臺灣博碩士論文加值系統

本研究以含浸法製備PtRuTa/C複合電極觸媒，有系統地探討各不同組成PtRuTa/C電極觸媒對甲醇氧化之催化活性及穩定性；藉由循環伏安法(CV)、計時安培法(CA)以及一氧化碳剝除法(CO-stripping voltammetry)進行電化學特性分析；並使用X光繞射儀(XRD)、能量散射光譜儀(EDS)、電子能譜儀(XPS)、穿透式電子顯微鏡(TEM)以及掃描式電子顯微鏡(SEM)等儀器量測觸媒表面結構特性、組成比例與顆粒大小分佈。
結果顯示：PtRuTa 觸媒表面呈多孔洞結構，其平均粒徑介於4.3至6.1 nm之間，粒徑大小隨著Ta成分比例增加而增加，而Pt在觸媒表面之分布則隨著Ta成分比例增加而有趨於團聚的現象。
經由實驗研究不同掃描速率對於PtRu及PtRuTa組成觸媒對甲醇起始氧化電位(Methanol oxidation on-set potential, VMOSP)判讀之影響，發現PtRuTa/C電極觸媒中的VMOSP遲滯現象，包括正向和逆向掃描，隨著掃描速率降低而減小並趨近於同一值，經由此方式可求得各PtRu及PtRuTa 觸媒之VMOSP精確值。其結果顯示Pt與Ru之最佳成分比例為1: 1，且觸媒中Ta成分比例對於PtRu (Ru 50 atom %)觸媒之VMOSP影響並不明顯。而PtRuTa/C觸媒對於甲醇氧化反應之穩定性分析顯示：複合電極觸媒中添加Ta組成可發揮其在酸液中之耐腐蝕特性，有效降低PtRu在酸液中之溶解現象，其安定PtRu觸媒的作用隨著鉭含量增加而上升，且當Ta含量小於5 atom %時，可有效分散PtRu觸媒，使Pt 之比催化活性隨著Ta含量增加而增加，提升觸媒之催化效果；然而當Ta含量大於5 atom %時，因Ta過多造成的遮蔽作用，使Pt 之比催化活性隨著Ta含量增加而減少。
另一方面，不同組成之PtRuTa/C電極觸媒在0.5 M硫酸的甲醇水溶液中之浸泡實驗結果顯示：在非操作測試中，由於Ta2O5之形成可增加PtRuTa觸媒表面元素之束縛能，使觸媒中之Ta成分有效地抑制Pt及Ru在酸液中之溶解現象。

PtRuTa/C tri-metal electrocatalysts were prepared by impregnation method for use as anode catalysts, with an attempt to improve the stability and electrocatalytic activity of the PtRu for methanol oxidation reaction (MOR). The lattice parameters, composition, and particle size distribution of catalysts were characterized by the means of X-ray diffractometer (XRD), X-ray energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), and scanning electron microscope (SEM), respectively. The electrochemical behaviors of the electrodes were studied by cyclic voltammetry (CV), chronoamperometry (CA), and CO-stripping voltammetry. The inductively coupled plasma-mass spectrometer (ICP-MS) was used to detect the dissolved species in the immersing solutions (0.5 M H2SO4 + 2.0 M CH3OH), used for examining the degradation and dissolution of the PtRu catalysts during the out-of-service time.
The results show that the atomic ratios of Pt, Ru, and Ta in the PtRuTa/C catalysts are approximately equal to the known values in the original precursor solutions, indicating the successful preparation of the PtRuTa catalysts. The particle size of the PtRuTa/C catalysts is 4.3 to 6.1 nm with a spherical structure. The catalysts are well dispersed on the carbon black supports; however, the distributions of Pt atoms decrease, while the agglomeration increases, with the increase of Ta content.
On the other hand, the exact methanol oxidation on-set potential (VMOSP) at various PtRu based catalysts are obtained accurately by extrapolation at a scan rate of zero. The results show that the optimum ratio of Pt: Ru is ca. 1:1, and the dependence of VMOSP on the Ta content in the catalyst is insignificant。In addition, the stability of the catalysts for MOR increases significantly with the increase of Ta contents, while the specific activity of the catalysts increases when the Ta content is less than 5 atom %.
Additionally, the degradation and dissolution of the PtRu catalysts during the out-of-service time examined by immersing tests shows that, as well as that in the operation time, the dissolution of Ru on the catalysts is effectively depressed in the presence of Ta due to the formation of Ta2O5.

摘要
ABSTRACT
誌謝
Contents
Table of contents
Figure of contents
Chapter 1 Introduction
Chapter 2 Literature Review
2.1. The anode catalysts of DMFC
2.1.1. Pt-M bimetal electrocatalyst
2.2. Preparation of Pt-Ru catalysts
2.3. The stability of PtRu electrocatalysts
2.3.1. Degradation of PtRu electrocatalysts
2.3.2. Improvement of the stability of the PtRu based catalysts
2.4. Motivation
Chapter 3 Experimental
3.1. Preparation of catalysts
3.2. Preparation of working electrodes
3.3. Electrochemical measurements
3.4. Characterization of catalyst
3.5. The reagents
3.6. Instruments and equipments
Chapter 4 Results and discussion
4.1. Electrocatalyst characterizations
4.2. The catalytic activity of PtRuTa/C electrocatlysts for MeOH oxidation
4.2.1. Measurements of exact VMOSP for the PtRuTa and PtRu electrocatalysts
4.2.2. Effects of Ta contents on the catalytic activity of PtRuTa/C electrocatalyst for MeOH oxidation
4.3. Effects of Ta contents on the stability of PtRuTa/C elecrocatalysts for MOR
4.3.1. Degradation tests for the PtRuTa/C used as anode for MOR
4.3.2. Dependence of the stability of PtRuTa/C on the Ta contents in the catalysts
4.3.3. Structure and morphology analysis for the anodic degradation of the PtRuTa/C
4.3.4. Degradation tests for the PtRuTa/C immersed in acid aqueous MeOH
Chapter 5 Conclusion
References
自傳

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