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Mechanical degradation under hydrogen of yttrium doped barium zirconate electrolyte material prepared with NiO additive

Authors D. Ciria, M. Ben Hassine, M. Jiménez-Melendo, A. Iakovleva, P. Haghi-Ashtiani, V. Aubin, G. Dezanneau
Source
Journal of Power Sources
Volume: 321, Pages: 226–232
Time of Publication: 2016
Abstract Recently, a novel process was presented to fabricate dense yttrium-doped barium zirconate electrolytes with high proton conductivity. This process was based on the use of a NiO additive during reactive sintering. We show here that materials made from this process present a fast degradation of mechanical properties when put in hydrogen-rich conditions, while material made from conventional sintering without NiO aid remains intact in the same conditions. The fast degradation of samples made from reactive sintering, leading to sample failure under highly compressive conditions, is due to the reduction of NiO nanoparticles at grain boundaries as shown from structural and chemical analyses using Transmission Electron Microscopy. By the present study, we alert about the potential risk of cell failure due to this mechanical degradation.
Keywords PCFCs; Mechanical properties; BZY; Solid state reactive sintering
Remark doi:10.1016/j.jpowsour.2016.05.001
Link

Electrochemical Property Assessment of Pr2CuO4 Submicrofiber Cathode for Intermediate-Temperature Solid Oxide Fuel Cells

Authors Ting Zhao, Li-Ping Sun, Qiang Li, Li-Hua Huo, Hui Zhao, Jean-Marc Bassat, Aline Rougier, Sébastien Fourcade and Jean-Claude Grenier
Source
Journal of Electrochemical Energy Conversion and Storage
Volume: 13, Issue: 1, Pages: 011006
Time of Publication: 2016
Abstract The Pr2CuO4 (PCO) submicrofiber precursors are prepared by electrospinning technique and the thermo-decomposition procedures are characterized by thermal gravity (TG), X-ray diffraction (XRD), Fourier transform infrared spectoscopy (FT-IR), and scanning electron microscopy (SEM), respectively. The fibrous PCO material was formed by sintering the precursors at 900 °C for 5 hrs. The highly porous PCO submicrofiber cathode forms good contact with the Ce0.9Gd0.1O1.95 (CGO) electrolyte after heat-treated at 900 °C for 2 hrs. The performance of PCO submicrofiber cathode is comparably studied with the powder counterpart at various temperatures. The porous microstructure of the submicrofiber cathode effectively increases the three-phase boundary (TPB), which promotes the surface oxygen diffusion and/or adsorption process on the cathode. The PCO submicrofiber cathode exhibits an area specific resistance (ASR) of 0.38 Ω cm2 at 700 °C in air, which is 30% less than the PCO powder cathode. The charge transfer process is the rate limiting step of the oxygen reduction reaction (ORR) on the submicrofiber cathode. The maximum power densities of the electrolyte-support single cell PCO|CGO|NiO-CGO reach 149 and 74.5 mW cm−2 at 800 and 700 °C, respectively. The preliminary results indicate that the PCO submicrofiber can be considered as potential cathode for intermediate temperature solid fuel cells (IT-SOFCs).
Remark doi: 10.1115/1.4033526
Link

Direct conversion of methane to aromatics in a catalytic co-ionic membrane reactor

Authors S.H.Morejudo, R.Zanon, S.escolastico, I. Yuste-Tirados, H. Malerřd-Fjeld, P.K. Vestre, W.G.Coors, A.Martinez, T.Norby, J.M.Serra, C.Kjřlseth
Source
Science
Volume: 353, Issue: 6299, Pages: 563-566
Publisher: American Association for the Advancement of Science (AAAS), ISBN: Print ISSN:0036-8075 Online ISSN:1095-9203, Time of Publication: 2016-08
Abstract Nonoxidative methane dehydroaromatization (MDA: 6CH4 ↔ C6H6 + 9H2) using shape-selective Mo/zeolite catalysts is a key technology for exploitation of stranded natural gas reserves by direct conversion into transportable liquids. However, this reaction faces two major issues: The one-pass conversion is limited by thermodynamics, and the catalyst deactivates quickly through kinetically favored formation of coke. We show that integration of an electrochemical BaZrO3-based membrane exhibiting both proton and oxide ion conductivity into an MDA reactor gives rise to high aromatic yields and improved catalyst stability. These effects originate from the simultaneous extraction of hydrogen and distributed injection of oxide ions along the reactor length. Further, we demonstrate that the electrochemical co-ionic membrane reactor enables high carbon efficiencies (up to 80%) that improve the technoeconomic process viability. Methane gas is expensive to ship. It is usually converted into carbon monoxide and hydrogen and then liquefied. This is economically feasible only on very large scales. Hence, methane produced in small amounts at remote locations is either burned or not extracted. A promising alternative is conversion to benzene and hydrogen with molybdenumzeolite catalysts. Unfortunately, these catalysts deactivate because of carbon buildup; plus, hydrogen has to be removed to drive the reaction forward. Morejudo et al. address both of these problems with a solid-state BaZrO3 membrane reactor that electrochemically removes hydrogen and supplies oxygen to suppress carbon buildup.
Keywords CMR, MDA, catalytic membrane reactor, ZSM-5, MCM-22, FBR, FBR-PolyM, Pd-CMR, Co-ionic CMR, FT, ProboStat CMR base unit (NorECs)
Remark http://science.sciencemag.org/highwire/filestream/682540/field_highwire_adjunct_files/0/Morejudo.SM.pdf
BaZrO3
BaZrO3
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Magnetron-Sputtered YSZ and CGO Electrolytes for SOFC

Authors A. A. Solovyev , A. V. Shipilova, I. V. Ionov, A. N. Kovalchuk, S. V. Rabotkin, V. O. Oskirko
Source
Journal of Electronic Materials
Time of Publication: 2016
Abstract Reactive magnetron sputtering has been used for deposition of yttria-stabilized ZrO2 (YSZ) and gadolinium-doped CeO2 (CGO) layers on NiO-YSZ commercial anodes for solid oxide fuel cells. To increase the deposition rate and improve the quality of the sputtered thin oxide films, asymmetric bipolar pulse magnetron sputtering was applied. Three types of anode-supported cells, with single-layer YSZ or CGO and YSZ/CGO bilayer electrolyte, were prepared and investigated. Optimal thickness of oxide layers was determined experimentally. Based on the electrochemical characteristics of the cells, it is shown that, at lower operating temperatures of 650°C to 700°C, the cells with single-layer CGO electrolyte are most effective. The power density of these fuel cells exceeds that of the cell based on YSZ single-layer electrolyte at the same temperature. Power densities of 650 mW cm−2 and 500 mW cm−2 at 700°C were demonstrated by cells with single-layer YSZ and CGO electrolyte, respectively. Significantly enhanced maximum power density was achieved in a bilayer-electrolyte single cell, as compared with cells with a single electrolyte layer. Maximum power density of 1.25 W cm−2 at 800°C and 1 W cm−2 at 750°C under voltage of 0.7 V were achieved for the YSZ/CGO bilayer electrolyte cell with YSZ and CGO thickness of about 4 μm and 1.5 μm, respectively. This signifies that the YSZ thin film serves as a blocking layer to prevent electrical current leakage in the CGO layer, leading to the overall enhanced performance. This performance is comparable to the state of the art for cells based on YSZ/CGO bilayer electrolyte.
Keywords Solid oxide fuel cell CGO YSZ bilayer electrolyte magnetron sputtering pulse electron-beam treatment
Remark Link

Characteristics of Cu and Mo-doped Ca3Co4O9−δ cathode materials for use in solid oxide fuel cells

Authors Sea-Fue Wang, Yung-Fu Hsu, Jing-Han Chang, Soofin Cheng, Hsi-Chuan Lu
Source
Ceramics International
Time of Publication: 2016
Abstract In this study, Cu and Mo ions were doped in Ca3Co4O9−δ to improve the electrical conductivity and electrochemical behavior of Ca3Co4O9−δ ceramic and the performance of a solid oxide fuel cell (SOFC) single cell based on NiO-SDC/SDC/doped Ca3Co4O9−δ-SDC were examined. Cu substitution in the monoclinic Ca3Co4O9−δ ceramic effectively enhanced the densification, slightly increased the grain size, and triggered the formation of some Ca3Co2O6; however, no second phase was found in porous Mo-doped Ca3Co4O9−δ ceramics even when the sintering temperature reached 1050 °C. Substitution of Cu ions caused slight increase in the Co3+ and Co4+ contents and decrease in the Co2+ content; however, doping with Mo ions showed the opposite trend. Doping the Ca3Co4O9−δ ceramic with a small amount of Cu or Mo increased its electrical conductivity. The maximum electrical conductivity measured was 218.8 S cm−1 for the Ca3Co3.9Cu0.1O9−δ ceramic at 800 °C. The Ca3Co3.9Cu0.1O9−δ ceramic with a coefficient of thermal expansion coefficient of 12.1×10−6 K−1 was chosen as the cathode to build SOFC single cells consisting of a 20 μm SDC electrolyte layer. Without optimizing the microstructure of the cathode or hermetically sealing the cell against the gas, a power density of 0.367 Wcm−2 at 750 °C was achieved, demonstrating that Cu-doped Ca3Co4O9−δ can be used as a potential cathode material for IT-SOFCs.
Keywords Solid oxide fuel cell; Cathode; Impedance; Cell performance
Remark In Press, doi:10.1016/j.ceramint.2016.04.037
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Synthesis and characterization of robust, mesoporous electrodes for solid oxide fuel cells

Authors Laura Almar, Alex Morata, Marc Torrell, Mingyang Gong, Meilin Liu, Teresa Andreu and Albert Tarancón
Source
Journal of Materials Chemistry A
Time of Publication: 2016
Abstract The use of mesoporous electrodes in solid oxide cells would lead to a significant enhancement of the performance due to their high surface area and large number of active sites for electrochemical reactions. However, their application in real devices is still hindered by the potential instability of the mesostructure and morphology at high temperatures required for device fabrication and under severe conditions for high-current, long-term operation. Here we report our findings on the preparation and characterization of mesoporous electrodes based on ceria infiltrated with catalysts: an anode consisting of a Ce0.8Sm0.2O1.9 (SDC) scaffold infiltrated with Ni and a cathode consisting of an SDC scaffold infiltrated with Sm0.5Sr0.5CoO3−δ (SSC). In particular, a doped-zirconia electrolyte supported cell with a mesoporous Ni–SDC anode and a mesoporous SSC–SDC cathode demonstrates an excellent peak power density of 565 mW cm−2 at 750 °C (using humidified hydrogen as the fuel). More importantly, both mesoporous electrodes display remarkable stability, yielding a combined electrode virtual non-degradation for the last 500 hours of the test at a constant current density of 635 mA cm−2 at 750 °C, demonstrating the potential of these mesoporous materials as robust electrodes for solid oxide fuel cells or other high-temperature electrochemical energy storage and conversion devices.
Remark DOI: 10.1039/C6TA00321D
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Fluorite-like compounds with high anionic conductivity in Nd2MoO6 – Bi2O3 system

Authors E.P. Kharitonova, V.I. Voronkova, D.A. Belov, E.I. Orlova
Source
International Journal of Hydrogen Energy
Time of Publication: 2016
Abstract A wide range of (Bi2O3)x(Nd2O3)(1−x)/2(MoO3)(1−x)/2 solid solutions with the structure of the anion-conducting bismuth oxide was found in the Bi2O3–Nd2MoO6 join of ternary Bi2O3–MoO3–Nd2O3 system at 0.5 ≤ x ≤ 1. In said concentration range the compounds with large (0.92 ≤ x ≤ 0.98) and small (0.5 ≤ x < 0.6) bismuth content are tetragonal at room temperature. In the intermediate concentration range (0.67 ≤ x ≤ 0.9) cubic δ-Bi2O3 structure is stabilized at room temperature. It is shown that two tetragonal phases observed at different bismuth concentrations differ from each other in their polymorphism and behavior of the unit cell parameters. All the obtained compounds show high conductivity that reaches 0.1 S/cm (for a cubic sample with x = 0.8 at 800 °C).
Keywords Bi2O3; Nd2O3; MoO3; Polymorphism; Oxygen conductivity
Remark In press, doi:10.1016/j.ijhydene.2016.03.046
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Structural study and proton conductivity in BaCe0.7Zr0.25−xYxZn0.05O3 (x = 0.05, 0.1, 0.15, 0.2 & 0.25)

Authors Ahmed Afif, Nikdalila Radenahmad, Chee Ming Lim, Mohamad Iskandar Petra, Md. Aminul Islam, Seikh Mohammad Habibur Rahman, Sten Eriksson, Abul Kalam Azad
Source
International Journal of Hydrogen Energy
Time of Publication: 2016
Abstract Solid oxide fuel cell (SOFC) has been considered to generate power represented by conductivity. Zinc doped Barium Cerium Zirconium Yttrium oxide (BCZYZn) has been found to offer high protonic conductivity and high stability as being electrolyte for proton-conducting SOFCs. In this study, we report a new series of proton conducting materials, BaCe0.7Zr0.25−xYxZn0.05O3 (x = 0.05, 0.1, 0.15, 0.2 and 0.25). The materials were synthesized by solid state reaction route and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal expansion, particle size and impedance spectroscopy (IS). Rietveld analysis of the XRD data reveal a cubic perovskite structure with Pm-3m space group up to composition x = 0.15. For x = 0.15 and 0.20, the materials have structural phase change to orthorhombic in the Pbnm space group. Scanning electron microscopy images show high density materials. Thermal expansion measurements show that the thermal expansion coefficient is in the range 10.0–11.0 × 10−6/°C. Impedance spectroscopy shows higher ionic conduction under wet condition compared to dry condition. Y content of 25% (BCZYZn25) exhibits highest conductivity of 1.84 × 10−2 S/cm in wet Argon. This study indicated that perovskite electrolyte BCZYZn is promising material for the next generation of intermediate temperature solid oxide fuel cells (IT-SOFCs).
Keywords Proton conductor; Sinterability; Rietveld refinement; Conductivity; SOFC electrolyte
Remark In Press, doi:10.1016/j.ijhydene.2016.02.135
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Ca-doped fluorite-like compounds based on Nd5Mo3O16

Authors V.I. Voronkova, E.P. Kharitonova, E.I. Orlova, A.V. Levchenko, A.M. Antipin, N.I. Sorokina, D.A. Belov
Source
Journal of Alloys and Compounds
Time of Publication: 2016
Abstract We have studied phase relations in a molybdenum oxide-rich region of the ternary system CaO–Nd2O3–MoO3. Using polycrystalline samples prepared by solid-state reactions in air, the system has been shown to contain a rather broad region of cubic fluorite-like phases isostructural with Nd5Mo3O16. The atomic structure of a calcium-doped fluorite-like Nd5Mo3O16+δ single crystal grown from an off-stoichiometric melt has been studied by X-ray diffraction. The peculiarities of the structure of calcium-doped fluorite-related compounds were revealed. Experimental structural data demonstrate partial mutual substitutions of Nd and Mo cations, splitting of the O2 position into several additional positions, and the presence of excess oxygen, which occupies octahedral sites in the voids of the structure. Some of the fluorite-like samples have high electrical conductivity, on the order of 10−2 S/cm at 800 °C.
Keywords Ceramics; Oxides; Crystal growth; Crystal structure; Ionic conductivity
Remark doi:10.1016/j.jallcom.2016.03.013
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Crystal structure and proton conductivity of BaSn0.6Sc0.4O3-δ: Insights from neutron powder diffraction and solid state NMR

Authors Francis Gachau Kinyanjui, Stefan Tommy Norberg, Christopher Knee, Istaq Ahmed, Stephen Hull, Lucienne Buannic, Ivan Hung, Zhehong Gan, Frédéric Blanc, Clare P. Grey and Sten Eriksson
Source
Journal of Materials Chemistry A
Time of Publication: 2016
Remark DOI: 10.1039/C5TA09744D
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Optically-transparent and electrically-conductive AgI–AgPO3–WO3 glass fibers

Authors Maxime Rioux, Yannick Ledemi, Jeff Viens, Steeve Morency, Seyed Alireza Ghaffari and Younčs Messaddeq
Source
RSC Advances
Volume: 5, Pages: 40236-40248
Time of Publication: 2015
Abstract In this study, we report to our knowledge the first optically-transparent and electrically-conductive optical glass fiber belonging to the system AgI–AgPO3–WO3. The addition of tungsten oxide (WO3) into the phosphate glassy network allowed the adjustment of the glass transition temperature, thermal expansion coefficient, refractive index, optical band edge, and electrical conductivity, which are all very important parameters in view of drawing glass fibers with a desired set of electrical and optical properties. Furthermore, the addition of WO3 can improve considerably glass stability against water and humidity in the environment. AgI–AgPO3–WO3 glass fibers with 15 mol% WO3 showed 2 dB m−1 optical propagation loss from 800 to 950 nm wavelength range, and 10−3 S cm−1 electrical conductivity at 1 MHz AC frequency. Complex impedance spectra and thermal activation energies ranging from 0.15 to 0.30 eV are indicative of a dominant conductivity mechanism being ionic in nature within the range of AC frequencies from 1 Hz to 1 MHz. Fibers exhibited higher electrical conductivities than the bulk glasses. Glasses in the AgI–AgPO3–WO3 system can be used for fibers that require a set of adjustable properties pertaining to electrical conductivity, optical transparency, and environmental stability.
Remark DOI: 10.1039/C5RA00681C
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Phase Relations and Physical Properties of Layered Pb-Containing Nd2MoO6 Compounds

Authors Valentina Voronkova, Ekaterina Orlova, Sergey Kazakov, Elena Kharitonova and Dmitry Belov
Source
European Journal of Inorganic Chemistry
Volume: 2016, Issue: 7, Pages: 1022-1029
Time of Publication: 2016
Abstract The phase relations along the Nd2MoO6–PbO join of the ternary Nd2O3–MoO3–PbO system have been studied by means of solid-state synthesis in air. The samples with high Pb content underwent a reversible first-order phase transition near 820 °C. XRD analysis revealed two tetragonal phases, the high-temperature centric phase (I41/acd) and the low-temperature acentric phase (Iequation image2m). In the region of the phase transition, the permittivity of the Pb-containing samples show a strong lambda-type anomaly and electrical conductivity increases sharply by one and half orders of magnitude. The conductivities of the Pb-containing samples reach 10–2 S/cm at 850 °C, which is two orders of magnitude greater than the conductivity of pure Nd2MoO6. The conductivity in such compounds may be due to oxygen ions. A permittivity anomaly, existence of a piezoelectric effect, and the symmetry change from acentric Iequation image2m to centric I41/acd may indicate an antiferroelectric nature of the phase transition.
Keywords Conducting materials;Layered compounds;Lead;Rare earths;Solid-phase synthesis
Remark DOI: 10.1002/ejic.201501167
Link

Phase stability and thermoelectric properties of Cu10.5Zn1.5Sb4S13 tetrahedrite

Authors Subramaniam Harish, Duraisamy Sivaprahasama, Manjusha Battabyal, Raghavan Gopalan
Source
Journal of Alloys and Compounds
Volume: 667, Pages: 323–328
Time of Publication: 2016
Abstract Cu10.5Zn1.5Sb4S13 tetrahedrite compound was prepared by mechanical milling of Cu2S, ZnS and Sb2S3 powders and spark plasma sintered (SPS) to dense samples. The phase formation, chemical homogeneity, thermal stability of the compound and the thermoelectric properties of the sintered samples were evaluated. Single phase tetrahedrite with the crystallite size of 40 nm was obtained after 30 h of milling followed by annealing at 573 K for 6 h in an argon atmosphere. In-situ high-temperature X-ray diffraction studies revealed that the phase is stable up to 773 K. The Seebeck coefficient of the sintered samples of density >98% shows p-type behavior with maximum thermopower of 170 μV/K at 573 K. The electrical resistivity (ρ) decreases with temperature up to 475 K and then increases. A low thermal conductivity of 0.5 W/(m⋅K), in combination with moderate power factor gave a maximum ZT of ∼0.038 at 573 K in Cu10.5Zn1.5Sb4S13 sample having a grain size of ∼200 nm.
Keywords Thermoelectric; Tetrahedrite; Solid state reactions; Spark plasma sintering; Figure of merit
Remark doi:10.1016/j.jallcom.2016.01.094
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New ferroelastic K2Sr(MoO4)2: Synthesis, phase transitions, crystal and domain structures, ionic conductivity

Authors Galina D. Tsyrenova, Erzhena Т. Pavlova, Sergey F. Solodovnikov, Nadezhda N. Popova, Tatyana Yu. Kardash, Sergey Yu. Stefanovich, Irina А. Gudkova, Zoya A. Solodovnikova, Bogdan I. Lazoryak
Source
Journal of Solid State Chemistry
Volume: 237, Pages: 64–71
Time of Publication: 2016
Abstract K2Sr(MoO4)2 crystals were synthesized and their properties examined. The distortive polymorphic transformations at 421 K (α (LT)→ β(MT)) and 744 K (β(MT)→γ (HT)) of K2Sr(MoO4)2 were studied. It has been shown that the transitions go in sequence from the high-temperature palmierite K2Pb(SO4)2-type γ-phase (R View the MathML source3Żm) to an intermediate β-phase with a probable incommensurate structure and then to a low-temperature α-phase. Domain structures peculiarities in ferroelastic α-K2Sr(MoO4)2 have been investigated. The electrical conductivity of K2Sr(MoO4)2 rises tenfold in the vicinity of the phase transition at 744 K that may be associated with a change conductivity path from quasi-one-dimensional to two-dimensional. The crystal structure of the α-phase (sp. gr. С2/c, а=14.318(3) Ĺ, b=5.9337(12) Ĺ, с=10.422(2) Ĺ, β=105.83(3)°, Z=4, R=0.0219) is similar to that of α-Pb3(PO4)2. Sr-atoms are mainly located at site with the coordination number CN=8 (a tetragonal antiprism with bond lengths of 2.578(2)–2.789(2) Ĺ) and K atoms are located at site with CN=9+1.
Keywords Potassium; Strontium; molybdates; Phase transitions; Ferroelastics; Crystal structure; Crystal optics analysis; Domain structure; Ionic conductivity
Remark doi:10.1016/j.jssc.2016.01.011
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New methods for the preparation and dielectric properties of Lа2 − xSrxNiO4 (х = 1/8) ceramic

Authors T.I. Chupakhina, N.I. Kadyrova, N.V. Melnikova, O.I. Gyrdasova, E.A. Yakovleva, Yu.G. Zainulin
Source
Materials Research Bulletin
Volume: 77, Pages: 190–198
Time of Publication: 2016
Abstract The perovskite-type oxide La2−xSrxNiO4 (x = 1/8) was prepared by a new precursor route. The reaction proceeds in the self-ignition mode. Single-phase powder and gas-tight ceramic samples can be produced by single annealing of decomposition products. It was shown that as a result of thermobaric treatment of La2−xSrxNiO4 (x = 1/8) the solid solution La2−xSrxNiO4 with a higher concentration of strontium and the second phase La3Ni2O7 are formed. Short-term (5 min) thermobaric treatment (P = 2.5 GPa) at t° = 900 °С changes the unit cell parameters, but is not accompanied by structural transitions. At the same time, morphological restructuring of the sample occurs—the agglomerates delaminate into thin plates crystals. It was established that the permittivity of the material exposed to thermobaric treatment is much higher compared to that of the sample annealed at atmospheric pressure and virtually does not depend on frequency in a wide temperature range.
Keywords Oxides; X-ray diffraction; High pressure; Impedance spectroscopy; Dielectric properties
Remark doi:10.1016/j.materresbull.2016.01.023
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Chemical stability and H2 flux degradation of cercer membranes based on lanthanum tungstate and lanthanum chromite

Authors Jonathan M. Polfus, , Zuoan Li, Wen Xing, Martin F. Sunding, John C. Walmsley, Marie-Laure Fontaine, Partow P. Henriksen, Rune Bredesen
Source
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
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Nb-doped TiO2 sol–gel films for CO sensing applications

Authors M. Duta, L. Predoana, J.M. Calderon-Moreno, S. Preda, M. Anastasescu, A. Marin, I. Dascalu, P. Chesler, C. Hornoiu, M. Zaharescu, P. Osiceanu, M. Gartner
Source
Materials Science in Semiconductor Processing
Volume: 42, Issue: 3, Pages: 397–404
Time of Publication: 2016
Abstract Nb doped titania (TiO2:Nb) multilayered films (1–10 layers) with anatase structure were obtained by the low-cost sol–gel and dipping method on microscope glass substrates, followed by thermal treatment at 450 °C for 1 h. After each layer deposition, an intermediate annealing step was performed at 300 °C for 30 min. Doping TiO2 sol–gel films with a low amount of Nb (0.8 at%) allows obtaining an improved CO sensor able to operate under environmental atmosphere (air). It was found that the sensor sensitivity is less dependent on the film thickness but is significantly influenced by Nb doping at the optimal working temperature of 400 °C. Good recovery characteristics were obtained for a wide CO detection range, between 0 and 2000 ppm. The gas-sensing behavior of the films was correlated with the structural, chemical and morphological properties of the multi-layered structures.
Keywords Sol–gel method; Nb-doped TiO2 films; Microstructure; CO sensor
Remark doi:10.1016/j.mssp.2015.11.004
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Synthesis and properties of La0.05Ba0.95Ti1 −xMyO3 (M = Mn, Ce) as anode materials for solid oxide fuel cells

Authors Cédric Périllat-Merceroz, Pascal Roussel, Edouard Capoen, Sébastien Rosini, Patrick Gélin, Rose-Noëlle Vannier, Gilles Gauthier
Source
Solid State Ionics
Volume: 283, Pages: 21–29
Time of Publication: 2015
Abstract Stoichiometric and sub-stoichiometric lanthanum barium titanates (LBT) of perovskite structure type, substituted or not with Mn and/or Ce at the Ti-site, were prepared by sol–gel route with heat treatment in air. All the compounds display a cubic Pm-3m symmetry, which remains stable in reducing atmosphere. Whereas Mn substitution highly promotes the reducibility of the material, the electrical and electrochemical performance of Mn-doped compounds is decreased with respect to non-doped sub-stoichiometric LBT. In contrast, the electrical conductivity and resistance polarization of Ce-substituted LBT are close to those of non-doped LBT and Ce-substituted LBT appears especially efficient in improving the catalytic properties for methane steam reforming and avoiding carbon formation.
Keywords SOFC; Anode; Perovskite; Barium titanate; Impedance electrochemical spectroscopy; Methane steam reforming
Remark doi:10.1016/j.ssi.2015.11.005
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Molybdenum doped Pr0.5Ba0.5MnO3−δ (Mo-PBMO) double perovskite as a potential solid oxide fuel cell anode material

Authors Yi-Fei Sun, Ya-Qian Zhang, Bin Hua, Yashar Behnamian, Jian Li, Shao-Hua Cui, Jian-Hui Lid, Jing-Li Luo
Source
Journal of Power Sources
Volume: 301, Pages: 237–241
Time of Publication: 2016
Abstract A layered Mo doped Pr0.5Ba0.5MnO3−δ (Mo-PBMO) double perovskite oxide was prepared by a modified sol–gel method and the properties of the fabricated material are characterized by various technologies. The results of X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), NH3-temperature programmed desorption (NH3-TPD), and thermogravimetric analysis (TGA) demonstrate that the treatment in reducing atmosphere at high temperature lead to a significant phase transformation of the material to a single cubic phase as well as with the Mo in multiple oxidized states. Such character leads to the production of large amount of oxygen deficiency with facilitated oxygen diffusion. The electrochemical performance tests of half-cell and single cell SOFCs exhibit the promoted effect of Mo on catalytic activity for the oxidation of H2 and CH4, indicating that Mo-PBMO could serve as an anode material candidate for SOFCs.
Keywords Mo; Pr0.5Ba0.5MnO3−δ; Double perovskite; Anode; SOFC
Remark doi:10.1016/j.jpowsour.2015.09.127
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Experimental and molecular dynamics study of thermo-physical and transport properties of ThO2-5wt.%CeO2 mixed oxides

Authors P.S. Somayajulu, P.S. Ghosh, J. Banerjee, K.L.N.C. Babu, K.M. Danny, B.P. Mandal, T. Mahata, P. Sengupta, S.K. Sali, A. Arya
Source
Journal of Nuclear Materials
Volume: 467, Issue: 2, Pages: 644–659
Time of Publication: 2015
Abstract We have determined the thermo-physical (elastic modulus, specific heat, thermal expansion and thermal conductivity) and transport (ionic conductivity) properties of ThO2-5wt.%CeO2 mixed oxide (MOX) using a combined experimental and theoretical methodology. The specific heat, ionic conductivity and elastic properties of ThO2-5wt.%CeO2 pellets prepared by conventional powder metallurgy (POP) and coated agglomerate pelletization (CAP) routes (sintered in both air and Ar-8%H2 atmosphere) are compared with respect to homogeneity (CeO2 distribution in ThO2 matrix), microstructure, porosity and oxygen to metal ratio. The effects of inhomogeneity and pore distribution on thermal expansion and thermal conductivity of the mixed-oxide pellets are identified. Molecular dynamics (MD) simulations using the Coulomb-Buckingham-Morse-many-body model based interatomic potentials are used to predict elastic properties in the temperature range between 300 and 2000 K and thermodynamic properties, viz., enthalpy increment and specific heats of ThO2. Finally, the thermal expansion coefficient and thermal conductivity of ThO2 and (Th,Ce)O2 mixed-oxides obtained from MD are compared with available experimental results.
Keywords ThO2-5%CeO2 MOX; Specific heat; Ionic conductivity; Temperature dependent elastic properties; Molecular dynamics simulation
Remark doi:10.1016/j.jnucmat.2015.10.053
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Effect of Cerium on the Electrical Properties of a Cobalt Conversion Coating for Solid Oxide Fuel Cell Interconnects – A Study Using Impedance Spectroscopy

Authors Jan Gustav Grolig, Jan Froitzheim, Jan-Erik Svensson
Source
Electrochimica Acta
Volume: 184, Pages: 301–307
Time of Publication: 2015
Abstract Coatings of metallic cobalt, which convert into a cobalt manganese spinel oxide are known to improve the properties of interconnects for solid oxide fuel cells (SOFCs). The addition of cerium to the cobalt coating further improves the corrosion properties of the material. For this study traditional four-point DC measurements at high temperatures were combined with impedance spectroscopy at low temperatures in order to investigate the effect of cerium on the electrical properties of a cobalt conversion coating. It was found that combination-coatings of cerium and cobalt exhibit superior electrical properties compared to pure cobalt coatings. Cerium slows down the growth of chromia and prevents the outward diffusion of iron into the cobalt spinel layer. Both effects are beneficial for the electrical properties of the interconnect. Impedance spectroscopy measurements revealed that even after more than 3000 h of exposure the outer cobalt manganese spinel layer still has a higher electrical conductivity when cerium was present.
Remark doi:10.1016/j.electacta.2015.10.111
Link

Lithium Polymer Electrolytes Based on Sulfonated Poly(ether ether ketone) for Lithium Polymer Batteries

Authors Savitha Thayumanasundaram, Vijay Shankar Rangasamy, Jin Won Seo andJean-Pierre Locquet
Source
European Journal of Inorganic Chemistry
Volume: 2015, Issue: 32, Pages: 5395–5404
Time of Publication: 2015
Abstract We studied a lithium-ion conducting polymer based on sulfonated poly(ether ether ketone) (SPEEK) doped with lithium bis(trifluoromethane)sulfonimide (LiTFSI). Self-standing membranes were prepared by the solvent-casting technique with a LiTFSI loading of 0 to 30 wt.-%. The thermogravimetric analysis curves showed that the SO3H groups decompose earlier in the SPEEK–LiTFSI membranes than in pure SPEEK, owing to interactions between the Li+ ions and the SO3H groups. X-ray diffraction and differential scanning calorimetry studies showed that the addition of LiTFSI decreased the crystallinity and the glass-transition temperature of the polymer, which revealed the plasticizing effect of the lithium salt on the polymer matrix. The 7Li NMR spectroscopy results showed a single central transition line at around δ = –1.2 ppm, which indicated the presence of free mobile lithium ions. Dynamic mechanical analysis of the membrane showed it to be mechanically stable up to 100 °C, a prerequisite for flexible lithium polymer batteries. The highest room-temperature conductivity in the order of 10–5 S cm–1 was observed for the 20 wt.-% LiTFSI-doped SPEEK membrane, which increased to 5 × 10–4 S cm–1 at 100 °C.
Keywords Lithium batteries;Polymer electrolytes;Dynamic mechanical analysis;Raman spectroscopy;Ion pairs
Remark DOI: 10.1002/ejic.201500649
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Exceptional hydrogen permeation of all-ceramic composite robust membranes based on BaCe0.65Zr0.20Y0.15O3−δ and Y- or Gd-doped ceria

Authors Elena Rebollo, Cecilia Mortalň, Sonia Escolástico, Stefano Boldrini, Simona Barison, José M. Serra and Monica Fabrizio
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

The effect of Cu2O nanoparticle dispersion on the thermoelectric properties of n-type skutterudites

Authors M Battabyal, B Priyadarshini, D Sivaprahasam, N S Karthiselva and R Gopalan
Source
Journal of Physics D: Applied Physics
Volume: 48, Issue: 45 Time of Publication: 2015
Abstract We report the thermoelectric properties of Ba0.4Co4Sb12 and Sn0.4Ba0.4Co4Sb12 skutterudites dispersed with Cu2O nanoparticles. The samples were synthesized by ball milling and consolidated by spark plasma sintering. Dispersion of Cu2O is found to significantly influence the electrical resistivity and thermopower at high temperatures with a more pronounced effect on the electrical resistivity due to the energy filtering effect at the interface between Cu2O nanoparticles and a Ba0.4Co4Sb12 and Sn0.4Ba0.4Co4Sb12 matrix. At 573 K, the electrical resistivity of Ba0.4Co4Sb12 decreases from 5.01  ×  10−5 Ωm to 2.98  ×  10−5 Ωm upon dispersion of Cu2O. The dispersion of Cu2O reduces the thermal conductivity of the samples from 300 K and above by increasing the phonon scattering. The lowest observed thermal conductivity at 573 K is found to be 2.001 W mK−1 in Cu2O dispersed Ba0.4Co4Sb12 while it is 2.91 W mK−1 in the Ba0.4Co4Sb12 sample without Cu2O dispersion. Hence Cu2O dispersion plays a significant role in the thermoelectric properties and a maximum figure of merit (ZT ) ~ 0.92 is achieved in Cu2O dispersed Ba0.4Co4Sb12 at 573 K which is more than 200% compared to the pure Ba0.4Co4Sb12 sample. The results from nanoindentation experiments show that the Cu2O dispersed sample (Cu2O  +  Sn0.4Ba0.4Co4Sb11.6) has a higher reduced Youngs modulus (~139 GPa) than the pure Sn0.4Ba0.4Co4Sb11.6 sample (~128 GPa).
Remark Link

Oxygen permeation and creep behavior of Ca1−xSrxTi0.6Fe0.15Mn0.25O3−δ (x=0, 0.5) membrane materials

Authors Jonathan M. Polfus, Wen Xing, Goran Pećanac, Anita Fossdal, Sidsel M. Hanetho, Yngve Larring, Jürgen Malzbender, Marie-Laure Fontaine, Rune Bredesen
Source
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
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