Stability of Vanadium Electrolytes in the Vanadium Redox Flow Battery
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Stability of Vanadium Electrolytes in the Vanadium Redox Flow Battery Shu-Yuan Chuang1,2, Chih-Hsing Leu1*, Kan-Lin Hsueh1, Chun-Hsing Wu1, Hsiao-Hsuan Hsu1, Yi-Ray Chen1, Wen-Sheng Chang1 1
Green Energy and Environment Research Laboratories, Industrial Technology Research Institute, Hsinchu 310,
Taiwan, Republic of China 2
Department of Materials Engineer, Ming Chi University of Technology, Taipei 243, Taiwan, Republic of China
* Corresponding author. Fax: +886-3-5820030, E-mail address: [email protected]
ABSTRACT The stability of the negative electrode electrolyte affects the efficiency and capacity of energy storage in the vanadium redox flow battery (VRFB) system.
To explore the stability of
vanadium electrolytes, the study prepared five types of V(II) electrolytes that were exposed to air in a fixed open area and monitored the charge state of vanadium ions over time by UV/Visible spectrophotometer. This study succeeded in preparing pure V(II) electrolytes. Five characteristics are found in the UV/Visible spectra, respectively, during the oxidation process from V(II) electrolytes to V(III) electrolytes and V(III) electrolytes to V(IV) electrolytes. The experimental results show that the oxidation rate of a solution of 1 M V(II) electrolytes to V(III) electrolytes and 1 M V(III) electrolytes to V(IV) electrolytes under an atmosphere of air is 4.79 and 0.0089 mol/h per square meter. The oxidation rates of 0.05-1 M V(II) electrolytes to V(III) electrolytes are approximately 96-538 times than that of V(III) electrolytes to V(IV) electrolytes. Keywords: Electrolyte᧷UV/Visible spectra᧷Energy storage᧷Vanadium redox flow battery
1. INTRODUCTION The concept of redox flow cell was proposed by Thaller et al. [1] in 1974. Skyllas-Kazacos et al. [2-4] proposed the all vanadium redox flow battery (VRFB) in 1985. Compared to varied electric storage technologies, the VRFB is one of most promising storage energy systems considering the capital cost, the power rating and discharge time [5, 6]. In Japan and South Africa, the VRFB system closed to commercialization in load leveling, wind power and solar power [7] according to an expected long cycle life for the rechargeable cell [8, 9]. Compared to alternative battery solutions, the VRFB has unique and highly competitive features including no cross contamination, easy scale-up the battery storage capacity at low capital cost, high energy efficiencies possible, long cycle life, minimal safety etc. [10]. However, a number of side reactions can occur during operation and can cause loss of capacity over extended charge–discharge cycling including the oxidation of vanadium ion in air, gassing side reaction during charging, differential transfer of vanadium ion or volumetric transfer of electrolytes from one half-cell to the other [10]. It is easy to find that the violet V(II) oxidizes
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to the green V(III) in a short time in air.
During charge-discharge cycles, the energy efficiency
and battery capacity of VRFB will lose due to the oxidation of vanadium electrolytes in air
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