Operando insights on stable Cu2+ active sites for efficient electrochemical CO2-to-C2H4 conversion

Copper catalysts feature unique superiorities for the electrochemical conversion of CO2 to C2+ fuels and chemicals. Their surface oxidation states dominantly determine the reaction pathways to various products. However, most Cu-based catalysts inevitably undergo electroreduction from Cu2+ to Cu1+ or Cu0 species during the electrochemical CO2 reduction. Herein, we propose a straightforward strategy to stabilize Cu2+ ions by coordinating them with benzobistriazole (H2BBTA), producing a metal-organic polymer (CuBBTA) with periodically adjacent copper atoms. Remarkably, CuBBTA delivers a high Faradaic efficiency of 62.0 ± 1.9% for CO2-to-C2H4 conversion and a half-cell power conversion efficiency of 34.4% in a flow cell. It also maintains stable operation for over 50 hours in a zero-gap electrolyzer, sustaining a FE > 55% at ≈ 1 A total current density. Operando X-ray absorption, Raman, and attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) reveal that the catalyst remains structurally stable with no dynamic transformation during the reaction. Online differential electrochemical mass spectrometry (DEMS), operando ATR-SEIRAS and theoretical calculations show that neighboring Cu2+ ions in the polymer provide suitably-distanced dual sites that enable the energetically favorable formation of an *COCHO intermediate. This study presents a strategic method for developing stable catalysts for efficient CO2-to-ethylene electroconversion. Producing multi-carbon fuels from carbon dioxide requires catalysts that remain stable under reaction conditions. Here, the authors report operando evidence identifies stable Cu2+ sites that enable efficient and selective ethylene generation.