ACTIVE CATHODES FOR SUPER-HIGH POWER DENSITY SOLID OXIDE FUEL CELLS THROUGH SPACE CHARGE EFFECTS

This report summarizes the work done during the first quarter of the project. Effort was directed in three areas: (1) The determination of the role of ionic conductor morphology, used in composite cathodes, on the ionic conductivity of the ionic conductor. It was shown that if the particles are not well sintered, the necks formed between particles will be very narrow, and the resulting conductivity will be too low (resistivity will be too high). Specifically, a mathematical equation was derived to demonstrate the singular nature of conductivity. (2) Nanosize powders of Sc-doped CeO{sub 2} were prepared by combustion synthesis. The rationale is that the particle size of the composite electrode must be as small as possible to ensure a high ionic conductivity--and resulting in high performance in fuel cells. Di-gluconic acid (DGA) was used as fuel. The process led to the formation of nanosize Sc-doped CeO{sub 2}. The powder was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). (3) Samples were sintered to form materials containing various levels of porosity, from {approx}3% to {approx}43%. Conductivity was measured over a range of temperatures by four probe DC method. It was observed that in highly porous samples, the conductivity was far lower than can be expected purely based on total porosity. The difference could be rationalized on the basis of the theoretical model developed