1, 2-Dimethylimidazole based bromine complexing agents for vanadium bromine redox flow batteries. (3rd May 2019)

• Record Type: Journal Article
• Authors: Kim, Donghyeon; Kim, Yongbeom; Lee, Youngho; Jeon, Joonhyeon
• Is Part Of: International journal of hydrogen energy. Volume 44:Number 23(2019)
• Page Start: 12024
• Page End: 12032
• Publication Date: 2019-05-03
• Subjects: Energy storage system -- Redox flow battery -- Vanadium bromine redox flow battery -- Bromine complexing agents -- 1, 2-Dimethylimidazole; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2019.03.050
• Languages: English
• ISSNs: 0360-3199

Abstract

Abstract: To stabilize bromine produced during a vanadium-bromine redox flow batteries (VBr RFBs) charging, a bromine complexing agent (BCA) should be effectively used as a supporting material in VBr electrolyte. However, there remains a problem of improving the unstable reversibility between V 2+ and V 3+ in electrolyte including halogen elements (Br and Cl). This paper describes two imidazole-based BCAs, which are 1, 2-dimethyl-3-ethylimidazolium bromide (DMEIm: C7 H13 BrN2 ) and 1, 2-dimethyl-3-propylimidazolium bromide (DMPIm: C8 H15 BrN2 ), for not only confirming the capture of bromine but also improving the redox reaction of vanadium ions in VBr electrolyte. The effectiveness of the proposed two imidazole-based BCAs is demonstrated through the following experiments: cyclic voltammetry (CV), nuclear magnetic resonance analysis (NMR), scanning electron microscopy (SEM) analysis and cyclic cell operation test. Experimental results show that both the diffusion coefficient and the peak currents of each electrolyte using the proposed imidazole-based BCAs increases linearly with the rise of scan rate on the recorded CV curves, providing improved reversible reaction of V 2+ /V 3+ in negative electrolyte. It also exhibits that the electrolytes using the DMEIm and DMPIm provide significantly improved charge (discharge) capacities which are 9.38 (31.01) % and 11.8 (35.66) % higher than the pristine one, respectively, resulting in 13.27% and 14.36% higher current efficiencies. In addition, corrosion cracks on the separator surface due to bromine attack are not observed after the cyclic cell operation. Consequently, these results indicate that the proposed two imidazole-based BCAs can not only sequester bromine during the VBr RFB charging, but also enhance electrochemical reversibility caused by improving diffusion coefficient of vanadium. Highlights: Two Imidazole-based bromine-complexing agents are newly proposed for flow batteries. These are C7 H13 BrN2 and C8 H15 BrN2, more suitable to Vanadium-Bromide electrolyte. They provide the improved reversible reaction of V 2+ and V 3+ in negative electrolyte. Overall discharge capacities are 31%–36% higher than the pristine one. Performance potentially leads to 13.27%–14.36% higher current efficiencies.