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

The polarization behavior in He-O-2 atmosphere was studied on a Ag ele ctrode deposited on yttria-stabilized zirconia (YSZ) solid electrolyte . It was seen that the open circuit potential followed the Nemst equat ion under experimental conditions. If the cathodic overpotential appli ed 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 diffu sion of adsorbed oxygen. For P-O2 above 0.05 atm, however, a remarkabl y steep increase in currents was observed above a certain anodic overp otential. After this unexpected phenomenon had happened, the time requ ired to attain a stable open circuit potential became longer and the c athodic 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 exa mined by SEM and XPS, and the results showed that anodic polarization severely and irreversibly deformed the surface structure of the electr ode. However, little change in the surface state was observed with pol arization from the XPS analysis. The decomposition of the oxides which were formed during anodic polarization was presumed to result in a ch ange in the surface structure, leading to an increase in cathodic limi ting current.