Controlling the Phase Composition of Pre‐Catalysts to Obtain Abundant Cu(111)/Cu(200) Grain Boundaries for Enhancing Electrocatalytic CO₂ Reduction Selectivity to Ethylene

The preparation of ethylene (C₂H₄) by electrochemical CO₂ reduction (ECO₂R) has dramatically progressed in recent years. However, the slow kinetics of carbon-carbon (C-C) coupling remains a significant challenge. A generalized facet reconstruction strategy is reported to prepare a 3-phase mixed pre-catalyst (Cu₃N-300) of Cu₃N, Cu₂O, and CuO by controlling the calcination temperature and to obtain the derived Cu catalyst (A-Cu₃N-300-0.5) enriched with Cu(111)/Cu(200) grain boundaries (GBs) by subsequent constant potential reduction. Its Faraday efficiency (FE) toward C₂H₄ at a low reaction potential of -1.07 V (vs reversible hydrogen electrode (RHE)) is 46.03%, which is much higher than the other 3 derived Cu catalysts containing single Cu(111) facets (24.89% and 24.52%) and Cu(111)/Cu(111) GBs (28.66%). Combining in situ experimental and theoretical computational studies, abundant Cu(111)/Cu(200) GBs is found to enhance CO₂ activation and significantly promote the formation and adsorption of *CO intermediates, thereby lowering the activation energy barrier of C-C coupling and increasing the FE of C₂H₄.