Hydrocarbon-Nafion composite membrane with three-dimensional interlocking interfacial layer for improved cycle-stability of vanadium redox flow battery

Abstract

Hydrocarbon (HC) membranes for vanadium redox flow battery (VRFB) have attracted a great deal of interest, owing to their cost-effectiveness and high ion selectivity. However, they suffer from severe chemical degradation by highly oxidative $VO_2^{+}$ ion in positive electrolyte. Here, in order to improve the cycle-stability of a sulfonated poly(arylene ether sulfone) (SPAES) membrane, a SPAES-Nafion composite (S-N) membrane is suggested. The S-N membrane is composed of a SPAES substrate, a thin recast Nafion layer and a three-dimensional interlocked interfacial layer (3-D IIL) in which two different polymers are tightly bound forming 3-D structure. The SPAES substrate provides high ion selectivity which can contributes to high VRFB performance and the thin Nafion layer protects the SPAES substrate from $VO_2^{+}$ ion, improving the chemical stability of membrane. The 3-D IIL binds two different membranes, not generating additional interfacial resistance for proton conduction. As a result, the VRFB with the S-N membrane exhibits higher coulombic efficiencies and energy efficiencies than that with Nafion 115 at various current densities from 40 to 200 mA $cm^{-2}$. Moreover, the VRFB with the S-N membrane can operate more than 200 cycles in contrast to the sudden death of the VRFB with the SPAES membrane at 110th cycle due to the membrane failure, demonstrating the efficacy of this approach in improving membrane durability.