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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