Effect of the synthesis conditions on the properties of La0.15Sm0.35Sr0.08Ba0.42FeO3-a cathode material for SOFCs

Abstract

The perovskite La0.15Sm0.35Sr0.08Ba0.42FeO3-a has been prepared by the glycine nitrate (GNC) route, varying the fuel/oxidizer ratio (glycine/nitrate, G/N= 1 and 2) and cooling rate (slow cooling and air-quenched), in order to study the influence of sample preparation on the materials’ properties, in the context of their application as a cathode material for SOFCs. For this, the performance of the prepared mixed ion and electron conducting perovskite oxides is dictated by their structure, oxygen stoichiometry (3-δ), chemical composition and thermal expansion properties. High-resolution Synchrotron X-ray powder diffraction patterns were collected at room temperature and at 700 and 800ºC. It was found that the materials had a cubic crystal structure at these temperatures. As expected, 3-δ decreased as temperature increased, and was slightly smaller for the quenched sample. Higher electrical conductivity values were obtained for the sample with G/N = 1 (air-quenched) in the cooling rate. At 700 and 800°C the cathode synthesized with G/N = 1 and air-quenched showed the smallest polarization resistance values in impedance spectroscopy studies. Therefore, the physicochemical and electrochemical characterization clearly demonstrated the influence of the synthetic conditions on the cathode performance.