- CO-SINTERING OF MULTILAYER CERAMICS
Lee S-H; Messing, GL; Twiname, ER; Mohanram, A; Randall, CA; Green, DJ
Euro Ceramics VII Pt.1. Trans Tech Publications, Switzerland, 2002, p.257-260. Key Engineering Materials Vol.206-213
A better understanding of stress evolution and the origin of damage during the co-sintering of dissimilar materials is needed for the next generation of integrated ceramic packaging and solid oxide fuel cells. This requires the determination of the sintering strain history as a function of heating rate, powder characteristics and green body properties. In addition, changes in the viscoelastic properties of the porous materials during sintering need to be quantified. In Low Temperature Co-fired Ceramics (LTCC) it is important to monitor liquid phase redistribution during sintering. The establishment of a testing protocol for developing a fundamental understanding of the co-sintering process is discussed. The protocol is based on the determination of the modulus, sintering strain rate and viscosity of the individual components. Some of the tools discussed include cyclic loading dilatometry and asymmetric bilayer experiments. Results from work on co-sintering of laminated structures and inductors embedded in an LTCC package are presented. 6 refs.
- OXIDE-ION CONDUCTING CERAMICS FOR SOLID OXIDE FUEL CELLS
Huang, K; Wan, J; Goodenough, JB
J.Mat.Sci. Vol.36, No.5, 2001, p.1093-1098.
Realisation of a solid oxide fuel cell (SOFC) operating at 700 C on a hydrocarbon fuel or gaseous H2 is an outstanding technical target. For the past 25 years, efforts to achieve this goal have been based on yttria-stabilised zirconia as the electrolyte, a NiO + electrolyte composite as the anode, a porous La0.85Sr0.15MnO3 (LSM) metallic perovskite as the cathode, and a La1-xSrxCrO3 ceramic as the interconnect material. An alternate approach that would use a Sr- and Mg-doped LaGaO3 perovskite as the electrolyte, a Sm-doped ceria (SDC) as the anode or as a buffer layer with a NiO + SDC composite as the anode, a mixed oxide ion/electronic conductor (MIEC) as the cathode, and a stainless steel as the metallic interconnect is presented. 13 refs.
- CERIA-BASED MATERIALS FOR SOLID OXIDE FUEL CELLS
Kharton, VV; Figueiredo, FM; Navarro, L; Naumovich, EN; Kovalevsky, AV; Yaremchenko, AA; Viskup, AP; Carneiro, A; Marques, FMB; Frade, JR
J.Mat.Sci. Vol.36, No.5, 2001, p.1105-1117.
Electronic and ionic conduction in gadolinia-doped ceria (CGO) ceramics is analysed and the electrochemical properties of various oxide electrodes in contact with ceria-based solid electrolytes investigated. Properties of electrode materials, having thermal expansion compatible with that of doped ceria, are briefly reviewed. At temperatures below 1000 K, Ce0.90Gd0.10O2-delta (CGO10) was found to possess a better stability at reduced oxygen pressures than Ce0.80Gd0.20O2-delta (CGO20). Incorporation of small amounts of praseodymium oxide into CGO20 leads to a slight improvement of the stability of CGO20 at intermediate temperatures, but the difference between electrolytic domain boundaries of the Pr-doped material and CGO10 is insignificant. Since interaction of ceria-based ceramics with electrode materials, such as lanthanum strontium manganites, may result in the formation of low-conductive layers at the electrode /electrolyte interface, optimisation of electrode fabrication conditions is needed. A good electrochemical activity in contact with CGO20 electrolyte is pointed out for electrodes of perovskite-type La0.8Sr0.2Fe0.8Co0.2O3-delta and LaFe0.5Ni0.5O3-delta, and LaCoO3-delta/La2Zr2O7 composites; surface modification of the electrode layers with praseodymium oxide results in considerable decrease of cathodic overpotentials. Using highly dispersed ceria for the activation of SOFC anodes significantly improves the fuel cell performance. 55 refs.
- 50 YEARS OF CERAMICS IN THE US - LOOKING BACK, LOOKING FORWARD
Interceram. Vol.50, No.4, 2001, p.310-312, 314-316.
An overview of technological development in the ceramics industry in the last 50 years is presented and the status of the US industry examined. Information is included on the contribution of ceramics to the top 20 engineering achievements as listed by the US National Academy of Engineering, the most important ceramic innovations in the USA, the market value of the US ceramics industry (by segment), and ceramics technology and engineering educational programmes in the USA. The future prospects for the industry are discussed with particular reference to nanotechnology, bioceramics, fuel cells, microelectronic applications, ceramic matrix composites, high-temperature superconductors, microelectromechanical devices, and combinatorial engineering.
- HIGH TEMPERATURE ION CONDUCTING CERAMICS
Ramanarayanan, TA; Singhal, SC; Wachsman, ED
Interface. Vol.10, No.2, 2001, p.22-27.
Tremendous progress has been made in understanding the defect chemistry and electronic and ionic conduction in many high-temperature ceramics over the last four decades. Such ceramics are now attracting increasing attention for a variety of applications, notable among these being fuel cells for power generation, production of chemicals, oxygen generation for life support systems, and high-temperature electrochemical sensors. Many of these applications promise to become wide-spread commercial successes in the coming years as the cost is brought down through further technical advances and mass production. Details of three related symposia are included. 14 refs.
- IMPROVEMENT OF MECHANICAL AND ELECTRICAL PROPERTIES OF SCANDIA-DOPED ZIRCONIA CERAMICS BY POST-SINTERING WITH HOT ISOSTATIC PRESSING
Hirano, M; Inagaki, M; Mizutani, Y; Nomura, K; Kawai, M; Nakamura, Y
J.Am.Ceram.Soc. Vol.83, No.10, 2000, p.2619-2621.
Significant improvement in the fracture strength, accompanied by an enhancement in the electrical conductivity, of zirconia polycrystals that were doped with 3-7 mol% Sc2O3 has been obtained. The crystals were sintered at 1300 C for 1 h in air, followed by hot isostatic pressing (HIP) at 196 MPa at 1300 and 1450 C for 1.5 h in an argon-gas atmosphere. Dense bodies (with an average grain size of <0.5 micron), doped with 3.5 mol% of Sc2O3, showed the highest average fracture strength up to 1770 MPa and an electrical conductivity of 0.08 S/cm at 1000 C. Bodies which consisted of submicron-sized grains of tetragonal phases and were stabilised with 5 and 6 mol% of Sc2O3, exhibited high strength (1330 and 1140 MPa, respectively) and good conductivity (0.15 and 0.18 S/cm, respectively); values for both properties were greater than those previously reported. The HIPed zirconia ceramics, are candidates for an electrolyte of planar-type solid oxide fuel cells. 17 refs.
- USA CERAMIC COMPANY TO PLAY KEY ROLE IN NEW GENERATION FUEL CELLS
Global Ceram.Rev. No.1, 2000, p.6.
A number of power generation technologies are currently available to meet future energy demands; however, they generally have relatively low efficiencies and produce undesired pollutant emissions. Fuel cells have emerged as the most promising class of technology for meeting the forecast demand during the 21st century in a manner that is energy efficient, environmentally friendly and cost competitive. ART (Advanced Refractory Technologies) has teamed up with McDermott International to develop and commercialise low cost solid oxide fuel cells (SOFC) for electric power generation. Using fuels such as natural gas or propane, SOFC stacks based on oxide ceramics will provide electricity at very high efficiency rates, while being extremely friendly to the environment.
- DEVELOPMENT OF GAS SEPARATORS FOR SOLID OXIDE FUEL CELLS -JOINING OF MgO/MgAl2O4 COMPOSITE AND LaCrO3
Izumi, M; Shimotsu, M
J.Ceram.Soc.Jap. Vol.107, No.4, 1999, p.349-352.
One of the features of Mitsui-type solid oxide fuel cells (SOFC) is that the gas separators are made of MgO/MgAl2O4 composite ceramics, onto which several LaCrO3 ceramics are joined to connect the cells electrically in series. Since one of the functions of the gas separator is the separation of fuel gas and oxidant gas, the joining interface of MgO/MgAl2O4 composite and LaCrO3 must maintain gas tightness at the operating temperature over 1200 K for a long term. A ceramic joining technique has been developed in which a ceramics slurry is coated onto the joining surfaces and then firing is performed at 1773 K. The average bending strength of the joints was 65 MPa at 1273 K. The joining interface held gas tightness after four thermal cycles from 1773 K to room temperature. The vicinity of the joining interface showed an altered structure due to the joining process. However, the altered area was not extended and the interface held gas tightness for not less than 8000 h under the operating condition of the SOFC. 12 refs.
- HIGH ELECTRICAL CONDUCTIVITY AND HIGH FRACTURE STRENGTH OF Sc2O3-DOPED ZIRCONIA CERAMICS WITH SUBMICROMETRE GRAINS
Hirano, S; Watanabe, S; Kato, E; Mizutani, Y; Kawai, M; Nakamura, Y
J.Am.Ceram.Soc. Vol.82, No.10, 1999, p.2861-2864.
The microstructure, crystalline phases, electrical conductivity, and strength of less than 7 mol% Sc2O3-doped ZrO2 ceramics fabricated by comparatively low-temperature sintering at 1200-1300 C for 1 h were studied. ZrO2 ceramics having a uniform microstructure (grain size below 0.5 micron) stabilised with 6 mol% Sc2O3 showed high electrical conductivity (0.15 S/cm at 1000 C) and high fracture strength (660 MPa). With increasing Sc2O3 content from 3.5 to 7 mol%, the grain size, fracture strength, and electrical conductivity at 1000 C changed from 0.2 to 0.5 micron, 970 to 440 MPa, and 0.07 to over 0.2 S/cm, respectively. Sc2O3-doped ZrO2 polycrystals with high fracture strength and high electrical conductivity are promising candidates for the electrolyte material of solid oxide fuel cells. 23 refs.
- SOLID FREEFORM FABRICATION METHODS FOR ENGINEERING CERAMICS
Better Ceramics Through Processing. London, 1998, p.125-132. Br.Ceram.Proc.No.58
In recent years a new generation of solid freeform fabrication (SFF) methods have been investigated for forming engineering ceramics and their composites. SFF allows the rapid computer aided mouldless manufacture of engineering ceramics by the addition of material to, rather than the subtraction of material from, the part being produced. Laminated ceramic object manufacturing, fused deposition of ceramics, 3D ceramic printing, direct ceramic jet printing and electrostatic atomisation of ceramic inks are some of the methods that have been investigated recently. Recent developments in SFF of ceramics are briefly reviewed, and on-going research into ink-jet printing and electrostatic atomisation is summarised. Direct ink-jet printing and electrostatic atomisation of ceramic inks offer opportunities for miniaturisation of multilayer circuits, for the production of functionally graded materials, ordered composites and small complex-shaped components, particularly those involving co-firing of several ceramic layers (PEN structures) such as in solid oxide fuel cells. 11 refs.
- Ceramic matrix composites of zirconia reinforced with metal particles
Wildan, M; Edrees, HJ; Hendry, A
Materials Chemistry and Physics (Switzerland), vol. 75, no. 1-3, pp. 276-283, 28 Apr. 2002
The behaviour of commercial zirconia ceramics containing metal particles is of interest in the development of anodes for solid oxide fuel cells. The present work describes a study of zirconia reinforced with iron, chromium and stainless steel particles in which the electrical and thermal conductivity have been measured. Both of these properties increase with increasing metal content and in the case of electrical conductivity a discontinuous increase occurs when a critical concentration (20 vol.%) of metal particles are incorporated into the insulating zirconia matrix. The three systems studied show distinctly different behaviour and this is reported and explained. With chromium particles there is no chemical or physical reaction between reinforcant and matrix. However, with iron particles there is a chemical interfacial reaction between iron and the stabilising oxide (yttria) in the zirconia solid solution. Finally, with stainless steel particles the difference in coefficient of thermal expansion between the steel and zirconia leads to extensive microcracking of the composite after cooling from fabrication temperature. These phenomena are described and interpreted in terms of a functional model for thermal diffusivity and a microstructural model for the electrical percolation threshold in the zirconia composites.
- Materials for Electrochemical Energy Conversion and Storage
Manthiram, A; Kumta, PN; Sundaram, SK; Ceder, G
Ceramic Transactions (USA), vol. 127, pp. 1-260, 2002
25 papers consider topics including gas separation membranes, fuel cell materials, and materials for lithium-ion batteries. Synthesis and processing issues examined.
- Electrical characterisation of ceramic conductors for fuel cell applications
Martinez-Juarez, A; Sanchez, L; Chinarro, E; Recio, P; Pascual, C; Jurado, JR
Solid State Ionics (Netherlands), vol. 135, no. 1-4, pp. 525-528, Nov. 2000
In electrochemical devices, such as direct methanol fuel cells (DMFCs) or proton exchange membrane fuel cells (PEMFCs), it is necessary to reduce Pt loading to 0.3 mg/cm exp 2 at the electrodes. Furthermore, partial Pt replacement by other electrocatalysts is desirable. Use of ceramic compounds as electrodes might be an important technology innovation. The transition metal perovskite oxides LaNiO sub 3- delta , SmCoO sub 3 , which have been selected as candidate materials for this application, are metallic conductors and some undergo metallic-semiconductor transitions. The combustion synthesis method is used to prepare the corresponding powders. Specific surface areas as high as 10 m exp 2 /g and average particle size of the order of 10 nm were achieved, depending on precursors/fuel rate used. The as-prepared powders were XRD amorphous. The electrical characterisation of these materials was carried out by Complex Impedance Spectroscopy on four-probe arrangement samples.
- Mechanical and electrical properties of Sc sub 2 O sub 3 -doped zirconia ceramics improved by postsintering with HIP
Hirano, M; Inagaki, M; Mizutani, Y; Nomura, K; Kawai, M; Nakamura, Y
Solid State Ionics (Netherlands), vol. 133, no. 1-2, pp. 1-9, Aug. 2000
The microstructure, fracture strength, and electric conductivity of 3-7 mol% Sc sub 2 O sub 3 -doped zirconia polycrystals fabricated by sintering at 1300 deg C for 1 h in air, followed by hot isostatic pressing (HIP) at 196 MPa at 1300 and 1450 deg C for 1.5 h in an Ar gas atmosphere, have been investigated. Significant improvements in the fracture strength and also enhancement in the electric conductivity were obtained by the HIP treatment. We obtained HIPed zirconia polycrystals doped with 3.5 mol% Sc sub 2 O sub 3 having an average fracture strength as high as 1770 MPa, high fracture toughness as 5.6 MPa m exp 1/2 , and an electric conductivity of 0.08 S cm exp -1 at 1000 deg C. The present zirconia ceramics which had uniform submicron gains of tetragonal phases and were stabilized with 5 and 6 mol% Sc sub 2 O sub 3 doping showed excellent mechanical strength (1330, 1140 MPa), good fracture toughness (4.8, 4.1 MPa m exp 1/2 ), and good conductivity (0.15, 0.18 S cm exp -1 , respectively), both being higher than those reported before. The present HIPed zirconia ceramics are some of the candidate materials for an electrolyte of planar-type solid oxide fuel cells.
- High electrical conductivity and high fracture strength of Sc sub 2 O sub 3 -doped zirconia ceramics with submicrometer grains
Hirano, M; Watanabe, S; Kato, E; Mizutani, Y; Kawai, M; Nakamura, Y
Journal of the American Ceramic Society (USA), vol. 82, no. 10, pp. 2861-2864, Oct. 1999
The microstructure, crystal phase, electrical conductivity, and mechanical strength of <7-mol.%-Sc sub 2 O sub 3 -doped zirconia ceramics fabricated by comparatively low-temperature sintering at 1200-1300 deg C for 1 h were investigated. Zirconia ceramics having a uniform microstructure (grain size <0.5 mu m) stabilized with 6 mol.% Sc sub 2 O sub 3 showed high electrical conductivity (0.15 S/cm at 1000 deg C) and high fracture strength (660 MPa). With the increase of Sc sub 2 O sub 3 content from 3.5-7 mol.%, the grain size, fracture strength, and electrical conductivity at 1000 deg C changed from 0.2-0.5 mu m, 970-440 MPa, and 0.07 to >0.2 S/cm, respectively. Sc sub 2 O sub 3 -doped zirconia polycrystals with high fracture strength and high electrical conductivity are promising candidates for the electrolyte material of solid oxide fuel cells.
- Fast ionic conducting film ceramic membranes with advanced applications
Solid State Ionics (Netherlands), vol. 119, no. 1-4, pp. 305-310, Apr. 1999
Fast ionic conducting film ceramic membrane materials have been successfully prepared via the soft-chemical synthesizing procedure, e.g. sol-gel and suspension processes. These film membranes are ionic and proton conducting Li sub 2 SO sub 4 -Al sub 2 O sub 3 , Li sub 2 SO sub 4 -SiO sub 2 composites, oxide ionic dominating conductors based on ceria-based oxides, and mixed conducting ceria-zirconia solid solutions. These thin film ceramic membranes are nanostructured with a thickness from 0.1 to several mu m. Co-development of these conducting thin films as functional ceramic membranes is promising. One film can be thus used for a number of applications in advanced electrochemical or opto-ionic devices, e.g. fuel cells, electrochromic devices, and micro-batteries. A good example is CeO sub 2 -ZrO sub 2 films which were used as the electrode material for the fuel cell, transparent counter electrode for the electrochromic or opto-ionic devices and Li exp + -intercalated electrode for secondary micro-batteries. This paper gives a brief overview of these new fast ionic conducting film ceramic membranes mainly in terms of their electrical properties and applications in the advanced ionic /electrochemical devices.
- Nanocrystalline and nanoporous ceramics
Advanced Materials (FRG) (Germany), vol. 10, no. 17, pp. 1483-1486, 1 Dec. 1998
Nanocrystalline and nanoporous ceramics, renowned for their special transport properties, have typical applications in the fields of energy, the environment, and separation technology. One example is a solid oxide fuel cell, where an anode with improved characteristics was obtained by an optimized nanoscale porous composite architecture. In this article the author also emphasizes the requirements for nanoscale compaction processing and outlines new results of nanoparticle synthesis by emulsion techniques, such as the preparation of aggregate-free oxide particles of 5-10 nm diameter. Materials include silica and YSZ.
- The ceramography of high performance ceramics. XI. Beta-Aluminates - description of materials, preparation, etching techniques and description of microstructures
Trippel, B; Schafer, U; Hachtel, A; Schafer, G; Eschner, TH
Praktische Metallographie (Germany), vol. 35, no. 12, pp. 646-664, Dec. 1998
This article deals with the microstructural characterisation of Na- and K-Beta-Aluminates which are used as ion conductors, for example in batteries, electrochemical gas sensors and fuel cells or which are considered to be potential materials with improved characteristics. In addition to the specific effects which the different materials, sintering additives and sintering conditions have on the microstructures formed, the particular problems encountered in the ceramographic preparation of Beta-Aluminates are discussed.
- Fuel cell development at CFCL--the transition phase
Materials Australia (Australia), vol. 30, no. 4, pp. 8-10, July-Aug. 1998
Ceramic Fuel Cells Limited (CFCL) is involved in the commercialisation of an Australian developed version of a solid oxide fuel cell. The technology was developed in the Materials Science and Technology Division of CSIRO, based on the pioneering work done in that division on many aspects of zirconia technology. From a materials perspective, this is a very "high tech" prject which is dependent on a mix of unusual/specialised ceramics and metals with bread-and-butter ones.
- Phase diagrams and thermodynamic properties of zirconia based ceramics
Key Engineering Materials (Switzerland), vol. 153-154, pp. 37-73, 1998
The thermodynamic properties of the zirconia-based ceramics have been discussed in terms of the valence stability of binary oxides and the stabilization energy/interaction parameter in ternary or higher order systems. The stabilization energy and the interaction parameters can be well correlated with the ionic size of involved ions. Those properties are numerically expressed in the chemical potential diagrams. This makes it possible to understand the chemical reactivity of the oxides in terms of the physicochemical properties of constituent ions in the oxides. This approach has been compared with the acid-base theory. As examples, analyses have been made on reactions of stabilized zirconia with perovskite electrodes in solid oxide fuel cells, with vanadium oxide in combustion gas, with molten carbonates and with silica-based glasses.
- Residual stress generation during constrained sintering of layered ceramic thin film structures
Busso, EP; Travis, RP; Chandra, L
Materials Research Society, Thin-Films - Stresses and Mechanical Properties VII Symposium Proceedings (USA), pp. 547-552, 1998
This work investigates the sintering kinetics and residual stresses which develop in thin layered ceramic structures when sintered on a rigid substrate. A continuum constitutive framework to model the evolution of the microstructure and stresses in the sintering layers under non-isothermal conditions is presented. The sintering model is used to investigate the constrained sintering behaviour of layered ceramic structures used in solid oxide fuel cells (SOFC). Samples of a 50 mu n thick SOFC film were screen- printed on a fully dense yttria-stabilised zirconia substrate and then sintered at temperatures ranging from 1100 deg C to 1300 deg C. Measured values of relative density and average grain size are compared with model predictions. A correlation between residual stresses extracted from curvature measurements and analytical predictions revealed these stresses to have been mostly relieved during the subsequent cooling by microcrack formation.
- Brazing of metallic conductors onto ceramic plates in solid oxide fuel cells. I. Attaching a current collector
Wilkenhoener, R; Buchkremer, HP; Stoever, D; Stolten, D; Koch, A
Journal of Materials Science (USA), vol. 36, no. 7, pp. 1775-1782, 1 Apr. 2001
Furnace brazing to attach metallic plates to LaCrO sub 3 end plates in solid oxide fuel cell (SOFC) was investigated. The metallic plates act as a current collector to which a few conducting wires made of conventional heat-resisting alloys can be attached. The alloy CrFe5Y sub 2 O sub 3 1 was found to be a suitable material for the current collector because its thermal expansion coefficient matches that of LaCrO sub 3 better than heat-resisting nickel- or iron-based alloys. Among various filler alloys tested, SCP6 (Cu with 18 wt.% Pd) enables the best wetting of LaCrO sub 3 and CrFe5Y sub 2 O sub 3 1 plates, leading to good adhesion between them. Several approaches were successfully pursued to reduce the bending of brazed LaCrO sub 3 /SCP6/CrFe5Y sub 2 O sub 3 1 joints. The area specific resistance of some LaCrO sub 3 /SCP6/CrFe5Y sub 2 O sub 3 1 joints increased slightly during annealing (1000 deg C in air for 2400 h) due to oxidation in the filler alloy. Nevertheless, it remained below the target limit of 0.2 Omega cm exp 2 .
- A novel Ni-CERMET electrode based on a proton conducting electrolyte
Van Rij, LN; Le, J; Van Landschoot, RC; Schoonman, J
Journal of Materials Science (USA), vol. 36, no. 5, pp. 1069-1076, 1 Mar. 2001
Based on the one-chamber fuel cell design by Iwahara a catalytic methane sensor has been developed. The working principle of this sensor is based on the difference in catalytic properties of two electrodes for the CO sub 2 reforming reaction of methane. The sensor is based on a high-temperature proton conducting electrolyte, i.e. SrCe sub 0.95 Yb sub 0.05 O sub 3- alpha or CaZr sub 0.9 In sub 0.1 O sub 3- alpha . At 500 deg C a linear sensor response on the methane partial pressure has been found for a Ru /SrCe sub 0.95 Yb sub 0.05 O sub 3- alpha /Pt cell. This cell, however, shows poor long-term stability. The long-term stability of the Ru/SrCe sub 0.95 Yb sub 0.05 O sub 3- alpha /Pt cell is improved using a more stable electrolyte material, i.e. CaZr sub 0.9 In sub 0.1 O sub 3- alpha (CZl10). Further improvement of the long-term stability of the sensor is achieved using a nickel-CaZr sub 0.9 In sub 0.1 O sub 3- alpha CERMET (Ni-CZl10) electrode. The sensor response of a Ni-CZl10/CaZr sub 0.9 In sub 0.1 O sub 3- alpha /Pt cell is found to be linear at 600 deg C and 700 deg C, respectively. The temperature dependence of both the Ru/SrCe sub 0.95 Yb sub 0.05 O sub 3- alpha /Pt and the Ni-CZl10/CaZr sub 0.9 In sub 0.1 O sub 3- alpha /Pt cell can be explained by the temperature dependence of the catalytic activity of the electrode materials used. This confirms that the obtained EMF is established by a catalytic activity difference between both electrodes. The power output of a Ni-CZl10/CaZr sub 0.9 In sub 0.1 O sub 3- alpha /Pt cell is also determined. A combined sensor-fuel cell would have the advantage that it is able to detect the fuel concentration in the gas and, therefore, correct in situ for fluctuations in the fuel concentration. The power output of the Ni-CZl10/CaZr sub 0.9 In sub 0.1 O sub 3- alpha /Pt cell, however, is found to be 0.01 mWcm exp -2 . This low power output, with respect to values reported in literature for the one-chamber fuel cell, can be explained by the relatively thick electrolyte used, the electrode materials chosen, and the use of the reforming reaction of methane instead of the partial oxidation of methane. However, the feasiblity of the combined sensor-fuel cell has been demonstrated.
- Development of components for fuel cell working at moderate temperature
Taiheiyo Cement Kenkyu Hokoku (Journal of the Taiheiyo Cement Corporation) Japan (Japan), vol. 140, pp. 117-125, 2001
In order to develop components which is desirable for promising SOFC working at moderate temperature (600-800 deg C), Taiheiyo Cement Corp., Ltd attempted strengthening of lanthanum gallate solid oxide (LSGM) electrolyte and manufacturing of porous cermet electrode collaborating with Tokyo Gas Co., Ltd. As for electrode, our ceramics processing techniques was applied to manufacture porous cermet electrode and succeed to realize a series of cermet having a widely range of open porosity (5-60 vol%). Further more, by using air filter made of resin as template, a new porous structure with surprisingly high air permeability was obtained and named 'KAMINARI-OKOSHI' -type one. As for electrolyte, addition of alumina, especially from 2 to 5 mass%, was found to be effective to strengthen LSGM without lowering its intrinsically high electric conductivity owing to oxide ion. In a case of LSGM added 2mass% of alumina, its 3-point bending strength of 255 MPa at room temperature and 190 MPa at 800 deg C is to be compatible to engineering ceramics such as pure mullite and its electric conductivity of 8.8 S/m at 800 deg C is four times higher than YSZ at 800 deg C. A planar electrolyte-supporting-type unit cell using this alumina added LSGM (thickness: 200 mu m) was assembled and showed power density of 0.58 W/cm exp 2 (1.0A/cm exp 2 ) at 750 deg C. This unit cell showed no degradation of voltage over 1000 hr and kept 0.9V (0.3A/cm exp 2 ) at 750 deg C.
- Oxidation properties of Fe-Cr ferritic alloys coated with (La,Sr)CoO sub 3 for SOFC application
Przybylski, K; Prazuch, J; Brylewski, T; Maruyama, T
Corrosion Institute of Southern Africa, 14th International Corrosion Congress (ICC) Proceedings (South Africa), pp. 122.0, Oct. 1999
Recently, high-temperature iron-base scaling-resistant alloys (Fe-Cr) have been tested for application in construction of separators for planar type solid oxide fuel cells (SOFC) operating at 1073 K, on account of their advantages in comparison with other Ni or Co-based alloys and ceramics (e.g. (La,Sr)CrO sub 3 ). The oxidation kinetics of Fe-16 wt.-% Cr and Fe-25 wt.-%Cr steels (Ni < 1.0%, Mn < 0.4%, Si <0.8%) have been studied in air at 1073 K and 1173 K and in H sub 2 -H sub 2 O gas mixtures (p sub H2 /p sub H2O =94/6), corresponding to the anode and cathode operating conditions of SOFC for 85, 119, 140 and 180 h using thermogravimetric method. It has been found that the oxide scale, composed mainly of Cr sub 2 O sub 3 , grows in accordance with the parabolic rate law and the determined parabolic rate constants k sub p was independent of the oxygen partial pressure in the range of 2.35 x 10 exp -21 to 0.21 atm at 1073 K. The increase in the electrical resistance of the chromia scale on the Fe-Cr steel tested vs time, calculated on the basis of k sub p , in comparison with constant value of the electrical resistance of (La,Sr)CrO sub 3 ceramic separator indicate the necessity to modify the alloy surface. The resistance of the alloy coated with (La,Sr)CoO sub 3 by screen-printing method does not exceed the resistance of ceramic separator in air at 1073 K, showing the applicability of the tested commercial steels for construction of metallic separators for SOFC. The TEM and EDS investigations of the interface between (La,Sr)CoO sub 3 coating layer and Fe-25Cr steel showed the formation of strontium-chromium oxide precipitates at grain boundaries of Cr sub 2 O sub 3 as a result of strontium segregation to chromia scales during the oxidation process. The effect of Sr incorporation to chromia scales on the microstructure and chemical composition will be discussed.
- Stainless steels in solid oxide fuel cells
Associazione Italiana di Metallurgia, International Congress Stainless Steel '99 Science and Market 3rd European Congress Proceedings, Vol. 1: Marketing and Application (Italy), pp. 353-361, June 1999
Fuel cells are devices for the electrochemical production of electricity from streams of fuel and air at high temperatures, 750 deg C - 1000 deg C, with moderate to high levels of moisture. This environment creates many problems for materials, especially the interconnect (or bipolar) plates. Some design use advanced ceramics whereas others use heat resistance steels, nickel-chromium alloys or chromium alloys. CFCL has researched the technical and commercial aspects of planar solid oxide fuel cells (SOFC) over the last 6 years, and has concluded that the replacement of all expensive metals by commercial grades of heat resistant steels is essential if this power generation technology is to become commercially viable. The components for which stainless steels are being trailed in CFCL's fuel cell units are described and the unresolved issues and problems detailed. Experimental work conducted with ferritic steels produced to a modified 446 grade specification are presented, and the methods used to protect the steel from degradation discussed. Overlying all these concerns is cost. Our analysis shows that the future of SOFC technology is quite sensitive to the price and availability of suitable stainless steels in appropriate sheet form.
- Ceramic opportunities in fuel cells
Ceramic Industry (USA), vol. 152, no. 6, pp. 35-37,39, June 2002
Fuel cells are still a number of years away from full commercialization, but the outlook for ceramic applications in this emerging market is promising. A number of different types of fuel cells are currently in development. Of the different technologies, solid oxide fuel cells (SOFCs), which incorporate ceramic-based electrolytes as well as ceramic anode and cathode materials, hold the most promise for the ceramic industry. Most fuel cell developers agree that wide commercialization of fuel cells probably won't occur until at least 2010 or later, and it is unclear which technology will capture the largest market share. Even if SOFCs do not emerge as the biggest player, ceramics will likely find applications in other areas related to fuel cells. Article online at www.ceramicindustry.com.
- Cooler fuel cells
Advanced Ceramics Report (UK), pp. 7, Aug. 2000
One of the main reasons fuel cells have yet to become a commercial success is the fact that they run at high temperatures, approx1000 deg C in the case of zirconia-based membrane types. However, a new design of ceramic fuel cell made by Japanese researchers runs at just 500 deg C, approx100 deg C cooler than its closest ceramic competitor. Developed by Takashi Hibino of the National Industrial Research Institute of Nagoya, Japan, and his colleagues at Nagoya University, the new design uses a cell with a cerium dioxide membrane that lets ions through at lower temperatures. Contact: Takashi Hibino, National Industrial Research Institute, 1, Hirate-cho, Kita-ku, Nagoya City, Aichi 462, Japan; tel +81-52-911-2111, fax +81-52-916-2802.
- MIXED ELECTRONIC-IONIC CONDUCTIVITY OF COBALT DOPED CERIUM GADOLINIUM OXIDE
Kleinlogel, CM; Gauckler, LJ
J.Electroceramics. Vol.5, No.3, 2000, p.231-243.
The effect of small amounts (< 5 mol%) of cobalt oxide on the electrical properties of cerium oxide solid solutions has been evaluated. Ce0.8Gd0.2O2-x (CGO) powder with an average crystallite size of 20 nm served as a model substance for the electrolyte material with a high oxygen ion conductivity and low electronic conductivity in its densified state. Doping the CGO powder by transition metal oxides (MeO) with concentrations below 2 mol% did not change the ionic conductivity nor the electrolytic domain boundary. After long sintering times (2 h) at temperatures above 900 C, MeO and CeO2 form solid solutions. However, short sintering times or high dopant concentrations lead to an electronic conducting grain boundary phase short circuiting the ionic conductivity of the CGO grains. Choosing proper doping levels, sintering time and temperature allows mixed conducting oxides based on CGO to be tailored. These materials have potential use as electrolytes and/or anodes in solid oxide fuel cells and ion separation membranes. 56 refs.
- EVALUATION OF COMMERCIAL NICKEL OXIDE POWDERS FOR COMPONENTS IN SOLID OXIDE FUEL CELLS
Tietz, F; Dias, FJ; Simwonis, D; Stover, D
J.Eur.Ceram.Soc. Vol.20, No.8, 2000, p.1023-1034.
Various commercial nickel oxides were examined with respect to their relevant powder properties for application as anodes or anode substrates in SOFCs. The powders were characterised regarding their morphology, grain size distribution, BET surface and sintering behaviour. Furthermore, anode substates were produced from these powders together with yttria-stabilised zirconia (YSZ) powder. The sintering behaviour, gas permeability and electrical conductivity of these components were determined and compared with the current standard material used for SOFC development. A comparison of the powder and component properties indicate a significant influence of the powder properties on the components produced. 30 refs.
- LANTHANUM ALKALINE-EARTH MANGANITES AS A CATHODE MATERIAL IN HIGH-TEMPERATURE SOLID OXIDE FUEL CELLS
Mori, M; Hiei, Y; Yamamoto, T; Itoh, H
J.Electrochem.Soc. Vol.146, No.11, 1999, p.4041-4047.
The effect of RE (RE = Ce and Pr) doping of LaMnO3 perovskite on its crystallographic properties, phase relationships, electrical conductivity, thermal expansion, sintering, and reaction with Y2O3-stabilised ZrO2 electrolyte is presented. La1-xRExMnO3 showed a single perovskite phase in the region x = 0-0.05 for Ce substitution and over the entire composition range of Pr content. No effect of RE doping on conductivity was observed but a decrease in thermal expansion coefficients was. Ce doping of LaMnO3 increased its morphological stability and suppressed its reaction with the electrolyte. Ln1-xAExMnO3 (Ln: lanthanum concentration with La, Ce, and Pr, AE = Sr, Ca) materials were examined as cathodes in solid oxide fuel cells. XRD analysis indicated that Ln1-xAExMnO3 (x = 0-0.3) showed a single perovskite phase. Conductivities of these oxides increased with AE content and ranged from 80 to 200 S/cm at 1000 C in air, and thermal expansion coefficients ranged from 9.5 to 11.6 x 10 exp(-6)/C. Ln1-xAExMnO3 showed less reactivity with the electrolyte compared with La1-xAExMnO3. The cathodic polarisation of the (Ln0.8Sr0.2)0.95MnO3 at 1000 C was 60 mV at 500 mA/cm2 in air. 22 refs.
- SOLID OXIDE FUEL CELL AND DOPED PEROVSKITE LANTHANUM GALLATE ELECTROLYTE THEREFOR
QPAT-US US Pat.6004688
A perovskite lanthanum gallate electrolyte doped with strontium and Mg and a solid oxide fuel cell incorporating a doped lanthanum gallate electrolyte with a cathode on one side, an anode on the other side and a buffer layer comprising a mixed electronic and oxide-ion conductor between the anodes and/or the cathode and the electrolyte to block unwanted chemical reactions while permitting electronic and oxide-ion transport.
- INTERMEDIATE TEMPERATURE SOLID OXIDE FUEL CELLS USING A NEW LaGaO3 BASED OXIDE ION CONDUCTOR. PT.1. DOPED SmCoO3 AS A NEW CATHODE MATERIAL
Ishihara, T; Honda, M; Shibayama, T; Minami, H; Nishiguchi, H; Takita
J.Electrochem.Soc. Vol.145, No.9, 1998, p.3177-3183.
LaGaO3-based perovskite oxides doped with Sr and Mg exhibit high ionic conductivity over a wide range of pO2. The LaGaO3-based oxide was found to be very stable in reducing, oxidising and CO2 atmospheres. SOFCs using LaGaO3-based perovskite-type oxide as the electrolyte were studied for use in intermediate temperature SOFCs. The power generation characteristics of cells were strongly affected by the electrodes. Both Ni and LnCoO3 (Ln = rare earth) were suitable for use as anode and cathode, respectively. Rare earth cations in the Ln site of the Co-based perovskite cathode also had a significant effect on the power generation characteristics. In particular, a high power density could be attained in the temperature range 973-1273 K by using a doped SmCoO3 for the cathode. The study revealed that a LaGaO3-based oxide for electrolyte and a SmCoO3-based oxide for the cathode are promising components for SOFCs operating at intermediate temperature. 25 refs.
- Ag-PEROVSKITE CERMETS FOR THIN FILM SOLID OXIDE FUEL CELL AIR-ELECTRODE APPLICATIONS
QPAT-US US Pat.6004696
An air electrode for a solid oxide fuel cell having high conductivity and low interfacial resistance is disclosed. Said air electrode is composed of an Ag-perovskite cermet.
- ELECTRICALLY CONDUCTING CERAMIC AND FUEL CELL USING THE SAME
Invention is an electrically conducting ceramic having improved electrical conductivity which comprises a perovskite-type composite oxide of a composition represented by the following formula (La sub1- x-y A subx B suby) subz (Mn sub1-u C subu) subv O sub delta wherein A represents at least one type of atom selected from the group consisting of Sc, Y, Nd, Yb, Er, Gd, Sm, and Dy, B represents at least one type of atom selected from the group consisting of Ba, Sr, and Ca, and C represents at least one type of atom selected from the group consisting of Co, Fe, Ni, Ce, Zr, Mg, Al, Sb, and Cr, and x, y, z, u, v, and delta are the numbers that satisfy the following formulas: x=0.02-0.5, y=0.1-0.6, z=0.9-1.05, u=0-0.5, v=1, and at 1000 C in open air, delta=2.97-3.04. A tubular-type fuel cell containing an electroconductive ceramic in accordance with this invention as an air electrode does not deform during operation for long period of time and yields a stabilized output and a planar type fuel cell which is free from peeling of air electrodes or does not decrease its output by the deformation of the cell.
- DEVELOPMENT OF CATHODE MATERIALS FOR LOW TEMPERATURE SOFC
Christie, GM; Van, HeuvelnFH; Van, BerkelFPF
Riso Int.Symp.Mater.Sci. High-Temperature Electrochemistry: Ceramics and Metals Roskilde,2-6 September 1996,17,1996,p.205-211
Electrochemical techniques are used to evaluate the performance of porous LA0.6Sr0.4Co0.2Fe0.8O3-delta electrodes when used in conjunction with Ce0.9Gd0.1O1.95 electrolytes at 700 C in air. Two distinct regimes of behavior are identified: at low electrode overpotential, a poor performance is observed; at higher electrode overpotential, a transition to a higher performance regime occurs. Variations in electrode microstructure have the most significant effect on electrode performance in the high performance regime, where the electrodes with the smallest particles exhibit the lowest resistances. Impregnation of the oxide electrode with microcrystalline particles of Pt significantly enhance the electrode performance. 7 refs.
- INFLUENCE OF A-SITE DEFICIENCY ON THE PERFORMANCE OF STRONTIUM DOPED LANTHANUM-MANGANATE PEROVSKITE TYPE SOFC CATHODES
Weber, A; Manner, R; Jobst, B; Schiele, M; Cerva, H; Waser, R
Riso Int.Symp.Mater.Sci. High-Temperature Electrochemistry: Ceramics and Metals Roskilde,2-6 September 1996,17,1996,p.473-478
SOFC cathodes of La sub(0.8-x)Sr sub0.2 MnO sub3 (LSM) with different La deficiencies (x=0, 0.05, 0.075, 0.1) are studied. The LSM powders and sintered cathode layers are analyzed. The electrical properties of the cathodes are determined. All the cathodes show a significant decrease of the cathode resistance during the first electrical loading of the cell. 8 refs.
- PREPARATION AND CHARACTERISATION OF NEW MIXED CONDUCTING OXIDES BASED ON BaCe1-xGdxO3-x/2
Mukundan, R; Davies, PK; Worrell, WL
Role of Ceramics in Advanced Electrochemical Systems. Proc.Symp. Cincinnati, 30 April-3 May 1995, p.13-21. Ceram.Trans.Vol.65
The high protonic conductivities of barium cerium gadolinium oxides (Ba(Ce1-xGdx)O3-x/2, x between 0-0.2) have led to their incorporation as electrolytes in fuel cells operating at 873-1073 K. In an effort to develop new mixed-conducting electrodes that are compatible with the cerate electrolyte, the electrochemical properties of Pr- and Tb-doped barium gadolinium cerate were examined. It is shown that for both systems the doping increases the electronic contribution to the total conductivity and for Ba(Ce0.5Pr0.4Gd0.1)O3-delta a conductivity exceeding approximately 0.1 S/cm at 1173 K in dry air was obtained. The high conductivities induced by the substitution of Pr may result in their application as cathodes in a cerate-based protonic fuel cell. 7 refs.
- Preparation and characterization of new mixed conducting oxides based on BaCe sub 1 sub - sub x Gd sub x O sub 3 sub - sub x sub /2 [0
Mukundan, R; Davies, PK; Worrell, WL
Ceramic Transactions, 65, pp. 13-21, 1996
The high protonic conductivities of title oxides led to their incorporation as electrolytes in fuel cells. In an effort to develop new mixed conducting electrodes that are compatible with the cerate electrolyte, authors examine the electrochemical properties of Pr- and Tb-doped barium gadolinium cerate. For both systems, doping increases the electronic contribution to the total conductivity, and for Ba(Ce sub 0.5 Pr sub 0.4 Gd sub 0.1 )O sub 3- delta , a conductivity exceeding >0.1 S/cm at 1173 K in dry air is obtained. The high conductivities induced by the substitution of Pr may result in application as cathodes in a cerate-based protonic fuel cell. (meeting proceedings)
- SILVER-BaCe0.8Gd0.2O3 COMPOSITES AS CATHODE MATERIALS FOR SOFCS USING BaCeO3-BASED ELECTROLYTES
Hu, H; Liu, M
J.Electrochem.Soc. Vol.143, No.3, 1996, p.859-864.
Composites of silver and BaCe0.8Gd0.2O3 ceramics were studied as cathode materials for intermediate-temperature solid oxide fuel cells using BaCeO3-based electrolytes. Results indicate that the electrochemical properties of these composites are quite sensitive to the composition and microstructure of the electrodes. The optimal silver content of the composites seems to fall within the range of 50 to 70 vol%, depending on the particular microstructure of the electrode. As compared to pure silver electrodes, the composite electrodes show better adhesion to the electrolyte, higher exchange current densities, and lower cathodic overpotentials under various conditions. The observed high performance of the composite electrodes is attributed primarily to the fine-grained microstructure and high porosity of the composites, as the BaCe0.8Gd0.2O3 phase inhibits grain growth of the silver phase in the composites. 12 refs.
- AN EVALUATION OF Ce-Pr OXIDES AND Ce-Pr-Nb OXIDES MIXED CONDUCTORS FOR CATHODES OF SOLID OXIDE FUEL CELLS: STRUCTURE, THERMAL EXPANSION AND ELECTRICAL CONDUCTIVITY
Nauer, M; Ftikos, C; Steele, BCH
J.Eur.Ceram.Soc. Vol.14, No.6, 1994, p.493-499.
CeO2 doped with PrO2 and Nb2O5 was evaluated as a cathode material for solid oxide fuel cells. One fluorite phase was detected in CeO2-PrO2-x for PrO2-x up to 20 mol%, and two fluorite phases, with different lattice parameters, for higher PrO2-x concentrations. The addition of 3 mol% Nb2O5 stabilised a single fluorite phase for up to 50 mol% PrO2-x. The thermal expansion coefficient varied between 0 and 3 x 10 exp(-6)/K, depending upon composition and temperature. The electrical conductivity was mainly electronic and thermally activated. 12 refs.
- SINTERING AND MICROSTRUCTURAL DEVELOPMENT OF CERIA-GADOLINIA DISPERSED POWDERS
Duran, P; Moure, C; Juraldo, JR
J.Mat.Sci. 29, No.7, 1994, p.1940-1948
Well-dispersed ceria-gadolinia oxide powders were obtained from thoroughly isopropanol-washed coprecipitated oxalates, followed by calcination at 800 C. The characteristics of the calcined powders and the microstructure of the green compacts were found to be of great importance in the sintering behaviour. Those green bodies in which some agglomerate survived after compaction reached a lower final density, while those having soft agglomerates were almost fully densified at a sintering temperature as low as 1400 C. The densification process was studied by isothermal and constant heating rate dilatometry, and microstructural development at each stage in the processing was followed by SEM. By controlling the processing variables it was possible to obtain low-temperature near fully dense (better than 99%) and tough CeO2-Gd2O3 bodies with homogeneous microstructures. Ceria-doped ceramics are considered as good electrolytes or electrodes for high-temperature fuel cells and as oxygen sensors. 17 refs.
- STATUS OF SOFC DEVELOPMENT IN AUSTRALIA
Badwal, SPS; Foger, K
Solid Oxide Fuel Cells.Proc.3rd Int.Symp. Honolulu, 16-21 May 1993, p.21-27. Vol.93-4
CSIRO, through its Division of Materials Science and Technology, has been involved in research on zirconia ceramics (Both electrical and mechanical properties) and oxidation catalysis for more than 20 years. Based on this experience and expertise in a number of other key areas around the country a company, Ceramic Fuel Cells, was formed by a consortium to provide focus for R & D and commercialisation of solid oxide fuel cell technology. The consortium will invest $30 million over the first five year R & D stage. The SOFC development programme is relatively new in Australia. Performance of individual electrode and electrolyte materials has been optimised and planar single cells with LSM air and Ni/zirconia cermet electrodes and zirconia doped with yttria are currently undergoing evaluation. 2 refs.
- Application of electrophoretic and electrolytic deposition techniques in ceramics processing
Boccaccini, AR; Zhitomirsky, I
Current Opinion in Solid State & Materials Science (Netherlands), vol. 6, no. 3, pp. 251-260, June 2002
Electrodeposition is gaining increasing interest as a ceramic processing technique for a variety of technical applications. Major advances in the areas of electrophoretic deposition (EPD) and electrolytic deposition (ELD) achieved in the last 24 months include the fabrication of: electrodes and films for solid oxide fuel cells, fibre-reinforced and graded ceramic composites, nanostructured materials as well as a variety of advanced films and coatings for electronic, biomedical, optical, catalytic and electrochemical applications.
- Ni-YSZ cermet anodes prepared by citrate/nitrate combustion synthesis
Marinsek, M; Zupan, K; Maeek, J
Elsevier Science SA, Journal of Power Sources (Switzerland), vol. 106, no. 1-2, pp. 178-188, 1 Apr. 2002
The synthesis of Ni-YSZ cermets with tailored particle package, shape and microstructural characteristics is essential when preparing anodes for solid oxide fuel cells (SOFC). These materials are generally prepared by sintering and subsequent reduction of the mixture of metal oxides. In order to obtain cermets with an adequate contact area between electrocatalyst (Ni) and ionic conductor (YSZ), an alternative route was used based on mixed gel combustion with the material synthesis, calcination and partial sintering achieved in one step. The precursor for the combustion synthesis was a mixed citrate/nitrate gel prepared from nickel, zirconium and yttrium nitrates and citric acid by vacuum evaporation of the solution. The combustion reaction of this gel produces submicrometer crystalline NiO-YSZ composite. The influence of the fuel/oxidant molar ratio of the precursor on the combustion rate and end product characteristics was investigated. The reaction period, phase composition, morphology and agglomerate formation were studied in detail. It was shown that the initial fuel/oxidant ratio strongly influences the characteristics of the powder mixtures thus obtained. The morphological properties of the prepared mixed oxides after the combustion synthesis reveal that the particle size distribution and the agglomerate formation in the voluminous intermediate mixed oxide product (green body) differ with the initial fuel/oxidant molar ratio. Narrower agglomerate and pore size distribution has a great influence on the subsequent sintering and reduction of the mixed material. If the particle and pore size distribution in the green body are narrow, the coarsening of the YSZ and NiO grains, and subsequently, YSZ and Ni grains are less pronounced.
- Electrochemical performance of mixed ionic-electronic conducting oxides as anodes for solid oxide fuel cell
Jiang, Y; Wang, S; Zhang, Y; Li, W; Yan, J; Lu, Z
Solid State Ionics (Netherlands), vol. 120, no. 1-4, pp. 75-84, May 1999
Mixed ionic-electronic conducting (MIEC) oxides, SrFeCo sub 0.5 O sub x , SrCo sub 0.8 Fe sub 0.2 O sub 3- delta and La sub 0.6 Sr sub 0.4 Fe sub 0.8 Co sub 0.2 O sub 3- delta have been synthesized and prepared on yttria-stabilized zirconia as anodes for solid oxide fuel cells. Power output measurements show that the anodes composed of such kinds of oxides exhibit modest electrochemical activities to both H sub 2 and CH sub 4 fuels, giving maximum power densities of around 0.1 W/cm exp 2 at 950 deg C. Polarization and AC impedance measurements found that large activation overpotentials and ohmic resistance drops were the main causes for the relative inferior performance to the Ni-YSZ anode. While interlayered with an Ni-YSZ anode, a significant improvement in the electrochemical performance was observed. In particular, for the SrFeCo sub 0.5 O sub x oxide interlayered Ni-YSZ anode, the maximum power output reaches 0.25 W/cm exp 2 on CH sub 4 , exceeding those of both SrFeCo sub 0.5 O sub x and the Ni-YSZ, as anodes alone. A synergetic effect of SrFeCo sub 0.5 O sub x and the Ni-YSZ has been observed. Future work is needed to examine the long-term stability of MIEC oxide electrodes under a very reducing environment.
- Thermal spraying and performance of graded composite cathodes as SOFC-component
Barthel, K; Rambert, S
Materials Science Forum (Switzerland), vol. 308-311, pp. 800-805, 1999
Porous compositionally graded composite cathodes containing (La sub 0.8 Sr sub 0.2 ) sub 0.98 MnO sub 3 (LSM) and ZrO sub 2 -12% Y sub 2 O sub 3 (YSZ) were prepared by vacuum plasma spraying (VPS) and flame spraying (FS) on prefabricated planar cells with 60 mm diameter. Besides microstructural observations their electrochemical behavior has been investigated by impedance spectroscopy. The results of graded cathodes compared with non-gradient- and bi-layered ones concerning the cathodic polarization resistance between 750 and 950 deg C are discussed.
- Development of graded composite electrodes for the SOFC
Gerk, C; Willert-Porada, M
Materials Science Forum (Switzerland), vol. 308-311, pp. 806-813, 1999
The simultaneous increase of electrochemical activity (i.e. fineness) and thermal stability of SOFC-electrodes is possible using eutectic microstructures. On the basis of a lamellar NiO-YSZ eutectic a microwave melting process was developed which allows crystallization in a large temperature gradient. The microstructures obtained by melting the electrodes directly onto the top of a YSZ substrate (electrolyte) consist of partially aligned lamellae perpendicular to the surface of the substrate. The thickness of the alternating NiO-YSZ lamellae is graded over the thickness of the electrode, i.e. it increases with increasing distance from the substrate. In terms of functionality this means an inverse gradient of electrochemical active three phase boundaries (gas-Ni-YSZ) after reduction of NiO to Ni. During the reduction process the microstructural gradient of lamellae thickness is converted into a functional gradient of electrochemical active sites. The models taken into account show that this functionally graded micro structure should lower the overpotentials of SOFC-devices. The paper concentrates on modelling and experimental details for the preparation of partially aligned eutectic lamellae with a graded interlamellar spacing.
- Synthesis of ultrafine NiO/8YSZ composite powders
Kim, S-J; Jung, C-H
Journal of Materials Synthesis and Processing (USA), vol. 4, no. 6, pp. 405-411, Nov. 1996
Ultrafine NiO/8YSZ (8 mol% yttria-stabilized zirconia) composite powders were prepared using a glycine nitrate process (GNP) for anode material of solid oxide fuel cells. The specific surface areas of synthesized NiO/8YSZ composite powders were examined by controlling the pH of a precursor solution and the content of glycine. The binding of glycine with metal ions in the precursor solution was analyzed by using FTIR. The characteristics of synthesized composite powders were examined with an x-ray diffractometer, a BET method with N sub 2 absorption, and scanning and transmission electron microscopies. Ultrafine NiO/8YSZ composite powders of 15-18 m exp 2 /g were produced through the GNP when the content of glycine was controlled one to two times the stoichiometric ratio in the precursor solution. A strongly acidic precursor solution increased the specific surface area of the synthesized composite powders. This results from the increased binding of metal ions and glycine under strongly acidic solution (pH=0.5) conditions, where glycine consists of mainly the amine group of NH sub 3 exp + . After sintering and reducing treatment of NiO/8YSZ composite powders synthesized by GNP, the Ni/8YSZ pellet showed an ideal microstructure: fine Ni particles of 3 to 5 mu m were distributed uniformly and fine pores around Ni metal particles were formed, thus leading to an increase in the triple-phase boundary among gas, Ni, and 8YSZ.
- Dependence of SOFC cathode degradation by chromium-containing alloy on compositions of electrodes
Matsuzaki, Y; Yasuda, I
Journal of the Electrochemical Society (USA), vol. 148, no. 2, A126-A131, Feb. 2001
Although many benefits are expected by reducing the operating temperature of solid oxide fuel cells (SOFCs) with alloy interconnectors, it should be of concern that chromium oxyhydroxide vapor generated from an oxide scale (Cr sub 2 O sub 3 ), which is formed on the surface of most high temperature oxidation-resistant alloys, degrades the performance of the cathode under polarization. We have investigated a relationship between resistance against the Cr poisoning and compositions of electrode and electroltye to show the possibility of a mitigating the Cr poisoning without reducing the chromium oxyhydroxide vapor pressure. Strontium-doped LaMnO sub 3 (LSM) electrode on yttria-stabilized zirconia electrolyte with a current collector made of a Cr-containing alloy showed fast degradation under a polarization, which was due to the precipitation of Cr sub 2 O sub 3 at the electrode/electrolyte interface as a result of the reduction of the chromium oxyhydroxide vapor. In the present study, the degradation by the Cr poisoning has been investigated for the LSM electrode on four types of electrolytes. The degree of the degradation was found to depend on the composition of the electrolyte on which the electrode was prepared. This suggests that the electrochemical properties of the electrode/electrolyte interface influence the reduction of the chromium oxyhydroxide vapor. We have found that when La sub 0.6 Sr sub 0.4 Co sub 0.2 Fe sub 0.8 O sub 3 and Ce sub 0.8 Sm sub 0.2 O sub 1.9 were used as the electrode and the electrolyte, respectively, the significant Cr poisoning is not caused even in the presence of the chromium oxyhydroxide vapor at the temperature range from 923-1173K. Alloy used in study: Inconel 600.
- Development of metallic substrate supported planar solid oxide fuel cells fabricated by atmospeheric plasma spraying
Takenoiri, S; Kadokawa, N; Koseki, K
Journal of Thermal Spray Technology (USA), vol. 9, no. 3, pp. 360-363, Sept. 2000
A planar solid oxide fuel cell (SOFC) consisting of a cell supported with a porous metallic substrate and a metallic separator has been developed. In the fabrication of the cell, anodes and electrolytes were formed on sintered Ni-felt substrates using flame spraying (FS) and atmospheric plasma spraying (APS), respectively. The APS is also applied to form (LaSr)MnO sub 3 protective coatings on the metallic separators. With these metallic cells and separators, a 3 kW-class stack, which consisted of 30 cells (15-cell block x 2) was constructed and operated. The active electrode area of the cell was 600 cm exp 2 . The stack generated 3.3 kW at 970 deg C when the current density was 0.3 Acm exp -2 and the fuel utilization 50%. It did not show any degradation for the intitial 2100 h, but a few cells in the lower 15-cell block became unstable after 2100 h. On the other hand, the upper 15-cell block was stably operated for 3200 h.
- Synthesis and properties of dense nickel and cobalt zirconia cermet anodes for solid oxide fuel cells
Sammes, NM; Brown, M; Brown, IWM
Journal of Materials Science (UK), vol. 31, no. 22, pp. 6069-6072, 15 Nov. 1996
Porous Ni/zirconia cermets have been traditionally used as anodes in solid oxide fuel cell configurations. They show excellent catalytic activity towards hydrogen oxidation and a number of other attributes. However, they are prone to sintering during long term operation, thus causing a drop in the efficiency of the cell. This paper describes the fabrication and properties of a dense cermet which, we suggest, may act as an intermediate layer between the electrolyte and the porous anode and possibly reduce anode degradation. Cobalt and nickel based cermet systems were investigated and a 30 vol.% Co/zirconia system could be fabricated with <20% porosity after being sintered at 1300 deg C.
- Sputter deposition of yttria-stabilized zirconia onto a porous gold substrate
Jankowski, AF; Hayes, JP
J. Vac. Sci. Technol. A (USA), vol. 13, no. 3, Part I, pp. 658-661, May-June 1995
Process issues key to thin-film/solid-oxide fuel cells include the deposition of defect-free electrolyte layers on porous electrodes, gas transport through the porous conducting electrodes, and sufficient structural integrity for stack assembly and temperature cycling. This study addresses the method of electrolyte layer deposition. The initial approach uses a porous metal substrate to permit measurement of the electrolyte performance as well as provide a pore size similar to conventional cermet electrodes. The sputter deposition of Au under controlled process parameters provides the porous substrate. An optimum choice for the electrolyte material is yttria-stabilized zirconia (YSZ). The focus is to evaluate the process parameters of rf sputtering as YSZ target to densely coat the porous (Au) substrate. A high sputter gas pressure of argon facilitates filling surface voids of the porous substrate leading to the formation of a defect-free layer of cubic YSZ as examined with electron microscopy techniques.
- Sputter deposition of cermet fuel electrodes for solid oxide fuel cells
Tsai, T; Barnett, SA
J. Vac. Sci. Technol. A (USA), vol. 13, no. 3, Part I, pp. 1073-1077, May-June 1995
The structure and electrochemical properties of cermet thin films composed of 50 vol.% nickel and yttrium-stabilized ZrO sub 2 (YSZ) of interest for solid-oxide fuel cell (SOFC) electrode applications are described. The Ni-YSZ films-deposited by dc reactive magnetron sputtering of Ni-Zr-Y targets in Ar-O sub 2 mixtures-were porous, two-phase, and exhibited an equiaxed structure with grain sizes approx35 nm. The typical conductivity of 10 exp 3 Omega exp -1 cm exp -1 was similar to that of bulk Ni-YSZ. Impedance spectroscopy was used to characterize reactions of H sub 2 /H sub 2 O fuel gases at the interfaces between Ni-YSZ films and YSZ electrolytes. The spectra typically showed two arcs, attributed to charge transfer and gas diffusion. Either high sputter gas pressures of 40 m Torr or roughened YSZ substrate surfaces were necessary to obtain sufficient film porosity. Electrochemical resistance values of 0.15-0.35 Omega cm exp 2 were measured at 750 deg C in 97% H sub 2 +3% H sub 2 O, lower than those for bulk Ni-YSZ and low enough for high-power-density SOFC operation. The low resistance values were probably due to a small grain size. Using a 40 m Torr pressure and a roughened substrate led to film cracking, apparently due to tensile stresses, while using a 20 m Torr and a polished substrate led to a too-dense film. Either change increased the electrochemical resistance by >100 times.
- Synthesis, sintering and electrical properties of YNi0.33Mn0.67O3 perovskite prepared by a polymerized method
Moure, C; Gutierrez, D; Tartaj, J; Duran, P
Journal of the European Ceramic Society, vol. 23, no. 5, pp. 729-736, April 2003
The YNi0.33Mn0.67O3 solid solution is a semiconducting material that shows perovskite-like structure, orthorhombic symmetry, and spatial group Pbnm. Their electrical and magnetic properties are typical of materials with potential applications in sensor systems or as cathodes in solid oxide fuel cells (SOFC's). Usually, the conventional method of mixing oxides used to obtain these materials requires high-temperature synthesis. By means of a polymerisation method (the Pechini method, slightly modified) we have obtained an amorphous, porous, and soft powder from which the YNi0.33Mn0.67O3 solid solution can be synthesized as a single phase. The powder is characterised by a nanometric particle size and a low-temperature synthesis within the interval 750--800 deg C. The formation reaction has been studied by DTA/TG analysis, X-ray diffraction (XRD) analysis and infrared absorption technique (FTIR). Also, a comparison of the sintering process and the electrical behaviour is made between the samples prepared by the chemical and the mixing oxides methods.
- Composition control of radio-frequency magnetron sputter-deposited La sub 0.5 Sr sub 0.5 CoO sub 3- delta thin films
Klenov, DO; Donner, W; Chen, L; Jacobson, AJ; Stemmer, S
Journal of Materials Research, vol. 18, no. 1, pp. 188-194, January 2003
Mixed-conducting oxides based on the perovskite sturcture are of interest as cathodes in solid oxide fuel cells and as dense oxygen separation membranes. For this paper, we used radio-frequency (rf) sputter deposition to synthesize epitaxial La sub 0.5 Sr sub 0.5 CoO sub 3- delta (LSCO) films. We investigated the influence of sputter deposition parameters, in particular, oxygen partial pressure, plasma power, total sputter pressure, and post-deposition cooling atmosphere on film composition, microstructure, and electrical resistivity. We show that rf sputtering from a single target can produce LSCO films with La/Sr and (La + Sr)/Co ratios of unity and with low electrical resistivities of about 1 m Omega cm. Film microstructures were characterized by high-resolution transmission electron microscopy and x-ray diffraction. Formation of an ordered film superlattice, most likely due to oxygen vacancy ordering, was observed. In this paper, we discuss the relationship between the film microstructure and the electrical resistivity. Graphs, Diffraction Patterns, Photomicrographs., 28 ref.
- APPLICATION OF MICROWAVES IN THE SYNTHESIS OF Ce0.9Pr0.1O2 NANOSTRUCTURED POWDERS
Bondioli, F; Ferrari, AM; Leonelli, C; Siligardi, C; Hart, NA; Evans, NG
J.Mater.Chem. Vol.11, No.10, 2001, p.2620-2624.
Several rare-earth-doped cerium oxides exhibit high oxygen ion conductivity, making them of interest for use as solid electrolytes in solid oxide fuel cells. While various techniques have been developed to produce ceria or cation-doped ceria particles and their precursors, little effort has been directed at preparing ultrafine particles in aqueous solution through microwave irradiation. Nanostructured Ce0.9Pr0.1O2 powders were synthesised by the coprecipitation method, starting from a solution of the cation nitrates. The possible use of microwave technology in both drying and calcination steps was evaluated. XRD analysis, dielectric properties measurements, and colour characterisation were used in order to determine the benefits of using microwaves. The use of microwaves in both drying and calcination of coprecipitated powders seems to be an efficient method to improve powder quality, leading to shorter processing schedules and enhanced colour development. The presence of praseodymium increases the dielectric loss factor of ceria precursors by approximately one order of magnitude, while the linear response of the log of the loss factor with temperature indicated that conductivity is the predominant loss mechanism. 37 refs.
- PERFORMANCE OF INTERMEDIATE TEMPERATURE SOFCs WITH COMPOSITE ELECTROLYTES
Zhu, B; Mellander B-E
Solid Oxide Fuel Cells (SOFC VI). Proc.Sixth Int.Symp. Honolulu, 17-22 October 1999, p.244-253. Vol.99-19
Intermediate temperature (400 to 800 C) solid oxide fuel cells using composites of ceria-based oxides, chlorides and fluorides as electrolytes were studied. A typical oxide ion conductor used for ITSOFCs is gadolinium-doped ceria (GCO). Due to reduction in a H2 atmosphere, GCO develops significant electronic conduction, which causes a power loss when used in a fuel cell. Using salt-, or alumina-GCO composites, the electronic conduction can be suppressed significantly. The Al2O3-GCO composite showed a decreased conductivity, resulting in a poorer fuel cell performance; while the salt-GCO composite enhanced the conductivity and related enhanced SOFC performance, providing a way to develop practical ITSOFC devices. Very recent new discoveries on proton and oxygen ionic conduction in chloride- and fluoride-alumina composite materials provide great opportunities to develop new advanced ITSOFCs. For example, fuel cells using hydrofluoride composites as the electrolytes, typically CaH2-NaF-Ba2F2-Al2O3, showed a peak power density of 160 mW/cm2 at 400 mA/cm2 and 0.4 V. 16 refs.
- EFFECT OF MICROSTRUCTURE AND DOPANT ON THE ELECTROCHEMICAL PROPERTIES OF BARIUM CERATE-BASED ELECTROLYTES
Rauch, WL; Liu, M
Ceramic Membranes I. Proc.1st Int.Symp. New Jersey, 8-13 October 1995, p.146-165. Electrochemical Society Proc. Vol.95-24
Barium cerate-based electrolytes have great potential for intermediate temperature solid oxide fuel cells. Variable-valence dopants were introduced to barium cerate and the effect of dopants on structure, microstructure, and electrochemical properties studied. Results indicate that oxides of niobium, cobalt, copper, bismuth, chromium, neodymium, and gadolinium readily dissolve into barium cerate at 10 mol% or more to form a homogeneous perovskite phase. Several dopants were found to have dramatic effects on sintering rates. Niobium-doped barium cerates exhibited high ambipolar conductivity in hydrogen and are potential candidates for anode materials. The addition of manganese, cobalt, and nickel oxides increased the bulk resistivity dramatically. Further, the effect of microstructure on transport properties was investigated using the niobium-doped barium cerates as examples. While the total conductivity increased with grain size, the resistivity of the grain boundaries seemed insensitive to microstructure. 21 refs.
- MICROSTRUCTURE AND PROPERTIES OF BARIUM CERATE BASED ELECTROLYTES FOR SOLID OXIDE FUEL CELLS
Rauch, WL; Liu, M
Role of Ceramics in Advanced Electrochemical Systems. Proc.Symp. Cincinnati, 30 April-3 May 1995, p.73-83. Ceram.Trans.Vol.65
Barium cerate based ceramics have been widely reported to have high ionic conductivity and hold promise as electrolyte materials for intermediate-temperature solid oxide fuel cells (SOFCs). Samples of niobium-doped barium cerate were produced with a variety of microstructures and sintering parameters affecting the final microstructure of the electrolyte materials systematically investigated. The conductivity of the electrolyte materials produced were studied using impedance spectroscopy to understand the effect of microstructure (in particular grain size) on the desired properties of barium cerate based electrolytes. The processing and data presented here are for BaCe0.85Nb0.15O3. 2 refs.
- SOFC USING Dy-DOPED BaCeO3 CERAMICS AS A SOLID ELECTROLYTE
Iwahara, H; Hibino, T; Yamada, M
Solid Oxide Fuel Cells.Proc.3rd Int.Symp. Honolulu, 16-21 May 1993, p.137-145. Vol.93-4
Based on BaCe1-xDyxO3-a (x less than or equal to 0.20) solid electrolytes, hydrogen-air fuel cells have been constructed and operated at temperature above 800 C. The terminal voltage was 0.65 V at 400 mA/cm2 with 0.26 W/cm2 at 1000 C and 0.67 V at 200 mA/cm2 with 0.14 W/cm2 at 800 C. These values are rather high considering the thickness of the electrolyte (0.5 mm). Both the anodic and cathodic polarisations are sufficiently small, indicating that the voltage drop on discharging the cell is mainly due to the ohmic resistance of the solid electrolyte. From the measurements of water vapour evolution rates in the anode and cathode compartments, respectively, the charge carriers in the solid electrolyte were determined to be protons and oxide ions, the ratio of which depended on operating temperature. 15 refs.
- SOFC/CeO sub 2 doped electrolyte deposition using suspension plasma spraying
Bonneau, M; Gitzhofer, F; Boulos, M
ASM International, Thermal Spray: Surface Engineering via Applied Research (USA), pp. 929-934, May 2000
Ceria (CeO sub 2 ) based electrolytes have been considered for use in solid oxide fuel cells (SOFC) for more than 20 years. There are however some limitations to this usage that this study has tried to address, indeed the study objective has been that of synthesizing and thermal spraying thin layers (50-100 mu m) of doped CeO sub 2 by the technique of suspension plasma spraying, using radio frequency (RF) plasma technology. Various dopant combinations and concentrations have been selected for this work in order to increase the useful partial oxygen pressure range for satisfactory ionic conductivity development, thereby increasing the anionic conductivity and preventing CeO sub 2 reduction in fuel cell service. Ceria possesses the fluorite crystal structure at low temperatures but does not have enough oxygen vacancies to be a good ionic conductor. In ceria the cerium have 4 exp + oxidation state within the fluorite structure, and by substituting a certain amount of Ce exp 4+ ions by trivalent dopant ions, oxygen vacancies are induced into the structure. Recent studies have demonstrated that at low temperatures doped ceria seems to be a better electrolyte than doped zirconia. Also, it seems that dopants with ionic radii close to Ce exp 4+ ions give rise to better ionic conductivities. The doped ceria conductivity increases with the dopant concentration because more oxygen vacancies are created, but at higher concentrations vacancy ordering occurs which results in decreased ionic conductivity.
- TAPE CAST SOLID OXIDE FUEL CELLS FOR THE DIRECT OXIDATION OF HYDROCARBONS
Park, S; Gorte, RJ; Vohs, JM
J.Electrochem.Soc. Vol.148, No.5, 2001, p.A443-A447.
The method relies on the inclusion of pyrolysable pore formers in the anode green tape in order to produce a porous YSZ anode matrix. Wet impregnation was used to add both a metal current collector and an oxidation catalyst to the anode. The performance characteristics for cells produced using this method while operating on H2, CH4, and C4H10 are presented. 10 refs.
- FABRICATION AND PERFORMANCE OF THIN-FILM YSZ SOLID OXIDE FUEL CELLS
Wang, C; Worrell, WL; Park, S; Vohs, JM; Gorte, RJ
J.Electrochem.Soc. Vol.148, No.8, 2001, p.A864-A868.
A new technique for fabricating dense YSZ thin-film electrolytes (between 3 and 10 micron) on porous electrode substrates was used to make planar solid-oxide fuel cells (SOFCs). The YSZ electrolyte is strongly bonded to the Ni-YSZ and La0.89Sr0.1MnO3 (LSM)-YSZ electrode substrates, and the power density of a Ni-YSZ /YSZ/LSM-YSZ cell is over 0.8 W/cm2 at 800 C. Initial investigations of doped YSZ mixed-conducting electrodes in the thin-film YSZ cells indicate that Tb-and Ti-doped YSZs enhance cell power densities from 15 to 50% at 800 C. New Cu-CeO2-YSZ anodes for the dry oxidation of methane were also investigated. Initial results show that the Cu-CeO2-based anodes are stable in hydrocarbon fuels, and that the principal anodic reaction is a direct, electrocatalytic oxidation of the hydrocarbon fuel. 24 refs.
- Oxygen exchange measurements on perovskites as cathode materials for solid oxide fuel cells.
Preis, W; Bucher, E; Sitte, W
Journal of Power Sources, vol. 106, no. 1-2, pp. 116-121, 1 Apr. 2002
Oxygen exchange measurements have been applied to determine simultaneously the chemical diffusion coefficient and the surface exchange coefficient of oxide perovskites. The oxygen partial pressure is changed in a step-wise manner and the relaxation of the oxide ceramics is followed as a function of time. Instead of recording the amount of exchanged oxygen, the rate of oxygen incorporation reactions is measured directly. It is shown how the kinetic parameters can be extracted from the time dependence of the oxygen flux between the sample and the surrounding gas phase. The effect of finite switching times of the reactor on the relaxing oxygen flux is investigated theoretically. The time constant of the reactor is shown to be negligibly small under the chosen experimental conditions. The oxygen exchange measurements have been performed on La(sub)0.6 Sr(sub)0.4 CoO(sub)3-(delta) (LSC) at 725 and 825(degree)C as a function of the oxygen partial pressure p(O(sub)2 ) ranging from 10(exp)-4 to 10(exp)-3 bar. The chemical diffusion coefficient is almost independent of p(O(sub)2 ) constant temperature, whereas the exchange coefficient increases significantly with increasing p(O(sub)2 ). Finally, the dependence of the chemical exchange coefficient on the oxygen partial pressure is interpreted in terms of different mechanisms for the surface reaction.
- Chemically-induced stresses in ceramic oxygen ion-conducting membranes
Atkinson, A; Ramos, TMGM
Solid State Ionics [SOLID STATE IONICS]. Vol. 129, no. 1, pp. 259-269. 2000.
Many oxygen-ion conducting ceramics for potential application as membranes in solid oxide fuel cells, oxygen separators and partial oxidation reactors, suffer from a chemically-induced stress when subjected to a gradient in the thermodynamic activity of oxygen. The relationships between the oxide properties, the membrane operating conditions, the membrane geometry and the resulting stresses are explored. Ceria and acceptor-doped lanthanum chromite are given as typical examples for which relevant materials data have been published. Analysis of the experimental data shows that although the lattice expansion on reduction, that gives rise to the stress, depends mainly on the deviation from stoichiometry in their oxide, the crystal structure and the dopant also have a significant influence. The induced stresses are predicted to be lowest for planar membranes that are free to bend in order to relax the stresses. However, the stresses in a planar membrane that is constrained not to bend are predicted to be similar to those induced in a tubular membrane.
- Deformation of perovskite electronic ceramics - a review
Routbort, JL; Goretta, KC; Cook, RE; Wolfenstine, J
Solid State Ionics [SOLID STATE IONICS]. Vol. 129, no. 1, pp. 53-62. 2000.
Steady-state deformation of several important electronic ceramics, all having a perovskite structure, is reviewed and discussed in terms of their common prominent features. Of particular importance are the ferroelectric BaTiO sub(3), a leading candidate for electrodes in solid-oxide fuel cells, (La sub(1-y)Sr sub(y)) sub(1-x)MnO sub(3- delta ), and the high-temperature superconductor YBa sub(2)Cu sub(3)O sub(x). In all cases, deformation occurs by grain-boundary sliding accommodated by diffusion. Cations are the rate-controlling species and their diffusivities can be calculated and compared to existing tracer diffusion data. In some cases, the tracer diffusion coefficients have not been measured, but measurements of steady-state creep can provide these values.
- Fabrication, electrical conductivity and mechanical properties of Sc sub(2)O sub(3)-doped tetragonal zirconia ceramics
Hirano, Masanori; Watanabe, Shinzi; Kato, Etsuro; Mizutani, Yasunobu; Kawai, Masayuki; Nakamura, Yasuhisa
Solid State Ionics [SOLID STATE IONICS]. Vol. 111, no. 1-2, pp. 161-169. 1 Aug 1998.
The fracture strength, fracture toughness, and electrical conductivity of less than 7 mol % Sc sub(2)O sub(3)-doped zirconia polycrystals consisting of submicron grains were investigated, which were fabricated from fine powders prepared by the homogeneous precipitation method using zirconia sols previously formed by the thermal hydrolysis of ZrOCl sub(2) solution. An electrical conductivity of 0.09 S/cm at 1000 degree C was observed in 4 mol % Sc sub(2)O sub(3)-doped zirconia having a uniform microstructure (grain size <0.4 mu m) and consisting of a fully tetragonal phase. This value corresponds to nearly twice that of 3 mol % Y sub(2)O sub(3)-doped tetragonal zirconia, and the activation energy of the ionic conductivity was 0.82 eV (800 approximately 1000 degree C). The average bending strength for 4 mol % Sc sub(2)O sub(3)-doped tetragonal zirconia was 640 MPa, and its fracture toughness was 3.9 MPa times m super( one half ). The present Sc sub(2)O sub(3)-doped tetragonal zirconia ceramics with high electrical conductivity and high fracture strength have another possibility as a candidate electrolyte material for planar type solid oxide fuel cells.
- Materials for methane-fueled SOFC systems (electroceramics for solid oxide fuel cells)
Van Herle, J; Diethelm, S; Sfeir, J; Ihringer, R
Proceeding of the 7th Conference & Exhibition of the European Ceramic Society, Part 2; 7th Conference & Exhibition of the European Ceramic Society (Euro Ceramics VII), Brugge, Belgium, Sept. 9-13, 2001, Zurich, Switzerland, Trans Tech Publications Ltd, 2001, p. 1213-1220
A short overview of recent work on electroceramic materials relevant to methane-fueled SOFC systems is given. Various fuel feed options are considered, such as pure methane, biogas, and the addition of reforming agents. The principle and implementation into SOFC systems of mixed conducting ceramics for oxygen separation is described, as well as their characterization by electrochemical methods. Ceramic anodes capable of operating with methane-rich fuel injection are presented. The document concludes with electrochemical results on planar anode supported ceramic fuel cells operating at reduced temperature. (Author)
- Oxygen transport in LaFeO3
Waernhus, I; Wiik, K; Grande, T
Proceeding of the 7th Conference & Exhibition of the European Ceramic Society, Part 2; 7th Conference & Exhibition of the European Ceramic Society (Euro Ceramics VII), Brugge, Belgium, Sept. 9-13, 2001, Zurich, Switzerland, Trans Tech Publications Ltd, 2001, p. 1221-1222
Oxygen diffusion coefficients (D) and surface exchange coefficients (k) have been measured in LaFeO3 by conductivity relaxation. Differences in the transport properties with different La/Fe ratio and different microstructure. Calculations of defect structure and electronic properties are also presented. (Author)
- Present several items on ceria-based ceramic electrolytes - Synthesis, additive effects, reactivity and electrochemical behaviour
Jurado, J R
Journal of Materials Science (0022-2461), vol. 36, no. 5, 1 Mar. 2001, p. 1133-1139
Ceria-doped electrolytes have been extensively studied, because they are promising candidates for intermediate temperature solid oxide fuel cells (ITSOFC). In this work, several relevant aspects, such as powder synthesis, small additive effects, reactivity of electrode/electrolyte, and interface microstructure are described. The combustion synthesis is a really suitable synthesis route to achieve, at low temperatures, finely homogeneous and reactive powders for ceria based electrolytes. The presence of small amounts of titania is beneficial, since it produces a significant reduction of the grain boundary resistance. On the other hand, the reactivity of the ceria electrolyte against lanthanum-NiO perovskites at high temperatures (1475 C), enhances both the LaNiO(3-delta) decomposition and the diffusion of Ni and La ions as is noted in the reactivity analysis. (Author)
- Materials for lower temperature solid oxide fuel cells
Ralph, J M; Schoeler, A C; Krumpelt, M
Journal of Materials Science (0022-2461), vol. 36, no. 5, 1 Mar. 2001, p. 1161-1172
The solid oxide fuel cell (SOFC) continues to show great promise for the generation of electricity for an increasing range of applications. The present SOFC technology is based on an all-ceramic design, which eliminates the corrosion problems associated with fuel cells containing liquid electrolytes. To obtain good electrochemical performance with the currently used materials, this all-ceramic fuel cell operates at 1000 C. Despite a significant amount of research and several successful demonstrations at the 100 kW level, commercialization of the technology is not as rapid as anticipated. This is, in part, due to the high operating temperatures required, necessitating the use of expensive materials. As a result of these problems, there has been an effort over the past few years to lower the SOFC operating temperature. This paper will address the issues concerning the development of new materials that can operate at lower temperatures. Many of these issues have been or are being addressed in the research performed at Argonne National Laboratory, and some recent results are discussed. (Author)
- Hydrothermal synthesis and properties of Ce(1-x)M(x)O(2-delta) (M = La, Bi, Sm, Pr, Tb) solid solutions
Greenblatt, M; Shuk, P; Huang, W; Dikmen, S; Croft, M
Solid State Ionics V; Proceedings of the Symposium, Boston, MA, Nov. 28 - Dec. 3, 1998 (A01-29828 07-23), Warrendale, PA, Materials Research Society, 1999, p. 511-517
A systematic study of hydrothermally prepared Ce(1-x)M(x)O(2-delta)
(M= Sm, Bi, Pr, Tb; x = 0-0.30) solid solutions, promising
materials for application in solid oxide fuel cells and oxygen
membranes, is presented. Ultrafine particles of uniform crystallite
dimension (20 nm) can be formed in 30 min under hydrothermal
conditions (260 C, 10 MPa). The small particle size (20-50
nm) of the hydrothermally prepared materials allows sintering
of the samples into highly dense ceramics at 900-1350 C, significantly
lower temperatures than 1600-1650 C required for samples prepared
by solid state techniques. The solubility limit of Bi2O3 in
CeO2 was determined to be around 20 mol pct. The maximum conductivity
was found at x = 0.20 and x = 0. 17 for Bi and Sm, respectively.
In the Ce-Pr/Tb oxide systems, in addition to the high oxide
ion conductivity, electronic conductivity occurs through the
hopping of small polarons by a thermally activated mechanism.