CATHODIC AND ANODIC POLARIZATION PHENOMENA AT PLATINUM-ELECTRODES WITH DOPED CEO2 AS ELECTROLYTE .2. TRANSIENT OVERPOTENTIAL AND AC IMPEDANCE

The preceding paper (Part I) dealt with the study of electrode polarization phenomena by means of steady-state overpotential measurements. In this paper, two other manifestations of polarization are explored simultaneously with the steady-state measurements. The first is the transient decay of overpotential with time following current interruption, while the second is the a-c response as a function of frequency, best described in terms of complex impedance plots. It is shown that at high pO2 where the charge-transfer mechanism dominates, the overpotential decay curves can be quantitatively interpreted, while the contribution of the electrode behavior to the complex impedance is a single depressed circular arc. Both measurements give a double layer capacitance at each electrode ~100, μF/cm2. At low PO2, where concentration polarization develops at the cathode, the transient curves show a variable effective exchange current which can be calculated from the limiting current of the steady-state data. Correspondingly, the a-c impedance plots show the beginning of an additional arc. These results are completely consistent with the mechanisms developed in Part I. © 1979, The Electrochemical Society, Inc. All rights reserved.