Hydrogen storage capacity of titanium met-cars

Abstract

The adsorption of hydrogen molecules on the titanium metallocarbohedryne (met-car) clusterhas 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 Tiatom on the surface of the cluster can bind only one hydrogen molecule. Accordingly, aTi8C12 met-car canbind 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 affectH2 storage capacity slightly. Increasing the storage capacity by directly insertingH2 intothe met-car or by functionalizing it with an Na atom have been explored. It is found that the insertion ofneither an H2 molecule nor an Na atom could further promote theH2 storagecapacity of a Ti8C12 cluster. We have also tested the stability of theH2-adsorbed Ti8C12 met-car with ab initio molecular dynamics calculations which have been carried out atroom temperature.