Computational Insights into the Catalytic Activity of Two-Dimensional Janus WSO for Hydrogen Evolution Reaction

Janus two-dimensional materials have been synthesized and several of their applications as electronic and optical properties already studied in detail. In this study, we utilized density functional theory to computationally model janus WSO, which is derived from replacing a sulfur layer with oxygen in the parent two-dimensional material WS2. Our findings reveal that janus WSO is a p-type semiconductor with an indirect band gap. We also investigated its catalytic behaviour for the hydrogen evolution reaction (HER) by calculating the free energy change for hydrogen evolution. Similar to other two-dimensional materials, the janus WSO basal plane does not show significant HER activity; however, the defective material exhibits enhanced activity. We delved into the formation of single and multiple defect structures due to sulfur and oxygen vacancies and compared their HER activities. Our calculations demonstrate that some of the defect structures exhibit the potential for nearly zero free energy change for HER. Furthermore, we explored the effects of increased hydrogen coverage on the material's activity. Our reaction pathway modeling indicates that HER occurs via the Heyrovsky mechanism. Janus WSO proves to be a promising HER catalyst, with natural intrinsic strain and vacancies synergistically contributing to its appreciable catalytic activity.