Formic Acid Electro-Synthesis by Concurrent Cathodic CO₂ Reduction and Anodic CH₃OH Oxidation

The electrochemical conversion of carbon dioxide into energy-carrying compounds or value-added chemicals is of great significance for diminishing the greenhouse effect and the efficient utilization of carbon-dioxide emissions, but it suffers from the kinetically sluggish anodic oxygen evolution reaction (OER) and its less value-added production of O₂. We report a general strategy for efficient formic-acid synthesis by a concurrent cathodic CO₂ reduction and anodic partial methanol-oxidation reaction (MOR) using mesoporous SnO₂ grown on carbon cloth (mSnO₂/CC) and CuO nanosheets grown on copper foam (CuONS/CF) as cathodic and anodic catalysts, respectively. Anodic CuONS/CF enables an extremely lowered potential of 1.47 V vs. RHE (100 mA cm⁻²), featuring a significantly enhanced electro-activity in comparison to the OER. The cathodic mSnO₂/CC shows a rather high Faraday efficiency of 81 % at 0.7 V vs. RHE for formic-acid production from CO₂. The established electrolyzer equipped with CuONS/CF at the anode and mSnO₂/CC at the cathode requires a considerably low cell voltage of 0.93 V at 10 mA cm⁻² for formic-acid production at both sides.