Crystal structure, cobalt and iron speciation and oxygen non-stoichiometry of La0.6Sr0.4Co1-yFeyO3-d nanorods for IT-SOFC cathodes

TL;DR

This study investigates the crystal structure, oxidation states, and oxygen non-stoichiometry of La0.6Sr0.4Co1-yFeyO3-d nanorods, revealing higher defect levels and their implications for SOFC cathode performance.

Contribution

It provides detailed analysis of nanostructured La0.6Sr0.4Co1-yFeyO3-d, highlighting differences from bulk materials and linking defect levels to electrochemical performance.

Findings

Co cations have a lower oxidation state than Fe cations.

Oxygen non-stoichiometry d is higher in nanorods than in bulk materials.

Higher defect levels contribute to improved oxygen reduction reaction performance.

Abstract

Single-phased La0.6Sr0.4Co1-yFeyO3-d (y = 0.2, 0.5, 0.8) nanorods exhibiting the rhombohedral perovskite-type phase were synthesized by a pore-wetting technique. We studied their chemical composition, crystal and electronic structures, morphology and hyperfine properties as a function of the Co/Fe content of the samples. Our results demonstrate that Co cations exhibit a slightly lower oxidation state than Fe ones, resulting in a higher oxygen non-stoichiometry d for Co-rich samples. In addition, the values of d determined in this work for nanostructured samples are much higher than those reported in the literature for bulk materials. This can be attributed to the high degree of defects in nanomaterials and is probably one important factor in the high electrochemical performance for the oxygen reduction reaction of nanostructured La0.6Sr0.4Co1-yFeyO3-d IT-SOFC cathodes, which have been reported in a previous work. Keywords: electrode materials; nanostructured materials; X-ray diffraction; NEXAFS; M\"ossbauer spectroscopy