bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Measurements of a Single-cell Stack Using Various Designs of Flow Distributors for Planar SOFC
Authors: Huang C.M. , Shy S.S. , Huang S.C. , Lee C.H.
Published: September 2009

In 2008, Shy and his co-workers proposed that flow uniformity may play a role on the cell performance of a single SOFC stack based on 3D numerical models, in which four different designs of flow distributors with the same 12 rectangular flow channels divided by eleven ribs having different degrees of flow uniformity were studied. This work provides direct experimental measurements for the first time to show how exactly the cell performance of a single-cell stack would vary with a change in the degree of flow uniformity in these aforementioned flow distributors. It is found that by improving the degree of flow uniformity in flow distributors, the cell's peak power density of the single-cell stack can be increased up to 14%. Also discussed are the start-up procedure and effects of operating temperatures and air and hydrogen flow rates to cell performance.
Operating Characteristics of Solid Oxide Fuel Cell Stacks and Systems
Authors: Minh Nguyen Q.
Published: September 2009

Solid oxide fuel cells (SOFCs) have been developed for power generation applications and in the reverse operating mode for hydrogen and oxygen production. In both operating modes, stable performance and high efficiency are very much dependent on operating characteristics of the stack within the system. Several of the critical parameters include temperature gradient across the cell, voltage and temperature variations between cells, cell-to-cell contacts, and fuel and oxidant utilizations. This paper discusses certain factors important to the operation of SOFC stacks and systems including cyclic operation between power generation and hydrogen production modes.
Single Chamber Solid Oxide Fuel Cells (SC-SOFCs) based on a Proton Conducting Electrolyte
Authors: D'Epifanio Alessandra , Fabbri Emiliana , Di Bartolomeo Elisabetta , Licoccia Silvia , Traversa Enrico
Published: September 2009

Single chamber solid oxide fuel cells (SC-SOFCs) are promising for portable power applications because they are simpler than the conventional dual-chamber cells. SC-SOFCs based on the cell Ni/BaCe0.3Zr0.5Y0.2O3-δ (BCZY)/Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) were investigated under gas mixtures of propane (C3H8), oxygen (O2), and helium (He) with different compositions. To enhance the fuel partial oxidation at low temperatures, a porous layer of Ru was added onto the anode surface. Two configurations, finger (with parallel electrodes) and sandwich (with electrodes on opposite sides of the pellets), were analyzed
Non-Ionic Conduction Phenomena in Yttria Stabilised Zirconia Electrolyte in SOFC operated in the Electrolysis Mode
Authors: Schefold Josef , Brisse Annabelle , Zahid Mohsine
Published: September 2009

Anode supported solid oxide fuel cells (SOFCs) with yttria stabilised zircona (YSZ) electrolytes were operated at ~800{degree sign}C as solid oxide H2O electrolyser cells (SOECs). Typical operation voltages were 1.0 to 1.3 V. When operation was extended to current densities j corresponding to a steam conversion rate above 100%, or when the steam supply was interrupted under constant current conditions, cell voltages saturated at about 1.8 to 2.0 V. Cells survived long-term current polarisation with j ~ -0.3 to -0.5 Acm-2 without steam supply. The mechanism limiting the cell voltage is attributed to electronic conduction in the YSZ electrolyte. Electrolyte conduction in the normal SOEC mode (with reasonable steam conversion rates) remains predominantly ionic in the investigated temperature range. Depending on the cell characteristics and the operation conditions (notably the temperature), however, the ionic transfer number may be significantly lower compared to the SOFC operation.
On the Development of an Electrochemical Sensor to Measure SOFC Fuel Gas Compositions
Authors: Wu Yiing Mei , Zhen Yongda
Published: September 2009

SOFC fuel composition sensing is vital for operation control, monitoring and performance diagnosis. Sensors based on potentiometric measurements can yield accurate compositional correlations provided that chemical equilibrium is established on the electrode. For syngas sensing, sensitivity of open circuit potential to H2:CO ratio change was less than that of the humidification level variation. For methane systems, OCP sensors studied either failed to reach equilibrium due to inadequate catalytic activity or suffered from carbon deposition. Impedancemetric sensors provided reasonable responses in syngas and methane systems. Rh-impregnated LSCM/GDC sensors showed good catalytic ability and sensitivity toward methane without coking. Careful calibration is required to rule out ambiguity.
Detailed Modeling of an Anode-supported Solid Oxide Fuel Cell Using a Fully Three-dimensional Approach
Authors: Ho Thinh X. , Kosinski Pawel , Hoffmann Alex C. , Vik Arild
Published: September 2009

This paper presents a numerical investigation of a repeating unit of an anode-supported solid oxide fuel cell (SOFC) using a three-dimensional (3D) model. The modeling domain consists of fuel and air channels, composite anode and cathode electrodes, an electrolyte and anode and cathode interconnects. Electrochemical reactions are assumed to take place in a thin layer of finite thickness at electrode-electrolyte interfaces. Equations describing balances of mass, momentum, chemical and electrochemical processes taking place in the cell are solved simultaneously. The co-flow configuration with direct internal reforming is investigated. Results for temperature, chemical species, current density and electrical potential distributions in the cell are shown and discussed. The potential of the electronic phase is found to vary only slightly over the ribbed interconnects and the electrodes.
Mathematical Modelling of Mass and Charge Transport and Reaction in the Central Membrane of the IDEAL-Cell
Authors: Ou Tengjiao , Delloro Francesco , Nicolella Cristiano , Bessler Wolfgang G. , Thorel Alain S.
Published: September 2009

The IDEAL-Cell is an innovative SOFC concept, comprising the anode and the electrolyte of a protonic SOFC and the cathode and the electrolyte of an anionic SOFC, connected through a central membrane (CM), a composite layer of proton-conducting and anion-conducting materials. Protons formed at the anode migrate through the protonic electrolyte to the CM, where they react to produce water with oxygen anions migrated from the cathode through the anionic electrolyte. In this work, a two-dimensional mathematical model of charge transfer, mass transfer and electrochemical reaction in the CM is developed to support experimental tests aimed at demonstrating the IDEAL-Cell concept. The model enables the prediction of the steady-state response of the IDEAL-Cell under varying operating conditions. The model can be used to fit experimental polarization data for the estimation of kinetic parameters, and to support the design of IDEAL-Cell prototypes.
Characterization of La0.8Sr0.2Co0.5Mn0.5O3-δ Coating on Alloy Interconnect in SOFC
Authors: Han Min-Fang , Du Xiaojia , Liu Ze
Published: September 2009

Chromia-forming ferritic stainless steels are being considered for interconnector applications in planar solid oxide fuel cell (SOFC) stacks because of their low cost and excellent physical properties. Nevertheless, some problems still need to be solved as the performance degradation due to the oxide scale growth at the cathode contact surface and the evaporation of volatile Cr-containing species, which poisons the cathode materials. An alternative and probably simple way is to coat one thin protective layer to limit Cr evaporation and to develop a conductive scale. In this study, La0.8Sr0.2Co0.5Mn0.5O3-δ (LSCM8255) has been considered to obtain a conductive layer. Steel SUS430 surface had been coated with LSCM8255 layer using screen printing combined with dry press method. The microstructure evolution of the interface between the metallic substrate and oxide layers had been investigated by scanning electron microscopy and energy dispersive X-ray spectroscopy line scan analysis. There was few Cr evaporated into the LSCM8255 coating, and small peaks of Cr2O3 and 3Cr2O3•Fe2O3 after isothermal oxidation at 850oC for 500hrs. The variation with time of the area specific resistance (ASR) at 850{degree sign}C had been recorded up to 500h, and low ASR 0.03 Ω•cm2 was observed by a four probe dc technique.
Influence of the Processing Method on the Quality of the Protective Coatings for SOFC Applications
Authors: Comminges Clément , Zahid Mohsine , Larring Ingve , Tietz Frank
Published: September 2009

Protective layers for Solid Oxide Fuel Cells (SOFC) interconnects (IC) were developed. The contacting layers are made of La0.8Sr0.2Mn0.5Co0.5O3 (LSMC) and were prepared by wet powder spraying. In order to avoid IC oxidation and a dramatic increase of ASR, MnCo2O4 spinel protective coatings were processed either by Atmospheric Plasma Spraying (APS) or by a Metal Organic route (MO). The influence of the processing method of these layers on the resistance of their assembly with an IC was investigated on Crofer22APU and F17TNb substrates. The measured ASR is stable after about one hundred hours. Their efficiency in Single Repeated Unit (SRU) configuration was also investigated. The MO process gave the thinnest layer, thereby the lowest resistance. The APS process gives thicker and denser layers, thus preventing completely the chromium diffusion through the cathode, but a slightly higher resistance is observed.
Oxidation Behavior and Chromium Vaporization of Ion Implanted Crofer22APU
Authors: Hong SeungHee , Madakashira Phaniraj , Kim Dong-Ik , Cho Young Whan , Han Seung Hee , Han Heung Nam
Published: September 2009

Crofer 22APU, used for interconnects in solid oxide fuel cells (SOFCs), is studied to improve its oxidation resistance and to suppress chromium vaporization from the oxide scales. Carbon and nitrogen were implanted on the plate surface by the ion implantation method. These samples were subjected to oxidation at 800oC for 500 hours. Oxidation kinetics was determined by measuring weight gains at regular time intervals. Experiments to determine chromium volatility from the samples were conducted at 800 {degree sign}C in a tube furnace in flowing air. The chromium vapors were collected on a silicon wafer and Rutherford Backscattering Spectroscopy (RBS) was used to measure the chromium vaporization rates. ASR measurements were also carried out on the samples. AES, SEM/EDS and TEM were used to characterize the initial and oxidized surface of the samples. The ion-implanted samples show significantly less chromium vaporization rate than the unimplanted samples.
Influence of Electrical Load on the Stability of Glass Sealings
Authors: Rost Axel , Schilm Jochen , Kusnezoff Mihails
Published: September 2009

Gastight and stable sealings are crucial for reliable service of solid oxide fuel cells (SOFCs). Failures of sealings are conceivable for many reasons resulting in damage of the whole SOFC-stack. Reactions between sealing and interconnector materials (Crofer 22 APU) at high temperatures under oxidizing and reducing conditions affect the bonding strength and microstructure of the glass to metal interface. Electric voltage across the glass sealings lead to additional effects at anodically and cathodically polarized interfaces. Tests of model sealings under electric voltage in combination with dual atmosphere provide information about the stability of sealing glasses under SOFC-relevant operating conditions.
Effects of Fe Addition on Densification and Conduction Property of Gadolinia Doped Ceria
Authors: Limthongkul Pimpa , Jivaganont Pranuda , Loyma Wararat , Panaram Noppakao , Charojrochkul Sumittra
Published: September 2009

In this paper, the effects of Fe addition on densification and conduction property of commercial grade 10 mol% GDC were studied. Effects of Fe doping along with sintering temperatures on the density of the GDC were investigated. Without the Fe addition, it was found that GDC could not be densified to above 90% theoretical density even at a sintering temperature of 1500oC. A small addition of Fe, however, was found to greatly enhance the densification of GDC, in that > 98% density could be obtained even when as little as 0.01 % at Fe was added. Impedance analysis revealed correlations between electrical behavior of the Fe-doped GDC and the amount of Fe doping. Little effect of Fe doping was found on the bulk conductivity of the GDC, while the addition of Fe had higher influence on grain boundary conductivity.
Deformation and Fracture Characteristics of Zirconia and Ceria-Based Electrolytes for SOFCs under Reducing Atmospheres
Authors: Hashida Toshiyuki , Sato Kazuhisa , Takeyama Yohei , Kawada Tatsuya , Mizusaki Junichiro
Published: September 2009

In this paper, we discuss the effects of different oxygen partial pressures on the elastic modulus and fracture strength of 8 mol% yittria stabilized zirconia (8YSZ) and 10 mol% gadolinia doped ceria (10GDC). The specimens of 8YSZ and 10GDC prepared by a sintering process were treated at 800 åC under different oxygen partial pressures in the range of 0.2 to 10-22 atm for 1 hour. The treated specimens were then fast cooled down to a room temperature, and their mechanical properties were measured under an atmospheric pressure condition by using the small-punch testing method. The experimental results revealed that both the elastic modulus and fracture strength of the 10GDC decreased drastically when the oxygen partial pressure of the treatment was less than 10-15 atm, whereas no significant variation in both the mechanical properties was observed for the 8YSZ.
IR-assisted Sol-gel Synthesis of Ce0.8Gd0.2O2-δ for SOFCs Applications
Authors: Mercadelli Elisa , Danesin Manuel , Sanson Alessandra , Doubova Lioudmila , Boldrini Stefano
Published: September 2009

Gadolinia-doped ceria (Ce0.8Gd0.2O2-δ, GDC) is an alternative electrolyte for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC). Nanostructured materials have recently attracted extensive attention because of their high reactivity that allowed milder sintering conditions. Although several methods were proposed for the synthesis of ultrafine powders, most of them generally require a subsequent calcination step. The aim of this work was to produce ultrafine, pure GDC powders using a standard chemical route (aqueous sol-gel) coupled with non-conventional heating processes (infrared heating). Nanocrystalline non-agglomerated GDC particles were successfully produced under mild conditions (170{degree sign}C, 1h) without the intermediate decomposition and/or calcining steps. Moreover the GDC obtained through the optimization of the IR-assisted sol-gel synthesis parameters exhibited values of ionic conductivity higher than the ones showed by commercial and conventional sol-gel produced powders of similar composition.
Complementarity of Experimental and Theoretical Nuclear Magnetic Resonance Spectroscopic Studies for the Study of Candidate ITSOFC Electrolytes
Authors: Middlemiss Derek S. , Blanc Frederic , Grey Clare P.
Published: September 2009

Issues inherent to the determination of the local structure and transport properties of doped oxide phases of interest as candidate intermediate temperature solid oxide fuel cell electrolytes are described. In partial mitigation of such difficulties, an approach combining experimental solid state NMR spectroscopy with periodic DFT-based NMR and total energy calculations is outlined. It is anticipated that this method will permit for the more routine assignment of the NMR spectra of such doped phases, which has been hampered to-date by uncertainties in the ranges anticipated for the spectroscopic parameters of species in novel coordination environments.
Effect of Slight ZnO Addition on the Structural, Morphological and Electrical Properties of Barium Zirconate Pellets
Authors: Briois Pascal , Arab Pour Yazdi Mohammad , Georges Samuel , Shaula Aliaksandr , Cavaleiro Albano , Billard Alain
Published: September 2009

In this paper, BaZr0,84Y0,16O3-α (BZY16) pellets were synthesized by solid state reaction. ZnO was added at different contents to improve sintering. The effect is investigated as a function of its content in the powder mixture prior to sintering. Whatever the ZnO content, the sole phase observed by X-ray diffraction presents the perovskite structure of BaZrO3 and no trace of crystallized ZnO can be detected. Scanning electron microscopy observations show that the pellets density increases with the ZnO content to reach a maximum around 2 wt.% ZnO. Over this value, a significant increase of macroporosities occurs. On the another hand, the best ionic conductivity is obtained for 1 wt.% ZnO.
Nondestructive Imaging and Analysis of Transport Processes in the Solid Oxide Fuel Cell Anode
Authors: Grew Kyle , Peracchio Aldo A. , Izzo John R. , Chiu Wilson
Published: September 2009

Three-dimensional reconstruction methods, such as the non-destructive transmission x-ray imaging with tomographic reconstruction, have enabled the micro- to nano-scale characterization of the porous solid oxide fuel cell electrode structures. This work provides an examination on the use of several methods being developed by the authors to quantitatively characterize and examine electrode structures in the SOFC. The porous Ni-YSZ cermet anode is used as a framework for this study. Specific attention is paid to the effect these types of structures may have on the functional electrochemical behavior that must be supported by the SOFC; including transport phenomena in the electrode structure in addition to accounts of the interfaces associated with the electrochemical and heterogeneous catalytic phenomena. Phenomenological structures are used to support these efforts. Further, a quantitative description of the characteristic lengths of the electrode structure is discussed in this work.
High Performance SOFC Anode with Metal Nano-Particles Produced by Partial Reduction Reaction
Authors: Osada Norikazu , Fukasawa Takayuki , Yamada Masahiko
Published: September 2009

We have proposed a new design concept of the SOFC anode with metal nano-particles produced by partial reduction reaction. NiAl2O4 was employed as the precursor of Ni catalysts. After reduction of it, the Ni nano-particles of 20-50 nm were formed and acted as the good anodic catalysts. Furthermore, the SDC coating on NiAl2O4 surface enhanced anode performance and the 20 wt.% NiAl2O4-SDC with SDC coating in the anode showed high performance and high catalytic activity.
Electrochemical Properties of NiO-ScSZ Anodes Prepared from Composite Precursor Containing Ni and Zr
Authors: Doumae Kyousuke , Usui Takeshi , Yasui Tadashi , Watanabe Satoshi , Oshima Toshihiro , Shiratori Yusuke , Sasaki Kazunari
Published: September 2009

Generally, cermet anode is produced by mixing nickel oxide with stabilized zirconia. Improvement of the conventional anode is necessary in the viewpoints of electrochemical performance and its productivity. In this study, two approaches were tested in order to enhance the anode performance. First, wet blended Ni-Zr composite hydroxide was applied as a precursor to obtain homogeneous Ni-stabilized zirconia cermet. In the next phase, doping of Mg, Mn and Co to the nickel precursor is performed by co-precipitation method aiming at positive effects of these elements, and electrochemical properties of these anodes are evaluated and compared to those of conventional anode.
Phase Transformation of ScSZ by Reduction of NiO-ScSZ Mixture
Authors: Kishimoto Haruo , Yoshinaga Masashi , Yamaji Katsuhiko , Brito Manuel , Horita Teruhisa , Yokokawa Harumi
Published: September 2009

The phase transformation behavior of scandia stabilized zirconia in Ni-ScSZ cermet anodes was investigated in details by X-ray diffractometry (XRD) and Raman spectroscopy. Since explanations for the appearance of the tetragonal phase is not straight for word, possible effects of porosity, NiO dissolution and coexistence nickel metal were investigated. Dense or porous 10Sc1CeSZ disks, NiO doped 10Sc1CeSZ disks (0.5 to 2.0 mol% NiO) and sintered or porous NiO-10Sc1CeSZ mixture (Ni-10Sc1CeSZ cermet after reduction) were reduced under Ar-H2 mixture gas. Raman spectroscopy shows that 10Sc1CeSZ in the Ni-10Sc1CeSZ cermet partly transformed to the tetragonal phase on reduction. No transformation was observed for the 10Sc1CeSZ disk alone nor NiO doped samples. Although the presence of nickel is necessary for transformation, nickel dissolved into 10Sc1CeSZ has not apparent effect. Contact of nickel metal with 10Sc1CeSZ, i.e. three phase boundaries, has an important role in the transformation of 10Sc1CeSZ. Three different mechanisms are discussed.
Aspects of Metal-YSZ Electrode Kinetics Studied using Model Electrodes
Authors: Graves Christopher R. , Ebbesen Sune D. , Mogensen Mogens
Published: September 2009

The electrode kinetics of oxidation and reduction of H2/H2O and CO/CO2 at the metal/yttria stabilized zirconia (YSZ) interface were studied using model metal wire electrodes contacting polished YSZ pellets. The intent was to probe the reaction mechanisms by comparing the same reactions using different metals (Ag, Au, Cu, Ni, Pd, and Pt) under identical conditions relevant to fuel cell and electrolysis cell operation (e.g. including 50% H2/H2O and 50% CO/CO2). Impedance spectra were measured at open-circuit voltage and under polarization, and polarization sweeps were performed. The gas composition and temperature were varied to examine how the electrochemical measurements varied, to facilitate identifying the electrode rate-limiting processes. Possible mechanisms that may explain these and other details are discussed.
Optimization of the Charge Transfer Process in the Composite Ni-YSZ Cermet Anodes
Authors: Bredikhin Ivan S. , Bredikhin Sergey I. , Kveder Vitaly V.
Published: September 2009

Modeling and subsequent examination of ambipolar conductivity and surface reaction resulted in a noticeable optimization of the total anode conductivity. The electrochemical properties of solid oxide fuel cells (SOFCs) were investigated as a function of the Ni volume content in composite Ni/YSZ anodes. The dependence of experimentally measured SOFC characteristics on the anode thickness agreed well with the numerical calculation results. The maximum power output was achieved for the SOFC with an anode thickness 10-20 µm, and the part of the electrode exceeding this thickness mainly operated as a current collector for that functional layer.
Stability of Ni/Y-doped SrTiO3-YSZ Anode in Reduction-oxidation Cycles
Authors: Ikebe Tsugio , Muroyama Hiroki , Matsui Toshiaki , Eguchi Koichi
Published: September 2009

A composite anode consisting of 3 vol% Ni, Y-doped SrTiO3 (YST) and Y2O3 stabilized ZrO2 (YSZ) was fabricated: the Ni species was impregnated to YST-YSZ powder and then the resulting powder was fired onto the electrolyte at 1200ºC for 5 h in air. A single cell employing this anode exhibited the power density of 0.28 W cm-2 at 0.7 V at 1000ºC despite its extremely low content of Ni. Stable power generation was attained at the constant terminal voltage of 0.7 V in humidified hydrogen (0.6% H2O-H2) for 22 h. Even after five consecutive redox cycles, the cell performance remained unchanged mainly due to the stable porous framework of YST-YSZ with low Ni content.
Electrode Behavior of Ni/GDC and Pd-Ni/GDC Cermets in H2/H2S Fuels of Solid Oxide Fuel Cells
Authors: Jiang San Ping , Zhang Lan , He Hongquan
Published: September 2009

The effect of H2S on the hydrogen oxidation on Ni/gadolinia doped ceria (Ni/GDC) anodes with/without Pd-impregnation was investigated using the electrochemical impedance spectroscopy (EIS) and galvanostatic polarization techniques at 800oC. The polarization performance of Ni/GDC anodes degraded rapidly and the presence of 100 ppm H2S in H2 fuel causes structural damage to the Ni/GDC anodes after polarized at 200 mA/cm2 for 55 h. The infiltrated Pd nanoparticles significantly reduce the electrode polarization resistance, and promote the stability of the Ni/GDC anodes. The impregnated Pd nanoparticles on the surface of Ni/GDC anodes significantly reduced the structural damage and modification effect of H2S on the Ni and GDC particles of the anodes.
Ni-Fe Cermet as Stable Anode for Direct CH4 Type SOFC
Authors: Zhong Hao , Matsumoto Hiroshige , Ishihara Tatsumi
Published: September 2009

Ni-Fe/La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) (90:10) cermet anode for direct CH4 used SOFC was studied. Among the various cermet studied, it was found that Ni-Fe/LSGM exhibits the superior catalytic activity for CH4 oxidation and also stability in CH4, and so the carbon deposition was highly suppressed. This improvement could be explained by the increase in basic property of LSGM. The further kinetic study was performed and this cermet anode shows the almost zero PCH4 dependence of anodic overpotential. Therefore, the rate-determining step of CH4 electrochemical oxidation on this cermet seems to be charge transfer process due to a high surface activity of NiFe-LSGM catalyst.
Composite Anode of Ce0.6Mn0.3Fe0.1O2 and La0.6Sr0.4Fe0.9Mn0.1O3 for Oxidation Tolerant SOFC
Authors: Ishihara Tatsumi , Shin Tae Ho , Vanalabhpatana Parichatr
Published: September 2009

Anodic performance of oxide composites consisting of Ce(Mn,Fe)O2-La(Sr)Fe(Mn)O3 was studied. It was found that the open circuit potential close to the theoretical value exhibited the cell using oxide composite of Ce(Mn,Fe)O2-La(Sr)Fe(Mn)O3. On the other hand, the maximum power density is much improved by mixing two oxides for anode and the highest power density is achieved on the cell using 12.5 wt% Ce(Mn,Fe)O2 mixed with La(Sr)Fe(Mn)O3 for anode at intermediate temperature. The maximum power density was achieved values of 970 and 23 mW/cm2 at 1273 and 773 K, respectively. Exposure of anode to air at 1073 K, the maximum power density was returned to an almost original level after changing air to H2. Therefore, this study reveals that the composite of doped CeO2 and LaFeO3 based perovskite is useful as an oxide anode for SOFC using LSGMC based electrolyte.
Use of Electroless Anode Active Layer in Anode-supported Planar SOFC
Authors: Mukhopadhyay Madhumita , Mukhopadhyay Jayanta , Das Sharma Abhijit , Basu Rajendra N.
Published: September 2009

In SOFC, a novel Ni-YSZ cermet developed through electroless technique is used as an anode as well as anode active layer (AAL). In the present investigation, thickness of such AAL (varied in the range 15 - 140 micrometer) is optimized sequentially for fabricating high performance single cell. The fabrication technique involves tape casting followed by room temperature lamination to form the half cells. Effect of sintering temperature of half cells on the electrochemical performance has been carried out in the range of 1300 degC to 1400 degC. A typical I-V characteristics of coupon cell (active area of ~ 0.3 cm2) sintered at 1400 degC with an optimum AAL thickness show current density of ~ 3 A/cm2 and power density of ~ 2 W/cm2 at 0.7 V and 800 degC. Electrochemical performances of single cells using only electroless anode are also evaluated for comparison. Microstructures of these single cells are correlated with the electrochemical performances.
Correlations of Electronic and Chemical State on La0.7Sr0.3MnO3 Dense Thin-Film Cathode Surfaces
Authors: Khabibulakh Katsiev , Yildiz Bilge , Kavaipatti Balasubramaniam , Salvador Paul
Published: September 2009

We report on the surface topography, electron tunneling and chemical characteristics of 10nm- and 50nm-thick La0.7Sr0.3MnO3 (LSM) thin-films at temperatures up to 580oC in 10-3 mbar oxygen pressure, using in situ scanning tunneling microscopy and spectroscopy (STM/STS). Coarsening of the grains was found on the 10nm-thick LSM film. High resolution mapping of the tunneling spectra onto the surface topography showed a higher electron exchange rate at select grain boundaries compared to grain surfaces. A threshold-like drop in the tunneling current was observed at positive bias in STS, and is suggested as a unique indicator to the activation polarization in cation-oxygen bonding on LSM. Sr-enrichment and Mn-depletion were found on the surface at high temperature using Auger electron spectroscopy, accompanied by a reduction in tunneling conductance in STS. This suggests that the Mn-terminated surfaces are more active for electron exchange in oxygen reduction compared to the (La,Sr)-terminated surfaces on LSM.
Scandia-Stabilized Zirconia Impregnated (La, Sr)MnO3 Cathode for Tubular Solid Oxide Fuel Cells
Authors: Liu Renzhu , Zhao Chunhua , Li Junliang , Wang Shao Rong , Wen Zhaoyin , Wen Ting Lian
Published: September 2009

A LSM-ScSZ composite cathode for anode-supported tubular solid oxide fuel cell (SOFC) has been successfully developed. The fabrication method is a two-step process including dip-coating LSM framework and ion-impregnating ScSZ. A preliminary examination of the single tubular cell, which consists of a Ni-YSZ anode support tube, a Ni-ScSZ anode functional layer, a ScSZ electrolyte film, and the LSM-ScSZ cathode, has been carried out, and an improved performance is obtained. The polarization resistance of the cathode side is significantly decreased by impregnating the electronic conducting phase (LSM) with the ionic conducting phase (ScSZ). And the single cell generates the maximum power density of 433 mW cm-2 at 850 ºC, being operated with humidified hydrogen.
Electrochemical Characterization of Micro-Patterned La0,6Sr0,4Co0,2Fe0,8O3 Thin Film Structures on Fused Silica
Authors: Ryll Thomas , Scherrer Barbara , Toelke Rene , Rupp Jennifer L. , Bieberle-Hutter Anja , Gauckler Ludwig J.
Published: September 2009

The polarization resistance of solid oxide fuel cell (SOFC) cathodes strongly depends on the structure of the cathode-electrolyte interface. Therefore measurements of the polarization resistance of cathode thin films on electrolyte thin films are required in order to predict the performance of thin film SOFCs. In this study La0,6Sr0,4Co0,2Fe0,8O3 (LSCF) thin films were deposited by pulsed laser deposition on fused silica wafers carrying pre-structured Pt/Ta electrodes and a (Y2O3)0.08(ZrO2)0.92 (YSZ) thin film. Photolithography and argon sputtering were used to fabricate micro-patterns which proved to be applicable for the simultaneous characterization of LSCF thin films with respect to electrical in-plane and cross-plane conductivity as well as polarization resistance. In the future such test platforms are destined for the characterization of different cathode thin films with respect to conduction and oxygen reduction properties.
Impact of Alkali Earth Elements Incorporation on Electrical Characteristics of La2O3 Gated MOS Device
Authors: Koyanagi Tomotsune , Okamoto Kouichi , Kakushima Kuniyuki , Ahmet Parhat , Tsutsui Kazuo , Nishiyama Akira , Sugii Nobuyuki , Natori Kenji , Hattori Takeo , Iwai Hiroshi
Published: September 2009

The impacts of Mg, SrO or BaO capping, alkali earth oxides, into La2O3 MOS devices have been examined. A roll-off characteristic in flat-band voltage (Vfb) dependence on equivalent oxide thickness (EOT) has been suppressed with Mg capping and incorporation. On the other hand, capping with SrO and BaO have showed roll-up characteristics below an EOT of 1.2 nm. The main reason can be considered as the change in the number of fixed charges. No notable change in leakage current (Jg) has been observed.
Impact of Voltage and Current Stress on TiN/HfSixOy/TiN MIM Capacitors
Authors: Jyothi K. , Chandorkar Arun , Misra D.
Published: September 2009

In this paper we have investigated the long-term reliability of TiN/HfSixOy/TiN Metal-Insulator-Metal (MIM) capacitors by using constant voltage stress (CVS) and constant current stress (CCS). No significant increase in leakage current was observed as a function of stress time. On the other hand stress induced capacitance changes were observed due to change in dielectric constant.
Electrical Characteristics of HfO2 and La2O3 Gate Dielectrics for In0.53Ga0.47As MOS Structure
Authors: Funamizu Kiyohisa , Lin Yueh Chin , Kakushima Kuniyuki , Ahmet Parhat , Tsutsui Kazuo , Sugii Nobuyuki , Chang Edward Yi , Hattori Takeo , Iwai Hiroshi
Published: September 2009

InGaAs MOS capacitors with HfO2 and La2O3 gate dielectrics have been investigated. La2O3 capacitor has revealed large leakage current. It can be considered that As atoms scattering into La2O3 layer from InGaAs substrate by annealing cause large leakage current. So, by inserting HfO2 in a substrate surface, La2O3/HfO2 stacking enables both the low leakage current as well as large capacitance density.
Interface and Bulk Properties of MBE-Grown Rare-Earth Metal Oxides on Silicon
Authors: Gomeniuk Yuri V. , Gomeniuk Yuri V. , Nazarov Alexei , Lysenko Vladimir , Osten Hans Jörg , Laha Apurba
Published: September 2009

The paper presents the results of electrical characterization of the interface and bulk properties of high-k Gd2O3 and Nd2O3 dielectrics epitaxially grown on silicon substrates. The limitations of the conductance technique for correct determination of the interface state density due to the presence of leakage currents through the dielectric are discussed. The charge carrier transport through the dielectric film was found to occur via the variable-range hopping conductance mechanism.
Characterization of Stacked Hafnium Oxide (HfO2)/Silicon Dioxide (SiO2) Metal-Oxide-Semiconductor (MOS) Tunneling Temperature Sensors
Authors: Wang Chih-Yao , Hwu Jenn-Gwo
Published: September 2009

In this paper, the stacked HfO2/SiO2 MOS tunneling temperature sensors prepared by low temperature processing are investigated. The temperature responses of the stacked HfO2/SiO2 MOS tunneling temperature sensors at high and low temperature regions are not the same. The saturation current of the stacked HfO2/SiO2 MOS tunneling temperature sensor may affected by Frenkel-Poole effect at high temperature. It was also observed that the thicker stacked HfO2/SiO2 MOS tunneling temperature sensors are easier to be affected by Frenkel-Poole effect at high temperature. The stacked HfO2/SiO2 MOS tunneling temperature sensors can operate under low voltage and therefore consume less power as compared with the pure SiO2 tunneling temperature sensors.
Demonstration of Transconductance Enhancement on (110) and (001) Strained-Nanowire FETs
Authors: Seike Aya , Takai Hajime , Tsuchida Ikushin , Masuda Junichi , Kosemura Daisuke , Ogura Atsushi , Watanabe Takanobu , Ohdomari Iwao
Published: September 2009

Enhancement of transconductance for strained nanowire transistors (s-nwFETs) on (001) and (110) planes are demonstrated by evaluating Ids-Vbg curves of the devices. Normalized transconductance, gm*, for <100> direction s-nwFETs is enhanced by a factor of 2.16 for n-type on (001) plane and 1.83 for p-type on (110) plane. This is due to the lighter effective mass of electrons/holes along the selected channel direction.
Electron-phonon Scattering Effect on Strained Si Nanowire FETs at Low Temperature
Authors: Tsuchida Ikushin , Seike Aya , Takai Hajime , Masuda Junichi , Kosemura Daisuke , Ogura Atsushi , Watanabe Takanobu , Ohdomari Iwao
Published: September 2009

Strained Si nanowire FETs of nanowire width (W) of W=155nm and W=5000nm, are evaluated by Id-Vbg characteristics at various temperatures. Transconductance (gm) and subthreshold slope are obtained from the Id-Vbg characteristics. The normalized gm (gm*) increases by a factor of 1.38 for W=155nm and 3.13 for W=5000nm. Subthreshold slope decreases 22% for W=5000nm and 42% for W=155nm. This improvement is due to suppression of electron-phonon scattering at low temperature. This also indicates that the influence of electron-phonon interaction on gm enhancement is different compared to that in bulk Si.
Nonvolatile Memory Capacitors Based on Double Gold nanocrystals and HfO2 Tunneling and HfNO/HfTiO Laminate Control High-k Insulator Layers
Authors: Mikhelashvili Vissarion , Meyler Boris , Salzman Jossef , Salzman Jossef , Garbrecht Magnus , Cohen-Hyams T. , Kaplan Wayne , Eisenstein Gadi
Published: September 2009

We describe a new, all high-k, nonvolatile MIS memory capacitor with an equivalent oxide thickness of 7.3 nm that makes use of two gold nanocrystal charge storage layers. The device exhibits a large memory hysteresis of about 0.75 V and 15 V, respectively at a sweeping gate voltages of 1V and +11V to -8V with a maximum storage charge density of ~2.75e13 cm^-2. The leakage current density is 3.6e-5 A/cm^2 at -10 V and the breakdown voltage is in the range of 12.3V - 13.3V. A large memory hysteresis window of ~10 V was also observed after more than 10 hours of consecutive write / erase operations with a +-7 V swing.
Cat-CVD (Catalytic-CVD); Its Fundamentals and Application
Authors: Matsumura Hideki , Ohdaira Keisuke
Published: September 2009

Cat-CVD (Catalytic Chemical Vapor Deposition), often called "Hot-Wire CVD", is a new deposition method, in which source gas molecules are decomposed by catalytic cracking reaction with a heated catalyzer. The difference between Cat-CVD and the conventional plasma enhanced CVD (PECVD) is explained through discussion on their deposition mechanisms. The various films prepared by Cat-CVD and their qualities are summarized along with their applications.
Major Precursors of Pyrocarbon Deposition from Propane Pyrolysis
Authors: Lacroix Remy , Fournet Rene , Ziegler-Devin Isabelle , Marquaire Paul-Marie
Published: September 2009

A detailed kinetic mechanism modeling gas and surface reactions involved in pyrocarbon deposition by propane pyrolysis (CVD) was recently proposed. Simulated results were compared with experimental data obtained with a perfectly stirred reactor at low pressure (20 torr). The kinetic mechanism, which is comprised of 608 gas and 275 surface elementary steps, is efficient to predict both pyrocarbon deposition rate and gas phase composition for temperature ranging from 1173 to 1323 K, residence time ranging from 0.5 to 4 seconds and surface to volume ratio ranging from 20 to 170 cm-1. In this paper, we discuss the main pyrocarbon deposition pathways using flow rate and sensitivity analysis. In our experimental conditions, pyrocarbon is mostly formed by deposition of small unsaturated species (acetylene and ethylene) and methyl radicals. The pyrocarbon deposition rate is controlled by mole fractions of H, CH3, C2H2 and C2H4 in the gas phase and by the value of the kinetic rate of a few key surface reactions.
A Comprehensive Insight in the MOCVD of Aluminum through Interaction between Reactive Transport Modeling and Targeted Growth Experiments
Authors: Xenidou Theodora C. , Prud'Homme Nathalie , Vahlas Constantin , Markatos Nicholas C. , Boudouvis Andreas G.
Published: September 2009

Growth experiments and reactive transport modeling were combined to formulate a comprehensive predictive model for aluminum growth from dimethylethylamine alane. The growth-rate profile was experimentally investigated as a function of substrate temperature. The reactive transport model, built under the computational fluid dynamics software PHOENICS, was used to reproduce the experimental measurements and to contribute to the understanding of the aluminum growth process, under sub-atmospheric pressure conditions. The growth mechanism of aluminum films was based on well established in literature reaction order and activation energy of homogeneous and heterogeneous chemical reactions. The reactive transport model was used further to investigate the effect of some key operating parameters on the process output. Simulation results are suggestive of modifications in the operating parameters that could enhance the growth rate and the spatial uniformity of the film thickness.
Optimization of Calcium Precursor Transport for High Vacuum Chemical Vapor Deposition (HVCVD)
Authors: Luo Lu , Kuzminykh Yury , Catalano Maria Rita , Malandrino Graziella , Hoffmann Patrik
Published: September 2009

High-k films of CaCu3Ti4O12 are of interest for industrial multifunctional electronics. For oriented flow High Vacuum CVD processes, precursors are needed that they can be safely transported in the gas phase without carrier gas. We investigated the vapor pressure, and transport rate and temporal stability of a potential Ca precursor [Ca(hfa)2tgte] (hfa: hexafluoroacetylacetonate, tgte: tetraethylene glycol dimethyl ether) under HV conditions by varying the evaporation temperature. At 115{degree sign}C, the transport rate for the Ca(hfa)2tgte precursor of 4.3 mmol per hour was achieved allowing for high film deposition rates.
Iron Amidinates as Precursors for the MOCVD of Iron Containing Thin Films
Authors: Gleizes Alain N. , Krisyuk Vladislav , Aloui Lyacine , Turgambaeva Asiya E. , Sarapata Bartosz , Prud'Homme Nathalie , Senocq François , Samelor Diane , Zielinska-Lipiec Anna , Dumestre Frédéric , Vahlas Constantin
Published: September 2009

Two iron imidinates, iron bis(N,N'-di-iso-propylacetamidinate) (1) and iron bis(N,N'-di-tert-butylacetamidinate) (2), were used as oxygen-free and Fe-C bond-free precursors to tentatively grow oxygen-free and possibly carbon-free iron thin films. The thermal decomposition of 1 and 2 was studied by mass spectrometry. The films were grown on polycrystalline copper and submitted to EPMA, EDX, XPS and XRD analyses. α-Fe is present in small amount. The other components are Fe3C, and Fe4C or Fe4N depending on the precursor and the temperature.
High-speed Growth and Characterization of Polycrystalline AlN Layers by High Temperature Chemical Vapor Deposition (HTCVD)
Authors: Claudel Arnaud , Blanquet Elisabeth , Chaussende Didier , Martin Rachel , Pique Didier , Pons Michel
Published: September 2009

In this paper, AlN synthesis is achieved by High Temperature CVD which consists of a graphite susceptor heated by induction in a home-built vertical cold-wall reactor working at low pressure. The reactants used are ammonia NH3 and aluminium chlorides AlClx species formed in situ via Cl2 reaction with high purity Al wire. AlN films were deposited on a 55 mm diameter graphite susceptor between 1200{degree sign}C and 1600{degree sign}C. The influence of deposition temperature on growth rate, surface morphology, grain size and crystalline state is presented. Growth rates of up to 230 µm.h-1 were reached. AlN layers were characterized by SEM, X-ray Diffraction, Raman spectroscopy and Optical Profilometry.
Characterization of High-Rate Deposited Microcrystalline Si Films Prepared using Atmospheric-Pressure Very High-Frequency Plasma
Authors: Tabuchi Keita , Ouchi Kentato , Ohmi Hiromasa , Kakiuchi Hiroaki , Yasutake Kiyoshi
Published: September 2009

Using stable plasma excited at atmospheric pressure by supplying 150-MHz very high-frequency (VHF) power, low-temperature and high-rate deposition of hydrogenated microcrystalline silicon (mc-Si:H) films is investigated. H2/SiH4 ratio and substrate temperature (Tsub) are varied as parameters under supplying an optimized VHF power density of 24 W/cm2. It is observed that increasing H2/SiH4 ratio leads to the improvement of both deposition rate and crystalline volume fraction (ICRS). It is worth to note that ICRS of approximately 72% is obtained even at H2/SiH4 = 0. The Tsub dependence of Raman crystallinity of the mc-Si:H films indicates that a highly crystallized mc-Si:H film grows even when Tsub is reduced down to 90 ºC. One of the contributing factors to this low-temperature deposition of mc-Si:H is the moderate heating effect of the growing film surface by the atmospheric-pressure VHF plasma while suppressing ion damage of the surface.
MOCVD of Zirconium Oxide from the Zirconium Guanidinate Complex [ZrCp′{η2-(iPrN)2CNMe2}2Cl]
Authors: Blackman Chris , Carmalt Claire , Moniz Savio , Potts Stephen E. , Davies Hywel , Pugh David
Published: September 2009

Parallel to successful studies into use of [ZrCp′{η2-(iPrN)2CNMe2}2Cl] as a precursor to the deposition of zirconium carbonitride via CVD the same precursor was utilised for the MOCVD of thin films of ZrO2 using borosilicate glass substrates. The deposited films were of mixed phase; films deposited at temperatures below 550 deg. C were predominantly orthorhombic (or tetragonal), whilst films deposited at 600 deg. C were approximately 1:1 mixtures of monoclinic and orthorhombic (or tetragonal) ZrO2. Additionally the monoclinic phase displayed preferred orientation. Compositional analysis showed that whilst the films had significant amounts of, principally graphitic, carbon contamination, which increased with increasing deposition temperature, chlorine contamination was negligible.
New Complexes of Alkali-Metals as Precursors for MOCVD of Ferroelectric (K, Na)NbO3 Thin Films
Authors: Tsymbarenko Dmitry , Korsakov Igor , Mankevich Aleksey , Girichev Georgiy , Pelevina Elena , Kaul Andrey
Published: September 2009

Three new mixed ligand complexes of Na and K were synthesized and characterized. The thermal behavior of synthesized compounds was investigated by TGA in vacuum and mass spectrometry from Knudsen cell. Obtained compounds demonstrate sufficient volatility in vacuum and were tested as precursor for MOCVD deposition of KNbO3 films. Single phase highly oriented films were obtained.
Normal Pressure CVD - an Easy and Sustainable Method for Technical Surface Functionalisation
Authors: Heft Andreas , Pfuch Andreas , Horn Kerstin , Schimanski Arnd
Published: September 2009

The PYROSIL ® technique is a well known process which is used to produce SiOx layers by using Combustion Chemical Vapour Deposition (C-CVD) in order to modify surfaces and their properties like the adhesion promotion. Another method to deposit oxides at atmospheric pressure is the use of potential free plasmas like plasma blaster or plasma jets for the decomposition of the precursors (AP-CVD). As precursors liquid and gaseous compounds or suspensions with nanoparticles can be used, which are pyrolysed by flame or plasma. The process energy especially during the flame treatment serves additional as a heating source for the substrate. The AP- or C-CVD coatings have the potential for several different applications e.g. antireflective coatings on glass for solar industry, antimicrobial or photo catalytic coatings. Current results and several different aspects for the application of this technology will be presented.
Influencing Factors towards a Scalable Synthesis of Aligned Carbon Nanotubes by Chemical Vapour Deposition
Authors: Nitodas Stephanos F. , Karachalios Theodoros K.
Published: September 2009

The synthesis of arrays of aligned multi-wall carbon nanotubes (CNTs) by thermal chemical vapor deposition is addressed in this study. Deposition experiments are carried out in a hot-wall reactor from mixtures of acetylene and helium, using iron coated silicon wafers as substrates. Scanning electron microscopy (SEM) is employed to discuss the growth mechanisms and the interaction between the substrate and the aligned CNTs film. Methods for improved substrate-CNTs film interaction are proposed, aiming at fabricating a more efficiently controllable and scalable process, adjusted to meet the forthcoming industrial demands.
Vapor Phase Synthesis of Pt Nanoparticles on Carbon Nanotube-Active Carbon Hierarchical Composites
Authors: Jin Chen , Holz Marie , Xia Wei , Mei Bastian , Kundu Shankhamala , Muhler Martin
Published: September 2009

Active carbon was used as substrate for the CVD of iron in a fluidized-bed reactor. Carbon nanotubes were subsequently grown from ethylene to obtain CNT-AC composites. The functionalization of the carbon composite was performed by conventional HNO3 treatment in liquid phase and by a recently developed treatment method using HNO3 vapor. The CVD of Pt was carried out with two different precursors, i.e., Pt(acac)2 and (CH3)3Pt(C5H5). One-step CVD in a fluidized-bed reactor was compared with two-step CVD in a fixed-bed reactor. X-ray diffraction, scanning and transmission electron microscopy, online mass spectrometry and X-ray photoelectron spectroscopy were employed for the characterization of the samples. It was found that the HNO3 vapor treatment was not only more effective in oxygen functionalization, but also more reliable for maintaining the structure/morphology of the hierarchical carbon composite. Highly dispersed Pt nanoparticles supported on CNT-AC were achieved by two-step CVD from (CH3)3Pt(C5H5) in a fixed-bed reactor.