利用水熱法生長鎳氧化物於噴塗式奈米碳管之超級電容研究

Study on the Hydrothermally-Grown Nickel Oxides on the Sprayed Carbon Nanotubes for the Supercapacitors

石雅琪(Ya-Chi Shih)

指導教授 ： 鄭晃忠

國立交通大學/電機學院/電子工程系所/碩士(2019年)

摘要

超級電容(Supercapacitors, Ultracapacitors, Electrochemical Capacitors)由於其優異的電氣特性，像是：充電速率短，功率密度高，可靠性高，循環壽命長和安全性高，進而成為目前最具創新性和吸引力的儲能設備。因此，它們被認為是目前最具有展望性的儲能裝置。但由於目前技術無法使它們的能量密度超越鋰離子電池，造成超級電容應用受到限制，因此提升超級電容的能量密度為目前研究的主流。
根據超級電容存儲原理，主要分成兩種形式：雙電層電容器(Electric Double Layer Capacitors)和擬電容器(Pseudocapacitors)。在新穎的超級電容應用中有一種提高整體電特性，亦可以維持循環穩定性的方式，即是將上述兩種類型結合成為混合結構的超級電容。有鑑於此，本論文希望能結合奈米碳管(Carbon Nanotubes)和氧化鎳(Nickel Oxide)，以製作成混合結構之超級電容電極，來達到提升比電容值(Specific Capacitance)的目的。本論文共分為四個部分：第一部分將利用低溫水熱法成長二維結構的氫氧化鎳於奈米碳管薄膜上，第二部分利用低溫水熱氫氧化鎳混合六亞甲基四胺(Hexamethylenetetramine, HMTA, C6H12N4)製作於奈米碳管薄膜上，以形成三維結構，第三及第四部分將這兩者的最佳參數進行退火處理，以提升奈米碳管薄膜上的二維氧化鎳結構及三維氧化鎳混合HMTA結構之特性。
首先，討論不同六水合硝酸鎳濃度和不同水熱法生長時間製作的超級電容電極對於比電容值和其他電特性的影響。本研究分別利用掃描電子顯微鏡(SEM)，穿隧式電子顯微鏡(TEM)，能量色散X-射線光譜(EDX)和X射線光電子能譜(XPS)，以分析在奈米碳管薄膜上製備的二維氫氧化鎳結構表面形態和化學鍵合。此外，透過循環伏安法(Cyclic Voltammetry Measurement)，充電和放電時間(Charge and Discharge Time)，電化學阻抗譜(Electrochemical Impedance Spectroscopy, EIS)和在不同的掃描速率下之測量(Different Scan-Rate Measurement)來研究在奈米碳管薄膜上合成的二維氫氧化鎳電特性。利用濃度為0.5 M之六水和硝酸鎳，進行30分鐘的水熱法處理後所獲得之二維氫氧化鎳薄膜可以使比電容值提高到912 F/g。根據SEM圖像的觀察結果，我們認為不同濃度的六水合硝酸鎳會影響的是成核點的數量，而不同的水熱法生長時間會影響的則是二維氫氧化鎳薄膜的生長大小。
第二部分中，為了可以獲得更佳的超級電容特性，本論文引入「添加HMTA來將二維氫氧化鎳的結構改變為三維」之概念，以大幅提升整體的比電容值。這部分討論了在0.1 M之六水合硝酸鎳情況下，HMTA添加的多寡和水熱法生長時間長短對於比電容值的影響。為了證明水熱法處理後會有Ni(OH)2的存在，我們對其進行SEM和XPS等料分析來對表面形貌進行探討。通過SEM圖像，我們提出了HMTA添加比例對電性能的影響。在六水合硝酸鎳與HMTA的溶液比例為20：1的情況下，將會形成更立體的三維結構，提供電解質離子進行反應的傳輸通道，使得整體比電容值大幅提高。將噴塗在鈦基板上奈米碳管薄膜浸泡到0.1 M六水合硝酸鎳與0.005 M 的HMTA混合溶液中，並以水熱法沉積30分鐘，可以將比電容值提高到1481 F/g。
在最後兩章節中，將對前兩部分最佳參數的條件進行退火處理，讓Ni(OH)2轉換為NiO。這部分也進行了一系列電特性分析，例如：CV量測，循環穩定性測試，以觀察將奈米碳管上製備的Ni(OH)2轉換為NiO是否會對電性能有所改善。此外，還進行了XPS分析，以進一步確認退火後Ni(OH)2是否成功轉變為NiO。結果所示，退火過程不僅轉換晶相，還能提高比電容值。最重要的是，退火程序亦可改善附著性，將循環穩定性提高約2至3倍，並確保在不同掃描速率下，CV曲線的形狀仍可以維持良好的氧化還原峰。經過300 °C的3小時退火處理後，原先在0.5 M的六水合硝酸鎳進行30分鐘水熱法處理的樣品之比電容值可以從912 F/g提升至1593 F/g。另一方面，經過300 °C的3小時退火處理後，原先在0.1 M 六水合硝酸鎳添加0.005 M HMTA的混合溶液中，進行30分鐘水熱法處理的樣品之比電容值可以從1481 F/g提升至1763 F/g。因此，我們認為三維的奈米碳管/氧化鎳/HMTA混合結構將是未來在超級電容應用中最有前景的混合結構電極。

關鍵字

超級電容 ； 鎳氧化物 ； 奈米碳管 ； 水熱法

並列摘要

Supercapacitors have become the most innovative and attractive energy storage device owing to their excellent electrical characteristics such as short charging rate, high power density, high reliability, long cycle life, and safety. Therefore, they are considered as the most promising energy storage device in the next generation. However, they are limited since their energy density has not been able to surpass that of the lithium-ion batteries, so increasing the energy density of the supercapacitor is the current research mainstream.
There are two types of supercapacitors based on storage principle: Electric Double Layer Capacitors (EDLCs) and pseudocapacitors. In novel supercapacitors application, combining the two types mentioned above to increase promote the specific capacitance and the other electrical characteristics is considered to be a potential method. Therefore, the hybrid structure electrode combined with carbon nanotubes and nickel oxide(NiO) was utilized herein. There are four parts of this thesis: the first part is using the low-temperature hydrothermal method to grow 2-D structure of nickel hydroxide (Ni(OH)2) on the CNT thin films, while the second part using the low-temperature hydrothermal Ni(OH)2 with HMTA on the CNT thin films to obtain 3-D structure. The third and fourth parts is to anneal the best parameters of the former two parts to enhance the character of the 2-D NiO on CNT thin films and the 3-D NiO with HMTA on CNT thin films.
First, the influences of specific capacitance and other electrical properties of supercapacitor electrodes synthesized with different nickel nitrate hexahydrate (Ni(NO3) · 6H2O) concentrations and different hydrothermal growth times were discussed. A series of material analyses including scanning electron microscopy (SEM), transmission electron microscopy (TEM), EDS mapping and X-ray photoelectron spectroscopy (XPS) were used to analyze the surface morphology and chemical bonding of the nickel hydroxide synthesized on the CNTFs. Besides, Cyclic Voltammetry measurement (CV), charge and discharge time, Electrochemical Impedance Spectroscopy (EIS), and different scan rate measurements were used to investigate the electrical property of the nickel hydroxide synthesized on the CNTFs. The Csp would be promoted to 912 F/g with the 2-D Ni(OH)2 thin film synthesized by hydrothermal treatment with 0.5 M Ni(NO3) · 6H2O for 30 minutes. According to the observation results of SEM images, we consider that different Ni(NO3) · 6H2O concentrations affect the number of nuclei sites, while different hydrothermal growth times affect the size of the growth.
Changing the structure of Ni(OH)2 into a 3-D structure by adding HMTA was an ideal strategy to get better supercapacitor performance, so this idea was introduced to this thesis in order to further increase the Csp performance of the CNTFs in the second part. The influences of the HMTA adding ratio and hydrothermal reaction time of hydrothermal deposition on the Csp were discussed in this part. The material analyses including SEM and XPS were used to analyze the surface morphology and prove the existence of Ni(OH)2 after hydrothermal treatment. By comparing the SEM images, we proposed the effect of the HMTA adding ratio on the electrical properties. The ratio of 20:1 solution forms better 3-D structures, providing the transportation channel for electrolyte ions to reaction, and having better specific capacitance. The specific capacitance can be promoted to 1481 F/g through 0.1 M Ni(NO3) · 6H2O + 0.005 M HMTA hydrothermal treatment for 30 minutes.
In the last two sections, the best parameter samples of the previous two parts would be annealed, and the samples will be converted from Ni(OH)2 to NiO. A series of electrical analyses including CV measurement, cycling performance were used to observe if the conversion of Ni(OH)2 to NiO synthesized on the CNTFs would improve the electrical properties. Moreover, XPS analysis was also performed to further confirm whether Ni(OH)2 was successfully converted to NiO after annealing. The results showed that the annealing process not only converts the crystal phase but also increases the specific capacitance. The specific capacitance of sample under 0.5 M Ni(NO3) · 6H2O hydrothermally treated for 30 minutes can be promoted from 912 to 1593 F/g through 300 °C annealing treatment for 3 hours. On the other hand, the specific capacitance of sample under 0.1 M Ni(NO3) · 6H2O + 0.005 M HMTA hydrothermally treated for 30 minutes can be promoted from 1481 to 1763 F/g through 300 °C annealing treatment for 3 hours. Furthermore, the annealing procedure could improve the adhesion, enhance the cycle stability by approximately 2 to 3 times and ensure that the CV profile well maintained under different scan rate. Therefore, we believed that the CNTFs/nickel oxide/HMTA hybrid structure would be a promising electrode for use in supercapacitor applications.

並列關鍵字

Supercapacitors ； Nickel Oxide ； Carbon Nanotubes ； Hydrothermal Method

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