Synthesis of multi-walled carbon nanotubes in high yield using Mm based AB2 alloy hydride catalysts and the effect of purification on their hydrogen adsorption properties

Catalytic synthesis of multi-walled carbon nanotubes (MWNTs) by the pyrolysis of acetylene over mischmetal (Mm) based MmNi(2) and MmFe(2) hydride catalysts is reported. The hydrogen decrepitation technique has been used to prepare the catalyst particles of these Mm based hydrogen storage alloys. Large hydrogen decrepitation and low cost make these hydrides potential catalysts for large-scale production of CNTs. The samples were purified by air oxidation and acid treatment and were characterized by XRD, SEM, TEM, HRTEM, Raman spectroscopy and XPS. The yield of MWNTs was estimated to be similar to 60% and the purity of MWNTs thus obtained was more than 90%, as characterized by TGA. In addition, hydrogen adsorption measurements were carried out for as-prepared and purified MWNTs at 125 and 298 K using a high pressure hydrogen adsorption set-up. A maximum hydrogen storage capacity of 3.2 wt% at 60 bar is obtained at 125 K for purified CNTs prepared with MmFe(2) hydride catalysts.