Oxygen Partial Pressure Dependence of In Situ X-Ray Absorption Spectroscopy at Co and Fe K-Edge for (La0.6Sr0.4)(Co0.2Fe0.8)O3–δ

Abstract

(La0.6Sr0.4)(Co0.2Fe0.8)O3–δ (LSCF) has been promised as a cathode material of solid oxide fuel cells at intermediate temperatures. Despite the many previous studies of LSCF that have been reported, the role of Co and Fe atoms in the oxygen ion conduction is still unclear. In this work, we aimed at presenting each valence, oxygen chemical diffusion coefficient (Dchem) and activation energy (Ea) related to Co and Fe in LSCF by in situ X-ray absorption spectroscopy (XAS) at high temperatures and during reduction. For quantitative analysis of X-ray absorption near edge structure (XANES) spectroscopy, these results indicated that the Co valence decreased more easily than the Fe valence. On the other hand, from relaxation plots of the Co and Fe valence during reduction, the values of Dchem and Ea related to Co and Fe were nearly equal. Considering equations showing the oxygen ion conductivity, these results would indicate that oxygen ion conductivity was contributed by Co with more oxygen vacancies rather than Fe. According to these results, a structural model with and without oxygen vacancies and the oxygen ion conduction mechanism of LSCF was speculated, that is, we found that oxygen ion conductivity was more closely related to Co than Fe in LSCF by direct observations of in situ XAS.

Cobalt–iron red–ox behavior in nanostructured La0.4Sr0.6Co0.8Fe0.2O3− cathodes

“…Regarding the thermal treatments under reductive and oxidative atmospheres (Fig. 4), the general behavior follows the tendency observed for cobalt: an intensity transfer from the white line to lower energies appears upon reduction, indicating a decrease of the Fe formal oxidation state or changes in the coordination environment around the Fe atoms [4,7,8]. Compared to the intensity of the untreated samples, the WL (SH) intensity decreases (increases) 6.9% (8.0%) in the LSCF_A samples and 1.6% (36.4%) in the LSCF_H samples under reducing atmospheres.…”

“…Much effort has recently been done investigating perovskite materials such as La 1 À x Sr x Co 1 À y Fe y O 3 À d (LSCF) as cathodes for solid oxide fuel cells (SOFC) [1][2][3][4][5][6][7][8][9][10]. These ceramics, appropriated for intermediate temperature (IT)-SOFC design, are especially interesting due to its ability to conduct both oxygen ions and electrons, thus enlarging the performance of the cell.…”