Guanidinium/Hydroxyl-Functionalized Polybenzimidazole for High-Temperature Proton Exchange Membrane Fuel Cell Applications

In this study, polybenzimidazole (PBI) functionalized with hydroxyl groups (OH-PBI) is synthesized by the polycondensation of 3,3′-diaminobenzidine, 4,4′-dicarboxydiphenyl ether, and 2,5-dihydroxyterephthalic acid. To enhance the phosphoric acid uptake and proton conductivity of PBI-based membranes, tetramethylguanidinium-functionalized PBI (TMG/PBI) is synthesized by introducing guanidinium salts into OH-PBI. The as-prepared TMG/PBI-based membranes show good oxidization and thermal and dimensional stability. Owing to guanidinium functionalization, the TMG/PBI-based membranes show higher PA uptake, PA retention, and proton conductivity values than pure PBI and OH-PBI-based membranes. Additionally, single fuel cells comprising TMG/PBI-10 exhibit a significantly higher maximum power density (545.49 mW cm–2) at 120 °C than those comprising pure PBI membranes (196.15 mW cm–2). Thus, the as-prepared TMG/PBI-X membranes are promising materials for high-temperature proton exchange membrane fuel cell applications.