Polybenzimidazole enhance sulfonated polyimide composite proton exchange membrane with acid–base interaction

Abstract

To mitigate the damage to the mechanical strength and stability of sulfonated polyimide (SPI) proton exchange membranes caused by sulfonic acid groups, polybenzimidazole (PBI) was introduced into the SPI skeleton to prepare composite membranes. The incorporation of rigid structure enhanced the mechanical strength of the SPI/PBI composite membranes. Meanwhile, the acid–base interactions between the imidazole rings and sulfonic acid groups formed a crosslinked structure between the polymer chains, significantly improving the thermal stability, oxidative stability, and dimensional stability of the SPI/PBI composite membranes. Specifically, the tensile strength of the 3SPI/PBI composite membrane reached 106 MPa, which was 3.23 times that of pure SPI membrane. Fortunately, the SPI/PBI composite membranes maintained good proton conductivity in both high-humidity and low-humidity environments, and it was able to maintain stable proton conductivity at 60 °C/98% RH. Theoretical calculations revealed that the binding energy between the SPI and PBI structural units reached -37.41 kcal mol⁻¹, indicating a significant interaction.