Electrochemical CO2 reduction to formic acid on crystalline SnO2 nanosphere catalyst with high selectivity and stability

A novel catalyst for CO2 electroreduction based on nanostructured SnO2 was synthesized using a facile hydrothermal self-assembly method. The electrochemical activity showed that the catalyst gave outstanding catalytic activity and selectivity in CO2 electroreduction. The catalytic activity and formate selectivity depended strongly on the electrolyte conditions. A high faradaic efficiency, i.e., 56%, was achieved for formate formation in KHCO3 (0.5 mol/L). This is attributed to control of formate production by mass and charge transfer processes. Electrolysis experiments using SnO2-50/GDE (an SnO2-based gas-diffusion electrode, where 50 indicates the 50% ethanol content of the electrolyte) as the catalyst, showed that the electrolyte pH also affected CO2 reduction. The optimum electrolyte pH for obtaining a high faradaic efficiency for formate production was 8.3. This is mainly because a neutral or mildly alkaline environment maintains the oxide stability. The faradaic efficiency for formate production declined with time. X-ray photoelectron spectroscopy showed that this is the result of deposition of trace amounts of fluoride ions on the SnO2-50/GDE surface, which hinders reduction of CO2 to formate.

Graphical AbstractThe influence of electrolyte conditions on selectivity and activity were studied by electrochemical characterization. A faradaic efficiency of 56% HCOOH was achieved at −1.7 V vs SHE. The deposition of the trace fluoride ions has some influences on formate information.Figure optionsDownload as PowerPoint slide