Nanostructured electrochemical capacitors (ECs) are advantageous for charge and energy storage due to their large surface area-to-volume ratio, which contributes to a large electrostatic/double layer capacitance (). However, the intrinsically small density of states in nanostructures results in a quantum capacitance () in series with which could diminish the measured device capacitance (). The lack of available states in the electrodes for the charges to occupy, is then posited as a major obstacle to achieving greater capacitances and concomitant energy densities.
While such issues are just beginning to be investigated for graphene systems in the EC community, we show that higher capacitances may be harnessed in carbon nanotube arrays due to more efficient electric field screening. We have then investigated, through extensive modeling and comparison with experiment, the relative magnitudes of and in electrodes constituted of carbon nanotube arrays . We will also present an equivalent circuit of and in series based on the voltage drop across . Consequently, we attribute the increase in resulting from ionizing radiation and plasma processing to an increased . Our study has deep implications for the maximum capacitance that can be obtained and measured in practical ECs.
 H. Yamada and P. R. Bandaru, Appl. Phys. Lett. 102, 173113 (2013).