Theoretical insights into the hydrogen evolution activity of layered transition metal dichalcogenides

A thermodynamic descriptor-based approach using density functional theory calculations was used to investigate the activity and stability of 26 different transition metal dichalcogenide catalysts for the hydrogen evolution reaction (HER). We considered variations in the transition metal (Ti, V, Nb, Ta, Mo, W, Pd, Pt), the chalcogen (S and Se), the crystal structure (1T and 2H), and the surface termination (basal plane or edge). We find that the HER activity is strongly related to the stability of the catalyst, setting practical limitations on their potential application in HER. For the basal planes, the metallicity is found to be the most important parameter in determining the activity rather than structure or composition. However, systematic improvements in activity are strongly limited by a decrease in stability. For the edges, the activity and stability relationship are similar regardless of structure or chalcogen, and it is possible to achieve optimal hydrogen binding with a stable surface. Nudged elastic band calculations were carried out to probe the possible mechanisms for HER; the insurmountably high barrier for the Tafel mechanism suggests that HER may occur solely via the Volmer-Heyrovsky route for these materials.