Adsorption equilibrium of supercritical hydrogen on multi-walled carbon nanotubes

Based on the isotherms of excess adsorption amounts of hydrogen on multi-walled carbon nanotubes (MWCNTs) volumetrically measured at the temperatures from 123 K to 310 K under the pressures up to 12.5 MPa, the intermolecular interaction energy among hydrogen molecules was calculated by use of a lattice theory-based approximation adsorption model. The maximum surface concentration of hydrogen molecules upon the MWCNTs was fitted by way of linear regression. The interaction potential of hydrogen-MWCNTs and the isosteric heat of hydrogen adsorption in the low limit surface concentration were determined by use of gas-surface virial coefficients. It shows that hydrogen molecules accumulate mainly in the place where the potential is the minimum within the central tubular pore of the MWCNTs and they are likely to be in a state similar to that of compressed gas. However, there is no evidence to suggest that a significant adsorption of hydrogen molecules occurs on the MWCNTs. The hydrogen-hydrogen interaction energy increases linearly with the increase of adsorption temperature and surface loading, but its variation does not indicate any optimum temperatures for hydrogen storage in terms of adsorption on the MWCNTs. (c) 2004 Elsevier B.V. All rights reserved.