Molecular-Scale Resolution Mapping of Electrified MoS₂–Water Interfaces by Operando 3D-AFM

Understanding the interfacial water structure on electrified surfaces, in particular few-layer transition metal dichalcogenides MoS2, is relevant for advancing applications in biosensing, wearable electronics and catalysis. In this work, we implemented an operando 3D-AFM technique to probe the interfacial water layer structure on electrified surfaces with molecular-scale resolution. This method enabled us to study the interfacial hydration layer structure of MoS2 crystals under varying surface potential and electrochemical current density conditions. On pristine surfaces we observed the existence of two-to-four hydration layers. The interlayer distance (∼0.3 nm) was independent of the surface potential (−0.6 to 1.9 VSHE) and the current density. More hydration layers were observed at high positive potentials. Operando 3D-AFM compatibilized simultaneous current density and interfacial hydration layer structure measurements.