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.