Endohedral Metallofullerenes: A Smart Material for Hydrogen Storage

We report a first-principle computational study on tunable hydrogenation of the fullerene C$_{60}$ and endohedral metallofullerenes M@C$_{60}$ and M$_{2}$@C$_{60}$ (M = Li, Be, Mg, Ca, Al, and Sc). The interaction between the encapsulated metal atoms and the C$_{60}$ cage leads to a smart-material behavior, which tunes the hydrogen binding in a desired manner as the hydrogenation proceeds. At lower H densities, when H atoms are too strongly bound to pure C$_{60}$, the endohedral dopants weaken the binding. The dopants also enhance the hydrogen binding energy at higher coverages, and enable the degree of hydrogenation to be substantially increased relative to that available with un-modified C$_{60}$. Overall, the encapsulated metals increase the capacity and improve the energy efficiency for hydrogen storage in hydroendofullerides.