Electrocatalyst Support Materials Research Articles

Alternative Electrocatalyst Support Materials for Polymer Electrolyte Fuel Cells

Durability of electrocatalysts under severe operational conditions of polymer electrolyte fuel cells (PEFCs) is one of the most important technological issues to be improved. Alternative electrocatalyst support materials are desired, the use of which may solve problems such as oxidation-induced carbon support corrosion. One interesting solution is to use conductive oxide-based catalyst support. We focus our attention to SnO2, known as an oxide semiconductor with a high electronic conductivity. Nano-carbon support materials are also studied as an another option of electrocatalyst support design. Technical merits and remaining issues in alternative electrocatalyst support materials selection are discussed.

Pd Supported on Titanium Nitride for Efficient Ethanol Oxidation

The excellent metal−support interaction between palladium (Pd) and titanium nitride (TiN) is exploited in designing an efficient anode material, Pd-TiN, that could be useful for direct ethanol fuel cell in alkaline media. The physicochemical and electrochemical characterization of the Pd-TiN/electrolyte interface reveals an efficient oxidation of ethanol coupled with excellent stability of the catalyst under electrochemical conditions. Characterization of the interface using in situ Fourier transform infrared spectroscopy (in situ FTIR) shows the production of CO2 at low overvoltages revealing an efficient cleaving of the C−C bond. The performance comparison of Pd supported on TiN (Pd-TiN) with that supported on carbon (Pd-C) clearly demonstrates the advantages of TiN support over carbon. A positive chemical shift of Pd (3d) binding energy confirms the existence of metal−support interaction between Pd and TiN, which in turn helps weaken the Pd−CO synergetic bonding interaction. The remarkable ability of TiN to accumulate −OH species on its surface coupled with the strong adhesion of Pd makes TiN an active support material for electrocatalysts.

Alternative Electrocatalyst Support Materials for Polymer Electrolyte Fuel Cells

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KOH-activated multi-walled carbon nanotubes as platinum supports for oxygen reduction reaction

In the present investigation, multi-walled carbon nanotubes (MWCNTs) thermally treated by KOH were adopted as the platinum supporting material for the oxygen reduction reaction electrocatalysts. FTIR and Raman spectra were used to investigate the surface state of MWCNTs treated by KOH at different temperatures (700, 800, and 900 °C) and showed MWCNTs can be successfully functionalized. The structural properties of KOH-activated MWCNTs supported Pt were determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and their electrochemical performance was evaluated by the aid of cyclic voltammetry (CV) and rotating disk electrode (RDE) voltammetry. According to the experimental findings of the present work, the surrface of MWCNTs can be successfully functionalized with oxygen-containing groups after activation by KOH, favoring the good dispersion of Pt nanoparticles with narrow size distribution. The as-prepared Pt catalysts supported on KOH treated MWCNTs at higher temperature, possess higher electrochemical surface area and exhibit desirable activity towards oxygen reduction reaction (ORR). More precisely, it has been found that the electrochemical active area of Pt/MWCNTs-900 is approximately two times higher than that of Pt/MWCNTs. It can be concluded that KOH activation is an effective way to decorate MWCNTs’ surface with oxygen-containing groups and bigger surface area, which makes them more suitable as electrocatalyst support materials.

Carbon-free Pt Electrocatalysts Supported on Doped SnO2 for Polymer Electolyte Fuel Cells

Oxidation-induced carbon support corrosion especially in cathode electrocatalysts for polymer electrolyte fuel cells (PEFCs) is one of the important technological issues to be solved. We focus our attention to SnO2, known as a broad-band oxide semiconductor with a high electronic conductivity, as a possible electrocatalyst support material. In this study, nanostructure, electrochemical properties and durability of carbon-free electrocatalysts, Pt/SnO2, Pt/Nb-SnO2, Pt/Al-SnO2, are investigated.

Facet-Selective Platinum Electrodeposition at Free-standing Polycrystalline Boron-Doped Diamond Films

In the present investigation, electrochemical deposition of platinum particles was carried out on boron doped diamond (BDD) films by using cyclic voltammetry at different potential sweep rates while maintaining the Pt concentration and number of potential cycles during the deposition as constant for all samples. The BDD film surfaces were studied using Raman spectroscopy, X-ray diffraction, and scanning electrochemical microscopy. The deposited particles were characterized by scanning electron microscopy/X-ray energy dispersive analysis, X-ray photoelectron spectroscopy, and cyclic voltammetry before and after methanol oxidation. The platinum nanoparticles are found to be selectively electrodeposited on the (111) facets of the BDD. In addition, the location of the Pt particles on the diamond facets was affected by the potential sweep rate. For higher sweep rates, the particle size was dependent on the facet on which the particles are electrodeposited with smooth (110) facets exhibiting a smaller number of particles but with a larger particle diameter. After methanol oxidation studies using cyclic voltammetry and controlled potential electrolysis for several hours, the platinum particles remained attached to the (111) facets of the BDD, while the particles on the (110) facets of the BDD became agglomerated along grain boundaries. Functional groups present on the (111) facet of the diamond surface play an important role on the stability of the particles attached to the diamond surface. After methanol oxidation, the particles deposited on other facets appeared to lose their adhesion leading to agglomeration on the grain boundaries. BDD appears to be a promising electrocatalyst support material that can help to resist platinum nanoparticle agglomeration in direct methanol and other low temperature fuel cell applications.

The Physicochemical and Electrochemical Properties of 100 and 500 nm Diameter Diamond Powders Coated with Boron-Doped Nanocrystalline Diamond

There is a need for advanced, corrosion-resistant electrocatalyst support materials for use in fuel cells. To this end, electrically conducting diamond powder was prepared by depositing a layer of boron-doped nanocrystalline diamond on 100 and diamond powders. The doped layer was deposited by microwave plasma-assisted chemical vapor deposition using an -rich source gas mixture. After coating, the doped diamond powder had a specific surface area of and an electrical conductivity of . The doped diamond powder had a specific surface area of and an electrical conductivity of after coating. The specific surface area of both powders decreased by ca. 50% after diamond coating due mainly to particle–particle fusion. The electrical measurements provided conclusive evidence for a doped diamond overlayer as the uncoated powders possessed no electrical conductivity. Furthermore, the fact that the electrical properties were unaltered by acid washing confirmed that the conductivity arises from the doped diamond overlayer and not any adventitious carbon impurity on the particle surface, which is removed by such chemical treatment. Scanning electron microscopy images and Raman spectroscopy yielded further evidence in support of a nanocrystalline diamond overlayer. Both powders exhibited electrochemical responses for , , and that were comparable to typical responses seen for high-quality, boron-doped nanocrystalline diamond thin-film electrodes. The electrochemical behavior of the powders was assessed using a pipette electrode that housed the packed powder with no binder. The doped diamond powder electrodes were more plagued by ohmic resistance effects than were the powder electrodes because of reduced particle contact. Importantly, it was found that the doped diamond powder electrodes are dimensionally stable and corrosion-resistant during anodic polarization at vs in at . In contrast, glassy carbon powder polarized under identical conditions underwent significant microstructural degradation and corrosion.

Degradation Mechanisms of Powderous sp2 Carbon Electrocatalyst Support Materials and Development of Advanced sp3 Carbon Materials

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Evaluation of the Stability of sp2 Carbon Electrocatalyst Support Materials and Development of an Advanced Support Based on Electrically Conducting Diamond

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Development of Durable and High-Performance Electrocatalysts and Electrocatalyst Support Materials

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Preparation and Characterization of Boron-Doped Diamond Powder: A Possible Dimensionally Stable Electrocatalyst Support Material

Electrically conducting diamond powder was prepared by coating insulating diamond powder ( diam, ) with a thin boron-doped layer using microwave plasma-assisted chemical vapor deposition. Deposition times from 1 to 6 h were evaluated. Scanning electron microscopy (SEM) revealed that the diamond powder particles become more faceted and more secondary growths form with increasing deposition time. Fusion of neighboring particles was also observed with increasing growth time. The first-order diamond phonon line appeared in the Raman spectrum at ca. for deposition times up to 4 h, and was downshifted to as low as for some particles after the 6-h growth. Electrical resistance measurements of the bulk powder (no binder) confirmed that a conductive diamond overlayer formed, as the conductivity increased from near zero (insulating, ) for the uncoated powder to after the 6-h growth. Ohmic behavior was seen in current-voltage curves recorded for the 4-h powder between . Cyclic voltammetric i-E curves for and were recorded to evaluate the electrochemical properties of the conductive powder when mixed with a polytetrafluoroethylene binder. At scan rates between 10 and , for both redox systems was high, ranging from 140 to 350 mV, consistent with significant ohmic resistance within the powder/binder electrode. Our results at this point suggest that the resistance is mainly due to poor particle-particle connectivity. Anodic polarization at 1.6 V vs for 1 h (25°C) was performed to evaluate the morphological and microstructural stability of the conductive diamond in comparison with graphite and glassy carbon (GC) powders. The total charge passed during polarization was largest for the GC powder and smallest for conductive diamond powder . SEM images taken of conductive diamond powder after polarization showed no evidence of microstructural degradation, while significant morphological and microstructural changes were seen for the GC powder.