Hydrogen storage capacity of titanium met-cars

The adsorption of hydrogen molecules on the titanium metallocarbohedryne (met-car) cluster has been investigated by using the first-principles plane wave method. We have found that, while a single Ti atom at the corner can bind up to three hydrogen molecules, a single Ti atom on the surface of the cluster can bind only one hydrogen molecule. Accordingly, a Ti8C12 met-car can bind up to 16 H-2 molecules and hence can be considered as a high-capacity hydrogen storage medium. Strong interaction between two met-car clusters leading to the dimer formation can affect H-2 storage capacity slightly. Increasing the storage capacity by directly inserting H-2 into the met-car or by functionalizing it with an Na atom have been explored. It is found that the insertion of neither an H-2 molecule nor an Na atom could further promote the H-2 storage capacity of a Ti8C12 cluster. We have also tested the stability of the H-2-adsorbed Ti8C12 metcar with ab initio molecular dynamics calculations which have been carried out at room temperature.