Defects-enhanced dissociation of H2 on boron nitride nanotubes.

With the density-functional theory and nudged elastic band method, the adsorption and dissociation of the hydrogen molecule on the boron nitride (BN) nanotubes with and without defects are studied theoretically. Hydrogen molecule physically adsorbs on the surface of the BN layer and nanotubes. The dissociation of the hydrogen molecule on the surface of the perfect BN layer and nanotubes is endothermic, and the energy barrier reduces with the decrease of the diameter of the tubes, while it is still larger than 2.0 eV for the (7,0) BN nanotube. Antisite, carbon substitutional, vacancy, and Stone-Wales 5775 defects on the wall of the tube are considered. With the presence of the defects, the dissociation of the hydrogen molecule becomes exothermic and the dissociation barrier can be reduced to about 0.67 eV.