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In this work, we have studied La0.4Sr0.6Co0.8Fe0.2O3-δ/Ce0.8Gd0.2O2-δ/La0.4Sr0.6Co0.8Fe0.2O3-δ symmetrical cells containing Ce0.8Gd0.2O2-δ electrolytes synthetized with and without the addition of cobalt as sintering aid. Electrochemical impedance spectroscopy results indicate that both electrolyte and cathode impedance response are affected by the addition of Co to the electrolyte, despite using cathodes with similar nano/microstructure according to scanning electron microscopy observations. Transmission electron microscopy characterization revealed the formation of columnar structures at the cathode/electrolyte interface of the cell with Co-doped electrolyte. These columnar structures would negatively affect the cell performance hindering the diffusion of oxide ions from the cathode to the electrolyte.

Solid oxide fuel cell performance is usually limited by high cathodic area specific resistance (ASR) at intermediate temperatures (500-700°C). ASR can be decreased by reducing particle size to nanometer range. This improvement is usually ascribed to the area/volume ratio increase and a higher concentration of active sites for the oxygen reduction reaction (ORR). Nevertheless, this solely explanation seems not to be enough for explaining the high electrochemical performance of some nanostructured La0.4Sr0.6Co0.8Fe0.2O3-d cathodes previously reported (Baqué et al., Electrochemistry Comm. 10 (2008) 1905-1908). Accordingly, the ORR of these cathodes was studied by electrochemical impedance spectroscopy (EIS) under air and under pure oxygen within the 400-700°C range. The nanostructure was characterized even at atomic level by transmission electron microscopy (TEM), revealing that the cathode is composed of nanocrystals surrounded by zones with some degree of crystalline disorder. These results suggest that this kind of nanostructure facilitate the ORR in this compound. Fil: Baque, Laura Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Technical University Of Denmark; Dinamarca Fil: Soldati, Analía Leticia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina Fil: Troiani, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina Fil: Schreiber, Anja. Helmholtz Gemeinschaft; Alemania Fil: Caneiro, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina Fil: Serquis, Adriana Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina

In this work we successfully applied a FIB/lift-out technique to prepare site-specific thin samples containing the cathode/electrolyte interface between two La0.4Sr0.6Co0.8Fe0.2O3-δ (LSCF) / Ce0.9Gd0.1O2-δ (CGO) half cells. Despite different cathode thickness (15 μm and a 5 μm), both samples presented similar composition and nanostructure. However, an exhaustive microscopic analysis by SEM and TEM at high resolution modes, revealed that: the 15 μm sample presented a perfectly attached interface, while the other showed pores at the interfacial boundary, decreasing the real LSCF/CGO contact. In this way we could explain part of the difference in area specific resistance between measured between them.