Reinforced Polybenzimidazole Membranes by Crosslinked Fiber Mats for High Temperature Polymer Electrolyte Membrane Fuel Cells

• Polybenzimidazole nanofibers and mats prepared by electrospinning. • Nanofibers crosslinked by thermal curing with structure stability. • Nanofiber reinforced membranes exhibit anisotropic swelling upon acid doping. • Acid inventory issue identified for thin membranes. Thin and robust polybenzimidazole membranes are reinforced with polybenzimidazole fiber mats. The fiber mats are prepared by electrospinning followed by thermal curing to enhance their dimensional and structural stability in phosphoric acid. These properties are assessed by solubility tests in dimethylacetamide and swelling tests by phosphoric acid doping. The fiber reinforced membranes consist of two distinct phases, a rigid crosslinked polybenzimidazole fiber mat embedded in a continuous polybenzimidazole matrix. This was found to promote the anisotropic swelling during the subsequent phosphoric acid doping, i.e. suppressing the area swelling while enhancing the thickness swelling. Fuel cells equipped with thin composite membranes show high open circuit voltages and reasonable hydrogen crossover rate indicating dense morphology. The expected reduction in the ohmic resistance of fuel cells is not observed due to a reduced amount of acid in thinner membranes. Strategies to increase the acid inventory of the membrane electrode assemblies are under further evaluation.