Low-Overpotential Electrochemical Reduction of CO₂ to Formic Acid on Surface-Modified Doped Tin Oxide Pellets

Gas sensors fabricated with antimony doped tin oxide (ATO) nanomaterials exhibit remarkable sensitivity for detecting oxidizing and reducing gases. This study highlights the enhanced selectivity and stability of the porous ATO nanomaterial electrode made for electrochemical reduction of CO2 in aqueous media. During electrochemical reduction, these electrodes prepared from compressed powders tend to crumble within a few hours in aqueous media. To overcome this electrode disintegration effect, we modified the surface of the doped tin-Oxide nanoparticles and nanowires with Nafion and a dipodal silane (1,2-Bis(triethoxysilyl)ethane). The electrode characterization studies include Cyclic Voltammetry (CV), and Electrochemical Impedance Spectroscopy (EIS). Scanning electron microscopic investigation of electrode surface morphology and roughness before and after electrochemical CO2 reduction for derivatized and underivatized electrode revealed lower surface roughness for former than the latter. The derivatized electrodes allowed CO2 electrochemical reduction at low overpotentials and high current density without any electrode crumbling over more than 24 hours of continuous operation. Formate/formic acid and methanol were the major products of reduction at electrode potentials ranging from -0.4 to -1.0V vs. RHE in the CO2 saturated 0.1M KHCO3 electrolyte. Higher current density and Faradaic Efficiency of formic acid was observed when compared to planar tin electrode materials and tin oxide nanoparticles deposited on FTO glass.