Enhanced Hydrogen Storage on Li-Dispersed Carbon Nanotubes

Abstract

High storage capacity and a moderate binding strength are two important requirements that must be met for the successful development of hydrogen storage materials. In the present work we demonstrate that optimizing the number and position of dopants, a configuration of eight Li dispersed at the hollow sites above the hexagonal carbon rings, can lead to an extremely high H2 storage capacity of 13.45 wt %. Moreover, our local density approximation calculations predict that the average adsorption energy is −0.17 eV/H2, which is close to the lowest requirement (−0.20 eV/H2) as proposed by the U.S. Department of Energy. The electronic analysis demonstrates two salient points, namely that the best dopants are those whose bands overlap strongly with those of H2 and the nanotube simultaneously; second, all carbon atoms in the nanotube are fully ionized and thus the high capacity is attainable. These results provide insight into the binding mechanisms that govern hydrogen storage.