Chemical degradation of fluorosulfonamide fuel cell membrane polymer model compounds

• Aromatic trifluoromethyl sulfonamide model compounds were prepared and degraded.
• Mono-, di- and tri-substituted compounds were compared.
• The mono-substituted compound shows greater stability than the di-substituted species.
• Loss of perfluorinated sulfonamide side chains is an important pathway.
• Dimerization and aromatic ring hydroxylation are also degradation pathways.

The durability of a polymer electrolyte fuel cell membrane, along with high proton conductivity and mechanical performance is critical to the success of these energy conversion devices. Extending our work in perfluorinated membrane stability, aromatic trifluoromethyl sulfonamide model compounds were prepared, and their oxidative degradation was examined. The chemical structures for the models were based on mono-, di- and tri-perfluorinated sulfonamide modified phenyl rings. Durability of the model compounds was evaluated by exposure to hydroxyl radicals generated using Fenton reagent and UV irradiation of hydrogen peroxide. LC–MS results for the mono-substituted model compound indicate greater stability to radical oxidation than the di-substituted species; loss of perfluorinated fonamide side chains appears to be an important pathway, along with dimerization and aromatic ring hydroxylation. The tri-substituted model compound also shows loss of side chains, with the mono-substituted compound being a major oxidation product, along with a limited amount of hydroxylation and dimerization of the starting material.