Stepped high-index Cu(211)/(100) interface for enhanced electrochemical CO2 reduction

Engineering the local coordination and electronic environment of Cu active sites is critical for controlling intermediate stabilization and C-C coupling during the electrochemical CO 2 reduction reaction (CO 2 RR). However, the influence of stepped high-index facets within Cu interfacial structures remains insufficiently understood. Here, density functional theory (DFT) calculations are used to investigate the electronic structures and CO 2 adsorption characteristics of the stepped high-index Cu(211)/(100) and Cu(111)/(100) interfaces in comparison with pristine Cu(100). The Cu(211)/(100) interface promotes CO 2 adsorption and activation and facilitates interfacial charge transfer. The subsequent proton-coupled electron transfer (PCET) energetics and C-C coupling kinetics on Cu(211)/(100) are further evaluated relative to pristine Cu(100). The calculated free-energy profiles show that energetically unfavorable PCET steps following *CO formation limit further reduction on Cu(100), whereas the Cu(211)/(100) interface stabilizes *CO and facilitates its subsequent conversion to *CHO. The *CO → *CHO step is identified as the potential-determining step (PDS) with a limiting potential (U L ) of -0.55 V vs RHE. Among the C-C coupling pathways considered, *CHO-*CHO coupling is kinetically favored, with an activation barrier of 0.43 eV, substantially lower than those for *CO-*CHO (0.97 eV) and *CO-*CO coupling (1.58 eV). The results demonstrate that the Cu(211)/(100) interface facilitates the conversion of *CO to CHO and promotes CHO-mediated C-C coupling, highlighting the role of stepped high-index interfaces in directing CO 2 RR pathways toward C 2 products.