Teaching an Old Dog New Tricks: Synthesis, Processing, and Application of Polybenzimidazole (PBI) Membranes

A novel processing technique was developed in which gel polybenzimidazole (PBI) membranes, produced by the polyphosphoric acid (PPA) process, are converted into dense polymer films and re-doped in phosphoric acid. This process, termed the PPA+ process, provides a 5 times improvement in creep resistance due to a 2-fold increase in the solids content within the membrane. Remarkably, the dense p-PBIs re-doped in phosphoric acid also exhibit excellent ionic conductivities at high temperatures. Thus, the performance of such membranes in high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) is enhanced under various operating conditions and long lifetimes.