  Ab initio density-functional theory study suggests that pillared Li-dispersed
boron carbide nanotubes is capable of storing hydrogen with a mass density
higher than 6.0 weight% and a volumetric density higher than 45 g/L. The boron
substitution in carbon nanotube greatly enhances the binding energy of Li atom
to the nanotube, and this binding energy (~ 2.7 eV) is greater than the
cohesive energy of lithium metal (~1.7 eV), preventing lithium from aggregation
(or segregation) at high lithium doping concentration. The adsorption energy of
hydrogen on the Li-dispersed boron carbide nanotube is in the range of 10 ~24
kJ/mol, suitable for reversible H2 adsorption/desorption at room temperature
and near ambient pressure.
