Influence of strontium co-doping on the structural, optical, and electrical properties of erbium-doped ceria electrolyte for intermediate temperature solid oxide fuel cells

This study mainly aimed to elucidate the effects of strontium co-doping on the structural, optical, and electrical properties of erbium-doped ceria (Ce0.8Er0.2O2-delta). Ce1-x-yErxSryO2-delta co-doped electrolytes were synthesized through sol-gel-assisted citric acid-nitrate combustion technique and sintered at 1500 degrees C for 6 h. X-ray diffraction results confirmed that the sintered electrolytes possessed a cubic fluorite crystal structure. However, a perovskite secondary phase (SrCeO3) was observed in Ce0.8Er0.125Sr0.075O2-delta co-doped composition due to the low solubility limit of strontium (similar to 5 mol%) in ceria. UV-Vis spectroscopy showed that the co-doping of strontium from 0 mol% to 7.5 mol% increased the direct band gap from 3.41 eV to 3.43 eV. The relative densities and the grain size were in the range of 96.02-97.68% and 1.5-3.28 mu m, respectively, with increasing the strontium content from 0 mol% to 7.5 mol%. Electrochemical impedance spectroscopy showed that the total resistance of Ce0.8Er0.2O2-delta increased as the strontium content increased. Singly doped Ce0.8Er0.2O2-delta electrolyte exhibited the highest ionic conductivity of 18.22 mS/cm at 700 degrees C and the lowest activation energy of 0.55 eV within 600-800 degrees C among all other studied electrolytes.