Soluble ultra-high molecular weight poly(4,4′-diphenylether-5,5′-bibenzimidazole) based membranes with remarkable mechanical strength and specific proton conductivity for high temperature proton exchange membrane fuel cells

Reducing the thickness of membrane electrolyte is one important direction to improve Ohmic polarization and the according performance of high-temperature proton exchange membrane fuel cells for its widespread applications. Herein, we report that robust thin membranes can be formed using a soluble ether-contained poly(4,4′-diphenylether-5,5′-bibenzimidazole) with an ultra-high molecular weight of 170 kDa. Due to the enhanced chain entanglement of high molecular weight polymers, the formed thin membrane exhibits promising mechanical strength, thermal and oxidation stability. The optimized membrane with thickness of 61 μm and phosphoric acid uptake of 606 wt% has the high specific proton conductivity of 25.9 S cm−2 at 160 °C under anhydrous conditions and mechanical strength of 11.2 MPa. The accordingly fabricated membrane electrode assembly delivers a peak power density of 0.544 W cm−2 with the open circuit voltage of 0.915 V at 160 °C using air as oxidant, outperforming the value of 0.522 W cm−2 for the commercial membrane electrode assembly with thickness of 250 μm and phosphoric acid uptake of 1018 wt%.