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

Electrosynthesis of value-added chemicals from CO₂ offers a sustainable solution to climate change, renewable energy use, and raw material shortages. This study examines the high-rate production of ethylene (C₂H₄) and ethanol (CH₃CH₂OH) through CO₂ 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 C₂H₄ and CH₃CH₂OH selectivity decreases, while CH₄ and H₂ selectivity increases. However, an alternating operation by interrupting and restarting the polarization fully restores the C₂H₄ and CH₃CH₂OH 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 C₂H₄ selectivity. Under alternating operation, some oxidized Cu species remains, and the C₂H₄ selectivity is also preserved. This outcome suggests a close link between cationic Cu species and C₂H₄ production, offering insights into stabilizing these species for prolonged C₂H₄ production.