Electrochemical reduction of carbon dioxide on copper in methanol with various potassium supporting electrolytes at low temperature

The electrochemical reduction of CO2 at a Cu electrode was investigated in a methanol-based electrolyte using such potassium supporting salts as CH3COOK, KBr, KI and KSCN at extremely low temperature (-30°C). The main products obtained from CO2 by the electrochemical reduction were methane, ethylene, ethane, carbon monoxide and formic acid. The maximum Faradaic efficiency, of ethylene was 19.9% in KI/methanol-based catholyte at -3.0 V vs. Ag/AgCl saturated KCl. The best methane formation (27.0%) was obtained in CH3COOK/methanol electrolyte at -3.0 V. In the system containing a potassium halide, the efficiency of hydrogen formation, being a competitive reaction against CO2 reduction, was suppressed to less than 8.1%. The product selectivity of the electrochemical reduction of CO2 in methanol was greatly affected by the anionic species. This research can contribute to the large-scale manufacturing of useful organic products from readily available and cheap raw materials: CO2-saturated methanol from industrial absorbers (the Rectisol process).