Hydrogen Atom Adsorption-Induced Spin Reversal and Vacancies Boosting Hydrogen Evolution Reaction in Defective H-VS2 Monolayers

Spin reversal induced by adsorbates will cause intersite communication between the active and adjacent sites, which modulates the exchange coupling strength and spin alignment direction of adjacent atoms. Here, spin reversal induced by H adsorption and hydrogen evolution reaction (HER) performance of defective H-VS2 are studied by density-functional theory. The spin of V/S atoms around double S vacancies on different atomic layers (V2S) exhibits continuous reversals with H adsorption, which reverses once for S atoms around single V vacancy (VV). Moreover, the adsorption energies of the second H atom decreased in V2S- and VV-modified H-VS2 systems. Additionally, V2S and VV can activate the inert basal plane of H-VS2, and the increased antibonding filling and p-band center in H-VS2 with VV will weaken the interaction between S–H atoms and promote the desorption of H2, which causes lower Gibbs free energy in H-VS2 with VV than V2S and the pure H-VS2 monolayer.