Permeability measurements
In typical permeability experiments, a disk sample is sealed gas tight over a support tube. A gas or gas mixture is supplied to one side, and one or more species permeate to the other side, where a sweep gas and/or pump collect the gas. The modes of operation are numerous, and so are the ways to analyze the permeation, including gas chromatography (GC) and mass spectroscopy (MS). Typically, an inert gas added to the entry side gas mixture is used for monitoring the presence or absence of background leakage through seal leaks or sample cracks and porosity.
In general, a large sample area or tubular sample is preferable, as it reduces the relative effects of leakage from seal ring and general equipment. It also simplifies the considerations of sample geometry for samples where the thickness is not much smaller than the diameter so that permeation from the side is significant. However, a large sample may put higher requirements to the mechanical assembly and seal.
These articles refer to ProboStat or other NORECS products, filtered with keywords: 'permeability, permibility, ProGasMix'
ID=614
Modification of Ruddlesden-Popper-type Nd2-xNi0.75Cu0.2M0.05O4±δ by the Nd-site cationic deficiency and doping with Sc, Ga or In: Crystal structure, oxygen content, transport properties and oxygen permeability
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Journal of Solid State Chemistry
Volume: 296,
Pages: 121982 Time of Publication: 2021 |
| Abstract | Nd2-xNi0.75Cu0.2M0.05O4±δ (x ​= ​0 and 0.1; M ​= ​Sc, Ga, and In) Ruddlesden-Popper-type oxides are obtained by a sol-gel route and characterized concerning phase composition and crystal structure. It is found that the largest In3+ cannot be effectively introduced into the structure, while Nd stoichiometric and cation-deficient Nd2-xNi0.75Cu0.2Sc0.05O4±δ and Nd2-xNi0.75Cu0.2Ga0.05O4±δ (x ​= ​0; 0.1) can be obtained as single-phase materials. Systematic characterization of the crystal structure at high temperatures, oxygen content, as well as transport properties reveals that while the Nd-site deficiency has rather negligible influence on the structure, it causes a substantial decrease of the oxygen content, which at high temperatures leads to a change of the dominant type of defects from the oxygen interstitials to the vacancies for Nd1.9Ni0.75Cu0.2Sc0.05O4±δ and Nd1.9Ni0.75Cu0.2Ga0.05O4±δ. The Nd-site deficiency also causes a decrease of the total conductivity. Importantly, all the examined materials exhibit full chemical stability in CO2 atmosphere, which together with moderate thermal expansion makes them good candidates for the oxygen transport membranes, which can be used e.g. in the air separation technologies. The selected Sc- and Ga-doped compounds evaluated as ceramic membranes show relatively high oxygen fluxes, with the highest value of 0.78 ​mL ​cm-2 min-1 at ca. 880 ​°C registered for 0.9 ​mm thick, dense Nd1.9Ni0.75Cu0.2Ga0.05O4±δ membrane. |
| Keywords | Ruddlesden-Popper oxides; Nonstoichiometric compounds; Crystal structure; Transport properties; Oxygen permeation membranes |
| Remark | Link |
ID=566
Ruddlesden-Popper-type Nd2-xNi1-yCuyO4±δ layered oxides as candidate materials for MIEC-type ceramic membranes
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Journal of the European Ceramic Society
Volume: 40,
Issue: 12,
Pages: 4056-4066 Time of Publication: 2020 |
| Abstract | Series of Nd2-xNi1-yCuyO4±δ Ruddlesden-Popper-type oxides is obtained by auto-combustion synthesis method and systematically characterized concerning phase composition, formation of solid state solution, crystal structure, oxygen content, as well as regarding transport properties and oxygen permeability when applied as mixed conducting ceramic membranes. The A-site deficiency x is discussed in terms of structural stability and its effect on the oxygen content, with ongoing modification of total electrical conductivity observed. In selected Nd2-xNi0.75Cu0.25O4±δ oxides the dominating oxygen defects at high temperatures can be changed from oxygen interstitials to vacancies by the induced A-site deficiency, which affects bulk- and surface-related transport coefficients, as it is observed in electrical conductivity relaxation studies. The optimized Nd1.9Ni0.75Cu0.25O4±δ sinters having increased ionic conductivity, as well as fine, well-sintered microstructure allow to achieve one of the higher reported oxygen fluxes for CO2-stable Ruddlesden-Popper-based ceramic membranes (e.g. 0.49 mL cm−2 min−1 at ca. 880 °C for 1.05 mm thickness). |
| Keywords | Ruddlesden-Popper oxides, Nonstoichiometric compounds, Crystal structure, Transport properties, Oxygen permeation membranes |
| Remark |
https://doi.org/10.1016/j.jeurceramsoc.2020.04.054 Link |
ID=551
A CO2-Tolerant Perovskite Oxide with High Oxide Ion and Electronic Conductivity
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Adv. Mater.
Time of Publication: 2019
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| Abstract | Mixed ionic–electronic conductors (MIECs) that display high oxide ion con-ductivity (σo) and electronic conductivity (σe) constitute an important family of electrocatalysts for a variety of applications including fuel cells and oxygen sepa-ration membranes. Often MIECs exhibit sufficient σe but inadequate σo. It has been a long-standing challenge to develop MIECs with both high σo and stability under device operation conditions. For example, the well-known perovskite oxide Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) exhibits exceptional σo and electrocatalytic activity. The reactivity of BSCF with CO2, however, limits its use in practical applications. Here, the perovskite oxide Bi0.15Sr0.85Co0.8Fe0.2O3−δ (BiSCF) is shown to exhibit not only exceptional bulk transport properties, with a σo among the highest for known MIECs, but also high CO2 tolerance. When used as an oxygen separation membrane, BiSCF displays high oxygen permeability comparable to that of BSCF and much higher stability under CO2. The combination of high oxide transport properties and CO2 tolerance in a single-phase MIEC gives BiSCF a significant advantage over existing MIECs for practical applications. |
| Remark |
DOI: 10.1002/adma.201905200 Link |
ID=542
Factors Limiting the Apparent Hydrogen Flux in Asymmetric Tubular Cercer Membranes Based on La27W3.5Mo1.5O55.5 and La0.87Sr0.13CrO3
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Membranes
Volume: 9
Time of Publication: 2019
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| Abstract | Asymmetric tubular ceramic–ceramic (cercer) membranes based on La27W3.5Mo1.5O55.5-La0.87Sr0.13CrO3 were fabricated by a two-step firing method making use of water-based extrusion and dip-coating. The performance of the membranes was characterized by measuring the hydrogen permeation flux and water splitting with dry and wet sweep gases, respectively. To explore the limiting factors for hydrogen and oxygen transport in the asymmetric membrane architecture, the effect of different gas flows and switching the feed and sweep sides of the membrane on the apparent hydrogen permeability was investigated. A dusty gas model was used to simulate the gas gradient inside the porous support, which was combined with Wagner diffusion calculations of the dense membrane layer to assess the overall transport across the asymmetric membrane. In addition, the stability of the membrane was investigated by means of flux measurements over a period of 400 h. |
| Keywords | hydrogen permeation; water splitting; surface kinetics; asymmetric tubular membrane; lanthanum tungstate; lanthanum chromite |
| Remark |
doi:10.3390/membranes9100126 Link |
ID=540
Ceria-Based Dual-Phase Membranes for High-Temperature Carbon Dioxide Separation: Effect of Iron Doping and Pore Generation with MgO Template
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Membranes
Volume: 9,
Issue: 9,
Pages: 108 Time of Publication: 2019 |
| Abstract | Dual-phase membranes for high-temperature carbon dioxide separation have emerged as promising technology to mitigate anthropogenic greenhouse gases emissions, especially as a pre- and post-combustion separation technique in coal burning power plants. To implement these membranes industrially, the carbon dioxide permeability must be improved. In this study, Ce0.8Sm0.2O2−δ (SDC) and Ce0.8Sm0.19Fe0.01O2−δ (FSDC) ceramic powders were used to form the skeleton in dual-phase membranes. The use of MgO as an environmentally friendly pore generator allows control over the membrane porosity and microstructure in order to compare the effect of the membrane’s ceramic phase. The ceramic powders and the resulting membranes were characterized using ICP-OES, HSM, gravimetric analysis, SEM/EDX, and XRD, and the carbon dioxide flux density was quantified using a high-temperature membrane permeation setup. The carbon dioxide permeability slightly increases with the addition of iron in the FSDC membranes compared to the SDC membranes mainly due to the reported scavenging effect of iron with the siliceous impurities, with an additional potential contribution of an increased crystallite size due to viscous flow sintering. The increased permeability of the FSDC system and the proper microstructure control by MgO can be further extended to optimize carbon dioxide permeability in this membrane system. |
| Keywords | samarium doped ceria; SDC; FSDC; CO2 separation membranes; scavenging effect of iron; permeability |
| Remark |
https://doi.org/10.3390/membranes9090108 Link |
ID=527
Long-term stability of iron-doped calcium titanate CaTi0.9Fe0.1O3−δ oxygen transport membranes under non-reactive and reactive atmospheres
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Journal of Membrane Science
Volume: 583,
Pages: 171-179 Time of Publication: 2019 |
| Abstract | Oxygen transport membranes (OTM) are widely considered as a possible solution to limit the carbon footprint, but are notoriously afflicted by performance issues due to chemical instability observed during long-term operation. This paper reports on the stability of an OTM made of CaTi0.9Fe0.1O3−δ (CTF), and addresses its applicability. The redox stability of CTF was investigated using thermal gravimetry up to 1000 °C under air and H2, coupled with XRD and Mössbauer analyses. The redox potential of iron was measured using an electrochemical potential relaxation as a function of temperature. The baseline oxygen semi-permeability flux of dense CTF membranes was measured in inert atmospheres (air/argon or air/helium), and the long-term stability established for up to 1600 h under simulated operation atmospheres containing CO, CO2, H2 and CH4. CTF shows a remarkable performance stability and post mortem XRD, SEM-EDS and Raman analyses show no evidence of decomposition or reaction byproducts. |
| Remark |
https://doi.org/10.1016/j.memsci.2019.04.049 Link |
ID=452
Enhanced O2 Flux of CaTi0.85Fe0.15O3−δ Based Membranes by Mn Doping
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Journal of the American Ceramic Society
Volume: 99,
Issue: 3,
Pages: 1071–1078 Time of Publication: 2016 |
| Abstract | Dense symmetric membranes of CaTi0.85−xFe0.15MnxO3−δ (x = 0.1, 0.15, 0.25, 0.4) are investigated in order to determine the optimal Mn dopant content with respect to highest O2 flux. O2 permeation measurements are performed as function of temperature between 700°C–1000°C and as function of the feed side math formula ranging between 0.01 and 1 bar. X-ray photoelectron spectroscopy is utilized to elucidate the charge state of Mn, and synchrotron radiation X-ray powder diffraction (SR-XPD) is employed to investigate the structure symmetry and cell volume of the perovskite phase at temperatures up to 800°C. The highest O2 permeability is found for x = 0.25 over the whole temperature and math formula ranges, followed by x = 0.4 above 850°C. The O2 permeability for x = 0.25 reaches 0.01 mL(STP) min−1 cm−1 at 925°C with 0.21 bar feed side math formula and Ar sweep gas. X-ray photoelectron spectroscopy indicates that the charge state of Mn changes from approx. +3 to +4 when x > 0.1, which implies that Mn mainly improves electronic conductivity for x > 0.1. The cell volume is found to decrease linearly with Mn content, which coincides with an increase in the activation energy of O2 permeability. These results are consistent with the interpretation of the temperature and math formula dependency of O2 permeation. The sintering behavior and thermal expansion properties are investigated by dilatometry, which show improved sinterability with increasing Mn content and that the thermal expansion coefficient decreases from 12.4 to 11.9 × 10−6 K−1 for x = 0 and x = 0.25, respectively. |
ID=381
Stability of NASICON materials against water and CO2 uptake
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Solid State Ionics
Time of Publication: 2016
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| Abstract | The stability in ambient conditions of a scandium-based NASICON material, Na3.4Sc2Si0.4P2.6O12, was investigated using impedance spectroscopy, thermogravimetry/differential scanning calorimetry (TG/DSC) and multinuclear magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). The presence of H2O and CO2 in samples stored in ambient air could be evidenced as well as its impact on the ionic conductivity of the samples. The detected amounts of water and CO2 in the samples had no influence on the measured conductivities at room temperature, which confirmed the absence of protonic conduction in hydrated samples. A loss of conductivity during heating of hydrated samples was due to a loss of contact between the ceramic and the electrode used for the conductivity measurement. The recommendation for handling of NASICON-type materials is therefore: samples require storage in an Ar-filled glove box or in a dry environment to avoid artefacts during high temperature measurements. Nevertheless, the stability of the NASICON-type materials is confirmed since their conductivity is not affected by the moisture. |
| Keywords | Ionic conductivity; NASICON; Sodium; Scandium; ProGasMix |
| Remark |
http://dx.doi.org/10.1016/j.ssi.2016.11.006 Link |
ID=339
Chemical stability and H2 flux degradation of cercer membranes based on lanthanum tungstate and lanthanum chromite
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Journal of Membrane Science
Volume: 503,
Pages: 42–47 Time of Publication: 2016 |
| Abstract | Ceramic–ceramic composite (cercer) membranes of (Mo-doped) lanthanum tungstate, La27(W,Mo)5O55.5−δ, and lanthanum chromite, La0.87Sr0.13CrO3−δ, have recently been shown to exhibit H2 permeabilities among state-of-the-art. The present work deals with the long-term stability of these cercer membranes in line with concern of flux degradation and phase instability observed in previous studies. The H2 permeability of disc shaped membranes with varying La/W ratio in the lanthanum tungstate phase (5.35≤La/W≤5.50) was measured at 900 and 1000 °C with a feed gas containing 49% H2 and 2.5% H2O for up to 1500 h. It was observed that the H2 permeability decreased by a factor of up to 5.3 over 1500 h at 1000 °C. Post-characterization of the membranes and similarly annealed samples was performed by SEM, STEM and XRD, and segregation of La2O3 was observed. The decrease in H2 permeability was ascribed to the compositional instability of the cation-disordered lanthanum tungstate under the measurement conditions. Equilibration of the La/W ratio by segregation of La2O3 leads to a lower ionic conductivity according to the materials inherent defect chemistry. Partial decomposition and reduction of the lanthanum tungstate phase, presumably to metallic tungsten, was also observed after exposure to nominally dry hydrogen. |
| Keywords | Hydrogen separation; Dense ceramic membrane; Ceramic–ceramic composite; Lanthanum tungstate; Lanthanum chromite |
| Remark |
doi:10.1016/j.memsci.2015.12.054 Link |
ID=332
Exceptional hydrogen permeation of all-ceramic composite robust membranes based on BaCe0.65Zr0.20Y0.15O3−δ and Y- or Gd-doped ceria
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| Source |
Energy Environ. Sci.
Volume: 8,
Pages: 3675-3686 Time of Publication: 2015 |
| Abstract | Mixed proton and electron conductor ceramic composites were examined as hydrogen separation membranes at moderate temperatures (higher than 500 °C). In particular, dense ceramic composites of BaCe0.65Zr0.20Y0.15O3−δ (BCZ20Y15) and Ce0.85M0.15O2−δ (M = Y and Gd, hereafter referred to as YDC15 and GDC15), as protonic and electronic conducting phases respectively, were successfully prepared and tested as hydrogen separation membranes. The mixture of these oxides improved both chemical and mechanical stability and increased the electronic conductivity in dual-phase ceramic membranes. The synthetic method and sintering conditions were optimized to obtain dense and crack free symmetric membranes. The addition of ZnO as a sintering aid allowed achieving robust and dense composites with homogeneous grain distribution. The chemical compatibility between the precursors and the influence of membrane composition on electrical properties and H2 permeability performances were thoroughly investigated. The highest permeation flux was attained for the 50 : 50 volume ratio BCZ20Y15–GDC15 membrane when the feed and the sweep sides of the membrane were hydrated, reaching values of 0.27 mL min−1 cm−2 at 755 °C on a 0.65 mm thick membrane sample, currently one of the highest H2 fluxes obtained for bulk mixed protonic–electronic membranes. Increasing the temperature to 1040 °C, increased the hydrogen flux up to 2.40 mL min−1 cm−2 when only the sweep side was hydrated. The H2 separation process is attributed to two cooperative mechanisms, i.e. proton transport through the membrane and H2 production via the water splitting reaction coupled with oxygen ion transport. Moreover, these composite systems demonstrated a very good chemical stability under a CO2-rich atmosphere such as catalytic reactors for hydrogen generation. |
| Remark |
DOI: 10.1039/C5EE01793A Link |
ID=329
Oxygen permeation and creep behavior of Ca1−xSrxTi0.6Fe0.15Mn0.25O3−δ (x=0, 0.5) membrane materials
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Journal of Membrane Science
Volume: 449,
Pages: 172–178 Time of Publication: 2016 |
| Abstract | Oxygen permeation measurements were performed on dense symmetric samples of Ca0.5Sr0.5Ti0.6Fe0.15Mn0.25O3−δ and compared to CaTi0.6Fe0.15Mn0.25O3−δ in order to assess the influence of the perovskite lattice volume on oxygen permeation. Oxygen flux measurements were performed in the temperature range 700–1000 °C and as function of feed side pO2pO2 from 10−2 to 1 bar, and at high pressures up to 4 bar with a pO2pO2 of 3.36 bar. The O2 permeability of the Sr-doped sample was significantly lower than that of the Sr-free sample, amounting to 3.9×10−3 mL min−1 cm−1 at 900 °C for a feed side pO2pO2 of 0.21 bar. The O2 permeability of CaTi0.6Fe0.15Mn0.25O3−δ shows little variation with increased feed side pressures and reaches 1.5×10−2 mL min−1 cm−1 at 900 °C for a feed side pO2pO2 of 3.36 bar. This is approximately 1.5 times higher than the O2 permeability with a feed side pO2pO2 of 0.21 bar. Furthermore, in order to assess the applicability of CaTi0.6Fe0.15Mn0.25O3−δ as an oxygen membrane material, creep tests were performed under compressive loads of 30 and 63 MPa, respectively, in air in the temperature range 700–1000 °C; the results indicate a high creep resistance for this class of materials. The measured O2 permeabilities and creep rates are compared with other state-of-the-art membrane materials and their performance for relevant applications is discussed in terms of chemical and mechanical stability. |
| Keywords | Dense ceramic oxygen membrane; Ambipolar transport; Creep; CaTiO3; Calcium titanate |
| Remark |
doi:10.1016/j.memsci.2015.10.016 Link |
ID=303
Doping strategies for increased oxygen permeability of CaTiO3 based membranes
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Journal of Membrane Science
Volume: 482,
Pages: 137–143 Time of Publication: 2015 |
| Abstract | Oxygen permeation measurements are performed on dense samples of CaTi0.85Fe0.15O3−δ, CaTi0.75Fe0.15Mg0.05O3−δ and CaTi0.75Fe0.15Mn0.10O3−δ in combination with density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) in order to assess Mg and Mn as dopants for improving the O2 permeability of CaTi1−xFexO3−δ based oxygen separation membranes. The oxygen permeation measurements were carried out at temperatures ranging between 700 and 1000 °C with feed side oxygen partial pressures between 0.01 and 1 bar. The O2 permeability was experimentally found to be highest for the Mn doped sample over the whole temperature range, reaching 4.2×10−3 ml min−1 cm−1 at 900 °C and 0.21 bar O2 in the feed which corresponds to a 40% increase over the Fe-doped sample and similar to reported values for x=0.2. While the O2 permeability of the Mg doped sample was also higher than the Fe-doped sample, it approached that of the Fe-doped sample above 900 °C. According to the DFT calculations, Mn introduces electronic states within the band gap and will predominately exist in the effectively negative charge state, as indicated by XPS measurements. Mn may therefore improve the ionic and electronic conductivity of CTF based membranes. The results are discussed in terms of the limiting species for ambipolar transport and O2 permeability, i.e., oxygen vacancies and electronic charge carriers. |
| Keywords | Dense ceramic oxygen membrane; Ambipolar transport; Mixed ionic-electronic conduction; CaTiO3; Calcium titanate |
| Remark |
doi:10.1016/j.memsci.2015.02.036 Link |
ID=295
Binder Jetting: A Novel Solid Oxide Fuel-Cell Fabrication Process and Evaluation
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JOM
Volume: 67,
Issue: 3,
Pages: 660-667 Time of Publication: 2015 |
| Abstract | With an ever-growing concern to find a more efficient and less polluting means of producing electricity, fuel cells have constantly been of great interest. Fuel cells electrochemically convert chemical energy directly into electricity and heat without resorting to combustion/mechanical cycling. This article studies the solid oxide fuel cell (SOFC), which is a high-temperature (100°C to 1000°C) ceramic cell made from all solid-state components and can operate under a wide range of fuel sources such as hydrogen, methanol, gasoline, diesel, and gasified coal. Traditionally, SOFCs are fabricated using processes such as tape casting, calendaring, extrusion, and warm pressing for substrate support, followed by screen printing, slurry coating, spray techniques, vapor deposition, and sputter techniques, which have limited control in substrate microstructure. In this article, the feasibility of engineering the porosity and configuration of an SOFC via an additive manufacturing (AM) method known as binder jet printing was explored. The anode, cathode and oxygen ion-conducting electrolyte layers were fabricated through AM sequentially as a complete fuel cell unit. The cell performance was measured in two modes: (I) as an electrolytic oxygen pump and (II) as a galvanic electricity generator using hydrogen gas as the fuel. An analysis on influence of porosity was performed through SEM studies and permeability testing. An additional study on fuel cell material composition was conducted to verify the effects of binder jetting through SEM–EDS. Electrical discharge of the AM fabricated SOFC and nonlinearity of permeability tests show that, with additional work, the porosity of the cell can be modified for optimal performance at operating flow and temperature conditions. |
| Remark |
DOI 10.1007/s11837-015-1296-9 Link |
ID=294
Hydrogen separation membranes based on dense ceramic composites in the La27W5O55.5–LaCrO3 system
| Authors |
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| Source |
Journal of Membrane Science
Volume: 479,
Pages: 39–45 Time of Publication: 2015 |
| Abstract | Some compositions of ceramic hydrogen permeable membranes are promising for integration in high temperature processes such as steam methane reforming due to their high chemical stability in large chemical gradients and CO2 containing atmospheres. In the present work, we investigate the hydrogen permeability of densely sintered ceramic composites (cercer) of two mixed ionic-electronic conductors: La27W3.5Mo1.5O55.5−δ (LWM) containing 30, 40 and 50 wt% La0.87Sr0.13CrO3−δ (LSC). Hydrogen permeation was characterized as a function of temperature, feed side hydrogen partial pressure (0.1–0.9 bar) with wet and dry sweep gas. In order to assess potentially limiting surface kinetics, measurements were also carried out after applying a catalytic Pt-coating to the feed and sweep side surfaces. The apparent hydrogen permeability, with contribution from both H2 permeation and water splitting on the sweep side, was highest for LWM70-LSC30 with both wet and dry sweep gas. The Pt-coating further enhances the apparent H2 permeability, particularly at lower temperatures. The apparent H2 permeability at 700 °C in wet 50% H2 was 1.1×10−3 mL min−1 cm−1 with wet sweep gas, which is higher than for the pure LWM material. The present work demonstrates that designing dual-phase ceramic composites of mixed ionic-electronic conductors is a promising strategy for enhancing the ambipolar conductivity and gas permeability of dense ceramic membranes. |
| Keywords | Hydrogen separation; Dense ceramic membrane; Ceramic–ceramic composite; Lanthanum tungstate; Lanthanum chromite |
| Remark |
doi:10.1016/j.memsci.2015.01.027 Link |
ID=291
Hydrogen permeation, water splitting and hydration kinetics in Nd5.4Mo0.3W0.7O12−δ
| Authors |
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| Source |
Journal of Membrane Science
Volume: 476,
Pages: 105–111 Time of Publication: 2015 |
| Abstract | To investigate transport properties of Mo-substituted Nd5.4Mo0.3W0.7O12−δ for hydrogen separation application, hydrogen fluxes of Nd5.4Mo0.3W0.7O12−δ have been measured in both dry and wet sweep gases. The fluxes in dry sweep gas show lower temperature dependence at high temperatures than at low temperatures. Comparing the hydrogen permeability among rare earth tungstates, it has been revealed that the larger the RE-site cation radius, the higher the hydrogen permeation. Water splitting effect for the wet sweep gas has been confirmed by mass spectrometry. Oxygen surface kinetics under oxidizing conditions has been studied by ToF-SIMS measurements, and is significantly faster under wet conditions than dry. Hydration kinetics has been studied by conductivity relaxation measurements under reducing conditions for the first time, showing a two-fold non-monotonic behavior. |
| Keywords | Hydrogen permeation; Hydration kinetics; Water splitting; Oxygen surface kinetics; Nd5.4Mo0.3W0.7O12−δ |
| Remark |
doi:10.1016/j.memsci.2014.11.013 Link |
ID=286
Functional properties of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ proton conductors where X is an alkaline earth cation
| Authors |
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| Source |
Journal of the European Ceramic Society
Time of Publication: 2014-12
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| Abstract | Lanthanum niobates with general formulas of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ (X = Mg, Ca, Sr or Ba) were synthesized via the conventional solid state reaction. Specimens with relative density above 96% were produced after sintering. Structural and phase composition studies revealed predominant monoclinic Fergusonite structure for the majority of samples. SEM and TEM studies elucidated the effect of the used dopant combinations on grain growth, micro-crack formation and secondary phase formation. Results from microstructural study were correlated to the grain interior and grain boundary conductivities for selected samples (La0.99Sr0.01Nb0.99Al0.01O4−δ and La0.99Sr0.01Nb0.99Ti0.01O4−δ). The majority of co-doped niobates exhibited appreciable protonic conductivity under humid atmospheres at intermediate temperatures. Sr- or Ca-doped compounds displayed the highest total conductivities with values for LSNA equal to 6 × 10−4 S/cm and 3 × 10−4 S/cm in wet air and in wet 4% H2–Ar (900 °C), respectively. Additionally, thermal expansion was studied to complete functional characterization of co-doped LaNbO4. |
| Keywords | Proton-conducting ceramic materials, Hydrogen transport ceramic membranes, Rare earth ortho-niobates, Acceptor-doped lanthanum niobates, ProGasMix |
| Remark | Link |
ID=278
Hydrogen permeability of SrCe0.7Zr0.25Ln0.05O3−δ membranes (Ln=Tm and Yb)
| Authors |
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| Source |
Journal of Membrane Science
Volume: 473,
Pages: 327–332 Time of Publication: 2015 |
| Abstract | Zr substituted acceptor doped SrCeO3 materials were synthesized by citric acid route and characterized by XRD and SEM. The hydrogen flux of the materials was measured as a function of temperature and hydrogen partial pressure on the feed side. The hydrogen permeability for SrCe0.7Zr0.25Tm0.05O3−δ and SrCe0.7Zr0.25Yb0.05O3−δ is similar under our measurement window and shows the same hydrogen partial pressure dependency. Under short circuit condition, the hydrogen permeability increased significantly by more than one order of magnitude indicating that the hydrogen transport is limited by electronic conduction under open circuit conditions. The observed data were discussed by applying defect chemistry and the conventional ambipolar transport theory. After the hydrogen permeation measurements, the indication of kinetic cation de-mixing was found by XRD analysis. |
| Keywords | Co-substitution of B site; Hydrogen flux; Permeability; Acceptor doping; SrCeO3 |
| Remark |
DOI: 10.1016/j.memsci.2014.09.027 Link |
ID=257
Hydrogen permeation characteristics of La27Mo1.5W3.5O55.5
| Authors |
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| Source |
Journal of Membrane Science
Volume: 461,
Pages: 81–88 Time of Publication: 2014 |
| Abstract | Hydrogen permeation in 30% Mo-substituted lanthanum tungsten oxide membranes, La27Mo1.5W3.5O55.5 (LWMo), has been measured as a function of temperature, hydrogen partial pressure gradient, and water vapor pressure in the sweep gas. Transport of hydrogen by means of ambipolar proton–electron conductivity and – with wet sweep gas – water splitting contributes to the measured hydrogen content in the permeate. At 700 °C under dry sweep conditions, the H2 permeability in LWMo was 6×10−46×10−4 mL min−1 cm-1, which is significantly higher than that for state-of-the-art SrCeO3-based membranes. Proton conductivity was identified as rate limiting for ambipolar bulk transport across the membrane. On these bases it is evident that Mo-substitution is a successful doping strategy to increase the n-type conductivity and H2 permeability compared to nominally unsubstituted lanthanum tungsten oxide. A steady-state model based on the Wagner transport theory with partial conductivities as input parameters predicted H2 permeabilities in good agreement with the measured data. LWMo is a highly competitive mixed proton–electron conducting oxide for hydrogen transport membrane applications provided that long term stability can be ensured. |
| Remark |
http://dx.doi.org/10.1016/j.memsci.2014.03.011 Link |
ID=249
Hydrogen permeation characteristics of La27Mo1.5W3.5O55.5
| Authors |
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| Source |
Journal of Membrane Science
Time of Publication: 2014
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| Abstract | Hydrogen permeation in 30 % Mo-substituted lanthanum tungsten oxide membranes, La27Mo1.5W3.5O55.5 (LWMo), has been measured as a function of temperature, hydrogen partial pressure gradient, and water vapour pressure in the sweep gas. Transport of hydrogen by means of ambipolar proton-electron conductivity and – with wet sweep gas – water splitting contribute to the measured hydrogen content in the permeate. At 700 °C under dry sweep conditions, the H2 permeability in LWMo was 6×10−46×10−4 mL min−1 cm-1, which is significantly higher than for state-of-the-art SrCeO3-based membranes. Proton conductivity was identified as rate limiting for ambipolar bulk transport across the membrane. On these bases it is evident that Mo-substitution is a successful doping strategy to increase the n-type conductivity and H2 permeability compared to nominally unsubstituted lanthanum tungsten oxide. A steady-state model based on Wagner transport theory with partial conductivities as input parameters predicted H2 permeabilities in good agreement with the measured data. LWMo is a highly competitive mixed proton-electron conducting oxide for hydrogen transport membrane applications provided that long term stability can be ensured. |
| Remark |
Available online 14 March 2014 Link |
ID=225
Synthesis and Investigation of Porous Ni–Al Substrates for SolidOxide Fuel Cells
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| Source |
Materials of power engineering and radiationresistant materials
Time of Publication: 2013-10
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| Abstract | Selfpropagating hightemperature synthesis (SHS) is applied for the production of porous supporting Ni–Al bases of solidoxide fuel cells. The effect of synthesis onditions and the composition of source powders on the phase composition, microstructure, gas permeability, corrosion resistance, and other proper ties of obtained Ni–Al samples is investigated. The possibility is shown for the formation of solidoxide fuel cells (SOFCs) on the surface of porous Ni–Al plates. The cells have the structure Ni–ZrO3:Y2O3 anode/ZrO3:Y2O3 electrolyte/La0.8Mn0.2SrO3 cathode and provide a specific power of 400 mW/cm2 at a temperature of 800°C. |
| Keywords | selfpropagating hightemperature synthesis, Ni–Al, solidoxide fuel cells, ZrO3:Y2O3 electrolyte, magnetron sputtering. |
| Remark | Link |
ID=214
Synthesis and Characterization of Nonsubstituted and Substituted Proton-Conducting La6–xWO12–y
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| Source |
Inorganic Chemistry
Publisher: ACS Publications,
Time of Publication: 2013
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| Abstract | Mixed proton–electron conductors (MPEC) can be used as gas separation membranes to extract hydrogen from a gas stream, for example, in a power plant. From the different MPEC, the ceramic material lanthanum tungstate presents an important mixed protonic–electronic conductivity. Lanthanum tungstate La6–xWO12–y (with y = 1.5x + δ and x = 0.5–0.8) compounds were prepared with La/W ratios between 4.8 and 6.0 and sintered at temperatures between 1300 and 1500 °C in order to study the dependence of the single-phase formation region on the La/W ratio and temperature. Furthermore, compounds substituted in the La or W position were prepared. Ce, Nd, Tb, and Y were used for partial substitution at the La site, while Ir, Re, and Mo were applied for W substitution. All substituents were applied in different concentrations. The electrical conductivity of nonsubstituted La6–xWO12–y and for all substituted La6–xWO12–y compounds was measured in the temperature range of 400–900 °C in wet (2.5% H2O) and dry mixtures of 4% H2 in Ar. The greatest improvement in the electrical characteristics was found in the case of 20 mol % substitution with both Re and Mo. After treatment in 100% H2 at 800 °C, the compounds remained unchanged as confirmed with XRD, Raman, and SEM. |
| Keywords | ProGasMix |
| Remark |
lanthanum tungstate La6–xWO12–y Link |
ID=123
An ion-plasma technique for formation of anode-supported thin electrolyte films for IT-SOFC applications
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| Source |
International Journal of Hydrogen Energy
Volume: 36,
Issue: 9,
Pages: 5550-5556 Time of Publication: 2011-05 |
| Abstract | This paper describes a preparation method and structural and electrochemical properties of a thin bilayer anode-electrolyte structure for a solid oxide fuel cell operating at intermediate temperatures (IT-SOFC). Thin anode-supported yttria-stabilized zirconia electrolyte films were prepared by reactive magnetron sputtering of a Zr–Y target in an Ar–O2 atmosphere. Porous anode surfaces of IT-SOFCs were modified by a pulsed low-energy high-current electron beam prior to film deposition; the influence of this pretreatment on the performance of both the deposited films and a single cell was investigated. The optimal conditions of the pulsed electron beam pretreatment were obtained. For the electrolyte thickness about 2.5 μm and the value of gas permeability of the anode/electrolyte structure 1.01 × 10−7 mol m−2 s−1 Pa−1, the maximum power density achieved for a single cell at 800 °C and 650 °C was found to be 620 and 220 mW cm−2 in air, respectively. |
| Keywords | Solid oxide fuel cell; YSZ electrolyte; Magnetron sputtering; Surface modification of material; Pulsed electron beam treatment; Electrical performance |
