Effects of salt composition on the electrical properties of samaria-doped ceria/carbonate composite electrolytes for low-temperature SOFCs

Samaria-doped ceria (SDC)/carbonate composite electrolytes were developed for low-temperature solid oxide fuel cells (SOFCs). SDC powders were prepared by oxalate co-precipitation method and used as the matrix phase. Binary alkaline carbonates were selected as the second phase, including (Li-Na)₂CO₃, (Li-K)₂CO₃ and (Na-K)₂CO₃. AC conductivity measurements showed that the conductivities in air atmosphere depended on the salt composition. A sharp conductivity jump appeared at 475 °C and 450 °C for SDC/(Li-Na)₂CO₃ and SDC/(Li-K)₂CO₃, respectively. However, the conductivities of SDC/(Na-K)₂CO₃ increase linearly with temperature. Single cells based on above composite electrolytes were fabricated by dry-pressing and tested in hydrogen/air at 500-600 °C. A maximum power density of 600, 550 and 550 mW cm^-2 at 600 °C was achieved with SDC/(Li-Na)₂CO₃, SDC/(Li-K)₂CO₃ and SDC/(Na-K)₂CO₃ composite electrolyte, respectively, which we attribute to high ionic conductivities of these composite electrolytes in fuel cell atmosphere. We discuss the conduction mechanisms of SDC/carbonate composite electrolytes in different atmospheres according to defect chemistry theory.