Durable High Polymer Content m/p-Polybenzimidazole Membranes for Extended Lifetime Electrochemical Devices

A series of high polymer content phosphoric acid-doped m/p-polybenzimidazole (PBI) copolymer membranes were prepared via the poly(phosphoric acid) (PPA) process. These copolymer membranes showed much higher solubility in solution (7–10 wt %) compared to the homopolymer para-PBI (typically <3.5 wt %), which translated to higher polymer solids content in the PPA-processed doped membranes. Concurrent with these changes, the compressive creep compliance (J) decreased from approximately 1 × 10–5 to <2 × 10–6 Pa–1. These membranes exhibited high proton conductivities, >150 mS/cm at typical operating temperatures of 160–200 °C, and showed exceptional low voltage decay, ∼0.67 μV/h when tested at 160 °C for more than 2 years.