臺灣博碩士論文加值系統

質子交換膜燃料電池(proton exchange membrane fuel cells; PEMFCs)被視為是極具潛力的新替代能源裝置，主要是因為它們利用氫或甲醇為燃料，具有環保潔淨及高能量轉換效率等優點。然而，現今PEMFC大都均利用活性碳負載貴金屬(如鉑、釕等)觸媒來做為陽極與陰極電極催化劑，故基於成本考量較不利於放大製程及後續商業化應用。因此，就PEMFC電極催化劑而論，低貴金屬含量或非貴金屬的觸媒的研發，是一項重要的課題。而以直接甲醇燃料電池(direct methanol fuel cells; DMFCs)而言，為克服一氧化碳毒化問題，通常其陽極電極採用孔洞碳材負載鉑基(Pt-based)雙金屬合金觸媒，如鉑釕(PtRu)觸媒等。研究發現，添加次要貴金屬(Ru)，可有效修飾其合金觸媒結構、電子與化學性質，有利於在陽極進行甲醇氧化反應(methanol oxidation reaction; MOR)，對於抗一氧化碳毒化具有良好的效果，進而提升觸媒穩定性及整體DMFC之效能。然而，基於燃料電池膜電極組(membrane electrode assembly; MEA)成本及整體效益(如電極觸媒壽命、運轉效能等)考量，若在維持特定電催化效能之條件下，能夠進一步降低貴金屬使用量以降低MEA製備成本，此一研究導向對基礎科學研究與未來可能產業應用應兼俱重要性。
基於以上述論，本研究之主要目的在於開發有序中孔碳材(ordered mesoporous carbons; OMCs)負載雙功能PtM (M = Ru, Fe, Mo, Sn)合金觸媒，並針對其應用於DMFC陽極電極之催化效能與穩定性做深入的探討。延續吾人過去在開發OMC負載單(Pt)及雙(PtRu)貴金屬合金觸媒製程的研究經驗與成果，本研究利用呋喃甲醇及三甲苯作為主要碳源，乙醯丙酮有機金屬(metal acetylacetonates)為主要金屬前軀物及次要碳源，以高度有序中孔洞氧化矽SBA-15為硬模板，在無氧環境下經高溫(800 oC)碳化後，再移除氧化矽模板，最後成功地合成出具有高分散度之奈米尺度PtM合金金屬顆粒披覆的OMCs。藉由各種分析與光譜技術，如氫氣化學吸附、氮氣等溫吸/脫附、粉末x-光繞射、穿透式電子顯微鏡，x-光光電子能譜、感應耦合電漿質譜分析及恆電位法或循環伏安法測量等分別鑑定其結構、物化特性及電催化活性。實驗結果得知，所製備得到擔載鉑基合金觸媒的PtM-OMCs均具有高比面積（> 1000 m2/g），均勻的孔徑分佈（? 3 nm），且高度分散的合金觸媒顆粒(大約2~3 nm)。進一步由電化學測試結果得知其MOR催化表現依序為：PtRu-OMC > PtMo-OMC ~ PtFe-OMC >> PtSn-OMC。即便PtRu-OMC如預期的具有較佳的催化活性，但由單位成本所產生的電流密度而論，PtFe-OMC相較於其他PtM-OMCs有不錯的催化效能與產業應用潛力。

Proton exchange membrane fuel cells (PEMFCs) have been regarded as potential energy-conversion power devices owing to the advantages of not only using renewable and eco-friendly energy sources such as hydrogen or methanol as fuels, but also highly efficient. However, majority of the current PEMFCs rely on the use of noble metals (e.g., Pt, Ru) supported on activated carbons as electrocatalysts at both anode and cathode, which put some limits in scale-up production and feasibility for commercialization in terms of cost-effective view point. Thus, considering electrocatalysts for PEMFCs, R&D directs toward utilization of lesser noble metals or metal-free catalyst is a demanding task. In view of the anodic electrocatalyst for direct methanol fuel cells (DMFCs), utilization of Pt-based bifunctional catalyst was found to overcome the critical issue of CO-poisoning. It has been shown that by introducing a secondary noble metal (e.g., Ru), the structural, electronic, and chemical properties of the catalyst may be greatly enhanced. As a result, the supported PtRu/C catalyst shows improve stability and tolerance over CO-poisoning, and hence, a superior electrocatalytic activity over methanol oxidation reaction (MOR). Nevertheless, from the viewpoints of cost-effectiveness of the membrane electrode assembly (MEA) and overall performance of the PEMFC, further reducing the MEA production cost while maintain a satisfactory MOR activity at anode should be beneficial for both fundamental research and potential industrial applications.
As such, the objectives of this research is to develop facile syntheses of Pt-based bifunctional PtM (M = Ru, Fe, Mo, Sn) alloy electrocatalysts supported on ordered mesoporous carbons (OMCs) and to explore their stability and electrocatalytic performances during MOR. In continuation of our previous research endeavor, we report herein the synthesis of bifunctional Pt-M (M = Ru, Fe, Mo, Sn) electrocatalysts. The syntheses were carried out by using furfuryl alcohol and trimethylbenzene as the primary carbon sources, acetylacetonate organometallic compounds as the metallic precursors and the secondary carbon sources, and SBA-15 as the hard template, followed by carbonization under oxygen-free environment at elevated temperature (800 oC) and subsequent removal of the silica template. The structures, physicochemical properties, and electrocatalytic activities of the resultant PtM-OMCs were characterized by a variety of different analytical and spectroscopic techniques, such as H2 and CO chemisorption, N2 adsorption/desorption isotherm measurements, powdered x-ray diffraction (PXRD), transmission microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and inductive-coupled plasma mass spectroscopy (ICP-MS). Moreover, their electrocatalytic performances were evaluated by chronoamperometry (CA), and cyclic voltammetry (CV) measurements.
It was found that the PtM-OMC supported alloy catalysts so obtained all possess high specific surface areas (> 1000 m2/g), uniform pore size distributions (ca. 3 nm), and highly dispersed nano-scale average particle sizes (2 ~ 3 nm). Further electrocatalytic tests revealed that the MOR activities of these electrocatalysts follow the order: PtRu-OMC > PtMo-OMC ~ PtFe-OMC >> PtSn-OMC. Although the PtRu-OMC catalyst exhibited the anticipated highest activity over the PtM-OMCs, it is less compelling in terms of cost over the observed current density per unit metal. It is noteworthy that the PtFe-OMC catalyst, which revealed a satisfactory electrocatalytic performance over the other PtM-OMCs during MOR, shows perspective industrial application as anodic electrocatalyst for DMFC.

目錄
第 一 章 緒論 1
1.1 中孔分子篩簡介 1
1.1.1. SBA-15簡介 4
1.1.2. SBA-15之合成機制 5
1.2 中孔碳材簡介 6
1.2.1. 中孔碳材之合成機制 7
1.2.2. 孔洞碳材之應用 8
1.3 燃料電池簡介 12
1.3.1. 直接甲醇燃料電池(DMFC) 16
1.3.2. 二元金屬合金觸媒之MOR催化機制 17
1.4 動機與目的 22
第 二 章 實驗方法與步驟 25
2.1 化學藥品與試劑 25
2.2 樣品製備與處理 26
2.2.1. SBA-15的合成步驟 26
2.2.2. 模板複製法製備碳材 27
2.3 樣品物化特性鑑定 29
2.3.1. 化學吸/脫附實驗 30
2.3.2. 氮氣等溫吸/脫附實驗 30
2.3.3. 粉末X-光繞射 34
2.3.4. 熱重分析 36
2.3.5. 穿透式電子顯微鏡 36
2.3.6. X-光吸收光譜原理[] 38
2.3.7. 感應耦合電漿質譜分析 44
2.3.8. 電化學分析 44
第 三 章 結果與討論 48
3.1 中孔氧化矽SBA-15模板之合成與鑑定 48
3.2 負載金屬觸媒之中孔碳材合成與鑑定 50
3.2.1. 負載單金屬觸媒之中孔碳材 50
3.2.2. 負載鉑基雙金屬觸媒中孔碳材 63
3.3 X光吸收光譜實驗 72
3.3.1. X-光吸收近邊緣結構 72
3.3.2. 延伸X-光吸收細微結構 73
3.4 電化學特性測試結果 80
3.4.1. 甲醇氧化效能測試 80
3.4.2. CO剝除 89
第 四 章 結論 93
附錄 97
參考文獻 101

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