An ab Initio Investigation of Hydrogen Adsorption in Li-Doped closo-Boranes

Ab initio studies on molecular hydrogen adsorption in lithium-doped hexaborane(6) (B6H6Li2) have been carried out. Our calculated results show that the lithium sites in the complex carry a partial positive charge, and the binding energy of Li to the borane framework, as calculated at the MP2/aug-cc-pVTZ level of theory, is found to be -196.467 kcal/mol per lithium, which is large enough to ensure the stability toward recyclability. This charged surface created around the metal atom is found to interact with molecular hydrogen through charge-induced dipole interaction. Each lithium site is found to adsorb a maximum of three hydrogen molecules which corresponds to a gravimetric density of 12 wt %. We have also verified the possibility of constructing a three-dimensional solid using the dilithium-doped B-6 unit as a building block and -C equivalent to C- units as a linking agent. The hydrogen adsorption properties of this designed structure show that it can adsorb hydrogen with a gravimetric density of 7.3 wt %, and binding energy per molecular hydrogen is found to be around -2.2 kcal/mol.