奈米結構與奈米孔洞薄膜之合成與其電化學應用

Synthesis and Electrochemical Applications of Nanostructural and Nanoporous Thin Films

龔仲偉(Chung-Wei Kung)

指導教授 ： 何國川

國立臺灣大學/工學院/化學工程學研究所/博士(2015年)

https://doi.org/10.6342/NTU.2015.10799

摘要

本論文將各種奈米結構與奈米孔洞之電極材料合成於導電基材上，並將所得到之修飾電極應用於多種電化學應用，包含電化學感測器、超電容器、染料敏化太陽能電池的對電極以及電致色變薄膜。
由於一維奈米結構陣列被預期能夠擁有較快的軸向電子傳輸，本論文的第一部分著重在一維奈米結構陣列之電活性材料。透過化學浴沉積法與燒結製程，氧化鈷的一維彎曲針葉狀奈米柱陣列可以被長在導電基材上。此修飾電極被成功應用於非酵素型之電化學葡萄糖感測器，並達到優良的表現。之後，具有三種不同表面結構(一維直立針葉狀奈米柱陣列、二維奈米片、二維網型奈米片)的氧化鈷奈米結構薄膜也被以類似的製程生長在導電基材上，並將之與原本的彎曲針葉狀奈米柱陣列比較。這些修飾電極被應用於電化學催化對乙酰氨基酚之氧化上，而結果發現氧化鈷的一維直立針葉狀奈米柱陣列擁有最好的電催化活性。接著，此氧化鈷的直立針葉狀奈米柱陣列被直接以溶劑熱法的方式轉換為硫化鈷的一維針葉狀奈米柱陣列。受限於其二維的材料特性，硫化鈷平常是很難直接生長出一維奈米結構的。此硫化鈷的一維針葉狀奈米柱陣列被應用於染料敏化太陽能電池的對電極以取代原本使用的白金，所組成的染料敏化太陽能電池可以達到與使用白金時相近的光電轉換效率。在第一部分的最後，透過溶劑熱之陰離子轉換製程，原本利用化學浴沉積法長在導電基材上的層狀碳酸鈷氫氧化物之直立針葉狀奈米柱陣列可以被轉換為氧化鈷的針葉狀奈米管陣列。利用奈米管具有比奈米柱較高之表面積的優勢，相對於透過燒結得到的氧化鈷針葉狀奈米柱陣列，此氧化鈷的針葉狀奈米管陣列可展現高出許多的比電容值。
另一方面，二維奈米結構被預期能夠展現較一維奈米結構高的表面積。在本論文的第二部分，將針對具電化學活性之二維奈米結構薄膜進行探討。透過定電位電鍍與紫外光臭氧的製程，二維之氧化鈷奈米片的薄膜可以被生長在可撓之鈦金屬基材上。此氧化鈷薄膜在超電容的應用上，可以在2.5 A/g的充放電電流之下達到1,033.3 F/g的比電容值。另外，透過以氧化鋅的微米花陣列當作模板，由許多二維空心奈米花瓣之聚3,4-二氧乙烯噻吩所組成的空心微米花陣列可以被生長在導電基材上。此具有二維奈米結構之聚3,4-二氧乙烯噻吩被預期可以提供許多的電催化位置，因此在應用於染料敏化太陽能電池的對電極時可以獲得優良的表現。
除了具奈米結構的材料之外，本論文也將探討擁有更高表面積的奈米孔洞材料。在所有分類的孔洞材料中擁有最高表面積的金屬有機骨架在本論文的最後一部分被選作電極材料。由鋯金屬節點與芘類有機連結器所組成的金屬有機骨架之一維針葉狀奈米柱薄膜可以長在導電玻璃基材上。這些芘類有機連結器具有電化學活性並且可以展現電致色變的行為。由於一維針葉狀奈米柱的奈米結構可以提供較快的軸向電荷傳輸速率，再加上此金屬有機骨架之中的規律一維孔洞可以提供迅速的離子傳輸，此金屬有機骨架薄膜可以展現快速且可逆的電致色變性質。為了尋求在水溶液中也可以進行電化學操作並且穩定的金屬有機骨架薄膜，另外一種由鋯金屬節點與具電活性的紫質類有機連結器所組成的金屬有機骨架之均勻薄膜被以溶劑熱法的方式成長在導電基材上。本研究發現此金屬有機骨架薄膜在水溶液中具備電化學活性及穩定性，進而開闢出許多適用於各種水相系統中的電化學應用。

關鍵字

針葉狀奈米柱 ； 染料敏化太陽能電池 ； 電化學感測器 ； 電致色變 ； 金屬有機骨架 ； 超電容器

並列摘要

In this dissertation, various nanostructural and nanoporous electrode materials were synthesized directly onto the conducting substrates, and the obtained modified electrodes were applied for various electrochemical applications, including electrochemical sensors, supercapacitors, counter electrodes (CEs) of dye-sensitized solar cells (DSSCs), and electrochromic thin films.
Since one-dimensional (1D) nanostructural arrays are expected to show a faster electronic conduction along the axial direction through the arrays to their substrate, 1D nanostructural arrays of electroactive materials were focused in the first part of this dissertation. The 1D bending acicular nanorod arrays (ANRAs) of cobalt oxide (Co3O4) were grown on conducting substrates by using chemical bath deposition (CBD) followed by calcination. The bending Co3O4 ANRAs were successfully applied for non-enzymatic electrochemical glucose sensors and achieved a promising performance. Thereafter, three different morphologies of Co3O4 nanostructural thin films, including the 1D straight ANRAs, 2D nanosheets, and 2D net-shaped nanosheets, were also grown on conducting substrates by similar approaches and compared with the original bending ANRAs. The electrocatalytic activities of these Co3O4 thin films for the oxidation of acetaminophen (AP) were investigated, and the result shows that the 1D straight ANRAs of Co3O4 exhibit the best electrocatalytic activity among them. Thereafter, the straight Co3O4 ANRAs were solvothermally converted into the 1D ANRAs of cobalt sulfide (CoS), which is very difficult to be grown as 1D nanostructure due to its two-dimensional (2D) nature. The obtained CoS ANRAs were used as the CEs of DSSCs to replace the conventional CE using platinum, and the obtained DSSC shows comparable cell efficiency compared to the DSSC using platinum. In the end of the first part of this dissertation, a solvothermal anion-exchange process was used to convert the straight ANRAs of layered cobalt carbonate hydroxide (LCCH), which were grown on conducting substrates by CBD, into the Co3O4 acicular nanotube arrays (ANTAs). Taking advantages of the higher surface area provided by nanotubes compared to that provided by nanorods, the Co3O4 ANTAs show a much higher specific capacitance compare to the original Co3O4 ANRAs obtained by calcining the LCCH ANRAs.
On the other hand, 2D nanostructures are expected to exhibit a higher surface area compared to the 1D nanostructures. In the second part of this dissertation, 2D nanostructural thin films of electrochemically active materials were explored. Thin films of Co3O4 2D nanosheets were electrodeposited on flexible titanium substrates by a potentiostatic method, followed by an UV-ozone treatment. The obtained thin film of Co3O4 nanosheets was applied for supercapacitors; a high specific capacitance of 1,033.3 F/g was obtained at a charge-discharge current density of 2.5 A/g. Also, poly(3,4-ethylenedioxythiophene) (PEDOT) hollow microflower arrays (HMFAs), with several 2D hollow nanopetals on each of the microflowers were fabricated on a conducting substrate, by using ZnO microflower arrays (MFAs) as the template. The 2D nanostructures of PEDOT are expected to provide numerous electrocatalytic sites, which result in the promising performance when they were utilized as the CEs of DSSCs.
Beyond the nanostructural materials, the nanoporous materials which possess even higher surface area started to be considered. Metal-organic frameworks (MOFs), which show the highest surface area among all categories of porous materials, were chosen as electrode materials in the last part of this dissertation. Thin films composed of 1D acicular nanorods of a MOF constructed from zirconium-based nodes and pyrene-based linkers were grown on conducting glass substrates. The pyrene-based linkers are electrochemically active and show electrochromic behavior. Due to the fast charge-transport rate provided by the 1D acicular nanorods and the facile ion diffusion in regular 1D pores of the MOF, the obtained MOF thin film can exhibit facile and reversible electrochromism. In order to make a MOF thin film that is electrochemically addressable and stable in aqueous solutions, uniform thin films of another MOF, which is constructed from the electrochemically active porphyrin linkers and zirconium-based nodes, were solvothermally grown on conducting substrates. The MOF thin films were found to be electrochemically addressable and stable in aqueous solution, which opens up several opportunities for utilizing such MOF thin films in various electrochemical applications operated in aqueous systems.

並列關鍵字

Acicular nanorods ； Dye-sensitized solar cells ； Electrochemical sensors ； Electrochromism ； Metal-organic frameworks ； Supercapacitors

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