Development of cobalt-free oxide (Sm_0.5Sr_0.5Fe_0.8Cr_0.2O_3-δ) cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs)

A cobalt-free perovskite oxide Sm_0.5Sr_0.5Fe_0.8Cr_0.2O_3-δ (SSFC) has been exploited as a novel cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The cathode model was synthesized with the addition of the chromium element in the B side of the composite metallic oxide system, which was then formed by the solid-state reaction method. The model system was further characterized in detail for getting the properties behavior. The solid-state reaction of the SSFC system was observed through thermal gravimetric analysis. Meanwhile, the structural properties were investigated by x-ray diffraction, and the weight loss was examined by the thermal gravimetric analysis as well. Furthermore, the thermal expansion coefficient was determined by the thermal-mechanical analysis, and the conductivity properties were tested by the thermal conductivity analysis. The result showed that the SSFC cathode demonstrated the crystalline structure based on the design with a perovskite phase. The oxygen content created on the model structure was obtained to be 2.98 after the calcination process. The average thermal expansion coefficient was achieved up to 5.0×10^-6 K^-1 as the heating given up to 800 °С. Moreover, the conductivity value reached from 2 S∙cm^-1 at 400 °С and it increased to be a maximum of 7.5 S∙cm^-1 at 700 °С. In addition, the presence of Cr⁶⁺ cation valence coordinated with the oxygen anion could lead to generating a large concentration of oxygen vacancies on the cathode surface, facilitating the transport of the O²⁻ anion in the cathode system. Based on these results, the SSFC cathode has good properties as a composite system promising for IT-SOFCs application in the future