Directly Imaging and Regulating the Nanoscale Inhomogeneity of S‐Vacancies in Molybdenum Disulfide Monolayer during Electrocatalytic Hydrogen Evolution

The study of electron transfer event on two-dimensional (2D) layered transition metal dichalcogenides has attracted tremendous attentions attributing to their promising applications in electrochemical devices. Herein, we demonstrate an opto-electrochemical strategy to directly map and regulate electron transfer event on molybdenum disulfide (MoS2) monolayer by combining bright field (BF) imaging technique with electrochemical modulation. The heterogeneity of electrochemical activity on MoS2 monolayer down to nanoscale is resolved spatiotemporally. The thermodynamics of MoS2 monolayer is measured during electrocatalytic hydrogen evolution, and the Arrhenius correlations are obtained. We validate that the defect generation engineered by oxygen plasma bombardment dramatically enhances the local electrochemical activity of MoS2 monolayer, which can be attributed to point defects of S-vacancies as evidenced. Furthermore, by comparing the difference of electron transfer event on MoS2 with various layers, the interlayer coupling effect is uncovered. This study represents a facile method to image the heterogeneity of electrochemical properties for nanomaterials with atomic thickness and regulate the local activity within the plane by extrinsic factors. It also has potential applications in the design and evaluation of high-performance layered electrochemical systems down to nanoscale.