CATHODIC AND ANODIC POLARIZATION PHENOMENA AT PLATINUM-ELECTRODES WITH DOPED CEO2 AS ELECTROLYTE .1. STEADY-STATE OVERPOTENTIAL

Electrode polarization is studied by means of a current interruption method with the aid of a reference electrode. In this way anodic and cathodic overpotentials, ri, can be measured separately, and the electrolyte polarization (IR drop) can be distinguished from the electrode overpotentials. Platinum paste electrodes are used with several doped ceria electrolytes in oxygen-argon gas atmospheres. At high P02, the η-I curves obey the Butler-Volmer equation, with transfer coefficients of unity, both for anodic and cathodic polarizations. This result implies a charge-transfer (or activation) mechanism. Study of the exchange current, I0, as a function of po2 and temperature shows that oxygen for the charge-transfer process is supplied through adsorbed adatoms on the Pt electrode surface, obeying the Langmuir isotherm. An activation energy of 1.75 eV is obtained for the charge-transfer step. At low po2, limiting-current behavior is obtained for the cathodic polarization, characteristic of a concentration polarization. A scanning electron microscope study of the electrode structure helps to understand the deterioration of electrical properties which occurs when samples are subjected to high temperatures and/or current densities. © 1979, The Electrochemical Society, Inc. All rights reserved.