Effects of different ratios of flexible links and rigid structures in side chains on membrane properties for HT-PEM applications.

A series of grafted polybenzimidazoles with ratios of flexible links and rigid structures in side chains based on amino polybenzimidazole (AmPBI) was successfully prepared by simple N-substitution reaction. Due to the adequate number of amino groups on the AmPBI backbone, sufficient N–H sites reduce consumption of imidazole group during grafting reactions, while simultaneously elevating the number of proton transfer site. The grafted polybenzimidazole membranes with ratios of flexible links and rigid structures in side chains have excellent properties especially in the phosphoric acid (PA) uptake, pretty swelling ratio and proton conductivity. Importantly, PA uptake, swelling ratio, mechanical property, proton conductivity and power density can be controlled by changing the ratios of flexible links and rigid structures. The grafted membrane (AmPBI-P3) with the longer flexible link in the side chain shows a low swelling ratio of 128.62%, which is lower than that of other AmPBI-PX and AmPBI. Moreover, AmPBI-P3 shows a high proton conductivity of 126.9 mS cm−1 which is about 1.74 times higher than pure AmPBI (73.1 mS cm−1) and still reaches 91.4 mS cm−1 at 180 °C after the PA retention capacity test under 160 °C/0%RH for 240 h. A great power density of 738.5 mW/cm2 at 180 °C with dry H 2 –O 2 and no backpressure is impressive among many reported membranes. [Display omitted] • A series of grafted polybenzimidazoles was successfully prepared. • The proton conductivity of AmPBI-P3 under 180℃ is about 1.74 times higher than AmPBI. • AmPBI-P3 shows pretty retention capacity after the PA retention capacity test under 160 ℃/0%RH for 240 h. • Great power density (738.5 mW/cm2) under 180 °C implies the potential applications in HT-PEMFCs. [ABSTRACT FROM AUTHOR]