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

Two-dimensional VS2 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 VS2 nanosheets with various intrinsic point defects are studied by using first-principles calculations. Compared to the most-studied 2H-phase MoS2 basal plane, both 2H- and IT-phase VS2 basal planes exhibit superior catalytic activity due to their metallic properties. With the introduction of intrinsic point defects onto VS2 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 Vad in the 1T phase can enhance the HER activity of basal planes, which implies that the synthesis of VS2 nanosheets at the V rich condition facilitates the achievement of high HER performance. The HER activity of pristine and defective VS2 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 VS2 and the guidance for synthesizing highly active electrocatalysts in transition-metal dichalcogenides.