Density functional studies on the hydrogen storage capacity of boranes and alanes based cages

The hydrogen storage (H-storage) capacity of various boranes and alanes have been investigated using density functional theory (DFT) based M05-2X method employing 6–31+G** basis set. The changes in the H-storage capacities of borane and alane upon substitution of antipodal atoms in the cages by C, Si, and N have also been investigated. It is found from the calculations that a maximum of 20 H<SUB>2</SUB> molecules can be adsorbed on the deltahedron faces of these cages. The maximum gravimetric density has been observed for boranes when compared to alanes. The H-storage capacity of closo-borane dianion [B<SUB>12</SUB>H<SUB>12</SUB>]<SUP>2-</SUP>, monocarborane [CB<SUB>11</SUB>H<SUB>12</SUB>]<SUP>1-</SUP>, dicarborane [C<SUB>2</SUB>B<SUB>10</SUB>H<SUB>12</SUB>], and closo-azaborane [NB<SUB>11</SUB>H<SUB>12</SUB>] cages is almost similar (∼22 wt.%). Among these cages, B<SUB>BB</SUB> dianion show higher binding energy (BE) and BE per H<SUB>2</SUB> molecule (BE/nH<SUB>2</SUB>) which are 181.06 and 9.03 kJ/mol, respectively. In the case of alanes, dicarbalane [C<SUB>2</SUB>A<SUB>10</SUB>H<SUB>12</SUB>] has maximum H-storage capacity of 11.6 wt.%. Based on these findings, a new MOF with carborane (MOF-5<SUB>CC</SUB>) as linker has been designed. The calculation on the new MOF-5B<SUB>CC</SUB> reveals that it has H-storage capacity of 6.4 wt.% with BE/nH<SUB>2</SUB> of 3.02 kJ/mol