Investigation of the interface structure and electronic state of nanocomposite La0.6Sr0.4Co0.2Fe0.8O3−δ and Ce0.9Gd0.1O2−δ electrodes 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) electrodes for solid oxide fuel cells were investigated using scanning transmission electron microscopy (STEM) and soft X-ray absorption spectroscopy (XAS). The fine interface structure with compressive and extensive strains for LSCF and GDC, respectively, was observed by high-angle annular dark field STEM. The Fe L_2,3-edge total-electron-yield (TEY) XAS results 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 could be attributed to the strain effect at the interface. The Co L_2,3-edge TEY XAS results revealed that the valence of Co for the nanocomposite was 2+ with a high-spin (HS) configuration, while that for LSCF bulk was almost 3+ with a low-spin configuration. The Co²⁺ HS state, which should be less stable than the Co³⁺ LS state, is evidence that the oxygen adsorption/desorption reactivity is enhanced by the nanocomposite structure.