Constructing grain boundary to stabilize Cu0/Cu+ interfacial sites for efficient CO2 reduction reaction

The electrochemical CO2 reduction reaction (CO2RR) to multi‐carbon (C2+) products derived by renewable energy represents a promising strategy for mitigating CO2 emissions. One of the intensively studied strategies is to stabilize Cu+ species on catalysts to facilitate the adsorption of *CO intermediates. However, the reductive environment during CO2RR renders the Cu+ species on the catalyst surface susceptible to reduction to Cu0. Here, we developed a GB‐Cu2O‐Cu catalyst featuring enriched grain boundaries via an in situ electrochemical reduction process to stabilize Cu+ species, resulting in an abundance of Cu0/Cu+ interfacial active sites. In situ x‐ray diffraction (XRD) and Raman spectroscopy further revealed that the presence of grain boundaries effectively shields the Cu+ species on the catalyst surface from undergoing reduction during CO2RR, facilitating the concentration of *CO intermediates and thus promoting C‐C dimerization to C2+ products.