Synthesis and electrochemical characterization of pure and composite cathode materials for solid oxide fuel cells

In this paper La0.6Sr0.4Co0.2Fe0.8O3-delta cathode and Ce0.8Gd0.2O2-alpha electrolyte materials were synthesized by using a glycine-nitrate combustion (GNC) technique whereas La0.9Sr0.1MnO3-delta and La0.9Sr0.1Mn0.7Fe0.3O3-delta cathode materials were synthesized according to the Pechini method. The structures of all the cathode materials are perovskite type and their particle sizes are around 300 nm (for samples prepared by the GNC technique) and around 150-200 nm (for samples prepared by the Pechini method). Pure La0.6Sr0.4Co0.2Fe0.8O3-delta, La0.9Sr0.1Mn0.7Fe0.3O3-delta and composite La0.6Sr0.4Co0.2Fe0.8O3-delta/Ce0.8Gd0.2O2-alpha, La0.9Sr0.1MnO3-delta - 8 mol % yttria stabilized zirconia (LSM/YSZ) cathodes were fabricated by screen printing methods. The morphologies of the cathodes were studied by scanning electron microscopy. The resistances of the cathodes were evaluated by electrochemical impedance spectroscopy and galvanostatic current interruption techniques. Both techniques gave identical results in evaluating the total polarization resistance of the cathodes. Preparing a composite La0.6Sr0.4Co0.2Fe0.8O3-delta/Ce0.8Gd0.2O2-alpha cathode at lower temperatures is an effective way to improve the electrochemical kinetics of IT-SOFC cathodes. The apparent activation energy of the composite La0.6Sr0.4Co0.2Fe0.8O3-delta/Ce0.8Gd0.2O2-alpha cathode is 41 KJ.mol(-1), less than that of pure La0.6Sr0.4Co0.2Fe0.8O3-delta cathode (51 - 59 kJ.mol(-1)). In addition, the total polarization resistances of composite LSM/YSZ cathodes are about one fifth of those of La0.9Sr0.1Mn0.7Fe0.3O3-delta cathodes. The total polarization resistances of the composite LSM/YSZ cathodes at 850degreesC and 800degreesC are smaller than those of pure LSMF cathodes at 950degreesC and 900degreesC, respectively.