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.