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.