Processing and characterization of CoO and Sm2O3 codoped ceria solid solution electrolyte

A series of ceria-based solid solution electrolytes, CoO and Sm2O3 codoped ceria Ce0.8Sm0.2−xCoxO2−δ (denoted as CSO for x = 0 and CSCx for x = 0.01–0.09), are synthesized via a carbonate co-precipitate method. The phase composition of the precursor is determined by XRD, EA and TG/DSC. The oxidation valence of Co in the samples calcined at different temperatures is probed by XPS and determined to be in +2 valence state at the temperature >1000 °C. The sintering investigation demonstrates that the addition of Co promotes densification to occur at lower temperatures with a uniform grain growth. Impedance spectroscopy measurements indicate an improvement in the grain and the grain boundary conductivities for the samples with appropriate Co/Sm ratio. The optimal amount of Co additive is proved to be 7 mol%. It shows that CSC0.07 exhibits higher conductivity (σt = 0.0538 S cm−1 at 600 °C) and lower activation energy (Ea = 0.567 eV) compared with CSO and other CSCx. The results suggest that cobalt oxide could be used not only as an effective sintering aid but as a favorable dopant to ceria as well.

► Solid solution electrolytes Ce0.8Sm0.2−xCoxO2−δ were synthesized via oxalate co-precipitation method.
► Sintering temperature and the cobalt concentration affect the distribution of Co.
► Codoping with right ratio of Sm and Co in CSO is beneficial to improve the conductivity.