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.