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 benzobistriazolate (H2BBTA), producing a novel metal-organic polymer (CuBBTA) with periodically adjacent copper atoms. Remarkably, CuBBTA exhibits superior CO2-to-C2H4 Faradic efficiency (FE) of 62.0 ± 1.9% and a half-cell C2H4 power conversion efficiency (PCE) of 34.4% in a flow cell. It also maintains stable operation for over 50 hours in a zero-gap electrolyzers, 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 provides 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.