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.
Wang et al. (2025) studied this question.