Hydrogen storage in organometallic structures grafted on silsesquioxanes

Using density functional theory we show that a recently synthesized silsesquioxanes (SQ) nano complex [RSiO3/2](n) with R = -C5H5 provides a novel material for hydrogen storage. Grafting cyclopentadienyl on SQ totally changes its electronic structure and chemistry: cyclopentadienyl becomes a reactive site where a transition metal atom (e.g., Sc) can be doped to serve as an effective adsorption site for hydrogen molecules. This nano complex has the following advantages: (I) The storage capacity in the fully grafted case is 5 wt % where hydrogen is bound molecularly with a binding energy of about 0.6 eV/H-2 molecule. (2) The structure of SQ itself is stable. Our study shows for the first time that the functionalized SQ complexes can be an effective and practical material for hydrogen storage.