Activity Enhancement of Molybdenum Carbide in Alkaline Hydrogen Evolution Reaction through Oxidation-Gradient Modulation

Featured by their Pt-like electronic structure, molybdenum carbides have been widely developed for efficiently catalyzing the hydrogen evolution reaction (HER). It is noteworthy that the oxophilicity of transition-metal atoms can give rise to the inevitable surface oxidation of molybdenum carbides, which has a noticeable impact on their HER activities. However, such a significant detail was usually documented in theory simulations and rarely explored by well-controlled experiments. Herein, advanced surface-science techniques using vacuum-connected setups are performed to deliberately prepare oxidation-gradient molybdenum carbide-oxide model electrocatalysts and evaluate the corresponding alkaline HER performance. The performance evaluations demonstrate that the minimal oxygen-modified Mo2C exhibits the best alkaline HER activity among all model electrocatalysts. In situ XPS combined with quasi in situ XPS under different applied negative potentials reveals that tailoring the Mo2C surface decorated with oxygen-containing species can facilitate the desorption of produced OH* intermediates from water activation, thus avoiding the deep oxidation issue of the catalyst surface and accelerating the regeneration of active sites in the alkaline HER process. Moreover, a comparable trend of HER performance is also observed on the synthetically practical Mo2C powder catalysts, which further proves our hypothesis deduced from the model system. Our strategy of oxygen-terminated Mo2C model electrocatalysts and the utilization of advanced spectroscopy characterizations may pave an interesting route for the rational design of low-cost but highly efficient oxygen-modified molybdenum carbide catalysts for practical water electrolysis.