Perovskite-type Membranes Research Articles

Reverse cation segregation and crack self-healing of Ba0.3Sr0.7Fe0.9Mo0.1O3-δ perovskite four-channel hollow fiber membrane

The cation segregation in a perovskite-type membrane deleteriously affects the membrane performance and durability. Recovery of segregation is a great challenge because of the complexity of segregation products and severe limitations from the stability of perovskite oxide. This work presents a novel approach for reversing the surface cation segregation by hydrogen-induced annealing which further shows the ability of healing defects and cracks in the oxide bulk. Ba0.3Sr0.7Fe0.9Mo0.1O3-δ (BSFM) four-channel hollow fiber membranes were prepared by one-step thermal processing. A low hydrogen concentration (5 vol %) and a mild temperature (900 °C) were used to anneal the as-prepared BSFM hollow fiber membrane and served to trigger outright reverse segregation of massive complex oxide precipitations at grain boundaries and a self-healing of cracks formed during the sintering stage. The reverse segregation significantly alters the composition and structure which directly affects the performance of BSFM membrane, such as mechanical strength, electrical conductivity, oxygen permeability, and stability. A maximum breaking load of 31.6 N is reached for the hydrogen-induced membrane which is approximately 6 times of the as-prepared BSFM membrane. Hydrogen-induced membranes, having high oxygen permeation flux and low activation energy, can operate stably in partial oxidation of methane catalytic membrane reactor for more than 120 h. Our results demonstrate the feasibility of hydrogen-induced reverse segregation and crack self-healing in the perovskite-type dense membrane, suggesting new directions to design the high-performance materials based on perovskite oxides for application in catalysis, electrocatalysis, and separations in the future.

Inhibiting in situ phase transition in Ruddlesden-Popper perovskite via tailoring bond hybridization and its application in oxygen permeation

Inhibiting in situ phase transition in Ruddlesden-Popper perovskite via tailoring bond hybridization and its application in oxygen permeation

The surface roughness effect on electrochemical properties of La0.5Sr0.5Fe0.7Ga0.3O3-δ perovskite for oxygen transport membranes

The effect of the membrane surface on the oxygen permeation performances is not studied to sufficient detail in the literature. However, this paper shows that the roughness, and the surface physico-chemistry can have a large effect on the oxygen semi-performances of the membrane, in particular on the kinetics of oxygen exchanges at the surface of the mixed electronic and ionic conductors. For instance, the kinetic coefficient of oxygen surface exchanges can increase by more than one order of magnitude in relation with the surface roughness for La0.5Sr0.5Fe0.7Ga0.3O3-δ perovskite-type membrane. Then, the best oxygen fluxes obtained in this work, i.e. 3.9 10−3 mol m−2 s−1, are close to the best performances reported in the literature for a dense 1 mm in thick membrane. Finally, some assumptions are discussed and argued in detail to explain the effect of the surface of the La0.5Sr0.5Fe0.7Ga0.3O3-δ perovskite membrane on their oxygen semi-permeation performances.

Silver-doped strontium niobium cobaltite as a new perovskite-type ceramic membrane for oxygen separation

In this work, we report the silver doping as a novel strategy for developing single-phase mixed conducting ceramic membranes with perovskite-type structure for the efficient oxygen separation from air. Specifically, perovskite-type oxide with a nominal composition of Sr0.95Ag0.05Co0.9Nb0.1O3-δ (SANC) was designed, synthesized and investigated, and a comparative study with the Ag-free SrCo0.9Nb0.1O3-δ (SNC) perovskite-type membrane was also conducted. The incorporation of silver into the perovskite lattice of SNC has been confirmed even after the sintering at 1175 °C using Ag2O as the silver source. An improved sintering feature, enhanced mechanical strength, and an increased electrical conductivity of the SANC membrane when compared to the Ag-free SNC have been observed. Furthermore the chemical bulk diffusion and surface exchange coefficients increased through the silver doping. Above all higher oxygen permeation fluxes were achieved for the SANC membrane when compared with the SNC membrane under the corresponding conditions. Therefore, SANC turned out to be a highly promising ceramic membrane material for oxygen separation.

Correction to Effect of Ba Content on Oxygen Permeation Performance of BaxSr1–xCo0.8Fe0.2O3-δ (x = 0.2, 0.5, and 0.8) Perovskite-Type Membrane

Correction to Effect of Ba Content on Oxygen Permeation Performance of Ba_<i>x</i>Sr_1–<i>x</i>Co_0.8Fe_0.2O_3-δ (<i>x</i> = 0.2, 0.5, and 0.8) Perovskite-Type Membrane

Water splitting for hydrogen generation over lanthanum-calcium-iron perovskite-type membrane driven by reducing atmosphere

Here, we systematically investigated the behavior of water splitting in a La0.9Ca0.1FeO3−δ (LCF-91) perovskite-type oxygen-transport membrane (OTM) reactor driven by different reducing atmospheres (i.e., CO, H2/CO and CH4). The LCF-91 membrane showed favorable oxygen permeability and hydrogen production rates toward different reducing atmospheres (0.0617, 0.0523 and 0.0390 μmol s−1 cm−2 for CO, H2/CO and CH4 reducing gases, respectively). The activation of CO is easier than that of CH4 over the surface of LCF-91, which promotes the surface oxygen diffusion and following oxygen permeation rate. Further crystallization of the membrane materials is observed during the water splitting test, which is much more serious for the side exposing in the oxidation atmosphere (steam side) compared with the reducing atmospheres. Grain growth of materials in both reduction and oxidation sides of membrane is associated with the reducing atmospheres, and the growth rate follows a rank order of CH4 > H2/CO > CO. This crystallization of LCF-9 membrane materials is beneficial for improving the stability of the reactor for successive generation of hydrogen. The LCF-91 membrane reveals a favorable stability during the CH4-driven water splitting test.

Copper oxide - perovskite mixed matrix membranes delivering very high oxygen fluxes

Here we show that copper substitution in perovskite-type barium strontium cobalt copper oxide (BSCC) membranes confers extremely high oxygen fluxes well beyond the state of art, reaching 27.5mlcm−2min−1 at 950°C. A key feature of BSCC is the formation of a mixed matrix catalyst-perovskite membrane caused by the segregation of copper, leading to the formation of an intergranular network of copper-rich oxide between perovskite grains. BSCC membranes delivered pressure normalised oxygen flux (i.e. permeance) of up to 86 times higher, above pressure difference of 18kPa, as compared to best perovskite membrane, BBSC, due to the catalytic effect of segregated copper oxide. Unlike conventional dual-phase membranes which contain ion and electron conducting phases, this work shows for the first time perovskite-type membranes consisting of a mixed matrix of oxygen ion/electron conducting (perovskite) and catalytic (copper oxide) phases, thus paving the way to the development of high performance membranes for oxygen separation from air for clean energy applications.

Comparison of microstructure and hydrogen permeability of perovskite type ACe0.9Y0.1O3-δ (A is Sr, Ba, La, and BaSr) membranes

Hydrogen permeation through ACe0.9Y0.1O3-δ (A = Sr, Ba, La, and BaSr) perovskite-type membranes was studied at high temperatures. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used to characterize phase structure and phase stability of the membrane. The XRD results showed the formation of a single phase of perovskite structure with configuration orthorhombic for BCY and BSCY membranes. Based on the TGA results, it was found that the phase stability increases in the order of LCY < SCY < BCY < BSCY. The microstructure examinations of the synthesized membranes studied by scanning electron microscopy (SEM) showed the formation of a dense-like grained microstructure membrane, which is applicable for permeation tests. The partial substitution of Sr by Ba in SCY membrane led to an increase of more than 90% in the hydrogen permeation flux; a high permeation flux of about 1.6 ml min−1 cm−2 was achieved at 900 °C with a partial pressure of 0.6 atm. The activation energies for hydrogen permeation increased in the order of BaSr < Ba < Sr < La.

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.

High-flux oxygen-transporting membrane Pr(0.6)Sr(0.4)Co(0.5)Fe(0.5)O(3-δ): CO2 stability and microstructure.

High oxygen permeability and good thermochemical stability of oxygen-transporting membranes (OTMs) are two main requirements concerning the applicability of these devices in chemical processes, such as CO2 capture using the oxyfuel concept or catalytic membrane reactors. In this work, a single-phase perovskite-type membrane Pr0.6Sr0.4Co0.5Fe0.5O3-δ (PSCF) with 0.6-mm thickness was subjected to periodic thermal cycling in the temperature range between 850 and 1000 °C in a 1000-h long-term permeation test with pure CO2 as the sweep gas. The results of this long-term permeation operation revealed a stepwise increase in oxygen permeation values at 1000 °C after each thermal cycle, reaching from 1.38 cm(3) (STP) min(-1) cm(-2) in the first cycle to 1.75 cm(3) (STP) min(-1) cm(-2) in the fourth cycle. Furthermore, the membrane showed very good CO2 stability at 900 °C and above. Despite a partial decrease in oxygen permeation fluxes at 850 °C, a steady state of 0.25 cm(3) (STP) min(-1) cm(-2) was reached and maintained for more than 100 h. The newly developed PSCF membrane also exhibited a higher oxygen permeation flux with He and CO2 sweeping at all measured temperatures compared to a similar La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) membrane.

Coupling effects of oxygen surface exchange kinetics and membrane thickness on chemically induced stresses in perovskite-type membranes

The durability of the perovskite-type ceramic oxygen ion-conducted membranes strongly depends on the magnitude of the chemically induced stresses. This paper examines the influence of both membrane thickness and exchange of oxygen vacancies at the interface between the membrane surface and surrounding gas phase on the chemically induced stresses in the tubular perovskite-type membrane under the gradient of oxygen partial pressure created between air and an inert gas. A mathematical model relating the chemically induced strains and stresses in the tubular membrane to oxygen non-stoichiometry in perovskite-type oxide has been developed, and solved numerically by the ANSYS codes. Calculation results show that when the membrane thickness is significantly higher than the so-called characteristic membrane thickness, the largest first principal stress on the air feeding side of the membrane is practically identical to the one found under the assumption of the constant oxygen non-stoichiometry condition on the permeate side. An analogous comparison for the largest von Mises stress on the permeate side of the membrane gives rise to the difference by 50%. The influence of the oxygen surface exchange kinetics on the stresses strongly increases with decreasing thickness of the membrane. In case of the membrane of 0.1mm thickness which is of the same order of magnitude as the characteristic membrane thickness, the largest first principal stress on the feeding side that was calculated without and with oxygen surface exchange effect is different by a factor of two, while the corresponding largest von Mises stresses on the permeate side are different by a factor of about four. In general, the presence of oxygen surface exchange resistance and reduced membrane thickness lower the chemically induced stresses.

Effects of Nano Powder Synthesis Methods, Shaping and Sintering Conditions on Microstructure and Oxygen Permeation of La0.6Sr0.4Co0.2Fe0.8O3-Δ (LSCF) Perovskite-type Membranes

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Effect of surface modification of Ba0.5Sr0.5Co0.8Fe0.2O3−δ membrane for oxygen separation

Abstract The effect of surface modification on the oxygen separation properties of permeation membranes is investigated in this work. For this purpose, dense perovskite type membranes of the composition Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ have been successfully prepared by polymerized complex method. Oxygen permeation experiments were conducted according to membrane thickness (1.0 mm and 1.6 mm) and surface modification. The surface modification of the Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ dense membranes for measurement of oxygen permeability was done mainly by screen printing technique Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ powders. The oxygen flux of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ membrane increased with increasing temperature and with decreasing membrane thickness. The oxygen permeation flux through 1.0 mm membrane thickness with modified surface exposed to flowing air (Ph=0.21 atm) and helium (Pl=10 −5 atm) was ca. 1.4 ml/cm 2 ⋅min at 950 °C.

Oxygen permeation of Ba xSr 1 − xCo 0.8Fe 0.2O 3 − δ perovskite-type membrane: Experimental and modeling

Ba x Sr 1 − x Co 0 .8 Fe 0 .2 O 0.3 − δ ( x = 0.2, 0.5, 0.8) dense membranes were prepared by a combined EDTA and citrate complexing method. In our previous works, effects of sintering temperature, sintering dwell time and pressing pressure on microstructure and theoretical densities of the membranes were examined and finally the best corresponding values were reported as 1100 °C, 8–9 h and 200–250 MPa, respectively. In the present work, effects of temperature (650–950 °C), feed flow rate (100–200 cm³/min), sweep gas flow rate (40–80 cm³/min) and membrane thickness (4–5 mm) on oxygen permeation behavior of the Ba x Sr 1 − x Co 0 .8 Fe 0 .2 O 0.3 − δ membranes were investigated. Also, a mathematical model based on Nernst–Planck equation was developed to predict oxygen permeation through the perovskite-type membranes. Both bulk diffusion and surface reactions were incorporated into the model. It was observed that surface reactions are not elementary and a correction term should be introduced into the model to compensate this effect. Also, using a dimensionless Reynolds number, effect of feed flow rate on oxygen flux was taken into account. With aids of these modifications, it was realized that, there is a reasonable agreement between predicted results and experimental data with correlation coefficient (R) of higher than 0.960 and mean squared relative error (MSRE) of lower than 0.022 for all the membranes. Oxygen vacancy bulk diffusion coefficient (D v), surface exchange rate constants (k f and k r), contribution of each resistance to oxygen permeation and characteristic thickness (L c) of the BSCF membranes were also estimated.

Preparation of asymmetric perovskite-type membranes by a settlement method

Asymmetric SrCe 0.95Yb 0.05O 3− α (SCYb) membranes were prepared by using a settlement method to deposit a thin dense SCYb layer on the green porous SCYb support, followed by conventional dry pressing and co-sintering. SCYb powder was mixed in a liquid media (isopropanol) and directly poured onto the pre-pressed green porous SCYb support placed in a beaker. After the powder fully settled onto the support, the green asymmetric sample was dried and co-sintered. The cross-sectional images of the asymmetric systems indicate that thin dense SCYb films in the asymmetric membranes had uniform thicknesses at this level of analysis and show excellent adhesion to the porous support without any undesirable defects, delamination or cracking. Further, different dense layer thicknesses (80–20 μm) were readily obtained by altering the amount of the SCYb powders in the liquid media. The minimum dense layer thickness obtained by the settlement method, with the synthesis conditions utilised in this study, was around 20 μm.

Performance of Zinc-doped Perovskite-type Cathodes at Intermediate Temperatures and Under Carbon Dioxide Atmosphere

Zinc-doped (BaSr)FeO3-δ perovskite-type membranes were found to exhibit an excellent long-term stability at high and intermediate temperatures under an oxygen partial pressure gradient. With carbon dioxide as sweep gas, the oxygen permeation diminishes almost completely. By X-ray diffraction a phase mixture of hexagonal, tetragonal and cubic perovskite with a (Ba0.4{plus minus}0.1Sr0.6{plus minus}0.1)CO3 layer and some zinc oxide was found. Transmission electron microscopy showed that the dense perovskite membrane is decomposed into phases with different morphologies accompanied by pore and crack formation in a surface layer of 5 µm. After switching to helium as the sweep gas, a hexagonal perovskite phase is still present, which reduces the oxygen permeation flux. A short heating to 950 {degree sign}C regenerates the oxygen permeation flux. The appearance of the carbonate structure leads to a breakdown of the oxygen permeation ability, but the effect of the carbon dioxide is totally reversal after a short high temperature treatment.

Performance of zinc-doped perovskite-type membranes at intermediate temperatures for long-term oxygen permeation and under a carbon dioxide atmosphere

Zinc-doped (BaSr)FeO 3− δ perovskite-type membranes were found to exhibit excellent long-term stability at high and intermediate temperatures under an oxygen partial pressure difference of p 1/ p 2 = 21/2.1 × 10 3 Pa at 950 °C and p 1/ p 2 = 21/0.8 × 10 3 Pa at 750 °C. After the change to carbon dioxide as the sweep gas, the oxygen permeation diminishes almost completely. By XRD, a phase mixture of hexagonal, tetragonal and cubic perovskite with a (Ba 0.4±0.1Sr 0.6±0.1)CO 3 layer and some zinc oxide was found. TEM showed that the dense perovskite membrane is decomposed into phases with different morphologies accompanied by pore and crack formation in a surface layer with a depth of approximately 5 μm. After switching to helium as the sweep gas, the carbonate layer is decomposed, but a hexagonal and tetragonal perovskite phase in addition to the cubic phase are still present. A short heating to 950 °C regenerates the oxygen permeation flux due to the abatement of hexagonal perovskite for the benefit of the cubic and tetragonal perovskite phase. The appearance of the carbonate structure, even to a small amount of 8%, leads to a breakdown of the oxygen permeation ability, but also the hexagonal perovskite is disadvantageous. In contrast, the cubic and tetragonal perovskite modifications exhibit good oxygen permeation abilities. The effect of the carbon dioxide is totally reversible after a short high temperature treatment.

Reinvestigation of the Permeation Behaviour of a Ba0.5Sr0.5Co0.8Fe0.2O3-δ Perovskite-type Membrane

Reinvestigation of the Permeation Behaviour of a Ba0.5Sr0.5Co0.8Fe0.2O3-δ Perovskite-type Membrane

Preparation and characterisation of BaxSr1–xCo0.8Fe0.2O3–δ perovskite-type membranes: Part II

This feature describes the preparation and characterisation of BaxSr1–xCo0.8Fe0.2O3–d perovskite-type membranes. The first instalment of this article [DOI: 10.1016/S0958-2118(09)70031-X], which was published in the February 2009 issue of Membrane Technology, provides an introduction to these materials and their use. It also looks at the effects of sintering dwell time and pressing pressure on membrane density. The second part, which appears here, discusses the effect that sintering temperature has on membrane density, briefly covers the X-ray diffraction results, and includes further analysis based on scanning electron microscopy.

The structure and oxygen permeation performance of Ba0.5Sr0.5Ga1-xFexO3-d perovskite-type oxides

Solid-state reaction was used to prepare mixed-conducting Ba0.5Sr0.5Ga1-xFexO3-d (BSGF) perovskite-type membranes. They were characterized by SEM, XRD and DSC and their oxygen permeation performance was examined. The experiments showed that the doping content of the Ga can play an important role in the structure of BSGF. It was found that the perovskite structure was sustained when Ga doping was lower than 0.4 or a little higher, but when Ga doping reached 0.6, the samples will not be perovskite structure. The oxygen permeation experiment showed that the temperature can affect the oxygen permeation of the BSGF membrane remarkably. At high temperature (about 940°C), its oxygen permeation property was higher and its oxygen permeation property will decrease with the temperature. The measured oxygen desorption activity energy of the Ba0.5Sr0.5Ga0.2Fe0.8O3-d measured is about 306.314 kJ·mol-1.