Enhancing electrocatalytic reduction of CO 2 to C 2+ products with high efficiency at Cu 0 /Cu δ + interfaces via iodine modification strategy

Abstract Electrocatalytic CO 2 reduction reaction (CO 2 RR) to produce multicarbon (C 2+ ) products over Cu‐based catalysts represents an ideal approach for renewable energy storage and carbon emissions reduction. The Cu 0 /Cu δ + interfaces are widely recognized as crucial sites that promote C–C coupling and enhance the generation of C 2+ products. However, a major challenge arises from the tendency of Cu δ + active sites within Cu 0 /Cu δ + interfaces to undergo reduction to Cu 0 during the CO 2 RR process, leading to a decline in catalytic performance. Hence, it is crucial to establish durable Cu 0 /Cu δ + interfaces to enhance the conversion of CO 2 to C 2+ products. In this work, an iodine modification strategy is proposed to prepare a stable Cu@CuI composite catalyst with well‐maintained Cu 0 /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 CO 2 RR, achieving a Faradaic efficiency of 75.7% for C 2+ 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 CO 2 RR due to the presence of adsorbed iodine ions, which prevent complete reduction of Cu δ + species to Cu 0 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 CO 2 and lowering the energy barriers associated with coupling the *CHO and *CO intermediates during CO 2 RR. Consequently, this phenomenon enhances the selectivity toward C 2+ products during electrocatalytic CO 2 reduction.