Nanoscale Defect Engineering to Tune Electronic Structure and Surface Property of Two-Dimensional MoS2 Film for Hydrogen Evolution Reaction

Molybdenum disulfide (MoS2), a typical transition metal dichalcogenide, has drawn massive attention in the field of electrocatalytic hydrogen (H2) production. Defect engineering is one of the most feasible ways to enhance the hydrogen evolution reaction (HER) activity of MoS2, while there still remains a great challenge to achieve precise adaptation of defect structures to desirable electronic structures and surface properties. Herein, MoS2 electrocatalysts with stepped edge defect structures are manufactured by focused ion beam etching for superior HER performance. Comparing with defects with ordinary vertical edges, the stepped samples demonstrate much lower overpotential (−115 mV at the current density of −10 mA·cm–2), tremendously accelerated kinetics (Tafel slope of 36.0 mV·dec–1), and relatively high stability. The great leap of HER activity mainly benefits from the direct control of both the electronic structure and surface property of the material via accurate manipulation. According to the results of density functional theory calculation, contact angle test, and COMSOL Multiphysics simulation, the stepped edges not only speed up the generation rate of H2 by more optimized free energy of hydrogen adsorption and more suitable band structure for higher conductivity but also shorten the desorption time of H2 on the electrode surface attributing to its unique hydrophilic structure. It is believed that this study would play a constructive role in extending the design ideas of ultrahigh-performance MoS2-based electrocatalysts.