由於目前化石燃料會增長碳化合物的含量導致溫室效應，導致對於替代能源的需求和環境保護的意識越來越高，促使大眾開始致力發展環境友善與高效率能量轉換的方法來取代傳統燃料，而在眾多的方法中，利用電解水方法產氫和氧受到注目，它的優點在於低成本、容易架設以及高的轉換效率，在此方法中，決定了效率的因素主要在於催化劑的選擇，目前轉換效率最好的材料為鉑與其化合物，由於其特別的催化活性與高導電度，指他們擁有了較高的轉換電流密度(4.5 × 10-4 A cm-2)和較小的塔弗斜率(~40 mV/dec)，但是由於鉑為稀有金屬，其含量少、價格高，限制了其發展性與普及性，因此，大家開始尋找相對價格較低，又具有相當好的轉換效果的材料才取代鉑。在此篇論文中，我們開發了過度金屬的奈米線，過度金屬磷化物的奈米管和三維的過度金屬奈米花用來取代鉑，他們有著相當好的效果，例如:很小的過電位(<300 mV 在電流密度為10 mA/cm2)，相當小的塔弗斜率還有很高的穩定度，可以操作超過1000次，這些優異的性能主要由於三點；1. 石墨烯在奈米線的表面有很多缺陷，這些缺陷提供了很多活化的位置利於轉換2. 獨特的中空管狀的奈米線，能讓電解液能流入並在加入非晶碳增加導電度，提升效果3. 特別的奈米花形狀的金屬相二維材料提供了較高的體表面積比和活化位置。

Growing energy demands and environment consciousness due to current carbon-based fossil fuels have endorsed extensive research on the development of alternative energy conversion and storage technologies with high efficiency and environmental friendliness. Among them, electrochemical water splitting is very attractive, and is receiving more and more attention due to its low setting up cost, easy operation, and high yield. The critical challenge in this renewable technology is in dependency of highly active catalysts. To date, noble metal like platinum (Pt) and Pt-based materials are the efficient electrocatalysts for hydrogen evolution reaction (HER) because they exhibit incredibly high exchange current density (4.5 × 10-4 A cm-2) and smaller Tafel slope (~40 mV dec-1) owing to its high conductivity and remarkable catalytic properties. However, its scarcity on earth and high price limited it's extensive usage and gained insights towards finding the alternative high efficiency and low-cost electrocatalysts to approach the green, sustainable energy supply. To this end, we developed one dimensional (1D) nanowire and nanotube structure based on transition metal (TM) and transition metal phosphide (TMP), as well as three dimensional (3D) nanoflower based on transition metal dichalcogenides (TMD). The prepared materials exhibits superior electrocatalytic behaviour towards HER by achieving lower overpotentials < 300 mV at the current density of 10 mA cm-2 with low Tafel slopes and excellent stability over 1000 cycles. These superior electrocatalytic performances are due to (1) presence of graphene at the surface of nanowires increases the active sites by its defective edges, (2) easy diffusion of electrolyte by helical nanotube structure as well as increase in conductivity by the amorphous carbon, and (3) higher active sites due to high surface area of nanoflower morphology and metallic 1T phase of TMD.

Chinese Abstract i
English Abstract ii
Acknowledgements iii

Chapter 1 Introduction
1.1 Hydrogen - a clean and green energy source 1
1.2 Water Electrolysis 2
1.2.1 HER mechanism in acidic and alkaline media 3
1.2.2 Evaluating performance of HER catalysts 4
1.3 Literatures Review 6

Chapter 2 Experiments
2.1 Synthesis of Copper nanowire 10
2.1.1 Electrode fabrication for HER 10
2.1.2 Growth of Graphene carbon-enclosed chemical vapor
deposition (CE-CVD) 10

2.1.3 Harsh environments test 12
2.2 Synthesis of Copper phosphide helical nanotubes 12
2.3 Synthesis of (1T/2H) MoS2/MoO3 nanoflowers 13
2.4 Material Analysis and Characterization 13
2.4.1 Scanning Electron Microscope (SEM) 14
2.4.2 Transmission Electron Microscope (TEM) 14
2.4.3 X-ray diffraction spectrometer 14
2.4.4 Raman Spectrometer 14
2.4.5 X-ray photoemission spectrometer and Ultraviolet
photoelectron Spectroscopy 15

2.4.6 Electrical measurements 15
2.4.7 Surface area measurements 15
2.4.8 Sea water analysis 15
2.4.9 Electrochemical hydrogen evolution reaction 15

Chapter 3 Transition Metal (Cu) as Electrocatalyst
3.1 Why Cu is not an efficient electrocatalyst for HER? 17
3.2 Structural and crystallinity evidence of as synthesized
Cu NWs 17
3.3 Optimization of graphene growth by CECVD process 19
3.4 Identification of stability towards high harsh environments 22
3.4.1 Basic test (0.5 M NaCl) 23
3.4.2 Acidic test (0.5M H2SO4) 23
3.4.3 Sea Water test (from Penghu Island, Taiwan) 24
3.5 Cu NWs and graphene coated Cu NWs as electrocatalyst for HER 26

Chapter 4 Transition Metal Phosphide (Cu3P) as Electrocatalyst
4.1 Phosphorization of aged Cu NW after annealing 31
4.2 Temperature optimization of phosphorization process 32
4.3 Reaction time and carrier gas optimization of phosphorization
process 35
4.4 Phosphorization at 400 °C of aged Cu NW without annealing 36
4.5 Chemical composition analysis 37
4.6 Helical nanotube growth mechanism 39
4.7 Cu3P NH @ 400 °C as electrocatalyst for HER 41
4.8 Cu3P dNH @ 400 °C as electrocatalyst for HER 44
4.9 Behind the superior catalytic property of Cu3P NH @ 400 °C prepared
at 60 min 46

Chapter 5 Transition Metal Dichalcogenide ((1T/2H) MOS2/α-MoO3) as Electrocatalyst
5.1 Synthesis and optimization of nanoflowers 48
5.2 Identification of phases of nanoflowers 49
5.3 Chemical composition and crystallinity analysis of nanoflowers 51
5.4 (1T/2H) MoS2/α-MoO3 as electrocatalyst for HER 55

Chapter 6 Conclusion and future perspectives 59

References 60
Appendix 67

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