In-situ and in-operando studies of cobalt doped titanates by XRD, XAS and electrochemical impedance spectroscopy simulating working conditions as SOFC anodes and cathodes

Full text: Perovskites with Ti on their B-site has recently been subject of study on the Solid Oxide Fuel Cell (SOFC) field since these materials presents good properties that enables their use as a possible anode materials. At the SOFC cathode side, the (La,Sr)CoO₃ is one the most studied cathode material. In this work we present the study of the La_0.4Sr_0.6(Ti,Co)O₃ family (LSTC) for their use as electrode material for new devices with symmetric designs (S-SOFC). In a first step, we completely characterized, for first time, their crystal and electronic structures at room temperature through X-ray diffraction and X-ray Absorption Spectroscopy. This study was followed by non-ambient experiments, simulating in-situ conditions as S-SOFC electrode (oxidizing and reducing atmospheres up to 750°C). We found that cobalt doping increases the electrical conductivity by 5 to 8 orders of magnitude under an oxidizing condition respect to the undoped sample (La_0.4Sr_0.6TiO₃-d), making these materials suitable to be used as cathodes but higher Co doping levels (x≤0.7) decrease the material stability as anode under reducing atmospheres. Besides, Co doping induces a slight rhombohedral distortion in the crystal symmetry at room temperature, favoring a transformation to a cubic phase at higher temperatures (100-500°C, depending of the Co/Ti ratio). On the other hand, recent advances on materials characterization techniques have provided new platforms that enable the in-situ study of crystallographic, mechanical, electronic, and electrochemical properties under a wide range of environmental conditions, not only for fundamental research but also in order to recreate a more realistic environment in the case of applied research. Here, we also present preliminary results on LSTC S-SOFC from our recently commissioned characterization device, capable to perform simultaneous XRD and Electrochemical Impedance Spectroscopy measurements. (author)