Hydrogen adsorption of carbon nanotubes grown on different catalysts

•SWCNTs were grown on transition metal catalysts at 800 °C.•Purified SWCNTs grown on Fe catalyst had the highest hydrogen uptake.•The purification by acid treatment is the most important parameter affecting the hydrogen uptake.•The amount and type of the catalyst have effect on the hydrogen storage capacities.

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.