Electrical properties of ceria-based oxides and their application to solid oxide fuel cells

Ionic conductivities of ceria-alkaline-earth and -rare-earth oxide systems were investigated in relation to their structures, electrical conductivities, and reducibilities. Samaria and gadolinia-doped ceria samples exhibited the highest electrical conductivity in ceria-based oxides because of the close ionic radii of Sm3+ and Gd3+ to that of Ce4+. The ionic conductivity of samaria- doped ceria was also measured by an ac four-probe method with electron blocking electrodes. A solid oxide fuel cell with a samaria ceria electrolyte produced high electric power, because of its highest oxygen ionic conductivity. The reduction of ceria electrolyte at the fuel side could be suppressed by a coating of stabilized zirconia thin film on the ceria surface. The anodic overvoltage of the doped ceria/anode interface was very small.