Electrocatalytic Reduction of Carbon Dioxide on Nanosized Fluorine Doped Tin Oxide in the Solution of Extremely Low Supporting Electrolyte Concentration: Low Reduction Potentials

Fluorine doped tin oxide (FTO) has been prepared via the direct chemical reaction of tin oxide powders and hydrofluoric acid at room temperature. The image of FTO displays a sphere-like structure with an average diameter of 40–100 nm. The spectra of X-ray photoelectron spectroscopy (XPS) demonstrate that fluorine is doped into SnO₂. A well-defined reduction peak at −0.50 V (vs SCE) is detected on the cyclic voltammogram (CV) of the nanosized FTO (n-FTO) electrode in CO₂-saturated 3.6 × 10^–4 μM H₂SO₄ solution of pH 5.5, which is strong evidence for the electrochemical reduction of CO₂. This result indicates that the n-FTO electrode in such an extremely low supporting electrolyte concentration exhibits good electrocatalytic ability toward CO₂ reduction under lower potentials. On the basis of reduction peak current as a function of scan rate, the reduction of CO₂ is first performed via adsorption of CO₂ on the n-FTO electrode surface, and then CO₂ is reduced. The product solution obtained under a constant potential of −0.90 V (vs Ag/AgCl with saturated KCl solution) is used for analysis of UV–vis spectra, ¹H NMR, and gas chromatography; the results demonstrate the presence of formic acid and methanol in the product solution, but formic acid is a main product. Faradaic efficiency for formic acid is 82.3%