Enhanced conductivity and stability via comb-shaped polymer anion exchange membrane incorporated with porous polymeric nanospheres

The comb-shaped benzyl piperidinium cations functionalized aryl-ether bonds-free poly(biphenyl-alkylene)s (PB-g-PipVBC) were synthesized by super-acid catalyzed Friedel-Crafts polycondensation and atom transfer radical polymerization (ATRP). To further construct ion transport channels and improve ion conductivity, the composite membranes were fabricated via doping the pre-designed ionic porous polymeric nanospheres. The resulting composite membrane loaded with 1 wt% nanospheres showed high chloride conductivity of 65.6 mS cm-1 at 80 °C, benefiting from the ordered ion conductive channel and ionic nanoaggregates. Meanwhile, the composite membranes doped with nanospheres all exhibited acceptable alkaline stability and maintained above 40% of the original ion conductivity after soaking in 1 M NaOH at 80 °C for 1000 h, and the oxidative durable remaining mass retained above 75% for 1 h in 80 °C Fenton's reagent. Among them, the composite membrane loaded with 3 wt% nanospheres possessed the highest alkaline stability (66.3% of the original hydroxide conductivity after storage in 1 M NaOH for 1000 h), which was ascribed to morphology and the absence of alkaline labile aryl-bonds in polymer backbone. Moreover, it exhibited a peak power density of 77.3 mW cm-2 at 143.4 mA cm-2 in a direct borohydride fuel cell, which was higher than that of Nafion®211 (67.4 mW cm-2 at 134.8 mA cm-2). Therefore, the poly(biphenyl-alkylene)s and ionic polymeric nanospheres grafting with benzyl piperidinium cations by ATRP have great potential for designing anion exchange membranes in diverse applications.