Assessing stability and performance of fluorine-doped tin oxide electrodes for peroxide formation in carbonate-based electrolytes

Hydrogen peroxide (H₂O₂) is a valuable chemical currently produced industrially on a large scale by the anthraquinone process. Recently, carbonate and/or bicarbonate-induced selective water oxidation to hydrogen peroxide has been suggested as an environmentally friendly alternative. In this manuscript, we discuss the effect of electrolyte concentration and type of cation in selective water oxidation using carbonate-based electrolytes (i.e., Na₂CO₃, K₂CO₃ and Cs₂CO₃) on fluorine-doped tin oxide (FTO) electrodes. Based on the experimental observations and a techno-economic evaluation we reveal that K₂CO₃ is preferred over Na₂CO₃ and Cs₂CO₃ electrolytes. Using 5 M K₂CO₃ a Faradaic efficiency of > 60 % was achieved at industrially relevant current densities of 100 mA cm⁻². Although for 5 M Cs₂CO₃ electrolytes lower potentials are required at otherwise similar process conditions, a lower efficiency for hydrogen peroxide formation has been observed which is assigned to higher degradation in Cs-containing electrolyte, rendering the use of potassium-based electrolytes more efficient. Independent of the electrolyte used, the electrodes suffered from stability issues as revealed by increasing concentrations of tin in the electrolyte and electrode failure after polarization for several hours. Overall, this work provides detailed knowledge about the impact of electrolyte concentration and type of cation and reveals the importance of appropriate cell design and process operation for meaningful hydrogen peroxide synthesis by mediated-anodic water oxidation.