Chinese Journal of Applied Chemistry ›› 2020, Vol. 37 ›› Issue (8): 912-922.DOI: 10.11944/j.issn.1000-0518.2020.08.200022

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Poly(ether ether ketone) Proton Exchange Membrane Containing Bisphenol Fluorene Unit for Vanadium Redox Flow Battery Application

SONG Xun, JIA Yuting, ZHANG Jieling, NING Jinfeng, ZUO Haiyan, HUANG Xuehong*   

  1. Key Laboratory of Polymer Science,College of Chemistry and Materials Science,Fujian Normal University,Fuzhou 350007,China
  • Published:2020-08-01 Online:2020-08-07
  • Contact: HUANG Xuehong, professor; Tel:0591-83465353; E-mail:xhhuang64@fjnu.edu.cn; Research interests:the molecular design of ion exchange membranes for fuel cells
  • Supported by:
    Natural Science Foundation of Fujian Province(No.2017J01407), and the Fujian Normal University College Students′ Innovative Entrepreneurial Training Plan(No.S201910394023, No.202010394020)

Abstract: Poly(ether ether ketone) (PEEK) containing methyl groups was synthesized by the aromatic nucleophilic polycondensation reaction of bisphenol fluorene unit, 4,4′-(Hexafluoroisopropylidene)diphenol, and 4,4′-difluoro-benzophenone. Poly(ether ether ketone) proton exchange membranes were post-sulfonated using concentrated sulfuric acid to give highly proton conductive sulfonic fluorenyl groups (SF-PEEK). The structure and morphology of SF-PEEK membranes were characterized by Fourier transform infrared spectroscopy (FTIR), hydrogen nuclear magnetic resonance spectroscopy (1H NMR), thermal gravimetric analyzer (TGA), atomic force microscope (AFM) and scanning electron microscopy (SEM). The SF-PEEK membranes have strong hydrophilic/hydrophobic phase separation. The conductivity of the SF80-PFEK608 membrane (IEC=1.97 mmol/g) is 4.15×10-2 S/cm which is lower than that of Nafion membrane (5.67×10-2 S/cm). SF-PEEK membranes show much lower vanadium ions permeability (3.15×10-7~1.48×10-6 cm2/min) than that of Nafion 117 membrane (7.04×10-6 cm2/min). As a result, the self-discharge duration of the vanadium redox flow battery (VRFB) cell with SF80-PEEK608 membrane (90 h) is longer than that of VRFB cell with Nafion 117 membrane (57 h). Furthermore, the VRFB cell with SF80-PEEK608 (IEC=1.97 mmol/g) membrane exhibits higher coulombic efficiency of 80.9% compare with that of VRFB cell with Nafion 117 membrane (coulombic efficiency of 78.8%) at current density of 40 mA/cm2. The results indicate that SF-PEEK membrane is high-performance and low-cost alternative membrane for VRFB application.

Key words: polyether ether ketone proton exchange membrane, vanadium redox battery, vanadium ion permeability, conductivity, bisphenol fluorene unit