Speciation of metals in a nanostructured iron-cobaltite Mixed Conductor used for SOFC design

SOLDATI, ANALIA L.; BAQUÉ, LAURA; NAPOLITANO, FEDERICO; SERQUIS, ADRIANA C.

Campinas

Congreso; RAU 22 - Reunión Anual Usuarios LNLS/CPEM; 2012

Laboratorio Nacional de Luz Sincrotrón

Nanocrystalline Cobalt-ferrite powders with composition La0.4Sr0.6Co0.8Fe0.2O3-d (LSCF) are being investigated as eficient cathode materials for solid oxide fuel cell devices. In this case, we compare two LSCF powders obtained by two different  chemical methods called Acetate and HMTA [1]. XRD and TEM analyses showed in both samples the formation of a new phase under reductive conditions (Ar at 500 C), which coexists with that characteristic of the oxidated state. We used XANES to determine whether or not the formation of this new phase implies a chemical change, i.e. in the oxidation state of the transition metals (Fe and Co). XANES spectra were taken at room temperature from 200 eV below to 800 eV above the metal s K absorption edge using a Si(111) monochromator crystal. We observed intensity shifts in the metals K-edge features of samples treated in a reductive atmosphere. These differences might be explained by a change in the valece of the Co and Fe atoms to slightly lower formal oxidation states. In addition, the spec- tral features of re-oxidized samples did not differ significantly from the untreated samples, supporting the reversibility of this transformation. This behavior was observed in the Acetate as well as in the HTMA samples and can be attributed to intrinsic microstructural defects (size and strain) related to these synthesis routes. [1] Baque L. et al., Electrochem.Comm. 10, 1905 (2008).