Polybenzimidazoles containing bulky substituents and ether linkages for high-temperature proton exchange membrane fuel cell applications

• Soluble PBIs are synthesized from new tetraamines using Eaton's reagent as solvent.
• These PBIs exhibit excellent oxidative, thermal stability and mechanical strength.
• PEMFC based on CF3-phenyl substituted PBI exhibits better performance than m-PBI.

Novel solution-processable polybenzimidazoles P1–P3 were prepared from three new teteraamines and 4,4′-oxybis(benzoic acid) in Eaton's reagent at 145 °C. These tetraamines were 4,4′,5,5′-tetraaminodiphenyldiphenyl ether containing bromide, phenyl and trifluoromethyl-substituted phenyl substituents at 2 and 2′ positions, respectively. P1–P3 exhibited good thermal stability, oxidative stability and mechanical properties. Phosphoric acid-doped P1–P3 membranes also exhibited high proton conductivity in the range of 5.30×10−2−8.80×10−2 S cm−1. They also demonstrated high performance on single cell test, with open circuit voltages of 0.84–0.98 V and peak power density of 478–636 mW cm−2 at 160 °C with acid uptakes of 199–241%. Especially, the fuel cell based on P3 with an open circuit voltage of 0.95 V and peak power density of 636 mW cm−2 exhibited better performance than the one based on m-PBI. These membranes provided new options as proton exchange membranes for high-temperature PEMFC applications.

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