Alkali-metal-doped B₈₀ as high-capacity hydrogen storage media

We study the feasibility of the alkali-metal (AM = Li, Na, K)-doped B ₈₀ fullerenes for hydrogen storage using first-principles calculations. It is found that the AM atoms are strongly attached at the centers of the pentagons of the B₈₀, forming B₈₀AMm complexes (1 ≤ m ≤ 12). This bonding can be attributed to the charge transfer between the AM atoms and fullerenes, such as the case of the C₆₀AM. The charge redistribution induces an electric field mainly around the positively charged AM atoms, which polarizes the H₂ molecules but does not make them dissociate. The B₈₀Na₁₂ and B₈₀K ₁₂ can store up to 72 H₂ molecules with binding energies of 1.67 and 1.99 kcal/mol, respectively, resulting in gravimetric densities of hydrogen of 11.2% and 9.8%. Moreover, the AM atoms do not cluster on the B ₈₀, which facilitates the reversible hydrogen adsorption/desorption.