Assessment of the Effect of Transition Metal Oxide Addition on the Conductivity of Commercial Gd-Doped Ceria

Abstract

The effect of addition of transition metal oxides on the charge transport of commercially available Gd-doped ceria (Ce0.9Gd0.1O2-δ) was assessed with special emphasis on the electronic partial conductivity. The samples were doped by adding 2, 4 or 6 cat% of CoO3/4 or FeO2/3, or 2 mol% of the transition metal oxides V2O5, MnO2, and CuO, respectively. It was found that even small amounts of transition metal oxides severely change the partial electronic conductivity of ceria while the majority oxygen ion conductivity was only mildly affected: for high oxygen ion conductivity, Fe or Mn oxide addition as well as small amounts of Co oxide are beneficial, as especially the grain boundary conductivity is slightly increased. Addition of V or Cu oxide in contrast increases the minority charge carrier conductivity of electrons and thus enhances the mixed ionic-electronic conductivity. For Co oxide addition, an increasing electronic conductivity with decreasing oxygen partial pressure from 10−8 to 10−4 bar at temperatures below 600°C indicates the changing redox state of Co from divalent at low oxygen partial pressures to trivalent under ambient oxygen partial pressure.