First-principles study of sulfur vacancy concentration effect on the electronic structures and hydrogen evolution reaction of MoS 2

Defect engineering has been widely used in experiments to modulate the electrocatalytic properties of molybdenum disulfide (MoS₂). However, the effect of vacancy concentration on the vacancy distribution, electronic properties, and hydrogen evolution reaction (HER) activity remains elusive. Herein, we perform density functional theory (DFT) studies to investigate defective MoS₂ with different numbers of sulfur vacancies. In the case of low S-vacancy concentration, the vacancies prefer to agglomerate rather than being dispersed, while at the higher-vacancy concentration, the combination of local point defect and clustered vacancy chain is preferred. The coupling between S-vacancies leads to decreased band gap and increased Mo-H adsorption strength with increasing vacancy concentration. The optimal HER activity is identified to occur below vacancy concentration of 12.50%. Our work provides an atomic-level understanding about the role of S-vacancies in the HER performance of MoS₂, and offers useful guidelines for the design of defective MoS₂ and other TMDs electrocatalysts.