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Research Article
Selectivity Trends Between Oxygen Evolution and Chlorine Evolution on Iridium-Based Double Perovskites in Acidic MediaClick to copy article linkArticle link copied!
- Johannes G. VosJohannes G. VosLeiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The NetherlandsMore by Johannes G. Vos
- Zhichao LiuZhichao LiuLeiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The NetherlandsMore by Zhichao Liu
- Florian D. SpeckFlorian D. SpeckDepartment of Chemical and Biological Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, GermanyMore by Florian D. Speck
- Nickson PeriniNickson PeriniSao Carlos Institute of Chemistry, Sao Paulo University, Avenida Trabalhador São Carlense, 400, 13566-590, São Carlos, Sao Paulo, BrazilMore by Nickson Perini
- Wentian FuWentian FuLeiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The NetherlandsMore by Wentian Fu
- Serhiy CherevkoSerhiy CherevkoHelmholtz-Institute Erlangen-Nürnberg for Renewable Energy (IEK-11), Forschungszentrum Jülich, Egerlandstrasse 3, 91058 Erlangen, GermanyMore by Serhiy Cherevko
- Marc T. M. Koper*Marc T. M. Koper*E-mail: [email protected]Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The NetherlandsMore by Marc T. M. Koper
Abstract
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The electrochemical chlorine evolution reaction (CER) and oxygen evolution reaction (OER) represent core processes in the production of chlorine, relevant to bulk chemical manufacturing, and water splitting, the most promising technology for renewable energy storage. Unfortunately, because of an apparent coupling between their key binding intermediates, the two reactions can easily occur simultaneously, which is never an attractive outcome. In this work, using a series of iridium-based double perovskites and rotating ring-disk voltammetry to deconvolute parallel OER and CER currents, we explored the interdependence of CER and OER in dilute acidic chloride solutions of up to 120 mM, where both reactions may occur in parallel with similar current densities. We also employed online inductively coupled plasma-mass spectrometry (ICP-MS) measurements to probe the material stability and its dependence on chloride concentration. For all studied materials, we found a strong linear correlation between CER and OER activity as well as a comparable selectivity, strengthening the suggestion that OER and CER follow a scaling relationship. It was also found that chloride selectively enhances the dissolution of the noble metal component. A reaction order analysis was performed to gain insight into the CER mechanism, the effect of surface area changes due to adventitious leaching, and the observed suppressing effect of chloride on OER.
Copyright © 2019 American Chemical Society
1. Introduction
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The electrochemical chlorine evolution reaction (CER) and oxygen evolution reaction (OER) both lie at the heart of large scale electricity-to-chemical conversion steps, making them highly important with regard to a renewable-based energy infrastructure. (1−5) During chlorine evolution, chloride ions are oxidized to chlorine gas (Cl2). Likewise, oxygen evolution involves the oxidation of water into O2, along with the release of protons. The reactions proceed via
Note that the equilibrium potential for the OER is pH-dependent on the normal hydrogen electrode (NHE) scale and therefore pH-independent of the reversible hydrogen electrode (RHE) scale, whereas the reverse is true for CER.
(1)
(2)
CER is the core reaction in the chlor-alkali process and allows the production of chlorine and caustic soda, bulk chemicals that are required in large amounts throughout the chemical industry. (6,7) The two-electron nature of the reaction means it exhibits very fast kinetics, (8) but due to its relatively high equilibrium potential, the chlor-alkali process is very energy intensive. The required power input to drive chlorine evolution is the most significant economic (and environmental) cost. (9−12) A substantial body of research has thus gone in studying optimum process conditions for CER, since the large scale of the process means that even small efficiency gains can have a large impact. (13−15)
OER represents the desired anodic reaction in water electrolysis, since O2 is environmentally harmless and can be safely vented into the atmosphere. Its desired function is to complete the electrical circuit in water splitting cells, allowing the capture and storage of electrical energy in the form of H2 as a chemical fuel and in this way dampening the heavy intermittency of renewable energy fluxes. (16) Its four electron nature means that OER has very sluggish kinetics, especially compared to CER, and the difficulty of catalyzing the reaction poses one of the main barriers preventing widespread implementation of water electrolysis for energy storage. (17−19) In fact, the facile CER kinetics relative to OER is what makes it possible to vigorously evolve chlorine in acidic aqueous media with a pH lower than ∼2, with minimal anodic decomposition of the aqueous solvent.
In a practical sense, it is difficult to envision a situation where the mixed evolution of both chlorine and oxygen is an attractive outcome. Whereas chlorine as a product is unwanted during water electrolysis due to its environmental toxicity, OER is unwanted in chlor-alkali since the oxygen represents a safety risk and its formation is linked to catalyst degradation. (15,20−22) Thus, studying the selectivity between these two highly relevant reactions is important, especially since an OER-selective anode would allow the direct splitting of saline water without the costly need of removing chloride from the system. (23,24) Although OER and CER seem fundamentally different reactions at first glance, it has been often observed that catalyst materials proficient at OER are also highly active for CER, which can be ascribed to a so-called scaling relationship between the binding energies of their key intermediates. (25−27) Such a relationship implies that OER and CER are linked on a fundamental kinetic level, perhaps in the form of a common intermediate surface species and/or a shared active site. (28−30) It also implies that control over selectivity between the two reactions can be a serious challenge. It may be exceedingly difficult, if not impossible, to efficiently separate the two reactions on the basis of kinetic considerations alone, such as by finding an appropriate catalyst. (31−33)
Both CER and OER are most readily catalyzed on metal oxides. (25,34) CER is usually carried out in acidic media because of thermodynamic restrictions (see eq 2), on anodes made of mixtures of RuO2 and TiO2, so-called dimensionally stable anodes (DSA). (9) OER can be carried out in a wide pH range, but performance wise, the current state of the art is represented by polymer electrolyte membrane (PEM) electrolyzers which employ acidic pH and are equipped with Ir-based mixed metal oxides. (1) Ir, either as a pure oxide or as a dopant, is the only material known to retain long-term stability during acidic OER operation, and virtually no acidic OER anode is known that does not rely on Ir. (35) Unfortunately, the scarcity of Ir is a crippling limitation to large-scale implementation of PEM electrolyzers, and a large body of research has been devoted to reducing the needed Ir loading, such as by increasing the active surface area or developing Ir-based materials with higher intrinsic activity.
A recent example of Ir-based materials with lower intrinsic Ir mass loading are Ir-based double perovskites, aiming to reduce the amount of Ir needed while retaining the high catalytic OER performance. (36) Previous work by some of us showed that the high OER performance of these materials is related to their instability in acid, leading to amorphization of the surface and formation of a highly active surface layer. (37) An interesting question is how these Ir-based double perovskites perform as CER electrocatalysts and how parallel CER impacts their stability. They represent an attractive system of study also because of the possibility of studying a series of closely related structures. The Ir double perovskite structure is represented by A2BIrO6 and allows a degree of freedom in the type of A and B cations, meaning that many different perovskites can be prepared.
In this work, we explore parallel OER and CER on a series of double perovskites and investigate their selectivity and stability as well as the interdependence between the two reactions in acidic media of pH ∼ 1. Under these conditions, the OER and CER have similar onset potentials and they are in direct kinetic competition. Additionally, the acidic environment allowed the use of an RRDE method to deconvolute parallel OER and CER currents, by using a Pt ring to quantitatively detect Cl2 evolved on the disk, as described in detail in a previous publication. (38) Relatively low chloride concentrations (0 < [Cl–] < 120 mM) were chosen to study the CER, since it was previously shown that competition between OER and CER is the most prevalent under these conditions. (38) We studied a series of double perovskites written as Ba2BIrO6, where B = Pr, Nd, La, Sn, Y, Tb, and Ce. The material Sr2YIrO6 was also included with the aim to vary the A cation. Commercial IrO2 was included as reference material.
2. Experimental Section
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2.1. Chemicals
HClO4 (60%) and NaCl (EMSURE/Analysis grade) were purchased from Merck. Ir-based double perovskites were synthesized as reported previously. (36) IrO2 nanoparticles (Premion, 99.99%) were purchased from Alfa-Aesar. All purchased chemicals were used as received. The water used for all experiments was prepared by a Merck Millipore Milli-Q system (resistivity 18.2 MΩ cm, TOC < 5 ppb).
2.2. Synthesis of the Double Perovskites and X-ray Powder Diffraction
Samples of A2BIrO6 (A = Ba and Sr; B = lanthanides, Y, and Sn) were prepared from BaCO3, SrCO3, La2O3, CeO2, Pr6O11, Nd2O3, Tb4O7, Y2O3, SnO2, and Ir metal using methods based on standard solid-state reactions. (39,40) The La2O3 and Nd2O3 powders were preheated at 950 °C overnight before use. The well-ground mixtures were placed in alumina crucibles and allowed to react at 800 °C overnight. The resultant powders were then sintered at 1250 °C for 2 days with intermittent regrinding, and finally, the samples were furnace cooled to room temperature. Every synthesis was carried out in air.
X-ray powder diffraction patterns were collected on a Philips X’Pert diffractometer in Bragg–Brentano geometry, equipped with a X’Celerator detector and a Cu–Kα source. Diffraction patterns were collected in steps of 2θ = 0.020°, with a 10 s counting time per step in the range 15° < 2θ < 90°.
2.3. Online Electrochemical ICP-MS Analysis
Investigations of the chloride impact on the stability of iridium based double perovskites were performed using an electrochemical scanning flow cell (SFC) with online inductively coupled plasma mass spectrometry (ICP-MS) analysis to detect dissolution products in direct correlation to potential and current density. The SFC is a small polycarbonate cell with an electrolyte flow of 192 μL min–1 able to perform classical three electrode electrochemical experiments. The cell’s inlet is connected to a counter electrode compartment, housing a graphite rod (Sigma-Aldrich, 99.995%), while a Ag/AgCl reference electrode (Metrohm) is connected by a separate channel directly to the working electrode. The reference electrode was calibrated vs the RHE, against which all potentials are reported. The working electrode can be moved with an xyz-stage (Physik Instrumente, M-403), which allows fast screening of multiple catalyst spots on a glassy carbon plate (HTW, SIGRADUR G, 5 cm × 5 cm). The outlet of the SFC is connected to the ICP-MS (PerkinElmer, NexION 350x) to detect dissolution products. The ICP-MS was calibrated for the elements A, B, and Ir with a four point calibration slope by adding specific amounts of standard solutions (Merck, Certipur, Ir, Pr, Y, Ba, Sr) to the electrolyte. More details about the online SFC ICP-MS system can be found in previous publications. (41−43) The SFC was operated using 0.1 M HClO4 (Merck, Suprapur) as an electrolyte in control experiments, and addition of 50 mM NaCl (Sigma-Aldrich, 99.5%) provided information on chloride impact on the stability. Catalysts were dropcasted from water based suspensions containing 0.27 mg(Ir)/mL and 20 μL of Nafion (Sigma-Aldrich, 5 wt % in aliphatic alcohols). Using 0.3 μL of those suspensions for dropcasting resulted in dried catalyst spots whose sizes (see Table S1) were measured using a Keyence laser profilometer (VK-X200 series). Surface area normalization was based on these spot sizes. Each measurement was carried out in duplicate to ensure reproducibility; data from single measurements are reported.
2.4. General Electrochemical Procedures
All experiments were carried out at room temperature (∼20 °C). Electrochemical experiments were done using homemade two-compartment borosilicate glass cells with solution volumes of 100 mL. Before first-time use, all glassware was thoroughly cleaned by boiling in a 3:1 mixture of concentrated H2SO4 and HNO3. When not in use, all glassware was stored in a 0.5 M H2SO4 solution containing 1 g/L KMnO4. Before each experiment, glassware was thoroughly rinsed with water and then submerged in a dilute (∼0.01 M) solution of H2SO4 and H2O2 to remove all traces of KMnO4 and MnO2. The glassware was then rinsed three times with water and boiled in water. The rinsing–boiling procedure was repeated two more times.
An IviumStat potentiostat (Ivium Technologies) was used during electrochemistry experiments. All experiments except voltammetric characterizations were 85% iR-compensated in situ. The solution resistance was measured with electrochemical impedance spectroscopy at 0.75 V vs RHE by observing the absolute impedance in the high-frequency domain (100–50 kHz) corresponding to a zero-degree phase angle.
2.5. Rotating Ring-Disk Electrode (RRDE) Procedures
RRDE experiments were performed in 0.1 M HClO4 solutions with a pH value of 1.20 ± 0.05, as measured with a Lab 855 m equipped with a glass electrode (SI Analytics). The solutions were saturated with Ar (Linde, purity 6.0) before experiments. Solutions were bubbled with Ar gas during forced convection experiments, and Ar was used to blanket the solution in stationary conditions. The reference electrode was a HydroFlex reversible hydrogen electrode (Gaskatel), separated from the main solution using a Luggin capillary, to fix the reference sensing point and to prevent mixed potentials at the reference due to dissolved Cl2 gas. The Luggin tip was distanced ∼2 cm from the working electrode to minimize distortion of the current distribution across the electrode surface, (44) and it was aligned to the center of the working electrode, to minimize electrical cross-talk. (45,46) All potentials in this paper are reported on the RHE scale. A Pt mesh was used as a counter electrode, separated from the main solution with a coarse sintered glass frit.
RRDE measurements were done with a MSR rotator and E6 ChangeDisk RRDE tips in a PEEK shroud (Pine Research). GC disks (Pine Research Instrumentation, surface area 0.196 cm2) were prepared to a mirror finish by hand polishing on Microcloth pads with diamond paste suspensions down to a 0.05 μm particle size (Buehler), followed by rinsing and sonication of the electrode in water for 3 min. The fine-ground catalyst powders were prepared as suspensions of 3 mg/mL (total catalyst mass) in EtOH (AR/Analysis grade, Acros Organics). After drying the prepared GC surface with compressed air, the RRDE tip was placed upside down in the MSR rotator. Thin films of catalyst were prepared by dropcasting 2.5 μL well-stirred EtOH suspension (formal loading ∼38 μg cm–2, total catalyst mass) onto the GC surface, followed by drying under rotation at 175 rpm. After the solvent had visibly evaporated, the surface was further dried with hot air for several minutes.
Before any RRDE experiment, the Pt ring was electrochemically reactivated by scanning from −0.1 to 1.7 V at 500 mV s–1 for 20 scans at 1500 rpm. Hydrodynamic experiments were done at 1500 rpm by scanning the disk electrode in the range of 1.3–1.55 V at 10 mV s–1. In between experiments, the disk electrode was kept at 1.3 V. Ring currents were corrected for constant background currents and product collection delay. The latter arises from the time needed for products formed on the disk to reach the ring, and was approximately 200 ms at 1500 rpm.
The liquid phase collection factor of the ring-disk system, Nl, was determined by studying the Fe[CN]63–/Fe[CN]64– redox couple in a solution of 10 mM K3Fe[CN]6 and 0.1 M KNO3, using the Pt ring with a freshly prepared blank GC electrode. The value was 0.241 within 5% accuracy. The collection factor for dissolved Cl2 was also measured in the same setup, by evolving chlorine selectively on Ba2PrIrO6 in 0.1 M HClO4 + 0.1 M NaCl at a potential of 1.48 V vs RHE, right before the kinetic onset of OER. The collection factor for dissolved chlorine, NCl2, was found to be 0.215 within 3% accuracy, slightly lower than Nl. The difference can be attributed to the higher solution pH compared to previous studies, (38) which causes an increase in the degree of Cl2 dissociation into Cl– and HClO, the latter of which is not detectable using present methods. The value for NCl2 was used in all calculations concerning OER and CER current separation.
2.6. Parallel OER and CER: Activity Measurements
Before initiating quantitative measurements, the GC-supported thin films were scanned 20 times in chloride-free 0.1 M HClO4 between 1.3 and 1.55 V, into the OER region, at 1500 rpm. This was done to ensure unchanging catalyst behavior during the experiments. The Pt ring was initially deactivated. The final scan of this procedure was taken as the data for “pure” OER activity. In the next step, the double layer capacitance was determined to allow a degree of normalization of the currents vs electrochemical surface area (see below). Finally, 20 mM NaCl was added to the solution, and the GC supported thin film was scanned once again between 1.3–1.55 V at 1500 rpm, with the Pt ring fixed at 0.95 V vs RHE for Cl2 detection. These three steps were performed right after one another using the same film and setup. The procedure of steps was repeated for each catalyst material at least three times, in independently prepared solutions and glassware, and using freshly prepared electrode films.
Measurement of the double layer capacitance (Cdl)E was done by scanning the electrode in the potential window of 0.05–0.15 V at scan rates of 25, 50, 75, and 100 mV/s (see Figure S7). The value of the double layer capacitance (Cdl)E was calculated from the slope of the charging current around 0.1 V vs scan rate, i(Cdl)0.1V = (Cdl)0.1V × ν (see Figure S8). From (Cdl)0.1V, the electrochemical surface area could be approximated for each individual experiment by normalizing the activity to the specific capacitance of the double layer, assuming 0.059 mF cm–2 for the latter. (47) Reported values for each type of catalyst are averaged from individually normalized activities.
2.7. Parallel OER and CER: CER Selectivity vs [Cl–] Measurements
Just like the activity measurements, the GC-supported thin films were scanned at least 20 times in chloride-free 0.1 M HClO4 between 1.3 and 1.55 V at 1500 rpm to ensure unchanging catalyst behavior during experiments. Following this, the ring was activated and kept at 0.95 V vs RHE during all measurements. The electrode was then again scanned between 1.3 and 1.55 V at 1500 rpm, while increasing the concentration of NaCl in steps from 0 mM to 120 mM. No attempt at normalization versus surface area was undertaken for these experiments, since we were interested in OER vs CER selectivity and their reaction orders only, which are not affected by current normalization. Details about the preparation of an amorphous, hydrated IrOx/GC catalyst can be found elsewhere. (38)
3. Results and Discussion
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3.1. ICP-MS Measurements and Effect of Chloride on Stability
A series of Ba2BIrO6 compounds (B = Pr, Nd, La, Sn, Y, Tb, Ce) and Sr2YIrO6 were synthesized and investigated for OER and CER activity and selectivity. We first investigated the stability of these materials under representative electrochemical conditions, since it has recently been shown that Ir-based perovskites are unstable in acidic media. Ba2PrIrO6 (36,37) and the single perovskite SrIrO3 (48) tend to leach out both Ir and non-noble metals from their lattice during sustained OER, leading to an amorphous IrOx outer surface layer that is highly active toward OER, expectedly more so than the bulk material. The main driver for this instability appears to be the favorable thermodynamics of non-noble metal dissolution in acidic media, followed by codissolution and/or collapse of the interspaced IrO6 octahedra. Since our experiments involve CER in addition to OER, it was necessary to study the effect of chloride on the leaching behavior of the studied materials.
We performed online electrochemical ICP-MS measurements to follow the dissolution of Ir and the A + B cations under electrochemical conditions in 0.1 M HClO4, in presence and absence of 50 mM NaCl. Each experiment was comprised of the same electrochemical protocol seen in Figure 1A (top). Contact was made at 0.05 V, while subsequent potential cycling at 200 mV s–1 to 1.6 V was used to reach reproducible CVs. After a “resting” period at 1.2 V in which the dissolution subsided to its background signal, a linear sweep voltammogram (LSV) at 10 mV s–1 to 1.65 V, along with the integral of Ir dissolution, was used to calculate the stability number (S-number). (37) In the presence of chlorides, the formula for calculating the S-number was adapted according to eq (S 1) to include the formation of chlorine gas. Ba2PrIrO6, Ba2YIrO6, Sr2YIrO6, and Ba2CeIrO6 were chosen as representative double perovskites.
Figure 1
Figure 1. Online electrochemical iridium dissolution from ICP-MS measurements. Panel A, Ir dissolution over time correlated with the applied E vs t protocol (red) for Ba2PrIrO6 (blue), Sr2YIrO6 (green), and Ba2YIrO6 (yellow) in 0.1 M HClO4 (solid) and 0.1 M HClO4 with 50 mM NaCl (pale). For clarity reasons, the initial contact peak is not shown (see Figure S 1 for the full version). Panel B, Ir dissolution along with the current density of the LSV of the E vs t protocol. Panel C, S-number (amount of gases evolved per amount of Ir dissolved) comparison in the presence and absence of 50 mM NaCl. Panel D, total dissolved amount of Ir during initial contact with the electrolyte, cycling, and the LSV, as determined from the initial spot loading (see also Table S 1).
Figure 1 summarizes online ICP-MS Ir dissolution from Ba2PrIrO6, Ba2YIrO6, and Sr2YIrO6 during the electrochemical protocol; additional dissolution data for Ba2CeIrO6 is shown in the Supporting Information. Similar to a previous report, (37) all materials experience major Ir leaching immediately upon contact with the acidic electrolyte (Figure 1D), during which the electrode is conditioned at 0.05 V vs RHE. Cycling of the electrode promotes the rate of iridium leaching, suggesting that the effect is strongly dependent on transient changes in the catalyst matrix. (49) Non-noble components (Ba, Pr, Sr, Y, and Ce) on the other hand show little to no potential dependent dissolution and merely dissolve upon electrolyte contact. Table S 2 offers an overview of all integrated dissolution rates. In this table, Ba2PrIrO6 in chloride-free electrolyte shows enhanced contact dissolution rates of Ba compared to Pr and Ir; this conforms to previously reported XPS data on Ba2PrIrO6 which was exposed to a similar environment. (36) Interestingly, Sr in Sr2YIrO6 shows a small but more pronounced potential dependent dissolution during cycling than Ba in Ba2PrIrO6 and Ba2YIrO6. A lack of a clear trend for the total dissolution of any element in the presence of chloride is due to the big percentage of the contact dissolution on the overall dissolved amount (90–100%). Since the contact peak is rarely reproducible for the same catalyst as it depends on many factors, we only discuss dissolution during potentiodynamic control in the following. Most importantly, the dissolution of Ir is increased significantly during both the cycling and the linear potential ramp (Figure 1D). To look into this aspect in more detail, the extent of Ir leaching was correlated with the catalytic current in the voltammogram during the final LSV (Figure 1B). This allowed the calculation of the S-numbers for both pure OER in HClO4 as well as a competitive OER and CER in the presence of chloride (Figure 1C). A faradaic efficiency of 100% toward OER and 90% CER to 10% OER was assumed according to RRDE experiments, respectively (see below). The stability number S (plotted in Figure 1C) had a very similar value for Ba2PrIrO6, Ba2YIrO6, and Sr2YIrO6. For Ba2CeIrO6, OER activity and Ir dissolution during the linear sweep were too low to accurately measure, and S could not be determined. In the presence of chloride, all materials experience more Ir dissolution, as illustrated by a roughly 50% decrease in S, which is in line with previous results on the stability of noble metals such as Pt and Rh in the presence of chloride. (50) These results suggest that the dissolution of noble metal centers is impacted very differently during CER than during OER. We speculate that whereas during OER, the dissolution is driven by formation of higher oxide species, Cl– may enhance Ir dissolution specifically by forming chloro-iridate complexes such as IrCl3 and Ir[Cl]63–. We note that the total amount of Ir that dissolved from the double perovskites during these experiments is several orders of magnitude larger than what has been reported for IrO2. (51) This means that IrO2 represents an interesting, transiently stable material for comparison in this study.
3.2. Catalyst Characterization
To verify the bulk properties of the materials tested in this study, powder XRD patterns were measured (Figure S 2). The patterns generally agree with those reported in the literature; (39,40,52) in particular, the presence of the super lattice lines at about 18° and 35°, which in the double cubic cell are indexed as (111) and (311), respectively, suggest an ordered arrangement of the BO6 and IrO6 octahedra. The IrO2 shows poor crystallinity, displaying a single broad peak of overlapping rutile (110) and (101) reflections around 28° and 35° as well as a wide (200) reflection around 40°. A trace of metallic Ir is also present; this trace disappeared quickly upon cycling (see Figure S 4).
For the RRDE measurements, ethanol suspensions of the fine powders were dropcasted directly onto polished GC substrates and dried, followed by submersion and electrochemical measurements. We avoided the use of binders such as Nafion, (36,53,54) since it was found that Nafion had a major depressing effect on CER selectivity, likely due to its permselective behavior for cations (see Figure S 3). (55) ICP-MS control experiments showed that Nafion slightly enhanced Ir dissolution in Ba2PrIrO6 during the electrocatalytic LSV (Table S 2); the S-number however decreased very similarly (−47% vs −48%) under the effect of chloride. These results suggest that dissolution is much less strongly affected by chloride mass transport than the CER. Figure 2 displays the voltammetric characterization of ∼38 μg cm–2 formal catalyst mass loadings of the investigated double perovskites and IrO2 in the potential window of 0–1.4 V.
Figure 2
Figure 2. Voltammetric characterization of the Ir-based double perovskites used in this study, in a 0.1 M HClO4 solution, supported on GC. All materials were scanned at least 20 times in the range of 1.30–1.55 V at 1500 rpm prior to characterization. Catalysts are shown in groups with pronounced Ir redox transitions (A) and those with less obvious features, plus the IrO2 reference (B). Scan rate: 50 mV s–1.
On the basis of the stability results (section 3.1), we expect transient dissolution in all double perovskites during the RRDE measurements. All characterizations in Figure 2 were therefore taken from electrodes that were scanned at least 20 times in the potential region 1.30–1.55 V in 0.1 M HClO4 at a rotation rate of 1500 rpm to ensure that the voltammograms correspond to the actual catalyst surfaces that were used for subsequent OER and CER catalysis. The plots cannot be ascribed to idealized double perovskite surface structures but should be considered as double perovskite-derived thin IrOx films in varying states of amorphization.
On the basis of their voltammetric characterization, we divided the materials into two groups. First, we consider Ba2PrIrO6, Ba2NdIrO6, Ba2LaIrO6, and Sr2YIrO6, which show strong redox transitions in the range of 0.6–1.4 V (Figure 2A). These transitions are tentatively ascribed to Ir redox transitions, as was done previously for Ba2PrIrO6. (37) Ba2PrIrO6 and Sr2YIrO6 show two sets of peaks in the forward scan (marked I and II) and in the backward scan (marked III and IV). Considering the position and irreversibility of the peaks, we ascribe these peaks to the formation of an amorphous IrOx surface layer as a result of the leaching of A and B cations. Peaks I and IV likely correspond to a transition between Ir3+ and Ir4+, whereas peaks II and III represent further Ir oxidation that may be beneficial for OER catalysis (either formation of Ir5+ centers (56−58) or the more recently proposed formation of Ir4+-O– moieties). (59,60) Second, the group of Ba2SnIrO6, Ba2YIrO6, Ba2TbIrO6, and Ba2CeIrO6 shows more subtle features (Figure 2B). It is somewhat surprising that Ba2YIrO6 and Ba2CeIrO6 do not have pronounced Ir redox peaks, since they also displayed significant dissolution upon contact in ICP-MS measurements (Table S 2). Possibly, an amorphous IrOx layer is formed not during contact dissolution but during potential scanning in the OER region; the rate of Ir dissolution during this scanning, which differs between catalysts, perhaps controls the extent to which the layer forms. The IrO2 reference shows a broad profile with small reversible peaks around 0.8 and 1.2 V, in accordance with previous studies on IrO2. (61) We observed a trace of hydrogen evolution near 0 V for “pristine” IrO2 before scanning repeatedly into OER, which we ascribe to a small amount of metallic Ir present in the bulk (see also Figure S 4). This behavior is no longer visible in Figure 2B because of the irreversible conversion of interfacial metallic Ir into its oxide, which is a much worse HER electrocatalyst. (62) See Figure S 4 for comparisons of the curves in Figure 2 with the catalysts in their “pristine” state.
We must note that, in the context of this paper, the focus is on selectivity and OER/CER interdependence, meaning we are not interested in absolute activities per se. It is however still desirable to apply normalization of current vs the catalytically active surface area to allow comparison between different catalysts, even though the “active site” could become ambiguous in the case of two distinct reactions. The most common and straightforward approach is normalization vs the electrochemically active surface area (ECSA) by measuring the double layer capacitance (Cdl)E around potential E, which is expected to scale with the ECSA according to
where Cdl* is the specific capacitance per surface area of the material. (Cdl)E can be determined from the slope of the double layer charging current vs the scan rate (Figure S 7). Unfortunately, accurate ECSA determination is a persistent problem throughout electrocatalysis, (63) for four main reasons: (i) accurate values of Cdl* generally do not exist, (ii) (Cdl)E has to be measured in a region completely free of faradaic processes, (iii) (Cdl)E may be affected by the (potential-dependent) conductivity of the material, (iv) determination of (Cdl)E is not a selective chemical surface titration method, so that its value may actually not be the best measure of the ECSA.
(3)
Ideally, (Cdl)E should be measured at the same potential for all materials. Considering Figure 2, there is large variation in behaviors for the studied materials within the potential window of 0–1.4 V; the Ir-related redox transitions in Figure 2A are visible in a wide potential range up until the OER/CER onset, meaning that any (Cdl)E measurement in this potential range is distorted by pseudocapacitive contributions. McCrory et al. recommend measuring Cdl around the open circuit potential, but almost all measured materials assumed an open-circuit potential value that fell in the pseudocapacitance area. In fact, the EOCP value is likely not suitable in this regard, since it almost invariably depends on mixed potentials, i.e., the occurrence of multiple surface reactions resulting in zero net-current. Other authors recommend electrochemical impedance modeling to measure the adsorption capacitance of reaction intermediates as an estimate of the ESCA. (64) In the end, we resorted to measuring (Cdl)E in a 0.1 V interval centered around 0.1 V, hereby termed (Cdl)0.1V; this area appeared free of pseudocapacitive processes for all materials (Figure 2). Assuming a specific capacitance Cdl* = 0.059 mF cm–2, an “average” of reported literature values for oxides in acidic conditions, (36,47) we obtained ECSAs with similar magnitudes as the geometrical surface area. The caveat of this method is the large separation of OER-relevant potentials and the ECSA determination. Under the assumption that the Ir centers dictate the observed pseudocapacitive behavior, we also cannot exclude interference from conductivity (category (iii), since amorphous Ir oxides show a notable decrease of conductivity below 0.5 V. (65) In effect, this means that part of (Cdl)0.1V may originate from the GC substrate. (66,67) Despite the shortcomings of this normalization method, we again note that the activity normalization affects neither the slope of Tafel curves, the reaction order analysis, or OER vs CER selectivity.
3.3. OER and CER Activity Trends
In consideration of sections 3.1 and 3.2, we will not theorize about catalyst structure vs catalytic activity relationships, since the true structure of the double perovskite surfaces is not known. The materials show rather diverse catalytic behavior as will be shown below.
During scanning rotating ring-disk electrode (RRDE) voltammetry involving parallel CER and OER, the two reactions can be separated by using eq 4:
In eq 4, the total current on the disk electrode iD is assumed to be the sum of CER current (iCER), OER current (iOER), and a residual current originating from scanning (pseudo)capacitance. The capacitive contribution can be effectively minimized by using a relatively slow scan rate of 10 mV s–1 and averaging forward and backward scans, yielding approximately only catalytic current from catalytic OER and CER (iD), which are solution-controlled processes. We were then able to separate the CER current contribution by fixing the potential of the Pt ring at 0.95 V vs RHE to selectively detect Cl2 evolved on the disk (where reducing current is thus measured). The obtained ring current (iR) is directly proportional to CER rates. A further correction for the ring collection factor of chlorine (NCl2 ≈ 0.215 in 0.1 M HClO4) yields iCER, the CER current contribution. The remaining current on the disk was then assumed to originate from OER. See Figure S 5 for an example curve measured during a typical experiment.
(4)
Due to the perceived instability of the catalysts under study, we must note that the ring measurements may be affected by dissolved species coming from the disk. These species could cause additional stray reduction reactions or interfere with Cl2 detection by redepositing as species which are not active toward Cl2 reduction. As evidenced by their Pourbaix diagrams, (68) most A and B cations used in this study are expected to be electrochemically inert at 0.95 V in acidic solution, meaning they will not react or deposit on the Pt ring. Only Sn and solution-phase iridium species may possibly deposit as oxides under the studied conditions. From the Ir dissolution rates in ICP-MS measurements, we estimate that the error due to reduction reactions involving Ir is at least 2 orders of magnitude lower than the smallest ring currents related to CER (Figure S 6). Furthermore, a rough estimate shows that it would take at least 10 min of continuous operation at high potential to form a perfect IrO2 monolayer on the ring. Serious interference at the Pt ring can thus be safely excluded (see the Supporting Information for full details).
The value of the Tafel slope has been used as a “benchmark” for catalytic OER performance, with a lower Tafel slope correlating with a “better catalyst”. (69−71) It must be noted that strictly speaking, the catalytic performance of a material is not governed by the Tafel slope only. A low Tafel slope is only favorable if it leads to a low(er) overpotential at the desired current density. We will discuss our experimental findings related to the Tafel slope in this spirit, namely, that catalytic performance and the Tafel slope are not by definition correlated.
We first set out to measure “pure OER” currents (in the absence of Cl–) as well as CER currents measured during parallel OER and CER. Figure 3A shows OER Tafel plots constructed from capacitance-corrected disk current densities, in the absence of Cl–. Figure 3B shows CER Tafel plots constructed from ring currents in the presence of 20 mM Cl–. The activities for OER roughly follow the order Pr ≈ Nd > La > Sn > Sr2Y ≈ Tb > Ba2Y > IrO2 > Ce. The most catalytically active DPs Ba2PrIrO6, Ba2NdIrO6, Ba2LaIrO6, and Sr2YIrO6 also show a redox transition in their blank CVs (see Figure 2A); we speculate that activities correlate to the extent of surface leaching, although a definite correlation between activity and total dissolved amounts could not be established (see sections 3.1 and 3.2). Interestingly, the same order in activity is observed for CER, indicating scaling between OER and CER activities.
Figure 3
Figure 3. OER (A) and CER (B) Tafel curves obtained by scanning the electrode between 1.30 and 1.55 V at 10 mV s–1: (A) “pure” OER current densities in a 0.1 M HClO4 solution and (B) CER current densities in a 0.1 M HClO4 + 20 mM NaCl solution, derived from ring currents on a Pt ring fixed at 0.95 V vs RHE. Values shown are the average of at least three independent measurements (see Figure S 9 for a version containing error bars). Solutions saturated with Ar, rotation rate 1500 rpm.
To minimize mass transport control in case of CER, the experiments were performed at 1500 rpm. The highest measured CER current densities per geometric area, as measured at 1.55 V on BaPr2IrO6, were approximately 10% of the theoretical diffusion limited current as predicted by the Levich equation. We thus assume that mass transport effects on CER are negligible in the potential ranges studied. OER is considered effectively immune to mass transport effects.
Figure 4A,B shows a comparison of CER and OER current densities for all materials, plotted at 1.50 and 1.55 V. As already faintly visible from Figure 3, there is a linear scaling relationship between OER and CER activity. Although such a relationship has been observed previously in the literature, it must be noted that this is one of the few reports directly showing a correlation between CER and OER activity among a group of catalysts. (25) Furthermore, all materials, including the least active ones, showed regions of linear Tafel phenomena for both OER and CER (R2 > 0.98). The slopes of these linear CER Tafel sections are shown in Figure 4C, in comparison to CER current densities at 1.50 V. In Figure 4C, a lower Tafel slope correlates with higher CER current densities, which is a reasonable finding due to the exponential nature of the j/E curves. Furthermore, the catalytically most active materials display linear Tafel slopes in the range 45–50 mV/dec for CER and slopes of 40–45 mV/dec for OER (Figure 4D); for the less active materials, higher Tafel slopes with a higher variance are observed (see Table S 3 for all numerical Tafel slope values).
Figure 4
Figure 4. Correlations between OER and CER activities, data derived from Figure 3 (CER measured in 20 mM NaCl). (A and B) OER vs CER current densities compared at 1.50 and 1.55 V, respectively. (C) Comparison of CER Tafel slope vs current densities measured at 1.50 V, the upper potential limit of the linear portion (see also Figure 3B). (D) Comparison of Tafel slopes from linear portions (1.45–1.50 V) of OER and CER. All data are averages of at least three independent measurements; error bars represent corresponding standard deviations.
In light of the instability of the materials, we must comment on the possible origin of the linear relation between OER and CER activity. As previously mentioned, the selective leaching of non-noble A and B cations from the lattice will to a varying extent form an amorphous IrOx surface layer on all materials. Since the double perovskites share identical structural motifs, one can expect them to follow comparable amorphization behavior. This could result in thin catalytically active IrOx layers with perhaps varying surface area but similar kinetics, and thus a linear OER vs CER relation would always be observed. However, the variance in Tafel slopes for CER strongly speaks against this effect being the only descriptor for OER and CER activity; (34,72) if identical IrOx is formed, then all semilogarithmic i–E curves should display nearly identical (±5 mV/dec) Tafel slopes, which is not the case. The IrO2 reference furthermore fits in the scaling trend very well, despite possessing a rather different structure compared to the double perovskites. All in all, although we cannot discern the true nature and structure of the active catalyst phases, we can still conclude that they vary among catalysts and that despite this, a linear scaling relationship between CER and OER is observed. The origin of the scaling has been commented on by Trasatti. (25) It is possibly a similarity between the way that chloride binds to surfaces, as compared to the several key oxygen intermediates believed to be involved in the OER. (26) Most importantly, scaling suggests that a catalyst with a kinetic preference toward only one of the reactions may be very hard to find.
3.4. CER Selectivity as a Function of Chloride Concentration
We further probed OER vs CER selectivity of the materials by varying the chloride concentration stepwise between 0 and 120 mM. Molar selectivities toward CER (εCER) were defined as a ratio of CER current and combined OER and CER current, where the individual CER and OER currents were normalized to the amount of electrons in each reaction (eq 5):
Measured values of εCER for all materials are shown in Figure 5, at 1.50 and 1.55 V.
(5)
Figure 5
At 1.50 V (Figure 5A), εCER is very similar among materials and shows a strong dependence on chloride concentration. At 1.55 V (Figure 5B), selectivity toward OER increases and there is more variance among materials. A group consisting of Ba2PrIrO6, Ba2NdIrO6, Ba2LaIrO6, and Sr2YIrO6 shows particularly high OER selectivity. At both potentials shown, the least active materials generally show higher selectivity toward CER. An important exception is Ba2SnIrO6; this material shows relatively high CER selectivity at both 1.50 and 1.55 V while also possessing relatively high activity. Despite these differences, it can be said that εCER is globally governed by a single relationship; none of the materials show extremely diverging values (>20%) in their selectivity between OER and CER. This conclusion is in-line with Figure 4A,B, where a scaling trend was seen at the single concentration [Cl–] = 20 mM; this tendency seems to be applicable to higher chloride concentrations as well. The effect of mass transport on the measured CER currents should not be high. A 10% decrease in CER current, the prediction for maximum mass transport control in the experiments (see also the discussion of Figure 3), should lead to a decrease in εCER of less than 2% for virtually all chloride concentrations. At potentials above 1.55 V, selectivity toward OER will presumably increase, since CER will become increasingly mass transport limited whereas OER is much less affected. We were unfortunately not able to probe this potential region due to formation of persistent O2 bubbles at high current densities on the electrode tip, which interfered with the collection efficiency. (38)
3.5. OER vs CER Interdependence and Effect of Chloride Concentration
In this section, we look more deeply into parallel OER and CER as a function of chloride concentration. Figure 6 shows the effect of chloride regarding the OER Tafel curves as well as relative OER and CER activity.
Figure 6
Figure 6. Effect of chloride concentration on OER and CER. (A) OER currents measured in the presence of 20 mM NaCl, in parallel with CER. (B and C) Relative OER current (B) and CER current (C) as a function of increasing chloride concentration. The % OER currents are shown relative to chloride free conditions (0 mM NaCl), and the % CER currents are shown relative to 30 mM NaCl. See Figure S 12 for versions of parts A and B containing absolute currents.
The chloride concentration exhibits a pronounced influence on all catalysts under study regarding both CER and OER. When comparing Figure 6A to Figure 3A, the presence of 20 mM Cl– induces a shift of the OER Tafel curves toward higher potentials, a reduction in the apparent OER exchange current density, and thus a decrease in OER activity (a factor of 2 for most materials). A scaling relationship was again apparent when OER data from Figure 6A was compared to CER data from Figure 3B (see Figure S 10). Figure 6B,C shows relative OER and CER currents as a function of increasing [Cl–]. For OER, all values are shown as percentages relative to the value at chloride free conditions ([Cl–] = 0 mM). Likewise, all values for CER are shown relative to [Cl–] = 30 mM, where the value of the current at this concentration was taken as “30%”. This normalization was done due to the different current densities and allows a clearer comparison between trends among materials as chloride concentrations increase (see Figure S 12 for the absolute currents). Figure 6B shows a nonlinear decrease in OER current as a function of [Cl–] on all materials, in some cases (Ba2TbIrO6 and Ba2CeIrO6) approaching virtually complete OER suppression at 120 mM. At the same time, all materials show a continuous CER increase with increasing [Cl–] (Figure 6C), but there is significant downward curvature in all plots except for the IrO2 reference.
For further analysis of the interdependence between OER and CER, we consider theoretical models of these reactions and their predictions for chloride reaction orders. As has been comprehensively described by Conway and co-workers, (73) and more recently by Rosestolato et al., (74) reaction orders (and also Tafel slopes) of reactions involving a chemisorbed intermediate are never expected to remain constant as a function of concentration in the bulk, because of varying surface coverage of the intermediate. In this regard, chlorine evolution is a multistep reaction which involves elementary reaction steps termed Volmer, Tafel, and Heyrovský, which correspond to electrochemical adsorption, recombinatio,n and electrochemical desorption, respectively,
Electrochemical adsorption (Volmer step)
Recombination (Tafel step)
(6)
(7)
(8)
One can additionally consider a mechanism involving a “fourth” elementary reaction, as formulated by Kristhalik: (75)
(9)
(10)
This mechanism, in which eq 9 is rate-limiting, involves the formation of a short-lived “chloronium” (Cl*+) intermediate, which is proposed to be stabilized by metal–oxygen groups. (13,76)
In the simplest method of deriving theoretical current–potential relationships from these reactions, the Volmer step is taken as a quasi-equilibrium, with the subsequent rate-limiting step as either recombination or electrochemical desorption. The observed current density then becomes dependent on θCl, the fractional surface coverage of chemisorbed intermediate Cl*. (73) As a further approximation, one can assume that the adsorption of chloride obeys the Langmuir isotherm and that the surface reaction rate follows the mean-field approximation. (77) In the case of a Volmer–Tafel mechanism, the current–potential relation can then be modeled according to
(11)
In this equation, kT is the (nonelectrochemical) rate constant for recombination, KV and ηV describe the chemical quasi-equilibrium constant and overpotential for the Volmer adsorption step, and f = F/(RT). Only the irreversible (activated) potential region is considered, such that the backward reaction may be neglected. From this equation, one can derive 
, the CER reaction order versus [Cl–] at a constant potential E, as
, the CER reaction order versus [Cl–] at a constant potential E, as(12)
An analogous treatment for consecutive Volmer–Heyrovský steps leads to
(13)
(14)
In these equations, KV′ is again the chemical quasi-equilibrium constant for the Volmer adsorption step (on the potential scale of the Heyrovský step), and k0H, αH, and ηH are the standard rate constant, transfer coefficient, and overpotential for the Heyrovský step. This model predicts that as [Cl–] increases, θCl approaches 1; in the case of a V–T mechanism, 
varies between 2 and 0. In the case of a V–H mechanism, 
varies between 2 and 1. The V–K mechanism is reminiscent of the V–H mechanism but predicts that 
varies between 1 and 0:
varies between 2 and 0. In the case of a V–H mechanism, varies between 2 and 1. The V–K mechanism is reminiscent of the V–H mechanism but predicts that varies between 1 and 0:(15)
The simplest model accounting for the chloride dependence of the OER current would be to assume a simple site blocking, similar to previous work by Fernández et al.: (78)
In this equation, iOER describes the measured OER current; iOER0 describes the OER current that would have been measured in absence of chloride. The other symbols again relate to a Volmer-type adsorption of chloride. For the corresponding OER reaction order versus [Cl–], the dependence is
From this expression, we expect 
to change from 0 to −1 as [Cl–] increases, with the rate of change depending on the overpotential and KV.
(16)
(17)
to change from 0 to −1 as [Cl–] increases, with the rate of change depending on the overpotential and KV.The above models all make use of a Langmuir model isotherm for chloride adsorption. In reality, repulsive interactions between adsorbed chloride (and halides in general) will exist. (77) If this is taken into account by using a Frumkin isotherm, this will lead to a broadening of the isotherm, i.e., a broader range of chloride concentrations is needed to reach maximum coverage. For the models described above, this implies that the basic predictions remain the same and only that the predicted change from one reaction order to another will take place over a broader range of chloride concentrations.
The experimental OER and CER reaction orders can be approximated from the derivative of log–log plots (see Figures S 15 and S 16) of the i vs [Cl–] curves. The results are shown in Figure 7. We previously performed RRDE studies similar to those described in this report using amorphous IrOx. (38) The reaction orders for OER and CER obtained in those studies have been included for comparison. We want to note that for all values of [Cl–] < 10 mM in Figure 7, the results may not be fully reliable due to possible interference of oxide formation on the Pt ring used for detection. (38)
Figure 7
Figure 7. Reaction orders vs chloride concentration ( for OER (A) and CER (B). Values were derived using the [Cl–]-dependent slopes of Figures S 15 and S 16.
We will first focus our discussion of the OER reaction order to [Cl–] concentrations of up to 50 mM (see Figure S 17 for a close-up of this region). In this range, 
has a negative fractional value between −0.2 and −0.4 for all materials tested in this study, as was already apparent from the continuous decrease in OER activity in Figure 6A. Interestingly, the previously characterized IrOx has a value of 
closest to 0, varying between 0 and −0.1. This is illustrative of this material’s OER kinetics being almost impervious to the presence of chloride or parallel chlorine evolution, in contrast with the materials in the present study. For the double perovskites, 
is generally less negative the higher the intrinsic activity of the material, except for the IrO2 reference, which shows relatively low activity but globally also one of the least negative values of 
. Furthermore, most OER Tafel curves exhibit negligible changes in slope after the addition of Cl–, except for Ba2CeIrO6 (see Figure S 11 for a comparison and Table S 3 for the full data). This suggests that Cl– does not change the OER mechanism, which (along with the decreasing fractional reaction order in Figure 6A) is in agreement with the simple site blocking model. However, the extent of blocking appears to depend sensitively on the type of material. We hypothesize that site blocking for a more amorphous catalyst is different from that in a less amorphous system. The OER data at [Cl–] exceeding 50 mM are subject to increasing levels of uncertainty, due to inherent limitations of the experiment; with rising chloride concentration, the CER contribution starts to dominate the OER current as a result of which the experimental noise is greatly amplified in subtle slope changes of the log–log plots. Extensive averaging or smoothing may alleviate the noise, but we chose to present the data as-is to illustrate limitations of the method. Despite the noise, the overall trend nonetheless suggests that the reaction order never reaches −1 but rather seems to increase again to sometimes even positive values. This may reflect the influence of chloride on the actual structure of the catalytic interface.
has a negative fractional value between −0.2 and −0.4 for all materials tested in this study, as was already apparent from the continuous decrease in OER activity in Figure 6A. Interestingly, the previously characterized IrOx has a value of closest to 0, varying between 0 and −0.1. This is illustrative of this material’s OER kinetics being almost impervious to the presence of chloride or parallel chlorine evolution, in contrast with the materials in the present study. For the double perovskites, is generally less negative the higher the intrinsic activity of the material, except for the IrO2 reference, which shows relatively low activity but globally also one of the least negative values of . Furthermore, most OER Tafel curves exhibit negligible changes in slope after the addition of Cl–, except for Ba2CeIrO6 (see Figure S 11 for a comparison and Table S 3 for the full data). This suggests that Cl– does not change the OER mechanism, which (along with the decreasing fractional reaction order in Figure 6A) is in agreement with the simple site blocking model. However, the extent of blocking appears to depend sensitively on the type of material. We hypothesize that site blocking for a more amorphous catalyst is different from that in a less amorphous system. The OER data at [Cl–] exceeding 50 mM are subject to increasing levels of uncertainty, due to inherent limitations of the experiment; with rising chloride concentration, the CER contribution starts to dominate the OER current as a result of which the experimental noise is greatly amplified in subtle slope changes of the log–log plots. Extensive averaging or smoothing may alleviate the noise, but we chose to present the data as-is to illustrate limitations of the method. Despite the noise, the overall trend nonetheless suggests that the reaction order never reaches −1 but rather seems to increase again to sometimes even positive values. This may reflect the influence of chloride on the actual structure of the catalytic interface.Regarding the CER in Figure 7B, 
also decreases continuously for all double perovskites, down to values of roughly 0.5, but for IrO2, it stays at a constant value close to unity, 
. The IrOx reference material shows even different values, with 
around [Cl–] = 10 mM, which then progressively decreases to a steady value of 1.07. A 
value close to one has often been reported on metal oxides. (13,25,73,79,80) Furthermore, a decrease in 
as a result of an increase in [Cl–] has been reported previously on RuO2. (81) Judging from reaction orders alone, it thus seems likely that both IrOx and IrO2 follow a Volmer–Heyrovský mechanism, as their reaction orders converge near 1 at higher [Cl–]. This is in agreement with previous reports. (13) On the other hand, reaction orders on all double perovskites continuously decrease to values much lower than 1. Such behavior is more expected of either a Volmer–Tafel or Volmer–Krishtalik mechanism dominating the kinetics. We further investigated the CER mechanism using methods devised by Conway et al. (82) and Ferro et al. (83) By reordering the measured CER i–E curves, one can test whether a Volmer–Tafel or Volme–-Heyrovský mechanism applies (see Figure S 13 and its description for details about the method). For IrO2, we obtained a straight line in a Ferro–de Battisti test plot only, indicating Volmer–Heyrovský kinetics. We note that a straight line in such a plot can also indicate Volmer–Krishtalik kinetics; however, the y-intercept is then expected to be independent of [Cl–]. Instead, the intercept shows an inverse [Cl–] dependence, which matches well with the V–H pathway (see Figure S 14 for more details). On the other hand, Ba2PrIrO6 only showed a straight line in a Conway–Novak test plot, suggesting that CER proceeds via a Volmer–Tafel mechanism on this material (and perhaps also on the other perovskites), in agreement with the reaction order findings.
also decreases continuously for all double perovskites, down to values of roughly 0.5, but for IrO2, it stays at a constant value close to unity, . The IrOx reference material shows even different values, with around [Cl–] = 10 mM, which then progressively decreases to a steady value of 1.07. A value close to one has often been reported on metal oxides. (13,25,73,79,80) Furthermore, a decrease in as a result of an increase in [Cl–] has been reported previously on RuO2. (81) Judging from reaction orders alone, it thus seems likely that both IrOx and IrO2 follow a Volmer–Heyrovský mechanism, as their reaction orders converge near 1 at higher [Cl–]. This is in agreement with previous reports. (13) On the other hand, reaction orders on all double perovskites continuously decrease to values much lower than 1. Such behavior is more expected of either a Volmer–Tafel or Volmer–Krishtalik mechanism dominating the kinetics. We further investigated the CER mechanism using methods devised by Conway et al. (82) and Ferro et al. (83) By reordering the measured CER i–E curves, one can test whether a Volmer–Tafel or Volme–-Heyrovský mechanism applies (see Figure S 13 and its description for details about the method). For IrO2, we obtained a straight line in a Ferro–de Battisti test plot only, indicating Volmer–Heyrovský kinetics. We note that a straight line in such a plot can also indicate Volmer–Krishtalik kinetics; however, the y-intercept is then expected to be independent of [Cl–]. Instead, the intercept shows an inverse [Cl–] dependence, which matches well with the V–H pathway (see Figure S 14 for more details). On the other hand, Ba2PrIrO6 only showed a straight line in a Conway–Novak test plot, suggesting that CER proceeds via a Volmer–Tafel mechanism on this material (and perhaps also on the other perovskites), in agreement with the reaction order findings.As a final note, it can be expected that the apparent OER and CER chloride reaction orders on the double perovskites are affected by adventitious surface leaching as described in section 3.1. This leaching should lead to transient changes of the active surface area, and its effect on either 
or 
can be modeled via
where i is the measured current for either OER or CER, j is the current density as modeled by either the V–T or V–H model, and A is the real electrochemical surface area, which is dependent on chloride concentration due to leaching. It then follows that
On the right-hand side, the first term corresponds to the “kinetic” reaction order, as discussed earlier in this section. The second term represents the influence of chloride on the real surface area. As seen in Figure 1 and Table S2, the leaching rates of both noble and non-noble components are chloride-dependent but not in the same manner; a complex interplay can be expected from surface area changes due to increasing chloride concentration. Not much is currently known on the growth of amorphous surface phases on these materials in acidic media, meaning that the value and range of the A term is not easy to quantify. A reasonable assumption is that the term 
is positive immediately upon contacting the pristine perovskite with acidic electrolyte, during which the majority of surface leaching takes place and the change in surface area should be the largest. Considering that the rate of leaching steadily decreases over time in Figure 1, we may expect A to approach a constant value for all values of [Cl–], and its contribution to the reaction order should then tend to 0. On the other hand, if the rate of leaching increases strongly with increasing [Cl–], increasing changes of A could explain the apparent rise in reaction orders for both OER and CER at higher [Cl–] concentrations.
or can be modeled via(18)
(19)
is positive immediately upon contacting the pristine perovskite with acidic electrolyte, during which the majority of surface leaching takes place and the change in surface area should be the largest. Considering that the rate of leaching steadily decreases over time in Figure 1, we may expect A to approach a constant value for all values of [Cl–], and its contribution to the reaction order should then tend to 0. On the other hand, if the rate of leaching increases strongly with increasing [Cl–], increasing changes of A could explain the apparent rise in reaction orders for both OER and CER at higher [Cl–] concentrations.4. Conclusions
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In this work, we report that iridium-based double perovskites with structures Ba2BIrO6 (B = Pr, Nd, La, Sn, Y, Tb, Ce) and Sr2YIrO6, previously reported having high oxygen evolution activity in acidic media, also show high catalytic activity toward chlorine evolution in relatively low chloride concentrations (0–120 mM). A strong linear correlation between CER and OER activity was found on all catalysts employed and also comparable selectivity. This strengthens the suggestion that OER and CER follow a scaling relationship, as suggested in previous studies. On the basis of these results, we expect that promoting one reaction over the other on the basis of kinetic considerations alone may be exceedingly difficult, if not impossible. Alternative pathways, such as affecting the CER thermodynamics through pH changes or the mass transport of chloride to the active catalyst, are likely more successful in enhancing selectivity. (24) Electrochemical ICP-MS measurements showed that chloride has mixed effects on the stability of the perovskites, whereas non-noble dissolution effects were inconclusive; it significantly enhanced iridium dissolution during potentiodynamic control and active OER/CER, as evidenced by a lower value of the S-number. Dissolution pathways related to OER and CER are therefore likely different, which must be taken into account when considering an active catalyst for either of the reactions. Reaction order analysis indicates that CER proceeds via the Volmer–Tafel mechanism on the double perovskites, whereas it follows a Volmer–Heyrovský mechanism on IrO2 and amorphous IrOx. Contrary to amorphous IrOx, the OER activity on the double perovskites and IrO2 is strongly impacted by chloride concentration, displaying fractional, negative reaction orders.
Supporting Information
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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acscatal.9b01159.
Supplementary ICP-MS data and methodology description, XRD data, RRDE data concerning voltammetric characterizations, estimation of errors concerning RRDE chlorine detection, effect of Nafion on CER selectivity, ECSA determination and error bars, numerical Tafel slope values, OER vs CER selectivity, and test plots for the CER mechanism (PDF)
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Author Information
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- Marc T. M. Koper - Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands;
http://orcid.org/0000-0001-6777-4594;
- Nickson Perini - Sao Carlos Institute of Chemistry, Sao Paulo University, Avenida Trabalhador São Carlense, 400, 13566-590, São Carlos, Sao Paulo, Brazil;http://orcid.org/0000-0002-3319-5102
- Serhiy Cherevko - Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (IEK-11), Forschungszentrum Jülich, Egerlandstrasse 3, 91058 Erlangen, Germany;http://orcid.org/0000-0002-7188-4857
Acknowledgments
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This research received funding from The Netherlands Organization for Scientific Research (NWO) in the framework of the fund New Chemical Innovations, Project 731.015.204 ELECTROGAS, with financial support of Akzo Nobel Chemicals, Shell Global Solutions, Magneto Special Anodes (an Evoqua Brand), and Elson Technologies. N. Perini acknowledges FAPESP (Grant Number 2017/05040-1) for a scholarship.
References
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This article references 83 other publications.
- 1Carmo, M.; Fritz, D. L.; Mergel, J.; Stolten, D. A Comprehensive Review on PEM Water Electrolysis. Int. J. Hydrogen Energy 2013, 38, 4901– 4934, DOI: 10.1016/j.ijhydene.2013.01.151Google Scholar1https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXjvFentbs%253D&md5=c1f7c8334cfdb00ca6d13812d29ce968A comprehensive review on PEM water electrolysisCarmo, Marcelo; Fritz, David L.; Mergel, Juergen; Stolten, DetlefInternational Journal of Hydrogen Energy (2013), 38 (12), 4901-4934CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)A review. Hydrogen is often considered the best means by which to store energy coming from renewable and intermittent power sources. With the growing capacity of localized renewable energy sources surpassing the gigawatt range, a storage system of equal magnitude is required. PEM electrolysis provides a sustainable soln. for the prodn. of hydrogen, and is well suited to couple with energy sources such as wind and solar. However, due to low demand in electrolytic hydrogen in the last century, little research has been done on PEM electrolysis with many challenges still unexplored. The ever increasing desire for green energy has rekindled the interest on PEM electrolysis, thus the compilation and recovery of past research and developments is important and necessary. In this review, PEM water electrolysis is comprehensively highlighted and discussed. The challenges new and old related to electrocatalysts, solid electrolyte, current collectors, separator plates and modeling efforts will also be addressed. The main message is to clearly set the state-of-the-art for the PEM electrolysis technol., be insightful of the research that is already done and the challenges that still exist. This information will provide several future research directions and a road map in order to aid scientists in establishing PEM electrolysis as a com. viable hydrogen prodn. soln.
- 2Lakshmanan, S.; Murugesan, T. The Chlor-Alkali Process: Work in Progress. Clean Technol. Environ. Policy 2014, 16, 225– 234, DOI: 10.1007/s10098-013-0630-6Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXks1Sitbo%253D&md5=8f7e109b04aa9c2e416535901e21ba6dThe chlor-alkali process: Work in ProgressLakshmanan, Shyam; Murugesan, ThanapalanClean Technologies and Environmental Policy (2014), 16 (2), 225-234CODEN: CTEPAI; ISSN:1618-954X. (Springer)A review. The chlor-alkali process has come a long way from the days of the diaphragm and mercury cell process to the present membrane cell process, with huge redn. in power consumption and hence its carbon footprint. Although there is redn. in the release of highly toxic mercury to the environment, there is increased release of less harmful substances such as chloride and chlorate because the membrane cell is less tolerant to contaminants, and hence requires higher purity brine. The technol. providers have continued to improve upon the process to reduce power consumption and to reduce the plant's footprint. This review looks briefly at the three technologies and attempts to look at where we currently are at. All new chlor-alkali plants being built are of the membrane process. This review mentions some of the areas where improvements can be made to the membrane process.
- 3Crook, J.; Mousavi, A. The Chlor-Alkali Process: A Review of History and Pollution. Environ. Forensics 2016, 17, 211– 217, DOI: 10.1080/15275922.2016.1177755Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XptFWiu7w%253D&md5=abd4cd643cfe79f26ee0d7367c229035The chlor-alkali process: A review of history and pollutionCrook, Jedidiah; Mousavi, AliyarEnvironmental Forensics (2016), 17 (3), 211-217CODEN: EFNOAI; ISSN:1527-5922. (Taylor & Francis, Inc.)The chlor-alkali process is a widely used electrolytic process that yields chlorine and caustic soda. It has been in use since the 19th century and is a primary industry in the United States, Western Europe, and Japan. There are three primary electrolytic processes for producing chlorine and caustic soda: the diaphragm cell process, the mercury cell process, and the membrane cell process. The first two have been used for over 100 years; the latter was developed in the past 60. The two oldest methods are used the most throughout the world and have been proven to be the most environmentally unfriendly through their use of asbestos and mercury, resp. The membrane cell process is a superior method in its energy efficiency and lack of harmful chems. This article reviews the history of each method, addresses changes in its modern technol. and use, and discusses the emissions and outputs of the processes.
- 4Lewis, N. S. Toward Cost-Effective Solar Energy Use. Science 2007, 315, 798– 801, DOI: 10.1126/science.1137014Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhsVShsrs%253D&md5=cc048d85ee8244f9d0d58802cc124395Toward Cost-Effective Solar Energy UseLewis, Nathan S.Science (Washington, DC, United States) (2007), 315 (5813), 798-801CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)A review. At present, solar energy conversion technologies face cost and scalability hurdles in the technologies required for a complete energy system. To provide a truly widespread primary energy source, solar energy must be captured, converted, and stored in a cost-effective fashion. New developments in nanotechnol., biotechnol., and the materials and phys. sciences may enable step-change approaches to cost-effective, globally scalable systems for solar energy use.
- 5Katsounaros, I.; Cherevko, S.; Zeradjanin, A. R.; Mayrhofer, K. J. J. Oxygen Electrochemistry as a Cornerstone for Sustainable Energy Conversion. Angew. Chem., Int. Ed. 2014, 53, 102– 121, DOI: 10.1002/anie.201306588Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFSkurvO&md5=2cf6c456485e619aa79750c752a4cf96Oxygen Electrochemistry as a Cornerstone for Sustainable Energy ConversionKatsounaros, Ioannis; Cherevko, Serhiy; Zeradjanin, Aleksandar R.; Mayrhofer, Karl J. J.Angewandte Chemie, International Edition (2014), 53 (1), 102-121CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A review; electrochem. will play a vital role in creating sustainable energy solns. in the future, particularly for the conversion and storage of elec. into chem. energy in electrolysis cells, and the reverse conversion and utilization of the stored energy in galvanic cells. The common challenge in both processes is the development of-preferably abundant-nanostructured materials that can catalyze the electrochem. reactions of interest with a high rate over a sufficiently long period of time. An overall understanding of the related processes and mechanisms occurring under the operation conditions is a necessity for the rational design of materials that meet these requirements. A promising strategy to develop such an understanding is the investigation of the impact of material properties on reaction activity/selectivity and on catalyst stability under the conditions of operation, as well as the application of complementary in situ techniques for the investigation of catalyst structure and compn.
- 6Fauvarque, J. The Chlorine Industry. Pure Appl. Chem. 1996, 68, 1713– 1720, DOI: 10.1351/pac199668091713Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XlvFSqt7c%253D&md5=2eb6ac463af7279bab685f72d71bb442The chlorine industryFauvarque, JacquelinePure and Applied Chemistry (1996), 68 (9), 1713-1720CODEN: PACHAS; ISSN:0033-4545. (Blackwell)A review with 8 refs. Numerous products, such as polymers, chems. or pharmaceuticals and ultra-pure metals, which often do not actually contain chlorine, are produced using either chlorine or its derivs. They are essential in all industrial sectors and in our daily lives. New chlorine prodn. units have adopted the membrane electrolytic process, but the century-old diaphragm and mercury processes retain their high-performance characteristics when appropriately modernized and improved.
- 7Euro Chlor. Chlor-alkali Industry Review 2017/2018, Manufacturing & Applications, https://chlorineindustryreview.com/manufacturing-applications/ (accessed on November 28, 2018).Google ScholarThere is no corresponding record for this reference.
- 8Koper, M. T. M. Thermodynamic Theory of Multi-Electron Transfer Reactions: Implications for Electrocatalysis. J. Electroanal. Chem. 2011, 660, 254– 260, DOI: 10.1016/j.jelechem.2010.10.004Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXht1WmurbO&md5=721e205053e181f126a3bcc25f219c59Thermodynamic theory of multi-electron transfer reactions: Implications for electrocatalysisKoper, Marc T. M.Journal of Electroanalytical Chemistry (2011), 660 (2), 254-260CODEN: JECHES; ISSN:1873-2569. (Elsevier B.V.)This paper summarizes the thermodn. theory of multi-electron transfer reactions and its implications for electrocatalysis. The fundamental differences between catalyzing reactions involving the transfer of one electron or no catalytic intermediates, two electron transfers with one catalytic intermediate, two electron transfer with two catalytic intermediates, and more than two electron transfers with more than one intermediate are discussed. These different classes of reactions imply different optimization problems for finding the best catalyst, dictated primarily by the thermodn. of binding of the catalytic intermediates. The application of this theory to H evolution and oxidn., O evolution and redn., and CO2 redn., is discussed.
- 9Trasatti, S. Electrocatalysis: Understanding the Success of DSA®. Electrochim. Acta 2000, 45, 2377– 2385, DOI: 10.1016/S0013-4686(00)00338-8Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXjvFymur0%253D&md5=b013814cb2d58f21970cab92f3766276Electrocatalysis: understanding the success of DSATrasatti, S.Electrochimica Acta (2000), 45 (15-16), 2377-2385CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Science Ltd.)A review with 92 refs. concerning dimensionally stable anodes fundamentals and technol. is presented. The "legend" of DSA (Dimensionally Stable Anodes), one of the greatest technol. breakthrough of the past 50 yr of electrochem., is reviewed with the aim to emphasize the reasons for their success. In this respect, the industrial success, which came first, was due to factors differing from those responsible for the successive boom of fundamental research on the same materials. This article scrutinizes these factors highlighting the aspects which make these materials so much intriguing.
- 10Moussallem, I.; Jörissen, J.; Kunz, U.; Pinnow, S.; Turek, T. Chlor-Alkali Electrolysis with Oxygen Depolarized Cathodes: History, Present Status and Future Prospects. J. Appl. Electrochem. 2008, 38, 1177– 1194, DOI: 10.1007/s10800-008-9556-9Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXptlWjtrs%253D&md5=692153cd985008879000a9c3822c4290Chlor-alkali electrolysis with oxygen depolarized cathodes: history, present status and future prospectsMoussallem, Imad; Joerissen, Jakob; Kunz, Ulrich; Pinnow, Stefan; Turek, ThomasJournal of Applied Electrochemistry (2008), 38 (9), 1177-1194CODEN: JAELBJ; ISSN:0021-891X. (Springer)A review. The historical development, current status and future prospects of chlor-alkali electrolysis with oxygen depolarized cathodes (ODCs) are summarized. Over the last decades, membrane chlor-alkali technol. has been optimized to such an extent that no substantial redn. of the energy demand can be expected from further process modifications. However, replacement of the hydrogen evolving cathodes in the classical membrane cells by ODCs allows for redn. of the cell voltage and correspondingly the energy consumption of up to 30%. This replacement requires the development of appropriate cathode materials and novel electrolysis cell designs. Due to their superior long-term stability, ODCs based on silver catalysts are very promising for oxygen redn. in concd. NaOH solns. Finite-gap falling film cells appear to be the tech. most mature design among the several ODC electrolysis cells that have been investigated.
- 11Jung, J.; Postels, S.; Bardow, A. Cleaner Chlorine Production Using Oxygen Depolarized Cathodes? A Life Cycle Assessment. J. Cleaner Prod. 2014, 80, 46– 56, DOI: 10.1016/j.jclepro.2014.05.086Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtVKhsbfL&md5=6ce2c4db81210720bb86424e9113eb08Cleaner chlorine production using oxygen depolarized cathodes? A life cycle assessmentJung, Johannes; Postels, Sarah; Bardow, AndreJournal of Cleaner Production (2014), 80 (), 46-56CODEN: JCROE8; ISSN:0959-6526. (Elsevier Ltd.)Chlorine and caustic soda are two indispensable chem. commodities co-produced in the so-called chlor-alkali electrolysis. Chlor-alkali electrolysis is today a target for cleaner prodn. because of its large electricity demand causing considerable environmental impacts. The electricity demand of chlor-alkali electrolysis can be reduced by 30% using oxygen depolarized cathodes (ODCs) instead of the std. cathodes (STCs) used today. However, ODCs require addnl. resources and do not produce hydrogen in contrast to existing chlor-alkali plants. This work investigates if the redn. in electricity demand also contributes to cleaner prodn. For this purpose, environmental impacts from chlor-alkali electrolysis using ODCs are compared to the impacts from best available existing chlor-alkali plants using STCs. The life cycle assessment includes manufg., operation and disposal of the plants. To account for utilization of hydrogen from existing chlor-alkali plants, two alternative utilization scenarios are studied: energy recovery by combustion of hydrogen and use of hydrogen as chem. commodity. Seven environmental impact categories are studied in detail using the ReCiPe method. Chlor-alkali electrolysis using ODCs yields lower environmental impacts in up to six environmental impact categories. Plant operation contributes most in six out of seven impact categories. Chlor-alkali electrolysis using ODCs has thus potential to contribute to cleaner prodn. in the chlor-alkali industry.
- 12Wang, X.; Tong, C.; Palazoglu, A.; El-Farra, N. H. Energy Management for the Chlor-Alkali Process with Hybrid Renewable Energy Generation Using Receding Horizon Optimization. In 53rd IEEE Conference on Decision and Control , Los Angeles, CA, December 15–17, 2014; pp 4838– 4843.Google ScholarThere is no corresponding record for this reference.
- 13Trasatti, S. Progress in the Understanding of the Mechanism of Chlorine Evolution at Oxide Electrodes. Electrochim. Acta 1987, 32, 369– 382, DOI: 10.1016/0013-4686(87)85001-6Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXhsVGrtb4%253D&md5=0a0ac5123b10b681827ce9499dffc9e6Progress in the understanding of the mechanism of chlorine evolution at oxide electrodesTrasatti, SergioElectrochimica Acta (1987), 32 (3), 369-82CODEN: ELCAAV; ISSN:0013-4686.A review with 78 refs. is given on the mechanism of Cl2 evolution at such oxides as RuO2, RuO2 + TiO2, Co3O4 and NiCo2O4. After introductory general thermodn. and kinetic considerations, the possible factors which can distort the kinetic measurements of Cl2 evolution at oxide electrodes, giving rise to mistaken mechanisms, are analyzed as resulting from a retrospective anal. of the literature. Such factors include: mixed potentials, porosity, removal of produced Cl2, bubble formation, support passivation, morphol. and compn. of the active layer, ion sp. adsorption, and pH effects. In the light of the insight gained step-by-step on the possible interference by the above exptl. factors, the various mechanism proposals are reviewed, mainly chronol., to highlight the conceptual and exptl. progress made in this field in the past 15 yr. Conclusions are finally drawn which enable some possible topics for further research in this area to be discussed.
- 14Duby, P. The History of Progress in Dimensionally Stable Anodes. JOM 1993, 45, 41– 43, DOI: 10.1007/BF03222350Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXitVWisr0%253D&md5=9d35cc062c68fd726c518203807c237eThe history of progress in dimensionally stable anodesDuby, PaulJOM (1993), 45 (3), 41-3CODEN: JOMMER; ISSN:1047-4838.A review with 50 refs. is presented. A brief history is provided of dimensionally stable anodes by reviewing innovations in the chlor-alkali industry, electroplating, and electrowinning. These anodes are attractive for numerous reasons (e.g., long life and reduced energy consumption), but they must still overcome the hurdle of cost to gain wider acceptance for applications in the metallurgical process industries.
- 15Karlsson, R. K. B.; Cornell, A. Selectivity between Oxygen and Chlorine Evolution in the Chlor-Alkali and Chlorate Processes. Chem. Rev. 2016, 116, 2982– 3028, DOI: 10.1021/acs.chemrev.5b00389Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XisFahsLk%253D&md5=bf845f24c741b49db6a0e169caf132bdSelectivity between Oxygen and Chlorine Evolution in the Chlor-Alkali and Chlorate ProcessesKarlsson, Rasmus K. B.; Cornell, AnnChemical Reviews (Washington, DC, United States) (2016), 116 (5), 2982-3028CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. Cl gas and Na chlorate are two base chems. produced through electrolysis of NaCl brine which find uses in many areas of industrial chem. Although the industrial prodn. of these chems. started over 100 years ago, there are still factors that limit the energy efficiencies of the processes. This review focuses on the unwanted prodn. of O gas, which decreases the charge yield by up to 5%. Understanding the factors that control the rate of O prodn. requires understanding of both chem. reactions occurring in the electrolyte, as well as surface reactions occurring on the anodes. The dominant anode material used in chlorate and chlor-alkali prodn. is the dimensionally stable anode (DSA), Ti coated by a mixed oxide of RuO2 and TiO2. Although the selectivity for Cl evolution on DSA is high, the fundamental reasons for this high selectivity are just now becoming elucidated. This review summarizes the research, since the early 1900s until today, concerning the selectivity between Cl and O evolution in chlorate and chlor-alkali prodn. It covers exptl. as well as theor. studies and highlights the relations between process conditions, electrolyte compn., the material properties of the anode, and the selectivity for O formation.
- 16Jefferson, M. A Renewable Energy Future? In Handbook on Energy and Climate Change; Edward Elgar Publishing, 2013; Vol. 285, pp 254– 269.Google ScholarThere is no corresponding record for this reference.
- 17Zeng, K.; Zhang, D. Recent Progress in Alkaline Water Electrolysis for Hydrogen Production and Applications. Prog. Energy Combust. Sci. 2010, 36, 307– 326, DOI: 10.1016/j.pecs.2009.11.002Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXis1OqtLw%253D&md5=fb3b70cabefcb81fd4fc2ab3a228a3fbRecent progress in alkaline water electrolysis for hydrogen production and applicationsZeng, Kai; Zhang, DongkeProgress in Energy and Combustion Science (2010), 36 (3), 307-326CODEN: PECSDO; ISSN:0360-1285. (Elsevier Ltd.)A review. Alk. water electrolysis is one of the easiest methods for hydrogen prodn., offering the advantage of simplicity. The challenges for widespread use of water electrolysis are to reduce energy consumption, cost and maintenance and to increase reliability, durability and safety. This literature review examines the current state of knowledge and technol. of hydrogen prodn. by water electrolysis and identifies areas where R&D effort is needed in order to improve this technol. Following an overview of the fundamentals of alk. water electrolysis, an elec. circuit analogy of resistances in the electrolysis system is introduced. The resistances are classified into three categories, namely the elec. resistances, the reaction resistances and the transport resistances. This is followed by a thorough anal. of each of the resistances, by means of thermodn. and kinetics, to provide a scientific guidance to minimising the resistance in order to achieve a greater efficiency of alk. water electrolysis. The thermodn. anal. defines various electrolysis efficiencies based on theor. energy input and cell voltage, resp. These efficiencies are then employed to compare different electrolysis cell designs and to identify the means to overcome the key resistances for efficiency improvement. The kinetic anal. reveals the dependence of reaction resistances on the alk. concn., ion transfer, and reaction sites on the electrode surface, the latter is detd. by the electrode materials. A quant. relationship between the cell voltage components and c.d. is established, which links all the resistances and manifests the importance of reaction resistances and bubble resistances. The important effect of gas bubbles formed on the electrode surface and the need to minimise the ion transport resistance are highlighted. The historical development and continuous improvement in the alk. water electrolysis technol. are examd. and different water electrolysis technologies are systematically compared using a set of the practical parameters derived from the thermodn. and kinetic analyses. In addn. to the efficiency improvements, the needs for redn. in equipment and maintenance costs, and improvement in reliability and durability are also established. The future research needs are also discussed from the aspects of electrode materials, electrolyte additives and bubble management, serving as a comprehensive guide for continuous development of the water electrolysis technol.
- 18Man, I. C.; Su, H. Y.; Calle-Vallejo, F.; Hansen, H. A.; Martínez, J. I.; Inoglu, N. G.; Kitchin, J.; Jaramillo, T. F.; Nørskov, J. K.; Rossmeisl, J. Universality in Oxygen Evolution Electrocatalysis on Oxide Surfaces. ChemCatChem 2011, 3, 1159– 1165, DOI: 10.1002/cctc.201000397Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotFyjsb0%253D&md5=f4103e77db6bcd3ba840b6376b33315aUniversality in Oxygen Evolution Electrocatalysis on Oxide SurfacesMan, Isabela C.; Su, Hai-Yan; Calle-Vallejo, Federico; Hansen, Heine A.; Martinez, Jose I.; Inoglu, Nilay G.; Kitchin, John; Jaramillo, Thomas F.; Noerskov, Jens K.; Rossmeisl, JanChemCatChem (2011), 3 (7), 1159-1165CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)Trends in electrocatalytic activity of the O evolution reaction (OER) were studied from a large database of HO* and HOO* adsorption energies on oxide surfaces. The theor. overpotential was calcd. by applying std. d. functional theory in combination with the computational std. H electrode (SHE) model. By the discovery of a universal scaling relation between the adsorption energies of HOO* vs. HO*, it is possible to analyze the reaction free energy diagrams of all the oxides in a general way. This gave rise to an activity volcano that was the same for a wide variety of oxide catalyst materials and a universal descriptor for the O evolution activity, which suggests a fundamental limitation on the max. O evolution activity of planar oxide catalysts.
- 19Fabbri, E.; Schmidt, T. J. Oxygen Evolution Reaction—The Enigma in Water Electrolysis. ACS Catal. 2018, 8, 9765– 9774, DOI: 10.1021/acscatal.8b02712Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhslSgu7%252FM&md5=afd99f985774534b72ffa335f84fbb2fOxygen Evolution Reaction-The Enigma in Water ElectrolysisFabbri, Emiliana; Schmidt, Thomas J.ACS Catalysis (2018), 8 (10), 9765-9774CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)A review is given. We aim at increasing the awareness among the scientific community devoted to progresses in water electrolyzers of the very recent development made in the fundamental understanding of the OER, particularly focusing on the increasing consciousness that several processes actually underpin the evolution of O from a metal oxide catalyst. Traditionally, the OER mechanism on metal oxides has been derived from that on metal catalysts, where the main parameter governing the reaction overpotential is the binding strength of O (or oxygenated species/intermediates) on the catalyst surface following the Sabatier principle: the best catalyst in terms of displaying the min. overpotential binds O on its surface neither too strongly nor too weakly.
- 20Panić, V. V.; Dekanski, A. B.; Milonjić, S. K.; Mišković-Stanković, V. B.; Nikolić, B. Ž. Electrocatalytic Activity of Sol-Gel-Prepared RuO2/Ti Anode in Chlorine and Oxygen Evolution Reactions. Russ. J. Electrochem. 2006, 42, 1055– 1060, DOI: 10.1134/S1023193506100107Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhtVKjtbfK&md5=bbe86d7b76e20e7460edf9c1176e0b4dElectrocatalytic activity of sol-gel-prepared RuO2/Ti anode in chlorine and oxygen evolution reactionsPanic, V. V.; Dekanski, A. B.; Milonjic, S. K.; Miskovic-Stankovic, V. B.; Nikolic, B. Z.Russian Journal of Electrochemistry (2006), 42 (10), 1055-1060CODEN: RJELE3; ISSN:1023-1935. (MAIK Nauka/Interperiodica Publishing)Electrocatalytic properties of RuO2/Ti anode with different coating masses, which were prepd. by the alkoxide sol-gel procedure, were studied in Cl and O evolution reactions by polarization measurements and electrochem. impedance spectroscopy in H2SO4 and NaCl electrolytes. According to polarization measurements, the activity of anodes at overpotentials <100 mV is independent of coating mass. However, impedance measurements >100 mV reveal changes in the activity of anodes in Cl evolution reaction for different coating masses. The diffusion limitations related to the evolved Cl are registered in low-frequency domain at 1.10 V (SCE), diminishing with the increase in potential to the 1.15 V (SCE). The obsd. impedance behavior is discussed with respect to the activity model for activated Ti anodes in Cl evolution reaction involving formation of gas channels within porous coating structure. Gas channels enhance the mass transfer rate similarly to the forced convection, which also increases the activity of anode. This is more pronounced for the anode of greater coating mass due to its more compact surface structure. The more compact structure appears to be beneficial for gas channels formation.
- 21Hoseinieh, S. M.; Ashrafizadeh, F.; Maddahi, M. H. A Comparative Investigation of the Corrosion Behavior of RuO[Sub 2]–IrO[Sub 2]–TiO[Sub 2] Coated Titanium Anodes in Chloride Solutions. J. Electrochem. Soc. 2010, 157, E50, DOI: 10.1149/1.3294569Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXjt1amsbw%253D&md5=bd7e7d7886dd3831fbdc3b8b10193a11A Comparative Investigation of the Corrosion Behavior of RuO2-IrO2-TiO2 Coated Titanium Anodes in Chloride SolutionsHoseinieh, S. M.; Ashrafizadeh, F.; Maddahi, M. H.Journal of the Electrochemical Society (2010), 157 (4), E50-E56CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Deactivation of a RuO2-IrO2-TiO2/Ti oxide anode was studied during an accelerated life test in 0.5 mol dm-3 NaCl using cyclic voltammetry, electrochem. impedance spectroscopy, and SEM/energy-dispersive x-ray anal. The variations in double-layer capacitance, film resistance, and charge-transfer resistance during electrolysis were recorded at different potentials. A comprehensive deactivation mechanism of Ti anodes is proposed by the growth of an insulating TiO2 layer at the coating-substrate interface due to the Ti substrate oxidn. The impedance interpretation of the deactivation mechanism in chloride solns. changes with an increase in potential due to an increase in oxygen evolution on the anode surface at higher potentials.
- 22Shao, D.; Yan, W.; Cao, L.; Li, X.; Xu, H. High-Performance Ti/Sb–SnO2/Pb3O4 Electrodes for Chlorine Evolution: Preparation and Characteristics. J. Hazard. Mater. 2014, 267, 238– 244, DOI: 10.1016/j.jhazmat.2013.12.064Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXis1Wqu7o%253D&md5=4ec2c535e138603bd0093ed6613c02f7High-performance Ti/Sb-SnO2/Pb3O4 electrodes for chlorine evolution: Preparation and characteristicsShao, Dan; Yan, Wei; Cao, Lu; Li, Xiaoliang; Xu, HaoJournal of Hazardous Materials (2014), 267 (), 238-244CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)Chlorine evolution via electrochem. approach has wide application prospects in drinking water disinfection and wastewater treatment fields. Dimensional stable anodes used for chlorine evolution should have high stability and adequate chlorine evolution efficiency. Thus a novel and cost-effective Ti/Sb-SnO2/Pb3O4 electrode was developed. The physicochem. and electrochem. properties as well as the chlorine evolution performances of the electrodes were investigated. The electrocatalytic activity and deactivation course of the electrodes were also explored. Results showed that this novel electrode had strong chlorine evolution ability with high current efficiency ranging from 87.3% to 93.4% depending on the operational conditions. The accelerated service life of Ti/Sb-SnO2/Pb3O4 electrode could reach 180 h at a c.d. of 10,000 A m-2 in 0.5 mol L-1 H2SO4. During the electrolysis process, it was found that the conversion of Pb3O4 into β-PbO2 happened gradually on the electrode surface, which not only inhibited the leakage of hazardous Pb2+ ion but also increased the anti-corrosion capacity of the electrode effectively.
- 23Fujimura, K.; Izumiya, K.; Kawashima, A.; Akiyama, E.; Habazaki, H.; Kumagai, N.; Hashimoto, K. Anodically Deposited Manganese-Molybdenum Oxide Anodes with High Selectivity for Evolving Oxygen in Electrolysis of Seawater. J. Appl. Electrochem. 1999, 29, 769– 775, DOI: 10.1023/A:1003492009263Google ScholarThere is no corresponding record for this reference.
- 24Vos, J. G.; Wezendonk, T. A.; Jeremiasse, A. W.; Koper, M. T. M. MnOx/IrOx as Selective Oxygen Evolution Electrocatalyst in Acidic Chloride Solution. J. Am. Chem. Soc. 2018, 140, 10270– 10281, DOI: 10.1021/jacs.8b05382Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtlCnt7vI&md5=10e93065fa3c8c339b1aa6b146b9608aMnOx/IrOx as Selective Oxygen Evolution Electrocatalyst in Acidic Chloride SolutionVos, Johannes G.; Wezendonk, Tim A.; Jeremiasse, Adriaan W.; Koper, Marc T. M.Journal of the American Chemical Society (2018), 140 (32), 10270-10281CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The oxygen evolution reaction (OER) and chlorine evolution reaction (CER) are electrochem. processes with high relevance to water splitting for (solar) energy conversion and industrial prodn. of commodity chems., resp. Carrying out the two reactions sep. is challenging, since the catalytic intermediates are linked by scaling relations. Optimizing the efficiency of OER over CER in acidic media has proven esp. difficult. In this regard, the OER vs. CER selectivity of manganese oxide (MnOx), a known OER catalyst is investigated. Thin films (∼5-20 nm) of MnOx were electrodeposited on glassy carbon-supported hydrous iridium oxide (IrOx/GC) in aq. chloride solns. of pH ∼0.9. Using rotating ring-disk electrode voltammetry and online electrochem. mass spectrometry, it was found that deposition of MnOx onto IrOx decreases the CER selectivity of the system in the presence of 30 mM Cl- from 86% to < 7%, making it a highly OER-selective catalyst. Detailed studies of the CER mechanism and ex-situ structure studies using SEM, TEM, and XPS suggest that the MnOx film is in fact not a catalytically active phase, but functions as a permeable overlayer that disfavors the transport of chloride ions.
- 25Trasatti, S. Electrocatalysis in the Anodic Evolution of Oxygen and Chlorine. Electrochim. Acta 1984, 29, 1503– 1512, DOI: 10.1016/0013-4686(84)85004-5Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXmvFWqtQ%253D%253D&md5=3293b9b686c89687a6f73387afb26de1Electrocatalysis in the anodic evolution of oxygen and chlorineTrasatti, S.Electrochimica Acta (1984), 29 (11), 1503-12CODEN: ELCAAV; ISSN:0013-4686.Requisites for electrode materials to be suitable for technol. applications are outlined and discussed. Oxides with metallic or quasi-metallic cond. meet these requirements best. Most of these electrodes are prepd. by thermal procedures. The temp. of prepn. affects the catalytic activity through the surface area and the chem. compn. (nonstoichiometry). The covariation of these parameters is best followed in situ by voltammetric curves and point of zero charge measurements. Examples are given for pure RuO2, IrO2, Co3O4 and IrO2 + RuO2 mixts. Kinetic and mechanistic details are discussed for O evolution on RuO2, IrO2 and Co3O4 and for Cl evolution on RuO2 and Co3O4. Finally the electrocatalytic properties of different oxides are correlated with the energy change involved in the lower → higher valency state transition. Exptl. data for both O and Cl evolution can thus be organized into a volcano curve enabling predictive interpolations to be made.
- 26Hansen, H. A.; Man, I. C.; Studt, F.; Abild-Pedersen, F.; Bligaard, T.; Rossmeisl, J. Electrochemical Chlorine Evolution at Rutile Oxide (110) Surfaces. Phys. Chem. Chem. Phys. 2010, 12, 283– 290, DOI: 10.1039/B917459AGoogle Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhsFektbbJ&md5=e4a886eb0187ffd787c43d2b301e8ef0Electrochemical chlorine evolution at rutile oxide (110) surfacesHansen, Heine A.; Man, Isabela C.; Studt, Felix; Abild-Pedersen, Frank; Bligaard, Thomas; Rossmeisl, JanPhysical Chemistry Chemical Physics (2010), 12 (1), 283-290CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)Based on d. functional theory (DFT) calcns. the authors study the electrochem. chlorine evolution reaction on rutile (110) oxide surfaces. First the authors construct the Pourbaix surface diagram for IrO2 and RuO2, and from this the chlorine evolution reaction intermediates and identify the lowest overpotential at which all elementary reaction steps in the chlorine evolution reaction are downhill in free energy were found. This condition is then used as a measure for catalytic activity. Linear scaling relations between the binding energies of the intermediates and the oxygen binding energies at cus-sites are established for MO2 (M being Ir, Ru, Pt, Ti). The linear relations form the basis for constructing a generalized surface phase diagram where 2 parameters, the potential and the binding energy of oxygen, are needed to det. the surface compn. The authors calc. the catalytic activity as function of the oxygen binding energy, giving rise to a Sabatier volcano. By combining the surface phase diagram and the volcano describing the catalytic activity, the reaction mechanism differs depending on catalyst material. The flexibility in reaction path means that the chlorine evolution activity is high for a wide range of oxygen binding energies. The required overpotential for chlorine evolution is lower than the overpotential necessary for oxygen evolution.
- 27Abbott, D. F.; Petrykin, V.; Okube, M.; Bastl, Z.; Mukerjee, S.; Krtil, P. Selective Chlorine Evolution Catalysts Based on Mg-Doped Nanoparticulate Ruthenium Dioxide. J. Electrochem. Soc. 2015, 162, H23– H31, DOI: 10.1149/2.0541501jesGoogle Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitVCrs7%252FO&md5=5e6cba0928045d7c7b39f0769e4782bdSelective Chlorine Evolution Catalysts Based on Mg-Doped Nanoparticulate Ruthenium DioxideAbbott, Daniel F.; Petrykin, Valery; Okube, Maki; Bastl, Zdenk; Mukerjee, Sanjeev; Krtil, PetrJournal of the Electrochemical Society (2015), 162 (1), H23-H31CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Nanocryst. Mg-doped ruthenium dioxide catalysts with the formula Ru1-xMgxO2 (0 ≤ x ≤ 20) were synthesized by the spray-freezing freeze-drying technique. Synthesized materials are of nanoparticulate nature and show a single phase diffraction pattern conforming to a tetragonal oxide of the rutile structural type. Magnesium ions are not distributed homogeneously in the material, but exist in Mg-rich clusters as shown by X-ray absorption spectroscopy. The refinement of the Mg EXAFS functions for materials with low Mg content shows that the magnesium rich clusters contain Mg in a highly strained environment similar to that of the rutile-type structure. The Mg environment shifts to an ilmenite-type inclusion when Mg occupies more than 10% of all cationic positions. All Mg modified materials are active in oxygen evolution and chlorine evolution reactions. Although the Mg contg. catalysts show lower overall activities compared with the non-doped ruthenia, they feature enhanced selectivity toward the chlorine evolution process, which is attributed primarily to the opening of a reaction pathway for chlorine evolution assocd. with presence of Mg modified active sites.
- 28Exner, K. S.; Anton, J.; Jacob, T.; Over, H. Controlling Selectivity in the Chlorine Evolution Reaction over RuO 2 -Based Catalysts. Angew. Chem., Int. Ed. 2014, 53, 11032– 11035, DOI: 10.1002/anie.201406112Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVWqsbrL&md5=382b59a5a1f1ca5b371990ef737695ceControlling selectivity in the chlorine evolution reaction over RuO2-based catalystsExner, Kai S.; Anton, Josef; Jacob, Timo; Over, HerbertAngewandte Chemie, International Edition (2014), 53 (41), 11032-11035CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)In the industrially important Chlor-Alkali process, the chlorine evolution reaction (CER) over a ruthenium dioxide (RuO2) catalyst competes with the oxygen evolution reaction (OER). This selectivity issue is elucidated on the microscopic level with the single-cryst. model electrode RuO2(110) by employing d. functional theory (DFT) calcns. in combination with the concept of volcano plots. We demonstrate that one monolayer of TiO2(110) supported on RuO2(110) enhances the selectivity towards the CER by several orders of magnitudes, while preserving the high activity for the CER. This win-win situation is attributed to the different slopes of the volcano curves for the CER and OER.
- 29Exner, K. S.; Anton, J.; Jacob, T.; Over, H. Full Kinetics from First Principles of the Chlorine Evolution Reaction over a RuO 2 (110) Model Electrode. Angew. Chem., Int. Ed. 2016, 55, 7501– 7504, DOI: 10.1002/anie.201511804Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xnslaisbk%253D&md5=8c0f3edbb62734f04d1406d686a49445Full Kinetics from First Principles of the Chlorine Evolution Reaction over a RuO2(110) Model ElectrodeExner, Kai S.; Anton, Josef; Jacob, Timo; Over, HerbertAngewandte Chemie, International Edition (2016), 55 (26), 7501-7504CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Current progress in modern electrocatalysis research is spurred by theory, frequently based on ab initio thermodn., where the stable reaction intermediates at the electrode surface are identified, while the actual energy barriers are ignored. This approach is popular in that a simple tool is available for searching for promising electrode materials. However, thermodn. alone may be misleading to assess the catalytic activity of an electrochem. reaction as the authors exemplify with the Cl evolution reaction (CER) over a RuO2(110) model electrode. The full procedure is introduced, starting from the stable reaction intermediates, computing the energy barriers, and finally performing microkinetic simulations, all performed under the influence of the solvent and the electrode potential. Full kinetics from 1st-principles allows the rate-detg. step in the CER to be identified and the exptl. obsd. change in the Tafel slope to be explained.
- 30Sohrabnejad-Eskan, I.; Goryachev, A.; Exner, K. S.; Kibler, L. A.; Hensen, E. J. M.; Hofmann, J. P.; Over, H. Temperature-Dependent Kinetic Studies of the Chlorine Evolution Reaction over RuO 2 (110) Model Electrodes. ACS Catal. 2017, 7, 2403– 2411, DOI: 10.1021/acscatal.6b03415Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXivFSqt74%253D&md5=99bb72640b1b2e973e79b4bd43904465Temperature-Dependent Kinetic Studies of the Chlorine Evolution Reaction over RuO2(110) Model ElectrodesSohrabnejad-Eskan, Iman; Goryachev, Andrey; Exner, Kai S.; Kibler, Ludwig A.; Hensen, Emiel J. M.; Hofmann, Jan P.; Over, HerbertACS Catalysis (2017), 7 (4), 2403-2411CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)Ultrathin single-cryst. RuO2(110) films supported on Ru(0001) are employed as model electrodes to ext. kinetic information about the industrially important Cl evolution reaction (CER) in a 5M concd. NaCl soln. under well-defined electrochem. conditions and variable temps. A combination of chronoamperometry (CA) and online electrochem. mass spectrometry (OLEMS) expts. provides insight into the selectivity issue: At pH = 0.9, the CER dominates over O evolution, whereas at pH = 3.5, O evolution and other parasitic side reactions contribute mostly to the total c.d. From temp.-dependent CA data for pH = 0.9, the authors det. the apparent free activation energy of the CER over RuO2(110) to be 0.91 eV, which compares reasonably well with the theor. value of 0.79 eV derived from 1st-principles microkinetics. The exptl. detd. apparent free activation energy of 0.91 eV is considered as a benchmark for assessing future improved theor. modeling from 1st principles.
- 31Lassali, T. A. F.; Boodts, J. F. C.; Trasatti, S. Electrocatalytic Activity of the Ternary Oxide Ru0.3PtxTi(0.7 — x)O2 for Chlorine Evolution. Electrochim. Acta 1994, 39, 1545– 1549, DOI: 10.1016/0013-4686(94)85133-6Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXmtFGktb0%253D&md5=2c8087570dc2a55036ac1128a9e44eefElectrocatalytic activity of the ternary oxide Ru0.3PtxTi(0.7-x)O2 for chlorine evolutionLassali, T. A. F.; Boodts, J. F. C.; Trasatti, S.Electrochimica Acta (1994), 39 (11-12), 1545-9CODEN: ELCAAV; ISSN:0013-4686.The electrocatalytic activity of ternary oxides of nominal compn. Ru0.3PtxTi(0.7-x)O2 was investigated over the whole compn. range using chlorine evolution as a model reaction. Compn. was changed in 10 mol.% steps and the surface was characterized in situ by cyclic voltammetry (cv). Surface properties are governed by the RuOx features at low PtOx content (<30%), while at higher PtOx content they are controlled by PtOx. A single Tafel line of 31 ± 1 mV slope was obsd. at all compns. The reaction order is zero with respect to H+ and 1.5 with respect to Cl-. At high PtOx content and low Cl- concn. (<1 mol dm-3) O2 formation appears to control the gas evolution process. An inhibition of Cl2 evolution is obsd. for PtOx ≥ 30 mol.%. On the whole, morphol. effects predominate over electronic effects.
- 32Macounová, K. M.; Makarova, M.; Jirkovský, J. S.; Franc, J.; Krtil, P. Parallel Oxygen and Chlorine Evolution on Ru1–xNixO2–y Nanostructured Electrodes. Electrochim. Acta 2008, 53, 6126– 6134, DOI: 10.1016/j.electacta.2007.11.014Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXntFGhsb8%253D&md5=9dd753c965e53ff07d2f771a3363d3a2Parallel oxygen and chlorine evolution on Ru1-xNixO2-y nanostructured electrodesMacounova, Katerina; Makarova, Marina; Jirkovsky, Jakub; Franc, Jiri; Krtil, PetrElectrochimica Acta (2008), 53 (21), 6126-6134CODEN: ELCAAV; ISSN:0013-4686. (Elsevier B.V.)Nanocryst. materials with chem. compn. corresponding to Ru1-xNixO2-y (0.02 < x < 0.30) were prepd. by sol-gel approach. Substitution of Ru by Ni has a minor effect on the structural characteristics extractable from x-ray diffraction patterns. The electrocatalytic behavior of Ru1-xNixO2-y with respect to parallel O (O evolution reaction, OER) and Cl (Cl evolution reaction, CER) evolution in acidic media was studied by voltammetry combined with differential electrochem. mass spectrometry (DEMS). The DEMS data indicate a significant decrease of the over-voltage for Cl evolution with respect to that of pure RuO2. The O evolution is slightly hindered. The increasing Ni content affects the electrode material activity and selectivity. The overall material's activity increases with increasing Ni content. The activity of the Ru-Ni-O oxides towards Cl2 evolution shows a distinguished max. for material contg. 10% of Ni. Further increase of Ni content results in suppression of Cl2 evolution in favor of O2 evolution. A model reflecting the cation-cation interactions resulting from Ni-doping is proposed to explain the obsd. trends in electrocatalytic behavior.
- 33Petrykin, V.; Macounová, K. M.; Okube, M.; Mukerjee, S.; Krtil, P. Local Structure of Co Doped RuO2 Nanocrystalline Electrocatalytic Materials for Chlorine and Oxygen Evolution. Catal. Today 2013, 202, 63– 69, DOI: 10.1016/j.cattod.2012.03.075Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XntVyrurw%253D&md5=b84968444c0e8740adb917cbb50e6005Local structure of Co doped RuO2 nanocrystalline electrocatalytic materials for chlorine and oxygen evolutionPetrykin, Valery; Macounova, Katerina; Okube, Maki; Mukerjee, Sanjeev; Krtil, PetrCatalysis Today (2013), 202 (), 63-69CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Nano-particulate Co doped ruthenium dioxide electrocatalysts of the general formula Ru1-xCoxO2-y (0 < x 0.3) were prepd. by a co-pptn. method. The electrocatalysts with x < 0.2 conform to a single phase nano-cryst. materials. On the local level the Co forms clusters dispersed in the original rutile-like matrix. The local environment of the Co conforms to a rutile model which preserves the cationic arrangement but suppresses the probability of the Ru-Ru and Co-Co neighbors along the shortest metal-metal bonds. The electrocatalytic activity of the synthesized Ru1-xCoxO2-y materials in oxygen evolution is comparable with that of the non-doped ruthenium dioxide and little depends on the actual Co content. In presence of chlorides the Co doped materials are more selective towards oxygen evolution compared with the non doped ruthenia. The enhanced oxygen evolution in the case of Co doped electrocatalysts can be attributed to a chem. recombination of surface confined oxo-species. The selectivity shift towards oxygen evolution can be linked with limited activity of the Ru1-xCoxO2-y materials in the chlorine evolution reaction which seems to be relatively weakly dependent on the chloride concn.
- 34Consonni, V.; Trasatti, S.; Pollak, F. H.; O’Grady, W. E. Mechanism of Chlorine Evolution on Oxide Anodes: Study of PH Effects. J. Electroanal. Chem. Interfacial Electrochem. 1987, 228, 393– 406, DOI: 10.1016/0022-0728(87)80119-5Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXls1eqs7g%253D&md5=2535558283f0b32b94ac4268ce77f6dbMechanism of chlorine evolution on oxide anodes. Study of pH effectsConsonni, V.; Trasatti, S.; Pollak, F.; O'Grady, W. E.Journal of Electroanalytical Chemistry and Interfacial Electrochemistry (1987), 228 (1-2), 393-406CODEN: JEIEBC; ISSN:0022-0728.The Cl evolution on oxides such as polycryst. RuO2, IrO2, Co3O4, RuO2 + IrO2 and the (110) face of RuO2 single crystals proceeds with the same Tafel slope of 40 mV and the same reaction order of 1 with respect to Cl-. On all oxides, except RuO2 (110), the reaction rate is depressed by the acidity, which results in a reaction order with respect to H+ of -1 for IrO2 and Co3O4, of 0 for RuO2 (110) and variable for RuO2. Possible reasons for pH effects are discussed, and several plausible reaction mechanisms are examd.
- 35Spöri, C.; Kwan, J. T. H.; Bonakdarpour, A.; Wilkinson, D. P.; Strasser, P. The Stability Challenges of Oxygen Evolving Catalysts: Towards a Common Fundamental Understanding and Mitigation of Catalyst Degradation. Angew. Chem., Int. Ed. 2017, 56, 5994– 6021, DOI: 10.1002/anie.201608601Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2snit1Citw%253D%253D&md5=26d32ba6c91db37de4e26e6e5e525261The Stability Challenges of Oxygen Evolving Catalysts: Towards a Common Fundamental Understanding and Mitigation of Catalyst DegradationSpori Camillo; Strasser Peter; Kwan Jason Tai Hong; Bonakdarpour Arman; Wilkinson David P; Strasser PeterAngewandte Chemie (International ed. in English) (2017), 56 (22), 5994-6021 ISSN:.This Review addresses the technical challenges, scientific basis, recent progress, and outlook with respect to the stability and degradation of catalysts for the oxygen evolution reaction (OER) operating at electrolyzer anodes in acidic environments with an emphasis on ion exchange membrane applications. First, the term "catalyst stability" is clarified, as well as current performance targets, major catalyst degradation mechanisms, and their mitigation strategies. Suitable in situ experimental methods are then evaluated to give insight into catalyst degradation and possible pathways to tune OER catalyst stability. Finally, the importance of identifying universal figures of merit for stability is highlighted, leading to a comprehensive accelerated lifetime test that could yield comparable performance data across different laboratories and catalyst types. The aim of this Review is to help disseminate and stress the important relationships between structure, composition, and stability of OER catalysts under different operating conditions.
- 36Diaz-Morales, O.; Raaijman, S.; Kortlever, R.; Kooyman, P. J.; Wezendonk, T.; Gascon, J.; Fu, W. T.; Koper, M. T. M. Iridium-Based Double Perovskites for Efficient Water Oxidation in Acid Media. Nat. Commun. 2016, 7, 12363, DOI: 10.1038/ncomms12363Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhtlaks7bE&md5=b10818629280e87dd1d7b358ce974f0cIridium-based double perovskites for efficient water oxidation in acid mediaDiaz-Morales, Oscar; Raaijman, Stefan; Kortlever, Ruud; Kooyman, Patricia J.; Wezendonk, Tim; Gascon, Jorge; Fu, W. T.; Koper, Marc T. M.Nature Communications (2016), 7 (), 12363CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)The development of active, cost-effective and stable oxygen-evolving catalysts is one of the major challenges for solar-to-fuel conversion towards sustainable energy generation. Iridium oxide exhibits the best available compromise between catalytic activity and stability in acid media, but it is prohibitively expensive for large-scale applications. Therefore, prepg. oxygen-evolving catalysts with lower amts. of the scarce but active and stable iridium is an attractive avenue to overcome this economical constraint. Here we report on a class of oxygen-evolving catalysts based on iridium double perovskites which contain 32 wt% less iridium than IrO2 and yet exhibit a more than threefold higher activity in acid media. According to recently suggested benchmarking criteria, the iridium double perovskites are the most active catalysts for oxygen evolution in acid media reported until now, to the best of our knowledge, and exhibit similar stability to IrO2.
- 37Geiger, S.; Kasian, O.; Ledendecker, M.; Pizzutilo, E.; Mingers, A. M.; Fu, W. T.; Diaz-Morales, O.; Li, Z.; Oellers, T.; Fruchter, L.; Ludwig, A.; Mayrhofer, K. J. J.; Koper, M. T. M.; Cherevko, S. The Stability Number as a Metric for Electrocatalyst Stability Benchmarking. Nat. Catal. 2018, 1, 508– 515, DOI: 10.1038/s41929-018-0085-6Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFGisLnK&md5=efb4882d145e58f72b41527eece25eedThe stability number as a metric for electrocatalyst stability benchmarkingGeiger, Simon; Kasian, Olga; Ledendecker, Marc; Pizzutilo, Enrico; Mingers, Andrea M.; Fu, Wen Tian; Diaz-Morales, Oscar; Li, Zhizhong; Oellers, Tobias; Fruchter, Luc; Ludwig, Alfred; Mayrhofer, Karl J. J.; Koper, Marc T. M.; Cherevko, SerhiyNature Catalysis (2018), 1 (7), 508-515CODEN: NCAACP; ISSN:2520-1158. (Nature Research)Reducing the noble metal loading and increasing the specific activity of the oxygen evolution catalysts are omnipresent challenges in proton-exchange-membrane water electrolysis, which have recently been tackled by utilizing mixed oxides of noble and non-noble elements. However, proper verification of the stability of these materials is still pending. Here we introduce a metric to explore the dissoln. processes of various iridium-based oxides, defined as the ratio between the amts. of evolved oxygen and dissolved iridium. The so-called stability no. is independent of loading, surface area or involved active sites and provides a reasonable comparison of diverse materials with respect to stability. The case study on iridium-based perovskites shows that leaching of the non-noble elements in mixed oxides leads to the formation of highly active amorphous iridium oxide, the instability of which is explained by the generation of short-lived vacancies that favor dissoln. These insights are meant to guide further research, which should be devoted to increasing the utilization of highly durable pure cryst. iridium oxide and finding solns. to stabilize amorphous iridium oxides.
- 38Vos, J. G.; Koper, M. T. M. Measurement of Competition between Oxygen Evolution and Chlorine Evolution Using Rotating Ring-Disk Electrode Voltammetry. J. Electroanal. Chem. 2018, 819, 260– 268, DOI: 10.1016/j.jelechem.2017.10.058Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslOisb%252FL&md5=01573b2aec0aa64422dd552b109a5c76Measurement of competition between oxygen evolution and chlorine evolution using rotating ring-disk electrode voltammetryVos, J. G.; Koper, M. T. M.Journal of Electroanalytical Chemistry (2018), 819 (), 260-268CODEN: JECHES; ISSN:1873-2569. (Elsevier B.V.)Selectivity between Cl evolution and O evolution in aq. media is a phenomenon of central importance in the chlor-alkali process, H2O treatment, and saline H2O splitting, which is an emerging technol. for sustainable energy conversion. An apparent scaling between O vs. Cl evolution was established, making it challenging to carry the two reactions out individually with 100% faradaic efficiency. To aid selectivity detn., the authors developed a new method to quickly measure Cl evolution rates using a conventional RRDE setup. A Pt ring fixed at 0.95 V vs. RHE in pH 0.88 can selectively reduce the Cl2 formed on the disk and this allows precise and flexible data acquisition. Using this method, O evolution and Cl evolution on a glassy C supported IrOx catalyst proceed independently, and the selectivity towards Cl evolution (εCER) rapidly approaches 100% as [Cl-] increases from 0 to 100 mM. The authors' results suggest that on IrOx, O evolution is not suppressed or influenced by the presence of Cl- or by the Cl evolution reaction taking place simultaneously on the surface.
- 39Fu, W. T.; IJdo, D. J. W. On the Space Group of the Double Perovskite Ba2PrIrO6. J. Solid State Chem. 2005, 178, 1312– 1316, DOI: 10.1016/j.jssc.2005.02.003Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXivFOhs7s%253D&md5=e76380dfe77e0bac61de4fe1c9a8921dOn the space group of the double perovskite Ba2PrIrO6Fu, W. T.; IJdo, D. J. W.Journal of Solid State Chemistry (2005), 178 (4), 1312-1316CODEN: JSSCBI; ISSN:0022-4596. (Elsevier)The structure of the double perovskite Ba2PrIrO6 was reexamd. by profile anal. of x-ray diffraction data. Neither the monoclinic P21/n nor the tetragonal P4/mnc space group correctly describes its structure. Ba2PrIrO6 has cubic symmetry, space group Fm‾3m, a 8.40135(6) Å. In agreement with earlier observations, Ba2PrIrO6 is an ordered perovskite contg. the valence pair Pr(IV)/Ir(IV).
- 40Fu, W. T.; IJdo, D. J. W. Re-Examination of the Structure of Ba2MIrO6 (M = La, Y): Space Group Revised. J. Alloys Compd. 2005, 394, L5, DOI: 10.1016/j.jallcom.2004.10.049Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXjslOitrg%253D&md5=367b9cf92279a2da7e4103ba4271bf1eRe-examination of the structure of Ba2MIrO6 (M = La, Y): space group revisedFu, W. T.; IJdo, D. J. W.Journal of Alloys and Compounds (2005), 394 (1-2), L5-L8CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)The structure of the double perovskites Ba2MIrO6 (M = La, Y) was studied by the profile anal. of x-ray diffraction data. Both compds. consist of an ordered arrangement of LaO6/YO6 and IrO6 octahedra but with different symmetries. Ba2LaIrO6 is rhombohedral, space group R‾3, with a 6.04542(5) Å and α 60.264(1), in which the LaO6 and IrO6 octahedra are tilted around the primitive [111]p-axis of the cubic aristotype. However, Ba2YIrO6 is double cubic, space group Fm‾3m, with a 8.35032(9) Å.
- 41Schuppert, A. K.; Topalov, A. A.; Katsounaros, I.; Klemm, S. O.; Mayrhofer, K. J. J. A Scanning Flow Cell System for Fully Automated Screening of Electrocatalyst Materials. J. Electrochem. Soc. 2012, 159, F670– F675, DOI: 10.1149/2.009211jesGoogle Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1ygsr3P&md5=24cc1bbea4bce7064ae797d051c39034A scanning flow cell system for fully automated screening of electrocatalyst materialsSchuppert, Anna K.; Topalov, Angel A.; Katsounaros, Ioannis; Klemm, Sebastian O.; Mayrhofer, Karl J. J.Journal of the Electrochemical Society (2012), 159 (11), F670-F675CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Electrocatalysts play an important role in sustainable energy-related fields. As these catalysts still require improvement on activity and stability, a lot of effort is invested in developing new materials. Due to the enormous parameter space spanned by material compn. and exptl. conditions, there is a great demand for high-throughput screening of the material performance. To address this issue, a scanning flow cell (SFC) is developed and utilized for catalyst research for the first time. The adaptation of a homemade LabVIEW program to the SFC setup enables fully automated, computer-controlled high-throughput measurements. A gas purging system is introduced to sat. the electrolyte with gases in a time frame comparable to typical rotating disk electrode (RDE) systems. To demonstrate the capabilities of the setup, the oxygen redn. reaction on polycryst. platinum is investigated as a sample system. The cyclic voltammograms are consistent with those expected from investigations in conventional electrochem. cells. Repetitive measurements show high reproducibility. Considering the potential of the system toward improvements and extensions, the SFC will be a valuable screening tool for electrocatalyst research.
- 42Klemm, S. O.; Topalov, A. A.; Laska, C. A.; Mayrhofer, K. J. J. Coupling of a High Throughput Microelectrochemical Cell with Online Multielemental Trace Analysis by ICP-MS. Electrochem. Commun. 2011, 13, 1533– 1535, DOI: 10.1016/j.elecom.2011.10.017Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFartL%252FE&md5=d9a7d73a9fde29a99f7cce7e135cfc14Coupling of a high throughput microelectrochemical cell with online multielemental trace analysis by ICP-MSKlemm, Sebastian O.; Topalov, Angel A.; Laska, Claudius A.; Mayrhofer, Karl J. J.Electrochemistry Communications (2011), 13 (12), 1533-1535CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)The successful coupling of a specially designed microelectrochem. cell and direct online multi-elemental trace anal. by ICP-MS is presented. The feasibility of this method is demonstrated by the example of copper dissoln. in HCl (1 and 10 mM), showing very high sensitivity and an excellent congruency between electrochem. expts. and copper concns. detected downstream. The complementary data allows for a precise detn. of the valence of Cu ions released during anodic dissoln., which undergoes changes depending on the electrolyte and the applied c.d. Moreover it provides a means of quantification of processes without net external currents that are not readily accessible by plain electrochem. techniques, in particular the exchange current densities at the open circuit potential, i.e. corrosion rate, and the dissoln. of native oxides. The system presented combines full spectrum electrochem. capabilities, convection control, and highly sensitive electrolyte anal. in an integrated, miniaturized arrangement under full computer control and automation.
- 43Kasian, O.; Geiger, S.; Mayrhofer, K. J. J.; Cherevko, S. Electrochemical On-Line ICP-MS in Electrocatalysis Research. Chem. Rec. 2018, DOI: 10.1002/tcr.201800162Google ScholarThere is no corresponding record for this reference.
- 44Gileadi, E. Problems in Interfacial Electrochemistry That Have Been Swept under the Carpet. J. Solid State Electrochem. 2011, 15, 1359– 1371, DOI: 10.1007/s10008-011-1344-5Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtVOnsLrK&md5=51674ff6d3a18ca23b29cafa8fc6203eProblems in interfacial electrochemistry that have been swept under the carpetGileadi, E.Journal of Solid State Electrochemistry (2011), 15 (7-8), 1359-1371CODEN: JSSEFS; ISSN:1432-8488. (Springer)A crit. view of interfacial electrochem. in the past 50 years is discussed, with emphasis on tacit assumptions, which are sometimes hard to justify. The important role of the Tafel equation in studies of the mechanism of electrode reactions and in the development of electrode kinetics in the past century is recognized. However, it is shown that the validity of the ways it was implemented can be questioned, particularly in view of the uncertainty in the value of the symmetry factor commonly assumed. For example, the value of β pertinent to a species in the outer-Helmholtz plane cannot be the same as that applicable to a species already adsorbed on the surface. Three factors are involved in considering charge transfer to an adsorbed species: (a) The electrostatic field at the adsorption site is highly distorted; thus, the overpotential imposed may not apply at the point where the reaction takes place; (b) the effective charge on the adsorbed species may not equal the nominal charge assigned to it; and (c) the metal surface may already be modified by a monolayer of adsorbed species of the same kind, which is, however, inactive with respect to the reaction taking place. Similarly, in studies of the kinetics of metal deposition and dissoln., where charge is transferred across the interface by the ions, one cannot legitimately assume a value of β, although it can be measured exptl. It is very risky to predict the future of interfacial electrochem., but one might extrapolate present trends. Thus, the importance of the fundamental aspects of the field may have declined in the past two or three decades, and this trend will probably continue. On the other hand, the importance of understanding interfacial electrochem. as a basis for related fields such as nano-science, biol., micro- and nano-implanted biosensors, interaction of tissue with metal implants, materials science, as well as technologies such as corrosion and alloy plating is likely to increase.
- 45Vesztergom, S.; Ujvári, M.; Láng, G. G. Dual Cyclic Voltammetry with Rotating Ring–Disk Electrodes. Electrochim. Acta 2013, 110, 49– 55, DOI: 10.1016/j.electacta.2013.01.142Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXivVGqt7s%253D&md5=0d7eedf2ea9c2af0804afa2ea26ec09fDual cyclic voltammetry with rotating ring-disk electrodesVesztergom, Soma; Ujvari, Maria; Lang, Gyozo G.Electrochimica Acta (2013), 110 (), 49-55CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)The simultaneous perturbation of the disk and ring electrode potentials of an RRDE with time-varying controlling waveforms seems to be an effective way of carrying out high-sensitivity collection expts. The method of dual cyclic voltammetry (i.e. applying dynamic potential programs to the disk and the ring electrodes of an RRDE simultaneously) has proven to be an esp. promising method for studying the mechanisms of electrochem. processes. The new 3D representation of the data can be effectively used in order to reveal the formation of electroactive species in the disk electrode process. However, some issues concerning the application of this method may also arise. The "dual dynamic" perturbation of the electrodes can cause transients to appear in the current-potential characteristics of the two electrodes, which often results in elec. cross-talk effects. In this paper it is shown that the afore-mentioned cross-talk (experienced mainly when perturbations of a high rate are applied) is caused by the common resistance shared by the current paths of the two working electrodes. Numerical simulations as well as expts. with a simple model system have been carried out in order to study the cross-talk effects, and a method is suggested for their elimination.
- 46Vesztergom, S.; Barankai, N.; Kovács, N.; Ujvári, M.; Siegenthaler, H.; Broekmann, P.; Láng, G. G. Electrical Cross-Talk in Four-Electrode Experiments. J. Solid State Electrochem. 2016, 20, 3165– 3177, DOI: 10.1007/s10008-016-3294-4Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFahs7bJ&md5=0d8b9365504a40466f3d19c79e97d1a3Electrical cross-talk in four-electrode experiments - A digital simulation approach to the example of rotating ring-disk electrodesVesztergom, Soma; Barankai, Norbert; Kovacs, Noemi; Ujvari, Maria; Siegenthaler, Hans; Broekmann, Peter; Lang, Gyozo G.Journal of Solid State Electrochemistry (2016), 20 (11), 3165-3177CODEN: JSSEFS; ISSN:1432-8488. (Springer)The subject of this paper is elec. cross-talk, an interference between the current/voltage characteristics of the two working electrodes in four-electrode (generator/collector) systems. Cross-talk arises in electrochem. cells of finite resistance due to the superposition of the elec. fields of the working electrodes, and often causes difficulties in the interpretation of measurement results. In this paper, we present an algorithm for modeling simple generation/collection expts. with a rotating ring-disk electrode (RRDE) immersed into a finite resistance soln. of a redox couple. We show that based on the anal. of the Kirchhoff (Laplace) matrix of the simulation mesh, the effect of elec. cross-talk may be accounted for in such expts. The intensity of cross-talk is found to be heavily influenced by the selection of the ref. point for potential measurements; in practice, this is the position of the ref. electrode or the tip of the Luggin probe. The devised model is validated by means of a simple and demonstrative expt. [Figure not available: see fulltext.].
- 47McCrory, C. C. L.; Jung, S.; Peters, J. C.; Jaramillo, T. F. Benchmarking Heterogeneous Electrocatalysts for the Oxygen Evolution Reaction. J. Am. Chem. Soc. 2013, 135, 16977– 16987, DOI: 10.1021/ja407115pGoogle Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhslSqtLnM&md5=105318a53866c4b147ae62288137536dBenchmarking heterogeneous electrocatalysts for the oygen evolution reactionMcCrory, Charles C. L.; Jung, Suho; Peters, Jonas C.; Jaramillo, Thomas F.Journal of the American Chemical Society (2013), 135 (45), 16977-16987CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Objective evaluation of the activity of electrocatalysts for water oxidn. is of fundamental importance for the development of promising energy conversion technologies including integrated solar water-splitting devices, water electrolyzers, and Li-air batteries. However, current methods employed to evaluate oxygen-evolving catalysts are not standardized, making it difficult to compare the activity and stability of these materials. We report a protocol for evaluating the activity, stability, and Faradaic efficiency of electrodeposited oxygen-evolving electrocatalysts. In particular, we focus on methods for detg. electrochem. active surface area and measuring electrocatalytic activity and stability under conditions relevant to an integrated solar water-splitting device. Our primary figure of merit is the overpotential required to achieve a c.d. of 10 mA cm-2 per geometric area, approx. the c.d. expected for a 10% efficient solar-to-fuels conversion device. Utilizing the aforementioned surface area measurements, one can det. electrocatalyst turnover frequencies. The reported protocol was used to examine the oxygen-evolution activity of the following systems in acidic and alk. solns.: CoOx, CoPi, CoFeOx, NiOx, NiCeOx, NiCoOx, NiCuOx, NiFeOx, and NiLaOx. The oxygen-evolving activity of an electrodeposited IrOx catalyst was also investigated for comparison. Two general observations are made from comparing the catalytic performance of the OER catalysts investigated: (1) in alk. soln., every non-noble metal system achieved 10 mA cm-2 current densities at similar operating overpotentials between 0.35 and 0.43 V, and (2) every system but IrOx was unstable under oxidative conditions in acidic solns.
- 48Seitz, L. C.; Dickens, C. F.; Nishio, K.; Hikita, Y.; Montoya, J.; Doyle, A.; Kirk, C.; Vojvodic, A.; Hwang, H. Y.; Norskov, J. K.; Jaramillo, T. F. A Highly Active and Stable IrO x /SrIrO 3 Catalyst for the Oxygen Evolution Reaction. Science (Washington, DC, U. S.) 2016, 353, 1011– 1014, DOI: 10.1126/science.aaf5050Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVemtLfN&md5=dc18e94836ca7e0f36d3349ab3254eb9A highly active and stable IrOx/SrIrO3 catalyst for the oxygen evolution reactionSeitz, Linsey C.; Dickens, Colin F.; Nishio, Kazunori; Hikita, Yasuyuki; Montoya, Joseph; Doyle, Andrew; Kirk, Charlotte; Vojvodic, Aleksandra; Hwang, Harold Y.; Norskov, Jens K.; Jaramillo, Thomas F.Science (Washington, DC, United States) (2016), 353 (6303), 1011-1014CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Oxygen electrochem. plays a key role in renewable energy technologies such as fuel cells and electrolyzers, but the slow kinetics of the oxygen evolution reaction (OER) limit the performance and commercialization of such devices. Here we report an iridium oxide/strontium iridium oxide (IrOx/SrIrO3) catalyst formed during electrochem. testing by strontium leaching from surface layers of thin films of SrIrO3. This catalyst has demonstrated specific activity at 10 milliamps per square centimeter of oxide catalyst (OER current normalized to catalyst surface area), with only 270 to 290 mV of overpotential for 30 h of continuous testing in acidic electrolyte. D. functional theory calcns. suggest the formation of highly active surface layers during strontium leaching with IrO3 or anatase IrO2 motifs. The IrOx/SrIrO3 catalyst outperforms known IrOx and ruthenium oxide (RuOx) systems, the only other OER catalysts that have reasonable activity in acidic electrolyte.
- 49Topalov, A. A.; Katsounaros, I.; Auinger, M.; Cherevko, S.; Meier, J. C.; Klemm, S. O.; Mayrhofer, K. J. J. Dissolution of Platinum: Limits for the Deployment of Electrochemical Energy Conversion?. Angew. Chem., Int. Ed. 2012, 51, 12613– 12615, DOI: 10.1002/anie.201207256Google Scholar49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1agtrnF&md5=1296fc70022054f908c9cf76d12c4006Dissolution of Platinum: Limits for the Deployment of Electrochemical Energy Conversion?Topalov, Angel A.; Katsounaros, Ioannis; Auinger, Michael; Cherevko, Serhiy; Meier, Josef C.; Klemm, Sebastian O.; Mayrhofer, Karl J. J.Angewandte Chemie, International Edition (2012), 51 (50), 12613-12615CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)This quantification of Pt dissoln. as a function of the exptl. parameters offers guidelines for designing and operating Pt-based materials to optimize their durability in fuel cells. The intrinsic properties of polycryst. Pt already indicate that more than mere material development will be required for achieving all of the desired performance targets, particularly regarding severe start/stop cycling. Only a combined engineering, electrochem. and materials science approach considering the complex interplay of individual components and operation modes within fuel cells can improve the durability of electrocatalysts.
- 50Geiger, S.; Cherevko, S.; Mayrhofer, K. J. J. Dissolution of Platinum in Presence of Chloride Traces. Electrochim. Acta 2015, 179, 24– 31, DOI: 10.1016/j.electacta.2015.03.059Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXkt1Olt7c%253D&md5=0d166273f08f0dadf72ec6e89b008b78Dissolution of Platinum in Presence of Chloride TracesGeiger, Simon; Cherevko, Serhiy; Mayrhofer, Karl J. J.Electrochimica Acta (2015), 179 (), 24-31CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)One of the main issues on the way to a com. use of fuel cells is the durability of the cell compartments, in particular electrocatalysts. Chloride impurities, originating from airborne salts or synthesis residues, can have severe effects on degrdn. in general. The quant. impact on dissoln. of Pt, which is the most common electrocatalyst material in polymer electrolyte membrane fuel cells, and the mechanism are still not fully understood. In the current work, potentiodynamic and potentiostatic measurements of platinum in acidic electrolytes contg. chlorides in the range of 1 to 1000 μM were carried out utilizing a scanning flow cell (SFC) coupled to an inductively coupled plasma mass spectrometer (ICP-MS). We show that during potentiodynamic measurements dissoln. accelerates with increase in amt. of chlorides, as expected. Similarly as in Cl--free electrolytes, dissoln. is a predominantly transient process taking place during oxidn. or redn. While thus in general the mechanism remains the same as reported before in the absence of chlorides, evidence for addnl. dissoln. processes during oxide formation and redn. are obsd. This leads to a variation in the ratio between anodic and cathodic dissoln. when chlorides are present. Based on the exptl. results a tentative dissoln. mechanism is proposed.
- 51Kasian, O.; Grote, J.-P.; Geiger, S.; Cherevko, S.; Mayrhofer, K. J. J. The Common Intermediates of Oxygen Evolution and Dissolution Reactions during Water Electrolysis on Iridium. Angew. Chem., Int. Ed. 2018, 57, 2488– 2491, DOI: 10.1002/anie.201709652Google Scholar51https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXit1Wlur8%253D&md5=6be0bb9168540d599321fb066942e37dThe Common Intermediates of Oxygen Evolution and Dissolution Reactions during Water Electrolysis on IridiumKasian, Olga; Grote, Jan-Philipp; Geiger, Simon; Cherevko, Serhiy; Mayrhofer, Karl J. J.Angewandte Chemie, International Edition (2018), 57 (9), 2488-2491CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Understanding the pathways of catalyst degrdn. during the O evolution reaction is a cornerstone in the development of efficient and stable electrolyzers, since even for the most promising Ir based anodes the harsh reaction conditions are detrimental. The dissoln. mechanism is complex and the correlation to the O evolution reaction itself is still poorly understood. Here, by coupling a scanning flow cell with inductively coupled plasma and online electrochem. mass spectrometers, the authors monitor the O evolution and degrdn. products of Ir and Ir oxides in situ. At high anodic potentials several dissoln. routes become possible, including formation of gaseous IrO3. From exptl. data, possible pathways are proposed for the O-evolution-triggered dissoln. of Ir and the role of common intermediates for these reactions is discussed.
- 52Wakeshima, M.; Harada, D.; Hinatsu, Y. Crystal Structures and Magnetic Properties of Ordered Perovskites Ba2LnIrO6 (Ln = Lanthanide). J. Mater. Chem. 2000, 10, 419– 422, DOI: 10.1039/a907586kGoogle Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXhslWksLY%253D&md5=1b0c511483eb4c1851a4c32f21a1cfa5Crystal structures and magnetic properties of ordered perovskites Ba2LnIrO6 (Ln = lanthanide)Wakeshima, Makoto; Harada, Daijitsu; Hinatsu, YukioJournal of Materials Chemistry (2000), 10 (2), 419-422CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)The crystal structures and magnetic properties of ordered perovskites Ba2LnIrO6 (Ln = lanthanide) are reported. They have monoclinic perovskite-type structures with space group P21/n. Their magnetic susceptibilities were measured from 2-350 K. Ba2CeIrO6 and Ba2PrIrO6 show antiferromagnetic transitions at 17 and 71 K, resp. In these compds., the Ce and Pr ions are in the tetravalent state from anal. of their crystal structures and magnetic susceptibilities.
- 53Massué, C.; Huang, X.; Tarasov, A.; Ranjan, C.; Cap, S.; Schlögl, R. Microwave Assisted Synthesis of Stable and Highly Active Ir-Oxohydroxides for Electrochemical Oxidation of Water. ChemSusChem 2017, 10, 1958, DOI: 10.1002/cssc.201601864Google Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXlvVGgu70%253D&md5=450ba8bb3ab8b89c4d89409859a23c4dMicrowave-Assisted Synthesis of Stable and Highly Active Ir Oxohydroxides for Electrochemical Oxidation of WaterMassue, Cyriac; Huang, Xing; Tarasov, Andrey; Ranjan, Chinmoy; Cap, Sebastien; Schloegl, RobertChemSusChem (2017), 10 (9), 1958-1968CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)Water splitting for H prodn. in acidic media has been limited by the poor stability of the anodic electrocatalyst devoted to the O evolution reaction (OER). To help circumvent this problem we synthesized a class of novel Ir oxohydroxides by rapid microwave-assisted hydrothermal synthesis, which bridges the gap between electrodeposited amorphous IrOx films and cryst. IrO2 electrocatalysts prepd. by calcination routes. For electrode loadings 2 orders of magnitude below current stds., the synthesized compds. present an unrivalled combination of high activity and stability under com. relevant OER conditions in comparison to reported benchmarks, without need for pretreatment. The best compd. achieved a lifetime 33 times longer than the best com. Ir benchmark. This efficient synthesis of an Ir oxohydroxide phase with superior intrinsic OER performance constitutes a major step towards the targeted design of cost-efficient Ir based OER electrocatalysts for acidic media.
- 54Zaharieva, I.; Chernev, P.; Risch, M.; Klingan, K.; Kohlhoff, M.; Fischer, A.; Dau, H. Electrosynthesis, Functional, and Structural Characterization of a Water-Oxidizing Manganese Oxide. Energy Environ. Sci. 2012, 5, 7081– 7089, DOI: 10.1039/c2ee21191bGoogle Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XmsVWqtrw%253D&md5=d57548e8d50ded4d13888602d170fbbaElectrosynthesis, functional, and structural characterization of a water-oxidizing manganese oxideZaharieva, Ivelina; Chernev, Petko; Risch, Marcel; Klingan, Katharina; Kohlhoff, Mike; Fischer, Anna; Dau, HolgerEnergy & Environmental Science (2012), 5 (5), 7081-7089CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)In the sustainable prodn. of non-fossil fuels, water oxidn. is pivotal. Development of efficient catalysts based on manganese is desirable because this element is earth-abundant, inexpensive, and largely non-toxic. We report an electrodeposited Mn oxide (MnCat) that catalyzes electrochem. water oxidn. at neutral pH at rates that approach the level needed for direct coupling to photoactive materials. By choice of the voltage protocol we could switch between electrodeposition of inactive Mn oxides (deposition at const. anodic potentials) and synthesis of the active MnCat (deposition by voltage-cycling protocols). Electron microscopy reveals that the MnCat consists of nanoparticles (100 nm) with complex fine-structure. X-ray spectroscopy reveals that the amorphous MnCat resembles the biol. paragon, the water-splitting Mn4Ca complex of photosynthesis, with respect to mean Mn oxidn. state (ca. +3.8 in the MnCat) and central structural motifs. Yet the MnCat functions without calcium or other bivalent ions. Comparing the MnCat with electrodeposited Mn oxides inactive in water oxidn., we identify characteristics that likely are crucial for catalytic activity. In both inactive Mn oxides and active ones (MnCat), extensive di-μ-oxo bridging between Mn ions is obsd. However in the MnCat, the voltage-cycling protocol resulted in formation of MnIII sites and prevented formation of well-ordered and unreactive MnIVO2. Structure-function relations in Mn-based water-oxidn. catalysts and strategies to design catalytically active Mn-based materials are discussed. Knowledge-guided performance optimization of the MnCat could pave the road for its technol. use.
- 55Balaji, R.; Kannan, B. S.; Lakshmi, J.; Senthil, N.; Vasudevan, S.; Sozhan, G.; Shukla, A. K.; Ravichandran, S. An Alternative Approach to Selective Sea Water Oxidation for Hydrogen Production. Electrochem. Commun. 2009, 11, 1700– 1702, DOI: 10.1016/j.elecom.2009.06.022Google Scholar55https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXps1WrtLs%253D&md5=290cd69262d6a8846a2cbc406e12df49An alternative approach to selective sea water oxidation for hydrogen productionBalaji, Rengarajan; Kannan, Balasingam Suresh; Lakshmi, Jothinathan; Senthil, Natarajan; Vasudevan, Subramanyan; Sozhan, Ganapathy; Shukla, Ashok Kumar; Ravichandran, SubbiahElectrochemistry Communications (2009), 11 (8), 1700-1702CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)Sea water electrolysis is one of the promising ways to produce hydrogen since it is available in plentiful supply on the earth. However, in sea water electrolysis toxic chlorine evolution is the preferred reaction over oxygen evolution at the anode. In this work, research has been focused on the development of electrode materials with a high selectivity for oxygen evolution over chlorine evolution. Selective oxidn. in sea water electrolysis has been demonstrated by using a cation-selective polymer. We have used a perm-selective membrane (Nafion), which electrostatically repels chloride ions (Cl-) to the electrode surface and thereby enhances oxygen evolution at the anode. The efficiency and behavior of the electrode have been characterized by means of anode current efficiency and polarization studies. The surface morphol. of the electrode has been characterized by using a scanning electron microscope (SEM). The results suggest that nearly 100% oxygen evolution efficiency could be achieved when using an IrO2/Ti electrode surface-modified by a perm-selective polymer.
- 56Mo, Y.; Stefan, I. C.; Cai, W.-B.; Dong, J.; Carey, P.; Scherson, D. A. In Situ Iridium L III -Edge X-Ray Absorption and Surface Enhanced Raman Spectroscopy of Electrodeposited Iridium Oxide Films in Aqueous Electrolytes. J. Phys. Chem. B 2002, 106, 3681– 3686, DOI: 10.1021/jp014452pGoogle Scholar56https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38Xhsl2ntLw%253D&md5=84af63dd364b67f17650aea86d5415ceIn Situ Iridium LIII-Edge X-ray Absorption and Surface Enhanced Raman Spectroscopy of Electrodeposited Iridium Oxide Films in Aqueous ElectrolytesMo, Yibo; Stefan, Ionel C.; Cai, Wen-Bin; Dong, Jian; Carey, Paul; Scherson, Daniel A.Journal of Physical Chemistry B (2002), 106 (14), 3681-3686CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)Structural and electronic aspects of IrO2 films prepd. by electrodeposition on Au substrates were investigated by in situ LIII-edge X-ray absorption and surface enhanced Raman spectroscopies in both acid and alk. aq. solns. Linear correlations were found between the extent of oxidn. of Ir3+ in the films detd. from a statistical fit of the white line, which includes contributions from each of the sites differing by a single electron, and from coulometric anal. of the voltammetric curves. Anal. of the extended X-ray absorption fine structure (EXAFS) yielded Ir-O bond lengths decreasing in the sequence 2.02, 1.97, and 1.93 Å for Ir3+, Ir4+, and Ir5+ sites, resp. Whereas SERS provided evidence for the presence of cryst. IrO2 in the highly hydrated films, the lack of intense shells in the Fourier transform of the EXAFS function beyond the nearest oxygen neighbors indicates that the films do not display long-range order.
- 57Sanchez Casalongue, H. G.; Ng, M. L.; Kaya, S.; Friebel, D.; Ogasawara, H.; Nilsson, A. In Situ Observation of Surface Species on Iridium Oxide Nanoparticles during the Oxygen Evolution Reaction. Angew. Chem., Int. Ed. 2014, 53, 7169– 7172, DOI: 10.1002/anie.201402311Google Scholar57https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXos1CjsLs%253D&md5=114dd5f9d7fc27964b33d8e1d1a3885cIn Situ Observation of Surface Species on Iridium Oxide Nanoparticles during the Oxygen Evolution ReactionSanchez Casalongue, Hernan G.; Ng, May Ling; Kaya, Sarp; Friebel, Daniel; Ogasawara, Hirohito; Nilsson, AndersAngewandte Chemie, International Edition (2014), 53 (28), 7169-7172CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)An Ir oxide nanoparticle electrocatalyst under O evolution reaction conditions was probed in situ by ambient-pressure XPS. Under OER conditions, Ir undergoes a change in oxidn. state from IrIV to IrV that takes place predominantly at the surface of the catalyst. The chem. change in Ir is coupled to a decrease in surface hydroxide, providing exptl. evidence which strongly suggests that the O evolution reaction on Ir oxide occurs through an OOH-mediated deprotonation mechanism.
- 58Minguzzi, A.; Lugaresi, O.; Achilli, E.; Locatelli, C.; Vertova, A.; Ghigna, P.; Rondinini, S. Observing the Oxidation State Turnover in Heterogeneous Iridium-Based Water Oxidation Catalysts. Chem. Sci. 2014, 5, 3591, DOI: 10.1039/C4SC00975DGoogle Scholar58https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtVOitbvL&md5=e515cad76597243d18a3785437372febObserving the oxidation state turnover in heterogeneous iridium-based water oxidation catalystsMinguzzi, Alessandro; Lugaresi, Ottavio; Achilli, Elisabetta; Locatelli, Cristina; Vertova, Alberto; Ghigna, Paolo; Rondinini, SandraChemical Science (2014), 5 (9), 3591-3597CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)In this work the oxidn. states assumed by Ir in oxide systems used as heterogeneous catalysts for water oxidn. are detd. by means of in situ X-ray Absorption Spectroscopy (XAS). Using a highly hydrated iridium oxide film allows the max. no. of Ir sites to be involved in the electrochem. processes occurring at the catalysts during water oxidn. (oxygen evolution reaction, OER). X-ray Absorption Near Edge Structure (XANES) spectra clearly indicate the co-existence of Ir(III) and Ir(V) at the electrode potentials where OER occurs. This represents a fundamental step both in the understanding of the water oxidn. mechanism catalyzed by heterogeneous Ir oxide systems, and in the possible tailoring of electrocatalysts for OER.
- 59Pfeifer, V.; Jones, T. E.; Velasco Vélez, J. J.; Massué, C.; Arrigo, R.; Teschner, D.; Girgsdies, F.; Scherzer, M.; Greiner, M. T.; Allan, J.; Hashagen, M.; Weinberg, G.; Piccinin, S.; Hävecker, M.; Knop-Gericke, A.; Schlögl, R. The Electronic Structure of Iridium and Its Oxides. Surf. Interface Anal. 2016, 48, 261– 273, DOI: 10.1002/sia.5895Google Scholar59https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitV2isbvF&md5=af071905b21db89137699595dac71081The electronic structure of iridium and its oxidesPfeifer, Verena; Jones, Travis E.; Velasco Velez, Juan J.; Massue, Cyriac; Arrigo, Rosa; Teschner, Detre; Girgsdies, Frank; Scherzer, Michael; Greiner, Mark T.; Allan, Jasmin; Hashagen, Maike; Weinberg, Gisela; Piccinin, Simone; Haevecker, Michael; Knop-Gericke, Axel; Schloegl, RobertSurface and Interface Analysis (2016), 48 (5), 261-273CODEN: SIANDQ; ISSN:0142-2421. (John Wiley & Sons Ltd.)Iridium-based materials are among the most active and stable electrocatalysts for the oxygen evolution reaction. Amorphous iridium oxide structures are found to be more active than their cryst. counterparts. Herein, we combine synchrotron-based X-ray photoemission and absorption spectroscopies with theor. calcns. to investigate the electronic structure of Ir metal, rutile-type IrO2, and an amorphous IrOx. Theory and expt. show that while the Ir 4f line shape of Ir metal is well described by a simple Doniach-Sunjic function, the peculiar line shape of rutile-type IrO2 requires the addn. of a shake-up satellite 1 eV above the main line. In the catalytically more active amorphous IrOx, we find that addnl. intensity appears in the Ir 4f spectrum at higher binding energy when compared with rutile-type IrO2 along with a pre-edge feature in the O K-edge. We identify these addnl. features as electronic defects in the anionic and cationic frameworks, namely, formally OI- and IrIII, which may explain the increased activity of amorphous IrOx electrocatalysts. We corroborate our findings by in situ X-ray diffraction as well as in situ X-ray photoemission and absorption spectroscopies. Copyright © 2015 John Wiley & Sons, Ltd.
- 60Massué, C.; Pfeifer, V.; van Gastel, M.; Noack, J.; Algara-Siller, G.; Cap, S.; Schlögl, R. Reactive Electrophilic O I– Species Evidenced in High-Performance Iridium Oxohydroxide Water Oxidation Electrocatalysts. ChemSusChem 2017, 10, 4786– 4798, DOI: 10.1002/cssc.201701291Google Scholar60https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslyhu7zP&md5=c2190dc12f35e4663a50694ae9ac6234Reactive Electrophilic O1- Species Evidenced in High-Performance Iridium Oxohydroxide Water Oxidation ElectrocatalystsMassue, Cyriac; Pfeifer, Verena; van Gastel, Maurice; Noack, Johannes; Algara-Siller, Gerardo; Cap, Sebastien; Schloegl, RobertChemSusChem (2017), 10 (23), 4786-4798CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)Although quasi-amorphous Ir oxohydroxides have been identified repeatedly as superior electrocatalysts for the O evolution reaction (OER), an exact description of the performance-relevant species has remained a challenge. Here, we report the characterization of hydrothermally prepd. Ir(III/IV) oxohydroxides that exhibit exceptional OER performances. Holes in the O 2p states of the Ir(III/IV) oxohydroxides result in reactive O1- species, which are identified by characteristic near-edge x-ray absorption fine structure (NEXAFS) features. A prototypical titrn. reaction with CO as a probe mol. shows that these O1- species are highly susceptible to nucleophilic attack at room temp. Similarly to the preactivated oxygen involved in the biol. OER in photosystem II, the electrophilic O1- species evidenced in the Ir(III/IV) oxohydroxides are suggested to be precursors to species involved in the O-O bond formation during the electrocatalytic OER. The CO titrn. also highlights a link between the OER performance and the surface/subsurface mobility of the O1- species. Thus, the superior electrocatalytic properties of the Ir(III/IV) oxohydroxides are explained by their ability to accommodate preactivated electrophilic O1- species that can migrate within the lattice.
- 61Kuznetsova, E.; Petrykin, V.; Sunde, S.; Krtil, P. Selectivity of Nanocrystalline IrO2-Based Catalysts in Parallel Chlorine and Oxygen Evolution. Electrocatalysis 2015, 6, 198– 210, DOI: 10.1007/s12678-014-0233-yGoogle Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsl2lsr3L&md5=90a63c3c24692733b9832d7ab238c6f2Selectivity of Nanocrystalline IrO2-Based Catalysts in Parallel Chlorine and Oxygen EvolutionKuznetsova, Elizaveta; Petrykin, Valery; Sunde, Svein; Krtil, PetrElectrocatalysis (2015), 6 (2), 198-210CODEN: ELECCF; ISSN:1868-2529. (Springer)Nanocryst. electrocatalysts with chem. compn. corresponding to Ir1-xMxO2 (M = Co, Ni, and Zn, 0.05 ≤ x ≤ 0.2) were prepd. by the hydrolysis of H2IrCl6·4H2O solns. combined with nitrates and acetates of Ni, Zn, and Co. X-ray diffraction (XRD) anal. indicates that the dopant Co, Ni, and Zn cations substitute the Ir atoms in the rutile lattice. The prepd. materials contain small inclusions of iridium metal on the level comparable with the detection of the XRD technique. The local environment of Co and Zn in the doped IrO2 materials conforms to a rutile model with a homogeneous distribution of the doping elements in the rutile lattice. The incorporated Ni is distributed in the rutile lattice non-homogeneously and tends to form clusters within rutile structure. The incorporation of Ni and Co enhances the activity of the prepd. electrocatalysts in oxygen evolution. The modification of the IrO2 via doping process alters also the material's selectivity in the parallel oxygen and chlorine evolution. Incorporation of Co and Zn cations shifts the selectivity of the catalysts toward oxygen evolution in chloride-contg. media; the Ni incorporation leads to an enhancement of the selectivity toward chlorine evolution. Chlorine evolution is apparently limited by the no. of the active catalytic sites on the electrode surface.
- 62Cherevko, S.; Geiger, S.; Kasian, O.; Kulyk, N.; Grote, J.-P.; Savan, A.; Shrestha, B. R.; Merzlikin, S.; Breitbach, B.; Ludwig, A.; Mayrhofer, K. J. J. Oxygen and Hydrogen Evolution Reactions on Ru, RuO2, Ir, and IrO2 Thin Film Electrodes in Acidic and Alkaline Electrolytes: A Comparative Study on Activity and Stability. Catal. Today 2016, 262, 170– 180, DOI: 10.1016/j.cattod.2015.08.014Google Scholar62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVCnu7%252FE&md5=4bf7a1f1ee5806594ba98f8c86990ebeOxygen and hydrogen evolution reactions on Ru, RuO2, Ir, and IrO2 thin film electrodes in acidic and alkaline electrolytes: A comparative study on activity and stabilityCherevko, Serhiy; Geiger, Simon; Kasian, Olga; Kulyk, Nadiia; Grote, Jan-Philipp; Savan, Alan; Shrestha, Buddha Ratna; Merzlikin, Sergiy; Breitbach, Benjamin; Ludwig, Alfred; Mayrhofer, Karl J. J.Catalysis Today (2016), 262 (), 170-180CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Metallic iridium and ruthenium as well as their oxides are among the most active oxygen evolution (OER) electrocatalysts in acidic media, and are also of interest for the catalysis of the hydrogen evolution (HER). The stability of these materials under different operating conditions is, however, still not fully understood. In the current work, activity and stability of well-defined Ru, RuO2, Ir, and IrO2 thin film electrodes are evaluated in acidic and alk. electrolytes using an electrochem. scanning flow cell (SFC) connected to an inductively coupled plasma mass spectrometer (ICP-MS). Identical exptl. protocols are intentionally employed for all electrodes and electrolytes, to obtain unambiguous and comparable information on intrinsic activity and stability of the electrodes. It is found that independent of the electrolyte, OER activity decreases as Ru > Ir ≈ RuO2 > IrO2, while dissoln. increases as IrO2 « RuO2 < Ir « Ru. Moreover, dissoln. of these metals in both solns. is 2-3 orders of magnitude higher compared to their resp. oxides, and dissoln. is generally more intense in alk. solns. Similarly to the OER, metallic electrodes are more active catalysts for HER. They, however, suffer from dissoln. during native oxide redn., while IrO2 and RuO2 do not exhibit significant dissoln. The obtained results on activity and stability of the electrodes are discussed in light of their potential applications, i.e. water electrolyzers or fuel cells.
- 63Stevens, M. B.; Enman, L. J.; Batchellor, A. S.; Cosby, M. R.; Vise, A. E.; Trang, C. D. M.; Boettcher, S. W. Measurement Techniques for the Study of Thin Film Heterogeneous Water Oxidation Electrocatalysts. Chem. Mater. 2017, 29, 120– 140, DOI: 10.1021/acs.chemmater.6b02796Google Scholar63https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVyhs7jF&md5=191adc3a9549a1b2df75ccf18d6fe224Measurement Techniques for the Study of Thin Film Heterogeneous Water Oxidation ElectrocatalystsStevens, Michaela Burke; Enman, Lisa J.; Batchellor, Adam S.; Cosby, Monty R.; Vise, Ashlee E.; Trang, Christina D. M.; Boettcher, Shannon W.Chemistry of Materials (2017), 29 (1), 120-140CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)Heterogeneous electrocatalysts for the O evolution reaction (OER) are complicated materials with dynamic structures. They can exhibit potential-induced phase transitions, potential-dependent electronic properties, variable oxidn. and protonation states, and disordered local/surface phases. These properties make understanding the OER, and ultimately designing higher efficiency catalysts, challenging. The authors report procedures and measurement techniques that the authors have adopted or developed to assess each of the above challenges in understanding materials for the OER. These include the targeted synthesis of hydrated oxyhydroxide phases, the assessment and elimination of electrolyte impurities, the use of a quartz crystal microbalance to monitor film loading and dissoln., and the use of an in situ cond. measurement to understand the flow of electrons from the catalyst active sites to the conductive support electrode. The authors end with a recipe for the synthesis and characterization of a std. Ni(Fe)OxHy catalyst that can be performed in any lab. with a basic electrochem. setup and used as a quant. comparison to aid the development of new OER catalyst systems.
- 64Watzele, S.; Bandarenka, A. S. Quick Determination of Electroactive Surface Area of Some Oxide Electrode Materials. Electroanalysis 2016, 28, 2394– 2399, DOI: 10.1002/elan.201600178Google Scholar64https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XptVyhs74%253D&md5=1b621ff762f0e18fa6005a297535c887Quick Determination of Electroactive Surface Area of Some Oxide Electrode MaterialsWatzele, Sebastian; Bandarenka, Aliaksandr S.Electroanalysis (2016), 28 (10), 2394-2399CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Quick and accurate detn. of the real electroactive surface area of oxide electrodes remains one of the most challenging but at the same time important unsolved methodol. tasks in the field of electroanal. For instance, the widely used Brunauer-Emmett-Teller (BET) method unfortunately provides no direct connection to it. However, its assessment through the double layer capacitance is complicated and not accurate enough, as the bulk oxide films themselves contribute to the measured capacitance, not mentioning the double layer frequency dispersion and other poorly understood factors. The authors propose a relatively simple methodol. for a quick assessment of the electroactive surface area of some electron conducting oxide and perovskite materials. The methodol. involves several steps. Initially, calibration expts. were performed aiming to form the thinnest (practically .ltorsim.100-200 nm) flat oxide films, which exhibit necessary functional properties (close to those expected for the bulk material) without significant side influence of the substrate. Then, AFM measurements are implemented to est. the surface roughness of the resulting samples. Finally, electrochem. impedance measurements are done at a small overpotential related to the O evolution reaction (OER) aiming to ext. not the double layer but the capacitance of adsorption Ca of the OER intermediates. The Ca values can then be used to evaluate the electroactive surface area of real-world high surface area oxide electrodes composed of the same material. Other words, similar to the H underpotential deposition or CO oxidn. in the case of metals, the authors propose to use the O evolution reaction as the probing reaction to evaluate the surface area of oxide electrocatalysts. However, instead of cyclic voltammetry, electrochem. impedance spectroscopy was used as the main probing technique. Due to relatively high reproducibility, clear phys. meaning and exclusive connection to the electroactive area, the measurements of Ca can become a viable method in numerous electrochem. applications. An example using Ni-oxide electrodes is given to illustrate the methodol.
- 65Chow, K. F.; Carducci, T. M.; Murray, R. W. Electronic Conductivity of Films of Electroflocculated 2 Nm Iridium Oxide Nanoparticles. J. Am. Chem. Soc. 2014, 136, 3385– 3387, DOI: 10.1021/ja413226jGoogle Scholar65https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXjtVeqt70%253D&md5=ba8c11946e5caf164f97314d744803a3Electronic Conductivity of Films of Electroflocculated 2 nm Iridium Oxide NanoparticlesChow, Kwok-Fan; Carducci, Tessa M.; Murray, Royce W.Journal of the American Chemical Society (2014), 136 (9), 3385-3387CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The electronic cond. of films of iridium oxide (IrOx) composed of ∼2 nm nanoparticles (NPs) is strongly dependent on the film oxidn. state. The IrIVOx NPs can be electrochem. converted to several oxidn. states, ranging from IrIII to IrV oxides. The NP films exhibit a very high apparent cond., e.g., 10-2 S cm-1, when the NPs are in the oxidized +4/+5 state. When the film is fully reduced to its IrIII state, the apparent cond. falls to 10-6 S cm-1.
- 66Jung, S.; McCrory, C. C. L.; Ferrer, I. M.; Peters, J. C.; Jaramillo, T. F. Benchmarking Nanoparticulate Metal Oxide Electrocatalysts for the Alkaline Water Oxidation Reaction. J. Mater. Chem. A 2016, 4, 3068– 3076, DOI: 10.1039/C5TA07586FGoogle Scholar66https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFWqt7vN&md5=d585b6ce247c8654b74a42f826a78f38Benchmarking nanoparticulate metal oxide electrocatalysts for the alkaline water oxidation reactionJung, Suho; McCrory, Charles C. L.; Ferrer, Ivonne M.; Peters, Jonas C.; Jaramillo, Thomas F.Journal of Materials Chemistry A: Materials for Energy and Sustainability (2016), 4 (8), 3068-3076CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)Nanoparticulate metal-oxide catalysts are among the most prevalent systems for alk. water oxidn. However, comparisons of the electrochem. performance of these materials have been challenging due to the different methods of attachment, catalyst loadings, and electrochem. test conditions reported in the literature. Herein, we have leveraged a conventional drop-casting method that allows for the successful adhesion of a wide range of nanoparticulate catalysts to glassy-carbon electrode surfaces. We have applied this adhesion method to prep. catalyst films from 16 cryst. metal-oxide nanoparticles with a const. loading of 0.8 mg cm-2, and evaluated the resulting nanoparticulate films for the oxygen evolution reaction under conditions relevant to an integrated solar fuels device. In general, the activities of the adhered nanoparticulate films are similar to those of thin-film catalysts prepd. by electrodeposition or sputtering, achieving 10 mA cm-2 current densities per geometric area at overpotentials of ∼0.35-0.5 V.
- 67Batchellor, A. S.; Boettcher, S. W. Pulse-Electrodeposited Ni–Fe (Oxy)Hydroxide Oxygen Evolution Electrocatalysts with High Geometric and Intrinsic Activities at Large Mass Loadings. ACS Catal. 2015, 5, 6680– 6689, DOI: 10.1021/acscatal.5b01551Google Scholar67https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFKru7bJ&md5=69976b3eb8103db04e6eab8e93c8c26ePulse-Electrodeposited Ni-Fe (Oxy)hydroxide Oxygen Evolution Electrocatalysts with High Geometric and Intrinsic Activities at Large Mass LoadingsBatchellor, Adam S.; Boettcher, Shannon W.ACS Catalysis (2015), 5 (11), 6680-6689CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)One practical metric for electrocatalyst performance is current per geometric area at a given applied overpotential. An obvious route to increase performance is to increase the catalyst mass loading-as long as the intrinsic performance (i.e., specific activity or turnover frequency) of the catalyst is independent of loading, and other elec., ionic, or mass-transfer resistances are not severe. Here we report the geometric and intrinsic oxygen evolution reaction (OER) activities of Ni(Fe)OOH films, the fastest known water oxidn. catalyst in basic media, as a function of mass loading from 0 to ∼100 μg cm-2. We discuss practices for measuring and reporting intrinsic activities, highlighting exptl. conditions where the film activity on a per-metal-cation basis can be accurately measured and where capacitance measurements of electrochem. active surface area fail. We find that the electrochem. reversibility of the (nominally) Ni2+/3+ redox wave correlates with the apparent intrinsic activity as a function of loading. We report a pulsed-electrodeposition method that dramatically improves the catalyst reversibility and performance at high loading compared to continuous electrodeposition, which we attribute to improved connectivity in the micro/nanostructure and better compn. control. Pulse electrodeposited films are shown to have geometric performance similar to a no. of advanced composite electrocatalyst structures and to maintain effective per-metal turnover frequencies of >0.4 s-1 at 300 mV overpotential, even for loadings of ∼100 μg/cm2.
- 68Takeno, N. Atlas of Eh-pH Diagrams Intercomparison of Thermodynamic Databases , Geological Survey of Japan Open File Report No. 419, National Institute of Advanced Industrial Science and Technology Research Center for Deep Geological Environments, 2005.Google ScholarThere is no corresponding record for this reference.
- 69Zou, X.; Liu, Y.; Li, G.-D.; Wu, Y.; Liu, D.-P.; Li, W.; Li, H.-W.; Wang, D.; Zhang, Y.; Zou, X. Ultrafast Formation of Amorphous Bimetallic Hydroxide Films on 3D Conductive Sulfide Nanoarrays for Large-Current-Density Oxygen Evolution Electrocatalysis. Adv. Mater. 2017, 29, 1700404, DOI: 10.1002/adma.201700404Google ScholarThere is no corresponding record for this reference.
- 70Pi, Y.; Shao, Q.; Wang, P.; Lv, F.; Guo, S.; Guo, J.; Huang, X. Trimetallic Oxyhydroxide Coralloids for Efficient Oxygen Evolution Electrocatalysis. Angew. Chem., Int. Ed. 2017, 56, 4502– 4506, DOI: 10.1002/anie.201701533Google Scholar70https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXkslKru74%253D&md5=ab834584b2db1fe64cfce3cbc757d587Trimetallic Oxyhydroxide Coralloids for Efficient Oxygen Evolution ElectrocatalysisPi, Yecan; Shao, Qi; Wang, Pengtang; Lv, Fan; Guo, Shaojun; Guo, Jun; Huang, XiaoqingAngewandte Chemie, International Edition (2017), 56 (16), 4502-4506CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Trimetallic oxyhydroxides are one of the most effective materials for oxygen evolution reaction (OER) catalysis, a key process for water splitting. Herein, a facile wet-chem. method is described to directly grow a series of coralloid trimetallic oxyhydroxides on arbitrary substrates such as nickel foam (NF) and carbon nanotubes (CNTs). The amt. of iron in these oxyhydroxide sponges on NF and CNTs was precisely controlled, revealing that the electrocatalytic activity of the WCoFe trimetallic oxyhydroxides depends on the Fe amt. in a volcano-like fashion. The optimized W0.5Co0.4Fe0.1/NF catalyst exhibited an overpotential of only 310 mV to deliver a large c.d. of 100 mA cm-2 and a very low Tafel slope of 32 mV dec-1. It also showed superior stability with negligible activity decay after use in the OER for 21 days (> 500 h). XPS revealed that the addn. of Fe leads to an on av. lower Co oxidn. state, which contributes to the enhanced OER performance.
- 71Nai, J.; Lu, Y.; Yu, L.; Wang, X.; Lou, X. W. D. Formation of Ni-Fe Mixed Diselenide Nanocages as a Superior Oxygen Evolution Electrocatalyst. Adv. Mater. 2017, 29, 1703870, DOI: 10.1002/adma.201703870Google ScholarThere is no corresponding record for this reference.
- 72Guerrini, E.; Trasatti, S. Recent Developments in Understanding Factors of Electrocatalysis. Russ. J. Electrochem. 2006, 42, 1017– 1025, DOI: 10.1134/S1023193506100053Google Scholar72https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhtVKjur%252FJ&md5=21b7197b88f8c0aeeac0707e56cfc87dRecent developments in understanding factors of electrocatalysisGuerrini, E.; Trasatti, S.Russian Journal of Electrochemistry (2006), 42 (10), 1017-1025CODEN: RJELE3; ISSN:1023-1935. (MAIK Nauka/Interperiodica Publishing)A review. After an introductory anal. of terms and concepts in the field of electrocatalysis, a no. of exptl. examples are reported to illustrate various factors. In particular, Tafel slope and PZC of oxide electrodes are able to disentangle electronic from geometric factors. The points under discussion are: effect of particle size and methods of prepn., surface vs. bulk compn., primary vs. secondary effects with redox systems depending on the mol. structure of the couple, single crystal vs. polycryst. surfaces. The last case is particularly relevant since for the 1st time vicinal faces of RuO2 behave at the extremes of the usually obsd. exptl. picture.
- 73Tilak, B. V.; Conway, B. E. Analytical Relations between Reaction Order and Tafel Slope Derivatives for Electrocatalytic Reactions Involving Chemisorbed Intermediates. Electrochim. Acta 1992, 37, 51– 63, DOI: 10.1016/0013-4686(92)80011-AGoogle Scholar73https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XntVeisw%253D%253D&md5=603ddfa1501120eb5b810e386b2d6b42Analytical relations between reaction order and Tafel slope derivatives for electrocatalytic reactions involving chemisorbed intermediatesTilak, B. V.; Conway, B. E.Electrochimica Acta (1992), 37 (1), 51-61CODEN: ELCAAV; ISSN:0013-4686.It is shown that characteristic relations between reaction order R and Tafel slope derivs. b can be deduced for the two principal desorption types of pathways, "electrochem." and "recombination", common in electrocatalytic reactions involving a single chemisorbed intermediate leading to dimeric product, e.g. H2, Cl2. The exptl. measureable R usually differs from the kinetically-significant surface reaction order in heterogeneous processes through the logarithmic deriv. d ln Θ/d ln c of the absorption isotherm function Θ(c), where Θ is the fractional coverage of the reaction surface by chemisorbed intermediates and/or reagent species. Cases where significant lateral interaction effects arise are considered and distinguished from those for which Langmuir adsorption behavior obtains. Results based on the quasi-equil. hypothesis in the treatment of consecutive electrochem. reaction kinetics are distinguished from those derived by the steady-state method; simple factors arise which relate the results for R and for b derived by the two methods. The dependence of R and b values for the two desorption mechanisms on coverage, Θ by the kinetically involved intermediate are evaluated and exhibit usefully distinguishable characteristics. Applications to some selected exptl. results are discussed with regard to conclusions about reaction mechanisms based on evaluation of R in relation to b values.
- 74Rosestolato, D.; Fregoni, J.; Ferro, S.; De Battisti, A. Influence of the Nature of the Electrode Material and Process Variables on the Kinetics of the Chlorine Evolution Reaction. The Case of IrO2-Based Electrocatalysts. Electrochim. Acta 2014, 139, 180– 189, DOI: 10.1016/j.electacta.2014.07.037Google Scholar74https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1KgsLnN&md5=248da2acb6856630d0fd5ebc1d03462aInfluence of the nature of the electrode material and process variables on the kinetics of the chlorine evolution reaction. The case of IrO2-based electrocatalystsRosestolato, Davide; Fregoni, Jacopo; Ferro, Sergio; De Battisti, AchilleElectrochimica Acta (2014), 139 (), 180-189CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Kinetic studies on the chlorine evolution reaction (ChlER) on oxide-based materials were the subject of a no. of papers since the seventies, following the introduction of DSAs (Dimensionally Stable Anodes) in chlor-alkali plants. From exptl. data, different pathways are proposed for the reaction over the years. Actually, specific exptl. conditions and different approaches in sample prepn. may lead to conflicting explanations. The ChlER kinetics was studied at four electrode materials based on iridium and titanium oxides (with a 1:2 molar ratio). Electrodes were synthesized at two temps. (350 and 450°) and by two different prepn. methods: phys. vapor deposition (radiofrequency-magnetron sputtering) and a conventional sol-gel technique, using special precursors developed in the authors' lab. Both methodologies guarantee a high level of reproducibility. As also obsd. by other authors, exptl. data showed a lack of linearity in Tafel plots, high b slopes and reaction orders with respect to chloride ≤ 1, which were justified from a Volmer-Heyrovsky pathway, by considering a model proposed by Tilak and Conway in 1992. This approach highlighted the role of the adsorbed intermediates, also at low overpotentials, for all electrode materials. To analyze further the kinetics, Langmuir and Frumkin models for intermediates adsorption were considered. Values for the lateral interaction parameter g were estd., which ranged between 1 and 10, in all cases. Concerning the effect of pH, its influence on the ChlER rate seems to be related only with electrode surface modifications, without any involvement of protons in the rate detg. step of the process. A slight inhibiting effect was assessed, by increasing the protons concn. Eventually, impedance spectroscopy anal. did not appear sensitive to intermediate adsorption, plausibly because of the low variation of the coverage within the Tafel region; a poorly resolved contribution related to porosity was found in the case of samples prepd. at 350°.
- 75Krishtalik, L. I. Kinetics and Mechanism of Anodic Chlorine and Oxygen Evolution Reactions on Transition Metal Oxide Electrodes. Electrochim. Acta 1981, 26, 329– 337, DOI: 10.1016/0013-4686(81)85019-0Google Scholar75https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3MXitFKns7s%253D&md5=8cb5a9acc55a091c083d00475382aba9Kinetics and mechanism of anodic chlorine and oxygen evolution reactions on transition metal oxide electrodesKrishtalik, L. I.Electrochimica Acta (1981), 26 (3), 329-37CODEN: ELCAAV; ISSN:0013-4686.The 3-step mechanism of the Cl evolution at RuO2 and RuO2-TiO2 electrodes with the rate-detg. transfer of the 2nd electron and the formation of the nominally unipos. Cl as an intermediate is substantiated from kinetic data. The applicability of an analogous mechanism to the O evolution reaction is discussed as well as the possibility of participation in the process of higher oxidn. states of Ru. Analogies were drawn between anodic processes at RuO2 and other transition metal oxides.
- 76Exner, K. S.; Anton, J.; Jacob, T.; Over, H. Chlorine Evolution Reaction on RuO2(110): Ab Initio Atomistic Thermodynamics Study - Pourbaix Diagrams. Electrochim. Acta 2014, 120, 460– 466, DOI: 10.1016/j.electacta.2013.11.027Google Scholar76https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFGrt7fO&md5=1d0ec013b4c360ccc2f3ca4a18192836Chlorine Evolution Reaction on RuO2(110): Ab initio Atomistic Thermodynamics Study - Pourbaix DiagramsExner, Kai S.; Anton, Josef; Jacob, Timo; Over, HerbertElectrochimica Acta (2014), 120 (), 460-466CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Constrained ab initio thermodn. as a Pourbaix diagram can greatly assist kinetic modeling of a particular electrochem. reaction such as the Cl evolution reaction (CER) over RuO2(110). Pourbaix diagrams reveal stable surface structures, as a function of pH and the potential. The present DFT study indicates that the Pourbaix diagram in the CER potential region >1.36 V and pH values around zero is dominated by a stable surface structure in which all coordinatively undercoordinated Ru sites (Rucus) are capped by on-top O (Oot). This O satd. RuO2(110) surface is considered to serve as the catalytically active phase in the CER, quite in contrast to the heterogeneously catalyzed HCl oxidn. (Deacon process), for which the active RuO2(110) surface is mainly covered by on-top Cl. The active sites in the CER probably are RucusOot surface complexes, while in the Deacon process both undercoordinated surface Ru and O sites must be available for the activation of HCl mols.
- 77Koper, M. T. M. A Lattice-Gas Model for Halide Adsorption on Single-Crystal Electrodes. J. Electroanal. Chem. 1998, 450, 189– 201, DOI: 10.1016/S0022-0728(97)00648-7Google Scholar77https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXjtlOlu7o%253D&md5=65bc9a7c8e2e24c0045f7ae3b4217c19A lattice-gas model for halide adsorption on single-crystal electrodesKoper, Marc T. M.Journal of Electroanalytical Chemistry (1998), 450 (2), 189-201CODEN: JECHES ISSN:. (Elsevier Science S.A.)A lattice-gas model is described for the adsorption of halides on single-crystal electrodes. The lateral interactions between the adsorbed halides include a short-range nearest-neighbor interaction and a long-range electrostatic interaction. By Monte Carlo simulations the model is used to fit the exptl. isotherm of bromide adsorption on Ag(100), giving information about the relative importance of the long-range and short-range interactions. The model reproduces the order-disorder transition obsd. exptl., and the way in which the long-ranged interactions influence the properties of this phase transition is discussed. The Monte Carlo simulations are also compared to anal. mean-field and quasi-chem. approxns. to the isotherm. Finally, the kinetics of the disorder-order transition is studied by dynamic Monte Carlo simulations, and some results on isotherms and ordered phases on (110) and (111) surfaces are described.
- 78Fernández, J. L.; Gennero de Chialvo, M. R.; Chialvo, A. C. Kinetic Study of the Chlorine Electrode Reaction on Ti/RuO2 through the Polarisation Resistance. Electrochim. Acta 2002, 47, 1137– 1144, DOI: 10.1016/S0013-4686(01)00838-6Google Scholar78https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XjvFegsA%253D%253D&md5=6ecbeef48fb95822b8928393ec9595ebKinetic study of the chlorine electrode reaction on Ti/RuO2 through the polarisation resistance. Part II: Mechanistic analysisFernandez, J. L.; Gennero de Chialvo, M. R.; Chialvo, A. C.Electrochimica Acta (2002), 47 (7), 1137-1144CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Science Ltd.)A new methodol. for the kinetic treatment of electrode reactions is presented. It is based on a theor. anal. of the predictive capability of different mechanisms for the dependence of the polarization resistance on the different operative variables. This procedure is applied in this case to the anal. of the chlorine electrode reaction on Ti/RuO2, for which the variation of the polarization resistance on the activity of the chloride ions and on the partial pressure of the chlorine gas is derived. The descriptive capability of the mechanisms under discussion at present for this reaction is discussed and the theor. dependences are compared with exptl. data.
- 79Santana, M. H. P.; De Faria, L. A. Oxygen and Chlorine Evolution on RuO2+TiO2+CeO2+Nb2O5Mixed Oxide Electrodes. Electrochim. Acta 2006, 51, 3578– 3585, DOI: 10.1016/j.electacta.2005.09.050Google Scholar79https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XjsFeht70%253D&md5=abb82f0ce7beb4e9a7d53550437bee1bOxygen and chlorine evolution on RuO2 + TiO2 + CeO2 + Nb2O5 mixed oxide electrodesSantana, Mario H. P.; De Faria, Luiz A.Electrochimica Acta (2006), 51 (17), 3578-3585CODEN: ELCAAV; ISSN:0013-4686. (Elsevier B.V.)A systematic study was conducted on the mechanism and electrocatalytic properties of O2 and Cl2 evolution on mixed oxide electrodes of nominal compn.: Ti/[Ru(0.3)Ti(0.6)Ce(0.1-x)]O2[Nb2O5](x) (0 ≤ x ≤ 0.1). For the oxygen evolution, a 30 mV Tafel slope is obtained in the presence of CeO2, while in its absence a 40 mV coeff. is obsd. The intrinsic electrocatalytic activity is mainly due to electronic factors, as result of the synergism between Ru and Ce oxides. For chlorine evolution, the Tafel slope (30 mV) is independent on oxide compn. The best global electrocatalytic activity for ClER (chlorine evolution reaction) was obsd. in the absence of Nb2O5 additive. Variation of the voltammetric charge throughout the expts. confirms high CeO2 content compns. are fragile, due mainly to the porosity caused by CeO2 presence. However, Nb2O5 addn. decreases considerably this instability.
- 80Boggio, R.; Carugati, A.; Lodi, G.; Trasatti, S. Mechanistic Study of Cl2 Evolution at Ti-Supported Co3O4 Anodes. J. Appl. Electrochem. 1985, 15, 335– 349, DOI: 10.1007/BF00615986Google Scholar80https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXit1yisrY%253D&md5=a928f99624f0bf71da545ca36a41820fMechanistic study of chlorine evolution at titanium-supported cobalt oxide (Co3O4) anodesBoggio, R.; Carugati, A.; Lodi, G.; Trasatti, S.Journal of Applied Electrochemistry (1985), 15 (3), 335-49CODEN: JAELBJ; ISSN:0021-891X.Co3O4 layers were prepd. by thermal decompn. of Co(NO3)2 at various temps. in the range 200-500° on a Ti support with and without an interlayer of RuO2. Kinetic studies were carried out with and without dissolved Cl at variouspartial pressures in NaCl solns. of concns. in the range 0.5-5 mol dm-3. The effect of the soln. pH was esp. investigated. Kinetic measurements were carried out both near and far from equil. The following parameters were detd.: transfer coeff., Tafel slope, stoichiometric no., reaction orders with respect to Cl-, H* and surface sites, activation energy. The most intriguing feature obsd. was the inhibiting effect of acidity on the anodic Cl reaction. This behavior was ascribed to the complex surface behavior of oxides in soln. A detailed mechanistic scheme is proposed and discussed. The stability of the oxide surface was monitored by measuring the voltammetric charge in alk. soln. after sets of expts.
- 81Conway, B. E.; Ping, G.; De Battisti, A.; Barbieri, A.; Battaglin, G. Behaviour of the Adsorbed Cl* Intermediate in Anodic Cl2 Evolution at Thin-Film RuO2 Surfaces. J. Mater. Chem. 1991, 1, 725, DOI: 10.1039/jm9910100725Google Scholar81https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXms1GgsLk%253D&md5=38491baeffbd0c5153284e3e17a282f7Behavior of the adsorbed atomic chlorine intermediate in anodic chlorine evolution at thin-film ruthenium dioxide surfacesConway, Brian E.; Ping, Gu; De Battisti, Achille; Barbieri, Andrea; Battaglin, G.Journal of Materials Chemistry (1991), 1 (5), 725-34CODEN: JMACEP; ISSN:0959-9428.Studies of the adsorption of the Cl• intermediate in anodic Cl2 evolution at a series of four thin-film RuO2 electrodes formed on a Ti substrate were made by means of potential-relaxation measurements, following interruption of previous steady-state currents, coupled with detn. of the current vs. overpotential kinetic relationships. Expts. at rotated RuO2 electrodes show only a small effect, indicating that neither diffusion-controlled supply of Cl- nor effects of Cl2 supersatn. in the boundary region at the electrode materially effect the kinetic behavior. This behavior is manifested as continuously curved Tafel relations, which approach limiting currents at overvoltages of 0.2-0.3 V. Therefore, on these thin-film RuO2 materials, kinetic control of Cl2 evolution seems to be by the Cl• recombination pathway; this is supported by linearity of Conway-Novak test plots for the recombination mechanism. Anal. of the potential-relaxation transients enables the pseudocapacitance, C.vphi., for adsorbed Cl• to be detd. The C.vphi. shows ascent to large values below 50-100 mV of overpotential, depending on temp. Some problems arise, however, in reconciling this adsorption behavior with expectations assocd. with recombination control. The near-surface compn. profiles of the RuO2 films were detd. by means of Rutherford backscattering and the av. compns., deeper into the films, by energy-dispersive x-ray emission analyses.
- 82Conway, B. E.; Novak, D. M. Chloride Ion Adsorption Effects in the Recombination-Controlled Kinetics of Anodic Chlorine Evolution at Pt Electrodes. J. Chem. Soc., Faraday Trans. 1 1979, 75, 2454– 2472, DOI: 10.1039/f19797502454Google Scholar82https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3cXjtVyrug%253D%253D&md5=5df00ef4deeacb318310d6eb6b1c7ee2Chloride ion adsorption effects in the recombination-controlled kinetics of anodic chlorine evolution at platinum electrodesConway, Brian E.; Novak, Dunja M.Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases (1979), 75 (11), 2454-72CODEN: JCFTAR; ISSN:0300-9599.The role of Cl- adsorption in the anodic evolution of Cl2 at Pt electrodes in aq. solns. was examd. over a range of Cl- concns. The rate const. for the rate-detg. recombination step and the quasiequil. const. of the prior Cl- discharge/Cl• electrosorption step were evaluated quant. as a function of the Cl- concn. Despite the approach of the anodic current/potential relation towards limiting current behavior, consistent with recombination-controlled kinetics, the limiting current densities vary with the Cl- concn. This behavior is due to effects of specifically adsorbed Cl- on the Cl• recombination rate const. and to changes of state of the Pt anode surface due to competitive effects of Cl- adsorption on the extent of Pt surface oxidn. These factors complicate the interpretation of reaction orders in Cl- concns. for the evolution of Cl2 because both effects must be considered.
- 83Ferro, S.; De Battisti, A. Electrocatalysis and Chlorine Evolution Reaction at Ruthenium Dioxide Deposited on Conductive Diamond. J. Phys. Chem. B 2002, 106, 2249– 2254, DOI: 10.1021/jp012195iGoogle Scholar83https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38Xps1artg%253D%253D&md5=8915bd5e962e7c344e2e48a80d1b504aElectrocatalysis and Chlorine Evolution Reaction at Ruthenium Dioxide Deposited on Conductive DiamondFerro, Sergio; De Battisti, AchilleJournal of Physical Chemistry B (2002), 106 (9), 2249-2254CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)The instability of the commonly adopted support (e.g., Ti, Ti-Pd alloys, Ta) for the prepn. and characterization of different electrode materials was overcome by depositing the electrode material of interest (RuO2) on conductive, boron-doped diamond (BDD). The present paper reports results on the model chlorine evolution reaction, studied at BDD surfaces modified by RuO2 loadings of 1.2 × 1013, 6.0 × 1014, and 2.65 × 1016 mols. cm-2. A radical spillover mechanism is proposed for the reaction occurring at the electrode having the lowest noble-metal oxide loading.
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Abstract
Figure 1
Figure 1. Online electrochemical iridium dissolution from ICP-MS measurements. Panel A, Ir dissolution over time correlated with the applied E vs t protocol (red) for Ba2PrIrO6 (blue), Sr2YIrO6 (green), and Ba2YIrO6 (yellow) in 0.1 M HClO4 (solid) and 0.1 M HClO4 with 50 mM NaCl (pale). For clarity reasons, the initial contact peak is not shown (see Figure S 1 for the full version). Panel B, Ir dissolution along with the current density of the LSV of the E vs t protocol. Panel C, S-number (amount of gases evolved per amount of Ir dissolved) comparison in the presence and absence of 50 mM NaCl. Panel D, total dissolved amount of Ir during initial contact with the electrolyte, cycling, and the LSV, as determined from the initial spot loading (see also Table S 1).
Figure 2
Figure 2. Voltammetric characterization of the Ir-based double perovskites used in this study, in a 0.1 M HClO4 solution, supported on GC. All materials were scanned at least 20 times in the range of 1.30–1.55 V at 1500 rpm prior to characterization. Catalysts are shown in groups with pronounced Ir redox transitions (A) and those with less obvious features, plus the IrO2 reference (B). Scan rate: 50 mV s–1.
Figure 3
Figure 3. OER (A) and CER (B) Tafel curves obtained by scanning the electrode between 1.30 and 1.55 V at 10 mV s–1: (A) “pure” OER current densities in a 0.1 M HClO4 solution and (B) CER current densities in a 0.1 M HClO4 + 20 mM NaCl solution, derived from ring currents on a Pt ring fixed at 0.95 V vs RHE. Values shown are the average of at least three independent measurements (see Figure S 9 for a version containing error bars). Solutions saturated with Ar, rotation rate 1500 rpm.
Figure 4
Figure 4. Correlations between OER and CER activities, data derived from Figure 3 (CER measured in 20 mM NaCl). (A and B) OER vs CER current densities compared at 1.50 and 1.55 V, respectively. (C) Comparison of CER Tafel slope vs current densities measured at 1.50 V, the upper potential limit of the linear portion (see also Figure 3B). (D) Comparison of Tafel slopes from linear portions (1.45–1.50 V) of OER and CER. All data are averages of at least three independent measurements; error bars represent corresponding standard deviations.
Figure 5
Figure 6
Figure 6. Effect of chloride concentration on OER and CER. (A) OER currents measured in the presence of 20 mM NaCl, in parallel with CER. (B and C) Relative OER current (B) and CER current (C) as a function of increasing chloride concentration. The % OER currents are shown relative to chloride free conditions (0 mM NaCl), and the % CER currents are shown relative to 30 mM NaCl. See Figure S 12 for versions of parts A and B containing absolute currents.
Figure 7
Figure 7. Reaction orders vs chloride concentration ( for OER (A) and CER (B). Values were derived using the [Cl–]-dependent slopes of Figures S 15 and S 16.
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- 10Moussallem, I.; Jörissen, J.; Kunz, U.; Pinnow, S.; Turek, T. Chlor-Alkali Electrolysis with Oxygen Depolarized Cathodes: History, Present Status and Future Prospects. J. Appl. Electrochem. 2008, 38, 1177– 1194, DOI: 10.1007/s10800-008-9556-910https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXptlWjtrs%253D&md5=692153cd985008879000a9c3822c4290Chlor-alkali electrolysis with oxygen depolarized cathodes: history, present status and future prospectsMoussallem, Imad; Joerissen, Jakob; Kunz, Ulrich; Pinnow, Stefan; Turek, ThomasJournal of Applied Electrochemistry (2008), 38 (9), 1177-1194CODEN: JAELBJ; ISSN:0021-891X. (Springer)A review. The historical development, current status and future prospects of chlor-alkali electrolysis with oxygen depolarized cathodes (ODCs) are summarized. Over the last decades, membrane chlor-alkali technol. has been optimized to such an extent that no substantial redn. of the energy demand can be expected from further process modifications. However, replacement of the hydrogen evolving cathodes in the classical membrane cells by ODCs allows for redn. of the cell voltage and correspondingly the energy consumption of up to 30%. This replacement requires the development of appropriate cathode materials and novel electrolysis cell designs. Due to their superior long-term stability, ODCs based on silver catalysts are very promising for oxygen redn. in concd. NaOH solns. Finite-gap falling film cells appear to be the tech. most mature design among the several ODC electrolysis cells that have been investigated.
- 11Jung, J.; Postels, S.; Bardow, A. Cleaner Chlorine Production Using Oxygen Depolarized Cathodes? A Life Cycle Assessment. J. Cleaner Prod. 2014, 80, 46– 56, DOI: 10.1016/j.jclepro.2014.05.08611https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtVKhsbfL&md5=6ce2c4db81210720bb86424e9113eb08Cleaner chlorine production using oxygen depolarized cathodes? A life cycle assessmentJung, Johannes; Postels, Sarah; Bardow, AndreJournal of Cleaner Production (2014), 80 (), 46-56CODEN: JCROE8; ISSN:0959-6526. (Elsevier Ltd.)Chlorine and caustic soda are two indispensable chem. commodities co-produced in the so-called chlor-alkali electrolysis. Chlor-alkali electrolysis is today a target for cleaner prodn. because of its large electricity demand causing considerable environmental impacts. The electricity demand of chlor-alkali electrolysis can be reduced by 30% using oxygen depolarized cathodes (ODCs) instead of the std. cathodes (STCs) used today. However, ODCs require addnl. resources and do not produce hydrogen in contrast to existing chlor-alkali plants. This work investigates if the redn. in electricity demand also contributes to cleaner prodn. For this purpose, environmental impacts from chlor-alkali electrolysis using ODCs are compared to the impacts from best available existing chlor-alkali plants using STCs. The life cycle assessment includes manufg., operation and disposal of the plants. To account for utilization of hydrogen from existing chlor-alkali plants, two alternative utilization scenarios are studied: energy recovery by combustion of hydrogen and use of hydrogen as chem. commodity. Seven environmental impact categories are studied in detail using the ReCiPe method. Chlor-alkali electrolysis using ODCs yields lower environmental impacts in up to six environmental impact categories. Plant operation contributes most in six out of seven impact categories. Chlor-alkali electrolysis using ODCs has thus potential to contribute to cleaner prodn. in the chlor-alkali industry.
- 12Wang, X.; Tong, C.; Palazoglu, A.; El-Farra, N. H. Energy Management for the Chlor-Alkali Process with Hybrid Renewable Energy Generation Using Receding Horizon Optimization. In 53rd IEEE Conference on Decision and Control , Los Angeles, CA, December 15–17, 2014; pp 4838– 4843.There is no corresponding record for this reference.
- 13Trasatti, S. Progress in the Understanding of the Mechanism of Chlorine Evolution at Oxide Electrodes. Electrochim. Acta 1987, 32, 369– 382, DOI: 10.1016/0013-4686(87)85001-613https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXhsVGrtb4%253D&md5=0a0ac5123b10b681827ce9499dffc9e6Progress in the understanding of the mechanism of chlorine evolution at oxide electrodesTrasatti, SergioElectrochimica Acta (1987), 32 (3), 369-82CODEN: ELCAAV; ISSN:0013-4686.A review with 78 refs. is given on the mechanism of Cl2 evolution at such oxides as RuO2, RuO2 + TiO2, Co3O4 and NiCo2O4. After introductory general thermodn. and kinetic considerations, the possible factors which can distort the kinetic measurements of Cl2 evolution at oxide electrodes, giving rise to mistaken mechanisms, are analyzed as resulting from a retrospective anal. of the literature. Such factors include: mixed potentials, porosity, removal of produced Cl2, bubble formation, support passivation, morphol. and compn. of the active layer, ion sp. adsorption, and pH effects. In the light of the insight gained step-by-step on the possible interference by the above exptl. factors, the various mechanism proposals are reviewed, mainly chronol., to highlight the conceptual and exptl. progress made in this field in the past 15 yr. Conclusions are finally drawn which enable some possible topics for further research in this area to be discussed.
- 14Duby, P. The History of Progress in Dimensionally Stable Anodes. JOM 1993, 45, 41– 43, DOI: 10.1007/BF0322235014https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXitVWisr0%253D&md5=9d35cc062c68fd726c518203807c237eThe history of progress in dimensionally stable anodesDuby, PaulJOM (1993), 45 (3), 41-3CODEN: JOMMER; ISSN:1047-4838.A review with 50 refs. is presented. A brief history is provided of dimensionally stable anodes by reviewing innovations in the chlor-alkali industry, electroplating, and electrowinning. These anodes are attractive for numerous reasons (e.g., long life and reduced energy consumption), but they must still overcome the hurdle of cost to gain wider acceptance for applications in the metallurgical process industries.
- 15Karlsson, R. K. B.; Cornell, A. Selectivity between Oxygen and Chlorine Evolution in the Chlor-Alkali and Chlorate Processes. Chem. Rev. 2016, 116, 2982– 3028, DOI: 10.1021/acs.chemrev.5b0038915https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XisFahsLk%253D&md5=bf845f24c741b49db6a0e169caf132bdSelectivity between Oxygen and Chlorine Evolution in the Chlor-Alkali and Chlorate ProcessesKarlsson, Rasmus K. B.; Cornell, AnnChemical Reviews (Washington, DC, United States) (2016), 116 (5), 2982-3028CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. Cl gas and Na chlorate are two base chems. produced through electrolysis of NaCl brine which find uses in many areas of industrial chem. Although the industrial prodn. of these chems. started over 100 years ago, there are still factors that limit the energy efficiencies of the processes. This review focuses on the unwanted prodn. of O gas, which decreases the charge yield by up to 5%. Understanding the factors that control the rate of O prodn. requires understanding of both chem. reactions occurring in the electrolyte, as well as surface reactions occurring on the anodes. The dominant anode material used in chlorate and chlor-alkali prodn. is the dimensionally stable anode (DSA), Ti coated by a mixed oxide of RuO2 and TiO2. Although the selectivity for Cl evolution on DSA is high, the fundamental reasons for this high selectivity are just now becoming elucidated. This review summarizes the research, since the early 1900s until today, concerning the selectivity between Cl and O evolution in chlorate and chlor-alkali prodn. It covers exptl. as well as theor. studies and highlights the relations between process conditions, electrolyte compn., the material properties of the anode, and the selectivity for O formation.
- 16Jefferson, M. A Renewable Energy Future? In Handbook on Energy and Climate Change; Edward Elgar Publishing, 2013; Vol. 285, pp 254– 269.There is no corresponding record for this reference.
- 17Zeng, K.; Zhang, D. Recent Progress in Alkaline Water Electrolysis for Hydrogen Production and Applications. Prog. Energy Combust. Sci. 2010, 36, 307– 326, DOI: 10.1016/j.pecs.2009.11.00217https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXis1OqtLw%253D&md5=fb3b70cabefcb81fd4fc2ab3a228a3fbRecent progress in alkaline water electrolysis for hydrogen production and applicationsZeng, Kai; Zhang, DongkeProgress in Energy and Combustion Science (2010), 36 (3), 307-326CODEN: PECSDO; ISSN:0360-1285. (Elsevier Ltd.)A review. Alk. water electrolysis is one of the easiest methods for hydrogen prodn., offering the advantage of simplicity. The challenges for widespread use of water electrolysis are to reduce energy consumption, cost and maintenance and to increase reliability, durability and safety. This literature review examines the current state of knowledge and technol. of hydrogen prodn. by water electrolysis and identifies areas where R&D effort is needed in order to improve this technol. Following an overview of the fundamentals of alk. water electrolysis, an elec. circuit analogy of resistances in the electrolysis system is introduced. The resistances are classified into three categories, namely the elec. resistances, the reaction resistances and the transport resistances. This is followed by a thorough anal. of each of the resistances, by means of thermodn. and kinetics, to provide a scientific guidance to minimising the resistance in order to achieve a greater efficiency of alk. water electrolysis. The thermodn. anal. defines various electrolysis efficiencies based on theor. energy input and cell voltage, resp. These efficiencies are then employed to compare different electrolysis cell designs and to identify the means to overcome the key resistances for efficiency improvement. The kinetic anal. reveals the dependence of reaction resistances on the alk. concn., ion transfer, and reaction sites on the electrode surface, the latter is detd. by the electrode materials. A quant. relationship between the cell voltage components and c.d. is established, which links all the resistances and manifests the importance of reaction resistances and bubble resistances. The important effect of gas bubbles formed on the electrode surface and the need to minimise the ion transport resistance are highlighted. The historical development and continuous improvement in the alk. water electrolysis technol. are examd. and different water electrolysis technologies are systematically compared using a set of the practical parameters derived from the thermodn. and kinetic analyses. In addn. to the efficiency improvements, the needs for redn. in equipment and maintenance costs, and improvement in reliability and durability are also established. The future research needs are also discussed from the aspects of electrode materials, electrolyte additives and bubble management, serving as a comprehensive guide for continuous development of the water electrolysis technol.
- 18Man, I. C.; Su, H. Y.; Calle-Vallejo, F.; Hansen, H. A.; Martínez, J. I.; Inoglu, N. G.; Kitchin, J.; Jaramillo, T. F.; Nørskov, J. K.; Rossmeisl, J. Universality in Oxygen Evolution Electrocatalysis on Oxide Surfaces. ChemCatChem 2011, 3, 1159– 1165, DOI: 10.1002/cctc.20100039718https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotFyjsb0%253D&md5=f4103e77db6bcd3ba840b6376b33315aUniversality in Oxygen Evolution Electrocatalysis on Oxide SurfacesMan, Isabela C.; Su, Hai-Yan; Calle-Vallejo, Federico; Hansen, Heine A.; Martinez, Jose I.; Inoglu, Nilay G.; Kitchin, John; Jaramillo, Thomas F.; Noerskov, Jens K.; Rossmeisl, JanChemCatChem (2011), 3 (7), 1159-1165CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)Trends in electrocatalytic activity of the O evolution reaction (OER) were studied from a large database of HO* and HOO* adsorption energies on oxide surfaces. The theor. overpotential was calcd. by applying std. d. functional theory in combination with the computational std. H electrode (SHE) model. By the discovery of a universal scaling relation between the adsorption energies of HOO* vs. HO*, it is possible to analyze the reaction free energy diagrams of all the oxides in a general way. This gave rise to an activity volcano that was the same for a wide variety of oxide catalyst materials and a universal descriptor for the O evolution activity, which suggests a fundamental limitation on the max. O evolution activity of planar oxide catalysts.
- 19Fabbri, E.; Schmidt, T. J. Oxygen Evolution Reaction—The Enigma in Water Electrolysis. ACS Catal. 2018, 8, 9765– 9774, DOI: 10.1021/acscatal.8b0271219https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhslSgu7%252FM&md5=afd99f985774534b72ffa335f84fbb2fOxygen Evolution Reaction-The Enigma in Water ElectrolysisFabbri, Emiliana; Schmidt, Thomas J.ACS Catalysis (2018), 8 (10), 9765-9774CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)A review is given. We aim at increasing the awareness among the scientific community devoted to progresses in water electrolyzers of the very recent development made in the fundamental understanding of the OER, particularly focusing on the increasing consciousness that several processes actually underpin the evolution of O from a metal oxide catalyst. Traditionally, the OER mechanism on metal oxides has been derived from that on metal catalysts, where the main parameter governing the reaction overpotential is the binding strength of O (or oxygenated species/intermediates) on the catalyst surface following the Sabatier principle: the best catalyst in terms of displaying the min. overpotential binds O on its surface neither too strongly nor too weakly.
- 20Panić, V. V.; Dekanski, A. B.; Milonjić, S. K.; Mišković-Stanković, V. B.; Nikolić, B. Ž. Electrocatalytic Activity of Sol-Gel-Prepared RuO2/Ti Anode in Chlorine and Oxygen Evolution Reactions. Russ. J. Electrochem. 2006, 42, 1055– 1060, DOI: 10.1134/S102319350610010720https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhtVKjtbfK&md5=bbe86d7b76e20e7460edf9c1176e0b4dElectrocatalytic activity of sol-gel-prepared RuO2/Ti anode in chlorine and oxygen evolution reactionsPanic, V. V.; Dekanski, A. B.; Milonjic, S. K.; Miskovic-Stankovic, V. B.; Nikolic, B. Z.Russian Journal of Electrochemistry (2006), 42 (10), 1055-1060CODEN: RJELE3; ISSN:1023-1935. (MAIK Nauka/Interperiodica Publishing)Electrocatalytic properties of RuO2/Ti anode with different coating masses, which were prepd. by the alkoxide sol-gel procedure, were studied in Cl and O evolution reactions by polarization measurements and electrochem. impedance spectroscopy in H2SO4 and NaCl electrolytes. According to polarization measurements, the activity of anodes at overpotentials <100 mV is independent of coating mass. However, impedance measurements >100 mV reveal changes in the activity of anodes in Cl evolution reaction for different coating masses. The diffusion limitations related to the evolved Cl are registered in low-frequency domain at 1.10 V (SCE), diminishing with the increase in potential to the 1.15 V (SCE). The obsd. impedance behavior is discussed with respect to the activity model for activated Ti anodes in Cl evolution reaction involving formation of gas channels within porous coating structure. Gas channels enhance the mass transfer rate similarly to the forced convection, which also increases the activity of anode. This is more pronounced for the anode of greater coating mass due to its more compact surface structure. The more compact structure appears to be beneficial for gas channels formation.
- 21Hoseinieh, S. M.; Ashrafizadeh, F.; Maddahi, M. H. A Comparative Investigation of the Corrosion Behavior of RuO[Sub 2]–IrO[Sub 2]–TiO[Sub 2] Coated Titanium Anodes in Chloride Solutions. J. Electrochem. Soc. 2010, 157, E50, DOI: 10.1149/1.329456921https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXjt1amsbw%253D&md5=bd7e7d7886dd3831fbdc3b8b10193a11A Comparative Investigation of the Corrosion Behavior of RuO2-IrO2-TiO2 Coated Titanium Anodes in Chloride SolutionsHoseinieh, S. M.; Ashrafizadeh, F.; Maddahi, M. H.Journal of the Electrochemical Society (2010), 157 (4), E50-E56CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Deactivation of a RuO2-IrO2-TiO2/Ti oxide anode was studied during an accelerated life test in 0.5 mol dm-3 NaCl using cyclic voltammetry, electrochem. impedance spectroscopy, and SEM/energy-dispersive x-ray anal. The variations in double-layer capacitance, film resistance, and charge-transfer resistance during electrolysis were recorded at different potentials. A comprehensive deactivation mechanism of Ti anodes is proposed by the growth of an insulating TiO2 layer at the coating-substrate interface due to the Ti substrate oxidn. The impedance interpretation of the deactivation mechanism in chloride solns. changes with an increase in potential due to an increase in oxygen evolution on the anode surface at higher potentials.
- 22Shao, D.; Yan, W.; Cao, L.; Li, X.; Xu, H. High-Performance Ti/Sb–SnO2/Pb3O4 Electrodes for Chlorine Evolution: Preparation and Characteristics. J. Hazard. Mater. 2014, 267, 238– 244, DOI: 10.1016/j.jhazmat.2013.12.06422https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXis1Wqu7o%253D&md5=4ec2c535e138603bd0093ed6613c02f7High-performance Ti/Sb-SnO2/Pb3O4 electrodes for chlorine evolution: Preparation and characteristicsShao, Dan; Yan, Wei; Cao, Lu; Li, Xiaoliang; Xu, HaoJournal of Hazardous Materials (2014), 267 (), 238-244CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)Chlorine evolution via electrochem. approach has wide application prospects in drinking water disinfection and wastewater treatment fields. Dimensional stable anodes used for chlorine evolution should have high stability and adequate chlorine evolution efficiency. Thus a novel and cost-effective Ti/Sb-SnO2/Pb3O4 electrode was developed. The physicochem. and electrochem. properties as well as the chlorine evolution performances of the electrodes were investigated. The electrocatalytic activity and deactivation course of the electrodes were also explored. Results showed that this novel electrode had strong chlorine evolution ability with high current efficiency ranging from 87.3% to 93.4% depending on the operational conditions. The accelerated service life of Ti/Sb-SnO2/Pb3O4 electrode could reach 180 h at a c.d. of 10,000 A m-2 in 0.5 mol L-1 H2SO4. During the electrolysis process, it was found that the conversion of Pb3O4 into β-PbO2 happened gradually on the electrode surface, which not only inhibited the leakage of hazardous Pb2+ ion but also increased the anti-corrosion capacity of the electrode effectively.
- 23Fujimura, K.; Izumiya, K.; Kawashima, A.; Akiyama, E.; Habazaki, H.; Kumagai, N.; Hashimoto, K. Anodically Deposited Manganese-Molybdenum Oxide Anodes with High Selectivity for Evolving Oxygen in Electrolysis of Seawater. J. Appl. Electrochem. 1999, 29, 769– 775, DOI: 10.1023/A:1003492009263There is no corresponding record for this reference.
- 24Vos, J. G.; Wezendonk, T. A.; Jeremiasse, A. W.; Koper, M. T. M. MnOx/IrOx as Selective Oxygen Evolution Electrocatalyst in Acidic Chloride Solution. J. Am. Chem. Soc. 2018, 140, 10270– 10281, DOI: 10.1021/jacs.8b0538224https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtlCnt7vI&md5=10e93065fa3c8c339b1aa6b146b9608aMnOx/IrOx as Selective Oxygen Evolution Electrocatalyst in Acidic Chloride SolutionVos, Johannes G.; Wezendonk, Tim A.; Jeremiasse, Adriaan W.; Koper, Marc T. M.Journal of the American Chemical Society (2018), 140 (32), 10270-10281CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The oxygen evolution reaction (OER) and chlorine evolution reaction (CER) are electrochem. processes with high relevance to water splitting for (solar) energy conversion and industrial prodn. of commodity chems., resp. Carrying out the two reactions sep. is challenging, since the catalytic intermediates are linked by scaling relations. Optimizing the efficiency of OER over CER in acidic media has proven esp. difficult. In this regard, the OER vs. CER selectivity of manganese oxide (MnOx), a known OER catalyst is investigated. Thin films (∼5-20 nm) of MnOx were electrodeposited on glassy carbon-supported hydrous iridium oxide (IrOx/GC) in aq. chloride solns. of pH ∼0.9. Using rotating ring-disk electrode voltammetry and online electrochem. mass spectrometry, it was found that deposition of MnOx onto IrOx decreases the CER selectivity of the system in the presence of 30 mM Cl- from 86% to < 7%, making it a highly OER-selective catalyst. Detailed studies of the CER mechanism and ex-situ structure studies using SEM, TEM, and XPS suggest that the MnOx film is in fact not a catalytically active phase, but functions as a permeable overlayer that disfavors the transport of chloride ions.
- 25Trasatti, S. Electrocatalysis in the Anodic Evolution of Oxygen and Chlorine. Electrochim. Acta 1984, 29, 1503– 1512, DOI: 10.1016/0013-4686(84)85004-525https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXmvFWqtQ%253D%253D&md5=3293b9b686c89687a6f73387afb26de1Electrocatalysis in the anodic evolution of oxygen and chlorineTrasatti, S.Electrochimica Acta (1984), 29 (11), 1503-12CODEN: ELCAAV; ISSN:0013-4686.Requisites for electrode materials to be suitable for technol. applications are outlined and discussed. Oxides with metallic or quasi-metallic cond. meet these requirements best. Most of these electrodes are prepd. by thermal procedures. The temp. of prepn. affects the catalytic activity through the surface area and the chem. compn. (nonstoichiometry). The covariation of these parameters is best followed in situ by voltammetric curves and point of zero charge measurements. Examples are given for pure RuO2, IrO2, Co3O4 and IrO2 + RuO2 mixts. Kinetic and mechanistic details are discussed for O evolution on RuO2, IrO2 and Co3O4 and for Cl evolution on RuO2 and Co3O4. Finally the electrocatalytic properties of different oxides are correlated with the energy change involved in the lower → higher valency state transition. Exptl. data for both O and Cl evolution can thus be organized into a volcano curve enabling predictive interpolations to be made.
- 26Hansen, H. A.; Man, I. C.; Studt, F.; Abild-Pedersen, F.; Bligaard, T.; Rossmeisl, J. Electrochemical Chlorine Evolution at Rutile Oxide (110) Surfaces. Phys. Chem. Chem. Phys. 2010, 12, 283– 290, DOI: 10.1039/B917459A26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhsFektbbJ&md5=e4a886eb0187ffd787c43d2b301e8ef0Electrochemical chlorine evolution at rutile oxide (110) surfacesHansen, Heine A.; Man, Isabela C.; Studt, Felix; Abild-Pedersen, Frank; Bligaard, Thomas; Rossmeisl, JanPhysical Chemistry Chemical Physics (2010), 12 (1), 283-290CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)Based on d. functional theory (DFT) calcns. the authors study the electrochem. chlorine evolution reaction on rutile (110) oxide surfaces. First the authors construct the Pourbaix surface diagram for IrO2 and RuO2, and from this the chlorine evolution reaction intermediates and identify the lowest overpotential at which all elementary reaction steps in the chlorine evolution reaction are downhill in free energy were found. This condition is then used as a measure for catalytic activity. Linear scaling relations between the binding energies of the intermediates and the oxygen binding energies at cus-sites are established for MO2 (M being Ir, Ru, Pt, Ti). The linear relations form the basis for constructing a generalized surface phase diagram where 2 parameters, the potential and the binding energy of oxygen, are needed to det. the surface compn. The authors calc. the catalytic activity as function of the oxygen binding energy, giving rise to a Sabatier volcano. By combining the surface phase diagram and the volcano describing the catalytic activity, the reaction mechanism differs depending on catalyst material. The flexibility in reaction path means that the chlorine evolution activity is high for a wide range of oxygen binding energies. The required overpotential for chlorine evolution is lower than the overpotential necessary for oxygen evolution.
- 27Abbott, D. F.; Petrykin, V.; Okube, M.; Bastl, Z.; Mukerjee, S.; Krtil, P. Selective Chlorine Evolution Catalysts Based on Mg-Doped Nanoparticulate Ruthenium Dioxide. J. Electrochem. Soc. 2015, 162, H23– H31, DOI: 10.1149/2.0541501jes27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitVCrs7%252FO&md5=5e6cba0928045d7c7b39f0769e4782bdSelective Chlorine Evolution Catalysts Based on Mg-Doped Nanoparticulate Ruthenium DioxideAbbott, Daniel F.; Petrykin, Valery; Okube, Maki; Bastl, Zdenk; Mukerjee, Sanjeev; Krtil, PetrJournal of the Electrochemical Society (2015), 162 (1), H23-H31CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Nanocryst. Mg-doped ruthenium dioxide catalysts with the formula Ru1-xMgxO2 (0 ≤ x ≤ 20) were synthesized by the spray-freezing freeze-drying technique. Synthesized materials are of nanoparticulate nature and show a single phase diffraction pattern conforming to a tetragonal oxide of the rutile structural type. Magnesium ions are not distributed homogeneously in the material, but exist in Mg-rich clusters as shown by X-ray absorption spectroscopy. The refinement of the Mg EXAFS functions for materials with low Mg content shows that the magnesium rich clusters contain Mg in a highly strained environment similar to that of the rutile-type structure. The Mg environment shifts to an ilmenite-type inclusion when Mg occupies more than 10% of all cationic positions. All Mg modified materials are active in oxygen evolution and chlorine evolution reactions. Although the Mg contg. catalysts show lower overall activities compared with the non-doped ruthenia, they feature enhanced selectivity toward the chlorine evolution process, which is attributed primarily to the opening of a reaction pathway for chlorine evolution assocd. with presence of Mg modified active sites.
- 28Exner, K. S.; Anton, J.; Jacob, T.; Over, H. Controlling Selectivity in the Chlorine Evolution Reaction over RuO 2 -Based Catalysts. Angew. Chem., Int. Ed. 2014, 53, 11032– 11035, DOI: 10.1002/anie.20140611228https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVWqsbrL&md5=382b59a5a1f1ca5b371990ef737695ceControlling selectivity in the chlorine evolution reaction over RuO2-based catalystsExner, Kai S.; Anton, Josef; Jacob, Timo; Over, HerbertAngewandte Chemie, International Edition (2014), 53 (41), 11032-11035CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)In the industrially important Chlor-Alkali process, the chlorine evolution reaction (CER) over a ruthenium dioxide (RuO2) catalyst competes with the oxygen evolution reaction (OER). This selectivity issue is elucidated on the microscopic level with the single-cryst. model electrode RuO2(110) by employing d. functional theory (DFT) calcns. in combination with the concept of volcano plots. We demonstrate that one monolayer of TiO2(110) supported on RuO2(110) enhances the selectivity towards the CER by several orders of magnitudes, while preserving the high activity for the CER. This win-win situation is attributed to the different slopes of the volcano curves for the CER and OER.
- 29Exner, K. S.; Anton, J.; Jacob, T.; Over, H. Full Kinetics from First Principles of the Chlorine Evolution Reaction over a RuO 2 (110) Model Electrode. Angew. Chem., Int. Ed. 2016, 55, 7501– 7504, DOI: 10.1002/anie.20151180429https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xnslaisbk%253D&md5=8c0f3edbb62734f04d1406d686a49445Full Kinetics from First Principles of the Chlorine Evolution Reaction over a RuO2(110) Model ElectrodeExner, Kai S.; Anton, Josef; Jacob, Timo; Over, HerbertAngewandte Chemie, International Edition (2016), 55 (26), 7501-7504CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Current progress in modern electrocatalysis research is spurred by theory, frequently based on ab initio thermodn., where the stable reaction intermediates at the electrode surface are identified, while the actual energy barriers are ignored. This approach is popular in that a simple tool is available for searching for promising electrode materials. However, thermodn. alone may be misleading to assess the catalytic activity of an electrochem. reaction as the authors exemplify with the Cl evolution reaction (CER) over a RuO2(110) model electrode. The full procedure is introduced, starting from the stable reaction intermediates, computing the energy barriers, and finally performing microkinetic simulations, all performed under the influence of the solvent and the electrode potential. Full kinetics from 1st-principles allows the rate-detg. step in the CER to be identified and the exptl. obsd. change in the Tafel slope to be explained.
- 30Sohrabnejad-Eskan, I.; Goryachev, A.; Exner, K. S.; Kibler, L. A.; Hensen, E. J. M.; Hofmann, J. P.; Over, H. Temperature-Dependent Kinetic Studies of the Chlorine Evolution Reaction over RuO 2 (110) Model Electrodes. ACS Catal. 2017, 7, 2403– 2411, DOI: 10.1021/acscatal.6b0341530https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXivFSqt74%253D&md5=99bb72640b1b2e973e79b4bd43904465Temperature-Dependent Kinetic Studies of the Chlorine Evolution Reaction over RuO2(110) Model ElectrodesSohrabnejad-Eskan, Iman; Goryachev, Andrey; Exner, Kai S.; Kibler, Ludwig A.; Hensen, Emiel J. M.; Hofmann, Jan P.; Over, HerbertACS Catalysis (2017), 7 (4), 2403-2411CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)Ultrathin single-cryst. RuO2(110) films supported on Ru(0001) are employed as model electrodes to ext. kinetic information about the industrially important Cl evolution reaction (CER) in a 5M concd. NaCl soln. under well-defined electrochem. conditions and variable temps. A combination of chronoamperometry (CA) and online electrochem. mass spectrometry (OLEMS) expts. provides insight into the selectivity issue: At pH = 0.9, the CER dominates over O evolution, whereas at pH = 3.5, O evolution and other parasitic side reactions contribute mostly to the total c.d. From temp.-dependent CA data for pH = 0.9, the authors det. the apparent free activation energy of the CER over RuO2(110) to be 0.91 eV, which compares reasonably well with the theor. value of 0.79 eV derived from 1st-principles microkinetics. The exptl. detd. apparent free activation energy of 0.91 eV is considered as a benchmark for assessing future improved theor. modeling from 1st principles.
- 31Lassali, T. A. F.; Boodts, J. F. C.; Trasatti, S. Electrocatalytic Activity of the Ternary Oxide Ru0.3PtxTi(0.7 — x)O2 for Chlorine Evolution. Electrochim. Acta 1994, 39, 1545– 1549, DOI: 10.1016/0013-4686(94)85133-631https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXmtFGktb0%253D&md5=2c8087570dc2a55036ac1128a9e44eefElectrocatalytic activity of the ternary oxide Ru0.3PtxTi(0.7-x)O2 for chlorine evolutionLassali, T. A. F.; Boodts, J. F. C.; Trasatti, S.Electrochimica Acta (1994), 39 (11-12), 1545-9CODEN: ELCAAV; ISSN:0013-4686.The electrocatalytic activity of ternary oxides of nominal compn. Ru0.3PtxTi(0.7-x)O2 was investigated over the whole compn. range using chlorine evolution as a model reaction. Compn. was changed in 10 mol.% steps and the surface was characterized in situ by cyclic voltammetry (cv). Surface properties are governed by the RuOx features at low PtOx content (<30%), while at higher PtOx content they are controlled by PtOx. A single Tafel line of 31 ± 1 mV slope was obsd. at all compns. The reaction order is zero with respect to H+ and 1.5 with respect to Cl-. At high PtOx content and low Cl- concn. (<1 mol dm-3) O2 formation appears to control the gas evolution process. An inhibition of Cl2 evolution is obsd. for PtOx ≥ 30 mol.%. On the whole, morphol. effects predominate over electronic effects.
- 32Macounová, K. M.; Makarova, M.; Jirkovský, J. S.; Franc, J.; Krtil, P. Parallel Oxygen and Chlorine Evolution on Ru1–xNixO2–y Nanostructured Electrodes. Electrochim. Acta 2008, 53, 6126– 6134, DOI: 10.1016/j.electacta.2007.11.01432https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXntFGhsb8%253D&md5=9dd753c965e53ff07d2f771a3363d3a2Parallel oxygen and chlorine evolution on Ru1-xNixO2-y nanostructured electrodesMacounova, Katerina; Makarova, Marina; Jirkovsky, Jakub; Franc, Jiri; Krtil, PetrElectrochimica Acta (2008), 53 (21), 6126-6134CODEN: ELCAAV; ISSN:0013-4686. (Elsevier B.V.)Nanocryst. materials with chem. compn. corresponding to Ru1-xNixO2-y (0.02 < x < 0.30) were prepd. by sol-gel approach. Substitution of Ru by Ni has a minor effect on the structural characteristics extractable from x-ray diffraction patterns. The electrocatalytic behavior of Ru1-xNixO2-y with respect to parallel O (O evolution reaction, OER) and Cl (Cl evolution reaction, CER) evolution in acidic media was studied by voltammetry combined with differential electrochem. mass spectrometry (DEMS). The DEMS data indicate a significant decrease of the over-voltage for Cl evolution with respect to that of pure RuO2. The O evolution is slightly hindered. The increasing Ni content affects the electrode material activity and selectivity. The overall material's activity increases with increasing Ni content. The activity of the Ru-Ni-O oxides towards Cl2 evolution shows a distinguished max. for material contg. 10% of Ni. Further increase of Ni content results in suppression of Cl2 evolution in favor of O2 evolution. A model reflecting the cation-cation interactions resulting from Ni-doping is proposed to explain the obsd. trends in electrocatalytic behavior.
- 33Petrykin, V.; Macounová, K. M.; Okube, M.; Mukerjee, S.; Krtil, P. Local Structure of Co Doped RuO2 Nanocrystalline Electrocatalytic Materials for Chlorine and Oxygen Evolution. Catal. Today 2013, 202, 63– 69, DOI: 10.1016/j.cattod.2012.03.07533https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XntVyrurw%253D&md5=b84968444c0e8740adb917cbb50e6005Local structure of Co doped RuO2 nanocrystalline electrocatalytic materials for chlorine and oxygen evolutionPetrykin, Valery; Macounova, Katerina; Okube, Maki; Mukerjee, Sanjeev; Krtil, PetrCatalysis Today (2013), 202 (), 63-69CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Nano-particulate Co doped ruthenium dioxide electrocatalysts of the general formula Ru1-xCoxO2-y (0 < x 0.3) were prepd. by a co-pptn. method. The electrocatalysts with x < 0.2 conform to a single phase nano-cryst. materials. On the local level the Co forms clusters dispersed in the original rutile-like matrix. The local environment of the Co conforms to a rutile model which preserves the cationic arrangement but suppresses the probability of the Ru-Ru and Co-Co neighbors along the shortest metal-metal bonds. The electrocatalytic activity of the synthesized Ru1-xCoxO2-y materials in oxygen evolution is comparable with that of the non-doped ruthenium dioxide and little depends on the actual Co content. In presence of chlorides the Co doped materials are more selective towards oxygen evolution compared with the non doped ruthenia. The enhanced oxygen evolution in the case of Co doped electrocatalysts can be attributed to a chem. recombination of surface confined oxo-species. The selectivity shift towards oxygen evolution can be linked with limited activity of the Ru1-xCoxO2-y materials in the chlorine evolution reaction which seems to be relatively weakly dependent on the chloride concn.
- 34Consonni, V.; Trasatti, S.; Pollak, F. H.; O’Grady, W. E. Mechanism of Chlorine Evolution on Oxide Anodes: Study of PH Effects. J. Electroanal. Chem. Interfacial Electrochem. 1987, 228, 393– 406, DOI: 10.1016/0022-0728(87)80119-534https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXls1eqs7g%253D&md5=2535558283f0b32b94ac4268ce77f6dbMechanism of chlorine evolution on oxide anodes. Study of pH effectsConsonni, V.; Trasatti, S.; Pollak, F.; O'Grady, W. E.Journal of Electroanalytical Chemistry and Interfacial Electrochemistry (1987), 228 (1-2), 393-406CODEN: JEIEBC; ISSN:0022-0728.The Cl evolution on oxides such as polycryst. RuO2, IrO2, Co3O4, RuO2 + IrO2 and the (110) face of RuO2 single crystals proceeds with the same Tafel slope of 40 mV and the same reaction order of 1 with respect to Cl-. On all oxides, except RuO2 (110), the reaction rate is depressed by the acidity, which results in a reaction order with respect to H+ of -1 for IrO2 and Co3O4, of 0 for RuO2 (110) and variable for RuO2. Possible reasons for pH effects are discussed, and several plausible reaction mechanisms are examd.
- 35Spöri, C.; Kwan, J. T. H.; Bonakdarpour, A.; Wilkinson, D. P.; Strasser, P. The Stability Challenges of Oxygen Evolving Catalysts: Towards a Common Fundamental Understanding and Mitigation of Catalyst Degradation. Angew. Chem., Int. Ed. 2017, 56, 5994– 6021, DOI: 10.1002/anie.20160860135https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2snit1Citw%253D%253D&md5=26d32ba6c91db37de4e26e6e5e525261The Stability Challenges of Oxygen Evolving Catalysts: Towards a Common Fundamental Understanding and Mitigation of Catalyst DegradationSpori Camillo; Strasser Peter; Kwan Jason Tai Hong; Bonakdarpour Arman; Wilkinson David P; Strasser PeterAngewandte Chemie (International ed. in English) (2017), 56 (22), 5994-6021 ISSN:.This Review addresses the technical challenges, scientific basis, recent progress, and outlook with respect to the stability and degradation of catalysts for the oxygen evolution reaction (OER) operating at electrolyzer anodes in acidic environments with an emphasis on ion exchange membrane applications. First, the term "catalyst stability" is clarified, as well as current performance targets, major catalyst degradation mechanisms, and their mitigation strategies. Suitable in situ experimental methods are then evaluated to give insight into catalyst degradation and possible pathways to tune OER catalyst stability. Finally, the importance of identifying universal figures of merit for stability is highlighted, leading to a comprehensive accelerated lifetime test that could yield comparable performance data across different laboratories and catalyst types. The aim of this Review is to help disseminate and stress the important relationships between structure, composition, and stability of OER catalysts under different operating conditions.
- 36Diaz-Morales, O.; Raaijman, S.; Kortlever, R.; Kooyman, P. J.; Wezendonk, T.; Gascon, J.; Fu, W. T.; Koper, M. T. M. Iridium-Based Double Perovskites for Efficient Water Oxidation in Acid Media. Nat. Commun. 2016, 7, 12363, DOI: 10.1038/ncomms1236336https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhtlaks7bE&md5=b10818629280e87dd1d7b358ce974f0cIridium-based double perovskites for efficient water oxidation in acid mediaDiaz-Morales, Oscar; Raaijman, Stefan; Kortlever, Ruud; Kooyman, Patricia J.; Wezendonk, Tim; Gascon, Jorge; Fu, W. T.; Koper, Marc T. M.Nature Communications (2016), 7 (), 12363CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)The development of active, cost-effective and stable oxygen-evolving catalysts is one of the major challenges for solar-to-fuel conversion towards sustainable energy generation. Iridium oxide exhibits the best available compromise between catalytic activity and stability in acid media, but it is prohibitively expensive for large-scale applications. Therefore, prepg. oxygen-evolving catalysts with lower amts. of the scarce but active and stable iridium is an attractive avenue to overcome this economical constraint. Here we report on a class of oxygen-evolving catalysts based on iridium double perovskites which contain 32 wt% less iridium than IrO2 and yet exhibit a more than threefold higher activity in acid media. According to recently suggested benchmarking criteria, the iridium double perovskites are the most active catalysts for oxygen evolution in acid media reported until now, to the best of our knowledge, and exhibit similar stability to IrO2.
- 37Geiger, S.; Kasian, O.; Ledendecker, M.; Pizzutilo, E.; Mingers, A. M.; Fu, W. T.; Diaz-Morales, O.; Li, Z.; Oellers, T.; Fruchter, L.; Ludwig, A.; Mayrhofer, K. J. J.; Koper, M. T. M.; Cherevko, S. The Stability Number as a Metric for Electrocatalyst Stability Benchmarking. Nat. Catal. 2018, 1, 508– 515, DOI: 10.1038/s41929-018-0085-637https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFGisLnK&md5=efb4882d145e58f72b41527eece25eedThe stability number as a metric for electrocatalyst stability benchmarkingGeiger, Simon; Kasian, Olga; Ledendecker, Marc; Pizzutilo, Enrico; Mingers, Andrea M.; Fu, Wen Tian; Diaz-Morales, Oscar; Li, Zhizhong; Oellers, Tobias; Fruchter, Luc; Ludwig, Alfred; Mayrhofer, Karl J. J.; Koper, Marc T. M.; Cherevko, SerhiyNature Catalysis (2018), 1 (7), 508-515CODEN: NCAACP; ISSN:2520-1158. (Nature Research)Reducing the noble metal loading and increasing the specific activity of the oxygen evolution catalysts are omnipresent challenges in proton-exchange-membrane water electrolysis, which have recently been tackled by utilizing mixed oxides of noble and non-noble elements. However, proper verification of the stability of these materials is still pending. Here we introduce a metric to explore the dissoln. processes of various iridium-based oxides, defined as the ratio between the amts. of evolved oxygen and dissolved iridium. The so-called stability no. is independent of loading, surface area or involved active sites and provides a reasonable comparison of diverse materials with respect to stability. The case study on iridium-based perovskites shows that leaching of the non-noble elements in mixed oxides leads to the formation of highly active amorphous iridium oxide, the instability of which is explained by the generation of short-lived vacancies that favor dissoln. These insights are meant to guide further research, which should be devoted to increasing the utilization of highly durable pure cryst. iridium oxide and finding solns. to stabilize amorphous iridium oxides.
- 38Vos, J. G.; Koper, M. T. M. Measurement of Competition between Oxygen Evolution and Chlorine Evolution Using Rotating Ring-Disk Electrode Voltammetry. J. Electroanal. Chem. 2018, 819, 260– 268, DOI: 10.1016/j.jelechem.2017.10.05838https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslOisb%252FL&md5=01573b2aec0aa64422dd552b109a5c76Measurement of competition between oxygen evolution and chlorine evolution using rotating ring-disk electrode voltammetryVos, J. G.; Koper, M. T. M.Journal of Electroanalytical Chemistry (2018), 819 (), 260-268CODEN: JECHES; ISSN:1873-2569. (Elsevier B.V.)Selectivity between Cl evolution and O evolution in aq. media is a phenomenon of central importance in the chlor-alkali process, H2O treatment, and saline H2O splitting, which is an emerging technol. for sustainable energy conversion. An apparent scaling between O vs. Cl evolution was established, making it challenging to carry the two reactions out individually with 100% faradaic efficiency. To aid selectivity detn., the authors developed a new method to quickly measure Cl evolution rates using a conventional RRDE setup. A Pt ring fixed at 0.95 V vs. RHE in pH 0.88 can selectively reduce the Cl2 formed on the disk and this allows precise and flexible data acquisition. Using this method, O evolution and Cl evolution on a glassy C supported IrOx catalyst proceed independently, and the selectivity towards Cl evolution (εCER) rapidly approaches 100% as [Cl-] increases from 0 to 100 mM. The authors' results suggest that on IrOx, O evolution is not suppressed or influenced by the presence of Cl- or by the Cl evolution reaction taking place simultaneously on the surface.
- 39Fu, W. T.; IJdo, D. J. W. On the Space Group of the Double Perovskite Ba2PrIrO6. J. Solid State Chem. 2005, 178, 1312– 1316, DOI: 10.1016/j.jssc.2005.02.00339https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXivFOhs7s%253D&md5=e76380dfe77e0bac61de4fe1c9a8921dOn the space group of the double perovskite Ba2PrIrO6Fu, W. T.; IJdo, D. J. W.Journal of Solid State Chemistry (2005), 178 (4), 1312-1316CODEN: JSSCBI; ISSN:0022-4596. (Elsevier)The structure of the double perovskite Ba2PrIrO6 was reexamd. by profile anal. of x-ray diffraction data. Neither the monoclinic P21/n nor the tetragonal P4/mnc space group correctly describes its structure. Ba2PrIrO6 has cubic symmetry, space group Fm‾3m, a 8.40135(6) Å. In agreement with earlier observations, Ba2PrIrO6 is an ordered perovskite contg. the valence pair Pr(IV)/Ir(IV).
- 40Fu, W. T.; IJdo, D. J. W. Re-Examination of the Structure of Ba2MIrO6 (M = La, Y): Space Group Revised. J. Alloys Compd. 2005, 394, L5, DOI: 10.1016/j.jallcom.2004.10.04940https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXjslOitrg%253D&md5=367b9cf92279a2da7e4103ba4271bf1eRe-examination of the structure of Ba2MIrO6 (M = La, Y): space group revisedFu, W. T.; IJdo, D. J. W.Journal of Alloys and Compounds (2005), 394 (1-2), L5-L8CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)The structure of the double perovskites Ba2MIrO6 (M = La, Y) was studied by the profile anal. of x-ray diffraction data. Both compds. consist of an ordered arrangement of LaO6/YO6 and IrO6 octahedra but with different symmetries. Ba2LaIrO6 is rhombohedral, space group R‾3, with a 6.04542(5) Å and α 60.264(1), in which the LaO6 and IrO6 octahedra are tilted around the primitive [111]p-axis of the cubic aristotype. However, Ba2YIrO6 is double cubic, space group Fm‾3m, with a 8.35032(9) Å.
- 41Schuppert, A. K.; Topalov, A. A.; Katsounaros, I.; Klemm, S. O.; Mayrhofer, K. J. J. A Scanning Flow Cell System for Fully Automated Screening of Electrocatalyst Materials. J. Electrochem. Soc. 2012, 159, F670– F675, DOI: 10.1149/2.009211jes41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1ygsr3P&md5=24cc1bbea4bce7064ae797d051c39034A scanning flow cell system for fully automated screening of electrocatalyst materialsSchuppert, Anna K.; Topalov, Angel A.; Katsounaros, Ioannis; Klemm, Sebastian O.; Mayrhofer, Karl J. J.Journal of the Electrochemical Society (2012), 159 (11), F670-F675CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)Electrocatalysts play an important role in sustainable energy-related fields. As these catalysts still require improvement on activity and stability, a lot of effort is invested in developing new materials. Due to the enormous parameter space spanned by material compn. and exptl. conditions, there is a great demand for high-throughput screening of the material performance. To address this issue, a scanning flow cell (SFC) is developed and utilized for catalyst research for the first time. The adaptation of a homemade LabVIEW program to the SFC setup enables fully automated, computer-controlled high-throughput measurements. A gas purging system is introduced to sat. the electrolyte with gases in a time frame comparable to typical rotating disk electrode (RDE) systems. To demonstrate the capabilities of the setup, the oxygen redn. reaction on polycryst. platinum is investigated as a sample system. The cyclic voltammograms are consistent with those expected from investigations in conventional electrochem. cells. Repetitive measurements show high reproducibility. Considering the potential of the system toward improvements and extensions, the SFC will be a valuable screening tool for electrocatalyst research.
- 42Klemm, S. O.; Topalov, A. A.; Laska, C. A.; Mayrhofer, K. J. J. Coupling of a High Throughput Microelectrochemical Cell with Online Multielemental Trace Analysis by ICP-MS. Electrochem. Commun. 2011, 13, 1533– 1535, DOI: 10.1016/j.elecom.2011.10.01742https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFartL%252FE&md5=d9a7d73a9fde29a99f7cce7e135cfc14Coupling of a high throughput microelectrochemical cell with online multielemental trace analysis by ICP-MSKlemm, Sebastian O.; Topalov, Angel A.; Laska, Claudius A.; Mayrhofer, Karl J. J.Electrochemistry Communications (2011), 13 (12), 1533-1535CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)The successful coupling of a specially designed microelectrochem. cell and direct online multi-elemental trace anal. by ICP-MS is presented. The feasibility of this method is demonstrated by the example of copper dissoln. in HCl (1 and 10 mM), showing very high sensitivity and an excellent congruency between electrochem. expts. and copper concns. detected downstream. The complementary data allows for a precise detn. of the valence of Cu ions released during anodic dissoln., which undergoes changes depending on the electrolyte and the applied c.d. Moreover it provides a means of quantification of processes without net external currents that are not readily accessible by plain electrochem. techniques, in particular the exchange current densities at the open circuit potential, i.e. corrosion rate, and the dissoln. of native oxides. The system presented combines full spectrum electrochem. capabilities, convection control, and highly sensitive electrolyte anal. in an integrated, miniaturized arrangement under full computer control and automation.
- 43Kasian, O.; Geiger, S.; Mayrhofer, K. J. J.; Cherevko, S. Electrochemical On-Line ICP-MS in Electrocatalysis Research. Chem. Rec. 2018, DOI: 10.1002/tcr.201800162There is no corresponding record for this reference.
- 44Gileadi, E. Problems in Interfacial Electrochemistry That Have Been Swept under the Carpet. J. Solid State Electrochem. 2011, 15, 1359– 1371, DOI: 10.1007/s10008-011-1344-544https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtVOnsLrK&md5=51674ff6d3a18ca23b29cafa8fc6203eProblems in interfacial electrochemistry that have been swept under the carpetGileadi, E.Journal of Solid State Electrochemistry (2011), 15 (7-8), 1359-1371CODEN: JSSEFS; ISSN:1432-8488. (Springer)A crit. view of interfacial electrochem. in the past 50 years is discussed, with emphasis on tacit assumptions, which are sometimes hard to justify. The important role of the Tafel equation in studies of the mechanism of electrode reactions and in the development of electrode kinetics in the past century is recognized. However, it is shown that the validity of the ways it was implemented can be questioned, particularly in view of the uncertainty in the value of the symmetry factor commonly assumed. For example, the value of β pertinent to a species in the outer-Helmholtz plane cannot be the same as that applicable to a species already adsorbed on the surface. Three factors are involved in considering charge transfer to an adsorbed species: (a) The electrostatic field at the adsorption site is highly distorted; thus, the overpotential imposed may not apply at the point where the reaction takes place; (b) the effective charge on the adsorbed species may not equal the nominal charge assigned to it; and (c) the metal surface may already be modified by a monolayer of adsorbed species of the same kind, which is, however, inactive with respect to the reaction taking place. Similarly, in studies of the kinetics of metal deposition and dissoln., where charge is transferred across the interface by the ions, one cannot legitimately assume a value of β, although it can be measured exptl. It is very risky to predict the future of interfacial electrochem., but one might extrapolate present trends. Thus, the importance of the fundamental aspects of the field may have declined in the past two or three decades, and this trend will probably continue. On the other hand, the importance of understanding interfacial electrochem. as a basis for related fields such as nano-science, biol., micro- and nano-implanted biosensors, interaction of tissue with metal implants, materials science, as well as technologies such as corrosion and alloy plating is likely to increase.
- 45Vesztergom, S.; Ujvári, M.; Láng, G. G. Dual Cyclic Voltammetry with Rotating Ring–Disk Electrodes. Electrochim. Acta 2013, 110, 49– 55, DOI: 10.1016/j.electacta.2013.01.14245https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXivVGqt7s%253D&md5=0d7eedf2ea9c2af0804afa2ea26ec09fDual cyclic voltammetry with rotating ring-disk electrodesVesztergom, Soma; Ujvari, Maria; Lang, Gyozo G.Electrochimica Acta (2013), 110 (), 49-55CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)The simultaneous perturbation of the disk and ring electrode potentials of an RRDE with time-varying controlling waveforms seems to be an effective way of carrying out high-sensitivity collection expts. The method of dual cyclic voltammetry (i.e. applying dynamic potential programs to the disk and the ring electrodes of an RRDE simultaneously) has proven to be an esp. promising method for studying the mechanisms of electrochem. processes. The new 3D representation of the data can be effectively used in order to reveal the formation of electroactive species in the disk electrode process. However, some issues concerning the application of this method may also arise. The "dual dynamic" perturbation of the electrodes can cause transients to appear in the current-potential characteristics of the two electrodes, which often results in elec. cross-talk effects. In this paper it is shown that the afore-mentioned cross-talk (experienced mainly when perturbations of a high rate are applied) is caused by the common resistance shared by the current paths of the two working electrodes. Numerical simulations as well as expts. with a simple model system have been carried out in order to study the cross-talk effects, and a method is suggested for their elimination.
- 46Vesztergom, S.; Barankai, N.; Kovács, N.; Ujvári, M.; Siegenthaler, H.; Broekmann, P.; Láng, G. G. Electrical Cross-Talk in Four-Electrode Experiments. J. Solid State Electrochem. 2016, 20, 3165– 3177, DOI: 10.1007/s10008-016-3294-446https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFahs7bJ&md5=0d8b9365504a40466f3d19c79e97d1a3Electrical cross-talk in four-electrode experiments - A digital simulation approach to the example of rotating ring-disk electrodesVesztergom, Soma; Barankai, Norbert; Kovacs, Noemi; Ujvari, Maria; Siegenthaler, Hans; Broekmann, Peter; Lang, Gyozo G.Journal of Solid State Electrochemistry (2016), 20 (11), 3165-3177CODEN: JSSEFS; ISSN:1432-8488. (Springer)The subject of this paper is elec. cross-talk, an interference between the current/voltage characteristics of the two working electrodes in four-electrode (generator/collector) systems. Cross-talk arises in electrochem. cells of finite resistance due to the superposition of the elec. fields of the working electrodes, and often causes difficulties in the interpretation of measurement results. In this paper, we present an algorithm for modeling simple generation/collection expts. with a rotating ring-disk electrode (RRDE) immersed into a finite resistance soln. of a redox couple. We show that based on the anal. of the Kirchhoff (Laplace) matrix of the simulation mesh, the effect of elec. cross-talk may be accounted for in such expts. The intensity of cross-talk is found to be heavily influenced by the selection of the ref. point for potential measurements; in practice, this is the position of the ref. electrode or the tip of the Luggin probe. The devised model is validated by means of a simple and demonstrative expt. [Figure not available: see fulltext.].
- 47McCrory, C. C. L.; Jung, S.; Peters, J. C.; Jaramillo, T. F. Benchmarking Heterogeneous Electrocatalysts for the Oxygen Evolution Reaction. J. Am. Chem. Soc. 2013, 135, 16977– 16987, DOI: 10.1021/ja407115p47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhslSqtLnM&md5=105318a53866c4b147ae62288137536dBenchmarking heterogeneous electrocatalysts for the oygen evolution reactionMcCrory, Charles C. L.; Jung, Suho; Peters, Jonas C.; Jaramillo, Thomas F.Journal of the American Chemical Society (2013), 135 (45), 16977-16987CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Objective evaluation of the activity of electrocatalysts for water oxidn. is of fundamental importance for the development of promising energy conversion technologies including integrated solar water-splitting devices, water electrolyzers, and Li-air batteries. However, current methods employed to evaluate oxygen-evolving catalysts are not standardized, making it difficult to compare the activity and stability of these materials. We report a protocol for evaluating the activity, stability, and Faradaic efficiency of electrodeposited oxygen-evolving electrocatalysts. In particular, we focus on methods for detg. electrochem. active surface area and measuring electrocatalytic activity and stability under conditions relevant to an integrated solar water-splitting device. Our primary figure of merit is the overpotential required to achieve a c.d. of 10 mA cm-2 per geometric area, approx. the c.d. expected for a 10% efficient solar-to-fuels conversion device. Utilizing the aforementioned surface area measurements, one can det. electrocatalyst turnover frequencies. The reported protocol was used to examine the oxygen-evolution activity of the following systems in acidic and alk. solns.: CoOx, CoPi, CoFeOx, NiOx, NiCeOx, NiCoOx, NiCuOx, NiFeOx, and NiLaOx. The oxygen-evolving activity of an electrodeposited IrOx catalyst was also investigated for comparison. Two general observations are made from comparing the catalytic performance of the OER catalysts investigated: (1) in alk. soln., every non-noble metal system achieved 10 mA cm-2 current densities at similar operating overpotentials between 0.35 and 0.43 V, and (2) every system but IrOx was unstable under oxidative conditions in acidic solns.
- 48Seitz, L. C.; Dickens, C. F.; Nishio, K.; Hikita, Y.; Montoya, J.; Doyle, A.; Kirk, C.; Vojvodic, A.; Hwang, H. Y.; Norskov, J. K.; Jaramillo, T. F. A Highly Active and Stable IrO x /SrIrO 3 Catalyst for the Oxygen Evolution Reaction. Science (Washington, DC, U. S.) 2016, 353, 1011– 1014, DOI: 10.1126/science.aaf505048https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVemtLfN&md5=dc18e94836ca7e0f36d3349ab3254eb9A highly active and stable IrOx/SrIrO3 catalyst for the oxygen evolution reactionSeitz, Linsey C.; Dickens, Colin F.; Nishio, Kazunori; Hikita, Yasuyuki; Montoya, Joseph; Doyle, Andrew; Kirk, Charlotte; Vojvodic, Aleksandra; Hwang, Harold Y.; Norskov, Jens K.; Jaramillo, Thomas F.Science (Washington, DC, United States) (2016), 353 (6303), 1011-1014CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Oxygen electrochem. plays a key role in renewable energy technologies such as fuel cells and electrolyzers, but the slow kinetics of the oxygen evolution reaction (OER) limit the performance and commercialization of such devices. Here we report an iridium oxide/strontium iridium oxide (IrOx/SrIrO3) catalyst formed during electrochem. testing by strontium leaching from surface layers of thin films of SrIrO3. This catalyst has demonstrated specific activity at 10 milliamps per square centimeter of oxide catalyst (OER current normalized to catalyst surface area), with only 270 to 290 mV of overpotential for 30 h of continuous testing in acidic electrolyte. D. functional theory calcns. suggest the formation of highly active surface layers during strontium leaching with IrO3 or anatase IrO2 motifs. The IrOx/SrIrO3 catalyst outperforms known IrOx and ruthenium oxide (RuOx) systems, the only other OER catalysts that have reasonable activity in acidic electrolyte.
- 49Topalov, A. A.; Katsounaros, I.; Auinger, M.; Cherevko, S.; Meier, J. C.; Klemm, S. O.; Mayrhofer, K. J. J. Dissolution of Platinum: Limits for the Deployment of Electrochemical Energy Conversion?. Angew. Chem., Int. Ed. 2012, 51, 12613– 12615, DOI: 10.1002/anie.20120725649https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1agtrnF&md5=1296fc70022054f908c9cf76d12c4006Dissolution of Platinum: Limits for the Deployment of Electrochemical Energy Conversion?Topalov, Angel A.; Katsounaros, Ioannis; Auinger, Michael; Cherevko, Serhiy; Meier, Josef C.; Klemm, Sebastian O.; Mayrhofer, Karl J. J.Angewandte Chemie, International Edition (2012), 51 (50), 12613-12615CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)This quantification of Pt dissoln. as a function of the exptl. parameters offers guidelines for designing and operating Pt-based materials to optimize their durability in fuel cells. The intrinsic properties of polycryst. Pt already indicate that more than mere material development will be required for achieving all of the desired performance targets, particularly regarding severe start/stop cycling. Only a combined engineering, electrochem. and materials science approach considering the complex interplay of individual components and operation modes within fuel cells can improve the durability of electrocatalysts.
- 50Geiger, S.; Cherevko, S.; Mayrhofer, K. J. J. Dissolution of Platinum in Presence of Chloride Traces. Electrochim. Acta 2015, 179, 24– 31, DOI: 10.1016/j.electacta.2015.03.05950https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXkt1Olt7c%253D&md5=0d166273f08f0dadf72ec6e89b008b78Dissolution of Platinum in Presence of Chloride TracesGeiger, Simon; Cherevko, Serhiy; Mayrhofer, Karl J. J.Electrochimica Acta (2015), 179 (), 24-31CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)One of the main issues on the way to a com. use of fuel cells is the durability of the cell compartments, in particular electrocatalysts. Chloride impurities, originating from airborne salts or synthesis residues, can have severe effects on degrdn. in general. The quant. impact on dissoln. of Pt, which is the most common electrocatalyst material in polymer electrolyte membrane fuel cells, and the mechanism are still not fully understood. In the current work, potentiodynamic and potentiostatic measurements of platinum in acidic electrolytes contg. chlorides in the range of 1 to 1000 μM were carried out utilizing a scanning flow cell (SFC) coupled to an inductively coupled plasma mass spectrometer (ICP-MS). We show that during potentiodynamic measurements dissoln. accelerates with increase in amt. of chlorides, as expected. Similarly as in Cl--free electrolytes, dissoln. is a predominantly transient process taking place during oxidn. or redn. While thus in general the mechanism remains the same as reported before in the absence of chlorides, evidence for addnl. dissoln. processes during oxide formation and redn. are obsd. This leads to a variation in the ratio between anodic and cathodic dissoln. when chlorides are present. Based on the exptl. results a tentative dissoln. mechanism is proposed.
- 51Kasian, O.; Grote, J.-P.; Geiger, S.; Cherevko, S.; Mayrhofer, K. J. J. The Common Intermediates of Oxygen Evolution and Dissolution Reactions during Water Electrolysis on Iridium. Angew. Chem., Int. Ed. 2018, 57, 2488– 2491, DOI: 10.1002/anie.20170965251https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXit1Wlur8%253D&md5=6be0bb9168540d599321fb066942e37dThe Common Intermediates of Oxygen Evolution and Dissolution Reactions during Water Electrolysis on IridiumKasian, Olga; Grote, Jan-Philipp; Geiger, Simon; Cherevko, Serhiy; Mayrhofer, Karl J. J.Angewandte Chemie, International Edition (2018), 57 (9), 2488-2491CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Understanding the pathways of catalyst degrdn. during the O evolution reaction is a cornerstone in the development of efficient and stable electrolyzers, since even for the most promising Ir based anodes the harsh reaction conditions are detrimental. The dissoln. mechanism is complex and the correlation to the O evolution reaction itself is still poorly understood. Here, by coupling a scanning flow cell with inductively coupled plasma and online electrochem. mass spectrometers, the authors monitor the O evolution and degrdn. products of Ir and Ir oxides in situ. At high anodic potentials several dissoln. routes become possible, including formation of gaseous IrO3. From exptl. data, possible pathways are proposed for the O-evolution-triggered dissoln. of Ir and the role of common intermediates for these reactions is discussed.
- 52Wakeshima, M.; Harada, D.; Hinatsu, Y. Crystal Structures and Magnetic Properties of Ordered Perovskites Ba2LnIrO6 (Ln = Lanthanide). J. Mater. Chem. 2000, 10, 419– 422, DOI: 10.1039/a907586k52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXhslWksLY%253D&md5=1b0c511483eb4c1851a4c32f21a1cfa5Crystal structures and magnetic properties of ordered perovskites Ba2LnIrO6 (Ln = lanthanide)Wakeshima, Makoto; Harada, Daijitsu; Hinatsu, YukioJournal of Materials Chemistry (2000), 10 (2), 419-422CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)The crystal structures and magnetic properties of ordered perovskites Ba2LnIrO6 (Ln = lanthanide) are reported. They have monoclinic perovskite-type structures with space group P21/n. Their magnetic susceptibilities were measured from 2-350 K. Ba2CeIrO6 and Ba2PrIrO6 show antiferromagnetic transitions at 17 and 71 K, resp. In these compds., the Ce and Pr ions are in the tetravalent state from anal. of their crystal structures and magnetic susceptibilities.
- 53Massué, C.; Huang, X.; Tarasov, A.; Ranjan, C.; Cap, S.; Schlögl, R. Microwave Assisted Synthesis of Stable and Highly Active Ir-Oxohydroxides for Electrochemical Oxidation of Water. ChemSusChem 2017, 10, 1958, DOI: 10.1002/cssc.20160186453https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXlvVGgu70%253D&md5=450ba8bb3ab8b89c4d89409859a23c4dMicrowave-Assisted Synthesis of Stable and Highly Active Ir Oxohydroxides for Electrochemical Oxidation of WaterMassue, Cyriac; Huang, Xing; Tarasov, Andrey; Ranjan, Chinmoy; Cap, Sebastien; Schloegl, RobertChemSusChem (2017), 10 (9), 1958-1968CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)Water splitting for H prodn. in acidic media has been limited by the poor stability of the anodic electrocatalyst devoted to the O evolution reaction (OER). To help circumvent this problem we synthesized a class of novel Ir oxohydroxides by rapid microwave-assisted hydrothermal synthesis, which bridges the gap between electrodeposited amorphous IrOx films and cryst. IrO2 electrocatalysts prepd. by calcination routes. For electrode loadings 2 orders of magnitude below current stds., the synthesized compds. present an unrivalled combination of high activity and stability under com. relevant OER conditions in comparison to reported benchmarks, without need for pretreatment. The best compd. achieved a lifetime 33 times longer than the best com. Ir benchmark. This efficient synthesis of an Ir oxohydroxide phase with superior intrinsic OER performance constitutes a major step towards the targeted design of cost-efficient Ir based OER electrocatalysts for acidic media.
- 54Zaharieva, I.; Chernev, P.; Risch, M.; Klingan, K.; Kohlhoff, M.; Fischer, A.; Dau, H. Electrosynthesis, Functional, and Structural Characterization of a Water-Oxidizing Manganese Oxide. Energy Environ. Sci. 2012, 5, 7081– 7089, DOI: 10.1039/c2ee21191b54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XmsVWqtrw%253D&md5=d57548e8d50ded4d13888602d170fbbaElectrosynthesis, functional, and structural characterization of a water-oxidizing manganese oxideZaharieva, Ivelina; Chernev, Petko; Risch, Marcel; Klingan, Katharina; Kohlhoff, Mike; Fischer, Anna; Dau, HolgerEnergy & Environmental Science (2012), 5 (5), 7081-7089CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)In the sustainable prodn. of non-fossil fuels, water oxidn. is pivotal. Development of efficient catalysts based on manganese is desirable because this element is earth-abundant, inexpensive, and largely non-toxic. We report an electrodeposited Mn oxide (MnCat) that catalyzes electrochem. water oxidn. at neutral pH at rates that approach the level needed for direct coupling to photoactive materials. By choice of the voltage protocol we could switch between electrodeposition of inactive Mn oxides (deposition at const. anodic potentials) and synthesis of the active MnCat (deposition by voltage-cycling protocols). Electron microscopy reveals that the MnCat consists of nanoparticles (100 nm) with complex fine-structure. X-ray spectroscopy reveals that the amorphous MnCat resembles the biol. paragon, the water-splitting Mn4Ca complex of photosynthesis, with respect to mean Mn oxidn. state (ca. +3.8 in the MnCat) and central structural motifs. Yet the MnCat functions without calcium or other bivalent ions. Comparing the MnCat with electrodeposited Mn oxides inactive in water oxidn., we identify characteristics that likely are crucial for catalytic activity. In both inactive Mn oxides and active ones (MnCat), extensive di-μ-oxo bridging between Mn ions is obsd. However in the MnCat, the voltage-cycling protocol resulted in formation of MnIII sites and prevented formation of well-ordered and unreactive MnIVO2. Structure-function relations in Mn-based water-oxidn. catalysts and strategies to design catalytically active Mn-based materials are discussed. Knowledge-guided performance optimization of the MnCat could pave the road for its technol. use.
- 55Balaji, R.; Kannan, B. S.; Lakshmi, J.; Senthil, N.; Vasudevan, S.; Sozhan, G.; Shukla, A. K.; Ravichandran, S. An Alternative Approach to Selective Sea Water Oxidation for Hydrogen Production. Electrochem. Commun. 2009, 11, 1700– 1702, DOI: 10.1016/j.elecom.2009.06.02255https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXps1WrtLs%253D&md5=290cd69262d6a8846a2cbc406e12df49An alternative approach to selective sea water oxidation for hydrogen productionBalaji, Rengarajan; Kannan, Balasingam Suresh; Lakshmi, Jothinathan; Senthil, Natarajan; Vasudevan, Subramanyan; Sozhan, Ganapathy; Shukla, Ashok Kumar; Ravichandran, SubbiahElectrochemistry Communications (2009), 11 (8), 1700-1702CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)Sea water electrolysis is one of the promising ways to produce hydrogen since it is available in plentiful supply on the earth. However, in sea water electrolysis toxic chlorine evolution is the preferred reaction over oxygen evolution at the anode. In this work, research has been focused on the development of electrode materials with a high selectivity for oxygen evolution over chlorine evolution. Selective oxidn. in sea water electrolysis has been demonstrated by using a cation-selective polymer. We have used a perm-selective membrane (Nafion), which electrostatically repels chloride ions (Cl-) to the electrode surface and thereby enhances oxygen evolution at the anode. The efficiency and behavior of the electrode have been characterized by means of anode current efficiency and polarization studies. The surface morphol. of the electrode has been characterized by using a scanning electron microscope (SEM). The results suggest that nearly 100% oxygen evolution efficiency could be achieved when using an IrO2/Ti electrode surface-modified by a perm-selective polymer.
- 56Mo, Y.; Stefan, I. C.; Cai, W.-B.; Dong, J.; Carey, P.; Scherson, D. A. In Situ Iridium L III -Edge X-Ray Absorption and Surface Enhanced Raman Spectroscopy of Electrodeposited Iridium Oxide Films in Aqueous Electrolytes. J. Phys. Chem. B 2002, 106, 3681– 3686, DOI: 10.1021/jp014452p56https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38Xhsl2ntLw%253D&md5=84af63dd364b67f17650aea86d5415ceIn Situ Iridium LIII-Edge X-ray Absorption and Surface Enhanced Raman Spectroscopy of Electrodeposited Iridium Oxide Films in Aqueous ElectrolytesMo, Yibo; Stefan, Ionel C.; Cai, Wen-Bin; Dong, Jian; Carey, Paul; Scherson, Daniel A.Journal of Physical Chemistry B (2002), 106 (14), 3681-3686CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)Structural and electronic aspects of IrO2 films prepd. by electrodeposition on Au substrates were investigated by in situ LIII-edge X-ray absorption and surface enhanced Raman spectroscopies in both acid and alk. aq. solns. Linear correlations were found between the extent of oxidn. of Ir3+ in the films detd. from a statistical fit of the white line, which includes contributions from each of the sites differing by a single electron, and from coulometric anal. of the voltammetric curves. Anal. of the extended X-ray absorption fine structure (EXAFS) yielded Ir-O bond lengths decreasing in the sequence 2.02, 1.97, and 1.93 Å for Ir3+, Ir4+, and Ir5+ sites, resp. Whereas SERS provided evidence for the presence of cryst. IrO2 in the highly hydrated films, the lack of intense shells in the Fourier transform of the EXAFS function beyond the nearest oxygen neighbors indicates that the films do not display long-range order.
- 57Sanchez Casalongue, H. G.; Ng, M. L.; Kaya, S.; Friebel, D.; Ogasawara, H.; Nilsson, A. In Situ Observation of Surface Species on Iridium Oxide Nanoparticles during the Oxygen Evolution Reaction. Angew. Chem., Int. Ed. 2014, 53, 7169– 7172, DOI: 10.1002/anie.20140231157https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXos1CjsLs%253D&md5=114dd5f9d7fc27964b33d8e1d1a3885cIn Situ Observation of Surface Species on Iridium Oxide Nanoparticles during the Oxygen Evolution ReactionSanchez Casalongue, Hernan G.; Ng, May Ling; Kaya, Sarp; Friebel, Daniel; Ogasawara, Hirohito; Nilsson, AndersAngewandte Chemie, International Edition (2014), 53 (28), 7169-7172CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)An Ir oxide nanoparticle electrocatalyst under O evolution reaction conditions was probed in situ by ambient-pressure XPS. Under OER conditions, Ir undergoes a change in oxidn. state from IrIV to IrV that takes place predominantly at the surface of the catalyst. The chem. change in Ir is coupled to a decrease in surface hydroxide, providing exptl. evidence which strongly suggests that the O evolution reaction on Ir oxide occurs through an OOH-mediated deprotonation mechanism.
- 58Minguzzi, A.; Lugaresi, O.; Achilli, E.; Locatelli, C.; Vertova, A.; Ghigna, P.; Rondinini, S. Observing the Oxidation State Turnover in Heterogeneous Iridium-Based Water Oxidation Catalysts. Chem. Sci. 2014, 5, 3591, DOI: 10.1039/C4SC00975D58https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtVOitbvL&md5=e515cad76597243d18a3785437372febObserving the oxidation state turnover in heterogeneous iridium-based water oxidation catalystsMinguzzi, Alessandro; Lugaresi, Ottavio; Achilli, Elisabetta; Locatelli, Cristina; Vertova, Alberto; Ghigna, Paolo; Rondinini, SandraChemical Science (2014), 5 (9), 3591-3597CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)In this work the oxidn. states assumed by Ir in oxide systems used as heterogeneous catalysts for water oxidn. are detd. by means of in situ X-ray Absorption Spectroscopy (XAS). Using a highly hydrated iridium oxide film allows the max. no. of Ir sites to be involved in the electrochem. processes occurring at the catalysts during water oxidn. (oxygen evolution reaction, OER). X-ray Absorption Near Edge Structure (XANES) spectra clearly indicate the co-existence of Ir(III) and Ir(V) at the electrode potentials where OER occurs. This represents a fundamental step both in the understanding of the water oxidn. mechanism catalyzed by heterogeneous Ir oxide systems, and in the possible tailoring of electrocatalysts for OER.
- 59Pfeifer, V.; Jones, T. E.; Velasco Vélez, J. J.; Massué, C.; Arrigo, R.; Teschner, D.; Girgsdies, F.; Scherzer, M.; Greiner, M. T.; Allan, J.; Hashagen, M.; Weinberg, G.; Piccinin, S.; Hävecker, M.; Knop-Gericke, A.; Schlögl, R. The Electronic Structure of Iridium and Its Oxides. Surf. Interface Anal. 2016, 48, 261– 273, DOI: 10.1002/sia.589559https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitV2isbvF&md5=af071905b21db89137699595dac71081The electronic structure of iridium and its oxidesPfeifer, Verena; Jones, Travis E.; Velasco Velez, Juan J.; Massue, Cyriac; Arrigo, Rosa; Teschner, Detre; Girgsdies, Frank; Scherzer, Michael; Greiner, Mark T.; Allan, Jasmin; Hashagen, Maike; Weinberg, Gisela; Piccinin, Simone; Haevecker, Michael; Knop-Gericke, Axel; Schloegl, RobertSurface and Interface Analysis (2016), 48 (5), 261-273CODEN: SIANDQ; ISSN:0142-2421. (John Wiley & Sons Ltd.)Iridium-based materials are among the most active and stable electrocatalysts for the oxygen evolution reaction. Amorphous iridium oxide structures are found to be more active than their cryst. counterparts. Herein, we combine synchrotron-based X-ray photoemission and absorption spectroscopies with theor. calcns. to investigate the electronic structure of Ir metal, rutile-type IrO2, and an amorphous IrOx. Theory and expt. show that while the Ir 4f line shape of Ir metal is well described by a simple Doniach-Sunjic function, the peculiar line shape of rutile-type IrO2 requires the addn. of a shake-up satellite 1 eV above the main line. In the catalytically more active amorphous IrOx, we find that addnl. intensity appears in the Ir 4f spectrum at higher binding energy when compared with rutile-type IrO2 along with a pre-edge feature in the O K-edge. We identify these addnl. features as electronic defects in the anionic and cationic frameworks, namely, formally OI- and IrIII, which may explain the increased activity of amorphous IrOx electrocatalysts. We corroborate our findings by in situ X-ray diffraction as well as in situ X-ray photoemission and absorption spectroscopies. Copyright © 2015 John Wiley & Sons, Ltd.
- 60Massué, C.; Pfeifer, V.; van Gastel, M.; Noack, J.; Algara-Siller, G.; Cap, S.; Schlögl, R. Reactive Electrophilic O I– Species Evidenced in High-Performance Iridium Oxohydroxide Water Oxidation Electrocatalysts. ChemSusChem 2017, 10, 4786– 4798, DOI: 10.1002/cssc.20170129160https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslyhu7zP&md5=c2190dc12f35e4663a50694ae9ac6234Reactive Electrophilic O1- Species Evidenced in High-Performance Iridium Oxohydroxide Water Oxidation ElectrocatalystsMassue, Cyriac; Pfeifer, Verena; van Gastel, Maurice; Noack, Johannes; Algara-Siller, Gerardo; Cap, Sebastien; Schloegl, RobertChemSusChem (2017), 10 (23), 4786-4798CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)Although quasi-amorphous Ir oxohydroxides have been identified repeatedly as superior electrocatalysts for the O evolution reaction (OER), an exact description of the performance-relevant species has remained a challenge. Here, we report the characterization of hydrothermally prepd. Ir(III/IV) oxohydroxides that exhibit exceptional OER performances. Holes in the O 2p states of the Ir(III/IV) oxohydroxides result in reactive O1- species, which are identified by characteristic near-edge x-ray absorption fine structure (NEXAFS) features. A prototypical titrn. reaction with CO as a probe mol. shows that these O1- species are highly susceptible to nucleophilic attack at room temp. Similarly to the preactivated oxygen involved in the biol. OER in photosystem II, the electrophilic O1- species evidenced in the Ir(III/IV) oxohydroxides are suggested to be precursors to species involved in the O-O bond formation during the electrocatalytic OER. The CO titrn. also highlights a link between the OER performance and the surface/subsurface mobility of the O1- species. Thus, the superior electrocatalytic properties of the Ir(III/IV) oxohydroxides are explained by their ability to accommodate preactivated electrophilic O1- species that can migrate within the lattice.
- 61Kuznetsova, E.; Petrykin, V.; Sunde, S.; Krtil, P. Selectivity of Nanocrystalline IrO2-Based Catalysts in Parallel Chlorine and Oxygen Evolution. Electrocatalysis 2015, 6, 198– 210, DOI: 10.1007/s12678-014-0233-y61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsl2lsr3L&md5=90a63c3c24692733b9832d7ab238c6f2Selectivity of Nanocrystalline IrO2-Based Catalysts in Parallel Chlorine and Oxygen EvolutionKuznetsova, Elizaveta; Petrykin, Valery; Sunde, Svein; Krtil, PetrElectrocatalysis (2015), 6 (2), 198-210CODEN: ELECCF; ISSN:1868-2529. (Springer)Nanocryst. electrocatalysts with chem. compn. corresponding to Ir1-xMxO2 (M = Co, Ni, and Zn, 0.05 ≤ x ≤ 0.2) were prepd. by the hydrolysis of H2IrCl6·4H2O solns. combined with nitrates and acetates of Ni, Zn, and Co. X-ray diffraction (XRD) anal. indicates that the dopant Co, Ni, and Zn cations substitute the Ir atoms in the rutile lattice. The prepd. materials contain small inclusions of iridium metal on the level comparable with the detection of the XRD technique. The local environment of Co and Zn in the doped IrO2 materials conforms to a rutile model with a homogeneous distribution of the doping elements in the rutile lattice. The incorporated Ni is distributed in the rutile lattice non-homogeneously and tends to form clusters within rutile structure. The incorporation of Ni and Co enhances the activity of the prepd. electrocatalysts in oxygen evolution. The modification of the IrO2 via doping process alters also the material's selectivity in the parallel oxygen and chlorine evolution. Incorporation of Co and Zn cations shifts the selectivity of the catalysts toward oxygen evolution in chloride-contg. media; the Ni incorporation leads to an enhancement of the selectivity toward chlorine evolution. Chlorine evolution is apparently limited by the no. of the active catalytic sites on the electrode surface.
- 62Cherevko, S.; Geiger, S.; Kasian, O.; Kulyk, N.; Grote, J.-P.; Savan, A.; Shrestha, B. R.; Merzlikin, S.; Breitbach, B.; Ludwig, A.; Mayrhofer, K. J. J. Oxygen and Hydrogen Evolution Reactions on Ru, RuO2, Ir, and IrO2 Thin Film Electrodes in Acidic and Alkaline Electrolytes: A Comparative Study on Activity and Stability. Catal. Today 2016, 262, 170– 180, DOI: 10.1016/j.cattod.2015.08.01462https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVCnu7%252FE&md5=4bf7a1f1ee5806594ba98f8c86990ebeOxygen and hydrogen evolution reactions on Ru, RuO2, Ir, and IrO2 thin film electrodes in acidic and alkaline electrolytes: A comparative study on activity and stabilityCherevko, Serhiy; Geiger, Simon; Kasian, Olga; Kulyk, Nadiia; Grote, Jan-Philipp; Savan, Alan; Shrestha, Buddha Ratna; Merzlikin, Sergiy; Breitbach, Benjamin; Ludwig, Alfred; Mayrhofer, Karl J. J.Catalysis Today (2016), 262 (), 170-180CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Metallic iridium and ruthenium as well as their oxides are among the most active oxygen evolution (OER) electrocatalysts in acidic media, and are also of interest for the catalysis of the hydrogen evolution (HER). The stability of these materials under different operating conditions is, however, still not fully understood. In the current work, activity and stability of well-defined Ru, RuO2, Ir, and IrO2 thin film electrodes are evaluated in acidic and alk. electrolytes using an electrochem. scanning flow cell (SFC) connected to an inductively coupled plasma mass spectrometer (ICP-MS). Identical exptl. protocols are intentionally employed for all electrodes and electrolytes, to obtain unambiguous and comparable information on intrinsic activity and stability of the electrodes. It is found that independent of the electrolyte, OER activity decreases as Ru > Ir ≈ RuO2 > IrO2, while dissoln. increases as IrO2 « RuO2 < Ir « Ru. Moreover, dissoln. of these metals in both solns. is 2-3 orders of magnitude higher compared to their resp. oxides, and dissoln. is generally more intense in alk. solns. Similarly to the OER, metallic electrodes are more active catalysts for HER. They, however, suffer from dissoln. during native oxide redn., while IrO2 and RuO2 do not exhibit significant dissoln. The obtained results on activity and stability of the electrodes are discussed in light of their potential applications, i.e. water electrolyzers or fuel cells.
- 63Stevens, M. B.; Enman, L. J.; Batchellor, A. S.; Cosby, M. R.; Vise, A. E.; Trang, C. D. M.; Boettcher, S. W. Measurement Techniques for the Study of Thin Film Heterogeneous Water Oxidation Electrocatalysts. Chem. Mater. 2017, 29, 120– 140, DOI: 10.1021/acs.chemmater.6b0279663https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVyhs7jF&md5=191adc3a9549a1b2df75ccf18d6fe224Measurement Techniques for the Study of Thin Film Heterogeneous Water Oxidation ElectrocatalystsStevens, Michaela Burke; Enman, Lisa J.; Batchellor, Adam S.; Cosby, Monty R.; Vise, Ashlee E.; Trang, Christina D. M.; Boettcher, Shannon W.Chemistry of Materials (2017), 29 (1), 120-140CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)Heterogeneous electrocatalysts for the O evolution reaction (OER) are complicated materials with dynamic structures. They can exhibit potential-induced phase transitions, potential-dependent electronic properties, variable oxidn. and protonation states, and disordered local/surface phases. These properties make understanding the OER, and ultimately designing higher efficiency catalysts, challenging. The authors report procedures and measurement techniques that the authors have adopted or developed to assess each of the above challenges in understanding materials for the OER. These include the targeted synthesis of hydrated oxyhydroxide phases, the assessment and elimination of electrolyte impurities, the use of a quartz crystal microbalance to monitor film loading and dissoln., and the use of an in situ cond. measurement to understand the flow of electrons from the catalyst active sites to the conductive support electrode. The authors end with a recipe for the synthesis and characterization of a std. Ni(Fe)OxHy catalyst that can be performed in any lab. with a basic electrochem. setup and used as a quant. comparison to aid the development of new OER catalyst systems.
- 64Watzele, S.; Bandarenka, A. S. Quick Determination of Electroactive Surface Area of Some Oxide Electrode Materials. Electroanalysis 2016, 28, 2394– 2399, DOI: 10.1002/elan.20160017864https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XptVyhs74%253D&md5=1b621ff762f0e18fa6005a297535c887Quick Determination of Electroactive Surface Area of Some Oxide Electrode MaterialsWatzele, Sebastian; Bandarenka, Aliaksandr S.Electroanalysis (2016), 28 (10), 2394-2399CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)Quick and accurate detn. of the real electroactive surface area of oxide electrodes remains one of the most challenging but at the same time important unsolved methodol. tasks in the field of electroanal. For instance, the widely used Brunauer-Emmett-Teller (BET) method unfortunately provides no direct connection to it. However, its assessment through the double layer capacitance is complicated and not accurate enough, as the bulk oxide films themselves contribute to the measured capacitance, not mentioning the double layer frequency dispersion and other poorly understood factors. The authors propose a relatively simple methodol. for a quick assessment of the electroactive surface area of some electron conducting oxide and perovskite materials. The methodol. involves several steps. Initially, calibration expts. were performed aiming to form the thinnest (practically .ltorsim.100-200 nm) flat oxide films, which exhibit necessary functional properties (close to those expected for the bulk material) without significant side influence of the substrate. Then, AFM measurements are implemented to est. the surface roughness of the resulting samples. Finally, electrochem. impedance measurements are done at a small overpotential related to the O evolution reaction (OER) aiming to ext. not the double layer but the capacitance of adsorption Ca of the OER intermediates. The Ca values can then be used to evaluate the electroactive surface area of real-world high surface area oxide electrodes composed of the same material. Other words, similar to the H underpotential deposition or CO oxidn. in the case of metals, the authors propose to use the O evolution reaction as the probing reaction to evaluate the surface area of oxide electrocatalysts. However, instead of cyclic voltammetry, electrochem. impedance spectroscopy was used as the main probing technique. Due to relatively high reproducibility, clear phys. meaning and exclusive connection to the electroactive area, the measurements of Ca can become a viable method in numerous electrochem. applications. An example using Ni-oxide electrodes is given to illustrate the methodol.
- 65Chow, K. F.; Carducci, T. M.; Murray, R. W. Electronic Conductivity of Films of Electroflocculated 2 Nm Iridium Oxide Nanoparticles. J. Am. Chem. Soc. 2014, 136, 3385– 3387, DOI: 10.1021/ja413226j65https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXjtVeqt70%253D&md5=ba8c11946e5caf164f97314d744803a3Electronic Conductivity of Films of Electroflocculated 2 nm Iridium Oxide NanoparticlesChow, Kwok-Fan; Carducci, Tessa M.; Murray, Royce W.Journal of the American Chemical Society (2014), 136 (9), 3385-3387CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The electronic cond. of films of iridium oxide (IrOx) composed of ∼2 nm nanoparticles (NPs) is strongly dependent on the film oxidn. state. The IrIVOx NPs can be electrochem. converted to several oxidn. states, ranging from IrIII to IrV oxides. The NP films exhibit a very high apparent cond., e.g., 10-2 S cm-1, when the NPs are in the oxidized +4/+5 state. When the film is fully reduced to its IrIII state, the apparent cond. falls to 10-6 S cm-1.
- 66Jung, S.; McCrory, C. C. L.; Ferrer, I. M.; Peters, J. C.; Jaramillo, T. F. Benchmarking Nanoparticulate Metal Oxide Electrocatalysts for the Alkaline Water Oxidation Reaction. J. Mater. Chem. A 2016, 4, 3068– 3076, DOI: 10.1039/C5TA07586F66https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFWqt7vN&md5=d585b6ce247c8654b74a42f826a78f38Benchmarking nanoparticulate metal oxide electrocatalysts for the alkaline water oxidation reactionJung, Suho; McCrory, Charles C. L.; Ferrer, Ivonne M.; Peters, Jonas C.; Jaramillo, Thomas F.Journal of Materials Chemistry A: Materials for Energy and Sustainability (2016), 4 (8), 3068-3076CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)Nanoparticulate metal-oxide catalysts are among the most prevalent systems for alk. water oxidn. However, comparisons of the electrochem. performance of these materials have been challenging due to the different methods of attachment, catalyst loadings, and electrochem. test conditions reported in the literature. Herein, we have leveraged a conventional drop-casting method that allows for the successful adhesion of a wide range of nanoparticulate catalysts to glassy-carbon electrode surfaces. We have applied this adhesion method to prep. catalyst films from 16 cryst. metal-oxide nanoparticles with a const. loading of 0.8 mg cm-2, and evaluated the resulting nanoparticulate films for the oxygen evolution reaction under conditions relevant to an integrated solar fuels device. In general, the activities of the adhered nanoparticulate films are similar to those of thin-film catalysts prepd. by electrodeposition or sputtering, achieving 10 mA cm-2 current densities per geometric area at overpotentials of ∼0.35-0.5 V.
- 67Batchellor, A. S.; Boettcher, S. W. Pulse-Electrodeposited Ni–Fe (Oxy)Hydroxide Oxygen Evolution Electrocatalysts with High Geometric and Intrinsic Activities at Large Mass Loadings. ACS Catal. 2015, 5, 6680– 6689, DOI: 10.1021/acscatal.5b0155167https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFKru7bJ&md5=69976b3eb8103db04e6eab8e93c8c26ePulse-Electrodeposited Ni-Fe (Oxy)hydroxide Oxygen Evolution Electrocatalysts with High Geometric and Intrinsic Activities at Large Mass LoadingsBatchellor, Adam S.; Boettcher, Shannon W.ACS Catalysis (2015), 5 (11), 6680-6689CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)One practical metric for electrocatalyst performance is current per geometric area at a given applied overpotential. An obvious route to increase performance is to increase the catalyst mass loading-as long as the intrinsic performance (i.e., specific activity or turnover frequency) of the catalyst is independent of loading, and other elec., ionic, or mass-transfer resistances are not severe. Here we report the geometric and intrinsic oxygen evolution reaction (OER) activities of Ni(Fe)OOH films, the fastest known water oxidn. catalyst in basic media, as a function of mass loading from 0 to ∼100 μg cm-2. We discuss practices for measuring and reporting intrinsic activities, highlighting exptl. conditions where the film activity on a per-metal-cation basis can be accurately measured and where capacitance measurements of electrochem. active surface area fail. We find that the electrochem. reversibility of the (nominally) Ni2+/3+ redox wave correlates with the apparent intrinsic activity as a function of loading. We report a pulsed-electrodeposition method that dramatically improves the catalyst reversibility and performance at high loading compared to continuous electrodeposition, which we attribute to improved connectivity in the micro/nanostructure and better compn. control. Pulse electrodeposited films are shown to have geometric performance similar to a no. of advanced composite electrocatalyst structures and to maintain effective per-metal turnover frequencies of >0.4 s-1 at 300 mV overpotential, even for loadings of ∼100 μg/cm2.
- 68Takeno, N. Atlas of Eh-pH Diagrams Intercomparison of Thermodynamic Databases , Geological Survey of Japan Open File Report No. 419, National Institute of Advanced Industrial Science and Technology Research Center for Deep Geological Environments, 2005.There is no corresponding record for this reference.
- 69Zou, X.; Liu, Y.; Li, G.-D.; Wu, Y.; Liu, D.-P.; Li, W.; Li, H.-W.; Wang, D.; Zhang, Y.; Zou, X. Ultrafast Formation of Amorphous Bimetallic Hydroxide Films on 3D Conductive Sulfide Nanoarrays for Large-Current-Density Oxygen Evolution Electrocatalysis. Adv. Mater. 2017, 29, 1700404, DOI: 10.1002/adma.201700404There is no corresponding record for this reference.
- 70Pi, Y.; Shao, Q.; Wang, P.; Lv, F.; Guo, S.; Guo, J.; Huang, X. Trimetallic Oxyhydroxide Coralloids for Efficient Oxygen Evolution Electrocatalysis. Angew. Chem., Int. Ed. 2017, 56, 4502– 4506, DOI: 10.1002/anie.20170153370https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXkslKru74%253D&md5=ab834584b2db1fe64cfce3cbc757d587Trimetallic Oxyhydroxide Coralloids for Efficient Oxygen Evolution ElectrocatalysisPi, Yecan; Shao, Qi; Wang, Pengtang; Lv, Fan; Guo, Shaojun; Guo, Jun; Huang, XiaoqingAngewandte Chemie, International Edition (2017), 56 (16), 4502-4506CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Trimetallic oxyhydroxides are one of the most effective materials for oxygen evolution reaction (OER) catalysis, a key process for water splitting. Herein, a facile wet-chem. method is described to directly grow a series of coralloid trimetallic oxyhydroxides on arbitrary substrates such as nickel foam (NF) and carbon nanotubes (CNTs). The amt. of iron in these oxyhydroxide sponges on NF and CNTs was precisely controlled, revealing that the electrocatalytic activity of the WCoFe trimetallic oxyhydroxides depends on the Fe amt. in a volcano-like fashion. The optimized W0.5Co0.4Fe0.1/NF catalyst exhibited an overpotential of only 310 mV to deliver a large c.d. of 100 mA cm-2 and a very low Tafel slope of 32 mV dec-1. It also showed superior stability with negligible activity decay after use in the OER for 21 days (> 500 h). XPS revealed that the addn. of Fe leads to an on av. lower Co oxidn. state, which contributes to the enhanced OER performance.
- 71Nai, J.; Lu, Y.; Yu, L.; Wang, X.; Lou, X. W. D. Formation of Ni-Fe Mixed Diselenide Nanocages as a Superior Oxygen Evolution Electrocatalyst. Adv. Mater. 2017, 29, 1703870, DOI: 10.1002/adma.201703870There is no corresponding record for this reference.
- 72Guerrini, E.; Trasatti, S. Recent Developments in Understanding Factors of Electrocatalysis. Russ. J. Electrochem. 2006, 42, 1017– 1025, DOI: 10.1134/S102319350610005372https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhtVKjur%252FJ&md5=21b7197b88f8c0aeeac0707e56cfc87dRecent developments in understanding factors of electrocatalysisGuerrini, E.; Trasatti, S.Russian Journal of Electrochemistry (2006), 42 (10), 1017-1025CODEN: RJELE3; ISSN:1023-1935. (MAIK Nauka/Interperiodica Publishing)A review. After an introductory anal. of terms and concepts in the field of electrocatalysis, a no. of exptl. examples are reported to illustrate various factors. In particular, Tafel slope and PZC of oxide electrodes are able to disentangle electronic from geometric factors. The points under discussion are: effect of particle size and methods of prepn., surface vs. bulk compn., primary vs. secondary effects with redox systems depending on the mol. structure of the couple, single crystal vs. polycryst. surfaces. The last case is particularly relevant since for the 1st time vicinal faces of RuO2 behave at the extremes of the usually obsd. exptl. picture.
- 73Tilak, B. V.; Conway, B. E. Analytical Relations between Reaction Order and Tafel Slope Derivatives for Electrocatalytic Reactions Involving Chemisorbed Intermediates. Electrochim. Acta 1992, 37, 51– 63, DOI: 10.1016/0013-4686(92)80011-A73https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XntVeisw%253D%253D&md5=603ddfa1501120eb5b810e386b2d6b42Analytical relations between reaction order and Tafel slope derivatives for electrocatalytic reactions involving chemisorbed intermediatesTilak, B. V.; Conway, B. E.Electrochimica Acta (1992), 37 (1), 51-61CODEN: ELCAAV; ISSN:0013-4686.It is shown that characteristic relations between reaction order R and Tafel slope derivs. b can be deduced for the two principal desorption types of pathways, "electrochem." and "recombination", common in electrocatalytic reactions involving a single chemisorbed intermediate leading to dimeric product, e.g. H2, Cl2. The exptl. measureable R usually differs from the kinetically-significant surface reaction order in heterogeneous processes through the logarithmic deriv. d ln Θ/d ln c of the absorption isotherm function Θ(c), where Θ is the fractional coverage of the reaction surface by chemisorbed intermediates and/or reagent species. Cases where significant lateral interaction effects arise are considered and distinguished from those for which Langmuir adsorption behavior obtains. Results based on the quasi-equil. hypothesis in the treatment of consecutive electrochem. reaction kinetics are distinguished from those derived by the steady-state method; simple factors arise which relate the results for R and for b derived by the two methods. The dependence of R and b values for the two desorption mechanisms on coverage, Θ by the kinetically involved intermediate are evaluated and exhibit usefully distinguishable characteristics. Applications to some selected exptl. results are discussed with regard to conclusions about reaction mechanisms based on evaluation of R in relation to b values.
- 74Rosestolato, D.; Fregoni, J.; Ferro, S.; De Battisti, A. Influence of the Nature of the Electrode Material and Process Variables on the Kinetics of the Chlorine Evolution Reaction. The Case of IrO2-Based Electrocatalysts. Electrochim. Acta 2014, 139, 180– 189, DOI: 10.1016/j.electacta.2014.07.03774https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1KgsLnN&md5=248da2acb6856630d0fd5ebc1d03462aInfluence of the nature of the electrode material and process variables on the kinetics of the chlorine evolution reaction. The case of IrO2-based electrocatalystsRosestolato, Davide; Fregoni, Jacopo; Ferro, Sergio; De Battisti, AchilleElectrochimica Acta (2014), 139 (), 180-189CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Kinetic studies on the chlorine evolution reaction (ChlER) on oxide-based materials were the subject of a no. of papers since the seventies, following the introduction of DSAs (Dimensionally Stable Anodes) in chlor-alkali plants. From exptl. data, different pathways are proposed for the reaction over the years. Actually, specific exptl. conditions and different approaches in sample prepn. may lead to conflicting explanations. The ChlER kinetics was studied at four electrode materials based on iridium and titanium oxides (with a 1:2 molar ratio). Electrodes were synthesized at two temps. (350 and 450°) and by two different prepn. methods: phys. vapor deposition (radiofrequency-magnetron sputtering) and a conventional sol-gel technique, using special precursors developed in the authors' lab. Both methodologies guarantee a high level of reproducibility. As also obsd. by other authors, exptl. data showed a lack of linearity in Tafel plots, high b slopes and reaction orders with respect to chloride ≤ 1, which were justified from a Volmer-Heyrovsky pathway, by considering a model proposed by Tilak and Conway in 1992. This approach highlighted the role of the adsorbed intermediates, also at low overpotentials, for all electrode materials. To analyze further the kinetics, Langmuir and Frumkin models for intermediates adsorption were considered. Values for the lateral interaction parameter g were estd., which ranged between 1 and 10, in all cases. Concerning the effect of pH, its influence on the ChlER rate seems to be related only with electrode surface modifications, without any involvement of protons in the rate detg. step of the process. A slight inhibiting effect was assessed, by increasing the protons concn. Eventually, impedance spectroscopy anal. did not appear sensitive to intermediate adsorption, plausibly because of the low variation of the coverage within the Tafel region; a poorly resolved contribution related to porosity was found in the case of samples prepd. at 350°.
- 75Krishtalik, L. I. Kinetics and Mechanism of Anodic Chlorine and Oxygen Evolution Reactions on Transition Metal Oxide Electrodes. Electrochim. Acta 1981, 26, 329– 337, DOI: 10.1016/0013-4686(81)85019-075https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3MXitFKns7s%253D&md5=8cb5a9acc55a091c083d00475382aba9Kinetics and mechanism of anodic chlorine and oxygen evolution reactions on transition metal oxide electrodesKrishtalik, L. I.Electrochimica Acta (1981), 26 (3), 329-37CODEN: ELCAAV; ISSN:0013-4686.The 3-step mechanism of the Cl evolution at RuO2 and RuO2-TiO2 electrodes with the rate-detg. transfer of the 2nd electron and the formation of the nominally unipos. Cl as an intermediate is substantiated from kinetic data. The applicability of an analogous mechanism to the O evolution reaction is discussed as well as the possibility of participation in the process of higher oxidn. states of Ru. Analogies were drawn between anodic processes at RuO2 and other transition metal oxides.
- 76Exner, K. S.; Anton, J.; Jacob, T.; Over, H. Chlorine Evolution Reaction on RuO2(110): Ab Initio Atomistic Thermodynamics Study - Pourbaix Diagrams. Electrochim. Acta 2014, 120, 460– 466, DOI: 10.1016/j.electacta.2013.11.02776https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFGrt7fO&md5=1d0ec013b4c360ccc2f3ca4a18192836Chlorine Evolution Reaction on RuO2(110): Ab initio Atomistic Thermodynamics Study - Pourbaix DiagramsExner, Kai S.; Anton, Josef; Jacob, Timo; Over, HerbertElectrochimica Acta (2014), 120 (), 460-466CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Constrained ab initio thermodn. as a Pourbaix diagram can greatly assist kinetic modeling of a particular electrochem. reaction such as the Cl evolution reaction (CER) over RuO2(110). Pourbaix diagrams reveal stable surface structures, as a function of pH and the potential. The present DFT study indicates that the Pourbaix diagram in the CER potential region >1.36 V and pH values around zero is dominated by a stable surface structure in which all coordinatively undercoordinated Ru sites (Rucus) are capped by on-top O (Oot). This O satd. RuO2(110) surface is considered to serve as the catalytically active phase in the CER, quite in contrast to the heterogeneously catalyzed HCl oxidn. (Deacon process), for which the active RuO2(110) surface is mainly covered by on-top Cl. The active sites in the CER probably are RucusOot surface complexes, while in the Deacon process both undercoordinated surface Ru and O sites must be available for the activation of HCl mols.
- 77Koper, M. T. M. A Lattice-Gas Model for Halide Adsorption on Single-Crystal Electrodes. J. Electroanal. Chem. 1998, 450, 189– 201, DOI: 10.1016/S0022-0728(97)00648-777https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXjtlOlu7o%253D&md5=65bc9a7c8e2e24c0045f7ae3b4217c19A lattice-gas model for halide adsorption on single-crystal electrodesKoper, Marc T. M.Journal of Electroanalytical Chemistry (1998), 450 (2), 189-201CODEN: JECHES ISSN:. (Elsevier Science S.A.)A lattice-gas model is described for the adsorption of halides on single-crystal electrodes. The lateral interactions between the adsorbed halides include a short-range nearest-neighbor interaction and a long-range electrostatic interaction. By Monte Carlo simulations the model is used to fit the exptl. isotherm of bromide adsorption on Ag(100), giving information about the relative importance of the long-range and short-range interactions. The model reproduces the order-disorder transition obsd. exptl., and the way in which the long-ranged interactions influence the properties of this phase transition is discussed. The Monte Carlo simulations are also compared to anal. mean-field and quasi-chem. approxns. to the isotherm. Finally, the kinetics of the disorder-order transition is studied by dynamic Monte Carlo simulations, and some results on isotherms and ordered phases on (110) and (111) surfaces are described.
- 78Fernández, J. L.; Gennero de Chialvo, M. R.; Chialvo, A. C. Kinetic Study of the Chlorine Electrode Reaction on Ti/RuO2 through the Polarisation Resistance. Electrochim. Acta 2002, 47, 1137– 1144, DOI: 10.1016/S0013-4686(01)00838-678https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XjvFegsA%253D%253D&md5=6ecbeef48fb95822b8928393ec9595ebKinetic study of the chlorine electrode reaction on Ti/RuO2 through the polarisation resistance. Part II: Mechanistic analysisFernandez, J. L.; Gennero de Chialvo, M. R.; Chialvo, A. C.Electrochimica Acta (2002), 47 (7), 1137-1144CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Science Ltd.)A new methodol. for the kinetic treatment of electrode reactions is presented. It is based on a theor. anal. of the predictive capability of different mechanisms for the dependence of the polarization resistance on the different operative variables. This procedure is applied in this case to the anal. of the chlorine electrode reaction on Ti/RuO2, for which the variation of the polarization resistance on the activity of the chloride ions and on the partial pressure of the chlorine gas is derived. The descriptive capability of the mechanisms under discussion at present for this reaction is discussed and the theor. dependences are compared with exptl. data.
- 79Santana, M. H. P.; De Faria, L. A. Oxygen and Chlorine Evolution on RuO2+TiO2+CeO2+Nb2O5Mixed Oxide Electrodes. Electrochim. Acta 2006, 51, 3578– 3585, DOI: 10.1016/j.electacta.2005.09.05079https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XjsFeht70%253D&md5=abb82f0ce7beb4e9a7d53550437bee1bOxygen and chlorine evolution on RuO2 + TiO2 + CeO2 + Nb2O5 mixed oxide electrodesSantana, Mario H. P.; De Faria, Luiz A.Electrochimica Acta (2006), 51 (17), 3578-3585CODEN: ELCAAV; ISSN:0013-4686. (Elsevier B.V.)A systematic study was conducted on the mechanism and electrocatalytic properties of O2 and Cl2 evolution on mixed oxide electrodes of nominal compn.: Ti/[Ru(0.3)Ti(0.6)Ce(0.1-x)]O2[Nb2O5](x) (0 ≤ x ≤ 0.1). For the oxygen evolution, a 30 mV Tafel slope is obtained in the presence of CeO2, while in its absence a 40 mV coeff. is obsd. The intrinsic electrocatalytic activity is mainly due to electronic factors, as result of the synergism between Ru and Ce oxides. For chlorine evolution, the Tafel slope (30 mV) is independent on oxide compn. The best global electrocatalytic activity for ClER (chlorine evolution reaction) was obsd. in the absence of Nb2O5 additive. Variation of the voltammetric charge throughout the expts. confirms high CeO2 content compns. are fragile, due mainly to the porosity caused by CeO2 presence. However, Nb2O5 addn. decreases considerably this instability.
- 80Boggio, R.; Carugati, A.; Lodi, G.; Trasatti, S. Mechanistic Study of Cl2 Evolution at Ti-Supported Co3O4 Anodes. J. Appl. Electrochem. 1985, 15, 335– 349, DOI: 10.1007/BF0061598680https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXit1yisrY%253D&md5=a928f99624f0bf71da545ca36a41820fMechanistic study of chlorine evolution at titanium-supported cobalt oxide (Co3O4) anodesBoggio, R.; Carugati, A.; Lodi, G.; Trasatti, S.Journal of Applied Electrochemistry (1985), 15 (3), 335-49CODEN: JAELBJ; ISSN:0021-891X.Co3O4 layers were prepd. by thermal decompn. of Co(NO3)2 at various temps. in the range 200-500° on a Ti support with and without an interlayer of RuO2. Kinetic studies were carried out with and without dissolved Cl at variouspartial pressures in NaCl solns. of concns. in the range 0.5-5 mol dm-3. The effect of the soln. pH was esp. investigated. Kinetic measurements were carried out both near and far from equil. The following parameters were detd.: transfer coeff., Tafel slope, stoichiometric no., reaction orders with respect to Cl-, H* and surface sites, activation energy. The most intriguing feature obsd. was the inhibiting effect of acidity on the anodic Cl reaction. This behavior was ascribed to the complex surface behavior of oxides in soln. A detailed mechanistic scheme is proposed and discussed. The stability of the oxide surface was monitored by measuring the voltammetric charge in alk. soln. after sets of expts.
- 81Conway, B. E.; Ping, G.; De Battisti, A.; Barbieri, A.; Battaglin, G. Behaviour of the Adsorbed Cl* Intermediate in Anodic Cl2 Evolution at Thin-Film RuO2 Surfaces. J. Mater. Chem. 1991, 1, 725, DOI: 10.1039/jm991010072581https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXms1GgsLk%253D&md5=38491baeffbd0c5153284e3e17a282f7Behavior of the adsorbed atomic chlorine intermediate in anodic chlorine evolution at thin-film ruthenium dioxide surfacesConway, Brian E.; Ping, Gu; De Battisti, Achille; Barbieri, Andrea; Battaglin, G.Journal of Materials Chemistry (1991), 1 (5), 725-34CODEN: JMACEP; ISSN:0959-9428.Studies of the adsorption of the Cl• intermediate in anodic Cl2 evolution at a series of four thin-film RuO2 electrodes formed on a Ti substrate were made by means of potential-relaxation measurements, following interruption of previous steady-state currents, coupled with detn. of the current vs. overpotential kinetic relationships. Expts. at rotated RuO2 electrodes show only a small effect, indicating that neither diffusion-controlled supply of Cl- nor effects of Cl2 supersatn. in the boundary region at the electrode materially effect the kinetic behavior. This behavior is manifested as continuously curved Tafel relations, which approach limiting currents at overvoltages of 0.2-0.3 V. Therefore, on these thin-film RuO2 materials, kinetic control of Cl2 evolution seems to be by the Cl• recombination pathway; this is supported by linearity of Conway-Novak test plots for the recombination mechanism. Anal. of the potential-relaxation transients enables the pseudocapacitance, C.vphi., for adsorbed Cl• to be detd. The C.vphi. shows ascent to large values below 50-100 mV of overpotential, depending on temp. Some problems arise, however, in reconciling this adsorption behavior with expectations assocd. with recombination control. The near-surface compn. profiles of the RuO2 films were detd. by means of Rutherford backscattering and the av. compns., deeper into the films, by energy-dispersive x-ray emission analyses.
- 82Conway, B. E.; Novak, D. M. Chloride Ion Adsorption Effects in the Recombination-Controlled Kinetics of Anodic Chlorine Evolution at Pt Electrodes. J. Chem. Soc., Faraday Trans. 1 1979, 75, 2454– 2472, DOI: 10.1039/f1979750245482https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3cXjtVyrug%253D%253D&md5=5df00ef4deeacb318310d6eb6b1c7ee2Chloride ion adsorption effects in the recombination-controlled kinetics of anodic chlorine evolution at platinum electrodesConway, Brian E.; Novak, Dunja M.Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases (1979), 75 (11), 2454-72CODEN: JCFTAR; ISSN:0300-9599.The role of Cl- adsorption in the anodic evolution of Cl2 at Pt electrodes in aq. solns. was examd. over a range of Cl- concns. The rate const. for the rate-detg. recombination step and the quasiequil. const. of the prior Cl- discharge/Cl• electrosorption step were evaluated quant. as a function of the Cl- concn. Despite the approach of the anodic current/potential relation towards limiting current behavior, consistent with recombination-controlled kinetics, the limiting current densities vary with the Cl- concn. This behavior is due to effects of specifically adsorbed Cl- on the Cl• recombination rate const. and to changes of state of the Pt anode surface due to competitive effects of Cl- adsorption on the extent of Pt surface oxidn. These factors complicate the interpretation of reaction orders in Cl- concns. for the evolution of Cl2 because both effects must be considered.
- 83Ferro, S.; De Battisti, A. Electrocatalysis and Chlorine Evolution Reaction at Ruthenium Dioxide Deposited on Conductive Diamond. J. Phys. Chem. B 2002, 106, 2249– 2254, DOI: 10.1021/jp012195i83https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38Xps1artg%253D%253D&md5=8915bd5e962e7c344e2e48a80d1b504aElectrocatalysis and Chlorine Evolution Reaction at Ruthenium Dioxide Deposited on Conductive DiamondFerro, Sergio; De Battisti, AchilleJournal of Physical Chemistry B (2002), 106 (9), 2249-2254CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)The instability of the commonly adopted support (e.g., Ti, Ti-Pd alloys, Ta) for the prepn. and characterization of different electrode materials was overcome by depositing the electrode material of interest (RuO2) on conductive, boron-doped diamond (BDD). The present paper reports results on the model chlorine evolution reaction, studied at BDD surfaces modified by RuO2 loadings of 1.2 × 1013, 6.0 × 1014, and 2.65 × 1016 mols. cm-2. A radical spillover mechanism is proposed for the reaction occurring at the electrode having the lowest noble-metal oxide loading.
Supporting Information
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acscatal.9b01159.
Supplementary ICP-MS data and methodology description, XRD data, RRDE data concerning voltammetric characterizations, estimation of errors concerning RRDE chlorine detection, effect of Nafion on CER selectivity, ECSA determination and error bars, numerical Tafel slope values, OER vs CER selectivity, and test plots for the CER mechanism (PDF)
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