The article presents a novel strategy to enhance the efficiency of CO₂ reduction to multicarbon (C₂ₓ) products using copper (Cu) catalysts. The key innovation is the in situ copper faceting approach, which enables the preferential exposure of Cu(100) facets through the co-adsorption of CO and hydroxide ions (CO&OH−). This method slows the reduction of Cu during electrochemical reduction, promoting the formation of Cu(100) facets. The resulting Cu catalyst exhibits high current densities (>500 mA cm⁻²) and Faradaic efficiencies (≥83%) for both CO₂ and CO reductions. The catalyst maintains its performance over 150 hours of operation, with a full-cell energy efficiency of 37% and a single-pass carbon efficiency of 95%. The study also includes density functional theory (DFT) calculations to explain the surface energy differences between Cu(III) and Cu(100) facets, and detailed characterization of the Cu precatalyst and derived Cu catalysts. The findings highlight the potential of this approach for economically viable CO₂ electrolysis.The article presents a novel strategy to enhance the efficiency of CO₂ reduction to multicarbon (C₂ₓ) products using copper (Cu) catalysts. The key innovation is the in situ copper faceting approach, which enables the preferential exposure of Cu(100) facets through the co-adsorption of CO and hydroxide ions (CO&OH−). This method slows the reduction of Cu during electrochemical reduction, promoting the formation of Cu(100) facets. The resulting Cu catalyst exhibits high current densities (>500 mA cm⁻²) and Faradaic efficiencies (≥83%) for both CO₂ and CO reductions. The catalyst maintains its performance over 150 hours of operation, with a full-cell energy efficiency of 37% and a single-pass carbon efficiency of 95%. The study also includes density functional theory (DFT) calculations to explain the surface energy differences between Cu(III) and Cu(100) facets, and detailed characterization of the Cu precatalyst and derived Cu catalysts. The findings highlight the potential of this approach for economically viable CO₂ electrolysis.