Dynamic Cu0/Cu+ Interface Promotes Acidic CO2 Electroreduction

Acidic CO2 electroreduction reaction (CO2RR) shows advantages in high carbon utilization efficiency yet encounters great challenges in suppressing undesired hydrogen evolution competition and increasing C2+ product selectivity. Although it is known that Cu0/Cu+ interfaces are conducive to C–C coupling processes, the oxidation state of copper cannot be well maintained under the strong reductive condition and large current electrolysis operation. Herein, we propose an I2 addition involved strategy to protect the oxidation state of Cu and promote dynamic Cu0/Cu+ interfaces during acidic CO2RR. With the addition of I2 in the electrolyte, a high C2+ product Faraday efficiency of above 70% can be achieved at 0.4–0.6 A cm–2 even under a low K+ concentration of 0.3 M, which is comparable to those reported performances with almost ten times higher K+ concentrations (2–3 M). This low K+ concentration in electrolytes significantly avoids salt crystallization in the CO2 transport channel to enhance the electrolyzer's stability. As proved by the surface Pourbaix diagram and experimental results, adding excessive I2 into the electrolyte boosts the generation of CuI; also, CuI and metallic Cu coexist under electrochemical reduction conditions, demonstrating that a redox loop of Cu → CuI → Cu exists. The loop holds the key to constructing the dynamic Cu0/Cu+ interface, which is tightly bound to the adsorption of the *CO reaction intermediate and further promotes the C–C coupling process.