Cobalt (catalyst) is sputtered at different power levels (20, 50, and 80 W) on graphite foil on which multiwalled carbon nanotubes are subsequently grown directly by chemical vapor deposition. Next, the multiwalled carbon nanotube electrodes are immersed in a nitric acid solution and then annealed at different temperatures (200, 350, and 500 degrees C). At the 1000th cycle of potential cycling, a maximum specific capacitance of 109 F/g is obtained under the best conditions (Co sputtering power=50 W and annealing temperature=350 degrees C). These show high electrochemical stability and good specific capacitance. Furthermore, viewed under transmission electron microscope and measured by electrochemical analyzer, the higher the annealing temperature, the more integral the sidewall surface and the lower the equivalent series resistance of the multiwalled carbon nanotubes.