Large cryogenic storage of hydrogen in carbon nanotubes at low pressures

We report up to 6 wt% storage of H2 at 2 atm and T ! 77 K in processed bundles of single-walled carbon nanotubes. The hydrogen storage isotherms are completely reversible; D2 isotherms confirmed this anomalous low-pressure adsorption and also revealed the effects of quantum mechanical zero point motion. We propose that our postsynthesis treatment of the sample improves access for hydrogen to the central pores within individual nanotubes and may also create a roughened tube surface with an increased binding energy for hydrogen. Such an enhancement may be needed to understand the strong adsorption at low pressure. We obtained an experimental isosteric heat qst ! 125 ± 5 meV. Calculations are also presented that indicate disorder in the tube wall enhances the binding energy of H2.