Hydrogen storage in MgH_2 coated single walled carbon nanotubes

摘要

We present a density functional theory (DFT) study on the hydrogen storage capacity of (5,5) arm-chair single walled carbon nanotubes (SWCNTs) functionalized with magnesium hydride (MgH_2). Being lightweight and rich in hydrogen, MgH_2 adsorbs H_2 molecules in the vicinity of carbon nanotubes. The H_2 molecules are adsorbed dissociatively on SWCNT + MgH_2 complex. The H-H distance gets increased by more than ten times of the initial bond length 0.74 A of the H_2 molecule. The hydrogen storage capacity of three configurations namely ClMgH_2, C5MgH_2 and C10MgH_2 is reported. The density of states is computed for all the systems. The average binding energies of C5MgH_2 and C10MgH2 when H_2 molecule is adsorbed are 1.86 eV/H_2 and 1.96 eV/H_2, which are approximately equal. Thus, increasing the number of MgH_2 molecule does not vary the binding energy of H_2 adsorption. The corresponding temperature, in which desorption will take place, is 2285 K and 2457 K for C5MgH_2 and C10MgH_2 systems respectively, which are much above the room temperature.