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 (VS) defects, as observed from the electronic structural changes that are in excellent agreement with DFT calculations for a VS 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 VS defects via annealing is a promising strategy for enhancing hydrogen adsorption on MoS2, paving the way for its potential use in future catalytic applications.