Small angle neutron scattering study on the morphology of imidazolium-based grafted anion-conducting fuel cell membranes

Two imidazolium based graft-type of anion-conducting electrolyte membranes (AEMs) for fuel cells with a moderate ion exchange capacity of ∼1.0 mmol/g were successfully prepared by radiation-induced grafting to introduce imidazolium and styrene units into a poly(ethylene-co-tetrafluoroethylene) (ETFE) base film. Though imidazolium groups were desired to connect with styrene groups via two different ways, i.e. parallel or perpendicular orientations to the graft-polymer chains via copolymerization (AEM1) or homo-polymerization (AEM2), both AEMs possess high ion conductivity (>100 mS/cm at 60 °C) and modest stability. The morphologies of these membranes were elucidated by small-angle neutron scattering method. Our results revealed that 1) both AEMs show clear microphase separation with a length scale of 30–40 nm, and the semi-crystalline structural feature of the hydrophobic microdomains contributes to the membrane mechanical property; 2) at the length scale