中文摘要
氧化還原液流電池（Redox flow batteries, RFBs）是一種具有發展潛力的大規模電能儲存系統，因其可彈性的調整電容量和功率，可以更有效地整合太陽能和風能等間歇性能源。當電位範圍超過接近1.23 V時，傳統氧化還原液流電池容易受到水電解的影響，但非水相有機氧化還原液流電池（Non-aqueous organic redox flow batteries, NAORFBs）不僅不受到水電解的影響，更可以實現高電池電位，從而達到更高的能量密度。然而，NAORFBs 仍處於發展的早期階段，仍有許多問題需要克服，其中氧化還原活性物質的降解、缺乏適當的隔離膜、有機溶劑的黏度過高是當前需要優先克服的挑戰。高溶解度、高電池電壓、動力學反應快、高穩定性和低成本都是 NAORFBs活性材料的理想特性，且陽極電解液和陰極電解液的特性對於電池性能都至關重要，不過如今，市面上僅有低氧化還原電位的陽極電解液，高氧化還原電位的陰極電解液十分稀少。
N-取代吩噻嗪被認為是有應用潛力的NAORFBs 陰極電解液，除了易於獲得之外，電化學和物理化學性質容易修飾，在不帶電和帶電狀態下都很穩定，溶解在二甲基甲醯胺(Dimethylformamide, DMF)和碳酸酯溶劑等有機溶劑中，與常用的輔助鹽類沒有強烈的交互作用。 N-烷基吩噻嗪可以發生可逆的氧化還原反應，故非常適合用於液流電池。兩個苯基以及連接在活性中心N原子上的烷基、苯基或其他有機部分的電子釋放和屏蔽作用使N-烷基吩噻嗪自由基陽離子具有良好的穩定性。利用空間位阻方法調節吩噻嗪的氧化還原電位和自由基穩定性。 N-異丁基吩噻嗪是由低成本前驅物、吩噻嗪和異丁基溴一步合成的。 N-異丁基吩噻嗪的穩定性是透過 500 個循環的循環伏安法測試和 100 個循環的液流電池充放電測試來評估。 TEABF4/DMF 中預先混合的N-異丁基吩噻嗪和BTD 表現出良好的穩定性，特別是在進行500 循環循環伏安法時沒有明顯的衰減，並且在100循環中液流電池性能幾乎穩定，在100 次循環後保留67.4% 的放電電容量，並且具有中等的電化學效率。吩噻嗪被認為是潛在的陰極電解質，因為可以透過在對氮的的修飾來調節溶解度、穩定性、氧化還原電位和二電子轉移的利用。

Abstract
Redox flow batteries (RFBs) are a promising technology for large-scale static electrical energy storage because of detached energy and power modulation, allowing for more efficient integration of intermittent energy sources from sun and wind. The specific energy of traditional RFBs is restricted because of the electrolysis of water when the potential range exceeds nearly 1.23 V. Non-aqueous organic redox flow batteries (NAORFBs) can achieve high cell potential and thus high energy density, which is impossible in aqueous electrolytes, as well contain naturally abundant elements (H, C, N, O, S). However, NAORFBs are yet in their early stages of development and face a number of problems. Degradation of the redox-active species, lack of appropriate membrane (separator), high viscosity of organic solvents are the major problems of NAORFBs. High solubility, large cell voltage, fast kinetics, high stability, and low cost are all desirable characteristics in electroactive materials for NAORFBs. The characteristics of both anolytes and catholytes are equally important for the battery performance. Nowadays, there are many anolytes with low redox potential available commercially, but very few or no catholytes with high redox potentials are easily accessible for application in NAORFBs.
N-substituted phenothiazines are thought to be promising catholytes for NAORFBs since they can be obtained easily and the electrochemical and physicochemical properties can easily be modified, stable both in uncharged and in charged states, dissolve in organic solvents like DMF and carbonate solvents, the interactions with commonly used supporting salts are not so strong, environmentally friendly. N-alkylphenothiazines can undergo reversible redox reactions making them ideal for utilization in flow batteries. The electron releasing and shielding effects of two phenyl groups and an alkyl, phenyl or other organic moiety attached to the active center, N-atom, give N-alkylphenothiazine radical cation good stability. The redox potentials and radical stability of phenothiazine were tuned by making use of steric hindrance approach. N-isobutylphenothiazine was synthesized from low cost precursors, phenothiazine and isobutyl bromide in a single step process. The stability of N-isobutylphenothiazine is accessed with repeated CV tests for 500 cycles and flow battery test for 100 cycles. Premixed N-isobutylphenothiazine and BTD in TEABF4/DMF demonstrated good stability, particularly when 500 CV cycles are performed without significant peak decay as well as with nearly stable flow battery performance for 100 cycles, retaining 67.4% capacity after 100 cycles and with moderate electrochemical efficiencies. Phenothiazines are regarded as potential catholytes since the solubility, stability, redox potentials and the utilization of two electrons could be modulated by appending appropriate moiety, particularly at positions para to nitrogen.

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