Alkali Metal Cations Induce Structural Evolution on Au(111) During Cathodic Polarization

The activity of the electrocatalytic CO₂ reduction reaction (CO₂RR) is substantially affected by alkali metal cations (AM⁺) in electrolytes, yet the underlying mechanism is still controversial. Here, we employed electrochemical scanning tunneling microscopy and in situ observed Au(111) surface roughening in AM⁺ electrolytes during cathodic polarization. The roughened surface is highly active for catalyzing the CO₂RR due to the formation of surface low-coordinated Au atoms. The critical potential for surface roughening follows the order Cs⁺ > Rb⁺ > K⁺ > Na⁺ > Li⁺, and the surface proportion of roughened area decreases in the order of Cs⁺ > Rb⁺ > K⁺ > Na⁺ > Li⁺. Electrochemical CO₂RR measurements demonstrate that the catalytic activity strongly correlates with the surface roughness. Furthermore, we found that AM⁺ is critical for surface roughening to occur. The results unveil the unrecognized effect of AM⁺ on the surface structural evolution and elucidate that the AM⁺-induced formation of surface high-activity sites contributes to the enhanced CO₂RR in large AM⁺ electrolytes.