二氧化钼及其复合材料的制备与电催化制氢性能的研究

发布时间：2018-09-12 11:11

【摘要】：20世纪以来人类社会进入高速发展的阶段,人口增长,科技创新,使人们的生活发生了翻天覆地的变化。而为了支撑起现代人的日常生活,我们对能源的需求也不断增大。化石燃料大量无节制的开采与使用虽然满足了一时的发展需求,但是长远来讲,其产生的污染则是无法忽视的问题。因此,研究探索新型的清洁能源材料对人类社会的可持续发展具有重要的意义。氢气是一个良好的能量载体,燃烧后只会产生水,对环境没有危害,因此世界各国都将氢气作为未来的重要能源进行研究。然而作为一种二次能源,想要得到氢气必须要经过能量转换的步骤。目前由于引入了化石燃料的使用,工业化的氢气制取方式在生产氢气的过程中会生成大量温室气体,因此,寻找新型无污染的制氢方法迫在眉睫。电解水制氢技术是一种高效且无污染的制氢方式,通过电解槽直接将电能转化为化学能储存。目前在生产中使用的电极主要是铂碳类材料,其过电势小,并且可以达到较大的电流密度。但是由于贵金属铂的含量稀少且价格昂贵限制了其大范围的应用,在这种情况下,寻找新型的电催化制氢材料具有很大的意义。二氧化钼作为一种具有金属性的半导体拥有良好的电导率,同时由于其特殊的结构也被广泛地用于有机催化领域。本论文主要是针对二氧化钼这一金属相半导体及其复合物的制备以及它们在电催化制氢领域的应用进行了深入的研究。首先,我们利用三氧化钼与钼粉间的氧化还原反应制备了附载在石墨烯上的二氧化钼纳米颗粒并测试其电催化制氢性能；之后,我们利用钼片代替钼粉在钼片上直接生长了一层二氧化钼薄膜,使钼片作为集流体来进一步提升二氧化钼的电催化制氢性能；在实验中我们发现二氧化钼与铂之间存在“贵金属——载体间强相互作用”,因此我们制备了均匀负载铂的二氧化钼／碳纳米管复合材料,并发现其展现了优异的电催化制氢性能,可以与商用铂碳电极媲美。通过以上一系列的研究,我们认为二氧化钼由于其特殊的性质,在电催化领域具有很大的应用前景。本论文的内容分为以下四章：第一章为绪论,文中首先概述电解水制氢技术与氢电极反应的概念和基本原理,然后简要介绍了氢析出反应催化剂的选择与其设计和制备原则,接着介绍了近年来这一领域的发展,以及常见的硫化物、磷化物与复合材料催化剂。最后讨论了本论文的研究内容及意义。在第二章中,我们介绍了一种利用简单的氧化还原反应机理制备二氧化钼／还原石墨烯复合物的方法,利用石墨烯的空间限制作用我们成功控制了二氧化钼颗粒的尺寸。由于石墨烯与二氧化钼间的协同效应,在二氧化钼和石墨烯本身都没有优异的电催化制氢活性的前提下,制备的二氧化钼/还原石墨烯复合物展示了优良的催化活性,190 mV的起始过电势,塔菲尔斜率达到49 mV/dec。除此之外,该材料在酸性和碱性条件下都显示了良好的循环稳定性。经过分析我们认为,这种非同寻常的性能提升可以归功于复合材料更小的粒径,更多的活性位点与更好的导电性。第三章中,我们报道了不含贵金属的高效电催化制氢电极：直接生长在钼片上的磷掺杂二氧化钼纳米颗粒。钼片作为集流体,得到的电极展示了良好的电催化制氢活性：小的起始过电势80 mV,达到10 mA cm-2的阴极电流时过电势为135 mV,塔菲尔斜率为62 mV/dec,优于其他的二氧化钼基的催化材料。另外,经过2000次CV测试之后,我们发现这种磷掺杂二氧化钼薄膜/钼片电极具有很好的酸性稳定性。这种新颖的直接在钼片上生长磷掺杂二氧化钼的方法得到了一种高效的HER催化剂,拓展了我们合成不含贵金属、高效、低廉并且环境友好的HER催化剂的视野。第四章中,在本章工作中,我们综合了铂、二氧化钼以及碳纳米管的特性,制备出一种超低铂含量的复合材料作为高效的电催化产氢催化剂,同时在酸性介质中体现了良好的稳定性。这种铂-二氧化钼-碳纳米管的复合材料由简单的氧化还原反应制备得到,同时显示出卓越的电催化活性和良好的稳定性,它展现出了几乎为0的起始过电势,43 mV/dec的塔菲尔斜率,以及在过电势为60 mV和84mV时达到10 mA cm-2和20 mA cm-2的法拉第电流密度。由于二氧化钼与铂之间的强作用力以及较高的电导率,这种铂-二氧化钼-碳纳米管的复合材料的电催化产氢效率和稳定性要优于商用的铂碳电催化剂。引人注目的是,如此高的催化活性和增强的稳定性仅仅是由含有0.5 wt%铂的复合催化剂得到的。我们的工作在研发高效率、低铂含量的电催化剂领域开启了一条新的道路,同时保证了理想的催化活性和耐用性。
[Abstract]:Since the 20th century, human society has entered a stage of rapid development, population growth, scientific and technological innovation, so that people's lives have undergone earth-shaking changes. In order to support the daily life of modern people, our demand for energy is increasing. Although a large number of uncontrolled exploitation and use of fossil fuels meet the development needs of the moment, but In the long run, the pollution caused by hydrogen is a problem that can not be ignored. Therefore, it is of great significance to study and explore new clean energy materials for the sustainable development of human society. However, as a secondary energy source, hydrogen must go through the steps of energy conversion. At present, due to the introduction of fossil fuels, industrialized hydrogen production will generate a large number of greenhouse gases in the process of hydrogen production, so it is urgent to find a new pollution-free hydrogen production method. Hydrogen production technology is an efficient and non-polluting way of hydrogen production. Electric energy is directly converted into chemical energy by electrolytic cells. The electrodes used in production are mainly platinum-carbon materials with low overpotential and high current density. As a kind of metal semiconductor, molybdenum dioxide has good conductivity and is widely used in the field of organic catalysis because of its special structure. This paper mainly focuses on molybdenum dioxide, a metal phase semiconductor and its application. The preparation of the composite and its application in the field of electrocatalytic hydrogen production have been studied in depth. Firstly, molybdenum dioxide nanoparticles supported on graphene have been prepared by the oxidation-reduction reaction between molybdenum trioxide and molybdenum powder, and their electrocatalytic hydrogen production performance has been tested. A layer of molybdenum dioxide film was grown to further enhance the electrocatalytic hydrogen production performance of molybdenum dioxide by using molybdenum sheet as a collector. In the experiment, we found that there was a "strong interaction between noble metal and support" between molybdenum dioxide and platinum, so we prepared a uniformly loaded platinum molybdenum dioxide / carbon nanotube composite. Through the above series of studies, we believe that molybdenum dioxide has a great application prospect in the field of electrocatalysis because of its special properties. The contents of this paper are divided into the following four chapters: Chapter 1 is an introduction, and the electrolytic water is first summarized in this paper. The concept and basic principle of hydrogen production technology and hydrogen electrode reaction are introduced. Then the selection of hydrogen precipitation catalyst, its design and preparation principle are briefly introduced. Then the recent development in this field, as well as the common sulfides, phosphides and composite catalysts are introduced. Finally, the research contents and significance of this paper are discussed. In Chapter 2, we introduce a method of preparing molybdenum dioxide/reduced graphene composites by a simple oxidation-reduction reaction mechanism. We have successfully controlled the size of molybdenum dioxide particles by using the space-limiting effect of graphene. Due to the synergistic effect between graphene and molybdenum dioxide, there is no molybdenum dioxide or graphene itself. On the premise of excellent electrocatalytic activity for hydrogen production, the prepared molybdenum dioxide/reduced graphene composite exhibited excellent catalytic activity. The initial overpotential of 190 mV and the slope of Tafel reached 49 mV/dec. In addition, the material exhibited good cyclic stability in both acidic and alkaline conditions. The unusual performance improvement can be attributed to the smaller particle size, more active sites and better conductivity of the composite. In Chapter 3, we report a highly efficient electrocatalytic hydrogen production electrode without precious metals: phosphorus-doped molybdenum dioxide nanoparticles grown directly on molybdenum sheets. Molybdenum sheets as a collector exhibit good performance. Electrocatalytic hydrogen production activity: low initial overpotential of 80 mV, cathode current of 10 mA cm-2, overpotential of 135 mV, Tafel slope of 62 mV / dec, better than other catalytic materials based on molybdenum dioxide. In addition, after 2000 CV tests, we found that this phosphorus-doped molybdenum dioxide film / molybdenum sheet electrode has good acidity stability. Qualitative. This novel method of directly growing phosphorus-doped molybdenum dioxide on molybdenum sheets yields an efficient HER catalyst, which broadens our vision for the synthesis of HER catalysts without precious metals, high efficiency, low cost and environmental friendliness. A composite material with ultra-low platinum content was prepared as a highly efficient electrocatalytic hydrogen production catalyst and exhibited good stability in acidic media. The composite material was prepared by simple oxidation-reduction reaction and showed excellent electrocatalytic activity and stability. The initial overpotential of almost zero, the Tafel slope of 43 mV/dec, and the Faraday current density of 10 mA cm-2 and 20 mA cm-2 at overpotential of 60 mV and 84 mV have been found. It is noticeable that such high catalytic activity and enhanced stability are obtained only from a composite catalyst containing 0.5 wt% platinum. Our work opens a new path in the development of high-efficiency, low-platinum electrocatalysts and ensures an ideal catalysis. Activity and durability.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ136.12;O643.36

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