Impact of electrode geometry, depth of immersion, and size on impedance measurements

Abstract

Although the platinum electrode is used regularly in the practice of electroanalytical chemistry, there are some caveats that should be considered in experimental design and data interpretation when ac impedance measurements are made. A wire electrode was immersed only partially with the purpose of decreasing its effective area. Impedance was used to study the effect of partial immersion. In the case of an NaOH solution, a good impedance fit was found if a transmission line was added to the equivalent circuit. Transmission line behavior corresponds to the transversal conductivity in the wet, though not immersed, surface. Impedance was further compared for a wire electrode, as well as for short wire electrodes with metal spheres attached to their end. The shorter, predominantly spherical, electrode minimizes impedance artifacts at higher frequencies, thus serving as a better electrode for impedance studies. The change in impedance after depositing platinum black was used to estimate the effective surface area increase. Keywords: electrochemical impedance spectroscopy, platinum, electrode shape, partial immersion, platinum black, sodium hydroxide.