Hydrogen storage studies of Co, Fe, Fe<inf>3</inf>C nanoparticles encapsulated nitrogen doped carbon nanotubes

The most crucial part of the hydrogen economy is the development of a hydrogen storage material which will be cost effective and its hydrogen storage capacity meets US DOE target. This study is an attempt to develop an efficient hydrogen storage material from a simple, one step synthesis technique. Herein, we synthesize metal nanoparticles encapsulated (M = Co, Fe, Fe3C) nitrogen doped carbon nanotubes (M/NCNT) for the efficient hydrogen adsorption within temperature range of 25°C to 100°C and at pressures 5 to 18 bar. The phase, morphology, surface area, and composition of the encapsulated metal nanoparticles NCNT were confirmed by different characterization techniques. Fe/NCNT is observed to have the highest hydrogen storage capacity of 3.3 wt% at room temperature, ~16 bar pressure, and the highest isosteric heat of adsorption (Qst) of 13 kJmol−1, among all. B,N-CNTs reported 0.35 wt% hydrogen storage capacity at ~16 bar H2 equilibrium pressure and room temperature. The large surface area, defects produced on the CNT due to N doping as well as the presence of metal nanoparticles both inside, on the CNTs which results in the spillover mechanism for the dissociation of the hydrogen molecules into atoms and its diffusion through carbon layers within the CNT, are the factors that contribute to the enhancement of hydrogen storage capacity in M/NCNT.