Flame Spray Synthesis of Nanoscale La0.65Sr0.4Co0.2Fe0.8O3-δ and Ba0.5Sr0.5Co0.8Fe0.2O3-δ as Cathode Materials for Intermediate Temperature Solid Oxide Fuel Cells

A single-step gas phase process, based on a liquid-fed flame spray synthesis (FSS) technique is presented, which allows a precise control of particle size and particle stoichiometry for the processing of nanostructured cathode layers. Crystalline La0.6Sr0.4Co0.2Fe0.8O3-delta and Ba0.5Sr0.5Co0.8Fe0.2O3-delta nanopowders, two mixed ionic-electronically conducting perovskite compositions for intermediate temperature cathodes were synthesised from aqueous solutions of cost-effective nitrates with production rates up to 400 g h(-1). By controlling the processing parameters, a specific surface area (SSA) of 12-48 m(2)g(-1) corresponding to Brunauer-Emmett-Teller (BET) equivalent particle diameter from 20-100 nm were synthesised. The influence of process parameters like production rate and solvent composition on size, morphology, crystal structure and phase purity were investigated by BET, high resolution electron microscopy (HR-TEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Dilatometry was used to determine the thermal expansion coefficient (TEC) and shrinkage behaviour as a function of particle size. A pronounced shift towards lower temperatures for the onset of shrinkage is observed for the nanoscale materials. Electrochemical performance and degradation was analysed by conductivity measurements as well as thermogravimetric analysis (TGA) under different atmospheres. CO, was identified as a critical parameter in terms of carbonate formation from Ba0.5Sr0.5Co0.8Fe0.2O3-delta and causes a strong increase in the material resistivity, whereas La0.6Sr0.4Co0.2Fe0.8O3-delta is unaffected. The oxygen exchange kinetic of both compositions is affected by CO2 containing atmospheres.