Hydrogen Storage Capacity of C120 Nanocapsules: Density Functional Theory Based Treatments

The adsorption of hydrogen molecule on the external surface of pure C120 nanocapsule and endohedrally H2@C120 complex has been examined using the density functional theory calculations. Several different bonding configurations are considered for the hydrogen molecule approaching the outer surface of the considered nanocages. It has been found that the adsorbed H2 molecule bound weakly to the outer surface of the pure C120 nanocapsules in agreement with the recent experimental and theoretical results while, it prefers to be adsorbed rather strongly on the side wall of the endohedrally H2@C120 complex. The adsorption of a single layer and bi-layer of two H2 molecules on the most stable states of the considered H2@C120 complex appears to be feasible, although the molecules of the second layer are weakly bound. Furthermore, it is found that the formation of 100% coverage is favorable thermodynamically, which corresponds to about 20% by weight storage of H2 molecules. Thus, surprisingly, we arrive at the prediction that the C120 nanocapsules can be implemented as a novel material for energy storage.