Physicochemical Mechanisms Of The Double-Layer Capacitance Dispersion And Dynamics: An Impedance Analysis

Gold, as the noblest metal, is an appropriate model electrode to study electrochemical double layers. This study examines the frequency dispersion of the double layer of polished gold electrodes in perchloric acid with impedance spectroscopy under amplitude, electrolyte concentration, and potential variation. The dynamic perturbation of the double layer equilibrium by impedance measurements shows a constant phase (CP) response (phase angle of approximately -75 degrees), which is responsible for a frequency dispersion of the capacitance. The response is almost independent of the excitation amplitude, for which the CP behavior is ascribed to resistive-capacitive (RC) contributions of the electric field-driven ion separation instead of the previously reported diffusion-limited adsorption processes. The RC character of the double layer in combination with the electrolyte resistance is accompanied by a relaxation that can damp the ion movement and the related ion separation. At the relaxation frequency, the capacitance is found to be independent of the electrolyte concentration, which is attributed to a constant ratio of the contributions of damped ion movement and dielectric polarization of water molecules.