Ti-Decorated Doped Silicon Fullerene: A Possible Hydrogen-Storage Material

From first-principles density functional electronic structure calculations, we show that Si60H60 forms a highly symmetric (meta)stable fullerene structure on which Ti atoms can be capped exohedrally in cationic form, enabling storage of hydrogen in the molecular state. Whereas the H atoms on a Si60H60 cage saturate the Si dangling bonds, the Ti+ ion sitting on the energetically favorable hexagonal face of the Si60H60 fullerene allows a maximum of four H-2 molecules to be attached, with a binding energy intermediate between those of physisorption and chemisorption. However, two Ti atoms added to Si fullerene tend to dimerize, thereby reducing the hydrogen-storage efficiency. This clustering tendency of the Ti atoms on the fullerene surface can be avoided by doping the fullerene with P atoms. Our first-principles results show that Ti-decorated P10Si50H50 clusters can serve as a potential hydrogen-storage material, with a storage capacity of up to 5.23 wt% corresponding to full Ti coverage.