臺灣博碩士論文加值系統

ABSTRACT

One of the major goals of this research was to investigate relationship between the catalyst structure and the electrochemical activity of the bimetallic electrocatalyst prepared in different protocol. The carbon-supported Pt-Co is one of electrocatalyst for oxygen reduction reaction which has the enchancement than platinum. The XAS technique had been used for investigating the structure aspects which extracted from EXAFS data. The electrochemical measurement had been employed for investigating oxygen reduction reaction (ORR) by thin film on rotating disk electrode (RDE).
Microwave synthesis method was applied to prepare PtCo/C oxygen reduction electrocatalysts. The microwave irradiation combine with the modified-Watanabe method and the urea method were used for preparation of PtCo/C electrocatalysts. The different preparation yield different electrocatalyst of structure aspect and electrochemical properties. The modified-Watanabe has developed in our group but some of midification has been done for obtaining different structure. The urea method combine with microwave irradiation has been introduced as new approach for preparing PtCo/C electrocatalysts. Hydrolysis of urea at 90 oC was used to achieve the homogeneous production of hydroxyl ions to increase the pH from acidic to around neutral at this temperature, a pH of around 6. But by using microwave irradiation, the final pH value attained at pH 8. After preparation, the heat treatment was applied for as-synthesized at 300 oC and 400 oC in 10% H2 atmosphere.
The synthesized PtCo/C were characterized by various techniques for investigating its structure. XRD and TEM data showed that the as-synthesized catalyst have average particles size about 2 - 3 nm for the samples synthesized by the Watanabe method and 8 - 11 nm for the samples synthesized by the urea method after heat treatment at 400 oC. The cyclic voltammogram measurement in 0.5 M H2SO4 have been performed on all the prepared as well as commercial Pt/C-Etek and PtCo/C-Etek. The linear scan voltammogram have also been performed for investigating ORR in 0.5 M H2SO4 after purging O2 for 30 minutes. The activities of some of the as-synthesized are nearly similar and some are slightly higher when compared to commercially available Pt/C-Etek and PtCo/C-Etek. Expecially the samples had prepared by modified-Watanabe microwave method offer good performance than any other samples
XAS analysis on all the prepared and commercial samples has shown that the the catalyst contains Pt rich in its core and Co rich in the shell of bimetallic catalyst. And some of the catalyst has reversed structure where Co rich in core and Pt rich in shell.




Keywords: Cathode electrocatalysts, Microwave, DMFCs, Urea method, Colloid method, X-ray absorption spectroscopy, Oxygen reduction reaction

LIST OF CONTENTS


ABSTRACT i
ACKNOWLEDGEMENT iii
TABLE OF CONTENTS iv
LIST OF FIGURES xiii
LIST OF TABLES xiv
CHAPTER I INTRODUCTION 1
1.1.GENERAL ASPECTS OF FUEL CELLS 1
1.2.DIRECT METHANOL FUEL CELL (DMFCS) 8
1.2.1. Solid Polymer Electrolyste: PEM 10
1.2.2. Direct Methanol Fuel Cell Anode 13
1.2.3. Direct Methanol Fuel Cell Cathode 15
1.3. THE OBJECTIVITY OF THESIS 19
1.4. ANALYSIS TECHNIQUE 19
CHAPTER II ELECTOCATALYST 21
2.1. GENERAL FEATURES OF ELECTROCATALYST 21
2.1.1. PREPARATION OF CARBON-SUPPORTED
METAL NANOPARTICLES 22
2.1.1.1. Impregnation Methods 22
2.1.1.2. Colloidal Methods 22
2.1.1.3. Microwave 24
2.1.1.4. The Homogeneous Deposition-Precipitation
Technique 26
2.1.2. CATALYST SUPPORT 27
2.1.3. ELECTROCATALYSTS FOR ORR 28
2.2.FUNDAMENTAL ASPECTS BEHIND CHARACTERISTIC
AND PROPERTIES OF ELECTROCATALYST 32
2.2.1. ELECTROCHEMICAL PROPERTIES 32
2.2.1.1. Cyclic Voltammogram 32
2.2.1.2. Determination of EAS Area 36
2.2.1.3. The Rotating Disk Electrode Setup 38
2.2.2. STRUCTURAL MODEL AND ATOMIC
DISTRIBUTION OF BIMETALLIC NPs
AS INVESTIGED BY XAS 42
CHAPTER III EXPERIMENTAL 45
3.1. EXPERIMENT MATERIALS AND EQUIPMEENTS 45
3.1.1. Experiment Materials 45
3.1.2. Instrument and Equipments 46
3.2. EXPERIMENT METHODS 46
3.2.1. Treatment of Carbon Black 46
3.2.2. Modified-Watanabe Method Using Microwave 46
3.2.2.1. Alloying Nanoparticles 47
3.2.2.2. Ptcore-Coshell Nanoparticles 47
3.2.2.3. Cocore-Ptshell Nanoparticles 50
3.2.3. Urea Method Using Microwave 51
3.2.4. Heat Treatment for PtCo/C as-synthesized 53
3.3.ELECTROCATALYST CHARACTERIZATION 54
3.3.1. X-ray Powder Diffraction (XRD) 54
3.3.2. Energy Disperse X-ray (EDX) Microanalysis 55
3.3.3. Transmission Electron Miscoscope (TEM) 55
3.3.4. X-ray Absorption Spectroscopy (XAS) 56
3.3.5. Temperature-Programmed Reduction (TPR) 56
3.4.ELECTROCHEMICAL MEASUREMENT 56
3.4.1. Electrode preparation 56
3.4.2. Cyclic Voltammetry (CV) and
Linear Sweep Voltammetry (LSV) 57
CHAPTER IV RESULTS 58
4.1.ELECTROCATALYST CHARACTERIZATION 59
4.1.1. X-Ray Diffraction 59
4.1.2. Energy Disperse X-ray (EDX) microanalysis 63
4.1.3. Transmission Electron Microscopy (TEM) 65
4.1.4. Temperature Programmed Reduction (TPR) 67
4.2.ELECTROCATALYST PROPERTIES 70
4.2.1. Cyclic Voltammograms (CVs) 70
4.2.2. Oxygen Reduction Reaction (ORR) 75
4.2.3. Effect of acid treatment on
electrochemical properties 77
4.2.4. Effect of heat treatment on
electrochemical properties 79
4.3. ELECTROCATALYST STRUCTURE 81
4.3.1. X-ray Absorption Near Edge Spectroscopy
(XANES) 81
4.3.2. Extended X-ray Absorption Fine Structure
(EXAFS) 85
CHAPTER V DISCUSSION 96
5.1. Structure Parameters of Oxygen Reduction Reaction
Electrocatalyst 96
5.2. Electrochemical Activity of ORR electrocatalysts 101
5.3. Comparison Between Electrochemical Activity
and Structure for Oxygen Reduction Reaction
(ORR) Electrocatalysts 106
CHAPTER VI CONCLUSION 108
REFERENCES xv

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