Enhancing electrocatalytic reduction of CO₂ to C₂₊ products with high efficiency at Cu⁰/Cu^δ+ interfaces via iodine modification strategy

Electrocatalytic CO₂ reduction reaction (CO₂RR) to produce multicarbon (C₂₊) products over Cu-based catalysts represents an ideal approach for renewable energy storage and carbon emissions reduction. The Cu⁰/Cu^δ+ interfaces are widely recognized as crucial sites that promote C–C coupling and enhance the generation of C₂₊ products. However, a major challenge arises from the tendency of Cu^δ+ active sites within Cu⁰/Cu^δ+ interfaces to undergo reduction to Cu⁰ during the CO₂RR process, leading to a decline in catalytic performance. Hence, it is crucial to establish durable Cu⁰/Cu^δ+ interfaces to enhance the conversion of CO₂ to C₂₊ products. In this work, an iodine modification strategy is proposed to prepare a stable Cu@CuI composite catalyst with well-maintained Cu⁰/Cu^δ+ interfaces through a one-step redox reaction between iodine and copper. The optimized Cu@CuI-3 composite catalyst demonstrates an excellent performance in CO₂RR, achieving a Faradaic efficiency of 75.7% for C₂₊ products and a partial current density of 288 mA·cm⁻² at − 1.57 V_RHE in a flow cell. Operando techniques reveal that a numerous persistent Cu^δ+ species exist on the surface of the Cu@CuI-X composite catalyst even after CO₂RR due to the presence of adsorbed iodine ions, which prevent complete reduction of Cu^δ+ species to Cu⁰ owing to their high electronegativity. Density functional theory calculations further verify that adsorbed iodine ions on the surface of Cu@CuI-X serve as charge regulators by adjusting local charge density, thereby facilitating the formation of *CHO intermediates from CO₂ and lowering the energy barriers associated with coupling the *CHO and *CO intermediates during CO₂RR. Consequently, this phenomenon enhances the selectivity toward C₂₊ products during electrocatalytic CO₂ reduction.