Oxygen Transport Membranes Research Articles

A review on dual-phase oxygen transport membranes: from fundamentals to commercial deployment

This review summarizes recent progress on dual-phase oxygen transport membranes. Existing challenges, research strategies and future application areas are discussed.

Tuning the ceria interfaces inside the dual phase oxygen transport membranes

Dual-phase oxygen transport membranes (DP-OTMs) offer a good alternative for the separation of oxygen from gas mixtures. As a promising candidate, the overall performance of the fluorite-spinel composite CexGd1-xO2-δ-FeyCo3-yO4 (CGO-FCO) is often dominated by the behavior of the CGO-CGO grain boundaries (GBs), such as solute and non-solute segregations and structural disorders within the boundary. Due to the largely unknown atomistic GB environment, any attempt to control the GBs for an optimized membrane performance is still severely limited. In order to bridge this essential gap, utilizing advanced transmission electron microscopy (TEM) techniques, we quantified both atomistic and chemical structures at the CGO GBs inside the CGO-FCO DP-OTMs down to sub-nm scale. The atomic-site specific lattice distortions, elemental distributions, and valence state variations were found to be well confined within ∼2 nm around the GB, where a clear dependence on the structural coherence of individual GBs can be established. Our results further unraveled the complicated CGO GB environment inside real DP-OTMs, and paved the path towards optimized processing of various types of functional membranes.

Effects of Cr Doping and Water Content on the Crystal Structure Transitions of Ba2In2O5

Temperature-dependent crystal structure alterations in the brownmillerite-type material Ba2In2O5 play a fundamental role in its applications: (i) photocatalytic CO2 conversion; (ii) oxygen transport membranes; and (iii) proton conduction. This is connected to a reversible uptake of up an equimolar amount of water. In this study, in situ X-ray and neutron diffraction were combined with Raman spectroscopy and solid-state nuclear magnetic resonance experiments to unravel the effects of Cr doping and water content on the crystal structure transitions of Ba2In2O5(H2O)x over a wide temperature range (10 K ≤ T ≤ 1573 K, x < 1). A mixture of isolated and correlated protons was identified, leading to a highly dynamic situation for the protons. Hence, localisation of the protons by diffraction techniques was not possible. Cr doping led to an overall higher degree of disorder and stabilisation of the tetragonal polymorph, even at 10 K. In contrast, a further disordering at high temperatures, leading to a cubic polymorph, was found at 1123 K. Cr doping in Ba2In2O5 resulted in severe structural changes and provides a powerful way to adjust its physical properties to the respective application.

CFD Simulation of Syngas Combustion in a Two-Pass Oxygen Transport Membrane Reactor for Fire Tube Boiler Application

The oxygen transport membrane reactor technology enables the stable combustion of syngas and reduction in NOx emission. Applying the syngas combustion membrane reactor to fire tube boiler can integrate oxygen separation, syngas combustion, and steam generation in a single apparatus. In this study, a CFD model for oxygen permeation and syngas combustion in a two-pass LSCoF-6428 tubular membrane reactor for fire tube boiler application was developed to study the effects of the inlet temperature, the sweep gas flow rate, and the syngas composition on the reactor performance. It is shown that the inlet temperature has a strong effect on the reactor performance. Increasing the inlet temperature can efficiently and significantly improve the oxygen permeability and the heat production capacity. A 34-times increase of oxygen permeation rate and a doubled thermal power output can be obtained when increasing the inlet temperature from 1073 to 1273 K. The membrane temperature, the oxygen permeation rate, and the thermal power output of the reactor all increase with the increase of sweep gas flow rate or H2/CO mass ratio in syngas. The feasibility of the syngas combustion membrane reactor for fire tube boiler application was elucidated.

Influences of Al substitution on the oxygen permeability through 60 wt%Ce0.9La0.1O2-δ-40 wt%La0.6Sr0.4Co1-Al O3-δ composite membranes

• New 60 wt%Ce 0.9 La 0.1 O 2-δ -40 wt%La 0.6 S 0.4 Co 1- x Al x O 3-δ composite membranes are reported. • CLO-LSCAO membranes show high oxygen permeability. • CLO-LSCAO membranes show excellent stability under CO 2 atmosphere. • Substitution for Co by Al is economic and ecological. There is a common trade-off between the oxygen permeability and stability of the oxygen permeable membranes, which significantly hinders their practical applications in modern clean energy industries like oxyfuel power plants and process intensifications like the reaction together with separation in one apparatus. Herein we reported a series of previously unreleased ceramic composite oxygen transport membranes 60 wt%Ce 0.9 La 0.1 O 2-δ -40 wt%La 0.6 Sr 0.4 Co 1- x Al x O 3-δ (denoted as 60CLO-40LSC 1- x A x O) with excellent CO 2 stability and acceptable oxygen permeability, where x = 0.05, 0.1, 0.2, 0.3, 0.35. Study results demonstrated that all compositions (60CLO-40LSC 1- x A x O; x = 0.1, 0.2, 0.3, 0.35) clearly consisted of two phases at all doping concentrations ( x = 0.05, 0.1, 0.2, 0.3, 0.35) after sintering at 1250 ℃ for 5 h except for x = 0.05. The oxygen permeation flux initially increases with the increment of aluminum doping content in the range of 0–0.1 and reaches the highest oxygen permeation flux for x = 0.1, followed by the decrease of oxygen permeation flux as x enhances. The optimal doping composition shows a comparable oxygen permeation rate of 1.02 mL cm −2 min −1 at 1000 ℃ under air/He gradient and works steadily under a pure CO 2 environment for 50 h, providing potential applications in oxy-fuel combustion.

CFD Simulation of Hydrogen Generation and Methane Combustion Inside a Water Splitting Membrane Reactor

Hydrogen production from water splitting remains difficult due to the low equilibrium constant (e.g., Kp ≈ 2 × 10−8 at 900 °C). The coupling of methane combustion with water splitting in an oxygen transport membrane reactor can shift the water splitting equilibrium toward dissociation by instantaneously removing O2 from the product, enabling the continuous process of water splitting and continuous generation of hydrogen, and the heat required for water splitting can be largely compensated for by methane combustion. In this work, a CFD simulation model for the coupled membrane reactor was developed and validated. The effects of the sweep gas flow rate, methane content and inlet temperature on the reactor performance were investigated. It was found that coupling of methane combustion with water splitting could significantly improve the hydrogen generation capacity of the membrane reactor. Under certain conditions, the average hydrogen yield with methane combustion could increase threefold compared to methods that used no coupling of combustion. The methane conversion decreases while the hydrogen yield increases with the increase in sweep gas flow rate or methane content. Excessive methane is required to ensure the hydrogen yield of the reactor. Increasing the inlet temperature can increase the membrane temperature, methane conversion, oxygen permeation rate and hydrogen yield.

Effects of Bi Substitution on the Cobalt-Free 60wt.%Ce0.9Pr0.1O2−δ-40wt.%Pr0.6Sr0.4Fe1−xBixO3−δ Oxygen Transport Membranes

The mixed ionic-electronic conducting (MIEC) oxygen transport membrane (OTM) can completely selectively penetrate oxygen theoretically and can be widely used in gas separation and oxygen-enriched combustion industries. In this paper, dual-phase MIEC OTMs doped with Bi are successfully prepared by a sol-gel method with high-temperature sintering, whose chemical formulas are 60wt.%Ce0.9Pr0.1O2−δ-40wt.%Pr0.6Sr0.4Fe1−xBixO3−δ (60CPO-40PSF1−xBxO, x = 0.01, 0.025, 0.05, 0.10, 0.15, 0.20). The dual-phase structure, element content, surface morphology, oxygen permeability, and stability are studied by XRD, EDXS, SEM, and self-built devices, respectively. The optimal Bi-doped component is 60wt.%Ce0.9Pr0.1O2−δ-40wt.%Pr0.6Sr0.4Fe0.99Bi0.01O3−δ, which can maintain 0.71 and 0.62 mL·min−1·cm−2 over 50 h under He and CO2 atmospheres, respectively. The oxygen permeation flux through these Bi-doped OTMs under air/CO2 gradient is 12.7% less than that under air/He gradient, which indicates that the Bi-doped OTMs have comparable oxygen permeability and excellent CO2 tolerance.

A comprehensive comparative study of CO2-resistance and oxygen permeability of 60 wt % Ce0.8M0.2O2–δ (M = La, Pr, Nd, Sm, Gd) - 40 wt % La0.5Sr0.5Fe0.8Cu0.2O3–δ dual-phase membranes

In this study, dual-phase membranes 60 wt % Ce0.8M0.2O2–δ (M = La, Pr, Nd, Sm, Gd) - 40 wt % La0.5Sr0.5Fe0.8Cu0.2O3–δ (CMO-LSFCO) were prepared via a combination of EDTA-citric acid complexing sol-gel and mechanical mixture method. Their chemical compatibility, CO2 tolerance, oxygen permeability, conductivity, and long-term regenerative durability regarding the phase structure and composition were systematically studied. Among the studied CMO-LSCFO dual-phase membranes, CGO-LSFCO shows the highest oxygen permeability under air/He and air/CO2 gradients, which can be associated with the small particle size and high electronic conductivity of the CGO phase resulting in a good percolation with different transfer paths based on the correlations between membrane material characterization and oxygen permeability. The comprehensive comparative study presented in this work identifies the critical factors influencing the oxygen permeability, which may provide guidelines for designing further high performance dual-phase oxygen transport membranes.

Structure Optimization of a High-Temperature Oxygen-Membrane Module Using Finite Element Analysis

The oxygen transport membrane (OTM) is a high-density ion-conducting ceramic membrane that selectively transfers oxygen ions and electrons through the pressure differential across its layers. It can operate at more than 800 °C and serves as an economical method for gas separation. However, it is difficult to predict the material properties of the OTM through experiments or analyses because its structure contains pores and depends on the characteristics of the ceramic composite. In addition, the transmittance of porous ceramic materials fluctuates strongly owing to their irregular structure and arbitrary shape, making it difficult to design such materials using conventional methods. This study analyzes the structural weakness of an OTM using CAE software (ANSYS Inc., Pittsburgh, PA, USA). To enhance the structural strength, a structurally optimized design of the OTM was proposed by identifying the relevant geometric parameters.

The effect of Strontium contents on novel MIEC1-MIEC2 dual-phase ceramic-based oxygen transport membranes

Although ceramic-based oxygen transport membranes (OTMs) have irreplaceable advantages over traditional oxygen production technologies, their oxygen permeability and stability need to be further improved. Based on the theoretical starting point of increasing the three-boundary reaction zone and reducing blocking effect, a set of new dual-phase membranes 75wt%Ce0.8Sm0.1Cu0.1O2-δ-25wt%-Sm0.8Sr0.2Co0.8Fe0.2O3-δ (CSC-8282) and 75wt%Ce0.8Sm0.1Cu0.1O2-δ-25wt%Sm0.3Sr0.7Co0.8Fe0.2O3-δ (CSC-3782) with different strontium contents were prepared by a one-pot sol-gel method ensuring that each element has the same chemical potential. The surface morphology, crystal structure and element distribution are systematically studied by SEM, XRD and EDS, which confirms that the synthesized membranes have an obvious dual-phase structure and excellent compactness. The results of the oxygen permeability experiment show that the oxygen permeability of CSC-3782 is always higher than that of CSC-8282 under any conditions due to the inducing effect of strontium on oxygen vacancies, and flow rate of CSC-3782 at 960°C reached 0.64 and 0.22mL⋅cm-2⋅min-1 for He and CO2 as a sweep gas, respectively. The final long-term stability test confirmed that the dual-phase composite membrane with great prospects for development has high temperature stability and CO2-tolerant property, and the doping of strontium to A-site of perovskite contributes to the improvement of its performance.

Importance of Mixed-Conducting Materials for High-Temperature Fuel Cells Applications

In many electrochemical devices, mixed ionic/electronic conduction have received great attention. For instance, oxygen transport membrane (OTM) based on (Ba,Sr)(Co,Fe)O3 perovskite exhibit unique hole/oxygen ion mixed conduction behavior for oxygen separation application.Accordingly, electrodes/electrolytes exhibiting both electronic and/or multiple ionic conducting properties have been used for high temperature fuel cell application. For example, mixed conducting electrodes based on composite electrode (e.g. LSM/SDC, LSM/YSZ) show improved SOFC performance in comparison to conventional electrode. Such unique conduction behavior may be rationalized based on defect chemistry consideration. Thus, the materials processing and microstructure design may become key issues to optimize their mixed conduction properties. For instance, better hole and oxygen conducing perovskite may be obtained when desired aliovalent dopant and oxidizing atmosphere are used.Thus, the objective of this work is to conduct (1) fabrication/design of MIEC through defect-favored processing, (2) microstructure development for better gas transport, (3) characterization of conduction/interfacial kinetics for better electrodes/electrolytes performance. Desired analytical equipment such as SEM, XRD, electrochemical impedance spectroscopy (EIS) and cell testing are performed to conduct microstructural, structural and impedance analyses. The electrical conduction behavior of composite electrode/electrolytes will be discussed based on defect chemistry consideration and individual microstructure and morphology including pore size, pore distribution and interface area.

Residual stress and mechanical strength of Ce0.8Gd0.2O2-δ-FeCo2O4 dual phase oxygen transport membranes

Ce0.8Gd0.2O2-δ-FeCo2O4 membranes, benefiting from their excellent chemical stability, exhibit a broad application potential in oxygen-consuming industrial processes running in harsh environments. For long-term reliable operation, the membrane needs to possess sufficient mechanical strength. This paper characterizes the typical aspects that challenge the mechanical stability of the sintered membrane, including composition and microstructural defects as well as residual stress and residual stress gradients. It is revealed that mechanical strengths of the sintered membranes increase with decreasing iron cobalt spinel content, that the high iron cobalt spinel content induces microcracks, and that high residual tensile stress gradually decreases from the as-sintered surface to the bulk. Although the residual tensile stress can be reduced by applying an extensive elevated temperature dwell time during cooling, it is suggested to limit the iron cobalt spinel content to a nominal value of 15 wt% to eliminate the residual tensile stress while maintaining a high mechanical strength.

Conductivity Transitions of La0.7Sr0.3MnO3±δ and La0.6Sr0.4Co0.2Fe0.8O3−δ in Ce0.9Gd0.1O2−δ Matrix for Dual-Phase Oxygen Transport Membranes

Using van der Pauw method, the conductivity of disk samples of La0.7Sr0.3MnO3±δ (LSM) and La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) in a Ce0.9Gd0.1O2−δ (GDC) matrix was accurately quasi-continuously measured over 800 °C to −73 °C, and the transition points in Arrhenius behavior were systematically obtained from the extremum points of the second derivatives. While LSM-containing samples showed reproducible conductivity trajectories, the LSCF system exhibited unsystematic changes which may be related to the substantial oxidation/reduction reactions accompanying the ferroelastic–paraelastic transitions with a substantial thermal hysteresis at 650 °C to 750 °C, corresponding to conductivity maxima. A sudden decrease in activation energies on cooling corresponds to the para-to-ferromagnetic, weak insulator–metal transitions and the Curie temperature of LSM appears to gradually decrease in composites to 90 °C, while LSCF composites exhibit blurred transitions at approximately −40 °C. Relatively insulating paramagnetic phases are characterized by activation energy values ~0.2 eV, change to the high temperature phase exhibiting activation energy 0.1 eV for small polaron hopping mechanisms at 300 °C to 500 °C with increasing GDC content in the LSM composites and by two transitions at ∼60 °C and ∼245 °C for the LSCF composites. LSCF single phase shows distinctly lower transition points which appear to match with the singularly large c lattice parameter whereas the composites exhibit decreasing c with LSCF amount together with increasing lattice parameter of GDC. Van der Pauw conductivity is a feasible and sensitive in situ tool for monitoring the status of oxygen transport membranes.

Oxygen permeability and stability of dual-phase Ce0.85Pr0.15O2-δ-Pr0.6Sr0.4Fe0.9Al0.1O3-δ membrane for hydrogen production by water splitting

A series of dense xCe0.85Pr0.15O2-δ (CP) -(100-x) Pr0.6Sr0·4Fe0·9Al0·1O3-δ (PSFA) (x = 30, 40, 50, 60, 70) dual-phase oxygen transport membranes were successfully synthesized by sol-gel method. The feasibility of xCP-(100-x) PSFA membranes for hydrogen production by thermochemical water splitting was explored by testing in the thermochemical stability, oxygen permeability, hydrogen production efficiency, and performance degradation mechanism of these membranes. The results show that the thermochemical stability of xCP-(100-x) PSFA membranes is improved with the CP content increasing. The oxygen permeation model demonstrates that appropriate CP content is beneficial to reduce the permeation resistance of xCP-(100-x) PSFA membranes, and the reaction of surface exchange plays a major role in the oxygen transport process at 925 °C. The formation of Fe(SiO3) and Sr3Fe2O7 on the sweep side leads to the decline in hydrogen production rate. The 60CP-40PSFA membrane showed the best comprehensive performance with a hydrogen production retention rate of 90% and a stable hydrogen production rate of 0.99 ml cm−2 min−1 in the 100-h test cycle.

Study of Enhanced Conduction from Ceramic/Carbonate Composite Electrolytes

Mixed ionic/electronic conduction in many electrochemical devices have received great attention. For instance, oxygen transport membrane (OTM) based on (Ba,Sr)(Co,Fe)O3 perovskite exhibit unique hole/oxygen ion mixed conduction behavior for oxygen separation application. Moreover, composite electrodes/electrolytes consisting of electronic and/or multiple ionic conductors 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. Similarly, mixed conducting electrodes based on composite electrode (e.g. LSM/SDC, LSM/YSZ) also show improved SOFC performance in comparison to conventional electrode. However, to optimize the mixed conduction, the materials/microstructure designs play an important role. Thus, the objective of this work is to conduct (1) fabrication/design of MIEC and composites (2) microstructure development, (3) characterization of conduction/interfacial kinetics for electrodes/electrolytes in high-temperature fuel cells. High-resolution SEM, XRD, and Electrochemical Impedance Spectroscopy are employed to conduct microstructural, structural and impedance analyses. The electrical conduction behavior of composite electrode/electrolytes will be rationalized based on the pore size, pore distribution and interface area.

Oxygen vacancy, permeability and stability of Si doping Pr0.6Sr0.4FeO3-δ ceramic membrane for water splitting

The high-valence inorganic metalloid element of silicon was used for doping perovskite type oxides Pr0.6Sr0.4Fe1-xSixO3-δ (PSFSix, x = 0−0.1), as the oxygen transport membranes (OTM) for thermochemical water splitting to hydrogen production, which were fabricated by sol-gel method successfully. The effects of Si doped on microstructure, thermal expansion, permeability, and stability were investigated systematically. Although the crystal structure does not change, the metal-oxygen average binging energy (ABE) and oxygen vacancy concentration at room temperature increase after Si4+ doped. Furthermore, the phase transition process is reduced below the operating temperature by silicon doped. Due to the increase of ABE, the oxygen vacancy concentration of PSF exceeds that of the Si-doping samples with the temperature elevated. This is why the oxygen permeation flux of Si-doping samples is gradually exceeded by PSF. The long-term stability of water splitting to hydrogen is enhanced because the Si-doping increases the chemical stability of samples in reducing atmosphere.

Demonstration of a ceria membrane solar reactor promoted by dual perovskite coatings for continuous and isothermal redox splitting of CO2 and H2O

The direct one-step CO2 and H2O splitting using an oxygen-transport membrane (OTM) reactor was investigated as a potentially ideal way to generate renewable fuels from concentrated solar energy. The solar-driven thermolysis of CO2 (or H2O) was promoted by in-situ oxygen removal across nonstoichiometric ceria-based membranes. A new solar membrane reactor integrating a tubular densified membrane made of either pure ceria or perovskite-coated ceria was designed and operated under high-flux concentrated solar radiation. A continuous flow of inert gas on the permeate side was used to create the required oxygen partial pressure gradient (driving force) and ensure continuous oxygen permeation via oxygen ion diffusion across the densified ceria membrane. The continuous OTM solar operation at high temperature was demonstrated through testing under various operating conditions. The CO and O2 production rates were sharply enhanced by increasing the operating temperature (up to 1550 °C). The increase of CO2 concentration or oxidant gas flow rate also enhanced the process performance. Unprecedented fuel production rates (>0.07 μmol s−1 cm−2 at 1550 °C) were achieved with a pure CO2 stream on the feed side and flowing Ar on the sweep side of the reactive ceria membrane. An original composite membrane integrating two different perovskite coatings on each side of the ceria membrane, with a sandwich-like structure, was designed and tested under concentrated sunlight. Thin layers of La0.5Sr0.5Mn0.9Mg0.1O3 on the inner side and Ca0.5Sr0.5MnO3 on the outer side were added to enhance oxygen ion transfer. With such a membrane configuration, a remarkable production of CO (>0.13 μmol s−1 cm−2) and oxygen (with CO:O2 ratio of 2) was obtained simultaneously, respectively on the inner and outer sides of the OTM. These results outperform the production rates achieved with the uncoated ceria membranes, and demonstrate the benefits of using composite membranes composed of a densified core material coated with (or sandwiched in between) redox active perovskite materials.

Effects of catalysts on water decomposition and hydrogen oxidation reactions in oxygen transport membrane reactors

Oxygen transport membrane reactors (OTMRs) are used for hydrogen separation through coupling water decomposition reaction (WDR) with hydrogen oxidation reaction (HOR). The activities of catalysts towards WDR and HOR play key roles in the hydrogen separation performance. It is of great practical significance to find suitable catalysts possessing high catalytic activities for WDR and HOR, respectively. In this work, M/SDC (M = Ru, Pd and Pt) catalysts were prepared and their catalytic activities towards WDR and HOR were evaluated systematically and separately on OTMR for hydrogen separation. It is demonstrated that Ru/SDC catalyst shows the highest activities towards both WDR and HOR, while the activity difference among the three noble metal catalysts is small. After testing for tens of hours at temperatures up to 940 °C, Ru nanoparticles in Ru/SDC catalyst still remain <20 nm. The formation of solid solution and strong metal-support interaction (SMSI) between Ru and SDC support keep Ru nanoparticles in small size in the long-time test.

Two-step sintering technique for enhancing mechanical and oxygen permeation properties of dual-phase oxygen transport membranes

The present work involved the application of a two-step sintering (TSS) technique for typical Ce0.9Gd0.1O2−δ–La0.6Sr0.4Co0.2Fe0.8O3–δ (GDC–LSCF) composites and its effect on the microstructure and resultantly mechanical and O2-permeating properties. The samples obtained by conventional sintering (CS) performed at 1100, 1250, and 1400 °C for 3 h exhibited maximum flexural strength and hardness values of 142 MPa and 8.71 GPa, respectively. However, the application of a TSS procedure produced fine-grained microstructures with improved mechanical properties. In particular, with the use of a typical 1250/1200 TSS protocol, increases of approximately 31 % and 7% in the flexural strength and hardness values, respectively, were observed compared to those obtained using the CS method. Moreover, thick-film (∼ 60 μm) GDC–LSCF membrane prepared by tape casting and the TSS technique showed remarkably 1.5–2 times higher oxygen permeation flux than membrane sintered by CS method. The results are discussed and explained in detail.

CO2-Tolerant Oxygen Permeation Membranes Containing Transition Metals as Sintering Aids with High Oxygen Permeability

Chemical doping of ceramic oxides may provide a possible route for realizing high-efficient oxygen transport membranes. Herein, we present a study of the previously unreported dual-phase mixed-conducting oxygen-permeable membranes with the compositions of 60 wt.% Ce0.85Pr0.1M0.05O2-δ-40 wt.%Pr0.6Sr0.4Fe0.8Al0.2O3-δ (M = Fe, Co, Ni, Cu) (CPM-PSFA) adding sintering aids, which is expected to not only improve the electronic conductivity of fluorite phase, but also reduce the sintering temperature and improve the sintering properties of the membranes. X-ray powder diffraction (XRD) results indicate that the CPM-PSFA contain only the fluorite and perovskite two phases, implying that they are successfully prepared with a modified Pechini method. Backscattered scanning electron microscopy (BSEM) results further confirm that two phases are evenly distributed, and the membranes are very dense after sintering at 1275 °C for 5 h, which is much lower than that (1450 °C, 5 h) of the composite 60 wt.%Ce0.9Pr0.1O2-δ-40 wt.%Pr0.6Sr0.4Fe0.8Al0.2O3-δ (CP-PSFA) without sintering aids. The results of oxygen permeability test demonstrate that the oxygen permeation flux through the CPCu-PSFA and CPCo-PSFA is higher than that of undoped CP-PSFA and can maintain stable oxygen permeability for a long time under pure CO2 operation condition. Our results imply that these composite membranes with high oxygen permeability and stability provide potential candidates for the application in oxygen separation, solid oxide fuel cell (SOFC), and oxy-fuel combustion based on carbon dioxide capture.