High pressure saturation of hydrogen stored by single-wall carbon nanotubes

Since the early report of adsorption on single-walled carbon nanotubes in 1997, a number of controversial publications have claimed the hydrogen capacity of these materials to be between 0.1 and 10.0 wt %. However, no study has yet demonstrated a plateau of adsorption with pressure that is consistent with monolayer saturation. Others have suggested that the tube bundle structure expand under high pressure to enable higher adsorption on newly uncovered surfaces, but received no confirmation. Using a high-pressure instrument with in situ electrical probes, we found that a plateau is nearly achieved at about 300 atm in the room temperature isotherm. And that nanotube bundles do not expand or swell, shown by the in situ electrical measurements of purified single-walled nanotube (SWNT) bundles. The monolayer saturation plateau was found on bundled SWNT at room temperature corresponding to an adsorption of 0.9 wt %.