Reaction‐Zone Expansions and Mechanism of the O 2, Ag/Yttria‐Stabilized Zirconia Electrode Reaction

Abstract

Experimental data obtained by impedance spectroscopy with silver droplet electrodes of different radii have been reanalyzed in the medium‐frequency range under the assumption of rate‐limiting oxygen diffusion through a thin slab of the electrode material. The model, which is based on literature data and has no adjustable parameters, gives a good fit. This demonstrates that in the medium‐frequency range, oxygen diffusion through the electrode material is evenly distributed over the whole electrode interface. On the other hand, under dc conditions it is concentrated along the electrode triple‐phase perimeter. Therefore, the distribution of the transfer current over the interface varies with the applied signal frequency. It follows that the electrode resistance and capacitance determined from the impedance diagram are related to an electrode reaction occurring over a reaction zone variable with the signal frequency.