Facile preparation of polybenzimidazole membrane crosslinked with three-dimensional polyaniline for high-temperature proton exchange membrane

Phosphoric acid (PA) doped polybenzimidazole (PBI) membrane has been regarded as one of most effective high temperature proton exchange membrane (HT-PEM). However, it has to face poor mechanical properties at high acid doping levels (ADLs) and significant acid loss at high temperature during the operation of fuel cell. Herein, we prepare cross-linked PBI membranes containing different contents of the cross-linker three-dimensional polyaniline (PANI) via a facile N-substitution reaction. The obtained cross-linked PBI membrane exhibits superior tensile strength, stability and proton conductivity. More importantly, robust mechanical strength and good acid retention of the PA-doped cross-linked PBI membrane are demonstrated even at high ADL (above 20). The cross-linked PANI-30%-g-OPBI membrane exhibits a high ADL of 22.9, high proton conductivity of 122.8 mS cm−1 at 160 °C. Furthermore, the peak power density reaches 447 mW cm−2 at 160 °C, which is 2.5 times than that based on the corresponding PBI membrane. Molecular dynamics simulation results indicate that the decreased mobility of polymer chains improve the mechanical properties of the cross-linked membranes, and the high intermolecular interaction energy of the aniline-biphosphate ion pair significantly decrease PA leaching in the membranes due to the introduction of 3D molecular structure of PANI.