A study of oxygen transport in mixed conducting oxides using isotopic exchange and conductivity relaxation

Mixed conducting oxygen ion conductors can be applied as membranes for the separation of oxygen from air, as electrodes for both oxygen pumps and solid oxide fuel cells. In these applications, oxygen molecules dissociate on the surface of the material. The atomic oxygen species pick up two electrons each before they are incorporated in the oxygen anion sublattice. Oxygen transport through the bulk usually occurs by a hopping process. The transport of oxygen through a mixed conducting membrane is impeded by the bulk diffusion resistance and the rate of the surface reaction on either side of the membrane. A way to enhance the permeation of oxygen is to decrease the membrane thickness, which increases the relative importance of the surface reaction rate in the overall oxygen transport. It is therefore desirable to improve the understanding of the surface process. In the current thesis, theory and experiments are combined which might add to the insight of surface processes.