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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 source3m) 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) , b=5.9337(12) , с=10.422(2) , 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) ) 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 Cdric Prillat-Merceroz, Pascal Roussel, Edouard Capoen, Sbastien Rosini, Patrick Glin, Rose-Nolle 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
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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 Mortal, Sonia Escolstico, Stefano Boldrini, Simona Barison, Jos 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
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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, Jrgen 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 3.910−3 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 1.510−2 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
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Comparative study of the electrochemical promotion of CO2 hydrogenation on Ru using Na+, K+, H+ and O2 − conducting solid electrolytes

Authors I. Kalaitzidou, M. Makri, D. Theleritis, A. Katsaounis, C.G. Vayenas
Source
Surface Science
Time of Publication: 2015
Abstract The kinetics and the electrochemical promotion of the hydrogenation of CO2 to CH4 and CO are compared for Ru porous catalyst films deposited on Na+, K+, H+ and O2 − conducting solid electrolyte supports. It is found that in all four cases increasing catalyst potential and work function enhances the methanation rate and selectivity. Also in all four cases the rate is positive order in H2 and exhibits a maximum with respect to CO2. At the same time the reverse water gas shift reaction (RWGS) which occurs in parallel exhibits a maximum with increasing pH2pH2 and is positive order in CO2. Also in all cases the selectivity to CH4 increases with increasing pH2pH2 and decreases with increasing pCO2pCO2. These results provide a lucid demonstration of the rules of chemical and electrochemical promotion which imply that (∂r/∂Φ)(∂r/∂pD) > 0 and (∂r/∂Φ)(∂r/∂pA) < 0, where r denotes a catalytic rate, Φ is the catalyst work function and pD and pA denote the electron donor and electron acceptor reactant partial pressures respectively.
Keywords Effect of Ru catalyst support and potential on product selectivity.
Remark In Press, doi:10.1016/j.susc.2015.09.011
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Electrochemical promotion of the hydrogenation of CO2 on Ru deposited on a BZY proton conductor

Authors I. Kalaitzidou, A. Katsaounis, T. Norby, C.G. Vayenas
Source
Journal of Catalysis
Volume: 331, Pages: 98–109
Time of Publication: 2015
Abstract he kinetics and the electrochemical promotion of the hydrogenation of CO2 on polycrystalline Ru deposited on BZY (BaZr0.85Y0.15O3−α + 1 wt% NiO), a proton conductor in wet atmospheres, with α ≈ 0.075, was investigated at temperatures 300–450 C and atmospheric pressure. Methane and CO were the only detectable products and the selectivity to CH4 could be reversibly controlled between 15% and 65% by varying the catalyst potential by less than 1.2 V. The rate and the selectivity to CH4 are very significantly enhanced by proton removal from the catalyst via electrochemically controlled spillover of atomic H from the catalyst surface to the proton-conducting support. The effect is strongly non-Faradaic and the apparent Faradaic efficiency of methanation takes values up to 500 and depends strongly on the porous Ru catalyst film thickness. The observed strong promotional effect, in conjunction with the observed reaction kinetics, is in good agreement with the rules of electrochemical and chemical promotion.
Keywords Hydrogenation of CO2; CO2 methanation; Ru catalyst; RWGS reaction; BZY proton conducting support; Selectivity modification; Electrochemical promotion of catalysis (EPOC); Non-faradaic electrochemical modification of catalytic activity (NEMCA effect)
Remark doi:10.1016/j.jcat.2015.08.023
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Electrochemical Promotion of Ir0.5Pt0.5O2/YSZ

Authors S. Balomenou, K. M. Papazisi, D. Tsiplakides
Source
Topics in Catalysis
Volume: 58, Issue: 18, Pages: 1270-1275
Time of Publication: 2015
Abstract A high surface area, nanostructured bimetallic oxide catalyst, Ir0.5Pt0.5O2, deposited on YSZ was studied for the electrochemical promotion of ethylene oxidation. The catalyst was synthesized using the modified Adams fusion method and was characterized regarding its structure, morphology and specific surface area via XPS, XRD, HRTEM, SEM and BET. Regarding the performance for electrochemical promotion, it was found that the rate of ethylene oxidation can be enhanced significantly and in a strongly non-faradaic manner via positive potential application, exhibiting strongly electrophobic behaviour.
Keywords Electrochemical promotion, EPOC, Ir0.5Pt0.5O2, Adams fusion method
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Enhanced Carbon Deposition Tolerance of SOFC Anodes Under Triode Operation

Authors Ioanna Petrakopoulou, Dimitrios Tsiplakides, Stella Balomenou
Source
Topics in Catalysis
Volume: 58, Issue: 18, Pages: 1303-1310
Time of Publication: 2015
Abstract The triode fuel cell design and operation concept was applied as an alternative means for controlling and enhancing the carbon tolerance of state-of-the-art solid oxide fuel cell (SOFC) anodes. The triode cell configuration entails the introduction of a third electrode in addition to the anode and cathode, driven by an auxiliary circuit which is run in electrolytic mode. In this way the cell is forced to operate at controlled potential differences that are inaccessible under standard operation, and thus introduces a controllable variable into fuel cell operation. In the present study, the effectiveness of the triode approach was evaluated for the in situ control of the rate of carbon deposition in commercial multilayer NiO–GDC and NiO–YSZ SOFC anodes. The study involved typical and triode operation of SOFC button cells under CH4 steam reforming conditions, and it was found that the application of a small electrolytic current under triode operation resulted in significantly less carbon built-up on the anode compared to the standard SOFC operation.
Keywords SOFC Triode fuel cell operation, Anode degradation, Carbon formation, CH4 steam reforming
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Development of a Coking-Resistant NiSn Anode for the Direct Methane SOFC

Authors N. Bogolowski, B. Iwanschitz and J.-F. Drillet
Source
Fuel Cells
Volume: 15, Issue: 5, Pages: 711–717
Abstract The present work reports on the development of a coking-resistant NiSn-based membrane electrode assembly (MEA) for internal CH4 reforming in solid oxide fuel cells (SOFCs). Catalyst powder was prepared in a centrifugal casting oven by melting stoichiometric amounts of Ni and Sn under vacuum. The formation of Ni3Sn2 intermetallic phase was confirmed by XRD analysis. Catalytic activity for CH4 reforming and stability of the NiSn powder were first evaluated in a quartz glass reactor for 4 h at 600–1,000 C. The main reaction products H2 and CO were detected by gas chromatography while no carbon formation was detected during the experiments. Then, 3YSZ electrolyte-supported MEAs were fabricated with a Ni3Sn2/YSZ anode and LSM/YSZ cathode and characterized under SOFC conditions. The MEA showed an excellent stability under CH4 atmosphere (3% H2O) at 850 C over more than 650 h. No substantial decrease in cell potential was observed during this period.
Keywords Anode Material;Intermetallic Phase;Internal Reforming;Methane;Nickel-Tin Alloy;Ni3Sn2;SOFC;Solid Oxide Fuel Cell
Remark DOI: 10.1002/fuce.201400187
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Hardening in non-stoichiometric (1−x)Bi0.5Na0.5TiO3–xBaTiO3 lead-free piezoelectric ceramics

Authors Sasiporn Prasertpalichat, David P. Cann
Source
Journal of Materials Science
Volume: 51, Issue: 1, Pages: 476-486
Time of Publication: 2016
Abstract The role of A-site non-stoichiometry was investigated in lead-free piezoelectric ceramics based on compositions in the 1 − x(Bi0.5Na0.5TiO3)–xBaTiO3 system near the morphotropic phase boundary, where x = 0.055, 0.06, and 0.07. Donor doping was introduced through the addition of excess Bi, however, there were no changes in the crystal structure. In contrast, acceptor doping was introduced through the addition of excess Na and was found to promote rhombohedral distortions. A significant improvement of dielectric properties was observed in donor-doped compositions and, in contrast, a degradation in properties was observed in acceptor-doped compositions. Compared to the stoichiometric composition, the acceptor-doped compositions displayed a significant increase in coercive field (E c) which is an indication of domain wall pinning as found in hard Pb(Zr x Ti1−x )O3. This result was further confirmed via remanent polarization hysteresis analyses. Moreover, all A-site acceptor-doped compositions also exhibited an increase in mechanical quality factor (Q m) as well as a decrease in piezoelectric coefficient (d 33), dielectric loss (tan δ), remanent polarization (P r), and dielectric permittivity, which are all the typical characteristics of the effects of “hardening.” The mechanism for the observed hardening in A-site acceptor-doped BNT-based systems is linked to changes in the long-range domain structure and defect chemistry.
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Copper Iron Conversion Coating for Solid Oxide Fuel Cell Interconnects

Authors Jan Gustav Grolig, , Patrik Alnegren, Jan Froitzheim, Jan-Erik Svensson
Source
Journal of Power Sources
Volume: 297, Pages: 534–539
Time of Publication: 2015
Abstract A conversion coating of iron and copper was investigated with the purpose of increasing the performance of Sanergy HT as a potential SOFC interconnect material. Samples were exposed to a simulated cathode atmosphere (air, 3 % H2O) for durations of up to 1000 h at 850 C. Their performance in terms of corrosion, chromium evaporation and electrical resistance (ASR) was monitored and compared to uncoated and cobalt-coated Sanergy HT samples. The copper iron coating had no negative effects on corrosion protection and decreased chromium evaporation by about 80%. An Area Specific Resistance (ASR) of 10 mΩcm2 was reached after 1000 h of exposure. Scanning Electron Microscopy revealed well adherent oxide layers comprised of an inner chromia layer and an outer spinel oxide layer.
Keywords Interconnect; Corrosion; Chromium volatilization; Sanergy HT; SOFC; Area specific resistance
Remark doi:10.1016/j.jpowsour.2015.06.139
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Atomic structure and ionic conductivity of glassy materials based on silver sulfide

Authors N. V. Melnikova, K. V. Kurochka, O. L. Kheifets, N. I. Kadyrova, Ya. Yu. Volkova
Source
Volume: 79, Issue: 6, Pages: 719-722
Time of Publication: 2015
Abstract The effect of the composition of glassy ionic conductors AgGe1 + x As1–x S3 and the composites based on these materials containing single-walled carbon nanotubes (CNT) AgGe1+x As1–x (S + CNT)3, on the atomic structure and ionic conductivity is analyzed.
Remark Link

Protons in piezoelectric langatate; La3Ga5.5Ta0.5O14

Authors Tor Svendsen Bjrheim, Vijay Shanmugappirabu, Reidar Haugsrud, Truls E. Norby
Source
Solid State Ionics
Volume: 278, Pages: 275–280
Time of Publication: 2015
Abstract This contribution reports the hydration and electrical transport properties of effectively acceptor doped single crystalline and polycrystalline langatate, La3Ga5.5Ta0.5O14. The electrical properties are investigated over wide ranges of pH2OpH2O, pD2OpD2O and pO2pO2 in the temperature range 400 to 1000 C. Acceptor doped langatate is dominated by oxygen vacancies in dry atmospheres and at high temperatures, and by protonic defects in wet atmospheres and at lower temperatures. The corresponding standard hydration enthalpy and entropy are − 90 5 kJ/mol and − 130 5 J/mol K, respectively. Further, all compositions display pure proton conductivity in wet atmospheres below 700 C with a proton mobility enthalpy in the range of 70–75 kJ/mol, depending on doping level and crystallographic direction. Hence, protons are important for the physiochemical properties of langatate even at 1000 C, and could therefore influence the behavior of langatate-based resonator devices. The proton conductivity is slightly anisotropic, being higher in the X- and Y- than in the Z-direction. At high temperatures and under dry conditions, electron holes and oxide ions dominate the conductivity, and the enthalpy of mobility of vacancies is 140 5 kJ/mol.
Keywords Langatate; Piezoelectric; Defects; Protons; Conductivity
Remark doi:10.1016/j.ssi.2015.06.024
Link

Tetragonal tungsten bronzes Nb8−xW9+xO47−δ: optimization strategies and transport properties of a new n-type thermoelectric oxide

Authors Christophe P. Heinrich, Matthias Schrade, Giacomo Cerretti, Ingo Lieberwirth, Patrick Leidich, Andreas Schmitz, Harald Fjeld, Eckhard Mueller, Terje G. Finstad, Truls Norby and Wolfgang Tremel
Source
Materials Horizons
Issue: 5, Pages: 519-527
Time of Publication: 2015
Abstract Engineering of nanoscaled structures may help controlling the electrical and thermal transport in solids, in particular for thermoelectric applications that require the combination of low thermal conductivity and low electrical resistivity. The tetragonal tungsten bronzes Nb8−xW9+xO47 (TTB) allow a continuous variation of the charge carrier concentration while fulfilling at the same time the concept of a “phonon-glass electron-crystal” through a layered nanostructure defined by intrinsic crystallographic shear planes. The thermoelectric properties of the tetragonal tungsten bronzes Nb8−xW9+xO47−δ (0 < x < 2) were studied in the temperature range from 373 to 973 K. Structural defects and the thermal stability under various oxygen partial pressure pO2 were investigated by means of thermogravimetry, HR-TEM, and XRD. Nb8W9O47−δ was found stable at 973 K and a pO2 of ≈10−15 atm. The oxygen nonstoichiometry δ can reach up to 0.3, depending on the applied atmosphere. By increasing the substitution level x, the electrical resistivity ρ and the Seebeck coefficient S decreased. For x = 2, ρ reached 20 mΩ cm at 973 K, combined with a Seebeck coefficient of approximately −120 μV K−1. The thermal conductivity was low for all samples, ranging from 1.6 to 2.0 W K−1 m−1, attributed to the complex crystal structure. The best thermoelectric figure of merit zT of the investigated samples was 0.043, obtained for x = 2 at 973 K, but it is expected to increase significantly upon a further increase of x. The control of the oxygen non-stoichiometry δ opens a second independent optimization strategy for tetragonal tungsten bronzes.
Remark DOI: 10.1039/C5MH00033E
Link

EuBaCo2O5+δ-Ce0.9Gd0.1O2−δ composite cathodes for intermediate-temperature solid oxide fuel cells: high electrochemical performance and oxygen reduction kinetics

Authors Zhan Shi, Tian Xia, Fuchang Meng, Jingping Wang, Shengming Wu, Jie Lian, Hui Zhao, Chunbo Xu
Source
Electrochimica Acta
Volume: 174, Pages: 608–614
Time of Publication: 2015
Abstract The characteristics and electrochemical performance of double perovskite EuBaCo2O5+δ (EBCO) have been investigated as a composite cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The thermal expansion coefficients can be effectively reduced in the case of EBCO-Ce0.9Gd0.1O2−δ (CGO) composite cathodes. No chemical reactions between EBCO cathode and CGO electrolyte are observed after sintering at 1000 C for 24 h. The maximum electrical conductivities of EBCO-CGO materials reach 28-77 S cm−1 with the change of CGO weight ratio from 40 wt. % to 5 wt. %. Among all these components, the EBCO-10 wt. % CGO (EBCO-10CGO) composite cathode gives the lowest area-specific resistance of 0.055 and 0.26 Ω cm2 in air at 700 and 600 C, respectively. The maximum power density of Ni-CGO anode-supported single cell consisted of the EBCO-10CGO composite cathode and CGO electrolyte achieves 0.81 W cm−2 at 700 C. These results indicate that the EBCO-10CGO composite materials can be used as a promising cathode candidate for IT-SOFCs. Furthermore, the rate-limiting steps for the oxygen reduction reaction at the EBCO-10CGO composite cathode interface are determined to be the charge transfer and dissociation of adsorbed molecule oxygen processes.
Keywords Intermediate-temperature solid oxide fuel cells; cathode materials; electrochemical performance; oxygen reduction kinetics
Remark doi:10.1016/j.electacta.2015.06.059
Link

Multilayer ceramic capacitors based on relaxor BaTiO3-Bi(Zn1/2Ti1/2)O3 for temperature stable and high energy density capacitor applications

Authors Nitish Kumar, Aleksey Ionin, Troy Ansell, Seongtae Kwon, Wesley Hackenberger and David Cann
Source
Applied Physics Letters
Volume: 106, Pages: 252901
Time of Publication: 2015
Abstract The need for miniaturization without compromising cost and performance continues to motivate research in advanced capacitor devices. In this report, multilayerceramiccapacitors based on relaxor BaTiO3-Bi(Zn1/2Ti1/2)O3 (BT-BZT) were fabricated and characterized. In bulk ceramic embodiments, BT-BZT has been shown to exhibit relative permittivities greater than 1000, high resistivities (ρ > 1 GΩ-cm at 300 C), and negligible saturation up to fields as high as 150 kV/cm. Multilayercapacitor embodiments were fabricated and found to exhibit similar dielectric and resistivity properties. The energy density for the multilayerceramics reached values of ∼2.8 J/cm3 at room temperature at an applied electric field of ∼330 kV/cm. This represents a significant improvement compared to commercially available multilayercapacitors. The dielectric properties were also found to be stable over a wide range of temperatures with a temperature coefficient of approximately −2000 ppm/K measured from 50 to 350 C, an important criteria for high temperature applications. Finally, the compatibility of inexpensive Ag-Pd electrodes with these ceramics was also demonstrated, which can have implications on minimizing the device cost.
Remark http://dx.doi.org/10.1063/1.4922947
Link
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