Reaction-Driven Varieties of Active Sites on Cu(100) in Electrochemical CO₂ Reduction Reaction

The development of electrochemical CO2 reduction reaction (eCO2RR) on Cu-based electrodes is one of the promising strategies for environmentally friendly progress. Recent experimental findings have shown that the low-index single-crystal Cu surfaces undergo significant reconstruction by CO as reactants/products, greatly affecting their catalytic activity. It is crucial to understand how the reconstruction takes place in real time and affects the catalytic performance at atomic scale. Herein, we conducted a systematic investigation on the surface reconstruction of Cu(100) and its influence on eCO2RR using potential-dependent grand canonical Monte Carlo (GCMC), environmental kinetic Monte Carlo (EKMC), and density functional theory (DFT) methods. At the experimental onset potential of CO formation, we elucidate the atomistic mechanism of surface reconstruction under CO and H coadsorption. Adsorbate-driven formation of adatoms and vacancies appears on the surface first, and then square-like clusters are generated via the adatom aggregation. The reconstructed surfaces are identified to be stable for a long time (over hours) at a wide range of electrode potentials, which enhances the catalytic activity. Moreover, the formation of products shows an ensemble effect: Surface Cu atom vacancy is the most favorable for the formation of methane; adatom is the most favorable for the formation of hydrogen and formic acid; and 4-atom cluster is the most favorable for the formation of CO and C2 products. These results highlight the possibility of tuning the ensemble of reaction-driven species to enhance eCO2RR selectivity on the Cu(100) surface.