Dual cross-linked polymer electrolyte membranes based on poly(aryl ether ketone) and poly(styrene-vinylimidazole-divinylbenzene) for high temperature proton exchange membrane fuel cells

One critical issue to phosphoric acid (PA) doped high-temperature proton exchange membranes (HT-PEMs) is to balance the proton conductivity and mechanical properties for overall application performance in fuel cells. Addressing the issue, we prepare durable HT-PEMs having the dual crosslinking structure by employing poly(vinylimidazole-divinylbenzene-styrene) (poly(VIm-DVB-St)) copolymer as a crosslinker and using the poly (aromatic ether ketone) (PAEK) polymer containing four methyl groups as the host membrane matrix. The imidazole groups of poly(VIm-DVB-St) react with benzyl bromide groups of brominated PAEK for both the primary cross-linking network and high PA doping. The divinylbenzene crosslinked poly (styrene-co-vinylimidazole) network generates the secondary cross-linking structure. The formed reticular polymer chain structure brings on low swelling and high mechanical strength of the HT-PEMs. The fuel cell based on the acid doped PAEK₄₁-85%VIm/233.0 PA shows a H₂-air fuel cell peak power density of 306 mW cm⁻² at 200 °C without back pressure, and a low degradation rate of 3.9 × 10⁻⁵ V h⁻¹ during a period of 600 h under a constant current density of 200 mA cm⁻² at 160 °C.