Imidazole based ionenes, their blends with PBI-OO and applicability as membrane in a vanadium Redox flow battery. (November 2017)

• Record Type: Journal Article
• Authors: Strużyńska-Piron, Izabela; Jung, Mina; Maljusch, Artjom; Conradi, Oliver; Kim, Sangwon; Jang, Jong Hyun; Kim, Hyoung-Juhn; Kwon, Yongchai; Nam, Suk Woo; Henkensmeier, Dirk
• Is Part Of: European polymer journal. Volume 96(2017)
• Page Start: 383
• Page End: 392
• Publication Date: 2017-11
• Subjects: Vanadium Redox Flow Battery (VRFB) -- anion exchange membrane (AEM) -- PBI-OO -- Ionenes -- 2-Mesityl-benzimidazole; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; Polymerization; Polymers; Periodicals; Electronic journals; 547.705
• DOI: 10.1016/j.eurpolymj.2017.09.031
• Languages: English
• ISSNs: 0014-3057

Abstract

Graphical abstract: Highlights: Synthesis of ionenes based on dibromoxylene and mesitylbenzimidazole. To reduce brittleness, the ionene was blended with PBI-OO. IEC of blends ranges between 1.33 and 1.78 mmol chloride/g. Voltage efficiency of a vanadium redox flow battery increases with amount of ionene. Coulomb efficiency increases with amount of PBI-OO, all show very low self discharge. Abstract: A new cationic ionene was synthesised from dibromoxylene and 2-(2, 4, 6-trimethylphenyl)benzimidazole. Even though the weight average molecular weight Mw reached values around 40, 000 g/mole, no membranes could be prepared from this ionene, probably because of its rigid backbone. Blending with 33, 41 and 50 wt% PBI-OO gave access to self-supporting membranes. In comparison with pure PBI-OO, these membranes have a higher water uptake (30–50%) and show a chloride conductivity around 0.5 mS/cm at 60 °C. In the VRFB, the membranes absorb sulfuric acid, which increases the conductivity. Nevertheless, the voltage efficiency (VE) of PBI-OO was surprisingly low. Further analysis suggests that the polymer gets easily sulfonated, leading to ionic crosslinking and thus reduced conductivity. At OCV, the PBI-OO based membrane showed a very low potential degradation rate of 0.19 mV/h even over 280 h, while the OCV decreased 60% within 60 h for Nafion 212. Charge/discharge curves revealed that the coulomb efficiency (CE) decreases with increasing amount of the ionene, while the VE increases. This indicates a potential for improved membranes by blending PBI or its derivatives (responsible for high CE) with highly conducting ion exchange materials to increase the VE in comparison to the pure polymer.