Stability of In2O3 Nanoparticles in PTFEcontaining Gas Diffusion Electrodes for CO2 electroreduction to Formate

Electrocatalytic conversion of CO2 to fuels and chemicals can help mitigate climate change by reuse of the greenhouse gas. Formic acid is an interesting product of electrochemical CO2 reduction, because it can serve as a liquid hydrogen carrier. Indium-based electrodes show promising activity and selectivity towards formic acid formation during CO2 electroreduction. However, the low stability of such electrodes at high current density limits their implementation in industry. Herein, we optimize a gas diffusion electrode (GDE) containing ∼6 nm In2O3 nanoparticles obtained by flame spray pyrolysis. The catalyst exhibits high initial faradaic efficiency towards formate (> 80%) at current densities up to 200 mA/cm2. In situ Raman spectroscopy reveals that the In2O3 particles rapidly reduce under reaction conditions, demonstrating that metallic indium is the active phase for CO2 reduction. Degradation mechanisms of the catalyst during 50 h at high current density were studied using XPS, in situ Raman, TEM and SEM, and elemental analysis of the electrolyte. Catalyst reduction, sintering of the active phase and dissolution of indium could be excluded as a cause of the declining FE. Adding carbon and hydrophobic PTFE particles to the catalyst in the GDE improves CO2 supply and prevents early saturation of the GDE by liquid electrolyte. The optimized GDE configuration inhibits hydrogen evolution and demonstrates increased stability during 50 h of CO2 electroreduction.