A density functional study of hydrogen storage in Li decorated C20 fullerene

Molecular adsorption of hydrogen in lithium decorated smallest fullerene (C20Li2) has been carried out within the framework of density functional theory (DFT) at B3LYP/6311+G(d,p) level. Hydrogen molecules were added sequentially till maximum number of hydrogen molecules could be accommodate by the C20Li2. The kinetic stabilities of the hydrogenated clusters were confirmed through global reactivity descriptors and electronic band gaps. It was observed that the C20Li2 clusters could hold maximum up to eight hydrogen molecule with average adsorption energy in the range 0.11 - 0.06 eV/H2 resulting in gravimetric density of 5.98 wt% which was in accordance with the target set by US Department of Energy (US-DOE) for optimal hydrogen adsorption. The average adsorption energy value and the distance between Li atom and hydrogen molecules indicated the process to be physisorption type. Topological analysis using Bader's quantum theory of atoms in molecules (QTAIM) concluded that the interaction between H2 and Li atom to be closed shell type with ρ < 0.20 a.u with positive ∇2ρ corresponding to ionic or van der Walls bonds.