  Towards the development of a useful mechanism for hydrogen storage, we have
studied the hydrogenation of single-walled carbon nanotubes with atomic
hydrogen using core-level photoelectron spectroscopy and x-ray absorption
spectroscopy. We find that atomic hydrogen creates C-H bonds with the carbon
atoms in the nanotube walls and such C-H bonds can be com-pletely broken by
heating to 600 oC. We demonstrate approximately 65+/-15 at % hydrogenation of
carbon atoms in the single-walled carbon nanotubes which is equivalent to
5.1+/-1.2 weight % hydrogen capacity. We also show that the hydrogenation is a
reversible process.
