Retarding of electrochemical oxidation of formate on the platinum anode by a coat of Nafion membrane

• Pt@Nafion electrode used as anode can prevent the oxidization of formate.
• The oxidation rate of formate on Pt@Nafion anode is much slow than that on Pt anode.
• The concentration of the formate in the electrolyte can reach to 0.12 mol L−1.
• Both the Sn cathode and the Pt@Nafion anode can be reused.

It has been found that the faradaic efficiency is decreasing with the electrolysis time for electrochemical reduction of CO2 to formate on a Sn cathode with a Pt anode in an undivided electrolytic cell, because the oxidation of formed formate takes place on the Pt anode, which also limits seriously the highest concentration of formate in the system. Here, we report that a coat of Nafion membrane on the Pt anode can retard the oxidation of formate: even if the concentration of the formate in the electrolyte reaches to 0.12 mol L−1, the faradaic efficiency still maintains above 61.3%; in contrast, the oxidation reaction of the formate on the naked Pt electrode is very fast, when the concentration of the formate in the electrolyte reaches to 0.023 mol L−1, the faradaic efficiency decreases to 35.3%. This is very important because the separation of formic acid could not be economical when its concentration is not high enough, and it is also costly if the depleted solution allows too less of its concentration because the solution has to be reused in the electrochemical process.

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