Crosslinked polybenzimidazole high temperature-proton exchange membranes with a polymers of intrinsic microporosity (PIM) macromolecular crosslinker

The macromolecular crosslinkers of bromomethylated polymer of intrinsic microporosity (PIM-BM) are successfully introduced into the poly(2,2'-(1,4-naphthalene)-5,5′-bibenzimidazole) (NPBI) to improve the phosphoric acid retention in high temperature proton exchange membrane fuel cell (HT-PEMFC). Thanks to the excellent miscibility between two polymers, the transparent and tough crosslinked membranes (NPBI/PIM-BM-x) have been obtained by the solution-casting. Compared with pristine NPBI membrane, the crosslinked membranes exhibit higher retention of phosphoric acid (PA) in various complicated temperature/humidity conditions due to the microporosity resulting from the micropore polymer of intrinsic microporosity (PIM) crosslinker. Specifically, the PA doped NPBI/PIM-BM-15 (NPBI/PIM-BM-15/PA) membrane shows 57.73% PA retention under 80 °C/40% relative humidity (RH), higher than PA doped NPBI (NPBI/PA) membrane (48.12%). Therefore, under accelerate stress test (AST) in fuel cells, the crosslinked NPBI/PIM-BM-15/PA membrane shows an excellent retention of peak power density, e.g. remaining 88.99% after 200 cycles of testing at 80 °C. This value is much better than pristine NPBI based fuel cell (only remaining 52.01% after 200 cycles under the same testing conditions). At a higher temperature of 160 °C without extra humidity, the fuel cells based on PA doped crosslinked membranes show comparable peak power density of 565–627.5 mW cm−2 to NPBI (632.5 mW cm−2) without an obvious sacrificing of initial fuel cell performance. Thus, the improved PA retention of the HT-PEM based on with PIMs crosslinker shows a great potential to broaden the operational temperature range and to be used for the next-generation HT-PEMs.