Limits to the magnitude of capacitance in carbon nanotube array electrode based electrochemical capacitors

Nanostructured electrochemical capacitors (ECs) are advantageous for charge and energy storage due to their intrinsically large surface area, which contributes to a large electrostatic/double layer capacitor (C-dl). However, the intrinsically small density of states in nanostructures results in a quantum capacitor (C-Q) in series with C-dl which could diminish the total device capacitance value (C-tot). We investigate, through comparison with experiment, the relative magnitudes of C-dl and C-Q in electrodes constituted of carbon nanotube arrays. Consequently, we attribute the increase in C-tot resulting from ionizing radiation to an increase in C-Q and suggest limits to the capacitance in ECs. (C) 2013 AIP Publishing LLC.