Hydrogen adsorption and cohesive energy of single-walled carbon nanotubes

Hydrogen adsorption on crystalline ropes of carbon single-walled nanotubes (SWNT) was found to exceed 8 wt.%, which is the highest capacity of any car bon material. Hydrogen is first adsorbed on the outer surfaces of the cryst alline ropes. At pressures higher than about 40 bar at 80 K, however, a pha se transition occurs where there is a separation of the individual SWNTs, a nd hydrogen is physisorbed on their exposed surfaces. The pressure of this phase transition provides a tube-tube cohesive energy for much of the mater ial of 5 meV/C atom. This small cohesive energy is affected strongly by the quality of crystalline order in the ropes. (C) 1999 American Institute of Physics. [S0003-6951(99)04816-0].