Dynamic Relocation of Copper Catalysts in Gas Diffusion Electrodes during CO<sub>2</sub> Electroreduction
Daiko Takamatsu, N. Fukatani, Akio Yoneyama, Tatsumi Hirano, Kakuro Hirai, Shin Yabuuchi, Koichi Watanabe, Kazuhide Kamiya, Shuji Nakanishi
Abstract
High Resolution Image Download MS PowerPoint Slide Developing technologies that convert CO 2 into valuable carbon products using renewable energy is of growing significance. Copper (Cu) is a unique electrocatalyst capable of reducing CO 2 to value-added multicarbon (C 2+ ) compounds. While recent in situ studies have elucidated the dynamic evolution of Cu catalysts during electrochemical CO 2 reduction reactions (CO 2 RR), the relationship between catalyst behavior in gas diffusion electrodes (GDEs) and C 2+ product selectivity at industrially relevant current densities remains insufficiently understood. In this study, we examined the correlation between the structure, chemical state, and C 2+ selectivity of Cu catalysts in Cu-GDEs during CO 2 RR operation at current densities exceeding 200 mA/cm 2 . Ex situ and in situ scanning X-ray fluorescence microscopy revealed significant relocation of Cu within the GDE after CO 2 RR. In situ X-ray absorption spectroscopy identified the presence of Cu 1+ 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 C 2+ selectivity over time was primarily due to flooding, overshadowing the impact of Cu relocation on C 2+ selectivity. These findings provide important insights for designing stable and highly selective Cu-based GDEs for practical CO 2 electrolyzers.