Unveiling the in-situ hydrogen intercalation in Mo2COx for promoting the alkaline hydrogen evolution reaction

Dimolybdenum carbide (Mo2C) is an efficient electrocatalyst for the hydrogen evolution reaction (HER). However, Mo2C tends to undergo surface chemical reconstruction under reaction conditions, which presents difficulties for optimization and characterization. Here, we report an HER activated Mo2COx–Ni(OH)2 catalyst and demonstrate that structural transformations including the surface oxidation of Mo2C and the in-situ hydrogen intercalation of Mo2COx govern the promoted HER performance. The electrochemically induced hydrogen intercalation from Mo2COx to HxMo2COx was identified by in-situ cyclic voltammetry characterization, and the significant role of hydrogen intercalation in surface-mediated HER pathway has been revealed by in-situ electrochemical impedance characterization. Density functional theory calculations indicate that hydrogen intercalation enables the HER by addressing sluggish water dissociation toward fast kinetics. Overall, this work underscores the importance of tracking the structure dynamic alteration of Mo2C-based material under the reaction conditions.