Electrochemical Reduction of Carbon Dioxide I. Effects of the Electrolyte on the Selectivity and Activity with Sn Electrode

The effects of electrolyte on selectivity and activity were investigated in the electrochemical reduction of CO2 on the Sn electrode. The production of formate, the primary product in our three-electrode cell was quantitatively characterized by solution phase 1H NMR spectroscopy. Both SO42− and Na+ favor higher faradaic and energy efficiencies, while HCO3− and K+ enable a higher rate of formate production. The faradaic efficiency was as high as ∼95% for 0.1 M Na2SO4 at a potential of −1.7 V vs. a Saturated Calomel Electrode (SCE). 0.5 M KHCO3 was an optimal electrolyte for obtaining a high production rate of formate which can reach over 3.8 μmol min−1 cm−2 at a potential of −2.0 V vs. SCE while maintaining a faradaic efficiency of ∼63%. A trend we observed was that the faradaic efficiency increases as the concentration of electrolyte is diluted. Our studies also show the degradation of electrocatalytic activity of the Sn electrode in this three-electrode cell can be attributed to the electrodeposition of trace amounts of Zn onto the surface of the Sn electrode, which reduces the active surface area.