Computationally guided construction of optimal Mo2C/C electrocatalysts toward high-efficiency hydrogen evolution reaction

Abstract

During the synthesis of beta-molybdenum carbide (Mo₂C), hydrocarbons and their derivatives are typically used as carbon (C) sources and reducing agents, resulting in unavoidable residual carbon. The residual carbon layer may accelerate the sluggish desorption kinetics on the Mo₂C surface via electronic interactions, and intrinsically enhance the hydrogen evolution catalytic activity of the Mo₂C/C composite material. To discover the optimal configuration of Mo₂C/C electrocatalysts for the hydrogen evolution reaction (HER), the hydrogen adsorption free energies (ΔG_H*) of numerous inequivalent carbon sites were calculated. The corresponding results show that when a monolayer of carbon decorates the surface of Mo₂C, most of the carbon sites exhibit ideal ΔG_H*, but once the surface carbon layer increases to a double layer, no significant improvement can be observed. Guided by the computational results, a mild static hydrogen atmosphere calcination strategy was proposed to selectively etch the residual carbon layer on the Mo₂C surface and achieve accelerated HER kinetics with a low Tafel slope of 46 mV dec⁻¹. This work demonstrates that reducing the surface residual carbon layer provides a facile tactic to optimize catalytic activity for metal carbide electrocatalysts.