Nanoparticulate Cathode Films for Low Temperature Solid Oxide Fuel Cells

The thesis aimed to investigate the impact of morphological and compositional architecture on enhancement of electrochemical performance of the cathode. Nanocrystalline particles of cathode materials (La0.75 Sr0.2 Mn O3–δ , La0.6Sr0.4Co0.2Fe0.8O3−δ and La0.25Ba0.25Sr0.5Co0.2Fe0.8O3−δ ) with high phase purity and high specific surface area were synthesized via. Nebulized spray pyrolysis method. The powders were characterized by various analytical methods such as X-ray diffraction, electron microscopy, Inductively Coupled Plasma and Nitrogen adsorption. The hollow sphere morphology of as synthesized powder was modified by application of ultrasonic energy into non-agglomerated nanoparticles. The surface potential behavior of each material system was characterized by Zeta-potential measurement and consequently, the stabilized dispersions of cathode nanoparticles were prepared. Nanoparticulate cathode thin films were deposited by Spin-coating of stabilized dispersions. The half cells (symmetrical samples) were characterized electrochemically by high temperature impedance spectroscopy and the cathode performance were analyzed by the area normalized polarization resistance e.g. Area Specific Resistance (ASR). A new approach for the preparation of thin film functional cathode layers by spin coating of nanocomposite dispersions has been examined for mixed conductive cathode material systems. The cathodes prepared by this process achieved very high electrochemical activity, as a result of the precise control of the morphology and microstructure of the cathode layers by maximizing the surface area over for the oxygen exchange reaction. Very low cathode polarization resistance realizes the reduction of SOFC working temperature below 500 °C. Therefore, several problems associated with aging, sealing, corrosion etc. over long term operation will be bypassed. Furthermore, the method offers a time saving and cost effective single step coating process compared to the conventional methods for thin film fabrication like sputtering, pulsed laser deposition and metal organic chemical vapor deposition. Moreover, the small thickness (~1 μm) is at least 10–20 times lower than that of cathode layers prepared by conventional methods. This represents not only a considerable reduction in ohmic resistance of the whole cell but also a significant reduction in material costs. This novel preparation technique for nanoparticulate thin cathode films provides an immense benefit for applications in Micro Solid Oxide Fuel Cells operating below 500 °C