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It is known that uniaxially drawn perfluoronated sulfonic-acid ionomers (PFSAs) show diffusion anisotropy because of the aligned water channels along the deformation direction. We apply the uniaxially stretched membranes to vanadium redox flow batteries (VRFBs) to suppress the permeation of active species, vanadium ions through the transverse directions. The aligned water channels render much lower vanadium permeability, resulting in higher Coulombic efficiency (>98%) and longer self-discharge time (>250 h). Similar to vanadium ions, proton conduction through the membranes also decreases as the stretching ratio increases, but the thinned membranes show the enhanced voltage and energy efficiencies over the range of current density, 50-100 mA/cm. Hydrophilic channel alignment of PFSAs is also beneficial for long-term cycling of VRFBs in terms of capacity retention and cell performances. This simple pretreatment of membranes offers an effective and facile way to overcome high vanadium permeability of PFSAs for VRFBs.

We present cross-linkable precursor-type gel polymer electrolytes (GPEs) that have large ionic liquid uptake capability, can easily penetrate electrodes, have high ion conductivity, and are mechanically strong as high-performance, flexible all-solid-state supercapacitors (SC). Our polymer precursors feature a hydrophilic-hydrophobic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock main-chain structure and trifunctional silane end groups that can be multi-cross-linked with each other through a sol-gel process. The cross-linked solid-state electrolyte film with moderate IL content (200 wt %) shows a well-balanced combination of excellent ionic conductivity (5.0 × 10 S cm) and good mechanical stability (maximum strain = 194%). Moreover, our polymer electrolytes have various advantages including high thermal stability (decomposition temperature > 330 °C) and the capability to impregnate electrodes to form an excellent electrode-electrolyte interface due to the very low viscosity of the precursors. By assembling our GPE-impregnated electrodes and solid-state GPE film, we demonstrate an all-solid-state SC that can operate at 3 V and provides an improved specific capacitance (112.3 F g at 0.1 A g), better rate capability (64% capacity retention until 20 A g), and excellent cycle stability (95% capacitance decay over 10 000 charge/discharge cycles) compared with those of a reference SC using a conventional PEO electrolyte. Finally, flexible SCs with a high energy density (22.6 W h kg at 1 A g) and an excellent flexibility (>93% capacitance retention after 5000 bending cycles) can successfully be obtained.

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For a mechanically tough proton exchange membrane, a composite membrane incorporated with a porous polymer substrate is of great interest to suppress the ionomer swelling and to improve the dimensional stability and mechanical strength of the ionomers. For the composite membranes, good impregnation of substrate-incompatible ionomer solution into the substrate pores still remains one of the challenges to be solved. Here, we demonstrated a facile process (surface treatment with solvents compatible with both substrate and the ionomer solution) for the fabrication of the composite membranes using polytetrafluoroethylene (PTFE) as a porous substrate and poly­(arylene ether sulfone) (SPAES) as a hydrocarbon-based (HC) ionomer. Appropriate solvents for the surface treatment were sought through the contact angle measurement, and it was found that alcohol solvents effectively tuned the surface property of PTFE pores to facilitate the penetration of the SPAES/N-methyl-2-pyrrolidone (NMP) solution into ∼300 nm pores of the substrate. Using this simple alcohol treatment, the SPAES/NMP contact angle was reduced in half, and we could fabricate the mechanically tough PTFE/HC composite membranes, which were apparently translucent and microscopically almost void-free composite membranes.

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PErC(5)QPS-QPPO exhibited 20.7% higher MPD than commercial AEM (AMV).