A DFT study of the hydrogen storage potentials and properties of Na- and Li-doped fullerenes

Developing solid-state materials with high gravimetric and volumetric densities is critical for the use of hydrogen as an alternative to fossil fuels. However, the hydrogen storage process must be reversible under moderate temperature, pressure and a high sorption rate. Li- (Li6C60) and Na- (Na6C60) doped fullerenes represent strongly promising storage materials, but their structures, stabilities and electronic properties remain unclear. The hydrogen interaction mechanisms with these materials are still not explored up to now. In this study, these properties and hydrogen storage potentials of four stable Na6C60 and four Li6C60 isomers were analyzed based on the density functional calculations. Moreover, the influences of temperature and pressure on the stability of the eight isomers were explored using standard statistical thermodynamic methods. The calculated Infrared spectra are in good agreement with the corresponding experimental observations. Li6C60-a3 and Na6C60-b4 are the most stable isomers among the Li- and Na-doped fullerenes, of which the Li-doped fullerene represents a more preferable storage material than Na-doped fullerene.