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.