Storage of hydrogen on carbon materials: Experiments and analyses

Superactivated carbon and carbon nanotubes are both considered potential hydrogen carriers. Adsorption isotherms of H-2 on activated carbon AX-21 and multi-wall carbon nanotubes were collected with a volumetric method for the temperature range of 77, 233-298 K and pressures up to 7 or 10 MPa. Based on the experimental data for 233-298 K, the limiting heats of adsorption of 7.6 and 1.8 kJ/mol were obtained for activated carbon and carbon nanotubes, respectively. The absolute adsorption was determined with a recently presented method, and the adsorption behavior of H-2 on carbon nanotubes was thus reasonably explained. A comparison was given for the storage capacities of compression alone and of filling powder or pellets of the two materials. It was concluded that adsorption of H 2 on carbon nanotubes is too weak to enhance storage, but activated carbon enhances storage capacity considerably. The weight percentage of hydrogen stored in carbon powder reaches 10.8% at 77 K and 6 MPa, including the quantity compressed in the void space, and 4.1 kg H-2 was stored in a 100-liter container filled with carbon pellets for the same condition.