在溫和鹼性環境操作的環境友善鈦鐵氧化還原液流電池

Abstract

近年來，氧化還原液流電池（RFBs）因具有多種優勢，如低自放電率、高能量容量、長期能量儲存時間、長循環壽命與水基系統的高安全性，逐漸受到作為鋰離子電池替代能源儲存技術的關注。然而，商用釩氧化還原液流電池（VRFBs）需要在強酸性環境下運行，以確保釩離子具有良好的溶解性，這大幅增加了電極、膜和其他運行組件對強酸耐受性的基礎設施成本。此外，釩礦的高成本以及與強酸性電解質相關的長期維護和環境問題也需加以解決。本研究旨在構建成本效益高且環境友好的鈦鐵液流電池，因為鈦和鐵在地球上價格低廉且資源豐富。為此，我們在陽極使用兒茶酚螯合鈦以形成Ti(cat)3-2，而在陰極則採用Fe(CN)64-複合物；這兩種電解質在弱鹼性條件下可形成均勻溶液，從而促進更環保的系統。 在本研究中，我們開發了一種製備Ti(cat)3-2的新型一步法，使用鈦醇鹽作為起始材料，避免了已發表文獻中使用強酸溶解鈦氧化物的步驟。所得到的電解質可在空氣中穩定存放數月。我們也組建了相應的鈦鐵液流電池，以評估電池在40 mA cm-2電流密度下的性能和循環穩定性。系統化改變電解質的組成，包括陽離子的類型、支持電解質的濃度以及混合陽離子的使用等，並調整運行條件，如電解質的流速，以優化電池性能。

In recent years, redox flow batteries (RFBs) have gained increasing attention as alternative energy storage technology besides lithium-ion batteries due to several advantages, such as low self-discharge rate, high energy capacity, prolonged energy storage time, long cycle life and high safety water based systems. However, commercial vanadium redox flow batteries (VRFBs) need to operate in strong acidic environments to ensure good solubility of vanadium ions, which severely add up the infrastructure costs for the strong acid tolerance requirements for electrodes, membranes, and other operating components. Furthermore, the high cost of vanadium ore and long-term maintenance and environmental issues associated with strong acidic electrolytes also need to address. This study aims to construct cost-effective and environmentally friendly titanium-iron flow batteries, as titanium and iron are inexpensive and abundantly available on Earth. Hereby, titanium is chelated with catechol to form Ti(cat)32- at the negative electrode while Fe(CN)64- complexes are adopted for the positive electrode; and both the electrolytes could form a homogeneous solution under mild alkaline conditions to facilitate a more environmentally friendly system. In this study, we also develop a novel one-step method to prepare Ti(cat)32-, by employing titanium alkoxides as the starting materials to avoid the use of strong acid to dissolve raw titanium oxides in the published works. The resulting electrolytes could be stably stored in air for several months. We also build corresponding Ti-Fe flow batteries to evaluate the cell performance and the cycling stability at a current density of 40 mA cm-2. The composition of the electrolytes, including the types of cations, the concentration of supporting electrolytes and the use of mixed cations as well as the operation conditions such as the flow rate of the electrolytes are systematically varied to optimize the battery.