Structural and microstructural characterization and properties of new phases in the Nd-Sr-Co-(Fe/Mn)-O system as air-electrodes in SOFCs .

Abstract

New oxides of the (Nd-Sr)n+1MO3n+1 (M=Co and Mn or Fe) series are reported. Compounds of composition NdSrCo0.75Fe0.25O4.10, NdSrCo0.75Mn0.25O4.08 and Nd0.5Sr1.5Co0.75Mn0.25O3.86 are the n=1 members of the Ruddlesden–Popper homologous series (K2NiF4 structural type) as determined by X-ray diffraction and different transmission electron microscopy techniques. Their crystal structure consist of connected (Co-Fe/Mn)O6 octahedra blocks separated by (Nd/Sr)O rock-salt like layers along the c-axis. Interstitial oxygen atoms or anion vacancies are induced depending on composition. Oxides with interstitial oxygen show good performances as intermediate temperature solid oxide fuel cells (IT-SOFC) cathode. The area-specific resistance values of electrodes made of these oxides at 973 K in air are 0.18 cm 2 for NdSrCo0.75Fe0.25O4.10 and NdSrCo0.75Mn0.25O4.08 (comparable to the one of state-of-the-art materials proposed as cathodes in IT-SOFC) and 1.38  cm 2 for Nd0.5Sr1.5Co0.75Mn0.25O3.86.