氧化沉積法製備可調微結構之釕基氧化物於超電容上的應用

Oxidation Precipitation of Porous Ruthenium-Based Oxides with Tunable Microstructures for Supercapacitors

陳怡利(I-LI CHEN)

指導教授 ： 胡啟章

國立清華大學/工學院/化學工程學系/博士(2014年)

摘要

本研究結合化學氧化沉澱法以及後熱處理之方法來製備可調微結構與多孔性釕基氧化物並將其應用於超高電容器。在此研究，我們提供一個系統性的實驗平台來深入探討氧化物的結構、表面型貌以及電化學充放電之機制。因此，本研究焦點著重於藉由摻雜鈦元素和界面活性劑修飾釕氧化物的電容特性。
第一部分介紹透過化學氧化沉澱法合成釕鈦雙元氧化複合物，伴隨著後續溫度範圍從150至300oC熱退火處理。X光吸收光譜結果可看出熱處理使得部分鈦原子佔據八隅體RuO6結構的特定位置而固溶到二氧化釕之結構。這現象導致原本二氧化釕晶格扭曲，並產生額外的電化學活性位置。因此電化學結果可以發現釕鈦氧化物經200oC熱處理後與純二氧化釕相比，能有最佳的比電容值（約是純二氧化釕經200oC熱處理後的1.5倍），同時也擁有較好的電容維持率。另一方面，藉由高溫(大於250oC)熱退火情況下，因為摻入的鈦原子提供一個異相介面導致釕鈦氧化物奈米柱沿著二氧化釕晶面的c軸方向成長出來。
在第二部分中結合不同的介面活性劑如Pluronic F127和溴化十六烷三甲基銨（CTAB），並透過後續的熱退火步驟製備沿著{101}面擇優取向方式成長的二氧化釕。基於異質表面化學的觀點，擇優取向沿著{101}面生長的二氧化釕，是由於表面活性劑的鏈結對二氧化釕較高表面能的晶面產生吸附所致，此現象在經過熱退火處理後產生大量沿著{101}面生長的二氧化釕。Pluronic F127的系統可明顯的發現比電容與電容維持率的提升是由於{101}結晶面上佈滿著金屬態的釕原子，而這些金屬態的釕原子可增加電子的傳遞效率進而增進活性。另外， CTAB的系統中，電化學性能的提升是由於殘餘的介面活性劑於在二氧化釕的奈米顆粒表面形成離子和電子導電的緩衝層或局部形成二氧化釕的奈米結晶。
為了進一步增加電容特性，系統性的組合摻雜鈦原子與介面活性劑 (Pluronic F127 和CTAB) 於二氧化釕結構中。因此，經由相同化學氧化沉澱方式合成Pluronic F127或CTAB的釕鈦雙元氧化物。初步結果表示，藉由Pluronic F127或CTAB改質的釕鈦氧化物其電容提升除了摻雜的鈦增加其電化學活性位置，並且有著界面活性劑的輔助，得以促進各種方向的異相結晶和提高分散性的奈米氧化物。

關鍵字

二氧化釕 ； 釕鈦氧化物 ； 奈米柱 ； 擇優取向成長 ； Pluronic F127 ； 溴化十六烷三甲基銨 ； X-ray吸收光譜 ； 超高電容器

並列摘要

The aim of this study is to utilize chemical oxidation precipitation method accompanied by the post thermal conditioning for the synthesis of porous ruthenium-based oxides with tunable microstructure. Here, we provide a systematic platform to meet our experimental concepts for the better understanding of dependency between structure, surface morphology and electrochemical charge-discharge mechanism. Hence, our spotlights focus on the investigation of RuO2 electrochemical performance enhancement by the incorporation of second Ti dopants and the modification by templating surfactants.
In the 1st part, a binary ruthenium-titanium (Ru-Ti) oxide nanocomposite has been synthesized through chemically oxidative precipitation method, followed by the thermal annealing treatment at different temperatures ranging from 150 to 300oC. X-ray absorption spectroscopy (XAS) demonstrates that a minor amount of Ti atoms are incorporated into crystalline RuO2, which partially occupy Ru sites in the octahedral RuO6 structure. This would induce the distortion of original RuO2 lattice and generate additional electrochemically active sites. Therefore, it is found that Ru-Ti oxides annealed at 200oC exhibits much higher specific capacitance (near 1.5 fold improvement) and better capacitance retention relative to pure RuO2. On the other hand, the growth of RuO2 nanorods has been thermally induced from binary Ru-Ti oxides at a higher annealing temperature region (> 250oC) since the presence of incorporated Ti dopants provide an inhomogeneous interface for facilitating the crystallization and growth of RuO2 along c-aixs to form Ru1-TiO2 nanorods.
In the 2nd part, we demonstrates that the combination of different surfactants containing Pluronic F127 along with cetyltrimethylammonium bromide (CTAB), and post annealing treatment can prepare well-crystalline RuO2 with the preferential orientation growth of facet {101}. Based on the heterogeneous surface chemistry viewpoints, the preferential orientation growth along the {101} facet of RuO2 is due to the adsorption of ligands of surfactants on the higher surface energy facets and it is proposed to promote the prosperous crystal growth along the {101} plane. Apparently, in F127 system, the specific capacitance and capacitance rate-retention are promoted substantially since the topmost surface of facet {101} is occupied by Ru atoms, probably favoring the construction of the electron pathways. Besides, in the case of CTAB system, the electrochemical performance enhancement is owing to the transformation of residue polymer into ionic and electronic conducting buffer layer on the topmost surface of RuO2 nanoparticles or locally robustness formation of RuO2 nanocrystallites.
In order to further promote the capacitive property, the synergy combination of Ti intercalation and surfactants introduction has been executed. As a consequence, the synthesis of Ru-Ti oxides trapped with Pluronic F127 or CTAB has been prepared by virtue of the identical approach. It is suggested that the specific capacitance of Ru-Ti oxides modified with F127 or CTAB is considerably enhanced because of the synergistic effects from Ti incorporation to create more electrochemical sites and surfactant assistance to promote the anisotropic crystal growth along with well dispersion of oxide nanoparticles.

並列關鍵字

Ruthenium oxides ； Ruthenium - Titanium oxides ； Nanorods ； Preferential orientation growth ； Pluronic F127 ； Cetyltrimethylammonium bromide ； X-ray absorption spectroscopy ； Supercapacitors

參考文獻

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