3DOM Perovskite Enabled Interfacial Microenvironment Regulation With Accelerated Complete Reconstruction to Grain‐Boundary‐Rich Nano‐Copper for High‐Current C ₂₊ Electrosynthesis

Electrochemical CO₂ reduction reaction (CO₂RR) offers a compelling pathway to convert carbon emissions into value-added chemicals, yet achieving high activity, selectivity, and durability under industrial conditions remains challenging. Though copper oxides could uniquely promote C₂₊ electrosynthesis, their performance is dictated by dynamic oxide reconstruction, which is strongly governed by the interfacial microenvironment. Here, we report direct interfacial microenvironment regulation by constructing a 3D ordered macroporous (3DOM) architecture from layered perovskite La₂CuO₄. The 3DOM architecture simultaneously strengthens the surface electric field, elevates local pH, and accelerates mass transport at the interface, driving accelerated and complete reconstruction of La₂CuO₄ into dendritic grain-boundary-rich nano-copper. Consequently, 3DOM-La₂CuO₄ delivers a high C₂₊ partial current density of 585 mA cm⁻² in a flow cell, outperforming bulk counterpart and most reported Cu-oxide-based catalysts. In a membrane-electrode assembly, stable operation is sustained for ∼ 200 h at 600 mA cm⁻² with high C₂₊ selectivity. Combined experimental and theoretical analysis identify undercoordinated, compressively strained Cu atoms at grain boundaries as the intrinsic active sites for C₂₊ formation, by facilitating *COH formation, stabilizing *OCCOH intermediate, and suppressing the competing hydrogen production. This work establishes electrode-architecture-driven microenvironment engineering as a general strategy for directing oxide reconstruction and designing high-performance CO₂RR catalysts.