Lanthanum Tungstate Research Articles

Spectroscopic analysis of La2(WO4)3:Tb3+ phosphor and the delayed concentration quenching of 5D4 →7FJ emission

Trivalent terbium ion doped lanthanum tungstate (La2-xTbx(WO4)3; x = 0.6,1.0,1.4) and terbium tungstate (Tb2(WO4)3) phosphors were successfully synthesized via optimized microwave-assisted co-precipitation technique. The phase purity and crystallinity of the prepared samples were confirmed using the powder XRD technique. The photoluminescence studies revealed a quenching-free emission up to 70 % of Tb3+ doping concentration, even though the emission intensity slightly decreases under host excitation since it becomes less relevant at higher doping concentrations. The experimental and calculated oscillator strengths were evaluated using absorption data and further used to quantify the Judd - Ofelt (JO) intensity parameters, which appeared in a trend of Ω2>Ω4>Ω6 for all samples. As a theoretical approach to assure the excellency of the tungstate host, the radiative parameters were calculated from the emission data using the JO analysis technique. The dominance in the values of stimulated emission cross section and gain bandwidth corresponding to 5D4→7F5 transition of Tb3+ ion of lanthanum tungstate proclaims it as an excellent green phosphor. Hence, the less susceptibility of the tungstate host towards concentration quenching is confirmed in the present work.

Negative effect of lanthanum tungstate on the mechanical properties of W-La2O3 alloys

With the rapid development of the photovoltaic industry, tungsten alloys have been selected to replace the high‑carbon steel to fabricate the busbars for diamond wire saws due to their superior mechanical properties, and the La2O3 doped tungsten alloy has been widely used. However, the yield of eligible W alloy wires is not very high due to serious wire breakage problems during the production process, especially in the solid-liquid mixing route. To discover the possible reason, the commonly produced lanthanum tungstate (La30W17O96) in the solid-liquid mixing route has been systematically studied in the work, and its possible influence on the mechanical properties is also explored. It is found that the La30W17O96 leads to the formation of brittle second phases at grain boundaries (GBs), which weakens the intergranular bonding, resulting in a significant decrease in the compressive strength of tungsten alloys, manifested as intergranular fracture. Transmission electron microscopy (TEM) analysis reveals that these second phases are consisted of polycrystalline La6W2O15, La2W3O12 and amorphous states, and the La30W17O96 can decompose into a more stable structure during sintering. This work highlights the destructive effect of La30W17O96 on the intrinsic properties of tungsten alloys and provides a new perspective for solving the problem of tungsten wire breakage.

Studies on the effect of Tb doping on the structural and optical properties of La2(WO4)3 nanoparticles

Pristine and terbium ion-doped lanthanum tungstate nanoparticles were synthesized by the chemical precipitation method. In the present work, the effect of Tb doping on the structural and optical properties of lanthanum tungstate nanoparticles is studied. The structure and surface morphology of the prepared samples were analysed using the X-ray diffraction technique and scanning electron microscopy technique. Both the samples exhibit monoclinic scheelite structure. The optical properties of the samples were studied using UV–Visible absorption spectroscopy and photoluminescence spectroscopy. By Tb ion doping, the optical bandgap value reduces and the colour of emission of the sample changes from blue to green region.

An effective strategy to boost hydrogen separation performance through stable mixed proton‐electron conducting membrane

AbstractHydrogen separation and purification are key to widespread application of hydrogen energy. Hydrogen permeable membranes based on lanthanum tungstate (LWO) attract attention due to favorable mechanical strength and chemical stability. However, industrial application of LWO‐based membranes has remained challenging because of modest hydrogen permeances. Here we report a novel graded porous supported symmetric (GPSS) LWO‐based membrane with improved transport properties, gas exchange dynamics, and operational stability, boosting stable hydrogen flux by several times over previously reported state‐of‐the‐art membranes.

Bilayer Cell Model and System Design of Highly Efficient Protonic Ceramic Fuel Cells

A highly efficient power generation system was designed by minimizing leakage current in protonic ceramic fuel cells (PCFCs) using bilayer electrolytes. The best electrolyte designs are achieved by optimizing the cell efficiency based on the transport properties of electrolyte materials assuming hydrogen as fuel. In parallel, the effect of the electrodes on the overall cell performance was also considered. Additionally, a PCFC system was modeled using the designed cells. Two PCFC systems were investigated. One based on hydrogen as a fuel, and another based on methane as fuel. It was found that a bilayer electrolyte consisting of BaZr0.8Y0.2O3−δ (BZY) with a thin layer of lanthanum tungstate (La28-xW4+xO54+3x/2v2-3x/2) is the most effective at reducing leakage current at 600°C. For this cell, a system efficiency of 69% (LHV, DC) and 65% (LHV, AC) were obtained under the cell voltage of 0.93 V, with a leakage current ratio of less than 1%, and fuel utilization of 95% when using hydrogen as fuel. On the other hand, when methane was used as fuel, the efficiency increased up to 78% (LHV, DC) and 74% (LHV, AC).

Dazzling green luminescent and biocompatible Tb3+ -activated lanthanum tungstate nanophosphors for group-III evaluation of latent fingerprints and anticancer applications

Dazzling green emission exhibiting Tb3+ ions doped lanthanum tungstate (LWO) nanophosphors were synthesized by a facile hydrothermally assisted solid-state reaction method. The nanophosphors were determined to have an orthorhombic structure using XRD analysis. In the optimized Tb3+: LWO nanophosphor, FE-SEM revealed aggregated non-uniform nanorods. TEM, FTIR, and XPS studies were performed to examine the material properties. A predominant excitation band was recorded at 488 nm (7F6→5D4) for the Tb3+ doped LWO nanophosphors, along with a moderately intense excitation band at 378 nm (7F6→5G6). Ravishing green emission at 544 nm (5D4→7F5) was obtained from Tb3+ ions containing LWO nanophosphors under excitation at 378 nm and 488 nm. We improved the green emission intensity by increasing the Tb3+ ion concentration up to 14 mol%, which was reduced after 14 mol% due to concentration quenching. The energy-level diagram shows the green radiative transition pathway. The CIE coordinates and color purity were computed for Tb3+: LWO nanophosphors from their emission profiles, and the evaluated coordinates were centralized in the strong green region. A high color purity of 90.1% was obtained appreciably from the optimized Tb3+: LWO nanophosphor. The lifetime of the green emission transition was systematically evaluated based on decay dynamics. The visualization of fingerprints was examined using the optimized green phosphor with an in-depth analysis of the Group-III level details. The non-cytotoxicity of Tb3+ (14 mol%): LWO nanophosphor was confirmed in normal WI-38 lung fibroblast cells. Moreover, these phosphors exhibited strong cytotoxicity against human breast cancer cells of MCF-7. From these results, the synthesized Tb3+ (14 mol%): LWO non-cytotoxic nanophosphor material is considered the best green luminescent material for latent fingerprints in forensic investigation, photonic and anticancer applications.

Optimized microwave assisted synthesis of La2(WO4)3:Tb3+ phosphors and analysis of photoluminescence behavior

NUV/blue LED excitable green emitting terbium doped lanthanum tungstate nanophosphors were successfully synthesized via optimized microwave assisted co–precipitation technique for the first time. Powder XRD analysis confirms that the nanophosphor have monoclinic structure and belongs to space group C2/c. FTIR spectrum identified the characteristic vibrational modes of tungstate group. The chemical composition of the sample was confirmed with the help of EDS technique. Thermogravimetric analysis (TGA) ascertained the outstanding thermal stability of the prepared sample. The strong and wide charge transfer band in the excitation spectrum clearly demonstrates the efficient energy transfer from the host matrix to the terbium ion. This broad band allows for NUV excitation, and the sharp peak at 487 nm indicates that blue LED sources can also be used for excitation. The presence of prominent peak at 543 nm in the emission spectrum, due to 5D4→7F5 transition irrespective of the excitation wavelength, uplifts terbium doped lanthanum tungstate to the group of excellent green emitting phosphors. Decay curves shows single exponential nature and fluorescence life time was obtained. The small value of decay time implies that the synthesized material is suitable for display applications. The calculated CIE chromaticity co–ordinates are close to green emitting phosphors. Thus, terbium doped lanthanum tungstate phosphors are potential phosphors with green emission for WLED applications.

Up-scaling and processing related characterisation of hydrogen permeation membranes based on pristine and Mo substituted La28−xW4+xO54+1.5x

Mixed protonic and electronic conducting ceramic membranes offer a high potential to separate pure hydrogen from gas mixtures or in the field of membrane reactors. The water-gas-shift reaction is an example for the possible application of lanthanum tungstate based materials with general formula La28−xW4+xO54+1.5x (LaWO) due to their high stability under the reaction conditions. To bring ceramic membranes one step closer to commercialisation, high effort is needed to find optimised material compositions and transfer them into suitable fabrication techniques. Both is done in the present work. First, a detailed XRD-study, supported by microstructural analysis, was performed to find a suitable composition for Mo-substituted LaWO. As it was demonstrated, with increasing the Mo concentration as a substitute for W leading to enhanced electronic conductivity, the single phase region narrows and La/W ratio shifts to the higher values. In order to ensure single phase composition of the powder used in the membrane fabrication, 20 mol.% Mo substituted LWO was the material of choice. Subsequently tape-casting was performed to produce asymmetric membranes consisting of a thin functional membrane made of LaWO-Mo20 and a porous support layer of pure LaWO. Such asymmetric component could be scaled-up to 100 cm² active membrane area. The sintering behaviour was characterised by optical dilatometry. The more cost-efficient support material MgO was shown to be incompatible with the LaWO-Mo20 material. Therefore, an advanced fabrication route was developed by introducing an intermediate layer to overcome interdiffusion and secondary phase formation.

BiLaWO6: Er3+/Tm3+/Yb3+ phosphor: Study of multiple fluorescence intensity ratiometric thermometry at cryogenic temperatures

Highly thermally stable Er3+/Tm3+/Yb3+ tri-doped bismuth lanthanum tungstate phosphors were prepared by high temperature solid-state reaction method. The structural and morphological properties of the prepared phosphors were analysed by X-ray diffraction (XRD), Raman spectroscopy and Scanning electron microscopy (SEM) coupled with energy dispersion spectrum (EDS). Visible upconversion (UC) luminescence was measured by exciting the phosphors with 980 nm laser radiation. The dependence of the UC intensity of each emission band of Er3+ and Tm3+ ions as a function of temperature in the range from 30 to 300 K was monitored. Fluorescence intensity ratios (FIR) of thermally coupled levels (TCL) and non-thermally coupled levels (NTCL) were analysed and verified with appropriate theoretical validation. The absolute (SA) and relative sensitivities (SR) were estimated and compared with the reported systems. In the present case of BiLaWO6: Er3+/Tm3+/Yb3+, SR (0.43 % K−1) related to TCL of Er3+ UC is found to have maximum sensitivity compared to any of the NTCL combinations at 300 K. From this study we inferred that the SR values estimated from NTCL are smaller than that of TCL involved in BLW: Er3+/Tm3+/Yb3+ phosphor. The temperature dependent CIE color coordinates were also evaluated in the cryogenic temperature region.

Enhanced Hydrogen Permeability of Mixed Protonic–Electronic Conducting Membranes through an In‐Situ Exsolution Strategy

AbstractMixed protonic–electronic conducting (MPEC) ceramic membranes with high H2 permeability and stability are significant for practical H2 separation. CO2‐tolerant lanthanum tungstate oxides have received much attention, but their low H2 permeability is their main problem for membrane applications. Herein, an efficient in‐situ exsolution strategy is proposed to enhance the H2 permeability and CO2 stability of lanthanum tungstate‐type membranes. During H2 permeation, the catalytic Pd nanoparticles are in‐situ generated from the bulk oxide lattices and dispersed evenly on the membrane surfaces, which greatly promotes the H2 surface exchange kinetics. Also, the protonic conductivity of the membranes is effectively improved through the introduction of Pd. Consequently, the H2 permeation flux is increased by 3.5 times and a maximum H2 flux of 1.3 mL min−1 cm−2 is achieved at 1000 °C through the La5.5(W0.6Mo0.4)0.95Pd0.05O11.25‐δ (LWMPd) membrane. The LWMPd membrane shows outstanding long‐term chemical stability during 300 h continuous operation in a CO2‐containing atmosphere. Therefore, this in‐situ exsolution formation of Pd nanoparticles provides effective guidance for developing competitive MPEC membranes for H2 separation and purification.

Cation-deficient Ca-doping lanthanum tungstate Ca2.06La2.61□0.33W2O12: Structure and transport property study

A new cation-deficient Ca-doping lanthanum tungstate compound with the exact formula Ca2.06La2.61□0.33W2O12 (□ indicating a vacancy) is presented in this work. It crystallizes in the space group R 3¯ C (No.167), Z ​= ​18 with the hexagonal parameters a ​= ​9.7747(1) Å and c ​= ​55.7833(4) Å, similar to Ca5Re2O12. This compound belongs to a rare small crystallographic family A5B2X12 having large cells. The thermodynamic and kinetic processes of synthesizing this white powder compound are very slow. Its structure is analyzed by X-ray, neutron powder and electron diffraction. The conduction properties are investigated with complex impedance spectroscopy.

Evaluation of La2-x(Ca/Sr)xNi1-yFeyO4+δ (x = 0.5, 0.6; y = 0.4, 0.5) as cathodes for proton-conducting SOFC based on lanthanum tungstate

La2NiO4+δ, La1.4Ca0.6Ni0.6Fe0.4O4+δ (LCNF0604), La1.4Sr0.6Ni0.6Fe0.4O4+δ (LSNF0604), La1.4Sr0.6Ni0.5Fe0.5O4+δ (LSNF0605) and La1.5Sr0.5Ni0.6Fe0.4O4+δ (LSNF0504) were synthesized by the citrate-nitrate technique with the following four annealing steps at 950 °C in air (La2NiO4+δ, LCNF0604, LSNF0604) or in atmosphere with the reduced (10−5 atm) oxygen partial pressure (LSNF0605, LSNF0504). Phase purity of the samples is confirmed by the X-ray powder diffraction (XRPD). Electrochemical impedance spectroscopy studies of the symmetrical cells based on the proton-conducting La28−zW4+zO54+1.5z (z = 0.85, LWO85) electrolyte reveal that the polarization resistance (Rp) decreases in the row LCNF0604>La2NiO4+δ>LSNF0504>LSNF0604>LSNF0605 in the temperature interval of 600–800 °C in wet air. The process at low frequencies related to the surface exchange, provides the most significant contribution to the polarization resistance of the studied cells. Higher polarization resistance for the La2NiO4+δ/LWO85 cell can be associated with blocking of protons/protonic species. The minimal Rp value of 1 Ω cm2 at 800 °C in wet air is demonstrated by the LSNF0605/LWO85 symmetrical cell. The maximal power density for the anode-supported LSNF0605/LWO85/Ni-LWO85 single fuel cell is equal to 55 mW cm−2 at 750 °C. The performance of the fuel cell is limited by the formation of La2O3 at the LWO85/Ni-LWO85 interface due to chemical interaction between NiO and LWO85. To improve the performance of the studied fuel cell the development of new proton-conducting buffer layer stable to LWO85 is required.

Pilot scale fabrication of lanthanum tungstate supports for H2 separation membranes

This paper reports the fabrication of asymmetric tubular geometry lanthanum tungstate-based membranes for high temperature H2 separation applications. As starting materials, powders with the compositions La28-yW4+yO54+δ (y = 0.848), La28-yW4+yO54+δ (y = 1) and La28-y(W1-xMox)4+yO54+δ (x = 0.3, y = 1) were synthesized by solid state reaction method. Porous, thick-wall tubes made of lanthanum tungstate-based powders with high gas permeability (7–8 x10-15 m2 at 2 bar overpressure) and homogeneous porous microstructure were made by combining a cost-effective solid-state synthesis and thermoplastic extrusion method. Deposition of lanthanum tungstate-based dense thin film (∼20 μm) was achieved on top of porous supports through dip coating technique. The influence of conformation routes, thermal debindering and sintering processes were investigated in detail to achieve defect free H2 transport membranes. Asymmetric geometry membranes with ∼20 μm dense layer thickness supported on porous tubular (∼ 7.5 mm diameter and ∼0.8 mm thick) supports.As a result, a procedure for proton conducting ceramics manufacture was established which can be deployed to fabricate high temperature catalytic membrane reactors for synthetic fuel from gas-to-liquid (GTL) processes.

Development and application of lanthanum tungstate series proton conductors

<p indent=0mm>As one of the most important clean energy and commodity chemicals, hydrogen is widely used in human life and industrial production. In the present decade, three main technologies for hydrogen recovery have been developed, namely pressure swing adsorption (PSA), cryogenic separation, and membrane separation. Among these three different hydrogen recovery technologies, the membrane separation method is favored for its high efficiency. Benefiting from its absolute selectivity of hydrogen and the low cost, mixed protonic-electronic conductors (MPEC) have become an important research object in the field of hydrogen separation membrane materials, which enable a significant approach for the purification and utilization of hydrogen energy. For the traditional proton-conducting perovskite oxides doped with Ce and Zr, although they have high proton conductivity, their poor chemical stability under the atmosphere in the presence of CO₂ and H₂O hinders the commercial application. Rare-earth metal compound lanthanum tungstate material (LWO) is a kind of crucial proton conductor, which has good chemical stability in CO₂ atmosphere. However, the hydrogen permeability of LWO is not satisfactory because of the low electronic conductivity. A variety of effective methods to improve the hydrogen permeability of lanthanum tungstate film are summarized in this review. This review introduces the basic electronic conductivity of LWO-based single-phase materials, with the emphasis on improving the electronic conductivity of LWO by adjusting La/W ratio, cation doping strategies, and preparation methods. Furthermore, it reviews breakthroughs in their application in proton-conducting solid oxide fuel cells (SOFC) as well as hydrogen separation membranes. The problems now faced by LWO oxides are analyzed and their future development is predicted. Firstly, the proton conductivity of LWO is positively correlated with the La/W ratio. Adjusting the La/W ratio improves proton conductivity of LWO. For cation doping, the substitution of W rather than La more effectively improves the proton conductivity of LWO. Secondly, compositing LWO and the electronic conductors effectively enhance the performance of the hydrogen permeation membranes. Thirdly, in terms of the SOFC applications, an additional oxide layer between the LWO electrolyte layer and the electrode layer avoids the phase reaction on the interface, which prevents the chemical incompatibility between the LWO and electrode materials. Many studies show that the maximum utilization of LWO can be realized by optimizing crystal structure, phase composition, and the SOFC structure. In view of the problems existing in the research of LWO materials, future research can be focused on the following aspects: (1) Further exploring the electronic-ionic conducting pathway and catalytic mechanism of LWO series materials, and then optimizing the electrochemical properties under the guidance. (2) Developing the electrode materials with good catalytic performance and good chemical compatibility with LWO which is significant to the stable operation of SOFC. Also, it is necessary to improve the cell preparation process in which the unbeneficial interface reaction between the electrode and the LWO can be avoided. (3) For hydrogen permeation membrane, future research can be developed towards optimization with cation doping, surface engineering, and composite materials preparation.

Enhanced H2 production by using La5.5WO11.25-δ-La0.8Sr0.2FeO3-δ mixed oxygen ion-proton-electron triple-conducting membrane

Although lanthanum tungstates (LnnWO12-δ) show superior CO2-tolerance compared to the traditional perovskite-type oxides, their hydrogen permeation fluxes are not competitive. Herein, a mixed oxygen ion-proton-electron triple-conducting membrane with a nominal composition of La5.5WO11.25-δ-La0.8Sr0.2FeO3-δ (LWO-LSF) was developed for H2 production. The triple-conducting membrane is composed of a LWO phase with proton conductivity and a LSF phase with mixed oxygen ion-electron conductivities. In the LWO-LSF membrane, proton (H+) permeation and oxygen ion (O2−) counter-permeation property was simultaneously displayed. The improved H2 production can be ascribed to (1) hydrogen permeated as H+ through LWO phase, and (2) hydrogen produced from water splitting that is enhanced by O2− counter-permeation through LSF phase. A higher H2 flux of 0.15 mL min−1 cm−2 was achieved at 900 °C using LWO-LSF triple-conducting membrane, compared with the conventional proton-electron conducting membranes LWO or La5.5WO11.25-δ-La0.8Sr0.2CrO3-δ (LWO-LSC). Furthermore, the constant H2 fluxes in various atmospheres indicated the good stability of LWO-LSF membrane in simulated raw hydrogen.

Design and Modeling of Proton-Conducting Bilayer Electrolytes Using a Nernst-Planck-Poisson Formulation

Proton-conducting oxides have attracted much attention in recent years due to their good ion conductivity at intermediate temperatures (500-700°C), as opposed to conventional oxide ion-conducting oxides that require high temperatures (usually, >900°C). Lowering the operating temperature of reversible protonic ceramic electrochemical cells (RePCECs) is desirable as it reduces material, heating, and insulation costs, while also increasing the operating life of the cell. Nevertheless, along with the desired proton conductivity, typical proton-conducting solid electrolytes also allow the transport of other charged defects like oxygen-vacancies, electrons, and electron holes. The presence of these other defects, especially the electron holes, causes leakage current that significantly reduces the cell’s electrical efficiency. Therefore, an electrolyte capable of reducing leakage current is necessary. Unfortunately, there is usually a trade-off between high ionic conductivity and low hole conduction. For example, while lanthanum tungstate (LWO) has a low electron conductivity and is capable of suppressing hole conduction below 800°C, its proton conductivity is lower than that of commonly used perovskite materials like yttria-doped barium cerate (BCY) or yttria-doped barium zirconate (BZY). Nonetheless, previous studies showed that LWO67 can act as a leakage current-blocking layer when deposited on a BZY82 base electrolyte and the estimated leakage current was almost 200 times lower than that of a BZY82 single layer electrolyte under open-circuit conditions. This suggests that under certain operating conditions, bilayer electrolytes can achieve better performance when compared to their corresponding single-layer electrolytes. Therefore, in this study, we design proton-conducting bilayer electrolytes by investigating the incorporation and transport of charged defects using a steady-state Nernst-Planck-Poisson (NPP) model.The main goals of this work are twofold. Firstly, to find the combination of electrolytes that better suppresses leakage current. For this purpose, we calculate the defect concentration, flux, and electrostatic profiles inside common materials like BCY, BZY, BZCYYb, BZCY, LWO, and different combinations of bilayer electrolytes to better understand how the addition of a leakage current-blocking layer affects proton conduction and overall efficiency. We consider three mobile defects when solving the NPP equation, protons (OHO •), oxygen vacancies (vO ••), and electron holes that are treated as small polarons localized at oxygen sites (OO •). Afterward, the I-V curve and relevant theoretical efficiency are predicted within and A cm-2 (fuel cell and electrolyzer operation) at 500, 600 and 700°C, in order to identify the most promising one. Secondly, to design a cell by finding the optimal thickness of the better performing bilayer electrolyte that maximizes efficiency.

Design and Modeling of Proton-Conducting Bilayer Electrolytes Using a Nernst-Planck-Poisson Formulation

In this study, the efficiency of proton-conducting ceramic fuel cells was improved by designing bilayer electrolytes with high ion conductivity and low hole conduction. The designs were carried out by finding the thicknesses of anode and cathode-side electrolytes that optimizes efficiency using integral equations based on Wagner theory. Results obtained for bilayer electrolytes were compared with those of single-layer electrolytes. Best performances were found when thin layers of lanthanum tungstate (La28-x W4+x O54+3x/2v2-3x/2) with an La/W ratio of 6.7 (LWO67) were used as cathode-side electrolytes attached to commonly used perovskite materials like BaCe0.9Y0.1O3- δ (BCY10), BaZr0.8Y0.2O3- δ (BZY20), and BaZr0.1Ce0.7Y0.1Yb0.1O3- δ (BZCYYb1711). In addition, the transport properties of a single-layer LWO67 electrolyte were further analyzed by using the Nernst-Planck-Poisson (NPP) model for which parameters were fitted. Finally, a bilayer NPP formulation was explored to obtained the charged defect fluxes and other useful information to enhance the efficiency of a bilayer BZY20|BZCYYb1711 electrolyte.

Development of Mn and Mo double-substituted La5.5WO11.25-δ based membranes with enhanced hydrogen permeation flux

Mixed protonic-electronic ceramic lanthanum tungstate membranes of La5.5W1-xMnxO11.25-δ (LWMnx, x = 0.1, 0.15 and 0.2) and La5.5W0.8-yMn0.2MoyO11.25-δ (LWMn0.2Moy, y = 0.1, 0.2, 0.3 and 0.4) were developed in present work. The H2 permeation flux through lanthanum tungstate membrane was increased by substitution of Mn ions into W sites. However, the impurity of La2O3 formed in LWMn0.15 and LWMn0.2 membranes. Introduction of a moderate amount of Mo ions in LWMn0.2 was beneficial to single phase formation and H2 permeation. LWMn0.2Mo0.2 exhibited a pure cubic phase structure without any impurities. LWMn0.2Mo0.2 membrane had a H2 permeation flux about 0.12 mL/min∙cm2 at 1000 °C, which was 1.7 times higher than that through LWMn0.2 membranes.

Effect of lanthanum tungstate hole-blocking layer for improvement of energy efficiency in anode-supported protonic ceramic fuel cells

Effect of lanthanum tungstate hole-blocking layer for improvement of energy efficiency in anode-supported protonic ceramic fuel cells

Influence of Cr doping on hydrogen permeation performance of lanthanum tungstate membrane

A series of La5.5W1-xCrxO11.25-δ (LWCrx, x = 0.1, 0.2, 0.3 and 0.4) powders were successfully synthesized by a traditional solid-state reaction method. The influences of Cr doping on phase structure, microstructure, hydrogen permeation and chemical stability of lanthanum tungstate were investigated in details. The oxygen vacancy concentration in LWCr0.2 was higher than the other three samples. Moreover, the hydrogen permeation fluxes through LWCrx membranes increased with the increase of Cr content when x ≤ 0.2, and LWCr0.2 exhibited the highest hydrogen permeation flux because of its higher oxygen vacancy concentration. Besides, the hydrogen permeation fluxes through LWCr0.2 membrane were comparable to that through La5.5W0.8Mo0.2O11.25-δ (LWMo0.2) membrane. During a 104 h of hydrogen permeation test, the hydrogen permeation flux and phase structure changed slightly, revealing a good stability of LWCr0.2 membrane.