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

Abstract

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 −SO 3 H. 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.

Sulfonated Polyphosphazene-Blended Self-Cross-Linked Polybenzimidazole-Based High-Temperature Proton Exchange Membranes: High Efficiency in Proton Transport at Low Humidity

“…The peak at 1530 cm –1 identified the existence of the CN stretching mode in the imidazole ring in m-PBI, HOM-mPBI, and CM-mPBI . The observable peaks at 3050 and 2918 cm –1 were assigned as the N–H bonds and the stretching of C–H bonds associated with the aromatic rings and −CH 2 –, respectively . The typical hydroxyl association peak at 3390 cm –1 was observed in the curve of HOM-mPBI.…”

“…40 The observable peaks at 3050 and 2918 cm −1 were assigned as the N−H bonds and the stretching of C−H bonds associated with the aromatic rings and −CH 2 −, respectively. 31 The typical hydroxyl association peak at 3390 cm −1 was observed in the curve of HOM-mPBI. As for CM-mPBI, the peak at 610 cm −1 was ascribed to the stretching vibration of C−Cl bonds, and the band at 2918 cm −1 was assigned to the bending vibration of the −CH 2 − group.…”

“…The precursor of the chloromethylation reaction, mPBI, was synthesized according to the previously reported methods . Five grams of mPBI was weighted and added to 20 mL of N -methylpyrrolidone (NMP) to obtain a homogeneous solution.…”

“…The precursor of the chloromethylation reaction, mPBI, was synthesized according to the previously reported methods. 31 Five grams of mPBI was weighted and added to 20 mL of N-methylpyrrolidone (NMP) to obtain a homogeneous solution. Then, 1.06 g of paraformaldehyde and 2−3 drops of triethylamine were added to the solution of mPBI to obtain the hydroxymethylated product (HOM-mPBI).…”

Anchoring Highly Sulfonated Hyperbranched PBI onto oPBI: Fast Proton Conduction with Low Leaching

“…Several methods have been developed to address these issues. Covalent cross-linking could effectively retard the decline in mechanical strength at a high doping level of proton conductors. − Multilayered membranes exhibited good PA retention ability and mechanical property. , Inorganic acids are anchored onto polymers, ionic liquids, and additives such as silica, graphene oxide, and carbon nanotubes. ,− Encapsulation or intercalation of inorganic acids is also effective in alleviating acid leaching. − During recent years, insoluble organic-inorganic hybrid proton conductors such as phosphonates, sulfophenyl phosphates, and phytates were also developed by our research group. − Doping of such proton conductors could enhance the mechanical property at certain doping levels, and avoid leaching and phase separation problems due to their inorganic–organic nature and insolubility. However, during preparation of such proton conductors, the hydroxyl groups in the phosphonic acid groups partially react with metal ions to ensure the insolubility, which reduces the content of the proton-conducting groups and affects the conductivity.…”