Dynamic Copper Dissolution Enables a Facile C–C Coupling Pathway in CO ₂ Electroreduction: A First-Principles Study

Electrochemical CO2 reduction offers a sustainable route to lower carbon emissions while producing valuable multicarbon (C2+) products. Yet, the efficiency of C2+ formation is limited by the C–C coupling step, traditionally assumed to proceed exclusively via the dimerization of two surface-bound *CO species. However, recent studies reveal that copper catalysts undergo dynamic dissolution and redeposition during electrolysis, generating transient Cu+ carbonyl complexes whose potential participation in C–C bond formation has been overlooked. Here, we apply density functional theory with a constant potential model to explore this previously unconsidered C–C bond formation mechanism, wherein the CO ligand of the dissolved Cu+ carbonyl complex couples with surface-adsorbed *CO. We find that the Cu-CO + *CO coupling pathway is kinetically accessible with free energy barriers of approximately 0.77 eV on Cu(100), Cu(110), Cu(211), and Cu(331), largely independent of the surface morphology. Notably, this pathway emerges as a competitive parallel route on stepped surfaces, such as Cu(211) and Cu(331), offering a low-barrier alternative to conventional *CO + *CO dimerization. The coupling process is best described as the reaction of a Cu+-coordinated CO with a Cu0-adsorbed *CO, aligning with the established two-site cooperative mechanism involving adjacent Cu+ and Cu0 sites. Moreover, we demonstrate that C–C coupling between the CO ligand of the Cu+ complex and other *C1 species derived from further *CO reduction is even more kinetically facile with an average barrier of only 0.44 eV. These results reveal a Cu+-mediated C–C formation pathway, expanding the mechanistic landscape and highlighting copper dissolution kinetics as a new approach for catalytic system design.