臺灣博碩士論文加值系統

控制鉑奈米結構之形貌，是一增益其催化活性的有效方法，特別是在相同質量的基礎上活性之機會。本研究利用甲酸還原法(formic acid method, FAM)製備高效能雙元鉑基合金(PtM, M= Au, Pd, or Cu)奈米顆粒(nanoparticles, NPs)及奈米棒(nanorods, NRs)觸媒以應用於氧氣還原反應(oxygen reduction reaction, ORR)。所製備觸媒之合金相、表面組成、化學組成、微結構、形貌以及電催化活性分析分別使用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, ICP-AES), X光吸收光譜(X-ray absorption spectroscopy, XAS), 高解析度穿透式電子顯微鏡(high resolution transmission electron microscopy, HRTEM) 以及旋轉盤電極(rotating disk electrode, RDE)等儀器做鑑定。
本研究分為三部分，第一部分成功地以FAM製備金屬負載量 45 wt % 之PtM NPs觸媒，其ORR活性以及穩定度均優於商用材Pt/C，其中又以PtAu之整體特性提升最為顯著，此乃歸因於次表層之金金屬修飾了表層鉑之電子結構和親氧力。
第二部分同樣用FAM製備金屬負載量45 wt%，平均直徑3 nm及長度10-20 nm之Pt和PtM NRs觸媒。從XAS分析中利用鉑之LIII和LII之峰值面積可鑑定出PtCu和PtPd NRs有較少之未填滿d軌域(number of unoccupied d-states, hTs)，此表示d軌域電子由添加金屬中轉移至鉑，同時也降低了氧氣之吸附強度。而Pt和PtM NRs 之電子轉移數大於3.8，因此有較佳的ORR活性。此外在加速穩定度測試(accelerated durability test, ADT)後，PtCu NRs質量活性為34.4 mA cm−2 mg-1 Pt ，是商用材Pt/C之2.2倍。此結果可歸因於一維奈米結構有助於ORR活性及穩定度之提升。
第三部分針對PtCu NRs和Pt/C 在不同電解液環境下進行ORR測試，結果顯示PtCu NRs和Pt/C在HClO4 中ORR活性分別為在H2SO4中之3.0和1.5倍。此乃歸因於硫離子容易吸附在Pt (111)表面阻礙ORR活性位點進而影響ORR活性。

Controlling the morphology of Pt nanostructures can provide a great opportunity to improve their catalytic properties and increase their activity on a mass basis. In this study, highly effective carbon supported PtM (M= Au, Pd, or Cu) nanoparticles (NPs), Pt and PtM nanorods (NRs) prepared by formic acid method (FAM) are studied for their activity and durability toward oxygen reduction reaction (ORR). The structures, surface compositions, chemical compositions, morphologies, electrochemical properties and local structural parameters 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), rotating disk electrode (RDE) technique and X-ray absorption spectroscopy (XAS), respectively.
The study is divided into three parts. In the first part, the 45 wt% PtM NPs are prepared by FAM successfully. The ORR activity and long-term durability of the PtM NPs is better than that of the Pt/C after 1000th potential cycles of accelerated durability test (ADT), especially PtAu NPs. The promotion of ORR performance is attributed to the modified electronic structure of the surface Pt and oxophilicity through the underlying Au sublayer.
In the second part, the 45 wt% Pt and PtM NRs catalysts with an average diameter of 3 nm and length of 10-20 nm are prepared by FAM. The number of unoccupied d-states (hTs) extracted from Pt LIII and LII –edge of XAS spectra show that PtCu and PtPd NRs have lower unfilled Pt d-states, indicating more d-band electrons transfer from the metal to Pt and a decrease of the adsorption strength of oxygenated adsorbates. The as-prepared Pt and PtM NRs have significantly enhanced ORR activity with an electrons transfer number per oxygen molecule of more than 3.8. Besides, after ADT of 1000 cycles, PtCu NRs display a mass activity of 34.4 mA cm−2 mg-1 Pt, which is nearly 2.2 times higher than that of commercial Pt/C. Thus, these results lead to the conclusion that the promotional effect of Pt and PtM NRs may be attributed to the 1D morphology, favorably enhancing the electrochemical activity and stability of ORR.
In the third part, the LSV results exhibit that the current density of PtCu NRs and Pt/C in HClO4 is about 3.0 and 1.5 times higher than that in H2SO4 because strongly adsorbed sulfate (or bisulfate) anions block the ORR active sites on Pt, especially on Pt (111) surface.

摘要 I
Abstract III
Table of contents VII
List of figure IX
List of Tables XII
Chapter 1 Introduction 1
1.1 Mechanism of the ORR 1
1.2 Cathode catalysts in the PEMFCs 3
1.3 Nanostructured materials 5
1.4 Correlation between fine structure and ORR activity 9
1.5 Effect of adsorbed anions on the oxygen reduction activities of Pt in different electrolyte solutions 13
1.6 Motivation and approach 16
Chapter 2 Experimental section 17
2.1 Preparation of PtM NPs 17
2.2 Preparation of Pt and PtM NRs 17
2.3 Characterization of catalysts 19
2.3.1 Thermal gravimetric analysis (TGA) 19
2.3.2 Inductively coupled plasma – atomic emission spectroscopy (ICP-AES) 19
2.3.3 X-ray diffraction (XRD) 22
2.3.4 X-ray absorption spectroscopy (XAS) 22
2.3.5 High resolution transmission electron microscopy (HRTEM) 23
2.3.6 X-ray photoelectron spectroscopy (XPS) 24
2.3.7 Rotating disk electrode (RDE) 24
2.3.8 Cyclic voltammograms (CV) 25
2.3.9 Accelerated durability tests (ADT) 26
Chapter 3 Results and Discussion 27
3.1 The structural and electrochemical characterizations of PtM NPs 27
3.1.1 XRD characterization 27
3.1.2 HRTEM characterization 30
3.1.3 XPS characterization 30
3.1.4 LSV characterization 33
3.1.5 ADT characterization 33
3.1.6 Summary 39
3.2 The structural and electrochemical characterizations of PtM NRs 40
3.2.1 XRD characterization 40
3.2.2 HRTEM characterization 43
3.2.3 XPS characterization 43
3.2.4 LSV characterization 46
3.2.5 XAS characterization 53
3.2.6 ADT characterization 56
3.2.7 Summary 59
3.3 Effect of adsorbed anions of PtM NPs and NRs in different electrolyte solutions 60
Chapter 4 Conclusions 62
References 64

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