Structure of cathode-electrolyte interfaces and correlation with ionic conductivity in Solid Oxide Fuel Cell devices

A multiple analysis approach has been used in order to investigate the chemical compatibility between different promising cathode and electrolyte materials for It-SOFC (Intermediate Temperature-Solid Oxide Fuel Cell) application, in order to evaluate how the chemical reactivity can affect the fuel cell performance. The cathodes investigated are: (Ba.La)FeO3, Sm0.5Sr0.5CoO3 and La0.8Sr0.2MnO3. The electrolytes investigated are: Ce0.8Gd0.2O2, Ce0.8Sm0.2O2, BaCe0.9Y0.1O3 and Ba1.015Zr0.825Y0.175O3. The cathode/electrolyte compatibility study was carried out with X-ray Diffraction (XRD), Secondary Electrons Microscopy (SEM), X-ray microspectroscopy, X-ray Absorption Near Edge Structure (XANES) and electrochemical Impedance spectroscopy (EIS). XRD was used to evaluate the materials chemical reactivity through Rietveld analysis. SEM and X-ray microspectrscopy were used to study the cathode/electrolyte interface at micrometric scale and evaluate the materials chemical reactivity, XANES was used to investigate the structural change due to the chemical reactivity. EIS was used to evaluate the influence of the chemical reactivity on the electrical response of the cell. The obtained results show a chemical reactivity both on macro and micro scale because of the formation of unwanted secondary phases such as La2Zr2O7. Moreover the impedance reveals a clear influence of the cathode/electrolyte interface reactivity on the electrical properties of the cell.