Mechanical bending effects on hydrogen storage of Ni decorated (8, 0) boron nitride nanotube : DFT study

Abstract

The influence of mechanical bending to tuning the hydrogen storage of Ni-functionalized of zigzag type of boron nitride nanotubes (BNNTs) has been investigated using density functional theory (DFT) with reference to the ultimate targets of the US Department of Energy (DOE). Single Ni atoms prefer to bind strongly at the axial bridge site of BN nanotube, and each Ni atom bound on BNNT may adsorb up to five, H2 molecules, with average adsorption energies per hydrogen molecule of )-1.622,-0.527 eV( for the undeformed B40N40-? = 0 , ) -1.62 , 0-0.308 eV( for the deformed B40N40-? = 15, ) -1.589, -0.310 eV( for the deformed B40N40-? = 30, and ) -1.368- -0.323 eV( for the deformed B40N40-? = 45 nanotubes respectively. with the H-H bonds between H2 molecules significantly elongated. The curvature attributed to the bending angle has effect on average adsorption energies per H2 molecule. With no metal clustering, the system gravimetric capacities are expected to be as large as 5.691 wt % for 5H2 Ni B40N40-? = 0, 15, 30, 45. While the desorption activation barriers of the complexes nH2 + Ni B40N40-? = 0 (n = 1-4) are outside the (DOE) domain (-0.2 to -0.6 eV), the complexes nH2 + Ni- B40N40-? = 0 (n = 5) is inside this domain. For nH2 + Ni- B40N40-? = 15, 30, 45 with (n = 1-2) are outside the (DOE) domain, the complexes nH2 + Ni- B40N40-? = 15, 30, 45 with (n = 3-5) are inside this domain. The hydrogen storage of the irreversible 4H2+ Ni- B40N40-? = 0, 2H2+ Ni- B40N40-? = 15, 30, 45 and reversible 5H2+ Ni- B40N40-? = 0, 3H2+ Ni- B40N40-? = 15, 30, 45 interactions are characterized in terms of density of states, pairwise and non-pairwise additivity, infrared, Raman, electrophilicity and molecular electrostatic potentials. Our calculations expect that 5H2- Ni- B40N40-j = 0, 15, 30, 45 complexes are promising hydrogen storage candidates.