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 H2 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 H2 storage capacity slightly. Increasing the storage capacity by directly inserting H2 into the met-car or by functionalizing it with an Na atom have been explored. It is found that the insertion of neither an H2 molecule nor an Na atom could further promote the H2 storage capacity of a Ti8C12 cluster. We have also tested the stability of the H2-adsorbed Ti8C12 met-car with ab initio molecular dynamics calculations which have been carried out at room temperature