Gaseous nitrogen has a wide variety of applications in industry. Currently, nitrogen is produced by energy-intensive cryogenic fractional distillation of liquefied air, pressure swing adsorption (PSA), and membranes. In this paper, a novel process was proposed and experimentally verified for production of nitrogen. In this process, oxygen in air is extracted through a dense oxygen–permeable membrane, which is then reacted with methane. By optimizing the air and methane flow rate, the process can produce nearly pure nitrogen as well as a syngas (a mixture of CO and H2). At 800 °C, the reactor produced nitrogen at a rate of 9.2 mL cm–2·min–1 with purity over 99%, and methane was reformed to syngas with CH4 throughput conversion over 90%, H2 selectivity of 92%, and CO selectivity of 92%. The syngas can be burned to generate heat or used as intermediate chemicals for production of liquid fuels and hydrogen. Since the membrane reactor is driven by the energy released by the reaction and does not consume high grade energy electricity, it has a much higher overall energy efficiency than the current industrial nitrogen separation processes.

•LSCF membrane with a support, a dense layer, and a catalytic layer was obtained.•Large and open finger-like pores led to fast gas transport in the support.•Concentration polarization was markedly reduced.•Oxygen permeation flux was 1.54 ml cm−2 min−1 in air/He gradient at 900 °C.•High performance was related with the pore structure and thin dense layer.A three-layered La0.6Sr0.4Co0.2Fe0.8O3-δ membrane was prepared via a modified phase-inversion tape casting method combined with warm pressing and screen-printing. The membrane comprised a thick porous support with straight and large open finger-like pores, a dense separation layer with reduced thickness of 40 µm, and a thin catalytic layer. Oxygen permeation performance was studied under various conditions, and compared with that for a similar membrane, the support of which was fabricated by conventional tape casting and associated with a distinctly different pore structure. Under an air/He gradient, an oxygen flux as high as 1.54 ml (STP) cm−2 min−1 was achieved at 900 °C for the former membrane, about 2.5 times higher than that for the latter. When pure oxygen was used instead of air as the feed gas, their oxygen permeation fluxes were only slightly differed. The obtained results clearly indicated serious presence of concentration polarization in air feed gas in the membrane made by conventional tape casting, which was markedly reduced in the phase-inversion derived membrane. The significantly improved oxygen permeation performance of the latter membrane could be ascribed to its unique pore structure, which allowed fast gas transport through the porous support.

•A novel ceramic membrane covered by α-Si3N4 nanowires has been prepared.•Modified the membrane surface to superhydrophobic by inorganic SiNCO.•This membrane can be used in harsh environments (20 wt% NaCl solution, 90 °C).•The membrane has been used in membrane distillation for 500 h.The α-Si3N4 membrane was prepared by tape casting of silicon slurry, followed by calcination at 1300 °C in flowing NH3 gas. It comprised of α-Si3N4 nanowire of diameter 70 nm which were converted from silicon powder via the vapor–liquid–solid (VLS) growth mechanism. The surface of the obtained membrane was transformed from hydrophilic to superhydrophobic, with a high water contact angle of ~ 160°, by coating with a vesicular SiNCO nano-layer. The experimental results showed that nanowire structure also favored superhydrophobicity. Water desalination performance of the membrane was tested with a sweeping gas membrane distillation (SGMD) device. High water flux of 8.09 l m−2 h−1 was achieved for 20 wt% NaCl aqueous solution in the feed at 90 °C, which was maintained for more than 500 h.

Porous nickel electrodes were fabricated by the phase inversion tape casting method. The as-prepared nickel electrode contained finger-like straight open pores with an average diameter of ∼100 μm and smaller pores with an average diameter of 1–3 μm in the walls. When used as an anode for the oxygen evolution reaction (OER), the porous nickel electrode shows high catalytic activity, reaching a catalytic current density of 10 mA cm−2 under an overpotential of only 300 mV in 1.0 M KOH. It also exhibited excellent performance for the hydrogen evolution reaction (HER), resulting in a current density of 10 mA cm−2 under an overpotential of 125 mV in the same electrolyte. For both OER and HER, the electrode shows great catalytic stability and much better catalytic performance than commercial nickel foam. Moreover, an alkaline electrolyzer using identical porous nickel electrodes as both the anode and cathode required a cell voltage of only 1.65 V to reach 10 mA cm−2 for overall water splitting. The improved electrocatalytic performance of the electrode can be attributed to its unique dual-pore structure.

Hydrophobic surfaces are required for a variety of applications owing to their water repellent and self-cleaning properties. In this work, we present a novel approach to prepare durable hydrophobic surfaces on porous ceramics. A polydimethylsiloxane (PDMS) film was applied to a porous alumina wafer, followed by pyrolysis at 400 °C in a non-oxidizing atmosphere (H2:N2 = 5:95), giving rise to nanoparticles. In these particles, Si, C and O elements formed amorphous networks to which methyl groups that had survived the pyrolysis were bonded. The as-modified porous alumina wafer was hydrophobic with a water contact angle of 136°, which is attributed to the presence of the methyl groups. The hydrophobicity was maintained after immersion in aqueous solutions in a pH range of 2–12 and acetone. The hydrophobicity was also retained after exposure to temperatures as high as 450 °C in an oxidative atmosphere (air) and after mechanical abrasion with sandpaper. The hydrophobic porous alumina ceramics developed in the present study are promising for use as membranes in various separation processes.

•Planar YSZ-LSCrF membranes comprising a separation layer of various thickness have been prepared.•Oxygen permeation is mainly limited by surface oxygen exchange in the thickness range of 75–25 μm.•Membranes with a thin separation layer and modified surfaces show very high oxygen permeability.Zr0.84Y0.16O1.92 (YSZ)-La0.8Sr0.2Cr0.5Fe0.5O3−δ (LSCrF) planar membranes consisting of an oxygen-permeable dense layer and a finger-like porous support were prepared using the phase inversion tape casting/sintering method. The thickness of the dense layer was varied in the range of 75–25 μm by adjusting the blade gap for the tape casting. The oxygen permeation flux through the membranes was measured at elevated temperatures with the dense layer side exposed to air and the porous support side swept with CO to remove the permeated oxygen. At 850 °C, oxygen permeation fluxes of 0.8, 0.9, 1.1 ml cm−2 min−1 (STP) were observed for the membranes with a 75, 50, 25 μm thick dense layer, respectively. The oxygen permeation flux increased with decreasing the thickness of the dense layer appreciably, but the increment was much smaller than the extrapolated value assuming the linear dependence of the oxygen permeation flux on the reciprocal thickness, revealing that the overall oxygen permeation process was mainly controlled by the surface oxygen exchange step in the given thickness range. To enhance the surface oxygen exchange activity, the membrane was modified by applying a 10 μm thick porous YSZ-LSCrF layer on the dense layer side surface and depositing samarium doped ceria (SDC) nano-particles on the inner surface of the porous support. The membranes with modified surfaces exhibited much increased oxygen permeation flux. An increased flux of 2.1 ml cm−2 min−1 was obtained at 850 °C for the membranes with a 25 μm thick dense layer, which was almost twice as large as that for the un-modified membrane. The membrane with a thin dense separation layer and modified surfaces shows much increased oxygen permeation flux, promising for practical applications.

•Supported planar Zr0.84Y0.16O1.92–La0.8Sr0.2Cr0.5Fe0.5O3 − δ membrane has been prepared.•The membrane exhibits much increased oxygen permeability, promising for chemical reactor applications.•The phase inversion tape casting method can be generalized for preparation of other ceramic membranes.The Zr0.84Y0.16O1.92 (YSZ)–La0.8Sr0.2Cr0.5Fe0.5O3 − δ (LSCrF) composite membrane was prepared using the phase inversion tape casting method. Two slurries, one composed of YSZ and LSCrF powder, and the other composed also graphite, were used for preparation of the membrane. They were co-tape cast onto a Mylar sheet, and then immersed in a water bath for solidification into a green tape through phase inversion mechanism. After sintering at 1450 °C in the air, the green tape was converted into a ceramic membrane. The sintered membrane possessed an asymmetric structure: a dense layer of thickness ~ 30 μm and a finger-like porous support of thickness ~ 1 mm. The membrane was further modified by applying a porous YSZ–LSCrF layer on its surfaces at the dense layer side and depositing Sm0.2Ce0.8O2 nano-particles on the inner surfaces of the support. The oxygen permeability of the as-prepared membrane was measured by exposing its dense layer side to air and the support side to CO at elevated temperatures. The membrane exhibited desired oxygen permeability under the given measurement conditions. An oxygen permeation flux as large as 2.4 ml·cm− 2·min− 1 (STP) was observed at 900 °C, which is comparable to the hollow fiber membrane of the same composition. Owing to its desired oxygen permeability and good stability, the supported planar YSZ–LSCrF membrane developed in the present study holds promise for applications in chemical reactors integrating oxygen separation and oxygen-consuming chemical reactions such as partial oxidation of methane (POM). The phase inversion tape casting method explored in the present study can be applied to the preparation of other ceramic membranes.

Most of the alkaline earth-containing perovskite-based oxygen-transporting membranes (OTMs) have insufficient tolerance toward CO2 that potentially limits their commercial applications, for example, oxy-fuel combustion processes with CO2 capture. One concern regarding the chemical potential of oxygen that may influence the CO2 tolerance of perovskites, however, is lacking effective investigations. In the present work, we demonstrate that the approach to increase the chemical potential of oxygen at the feed side contributes to stabilize the oxygen permeation fluxes of the fluorite–perovskite dual-phase OTM under CO2-rich atmosphere, and we further verify that oxygen can effectively act as a “buffer” to prevent the carbonate formation. Remarkably, we achieve high and stable oxygen permeation fluxes over 0.84 mL cm–2 min–1 during long-term operation at 900 °C with a 0.5 mm thickness 80 wt % Ce0.8Gd0.15Cu0.05O2−δ-20 wt % SrFeO3−δ (CGCO-SFO, nominal composition) dual-phase membrane using oxygen-enriched air as the feed gas and pure CO2 as the sweep gas.

A planar alumina membrane was prepared by a one-step phase-inversion tape casting method. The membrane consisted of a thick support layer with finger-like large pores and a thin separation layer containing small pores with an average diameter of ∼0.76 μm. The overall porosity of the membrane was ∼59%, as determined with the Archimedes method, and the porosity associated with the large, finger-like pores in the support layer was ∼34% as derived from image analysis. The surface of this alumina membrane was converted from hydrophilic to hydrophobic via grafting with a fluoroalkylsilane. The water desalination performance was tested by exposing the hydrophobic separation layer to an aqueous solution of 2 wt.% NaCl at 80 °C, while a sweep of distilled water at 20 °C was used, resulting in a water flux of 19.1 L m−2 h−1 and a salt rejection over 99.5%. Due to the excellent water desalination performance, the hydrophobic porous ceramic membrane holds promise for practical applications.

Brittleness is the main obstacle for commercial implementation of ceramic hollow fiber membranes. Here we report the reinforcement of porous alumina hollow fiber membranes by using commercial SiC nanofibers. The SiC reinforced alumina hollow fiber membranes were produced by the polymer-assisted phase inversion method and subsequent removal of the polymer and sintering at high temperatures. The effects of the amounts of SiC nanofibers (2.5–10.0 wt%) on the mechanical strength, microstructure and water flux of the hollow fiber membranes were investigated. The results showed that without addition of SiC nanofibers, the maximum bending strength was about 154 MPa for the porous alumina hollow fiber sintered at 1510 °C. However, the maximum bending strength of the reinforced membrane reached 218 MPa, in which 5 wt% SiC was incorporated and sintered at 1450 °C; in other words, a 40% improvement in bending strength was achieved. After being sintered at 1450 °C, the 5% SiC reinforced membrane exhibits a porosity of 41.7% and a peak pore size of 1.35 μm whereas the pure alumina membrane has a porosity of 37.5% and a peak pore size of 1.25 μm; the former shows a water permeability of 7.99 L m−2 h−1 kPa−1, which is 3.3 times higher than that of the latter. Therefore, the ceramic nanofiber reinforcement is promising for the development of high-performance ceramic hollow fiber membranes for practical applications.

Ce0.8Sm0.2O1.9–La0.8Sr0.2Cr0.5Fe0.5O3−δ (SDC-LSCrF) composite hollow fiber membranes were prepared by phase inversion followed by sintering. Average oxygen fluxes of 0.5 cm3·cm–2·min–1(STP) were measured, at 950 °C, by feeding either He or CO2 (30 mL·min–1) into the lumen of the hollow fiber (with length 48 mm), while exposing the shell side to ambient air. The oxygen flux at given conditions increases to 4.8 cm3·cm–2·min–1 (STP) when the reactive sweep gas CO is employed. The profound lowering of the activation energy for the oxygen flux relative to that observed upon using He and CO2 as sweep gas suggests that rate limitations by the surface exchange reaction occur when using the latter sweep gases. The developed hollow fiber membranes show excellent stability over the 750 h duration of the tests and therefore hold promise for application in oxyfuel combustion processes and membrane reactors.

Zr0.84Y0.16O1.92–La0.8Sr0.2Cr0.5Fe0.5O3−δ (YSZ-LSCrF) dual-phase composite hollow fiber membranes were prepared by a combined phase-inversion and sintering method. The shell surface of the hollow fiber membrane was modified with Ce0.8Sm0.2O1.9 (SDC) via a drop–coating method. As the rate of oxygen permeation of the unmodified membrane is partly controlled by the surface exchange kinetics, coating of a porous layer of SDC on the shell side (oxygen reduction side) of the hollow fiber membrane was found to improve its oxygen permeability. Rate enhancements up to 113 and 48% were observed, yielding a maximum oxygen flux of 0.32 and 4.53 mL min–1 cm–2 under air/helium and air/CO gradients at 950 °C, respectively. Excess coating of SDC was found to induce significant gas phase transport limitations and hence lower the rate of oxygen permeation. A model was proposed to calculate the length of triple phase boundaries (TPBs) for the coated dual-phase composite membrane and to explain the effect of coating on the oxygen permeability.Keywords: dual-phase composite; hollow fiber; oxygen separation membrane; samaria-doped ceria; surface modification; triple-phase boundary;

A variant of tape casting based on the phase inversion phenomenon was adopted for fabrication of porous ceramic wafer. A slurry was prepared by dispersing alumina powder in an N-methyl-2-pyrrolidone (NMP) solution of the polymers polyethersulfone (PES) and polyvinylpyrrolidone (PVP). The slurry was cast using a doctor blade, and immersed in water to solidify the polymer solution via phase inversion. The green tape was dried and sintered at 1500 °C. The as-prepared ceramic wafer was characterized using synchrotron-radiation computed tomography (SR-CT). It was revealed that the ceramic wafer contained typical finger-like macrovoids, and the porosity resulting from these macrovoids was ~30%. The overall porosity of the wafer was 59%, as derived from the density data measured by Archimedes method in mercury. It is concluded that the phase inversion tape casting is a simple and effective method for preparation of porous ceramics.

This paper reports the development of hydrophobic porous alumina ceramic hollow fiber membranes for water desalination based on the membrane distillation process. The alumina hollow fiber with an average pore size of 0.7 μm was prepared by the phase inversion and sintering method. The surface of the hollow fiber was converted from hydrophilic to hydrophobic via grafting with fluoroalkylsilane (FAS). The water desalination performance of the as-prepared hydrophobic hollow fiber was tested using the vacuum membrane distillation method. By exposing the shell side of the fiber to an aqueous solution of 4 wt% NaCl at 80 °C and vacuuming the lumen side of the fiber to a pressure of 0.04 bar, a water flux of 42.9 L m−2 h−1 was attained with a salt rejection over 99.5%, which is comparable with the best performance of polymer membrane. The water flux and salt rejection was found to decrease slowly with time, but after water washing–drying the rejection was recovered completely, and the water flux largely. The hydrophobic ceramic hollow fiber membrane developed in this work is promising for practical applications.Highlights► Hydrophobic porous alumina hollow fiber has been prepared. ► The hollow fiber can separate pure water from NaCl solution at a fast rate. ► The hollow fiber holds promise for membrane distillation desalination applications.

A membrane reactor has been investigated to reform methane into fuel suitable for solid oxide fuel cells (SOFCs). An oxygen-permeable Zr.84Y0.16O1.92 (YSZ)–La0.8Sr0.2Cr0.5Fe0.5O3−δ (LSCF) hollow fiber membrane coated with Ru catalyst at the lumen side is used to construct the reactor. The reactor is tested at elevated temperatures with the shell and lumen sides of the hollow fiber exposed to the atmosphere air and methane, respectively. The reaction of methane with the permeated oxygen proceeds at a remarkably fast rate. Methane throughput conversion over 90% is attained at 950 °C at a high methane feed rate of 14.7 cm3 CH4 min−1 cm−2 membrane surface and oxygen permeation rate 7.9 cm3 min−1 cm−2; the effluent from the reactor is composed mainly of H2 (53.5%) and CO (35.7%), revealing that the dominating reaction occurring in the reactor is partial oxidation of the methane (POM). When the effluent is fed into a disk-shaped SOFC single cell, it exhibits stable performance. The mild exothermal nature of POM reaction and the high surface to volume ratio of hollow fiber membrane may allow us to construct and operate a compact autothermal methane reformer for SOFC applications.Highlights► A hollow fiber membrane reactor can convert methane into H2 and CO efficiently. ► SOFC can run on the fuel converted from methane by the membrane reactor. ► The membrane reactor is promising for methane fuel processing application in SOFCs.

Perovskite-type Sr(Co0.8Fe0.2)0.8Ti0.2O3−δ (SCFT20) hollow fiber membrane was prepared using the phase inversion spinning/sintering method. The hollow fiber became permeable to oxygen at elevated temperatures. At 950 °C, an oxygen permeation flux of 1.4 × 10−6 mol cm−2 s−1 was observed with a hollow fiber membrane of length 20.00 mm, outer diameter 2 mm, wall thickness 0.3 mm by exposing its shell side to the ambient air and sweeping its core side with high purity helium at a rate of 30 cm3 min−1. The hollow fiber exhibited lower, yet reasonably stable oxygen permeation flux when its core side was swept with CO2. The oxygen permeation of the membrane could be recovered to a large extent by temporarily switching off the CO2 sweep gas. The lower oxygen permeation flux under air/CO2 gradient compared with the air/He gradient was attributed to the partial decomposition of SCFT20 caused by the reaction with CO2.Research highlights▶ The SCFT20 membrane is fabricated into hollow fiber geometry. ▶ The hollow fiber allows oxygen to permeate at faster rate than the disk-shaped membrane. ▶ The oxygen permeation performance of the hollow fiber degrades gradually when its core side is swept with 100% of CO2, which however can be recovered to a large extent by temporarily switching off the CO2 sweep gas.

The effect of Zr doping in SrCo0.8Fe0.2O3 − δ (SCF) membranes was investigated. The lattice parameter of SCF increased with the Zr content until 4 at.%, and then leveled off with further increase in the Zr content, revealing that the Zr solubility limit lies at ∼ 4%. The Zr doping resulted in an increase in oxygen stoichiometry (3 − δ) of SCF membranes especially at low oxygen partial pressure. The brownmillerite to perovskite phase transition was investigated by dilatometry in nitrogen (pO2 = 2 × 10− 3 atm). The phase transition temperature was lowered by Zr doping: 770 °C for undoped SCF and 710 °C for SCF doped with 4 at.% of Zr. The change in volume associated to the phase transition also became less pronounced for the Zr-doped samples. Compared to the undoped membrane, the Zr-doped SCF exhibited a somewhat lower oxygen permeability, but it remained well-permeable to oxygen at lower operation temperatures due to the stabilization of the perovskite structure.

The oxygen transport in the nickel-zirconia composite was investigated using the oxygen permeation method. A disk-shaped sample made of nickel (40 vol%) and yttria-stabilized zirconia (YSZ) was used to construct a permeation cell. By exposing one side of the sample to a CO2 gas stream and the other side to a CO stream at elevated temperatures, oxide ions were extracted from CO2 and transported to the other side to oxidize CO. The oxygen permeation flux through the composite was determined by analyzing the effluent from the permeation cell, and the oxygen ionic conductivity of the composite was derived from the permeation data and the oxygen partial pressures. It was shown that the oxygen ionic conductivity of the composite YSZ fraction was about one third of that for the single-phase zirconia ceramic, and the activation energy associated with the transport of oxide ions in the composite is somewhat greater than that of the single-phase zirconia.

Burning fossil fuels with O2/CO2 mixture produces a concentrated CO2 stream and thus enables efficient CO2 capture. In an attempt to improve the economic competiveness of this oxy-fuel combustion technology, intensive efforts have been made to develop ceramic oxygen separation membranes that have a potential to reduce the oxygen production costs over the present cryogenic air separation process. In this paper it is proposed that the O2/CO2 mixture could be supplied by using CO2 as sweeping gas to remove the oxygen separated from air by an oxygen selective membrane. State-of-the-art membranes with the perovskite structure, such as SrCo0.8Fe0.2O3−δ (SCF), suffer degradation upon exposure to the acidic gas CO2. This paper reports that the stability of SCF in CO2 can be improved remarkably by reducing its surface basicity through the introduction of Ti ions, while the oxygen permeability is largely retained. The membrane-based O2/CO2 production concept is also verified with a CO2-tolerant membrane tube.

The dense ceramic oxygen separation membrane holds promise to reduce the oxygen production cost significantly over the current mature cryogenic distillation process. Preparation of membranes in hollow fiber geometry is expected to lead to a remarkable increase in the oxygen production capacity of the membrane unit. Gas-tight Ce0.8Sm0.2O2−δ−La0.8Sr0.2MnO3−δ dual-phase composite hollow fibers were prepared by a phase-inversion/sintering technique. A stable oxygen permeation rate of 3.2 × 10−7 mol·cm−2·s−1 was measured under air/He gradient at 950 °C, and 3.0 × 10−7 mol·cm−2·s−1 was found under air/CO2 gradient. It was also found that oxygen permeation through the hollow fiber can be well-described by the Wagner equation and assuming that the gas flow in the core of the fiber conforms to the plug flow model.

Effect of thermal history and chemical composition on aging of NixMn3 − xO4 + δ (0.56 ≤ x ≤ 1.0) ceramics was investigated. It was found that all the NixMn3 − xO4 + δ ceramic samples metallized by co-firing at 1050°C showed significant electrical stability with an aging coefficient less than 1.0%, while aging of those metallized by annealing at 850°C was increasingly serious with a rise in Ni content x, the aging coefficient ranging from 0.2% to 3.8%. However, the ceramic samples with Ni content x ≤ 0.70, whether metallized by co-firing or by annealing, exhibited extraordinarily high electrical stability with an aging coefficient less than 0.5%. The composition dependence of aging of the ceramic samples was explained qualitatively, based on the electrical conduction mechanism of small polaron hopping and on the aging mechanism of the cationic vacancy-assisted migration of cations to their thermodynamically preferable sites under thermal stress.

In this paper, the dense FexCu0.10Ni0.66Mn2.24−xO4 (0 ≤ x ≤ 0.90) ceramics with accurate stoichiometry are prepared by the route of solid-state coordination reaction. The effect of Fe addition on the electrical properties of the ceramics has been investigated by powder X-ray diffraction (XRD), electrical measurement and thermogravimetric analysis. With Fe content x increasing from 0 to 0.45, the resistivity remains almost unchanged, whereas the thermal constant B decreases drastically. With a further increase in x from 0.45 to 0.90, both the resistivity and the thermal constant B increase. With a rise in x from 0 to 0.9, the aging coefficient drops from 19.9 to 0.6%. The remarkable improvement of the electrical stability can be attributed to the mechanism that substitution of Fe3+ for Mn2+ and Mn3+ restrains the formation of cation vacancies in spinel lattice, thus the modification of cation distribution and the consequent aging under thermal stress is greatly alleviated.

A method based on the X-ray diffraction intensity ratio was developed to determine the maximum deficiency that the perovskite-structured La1−xMnO3±δ can accommodate at the A-site. Computer simulation predicts that the intensity ratio of (024) and (012) reflections for La1−xMnO3±δ in hexagonal setting increases with increasing the La deficiency x. XRD analysis shows that with increasing x until 0.09, the ratio increases as predicted, then levels off with further increase in x. An abrupt change in electrical conductivity is also observed at x of ∼0.10. It is concluded that the maximum deficiency lies in between 0.09 and 0.10 for La1−xMnO3±δ. The methodology presented in this paper in principle can be applied to other perovskite-structured materials.The X-ray diffraction intensity ratio of (024) and (012) reflections of La1−xMnO3±δI0 2 4/I0 1 2 increases with x until x=0.09 as predicted by the computer simulation, and at x>0.09 the intensity ratio levels off, showing that the maximum lanthanum deficiency is around 0.09.

The composites made of spinel-structured (Ni,Mn)3O4 and perovskite-structured La(Mn,Ni)O3 were investigated for potential application as negative temperature coefficient (NTC) thermistor. The composites were prepared using the standard ceramic route. The electrical resistivity of the composite at 25°C was found to decrease by one to two orders of magnitude depending the amount of the low-resistivity perovskite phase, while the thermal constant determining the temperature sensitivity of the NTC thermistor was still reasonably large in the range of 4,000 to 3,000 K, and the resistivity drift after annealing at 150°C for 1,000 h in air was relatively small (∼1.2%). The general effective media model was adopted to fit the electrical resistivity data of the composites, giving a value of 0.37 for the percolation volume fraction of the perovskite phase. This work demonstrates that it is possible to tune the electrical resistivity and thermal constant of the spinel-structured oxide through making composite with low-resistivity perovskite-structured oxide.

A dense La0.7Sr0.3Ga0.3Fe0.7O3 − δ membrane tube was treated with hydrogen by exposing its tube side to a H2 stream and the shell side to the ambient air at 950 °C. A porous layer of thickness ~ 500 μm was formed on the membrane surface (tube side) after 16 h treatment. The oxygen permeation measurement was performed by sweeping the tube side of the membrane with helium to carry away the permeated oxygen. The H2-treated membrane exhibited a large increase in oxygen permeation flux (by a factor of 4.5 at 950 °C and 10.5 at 800 °C) and a significant reduction in the apparent activation energy, which is attributed to the increased porosity on the tube-side surface. It is suggested that the H2 treatment altered the rate-limiting step from the surface oxygen exchange to the transport of oxygen in the bulk of the membrane. The H2 treatment also led to an enhanced depletion of Ga from the membrane surface, which could affect the applicability of the membrane.

The stability and oxygen permeation behavior of the Ce0.8Sm0.2O2−δ–La0.8Sr0.2CrO3−δ dual-phase composite were investigated under a large oxygen gradient with one side of it exposed to air and the other side to CO, CH4 or H2 at elevated temperatures. An oxygen permeation flux of 8.6 × 10−7 mol cm−2 s−1 was obtained with a 1.1 mm thick membrane tube under air/CO gradient at 950 °C, and no decrease in the flux was observed within a period of 110 h. The oxygen flux under air/CO gradient was found to be about twice that under air/CH4 or air/H2 gradients, which may be attributed to the higher catalytic activity of the membrane towards the oxidation of CO. The membrane tube remained intact after high temperature operation for over 1000 h, and no significant change in the phase composition and microstructure occurred. The dual-phase composite may satisfy the stability requirement under the stringent membrane reactor conditions.

Perovskite phase dominant SrFeCo0.5Oy ceramic membranes were made from powders prepared by a glycine–nitrate combustion process (GNP). The sample sintered at 1150 °C consisted of perovskite and spinel phase. The grain size of the sintered sample increased remarkably with the calcination temperature of the starting powder. The phase composition of a coarse-grained sample remained almost unchanged after annealing at 900 °C in air, whereas, annealing of a fine-grained sample resulted in the formation of an intergrowth oxide as a dominant phase. In comparison with solid state reaction (SSR) and sol–gel derived membranes, the GNP-derived membrane exhibited greater oxygen permeability, which could be attributed to the oxygen-deficient perovskite phase that is highly permeable to oxygen.

Brittleness is the main obstacle for commercial implementation of ceramic hollow fiber membranes. Here we report the reinforcement of porous alumina hollow fiber membranes by using commercial SiC nanofibers. The SiC reinforced alumina hollow fiber membranes were produced by the polymer-assisted phase inversion method and subsequent removal of the polymer and sintering at high temperatures. The effects of the amounts of SiC nanofibers (2.5–10.0 wt%) on the mechanical strength, microstructure and water flux of the hollow fiber membranes were investigated. The results showed that without addition of SiC nanofibers, the maximum bending strength was about 154 MPa for the porous alumina hollow fiber sintered at 1510 °C. However, the maximum bending strength of the reinforced membrane reached 218 MPa, in which 5 wt% SiC was incorporated and sintered at 1450 °C; in other words, a 40% improvement in bending strength was achieved. After being sintered at 1450 °C, the 5% SiC reinforced membrane exhibits a porosity of 41.7% and a peak pore size of 1.35 μm whereas the pure alumina membrane has a porosity of 37.5% and a peak pore size of 1.25 μm; the former shows a water permeability of 7.99 L m−2 h−1 kPa−1, which is 3.3 times higher than that of the latter. Therefore, the ceramic nanofiber reinforcement is promising for the development of high-performance ceramic hollow fiber membranes for practical applications.

Porous nickel electrodes were fabricated by the phase inversion tape casting method. The as-prepared nickel electrode contained finger-like straight open pores with an average diameter of ∼100 μm and smaller pores with an average diameter of 1–3 μm in the walls. When used as an anode for the oxygen evolution reaction (OER), the porous nickel electrode shows high catalytic activity, reaching a catalytic current density of 10 mA cm−2 under an overpotential of only 300 mV in 1.0 M KOH. It also exhibited excellent performance for the hydrogen evolution reaction (HER), resulting in a current density of 10 mA cm−2 under an overpotential of 125 mV in the same electrolyte. For both OER and HER, the electrode shows great catalytic stability and much better catalytic performance than commercial nickel foam. Moreover, an alkaline electrolyzer using identical porous nickel electrodes as both the anode and cathode required a cell voltage of only 1.65 V to reach 10 mA cm−2 for overall water splitting. The improved electrocatalytic performance of the electrode can be attributed to its unique dual-pore structure.