We tested the performance of SnO2/C, Au/C and Cu/C (fig. ) in electrolyte solutions containing 0.1 M H2SO4 + 0.4 M K2SO4 (pH = 1.5). This combination of electrolytes is more practical than the combination of HOTf + KOTf, even though addition of K + ions slightly changes the pH of H2SO4 solutions. For SnO2/C, formic acid was the major product of CO2 reduction. The maximum Faradaic efficiency and partial current density were 88% and 314 mA/cm 2 , respectively (fig. ). These performance metrics are comparable to state-of-theart results of formic acid production from a solid-state electrolyzer 20 and formate formation in near neutral solutions 21 . Aqueous solution of formic acid could be separated from the electrolyte solution by distillation (fig. ). This result demonstrated the advantage of an acidic reaction medium for formic acid generation compared to a near neutral or alkaline medium where only formate would be generated. For Au/C, CO was the major product with the maximum Faradaic efficiency and partial current density as 91% and 227 mA/cm 2 , respectively (fig. ). For Cu/C, formic acid, CO, methane, ethylene, propene, acetic acid, ethanol and 1-propanol were detected as the products of CO2 reduction (fig. ). The minimum Faradaic efficiency of HER was 16%, lower than that of Cu/PFSA catalyst (PFSA = perfluorosulfonic acid) in H3PO4-KCl medium (Faradaic efficiency of HER = 36%) reported by Huang et al. Among the products of > 2e reduction, ethylene was the major product with the partial current density of 136 mA/cm 2 (fig. ). Its Faradaic efficiency was 25%, similar to the highest Faradaic efficiency for ethylene production on Cu/PFSA in H3PO4-KCl medium by Huang et al. The maximum partial current densities of CO formation on Au/C and ethylene formation on Cu/C in acidic media are comparable to those on state-of-the-art catalysts in near neutral and alkaline media. We also directly compared the performances of Au/C in CO2 electroreduction in acidic, near neutral (0.8 M KHCO3) and alkaline (0.8 M KOH) media in a two-electrode cell (fig. ).