Equilibrium, kinetic and thermodynamic studies of hydrogen adsorption on multi-walled carbon nanotubes

In this study, the quilibrium adsorption of hydrogen on multi-walled carbon nanotubes (MWCNT) were experimentally investigated using volumetric method in a dual sorption vessels at temperature range of 288–318 K and pressures up to 40 bars. The result obtained indicated that the equilibrium uptake of hydrogen by MWCNT rapidly increases with pressure while temperature had a marginal effect on it at the temperature range under study. The maximum storage capacity did not exceed 3% at the lowest temperature and highest pressure under study. The experimental data was well fitted by the Frendlich model isotherm considering the values of regression correlation coefficients. The kinetic study revealed a very fast sorption of hydrogen onto MWCNT adsorbent. The parameters of the pseudo-first-order kinetic model were confidently recovered from a nonlinear fit to the experimental data which indicated the adsorption of hydrogen onto MWCNT was dominated by physisorption. Isosteric heat of adsorption was evaluated from a set of isotherms based on the Clausius–Clapeyron equation. Results showed that although the adsorption of hydrogen on MWCNT was exothermic, but the heat of adsorption was too low. The kinetic study revealed a very fast sorption of hydrogen onto MWCNT occureded in few seconds. The results emphasized that lower temperature and higher pressure is needed to improve the storage capacity of hydrogen on MWCNT adsorbent.