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Effect of Firing Temperature on the Kinetics of Oxygen Reduction in La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) Cathodes for Solid Oxide Fuel Cells

Author Brage Braathen Kjeldby
Source
dissertation
Time of Publication: 2015
Remark Norwegian University of Science and Technology, Department of Materials Science and Engineering
Link

DC-bias dependent impedance spectroscopy of BaTiO3–Bi(Zn1/2Ti1/2)O3 ceramics

Authors Nitish Kumar, Eric A. Patterson, Till Frömling and David P. Cann
Source
J. Mater. Chem. C
Volume: 4, Pages: 1782-1786
Time of Publication: 2016
Remark DOI: 10.1039/C5TC04247J
Link

Surface Protonics Promotes Catalysis

Authors R. Manabe, S. Okada, R. Inagaki, K. Oshima, S. Ogo & Y. Sekine
Source
Nature Scientific Reports 6
Time of Publication: 2016
Abstract Catalytic steam reforming of methane for hydrogen production proceeds even at 473 K over 1 wt% Pd/CeO2 catalyst in an electric field, thanks to the surface protonics. Kinetic analyses demonstrated the synergetic effect between catalytic reaction and electric field, revealing strengthened water pressure dependence of the reaction rate when applying an electric field, with one-third the apparent activation energy at the lower reaction temperature range. Operando–IR measurements revealed that proton conduction via adsorbed water on the catalyst surface occurred during electric field application. Methane was activated by proton collision at the Pd–CeO2 interface, based on the inverse kinetic isotope effect. Proton conduction on the catalyst surface plays an important role in methane activation at low temperature. This report is the first describing promotion of the catalytic reaction by surface protonics.
Remark doi:10.1038/srep38007
Link

Structural- and Compositional Investigations of Grain Boundaries in Y-Doped BaZrO3 A proton-conducting electrolyte for electrochemical applications

Author Adrian Lervik
Source
Master’s Thesis
Time of Publication: 2016
Remark University of Oslo
Link

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
Volume: 646, Pages: 194-203
Time of Publication: 2016
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 and is positive order in CO2. Also in all cases the selectivity to CH4 increases with increasing and decreases with increasing . 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 Electrochemical promotion of catalysis, Ion conducting support, Hydrogenation of CO2, Ruthenium catalyst, Rules of promotion, Metal–support interactions
Remark https://doi.org/10.1016/j.susc.2015.09.011
Link

Defect mechanisms in BaTiO3-BiMO3 ceramics

Authors Nitish Kumar, Eric A. Patterson, Till Frömling, Edward P. Gorzkowski, Peter Eschbach, Ian Love, Michael P. Müller, Roger A. De Souza, Julie Tucker, Steven R. Reese and David P. Cann
Source
Journal of the American Ceramic Society
Time of Publication: 2018
Abstract Often, addition of BiMO3 to BaTiO3 (BT) leads to improvement in resistivity with a simultaneous shift to n-type conduction from p-type for BT. In considering one specific BiMO3 composition, that is, Bi(Zn1/2Ti1/2)O3 (BZT), several prospective candidates for the origin of this n-type behavior in BT-BZT were studied—loss of volatile cations, oxygen vacancies, bismuth present in multiple valence states and precipitation of secondary phases. Combined x-ray and neutron diffraction, prompt gamma neutron activation analysis and electron energy loss spectroscopy suggested much higher oxygen vacancy concentration in BT-BZT ceramics (>4%) as compared to BT alone. X-ray photoelectron spectroscopy and x-ray absorption spectroscopy did not suggest the presence of bismuth in multiple valence states. At the same time, using transmission electron microscopy, some minor secondary phases were observed, whose compositions were such that they could result in effective donor doping in BT-BZT ceramics. Using experimentally determined thermodynamic parameters for BT and slopes of Kröger-Vink plots, it has been suggested that an ionic compensation mechanism is prevalent in these ceramics instead of electronic compensation. These ionic defects have an effect of shifting the conductivity minimum in the Kröger-Vink plots to higher oxygen partial pressure values in BT-BZT ceramics as compared to BT, resulting in a significantly higher resistivity values in air atmosphere and n-type behavior. This provides an important tool to tailor transport properties and defects in BT-BiMO3 ceramics, to make them better suited for dielectric or other applications.
Remark DOI: 10.1111/jace.15403, Version of Record online: 8 JAN 2018
Link

The Effect of Ni Doping on the Performance and Electronic Structure of LSCF Cathodes Used for IT-SOFCs

Authors Alessandro Longo, Leonarda F. Liotta, Dipanjan Banerjee, Valeria La Parola, Fabrizio Puleo, Chiara Cavallari, Christoph J. Sahle, Marco Moretti Sala, and Antonino Martorana
Source
J. Phys. Chem.: C
Time of Publication: 2017
Abstract We investigated the effect of nickel doping on the electronic structure and performance of nanostructured La0.6Sr0.4Co0.2Fe0.8–0.03Ni0.03O3−δ prepared by the one-pot sol–gel method. The commercial undoped La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF0.8) was used as reference. Moreover, for comparison, Ni (3 mol %) was deposited by wetness impregnation over the La0.6Sr0.4Co0.2Fe0.8O3−δ. We show by in situ X-ray absorption spectroscopy at 900 °C under air flow that nickel enters the B perovskite site of the material and favors the stabilization of the cobalt oxidation state, as evidenced by the delay in the decrease of the average Co valence with respect to undoped samples. Our results are further supported by in situ X-ray Raman spectroscopy (XRS) that allowed us to monitor the temperature evolution of the O K-edge. XRS evidences that nickel-doped LSCF shows unmodified O2p-TM3d density of states, which proves that the Co oxidation state is preserved. Electrochemical impedance spectroscopy measurements were carried out over half-cell systems consisting of LSCF-based materials deposited onto a Ce0.8Gd0.2O2−δ electrolyte. The improvement of the electrochemical performances of the Ni-doped La0.6Sr0.4Co0.2Fe0.8–0.03Ni0.03O3−δ sample with respect to a reference Ni-impregnated LSCF is attributed to the stabilization of the TM-O6 structural units, which were recently proposed as the functional units for oxygen reduction.
Remark DOI: 10.1021/acs.jpcc.7b07626
Link

Protonic Conductors for Intermediate Temperature Fuel Cell Electrolytes: Superprotonic CsH2PO4 Stabilization and in-Doped SnP2O7 Structure Study

Author Heber Jair Martinez Salinas
Source
Dissertation
Time of Publication: 2017
Remark The University of Texas at El Paso
Link

Optimisation of growth parameters to obtain epitaxial Y-doped BaZrO3 proton conducting thin films

Authors A. Magrasó, B. Ballesteros, R. Rodríguez-Lamas, M.F. Sunding, J. Santiso
Source
Volume: 314, Pages: 9–16
Time of Publication: 2018
Abstract We hereby report developments on the fabrication and characterization of epitaxial thin films of proton conducting Y-doped BaZrO3 (BZY) by pulsed laser deposition (PLD) on different single crystal substrates (MgO, GdScO3, SrTiO3, NdGaO3, LaAlO3 and sapphire) using Ni-free and 1% Ni-containing targets. Pure, high crystal quality epitaxial films of BZY are obtained on MgO and on perovskite-type substrates, despite the large lattice mismatch. The deposition conditions influence the morphology, cell parameters and chemical composition of the film, the oxygen partial pressure during film growth being the most determining. Film characterization was carried out using X-ray diffraction, transmission electron and atomic force microscopies, wavelength dispersive X-ray spectroscopy and angle-resolved X-ray photoelectron spectroscopy. All films show a slight tetragonal distortion that is not directly related to the substrate-induced strain. The proton conductivity of the films depends on deposition conditions and film thickness, and for the optimised conditions its total conductivity is slightly higher than the bulk conductivity of the target material (3 mS/cm at 600 °C, in wet 5% H2/Ar). The conductivities are, however, more than one order of magnitude lower than the highest reported in literature and possible reasoning is elucidated in terms of local and extended defects in the films.
Keywords BaZrO3; Thin film; Electrolyte; Proton conductivity; SOFC; PC-SOFC
Remark https://doi.org/10.1016/j.ssi.2017.11.002
Link

Improvement of thermoelectric properties of lanthanum cobaltate by Sr and Mn co-substitution

Authors Ashutosh Kumar, D. Sivaprahsam, Ajay D. Thakur
Source
Journal of Alloys and Compounds
Volume: 735, Pages: 1787–1791
Time of Publication: 2018
Abstract We report thermoelectric (TE) properties of Sr and Mn co-substituted LaCoO3 system from room temperature to 700 K. Sr-substitutions at La and Mn at Co site in LaCoO3 improves the electrical conductivity (σ). Thermal conductivity (κ) of all the samples increases with the increase in temperature but decreases with the substitution in LaCoO3. An estimation of the electronic thermal conductivity (κe) suggests a dominant phonon contribution to thermal conductivity in this system. A maximum value of the figure of merit is 0.14 at 480 K for La0.95Sr0.05Co0.95Mn0.05O3.
Keywords Powders: solid-state reaction; Thermal conductivity; Electrical conductivity; Perovskites
Remark https://doi.org/10.1016/j.jallcom.2017.11.334
Link

Microstructural engineering and use of efficient poison resistant Au-doped Ni-GDC ultrathin anodes in methane-fed solid oxide fuel cells

Authors F.J. Garcia-Garciaa, F. Yubero, A.R. González-Elipe, R.M. Lambert
Source
International Journal of Hydrogen Energy
Volume: 43, Issue: 2, Pages: 885–893
Time of Publication: 2018
Abstract Ultrathin porous solid oxide fuel cell (SOFC) anodes consisting of nickel-gadolinia-doped-ceria (Ni-GDC) cermets with a unique porous micro-columnar architecture with intimate contact between the GDC and the Ni phases were made by magnetron sputtering at an oblique deposition angle and characterised in detail by a variety of methods prior to use in hydrogen or methane-fuelled SOFCs. These Ni-GDC anodes exhibited excellent transport properties, were robust under thermal cycling and resistant to delamination from the underlying yttria-stabilised zirconia electrolyte. Similarly prepared Au-doped Ni-GDC anodes exhibited the same morphology, porosity and durability. The gold associated exclusively with the Ni component in which it was present as a surface alloy. Strikingly, whatever their treatment, a substantial amount of Ce3+ persisted in the anodes, even after operation at 800 °C under fuel cell conditions. With hydrogen as fuel, the un-doped and Au-doped Ni-GDC anodes exhibited identical electrochemical performances, comparable to that of much thicker commercial state-of-the-art Ni-GDC anodes. However, under steam reforming conditions with CH4/H2O mixtures the behaviour of the Au-doped Ni-GDC anodes were far superior, exhibiting retention of good power density and dramatically improved resistance to deactivation by carbon deposition. Thus two distinct beneficial effects contributed to overall performance: persistence of Ce3+ in the working anodes could induce a strong metal-support interaction with Ni that enhanced the catalytic oxidation of methane, while formation of a Nisingle bondAu surface alloy that inhibited carbonisation and poisoning of the active nickel surface.
Keywords SOFC; Ultrathin film anodes; Magnetron sputtering; Gadolinia doped ceria; Carbon-tolerant; Gold doping
Remark https://doi.org/10.1016/j.ijhydene.2017.11.020
Link

Electrical properties of polycrystalline materials from the system Cu-As-Ge-Se under high pressure condition

Authors V E Zaikova, N V Melnikova, A V Tebenkov , A A Mirzorakhimov, O P Shchetnikov, A N Babush kin and G V Sukhanova
Source
Journal of Physics: Conference Series
Volume: 917 Time of Publication: 2017
Abstract The paper deals with electrical properties of polycrystalline materials (GeSe)x(CuAsSe2)1-x(x= 0.5 and 0.7) under high pressure (up to 45 GPa) conditions. The phenomenon of negative magnetoresistance was observed for studied materials.
Remark doi :10.1088/1742-6596/917/8/082009
Link

Asymmetric tubular CaTi0.6Fe0.15Mn0.25O3-δ membranes: Membrane architecture and long-term stability

Authors Wen Xing, Marie-Laure Fontaine, Zuoan Li, Jonathan M. Polfus, Yngve Larring, Christelle Denonville, Emmanuel Nonnet, Adam Stevenson, Partow P. Henriksen, Rune Bredesen
Source
Journal of Membrane Science
Volume: 548, Pages: 372-379
Time of Publication: 2018
Abstract Three architectures of asymmetric tubular oxygen transport membranes (OTM) based on CaTi0.6Fe0.15Mn0.25O3-δ were fabricated with various thicknesses of the tubular porous supports and the dense membrane layers. This was achieved by a two-step firing method combining water based extrusion and dip-coating. The oxygen flux of the tubular membranes was characterized as a function of temperature and oxygen partial pressure on both feed and sweep sides for the different architectures. The flux exhibits different functional dependencies with respect to the oxygen partial pressure gradient and the membrane architecture. Numerical simulations using a Dusty-gas model were conducted to evaluate the effect of the porous support microstructure and thickness on oxygen partial pressure gradient inside the porous media. Results from this work were used to establish dependency of the flux with respect to bulk transport properties of the material, surface kinetics and architecture of the porous support. Furthermore, long-term stability of the produced tubular asymmetric membrane operated in CO2-containing atmospheres was assessed over half a year. The membrane exhibited a stable oxygen flux without showing significant flux degradation.
Keywords OTM, Asymmetric tubular membrane, Oxygen flux, CaTiO3, Long-term stability
Remark https://doi.org/10.1016/j.memsci.2017.11.042
Link

Three-dimensional printed yttria-stabilized zirconia self-supported electrolytes for solid oxide fuel cell applications

Authors S.Masciandaro, M. Torrell, P. Leone, A. Tarancón
Source
Journal of the European Ceramic Society
Time of Publication: 2017
Abstract Additive manufacturing represents a revolution due to its unique capabilities for freeform fabrication of near net shapes with strong reduction of waste material and capital cost. These unfair advantages are especially relevant for expensive and energy-demanding manufacturing processes of advanced ceramics such as Yttria-stabilized Zirconia, the state-of-the-art electrolyte in Solid Oxide Fuel Cell applications. In this study, self-supported electrolytes of yttria-stabilized zirconia have been printed by using a stereolithography three-dimensional printer. Printed electrolytes and complete cells fabricated with cathode and anode layers of lanthanum strontium manganite- and nickel oxide-yttria-stabilized zirconia composites, respectively, were electrochemical characterized showing full functionality. In addition, more complex configurations of the electrolyte have been printed yielding an increase of the performance entirely based on geometrical aspects. Complementary, a numerical model has been developed and validated as predictive tool for designing more advanced configurations that will enable highly performing and fully customized devices in the next future.
Keywords Solid oxide fuel cell, 3D printing, Stereolithography, Yttria-stabilized zirconia, Electrolyte
Remark Available online 15 November 2017, https://doi.org/10.1016/j.jeurceramsoc.2017.11.033
Link

Characteristics of LaCo0.4Ni0.6-xCuxO3-δ ceramics as a cathode material for intermediate-temperature solid oxide fuel cells

Authors Yi-XinLiu, Sea-Fue Wang,Yung-Fu Hsu, Hung-Wei Kai, Piotr Jasinski
Source
Journal of the European Ceramic Society
Time of Publication: 2017
Abstract In this study, the effects of Cu-ion substitution on the densification, microstructure, and physical properties of LaCo0.4Ni0.6-xCuxO3-δ ceramics were investigated. The results indicate that doping with Cu ions not only enhances the densification but also promotes the grain growth of LaCo0.4Ni0.6-xCuxO3-δ ceramics. The Cu substitution at x ≤ 0.2 can suppress the formation of La4Ni3O10, while the excess Cu triggers the formation of La2CuO4.032 phase. The p-type conduction of LaCo0.4Ni0.6O3-δ ceramic was significantly raised by Cu substitution because the acceptor doping () triggered the formation of hole carriers; this effect was maximized in the case of LaCo0.4Ni0.4Cu0.2O3-δ composition (1480 S cm−1 at 500 °C). Thermogravimetric data revealed a slight weight increase of 0.29% for LaCo0.4Ni0.4Cu0.2O3-δ compact up to 871 °C; this is due to the incorporation of oxygen that creates metal vacancies and additional carriers, partially compensating the conductivity loss due to the spin-disorder scattering. As the temperature of the LaCo0.4Ni0.4Cu0.2O3-δ compacts rose above 871 °C, significant weight loss with temperature was observed because of the release of lattice oxygen to the ambient air as a result of Co (IV) thermal reduction accompanied by the formation of oxygen vacancies. A solid oxide fuel cell (SOFC) single cell with Sm0.2Ce0.8O2-δ (electrolyte) and LaCo0.4Ni0.4Cu0.2O3-δ (cathode) was built and characterized. The Ohmic (0.256 Ω cm2) and polarization (0.434 Ω cm2) resistances of the single cell at 700 °C were determined; and the maximum power density was 0.535 W cm−2. These results show that LaCo0.4Ni0.4Cu0.2O3-δ is a very promising cathode material for SOFC applications.
Keywords Solid oxide fuel cells, Cell performance, Impedance Cathode
Remark Available online 8 November 2017, https://doi.org/10.1016/j.jeurceramsoc.2017.11.019
Link

Influence of processing on stability, microstructure and thermoelectric properties of Ca3Co4 − xO9 + δ

Authors Nikola Kanasac Sathy, Prakash Singh, Magnus Rotan, Mohsin Saleemi, Michael Bittner, Armin Feldhoff, Truls Norby, Kjell Wiika, Tor Grande, Mari-Ann Einarsrud
Source
Journal of the European Ceramic Society
Time of Publication: 2017
Abstract Due to high figure of merit, Ca3Co4 − xO9 + δ (CCO) has potential as p-type material for high-temperature thermoelectrics. Here, the influence of processing including solid state sintering, spark plasma sintering and post-calcination on stability, microstructure and thermoelectric properties is reported. By a new post-calcination approach, single-phase materials were obtained from precursors to final dense ceramics in one step. The highest zT of 0.11 was recorded at 800 °C for CCO with 98 and 72% relative densities. In situ high-temperature X-ray diffraction in air and oxygen revealed a higher stability of CCO in oxygen (∼970 °C) than in air (∼930 °C), with formation of Ca3Co2O6 which also showed high stability in oxygen, even at 1125 °C. Since achievement of phase pure high density CCO by post-calcination method in air is challenging, the phase stability of CCO in oxygen is important for understanding and further improvement of the method.
Keywords Ca3Co4 − xO9 + δ, Post calcination, Phase stability, Microstructure, Thermoelectric performance
Remark Available online 6 November 2017, https://doi.org/10.1016/j.jeurceramsoc.2017.11.011
Link

Analysis of potential materials for single component fuel cells

Authors Monica Lin, Ashgar Imran, and Peter Lund
Source
FUNCTIONAL NANOSTRUCTURES PROCEEDINGS
Time of Publication: 2017
Abstract The following paper summarizes the results of systematic analysis on single component fuel cell. This recent technology in the solid oxide fuel cell field consists of a unique layer in place of the conventional three-layers structure. The single layer is a mixture of ionic and semi-conductor material. Surprisingly, the expected short circuit has not shown up. On the contrary, the performance is even higher, as reported in literature [1]. This work aims to compare different combinations of materials in terms of performance. La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF), LiNi0.8Co0.15Al0.05O2 (NCAL), La0.8Sr0.2CoO3(LSC), LiNiZn oxide (LNZ) and a new kind of material, CuFe2O4 are analysed as semi-conductor material. As ionic conductor, CeO2/Gd (GDC) is mainly tilised. Also, CeO2/Sm (SDC) and CeO2/Sm/Ca SCDC are considered too.
Remark Link

Thermoelectrochemical Heat Converter

Source
Time of Publication: 2017
Abstract A direct thermoelectrochemical heat-to-electricity converter includes two electrochemical cells at hot and cold temperatures, each having a gas-impermeable, electron-blocking membrane capable of transporting an ion I, and a pair of electrodes on opposite sides of the membrane. Two closed-circuit chambers A and B each includes a working fluid, a pump, and a counter-flow heat exchanger. The chambers are connected to opposite sides of the electrochemical cells and carry their respective working fluids between the two cells. The working fluids are each capable of undergoing a reversible redox half-reaction of the general form R→O+I+e−, where R is a reduced form of an active species in a working fluid and O is the oxidized forms of the active species. One of the first pair of electrodes is electrically connected to one the second pair of electrodes via an electrical load to produce electricity. The device thereby operates such that the first electrochemical cell runs a forward redox reaction, gaining entropy, and the second electrochemical cell runs a reverse redox reaction, expelling entropy.
Remark United States Patent Application 20170288253
Link

High-temperature properties of (La,Ca)(Fe,Mg,Mo)O3-δ perovskites as prospective electrode materials for symmetrical SOFC

Authors S.Ya.Istomin, A.V.Morozov, M.M.Abdullayev, M.BatukbJ.Hadermann, S.M.Kazakov, A.V.Sobolev, I.A.Presniakov, E.V.Antipov
Source
Journal of Solid State Chemistry
Volume: 258, Pages: 1-10
Time of Publication: 2018
Abstract La1−yCayFe0.5+x(Mg,Mo)0.5−xO3-δ oxides with the orthorhombic GdFeO3-type perovskite structure have been synthesized at 1573 K. Transmission electron microscopy study for selected samples shows the coexistence of domains of perovskite phases with ordered and disordered B-cations. Mössbauer spectroscopy studies performed at 300 K and 573 K show that while compositions with low Ca-content (La0.55Ca0.45Fe0.5Mg0.2625Mo0.2375O3-δ and La0.5Ca0.5Fe0.6Mg0.175Mo0.225O3-δ) are nearly oxygen stoichiometric, La0.2Ca0.8Fe0.5Mg0.2625Mo0.2375O3-δ is oxygen deficient with δ ≈ 0.15. Oxides are stable in reducing atmosphere (Ar/H2, 8%) at 1173 K for 12 h. No additional phases have been observed at XRPD patterns of all studied perovskites and Ce1−xGdxO2−x/2 electrolyte mixtures treated at 1173–1373K, while Fe-rich compositions (x≥0.1) react with Zr1−xYxO2−x/2 electrolyte above 1273 K. Dilatometry studies reveal that all samples show rather low thermal expansion coefficients (TECs) in air of 11.4–12.7 ppm K−1. In reducing atmosphere their TECs were found to increase up to 12.1–15.4 ppm K−1 due to chemical expansion effect. High-temperature electrical conductivity measurements in air and Ar/H2 atmosphere show that the highest conductivity is observed for Fe- and Ca-rich compositions. Moderate values of electrical conductivity and TEC together with stability towards chemical interaction with typical SOFC electrolytes make novel Fe-containing perovskites promising electrode materials for symmetrical solid oxide fuel cell.
Keywords Symmetrical solid oxide fuel cell, Perovskites, Crystal structure, High-temperature electrical conductivity
Remark https://doi.org/10.1016/j.jssc.2017.10.005
Link

New Solid Electrolyte Na9Al(MoO4)6: Structure and Na+ Ion Conductivity

Authors Aleksandra A. Savina, Vladimir A. Morozov, Anton L. Buzlukov, Irina Yu. Arapova, Sergey Yu. Stefanovich, Yana V. Baklanova, Tatiana A. Denisova, Nadezhda I. Medvedeva, Michel Bardet, Joke Hadermann, Bogdan I. Lazoryak, and
Source
Chem. Mater.
Volume: 29, Issue: 20, Pages: 8901–8913
Time of Publication: 2017
Abstract Solid electrolytes are important materials with a wide range of technological applications. This work reports the crystal structure and electrical properties of a new solid electrolyte Na9Al(MoO4)6. The monoclinic Na9Al(MoO4)6 consists of isolated polyhedral [Al(MoO4)6]9– clusters composed of a central AlO6 octahedron sharing vertices with six MoO4 tetrahedra to form a three-dimensional framework. The AlO6 octahedron also shares edges with one Na1O6 octahedron and two Na2O6 octahedra. Na3–Na5 atoms are located in the framework cavities. The structure is related to that of sodium ion conductor II-Na3Fe2(AsO4)3. High-temperature conductivity measurements revealed that the conductivity (σ) of Na9Al(MoO4)6 at 803 K equals 1.63 × 10–2 S cm–1. The temperature behavior of the 23Na and 27Al nuclear magnetic resonance spectra and the spin-lattice relaxation rates of the 23Na nuclei indicate the presence of fast Na+ ion diffusion in the studied compound. At T<490 K, diffusion occurs by means of Na+ ion jumps exclusively through the sublattice of Na3–Na5 positions, whereas Na1 and Na2 become involved in the diffusion processes (through chemical exchange with the Na3–Na5 sublattice) only at higher temperatures.
Remark DOI: 10.1021/acs.chemmater.7b03989
Link

Alkali and Alkaline Earth Oxoacid Salts; Synthesis, Hydration, Stability, and Electrical Conductivity

Author AA Elstad
Source
Time of Publication: 2017
Abstract Proton-conducting electrolytes are sough after for use in various applications within the field of electrochemistry. Pure and high proton conductivity has been found in many perovskite-type oxides like BaZrO3 (BZY) and BaCeO3, with BaCeO3-based materials being among the best proton-conducting oxides. In the intermediate temperature range of 400 to 800 C, BZY has been established as one of the most promising materials, exhibiting a protonic conductivity higher than 1  10􀀀2 S cm􀀀1 over the whole temperature range. However, it is difficult to process, and the resulting materials are usually grainy and possess highly resistive grain-boundaries [1]. For low-temperature regions, compounds like CsHSO4 and CsH2PO4 show great potential with respect to protonic conductivity, even displaying superprotonic transitions that immensely increase their conductivity, however their stability is lacking with respect to temperature and solubility in water [2]. With this project, the aim is to broaden the horizon and investigate compounds that fall outside the common perovskite-definition. In this work, various solid acids (E.g. KBaPO4, NaCaHSiO4 and BaH2SiO4), in which the cations are alkali and alkaline earth metals and the anionic groups are separated XO4 tetrahedra, are synthesized and subsequently characterized by X-Ray Diffraction (XRD), Thermogravimetric Analysis (TG), as well as electrical characterization by Impedance Spectroscopy (IS). The work on KBaPO4 culminated in a submitted paper [3]. KBaPO4 has been proposed to transform into a great protonic conductor upon hydration at low temperatures. Effectively, hydration through steam at 80 C is said to give the compound a protonic conductivity of 1  10􀀀2 S cm􀀀1 just below 100 C [4]. This is a remarkable result and, if it can be reproduced, it can become a viable rival to BZY. For this reason, KBaPO4 was chosen as a topic for this work. Here, we synthesize KBaPO4 through a high-temperature solid state reaction, and subsequently characterize the system with respect to thermal stability and its inherent electrical conductivity. Through electrical measurements, we found that the conductivity of pure KBaPO4 was very low, around 2  10􀀀6 S cm􀀀1 at 600 C, with an activation energy exceeding 1 eV. The compound is indifferent to the presence of humidity, and results indicate that the charge carrier in the compound is not protonic, but rather it is theorized to be potassium ions, with potassium Frenkel defects being the predominating defect, however this has not been explicitly confirmed. All in all, we propose a defect model for KBaPO4 with Frenkel defects as the predominating defects. Through attempts at hydrating KBaPO4 in accordance to the method proposed by Goodenough, we found that it does not transform into a high-conductivity phase, but rather decomposes into potassium doped Ba3(PO4)2, and that the resulting system shows similar properties, such as thermal stability (Decomposing at 300 C) and protonic conductivity (1:6  10􀀀6 S cm􀀀1 at 250 C), to the system Ba3-xKxHx(PO4)2 previously investigated by Haile et al. [5], albeit with a significantly lower potassium content than the systems they have characterized, possibly indicating that a saturation of K in Ba3(PO4)2 has been reached. By subsequently heating Ba3-xKxHx(PO4)2 to high temperatures, the system is found to expel potassium and form a two-phase system of Ba3(PO4)2 and a secondary phase of KBaPO4, showing similarities to the system Ba3(1-x)K3x(PO4)2-x previously investigated by Iwahara et al. [6]. Through impedance spectroscopy of said system, we found evidence that points toward the system being a protonic conductor, with a bulk conductivity slightly higher than 1  10􀀀3 S cm􀀀1 at 600 C, and an activation energy of around 0:67 eV. This is one order of magnitude higher than the one previously reported by Iwahara et al., and only one order of magnitude lower than that of BaZrO3. Parallelly, NaCaHSiO4 and related compounds ABHXO4 (A􀀀􀀀 Li, Na or K. B􀀀􀀀 Ca, Sr or Ba. X􀀀􀀀 Si, Ge or Sn) were synthesized hydrothermally and subsequently characterized. Electrical characterization of NaCaHSiO4 gave low conductivities, although protonic, of 1:8  10􀀀8 S cm􀀀1 at 250 C, with an activation energy of 0:9 eV. Based on the results, we propose a defect model in which interstitial hydroxide ions and interstitial protons str significant defects in the compound. However, although NaCaHSiO4 could be successfully synthesized and subsequently characterized, the other syntheses did not yield the desired results. In fact, the only synthesis that yielded a pure product was that which gave Sr2SiO4, possibly providing a hydrothermal approach to synthesizing a compound previously produced by a hightemperature solid state reaction. Lastly, the compound BaH2SiO4 was synthesized, according to a hydrothermal route, and characterized with respect to thermal stability and electrical conductivity. It was found to exhibit a conductivity of 2:5  10􀀀8 S cm􀀀1 at 200 C with an activation energy of 0:88 eV, comparable to that of NaCaHSiO4. Due to BaH2SiO4 showing similar response to various atmospheres as NaCaHSiO4, a defect model containing hydroxide and hydrogen interstitials is proposed for BaH2SiO4 as well. Compared to earlier reports, a discrepancy was found in that the BaH2SiO4 decomposes prior to temperature regions in which data on electrical conductivity has been previously reported. Another, separate investigation into BaH2SiO4 is therefore recommended.
Remark Thesis for the degree of ’Master of Science’, Depertment of Chemistry, University of Oslo
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Defect chemistry and electrical properties of BiFeO3

Authors Matthias Schrade, Nahum Masó, Antonio Perejón, Luis A. Pérez-Maqueda and Anthony R. West
Source
Journal of Materials Chemistry C
Issue: 38 Time of Publication: 2017
Abstract BiFeO3 attracts considerable attention for its rich functional properties, including room temperature coexistence of magnetic order and ferroelectricity and more recently, the discovery of conduction pathways along ferroelectric domain walls. Here, insights into the defect chemistry and electrical properties of BiFeO3 are obtained by in situ measurements of electrical conductivity, σ, and Seebeck coefficient, α, of undoped, cation-stoichiometric BiFeO3 and acceptor-doped Bi1−xCaxFeO3−δ ceramics as a function of temperature and oxygen partial pressure pO2. Bi1−xCaxFeO3−δ exhibits p-type conduction; the dependencies of σ and α on pO2 show that Ca dopants are compensated mainly by oxygen vacancies. By contrast, undoped BiFeO3 shows a simultaneous increase of σ and α with increasing pO2, indicating intrinsic behavior with electrons and holes as the main defect species in almost equal concentrations. The pO2-dependency of σ and α cannot be described by a single point defect model but instead, is quantitatively described by a combination of intrinsic and acceptor-doped characteristics attributable to parallel conduction pathways through undoped grains and defect-containing domain walls; both contribute to the total charge transport in BiFeO3. Based on this model, we discuss the charge transport mechanism and carrier mobilities of BiFeO3 and show that several previous experimental findings can readily be explained within the proposed model.
Remark Link

Performance and stability in H2S of SrFe0.75Mo0.25O3-δ as electrode in proton ceramic fuel cells

Authors S.Wachowski, M.Polfus, T.Norby
Source
Journal of the European Ceramic Society
Volume: 38, Issue: 1, Pages: 163-171
Time of Publication: 2018
Abstract The H2S-tolerance of SrFe0.75Mo0.25O3-δ (SFM) electrodes has been investigated in symmetric proton ceramic fuel cells (PCFC) with BaZr0.8Ce0.1Y0.1O3-δ (BZCY81) electrolyte. The ionic conductivity of the electrolyte under wet reducing conditions was found to be insignificantly affected in the presence of up to 5000 ppm H2S. The fuel cell exhibited an OCV of about 0.9 V at 700 °C, which dropped to about 0.6 V and 0.4 V upon exposure to 500 and 5000 ppm H2S, respectively, on the fuel side. Post characterization of the fuel cell revealed significant degradation of the anode in terms of microstructure and chemical composition due to formation of sulfides such as SrS, MoS2 and Fe3S4. Nevertheless, the fuel cell was still functional due to the sufficient electronic conductivity of some of these sulfides.
Keywords Proton ceramic fuel cells (PCFC), Sulfur tolerance, H2S, Strontium ferrite, Barium zirconate
Remark https://doi.org/10.1016/j.jeurceramsoc.2017.08.020
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Improvement of thermoelectric properties of lanthanum cobaltate by Sr and Mn co-substitution

Authors Ashutosh Kumar, D. Sivaprahsam, Ajay D. Thakur
Source
Journal of Alloys and Compounds
Volume: 735, Pages: 1787–1791
Time of Publication: 2017-12
Abstract We report thermoelectric (TE) properties of Sr and Mn co-substituted LaCoO3 system from room temperature to 700 K. Sr-substitutions at La and Mn at Co site in LaCoO3 improves the electrical conductivity (σ). Thermal conductivity (κ) of all the samples increases with the increase in temperature but decreases with the substitution in LaCoO3. An estimation of the electronic thermal conductivity (κe) suggests a dominant phonon contribution to thermal conductivity in this system. A maximum value of the figure of merit is 0.14 at 480 K for La0.95Sr0.05Co0.95Mn0.05O3.
Keywords Seebsys, Powders: solid-state reaction, Thermal conductivity, Electrical conductivity, Perovskites
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Fabrication and testing of unileg oxide thermoelectric device

Authors Jyothi Sharma, R. D. Purohit, Deep Prakash, and P. K. Sinha
Source
API Conference Proceedings
Time of Publication: 2017
Abstract A prototype of oxide thermoelectric unileg device was fabricated. This device was based on only n-legs made of La doped calcium manganate. The powder was synthesized, characterised and consolidated in rectangular thermoelements. A 3×3 device was fabricated by fitting 9 rectangular bars in alumina housing and connected by silver strips. The device has been tested under large temperature difference (ΔT=480°C) using an indegenous system. An open circuit voltage of 468 mV was obtained for a nine leg unileg device. The device exhibits a internal resistance of ∼1Ω. The maximum power output for this nine leg device reached upto 50 mW in these working condition
Keywords Seebsys
Remark Link
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