Reconstructing Cu nanoparticle supported on vertical graphene surfaces via electrochemical treatment to tune the selectivity of CO₂ reduction toward valuable products

Reconstructing a catalyst with tunable properties is essential for achieving selective electrochemical CO₂ reduction reaction (CO2RR). Here, a reduction–oxidation–reduction (ROR) electrochemical treatment is devised to advisedly reconstruct copper nanoparticles on vertical graphene. Undercoordinated sites and oxygen vacancies constructed on the Cu active sites during the ROR treatment enhance the CO2RR activity. Moreover, by varying the oxidation potential while maintaining the reduction potential during the ROR treatment, CO2RR selectivity can be tuned between *COOH- and *OCHO-derived products. Specifically, rich grain boundaries are formed on the ROR catalyst with a high oxidation potential (+1.2 V_RHE), favoring the *COOH/*OCCO adsorption and leading C–C coupling to *COOH-derived products, while the catalyst undergoing ROR at a low oxidation potential (+0.8 V_RHE) lacks grain boundaries, resulting in highly selective formate (*OCHO-derived) production. Our findings are evidenced by combined in situ and ex situ characterizations and theoretical calculations.