利用熱處理改質引發表面偏析現象以增進鉑釕觸媒之甲醇氧化反應活性; Promotion of Pt-Ru/C Catalysts Driven by Heat Treated Induced Surface Segregation for Methanol Oxidation Reaction

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题名:	利用熱處理改質引發表面偏析現象以增進鉑釕觸媒之甲醇氧化反應活性;Promotion of Pt-Ru/C Catalysts Driven by Heat Treated Induced Surface Segregation for Methanol Oxidation Reaction
作者:	張維蓉;Wei-jung Chang
贡献者:	材料科學與工程研究所
关键词:	合金度;表面偏析;甲醇氧化;熱處理;鉑釕觸媒;PtRu/C catalysts;heat treatment;methanol oxidation;surface segregation;degree of alloying
日期:	2009-07-09
上传时间:	2009-09-21 11:29:20 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	直接甲醇燃料電池(DMFC)具有體積小、工作溫度低且使用液態燃料等特性，因此在可攜式電源的應用領域裡具有極大的發展潛力，但也因其具有較低的功率密度、陽極白金觸媒易遭一氧化碳毒化、甲醇穿透(crossover)與觸媒價格相對高之缺點，故在產業界與學術界皆被廣泛的研究，特別是關於提升觸媒效能的研究，更是近二十年來的研究重點之ㄧ。本研究採用最為廣泛使用的E-tek商用觸媒，重量組成比為Pt : Ru : C = 13.4 : 6.6 : 80之鉑釕陽極觸媒 (PtRu/C)，並以不同氣氛的熱處理改質，期望能了解觸媒組成、結構、成份偏析以及電化學活性之關連性，並且也透過改質，製備出甲醇氧化效能超越原始商用材之優良觸媒。所改質的觸媒，以X光繞射分析儀(X-ray diffraction, XRD)鑑定其結構，並以程式溫度還原系統(temperature-programmed reduction, TPR)與X射線光電子光譜(X-ray photoelectron spectroscopy, XPS)分析其表面組成，而電催化特性則以電化學循環伏安法(cyclic voltammetry, CV)分析。從XRD與XPS分析發現原始的商用材表面成份多為RuO2與Pt還有部份的Pt(OH)2。熱處理會造成Ru的表面偏析，並且因為過多的非晶質Ru偏析至表面導致觸媒的合晶度降低，然而在本研究中，合金度並不直接影響電化學活性。比較I07 (0.7 V vs. NHE)可發現，氫氣熱處理的樣品具有相似的表面組成且具有優秀的抗一氧化碳毒化之特性。而氮氣熱處理會抑制Ru的偏析，進而促進甲醇氧化效應，其改質效果最佳。 The direct methanol fuel cells (DMFC) have many advantages, such as small volume, low operational temperature, and liquid fuel feeding, therefore, DMFC has potential applications in mobile electronics. However, the low power density, methanol crossover, expensive Pt catalysts, and catalyst poisoning are needed to be solved. The research of DMFC has attracted much attention, especially the development and promotion of catalysts, has been studied comprehensively in last two decades. Alloy catalysts of commercial E-tek with a weight ratio of Pt : Ru : C = 13.4 : 6.6 : 80, heat treated in different atmospheres were prepared for the methanol oxidation reaction (MOR) and their structure-activity relationship (SAR) investigation. The alloy structures, surface species,and electro-catalytic activities of prepared alloy catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) technique, respectively. The electro-oxidation performance was studied by cyclic voltammetry (CV). It has been found that the surface of as-received Pt-Ru/C catalysts was consisted of mainly RuO2, Pt, and some Pt(OH)2. Thermal treatments induce Ru surface segregation in different extents, especially in O2 and H2 environments. The segregation of amorphous Ru in the catalysts altered the alloying degrees significantly. However, the Pt-Ru alloying degree is not significantly influence the electrochemical properties in this study. Catalysts involved in H2 heat treatment have a excellent CO depoisoning ability and have similar surface compositions and species. The N2 treatment seems to serve as a surface composition and structure adjustment process, which suppresses the surface Pt depletion and makes the components more stable and promotes the MOR.
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