High-temperature proton-exchange membrane fuel cells (HT-PEMFCs) are mostly based on acid-doped membranes composed of polybenzimidazole (PBI). A severe drawback of acid-doped membranes is the deterioration of mechanical properties upon increasing acid-doping levels. Cross-linking of different polymers is a way to mitigate stability issues. In this study, a new ion-pair-coordinated membrane (IPM) system with quaternary ammonium groups for the application in HT-PEMFCs is introduced. PBI cross-linked with poly(vinylbenzyl chloride) and quaternized with three amines (DABCO, quinuclidine, and quinuclidinol) are manufactured and compared to the state-of-the-art commercial Dapazol PBI membrane ex situ as well as by evaluating their HT-PEMFC performance. The IPMs show reduced swelling and better mechanical properties upon doping, which enables a reduction in membrane thickness while maintaining a comparably low gas crossover and mechanical stability. The HT-PEMFC based on the best-performing IPM reaches up to 530 mW cm-2 at 180 °C under H2/air conditions at ambient pressure, while Dapazol is limited to less than 430 mW cm-2 at equal parameters. This new IPM system requires less acid doping than conventional PBI membranes while outperforming conventional PBI membranes, which renders these new membranes promising candidates for application in HT-PEMFCs.
Keywords: Proton-exchange membrane; high-temperature proton-exchange membrane fuel cell; hydrogen gas crossover; ion pair; phosphoric acid; quaternary ammonium groups.