Crosslinked Hexafluoropropylidene Polybenzimidazole Membranes with Chloromethyl Polysulfone for Fuel Cell Applications

Abstract Hexafluoropropylidene polybenzimidazole (F 6 PBI) was synthesized with excellent chemical stability and improved solubility. When doped with phosphoric acid, however, the F 6 PBI membranes showed plastic deformation at elevated temperatures. Further efforts were made to covalently crosslink F 6 PBI membranes with chloromethyl polysulfone as a polymeric crosslinker. Comparing with linear F 6 PBI and m PBI membranes, the polymer crosslinked F 6 PBI membranes exhibited little organo solubility, excellent stability towards the radical oxidation, high resistance to swelling in concentrated phosphoric acid solutions, and improved mechanical strength, especially at elevated temperatures. The superior characteristics of crosslinked membranes allowed for higher acid doping levels and therefore increased proton conductivity as well as significantly improved fuel cell performance and durability, as compared with the linear F 6 PBI and m PBI membranes.