Dynamic Relocation of Copper Catalysts in Gas Diffusion Electrodes during CO2 Electroreduction.

Developing technologies that convert CO2 into valuable carbon products using renewable energy is of growing significance. Copper (Cu) is a unique electrocatalyst capable of reducing CO2 to value-added multicarbon (C2+) compounds. While recent in situ studies have elucidated the dynamic evolution of Cu catalysts during electrochemical CO2 reduction reactions (CO2RR), the relationship between catalyst behavior in gas diffusion electrodes (GDEs) and C2+ product selectivity at industrially relevant current densities remains insufficiently understood. In this study, we examined the correlation between the structure, chemical state, and C2+ selectivity of Cu catalysts in Cu-GDEs during CO2RR operation at current densities exceeding 200 mA/cm2. Ex situ and in situ scanning X-ray fluorescence microscopy revealed significant relocation of Cu within the GDE after CO2RR. In situ X-ray absorption spectroscopy identified the presence of Cu1+ species during operation, indicating that Cu relocation proceeds via a dissolution-redeposition. The dissolution-redeposition behavior was found to be pH-dependent and more pronounced at high pH. Online gas chromatography demonstrated that the decrease in C2+ selectivity over time was primarily due to flooding, overshadowing the impact of Cu relocation on C2+ selectivity. These findings provide important insights for designing stable and highly selective Cu-based GDEs for practical CO2 electrolyzers.