The effect of nitrogen positive sites on the proton conductivity and acid stability of polybenzimidazole-based proton exchange membranes

Abstract

High-temperature proton exchange membranes (HT-PEMs) based on amino-type polybenzimidazole (AmPBI) and double-bonded ionic liquids (ILs) are prepared. To prevent leakage of ILs, three kinds of polymeric ionic liquids (PILs) with different nitrogen positive sites are synthesized through in-situ free radical polymerization, and then the AmPBI-PIL membranes are prepared. The ion pairs (N+ - H2PO4−) formed after treatment with KOH and PA have a good effect on both proton conductivity and PA retention. After acid doping, the nitrogen positive sites in the PILs form ion pairs with PA, which serves as a jumping site for protons and promotes proton transport. The excellent proton conductivity and PA remaining of the AmPBI-PIL membranes are noteworthy. In particular, the proton conductivity of AmPBI-CTDTr is as high as 184.9 mS cm−1 at 180 °C, and the acid reservation is 83 % at 160 °C after 240 h. AmPBI-CTDTr has a 550.9 mW cm−2 peak power density when it is anhydrous at 160 °C.