||Investigation of tunable MoS2-conductive composites by hot-injection method for electrocatalytic water splitting
||Department of Materials Science and Engineering
水分解產氫(Hydrogen evolution reaction by water splitting)是個乾淨、環保，對環境友善的製程，堪稱是現今最具有潛力的再生能源之一。傳統產氫效率低，需要藉由電觸媒的協助，二硫化鉬(Molybdenum disulfide, MoS2)擁有催化活性大及適中氫吸附自由能等優勢，然而其最大瓶頸為導電性較低、反應點侷限及製程時間長。為了改善這些缺點，通常會透過與導電性良好的材料結合，提升電子傳遞速率並可扮演MoS2生長基材的角色。本研究成功利用簡易、低成本之熱注入法製備油胺包覆之單層二硫化鉬(OLA-protected monolayer MoS2)，並透過製程參數改變，即可形成不同種與導電材結合的複合物(MoS2-MoO2, MoS2-carbon)。其中透過反應溫度及時間的增加，產生MoO3→MoO2→MoS2的趨勢，顯微結構證實形成二硫化鉬-二氧化鉬核殼結構(MoS2-MoO2 core-shell structure)；除此之外，利用油胺(Oleylamine, OLA)作為製備溶劑，它更會滲入MoS2層間將之分離成單層MoS2，並透過進一步退火將缺乏導電及催化性之OLA高溫碳化成carbon。MoS2層間膨脹，其層間距從0.61 nm膨脹至1.02 nm，且單層MoS2和carbon彼此交層排列，形成二硫化鉬-碳材交層結構(MoS2-carbon interoverlapped structure)。MoS2-導電材複合材料之電催化效能，皆較純相MoS2、MoO2大幅提升，起始電位及塔弗斜率有效降低。MoS2-MoO2顯著的效果提升主要是來自MoS2豐富的活性點及MoO2有助於載子傳遞方向的改善；而MoS2-carbon則是因為OLA將MoS2層間距增加，形成單層結構，單層MoS2及硫缺陷貢獻豐富活性催化點，且交替碳層造成MoS2層間導電性提升。
Hydrogen has been considered as one of the most promising renewable energy for production and storage. MoS2-MoO2 composite can act as an excellent electrocatalyst for hydrogen evolution reaction (HER) because of the presence of high concentration of effective active sites and good conductivity. Here, we report an efficient method to synthesize MoS2-MoO2 composite by hot-injection method using MoO3 and S powder as precursors with oleic acid (OA) and oleylamine (OLA) as solvent, respectively. With increasing reaction temperature and time, OA will reorganize the octahedral units of MoO3 and gradually turn into low valence of Mo. After injecting S-precursor, OLA will first reduce Mo-precursor to MoO2 as core, and then S atoms replace O atoms to form MoS2 as shell, eventually forming MoS2-MoO2 core-shell structure. A Tafel slope of 129 mV/dec was measured for MoS2-MoO2 composite, which is much better than MoS2 and MoO2 alone. The enhanced HER performance is attributed to the improved charge transfer direction by MoO2 and the abundance active sites from MoS2.
Extended Abstract II
1.1 前言 1
1.2 二硫化鉬的發展 3
1.3 二硫化鉬用於水分解產氫的發展史 4
1.4 研究動機與目的 6
2.1 水分解產氫反應 (Water Splitting for Hydrogen Evolution Reaction) 7
2.2 電催化材料選用 12
2.2.1 電催化材料選用要求 12
2.2.2 評斷性質表現的重要參數 14
2.2.3 常用的電催化材料 19
2.3 二硫化鉬 (Molybdenum disulfide, MoS2) 27
2.3.1 結構與其多形體 (Polymorph) 27
2.3.2 催化性質 29
2.3.3 製程 32
2.4 二硫化鉬應用於電催化產氫 36
2.4.1 少層數(Few-layer)、層間膨脹(Layer-expanded)之MoS2 36
2.4.2 MoS2與導電材結合 39
3.1 實驗藥品 49
3.2 實驗裝置 50
3.2.1 熱注入裝置 50
3.2.2 管狀高溫爐裝置 51
3.2.3 電化學量測裝置 52
3.3 實驗流程 53
3.3.1 油胺包覆之單層二硫化鉬 (OLA-protected Monolayer MoS2) 53
3.3.2 二硫化鉬-二氧化鉬複合材料 (MoS2-MoO2) 55
3.3.3 二硫化鉬-碳材複合材料 (MoS2-carbon) 57
3.3.4 製備工作電極 (Working electrode preparation) 59
3.4 分析儀器 60
3.4.1 微結構與成分分析 60
3.4.2 電化學性質分析 61
Part 1 純相二硫化鉬 62
4.1 油胺包覆之單層二硫化鉬 (OLA-protected Monolayer MoS2) 62
4.1.1 成分與鍵結分析 62
4.1.2 微結構分析 65
4.1.3 價數態與元素能譜分析 67
4.1.4 電催化產氫效能量測與機制探討 69
4.1.5 小結 71
Part 2 二硫化鉬與導電材之複合相 72
4.2 二硫化鉬-二氧化鉬核殼結構 (MoS2-MoO2 core-shell structure) 72
4.2.1 成分與鍵結分析 73
§ 注入前Mo-precursor隨反應溫度與時間的變化 73
§ 注入S源後隨反應溫度與時間的變化 76
4.2.2 微結構分析 81
4.2.3 價數態與元素能譜分析 86
4.2.4 電催化產氫效能量測與機制探討 88
4.2.5 小結 91
4.3 二硫化鉬-碳交互層狀結構 (MoS2-carbon interoverlapped structure) 92
4.3.1 成分與鍵結分析 92
4.3.2 微結構分析 95
4.3.3 價數態與元素能譜分析 97
4.3.4 電催化產氫效能量測與機制探討 99
4.3.5 小結 102
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