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

Abstract

The activity of the electrocatalytic CO 2 reduction reaction (CO 2 RR) 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 CO 2 RR 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 CO 2 RR 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 CO 2 RR in large AM + electrolytes.