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.