A Physical Model for Understanding the Activation of MoS₂ Basal-Plane Sulfur Atoms for the Hydrogen Evolution...

Weak binding of hydrogen atoms to the 2H-MoS₂ basal plane renders MoS₂ inert as an electrocatalyst for the hydrogen evolution reaction. Transition-metal doping can activate neighboring sulfur atoms in the MoS₂ basal plane to bind hydrogen more strongly. Our theoretical studies show strong variation in the degree of activation by dopants across the 3d transition-metal series. To understand the trends in activation, we propose a model based on the electronic promotion energy required to partially open the full valence shell of a local S atom and therefore enable it to bond with a H atom. In general, the promotion is achieved through an electron transfer from the S to neighboring metal-atom sites. Furthermore, we demonstrate a specific, electronic-structure-based descriptor for the hydrogen-binding strength: Δ_dp , the local interband energy separation between the lowest empty d-states on the dopant metal atoms and occupied p-states on S. This model can be used to provide guidelines for chalcogen activation in future catalyst design based on doped transition-metal dichalcogenides.