Fabrication of SPAEK–cerium zirconium oxide nanotube composite membrane with outstanding performance and durability for vanadium redox flow batteries

Abstract

Herein, an alternative sulfonated poly(arylene ether ketone) (SPAEK)–cerium zirconium oxide nanotube (Ce₂Zr₂O₇NT) composite (SPAEK/Ce₂Zr₂O₇) membrane has been proposed as a potential polymer electrolyte membrane for all vanadium redox flow batteries (VRFBs) performance. The as-prepared composite membrane showed higher ion selectivity and reduced vanadium ion crossover than the pristine SPAEK and NRE-212 (Nafion-212) membranes in VRFB operation. The vanadium ion permeability rate of SPAEK/Ce₂Zr₂O₇ (2%) composite membrane was found to be 27-fold and 12-fold lower than that of commercial NRE-212 and pristine SPAEK membranes, respectively. VRFBs operated with SPAEK/Ce₂Zr₂O₇ (441 h) were shown to have a lower self-discharge rate than pristine SPAEK (172 h) and NRE-212 (42 h) membranes, respectively. Finally, an electrochemical test of VRFB exhibited high retention capacity after 100 cycles for SPAEK/Ce₂Zr₂O₇ membrane as compared to NRE-212 and pristine SPAEK, while the coulombic efficiency (99.42%) at 40 mA cm⁻². The structure and morphology of Ce₂Zr₂O₇NT and the composite membrane were investigated by means of XRD, SEM, and TEM, and a consistent chemical structure of SPAEK/Ce₂Zr₂O₇ (2%) composite membrane before and after the chemical stability test was confirmed using ¹H NMR. The composite with 2% filler exhibits improved thermal, mechanical, oxidative, and chemical stability with superior ion selectivity. Also, X-ray photoelectron spectroscopy (XPS) analysis of SPAEK/Ce₂Zr₂O₇ (2%) composite membrane reveals the existence of a vanadium peak after 100 VRFB cycles.