The effect of Cu oxidation states on C₂H₄ production from electrochemical CO₂ conversion

Recently, many studies have reported on the significant role of Cu delta+/Cu-0 in the production of C2H4, highlighting the enhanced activity of oxidized Cu electrodes compared to metallic Cu electrodes. However, there is relatively little research that compares catalytic performance for C2H4 production in membrane electrode assembly (MEA)type cells. Herein, we present an analysis of the performance of Cu-based oxidized cathodes in MEA-type cells, specifically focusing on the Cu oxidation state in relation to the CO2 reduction reaction (CO2RR). Both metallic Cu and oxidized Cu cathodes were prepared via a simple electroless deposition and subsequent oxidation process. The electric, chemical, and thermal oxidation methods yielded Cu electrodes with distinct electronic structures. Subsequently, the CO2RR performance of these electrodes was evaluated in single MEA-type cells, and the correlation between the Cu0-1+ ratio and their performance was studied. Our findings confirmed that the ability to form C2H4 follows a volcano-shaped trend based on the Cu0-1+ ratio. Furthermore, a stability test was conducted for CO2RR at a cell voltage of 3.2 V, revealing that the initially highly active Cu-based cathode exhibited notably poor stability in the MEA-type cell test.