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

[Image: see text] 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.