原子级厚二维结构的设计、合成及其光电催化性能研究

发布时间：2018-02-09 03:49

本文关键词： 原子级厚二维结构构效关系二氧化碳还原光电解水　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：全球变暖与化石能源大量开采使用息息相关,人类社会的快速发展对能源需求持续快速增长,目前化石燃料仍占全球能源消费的80%,建立在不可重复利用的化石能源基础上的传统能源发展方式难以为继。解决能源危机和温室效应的根本出路是开发新能源、构建全球能源互联网,加快绿色能源替代,实现绿色能源大规模开发、高效率利用,从根本上解决化石能源污染和温室气体排放问题。为了实现更有效、更环保的能源利用,针对太阳能、氢能以及二氧化碳还原为碳氢燃料能源的开发,有利于建造一个清洁、高效、可持续的全球能源网络。而在众多已发展的光电解水、二氧化碳还原半导体催化剂中,原子级厚二维结构催化剂因其特殊的原子结构、电子结构特征,以及因为原子的缺失引入的缺陷结构等特征,被认为是光电解水、二氧化碳还原催化剂的有利候选者。本论文以原子级厚二维材料为研究对象,以宏观功能(光还原二氧化碳、电解水及光电解水)与微观结构(原子结构、电子结构和缺陷结构)之间内在关系为主线,旨在揭示原子级厚二维材料宏观性质与其微观结构之间的构效关系,深化对原子级厚二维材料宏观性能和结构本质的认识,为实现原子级厚二维材料功能导向的结构设计和可控制备提供新思路、新方法和新材料体系。本论文对具有应用前景的功能原子级厚二维材料的进行设计,补充及发展了可控制备方法以及表征手段,对宏观功能进行探索研究,从原子级尺度上揭露了原子级厚二维材料宏观功能与微观结构之间的关系。本论文主要研究内容如下:1.我们首次构建了一个原子级厚二维半导体的结构模型,它能提供丰富的催化活性位点,具有良好的二维电导率和优越的结构稳定性。我们通过制备Bi-油酸根层状杂化中间体得到正交相钨酸铋二维超薄结构。二维超薄结构使更多的内部原子暴露在表面,不仅有利于增加二氧化碳的吸附量,还有助于获得更高的光吸收能力。第一性原理计算显示二维超薄结构具有显著增加的态密度,进而有利于载流子传输。时间分辨荧光光谱显示二维超薄结构有利于电子-空穴的分离,进而促使光还原二氧化碳性能得到提升,为设计高效的光催化还原二氧化碳催化剂提供了新的思路。2.我们首次构建了一个具有金属性的非金属物质的原子级厚二维结构模型。以CoSe_2为例,通过制备CoSe_2-DETA(二乙烯三胺)层状杂化中间体得到正交相CoSe_2单胞厚二维结构。密度泛函理论计算和变温电导率测试均证实原子级厚正交相CoSe_2二维结构具有金属性的导电行为。同步辐射X射线吸收精细结构谱表明,相对于块材,原子级厚CoSe_2二维结构表面钴原子的配位数明显降低,这有利于提高其本征催化活性。基于此,原子级厚CoSe_2二维结构表现出相较于CoSe_2-DETA层状杂化中间体和块材更高的电流密度、更低的Tafel斜率和更高的转换频率(TOF),进而获得更好的电解水性能。3.我们建构了一个可控厚度的p型半导体纳米片模型,研究其厚度与光电解水性能之间的关系。首先通过简单的液相剥离法得到不同厚度的超薄氧化亚锡二维结构。氧化亚锡二维结构厚度越薄,比表面积越大,提供的活性位点越多,同时通过第一性原理计算得知相较于氧化亚锡块材,超薄氧化亚锡二维结构费米能级附近的态密度增强,提高了载流子的分离效率,从而获得高的可见光光转化效率。光电解水实验结果表明,3 nm厚的超薄氧化亚锡二维结构具有相对较高的光电转化效率,揭示了超薄p型半导体纳米片的厚度与光电解水分解效率的关系。
[Abstract]:Global warming and a large number of fossil energy exploitation is closely related to the rapid development of human society to the sustained and rapid growth in energy demand, the current fossil fuel still accounts for 80% of global energy consumption, the traditional energy development mode establishment in the repeated use of fossil energy on the basis of hard to continue. The fundamental way to solve the energy crisis and the greenhouse effect is developed new energy, building global energy Internet, accelerate the implementation of large-scale development of alternative green energy, green energy, efficient use of fossil energy, solve the problem of pollution and greenhouse gas emissions fundamentally. In order to achieve more efficient, more environmentally friendly energy utilization, for solar energy, hydrogen and carbon dioxide reduction for the development of hydrocarbon fuel energy, is conducive to the construction of a a clean, efficient and sustainable global energy network. And has developed in many photoelectric semiconductor solutions of water, carbon dioxide reduction In the catalyst, the atomic structure of two-dimensional thick catalyst because of its special characteristics of atomic structure, electronic structure, and because of lack of the defects induced by atomic structure characteristics, considered photoelecirolysis water, favorable candidates for reduction of carbon dioxide catalyst. The atomic level thick two-dimensional material as the research object, to the macro function (light reduction carbon dioxide, water electrolysis and photoelecirolysis water) and microstructure (electronic structure and defect structure of atomic structure, the intrinsic relationship between) as the main line, in order to reveal the relationship between the macroscopic properties of atomic thick two-dimensional material and its microstructure, deepen understanding of the macroscopic properties of atomic thick two-dimensional materials and structural nature, structure design the atomic level thick two-dimensional material function oriented and controllable preparation to provide new ideas, new methods and new materials system. This paper has the application prospect of the function of atomic level The design of thick two-dimensional materials, supplementary and the development of the controllable preparation method and characterization method, studies the macro function, from the atomic scale reveals the relationship between the macro function of atomic thickness and microstructure of two-dimensional materials. The main research contents of this paper are as follows: 1. we first constructed an atomic level the thickness of two-dimensional semiconductor structure model, it can provide the catalytic active sites rich, has good conductivity and excellent dimensional stability. We prepared Bi- structure of oleate layered hybrid system get through intermediate orthorhombic structure. Two dimensional 2D thin bismuth tungstate thin structure make more atoms exposed on the surface, not only conducive to the increase of adsorption capacity carbon dioxide, also helps to obtain higher light absorption ability. The first principle calculations show that the two-dimensional ultrathin structure has significantly increased the density of States, and For carrier transport. Time resolved fluorescence spectra display two-dimensional ultrathin structure is conducive to the separation of electron hole, and then promote the light reduction of carbon dioxide to improve the performance, for the design of efficient photocatalytic reduction of carbon dioxide catalyst provides a new idea of.2. for the first time we build the atomic level thick two-dimensional structure model with a metal non metal material. In the case of CoSe_2, the preparation of CoSe_2-DETA by (two three ethylene amine) layered hybrid intermediate orthorhombic CoSe_2 single cell thick two-dimensional structure. Density functional theory calculation and variable temperature conductivity test were confirmed the electrical behavior of atomic thick orthorhombic CoSe_2 two-dimensional structure with metallic. Synchrotron radiation X ray absorption fine structure spectra show that relative to the bulk coordination number of atomic level surface cobalt atoms thick CoSe_2 two-dimensional structure is significantly reduced, which is beneficial to improve the intrinsic catalytic activity. At the atomic level CoSe_2 thick two-dimensional structure show compared to the current density of CoSe_2-DETA layered hybrid intermediate and bulk higher Tafel, lower slope and higher switching frequency (TOF), electrolysis of water and get better performance of.3., we construct a p type semiconductor nano sheet model of a controllable thickness and its research the thickness and relationship between the performance of photoelecirolysis water. First, by a simple liquid phase separation method by thin SnO two-dimensional structure with different thickness. The thickness of tin oxide two-dimensional structure thinner, larger specific surface area, active site provides more, at the same time by first principle calculation that compared to the bulk of stannous oxide the density of state, near the thin SnO two-dimensional structure of Fermi level enhancement, to improve the separation efficiency of the carrier, so as to obtain high visible light photoelectric conversion efficiency. The experimental results show that the solution of water, 3 nm thick The two-dimensional structure of ultra-thin tin oxide has relatively high photoelectric conversion efficiency, revealing the relationship between the thickness of ultra-thin P semiconductor nanosheets and the efficiency of photoelectric decomposition of water.

【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】：2017
【分类号】：O643.36

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