Synthesis and Characterization of Gd(1−x)SrxCo(1−y)FeyO(3−Δ) as a Cathode Material for Intermediate Temperature Solid Oxide Fuel Cells

Abstract

ABSTRACTGd(1−x)SrxCoO(3−Δ) (GSC) is a promising cathode material system for use in IT-SOFCs due to its high catalytic activity for oxygen reduction and appreciable conductivity. However, it has a high thermal expansion coefficient that is unmatched to the common IT-SOFC electrolyte material, Ce0.8Gd0.2O(2−Δ) (CGO). Gd0.8Sr0.2CoO(3−Δ) (GS20C) was determined to provide the best balance of properties as a base composition in the GSC system for further study. GS20C exhibited electrical conductivity of 400 S cm−1 at 600°C and a linear thermal expansion coefficient of 23 ppm/°C. Manipulation of the Co-site in GS20C by Fe substitution to form Gd(0.8)Sr(0.2)Co(1−y)FeyO(3−Δ) (GS20CFY, Y= 0, 20, 40, 60, 80, 100 atomic%) resulted in a dramatic decrease in the thermal expansion coefficient to a level close to that of the electrolyte (∼13 ppm/°C). However, the decrease in thermal expansion was accompanied by a large decrease in the conductivity as the iron content was increased in the system (to ∼10 S cm−1). Alternatively, formation of GS20C/CGO composite cathodes resulted in thermal matching with the electrolyte material up to the IT-SOFC operating temperature of approximately 600°C with the maintenance of high electrical conductivity. Composite GS20C/CGO cathodes may reduce the problems associated with poor GSC thermal matching to the electrolyte without compromising other important cathodic properties.