Ab initio calculations predicting the existence of an oxidized calcium dihydrogen complex to store molecular hydrogen in densities up to 100 g/L

We propose a system that can store molecular hydrogen in densities up to $\ensuremath{\sim}100\text{ }\text{g}/\text{L}$. Our ab initio calculations predict the existence of an oxidized calcium dihydrogen complex, which holds up to eight ${\text{H}}_{2}$, i.e., $\text{Ca}(\text{ion}){({\text{H}}_{2})}_{8}$. The dihydrogen binding to the Ca is via a weak electron-donation mechanism from the occupied ${\text{H}}_{2}$ $\ensuremath{\sigma}$ orbital to the unoccupied, but bound, $\text{Ca}\text{ }3d$ orbitals. Because of the high concentration of the hydrogen in such complexes, even in calcium-intercalated pillared graphite, one can obtain reversible hydrogen storage denser than that of liquid hydrogen, 70 g/L.