1 Electroceramics, Fuel Cells and Solid State Chemistry Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark2 Fuel Cells and Solid State Chemistry Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark3 Risø National Laboratory for Sustainable Energy, Technical University of Denmark
Due to global warming as well as other factors, it is necessary to find alternatives to the current consumption of fossil fuels. Oxide materials with high protonic conductivity can potentially find application within many different technological fields in a society that is based on renewable energy to a wider extent. Materials that also have electronic conductivity can find use in hydrogen permeable membranes, which is the main subject of this thesis. The focus of the thesis is experimental aspects of development of new membrane materials. The necessary theoretical background is treated, and three primary methods of characterising potential materials are presented, paying specific attention to how they can be applied to materials with mixed protonic and electronic conductivity; conductivity measurements, concentration cell measurements and flux measurements. Experimental results achieved with all three methods will also be presented. DC conductivity measurements on yttrium doped strontium cerate are shown and compared to previous measurements. Impedance spectroscopy is used to characterise the conductivity as a function of temperature and partial pressures of oxygen and water vapour in calcium doped samarium titanate, lanthanum magnesium titanate and strontium cerate doped with yttrium and nickel. Concentration cell measurements were used to estimate transport numbers for protons and oxide ions in yttrium doped strontium cerate and calcium doped samarium titanate. Furthermore, the voltage of a concentration cell with hydrogen on one side and deuterium on the other was examined as a function of temperature. Results of flux measurements on strontium cerate doped with yttrium or yttrium and nickel are presented and compared to theoretically calculated fluxes and results of similar studies in literature.