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Structure and transport properties in un-doped and acceptor-doped gadolinium tungstates

Authors Wen Xing, Protima Rauwel, Charles H. Hervoches, Zuoan Li, Reidar Haugsrud
Source
Solid State Ionics
Volume: 261, Pages: 87-94
Time of Publication: 2014
Abstract Nominal Gd6WO12, Gd5.94Ca0.06WO12 − δ, Gd5.7Ca0.3WO12 − δ and Gd5.7WO12 − δ were synthesized by solid state reaction and wet chemistry methods. The structure and morphology of the materials were analyzed by XRD, SEM and TEM and the electrical conductivity was measured as a function of temperature in reducing and oxidizing atmospheres under wet and dry conditions. The total conductivity is essentially independent of composition above 700 C. Below 700 C, the conductivity of Ca-doped samples is higher than that of Gd6WO12 and Gd5.7WO12 − δ and increases with increasing doping concentration. The conductivity below 700 C is also higher under wet compared to dry conditions and, moreover, the H–D isotope effect on the conductivity is significant. Based on this, and on conductivity characterization as a function of pO2pO2 and pH2OpH2O, it was concluded that the materials are mixed ionic and electronic conductors where electrons and holes dominate at high temperatures and intermediate temperatures under sufficiently reducing and oxidizing conditions, respectively. Protons are the predominating ionic charge carriers below approximately 700 C. The hydrogen flux through Gd5.7Ca0.3WO12 − δ was measured as a function of temperature under wet and dry sweep gas conditions, as well as with varying pH2pH2 on the feed side, confirming the picture outlined by the conductivity measurements. A defect chemical model has been derived to which the conductivity data were fitted yielding thermodynamic and transport parameters describing the functional characteristics of the materials.
Keywords Proton; Structure; Gd6WO12; Ambipolar conductivity; Hydrogen flux
Remark Link

Solid Oxide-Molten Carbonate Nano-composite Fuel Cells: Particle Size Effect

Authors Shalima Shawuti, Mehmet A. Gulgun
Source
Journal of Power Sources
Time of Publication: 2014
Abstract Varying the amount of specific interface area in the CeO2-Na2CO3 nano-composite fuel cell electrolyte helped reveal the role of interfaces in ionic conductivity. We mixed ceria particles with micrometer or nanometer size distributions to obtain a specific surface area (SSA) in the composite from 47 m2/g to 203 m2/g. Micro-structural investigations of the nano-composite showed that the Na2CO3 phase serves as the glue in the microstructure, while thermal analysis revealed a glass transition-like behavior at 350 C. High SSA enhanced the ionic conductivity significantly at temperatures below 400 C. Moreover, the activation energy for the Arrhenius conductivity (σT) of the composites was lower than that of the Na2CO3 phase. This difference in the activation energies is consistent with the calculated dissociation energy of the carbonate phase. The strong dependence of conductivity on the SSA, along with differences in the activation energies, suggests that the oxide surface acted as a dissociation agent for the carbonate phase. A model for the solid composite electrolyte is proposed: in the nano-composite electrolyte, the oxide surface helps Na2CO3 dissociate, so that the "liberated" ions can move more easily in the interaction region around the oxide particles, thus giving rise to high ionic conductivities.
Keywords composite electrolyte; ionic conductivity; impedance spectroscopy; SOFC; interphase; activation energy
Remark in press, http://dx.doi.org/10.1016/j.jpowsour.2014.05.010
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Hydrogen permeation characteristics of La27Mo1.5W3.5O55.5

Authors Einar Vllestad, Camilla K. Vigen, Anna Magras, Reidar Haugsrud
Source
Journal of Membrane Science
Time of Publication: 2014
Abstract Hydrogen permeation in 30 % Mo-substituted lanthanum tungsten oxide membranes, La27Mo1.5W3.5O55.5 (LWMo), has been measured as a function of temperature, hydrogen partial pressure gradient, and water vapour pressure in the sweep gas. Transport of hydrogen by means of ambipolar proton-electron conductivity and – with wet sweep gas – water splitting contribute to the measured hydrogen content in the permeate. At 700 C under dry sweep conditions, the H2 permeability in LWMo was 610−4610−4 mL min−1 cm-1, which is significantly higher than for state-of-the-art SrCeO3-based membranes. Proton conductivity was identified as rate limiting for ambipolar bulk transport across the membrane. On these bases it is evident that Mo-substitution is a successful doping strategy to increase the n-type conductivity and H2 permeability compared to nominally unsubstituted lanthanum tungsten oxide. A steady-state model based on Wagner transport theory with partial conductivities as input parameters predicted H2 permeabilities in good agreement with the measured data. LWMo is a highly competitive mixed proton-electron conducting oxide for hydrogen transport membrane applications provided that long term stability can be ensured.
Remark Available online 14 March 2014
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Performance Variability and Degradation in Porous La1-xSrxCoO3-δ Electrodes

Authors Yunxiang Lu, Cortney R. Kreller, Stuart B. Adler, James R. Wilson, Scott A. Barnett, Peter W. Voorhees, Hsun-Yi Chen and Katsuyo Thornton
Source
J. of the Electrochemical Society
Volume: 161, Issue: 4, Pages: F561-F568
Time of Publication: 2014
Abstract Porous La1-xSrxCoO3-δ (LSC) electrodes with Sr composition x = 0.2 (LSC-82) and x = 0.4 (LSC-64) were prepared by screenprinting LSC powders onto rare-earth doped ceria electrolytes, followed by sintering at 950 ∼ 1100C, and characterization using scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface-area analysis, 3-D morphological imaging based on focused ion beam scanning electron microscopy (FIB-SEM), and energy dispersion X-ray spectroscopy (EDX/EDS). The batch-to-batch variability and degradation (over 1000 ∼ 2000 hours) of the electrochemical performance of these cells were studied using electrochemical impedance spectroscopy (EIS) and measurements of nonlinear electrochemical impedance (NLEIS). These measurements reveal a strong correlation between the characteristic frequency (ωc) and characteristic resistance (Rc) of the electrodes, which, when analyzed in light of microstructural data, indicates that performance variability and degradation are caused primarily by variations in the surface rate coefficient k(T) for O2 exchange.
Remark doi: 10.1149/2.101404jes
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Doped Germanate-Based Apatites as Electrolyte for Use in Solid Oxide Fuel Cells

Authors S.-F. Wang, Y.-F. Hsu, W.-J. Lin and K. Kobayashi
Source
Fuel Cells
Time of Publication: 2014
Abstract Apatite ceramics, known for their good electrical conductivities, have garnered substantial attention as an alternative electrolyte for solid oxide fuel cells (SOFCs). However, studies focusing on the electrochemical performances of SOFCs with apatities as electrolytes remain rare, partly due to their high sintering temperature. In this study, the effects of Mg2+, Al3+, Ga3+, and Sn4+ dopants on the characteristics of La9.5Ge6O26  δ are examined and their potential for use as SOFC electrolytes evaluated. The results indicate that La9.5Ge5.5Al0.5O26 is stabilized into a hexagonal structure, while the La9.5Ge5.5Sn0.5O26.25, La9.5Ge5.5Ga0.5O26, and La9.5Ge5.5Mg0.5O25.75 ceramics reveal triclinic cells accompanied with the second phase La2Sn2O7 or La2GeO5. The study further demonstrates that a high sintering temperature is needed for both the La9.5Ge5.5Mg0.5O25.75 and the La9.5Ge5.5Sn0.5O26.25 ceramics, and the worst electrical conductivity among the examined systems appears in the La9.5Ge5.5Ga0.5O26 ceramic. The La9.5Ge5.5Al0.5O26 ceramic is accordingly selected for cell evaluation due to its ability to reach densification at 1,350 C, its good electrical conductivity of 0.026 S cm–1 at 800 C, and its acceptable thermal expansion coefficient of 10.1  10–6 K–1. The maximum power densities of the NiO-SDC/La9.5Ge5.5Al0.5O26/LSCF-SDC single cell are found to be respectively 0.22, 0.16, 0.11, and 0.07 W cm–2 at 950, 900, 850, and 800 C.
Keywords Apatites; Cell Performance; Electrolyte; Impedance; Solid Oxide Fuel Cell
Remark Article first published online: 19 FEB 2014 DOI: 10.1002/fuce.201300093
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Effect of Nb substitution for Ti on the electrical properties of Yb2Ti2O7-based oxygen ion conductors

Authors L.G. Shcherbakova, J.C.C. Abrantes, D.A. Belov, E.A. Nesterova, O.K. Karyagina, A.V. Shlyakhtina
Source
Solid State Ionics
Time of Publication: 2014
Abstract We have studied the effect of niobium doping on the electrical conductivity of Yb2Ti2O7-based oxygen ion conductors. Yb2[Ti1 − xNbx]2O7 (x = 0.01, 0.04, 0.1) and (Yb0.8Tb0.1Ca0.1)2[Ti1 − xNbx]2O6.9 (x = 0; 0.05; 0.1) pyrochlore solid solutions were synthesized through coprecipitation followed by firing at 1550 C for 4 h. The materials were examined by XPS, XRD, scanning electron microscopy and impedance spectroscopy. Yb2(Ti0.99Nb0.01)2O7 was shown to have the highest oxygen ion conductivity in air (2.3 10− 3 S/cm at 750 C), which is however markedly lower than that of undoped Yb2Ti2O7. In the (Yb0.8Tb0.1Ca0.1)2[Ti1 − xNbx]2O6.9 (x = 0; 0.05; 0.1) system, the highest conductivity is offered by (Yb0.8Tb0.1Ca0.1)2[Ti0.95Nb0.05]2O6.9 (σ = 4.44 10− 3 S/cm at 650 C). Additional oxygen vacancies created by Ca doping in pyrochlore structure reduce the detrimental effect of Nb4 + doping on the oxide ion transport up to 5% Nb. The conductivity of the Yb2(Ti0.99Nb0.01)2O7 and (Yb0.8Tb0.1Ca0.1)2[Ti0.95Nb0.05]2O6.9 solid solutions was measured both in air and under reducing conditions (5% H2 in N2 and CO2 atmospheres). A comparative study of both these compositions under 5% H2 in N2 atmosphere showed that the transport mechanism was not affected by complex doping of the lanthanide and titanium sublattices in the Yb2Ti2O7-based materials and was related to oxygen vacancies. Conductivity measurements in CO2 were done to ensure correct evaluation of the ionic conductivity of (Yb0.8Tb0.1Ca0.1)2[Ti0.95Nb0.05]2O6.9, because in air it seems to be a mixed p-type and ionic conductor.
Keywords Oxide ion conductivity; Pyrochlore; Acceptor doping; Donor doping; Impedance spectroscopy
Remark Available online 1 February 2014; http://dx.doi.org/10.1016/j.ssi.2014.01.019
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Zr-doped samarium molybdates — potential mixed electron–proton conductors

Authors S.N. Savvin, A.V. Shlyakhtina, I.V. Kolbanev, A.V. Knotko, D.A. Belov, L.G. Shcherbakova, P. Nuez
Source
Solid State Ionics
Time of Publication: 2014
Abstract Two Zr-doped samarium molybdates View the MathML sourceSm6−x7Zrx7Mo17O127+x24−δ corresponding to x = 0.6 and 1 (SZMO) have been synthesized at 1600 C for 3 h using mechanically activated mixtures of starting oxides. Fluorite-like Sm0.771Zr0.086Mo0.143O1.739 − δ (06SZMO) and Sm0.714Zr0.143Mo0.143O1.756 − δ (10SZMO) have similar total conductivity of about 4 10− 4 S/cm at 800 C in air. Below 600 C, the total conductivity of 06SZMO in air exceeds that of 10SZMO. An increase in bulk and grain boundary conductivity of 06SZMO observed at low temperate under wet conditions suggests there may be a proton contribution to the total conductivity. Under reducing conditions (5% H2–Ar) 06SZMO becomes essentially an electronic conductor. Its conductivity reaches 0.25 S/cm at 800 C and the activation energy decreases to 0.3 eV.
Keywords Rare-earth; Sm molybdate; Fluorite; Oxide ion conductivity; Proton conductivity; Electron conductivity; Impedance spectroscopy
Remark Available online 6 February 2014; http://dx.doi.org/10.1016/j.ssi.2014.01.031
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Interstitial oxide ion conduction in (Sm2 − xZrx)Zr2O7 + δ

Authors A.V. Shlyakhtina, D.A. Belov, A.V. Knotko, I.V. Kolbanev, A.N. Streletskii
Source
Solid State Ionics
Time of Publication: 2014
Abstract The crystal structure and transport properties of (Sm2 − xZrx)Zr2O7 + x/2 (x = 0; 0.2; 0.32; 0.39; 0.48; 0.67; 0.78; 0.96; 1.14; 1.27) solid solutions have been investigated by X-ray techniques and impedance spectroscopy, respectively. The excess oxygen content of the composition with x = 0.2 has been determined by thermal analysis and mass spectrometry in a reducing atmosphere. The SmZrO system includes a two-phase (fluorite + pyrochlore) region for the (Sm2 − xZrx)Zr2O7 + x/2 (0.48 ≤ x < 0.96) solid solutions. The interstitial oxide ion conductivity of the (Sm2 − xZrx)Zr2O7 + x/2 (0.2 ≤ x < 0.48), 3 10− 3 S/cm at 750 C, is comparable to the vacancy-mediated conductivity of undoped Sm2Zr2O7. The bulk conductivity of the interstitial oxide ion conductors (Sm2 − xZrx)Zr2O7 + x/2 (0.2 ≤ x < 0.48) was shown to vary little in a wide range of Sm2O3 concentrations in contrast to the vacancy mediated oxide ion conductors Sm2(Zr2 − xSmx)O7 − δ (0 ≤ x < 0.29).
Remark Available online 2 February 2014; http://dx.doi.org/10.1016/j.ssi.2014.01.028
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Atmosphere controlled conductivity and Maxwell-Wagner relaxation in Bi0.5K0.5TiO3—BiFeO3 ceramics

Authors Morozov, Maxim I.; Einarsrud, Mari-Ann; Grande, Tor
Source
Journal of Applied Physics
Volume: 115, Issue: 4, Pages: 044104 - 044104-6
Time of Publication: 2014
Abstract Here, we report on a giant dielectric relaxation in (1 − x)Bi0.5K0.5TiO3—xBiFeO3 ceramics below ∼300 C, which becomes more pronounced with increasing BiFeO3 content. The relaxation was shown to be of Maxwell-Wagner type and associated with charge depletion at the electroded interfaces. It was also shown that the relaxation could be controlled or, eventually, removed by heat treatment in controlled partial pressure of oxygen. This was rationalized by the relationship between the electrical conductivity and variation in the oxidation state of Fe, which is strongly coupled to the partial pressure of oxygen. The results are discussed with emphasis on oxygen diffusion and point defect equilibria involving oxygen vacancies and iron in divalent and tetravalent state. Finally, the barrier-free dielectric properties of the (1 − x)Bi0.5K0.5TiO3—xBiFeO3 ceramics are reported.
Remark Link

Atmosphere controlled conductivity and Maxwell-Wagner relaxation in Bi0.5K0.5TiO3—BiFeO3 ceramics

Authors Maxim I. Morozov, Mari-Ann Einarsrud and Tor Grande
Source
J. Appl. Phys.
Volume: 115, Pages: 044104
Time of Publication: 2014
Abstract Here, we report on a giant dielectric relaxation in (1 − x)Bi0.5K0.5TiO3 — xBiFeO3 ceramics below ∼300 C, which becomes more pronounced with increasing BiFeO3 content. The relaxation was shown to be of Maxwell-Wagner type and associated with charge depletion at the electroded interfaces. It was also shown that the relaxation could be controlled or, eventually, removed by heat treatment in controlled partial pressure of oxygen. This was rationalized by the relationship between the electrical conductivity and variation in the oxidation state of Fe, which is strongly coupled to the partial pressure of oxygen. The results are discussed with emphasis on oxygen diffusion and point defect equilibria involving oxygen vacancies and iron in divalent and tetravalent state. Finally, the barrier-free dielectric properties of the (1 − x)Bi0.5K0.5TiO3 — xBiFeO3 ceramics are reported.
Remark Link

Characterisation of structure and conductivity of BaTi0.5Sc0.5O3 − δ

Authors S.M.H. Rahman, I. Ahmed, R. Haugsrud, S.G. Eriksson, C.S. Knee
Source
Solid State Ionics
Volume: 225, Pages: 140–146
Time of Publication: 2014
Abstract BaTi0.5Sc0.5O3 − δ was prepared via solid state reaction route and final sintering at 1550 C. High resolution X-ray powder diffraction on the as-prepared material reveals a cubic perovskite structure with a unit cell parameter, a = 4.1343(1) . Thermogravimetric analysis revealed the presence of significant levels of protons in the as-prepared material and 74% of the theoretically achievable protonation through filling of oxide ion vacancies was attained on exposure to a humid environment at 185 C. Infrared spectroscopy revealed a broad Osingle bondH stretching band confirming the presence of OHO• defects. Electrical conductivity was measured with variable frequency AC impedance methods in oxygen, argon, and hydrogen under dry, hydrated (H2O) and heavy water (D2O) conditions. In the temperature range of 150–550 C in a wet gas atmosphere the conductivity is significantly higher than that observed for dry conditions, indicating that protons are the dominant charge carriers. Conductivity is also found to be higher in dry oxygen in comparison with dry argon over the whole temperature range of 150–1000 C, characteristic of contribution from p-type charge carriers under oxidising atmospheres. At 550 C the proton conductivity was estimated to be 2.89 10− 4 S cm− 1 in wet Ar. Fitting of conductivity data provides a hydration enthalpy change (ΔHhydr0) of − 100 5 kJ/mol and hydration entropy change (ΔShydr0) of − 160 10 J/mol K.
Keywords Barium titanate; BaTiO3; Perovskite; Proton conductivity; X-ray diffraction; Hydration
Remark Link

Stability of La-Sr-Co-Fe Oxide-Carbonate Dual-Phase Membranes for Carbon Dioxide Separation at High Temperatures

Authors Tyler Norton , Jose Ortiz-Landeros , and Jerry Y.S. Lin
Source
Ind. Eng. Chem. Res.
Time of Publication: 2014
Abstract Dual-phase membranes consisting of a mixed ionic and an electronic conducting ceramic phase and an ionically conductive molten carbonate phase have the ability to selectively separate CO2 at high temperature with or without the presence of O2. This study examines the stability of a dual-phase ceramic-carbonate membrane consisting of La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) and an eutectic molten carbonate phase composed of Li2CO3, Na2CO3, and K2CO3. LSCF-carbonate membranes exposed to a CO2/He gradient at temperatures between 800-900oC result in a drastic decrease in CO2 permeation before reaching steady-state after more than 60 hours of exposure to the permeating gases due to surface reaction between CO2 and the LSCF ceramic phase of the membrane, resulting in decomposition of the membrane surface. The introduction of O2 in the feed gas, however, helps maintain the LSCF ceramic phase structure and results in stable CO2 permeation flux at much higher value due to a change in transport mechanism in the membrane. The results suggest finding oxygen ionic or mixed-conducting ceramic material stable in CO2 for the dual-phase membrane is critical to ensure stability of the membrane for CO2 permeation.
Remark DOI: 10.1021/ie4033523
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Synthesis and characterization of the micro-mesoporous anode materials and testing of the medium temperature solid oxide fuel cell single cells

Author Kadi Tamm
Source
Time of Publication: 2013
Remark Dissertation
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Polymorphism and properties of Bi2WO6 doped with pentavalent antimony

Authors E.P. Kharitonova, D.A. Belov, A.B. Gagor, A.P. Pietraszko, O.A. Alekseeva, V.I. Voronkova
Source
Journal of Alloys and Compounds
Time of Publication: 2014
Abstract Antimony-containing solid solutions isostructural with bismuth tungstate, Bi2WO6, have been prepared in air as polycrystalline samples by solid-state reactions and as single crystals by unseeded flux growth. The antimony in the solid solutions is in a pentavalent state and substitutes for tungsten in the structure of Bi2WO6. The Bi2W1–xSbxO6–y solid solutions have been shown to exist in the composition range 0 ⩽ x ⩽ 0.05. We have examined the effect of Sb5+ doping on the polymorphism and properties of Bi2WO6. In contrast to undoped Bi2WO6, antimony-substituted bismuth tungstate does not completely transform into its high-temperature, monoclinic phase at 960 C and remains two-phase up to temperatures approaching its melting point. Antimony substitution for tungsten has a weak effect on the temperatures of the ferroelectric phase transitions. Heterovalent substitution of Sb5+ for W6+ is accompanied by the formation of extra oxygen vacancies and an increase in the electrical conductivity of the solid solutions by one to two orders of magnitude relative to undoped Bi2WO6.
Keywords Aurivillius phases; Bi2WO6; Ceramics; Phase transitions; Electrophysical properties; Differential scanning calorimetry
Remark Available online 3 January 2014
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Effect of Ni Concentration on Phase Stability, Microstructure and Electrical Properties of BaCe0.8Y0.2O3-δ - Ni Cermet SOFC Anode and its application in proton conducting ITSOFC

Authors Pooja Sawant, S. Varma, M.R. Gonal, B.N. Wani, Deep Prakash, S.R. Bharadwaj
Source
Electrochimica Acta
Time of Publication: 2013
Abstract In this work we have studied the effect of Ni concentration on phase stability, microstructure and electrical properties of BaCe0.8Y0.2O3-δ (BCY)-Ni cermet SOFC anode. It has been seen that Ni forms composite with BCY without forming any solid solution in both oxidized and reduced state. Also, microstructural analysis reveals the effect of Ni on porosity and triple phase boundaries necessary for electrochemical reactions during cell operation. Electrical conductivity values obtained from dc four probe technique in H2 atmosphere increase with an increase in Ni content. Composites with low vol% of Ni contents i.e. 19% (Ni19) and 26% (Ni26) show predominantly semiconductor-like behaviour whereas higher vol% viz. 35% (Ni35), 45% (Ni45) and 56% (Ni56) composites show electronic conductivity behaviour. This confirms that electronic conduction occurs through metallic Ni phase. Also, anode supported single cell for proton conducting SOFC has been fabricated using Ni35 composition and its current-potential characteristics measured at different temperatures.
Keywords Cermet; X-ray diffraction; Electrical conductivity; Four probe; Single Cell
Remark Available online 25 December 2013
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Cathode compatibility, operation, and stability of LaNbO4-based proton conducting fuel cells

Authors Anna Magras, Marie-Laure Fontaine, Rune Bredesen, Reidar Haugsrud, Truls Norby
Source
Solid State Ionics
Time of Publication: 2013
Abstract Cathodes compatible with Ca-doped LaNbO4 (LCNO) and the operation of a complete proton conducting fuel cell based on this electrolyte are presented. The best performing cathode was a 50 vol.% La0.8Sr0.2MnO3 (LSM)–50 vol.% LCNO composite, with an overall area specific resistance (ASR) of ~ 10 Ω cm2 at 800 C in wet air. Pt and La0.8Sr0.2(Cr0.5Mn0.5)O3-based cathodes exhibit higher ASRs. The performance of a complete Ni–LCNO//LCNO//LSM–LCNO fuel cell shows a high open circuit voltage but with relatively low performance, in agreement with the modest proton conductivity of LaNbO4-based materials and cathode performances. The cell exhibits stable operation with CO2 containing atmosphere on the cathode side, confirming the chemical robustness of LaNbO4-based electrolytes.
Keywords Proton conducting fuel cells; Manufacturing; Impedance spectroscopy; LaNbO4; Characterization; Cathode performance
Remark Available online 22 December 2013;
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Determination of Oxygen Diffusion Coefficients in La1-xSrxFe1-yGayO3-δ Perovskites Using Oxygen Semi-Permeation and Conductivity Relaxation Methods

Authors P. M. Geffroy, Y. Hu, A. Vivet, T. Chartier and G. Dezanneau
Source
Journal of the Electrochemical Society
Volume: 161, Issue: 3, Pages: F153-F160
Time of Publication: 2014
Abstract This paper reports new evidence that oxygen surface exchange and bulk diffusion in a mixed conductor can be simultaneously determined via the oxygen semi-permeation method. Herein, we report the use of an original apparatus for oxygen activity measurements at both membrane surfaces to evaluate the oxygen surface exchange and bulk diffusion coefficients. Oxygen surface exchange and bulk diffusion in the La1-xSrxFe1-yGayO3-δ perovskite series are also determined and compared with the results from three different methods: isotopic exchange, conductivity relaxation, and oxygen semi-permeation. Although the thermodynamic conditions for these methods are not exactly the same, the values obtained for the oxygen surface exchange and bulk diffusion coefficients are in good agreement.
Remark Link

Entwicklung protonenleitender Werkstoffe und Membranen auf Basis von Lanthan-Wolframat fr die Wasserstoffabtrennung aus Gasgemischen

Author J Seeger
Source
Book of its own
Time of Publication: 2013
Remark Link

Porous La 0.6 Sr 0.4 CoO 3-δ thin film cathodes for large area micro solid oxide fuel cell MEMS power generators

Authors I. Garbayo, V. Esposito, S. Sanna, A. Morata, D. Pla, L. Fonseca, N. Sabat, A. Tarancn
Source
Journal of Power Sources
Time of Publication: 2013
Abstract Porous La0.6Sr0.4CoO3-δ thin films were fabricated by pulsed laser deposition for being used as a cathode for micro solid oxide fuel cell applications as MEMS power generators. Symmetrical La0.6Sr0.4CoO3-δ/yttria-stabilized zirconia/La0.6Sr0.4CoO3-δ free-standing membranes were fabricated using silicon as a substrate. A novel large-area membrane design based on grids of doped-silicon slabs. Thermo-mechanical stability of the tri-layer membranes was ensured in the intermediate range of temperatures up to 700C. In-plane conductivity of ca. 300 S/cm was measured for the cathode within the whole range of application temperatures. Finally, area specific resistance values below 0.3 Ωcm2 were measured for the cathode/electrolyte bi-layer at 700C in the exact final micro solid oxide fuel cell device configuration, thus presenting La0.6Sr0.4CoO3-δ as a good alternative for fabricating reliable micro solid oxide fuel cells for intermediate temperature applications.
Keywords Micro Solid Oxide Fuel Cell, thin film cathode, self-supported electrolyte
Remark DOI: 10.1016/j.jpowsour.2013.10.038

Nanocrystalline Sm0.5Sr0.5CoO3−δ synthesized using a chelating route for use in IT-SOFC cathodes: microstructure, surface chemistry and electrical conductivity

Authors Rares Scurtu, Simona Somacescu, Jose Maria Calderon-Moreno, Daniela Culita, Ion Bulimestru, Nelea Popa, Aurelian Gulea, Petre Osiceanu
Source
Journal of Solid State Chemistry
Time of Publication: 2013
Abstract Nanocrystalline Sm0.5Sr0.5CoO3−δ powders were synthesized by a chelating route using different polyfunctional HxAPC acids (APC=aminopolycarboxylate; x= 3, 4, 5). Different homologous aminopolycarboxylic acids, namely nitrilotriacetic (H3nta), ethylenediaminetetraacetic (H4edta), 1,2-cyclohexanediaminetetracetic (H4cdta) and diethylenetriaminepentaacetic (H5dtpa) acid, were used as chelating agents to combine Sm, Sr, Co elements into a perovskite structure. The effects of the chelating agents on the crystalline structure, porosity, surface chemistry and electrical properties were investigated. The electrical properties of the perovskite-type materials emphasized that their conductivities in the temperature range of interest (600–800 C) depend on the nature of the precursors as well as on the presence of a residual Co oxide phase as shown by XRD and XPS analysis. The surface chemistry and the surface stoichiometries were determined by XPS revealing a complex chemical behavior of Sr that exhibits a peculiar „surface phase” and „bulk phase” chemistry within the detected volume (<10 nm).
Keywords Cathode; Perovkites; Electrical Conductivity; XPS; IT-SOFC
Remark Available online 5 November 2013
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Effects of temperature, triazole and hot-pressing on the performance of TiO2 photoanode in a solid-state photoelectrochemical cell

Authors Kingsley O. Iwu, Augustinas Galeckas, Spyros Diplas, Frode Seland, Andrej Yu. Kuznetsov,Truls Norby
Source
Electrochimica Acta
Time of Publication: 2013
Abstract The photocurrent of hydrogen generating solid-state photoelectrochemical cell utilising a polybenzimidazole proton-conducting membrane and gaseous anode reactants has been enhanced by operation at higher temperatures. With a bias of 0 V for example, photocurrent increased from 15 to 30 μA/cm2 on moving from 25 C to 45 C. The increase in photocurrent, which was limited by the dehydration of the cell, was shown to have contribution from improved electrode kinetics. Modification of TiO2 surface with triazole, a conjugated heterocyclic compound, led to significant increase in photocurrent - up to 4 fold increase at 0 V and 25 C. This was attributed to improved separation of photogenerated charge carriers, as confirmed by correspondingly increased carrier lifetimes from 50 ns to 90 ns for triazole-modified TiO2. Assembly of the photoelectrochemical cell by hot-pressing induced a ̴ 0.3 eV red shift in optical absorption edge of TiO2, in agreement with a shift of its valence band maximum to higher binding energy.
Keywords Solid-state; photoelectrochemical; XPS; carrier lifetime; triazole
Remark Available online 28 October 2013
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Synthesis and Investigation of Porous Ni–Al Substrates for SolidOxide Fuel Cells

Authors A. A. Solov’ev, N. S. Sochugov , I. V. Ionov , A. I. Kirdyashkin , V. D. Kitler , A. S. Maznoi , Yu. M. Maksimov , and T. I. Sigfusson
Source
Materials of power engineering and radiationresistant materials
Time of Publication: 2013-10
Abstract Selfpropagating hightemperature synthesis (SHS) is applied for the production of porous supporting Ni–Al bases of solidoxide fuel cells. The effect of synthesis onditions and the composition of source powders on the phase composition, microstructure, gas permeability, corrosion resistance, and other proper ties of obtained Ni–Al samples is investigated. The possibility is shown for the formation of solidoxide fuel cells (SOFCs) on the surface of porous Ni–Al plates. The cells have the structure Ni–ZrO3:Y2O3 anode/ZrO3:Y2O3 electrolyte/La0.8Mn0.2SrO3 cathode and provide a specific power of 400 mW/cm2 at a temperature of 800C.
Keywords selfpropagating hightemperature synthesis, Ni–Al, solidoxide fuel cells, ZrO3:Y2O3 electrolyte, magnetron sputtering.
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Galliosilicate glasses for viscous sealants in solid oxide fuel cell stacks: Part III: Behavior in air and humidified hydrogen

Authors T. Jin, M.O. Naylor, J.E. Shelby, S.T. Misture
Source
International Journal of Hydrogen Energy
Time of Publication: 2013
Abstract Optimized boro-galliosilicate glasses were selected to evaluate their viscous sealing performance in both air and humidified hydrogen atmospheres. Selected low-alkali and alkali-free glasses show excellent performance, with viscous behavior maintained for more than 1000 h in wet hydrogen. Candidate sealants were thermally treated at 850 and 750 C for up to 1000 h in contact with alumina coated 441 stainless steel (Al-SS) and 8 mol% yttria-stabilized zirconia (8YSZ). Each sealant crystallizes appreciably by 1000 h, and their coefficients of thermal expansion range from 10.2 to 11.7 10−6 K−1, 100–400 C. The remnant amorphous phases in most of the partially crystallized sealants show softening points near or below the target operating temperatures, thus enabling viscous sealing. Humidified hydrogen in general increases the rate of crystallization but does not change the crystalline phases formed or interactions with 8YSZ. For the low-alkali GaBA series, wet H2 enhances the interfacial interaction between potassium in the glass phase and the protective alumina coating on the stainless steel.
Keywords Solid oxide fuel cell; Sealing glass; Galliosilicate; Thermal expansion; Hydrogen
Remark Available online 25 October 2013
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Porous La0.6Sr0.4CoO3-δ thin film cathodes for large area micro solid oxide fuel cell MEMS power generators

Authors I. Garbayo, V. Esposito, S. Sanna, A. Morata, D. Pla, L. Fonseca, N. Sabat, A. Tarancn
Source
Journal of Power Sources
Time of Publication: 2013
Abstract Porous La0.6Sr0.4CoO3-δ thin films were fabricated by pulsed laser deposition for being used as a cathode for micro solid oxide fuel cell applications as MEMS power generators. Symmetrical La0.6Sr0.4CoO3-δ/yttria-stabilized zirconia/La0.6Sr0.4CoO3-δ free-standing membranes were fabricated using silicon as a substrate. A novel large-area membrane design based on grids of doped-silicon slabs. Thermo-mechanical stability of the tri-layer membranes was ensured in the intermediate range of temperatures up to 700C. In-plane conductivity of ca. 300 S/cm was measured for the cathode within the whole range of application temperatures. Finally, area specific resistance values below 0.3 Ωcm2 were measured for the cathode/electrolyte bi-layer at 700C in the exact final micro solid oxide fuel cell device configuration, thus presenting La0.6Sr0.4CoO3-δ as a good alternative for fabricating reliable micro solid oxide fuel cells for intermediate temperature applications.
Remark Available online 18 October 2013
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Nano Coated Interconnects for SOFC (NaCoSOFC)

Authors Jan Froitzheim, Anna Magraso, Tobias Holt, Mats W Lundberg, Hannes Falk Windisch, Robert Berger, Rakshith Nugehalli Sachitanand, Jrgen Westlinder, Jan-Erik Svensson and Reidar Haugsrud
Source
ECS Transactions
Volume: 57, Issue: 1, Pages: 2187-2193
Time of Publication: 2013
Abstract The NaCoSOFC project is focused on the development of nano coatings for SOFC interconnects. The project is sponsored by the Nordic Top Level Research Initiative and has four project partners: Sandvik Materials Technology which is producing coated interconnects, Chalmers University of Technology and the University of Oslo that characterize samples with respect to e.g. corrosion, Cr evaporation and ASR as well as Topsoe Fuel Cell that is testing the developed interconnects in its stacks. The developed coatings are based on a combination of Co with RE elements and exhibit high corrosion resistance, 10 fold decrease in Cr evaporation and ASR values that are approximately 50% of the uncoated material.
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