Self-Similar Interfacial Impedance of Electrodes in High Conductivity Media: II. Disk Electrodes.

Electrode polarization effects were investigated using impedance spectroscopy measurements for planar and nanorod-structured gold disk electrodes at 100 Hz to 1 MHz frequency range and in 0.25 S/m to 1.5 S/m conductivity KCl solutions. Diameters of planar electrodes were varied from 50 mu m to 2 mm to examine the effect of electrode size on impedance spectra. Normalizing the impedance magnitude with the spreading resistance and frequency with the characteristic time scale, all experimental data collapsed onto a universal curve, proving self-similarity. Experimental impedance results were compared well with that obtained from the numerical solution of Poisson-Nernst-Planck equations in axisymmetric domain. The influence of surface morphology was also investigated by generating cylindrical nanorods on a planar electrode. The 500 pm diameter electrode surface was covered with cylindrical nanorods with known height, diameter, and separation distance, which were characterized using scanning electron microscopy. The characteristic time scale for the nanorod-structured electrode increased by the surface enlargement factor obtained by cyclic voltammetry measurements. Self-similar interfacial impedance of electrodes was modeled using a constant phase element model. Current findings describe the coupled effects of electrode diameter, electrolyte conductivity, and electrode surface morphology on the impedance spectra of electrode/electrolyte system when the electric double layer between the nanorods does not overlap.