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First-principles Study On The Hydrogen Storage Properties Of Metal-modified Point Defect Graphene And Carbon Nanotubes

Posted on:2019-09-03Degree:MasterType:Thesis
Country:ChinaCandidate:M M HuFull Text:PDF
GTID:2371330545450135Subject:Atomic and molecular physics
Abstract/Summary:PDF Full Text Request
Due to the limitation of production technology,the defects of carbon nanomaterials are widespread,and the defects have an important influence on the physical and chemical properties of carbon nanomaterials.Based on density functional theory(DFT),the hydrogen storage properties and electronic properties of intrinsic defects caused by single extra carbon atom doping and two extra carbon atoms doping in graphene and carbon nanotubes are studied in this paper.On this basis,the electronic modification and hydrogen storage properties of C-Bridge defects of single carbon atom and the electronic modification and hydrogen storage properties of two carbon atom C7557 defects were studied.The electronic properties and hydrogen storage properties of B,N and Li doped single carbon atoms C-Bridge defects in the carbon nanotubes system were investigated.The electronic properties and hydrogen storage properties of two kinds of carbon atoms doped C7557 defects were investigated.The effect of lithium doping on the hydrogen storage capacity of graphene with two intrinsic defects was investigated by first principle calculation.The results of calculation and analysis show that:(1)C-Bridge and C7557,the two different structures of intrinsic defects have proper formation energy,which indicates that they are stable structures.(2)The binding energy of Li atoms on C-Bridge and C7557 is higher than the cohesive energy of Li atoms and the binding energy of Li atoms on graphene atoms.The magnetic properties caused by C-Bridge defects depend on the characteristics of Li doping,but there is no magnetic moment when Li is adsorbed at C7557 position.(3)The doping of Li atoms can regulate the Dirac cone and Fermi surface in the graphene band structure.(4)The ability of hydrogen storage at intrinsic defect points is weak and the storage capacity of defected graphene can be improved by proper selection of Li doping.We believe that these two systems may be expected to be used in hydrogen storage in the near future.The electronic properties and hydrogen storage properties of small-diameter single-walled carbon nanotubes(5 * 5)containing interstitial defects were simulated by the first principle.The conclusions are summarized as follows:(1)The single carbon atom doped C-Bridge defect is a stable structure.The introduction of defects increases the chemical activity of carbon nanotubes.On this basis,the substitutionof B and N represents the introduction of carriers of two forms,hole and electron,respectively.(2)These operations reduce the band gap of the carbon nanotubes and change the electronic structure within the defect local area.The alkali metal Li atoms can be doped above the C-Bridge-SWCNT and the N/C-Bridge/SWCNT,and the adsorption energy of Li can be greater than that of Li,and Li atoms can be well dispersed on both defects and do not have clusters.(3)Compared with the absence of Li atoms,the doping of Li atoms leads to the redistribution of electrons at the defects,which results in a very good hydrogen storage effect.The Li/C Bridge can adsorb 6 hydrogen molecules,Li/N/C-Bridge can adsorb 8hydrogen molecules.It can be predicted that there will be a very high mass fraction of hydrogen storage when Li doping is extended to the whole plane.(4)The defect structure C7557 with two interstitial carbon atoms is a highly symmetric defect type.Alkali metal Li,alkali earth metal Ca and transition metal Ti can all be doped on C7557-SWCNT,and the adsorption energy is 3.065 eV,3.405 eV,5.133 eV,respectively.(5)Li/C7557 can adsorb 6 hydrogen molecules and Ca/C7557 can absorb 9 hydrogen molecules.
Keywords/Search Tags:First-principles, Defects, Graphene, Carbon nanotubes, Hydrogen storage
PDF Full Text Request
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