Development of Multi-element Nanocatalysts and Nanocomposites for Direct Methanol Fuel Cell and Advanced Eenergy Applications

發展多元奈米觸媒粒子及奈米複合材料及應用於直接甲醇燃料電池等能源相關科技應用

陳燦耀(Tsan-Yao Chen)

指導教授 ： 林滄浪

國立清華大學/原子科學院/工程與系統科學系/博士(2009年)

摘要

In this thesis, three types of hybrid nanocomposites including nanocatalysts-carbon nanotube, metal-silica-polymer porous materials, and metal nanowire/titanium oxide nanoparticle electrode were developed for the applications of direct methanol fuel cell (DMFC), direct glucose bio-fuel cell (DGBFC), and dye-sensitized solar cell (DSSC), repectively. The DMFC electrode was fabricated by combining the nanocatalysts synthesis, multi-walled carbon nanotube (MWCNT) growth, MWCNT surface functionalization treatments, and the nanocatalysts dispersion techniques. The output power of the fabricated DMFC stack with Pt nanocatalysts dispersed on MWCNT by surface modification treatment as the electrode of the membrane-electrolyte-assembly (MEA) was improved by more than 300% (from 4.6 to 20.1 mW/cm2). For the applications in DSSC, in order to improve the electron conduction, TiO2 coated silver nanowires were added in the TiO2 electrode thin film at silver nanowires ~1.4 – 1.5 wt% and conventional titanium oxides nanoparticles P25 at ~98 wt%. Photo-excited electrons can be efficiently transferred to the electrode through the network of the dispersed metallic nanowires added in the anode. We compared the photovoltaic performance with the anodes of standard P-25, the silver nanowire/P-25, and the TiO2 coated silver nanowire/P-25 DSSC. The DSSC with TiO2 coated silver nanowires shows significantly improved (about 1.5 and 2.0 times) photovoltaic efficiency and structural durability compared with that of the standard P-25 and the silver nanowires without coating DSSC. The TiO2 coated silver nanowire can resist the redox chemical corrosions by iodide ions since they are protected from contact with electrolytes during the photovoltaic reaction by the coated thin TiO2 layer. The presence of the metal network (silver nanowires) improves the production and transportation of light generated current so as to the photovoltaic efficiency. For Developing bio-friendly composites as the anode for supporting enzyme is the main research goal in DGBFC researches. A low metal loading (~10 – 15%) and highly conductive hybrid porous nanocomposite containing polyvinylpyrrolidone, silica, and Ag was synthesized using a novel solid-state polyol reduction process. This hybrid nanocompsoite was initially solidified by sol-gel reaction then heat-treated at 160˚C in ambient environment. The dark-glassy transparent hybrid nanocompsoite turned into silver reflective appearance after the heat-treatment. The resulted solid film showed drasmatic increase in electrical conductivity by about 5 millions folds. The synthesized nanocomposite can be used as a new silica-based electronic conductor with low metal loading and bulk density.

關鍵字

奈米複合材料 ； 直接甲醇燃料電池 ； 奈米觸媒 ； 生物燃料電池 ； 染料敏化太陽能電池 ； X 光吸收光譜 ； 小角度X 光散射

並列摘要

本研究論文主軸為開發可應用於先進能源科技(如甲醇氧化燃料電池、生物燃料電池以及太陽能電池)之金屬-碳/矽/鈦氧化物奈米複合材料。研究進程包含整合材料設計、製造方法、元件組裝與結構、特性分析等步驟。內容包含三項奈米複合材料之系統分別為:1.可應用於甲醇氧化燃料電池(Direct Methanol Fuel Cell, DMFC)之奈米金屬觸媒粒子/奈米碳管複合結構; 2.可應用於生物燃料電池(Direct Glucose Bio-Fuel Cell, DGBFC)之多孔隙奈米金屬/矽氧化物複合結構; 以及3.可應用於太陽光-電能轉化電池(Dye Sensitize Solar Cell, DSSC)之奈米金屬/鈦氧化物複合結構。
在DMFC系統中，控制金屬奈米觸媒粒子之原子結構、製做具有多孔隙導電電極以及改善觸媒粒子在與電極材料上之分散性、附著性將為提升元件工作效率之關鍵因素。其中金屬奈米粒子之原子結構以改變反應組成與反應程序等規畫方法控制，結果顯示白金/銠(Pt/Ru)之雙元奈米粒子之尺寸隨白金組成增加。改變反應組成可製備雙元合金系統，其中白金原子傾向分布在粒子表面隨組成增加逐步主導粒子之晶體結構。改變反應程序則可製作具有白金殼-銠核結構之雙元奈米粒子，其白金原子將透過兩種化學反應在銠顆粒表面成長:1.白金離子受熱活化之乙二醇分子(醛基)在銠顆粒表面還原; 2.白金離子以氧化電位差與銠金屬原子發生交換反應還原在顆粒表面。DMFC的陽極系統利用奈米金屬觸媒粒子在奈米碳管表面分散製做，過程輔以碳管表面硫化改質技術顯著提升觸媒粒子之表面之分散性使得全電池輸出功率得以提升300%以上(由4.6到20.1 mW*cm-2, 金屬含量約0.5 mg*cm-2)。
複合材料在染料敏化太陽能電池之應用則著墨在開發具有高導電性、持久化學穩定性之陽極結構。系統中陽極為光-電化學轉換層其厚度約為10微米:其組成為銀金屬奈米線(AgNWs)、商用鈦氧化物奈米粉(P25)以及銠錯合鹽離子基組成的光染劑(N3 dye)，電解質則為慣用的碘-碘離子溶液(I-I3-)，陽極背基板為導電玻璃(FTO)。經由表面改質技術處理後，改質金屬奈米線(AgNWs@TiO2)的添加(約1.6 wt%)可使陽極複合結構(AgNWs@TiO2/P25)之工作效率相對於標準電極(由同厚度之P25鍍膜)約提升200%(由2.2 到4.2 %)、相對於含有未改質金屬奈米線的陽極提升約35%，此外表面改質可使得陽極工作電流得以在二十分鐘內穩定維持(僅下降~5.0 - 6.0%，由11.4 – 10.9 mA*cm-2)。
奈米金屬-矽氧化物複合材料則在結合溶膠凝膠法合成之結構中以多醇反應將金屬還原合成，製做含有12-15 wt%金屬的奈米金屬-矽氧化物-高分子複合材料。流程中將高分子材料與金屬鹽溶液、醇類、矽氧化物溶膠混合，於第一階段進行水解反應使矽氧化物形成凝膠將金屬鹽類與水、醇等溶液侷限在內部之奈米孔隙中，隨後在定溫控制濕度系統中將凝膠內水分子緩慢揮發使金屬鹽得以由水-醇介面轉換到醇溶液相。待乾燥完成後，樣品置入定溫系統以攝氏160度進行熱處理使醇類活化對金屬離子進行還原作用，過程中金屬奈米結構將緩慢在材料內外之奈米孔徑內還原成為緊密連結的奈米金屬結構。經過熱處理之材料其薄膜阻抗(sheet resistance)可顯著降低約105倍(由~25.0降低至3*10-3 歐姆/平方)。

並列關鍵字

nanocomposite ； direct methanol fuel cell ； nanocatalyst ； bio-fuel cell ； solar cell ； X-ray absorption spectroscopic ； small angle x-ray scattering

參考文獻

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