Mixed transport properties of Ce1−xSmxO2−x/2 system under fuel cell operating conditions

Ceria-samaria compositions were prepared by freeze-drying, yielding very homogeneous and fluorite single phase powders at temperatures as low as 375 °C. These powders were used to obtain dense ceramics by sintering at 1600 °C for 10 h. The mixed transport properties of these materials were characterized by impedance spectroscopy and the Hebb-Wagner ion-blocking method, at temperatures in the range 700-950 °C. The onset of n-type electronic conductivity was expressed as a function of oxygen partial pressure and temperature, and was found dependent on the Sm-content. Mixed transport properties were also analyzed for conditions in which the samples are exposed to fuels in a SOFC, either as electrolyte or component of cermet anodes. The degree of fuel conversion and corresponding changes in gas composition produce changes in the mixed transport properties of SOFC electrolytes, with emphasis on the fuel side. The mixed transport properties were also used to estimate open cell voltage as a function of fuel conversion.