A structure-sensitive descriptor for the design of active sites on MoS2 catalysts†

MoS₂ catalysts hold great promise for numerous reactions of industrial and technological interest. However, general guidelines for the design of their active sites remain elusive. We hypothesize that this is because the link between their geometric structure and reactivity is yet to be established at the atomic scale. Here we show that cn, a metric based on the number of sulfur atoms coordinated to Mo atoms, captures the trends in reactivity of MoS₂ catalysts with various sulfur vacancy contents. This is illustrated for the adsorption energies of numerous monatomic and polyatomic species. More importantly, cn can be used to predict the reaction and activation energies of common formation and dissociation reactions in catalysis. Finally, cn is used to outline the optimal configuration of MoS₂ active sites for the electrocatalytic hydrogen evolution reaction: the highest exchange current density corresponds to terrace sites with adjacent S vacancies with cn in the range of 4.33 to 4.67.