摘 要

 

自2010年成功制备以来，二维材料石墨炔已经成为国内外的研究热点。石墨炔具有丰富的化学键、大的共轭体系和高比表面积，拥有良好的半导体性能和独特的物理化学性能，有望在环境和能源方面得到广泛的应用。现有研究表明，应变不仅会对材料的结构产生影响，同样还会改变材料的电子结构，所以研究石墨炔的应变效应具有很重要的意义。石墨炔具有较大的比表面积和丰富的多孔结构，是理想的金属单原子载体，有利于最大程度地提高金属单原子的利用率，在CO氧化和氢气存储等方面具有独特的应用潜质。本文通过密度泛函理论对外加应变和非贵金属修饰对石墨炔的电子结构、CO氧化和储氢性能展开研究，具体的工作和主要结论概括如下。

 

(1) 研究了外加拉伸和压缩应变对石墨炔几何结构和电子结构的影响。研究表明石墨炔能承受的应变范围为-13%的压缩应变到15%的拉伸应变。在此应变范围内石墨炔的碳碳键长随应变发生线性变化。随着外加应变的不断增大，应变能呈现单调递增趋势。石墨炔的禁带宽度随压缩应变的增大缓慢减小，随拉伸应变的增大缓慢增大。

 

(2) 以石墨炔作为Ni和Cu的单原子催化剂载体，研究其对CO氧化的催化性能。吸附能和扩散势垒计算表明，Ni和Cu原子可以稳定地吸附在石墨炔表面。进一步建立多种CO氧化反应路径，通过过渡态搜索确定CO氧化的最优反应路径和反应机理。研究表明，在Ni和Cu原子修饰石墨炔表面CO氧化反应是通过Langmuir-Hinshelwood机制和随后的Eley-Rideal机制完成的。Ni修饰石墨炔CO氧化反应的限速步骤反应势垒是0.81 eV，Cu修饰石墨炔CO氧化反应的限速步骤反应势垒是0.75 eV。上述研究表明，低成本、高活性的Ni和Cu原子修饰石墨炔是性能优异的CO氧化反应催化剂。

 

(3) 研究了Ca和Li原子修饰石墨炔的储氢性能。通过几何优化确定Ca原子和Li原子在石墨炔表面的稳定吸附位置。在储氢性能的研究中，单个和两个Ca原子修饰石墨炔可分别稳定吸附10个和20个氢气分子，氢气存储质量比分别为7.29 wt%和11.90 wt%。单个和两个Li原子修饰石墨炔可分别稳定吸附10个和16个氢气分子，氢气存储质量比分别为8.23 wt%和12.21 wt%。上述研究表明，Ca和Li原子修饰石墨炔具有优异的氢气存储性能。

 

关键词：石墨炔； 非贵金属修饰； 应变； CO氧化； 氢气存储

 

Abstract

 

Since its successful preparation in 2010,the two-dimensional graphdiyne has become the research hotspot due to its rich chemical bonds, large conjugated structure, high specific surface area, excellent semiconducting properties and unique physicochemical properties, which is expected to be widely used in the fields of environment and energy. The current studies show that the strain will not only affect the geometrical structure of the materials, but also change the electronic structure. Therefore, it is of great significance to study the strain effect of graphdiyne.Graphdiyne has large specific surface area and porous structure, which is an ideal support for single metal atom. The embedding of single metal atom on graphdiyne can maximize the utilization of singlemetal atom, which will have potential applications in CO oxidation and hydrogen storage. In this dissertation, the external strain and non-noble metal decoration on the electronic structure,CO oxidation and hydrogen storage properties of graphdiyne have been investigated using density functional theory. The detailed results and main conclusions are summarized as follows.

 

(1) The effects of external tensile and compressive strains on the geometrical structure and electronic structure of graphdiyne are studied. The results show that graphdiyne can withstand the strain inthe range from -13% compressive strain to 15% tensile strain. In this range of strain, the C-C bond length of graphdiyne changes linearly with strain.With the increase of the external strain,the strain energy presents a monotonous increasing trend. The band gap of graphdiyne decreases slowly with the increase of the compressive strain and increases slowly with the increase of the tensile strain.

 

(2) The CO oxidation of graphdiyne embedded with Ni and Cu atoms have been detailedly investigated.The results of the adsorption energy and the diffusion barrier show that Ni and Cu atoms can be stably adsorbed on the surface of graphdiyne. Furthermore, several CO oxidation reaction paths are established,and the optimal reaction path and the reaction mechanism of CO oxidation are determined through transition state search. The results show that the CO oxidation on the surface of graphdiyne embedded with Ni and Cu atomsis completed through the Langmuir-Hinshelwood mechanism and the subsequent Eley-Rideal mechanism. The reaction barrier of the rate-limiting step for the CO oxidation on Ni embedded graphdiyne is 0.81 eV, and reaction barrier of the rate-limiting stepfor the CO oxidation on Cu embedded graphdiyne is 0.75 eV.The above studies show that low-cost and high active Ni and Cu embedded graphdiyne are excellent catalysts for CO oxidation.

 

(3) The hydrogen storage performance of graphdiyne embedded with Ca and Li atoms have been detailed studied. The stable adsorption positions of Ca and Li atoms on the surface of graphdiyne are determined by the geometrical optimization. In the investigation of the hydrogen storage performance,10 and 20 hydrogen molecules can be stably adsorbed on the surface of the single and double Ca atoms embedded graphdiyne, respectively, and the corresponding hydrogen storage gravimetric density are 7.29 wt% and 11.90 wt%, respectively.At the same time, 10 and 16 hydrogen molecules can be stably adsorbed on the surface of single and double Li atoms embedded graphdiyne,respectively, and the corresponding hydrogen storage gravimetric density are 8.23 wt% and 12.21 wt%, respectively.The above studies show that the Ca and Li embedded graphdiyne exhibit excellent hydrogen storage performance.

 

Key words: Graphdiyne; Non-noble metal decoration;Strain; CO oxidation; Hydrogen storage