Insights into the Hydrogen Evolution Reaction on 2D Transition-Metal Dichalcogenides

Understanding hydrogen evolution reaction (HER) behaviors over two-dimensional transition-metal dichalcogenides (2D-TMDs) is critical for the development of nonprecious HER electrocatalysts with better activity. In this work, by combining density functional theory calculations with microkinetic modeling, we thoroughly investigated the HER mechanism on 2D-TMDs. We find an important dependence of simulated cell size on the calculated hydrogen adsorption energy and the activation barrier for MoS2. Distinct from previous H migration mechanisms proposed for the Heyrovsky reaction, the rate-determining step for MoS2, we propose that the Mo site only serves as the stabilized transition state rather than H adsorption. In comparison to transition-metal electrocatalysts, we find that the activation barrier of the Heyrovsky reaction on 2D-TMDs scales with the hydrogen adsorption energy exactly as for transition metals except that all activation energies are displaced upward by ca. 0.4 eV. This higher Heyrovsky activation barrier is responsible for the substantially lower activity of 2D-TMDs. We further show that this higher activation barrier stems from the more positively charged adsorbed hydrogen on the chalcogenides interacting repulsively with the incoming proton. Based on these insights, we discuss potential strategies for the design of nonprecious HER catalysts with activity comparable to Pt.

Automated summary

In this work, the HER mechanism on 2D-TMDs was thoroughly investigated using density functional theory calculations and microkinetic modeling. It was found that the simulated cell size has an important influence on the calculated hydrogen adsorption energy and the activation barrier. The study proposes that the Mo site on MoS2 serves as a stabilized transition state rather than hydrogen adsorption. The activation barrier of the Heyrovsky reaction on 2D-TMDs scales with the hydrogen adsorption energy, but is displaced upward by approximately 0.4 eV compared to transition metals. This higher activation barrier is responsible for the lower activity of 2D-TMDs.