Mechanistic Implications of Low CO Coverage on Cu in the Electrochemical CO and CO 2 Reduction Reactions.

Electrochemical CO or CO 2 reduction reactions (CO (2) RR), powered by renewable energy, represent one of the promising strategies for upgrading CO 2 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 (CO ad ) is the most commonly reported reaction intermediate in the CO (2) RR, and its surface coverage (θ CO ) and binding energy are proposed to be key to the catalytic performance. Recent experimental evidence sugguests that θ CO on Cu electrode at electrochemical conditions is quite low (∼0.05 monolayer), while relatively high θ CO is often assumed in literature mechanistic discussion. This Perspective briefly summarizes existing efforts in determining θ CO on Cu surfaces, analyzes mechanistic impacts of low θ 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.