bluuebunny/crossref_metadata_2025 huggingface dataset:
Ni/YSZ Anode Interactions with Impurities in Coal Gas
Authors: Marina Olga A. , Pederson Larry R. , Coyle Christopher A. , Thomsen Ed C. , Coffey Greg W.
Published: September 2009

Performance of solid oxide fuel cell (SOFC) with nickel/zirconia anodes on synthetic coal gas in the presence of low levels of phosphorus, arsenic, selenium, sulfur, hydrogen chloride, and antimony impurities were evaluated. The presence of phosphorus and arsenic led to the slow and irreversible SOFC degradation due to the formation of secondary phases with nickel, particularly close to the gas inlet. Phosphorus and antimony surface adsorption layers were identified as well. Hydrogen chloride and sulfur interactions with the nickel were limited to the surface adsorption only, whereas selenium exposure also led to the formation of nickel selenide for highly polarized cells.
Generalized Ellingham Diagrams for Utilization in Solid Oxide Fuel Cells with an Emphasis on Interactions of Nickel Cermet Anode with Impurities in Coal Synthesis Gas
Authors: Yokokawa Harumi , Kishimoto Haruo , Yamaji Katsuhiko , Horita Teruhisa
Published: September 2009

Generalized Ellingham diagrams have been constructed for those systems which are important in thermodynamic investigations on the chemical stability of nickel cermet anode against gaseous impurities contained in coal derived gases. In the same way as the original Ellingham diagram, the oxygen potential and temperature are adopted as the vertical and horizontal axes to make detailed examinations on related phase equilibria in terms of operational parameters of solid oxide fuel cells. As impurities, S, Se, As, and P are considered in their interactions with nickel as the metal component in cermet anode, and with zirconia, yttria, and ceria as the oxide component in the cermet anode.
Suppression of Anode Degradation by Sulfur using an Anionic Catalyst
Authors: Thampi K. R. , Rambert Serge , McEvoy Augustin J.
Published: September 2009

Fuel cells can be regarded as catalysed chemical reactors. They can therefore be highly sensitive to the purity of the relevant reagent, the fuel. The anode catalyst in the standard SOFC is a metal-ceramic composite characterised by rapid and significant deterioration of its activity when exposed to sulfur contaminants in the fuel, even in ppm. concentrations. However commercial hydrocarbon liquid fuels regularly contain some quantity of sulfur compounds as impurities, and sulfur compounds are even deliberately added as odorants for safety reasons in gaseous fuels. Therefore a desulfuriser unit is a normal subsystem in any SOFC installation. An anode with high intrinsic sulfur tolerance would clearly simplify SOFC system design, as well as offering lower capital and operation costs. In a technology transfer from petrochemicals practice, hydrodesulfurisation catalysts using heavy metals have been investigated and showed partial protection of the anode. However a recent observation established an even more effective desensitisation to sulfur of a Ni-YSZ cermet anode modified by an anionic activator.
Improvement of Ni/SDC Anode by Alkaline Earth Metal Oxide Addition for Direct Methane-SOFC
Authors: Asamoto Makiko , Miyake Shinji , Sugihara Kazunari , Yamaguchi Shuhei , Yahiro Hidenori
Published: September 2009

The anodic performances of Ni/CeO2-Sm2O3(Ni/SDC) modified by the addition of alkaline earth metal oxides (MgO, CaO, SrO, and BaO) were investigated for direct oxidation of CH4 in solid oxide fuel cells (SOFCs). Although the initial power density of cell with Ni/SDC anode modified by the addition of CaO (Ni-CaO/SDC) was slightly lower than that of cell with Ni/SDC, the former anode exhibited an excellent stability compared to the latter one. After continuous operation of SOFC for 24 h, no or less amount of carbon deposition was observed over Ni-CaO/SDC.
Methane Oxidation at the Ni1-XCoX-Samaria-doped Ceria Cermet Anode
Authors: Hiromasa Tsuchiya , Weerapakkaroon Wichapun , Kanjanaboonmalert Tanawat , Wah Tzu Teoh , Sato Kazunori
Published: September 2009

Substitution of Co atoms for Ni atoms in the Ni-based cermet anode resulted in a decrease in the anodic overvoltage and interfacial resistance between the anode and electrolyte. This effect has been confirmed for a samaria-doped ceria (SDC) electrolyte and a scandia-stabilized zirconia (ScSZ) electrolyte. The results of electrochemical measurements revealed that the enhancement of the direct oxidation of methane was caused by the modification of microstructure in the cermet anode.
Study of CuFe-Ce0.9Gd0.1O2-δ as IT-SOFC Anode: Catalytic Activity, Thermal Expansion, Morphology, Electrical Conductivity and Chemical Compatibility
Authors: Fuerte Araceli , Hornes Aitor , Bera Parthasarathi , Martínez-Arias Arturo , Escudero María J. , Daza Loreto
Published: September 2009

CuFe-Ce0.9Gd0.1O2- (CF-CG) has been prepared in order to explore its potential as anode material for Intermediate Temperature Fuel Cell (IT-SOFC) for direct oxidation of methane. In this work, the catalytic activity, the thermal expansion coefficient, the morphology, the electrical conductivity and the chemical compatibility of this anode material with YSZ, LSGM and CGO, common electrolytes used in SOFC, have been studied. Catalytic activity results reveal that the presence of Fe affects both the CH4 reactivity and the formation of carbon deposits. The sample shows metallic behavior having an electrical conductivity value of 7.8 S cm-1 at 750°C under reducing atmosphere. The thermal expansion coefficients in both reducing and oxidizing atmosphere are matched to that of SOFC electrolytes. Reactivity studies have demonstrated an excellent chemical compatibility between this material and common SOFC electrolytes.
Microstructural Studies and Performance of Impregnated Manganese Containing Perovskite Solid Oxide Fuel Cell Anodes
Authors: Corre Gael , Kim Gun Tae , Cassidy Mark , Gorte Raymond , Vohs John , Irvine John
Published: September 2009

We report here on the development of a novel type of solid oxide fuel cell anodes that are based on Mn containing perovskites and prepared by infiltration of electrode precursor solutions into Yttria stabilized zirconia scaffolds. The presence of Mn, even in small amount, on the B-site of the ABO3 structure leads to electrode microstructures that offer a large surface area that is available for electrochemical reactions. The oxides form a remarkable thin coating on the electrode scaffold after high temperature sintering. The evolution of those films in reducing environments creates arrays of interconnected ~10nm scale particles covering the electrode scaffold. Such electrodes, based on LSCM with small amounts of added catalyst, provide outstanding performance, both for the direct oxidation of methane in solid oxide fuel cells, and the reduction of pure CO2 in solid oxide electrolyzers.
Intermediate Temperature SOFC Anode Component based on A-site Deficient La-doped SrTiO3
Authors: Savaniu Cristian D. , Irvine John
Published: September 2009

Surface modified A-site deficient lanthanum-doped SrTiO3 (La0.2Sr0.7TiO3) was evaluated as a potential anode component material for intermediate temperatures SOFCs. The reduction of the material has been investigated and results of thermal expansion and conductivity dependence of the oxygen partial pressures are presented revealing a strong dependence of the material's thermal and electrical properties on temperature and atmosphere and the fact that reduction may become more facile as the extent of reduction increases. Button fuel cells were produced by tape casting and impregnation, comprising YSZ electrolyte, a porous, conductive backbone of La0.2Sr0.7TiO3 anode impregnated via solutions with Gd-doped ceria and copper and thin films of La0.6Sr0.4CoO3 cathode produced in-situ in the fuel cell test experiment. Fuel cells tests using pure, humidified H2 as fuel demonstrated that remarkable power densities in excess of 0.5 W/cm2 at 750oC can be achieved using these cells with suitable pre-reduction of the titanate material.
Ni-Modified Perovskite Materials for Solid Oxide Fuel Cell Anodes Fed With Glycerol
Authors: Lo Faro Massimiliano , La Rosa Daniela , Minutoli Maurizio , Monforte Giuseppe , Antonucci Vincenzo , Aricò Antonino Salvatore
Published: September 2009

An investigation of the electrochemical oxidation of glycerol as alternative to hydrogen and methane in an intermediate temperature solid oxide fuel cell (IT-SOFC) by using a noble metal-free anode catalyst was carried out. The anode electrocatalyst was based on a Ni-modified La0.6Sr0.4Fe0.8Co0.2O3 (LSFCO) perovskite. After thermal activation, Ni was mainly present as ultrafine La2NiO4 particles homogeneously dispersed on the perovskite surface. The thermal treatment also caused a modification of perovskite into a lanthanum depleted SrFe0.8Co0.2O3 (SFCO) structure. These results were corroborated by x-ray diffraction (XRD) and transmission electron microscopy (TEM). By using this modified perovskite, a low ohmic resistance was recorded and suitable power density achieved for an electrolyte supported IT-SOFC. The effects on the electrochemical performance produced by the variation of the ratio of glycerol / water for the anode feed were investigated.
Analysis of LSM-YSZ Composite Cathode Phase Connectivity Using Three-Dimensional Reconstructions
Authors: Wilson James , Cronin J. Scott , Rukes Sherri , Duong Anh , Mumm Daniel , Barnett Scott A.
Published: September 2009

Composite electrodes commonly consist of interconnected pore, electronic-conductor, and ionic-conductor phases that are responsible for the transport of gas phase species, electrons, and oxygen ions, respectively. Attempts to understand how this complicated structure influences electrochemical performance can be facilitated through the acquisition of quantitative microstructural data. In this work, nine different cathode compositions ranging from 30wt% La0.8Sr0.2MnO3 (LSM) - 70wt% Y2O3-stabilized ZrO2 (YSZ) to 70wt% LSM - 30wt% YSZ were screen printed symmetrically on both sides of YSZ-electrolytes. 3D reconstructions of the cathodes were achieved using focused ion beam (FIB) tomography techniques, and the connectivity of the phases was quantified to determine the electrochemically active triple-phase boundary (EA-TPB) densities. The composition dependence of the polarization resistance, calculated with an electrochemical model that employed the EA-TPB densities along with measured YSZ tortuosities, was compared with the measured resistances.
Solid-state Synthesis of La0.7Sr0.3MnO3 Powders using Different Grinding Times
Authors: Conceição Leandro , Silva Camila R. , Ribeiro Nielson F. , Souza Mariana M.
Published: September 2009

Sr-doped lanthanum manganites (LSM) have been studied as promising materials for cathodes in solid oxide fuel cells (SOFC). In the present work La0.7Sr0.3MnO3 powders were synthesized by solid-state method evaluating the influence of dry or wet (using isopropanol) routes and different grinding times on the morphological and microstructural properties of LSM. The results of the synthesis of LSM powders pointed out that the use of solvent during homogenization results in poor crystallinity and only 6 hours of grinding at low speed in the ball mill is enough to obtain nano-sized crystalline phase by dry route. Scanning electron micrographs showed formation of agglomerates of fine primary particles. The electrical conductivity of the sintered LSM (La1-xSrxMnO3, x= 0.2, 0.3 and 0.4) pellets with about 35% of porosity was measured by the two probe technique, showing a slight increase in the conductivity with strontium content.
Structural Characterization of Sr-doped LaMnO3 and LaCrO3 Powders Synthesized by Combustion Method
Authors: Silva Adney Luis A. , Conceição Leandro , Rocco Ana Maria , Souza Mariana M.
Published: September 2009

Lanthanum strontium manganite (LSM) and chromite (LSC) are good candidates for cathode and interconnect application in SOFC, respectively. This paper reports the synthesis of LSM and LSC powders from nitrate precursors by the combustion method, using two different fuels (urea and glycine). The ignition of the reagent mixture with urea takes a longer time and the maximum temperature is higher than using glycine. However, the adiabatic flame temperatures using urea are lower. X-ray diffraction patterns showed formation of only perovskite phase for the samples synthesized with urea, whereas secondary phases were also found for the samples prepared from glycine. The crystallite size calculated using the Scherrer equation is in the range of 23-31 nm. Thermogravimetric analysis revealed that the weight loss is much higher for manganites, with complete burn out of organics at 850-900oC. Scanning electron microscopy showed the presence of agglomerates, formed by fine particles of different shapes.
Studies of Model SOFCs with Sr0.7Ce0.3MnO3 Cathode Material
Authors: Sinitsyn Vitaly , Kuritsyna Irina , Khasanov Salavat , Matveev Danila , Bredikhin Sergey I.
Published: September 2009

Model SOFCs with Sr0.7Ce0.3MnO3 cathode were found to display nonlinear current-voltage characteristics resulting from changes in the interface resistance with varying current load. Short-term tests (~200 hours) of the cell performance were carried out at a current load of 81.5 mA/cm2. The resource tests demonstrated high stability of power performance of the model SOFCs. The Sr0.7Ce0.3MnO3 material was concluded to be a promising cathode for intermediate-temperature SOFCs.
Transient Response of LSM Electrode under Cathodic Polarization
Authors: Jun Yang , Muroyama Hiroki , Matsui Toshiaki , Eguchi Koichi
Published: September 2009

A dynamic model of oxygen concentration in the vicinity of TPB was established. From the simulation of the transient variation of oxygen concentration, it was revealed that a drastic change occurred soon after the high current loading. Considering the defect chemistry of LSM, the dynamic response of LSM cathode under cathodic polarization with time was simulated. This simulation shows that the dynamic response of cathodic potential with time proceeds in two steps with different time domain. The simulated phenomenon was validated by experimental results.
Study on the Role of the Morphology of SOFC Cathodes
Authors: Grunbaum Nicolas , Sant'Ana Gallo Leonardo , Steil Marlu Cesar , Dessemond Laurent
Published: September 2009

The role of the morphology of strontium doped lanthanum manganite (LSM) and LSM/yttria stabilized zirconia (YSZ) composite electrodes was studied by using DC polarization measurement and impedance spectroscopy. Different electrodes were tested: single pure LSM with small porosity layer, porous LSM layer over pure LSM layer and LSM-YSZ composite (50wt% YSZ) with a porous LSM layer. Electrochemical properties of these structures were investigated as a function of temperature. Impedance diagrams show that the electrode reaction of pure LSM electrodes could be related to a high frequency contribution attributed to a charge transfer between LSM and YSZ and a low frequency one semicircle related to an oxygen adsorption step. The impedance response of the electrode based on a LSM-YSZ composite could be related to only the high frequency contribution. No electrochemical activation was evidenced in this case. Maximum current density was around -0.1 A.cm-2 for a cathodic overpotential equal to -0.1 V.
Structural and Chemical Investigations of (La, Sr)CoO3-δ Thin Film Electrodes Exhibiting Very Fast Oxygen Reduction Kinetics
Authors: Januschewsky Judith , Kubicek Markus , Stoeger-Pollach Michael , Bernardi Johannes , Fleig Juergen
Published: September 2009

The polarization resistance of La0.6Sr0.4CoO3-δ thin film electrodes prepared via pulsed laser deposition (PLD) is investigated by impedance spectroscopy for various film deposition temperatures. The electrodes were deposited on yttria stabilized zirconia (YSZ) single crystals and polycrystals and on polycrystalline gadolinia doped ceria (CGO). Structure-property relations emphasizing the correlation between crystallinity and performance are determined by additional XRD, SEM and TEM measurements. These experiments revealed that thin film electrodes of extraordinary low polarization resistance and little degradation may be produced on YSZ by optimizing the deposition conditions.
Design and Characterization of Functionally Graded Cathode Materials for Solid Oxide Fuel Cells
Authors: Sadykov Vladislav A. , Pavlova Svetlana , Zarubina Valeria , Bobin Aleksei , Alikina Galina , Lukashevich Anton , Muzykantov Vitalii , Usoltsev Vladimir , Kharlamova Tamara , Boronin Andrei , Koscheev Sergei , Krieger Tamara , Ishchenko Arcady , Mezentseva Natalia , Salanov Aleksei , Smirnova Alevtina , Bobrenok Oleg , Uvarov Nikolai
Published: September 2009

This work presents results on synthesis and characterization of mixed ionic-electronic conducting nanocomposite cathode materials for Intermediate Temperature Solid Oxide Fuel Cells. The corresponding materials are comprised of La0.8Sr0.2MnO3 (LSM) or La0.8Sr0.2Fe1-xNixO3-δ (x=0.1-0.4) (LSFNx) perovskites and Sc0.1Ce0.01Zr0.89O2-x (ScCeSZ) or Ce0.9Gd0.1O2-δ (GDC) fluorites mixed via powerful ultrasonic dispersion of powders in isopropanol. Genesis of their structural properties was studied in detail by transmission electron microscopy with elemental analysis and X-ray diffraction; surface features were characterized by X-ray Photoelectron Spectroscopy. Perovskite-fluorite nanodomain interfaces appear to provide a path for fast oxygen diffusion as revealed by the oxygen isotope exchange and temperatureprogrammed desorption. Testing in wet H2/air for button-size fuel cells with thin Y-doped zirconia layer and nanocomposite functionally graded cathodes demonstrated promising and stable performance in some combinations in the intermediate temperature range.
Synthesis and Study of LSCF Perovskites for IT SOFC Cathode Application
Authors: Ushkalov Leonid , Vasylyev Oleksandr D. , Pryschepa Yevgen , Samelyuk Anatolyy , Melakh Viktor
Published: September 2009

Iron- and cobalt-containing perovskites LaxSr1 xCoyFe1-yO3{plus minus}δ, (х = 0.8; 0.6 and у = 0.8; 0.2) were synthesized via solid state reaction method. Some samples were synthesized using two different iron oxides (Fe2O3 and Fe3O4). Phase composition of synthesized powders was studied by XRD. It was revealed that formation of the perovskite structure occurs at temperatures higher 900 {degree sign}C. Mixing LSCF powder with gadolinia doped ceria (GDC) in proportion 50:50 mas. % composite materials were prepared. Conductivity measurements were carried out with circle-shaped samples. The highest conductivity at the target temperature of 600 {degree sign}C was observed on composite La0,6Sr0,4Co0,8Fe0,2O3-δ-GDC samples. Study of a fracture surface of compacted samples has shown that adding of GDC enhances the both conductivity and sinterability of powders changing the fracture mechanism of cathode material from intergranular to the cleavage one.
Composite Cathode Study for Low Temperature SOFC
Authors: Zhang Xinge , Robertson Mark , Decès-Petit Cyrille , Kesler Olivera
Published: September 2009

Since the kinetics of cathode is slow In low temperature solid oxide fuel cells, full attention has to be given to boost cathode performance through optimization of cathode composition and microstructure. In this contribution, the effect of composition of (1-x) Sm0.5Sr0.5CoO3 (SSC) + x Sm0.2Ce0.8O1.9 (SDC) cathodes (x=0, 10, 25, 40 wt%) sintered at 1000{degree sign}C for 2hrs has been investigated using symmetric cells with Sm0.2Ce0.8O1.9 (SDC) electrolytes. The results showed that an increase in SDC content in the composite cathodes led to an increase in cathode polarization resistance (Rc). The Rc values on average were 0.042 W cm2 for the cathode without SDC addition, 0.063 W cm2 for the cathode with 10 wt% SDC, 0.079 W cm2 for the cathode with 25 wt% SDC, and 0.207 W cm2 for the cathode with 40 wt% SDC at 650{degree sign}C. The calculated activation energy values of the composite cathodes were in the range of 120{plus minus}20 kJ mol-1. We also investigated an in-situ (650{degree sign}C) sintered SSC cathode, and found that it showed the lowest electrochemical polarization resistance, approximately 0.028 W cm2 at 650{degree sign}C. The cathode stability of the symmetric cells has also been tested at 650{degree sign}C in air. No obvious voltage degradation under constant current density (0.5 A cm-2) has been observed in the cells with 1000oC-sintered SSC with 25 wt% SDC. However, the cell with in-situ sintered SSC cathode showed a steady decay rate of -4mV/hr. EIS analysis of the cell before and after the stability test revealed that the
Characterisation and Performance of SOFC Components made by Reactive Spray Deposition Technology
Authors: Neagu Roberto , Zhang Xinghe , Maric Radenka , Roller Justin M.
Published: September 2009

The paper presents an overview of the results obtained by using a newly developed flame based deposition technique to fabricate SOFC components. Gadolinia doped ceria (20% mol gadolinia), yttria stabilised zirconia (8% mol yttria) and samarium strontium cobaltite (50% at Sm) ceramics have been deposited on various substrates, including SOFC anode materials and half cells. Thin and dense electrolyte layers having thicknesses in the range of 100 nm to 2 mm have been successfully fabricated. Porous cathode layers deposited on half cell substrates have shown a 25-30% increase in performance compared to samaria doped ceria - samarium strontium cobaltite screen printed cathodes tested in the same conditions.
A2MO4+δ Oxides: Flexible Electrode Materials for Solid Oxide Cells
Authors: Grenier Jean C. , Mauvy Fabrice , Lalanne Cécile , Bassat Jean-Marc , Chauveau Florent , Mougin Julie , Dailly Julian , Marrony Mathieu
Published: September 2009

Until now, most cathode materials used in high temperature ceramic solid electrolyte oxide cells (SEOC) are perovskite-type MEIC compounds, AMO3-δ, showing oxygen sub-stoichiometry. Recently, a new family of overstoichiometric oxides, formulated A2MO4+δ with A = La, Nd, Pr, Sr and M = Ni, Cu, has been investigated. Due to their basic properties (large D* and k coefficients, high electrical conductivity), the nickelate compounds have been especially used in various applications. Nd2NiO4 and Pr2NiO4 exhibit very promising electrochemical properties down to temperature as low as 600{degree sign}C, as ITSOFC cathodes as well as PCFC cathodes (they are stable under moist air (3 -10 % H2O). In addition, encouraging cell tests (SOFC and PCFC) have been performed with both nickelates. Furthermore, these materials have been also used as HTSE anodes and first results show excellent performances. Thus, it appears that these materials show an extremely high flexibility for being used as air electrode in very different conditions in terms of oxygen partial pressure or/and water content. This is explained on the basis of structural features of these materials and the great ability of these compounds for accommodating the oxygen non-stoichiometry.
Oxygen Exchange Kinetics and Chemical Stability of the IT-SOFC Cathode Material Nd2NiO4+δ
Authors: Egger Andreas , Bucher Edith , Sitte Werner , Lalanne Cécile , Bassat Jean-Marc
Published: September 2009

Chemical surface exchange coefficients k_chem and chemical diffusion coefficients D_chem of Nd2NiO4+δ have been determined by the conductivity relaxation technique at 575{less than or equal to}T/{degree sign}C{less than or equal to}725 between oxygen partial pressures of 0.01 and 0.02 bar. At 700 {degree sign}C values of 1E-4 cm/s and 6E-7 cm2/s were measured for k_chem and D_chem, respectively. A strong decrease upon cooling was observed for both kinetic parameters due to high activation energies. Electronic conductivities range between 100 and 120 S/cm and are found to decrease for increasing temperature in the investigated temperature region of 575{less than or equal to}T/{degree sign}C{less than or equal to}725. Thermogravimetry/mass spectroscopy was performed at 20<T/{degree sign}C<900 in atmospheres of constant pO2=0.2 bar, with and without CO2 and H2O, as well as in pure Ar. Oxygen exchange starts at T~300-400 {degree sign}C and shows a maximum in the range 500<T/{degree sign}C<550 which can be ascribed to a structural transition. First results indicate good stability of Nd2NiO4+δ vs. CO2- and H2O-containing atmospheres at 500<T/{degree sign}C<900.
Electrochemical Behaviour of La2Ni0.6Cu0.4O4+δ Oxide on SDC Electrolyte as Cathode for IT-SOFC
Authors: Pérez-Coll Domingo , Aguadero Ainara , Escudero María J. , Daza Loreto
Published: September 2009

La2Ni0.6Cu0.4O4+δ, a mixed conductor oxide with K2NiF4-type structure, was evaluated as cathode material for IT-SOFC based on Sm0.2Ce0.8O1.9 (SDC) electrolyte. A single cell with La2Ni0.6Cu0.4O4+δ as cathode, SDC as electrolyte and Ni-SDC as anode was fabricated and tested with humidified H2 as fuel and stationary air as oxidant. The electrochemical behavior was analyzed by current voltages curves, ac impedance spectroscopy and load demands at 750, 800 and 850° C. The maximum power density reached by the cell was 120, 166 and 217 mW/cm2 at 750, 800 and 850° C using a 0.4 mm-thick electrolyte. In addition, the cell performance was very stable at 800 ºC for a current density of 421 mA/cm2 demanded for 40 h and at 750 ºC for different current loads (from 84 to 336 mA/cm2) for 80 h. The use of a thinner SDC electrolyte encourages to obtain better performances.
Synthesis and Characterization of Ba0.5Sr0.5Co0.8Fe0.2O3-δ for Intermediate Temperature Solid Oxide Fuel Cell Cathode by Solid-State Reaction, Pechini and Citrate-EDTA Complexing Methods
Authors: Hung I-Ming , Laing Chen-Yu
Published: September 2009

In this study, perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-δ cathode powders prepared by solid-state reaction, pechini method and citrate-EDTA complexing method, respectively. From the result of XRD, it was found that single perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-δ can be prepared above 1000 oC and 950 oC, respectively, for solid-state reaction and citrate-EDTA complexing method. The average grain size of BSCF samples is respectively between 4~10μm, 1~10μm and 3~6μm prepared from solid-state reaction, pechini and citrate-EDTA complexing method. It was found that the maximum conductivity of all samples increased with temperature increased from 50° to 400° and then decreased slowly with temperature increased. The sample prepared from citrate-EDTA complexing method had the highest conductivity of 50.2 S/cm which is higher about 90% and 42% respectively than that of sample prepared from solid-state reaction and pechini method.
Combustion Synthesis of La0.6Sr0.4Co0.98Ni0.02O3 Cathode and Evaluation of its Electrical and Electrochemical Properties for IT-SOFC
Authors: Dutta Atanu , Götz Holger , Ghosh Sawati , Basu Rajendra N.
Published: September 2009

Nanocrystalline powder (30-40 nm) of 2 mol% Ni-doped lanthanum strontium cobaltite (La0.6Sr0.4Co0.98Ni0.02O3) was synthesized by combustion technique using glycine as fuel with various combinations of fuel to nitrate ratios. The thermal analysis revealed that the crystallization process is not single step and remained incomplete even up to 700{degree sign}C. In XRD analysis, existence of two minor phases was observed in addition to lanthanum strontium cobaltite phase. One particular synthesis condition i.e., with a slightly fuel excess ratio (0.45) showed highest electrical conductivity of 96 S/cm at 800{degree sign}C in air. For the application as cathode in SOFC, this material was studied in the symmetric cell mode with Gd-doped CeO2 as electrolyte and it showed lowest interfacial polarization resistance of 0.158 Ω·cm2 when sintered at 1000{degree sign}C. Significantly high current density of ~ 3.4 A/cm2 and power density of ~ 2.4 W/cm2 at 800{degree sign}C was obtained with this cathode in anode-supported single cell with doped CeO2 as a buffer layer.
Doped Ceria Diffusion Barrier Layers for La0.8Sr0.2CoO3 Infiltrated into YSZ
Authors: Küngas Rainer , Bidrawn Fred , Vohs John , Gorte Raymond
Published: September 2009

The possibility of improving the long-term stability of La0.8Sr0.2CoO3 (LSCo)-YSZ cathodes, formed by infiltration, through the use of samaria-doped ceria (SDC) barrier coatings, was studied. The barrier coatings did not affect the initial performance of the LSCo-YSZ composite cathodes following calcination at 973 K, and cells with the barrier coatings showed significantly lower impedances following calcination to higher temperatures.
Insight into Rate Limiting Mechanisms of Porous La1-xSrxCoO3-δ Electrodes through Nonlinear Electrochemical Impedance Spectroscopy (NLEIS)
Authors: Kreller Cortney R. , Adler Stuart
Published: September 2009

The rate-limiting mechanisms of mixed ionic electronic conducting solid oxide fuel cell cathode materials have small nonlinearities arising from non-ideal thermodynamic behavior and the surface exchange reaction. The nonlinear current-voltage characteristics of these electrodes are measured using nonlinear electrochemical impedance spectroscopy (NLEIS). Experimentally measured harmonics are compared to a theoretical model approximating a porous mixed-conducting electrode as an array of uniform cylindrical rods to examine the relative roles of defect thermodynamics, exchange kinetics, and surface and bulk diffusion on the nonlinear harmonic response. NLEIS measurements on porous LaSrCoO over a range of temperatures and pO2 have shown that the nonlinear behavior of these materials cannot be solely attributed to the surface reduction of oxygen coupled to a vacancy diffusion transport pathway. Furthermore, our results indicate that the surface of these materials has different thermodynamic characteristics and transport species in situ than that measured independently on bulk samples of these materials.
Ab initio Defect Energetics in LaBO3 Perovskite Solid Oxide Fuel Cell Materials
Authors: Lee Yueh-Lin , Morgan Dane , Kleis Jesper , Rossmeisl Jan
Published: September 2009

Perovskite materials of the form ABO3 are a promising family of compounds for use in solid oxide fuel cell (SOFC) cathodes. Study of the physics of these compounds under SOFC conditions with ab initio methods is particularly challenging due to high temperatures, exchange of oxygen with O2 gas, and correlated electron effects. This paper discusses an approach to performing ab initio studies on these materials for SOFC applications and applies the approach to calculate vacancy formation energies in LaBO3 (B = Mn, Fe, Co, Ni) compounds.
Flexible Contact Layer Between Cathode and Interconnect of SOFC
Authors: Xie Zhaohui , Zhu Qingshan , Fang Liping
Published: September 2009

The contact resistance between the cathodes and interconnects constitutes a significant part of the overall resistance in an SOFC stack. In order to enhance the conductibility between the cathode and interconnect, a new stack configuration of SOFC is proposed, with flexible contact layers of strontium-doped lanthanum manganite inserted to between the cathodes and interconnects as separated components. The conduct material is in fabric structure prepared from template via wet-chemical method. The preparation process and performance of the conduct material are described.
Sulfur as Pollutant Species on the Cathode Side of a SOFC System
Authors: Schuler Andreas J. , Wuillemin Zacharie , Hessler-Wyser Aïcha , Van Herle Jan
Published: September 2009

In order to link electrochemical performance degradation of the cathode in a large solid oxide fuel cell (SOFC) to the presence of pollutant species, a spatially-resolved study of contaminants was performed. Distribution maps of pollutants over the cell allowed to identify their sources. Besides chromium and silicon, sulfur was found as a major pollutant species. Its preferential reaction with strontium doped lanthanum cobaltite (LSC), forming strontium sulfate SrSO4, compared to strontium doped lanthanum manganite (LSM) is revealed here. When sulfur poisoning arises in combination with chromium, a sulfur-containing strontium chromate compound is formed.
Effect of SO2 Concentration on Degradation of Sm0.5Sr0.5CoO3 Cathode
Authors: Yamaji Katsuhiko , Xiong YuePing , Yoshinaga Masashi , Kishimoto Haruo , Brito Manuel , Horita Teruhisa , Yokokawa Harumi , Akikusa Jun , Kawano Mitsunobu
Published: September 2009

A trace amount of SO2 in air is not a negligible factor on degradation of SOFC cathode. SO2 acts like Cr vapors which cause Cr-poisoning, and easily reacts with the strontium component in lanthanum-cobaltite based SOFC cathodes. Effects of SO2 concentration on degradation of an Sm0.5Sr0.5CoO3 (SSC) cathode were investigated in order to evaluate degradation of SSC cathode in an accelerated mode. Three different concentrations of SO2 (100 ppm, 1 ppm, and 5 ppb) were supplied to the cathode with air during cell tests at T = 1073 K Degradation of SSC cathode was accelerated with increasing SO2 concentration. In the thin SO2 conditions (1 ppm and 5 ppb SO2), SO2 in air was captured on the surface of the SSC cathode. SO2 reacted with the strontium component in the SSC cathode to form SrSO4. In the thick SO2 condition (100 ppm SO2), SO2 reacted with the strontium and samarium components. Too excess SO2 concentration in air was not suitable to examine cathode degradation in an accelerated mode because other degradation modes were appeared. One ppm - SO2 in air was applicable to accelerate the degradation of SSC cathode.
Mechanistic Understanding of Cr Poisoning on La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)
Authors: Wachsman Eric D. , Oh Dongjo , Armstrong Eric , Jung Doh Won , Kan Cynthia
Published: September 2009

The effects of Cr poisoning on the catalytic activity of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and the poisoning mechanism was investigated. AC impedance spectroscopy and temperature programmed isotopic exchange (TPX) were consistent in proving poisoning mainly degraded the surface catalytic activity as a passive layer evolved on the surface or near-surface region. The formation of small particles was clearly observed in scanning electron microscopy when LSCF was heat treated in the presence of Crofer22APU. Low angle X-ray diffraction identified these were SrCrO4. As a result of Sr diffusion to form SrCrO4 particles, it was found that a Sr-deficient phase was formed and a phase transition from rhombohedral to cubic perovskite occurred in the near surface region. While previous Cr poisoning studies on LSCF mostly emphasized the effects of SrCrO4 formation, the Sr deficient surface layer also significantly degrades the catalytic activity of LSCF due to reduction of oxygen vacancies and surface Co/Fe concentration.
La(Ni,Fe)O3 Stability in the Presence of Cr Species- solid-state Reactivity Study
Authors: Stodolny Maciej K. , Van Berkel Frans P. , Boukamp Bernard A.
Published: September 2009

The solid-state reactivity between La(Ni0.6Fe0.4)O3 (LNF) and Cr2O3 in the IT-SOFC operating temperature range of 600-800 ºC has been investigated using XRD analysis. Because LNF material can be used as a cathode, as a current collecting layer and/or an interconnect coating, a thorough investigation of its chemical stability is of importance for SOFC systems utilizing ferritic stainless steel interconnects. This study demonstrates the intrinsic instability of LNF when exposed to direct contact with Cr2O3 at 800 ºC. It has been observed that Cr enters the perovskite phase, replacing first Ni and then Fe already after 200 h. The rate of the Cr reaction with LNF depends on temperature and exposure time. After 1000 h at 600 ºC no reaction products could be detected with XRD. Although this is a promising result, long-term testing under fuel cell operating conditions is needed to prove LNF as a viable IT-SOFC cathode material.
Anomalous VFB Shift in High-k Gate Stacks - Is its Origin at the Top or Bottom Interface ? -
Authors: Toriumi AKira , Nabatame Toshihide
Published: September 2009

Metal/high-k gate stack technology is now about to be in production. However, there are so many issues which have not been understood yet. VTH control is the most serious concern for high performance and low power CMOS application. In this paper, our understandings of anomalous VFB shift observed in high-k gate stacks is presented from the viewpoint of dipole formation at high-k interface.
Flat-band Voltage and Structural Properties of Hafnium Dioxide Films Grown by Liquid-injection MOCVD
Authors: Ducroquet Frédérique , Rauwel Erwan , Dubourdieu Catherine
Published: September 2009

The flat-band voltage shift of bilayer SiO2/HfO2 MOS structures is investigated as a function of the structural properties of the HfO2 films. It was demonstrated that for amorphous HfO2 films, the flat-band voltage vs HfO2 thickness relationship is well described by a second-order polynomial resulting from a bilayer model including two interfacial charge densities and bulk high-k charges. When the crystalline structure of HfO2 is stabilized in a monoclinic phase, the flat-band voltage is shifted to positive voltages and becomes nearly independent on the HfO2 thickness. These results confirm that the high-k/SiO2 interface can significantly contribute to the flat-band voltage shift. However, this contribution appears greatly dependent on the microstructural properties of HfO2.
High-k Dielectrics and Interface Passivation for Ge and III/V Devices on Silicon for Advanced CMOS
Authors: Heyns Marc M. , Bellenger Florence , Brammertz Guy , Caymax Matty , De Jaeger Brice , Delabie Annelies , Eneman Geert , Houssa Michel , Lin Dennis , Martens Koen , Merckling Clement , Meuris Marc , Mitard Jerome , Penaud Julien , Pourtois Geoffrey , Scarrozza Marco , Simoen Eddy , Sioncke Sonja , Van Elshocht S. , Wang Wei-E
Published: September 2009

The use of Ge and III/V materials for future CMOS applications is investigated. Passivation of the Ge surface can be obtained by either GeO2 or a thin Si layer. Short channel Ge pMOS devices with low EOT are fabricated. The passivation of III/V materials is a very challenging topic. Some critical issues and passivation schemes are investigated and the performance of inversion channel MOSFET's on In0.53Ga0.47As with ALD Al2O3 is discussed.
Electrical Properties of Lanthanum-scandate Gate Dielectric Directly Deposited on Ge
Authors: Bera M.K. K. , Song J. , Kakushima Kuniyuki , Ahmet Parhat , Tsutsui Kazuo , Sugii Nobuyuki , Hattori Takeo , Iwai Hiroshi
Published: September 2009

The electrical performance of both Ge MOSCAP and MOSFET with LaScOx high-k gate dielectric directly deposited on Ge (100) without utilizing any interfacial passivation layer has been investigated. This study also reports about the control of Vfb/Vth through ScO concentration. Accordingly, a relatively larger hysteresis and higher density of interface states with ScO concentration having lower or higher than 50% along with increasing annealing temperatures were observed in general as a result of deterioration caused by the formation of GeOx at the interface in conjunction with more pronounce intermixing or Ge out-diffusion into LaScOx. Nevertheless, an ultrathin Si passivation layer is found to be advantageous to inhibit Ge incorporation into high-k bulk in the form of GeOx, thereby diminishing the resultant oxide charge trapping as well as improves the thermal stabilities of the entire LaScOx/Ge MOS structures. Besides, reasonably good electrical properties of Ge p-MOSFETs with LaScOx gate dielectric have been demonstrated.
Defects Generation under Constant Voltage Stress in La2O3/HfO2 Gate Stacks Grown on Ge Substrates
Authors: Evangelou Evangelos K. , Rahman M. S. , Dimoulas Athanasios , Galata Sotiria
Published: September 2009

We report on the defect generation under constant voltage stress in La2O3/HfO2 gate stacks grown on Germanium (001) substrates by molecular beam deposition utilizing a stress and sense technique. A voltage range from 0.5V up to 2.4V was used for the measurements. At low applied gate voltages, the stress induced current decrease could be explained by a field lowering model due to charge trapping, while at higher voltages the generation of shallow traps in the Lanthanum oxide layer becomes more important.
Structural and Electrical Properties of HfO2/n-InxGa1-xAs structures (x: 0, 0.15, 0.3 and 0.53)
Authors: Hurley Paul K. , O'Connor Eamon , Monaghan Scott , Long Rathnait , O'Mahony Aileen , Povey Ian M. , Cherkaoui Karim , MacHale John , Quinn Aidan , Brammertz Guy , Heyns Marc M. , Newcomb Simon , Afanas'ev Valeri V. , Sonnet Arif , Galatage Rohit , Jivani Naqi , Vogel Eric , Wallace Robert M. , Pemble Martyn
Published: September 2009

In this work results are presented of an investigation into the structural and electrical properties of HfO2 films on GaAs and InxGa1-xAs substrates for x: 0.15, 0.30, and 0.53. The capacitancevoltage responses of the GaAs and InxGa1-xAs (x: 0.15 and 0.30) are dominated by an interface defect response. Analysis of these samples at 77K indicates that the defect density is > 2.5x1013 cm-2. For the HfO2/In0.53Ga0.47As system, 77K capacitance-voltage responses indicate surface accumulation is achieved. The results are consistent with a high defect density, with an energy level {greater than or equal to}0.75 eV above the valence band in the HfO2/InxGa1-xAs system, where the defect energy with respect to the valence band, does not change with the composition of the InxGa1-xAs. The HfO2/In0.53Ga0.47As interface exhibits two defects at 0.3eV (1.7x1013cm-2eV) and 0.61eV (1.5x1013cm-2eV) above the valance band edge. The defect at 0.61eV is removed by forming gas annealing at 325oC.
Modeling of Alternative High-k Dielectrics for Memory Based Applications
Authors: Pourtois Geoffrey , Clima Sergiu , Sankaran Kiroubanand , Delugas Pietro , Fiorentini Vincenzo , Magnus Wim , Soree Bart , Van Elshocht S. , Adelman Christof , Van Houdt Jan , Wouters Dirk , De Gendt Stefan , Heyns Marc M. , Kittl Jorge
Published: September 2009

Significant research efforts are devoted to the development of alternative high dielectric constant oxides (high-k) to sustain the requirements of the next generations of DRAM and FLASH memories. For the metal-insulator-metal applications, the identification of an oxide with a dielectric constant higher than 50 and a crystallization temperature lower than 650 C is a corner stone in the selection of the materials; while for non volatile memory (NVM) applications, an oxide with a dielectric constant ranging between 9 and 30, a large band gap (> 6 eV) are targeted. While significant efforts have been dedicated to the integration of possible material candidates, little is known on their intrinsic properties. Through this paper, we provide an overview of the parameters that determine the electronic and the polarizability response of tantalates, niobiates and rare-earth based scandates oxides eligible for the development of the next generation of memory based applications.
Stable HfO2 based Layers Fabricated by RF Magnetron Sputtering
Authors: Khomenkova Larysa , Dufour Christian , Coulon Pierre-Eugène , Bonafos Caroline , Gourbilleau Fabrice
Published: September 2009

Structural and composition properties of HfO2-based layers fabricated by RF magnetron sputtering were studied by means of X-ray diffraction and transmission electron microscopy, Energy dispersive spectroscopy and ATR-FTIR techniques versus the deposition parameters and post-deposition annealing treatment. It was observed that the temperature at which amorphous-crystalline transformation of pure HfO2 layers occurs depends on deposition conditions. It was found that silicon incorporation in HfO2 matrix plays main role in the stability of the layers and allows to increase the temperature of layer crystallization up to 900-1100{degree sign}C.
Structure of Hafnium Silicate Films Formed by Atomic Layer Deposition
Authors: Liu Jian , Wu Xiaohua , Lennard William , Landheer D.
Published: September 2009

Hf distributions in as-grown and annealed (HfO2)0.25(SiO2)0.75 films with thicknesses in the range 4-13 nm were investigated by high resolution transmission electron microscopy (HRTEM), angle resolved X-ray photoelectron spectroscopy (ARXPS) and medium energy ion scattering (MEIS). HRTEM images show a layered structure in films thinner than 8 nm. ARXPS data also show a non-uniform distribution of Hf throughout the film depth. A diffusion of SiO2 to the film surface after a longer time anneal was observed by MEIS. All these observations provide evidence for surface-directed spinodal decomposition in the pseudobinary (HfO2)x(SiO2)1-x alloy system.
Formation and Characterization of Thin Silicon Dioxide Films Obtained by Inductively-Coupled High-Density Plasmas using a Dual Rotated Spiral Antenna System
Authors: Kim Yil Wook , Woo Sang Ho , Kim Hai-Won , Um Pyung Yong , Ji Jung-Min , Kim Chang-Koo
Published: September 2009

Thin silicon dioxide films were obtained by low-temperature plasma oxidation. Plasma oxidation was performed using a specially-designed new plasma source, called dual rotated spiral antenna (DuRoSA) system. This new plasma source produced high density plasmas (~ 1012 cm-3) having relatively low electron temperatures (2.5 ~ 4 eV). The temperature dependence of the plasma oxidation was found to be less sensitive than that of the high temperature thermal oxidation. The decrease in both oxidation rate and electron density with increasing oxygen fraction suggested that the negative oxygen ions may play the key role in plasma oxidation.
Nitrogen Incorporation in Al2O3 Thin Films Prepared by Pulsed Ultrasonic Sprayed Pyrolysis
Authors: Carmona-Tellez Salvador , Palacio Carlos , Gallardo Salvador , Rivera Zacarias , Guzman-Mendoza Jose , Aguilar-Frutis Miguel , Garcia-Hipolito Manuel , Alarcon-Flores Gilberto , Falcony Ciro
Published: September 2009

The electrical characteristics and the chemical composition profiles determined by XPS and SIMS for aluminum oxide thin films deposited by pulsed ultrasonic spray pyrolysis are reported. The films were deposited on c-Si at 550 ºC using a chemical solution of aluminum acetylacetonate as source of aluminum and N,N-Dimethylformamide as solvent, in addition a H2O-NH4OH mist was supplied simultaneously during deposition to improve the overall properties of these films. The results show that there is nitrogen incorporation in the films at the interface with the Si substrate. There is also a clear migration of silicon into the deposited film. The thickness of the films was in the range of 30 nm. Infrared spectroscopy also shows the presence of Si-O bonds. The dielectric constant for these films was higher than 8 and their interface trap density at midgap was in the 1010 eV-1cm-2 range.
High Density MIM Capacitors Using HfAlOx
Authors: Hota Mrinal K. , Mahata Chandreswar , Sarkar Chandan K. , Maiti C.K.
Published: September 2009

Amorphous HfAlOx films deposited by RF magnetron co-sputtering of HfO2 and Al2O3 targets at a substrate temperature of 50{degree sign}C have been used for the fabrication of Metal-insulator-metal capacitor structures. Effects of different metal electrodes (Au and Al) are investigated and the electrical properties are compared. The electrical properties of the MIM capacitors are investigated by using current-voltage (I-V) and capacitance-voltage (C-V) characteristics in the 1 kHz - 1 MHz frequency range. Using high work function (5.1 eV) top electrode Au, low leakage current and low energy dissipation is obtained in high density (~5fF/μm2) HfAlOx MIM capacitors with improved voltage coefficients of capacitance values. The leakage current density is approximately one order of magnitude higher than devices with Al electrodes. In addition, effects of constant voltage stressing and temperature on the leakage current and voltage linearity are also investigated. Stress voltage frequency dependence of quadratic voltage coefficient of capacitance is discussed.