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 CO 2 reduction reaction (CO 2 RR). The presence of Cu + species plays a crucial role in facilitating CO 2 activation and C–C coupling, promoting the formation of multicarbon (C 2+ ) 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 C 2+ products (57.4% for ethylene) at a CO 2 RR 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 + /Cu 0 interface during CO 2 RR. Moreover, in situ time-resolved attenuated total reflection-surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) studies reveal that the optimized Cu + /Cu 0 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 CO 2 RR.