Effect of Microstructure on Ionic Conduction of Composite Electrolytes Consisting of Doped Ceria and Carbonates

Abstract

Composite Electrolytes consisting of oxygen ion conductors and carbonates have received great attention for high temperature fuel cell application. For example, enhanced conduction was observed when the oxygen ion conductor, doped ceria was directly mixed with Li/K carbonates. The electrical conduction of composite electrolyte was contributed by the migration of oxygen ions in solid state and carbonate ions in liquid state. It was observed that the two-phase electrolytes exhibit coionic (O=/H+) conductors during fuel cell operation under the H2/ air atmosphere. It is believed that highly mobile ions at the interface between doped ceria and carbonates may contribute to the high conductivity of the composite electrolyte. In other words, the super-ionic phase might exist at the interface between doped ceria and carbonates, where the defect concentrations are high. Thus, the electrical conduction of composite electrolytes with various types of microstructures were evaluated at temperatures ranging from 300℃to 700℃. For powder mixture, the composite samples were prepared by direct mixing of doped ceria and carbonate powders. For infiltrated composite, the carbonates were infiltrated into porous ceria substrates at 600℃. SEM, XRD, and Electrochemical Impedance Spectroscopy were employed to conduct microstructural, structural and impedance analyses. The electrical conduction behavior of composite electrolytes will be rationalized based on the pore size, pore distribution and interface area.