Oxygen Permeation and Stability of Ce0.8Gd0.2O2−δ-PrBaCo2−xFexO5+δ Dual-phase Composite Membranes

Dual-phase membranes of 60 wt% Ce0.8Gd0.2O2−δ-40 wt% PrBaCo2-xFexO3−δ (0 ≤ x ≤ 2) were prepared by a combined citrate and ethylene diamine tetraacetic acid (EDTA) complexing method. X-ray diffraction (XRD) results revealed the good chemical compatibility between ion-conducting phase CGO and electron-conducting phases PBC2−xFxO after sintering in air. The Fe ionic dopant had a significant effect on the phase structure stability and oxygen permeability under CO2 atmosphere, which was confirmed by XRD, thermogravimetry-differential scanning calorimetry (TG-DSC), scanning electron microscopy (SEM) and oxygen permeation experiments. CGO-PBC0.5F1.5O dual-phase membrane demonstrated a stable oxygen permeation flux of 2.71 × 10−7 mol cm−2 s−1 with 50 mol% He/CO2 as the sweep gas at 925 °C, and this value was much higher than that of perovskite-type membranes. The rate-limiting step in the oxygen permeation process changed from the bulk diffusion to the surface oxygen exchange when the CGO-PBC0.5F1.5O membrane thickness decreased to 0.8 mm or less. Due to the high oxygen permeation fluxes and the excellent structural stability under CO2 atmosphere, the CGO-PBC0.5F1.5O membrane is a great potential candidate material for separating oxygen from air in the oxy-fuel combustion techniques.