Wenjia Wu

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

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(-1) at 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.

Molecular‐Level Hybridization of Nafion with Quantum Dots for Highly Enhanced Proton Conduction

Nanophase-separated membranes hold promise for fast molecule or ion transfer. However, development and practical application are significantly hindered by both the difficulty of chemical modification and nanophase instability. This can be addressed by organic-inorganic hybridization of functional fillers with a precise distribution in specific nanophase. Here, a molecular-level hybridization for nanophase-separated Nafion using 2-5 nm quantum dots (QDs) as a new smart filler is demonstrated. Two kinds of QDs are prepared and used: hydrophilic polymer-like QDs (PQDs) and hydrophobic graphene oxide QDs (GQDs). Because of selective interactions, QDs offer advantages of matched structural size and automatic recognition with the nanophase. A distinctive synthesis of subordinate-assembly, in which QDs are driven by the self-assembly of Nafion affinity chains, is reported. This results in a precise distribution of QDs in the ionic, or backbone, nanophases of Nafion. The resulting PQDs in the ionic nanophase significantly increase membrane proton conduction and device output-power without loss of mechanical stability. This is difficult to realize with conventional fillers. The GQDs in the backbone nanophase reduce the crystallinity and significantly augment membrane water uptake and swelling capacities.