Stability of Residual Oxides in Oxide‐Derived Copper Catalysts for Electrochemical CO₂ Reduction Investigated with ¹⁸O Labeling

Oxide-derived (OD) Cu catalysts have high selectivity towards the formation of multi-carbon products (C2 /C3 ) for aqueous electrochemical CO2 reduction (CO2 R). It has been proposed that a large fraction of the initial oxide can be surprisingly resistant to reduction, and these residual oxides play a crucial catalytic role. The stability of residual oxides was investigated by synthesizing 18 O-enriched OD Cu catalysts and testing them for CO2...