Realization of hydrogen economies depends on finding feasible materials that can store hydrogen with high capacity. To develop economical hydrogen energy, carbon nanostructures with sp2-like bonding functionalized by transition metal (TM), alkali metal (AM) and alkaline-earth metal (AEM) atoms have been expected to be promising storage materials due to their light weights and large surface areas.

Recently, researchers in Institute of Solid State Physics, Chinese Academy of Sciences, employ all-electron density functional theory to study of high-capacity hydrogen storage media consisting of a Ti atom capped on two kinds of atomic carbon chains, cumulene (with double C–C bonds) or polyyne (with alternating singlet and triplet bonds). The number of adsorbed H2 molecules is only determined by the type of chain. Each Ti atom in TiC5 and TiC8 can bind up to six and five H2 molecules, respectively, corresponding to storage capacities of 10 wt% and 6.5 wt%. The average binding energy of H2 molecules is between the physisorption and chemisorption energies.

Researchers choose C20 fullerene as the end-capping candidate, as it is the most frequently experimentally synthesized curved sp2 system. The TiC5 chain assembled on the C20 structure can hold 6 H2 molecules, with an average binding energy of 0.52 eV per H2 molecule.

The theoretical results will provide a useful reference for the design of high-capacity hydrogen storage materials in the laboratory. This work has been published in Phys. Chem. Chem. Phys. 13, 2323 (2011).

Titanium-capped sp+sp2 system as hydrogen storage materials