First-Principles Study Of Adsorbability Of Graphene

In this thesis, we investigated the adsorption of graphene based on den-sity functional theory(DFT), including transition metal adatom adsorption on graphene and Titanium-Embedded Graphene as High-Capacity Hydrogen-Storage Media.Graphene is a two-dimensional(2D) honeycomb-structured lattice of car-bon atoms. The bonding is very strong and graphene is highly stable. Based on its chemical structure, graphene has many unique physical and chemical proper-ties, such as high surface area, high conductivity, high strength, easy to modify and so on. Recently, graphene, due to its large surface and unusual nature, at-tracted a lot of attention, and a growing number of researchers research on that pure and doped graphene storage small molecules or gases though theoretical and experimental methods. DFT is a very useful theoretical method to study this kind of materials.At first we gived a short introduction to the development and the basic concept of DFT. Only simple H atom can be calculated by quantum mechanics at the very beginning of its foundation. Several years later, E. A. Hylleraas and D. R. Hartree calculated the ground state of Helium atom by variational and self-consistent field method, respectively; V. Fork improved the self-consistent field method forming the well-know Hartree-Fork method. This method is the prototype of many modern methods for electronic structure calculation, The DFT was founded in 1960's, it is widely used in materials simulations and com-putational chemistry because of its high precision and moderate computational consumption.In the third chapter, the adsorption of 15 different transition metal adatoms on graphene is studied. The adsorption energy, stable geometry, density of state, and magnetic moment of each adatom-graphene system are calculated. The dis-tortion of the graphene layer on B of T sites are quite significant in some casees, and the adsorption is characterized by strong hybridization between adatom and graphene electronic states. The favorable adsorption site indicates the main chemical bond between adsorbate and graphene. Half filled d shell TM atoms and Au, Ag, Zn have small adsorption energy. The reduction in magnetic mo-ment from the isolated to the adsorbed atom is explained by the perspective of charge transfer, and electron shift between different orbits states of the adatom.In the fourth chapter, we propose a system that can store hydrogen molecules in densities up to 68 g/L, which is denser than the most practical high-pressure tank,39g/L. Our first-principles calculations predict that this complex, Ti atoms embedded in double-vacancy graphene (Ti@DV), holds up to eight H2 per unit. The hydrogen molecules are not dissociated and are all stored in molecu-lar form, so the adsorption and desorption of hydrogen is feasible to achieve. Also, this type of structural is stable in charging-discharging process. The DOS of Hydrogen-Storage Media indicates little charge transfer between H2 and Ti@DV graphene.In the final chapter, we made a conclusion for this thesis, and made a plan for the following work.