Optimisation of Spray Pyrolysed (La0.6Sr0.4)0.99CoO3 Cathodes for Solid Oxide Fuel Cells
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The effect of the precursor concentration and the concentration of citric acid (CA) on the properties of (La0.6Sr0.4)0.99CoO3 (LSC), prepared by spray pyrolysis, has been studied. Precursor solutions with concentrations ranging from 67 to 222 g/L, and with CA:LSC ratios of 0.1, 0.5, and 1, were used to synthesise LSC powder. The samples were cal- cined at 750 °C for 6 hours, and subsequently milled for 48 hours. The powders were characterised by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, gas adsorption, and laser diffraction spectrometry.The morphology of the as-prepared powders was found to vary with precursor concentration and amount of citric acid used. More evenly sized agglomerates, and thinner core shells were observed for powders produced from low concentration precursor solutions with high CA:LSC ratios. Post calcination, all samples were found to be phase pure LSC with rhombohedral symmetry. The highest surface area, with a value of 21.2 m2g−1, was measured for the sample made from the precursor solution with the lowest concentration and highest CA:LSC ratio. The particle size distribution was found to be the most narrow for the high concentration sample with the highest CA:LSC ratio. This sample also had the lowest median particle size. The crystallite size calculated from the XRD patterns varied from 42 to 45 nm. The particle size measured from SEM images had larger variations with the smallest value, 85 nm, measured for the sample from the high concentration batch with the lowest ratio of CA:LSC. Symmetric cells with LSC cathodes on Ce0.8Gd0.2O2 (CGO) electrolytes were fabricated by spray deposition and fired at various temperature programs. The deposited cathodes were uniform, with a thickness of 1-2 μm. A firing temperature of 800 °C with no annealing time was found to give good adhesion between cathode and electrolyte. The cell was analysed by electrochemical impedance spectroscopy in oxygen atmosphere at 600, 700, and 800 °C, and the area specific resistance was determined to 3.02, 1.27, and 0.32 Ωcm2 respectively. The results in this work indicate that LSC powders produced by spray pyrolysis are suitable as cathode materials for use in IT-solid oxide fuel cells.