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

Understanding the <i>in situ</i> surface structure of electrodes is crucial for unraveling the synergistic mechanisms of electrolytes in interfacial electrocatalysis. Herein, using <i>in situ</i> 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 <i>via</i> 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 <i>in situ</i> surface structures, which is important for understanding electrolyte-mediated surface structure-activity relationships.