Studies on the faradaic efficiency for electrochemical reduction of carbon dioxide to formate on tin electrode

• pH value in CO2-saturated KHCO3 solution has an effect on CO2 reduction.
• Oxidation of formate is main reason for efficiency decreasing with time lasted.
• Formate oxidization accelerates as formate concentration in electrolyte increases.
• Faradaic efficiency is >91% when formate concentration is <0.01 mol L−1.

The electrochemical reduction of carbon dioxide (CO2) on Sn electrode has been investigated in aqueous KHCO3 solution by cyclic voltammetry and controlled potential electrolysis. The results show that the faradaic efficiency for producing formate is affected by the electrolysis potential, the concentration and pH value of KHCO3 solution; the reason for the decrease of faradaic efficiency as the electrolysis time lasts is the oxidation of formate on the Pt anode. When the concentration of the formate in the electrolyte is less than 0.01 mol L−1, the faradaic efficiency can reach above 91%.