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Energy, Environmental, and Catalysis Applications

Hydrogen-Assisted Thermal Treatment of Electrode Materials for Electrochemical Double-Layer Capacitors
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  • Matteo Gentile
    Matteo Gentile
    BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
    Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, Milano 20133, Italy
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  • Sebastiano Bellani*
    Sebastiano Bellani
    BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
    *Email: [email protected]
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  • Marilena I. Zappia
    Marilena I. Zappia
    BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
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  • Agnese Gamberini
    Agnese Gamberini
    BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
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  • Valentina Mastronardi
    Valentina Mastronardi
    BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
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  • Matteo Abruzzese
    Matteo Abruzzese
    BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
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  • Luca Gabatel
    Luca Gabatel
    BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
    Department of Mechanical, Energy, Management and Transport Engineering - DIME, Università di Genova, Via all’Opera Pia 15, Genova 16145, Italy
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  • Lea Pasquale
    Lea Pasquale
    Materials Characterization Facility, Istituto Italiano di Tecnologia, Via Morego 30, Genova 16163, Italy
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    Orcidhttps://orcid.org/0000-0002-3919-8873
  • Sergio Marras
    Sergio Marras
    Materials Characterization Facility, Istituto Italiano di Tecnologia, Via Morego 30, Genova 16163, Italy
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  • Ahmad Bagheri
    Ahmad Bagheri
    Graphene Laboratories, Istituto Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy
    Center for Advancing Electronics Dresden (CFAED) & Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, Dresden 01062, Germany
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  • Hossein Beydaghi
    Hossein Beydaghi
    BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
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  • Evie L. Papadopoulou
    Evie L. Papadopoulou
    BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
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    Orcidhttps://orcid.org/0000-0001-5959-9730
  • Guglielmo Lanzani
    Guglielmo Lanzani
    Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, Milano 20133, Italy
    Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia, Via Pascoli 70/3, Milano 20133, Italy
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  • Francesco Bonaccorso*
    Francesco Bonaccorso
    BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
    Graphene Laboratories, Istituto Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0001-7238-9420
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ACS Applied Materials & Interfaces

Cite this: ACS Appl. Mater. Interfaces 2024, 16, 11, 13706–13718
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https://doi.org/10.1021/acsami.3c18629
Published March 8, 2024

Copyright © 2024 The Authors. Published by American Chemical Society. This publication is licensed under

CC-BY-NC-ND 4.0 .

Abstract

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The capacitance of electrode materials used in electrochemical double-layer capacitors (EDLCs) is currently limited by several factors, including inaccessible isolated micropores in high-surface area carbons, the finite density of states resulting in a quantum capacitance in series to Helmholtz double-layer capacitance, and the presence of surface impurities, such as functional groups and adsorbed species. To unlock the full potential of EDLC active materials and corresponding electrodes, several post-production treatments are commonly proposed to improve their capacitance and, thus, the energy density of the corresponding devices. In this work, we report a systematic study of the effect of a prototypical treatment, namely H2-assisted thermal treatment, on the chemical, structural, and thermal properties of activated carbon and corresponding electrodes. By combining multiple characterization techniques, we clarify the actual origins of the improvement of the performance (e.g., > +35% energy density for the investigated power densities in the 0.5–45 kW kg–1 range) of the EDLCs based on treated electrodes compared to the case based on the pristine electrodes. Contrary to previous works supporting a questionable graphitization of the activated carbon at temperatures <1000 °C, we found that a “surface graphitization” of the activated carbon, detected by spectroscopic analysis, is mainly associated with the desorption of surface contaminants. The elimination of surface impurities, including adsorbed species, improves the surface capacitance of the activated carbon (CsurfAC) by +37.1 and +36.3% at specific currents of 1 and 10 A g–1, respectively. Despite the presence of slight densification of the activated carbon upon the thermal treatment, the latter still improves the cell gravimetric capacitance normalized on the mass of the activated carbon only (CgAC), e.g., + 28% at 1 A g–1. Besides, our holistic approach identifies the change in the active material and binder contents as a concomitant cause of the increase of cell gravimetric capacitance (Cg), accounting for the mass of all of the electrode materials measured for treated electrodes compared to pristine ones. Overall, this study provides new insights into the relationship between the modifications of the electrode materials induced by H2-assisted thermal treatments and the performance of the resulting EDLCs.

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Introduction

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Electrochemical double-layer capacitors (EDLCs) are energy storage systems that rely on the electric double-layer formation by means of ion adsorption and swapping of co-ions for counterions at the carbon electrode/electrolyte interfaces. (1) Consequently, basic mechanistic views consider a large specific surface area of electrode materials as a primary requirement to achieve large gravimetric energy densities. (2) In addition, the meso/microporosities of the electrodes must be properly balanced to ensure the access of the electrolyte ions to the pores, avoiding the presence of inaccessible isolated micropores (i.e., blocked pores). (2−4) Despite these general aspects, the capacitance of carbon electrodes also depends on other factors, (5) including: 1) the electronic properties of the carbonaceous materials, i.e., their density of states (DOS), determining their space-charge capacitance (CSC) (6−8) and the quantum capacitance (CQ); (9,10) 2) the electrolyte ions/electrode electron correlations, regulating the ion packing in the electrical double layer at high-specific surface area carbon/electrolyte interfaces; (10) 3) the electrical resistivity associated with the graphitization degree; (11) and 4) the presence of impurities, such as adsorbates, e.g., hydrocarbons (12,13) and water. (14) In this scenario and based on theory-driven guidelines, (8−10) carbon materials with controlled properties have been designed by means of specific syntheses or postproduction treatments to support the leading role of one or more of these factors (sometimes to the detriment of the others) in determining the electrode capacitance.
In this work, we attempt to elucidate the effects of a prototypical H2-assisted thermal treatment of carbonaceous materials (15−20) on capacitance-determining phenomena in electrodes based on commercially available activated carbon as the active material. Driven by previous studies, (17−22) a moderate temperature (≤1000 °C) thermal treatment of the electrode materials in a H2-rich atmosphere was specifically studied to enhance the cell gravimetric capacitance (Cg). Despite it not being the scope of this work, H2-assisted thermal treatment has also been for innovative active materials, including carbide-derived carbons and graphene derivatives, to remove synthesis-derived byproducts (e.g., halogens used for selective carbide etching). (23−25) The combination of compositional, thermal, structural, and gas physisorption characterizations indicates that the H2-assisted thermal treatment is responsible for a stable surface modification of the active materials. Such a modification involves the desorption of physiosorbed species and the stabilization of the active material surface by forming stable C–H bonds involving unsaturated carbons originating from the reduction of oxygen functionalities. Meanwhile, contrary to expectations from previous works, (19,20) no substantial structural modifications of active material take place in terms of graphitic order, even though the specific surface area reveals a densification process. Similar conclusions were also derived in previous studies on carbon nano-onions, whose capacitive properties were mainly attributed to defects such as dislocation, stacking faults, or atom vacancies located in the edges of graphitic structures. (18) In our case, the H2-assisted thermal treatment of the EDLC electrodes led to a significant enhancement of the Cg by 39.4% at 1 A g–1 (38.6% at 10 A g–1) that, despite everything, agrees with previous studies supporting the graphitization of the treated activated carbon. (19,20) More in detail, we show the stable removal of oxygen groups and surface impurities (i.e., “surface graphitization”) in the treated activated carbon surface capacitance of the activated carbon (CsurfAC), as expected for highly graphitic active materials, e.g., nanostructured graphite. (26) Even though a slight densification of the activated carbon occurs during the H2-assisted thermal treatment, the cell capacitance normalized on the mass of activated carbon only (CgAC) still increases compared to that of EDLCs based on untreated activated carbon. In addition, by systematically determining the amount of adsorbed species as well as the binder residues in the treated electrodes compared to pristine ones, it becomes evident that the Cg of EDLCs, accounting for the mass of all the electrode materials, increases because of the higher content of active materials in the thermally treated electrodes. Compared to previous studies, (19,20) this observation leads to a more truthful interpretation of the effect of H2-assisted thermal treatment on the EDLC performances.

Materials and Methods

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Materials

Activated carbon powder (AB-520) was purchased from MTI Corp., while poly(vinylidene fluoride) (PVDF) and N-Methyl-2-pyrrolidone (NMP) were supplied by Sigma-Aldrich. Pyrolytic graphite sheets (Graphite 1000 W mK–1) were purchased from Panasonic.

Materials Characterization

X-ray photoelectron spectroscopy (XPS) analysis was carried out with a Kratos Axis UltraDLD spectrometer, equipped with a monochromatic Al Kα source, operated at 20 mA and 15 kV. Specimens for the XPS measurements were prepared by pressing a few milligrams of powder onto Cu adhesive tape. Wide scans were carried out with an analysis area of 300 μm × 700 μm and a pass energy of 160 eV. High-resolution spectra were collected over the same analysis area at a pass energy of 10 eV. The C KLL Auger spectra were recorded at a pass energy of 40 eV with a step size of 0.1 eV. The Kratos charge neutralizer system was used on all specimens. Spectra have been charge-corrected to the C 1s peak at 284.5 eV for sp2 carbon (C═C) and were analyzed using CasaXPS software (version 2.3.25).
Thermogravimetric analysis (TGA) was performed on material powders with a TGA Q500 (TA Instruments, USA) thermogravimetric analyzer in both N2 and O2 flow from 25 to 870 °C at a heating rate of 10 °C min–1.
Raman spectroscopy measurements were carried out on powders using a Renishaw inVia spectrometer using a 50× objective (numerical aperture 0.75) and a laser with a wavelength of 514.5 nm and an incident power of ∼5 mW. A total of 30 points per sample were measured to perform the statistical analysis of the data. OriginPro 2020 was used to perform Raman peak deconvolution and statistics.
X-ray diffraction (XRD) measurements of material powders were carried out on a Malvern-PANalytical third-generation Empyrean X-ray powder diffractometer. The instrument was equipped with a 1.8 kW CuKα ceramic X-ray tube operating at 45 kV and 40 mA. The diffraction patterns were collected in the air at room temperature, in transmission geometry and 1D mode, using a Cu focusing mirror, a reflection-transmission spinner sample stage (rotation speed = 1 rps), and 7 mm thick mylar foil as the sample substrate.
Specific surface area and porosity measurements of the electrodes were carried out by N2 adsorption at 77 K and Ar adsorption at 87 K with an automated gas sorption analyzer (AutoSorb iQ, Quantachrome Instruments, USA). Prior to measurements, the powder samples were degassed in a vacuum at 250 °C for 4 h to remove any adsorbed species. The Brunauer, Emmett, and Teller (BET) surface area (SBET) was calculated from the N2 isotherms using the multipoint BET method, (27) considering equally spaced points in a relative pressure range, P/P0, from 0.05 to 0.30 with a correlation coefficient exceeding 0.999. The total pore volume (VT) was directly calculated from the volume of N2 held at the highest relative pressure (P/P0 = 0.99), and the micropore volume (VDR) was determined after the application of the Dubinin–Radushkevic (DR) equation (28) to the adsorption data up to P/P0 < 0.1. The quenched solid density functional theory (QSDFT) (29) (implemented into Quantachrome’s data reduction software) was applied to the Ar adsorption data using a slit-shape model to describe the pore size distribution (PSD) of the samples.
Zeta potential measurements were carried out with a Malvern Instruments Zeta Sizer Nano ZS system (Malvern, U.K.). The measurements for zeta potential of pristine and treated activated carbon were performed in water/acetonitrile (70:30 vol/vol) at 25 °C.

Electrodes Fabrication and H2-Assisted Thermal Treatment

Commercial activated carbon, few-layer graphene (FLG, BeDimensional S.p.A.), produced by wet-jet milling exfoliation of graphite, (30−34) and PVDF were mixed with an 80:10:10 weight ratio in NMP (1:3 solid/liquid weight content ratio) using a planetary centrifugal mixer until obtaining a homogenized slurry. (35−37) The as-produced slurry was subsequently deposited onto a pyrolytic graphite sheet by doctor blading using a MSK-AFA-H200A coater (MTI Corp.) and dried at 70 °C in a vacuum oven (Binder, VD 53-UL) overnight to remove solvent residues. In the resulting EDLC electrodes, the mass loading of the electrode materials was ∼4 mg cm–2 to be compatible with practical requirements, as recommended in ref (38). The H2-assisted thermal treatment of the electrode materials and the electrodes was conducted for 2 h at different temperatures (i.e., 500, 600, 700 and 800 °C, temperature ramp = 10 °C min–1) in a three-zone split furnace (PSC 12/600H, Lenton, Hope, UK). The pressure of the chamber was set to 20 Torr via a homemade valve-controlling system, keeping a 100 sccm flow of a H2:Ar 10:90 vol/vol gas mixture as controlled upstream through an array of mass flow controllers (1479A, MKS Instruments, Andover, MA, USA). After the treatment, the furnace was left to cool to room temperature.

Electrochemical Double-Layer Capacitor Fabrication

The EDLCs were fabricated by stacking two electrodes in a Swagelok-type cell based on 316L stainless steel pistons, a polytetrafluoroethylene insulating body, and fluorelastomer sealing rings by using a glass fiber membrane (Whatman glass microfiber filter) as the separator. The electrolyte was formulated inside a N2-filled glovebox (MBRAUN UNIlab) by mixing tetraethylammonium-tetrafluoroborate (TEABF4) salts in acetonitrile to a 1 M concentration.

Electrochemical Characterization

Electrochemical measurements of the EDLCs were performed at room temperature using a potentiostat/galvanostat (VMP3, Biologic) station controlled via its own software. Cyclic voltammetry (CV) measurements were performed at various voltage scan rates, from 5 to 1000 mV s–1, after 10 preconditioning cycles at 100 mV s–1. Once the CVs were completed, galvanostatic charge/discharge (GCD) curves were collected at specific currents ranging from 0.05 to 50 A g–1. The Cg of the EDLCs was calculated from the GCD profiles as Cg = (I × td)/(ΔV × m), in which I is the applied current, td is the discharge time, ΔV is the voltage window, and m is the mass of the electrode materials of both electrodes. The energy and power density of the EDLCs were calculated using integral equations that consider the nonlinearity of the GCD profiles, as discussed in refs (35,39,and40).

Results and Discussion

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Relationship between Active Material Properties and Electrode Capacitance

The interfacial capacitance of the carbon electrode/electrolyte interface has been modeled by the series of different capacitances, C–1 = Cdiff–1 + CH–1 + CX–1, in which Cdiff is the capacitance of the diffusive layer of the electrical double layer, CH is the Helmholtz double-layer capacitance, and quantum/space-charge capacitance (CX) includes the CSC (6−8) and the CQ of the electrode active materials. (10) More in detail, the series between CH and Cdiff forms the electrical double-layer capacitance (CEDL). CX accounts for the variation of Fermi energy with charge accumulated in the electrode close to its surface (10) and is often considered the contribution limiting the overall capacitance of graphitic electrodes. (10) In single-layer graphene, CX is given by CQ as determined by the linear dispersion of the Dirac cone structure, leading to small capacitance near charge neutrality corresponding to the potential of zero charge and the characteristic “V shape” of the capacitance as a function of applied voltage. In multilayer graphene, CX has been modeled in ref (10) by coupling the Poisson–Schrodinger equations to consider both CQ and CSC. Even if CX increases with the number of graphene layers, the electrostatic correlation effects between the π-band electron Fermi liquid and ions in the Helmholtz layer can instead lead to an enhancement of the interface capacitance with a decreasing number of layers, as in the case of single-layer graphene. (10) Despite the advent of advanced graphene-based active materials, (41) the most common electrode material for EDLCs is activated carbon due to its high surface area, tunable porosity, and scalable synthesis by means of either thermal or chemical activation processes. (42) Activated carbon is composed of randomly oriented single-layer graphene and graphitic layers (e.g., few-/multilayer graphene) without exhibiting a long-range three-dimensional order. (43) Based on these general considerations and experimental studies from our group, (3,4,35) a mixture of activated carbon and single/few-layer graphene, produced by the wet-jet milling exfoliation method, (30−32) was used in this work as the highly conductive high-surface area carbon network.
Beyond the above-discussed capacitance contribution, although often neglected in consolidated capacitance models, surface impurities, including adsorbed species, such as hydrocarbons and water, can also form a dielectric layer on carbon materials, leading to an additional capacitance (Ci) limiting the overall C. (12,44) Figure 1a shows an electrical equivalent circuit that can be used for the carbon electrode/electrolyte interfacial region, including the capacitance contribution discussed above, which is schematized in Figure 1b. The circuit is similar to those reported in previous literature, (45) but it includes Ci, in series to CEDL2, given by the electrical double-layer formed at the impurities-covered electrode materials/electrolyte interface. The electrical resistivity associated with the graphitization degree of the carbon active materials has been also considered as a universal parameter regulating their CQ. (11) Importantly, the effect of the electrical resistivity on the overall C has also been observed in pioneering works on ordered graphitic materials with anisotropic electric properties, showing that the edge of graphite exhibits a C 1 order of magnitude higher than that of graphitic basal planes. (47,48) In this context, experimental studies reported moderate temperature (≤1000 °C) thermal treatments in H2-rich atmosphere to induce a graphitization of activated carbons, improving the overall Cg and the cyclic stability of the resulting EDLCs. (19,20) Furthermore, these treatments have been recently reported to improve the capacity and rate capability of graphene-like graphite anodes for Li-ion batteries. (15,16) Meanwhile, temperature-programmed reduction experiments revealed that activated carbons start reacting with H2 at a temperature higher than 400 °C, completing the reaction at ca. 800 °C. (22) Contrary to annealing in N2, the H2-assisted thermal treatment is effective not only for removing oxygen groups (e.g., COOH, C═O, and C–O–C) (49) but also for eliminating and stabilizing unsaturated carbon atoms by hydrogasification and forming C–H bonds (hydrogenation), respectively. (49) Thus, H2-assisted thermal treatment was selected in this work as a case treatment of electrode materials to enhance the electrochemical performances of carbon electrodes for EDCLs, with the aim of elucidating the role of the above-discussed phenomena that determine the performance of an EDCL (Figure 1c).

Figure 1

Figure 1. (a) Electrical modeling of the electrode/electrolyte interface, including various capacitances contributing to the overall interfacial capacitance. The capacitance associated with the impurity-free electrode material/electrolyte interface is modeled as CEDL1, while the capacitance of the impurity-covered electrode material/electrolyte is represented by CEDL2. Beyond the capacitance terms associated with the dielectric layer of surface impurities, i.e., Ci and CX, the electrical equivalent circuit includes the leakage resistance (RLEAK) associated with self-discharge processes. Other impedance elements completing the modeling of the whole EDLC (e.g., ZW, CC/E, RC/E, etc...) are discussed in the relevant literature. (45,46) (b) Sketch of the Dirac cone electronic structure of the graphene, the Helmholtz double-layer, and dielectric layer atop active materials determining CQ, CH, and Ci, respectively. (c) Sketch of the furnace used for H2-assisted thermal treatment of electrode materials, which were initially supposed to undergo graphitization and/or cleaning processes.

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Chemical, Structural, and Electrochemical Characterization of the Electrode Materials

As detailed in the Materials and Methods section, the active materials of the EDLC electrodes were obtained by mixing commercial activated carbon with FLG, produced by wet-jet milling exfoliation of graphite, (30−32) and PVDF binder, following the procedures reported in our previous studies. (3,4,35)
The material weight ratio of activated carbon, FLG, and PVDF was 80:10:10. Despite this, the electrode formulation has a limited weight content of active material (80 wt % vs. > 90 wt % used in commercial EDLCs) and is not intended for high-energy density EDLCs. It has been used in this work to assess the effects of the H2-assisted thermal treatment on electrode materials commonly established for EDLC applications. (3,4,35) The effects of H2-assisted thermal treatment on the surface chemistry of the electrode materials were evaluated by XPS measurements. Hereafter, untreated samples are named pristine, while H2-500 °C, H2-600 °C, H2-700 °C, and H2-800 °C indicate the samples thermally treated in a H2:Ar 90:10 vol/vol mixture (flow rate = 100 sccm) at 500, 600, 700, and 800 °C, respectively. The survey spectra of the investigated electrode materials (Figure S1) exhibit characteristic peaks for C 1s, O 1s, and F 1s arising from active and/or conductive materials (activated carbon, graphene, and carbon black) and PVDF. The atomic content (at. %) of C, O, and F is reported in Figure 2a and Table S1. The at. % of O and F are significantly reduced after H2-assisted thermal treatments, which consequently increases the at. % of C. Also, the at. % of O and F decreases with increasing temperature of the thermal treatment from 500 to 800 °C. At the highest temperature of 800 °C, F is completely removed via the formation of volatile HF, (50,51) and the at % of O is as low as 0.7. This preliminary analysis indicates that the H2-assisted thermal treatment effectively decomposes the binder and, more importantly, eliminates surface impurities. The latter may include either functional groups or amorphous carbon, which, in turn, may be linked to the presence of adsorbed carbonaceous species, e.g., hydrocarbons (adventitious carbon). (12,13) High-resolution C 1s, O 1s, and F 1s XPS spectra were then acquired, as shown in Figure S2 for a pristine sample, to evaluate the at % of the functionalities based on the detected elements. The C 1s spectra were deconvoluted into nine peaks at 283.7 ± 0.2 eV, 284.5 ± 0.2 eV, 285.0 ± 0.2 eV, 286.5 ± 0.2 eV, 287.9 ± 0.2 eV, 288.9 ± 0.2 eV, 289.3 ± 0.2 eV, 290.0 ± 0.2 eV, and 290.9 ± 0.2 eV. These peaks correspond to C vacancies, C═C (sp2-hybridized carbon), C–C (sp3-hybridized carbon), C–O (hydroxyl), C═O (carbonyl), O═C–O (carboxyl), R–(CO)–O–(CO)–R, R-O–(CO)–O-R, and the π–π* satellite peak, respectively. (52,53) Their atom %, with respect to C, is reported in Table S2. The spectra of the pristine, H2-500 °C and H2-600 °C samples comprise four additional peaks associated with the PVDF binder and located at 285.9 ± 0.2 eV (attributed to the CH2 group), 290.5 ± 0.2 eV (CF2–CH2), 291.5 ± 0.2 eV (CF2–CF2), and 292.8 ± 0.2 eV (CF3). (53,54) Figure 2b shows the at % of C-based functionalities, referred to as the sum of the contents of detected elements, evidencing that the at. % of components associated with PVDF gradually decreases with increasing temperature up to 600 °C and approaches 0 at. % for H2-700 °C and H2-800 °C samples. The latter samples show the highest contents of sp2-hybridized C (C═C) (68.3 and 69.5 at. %, respectively) and the lowest content of sp3-hybridized C (C–C) (4.8 and 5.1 at. %, respectively). The O 1s spectra of the investigated samples were deconvoluted into four main components, the main two corresponding to C═O (531.3 ± 0.2 eV) and the O–C═O/–OH (533.4 ± 0.2 eV) groups (Figure S2). The two peaks at 535.4 ± 0.2 and 538.0 ± 0.2 eV, labeled O–Fa and O–Fb, respectively, and featured by pristine, H2-500 °C, and H2-600 °C samples, are assigned to O bonded to a highly electronegative F to form O–F bonds. (55,56) This consequently results in the appearance of two peaks in the corresponding F 1s spectra at 691.0 ± 0.2 and at 693.2 ± 0.2 eV, labeled F–Oa and F–Ob (Figure S2). (56) The other two components in the F 1s spectra, at 687.5 ± 0.2 and at 689.0 ± 0.2 eV, assigned to CF2 and CF2–CF2 groups, respectively, are associated with the PVDF. (54,56) Furthermore, the O-based functionalities derived from the O 1s spectra are reported in Table S3, while Figure 2c shows the at. % of the O-based groups referred to as the sum of the contents of detected elements. Clearly, the O-based groups are progressively removed with the increase of the annealing temperature. In order to determine the at. % of C sp2 and sp3, we have used the parameter D, defined as the energy distance between the minimum and maximum of the first derivatives of the X-ray excited Auger spectra (XAES C KLL). (53,54,57,58) In detail, the linear interpolation of the parameter D values for graphite and diamond allows for evaluation of the C sp2/sp3 at. % in carbon materials, in which, qualitatively, the higher the parameter D, the higher the at. % of C sp2. (53,54,57,58) As shown in Figure 2d, parameter D increases from 20.8 eV for the pristine sample up to 22.4 eV for H2-800 °C, indicating that, at the surface of the electrode materials, the content of sp2-hybridized C increases with increasing annealing temperature. In previous studies, (59) parameter D values between 21.5 and 23.1 eV have been ascribed to “clean” graphite obtained by cleaving pyrolithic graphite under ultrahigh vacuum conditions. Following exposure to ambient conditions, the parameter D values of pyrolytic graphite decreased, indicating possible surface contamination. Noteworthily, the information depth (ID), i.e., the thickness of the layer from which a given percentage (P) of the detected signal electrons originates, ID (P = 99%) for C KLL Auger electrons (<4 nm) is more than two times smaller than that of C 1s photoelectrons (∼9.7 nm for Al Kα X-rays). (57) Therefore, parameter D can be more sensitive to surface contamination compared to the C 1s signal. Table S4 reports the C sp2 at. % deduced from the analysis of parameter D according to the linear interpolation proposed by Lascovich et al. (who measured parameter D values of 13.2 eV and 23.1 eV for diamond and graphite, respectively). (57,58) Hereafter, we show, in agreement with literature, (60) that surface graphitization may also be associated with the removal of adsorbed species (e.g., hydrocarbons), which may instead remain in the pristine sample even when subjected to the ultrahigh vacuum (∼10–10 Torr) of the XPS chamber. (60)

Figure 2

Figure 2. (a) Elemental composition of the electrode materials before and after H2-assisted thermal treatment at various temperatures (from 500 to 800 °C). (b) C and (c) O functionalities at. % (normalized on the overall C and at. %, respectively) of the investigated electrode materials. The data have been estimated from the analysis of the XPS spectra (wide scan, C 1s, and O 1s spectra). (d) First derivative of the XAES C KLL spectra (parameter D) of the investigated electrode materials.

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Based on the XPS results, TGA measurements were performed to further assess the effects of the H2-assisted thermal treatment on the activated carbon, under either N2 or O2 flow, determining the weight losses attributed to adsorbed species, functional groups, and carbon decomposition. Figure 3a shows the thermographs measured under a N2 flow for the investigated samples. The weight loss at temperatures inferior to 100 °C is ascribed to the loss of adsorbed water (moisture). (61) The weight loss occurring above 100 °C is due to the decomposition/volatilization of oxygen functionalities (62) and nongraphitic carbons, (63) as well as to the desorption of adsorbed species, e.g., hydrocarbons in the 100–600 °C temperature range. (64) The pristine sample shows a high adsorbed water content (∼13.7%), which was reduced to less than 3% after the H2-assisted thermal treatments. Clearly, in preparing an electrode material mixture, the presence of moisture in the pristine material may cause underweight issues with the activated carbon, leading to an electrode composition different from the targeted one, as discussed later. In addition, the pristine sample shows significant weight loss associated with the elimination of oxygen functionalities or adsorbed species (11.9% at 310 °C). This weight loss is almost negligible in the treated samples, in agreement with the oxygen removal observed by XPS analysis. Figure 3b shows the thermographs of the investigated materials measured under an O2 flow. The weight losses are associated with adsorbed water elimination (<100 °C), decomposition of oxygen functionalities, and desorption of adsorbed species such as hydrocarbons (≥100 °C, typically less than 500 °C) and carbon combustion (typically >350 °C). (61,64,65) The weight loss associated with adsorbed water is 16.3%, higher than the one observed under N2 flow. In the treated samples, the weight loss associated with adsorbed water elimination is less than 2%. Between 100 and 450 °C, the pristine sample shows weight losses attributed to the elimination of oxygen functionalities and adsorbed species. These weight losses are not observed in the treated samples. Importantly, H2-assisted thermal treatment stabilizes reactive sites by forming stable C–H bonds, (49) which impede subsequent adsorption processes in ambient conditions. The TGA data also show a weight gain of the treated samples at temperatures between 180 and 420 °C (inset panel of Figure 3b), suggesting that O2 can react with reactive unsaturated C atoms. (22,49) The latter is likely formed by reductive deoxygenation processes induced by H2-assisted thermal treatments. However, this weight increase is less than 1%, confirming that H2-assisted thermal treatment stabilizes reactive sites by forming stable C–H bonds. (49)

Figure 3

Figure 3. TGA curves measured in (a) N2 and (b) O2 for activated carbons before (pristine) and after H2-assisted thermal treatments at various temperatures (H2-500 °C, H2-600 °C, H2-700 °C, and H2-800 °C).

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Notably, in the C 1s XPS spectrum (Figure 2b), C–H bonds exhibit the same binding energy as the C–C bonds, impeding reliable quantification. Previous studies supported the idea that the carbon surface resulting from H2-assisted thermal treatment shows stable basic properties, contrasting subsequent adsorption processes in ambient conditions. (49) A pronounced carbon combustion is observed at temperatures above 450 °C, similar to highly defective graphitic samples, including activated carbons. (65) The kinetics of the combustion reaction are faster for treated samples. This is consistent with experimental studies on graphene derivatives. (62,65) XRD and Raman spectroscopy measurements were carried out to further evaluate the structural changes of the electrode materials after various H2-assisted thermal treatments. Considering the microporous morphology of the activated carbon, the removal of oxygen functionalities should be inevitably associated with structural changes, as shown in previous studies on graphitic structures. (15) According to other works, (19,20) H2-assisted treatment could allow a low-temperature graphitization of porous carbons, whose porosity would increase at temperatures below 1000 °C. The use of an H2-rich reductive atmosphere was considered the key in avoiding the reduction of surface area and porosity that takes place during graphitization processes in inert gases. (19,20) In principle, the use of H2 for the synthesis of porous graphitic structures renders unnecessary the complex multistep processes involving sacrificial templates, such as polymers, nanostructured oxides (e.g., SiO2, MgO, and ZnO), (66,67) layered hydroxydes, (68) and salts, which hinder the densification of carbons during their graphitization. (69) Also, H2 may catalyze the graphitization processes at low-temperature, (19,20) without requiring the use of metal (e.g., Ni, Fe, Co, and Mo)-based catalysts, (70,71) which then require purification steps for their removal. However, the effect of H2-assisted thermal treatments on the structure of carbon materials is still under debate, and other experimental studies have supported negligible differences between pristine and H2-treated activated carbons. (72) Figure 4a shows the Raman spectra measured for the pristine and thermally treated samples. In all samples, the spectra show distinct peaks located at ca. 1343 and 1599 cm–1, corresponding to the D and G bands of nonordered graphitic structures in the activated carbon. (43,73) In general, the G peak corresponds to the in-plane bond-stretching motion of the pairs of C atoms in sp2 configuration with E2g symmetry (E2g optical mode at the Brillouin zone center). (74−77) This mode occurs at all sp2 sites, and not only for the atoms located in the 6-fold aromatic C rings. (74−77) The D peak is a breathing mode of sp2 rings with A1g symmetry and refers to a defective graphitic material, where defect-induced double resonance Raman scattering processes involve the electronic π–π* transitions. (74−76) Based on the interpretation of the G and D peaks, the ratio between the intensity of the D and G peaks (I(D)/I(G)) can be used to approximately evaluate the graphitization degree of porous carbons, including activated carbon. (75,76) As shown in Figure 4b, the H2-assisted treatment of the samples slightly decreases the I(D)/I(G), from 1.19 to a minimum of 1.07 for the annealing temperature of 600 °C, suggesting a negligible increase in the graphitization degree of the treated activated carbon compared to the pristine one. This seems to be in contrast with our XPS analysis (Figure 2d), which, however, is more sensitive to the sample surface as well as to amorphous species.

Figure 4

Figure 4. Structural characterization of the activated carbon before (pristine) and after the H2-assisted thermal treatments at various temperatures (H2-500 °C, H2-600 °C, H2-700 °C, and H2-800 °C). (a) Raman spectra and (b) I(D)/I(G) vs. annealing temperature plot measured for the investigated samples. (c) XRD patterns measured for the investigated samples. (d) N2 adsorption/desorption isotherms measured for the investigated electrode materials, before (pristine) and after H2-assisted thermal treatments at various temperatures (H2-500 °C, H2-600 °C, H2-700 °C, and H2-800 °C). The inset panel shows the PSD, calculated by applying QSDFT to the Ar adsorption data at 87 K, for the investigated electrode materials.

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In agreement with the Raman spectroscopy data, analysis of the XRD patterns of the investigated samples reveals similar patterns, regardless of the thermal treatment process (Figure 4c). More in detail, the XRD patterns exhibit two main reflection peaks at 2θ of 23.8 and 43.8°, which are attributed to (002) and (100) reflections of graphitic domains, respectively. From the broadening of the (100) peak, the mean lateral size of the graphitic domains (La) can be estimated, while the number of graphene sheets in the domains (N) is correlated to the width of the (002) peak. (78)
Pioneering work showed that, in activated carbons, the decrease in La is correlated to an increase in their capacitance. (43) Thus, it has been suggested that defects located at the edges of the graphitic domains have a significant capacitance contribution. (18) However, the diffractograms of the investigated samples do not present any difference that would indicate structural modifications of the starting activated carbon after H2-assisted thermal treatment, which may instead be expected by the interpretation of the XPS and TGA data. To further evaluate the effects induced by the H2-assisted thermal treatment on the properties of the electrode materials, N2 adsorption measurements at 77 K were carried out to estimate the surface area, total pore volume, and micro- and mesopore volumes of the investigated EDLC electrodes. The estimation of the micropore size in the samples was carried out by Ar adsorption at 87 K. (29) In fact, Ar adsorption in narrow carbon micropores takes place at a higher relative pressure compared to N2 due to a weaker effective adsorption potential, i.e., the absence of specific interactions between Ar and the activated carbon surface. (29) Table S5 lists the main parameters extrapolated by the N2/Ar adsorption data. Figure 4d compares the N2 adsorption–desorption isotherms for the investigated electrode materials. Based on the International Union of Pure and Applied Chemistry (IUPAC) classification, all the isotherms can be classified as Type I with a narrow micropore size distribution. (29,79) The Brunauer SBET of the investigated electrode materials decreases from 1924 m2 g–1 in the pristine sample to a minimum value of 1752 m2 g–1 for H2-700 °C (Table S5). The SBET trend is different from those reported in previous studies on carbonaceous active materials treated in a H2-rich atmosphere. The superior electrochemical performance of the treated materials compared to native ones was attributed both to an SBET increase and surface graphitization. (19,20) In our case, the densification of the treated materials is reasonably associated with the elimination of oxygen functionalities, followed by the formation of C–H bonds. The PSD curves of the investigated electrode materials (Figure 4d, inset), obtained by applying the QSDFT to the Ar adsorption data at 87 K, indicate that the samples exhibit a microporous structure without remarkable changes in the size of the micropores. As summarized in Table S5, the VT and the VDR obtained from the N2 adsorption data, as well as the micropore volume (Vt) and the average micropore width (L) obtained from the Ar adsorption data, decrease after the H2-assisted thermal treatments, which is consistent with the trend observed for SBET. The slight discrepancy observed between VT and Vt (lower values for Vt) is likely due to different pore-filling mechanisms of the adsorptive for N2 and Ar adsorbents, as associated with adsorption of Ar on a carbonaceous surface weaker than that of N2. (29)
The combination of our chemical, thermal, structural, and gas adsorption characterizations supports the fact that the H2-assisted thermal treatment is effective in removing surface impurities, which are mainly adsorbed species. The latter has been determined in previous studies, (44) and the rapid kinetics of their adsorption on an ideally flat graphitic surface lead to saturated coverage over an hour-time scale. (60,80) The presence of defective graphitic structures, such as those exhibited by activated carbon, can further accelerate the contaminant adsorption processes. (80) However, the porous morphology of activated carbon can significantly slow down the contaminant absorption/desorption kinetics. Consequently, the readsorption of atmospheric contaminants onto treated activated carbons may be prevented on a day-time scale. The elimination of oxygen groups by a H2-assisted treatment does not substantially alter the structural properties of the activated carbon, even though the introduction of C–H bonds can stabilize the surface chemistry by impeding subsequent adsorption processes in ambient conditions, (49) as evidenced by both XPS and TGA analyses.
Zeta potential measurements of pristine and treated activated carbon (H2-700 °C) were carried out to evaluate their surface charge. In the water/acetonitrile (70:30 vol/vol), the pristine sample shows a negative zeta potential (−24.8 mV), which turns positive after H2-assisted thermal treatment (12 mV), indicating a basic surface. The latter is likely associated with Lewis basic sites assigned to π electron-rich graphitic regions, (22) in accordance with our XPS analysis. Notably, despite the effects induced by the H2-assisted thermal treatment, contact angle measurements with a prototypical organic electrolyte (1 M TEABF4 in acetonitrile, as studied hereafter) showed optimal wettability for both pristine and treated electrodes. The electrolyte drops completely spread out on the surface of the electrodes, meaning contact angles of 0°.
To further illustrate the effects of the H2-assisted thermal treatment on the electrochemical behavior of the electrode materials in EDLCs based on 1 M TEABF4 in acetonitrile as the electrolyte, CV and GCD measurements were carried out on symmetric EDLCs based on pristine and treated electrodes (hereafter named similarly to the material samples, i.e., pristine, H2-500 °C, H2-600 °C, H2-700 °C, and H2-800 °C). Figure 5a shows the CV curves measured for the investigated EDCLs at a voltage scan rate of 500 mV s–1. The quasi-rectangular shape of the CV curves confirms the capacitive behavior of the EDLCs. Importantly, the H2-assisted thermal treatments increase the capacitive current of the EDLCs, with maximum values recorded for H2-700 °C. In general, the current density of the EDLCs increases with increasing voltages, leading to the appearance of the so-called butterfly-shaped CV curves commonly shown for devices based on active carbonaceous materials. (10,11) This effect, resulting in the characteristic “V shape” of the CQ as a function of voltage, is generally attributed to the potential-dependent DOS of graphitic materials, i.e., their charge carrier density increases with the position of the Fermi level within the DOS (electrochemical doping). (10,11) Nevertheless, similar effects may also originate from the dielectric layer made of surface impurities, including adsorbed species, leading to Ci. (12,44) Importantly, the effects of the adsorbed species on the capacitance of the activated carbon have been scarcely reported, (12,44) even though they may form a dielectric layer that may limit the overall capacitance of the active materials. Figure 5b reports the GCD profiles measured for the EDLCs at a specific current of 1 A g–1. The triangular shape of the profiles further confirms the capacitive behavior of the EDLCs. The highest discharge time was recorded for the H2-700 °C electrode, which is consistent with our CV analysis. Figure 5c shows the Cg measured for the EDLCs as a function of the specific current, as calculated from the GCD curves. All the devices show excellent rate capabilities, indicating low internal areal resistance (<0.9 Ω cm2). The latter, corresponding to the equivalent series resistance (ESR) multiplied by the electrode geometric area, was estimated by the voltage drops (Vdrop) at the initial stage of charge and discharge, being associated with the resistive losses, i.e., Vdrop = 2I × ESR, where I is the applied current. Figure 5d shows the energy density vs. power density plot (i.e., Ragone plot) extrapolated from the GCD data. The H2-700 °C electrode showed the highest energy density and the best rate capability among the investigated EDCLs, reaching energy densities of 17.2 and 10.6 W h kg–1 at the power density of 1.2 and 40.2 kW kg–1, respectively. These energy densities represent an improvement of 36.9 and 47.3%, respectively, compared to those measured for EDLC based on pristine electrodes. By increasing the temperature of the H2-assisted thermal treatment to 800 °C, the rate capability of the resulting EDLC decreased compared to the optimal case (H2-700 °C). This behavior is likely due to the worsening of the adhesion of the electrode materials to the graphitic substrate used as the current collector, even causing, in some cases, the entire delamination of the electrode material coating. The electrochemical results indicate that the H2-assisted thermal treatment at the optimal temperature, i.e., 700 °C, is an effective route to improve the overall performance of the EDLCs, in accordance with previous works. (19)

Figure 5

Figure 5. (a) CV curves (voltage scan rate = 500 mV s–1) and (b) GCD profiles (specific current = 1 A g–1) measured for the investigated ELDCs (pristine, H2-500 °C, H2-600 °C, H2-700 °C, and H2-800 °C). (c) Cg of the investigated EDLCs as a function of the specific current (data extrapolated from the analysis of the GCD profiles). (d) Ragone plots measured for the investigated EDLCs.

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At first instance, this behavior could be associated with an increase in the electrochemical performances of the active materials, i.e., activated carbon. However, this deduction may be simplistic since it does not consider that the percentage content of active materials in the final electrode formulation significantly increases after the H2-assisted treatment. In fact, the PVDF binder is decomposed at high temperatures and lost in the form of volatile products, as shown by our XPS analysis (F atom % = 0 for H2-700 °C and H2-800 °C samples). As shown in the literature, PVDF undergoes thermal degradation at temperatures higher than 500 °C, initiated by the carbon–hydrogen scission, which is followed by H–X elimination (dehydrohalogenation) (50,51) and complex reactions, e.g., polyaromatization. (20,50,51) A second degradation mechanism, namely homolytic scission, originated from the backbone scission with the formation of halogenated or oxygenated compounds, monomers, H–F, and other alkyl radicals. (50,51) In an inert atmosphere, these degradation processes lead to PVDF weight losses higher than 70% at temperatures higher than 500 °C. (50) Also, the presence of adsorbed species in pristine activated carbon can result in an underestimation of the weight of activated carbon during the formulation of the corresponding slurries used for electrode preparation. Consequently, the content of the activated carbon in the electrode is reduced from the targeted value of 85.0 to 76.2 wt %, assuming a content of adsorbed water of 13.7 wt %, as estimated by TGA in N2. In this case, the actual PVDF content would be ∼11.6%. If adsorbed carbonaceous species are also considered and their content is estimated at around 16.2 wt % from TGA N2 (excluding reduction of functionalities present on the activated carbon), the activated carbon content can deviate further from the targeted value of 80.0 wt %, decreasing to 71.6 wt %, while leading to a PVDF content of ∼14.2%. In addition, according to literature studies, (50,51) it is reasonable to assume that, after the H2-assisted thermal treatment, ∼80% of the initial PVDF content is lost in the form of volatile products in the most performant electrodes, i.e., H2-700 °C.
Figure 6a shows the gravimetric capacitances for pristine and H2-700 °C EDCLs obtained by normalizing the cell capacitance on the total mass of the activated carbon only (metric hereafter referred to as CgAC) as a function of the specific current, calculated considering two cases: (1) 13.7 wt % of adsorbed water in the pristine activated carbon powder, removed after the H2-assisted thermal treatment together with 80 wt % of PVDF; (2) 29.9 wt % of various adsorbed species (including water and carbonaceous species) in the pristine activated carbon powder, removed after the H2-assisted thermal treatment together with 80 wt % of PVDF. These data support that the H2-assisted treatment effectively increases CgAC (e.g., by ∼+28% at 1 A g–1 for case 2), as expected from the elimination of the double layer of surface impurities associated with Ci (limiting the overall C). (12,44) The similar rate capability of the EDLCs may be associated with similar PSDs of the corresponding electrodes (see the inset panel of Figure 4d), which also exhibited similar electrical resistivities (Figure S3). According to previous work, (11) the removal of surface impurities (including oxygen functionalities and adsorbed species), leading to “surface graphitization”, should improve the CsurfAC, calculated as CsurfAC = 4 × CgAC/SBET (CgAC values herein taken from case 2). Figure 6b shows the CsurfAC in pristine and H2-700 °C EDLCs. Importantly, these data reveal that H2-assisted thermal treatment improves the CsurfAC by 37.1 and 36.3% at the specific currents of 1 and 10 A g–1, respectively. Overall, by focusing on the specific performance of the activated carbon, our analysis indicates that the improvement of the electrochemical performances of the treated electrodes compared to the pristine ones is actually associated with 1) the higher content of active materials, being most of the binder content volatilized and moisture and contaminants desorbed during the H2-assisted thermal treatment; and 2) the higher CsurfAC as a consequence of the elimination of the dielectric layer made of surface impurities (thus, the canceling of Ci contribution). In the overall EDLC CgAC, the CsurfAC improvement is counterbalanced by a slight densification of the AC, expressed as a decrease of its SBET. However, the trade-off between “surface graphitization” and densification effects still results in a significant increase of the CgAC after the thermal treatment.

Figure 6

Figure 6. (a) CgAC of the pristine and H2-700 °C EDLCs as a function of the specific current. Case 1 refers to data calculated considering 13.7 wt % of adsorbed water in the pristine activated carbon powder and the removal of 80 wt % of PVDF after the H2-assisted thermal treatment. Case 2 refers to data calculated assuming 29.9 wt % of adsorbed species (including water and carbonaceous species) in the pristine activated carbon powder and the removal of 80 wt % of PVDF after the H2-assisted thermal treatment. (b) Comparison between CsurfAC of pristine and H2-700 °C EDLCs at 1 and 10 A g–1.

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Conclusions

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In summary, we have systematically evaluated the effect of the H2-assisted thermal treatment, performed at temperatures ranging from 500 to 800 °C, on the properties of the carbonaceous electrode materials, aiming at determining possible correlations of their surface chemistry and structural characteristics with the electrochemical performances of the corresponding EDLCs using conventional organic electrolytes (1 M TEABF4 in acetonitrile). This study was inspired by previous reports, (17−20) reporting contradictory conclusions regarding the effects of H2-assisted thermal treatment and calling for a systematic study to clarify controversial aspects. We show that, by optimizing the temperature of the H2-assisted thermal treatment of the electrodes, the resulting EDLCs can achieve an enhancement of the energy density higher than 35% for power densities in the 0.5–45 kW kg–1 range. The combination of multiple characterization techniques, including compositional, thermal, and structural characterizations, allows us to clarify the actual origins of this remarkable EDLC performance improvement. The removal of surface impurities, including adsorbed species, significantly improves the CsurfAC. The trade-off between chemical (“surface graphitization”) and structural (densification) effects upon the thermal treatment still results in a significant increase in the CgAC. Besides, as proved by an accurate calculation of the actual contents of the electrode materials, the increase of the active material and the decrease of the binder contents are also primary causes of the increase of Cg after the thermal treatment of the electrodes. Overall, our study sheds light on the effects of the H2-assisted thermal treatment on activated carbon-based electrodes for EDLCs, clarifying the origin of discordant conclusions reported in the previous literature.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.3c18629.

  • Supplementary XPS, electrical resistivity and gas physisorption measurements, and analyses of electrode materials and electrodes (PDF)

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Author Information

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  • Corresponding Authors
    • Sebastiano Bellani - BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy;  Email: [email protected]
    • Francesco Bonaccorso - BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy;  Graphene Laboratories, Istituto Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy;  Orcidhttps://orcid.org/0000-0001-7238-9420;  Email: [email protected]
  • Authors
    • Matteo Gentile - BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy;  Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, Milano 20133, Italy
    • Marilena I. Zappia - BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
    • Agnese Gamberini - BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
    • Valentina Mastronardi - BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
    • Matteo Abruzzese - BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
    • Luca Gabatel - BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy;  Department of Mechanical, Energy, Management and Transport Engineering - DIME, Università di Genova, Via all’Opera Pia 15, Genova 16145, Italy
    • Lea Pasquale - Materials Characterization Facility, Istituto Italiano di Tecnologia, Via Morego 30, Genova 16163, Italy;  Orcidhttps://orcid.org/0000-0002-3919-8873
    • Sergio Marras - Materials Characterization Facility, Istituto Italiano di Tecnologia, Via Morego 30, Genova 16163, Italy
    • Ahmad Bagheri - Graphene Laboratories, Istituto Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy;  Center for Advancing Electronics Dresden (CFAED) & Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, Dresden 01062, Germany
    • Hossein Beydaghi - BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy
    • Evie L. Papadopoulou - BeDimensional S.p.A., Via Lungotorrente Secca 30R, Genova 16163, Italy;  Orcidhttps://orcid.org/0000-0001-5959-9730
    • Guglielmo Lanzani - Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, Milano 20133, Italy;  Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia, Via Pascoli 70/3, Milano 20133, Italy
  • Author Contributions

    M.G. and S.B. contributed equally. Matteo Gentile: conceptualized the idea and led laboratory research. Sebastiano Bellani: conceptualized the idea, carried out electrochemical characterizations and corresponding data analysis, supervised research activities, acquired funding, and wrote the draft of the manuscript. Marilena Zappia, Agnese Gamberini, Valentina Mastronardi, Matteo Abruzzese, Luca Gabatel, Ahmad Bagheri, Hossein Beydaghi, and Evie L. Papadopoulou performed Raman, TGA, contact angle, zeta potential, and electrochemical characterizations. Lea Pasquale carried out XPS and gas physisorption measurements and corresponding data analyses. Sergio Marras carried out XRD measurements and corresponding data analysis. Guglielmo Lanzani supervised research activities and acquired funding. Francesco Bonaccorso supervised research activities and acquired funding. The manuscript was written through the contributions of all authors. All authors have given approval to the final version of the manuscript.

  • Funding

    This project received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement no. 881603-GrapheneCore3, the European Union’s Horizon 2020 Research and Innovation Program under the Marie Skłodowska-Curie grant agreement no. 813036, the European Union’s SENSIBAT project under grant agreement no. 957273, the European Union’s GREENCAP Horizon Europe research and innovation program under grant agreement no. 101091572 and the European Union’s 2D-PRINTABLE Horizon Europe research and innovation program under grant agreement no. 694101.

  • Notes
    The authors declare the following competing financial interest(s): S.B., M.I.Z., A.G., V.M., M.A., L.G., A.B., H.B., E.L.P. and F.B. are employees of BeDimensional S.p.A., a company that is commercializing 2D materials.

Acknowledgments

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We thank the Electron Microscopy and Material Characterization facilities for their support in XRD data acquisition.

References

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This article references 80 other publications.

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    Garakani, M. A.; Bellani, S.; Pellegrini, V.; Oropesa-Nuñez, R.; Castillo, A. E. D. R.; Abouali, S.; Najafi, L.; Martín-García, B.; Ansaldo, A.; Bondavalli, P.; Demirci, C.; Romano, V.; Mantero, E.; Marasco, L.; Prato, M.; Bracciale, G.; Bonaccorso, F. Scalable Spray-Coated Graphene-Based Electrodes for High-Power Electrochemical Double-Layer Capacitors Operating over a Wide Range of Temperature. Energy Storage Mater. 2021, 34, 1– 11,  DOI: 10.1016/j.ensm.2020.08.036
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  4. 4
    Bellani, S.; Martín-García, B.; Oropesa-Nuñez, R.; Romano, V.; Najafi, L.; Demirci, C.; Prato, M.; Del Rio Castillo, A. E.; Marasco, L.; Mantero, E.; D’Angelo, G.; Bonaccorso, F. Ion Sliding” on Graphene: A Novel Concept to Boost Supercapacitor Performance. Nanoscale Horiz. 2019, 4 (5), 1077– 1091,  DOI: 10.1039/C8NH00446C
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    4
    "Ion sliding" on graphene: a novel concept to boost supercapacitor performance
    Bellani, Sebastiano; Martin-Garcia, Beatriz; Oropesa-Nunez, Reinier; Romano, Valentino; Najafi, Leyla; Demirci, Cansunur; Prato, Mirko; Del Rio Castillo, Antonio Esau; Marasco, Luigi; Mantero, Elisa; D'Angelo, Giovanna; Bonaccorso, Francesco
    Nanoscale Horizons (2019), 4 (5), 1077-1091CODEN: NHAOAW; ISSN:2055-6764. (Royal Society of Chemistry)
    Efficient ionic transport in nanoporous carbon electrodes is pivotal for the development of high-rate electrochem. capacitive energy storage in supercapacitors (SCs). Over the past decade, the understanding of the charging/discharging mechanisms in nanostructured carbon electrodes and the elucidation of confinement and desolvation of ions in elec. charged carbon nanopores have spurred the development of advanced SCs holding ever-increasing energy d. Crucially, these advancements have to be accomplished without sacrificing the extraordinary power handling and cycling lifetime of the SC. In this work, we investigated the interaction between single-/few-layer graphene (SLG/FLG) flakes or activated carbon (AC) films and 1 M tetraethylammonium tetrafluoroborate (TEABF4) in propylene carbonate (PC) by lateral force microscopy (LFM) measurements. We unravel that the electrolyte nanotribol. on SLG/FLG flakes incorporated into AC-based electrodes is effective at boosting the power performance of com.-like SCs (active material mass loading ∼10 mg cm-2), thus maximizing the advantage of using nanoporous nanocarbon electrodes with high energy d. At a charge/discharge (CD) c.d. of 0.1 A g-1, our hybrid AC:SLG/FLG-based SC shows a 30% increase of specific capacitance (Cg) compared to the ref. device, i.e., the AC-based one (Cg from 76.8 F g-1 to 98.2 F g-1). At higher CD current densities (>1 A g-1), the AC-based device displays a resistive behavior, while the AC:SLG/FLG-based SCs still exhibit a Cg of 23.9 and 5.2 F g-1 at CD current densities as high as 2.5 and 5 A g-1, resp. Beyond the control of the nanoporosity of carbon materials and the inter-ionic interaction of the electrolytes, the rationalization of the relationship between the nanotribol. of nanocarbons and the performance of the corresponding SCs offers new opportunities to optimize the SC design compatibly with established high-throughput industrial manufg.
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  5. 5
    Wu, J. Understanding the Electric Double-Layer Structure, Capacitance, and Charging Dynamics. Chem. Rev. 2022, 122 (12), 10821– 10859,  DOI: 10.1021/acs.chemrev.2c00097
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    5
    Understanding the Electric Double-Layer Structure, Capacitance, and Charging Dynamics
    Wu, Jianzhong
    Chemical Reviews (Washington, DC, United States) (2022), 122 (12), 10821-10859CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. Significant progress has been made in recent years in theor. modeling of the elec. double layer (EDL), a key concept in electrochem. important for energy storage, electrocatalysis, and multitudes of other technol. applications. However, major challenges remain in understanding the microscopic details of the electrochem. interface and charging mechanisms under realistic conditions. This review delves into theor. methods to describe the equil. and dynamic responses of the EDL structure and capacitance for electrochem. systems commonly deployed for capacitive energy storage. Special emphasis is given to recent advances that intend to capture the nonclassical EDL behavior such as oscillatory ion distributions, polarization of nonmetallic electrodes, charge transfer, and various forms of phase transitions in the micropores of electrodes interfacing with an org. electrolyte or ionic liq. This comprehensive anal. highlights theor. insights into predictable relationships between materials characteristics and electrochem. performance and offers a perspective on opportunities for further development toward rational design and optimization of electrochem. systems.
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  6. 6
    Barbieri, O.; Hahn, M.; Herzog, A.; Kötz, R. Capacitance Limits of High Surface Area Activated Carbons for Double Layer Capacitors. Carbon 2005, 43 (6), 1303– 1310,  DOI: 10.1016/j.carbon.2005.01.001
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    Capacitance limits of high surface area activated carbons for double layer capacitors
    Barbieri, O.; Hahn, M.; Herzog, A.; Koetz, R.
    Carbon (2005), 43 (6), 1303-1310CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    A large sp. surface area (SSA) of carbon materials used for electrochem. double layer capacitors (EDLC) is the most important parameter leading to a large gravimetric capacitance (Cg). However, for a SSA detd. with the differential functional theory (DFT) model above a value of 1200 m2/g the plot of Cg vs. SDFT exhibits a plateau. We suggest that this limitation of Cg can be ascribed to a space constriction for charge accommodation inside the pore walls. As a consequence, the use of extremely high surface area carbons for EDLCs may be unprofitable.
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  7. 7
    Hahn, M.; Baertschi, M.; Barbieri, O.; Sauter, J.-C.; Kötz, R.; Gallay, R. Interfacial Capacitance and Electronic Conductance of Activated Carbon Double-Layer Electrodes. Electrochem. Solid-State Lett. 2004, 7 (2), A33,  DOI: 10.1149/1.1635671
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    Gerischer, H. An Interpretation of the Double Layer Capacity of Graphite Electrodes in Relation to the Density of States at the Fermi Level. J. Phys. Chem. 1985, 89 (20), 4249– 4251,  DOI: 10.1021/j100266a020
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    8
    An interpretation of the double layer capacity of graphite electrodes in relation to the density of states at the Fermi level
    Gerischer, H.
    Journal of Physical Chemistry (1985), 89 (20), 4249-51CODEN: JPCHAX; ISSN:0022-3654.
    The double layer capacitance of stress-annealed graphite electrodes in contact with electrolytes is relatively low in comparison to metal electrodes. This behavior is interpreted as due to a low d. of electronic states around the Fermi level of graphite. Exptl. data from the literature are analyzed and a d. of states of the order of 2.4 × 1020 cm-3 eV-1 is obtained. This interpretation is in qual. agreement with theor. calcns. of the band structure of graphite and fits to the concn. of electrons and holes derived from cond. data.
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    Luryi, S. Quantum Capacitance Devices. Appl. Phys. Lett. 1988, 52 (6), 501– 503,  DOI: 10.1063/1.99649
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    Ji, H.; Zhao, X.; Qiao, Z.; Jung, J.; Zhu, Y.; Lu, Y.; Zhang, L. L.; MacDonald, A. H.; Ruoff, R. S. Capacitance of Carbon-Based Electrical Double-Layer Capacitors. Nat. Commun. 2014, 5 (1), 3317,  DOI: 10.1038/ncomms4317
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    Capacitance of carbon-based electrical double-layer capacitors
    Ji Hengxing; Zhao Xin; Qiao Zhenhua; Jung Jeil; Zhu Yanwu; Lu Yalin; Zhang Li Li; Ruoff Rodney S; MacDonald Allan H
    Nature communications (2014), 5 (), 3317 ISSN:.
    Experimental electrical double-layer capacitances of porous carbon electrodes fall below ideal values, thus limiting the practical energy densities of carbon-based electrical double-layer capacitors. Here we investigate the origin of this behaviour by measuring the electrical double-layer capacitance in one to five-layer graphene. We find that the capacitances are suppressed near neutrality, and are anomalously enhanced for thicknesses below a few layers. We attribute the first effect to quantum capacitance effects near the point of zero charge, and the second to correlations between electrons in the graphene sheet and ions in the electrolyte. The large capacitance values imply gravimetric energy storage densities in the single-layer graphene limit that are comparable to those of batteries. We anticipate that these results shed light on developing new theoretical models in understanding the electrical double-layer capacitance of carbon electrodes, and on opening up new strategies for improving the energy density of carbon-based capacitors.
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  11. 11
    Weingarth, D.; Zeiger, M.; Jäckel, N.; Aslan, M.; Feng, G.; Presser, V. Graphitization as a Universal Tool to Tailor the Potential-Dependent Capacitance of Carbon Supercapacitors. Adv. Energy Mater. 2014, 4 (13), 1400316,  DOI: 10.1002/aenm.201400316
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    11
    Graphitization as a Universal Tool to Tailor the Potential-Dependent Capacitance of Carbon Supercapacitors
    Weingarth, Daniel; Zeiger, Marco; Jaeckel, Nicolas; Aslan, Mesut; Feng, Guang; Presser, Volker
    Advanced Energy Materials (2014), 4 (13), 1400316/1-1400316/13CODEN: ADEMBC; ISSN:1614-6840. (Wiley-Blackwell)
    Most efforts to improve the energy d. of supercapacitors are currently dedicated to optimized porosity or hybrid devices employing pseudocapacitive elements. Little attention has been given to the effects of the low charge carrier d. of carbon on the total material capacitance. To study the effect of graphitization on the differential capacitance, carbon onion (also known as onion-like carbon) supercapacitors are chosen. The increase in d. of states (DOS) related to the low d. of charge carriers in carbon materials is an important effect that leads to a substantial increase in capacitance as the electrode potential is increased. Using carbon onions as a model, it is shown that this phenomenon cannot be related only to geometric aspects but must be the result of varying graphitization. This provides a new tool to significantly improve carbon supercapacitor performance, in addn. to having significant consequences for the modeling community where carbons usually are approximated to be ideal metallic conductors. Data on the structure, compn., and phase content of carbon onions are presented and the correlation between electrochem. performance and elec. resistance and graphitization is shown. Highly graphitic carbons show a stronger degree of electrochem. doping, making them very attractive for enhancing the capacitance.
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  12. 12
    Duignan, T. T.; Zhao, X. S. Impurities Limit the Capacitance of Carbon-Based Supercapacitors. J. Phys. Chem. C 2019, 123 (7), 4085– 4093,  DOI: 10.1021/acs.jpcc.8b12031
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    12
    Impurities Limit the Capacitance of Carbon-Based Supercapacitors
    Duignan, Timothy T.; Zhao, Xiu Song
    Journal of Physical Chemistry C (2019), 123 (7), 4085-4093CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Supercapacitors cannot fulfill their potential as energy storage devices without substantially improving their comparatively low energy d. Doing so requires improving their capacitance. Unfortunately, predicting the capacitance of the carbon-based materials that typically make up supercapacitor electrodes is very difficult. Carbon materials can have an areal capacitance that is an order of magnitude lower than both that of std. metals and theor. expectations. Here, we provide new quantum mech. calcns. to demonstrate that the std. explanation of this unusually low capacitance in terms of the space charge capacitance is inadequate. We then demonstrate that a layer of hydrocarbon impurities, which has recently been shown to form on graphite, is likely the dominant cause of the low capacitance of graphite. We develop a model of this effect, which accounts for the penetration of solvent into the hydrocarbon layer as the voltage increases. This model explains the characteristic V shape of the capacitance as a function of voltage. We present evidence that this layer may also play a role in limiting the capacitance in real supercapacitor materials such as activated carbon.
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  13. 13
    Tolman, N. L.; Mukai, J. M.; Wang, S.; Zito, A.; Luo, T.; Liu, H. The Effect of Physical Adsorption on the Capacitance of Activated Carbon Electrodes. Carbon 2019, 150, 334– 339,  DOI: 10.1016/j.carbon.2019.05.005
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    13
    The effect of physical adsorption on the capacitance of activated carbon electrodes
    Tolman, Nathan L.; Mukai, Jason M.; Wang, Shuqing; Zito, Alessandra; Luo, Tianyi; Liu, Haitao
    Carbon (2019), 150 (), 334-339CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    This work reports the effect of physisorption of org. compds. on the double layer capacitance of activated carbon electrodes. Exposure of activated carbon electrodes to toluene or chloroform vapor for less than 10 min resulted in a capacitance loss of 77% and 84%, resp. Even adsorbates, such as acetone and ethanol, miscible with the aq. Li2SO4 electrolyte caused 20-30% losses in capacitance. It was also found that there was an adsorbate size dependence: above a certain threshold, a larger adsorbate could have more than twice the impact on capacitance than a slightly smaller one. The results were consistent with the hypothesis that volatile org. contaminants (VOC) block access of the aq. electrolyte to the carbon electrode surface. Porous activated carbon is currently the material of choice for supercapacitor electrodes in both research labs. and com. supercapacitor applications. These facilities also often house and use many volatile org. solvents either for research and development or simply for cleaning purposes. Because of this, our work has significant implications to the research and development of carbon-based supercapacitors.
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  14. 14
    Wang, H.; Yoshio, M. Effect of Water Contamination in the Organic Electrolyte on the Performance of Activated Carbon/Graphite Capacitors. J. Power Sources 2010, 195 (1), 389– 392,  DOI: 10.1016/j.jpowsour.2009.06.097
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    14
    Effect of water contamination in the organic electrolyte on the performance of activated carbon/graphite capacitors
    Wang, Hongyu; Yoshio, Masaki
    Journal of Power Sources (2010), 195 (1), 389-392CODEN: JPSODZ; ISSN:0378-7753. (Elsevier B.V.)
    The effect of water contamination in the electrolyte on the performance of AC/graphite capacitor has been investigated by electrochem. tests and in situ XRD measurements. The deterioration mechanisms for the charge storage ability of the electrodes in the capacitors using polluted electrolytes have also been addressed.
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  15. 15
    Inamoto, J.; Matsuo, Y.; Katsumi, M.; Uchida, S.; Ishikawa, M.; Masuyama, T.; Tsukamoto, K.; Sato, Y. Effect of Hydrogen-Gas Treatment on the Local Structure of Graphene-like Graphite. Carbon 2020, 163, 162– 168,  DOI: 10.1016/j.carbon.2020.03.016
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    15
    Effect of hydrogen-gas treatment on the local structure of graphene-like graphite
    Inamoto, Junichi; Matsuo, Yoshiaki; Katsumi, Maeda; Uchida, Satoshi; Ishikawa, Masashi; Masuyama, Takuya; Tsukamoto, Kaoru; Sato, Yuta
    Carbon (2020), 163 (), 162-168CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    Graphene-like graphite (GLG) has been expected as a new candidate for a large-capacity neg. electrode material of a lithium-ion battery. Recently, our group has reported that hydrogen-gas treatment of GLG lowered the mean-discharge potential and increased its capacity. In order to clarify the origin of this improvement, scanning tunneling microscopy (STM) was conducted together with simulation using d. functional theory calcn. A GLG mono-sheet suitable for STM observation was synthesized from highly oriented pyrolytic graphite (HOPG) as a raw material. A distorted honeycomb region surrounded by triangular one was obsd. for GLG mono-sheets and it was well simulated using a model consisting of a topmost graphene with pairwisely introduced ether groups underneath. The above honeycomb region disappeared for GLG treated with hydrogen gas (GLG-H), and it was also well simulated using a model in which each oxygen atom introduced in the graphene was substituted by two hydrogen atoms. Since the resulting local structure of GLG-H was similar to that of graphite which shows low discharge potential, this would lead to the increased accessible capacity under 2.0 V of cut-off voltage.
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  16. 16
    Matsuo, Y.; Taninaka, J.; Hashiguchi, K.; Sasaki, T.; Cheng, Q.; Okamoto, Y.; Tamura, N. Effect of Oxygen Contents in Graphene like Graphite Anodes on Their Capacity for Lithium Ion Battery. J. Power Sources 2018, 396, 134– 140,  DOI: 10.1016/j.jpowsour.2018.06.022
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    16
    Effect of oxygen contents in graphene like graphite anodes on their capacity for lithium ion battery
    Matsuo, Yoshiaki; Taninaka, Junichi; Hashiguchi, Katsuki; Sasaki, Toshiyuki; Cheng, Qian; Okamoto, Yasuharu; Tamura, Noriyuki
    Journal of Power Sources (2018), 396 (), 134-140CODEN: JPSODZ; ISSN:0378-7753. (Elsevier B.V.)
    Graphene like graphite (GLG) samples contg. various amts. of oxygen are prepd. from the thermal redn. of graphite oxide (GO) and are used as anodes of lithium ion battery. The oxygen/carbon (O/C) ratios in GLG varied from 0 to 0.08, depending on the thermal redn. temp., oxygen gas pressure during heat treatment and degree of oxidn. of the starting GO. The cell voltage during discharge almost linearly increases below 1 V independent of the oxygen contents in them. The discharge capacity of GLG above 1 V increases with the increase in the oxygen content with a slope of lithium/oxygen ratio of 3 at lower O/C ratios. Then the slope becomes smaller and the discharge capacity reaches 673 mAhg-1 for GLG with O/C = 0.08. When GLG is treated with hydrogen gas, considerable amts. of oxygen atoms are substituted by hydrogen ones. The discharge capacity of the resulting GLG samples is larger than that expected form their oxygen contents and coulombic efficiency is slightly improved up to 59%. Introduction of oxygen atoms within carbon layers results in the large increase in the interlayer spacing during charging, which leads to accommodation of large amts. of lithium ions.
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  17. 17
    Takeuchi, M.; Maruyama, T.; Koike, K.; Mogami, A.; Oyama, T.; Kobayashi, H. Non-Porous Carbon for a High Energy Density Electric Double Layer Capacitor. Electrochemistry 2001, 69 (6), 487– 492,  DOI: 10.5796/electrochemistry.69.487
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    17
    Non-porous carbon for a high energy density electric double layer capacitor
    Takeuchi, Makoto; Maruyama, Takamichi; Koike, Katsumi; Mogami, Akinori; Oyama, Takashi; Kobayashi, Hiroshi
    Electrochemistry (Tokyo, Japan) (2001), 69 (6), 487-492CODEN: EECTFA; ISSN:1344-3542. (Electrochemical Society of Japan)
    Apparently non-porous activated carbon with a sp. surface area less than 100 m2/g (BET) prepd. from calcined carbon of petroleum coke is studied as the polarized electrode for an Elec. Double Layer Capacitor (EDLC). The non-porous carbon makes negligibly small elec. double layer when it is dipped into an electrolyte soln. in the beginning. During the initial charging process, however, "solvent co-intercalation of ions" builds double layers in the pos. and the neg. electrodes, and during the discharging process, the excess ions go out, while the opposite ions come in, to maintain the double layers elec. neutral. After that, the electrodes behave like conventional activated porous carbon electrodes with an extra high dense capacitance. The obsd. phenomenon is discussed from the viewpoints of the interlayer distance in graphitelike structure, the mol. vol. of solvent for electrolyte, the residual functional groups such as active oxidized hydrogen obsd. by NMR, and of the elimination method for the residual active oxidized hydrogen by heat treatment in H2 atmosphere, as well as the prepn. method for source carbon.
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  18. 18
    Moussa, G.; Matei Ghimbeu, C.; Taberna, P.-L.; Simon, P.; Vix-Guterl, C. Relationship between the Carbon Nano-Onions (CNOs) Surface Chemistry/Defects and Their Capacitance in Aqueous and Organic Electrolytes. Carbon 2016, 105, 628– 637,  DOI: 10.1016/j.carbon.2016.05.010
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    18
    Relationship between the carbon nano-onions (CNOs) surface chemistry/defects and their capacitance in aqueous and organic electrolytes
    Moussa, Georges; Matei Ghimbeu, Camelia; Taberna, Pierre-Louis; Simon, Patrice; Vix-Guterl, Cathie
    Carbon (2016), 105 (), 628-637CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    The effect of surface functionalities on supercapacitor performance was highlighted often in many works. However, studies devoted to the influence of C defects did not gain particular attention due to the difficulty to quantify such parameter. In this context, C nano-onions were used as model material to understand the influence of the surface chem. (nature and amt. of O groups) and structural defects (active surface area, ASA) on the capacitance. Different types of thermal treatments in oxidizing or reducing atms. allowed to finely tune the surface chem. and the ASA as demonstrated by temp. programmed desorption coupled with mass spectrometry (TPD-MS). For the 1st time, the exact control of these characteristics independently one of each other allowed to highlight an important influence of the C defects on the capacitance in org. and aq. electrolytes which outbalance the O functional group effect.
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  19. 19
    Hu, W.; Sun, X. N.; Xu, D.; Xiao, Z. H.; Chen, X. Y. Microporous Carbon Materials by Hydrogen Treatment: The Balance of Porosity and Graphitization upon the Capacitive Performance. Ind. Eng. Chem. Res. 2017, 56 (25), 7253– 7259,  DOI: 10.1021/acs.iecr.7b01626
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    19
    Microporous Carbon Materials by Hydrogen Treatment: The Balance of Porosity and Graphitization upon the Capacitive Performance
    Hu, Wei; Sun, Xiao Na; Xu, Dong; Xiao, Zheng Hui; Chen, Xiang Ying
    Industrial & Engineering Chemistry Research (2017), 56 (25), 7253-7259CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)
    The balance of porosity and graphitization toward carbon materials plays a crucial role in detg. the capacitive performance. In this work, this purpose has been successfully implemented by adjusting the carbonization temp. and hydrogen gas treatment. Oxygen contg. functional groups have conspicuously reduced by the coeffects of hydrogen gas and high temp. on carbon materials. Besides, by treatment at a temp. of 800 °C with hydrogen, the electrochem. performances have been greatly improved. The electrode treated at the temp. of 800 °C with hydrogen displays higher specific capacitances of 171 F g-1 compared with that of bare carbon electrode of 145 F g-1, owing to enlarged BET surface area and pore vol. and reduced resistance. At the same time, the electrode treated at the temp. of 800 °C with hydrogen exhibits a higher cycling stability of 96.3% of primary specific capacitances after 5000 cycles and energy d. of 8.36 Wh kg-1, resp.
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  20. 20
    Qin, T.; Shi, Z.; Li, M.; Wang, C. Effect of Reduction Heat Treatment in H2 Atmosphere on Structure and Electrochemical Properties of Activated Carbon. J. Solid State Electrochem. 2015, 19 (5), 1437– 1446,  DOI: 10.1007/s10008-015-2767-1
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    20
    Effect of reduction heat treatment in H2 atmosphere on structure and electrochemical properties of activated carbon
    Qin, Ting-ting; Shi, Zhi-qiang; Li, Ming-wei; Wang, Cheng-yang
    Journal of Solid State Electrochemistry (2015), 19 (5), 1437-1446CODEN: JSSEFS; ISSN:1432-8488. (Springer)
    Activated carbon is heat-treated in a H2 atmosphere at 600, 800, and 1000 °C for 1 h, resp., to be used as electrode material for elec. double layer capacitors (EDLCs). After heat treatment, the surface morphol. has no obvious change as compared with the raw material. The sp. surface area and pore vol. of sample treated at 600 °C have a slightly increase while those of samples treated at higher temp. decrease. XPS and elemental anal. indicate that oxygen contg. functional groups on the sample are significantly reduced after treatment. The electrochem. performance of samples was evaluated using cyclic voltammetry and galvanostatic charge-discharge tests in 1 M TEABF4/PC electrolyte. The sample treated at 600 °C shows the optimized electrochem. performance with increase capacitance, enhanced stability, and improved energy d. Its initial specific capacitance is near 127 F/g, and initial coulombic efficiency is about 52 %. At 3.0 V, its energy d. reaches 32 Wh/kg and specific capacitance is about 70 F/g at 1 A/g even after 10,000 charge-discharge cycles. Thus, heat treatment at 600 °C under H2 atmosphere is an effective method to improve electrochem. properties of EDLCs based on activated carbon material.
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  21. 21
    Zhong, Z.; Aika, K. Effect of Hydrogen Treatment of Active Carbon as a Support for Promoted Ruthenium Catalysts for Ammonia Synthesis. Chem. Commun. 1997, (13), 1223– 1224,  DOI: 10.1039/a702273e
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    Effect of hydrogen treatment of active carbon as a support for promoted ruthenium catalysts for ammonia synthesis
    Zhong, Zhihua; Aika, Ken-ichi
    Chemical Communications (Cambridge) (1997), (13), 1223-1224CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    Hydrogen treatment of active carbon (A.C.) at temps. ranging from 1073 to 1188 K for 12 h is an effective method for eliminating surface impurities, leading to the prepn. of useful ruthenium catalysts; for example, 2 mass% Ru-BaO/A.C. (Ba/Ru = 5) yields 2 mmol NH3 h-1 g-1 at 588 K under 1 atm.
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  22. 22
    Oliveira, L. C. A.; Silva, C. N.; Yoshida, M. I.; Lago, R. M. The Effect of H2 Treatment on the Activity of Activated Carbon for the Oxidation of Organic Contaminants in Water and the H2O2 Decomposition. Carbon 2004, 42 (11), 2279– 2284,  DOI: 10.1016/j.carbon.2004.05.003
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    22
    The effect of H2 treatment on the activity of activated carbon for the oxidation of organic contaminants in water and the H2O2 decomposition
    Oliveira, Luiz C. A.; Silva, Cristina N.; Yoshida, Maria I.; Lago, Rochel M.
    Carbon (2004), 42 (11), 2279-2284CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Science Ltd.)
    H2O2 reactions, i.e. H2O2 decompn. and oxidn. of orgs. in aq. medium, were studied in the presence of activated C. It was obsd. that the C pre-treatment with H at 300, 500, 700 and 800° resulted in an increase in activity for both reactions. The carbons were characterized by BET N adsorption, thermogravimetric analyses (TG), temp. programmed redn. (TPR), ESR (EPR), iodometric titrn. and detn. of the acid/basic sites. TPR expts. showed that activated C reacts with H at temps. >400°. The treatment produces a slight increase in the surface area. EPR analyses indicate the absence of unpaired electrons in the C. Iodometric titrns. and TG analyses suggested that the treatment with H generates redn. sites in the C structure, with concn. of approx. 0.33, 0.53, 0.59, 0.65 and 0.60 mmol/g for carbons treated at 25, 300, 500, 700 and 800°, resp. It was also obsd. the appearance of basic sites which might be related to the redn. sites. It is proposed that these reducing sites in the C can activate H2O2 to generate HO* radicals which can lead to 2 competitive reactions, i.e. the H2O2 decompn. or the oxidn. of orgs. in water.
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  23. 23
    Malmberg, S.; Arulepp, M.; Tarasova, E.; Vassiljeva, V.; Krasnou, I.; Krumme, A. Electrochemical Evaluation of Directly Electrospun Carbide-Derived Carbon-Based Electrodes in Different Nonaqueous Electrolytes for Energy Storage Applications. C 2020, 6, 59,  DOI: 10.3390/c6040059
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    23
    Electrochemical evaluation of directly electrospun carbide-derived carbon-based electrodes in different nonaqueous electrolytes for energy storage applications
    Malmberg, Siret; Arulepp, Mati; Tarasova, Elvira; Vassiljeva, Viktoria; Krasnou, Illia; Krumme, Andres
    C (2020), 6 (4), 59CODEN: CABCC3; ISSN:2311-5629. (MDPI AG)
    This study focuses on the electrochem. behavior of thin-layer fibrous carbide-derived carbon (CDC) electrospun electrodes in com. and research and development stage org.-solvent and ionic liq. (IL) based electrolytes. The majority of earlier published works stated various electrolytes with asym. cells of powder-based pressure-rolled (PTFE), or slurry-cast electrodes, were significantly different than the presented CDC-based fibrous spun electrodes. The benefits of the fibrous structure are relatively low thickness (20μm), flexibility and mech. durability. Thin-layered durable electrode materials are gaining more interest and importance in mech. more demanding applications such as the space industry and in wearable devices, and need to achieve a targeted balance between mech., elec. and electrochem. properties. The existing com. electrode technologies lack compatibility in such applications due to their limited mech. properties and high cost. The test results showed that the widest potential window dU ≤ 3.5 V was achieved in 1.5 M 1-ethyl-3-methylimidazoliumbis(trifluoromethyl-sulfonyl)imide (EMIm-TFSI) soln. in acetonitrile (ACN). Gravimetric capacitance reached 105.6 F g-1 for the pos. charged electrode. Cycle-life results revealed stable material capacitance and resistance over 3000 cycles.
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  24. 24
    Malmberg, S.; Arulepp, M.; Savest, N.; Tarasova, E.; Vassiljeva, V.; Krasnou, I.; Käärik, M.; Mikli, V.; Krumme, A. Directly Electrospun Electrodes for Electrical Double-Layer Capacitors from Carbide-Derived Carbon. J. Electrost. 2020, 103, 103396,  DOI: 10.1016/j.elstat.2019.103396
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    24
    Directly electrospun electrodes for electrical double-layer capacitors from carbide-derived carbon
    Malmberg, Siret; Arulepp, Mati; Savest, Natalja; Tarasova, Elvira; Vassiljeva, Viktoria; Krasnou, Illia; Kaarik, Maike; Mikli, Valdek; Krumme, Andres
    Journal of Electrostatics (2020), 103 (), 103396CODEN: JOELDH; ISSN:0304-3886. (Elsevier B.V.)
    This work aims towards the optimization of porous carbon satd. nanofibres compn. for elec.-double layer (EDL) electrode's prepn. The properties of microporous carbide-derived carbon (CDC) based electrospun electrodes are discussed. The variable electrode compn. and their mech. properties were obsd. to obtain the highest EDL capacitance. Effect of densification pressure and -temp. of electrospun electrodes are discussed. Thin electrode layer enables faster charge-discharge capability and perform higher power with same consumption of electrode materials. The EDL capacitance of 114 Fg-1, detd. by cyclic voltammetry method within the voltage range of 0-2.7 V, was achieved.
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  25. 25
    Rose, M.; Korenblit, Y.; Kockrick, E.; Borchardt, L.; Oschatz, M.; Kaskel, S.; Yushin, G. Hierarchical Micro- and Mesoporous Carbide-Derived Carbon as a High-Performance Electrode Material in Supercapacitors. Small 2011, 7 (8), 1108– 1117,  DOI: 10.1002/smll.201001898
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    25
    Hierarchical Micro- and Mesoporous Carbide-Derived Carbon as a High-Performance Electrode Material in Supercapacitors
    Rose, Marcus; Korenblit, Yair; Kockrick, Emanuel; Borchardt, Lars; Oschatz, Martin; Kaskel, Stefan; Yushin, Gleb
    Small (2011), 7 (8), 1108-1117CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Ordered mesoporous carbide-derived carbon (OM-CDC) materials produced by nanocasting of ordered mesoporous silica templates are characterized by a bimodal pore size distribution with a high ratio of micropores. The micropores result in outstanding adsorption capacities and the well-defined mesopores facilitate enhanced kinetics in adsorption processes. Here, for the first time, a systematic study is presented, in which the effects of synthesis temp. on the electrochem. performance of these materials in supercapacitors based on a 1 M aq. soln. of sulfuric acid and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liq. are reported. Cyclic voltammetry shows the specific capacitance of the OM-CDC materials exceeds 200 F g-1 in the aq. electrolyte and 185 F g-1 in the ionic liq., when measured in a sym. configuration in voltage ranges of up to 0.6 and 2 V, resp. The ordered mesoporous channels in the produced OM-CDC materials serve as ion-highways and allow for very fast ionic transport into the bulk of the OM-CDC particles. At room temp. the enhanced ion transport leads to 75% and 90% of the capacitance retention at current densities in excess of ∼10 A g-1 in ionic liq. and aq. electrolytes, resp. The supercapacitors based on 250-300 μm OM-CDC electrodes demonstrate an operating frequency of up to 7 Hz in aq. electrolyte. The combination of high specific capacitance and outstanding rate capabilities of the OM-CDC materials is unmatched by state-of-the art activated carbons and strictly microporous CDC materials.
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    Gomibuchi, E.; Ichikawa, T.; Kimura, K.; Isobe, S.; Nabeta, K.; Fujii, H. Electrode Properties of a Double Layer Capacitor of Nano-Structured Graphite Produced by Ball Milling under a Hydrogen Atmosphere. Carbon 2006, 44 (5), 983– 988,  DOI: 10.1016/j.carbon.2005.10.006
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    26
    Electrode properties of a double layer capacitor of nano-structured graphite produced by ball milling under a hydrogen atmosphere
    Gomibuchi, Emi; Ichikawa, Takayuki; Kimura, Koichi; Isobe, Shigehito; Nabeta, Koji; Fujii, Hironobu
    Carbon (2006), 44 (5), 983-988CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    Nano-structural graphite prepd. by ball milling under H2 or Ar atm. was studied as an electrode for elec. double layer capacitors (EDLCs) by means of a conventional 2-electrode galvanostatic method. Esp., the product prepd. under H2 atmosphere using zirconia balls revealed 500 m2 g-1 surface area and showed 12 F g-1 specific capacitance, which was comparable to that of an activated carbon with large sp. surface area of 3000 m2 g-1 examd. as a ref. A proper condition of the milling time is rather a shorter time than ∼8 h, where the graphitic feature is remained in the ball milled product. On the other hand, for the sample prepd. by using steel balls, the specific capacitance per surface area was several hundreds times smaller than the others, indicating that the small amt. of Fe contamination during milling played a neg. role for the EDLC properties.
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    Brunauer, S.; Emmett, P. H.; Teller, E. Adsorption of Gases in Multimolecular Layers. J. Am. Chem. Soc. 1938, 60 (2), 309– 319,  DOI: 10.1021/ja01269a023
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    Adsorption of gases in multimolecular layers
    Brunauer, Stephen; Emmett, P. H.; Teller, Edward
    Journal of the American Chemical Society (1938), 60 (), 309-19CODEN: JACSAT; ISSN:0002-7863.
    The polarization theory of multimolecular adsorption is discussed critically. The adsorption energy due to attraction of dipoles induced into a nonpolar gas such as A is insufficient to constitute a major portion of the binding energy between adsorbed layers. Adsorption-isotherm equations for multimolecular adsorption are derived on the assumption that the same forces that produce condensation are responsible also for multimolecular adsorption. Numerous applications of the equations are given to exptl. adsorption isotherms. Cf. C. A. 32, 1159.3.
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    Dubinin, M. M. Fundamentals of the Theory of Adsorption in Micropores of Carbon Adsorbents: Characteristics of Their Adsorption Properties and Microporous Structures. Carbon 1989, 27 (3), 457– 467,  DOI: 10.1016/0008-6223(89)90078-X
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    28
    Fundamentals of the theory of adsorption in micropores of carbon adsorbents: characteristics of their adsorption properties and microporous structures
    Dubinin, M. M.
    Carbon (1989), 27 (3), 457-67CODEN: CRBNAH; ISSN:0008-6223.
    Quant. methods of characterization of the adsorption properties and microporous structure covering the entire variety of micropore types have been elaborated on the basis of the theory of vapor adsorption in micropores. The general situation is encompassed by the three parameters of the Dubinin-Stoeckli equation (micropore vol., the characteristic adsorption energy, and variance) plus the sp. surface area of mesopores. They allow one to predict adsorption of different vapors and the adsorption vs. temp. relationships. The same parameters can be used to calc. the micropore size distribution patterns, the geometric surface area of micropores, and, where necessary, the vol. of micropores within a given size range. Benzene at 293 K and nitrogen at 77 K are not equiv. ref. vapors. Benzene is more appropriate to obtain a comprehensive characteristic of both the adsorption properties and the microporous structure.
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    Silvestre-Albero, J.; Silvestre-Albero, A.; Rodríguez-Reinoso, F.; Thommes, M. Physical Characterization of Activated Carbons with Narrow Microporosity by Nitrogen (77.4K), Carbon Dioxide (273K) and Argon (87.3K) Adsorption in Combination with Immersion Calorimetry. Carbon 2012, 50 (9), 3128– 3133,  DOI: 10.1016/j.carbon.2011.09.005
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    Physical characterization of activated carbons with narrow microporosity by nitrogen (77.4 K), carbon dioxide (273 K) and argon (87.3 K) adsorption in combination with immersion calorimetry
    Silvestre-Albero, J.; Silvestre-Albero, A.; Rodriguez-Reinoso, F.; Thommes, M.
    Carbon (2012), 50 (9), 3128-3133CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    To get more insight into the characterization of nanoporous carbons by gas adsorption, the use of different probe mols. was compared. A series of activated carbons with ranging porosity (burn-off) were prepd. from olive stones using CO2 as activating agent and characterized using N2 and Ar adsorption at low temp. (77.4 K for N2 and 87.3 K for Ar) together with CO2 adsorption at 273 K and immersion calorimetry into liqs. of different mol. dimensions. Ar adsorption in narrow carbon micropores takes place at a higher relative pressure compared to N2 due to a weaker effective adsorption potential (lower strength of dispersion forces), including the absence of specific interactions of Ar with the adsorbent surface. Application of advanced theor. approaches based on the d. functional theory (NLDFT and QSDFT) provides an accurate description of the pore-size distribution (PSD). The PSD obtained from the Ar adsorption data at 87.3 K is in good agreement with immersion calorimetry measurements. Ar adsorption at 87.3 K in combination with the application of advanced DFT methods (e.g. QSDFT) allows for a reliable characterization of the narrow microporosity in highly heterogeneous activated carbons.
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  30. 30
    Del Rio Castillo, A. E.; Pellegrini, V.; Ansaldo, A.; Ricciardella, F.; Sun, H.; Marasco, L.; Buha, J.; Dang, Z.; Gagliani, L.; Lago, E.; Curreli, N.; Gentiluomo, S.; Palazon, F.; Prato, M.; Oropesa-Nuñez, R.; Toth, P. S.; Mantero, E.; Crugliano, M.; Gamucci, A.; Tomadin, A.; Polini, M.; Bonaccorso, F. High-Yield Production of 2D Crystals by Wet-Jet Milling. Mater. Horiz. 2018, 5 (5), 890– 904,  DOI: 10.1039/C8MH00487K
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    High-yield production of 2D crystals by wet-jet milling
    Del Rio Castillo, A. E.; Pellegrini, V.; Ansaldo, A.; Ricciardella, F.; Sun, H.; Marasco, L.; Buha, J.; Dang, Z.; Gagliani, L.; Lago, E.; Curreli, N.; Gentiluomo, S.; Palazon, F.; Prato, M.; Oropesa-Nunez, R.; Toth, P. S.; Mantero, E.; Crugliano, M.; Gamucci, A.; Tomadin, A.; Polini, M.; Bonaccorso, F.
    Materials Horizons (2018), 5 (5), 890-904CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
    Efficient and scalable prodn. of two-dimensional (2D) materials is required to overcome technol. hurdles towards the creation of a 2D-material-based industry. Here, we present a novel approach developed for the exfoliation of layered crystals, i.e., graphite, hexagonal-boron nitride and transition metal dichalcogenides. The process is based on high-pressure wet-jet-milling (WJM), resulting in a 2 L h-1 prodn. of 10 g L-1 of single- and few-layer 2D crystal flakes in dispersion making the scaling-up more affordable. The WJM process enables the prodn. of defect-free and high quality 2D-crystal dispersions on a large scale, opening the way for their full exploitation in different com. applications, e.g., as anode active material in lithium ion batteries, as reinforcement in polymer-graphene composites, and as conductive inks, as we demonstrate in this report.
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    Bellani, S.; Petroni, E.; Del Rio Castillo, A. E.; Curreli, N.; Martín-García, B.; Oropesa-Nuñez, R.; Prato, M.; Bonaccorso, F. Scalable Production of Graphene Inks via Wet-Jet Milling Exfoliation for Screen-Printed Micro-Supercapacitors. Adv. Funct. Mater. 2019, 29 (14), 1807659,  DOI: 10.1002/adfm.201807659
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    Beydaghi, H.; Abouali, S.; Thorat, S. B.; Del Rio Castillo, A. E.; Bellani, S.; Lauciello, S.; Gentiluomo, S.; Pellegrini, V.; Bonaccorso, F. 3D Printed Silicon-Few Layer Graphene Anode for Advanced Li-Ion Batteries. RSC Adv. 2021, 11 (56), 35051– 35060,  DOI: 10.1039/D1RA06643A
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    3D printed silicon-few layer graphene anode for advanced Li-ion batteries
    Beydaghi, Hossein; Abouali, Sara; Thorat, Sanjay B.; Del Rio Castillo, Antonio Esau; Bellani, Sebastiano; Lauciello, Simone; Gentiluomo, Silvia; Pellegrini, Vittorio; Bonaccorso, Francesco
    RSC Advances (2021), 11 (56), 35051-35060CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
    The printing of three-dimensional (3D) porous electrodes for Li-ion batteries is considered a key driver for the design and realization of advanced energy storage systems. While different 3D printing techniques offer great potential to design and develop 3D architectures, several factors need to be addressed to print 3D electrodes, maintaining an optimal trade-off between electrochem. and mech. performances. Herein, we report the first demonstration of 3D printed Si-based electrodes fabricated using a simple and cost-effective fused deposition modeling (FDM) method, and implemented as anodes in Li-ion batteries. To fulfil the printability requirement while maximizing the electrochem. performance, the compn. of the FDM filament has been engineered using polylactic acid as the host polymeric matrix, a mixt. of carbon black-doped polypyrrole and wet-jet milling exfoliated few-layer graphene flakes as conductive additives, and Si nanoparticles as the active material. The creation of a continuous conductive network and the control of the structural properties at the nanoscale enabled the design and realization of flexible 3D printed anodes, reaching a specific capacity up to ∼345 mA h g-1 at the c.d. of 20 mA g-1, together with a capacity retention of 96% after 350 cycles. The obtained results are promising for the fabrication of flexible polymeric-based 3D energy storage devices to meet the challenges ahead for the design of next-generation electronic devices.
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  33. 33
    Levchenko, S.; Marangon, V.; Bellani, S.; Pasquale, L.; Bonaccorso, F.; Pellegrini, V.; Hassoun, J. Influence of Ion Diffusion on the Lithium-Oxygen Electrochemical Process and Battery Application Using Carbon Nanotubes-Graphene Substrate. ACS Appl. Mater. Interfaces 2023, 15 (33), 39218– 39233,  DOI: 10.1021/acsami.3c05240
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    Influence of Ion Diffusion on the Lithium-Oxygen Electrochemical Process and Battery Application Using Carbon Nanotubes-Graphene Substrate
    Levchenko, Stanislav; Marangon, Vittorio; Bellani, Sebastiano; Pasquale, Lea; Bonaccorso, Francesco; Pellegrini, Vittorio; Hassoun, Jusef
    ACS Applied Materials & Interfaces (2023), 15 (33), 39218-39233CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Lithium-oxygen (Li-O2) batteries are nowadays among the most appealing next-generation energy storage systems in view of a high theor. capacity and the use of transition-metal-free cathodes. Nevertheless, the practical application of these batteries is still hindered by limited understanding of the relationships between cell components and performances. In this work, we investigate a Li-O2 battery by originally screening different gas diffusion layers (GDLs) characterized by low sp. surface area (<40 m2 g-1) with relatively large pores (absence of micropores), graphitic character, and the presence of a fraction of the hydrophobic PTFE polymer on their surface (<20 wt %). The electrochem. characterization of Li-O2 cells using bare GDLs as the support indicates that the oxygen redn. reaction (ORR) occurs at potentials below 2.8 V vs Li+/Li, while the oxygen evolution reaction (OER) takes place at potentials higher than 3.6 V vs Li+/Li. Furthermore, the relatively high impedance of the Li-O2 cells at the pristine state remarkably decreases upon electrochem. activation achieved by voltammetry. The Li-O2 cells deliver high reversible capacities, ranging from ~ 6 to ~ 8 mA h cm-2 (referred to the geometric area of the GDLs). The Li-O2 battery performances are rationalized by the investigation of a practical Li+ diffusion coeff. (D) within the cell configuration adopted herein. The study reveals that D is higher during ORR than during OER, with values depending on the characteristics of the GDL and on the cell state of charge. Overall, D values range from ~ 10-10 to ~ 10-8 cm2 s-1 during the ORR and ~ 10-17 to ~ 10-11 cm2 s-1 during the OER. The most performing GDL is used as the support for the deposition of a substrate formed by few-layer graphene and multiwalled carbon nanotubes to improve the reaction in a Li-O2 cell operating with a max. specific capacity of 1250 mA h g-1 (1 mA h cm-2) at a c.d. of 0.33 mA cm-2. XPS on the electrode tested in our Li-O2 cell setup suggests the formation of a stable solid electrolyte interphase at the surface which extends the cycle life.
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  34. 34
    Zappia, M. I.; Mastronardi, V.; Bellani, S.; Zuo, Y.; Bianca, G.; Gabatel, L.; Gentile, M.; Bagheri, A.; Beydaghi, H.; Drago, F.; Ferri, M.; Moglianetti, M.; Pompa, P. P.; Manna, L.; Bonaccorso, F. Graphene vs. Carbon Black Supports for Pt Nanoparticles: Towards next-Generation Cathodes for Advanced Alkaline Electrolyzers. Electrochim. Acta 2023, 462, 142696,  DOI: 10.1016/j.electacta.2023.142696
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    Graphene vs. carbon black supports for Pt nanoparticles: Towards next-generation cathodes for advanced alkaline electrolyzers
    Zappia, Marilena Isabella; Mastronardi, Valentina; Bellani, Sebastiano; Zuo, Yong; Bianca, Gabriele; Gabatel, Luca; Gentile, Matteo; Bagheri, Ahmad; Beydaghi, Hossein; Drago, Filippo; Ferri, Michele; Moglianetti, Mauro; Pompa, Pier Paolo; Manna, Liberato; Bonaccorso, Francesco
    Electrochimica Acta (2023), 462 (), 142696CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)
    The development of efficient and cost-effective H2O splitting electrolyzers is a fundamental step to support the achievement of climate neutrality by using renewable energy sources to produce green H2 as a form of clean fuel. The authors studied Pt-based nanostructured cathodes for high-performance alk. electrolyzers (AELs), showing the beneficial effect of graphene over traditional C black as nanocatalysts support. By relying on a H2O-based, scalable, synthetic method, surface-cleaned Pt nanoparticles were successfully produced and strongly anchored to defect-free graphene flakes, the latter produced through wet-jet milling exfoliation of natural graphite. Once deposited on conventional gas diffusion layers, Pt/graphene catalysts outperform traditional Pt on Vulcan (Pt/C) in terms of H evolution reaction (HER) activity and performance durability. The two-dimensional morphol. of graphene flakes strongly retains the catalysts in the electrode even in the absence of any binder, while intrinsically ensuring the exposure of the catalytic sites for the HER. This rationale enables the fabrication of high-performance AELs based on Pt/graphene cathodes. By using com. available cost-effective anodes (stainless-steel meshes), the authors' AELs reached current densities of 1 A cm-2 at a voltage of ≥1.71 V. These AELs can even operate up to >2 A cm-2 (e.g., 2.2 A cm-2 at 1.90 V), with stable performance during accelerated stress tests. The authors' study discloses two main aspects: (1) graphene is an effective conductive support for 1-10 nm-scale catalysts for the development of nanostructured cathodes with elevated catalytic properties and durable performance; (2) the use of efficient nanostructured cathodes can boost the AEL's performance to state-of-the-art values reported for proton-exchange membrane electrolyzers, avoiding the use of expensive anodes (e.g., Ir-based ones).
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  35. 35
    Eredia, M.; Bellani, S.; Zappia, M. I.; Gabatel, L.; Galli, V.; Bagheri, A.; Beydaghi, H.; Bianca, G.; Conticello, I.; Pellegrini, V.; Bonaccorso, F. High-Energy Density Aqueous Supercapacitors: The Role of Electrolyte PH and KI Redox Additive. APL Mater. 2022, 10 (10), 101102,  DOI: 10.1063/5.0106932
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    High-energy density aqueous supercapacitors: The role of electrolyte pH and KI redox additive
    Eredia, Matilde; Bellani, Sebastiano; Zappia, Marilena I.; Gabatel, Luca; Galli, Valerio; Bagheri, Ahmad; Beydaghi, Hossein; Bianca, Gabriele; Conticello, Irene; Pellegrini, Vittorio; Bonaccorso, Francesco
    APL Materials (2022), 10 (10), 101102CODEN: AMPADS; ISSN:2166-532X. (American Institute of Physics)
    Supercapacitors (SCs), including the most established electrochem. double layer capacitors (EDLCs), are energy storage systems that can be charged in the second timescale, while sustaining a great no. of re-charge cycles without losing efficiency. Undoubtedly, their major drawback is their insufficient energy d. compared to batteries. Meanwhile, the redn. of the SC costs using cheap and sustainable electrolytes is also a trivial criterion to be considered in the competition race of the energy storage technologies. In this work, we report an extended characterization of aq. SCs, screening acidic, neutral and alk. electrolytes, as well as the addn. of KI as a prototypical redox additive, and performing both two- and three-electrode configuration measurements. By using near-neutral electrolytes, our aq. EDLCs can reach a max. cell voltage superior to 2 V, enabling energy densities higher than 18 W h kg-1 (comparable or approaching those of lead acid and Ni-Cd batteries) at a power d. up to almost 7 kW kg-1 (significantly superior to those of competing battery technologies). The introduction of redox additives can significantly increase the capacity of the SCs. However, compared to EDLCs, both the cell voltage and the energy efficiency of the SCs decrease because of partially irreversible faradaic redox reactions and overpotentials of kinetically limited redox reactions. While debunking the myth that aq. SCs exhibit low energy d., our study also remarks the importance of adequately assessing aq. SCs, showing the current challenges of advanced SC architectures alternative to EDLCs. (c) 2022 American Institute of Physics.
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  36. 36
    Bagheri, A.; Bellani, S.; Beydaghi, H.; Eredia, M.; Najafi, L.; Bianca, G.; Zappia, M. I.; Safarpour, M.; Najafi, M.; Mantero, E.; Sofer, Z.; Hou, G.; Pellegrini, V.; Feng, X.; Bonaccorso, F. Functionalized Metallic 2D Transition Metal Dichalcogenide-Based Solid-State Electrolyte for Flexible All-Solid-State Supercapacitors. ACS Nano 2022, 16 (10), 16426– 16442,  DOI: 10.1021/acsnano.2c05640
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    Functionalized Metallic 2D Transition Metal Dichalcogenide-Based Solid-State Electrolyte for Flexible All-Solid-State Supercapacitors
    Bagheri, Ahmad; Bellani, Sebastiano; Beydaghi, Hossein; Eredia, Matilde; Najafi, Leyla; Bianca, Gabriele; Zappia, Marilena Isabella; Safarpour, Milad; Najafi, Maedeh; Mantero, Elisa; Sofer, Zdenek; Hou, Guorong; Pellegrini, Vittorio; Feng, Xinliang; Bonaccorso, Francesco
    ACS Nano (2022), 16 (10), 16426-16442CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Highly efficient and durable flexible solid-state supercapacitors (FSSSCs) are emerging as low-cost devices for portable and wearable electronics due to the elimination of leakage of toxic/corrosive liq. electrolytes and their capability to withstand elevated mech. stresses. Nevertheless, the spread of FSSSCs requires the development of durable and highly conductive solid-state electrolytes, whose electrochem. characteristics must be competitive with those of traditional liq. electrolytes. Here, we propose an innovative composite solid-state electrolyte prepd. by incorporating metallic two-dimensional group-5 transition metal dichalcogenides, namely, liq.-phase exfoliated functionalized niobium disulfide (f-NbS2) nanoflakes, into a sulfonated poly(ether ether ketone) (SPEEK) polymeric matrix. The terminal sulfonate groups in f-NbS2 nanoflakes interact with the sulfonic acid groups of SPEEK by forming a robust hydrogen bonding network. Consequently, the composite solid-state electrolyte is mech./dimensionally stable even at a degree of sulfonation of SPEEK as high as 70.2%. At this degree of sulfonation, the mech. strength is 38.3 MPa, and thanks to an efficient proton transport through the Grotthuss mechanism, the proton cond. is as high as 94.4 mS cm-1 at room temp. To elucidate the importance of the interaction between the electrode materials (including active materials and binders) and the solid-state electrolyte, solid-state supercapacitors were produced using SPEEK and poly(vinylidene fluoride) as proton conducting and nonconducting binders, resp. The use of our solid-state electrolyte in combination with proton-conducting SPEEK binder and carbonaceous electrode materials (mixt. of activated carbon, single/few-layer graphene, and carbon black) results in a solid-state supercapacitor with a specific capacitance of 116 F g-1 at 0.02 A g-1, optimal rate capability (76 F g-1 at 10 A g-1), and electrochem. stability during galvanostatic charge/discharge cycling and folding/bending stresses.
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  37. 37
    Najafi, M.; Bellani, S.; Galli, V.; Zappia, M. I.; Bagheri, A.; Safarpour, M.; Beydaghi, H.; Eredia, M.; Pasquale, L.; Carzino, R.; Lauciello, S.; Panda, J.-K.; Brescia, R.; Gabatel, L.; Pellegrini, V.; Bonaccorso, F. Carbon- α-Fe2O3 Composite Active Material for High-Capacity Electrodes with High Mass Loading and Flat Current Collector for Quasi-Symmetric Supercapacitors. Electrochem 2022, 3 (3), 463– 478,  DOI: 10.3390/electrochem3030032
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    Carbon-α-Fe2O3 Composite Active Material for High-Capacity Electrodes with High Mass Loading and Flat Current Collector for Quasi-Symmetric Supercapacitors
    Najafi, Maedeh; Bellani, Sebastiano; Galli, Valerio; Zappia, Marilena Isabella; Bagheri, Ahmad; Safarpour, Milad; Beydaghi, Hossein; Eredia, Matilde; Pasquale, Lea; Carzino, Riccardo; Lauciello, Simone; Panda, Jaya-Kumar; Brescia, Rosaria; Gabatel, Luca; Pellegrini, Vittorio; Bonaccorso, Francesco
    Electrochem (2022), 3 (3), 463-478CODEN: ELECHK; ISSN:2673-3293. (MDPI AG)
    In this work, we report the synthesis of an active material for supercapacitors (SCs), namely α-Fe2O3/carbon composite (C-Fe2O3) made of elongated nanoparticles linearly connected into a worm-like morphol., by means of electrospinning followed by a calcination/carbonization process. The resulting active material powder can be directly processed in the form of slurry to produce SC electrodes with mass loadings higher than 1 mg cm-2 on practical flat current collectors, avoiding the need for bulky porous substrate, as often reported in the literature. In aq. electrolyte (6 M KOH), the so-produced C-Fe2O3 electrodes display capacity as high as ∼140 mAh g-1 at a scan rate of 2 mV s-1, while showing an optimal rate capability (capacity of 32.4 mAh g-1 at a scan rate of 400 mV s-1). Thanks to their poor catalytic activity towards water splitting reactions, the electrode can operate in a wide potential range (-1.6 V-0.3 V vs. Hg/HgO), enabling the realization of performant quasi-sym. SCs based on electrodes with the same chem. compn. (but different active material mass loadings), achieving energy d. approaching 10 Wh kg-1 in aq. electrolytes.
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    Gogotsi, Y.; Simon, P. True Performance Metrics in Electrochemical Energy Storage. Science 2011, 334 (6058), 917– 918,  DOI: 10.1126/science.1213003
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    True performance metrics in electrochemical energy storage
    Gogotsi, Y.; Simon, P.
    Science (Washington, DC, United States) (2011), 334 (6058), 917-918CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    There is no expanded citation for this reference.
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    Laheäär, A.; Przygocki, P.; Abbas, Q.; Béguin, F. Appropriate Methods for Evaluating the Efficiency and Capacitive Behavior of Different Types of Supercapacitors. Electrochem. Commun. 2015, 60, 21– 25,  DOI: 10.1016/j.elecom.2015.07.022
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    Appropriate methods for evaluating the efficiency and capacitive behavior of different types of supercapacitors
    Laheaar, A.; Przygocki, P.; Abbas, Q.; Beguin, F.
    Electrochemistry Communications (2015), 60 (), 21-25CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)
    The development of new brands of supercapacitors (SCs) has led to a variety of energy storage mechanisms and frequently to performance overestimation or erroneous presentation of the capacitive behavior through applying math. relations valid only for elec. double-layer capacitors (EDLCs). This paper addresses a realistic evaluation of capacitive performance and efficiency of SCs based on carbon electrodes. The presented examples of imprecise data processing include misleading information, such as seeming discharge capacitance increase during SC aging and coulombic efficiencies of 90% for SCs involving redox processes while energy efficiency is only 50%. Even in typical EDLCs, energy efficiency is 5-10% lower than coulombic efficiency.
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    Noori, A.; El-Kady, M. F.; Rahmanifar, M. S.; Kaner, R. B.; Mousavi, M. F. Towards Establishing Standard Performance Metrics for Batteries, Supercapacitors and Beyond. Chem. Soc. Rev. 2019, 48 (5), 1272– 1341,  DOI: 10.1039/C8CS00581H
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    Towards establishing standard performance metrics for batteries, supercapacitors and beyond
    Noori, Abolhassan; El-Kady, Maher F.; Rahmanifar, Mohammad S.; Kaner, Richard B.; Mousavi, Mir F.
    Chemical Society Reviews (2019), 48 (5), 1272-1341CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    Over the past decade, electrochem. energy storage (EES) devices have greatly improved, as a wide variety of advanced electrode active materials and new device architectures have been developed. These new materials and devices should be evaluated against clear and rigorous metrics, primarily based on the evidence of real performances. A series of criteria are commonly used to characterize and report performance of EES systems in the literature. However, as advanced EES systems are becoming more and more sophisticated, the methodologies to reliably evaluate the performance of the electrode active materials and EES devices need to be refined to realize the true promise as well as the limitations of these fast-moving technologies, and target areas for further development. In the absence of a commonly accepted core group of metrics, inconsistencies may arise between the values attributed to the materials or devices and their real performances. Herein, we provide an overview of the energy storage devices from conventional capacitors to supercapacitors to hybrid systems and ultimately to batteries. The metrics for evaluation of energy storage systems are described, although the focus is kept on capacitive and hybrid energy storage systems. In addn., we discuss the challenges that still need to be addressed for establishing more sophisticated criteria for evaluating EES systems. We hope this effort will foster ongoing dialog and promote greater understanding of these metrics to develop an international protocol for accurate assessment of EES systems.
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    Pomerantseva, E.; Bonaccorso, F.; Feng, X.; Cui, Y.; Gogotsi, Y. Energy Storage: The Future Enabled by Nanomaterials. Science 2019, 366 (6468), eaan8285  DOI: 10.1126/science.aan8285
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    Zhang, L. L.; Zhao, X. S. Carbon-Based Materials as Supercapacitor Electrodes. Chem. Soc. Rev. 2009, 38 (9), 2520– 2531,  DOI: 10.1039/b813846j
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    Carbon-based materials as supercapacitor electrodes
    Zhang, Li Li; Zhao, X. S.
    Chemical Society Reviews (2009), 38 (9), 2520-2531CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. This tutorial review provides a brief summary of recent research progress on carbon-based electrode materials for supercapacitors, as well as the importance of electrolytes in the development of supercapacitor technol. The basic principles of supercapacitors, the characteristics and performances of various nanostructured carbon-based electrode materials are discussed. Aq. and nonaq. electrolyte solns. used in supercapacitors are compared. The trend on future development of high-power and high-energy supercapacitors is analyzed.
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    Qu, D. Studies of the Activated Carbons Used in Double-Layer Supercapacitors. J. Power Sources 2002, 109 (2), 403– 411,  DOI: 10.1016/S0378-7753(02)00108-8
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    Studies of the activated carbons used in double-layer supercapacitors
    Qu, Deyang
    Journal of Power Sources (2002), 109 (2), 403-411CODEN: JPSODZ; ISSN:0378-7753. (Elsevier Science B.V.)
    The specific capacitance of activated carbons is detd. by both the ratio of edge/basal orientation and the nature of functional group on the surface. The difference between the edge and the basal layers results from the semiconductive properties of basal layer. The ratio of edge/basal orientation can be estd. by XRD. The wettability of activated carbons is detd. by the nature of functional groups on the surface. Most of the surface groups are electrochem. active. The impact of the surface groups on electrochem. performance of the activated C electrodes was studied by various surfactant treatments. The a.c. impedance and const. current discharge techniques were used. Two types of surface groups which had capacitor-like or battery-like behaviors, resp., were revealed and discussed. The surface groups with battery-like behavior should be avoided. Non-sym. electrode arrangement should be considered for a double-layer supercapacitor to take the advantages of pseudo-capacitance of the surface groups with capacitor-like behaviors.
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    Hurst, J. M.; Li, L.; Liu, H. Adventitious Hydrocarbons and the Graphite-Water Interface. Carbon 2018, 134, 464– 469,  DOI: 10.1016/j.carbon.2018.04.020
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    Adventitious hydrocarbons and the graphite-water interface
    Hurst, Justin M.; Li, Lei; Liu, Haitao
    Carbon (2018), 134 (), 464-469CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    This paper reports the adsorption of airborne and waterborne hydrocarbon contaminants on graphite and their impact on the graphite-water interfacial properties. Exposing a freshly exfoliated highly oriented pyrolytic graphite (HOPG) surface to ambient air and 1-octadecene vapor (ca. 1 ppm) caused a ca. 30% and 70% decrease in its double layer capacitance, resp. Similarly, a 38% decrease of capacitance was obsd. within 1500 min after a freshly cleaved HOPG was immersed in 1 M NaCl soln.; liq. phase ellipsometry data showed that a contamination layer of ca. 0.6-2 nm was formed on the HOPG surface within the same time frame. The capacitance of a contaminated sample can be partially and temporarily restored by applying a high or low potential (-1.222 V or 0.778 V vs. Ag/AgCl). Herein we report that hydrocarbon contamination on graphite is significant in both water and air.
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    Kang, J.; Wen, J.; Jayaram, S. H.; Yu, A.; Wang, X. Development of an Equivalent Circuit Model for Electrochemical Double Layer Capacitors (EDLCs) with Distinct Electrolytes. Electrochim. Acta 2014, 115, 587– 598,  DOI: 10.1016/j.electacta.2013.11.002
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    Development of an equivalent circuit model for electrochemical double layer capacitors (EDLCs) with distinct electrolytes
    Kang, Jinhee; Wen, John; Jayaram, Shesha H.; Yu, Aiping; Wang, Xiaohui
    Electrochimica Acta (2014), 115 (), 587-598CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)
    An equivalent circuit model for electrochem. double layer capacitors (EDLCs) is proposed through analyzing the electrochem. impedance spectroscopy (EIS) measurements. The model is developed based on the Grahame theory, while these capacitive or resistive behaviors in the presence of charge diffusion and the ion adsorption at the double layer interface and bulk media were studied. This circuit model, upon its validation against the EIS data, is successfully applied to characterize the practical EDLC devices. Meanwhile, exptl. results were obtained from different EDLC cells that consist of the activated C-based electrodes and two electrolytes, namely, aq. (H2SO4) and org. (Et4NBF4/PC). The model predicts the useful parameters (such as resistance and capacitance) which help interpret electrochem. reactions at the electrode/electrolyte interface. The quant. dependence of impedance on the applied electrode potential is analyzed for two electrolytes during charging/discharging, and its correlation with the internal resistance (referred ESR) was studied.
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    Gamby, J.; Taberna, P. L.; Simon, P.; Fauvarque, J. F.; Chesneau, M. Studies and Characterisations of Various Activated Carbons Used for Carbon/Carbon Supercapacitors. J. Power Sources 2001, 101 (1), 109– 116,  DOI: 10.1016/S0378-7753(01)00707-8
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    Studies and characterisations of various activated carbons used for carbon/carbon supercapacitors
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    Journal of Power Sources (2001), 101 (1), 109-116CODEN: JPSODZ; ISSN:0378-7753. (Elsevier Science B.V.)
    Various activated carbons from the PICA Company have been tested in supercapacitor cells in order to compare their performances. The differences measured in terms of sp. capacitance and cell resistance are presented. Porosity measurements made on activated carbon powders and electrode allowed a better understanding of the electrochem. behavior of these activated carbons. In this way, the PICACTIF SC carbon was found to be an interesting active material for supercapacitors, with a sp. capacitance as high as 125 F/g.
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    Randin, Jean P.; Yeager, Ernest
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    In a continuation of previous work (J. P. Randin and E. Yeager, 1971) the nonfaradaic differential electrode capacitance of the basal plane of high-pressure, stress-annealed pyrolytic graphite was detd. in contact with an aq. soln. by using an a.c. impedance bridge. The capacitance had almost a parabolic dependence on elec. potential in concd. electrolytes, and was independent of pH. The measured capacitance compares favorably with the theoretical value.
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    Kim, T.; Lim, S.; Kwon, K.; Hong, S.-H.; Qiao, W.; Rhee, C. K.; Yoon, S.-H.; Mochida, I. Electrochemical Capacitances of Well-Defined Carbon Surfaces. Langmuir 2006, 22 (22), 9086– 9088,  DOI: 10.1021/la061380q
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    Electrochemical Capacitances of Well-Defined Carbon Surfaces
    Kim, Taegon; Lim, Seongyop; Kwon, Kihyun; Hong, Seong-Hwa; Qiao, Wenming; Rhee, Choong Kyun; Yoon, Seong-Ho; Mochida, Isao
    Langmuir (2006), 22 (22), 9086-9088CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    Reported is the capacitive behavior of homogeneous and well-defined surfaces of pristine C nanofibers (CNFs) and surface-modified CNFs. The capacitances of the well-defined CNFs were measured with cyclic voltammetry to correlate the surface structure with capacitance. Among the studied pristine CNFs, the edge surfaces of platelet CNFs (PCNF) and herringbone CNFs were more effective in capacitive charging than the basal plane surface of tubular CNF by a factor of 3-5. Graphitization of PCNF (GPCNF) changed the edge surface of PCNF into a domelike basal plane surface, and the corresponding capacitances decreased from 12.5 to 3.2 F/g. A chem. oxidn. of the GPCNF, however, recovered a clear edge surface by removal of the curved basal planes to increase the capacitance to 5.6 F/g. The difference in the contribution of the edge surface and basal-plane surface to the capacitance of CNF was discussed in terms of the anisotropic cond. of graphitic materials.
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    Menéndez, J. A.; Phillips, J.; Xia, B.; Radovic, L. R. On the Modification and Characterization of Chemical Surface Properties of Activated Carbon: In the Search of Carbons with Stable Basic Properties. Langmuir 1996, 12 (18), 4404– 4410,  DOI: 10.1021/la9602022
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    On the Modification and Characterization of Chemical Surface Properties of Activated Carbon: In the Search of Carbons with Stable Basic Properties
    Menendez, J. Angel; Phillips, Jonathan; Xia, Bo; Radovic, Ljubisa R.
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    Differences between the surface chem. properties of H- and N-treated samples of an activated carbon were quantified by using several complementary techniques. Calorimetric studies conducted at 303 K revealed that the sample treated in N2 at 1223 K adsorbs a great deal of O with unusually high differential heats. In fact, both the quantity and the heat of adsorption increased when the treatment temp. was increased at 773-1223 K. In contrast, samples treated in H2 adsorbed less and less O2 as the treatment temp. was raised; after treatment at 1223 K, virtually no O2 adsorption occurred. At the same time, the H/C ratio in the H2-treated samples decreased with increasing treatment temp. Point of zero charge measurements revealed that only H2 treatments at high temp. (> 1073 K) create basic (hydrophobic) surfaces which are stable after prolonged air exposure. These results are consistent with the notion that the removal of O in the form of CO and CO2 during high-temp. N2 treatment leaves unsatd. carbon atoms at crystallite edges; these sites are very active for subsequent O adsorption. In contrast, high-temp. H2 treatment accomplishes 3 tasks: (1) it also removes surface O; (2) it stabilizes some of the (re)active sites by forming stable C-H bonds; (3) it gasifies the most reactive unsatd. carbon atoms. The relative contributions of these 3 effects depend on the temp. of H2 treatment. The carbon surface resulting from high-temp. H2 treatment is stable against subsequent O2 adsorption in ambient conditions.
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    de Jesus Silva, A. J.; Contreras, M. M.; Nascimento, C. R.; da Costa, M. F. Kinetics of Thermal Degradation and Lifetime Study of Poly(Vinylidene Fluoride) (PVDF) Subjected to Bioethanol Fuel Accelerated Aging. Heliyon 2020, 6 (7), e04573  DOI: 10.1016/j.heliyon.2020.e04573
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    Polymer Degradation and Stability (1994), 43 (3), 423-30CODEN: PDSTDW; ISSN:0141-3910.
    A systematic study of the thermal degrdn. of a series of homopolymers and copolymers of chlorotrifluoroethylene and vinylidene fluoride was carried out using thermogravimetry and thermal volatilization anal. (TVA). Volatile products were sepd. by subambient TVA and characterized by means of IR spectroscopy and mass spectrometry. On degrdn., poly(chlorotrifluoroethylene) gives the monomer as the major product and CO2, C2F2Cl2, C3F5Cl and C2F3Cl3 in traces. Poly(vinylidene fluoride) forms hydrogen fluoride in appreciable quantity along with the monomer and C4H3F3. The copolymers show a similar type of degrdn. pattern. The structural changes which take place during degrdn. have also been studied and mechanisms of formation of the various products are discussed.
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    Stobinski, L.; Lesiak, B.; Zemek, J.; Jiricek, P. Time Dependent Thermal Treatment of Oxidized MWCNTs Studied by the Electron and Mass Spectroscopy Methods. Appl. Surf. Sci. 2012, 258 (20), 7912– 7917,  DOI: 10.1016/j.apsusc.2012.04.127
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    Applied Surface Science (2012), 258 (20), 7912-7917CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
    Purified and functionalized in boiling concd. (68%) HNO3 acid the oxidized multiwall C nanotubes (ox-MWCNTs) under thermal treatment from RT to 630° and at 350° time dependent (1-4 h) were studied using the surface sensitive electron and mass spectroscopy methods. Mass spectroscopy indicates significant desorption of H2 and H2O to ∼300°. Higher H2 desorption rate from RT up to ∼100° is most likely caused by decompn. of org. acid impurities included within a bundle and in channels of the ox-MWCNTs after their functionalization by HNO3. In the range of 100-300° part of the detected H2, accompanied by desorption of CO2, may origin from desorbed H2O. Above 300°, the small amt. of desorbing H2O may result from transformation of carboxylic groups into carboxylic acid anhydride. Significant desorption of CO2 starting from 150° may result from decompn. of carboxylic groups, whereas desorption of CO starting at ∼300° from decompn. of acid anhydride groups created from carboxylic groups during thermal dehydration. Desorption of CO and CO2 at ∼470° may be due to decompn. of hydroxyl OH and carbonyl CO groups. Above 600° mainly decompn. of CO groups takes place and results in small desorption of CO. Time dependent (1-4 h) thermal treatment of ox-MWCNTs at 350° shows in XPS spectra decreasing amt. of CO in carboxyl groups and increasing amt. of CO in carbonyl and acid anhydride groups arising from carboxyl groups decompn. Between 350° and 470° the higher desorption rate of CO2 than CO indicates significant decompn. of carboxyl and carboxyl anhydride groups. At 350° the dynamic changes are indicated by the energy, intensity and full width at half max. (FWHM) of the π → π* interband transition and π loss peak, and quasi-elastic peak FWHM. During 4 h at 350° no C sp2 reconstruction is obsd. For the applied procedure of MWCNTs oxidn., large amt. of H2O and some org. acid impurities, resulting from the MWCNTs oxidn., remain in the CNTs channels, interstitial channels between tubes and at nanotubes surface.
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    Morgan, D. J. Comments on the XPS Analysis of Carbon Materials. C 2021, 7, 51,  DOI: 10.3390/c7030051
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    Comments on the XPS Analysis of Carbon Materials
    Morgan, David J.
    C (2021), 7 (3), 51CODEN: CABCC3; ISSN:2311-5629. (MDPI AG)
    The surface chem. of carbon materials is predominantly explored using XPS. However, many published papers have crit. failures in the published anal., stemming from an ill-informed approach to analyzing the spectroscopic data. Herein, a discussion on line shapes and changes in the spectral envelope of predominantly graphitic materials are explored, together with the use of the D-parameter, to ascertain graphitic content, using this information to highlight a simple and logical approach to strengthen confidence in the functionalization derived from the carbon core-level spectra.
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    Gieu, J.-B.; Winkler, V.; Courrèges, C.; El Ouatani, L.; Tessier, C.; Martinez, H. New Insights into the Characterization of the Electrode/Electrolyte Interfaces within LiMn2O4/Li4Ti5O12 Cells, by X-Ray Photoelectron Spectroscopy, Scanning Auger Microscopy and Time-of-Flight Secondary Ion Mass Spectrometry. J. Mater. Chem. A 2017, 5 (29), 15315– 15325,  DOI: 10.1039/C7TA02529G
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    New insights into the characterization of the electrode/electrolyte interfaces within LiMn2O4/Li4Ti5O12 cells, by X-ray photoelectron spectroscopy, scanning Auger microscopy and time-of-flight secondary ion mass spectrometry
    Gieu, Jean-Baptiste; Winkler, Volker; Courreges, Cecile; El Ouatani, Loubna; Tessier, Cecile; Martinez, Herve
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2017), 5 (29), 15315-15325CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    This work aims to study the electrode/electrolyte interfaces in a Li4Ti5O12 (LTO)/LiMn2O4 (LMO) cell assembled with a VC-contg. electrolyte and operating at 60°. LMO and LTO electrodes were mainly analyzed by XPS after the first and tenth galvanostatic cycles. The XPS results indicate that both electrodes are covered by surface layers during the first charge, coming from the degrdn. of electrolyte species, inducing irreversible capacity losses. Although the compns. of both layers are similar, the one formed on LTO electrodes is thicker than the one formed on LMO electrodes and contains small amts. of MnF2, homogeneously spread over the surface, as revealed by the fluorine elemental mapping obtained by a complementary scanning Auger microscopy expt. An addnl. measurement by time-of-flight secondary ion mass spectrometry indicates that the MnF2 is located on top of the surface layer. XPS anal. also indicates that during the first discharge, the thickness of the LTO electrode surface layer slightly decreases, due to a partial dissoln., while no changes are obsd. on the LMO electrode. After the tenth charge, the layers do not present any noticeable changes compared to the first charge. Interfacial layers in the LMO/LTO cell are mainly formed during the first charge, inducing an irreversible capacity loss. During the following cycles, the surface layer on LMO electrodes is stable, while it is slightly dissolved and reformed in each cycle on LTO electrodes, as suggested by the electrochem. data showing smaller and decreasing capacity losses, characteristic of the gradual passivation of these electrodes.
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    Bartnik, A.; Lisowski, W.; Sobczak, J.; Wachulak, P.; Budner, B.; Korczyc, B.; Fiedorowicz, H. Simultaneous Treatment of Polymer Surface by EUV Radiation and Ionized Nitrogen. Appl. Phys. A: Mater. Sci. Process. 2012, 109 (1), 39– 43,  DOI: 10.1007/s00339-012-7243-5
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    Simultaneous treatment of polymer surface by EUV radiation and ionized nitrogen
    Bartnik, Andrzej; Lisowski, Wojciech; Sobczak, Janusz; Wachulak, Przemyslaw; Budner, Boguslaw; Korczyc, Barbara; Fiedorowicz, Henryk
    Applied Physics A: Materials Science & Processing (2012), 109 (1), 39-43CODEN: APAMFC; ISSN:0947-8396. (Springer)
    The chem. modification of a poly(vinylidene fluoride) surface by extreme UV (EUV) irradn. in presence of ionized nitrogen was demonstrated for the first time. Nitrogen gas, injected into an interaction region, was ionized and excited by the EUV radiation from a laser-plasma source. The ionization degree and excited states of nitrogen were investigated using EUV spectrometry and the corresponding spectra are presented. Chem. modification of polymer after combined EUV and ionized nitrogen treatment was investigated using XPS. A significant contribution of nitrogen atoms in near-surface layer of the polymer after the treatment was demonstrated.
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    Wijaya, O.; Hartmann, P.; Younesi, R.; Markovits, I. I. E.; Rinaldi, A.; Janek, J.; Yazami, R. A Gamma Fluorinated Ether as an Additive for Enhanced Oxygen Activity in Li-O2 Batteries. J. Mater. Chem. A 2015, 3 (37), 19061– 19067,  DOI: 10.1039/C5TA03439F
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    A gamma fluorinated ether as an additive for enhanced oxygen activity in Li-O2 batteries
    Wijaya, Olivia; Hartmann, Pascal; Younesi, Reza; Markovits, Iulius I. E.; Rinaldi, Ali; Janek, Jurgen; Yazami, Rachid
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2015), 3 (37), 19061-19067CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    Perfluorocarbons (PFCs) are known for their high O2 soly. and have been investigated as additives in Li-O2 cells to enhance the cathode performance. However, the immiscibility of PFCs with org. solvents remains the main issue to be addressed as it hinders PFC practical application in Li-O2 cells. Furthermore, the effect of PFC additives on the O2 mass transport properties in the catholyte and their stability has not been thoroughly investigated. In this study, we investigated the properties of 1,1,1,2,2,3,3,4,4-nonafluoro-6-propoxyhexane (TE4), a gamma-fluorinated ether, and found it to be miscible with tetraglyme (TEGDME), a solvent commonly used in Li-O2 cells. The results show that with the TE4 additive up to 4 times higher O2 soly. and up to 2 times higher O2 diffusibility can be achieved. With 20 vol% TE4 addn., the discharge capacity increased about 10 times at a high discharge rate of 400 mA gC-1, corresponding to about 0.4 mA cm-2. The chem. stability of TE4 after Li-O2 cell discharge is investigated using 1H and 19F NMR, and the TE4 signal is retained after discharge. FTIR and XPS measurements indicate the presence of Li2O2 as a discharged product, together with side products from the parasitic reactions of LiTFSI salt and TEGDME.
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    Lesiak, B.; Kövér, L.; Tóth, J.; Zemek, J.; Jiricek, P.; Kromka, A.; Rangam, N. C Sp2/Sp3 Hybridisations in Carbon Nanomaterials - XPS and (X)AES Study. Appl. Surf. Sci. 2018, 452, 223– 231,  DOI: 10.1016/j.apsusc.2018.04.269
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    C sp2/sp3 hybridizations in carbon nanomaterials - XPS and (X)AES study
    Lesiak, B.; Kover, L.; Toth, J.; Zemek, J.; Jiricek, P.; Kromka, A.; Rangam, N.
    Applied Surface Science (2018), 452 (), 223-231CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
    The C KLL (KVV) Auger spectrum shape provides a measure of C sp2/sp3 hybridizations, alternative to C 1s spectra fitting. Due to a smaller kinetic energy of C KLL electrons vs. C 1s photoelectrons, the examd. information depths were attributed to lower or higher surface sensitivity, resp. The C nanostructures KLL Auger spectrum shape reflects d. of electronic states (DOS) and contains contributions of sp2 (graphite) and/or sp3 (diamond) hybridizations; for O- and H-contg. nanostructures this shape reflects chem. effects. C sp2/sp3 content was evaluated from parameter D, defined as an energy difference between the max. and min. of the first-deriv. C KLL spectrum, where dependence of parameter D on C sp2/sp3 hybridizations was assumed to be linear between graphite and diamond D values. Derived parameter D and thus C sp2/sp3 hybridization values were affected by procedure Auger spectrum smoothing procedures and D values used for ref. materials with pure sp3 and pure sp2 hybridizations. This work estd. the reliability of C sp2/sp3 hybridizations derived from parameter D detd. for a set of C nanomaterials and assessed chem. and morphol. effects on measured parameter D values. The presence of an inhomogeneous distribution of hybridization as a function of depth from the surface was identified mainly in graphene oxides vs. graphite and reduced graphene oxide. The largest effect on parameter D and then evaluated C sp2/sp3 content resulted from O and H at the surface and applied smoothing procedure in contrary to C nanomaterial structural properties (crystallinity, grain size). Parameter D values for C sp3 and C sp2 hybridizations, i.e., 13.2 and 23.1 eV, resp., were recommended to be used for linear interpolation proposed by Lascovich, et al. (1994).
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    Lascovich, J. C.; Scaglione, S. Comparison among XAES, PELS and XPS Techniques for Evaluation of Sp2 Percentage in a-C:H. Appl. Surf. Sci. 1994, 78 (1), 17– 23,  DOI: 10.1016/0169-4332(94)90026-4
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    Comparison among XAES, PELS and XPS techniques for evaluation of Sp2 percentage in a-C:H
    Lascovich, J. C.; Scaglione, S.
    Applied Surface Science (1994), 78 (1), 17-23CODEN: ASUSEE; ISSN:0169-4332.
    The ratio R of sp3 to sp2 in hydrogenated amorphous carbon (a-C:H) was evaluated by x-ray Auger electron spectroscopy (XAES), photo-EELS (PELS) and XPS. Hydrogenated amorphous carbon samples were deposited by a dual ion beam sputtering technique (DIBS). Percentages of Sp2 sites are at 45-70% for all analyzed samples. Values measured by XAES are ∼ 10% greater than values measured by PELS and the XPS evaluation appears in agreement with them. The R values also appear to be influenced not only by H contents, but even by deposition parameters (i.e., energy of the H ion beam and growth rate).
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    Lesiak, B.; Zemek, J.; Houdkova, J.; Kromka, A.; Jóźwik, A. Electron Spectra Line Shape Analysis of Highly Oriented Pyrolytic Graphite and Nanocrystalline Diamond. Anal. Sci. 2010, 26 (2), 217– 222,  DOI: 10.2116/analsci.26.217
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    Electron spectra line shape analysis of highly oriented pyrolytic graphite and nanocrystalline diamond
    Lesiak, Beata; Zemek, Josef; Houdkova, Jana; Kromka, Alexander; Jozwik, Adam
    Analytical Sciences (2010), 26 (2), 217-222CODEN: ANSCEN; ISSN:0910-6340. (Japan Society for Analytical Chemistry)
    The x-ray excited Auger electron spectroscopy (XAES), XPS and elastic peak electron spectroscopy (EPES) methods were applied in investigating samples of nanocryst. diamond and highly oriented pyrolytic graphite of various C sp2/sp3 ratios, crystallinity conditions and grain sizes. The compn. at the surface was estd. from the XPS. The C sp2/sp3 ratio was evaluated from the width of the XAES first deriv. C KLL spectra and from fitting of XPS C 1s spectra into components. The pattern recognition (PR) method applied for analyzing the spectra line shapes exhibited high accuracy in distinguishing different carbon materials. The PR method was found to be a potentially useful approach for identification, esp. important for technol. applications in fields of materials engineering and for controlling the chem. reaction products during synthesis.
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    Li, Z.; Wang, Y.; Kozbial, A.; Shenoy, G.; Zhou, F.; McGinley, R.; Ireland, P.; Morganstein, B.; Kunkel, A.; Surwade, S. P.; Li, L.; Liu, H. Effect of Airborne Contaminants on the Wettability of Supported Graphene and Graphite. Nat. Mater. 2013, 12 (10), 925– 931,  DOI: 10.1038/nmat3709
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    Effect of airborne contaminants on the wettability of supported graphene and graphite
    Li, Zhiting; Wang, Yongjin; Kozbial, Andrew; Shenoy, Ganesh; Zhou, Feng; McGinley, Rebecca; Ireland, Patrick; Morganstein, Brittni; Kunkel, Alyssa; Surwade, Sumedh P.; Li, Lei; Liu, Haitao
    Nature Materials (2013), 12 (10), 925-931CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
    It is generally accepted that supported graphene is hydrophobic and that its water contact angle is similar to that of graphite. The authors show that the water contact angles of freshly prepd. supported graphene and graphite surfaces increase when they are exposed to ambient air. By using IR spectroscopy and XPS, the authors demonstrate that airborne hydrocarbons adsorb on graphitic surfaces, and that a concurrent decrease in the water contact angle occurs when these contaminants are partially removed by both thermal annealing and controlled UV-O3 treatment. Graphitic surfaces are more hydrophilic than previously believed, and these results suggest that previously reported data on the wettability of graphitic surfaces may have been affected by unintentional hydrocarbon contamination from ambient air.
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    Farivar, F.; Yap, P. L.; Hassan, K.; Tung, T. T.; Tran, D. N. H.; Pollard, A. J.; Losic, D. Unlocking Thermogravimetric Analysis (TGA) in the Fight against “Fake Graphene” Materials. Carbon 2021, 179, 505– 513,  DOI: 10.1016/j.carbon.2021.04.064
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    Unlocking thermogravimetric analysis (TGA) in the fight against "Fake graphene" materials
    Farivar, Farzaneh; Yap, Pei Lay; Hassan, Kamrul; Tung, Tran Thanh; Tran, Diana N. H.; Pollard, Andrew J.; Losic, Dusan
    Carbon (2021), 179 (), 505-513CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    The absence of rapid, reliable and cost-effective quality control for industrially manufd. graphene materials is an immediate problem for the emerging graphene industry. Recent studies have alarmingly revealed that a large percentage of manufd. graphene materials traded worldwide have a large variation of properties, and some of them are overpriced graphite powders. Currently, benchmark graphene characterization methods based on localized anal. can provide information of key properties of graphene such as the no. of layers, particle size, and defects, only on individual graphene particles, which do not represent the properties of "bulk" material. To address these limitations, we developed and validated thermogravimetric anal. (TGA) as a simple anal. tool for characterization and quality control of manufd. few-layer graphene (FLG) and their non-graphene impurities in powder forms. Our results, using verified control and industrial samples, revealed that the deriv. TGA graphs of FLG, graphene oxide and graphite powders have signatory distinctive peaks with temp. of max. mass decompn. rates (Tmax) in specific ranges, reflecting differences of their structural, chem., and thermal properties, which are suitable for their qual. and quant. anal. The method is applicable for graphene manufacturers and end-users for simple, low-cost and reliable quality control of graphene materials that will not fail to detect "fake" graphene.
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    Strzemiecka, B.; Voelkel, A.; Donate-Robles, J.; Martín-Martínez, J. M. Assessment of the Surface Chemistry of Carbon Blacks by TGA-MS, XPS and Inverse Gas Chromatography Using Statistical Chemometric Analysis. Appl. Surf. Sci. 2014, 316, 315– 323,  DOI: 10.1016/j.apsusc.2014.07.174
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    Assessment of the surface chemistry of carbon blacks by TGA-MS, XPS and inverse gas chromatography using statistical chemometric analysis
    Strzemiecka, Beata; Voelkel, Adam; Donate-Robles, Jessica; Martin-Martinez, Jose Miguel
    Applied Surface Science (2014), 316 (), 315-323CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
    Four carbon blacks with different sp. surface areas and surface chemistries (C32, C71, C159 and C178) were analyzed by transmission electron microscopy (TEM) and nitrogen adsorption isotherms at 77 K. Their surface chemistries were analyzed by XPS, thermal gravimetric anal. coupled with mass spectrometry (TGA-MS) and inverse gas chromatog. (IGC). The carbon blacks contained 2.7-5.8 wt% volatiles corresponding to -OH, C-O, C = O and COO groups. The surface chem. parameters obtained with the different exptl. techniques were inter-related by using chemometric statistical anal. tools. The application of this methodol. showed that the carbon blacks with lower sp. surface area (C32 and C71) had basic character (electron donor) mainly due to C = O and C-O groups, whereas the carbon black with the highest sp. surface area (C178) showed acidic character (acceptor electron) due to its high content of OH groups. Moreover, the total surface energy and the dispersive component of the surface energy of the carbon blacks increased with the increase of their sp. surface area. In general the specific interactions of the carbon blacks also increased with the increase of their sp. surface area although C71 is exceptional due to higher oxygen content corresponding to C-O groups.
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    Cataldo, F. A Study on the Theraml Stability to 1000°C of Various Carbon Allotropes and Carbonaceous Matter both under Nitrogen and in Air. Fullerenes, Nanotubes Carbon Nanostruct. 2002, 10 (4), 293– 311,  DOI: 10.1081/FST-120016451
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    A study on the thermal stability to 1000° of various carbon allotropes and carbonaceous matter both under nitrogen and in air
    Cataldo, Franco
    Fullerenes, Nanotubes, and Carbon Nanostructures (2002), 10 (4), 293-311CODEN: FNCNAR; ISSN:1536-383X. (Marcel Dekker, Inc.)
    The thermal behavior of graphite, C60 fullerene, fullerene black (carbon soot contg. fullerenes), extd. fullerene black and diamond has been analyzed at ≤1000° by using TGA-DTA under flowing nitrogen at a heating rate of 20°/min. Small wt. losses have been recorded in the case of graphite and diamond. Furthermore no diamond graphitization was obsd. The sublimation of C60 and the fullerene fraction of fullerene black (both pristine and extd.) has been obsd. and discussed. The combustion reaction in flowing air of graphite, C60 and C70 fullerenes, fullerene black (both unextd. and extd.), carbon nanotubes and diamond has been studied by using TGA-DTA at 20°/min. C70 fullerene and fullerene black were the most reactive carbon materials with O2. The role played by C70 in the degrdn. of fullerites has been discussed. Among the carbon materials examd., the highest resistance to O2 attack has been shown by diamond and carbon nanotubes. The behavior of graphite is intermediate between diamond and fullerene blacks. The behavior of C60 fullerene appears closer to that of graphite, although it appears to be more reactive with O2. Specimens of graphite and carbon blacks N375 and N234 have been studied by using TGA-DTA in flowing air before and after a radiation treatment with neutrons or γ-radiation. The effect of the radiation damage on the combustion reaction of these carbon materials has been discussed.
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    Jahandar Lashaki, M.; Hashisho, Z.; Phillips, J. H.; Crompton, D.; Anderson, J. E.; Nichols, M. Mechanisms of Heel Buildup during Cyclic Adsorption-Desorption of Volatile Organic Compounds in a Full-Scale Adsorber-Desorber. Chem. Eng. J. 2020, 400, 124937,  DOI: 10.1016/j.cej.2020.124937
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    Mechanisms of heel buildup during cyclic adsorption-desorption of volatile organic compounds in a full-scale adsorber-desorber
    Jahandar Lashaki, Masoud; Hashisho, Zaher; Phillips, John H.; Crompton, David; Anderson, James E.; Nichols, Mark
    Chemical Engineering Journal (Amsterdam, Netherlands) (2020), 400 (), 124937CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
    This study elucidates the different mechanisms contributing to heel formation during cyclic adsorption-desorption of volatile org. compds. (VOCs) from a painting process in a full-scale adsorber-desorber. Two batches of beaded activated carbon (BAC), one subjected to normal operation and the other inadvertently exposed to oxygen during desorption, were investigated. Both batches displayed sharp increases in apparent d. during early cycles, which indicate high heel formation due to occupation/blockage of high-energy adsorption sites. Thermogravimetric anal. and gas chromatog.-mass spectrometry results identified non-desorbed adsorbates, adsorbate reaction byproducts and char from adsorbate decompn. The main heel formation mechanisms include physisorption and chemisorption followed by thermal oxidn., pyrolysis and eventually char formation. We hypothesize that non-ideal heat and purge gas distribution across the desorber is the reason for the accumulation of non-desorbed species and heel formation, shortening the lifetime of the adsorbent. In addn. to pyrolysis reactions that partially contributed to heel formation in the absence of oxygen, accumulation of thermal oxidn. products also contributed to the deterioration of adsorbent performance in the presence of oxygen during desorption. Moreover, extended exposure of the non-desorbed physisorbed and chemisorbed heel species to repetitive desorption cycles ultimately transformed them to permanent (non-desorbable) heel via polymn. and char formation. Therefore, to reduce heel buildup and maximize long-term adsorber performance, it is recommended to (i) ensure effective desorption conditions to prevent or minimize the accumulation of non-desorbed physisorbed species, and (ii) maintain sufficiently low oxygen levels in the desorption purge gas to minimize the detrimental effects of any species that do accumulate.
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    Losic, D.; Farivar, F.; Yap, P. L.; Karami, A. Accounting Carbonaceous Counterfeits in Graphene Materials Using the Thermogravimetric Analysis (TGA) Approach. Anal. Chem. 2021, 93 (34), 11859– 11867,  DOI: 10.1021/acs.analchem.1c02662
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    Accounting Carbonaceous Counterfeits in Graphene Materials Using the Thermogravimetric Analysis (TGA) Approach
    Losic, Dusan; Farivar, Farzaneh; Yap, Pei Lay; Karami, Afshin
    Analytical Chemistry (Washington, DC, United States) (2021), 93 (34), 11859-11867CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    Counterfeits in the supply chain of high-value advanced materials such as graphene and their derivs. have become a concerning problem with a potential neg. impact on this growing and emerging industry. Recent studies have revealed alarming facts that a large percentage of manufd. graphene materials on market are not graphene, raising considerable concerns for the end users. The common and recommended methods for the characterization of graphene materials, such as transmission electron microscopy (TEM), at. force microscopy (AFM), and Raman spectroscopy based on spot anal. and probing properties of individual graphene particles, are limited to provide the detn. of the properties of "bulk" graphene powders at a large scale and the identification of non-graphene components or purposely included additives. These limitations are creating counterfeit opportunities by adding low-cost black carbonaceous materials into manufd. graphene powders. To address this problem, it is crit. to have reliable characterization methods, which can probe the specific properties of graphene powders at bulk scale, confirm their typical graphene signature, and detect the presence of unwanted addnl. compds., where the thermogravimetric anal. (TGA) method is one of the most promising methods to perform this challenging task. This paper presents the evaluation of the TGA method and its ability to detect low-cost carbon additives such as graphite, carbon black, biochar, and activated carbon as potential counterfeiting materials to graphene materials and their derivs. such as graphene oxide (GO) and reduced GO. The superior performance of the TGA method is demonstrated here, showing its excellent capability to successfully detect these additives when mixed with graphene materials, which is not possible by two other comparative methods (Raman spectroscopy and powder X-ray diffraction (XRD)), which are used as the common characterization methods for graphene materials.
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    Fuertes, A. B.; Alvarez, S. Graphitic Mesoporous Carbons Synthesised through Mesostructured Silica Templates. Carbon 2004, 42 (15), 3049– 3055,  DOI: 10.1016/j.carbon.2004.06.020
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    Graphitic mesoporous carbons synthesised through mesostructured silica templates
    Fuertes, Antonio B.; Alvarez, Sonia
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    Different mico-mesoporous silicon carbide-derived carbons (SiC-CDC) were synthesized via gas phase chlorination at 1100°C and thereafter activated at 900°C and 1000°C with H2O steam using Ar and CO2 as the carrier gases. The phys. characterization data show that these materials are mainly amorphous, the structure does not change remarkably during the activation process and the surface chem. of the differently activated and treated materials remains the same and there are no functional groups at the SiC-CDC surface. N2, Ar and CO2 sorption measurements indicate an increase in the sp. surface area and pore size distribution with increasing the activation temp., whereas the influence of the carrier gas during synthesis is minimal. Although the sp. surface areas and pore size distributions differed, the electrochem. parameters in 1 M (C2H5)3CH3NBF4 acetonitrile soln. for all SiC-CDC materials were similar - specific gravimetric capacitances 130 ± 18 F g-1 and volumetric capacitance 67 ± 14 F cm-3 were calcd. Abs. phase angle values from -85° to -88° at low frequencies and very high energy and power densities 22 Wh kg-1 at 20 kW kg-1 and 12 Wh dm-3 at 10 kW dm-3 have been achieved.
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  • Abstract

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    Figure 1. (a) Electrical modeling of the electrode/electrolyte interface, including various capacitances contributing to the overall interfacial capacitance. The capacitance associated with the impurity-free electrode material/electrolyte interface is modeled as CEDL1, while the capacitance of the impurity-covered electrode material/electrolyte is represented by CEDL2. Beyond the capacitance terms associated with the dielectric layer of surface impurities, i.e., Ci and CX, the electrical equivalent circuit includes the leakage resistance (RLEAK) associated with self-discharge processes. Other impedance elements completing the modeling of the whole EDLC (e.g., ZW, CC/E, RC/E, etc...) are discussed in the relevant literature. (45,46) (b) Sketch of the Dirac cone electronic structure of the graphene, the Helmholtz double-layer, and dielectric layer atop active materials determining CQ, CH, and Ci, respectively. (c) Sketch of the furnace used for H2-assisted thermal treatment of electrode materials, which were initially supposed to undergo graphitization and/or cleaning processes.

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    Figure 2

    Figure 2. (a) Elemental composition of the electrode materials before and after H2-assisted thermal treatment at various temperatures (from 500 to 800 °C). (b) C and (c) O functionalities at. % (normalized on the overall C and at. %, respectively) of the investigated electrode materials. The data have been estimated from the analysis of the XPS spectra (wide scan, C 1s, and O 1s spectra). (d) First derivative of the XAES C KLL spectra (parameter D) of the investigated electrode materials.

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    Figure 3

    Figure 3. TGA curves measured in (a) N2 and (b) O2 for activated carbons before (pristine) and after H2-assisted thermal treatments at various temperatures (H2-500 °C, H2-600 °C, H2-700 °C, and H2-800 °C).

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    Figure 4

    Figure 4. Structural characterization of the activated carbon before (pristine) and after the H2-assisted thermal treatments at various temperatures (H2-500 °C, H2-600 °C, H2-700 °C, and H2-800 °C). (a) Raman spectra and (b) I(D)/I(G) vs. annealing temperature plot measured for the investigated samples. (c) XRD patterns measured for the investigated samples. (d) N2 adsorption/desorption isotherms measured for the investigated electrode materials, before (pristine) and after H2-assisted thermal treatments at various temperatures (H2-500 °C, H2-600 °C, H2-700 °C, and H2-800 °C). The inset panel shows the PSD, calculated by applying QSDFT to the Ar adsorption data at 87 K, for the investigated electrode materials.

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    Figure 5

    Figure 5. (a) CV curves (voltage scan rate = 500 mV s–1) and (b) GCD profiles (specific current = 1 A g–1) measured for the investigated ELDCs (pristine, H2-500 °C, H2-600 °C, H2-700 °C, and H2-800 °C). (c) Cg of the investigated EDLCs as a function of the specific current (data extrapolated from the analysis of the GCD profiles). (d) Ragone plots measured for the investigated EDLCs.

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    Figure 6

    Figure 6. (a) CgAC of the pristine and H2-700 °C EDLCs as a function of the specific current. Case 1 refers to data calculated considering 13.7 wt % of adsorbed water in the pristine activated carbon powder and the removal of 80 wt % of PVDF after the H2-assisted thermal treatment. Case 2 refers to data calculated assuming 29.9 wt % of adsorbed species (including water and carbonaceous species) in the pristine activated carbon powder and the removal of 80 wt % of PVDF after the H2-assisted thermal treatment. (b) Comparison between CsurfAC of pristine and H2-700 °C EDLCs at 1 and 10 A g–1.

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  • References

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      "Ion sliding" on graphene: a novel concept to boost supercapacitor performance
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      Efficient ionic transport in nanoporous carbon electrodes is pivotal for the development of high-rate electrochem. capacitive energy storage in supercapacitors (SCs). Over the past decade, the understanding of the charging/discharging mechanisms in nanostructured carbon electrodes and the elucidation of confinement and desolvation of ions in elec. charged carbon nanopores have spurred the development of advanced SCs holding ever-increasing energy d. Crucially, these advancements have to be accomplished without sacrificing the extraordinary power handling and cycling lifetime of the SC. In this work, we investigated the interaction between single-/few-layer graphene (SLG/FLG) flakes or activated carbon (AC) films and 1 M tetraethylammonium tetrafluoroborate (TEABF4) in propylene carbonate (PC) by lateral force microscopy (LFM) measurements. We unravel that the electrolyte nanotribol. on SLG/FLG flakes incorporated into AC-based electrodes is effective at boosting the power performance of com.-like SCs (active material mass loading ∼10 mg cm-2), thus maximizing the advantage of using nanoporous nanocarbon electrodes with high energy d. At a charge/discharge (CD) c.d. of 0.1 A g-1, our hybrid AC:SLG/FLG-based SC shows a 30% increase of specific capacitance (Cg) compared to the ref. device, i.e., the AC-based one (Cg from 76.8 F g-1 to 98.2 F g-1). At higher CD current densities (>1 A g-1), the AC-based device displays a resistive behavior, while the AC:SLG/FLG-based SCs still exhibit a Cg of 23.9 and 5.2 F g-1 at CD current densities as high as 2.5 and 5 A g-1, resp. Beyond the control of the nanoporosity of carbon materials and the inter-ionic interaction of the electrolytes, the rationalization of the relationship between the nanotribol. of nanocarbons and the performance of the corresponding SCs offers new opportunities to optimize the SC design compatibly with established high-throughput industrial manufg.
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      A review. Significant progress has been made in recent years in theor. modeling of the elec. double layer (EDL), a key concept in electrochem. important for energy storage, electrocatalysis, and multitudes of other technol. applications. However, major challenges remain in understanding the microscopic details of the electrochem. interface and charging mechanisms under realistic conditions. This review delves into theor. methods to describe the equil. and dynamic responses of the EDL structure and capacitance for electrochem. systems commonly deployed for capacitive energy storage. Special emphasis is given to recent advances that intend to capture the nonclassical EDL behavior such as oscillatory ion distributions, polarization of nonmetallic electrodes, charge transfer, and various forms of phase transitions in the micropores of electrodes interfacing with an org. electrolyte or ionic liq. This comprehensive anal. highlights theor. insights into predictable relationships between materials characteristics and electrochem. performance and offers a perspective on opportunities for further development toward rational design and optimization of electrochem. systems.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXjtlCqtbs%253D&md5=4dea38a3b76a017d6e06392172860788
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      The double layer capacitance of stress-annealed graphite electrodes in contact with electrolytes is relatively low in comparison to metal electrodes. This behavior is interpreted as due to a low d. of electronic states around the Fermi level of graphite. Exptl. data from the literature are analyzed and a d. of states of the order of 2.4 × 1020 cm-3 eV-1 is obtained. This interpretation is in qual. agreement with theor. calcns. of the band structure of graphite and fits to the concn. of electrons and holes derived from cond. data.
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      Capacitance of carbon-based electrical double-layer capacitors
      Ji Hengxing; Zhao Xin; Qiao Zhenhua; Jung Jeil; Zhu Yanwu; Lu Yalin; Zhang Li Li; Ruoff Rodney S; MacDonald Allan H
      Nature communications (2014), 5 (), 3317 ISSN:.
      Experimental electrical double-layer capacitances of porous carbon electrodes fall below ideal values, thus limiting the practical energy densities of carbon-based electrical double-layer capacitors. Here we investigate the origin of this behaviour by measuring the electrical double-layer capacitance in one to five-layer graphene. We find that the capacitances are suppressed near neutrality, and are anomalously enhanced for thicknesses below a few layers. We attribute the first effect to quantum capacitance effects near the point of zero charge, and the second to correlations between electrons in the graphene sheet and ions in the electrolyte. The large capacitance values imply gravimetric energy storage densities in the single-layer graphene limit that are comparable to those of batteries. We anticipate that these results shed light on developing new theoretical models in understanding the electrical double-layer capacitance of carbon electrodes, and on opening up new strategies for improving the energy density of carbon-based capacitors.
      >> More from SciFinder ®
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      Graphitization as a Universal Tool to Tailor the Potential-Dependent Capacitance of Carbon Supercapacitors
      Weingarth, Daniel; Zeiger, Marco; Jaeckel, Nicolas; Aslan, Mesut; Feng, Guang; Presser, Volker
      Advanced Energy Materials (2014), 4 (13), 1400316/1-1400316/13CODEN: ADEMBC; ISSN:1614-6840. (Wiley-Blackwell)
      Most efforts to improve the energy d. of supercapacitors are currently dedicated to optimized porosity or hybrid devices employing pseudocapacitive elements. Little attention has been given to the effects of the low charge carrier d. of carbon on the total material capacitance. To study the effect of graphitization on the differential capacitance, carbon onion (also known as onion-like carbon) supercapacitors are chosen. The increase in d. of states (DOS) related to the low d. of charge carriers in carbon materials is an important effect that leads to a substantial increase in capacitance as the electrode potential is increased. Using carbon onions as a model, it is shown that this phenomenon cannot be related only to geometric aspects but must be the result of varying graphitization. This provides a new tool to significantly improve carbon supercapacitor performance, in addn. to having significant consequences for the modeling community where carbons usually are approximated to be ideal metallic conductors. Data on the structure, compn., and phase content of carbon onions are presented and the correlation between electrochem. performance and elec. resistance and graphitization is shown. Highly graphitic carbons show a stronger degree of electrochem. doping, making them very attractive for enhancing the capacitance.
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    12. 12
      Duignan, T. T.; Zhao, X. S. Impurities Limit the Capacitance of Carbon-Based Supercapacitors. J. Phys. Chem. C 2019, 123 (7), 4085– 4093,  DOI: 10.1021/acs.jpcc.8b12031
      12
      Impurities Limit the Capacitance of Carbon-Based Supercapacitors
      Duignan, Timothy T.; Zhao, Xiu Song
      Journal of Physical Chemistry C (2019), 123 (7), 4085-4093CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Supercapacitors cannot fulfill their potential as energy storage devices without substantially improving their comparatively low energy d. Doing so requires improving their capacitance. Unfortunately, predicting the capacitance of the carbon-based materials that typically make up supercapacitor electrodes is very difficult. Carbon materials can have an areal capacitance that is an order of magnitude lower than both that of std. metals and theor. expectations. Here, we provide new quantum mech. calcns. to demonstrate that the std. explanation of this unusually low capacitance in terms of the space charge capacitance is inadequate. We then demonstrate that a layer of hydrocarbon impurities, which has recently been shown to form on graphite, is likely the dominant cause of the low capacitance of graphite. We develop a model of this effect, which accounts for the penetration of solvent into the hydrocarbon layer as the voltage increases. This model explains the characteristic V shape of the capacitance as a function of voltage. We present evidence that this layer may also play a role in limiting the capacitance in real supercapacitor materials such as activated carbon.
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    13. 13
      Tolman, N. L.; Mukai, J. M.; Wang, S.; Zito, A.; Luo, T.; Liu, H. The Effect of Physical Adsorption on the Capacitance of Activated Carbon Electrodes. Carbon 2019, 150, 334– 339,  DOI: 10.1016/j.carbon.2019.05.005
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      The effect of physical adsorption on the capacitance of activated carbon electrodes
      Tolman, Nathan L.; Mukai, Jason M.; Wang, Shuqing; Zito, Alessandra; Luo, Tianyi; Liu, Haitao
      Carbon (2019), 150 (), 334-339CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      This work reports the effect of physisorption of org. compds. on the double layer capacitance of activated carbon electrodes. Exposure of activated carbon electrodes to toluene or chloroform vapor for less than 10 min resulted in a capacitance loss of 77% and 84%, resp. Even adsorbates, such as acetone and ethanol, miscible with the aq. Li2SO4 electrolyte caused 20-30% losses in capacitance. It was also found that there was an adsorbate size dependence: above a certain threshold, a larger adsorbate could have more than twice the impact on capacitance than a slightly smaller one. The results were consistent with the hypothesis that volatile org. contaminants (VOC) block access of the aq. electrolyte to the carbon electrode surface. Porous activated carbon is currently the material of choice for supercapacitor electrodes in both research labs. and com. supercapacitor applications. These facilities also often house and use many volatile org. solvents either for research and development or simply for cleaning purposes. Because of this, our work has significant implications to the research and development of carbon-based supercapacitors.
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    14. 14
      Wang, H.; Yoshio, M. Effect of Water Contamination in the Organic Electrolyte on the Performance of Activated Carbon/Graphite Capacitors. J. Power Sources 2010, 195 (1), 389– 392,  DOI: 10.1016/j.jpowsour.2009.06.097
      14
      Effect of water contamination in the organic electrolyte on the performance of activated carbon/graphite capacitors
      Wang, Hongyu; Yoshio, Masaki
      Journal of Power Sources (2010), 195 (1), 389-392CODEN: JPSODZ; ISSN:0378-7753. (Elsevier B.V.)
      The effect of water contamination in the electrolyte on the performance of AC/graphite capacitor has been investigated by electrochem. tests and in situ XRD measurements. The deterioration mechanisms for the charge storage ability of the electrodes in the capacitors using polluted electrolytes have also been addressed.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtV2jtrrE&md5=47ea41d09051b1a16161233fc6ecc49a
    15. 15
      Inamoto, J.; Matsuo, Y.; Katsumi, M.; Uchida, S.; Ishikawa, M.; Masuyama, T.; Tsukamoto, K.; Sato, Y. Effect of Hydrogen-Gas Treatment on the Local Structure of Graphene-like Graphite. Carbon 2020, 163, 162– 168,  DOI: 10.1016/j.carbon.2020.03.016
      15
      Effect of hydrogen-gas treatment on the local structure of graphene-like graphite
      Inamoto, Junichi; Matsuo, Yoshiaki; Katsumi, Maeda; Uchida, Satoshi; Ishikawa, Masashi; Masuyama, Takuya; Tsukamoto, Kaoru; Sato, Yuta
      Carbon (2020), 163 (), 162-168CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      Graphene-like graphite (GLG) has been expected as a new candidate for a large-capacity neg. electrode material of a lithium-ion battery. Recently, our group has reported that hydrogen-gas treatment of GLG lowered the mean-discharge potential and increased its capacity. In order to clarify the origin of this improvement, scanning tunneling microscopy (STM) was conducted together with simulation using d. functional theory calcn. A GLG mono-sheet suitable for STM observation was synthesized from highly oriented pyrolytic graphite (HOPG) as a raw material. A distorted honeycomb region surrounded by triangular one was obsd. for GLG mono-sheets and it was well simulated using a model consisting of a topmost graphene with pairwisely introduced ether groups underneath. The above honeycomb region disappeared for GLG treated with hydrogen gas (GLG-H), and it was also well simulated using a model in which each oxygen atom introduced in the graphene was substituted by two hydrogen atoms. Since the resulting local structure of GLG-H was similar to that of graphite which shows low discharge potential, this would lead to the increased accessible capacity under 2.0 V of cut-off voltage.
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    16. 16
      Matsuo, Y.; Taninaka, J.; Hashiguchi, K.; Sasaki, T.; Cheng, Q.; Okamoto, Y.; Tamura, N. Effect of Oxygen Contents in Graphene like Graphite Anodes on Their Capacity for Lithium Ion Battery. J. Power Sources 2018, 396, 134– 140,  DOI: 10.1016/j.jpowsour.2018.06.022
      16
      Effect of oxygen contents in graphene like graphite anodes on their capacity for lithium ion battery
      Matsuo, Yoshiaki; Taninaka, Junichi; Hashiguchi, Katsuki; Sasaki, Toshiyuki; Cheng, Qian; Okamoto, Yasuharu; Tamura, Noriyuki
      Journal of Power Sources (2018), 396 (), 134-140CODEN: JPSODZ; ISSN:0378-7753. (Elsevier B.V.)
      Graphene like graphite (GLG) samples contg. various amts. of oxygen are prepd. from the thermal redn. of graphite oxide (GO) and are used as anodes of lithium ion battery. The oxygen/carbon (O/C) ratios in GLG varied from 0 to 0.08, depending on the thermal redn. temp., oxygen gas pressure during heat treatment and degree of oxidn. of the starting GO. The cell voltage during discharge almost linearly increases below 1 V independent of the oxygen contents in them. The discharge capacity of GLG above 1 V increases with the increase in the oxygen content with a slope of lithium/oxygen ratio of 3 at lower O/C ratios. Then the slope becomes smaller and the discharge capacity reaches 673 mAhg-1 for GLG with O/C = 0.08. When GLG is treated with hydrogen gas, considerable amts. of oxygen atoms are substituted by hydrogen ones. The discharge capacity of the resulting GLG samples is larger than that expected form their oxygen contents and coulombic efficiency is slightly improved up to 59%. Introduction of oxygen atoms within carbon layers results in the large increase in the interlayer spacing during charging, which leads to accommodation of large amts. of lithium ions.
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    17. 17
      Takeuchi, M.; Maruyama, T.; Koike, K.; Mogami, A.; Oyama, T.; Kobayashi, H. Non-Porous Carbon for a High Energy Density Electric Double Layer Capacitor. Electrochemistry 2001, 69 (6), 487– 492,  DOI: 10.5796/electrochemistry.69.487
      17
      Non-porous carbon for a high energy density electric double layer capacitor
      Takeuchi, Makoto; Maruyama, Takamichi; Koike, Katsumi; Mogami, Akinori; Oyama, Takashi; Kobayashi, Hiroshi
      Electrochemistry (Tokyo, Japan) (2001), 69 (6), 487-492CODEN: EECTFA; ISSN:1344-3542. (Electrochemical Society of Japan)
      Apparently non-porous activated carbon with a sp. surface area less than 100 m2/g (BET) prepd. from calcined carbon of petroleum coke is studied as the polarized electrode for an Elec. Double Layer Capacitor (EDLC). The non-porous carbon makes negligibly small elec. double layer when it is dipped into an electrolyte soln. in the beginning. During the initial charging process, however, "solvent co-intercalation of ions" builds double layers in the pos. and the neg. electrodes, and during the discharging process, the excess ions go out, while the opposite ions come in, to maintain the double layers elec. neutral. After that, the electrodes behave like conventional activated porous carbon electrodes with an extra high dense capacitance. The obsd. phenomenon is discussed from the viewpoints of the interlayer distance in graphitelike structure, the mol. vol. of solvent for electrolyte, the residual functional groups such as active oxidized hydrogen obsd. by NMR, and of the elimination method for the residual active oxidized hydrogen by heat treatment in H2 atmosphere, as well as the prepn. method for source carbon.
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    18. 18
      Moussa, G.; Matei Ghimbeu, C.; Taberna, P.-L.; Simon, P.; Vix-Guterl, C. Relationship between the Carbon Nano-Onions (CNOs) Surface Chemistry/Defects and Their Capacitance in Aqueous and Organic Electrolytes. Carbon 2016, 105, 628– 637,  DOI: 10.1016/j.carbon.2016.05.010
      18
      Relationship between the carbon nano-onions (CNOs) surface chemistry/defects and their capacitance in aqueous and organic electrolytes
      Moussa, Georges; Matei Ghimbeu, Camelia; Taberna, Pierre-Louis; Simon, Patrice; Vix-Guterl, Cathie
      Carbon (2016), 105 (), 628-637CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      The effect of surface functionalities on supercapacitor performance was highlighted often in many works. However, studies devoted to the influence of C defects did not gain particular attention due to the difficulty to quantify such parameter. In this context, C nano-onions were used as model material to understand the influence of the surface chem. (nature and amt. of O groups) and structural defects (active surface area, ASA) on the capacitance. Different types of thermal treatments in oxidizing or reducing atms. allowed to finely tune the surface chem. and the ASA as demonstrated by temp. programmed desorption coupled with mass spectrometry (TPD-MS). For the 1st time, the exact control of these characteristics independently one of each other allowed to highlight an important influence of the C defects on the capacitance in org. and aq. electrolytes which outbalance the O functional group effect.
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    19. 19
      Hu, W.; Sun, X. N.; Xu, D.; Xiao, Z. H.; Chen, X. Y. Microporous Carbon Materials by Hydrogen Treatment: The Balance of Porosity and Graphitization upon the Capacitive Performance. Ind. Eng. Chem. Res. 2017, 56 (25), 7253– 7259,  DOI: 10.1021/acs.iecr.7b01626
      19
      Microporous Carbon Materials by Hydrogen Treatment: The Balance of Porosity and Graphitization upon the Capacitive Performance
      Hu, Wei; Sun, Xiao Na; Xu, Dong; Xiao, Zheng Hui; Chen, Xiang Ying
      Industrial & Engineering Chemistry Research (2017), 56 (25), 7253-7259CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)
      The balance of porosity and graphitization toward carbon materials plays a crucial role in detg. the capacitive performance. In this work, this purpose has been successfully implemented by adjusting the carbonization temp. and hydrogen gas treatment. Oxygen contg. functional groups have conspicuously reduced by the coeffects of hydrogen gas and high temp. on carbon materials. Besides, by treatment at a temp. of 800 °C with hydrogen, the electrochem. performances have been greatly improved. The electrode treated at the temp. of 800 °C with hydrogen displays higher specific capacitances of 171 F g-1 compared with that of bare carbon electrode of 145 F g-1, owing to enlarged BET surface area and pore vol. and reduced resistance. At the same time, the electrode treated at the temp. of 800 °C with hydrogen exhibits a higher cycling stability of 96.3% of primary specific capacitances after 5000 cycles and energy d. of 8.36 Wh kg-1, resp.
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    20. 20
      Qin, T.; Shi, Z.; Li, M.; Wang, C. Effect of Reduction Heat Treatment in H2 Atmosphere on Structure and Electrochemical Properties of Activated Carbon. J. Solid State Electrochem. 2015, 19 (5), 1437– 1446,  DOI: 10.1007/s10008-015-2767-1
      20
      Effect of reduction heat treatment in H2 atmosphere on structure and electrochemical properties of activated carbon
      Qin, Ting-ting; Shi, Zhi-qiang; Li, Ming-wei; Wang, Cheng-yang
      Journal of Solid State Electrochemistry (2015), 19 (5), 1437-1446CODEN: JSSEFS; ISSN:1432-8488. (Springer)
      Activated carbon is heat-treated in a H2 atmosphere at 600, 800, and 1000 °C for 1 h, resp., to be used as electrode material for elec. double layer capacitors (EDLCs). After heat treatment, the surface morphol. has no obvious change as compared with the raw material. The sp. surface area and pore vol. of sample treated at 600 °C have a slightly increase while those of samples treated at higher temp. decrease. XPS and elemental anal. indicate that oxygen contg. functional groups on the sample are significantly reduced after treatment. The electrochem. performance of samples was evaluated using cyclic voltammetry and galvanostatic charge-discharge tests in 1 M TEABF4/PC electrolyte. The sample treated at 600 °C shows the optimized electrochem. performance with increase capacitance, enhanced stability, and improved energy d. Its initial specific capacitance is near 127 F/g, and initial coulombic efficiency is about 52 %. At 3.0 V, its energy d. reaches 32 Wh/kg and specific capacitance is about 70 F/g at 1 A/g even after 10,000 charge-discharge cycles. Thus, heat treatment at 600 °C under H2 atmosphere is an effective method to improve electrochem. properties of EDLCs based on activated carbon material.
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    21. 21
      Zhong, Z.; Aika, K. Effect of Hydrogen Treatment of Active Carbon as a Support for Promoted Ruthenium Catalysts for Ammonia Synthesis. Chem. Commun. 1997, (13), 1223– 1224,  DOI: 10.1039/a702273e
      21
      Effect of hydrogen treatment of active carbon as a support for promoted ruthenium catalysts for ammonia synthesis
      Zhong, Zhihua; Aika, Ken-ichi
      Chemical Communications (Cambridge) (1997), (13), 1223-1224CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      Hydrogen treatment of active carbon (A.C.) at temps. ranging from 1073 to 1188 K for 12 h is an effective method for eliminating surface impurities, leading to the prepn. of useful ruthenium catalysts; for example, 2 mass% Ru-BaO/A.C. (Ba/Ru = 5) yields 2 mmol NH3 h-1 g-1 at 588 K under 1 atm.
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    22. 22
      Oliveira, L. C. A.; Silva, C. N.; Yoshida, M. I.; Lago, R. M. The Effect of H2 Treatment on the Activity of Activated Carbon for the Oxidation of Organic Contaminants in Water and the H2O2 Decomposition. Carbon 2004, 42 (11), 2279– 2284,  DOI: 10.1016/j.carbon.2004.05.003
      22
      The effect of H2 treatment on the activity of activated carbon for the oxidation of organic contaminants in water and the H2O2 decomposition
      Oliveira, Luiz C. A.; Silva, Cristina N.; Yoshida, Maria I.; Lago, Rochel M.
      Carbon (2004), 42 (11), 2279-2284CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Science Ltd.)
      H2O2 reactions, i.e. H2O2 decompn. and oxidn. of orgs. in aq. medium, were studied in the presence of activated C. It was obsd. that the C pre-treatment with H at 300, 500, 700 and 800° resulted in an increase in activity for both reactions. The carbons were characterized by BET N adsorption, thermogravimetric analyses (TG), temp. programmed redn. (TPR), ESR (EPR), iodometric titrn. and detn. of the acid/basic sites. TPR expts. showed that activated C reacts with H at temps. >400°. The treatment produces a slight increase in the surface area. EPR analyses indicate the absence of unpaired electrons in the C. Iodometric titrns. and TG analyses suggested that the treatment with H generates redn. sites in the C structure, with concn. of approx. 0.33, 0.53, 0.59, 0.65 and 0.60 mmol/g for carbons treated at 25, 300, 500, 700 and 800°, resp. It was also obsd. the appearance of basic sites which might be related to the redn. sites. It is proposed that these reducing sites in the C can activate H2O2 to generate HO* radicals which can lead to 2 competitive reactions, i.e. the H2O2 decompn. or the oxidn. of orgs. in water.
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    23. 23
      Malmberg, S.; Arulepp, M.; Tarasova, E.; Vassiljeva, V.; Krasnou, I.; Krumme, A. Electrochemical Evaluation of Directly Electrospun Carbide-Derived Carbon-Based Electrodes in Different Nonaqueous Electrolytes for Energy Storage Applications. C 2020, 6, 59,  DOI: 10.3390/c6040059
      23
      Electrochemical evaluation of directly electrospun carbide-derived carbon-based electrodes in different nonaqueous electrolytes for energy storage applications
      Malmberg, Siret; Arulepp, Mati; Tarasova, Elvira; Vassiljeva, Viktoria; Krasnou, Illia; Krumme, Andres
      C (2020), 6 (4), 59CODEN: CABCC3; ISSN:2311-5629. (MDPI AG)
      This study focuses on the electrochem. behavior of thin-layer fibrous carbide-derived carbon (CDC) electrospun electrodes in com. and research and development stage org.-solvent and ionic liq. (IL) based electrolytes. The majority of earlier published works stated various electrolytes with asym. cells of powder-based pressure-rolled (PTFE), or slurry-cast electrodes, were significantly different than the presented CDC-based fibrous spun electrodes. The benefits of the fibrous structure are relatively low thickness (20μm), flexibility and mech. durability. Thin-layered durable electrode materials are gaining more interest and importance in mech. more demanding applications such as the space industry and in wearable devices, and need to achieve a targeted balance between mech., elec. and electrochem. properties. The existing com. electrode technologies lack compatibility in such applications due to their limited mech. properties and high cost. The test results showed that the widest potential window dU ≤ 3.5 V was achieved in 1.5 M 1-ethyl-3-methylimidazoliumbis(trifluoromethyl-sulfonyl)imide (EMIm-TFSI) soln. in acetonitrile (ACN). Gravimetric capacitance reached 105.6 F g-1 for the pos. charged electrode. Cycle-life results revealed stable material capacitance and resistance over 3000 cycles.
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    24. 24
      Malmberg, S.; Arulepp, M.; Savest, N.; Tarasova, E.; Vassiljeva, V.; Krasnou, I.; Käärik, M.; Mikli, V.; Krumme, A. Directly Electrospun Electrodes for Electrical Double-Layer Capacitors from Carbide-Derived Carbon. J. Electrost. 2020, 103, 103396,  DOI: 10.1016/j.elstat.2019.103396
      24
      Directly electrospun electrodes for electrical double-layer capacitors from carbide-derived carbon
      Malmberg, Siret; Arulepp, Mati; Savest, Natalja; Tarasova, Elvira; Vassiljeva, Viktoria; Krasnou, Illia; Kaarik, Maike; Mikli, Valdek; Krumme, Andres
      Journal of Electrostatics (2020), 103 (), 103396CODEN: JOELDH; ISSN:0304-3886. (Elsevier B.V.)
      This work aims towards the optimization of porous carbon satd. nanofibres compn. for elec.-double layer (EDL) electrode's prepn. The properties of microporous carbide-derived carbon (CDC) based electrospun electrodes are discussed. The variable electrode compn. and their mech. properties were obsd. to obtain the highest EDL capacitance. Effect of densification pressure and -temp. of electrospun electrodes are discussed. Thin electrode layer enables faster charge-discharge capability and perform higher power with same consumption of electrode materials. The EDL capacitance of 114 Fg-1, detd. by cyclic voltammetry method within the voltage range of 0-2.7 V, was achieved.
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    25. 25
      Rose, M.; Korenblit, Y.; Kockrick, E.; Borchardt, L.; Oschatz, M.; Kaskel, S.; Yushin, G. Hierarchical Micro- and Mesoporous Carbide-Derived Carbon as a High-Performance Electrode Material in Supercapacitors. Small 2011, 7 (8), 1108– 1117,  DOI: 10.1002/smll.201001898
      25
      Hierarchical Micro- and Mesoporous Carbide-Derived Carbon as a High-Performance Electrode Material in Supercapacitors
      Rose, Marcus; Korenblit, Yair; Kockrick, Emanuel; Borchardt, Lars; Oschatz, Martin; Kaskel, Stefan; Yushin, Gleb
      Small (2011), 7 (8), 1108-1117CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Ordered mesoporous carbide-derived carbon (OM-CDC) materials produced by nanocasting of ordered mesoporous silica templates are characterized by a bimodal pore size distribution with a high ratio of micropores. The micropores result in outstanding adsorption capacities and the well-defined mesopores facilitate enhanced kinetics in adsorption processes. Here, for the first time, a systematic study is presented, in which the effects of synthesis temp. on the electrochem. performance of these materials in supercapacitors based on a 1 M aq. soln. of sulfuric acid and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liq. are reported. Cyclic voltammetry shows the specific capacitance of the OM-CDC materials exceeds 200 F g-1 in the aq. electrolyte and 185 F g-1 in the ionic liq., when measured in a sym. configuration in voltage ranges of up to 0.6 and 2 V, resp. The ordered mesoporous channels in the produced OM-CDC materials serve as ion-highways and allow for very fast ionic transport into the bulk of the OM-CDC particles. At room temp. the enhanced ion transport leads to 75% and 90% of the capacitance retention at current densities in excess of ∼10 A g-1 in ionic liq. and aq. electrolytes, resp. The supercapacitors based on 250-300 μm OM-CDC electrodes demonstrate an operating frequency of up to 7 Hz in aq. electrolyte. The combination of high specific capacitance and outstanding rate capabilities of the OM-CDC materials is unmatched by state-of-the art activated carbons and strictly microporous CDC materials.
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    26. 26
      Gomibuchi, E.; Ichikawa, T.; Kimura, K.; Isobe, S.; Nabeta, K.; Fujii, H. Electrode Properties of a Double Layer Capacitor of Nano-Structured Graphite Produced by Ball Milling under a Hydrogen Atmosphere. Carbon 2006, 44 (5), 983– 988,  DOI: 10.1016/j.carbon.2005.10.006
      26
      Electrode properties of a double layer capacitor of nano-structured graphite produced by ball milling under a hydrogen atmosphere
      Gomibuchi, Emi; Ichikawa, Takayuki; Kimura, Koichi; Isobe, Shigehito; Nabeta, Koji; Fujii, Hironobu
      Carbon (2006), 44 (5), 983-988CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      Nano-structural graphite prepd. by ball milling under H2 or Ar atm. was studied as an electrode for elec. double layer capacitors (EDLCs) by means of a conventional 2-electrode galvanostatic method. Esp., the product prepd. under H2 atmosphere using zirconia balls revealed 500 m2 g-1 surface area and showed 12 F g-1 specific capacitance, which was comparable to that of an activated carbon with large sp. surface area of 3000 m2 g-1 examd. as a ref. A proper condition of the milling time is rather a shorter time than ∼8 h, where the graphitic feature is remained in the ball milled product. On the other hand, for the sample prepd. by using steel balls, the specific capacitance per surface area was several hundreds times smaller than the others, indicating that the small amt. of Fe contamination during milling played a neg. role for the EDLC properties.
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    27. 27
      Brunauer, S.; Emmett, P. H.; Teller, E. Adsorption of Gases in Multimolecular Layers. J. Am. Chem. Soc. 1938, 60 (2), 309– 319,  DOI: 10.1021/ja01269a023
      27
      Adsorption of gases in multimolecular layers
      Brunauer, Stephen; Emmett, P. H.; Teller, Edward
      Journal of the American Chemical Society (1938), 60 (), 309-19CODEN: JACSAT; ISSN:0002-7863.
      The polarization theory of multimolecular adsorption is discussed critically. The adsorption energy due to attraction of dipoles induced into a nonpolar gas such as A is insufficient to constitute a major portion of the binding energy between adsorbed layers. Adsorption-isotherm equations for multimolecular adsorption are derived on the assumption that the same forces that produce condensation are responsible also for multimolecular adsorption. Numerous applications of the equations are given to exptl. adsorption isotherms. Cf. C. A. 32, 1159.3.
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    28. 28
      Dubinin, M. M. Fundamentals of the Theory of Adsorption in Micropores of Carbon Adsorbents: Characteristics of Their Adsorption Properties and Microporous Structures. Carbon 1989, 27 (3), 457– 467,  DOI: 10.1016/0008-6223(89)90078-X
      28
      Fundamentals of the theory of adsorption in micropores of carbon adsorbents: characteristics of their adsorption properties and microporous structures
      Dubinin, M. M.
      Carbon (1989), 27 (3), 457-67CODEN: CRBNAH; ISSN:0008-6223.
      Quant. methods of characterization of the adsorption properties and microporous structure covering the entire variety of micropore types have been elaborated on the basis of the theory of vapor adsorption in micropores. The general situation is encompassed by the three parameters of the Dubinin-Stoeckli equation (micropore vol., the characteristic adsorption energy, and variance) plus the sp. surface area of mesopores. They allow one to predict adsorption of different vapors and the adsorption vs. temp. relationships. The same parameters can be used to calc. the micropore size distribution patterns, the geometric surface area of micropores, and, where necessary, the vol. of micropores within a given size range. Benzene at 293 K and nitrogen at 77 K are not equiv. ref. vapors. Benzene is more appropriate to obtain a comprehensive characteristic of both the adsorption properties and the microporous structure.
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    29. 29
      Silvestre-Albero, J.; Silvestre-Albero, A.; Rodríguez-Reinoso, F.; Thommes, M. Physical Characterization of Activated Carbons with Narrow Microporosity by Nitrogen (77.4K), Carbon Dioxide (273K) and Argon (87.3K) Adsorption in Combination with Immersion Calorimetry. Carbon 2012, 50 (9), 3128– 3133,  DOI: 10.1016/j.carbon.2011.09.005
      29
      Physical characterization of activated carbons with narrow microporosity by nitrogen (77.4 K), carbon dioxide (273 K) and argon (87.3 K) adsorption in combination with immersion calorimetry
      Silvestre-Albero, J.; Silvestre-Albero, A.; Rodriguez-Reinoso, F.; Thommes, M.
      Carbon (2012), 50 (9), 3128-3133CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      To get more insight into the characterization of nanoporous carbons by gas adsorption, the use of different probe mols. was compared. A series of activated carbons with ranging porosity (burn-off) were prepd. from olive stones using CO2 as activating agent and characterized using N2 and Ar adsorption at low temp. (77.4 K for N2 and 87.3 K for Ar) together with CO2 adsorption at 273 K and immersion calorimetry into liqs. of different mol. dimensions. Ar adsorption in narrow carbon micropores takes place at a higher relative pressure compared to N2 due to a weaker effective adsorption potential (lower strength of dispersion forces), including the absence of specific interactions of Ar with the adsorbent surface. Application of advanced theor. approaches based on the d. functional theory (NLDFT and QSDFT) provides an accurate description of the pore-size distribution (PSD). The PSD obtained from the Ar adsorption data at 87.3 K is in good agreement with immersion calorimetry measurements. Ar adsorption at 87.3 K in combination with the application of advanced DFT methods (e.g. QSDFT) allows for a reliable characterization of the narrow microporosity in highly heterogeneous activated carbons.
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    30. 30
      Del Rio Castillo, A. E.; Pellegrini, V.; Ansaldo, A.; Ricciardella, F.; Sun, H.; Marasco, L.; Buha, J.; Dang, Z.; Gagliani, L.; Lago, E.; Curreli, N.; Gentiluomo, S.; Palazon, F.; Prato, M.; Oropesa-Nuñez, R.; Toth, P. S.; Mantero, E.; Crugliano, M.; Gamucci, A.; Tomadin, A.; Polini, M.; Bonaccorso, F. High-Yield Production of 2D Crystals by Wet-Jet Milling. Mater. Horiz. 2018, 5 (5), 890– 904,  DOI: 10.1039/C8MH00487K
      30
      High-yield production of 2D crystals by wet-jet milling
      Del Rio Castillo, A. E.; Pellegrini, V.; Ansaldo, A.; Ricciardella, F.; Sun, H.; Marasco, L.; Buha, J.; Dang, Z.; Gagliani, L.; Lago, E.; Curreli, N.; Gentiluomo, S.; Palazon, F.; Prato, M.; Oropesa-Nunez, R.; Toth, P. S.; Mantero, E.; Crugliano, M.; Gamucci, A.; Tomadin, A.; Polini, M.; Bonaccorso, F.
      Materials Horizons (2018), 5 (5), 890-904CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
      Efficient and scalable prodn. of two-dimensional (2D) materials is required to overcome technol. hurdles towards the creation of a 2D-material-based industry. Here, we present a novel approach developed for the exfoliation of layered crystals, i.e., graphite, hexagonal-boron nitride and transition metal dichalcogenides. The process is based on high-pressure wet-jet-milling (WJM), resulting in a 2 L h-1 prodn. of 10 g L-1 of single- and few-layer 2D crystal flakes in dispersion making the scaling-up more affordable. The WJM process enables the prodn. of defect-free and high quality 2D-crystal dispersions on a large scale, opening the way for their full exploitation in different com. applications, e.g., as anode active material in lithium ion batteries, as reinforcement in polymer-graphene composites, and as conductive inks, as we demonstrate in this report.
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    31. 31
      Bellani, S.; Petroni, E.; Del Rio Castillo, A. E.; Curreli, N.; Martín-García, B.; Oropesa-Nuñez, R.; Prato, M.; Bonaccorso, F. Scalable Production of Graphene Inks via Wet-Jet Milling Exfoliation for Screen-Printed Micro-Supercapacitors. Adv. Funct. Mater. 2019, 29 (14), 1807659,  DOI: 10.1002/adfm.201807659
      There is no corresponding record for this reference.
    32. 32
      Beydaghi, H.; Abouali, S.; Thorat, S. B.; Del Rio Castillo, A. E.; Bellani, S.; Lauciello, S.; Gentiluomo, S.; Pellegrini, V.; Bonaccorso, F. 3D Printed Silicon-Few Layer Graphene Anode for Advanced Li-Ion Batteries. RSC Adv. 2021, 11 (56), 35051– 35060,  DOI: 10.1039/D1RA06643A
      32
      3D printed silicon-few layer graphene anode for advanced Li-ion batteries
      Beydaghi, Hossein; Abouali, Sara; Thorat, Sanjay B.; Del Rio Castillo, Antonio Esau; Bellani, Sebastiano; Lauciello, Simone; Gentiluomo, Silvia; Pellegrini, Vittorio; Bonaccorso, Francesco
      RSC Advances (2021), 11 (56), 35051-35060CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
      The printing of three-dimensional (3D) porous electrodes for Li-ion batteries is considered a key driver for the design and realization of advanced energy storage systems. While different 3D printing techniques offer great potential to design and develop 3D architectures, several factors need to be addressed to print 3D electrodes, maintaining an optimal trade-off between electrochem. and mech. performances. Herein, we report the first demonstration of 3D printed Si-based electrodes fabricated using a simple and cost-effective fused deposition modeling (FDM) method, and implemented as anodes in Li-ion batteries. To fulfil the printability requirement while maximizing the electrochem. performance, the compn. of the FDM filament has been engineered using polylactic acid as the host polymeric matrix, a mixt. of carbon black-doped polypyrrole and wet-jet milling exfoliated few-layer graphene flakes as conductive additives, and Si nanoparticles as the active material. The creation of a continuous conductive network and the control of the structural properties at the nanoscale enabled the design and realization of flexible 3D printed anodes, reaching a specific capacity up to ∼345 mA h g-1 at the c.d. of 20 mA g-1, together with a capacity retention of 96% after 350 cycles. The obtained results are promising for the fabrication of flexible polymeric-based 3D energy storage devices to meet the challenges ahead for the design of next-generation electronic devices.
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    33. 33
      Levchenko, S.; Marangon, V.; Bellani, S.; Pasquale, L.; Bonaccorso, F.; Pellegrini, V.; Hassoun, J. Influence of Ion Diffusion on the Lithium-Oxygen Electrochemical Process and Battery Application Using Carbon Nanotubes-Graphene Substrate. ACS Appl. Mater. Interfaces 2023, 15 (33), 39218– 39233,  DOI: 10.1021/acsami.3c05240
      33
      Influence of Ion Diffusion on the Lithium-Oxygen Electrochemical Process and Battery Application Using Carbon Nanotubes-Graphene Substrate
      Levchenko, Stanislav; Marangon, Vittorio; Bellani, Sebastiano; Pasquale, Lea; Bonaccorso, Francesco; Pellegrini, Vittorio; Hassoun, Jusef
      ACS Applied Materials & Interfaces (2023), 15 (33), 39218-39233CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Lithium-oxygen (Li-O2) batteries are nowadays among the most appealing next-generation energy storage systems in view of a high theor. capacity and the use of transition-metal-free cathodes. Nevertheless, the practical application of these batteries is still hindered by limited understanding of the relationships between cell components and performances. In this work, we investigate a Li-O2 battery by originally screening different gas diffusion layers (GDLs) characterized by low sp. surface area (<40 m2 g-1) with relatively large pores (absence of micropores), graphitic character, and the presence of a fraction of the hydrophobic PTFE polymer on their surface (<20 wt %). The electrochem. characterization of Li-O2 cells using bare GDLs as the support indicates that the oxygen redn. reaction (ORR) occurs at potentials below 2.8 V vs Li+/Li, while the oxygen evolution reaction (OER) takes place at potentials higher than 3.6 V vs Li+/Li. Furthermore, the relatively high impedance of the Li-O2 cells at the pristine state remarkably decreases upon electrochem. activation achieved by voltammetry. The Li-O2 cells deliver high reversible capacities, ranging from ~ 6 to ~ 8 mA h cm-2 (referred to the geometric area of the GDLs). The Li-O2 battery performances are rationalized by the investigation of a practical Li+ diffusion coeff. (D) within the cell configuration adopted herein. The study reveals that D is higher during ORR than during OER, with values depending on the characteristics of the GDL and on the cell state of charge. Overall, D values range from ~ 10-10 to ~ 10-8 cm2 s-1 during the ORR and ~ 10-17 to ~ 10-11 cm2 s-1 during the OER. The most performing GDL is used as the support for the deposition of a substrate formed by few-layer graphene and multiwalled carbon nanotubes to improve the reaction in a Li-O2 cell operating with a max. specific capacity of 1250 mA h g-1 (1 mA h cm-2) at a c.d. of 0.33 mA cm-2. XPS on the electrode tested in our Li-O2 cell setup suggests the formation of a stable solid electrolyte interphase at the surface which extends the cycle life.
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    34. 34
      Zappia, M. I.; Mastronardi, V.; Bellani, S.; Zuo, Y.; Bianca, G.; Gabatel, L.; Gentile, M.; Bagheri, A.; Beydaghi, H.; Drago, F.; Ferri, M.; Moglianetti, M.; Pompa, P. P.; Manna, L.; Bonaccorso, F. Graphene vs. Carbon Black Supports for Pt Nanoparticles: Towards next-Generation Cathodes for Advanced Alkaline Electrolyzers. Electrochim. Acta 2023, 462, 142696,  DOI: 10.1016/j.electacta.2023.142696
      34
      Graphene vs. carbon black supports for Pt nanoparticles: Towards next-generation cathodes for advanced alkaline electrolyzers
      Zappia, Marilena Isabella; Mastronardi, Valentina; Bellani, Sebastiano; Zuo, Yong; Bianca, Gabriele; Gabatel, Luca; Gentile, Matteo; Bagheri, Ahmad; Beydaghi, Hossein; Drago, Filippo; Ferri, Michele; Moglianetti, Mauro; Pompa, Pier Paolo; Manna, Liberato; Bonaccorso, Francesco
      Electrochimica Acta (2023), 462 (), 142696CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)
      The development of efficient and cost-effective H2O splitting electrolyzers is a fundamental step to support the achievement of climate neutrality by using renewable energy sources to produce green H2 as a form of clean fuel. The authors studied Pt-based nanostructured cathodes for high-performance alk. electrolyzers (AELs), showing the beneficial effect of graphene over traditional C black as nanocatalysts support. By relying on a H2O-based, scalable, synthetic method, surface-cleaned Pt nanoparticles were successfully produced and strongly anchored to defect-free graphene flakes, the latter produced through wet-jet milling exfoliation of natural graphite. Once deposited on conventional gas diffusion layers, Pt/graphene catalysts outperform traditional Pt on Vulcan (Pt/C) in terms of H evolution reaction (HER) activity and performance durability. The two-dimensional morphol. of graphene flakes strongly retains the catalysts in the electrode even in the absence of any binder, while intrinsically ensuring the exposure of the catalytic sites for the HER. This rationale enables the fabrication of high-performance AELs based on Pt/graphene cathodes. By using com. available cost-effective anodes (stainless-steel meshes), the authors' AELs reached current densities of 1 A cm-2 at a voltage of ≥1.71 V. These AELs can even operate up to >2 A cm-2 (e.g., 2.2 A cm-2 at 1.90 V), with stable performance during accelerated stress tests. The authors' study discloses two main aspects: (1) graphene is an effective conductive support for 1-10 nm-scale catalysts for the development of nanostructured cathodes with elevated catalytic properties and durable performance; (2) the use of efficient nanostructured cathodes can boost the AEL's performance to state-of-the-art values reported for proton-exchange membrane electrolyzers, avoiding the use of expensive anodes (e.g., Ir-based ones).
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    35. 35
      Eredia, M.; Bellani, S.; Zappia, M. I.; Gabatel, L.; Galli, V.; Bagheri, A.; Beydaghi, H.; Bianca, G.; Conticello, I.; Pellegrini, V.; Bonaccorso, F. High-Energy Density Aqueous Supercapacitors: The Role of Electrolyte PH and KI Redox Additive. APL Mater. 2022, 10 (10), 101102,  DOI: 10.1063/5.0106932
      35
      High-energy density aqueous supercapacitors: The role of electrolyte pH and KI redox additive
      Eredia, Matilde; Bellani, Sebastiano; Zappia, Marilena I.; Gabatel, Luca; Galli, Valerio; Bagheri, Ahmad; Beydaghi, Hossein; Bianca, Gabriele; Conticello, Irene; Pellegrini, Vittorio; Bonaccorso, Francesco
      APL Materials (2022), 10 (10), 101102CODEN: AMPADS; ISSN:2166-532X. (American Institute of Physics)
      Supercapacitors (SCs), including the most established electrochem. double layer capacitors (EDLCs), are energy storage systems that can be charged in the second timescale, while sustaining a great no. of re-charge cycles without losing efficiency. Undoubtedly, their major drawback is their insufficient energy d. compared to batteries. Meanwhile, the redn. of the SC costs using cheap and sustainable electrolytes is also a trivial criterion to be considered in the competition race of the energy storage technologies. In this work, we report an extended characterization of aq. SCs, screening acidic, neutral and alk. electrolytes, as well as the addn. of KI as a prototypical redox additive, and performing both two- and three-electrode configuration measurements. By using near-neutral electrolytes, our aq. EDLCs can reach a max. cell voltage superior to 2 V, enabling energy densities higher than 18 W h kg-1 (comparable or approaching those of lead acid and Ni-Cd batteries) at a power d. up to almost 7 kW kg-1 (significantly superior to those of competing battery technologies). The introduction of redox additives can significantly increase the capacity of the SCs. However, compared to EDLCs, both the cell voltage and the energy efficiency of the SCs decrease because of partially irreversible faradaic redox reactions and overpotentials of kinetically limited redox reactions. While debunking the myth that aq. SCs exhibit low energy d., our study also remarks the importance of adequately assessing aq. SCs, showing the current challenges of advanced SC architectures alternative to EDLCs. (c) 2022 American Institute of Physics.
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    36. 36
      Bagheri, A.; Bellani, S.; Beydaghi, H.; Eredia, M.; Najafi, L.; Bianca, G.; Zappia, M. I.; Safarpour, M.; Najafi, M.; Mantero, E.; Sofer, Z.; Hou, G.; Pellegrini, V.; Feng, X.; Bonaccorso, F. Functionalized Metallic 2D Transition Metal Dichalcogenide-Based Solid-State Electrolyte for Flexible All-Solid-State Supercapacitors. ACS Nano 2022, 16 (10), 16426– 16442,  DOI: 10.1021/acsnano.2c05640
      36
      Functionalized Metallic 2D Transition Metal Dichalcogenide-Based Solid-State Electrolyte for Flexible All-Solid-State Supercapacitors
      Bagheri, Ahmad; Bellani, Sebastiano; Beydaghi, Hossein; Eredia, Matilde; Najafi, Leyla; Bianca, Gabriele; Zappia, Marilena Isabella; Safarpour, Milad; Najafi, Maedeh; Mantero, Elisa; Sofer, Zdenek; Hou, Guorong; Pellegrini, Vittorio; Feng, Xinliang; Bonaccorso, Francesco
      ACS Nano (2022), 16 (10), 16426-16442CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Highly efficient and durable flexible solid-state supercapacitors (FSSSCs) are emerging as low-cost devices for portable and wearable electronics due to the elimination of leakage of toxic/corrosive liq. electrolytes and their capability to withstand elevated mech. stresses. Nevertheless, the spread of FSSSCs requires the development of durable and highly conductive solid-state electrolytes, whose electrochem. characteristics must be competitive with those of traditional liq. electrolytes. Here, we propose an innovative composite solid-state electrolyte prepd. by incorporating metallic two-dimensional group-5 transition metal dichalcogenides, namely, liq.-phase exfoliated functionalized niobium disulfide (f-NbS2) nanoflakes, into a sulfonated poly(ether ether ketone) (SPEEK) polymeric matrix. The terminal sulfonate groups in f-NbS2 nanoflakes interact with the sulfonic acid groups of SPEEK by forming a robust hydrogen bonding network. Consequently, the composite solid-state electrolyte is mech./dimensionally stable even at a degree of sulfonation of SPEEK as high as 70.2%. At this degree of sulfonation, the mech. strength is 38.3 MPa, and thanks to an efficient proton transport through the Grotthuss mechanism, the proton cond. is as high as 94.4 mS cm-1 at room temp. To elucidate the importance of the interaction between the electrode materials (including active materials and binders) and the solid-state electrolyte, solid-state supercapacitors were produced using SPEEK and poly(vinylidene fluoride) as proton conducting and nonconducting binders, resp. The use of our solid-state electrolyte in combination with proton-conducting SPEEK binder and carbonaceous electrode materials (mixt. of activated carbon, single/few-layer graphene, and carbon black) results in a solid-state supercapacitor with a specific capacitance of 116 F g-1 at 0.02 A g-1, optimal rate capability (76 F g-1 at 10 A g-1), and electrochem. stability during galvanostatic charge/discharge cycling and folding/bending stresses.
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    37. 37
      Najafi, M.; Bellani, S.; Galli, V.; Zappia, M. I.; Bagheri, A.; Safarpour, M.; Beydaghi, H.; Eredia, M.; Pasquale, L.; Carzino, R.; Lauciello, S.; Panda, J.-K.; Brescia, R.; Gabatel, L.; Pellegrini, V.; Bonaccorso, F. Carbon- α-Fe2O3 Composite Active Material for High-Capacity Electrodes with High Mass Loading and Flat Current Collector for Quasi-Symmetric Supercapacitors. Electrochem 2022, 3 (3), 463– 478,  DOI: 10.3390/electrochem3030032
      37
      Carbon-α-Fe2O3 Composite Active Material for High-Capacity Electrodes with High Mass Loading and Flat Current Collector for Quasi-Symmetric Supercapacitors
      Najafi, Maedeh; Bellani, Sebastiano; Galli, Valerio; Zappia, Marilena Isabella; Bagheri, Ahmad; Safarpour, Milad; Beydaghi, Hossein; Eredia, Matilde; Pasquale, Lea; Carzino, Riccardo; Lauciello, Simone; Panda, Jaya-Kumar; Brescia, Rosaria; Gabatel, Luca; Pellegrini, Vittorio; Bonaccorso, Francesco
      Electrochem (2022), 3 (3), 463-478CODEN: ELECHK; ISSN:2673-3293. (MDPI AG)
      In this work, we report the synthesis of an active material for supercapacitors (SCs), namely α-Fe2O3/carbon composite (C-Fe2O3) made of elongated nanoparticles linearly connected into a worm-like morphol., by means of electrospinning followed by a calcination/carbonization process. The resulting active material powder can be directly processed in the form of slurry to produce SC electrodes with mass loadings higher than 1 mg cm-2 on practical flat current collectors, avoiding the need for bulky porous substrate, as often reported in the literature. In aq. electrolyte (6 M KOH), the so-produced C-Fe2O3 electrodes display capacity as high as ∼140 mAh g-1 at a scan rate of 2 mV s-1, while showing an optimal rate capability (capacity of 32.4 mAh g-1 at a scan rate of 400 mV s-1). Thanks to their poor catalytic activity towards water splitting reactions, the electrode can operate in a wide potential range (-1.6 V-0.3 V vs. Hg/HgO), enabling the realization of performant quasi-sym. SCs based on electrodes with the same chem. compn. (but different active material mass loadings), achieving energy d. approaching 10 Wh kg-1 in aq. electrolytes.
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    38. 38
      Gogotsi, Y.; Simon, P. True Performance Metrics in Electrochemical Energy Storage. Science 2011, 334 (6058), 917– 918,  DOI: 10.1126/science.1213003
      38
      True performance metrics in electrochemical energy storage
      Gogotsi, Y.; Simon, P.
      Science (Washington, DC, United States) (2011), 334 (6058), 917-918CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      There is no expanded citation for this reference.
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    39. 39
      Laheäär, A.; Przygocki, P.; Abbas, Q.; Béguin, F. Appropriate Methods for Evaluating the Efficiency and Capacitive Behavior of Different Types of Supercapacitors. Electrochem. Commun. 2015, 60, 21– 25,  DOI: 10.1016/j.elecom.2015.07.022
      39
      Appropriate methods for evaluating the efficiency and capacitive behavior of different types of supercapacitors
      Laheaar, A.; Przygocki, P.; Abbas, Q.; Beguin, F.
      Electrochemistry Communications (2015), 60 (), 21-25CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)
      The development of new brands of supercapacitors (SCs) has led to a variety of energy storage mechanisms and frequently to performance overestimation or erroneous presentation of the capacitive behavior through applying math. relations valid only for elec. double-layer capacitors (EDLCs). This paper addresses a realistic evaluation of capacitive performance and efficiency of SCs based on carbon electrodes. The presented examples of imprecise data processing include misleading information, such as seeming discharge capacitance increase during SC aging and coulombic efficiencies of 90% for SCs involving redox processes while energy efficiency is only 50%. Even in typical EDLCs, energy efficiency is 5-10% lower than coulombic efficiency.
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    40. 40
      Noori, A.; El-Kady, M. F.; Rahmanifar, M. S.; Kaner, R. B.; Mousavi, M. F. Towards Establishing Standard Performance Metrics for Batteries, Supercapacitors and Beyond. Chem. Soc. Rev. 2019, 48 (5), 1272– 1341,  DOI: 10.1039/C8CS00581H
      40
      Towards establishing standard performance metrics for batteries, supercapacitors and beyond
      Noori, Abolhassan; El-Kady, Maher F.; Rahmanifar, Mohammad S.; Kaner, Richard B.; Mousavi, Mir F.
      Chemical Society Reviews (2019), 48 (5), 1272-1341CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      Over the past decade, electrochem. energy storage (EES) devices have greatly improved, as a wide variety of advanced electrode active materials and new device architectures have been developed. These new materials and devices should be evaluated against clear and rigorous metrics, primarily based on the evidence of real performances. A series of criteria are commonly used to characterize and report performance of EES systems in the literature. However, as advanced EES systems are becoming more and more sophisticated, the methodologies to reliably evaluate the performance of the electrode active materials and EES devices need to be refined to realize the true promise as well as the limitations of these fast-moving technologies, and target areas for further development. In the absence of a commonly accepted core group of metrics, inconsistencies may arise between the values attributed to the materials or devices and their real performances. Herein, we provide an overview of the energy storage devices from conventional capacitors to supercapacitors to hybrid systems and ultimately to batteries. The metrics for evaluation of energy storage systems are described, although the focus is kept on capacitive and hybrid energy storage systems. In addn., we discuss the challenges that still need to be addressed for establishing more sophisticated criteria for evaluating EES systems. We hope this effort will foster ongoing dialog and promote greater understanding of these metrics to develop an international protocol for accurate assessment of EES systems.
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    41. 41
      Pomerantseva, E.; Bonaccorso, F.; Feng, X.; Cui, Y.; Gogotsi, Y. Energy Storage: The Future Enabled by Nanomaterials. Science 2019, 366 (6468), eaan8285  DOI: 10.1126/science.aan8285
      There is no corresponding record for this reference.
    42. 42
      Zhang, L. L.; Zhao, X. S. Carbon-Based Materials as Supercapacitor Electrodes. Chem. Soc. Rev. 2009, 38 (9), 2520– 2531,  DOI: 10.1039/b813846j
      42
      Carbon-based materials as supercapacitor electrodes
      Zhang, Li Li; Zhao, X. S.
      Chemical Society Reviews (2009), 38 (9), 2520-2531CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. This tutorial review provides a brief summary of recent research progress on carbon-based electrode materials for supercapacitors, as well as the importance of electrolytes in the development of supercapacitor technol. The basic principles of supercapacitors, the characteristics and performances of various nanostructured carbon-based electrode materials are discussed. Aq. and nonaq. electrolyte solns. used in supercapacitors are compared. The trend on future development of high-power and high-energy supercapacitors is analyzed.
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    43. 43
      Qu, D. Studies of the Activated Carbons Used in Double-Layer Supercapacitors. J. Power Sources 2002, 109 (2), 403– 411,  DOI: 10.1016/S0378-7753(02)00108-8
      43
      Studies of the activated carbons used in double-layer supercapacitors
      Qu, Deyang
      Journal of Power Sources (2002), 109 (2), 403-411CODEN: JPSODZ; ISSN:0378-7753. (Elsevier Science B.V.)
      The specific capacitance of activated carbons is detd. by both the ratio of edge/basal orientation and the nature of functional group on the surface. The difference between the edge and the basal layers results from the semiconductive properties of basal layer. The ratio of edge/basal orientation can be estd. by XRD. The wettability of activated carbons is detd. by the nature of functional groups on the surface. Most of the surface groups are electrochem. active. The impact of the surface groups on electrochem. performance of the activated C electrodes was studied by various surfactant treatments. The a.c. impedance and const. current discharge techniques were used. Two types of surface groups which had capacitor-like or battery-like behaviors, resp., were revealed and discussed. The surface groups with battery-like behavior should be avoided. Non-sym. electrode arrangement should be considered for a double-layer supercapacitor to take the advantages of pseudo-capacitance of the surface groups with capacitor-like behaviors.
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    44. 44
      Hurst, J. M.; Li, L.; Liu, H. Adventitious Hydrocarbons and the Graphite-Water Interface. Carbon 2018, 134, 464– 469,  DOI: 10.1016/j.carbon.2018.04.020
      44
      Adventitious hydrocarbons and the graphite-water interface
      Hurst, Justin M.; Li, Lei; Liu, Haitao
      Carbon (2018), 134 (), 464-469CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      This paper reports the adsorption of airborne and waterborne hydrocarbon contaminants on graphite and their impact on the graphite-water interfacial properties. Exposing a freshly exfoliated highly oriented pyrolytic graphite (HOPG) surface to ambient air and 1-octadecene vapor (ca. 1 ppm) caused a ca. 30% and 70% decrease in its double layer capacitance, resp. Similarly, a 38% decrease of capacitance was obsd. within 1500 min after a freshly cleaved HOPG was immersed in 1 M NaCl soln.; liq. phase ellipsometry data showed that a contamination layer of ca. 0.6-2 nm was formed on the HOPG surface within the same time frame. The capacitance of a contaminated sample can be partially and temporarily restored by applying a high or low potential (-1.222 V or 0.778 V vs. Ag/AgCl). Herein we report that hydrocarbon contamination on graphite is significant in both water and air.
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    45. 45
      Kang, J.; Wen, J.; Jayaram, S. H.; Yu, A.; Wang, X. Development of an Equivalent Circuit Model for Electrochemical Double Layer Capacitors (EDLCs) with Distinct Electrolytes. Electrochim. Acta 2014, 115, 587– 598,  DOI: 10.1016/j.electacta.2013.11.002
      45
      Development of an equivalent circuit model for electrochemical double layer capacitors (EDLCs) with distinct electrolytes
      Kang, Jinhee; Wen, John; Jayaram, Shesha H.; Yu, Aiping; Wang, Xiaohui
      Electrochimica Acta (2014), 115 (), 587-598CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)
      An equivalent circuit model for electrochem. double layer capacitors (EDLCs) is proposed through analyzing the electrochem. impedance spectroscopy (EIS) measurements. The model is developed based on the Grahame theory, while these capacitive or resistive behaviors in the presence of charge diffusion and the ion adsorption at the double layer interface and bulk media were studied. This circuit model, upon its validation against the EIS data, is successfully applied to characterize the practical EDLC devices. Meanwhile, exptl. results were obtained from different EDLC cells that consist of the activated C-based electrodes and two electrolytes, namely, aq. (H2SO4) and org. (Et4NBF4/PC). The model predicts the useful parameters (such as resistance and capacitance) which help interpret electrochem. reactions at the electrode/electrolyte interface. The quant. dependence of impedance on the applied electrode potential is analyzed for two electrolytes during charging/discharging, and its correlation with the internal resistance (referred ESR) was studied.
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    46. 46
      Gamby, J.; Taberna, P. L.; Simon, P.; Fauvarque, J. F.; Chesneau, M. Studies and Characterisations of Various Activated Carbons Used for Carbon/Carbon Supercapacitors. J. Power Sources 2001, 101 (1), 109– 116,  DOI: 10.1016/S0378-7753(01)00707-8
      46
      Studies and characterisations of various activated carbons used for carbon/carbon supercapacitors
      Gamby, J.; Taberna, P. L.; Simon, P.; Fauvarque, J. F.; Chesneau, M.
      Journal of Power Sources (2001), 101 (1), 109-116CODEN: JPSODZ; ISSN:0378-7753. (Elsevier Science B.V.)
      Various activated carbons from the PICA Company have been tested in supercapacitor cells in order to compare their performances. The differences measured in terms of sp. capacitance and cell resistance are presented. Porosity measurements made on activated carbon powders and electrode allowed a better understanding of the electrochem. behavior of these activated carbons. In this way, the PICACTIF SC carbon was found to be an interesting active material for supercapacitors, with a sp. capacitance as high as 125 F/g.
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    47. 47
      Randin, J.-P.; Yeager, E. Differential Capacitance Study on the Basal Plane of Stress-Annealed Pyrolytic Graphite. J. Electroanal. Chem. Interfacial Electrochem. 1972, 36 (2), 257– 276,  DOI: 10.1016/S0022-0728(72)80249-3
      47
      Differential capacitance study on the basal plane of stress-annealed pyrolytic graphite
      Randin, Jean P.; Yeager, Ernest
      Journal of Electroanalytical Chemistry and Interfacial Electrochemistry (1972), 36 (2), 257-76CODEN: JEIEBC; ISSN:0022-0728.
      In a continuation of previous work (J. P. Randin and E. Yeager, 1971) the nonfaradaic differential electrode capacitance of the basal plane of high-pressure, stress-annealed pyrolytic graphite was detd. in contact with an aq. soln. by using an a.c. impedance bridge. The capacitance had almost a parabolic dependence on elec. potential in concd. electrolytes, and was independent of pH. The measured capacitance compares favorably with the theoretical value.
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    48. 48
      Kim, T.; Lim, S.; Kwon, K.; Hong, S.-H.; Qiao, W.; Rhee, C. K.; Yoon, S.-H.; Mochida, I. Electrochemical Capacitances of Well-Defined Carbon Surfaces. Langmuir 2006, 22 (22), 9086– 9088,  DOI: 10.1021/la061380q
      48
      Electrochemical Capacitances of Well-Defined Carbon Surfaces
      Kim, Taegon; Lim, Seongyop; Kwon, Kihyun; Hong, Seong-Hwa; Qiao, Wenming; Rhee, Choong Kyun; Yoon, Seong-Ho; Mochida, Isao
      Langmuir (2006), 22 (22), 9086-9088CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      Reported is the capacitive behavior of homogeneous and well-defined surfaces of pristine C nanofibers (CNFs) and surface-modified CNFs. The capacitances of the well-defined CNFs were measured with cyclic voltammetry to correlate the surface structure with capacitance. Among the studied pristine CNFs, the edge surfaces of platelet CNFs (PCNF) and herringbone CNFs were more effective in capacitive charging than the basal plane surface of tubular CNF by a factor of 3-5. Graphitization of PCNF (GPCNF) changed the edge surface of PCNF into a domelike basal plane surface, and the corresponding capacitances decreased from 12.5 to 3.2 F/g. A chem. oxidn. of the GPCNF, however, recovered a clear edge surface by removal of the curved basal planes to increase the capacitance to 5.6 F/g. The difference in the contribution of the edge surface and basal-plane surface to the capacitance of CNF was discussed in terms of the anisotropic cond. of graphitic materials.
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    49. 49
      Menéndez, J. A.; Phillips, J.; Xia, B.; Radovic, L. R. On the Modification and Characterization of Chemical Surface Properties of Activated Carbon: In the Search of Carbons with Stable Basic Properties. Langmuir 1996, 12 (18), 4404– 4410,  DOI: 10.1021/la9602022
      49
      On the Modification and Characterization of Chemical Surface Properties of Activated Carbon: In the Search of Carbons with Stable Basic Properties
      Menendez, J. Angel; Phillips, Jonathan; Xia, Bo; Radovic, Ljubisa R.
      Langmuir (1996), 12 (18), 4404-4410CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      Differences between the surface chem. properties of H- and N-treated samples of an activated carbon were quantified by using several complementary techniques. Calorimetric studies conducted at 303 K revealed that the sample treated in N2 at 1223 K adsorbs a great deal of O with unusually high differential heats. In fact, both the quantity and the heat of adsorption increased when the treatment temp. was increased at 773-1223 K. In contrast, samples treated in H2 adsorbed less and less O2 as the treatment temp. was raised; after treatment at 1223 K, virtually no O2 adsorption occurred. At the same time, the H/C ratio in the H2-treated samples decreased with increasing treatment temp. Point of zero charge measurements revealed that only H2 treatments at high temp. (> 1073 K) create basic (hydrophobic) surfaces which are stable after prolonged air exposure. These results are consistent with the notion that the removal of O in the form of CO and CO2 during high-temp. N2 treatment leaves unsatd. carbon atoms at crystallite edges; these sites are very active for subsequent O adsorption. In contrast, high-temp. H2 treatment accomplishes 3 tasks: (1) it also removes surface O; (2) it stabilizes some of the (re)active sites by forming stable C-H bonds; (3) it gasifies the most reactive unsatd. carbon atoms. The relative contributions of these 3 effects depend on the temp. of H2 treatment. The carbon surface resulting from high-temp. H2 treatment is stable against subsequent O2 adsorption in ambient conditions.
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    50. 50
      de Jesus Silva, A. J.; Contreras, M. M.; Nascimento, C. R.; da Costa, M. F. Kinetics of Thermal Degradation and Lifetime Study of Poly(Vinylidene Fluoride) (PVDF) Subjected to Bioethanol Fuel Accelerated Aging. Heliyon 2020, 6 (7), e04573  DOI: 10.1016/j.heliyon.2020.e04573
      There is no corresponding record for this reference.
    51. 51
      Zulfiqar, S.; Zulfiqar, M.; Rizvi, M.; Munir, A.; McNeill, I. C. Study of the Thermal Degradation of Polychlorotrifluoroethylene, Poly(Vinylidene Fluoride) and Copolymers of Chlorotrifluoroethylene and Vinylidene Fluoride. Polym. Degrad. Stab. 1994, 43 (3), 423– 430,  DOI: 10.1016/0141-3910(94)90015-9
      51
      Study of the thermal degradation of poly(chlorotrifluoroethylene), poly(vinylidene fluoride) and copolymers of chlorotrifluoroethylene and vinylidene fluoride
      Zulfiqar, S.; Zulfiqar, M.; Rizvi, Masroor; Munir, Arshad; McNeill, I. C.
      Polymer Degradation and Stability (1994), 43 (3), 423-30CODEN: PDSTDW; ISSN:0141-3910.
      A systematic study of the thermal degrdn. of a series of homopolymers and copolymers of chlorotrifluoroethylene and vinylidene fluoride was carried out using thermogravimetry and thermal volatilization anal. (TVA). Volatile products were sepd. by subambient TVA and characterized by means of IR spectroscopy and mass spectrometry. On degrdn., poly(chlorotrifluoroethylene) gives the monomer as the major product and CO2, C2F2Cl2, C3F5Cl and C2F3Cl3 in traces. Poly(vinylidene fluoride) forms hydrogen fluoride in appreciable quantity along with the monomer and C4H3F3. The copolymers show a similar type of degrdn. pattern. The structural changes which take place during degrdn. have also been studied and mechanisms of formation of the various products are discussed.
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    52. 52
      Stobinski, L.; Lesiak, B.; Zemek, J.; Jiricek, P. Time Dependent Thermal Treatment of Oxidized MWCNTs Studied by the Electron and Mass Spectroscopy Methods. Appl. Surf. Sci. 2012, 258 (20), 7912– 7917,  DOI: 10.1016/j.apsusc.2012.04.127
      52
      Time dependent thermal treatment of oxidized MWCNTs studied by the electron and mass spectroscopy methods
      Stobinski, L.; Lesiak, B.; Zemek, J.; Jiricek, P.
      Applied Surface Science (2012), 258 (20), 7912-7917CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
      Purified and functionalized in boiling concd. (68%) HNO3 acid the oxidized multiwall C nanotubes (ox-MWCNTs) under thermal treatment from RT to 630° and at 350° time dependent (1-4 h) were studied using the surface sensitive electron and mass spectroscopy methods. Mass spectroscopy indicates significant desorption of H2 and H2O to ∼300°. Higher H2 desorption rate from RT up to ∼100° is most likely caused by decompn. of org. acid impurities included within a bundle and in channels of the ox-MWCNTs after their functionalization by HNO3. In the range of 100-300° part of the detected H2, accompanied by desorption of CO2, may origin from desorbed H2O. Above 300°, the small amt. of desorbing H2O may result from transformation of carboxylic groups into carboxylic acid anhydride. Significant desorption of CO2 starting from 150° may result from decompn. of carboxylic groups, whereas desorption of CO starting at ∼300° from decompn. of acid anhydride groups created from carboxylic groups during thermal dehydration. Desorption of CO and CO2 at ∼470° may be due to decompn. of hydroxyl OH and carbonyl CO groups. Above 600° mainly decompn. of CO groups takes place and results in small desorption of CO. Time dependent (1-4 h) thermal treatment of ox-MWCNTs at 350° shows in XPS spectra decreasing amt. of CO in carboxyl groups and increasing amt. of CO in carbonyl and acid anhydride groups arising from carboxyl groups decompn. Between 350° and 470° the higher desorption rate of CO2 than CO indicates significant decompn. of carboxyl and carboxyl anhydride groups. At 350° the dynamic changes are indicated by the energy, intensity and full width at half max. (FWHM) of the π → π* interband transition and π loss peak, and quasi-elastic peak FWHM. During 4 h at 350° no C sp2 reconstruction is obsd. For the applied procedure of MWCNTs oxidn., large amt. of H2O and some org. acid impurities, resulting from the MWCNTs oxidn., remain in the CNTs channels, interstitial channels between tubes and at nanotubes surface.
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    53. 53
      Morgan, D. J. Comments on the XPS Analysis of Carbon Materials. C 2021, 7, 51,  DOI: 10.3390/c7030051
      53
      Comments on the XPS Analysis of Carbon Materials
      Morgan, David J.
      C (2021), 7 (3), 51CODEN: CABCC3; ISSN:2311-5629. (MDPI AG)
      The surface chem. of carbon materials is predominantly explored using XPS. However, many published papers have crit. failures in the published anal., stemming from an ill-informed approach to analyzing the spectroscopic data. Herein, a discussion on line shapes and changes in the spectral envelope of predominantly graphitic materials are explored, together with the use of the D-parameter, to ascertain graphitic content, using this information to highlight a simple and logical approach to strengthen confidence in the functionalization derived from the carbon core-level spectra.
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    54. 54
      Gieu, J.-B.; Winkler, V.; Courrèges, C.; El Ouatani, L.; Tessier, C.; Martinez, H. New Insights into the Characterization of the Electrode/Electrolyte Interfaces within LiMn2O4/Li4Ti5O12 Cells, by X-Ray Photoelectron Spectroscopy, Scanning Auger Microscopy and Time-of-Flight Secondary Ion Mass Spectrometry. J. Mater. Chem. A 2017, 5 (29), 15315– 15325,  DOI: 10.1039/C7TA02529G
      54
      New insights into the characterization of the electrode/electrolyte interfaces within LiMn2O4/Li4Ti5O12 cells, by X-ray photoelectron spectroscopy, scanning Auger microscopy and time-of-flight secondary ion mass spectrometry
      Gieu, Jean-Baptiste; Winkler, Volker; Courreges, Cecile; El Ouatani, Loubna; Tessier, Cecile; Martinez, Herve
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2017), 5 (29), 15315-15325CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      This work aims to study the electrode/electrolyte interfaces in a Li4Ti5O12 (LTO)/LiMn2O4 (LMO) cell assembled with a VC-contg. electrolyte and operating at 60°. LMO and LTO electrodes were mainly analyzed by XPS after the first and tenth galvanostatic cycles. The XPS results indicate that both electrodes are covered by surface layers during the first charge, coming from the degrdn. of electrolyte species, inducing irreversible capacity losses. Although the compns. of both layers are similar, the one formed on LTO electrodes is thicker than the one formed on LMO electrodes and contains small amts. of MnF2, homogeneously spread over the surface, as revealed by the fluorine elemental mapping obtained by a complementary scanning Auger microscopy expt. An addnl. measurement by time-of-flight secondary ion mass spectrometry indicates that the MnF2 is located on top of the surface layer. XPS anal. also indicates that during the first discharge, the thickness of the LTO electrode surface layer slightly decreases, due to a partial dissoln., while no changes are obsd. on the LMO electrode. After the tenth charge, the layers do not present any noticeable changes compared to the first charge. Interfacial layers in the LMO/LTO cell are mainly formed during the first charge, inducing an irreversible capacity loss. During the following cycles, the surface layer on LMO electrodes is stable, while it is slightly dissolved and reformed in each cycle on LTO electrodes, as suggested by the electrochem. data showing smaller and decreasing capacity losses, characteristic of the gradual passivation of these electrodes.
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    55. 55
      Bartnik, A.; Lisowski, W.; Sobczak, J.; Wachulak, P.; Budner, B.; Korczyc, B.; Fiedorowicz, H. Simultaneous Treatment of Polymer Surface by EUV Radiation and Ionized Nitrogen. Appl. Phys. A: Mater. Sci. Process. 2012, 109 (1), 39– 43,  DOI: 10.1007/s00339-012-7243-5
      55
      Simultaneous treatment of polymer surface by EUV radiation and ionized nitrogen
      Bartnik, Andrzej; Lisowski, Wojciech; Sobczak, Janusz; Wachulak, Przemyslaw; Budner, Boguslaw; Korczyc, Barbara; Fiedorowicz, Henryk
      Applied Physics A: Materials Science & Processing (2012), 109 (1), 39-43CODEN: APAMFC; ISSN:0947-8396. (Springer)
      The chem. modification of a poly(vinylidene fluoride) surface by extreme UV (EUV) irradn. in presence of ionized nitrogen was demonstrated for the first time. Nitrogen gas, injected into an interaction region, was ionized and excited by the EUV radiation from a laser-plasma source. The ionization degree and excited states of nitrogen were investigated using EUV spectrometry and the corresponding spectra are presented. Chem. modification of polymer after combined EUV and ionized nitrogen treatment was investigated using XPS. A significant contribution of nitrogen atoms in near-surface layer of the polymer after the treatment was demonstrated.
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    56. 56
      Wijaya, O.; Hartmann, P.; Younesi, R.; Markovits, I. I. E.; Rinaldi, A.; Janek, J.; Yazami, R. A Gamma Fluorinated Ether as an Additive for Enhanced Oxygen Activity in Li-O2 Batteries. J. Mater. Chem. A 2015, 3 (37), 19061– 19067,  DOI: 10.1039/C5TA03439F
      56
      A gamma fluorinated ether as an additive for enhanced oxygen activity in Li-O2 batteries
      Wijaya, Olivia; Hartmann, Pascal; Younesi, Reza; Markovits, Iulius I. E.; Rinaldi, Ali; Janek, Jurgen; Yazami, Rachid
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2015), 3 (37), 19061-19067CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      Perfluorocarbons (PFCs) are known for their high O2 soly. and have been investigated as additives in Li-O2 cells to enhance the cathode performance. However, the immiscibility of PFCs with org. solvents remains the main issue to be addressed as it hinders PFC practical application in Li-O2 cells. Furthermore, the effect of PFC additives on the O2 mass transport properties in the catholyte and their stability has not been thoroughly investigated. In this study, we investigated the properties of 1,1,1,2,2,3,3,4,4-nonafluoro-6-propoxyhexane (TE4), a gamma-fluorinated ether, and found it to be miscible with tetraglyme (TEGDME), a solvent commonly used in Li-O2 cells. The results show that with the TE4 additive up to 4 times higher O2 soly. and up to 2 times higher O2 diffusibility can be achieved. With 20 vol% TE4 addn., the discharge capacity increased about 10 times at a high discharge rate of 400 mA gC-1, corresponding to about 0.4 mA cm-2. The chem. stability of TE4 after Li-O2 cell discharge is investigated using 1H and 19F NMR, and the TE4 signal is retained after discharge. FTIR and XPS measurements indicate the presence of Li2O2 as a discharged product, together with side products from the parasitic reactions of LiTFSI salt and TEGDME.
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    57. 57
      Lesiak, B.; Kövér, L.; Tóth, J.; Zemek, J.; Jiricek, P.; Kromka, A.; Rangam, N. C Sp2/Sp3 Hybridisations in Carbon Nanomaterials - XPS and (X)AES Study. Appl. Surf. Sci. 2018, 452, 223– 231,  DOI: 10.1016/j.apsusc.2018.04.269
      57
      C sp2/sp3 hybridizations in carbon nanomaterials - XPS and (X)AES study
      Lesiak, B.; Kover, L.; Toth, J.; Zemek, J.; Jiricek, P.; Kromka, A.; Rangam, N.
      Applied Surface Science (2018), 452 (), 223-231CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
      The C KLL (KVV) Auger spectrum shape provides a measure of C sp2/sp3 hybridizations, alternative to C 1s spectra fitting. Due to a smaller kinetic energy of C KLL electrons vs. C 1s photoelectrons, the examd. information depths were attributed to lower or higher surface sensitivity, resp. The C nanostructures KLL Auger spectrum shape reflects d. of electronic states (DOS) and contains contributions of sp2 (graphite) and/or sp3 (diamond) hybridizations; for O- and H-contg. nanostructures this shape reflects chem. effects. C sp2/sp3 content was evaluated from parameter D, defined as an energy difference between the max. and min. of the first-deriv. C KLL spectrum, where dependence of parameter D on C sp2/sp3 hybridizations was assumed to be linear between graphite and diamond D values. Derived parameter D and thus C sp2/sp3 hybridization values were affected by procedure Auger spectrum smoothing procedures and D values used for ref. materials with pure sp3 and pure sp2 hybridizations. This work estd. the reliability of C sp2/sp3 hybridizations derived from parameter D detd. for a set of C nanomaterials and assessed chem. and morphol. effects on measured parameter D values. The presence of an inhomogeneous distribution of hybridization as a function of depth from the surface was identified mainly in graphene oxides vs. graphite and reduced graphene oxide. The largest effect on parameter D and then evaluated C sp2/sp3 content resulted from O and H at the surface and applied smoothing procedure in contrary to C nanomaterial structural properties (crystallinity, grain size). Parameter D values for C sp3 and C sp2 hybridizations, i.e., 13.2 and 23.1 eV, resp., were recommended to be used for linear interpolation proposed by Lascovich, et al. (1994).
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    58. 58
      Lascovich, J. C.; Scaglione, S. Comparison among XAES, PELS and XPS Techniques for Evaluation of Sp2 Percentage in a-C:H. Appl. Surf. Sci. 1994, 78 (1), 17– 23,  DOI: 10.1016/0169-4332(94)90026-4
      58
      Comparison among XAES, PELS and XPS techniques for evaluation of Sp2 percentage in a-C:H
      Lascovich, J. C.; Scaglione, S.
      Applied Surface Science (1994), 78 (1), 17-23CODEN: ASUSEE; ISSN:0169-4332.
      The ratio R of sp3 to sp2 in hydrogenated amorphous carbon (a-C:H) was evaluated by x-ray Auger electron spectroscopy (XAES), photo-EELS (PELS) and XPS. Hydrogenated amorphous carbon samples were deposited by a dual ion beam sputtering technique (DIBS). Percentages of Sp2 sites are at 45-70% for all analyzed samples. Values measured by XAES are ∼ 10% greater than values measured by PELS and the XPS evaluation appears in agreement with them. The R values also appear to be influenced not only by H contents, but even by deposition parameters (i.e., energy of the H ion beam and growth rate).
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    59. 59
      Lesiak, B.; Zemek, J.; Houdkova, J.; Kromka, A.; Jóźwik, A. Electron Spectra Line Shape Analysis of Highly Oriented Pyrolytic Graphite and Nanocrystalline Diamond. Anal. Sci. 2010, 26 (2), 217– 222,  DOI: 10.2116/analsci.26.217
      59
      Electron spectra line shape analysis of highly oriented pyrolytic graphite and nanocrystalline diamond
      Lesiak, Beata; Zemek, Josef; Houdkova, Jana; Kromka, Alexander; Jozwik, Adam
      Analytical Sciences (2010), 26 (2), 217-222CODEN: ANSCEN; ISSN:0910-6340. (Japan Society for Analytical Chemistry)
      The x-ray excited Auger electron spectroscopy (XAES), XPS and elastic peak electron spectroscopy (EPES) methods were applied in investigating samples of nanocryst. diamond and highly oriented pyrolytic graphite of various C sp2/sp3 ratios, crystallinity conditions and grain sizes. The compn. at the surface was estd. from the XPS. The C sp2/sp3 ratio was evaluated from the width of the XAES first deriv. C KLL spectra and from fitting of XPS C 1s spectra into components. The pattern recognition (PR) method applied for analyzing the spectra line shapes exhibited high accuracy in distinguishing different carbon materials. The PR method was found to be a potentially useful approach for identification, esp. important for technol. applications in fields of materials engineering and for controlling the chem. reaction products during synthesis.
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    60. 60
      Li, Z.; Wang, Y.; Kozbial, A.; Shenoy, G.; Zhou, F.; McGinley, R.; Ireland, P.; Morganstein, B.; Kunkel, A.; Surwade, S. P.; Li, L.; Liu, H. Effect of Airborne Contaminants on the Wettability of Supported Graphene and Graphite. Nat. Mater. 2013, 12 (10), 925– 931,  DOI: 10.1038/nmat3709
      60
      Effect of airborne contaminants on the wettability of supported graphene and graphite
      Li, Zhiting; Wang, Yongjin; Kozbial, Andrew; Shenoy, Ganesh; Zhou, Feng; McGinley, Rebecca; Ireland, Patrick; Morganstein, Brittni; Kunkel, Alyssa; Surwade, Sumedh P.; Li, Lei; Liu, Haitao
      Nature Materials (2013), 12 (10), 925-931CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
      It is generally accepted that supported graphene is hydrophobic and that its water contact angle is similar to that of graphite. The authors show that the water contact angles of freshly prepd. supported graphene and graphite surfaces increase when they are exposed to ambient air. By using IR spectroscopy and XPS, the authors demonstrate that airborne hydrocarbons adsorb on graphitic surfaces, and that a concurrent decrease in the water contact angle occurs when these contaminants are partially removed by both thermal annealing and controlled UV-O3 treatment. Graphitic surfaces are more hydrophilic than previously believed, and these results suggest that previously reported data on the wettability of graphitic surfaces may have been affected by unintentional hydrocarbon contamination from ambient air.
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    61. 61
      Farivar, F.; Yap, P. L.; Hassan, K.; Tung, T. T.; Tran, D. N. H.; Pollard, A. J.; Losic, D. Unlocking Thermogravimetric Analysis (TGA) in the Fight against “Fake Graphene” Materials. Carbon 2021, 179, 505– 513,  DOI: 10.1016/j.carbon.2021.04.064
      61
      Unlocking thermogravimetric analysis (TGA) in the fight against "Fake graphene" materials
      Farivar, Farzaneh; Yap, Pei Lay; Hassan, Kamrul; Tung, Tran Thanh; Tran, Diana N. H.; Pollard, Andrew J.; Losic, Dusan
      Carbon (2021), 179 (), 505-513CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      The absence of rapid, reliable and cost-effective quality control for industrially manufd. graphene materials is an immediate problem for the emerging graphene industry. Recent studies have alarmingly revealed that a large percentage of manufd. graphene materials traded worldwide have a large variation of properties, and some of them are overpriced graphite powders. Currently, benchmark graphene characterization methods based on localized anal. can provide information of key properties of graphene such as the no. of layers, particle size, and defects, only on individual graphene particles, which do not represent the properties of "bulk" material. To address these limitations, we developed and validated thermogravimetric anal. (TGA) as a simple anal. tool for characterization and quality control of manufd. few-layer graphene (FLG) and their non-graphene impurities in powder forms. Our results, using verified control and industrial samples, revealed that the deriv. TGA graphs of FLG, graphene oxide and graphite powders have signatory distinctive peaks with temp. of max. mass decompn. rates (Tmax) in specific ranges, reflecting differences of their structural, chem., and thermal properties, which are suitable for their qual. and quant. anal. The method is applicable for graphene manufacturers and end-users for simple, low-cost and reliable quality control of graphene materials that will not fail to detect "fake" graphene.
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    62. 62
      Strzemiecka, B.; Voelkel, A.; Donate-Robles, J.; Martín-Martínez, J. M. Assessment of the Surface Chemistry of Carbon Blacks by TGA-MS, XPS and Inverse Gas Chromatography Using Statistical Chemometric Analysis. Appl. Surf. Sci. 2014, 316, 315– 323,  DOI: 10.1016/j.apsusc.2014.07.174
      62
      Assessment of the surface chemistry of carbon blacks by TGA-MS, XPS and inverse gas chromatography using statistical chemometric analysis
      Strzemiecka, Beata; Voelkel, Adam; Donate-Robles, Jessica; Martin-Martinez, Jose Miguel
      Applied Surface Science (2014), 316 (), 315-323CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
      Four carbon blacks with different sp. surface areas and surface chemistries (C32, C71, C159 and C178) were analyzed by transmission electron microscopy (TEM) and nitrogen adsorption isotherms at 77 K. Their surface chemistries were analyzed by XPS, thermal gravimetric anal. coupled with mass spectrometry (TGA-MS) and inverse gas chromatog. (IGC). The carbon blacks contained 2.7-5.8 wt% volatiles corresponding to -OH, C-O, C = O and COO groups. The surface chem. parameters obtained with the different exptl. techniques were inter-related by using chemometric statistical anal. tools. The application of this methodol. showed that the carbon blacks with lower sp. surface area (C32 and C71) had basic character (electron donor) mainly due to C = O and C-O groups, whereas the carbon black with the highest sp. surface area (C178) showed acidic character (acceptor electron) due to its high content of OH groups. Moreover, the total surface energy and the dispersive component of the surface energy of the carbon blacks increased with the increase of their sp. surface area. In general the specific interactions of the carbon blacks also increased with the increase of their sp. surface area although C71 is exceptional due to higher oxygen content corresponding to C-O groups.
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    63. 63
      Cataldo, F. A Study on the Theraml Stability to 1000°C of Various Carbon Allotropes and Carbonaceous Matter both under Nitrogen and in Air. Fullerenes, Nanotubes Carbon Nanostruct. 2002, 10 (4), 293– 311,  DOI: 10.1081/FST-120016451
      63
      A study on the thermal stability to 1000° of various carbon allotropes and carbonaceous matter both under nitrogen and in air
      Cataldo, Franco
      Fullerenes, Nanotubes, and Carbon Nanostructures (2002), 10 (4), 293-311CODEN: FNCNAR; ISSN:1536-383X. (Marcel Dekker, Inc.)
      The thermal behavior of graphite, C60 fullerene, fullerene black (carbon soot contg. fullerenes), extd. fullerene black and diamond has been analyzed at ≤1000° by using TGA-DTA under flowing nitrogen at a heating rate of 20°/min. Small wt. losses have been recorded in the case of graphite and diamond. Furthermore no diamond graphitization was obsd. The sublimation of C60 and the fullerene fraction of fullerene black (both pristine and extd.) has been obsd. and discussed. The combustion reaction in flowing air of graphite, C60 and C70 fullerenes, fullerene black (both unextd. and extd.), carbon nanotubes and diamond has been studied by using TGA-DTA at 20°/min. C70 fullerene and fullerene black were the most reactive carbon materials with O2. The role played by C70 in the degrdn. of fullerites has been discussed. Among the carbon materials examd., the highest resistance to O2 attack has been shown by diamond and carbon nanotubes. The behavior of graphite is intermediate between diamond and fullerene blacks. The behavior of C60 fullerene appears closer to that of graphite, although it appears to be more reactive with O2. Specimens of graphite and carbon blacks N375 and N234 have been studied by using TGA-DTA in flowing air before and after a radiation treatment with neutrons or γ-radiation. The effect of the radiation damage on the combustion reaction of these carbon materials has been discussed.
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    64. 64
      Jahandar Lashaki, M.; Hashisho, Z.; Phillips, J. H.; Crompton, D.; Anderson, J. E.; Nichols, M. Mechanisms of Heel Buildup during Cyclic Adsorption-Desorption of Volatile Organic Compounds in a Full-Scale Adsorber-Desorber. Chem. Eng. J. 2020, 400, 124937,  DOI: 10.1016/j.cej.2020.124937
      64
      Mechanisms of heel buildup during cyclic adsorption-desorption of volatile organic compounds in a full-scale adsorber-desorber
      Jahandar Lashaki, Masoud; Hashisho, Zaher; Phillips, John H.; Crompton, David; Anderson, James E.; Nichols, Mark
      Chemical Engineering Journal (Amsterdam, Netherlands) (2020), 400 (), 124937CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
      This study elucidates the different mechanisms contributing to heel formation during cyclic adsorption-desorption of volatile org. compds. (VOCs) from a painting process in a full-scale adsorber-desorber. Two batches of beaded activated carbon (BAC), one subjected to normal operation and the other inadvertently exposed to oxygen during desorption, were investigated. Both batches displayed sharp increases in apparent d. during early cycles, which indicate high heel formation due to occupation/blockage of high-energy adsorption sites. Thermogravimetric anal. and gas chromatog.-mass spectrometry results identified non-desorbed adsorbates, adsorbate reaction byproducts and char from adsorbate decompn. The main heel formation mechanisms include physisorption and chemisorption followed by thermal oxidn., pyrolysis and eventually char formation. We hypothesize that non-ideal heat and purge gas distribution across the desorber is the reason for the accumulation of non-desorbed species and heel formation, shortening the lifetime of the adsorbent. In addn. to pyrolysis reactions that partially contributed to heel formation in the absence of oxygen, accumulation of thermal oxidn. products also contributed to the deterioration of adsorbent performance in the presence of oxygen during desorption. Moreover, extended exposure of the non-desorbed physisorbed and chemisorbed heel species to repetitive desorption cycles ultimately transformed them to permanent (non-desorbable) heel via polymn. and char formation. Therefore, to reduce heel buildup and maximize long-term adsorber performance, it is recommended to (i) ensure effective desorption conditions to prevent or minimize the accumulation of non-desorbed physisorbed species, and (ii) maintain sufficiently low oxygen levels in the desorption purge gas to minimize the detrimental effects of any species that do accumulate.
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    65. 65
      Losic, D.; Farivar, F.; Yap, P. L.; Karami, A. Accounting Carbonaceous Counterfeits in Graphene Materials Using the Thermogravimetric Analysis (TGA) Approach. Anal. Chem. 2021, 93 (34), 11859– 11867,  DOI: 10.1021/acs.analchem.1c02662
      65
      Accounting Carbonaceous Counterfeits in Graphene Materials Using the Thermogravimetric Analysis (TGA) Approach
      Losic, Dusan; Farivar, Farzaneh; Yap, Pei Lay; Karami, Afshin
      Analytical Chemistry (Washington, DC, United States) (2021), 93 (34), 11859-11867CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Counterfeits in the supply chain of high-value advanced materials such as graphene and their derivs. have become a concerning problem with a potential neg. impact on this growing and emerging industry. Recent studies have revealed alarming facts that a large percentage of manufd. graphene materials on market are not graphene, raising considerable concerns for the end users. The common and recommended methods for the characterization of graphene materials, such as transmission electron microscopy (TEM), at. force microscopy (AFM), and Raman spectroscopy based on spot anal. and probing properties of individual graphene particles, are limited to provide the detn. of the properties of "bulk" graphene powders at a large scale and the identification of non-graphene components or purposely included additives. These limitations are creating counterfeit opportunities by adding low-cost black carbonaceous materials into manufd. graphene powders. To address this problem, it is crit. to have reliable characterization methods, which can probe the specific properties of graphene powders at bulk scale, confirm their typical graphene signature, and detect the presence of unwanted addnl. compds., where the thermogravimetric anal. (TGA) method is one of the most promising methods to perform this challenging task. This paper presents the evaluation of the TGA method and its ability to detect low-cost carbon additives such as graphite, carbon black, biochar, and activated carbon as potential counterfeiting materials to graphene materials and their derivs. such as graphene oxide (GO) and reduced GO. The superior performance of the TGA method is demonstrated here, showing its excellent capability to successfully detect these additives when mixed with graphene materials, which is not possible by two other comparative methods (Raman spectroscopy and powder X-ray diffraction (XRD)), which are used as the common characterization methods for graphene materials.
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    66. 66
      Fuertes, A. B.; Alvarez, S. Graphitic Mesoporous Carbons Synthesised through Mesostructured Silica Templates. Carbon 2004, 42 (15), 3049– 3055,  DOI: 10.1016/j.carbon.2004.06.020
      66
      Graphitic mesoporous carbons synthesised through mesostructured silica templates
      Fuertes, Antonio B.; Alvarez, Sonia
      Carbon (2004), 42 (15), 3049-3055CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      In this paper the fabrication and characterization of graphitizable and graphitized porous carbons with a well-developed mesoporosity is described. The synthetic route used to prep. the graphitizable carbons was: (a) the infiltration of the porosity of mesoporous silica with a soln. contg. the carbon precursor (i.e. poly-vinyl chloride, PVC), (b) the carbonization of the silica-PVC composite and (c) the removal of the silica skeletal. Carbons obtained in this way have a certain graphitic order and a good elec. cond. (0.3 S cm-1), which is two orders larger than that of a non-graphitizable carbon. In addn., these materials have a high BET surface area (>900 m2.g-1), a large pore vol. (>1 cm3 g-1) and a bimodal porosity made up of mesopores. The pore structure of these carbons can be tailored as a function of the type of silica selected as template. Thus, whereas a graphitizable carbon with a well-ordered porosity is obtained from SBA-15 silica, a carbon with a wormhole pore structure results when MSU-1 silica is used as template. The heat treatment of a graphitizable carbon at a high temp. (2300°C) allows it to be converted into a graphitized porous carbon with a relatively high BET surface area (260 m2.g-1) and a porosity made up of mesopores in the 2-15 nm range.
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    67. 67
      Díez, N.; Sevilla, M.; Fuertes, A. B. Synthesis Strategies of Templated Porous Carbons beyond the Silica Nanocasting Technique. Carbon 2021, 178, 451– 476,  DOI: 10.1016/j.carbon.2021.03.029
      67
      Synthesis strategies of templated porous carbons beyond the silica nanocasting technique
      Diez, Noel; Sevilla, Marta; Fuertes, Antonio B.
      Carbon (2021), 178 (), 451-476CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      A review. Porous carbons have become extremely important in many applications related to environmental remediation and, more recently, to challenging energy issues. Then, great efforts have been addressed to the design and prodn. of carbon materials for emergent energy applications. Various templating approaches have emerged as suitable alternatives to traditional methods based on phys. or chem. activation procedures. This review focuses on simple, sustainable templating strategies based on the use of easily removable inorg. particles (e.g., NaCl, MgO, CaCO3, ZnO) or polymeric materials (i.e., HIPE emulsions, block copolymers, surfactants). The fundamental aspects, advances, applications, and challenges are analyzed in detail. This review provides useful information for researchers interested in easy methodologies for producing porous carbons with a variety of morphologies and pore structures intended for a wide range of applications, including energy storage and prodn.
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    68. 68
      Yan, J.; Wang, Q.; Wei, T.; Jiang, L.; Zhang, M.; Jing, X.; Fan, Z. Template-Assisted Low Temperature Synthesis of Functionalized Graphene for Ultrahigh Volumetric Performance Supercapacitors. ACS Nano 2014, 8 (5), 4720– 4729,  DOI: 10.1021/nn500497k
      68
      Template-assisted low temperature synthesis of functionalized graphene for ultrahigh volumetric performance supercapacitors
      Yan, Jun; Wang, Qian; Wei, Tong; Jiang, Lili; Zhang, Milin; Jing, Xiaoyan; Fan, Zhuangjun
      ACS Nano (2014), 8 (5), 4720-4729CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      We demonstrated the fabrication of functionalized graphene nanosheets via low temp. (300 °C) treatment of graphite oxide with a slow heating rate using Mg(OH)2 nanosheets as template. Because of its dented sheet with high surface area, a certain amt. of oxygen-contg. groups, and low pore vol., the as-obtained graphene delivers both ultrahigh specific gravimetric and volumetric capacitances of 456 F g-1 and 470 F cm-3, almost 3.7 times and 3.3 times higher than hydrazine reduced graphene, resp. Esp., the obtained volumetric capacitance is the highest value so far reported for carbon materials in aq. electrolytes. More importantly, the assembled supercapacitor exhibits an ultrahigh volumetric energy d. of 27.2 Wh L-1, which is among the highest values for carbon materials in aq. electrolytes, as well as excellent cycling stability with 134% of its initial capacitance after 10 000 cycles. Therefore, the present work holds a great promise for future design and large-scale prodn. of high performance graphene electrodes for portable energy storage devices.
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    69. 69
      Yoon, S. B.; Chai, G. S.; Kang, S. K.; Yu, J.-S.; Gierszal, K. P.; Jaroniec, M. Graphitized Pitch-Based Carbons with Ordered Nanopores Synthesized by Using Colloidal Crystals as Templates. J. Am. Chem. Soc. 2005, 127 (12), 4188– 4189,  DOI: 10.1021/ja0423466
      69
      Graphitized Pitch-Based Carbons with Ordered Nanopores Synthesized by Using Colloidal Crystals as Templates
      Yoon, Suk Bon; Chai, Geun Seok; Kang, Soon Ki; Yu, Jong-Sung; Gierszal, Kamil P.; Jaroniec, Mietek
      Journal of the American Chemical Society (2005), 127 (12), 4188-4189CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A highly graphitized ordered nanoporous carbon (ONC) was synthesized by using com. mesophase pitch as carbon precursor and siliceous colloidal crystal as template. Since silica colloids of different sizes (>6 nm) and narrow particle size distribution are com. available, the pore size tailoring in the resulting ONCs is possible.
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    70. 70
      O̅ya, A.; O̅tani, S. Catalytic Graphitization of Carbons by Various Metals. Carbon 1979, 17 (2), 131– 137,  DOI: 10.1016/0008-6223(79)90020-4
      70
      Catalytic graphitization of carbons by various metals
      Oya, Asao; Otani, Sugio
      Carbon (1979), 17 (2), 131-7CODEN: CRBNAH; ISSN:0008-6223.
      The effect of various metals on the catalytic graphitization of a graphitizing and a nongraphitizing C was studied by x-ray diffractometry and optical microscopy. Graphitic C was formed in a graphitizing 3,5-Me2C6H3OH-HCHO resin derived C; addn. of Al, Cr, Mn, Fe, Co, and Ni gave large crystal flakes whereas addn. of Ca, Ti, V, Mo, and W gave fine crystals through a carbide formation-decompn. mechanism. In the nongraphitizing PhOH-HCHO derived C, addn. of Mg, Si, Ca, Cu, and Ge led to the formation of graphitic C whereas addn. of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Mo, and W gave graphitic and turbostratic C. B accelerated homogeneous graphitization of both carbons.
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    71. 71
      Hunter, R. D.; Ramírez-Rico, J.; Schnepp, Z. Iron-Catalyzed Graphitization for the Synthesis of Nanostructured Graphitic Carbons. J. Mater. Chem. A 2022, 10 (9), 4489– 4516,  DOI: 10.1039/D1TA09654K
      71
      Iron-catalyzed graphitization for the synthesis of nanostructured graphitic carbons
      Hunter, R. D.; Ramirez-Rico, J.; Schnepp, Z.
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2022), 10 (9), 4489-4516CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      A review. Carbons are versatile and diverse materials that have numerous applications across energy and environmental sciences. Carbons with a graphitic structure are particularly appealing due to their high chem. stability, large surface areas and high thermal and electronic cond. Numerous methods exist to produce nanostructured graphitic carbons but some of these can be energy-intensive and/or have problems with scalability. One option that is being increasingly explored is the process of iron-catalyzed graphitization. This simply involves the pyrolysis of carbon-rich precursors in the presence of an iron catalyst and has been used to produce carbons with a wide range of structures and properties. This review will examine the current field of iron-catalyzed graphitization, with a focus on mol. org. or biomass precursors. Bio-derived precursors are particularly attractive as a potential option for sustainable prodn. of graphitic carbons. We start with a brief introduction to some key carbon structures, the current applications in which they are employed and some of the key methods that have been developed to produce nanostructured graphitic carbons. We will then review the history of catalytic graphitization before evaluating the wide range of conditions and precursors that have been employed in catalytic graphitization. Finally, this review will investigate the current challenges facing iron-catalyzed graphitization, looking particularly at the limitations of the current understanding of the mechanistic aspects of graphitization, with a view to outlining where research in this field might progress.
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    72. 72
      Tee, E.; Tallo, I.; Thomberg, T.; Jänes, A.; Lust, E. Steam and Carbon Dioxide Co-Activated Silicon Carbide-Derived Carbons for High Power Density Electrical Double Layer Capacitors. J. Electrochem. Soc. 2018, 165 (10), A2357– A2364,  DOI: 10.1149/2.1261810jes
      72
      Steam and Carbon Dioxide Co-Activated Silicon Carbide-Derived Carbons for High Power Density Electrical Double Layer Capacitors
      Tee, Ester; Tallo, Indrek; Thomberg, Thomas; Janes, Alar; Lust, Enn
      Journal of the Electrochemical Society (2018), 165 (10), A2357-A2364CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)
      Different mico-mesoporous silicon carbide-derived carbons (SiC-CDC) were synthesized via gas phase chlorination at 1100°C and thereafter activated at 900°C and 1000°C with H2O steam using Ar and CO2 as the carrier gases. The phys. characterization data show that these materials are mainly amorphous, the structure does not change remarkably during the activation process and the surface chem. of the differently activated and treated materials remains the same and there are no functional groups at the SiC-CDC surface. N2, Ar and CO2 sorption measurements indicate an increase in the sp. surface area and pore size distribution with increasing the activation temp., whereas the influence of the carrier gas during synthesis is minimal. Although the sp. surface areas and pore size distributions differed, the electrochem. parameters in 1 M (C2H5)3CH3NBF4 acetonitrile soln. for all SiC-CDC materials were similar - specific gravimetric capacitances 130 ± 18 F g-1 and volumetric capacitance 67 ± 14 F cm-3 were calcd. Abs. phase angle values from -85° to -88° at low frequencies and very high energy and power densities 22 Wh kg-1 at 20 kW kg-1 and 12 Wh dm-3 at 10 kW dm-3 have been achieved.
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    73. 73
      Bokobza, L.; Bruneel, J.-L.; Couzi, M. Raman Spectra of Carbon-Based Materials (from Graphite to Carbon Black) and of Some Silicone Composites. C 2015, 1, 77– 94,  DOI: 10.3390/c1010077
      There is no corresponding record for this reference.
    74. 74
      Wu, J.-B.; Lin, M.-L.; Cong, X.; Liu, H.-N.; Tan, P.-H. Raman Spectroscopy of Graphene-Based Materials and Its Applications in Related Devices. Chem. Soc. Rev. 2018, 47 (5), 1822– 1873,  DOI: 10.1039/C6CS00915H
      74
      Raman spectroscopy of graphene-based materials and its applications in related devices
      Wu, Jiang-Bin; Lin, Miao-Ling; Cong, Xin; Liu, He-Nan; Tan, Ping-Heng
      Chemical Society Reviews (2018), 47 (5), 1822-1873CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      Graphene-based materials exhibit remarkable electronic, optical, and mech. properties, which has resulted in both high scientific interest and huge potential for a variety of applications. Furthermore, the family of graphene-based materials is growing because of developments in prepn. methods. Raman spectroscopy is a versatile tool to identify and characterize the chem. and phys. properties of these materials, both at the lab. and mass-prodn. scale. This technique is so important that most of the papers published concerning these materials contain at least one Raman spectrum. Thus, here, we systematically review the developments in Raman spectroscopy of graphene-based materials from both fundamental research and practical (i.e., device applications) perspectives. We describe the essential Raman scattering processes of the entire first- and second-order modes in intrinsic graphene. Furthermore, the shear, layer-breathing, G and 2D modes of multilayer graphene with different stacking orders are discussed. Techniques to det. the no. of graphene layers, to probe resonance Raman spectra of monolayer and multilayer graphenes and to obtain Raman images of graphene-based materials are also presented. The extensive capabilities of Raman spectroscopy for the investigation of the fundamental properties of graphene under external perturbations are described, which have also been extended to other graphene-based materials, such as graphene quantum dots, carbon dots, graphene oxide, nanoribbons, chem. vapor deposition-grown and SiC epitaxially grown graphene flakes, composites, and graphene-based van der Waals heterostructures. These fundamental properties have been used to probe the states, effects, and mechanisms of graphene materials present in the related heterostructures and devices. We hope that this review will be beneficial in all the aspects of graphene investigations, from basic research to material synthesis and device applications.
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    75. 75
      Ferrari, A. C.; Basko, D. M. Raman Spectroscopy as a Versatile Tool for Studying the Properties of Graphene. Nat. Nanotechnol. 2013, 8 (4), 235– 246,  DOI: 10.1038/nnano.2013.46
      75
      Raman spectroscopy as a versatile tool for studying the properties of graphene
      Ferrari, Andrea C.; Basko, Denis M.
      Nature Nanotechnology (2013), 8 (4), 235-246CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
      A review. Raman spectroscopy is an integral part of graphene research. It is used to det. the no. and orientation of layers, the quality and types of edge, and the effects of perturbations, such as elec. and magnetic fields, strain, doping, disorder and functional groups. This, in turn, provides insight into all sp2-bonded carbon allotropes, because graphene is their fundamental building block. Here we review the state of the art, future directions and open questions in Raman spectroscopy of graphene. We describe essential phys. processes whose importance has only recently been recognized, such as the various types of resonance at play, and the role of quantum interference. We update all basic concepts and notations, and propose a terminol. that is able to describe any result in literature. We finally highlight the potential of Raman spectroscopy for layered materials other than graphene.
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    76. 76
      Pimenta, M. A.; Dresselhaus, G.; Dresselhaus, M. S.; Cançado, L. G.; Jorio, A.; Saito, R. Studying Disorder in Graphite-Based Systems by Raman Spectroscopy. Phys. Chem. Chem. Phys. 2007, 9 (11), 1276– 1290,  DOI: 10.1039/B613962K
      76
      Studying disorder in graphite-based systems by Raman spectroscopy
      Pimenta, M. A.; Dresselhaus, G.; Dresselhaus, M. S.; Cancado, L. G.; Jorio, A.; Saito, R.
      Physical Chemistry Chemical Physics (2007), 9 (11), 1276-1291CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      A review. Raman spectroscopy has historically played an important role in the structural characterization of graphitic materials, in particular providing valuable information about defects, stacking of the graphene layers and the finite sizes of the crystallites parallel and perpendicular to the hexagonal axis. Here the authors review the defect-induced Raman spectra of graphitic materials from both exptl. and theor. standpoints and the authors present recent Raman results on nanographites and graphenes. The disorder-induced D and D' Raman features, as well as the G'-band (the overtone of the D-band which is always obsd. in defect-free samples), are discussed in terms of the double-resonance (DR) Raman process, involving phonons within the interior of the 1st Brillouin zone of graphite and defects. In this review, exptl. results for the D, D' and G' bands obtained with different laser lines, and in samples with different crystallite sizes and different types of defects are presented and discussed. The authors also present recent advances that made possible the development of Raman scattering as a tool for very accurate structural anal. of nano-graphite, with the establishment of an empirical formula for the in- and out-of-plane cryst. size and even fancier Raman-based information, such as for the at. structure at graphite edges, and the identification of single vs. multi-graphene layers. Once established, this knowledge provides a powerful machinery to understand newer forms of sp2 C materials, such as the recently developed pitch-based graphitic foams. Results for the calcd. Raman intensity of the disorder-induced D-band in graphitic materials as a function of both the excitation laser energy (Elaser) and the in-plane size (La) of nano-graphites are presented and compared with exptl. results. The status of this research area is assessed, and opportunities for future work are identified.
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    77. 77
      Dresselhaus, M. S.; Dresselhaus, G.; Hofmann, M. Raman Spectroscopy as a Probe of Graphene and Carbon Nanotubes. Philos. Trans. R. Soc., A 2008, 366 (1863), 231– 236,  DOI: 10.1098/rsta.2007.2155
      77
      Raman spectroscopy as a probe of graphene and carbon nanotubes
      Dresselhaus, M. S.; Dresselhaus, G.; Hofmann, M.
      Philosophical Transactions of the Royal Society, A: Mathematical, Physical & Engineering Sciences (2008), 366 (1863), 231-236CODEN: PTRMAD; ISSN:1364-503X. (Royal Society)
      A review. Progress in the use of Raman spectroscopy to characterize graphene samples for the no. of graphene layers and doping level they contain is briefly reviewed. Comparisons to prior studies on graphites and carbon nanotubes are used for inspiration to define future promising directions for Raman spectroscopy research on few layer graphenes.
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    78. 78
      Langford, J. I.; Wilson, A. J. C. Scherrer after Sixty Years: A Survey and Some New Results in the Determination of Crystallite Size. J. Appl. Crystallogr. 1978, 11 (2), 102– 113,  DOI: 10.1107/S0021889878012844
      78
      Scherrer after sixty years: a survey and some new results in the determination of crystallite size
      Langford, J. I.; Wilson, A. J. C.
      Journal of Applied Crystallography (1978), 11 (2), 102-13CODEN: JACGAR; ISSN:0021-8898.
      The interpretation of the broadening arising from small crystallites is summarized. Studies of the half-width as a measure of breadth were completed Scherrer consts. of simple regular shapes were detd. for all low-angle reflections (h2 + k2 + l2 ≤ 100) for 4 measures of breadth. The systematic variation of Scherrer consts. with hkl is discussed, and a convenient representation in the form of contour maps is applied to simple shapes. The relation between the apparent and true size is considered for crystallites with the same shape. If they are of the same size, then the normal Scherrer const. applies, but if there is a distribution of sizes, a modified Scherrer const. must be used.
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    79. 79
      Thommes, M.; Kaneko, K.; Neimark, A. V.; Olivier, J. P.; Rodriguez-Reinoso, F.; Rouquerol, J.; Sing, K. S. W. Physisorption of Gases, with Special Reference to the Evaluation of Surface Area and Pore Size Distribution (IUPAC Technical Report). Pure Appl. Chem. 2015, 87 (9–10), 1051– 1069,  DOI: 10.1515/pac-2014-1117
      79
      Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report)
      Thommes, Matthias; Kaneko, Katsumi; Neimark, Alexander V.; Olivier, James P.; Rodriguez-Reinoso, Francisco; Rouquerol, Jean; Sing, Kenneth S. W.
      Pure and Applied Chemistry (2015), 87 (9-10), 1051-1069CODEN: PACHAS; ISSN:0033-4545. (Walter de Gruyter, Inc.)
      Gas adsorption is an important tool for the characterization of porous solids and fine powders. Major advances in recent years have made it necessary to update the 1985 IUPAC manual on Reporting Physisorption Data for Gas/Solid Systems. The aims of the present document are to clarify and standardise the presentation, nomenclature and methodol. assocd. with the application of physisorption for surface area assessment and pore size anal. and to draw attention to remaining problems in the interpretation of physisorption data.
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    80. 80
      Kozbial, A.; Li, Z.; Sun, J.; Gong, X.; Zhou, F.; Wang, Y.; Xu, H.; Liu, H.; Li, L. Understanding the Intrinsic Water Wettability of Graphite. Carbon 2014, 74, 218– 225,  DOI: 10.1016/j.carbon.2014.03.025
      80
      Understanding the intrinsic water wettability of graphite
      Kozbial, Andrew; Li, Zhiting; Sun, Jianing; Gong, Xiao; Zhou, Feng; Wang, Yongjin; Xu, Haochen; Liu, Haitao; Li, Lei
      Carbon (2014), 74 (), 218-225CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      We report the effect of airborne hydrocarbon contamination on the water wettability of graphite. Graphite is traditionally known to be hydrophobic with water contact angle (WCA) within the 75-95° range. The WCA of highly ordered pyrolytic graphite (HOPG) was 64.4 ± 2.9° when measured within 10 s after exfoliation in air and increased to ca. 90° after exposure to the ambient air. Ellipsometry measurement showed growth of an adsorptive layer on exfoliated HOPG and attenuated total reflectance-Fourier transform IR spectroscopy (ATR-FTIR) data indicated that the layer is airborne hydrocarbon. Theor. calcn. confirms that adsorption of only a monolayer amt. of hydrocarbon is enough to reproduce the hydrophobic behavior previously obsd. on HOPG. Graphite is intrinsically more hydrophilic than previously believed and that surface adsorbed airborne hydrocarbon is the source of hydrophobicity.
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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.3c18629.

    • Supplementary XPS, electrical resistivity and gas physisorption measurements, and analyses of electrode materials and electrodes (PDF)


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