新型鎢金屬有機框架衍生物複合石墨烯應用於超級電容器負極材料之開發

Abstract

面對氣候變遷與能源轉型的挑戰，可再生能源因其低碳排與永續特性，被視為未來能源系統的關鍵因素。然而，風能與太陽能等再生能源受限於其間歇性難以穩定供電，迫切需要高效儲能的研發。超級電容器具備高功率密度、快速充放電能力與長循環壽命等優勢，在穩定能源供需中展現出極大潛力。本研究以設計具備優異儲能能力的負極電極材料為目標，提出一種基於鎢金屬有機框架(W-MOF)衍生之複合材料，應用於超級電容器負極。鎢元素具多種氧化態(+2至+6)，在氧化還原反應中具備高度活性，但以鎢作為金屬中心的 MOF 材料仍鮮有文獻深入探討。本研究使用六氯化鎢(WCl6)、均苯四甲酸(PMA)與硝酸(HNO3)透過一步水熱法合成W-MOF材料，並藉由煅燒形成鎢金屬框架衍生物材料(D-WO3)。為進一步提升其導電性與倍率性能，將不同含量之氧化還原石墨烯(rGO)摻雜其中，合成D-WO3@rGO複合材料。該材料兼具電雙層與擬電容儲能機制，並藉由D-WO3本身結構與rGO的協同效應，大幅提升其比表面積與導電性。本研究所製備的D-WO3@rGO60材料，擁有低電解液電阻(Rs) 2.31 Ω與電荷轉移電阻(Rct) 0.56 Ω，在電流密度為1 A g-1下可獲得高比電容值998.8 Fg-1。相比D-WO3(350A) (654.2 F g-1)、D-WO3@rGO40 (751.2 F g-1)與D-WO3@rGO80 (816.2 F g-1)材料，分別提升1.53、1.33及1.22倍，顯示D-WO3@rGO60具有優異的電容性能。當電流密度提升至5 A g-1時，仍保有40.5 %的倍率性能，驗證D-WO3透過水熱法複合rGO能有效提升其倍率性能。最後，以D-WO3@rGO60為負極材料，活性碳(Activated carbon, AC)為正極材料組裝成混合式超級電容器(Hybrid supercapacitor, HSC)，該HSC在15.7 W h kg-1的能量密度下具有3000 W kg-1的高功率密度。它可點亮排列有NTNU ME圖樣的88顆並聯紅光LED燈，持續時間可達240秒，也透過相同方式成功驅動計算機20秒，證實本研究所開發的HSC具有作為儲能元件的實際應用能力，而其所使用之D-WO3@rGO60複合材料，可在高性能儲能領域，提供一條兼具材料創新性與應用導向性的技術路徑，對次世代可攜式與再生能源整合型儲能系統具有重要意義。Facing the challenges of climate change and energy transition, renewable energy has emerged as a key component of future energy systems due to its low carbon emissions and sustainability. However, renewable sources such as wind and solar power are inherently intermittent, making it difficult to ensure a stable power supply. This underscores the urgent need for the development of efficient energy storage technologies. Supercapacitors, with their high power density, rapid charge-discharge capabilities, and long cycle life, show great promise in stabilizing energy supply and demand. This study aims to design an anode electrode material with superior energy storage performance by proposing a novel composite material derived from a tungsten-based metal-organic framework (W-MOF) for use in supercapacitor electrodes. Tungsten, known for its multiple oxidation states (+2 to +6), exhibits high redox activity. Yet, MOF materials with tungsten as the central metal have rarely been studied in depth. In this research, W-MOF was synthesized via a one-step hydrothermal method using tungsten hexachloride (WCl6), pyromellitic acid (PMA), and nitric acid (HNO3). The resulting material was then calcined to form a tungsten oxide-based derivative (D-WO3).To further enhance conductivity and rate performance, reduced graphene oxide (rGO) with varying contents was introduced to form the D-WO3@rGO composite. This material exhibits a combination of electric double-layer and pseudocapacitive energy storage mechanisms. The synergistic effect between the structure of D-WO3 and rGO significantly increases both the specific surface area and electrical conductivity. The D-WO3@rGO60 material prepared in this study exhibits a low electrolyte resistance (Rs) of 2.31 Ω and a charge transfer resistance (Rct) of 0.56 Ω. It achieves a high specific capacitance of 998.8 F g⁻¹ at a current density of 1 A g⁻¹, outperforming D-WO3(350A) (654.2 F g⁻¹), D-WO3@rGO40 (751.2 F g⁻¹), and D-WO3@rGO80 (816.2 F g⁻¹) by factors of 1.53, 1.33, and 1.22, respectivelydemonstrating its excellent capacitive performance. Even at a high current density of 5 A g⁻¹, it retains 40.5% of its capacitance, confirming that rGO incorporation via hydrothermal synthesis effectively enhances the rate capability of D-WO3.Finally, a hybrid supercapacitor (HSC) was assembled using D-WO3@rGO60 as the negative electrode and activated carbon (AC) as the positive electrode. This HSC achieved a high power density of 3000 W kg⁻¹ at an energy density of 15.7 Wh kg⁻¹. It successfully powered 88 parallel-connected red LEDs shaped into the pattern"NTNU ME" for 240 seconds and operated a computer for 20 seconds, demonstrating its practical energy storage capability. The D-WO3@rGO60 composite developed in this study offers an innovative and application-oriented approach for high-performance energy storage, holding significant potential for next-generation portable and renewable-integrated storage systems.