Cage-like cross-linked membranes with excellent ionic liquid retention and elevated proton conductivity for HT-PEMFCs

Polybenzimidazole/ionic liquid (IL) composite membranes with cage-like cross-linked structure were prepared based on polybenzimidazole containing hydroxyl groups (PBIOH30), 3-(triethoxysilyl) propyl isocyanate (IPTS) and 1-butyl-3-methylimidazolium dihydrogen phosphate (BMI-DHPH). The basic characteristic of imidazole rings in IL enhanced the phosphoric acid (PA) doping ability of the obtained cPBI-IL X membranes, thus, the proton conductivity of which was elevated. The cage-like cross-linked structure was formed under acidic conditions, and such structure can not only strengthen the mechanical properties of cPBI-IL X membranes but also prevent the leakage of the IL to some extent. The IL retention ability of cPBI-IL 10 was significantly improved, the residual weight percentage of IL was 71.6 wt%, while that of PBI-IL 10 membrane without cage-like cross-linked structure was only 2 wt%. The membrane with 8 wt% IL content exhibited the highest proton conductivity of 0.133 S cm−1 at 160 °C.