High-Performance MoC Electrocatalyst for Hydrogen Evolution Reaction Enabled by Surface Sulfur Substitution.

Molybdenum carbides have been expected to be one of the promising catalysts for the hydrogen evolution reaction (HER) due to their similar d-band electronic structures to the Pt-group metals. However, the weaker hydrogen-adsorption ability of MoC severely hinders its applications. Guided by density functional theory calculations, we put forward a strategy to design the novel MoC-based electrocatalyst with surface reconstruction through sulfur doping. The incorporation of minor sulfur not only greatly increases the number of active sites and intrinsic activity but also optimizes the electronic structure to improve the electron transfer efficiency. As a result, the as-prepared sulfur-substituted MoC tackles the limitation of the Volmer step and exhibits superior HER performance with a small Tafel slope of 48 mV dec. Theoretical investigations demonstrate that the terminal sulfur plays a critical role in facilitating a close to zero hydrogen adsorption energy (Δ) and a lower hydrogen release barrier.