Actas de congresos
X-ray absorption spectroscopy study on La0.6Sr0.4CoO3 and La0.6Sr0.4Co1¡yFeyO3 nanotubes and nanorods for IT-SOFC cathodes.
Fecha
2013-02-26Registro en:
Reunião Anual do LNLS, 23, 2013, Campinas.
Autor
Mejía-Gómez, A.
Sacanell, J.
Soldati, A. L.
Fantini, Marcia Carvalho de Abreu
Lamas, D. G.
Institución
Resumen
In the last years, extensive research has been devoted to develop novel materials
and structures with high electrochemical performance for intermediate-temperatures
solid-oxide fuel cells (IT-SOFCs) electrodes. In recent works, we have investigated the structural and electrochemical properties of La0:6Sr0:4CoO3 (LSCO) and
La0:6Sr0:4Co1¡yFeyO3 (LSCFO) nanostructured cathodes, finding that they exhibit
excellent electrocatalytic properties for the oxygen reduction reaction [1,2]. These materials were prepared by a pore-wetting technique using polycarbonate porous membranes as templates. Two average pore sizes were used: 200 nm and 800 nm. Our scanning electronic microscopy (SEM) study showed that the lower pore size yielded nanorods, while nanotubes were obtained with the bigger pore size. All the samples
were calcined at 1000oC in order to produce materials with the desired perovskite-type
crystal structure.
In this work, we analyze the oxidation states of Co and Fe and the local atomic order
of LSCO and LSCFO nanotubes and nanowires for various compositions. For this pur-
pose we performed XANES and EXAFS studies on both Co and Fe K edges. These
measurements were carried out at the D08B-XAFS2 beamline of the Brazilian Synchrotron Light Laboratory (LNLS). XANES spectroscopy showed that Co and Fe only
change slightly their oxidation state upon Fe addition. Surprisingly, XANES results
indicated that the content of oxygen vacancies is low, even though it is well-known that
these materials are mixed ionic-electronic conductors. EXAFS results were consistent
with those expected according to the rhombohedral crystal structure determined in
previous X-ray powder dffraction investigations.
[1] M.G. Bellino et al, J. Am. Chem. Soc. 129 (2007) 3066
[2] J.G. Sacanell et al., J. Power Sources 195 (2010) 1786