| 摘要: | 為了要增益白金基催化劑之乙醇氧化反應(ethanol oxidation reaction, EOR)活性，本研究製備具有不同程度親氧性之鉑基二元與三元包含鉑金、鉑銀、鉑錫和鉑錫銀奈米棒(nanorods, NRs)，並探討一維結構及去合金效應對三元鉑錫銀奈米棒之EOR活性的增益。所製備觸媒之結構、表面組成、化學組成、形貌、電化學性質分析可藉由X光繞射儀(X-ray diffraction, XRD)，光電子能譜儀(X-ray photoelectron spectroscopy, XPS)，感應耦合電漿原子發射光譜分析儀(inductively coupled plasma-atomic emission spectrometer)，高解析度穿透式電子顯微鏡(high resolution transmission electron microscopy, HRTEM)，循環伏安法(cyclic voltammetry, CV)等儀器鑑定。
研究結果分為三個部分，第一部分以甲酸還原法製備長寬比約2.7的碳支撐鉑基二元和三元奈米棒。在EOR的結果中，PtSnAg在0.6 V擁有最高的電流值，說明PtSnAg表面的氧化物可藉由雙功能機制(bi-functional mechanism)來促進乙醇解離吸附於鉑表面和CO的氧化，並進一步提升EOR活性。此外，根據常溫下計時伏安法(chronoamperometric, CA)的結果，PtSnAg觸媒相較於其他觸媒仍展現了最佳的活性與穩定性，這可歸因於觸媒表面的含氧物質像是PtOx、SnO2和銀的合金化效應。
第二部分則是利用去合金法進一步提升PtSnAg的活性。經過5圈的去合金化過程後，PtSnAg的電化學表面積可增益至3倍，這是因為Ag會部分溶解使得鉑的活性位置數量增加。此外，PtSnAg在去合金化10圈後展現了最佳的EOR活性與穩定性，或許可以歸因表面Pt/Sn/Ag組成的最佳化。
第三部分是用不同溫度製備長寬比分別為7.2，5.7，2.7的碳支撐PtSnAg奈米棒，並命名為PtSnAg-5 oC，PtSnAg-15 oC和PtSnAg-RT。在EOR活性結果中，PtSnAg-5 oC在0.6 V的活性約為PtSnAg-15 oC和PtSnAg-RT的1.2與2.1倍。此外，經過2小時的CA測試後，在PtSnAg-5 oC之奈米棒顯示了最佳的穩定性，此結果可歸因於此奈米棒有較高的長寬比與表面氧化物以利去除COads和CHx。由第二第三部分的研究結果可以發現，控制形貌比起去合金更能有效提升PtSnAg之EOR性能。
;In order to prepare Pt-based catalysts with high ethanol oxidation reaction (EOR) performance, binary and ternary nanorods (NRs) including PtAu, PtAg, PtSn, and PtSnAg with different degrees of oxophilicity is systematically elucidated. Besides, the effect of dealloying and one-dimentional (1-D) structures on the EOR performance of ternary PrSnAg NRs has been studied. The structures, surface compositions, chemical compositions, morphologies and electrochemical properties of prepared catalysts are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-atomic emission spectrometer (ICP-AES), high resolution transmission electron microscopy (HRTEM), and cyclic voltammetry (CV) technique, respectively.
This study is divided into three parts. In the first part, the carbon-supported Pt-based binary and ternary NRs with an aspect ratio of about 2.7 are prepared via formic acid method. In EOR results, the current density of PtSnAg at 0.6 V is the highest, suggesting the surface oxides in PtSnAg can improve EOR activity by promotion of dissociative adsorption of ethanol on Pt surface and the CO oxidation reaction through bi-functional mechanism. Moreover, chronoamperometric (CA) results obtained at ambient temperature show that ternary PtSnAg catalyst have the highest current density and stability among all samples, attributed to the surface oxygen containing species (OCS) such as PtOx, and SnO2 and Ag alloying effect.
In the second part, the dealloying process has been used to further improve the activity of the PtSnAg catalysts. After dealloying process of 5 cycles, the electrochemical surface area of PtSnAg can be enhanced about 3 folds, owing to Ag partial dissolution and the increase in the number of Pt active sites. Besides, the PtSnAg after dealloying of 10 cycles has the best EOR performance and durability, maybe attributed to the optimized surface Pt/Sn/Ag compositions.
In the third part, the PtSnAg/C NRs with an aspect ratio of 7.2, 5.7, and 2.7 have been prepared at different temperatures (named as PtSnAg-5, PtSnAg-15 oC, and PtSnAg-RT, respectively). For the EOR performance of PtSnAg/C catalysts with different aspect ratios, the current density of PtSnAg-5 oC at 0.6 V is about 1.2 and 2.1 times higher than that of PtSnAg-15 oC and PtSnAg-RT. Besides, after CA test for 2 h, NRs prepared at 5 oC display the best durability, because the synergic effect of the higher aspect ratio and surface oxide can remove the COads and CHx. Compared the results in parts 2 and 3, it seems that morphologies control is more effective than the dealloying to promote the EOR performance of PtSnAg. |
