Reversible hydrogen storage on alkali metal (Li and Na) decorated C20 fullerene: A density functional study

Abstract

This work reports the reversible hydrogen storage capacities of Li and Na decorated C20 fullerene using dispersion corrected density functional theory calculation. The alkali metal (AM) atoms are found to bind on the C–C bridge position of C20 through non-covalent closed-shell interaction. Their thermodynamic stabilities are verified through HOMO-LUMO gaps and different reactivity descriptors. Each Li and Na atoms decorated on C20 adsorb maximum up to five H2 molecules through Niu-Rao-Jena interaction. The adsorption energy decreases with successive addition of H2 molecules with average binding energy lying in the range of 0.12 eV–0.13 eV. The systems can have a maximum gravimetric density of 13.08 wt% and 10.82 wt% for C20Li4–20H2 and C20Na4–20H2 respectively. ADMP molecular dynamic simulations illustrate the reversibility of adsorbed hydrogen molecules at higher temperature (≧ 300 K). The calculated thermodynamic useable hydrogen capacity shows the room temperature H2 desorption condition of AM decorated C20. Consistent with criteria set by the US-DOE, C20Li4 and C20Na4 can be used as promising hydrogen storage materials.