Ce-doped strontium cobalt ferrite perovskites as cathode catalysts for solid oxide fuel cells: Effect of dopant concentration

The bulk structure, oxygen mobility, and button cell performance of perovskite-type oxides with the formula Sr1-xCexCo0.2Fe0.8O3-delta for x=0.10, 0.15, and 0.20 have been investigated using in situ X-ray diffraction (XRD), oxygen temperature-programmed desorption (O-2-TPD), CO2-temperature-programmed oxidation (TPO) and button cell/impedance measurements. XRD results indicate that cerium-doped perovskites have a cubic structure and do not undergo structural changes with increasing temperature. An additional CeO2 phase was observed when the concentration of Ce exceeded 15%. Addition of cerium lowers the thermal expansion coefficient (TEC), bringing the TEC closer to that of gadolinia-doped ceria (GDC) electrolyte. The oxygen vacancy generation was inversely proportional to the doping concentration of Ce. However, the best unit cell performance and the lowest impedance were achieved with intermediate levels of Ce doping, suggesting that the ceria phase which segregates at higher doping levels has a detrimental effect on the cell performance. CO2-TPO experiments which were used to examine the rate of intra-facial transport of oxygen were found to be a good probe for button cell performance. (C) 2012 Elsevier B.V. All rights reserved.