New anhydrous proton exchange membranes based on polypyrrolone (PPy) for high-temperature polymer electrolyte fuel cells

Polypyrrolone (PPy) possesses excellent heat resistance and mechanical properties, moreover, the N-heterocycle contained in the PPy allows the absorption of phosphoric acid (PA) for proton conduction. In the present work, PPy is synthesized by a two-step method and evaluated for the first time as the polymeric material for high temperature proton exchange membranes (HT-PEMs). The PA-doped PPy membrane reaches a peak power density of 582 mW cm-2 at 160 degrees C under fully anhydrous conditions, besides, the fuel cell exhibits excellent durability over a period of 300 h with a load voltage decay of only 0.032% per hour and remains 0.647 V after the test. Further, the PPy-impregnated polyimide (PI) nanofiber mat composite membrane (PI@PPy) with an optimal thickness is fabricated with enhanced dimensional stability, of which acid swelling ratio noticeably declined by 51% in area and 25% in volume. A higher peak power density (634 mW cm-2) and less cell voltage reduction is also observed in the composite membrane, benefits from the trade-off between proton conductivity and PA retention ability. The results of the present study may contribute to further studies on polypyrrolonebased HT-PEMs and composite membranes.