Highly durable polymer electrolyte membranes at elevated temperature: Cross-linked copolymer structure consisting of poly(benzoxazine) and poly(benzimidazole)

For polymer electrolyte membrane fuel cell (PEMFC) applications at elevated temperature (>100 degrees C), a series of cross-linked benzoxazine benzimidazole copolymer, P(HFa-co-BI), membranes are prepared by casting a solution of poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole] (PBI) and di-functional benzoxazine monomer, 6,6'-(hexafluoroisopropylidene)bis(3-phenyl-3,4-dihydro-2H-benzoxazine) (HFa), in N,N-dimethylacetamide prior to stepwise heating to 250 degrees C. The films are also viable to manufacture to large quantities and area by roll-to-roll coating. The resulting cross-linked copolymer, P(HFa-co-BI), membranes are found to be thermally and mechanically stable. Although the proton conductivity values of P(HFa-co-BI) membranes are smaller than that of the PBI membrane, their cell performance (0.68 V at 0.2 A cm(-2) at 150 degrees C) is close to that of FBI membrane and their long-term durability (ca. 3116 cycles on in situ accelerated lifetime mode of load cycling testing) is found to be far superior to the PBI membrane. (C) 2012 Elsevier B.V. All rights reserved.