Electrochemical CO2-to-Formate Conversion on Scalable Cu3Sn Gas Diffusion Electrodes via an OCHO-Mediated Pathway

Abstract Electrochemical CO2 reduction to formate (HCOO−) presents a sustainable strategy for carbon valorisation but remains challenging due to low selectivity and competing side reactions. In this work, we report a Cu3Sn gas diffusion electrode (GDE) synthesized via a scalable electrochemical spontaneous deposition (ESD) method, enabling highly selective CO2-to-formate conversion. The optimised CuSn35min electrode, corresponding to the Cu3Sn alloy phase, achieves a Faradaic efficiency of ∼90% for HCOO− at −0.85 V vs RHE in half-cell testing, while effectively suppressing hydrogen evolution and C2 product formation. Mechanistic and electrokinetic analyses, supported by in situ Raman spectroscopy, reveal a shift from *CO dimerization to an *OCHO-mediated pathway, driven by the synergistic interaction between Cu and Sn. Post-electrolysis structural characterization indicates the formation of surface SnO2 and Cu2O species on the Cu3Sn framework, suggesting a dynamically reconstructed alloy-oxide interface as the catalytically active phase. Full-cell evaluation in a Cu3Sn GDE∥Pt mesh configuration under continuous CO2 flow delivers ∼82% formate Faradaic efficiency and ∼73% energy efficiency at 180 mA cm−2, with formate Faradaic efficiency retained above 76% over 60 h of continuous operation. This work demonstrates a cost-effective and scalable route for designing alloy-based GDEs for efficient CO2 electroreduction.