Electrolyte concentration modulates the surface structure evolution of Au(111) cathodes

Understanding the in situ surface structure of electrodes is crucial for unraveling the synergistic mechanisms of electrolytes in interfacial electrocatalysis. Herein, using in situ electrochemical scanning tunneling microscopy (EC-STM), we unveil the electrolyte concentration-driven roughening of Au(111) surfaces under cathodic polarization. As the concentration of alkali metal cations (AM⁺) ([AM⁺]) decreases, the AM⁺-induced surface structure evolution proceeds from surface corrosion at 1 M to the formation of surface pits alongside surface nanoclusters composed of released Au atoms at 0.5-0.3 M and ultimately to the generation of pit-free nanoclusters via surface atomic migration at 0.2 M. Moreover, surface modifications modulate the electrode surface structure, enabling more pronounced structure evolution at lower bulk [AM⁺]. Electrochemical measurements correlate increased surface roughness with enhanced CO₂ reduction reaction (CO₂RR) performance. The results provide a new perspective on understanding the role of AM⁺ in regulating the electrochemical interface and microscopic insights into AM⁺ concentration-driven in situ surface structures, which is important for understanding electrolyte-mediated surface structure-activity relationships.