Robust and high-conductivity poly(biphenyl-co-terphenyl pyridine) copolymers for high temperature proton exchange membrane fuel cell applications

High temperature proton exchange membrane (HT-PEM) is a core component for high temperature proton exchange membrane fuel cells (HT-PEMFCs). Although phosphoric acid (PA) doped polybenzimidazole (PBI) membranes are widely applied in HT-PEMFCs, the synthetic procedure is rather tough and the carcinogenic monomer should be used. Thus, it is of significance to obtain cheaper and easily prepared HT-PEMs with moderate physicochemical properties and good fuel cell performance. Herein, using a straightforward Friedel-Crafts reaction between 4-acetylpyridine, biphenyl and para-terphenyl, a series of poly(biphenyl-co-terphenyl pyridine) copolymers (Co-x%BP-y%TP) are developed. The obtained Co-x%BP-y%TP membranes exhibit excellent capability of absorbing PA owing to the existence of pyridine units in polymers, and meanwhile PA absorption capacity of membranes increase with the increased percentage of the biphenyl moiety in copolymers. Through immersing in 85 wt% PA at 100 °C, the Co–25%BP-75%TP membrane achieves a PA uptake of 274%, displays a moderate tensile strength of 4.7 MPa and possesses a high conductivity of 0.099 S cm−1 at 180 °C. Consequently, under 200 °C and no backpressure condition, the peak power density of the H2–O2 cell equipped with Co–25%BP-75%TP/274%PA membrane reached a high value of 773 mW cm−2, demonstrating a big potential to be operated in HT-PEMFCs.