Current distribution effects in AC impedance spectroscopy of electroceramic point contact and thin film model electrodes

The Finite-Element-Method (FEM) was used for the simulations of the effect of a changing current distribution during AC impedance spectrum recording on electroceramic point contact and thin film model electrodes. For pure electronic conducting point contact electrodes the transition from the primary current distribution to the DC current distribution restricted to the Three-Phase-Boundary (TPB) zone introduces an error in the determination of the reaction resistance, Rreac = Z(freq. → 0) − Z(freq. → ∞).

The error is estimated for different width of the effective TPB zone and a rule of thumb regarding its significance is provided. The associated characteristic impedance spectrum shape change is simulated and its origin discussed. Furthermore, the characteristic shape of impedance spectra of thin electroceramic film electrodes with lateral ohmic resistance is studied as a function of an increasing lateral ohmic resistance.

The characteristic change in the shape of the complex plane impedance plot with increasing lateral ohmic resistance is discussed in terms of extracting kinetic parameters such as electrolyte and reaction resistance.