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

Abstract

We propose a system that can store molecular hydrogen in densities up to $\sim 100\text{g}/\text{L}$. Our ab initio calculations predict the existence of an oxidized calcium dihydrogen complex, which holds up to eight ${\text{H}}_2$, i.e., $\text{Ca}\left(\text{ion}\right){\left({\text{H}}_2\right)}_8$. The dihydrogen binding to the Ca is via a weak electron-donation mechanism from the occupied ${\text{H}}_2$ $\sigma$ orbital to the unoccupied, but bound, $\text{Ca}3d$ 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.