掺杂对碳纳米材料性质影响的第一性原理研究

发布时间：2018-01-06 18:36

本文关键词：掺杂对碳纳米材料性质影响的第一性原理研究　出处：《中国科学技术大学》2015年博士论文　论文类型：学位论文

【摘要】：碳纳米材料是指至少有一个维度在尺寸上达到纳米量级的碳材料,主要包括几种类型：富勒烯、碳纳米粒子(碳纳米球、碳纳米胶囊)、碳纳米管(碳纳米纤维)、石墨烯以及其他的碳纳米多孔材料。碳纳米材料在力学、电学、磁学、光学和催化等方面均有着良好的性质和应用潜力,自从发现以来就引起了人们广泛的研究兴趣和热潮,成为纳米科学研究的重点对象。直到现在对碳纳米材料性质和技术的研究依然是科学研究的前沿。随着技术的发展,纯的碳纳米材料本身的性质已经满足不了人们对新材料、新性质的需求,人们不断地尝试和研究各种调制碳纳米材料的性质的新方法和新技术。实验上,掺杂作为一种传统的方法被广泛地用来调制碳纳米材料的性质。但是由于缺乏大量的实验数据,仅从实验很难从根本上理解调制碳纳米材料性质的微观机理。因此,理论模拟对于揭示这种掺杂调制的机理有着非常重要的作用。在纳米材料的研究中,量子力学是支配这些微观体系的基本规律,但是作为量子力学核心的薛定谔方程却很难解析求解,因此计算化学作为近似求解薛定谔方程的一种方法应运而生。在采用各种近似后,薛定谔方程大大简化,通过高性能计算方法可近似求解薛定谔方程。随着近二十年来计算机硬件的飞速发展,计算成本急剧降低,计算化学已经在理论模拟中表现出越来越重要的地位。而基于密度泛函理论的第一性原理计算由于其快速而可靠的计算结果使其成为计算化学中最主流的方法之一,并且成为材料科学、凝聚态物理学中重要的理论模拟手段。在本论文中,我们主要采用第一性原理计算方法研究掺杂对碳纳米材料性能的影响。本论文分为五章。第一章我们首先简要介绍了计算化学的方法,重点介绍密度泛函理论的理论框架,发展过程和常用的交换相关泛函。密度泛函理论的核心是构建单电子模型。具体实现是通过假想一个和真实体系同样电荷密度的非相互作用的单电子体系,用非相互作用体系的电子的动能和Hartree势能来近似真实的动能和电子之间相互作用能,差额的部分被归结到交换相关泛函中去,所以密度泛函理论从原理上说是精确的,其发展的核心就是找到合适的交换相关泛函,使得计算结果尽可能逼近实验。随后我们介绍了固体能带的计算方法,这些方法使得密度泛函理论在固体领域得到广泛应用。此外,我们简单介绍了采用准粒子模型的GW方法以及含时密度泛函理论。由于本文中涉及到了大量化学反应能垒的计算,所以最后简要介绍了计算化学反应能垒的方法,并简要介绍了本论文中用到的第一性原理软件包。第二章中,我们主要研究氮杂富勒烯对碳纳米管输运性质的调制。首先简要介绍了碳纳米管材料的研究进展,随后我们希望通过理论计算对一组矛盾的实验结果做出合理的解释。对于相同的封装了氮掺杂富勒烯分子的碳纳米管(“纳米豆荚”),不同的实验组测出了不同的单向导电性。通过对体系电子结构的计算,我们从理论上解释了这种不同输运性质的原因：不同的碳纳米管结构可以导致不同的输运行为,有着类似5-8-5缺陷结构的碳纳米管封装了掺氮富勒烯分子才能使得碳纳米管从p-型半导体转变为n-型半导体。第三章中,我们研究了氮掺杂的碳纳米材料。作为电极材料有着良好的催化氧气还原反应的能力并且避免了传统Pt基催化剂的缺点,如价格较高、会对CO气体中毒、对甲醇容忍性差和耐久性差。尽管这种材料的催化效率还没有完全赶上Pt基催化剂,但是有潜力作为新兴的电极材料,并在近年来得到了广泛的实验和理论研究,因此有可能取代传统Pt电极材料。由于实际催化过程的复杂性,到目前为止这种掺杂氮的碳纳米材料的催化活性中心问题依然存在争论,真正的催化机理仍然有待发展。在本章中,我们通过一个简化的模型模拟了氧气在氮掺杂的碳纳米材料上的解离过程,通过解离能垒的计算来研究氧气在不同氮掺杂结构上的反应活性。计算结果表明：氮掺杂可以提高碳纳米材料电催化的活性；在不同的氮掺杂结构中,类似石墨结构的氮掺杂方式的催化活性最好。第四章和第五章是第三章工作的深化和扩展。由于氮掺杂的碳纳米材料表现出良好的催化氧气还原反应的能力。随着研究的深入,各种不同的元素包括硼、硫等都被掺杂到碳纳米材料中。这些元素单掺杂的材料往往没有氮掺杂材料的催化活性好,但是硼氮、硫氮以及其他形式的共掺杂却表现出良好的催化氧气还原反应的活性。在第四章中,我们主要研究了硼掺杂和硼氮共掺杂的碳纳米管作为电极材料对还原氧气所起到的催化作用。我们计算了氧气在这些材料上的解离能垒,计算结果表明：硼掺杂的碳纳米管催化活性不高,而硼氮共掺杂的碳纳米管催化活性比氮掺杂的碳纳米管要好,和实验结果一致。在第五章中,我们简单测试了硫氮共掺杂对石墨烯催化氧气还原反应能力的影响,结果表明硫氮共掺杂可以有效降低氧气还原反应的能垒。
[Abstract]:Carbon nano material is refers to at least one dimension carbon material at nanometer scale in size, including several types: fullerene, carbon nanoparticles (nano carbon ball, carbon nano capsule), carbon nanotubes (CNFs), graphene and other carbon nano porous materials. Carbon nano materials in mechanical and electrical, magnetism, optics and catalysis has good properties and potential applications, have attracted extensive research interest and boom since the discovery, become the focus of nano science. Until now, the research on carbon nano material properties and technology is still the forefront of scientific research.
With the development of technology, properties of pure carbon nano material itself has been unable to meet the people of the new material, the new nature of the demand, new method and new technology of nature people constantly try and study the modulation of carbon nano materials. The doping, as a traditional method is widely used for modulation properties of carbon nano materials. But due to the lack of a large number of experimental data, only from the experiment is very difficult to fundamentally understand the microscopic mechanism of modulation of carbon nano materials in nature. Therefore, the theoretical simulation plays a very important role in the mechanism of doping modulation. In the research of nano materials, quantum mechanics is the basic rule of the micro system control however, as the core of the Schrodinger equation in quantum mechanics is difficult to solve, so the computational chemistry as an approximate method for solving the Schrodinger equation in the various came into being. Approximate, the Schrodinger equation is greatly simplified, approximate solution of Schrodinger equation by high performance computing method. As in the past twenty years the rapid development of computer hardware, the computational cost decreases sharply, computational chemistry has in the theoretical simulation shows more and more important role. And the first principle calculations based on density functional theory because of its rapid and reliable results make it become one of the most mainstream method in chemical calculation, and has become an important means of material science, simulation theory in condensed state physics. In this thesis, we mainly use the first principle calculation method of the effect of doping on the properties of carbon nano materials.
This paper is divided into five chapters. The first chapter, we first briefly introduce the computational chemistry method, focuses on the theoretical framework of the density functional theory, the development process and the common exchange correlation functional. The core density functional theory is to construct a single electron model. The specific implementation is through a single electronic system of non interaction of a hypothetical and real system the same charge density, non interaction system of the kinetic energy of the electrons and the Hartree potential approximation between real kinetic energy and electron interaction can be attributed to the difference, part of the exchange correlation functional, so the density functional theory from the principle that is accurate, the core of its development is to find the exchange correlation functionals right, so the calculation results can approximate experiment. Then we introduced the calculation method of solid band, this method makes the density functional theory in solid field widely Widely used. In addition, we introduce a simple method using GW quasi particle model and time-dependent density functional theory. The calculation of this paper involves a large number of chemical reaction energy barrier, so finally briefly introduces a method for calculating the energy barrier of chemical reaction, and the first principle used in the software package in brief introduction.
In the second chapter, on the transport properties of carbon nanotubes. We mainly study the modulation azafullerence. First briefly introduces the research progress of carbon nanotube materials, then we hope that through theoretical calculation to make a reasonable explanation for a set of contradictory experimental results. For the same package of nitrogen doped fullerene carbon nanotubes ("Nanopeapods"), the experimental group has been measured by different one-way conductivity different. Through the calculation of the electronic structure of the system, we explain the reason of different transport properties theoretically: carbon nanotube structure can lead to different transport behavior of different carbon nanotubes, a package similar to the 5-8-5 defect structure of nitrogen doped fullerene in order to make the transition from molecular carbon nanotubes p- type semiconductor is n- type semiconductor.
In the third chapter, we studied the nitrogen doped carbon nano materials. As the electrode material with good catalytic oxygen reduction reaction and avoid the shortcomings of traditional Pt based catalysts, such as high prices, will the CO gas poisoning, poor tolerance and poor durability of methanol. Although the catalytic efficiency of this kind of material is also not fully catch up with the Pt based catalyst, but has the potential as an electrode material emerging, and obtained the extensive experimental and theoretical studies in recent years, it is possible to replace the traditional Pt electrode materials. Because of the complexity of the actual catalytic processes, the catalytic center problem of carbon nano materials so far this nitrogen doped remains debatable true, the catalytic mechanism remains to be developed. In this chapter, we through the dissociation process of a simplified model of oxygen in nitrogen doped carbon nano materials on the solution from the energy barrier by Calculations were carried out to study the reactivity of oxygen on different nitrogen doped structures. The results show that nitrogen doping can improve the electrocatalytic activity of carbon nanomaterials, and in different nitrogen doped structures, graphite like structure has the best catalytic activity.
The fourth chapter and the fifth chapter is to deepen and expand the work of the third chapter. The nitrogen doped carbon nano materials exhibit good electrocatalytic activity for oxygen reduction reaction ability. With the in-depth study, the various elements including boron, sulfur and so on were doped into the carbon nano materials. These materials are often not single doped catalytic element the activity of nitrogen doped materials, but boron nitrogen, sulfur and nitrogen Co doped other forms but exhibited good catalytic activity for oxygen reduction reaction. In the fourth chapter, we mainly study the boron doped boron and nitrogen doped carbon nanotubes as electrode materials for catalytic reduction of oxygen plays. We calculated the oxygen dissociation in these materials on the energy barrier, the calculation results show that the catalytic activity of boron doped carbon nanotubes and carbon nanotubes is not high, the catalytic activity of boron nitrogen Co doped ratio of nitrogen doped carbon nanotubes to Well, it is consistent with the experimental results. In the fifth chapter, we simply tested the effect of sulfur and nitrogen co doping on the ability of graphene catalyzed oxygen reduction reaction. The results showed that sulfur and nitrogen co doping can effectively reduce the barrier of oxygen reduction reaction.

【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】：2015
【分类号】：TB383.1;O613.71

【共引文献】