Surface adsorption and micropore filling of the hydrogen in activated MWCNTs

Hydrogen uptake of KOH-activated MWCNTs measured at ambient temperature and moderate equilibrium pressures ranging 0.3-1.9 MPa is compared with that of the pristine nanotubes. In the pressure range considered, the hydrogen uptake of nanotubes stems from micropore volume filling and adsorption on the external and the mesoporous surfaces. Pristine nanotubes store 0.2 wt.% of hydrogen which increases to 0.32 wt.% upon activation, corresponding to an enhancement of 60%. The pore width in the micropore region derived using the Horváth-Kawazoe equation suggests no widening of micropores. The contributions of hydrogen adsorbed on the meso- and micropores are resolved by applying the Langmuir kinetics to the external surface and micropore surface areas and micropore volume; the latter are derived from BET, Dubinin-Astakhov, and Lippen's-de Boer's t-plot analysis.