微波輔助法合成四氧化三鈷/石墨烯奈米複合材料製作超級電容器之研究

Microwave-assisted synthesis of cobalt oxide/graphene nanocomposite for supercapacitors

吳維瀚(Wei-Han Wu)

指導教授 ： 劉宗平

元智大學/電機通訊學院/光電工程學系/碩士(2012年)

摘要

超級電容器是一種高循環壽命的儲能元件，它具有高效率的充放電能力。在很小的區域內，可以得到法拉級的電容量。由於石墨烯內載子的傳輸速率高，這可以大幅縮短充電的時間。利用石墨烯合成奈米複合材料製作而成之電極，可兼具高能量密度與高功率密度。在未來，它將成為一個重要的能源存儲元件。
在實驗的過程中，採用四氧化三鈷/石墨烯奈米複合材料作為活性物質，來製作超級電容器的半電極。製作電極的過程，可分為三個部份。首先，採用改良式Hummers法製備氧化石墨烯。其次，再利用微波輔助合成法，製備四氧化三鈷/石墨烯奈米複合材料的前驅物。最後，高溫還原後，將前驅物粉末混合成為電化學材料，然後製作成電極。
在此研究中，選擇微波功率、微波時間及還原溫度作為參數，來探討電極的性質。透射式電子顯微鏡照片顯示，四氧化三鈷之球形粒子均勻地分佈在石墨烯薄片上，且其晶粒之大小約為20-40 nm。採用循環伏安法（CV），在掃描速率為10 mV/s時所獲得的最大電容量為329 F/g。通過定電流充放電測試，所獲得最大的能量密度和功率密度分別為7.3 W-h/kg及 0.488 kW/kg。
總結而言，製備活性物質的最佳參數：微波功率為700 W、微波時間為60 min、還原溫度在400 ℃。最終，所合成電化學材料的最佳成分比例為活性物質：碳黑：聚偏氟乙烯等於7：2：1。

關鍵字

石墨烯 ； 奈米複合材料 ； 微波輔助法 ； 電極 ； 超級電容器

並列摘要

The supercapacitor is an energy storage device of high cycle life, which has a high efficiency capacity of charging and discharging. In a small region, a capacitance with an order of Faraday can be obtained. Since the transport rate of carriers in graphene is high, this can significantly shorten the charging time. The electrode made of nanocomposite material with graphene synthesis has high energy density and power density; it becomes one of the important energy storage devices in the future.
In experimental process, Co3O4/graphene nanocomposites were used as active substances to fabricate the half-electrode of supercapacitors. The process for fabricating the electrode can be divided into three parts. Firstly, the modified Hummers method is used to prepare of graphene oxide. Secondly, the precursors of Co3O4/graphene nanocomposite material can be prepared by microwave-assisted synthesis. Finally, after reduction at high temperature, the precursor powder was mixing become electrochemical materials and then made into the electrode.
In this study, the microwave power, the microwave time, and the reduction temperature are selected as parameters to explore the properties of the electrode. Transmission electron microscope photographs show that spherical particles of Co3O4 are uniformly distributed on the graphene sheet and their grain sizes are approximately 20-40 nm. By using the cyclic voltammetry (CV), the maximum capacitance obtained at a scanning rate of 10 mV/s is 329 F/g. Through galvanostatic charge/discharge tests, the maximum of the energy density and the power density obtained are respectively 7.3 W-h/kg and 0.488 kW/kg.
In summary, the optimized parameters for synthesizing active substances are the microwave power of 700 W, the microwave time of 60 min, the reduction temperature at 400 ℃. Consequently, the optimal composition ratio of electrochemical materials is active material: carbon black: polyvinylidene fluoride (PVDF) equal to 7:2:1.

並列關鍵字

supercapacitor ； graphene ； nanocomposite ； microwave-assisted method ； electrode

參考文獻

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