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

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.