Abstract:A tetraamine monomer, 4,4’-bis(3,4-diaminophenoxy)biphenyl (BDAPB) was randomly copolymerized with a dicarboxylic monomer, 4,4’-dicarboxyldiphenyl ether (DCDPE), and another tetraamine monomer, 3,3’-diaminobenzidine (DAB) in Eaton’s reagent (the mass ratio of methanesulfonic acid to phosphorus pentoxide was 10:1) yielding a series of polybenzimidazole copolymers (PBI-x, x refers to the molar fraction of BDAPB in the tetraamine monomers). The resulting PBI-x were further post-sulfonated and subsequently covalently cross-linked (cross-linker: bisphenol A epoxy resin) to give a series of covalently cross-linked sulfonated polybenzimidazole copolymer membranes (S-PBI-x-Cy, here, y refers to the molar ratio of epoxy groups to benzimidazole groups). The thermal stability, mechanical properties, water uptake, swelling ratio, proton conductivity, radical oxidative stability and single cell performance of the exchange proton membranes were investigated. The prepared cross-linked membranes exhibited good mechanical properties. With an increase in molar fraction of BDAPB moiety, the proton conductivities of the membranes increased remarkably. As the molar fraction of BDAPB reached 30%, its proton conductivity was higher than that of Nafion 212. The covalent cross-linking treatment led to reduction in membrane swelling ratio, and the higher cross-linking density, the more significant reduction in swelling ratio. The single cell assembled with the S-PBI-30-C15 membrane exhibited excellent performance (H2-O2), and its maximum output power density reached 1.11 W/cm2 at 90 oC and 70% relative humidity, which is higher than that of Nafion 212 (0.95 W/cm2) under the same conditions.