Fluorinated poly(arylene ether)s functionalized by bulky imidazolium with excellent chemical stability for high-durability high temperature proton exchange membrane fuel cell applications

The development of polymer electrolyte membranes with superior chemical stability is critical for the widespread application and commercialization of high temperature proton exchange membrane fuel cells (HT-PEMFCs). Herein, we report the synthesis of fluorinated poly(aryl ether) (FPAE) copolymers via nucleophilic polycondensation of decafluorobiphenyl (DFBP) and methylhydroquinone, incorporating 4,4′-(hexafluoroisopropylidene)diphenol (6FDP) as a co-monomer. To enhance phosphoric acid (PA) doping capacity and simultaneously control dimensional swelling, bulky 1-decyl-2-methylimidazole (DeIm) groups are grafted onto the polymer backbone. The resulting homopolymer FPAE-DeIm membrane exhibits an excellent oxidative stability, retaining 68 % of their initial mass after 120 h in Fenton’s reagent (3 wt% H₂O₂ + 4 ppm Fe²⁺) at 80 °C, vastly outperforming conventional DeIm-grafted poly(2,6-dimethyl-1,4-phenylene oxide), which degrades within 2 h. The introduction of rigid and hydrophobic poly(DFBP-6FDP) units further enhances chemical durability and suppresses volume swelling. Consequently, Co-FPAE_0.65-DeIm exhibits an optimal balance of properties: 73 % mass retention after Fenton test, a volume swelling of 55 % in 85 wt% PA at 150 °C, a tensile strength of 15.5 MPa at room temperature, and a proton conductivity of 78.3 mS cm^-1 at 180 °C. Remarkably, under constant current operation (200 mA cm^-2) at 160 °C in dry H₂/air without backpressure, the membrane showed no signs of degradation over a 617-hour test. During this period, the peak power density increased from 319 to 420 mW cm^-2, while the cell voltage improved from 0.633 V to 0.683 V. These results position Co-FPAE_x-DeIm membranes as highly durable and efficient HT-PEMs, underscoring the potential for long-term operation in HT-PEMFCs.