Coordination modulation of iodide at the CuI-Cu2O interface to stabilize Cu+ and promote carbon dioxide-to-ethylene conversion.

Electrochemical conversion of CO2 to value-added chemicals is a promising carbon recycling strategy for mitigating CO2 emissions from fossil fuels and addressing associated environmental challenges. In copper-based catalysts, Cu+ species promote the reduction of CO2 to multi‑carbon products, such as ethylene (C2H4). However, under typical electroreduction, Cu+ is prone to reduction to Cu0, leading to degradation of catalytic performance and poor stability. Herein, we present an interfacial engineering strategy to design a CuI-Cu2O composite catalyst with densely packed Cu2O nanoparticles on tetrahedral CuI substrates and self-stabilizing Cu+ ability for selective CO2 electroreduction to C2H4. Density functional theory (DFT) calculations and spectroscopic characterizations demonstrated that the CuI-Cu2O catalyst combined the efficient generation of *CO intermediates by Cu2O with the efficient CC coupling functionality of CuI, and the iodide ions within the catalyst autonomously modulated the copper oxidation state to stabilize Cu+, collectively enhancing CO2-to-C2H4 selectivity. Consequently, the CuI-Cu2O catalyst achieved a C2H4 Faradaic efficiency of 62.98 ± 1.05% along with a high current density of 275.16 mA·cm-2 at -0.97 V vs. the reversible hydrogen electrode (RHE). In the stability test, the CuI-Cu2O catalyst operated stably for over 16 h at a current density of approximately 279.95 mA·cm-2. This study provides a catalyst design strategy that simultaneously enhances *CO supply and CC coupling while autonomously modulating the active Cu+ state, offering an effective approach for achieving stable and highly selective CO2-to-C2H4 conversion.