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Al-decorated, single-walled carbon nanotube has been investigated for hydrogen storage applications by using Density Functional Theory (DFT) based calculations. Single Al atom-decorated on (8,0) CNT adsorbs upto six H2 molecules with a binding energy of 0.201 eV/H2. Uniform decoration of Al atom is considered for hydrogen adsorption. The first Al atom has a binding energy of 1.98 eV on (8,0) CNT and it decreases to 1.33 eV/Al and 0.922 eV/Al respectively, when the number of Al atoms is increased to four and eight. Each Al atom in (8,0) CNT-8Al adsorbs four H2 molecules, without clustering of Al atoms, and the storage capacity reaches to 6.15 wt%. This gravimetric storage capacity is higher than the revised 2015 target of U.S Department of Energy (DOE). The average adsorption binding energy of H2 in (8,0) CNT-8(Al+4H2), i.e. 0.214 eV/H2, lies between 0.20 and 0.60 eV/H2 which is required for adsorbing and desorbing H2 molecules at near ambient conditions. Thus, Al-decorated (8,0) CNT is proposed as a good hydrogen storage medium which could be useful for onboard automobile applications, at near ambient conditions. [ABSTRACT FROM AUTHOR]

Abstract: Lithium decoration is an effective strategy for improving the hydrogen adsorption binding energy and the storage capacity in carbon nanostructures. Here, it is shown that Li-decorated double carbon vacancy graphene (DVG) can be used as an efficient hydrogen storage medium by means of Density Functional Theory (DFT) based calculations. The Li binding energy in DVG is 4.04 eV, which is much higher than that of pristine graphene. A maximum of four hydrogen molecules adsorb on Li decorated on one side of DVG and this leads to a gravimetric storage capacity of 3.89 wt% with an average adsorption binding energy of 0.23 eV/H2. When Li is decorated on both sides of DVG, the gravimetric storage capacity reaches 7.26 wt% with a binding energy of 0.26 eV/H2 which shows that desorption would take place at ambient conditions. [Copyright &y& Elsevier]

Abstract: Adsorption binding energies have been calculated for Nickel-doped single-walled carbon nanotubes (CNTs). Density Functional Theory (DFT) with double numerical polarization (DNP) has been used for finding the total energies of the structures. It is found that the Nickel doped CNTs show fluctuation in the binding energies of hydrogen adsorption which is overcome by passivating the Nickel atom with two hydrogen atoms. The density of states (DOS) and Mullikan atomic charge analysis have been carried to confirm the charge transfer from Ni to the carbon atoms of the CNT. The smallest CNT (diameter ≈ 4 Å) with the chirality of (5,0) has been taken for hydrogen adsorption studies. Geometry optimization shows that Ni atom prefers bridge site rather than the centre of the hexagon. The H2 binding energies obtained in the present study reveal that desorption would take place above room temperature in Ni doped (5,0) CNTs. [Copyright &y& Elsevier]