Correlation between Structural, Chemical, and Electrochemical Properties of La0.6Sr0.4CoO3−d Nanopowders for Application in Intermediate Temperature Solid Oxide Fuel Cells

LEANDRO M. ACUÑA; FERNANDO F. MUÑOZ; RODOLFO O. FUENTES

JOURNAL OF PHYSICAL CHEMISTRY C

AMER CHEMICAL SOC

Lugar: Washington; Año: 2016 p. 20387 - 20399

1932-7447

Lanthanum−strontium cobaltites are excellent mixed ionic andelectronic conductors and exhibit good activity for the oxygen reductionreaction (ORR) at temperatures higher than 500 °C. This led to these materials beingproposed as cathodes for solid-oxide fuel cell devices, either for the standardhigh temperature (SOFC, 900−1000 °C) or theintermediate temperature (IT-SOFC, 500−700 °C) range. Although it was determined that crystalstructure and oxygen vacancies play a central role in these properties, littleis known about cobalt speciation at SOFC or IT-SOFC working temperatures. Inthis study the cobalt speciation and local order of La0.6Sr0.4CoO3−d (LSC) is analyzed in detailfor the first time in nano- and microstructured powders by means of in situexperiments using X-ray absorption spectroscopy (XAS) in the temperature rangeof 20−700 °C. The electrochemical performance of LSC-based cathodes in symmetricalcells under the same conditions is also studied using electrochemical impedancespectroscopy (EIS). Cobalt atoms can be found in any of the three possibleoxidation states. Their relative amount depends on temperature and crystallitesize. In crystallites of a few tens of nanometers, the ease with which Co atomschange their oxidation state is enhanced. This effect probably facilitates oxide transport in LSC-based cathodes.