Quaternized porphyrin crosslinked polybenzimidazole membrane with dual-ion pair structure as HT-PEM: Enhanced proton conductivity and stability

High phosphoric acid (PA) retention stability and exceptional proton conductivity are critical for practical applications of PA-doped polybenzimidazole (PBI) membranes as high-temperature proton exchange membranes (HT-PEMs). In this study, TBPP-OPBI membranes were fabricated by crosslinking poly[2,2′-(p-oxydiphenylene)-5,5′-bibenzimidazole] (OPBI) with halogen-functionalized porphyrin (TBPP), followed by quaternization to produce quaternized porphyrin (QTBPP) crosslinked OPBI membranes (QTBPP-OPBI). Building upon the mechanically robust crosslinked framework, dual ionic pair structures were constructed through protonation of porphyrin rings and incorporation of quaternary ammonium groups. This design simultaneously enhances polymer-PA interaction energy and increases H 2 PO 4 − content within the membrane, thereby significantly improving PA doping stability and proton conductivity. The 0.81-QTBPP-OPBI membrane demonstrated a proton conductivity of 345 mS cm −1 at 180 °C and a peak power density of 576.6 mW cm −2 at 160 °C, representing 5.1-fold and 3.2-fold enhancements over the OPBI membrane, respectively, while maintaining excellent fuel cell stability beyond 200 h. This work thus establishes a straightforward structural design strategy to enhance the application performance of PA-PBI proton exchange membranes.