Reducing sintering temperature while maintaining high conductivity for SOFC electrolyte: Copper as sintering aid for Samarium Doped Ceria

High sintering temperature (up to 1400 °C), a requirement for near complete density of common solid oxide fuel cell (SOFC) electrolytes, leads to physical strain on porous electrode structures when co-sintered with electrolyte, and to high manufacturing cost. Lowering sintering temperature can hence be another step towards commercialization of SOFC technology. The efficacy of copper as sintering additive for Samarium Doped Ceria (SDC) was evaluated by characterizing the crystal structure and microstructure of sintered samples, the shrinkage behavior during sintering, and the electrical conductivity of SDC samples with and without copper. Copper contents of 0.1, 0.5, 1.0, 3.0, and 5.0 mol % were studied, among which 0.5 mol% copper and above led to segregation of a copper oxide phase on the surface and grain boundaries of SDC. Copper content as low as 0.5 mol% led to significant reduction in sintering temperature, approximately 300 °C from conventional sintering temperature of 1400 °C. If copper content is too low, e.g. 0.1 mol%, it has minimum effect in lowering the sintering temperature. In addition, 0.5 mol% copper led to the smallest decrease in total conductivity; for example, at 800 °C it reduced by 17% from 0.077 to 0.0642 S/cm. Finally, addition of copper up to 5.0 mole% does not affect the thermal expansion coefficient of the electrolyte.