Defect‐Rich Porous Cu with Abundant Cu(100) for Acidic CO ₂ Electroreduction in Membrane Electrode Assembly

Acidic electrocatalytic CO₂ reduction (CO₂RR) faces slow C-C coupling kinetics and dominant hydrogen evolution, resulting in low C₂₊ yields and selectivity. Here, the porous copper nanosheets (pCu NS) are reported with abundant Cu(100) and defect sites for efficient acidic CO₂RR to C₂₊ products. In a membrane electrode assembly (MEA), the pCu NS electrodes achieved a remarkable 75.01% C₂₊ production Faradaic efficiency (FE) at a current density of 300 mA cm^-2 with a full-cell voltage of 3.8 V. A CO₂ single-pass conversion efficiency of up to 74.38% is achieved. In situ Raman spectra and density functional theory calculations revealed that pCu NS not only gives abundant nanopores and defect sites but also preferentially exposes Cu(100) facets, synergistically creating local alkaline microenvironment, maximizing the *CO intermediate coverage, and promoting *CO hydrogenation for C₂₊ production. This work offers a crucial insight for designing an efficient catalyst for efficient acidic CO₂-to-C₂₊ conversion.