Properties of La0.6Sr0.4Co0.2Fe0.8O3-x (LSCF) double layer cathodes on gadolinium-doped cerium oxide (CGO) electrolytes - II. Role of oxygen exchange and diffusion

Abstract

The area specific resistivity (ASR) of La0.6Sr0.4Co0.2Fe0.8O3-x cathodes on Gd-doped ceria electrolytes has been measured over the temperature range 325-725 degrees C, The ASR values for single layer porous cathodes could be satisfactorily interpreted in terms of available data for oxygen surface exchange coefficients. By introducing a thin (similar to 1 mu m) dense layer of La0.6Sr0.4Co0.2Fe0.8O3-x (LSCF) adjacent to the gadolinium-doped cerium oxide (CGO) electrolyte the resistivity values were decreased by a factor of 2-3 times; which could be explained by increasing the effective interfacial contact area between the LSCF and GGO. However calculations using data for oxygen self diffusion coefficients indicated much higher ASR values than determined experimentally for these duplex layer cathode structures. It is necessary, therefore, to invoke enhanced oxygen ion transport through the dense layer which could arise either due to the development of A-site deficient LSCF material, or too rapid diffusion via grain boundaries.