Polybenzimidazole membrane crosslinked with quaternized polyaniline as high-temperature proton exchange membrane: Enhanced proton conductivity and stability

Despite the phosphoric acid (PA) doped polybenzimidazole (PBI) membrane demonstrates excellent proton conductivity, the higher loss rate of PA and the lower mechanical strength at high PA doping level (ADL) will lead to a significant deterioration of its performance. The traditional cross-linking method can construct compact PBI molecular structure to enhance the mechanical properties, but it prevents the doping of PA in PBI membrane, thus reducing the ADL. Herein, we prepare cross-linked poly[2,2′-(p-oxydiphenylene)-5,5′-benzimidazole] (OPBI) membranes with polyaniline (PANI) cross-linker containing different quaternary ammonium (QA) group contents to balance the relationship between ADL and mechanical properties. Based on the aniline-diphosphate ion pair constructed by PANI and PA, more QA-diphosphate ion pairs are constructed through tuning the content of alkaline QA group in PANI to increase ADL and reduce the loss of PA. Quaternized PANI cross-linked OPBI membranes (QPANI-OPBI) exhibit superior mechanical properties, high ADL and proton conductivity. The cross-linked membrane containing QA group at a molar ratio of 0.30 to the OPBI repeating unit (0.30-QPANI-OPBI) exhibits the smallest PA loss rate of 15.2% after 120 h even at the highest ADL of 17.2. The 0.30-QPANI-OPBI membrane exhibits much better proton conductivity and peak power density than OPBI membrane at high temperature (160 °C), which are respectively 145.6 mS cm−1 and 459 mW cm−2. Our present work demonstrates that the quaternized PANI would be a promising cross-linker to prepare the PA-PBI membrane with excellent properties as High-temperature proton exchange membrane (HT-PEM).