The catalytic synthesis of three-dimensional hierarchical carbon nanotube composites was based on the electrodeposition of iron and the subsequent iron-catalyzed growth of carbon nanotubes from cyclohexane. Electrochemical studies provided evidence for the strong interaction between the graphite foil, the long primary CNTs, and the short secondary CNTs, which are essential for the application of the hierarchical nanocomposite in fuel cell catalysis and in sensor systems.