%0 Journal Article %J Journal of the Electrochemical Society %D 2009 %T Carbon Nanotube Yarn Actuators: An Electrochemical Impedance Model %A Mirfakhrai J. D. W., and Oh and Kozlov and Fang and Zhang and Baughman and Madden %P K97--K103 %V 156 %X Twist-spun yarns made of carbon nanotubes have been shown to work as electrochemical actuators and force sensors. The electrochemical response of these yarns at different bias potentials was studied using electrochemical impedance spectroscopy (EIS) and compared with results from cyclic voltammetry. Based on the EIS results, the capacitance is estimated first by directly fitting a resistance-capacitance circuit and then by fitting a circuit including a constant phase element (CPE), estimating the capacitance based on the CPE. The gravimetric capacitance in aqueous electrolyte is found to be about 12 F/g and relatively independent of bias, while in an acetonitrile-based electrolyte it is a function of the bias potential, increasing to nearly 20 F/g when the bias potential is larger. The capacitance per unit surface area of the multiwalled nanotubes bundles in the yarn is estimated to be about 0.05 F/m(2).