Insights into the stability of copper gas diffusion electrodes for carbon dioxide reduction at high reaction rates

Electrosynthesis of value-added chemicals from CO 2 offers a sustainable solution to climate change, renewable energy use, and raw material shortages. This study examines the high-rate production of ethylene (C 2 H 4 ) and ethanol (CH 3 CH 2 OH) through CO 2 reduction reaction on copper (Cu) gas diffusion electrodes (GDEs) made by sputtering deposition. The catalyst layer thickness of the GDEs, adjusted by deposition time, significantly affects the electrode stability. During testing, a selectivity shift is observed, where C 2 H 4 and CH 3 CH 2 OH selectivity decreases, while CH 4 and H 2 selectivity increases. However, an alternating operation by interrupting and restarting the polarization fully restores the C 2 H 4 and CH 3 CH 2 OH selectivity. Operando X-ray absorption spectroscopy with online product analysis reveals that at constant potentials, the dominant oxidized Cu species gradually reduces to metallic Cu, along with a decline in C 2 H 4 selectivity. Under alternating operation, some oxidized Cu species remains, and the C 2 H 4 selectivity is also preserved. This outcome suggests a close link between cationic Cu species and C 2 H 4 production, offering insights into stabilizing these species for prolonged C 2 H 4 production.