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Sc-decorated Porous Graphene For Hydrogen Storage Properties:First-Principles Study

Posted on:2019-03-09Degree:MasterType:Thesis
Country:ChinaCandidate:J WangFull Text:PDF
GTID:2321330569977969Subject:Theoretical Physics
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Carbon nanostructures have been investigated for solid-state hydrogen storage due to the high specific surface area,fast kinetics,and reversible hydrogen storage etc.Porous graphene?PG?is one of the few two-dimensional carbon materials successfully prepared experimentally.The inherent nanopores in porous graphene are well-developed and uniformly distributed,therefore,it has a higher specific surface area,which portend highly effective hydrogen storage.Sc is the lightest TM atom,indicating that Sc-decorated PG could produce higher hydrogen storage capacity.However,there are few studies on Sc-modified porous graphene at home and abroad,and the adsorption mechanism and hydrogen storage capacity are still not clear.Therefore,using the generalized gradient approximation in density functional theory,the optimized geometrical structure,adsorption mechanism and hydrogen storage performance of Sc modified porous graphene?PG?are studied.By studying the hydrogen storage properties for Sc modified porous graphene system,it is found that the carbon ring center is the most stable adsorbed position for single Sc atom on PG,and the maximum number of adsorbed H2 molecules is four with the average adsorption energy of-0.429 eV/H2.By adding second Sc atom on the other side of the system,the hydrogen storage capacity of the system can be improved effectively.Two Sc atoms located on the opposite side of the PG carbon ring center hole is the most suitable hydrogen storage structure,and the hydrogen storage capacity reach for maximum 9.09 wt.%at the average adsorption energy of-0.296 eV/H2.The adsorption of H2 molecules in PG system is mainly attributed to orbital interaction among H,Sc,C atoms,and Coulomb attraction between negatively charged H2 molecules and positively charged Sc atoms.By studying the hydrogen storage properties of Sc decorated B doped PG system,it is found that for a single Sc atom,the most stable adsorption position on B-PG is boron-carbon hexagon center after doping with B atom.The corresponding adsorption energy is-4.004 eV,and five H2 molecules can be adsorbed around a Sc atom with the average adsorption energy of-0.515 eV/H2.Analyzing the density of states?DOS?and the charge population of the system,the adsorption of H2 molecules in Sc-B/PG system is mainly attributed to orbital interaction between H and Sc atoms,and the Coulomb attraction between the negatively charged H2 molecule and the positively charged Sc atom,after H2 molecule is polarized by Sc atoms and B-PG electrostatic field.For the system of Sc-B/PG,the largest hydrogen storage capacity structure is two Sc atoms located above the boron-carbon hexagon center in a double side of PG.This structure can absorb twelve H2 molecules with an average adsorption energy of-0.225 eV/H2,and the hydrogen storage capacity is 9.13 wt.%.The doping of B atom can increase the adsorption energy of Sc atom and H2 molecule on the system,effectively prevent the Sc atom from aggregating and improve the hydrogen storage performance.Therefore,Sc-decorated B doped porous graphene may become one of the most promising hydrogen storage materials.
Keywords/Search Tags:first principles, Sc modification, porous graphene, hydrogen storage, B doping
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