The gadolinia-doped ceria electrolyte, Ce0.8Gd0.2O2-δ, and the perovskite-type mixed conductor, La0.8Sr0.2Fe0.8Co0.2O3-δ, were combined into dual-phase ceramic membranes for O separation. The O permeability of both La0.8Sr0.2Fe0.8Co0.2O3-δ and composite membranes at 970 to 1220K was found to be limited by the bulk ambipolar conductivity. The La0.8Sr0.2Fe0.8Co0.2O3-δ exhibited a relatively low ionic conductivity and a high activation energy for ionic transport (~200kJ/mol) as compared with doped ceria. As a result, the O permeation through composite membranes which contained similar volume fractions of the phases was governed by the ionic transport in Ce0.8Gd0.2O2-δ. The permeation fluxes through composite membranes and La0.7Sr0.3MnO3-δ/Ce0.8Gd0.2O2-δ composites had comparable values. An increase in the p-type electronic conductivity of ceria under oxidizing conditions, which could be achieved by co-doping with variable-valence metal cations such as Pr, led to a greater permeability. The O ionic conductivity of composites which consisted of Ce0.8Gd0.2O2-δ and perovskite oxides depended strongly upon the processing conditions. It decreased with interdiffusion of the phase components; particularly La and Sr cations from the perovskite and into the Ce0.8Gd0.2O2-δ phase.

Oxygen Transport in Ce0.8Gd0.2O2-δ-Based Composite Membranes. V.V.Kharton, A.V.Kovalevsky, A.P.Viskup, A.L.Shaula, F.M.Figueiredo, E.N.Naumovich, F.M.B.Marques: Solid State Ionics, 2003, 160[3-4], 247-58