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標題: | a-氫氧化鎳/石墨烯衍生物及a-氫氧化鎳/脫層奈米蒙托土混摻複合材料於高效能超級電容電極之製備與應用 Fabrication and application of a-Ni(OH)2/graphene derivative and a-Ni(OH)2/exfoliated montmorillonite composites and their hybrids for high-performance supercapacitor electrodes |
作者: | Ching-Ting Tai 戴晶婷 |
指導教授: | 林金福(King-Fu Lin) |
關鍵字: | 超級電容,氫氧化鎳,鋁基取代,氧化石墨烯,還原氧化石墨烯,脫層蒙托土,泡沫鎳電極, Supercapacitor,Nickel Hydroxide,Al-substituted,Graphene Oxide,Reduced Graphene Oxide,Exfoliated Clay,Nickel Foam, |
出版年 : | 2016 |
學位: | 碩士 |
摘要: | 近年來超級電容的發展可歸因於高功率密度、長效穩定性、可瞬間充放電之性質,為了更進一步縮短充放電時間,提高能量密度以及在高電流密度下的電容保持率,本論文利用簡單且對乾淨的化學析出法製備出一種被鋁基局部取代的a相氫氧化鎳(Al-Ni(OH)2),作為超級電容之工作電極,再藉由額外添加石墨烯衍生物(氧化石墨烯、還原氧化石墨烯、 改質之帶正電石墨烯、改質之帶正電還原氧化石墨烯)和脫層奈米蒙托土作為氫氧化鎳的成核基板,成功合成出氫氧化鎳複合材料。此外,若將exMMT/Al-Ni(OH)2與石墨烯衍生物/Al-Ni(OH)2這兩種複材混合可再製成Al-Ni(OH)2混摻複合材料,其在高電流密度下擁有較高的電容保持率與穩定性。
上述之石墨烯衍生物與脫層蒙托土由以下方法所製成,氧化石墨烯(GO)是由modified Hummers method製成,再藉由添加聯氨使GO還原為還原氧化石墨烯(rGO),若再將乙二胺加入GO與rGO的溶液中,可以利用化學改質法製成帶正電石墨烯(GO+)與帶正電還原氧化石墨烯(rGO+)。脫層蒙托土(exMMT)則是由本實驗室的無乳化劑聚合法製備而成,接著在a相氫氧化鎳合成過程中加入四種不同重量百分比(0.8%, 1.59%, 3.13%, 6.09%)的添加物,便可得到相氫氧化鎳與石墨烯衍生物及脫層奈米蒙托土之複合材料。 本實驗利用XRD、TEM、SEM、Raman等儀器分析材料特性,再進一步利用GCD、CV、EIS測量電化學性質。由實驗結果發現,那些帶負電之複材(GO/Al-Ni(OH)2, rGO/Al-Ni(OH)2, and exMMT/Al-Ni(OH)2),氫氧化鎳奈米薄片會散亂地直立在添加物上,呈現一個3D孔隙結構。然而,對於那些帶正電之複材(GO+/Al-Ni(OH)2 and rGO+/Al-Ni(OH)2),表面卻呈現相對平坦的形貌,我們甚至觀察到rGO+/Al-Ni(OH)2 有局部層狀堆疊結構。所有複材中,以1.59% GO/Al-Ni(OH)2表現最為優異,在1A/g之電流密度,電容值高達2759.32 F/g,在20A/g尚餘1279.94 F/g,電容保持率為46%。1.59% GO/Al-Ni(OH)2相較於純Al-Ni(OH)2,在1A/g與20A/g下電容值分別高出30%與70%,這個結果可以用兩個理由解釋:(1) 3D結構提供較高的比表面積讓電解液與電極材料接觸,大幅增加有效氧化反應面積。(2)氧化石墨烯在合成過程中還原為還原氧化石墨烯,故能大幅增加氫氧化鎳複合材料之導電性。 在Al-Ni(OH)2混摻複合材料中,exMMT/Al-Ni(OH)2與rGO+Al-Ni(OH)2 以重量比1:1混摻時,具有最突出的電容表現,在1A/g之電流密度,電容值為2498.81 F/g,在20A/g尚餘1760.76 F/g,電容保持率高達70%。由EIS結果我們發現,將兩種不同的複材混摻後,Rct大幅度下降,幾乎與1.59% GO/Al-Ni(OH)2之Rct相等。推測原因是由於exMMT和rGO+表面所帶之相反電荷造成庫倫引力作用,使兩種複材在混摻過程中吸附在一起。在這個混摻複合材料中,exMMT的陽離子交換特性有利於電解液之擴散,而rGO+則可增加整體複材之導電度,因此,Al-Ni(OH)2混摻複合材料的特殊結構能有效提升電化學之氧化還原反應動力學,成功製備出一種高效能超級電容之電極材料。 In recent years, supercapacitor has attracted significant attention by its superior performance such as high specific power, long lifecycle, short charging time, and environment-friendly. To improve the specific energy, rate capability, and cycle stability of electrode materials for supercapacitor, in this thesis a facile one-step solution precipitation method was conducted to prepare 3D structural Al-Ni(OH)2 composites in a-phase. The composites are composed of Al-Ni(OH)2 and 2D supporting additives (graphene oxide, reduced graphene oxide, modified graphene oxide with positive charges, modified reduced graphene oxide, and exfoliated montmorillonite). In addition, the “Al-Ni(OH)2 composite hybrid” as a final product is made by mixing with two composites: graphene-based materials/Al-Ni(OH)2 and exMMT/Al-Ni(OH)2, and it provides new properties and high performance. The 2D supporting additives are prepared by the following methods. The graphene oxide (GO) is prepared by modified Hummers method and then reduces it with hydrazine as reducing agent to obtain reduced graphene oxide (rGO). The functionalized GO and rGO with positive charges (GO+ and rGO+, respectively) was made by chemical modification with ethylenediamine. Furthermore, the exfoliated montmorillonite (exMMT) is fabricated through soap-free emulsion polymerization of methyl methacrylate (MMA) in the presence of montmorillonite. The Al-Ni(OH)2 based composites are fabricated by controlling the additives mass ratio with 0.8%, 1.59%, 3.13%, and 6.09%. XRD, TEM, SEM, Raman, and electrochemical measurements including GCD, CV, and EIS are used to characterize the Al-Ni(OH)2 based materials. The surface morphology of those composites with negatively charged substrates (GO, rGO, and exMMT) were a 3D open-porous nanostructure constructed by randomly decorated Al-Ni(OH)2 nanosheets as building blocks. Whereas, for those with positively charged substrates (GO+ and rGO+), the relatively flat structure was observed. Among these composites, the best one was 1.59% GO/Al-Ni(OH)2 (GO accounts for 1.59wt% of this composite) with 2759.32 F/g at 1A/g and 1279.94 F/g at 20A/g with a capacitance retention of about 46%. The specific capacitance at 1 A/g and 20 A/g were 30% and 70% higher than that of pure Al-Ni(OH)2, respectively. This improved capacitance could be explained by both the increasing effective redox areas related to 3D porous morphology and enhanced conductivity by incorporating graphitic sheet. In the hybrid system, the exMMT/Al-Ni(OH)2 and rGO+/Al-Ni(OH)2 hybridized in 1:1 mass ratio showed the highest specific capacitance with 2498.81 F/g at 1A/g and retained 1760.76 F/g at 20A/g with a significantly improved capacitance retention of about 70%. Note that after the hybrid process, Rct dramatically decreased and almost equaled to the Rct of 1.59% GO/Al-Ni(OH)2. It is presumable that exMMT nanosheets would raise ionic transportability and rGO+ sheets enhanced electrical conductivity. Therefore, such Al-Ni(OH)2 hybrid is an excellent choice for high-performance supercapacitor electrode. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/48797 |
DOI: | 10.6342/NTU201603701 |
全文授權: | 有償授權 |
顯示於系所單位: | 材料科學與工程學系 |
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