Defect Engineering in MoSe2 for the Hydrogen Evolution Reaction: From Point Defects to Edges

Superior catalytic activity and high chemical stability of inexpensive electrocatalysts for the hydrogen evolution reaction (HER) are crucial to the large-scale production of hydrogen from water. The nonprecious two-dimensional MoSe 2 materials emerge as a potential candidate, and the improvement of their catalytic activity depends on the optimization of active reaction sites at both the edges and the basal plane. Herein, the structural stability, electrocatalytic activity, and HER mechanisms on a series of MoSe 2 catalytic structures including of point defects, holes, and edges have been explored by using first-principles calculations. Our calculated results demonstrate that thermodynamically stable defects (e.g., V Se, V Se 2, Se Mo, and V Mo 3 Se 2 ) and edges (e.g., Mo-R and Se-R) in MoSe 2 are very similar to the case of MoS 2, but their HER activity is higher than that of the corresponding structures in MoS 2, which is in good agreement with experimental observations. Furthermore, a Fermi-abundance model is proposed to explain the fundamental correlation between the HER activity of various MoSe 2 catalysts and their intrinsic electronic structures, and this model is also applicable for assessing the HER activity of other types of catalysts, such as MoS 2 and Pt. Moreover, two different HER mechanisms have been revealed in the MoSe 2 catalytic structures: the Volmer–Tafel mechanism is preferred for the V Se and V Se 2 structures, whereas the Volmer–Heyrovsky mechanism is more favorable for other MoSe 2 catalytic structures. The present work suggests that MoSe 2 with appropriate defects and edges is able to compete against the Pt-based catalysts and also opens a route to design highly active electrocatalysts for the HER.