A comparative study of hydrogen adsorption on superactivated carbon versus carbon nanotubes

Adsorption isotherms of hydrogen on activated carbon and multiwalled carbon nanotubes (MWNT) were collected using volumetric method for the range of 233–298 K and pressures up to 11 Mpa. The same shape of isotherms revealed a common mechanism of adsorption. However, the amount of H2 adsorbed on MWNT is 3–5 times less than on activated carbon, but the surface concentration of H2 on MWNT is 4–6 times higher than on activated carbon. Temperature exerts much less effect on the adsorption of H2 on MWNT than on the adsorption of H2 on activated carbon. Isosteric heat of adsorption was evaluated from a set of isotherms basing on the Clausius–Clapeyron equation, and −1.7 kJ/mol was obtained for MWNT, −6.4 kJ/mol was obtained for activated carbon. Considering the much less quantity adsorbed, the much less heat of adsorption and the much smaller surface area, carbon nanotubes seem not to be a promising carrier of hydrogen for practical applications.