Visualizing the role of applied voltage in non-metal electrocatalysts.

Understanding how applied voltage drives the electrocatalytic reaction at the nanoscale is a fundamental scientific problem, particularly in non-metallic electrocatalysts, due to their low intrinsic carrier concentration. Herein, using monolayer molybdenum disulfide (MoS) as a model system of non-metallic catalyst, the potential drops across the basal plane of MoS (ΔV) and the electric double layer (ΔV) are decoupled quantitatively as a function of applied voltage through surface potential microscopy. We visualize the evolution of the band structure under liquid conditions and clarify the process of E keeping moving deep into E, revealing the formation process of the electrolyte gating effect. Additionally, electron transfer (ET) imaging reveals that the basal plane exhibits high ET activity, consistent with the results of surface potential measurements. The potential-dependent behavior of k and n in the ET reaction are further decoupled based on the measurements of ΔV and ΔV. Comparing the ET and hydrogen evolution reaction imaging results suggests that the low electrocatalytic activity of the basal plane is mainly due to the absence of active sites, rather than its electron transfer ability. This study fills an experimental gap in exploring driving forces for electrocatalysis at the nanoscale and addresses the long-standing issue of the inability to decouple charge transfer from catalytic processes.