Hydrogen adsorption of carbon nanotubes grown on different catalysts

Single wall carbon nanotubes (SWCNTs) were synthesized by catalytic chemical vapor deposition of C₂H₂ at 800 °C for 60 min. Catalysts were prepared by impregnation of transition metals (Fe, Co, Ni, V and bimetallic mixture of Fe-Co) on MgO powder substrate with a metal to MgO ratio of 5:100. After the synthesis, the samples were purified by liquid phase oxidation method with 1.5 M HNO₃ for 30 min at 210 °C. The samples were characterized by thermal gravimetric analysis, scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The hydrogen storage capacities of purified SWCNTs were investigated by volumetric method. It was found that the hydrogen uptake was in the range of 2.76-5.25 wt% at cryogenic temperature and 100 bar pressure. The maximum capacity was obtained with purified SWCNTs produced on Fe catalyst whereas purified SWCNTs grown on Fe-Co catalyst had the minimum hydrogen uptake.