Optimizing edges and defects of supported MoS2 catalysts for hydrogen evolution via an external electric field.

As a fascinating non-precious catalyst for hydrogen evolution reaction (HER), two-dimensional (2D) molybdenum disulphide (MoS2) has attracted ever-growing interest. While the pristine basal plane of MoS2 is chemically inactive, certain edges and defects have been recognized to be catalytically active for HER. Nevertheless, the per-site activity of MoS2 is still much lower than that of Pt. Therefore, further optimization of active sites becomes highly desirable to enhance the overall catalytic activity of MoS2. In this work, we propose to use an electric field to engineer the electronic structure of edges and defects of MoS2, aiming to optimize its catalytic performance. Via systematic density functional theory based first-principles calculations, we investigated the adsorption of H atoms on different edges of free-standing and supported MoS2, revealing the critical role of S p-resonance states near the Fermi level in determining H adsorption, which offers an excellent descriptor for the catalytic activity associated with the electronic structure. Remarkably, by introducing an external electric field, we demonstrate the ability to fine tune the position of S p-resonance states, which can give an optimal H adsorption strength on MoS2 for HER. We also explored field effects on S vacancies in the basal plane, which show a different behavior for H adsorption due to the presence of Mo d states that are insensitive to the electric field. We expect these findings to shed new light on the design and control of MoS2-based catalysts for industrial applications.