Base-acid doped polybenzimidazole with high phosphoric acid retention for HT-PEMFC applications

Abstract A major problem faced by phosphoric acid doped polymer electrolyte membranes is leaking out easily as the reaction proceeds. Here, the long alkyl side chains with quaternary ammonium groups grafted the polybenzimidazole membranes (PBI-Sc-X) are prepared. The strong interaction between quaternary ammonium and biphosphate ion-pairs keep phosphoric acid (PA) in base-acid doped membranes. As a result, the remaining PA weight of PBI-Sc-X membranes could hold above 80%, which is better than that of pure PBI. Besides, it is observed that the highest power density of 411.7 mW/cm2 at 160 °C under current density 1000 mA/cm2 is obtained with base-acid doped PBI-Sc-5 membranes. Furthermore, the PBI-Sc-X membranes show considerable performance in oxidative stability, mechanical strength and thermal stability, which gave a basis for HT-PEMFCs application.