质子交换膜是全钒液流电池的重要组件，应具备高质子传导和阻隔钒离子渗透的能力。但质子交换膜普遍存在质子传导率与溶胀度不易兼得，成为其面临的巨大挑战。本文提出膜材料的同轴电纺纤维化方法，在膜中构建长程质子传导通道，同时提高膜的耐溶胀性。磺化聚醚醚酮（SPEEK）同轴纤维膜兼具高质子传导和低溶胀特性，内、外轴采用相同磺化度的同轴纤维膜性能明显优于单轴纤维膜，溶胀度降低了41.3%，钒渗透率降低了6.9%，质子传导率提高了13.9%，质子/钒离子选择性提高了22.5%。在液流电池性能测试中，100mA/cm2电流密度下，同轴电纺纤维膜电池的能量效率达到83.7%，高于单轴电纺纤维膜和商业化Nafion211膜（74.9%），表明同轴电纺方法在全钒液流电池中应用前景广阔。

Proton exchange membrane is an important component of all-vanadium redox flow batteries, which should have high proton conductivity and the ability to block the penetration of vanadium ions. However, it is challenging for membrane to obtain high proton conductivity and low swelling ratio. In this work, the coaxial electrospinning method is proposed. By fiberizing the membrane materials, interconnective proton pathways could be built in the membranes to improve anti-swelling ability. The properties of the sulfonated poly (ether ether ketone) coaxial electrospun membrane is much better than that of the uniaxial electrospun membrane, with the same degree of sulfonation material. Coaxial electrospun membranes have a 41.3% reduction in swelling ratio, a 6.9% reduction in vanadium permeability, an 13.9% increase in conductivity and a 22.5% increase in proton/vanadium ions selectivity. In the single cell performance test, at a current density of 100mA/cm2, the energy efficiency of the cell assembled with coaxial electrospun membrane reaches 83.7%, which is higher than that assembled with the uniaxial electrospun membrane and Nafion211. Coaxial electrospinning method has potential applications in all-vanadium redox flow batteries.

[1] Park, M，Ryu, J; Cho, J, Nanostructured electrocatalysts for all-vanadium redox flow batteries[J]. Chem Asian J, 2015, 10 (10), 2096-110.
[2] Skyllas-Kazacos; M., New all-vanadium redox flow cell[J]. J Electrochem Soc, 1986, 133 (5), 1057.
[3] Wang, S，Owusu, K A，Mai, L, et al., Vanadium dioxide for energy conservation and energy storage applications: Synthesis and performance improvement[J]. APPL ENERG, 2018, 211, 200-217.
[4] Shi, Y，Eze, C，Xiong, B, et al., Recent development of membrane for vanadium redox flow battery applications: A review[J]. APPL ENERG, 2019, 238, 202-224.
[5] Wang, K，Liu, L，Xi, J, et al., Reduction of capacity decay in vanadium flow batteries by an electrolyte-reflow method[J]. J Power Sources, 2017, 338, 17-25.
[6] Oldenburg, F J，Nilsson, E，Schmidt, T J, et al., Tackling capacity fading in vanadium redox flow batteries with amphoteric polybenzimidazole/nafion bilayer membranes[J]. ChemSusChem, 2019, 12 (12), 2620-2627.
[7] Li, B，Luo, Q，Wei, X, et al., Capacity decay mechanism of microporous separator-based all-vanadium redox flow batteries and its recovery[J]. ChemSusChem, 2014, 7 (2), 577-84.
[8] Hossain, S I，Aziz, M A; Shanmugam, S, Ultra-high ion-selective and durable nafion-ndzr composite layer membrane for all-vanadium redox flow batteries[J]. ACS Sustain Chem Eng, 2020, 8(4):1998-2007.
[9] Ye, J，Cheng, Y，Sun, L, et al., A green speek/lignin composite membrane with high ion selectivity for vanadium redox flow battery[J]. J Membr Sci, 2019, 572, 110-118.
[10] Skyllas-Kazacos, M，Chakrabarti, M H，Hajimolana, S A, et al., Progress in flow battery research and development[J]. J Electrochem Soc, 2011, 158 (8).
[11] Mögelin, H，Yao, G，Zhong, H, et al., Porous glass membranes for vanadium redox-flow battery application - effect of pore size on the performance[J]. J Power Sources, 2018, 377, 18-25.
[12] Cha, M S，Jeong, H Y，Shin, H Y, et al., Crosslinked anion exchange membranes with primary diamine-based crosslinkers for vanadium redox flow battery application[J]. J Power Sources, 2017, 363, 78-86.
[13] Peng, S，Wu, X，Yan, X, et al., Polybenzimidazole membranes with nanophase-separated structure induced by non-ionic hydrophilic side chains for vanadium flow batteries[J]. J Mater Chem A, 2018, 6 (9), 3895-3905.
[14] Shukla, G; Shahi, V K, Amine functionalized graphene oxide containing c16 chain grafted with poly(ether sulfone) by dabco coupling: Anion exchange membrane for vanadium redox flow battery[J]. J Membr Sci, 2019, 575, 109-117.
[15] Lim, D W，Sadakiyo, M; Kitagawa, H, Proton transfer in hydrogen-bonded degenerate systems of water and ammonia in metal-organic frameworks[J]. Chem Sci, 2019, 10 (1), 16-33.
[16] Zeng, L，Ye, J，Zhang, J, et al., A promising speek/mcm composite membrane for highly efficient vanadium redox flow battery[J]. Surf Coat Technol, 2019, 358, 167-172.
[17] Gong, X，He, G，Yan, X, et al., Electrospun nanofiber enhanced imidazolium-functionalized polysulfone composite anion exchange membranes[J]. RSC Adv, 2015, 5 (115), 95118-95125.
[18] Gong, X，He, G，Wu, Y, et al., Aligned electrospun nanofibers as proton conductive channels through thickness of sulfonated poly (phthalazinone ether sulfone ketone) proton exchange membranes[J]. J Power Sources, 2017, 358, 134-141.
[19] Li, J，Zhang, Q，Peng, S, et al., Electrospinning fiberization of carbon nanotube hybrid sulfonated poly (ether ether ketone) ion conductive membranes for a vanadium redox flow battery[J]. J Membr Sci, 2019, 583, 93-102.
[20] Jia, C，Cheng, Y，Ling, X, et al., Sulfonated poly(ether ether ketone)/functionalized carbon nanotube composite membrane for vanadium redox flow battery applications[J]. Electrochim Acta, 2015, 153, 44-48.
[21] Yuan, Q，Fu, Z，Wang, Y, et al., Coaxial electrospun sulfonated poly (ether ether ketone) proton exchange membrane for conductivity-strength balance[J]. J Membr Sci, 2019, 595:117516.