Improved electrochemical capacitive characteristics of the carbon nanotubes grown on the alumina templates with high pore density

Specific capacitances of the carbon nanotube (CNT) electrodes are significantly enhanced by using the nanoporous alumina templates with high pore density and uniform pore diameter. Well-ordered nanoporous alumina templates were fabricated by a two-step anodization method by applying a constant voltage of 25.0 V or 20.0 V in sulfuric acid solution. The cylindrical pore diameter and pore density of the templates prepared at the anodizing voltage of 25.0 V or 20.0 V were 53 ± 1 nm and 3.1 × 1010 cm−2 or 38 ± 2 nm and 3.8 × 1010 cm−2, respectively. The CNTs with uniform diameters of 44 ± 2 nm in the 53 nm pores and of 32 ± 5 nm in the 38 nm pores, respectively, were grown on the porous alumina template. For the electrochemical double layer capacitors (EDLCs), the aluminum metal below the porous alumina layer was used as a current collector for the CNT electrode without any binding material. The EDLC characteristics were analyzed by measuring the capacitances from cyclic voltammograms and the charge–discharge curves. A maximum value of 175 F g−1 was achieved for the specific capacitances of the CNT electrodes prepared on the alumina templates with high pore density.