THE EFFECT OF ANODIC POLARIZATION ON A AG ELECTRODE DEPOSITED ON YSZ SOLID-ELECTROLYTE

Abstract

The polarization behavior in He-O-2 atmosphere was studied on a Ag electrode deposited on yttria-stabilized zirconia (YSZ) solid electrolyte. It was seen that the open circuit potential followed the Nemst equation under experimental conditions. If the cathodic overpotential applied was lower than - 100 mV, a limiting current was observed for a wide range of P-O2 and this was found to result from the interfacial diffusion of adsorbed oxygen. For P-O2 above 0.05 atm, however, a remarkably steep increase in currents was observed above a certain anodic overpotential. After this unexpected phenomenon had happened, the time required to attain a stable open circuit potential became longer and the cathodic limiting current increased by about ten times. To investigate the effect of anodic polarization on the Ag electrode, changes in the surface of the electrode before and after anodic polarization were examined by SEM and XPS, and the results showed that anodic polarization severely and irreversibly deformed the surface structure of the electrode. However, little change in the surface state was observed with polarization from the XPS analysis. The decomposition of the oxides which were formed during anodic polarization was presumed to result in a change in the surface structure, leading to an increase in cathodic limiting current.