Ca、B掺杂对石墨烯和碳纳米管储氢性能影响的第一原理研究

发布时间：2018-01-26 23:12

本文关键词： 石墨烯碳纳米管第一原理计算储氢性能　出处：《重庆师范大学》2015年硕士论文　论文类型：学位论文

【摘要】：在人类赖以生存的环境中,我们所依靠的能源80%以上仍然来源于化石燃料的燃烧。由此产生的环境问题对人类的生存威胁越来越大。我们不得不开发一种对环境污染小的新型能源,氢能源应运而生。但是氢能源主要是以氢气的气体形式存在,易燃易爆炸,所以氢能源的储存问题便成为各国学术研究的一大热点。目前氢能源的储存研究主要集中在金属材料储氢、炭质材料储氢、金属有机骨架储氢等方面。炭质材料质量轻,比表面积大、孔状结构多使得其自从被发现以来便成为储氢研究的一大热点,尤其是对石墨烯和碳纳米管的储氢性能研究。本文采用基于密度泛函理论的第一原理计算方法,利用MS(Material Studio)软件中的CASTEP程序,对Ca、B掺杂前后的石墨烯和碳纳米管的储氢性能进行了研究。计算并分析了掺杂前后体系的形成热、原子的净电荷、Mulliken集居数、重叠集居数、态密度、能带结构、电子密度等相关量。对于石墨烯系统,研究表明:在没有掺杂之前,C原子和H原子之间不存在相互作用力,石墨烯对氢的吸附主要为物理吸附。掺杂B原子之后,体系的形成热升高,稳定性增强,电子向C原子移动,费米能级附近带隙宽度由原来的绝缘体范围变为金属范围,增强了体系内部原子之间电子的自由移动,提高了体系的储氢能力;此时体系的理论储氢量可以达到8.0wt%。掺入Ca原子之后,体系变为半导体性质,电子向C原子转移,C原子处电子密度最大,C-H之间形成较强的共价键作用,但不如B掺杂性能好。对于碳纳米管体系,Ca的掺杂使得C原子和H原子处电子密度增大,C-H之间的化学键作用增强,相比未掺杂的碳纳米管体系,导带和价带的重叠程度更强,增强了体系的储氢能力。B的掺杂,使得体系由金属性向半导体性质转变,抑制了体系中电子的移动,但部分电子仍能跨越能隙,由B原子向C原子和H原子转移,C-H之间的电子密度部分增大,使得C原子和H原子之间的化学键作用有所增强,但不如Ca掺杂对体系储氢性能的影响好。综上所述,B原子和Ca原子掺杂都有利于提高石墨烯和碳纳米管的的储氢性能,但B原子掺杂有利于提高石墨烯体系储氢性能,而Ca原子掺杂则更适用于提高碳纳米管体系的储氢性能。
[Abstract]:In the environment on which human beings depend. More than 80% of the energy we rely on still comes from the burning of fossil fuels. The resulting environmental problems are increasingly threatening the survival of mankind. We have to develop a new energy source with little environmental pollution. Hydrogen energy comes into being. However, hydrogen energy mainly exists in the form of hydrogen gas, which is flammable and explosive. Therefore, the storage of hydrogen energy has become a hot topic of academic research in many countries. At present, the research of hydrogen energy storage mainly focuses on metal materials, carbon materials, hydrogen storage. Carbon materials with light weight, large specific surface area and porous structure have become a hot spot in hydrogen storage research since they were discovered. In particular, the hydrogen storage properties of graphene and carbon nanotubes are studied. In this paper, the first principle method based on density functional theory is used to calculate the hydrogen storage properties of graphene and carbon nanotubes. Using MS(Material Studio software in the CASTEP program, Ca. The hydrogen storage properties of graphene and carbon nanotubes before and after B doping were studied. The heat of formation, the net charge of atoms and the overlapping population were calculated and analyzed. The density of states, band structure, electron density and so on. For graphene system, it is shown that there is no interaction between C atom and H atom before doping. The adsorption of graphene on hydrogen is mainly physical adsorption. After doping B atom, the formation heat of the system increases, the stability of the system increases, and the electron moves to the C atom. The band gap width near the Fermi energy level is changed from the original insulator range to the metal range, which enhances the free movement of electrons between atoms in the system and improves the hydrogen storage capacity of the system. In this case, the theoretical hydrogen storage capacity of the system can reach 8.0 wt.The system becomes semiconductor property after the addition of Ca atom, and the electron density of the C atom is the highest when the electron is transferred to the C atom. There is a strong covalent bond between C-H, but it is not as good as B-doping. For carbon nanotube system, the electron density between C atom and H atom increases with Ca doping. Compared with the undoped carbon nanotube system, the chemical bond interaction between C-H is stronger, the overlap of conduction band and valence band is stronger, which enhances the hydrogen storage ability of the system. B doping. The system changes from the gold property to the semiconductor property, which inhibits the electron movement in the system, but some electrons can still cross the energy gap and transfer from B atom to C atom and H atom. The increase of electron density between C-H and H atoms makes the chemical bond between C atom and H atom stronger, but the effect of Ca doping on hydrogen storage property of the system is not as good as that of Ca doping. Doping of B atom and Ca atom can improve the hydrogen storage performance of graphene and carbon nanotubes, but B atom doping can improve the hydrogen storage performance of graphene system. However, Ca doping is more suitable for improving the hydrogen storage performance of carbon nanotube system.
【学位授予单位】：重庆师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB34;TB383.1

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