Solid Solution In Situ‐Reconstructed Mg‐Cu ₂ O/Cu Heterointerface for CO ₂ Reduction to C ₂₊ Alcohols in Neutral and Acidic Media

Electrochemical CO₂ reduction presents a sustainable route for producing value-added liquid C₂₊ alcohols. Using neutral and acidic media enables high CO₂ utilization, but suffers low C₂₊ alcohols selectivity and production rate, due to high energy barrier of C─C coupling and competing C₂H₄ pathway on conventional Cu catalysts. Herein, we report porous Mg-stabilized Cu₂O/metallic Cu (Mg-Cu₂O/Cu) heterointerface, in situ reconstructed from block copolymer-derived mesoporous MgCuO solid solution under operating CO₂ reduction conditions, that realizes extraordinary neutral and acidic CO₂-to-C₂₊ alcohols performance. In situ spectroscopic and computational investigations disclose that Mg-Cu₂O/Cu heterointerface facilitates *CO hydrogenation and triggers energy-favorable asymmetric *CO─CHO coupling, distinctive to energy-intensive symmetric *CO─CO dimerization catalyzed by bare CuO-derived Cu surface. More importantly, the heterostructure modulates bonding strength of key C₂₊ intermediate with enhanced O─C yet weakened Cu─O bonds, switching selectivity from C₂H₄ on Cu to C₂₊ alcohols on Mg-Cu₂O/Cu. Along with porous architecture affording abundant accessible sites, we achieve remarkable Faradaic efficiencies of 70.4% at an industrial current density of 448.7 mA cm^-2 in neutral electrolyte and 61.4% at 316.1 mA cm^-2 in acid for C₂₊ alcohols, placing among the highest levels reported hitherto. This work provides a general catalyst design framework for steering reaction pathways in practical CO₂ electrolysis.