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Influence of Pr substitution on defects, transport, and grain boundary properties of acceptor-doped BaZrO3

Authors Anna Magras, Christian Kjlseth, Reidar Haugsrud, Truls Norby
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 7962–7969
Time of Publication: 2012-05
Abstract We report on effects of partially substituting Zr with the multivalent Pr on the conductivity characteristics of acceptor (Gd) doped BaZrO3-based materials. BaZr0.6Pr0.3Gd0.1O3−δ was sintered 96% dense at 1550 C with grains of 1–4 μm. The electrical conductivity was characterised by impedance spectroscopy and EMF transport number measurements as a function of temperature and the partial pressures of oxygen and water vapour. H2O/D2O exchanges were applied to further verify proton conduction. The material is mainly a mixed proton–electron conductor: the p-type electronic conductivity is ∼0.004 and ∼0.05 S/cm in wet O2 at 500 and 900 C, respectively, while the protonic conductivity is ∼10−4 S/cm and ∼10−3 S/cm. The material is expectedly a pure proton conductor at sufficiently low temperatures and wet conditions. The specific grain boundary conductivity is essentially equal for the material with or without Pr, but the overall resistance is significantly lower for the former. We propose that replacing Pr on the Zr site reduces the grain boundary contribution due to an increased grain size after otherwise equal sintering conditions.
Keywords BaZrO3; BaPrO3; Defects and transport; Grain boundaries; Grain boundary specific conductivity
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Effects of A and B site acceptor doping on hydration and proton mobility of LaNbO4

Authors Morten Huse, Truls Norby, and Reidar Haugsrud
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 8004–8016
Time of Publication: 2012-05
Abstract Acceptor doping of the high temperature proton conductor LaNbO4 has been studied by impedance spectroscopy in various atmospheres at 300–1100 C and by X-ray powder diffraction and scanning electron microscopy. Doping LaNbO4 on both A and B site (with Ca and Ti, respectively) resulted in a two-phase composition of LaNbO4 and LaNb3O9. This composite is interesting as the two phases make it a mixed proton and electron conductor. The electrical characterisation of Ti-doped LaNbO4 revealed mixed electronic (n- and p-type) and ionic conductivity at temperatures above approx. 750 C, while proton conductivity was dominating below this temperature under wet conditions. Ti-doping resulted in higher activation enthalpy and lower mobility of protons as compared to Ca-doping, attributed to stronger proton–acceptor association in the former case. Thermodynamic constants for hydration of associated protons and proton–acceptor association as well as mobility parameters were fitted to the experimental data and came out as , , , and , and . Neither B site doping nor A and B site co-doping showed indications of increased solubility relative to sole A site doping in LaNbO4.
Keywords LaNbO4; Ti-doped LaNbO4; Defect association; Proton mobility; Proton conductivity; Hydration thermodynamics
Remark Link

Effects of (LaSr)(CoFeCu)O3-δ Cathodes on the Characteristics of Intermediate Temperature Solid Oxide Fuel Cells

Authors Sea-Fue Wang, Chun-Ting Yeh, Yuh-Ruey Wang, Yung-Fu Hsu
Source
Journal of Power Sources
Volume: 201, Pages: 18–25
Time of Publication: 2012-03
Abstract In this study, Cu2+ ions doped La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes are prepared for use in solid oxide fuel cells (SOFCs). The maximum electrical conductivities of the La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ (438 S cm−1) and the La0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ (340 S cm−1) discs are higher than that of the La0.6Sr0.4Co0.2Fe0.8O3−δ disc (LSCF; 81 S cm−1) sintered at 1100 C. The substitution of Cu2+ over Fe3+ leads to a higher coefficients of thermal expansion (CTE), while the replacement of Co3+ by Cu2+ results in a lower CTE. Single cells with the La0.6Sr0.4Co0.2Fe0.8O3−δ, La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ, and La0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ cathodes operating at 650 C and 550 C show similar ohmic resistance (R0) values while the polarization resistance (RP) values of the cells with the La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ and a0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ cathodes are slightly lower than that of the single cell with the La0.6Sr0.4Co0.2Fe0.8O3−δ cathode, indicating that the Cu2+-doped LSCF cathode exhibits a greater electrochemical catalytic activity for oxygen reduction. Maximum power densities of the cells with the La0.6Sr0.4Co0.2Fe0.8O3−δ, La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ, and La0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ cathodes operating at 700 C read respectively 1.07, 1.15, and 1.24 W cm−2. It is evident that the doping of Cu2+ ions in LSCF is beneficial to the electrochemical performance of the cells.
Keywords Solid oxide fuel cell; cathode; cathode; impedance; Cell performance
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Synthesis and Enhanced Proton Conduction in a 20 mol% Ytterbium Doped Barium Zirconate Ceramic Using Zn as Sintering Aid

Authors Seikh M.H. Rahman, Istaq Ahmed, Sten G. Eriksson
Source
Applied Mechanics and Materials
Mechanical and Aerospace Engineering
Volume: 110-116 Time of Publication: 2011-10
Abstract 20% Ytterbium (III)-doped perovskite structured barium zirconate, BaZrO3, was prepared by two different synthesis routes: solid state and sol-gel routes. 2 % Zinc (II) was added as an acceptor dopant at the Zr (IV) site according to stoichiometry. It was also added as 2 % excess of the formula. The purpose of this study is to see how zinc (II) acts as a sintering aid in view of synthesis route, densification and conductivity of the material. A dense ceramic (90% of theoretical density) was achieved by the sol-gel method when stoichiometry was adjusted. Phase purity of the samples was checked by X-ray powder diffraction (XRD). Thermogravimetric analysis (TGA) and Impedance spectroscopy (IS) was used to characterize hydration and electrical conductivity respectively.The data shows that the addition of stoichiometric amounts of Zn2+ via sol-gel synthesis route promotes not only densification but also water incorporation and conductivity in comparison with the solid state route, keeping the same final sintering temperature of 1500C. For example, pre-hydrated BaZr0.78Zn0.02Yb0.2O3-δ, prepared via the sol-gel method shows total conductivity (σtot) value of 3.14*10-5 and 3.8*10-3 Scm-1, whereas for the solid state route, σtot values are 1.74*10-5 and 8.87*10-4 Scm-1 under dry Ar (heating cycle) at 300 C and 600 C, respectively.
Keywords BaZrO3, Impedance Spectroscopy, Proton Conductivity, Sintering Aid, TGA, X-Ray Diffraction (XRD)
Editor Wu Fan
Remark Online since October, 2011; DOI 10.4028/www.scientific.net/AMM.110-116.1181
Link

Effect of nano-grain size on the ionic conductivity of spark plasma sintered 8YSZ electrolyte

Authors K. Rajeswari, M. Buchi Suresh, Dibyendu Chakravarty, Dibakar Das, Roy Johnson
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 1, Pages: 511–517
Time of Publication: 2012-01
Abstract Densification and micro-structural development of ultra fine 8 mol% yttria stabilized zirconia (8YSZ) nano powder were investigated systematically by varying the SPS sintering temperature at constant applied pressure of 50 MPa. A hundred fold decrease in average grain size ranging from 10 μm to 80 nm is observed on decreasing the SPS sintering temperature from 1200 C to 1050 C with >99% of theoretical densities. Impedance measurements on the samples indicated an enhancement in the ionic conductivity at 700 C from 0.004 S/cm to 0.018 S/cm with decrease in grain size from 10 μm to 0.51 μm and a significant increase in conductivity from 0.018 S/cm to 0.068 S/cm on further reduction of grain size to 80 nm. A significant change in the grain-boundary conductivity is noticed on reducing the grain sizes to nano regime. The diverse microstructure with ultra fine grain size resulting from SPS at 1050 C could contribute to the enhanced ionic conductivity, which is supported by the activation energy data.
Keywords Solid oxide fuel cells; Electrolyte; Microstructure; Spark plasma sintering
Remark Link

Dielectric relaxation in a thermosetting polyimide modified with a thermoplastic polyimide

Authors D. A. Belov, S. Yu. Stefanovich and M. Yu. Yablokova
Source
Polymer Science Series A
Volume: 53, Issue: 10, Pages: 963-967
Time of Publication: 2011-10
Abstract Relaxation processes in glass-fiber-reinforced composites with a polymer matrix based on blends of thermosetting and thermoplastic polyimides are studied via dielectric-relaxation spectroscopy. For all investigated blends, two relaxation processes related to the β relaxation of different fragments of the polymer chain are found. Linear flexiblechain polyimide incorporated into the polymer matrix serves as a plasticizer.
Remark DOI: 10.1134/S0965545X11100014
Link

Autothermal Reforming of Methane in Proton-Conducting Ceramic Membrane Reactor

Authors Jay Kniep , Matthew Anderson , and Jerry Y.S. Lin
Source
Ind. Eng. Chem. Res.
Volume: 50, Issue: 22, Pages: 12426–12432
Time of Publication: 2011-10
Abstract Endothermic steam reforming of methane for hydrogen production requires heat input with selective oxidation of methane. Dense SrCe0.75Zr0.20Tm0.05O3-δ perovskite membranes were combined with a reforming catalyst to demonstrate the feasibility of a heat-exchange membrane reactor for steam reforming of methane coupled with selective oxidation of permeated hydrogen. The reforming catalyst used was a prereduced nickel based catalyst supported on γ-Al2O3. Hydrogen produced via the steam reforming of methane or water gas shift reaction was able to diffuse through the catalyst bed and transport through the membrane. The permeated hydrogen reacted with oxygen (from air) to produce heat for the steam reforming of methane on the other side of the membrane. The membrane reactor avoids the use of an expensive air separation unit to produce pure oxygen. The influence of experimental conditions, such as temperature, gas hourly space velocity, and the steam to carbon (S/C) ratio, on the membrane reactor was investigated. SrCe0.75Zr0.20Tm0.05O3-δ showed good chemical stability in steam reforming conditions as X-ray diffraction analysis of the membrane surface exposed to steam-reforming conditions for 425 h showed only minor CeO2 formation. The experimental data demonstrate the feasibility of using a proton conducting ceramic membrane in the heat-exchange membrane reactor for steam reforming of methane coupled with selective oxidation.
Remark Link

Post-heat treatment pressure effect on performances of metal-supported solid oxide fuel cells fabricated by atmospheric plasma spraying

Authors Chun-Huang Tsai, Chang-sing Hwang, Chun-Liang Chang, Jen-Feng Yu, Sheng-Hui Nien
Source
Journal of Power Sources
Volume: 197, Pages: 145–153
Time of Publication: 2012-01
Abstract The nickel metal-supported cells fabricated by atmospheric plasma spraying are post-heat treated in air at 960 C for 2 h with different pressures. The current–voltage–power and AC impedance measurements show the prepared cell with an applied pressure of 450 g cm−2 in the post-heat treatment has a better electrochemical performance at test temperatures ≥ 650 C. For test temperatures < 650 C, the maximum power densities at 450 g cm−2 pressure are about the same as the maximum power densities at 1250 g cm−2 pressure. The SEM micrograph indicates that the cathode including the cathode interlayer and the cathode collector is the most porous region in the cell. AC impedance results show this cathode is the most sensitive part to the applied pressure in the post-heat treatment and the cell with 450 g cm−2 pressure has the smallest low frequency intercept R2 and the polarization resistance Rp at temperatures from 600 to 800 C. The performance durability test of the cell post-heat treated at 450 g cm−2 pressure shows a degradation rate of 0.0087 mV h−1 or 0.0026 mW h−1 at 300 mA cm−2 constant current density and 750 C test temperature.
Keywords Atmospheric plasma spray; Solid oxide fuel cells; Metal-supported; Nanostructured
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The morphotropic phase boundary in the (1 − x)PbZrO3–x[0.3Bi(Zn1/2Ti1/2)O3–0.7PbTiO3] perovskite solid solution

Authors T. Sareein, W. Hu, X. Tan and R. Yimnirun
Source
Journal of Materials Science
Volume: 47, Issue: 4, Pages: 1774-1779
Time of Publication: 2012-04
Abstract Ceramics in the (1 − x)PbZrO3–x[0.3Bi(Zn1/2Ti1/2)O3–0.7PbTiO3] solid solution system with 0.48 ≤ x ≤ 0.56 were investigated. A morphotropic phase boundary separating rhombohedral and tetragonal perovskite phases was identified at x = 0.52. This composition displays the maximum remanent polarization P r of 40.7 μC/cm2 and the best piezoelectric coefficient d 33 of 311 pC/N in the pseudo-binary system. However, the Curie temperature T c for this MPB composition is 291 C, much lower than initially expected.
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Synthesis and electrical properties of lead free (Bi0.5K0.5)TiO3–BaTiO3–Bi(Zn0.5Ti0.5)O3 ceramics

Authors A. Prasatkhetragarn, B. Yotburut, N. Triamnak, R. Yimnirun and D.P. Cann
Source
Ceramics International
Volume: 38, Issue: 1, Pages: 827–830
Time of Publication: 2012-01
Abstract Lead free ferroelectric materials with high Curie temperature in (x)[(Bi0.5K0.5)TiO3]− (1-x)[0.5Bi(Zn0.5Ti0.5)O3 − 0.5BaTiO3] or (x)BKT − (1-x)[BZT − BT] ternary system, where x = 0.4, 0.5, 0.6 and 0.8, were synthesized. The single phase perovskite for all ceramics were formed at 900 C for 6 h in air. The ceramic compositions with x = 0.5 and 0.6 exhibited the dielectric properties with relaxor-like phase transition behavior, while the ceramic with x = 0.8 showed the dielectric behavior of normal ferroelectric materials. From room temperature P–E measurement, the maximum remnant polarization (Pr of 2.75 μC/cm2) and coercive field (Ec of 12.41 kV/cm) were obtained in the composition with x = 0.6. In addition, the TC, Pr and Ec were found trend to increase with increasing BKT content.
Keywords Ferroelectric; Dielectric; Relaxor-like behavior; High Curie temperature
Remark Link

Characterization of individual barium titanate nanorods and their assessment as building blocks of new circuit architectures

Authors K. Zagar, F. Hernandez-Ramirez, J. D. Prades, J. R. Morante, A. Rečnik and M. Čeh
Source
Nanotechnology
Volume: 22, Issue: 38, Pages: 385501
Time of Publication: 2011-09
Abstract In this work, we report on the integration of individual BaTiO3 nanorods into simple circuit architectures. Polycrystalline BaTiO3 nanorods were synthesized by electrophoretic deposition (EPD) of barium titanate sol into aluminium oxide (AAO) templates and subsequent annealing. Transmission electron microscopy (TEM) observations revealed the presence of slabs of hexagonal polymorphs intergrown within cubic grains, resulting from the local reducing atmosphere during the thermal treatment. Electrical measurements performed on individual BaTiO3 nanorods revealed resistivity values between 10 and 100 Ω cm, which is in good agreement with typical values reported in the past for oxygen-deficient barium titanate films. Consequently the presence of oxygen vacancies in their structure was indirectly validated. Some of these nanorods were tested as proof-of-concept humidity sensors. They showed reproducible responses towards different moisture concentrations, demonstrating that individual BaTiO3 nanorods may be integrated in complex circuit architectures with functional capacities.
Remark doi: 10.1088/0957-4484/22/38/385501
Link

Structure, chemical stability and mixed proton–electron conductivity in BaZr0.9−xPrxGd0.1O3−δ

Authors A. Magras, C. Frontera, A.E. Gunns, A. Tarancn, D. Marrero-Lpez, T. Norby and R. Haugsrud
Source
Journal of Power Sources
Time of Publication: 2011-08
Abstract BaZr0.9−xPrxGd0.1O3−δ (x = 0.3 and 0.6) was prepared by combustion synthesis and characterised with respect to conductivity and stability in an attempt to combine the desirable properties of the end members. The polycrystalline materials exhibit a cubic or pseudo-cubic structure as determined by X-ray synchrotron radiation and transmission electron microscopy. The chemical stability of the compositions is strongly dependent on the praseodymium content, the materials with more Pr present lower stability. Electron holes dominate the conductivity under oxidising atmospheres in BaZr0.3Pr0.6Gd0.1O3−δ, while BaZr0.6Pr0.3Gd0.1O3−δ exhibits a mixed electron hole–proton conducting behaviour. Substitution of Zr by Pr in acceptor-doped BaZrO3 decreases the sintering temperature and increases the grain growth rate.
Remark Article in press, DOI:10.1016/j.jpowsour.2011.06.076

Impedance and modulus spectroscopic studies on 40PrTiTaO6 + 60YTiNbO6 ceramic composite

Authors D. B. Dhwajam, M. Buchi Suresh, U. S. Hareesh, J. K. Thomas, S. Solomon, Annamma John
Source
Journal of Materials Science: Materials in Electronics
Volume: 23, Issue: 3, Pages: 653-658
Time of Publication: 2012-03
Abstract The 40PrTiTaO6 + 60YTiNbO6 ceramic composite is prepared through the solid state ceramic route. The structure is discussed using X-ray diffraction analysis. Surface morphology is examined by Scanning Electron Microscopy (SEM). Impedance and modulus spectroscopic studies are carried out. A decrease in the resistive behavior of the sample assisted by the grain boundary conduction with rise in temperature is found. The experimental results on electrical properties indicate that the material exhibits conduction both due to bulk and grain boundary effect. The microstructure was investigated by SEM micrographs in which grains separated by grain boundaries are visible. There is a probable change in the capacitance values of the material as a function of temperature. The relaxation time is small at higher temperatures than at lower temperatures. The activation energy is found as 1.52 eV, which suggests the possibility of electrical conduction due to the mobility of oxide ions (O2−) or oxide ion vacancies at higher temperature.
Remark Link

Proton Conductivity in Acceptor-Doped LaVO4

Authors Morten Huse, Truls Norby, and Reidar Haugsrud
Source
J. Electrochem. Soc.
Volume: 158, Issue: 8, Pages: B857-B865
Time of Publication: 2011-06
Abstract Electrical characterization of nominally undoped LaVO4, La0.99Ca0.01VO4− and La0.95Ca0.05VO4− was performed in various partial pressures of oxygen, water vapor and hydrogen isotopes, from 300 to 1100C by impedance spectroscopy, AC conductivity measurements (10 kHz) and EMF-measurements. XRD, SEM and EDS were used for structural, micro structural and compositional analysis. Acceptor doped LaVO4 is a pure ionic conductor in oxidizing atmospheres in the entire measured temperature range; dominated by proton conductivity at low temperatures (T < 450C) under wet conditions and oxide ion conductivity at high temperatures. A maximum in the partial proton conductivity of ~ 6 10−5 S/cm was reached at 900C (pH2O2.510-2 atm). Thermodynamics of hydration and transport parameters for charge carriers in La0.99Ca0.01VO4 were derived from relations between defect chemistry, transport properties and the measured conductivity data and revealed: S=− 130 10 J/mol K, S =− 142 10 J/mol K, H=− 110 10 kJ/mol, 0,H+ = 50 6 cm2 K/Vs, Hmob,H+ = 75 10 kJ/mol, 0,v= 120 20 cm2 K/Vs and Hmob,v = 85 10 kJ/mol. The tetrahedron (XO4) volume and migration enthalpy were found to be correlated for the series of monoclinic LaXO4.

Nanostructuring phenomena in oxygen-conducting complex oxides of heavy REE

Authors A. V. Shlyakhtina, D. A. Belov, S. Yu. Stefanovich and L. G. Shcherbakova
Source
Russian Journal of Electrochemistry
Volume: 47, Issue: 5, Pages: 620-627
Time of Publication: 2011-05
Abstract In complex oxides of REE (Ln4M3O12 (Ln = Tm, Lu; M = Zr, Hf), Ln2TiO5 (Ln = Er-Yb)) and Ho2TiO5, the following phase transitions of the order-disorder type are studied for different cooling rates: rhombohedral δ-phase-defective fluorite in Ln4M3O12 (Ln = Tm, Lu; M = Zr, Hf), pyrochlor-like phasedefective fluoride in Ln2TiO5 (Ln = Er-Yb), and hexagonal β-phase-pyrochlor in Ho2TiO5. The presence of nanostructuring phenomena typical of fluorite-like polymorphous modifications of complex oxides in the Ln2O3-MO2 (Ln = Ho-Lu; M = Ti, Zr, Hf) systems is confirmed. The conductivity of polymorphous modifications of Ln4Zr3O12 (Ln = Tm, Lu;) and Ln2TiO5 (Ln = Ho-Yb) with different thermal prehistory is studied. The comparative studies of the oxygen-ionic conductivity of fluorite- and pyrochlor-like Ln2TiO5 (Ln = Ho-Yb), pyrochlor Ho2TiO5, and β-Ho2TiO5 and also of the conductivity of fluorite-like compounds and δ-Ln4Zr3O12 (Ln = Tm, Lu) are carried out. The oxygen-ionic conductivity of complex oxides in the Ln2O3-MO2 (Ln = Er-Lu; M = Ti, Zr, Hf) system is shown to decrease in the following series: defective pyrochlor-defective fluorite-rhombohedral δ-phase ∼ hexagonal β-phase.

Partial Oxidation of Methane and Oxygen Permeation in SrCoFeOx Membrane Reactor with Different Catalysts

Author Jay Kniep and Y.S. Lin
Source
Ind. Eng. Chem. Res.
Volume: 50, Issue: 13, Pages: 7941–7948
Time of Publication: 2011-05
Abstract Partial oxidation of methane (CH4) and oxygen permeation in a dense SrCoFeOx disk membrane reactor were studied with the reducing side of the membrane packed with different catalysts (catalyst support γ-Al2O3, La0.6Sr0.4Co0.8Fe0.2O3−δ, and 10 wt % Ni/γ-Al2O3) of increasing reaction activities for CH4 oxidation. The influence of temperature, flow rates, and inlet CH4 concentration (diluted with helium) on the performance of the different membrane reactors was investigated. The oxygen permeation flux and CH4 conversion increased in the following order: γ-Al2O3 < La0.6Sr0.4Co0.8Fe0.2O3−δ < 10% Ni/γ-Al2O3. The membrane reactor with the reforming catalyst of 10 wt % Ni/γ-Al2O3 had the highest CH4 conversion (90%), CO selectivity (97%), and oxygen permeation flux (2.40 mL/(cm2 min)) at 900 C. The improvement of the oxygen permeation through the membranes with different catalysts emphasizes the effect of the CH4 oxidation reaction rate on the reducing side of the membrane on the oxygen permeation flux through the mixed-conducting ceramic membranes. Under identical conditions, the oxygen permeation flux through mixed-conducting ceramic membrane with a reducing gas is a strong function of the catalytic activity for the oxidation of the reducing gas.
Remark Link

Phase transition and electrical properties of gallium- and indium-doped Bi10Ti3W3O30

Authors E. P. Kharitonova, D. A. Belov, A. V. Mosunov and V. I. Voronkova
Source
Inorganic Materials
Volume: 47, Issue: 5, Pages: 513-520
Time of Publication: 2011-05
Abstract Polycrystalline samples of gallium- and indium-doped Bi10Ti3W3O30 (mixed-layer Aurivillius phase with the Ti4+ and W6+ distributed at random over the perovskite-like slabs) have been prepared by solid-state reactions, and their polymorphism and electrical properties have been studied. Doping with both In3+ and Ga3+ yields limited solid solutions and shifts the ferroelectric phase transition to lower temperatures. The heterovalent substitutions of In3+ and Ga3+ for Ti4+ and W6+ increase the oxygen vacancy concentration and, accordingly, the conductivity of the material relative to the undoped compound.

Lamellar Titanates: A Breakthrough in the Search for New Solid Oxide Fuel Cell Anode Materials Operating on Methane

Authors Cdric Prillat-Merceroz, Pascal Roussel, Rose-Nolle Vannier, Patrick Glin, Sbastien Rosini, Gilles Gauthier
Source
Advanced Energy Materials
Volume: 1, Issue: 4, Pages: 573–576
Time of Publication: 2011-07
Abstract Decreasing the dimensionality of the LaxSr1–xTiOmath image family structure from 3D to 2D by increasing the La content greatly enhances the electrochemical performance of the material as an SOFC anode. This is attested to by the strong decrease in the polarization resistance values deduced from the complex impedance spectra (Nyquist plot) recorded at 900 C in H2/H2O(3%) on a symmetrical cell.
Keywords Solid oxide fuel cells; Anode materials; Titanate; Methane
Remark Link

An ion-plasma technique for formation of anode-supported thin electrolyte films for IT-SOFC applications

Authors N.S. Sochugov, A.A. Soloviev, A.V. Shipilova, V.P. Rotshtein
Source
International Journal of Hydrogen Energy
Volume: 36, Issue: 9, Pages: 5550-5556
Time of Publication: 2011-05
Abstract This paper describes a preparation method and structural and electrochemical properties of a thin bilayer anode-electrolyte structure for a solid oxide fuel cell operating at intermediate temperatures (IT-SOFC). Thin anode-supported yttria-stabilized zirconia electrolyte films were prepared by reactive magnetron sputtering of a Zr–Y target in an Ar–O2 atmosphere. Porous anode surfaces of IT-SOFCs were modified by a pulsed low-energy high-current electron beam prior to film deposition; the influence of this pretreatment on the performance of both the deposited films and a single cell was investigated. The optimal conditions of the pulsed electron beam pretreatment were obtained. For the electrolyte thickness about 2.5 μm and the value of gas permeability of the anode/electrolyte structure 1.01 10−7 mol m−2 s−1 Pa−1, the maximum power density achieved for a single cell at 800 C and 650 C was found to be 620 and 220 mW cm−2 in air, respectively.
Keywords Solid oxide fuel cell; YSZ electrolyte; Magnetron sputtering; Surface modification of material; Pulsed electron beam treatment; Electrical performance

Microwave-assisted synthesis of gadolinia-doped ceria powders for solid oxide fuel cells

Authors A. Gondolini, E. Mercadelli, A. Sanson, S. Albonetti, L. Doubova and S. Boldrini
Source
Ceramics International
Volume: 37, Issue: 4, Pages: 1423-1426
Time of Publication: 2011-05
Abstract Gadolinia doped ceria (GDC) is an attractive electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs) for its high ionic conductivity at low temperature (500–700 C). A number of different methods are currently used to prepare nano-sized doped-ceria powder. Among the others, precipitation in solution remains the best method to obtain well-dispersed particles of controlled properties. In this work, nanocrystalline Ce1−xGdxO2−δ (GDC) particles were produced by polyol microwave assisted method in very mild conditions (170 C, 2 h, 1 atm). The as-synthesized powder showed good sinterability and ionic conductivity comparable to the ones of the corresponding nanometric commercial GDC.
Keywords GDC; Microwave heating; Polyol method; IT-SOFC

Solid oxide fuel cells with Sm0.2Ce0.8O2−δ electrolyte film deposited by novel aerosol deposition method

Authors Sea-Fue Wang, Yung-Fu Hsu, Chih-Hao Wang and Chin-Ting Yeh
Source
Journal of Power Sources
Volume: 196, Issue: 11, Pages: 5064-5069
Time of Publication: 2011-06
Abstract In this study, dense electrolyte ceramic Sm0.2Ce0.8O2−δ (SDC) thin films are successfully deposited on NiO-SDC anode substrate by aerosol deposition (AD) with oxygen as the carrier gas at the substrate temperature ranging from room temperature to 300 C. To remove the effect of humidity on the starting powders, this study found that, in depositing SDC films, having the starting powders preheat-treated at 200 C helped generate a smooth and dense layer, though a lower deposition rate was achieved. At a deposition time of 22 min, SDC films with a uniform thickness of 1.5 μm and grain sizes of ≈67 nm are obtained. SOFC single cells are then built by screen printing a LSCF cathode on the anode-supported substrates with SDC electrolyte. The cross-sectional SEM micrographs exhibit highly dense, granular, and crack-free microstructures. The open circuit voltages (OCV) of the single cells decrease with the rise in temperature, dropping from 0.81 V at 500 C to 0.59 V at 700 C. Maximum power densities (MPD) decline with decreasing operating temperature from 0.34 to 0.01 W cm−2 due to the increase of the R0 and RP of the single cells. The electrochemical results testify to the fine quality of SDC films as well as illustrate the electrolyte thickness effect and the effect of mixed ionic and electronic conduction of the SDC electrolyte in the reducing atmosphere.
Keywords SDC films, NiO-SDC substrate, aerosol deposition, Very dense SDC films, uniform thickness of 1.5 μm, Single cell with a MPD of 0.34 W cm−2, 700 C, Solid oxide fuel cell; Ceria; Aerosol deposition; Electrolyte

Conductivity, transport number measurements and hydration thermodynamics of BaCe0.2Zr0.7Y(0.1 − ξ)NiξO(3 − δ)

Authors S. Ricotea, The Corresponding Author, N. Bonanos, H.J. Wang and R. Haugsrud
Source
Solid State Ionics
Volume: 185, Issue: 1, Pages: 11-17
Time of Publication: 2011-03
Abstract BaCe0.2Zr0.7Y(0.1 − ξ)NiξO(3 − δ) compounds with ξ = 0.01 and 0.02 have been synthesized by solid state reaction at 1400 C and sintered at 1450 C. TEM analyses were performed and showed a segregation of nickel at the grain boundaries for ξ = 0.02. This apparent solubility limit of Ni in the B-site of the perovskite is in agreement with similar data obtained earlier for the two compositions. The first aim of this work was to evaluate the conductivity of BaCe0.2Zr0.7Y(0.1 − ξ)NiξO(3 − δ) at temperature between 500 and 900 C, using impedance spectroscopy at different oxygen partial pressures and water vapor pressures, as well as the emf technique. The compounds exhibit p-type conduction in oxidizing atmosphere, and ionic conduction elsewhere. The oxide ion contribution of the conductivity is negligible only for temperatures below 600 C. The determination of hydration enthalpies, our second goal, was achieved by modelling of the conductivity data and by thermogravimetric measurements (TG-DSC).

Fabrication and Characterization of Anode-Supported BaIn0.3Ti0.7O2.85 Thin Electrolyte for Solid Oxide Fuel Cell

Authors M. Rieu, P. K. Patro, T. Delahaye*, E. Bouyer
Source
International Journal of Applied Ceramic Technology
Article first published online: 28 MAR 2011
Time of Publication: 2011-03
Abstract BaIn0.3Ti0.7O2.85 (BIT07) is a promising electrolyte for solid oxide fuel cells, due to its chemical compatibility with most of the cathode electrode material such as LSM and Ln2NiO4. The present work is aimed on the fabrication of anode-supported half cells with thin BIT07 electrolyte. For this, Ni-8YSZ cermet was chosen due to its excellent mechanical and electrochemical properties, in addition to its low cost. The NiO–8YSZ anode support was prepared by tape casting, and for this, an organic slurry formulation was optimized. The BIT07 electrolyte thin film was deposited through screen printing on the green anode. The formulation of the ink was optimized, and sintering at 1350C for 3 h led to a dense electrolyte with controlled thickness varying from 2 to 12 μm. Further, the cermet electrode still had a homogeneous microstructure with well-defined anode/electrolyte interface. The electrode ASR was about 0.5 Ω cm2 and was stable over 500 h at 800C under H2–3% H2O. The fabrications of half cells were successfully scaled up to 100 mm 100 mm retaining the dimensional control and without any surface defects.

Curing of a network polyimide modified with a linear component

Authors D.A. Belov, S.Yu. Stefanovich, M.Yu. Yablokova
Source
Russian Journal of Applied Chemistry
Volume: 84, Issue: 2, Pages: 301-306
Time of Publication: 2011-03
Abstract The curing and relaxation processes in polymeric composites based on blends of network and linear polyimides applied onto a filler were studied by dielectric spectroscopy. The sensitivity of dielectric spectroscopy to processes occurring in the course of curing was examined.

Structure, Water Uptake, and Electrical Conductivity of TiP2O7

Authors Vajeeston Nalini, Magnus H. Srby, Koji Amezawa, Reidar Haugsrud, Helmer Fjellvg, Truls Norby
Source
Journal of the American Ceramic Society
Volume: 94, Issue: 5, Pages: 1514–1522
Time of Publication: 2011-05
Abstract We report here on the structure of TiP2O7 and electrical properties of nominally acceptor (Sc, Fe)-doped TiP2O7 synthesized by an aqueous phosphoric acid route. Structural characterization, including studies of the high-temperature phase transition in TiP2O7, was carried out by powder X-ray and neutron diffraction. Ceramic disks were sintered by the spark plasma technique and their conductivities were characterized as a function of p(O2) and p(H2O) in the temperature range of 500–1000C by means of AC constant frequency measurements and impedance spectroscopy. As reported earlier, the acceptor doping appears not to influence the defect structure of TiP2O7 significantly. Effects of H+/D+ isotope shift were utilized to identify proton conduction. The conductivity was independent of p(O2) at 500–900C under oxidizing conditions suggesting predominantly protonic conduction at these temperatures. Under reducing atmosphere n-type conductivity contributed to the total conductivity at the higher temperatures. p(H2O) dependencies of the conductivities are interpreted in terms of a defect-chemical model involving protons and oxygen interstitials as the dominating defects. The uptake of water was studied by thermogravimetry at high p(H2O) and the thermodynamics of the hydration reaction was derived. Finally, parameters for the mobility of protons were extracted by combining the conductivity and thermogravimetry data.
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