Hydrogen storage properties of multi-walled carbon nanotubes and carbon nano-onions grown on single and bi-catalysts including Fe, Mo, Co and Ni supported by MgO

The effects of various catalysts including Fe, Mo, Ni, Co and their dual compounds supported by MgO, on production yield, diameter, quality and hydrogen storage properties of carbon nanostructures (CNSs) containing multi-walled carbon nanotubes and carbon nano-onions are studied. It is shown that the production yield of CNSs depends on applied catalyst. The production yields of CNSs are in descending order by using the following catalyst as: Co/Mo, Fe/Mo, Ni/Mo, Mo, Fe/Co, Fe/Ni, Fe, Ni, Co and Ni/Co. Moreover, the CNSs grown on Fe/Co@MgO catalyst have the highest quality, and those grown on Mo@MgO catalyst have the highest surface area, micro-pore distribution and dangling bands, compared to the others. The results of Raman spectroscopy and N2 adsorption confirm the relation between D′ peak area and pores volume less than 10 nm. The hydrogen storage capacities of CNSs grown on the catalysts with production yield more than 45% are in the ascending order as: Mo, Ni/Mo, Fe/Mo, Co/Mo and Fe/Co. It inferred that the CNSs grown on catalysts including Mo are more suitable for hydrogen storage applications, due to high micro-pores (vacancy-like defects) and likely presence of molybdenum carbide structures for enhancing hydrogen uptake. The findings elucidate that specific surface area, micro and meso-pore (certainly less than 10 nm), and vacancy-like defects of the CNSs affect hydrogen uptake and desorption temperature of the stored hydrogen.