Hydrogen adsorption on magnesium-decorated (3, 3) and (5, 0) boron nitride nanotubes

Hydrogen is one of the cleanest ways to store energy in a post-fossil fuel economy. However, it can be dangerous as bulk gas and additional methods for hydrogen storage are needed. Physisorption on graphene sheets and nanotubes has been proposed as an effective approach due to their exceedingly high surface area and storage capacity similar to, or exceeding, highly compressed gas. Magnesium-doping has been demonstrated to significantly enhance hydrogen storage on boron-doped graphene sheets, but Mg-doped boron nitride nanotubes (BNNT), a potentially far more promising material due to the inherent dipoles in the surface providing stronger affinity for hydrogen, remain unexplored. In this in silico investigation, both the armchair (3,3) and zigzag (5,0) BNNT architectures, doped with Mg atoms, were examined for hydrogen storage capacity using first-principles density functional theory. Our calculations revealed that highly Mg-doped armchair and zigzag polymorphs of BNNTs could adsorb up to 9.65 and 8.77 weight percent hydrogen respectively, above the targets sought by the US Department of Energy for future hydrogen storage materials.