本研究利用單層至少數層二硒化鉬奈米花之壓電效應進行分解水產氫。單層至少數層二硒化鉬奈米花為n型半導體且具有非對稱中心結構，使其具有壓電材料特性。在壓電產氫應用中，選用甲醇作為犧牲劑並且在以超音波震盪機 (300 W, 59 kHz) 作為機械能之外力系統中，二硒化鉬奈米花之最佳產氫速率達4649 μmolg-1h-1，氫氣量隨著增加超音波震盪機系統之頻率和功率而有顯著上升。經由三次循環產氫試驗後，二硒化鉬奈米花具有86 ％之催化活性。此外，二硒化鉬奈米花經由TEM、XPS儀器鑑定為具有1T金屬相及2H半導體相，可藉由1T金屬相轉為2H半導體相之相轉變處理，在氬氣氛圍中進行250 ℃退火兩小時後，以XPS儀器鑑定，其1T金屬相之比例從77.0 %下降至31.5 %，而2H半導體相比例從23.0 %上升至68.5 %。將退火前後之二硒化鉬奈米花進行壓電產氫試驗，結果顯示退火前具有較高比例之1T金屬相及較低比例之2H半導體相的二硒化鉬奈米花有較高的產氫量。此結果可支持1T金屬相在水分解產氫之氧化還原過程中，作為載子之通道，減少電子和電洞之再結合現象，而2H半導體相作為壓電效應之來源，可經由機械能驅動產生極化現象，使電子電動對分離。

The piezocatalytic effect of the single-and few-layered MoSe⁠2 nanoflowers for generating hydrogen gas from water splitting was demonstrated in this study. The single-and few-layered MoSe⁠2 nanoflowers possessed non-centrosymmetric structure with piezoelectric property, which showed a piezocatalytic activity in hydrogen production. The maximal piezocatalytic hydrogen evolution rate of MoSe2 nanoflowers reached to 4649 µmol·g-1 h-1 by using methanol as sacrificial reagent under ultrasonic-wave vibration (300 W, 59 kHz). Higher amount of hydrogen gas output could be observed at higher frequency- and power-modulation of ultrasonic-wave vibration system. After the three consecutive cycling tests, it showed 86 % of catalytic activity remained. Furthermore, TEM and XPS confirmed that 1T metallic phase and 2H semiconducting phase coexisted in MoSe2 nanoflowers. The phase transformation was conducted by 250 °C thermal annealing treatment under argon atmosphere for 2 h. The ratio of 1T metallic decreased from 77.0 % to 31.5 %, while the ratio of 2H semiconducting phase increased from 23.0 % to 68.5 %. The MoSe2 nanoflowers was compared to annealed MoSe2 nanoflowers by piezocatalytic hydrogen evolution experiment. The MoSe2 nanoflowers with high ratio of 1T metallic and low ratio of 2H semiconducting phase exhibited an enhanced hydrogen evolution yields. This result could suggest that the 1T metallic phase acted as the channel for electron carriers during the redox process, reducing the recombination of electron and hole pairs. On the other hand, 2H semiconducting phase contributed to piezoelectric polarization process.

摘要 I
Abstract III
致謝 V
Chapter 1 Introduction 1
1.1 Background information 1
1.2 Motivation 3
Chapter 2 Literature Review 4
2.1 Photocatalytic water splitting 4
2.1.1 Principle of photocatalytic water splitting 5
2.1.2 Photocatalyst for water splitting 6
2.1.3 Methods for improving photocatalytic activity 8
2.2 Piezocatalytic water splitting 15
2.2.1 Piezoelectric effect 15
2.2.2 Principle of piezocatalytic water splitting 16
2.2.3 Recent development of piezocatalytic water splitting 21
2.3 2D Transition‐metal dichalcogenides (TMDs) 25
2.3.1 Brief introduction 26
2.3.2 Piezoelectric properties of TMDs 28
2.3.3 TMDs as piezocatalysts 32
2.4 MoSe2 35
2.4.1 Brief introduction 35
2.4.2 Synthesis methods of MoSe2 37
2.4.2.1 Chemical vapor deposition 37
2.4.2.2 Hydrothermal method 39
2.4.2.3 Liquid exfoliation 41
2.4.3 1T and 2H phase of MoSe2 on H2 evolution application 42
Chapter 3 Experimental Designs 45
3.1 Experimental procedures 45
3.1.1 Synthesis procedures of MoSe2 nanoflowers 47
3.1.2 Experimental setup of piezocatalytic water splitting 49
3.2 Piezocatalytic water splitting measurements 51
3.2.1 Ultrasonic cleaner 51
3.2.2 Gas chromatography (GC) 52
3.3 Instruments for characterization analysis 55
3.3.1 X-ray diffractometer (XRD) 55
3.3.2 Scanning electron microscopy (SEM) 56
3.3.3 Field-emission transmission electron microscopy (FETEM) 57
3.3.4 X-ray photoelectron spectrometry (XPS) 58
3.3.5 Piezoresponse force microscopy (PFM) 59
Chapter 4 Results and Discussion 61
4.1 Characterizations of MoSe2 nanoflowers 61
4.1.1 SEM analysis 61
4.1.2 XRD analysis 63
4.1.3 TEM analysis 65
4.1.4 XPS analysis 70
4.1.5 PFM analysis 73
4.2 Piezocatalytic water splitting of hydrogen evolution 75
4.2.1 Effect of alcohol sacrificial reagent 75
4.2.2 Effect of vibration frequency 77
4.2.3 Effect of vibration power 79
4.2.4 Effect of 1T and 2H phases 80
4.2.5 Long-term stability test 82
4.2.6 Cycling test 83
4.2.7 Mechanism of piezocatalytic hydrogen evolution 84
4.2.8 Piezocatalytic H2 evolution rate analysis 86
Chapter 5 Conclusions 88
Chapter 6 Future Prospects 90
References 91

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