Physico-chemical properties of Ln0.5A0.5Co0.5Fe0.5O3-δ (Ln: La, Sm; A: Sr, Ba) cathode materials and their performance in electrolyte-supported Intermediate Temperature Solid Oxide Fuel Cell

Oxides with perovskite structure and composition: La0.5Sr0.5Co0.5Fe0.5O3-delta, La0.5Ba0.5Co0.5Fe0.5O3-delta, Sm0.5Sr0.5Co0.5Fe0.5O3-delta and Sm0.5Ba0.5Co0.5Fe0.5O3-delta were synthesized by a sol-gel EDTA based method. Their physico-chemical properties were evaluated by structural (XRD), transport (electrical conductivity, Seebeck coefficient), and high temperature oxygen nonstoichiometry measurements (TG, delta). A distorted perovskite structure was observed for all of the samples, varying with A-site average radius of cations and tolerance factor t. TG measurements, which were performed in air and in reducing atmosphere allowed to determine the initial, as well as the high temperature dependence of the oxygen nonstoichiometry delta for all materials. At high temperatures the electrical conductivity of the measured samples showed a characteristic maximum and corresponding increase of the Seebeck coefficient. Both effects can be interpreted as a result of a formation of the oxygen vacancies. Apart from Sm0.5Ba0.5Co0.5Fe0.5O3-delta composition, all other materials possess very high electrical conductivity at high temperatures, well exceeding 100 S cm(-1). A custom made IT-SOFC cells were constructed with Ce0.85Gd0.15O1.925 sinters as a support. Their performance was evaluated in 600-800 degrees C range. Despite rather similar transport properties of La0.5Sr0.5Co0.5Fe0.5O3-delta, La0.5Ba0.5Co0.5Fe0.5O3-delta and Sm0.5Sr0.5Co0.5Fe0.5O3-delta perovskites, the best electrochemical properties were recorded in case of the cell with La0.5Sr0.5Co0.5Fe0.5O3-delta based cathode. (C) 2010 Elsevier B.V. All rights reserved.