標題: 利用 X 光吸收光譜研究鉑原子在釕奈米顆粒的置換反應
Investigation of Displacement Reaction for Pt on Ru/C Nanoparticles by X-ray Absorption Spectroscopy
作者: 張立忠
Chang, Li-Chung
吳樸偉
李志甫
Wu, Pu-Wei
Lee, Jyh-Fu
加速器光源科技與應用碩士學位學程
關鍵字: X光吸收光譜;置換反應;鉑釕合金;X-ray Absorption Spectroscopy;Displacement Reaction;PtRu alloy
公開日期: 2009
摘要: 置換反應為一個新穎的觸媒製備方式,對於直接甲醇燃料電池陽極或陰極觸媒都有相關的應用。該方法解決了傳統觸媒製備時遭遇的問題,例如貴重金屬的乘載量太高和使用率太低。利用置換反應所製備的觸媒可以降低貴重金屬的承載量到單一原子層或甚至更低。可以提升貴重金屬參與觸媒反應的使用率,減少貴重金屬的浪費便可以降低燃料電池系統單價。然而,置換反應的反應機制相當複雜,需要投入更多的研究加以釐清。藉由增加對反應過程的基礎知識,使得置換反應所製備出來的觸媒得以最佳化。 在本研究中,置換反應中所參與的元素為鉑與釕。選擇這兩個元素做為研究對象的原因,除了鉑釕合金之間會進行置換反應外,鉑釕合金也是一個效能優異的直接甲醇燃料電池陽極觸媒。首先,我們使用化學還原法製備的碳承載之釕奈米顆粒,緊接著將他們浸泡入鉑的前驅物中進行置換反應後進行分析。並且,在不同酸鹼值下的鉑前驅物,對於釕的置換反應中的影響也進行深入的探討。研究方法主要使用X光吸收光譜來鑑定置換反應過程中,鉑的氧化價數和微結構變化情形。同時,釕的氧化價數和微結構變化也進行分析,使得我們可以分別用鉑與釕的變化建構一個合理的反應機制。另一方面,由穿透式電子顯微鏡得知釕奈米顆粒均勻分布在碳的承載物上,並且置換上鉑之後的顆粒大小並沒有明顯的變化;X光繞射圖顯示釕受到了鉑的影響,晶格有變大的情形;能量分散X光譜儀和感應耦合電漿質譜分析儀指出置換反應中,鉑的沉積量和釕被置換的量受鉑前驅物酸鹼值有相當的影響。 總結以上分析結果,利用置換反應將鉑沉積在釕奈米顆粒的反應過程中:鉑離子被釕還原至較低的氧化價數並沉積在釕奈米顆粒的表面,而釕氧化成離子並解離入前驅物水溶液當中。然而,鉑並非直接與釕形成鍵結,是藉由氧的嫁接形成鍵結在釕的表面。
An investigation to the displacement reaction mechanism for Pt on Ru/C nanoparticles was carried out by analyzing the immersion of Ru/C nanoparticles into hexachloroplatinic acids with various pH values. X-ray diffraction patterns indicated slight Ru lattice expansion of Pt deposition. The exact variation of Pt and Ru during displacement reaction was determined by inductively coupled plasma mass spectrometry, which suggested that the dissolution of Ru was mainly resulted from the displacement by Pt. The Ru/C and PtRu/C were approximately 2 to 3 nm in sizes from TEM images from transmission electron microscope. Energy dispersive x-ray spectroscopy determined the composition of Pt on Ru nanoparticles. X-ray absorption spectroscopy analysis provided a detailed reaction mechanism which indicated that Pt cations were reduced to moderate oxidation states or merely physically adsorbed contingent on the types of complexing ligands. In addition, the Pt was deposited onto Ru through bridged-oxygen instead of forming a direct Pt-Ru bonding during displacement reaction.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT079701506
http://hdl.handle.net/11536/44181
Appears in Collections:Thesis


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