Minority Sites on Cu Surfaces Drive C–C Coupling in the Electrochemical Reduction of CO 2

The electrochemical CO 2 reduction reaction (CO 2 RR) on Cu has been extensively investigated as a strategy to valorize a prominent greenhouse gas; however, key mechanistic questions remain unresolved. In this work, we propose a mechanistic framework to rationalize the contradiction between CO coverages on Cu under electrochemical conditions and the reaction orders of CO 2 and CO in the formation of C 2+ products by recognizing the site heterogeneity on Cu surfaces. OC–CO coupling occurs primarily on highly active minority sites with a strong CO affinity, while the majority of surface Cu sites are relatively inert in OC–CO coupling. Further, correlations between the structure and effectiveness of molecular inhibitors reveal that Cu CO sites are likely located on highly curved nanostructures. This work proposes a general mechanistic framework to rationalize the Cu-catalyzed CO 2 RR and provides insights into the structure of active sites.