Synthesis and characterization of gadolinium(1-x) strontium(x) cobalt(1-y) iron(y) oxygen(3-delta) as a cathode material for intermediate-temperature solid oxide fuel cells

Gd_(1−x)Sr_xCoO_(3−δ) is a promising cathode material system for use in intermediate temperature solid oxide fuel cells (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 IT-SOFC electrolyte material, Ce _0.8Gd_0.2O_(2−δ).; It was determined that Gd_0.8Sr_0.2CoO_(3−δ) , consisting of orthorhombic and cubic perovskite phases, provided the best balance of properties as a base cathode composition for further study. Two strategies were selected as potential methods to improve the thermal matching of Gd_0.8Sr_0.2CoO_(3−δ) to the Ce_0.8Gd_0.2O_(2−δ) electrolyte: the replacement of cobalt by iron; and the introduction of electrolyte material to form a cathode composite.; Manipulation of the Co-site in the Gd_0.8Sr_0.2CoO _(3−δ) orthorhombic and cubic lattices resulted in a dramatic decrease in the thermal expansion coefficient to a level close to that of the electrolyte. However, the decrease in thermal expansion was accompanied by a large decrease in the conductivity as the iron content was increased in the Gd_0.8Sr_0.2Co_(1−y)Fe_yO _(3−δ) System.; Formation of Gd_0.8Sr_0.2CoO_(3−δ) /Ce_0.8Gd_0.2O_(2−δ) 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 Gd_0.8Sr_0.2CoO _(3−δ)/Ce_0.8Gd_0.2O_(2−δ) cathodes solve the problems associated with poor Gd_0.8Sr _0.2CoO_(3−δ) thermal matching without compromising other important cathodic properties.