<i>In Situ</i> DXAFS Reveals Active Cu ^δ+ Intermediates of F-CuO Enhancing CO ₂ -to-C ₂₊ Electrocatalysis

Electrochemical CO2 reduction reaction (CO2RR) represents a promising strategy for converting CO2 into value-added chemicals and fuels, contributing to carbon neutrality. Copper (Cu)-based catalysts hold particular promise in this field due to their capability of producing multicarbon (C2+) products. However, copper-based catalysts still suffer from structural instability and unclear dynamic evolution under operating conditions. This study elucidates the crucial role of fluorine (F) doping in enhancing the structural stability of copper oxide (CuO) during the electrocatalytic CO2RR. Using in situ dispersive X-ray absorption fine structure (DXAFS) coupled with unsupervised machine learning analysis, we directly observed the formation and stabilization of a Cuδ+ intermediate phase (0 < δ < 2) in the F-CuO catalyst under applied potential. In contrast, undoped CuO underwent a rapid and direct transformation to metallic Cu0 under identical conditions, with no detectable intermediate state. This study establishes anionic doping as an effective strategy to modulate the electronic structure of copper catalysts, thereby stabilizing critical reaction intermediates and enabling highly efficient and stable CO2-to-C2+ conversion.