Formate-Induced Dissolution and Reprecipitation of a Copper Electrocatalyst during Electrochemical CO₂ Reduction Reaction

Catalyst size, morphology, and crystal structure play crucial roles in determining the activity and selectivity of electrochemical CO2 reduction reactions, which are known to change during the reaction process. A comprehensive understanding of how, when, and why these parameters evolve under operational conditions is essential for developing stable, efficient, and selective catalysts. In this study, we reveal that formate, one of the reaction products, contributes to the degradation of copper catalysts through a ligand-assisted dissolution mechanism. Utilizing in situ electrochemical atomic force microscopy and ex-situ scanning and transmission electron microscopies, we observed a significant reduction in the size of copper nanoparticles, which decreased from over 30 nm to less than 10 nm in diameter within 60 min of CO2RR. The temporal production of formate correlated with the particle size changes. Furthermore, analysis of the electrolyte using inductively coupled plasma optical emission spectroscopy confirmed the dissolution of copper nanoparticles. Control experiments involving various reaction products (H2, CO, and HCOO–) demonstrated that formate significantly promotes copper dissolution, thereby highlighting its role in the ligand-assisted dissolution mechanism of copper electrocatalysts. Our findings provide critical insights into copper catalyst behavior during electrochemical CO2 reduction, facilitating the design of more resilient and effective electrocatalysts.