Published references
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These publications have a reference to ProboStat™ or other NORECS products
All 1-25 26-50 51-75 76-100 101-125 126-150 151-175 176-200 201-225 226-250 251-275 276-300 301-325 326-350 351-375 376-400 401-425 426-450 451-475 476-500 501-525 526-550 551-575 576-600 601-625 626-650 651-675 676-Hydrogen flux in La0.87Sr0.13CrO3–δ
ID=259| Authors |
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| 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
ID=258| Authors |
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| 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
ID=257| Authors |
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| 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 6×10−46×10−4 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 Link |
Mesoporous NiO-Samaria Doped Ceria for Low-Temperature Solid Oxide Fuel Cells
ID=256| Authors |
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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 Link |
Oxide ion transport in (Nd2−xZrx)Zr2O7+δ electrolytes by an interstitial mechanism
ID=255| Authors |
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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 Link |
Application of PVD methods to solid oxide fuel cells
ID=254| Authors |
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| Source |
Applied Surface Science
Time of Publication: 2014
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| 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 Link |
Proton conduction in oxygen deficient Ba3In1.4Y0.3M0.3ZrO8 (M = Ga3+ or Gd3+) perovskites
ID=253| Authors |
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| 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
ID=252| Authors |
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| 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 |
Structure and transport properties in un-doped and acceptor-doped gadolinium tungstates
ID=251| Authors |
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| 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
ID=250| Authors |
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| Source |
Journal of Power Sources
Time of Publication: 2014
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| 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 Link |
Hydrogen permeation characteristics of La27Mo1.5W3.5O55.5
ID=249| Authors |
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| Source |
Journal of Membrane Science
Time of Publication: 2014
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| 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 6×10−46×10−4 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 Link |
Performance Variability and Degradation in Porous La1-xSrxCoO3-δ Electrodes
ID=248| Authors |
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| 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 ∼ 1100°C, 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 Link |
Doped Germanate-Based Apatites as Electrolyte for Use in Solid Oxide Fuel Cells
ID=247| Authors |
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| Source |
Fuel Cells
Time of Publication: 2014
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| 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 Link |
Effect of Nb substitution for Ti on the electrical properties of Yb2Ti2O7-based oxygen ion conductors
ID=246| Authors |
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| Source |
Solid State Ionics
Time of Publication: 2014
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| 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 Link |
Zr-doped samarium molybdates — potential mixed electron–proton conductors
ID=245| Authors |
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| Source |
Solid State Ionics
Time of Publication: 2014
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| 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 Link |
Interstitial oxide ion conduction in (Sm2 − xZrx)Zr2O7 + δ
ID=244| Authors |
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| Source |
Solid State Ionics
Time of Publication: 2014
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| 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 Link |
Atmosphere controlled conductivity and Maxwell-Wagner relaxation in Bi0.5K0.5TiO3—BiFeO3 ceramics
ID=243| Authors |
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| 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
ID=242| Authors |
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| 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
ID=241| Authors |
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| 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) Å. 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
ID=240| Authors |
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| Source |
Ind. Eng. Chem. Res.
Time of Publication: 2014
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| 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 Link |
Synthesis and characterization of the micro-mesoporous anode materials and testing of the medium temperature solid oxide fuel cell single cells
ID=239| Author |
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| Source |
Time of Publication: 2013
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| Remark |
Dissertation Link |
Polymorphism and properties of Bi2WO6 doped with pentavalent antimony
ID=238| Authors |
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| Source |
Journal of Alloys and Compounds
Time of Publication: 2014
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| 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 Link |
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
ID=237| Authors |
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| Source |
Electrochimica Acta
Time of Publication: 2013
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| 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 Link |
Cathode compatibility, operation, and stability of LaNbO4-based proton conducting fuel cells
ID=236| Authors |
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| Source |
Solid State Ionics
Time of Publication: 2013
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| 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; Link |
Determination of Oxygen Diffusion Coefficients in La1-xSrxFe1-yGayO3-δ Perovskites Using Oxygen Semi-Permeation and Conductivity Relaxation Methods
ID=235| Authors |
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| 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 |
