Unlocking power of neighboring vacancies in boosting hydrogen evolution reactions on two-dimensional NiPS3 monolayer

This study investigates the effect of defect engineering on the catalytic activity of a NiPS₃ monolayer catalyst for the hydrogen evolution reaction (HER). Three different types of vacancies on the basal plane of the monolayer are explored through a multi-step mechanism involving the dissociative adsorption of a water molecule and subsequent electrochemical adsorption of the dissociated proton. Co-formation of vacancies in both Ni and S sites is found to be the most effective in enhancing the catalytic performance of the monolayer. A key resource for the reaction thermodynamics is the S-substitution-like physisorption of a water molecule on a vacant S site, followed by the dissociative occupation of OH and H into vacant sites of S and Ni elements, boosted by the NiS di-vacancy configuration with low activation energy barriers. Investigation reveals the highest contribution of bonding orbitals to the monolayer-H bond makes it the most desirable defect engineering approach for transition metal phosphorus chalcogenides with high HER activities. Overall, this study highlights the significance of controlled defect engineering in augmenting the catalytic performance of NiPS₃ monolayer catalysts for HER.