Ionically Crosslinked Composite Membranes from Polybenzimidazole and Sulfonated Poly (fluorenyl ether ketone) for High-Temperature PEM Fuel Cells

A series of composite polymer membranes composed of poly [2,2''-(p-oxydiphenylene)-5,5''-benzimidazole] (OPBI) and sulfonated poly (fluorenyl ether ketone) (SPFEK) were developed with enhanced mechanical integrity and superior oxidative stability. The phosphonic acid (PA) doped OPBI-SPFEK membranes were then fabricated for the high temperature-proton exchange membrane fuel cells (HT-PEMFCs) application. It is suggested that an ionically crosslinked structure can be formed by the intense interaction among the protonated benzimidazolium, sulfonate groups, and PA molecules. With lower acid content and swelling ratio, the composite membranes afforded satisfactory proton conductivity and much higher tensile strength than the pristine OPBI. A maximum conductivity of 0.050 S cm−1 was reached by OPBI-SPFEK-10% at 180 °C, with tensile strength as high as 24.7 MPa. The single fuel cell from the optimized OPBI-SPFEK-10% exhibited the highest peak power density of 727 mW cm−2 at 160 °C, which was 21% higher than that from the pristine OPBI.