Constructing Ionic Liquid-Filled Proton Transfer Channels within Nanocomposite Membrane by Using Functionalized Graphene Oxide

Abstract

© 2015 American Chemical Society. Herein, nanocomposite membranes are fabricated based on functionalized graphene oxides (FGOs) and sulfonated poly(ether ether ketone) (SPEEK), followed by being impregnated with imidazole-type ionic liquid (IL). The functional groups (acidic group or basic group) on FGOs generate strong interfacial interactions with SPEEK chains and then adjust their motion and stacking. As a result, the nanocomposite membranes possess tunable interfacial domains as determined by its free volume characteristic, which provides regulated location for IL storage. The stored ILs act as hopping sites for water-free proton conduction along the FGO-constructed interfacial channels. The microstructure at SPEEK-FGO interface governs the IL uptake and distribution in nanocomposite membrane. Different from GO and vinyl imidazole functionalized GO (VGO), the presence of acidic (-SO3H) groups confers the p-styrenesulfonic acid functionalized GO (SGO) incorporated nanocomposite membrane loose interface and strong electrostatic attraction with imidazole-type IL, imparting an enhanced IL uptake and anhydrous proton conductivity. Nanocomposite membrane containing 7.5% SGO attains the maximum IL uptake of 73.7% and hence the anhydrous conductivity of 21.9 mS cm-1at 150 °C, more than 30 times that of SPEEK control membrane (0.69 mS cm-1). In addition, SGOs generate electrostatic attractions to the ILs confined within SGO-SPEEK interface, affording the nanocomposite membrane enhanced IL retention ability.