LA_0.4SR_0.6TI_1-xCo_xO_3-d (0 <= X <= 1) electrode characterization simulating operation conditions at intermediate temperature symmetric solid oxide fuel cells (S-SOFC)

Full text: In this work, a combined synchrotron X-ray diffraction (XPD), X-ray Absorption Near Edge Spectroscopy (XANES) and Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) study of LSTC (La_0.4Sr_0.6Ti_xCo_1-xO_3-d with 0<=x<=1), intended as symmetric solid oxide fuel cells (S-SOFC) electrode, is presented. Crystallographic and Electronic structure were characterized at room temperature and under reductive and oxidising temperature cycles (20-700°C) simulating operation conditions in a S-SOFC. LSTC has a perovskite pseudocubic structure with an A-site vacancy concentration related with Co doping level. This result seems to be triggered by the fact that Ti remains in a higher formal valence (around 4⁺) independent of the Co concentrations. On the contrary, Co K-edge XANES spectra shows a dependency with the doping level but this seems to be related to structural changes. In-situ measurements simulating the working environment show that LSTC undergoes a rhombohedric to cubic perovskite phase transition with critical temperature being dependent of the structural distortion level. On the other side, XANES/EXAFS in situ experiments show that Co oxidation state moves toward more reduced values with temperature, in both oxidising and reductive environments, while Ti remains always close to 4⁺. (author)