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 (V-2S) exhibits continuous reversals with H adsorption, which reverses once for S atoms around single V vacancy (V-V). Moreover, the adsorption energies of the second H atom decreased in V-2S- and V-V-modified H-VS2 systems. Additionally, V-2S and V-V can activate the inert basal plane of H-VS2, and the increased antibonding filling and p-band center in H-VS2 with V-V will weaken the interaction between S-H atoms and promote the desorption of H-2, which causes lower Gibbs free energy in H-VS2 with V-V than V-2S and the pure H-VS2 monolayer.