The interaction of hydrogen with Li-coated C70 fullerene: A DFT study

Abstract

We have applied density functional calculations to study the structure, stability and hydrogen storage properties of Li-coated C70 fullerenes. Our results show that among different possibilities for the geometry of Li-coated C70 fullerenes, Li atoms prefer to occupy exohedral and endohedral positions on top of the pentagons. Among isomers of Li2C70 and Li6C70, those in which one of the Li atoms occupy the endohedral position of one of the polar pentagonal rings and the other ones situate on the top of the pentagons around the opposite polar pentagon, have higher binding energies. Charge transfer is occurred from Li to C70, putting extra electrons in the vicinity of the Li atom. This results in the binding of hydrogen in atomic form to the on-top C site that is nearest to the Li atom in the preferred configuration of hydrogenated Li-coated C70 fullerene. Therefore, there are two types of hydrogen binding in Li6C70. One group of hydrogen bind to Li atoms in quasi-molecular form, which will desorb at a lower temperature, and the other group of H atoms bind to C in atomic form, which will desorb at higher temperatures.