Fabrication and characterization of functionally graded CeO₂-YSZ solid electrolyte materials

Functionally graded materials (FGM) have been studied for many kinds of materials in order to improve mechanical or thermal properties. We have applied the FGM concept to solid electrolyte materials in order to improve electrical properties as well as mechanical stability of solid oxide fuel cells (SOFC). In this study, we have adopted yttria-stabilized zirconia (YSZ) as a base electrolyte material, because YSZ is the key material for SOFC. The matching is quite important in both chemical and mechanical properties between electrolyte and electrodes for the SOFC system. From this point of view, we have studied a single-component SOFC using electron-ion mixed conducting CeO₂ doped YSZ as the electrode material. The aim of this work is improving the electrical and electrochemical properties as well as mechanical properties of the single-component SOFC by functionally graded CeO₂ concentration in the mixed conducting Ce-YSZ electrode. The oxygen transport properties of FG electrolytes were studied by electrical impedance and SIMS measurements. We have found that the oxygen diffusion property at the electrode/electrolyte interface is improved in FG electrolytes. In addition, the over-potential of the FG electrode measured by current interrupt method shows low values compared with the non-FG electrodes.