H2 storage on single- and multi-walled carbon nanotubes

The adsorption of hydrogen on single-walled and multi-walled carbon nanotubes (CNTs) was investigated at 77 and 298 K, in the pressure range of 0–1000 Torr. The adsorption isotherms indicate that adsorption follows the Langmuir model. Hydrogen uptakes were found to depend strongly on the nature of the CNTs. Single-walled CNTs adsorb significantly higher quantities of hydrogen per unit mass of the solid, while the opposite is true on a per unit surface area basis. This observation implies that adsorption takes place selectively on specific sites on the surface. The hydrogen uptake capacity of CNTs was also found to be affected by the purity of the materials, increasing with increasing purity. Temperature programmed desorption indicated that relatively strong adsorption bonds develop between adsorbent and adsorbate and that a single type of adsorption site exists on the solid surface.