Ca, Sr or Mg-doped Ceria Electrolytes Prepared by Citrate-Nitrate Combustion Synthesis: Effect of Doping Concentration

In this work, it was aimed to synthesize and characterize rare earth metal-free cerium-based electrolytes that might be used in solid oxide fuel cells (SOFCs) by doping calcium, strontium, or magnesium to CeO2. For this purpose, CeO2, CaxCe(1-x)O(2-delta) (0.16 <= x <= 0.24), SrxCe(1-x)O(2-delta) (0.02 <= x <= 0.08) and MgxCe(1-x)O(2-delta) (0.07 <= x <= 0.13) were prepared by using citrate-nitrate combustion method. The solubility limits, microstructural and physical properties of the samples were characterized with XRD, SEM, TG-DTA and impedance analysis. It was found that all samples were in fluorite structure similar to the undoped ceria. The solubility limits of Ca2+, Sr2+ and Mg2+ were 21%, 6% and 12% (by mole) respectively based on XRD analysis results. The relative densities of sintered pellets at 1400 degrees C were more than 90%. Electrochemical impedance spectroscopy analysis, in which the ionic conductivities of the samples were measured, revealed that the Ca0.2Ce0.8O2-delta (CCO20) sample sintered at 1400 degrees C showed the highest ionic conductivity value of 4.47 x10(-2) S.cm(-1) at 800 degrees C. It was determined that the O2- ion conductivity decreased with the order of Ca2+ approximate to Sr2+ >> Mg2+. Conductivities increased with increasing dopant ratio, reached a maximum below the ratios of solubility limits, and then decreased. The obtained results showed that Ca or Sr doped electrolytes prepared by the citrate-nitrate method can show ionic conductivities close to the state-of-the-art Sm doped Ceria electrolytes. It has been determined that Mg doping is quite ineffective.

Automated summary

This research aimed to synthesize and characterize rare earth metal-free cerium-based electrolytes for solid oxide fuel cells (SOFCs) by doping calcium, strontium, or magnesium to CeO2. Various samples were prepared and characterized for their solubility limits, microstructural and physical properties, which revealed that Ca or Sr doped electrolytes showed good ionic conductivity close to state-of-the-art Sm doped Ceria electrolytes, while Mg doping was ineffective.