Impedance Spectroscopy and Cyclic Voltammetry to Determine Double Layer Capacitances and Electrochemically Active Surface Areas

The electrochemically active surface area (ECSA) of an electrode can be estimated by means of double layer capacitance (DLC) measurements using impedance spectroscopy and cyclic voltammetry. In this study, the responses of smooth and porous gold electrodes (chosen as model systems) to both methods are measured and described by physical models. I point out that diffusion limited adsorption processes significantly contribute to the measured responses and thus complicate the estimation of DLCs. Impedance is derived to be in most cases more suitable for measuring DLCs as higher frequencies are available and as contributions of serial resistances and capacitances can be separately evaluated in the frequency domain. The relaxation properties in the frequency domain are shown to display a useful tool to survey the accuracy of the DLC estimation. The DLCs of polished gold electrodes are shown to be proportional to their geometric surface area. From these measurements a specific DLC of 6±2 μF/cm² of gold in perchloric acid is determined, which agrees with the lowest reported values of strongly scattering data in the literature. A handy flow chart for experimentalists to determine electrode capacitances from impedance spectra is proposed.