Amphoteric membranes were obtained from imidazoliumfunctionalized polyphenylene oxide (ImPPO) and sulfonated poly(ether ether ketone) (SPEEK) for an all-vanadium redox flow battery (VRFB) application. The SPEEK/ImPPO amphoteric membranes showed a considerably lower swelling degree and water uptake compared to those of pure SPEEK membranes, owing to the formation of ionic bonds between the cationic imidazolium groups of ImPPO and the anionic sulfonate groups of SPEEK. The cationic imidazolium groups of the ImPPO exhibited a Donnan exclusion effect on vanadium ions; therefore, the amphoteric membranes showed a much lower vanadium permeability than the pure SPEEK membrane. In addition, the vanadium permeability of the amphoteric membranes deceased with an increase in the ImPPO content. SPEEK-ImPPO20 with 20 wt% ImPPO showed a vanadium permeability of 0.43 × 10 À 9 cm 2 s À 1 at room temperature, which is 17 times lower than that of Nafion 212 (8 × 10 À 9 cm 2 s À 1 ). The VRFB assembled with SPEEK-ImPPO20 showed a coulombic efficiency of 97.2 % and a voltage efficiency of 85.8 % at a current density of 60 mA cm À 2 , whereas the values for Nafion 212 were 92.4 % and 86.7 % under the same conditions. In addition, the VRFB assembled with SPEEK-ImPPO20 exhibited much better capacity retention than that assembled with Nafion 212. These results indicate that the SPEEK-ImPPO amphoteric membrane is a promising material for VRFB applications.[a] Dr.
In this study, a series of polyether ether ketone (PEEK)-based un-cross-linked and cross-linked anion exchange membranes (AEMs) with bisimidazolium cations are prepared to fabricate all-vanadium redox flow batteries (VRFBs). Compared with a Nafion 212 membrane, these AEMs exhibit significantly lower vanadium-ion permeabilities because of the Donnan exclusion effect of bis-imidazolium cations. Moreover, owing to their denser structure, the vanadium permeability of the cross-linked PEEK-based AEMs (CImPEEK) is less than that of the un-cross-linked PEEK-based AEMs (ImPEEK) with similar ion exchange capacity (IEC) values. The ImPEEK and CImPEEK membranes exhibited the vanadium-ion permeabilities of 4.7 × 10 −10 and 5.5 × 10 −11 cm 2 s −1 at room temperature, respectively, which are considerably lower than the permeability of the Nafion 212 membrane (8.9 × 10 −9 cm 2 s −1 ) under the same conditions. Furthermore, the PEEK-based AEMs are more chemically stable in an electrolyte solution than the Nafion 212 membrane. The VRFB containing a CImPEEK membrane demonstrate a Coulombic efficiency of 99.5% at a current density of 120 mA cm −2 , whereas the corresponding value obtained for the VRFB with a Nafion 212 membrane under the same conditions was 95.8%. Finally, the capacity retention of the former battery is superior to those of the VRFBs containing Nafion 212 and ImPEEK membranes. The results of this work indicate that CImPEEK is a promising membrane material for VRFB applications.
The alkaline stability of anion exchange membranes (AEMs) is crucial to the performance of alkaline anion exchange membrane fuel cells (AEMFCs). Here, we have prepared and characterization of a series of new spirocyclic quaternary ammonium‐based AEMs with good alkaline stability. The AEMs was obtained by UV‐initiated polymerization of N, N‐diallylpiperidinium bromide ([DAPip][Br]), styrene and acrylonitrile. The water uptake, swelling ratio, IEC and conductivity of the AEMs increase with increasing the [DAPip][Br] content. The transparent and mechanically robust AEMs show high conductivities (7.99×10−2 S cm−1 at 80 °C) and good alkaline stability in 1 M KOH solution at 80 °C. The single cell with [DAPip][OH]20 showed a maximum power density of 93.9 mW cm−2. The spirocyclic quaternary ammonium‐based AEMs with an aliphatic backbone will open up new prospects for the preparation of AEMs with excellent alkaline stability and high conductivity.
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