Novel sulfonated poly(arylene ether ketone) containing benzoxazole membranes for proton exchange membrane fuel cell

Abstract

Novel sulfonated poly(aryl ether ketones) containing benzoxazole were directly synthesized by aromatic nucleophilic polycondensation using various ratios of 2,2′-bi[2-(4-flurophenyl)benzoxazol-6-yl]hexafluoropropane to sodium 5,5′-carbonylbis(2-fluorobenzenesulfonate). The copolymers were soluble in polar aprotic solvents such asN-methyl-2-pyrrolidone,N,N-dimethylacetamide, andN,N-dimethylformamide at a relatively high solid composition (>15 wt%) and formed tough, flexible and transparent membranes. The membranes exhibited a degradation temperature of above 290 °C. The exact dissolution times of these membranes at 80 °C in Fenton’s reagent (3 wt% H₂O₂ containing 2 ppm FeSO₄) were undetectable, confirming their excellent chemical stability in fuel cell application. The membranes showed a moderate increase in water uptake with respect to increasing temperature. The proton conductivities of the membranes were dependent on the composition and ranged from 1.10× 10⁻² to 5.50×10⁻² Scm⁻¹ at 80 °C and 95% relative humidity (RH). At 120 °C without externally humidified conditions, the conductivities increased above 10⁻² Scm⁻¹ with respect to increasing benzoxazole content, which suggested that the benzoxazole moieties contributed to the proton conduction.