Sr_0.7R_0.3CoO_3-δ (R = Gd, Eu, and Sm) Perovskites Infiltrated with Pd: Enhancing the Performance as Cathode Materials in Solid Oxide Fuel Cells

Perovskites based on Sr0.7R0.3CoO3-δ (R = Gd, Eu, and Sm) were prepared to be used as cathodes in solid oxide fuel cells (SOFC). The materials were synthesized using the citrate-nitrate route and thermal treatments in air atmosphere. The identification of the phases was performed using high-resolution synchrotron X-ray powder diffraction (SXRD) at room temperature to determine the features of the crystalline structure and to identify oxygen vacancies in the materials. SXRD data revealed a significant presence of long-range ordered oxygen vacancies concentrated at the O2 and O4 oxygen positions, exhibiting large displacement factors, defined in a tetragonal perovskite-type superstructures with I4/mmm space group. Subsequently, thermal properties were analyzed to determine the thermal expansion coefficients and their compatibility with the other components of the cell. Additionally, thermal analysis allowed us to identify a reduction in the oxygen content as the temperature increases. A single-cell test conducted in electrolyte-supported configuration at 800 and 850 °C with values surpassing 750 mW/cm2 demonstrated the successful utilization of these perovskites as cathode materials in SOFCs. Furthermore, the materials were further optimized by improving the performance of the cells with an additional process: infiltration with a Pd(NO3)2 solution.