Ca-Coated Boron Fullerenes and Nanotubes as Superior Hydrogen Storage Materials

A comprehensive study was performed on hydrogen adsorption and storage in Ca-coated boron fullerenes and nanotubes by means of density functional computations. Ca strongly binds to boron fullerene and nanotube surfaces due to charge transfer between Ca and the B substrate. Accordingly, Ca atoms do not cluster on the surface of the boron substrate, while transition metals (such as Ti and Sc) persist in clustering on the B-80 surface. B-80 fullerene coated with 12 Ca atoms can store up to 60 H-2 molecules with a binding energy of 0.12-0.40 eV/H-2, corresponding to a gravimetric density of 8.2 wt %, while the hydrogen storage capacity in a (9,0) B nanotube is 7.6 wt % with a binding energy of 0.10-0.30 eV/H-2. The Ca-coated boron fullerenes and nanotubes proposed in this work are favorable for reversible adsorption and desorption of hydrogen at ambient conditions.