Preanodized Cu Surface for Selective CO₂ Electroreduction to C₁ or C₂₊ Products

The electrochemical CO2 reduction over Cu catalysts has shown great potential in producing a wide range of valuable chemicals, but it is still plagued by a poor controllability on product distribution. Herein, we demonstrate an effective regulation of CO2 reduction paths through a preanodization treatment of Cu foil electrodes in different electrolytes. The Cu electrode exhibits a superior C1 and C2+ product selectivity after being preanodized in NaClO4 (Cu-NaClO4) and Na2HPO4 electrolyte (Cu-Na2HPO4), respectively. Combined with in situ electrochemical Raman, ATR-SEIRAS, and SEM characterizations, the preferential C1 path is due to the deposition of many Cu nanocrystals with dominant Cu(111) facets on the Cu-NaClO4 electrode. In contrast, the preferential C2+ path over the Cu-Na2HPO4 is attributed to formation of a unique Cu nanodendritic morphology, which strengthens the *CO intermediate adsorption and induces an environment of low local H2O/CO2 stoichiometric ratio, thus facilitating C–C coupling for C2+ production. Our findings may shed light on the rational control of the CO2 reduction path through engineering of the Cu surface structure.