Investigation of the interface structure and electronic state of nanocomposite La0.6Sr0.4Co0.2Fe0.8O3-δ and Ce0.9Gd0.1O2-δ electrode for solid oxide fuel cells

Abstract

The interface structure and electronic state of nanocomposite La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) and Ce_0.9Gd_0.1O_2-δ (gadolinium doped ceria: GDC) electrode for solid oxide fuel cell were investigated by scanning transmission electron microscopy (STEM) and soft X-ray absorption spectroscopy (XAS). Fine interface structure with compressive and extensive strains respectively for LSCF and GDC was observed by the high-angle annular dark field STEM. The Fe L_2,3-edge XAS showed a slight difference: the crystal field splitting for the FeO₆ octahedron of the LSCF and GDC nanocomposites is smaller than that of the LSCF bulk and thin film. This should be related to the strain effect at the interface. The Co L_2,3-edge XAS revealed that the valence of Co for the nanocomposite was 2+ with a high-spin (HS) configuration while that for LSCF bulk was mostly attributed to 3+ with a low-spin configuration. The Co²⁺ HS state, which should be less stale than the Co³⁺ LS state, is evidence that the oxygen adsorption/desorption reactivity is increased by the nanocomposite structure.