Monolithic Macromolecule Membrane Based on Polybenzimidazole: Achieving High Proton Conductivity and Low Fuel Permeability through Multiple Cross-Linking

Increasing the proton-conducting durability and structural stability of acid-doped polybenzimidazole (PBI) proton exchange membranes (PEMs) is helpful for their application at high temperatures. However, these membranes tend to show a high swelling degree and easy leaching of acidic proton conductors. To effectively improve the comprehensive performance of PEMs, a multifunctional and cross-linkable proton conductor (TTPSA) is used to form a high-temperature PEM (HTPEM) by multiple cross-linking with chloromethylated polyetherimide (CMPEI) and mPBI. The CMPEI, as a “bridge”, is covalently bonded with mPBI and TTPSA to form a monolithic macromolecule. Different from the blending and doping strategy, TTPSA can be firmly immobilized onto the membrane matrix to avoid leaching. Besides, more basic nitrogen sites formed by covalent cross-linking on TTPSA and mPBI can enhance the ionic and hydrogen-bond interactions with −SO3H. Therefore, the resulting mPBI-CMPEI-TTPSA membrane demonstrated excellent overall performance, in terms of oxidative and dimensional stability and fuel crossover resistance. The conductivity of mPBI-CMPEI(20)-TTPSA(30) reached 0.113 and 0.057 S/cm under 100% RH and 50% RH at 180 °C, respectively. More importantly, the conductivity almost not changed even after 48 h washing. This research offers a promising approach to the design of HTPEMs.