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

摘要

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)_2CO_3, (Li-K)_2CO_3 and (Na-K)_2CO_3. AC conductivity measurements showed that the conductivities in air atmosphere depended on the salt composition. A sharp conductivity jump appeared at 475 ℃ and 450 ℃ for SDC/ (Li-Na)_2CO_3 and SDC/(Li-K)_2CO_3. respectively. However, the conductivities of SDC/(Na-K)_2CO_3 increase linearly with temperature. Single cells based on above composite electrolytes were fabricated by dry-pressing and tested in hydrogen/air at 500-600 ℃. A maximum power density of 600, 550 and 550 mWcm~(-2) at 600 ℃ was achieved with SDC/ (Li-Na)_2CO_3, SDC/(Li-K)_2CO_3 and SDC/(Na-K)_2CO_3 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 elec-trolvtes in different atmospheres according to defect chemistrv theory.