RELATION BETWEEN SOLID OXIDE ELECTROLYTE SURFACE-PROPERTIES AND ELECTRODE-REACTION KINETICS

The gaseous electrode reaction on solid electrolytes has traditionally been studied as localized in the vicinity of the contact between a metallic electrode, the electrolyte and the gas phase (microsystem). The rate of such reactions was usually analyzed in terms of gas supply in the reaction zone. This paper presents recent results on O//2, CO-CO//2, H//2-H//2O electrode reactions on various types of solid oxide electrolytes. They are interpreted as resulting from a direct participation of the electrolyte surface. In fact, a marked influence of the oxygen vacancy concentration and electronic conductivity of the interface are observed on the electrode reaction rate. The presence of oxygen vacancies and mobile electrons at the surfaces are properties typically required in solid state chemistry for catalyzed gas oxidation. This led the author to introduce the concept of an 'electrocatalytic effect' of the electrolyte surface. This effect is demonstrated in the case of water vapor reduction on yttria stabilized zirconia, superficially doped at the cathodic interface with appropriate redox couples.