鉑錫合金觸媒對於乙醇氧化反應表現與機構之探討

Abstract

本實驗主要探討Pt及PtSn合金觸媒對於乙醇氧化反應的催化活性與觸媒穩定度，並分析其產物及反應機構。以含浸法合成觸媒，並利用粉末繞射分析儀 (XRD) 、能量散射光譜儀 (EDS) 及X光光電子光譜 (XPS) 鑑定觸媒的晶格結構、元素組成以及各元素氧化態。以電位儀利用循環伏安法 (CV) 及計時安培法 (CA) 檢測觸媒在乙醇氧化反應中的反應活性表面積，催化活性與穩定度，最後再以傅立葉紅外光光譜儀分析反應後產物，推測反應途徑。在實驗的結果中我們觀察到，因Sn的加入會對Pt的氧化態造成影響，可以幫助乙醇吸附以及反應的活性與穩定度。實驗結果中發現合金的表現確實都比單金屬Pt來的好，而在不同比例的PtSn合金中以Pt5Sn1的表現最佳。另外在紅外光譜儀的結果中顯示乙酸為主要的反應產物，也間接說明了釋出4電子的C2路徑為乙醇氧化反應的主要反應途徑。

The present study investigates ethanol oxidation reactions (EOR), the anodic reactions for direct ethanol fuel cells (DDEFC), on Pt and PtSn alloys with the ratios of Pt/Sn = 10/1, 5/1, 3/1, 1/1 and 1/3 (Pt¬10Sn1, Pt¬5Sn1, Pt¬3Sn1, Pt¬1Sn1, Pt¬1Sn3) on carbon black XC-72. All bimetallic catalysts are synthesized by impregation method and characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) to confirm the cystal structure, composition and oxidation state of each element. The fabricated catalysts have been examined by the electrochemical tests of cyclic voltammetry (CV) and chronoamperometry (CA) to study the ECSA, EOR activity and stability. Furthermore, we employed in situ FTIR to investigate the product evolution in the reaction for the mechanism understanding. The experimental observation found that proper amount of Sn addition can change the oxidation state of Pt to strengthen the ethanol adsorption and improve the EOR activity and stability. As a result, Pt5Sn1 has the best EOR performance. Additionally, the FTIR spectra show the main product on those PtSn bimentals is acetic acid corresponding to the four – electron – oxidation pathway.