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An ultra-high ion-selective SPAEK/ZrNT composite membrane is developed and exhibits an improved VRB self-discharge time compared with SPAEK and Nafion-212 membranes.

A SPEKS/sGO composite membrane with superior ion selectivity and chemical stability was synthesized. The composite and pristine SPEKS membranes exhibited a 10.4- and 6.5-times greater self-discharge time compared with the commercial Nafion-212 membrane.

A thin Nafion-neodymium zirconium oxide nanotube (NdZr) composite (Nafion-NdZr) membrane has been fabricated and further modified by the polycation, poly­(diallyldimethylammonium chloride) (PDDA), and polyanion, poly­(sodium styrene sulfonate) (PSS). The ion selectivity of the Nafion-NdZr (1%)/[P-S]2 composite layer membrane was found to be 6.9, 3.5, and 2.3 times higher than those of recast Nafion, Nafion/[P-S]2 layer, and Nafion-NdZr (1%) composite membranes, respectively. As a result, the vanadium redox flow batteries (VFBs) assembled with Nafion-NdZr (1%) composite and Nafion-NdZr (1%)/[P-S]2 composite layer membranes have surpassed the VFB performance operated with recast Nafion and Nafion/[P-S]2 layer membranes. Noticeably, VFB operated with the Nafion-NdZr (1%)/[P-S]2 composite layer membrane (513.7 h) exhibited a longer self-discharge time than those with Nafion-NdZr (1%) (293.2 h), Nafion/[P-S]2 (124.1 h), and recast Nafion (32.7 h) membranes. Finally, the single VFB cell constructed with Nafion-NdZr (1%)/[P-S]2 and Nafion-NdZr (1%) membranes remarkably showed 80.1 and 73.4% capacity retention, respectively, over 200 charge–discharge cycles, whereas recast Nafion exhibited a 41.5% capacity retention over 100 cycles at a 40 mA cm–2 current density. The structure and morphology of the Nd2Zr2O7 nanotube, Nafion-NdZr composite, and Nafion-NdZr (1%)/[P-S]2 composite layer membranes were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared, and atomic force microscopy analyses. Longer cyclic performance and excellent oxidative, chemical, and thermal stability further prove the durability of proposed membranes.

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Ce2Zr2O7 nanotube in SPAEK block copolymer enhance ion selectivity and VRFB performance. The self-discharge time of SPAEK/Ce2Zr2O7 membrane was higher than pristine SPAEK and NRE-212 membrane.

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A highly ion-selective membrane for vanadium redox flow batteries (VRBs) consisting of sulfonated poly(arylene ether ketone) (SPAEK) and polyoxometalate coupled with a graphene oxide was designed and fabricated. The SPAEK/PW-mGO composite membrane showed an effectively low self-discharge rate and excellent Coulombic efficiency (98.73%) in VRBs.