Highly efficient formic acid and carbon dioxide electro-reduction to alcohols on indium oxide electrodes

Abstract

Formic acid is often assumed to be the first intermediate of carbon dioxide reduction to alcohols or hydrocarbons. Here we use co-electrolysis of water and aqueous formic acid in a PEM electrolysis cell with Nafion® as a polymer electrolyte, a standard TaC-supported IrO₂ water-splitting catalyst at the anode, and nanosize In₂O₃ with a small amount of added polytetrafluoroethylene (PTFE) as the cathode. This results in a mixture of methanol, ethanol and iso-propanol with a maximum combined Faraday efficiency of 82.5%. In the absence of diffusion limitation, a current density up to 70 mA cm⁻² is reached, and the space-time-yield compares well with results from heterogeneous In₂O₃ catalysis. Reduction works more efficiently with dissolved CO₂ than with formic acid, but the product distribution is different, suggesting that CO₂ reduction occurs primarily via a competing pathway that bypasses formic acid as an intermediate.