Sulfonation Modification of Halloysite Nanotubes for the In-Situ Synthesis of Polybenzimidazole-Based Composite Proton Exchange Membranes in Wide-Temperature Range Applications

Phosphoric acid-doped polybenzimidazole (PA-PBI) membranes face challenges, such as the easy loss of free PA and the reduced mechanical strength caused by the "plasticization effect" of PA, limiting their application in a wide temperature range. In this study, sulfonated halloysite (sHNT) was used to modify poly(2,5-benzimidazole) (ABPBI) for the in-situ synthesis of a composite proton exchange membrane. The introduction of halloysites in the composite membrane enabled the capturing of PA and water, while its nanoporous structure provided additional paths for proton conduction. Sulfonation modification of halloysite improved the interfacial compatibility between the inorganic particles and the polymer matrix, with the -SO3H groups providing extra proton hopping sites. Due to the well-constructed interface, the resulting sHNT/ABPBI composite membrane exhibited high mechanical strength and excellent proton conductivity across a wide temperature range. The 3 % sHNT/ABPBI composite membrane exhibited a breaking strength of approximately 130 MPa, which was 1.6 times that of pure ABPBI. Moreover, the proton conductivity of the composite exceeded 0.01 S cm(-1) at temperatures ranging from 40 to 180 degrees C. At 160 degrees C, the peak power density of the PA-doped 3 % sHNT/ABPBI composite membrane was 0.212 W cm(-2), which was 1.33 times higher than that of the pure ABPBI membrane. These results show that the composite membrane has potential applications in a wide temperature range.