Supergrowth of Aligned Carbon Nanotubes Directly on Carbon Papers and Their Properties as Supercapacitors

We demonstrate that vertically aligned carbon nanotubes can be synthesized directly on conductive carbon papers and used as excellent electrochemical capacitors. The carbon nanotubes were synthesized with use of an Al/Fe catalyst via water-assisted chemical vapor deposition. They grew as fast as similar to 100 mu m/min and approximately 70% of them had double walls with an average diameter of similar to 6 nm. Interestingly, the carbon nanotube forest showed microscale patterns defined by the structure of underlying carbon papers. The nanotubes were attached well to the carbon papers and maintained their adhesion under mild ultrasonication in solution. Owing to the direct integration, naturally patterned structure, and good alignment, the carbon nanotubes showed excellent performance as supercapacitors. In aqueous 1 M H2SO4 solution, specific capacitance, energy, and power measured at the current density of 20 A/g were ca. 200 F/g, 20 Wh/kg, and 40 kW/kg, respectively. A specific energy of >100 Wh/kg was achieved when organic electrolyte was used. Demonstrated facile and direct integration of carbon nanotubes on conductive substrates and their excellent electrochemical properties may hold great promise for electrochemical energy storage applications.