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

Thin and robust polybenzimidazole membranes are reinforced using 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 evaluated through solubility tests in dimethylacetamide and swelling tests by phosphoric acid doping. The fiber reinforced membranes are in two distinct phases, a rigid crosslinked polybenzimidazole fiber mat within 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 composite membranes. The expected reduction in the ohmic resistance of fuel cells is not observed due to a reduced amount of acid in thinner membranes. Approaches to increasing the acid inventory in MEAs are under further evaluation.