Localized Geometry Determined Selectivity of Iodide‐Derived Copper for Electrochemical CO₂ Reduction

Abstract Two iodide‐derived copper (ID‐Cu) electrocatalysts (E‐ID‐Cu and W‐ID‐Cu) are prepared by electrochemical/wet chemical iodination of Cu foil and subsequent in situ electrochemical reduction reaction. In comparison to electropolished Cu (EP‐Cu), both E‐ID‐Cu and W‐ID‐Cu can produce multicarbon (C₂₊) products with much‐improved selectivity, with Faradic efficiency (FE) reaching 64.39% for E‐ID‐Cu and 71.16% for W‐ID‐Cu at −1.1 V versus reversible hydrogen electrodes (RHE), which can be attributed to their localized geometry features with high defect density and high surface roughness. Given the well‐determined FEs towards C₂₊ products, the partial current densities for C₂₊ production can be estimated to be 251.8 mA cm⁻² for E‐ID‐Cu and 290.0 mA cm⁻² for W‐ID‐Cu at −1.2 V versus RHE in a flow cell. In situ characterizations and theoretical calculations reveal that the high‐density defects and high surface roughness can promote *CO adsorption by raising the d band center and then facilitate C–C coupling, contributing to the high selectivity of C₂₊ products for ID‐Cu. Interestingly, the high surface roughness can increase the residence time of *C–H intermediates and decrease the formation energy of the *OCCO and*CH₃CH₂O intermediates, thus favoring C₂₊ production, with a unique C₂H₆ product observed over W‐ID‐Cu with FE of 10.14% at −0.7 V versus RHE.