二氧化鈦奈米管/碳黑複合物應用於觸媒載體; High Performance DMFC PtRu-Catalyst using TiO2 Nano-tube (TNT) and Vulcan XC-27R mixture as Support

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題名:	二氧化鈦奈米管/碳黑複合物應用於觸媒載體;High Performance DMFC PtRu-Catalyst using TiO2 Nano-tube (TNT) and Vulcan XC-27R mixture as Support
作者:	楊志偉;Jhih-Wei Yang
貢獻者:	化學研究所
關鍵詞:	二氧化鈦奈米管;觸媒;直接甲醇燃料電池;化學活性面積;TiO2 nanotube;anode catalyst;DMFC;ECSA
日期:	2008-07-09
上傳時間:	2009-09-22 10:18:49 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	直接甲醇燃料電池具有高能量密度、燃料穩定容易儲存、填充方便等優勢，相當具發展潛力，由於觸媒催化效率不良，使成本居高不下。觸媒催化效率低，原因包含 (1)甲醇氧化與氧氣還原反應步驟複雜，需克服相當高之活化能，因此反應速率低； (2)反應過程中間產物毒化Pt； (3)觸媒金屬在載體上分散與吸附不良、金屬穩定度不足經過使用後，金屬流失或是聚集。本論文使用TNT/XC72R的混合物為直接甲醇燃料電池觸媒載體，藉以提昇燃料電池觸媒效能。混合物兼具TNT的高表面積與XC-72R的導電度。使用乙二醇為溶劑間還原劑，並以微波加熱或是回流加熱還原PtRu。PtRu顆粒能均勻分佈在TNT與XC-72R上。利用迴流法製備之觸媒，較微波法擁有較小粒徑。金屬顆粒的大小鑑定，採直接利用穿透式電子顯微鏡(TEM)，或是間接以Debye Function Analysis(DFA)與Williamson-Hall Plot分析粉末X光繞射圖譜，求得粒徑大小為2-5nm。電化學性質分別採用循環伏安法 (Cyclic Voltammetry, CV)測試甲醇氧化活性抗CO毒化率 (CO Tolerance)；CO脫附 (CO Stripping)測試化學活性面積 (Electrochemical Surface Area, ECSA)；掃瞄速率 (Scan Rate Test)測試分析甲醇擴散效應；定電壓安培法 (Chronoamperometry, CA)測試觸媒長時間使用效能。這些特性顯示PtRu奈米粒子，能夠在TNT/XC-72R混合物上，保持高的表面積與導電度。TNT能與PtRu有強作用力，能夠穩定金屬，高TNT含量的觸媒在經過長時間使用後，依然維持良好合金度，不因使用出現PtRu分相。XC-72R用來補償TNT導電性的不足，TNT則扮演降低CO毒化與降低起始電位，SEM的結果顯示較高TNT含量觸媒結構呈現多孔隙結構，使觸媒能夠加分散增加電化學活性面積。並且提供燃料進入之通道，當TNT含量增加至40 wt %~ 50 wt %時，會與導電度出現最適化點。若TNT量繼續增加，則因XC-72R 量不足造成導電度下降，進而使觸媒效能下降 Direct methanol fuel cells (DMFC) shows potential as new energy source due to its relatively high energy density, easy to store and transport fuel, and easy to reload. However, the low catalyst efficiency, insufficient durability and high cost to manufacture are hurdles for immediate commercialization. The technical issues to overcome includes (1) lowering the activation so that catalytical reaction rates for both methanol oxidation and oxygen reduction can be improved, (2) to alleviate Pt poisoning by CO in fuel stream and intermediate product, (3) to improve the metal nanoparticle stability and adhesion such that metal aggregation and losses due to poor stability and low adhesion can be eradicated. . Present study disclosed a novel high performance catalyst for DMFC where the efficiency, activity, stability and durability can all be improved. The catalyst was prepared by using TiO2 Nano-tube (TNT) and XC-72R mixture as the metal catalyst support which preserved both the high surface area (from TNT) for reaction and high electronic conductivity (from XC-72). The PtRu catalysts had been prepared by glycol reduction with either microwave or reflux heating methods. The reflux prepared catalyst shows the best performance due to the smaller size than that prepared by microwave heating. The particle size, particle size distribution and Pt and Ru atomic partition within the nanoparticle is characterized Debye functional analysis (DFA) and Williamson-Hall Plot. This analysis indicated bi-modal particle size distributions with size averaged at 2 and 5 nm. The methanol oxidation activity and CO tolerance are measured by cyclic voltammetry. Using CO-stripping assesses the electrochemical surface area. The scan rate test analysis the methanol diffusion property. The catalysts life time are determined by chronoamperometry. These characterizations showed PtRu nano particle on TNT and XC-72R mixture exhibits high surface area and good electric conductivity, displayed excellent catalytic activities compared with the single component substrate using either TNT or XC-72R. Furthermore, the TNT exhibited strong interaction which stabilized the PtRu nano-particle. The high TNT content catalyst after long time test remains well alloy and preserved high activity. It is interesting to observe that XC-72R beads forms connected strings which sustained the electronic conductivity. In addition, TNT substrate also plays an imperative role in decreasing CO poisoning and on-set pontential, the morphology obtained by SEM shows that the nanocomposite substrate is highly miscible and displayed conspicuous porous structure which make catalyst more disperse to increase the electrochemical surface area. These characters enhance the degree of metal particles dispersion and provided fluent fuel transmission path when TNT content reached above 40wt%. The best catalytic performance is reached with 50wt % TNT and 50 wt% XC-72R. The performance decays with higher TNT since at low XC-72R content, the electronic conductivity is lost and the catalytical activity is reduced.
顯示於類別:	[化學研究所] 博碩士論文

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