This extended electrochemical window provides ample room for accommodating diverse redox chemistries, a considerable advantage compared to the constraints posed by water as a solvent, with its electrochemical window typically around 2.06 V (the exact value may depend on the solution's pH). The advantages discussed above have spurred investigations into CO2 reduction in non-aqueous media, although the number of such studies is not as extensive as those conducted in aqueous media. By utilizing a two-layered carbon-free lead (Pb) gas diffusion electrode (GDE), Konig et al.34 demonstrated a 53% Faradaic efficiency for oxalate production at a current density of approximately 80 mA/cm2 and a potential of approximately -2.5 V vs. Ag/Ag+. Their study employed a 0.1 M tetraethylammonium tetrafluoroborate solution in acetonitrile as the electrolyte. In a different study, Tomita et al.35 observed that for a Pt electrode, the main product was oxalic acid at a current density of 5 mA/cm2 using a 0.1 M tetraethylammonium perchlorate acetonitrile-water mixture. However, an increase in water concentration led to a decrease in oxalic acid formation and an increase in formic acid production. At higher water concentrations, hydrogen evolution became dominant. Another study by Figueiredo et al.21 reported CO as the primary product in wet acetonitrile using an ammonium-based electrolyte. The formation of CO, accompanied by formate and carbonate, was also reported by Christensen and Hamnett36 using a 0.1 M tetrabutylammonium tetrafluoroborate solution in acetonitrile over an Au electrode. As we can observe, the performance of CO2 reduction in non-aqueous media has exhibited significant variations dependent on factors such as the composition of the electrolyte, the nature of the electrode, and the availability of proton donors. For readers interested in an extensive review, a recent work by Reis et al.37 offers a comprehensive overview of CO2 electrochemical reduction studies in non-aqueous media.
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