Performance and stability of mixed conducting composite membranes based on substituted ceria

High-temperature dual-phase oxygen separation membranes were successfully prepared from different Ce0.8Gd0.2O2- (CG)-spinel mixtures according to the mixed oxide route. MnCo1.9Fe0.1O4 (C19) and Cu0.6Ni0.4Mn2O4 (M2) were used as the spinel components with volume fractions of 10, 20, 30, 40 and 50 vol% respectively. The formation of an electron-conducting percolative network by the spinel components was investigated based on electrical resistivity measurements at room temperature. The oxygen permeation behaviour of the composites was determined as a function of the material composition and the temperature. The highest oxygen flux of approximately 0.14 ml (STP)/cm2min was obtained with samples of 0.8mm thickness at 900°C and a spinel content of 30 vol%. The stability of the individual phases was proven by means of X-ray-diffraction (XRD) and microstructural investigations after sintering and high-temperature exposure experiments at 850°C in a CO2- and SO2-containing model flue gas. No degradation of the composite materials was observed. However, semi-long-term permeation experiments in an air/CO2 gradient revealed a strong increase of the oxygen flux as a function of time accompanied by intensive material corrosion probably caused by kinetic demixing.