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The magnesium hydride (MH)-doped carbon nanotubes (CNTs) are studied by density functional theory (DFT). MH is doped at three different sites of CNTs and the corresponding binding energies have been calculated. The hydrogen adsorption binding energies on these structures have been determined. The binding energy of adsorption for third and fourth H2molecule addition is exactly nearer to the applicable target, for achieving room temperature kinetics. The H site on CNT is the effective site for MH doping compared to other sites. The storage capacity of H2molecules, when five H2molecules are adsorbed on MH is 1.6wt%. It is shown that MH doped at various sites of CNT can be used as a good hydrogen storage medium at ambient temperatures. [ABSTRACT FROM PUBLISHER]

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: 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]