(254c) Trends in the Hydrogen Evolution Activity of Metal Carbide Catalysts
The hydrogen evolution reaction (HER) can be employed to generate hydrogen as a potentially carbon-neutral feedstock for the synthesis of ammonia, as a reducing source for the deoxygenation of biofuels, or as a fuel source for hydrogen fuel cells for automotive or stationary applications. In other electrochemical applications, the HER is a major side reaction that affects the product selectivity in electrocatalytic reduction of CO2 into hydrocarbons or N2 into ammonia or the local pH and the development of structural properties during metal electrodeposition. Metal carbide catalysts are alternative nonprecious electrode materials for electrochemical energy conversion devices, such as for hydrogen fuel cells or electrolyzers. This talk presents the experimental exchange current densities for the HER on eight mono- and bimetallic metal carbide electrocatalysts (B4C, TiC, Fe3C, Co3C, Ni/C, Mo2C, WC, and CoWC) and correlates the current densities to the hydrogen binding energies that we have calculated via electronic structure computations. We find these electrode materials to have activities higher than those of their parent metals and intermediate between the catalytic activities of the Pt-group and early transition-metal surfaces. Increased HER activities on metal carbides relative to the activities of their parent metals can be understood with a three-fold higher sensitivity of metal carbides to the coverage-induced weakening of hydrogen adsorption relative to metal surfaces. The discussed trends can be useful for the design of bimetallic carbide electrocatalysts.