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First Principles Study On Hydrogen Storage Behavior Of Ca And TiO2Decorated Graphene

Posted on:2013-09-01Degree:MasterType:Thesis
Country:ChinaCandidate:Y GaoFull Text:PDF
GTID:2251330392970365Subject:Materials science
Abstract/Summary:PDF Full Text Request
Hydrogen is one of the most desirable renewable energy sources, due to itsnon-pollution, efficiency and low mass density. How to develop hydrogen storagesystems that can operate at ambient conditions with enough gravimetric andvolumetric capacities is a critical issue. Graphene, a single atomic layer of graphite,which is considered as a relatively light and cheap material, has generated greatinterest as a potential hydrogen storage system.In this work, first-principles total energy calculations were performed in order tostudy the structure and hydrogen storage behavior on Ca-decorated graphene. On thestable structure of Ca-decorated graphene with3×3300reconstruction, thefirst hydrogen molecule adsorbed is dissociative, with the energy barrier of only0.05eV. Further adsorption of hydrogen molecules on Ca-adsorbed graphene is weak,which indicates Ca-adsorbed graphene does not suit for the hydrogen storage viaphysical adsorption of hydrogen molecules. On the other hand, hydrogen spillovermechanism could exist on Ca-decorated graphene. On the graphene with one Cadimer adsorbed, one of the four H atoms adsorbed on the Ca dimer adsorbeschemically on C in graphene more stably by0.37eV than on the Ca dimer. With thenumber of hydrogen atoms adsorbed on Ca-decorated graphene increasing, thebinding energy of hydrogen atoms tends to increase. Thus, the spillover process isenergetically favorable. The hydrogen storage capacity via the spillover mechanism inCa-adsorbed graphene depends on the Ca content and could approach7.7wt.%.In the case of hydrogen atom absorption in TiO2cluster decorated graphene, TiO2cluster is chemisorbed on graphene via C-O bond. The C atoms near TiO2cluster actas the nucleation positions for the hydrogen atom adsorption, and the binding energyof hydrogen atoms on graphene (2.8eV) is significantly enhanced due to thedecoration of TiO2clusters, which is larger than the binding energy of hydrogenatoms (2.4eV) in hydrogen molecules. It can be deduced that the hydrogen storagecapacity could reach7.3wt.%, provided that the content of TiO2in graphene is5wt.%. The results give a comprehensive understanding on electrochemical hydrogenstorage behavior of graphene-based nanocomposites.
Keywords/Search Tags:hydrogen storage, graphene, First-principles calculations, Ca, TiO2
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