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.