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 should be reversible under moderate temperature and pressure and a high sorption rate. Li- (Li6C60) and Na- (Na6C60) doped fullerenes represent potential storage materials, but their structures, stabilities and electronic properties remain unclear. The hydrogen interaction mechanisms of these materials have not been explored. These factors and the hydrogen storage potentials of the materials based on the density functional calculations of four Na6C60 isomers and four Li6C60 isomers were analyzed in this study. Moreover, the influences of temperature and pressure on the stability of the eight isomers were analyzed using standard statistical thermodynamic methods. The calculated results were compared with the corresponding experimental observations. Li6C60-a3 and Na6C60-b4 are the most stable isomers among the Li- and Na-doped fullerenes. Li-doped fullerene represents a more preferable storage material than Na-doped fullerene.218