Stability of Residual Oxides in Oxide-Derived Copper Catalysts for Electrochemical CO Reduction Investigated with O Labeling.

Oxide-derived (OD) Cu catalysts have high selectivity towards the formation of multi-carbon products (C /C ) for aqueous electrochemical CO reduction (CO 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 O-enriched OD Cu catalysts and testing them for CO R. These catalysts maintain a high selectivity towards C /C products (ca. 60 %) for up to 5 h in 0.1 m KHCO at -1.0 V vs. RHE. However, secondary-ion mass spectrometry measurements show that only a small fraction (<1 %) of the original O content remains, showing that residual oxides are not present in significant amounts during CO R. Furthermore, we show that OD Cu can reoxidize rapidly, which could compromise the accuracy of ex situ methods for determining the true oxygen content.