金属钇修饰硼富勒烯储氢性能的第一性原理研究

发布时间：2018-05-15 13:10

本文选题：第一性原理 + 储氢　；参考：《中国海洋大学》2015年硕士论文

【摘要】：随着工业的发展和人们对能源需求的不断增加,传统能源也面临着枯竭等难题。从可持续发展角度来看,人们亟需开发一种新型可再生的清洁能源来替代传统能源。氢能作为一种来源丰富、无污染的可再生能源,目前受到广泛的关注和研究。利用氢能首先面对的就是氢气的存储问题,这是氢能开发利用的瓶颈。传统储氢技术不仅成本高、安全性能低,而且储氢率也不能满足实际的需求。近十几年来,纳米材料具有独特的纳米尺寸效应和性能,被认为是极具潜力的储氢材料。本论文主要讨论在吸附过渡金属后,富勒烯对氢气的存储情况。主要内容如下：(1)富勒烯对过渡金属的吸附。我们研究了单个金属Y原子在硼富勒烯(B80)表面上可能的吸附位,包括硼环的正上方和B-B键的正上方。计算结果发现,金属Y原子更容易稳定吸附在硼五元环的正上方。同时,我们还选取了碳富勒烯(C70)作为吸附基底,研究了过渡金属Sc原子在C70富勒烯表面可能的吸附位。通过吸附位置、吸附能、键长等参数的比较,选取了最稳定的吸附位置,为接下来氢气的吸附做好基础。(2)吸附过渡金属对富勒烯储氢的影响。采用密度泛函理论,模拟计算了吸附单个过渡金属后纳米材料体系的储氢性能,结果表明吸附金属原子后,富勒烯储氢性能有了很大的提高。在BsoY体系中,每个Y原子最多可以吸附六个氢分子,平均吸附能为-0.55eV,这个能量值在常温下对氢分子的吸附脱附都非常有利。当在B8o富勒烯表面所有五元环上均吸附Y原子后,体系的储氢率可达6.85wt%。与Bso富勒烯吸附情况相比较,C70Sc体系中金属原子最多可以吸附四个氢分子,当在C70富勒烯表面可能吸附位均吸附上金属Sc原子后,体系理论储氢率可达6.50wt%,但模拟结果显示有部分氢分子游离于体系外,并没有与金属原子成键。(3)吸附机理探究。进一步探究修饰过渡金属后纳米材料储氢率大幅度提高的原因,并分析了相应体系的差分电荷密度图和投影态密度图。通过比较分析可知,在氢气的吸附过程中,过渡金属扮演着“桥梁”的作用,即氢分子被吸附后,首先将成键轨道中的电子转移到了金属的d轨道上,填充满的d轨道会反过来将部分电子反馈给氢分子的反键轨道,也就是所谓的"Dewar-Chatt-Duncanson"作用。此时,金属原子在电子转移过程中形成的极化电场也对氢分子的吸附起到促进作用。
[Abstract]:With the development of industry and the increasing demand for energy, traditional energy is also faced with problems such as exhaustion. From the perspective of sustainable development, people urgently need to develop a new renewable clean energy to replace traditional energy. Hydrogen energy, as a kind of renewable energy with abundant sources and no pollution, has received extensive attention and research. Hydrogen energy is first used in hydrogen storage, which is the bottleneck of hydrogen energy development and utilization. Traditional hydrogen storage technology not only has high cost and low safety performance, but also can not meet the actual demand. In recent years, nanomaterials have been considered as potential hydrogen storage materials because of their unique nanometer size effect and properties. This paper mainly discusses the hydrogen storage of fullerene after adsorption of transition metal. The main contents are as follows: 1) adsorption of transition metals by fullerene. We have studied the possible adsorption sites of a single metal Y atom on the surface of boron fullerene (B80), including the positive surface of the boron ring and the positive top of the B-B bond. The calculated results show that the Y atom is more stable to adsorb on the straight top of the boron quaternary ring. At the same time, the possible adsorption sites of transition metal SC on the surface of C70 fullerenes were studied by using carbon fullerenes (C70) as the adsorption substrate. By comparing the adsorption site, adsorption energy, bond length and other parameters, the most stable adsorption sites were selected, and the effect of transition metal adsorption on the hydrogen storage of fullerenes was established for the subsequent hydrogen adsorption. The hydrogen storage properties of nanomaterials adsorbed on a single transition metal were simulated by using density functional theory. The results showed that the hydrogen storage performance of fullerenes was greatly improved after adsorption of metal atoms. In BsoY system, up to six hydrogen molecules can be adsorbed by each Y atom, with an average adsorption energy of -0.55 EV. This energy value is very favorable for the adsorption and desorption of hydrogen molecules at room temperature. When Y atoms are adsorbed on all five-member rings on the surface of B8o fullerene, the hydrogen storage rate of the system can reach 6.85 wt. Compared with the adsorption of Bso fullerenes, metal atoms can adsorb up to four hydrogen molecules in C _ (70) S _ (c) system. When the possible adsorption sites on the surface of C _ (70) fullerene are all adsorbed on metal SC atoms, The theoretical hydrogen storage rate of the system can reach 6.50 wts. but the simulation results show that some hydrogen molecules are dissociated outside the system without bonding with metal atoms. The reasons for the increase of hydrogen storage rate after modification of transition metal were investigated and the differential charge density and projected state density of the corresponding system were analyzed. Through comparison and analysis, it can be seen that transition metals play a "bridge" role in the hydrogen adsorption process, that is, after the hydrogen molecules are adsorbed, the electrons in the bonding orbitals are first transferred to the d orbitals of the metals. Filled d orbitals will in turn feed some electrons back to the antibonding orbitals of hydrogen molecules, known as "Dewar-Chatt-Duncanson". At this point, the polarized electric field formed by metal atoms during electron transfer also promotes the adsorption of hydrogen molecules.
【学位授予单位】：中国海洋大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB34;TQ116.2

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