Mechanisms and Potential-Dependent Energy Barriers for Hydrogen Evolution on Supported MoS2 Catalysts

Periodic density functional theory calculations are used to elucidate the mechanism of the hydrogen evolution reaction on the Mo edge of graphene- and Au(111)-supported molybdenum disulfide (MoS2) electrocatalysts. Calculated potential-dependent energy barriers, employing a detailed model of the electrochemical cell, reveal that the Volmer–Heyrovský mechanism (barrier: 1.3 eV) is favored over the Volmer–Tafel mechanism at potentials close to 0 V vs the standard hydrogen electrode (SHE). In this mechanism, H preferentially adsorbs to a S atom, but the formation of H2 occurs with Hads on Mo. Therefore, surface diffusion of Hads is required, which contributes to the overall barrier. The Volmer–Heyrovský barrier is similar on both supports, which is consistent with experimental rate measurements. However, Hads diffusion is the limiting step in the overall reaction on graphene-supported MoS2, whereas on Au-supported MoS2, the Volmer and Heyrovský barriers both contribute. This differing behavior between supports affects how the reaction rate changes with the potential, showing the importance of considering explicit reaction barriers. Our results provide a thorough understanding of hydrogen evolution kinetics and support-tuning effects, contributing to the optimization of MoS2 as a catalyst for this key reaction in sustainable energy production.