High Efficiency Electrochemical CO2-to-Methane Conversion Method Using Methanol with Lithium Supporting Electrolytes

The electrochemical reduction of CO2 at a Cu electrode was investigated in a methanol-based electrolyte using such lithium supporting salts as LiCl, LiBr, LiI, LiClO4, and CH3COOLi at low temperature (−30 °C). The main products from CO2 by the electrochemical reduction were methane, ethylene, carbon monoxide, and formic acid. A maximum faradic efficiency of methane was 71.8% in LiClO4/methanol-based electrolyte at −3.0 V versus Ag/AgCl saturated KCl. In the lithium salts/methanol-based electrolyte system, except for the case of acetate, the efficiency of hydrogen formation, being a competitive reaction against CO2 reduction, was depressed below 12%. On the basis of this work, the high efficiency electrochemical CO2-to-methane conversion method appears to be achieved. Future work to advance this technology may include the use of solar energy as the electric energy source. This research can contribute to large-scale manufacturing of useful organic products from readily available and cheap raw materials: CO2-saturated methanol from industrial absorbers (the Rectisol process).