Hydrogen absorption boosting in mildly annealed bulk MoS2

Abstract

The basal plane of MoS₂ has been considered a potential source of active catalytic sites in hydrogen absorption. Sulfur vacancies can activate the inert basal plane of MoS₂; however, achieving sufficient catalytic efficiency requires a high defect concentration of about 12%. We investigated the effect of defects on the hydrogen adsorption on the basal plane of MoS₂ using angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations. Mild annealing in terms of temperature and time effectively introduces single sulfur vacancy (V_S) defects, as observed from the electronic structural changes that are in excellent agreement with DFT calculations for a V_S concentration of ∼4%. Subsequent exposure to molecular hydrogen showed that the higher hydrogen pressure facilitates hydrogen adsorption, as predicted by theoretical calculations. Interestingly, hydrogen exposure restores the electronic structure to a state similar to that of pristine MoS₂. These results suggest that the controlled introduction of V_S defects via annealing is a promising strategy for enhancing hydrogen adsorption on MoS₂, paving the way for its potential use in future catalytic applications.