Novel double cross-linked membrane based on poly (ionic liquid) and polybenzimidazole for high-temperature proton exchange membrane fuel cells

Novel double cross-linked composite membranes are fabricated based on diazoniabicyclo-type poly (ionic liquid) with trimethoxysilane groups ([TSPDO]BrCl) and norbornene-type polybenzimidazole (NbPBI). During membrane fabrication, in-situ free radical polymerizations and in-situ sol-gel reactions are completed to form the poly (ionic liquid)-NbPBI cross-linked networks and the Si-O-Si networks, respectively. An obvious advantage of this strategy is that the trimethoxysilane groups are fixed by the first cross-linked networks before hydrolysis reaction. Such method can avoid structural defects caused by SiO2 particle aggregation in the membranes. Compared to the pristine NbPBI cross-linked membrane, the NbPBI-TSPDO cross-linked membranes exhibit enhanced thermal stability, mechanical properties, and proton conductivity. Considering the comprehensive performance, the NbPBI-TSPDO30 membrane has the highest proton conductivity of 0.061 S cm−1 at 170 °C under anhydrous conditions. Moreover, NbPBI-TSPDO membranes display an improved PA retention rate of up to 81% and 64% at 160 °C for 400 h and 80 °C/40% RH for 96 h, respectively. [Display omitted] •Double cross-linked membranes based on NbPBI and PIL with siloxane were prepared.•Double cross-linked network improves proton conductivity and mechanical strength.•NbPBI-TSPDO30 has a proton conductivity of 61 mS cm−1 at 170 °C with highly cross-linked.•NbPBI-TSPDO exhibits enhanced PA retention (up to 81%) than that of NbPBI (75%).•Fuel cell with NbPBI-TSPDO30 exhibits a power density of 159 mW cm−2 at 120 °C.