1,2-Dimethylimidazole based bromine complexing agents for vanadium bromine redox flow batteries

• Published in: International journal of hydrogen energy Vol. 44; no. 23; pp. 12024 - 12032
• Main Authors: Kim, Donghyeon, Kim, Yongbeom, Lee, Youngho, Jeon, Joonhyeon
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 03.05.2019
• Subjects: 1,2-Dimethylimidazole; Bromine complexing agents; Energy storage system; Redox flow battery; Vanadium bromine redox flow battery; 1,2-Dimethylimidazole; Vanadium bromine redox flow battery; Energy storage system; Bromine complexing agents; Redox flow battery
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2019.03.050

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 V2+ and V3+ in electrolyte including halogen elements (Br and Cl). This paper describes two imidazole-based BCAs, which are 1,2-dimethyl-3-ethylimidazolium bromide (DMEIm: C7H13BrN2) and 1,2-dimethyl-3-propylimidazolium bromide (DMPIm: C8H15BrN2), 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 V2+/V3+ 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. •Two Imidazole-based bromine-complexing agents are newly proposed for flow batteries.•These are C7H13BrN2 and C8H15BrN2, more suitable to Vanadium-Bromide electrolyte.•They provide the improved reversible reaction of V2+ and V3+ 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.