Segregation Resistant Nanocrystalline/Amorphous (La, Sr) CoO3-(La,Sr)(2)CoO4 Composite Cathodes for IT-SOFCs

Abstract

There is a considerable interest in lowering the operating temperature of solid oxide fuel cells. In this respect, (La,Sr)CoO3(La,Sr)(2)CoO4 dual phase oxides have attracted much attention as cathode materials due to their enhanced oxygen reduction reaction kinetics. The main drawback in lanthanum strontium cobaltite cathodes is Sr-segregation at operating temperatures which causes a sudden degradation in performance. In the current study, this segregation is verified by a specially designed experiment where a (La0.8Sr0.2)CoO3 - (La0.5Sr0.5)(2)CoO4 bilayer is deposited and annealed for an extended period of time. Thin film cathodes are then deposited via co-sputtering of (La0.8Sr0.2)CoO3 and (La0.5Sr0.5)(2)CoO4 yielding non-crystalline structures with acceptable area specific resistance values at temperatures as low as 575 degrees C. The stability of these cathodes is investigated over an extensive range of compositions (La0.8Sr0.2)CoO3: (La0.5Sr0.5)(2)CoO4 = 0.10:0.90 - 0.90:0.10. Prolonged annealing of cathodes at temperature of the same initial area specific resistance shows an exceptionally stable cathode performance as measured by electrochemical impedance spectroscopy responses. It is therefore concluded that co-sputtered (La0.8Sr0.2)CoO3 - (La0.5Sr0.5)(2)CoO4 dual phase cathodes with their amorphous/nanocrystalline structures, especially at mid-compositions, provide an extremely stable microstructure with a strong resistance to Sr segregation. (C) 2019 The Electrochemical Society.