Hydrogen storage in single-walled carbon nanotubes

We perform density-functional calculations to search for hydrogen adsorption sites and predict maximum storage capacity in single-walled carbon nanotubes. We find two chemisorption sites at top sites of the exterior and the interior of the tube wall. We further find that a form of H-2 molecule can exist in an empty space inside nanotubes. The storage capacity of hydrogen in an empty space increases linearly with tube diameter. The maximum storage capacity is limited by the repulsive energies between H-2 molecules inside nanotubes and those between H-2 molecules and the tube wall. We predict that hydrogen storage capacity in (10,10) nanotube can exceed 14 wt % (160 kg H-2/m(3)). (C) 2000 American Institute of Physics. [S0003-6951(00)04520-4].