Electrochemical CO₂ reduction to formic acid on crystalline SnO₂ nanosphere catalyst

In this work, the morphology controlled SnO₂ nanosphere catalyst has been successfully synthesized and applied to electrochemical CO₂ reduction to formic acid in 0.5 M KHCO₃. The catalysts were synthesized by a simple hydrothermal method under controlling the different proportions of ethanol to distilled water as mixed solvent. The obtained catalysts were then coated on gas diffusion electrode (SnO₂/GDE) as working electrode. It was found that the catalyst prepared from 50% content of ethanol gives the best catalytic activity towards CO₂ reduction, where the onset potential was found to be 300 mV more anodic than that of hydrogen evolution. Meanwhile, the SnO₂/GDE-50 showed the most stable property for CO₂ reduction. The current density and faradaic efficiency increased as the potential increased, reaching a maximum at -1.7 V vs. SHE. At this stage, the maximum faradaic efficiency of 68% with a current density of 6 mA cm^-2 was obtained. Moreover, the production rate of format exhibits a maximum value of 518.2 mg L^-1 at the cathode potential of -1.9 V vs. SHE.