Hexagonal Antiprismatic Metallacarborane Clusters for Hydrogen Storage

We investigated the adsorption properties of molecular hydrogen attached to hexagonal antiprismatic metallacarborane clusters, RuNiC$_2$B$_{10}$H$_{12}$ and Ru$_2$C$_2$B$_{10}$H$_{12}$, using density functional theory. These clusters have been recently synthesized using the reduction-metallation (RedMet) approach [1] and their structures have been resolved. The hydrogen molecules are sequentially attached to these clusters until the H$_2$ binding energies fall below 0.2 eV, which is the minimum value of ideal H$_2$ binding energy in the range of 0.2-0.4 eV/H$_2$ for the practical vehicle applications [2]. We included the van der Waals interactions between metallacarborane clusters and molecular hydrogens. We also evaluated the contribution of zero point vibrational energies to the H$_2$ binding energy. The kinetic stability of these clusters before and after hydrogen adsorption is discussed by analyzing the energy gap. The results show that RuNiC$_2$B$_{10}$H$_{12}$ and Ru$_2$C$_2$B$_{10}$H$_{12}$ clusters can bind up to 8.5 wt \% and 9.8 wt \% molecular hydrogen, respectively. These results suggest that these metallacarborane clusters are potential hydrogen storage materials to meet the targets of DOE for 2015. \\[4pt] [1] D. Ellis et al., Chem. Commu. {\bf 14}, 1917 (2005).\\[0pt] [2] http://www.sc.doe.gov/bes/hydrogen.pdf.