Ether-free sulfonated poly(fluorene biphenyl indole) membranes and ionomer binders for proton exchange membrane fuel cells

Abstract

Because of the vulnerability of ether bonds to oxidative radicals, the ether-free polymer electrolytes are synthesized to prepare chemically more stable proton exchange membranes for long time durable fuel cell application. Here, we present a series of ether-free sulfonated poly(fluorene biphenyl indole)s (SPFBI) synthesized by a feasible and cost-effective process. Owing to the ether-free structure, SPFBI membranes display great chemical stability comparable to the commercial Pemion membranes from Fenton's test. SPFBI membranes exhibit high proton conductivity up to 0.1956 S cm−1 at 80 °C under the limited swelling ratio lower than 16.5%. Consequently, while the SPFBI-0.4 membrane shows the excellent cell performance reaching the maximum power density of 365 mW cm−2, it also plays a decent role as an ionomer binder for both SPFBI and Nafion membranes. In open circuit voltage stability test, the membrane electrode assemblies using SPFBI-0.2 membrane can sustain more than 620 h without any severe defects at 90 °C under low relative humidity of 30%, outweighing the Nafion counterpart. This study provides a remarkable approach for optimizing the ether-free hydrocarbon-based polymer structure for the application of both polymer electrolyte membrane and ionomer binder with high proton conductivity and chemical stability.