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Identification of Interface Structure for a Topological CoS2 Single Crystal in Oxygen Evolution Reaction with High Intrinsic Reactivity
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Energy, Environmental, and Catalysis Applications

Identification of Interface Structure for a Topological CoS2 Single Crystal in Oxygen Evolution Reaction with High Intrinsic Reactivity
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  • Yu Kang*
    Yu Kang
    Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0003-0336-454X
  • Yangkun He
    Yangkun He
    Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
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    Orcidhttps://orcid.org/0000-0002-5126-153X
  • Darius Pohl
    Darius Pohl
    Dresden Center for Nanoanalysis, cfaed, Technische Universität Dresden, Helmholtzstraße 18, 01069 Dresden, Germany
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  • Bernd Rellinghaus
    Bernd Rellinghaus
    Dresden Center for Nanoanalysis, cfaed, Technische Universität Dresden, Helmholtzstraße 18, 01069 Dresden, Germany
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  • Dong Chen
    Dong Chen
    Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
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  • Marcus Schmidt
    Marcus Schmidt
    Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
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  • Vicky Süß
    Vicky Süß
    Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
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  • Qingge Mu
    Qingge Mu
    Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
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  • Fan Li
    Fan Li
    Max Planck Institute for Microstructure Physics, Weinberg 2, D-06120 Halle, Sachsen-Anhalt, Germany
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  • Qun Yang
    Qun Yang
    Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
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  • Hedong Chen
    Hedong Chen
    Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
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  • Yufei Ma
    Yufei Ma
    Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
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  • Gudrun Auffermann
    Gudrun Auffermann
    Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
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  • Guowei Li*
    Guowei Li
    CAS Key Laboratory of Magnetic Materials and Devices, and Zhejiang Province Key Laboratory of Magnetic Materials and Application Technology, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China
    University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0003-1837-3967
  • Claudia Felser*
    Claudia Felser
    Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
    *Email: [email protected]
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Open PDFSupporting Information (1)

ACS Applied Materials & Interfaces

Cite this: ACS Appl. Mater. Interfaces 2022, 14, 17, 19324–19331
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https://doi.org/10.1021/acsami.1c24966
Published April 25, 2022

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Abstract

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Transition metal chalcogenides such as CoS2 have been reported as competitive catalysts for oxygen evolution reaction. It has been well confirmed that surface modification is inevitable in such a process, with the formation of different re-constructed oxide layers. However, which oxide species should be responsible for the optimized catalytic efficiencies and the detailed interface structure between the modified layer and precatalyst remain controversial. Here, a topological CoS2 single crystal with a well-defined exposed surface is used as a model catalyst, which makes the direct investigation of the interface structure possible. Cross-sectional transmission electron microscopy of the sample reveals the formation of a 2 nm thickness Co3O4 layer that grows epitaxially on the CoS2 surface. Thick CoO pieces are also observed and are loosely attached to the bulk crystal. The compact Co3O4 interface structure can result in the fast electron transfer from adsorbed O species to the bulk crystal compared with CoO pieces as evidenced by the electrochemical impedance measurements. This leads to the competitive apparent and intrinsic reactivity of the crystal despite the low surface geometric area. These findings are helpful for the understanding of catalytic origins of transition metal chalcogenides and the designing of high-performance catalysts with interface-phase engineering.

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1. Introduction

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Energy consumption together with CO2 emission has caused global concerns over the decades, this has given rise to the targets of peak carbon emission and carbon neutrality recently. (1−3) Electrochemical water splitting is one of the best possible solutions that transfer renewable energy into green hydrogen fuel. (4−6) The oxygen evolution reaction (OER) in water splitting is the rate-determining step because it is a complex four-electron process with high overpotential. (7−10) Many advanced nanocatalysts have been developed to promote the performance of OER, such as transition metal oxides, hydroxides, chalcogenides, and phosphides. (11−16) Among them, transition metal sulfides, usually with extremely low cost and high electric conductivity, are highly potential catalysts. (17−19) These nanosulfides may experience surface reconstruction at high potential during OER and are recognized as precatalysts. (20,21) In this case, the electron derived from adsorption oxygen species would transfer through surface-reconstructed layers and inner bulk precatalyst before reaching the electrode substrate. Therefore, both the reconstructed layer and bulk precatalysts play a role in promoting the performance, forming a so-called active structure. (22−24) However, previous works usually focused on identifying either the bulk sulfides or the reconstructed species. Little is known about the interface between the surface reconstructed layer and bulk precatalysts. This may be due to the complex surface structure of nanocatalysts, giving rise to the difficulty in understanding the interface. Hence, well-defined sulfide electrocatalysts with good performance are highly desired.
Recently, booming topological materials, which are also single crystals, seem to provide a new approach. Topological single crystals such as PtSn4, 1T′-MoTe2, Co3Sn2S2, and so forth have been introduced into water splitting. (25−29) These semimetals have extremely high charge carrier mobility and a protected topological surface state derived from the bulk band inversion of the valence and conduction band. (30−32) Such special properties can facilitate the electron transfer between the bulk crystal and adsorbates on the surface. (33−35) Recently, it was reported that the CoS2 single crystal hosts a topological nodal line and Fermi arc surface state in the band structure close to the Fermi level (Ef); therefore, it is also verified as a topological material. (36) This suggests it might be a good electrocatalyst with superior electric conductivity. As far as we know, the CoS2 single crystal has not yet been studied for water splitting, making it an ideal model catalyst to clarify the interface structure for OER.
In this work, we have successfully grown a well-crystallized topological CoS2 single crystal, which exhibits superior intrinsic reactivity based on its effective electrochemical surface area. Assisted by the focused ion beam (FIB) technique, electron microscopy, and electrochemical analysis, the surface evolution species, that is, CoO pieces and Co3O4, have been clearly identified after OER. The Co3O4 is observed to epitaxially grow on the bulk surface, such that the Co3O4–CoS2 with a compact interface could facilitate fast electron transfer and promote the intrinsic performance. Therefore, the CoS2 single crystal acts as a clean model catalyst for studying surface evolution and the interface structure, paving a way for further understanding of the electron transfer process between adsorbed O species and catalysts for OER.

2. Experimental Section

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2.1. Synthesis of a CoS2 Single Crystal

Single crystals of CoS2 were grown via chemical transport reaction using CoBr2 as the transport additive. CoS2 had first been synthesized by a direct reaction of elemental cobalt (powder 99.998%, Alfa Aesar) and sulfur (pieces 99.99%, Alfa Aesar) at 700 °C in an evacuated fused silica tube for 7 days. Starting from this microcrystalline powder, CoS2 was crystallized by a chemical transport reaction in a temperature gradient from 700 °C (source) to 640 °C (sink), with the addition of 3.5 mg/mL tube volume cobalt(II) bromide (Alfa Aesar 99.99%, ultradry). After 14 days, the experiment was stopped by quenching the ampoule in cold water. The obtained crystals showed a well-developed morphology. The preparation of RuO2, Co3O4, and CoOOH is shown in the Supporting Information.

2.2. Characterizations

CoS2 single crystal formation was confirmed with a pyrite structure by powder X-ray diffraction (XRD) using a monochromator’s Co Kα radiation and the Laue diffraction method. The surface morphology of the crystal was characterized by scanning electron microscopy (SEM) (Philips XL30). High resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray analysis were carried out by using a JEOL F200 with an operating voltage of 200 kV. Electron transparent samples were prepared by the FIB technique using an FEI Helios 660. Resistivity measurement was conducted on quantum design PPMS via the four-probe method. X-ray photoelectron spectroscopy (XPS) spectra were obtained from a UHV surface analysis system equipped with a Scienta-200 hemispherical analyzer. Raman spectra studies were carried out by a customary confocal micro-Raman spectrometer with an unpolarized HeNe laser (632.8 nm) as the light source.

2.3. Electrochemical Measurement

The electrochemical measurement was carried out on an Autolab PGSTAT302N electrochemistry workstation. Three electrode system was employed. A carbon rod and a Ag/AgCl electrode were used as the counter electrode and reference electrode, respectively, with 1 M KOH solution as the electrolyte. The solution was bubbled before and during the test. For the working electrode preparation, the CoS2 single crystal was attached with Ti wire by a silver paint, which was covered by resin after it dried up. Linear sweep voltammetry (LSV) was measured at a scan rate of 5 mV/s to avoid the interference of the capacitive current. The electrochemical impedance spectroscopy was conducted from 10 kHz to 0.01 Hz. The applied potential against the reference electrode was converted into potential versus RHE by
(1)
The effective electrochemical active surface area (ECSA) was calculated by
(2)
where the double-layer capacitance (Cdl) was obtained by plotting the difference of current density ΔJ = (Janodic – Jcathodic)/2 at 1.17 V versus RHE against the scan rate. Cs is the specific capacitance, which is estimated to be 0.02 mF/cm2, (37) and GSA is the geometric surface area of the single crystal.

3. Results and Discussion

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3.1. Crystal Structure

We have successfully prepared the CoS2 single crystal by the chemical vapor transport (CVT) method (see Experimental Section). The obtained well-crystallized polyhedron was around 2 mm in size (Figure 1a). The Laue diffraction pattern presenting clear ordered diffraction spots confirmed the high quality of the single crystal (Figure S1). CoS2 exists in the pyrite cubic structure (Figure 1b), with corner-shared [CoS6] connecting it together (Figure 1c), which could be expected as a metallic state owing to the octahedral Co2+ sites with 3d7 configuration. The powder XRD pattern has demonstrated the CoS2 phase with the space group of Pa3̅ (no. 205) (Figure 1d). The crystal structure was further confirmed by HRTEM and the corresponding fast Fourier transform (FFT) (Figure 1e), which presented clear lattice fringes of 0.55 nm distance, corresponding to the (100) plane of CoS2. In addition, the resistivity versus T curve of CoS2 is given in Figure 1f. The crystal exhibited typical metallic property owing to the increasing resistivity with temperature, although there was a resistivity slope variation at 120 K, ascribed to the phase transition from ferromagnetic to the paramagnetic state. The crystal presented around 260 μΩ·cm at room temperature, indicating excellent electric conductivity, which can facilitate electron transfer during electrochemistry. The residual resistivity ratio, defined as ρ300K/ρ0, was around 17.6, also suggesting the high crystallinity of CoS2.

Figure 1

Figure 1. (a)Photograph and (b,c) pyrite structure of the CoS2 single crystal. (d) XRD pattern, (e) HRTEM with the corresponding FFT image, and (f) resistivity vs temperature curve of the CoS2 crystal.

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3.2. OER Performance and Characterizations

The OER performance of the CoS2 single crystal was studied in 1 M KOH electrolyte, and the results are shown in Figure 2. Typical RuO2, Co3O4, and CoOOH powders were also compared by using a rotating disk electrode in the same solution. Linear sweep voltammetry (LSV) presented that the overpotential for CoS2 at 10 mA cm–2 was around 300 mV (Figure 2a), much lower than those reference RuO2, Co3O4, and CoOOH materials alone. This indicated that CoS2 can be a good precatalyst for OER, although the Tafel slope of the CoS2 crystal was 81 mV dec–1 (Figure 2b), slightly higher than the value of typical CoOOH and Co3O4 (46 and 65 mV dec–1) in water splitting. To reveal the intrinsic OER performance, we measured the effective ECSAs of the single crystal, as shown in Figure S2, and the electrochemical double-layered capacitance (Cdl) was estimated to be only 0.021 mF cm–2 (inset in Figure 2c), almost orders of magnitude lower than those of other nanomaterials reported. It is interesting to note that such a low Cdl has still ensured a superior activity of CoS2. The specific cyclic voltammetry normalized to ECSA showed that the overpotential only increased slightly to 310 mV, similar to the geometric surface-normalized results, indicating that the ECSA was almost approximate to the surface area. We compared the results with previously reported nanomaterials; as shown in Figure 2d, the single crystal exhibited competitive apparent overpotential, and most importantly, the current density of CoS2 based on ECSA was nearly orders of magnitude higher than other works under the potential of 1.55 V, demonstrating its excellent intrinsic electrochemical activity for OER. The stability was also investigated at a static current density of 10 mA cm–2 (Figure 2e). A relatively stable performance can be guaranteed, with no obvious potential increase during 10 h. The faradaic efficiency of CoS2 was around 90% (Figure S3), indicating the slow oxidation of the crystal during OER, which may affect the long-term stability of CoS2.

Figure 2

Figure 2. OER performance of the CoS2 single crystal and reference materials with 90% iR correction. (a) LSV curves with the scanning rate of 5 mV s–1 and (b) Tafel slope (CoS2 was tested at the steady state from 1.40 to 1.66 V at the interval of 0.02 V). (c) Cyclic voltammetry results comparison based on the geometric area and ECSA of the single crystal. The inset is the difference in current density between anodic and cathodic sweeps vs scan rate. (d) Apparent overpotential comparison (left) at 10 mA cm–2 normalized to the geometric surface area and the intrinsic current density comparison (right) at 1.55 V based on ECSA. (e) Stability test at a static current density of 10 mA cm–2. (f) Nyquist plots under different potentials. The inset shows the equivalent circuit for the two semicircles.

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Electrochemical impedance spectroscopy (EIS) was used to investigate the electron transfer process. The measurement was carried out at different potentials in the OER region. Two obvious semicircles in the Nyquist plots in Figure 2f can be observed and fitted with two time constants in series with each other. The semicircle at low frequency was effectively influenced by the applied overpotential, with a smaller Rp2 value at higher potential (Table S1), which can be ascribed to the charge transfer process of OER between the catalyst and adsorption species. Additionally, the small semicircle at high frequency was almost independent concerning the applied potential due to the small change in Rs (also see Figure S4 and Table S1). This might be related to the fast electron transfer from the bulk single crystal to the surface active layers, in which the high electrical conductivity of CoS2 played an important role. (38)
Compared with nano-electrocatalysts, the single crystal can provide a better platform to understand the mechanism of high intrinsic reactivity of CoS2 and its real active structure during water splitting. The SEM image in Figure 3a showed that there were many sheet-like pieces with the size of around 50 μm stacked on the crystal surface after OER. This might be the oxidation product. We used the FIB technique to cut the piece and expose the cross section (see details in Figure S5). Before cutting, the protective layer was first deposited onto the piece (Figure 3b). It can be seen from the cross section that there was a gap between the surface piece and bulk CoS2 (Figure 3c), and this is not facile to charge transfer between them. Figure 3d–g presents the scanning TEM (STEM) images and the corresponding energy-dispersive X-ray spectroscopy (EDS). In the red rectangle area of the cross section, the sulfur element mapping has disappeared, with only Co and O left in the cut piece, demonstrating that the crystal was indeed oxidized forming pieces of the layer on the surface during water splitting. We performed the selected area electron diffraction (SAED) measurements and had a fit (Figure 3h). As a result, the cut piece could be attributed to the textured nanocrystalline CoO (ICSD #9865) owing to the appearance of broad (200) reflections and otherwise ring patterns.

Figure 3

Figure 3. SEM image of (a) surface pieces on the CoS2 single crystal after OER, (b) one of the pieces after depositing the protective layer for FIB, and (c) cross section of the cut piece after FIB. (d) STEM annular dark-field (ADF) image of the cross-section and (e–g) corresponding EDS elemental mappings. (h) SAED pattern of the cut piece, which was fitted with (111), (200), and (220) reflections of CoO.

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Besides the CoO on the single crystal, there is still a question considering the state of other surface places without pieces. Therefore, we cut the surface of CoS2 after OER along the red line, as shown in Figure 4a, by the FIB technique (see details in Figure S6). Figure 4b shows the TEM of the cut cross section, with an obvious shell layer covered on the surface of CoS2. Figure 4c clearly presents the lattice stripes of the shell. It was observed that the shell closely grew on the surface of the bulk crystal, which was different from those pieces of CoO. We measured the lattice distance along the red line, and the profile is given in Figure S7, which gave a plane distance of around 0.24 nm, consistent with the (311) plane of the Co3O4 phase. (39) STEM and EDS mappings of near surface in Figure 4d–g showed that the Co element layer was thicker than the S layer, and the O layer had indeed overlapped with the Co layer. This further demonstrated the formation of the surface oxidation layer. Line scanning also indicated the existence of a surface layer (Figure S8). Therefore, it can be concluded that the Co3O4 layer formed on the surface after OER. In addition, we also found that the distance in the (311) plane of cubic Co3O4 (0.24 nm) along the red line direction was approximately equal to the (021) plane spacing of cubic CoS2 (Figure 4c), although the lattice of Co3O4 was not much clear, suggesting that the Co3O4 layer seemed to epitaxially grow on the bulk crystal, as illustrated in Figure 4h. This kind of structure may promote electron transfer and contribute to the superior intrinsic reactivity of the CoS2 crystal.

Figure 4

Figure 4. SEM image of (a) thin oxidation layer on CoS2 surface after OER. (b) High-resolution TEM of the cross section of the surface oxidation layer (c) and the corresponding amplified area in the red square frame. (d) STEM ADF of the cross section and (e–g) corresponding EDS elemental mappings of the marked area in (d). (h) Illustration of the interface of Co3O4 and CoS2 crystal in the TEM.

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We compared the XPS of the samples before and after OER with the XPS survey, as shown in Figure S9. The Co spectrum of the fresh one (Figure 5a) was deconvoluted, and the main binding energy at 778.9 and 794.1 eV were ascribed to 2p3/2 and 2p1/2 of Co2+ in CoS2 single crystal, respectively. (40) The smaller peaks at 780.8 and 797.0 eV can be attributed to the Co3+ species due to the slight oxidation of the surface. The left two peaks at 784.6 and 802.9 eV correspond to the Co 2p satellites. After OER, it can be observed that the whole Co 2p3/2 peak shifted into higher binding energy, consistent with previous results. (24) The resulting area of Co3+ species became much larger than that of Co2+, further demonstrating the existence of the oxidation layers. In addition, the O 1s spectrum of fresh and reacted crystal was also deconvoluted into two peaks and three peaks, respectively (Figure 5b). The binding energy at 532.1 eV was assigned to the adsorbed water species, (41) with similar peak areas for the two samples. The binding energy at 531.4 eV was associated with the nonstoichiometric oxygen on the surface. Here, for the reacted sample, both CoO and Co3O4 might contribute to this peak due to their defects, leading to a much larger area than that of the fresh one. For the peak at 529.9 eV after OER, it was produced from the lattice oxygen of the surface cobalt oxides pieces. Hence, the XPS analysis was consistent with the results of electron microscopy. Besides, we compared the O 1s spectra of this work and those of the pure CoOOH. (42) It was found that their peak shapes were rather different from each other, indicating the O species did not come from CoOOH. On the contrary, the O 1s peak shape was much similar to the result of the Co3O4 structure (Figure S10). (43) This also suggested the existence of Co3O4.

Figure 5

Figure 5. XPS spectra of (a) Co 2p and (b) O 1s. (c) Raman spectra of the CoS2 crystal after the measurements at 1.4, 1.5, and 1.6 V.

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To further understand the oxidation of the single crystal at different potentials, a Raman spectrum was further carried out. As shown in Figure 5c, there were two main peaks after the potentiostatic measurement at 1.4 eV, which can be assigned to the Ag and Eg vibration modes of the CoS2 structure, (44) indicating that very little oxidation has occurred on the surface. When increasing the potential to 1.5 and 1.6 V, besides the CoS2 phase, another three vibration peaks ascribing to the F2g, Eg, and A1g Raman active modes of Co3O4 were also observed. (45) This suggested that the surface oxidation layer quickly generated at above 1.5 V. Besides, the significantly increased OER performance over 1.5 V indicated that the Co3O4 layer formation may play an important role in water splitting.

3.3. Discussion

Although previous work reported the surface evolution of nanocatalysts during water splitting, there is still a lack of knowledge about the detailed interface structure between the surface reconstructed layer and the bulk precatalysts due to their complex structure. In this work, we used the topological CoS2 single crystal with excellent conductivity as the model catalyst and identified two kinds of oxidation species on the surface of CoS2 after OER. They are the CoO pieces and Co3O4. Most importantly, it was revealed that the thin Co3O4 layer epitaxially grew on the CoS2 surface (Figure 4b,c), while the pieces of CoO were loosely attached to the crystal (Figure 3a). Thus, such a compact Co3O4–CoS2 interface would be more facile for the transfer of electrons between single crystal and adsorbed O species, which has already been demonstrated by the very small semicircle at high frequency in Figure S4. In addition, the intrinsic activity based on ECSA was quite close to the geometric surface normalized results (Figure 2c), indicating that the ECSA is approximate to the geometric area. From the abovementioned discussion, we know the Co3O4 thin layer is covered on the CoS2 geometric surface. This further demonstrated that Co3O4–CoS2 with a compact interface formed the active structure for OER instead of the CoO pieces. Although some work has indicated that Co3O4 can be transformed into CoOOH during the reaction, (46−49) only our result has definitively identified Co3O4 species on the surface after OER. This might be due to the reversible transformation between the oxy-hydroxide and Co3O4 layer (Co3O4 + OH– + H2O ↔ 3CoOOH + e–) at a different potential, (50,51) and the compact interface between Co3O4 and bulk crystal could facilitate such a fast transformation and thus contribute to the high performance. Therefore, we can conclude that the Co3O4–CoS2 with such a compact interface was the active structure owing to the fast and efficient electron transfer during OER.

4. Conclusions

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In summary, we have successfully grown high-quality topological CoS2 single crystal via the CVT method, which exhibited superior intrinsic OER performance compared with nanocounterparts. Further electron microscopes with the FIB technique identified two kinds of oxidation species in situ formed on the surface after the reaction, that is, the CoO pieces and Co3O4. The Co3O4 thin layer with several nanometers grew epitaxially on the surface of the conductive CoS2 crystal, facilitating the electron transfer between bulk crystal and adsorbed O species. Thus, the formed Co3O4–CoS2 with a compact interface was revealed as the active structure for OER and contributed to the high intrinsic reactivity. Overall, this work reveals the interface structure of CoS2 for OER and helps in further understanding of the connection between surface evolution species and bulk precatalysts for efficient electron transfer.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.1c24966.

  • Additional experimental details, Laue diffraction, electrochemical OER results, electron microscopy, XPS, and the fitting parameters of EIS (PDF)

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Author Information

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  • Corresponding Authors
    • Yu Kang - Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany;  Orcidhttps://orcid.org/0000-0003-0336-454X;  Email: [email protected]
    • Guowei Li - CAS Key Laboratory of Magnetic Materials and Devices, and Zhejiang Province Key Laboratory of Magnetic Materials and Application Technology, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China;  University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China;  Orcidhttps://orcid.org/0000-0003-1837-3967;  Email: [email protected]
    • Claudia Felser - Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany;  Email: [email protected]
  • Authors
    • Yangkun He - Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany;  Orcidhttps://orcid.org/0000-0002-5126-153X
    • Darius Pohl - Dresden Center for Nanoanalysis, cfaed, Technische Universität Dresden, Helmholtzstraße 18, 01069 Dresden, Germany
    • Bernd Rellinghaus - Dresden Center for Nanoanalysis, cfaed, Technische Universität Dresden, Helmholtzstraße 18, 01069 Dresden, Germany
    • Dong Chen - Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
    • Marcus Schmidt - Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
    • Vicky Süß - Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
    • Qingge Mu - Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
    • Fan Li - Max Planck Institute for Microstructure Physics, Weinberg 2, D-06120 Halle, Sachsen-Anhalt, Germany
    • Qun Yang - Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
    • Hedong Chen - Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
    • Yufei Ma - Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
    • Gudrun Auffermann - Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
  • Funding

    Open access funded by Max Planck Society.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This work was financially supported by the European Research Council (ERC Advanced grant no. 742068 “TOPMAT”). We also acknowledge funding by the DFG through SFB 1143 (project ID. 247310070) and the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter ct.qmat (EXC2147, project ID. 39085490). G.L. thanks the start-up funding and the foundation of the President of Ningbo Institute of Materials Technology and Engineering (NIMTE) of the Chinese Academy of Sciences (CAS).

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    Seo, Hyowon; Rahimi, Mohammad; Hatton, T. Alan
    Journal of the American Chemical Society (2022), 144 (5), 2164-2170CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Anthropogenic carbon dioxide (CO2) emission from the combustion of fossil fuels is a major contributor to global climate change and ocean acidification. The implementation of carbon capture and storage technologies has been proposed to mitigate the buildup of this greenhouse gas in the atm. Among these technologies, direct air capture is regarded as a plausible CO2 removal tool whereby net neg. emissions can be achieved. However, the sepn. of CO2 from air is particularly challenging due to the ultradilute concn. of CO2 in the presence of high concns. of dioxygen and water. Here, we report a robust electrochem. redox-active amine system demonstrating a high electron utilization (i.e., mole of CO2 per mol of electrons) of up to 1.25 with the capture of two CO2 mols. per amine in an aq. soln. with a work of 101 kJe per mol of CO2. The capture of CO2 directly from ambient air as the feed gas presented an electron utilization of 0.78.
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  2. 2
    Zhang, L.; Dang, Y.; Zhou, X.; Gao, P.; Petrus van Bavel, A.; Wang, H.; Li, S.; Shi, L.; Yang, Y.; Vovk, E. I.; Gao, Y.; Sun, Y. Direct Conversion of CO2 to a Jet Fuel over Cofe Alloy Catalysts. Innovation 2021, 2, 100170,  DOI: 10.1016/j.xinn.2021.100170
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    2
    Direct conversion of CO2 to a jet fuel over CoFe alloy catalysts
    Zhang, Lei; Dang, Yaru; Zhou, Xiaohong; Gao, Peng; Petrus van Bavel, Alexander; Wang, Hao; Li, Shenggang; Shi, Lei; Yang, Yong; Vovk, Evgeny I.; Gao, Yihao; Sun, Yuhan
    Innovation (2021), 2 (4), 100170CODEN: INNOCI; ISSN:2666-6758. (Elsevier Inc.)
    The direct conversion of carbon dioxide (CO2) using green hydrogen is a sustainable approach to jet fuel prodn. However, achieving a high level of performance remains a formidable challenge due to the inertness of CO2 and its low activity for subsequent C-C bond formation. In this study, we prepd. a Na-modified CoFe alloy catalyst using layered double-hydroxide precursors that directly transforms CO2 to a jet fuel composed of C8-C16 jet-fuel-range hydrocarbons with very high selectivity. At a temp. of 240°C and pressure of 3 MPa, the catalyst achieves an unprecedentedly high C8-C16 selectivity of 63.5% with 10.2% CO2 conversion and a low combined selectivity of less than 22% toward undesired CO and CH4. Spectroscopic and computational studies show that the promotion of the coupling reaction between the carbon species and inhibition of the undesired CO2 methanation occur mainly due to the utilization of the CoFe alloy structure and addn. of the Na promoter. This study provides a viable technique for the highly selective synthesis of eco-friendly and carbon-neutral jet fuel from CO2.
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  3. 3
    Yang, D.; Zhu, Q.; Han, B. Electroreduction of CO2 in Ionic Liquid-Based Electrolytes. Innovation 2020, 1, 100016,  DOI: 10.1016/j.xinn.2020.100016
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    3
    Electroreduction of CO2 in Ionic Liquid-Based Electrolytes
    Yang Dexin; Yang Dexin; Zhu Qinggong; Han Buxing; Zhu Qinggong; Han Buxing
    Innovation (Cambridge (Mass.)) (2020), 1 (1), 100016 ISSN:.
    Electroreduction of carbon dioxide (CO2) to value-added chemicals and fuels is a promising approach for sustainable energy conversion and storage. Many electrocatalysts have been designed for this purpose and studied extensively. The role of the electrolyte is particularly interesting and is pivotal for designing electrochemical devices by taking advantage of the synergy between electrolyte and catalyst. Recently, ionic liquids as electrolytes have received much attention due to their high CO2 adsorption capacity, high selectivity, and low energy consumption. In this review, we present a comprehensive overview of the recent progress in CO2 electroreduction in ionic liquid-based electrolytes, especially in the performance of different catalysts, the electrolyte effect, as well as mechanism studies to understand the reaction pathway. Perspectives on this interesting area are also discussed for the construction of novel electrochemical systems.
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  4. 4
    Li, L.; Wang, P.; Shao, Q.; Huang, X. Metallic Nanostructures with Low Dimensionality for Electrochemical Water Splitting. Chem. Soc. Rev. 2020, 49, 3072– 3106,  DOI: 10.1039/d0cs00013b
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    4
    Metallic nanostructures with low dimensionality for electrochemical water splitting
    Li, Leigang; Wang, Pengtang; Shao, Qi; Huang, Xiaoqing
    Chemical Society Reviews (2020), 49 (10), 3072-3106CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Metallic nanostructures with low dimensionality (one-dimension and two-dimension) possess unique structural characteristics and distinctive electronic and physicochem. properties including high aspect ratio, high sp. surface area, high d. of surface unsatd. atoms and high electron mobility. These distinctive features have rendered them remarkable advantages over their bulk counterparts for surface-related applications, for example, electrochem. water splitting. In this review article, we highlight the recent research progress in low-dimensional metallic nanostructures for electrochem. water splitting including hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Fundamental understanding of the electrochem. of water splitting including HER and OER is firstly provided from the aspects of catalytic mechanisms, activity descriptors and property evaluation metrics. Generally, it is challenging to obtain low-dimensional metallic nanostructures with desirable characteristics for HER and OER. We hereby introduce several typical methods for synthesizing one-dimensional and two-dimensional metallic nanostructures including org. ligand-assisted synthesis, hydrothermal/solvothermal synthesis, carbon monoxide confined growth, topotactic redn., and templated growth. We then put emphasis on the strategies adopted for the design and fabrication of high-performance low-dimensional metallic nanostructures for electrochem. water splitting such as alloying, structure design, surface engineering, interface engineering and strain engineering. The underlying structure-property correlation for each strategy is elucidated aiming to facilitate the design of more advanced electrocatalysts for water splitting. The challenges and perspectives for the development of electrochem. water splitting and low-dimensional metallic nanostructures are also proposed.
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  5. 5
    Sun, H.; Xu, X.; Song, Y.; Zhou, W.; Shao, Z. Designing High-Valence Metal Sites for Electrochemical Water Splitting. Adv. Funct. Mater. 2021, 31, 2009779,  DOI: 10.1002/adfm.202009779
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    5
    Designing High-Valence Metal Sites for Electrochemical Water Splitting
    Sun, Hainan; Xu, Xiaomin; Song, Yufei; Zhou, Wei; Shao, Zongping
    Advanced Functional Materials (2021), 31 (16), 2009779CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Electrochem. water splitting is a crit. energy conversion process for producing clean and sustainable hydrogen; this process relies on low-cost, highly active, and durable oxygen evolution reaction/hydrogen evolution reaction electrocatalysts. Metal cations (including transition metal and noble metal cations), particularly high-valence metal cations that show high catalytic activity and can serve as the main active sites in electrochem. processes, have received special attention for developing advanced electrocatalysts. In this , heterogenous electrocatalyst design strategies based on high-valence metal sites are presented, and assocd. materials designed for water splitting are summarized. In the discussion, emphasis is given to high-valence metal sites combined with the modulation of the phase/electronic/defect structure and strategies of performance improvement. Specifically, the importance of using advanced in situ and operando techniques to track the real high-valence metal-based active sites during the electrochem. process is highlighted. Remaining challenges and future research directions are also proposed. It is expected that this comprehensive discussion of electrocatalysts contg. high-valence metal sites can be instructive to further explore advanced electrocatalysts for water splitting and other energy-related reactions.
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  6. 6
    Ifkovits, Z. P.; Evans, J. M.; Meier, M. C.; Papadantonakis, K. M.; Lewis, N. S. Decoupled electrochemical water-splitting systems: a review and perspective. Energy Environ. Sci. 2021, 14, 4740– 4759,  DOI: 10.1039/d1ee01226f
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    6
    Decoupled electrochemical water-splitting systems: a review and perspective
    Ifkovits, Zachary P.; Evans, Jake M.; Meier, Madeline C.; Papadantonakis, Kimberly M.; Lewis, Nathan S.
    Energy & Environmental Science (2021), 14 (9), 4740-4759CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
    A review. Electrochem. water splitting is a promising technol. to renewably generate hydrogen fuel from water. One particular drawback of conventional water splitting is that the hydrogen-forming redn. reaction is tightly coupled, both spatially and temporally, to the oxygen-forming oxidn. reaction. This coupling poses challenges in both conventional and direct-solar-powered electrolysis systems, including gas crossover and separator degrdn., sometimes necessitating the use of precious metal catalysts. In decoupled water splitting, the conventional electrolysis reactions are sepd. spatially, temporally, or both, via coupling to an intermediate redox mediator. Decoupled water-splitting systems are flexible and modular by nature, with other proposed benefits including facile coupling to renewable power sources, utilization of earth-abundant catalysts, and intrinsically safe operation. Here we review recent advances in decoupled water splitting and related fields, mainly categorizing decoupled systems by mediator phase and std. potential. We offer insight to how decoupling may be advantageous, and which tradeoffs need to be considered for practical implementation. We conclude our review with discussion of known technol. hurdles and note opportunities for future discovery.
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  7. 7
    Shan, J.; Ye, C.; Chen, S.; Sun, T.; Jiao, Y.; Liu, L.; Zhu, C.; Song, L.; Han, Y.; Jaroniec, M.; Zhu, Y.; Zheng, Y.; Qiao, S.-Z. Short-Range Ordered Iridium Single Atoms Integrated into Cobalt Oxide Spinel Structure for Highly Efficient Electrocatalytic Water Oxidation. J. Am. Chem. Soc. 2021, 143, 5201– 5211,  DOI: 10.1021/jacs.1c01525
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    7
    Short-Range Ordered Iridium Single Atoms Integrated into Cobalt Oxide Spinel Structure for Highly Efficient Electrocatalytic Water Oxidation
    Shan, Jieqiong; Ye, Chao; Chen, Shuangming; Sun, Tulai; Jiao, Yan; Liu, Lingmei; Zhu, Chongzhi; Song, Li; Han, Yu; Jaroniec, Mietek; Zhu, Yihan; Zheng, Yao; Qiao, Shi-Zhang
    Journal of the American Chemical Society (2021), 143 (13), 5201-5211CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Noble metals manifest themselves with unique electronic structures and irreplaceable activity toward a wide range of catalytic applications but are unfortunately restricted by limited choice of geometric structures spanning single atoms, clusters, nanoparticles, and bulk crystals. Herein, we propose how to overcome this limitation by integrating noble metal atoms into the lattice of transition metal oxides to create a new type of hybrid structure. This study shows that iridium single atoms can be accommodated into the cationic sites of cobalt spinel oxide with short-range order and an identical spatial correlation as the host lattice. The resultant Ir0.06Co2.94O4 catalyst exhibits much higher electrocatalytic activity than the parent oxide by 2 orders of magnitude toward the challenging oxygen evolution reaction under acidic conditions. Because of the strong interaction between iridium and cobalt oxide support, the Ir0.06Co2.94O4 catalyst shows significantly improved corrosion resistance under acidic conditions and oxidative potentials. This work eliminates the "close-packing" limitation of noble metals and offers promising opportunity to create analogs with desired topologies for various catalytic applications.
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  8. 8
    Liang, X.; Shi, L.; Liu, Y.; Chen, H.; Si, R.; Yan, W.; Zhang, Q.; Li, G. D.; Yang, L.; Zou, X. Activating Inert, Nonprecious Perovskites with Iridium Dopants for Efficient Oxygen Evolution Reaction under Acidic Conditions. Angew. Chem., Int. Ed. 2019, 131, 7713– 7717,  DOI: 10.1002/ange.201900796
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  9. 9
    Seitz, 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 IrOx/SrIrO3 Catalyst for the Oxygen Evolution Reaction. Science 2016, 353, 1011– 1014,  DOI: 10.1126/science.aaf5050
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    9
    A highly active and stable IrOx/SrIrO3 catalyst for the oxygen evolution reaction
    Seitz, 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.
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  10. 10
    Wang, J.; Tran, D. T.; Chang, K.; Prabhakaran, S.; Kim, D. H.; Kim, N. H.; Lee, J. H. Bifunctional Catalyst Derived from Sulfur-Doped VMoOx Nanolayer Shelled Co Nanosheets for Efficient Water Splitting. ACS Appl. Mater. Interfaces 2021, 13, 42944– 42956,  DOI: 10.1021/acsami.1c13488
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    10
    Bifunctional Catalyst Derived from Sulfur-Doped VMoOx Nanolayer Shelled Co Nanosheets for Efficient Water Splitting
    Wang, Jingqiang; Tran, Duy Thanh; Chang, Kai; Prabhakaran, Sampath; Kim, Do Hwan; Kim, Nam Hoon; Lee, Joong Hee
    ACS Applied Materials & Interfaces (2021), 13 (36), 42944-42956CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    A novel sulfur-doped vanadium-molybdenum oxide nanolayer shelling over two-dimensional cobalt nanosheets (2D Co@S-VMoOx NSs) was synthesized via a facile approach. The formation of such a unique 2D core@shell structure together with unusual sulfur doping effect increased the electrochem. active surface area and provided excellent elec. cond., thereby boosting the activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). As a result, only low overpotentials of 73 and 274 mV were required to achieve a current response of 10 mA cm-2 toward HER and OER, resp. Using the 2D Co@S-VMoOx NSs on nickel foam as both cathode and anode electrode, the fabricated electrolyzer showed superior performance with a small cell voltage of 1.55 V at 10 mA cm-2 and excellent stability. These results suggested that the 2D Co@S-VMoOx NSs material might be a potential bifunctional catalyst for green hydrogen prodn. via electrochem. water splitting.
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  11. 11
    Hwang, J.; Rao, R. R.; Giordano, L.; Katayama, Y.; Yu, Y.; Shao-Horn, Y. Perovskites in Catalysis and Electrocatalysis. Science 2017, 358, 751– 756,  DOI: 10.1126/science.aam7092
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    11
    Perovskites in catalysis and electrocatalysis
    Hwang, Jonathan; Rao, Reshma R.; Giordano, Livia; Katayama, Yu; Yu, Yang; Shao-Horn, Yang
    Science (Washington, DC, United States) (2017), 358 (6364), 751-756CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    A review. Catalysts for chem. and electrochem. reactions underpin many aspects of modern technol. and industry, from energy storage and conversion to toxic emissions abatement to chem. and materials synthesis. This role necessitates the design of highly active, stable, yet earth-abundant heterogeneous catalysts. In this Review, we present the perovskite oxide family as a basis for developing such catalysts for (electro)chem. conversions spanning carbon, nitrogen, and oxygen chemistries. A framework for rationalizing activity trends and guiding perovskite oxide catalyst design is described, followed by illustrations of how a robust understanding of perovskite electronic structure provides fundamental insights into activity, stability, and mechanism in oxygen electrocatalysis. We conclude by outlining how these insights open exptl. and computational opportunities to expand the compositional and chem. reaction space for next-generation perovskite catalysts.
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  12. 12
    Mefford, J. T.; Akbashev, A. R.; Kang, M.; Bentley, C. L.; Gent, W. E.; Deng, H. D.; Alsem, D. H.; Yu, Y.-S.; Salmon, N. J.; Shapiro, D. A.; Unwin, P. R.; Chueh, W. C. Correlative Operando Microscopy of Oxygen Evolution Electrocatalysts. Nature 2021, 593, 73,  DOI: 10.1038/s41586-021-03454-x
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  13. 13
    Wang, J.; Han, L.; Huang, B.; Shao, Q.; Xin, H. L.; Huang, X. Amorphization Activated Ruthenium-Tellurium Nanorods for Efficient Water Splitting. Nat. Commun. 2019, 10, 5692,  DOI: 10.1038/s41467-019-13519-1
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    13
    Amorphization activated ruthenium-tellurium nanorods for efficient water splitting
    Wang, Juan; Han, Lili; Huang, Bolong; Shao, Qi; Xin, Huolin L.; Huang, Xiaoqing
    Nature Communications (2019), 10 (1), 5692CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
    Pursuing active and durable water splitting electrocatalysts is of vital significance for solving the sluggish kinetics of the oxygen evolution reaction (OER) process in energy supply. Herein, theor. calcns. identify that the local distortion-strain effect in amorphous RuTe2 system abnormally sensitizes the Te-pp coupling capability and enhances the electron-transfer of Ru-sites, in which the excellent inter-orbital p-d transfers det. strong electronic activities for boosting OER performance. Thus, a robust electrocatalyst based on amorphous RuTe2 porous nanorods (PNRs) is successfully fabricated. In the acidic water splitting, a-RuTe2 PNRs exhibit a superior performance, which only require a cell voltage of 1.52 V to reach a c.d. of 10 mA cm-2. Detailed investigations show that the high d. of defects combine with oxygen atoms to form RuOxHy species, which are conducive to the OER. This work offers valuable insights for constructing robust electrocatalysts based on theor. calcns. guided by rational design and amorphous materials.
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  14. 14
    Yu, X.; Zhao, J.; Johnsson, M. Interfacial Engineering of Nickel Hydroxide on Cobalt Phosphide for Alkaline Water Electrocatalysis. Adv. Funct. Mater. 2021, 31, 2101578,  DOI: 10.1002/adfm.202101578
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    14
    Interfacial Engineering of Nickel Hydroxide on Cobalt Phosphide for Alkaline Water Electrocatalysis
    Yu, Xiaowen; Zhao, Jun; Johnsson, Mats
    Advanced Functional Materials (2021), 31 (25), 2101578CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Catalysts based on earth-abundant non-noble metals are interesting candidates for alk. water electrolysis in sustainable hydrogen economies. However, such catalysts often suffer from high overpotential and sluggish kinetics in both the hydrogen and oxygen evolution reactions (HER and OER). In this study, a hybrid catalyst made of iron-doped cobalt phosphide (Fe-CoP) nanowire arrays and Ni(OH)2 nanosheets is introduced that displays strong electronic interactions at the interface, which significantly improves the interfacial reactivity of reactants and/or intermediates with the hybrid catalyst surface. The combined exptl. and theor. study further confirms that the hybrid catalyst promotes the sluggish rate-limiting steps in both the HER and OER. Full water electrolysis is thus enabled to take place at such a low cell voltage as 1.52 V to reach the c.d. of 10 mA cm-2 along with superior durability and high conversion efficiency.
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  15. 15
    Sun, Y.; Li, R.; Chen, X.; Wu, J.; Xie, Y.; Wang, X.; Ma, K.; Wang, L.; Zhang, Z.; Liao, Q.; Kang, Z.; Zhang, Y. A-Site Management Prompts the Dynamic Reconstructed Active Phase of Perovskite Oxide OER Catalysts. Adv. Energy Mater. 2021, 11, 2003755,  DOI: 10.1002/aenm.202003755
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    15
    A-Site Management Prompts the Dynamic Reconstructed Active Phase of Perovskite Oxide OER Catalysts
    Sun, Yu; Li, Ran; Chen, Xiaoxuan; Wu, Jing; Xie, Yong; Wang, Xin; Ma, Kaikai; Wang, Li; Zhang, Zheng; Liao, Qingliang; Kang, Zhuo; Zhang, Yue
    Advanced Energy Materials (2021), 11 (12), 2003755CODEN: ADEMBC; ISSN:1614-6840. (Wiley-Blackwell)
    Perovskites (ABX3) are promising oxygen evolution reaction (OER) catalysts for their highly intrinsic activity. The in-depth understanding and the adjustment of dynamic reconstruction of active phases for perovskites in OER are still a daunting challenge. Here, a refined A-site management strategy is proposed for perovskite oxides, which facilitates the surface reconstruction of the B-site element-based active phase to enhance the OER performance. Electrocatalyst lanthanum nickel oxide displays a dynamic reconstruction feature during OER with the growth of a self-assembled NiOOH active layer, based on the in situ electrochem. Raman technol. Precise A-site cerium-doping lowers the reconstruction potential for the active phase and the dynamic structure-activity correlation is well established. Theor. calcns. demonstrate that A-site cerium substitution upshifts the O 2p level for greater structural flexibility with optimized oxygen vacancy content, thereby activating the B-site atom and promoting the active phase reconstruction. These results suggest that A-site management prompts the B-site element-based active phase dynamic reconstruction via engineered X-site content as a bridge. Therefore, indicating the strong correlation of each-site component in perovskite oxides during OER and deepening the understanding of the fundamental processes of the structural transformation and further benefiting the accurate design of high-efficiency perovskite OER electrocatalysts.
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  16. 16
    Yuan, Y.; Adimi, S.; Thomas, T.; Wang, J.; Guo, H.; Chen, J.; Attfield, J. P.; DiSalvo, F. J.; Yang, M. Co3Mo3N─an Efficient Multifunctional Electrocatalyst. Innovation 2021, 2, 100096,  DOI: 10.1016/j.xinn.2021.100096
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  17. 17
    Hou, J.; Zhang, B.; Li, Z.; Cao, S.; Sun, Y.; Wu, Y.; Gao, Z.; Sun, L. Vertically Aligned Oxygenated-CoS2-MoS2 Heteronanosheet Architecture from Polyoxometalate for Efficient and Stable Overall Water Splitting. ACS Catal. 2018, 8, 4612– 4621,  DOI: 10.1021/acscatal.8b00668
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    17
    Vertically Aligned Oxygenated-CoS2-MoS2 Heteronanosheet Architecture from Polyoxometalate for Efficient and Stable Overall Water Splitting
    Hou, Jungang; Zhang, Bo; Li, Zhuwei; Cao, Shuyan; Sun, Yiqing; Wu, Yunzhen; Gao, Zhanming; Sun, Licheng
    ACS Catalysis (2018), 8 (5), 4612-4621CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
    To achieve efficient conversion of renewable energy sources through H2O splitting, low-cost, earth-abundant, and robust electrocatalysts for the O evolution reaction (OER) and H evolution reaction (HER) are required. Herein, vertically aligned oxygenated-CoS2-MoS2 (O-CoMoS) heteronanosheets grown on flexible C fiber cloth as bifunctional electrocatalysts have been produced using the Anderson-type (NH4)4[CoIIMo6O24H6].6H2O polyoxometalate as bimetal precursor. In comparison to different O-FeMoS, O-NiMoS, and MoS2 nanosheet arrays, the O-CoMoS heteronanosheet array exhibited low overpotentials of 97 and 272 mV to reach a c.d. of 10 mA cm-2 in alk. soln. for the HER and OER, resp. Assembled as an electrolyzer for overall H2O splitting, O-CoMoS heteronanosheets as both the anode and cathode deliver a c.d. of 10 mA cm-2 at a quite low cell voltage of 1.6 V. This O-CoMoS architecture is highly advantageous for a disordered structure, exposure of active heterointerfaces, a highway of charge transport on 2-dimensional conductive channels, and abundant active catalytic sites from the synergistic effect of the heterostructures, accomplishing a dramatically enhanced performance for the OER, HER, and overall H2O splitting. This work represents a feasible strategy to explore efficient and stable bifunctional bimetal sulfide electrocatalysts for renewable energy applications.
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    Zhao, M.; Li, W.; Li, J.; Hu, W.; Li, C. M. Strong Electronic Interaction Enhanced Electrocatalysis of Metal Sulfide Clusters Embedded Metal-Organic Framework Ultrathin Nanosheets toward Highly Efficient Overall Water Splitting. Adv. Sci. 2020, 7, 2001965,  DOI: 10.1002/advs.202001965
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    18
    Strong Electronic Interaction Enhanced Electrocatalysis of Metal Sulfide Clusters Embedded Metal-Organic Framework Ultrathin Nanosheets toward Highly Efficient Overall Water Splitting
    Zhao, Ming; Li, Wei; Li, Junying; Hu, Weihua; Li, Chang Ming
    Advanced Science (Weinheim, Germany) (2020), 7 (20), 2001965CODEN: ASDCCF; ISSN:2198-3844. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Unique metal sulfide (MS) clusters embedded ultrathin nanosheets of Fe/Ni metal-org. framework (MOF) are grown on nickel foam (NiFe-MS/MOFF) as a highly efficient bifunctional electrocatalyst for overall water splitting. It exhibits remarkable catalytic activity and stability toward both the oxygen evolution reaction (OER, n = 230 mV at 50 mA cm-2) and hydrogen evolution reaction (HER, n = 156 mV at 50 mA cm-2) in alk. media, and bi-functionally catalyzes overall alk. water splitting at a c.d. of 50 mA cm-2 by 1.74 V cell voltage without iR compensation. The enhancement mechanism is ascribed to the impregnated metal sulfide clusters in the nanosheets, which not only promote the formation of ultrathin nanosheet to greatly enlarge the reaction surface area while offering high elec. cond., but more importantly, efficiently modulate the electronic structure of the catalytically active atom sites to an electron-rich state via strong electronic interaction and strengthen the adsorption of oxygenate intermediate to facilitate fast electrochem. reactions. This work reports a highly efficient HER/OER bifunctional electrocatalyst and may shed light on the rational design and synthesis of uniquely structured MOF-derived catalysts.
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  19. 19
    Xiong, D.; Gu, M.; Chen, C.; Lu, C.; Yi, F.-Y.; Ma, X. Rational design of bimetallic metal-organic framework composites and their derived sulfides with superior electrochemical performance to remarkably boost oxygen evolution and supercapacitors. Chem. Eng. J. 2021, 404, 127111,  DOI: 10.1016/j.cej.2020.127111
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    19
    Rational design of bimetallic metal-organic framework composites and their derived sulfides with superior electrochemical performance to remarkably boost oxygen evolution and supercapacitors
    Xiong, Dengke; Gu, Minli; Chen, Chen; Lu, Chunxiao; Yi, Fei-Yan; Ma, Xinghua
    Chemical Engineering Journal (Amsterdam, Netherlands) (2021), 404 (), 127111CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
    Developing highly efficient and stable multi-functional metal-org. framework electrochem. materials is of prime importance for renewable energy technologies and electrocatalytic applications. Herein, a novel series of bimetallic metal-org. framework (MOF) hybrid materials were successfully designedly fabricated through an in-situ growth and MOF-on-MOF strategies, namely as NiFeMOF/NF, NiCoMOF/NF, FeMOF/NiMOF/NF, and CoMOF/NiMOF/NF. Benefiting from the synergistic effect of bimetallic centers, conductive substrate and unique fabrication, they exhibit remarking electrochem. performance. Among them, FeMOF/NiMOF/NF composite with ultrathin nanosheets displays the best electrochecatalytic performance with ultralow overpotentials of 293 mV at 50 mA cm-2 and 359 mV at 100 mA cm-2 for oxygen evolution reaction (OER), and remarking electrochem. stability with high c.d. of 100 mA cm-2 after testing for 24 h, that 88% of initial c.d. can be remained. Based on these fabricated bimetallic MOF hybrid materials as precursors, the corresponding MOF-derived nano sulfides were obtained with massive exposure of active sites. As an excellent supercapacitor electrode, NiCoS/NF-1 converted from CoMOF/NiMOF/NF shows admirable specific capacitance of 2815.4 F g-1 at 1 mA cm-2 and a remarkable rate capability of 82%.
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  20. 20
    Zang, Z.; Wang, X.; Li, X.; Zhao, Q.; Li, L.; Yang, X.; Yu, X.; Zhang, X.; Lu, Z. Co9S8 Nanosheet Coupled Cu2S Nanorod Heterostructure as Efficient Catalyst for Overall Water Splitting. ACS Appl. Mater. Interfaces 2021, 13, 9865– 9874,  DOI: 10.1021/acsami.0c20820
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    Co9S8 Nanosheet Coupled Cu2S Nanorod Heterostructure as Efficient Catalyst for Overall Water Splitting
    Zang, Zehao; Wang, Xuewei; Li, Xiang; Zhao, Qingling; Li, Lanlan; Yang, Xiaojing; Yu, Xiaofei; Zhang, Xinghua; Lu, Zunming
    ACS Applied Materials & Interfaces (2021), 13 (8), 9865-9874CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Electrocatalytic water splitting is a promising technol. for large-scale hydrogen prodn. However, it requires efficient catalysts to overcome the large overpotentials in the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, we report a novel heterostructure catalyst Co9S8/Cu2S on copper foam (Co9S8/Cu2S/CF) with multistep impregnation and electrodeposition. Due to the strong interfacial interaction, the interfacial electrons transfer from Co sites to S sites, which promote the adsorption of oxygen-contg. intermediates, water mols., as well as the dissocn. of water mols. Therefore, the heterostructure catalyst exhibits low overpotentials of 195 mV for OER and 165 mV for HER at 10 mA cm-2, resp. Moreover, it only needs 1.6 V to realize water splitting at 10 mA cm-2 in a two-electrode cell. This work provides an efficient method to tailor the surface electronic structure through specific morphol. design and construct a heterostructure interface to achieve alk. water splitting.
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  21. 21
    Shit, S.; Chhetri, S.; Jang, W.; Murmu, N. C.; Koo, H.; Samanta, P.; Kuila, T. Cobalt Sulfide/Nickel Sulfide Heterostructure Directly Grown on Nickel Foam: An Efficient and Durable Electrocatalyst for Overall Water Splitting Application. ACS Appl. Mater. Interfaces 2018, 10, 27712– 27722,  DOI: 10.1021/acsami.8b04223
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    21
    Cobalt Sulfide/Nickel Sulfide Heterostructure Directly Grown on Nickel Foam: An Efficient and Durable Electrocatalyst for Overall Water Splitting Application
    Shit, Subhasis; Chhetri, Suman; Jang, Wooree; Murmu, Naresh C.; Koo, Hyeyoung; Samanta, Pranab; Kuila, Tapas
    ACS Applied Materials & Interfaces (2018), 10 (33), 27712-27722CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Fabrication of high-performance noble metal-free bifunctional electrocatalysts for both H evolution reaction (HER) and O evolution reaction (OER) in H2O is a promising strategy toward future C-neutral economy. Herein, a 1-pot hydrothermal synthesis of Co sulfide/Ni sulfide heterostructure supported by Ni foam (CoSx/Ni3S2@NF) was performed. The Ni foam acted as the 3-dimensional conducting substrate as well as the source of Ni for Ni3S2. The formation of CoSx/Ni3S2@NF was confirmed by x-ray diffraction and XPS. The formation of CoSx/Ni3S2@NF facilitated easy charge transport and showed synergistic electrocatalytic effect toward HER, OER, and overall H2O splitting in alk. medium. Remarkably, CoSx/Ni3S2@NF showed catalytic activity comparable with that of benchmarking electrocatalysts Pt/C and RuO2. For CoSx/Ni3S2@NF, overpotentials of 204 and 280 mV were required to achieve current densities of 10 and 20 mA cm-2 for HER and OER, resp., in 1.0M KOH soln. A 2-electrode system was formulated for overall H2O splitting reaction, which showed current densities of 10 and 50 mA cm-2 at 1.572 and 1.684 V, resp. The prepd. catalyst exhibited excellent durability in HER and OER catalyzing conditions and also in overall H2O splitting operation. Therefore, CoSx/Ni3S2@NF could be a promising noble-metal-free electrocatalyst for overall H2O splitting application.
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  22. 22
    Chen, W.; Wang, H.; Li, Y.; Liu, Y.; Sun, J.; Lee, S.; Lee, J.-S.; Cui, Y. In Situ Electrochemical Oxidation Tuning of Transition Metal Disulfides to Oxides for Enhanced Water Oxidation. ACS Cent. Sci. 2015, 1, 244– 251,  DOI: 10.1021/acscentsci.5b00227
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    22
    In Situ Electrochemical Oxidation Tuning of Transition Metal Disulfides to Oxides for Enhanced Water Oxidation
    Chen, Wei; Wang, Haotian; Li, Yuzhang; Liu, Yayuan; Sun, Jie; Lee, Sanghan; Lee, Jang-Soo; Cui, Yi
    ACS Central Science (2015), 1 (5), 244-251CODEN: ACSCII; ISSN:2374-7951. (American Chemical Society)
    The development of catalysts with earth-abundant elements for efficient oxygen evolution reactions is of paramount significance for clean and sustainable energy storage and conversion devices. Our group demonstrated recently that the electrochem. tuning of catalysts via lithium insertion and extn. has emerged as a powerful approach to improve catalytic activity. Here we report a novel in situ electrochem. oxidn. tuning approach to develop a series of binary, ternary, and quaternary transition metal (e.g., Co, Ni, Fe) oxides from their corresponding sulfides as highly active catalysts for much enhanced water oxidn. The electrochem. tuned cobalt-nickel-iron oxides grown directly on the three-dimensional carbon fiber electrodes exhibit a low overpotential of 232 mV at c.d. of 10 mA cm-2, small Tafel slope of 37.6 mV dec-1, and exceptional long-term stability of electrolysis for over 100 h in 1 M KOH alk. medium, superior to most non-noble oxygen evolution catalysts reported so far. The materials evolution assocd. with the electrochem. oxidn. tuning is systematically investigated by various characterizations, manifesting that the improved activities are attributed to the significant grain size redn. and increase of surface area and electroactive sites. This work provides a promising strategy to develop electrocatalysts for large-scale water-splitting systems and many other applications.
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  23. 23
    Kou, Z.; Li, X.; Zhang, L.; Zang, W.; Gao, X.; Wang, J. Dynamic Surface Chemistry of Catalysts in Oxygen Evolution Reaction. Small Sci. 2021, 1, 2100011,  DOI: 10.1002/smsc.202100011
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    23
    Dynamic Surface Chemistry of Catalysts in Oxygen Evolution Reaction
    Kou, Zongkui; Li, Xin; Zhang, Lei; Zang, Wenjie; Gao, Xiaorui; Wang, John
    Small Science (2021), 1 (7), 2100011CODEN: SSMCBJ; ISSN:2688-4046. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Electrocatalytic oxygen evolution reaction (OER) is a crucial anode reaction where electrocatalysts are the key elements and their dynamic surface chem. runs throughout the entire process. Herein, we examine the latest advances and challenges in understanding of the dynamic surface chem. of OER electrocatalysts. There are electrochem. origin and driving force for the dynamic surface nature, where several processes can take place either concurrently or sequentially, including reconstruction (i.e., phase formation/transformation, morphol. change, and compositional change), vacancy generation and filling/refilling, and the intermediate adsorption-desorption process on catalytic surface. These dynamic surface processes of OER catalysts are impacted by not only the reaction and service conditions, including the (local) pH and its gradient distribution, applied potential, types and concn. of exotic ions and external fields on top of the nature of catalysts/precatalysts, but also their interactions. Due to the local, time-dependent and instant nature, there are considerable challenges in tracing, modeling and understanding of the complete dynamic surface chem. of catalysts in OER, by means of ex situ, in situ and operando exptl. investigations. Therefore, computational studies and dynamic simulations help provide key insights in future pursuits, where there is crit. need for a multiscale computational modeling approach encompassing all these aspects.
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  24. 24
    Fan, K.; Zou, H.; Lu, Y.; Chen, H.; Li, F.; Liu, J.; Sun, L.; Tong, L.; Toney, M. F.; Sui, M.; Yu, J. Direct Observation of Structural Evolution of Metal Chalcogenide in Electrocatalytic Water Oxidation. ACS Nano 2018, 12, 12369– 12379,  DOI: 10.1021/acsnano.8b06312
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    24
    Direct Observation of Structural Evolution of Metal Chalcogenide in Electrocatalytic Water Oxidation
    Fan, Ke; Zou, Haiyuan; Lu, Yue; Chen, Hong; Li, Fusheng; Liu, Jinxuan; Sun, Licheng; Tong, Lianpeng; Toney, Michael F.; Sui, Manling; Yu, Jiaguo
    ACS Nano (2018), 12 (12), 12369-12379CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    As one of the most remarkable O evolution reaction (OER) electrocatalysts, metal chalcogenides were intensively reported during the past few decades because of their high OER activities. It is reported that electron-chem. conversion of metal chalcogenides into oxides/hydroxides would take place after the OER. However, the transition mechanism of such unstable structures, as well as the real active sites and catalytic activity during the OER for these electrocatalysts, was not understood yet; therefore a direct observation for the electrocatalytic H2O oxidn. process, esp. at nano or even angstrom scale, is urgently needed. In this research, by employing advanced Cs-cor. TEM, a step by step oxidational evolution of amorphous electrocatalyst CoSx into crystd. CoOOH in the OER was in situ captured: irreversible conversion of CoSx to crystd. CoOOH is initiated on the surface of the electrocatalysts with a morphol. change via Co(OH)2 intermediate during the OER measurement, where CoOOH is confirmed as the real active species. Besides, this transition process also was confirmed by multiple applications of XPS, in situ FTIR spectroscopy, and other ex situ technologies. Also, from this discovery, a high-efficiency electrocatalyst of a N-doped graphene foam (NGF) coated by CoSx was explored through a thorough structure transformation of CoOOH. The authors believe this in situ and in-depth observation of structural evolution in the OER measurement can provide insights into the fundamental understanding of the mechanism for the OER catalysts, thus enabling the more rational design of low-cost and high-efficient electrocatalysts for H2O splitting.
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  25. 25
    Li, G.; Fu, C.; Shi, W.; Jiao, L.; Wu, J.; Yang, Q.; Saha, R.; Kamminga, M. E.; Srivastava, A. K.; Liu, E.; Yazdani, A. N.; Kumar, N.; Zhang, J.; Blake, G. R.; Liu, X.; Fahlman, M.; Wirth, S.; Auffermann, G.; Gooth, J.; Parkin, S.; Madhavan, V.; Feng, X.; Sun, Y.; Felser, C. Dirac Nodal Arc Semimetal PtSn4: An Ideal Platform for Understanding Surface Properties and Catalysis for Hydrogen Evolution. Angew. Chem., Int. Ed. 2019, 131, 13241– 13246,  DOI: 10.1002/ange.201906109
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    Yang, Q.; Li, G.; Manna, K.; Fan, F.; Felser, C.; Sun, Y. Topological Engineering of Pt-Group-Metal-Based Chiral Crystals toward High-Efficiency Hydrogen Evolution Catalysts. Adv. Mater. 2020, 32, 1908518,  DOI: 10.1002/adma.201908518
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    26
    Topological Engineering of Pt-Group-Metal-Based Chiral Crystals toward High-Efficiency Hydrogen Evolution Catalysts
    Yang, Qun; Li, Guowei; Manna, Kaustuv; Fan, Fengren; Felser, Claudia; Sun, Yan
    Advanced Materials (Weinheim, Germany) (2020), 32 (14), 1908518CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    It has been demonstrated that topol. nontrivial surface states can favor heterogeneous catalysis processes such as the hydrogen evolution reaction (HER), but a further decrease in mass loading and an increase in activity are still highly challenging. The observation of massless chiral fermions assocd. with large topol. charge and long Fermi arc (FA) surface states inspires the investigation of their relationship with the charge transfer and adsorption process in the HER. In this study, it is found that the HER efficiency of Pt-group metals can be boosted significantly by introducing topol. order. A giant nontrivial topol. energy window and a long topol. surface FA are expected at the surface when forming chiral crystals in the space group of P213 (#198). This makes the nontrivial topol. features resistant to a large change in the applied overpotential. As HER catalysts, PtAl and PtGa chiral crystals show turnover frequencies as high as 5.6 and 17.1 s-1 and an overpotential as low as 14 and 13.3 mV at a c.d. of 10 mA cm-2. These crystals outperform those of com. Pt and nanostructured catalysts. This work opens a new avenue for the development of high-efficiency catalysts with the strategy of topol. engineering of excellent transitional catalytic materials.
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  27. 27
    Li, G.; Xu, Q.; Shi, W.; Fu, C.; Jiao, L.; Kamminga, M. E.; Yu, M.; Tüysüz, H.; Kumar, N.; Süß, V. Surface States in Bulk Single Crystal of Topological Semimetal Co3Sn2S2 toward Water Oxidation. Sci. Adv. 2019, 5, eaaw9867  DOI: 10.1126/sciadv.aaw9867
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    There is no corresponding record for this reference.
  28. 28
    He, Y.; Boubeche, M.; Zhou, Y.; Yan, D.; Zeng, L.; Wang, X.; Yan, K.; Luo, H. Topologically Nontrivial 1T’-MoTe2 as Highly Efficient Hydrogen Evolution Electrocatalyst. J. Phys. Mater. 2020, 4, 014001,  DOI: 10.1088/2515-7639/abc40c
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    There is no corresponding record for this reference.
  29. 29
    Li, J.; Ma, H.; Xie, Q.; Feng, S.; Ullah, S.; Li, R.; Dong, J.; Li, D.; Li, Y.; Chen, X.-Q. Topological Quantum Catalyst: Dirac Nodal Line States and a Potential Electrocatalyst of Hydrogen Evolution in the TiSi Family. Sci. China Mater. 2018, 61, 23– 29,  DOI: 10.1007/s40843-017-9178-4
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    Topological quantum catalyst: Dirac nodal line states and a potential electrocatalyst of hydrogen evolution in the TiSi family
    Li, Jiangxu; Ma, Hui; Xie, Qing; Feng, Shaobo; Ullah, Sami; Li, Ronghan; Dong, Junhua; Li, Dianzhong; Li, Yiyi; Chen, Xing-Qiu
    Science China Materials (2018), 61 (1), 23-29CODEN: SCMCDB; ISSN:2095-8226. (Science China Press)
    Topol. nodal line (DNL) semimetals, a closed loop of the inverted bands in its bulk phases, result in the almost flat drumhead-like non-trivial surface states (DNSSs) with an unusually high electronic d. near the Fermi level. High catalytic active sites generally assocd. with high electronic densities around the Fermi level, high carrier mobility and a close-to-zero free energy of the adsorbed state of hydrogen (ΔGH*≈0) are prerequisite to design alternative of precious platinum for catalyzing electrochem. hydrogen prodn. from water. By combining these two aspects, it is natural to consider if the DNLs are a good candidate for the hydrogen evolution reaction (HER) or not because its DNSSs provide a robust platform to activate chem. reactions. Here, through first-principles calcns. we reported a new DNL TiSi-type family, exhibiting a closed Dirac nodal line due to the linear band crossings in ky=0 plane. The hydrogen adsorbed state on the surface yields ΔGH* to be almost zero and the topol. charge carries participate in HER. The results highlight a new routine to design topol. quantum catalyst utilizing the topol. DNL-induced surface bands as active sites, rather than edge sites-, vacancy-, dopant-, strain-, or heterostructure-created active sites.
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    Li, G.; Felser, C. Heterogeneous Catalysis at the Surface of Topological Materials. Appl. Phys. Lett. 2020, 116, 070501,  DOI: 10.1063/1.5143800
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    30
    Heterogeneous catalysis at the surface of topological materials
    Li, Guowei; Felser, Claudia
    Applied Physics Letters (2020), 116 (7), 070501CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    A review. Intriguing properties are frequently reported in various topol. non-trivial materials. They include robust metallic surface states, high carrier mobility, chiral fermions, and ultralong Fermi arcs. An exciting recent finding is that these properties are strongly related to adsorption and electron transfer in various heterogeneous catalysis reactions, such as hydrogen evolution, oxygen evolution, oxygen redn., enantiospecific adsorption, and hydrometallation. Thus, we expect that the introduction of non-trivial symmetry-protected topol. order will offer important freedom for designing high-performance heterogeneous catalysts. To uncover the contribution of the topol. non-trivial electronic structure to the heterogeneous reactions, in situ techniques are urgently needed to detect the interaction between surface states, topol. electrons, and reaction intermediates. (c) 2020 American Institute of Physics.
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  31. 31
    Shekhar, C.; Nayak, A. K.; Sun, Y.; Schmidt, M.; Nicklas, M.; Leermakers, I.; Zeitler, U.; Skourski, Y.; Wosnitza, J.; Liu, Z.; Chen, Y.; Schnelle, W.; Borrmann, H.; Grin, Y.; Felser, C.; Yan, B. Extremely Large Magnetoresistance and Ultrahigh Mobility in the Topological Weyl Semimetal Candidate NbP. Nat. Phys. 2015, 11, 645– 649,  DOI: 10.1038/nphys3372
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    Extremely large magnetoresistance and ultrahigh mobility in the topological Weyl semimetal candidate NbP
    Shekhar, Chandra; Nayak, Ajaya K.; Sun, Yan; Schmidt, Marcus; Nicklas, Michael; Leermakers, Inge; Zeitler, Uli; Skourski, Yurii; Wosnitza, Jochen; Liu, Zhongkai; Chen, Yulin; Schnelle, Walter; Borrmann, Horst; Grin, Yuri; Felser, Claudia; Yan, Binghai
    Nature Physics (2015), 11 (8), 645-649CODEN: NPAHAX; ISSN:1745-2473. (Nature Publishing Group)
    Recent expts. have revealed spectacular transport properties in semimetals, such as the large, non-satg. magnetoresistance exhibited by WTe2 (ref. ). Topol. semimetals with massless relativistic electrons have also been predicted as three-dimensional analogs of graphene. These systems are known as Weyl semimetals, and are predicted to have a range of exotic transport properties and surface states, distinct from those of topol. insulators. Here we examine the magneto-transport properties of NbP, a material the band structure of which has been predicted to combine the hallmarks of a Weyl semimetal with those of a normal semimetal. We observe an extremely large magnetoresistance of 850,000% at 1.85 K (250% at room temp.) in a magnetic field of up to 9 T, without any signs of satn., and an ultrahigh carrier mobility of 5 × 106 cm2 V-1 s-1 accompanied by strong Shubnikov-de Haas (SdH) oscillations. NbP therefore presents a unique example of a material combining topol. and conventional electronic phases, with intriguing phys. properties resulting from their interplay.
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  32. 32
    Xie, R.; Zhang, T.; Weng, H.; Chai, G.-L. Progress, Advantages, and Challenges of Topological Material Catalysts. Small Sci. 2022, 2, 2100106,  DOI: 10.1002/smsc.202100106
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    32
    Progress, Advantages, and Challenges of Topological Material Catalysts
    Xie, Ruikuan; Zhang, Tan; Weng, Hongming; Chai, Guo-Liang
    Small Science (2022), 2 (4), 2100106CODEN: SSMCBJ; ISSN:2688-4046. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Topol. materials is one of the hottest topics in condensed matter physics because of its exotic properties such as robust metallic boundary states, Fermi arcs, and the spin-momentum-locking helicity. The topol. protected conducting boundary states spanning the whole bandgap are expected to serve as robust and wide-range-energy transition states facilitating catalytic reactions. Recently, some topol. materials have been found to be high-performance catalysts, which might open an emerging research field. Herein, an overview of topol. materials is given and then recent progress in topol. material catalysts (TMCs) is presented. As it is a new field, more detailed and accurate mechanisms behind the high performance of TMCs are urgently needed. Combining theor. and exptl. studies is a promising way to resolve these puzzles. Heterostructures, dopants, and defects have the chance to tune the catalytic activity of TMCs while retaining topol. surface states (TSSs). Also, more TMCs are needed to be discovered, and more catalytic reactions are to be investigated for TMCs in the future.
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  33. 33
    Xiao, J.; Kou, L.; Yam, C.-Y.; Frauenheim, T.; Yan, B. Toward Rational Design of Catalysts Supported on a Topological Insulator Substrate. ACS Catal. 2015, 5, 7063– 7067,  DOI: 10.1021/acscatal.5b01966
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    Toward Rational Design of Catalysts Supported on a Topological Insulator Substrate
    Xiao, Jianping; Kou, Liangzhi; Yam, Chi-Yung; Frauenheim, Thomas; Yan, Binghai
    ACS Catalysis (2015), 5 (12), 7063-7067CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
    Exotic and robust metallic surface states of topol. insulators (TIs) have been expected to provide a promising platform for novel surface chem. and catalysis. However, it is still not fully known how TIs affect the activity of catalysts. In this work, we study the effects of topol. surface states (TSSs) on the activity of transition metal clusters (Au, Ag, Cu, Pt, and Pd), which are supported on a TI Bi2Se3 substrate. It was found the adsorption energy of oxygen on the supported catalysts can be always enhanced due to the TSSs. However, it does not necessarily mean an increase of the activity in catalytic oxidn. reaction. Rather, the enhanced adsorption behavior in the presence of TSSs exhibits dual effects, detd. by the intrinsic reactivity of these catalysts with oxygen. For the Au case, the activity of catalytic oxidn. can be improved because the TSSs can enhance the dissocn. rate of dioxygen. In contrast, a neg. effect is found for the Pt and Pd clusters since the TSSs will suppress the desorption process of reaction products. We also found that the effect of TSSs on the activity of hydrogen evolution reaction (HER) is quite similar (i.e., the metals with original weak reactivity can gain a pos. effect from TSSs). The present work can pave a way for more rational design and selection of catalysts when using TIs as substrates.
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  34. 34
    Li, L.; Zeng, J.; Qin, W.; Cui, P.; Zhang, Z. Tuning the Hydrogen Activation Reactivity on Topological Insulator Heterostructures. Nano Energy 2019, 58, 40– 46,  DOI: 10.1016/j.nanoen.2019.01.007
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    34
    Tuning the hydrogen activation reactivity on topological insulator heterostructures
    Li, Leiqiang; Zeng, Jiang; Qin, Wei; Cui, Ping; Zhang, Zhenyu
    Nano Energy (2019), 58 (), 40-46CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)
    The central challenge faced in hydrogen evolution reaction is the low reaction efficiency when using non-precious materials as potential new types of electrocatalysts. Here, we report an elegant synergistic effect of local bonding and topol. surface states (TSSs) for optimally enhanced hydrogen evolution reaction by invoking topol. insulator heterostructures purely composed of abundant elements. Using first-principles calcns. within d. functional theory, we demonstrate that the three-dimensional topol. insulator of Bi2Se3 covered with a single layer of ZnSe can function as an ideal platform for maximal hydrogen evolution reaction with optimal hydrogen adsorption free energy. Such a highly desirable functionality is attributed to the TSSs of Bi2Se3 serving as an electron bath in enhancing the hydrogen adsorption strength, which would be too weak on top of the ZnSe overlayer without considering topol. effects, but too strong upon increasing the ZnSe overlayer thickness. We also demonstrate precise tunability of the vertical location of the TSSs via the ZnSe overlayer thickness, which can be exploited for other functionalities of such topol. insulator heterostructures. The present study provides an important linkage between the topol. insulators as a new class of quantum matter and catalytic materials for clean energy.
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    Chen, H.; Zhu, W.; Xiao, D.; Zhang, Z. Co Oxidation Facilitated by Robust Surface States on Au-Covered Topological Insulators. Phys. Rev. Lett. 2011, 107, 056804,  DOI: 10.1103/PhysRevLett.107.056804
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    CO Oxidation Facilitated by Robust Surface States on Au-Covered Topological Insulators
    Chen, Hua; Zhu, Wenguang; Xiao, Di; Zhang, Zhen-Yu
    Physical Review Letters (2011), 107 (5), 056804/1-056804/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    Surface states-the electronic states emerging as a solid material terminates at a surface-are usually vulnerable to contaminations and defects. The robust topol. surface state(s) (TSS) on the three-dimensional topol. insulators provide a perfect platform for exploiting surface states in less stringent environments. Employing 1st-principles d. functional theory calcns., the TSS can play a vital role in facilitating surface reactions by serving as an effective electron bath. The authors use CO oxidn. on gold-covered Bi2Se3 as a prototype example, and show that the robust TSS can significantly enhance the adsorption energy of both CO and O2 mols., by promoting different directions of static electron transfer. The concept of TSS as an electron bath may lead to new design principles beyond the conventional d-band theory of heterogeneous catalysis.
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    Schröter, N. B.; Robredo, I.; Klemenz, S.; Kirby, R. J.; Krieger, J. A.; Pei, D.; Yu, T.; Stolz, S.; Schmitt, T.; Dudin, P. Weyl Fermions, Fermi Arcs, and Minority-Spin Carriers in Ferromagnetic CoS2. Sci. Adv. 2020, 6, eabd5000  DOI: 10.1126/sciadv.abd5000
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    Wei, C.; Sun, S.; Mandler, D.; Wang, X.; Qiao, S. Z.; Xu, Z. J. Approaches for Measuring the Surface Areas of Metal Oxide Electrocatalysts for Determining Their Intrinsic Electrocatalytic Activity. Chem. Soc. Rev. 2019, 48, 2518– 2534,  DOI: 10.1039/c8cs00848e
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    Approaches for measuring the surface areas of metal oxide electrocatalysts for determining their intrinsic electrocatalytic activity
    Wei, Chao; Sun, Shengnan; Mandler, Daniel; Wang, Xun; Qiao, Shi Zhang; Xu, Zhichuan J.
    Chemical Society Reviews (2019), 48 (9), 2518-2534CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Great attention has been recently drawn to metal oxide electrocatalysts for electrocatalysis-based energy storage and conversion devices. To find the optimal electrocatalyst, a prerequisite is an activity metric that reasonably evaluates the intrinsic electrocatalytic activity of a particular catalyst. The intrinsic activity is commonly defined as the specific activity which is the current per unit catalyst surface area. Thus, the precise assessment of intrinsic activity highly depends on the reliable measurement of catalyst surface area, which calls for the knowledge of exptl. approaches for detg. the surface areas of metal oxide electrocatalysts. This tutorial review aims to summarize and analyze the approaches for measuring the surface areas of metal oxide electrocatalysts for evaluating and comparing their intrinsic electrocatalytic activities. We start by comparing the popular metrics for activity estn. and highlighting the importance of surface-area-normalized activity (i.e. specific activity) for intrinsic chem. anal. Second, we provide some general guidelines for exptl. measuring the electrochem. active surface area (ECSA). Third, we review the methods for the surface area measurement of metal oxide electrocatalysts. The detailed procedure for each method is explicitly described to provide a step-by-step manual that guides researchers to perform the measurement; the rationales and uncertainties for each method are discussed to help readers justify the reliable assessment of surface area. Next, we give our recommendations on selecting a rational exptl. approach for the surface area measurement of a particular metal oxide electrocatalyst. Lastly, we discuss the future challenges of ECSA measurement and present an exemplary novel ECSA technique.
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    Li, G.; Khim, S.; Chang, C. S.; Fu, C.; Nandi, N.; Li, F.; Yang, Q.; Blake, G. R.; Parkin, S.; Auffermann, G.; Sun, Y.; Muller, D. A.; Mackenzie, A. P.; Felser, C. In Situ Modification of a Delafossite-Type PdCoO2 Bulk Single Crystal for Reversible Hydrogen Sorption and Fast Hydrogen Evolution. ACS Energy Lett. 2019, 4, 2185– 2191,  DOI: 10.1021/acsenergylett.9b01527
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    In Situ Modification of a Delafossite-Type PdCoO2 Bulk Single Crystal for Reversible Hydrogen Sorption and Fast Hydrogen Evolution
    Li, Guowei; Khim, Seunghyun; Chang, Celesta S.; Fu, Chenguang; Nandi, Nabhanila; Li, Fan; Yang, Qun; Blake, Graeme R.; Parkin, Stuart; Auffermann, Gudrun; Sun, Yan; Muller, David A.; Mackenzie, Andrew P.; Felser, Claudia
    ACS Energy Letters (2019), 4 (9), 2185-2191CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
    The observation of extraordinarily high cond. in delafossite-type PdCoO2 is of great current interest, and there is some evidence that electrons behave like a fluid when flowing in bulk crystals of PdCoO2. Thus, this material is an ideal platform for the study of the electron transfer processes in heterogeneous reactions. Here, the authors report the use of bulk single-crystal PdCoO2 as a promising electrocatalyst for H evolution reactions (HERs). An overpotential of only 31 mV results in a c.d. of 10 mA cm-2, accompanied by high long-term stability. The authors have precisely detd. that the crystal surface structure is modified after electrochem. activation with the formation of strained Pd nanoclusters in the surface layer. These nanoclusters exhibit reversible H sorption and desorption, creating more active sites for H access. The bulk PdCoO2 single crystal with ultrahigh cond., which acts as a natural substrate for the Pd nanoclusters, provides a high-speed channel for electron transfer.
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    Anantharaj, S.; Ede, S. R.; Sakthikumar, K.; Karthick, K.; Mishra, S.; Kundu, S. Recent Trends and Perspectives in Electrochemical Water Splitting with an Emphasis on Sulfide, Selenide, and Phosphide Catalysts of Fe, Co, and Ni: A Review. ACS Catal. 2016, 6, 8069– 8097,  DOI: 10.1021/acscatal.6b02479
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    Recent Trends and Perspectives in Electrochemical Water Splitting with an Emphasis on Sulfide, Selenide, and Phosphide Catalysts of Fe, Co, and Ni: A Review
    Anantharaj, Sengeni; Ede, Sivasankara Rao; Sakthikumar, Kuppan; Karthick, Kannimuthu; Mishra, Soumyaranjan; Kundu, Subrata
    ACS Catalysis (2016), 6 (12), 8069-8097CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
    A review. Increasing demand for finding eco-friendly and everlasting energy sources is now totally depending on fuel cell technol. Though it is an eco-friendly way of producing energy for the urgent requirements, it needs to be improved to make it cheaper and more eco-friendly. Although there are several types of fuel cells, the H (H2) and O (O2) fuel cell is the one with zero C emission and H2O as the only byproduct. However, supplying fuels in the purest form (at least the H2) is essential to ensure higher life cycles and less decay in cell efficiency. The current large-scale H2 prodn. is largely dependent on steam reforming of fossil fuels, which generates CO2 along with H2 and the source of which is going to be depleted. As an alternate, electrolysis of H2O was given greater attention than the steam reforming. The reasons are as follows: the very high purity of the H2 produced, the abundant source, no need for high-temp., high-pressure reactors, and so on. In earlier days, noble metals such as Pt (cathode) and Ir and Ru (anode) were used for this purpose. However, there are problems in employing these metals, as they are noble and expensive. In this review, the authors elaborate how the group VIII 3d metal sulfide, selenide, and phosphide nanomaterials have arisen as abundant and cheaper electrode materials (catalysts) beyond the oxides and hydroxides of the same. The authors also highlight the evaluation perspective of such electrocatalysts toward H2O electrolysis.
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    Tanwar, K.; Gyan, D. S.; Bhattacharya, S.; Vitta, S.; Dwivedi, A.; Maiti, T. Enhancement of Thermoelectric Power Factor by Inducing Octahedral Ordering in La2-xSrxCoFeO6 Double Perovskites. Phys. Rev. B: Condens. Matter Mater. Phys. 2019, 99, 174105,  DOI: 10.1103/physrevb.99.174105
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    Chuang, T. J.; Brundle, C. R.; Rice, D. W. Interpretation of the X-Ray Photoemission Spectra of Cobalt Oxides and Cobalt Oxide Surfaces. Surf. Sci. 1976, 59, 413– 429,  DOI: 10.1016/0039-6028(76)90026-1
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    Interpretation of the x-ray photoemission spectra of cobalt oxides and cobalt oxide surfaces
    Chuang, T. J.; Brundle, C. R.; Rice, D. W.
    Surface Science (1976), 59 (2), 413-29CODEN: SUSCAS; ISSN:0039-6028.
    CoO and Co3O4 were studied by high-resoln. x-ray photoemission. The characteristic binding energies in the Co 2p3/2, 2p1/2, and 3s regions, their band shapes and widths, the assocd. shake-up structure, the O(1s) and 0(2s) BE's, and the valence band spectra were examd. The 2 oxides are readily distinguished from their spectra though it is shown that the O(1s) BE's are identical at 529.50 ± 0.14 eV. Ar and O ion sputtered surfaces were examd. to establish the integrity of the oxides. A higher BE O(1s) component (530.7-531.6 eV), the intensity and BE of which vary with the treatments mentioned above, corresponds to nonstoichiometric surface O. The results are discussed with respect to the electronic structures of the oxides and the often conflicting earlier studies of these oxides.
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    Chen, Z.; Kronawitter, C. X.; Yeh, Y.-W.; Yang, X.; Zhao, P.; Yao, N.; Koel, B. E. Activity of Pure and Transition Metal-Modified CoOOH for the Oxygen Evolution Reaction in an Alkaline Medium. J. Mater. Chem. A 2017, 5, 842– 850,  DOI: 10.1039/c6ta07482k
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    Activity of pure and transition metal-modified CoOOH for the oxygen evolution reaction in an alkaline medium
    Chen, Zhu; Kronawitter, Coleman X.; Yeh, Yao-Wen; Yang, Xiaofang; Zhao, Peng; Yao, Nan; Koel, Bruce E.
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2017), 5 (2), 842-850CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    A new electrode structure enabling low overpotentials for the oxidn. of water, based on three-dimensional arrays of CoOOH nanowires, is presented. The electrocatalytic activities of pure and M-modified cobalt oxyhydroxides (M = Ni or Mn) nanowires have been investigated in detail for the oxygen evolution reaction (OER) in an alk. environment. The pure, Ni-, and Mn-modified nanowires, with preferentially exposed low-index surfaces, were fabricated directly on stainless steel mesh current collectors using an inexpensive and scalable chem. synthesis procedure. The unique electrode structure ensures excellent substrate-catalyst elec. contact and increases the surface area accessible to the electrolyte. The OER activity of CoOOH nanowires is shown to be significantly improved through incorporation of Ni. Specifically, optimal OER activity is obtained for CoOOH nanowires with 9.7% surface Ni content, which corresponds to four-times greater c.d. compared to pure CoOOH. In contrast, Mn modification of the CoOOH nanowires did not improve the OER activity. Tafel anal. suggests Ni incorporation leads to change in the OER rate-detg. step based on an obsd. decrease in the Tafel slope. Electrochem. impedance spectroscopy reveals that Ni incorporation improves the ability of the catalysts to stabilize surface intermediates, whereas Mn incorporation impedes intermediate stabilization. This study provides new insights regarding the influence of transition metal impurities on the OER activity of CoOOH and provides a clear strategy for the optimization of CoOOH-based OER catalysts in alk. electrolytes.
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    Wang, Q.; Xue, X.; Lei, Y.; Wang, Y.; Feng, Y.; Xiong, X.; Wang, D.; Li, Y. Engineering of Electronic States on Co3O4 Ultrathin Nanosheets by Cation Substitution and Anion Vacancies for Oxygen Evolution Reaction. Small 2020, 16, 2001571,  DOI: 10.1002/smll.202001571
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    Engineering of Electronic States on Co3O4 Ultrathin Nanosheets by Cation Substitution and Anion Vacancies for Oxygen Evolution Reaction
    Wang, Qichen; Xue, Xiongxiong; Lei, Yongpeng; Wang, Yuchao; Feng, Yexin; Xiong, Xiang; Wang, Dingsheng; Li, Yadong
    Small (2020), 16 (24), 2001571CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Due to the earth abundance and tunable electronic properties, etc., transition metal oxides (TMOs) show attractive attention in oxygen evolution reaction. O-vacancies (Vo) play important roles in tailoring the local surface and electronic environment to lower the activation barriers. Herein, an effective strategy is shown to enhance the oxygen evolution redn. (OER) performance on Co3O4 ultrathin nanosheets via combined cation substitution and anion vacancies. The oxygen-deficient Fe-Co-O nanosheets (3-4 nm thickness) display an overpotential of 260 mV@10 mA cm-2 and a Tafel slope of 53 mV dec-1, outperforming those of the benchmark RuO2 in 1.0 M KOH. Further calcns. demonstrate that the combined introduction of Fe cation and Vo with appropriate location and content finely tune the intermediate absorption, consequently lowering the rate-limiting activation energy from 0.82 to as low as 0.15 eV. The feasibility is also proved by oxygen-deficient Ni-Co-O nanosheets. This work not only establishes a clear at.-level correlation between cation substitution, anion vacancies, and OER performance, but also provides valuable insights for the rational design of highly efficient catalysts for OER.
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    Chen, C.-J.; Chen, P.-T.; Basu, M.; Yang, K.-C.; Lu, Y.-R.; Dong, C.-L.; Ma, C.-G.; Shen, C.-C.; Hu, S.-F.; Liu, R.-S. An Integrated Cobalt Disulfide (CoS2) Co-Catalyst Passivation Layer on Silicon Microwires for Photoelectrochemical Hydrogen Evolution. J. Mater. Chem. A 2015, 3, 23466– 23476,  DOI: 10.1039/c5ta06202k
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    An integrated cobalt disulfide (CoS2) co-catalyst passivation layer on silicon microwires for photoelectrochemical hydrogen evolution
    Chen, Chih-Jung; Chen, Po-Tzu; Basu, Mrinmoyee; Yang, Kai-Chih; Lu, Ying-Rui; Dong, Chung-Li; Ma, Chong-Geng; Shen, Chin-Chang; Hu, Shu-Fen; Liu, Ru-Shi
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2015), 3 (46), 23466-23476CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    An integrated cobalt disulfide (CoS2) co-catalyst passivation layer on Si microwires (MWs) was used as a photocathode for solar hydrogen evolution. Si MWs were prepd. by photolithog. and dry etching techniques. The CoS2-Si photocathodes were subsequently prepd. by chem. deposition and thermal sulfidation of the Co(OH)2 outer shell. The optimized onset potential and photocurrent of the CoS2-Si electrode were 0.248 V and -3.22 mA cm-2 (at 0 V), resp. The best photocatalytic activity of the CoS2-Si electrode resulted from lower charge transfer resistances among the photoabsorber, co-catalyst, and redox couples in the electrolyte. X-ray absorption near edge structure was conducted to investigate the unoccupied electronic states of the CoS2 layer. We propose that more vacancies in the S-3p unoccupied states of the CoS2-Si electrode were present with a lower neg. charge of S22- to form weaker S-H bond strength, promoting water splitting efficiency. Moreover, the CoS2 co-catalyst that completely covered underlying Si MWs served as a passivation layer to prevent oxidn. and reduce degrdn. during photoelectrochem. measurements. Therefore, the optimal CoS2-Si electrode maintained the photocurrent at about -3 mA cm-2 (at 0 V) for 9 h, and its hydrogen generation rate was approx. 0.833 μmol min-1.
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    Wang, G.; Shen, X.; Horvat, J.; Wang, B.; Liu, H.; Wexler, D.; Yao, J. Hydrothermal Synthesis and Optical, Magnetic, and Supercapacitance Properties of Nanoporous Cobalt Oxide Nanorods. J. Phys. Chem. C 2009, 113, 4357– 4361,  DOI: 10.1021/jp8106149
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    Hydrothermal Synthesis and Optical, Magnetic, and Supercapacitance Properties of Nanoporous Cobalt Oxide Nanorods
    Wang, Guoxiu; Shen, Xiaoping; Horvat, Josip; Wang, Bei; Liu, Hao; Wexler, David; Yao, Jane
    Journal of Physical Chemistry C (2009), 113 (11), 4357-4361CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Nanoporous cobalt oxide nanorods were synthesized by a hydrothermal method. TEM anal. showed that the individual Co3O4 nanorods have a nanoporous structure, consisting of the textured aggregations of nanocrystals. Optical properties of Co3O4 nanorods were characterized by Raman and UV-visible spectroscopy. Magnetic property measurement shows that Co3O4 nanorods have a low Neel transition temp. of 35 K. The authors obsd. quite significant exchange bias for nanoporous Co3O4 nanorods, indicating the existence of magnetic coupling between the nanocrystals in Co3O4 nanorods. When applied as electrode materials in supercapacitors, Co3O4 demonstrated a high capacitance of 280 F/g.
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    Bergmann, A.; Jones, T. E.; Moreno, E. M.; Teschner, D.; Chernev, P.; Gliech, M.; Reier, T.; Dau, H.; Strasser, P. Unified structural motifs of the catalytically active state of Co(oxyhydr)oxides during the electrochemical oxygen evolution reaction. Nat. Catal. 2018, 1, 711– 719,  DOI: 10.1038/s41929-018-0141-2
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    Unified structural motifs of the catalytically active state of Co(oxyhydr)oxides during the electrochemical oxygen evolution reaction
    Bergmann, Arno; Jones, Travis E.; Martinez Moreno, Elias; Teschner, Detre; Chernev, Petko; Gliech, Manuel; Reier, Tobias; Dau, Holger; Strasser, Peter
    Nature Catalysis (2018), 1 (9), 711-719CODEN: NCAACP; ISSN:2520-1158. (Nature Research)
    Efficient catalysts for the anodic oxygen evolution reaction (OER) are crit. for electrochem. H2 prodn. Their design requires structural knowledge of their catalytically active sites and state. Here, we track the at.-scale structural evolution of well-defined CoOx(OH)y compds. into their catalytically active state during electrocatalytic operation through operando and surface-sensitive X-ray spectroscopy and surface voltammetry, supported by theor. calcns. We find clear voltammetric evidence that electrochem. reducible near-surface Co3+-O sites play an organizing role for high OER activity. These sites invariably emerge independent of initial metal valency and coordination under catalytic OER conditions. Combining expts. and theory reveals the unified chem. structure motif as μ2-OH-bridged Co2+/3+ ion clusters formed on all three-dimensional cross-linked and layered CoOx(OH)y precursors and present in an oxidized form during the OER, as shown by operando X-ray spectroscopy. Together, the spectroscopic and electrochem. fingerprints offer a unified picture of our mol. understanding of the structure of catalytically active metal oxide OER sites.
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    Bergmann, A.; Martinez-Moreno, E.; Teschner, D.; Chernev, P.; Gliech, M.; De Araújo, J. F.; Reier, T.; Dau, H.; Strasser, P. Reversible Amorphization and the Catalytically Active State of Crystalline Co3O4 During Oxygen Evolution. Nat. Commun. 2015, 6, 8625,  DOI: 10.1038/ncomms9625
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    Reversible amorphization and the catalytically active state of crystalline Co3O4 during oxygen evolution
    Bergmann, Arno; Martinez-Moreno, Elias; Teschner, Detre; Chernev, Petko; Gliech, Manuel; Ferreira de Araujo, Jorge; Reier, Tobias; Dau, Holger; Strasser, Peter
    Nature Communications (2015), 6 (), 8625CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
    Water splitting catalyzed by earth-abundant materials is pivotal for global-scale prodn. of non-fossil fuels, yet our understanding of the active catalyst structure and reactivity is still insufficient. Here we report on the structurally reversible evolution of cryst. Co3O4 electrocatalysts during oxygen evolution reaction identified using advanced in situ X-ray techniques. At electrode potentials facilitating oxygen evolution, a sub-nanometer shell of the Co3O4 is transformed into an X-ray amorphous CoOx(OH)y which comprises di-μ-oxo-bridged Co3+/4+ ions. Unlike irreversible amorphizations, here, the formation of the catalytically-active layer is reversed by re-crystn. upon return to non-catalytic electrode conditions. The Co3O4 material thus combines the stability advantages of a controlled, stable cryst. material with high catalytic activity, thanks to the structural flexibility of its active amorphous oxides. We propose that cryst. oxides may be tailored for generating reactive amorphous surface layers at catalytic potentials, just to return to their stable cryst. state under rest conditions.
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    Xiao, Z.; Huang, Y.-C.; Dong, C.-L.; Xie, C.; Liu, Z.; Du, S.; Chen, W.; Yan, D.; Tao, L.; Shu, Z.; Zhang, G.; Duan, H.; Wang, Y.; Zou, Y.; Chen, R.; Wang, S. Operando Identification of the Dynamic Behavior of Oxygen Vacancy-Rich Co3O4 for Oxygen Evolution Reaction. J. Am. Chem. Soc. 2020, 142, 12087– 12095,  DOI: 10.1021/jacs.0c00257
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    Operando Identification of the Dynamic Behavior of Oxygen Vacancy-Rich Co3O4 for Oxygen Evolution Reaction
    Xiao, Zhaohui; Huang, Yu-Cheng; Dong, Chung-Li; Xie, Chao; Liu, Zhijuan; Du, Shiqian; Chen, Wei; Yan, Dafeng; Tao, Li; Shu, Zhiwen; Zhang, Guanhua; Duan, Huigao; Wang, Yanyong; Zou, Yuqin; Chen, Ru; Wang, Shuangyin
    Journal of the American Chemical Society (2020), 142 (28), 12087-12095CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The exact role of a defect structure on transition metal compds. for electrocatalytic oxygen evolution reaction (OER), which is a very dynamic process, remains unclear. Studying the structure-activity relationship of defective electrocatalysts under operando conditions is crucial for understanding their intrinsic reaction mechanism and dynamic behavior of defect sites. Co3O4 with rich oxygen vacancy (VO) has been reported to efficiently catalyze OER. Herein, pure spinel Co3O4 and VO-rich Co3O4 are constructed as catalyst models to study the defect mechanism and investigate the dynamic behavior of defect sites during the electrocatalytic OER process by various operando characterizations. Operando electrochem. impedance spectroscopy (EIS) and cyclic voltammetry (CV) implied that the VO could facilitate the pre-oxidn. of the low-valence Co (Co2+, part of which was induced by the VO to balance the charge) at a relatively lower applied potential. This observation confirmed that the VO could initialize the surface reconstruction of VO-Co3O4 prior to the occurrence of the OER process. The quasi-operando XPS and operando X-ray absorption fine structure (XAFS) results further demonstrated the oxygen vacancies were filled with OH• first for VO-Co3O4 and facilitated pre-oxidn. of low-valence Co and promoted reconstruction/deprotonation of intermediate Co-OOH•. This work provides insight into the defect mechanism in Co3O4 for OER in a dynamic way by observing the surface dynamic evolution process of defective electrocatalysts and identifying the real active sites during the electrocatalysis process. The current finding would motivate the community to focus more on the dynamic behavior of defect electrocatalysts.
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    Reith, L.; Triana, C. A.; Pazoki, F.; Amiri, M.; Nyman, M.; Patzke, G. R. Unraveling Nanoscale Cobalt Oxide Catalysts for the Oxygen Evolution Reaction: Maximum Performance, Minimum Effort. J. Am. Chem. Soc. 2021, 143, 15022– 15038,  DOI: 10.1021/jacs.1c03375
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    Unraveling Nanoscale Cobalt Oxide Catalysts for the Oxygen Evolution Reaction: Maximum Performance, Minimum Effort
    Reith, Lukas; Triana, Carlos A.; Pazoki, Faezeh; Amiri, Mehran; Nyman, May; Patzke, Greta R.
    Journal of the American Chemical Society (2021), 143 (37), 15022-15038CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The oxygen evolution reaction (OER) is a key bottleneck step of artificial photosynthesis and an essential topic in renewable energy research. Therefore, stable, efficient, and economical water oxidn. catalysts (WOCs) are in high demand and cobalt-based nanomaterials are promising targets. Herein, we tackle two key open questions after decades of research into cobalt-assisted visible-light-driven water oxidn.: What makes simple cobalt-based ppts. so highly active-and to what extent do we need Co-WOC design. Hence, we started from Co(NO3)2 to generate a precursor ppt., which transforms into a highly active WOC during the photocatalytic process with a [Ru(bpy)3]2+/S2O82-/borate buffer std. assay that outperforms state of the art cobalt catalysts. The structural transformations of these nanosized Co catalysts were monitored with a wide range of characterization techniques. The results reveal that the pptd. catalyst does not fully change into an amorphous CoOx material but develops some cryst. features. The transition from the ppt. into a disordered Co3O4 material proceeds within ca. 1 min, followed by further transformation into highly active disordered CoOOH within the first 10 min. Furthermore, under noncatalytic conditions, the precursor directly transforms into CoOOH. Moreover, fast pptn. and isolation afford a highly active precatalyst with an exceptional O2 yield of 91% for water oxidn. with the visible-light-driven [Ru(bpy)3]2+/S2O82- assay, which outperforms a wide range of carefully designed Co-contg. WOCs. We thus demonstrate that high-performance cobalt-based OER catalysts indeed emerge effortlessly from a self-optimization process favoring the formation of Co(III) centers in all-octahedral environments. This paves the way to new low-maintenance flow chem. OER processes.
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  50. 50
    Reikowski, F.; Maroun, F.; Pacheco, I.; Wiegmann, T.; Allongue, P.; Stettner, J.; Magnussen, O. M. Operando Surface X-Ray Diffraction Studies of Structurally Defined Co3O4 and CoOOH Thin Films During Oxygen Evolution. ACS Catal. 2019, 9, 3811– 3821,  DOI: 10.1021/acscatal.8b04823
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    50
    Operando Surface X-ray Diffraction Studies of Structurally Defined Co3O4 and CoOOH Thin Films during Oxygen Evolution
    Reikowski, Finn; Maroun, Fouad; Pacheco, Ivan; Wiegmann, Tim; Allongue, Philippe; Stettner, Jochim; Magnussen, Olaf M.
    ACS Catalysis (2019), 9 (5), 3811-3821CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
    In the search for precious-metal-free electrode materials for electrochem. water splitting, transition-metal oxides have been receiving much recent interest as active and stable electrocatalysts for the anodic oxygen evolution reaction (OER). We present operando surface X-ray diffraction studies of two structurally well-defined epitaxial cobalt oxide thin films: Co3O4(111) and CoOOH(001) electrodeposited on Au(111). The potential-dependent structural changes during cyclic voltammograms were monitored with high time resoln. up to OER current densities as high as 150 mA cm-2. The CoOOH(001) film is found to be smooth and perfectly stable over a wide potential range. In the case of Co3O4(111), fast and fully reversible structural changes are obsd. Specifically, the surface region of Co3O4(111) starts restructuring at potentials 300 mV neg. of the onset of the OER, indicating that the process is related to the thermodynamically predicted Co3O4/CoOOH(001) transition rather than to the catalytic reaction. The formed skin layer is of defined thickness, which changes linearly with applied potential, and is the OER active phase. Surprisingly, the catalytic activity of the skin layer covered Co3O4 film and that of the smooth CoOOH(001) are almost identical, if the true microscopic surface area is taken into account. This indicates that the no. of OER active sites on the two oxides is similar, despite the very different defect d., and is at variance with previous suggestions that di-μ-oxo bridged Co cations are exclusively responsible for the OER activity of Co oxides. For the smooth CoOOH(001), a turnover frequency of 4.2 s-1 per surface atom is detd. at an overpotential of 400 mV. Furthermore, our studies demonstrate that the pseudocapacitive charging current in the pre-OER potential range must be assigned to a bulk process that is accompanied by potential-dependent changes of the unit cell vol. in the Co3O4 bulk.
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  51. 51
    Rehman, A. U.; Fayaz, M.; Lv, H.; Liu, Y.; Zhang, J.; Wang, Y.; Du, L.; Wang, R.; Shi, K. Controllable Synthesis of a Porous PEI-Functionalized Co3O4/rGO Nanocomposite as an Electrochemical Sensor for Simultaneous as Well as Individual Detection of Heavy Metal Ions. ACS Omega 2022, 7, 5870– 5882,  DOI: 10.1021/acsomega.1c05989
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    51
    Controllable Synthesis of a Porous PEI-Functionalized Co3O4/rGO Nanocomposite as an Electrochemical Sensor for Simultaneous as Well as Individual Detection of Heavy Metal Ions
    Rehman, Afrasiab Ur; Fayaz, Muhammad; Lv, He; Liu, Yang; Zhang, Jiawei; Wang, Yang; Du, Lijuan; Wang, Ruihong; Shi, Keying
    ACS Omega (2022), 7 (7), 5870-5882CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
    The present study focuses on the strategy of employing an electrochem. sensor with a porous polyethylenimine (PEI)-functionalized Co3O4/reduced graphene oxide (rGO) nanocomposite (NCP) to detect heavy metal ions (HMIs: Cd2+, Pb2+, Cu2+, and Hg2+). The porous PEI-functionalized Co3O4/rGO NCP (rGO·Co3O4·PEI) was prepd. via a hydrothermal method. The synthesized NCP was based on a conducting polymer PEI, rGO, nanoribbons of Co3O4, and highly dispersed Co3O4 nanoparticles (NPs), which have shown excellent performance in the detection of HMIs. The as-prepd. PEI-functionalized rGO·Co3O4·PEI NCP-modified electrode was used for the sensing/detection of HMIs by means of both square wave anodic stripping voltammetry (SWV) and differential normal pulse voltammetry (DNPV) methods for the first time. Both methods were employed for the simultaneous detection of HMIs, whereas SWV was employed for the individual anal. as well. The limits of detection (LOD; 3σ method) for Cd2+, Pb2+, Cu2+, and Hg2+ detd. using the rGO·Co3O4·PEI NCP-modified electrode were 0.285, 1.132, 1.194, and 1.293 nM for SWV, resp. Similarly, LODs of Cd2+, Pb2+, Cu2+, and Hg2+ were 1.069, 0.285, 2.398, and 1.115 nM, resp., by DNPV during simultaneous anal., whereas they were 0.484, 0.878, 0.462, and 0.477 nM, resp., by SWV in individual anal.
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  1. Ezhava Manu Manohar, Soumalya Roy, Sujoy Bandyopadhyay, Manas Pal, Smita Singh, Vellaichamy Ganesan, Robert Pełka, Piotr Konieczny, Michał Rams, Hyosung Choi, Srinu Tothadi, Sourav Das. A Linear Trinuclear Acetate Bridged Cobalt Complex Containing Pyridine-Based Bicompartmental Ligand: Synthesis, Structural, Magnetic, and Electrocatalytic Oxygen Evolution Studies. Crystal Growth & Design 2024, 24 (3) , 1032-1041. https://doi.org/10.1021/acs.cgd.3c01061
  2. Yu Kang, Yujia Han, Hedong Chen, Horst Borrmann, Peter Adler, Darius Pohl, Martin Hantusch, Markus König, Yangkun He, Yufei Ma, Xiaodong Wang, Claudia Felser. Ruthenium-Alloyed Iron Phosphide Single Crystal with Increased Fermi Level for Efficient Hydrogen Evolution. ACS Applied Materials & Interfaces 2022, 14 (50) , 55587-55593. https://doi.org/10.1021/acsami.2c16419
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  • Abstract

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    Figure 1

    Figure 1. (a)Photograph and (b,c) pyrite structure of the CoS2 single crystal. (d) XRD pattern, (e) HRTEM with the corresponding FFT image, and (f) resistivity vs temperature curve of the CoS2 crystal.

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    Figure 2

    Figure 2. OER performance of the CoS2 single crystal and reference materials with 90% iR correction. (a) LSV curves with the scanning rate of 5 mV s–1 and (b) Tafel slope (CoS2 was tested at the steady state from 1.40 to 1.66 V at the interval of 0.02 V). (c) Cyclic voltammetry results comparison based on the geometric area and ECSA of the single crystal. The inset is the difference in current density between anodic and cathodic sweeps vs scan rate. (d) Apparent overpotential comparison (left) at 10 mA cm–2 normalized to the geometric surface area and the intrinsic current density comparison (right) at 1.55 V based on ECSA. (e) Stability test at a static current density of 10 mA cm–2. (f) Nyquist plots under different potentials. The inset shows the equivalent circuit for the two semicircles.

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    Figure 3

    Figure 3. SEM image of (a) surface pieces on the CoS2 single crystal after OER, (b) one of the pieces after depositing the protective layer for FIB, and (c) cross section of the cut piece after FIB. (d) STEM annular dark-field (ADF) image of the cross-section and (e–g) corresponding EDS elemental mappings. (h) SAED pattern of the cut piece, which was fitted with (111), (200), and (220) reflections of CoO.

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    Figure 4

    Figure 4. SEM image of (a) thin oxidation layer on CoS2 surface after OER. (b) High-resolution TEM of the cross section of the surface oxidation layer (c) and the corresponding amplified area in the red square frame. (d) STEM ADF of the cross section and (e–g) corresponding EDS elemental mappings of the marked area in (d). (h) Illustration of the interface of Co3O4 and CoS2 crystal in the TEM.

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    Figure 5

    Figure 5. XPS spectra of (a) Co 2p and (b) O 1s. (c) Raman spectra of the CoS2 crystal after the measurements at 1.4, 1.5, and 1.6 V.

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  • References

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      Innovation (Cambridge (Mass.)) (2020), 1 (1), 100016 ISSN:.
      Electroreduction of carbon dioxide (CO2) to value-added chemicals and fuels is a promising approach for sustainable energy conversion and storage. Many electrocatalysts have been designed for this purpose and studied extensively. The role of the electrolyte is particularly interesting and is pivotal for designing electrochemical devices by taking advantage of the synergy between electrolyte and catalyst. Recently, ionic liquids as electrolytes have received much attention due to their high CO2 adsorption capacity, high selectivity, and low energy consumption. In this review, we present a comprehensive overview of the recent progress in CO2 electroreduction in ionic liquid-based electrolytes, especially in the performance of different catalysts, the electrolyte effect, as well as mechanism studies to understand the reaction pathway. Perspectives on this interesting area are also discussed for the construction of novel electrochemical systems.
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      Chemical Society Reviews (2020), 49 (10), 3072-3106CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Metallic nanostructures with low dimensionality (one-dimension and two-dimension) possess unique structural characteristics and distinctive electronic and physicochem. properties including high aspect ratio, high sp. surface area, high d. of surface unsatd. atoms and high electron mobility. These distinctive features have rendered them remarkable advantages over their bulk counterparts for surface-related applications, for example, electrochem. water splitting. In this review article, we highlight the recent research progress in low-dimensional metallic nanostructures for electrochem. water splitting including hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Fundamental understanding of the electrochem. of water splitting including HER and OER is firstly provided from the aspects of catalytic mechanisms, activity descriptors and property evaluation metrics. Generally, it is challenging to obtain low-dimensional metallic nanostructures with desirable characteristics for HER and OER. We hereby introduce several typical methods for synthesizing one-dimensional and two-dimensional metallic nanostructures including org. ligand-assisted synthesis, hydrothermal/solvothermal synthesis, carbon monoxide confined growth, topotactic redn., and templated growth. We then put emphasis on the strategies adopted for the design and fabrication of high-performance low-dimensional metallic nanostructures for electrochem. water splitting such as alloying, structure design, surface engineering, interface engineering and strain engineering. The underlying structure-property correlation for each strategy is elucidated aiming to facilitate the design of more advanced electrocatalysts for water splitting. The challenges and perspectives for the development of electrochem. water splitting and low-dimensional metallic nanostructures are also proposed.
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      A review. Electrochem. water splitting is a crit. energy conversion process for producing clean and sustainable hydrogen; this process relies on low-cost, highly active, and durable oxygen evolution reaction/hydrogen evolution reaction electrocatalysts. Metal cations (including transition metal and noble metal cations), particularly high-valence metal cations that show high catalytic activity and can serve as the main active sites in electrochem. processes, have received special attention for developing advanced electrocatalysts. In this , heterogenous electrocatalyst design strategies based on high-valence metal sites are presented, and assocd. materials designed for water splitting are summarized. In the discussion, emphasis is given to high-valence metal sites combined with the modulation of the phase/electronic/defect structure and strategies of performance improvement. Specifically, the importance of using advanced in situ and operando techniques to track the real high-valence metal-based active sites during the electrochem. process is highlighted. Remaining challenges and future research directions are also proposed. It is expected that this comprehensive discussion of electrocatalysts contg. high-valence metal sites can be instructive to further explore advanced electrocatalysts for water splitting and other energy-related reactions.
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      A review. Electrochem. water splitting is a promising technol. to renewably generate hydrogen fuel from water. One particular drawback of conventional water splitting is that the hydrogen-forming redn. reaction is tightly coupled, both spatially and temporally, to the oxygen-forming oxidn. reaction. This coupling poses challenges in both conventional and direct-solar-powered electrolysis systems, including gas crossover and separator degrdn., sometimes necessitating the use of precious metal catalysts. In decoupled water splitting, the conventional electrolysis reactions are sepd. spatially, temporally, or both, via coupling to an intermediate redox mediator. Decoupled water-splitting systems are flexible and modular by nature, with other proposed benefits including facile coupling to renewable power sources, utilization of earth-abundant catalysts, and intrinsically safe operation. Here we review recent advances in decoupled water splitting and related fields, mainly categorizing decoupled systems by mediator phase and std. potential. We offer insight to how decoupling may be advantageous, and which tradeoffs need to be considered for practical implementation. We conclude our review with discussion of known technol. hurdles and note opportunities for future discovery.
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      Noble metals manifest themselves with unique electronic structures and irreplaceable activity toward a wide range of catalytic applications but are unfortunately restricted by limited choice of geometric structures spanning single atoms, clusters, nanoparticles, and bulk crystals. Herein, we propose how to overcome this limitation by integrating noble metal atoms into the lattice of transition metal oxides to create a new type of hybrid structure. This study shows that iridium single atoms can be accommodated into the cationic sites of cobalt spinel oxide with short-range order and an identical spatial correlation as the host lattice. The resultant Ir0.06Co2.94O4 catalyst exhibits much higher electrocatalytic activity than the parent oxide by 2 orders of magnitude toward the challenging oxygen evolution reaction under acidic conditions. Because of the strong interaction between iridium and cobalt oxide support, the Ir0.06Co2.94O4 catalyst shows significantly improved corrosion resistance under acidic conditions and oxidative potentials. This work eliminates the "close-packing" limitation of noble metals and offers promising opportunity to create analogs with desired topologies for various catalytic applications.
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      Seitz, 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 IrOx/SrIrO3 Catalyst for the Oxygen Evolution Reaction. Science 2016, 353, 1011– 1014,  DOI: 10.1126/science.aaf5050
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      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.
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      Wang, J.; Tran, D. T.; Chang, K.; Prabhakaran, S.; Kim, D. H.; Kim, N. H.; Lee, J. H. Bifunctional Catalyst Derived from Sulfur-Doped VMoOx Nanolayer Shelled Co Nanosheets for Efficient Water Splitting. ACS Appl. Mater. Interfaces 2021, 13, 42944– 42956,  DOI: 10.1021/acsami.1c13488
      10
      Bifunctional Catalyst Derived from Sulfur-Doped VMoOx Nanolayer Shelled Co Nanosheets for Efficient Water Splitting
      Wang, Jingqiang; Tran, Duy Thanh; Chang, Kai; Prabhakaran, Sampath; Kim, Do Hwan; Kim, Nam Hoon; Lee, Joong Hee
      ACS Applied Materials & Interfaces (2021), 13 (36), 42944-42956CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      A novel sulfur-doped vanadium-molybdenum oxide nanolayer shelling over two-dimensional cobalt nanosheets (2D Co@S-VMoOx NSs) was synthesized via a facile approach. The formation of such a unique 2D core@shell structure together with unusual sulfur doping effect increased the electrochem. active surface area and provided excellent elec. cond., thereby boosting the activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). As a result, only low overpotentials of 73 and 274 mV were required to achieve a current response of 10 mA cm-2 toward HER and OER, resp. Using the 2D Co@S-VMoOx NSs on nickel foam as both cathode and anode electrode, the fabricated electrolyzer showed superior performance with a small cell voltage of 1.55 V at 10 mA cm-2 and excellent stability. These results suggested that the 2D Co@S-VMoOx NSs material might be a potential bifunctional catalyst for green hydrogen prodn. via electrochem. water splitting.
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    11. 11
      Hwang, J.; Rao, R. R.; Giordano, L.; Katayama, Y.; Yu, Y.; Shao-Horn, Y. Perovskites in Catalysis and Electrocatalysis. Science 2017, 358, 751– 756,  DOI: 10.1126/science.aam7092
      11
      Perovskites in catalysis and electrocatalysis
      Hwang, Jonathan; Rao, Reshma R.; Giordano, Livia; Katayama, Yu; Yu, Yang; Shao-Horn, Yang
      Science (Washington, DC, United States) (2017), 358 (6364), 751-756CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      A review. Catalysts for chem. and electrochem. reactions underpin many aspects of modern technol. and industry, from energy storage and conversion to toxic emissions abatement to chem. and materials synthesis. This role necessitates the design of highly active, stable, yet earth-abundant heterogeneous catalysts. In this Review, we present the perovskite oxide family as a basis for developing such catalysts for (electro)chem. conversions spanning carbon, nitrogen, and oxygen chemistries. A framework for rationalizing activity trends and guiding perovskite oxide catalyst design is described, followed by illustrations of how a robust understanding of perovskite electronic structure provides fundamental insights into activity, stability, and mechanism in oxygen electrocatalysis. We conclude by outlining how these insights open exptl. and computational opportunities to expand the compositional and chem. reaction space for next-generation perovskite catalysts.
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    12. 12
      Mefford, J. T.; Akbashev, A. R.; Kang, M.; Bentley, C. L.; Gent, W. E.; Deng, H. D.; Alsem, D. H.; Yu, Y.-S.; Salmon, N. J.; Shapiro, D. A.; Unwin, P. R.; Chueh, W. C. Correlative Operando Microscopy of Oxygen Evolution Electrocatalysts. Nature 2021, 593, 73,  DOI: 10.1038/s41586-021-03454-x
      There is no corresponding record for this reference.
    13. 13
      Wang, J.; Han, L.; Huang, B.; Shao, Q.; Xin, H. L.; Huang, X. Amorphization Activated Ruthenium-Tellurium Nanorods for Efficient Water Splitting. Nat. Commun. 2019, 10, 5692,  DOI: 10.1038/s41467-019-13519-1
      13
      Amorphization activated ruthenium-tellurium nanorods for efficient water splitting
      Wang, Juan; Han, Lili; Huang, Bolong; Shao, Qi; Xin, Huolin L.; Huang, Xiaoqing
      Nature Communications (2019), 10 (1), 5692CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
      Pursuing active and durable water splitting electrocatalysts is of vital significance for solving the sluggish kinetics of the oxygen evolution reaction (OER) process in energy supply. Herein, theor. calcns. identify that the local distortion-strain effect in amorphous RuTe2 system abnormally sensitizes the Te-pp coupling capability and enhances the electron-transfer of Ru-sites, in which the excellent inter-orbital p-d transfers det. strong electronic activities for boosting OER performance. Thus, a robust electrocatalyst based on amorphous RuTe2 porous nanorods (PNRs) is successfully fabricated. In the acidic water splitting, a-RuTe2 PNRs exhibit a superior performance, which only require a cell voltage of 1.52 V to reach a c.d. of 10 mA cm-2. Detailed investigations show that the high d. of defects combine with oxygen atoms to form RuOxHy species, which are conducive to the OER. This work offers valuable insights for constructing robust electrocatalysts based on theor. calcns. guided by rational design and amorphous materials.
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    14. 14
      Yu, X.; Zhao, J.; Johnsson, M. Interfacial Engineering of Nickel Hydroxide on Cobalt Phosphide for Alkaline Water Electrocatalysis. Adv. Funct. Mater. 2021, 31, 2101578,  DOI: 10.1002/adfm.202101578
      14
      Interfacial Engineering of Nickel Hydroxide on Cobalt Phosphide for Alkaline Water Electrocatalysis
      Yu, Xiaowen; Zhao, Jun; Johnsson, Mats
      Advanced Functional Materials (2021), 31 (25), 2101578CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Catalysts based on earth-abundant non-noble metals are interesting candidates for alk. water electrolysis in sustainable hydrogen economies. However, such catalysts often suffer from high overpotential and sluggish kinetics in both the hydrogen and oxygen evolution reactions (HER and OER). In this study, a hybrid catalyst made of iron-doped cobalt phosphide (Fe-CoP) nanowire arrays and Ni(OH)2 nanosheets is introduced that displays strong electronic interactions at the interface, which significantly improves the interfacial reactivity of reactants and/or intermediates with the hybrid catalyst surface. The combined exptl. and theor. study further confirms that the hybrid catalyst promotes the sluggish rate-limiting steps in both the HER and OER. Full water electrolysis is thus enabled to take place at such a low cell voltage as 1.52 V to reach the c.d. of 10 mA cm-2 along with superior durability and high conversion efficiency.
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    15. 15
      Sun, Y.; Li, R.; Chen, X.; Wu, J.; Xie, Y.; Wang, X.; Ma, K.; Wang, L.; Zhang, Z.; Liao, Q.; Kang, Z.; Zhang, Y. A-Site Management Prompts the Dynamic Reconstructed Active Phase of Perovskite Oxide OER Catalysts. Adv. Energy Mater. 2021, 11, 2003755,  DOI: 10.1002/aenm.202003755
      15
      A-Site Management Prompts the Dynamic Reconstructed Active Phase of Perovskite Oxide OER Catalysts
      Sun, Yu; Li, Ran; Chen, Xiaoxuan; Wu, Jing; Xie, Yong; Wang, Xin; Ma, Kaikai; Wang, Li; Zhang, Zheng; Liao, Qingliang; Kang, Zhuo; Zhang, Yue
      Advanced Energy Materials (2021), 11 (12), 2003755CODEN: ADEMBC; ISSN:1614-6840. (Wiley-Blackwell)
      Perovskites (ABX3) are promising oxygen evolution reaction (OER) catalysts for their highly intrinsic activity. The in-depth understanding and the adjustment of dynamic reconstruction of active phases for perovskites in OER are still a daunting challenge. Here, a refined A-site management strategy is proposed for perovskite oxides, which facilitates the surface reconstruction of the B-site element-based active phase to enhance the OER performance. Electrocatalyst lanthanum nickel oxide displays a dynamic reconstruction feature during OER with the growth of a self-assembled NiOOH active layer, based on the in situ electrochem. Raman technol. Precise A-site cerium-doping lowers the reconstruction potential for the active phase and the dynamic structure-activity correlation is well established. Theor. calcns. demonstrate that A-site cerium substitution upshifts the O 2p level for greater structural flexibility with optimized oxygen vacancy content, thereby activating the B-site atom and promoting the active phase reconstruction. These results suggest that A-site management prompts the B-site element-based active phase dynamic reconstruction via engineered X-site content as a bridge. Therefore, indicating the strong correlation of each-site component in perovskite oxides during OER and deepening the understanding of the fundamental processes of the structural transformation and further benefiting the accurate design of high-efficiency perovskite OER electrocatalysts.
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    16. 16
      Yuan, Y.; Adimi, S.; Thomas, T.; Wang, J.; Guo, H.; Chen, J.; Attfield, J. P.; DiSalvo, F. J.; Yang, M. Co3Mo3N─an Efficient Multifunctional Electrocatalyst. Innovation 2021, 2, 100096,  DOI: 10.1016/j.xinn.2021.100096
      There is no corresponding record for this reference.
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    17. 17
      Hou, J.; Zhang, B.; Li, Z.; Cao, S.; Sun, Y.; Wu, Y.; Gao, Z.; Sun, L. Vertically Aligned Oxygenated-CoS2-MoS2 Heteronanosheet Architecture from Polyoxometalate for Efficient and Stable Overall Water Splitting. ACS Catal. 2018, 8, 4612– 4621,  DOI: 10.1021/acscatal.8b00668
      17
      Vertically Aligned Oxygenated-CoS2-MoS2 Heteronanosheet Architecture from Polyoxometalate for Efficient and Stable Overall Water Splitting
      Hou, Jungang; Zhang, Bo; Li, Zhuwei; Cao, Shuyan; Sun, Yiqing; Wu, Yunzhen; Gao, Zhanming; Sun, Licheng
      ACS Catalysis (2018), 8 (5), 4612-4621CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
      To achieve efficient conversion of renewable energy sources through H2O splitting, low-cost, earth-abundant, and robust electrocatalysts for the O evolution reaction (OER) and H evolution reaction (HER) are required. Herein, vertically aligned oxygenated-CoS2-MoS2 (O-CoMoS) heteronanosheets grown on flexible C fiber cloth as bifunctional electrocatalysts have been produced using the Anderson-type (NH4)4[CoIIMo6O24H6].6H2O polyoxometalate as bimetal precursor. In comparison to different O-FeMoS, O-NiMoS, and MoS2 nanosheet arrays, the O-CoMoS heteronanosheet array exhibited low overpotentials of 97 and 272 mV to reach a c.d. of 10 mA cm-2 in alk. soln. for the HER and OER, resp. Assembled as an electrolyzer for overall H2O splitting, O-CoMoS heteronanosheets as both the anode and cathode deliver a c.d. of 10 mA cm-2 at a quite low cell voltage of 1.6 V. This O-CoMoS architecture is highly advantageous for a disordered structure, exposure of active heterointerfaces, a highway of charge transport on 2-dimensional conductive channels, and abundant active catalytic sites from the synergistic effect of the heterostructures, accomplishing a dramatically enhanced performance for the OER, HER, and overall H2O splitting. This work represents a feasible strategy to explore efficient and stable bifunctional bimetal sulfide electrocatalysts for renewable energy applications.
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    18. 18
      Zhao, M.; Li, W.; Li, J.; Hu, W.; Li, C. M. Strong Electronic Interaction Enhanced Electrocatalysis of Metal Sulfide Clusters Embedded Metal-Organic Framework Ultrathin Nanosheets toward Highly Efficient Overall Water Splitting. Adv. Sci. 2020, 7, 2001965,  DOI: 10.1002/advs.202001965
      18
      Strong Electronic Interaction Enhanced Electrocatalysis of Metal Sulfide Clusters Embedded Metal-Organic Framework Ultrathin Nanosheets toward Highly Efficient Overall Water Splitting
      Zhao, Ming; Li, Wei; Li, Junying; Hu, Weihua; Li, Chang Ming
      Advanced Science (Weinheim, Germany) (2020), 7 (20), 2001965CODEN: ASDCCF; ISSN:2198-3844. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Unique metal sulfide (MS) clusters embedded ultrathin nanosheets of Fe/Ni metal-org. framework (MOF) are grown on nickel foam (NiFe-MS/MOFF) as a highly efficient bifunctional electrocatalyst for overall water splitting. It exhibits remarkable catalytic activity and stability toward both the oxygen evolution reaction (OER, n = 230 mV at 50 mA cm-2) and hydrogen evolution reaction (HER, n = 156 mV at 50 mA cm-2) in alk. media, and bi-functionally catalyzes overall alk. water splitting at a c.d. of 50 mA cm-2 by 1.74 V cell voltage without iR compensation. The enhancement mechanism is ascribed to the impregnated metal sulfide clusters in the nanosheets, which not only promote the formation of ultrathin nanosheet to greatly enlarge the reaction surface area while offering high elec. cond., but more importantly, efficiently modulate the electronic structure of the catalytically active atom sites to an electron-rich state via strong electronic interaction and strengthen the adsorption of oxygenate intermediate to facilitate fast electrochem. reactions. This work reports a highly efficient HER/OER bifunctional electrocatalyst and may shed light on the rational design and synthesis of uniquely structured MOF-derived catalysts.
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    19. 19
      Xiong, D.; Gu, M.; Chen, C.; Lu, C.; Yi, F.-Y.; Ma, X. Rational design of bimetallic metal-organic framework composites and their derived sulfides with superior electrochemical performance to remarkably boost oxygen evolution and supercapacitors. Chem. Eng. J. 2021, 404, 127111,  DOI: 10.1016/j.cej.2020.127111
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      Rational design of bimetallic metal-organic framework composites and their derived sulfides with superior electrochemical performance to remarkably boost oxygen evolution and supercapacitors
      Xiong, Dengke; Gu, Minli; Chen, Chen; Lu, Chunxiao; Yi, Fei-Yan; Ma, Xinghua
      Chemical Engineering Journal (Amsterdam, Netherlands) (2021), 404 (), 127111CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
      Developing highly efficient and stable multi-functional metal-org. framework electrochem. materials is of prime importance for renewable energy technologies and electrocatalytic applications. Herein, a novel series of bimetallic metal-org. framework (MOF) hybrid materials were successfully designedly fabricated through an in-situ growth and MOF-on-MOF strategies, namely as NiFeMOF/NF, NiCoMOF/NF, FeMOF/NiMOF/NF, and CoMOF/NiMOF/NF. Benefiting from the synergistic effect of bimetallic centers, conductive substrate and unique fabrication, they exhibit remarking electrochem. performance. Among them, FeMOF/NiMOF/NF composite with ultrathin nanosheets displays the best electrochecatalytic performance with ultralow overpotentials of 293 mV at 50 mA cm-2 and 359 mV at 100 mA cm-2 for oxygen evolution reaction (OER), and remarking electrochem. stability with high c.d. of 100 mA cm-2 after testing for 24 h, that 88% of initial c.d. can be remained. Based on these fabricated bimetallic MOF hybrid materials as precursors, the corresponding MOF-derived nano sulfides were obtained with massive exposure of active sites. As an excellent supercapacitor electrode, NiCoS/NF-1 converted from CoMOF/NiMOF/NF shows admirable specific capacitance of 2815.4 F g-1 at 1 mA cm-2 and a remarkable rate capability of 82%.
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    20. 20
      Zang, Z.; Wang, X.; Li, X.; Zhao, Q.; Li, L.; Yang, X.; Yu, X.; Zhang, X.; Lu, Z. Co9S8 Nanosheet Coupled Cu2S Nanorod Heterostructure as Efficient Catalyst for Overall Water Splitting. ACS Appl. Mater. Interfaces 2021, 13, 9865– 9874,  DOI: 10.1021/acsami.0c20820
      20
      Co9S8 Nanosheet Coupled Cu2S Nanorod Heterostructure as Efficient Catalyst for Overall Water Splitting
      Zang, Zehao; Wang, Xuewei; Li, Xiang; Zhao, Qingling; Li, Lanlan; Yang, Xiaojing; Yu, Xiaofei; Zhang, Xinghua; Lu, Zunming
      ACS Applied Materials & Interfaces (2021), 13 (8), 9865-9874CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Electrocatalytic water splitting is a promising technol. for large-scale hydrogen prodn. However, it requires efficient catalysts to overcome the large overpotentials in the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, we report a novel heterostructure catalyst Co9S8/Cu2S on copper foam (Co9S8/Cu2S/CF) with multistep impregnation and electrodeposition. Due to the strong interfacial interaction, the interfacial electrons transfer from Co sites to S sites, which promote the adsorption of oxygen-contg. intermediates, water mols., as well as the dissocn. of water mols. Therefore, the heterostructure catalyst exhibits low overpotentials of 195 mV for OER and 165 mV for HER at 10 mA cm-2, resp. Moreover, it only needs 1.6 V to realize water splitting at 10 mA cm-2 in a two-electrode cell. This work provides an efficient method to tailor the surface electronic structure through specific morphol. design and construct a heterostructure interface to achieve alk. water splitting.
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    21. 21
      Shit, S.; Chhetri, S.; Jang, W.; Murmu, N. C.; Koo, H.; Samanta, P.; Kuila, T. Cobalt Sulfide/Nickel Sulfide Heterostructure Directly Grown on Nickel Foam: An Efficient and Durable Electrocatalyst for Overall Water Splitting Application. ACS Appl. Mater. Interfaces 2018, 10, 27712– 27722,  DOI: 10.1021/acsami.8b04223
      21
      Cobalt Sulfide/Nickel Sulfide Heterostructure Directly Grown on Nickel Foam: An Efficient and Durable Electrocatalyst for Overall Water Splitting Application
      Shit, Subhasis; Chhetri, Suman; Jang, Wooree; Murmu, Naresh C.; Koo, Hyeyoung; Samanta, Pranab; Kuila, Tapas
      ACS Applied Materials & Interfaces (2018), 10 (33), 27712-27722CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Fabrication of high-performance noble metal-free bifunctional electrocatalysts for both H evolution reaction (HER) and O evolution reaction (OER) in H2O is a promising strategy toward future C-neutral economy. Herein, a 1-pot hydrothermal synthesis of Co sulfide/Ni sulfide heterostructure supported by Ni foam (CoSx/Ni3S2@NF) was performed. The Ni foam acted as the 3-dimensional conducting substrate as well as the source of Ni for Ni3S2. The formation of CoSx/Ni3S2@NF was confirmed by x-ray diffraction and XPS. The formation of CoSx/Ni3S2@NF facilitated easy charge transport and showed synergistic electrocatalytic effect toward HER, OER, and overall H2O splitting in alk. medium. Remarkably, CoSx/Ni3S2@NF showed catalytic activity comparable with that of benchmarking electrocatalysts Pt/C and RuO2. For CoSx/Ni3S2@NF, overpotentials of 204 and 280 mV were required to achieve current densities of 10 and 20 mA cm-2 for HER and OER, resp., in 1.0M KOH soln. A 2-electrode system was formulated for overall H2O splitting reaction, which showed current densities of 10 and 50 mA cm-2 at 1.572 and 1.684 V, resp. The prepd. catalyst exhibited excellent durability in HER and OER catalyzing conditions and also in overall H2O splitting operation. Therefore, CoSx/Ni3S2@NF could be a promising noble-metal-free electrocatalyst for overall H2O splitting application.
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    22. 22
      Chen, W.; Wang, H.; Li, Y.; Liu, Y.; Sun, J.; Lee, S.; Lee, J.-S.; Cui, Y. In Situ Electrochemical Oxidation Tuning of Transition Metal Disulfides to Oxides for Enhanced Water Oxidation. ACS Cent. Sci. 2015, 1, 244– 251,  DOI: 10.1021/acscentsci.5b00227
      22
      In Situ Electrochemical Oxidation Tuning of Transition Metal Disulfides to Oxides for Enhanced Water Oxidation
      Chen, Wei; Wang, Haotian; Li, Yuzhang; Liu, Yayuan; Sun, Jie; Lee, Sanghan; Lee, Jang-Soo; Cui, Yi
      ACS Central Science (2015), 1 (5), 244-251CODEN: ACSCII; ISSN:2374-7951. (American Chemical Society)
      The development of catalysts with earth-abundant elements for efficient oxygen evolution reactions is of paramount significance for clean and sustainable energy storage and conversion devices. Our group demonstrated recently that the electrochem. tuning of catalysts via lithium insertion and extn. has emerged as a powerful approach to improve catalytic activity. Here we report a novel in situ electrochem. oxidn. tuning approach to develop a series of binary, ternary, and quaternary transition metal (e.g., Co, Ni, Fe) oxides from their corresponding sulfides as highly active catalysts for much enhanced water oxidn. The electrochem. tuned cobalt-nickel-iron oxides grown directly on the three-dimensional carbon fiber electrodes exhibit a low overpotential of 232 mV at c.d. of 10 mA cm-2, small Tafel slope of 37.6 mV dec-1, and exceptional long-term stability of electrolysis for over 100 h in 1 M KOH alk. medium, superior to most non-noble oxygen evolution catalysts reported so far. The materials evolution assocd. with the electrochem. oxidn. tuning is systematically investigated by various characterizations, manifesting that the improved activities are attributed to the significant grain size redn. and increase of surface area and electroactive sites. This work provides a promising strategy to develop electrocatalysts for large-scale water-splitting systems and many other applications.
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    23. 23
      Kou, Z.; Li, X.; Zhang, L.; Zang, W.; Gao, X.; Wang, J. Dynamic Surface Chemistry of Catalysts in Oxygen Evolution Reaction. Small Sci. 2021, 1, 2100011,  DOI: 10.1002/smsc.202100011
      23
      Dynamic Surface Chemistry of Catalysts in Oxygen Evolution Reaction
      Kou, Zongkui; Li, Xin; Zhang, Lei; Zang, Wenjie; Gao, Xiaorui; Wang, John
      Small Science (2021), 1 (7), 2100011CODEN: SSMCBJ; ISSN:2688-4046. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Electrocatalytic oxygen evolution reaction (OER) is a crucial anode reaction where electrocatalysts are the key elements and their dynamic surface chem. runs throughout the entire process. Herein, we examine the latest advances and challenges in understanding of the dynamic surface chem. of OER electrocatalysts. There are electrochem. origin and driving force for the dynamic surface nature, where several processes can take place either concurrently or sequentially, including reconstruction (i.e., phase formation/transformation, morphol. change, and compositional change), vacancy generation and filling/refilling, and the intermediate adsorption-desorption process on catalytic surface. These dynamic surface processes of OER catalysts are impacted by not only the reaction and service conditions, including the (local) pH and its gradient distribution, applied potential, types and concn. of exotic ions and external fields on top of the nature of catalysts/precatalysts, but also their interactions. Due to the local, time-dependent and instant nature, there are considerable challenges in tracing, modeling and understanding of the complete dynamic surface chem. of catalysts in OER, by means of ex situ, in situ and operando exptl. investigations. Therefore, computational studies and dynamic simulations help provide key insights in future pursuits, where there is crit. need for a multiscale computational modeling approach encompassing all these aspects.
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    24. 24
      Fan, K.; Zou, H.; Lu, Y.; Chen, H.; Li, F.; Liu, J.; Sun, L.; Tong, L.; Toney, M. F.; Sui, M.; Yu, J. Direct Observation of Structural Evolution of Metal Chalcogenide in Electrocatalytic Water Oxidation. ACS Nano 2018, 12, 12369– 12379,  DOI: 10.1021/acsnano.8b06312
      24
      Direct Observation of Structural Evolution of Metal Chalcogenide in Electrocatalytic Water Oxidation
      Fan, Ke; Zou, Haiyuan; Lu, Yue; Chen, Hong; Li, Fusheng; Liu, Jinxuan; Sun, Licheng; Tong, Lianpeng; Toney, Michael F.; Sui, Manling; Yu, Jiaguo
      ACS Nano (2018), 12 (12), 12369-12379CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      As one of the most remarkable O evolution reaction (OER) electrocatalysts, metal chalcogenides were intensively reported during the past few decades because of their high OER activities. It is reported that electron-chem. conversion of metal chalcogenides into oxides/hydroxides would take place after the OER. However, the transition mechanism of such unstable structures, as well as the real active sites and catalytic activity during the OER for these electrocatalysts, was not understood yet; therefore a direct observation for the electrocatalytic H2O oxidn. process, esp. at nano or even angstrom scale, is urgently needed. In this research, by employing advanced Cs-cor. TEM, a step by step oxidational evolution of amorphous electrocatalyst CoSx into crystd. CoOOH in the OER was in situ captured: irreversible conversion of CoSx to crystd. CoOOH is initiated on the surface of the electrocatalysts with a morphol. change via Co(OH)2 intermediate during the OER measurement, where CoOOH is confirmed as the real active species. Besides, this transition process also was confirmed by multiple applications of XPS, in situ FTIR spectroscopy, and other ex situ technologies. Also, from this discovery, a high-efficiency electrocatalyst of a N-doped graphene foam (NGF) coated by CoSx was explored through a thorough structure transformation of CoOOH. The authors believe this in situ and in-depth observation of structural evolution in the OER measurement can provide insights into the fundamental understanding of the mechanism for the OER catalysts, thus enabling the more rational design of low-cost and high-efficient electrocatalysts for H2O splitting.
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    25. 25
      Li, G.; Fu, C.; Shi, W.; Jiao, L.; Wu, J.; Yang, Q.; Saha, R.; Kamminga, M. E.; Srivastava, A. K.; Liu, E.; Yazdani, A. N.; Kumar, N.; Zhang, J.; Blake, G. R.; Liu, X.; Fahlman, M.; Wirth, S.; Auffermann, G.; Gooth, J.; Parkin, S.; Madhavan, V.; Feng, X.; Sun, Y.; Felser, C. Dirac Nodal Arc Semimetal PtSn4: An Ideal Platform for Understanding Surface Properties and Catalysis for Hydrogen Evolution. Angew. Chem., Int. Ed. 2019, 131, 13241– 13246,  DOI: 10.1002/ange.201906109
      There is no corresponding record for this reference.
    26. 26
      Yang, Q.; Li, G.; Manna, K.; Fan, F.; Felser, C.; Sun, Y. Topological Engineering of Pt-Group-Metal-Based Chiral Crystals toward High-Efficiency Hydrogen Evolution Catalysts. Adv. Mater. 2020, 32, 1908518,  DOI: 10.1002/adma.201908518
      26
      Topological Engineering of Pt-Group-Metal-Based Chiral Crystals toward High-Efficiency Hydrogen Evolution Catalysts
      Yang, Qun; Li, Guowei; Manna, Kaustuv; Fan, Fengren; Felser, Claudia; Sun, Yan
      Advanced Materials (Weinheim, Germany) (2020), 32 (14), 1908518CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      It has been demonstrated that topol. nontrivial surface states can favor heterogeneous catalysis processes such as the hydrogen evolution reaction (HER), but a further decrease in mass loading and an increase in activity are still highly challenging. The observation of massless chiral fermions assocd. with large topol. charge and long Fermi arc (FA) surface states inspires the investigation of their relationship with the charge transfer and adsorption process in the HER. In this study, it is found that the HER efficiency of Pt-group metals can be boosted significantly by introducing topol. order. A giant nontrivial topol. energy window and a long topol. surface FA are expected at the surface when forming chiral crystals in the space group of P213 (#198). This makes the nontrivial topol. features resistant to a large change in the applied overpotential. As HER catalysts, PtAl and PtGa chiral crystals show turnover frequencies as high as 5.6 and 17.1 s-1 and an overpotential as low as 14 and 13.3 mV at a c.d. of 10 mA cm-2. These crystals outperform those of com. Pt and nanostructured catalysts. This work opens a new avenue for the development of high-efficiency catalysts with the strategy of topol. engineering of excellent transitional catalytic materials.
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    27. 27
      Li, G.; Xu, Q.; Shi, W.; Fu, C.; Jiao, L.; Kamminga, M. E.; Yu, M.; Tüysüz, H.; Kumar, N.; Süß, V. Surface States in Bulk Single Crystal of Topological Semimetal Co3Sn2S2 toward Water Oxidation. Sci. Adv. 2019, 5, eaaw9867  DOI: 10.1126/sciadv.aaw9867
      There is no corresponding record for this reference.
    28. 28
      He, Y.; Boubeche, M.; Zhou, Y.; Yan, D.; Zeng, L.; Wang, X.; Yan, K.; Luo, H. Topologically Nontrivial 1T’-MoTe2 as Highly Efficient Hydrogen Evolution Electrocatalyst. J. Phys. Mater. 2020, 4, 014001,  DOI: 10.1088/2515-7639/abc40c
      There is no corresponding record for this reference.
    29. 29
      Li, J.; Ma, H.; Xie, Q.; Feng, S.; Ullah, S.; Li, R.; Dong, J.; Li, D.; Li, Y.; Chen, X.-Q. Topological Quantum Catalyst: Dirac Nodal Line States and a Potential Electrocatalyst of Hydrogen Evolution in the TiSi Family. Sci. China Mater. 2018, 61, 23– 29,  DOI: 10.1007/s40843-017-9178-4
      29
      Topological quantum catalyst: Dirac nodal line states and a potential electrocatalyst of hydrogen evolution in the TiSi family
      Li, Jiangxu; Ma, Hui; Xie, Qing; Feng, Shaobo; Ullah, Sami; Li, Ronghan; Dong, Junhua; Li, Dianzhong; Li, Yiyi; Chen, Xing-Qiu
      Science China Materials (2018), 61 (1), 23-29CODEN: SCMCDB; ISSN:2095-8226. (Science China Press)
      Topol. nodal line (DNL) semimetals, a closed loop of the inverted bands in its bulk phases, result in the almost flat drumhead-like non-trivial surface states (DNSSs) with an unusually high electronic d. near the Fermi level. High catalytic active sites generally assocd. with high electronic densities around the Fermi level, high carrier mobility and a close-to-zero free energy of the adsorbed state of hydrogen (ΔGH*≈0) are prerequisite to design alternative of precious platinum for catalyzing electrochem. hydrogen prodn. from water. By combining these two aspects, it is natural to consider if the DNLs are a good candidate for the hydrogen evolution reaction (HER) or not because its DNSSs provide a robust platform to activate chem. reactions. Here, through first-principles calcns. we reported a new DNL TiSi-type family, exhibiting a closed Dirac nodal line due to the linear band crossings in ky=0 plane. The hydrogen adsorbed state on the surface yields ΔGH* to be almost zero and the topol. charge carries participate in HER. The results highlight a new routine to design topol. quantum catalyst utilizing the topol. DNL-induced surface bands as active sites, rather than edge sites-, vacancy-, dopant-, strain-, or heterostructure-created active sites.
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    30. 30
      Li, G.; Felser, C. Heterogeneous Catalysis at the Surface of Topological Materials. Appl. Phys. Lett. 2020, 116, 070501,  DOI: 10.1063/1.5143800
      30
      Heterogeneous catalysis at the surface of topological materials
      Li, Guowei; Felser, Claudia
      Applied Physics Letters (2020), 116 (7), 070501CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      A review. Intriguing properties are frequently reported in various topol. non-trivial materials. They include robust metallic surface states, high carrier mobility, chiral fermions, and ultralong Fermi arcs. An exciting recent finding is that these properties are strongly related to adsorption and electron transfer in various heterogeneous catalysis reactions, such as hydrogen evolution, oxygen evolution, oxygen redn., enantiospecific adsorption, and hydrometallation. Thus, we expect that the introduction of non-trivial symmetry-protected topol. order will offer important freedom for designing high-performance heterogeneous catalysts. To uncover the contribution of the topol. non-trivial electronic structure to the heterogeneous reactions, in situ techniques are urgently needed to detect the interaction between surface states, topol. electrons, and reaction intermediates. (c) 2020 American Institute of Physics.
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    31. 31
      Shekhar, C.; Nayak, A. K.; Sun, Y.; Schmidt, M.; Nicklas, M.; Leermakers, I.; Zeitler, U.; Skourski, Y.; Wosnitza, J.; Liu, Z.; Chen, Y.; Schnelle, W.; Borrmann, H.; Grin, Y.; Felser, C.; Yan, B. Extremely Large Magnetoresistance and Ultrahigh Mobility in the Topological Weyl Semimetal Candidate NbP. Nat. Phys. 2015, 11, 645– 649,  DOI: 10.1038/nphys3372
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      Extremely large magnetoresistance and ultrahigh mobility in the topological Weyl semimetal candidate NbP
      Shekhar, Chandra; Nayak, Ajaya K.; Sun, Yan; Schmidt, Marcus; Nicklas, Michael; Leermakers, Inge; Zeitler, Uli; Skourski, Yurii; Wosnitza, Jochen; Liu, Zhongkai; Chen, Yulin; Schnelle, Walter; Borrmann, Horst; Grin, Yuri; Felser, Claudia; Yan, Binghai
      Nature Physics (2015), 11 (8), 645-649CODEN: NPAHAX; ISSN:1745-2473. (Nature Publishing Group)
      Recent expts. have revealed spectacular transport properties in semimetals, such as the large, non-satg. magnetoresistance exhibited by WTe2 (ref. ). Topol. semimetals with massless relativistic electrons have also been predicted as three-dimensional analogs of graphene. These systems are known as Weyl semimetals, and are predicted to have a range of exotic transport properties and surface states, distinct from those of topol. insulators. Here we examine the magneto-transport properties of NbP, a material the band structure of which has been predicted to combine the hallmarks of a Weyl semimetal with those of a normal semimetal. We observe an extremely large magnetoresistance of 850,000% at 1.85 K (250% at room temp.) in a magnetic field of up to 9 T, without any signs of satn., and an ultrahigh carrier mobility of 5 × 106 cm2 V-1 s-1 accompanied by strong Shubnikov-de Haas (SdH) oscillations. NbP therefore presents a unique example of a material combining topol. and conventional electronic phases, with intriguing phys. properties resulting from their interplay.
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    32. 32
      Xie, R.; Zhang, T.; Weng, H.; Chai, G.-L. Progress, Advantages, and Challenges of Topological Material Catalysts. Small Sci. 2022, 2, 2100106,  DOI: 10.1002/smsc.202100106
      32
      Progress, Advantages, and Challenges of Topological Material Catalysts
      Xie, Ruikuan; Zhang, Tan; Weng, Hongming; Chai, Guo-Liang
      Small Science (2022), 2 (4), 2100106CODEN: SSMCBJ; ISSN:2688-4046. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Topol. materials is one of the hottest topics in condensed matter physics because of its exotic properties such as robust metallic boundary states, Fermi arcs, and the spin-momentum-locking helicity. The topol. protected conducting boundary states spanning the whole bandgap are expected to serve as robust and wide-range-energy transition states facilitating catalytic reactions. Recently, some topol. materials have been found to be high-performance catalysts, which might open an emerging research field. Herein, an overview of topol. materials is given and then recent progress in topol. material catalysts (TMCs) is presented. As it is a new field, more detailed and accurate mechanisms behind the high performance of TMCs are urgently needed. Combining theor. and exptl. studies is a promising way to resolve these puzzles. Heterostructures, dopants, and defects have the chance to tune the catalytic activity of TMCs while retaining topol. surface states (TSSs). Also, more TMCs are needed to be discovered, and more catalytic reactions are to be investigated for TMCs in the future.
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    33. 33
      Xiao, J.; Kou, L.; Yam, C.-Y.; Frauenheim, T.; Yan, B. Toward Rational Design of Catalysts Supported on a Topological Insulator Substrate. ACS Catal. 2015, 5, 7063– 7067,  DOI: 10.1021/acscatal.5b01966
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      Toward Rational Design of Catalysts Supported on a Topological Insulator Substrate
      Xiao, Jianping; Kou, Liangzhi; Yam, Chi-Yung; Frauenheim, Thomas; Yan, Binghai
      ACS Catalysis (2015), 5 (12), 7063-7067CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
      Exotic and robust metallic surface states of topol. insulators (TIs) have been expected to provide a promising platform for novel surface chem. and catalysis. However, it is still not fully known how TIs affect the activity of catalysts. In this work, we study the effects of topol. surface states (TSSs) on the activity of transition metal clusters (Au, Ag, Cu, Pt, and Pd), which are supported on a TI Bi2Se3 substrate. It was found the adsorption energy of oxygen on the supported catalysts can be always enhanced due to the TSSs. However, it does not necessarily mean an increase of the activity in catalytic oxidn. reaction. Rather, the enhanced adsorption behavior in the presence of TSSs exhibits dual effects, detd. by the intrinsic reactivity of these catalysts with oxygen. For the Au case, the activity of catalytic oxidn. can be improved because the TSSs can enhance the dissocn. rate of dioxygen. In contrast, a neg. effect is found for the Pt and Pd clusters since the TSSs will suppress the desorption process of reaction products. We also found that the effect of TSSs on the activity of hydrogen evolution reaction (HER) is quite similar (i.e., the metals with original weak reactivity can gain a pos. effect from TSSs). The present work can pave a way for more rational design and selection of catalysts when using TIs as substrates.
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    34. 34
      Li, L.; Zeng, J.; Qin, W.; Cui, P.; Zhang, Z. Tuning the Hydrogen Activation Reactivity on Topological Insulator Heterostructures. Nano Energy 2019, 58, 40– 46,  DOI: 10.1016/j.nanoen.2019.01.007
      34
      Tuning the hydrogen activation reactivity on topological insulator heterostructures
      Li, Leiqiang; Zeng, Jiang; Qin, Wei; Cui, Ping; Zhang, Zhenyu
      Nano Energy (2019), 58 (), 40-46CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)
      The central challenge faced in hydrogen evolution reaction is the low reaction efficiency when using non-precious materials as potential new types of electrocatalysts. Here, we report an elegant synergistic effect of local bonding and topol. surface states (TSSs) for optimally enhanced hydrogen evolution reaction by invoking topol. insulator heterostructures purely composed of abundant elements. Using first-principles calcns. within d. functional theory, we demonstrate that the three-dimensional topol. insulator of Bi2Se3 covered with a single layer of ZnSe can function as an ideal platform for maximal hydrogen evolution reaction with optimal hydrogen adsorption free energy. Such a highly desirable functionality is attributed to the TSSs of Bi2Se3 serving as an electron bath in enhancing the hydrogen adsorption strength, which would be too weak on top of the ZnSe overlayer without considering topol. effects, but too strong upon increasing the ZnSe overlayer thickness. We also demonstrate precise tunability of the vertical location of the TSSs via the ZnSe overlayer thickness, which can be exploited for other functionalities of such topol. insulator heterostructures. The present study provides an important linkage between the topol. insulators as a new class of quantum matter and catalytic materials for clean energy.
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    35. 35
      Chen, H.; Zhu, W.; Xiao, D.; Zhang, Z. Co Oxidation Facilitated by Robust Surface States on Au-Covered Topological Insulators. Phys. Rev. Lett. 2011, 107, 056804,  DOI: 10.1103/PhysRevLett.107.056804
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      CO Oxidation Facilitated by Robust Surface States on Au-Covered Topological Insulators
      Chen, Hua; Zhu, Wenguang; Xiao, Di; Zhang, Zhen-Yu
      Physical Review Letters (2011), 107 (5), 056804/1-056804/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      Surface states-the electronic states emerging as a solid material terminates at a surface-are usually vulnerable to contaminations and defects. The robust topol. surface state(s) (TSS) on the three-dimensional topol. insulators provide a perfect platform for exploiting surface states in less stringent environments. Employing 1st-principles d. functional theory calcns., the TSS can play a vital role in facilitating surface reactions by serving as an effective electron bath. The authors use CO oxidn. on gold-covered Bi2Se3 as a prototype example, and show that the robust TSS can significantly enhance the adsorption energy of both CO and O2 mols., by promoting different directions of static electron transfer. The concept of TSS as an electron bath may lead to new design principles beyond the conventional d-band theory of heterogeneous catalysis.
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    36. 36
      Schröter, N. B.; Robredo, I.; Klemenz, S.; Kirby, R. J.; Krieger, J. A.; Pei, D.; Yu, T.; Stolz, S.; Schmitt, T.; Dudin, P. Weyl Fermions, Fermi Arcs, and Minority-Spin Carriers in Ferromagnetic CoS2. Sci. Adv. 2020, 6, eabd5000  DOI: 10.1126/sciadv.abd5000
      There is no corresponding record for this reference.
    37. 37
      Wei, C.; Sun, S.; Mandler, D.; Wang, X.; Qiao, S. Z.; Xu, Z. J. Approaches for Measuring the Surface Areas of Metal Oxide Electrocatalysts for Determining Their Intrinsic Electrocatalytic Activity. Chem. Soc. Rev. 2019, 48, 2518– 2534,  DOI: 10.1039/c8cs00848e
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      Approaches for measuring the surface areas of metal oxide electrocatalysts for determining their intrinsic electrocatalytic activity
      Wei, Chao; Sun, Shengnan; Mandler, Daniel; Wang, Xun; Qiao, Shi Zhang; Xu, Zhichuan J.
      Chemical Society Reviews (2019), 48 (9), 2518-2534CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Great attention has been recently drawn to metal oxide electrocatalysts for electrocatalysis-based energy storage and conversion devices. To find the optimal electrocatalyst, a prerequisite is an activity metric that reasonably evaluates the intrinsic electrocatalytic activity of a particular catalyst. The intrinsic activity is commonly defined as the specific activity which is the current per unit catalyst surface area. Thus, the precise assessment of intrinsic activity highly depends on the reliable measurement of catalyst surface area, which calls for the knowledge of exptl. approaches for detg. the surface areas of metal oxide electrocatalysts. This tutorial review aims to summarize and analyze the approaches for measuring the surface areas of metal oxide electrocatalysts for evaluating and comparing their intrinsic electrocatalytic activities. We start by comparing the popular metrics for activity estn. and highlighting the importance of surface-area-normalized activity (i.e. specific activity) for intrinsic chem. anal. Second, we provide some general guidelines for exptl. measuring the electrochem. active surface area (ECSA). Third, we review the methods for the surface area measurement of metal oxide electrocatalysts. The detailed procedure for each method is explicitly described to provide a step-by-step manual that guides researchers to perform the measurement; the rationales and uncertainties for each method are discussed to help readers justify the reliable assessment of surface area. Next, we give our recommendations on selecting a rational exptl. approach for the surface area measurement of a particular metal oxide electrocatalyst. Lastly, we discuss the future challenges of ECSA measurement and present an exemplary novel ECSA technique.
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    38. 38
      Li, G.; Khim, S.; Chang, C. S.; Fu, C.; Nandi, N.; Li, F.; Yang, Q.; Blake, G. R.; Parkin, S.; Auffermann, G.; Sun, Y.; Muller, D. A.; Mackenzie, A. P.; Felser, C. In Situ Modification of a Delafossite-Type PdCoO2 Bulk Single Crystal for Reversible Hydrogen Sorption and Fast Hydrogen Evolution. ACS Energy Lett. 2019, 4, 2185– 2191,  DOI: 10.1021/acsenergylett.9b01527
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      In Situ Modification of a Delafossite-Type PdCoO2 Bulk Single Crystal for Reversible Hydrogen Sorption and Fast Hydrogen Evolution
      Li, Guowei; Khim, Seunghyun; Chang, Celesta S.; Fu, Chenguang; Nandi, Nabhanila; Li, Fan; Yang, Qun; Blake, Graeme R.; Parkin, Stuart; Auffermann, Gudrun; Sun, Yan; Muller, David A.; Mackenzie, Andrew P.; Felser, Claudia
      ACS Energy Letters (2019), 4 (9), 2185-2191CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
      The observation of extraordinarily high cond. in delafossite-type PdCoO2 is of great current interest, and there is some evidence that electrons behave like a fluid when flowing in bulk crystals of PdCoO2. Thus, this material is an ideal platform for the study of the electron transfer processes in heterogeneous reactions. Here, the authors report the use of bulk single-crystal PdCoO2 as a promising electrocatalyst for H evolution reactions (HERs). An overpotential of only 31 mV results in a c.d. of 10 mA cm-2, accompanied by high long-term stability. The authors have precisely detd. that the crystal surface structure is modified after electrochem. activation with the formation of strained Pd nanoclusters in the surface layer. These nanoclusters exhibit reversible H sorption and desorption, creating more active sites for H access. The bulk PdCoO2 single crystal with ultrahigh cond., which acts as a natural substrate for the Pd nanoclusters, provides a high-speed channel for electron transfer.
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    39. 39
      Anantharaj, S.; Ede, S. R.; Sakthikumar, K.; Karthick, K.; Mishra, S.; Kundu, S. Recent Trends and Perspectives in Electrochemical Water Splitting with an Emphasis on Sulfide, Selenide, and Phosphide Catalysts of Fe, Co, and Ni: A Review. ACS Catal. 2016, 6, 8069– 8097,  DOI: 10.1021/acscatal.6b02479
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      Recent Trends and Perspectives in Electrochemical Water Splitting with an Emphasis on Sulfide, Selenide, and Phosphide Catalysts of Fe, Co, and Ni: A Review
      Anantharaj, Sengeni; Ede, Sivasankara Rao; Sakthikumar, Kuppan; Karthick, Kannimuthu; Mishra, Soumyaranjan; Kundu, Subrata
      ACS Catalysis (2016), 6 (12), 8069-8097CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
      A review. Increasing demand for finding eco-friendly and everlasting energy sources is now totally depending on fuel cell technol. Though it is an eco-friendly way of producing energy for the urgent requirements, it needs to be improved to make it cheaper and more eco-friendly. Although there are several types of fuel cells, the H (H2) and O (O2) fuel cell is the one with zero C emission and H2O as the only byproduct. However, supplying fuels in the purest form (at least the H2) is essential to ensure higher life cycles and less decay in cell efficiency. The current large-scale H2 prodn. is largely dependent on steam reforming of fossil fuels, which generates CO2 along with H2 and the source of which is going to be depleted. As an alternate, electrolysis of H2O was given greater attention than the steam reforming. The reasons are as follows: the very high purity of the H2 produced, the abundant source, no need for high-temp., high-pressure reactors, and so on. In earlier days, noble metals such as Pt (cathode) and Ir and Ru (anode) were used for this purpose. However, there are problems in employing these metals, as they are noble and expensive. In this review, the authors elaborate how the group VIII 3d metal sulfide, selenide, and phosphide nanomaterials have arisen as abundant and cheaper electrode materials (catalysts) beyond the oxides and hydroxides of the same. The authors also highlight the evaluation perspective of such electrocatalysts toward H2O electrolysis.
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    40. 40
      Tanwar, K.; Gyan, D. S.; Bhattacharya, S.; Vitta, S.; Dwivedi, A.; Maiti, T. Enhancement of Thermoelectric Power Factor by Inducing Octahedral Ordering in La2-xSrxCoFeO6 Double Perovskites. Phys. Rev. B: Condens. Matter Mater. Phys. 2019, 99, 174105,  DOI: 10.1103/physrevb.99.174105
      There is no corresponding record for this reference.
    41. 41
      Chuang, T. J.; Brundle, C. R.; Rice, D. W. Interpretation of the X-Ray Photoemission Spectra of Cobalt Oxides and Cobalt Oxide Surfaces. Surf. Sci. 1976, 59, 413– 429,  DOI: 10.1016/0039-6028(76)90026-1
      41
      Interpretation of the x-ray photoemission spectra of cobalt oxides and cobalt oxide surfaces
      Chuang, T. J.; Brundle, C. R.; Rice, D. W.
      Surface Science (1976), 59 (2), 413-29CODEN: SUSCAS; ISSN:0039-6028.
      CoO and Co3O4 were studied by high-resoln. x-ray photoemission. The characteristic binding energies in the Co 2p3/2, 2p1/2, and 3s regions, their band shapes and widths, the assocd. shake-up structure, the O(1s) and 0(2s) BE's, and the valence band spectra were examd. The 2 oxides are readily distinguished from their spectra though it is shown that the O(1s) BE's are identical at 529.50 ± 0.14 eV. Ar and O ion sputtered surfaces were examd. to establish the integrity of the oxides. A higher BE O(1s) component (530.7-531.6 eV), the intensity and BE of which vary with the treatments mentioned above, corresponds to nonstoichiometric surface O. The results are discussed with respect to the electronic structures of the oxides and the often conflicting earlier studies of these oxides.
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    42. 42
      Chen, Z.; Kronawitter, C. X.; Yeh, Y.-W.; Yang, X.; Zhao, P.; Yao, N.; Koel, B. E. Activity of Pure and Transition Metal-Modified CoOOH for the Oxygen Evolution Reaction in an Alkaline Medium. J. Mater. Chem. A 2017, 5, 842– 850,  DOI: 10.1039/c6ta07482k
      42
      Activity of pure and transition metal-modified CoOOH for the oxygen evolution reaction in an alkaline medium
      Chen, Zhu; Kronawitter, Coleman X.; Yeh, Yao-Wen; Yang, Xiaofang; Zhao, Peng; Yao, Nan; Koel, Bruce E.
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2017), 5 (2), 842-850CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      A new electrode structure enabling low overpotentials for the oxidn. of water, based on three-dimensional arrays of CoOOH nanowires, is presented. The electrocatalytic activities of pure and M-modified cobalt oxyhydroxides (M = Ni or Mn) nanowires have been investigated in detail for the oxygen evolution reaction (OER) in an alk. environment. The pure, Ni-, and Mn-modified nanowires, with preferentially exposed low-index surfaces, were fabricated directly on stainless steel mesh current collectors using an inexpensive and scalable chem. synthesis procedure. The unique electrode structure ensures excellent substrate-catalyst elec. contact and increases the surface area accessible to the electrolyte. The OER activity of CoOOH nanowires is shown to be significantly improved through incorporation of Ni. Specifically, optimal OER activity is obtained for CoOOH nanowires with 9.7% surface Ni content, which corresponds to four-times greater c.d. compared to pure CoOOH. In contrast, Mn modification of the CoOOH nanowires did not improve the OER activity. Tafel anal. suggests Ni incorporation leads to change in the OER rate-detg. step based on an obsd. decrease in the Tafel slope. Electrochem. impedance spectroscopy reveals that Ni incorporation improves the ability of the catalysts to stabilize surface intermediates, whereas Mn incorporation impedes intermediate stabilization. This study provides new insights regarding the influence of transition metal impurities on the OER activity of CoOOH and provides a clear strategy for the optimization of CoOOH-based OER catalysts in alk. electrolytes.
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    43. 43
      Wang, Q.; Xue, X.; Lei, Y.; Wang, Y.; Feng, Y.; Xiong, X.; Wang, D.; Li, Y. Engineering of Electronic States on Co3O4 Ultrathin Nanosheets by Cation Substitution and Anion Vacancies for Oxygen Evolution Reaction. Small 2020, 16, 2001571,  DOI: 10.1002/smll.202001571
      43
      Engineering of Electronic States on Co3O4 Ultrathin Nanosheets by Cation Substitution and Anion Vacancies for Oxygen Evolution Reaction
      Wang, Qichen; Xue, Xiongxiong; Lei, Yongpeng; Wang, Yuchao; Feng, Yexin; Xiong, Xiang; Wang, Dingsheng; Li, Yadong
      Small (2020), 16 (24), 2001571CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Due to the earth abundance and tunable electronic properties, etc., transition metal oxides (TMOs) show attractive attention in oxygen evolution reaction. O-vacancies (Vo) play important roles in tailoring the local surface and electronic environment to lower the activation barriers. Herein, an effective strategy is shown to enhance the oxygen evolution redn. (OER) performance on Co3O4 ultrathin nanosheets via combined cation substitution and anion vacancies. The oxygen-deficient Fe-Co-O nanosheets (3-4 nm thickness) display an overpotential of 260 mV@10 mA cm-2 and a Tafel slope of 53 mV dec-1, outperforming those of the benchmark RuO2 in 1.0 M KOH. Further calcns. demonstrate that the combined introduction of Fe cation and Vo with appropriate location and content finely tune the intermediate absorption, consequently lowering the rate-limiting activation energy from 0.82 to as low as 0.15 eV. The feasibility is also proved by oxygen-deficient Ni-Co-O nanosheets. This work not only establishes a clear at.-level correlation between cation substitution, anion vacancies, and OER performance, but also provides valuable insights for the rational design of highly efficient catalysts for OER.
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    44. 44
      Chen, C.-J.; Chen, P.-T.; Basu, M.; Yang, K.-C.; Lu, Y.-R.; Dong, C.-L.; Ma, C.-G.; Shen, C.-C.; Hu, S.-F.; Liu, R.-S. An Integrated Cobalt Disulfide (CoS2) Co-Catalyst Passivation Layer on Silicon Microwires for Photoelectrochemical Hydrogen Evolution. J. Mater. Chem. A 2015, 3, 23466– 23476,  DOI: 10.1039/c5ta06202k
      44
      An integrated cobalt disulfide (CoS2) co-catalyst passivation layer on silicon microwires for photoelectrochemical hydrogen evolution
      Chen, Chih-Jung; Chen, Po-Tzu; Basu, Mrinmoyee; Yang, Kai-Chih; Lu, Ying-Rui; Dong, Chung-Li; Ma, Chong-Geng; Shen, Chin-Chang; Hu, Shu-Fen; Liu, Ru-Shi
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2015), 3 (46), 23466-23476CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      An integrated cobalt disulfide (CoS2) co-catalyst passivation layer on Si microwires (MWs) was used as a photocathode for solar hydrogen evolution. Si MWs were prepd. by photolithog. and dry etching techniques. The CoS2-Si photocathodes were subsequently prepd. by chem. deposition and thermal sulfidation of the Co(OH)2 outer shell. The optimized onset potential and photocurrent of the CoS2-Si electrode were 0.248 V and -3.22 mA cm-2 (at 0 V), resp. The best photocatalytic activity of the CoS2-Si electrode resulted from lower charge transfer resistances among the photoabsorber, co-catalyst, and redox couples in the electrolyte. X-ray absorption near edge structure was conducted to investigate the unoccupied electronic states of the CoS2 layer. We propose that more vacancies in the S-3p unoccupied states of the CoS2-Si electrode were present with a lower neg. charge of S22- to form weaker S-H bond strength, promoting water splitting efficiency. Moreover, the CoS2 co-catalyst that completely covered underlying Si MWs served as a passivation layer to prevent oxidn. and reduce degrdn. during photoelectrochem. measurements. Therefore, the optimal CoS2-Si electrode maintained the photocurrent at about -3 mA cm-2 (at 0 V) for 9 h, and its hydrogen generation rate was approx. 0.833 μmol min-1.
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    45. 45
      Wang, G.; Shen, X.; Horvat, J.; Wang, B.; Liu, H.; Wexler, D.; Yao, J. Hydrothermal Synthesis and Optical, Magnetic, and Supercapacitance Properties of Nanoporous Cobalt Oxide Nanorods. J. Phys. Chem. C 2009, 113, 4357– 4361,  DOI: 10.1021/jp8106149
      45
      Hydrothermal Synthesis and Optical, Magnetic, and Supercapacitance Properties of Nanoporous Cobalt Oxide Nanorods
      Wang, Guoxiu; Shen, Xiaoping; Horvat, Josip; Wang, Bei; Liu, Hao; Wexler, David; Yao, Jane
      Journal of Physical Chemistry C (2009), 113 (11), 4357-4361CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Nanoporous cobalt oxide nanorods were synthesized by a hydrothermal method. TEM anal. showed that the individual Co3O4 nanorods have a nanoporous structure, consisting of the textured aggregations of nanocrystals. Optical properties of Co3O4 nanorods were characterized by Raman and UV-visible spectroscopy. Magnetic property measurement shows that Co3O4 nanorods have a low Neel transition temp. of 35 K. The authors obsd. quite significant exchange bias for nanoporous Co3O4 nanorods, indicating the existence of magnetic coupling between the nanocrystals in Co3O4 nanorods. When applied as electrode materials in supercapacitors, Co3O4 demonstrated a high capacitance of 280 F/g.
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    46. 46
      Bergmann, A.; Jones, T. E.; Moreno, E. M.; Teschner, D.; Chernev, P.; Gliech, M.; Reier, T.; Dau, H.; Strasser, P. Unified structural motifs of the catalytically active state of Co(oxyhydr)oxides during the electrochemical oxygen evolution reaction. Nat. Catal. 2018, 1, 711– 719,  DOI: 10.1038/s41929-018-0141-2
      46
      Unified structural motifs of the catalytically active state of Co(oxyhydr)oxides during the electrochemical oxygen evolution reaction
      Bergmann, Arno; Jones, Travis E.; Martinez Moreno, Elias; Teschner, Detre; Chernev, Petko; Gliech, Manuel; Reier, Tobias; Dau, Holger; Strasser, Peter
      Nature Catalysis (2018), 1 (9), 711-719CODEN: NCAACP; ISSN:2520-1158. (Nature Research)
      Efficient catalysts for the anodic oxygen evolution reaction (OER) are crit. for electrochem. H2 prodn. Their design requires structural knowledge of their catalytically active sites and state. Here, we track the at.-scale structural evolution of well-defined CoOx(OH)y compds. into their catalytically active state during electrocatalytic operation through operando and surface-sensitive X-ray spectroscopy and surface voltammetry, supported by theor. calcns. We find clear voltammetric evidence that electrochem. reducible near-surface Co3+-O sites play an organizing role for high OER activity. These sites invariably emerge independent of initial metal valency and coordination under catalytic OER conditions. Combining expts. and theory reveals the unified chem. structure motif as μ2-OH-bridged Co2+/3+ ion clusters formed on all three-dimensional cross-linked and layered CoOx(OH)y precursors and present in an oxidized form during the OER, as shown by operando X-ray spectroscopy. Together, the spectroscopic and electrochem. fingerprints offer a unified picture of our mol. understanding of the structure of catalytically active metal oxide OER sites.
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    47. 47
      Bergmann, A.; Martinez-Moreno, E.; Teschner, D.; Chernev, P.; Gliech, M.; De Araújo, J. F.; Reier, T.; Dau, H.; Strasser, P. Reversible Amorphization and the Catalytically Active State of Crystalline Co3O4 During Oxygen Evolution. Nat. Commun. 2015, 6, 8625,  DOI: 10.1038/ncomms9625
      47
      Reversible amorphization and the catalytically active state of crystalline Co3O4 during oxygen evolution
      Bergmann, Arno; Martinez-Moreno, Elias; Teschner, Detre; Chernev, Petko; Gliech, Manuel; Ferreira de Araujo, Jorge; Reier, Tobias; Dau, Holger; Strasser, Peter
      Nature Communications (2015), 6 (), 8625CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Water splitting catalyzed by earth-abundant materials is pivotal for global-scale prodn. of non-fossil fuels, yet our understanding of the active catalyst structure and reactivity is still insufficient. Here we report on the structurally reversible evolution of cryst. Co3O4 electrocatalysts during oxygen evolution reaction identified using advanced in situ X-ray techniques. At electrode potentials facilitating oxygen evolution, a sub-nanometer shell of the Co3O4 is transformed into an X-ray amorphous CoOx(OH)y which comprises di-μ-oxo-bridged Co3+/4+ ions. Unlike irreversible amorphizations, here, the formation of the catalytically-active layer is reversed by re-crystn. upon return to non-catalytic electrode conditions. The Co3O4 material thus combines the stability advantages of a controlled, stable cryst. material with high catalytic activity, thanks to the structural flexibility of its active amorphous oxides. We propose that cryst. oxides may be tailored for generating reactive amorphous surface layers at catalytic potentials, just to return to their stable cryst. state under rest conditions.
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    48. 48
      Xiao, Z.; Huang, Y.-C.; Dong, C.-L.; Xie, C.; Liu, Z.; Du, S.; Chen, W.; Yan, D.; Tao, L.; Shu, Z.; Zhang, G.; Duan, H.; Wang, Y.; Zou, Y.; Chen, R.; Wang, S. Operando Identification of the Dynamic Behavior of Oxygen Vacancy-Rich Co3O4 for Oxygen Evolution Reaction. J. Am. Chem. Soc. 2020, 142, 12087– 12095,  DOI: 10.1021/jacs.0c00257
      48
      Operando Identification of the Dynamic Behavior of Oxygen Vacancy-Rich Co3O4 for Oxygen Evolution Reaction
      Xiao, Zhaohui; Huang, Yu-Cheng; Dong, Chung-Li; Xie, Chao; Liu, Zhijuan; Du, Shiqian; Chen, Wei; Yan, Dafeng; Tao, Li; Shu, Zhiwen; Zhang, Guanhua; Duan, Huigao; Wang, Yanyong; Zou, Yuqin; Chen, Ru; Wang, Shuangyin
      Journal of the American Chemical Society (2020), 142 (28), 12087-12095CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The exact role of a defect structure on transition metal compds. for electrocatalytic oxygen evolution reaction (OER), which is a very dynamic process, remains unclear. Studying the structure-activity relationship of defective electrocatalysts under operando conditions is crucial for understanding their intrinsic reaction mechanism and dynamic behavior of defect sites. Co3O4 with rich oxygen vacancy (VO) has been reported to efficiently catalyze OER. Herein, pure spinel Co3O4 and VO-rich Co3O4 are constructed as catalyst models to study the defect mechanism and investigate the dynamic behavior of defect sites during the electrocatalytic OER process by various operando characterizations. Operando electrochem. impedance spectroscopy (EIS) and cyclic voltammetry (CV) implied that the VO could facilitate the pre-oxidn. of the low-valence Co (Co2+, part of which was induced by the VO to balance the charge) at a relatively lower applied potential. This observation confirmed that the VO could initialize the surface reconstruction of VO-Co3O4 prior to the occurrence of the OER process. The quasi-operando XPS and operando X-ray absorption fine structure (XAFS) results further demonstrated the oxygen vacancies were filled with OH• first for VO-Co3O4 and facilitated pre-oxidn. of low-valence Co and promoted reconstruction/deprotonation of intermediate Co-OOH•. This work provides insight into the defect mechanism in Co3O4 for OER in a dynamic way by observing the surface dynamic evolution process of defective electrocatalysts and identifying the real active sites during the electrocatalysis process. The current finding would motivate the community to focus more on the dynamic behavior of defect electrocatalysts.
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    49. 49
      Reith, L.; Triana, C. A.; Pazoki, F.; Amiri, M.; Nyman, M.; Patzke, G. R. Unraveling Nanoscale Cobalt Oxide Catalysts for the Oxygen Evolution Reaction: Maximum Performance, Minimum Effort. J. Am. Chem. Soc. 2021, 143, 15022– 15038,  DOI: 10.1021/jacs.1c03375
      49
      Unraveling Nanoscale Cobalt Oxide Catalysts for the Oxygen Evolution Reaction: Maximum Performance, Minimum Effort
      Reith, Lukas; Triana, Carlos A.; Pazoki, Faezeh; Amiri, Mehran; Nyman, May; Patzke, Greta R.
      Journal of the American Chemical Society (2021), 143 (37), 15022-15038CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The oxygen evolution reaction (OER) is a key bottleneck step of artificial photosynthesis and an essential topic in renewable energy research. Therefore, stable, efficient, and economical water oxidn. catalysts (WOCs) are in high demand and cobalt-based nanomaterials are promising targets. Herein, we tackle two key open questions after decades of research into cobalt-assisted visible-light-driven water oxidn.: What makes simple cobalt-based ppts. so highly active-and to what extent do we need Co-WOC design. Hence, we started from Co(NO3)2 to generate a precursor ppt., which transforms into a highly active WOC during the photocatalytic process with a [Ru(bpy)3]2+/S2O82-/borate buffer std. assay that outperforms state of the art cobalt catalysts. The structural transformations of these nanosized Co catalysts were monitored with a wide range of characterization techniques. The results reveal that the pptd. catalyst does not fully change into an amorphous CoOx material but develops some cryst. features. The transition from the ppt. into a disordered Co3O4 material proceeds within ca. 1 min, followed by further transformation into highly active disordered CoOOH within the first 10 min. Furthermore, under noncatalytic conditions, the precursor directly transforms into CoOOH. Moreover, fast pptn. and isolation afford a highly active precatalyst with an exceptional O2 yield of 91% for water oxidn. with the visible-light-driven [Ru(bpy)3]2+/S2O82- assay, which outperforms a wide range of carefully designed Co-contg. WOCs. We thus demonstrate that high-performance cobalt-based OER catalysts indeed emerge effortlessly from a self-optimization process favoring the formation of Co(III) centers in all-octahedral environments. This paves the way to new low-maintenance flow chem. OER processes.
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    50. 50
      Reikowski, F.; Maroun, F.; Pacheco, I.; Wiegmann, T.; Allongue, P.; Stettner, J.; Magnussen, O. M. Operando Surface X-Ray Diffraction Studies of Structurally Defined Co3O4 and CoOOH Thin Films During Oxygen Evolution. ACS Catal. 2019, 9, 3811– 3821,  DOI: 10.1021/acscatal.8b04823
      50
      Operando Surface X-ray Diffraction Studies of Structurally Defined Co3O4 and CoOOH Thin Films during Oxygen Evolution
      Reikowski, Finn; Maroun, Fouad; Pacheco, Ivan; Wiegmann, Tim; Allongue, Philippe; Stettner, Jochim; Magnussen, Olaf M.
      ACS Catalysis (2019), 9 (5), 3811-3821CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
      In the search for precious-metal-free electrode materials for electrochem. water splitting, transition-metal oxides have been receiving much recent interest as active and stable electrocatalysts for the anodic oxygen evolution reaction (OER). We present operando surface X-ray diffraction studies of two structurally well-defined epitaxial cobalt oxide thin films: Co3O4(111) and CoOOH(001) electrodeposited on Au(111). The potential-dependent structural changes during cyclic voltammograms were monitored with high time resoln. up to OER current densities as high as 150 mA cm-2. The CoOOH(001) film is found to be smooth and perfectly stable over a wide potential range. In the case of Co3O4(111), fast and fully reversible structural changes are obsd. Specifically, the surface region of Co3O4(111) starts restructuring at potentials 300 mV neg. of the onset of the OER, indicating that the process is related to the thermodynamically predicted Co3O4/CoOOH(001) transition rather than to the catalytic reaction. The formed skin layer is of defined thickness, which changes linearly with applied potential, and is the OER active phase. Surprisingly, the catalytic activity of the skin layer covered Co3O4 film and that of the smooth CoOOH(001) are almost identical, if the true microscopic surface area is taken into account. This indicates that the no. of OER active sites on the two oxides is similar, despite the very different defect d., and is at variance with previous suggestions that di-μ-oxo bridged Co cations are exclusively responsible for the OER activity of Co oxides. For the smooth CoOOH(001), a turnover frequency of 4.2 s-1 per surface atom is detd. at an overpotential of 400 mV. Furthermore, our studies demonstrate that the pseudocapacitive charging current in the pre-OER potential range must be assigned to a bulk process that is accompanied by potential-dependent changes of the unit cell vol. in the Co3O4 bulk.
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    51. 51
      Rehman, A. U.; Fayaz, M.; Lv, H.; Liu, Y.; Zhang, J.; Wang, Y.; Du, L.; Wang, R.; Shi, K. Controllable Synthesis of a Porous PEI-Functionalized Co3O4/rGO Nanocomposite as an Electrochemical Sensor for Simultaneous as Well as Individual Detection of Heavy Metal Ions. ACS Omega 2022, 7, 5870– 5882,  DOI: 10.1021/acsomega.1c05989
      51
      Controllable Synthesis of a Porous PEI-Functionalized Co3O4/rGO Nanocomposite as an Electrochemical Sensor for Simultaneous as Well as Individual Detection of Heavy Metal Ions
      Rehman, Afrasiab Ur; Fayaz, Muhammad; Lv, He; Liu, Yang; Zhang, Jiawei; Wang, Yang; Du, Lijuan; Wang, Ruihong; Shi, Keying
      ACS Omega (2022), 7 (7), 5870-5882CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
      The present study focuses on the strategy of employing an electrochem. sensor with a porous polyethylenimine (PEI)-functionalized Co3O4/reduced graphene oxide (rGO) nanocomposite (NCP) to detect heavy metal ions (HMIs: Cd2+, Pb2+, Cu2+, and Hg2+). The porous PEI-functionalized Co3O4/rGO NCP (rGO·Co3O4·PEI) was prepd. via a hydrothermal method. The synthesized NCP was based on a conducting polymer PEI, rGO, nanoribbons of Co3O4, and highly dispersed Co3O4 nanoparticles (NPs), which have shown excellent performance in the detection of HMIs. The as-prepd. PEI-functionalized rGO·Co3O4·PEI NCP-modified electrode was used for the sensing/detection of HMIs by means of both square wave anodic stripping voltammetry (SWV) and differential normal pulse voltammetry (DNPV) methods for the first time. Both methods were employed for the simultaneous detection of HMIs, whereas SWV was employed for the individual anal. as well. The limits of detection (LOD; 3σ method) for Cd2+, Pb2+, Cu2+, and Hg2+ detd. using the rGO·Co3O4·PEI NCP-modified electrode were 0.285, 1.132, 1.194, and 1.293 nM for SWV, resp. Similarly, LODs of Cd2+, Pb2+, Cu2+, and Hg2+ were 1.069, 0.285, 2.398, and 1.115 nM, resp., by DNPV during simultaneous anal., whereas they were 0.484, 0.878, 0.462, and 0.477 nM, resp., by SWV in individual anal.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.1c24966.

    • Additional experimental details, Laue diffraction, electrochemical OER results, electron microscopy, XPS, and the fitting parameters of EIS (PDF)


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