Mechanistic Implications of Low CO Coverage on Cu in the Electrochemical CO and CO2 Reduction Reactions

Electrochemical CO or CO2 reduction reactions (CO(2)RR), powered by renewable energy, represent one of the promising strategies for upgrading CO2 to valuable products. To design efficient and selective catalysts for the CO(2)RR, a comprehensive mechanistic understanding is necessary, including a comprehensive understanding of the reaction network and the identity of kinetically relevant steps. Surface-adsorbed CO (COad) is the most commonly reported reaction intermediate in the CO(2)RR, and its surface coverage (theta(CO)) and binding energy are proposed to be key to the catalytic performance. Recent experimental evidence sugguests that theta(CO) on Cu electrode at electrochemical conditions is quite low (similar to 0.05 monolayer), while relatively high theta(CO) is often assumed in literature mechanistic discussion. This Perspective briefly summarizes existing efforts in determining theta(CO) on Cu surfaces, analyzes mechanistic impacts of low theta(CO) on the reaction pathway and catalytic performance, and discusses potential fruitful future directions in advancing our understanding of the Cu-catalyzed CO(2)RR.