The Role of Intrinsic Defects in Electrocatalytic Activity of Monolayer VS2 Basal Planes for the Hydrogen Evolution Reaction

Two-dimensional VS 2 nanomaterials have emerged as highly efficient and inexpensive electrocatalysts for the hydrogen evolution reaction (HER), and the further improvement of their HER performance depends on the understanding of the catalytic mechanism and activity in various pristine and defective structures. Here, structural stability, electronic properties, and HER activity of monolayer VS 2 nanosheets with various intrinsic point defects are studied by using first-principles calculations. Compared to the most-studied 2H-phase MoS 2 basal plane, both 2H- and 1T-phase VS 2 basal planes exhibit superior catalytic activity due to their metallic properties. With the introduction of intrinsic point defects onto VS 2 basal planes, we find that there are four types of stable defects in the 2H phase (i.e., S ad, S vac, V ad, and V S ) and three types of stable defects in the 1T phase (i.e., S ad, S vac, and V ad ). Moreover, the formation of S vac, V ad, and V S structures in the 2H phase and V ad in the 1T phase can enhance the HER activity of basal planes, which implies that the synthesis of VS 2 nanosheets at the V-rich condition facilitates the achievement of high HER performance. The HER activity of pristine and defective VS 2 structures can be well understood by a Fermi-abundance model that is also suitable to describe a broad class of electrocatalytic HER systems. This work provides a deep insight into the HER activity of single-layer VS 2 and the guidance for synthesizing highly active electrocatalysts in transition-metal dichalcogenides.