Screening of A-Substitution in the System A[sub 0.68]Sr[sub 0.3]Fe[sub 0.8]Co[sub 0.2]O[sub 3−δ] for SOFC Cathodes

Several elements were studied as potential A-site substituents in the perovskite system. The considered elements included , , , , , , , , and . The multicomponent oxides were prepared following a complexation-polymerization-pyrolysis method. The materials were characterized by X-ray diffraction, thermal dilatometry, and electrical conductivity under different oxidant atmospheres. The obtained materials were studied as solid oxide fuel cell cathodes, preparing porous films on top anode-supported cells with a yttria-stabilized zirconia electrolyte and a CGO protective layer. The complete cell was characterized by direct current voltamperometry using air and wet as fuel, whereas the porosity of the layer was studied by gas diffusion experiments after electrochemical testing. Oxygen conduction was investigated on gastight membranes prepared for - and -based materials under flow of air and helium (sweep) in the range from 650 to . Pure perovskite structure was not obtained for the cations with the smallest ionic radii. The materials with the best electrochemical performance at contained , , , and . The good electrochemical performance seems to be principally related to the intrinsic electrocatalytic properties of the material (perovskite or small clusters of the single oxide) because no clear correlations of the electrochemical performance and ionic conductivity, electronic conductivity, or gas diffusivity could be found. The electrochemical performance at could be correlated with the catalytic activity for methane oxidation in a fixed bed reactor in the same temperature range. Finally, the catalytic promotion of a -containing perovskite was evaluated by impregnation with .