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Superior electrochemical performance and oxygen reduction kinetics of layered perovskite PrBaxCo2O5+δ (x = 0.90–1.0) oxides as cathode materials for intermediate-temperature solid oxide fuel cells

Authors Jingping Wang, Fuchang Meng, Tian Xia, Zhan Shi, Jie Lian, Chunbo Xu, Hui Zhao, Jean-Marc Bassat, Jean-Claude Grenier
Source
International Journal of Hydrogen Energy
Time of Publication: 2014
Abstract The layered perovskite PrBaxCo2O5+δ (PBxCO, x = 0.90–1.0) oxides have been synthesized by a solid-state reaction technique, and evaluated as the potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Room temperature X-ray diffraction patterns show the orthorhombic structures which double the lattice parameters from the perovskite cell parameter as a ≈ ap, b ≈ ap and c ≈ 2ap (ap is the cell parameter of the primitive perovskite) in the Pmmm space group. There is a good chemical compatibility between the PBxCO cathode and the Ce0.9Gd0.1O1.95 (CGO) electrolyte at 1000 C. The electrical conductivity and thermal expansion coefficient of PBxCO are improved due to the increased amount of electronic holes originated from the Ba-deficiency. The results demonstrate the high electrochemical performance of PBxCO cathodes, as evidenced by the super low polarization resistances (Rp) over the intermediate temperature range. The lowest Rp value, 0.042 Ω cm2, and the cathodic overpotential, −15 mV at a current density of −25 mA cm−2, are obtained in the PrBa0.94Co2O5+δ cathode at 600 C in air, which thus allow to be used as a highly promising cathode for IT-SOFCs. A CGO electrolyte fuel cell with the PrBa0.94Co2O5+δ cathode presents the attractive peak power density of ∼1.0 W cm−2 at 700 C. Furthermore, the oxygen reduction kinetics of the PrBa0.94Co2O5+δ cathode is also studied, and the rate-limiting steps for oxygen reduction reaction are determined at different temperatures.
Remark DOI: 10.1016/j.ijhydene.2014.09.041
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Organic–Inorganic Hybrid Membranes Based on Sulfonated Poly(ether ether ketone) and Tetrabutylphosphonium Bromide Ionic Liquid for PEM Fuel Cell Applications

Authors Vijay Shankar Rangasamy, Savitha Thayumanasundaram, Niels de Greef, Jin Won Seo and Jean-Pierre Locquet
Source
European Journal of Inorganic Chemistry
Time of Publication: 2014
Abstract Ionic liquids (ILs), with their inherent ionic conductivity and negligible vapor pressure, can be exploited in proton exchange membrane (PEM) fuel cells for which thermal management is a major problem and the cell operation temperature is limited by the boiling point of water. In this work, sulfonated poly(ether ether ketone) (SPEEK) membranes were modified by the incorporation of tetrabutylphosphonium bromide ([P4 4 4 4]Br) by solvent-casting. Electrochemical impedance spectroscopy (EIS) was used to study the electrical properties of the modified membranes. Simultaneous TGA and FTIR studies were used to evaluate the thermal stability and chemical structure of the modified membranes, respectively. 1H NMR spectroscopy was applied to probe the changes in the chemical environment due to the interaction between the ionic liquid and the polymer. Mechanical properties were studied by dynamic mechanical analysis. The temperature-dependent behavior of the viscosity of the [P4 4 4 4]Br ionic liquid was observed to obey the Vogel–Fulcher–Tammann (VFT) equation, and was correlated to the ion-conducting properties of the IL-doped SPEEK membranes.
Remark DOI: 10.1002/ejic.201402558
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Crystal Structure and electrical properties of complex perovskite solid solutions based on (1-x) NaNbO3-xBi (Zn0.5Ti0.5) O3

Authors Sasiporn Prasertpalichat, David P. Cann
Source
Journal of Electroceramics
Time of Publication: 2014
Abstract Ceramics based on the perovskite solid solution (1-x) NaNbO3-xBi (Zn0.5Ti0.5) O3 were prepared using conventional solid state synthesis. The crystal structure, electrical, and optical properties were examined. According to diffraction data, a single perovskite phase could be identified up to the composition x = 0.09. As the Bi (Zn0.5Ti0.5) O3 content increased the crystal structure transitioned from orthorhombic to pseudocubic symmetry. Furthermore, dielectric data showed that the dielectric maximum shifted to lower temperatures with the addition of Bi (Zn0.5Ti0.5) O3. Polarization hysteresis data revealed a slim linear loop across the whole range of solid solutions. Optical data also showed a decrease in the optical band gap from 3.4 eV for pure NaNbO3 to 2.9 eV for the x = 0.09 composition. Using impedance spectroscopy, an electrically inhomogeneous microstructure was observed for compositions with increased Bi (Zn0.5Ti0.5) O3 content. Finally, the substitution of Ta on the B-site was shown to shift the dielectric maximum to temperatures as low as 100 K.
Remark DOI 10.1007/s10832-014-9953-x
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A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3

Authors Ming Li, Martha J. Pietrowski, Roger A. De Souza, Huairuo Zhang, Ian M. Reaney, Stuart N. Cook, John A. Kilner & Derek C. Sinclair
Source
Nature Materials
Volume: 13, Pages: 31-35
Time of Publication: 2014
Abstract Oxide ion conductors find important technical applications in electrochemical devices such as solid-oxide fuel cells (SOFCs), oxygen separation membranes and sensors1, 2, 3, 4, 5, 6, 7, 8, 9. Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free piezoelectric material; however, it is often reported to possess high leakage conductivity that is problematic for its piezo- and ferroelectric applications10, 11, 12, 13, 14, 15. Here we report this high leakage to be oxide ion conduction due to Bi-deficiency and oxygen vacancies induced during materials processing. Mg-doping on the Ti-site increases the ionic conductivity to ~0.01 S cm−1 at 600 C, improves the electrolyte stability in reducing atmospheres and lowers the sintering temperature. This study not only demonstrates how to adjust the nominal NBT composition for dielectric-based applications, but also, more importantly, gives NBT-based materials an unexpected role as a completely new family of oxide ion conductors with potential applications in intermediate-temperature SOFCs and opens up a new direction to design oxide ion conductors in perovskite oxides.
Remark doi:10.1038/nmat3782
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Thermoelectric Properties of A-site Deficient Lanthanum Substituted Strontium Titanate

Author Thomas Emdal Loland
Source
Time of Publication: 2014
Remark Link

Grain Size Dependent Comparison of ZnO and ZnGa2O4 Semiconductors by Impedance Spectrometry

Authors Shalima Shawuti, Musa Mutlu Can, Mehmet Ali Glgn,Tezer Fırat
Source
Electrochimica Acta
Time of Publication: 2014
Abstract We investigated the electrical properties of ZnGa2O4 via AC (alternating current) Impedance Spectroscopy method comparing with ZnO reference material. Experimentally, AC electrical conductivity of ZnO and ZnGa2O4 were found to be a function of temperature and grain size; i.e., the increase in grain size of the ZnO led a decrease in room temperature conductivity from 1.35 10−7 S cm−1 to 9.9 10−8 S cm−1. The temperature dependent resistivity variation of ZnGa2O4 and ZnO were similar to each other with varied responding temperature. Likewise, the conductivity for ZnGa2O4 decrease from 2.2 10−8 S cm−1 to 3.8 10−9 S cm−1 upon an increase in grain size from ∼0.5 μm to 100 μm, accordingly. In addition, a rise in temperature caused an increase in conductivity and led to a corresponding shift in the relaxation time towards the lower values. The semicircles in Nyquist plots disappeared at temperature above 250 C and 700 C for ZnO and ZnGa2O4, respectively. The AC measurements were also correlated with the size dependent activation energies (171 meV for 0.5 μm ZnO and 1200 meV for 0.5 μm ZnGa2O4).
Keywords Activation energy; Nyquist plots; AC Impedance spectrometry; Oxide semiconductors
Remark DOI: 10.1016/j.electacta.2014.08.084
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Effect of thermobaric treatment on the structure and properties of CaCu3Ti4O12

Authors N. I. Kadyrova, Y. G. Zainulin, N. V. Mel’nikova, I. S. Ustinova, I. G. Grigorov
Source
Bulletin of the Russian Academy of Sciences: Physics
Volume: 78, Issue: 8, Pages: 719-722
Time of Publication: 2014
Abstract CaCu3Ti4O12 is prepared by means of solid-state sintering. The effect of thermobaric treatment (P = 8.0 GPa and T = 1100C) and partial replacement of titanium by vanadium on the microstructure and dielectric properties of CaCu3Ti4O12 are investigated.
Remark Link

Conductivity and oxygen reduction activity changes in lanthanum strontium manganite upon low-level chromium substitution

Authors George Tsekouras, Artur Braun
Source
Solid State Ionics
Volume: 266, Pages: 19-24
Time of Publication: 2014
Abstract On the timescale of solid oxide fuel cell (SOFC) system lifetime requirements, the thermodynamically predicted low-level substitution of chromium on the B-site of (La,Sr)MnO3 could be a source of cathode degradation underlying more overt and well-known chromium poisoning mechanisms. To study this phenomenon in isolation, electronic conductivity (σ) and electrochemical oxygen reduction activity of the (La0.8Sr0.2)0.98CrxMn1−xO3 model series (x = 0, 0.02, 0.05 or 0.1) were measured in air between 850 and 650 C. Depending on the extent of chromium substitution and the measurement temperature, electrochemical impedance spectroscopy (EIS) results could be deconvoluted into a maximum of three contributions reflecting possible limiting processes such as oxide ion transport and dissociative adsorption. Chromium substitution resulted in lowered σ (from 174 S cm− 1 (x = 0) to 89 S cm− 1 (x = 0.1) at 850 C) and a steady rise in associated activation energy (Ea) (from 0.105 0.001 eV (x = 0) to 0.139 0.001 eV (x = 0.1)). From EIS analyses, ohmic and polarisation resistances increased, whilst Ea for the overall oxygen reduction reaction also increased from 1.39 0.04 eV (x = 0) to 1.48–1.54 0.04 eV upon chromium substitution.
Keywords Solid oxide fuel cell; Lanthanum strontium manganite; Chromium poisoning; Electronic conductivity; Electrochemical impedance spectroscopy
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The effect of calcination temperature on the electrochemical properties of La0.3Sr0.7Fe0.7Cr0.3O3−x (LSFC) perovskite oxide anode of solid oxide fuel cells (SOFCs)

Authors Yifei Sun, Ning Yan, Jianhui Li, Huayi Wu, Jing-Li Luo, Karl T. Chuang
Source
Sustainable Energy Technologies and Assessments
Volume: 8, Pages: 92-98
Time of Publication: 2014
Abstract A series of perovskite structure anode materials, LSFC, was successfully prepared by a glycine combustion process and further calcined at different temperatures. The electrochemical properties of anodes prepared at various calcination temperatures (1100 C, 1200 C and 1300 C) were investigated. The calcination temperature had no significant influence on the morphology of the material but showed obvious influences on the particle sizes and electrochemical properties of the materials. Higher calcination temperature results in sharper X-ray diffractometer (XRD) diffraction peaks of the materials with larger particle sizes and higher electrical conductivity. However materials calcined at higher temperature had much smaller BET surface area resulting in lower triple phase boundary (TPB). The electrochemical performance test exhibited that LSFC anode material sintered at 1100 C exhibited the smallest area specific resistance (ASR) value in H2 at operating temperatures from 700 to 900 C. For proton conducting SOFCs (PC-SOFCs) fed by syngas, the cell with anode calcined at 1100 C also showed highest power density output of 120 mW/cm2 at 750 C, which was almost three times higher than that of the cell with anode calcined at 1300 C.
Keywords Solid oxide fuel cell; Calcination temperature; Electrochemical properties; Perovskite
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Oxygen interstitial and vacancy conduction in symmetric Ln2 x Zr2 x O7 x/2 (Ln = Nd, Sm) solid solutions

Authors A. V. Shlyakhtina, D. A. Belov, A. V. Knotko, I. V. Kolbanev, A. N. Streletskii, O. K. Karyagina, L. G. Shcherbakova
Source
Inorganic Materials
Volume: 50, Issue: 10, Pages: 1035-1049
Time of Publication: 2014
Abstract We have compared (Ln2 − x Zr x )Zr2O7 + x/2 (Ln = Nd, Sm) pyrochlore-like solid solutions with interstitial oxide ion conduction and Ln2(Zr2 − x Ln x )O7 − δ (Ln = Nd, Sm) pyrochlore-like solid solutions with vacancy-mediated oxide ion conduction in the symmetric systems Nd2O3-ZrO2 (NdZrO) and Sm2O3-ZrO2 (SmZrO). We have studied their structure, microstructure, and transport properties and determined the excess oxygen content of the (Sm2 − x Zr x )Zr2O7 + x/2 (x = 0.2) material using thermal analysis and mass spectrometry in a reducing atmosphere (H2/Ar-He). The Ln2 x Zr2 x O7 x/2 (Ln = Nd, Sm) solid solutions have almost identical maximum oxygen vacancy and interstitial conductivities: (3–4) 10−3 S/cm at 750C. The lower oxygen vacancy conductivity of the Ln2(Zr2 − x Ln x )O7 − δ (Ln = Nd, Sm; 0 < x ≤ 0.3) solid solutions is due to the sharp decrease in it as a result of defect association processes, whereas the interstitial oxide ion conductivity of the (Ln2 − x Zr x )Zr2O7 + x/2 (Ln = Nd, Sm; 0.2 ≤ x < 0.48) pyrochlore-like solid solutions is essentially constant in a broad range of Ln2O3 concentrations.
Remark Link

MICROWAVE SINTERING OF Sr AND Mg-DOPED LANTHANUM GALLATE (LSGM) SOLID ELECTROLYTES

Authors Cristian Andronescu, Victor Fruth, Enikoe Volceanov, Rares Scurtu, Cornel Munteanu, Maria Zaharescu
Source
Romanian journal of materials
Time of Publication: 2014-01
Abstract Sr2+ and Mg2+ simultaneously doped lanthanum gallate (LSGM) powders, prepared by a modified Pechini route using polyvinyl alcohol (PVA) as polymeric alcohol, were densified using an activated microwave technique at 2.45 GHz, to develop a dense stable electrolyte for application in intermediate temperatures solid oxide fuel cells (IT-SOFC). Thermal behaviour of precursors was investigated by means of differential thermal analysis combined with thermogravimetric analysis (DTA/TGA). The powders and sintered samples were characterized using scanning electron microscopy and energy dispersive analysis (SEM-EDAX), X-ray diffraction (XRD) and infrared spectroscopy (FT-IR). The thermal expansion coefficient (TEC) and ionic conductivity of the sintered samples were also evaluated. Fine, homogeneous and high density pellets of almost pure LSGM phase were obtained after sintering at 14000C for a short period time in an activated microwave field. Using activated microwave field, due to the volumetric in situ heating, the sintering process is highly specific and instantaneous, leading to a faster kinetics compared to the conventional process (electric oven). With an optimized sintering schedule, a fine grained and dense microstructure of the samples were obtained.
Remark Link

Magnetron formation of Ni/YSZ anodes of solid oxide fuel cells

Authors A. A. Solov’ev, N. S. Sochugov, I. V. Ionov, A. V. Shipilova, A. N. Koval’chuk
Source
Russian Journal of Electrochemistry
Volume: 50, Issue: 7, Pages: 647-655
Time of Publication: 2014
Abstract Physico-chemical and structural properties of nanocomposite NiO/ZrO2:Y2O3 (NiO/YSZ) films applied using the reactive magnetron deposition technique are studied for application as anodes of solid oxide fuel cells. The effect of oxygen consumption and magnetron power on the discharge parameters is determined to find the optimum conditions of reactive deposition. The conditions for deposition of NiO/YSZ films, under which the deposition rate is maximum (12 μm/h), are found and the volume content of Ni is within the range of 40–50%. Ni-YSZ films reduced in a hydrogen atmosphere at the temperature of 800C have a nanoporous structure. However, massive nickel agglomerates are formed in the course of reduction on the film surface; their amount grows at an increase in Ni content in the film. Solid oxide fuel cells with YSZ supporting electrolyte and a LaSrMnO3 cathode are manufactured to study electrochemical properties of NiO/YSZ films. It is shown that fuel cells with a nanocomposite NiO/YSZ anode applied using a magnetron sputtering technique have the maximum power density twice higher than in the case of fuel cells with an anode formed using the high-temperature sintering technique owing to a more developed gas-anode-electrolyte three-phase boundary.
Remark Link

Full ceramic micro solid oxide fuel cells: towards more reliable MEMS power generators operating at high temperatures

Authors I. Garbayo, D. Pla, A. Morata, L. Fonseca, N. Sabat and A. Tarancn
Source
Energy Environ. Sci.
Time of Publication: 2014
Abstract Batteries, with a limited capacity, have dominated the power supply of portable devices for decades. Recently, the emergence of new types of highly efficient miniaturized power generators like micro fuel cells has opened up alternatives for continuous operation on the basis of unlimited fuel feeding. This work addresses for the first time the development of a full ceramic micro solid oxide fuel cell fabricated in silicon technology. This full-ceramic device represents a new generation of miniaturized power generators able to operate at high temperatures, and therefore able to work with a hydrocarbon fuel supply. Dense yttria-stabilized zirconia free-standing large-area membranes on micromachined silicon were used as the electrolyte. Thin-film porous electrodes of La0.6Sr0.4CoO3−δ and gadolinia-doped ceria were employed as cathode and anode materials, respectively. The electrochemical performance of all the components was evaluated by partial characterization using symmetrical cells, yielding excellent performance for the electrolyte (area specific resistance of 0.15 Ω cm2 at temperatures as low as 450 C) and the electrodes (area specific resistance of the cathode and anode below 0.3 Ω cm2 at 700 C). A micro solid oxide fuel cell with an active area of 2 mm2 and less than 1 micrometer in thickness was characterized under fuel cell conditions, using hydrogen as a fuel and air as an oxidant. A maximum power density of 100 mW cm−2 and 2 mW per single membrane was generated at 750 C, having an open circuit voltage of 1.05 V. Impedance spectroscopy of the all-ceramic membrane showed a total area-specific resistance of [similar]3.5 Ω cm2.
Remark DOI: 10.1039/C4EE00748D
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Proton conductivity of hexagonal and cubic BaTi1−xScxO3−δ (0.1 ≤ x ≤ 0.8)

Authors Seikh M. H. Rahman, Stefan T. Norberg, Christopher S. Knee, Jordi J. Biendicho, Stephen Hull and Sten G. Eriksson
Source
Dalton Transactions
Time of Publication: 2014
Abstract BaTi1−xScxO3−δ (x = 0.1–0.8) was prepared via solid state reaction. High resolution X-ray powder diffraction was used to characterise the synthesised materials. It was found that low substitution (x = 0.1 and 0.2) of Ti4+ for Sc3+ gives a hexagonal perovskite structure, whereas high substitution (x = 0.5–0.7) results in a cubic perovskite structure. Thermogravimetric analysis revealed significant levels of protons in both as-prepared and hydrated samples. Electrical conductivity was measured by AC impedance methods under oxygen, argon and under dry and humid, both H2O and D2O, conditions for BaTi1−xScxO3−δ (x = 0.2, 0.6 and 0.7). In the temperature range of 150–600 C, under humid conditions, the conductivity is significantly higher than that under the dry conditions. The increase in conductivity is especially prominent for the cubic phases, indicating that protons are the dominant charge carriers. The proton conductivity of hexagonal BaTi0.8Sc0.2O3−δ is approx. two orders of magnitude lower than that of the more heavily substituted cubic phases. Conductivity is also found to be higher in dry O2 than in Ar in the whole temperature range of 150–1000 C, characteristic of a significant contribution from p-type charge carriers under oxidising atmospheres. Greater Sc3+ substitution leads to a higher proton concentration and the highest proton conductivity (σ [similar] 2 10−3 S cm−1 at 600 C) is found for the BaTi0.3Sc0.7O3−δ composition.
Remark DOI: 10.1039/C4DT01280A
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Protons in acceptor doped langasite, La3Ga5SiO14

Authors Tor Svendsen Bjrheim, Reidar Haugsrud, Truls Norby
Source
Solid State Ionics
Volume: 264, Pages: 76–84
Time of Publication: 2014
Abstract The electrical and defect chemical properties of acceptor doped langasite have been investigated over wide ranges of pH2O, pO2 and temperature. All compositions are pure proton conductors up to 800 C in wet atmospheres and mixed oxide ion-p-type conductors at higher temperatures. The enthalpy of mobility of protons is 75 3 kJ/mol, while that of oxygen vacancies is 125 7 kJ/mol. The standard enthalpy and entropy of hydration are -100 3 kJ/mol and -157 5 J/mol K, respectively. Langasite based sensors may therefore be affected by dissolution of protons from H2O in the bulk crystal lattice up to temperatures as high as 1000 C.
Keywords Langasite; Piezoelectric; DFT; Defects; Hydrogen; Conductivity

Solid-State Synthesis and Properties of Relaxor (1−x)BKT–xBNZ Ceramics

Authors Espen T. Wefring, Maxim I. Morozov, Mari-Ann Einarsrud and Tor Grande
Source
J. of American Ceramic Society
Time of Publication: 2014
Abstract Conventional solid-state synthesis was used to synthesize dense and phase pure ceramics in the (1−x) Bi0.5K0.5TiO3–xBi0.5Na0.5ZrO3 (BKT–BNZ) system. Structural characterization was done using X-ray diffraction at both room temperature and elevated temperatures, identifying a transition from tetragonal xBi0.5Na0.5ZrO3 (xBNZ, x = 0–0.10) to pseudo cubic xBNZ for x = 0.15–0.80. Dielectric properties were investigated with respect to both temperature (RT = 600C) and frequency (1–106 Hz). Relaxor-like behavior was retained for all the materials investigated, evident by the broadening of the relative dielectric permittivity peaks at transition temperatures as well as frequency dispersion at their maximum. The maximum dielectric constant at elevated temperature was found for 0.15 BNZ. Electric field-induced strain and polarization response were also investigated for several compositions at RT and the largest field-induced strain was observed for the 0.10 BNZ ceramics. The composition range with best performance coincides with the transition from tetragonal to cubic crystal structure.
Remark DOI: 10.1111/jace.13066
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Ceramic–carbonate dual-phase membrane with improved chemical stability for carbon dioxide separation at high temperature

Authors Tyler T. Norton, Y.S. Lin
Source
Solid State Ionics
Volume: 263, Pages: 172–179
Time of Publication: 2014
Abstract This study examines membrane synthesis, structural stability, permeation properties, and long-term permeation stability of a new dense dual-phase membrane of composition La0.85Ce0.1Ga0.3Fe0.65Al0.05O3 − δ (LCGFA)–carbonate for high temperature CO2 separation. Porous ceramic supports made by sintering pressed powder at a temperature below its densification temperature resulted in a desired support with an open porosity ranging between 40 and 50%. The dual-phase membranes was prepared by direct infiltration of the ceramic supports in molten carbonate at 600 C, resulting in a four order of magnitude decrease in permeance when compared to the support. LCGFA–carbonate membranes are stable when exposed to gases ranging from gas mixtures containing N2 and various concentrations of CO2 to simulated syngas, and exhibit a stable long term CO2 permeation flux of 0.025 mLmin− 1cm− 2 for more than 275 h at 900 C. The CO2 permeation results show exponential dependence to increasing system temperature as well as a linear dependence to logarithmic change in CO2 partial pressure gradients across the membrane in the CO2 pressure range studied.
Keywords Ceramic–carbonate; Carbon dioxide permeation; Dual-phase membrane; Perovskite
Remark Link

Hydrogen flux in La0.87Sr0.13CrO3–δ

Authors Camilla K. Vigen, Reidar Haugsrud
Source
Journal of Membrane Science
Volume: 468, Pages: 317–323
Time of Publication: 2014
Abstract Acceptor doped LaCrO3 is a promising material for dense, ceramic hydrogen permeable membranes, displaying hydrogen flux in the order of 10−4 ml min−1 cm−1 in a 10% H2+2.5% H2O/dry Ar gradient at 1000 C. In this work we have characterized the ambipolar proton electron hole conductivity in La0.87Sr0.13CrO3–δ by means of hydrogen flux measurements. Proton transport parameters were extracted, yielding a pre-exponential factor of 3 cm2 K V−1 s−1 and an enthalpy of mobility of 65 kJ mol−1. Hydrogen flux measurements showed that applying a layer of Pt on both feed and sweep side surfaces significantly altered the temperature dependency and increased the hydrogen flux in a 550 μm thick membrane. This indicates that surface kinetics will limit the hydrogen flux in uncoated membranes. From hydrogen surface exchange measurements, a surface exchange coefficient ranging from 10−10 to 10−8 mol cm−2 s−1 at 325–600 C was obtained.
Keywords Hydrogen permeation; LaCrO3; Proton conductivity; Surface kinetics
Remark Link

Carbon dioxide permeation properties and stability of samarium-doped-ceria carbonate dual-phase membranes

Authors Tyler T. Norton, Bo Lu, Y.S. Lin
Source
Journal of Membrane Science
Volume: 467, Pages: 244–252
Time of Publication: 2014
Abstract This study examines high temperature carbon dioxide permeation properties and long-term permeation stability of samarium doped ceria (SDC)-carbonate dual-phase membranes. Hermetic SDC-carbonate membranes were prepared by infiltrating porous SDC ceramic support with Li/K/Na molten carbonate. Carbon permeation experiments on the SDC-carbonate membranes were conducted with either atmospheric or high pressure feed of CO2:N2 mixture or simulated syngas with composition of 50% CO, 35% CO2, 10% H2, and 5% N2. The SDC-carbonate membranes exhibit CO2 permeation flux in the range of 0.2–0.8 mL(STP) cm−2 min−1 in 700–950 C with measured CO2 to N2 separation factor above 1000. The CO2 permeation flux shows power function dependence with CO2 partial pressure and exponential dependence with temperature. The activation energy for CO2 permeation is 63 kJ mol−1, similar to that for oxygen ionic conduction in SDC. Essentially the same CO2 permeation characteristics are observed for the membranes with CO2:N2 and simulated syngas feeds. The membranes exhibit stable long-term permeation flux in 700–900 C with either CO2:N2 or simulated gas feed at atmospheric pressure or high pressure (5 atm) for various periods of testing time (as long as 35 days). The membranes, with remarkable permeation stability in the presence of H2, show only slight decomposition of the ceramic phase after long-term exposure to feed gas mixtures at high temperature.
Keywords Ceramic-carbonate; Samarium doped ceria; Carbon dioxide permeation; Fluorite; Membrane stability
Remark Link

Hydrogen permeation characteristics of La27Mo1.5W3.5O55.5

Authors Einar Vllestad, Camilla K. Vigen, Anna Magras, Reidar Haugsrud
Source
Journal of Membrane Science
Volume: 461, Pages: 81–88
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 vapor pressure in the sweep gas. Transport of hydrogen by means of ambipolar proton–electron conductivity and – with wet sweep gas – water splitting contributes 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 that 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 the 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 http://dx.doi.org/10.1016/j.memsci.2014.03.011
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Mesoporous NiO-Samaria Doped Ceria for Low-Temperature Solid Oxide Fuel Cells

Authors Kim, Jin-Yeop; Kim, Ji Hyeon; Choi, Hyung Wook; Kim, Kyung Hwan; Park, Sang Joon
Source
Journal of Nanoscience and Nanotechnology
Volume: 14, Issue: 8, Pages: 6399-6403(5)
Time of Publication: 2014
Abstract In order to prepare anode material for low-temperature solid oxide fuel cells (SOFCs), the mesoporous NiO-SDC was synthesized using a cationic surfactant (cetyltrimethyl-ammonium bromide; CTAB) for obtaining wide triple-phase boundary (TPB). In addition, Ni-SDC anode-supported SOFC single cells with YSZ electrolyte and LSM cathode were fabricated and the performance of single cells was evaluated at 600 C. The microstructure of NiO-SDC was characterized by XRD, EDX, SEM, and BET, and the results showed that the mesoporous NiO-SDC with 10 nm pores could be obtained. It was found that the surface area and the electrical performance were strongly influenced by the Ni content in Ni-SDC cermets. After calcined at 600 C, the surface area of NiO-SDC was between 90–117 m2/g at 35–45 Ni wt%, which was sufficiently high for providing large TPB in SOFC anode. The optimum Ni content for cell performance was around 45 wt% and the corresponding MPD was 0.36 W/cm2. Indeed, the mesoporous NiO-SDC cermet may be of interest for use as an anode for low-temperature SOFCs.
Remark DOI: http://dx.doi.org/10.1166/jnn.2014.8452
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Oxide ion transport in (Nd2−xZrx)Zr2O7+δ electrolytes by an interstitial mechanism

Authors A.V. Shlyakhtina, D.A. Belov, A.V. Knotko, M. Avdeev, I.V. Kolbanev, G.A. Vorobieva, O.K. Karyagina, L.G. Shcherbakova
Source
Journal of Alloys and Compounds
Volume: 603, Issue: 5, Pages: 274–281
Time of Publication: 2014
Abstract We have studied the structure and transport properties of ten (Nd2−xZrx)Zr2O7+x/2 (x = 0–1.27) solid solutions, which lie in the ZrO2–Nd2Zr2O7 isomorphous miscibility range. Major attention has been focused on the pyrochlore-like (Nd2−xZrx)Zr2O7+x/2 solid solutions with x = 0–0.78, which are thought to be potential interstitial oxide ion conductors. The X-ray and neutron diffraction results demonstrate that the (Nd2−xZrx)Zr2O7+x/2 (x = 0–1.27) solid solutions undergo an order–disorder (pyrochlore–defect fluorite) structural phase transition. The (Nd2−xZrx)Zr2O7+x/2 (x = 0.2–0.78) have the bulk conductivity, ∼(1.2–4) 10–3 S/cm at 750 C, which is two orders of magnitude higher than that of the ordered pyrochlore Nd2Zr2O7. An attempt has been made to determine the interstitial oxygen content of (Nd2−xZrx)Zr2O7+x/2 (x = 0.2; 0.67) in a reducing atmosphere using thermogravimetry and mass spectrometry. It has been shown that no reduction occurs in the NdZrO system, where neodymium has only one oxidation state, 3+.
Keywords Fuel cells; Ionic conduction; Electrochemical impedance spectroscopy; Neutron diffraction; X-ray diffraction; SEM
Remark http://dx.doi.org/10.1016/j.jallcom.2014.03.068
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Application of PVD methods to solid oxide fuel cells

Authors A.A. Solovyeva, N.S. Sochugov, S.V. Rabotkin, A.V. Shipilova, I.V. Ionov, A.N. Kovalchuk, A.O. Borduleva
Source
Applied Surface Science
Time of Publication: 2014
Abstract In this paper, attention is paid to the application of such a method of vacuum physical vapor deposition (PVD) as magnetron sputtering for fabrication of a solid oxide fuel cell (SOFC) materials and structures. It is shown that the YSZ (yttria-stabilized zirconia) electrolyte and Ni–YSZ anode layers with required thickness, structure and composition can be effectively formed by PVD methods. The influence of parameters of pulsed power magnetron discharge on the deposition rate and the microstructure of the obtained YSZ electrolyte films were investigated. It is shown that the deposition rate of the oxide layers by magnetron sputtering can be significantly increased by using asymmetric bipolar power magnetrons, which creates serious prerequisites for applying this method on the industrial scale. Porous Ni–YSZ anode films were obtained by reactive co-sputtering of Ni and Zr–Y targets and subsequent reduction in the H2 atmosphere at a temperature of 800 C. The Ni–YSZ films comprised small grains and pores of tens of nanometers.
Keywords Solid oxide fuel cell; Metal support; Magnetron sputtering; Thin film; YSZ electrolyte; NiO/YSZ anode
Remark http://dx.doi.org/10.1016/j.apsusc.2014.03.163
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Proton conduction in oxygen deficient Ba3In1.4Y0.3M0.3ZrO8 (M = Ga3+ or Gd3+) perovskites

Authors Francis G. Kinyanjui, Stefan T. Norberg, Christopher S. Knee, Sten-G. Eriksson
Source
Journal of Alloys and Compounds
Volume: 605, Pages: 56-62
Time of Publication: 2014
Abstract B -site disordered, oxygen deficient Ba3In1.4Y0.3M 0.3ZrO8 (M = Gd3+ or Ga3+) perovskites of space group View the MathML sourcePm3‾m, were prepared by a solid-state reactive sintering method. Thermogravimetric analysis of the as-prepared samples revealed 79.3% and 55.5% protonation of the available oxygen vacancies by OH groups in the Gd3+ and Ga3+ containing samples, respectively. Conductivity was found to be in the range of 0.3–1.1 10−3 S cm−1 (M = Gd3+) and 1.1–4.6 10−4 S cm−1 (M = Ga3+) for the temperature interval 300–600 C in wet Argon. Ba3In1.4Y0.3Ga0.3ZrO8 shows an approximate one order of magnitude increase in conductivity at T > 600 C under dry oxygen indicating a significant p-type contribution whereas Ba3In1.4Y0.3Gd0.3ZrO8 reveals a smaller enhancement. Ba3In1.4Y0.3Ga0.3ZrO8 displays considerable mixed proton–electronic conduction in the interval 400–800 C under wet oxidising conditions suggesting possibility of Ga-containing compositions as a cathode materials in a proton conducting fuel cell.
Keywords Proton conducting electrolyte; Oxygen deficient perovskite; Mixed conductor; Cathode material; Impedance spectroscopy

Role of point defects in bipolar fatigue behavior of Bi(Mg1/2Ti1/2)O3 modified (Bi1/2K1/2)TiO3-(Bi1/2Na1/2)TiO3 relaxor ceramics

Authors Nitish Kumar, Troy Y. Ansell and David P. Cann
Source
J. Applied Physics
Volume: 115, Pages: 154104
Time of Publication: 2014
Abstract Lead-free Bi(Mg1/2Ti1/2)O3-(Bi1/2K1/2)TiO3-(Bi1/2 Na 1/2)TiO3 (BMT-BKT-BNT) ceramics have been shown to exhibit large electromechanical strains under high electric fields along with negligible fatigue under strong electric fields. To investigate the role of point defects on the fatigue characteristics, the composition 5BMT-40BKT-55BNT was doped to incorporate acceptor and donor defects on the A and B sites by adjusting the Bi/Na and Ti/Mg stoichiometries. All samples had pseudo-cubic symmetries based on x-ray diffraction, typical of relaxors. Dielectric measurements showed that the high and low temperature phase transitions were largely unaffected by doping. Acceptor doping resulted in the observation of a typical ferroelectric-like polarization with a remnant polarization and strain hysteresis loops with significant negative strain. Donor-doped compositions exhibited characteristics that were indicative of an ergodic relaxor phase. Fatigue measurements were carried out on all of the compositions. While the A-site acceptor-doped composition showed a small degradation in maximum strain after 106 cycles, the other compositions were essentially fatigue free. Impedance measurements were used to identify the important conduction mechanisms in these compositions. As expected, the presence of defects did not strongly influence the fatigue behavior in donor-doped compositions owing to the nature of their reversible field-induced phase transformation. Even for the acceptor-doped compositions, which had stable domains in the absence of an electric field at room temperature, there was negligible degradation in the maximum strain due to fatigue. This suggests that either the defects introduced through stoichiometric variations do not play a prominent role in fatigue in these systems or it is compensated by factors like decrease in coercive field, an increase in ergodicity, symmetry change, or other factors.
Remark http://dx.doi.org/10.1063/1.487167
Link
norecs.com

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