|摘要: ||本文為探討全釩氧化還原液流電池(Vanadium Redox Battery, VRB)性能之改善，第一部分為基礎電池選定，選用硫酸氧釩和硫酸、硫酸氧釩和鹽酸、硫酸氧釩和硫酸、鹽酸等三種電解液組成，分別調整流速、濃度和使用不同離子交換膜做為參數條件，利用測量開路電壓(Open-circuit Voltage, OCV)方式，測量自放電率。再將上列最佳參數組合，使用四種不同處理方式的碳氈做OCV實驗，由實驗結果得知以2.5M硫酸氧釩、2.5M硫酸和6M鹽酸組成電解液，並使用雙氧水和硫酸浸泡後的薄膜和利用浸泡和加熱處理方式的碳氈，流量在50mL/min，有最佳開路電壓效能，並做為基礎電池參數條件。|
第二部分將以第一部分所得知最佳電解液、薄膜處理以及碳氈改質方式進行20次充放電循環，在電流密度為20mA/cm2、40mA/cm2和60 mA/cm2下，測量電壓效率、庫倫效率和能量效率並與2M VOSO4 in 3M H2SO4電解液比較。實驗過程中可發現在同樣電流密度下VOSO4- H2SO4-HCl電解液有較佳的電壓效率，是因硫酸和鹽酸中的陰離子和碳氈改質降低了VRB中的內電阻。隨著電流密度上升，電容量下降的趨勢有所趨緩，同時也增加了庫倫效率。為了解釩離子於VRB操作時濃度之變化，本研究利用光分分度計，建立釩離子的濃度之線性迴歸方程式，應用到未來進行VRB充放電過程中釩離子濃度之變化。
Vanandium redox battery (VRB) is known as the most suitable energy storage device for the renewable energy systems. However, it suffers the problem of energy capacity loss after long term charge-discharge operation. The main reasons for the capacity loss are mainly caused by the crossover of vanadium ions crossing the ion exchange membrane and the electrolyte stability. In this study, we aim to improve the VRB capacity by enhancing the electrolyte stability and reducing the ion crossover. The approaches used are modifications on the electrolyte composition, membrane, and carbon felt. Experiments are performed to identify effects produced from each component modification.
Based on the experimental results, it was found that with the electrolyte solution composed of 2.5M vanadyl sulfate, 2.5M sulfuric acid, and 6M hydrochloric acid, combined with the uses of heat treated carbon felt, and hydrogen peroxide/sulfuric acid soaked Nafion membrane, can produce the best result based on the battery self-charge current-voltage measurement. Using this combined electrolyte-membrane-carbon felt system, the battery charge-discharge performance shows that the capacity can be improved as compared with the battery operated using traditional electrolyte composed of 2M vanadyl sulfate and 2.5M sulfuric acid. The electrolyte volume changes in both positive and negative compartments were also measured and the variation trends agreed with those reported in the literatures. To realize the vanadium ion concentration changes during the self-discharge and charge-discharge processes, a concentration measurement technique based on spectrophotometer was also developed in this study. The measured ion concentrations results (V3+ and V4+) agreed with those reported in the literature. However, further development on ion concentration measurement is needed because spectrophotometer cannot be applied to the V2+ and V5+ concentrations measurement due to their stabilities in acid solution.
keywords: Vanandium redox battery, electrolyte composition, carbon felt, spectrophotometer