Tuning *CO Adsorption via Cu⁺/Cu⁰ Interface Engineering for Enhanced Ethylene Selectivity in Electrochemical CO₂ Reduction

Copper (Cu)-based catalysts exhibit a unique capability to produce various value-added products via the electrochemical CO₂ reduction reaction (CO₂RR). The presence of Cu⁺ species plays a crucial role in facilitating CO₂ activation and C-C coupling, promoting the formation of multicarbon (C₂₊) products. Nonetheless, Cu⁺ species suffer from limited stability under high current densities, necessitating further efforts to improve their robustness. Here, we show that copper iodide (CuI), upon high-temperature oxidation, generates an iodine-doped Cu catalyst that achieves a Faradaic efficiency of 69.7% for C₂₊ products (57.4% for ethylene) at a CO₂RR current density of 400 mA cm^-2. Spectroscopic characterizations indicate that the residual iodide species act as electronic modulators, stabilizing adjacent Cu⁺ species via strong coordination and preserving the Cu⁺/Cu⁰ interface during CO₂RR. Moreover, in situ time-resolved attenuated total reflection-surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) studies reveal that the optimized Cu⁺/Cu⁰ interface on the CuI-400 °C-60 min electrocatalyst maintains appropriate *CO coverage on the catalyst surface, thereby enhancing C-C coupling efficiency and promoting ethylene formation during CO₂RR.