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 CO 2 (scCO 2 ) can be used as a solvent itself to suppresses hydrogen evolution and tune the carbon‐based product yield; however, it has received little attention for this purpose. Therefore, the focus of this study was on the electrochemical reduction of scCO 2 . The conductivity of scCO 2 was increased through the addition of supporting electrolyte and a cosolvent (acetonitrile). Furthermore, the addition of protic solutions of different pH to scCO 2 was investigated. 1 m H 2 SO 4 , trifluoroethanol, H 2 O, KOH, and CsHCO 3 solutions were used to determine the effect on current density, faradaic efficiency, and selectivity of the scCO 2 reduction. The reduction of scCO 2 to methanol and ethanol are reported for the first time. However, methane and ethylene were not observed. Additionally, corrosion of the Cu electrode was noticed.