Supercapacitor Electrodes from Tubes-in-Tube Carbon Nanostructures

Supercapacitors occupying a region between batteries and dielectric capacitors have been touted as a solution to the mismatch between the fast growth in power required by devices and the inability of batteries to efficiently discharge at high rates. Here, we report the electrochemical characterization of tubes-in-tube carbon nanostructures to investigate their application to supercapacitors. The average specific capacitance has been calculated for the cyclic voltammetric plots at 50 mV/s. The tubes-in-tube multiwalled carbon nanotubes consisting of outer nanotubes with an average outer diameter of 50 nm and inner nanotubes with diameters in the range of 3–10 nm exhibit an average capacitance of 203 F/g and a specific capacitance of 315 F/g at 0.35 V in 0.5 mol/L H<sub>2</sub>SO<sub>4</sub>. Pure electrostatic attraction in the double layer and faradic reaction in the pseudocapacitor are responsible for the supercapacitance. The specific surface area of the samples characterized by a nitrogen isotherm at 77 K reveals that the higher supercapacitance can be realized by modifying the pore size, pore-size distribution, and conductivity of the carbon nanomaterials.