Chemical vapor deposition of 3D graphene/carbon nanotubes networks for hybrid supercapacitors

We present the direct synthesis of graphene as well as carbon nanotube within the vertically-aligned carbon nanotube (VACNT) forests to form either the 3D CNT-graphene or 3D CNT-CNT network by means of chemical vapor deposition (CVD). The multi-dimensional material assembly process is achieved by the electroplating of a thin nickel layer around the individual CNTs followed by a second CVD process for the synthesis of graphene or CNTs branching out of the original VACNT, respectively. The combinations of large surface areas (graphene and CNT), high electrochemical reactions sites (graphene), and metal particles as pseudocapacitor materials improve the electrochemical capacitance. Compared with as-grown CNT forests, the capacitance of 3D CNT/graphene networks increases 16 times to ∼20 F/cm3 and 3D CNT/CNT networks increase 25 times to ∼30 F/cm3. A flexible supercapacitor based on the CNT/CNT forest electrode is demonstrated to achieve 90 % retention of its original capacitance after 10,000 charging-discharging cycles.