Co‐firing technology for the preparation of asymmetric oxygen transporting membranes based on BSCF and Zr‐doped BSCF

Asymmetric tubular membranes with a length of 450 mm were prepared in one step by co‐firing of a green support coated by slurry. BSCF (Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3‐δ) and Zr‐doped BSCF3Zr (Ba_0.5Sr_0.5(Co_0.8Fe_0.2)_0.97Zr_0.03O_3‐δ) were used for the separation layer as well as for the porous support, latter one together with PMMA microspheres as a pore forming agent. The gas leakage at room temperature was below 0.003 mL STP/(cm²·min). Oxygen fluxes up to 12 mL STP/(cm²·min) were observed at 900°C in vacuo operation mode. The oxygen flux increased with growing driving force but the slope of the curve flattened at higher driving forces probably caused by limiting surface exchange and pressure losses inside the porous support. The oxygen permeation of asymmetric BSCF tubes was slightly higher compared to BSCF3Zr and exceeded the oxygen flux of a monolithic BSCF membrane by a factor of 4 at comparable operation conditions. © 2013 American Institute of Chemical Engineers AIChE J, 60: 15–21, 2014     

A robust mixed‐conducting multichannel hollow fiber membrane reactor

To accelerate the commercial application of mixed‐conducting membrane reactor for catalytic reaction processes, a robust mixed‐conducting multichannel hollow fiber (MCMHF) membrane reactor was constructed and characterized in this work. The MCMHF membrane based on reduction‐tolerant and CO₂‐stable SrFe_0.8Nb_0.2O_3‐δ (SFN) oxide not only possesses a good mechanical strength but also has a high oxygen permeation flux under air/He gradient, which is about four times that of SFN disk membrane. When partial oxidation of methane (POM) was performed in the MCMHF membrane reactor, excellent reaction performance (oxygen flux of 19.2 mL min^?1 cm^?2, hydrogen production rate of 54.7 mL min^?1 cm^?2, methane conversion of 94.6% and the CO selectivity of 99%) was achieved at 1173 K. And also, the MCMHF membrane reactor for POM reaction was operated stably for 120 h without obvious degradation of reaction performance. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2592–2599, 2015     

Partial Oxidation of Methane to Syngas in a Packed Bed Catalyst Membrane Reactor

The planar membrane reactor configuration was explored for partial oxidation of methane (POM) to syngas. A supported membrane composed of yttria‐stabilized zirconia and La_0.8Sr_0.2Cr_0.5Fe_0.5O_3‐δ was sealed to a stainless holder, and a Ni/Al₂O₃ catalyst bed was placed under the membrane plane with a small slit between them. This reactor configuration would facilitate the POM reaction via oxidation‐reforming mechanism: the oxidation reaction occurring at the membrane surface and the reforming reaction taking place in the catalyst bed. At 800°C and a methane feed rate of 32 mL min^?1, the reactor attained methane throughput conversion over 90%, CO and H₂ selectivity both over 95%, and an equivalent oxygen permeation rate 1.4 mL cm^?2 min^?1. The membrane and catalyst remained intact after the POM testing. The planar membrane reactor configuration explored in this study may lead to the development of a compact reactor for syngas production. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2170–2176, 2016     

Enhancing oxygen permeation via multiple types of oxygen transport paths in hepta‐bore perovskite hollow fibers

The multiple types of efficient oxygen transport paths were demonstrated in high‐mechanical‐strength hepta‐bore Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3‐δ hollow fiber membranes. These types of paths play a prominent role in enhancing oxygen permeation fluxes (17.6 mL min^?1 cm^?2 at 1223 K) which greatly transcend the performance of state‐of‐the‐art Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3‐δ hollow fiber membranes, showing a good commercialization prospect. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4273–4277, 2017     

High‐rate hydrogen separation using an MIEC oxygen permeable membrane reactor

In this study, we propose using mixed ionic‐electronic conducting (MIEC) oxygen permeable membrane to separate hydrogen via the water splitting reaction. To do that, steam was fed to one side of the membrane (side I) and a low‐purity hydrogen was fed to the other side (side II). Oxygen from water splitting on side I permeates through the membrane driven by an oxygen chemical potential gradient across the membrane to react with the low‐purity hydrogen on side II. After condensation and drying, high‐purity hydrogen is acquired from side I. Thus, the hydrogen separation process is realized based on the fact that the low‐purity hydrogen is consumed and high‐purity hydrogen is acquired. We achieved a high hydrogen separation rate (13.5 mL cm^?2 min^?1) at 950°C in a reactor equipped with a 0.5‐mm‐thick Ba_0.98Ce_0.05Fe_0.95O_3‐δ membrane. This research proofed that it is feasible to upgrade hydrogen purity using an MIEC oxygen permeable membrane. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1278–1286, 2017     

Fabrication of BSCF-based mixed oxide ionic-electronic conducting multi-layered membrane by sequential electrophoretic deposition process

The Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF)-based multi-layered oxygen separation membrane was fabricated by the sequential electrophoretic deposition (EPD) process. A thin porous/dense bi-layer of BSCF was formed on a thick porous support of BSCF. The porous support prepared by a sacrificial template method using BSCF powder mixed with wheat starch (30 wt%) as a pore-forming agent, followed by uniaxial pressing and low-temperature sintering, was directly used as an EPD electrode. A thin BSCF layer was first formed on the porous support, and then a thin BSCF + PMMA (polymethyl methacrylate) layer was sequentially formed on the thin BSCF layer using a bimodal suspension of BSCF and PMMA. A 30-μm thin porous/dense bi-layer of BSCF of which the total thickness was obtained by optimizing the processes of EPD and subsequent co-sintering. The oxygen separation performance of 3.7 ml (STP) min^?1 cm^?2 at 860 °C was achieved for the BSCF-based multi-layered oxygen separation membrane.     

Multichannel mixed‐conducting hollow fiber membranes for oxygen separation

A multichannel mixed‐conducting hollow fiber (MMCHF) membrane, 0.5 wt % Nb₂O₅‐doped SrCo_0.8 Fe_0.2O_3‐δ (SCFNb), has been successfully prepared by phase inversion and sintering technique. The crystalline structure, morphology, sintering behavior, breaking load, and oxygen permeability of the MMCHF membrane were studied systematically. The MMCHF membrane with porous‐dense asymmetrical microstructure was obtained with the outer diameter of 2.46 mm and inner tetra‐bore diameter of 0.80 mm. The breaking load of the MMCHF membrane was 3–6 times that of conventional single‐channel mixed‐conducting hollow fiber membrane. The MMCHF membrane showed a high oxygen flux which was about two times that of symmetric capillary membrane at similar conditions as well as a good long‐term stability under low oxygen partial pressure atmosphere. This work proposed a new configuration for the mixed‐conducting membranes, combining advantages of multichannel tubular membrane technology and conventional hollow fibers. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1969–1976, 2014     

Fabrication of BSCF-based mixed ionic-electronic conducting membrane by electrophoretic deposition for oxygen separation application

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF), which exhibits a high mixed oxide ionic-electronic conduction, was used for the fabrication of an oxygen separation membrane. An asymmetric structure, which was a thin and dense BSCF membrane layer supported on a porous BSCF substrate, was fabricated by the electrophoretic deposition method (EPD). Porous BSCF supports were prepared by the uniaxial pressing method using a powder mixture with BSCF and starch as the pore-forming agent (0–50 wt.%). The sintering behaviors of the porous support and the thin layer were separately characterized by dilatometry to determine the co-fired temperature at which cracking did not occur. A crack-free and thin dense membrane layer, which had about a 15 μm thickness and >95% relative density, was obtained after optimizing the processes of EPD and sintering. The dense/porous interface was well-bonded and the oxygen permeation flux was 2.5 ml (STP) min⁻¹ cm^-2 at 850 °C.     

Influence of the preparation methods on the microstructure and oxygen permeability of a CO2‐stable dual phase membrane

A CO₂‐stable dual phase membrane of the composition 40 wt % NiFe₂O₄‐60 wt % Ce_0.9Gd_0.1O_2‐δ (40NFO‐60CGO) was synthesized in three different ways: mixing of the starting powders (1) in a mortar and (2) in a ball‐mill as well as by (3) direct in situ one‐pot sol–gel powder synthesis. Backscattered scanning electron microscopy revealed that the direct one‐pot synthesis of 40NFO‐60CGO gives the smallest grains in a homogeneous distribution, compared with powder homogenization in the mortar or the ball‐mill. The smaller is the grains, the higher is the oxygen permeability. The permeation of the membrane can be improved by coating a porous La_0.6Sr_0.4CoO_3‐δ (LSC) layer on the surface of the air side. The dual phase membrane of 40NFO‐60CGO prepared by in situ synthesis shows a steady oxygen flux of 0.30 ml/(min cm²) over more than 100 h when pure CO₂ was used as sweep gas, which indicated that the dual phases membrane is CO₂‐resistant at least over this 5 days testing period. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Modeling study of oxygen permeation through an electronically short‐circuited YSZ‐based asymmetric hollow fiber membrane

Here, oxygen fluxes through an electronically short‐circuited asymmetric Ag‐YSZ|YSZ|LSM‐YSZ hollow fiber prepared via a combined spinning and sintering route were tested and correlated to an explicit oxygen permeation model. The average oxygen permeation through such asymmetric hollow fiber with a 27 μm‐thick YSZ dense layer reached 0.52 mL (STP) cm^?2 min^?1 at 1173 K. From the model results, we can obtain the characteristic thickness, the effects of the temperature, and the effect of He sweep gas flow rate to the individual step contribution. The oxygen partial pressure variation in the permeate side, the local oxygen flux, and the three‐different resistance distribution along the axial direction of the asymmetric hollow fiber are theoretically studied; providing guidelines to further improve the membrane performance for oxygen separation. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3491–3500, 2017     

Carbon dioxide separation and dry reforming of methane for synthesis of syngas by a dual‐phase membrane reactor

High‐temperature CO₂ selective membranes offer potential for use to separate flue gas and produce a warm, pure CO₂ stream as a chemical feedstock. The coupling of separation of CO₂ by a ceramic–carbonate dual‐phase membrane with dry reforming of CH₄ to produce syngas is reported. CO₂ permeation and the dry reforming reaction performance of the membrane reactor were experimentally studied with a CO₂–N₂ mixture as the feed and CH₄ as the sweep gas passing through either an empty permeation chamber or one that was packed with a solid catalyst. CO₂ permeation flux through the membrane matches the rate of dry reforming of methane using a 10% Ni/γ‐alumina catalyst at temperatures above 750°C. At 850°C under the reaction conditions, the membrane reactor gives a CO₂ permeation flux of 0.17 mL min^?1 cm^?2, hydrogen production rate of 0.3 mL min^?1 cm^?2 with a H₂ to CO formation ratio of about 1, and conversion of CO₂ and CH₄, respectively, of 88.5 and 8.1%. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2207–2218, 2013     

The Effect of Plasma Spraying Power on La0.58Sr0.4Co0.2Fe0.8O3–δ–La0.8Sr0.2Ga0.8Mg0.2O3–δ Composite Cathode Interlayer Microstructure and Cell Performance

The metal‐supported intermediate temperature solid oxide fuel cells with a porous nickel substrate, a nano‐structured LDC (Ce_0.55La_0.45O_2–δ)–Ni composite anode, an LDC diffusion barrier layer, an LSGM (La_0.8Sr_0.2Ga_0.8Mg_0.2O_3–δ) electrolyte, an LSCF (La_0.58Sr_0.4Co_0.2Fe_0.8O_3–δ)–LSGM composite cathode interlayer and an LSCF cathode current collector are fabricated by atmospheric plasma spraying. Four different plasma spraying powers of 26, 28, 30, and 34 kW are used to fabricate the LSCF–LSGM composite cathode interlayers. Each cell with a prepared LSCF–LSGM composite cathode interlayer has been post‐heat treated at 960 °C for 2 h in air with an applied pressure of 450 g cm^–2. The current‐voltage‐power and AC impedance measurements indicate that the LSCF–LSGM composite cathode interlayer formed at 28 kW plasma spraying power has the best power performance and the smallest polarization resistance at temperatures from 600 to 800 °C. The microstructure of the LSCF–LSGM composite cathode interlayer shows to be less dense and composed of smaller dense regions as the plasma spraying power decreases to 28 kW. The durability test of the cell with an optimized LSCF–LSGM composite cathode interlayer gives a degradation rate of 1.1% kh^–1 at the 0.3 A cm^–2 constant current density and 750 °C test temperature.     

Evaluation of mixed‐conducting lanthanum‐strontium‐cobaltite ceramic membrane for oxygen separation

In this study, La_0.4Sr_0.6CoO_3‐δ (LSC) oxide was synthesized via an EDTA‐citrate complexing process and its application as a mixed‐conducting ceramic membrane for oxygen separation was systematically investigated. The phase structure of the powder and microstructure of the membrane were characterized by XRD and SEM, respectively. The optimum condition for membrane sintering was developed based on SEM and four‐probe DC electrical conductivity characterizations. The oxygen permeation fluxes at various temperatures and oxygen partial pressure gradients were measured by gas chromatography method. Fundamental equations of oxygen permeation and transport resistance through mixed conducting membrane were developed. The oxygen bulk diffusion coefficient (D_v) and surface exchange coefficient (K_ex) for LSC membrane were derived by model regression. The importance of surface exchange kinetics at each side of the membrane on oxygen permeation flux under different oxygen partial pressure gradients and temperatures were quantitatively distinguished from the oxygen bulk diffusion. The maximum oxygen flux achieved based on 1.6‐mm‐thick La_0.4Sr_0.6CoO_3‐δ membrane was ～4.0 × 10^?7 mol cm^?2 s^?1at 950°C. However, calculation results show theoretical oxygen fluxes as high as 2.98 × 10^?5 mol cm^?2 s^?1 through a 5‐μm‐thick LSC membrane with ideal surface modification when operating at 950°C for air separation. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Promoting Influence of Doping Indium into BaCe0.5Zr0.3Y0.2O3‐δ as Solid Proton Conductor

The influence of indium doping on chemical stability, sinterability, and electrical properties of BaCe_0.5Zr_0.3Y_0.2O_3‐δ was investigated. The phase purity and the chemical stability of the powders in humid pure CO₂ were evaluated by XRD. The dense electrolyte pellets were formed after the calcination at 1450°C for 8 h. SEM images and shrinkage plot showed that the sinterability of the samples was apparently improved by doping indium. The electrical conductivity was measured by impedance test through two‐point method, at both low (200–350°C) and high temperature ranges (450–850°C) in different atmospheres. BaCe_0.4Zr_0.3In_0.1Y_0.2O_3‐δ has been proved to be the optimal composition which simultaneously maximized the chemical stability, sinterability, and electrical conductivity which reached 1.1 × 10^?2 S/cm in wet hydrogen at 700°C, comparing with the 1.3 × 10^?2 S/cm for original BaCe_0.5Zr_0.3Y_0.2O_3‐δ. Anode support fuel cell with a thin BaCe_0.4Zr_0.3In_0.1Y_0.2O_3‐δ electrolyte (15 μm) was fabricated by spin coating method. Maximum power density of 0.651 W/cm² was obtained when operating at 700°C and fed by humid H₂ (containing H₂O 3 vol%). The obtained fuel cell could efficiently run at 650°C for more than 100 h without any attenuation.     

Zr‐ and Tb‐doped barium cerate‐based cermet membrane for hydrogen separation application

Ba_0.8Ce_0.35Zr_0.5Tb_0.15O_3‐δ (BCZT) perovskite has been synthesized by glycine‐assisted solution combustion method. The Ni‐Ba_0.8Ce_0.35Zr_0.5Tb_0.15O_3‐δ‐based cermet membrane is obtained by cosintering NiO and BCZT powder mixture at 1550°C in reducing atmosphere. The X‐ray diffraction pattern of sintered pellet shows the characteristic peaks of both Ni and BCZT phases. FESEM image and elemental mapping confirm the presence of randomly distributed metallic nickel in the BCZT matrix. An electrical conductivity of ~14 S/cm at 700°C is achieved in Ni‐BCZT membrane, which reduced further with increase in temperature (>700°C). The cermet membrane (1.5 mm thick) shows a highest hydrogen permeation flux of ~0.07 mL/min/cm² at 900°C. Chemical stability of Ni‐BCZT membrane has also been examined under humid and carbon dioxide containing atmosphere. The membrane shows good structural stability without any significant change in hydrogen permeation flux.     

Bi1.4Er0.6O3‐(La0.74Bi0.10Sr0.16) MnO3‐δ Cathodes Fabricated By Ion‐impregnating Method For IT‐SOFCs

Bi_1.4Er_0.6O₃‐(La_0.74Bi_0.10Sr_0.16)MnO_3‐δ (ESB‐LBSM) composite cathodes were fabricated by impregnating the ionic conducting ESB matrix with the LBSM electronic conducting materials. The ion‐impregnated ESB‐LBSM cathodes were beneficial for the O₂ reduction reactions, and the performance of these cathodes was investigated at temperatures below 700 °C by AC impedance spectroscopy and the results indicated that the ion‐impregnated ESB‐LBSM system had an excellent performance. At 700 °C, the lowest cathode polarisation resistance (R_p) was only 0.07 Ω cm² for the ion‐impregnated ESB‐LBSM system. For the performance testing of single cells, the maximum power density was 1.0 W cm^–2 at 700 °C for a cell with the ESB‐LBSM cathode. The results demonstrated that the unique combination of the ESB ionic conducting matrix with electronic conducting LBSM materials was a valid method to improve the cathode performance, and the ion‐impregnated ESB‐LBSM was a promising composite cathode material for the intermediate‐temperature solid oxide fuel cells.     

Oxygen permeability and structural stability of a novel tantalum‐doped perovskite BaCo0.7Fe0.2Ta0.1O3−δ

Dense BaCo_0.7Fe_0.2Ta_0.1O_3?δ (BCFT) perovskite membranes were successfully synthesized by a simple solid state reaction. In situ high‐temperature X‐ray diffraction indicated the good structure stability and phase reversibility of BCFT at high temperatures. The thermal expansion coefficient (TEC) of BCFT was determined to amount 1.02 × 10^?5 K^?1, which is smaller than those of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ (BSCF) (1.15 × 10^?5 K^?1), SrCo_0.8Fe_0.2O_3?δ (SCF) (1.79 × 10^?5 K^?1), and BaCo_0.4Fe_0.4Zr_0.2O_3?δ (BCFZ) (1.03 × 10^?5 K^?1). It can be seen that the introduction of Ta ions into the perovskite framework could effectively lower the TEC. Thickness dependence studies of oxygen permeation through the BCFT membrane indicated that the oxygen permeation process was controlled by bulk diffusion. A membrane reactor made from BCFT was successfully operated for the partial oxidation of methane to syngas at 900°C for 400 h without failure and with the relatively high, stable oxygen permeation flux of about 16.8 ml/min cm². © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Actual air separation through poly(aniline‐co‐toluidine)/ethylcellulose blend thin‐film composite membranes

Several multilayer thin‐film composite membranes were fabricated of ethylcellulose (EC) and poly(aniline‐co‐ortho‐toluidine) or poly(ortho‐toluidine) blend as selective thin films and three ultrafiltration membranes with a 10‐ to 45‐nm pore size and 100‐ to 200‐μm thickness as porous supports. The relationships between the actual air‐separation performance through the composite membranes and layer number, composition, casting solution concentration of the thin selective film are discussed. The oxygen‐enriched air (OEA) flux through the composite membranes increases steadily with increasing operational temperature and pressure. The oxygen concentration enriched by the composite membranes appears to decrease with operating temperature, but increases with operating pressure. The actual air‐separation property through the composite membranes seems to remain nearly constant for at least 320 days. The respective highest OEA flux, oxygen flux, and oxygen concentration, respectively, were found to be 4.78 × 10⁻⁵ cm³ (STP)/s · cm², 2.2 × 10⁻⁵ cm³ (STP)/s · cm², and 46% across EC/poly(o‐toluidine) (80/20) blend monolayer thin‐film composite membranes in a single step at 20°C and 650 kPa operating pressure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 458–463, 2000     

A novel lanthanum strontium cobalt iron composite membrane synthesised through beneficial phase reaction for oxygen separation

Composite ceramic membrane is one of the most attractive concepts which combines the advantages of different phases into a single membrane matrix. Recently, the reported significant increased oxygen surface kinetics on the Perovskite/Ruddlesden-Popper composite system because of the formation of novel and fast oxygen transport paths along the hetero-interface has been implanted into the oxygen permeation membrane system. In this work, a novel La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ-(La_0.5Sr_0.5)₂CoO_4+δ (LSCF-LSC) composite hollow fiber membrane is synthesized with oxygen permeation flux of 4.52 mL min⁻¹ cm⁻² at 950 °C. It presents round 4 times and 2.3 times of that of the single LSCF membrane and LSC-coated LSCF membrane at 900 °C. For better comparison, (La_0.576Sr_0.424)_1.136Co_0.3Fe_0.7O_3-δ (LSCF-new) is prepared based on the composition of LSCF-LSC composite. The enhanced oxygen permeability was further investigated through electrochemical impedance spectroscopy (EIS) measurements. We also confirm that LSCF-LSC shows significantly lower area specific resistance (ASRs) for LSCF-LSC|Ce_0.8Sm_0.2O_1.9 (SDC)|LSCF-LSC symmetrical cell relative to other symmetrical cells. This novel LSCF-LSC composite membrane also presents high CO₂ tolerance, with stable oxygen permeation fluxes round 2.6 mL min⁻¹ cm⁻² at 900 °C for 100 h.     

Chitosan‐Tethered Iron Oxide Composites as an Antisintering Porous Structure for High‐Performance Li‐Ion Battery Anodes

Chitosan‐linked Fe₃O₄ (CL‐Fe₃O₄) is facilely prepared by electrostatic interactions between citrate‐capped Fe₃O₄ (C‐Fe₃O₄) (with negatively charged carboxylate groups) and chitosan oligosaccharide lactate (with positively charged amine groups), and utilized as anodes for lithium‐ion batteries. Inert‐atmosphere calcination of CL‐Fe₃O₄ at 400°C leads to the formation of chitosan‐tethered iron oxide composites (Fe₂O₃@chitosan) with an antisintering porous structure. As the calcination temperature changes from 400°C to 700°C, the size of primary particles increases from ca. 40 nm to ca. 100 nm, and the surface area decreases from 57.8 m²/g to 10.9 m²/g. The iron oxide composites exhibit a high discharge capacity and good rate performance. At a current density of 0.1 C after 50 cycles, Fe₂O₃@chitosan (400°C) exhibits a higher retention capacity of 732 mAh/g than those (544 and 634 mAh/g) of chitosan‐free Fe₂O₃ and Fe₂O₃@chitosan (700°C), respectively. The high performance of Fe₂O₃@chitosan (400°C) is attributed to the antisintering porous structure with high surface area that is beneficial for facilitating ion transport, demonstrating a useful chemical strategy for the direct formation of porous electrode materials at low calcination temperature.