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Electrical conductivity of Zn-doped high temperature proton conductor LaNbO4

Authors Yong Cao, Yuan Tan, Dong Yan, , Bo Chi, Jian Pu, Li Jian
Source
Solid State Ionics
Volume: 278, Pages: 152–156
Time of Publication: 2015
Abstract Zn-doped LaNbO4 (La1 − xZnxNbO4 − δ, LZ100x) was prepared by a solid-state reaction method with x = 0, 0.005, 0.01, 0.015, 0.03 and 0.05 and investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and conductivity measurement. There were no XRD and TEM evidences of formed secondary phases in the composition range of x ≤ 0.03 due to the sensitivity. However, the solubility of Zn, less than 1.0 mol.%, was reasonable, according the variety of the grain sizes, conductivity, as well as the activation energy for the conductivity, with the increasing concentration of Zn. The conductivity of LaNbO4 was improved by one to two orders of magnitude with Zn doping in the research range; and the highest conductivity of 9.8 10− 4 S cm− 1 was obtained with LZ0.5 at 900 C in wet air.
Keywords LaNbO4; Conductivity; Zn doping; Grain size
Remark doi:10.1016/j.ssi.2015.06.011
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Gd- and Pr-based double perovskite cobaltites as oxygen electrodes for proton ceramic fuel cells and electrolyser cells

Authors Ragnar Strandbakke, Vladimir A. Cherepanov, Andrey Yu. Zuev, Dmitry S. Tsvetkov, Christos Argirusis, Georgia Sourkouni, Stephan Prnte, Truls Norby
Source
Solid State Ionics
Volume: 278, Pages: 120–132
Time of Publication: 2015
Abstract Double perovskite oxides BaGd0.8La0.2Co2O6−δ (BGLC), BaGdCo1.8Fe0.2O6−δ (BGCF), BaPrCo2O6−δ (BPC) and BaPrCo1.4Fe0.6O6−δ (BPCF) were investigated as oxygen electrodes on mixed conducting BaZr0.7Ce0.2Y0.1O3 (BZCY72) electrolyte using impedance spectroscopy vs temperature, pO2, and pH2O. We propose and have applied a novel approach to extract and parameterise the charge transfer and diffusion impedances of the electrode reactions in a system comprising charge transport of protons, oxide ions, and electrons. Given by the properties of the BZCY72, transport of protons dominates at lower temperatures and high pH2O, oxide ions at higher temperatures, and electron holes increasingly at high temperatures and high pO2. The electrodes showed good performance, with the lowest total apparent polarisation resistance for BGLC/BZCY72 being 0.05 and 10 Ωcm2 at 650 and 350 C, respectively. The low temperature rate limiting reaction step is a surface related process, involving protonic species, with an activation energy of approximately 50 kJ mol−1 for BGLC/BZCY72. The oxide ion transport taking over at higher temperatures exhibits a higher activation energy typical of SOFC cathodes. Thermogravimetric studies revealed that BGLC exhibits considerable protonation at 300–400 C, which may be interpreted as hydration with an enthalpy of approximately –50 kJ mol−1. The resulting mixed proton electron conduction may explain its good performance as electrode on BZCY72.
Keywords PCFC; PCEC; P-MIEC; Proton conductor; Mixed conductivity; Double perovskite
Remark doi:10.1016/j.ssi.2015.05.014
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Praseodymium-deficiency Pr0.94BaCo2O6-δ double perovskite: A promising high performance cathode material for intermediate-temperature solid oxide fuel cells

Authors Fuchang Meng, Tian Xia, Jingping Wang, Zhan Shi, Hui Zhao
Source
Journal of Power Sources
Volume: 239, Pages: 741–750
Time of Publication: 2015
Abstract Praseodymium-deficiency Pr0.94BaCo2O6-δ (P0.94BCO) double perovskite has been evaluated as a cathode material for intermediate-temperature solid oxide fuel cells. X-ray diffraction pattern shows the orthorhombic structure with double lattice parameters from the primitive perovskite cell in Pmmm space group. P0.94BCO has a good chemical compatibility with Ce0.9Gd0.1O1.95 (CGO) electrolyte even at 1000 C for 24 h. It is observed that the Pr-deficiency can introduce the extra oxygen vacancies in P0.94BCO, further enhancing its electrocatalytic activity for oxygen reduction reaction. P0.94BCO demonstrates the promising cathode performance as evidenced by low polarization are-specific resistance (ASR), e. g. 0.11 Ω cm2 and low cathodic overpotential e. g. −56 mV at a current density of −78 mA cm−2 at 600 C in air. These features are comparable to those of the benchmark cathode Ba0.5Sr0.5Co0.8Fe0.2O3-δ. The fuel cell CGO-Ni|CGO|P0.94BCO presents the attractive peak power density of 1.05 W cm−2 at 600 C. Furthermore, the oxygen reduction kinetics of P0.94BCO material is also investigated, and the rate-limiting steps for oxygen reduction reaction are determined.
Keywords Intermediate-temperature solid oxide fuel cell; Cathode material; Double perovskite; Electrochemical performance; Oxygen reduction reaction
Remark doi:10.1016/j.jpowsour.2015.06.007
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Reduced long term electrical resistance in Ce/Co-coated ferritic stainless steel for solid oxide fuel cell metallic interconnects

Authors Anna Magrasa, Hannes Falk-Windisch, Jan Froitzheim, Jan-Erik Svensson, Reidar Haugsrud
Source
International Journal of Hydrogen Energy
Volume: 40, Issue: 27, Pages: 8579–8585
Abstract The present study is focused on the influence of selected coatings on a ferritic stainless steel (Sanergy HT™, Sandvik) on the evolution of the area specific resistance (ASR) as a function of time at high temperature. The samples are exposed in humidified air at 850 C for up to 4200 h. It combines long-term ASR measurements with the thermogravimetric behavior and microstructural analysis of the cross sections by scanning electron microscopy. The results show that uncoated and Co-coated Sanergy HT™ exhibit similar oxidation kinetics and comparable ASRs, while a combined Ce/Co coating improves oxidation resistance and, consequently, reduces the ASR significantly. Other reports have earlier shown that Co- (and Ce/Co)-coated Sanergy HT™ reduces the evaporation of volatile chromium species. Overall, the study indicates that Ce/Co-coatings will render substantially improved performance for ferritic steel interconnects for solid oxide fuel cells.
Keywords Metallic coating; SOFC; Interconnects; Stainless steel; Conductivity; ASR
Remark doi:10.1016/j.ijhydene.2015.04.147
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Resistivity Enhancement and Transport Mechanisms in (1 − x)BaTiO3–xBi(Zn1/2Ti1/2)O3 and (1 − x)SrTiO3–xBi(Zn1/2Ti1/2)O3

Author Nitish Kumar* andDavid P. Cann
Source
Journal of the American Ceramic Society
Time of Publication: 2015
Abstract Ceramics of composition (1−x)BaTiO3–xBi(Zn1/2Ti1/2)O3 (BT-BZT) were prepared by solid-state synthesis; they have been shown to exhibit excellent properties suited for high-temperature dielectric applications. The X-ray diffraction data showed a single-phase perovskite structure for all the compositions prepared (x ≤ 0.1 BZT). The compositions with less than 0.075 BZT exhibited tetragonal symmetry at room temperature and pseudo-cubic symmetry above it. Most notably, a significant improvement in insulation properties was measured with the addition of BZT. Both low-field AC impedance and high-field direct DC measurements indicated an increase in resistivity of at least two orders of magnitude at 400C with the addition of just 0.03 BZT (~107 Ω-cm) into the solid solution as compared to pure BT (~105 Ω-cm). This effect was also evident in dielectric loss data, which remained low at higher temperatures as the BZT content increased. In conjunction with band gap measurements, it was also concluded that the conduction mechanism transitioned from extrinsic for pure BT to intrinsic for 0.075 BZT suggesting a change in the fundamental defect equilibrium conditions. It was also shown that this improvement in insulation properties was not limited to BT-BZT, but could also be observed in the paraelectric SrTiO3–BZT system.
Remark DOI: 10.1111/jace.13666, Article first published online
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Triode operation for enhancing the performance of H2S-poisoned SOFCs operated under CH4–H2O mixtures

Authors Foteini M. Sapountzi, Michail N. Tsampas, Chunhua Zhao, Antoinette Boreave, Laurence Retailleau, Dario Montinaro, Philippe Vernoux
Source
Solid State Ionics
Volume: 277, Pages: 65–71
Time of Publication: 2015
Abstract Performances of Solid Oxide Fuel Cells (SOFCs) were investigated in triode operation mode under methane steam reforming in the presence of H2S. Both the catalytic performances for methane steam reforming and the electrochemical properties for the electrochemical oxidation of hydrogen of a Ni/GDC anode drastically dropped in the presence of 1 ppm H2S. Poisoned catalytic sites are different from those for the hydrogen electrochemical oxidation. Triode operation, i.e. application of moderate negative currents between the anode and an auxiliary electrode, can improve electrochemical properties, as a result of a local production of H2 coming from H2O electrolysis. Some specific triode operations were found to achieve a thermodynamic efficiency close to the unity to avoid any energy overconsumption.
Keywords SOFC; Triode operation; H2S poisoning; Ni/GDC anode
Remark doi:10.1016/j.ssi.2015.05.003
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High-temperature anion and proton conduction in RE3NbO7 (RE = La, Gd, Y, Yb, Lu) compounds

Authors A. Chesnauda, M.-D. Braidab, S. Estradd, F. Peird, A. Tarancnf, A. Morataf, G. Dezanneau
Source
Journal of the European Ceramic Society
Volume: 35, Issue: 11, Pages: 3051–3061
Time of Publication: 2015
Abstract The oxide-ion and proton conduction properties of RE3NbO7 (RE = La, Gd, Y, Yb, Lu) compounds were investigated. For the bigger rare-earth cation, i.e. La3+, the compound crystallises in a weberite-type structure and the oxide-ion conductivity is low owing to the lack of intrinsic oxygen vacancies. Consequently, the resultant proton incorporation and conductivity in La3NbO7 are also low. For small rare-earth cations, i.e. from Gd3+ to Lu3+ and for RE = Y, materials adopt a fluorite-like structure confirmed from X-ray powder diffraction. In this latter case, materials include intrinsic oxygen vacancies leading to a higher oxygen conductivity. For these compounds, a proton incorporation takes place at low temperature under wet conditions giving rise to proton conductivity. Nevertheless, both oxygen and proton conductivities are low in these materials, which can be explained by the ordering of oxygen vacancies observed by Transmission Electron Microscopy.
Keywords Protonic ceramic fuel cell; Rare-earth niobate; Combustion synthesis; Fluorite-type structure; Electrical properties
Remark doi:10.1016/j.jeurceramsoc.2015.04.014
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Proton transport properties of the RE3Ga5MO14 (RE = La, Nd and M = Si, Ti, Sn) langasite family of oxides

Authors Tor S. Bjrheim, Reidar Haugsrud
Source
Solid State Ionics
Volume: 275, Pages: 29–34
Time of Publication: 2015
Abstract Hydration and proton transport properties of novel, intrinsically acceptor doped compositions within the RE3Ga5MO14 family of oxides have been addressed by means of measurements of the electrical conductivity. Oxygen vacancies and protons charge compensate the acceptor in dry and wet atmospheres, respectively, and all compositions display significant proton conductivity below 1000 C. The hydration thermodynamics is affected by M-ion substitution, and becomes more favorable in the order Si < Ti < Sn. The enthalpy of proton mobility is also strongly dependent on the M-ion; M = Si, Ti and Sn exhibit enthalpies of proton mobility of 76 3, 61 1 and 80 2 kJ mol− 1, respectively.
Keywords Langasites; Conductivity; Defects; Acceptor; Hydration; Protons
Remark doi:10.1016/j.ssi.2015.03.014
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Diffusion of Nd and Mo in lanthanum tungsten oxide

Authors Einar Vllestad, Markus Teusner, Roger A. De Souza, Reidar Haugsrud
Source
Solid State Ionics
Volume: 274, Pages: 128–133
Time of Publication: 2015
Abstract Cation diffusion in functional oxides exposed to electrochemical gradients may lead to kinetic demixing or decomposition and, consequently, determine the life-time of the functional component. Here we present chemical diffusion coefficients of Nd and Mo in the mixed proton–electron conductor lanthanum tungsten oxide, La28 − xW4 + xO54 + 3x/2 (LWO), measured at 1000 to 1200 C in both oxidizing and reducing atmospheres. The bulk diffusivities of Nd and Mo were similar at all temperatures investigated and did not change significantly from oxidizing to reducing conditions. On these bases it is suggested that bulk diffusion of both Nd and Mo occurs via the La2 site on which both cations reside. Based on the low activation energy for bulk transport (~ 200 kJ∙mol− 1) at temperatures below 1200 C it is proposed that the cation defect concentrations are, in effect, frozen in. Preferential diffusion of Nd along the grain boundaries was rationalized based on space charge effects and depletion of W6 + and Mo6 + near the positively charged grain boundary core. Potential implications of kinetic demixing or decomposition of LWO membranes are also evaluated based on the present results.
Keywords Lanthanum tungstate; Cation diffusion; SIMS; Degradation; Tracer diffusion
Remark doi:10.1016/j.ssi.2015.03.011
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Crystal structure and high-temperature properties of the Ruddlesden–Popper phases Sr3−xYx(Fe1.25Ni0.75)O7−δ (0≤x≤0.75)

Authors Louise Samain, Philipp Amshoff, Jordi J. Biendicho, Frank Tietz, Abdelfattah Mahmoud, Raphal P. Hermann, Sergey Ya. Istomin, Jekabs Grins, Gunnar Svensson
Source
Journal of Solid State Chemistry
Volume: 227, Pages: 45–54
Time of Publication: 2015
Abstract Ruddlesden–Popper n=2 member phases Sr3−xYxFe1.25Ni0.75O7−δ, 0≤x≤0.75, have been investigated by X-ray and neutron powder diffraction, thermogravimetry and Mssbauer spectroscopy. Both samples as-prepared at 1300 C under N2(g) flow and samples subsequently air-annealed at 900 C were studied. The as-prepared x=0.75 phase is highly oxygen deficient with δ=1, the O1 atom site being vacant, and the Fe3+/Ni2+ ions having a square pyramidal coordination. For as-prepared phases with lower x values, the Mssbauer spectral data are in good agreement with the presence of both 5- and 4-coordinated Fe3+ ions, implying in addition a partial occupancy of the O3 atom sites that form the basal plane of the square pyramid. The air-annealed x=0.75 sample has a δ value of 0.61(1) and the structure has Fe/Ni ions in both square pyramids and octahedra. Mssbauer spectroscopy shows the phase to contain only Fe3+, implying that all Ni is present as Ni3+. Air-annealed phases with lower x values are found to contain both Fe3+ and Fe4+. For both the as-prepared and the air-annealed samples, the Y3+ cations are found to be mainly located in the perovskite block. The high-temperature thermal expansion of as-prepared and air-annealed x=0.75 phases were investigated by high-temperature X-ray diffraction and dilatometry and the linear thermal expansion coefficient determined to be 14.4 ppm K−1. Electrical conductivity measurements showed that the air-annealed samples have higher conductivity than the as-prepared ones.
Keywords Ruddlesden–Popper structure; Oxygen non-stoichiometry; Crystal structure; Mssbauer spectroscopy; Electrical conductivity; Thermal expansion
Remark doi:10.1016/j.jssc.2015.03.018
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Atmosphere dependence of anode reaction of intermediate temperature steam electrolysis using perovskite type proton conductor

Authors Takaaki Sakai, Keita Arakawa, Masako Ogushi, Tatsumi Ishihara, Hiroshige Matsumoto, Yuji Okuyama
Source
Journal of Solid State Electrochemistry
Volume: 19, Issue: 6, Pages: 1793-1798
Time of Publication: 2015
Abstract The effect of oxygen partial pressure on anode reaction of steam electrolysis using SrZr0.5Ce0.4Y0.1O3-α (SZCY-541) proton conducting electrolyte was investigated by AC impedance measurement in this work. The anode reaction was enhanced by increasing oxygen partial pressure, and this result was opposite to the expectation from the conventional anode reaction (water splitting reaction). The increase in the electrode reaction conductivity with oxygen chemical potential was proportional to PO21/4 at 600 C and at higher oxygen partial pressure region of 700 and 800 C, suggesting the possibility that the enhancement is caused by the increase in hole concentration on the electrolyte surface near the anode.
Remark Link

FD Electrolysis: Co-electrolysis of steam and CO2 in full-ceramic symmetrical SOECs: A strategy for avoiding the use of Hydrogen as a safe gas

Authors Marc Torrell, Sergio Garca-Rodrguez, Alex Morata, Germn Penelas and Alberto Tarancon
Source
Faraday Discussions
Time of Publication: 2015
Abstract The use of cermets as fuel electrodes for solid oxide electrolysis cells requires permanent circulation of reducing gas, e.g. H2 or CO, so called safe gas, in order to avoid oxidation of the metallic phase. Replacing metallic based electrodes by pure oxides is therefore proposed as an advantage for the industrial application of solid oxide electrolyzers. In this work, full-ceramic symmetrical solid oxide electrolysis cells have been investigated for steam/CO2 co-electrolysis. Electrolyte supported cells with La0.75Sr0.25Cr0.5Mn0.5O3-δ reversible electrodes have been fabricated and tested in co-electrolysis mode using different fuel compositions, from pure H2O to pure CO2, at temperatures of 850C – 900C. Electrochemical impedance spectroscopy and galvanostatic measurements have been carried out for the mechanistic understanding of the symmetrical cells performance. The content of H2 and CO in the product gas has been measured by in-line gas micro-chromatography. The effect of employing H2 as a safe gas has been also investigated. Maximum density currents of 750 mA/cm2 and 620 mA/cm2 have been applied at 1.7 V for pure H2O and for H2O:CO2 ratios of 1:1, respectively. Remarkable results were obtained for hydrogen-free fuel compositions, which confirmed the interest of using ceramic oxides as a fuel electrode candidate to reduce or completely avoid the use of safe gas in operation minimizing the contribution of the reverse water shift reaction (RWSR) in the process. H2:CO ratios close to two were obtained for hydrogen-free tests fulfilling the basic requirements for synthetic fuel production. An important increase of the operation voltage was detected under continuous operation leading to a dramatic failure by delamination of the oxygen electrode.
Remark Accepted Manuscript, DOI: 10.1039/C5FD00018A
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Doping strategies for increased oxygen permeability of CaTiO3 based membranes

Authors Jonathan M. Polfus, Wen Xing, Martin F. Sunding, Sidsel M. Hanetho, Paul Inge Dahl, Yngve Larring, Marie-Laure Fontaine, Rune Bredesen
Source
Journal of Membrane Science
Volume: 482, Pages: 137–143
Time of Publication: 2015
Abstract Oxygen permeation measurements are performed on dense samples of CaTi0.85Fe0.15O3−δ, CaTi0.75Fe0.15Mg0.05O3−δ and CaTi0.75Fe0.15Mn0.10O3−δ in combination with density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) in order to assess Mg and Mn as dopants for improving the O2 permeability of CaTi1−xFexO3−δ based oxygen separation membranes. The oxygen permeation measurements were carried out at temperatures ranging between 700 and 1000 C with feed side oxygen partial pressures between 0.01 and 1 bar. The O2 permeability was experimentally found to be highest for the Mn doped sample over the whole temperature range, reaching 4.210−3 ml min−1 cm−1 at 900 C and 0.21 bar O2 in the feed which corresponds to a 40% increase over the Fe-doped sample and similar to reported values for x=0.2. While the O2 permeability of the Mg doped sample was also higher than the Fe-doped sample, it approached that of the Fe-doped sample above 900 C. According to the DFT calculations, Mn introduces electronic states within the band gap and will predominately exist in the effectively negative charge state, as indicated by XPS measurements. Mn may therefore improve the ionic and electronic conductivity of CTF based membranes. The results are discussed in terms of the limiting species for ambipolar transport and O2 permeability, i.e., oxygen vacancies and electronic charge carriers.
Keywords Dense ceramic oxygen membrane; Ambipolar transport; Mixed ionic-electronic conduction; CaTiO3; Calcium titanate
Remark doi:10.1016/j.memsci.2015.02.036
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Coated stainless steel 441 as interconnect material for solid oxide fuel cells: Evolution of electrical properties

Authors Jan Gustav Grolig , Jan Froitzheim, Jan-Erik Svensson
Source
Journal of Power Sources
Volume: 284, Pages: 321–327
Time of Publication: 2015
Abstract AISI 441 coated with a double layer coating of 10 nm cerium (inner layer) and 630 nm cobalt was investigated and in addition the uncoated material was exposed for comparison. The main purpose of this investigation was the development of a suitable ASR characterization method. The material was exposed to a simulated cathode atmosphere of air with 3% water at 850 C and the samples were exposed for up to 1500 h. We compared two methods of ASR measurements, an in-situ method where samples were measured with platinum electrodes for longer exposure times and an ex-situ method where pre-oxidized samples were measured for only very short measurement times. It was found that the ASR of ex-situ characterized samples could be linked to the mass gain and the electrical properties could be linked to the evolving microstructure during the different stages of exposure. Both the degradation of the electric performance and the oxygen uptake (mass gain) followed similar trends. After about 1500 h of exposure an ASR value of about 15 mΩcm2 was reached. The in-situ measured samples suffered from severe corrosion attack during measurement. After only 500 h of exposure already a value of 35 mΩcm2 was obtained.
Keywords ASR; Interconnect; AISI 441; SOFC; Corrosion; Platinum
Remark doi:10.1016/j.jpowsour.2015.03.029
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Steam-promoted CO2 flux in dual-phase CO2 separation membranes

Authors Wen Xing, Thijs Peters, Marie-Laure Fontaine, Anna Evans, Partow Pakdel Henriksen, Truls Norby, Rune Bredesen
Source
Journal of Membrane Science
Volume: 482, Pages: 115–119
Time of Publication: 2015
Abstract Steam dissolving into molten carbonates through the formation of hydroxide ions could contribute to the permeation of CO2 in dual-phase membranes under certain conditions. In this work, ceria (CeO2) supported dual-phase membranes was fabricated and the effect of steam on the transport properties has been investigated by means of flux measurements. The results show an approximate 30% increase of the CO2 flux when 2.5% steam is introduced to the feed side, while an approximate 250–300% increase of the CO2 flux is observed when introducing the same amount of steam to the sweep side. These phenomena and transport mechanisms are explained by the theory of ambipolar permeation of CO2 via various combinations of charged species.
Keywords Dual-phase; CO2 separation membrane; Steam; Flux
Remark doi:10.1016/j.memsci.2015.02.029
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Electrical conductivity and thermopower of (1 − x) BiFeO3 – xBi0.5K0.5TiO3 (x = 0.1, 0.2) ceramics near the ferroelectric to paraelectric phase transition

Authors E. T. Wefring, M.-A. Einarsrud and T. Grande
Source
Physical Chemistry Chemical Physics
Volume: 17, Issue: 14, Pages: 9420-9428
Time of Publication: 2015
Abstract Ferroelectric BiFeO3 has attractive properties such as high strain and polarization, but a wide range of applications of bulk BiFeO3 are hindered due to high leakage currents and a high coercive electric field. Here, we report on the thermal behaviour of the electrical conductivity and thermopower of BiFeO3 substituted with 10 and 20 mol% Bi0.5K0.5TiO3. A change from p-type to n-type conductivity in these semi-conducting materials was demonstrated by the change in the sign of the Seebeck coefficient and the change in the slope of the isothermal conductivity versus partial pressure of O. A minimum in the isothermal conductivity was observed at [similar]10−2 bar O2 partial pressure for both solid solutions. The strong dependence of the conductivity on the partial pressure of O2 was rationalized by a point defect model describing qualitatively the conductivity involving oxidation/reduction of Fe3+, the dominating oxidation state of Fe in stoichiometric BiFeO3. The ferroelectric to paraelectric phase transition of 80 and 90 mol% BiFeO3 was observed at 648 15 and 723 15 C respectively by differential thermal analysis and confirmed by dielectric spectroscopy and high temperature powder X-ray diffraction.
Remark DOI: 10.1039/C5CP00266D
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Structure and conductivity of acceptor doped La2BaZnO5 and Nd2BaZnO5

Authors Md. Khairul Hoque, Reidar Haugsrud, Christopher S. Knee
Source
Solid State Ionics
Volume: 272, Pages: 160–165
Time of Publication: 2015
Abstract The effect of calcium substitution on the structure and electrical conductivity of Ln2 − xCaxBaZnO5 − δ, Ln = La and Nd, has been studied. Differing trends with respect to dependence of the unit cell volume were observed as a function of Ca substitution. For both series of materials the limit of Ca substitution was estimated to be x ≈ 0.2. The electrical conductivity was studied in the temperature range of 1000–350 C using electrochemical impedance spectroscopy in argon and oxygen atmospheres and via isotherms between 400 and 1000 C as function of oxygen pressure and the water vapour pressure. A marked increase in conductivity of approx. two orders of magnitude was explained by the presence of oxygen vacancies in the calcium doped samples. At pO2 < 10− 12 atm the x = 0.15 materials are predominantly oxygen ion conductors, and La1.85Ca0.15BaZnO5 − δ displays a peak conductivity of 0.002 S cm− 1 at 1000 C. The materials display a rise in conductivity in oxidizing conditions, indicating a significant p-type contribution.
Keywords Oxide ion conductor; Mixed conductor; Synthesis; Impedance spectroscopy; SOFC
Remark doi:10.1016/j.ssi.2015.02.001
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Dual atmosphere study of the K41X stainless steel for interconnect application in high temperature water vapour electrolysis

Authors M.R. Ardigo, I. Popa, L. Combemale, S. Chevalier, F. Herbst, P. Girardon
Source
International Journal of Hydrogen Energy
Volume: 40, Issue: 15, Pages: 5305–5312
Time of Publication: 2015
Abstract High temperature water vapour electrolysis (HTE) is one of the most efficient technologies for mass hydrogen production. A major technical difficulty related to high temperature water vapour electrolysis is the development of interconnects working efficiently for a long period. Working temperature of 800 C enables the use of metallic materials as interconnects. High temperature corrosion behaviour and electrical conductivity of a commercial stainless steel, K41X (AISI 441), were tested in HTE dual atmosphere (95%O2-5%H20/10%H2-90%H2O) at 800 C. The alloy exhibits a very good oxidation resistance compared to single atmosphere tests. However, a supplied electrical current significantly changes the nature of the oxides that form during the test. A very good Area Specific Resistance (ASR) parameter was measured in dual atmosphere, much lower than the values obtained in single atmosphere tests.
Remark doi:10.1016/j.ijhydene.2015.01.116
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Solid oxide fuel cells with (La,Sr)(Ga,Mg)O3-δ electrolyte film deposited by radio-frequency magnetron sputtering

Authors Sea-Fue Wang, His-Chuan Lu, Yung-Fu Hsu, Yi-Xuan Hu
Source
Journal of Power Sources
Volume: 281, Pages: 258–264
Time of Publication: 2015
Abstract In this study, solid oxide fuel cells (SOFCs) containing a high quality La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) film deposited on anode supported substrate using RF magnetron sputtering are successfully prepared. The anode substrate is composed of two functional NiO/Sm0.2Ce0.8O2-δ (SDC) composite layers with ratios of 60/40 wt% and 50/50 wt% and a current collector layer of pure NiO. The as-deposited LSGM film appears to be amorphous in nature. After post-annealing at 1000 C, a uniform and dense polycrystalline film with a composition of La0.87Sr0.13Ga0.85Mg0.15O3-δ and a thickness of 3.8 μm is obtained, which was well adhered to the anode substrate. A composite LSGM/La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) layer, with a ratio of 30/70 wt%, is used as the cathode. The SOFC prepared reveals a good mechanical integrity with no sign of cracking, delamination, or discontinuity among the interfaces. The total cell resistance of a single cell with LSGM electrolyte film declines from 0.60 to 0.10 Ω cm2 as the temperature escalates from 600 to 800 C and the open circuit voltage (OCV) ranges from 0.85 to 0.95 V. The maximum power density (MPD) of the single cell is reported as 0.65, 1.02, 1.30, 1.42, and 1.38 W cm−2 at 600, 650, 700, 750, and 800 C, respectively. The good cell performance leads to the conclusion that RF magnetron sputtering is a feasible deposition method for preparing good quality LSGM films in SOFCs.
Keywords Solid oxide fuel cell; Sputtering; Electrolyte; Doped lanthanum gallate
Remark doi:10.1016/j.jpowsour.2015.01.185
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Phase equilibria in the Cs2MoO4–ZnMoO4–Zr(MoO4)2 system, Crystal structures and properties of new triple molybdates Cs2ZnZr(MoO4)4 and Cs2ZnZr2(MoO4)6

Authors Galina D. Tsyrenova, Sergey F. Solodovnikov, Nadezhda N. Popova, Zoya A. Solodovnikova, Erzhena T. Pavlova, Dmitry Yu. Naumov, Bogdan I. Lazoryak
Source
Volume: 81, Pages: 93–99
Time of Publication: 2015
Abstract Subsolidus phase relations in the Cs2MoO4–ZnMoO4–Zr(MoO4)2 system were determined and two new compounds, Cs2ZnZr(MoO4)4 and Cs2ZnZr2(MoO4)6, were obtained. The structure of Cs2ZnZr(MoO4)4 (a=5.7919(1) , c=8.0490(3) ; space group P View the MathML source3m1; Z=0.5; R=0.0149) belongs to the layered glaserite-like KAl(MoO4)2 structure type where the octahedral Al3+ positions are statistically occupied by 0.5 Zn2++0.5 Zr4+. The second triple molybdate, Cs2ZnZr2(MoO4)6 (a=13.366(1) , c=12.253(3) , space group R View the MathML source3, Z=3, R=0.0324), is isostructural to Cs2MnZr2(MoO4)6 and Cs2M2Zr(MoO4)6 (M=Al, Fe) and contains a mixed 3D framework built of МоO4 tetrahedra and (Zn, Zr)O6 octahedra sharing common vertices. Cesium cations are located in large channels of the framework. The latter compound undergoes a first-order phase transition at 723 K with considerable increasing its ionic conductivity.
Keywords Cesium; Zinc; Zirconium; Triple molybdates; Crystal structure; X-ray diffraction; IR and Raman spectra; Conductivity
Remark doi:10.1016/j.jpcs.2015.01.015
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Binder Jetting: A Novel Solid Oxide Fuel-Cell Fabrication Process and Evaluation

Authors Guha Manogharan, Meshack Kioko, Clovis Linkous
Source
JOM
Volume: 67, Issue: 3, Pages: 660-667
Time of Publication: 2015
Abstract With an ever-growing concern to find a more efficient and less polluting means of producing electricity, fuel cells have constantly been of great interest. Fuel cells electrochemically convert chemical energy directly into electricity and heat without resorting to combustion/mechanical cycling. This article studies the solid oxide fuel cell (SOFC), which is a high-temperature (100C to 1000C) ceramic cell made from all solid-state components and can operate under a wide range of fuel sources such as hydrogen, methanol, gasoline, diesel, and gasified coal. Traditionally, SOFCs are fabricated using processes such as tape casting, calendaring, extrusion, and warm pressing for substrate support, followed by screen printing, slurry coating, spray techniques, vapor deposition, and sputter techniques, which have limited control in substrate microstructure. In this article, the feasibility of engineering the porosity and configuration of an SOFC via an additive manufacturing (AM) method known as binder jet printing was explored. The anode, cathode and oxygen ion-conducting electrolyte layers were fabricated through AM sequentially as a complete fuel cell unit. The cell performance was measured in two modes: (I) as an electrolytic oxygen pump and (II) as a galvanic electricity generator using hydrogen gas as the fuel. An analysis on influence of porosity was performed through SEM studies and permeability testing. An additional study on fuel cell material composition was conducted to verify the effects of binder jetting through SEM–EDS. Electrical discharge of the AM fabricated SOFC and nonlinearity of permeability tests show that, with additional work, the porosity of the cell can be modified for optimal performance at operating flow and temperature conditions.
Remark DOI 10.1007/s11837-015-1296-9
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Hydrogen separation membranes based on dense ceramic composites in the La27W5O55.5–LaCrO3 system

Authors Jonathan M. Polfus, Wen Xing, Marie-Laure Fontaine, Christelle Denonville, Partow P. Henriksen, Rune Bredesen
Source
Journal of Membrane Science
Volume: 479, Pages: 39–45
Time of Publication: 2015
Abstract Some compositions of ceramic hydrogen permeable membranes are promising for integration in high temperature processes such as steam methane reforming due to their high chemical stability in large chemical gradients and CO2 containing atmospheres. In the present work, we investigate the hydrogen permeability of densely sintered ceramic composites (cercer) of two mixed ionic-electronic conductors: La27W3.5Mo1.5O55.5−δ (LWM) containing 30, 40 and 50 wt% La0.87Sr0.13CrO3−δ (LSC). Hydrogen permeation was characterized as a function of temperature, feed side hydrogen partial pressure (0.1–0.9 bar) with wet and dry sweep gas. In order to assess potentially limiting surface kinetics, measurements were also carried out after applying a catalytic Pt-coating to the feed and sweep side surfaces. The apparent hydrogen permeability, with contribution from both H2 permeation and water splitting on the sweep side, was highest for LWM70-LSC30 with both wet and dry sweep gas. The Pt-coating further enhances the apparent H2 permeability, particularly at lower temperatures. The apparent H2 permeability at 700 C in wet 50% H2 was 1.110−3 mL min−1 cm−1 with wet sweep gas, which is higher than for the pure LWM material. The present work demonstrates that designing dual-phase ceramic composites of mixed ionic-electronic conductors is a promising strategy for enhancing the ambipolar conductivity and gas permeability of dense ceramic membranes.
Keywords Hydrogen separation; Dense ceramic membrane; Ceramic–ceramic composite; Lanthanum tungstate; Lanthanum chromite
Remark doi:10.1016/j.memsci.2015.01.027
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Bi1−xNbxO1.5+x (x=0.0625, 0.12) fast ion conductors: Structures, stability and oxide ion migration pathways

Authors Matthew L. Tate, Jennifer Hack, Xiaojun Kuang, Garry J. McIntyre, Ray L. Withers, Mark R. Johnson, Ivana Radosavljevic Evans
Source
Journal of Solid State Chemistry
Volume: 225, Pages: 383–390
Time of Publication: 2015
Abstract A combined experimental and computational study of Bi1−xNbxO1.5+x (x=0.0625 and 0.12) has been carried out using laboratory X-ray, neutron and electron diffraction, impedance measurements and ab-initio molecular dynamics. We demonstrate that Bi0.9375Nb0.0625O1.5625, previously reported to adopt a cubic fluorite-type superstructure, can form two different polymorphs depending on the synthetic method: a metastable cubic phase is produced by quenching; while slower cooling yields a stable material with a tetragonal √2√21 superstructure, which undergoes a reversible phase transition into the cubic form at ~680 C on subsequent reheating. Neutron diffraction reveals that the tetragonal superstructure arises mainly from ordering in the oxygen sublattice, with Bi and Nb remaining disordered, although structured diffuse scattering observed in the electron diffraction patterns suggests a degree of short-range ordering. Both materials are oxide ion conductors. On thermal cycling, Bi0.88Nb0.12O1.62 exhibits a decrease in conductivity of approximately an order of magnitude due to partial transformation into the tetragonal phase, but still exhibits conductivity comparable to yttria-stabilised zirconia (YSZ). Ab-initio molecular dynamics simulations performed on Bi0.9375Nb0.0625O1.5625 show that oxide ion diffusion occurs by O2− jumps between edge- and corner-sharing OM4 groups (M=Bi, Nb) via tetrahedral □M4 and octahedral □M6 vacancies.
Keywords Functional oxides; Fast ion conductors; Complex superstructures
Remark doi:10.1016/j.jssc.2015.01.006
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Functional properties of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ proton conductors where X is an alkaline earth cation

Authors Mariya E. Ivanova, Wilhelm A. Meulenberg, Justinas Palisaitis, Doris Sebold, Cecilia Sols, Mirko Ziegner, Jose M. Serra, Joachim Mayer, Michael Hnsel, Olivier Guillon
Source
Journal of the European Ceramic Society
Volume: 35, Issue: 4, Pages: 1239–1253
Time of Publication: 2015
Abstract Lanthanum niobates with general formulas of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ (X = Mg, Ca, Sr or Ba) were synthesized via the conventional solid state reaction. Specimens with relative density above 96% were produced after sintering. Structural and phase composition studies revealed predominant monoclinic Fergusonite structure for the majority of samples. SEM and TEM studies elucidated the effect of the used dopant combinations on grain growth, micro-crack formation and secondary phase formation. Results from microstructural study were correlated to the grain interior and grain boundary conductivities for selected samples (La0.99Sr0.01Nb0.99Al0.01O4−δ and La0.99Sr0.01Nb0.99Ti0.01O4−δ). The majority of co-doped niobates exhibited appreciable protonic conductivity under humid atmospheres at intermediate temperatures. Sr- or Ca-doped compounds displayed the highest total conductivities with values for LSNA equal to 6 10−4 S/cm and 3 10−4 S/cm in wet air and in wet 4% H2–Ar (900 C), respectively. Additionally, thermal expansion was studied to complete functional characterization of co-doped LaNbO4.
Keywords Proton-conducting ceramic materials; Hydrogen transport ceramic membranes; Rare earth ortho-niobates; Acceptor-doped lanthanum niobates
Remark doi:10.1016/j.jeurceramsoc.2014.11.009
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Hydrogen permeation, water splitting and hydration kinetics in Nd5.4Mo0.3W0.7O12−δ

Authors Zuoan Li, Christian Kjlseth, Reidar Haugsrud
Source
Journal of Membrane Science
Volume: 476, Pages: 105–111
Time of Publication: 2015
Abstract To investigate transport properties of Mo-substituted Nd5.4Mo0.3W0.7O12−δ for hydrogen separation application, hydrogen fluxes of Nd5.4Mo0.3W0.7O12−δ have been measured in both dry and wet sweep gases. The fluxes in dry sweep gas show lower temperature dependence at high temperatures than at low temperatures. Comparing the hydrogen permeability among rare earth tungstates, it has been revealed that the larger the RE-site cation radius, the higher the hydrogen permeation. Water splitting effect for the wet sweep gas has been confirmed by mass spectrometry. Oxygen surface kinetics under oxidizing conditions has been studied by ToF-SIMS measurements, and is significantly faster under wet conditions than dry. Hydration kinetics has been studied by conductivity relaxation measurements under reducing conditions for the first time, showing a two-fold non-monotonic behavior.
Keywords Hydrogen permeation; Hydration kinetics; Water splitting; Oxygen surface kinetics; Nd5.4Mo0.3W0.7O12−δ
Remark doi:10.1016/j.memsci.2014.11.013
Link
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