Engineering Isolated S Vacancies over 2D MoS₂ Basal Planes for Catalytic Hydrogen Evolution

The consensus has been built on the fact that the hydrogen evolution reaction (HER) activity of MoS2 basal planes can be activated by S vacancies. Currently, the popular strategy for fabricating S vacancies is to remove part of S atoms of MoS2. Owing to the same identity of S atoms, the removal process is usually random and does not have selectivity. Herein, we develop a defect-predesigned strategy to produce MoS2 with single-atomic S vacancies (SV-MoS2) simply by preparing Se-doped MoS2 (Se–MoS2) and subsequent removing the Se of Se–MoS2. S vacancies originates from the vaporization of the doped Se atoms, making the formation of S vacancies have a high selectivity and raising a good possibility for precisely modulating the concentration of S vacancies. The results show that the concentration of S vacancies can be controlled over the range from ∼7.46% to 13.54%. MoS1.76 with ∼12.10% of S vacancies exhibits outstanding HER performance: an overpotential of 100 mV at 10 mA cm–2 and a Tafel slope of 49 mV dec–1, corroborating the theoretical prediction about the optimum concentration of S vacancies. Density functional theory calculation further reveals that the activation of MoS2 basal planes may intrinsically originate from the modification of S vacancies to band structure and density of state of MoS2, optimizing the hydrogen adsorption energy. This defect-predesigned strategy reduces the probability of forming the aggregates of S vacancies and will be more helpful for understanding how S vacancies affect the properties of MoS2.