Hydrogen saturation limit of Ti-doped BN nanotube with B-N defects: An insight from DFT calculations

Ti-decorated (10,0) single-walled BN nanotubes (BNNTs) with B-N defects was fully examined by density functional theory (DFT). According to DFT formalisms, the HOMO-LUMO gap found for the Ti-BNNTs is small compared to that of a wide-gap semiconducting pristine BNNT. The Ti atom does not form any clusters and protrudes to the external surface of the sidewall. The calculations suggest that the Ti-BNNT assembly can attract small molecules and it has a good affinity towards H₂ molecules. Up to seven H₂ can partially attach to the system in quasi-molecular fashion due to the partially cationic character of the functionalized Ti and heteropolar bonds exhibited at the BNNT surface. The binding energies of H₂ with Ti-BNNTs are within the optimal range for H₂ storage. The unique electronic structure is barely perturbed upon adsorption and the (H₂)_7xTi_xBNNT systems hydrogen storage capacity is in compliance to the specifications mandated by the Department of Energy.