Electrochemical reduction of protic supercritical CO2 on copper electrodes

The electrochemical reduction of carbon dioxide is usually studied in aqueous solutions under ambient conditions. However, the main disadvantages of this method are high hydrogen evolution and low faradaic efficiencies of carbon based products. Supercritical CO2 (scCO2) can be used as a solvent itself to suppresses hydrogen evolution and tune carbon based product yield, however, it received low attention. Therefore, the focus of this study was on the electrochemical reduction of supercritical CO2 (at 40 @C and 80 bar). The conductivity of scCO2 was increased through addition of supporting electrolyte and co-solvent (acetonitrile). Besides, the addition of protic solutions with different pH to supercritical CO2 was investigated. 1 M H2SO4, trifluoroethanol, H2O, KOH, and CsHCO3 solutions were used to determine the effect on current density, faradaic efficiency, and selectivity of scCO2 reduction. Reduction of supercritical CO2 to methanol and ethanol were reported for the first time. However, methane and ethylene were not observed. Additionally, corrosion of Cu was noticed.