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 (NdSr)_n+1MO_3n+1 (M = Co and Mn or Fe) series are reported. Compounds of composition NdSrCo_0.75Fe_0.25O_4.10, NdSrCo_0.75Mn_0.25O_4.08 and Nd_0.5Sr_1.5Co_0.75Mn_0.25O_3.86 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 consists 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 cell (IT-SOFC) cathode. The area-specific resistance values of electrodes made of these oxides at 973 K in air are 0.18 Ω cm² for NdSrCo_0.75Fe_0.25O_4.10 and NdSrCo_0.75Mn_0.25O_4.08 (comparable to the one of the state-of-the-art materials proposed as cathodes in IT-SOFC), and 1.38 Ω cm² for Nd_0.5Sr_1.5Co_0.75Mn_0.25O_3.86.