Energy-Efficient Dual Formate Electrosynthesis via Coupled Formaldehyde Oxidation and CO₂ Reduction at Ultra-Low Cell...

Electrochemical formate (HCOO^-) production via CO₂ reduction reaction (CO₂RR) holds great promise for carbon-neutral energy systems; however, its practical implementation is significantly hindered by the high energy demand of anodic oxygen evolution reaction (OER). Replacing OER with a more energetically and economically favorable alternative anodic reaction is therefore essential. In this study, we developed a highly efficient Cu-Ag catalyst for anodic formaldehyde oxidation reaction (FOR). Systematic investigations employing in situ Raman spectroscopy and comprehensive electrochemical analyses revealed that Cu enables an earlier onset potential for FOR, and Ag enhances formaldehyde adsorption, leading to synergistically improved performance. The optimal Cu₃Ag₇ catalyst exhibited superior FOR performance, with an onset potential of -0.05 V versus the reversible hydrogen electrode (V_RHE) and Faradaic efficiencies for HCOO^- exceeding 90% from 0.1 to 0.5 V_RHE. When coupled with CO₂RR, the FOR||CO₂RR system enabled dual-side HCOO^- production, achieving a total HCOO^- yield rate of 0.39 mmol h^-1 cm^-2 at an ultra-low cell voltage of 0.5 V, surpassing the performance of previously reported electrochemical HCOO^- production systems. Furthermore, this study presents a versatile anodic strategy that integrates FOR with a range of cathodic reactions, offering an energy-efficient chemical synthesis approach for the advancement of sustainable electrochemical technologies.