Hydrogen storage capacity at high pressure of raw and purified single wall carbon nanotubes produced with a solar reactor

Samples of single wall carbon nanotubes (SWNTs) were prepared using a solar reactor. Graphite targets containing different catalysts (Ni/Co, Ni/Y, Ni/Ce) allowed the synthesis of SWNTs soot in which nanotubes had different diameter distributions. Several consecutive stages of HCl treatment and thermal oxidation in air (HCl protocol) purified the samples. Another protocol involving HNO3 treatment and H2O2 oxidation (HNO3 protocol) was also used. Isotherms of hydrogen adsorption were volumetrically measured at 253 K under pressures below 6 MPa on raw and treated samples. The highest adsorption capacity (0.7  wt%) was measured on raw soot. HCl protocol clearly increases the BET surface area (SBET)(SBET) and the microporous volume (W0(N2))(W0(N2)) measured by N2 at 77 K of the treated samples with respect to the as-produced materials, whereas HNO3 protocol decreases them. A correlation between textural properties and hydrogen storage capacities is discussed.