Polyether Ether Ketone-Based Anion Exchange Membranes with Bis-imidazolium Cations for All-Vanadium Redox Flow Batteries

Abstract

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.

Dual Cross-Linked Poly(vinyl alcohol)-Based Anion Exchange Membranes with High Ion Selectivity for Vanadium Flow Batteries

“…In detail, the mechanical strength and elongation of the PVAc-0.5BPTMA-0.5DBPX-GA membrane were 10.3 MPa and 4.9%, while those of the PVAc-0.5BPTMA-0.5DBPX membrane were 5.1 MPa and 104.8%. Since the tensile strength of the membrane is a crucial indicator for longtime operation in VFBs, 25 GA cross-linking is an effective method to improve the dimensional and mechanical stabilities.…”

“…Zhang et al prepared a series of bis(imidazolium)-containing PEEK-based AEMs, which exhibited the low VO 2+ permeability, resulting in a higher CE of 99.5% than Nafion 212 (∼95.8%) at 120 mA cm −2 . 25 It is reported that aryl ether free AEMs possessed the enhanced chemical resistance as demonstrated by quaternary ammonium (QA) grafted polybenzimidazole- 26,27 and poly-(terphenylene)-based 28,29 AEMs. Additionally, in our recent work, it is interesting to find that AEMs based on QA side chain functionalized poly(p-terphenyl-N-methylpiperidinium)s exhibited high H + permeability.…”

Side-Chain Grafting-Modified Sulfonated Poly(ether ether ketone) with Significantly Improved Selectivity for a Vanadium Redox Flow Battery

“…So far, because of its extraordinarily high conductivity and outstanding chemical stability, Nafion membranes are still one of the finest choices for VRFB ion-selective membranes . However, the drawbacks of a high expansion rate, substantial vanadium ion penetration, and high cost are the key issues for large-scale deployment of Nafion membranes in VRFBs. , Many efforts have been made to date to produce innovative ion-selective membranes with improved performance and cheaper costs, such as cross-linking-modified − and polymer-blended composite membranes. − Because of their low cost, stability, and ease of manufacture, sulfonated poly­(ether ether ketone) membranes (SPEEK) have received a lot of interest. ,,,− Amphoteric ion exchange membranes with fixed cations and anion exchange groups have received a lot of interest in recent years. , Due to electrostatic repulsion, the positive ion group can effectively prevent the positive diffusion of vanadium ions under battery operating conditions, while the negative ion group provides optimum proton conductivity. Sulfamic acid (SA) contains −SO 3 H (acidic) and −NH 2 (weak basic) groups, which can be used to replace the inherent conductivity/permeability balance of the proton exchange membrane …”

Radiation synthesis of imidazolium ionic liquid grafted PVDF as the anion exchange membrane for vanadium redox flow batteries

“…Xing et al 13 prepared a series of poly(sulfone)-based AEMs modified by C2-protected imidazolium through an efficient Cu( i )-catalyzed azide–alkyne cycloaddition reaction, and the membranes exhibited excellent durability. Yang et al 17 fabricated a series of polyether ether ketone (PEEK)-based AEMs with bis imidazolium through complex reactions. The above-mentioned AEMs showed very high coulombic efficiency, indicating their great potential for application in VRFBs.…”