Novel mechanism of hydrogen storage in carbon nanotubes

A novel mechanism of hydrogen storage in carbon nanotubes is proposed by us ing density functional calculations. Several key intermediate states are id entified for hydrogen adsorption. Up to a coverage of 1.0, hydrogen atoms c hemisorb on the nanotube wall as either an arch type or a zigzag type. Then at higher coverage, hydrogens can be further stored inside the nanotubes a s H-2 molecules. Hydrogen atoms call be inserted into the nanotubes through the tube wall via a flip-in and/or a kick-in mechanism with reasonably sma ll activation barriers of 1.5 and 2.0 eV, respectively. In the H extraction process, a HZ molecule inside a nanotube first dissociates onto the inner wall with an activation barrier of 1.6 eV. Then, as a second step, H atoms on the interior of the tube mall are further extracted to the outer mall by the flip-out mechanism with all activation barrier. of 2.0 eV. Our calcula tions suitably describe ail electrochemical process of hydrogen storage in carbon nanotubes.