Chemical vapor synthesis of secondary carbon nanotubes catalyzed by iron nanoparticles electrodeposited on primary carbon nanotubes

Carbon nanotubes (CNTs) were used as substrate for the growth of secondary carbon nanotubes. Iron was applied as catalyst, and cyclohexane was used as carbon source. The iron nanoparticles were synthesized from iron sulfate by electrodeposition on the primary CNTs by ramping the potential from 0 V to − 0.75 V. The influence of subsequent calcination and reduction on the Fe/CNT samples was studied by X-ray photoelectron spectroscopy and transmission electron microscopy. Calcination in air at 400 °C was identified as a key step to improve the dispersion of the iron nanoparticles, presumably due to solid- and gas-phase reactions on the Fe–C interface, where iron acts as the gasification catalyst. Secondary CNTs were grown catalyzed by the highly dispersed iron nanoparticles at 700 °C in a hot-wall reactor. Nitrogen physisorption isotherms demonstrated the formation of inter-nanotube pores due to the growth of the secondary CNTs into the voids between the primary CNTs. The resulting specific surface area was found to be significantly enhanced by a factor of 6. The obtained hierarchical carbon nanocomposite is very promising as structured catalyst support in fuel cells.