Exploring highly soluble ether-free polybenzimidazole as anion exchange membranes with long term durability

A series of ether-free polybenzimidazoles (PBIs) containing alicyclic and aliphatic segments were synthesized for the application of anion exchange membranes (AEMs). The PBI-based AEMs prepared in this work (denoted as Pip-PBIs) possessed both high anionic conductivity and alkaline stability by grafting long alkyl chain 1-methylpiperidinium. Benefiting from the random arrangement of aromatic-alicyclic/aliphatic in backbone and their flexible spatial configurations, most Pip-PBIs showed significantly improved solubility in low boiling point solvents namely methanol and isopropanol, which could allow it as ionomer to improve the phase interface between catalyst and AEMs. Meanwhile, the flexible segments in backbone contributed to the formation of ion conductive channel, the Pip-PBI-C achieved the highest hydroxide ions conductivity of 108.8 mS cm−1 at 80 °C, and the conductivity could retain 82.9% after soaking in a 2 M aqueous NaOH at 80 °C for 1536 h. Furthermore, Pip-PBIs demonstrated well oxidation stability in Fenton's reagent (4 ppm FeSO4 and 3% H2O2). Moreover, the H2–O2 fuel cell using Pip-PBI-C as membrane achieved a high open circuit voltage of 1.0 V and a peak power density of 785.6 mW cm−2 at the current density of 1802.9 mA cm−2.