Research On Graded Cathode And Composite Electrolyte Of Solid Oxide Fuel Cells

Solid oxide fuel cell (SOFC) is one of the most efficient electrochemical devices in converting chemical energy of hydrogen fuel to electrical power directly. SOFCs include the oxygen ion conducting SOFC (SOFC-O), proton conducting SOFC (SOFC-H) and mixed conducting SOFC. Nowadays, the research of intermediate/low SOFC (ITSOFC) is a trend. In this thesis, the graded cathode of SOFC-O and the composite electrolyte of SOFC-H for ITSOFC application are prepared and studied.(1) Graded cathode of SOFC-OFor ITSOFC, since the electrolyte is thinner, the main factor that affects the cell efficiency is the polarization losses of electrodes. For a good electrochemical performance in ITSOFC, the polarization resistance of cathode must be reduced. In this part, we use the cathode materials of mixed ionic and electronic conductivity and optimize the cathode micro structure through a functionally graded cathode approach.The results show that a synthesis route through spin coating of the composite slurry could prepare the graded cathode layers on the substrate surface effectively. We prepare the functionally graded cathode of the particle size gradient, composition gradient and porosity gradient successfully through using the powders with different particle sizes, slulrries with different relative contents of SSC/SDC, and different amounts of the pore-making agent.(2) Composite electrolyte of SOFC-HUsing electrolyte of proton conductivity properties is a trend on the development of SOFC. In this part, a proton conductive glass, which is developed for proton exchange membrane fuel cells, was used to form composite electrolyte with ceramic proton conductor. It is expected that their respective excellent proton conductivity under the different temperature could be engineered into one composite electrolyte. With such composite electrolyte, SOFCs with wider working temperature ranges were expected.The results show that a denser composite electrolyte could be formed through sintering at a rather low temperature. The single cell made of BaCe0.3Zr0.5Y0.2O3-x after incorporating of proton conductive glass, shows higher and more stable output characteristics in a quite low working temperature. That means such composite have good potentials in ITSOFC applications.