Timothy Armstrong Oak Ridge National Laboratory
Christian Masquelier University of Picardie-CNRS
Yoshihiko Sadaoka Ehime University
Enrico Traversa University of Rome Tor Vergata
AA1: High Temperature Protonic Conductors: Materials and Applications
Monday AM, November 27, 2006
Republic B (Sheraton)
9:15 AM - **AA1.1
Selected Topics in High Temperature Proton Conductor.
Wilhelm Meulenberg 1 , José Serra 1 Show Abstract
1 Institute for Materials and Processes in Energy Systems 1, Forschungszentrum Juelich GmbH, Juelich, North-Rhine Westphalia, Germany
High temperature proton conducting membranes can find application in different key energy processes such as hydrocarbon reforming and water-gas-shift, allowing obtaining in turn a hydrogen stream and a humid CO2 stream that can readily be liquefied. Moreover, protonic conductors such as doped BaCeO3 and BaZrxCe1-xO3 can be employed as solid oxide fuel cell (SOFC) electrolyte operating at intermediate temperatures as low as 500C. In contrast with oxygen-anion conducting SOFC, the great advantage of protonic SOFCs is the full fuel-utilization operation without affecting the cell performance, when employing pure hydrogen as fuel. For these purposes, thin electrolyte layers should be obtained preferably over porous substrates with good electronic conductivity. In this contribution different fabrication methods will be outlined, considering the different technologies and the alternatives to prepare thin membranes or electrolytes without passing through very high temperature (1600C) treatments, which typically lead to metals evaporation problems, support densification or degradation and expensive manufacture. Furthermore, manufacture methods, electrochemical performance and operation modus of protonic SOFC will be review and thoroughly compared with state-of-the-art SOFC (YSZ- or CGO-based electrolytes).
9:45 AM - **AA1.2
Non-Perovskite-Structured High-Temperature Proton and Mixed Proton-Electron Conductors.
Reidar Haugsrud 1 , Truls Norby 1 Show Abstract
1 Chemistry, Centre for Materials Science and Nanotechnology, University of Oslo, Oslo Norway
10:15 AM - AA1.3
Proton Transfer Mechanism in LaPO4.
Rong Yu 1 , Lutgard De Jonghe 1 2 Show Abstract
1 , Lawrence Berkeley National Lab, Berkeley, California, United States, 2 , University of California, Berkeley, California, United States
10:30 AM - AA1.4
Proton Diffusion in Hydrated Acceptor-Doped Barium Zirconate.
Dirk Wilmer 1 , Klaus-Dieter Kreuer 2 , Tilo Seydel 3 Show Abstract
1 Institute of Physical Chemistry, Münster University, Münster Germany, 2 , Max-Planck-Institute for Solid State Research, Stuttgart Germany, 3 , Institut Laue-Langevin, Grenoble France
Acceptor-doped perovskites incorporate water by dissociative absorption. Owing to the mobility of oxygen vacancies and protonic defects, these materials are ionic conductors. If such a material is fully hydrated, the transference number of the protonic defects is close to unity.For use in electrochemical devices such as solid oxide fuel cells (where reducing the operating temperature is a key objective), high proton conductivity has to be accompanied by reasonable thermodynamics phase stability. In this respect, acceptor-doped BaZrO3 exhibits promising properties .Despite its significantly higher ionic radius when compared to Zr4+, Y3+ turns out to be optimal as an acceptor-dopant for BaZrO3. For temperatures below 700 °C, the observed proton conductivities clearly exceed the oxide ion conductivites of the best oxide ion conductors.We performed incoherent quasielastic neutron scattering measurements on Y-doped and hydrated BaZrO3 in order to study the proton diffusion in this material. Key questions to be addressed are i) how does the proton conduction mechanism look like and ii) does the dopant play the role of a trap for the proton , or are the protonic defects more or less delocalized.Our spectra obtained at the backscattering spectrometer IN16 (ILL Grenoble) exhibited quasielastic broadening at all temperatures (473 K to 673 K) studied. Model-free fitting using two Lorentzians results in good agreement with the data. As expected, a simple description of proton diffusion in terms of the Chudley-Elliott model (random walk on a Bravais lattice) does not yield satisfactory results. The observed scattering with two Lorentzians exhibiting a characteristic dependence of linewidths and weights on scattering vector Q suggest the use of the two-state model [2,4] which describes the protons alternating between a state of relatively free diffusion and situations where they are trapped in the vicinity of a lattice defect, viz., the dopant heterovalent metal ion. Simultanous fitting of the two-state model to all spectra taken at a single temperature yields good agreement with the experimental data. The parameters, however, especially the trapping and escape rates, do not show the expected temperature dependence, whereas the mean jump distance obtained from the fit (3.3 to 4 Å) compares favorably with typical proton intersite distances. Given that the two-state model cannot give full account of all our experimental findings, we shall present an extended model description in our contribution. W. Münch, K.-D. Kreuer, G. Seifert, J. Maier, Solid State Ionics 137-137 (2000) 183. Ch. Karmonik, R. Hempelmann, Th. Matzke, T. Springer, Z. Naturforsch. 50a (1995) 539. K.-D. Kreuer, St. Adams, W. Münch, A. Fuchs, U. Klock, J. Maier, Solid State Ionics 145 (2001) 295. D. Richter, T. Springer, Phys. Rev. B 18 (1978) 126.
10:45 AM - AA1.5
Synthesis and Characterization of Perovskite-Type Oxide Ceramic Based on BaCexY1-xO3 and BaZrxY1-xO3 for Solid Oxide Fuel Cell (SOFCs).
Alessandra D'Epifanio 1 , Emiliana Fabbri 1 , Enrico Traversa 1 , Silvia Licoccia 1 Show Abstract
1 , university of Rome Tor Vergata, Rome Italy
11:30 AM - **AA1.6
Study on the Perovskite-type Oxide Cathodes in Proton-conducting SOFC.
Hidenori Yahiro 1 Show Abstract
1 Department of Materials Science and Biotechnology, Ehime University, Matsuyama Japan
Metal ion-doped perovskite-type oxides such as SrCe0.95Yb0.05O3 and BaCe0.8Y0.2O3 showed high protonic conductivities and are of interest for applying to solid oxide fuel cell (SOFC). In the present study, the polarizations of the perovskite-type oxide cathodes were investigated in the H2-O2 fuel cell employing high proton-conducting electrolytes mentioned above. Among the perovskite-type oxides tested, La0.7Sr0.3FeO3 showed the lowest cathodic overpotential in the temperature range 773-973 K. The overpotential of La0.7Sr0.3FeO3 cathode was smaller than that of the sputtered platinum at 973 K. In addition, it was demonstrated that the cathodic overpotential of La0.7Sr0.3FeO3 was comparable to the anodic overpotential of the sputtered platinum, in contrast to the general consensus that the cathodic overpotential was much higher than the anodic one in H2-O2 SOFC using oxygen ion-conducting electrolytes. The dependences of partial pressures of both oxygen and water vapor on the cathodic overpotential of La0.7Sr0.3FeO3 suggested that the rate-determining step is either the reaction of surface oxygen atom with proton to yield water or the desorption of water produced on cathode. In order to reduce the electrolyte resistance, thin films of SrCe0.95Yb0.05O3 and BaCe0.8Y0.2O3 were prepared on the substrate made of the perovskite-type oxides. The spin-coating technique employed in the present study resulted in the preparation of the dense SrCe0.95Yb0.05O3 and BaCe0.8Y0.2O3 thin films on La0.7Sr0.3FeO3 oxide substrate. The electrical peoperties were studied for the resulting electrolyte/electrode devices.
12:00 PM - AA1.7
Pulsed Laser Deposition of Proton-conducting Yttrium-doped Barium Zirconate Films.
Joon Shim 1 , Turgut Gür 2 , Fritz Prinz 1 2 Show Abstract
1 Mechanical Engineering, Stanford University, Stanford, California, United States, 2 Material Science Engineering, Stanford University, Stanford, California, United States
12:15 PM - **AA1.8
Cell Performance Stability of HMFC using Ba(Ce1-xZrx)0.8Y0.2O3 Perovskite Type Proton Conductor as Electrolyte.
Masahiko Iijima 1 , Naoki Ito 1 , Shinichi Matsumoto 1 , Satoshi Iguchi 1 Show Abstract
1 , Toyota Motor Corporation, Susono, Shizuoka Japan
The use of an on-board reformer with an FC system is a very attractive option for FC vehicles because of its long cruising range and no need for new hydrogen infrastructure. PEMFC is not suitable with a reformer because the PEMFC and reformer have different operating temperatures. We have developed a new type of FC which shows high performance at intermediate temperatures. The essence of this new FC is an ultra-thin proton conductor electrolyte supported by a metal hydrogen membrane. We named it Hydrogen Membrane Fuel Cell and believe that it is suitable not only for vehicle applications but also for stationary applications.The HMFC using BaCe0.8Y0.2O3 as the electrolyte and pure Palladium as the substrate exhibits a high cell performance of 2.0 A/cm2 @0.5V, 600C and 1.5 A/cm2 @0.5V, 400C. BaCeO3 proton conducting ceramics have high proton conductivity, in contrast to its low chemical and mechanical stability.Using BaCeO3 as the HMFC electrolyte, there is the concern that cell performance stability may drop because the cathode side electrolyte is dissolved by hydrothermal reaction caused by H2O vapor generated at the cathode.The electrolyte can be changed from BaCeO3 to BaZrO3, which has higher chemical and mechanical stability. However, BaZrO3 exhibits lower proton conductivity than BaCeO3. In this study, we investigated the possibility of Ba(Ce1-xZrx)0.8YO3 (x=0-1) electrolytes, in which the B site of BaCe0.8Y0.2O3 perovskite ceramics is exchanged from Ce to Zr to produce a high resistance against hydrothermal dissolution and high proton conductivity. Each electrolyte thin film on Pd substrate was treated in 100% H2O at 400C for 200Hrs to evaluate the resistance against hydrothermal dissolution. After 200Hrs of H2O treatment, Ba(OH)2 was generated on the surface of BaCe0.8Y0.2O3 (BCY). On the other hand, after 1100Hrs of treatment, the generation of Ba(OH)2 on the surface of Ba(Ce0.5Zr0.5)0.8YO3 (BCZY) and BaZr0.8Y0.2O3 (BZY) was not confirmed. Consequently, the resistance against the hydrothermal dissolution was increased as a result of the displacement of the B site of BCY from Ce to Zr The cell performance of the HMFC using BCZY as electrolyte was the same level as the cell using BCY. In addition, the durability of the cell using BCZY as electrolyte was higher than the cell using BCY. After measuring the cell performance stability, an interface between the electrolyte and cathode was observed by TEM-EDX to confirm the absence of products by hydrothermal dissolution. The condensation of Ba was observed at the interface between the electrolyte and cathode of the BCY cell. It was inferred that the phenomenon occurred by the generation of Ba(OH)2. On the other hand, the condensation of Ba was not observed at the interface between the electrolyte and cathode of the BCZY cell. Consequently, the reason for improvement in the durability of the BCZY cell was inferred to be the prevention of hydrothermal dissolution of the electroly
12:45 PM - AA1.9
Solid Oxide Fuel Cells based on Proton Conducting Electrolytes.
U. (Balu) Balachandran 1 , Tae Lee 1 , Beihai Ma 1 , Stephen Dorris 1 Show Abstract
1 Energy Systems/Ceramics Section, Argonne National Laboratory, Argonne, Illinois, United States
AA2: Mixed Ionic (Protonic and Oxygen) Electronic Conductors
Monday PM, November 27, 2006
Republic B (Sheraton)
2:30 PM - **AA2.1
Mixed-Conducting Membranes for Hydrogen Production and Separation.
U. (Balu) Balachandran 1 , Beihai Ma 1 , Tae Lee 1 , Sun-Ju Song 1 , Ling Chen 1 , Stephen Dorris 1 Show Abstract
1 Energy Systems/Ceramics Section, Argonne National Laboratory, Argonne, Illinois, United States
Mixed-conducting oxides, possessing both ionic and electronic charge carriers, have found wide application in recent years in solid-state electrochemical devices that operate at high temperatures, e.g., solid-oxide fuel cells, batteries, and sensors. These materials also hold promise as dense ceramic membranes that separate gases such as oxygen and hydrogen from mixed-gas streams. We are developing Sr-Fe-Co oxide (SFC) as a membrane that selectively transports oxygen during partial oxidation of methane to syngas (mixture of CO and H2) because of SFC's high combined electronic and ionic conductivities. We have evaluated extruded tubes of SFC for conversion of methane to syngas in a reactor that was operated at ≈850°C. Methane conversion efficiencies were >90%, and some of the reactor tubes were operated for >1000 h. We are also developing dense proton-conducting oxides to separate pure hydrogen from product streams that are generated during methane reforming and coal gasification. Hydrogen selectivity in these membranes is nearly 100%, because they are free of interconnected porosity. Although most studies of hydrogen separation membranes have focused on proton-conducting oxides by themselves, we have developed cermet (i.e., ceramic-metal composite) membranes in which metal powder is mixed with these oxides in order to increase their hydrogen permeability. The hydrogen flux through these membranes has been measured in the temperature range of 500-900°C. In this talk, the development of oxygen and hydrogen transport membranes for hydrogen production and separation will be presented.Work supported by U.S. Department of Energy, Office of Fossil Energy, National Energy Technology Laboratory’s Hydrogen and Gasification Technologies Program, under Contract W-31-109-Eng-38.
3:00 PM - **AA2.2
Hydrogen Production with Mixed Protonic-Electronic Conducting Perovskite Membranes.
Eric Wachsman 1 , Heesung Yoon 1 Show Abstract
1 UF-DOE High Temperature Electrochemistry Center, University of Florida, Gainesville, Florida, United States
4:30 PM - AA2.3
Measuring of Partial Ionic Conductivity of Donor Doped SrTiO3.
Wenhua Huang 1 , Srikanth Gopalan 1 , Uday Pal 1 Show Abstract
1 Manufacturing Engineering, Boston University, Boston, Massachusetts, United States
A-site donor doped strontium titanate (SrTiO3) is a n-type material suggested for use as an anode in solid oxide fuel cells (SOFC) due to its high electrical conductivity in reducing atmosphere. Its defect structure and electrical properties have been studied extensively. However, its partial ionic conductivity has not been accurately measured. The available ionic conductivity data is obtained by curve fitting the total conductivity data to a defect structure model based on some simplified assumptions. In this paper, the partial ionic conductivity of donor doped strontium titanate has been directly measured by blocking the electronic current and the data is reported as a function of oxygen partial pressure over a temperature range of 700 oC to 850 oC.
4:45 PM - AA2.4
Oxygen Permeation and Hydrogen Generation Using MIEC Membranes.
Hengdong Cui 1 , Srikanth Gopalan 1 , Annamalai Karthikeyan 1 , Uday Pal 1 Show Abstract
1 Manufacturing Engineering, Boston University, Brookline, Massachusetts, United States
Porous mixed ionic and electronic conducting (MIEC) oxides that conduct both ions (H+, O2-, etc) and electrons (or holes) are used as electrode materials in battery and fuel cell technology. Dense MIEC membranes are also recently receiving increasing attention due to their potential application as gas separation membranes to separate oxygen from air. We have been studying a new process that utilizes oxygen ion and electron conducting MIECs for generating and separating hydrogen from steam. This research aims at exploring new routes for high-purity hydrogen production for use in fuel cells and hydrogen-based IC engines. The MIEC membrane separation process involves steam dissociation on the steam-rich side of the membrane (feed side). The oxygen ions formed as a result of steam dissociation are transported across the membrane in a coupled transport process with electrons being transported in the opposite direction. Upon reaching the methane side of the membrane (permeate side) the oxygen ion reacts with the methane to form products of combustion such as carbon monoxide, carbon dioxide and water vapor and releasing two electrons. This process results in hydrogen production at the feed side. The oxygen partial pressure gradient is the driving force for this process. Membrane requirements for such process are (i) high ambipolar conductivity characterized by high chemical diffusion rates of oxygen, (ii) stability under the prevailing conditions of low oxygen partial pressure and high water content and (iii) high surface reaction rates.A new dual-phase composite mixed ionic and electronic conducting (MIEC) membrane system comprising of rare-earth doped ceria with high oxygen ion conductivity and donor-doped strontium titanate with high electronic conductivity has been developed. In this work, the oxygen chemical diffusion coefficient and the oxygen surface exchange coefficient of the dual-phase materials, two parameters which control the eventual rate of oxygen transport across the membrane have been measured as a function of oxygen partial pressure, using the electrical conductivity relaxation technique. We also present results of permeation experiments under oxygen partial pressure gradients representative of the methane assisted steam electrolysis process. Electrical conductivity relaxation and permeation experiments have been used as experimental tools to study the effect of electrocatalysts on oxygen transport through such membranes.
5:00 PM - AA2.5
Mixed Conductivity and Oxygen Permeability of(BaxSr1-x)0.98Fe1-yMyO3-δ (x=0.1-0.3, y=0.1-0.4 and M=Ga, Al).
Chun yong Kang 1 , Hajime Kusaba 2 , Yasutake Teraoka 2 Show Abstract
1 Department of Molecular and Material Sciences, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Hukuoka, Japan, 2 Department of Molecular and Material Sciences, Faculty of Engineering Sciences, Kyushu University, Kasuga, Hukuoka, Japan
1. INTRODUCTIONOxygen-permeable mixed ionic-electronic conductors (MIECs) can be applied in catalytic membrane reactors. La-Sr-Co-Fe-O perovskites (LSCFs), which is the first-generation materials for the oxygen permeation membrane, show high oxygen permeability, but the lack of reduction tolerance makes it difficult to apply LSCFs for membrane reactors. Although materials having both oxygen permeability and reduction tolerance have been reported such as SrFeCo0.5Ox, (La,Sr)(Ga,Fe)O3-δ and (Ca,Sr)(Ti,Fe)O3-δ, the development of more excellent materials is necessary to meet requirements in practical application. Recently, we have revealed that Ba-Sr-Fe-O perovskites (BSFs) show both relatively high oxygen permeability and reduction tolerance. In this study, the effect of partial substitution of Ga and Al for Fe in BSFs have been investigated with respect to electrical property, oxygen permeability and reduction tolerance. 2. EXPERIMENTAL Target materials in this study were (BaxSr1-x)0.98Fe1-yMyO3-δ (x=0.1-0.3, y=0.1-0.4), where M is Ga (BSFG) or Al (BSFA). Mixed aqueous solution of nitrates of Ba, Sr, Fe, Ga(Al) and malic acid was evaporated to dryness, and the residue was calcined at 350 oC for 2 h and then at 850 °C for 5 h. Sample powder was compressed into a disk by the successive pressing of uniaxial and isostatic methods, and the disk was sintered at 1200-1250 oC in air. Both surfaces of sintered disks were polished to reach 1.0 mm thicknesses. Crystal structure analysis was performed by XRD analysis. Electrical property was measured by the 4-point method and electrochemical cell technique. The oxygen permeability was measured with the air/He gradient of oxygen partial pressure between 900 and 600 oC with an interval of 50 oC. Concentration of oxygen permeated from the air to He sides was measured by TCD.3. RESULTS AND DISCUSSIONXRD investigation revealed that the solubility limits of Ga and Al were ca. 30 mol% and 20mol%, respectively, irrespective of the A-site composition (x=0.1-0.3). The cubic perovskite-type structure of BSFG and BSFA was maintained even after the reduction in 5%H2/95%N2 at 900 oC. All the materials synthesized were p-type semiconductor, and the total conductivity tended to decrease with increasing the Ga and Al contents. Ionic transference numbers (ti) of BSFs were between 0.37 and 0.41. The substitution with Al had little effect on ti, but that with Ga resulted in the increase in ti; for example, 0.51 (y=0.2) and 0.55(y=0.3). The oxygen permeability was little affected by the substitution with Ga and Al, and the permeation rate of BSFG and BSFA were ca.1.0-1.04(cm3 (STP) /cm2 min) at 900 oC. The present results have revealed that BSFG and BSFA are MIEC materials with excellent reduction tolerance.
5:15 PM - AA2.6
ITM Ceramic Membrane Technology to Produce Synthesis Gas.
Christopher Miller 1 , Michael Carolan 1 , Christopher Chen 1 , Eric Minford 1 , James Steppan 2 , William Waldron 1 Show Abstract
1 , Air Products and Chemicals, Inc., Allentown, Pennsylvania, United States, 2 , Ceramatec, Inc., Salt Lake City, Utah, United States
The ITM Syngas Team, led by Air Products and including Chevron, Ceramatec, and other partners, in collaboration with the U.S. Department of Energy, is developing Ion Transport Membrane (ITM) technology for the production of synthesis gas, a mixture of hydrogen and carbon monoxide. The ITM Syngas process is a breakthrough technology that combines air separation and high-temperature synthesis gas generation processes into a single ceramic membrane reactor, with significant savings in the capital cost of synthesis gas production. Because synthesis gas is a feedstock for a range of different processes, ITM Syngas represents a technology platform that has numerous applications, such as hydrogen, clean fuels and chemicals. ITM ceramic membranes are fabricated from non-porous, mixed-metal oxides and operate with exceptionally high oxygen flux and selectivity when exposed to an oxygen chemical potential gradient at high temperatures. Oxygen from low-pressure air permeates, as oxygen ions, through the ceramic membrane and is consumed through chemical reactions, thus creating the chemical driving force for the transport of oxygen ions across the membrane at high rates. This oxygen then reacts with high-pressure natural gas in a partial oxidation process to produce synthesis gas. Significant advances have been made in developing and scaling up the ITM Syngas technology. This paper describes the development of commercial-size ceramic membranes and the ITM Syngas reactor system. Recent laboratory and pilot unit test results will also be discussed.
5:30 PM - AA2.7
Characterization of (La0.9Sr0.1)0.95Cr0.85Mg0.1Ni0.05O3 Perovskite Ceramics for a Perovskite Related Membrane Reactor.
Rachel Rosten 1 , Mattew Swanson 1 , Nina Orlovskaya 1 Show Abstract
1 Materials Science and Engineering, Michigan Technological University, Houghton, Michigan, United States
AA3: Poster Session: Fuel Cells
Monday PM, November 27, 2006
Exhibition Hall D (Hynes)
9:00 PM - AA3.1
Sintering and Properties of Nano-porous Doped Ceria Synthesized via Direct Condensation Method.
Vincenzo Esposito 1 , Silvia Licoccia 1 , Enrico Traversa 1 Show Abstract
1 , Università di Roma Tor Vergata, Rome Italy
9:00 PM - AA3.10
Double Perovskite Cathodes for Intermediate Temperature Solid Oxide Fuel Cells.
Wenquan Gong 1 , Guntae Kim 1 , Susan Wang 1 , Manoj Yadav 1 , Allan Jacobson 1 Show Abstract
1 Chemistry, University of Houston, Houston, Texas, United States
The oxygen-deficient double perovskite PrBaCo2O5+x (PBCO) was synthesized and evaluated as a promising cathode material for intermediate temperature solid oxide fuel cells (SOFCs) based on a gadolinium doped ceria (CGO) electrolyte. The electrical conductivity relaxation (ECR) and oxygen-isotope exchange and depth profiling (IEDP) measurements revealed that PBCO had high electronic conductivity and rapid oxygen ion diffusion and surface exchange kinetics. PBCO also showed good compatibility with CGO electrolyte material. Moreover, AC impedance measurements of the symmetrical cells of PBCO/CGO composite cathodes on a CGO electrolyte indicated excellent area specific resistance (ASR) performance. The electrochemical performance of PBCO/CGO composite cathodes in CGO electrolyte- supported and nickel/CGO composite anode- supported single cells were subsequently studied at 500~700 C with humidified (3% H2O) hydrogen as fuel and air as oxidant.
9:00 PM - AA3.11
A Study of SOFC Cathode Materials Under Low Oxygen Partial Pressures.
Jeffrey White 1 , Scott Misture 1 Show Abstract
1 , Alfred University, Alfred, New York, United States
The SOFC cathode materials LaxSr1-xCoO3-δ (x = 0.2, 0.3, and 0.4) and La0.3Sr0.7FeO3-δ were studied at temperatures up to 1173K with oxygen partial pressures from 1 atm to 3 x 10-4 atm, as well as under 4% H2. In-situ high temperature X-ray diffraction was used to monitor the phase evolution as a function of time over multiple heating/cooling cycles. All four compositions phase separated on heating to form LSMe, SrLaMeO4 and MeO, (where Me = Fe or Co), but not necessarily during the first heating cycle. Diffraction data indicate that the reverse reaction caused by step changes to higher PO2 cause exceedingly rapid re-solution of SrLaMeO4 and MeO to form X-ray phase pure LSC and LSF. A new phenomenon was observed that is characterized by a slow drift in unit cell volume over the course of at least 24 hours after stepwise changes in the oxygen partial pressure. The implications of the phase stability and reaction rates on applications in the fuel cell environment will be discussed for LSC, LSF, and the newer cathode materials such as Ba0.5Sr0.5Co0.8Fe0.2O3-δ.
9:00 PM - AA3.12
High-Performance and Stable Intermediate Temperature Cathodes for Anode Supported Planar Solid Oxide Fuel Cells.
Peter Zink 1 , Kyung Yoon 1 , Wenhua Huang 1 , Guosheng Ye 1 , Srikanth Gopalan 1 , Uday Pal 1 , Donald Seccombe 2 Show Abstract
1 Manufacturing Engineering, Boston University, Boston, Massachusetts, United States, 2 , BTU International, North Billerica, Massachusetts, United States
Sintering characteristics of scandia-stabilized zirconia (ScSZ) and ytrria-stabilized zirconia (YSZ) were investigated with and without sintering aids at temperatures between 1250 and 1335°C for application as an electrolyte material in solid oxide fuel cells. In this temperature range, with sintering aids, both materials densified to over 96% theoretical density. Four probe DC conductivity tests were performed in air at 50 degree intervals between 700 and 900°C. The conductivity tests demonstrated the conductivity of ScSZ to be approximately 2.5 times that of YSZ. A one-step co-firing process was employed to manufacture complete SOFCs. SOFCs made with the ScSZ or YSZ electrolyte and Ni-stabilized zirconia cermet anode and lanthanum manganite-based cathode materials showed virtually no difference in electrical performance at intermediate temperatures (600-800C). Analytical investigation indicated that the limits on cell performance were not due to the electrolyte, but more likely due to polarization resistance in the cathode. To lower the polarization resistance of the cathode, A-site-deficient-acceptor-doped lanthanum ferrite and lanthanum cobaltite cathode materials with various dopants were synthesized for further investigation. Ongoing experiments include reactivity studies, as well as partial conductivity, dilatometry, and impedance spectroscopy measurements. Based on these measurements, optimum cathode compositions are being selected for fabricating and electrochemically evaluating complete Ni-stabilized zirconia-anode-supported SOFCs with stabilized zirconia electrolyte at intermediate temperatures.
9:00 PM - AA3.13
Nafion® Composite Membrane Modified by Phosphoric Acid-Functionalized 3-APTES.
Jung-Soo Kang 1 , Young-Taek Kim 1 , Jinhwa Piao 2 , Hee-Woo Rhee 1 Show Abstract
1 Chemical and Biomolecular Engineering, Sogang University, Seoul Korea (the Republic of), 2 chemical engineering, Harbin Institute of Technology, Harbin China
9:00 PM - AA3.14
Hybrid Inorganic-organic Polymer Composites for Polymer-electrolyte Membrane Fuel Cells.
Andrea Ambrosini 1 , Cy Fujimoto 1 , Zachariah Harris 1 Show Abstract
1 Chemical and Biological Systems, Sandia National Laboratories, Albuquerque, New Mexico, United States
9:00 PM - AA3.15
Carbon Nanotubes Doped Active Direct Methanol Fuel Cell Cable.
Jaewu Choi 1 , Yuan Xu 1 , Jayasri Narayanamoorthy 1 Show Abstract
1 , wayne state university, Detroit, Michigan, United States
9:00 PM - AA3.2
Rare Earth Stabilized Zirconia – Energetics and Phase Stability.
Petra Simoncic 1 , Alexandra Navrotsky 1 Show Abstract
1 Thermochemistry Facility, UC Davis, Davis, California, United States
9:00 PM - AA3.3
A Comparative Study Of Electrical And Electrochemical Transport In Nanoscale Oxide-Ion Conductors.
Annamalai Karthikeyan 1 , Shriram Ramanathan 1 Show Abstract
1 Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Space charge layers and their effects on electrical properties at nanoscales have been well studied in semiconductors and other dielectric materials. An analogous study of ionic conductors at nanoscale is largely unexplored. The field of nanoionics has a high potential for miniaturization of electrochemical devices and fundamental understanding of ionic migration properties. Of the various types of ionic conductors, oxide ion conductors and mixed oxide and electronic conductors are key components in energy conversion devices such as solid oxide fuel cells. Study of transport properties of these materials at nano-scale will provide useful information on the effect of space charge layers at the substrate-film interface and interactions between oxygen vacancies in thin film oxide sytems. Systematic electrical conductivity studies of nanoscale oxide conductors such as lanthanum-doped zirconia, gadolinium-doped ceria, lanthanum-doped ceria, and doped perovskites are being carried out as function of film thickness in the range of few nm to 200nm. The measurements have been performed as a function of temperature typically ranging from 700°C to about 950°C and also as a function of oxygen partial pressure. Theoretical calculations are being performed on space charge potentials as a function of doping level, temperatures and defect association energies by numerically solving Poisson’s equation. Dielectric and conductivity measurements at high temperatures using parallel plate geometry are also being carried out to study transport properties across the film interfaces. These calculated values and experimental observation are being analyzed using dielectric and conductivity relaxation profiles as a function of frequency. This poster will report the experimental observation of various oxide conductors at nano-scales and their analysis based on conductivity relaxation profiles and space charge potential calculations. Our initial results indicate that space charge effects play a significant role when the sample thickness is less than 200nm.
9:00 PM - AA3.4
Characterization of Sc2O3–CeO2-ZrO2 Powders as a Promising Electrolyte Ceramics for Lower Temperature Solid Oxide Fuel Cells.
Alexandra Zevalkink 1 , Allen Hunter 1 , Nina Orlovskaya 1 Show Abstract
1 Materials Science and Engineering, Michigan Technological University, Houghton, Michigan, United States
9:00 PM - AA3.5
Nano-composite Porous Pt/YSZ Thin Films for Micro-SOFC Electrodes.
Woo Sik Kim 1 , WooChul Jung 1 , Avner Rothschild 1 , Joshua Hertz 1 , Harry Tuller 1 Show Abstract
1 Material Science and Technology, MIT, Cambridge, Massachusetts, United States
Nano-porous electrodes are attractive for applications in solid state ionic devices such as fuel cells and chemical sensors. The conventional methods for fabricating such electrodes are typically based on wet processes such as electroplating and sol-gel techniques. In this work we report on novel methods to fabricate nano-composite porous thin film electrodes using physical vapor deposition (PVD) techniques. This approach is particularly attractive for micro-SOFCs since it enables fabricating the entire SOFC stack (anode/electrolyte/cathode) in the sputtering machine without breaking vacuum.The challenge in sputtered electrodes lies in making them porous in order to enhance their electrochemical performance by increasing the TPB length and gas permeability through the electrode. We developed a unique method for sputtering nano-composite porous Pt/YSZ thin film electrodes. We examined the electrode microstructure as function of deposition conditions and observed the electrochemical performance of porous electrodes compared with dense electrodes. The relationship between the porosity and electrochemical properties as well as nano-structure of the porous electrodes will be discussed in the presentation.
9:00 PM - AA3.6
Design of Anodes for IT SOFC: Effect of Complex Oxide Promoters and Pd on Activity and Stability in Methane Steam Reforming of Ni/YSZ (ScSZ) Cermets.
Vladislav Sadykov 1 , Natalia Mezentseva 1 , Rimma Bunina 1 , Galina Alikina 1 , Anton Lukashevich 1 , Vladimir Rogov 1 , Ella Moroz 1 , Vladimir Zaikovskii 1 , Oleg Bobrenok 2 , Alevtina Smirnova 3 , John Irvine 5 , Oleksandr Vasylyev 4 Show Abstract
1 , Boreskov Institute of Catalysis SB RAS, Novosibirsk Russian Federation, 2 , Institute of Thermophysics SB RAS, Novosibirsk Russian Federation, 3 Global Fuel Cells Center, University of Connecticut, Storrs, Connecticut, United States, 5 School of Chemistry, University of St Andrews, Fife United Kingdom, 4 , Institute for Problems of Materials Science, Kiev Ukraine
9:00 PM - AA3.7
Gd0.2Ce0.8O2-based Composite Ceramics for Lower Temperatures SOFC Cathodes.
Nina Orlovskaya 1 , Rachel Rosten 1 , Mattew Swanson 1 , Peter Moran 1 , Natee Tangtrakam 1 , Jakob Kuebler 2 Show Abstract
1 Materials Science and Engineering, Michigan Technological University, Houghton, Michigan, United States, 2 High Performance Ceramics, EMPA, Duebendorf Switzerland
9:00 PM - AA3.8
Electrochemical Properties of Nanocrystalline Y2-XPrxRu2O7 Pyrochlore for Electrodic Application in IT-SOFCS.
Chiara Abate 1 2 , Enrico Traversa 1 , Eric Wachsman 2 Show Abstract
1 , University of Rome Tor Vergata, Rome Italy, 2 , University of Florida, Gainesville, Florida, United States
Ru pyrochlore oxides have been evaluated as possible candidates for SOFCs’ cathodic applications because they showed excellent electro catalytic behaviour for oxygen reduction and good electrical conductivity. In this work, nanocrystalline powders of Praseodymium doped Yttrium Ruthenium Oxide Y2-xPrxRu2O7 were prepared by a co-precipitation method. Pr was chosen as the A-site dopant in order to increase the electrical conductivity of Y2Ru2O7. Phase and morphology were studied by XRD and FE-SEM, which showed single pyrochlore phase and particle size of about 100 nm.The electrical conductivity of Y2-xPrxRu2O7 was measured as function of praseodymium content, oxygen partial pressure and temperature by d.c. 4-probe method and a.c. 2-probe method. The temperature dependence of the electrical conductivity has been investigated for a range of 5-25% of dopant elements, in 473-1073K temperature range. The values of conductivity increased with increasing dopant concentration and holes are the main charge carries.The isothermal electrical conductivity of Y2-xPrxRu2O7 has been investigated at 800°C at different oxygen partial pressure in order to understand the Praseodymium function into the pyrochlore structure. The experimental results are presented and discussed.
9:00 PM - AA3.9
Structural Characterization and Chemical Stability of Nanoscale La0.5Sr0.5CoO3-δ Cathodes on YSZ.
Levin Dieterle 1 , Dagmar Gerthsen 1 , Christoph Peters 2 , André Weber 2 , Uwe Guntow 3 Show Abstract
1 Laboratorium für Elektronenenmikroskopie, Universität Karlsruhe, Karlsruhe Germany, 2 Institut für Werkstoffe der Elektrotechnik, Universität Karlsruhe, Karlsruhe Germany, 3 , Fraunhofer-Institut für Silicatforschung, Würzburg Germany
There is a considerable interest in low-to-medium temperature (500-800 °C) solid oxide fuel cells (SOFCs), because cells operating at reduced working temperatures exhibit less problems with thermal activated degradation. In this temperature range a new design of the cathode/electrolyte interface is necessary to compensate the lower diffusivity of oxygen ions and the reduced catalytic activity. One concept for the improvement of the cathode performance is the use of a nanocrystalline cathode material with mixed (ionic and electronic) conductivity like La0.5Sr0.5CoO3-δ.Nanocrystalline La0.5Sr0.5CoO3-δ layers were deposited on 3.5 mol% Yttria stabilized Zirconia (YSZ) electrolytes by a sol-gel process, a fabrication technique that is cheap and suitable for industrial mass production compared to other techniques like pulsed laser deposition (PLD). The sol was deposited by spin-coating and treated by a rapid thermal annealing (RTA) process to obtain a perovskite type thin film. A final annealing process was performed at temperatures of 700 °C and 1000 °C for 8 h to evaluate the stability of the thin film at elevated temperatures.Microstructural surface characterization of the deposited layers was carried out by scanning electron microscopy (SEM). It could be shown that the grain size distribution can be controlled by the annealing temperatures. However, the chemical inhomogeneity, which increases with increasing annealing temperature, could be visualized by SEM micrographs and verified by energy dispersive X-Ray spectroscopy (EDS). Several secondary phases like CoO and SrZrO3 could be identified by means of transmission electron microscopy (TEM) using electron diffraction, electron energy-loss spectroscopy (EELS) and TEM-EDS in the cathode layer. The distribution of the chemical elements could be directly imaged by electron spectroscopic imaging (ESI) in cross-section TEM samples. The analysis shows that a reaction between Sr and Zr takes place at cathode/electrolyte interface which leads to the formation of a SrZrO3 reaction layer. The thickness of this layer increases with increasing annealing temperatures.In addition to the different secondary phases electron-beam induced superstructures could be observed in the lanthan-strontium-cobaltate. They exhibit a doubling or tripling of the lattice constant depending on the local Sr stoichiometry. The ordered domains are rotated against each other by 90° and their size depends on the local electron radiation dose.The presence of secondary phases and the resulting chemical inhomogeneity of the lanthan-strontium-cobaltate shows that the thin film is not stable on a YSZ electrolyte at elevated temperatures. To suppress the reaction between LSC and the YSZ electrolyte a diffusion barrier layer was applied between cathode and electrolyte. First investigations of a Gd-doped CeO2 (GCO) barrier layer are promising and show that the formation of secondary phases can be strongly suppressed.
Timothy Armstrong Oak Ridge National Laboratory
Christian Masquelier University of Picardie-CNRS
Yoshihiko Sadaoka Ehime University
Enrico Traversa University of Rome Tor Vergata
AA4: Modelling/Fundamental Studies
Tuesday AM, November 28, 2006
Republic B (Sheraton)
9:30 AM - **AA4.1
From Perovskites to Apatites: Atomic-Scale Studies of Complex Oxide Materials for Fuel Cells.
M.Saiful Islam 1 Show Abstract
1 Chemistry, University of Bath, Bath United Kingdom
10:00 AM - AA4.2
The Effect of Point Defects on the Physical properties of Acceptor-Doped Ceria.
Keith Duncan 1 , Eric Wachsman 1 Show Abstract
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Point defects can have a significant effect on the physical properties of ceramics. This is particularly true for ceramics used in thermal barrier coatings, electrochromic devices, sensors, gas separation membranes and solid oxide fuel cells. Consequently, the development of ceramics for these applications requires an understanding of the effects that point defects have on their material properties. Moreover, it is important to be able to predict the defect population as a function of operating conditions, e.g., oxygen partial pressure, PO2. An analytical approach is developed herein to explore the relationship between point defect populations and material properties in ceramics. For clarity, model development is constrained to crystalline oxides with the fluorite structure, but is applicable to other crystalline ceramics.The introduction of point defects into a crystal lattice results in expansion or contraction [1, 2]. This is called chemical expansion, αchem. Measurement of the lattice constant, a, reveals that, for fluorite-structured oxides, a is linearly dependent on the dopant concentration, ca, and the vacancy concentration, cv, thusa = a0 + βcv + β'caorαchem = (a - a0 - β'ca)/ a0 = βcv/a0 (1)where a0 is the lattice constant in the absence of defects; and the constant β and β' are the increase in lattice parameter due to defect formation from external equilibria and doping, respectively.The bond energy, U, between atoms in a crystal, may be approximated byU = A/rn – B/rm (2)where r is the interatomic distance, A and B are empirically determined constants for the repulsive and attractive components of the ionic bond energy in a perfect (defect free) crystal, respectively, n is the Born exponent and m arises from Coulombic forces. By setting the first derivative of Eq. (2) to zero and evaluating it at r = req, the equilibrium interatomic distance (for the fluorite structure, req = 1.732a/4, ), the elastic modulus, E, may be estimated from the 2nd derivative of U, with the resultE = E0(1 + βcv/a0)-n-3 (3)where E0 is the elastic modulus of a perfect crystal. Eq. (3) provides the functional dependence of the elastic modulus on point defect concentration, predicting that the elastic modulus decreases as the oxygen lattice vacancy concentration increases. Good fits to experimental data were obtained for both chemical expansion and elastic modulus, using β ≈ 1.73 × 10-3 nm [2, 5], ca ≈ 1.25 nm-3 and n = 9.
10:15 AM - AA4.3
Ionic Conductivity and Red-ox Properties of Ceria Solid Solutions from First-principles Calculations.
David Andersson 1 , Sergei Simak 2 , Natalia Skorodumova 3 , Igor Abrikosov 2 , Börje Johansson 1 3 Show Abstract
1 Department of Materials Science & Engineering, Royal Institute of Technology, Stockholm Sweden, 2 Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping Sweden, 3 Department of Physics, Uppsala University, Uppsala Sweden
10:30 AM - AA4.4
Interfacial Structure and Point Defects in Ceria/Zirconia Superlattices.
Michael Dyer 1 , Anter El-Azab 1 2 , Fei Gao 3 Show Abstract
1 Mechanical Engineering, Florida State University, Tallahassee, Florida, United States, 2 School of Computational Science, Florida State University, Tallahassee, Florida, United States, 3 Fundamental Science Directorate, Pacific Northwest National Laboratory, Richland, Washington, United States
Ceria and zirconia have the ability to conduct oxygen ions rapidly, which makes them excellent candidates for use as electrolytes in devices such as oxygen sensors and solid oxide fuel cells. Ionic conductivity in these materials is limited by the oxygen vacancy diffusivity and concentration, which can be increased by doping. Recently, it has been found that the in-plane conductivity of ceria/zirconia superlattices with nanoscale layer thickness exceeds those of the individual materials. Although the exact mechanisms responsible for this conductivity increase are yet to be pinned down, they can be generally attributed to the role of interfaces, epitaxial strain and interfacial dislocations, which impact the point defect energetics in these materials. We report the results of a molecular dynamics simulation study aiming to understand the interfacial structure in ceria/zirconia superlattices and the impact of the interfaces on the energies of oxygen vacancy formation and Gd ion substitution in ceria and zirconia layers of the superlattice structure. It is found that the semi-coherent interface is characterized by misfit dislocations, paired at approximately 3-4 nm, with stacking-fault-like region in between, which agrees with the TEM observations. It is also found that the vacancy formation energy and the Gd substitution energy vary as a function of distance from the interface in the individual layers, and that these energies depend on the layer thickness. In addition, the simulations showed that the defect energy variations across the thickness of the ceria and zirconia layers are consistent with the XPS data for composition profile in the superlattice structure. Finally, in the semi-coherent superlattice structure, the formation energy of oxygen vacancies and the Gd substitution energy are found to depend on the position of these defects relative to the interfacial dislocation core. In particular, the oxygen vacancy formation energy is found to be negative close to the dislocation core, indicating that vacancy concentration will increase in such regions allowing for high conduction parallel to the interface.
10:45 AM - AA4.5
Chemical Stresses and Diffusion in Nonstochiometric Oxide Thin Films.
Sunil Mandowara 1 , Brian Sheldon 1 , Sidharth Bhatia 1 , Tai Hee Eun 1 , Janet Rankin 1 Show Abstract
1 , Brown University, Providence, Rhode Island, United States
11:30 AM - **AA4.6
Ab Initio Study of Dopant-Oxygen-Vacancy Coupling in Oxygen Conducting Perovskites.
Dane Morgan 1 Show Abstract
1 , Univ. of Wisconsin - Madison, Madison, Wisconsin, United States
High oxygen conductivity ceramics are important for a wide range of applications, including solid oxide fuel cell electrolytes and catalysts, solid-state oxygen sensors, solid-state oxygen separation systems, and ceramic membrane conversion systems. There are a number of fast ion-conducting perovskites, and their wide range of possible dopants make them a very promising structural family for developing optimized materials. Of particular interest are perovskites with stoichiometry A2B2O5 (e.g., Ba2In2O5), where there is a high concentration of vacancies (1/6 of the oxygen sites) available to mediate transport. The vacancies are so prevalent in these systems that they interact strongly, creating significant short- and long-range-order effects (e.g., the vacancy ordered Brownmillerite phase). The chemical ordering strongly influences the oxygen transport and can be tuned through different dopants. However, detailed understanding of the coupling between the dopants and chemical ordering is still lacking. We will discuss ab initio studies of dopant-oxygen-vacancy coupling in doped Ba2In2O5 materials. We construct an ab initio based thermodynamic model with the cluster expansion method, which makes it possible to model the finite temperature behavior of the oxygen-vacancy ordering (e.g., order-disorder transition temperatures, oxygen site preferences, and short-range-order). Finally, we will discuss how these thermodynamic effects can couple to oxygen conductivity.
12:00 PM - AA4.7
Simulations of Anisotropic Oxygen Ion Conductivity in Layered Perovskite Type Materials.
Antony Cleave 1 , Mark Levy 1 , John Kilner 1 , Stephen Skinner 1 , Robin Grimes 1 Show Abstract
1 Materials Department, Imperial College, London United Kingdom
The current impetus for the development of alternative forms of power generation has led to the rapid development of devices such as solid oxide fuel cells (SOFC’s). Despite significant progress, many problems still exit. The high temperatures at which the cells must operate to achieve sufficiently high electrical conductivities pose serious problems due to mechanical problems such as thermal fatigue and limits on the choice of materials for the cell components. Consequently, there is an emphasis towards the development of materials with high conductivities at lower temperatures. To this end, much current work is given to perovskite related, mixed conducting materials for next generation cathodes. Of this class of material, one of the most studied is La2NiO4+δ. This material consists of alternating layers of perovskite-like LaNiO3 and rocksalt-like LaO. The excess oxygen is usually considered to be accommodated as an interplanar interstitial species that has led to interest in a possible oxygen interstitial conductivity mechanism. Given the layer structure, the anisotropy has been closely studied. Here, the aim of this work is to use atomistic simulation to predict the lowest energy path for oxygen migration through this system assuming both interstitial and vacancy mechanisms, parallel and perpendicular to the layer planes.As a first step, the sites for single oxygen interstitial ions were identified; both O2- and O- ions were considered. Subsequently defect cluster formation was considered. Results will be discussed in the light of available experimental data.
12:15 PM - AA4.8
The Unusual Role of Electronic Entropy in the Defect Equilibrium and Phase Diagram of LixFePO4.
Fei Zhou 1 , Thomas Maxisch 1 , Gerbrand Ceder 1 Show Abstract
1 , MIT, Cambridge, Massachusetts, United States
12:30 PM - AA4.9
First Principles Study on the Coupling of Sodium Ordering and Co3+ / Co4+ Charge Ordering in P2-NaxCoO2.
Yoyo Hinuma 1 , Ying Meng 1 , Gerbrand Ceder 1 Show Abstract
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
The unusual electronic properties of NaxCoO2 are attracting considerable interest in recent years. At high sodium content, the system displays unusually strong thermoelectric effect and a low metallic resistance1. In addition, for low sodium content, the hydrated material shows superconducting behavior2.
NaxCoO2 is a mixed valence system with a fraction x Co4+ and (1- x) Co3+ ions. Mixed Co3+ / Co4+ systems tends to display rich physics as they are often close to spin transitions and metal insulator transitions, as has already been demonstrated in LixCoO23, 4. It is highly possible that there is ordering both in the Na/V sublattice and Co3+ / Co4+ sublattice, and that these ordering are coupled.
In this study, we analyze the coupling between the Na-vacancy and Co-charge ordering. Density Functional Theory (DFT) in the Generalized Gradient Approximation with Hubbard U correction (GGA+U) is combined with the coupled cluster expansion technique to study ordering in the 0.5 ≤ x ≤ 1 range. We have discovered a number of new ground states, and investigated in-plane ordering and stacking strategies in the lowest energy configurations. We will also discuss the key interactions that determine the ground states of the system, and which may be important for understanding the high thermopower of these mixed valence oxides.
1I. Terasaki, Y. Sasago, and K. Uchinokura, Physical Review B 56, 12685 (1997).
2K. Takada, H. Sakurai, E. Takayama-Muromachi, et al., Nature 422, 53 (2003).
3C. A. Marianetti, G. Kotliar, and G. Ceder, Nature Materials 3, 627 (2004).
4M. Ménétrier, I. Saadoune, S. Levasseur, et al., Journal of Materials Chemistry 9, 1135 (1999).
12:45 PM - AA4.10
Modeling of The Area Specific Resistance and Interpretation of Impedance Spectra of Composite Cathodes.
Martin Sogaard 1 , Mogens Mogensen 1 Show Abstract
1 , Risø National Laboratory, Roskilde Denmark
AA5/QQ2: Joint Session: Solid State Chemistry of Ionic Conductors
Tuesday PM, November 28, 2006
Grand Ballroom (Sheraton)
2:30 PM - **AA5.1/QQ2.1
Mesoporous Transition Metal Oxides for Energy Storage.
Feng Jiao 1 , Shaju Kuthanapillil 1 , Peter Bruce 1 Show Abstract
1 Chemisty, University of St Andrews, St Andrews United Kingdom
Mesoporous materials based on main group elements are well established; this is not the case for transition metal oxides, in part because their synthesis has proved more intractable. Yet mesoporous transition metal oxides can exhibit many unique and important properties leading to a diverse range of applications. The synthesis and characterisation of several ordered mesoporous transition metal oxides with highly crystalline walls, α-Fe2O3, γ-Fe2O3, Fe3O4 (inverse spinel), Mn3O4 (spinel), low temperature-LiCoO2, will be described as will the significance of such materials in enabling a step change in the performance of energy storage devices, vital to address the problem of global warming.The synthesis of mesoporous transition metal compounds is often limited to transition metals in oxidation states that are stable in solution. We have synthesised several of the above ordered mesoporous materials, e.g. Fe3O4 and Mn3O4, by reducing/oxidising other ordered mesoporous transition metal oxides, e.g. Fe2O3 and Mn2O3, while preserving the ordered mesostructures throughout, thus enabling access to new mesoporous transition metal compounds. LT - LiCoO2 was synthesised by reacting mesoporous Co3O4 with LiOH in the solid-state, converting the former to the low temperature polymorph of LiCoO2, with preservation of the ordered mesostructure and with a high level of crystallinity in the walls.The magnetic properties of crystalline mesoporous materials are distinct from those of the corresponding bulk phases and from nanoparticulate forms of the same material in which the nanoparticle diameter is comparable to the thickness of the walls. Data on the magnetic behaviour will be presented.LT-LiCoO2 is an intercalation host from which lithium may be removed and re-inserted. As a mesoporous material, when used as an electrode in key energy storage devices such as rechargeable lithium batteries, the electrolyte can flood the pores providing a high surface area in intimate contact with the electrode. Furthermore, the thin walls (typically 7 nm) provides short diffusion distances for Li+ and e– on intercalation/deintercalation. Both features lead to rapid intercalation processes and much greater reversibility than is the case for corresponding nanoparticulate LT-LiCoO2. The ordered mesostructure is preserved on repeated intercalation/deintercalation. Data on the superior properties of the mesoporous material as an energy storage electrode will be presented.
3:00 PM - AA5.2/QQ2.2
Nonstoichiometry of Vanadium (IV) Oxide.
Dilan Seneviratne 1 , Harry Tuller 1 Show Abstract
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
3:15 PM - AA5.3/QQ2.3
New Insights Into The Formation Of Organically Templated Vanadium Oxides.
Arunachalam Ramanan 1 2 , M Stanley Whittingham 2 Show Abstract
1 Chemistry, Indian Institute of Technology, Delhi, New Delhi , Delhi, India, 2 Chemistry and Materials Research Center, Binghamton University, Binghamton, New York, United States
3:30 PM - AA5.4/QQ2.4
Bio-controlled Synthesis of Nanostructured Vanadium Oxides.
Olivier Durupthy 1 , Axel Marchal 1 , Nathalie Steunou 1 , Thibaud Coradin 1 , Gervaise Mosser 1 , Jacques Livage 1 Show Abstract
1 Université Paris 6, Chimie de la Matière Condensée de Paris, Paris France
3:45 PM - AA5.5/QQ2.5
Exploring Ionic Conductivity Mechanisms in Interfaces and Nanoparticles Using Magic-angle Spinning Nuclear Magnetic Resonance (MAS NMR).
Stephen Boyd 1 , Clare Grey 1 Show Abstract
1 Chemistry, Stony Brook University, Stony Brook, New York, United States
Several systems, including solid oxide fuel cells (SOFC) and gas sensors, rely on fast, reliable ionic conductivity within particles and at interfaces. Consequently, much research has centered on finding new materials that can support fast ionic movement at a reasonable temperature and at understanding conduction mechanisms. Here, two systems were studied in an attempt to investigate interfacial and surface phenomena. First, a heterostructurual material consisting of thin, alternating layers of BaF2 and CaF2 deposited by molecular beam epitaxy (MBE) was investigated by using 19F MAS NMR. New resonances were observed, in addition to those due to BaF2 and CaF2, and the relaxation times of all these peaks were investigated as a function of temperature. Second, nanoparticles of BaF2, treated with the a super-Lewis acid, SbF5, were studied by NMR as a function of loading level. SbF5 treatment resulted in the creation of local environments with very short spin-lattice relaxation (T1) times, indicating enhanced ionic mobility. More detailed NMR experiments are currently in progress to correlate ionic mobility with local structure.We thank Prof. J. Maier for providing the heterostructure sample and for helpful discussions.
4:30 PM - **AA5.6/QQ2.6
Ionic and Mixed Conductors for Energy: Preparation and Properties.
Philippe Knauth 1 Show Abstract
1 MADIREL, University of Provence, Marseille France
5:00 PM - AA5.7/QQ2.7
Electrochemical Synthesis of Inorganic Films Containing Ordered Nanoporous Structures Using Interfacial Surfactant Templating.
Ellen Steinmiller 1 , Ryan Spray 1 , Matthew Yarger 1 , Nikhlendra Singh 1 , Kyoung-Shin Choi 1 Show Abstract
1 Department of Chemistry, Purdue University, West Lafayette, Indiana, United States
Porous electrodes have been the center of interest in the development of devices for use in energy production, catalysis, and sensing application. By providing an enhanced surface area per unit volume, porous structures can significantly improve the kinetics and mass transfer at the interfaces of electrodes, thus enhancing the efficiency of various chemical and electrochemical reactions. Creating electrodes with ordered nanoporous structures is of special interest because it not only increases surface areas enormously but also makes it possible to study the effect of specific nanostructural details (i.e. pore sizes and pore connections) on chemical and physical properties of the electrodes. In this presentation, we introduce an electrochemical strategy for producing inorganic nanoporous films by utilizing self-assembly of amphiphilic molecules at solid-liquid interfaces for electrodeposition. The spontaneous aggregation of amphiphiles at solid-liquid interfaces is a well-established phenomenon. Surface micelles form at concentrations well below the critical micelle concentration (cmc) because the surface forces increase the interfacial concentration of amphiphiles. The novelty of our approach lies in exploiting these phenomena for inorganic synthesis by combining it with electrodeposition. This can be achieved by using a working electrode for both the organic assemblies and inorganic deposition. By selecting surfactants with appropriate hydrophilic groups, the metal ions that need to be deposited can be strongly bound on the surface of surfactant micelles as counter ions, thereby forming stable organic-inorganic interfacial aggregates. When an electrical bias is applied to initiate the deposition process, the organization of these metal ions in the interfacial assemblies directly becomes the skeleton of the inorganic deposits, resulting in ordered inorganic nanostructures. In this presentation, we will explain the principles of our electrochemical interfacial surfactant templating method in detail and discuss synthesis and characterization of several oxide and hydroxide films (e.g. zinc oxide, tin oxide) containing various nanoporous structures.
5:15 PM - AA5.8/QQ2.8
Anisotropy in Layered Polymer-Clay Nanocomposite Electrolytes.
Jodie Lutkenhaus 1 , Paula Hammond 1 Show Abstract
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
5:30 PM - AA5.9/QQ2.9
The Effect of Na Content on the Electrical Properties of Polycrystalline Na0.7Ga4.7Ti0.3O8 (x~0.7).
Jake Amoroso 1 2 3 , Doreen Edwards 1 2 3 Show Abstract
1 , Alfred University, Alfred, New York, United States, 2 , New York State College of Cermaics, Alfred , New York, United States, 3 , Kazuo Inamori School of Engineering, Alfred , New York, United States
New Presenting AuthorTues 11/28AA5.9/QQ2.94:30 - 4:45 pmThe Effect of Na Content on the Electrical Properties of Polycrystalline. Doreen D. Edwards
5:45 PM - AA5.10/QQ2.10
New Developments in Fluoride and Oxyfluoride Structural Chemistry.
Philip Lightfoot 1 , Nicholas Stephens 1 , Anil Jayasundera 1 , David Aldous 1 Show Abstract
1 , University of St Andrews, St Andrews United Kingdom
The development of the solid state chemistry of fluorides and oxyfluorides has lagged significantly behind that of the corresponding oxides. This is partly due to the more difficult and hazardous synthetic conditions generally required. Recently, milder methods of synthesising novel fluoride-based materials have come to the fore, both using relatively high-temperature solid state methods, and also through the increased use of solvothermal methods. We have recently been exploring the scope for preparing novel fluoride-based materials using organically-templated hydrothermal reactions. Our interests in functional materials lie in the areas of optical activity, ferroelectricity, magnetism and luminescence. In each case, the exploitation of fluoride rather than oxide-based systems may have advantages. Our recent exploratory work in this field has produced more than fifty novel compounds and structure types This talk will focus on the structural chemistry and preliminary physical property measurements of these systems, including reduced vanadium oxyfluorides, rare-earth fluorides and d0 metal oxyfluorides.
AA6: Poster Session: Batteries
Tuesday PM, November 28, 2006
Exhibition Hall D (Hynes)
9:00 PM - AA6.1
Ion Mobility in PMMA Doped with Small Amounts of a Lithium Salt.
Peter Kohn 1 , Klaus Schroeter 1 , Thomas Thurn-Albrecht 1 Show Abstract
1 Physics Department, Martin Luther University Halle, Halle Germany
Polymer electrolytes are ionically conducting materials consisting of ions dissolved in a polymer matrix. As for other conducting materials the conductivity of these systems is determined by the product of the mobility and the number density of the free charge carriers. Apart from the mechanical properties the decisive quantity for application of these materials is the conductivity and its dependence on various variables, like temperature, salt concentration etc. For a basic understanding of this behaviour at least one of the quantities mentioned above, mobility or density of ions, is needed in addition to the conductivity. Normally NMR techniques are used to determine the mobilities of ions in polymer electrolytes (via determination of diffusion coefficients and use of the Einstein relation). We here discuss two electrical measurements in a parallel plate capacitor geometry as alternative methods to determine the density and the mobility of the ions, respectively. The basic idea for the first experiment is that if the density of free ions is small and a high, constant voltage is applied across the capacitor all the ions will accumulate near the electrodes in the Helmholtz double layers. Integration of the measured current during this charging of a double layer capacitor yields the total ionic charge in the system and the number of free ions can be calculated.In the second experiment like in the first one the ions of opposite charge are forced to separate and accumulate at the different electrodes by applying a constant voltage. Subsequently the voltage is reversed and the ions migrate from one electrode to the other. The current measured during this process gives the transit time which is directly related to the mobility of the charge carriers.For an exemplary application we used these methods to study ion mobility in amorphous polymethylmethacrylate (PMMA) doped with lithiumtrifluorosulfonate (LiCF3SO3) above the glass transition temperature of PMMA. The measurements were complemented by dielectric spectroscopy in the frequency domain. While the experiments described above allow a determination of the density and the mobility of the ions, the frequency dependent dielectric measurements give the temperature and salt-concentration dependence of the ohmic conductivity of the electrolyte.
9:00 PM - AA6.10
Magnetic Studies of Layered Cathode Materials for Lithium Ion Batteries.
Natasha Chernova 1 , Miaomiao Ma 1 , Jie Xiao 1 , M. Stanley Whittingham 1 Show Abstract
1 Institute for Materials Research, State University of New York at Binghamton, Binghamton, New York, United States
Temperature dependences of DC and AC magnetic susceptibilities and magnetization curves of Lix(NiyMnyCo1-2y)O2 and Lix(NiyMnyCo1-2y)2-xO2 were studied to understand transition metal (TM) ion distribution through the magnetic interactions between the TM ions. In LiNi1/3Mn1/3Co1/3O2 and LiNi0.4Mn0.4Co0.2O2 spin-glass transitions were found, which implies random distribution of the TMs in the layers. The absence of magnetization hysteresis indicates good layered structure with small amount of Ni2+ in the Li layer. In LiNi0.45Mn0.45Co0.1O2 cluster-glass transition is observed provided by magnetic clusters formation around Ni2+ ions in the Li layer. In LiNi0.5Mn0.5O2 series of magnetic transitions is observed and explained assuming imperfect flower order of the TMs. This model is consistent with NMR data and Monte-Carlo simulations by C. Grey’s and G. Ceder’s groups. Upon chemical removal of only 0.06Li from LiNi0.5Mn0.5O2 the large hysteresis of magnetization observed in the pristine compound due to magnetic moment of clusters around Ni2+ on Li sites drastically decreases. The same effect is observed upon electrochemical removal of Li. This indicates that Ni2+ ions on Li sites are affected from the very beginning of Li removal. Possible mechanisms may include preferential oxidation of interslab Ni2+ or their migration to tetrahedral sites. Upon discharge the magnetic properties are not retained, therefore the TM distribution should be different than at the corresponding charge stage. The latter two facts were observed using the neutron diffraction by C. Grey’s group. In Lix(Ni0.45Mn0.45Co0.1)1-xO2 the largest hysteresis loop was observed at x=0.9; with increasing Li content the hysteresis diminished indicating decrease of the Ni/Li disorder. At lower Li contents the hysteresis loop diminishes and changes shape; additional magnetic transition observed from the temperature dependence of susceptibility is likely due to the appearance of a second phase. At x=0.5 this second phase becomes dominant; its nature will be discussed. This work is supported by the US Department of Energy, Office of FreedomCAR and Vehicle Technologies through the BATT program and by NSF, DMR 0313963.
9:00 PM - AA6.11
Influence of Lithium Content on Performance of Layered Li1+x(Ni0.45Mn0.45Co0.1)1-xO2 in Lithium Ion Batteries.
Jie Xiao 1 , Natasha Chernova 1 , M. Stanley Whittingham 1 Show Abstract
1 Chemistry, State University of New York at Binghamton, Binghamton, New York, United States
9:00 PM - AA6.12
Effect of ZnO Coating on LiMn1.5Ni0.5O4 Cathode Materials or Application to Li Ion Rechargeable Batteries.
Rahul Singhal 1 , Juan Burgos 2 , Maharaj Tomar 1 , Ram Katiyar 2 Show Abstract
1 Physics, University of Puerto Rico, Mayaguez, Puerto Rico, United States, 2 Physics, University of Puerto Rico, San-Juan, Puerto Rico, United States
9:00 PM - AA6.13
A New Lithium Iron Phosphate LiFe2P3O10 Synthesized by Wet Chemistry.
Atmane Ait-Salah 1 , Chintalapalle Ramana 2 , Francois Gendron 3 , Jean Francois Morhange 4 , Alain Mauger 5 , Christian Julien 6 Show Abstract
1 INSP, Universite P & M Curie, Paris France, 2 Nanoscience and Surface Chemistry Laboratory, Michigan University, Ann Arbor, Michigan, United States, 3 INSP, Universite P & M Curie, Paris France, 4 INSP, Universite P & M Curie, Paris France, 5 MIPPU, CNRS, Paris France, 6 Institut des NanoSciences de Paris, Universite P & M Curie, Paris France
9:00 PM - AA6.14
Aligned LiFePO4 Nanorods: Formation, Modification and Electrochemistry.
Lin Xu 1 , Liqiang Mai 1 2 , Tao Hu 1 , Wanli Guo 1 Show Abstract
1 Institute of Materials Science and Engineering, Wuhan University of Technology, Wuhan, Hubei, China, 2 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
9:00 PM - AA6.15
Local Structure and Magnetic Properties of LixFePO4 (0≤x≤1) Glasses.
Pavel Jozwiak 1 , Jerzy Garbarczyk 2 , Francois Gendron 3 , Alain Mauger 4 , Christian Julien 5 Show Abstract
1 Faculty of Physics, Warsaw University of Technology, Warsaw Poland, 2 Faculty of Physics, Warsaw University of Technology, Warsaw Poland, 3 INSP, University of Paris 6, Paris France, 4 MIPPU, CNRS, Paris France, 5 Institut des NanoSciences de Paris, Universite P & M Curie, Paris France
9:00 PM - AA6.16
Synthesis and Characterization of Li4Ti5O12 Thin Films by Rapid Thermal Annealing.
Chen Hu 1 , Wen Zhang 1 , Hanxing Liu 1 Show Abstract
1 materials sicence, Wuhan university of technology, WuHan, HuBei , China
9:00 PM - AA6.18
Ionic Conductivity of NASICON-like Compounds in InPO4-Li3PO4 System.
Galina Zimina 1 , Irina Smirnova 1 , Anna Potapova 1 , Andrey Novoselov 1 , Felix Spiridonov 2 , Sergey Stefanovich 2 Show Abstract
1 Department of Chemistry and Chemical Engineering for Rare and Dispersed Elements, Lomonosov Moscow State Academy of Fine Chemical Technology, Moscow Russian Federation, 2 Department of Chemistry, Lomonosov Moscow State University, Moscow Russian Federation
9:00 PM - AA6.19
The Influence of Heteroatomic Nitrogen on Lithium Intercalation in Oligophenylenes.
Walter Doherty 1 , Rainer Friedlein 1 , Thierry Renouard 2 3 , Claude Mathis 2 , William Salaneck 1 Show Abstract
1 Surface Physics and Chemistry, Linköping University, Linköping Sweden, 2 , Institut Charles Sadron, Strasbourg France, 3 Equipe Chimie et Ingénierie des Procédés (CIP), Université de Rennes 1, Rennes France
9:00 PM - AA6.2
Development of Solid Electrolyte Membranes for Use in Lithium Water Batteries.
Clifford Cook 1 , Robert Doe 1 , Michael Wagner 1 Show Abstract
1 Chemistry, George Washington University, Washington, District of Columbia, United States
Lithium metal in combination with water is a highly attractive power source because of the high specific energy for this system. Because of the vigorous nature of the reaction between lithium and water, many obstacles must be overcome in order to harness the energy that this system is capable of producing. Parasitic reactions must be controlled so as not to passivate the lithium or consume it totally. In addition, production of hydrogen gas that may accompany the parasitic reactions presents a serious challenge. As a result it is difficult to maintain high voltage and control the current density in these systems.In order to overcome these obstacles we are developing composite membranes of various lithium-ion conducting solid electrolytes and polymers. Lithium-ion conducting solid electrolytes are known to achieve ionic conductivities as large as 10-3 S/cm2. Utilizing these materials in conjunction with polymers and other materials, we are striving to create durable, hydrophobic membranes that will allow us to limit the parasitic reactions, maintain low cell impedance and thus achieve Li/water batteries for long-term use in practical applications. Results of the experiments will be presented herein.
9:00 PM - AA6.3
Charge-Discharge Reaction of Cu2Sb as Anode Material for Lithium Ion Battery.
Masanobu Nakayama 1 , Makiko Noji 1 , Tomoaki Kashiwagi 1 , Shinsuke Matsuno 1 , Masataka Wakihara 1 , Yo Kobayashi 2 , Hajime Miyashiro 2 Show Abstract
1 , Tokyo Institute of Technology, Tokyo Japan, 2 , Central Research Institute of Electric Power Industry, Tokyo Japan
9:00 PM - AA6.4
LixCn as Anode Material for Lithium Ion Batteries.
Wang Shun 1 , Xie Haiming 1 Show Abstract
1 chemistry, Northeast Normal university, Changchun, Jilin, China
9:00 PM - AA6.5
Nanocrystalline Diamond Anodes for Rechargeable Lithium Ion Batteries.
Joel De Jesus 1 , Sri Katar 2 , Fabrice Piazza 1 , Ram Katiyar 1 , Carlos Cabrera 2 , Brad Weiner 2 , Gerardo Morell 1 Show Abstract
1 Physics, University of Puerto Rico, San Juan, Puerto Rico, United States, 2 Chemistry, University of Puerto Rico, San Juan, Puerto Rico, United States
9:00 PM - AA6.6
Acicular Silver Vanadium Oxide Nanofibers Prepared by Hydrothermal Synthesis.
Kenneth Takeuchi 1 , Amy Marschilok 2 , Randolph Leising 2 , Esther Takeuchi 2 Show Abstract
1 Department of Chemistry, University at Buffalo (SUNY), Buffalo, New York, United States, 2 Research and Development, Greatbatch, Inc., Clarence, New York, United States
Silver vanadium oxide (SVO, Ag2V4O11) has demonstrated commercial success as a solid-state cathode material in power sources for implantable biomedical devices. This report describes the synthesis of SVO via a hydrothermal method. This novel synthetic approach allows low temperature production of acicular SVO nanofibers with a high surface area. This material was investigated as a cathode material in primary lithium batteries for high rate pulse applications.
9:00 PM - AA6.7
The Effect of Rare-earth Doping LiMn2O4 on Its Use as a Cathode in Li-ion Batteries
Maharaj Tomar 1 , Osbert Oviedo 1 , Ricardo Melgarejo 1 , Rahul Singhal 1 , Ram Katiyar 2 Show Abstract
1 Physics, University of Puerto Rico, Mayaguez, Puerto Rico, United States, 2 Physics, University of Puerto Rico, San-Juan, Puerto Rico, United States
9:00 PM - AA6.8
Analysis of Composition and Valence States in Positive Electrode Materials (Fe-substituted Li2MnO3) for Lithium Ion Batteries by Analytical Transmission Electron Microscopy.
Jun Kikkawa 1 , Tomoki Akita 1 , Mitsuharu Tabuchi 1 , Masahiro Shikano 1 , Kuniaki Tatsumi 1 , Masanori Kohyama 1 Show Abstract
1 , National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka, Japan
9:00 PM - AA6.9
Li Batteries with Porous SOL-GEL Cathodes.
Antonela Dima 1 , Maurizio Casalino 1 , Francesco Della Corte 1 , Ivo Rendina 1 Show Abstract
1 IMM, CNR , Napoli Italy
Timothy Armstrong Oak Ridge National Laboratory
Christian Masquelier University of Picardie-CNRS
Yoshihiko Sadaoka Ehime University
Enrico Traversa University of Rome Tor Vergata
AA7/BB8: Joint Session: Solid State Ionics for Mobile Energy
Wednesday AM, November 29, 2006
Republic B (Sheraton)
9:30 AM - **AA7.1/BB8.1
Enabling Aspects of Metal Halide Nanocompositesfor Reversible Energy Storage.
Glenn Amatucci 1 , Fadwa Badway 1 , Nathalie Pereira 1 , Wei Tong 1 , Irene Plitz 1 , Jafar Al-Sharab 1 , Frederick Cosandey 1 , Adam Skrzypczak 1 , John Gural 1 Show Abstract
1 Energy Storage Research Group, Department of Materials Science and Engineering, Rutgers, the State University of New Jersey, North Brunswick, New Jersey, United States
10:00 AM - AA7.2/BB8.2
A Study on the LiMn2O4 Cathodes with Mesh-like Structures for Li Secondary Batteries.
Min Park 1 , Dong-Hoon Chung 1 , Bong-Kwan Shin 1 , Seung-Ki Joo 1 Show Abstract
1 School pf Material Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
10:15 AM - AA7.3/BB8.3
Nanosized Amorphous Materials as Anodes for Lithium Batteries.
Quan Fan 1 , M. Stanley Whittingham 1 Show Abstract
1 Department of Chemistry, State University of New York at Binghamton, Binghamton, New York, United States
10:30 AM - AA7.4/BB8.4
Macroporous Silicon Inverse Opals as Electrodes for Lithium-Ion Secondary Batteries.
Alexei Esmanski 1 , Geoffrey Ozin 1 Show Abstract
1 Chemistry, University of Toronto, Toronto, Ontario, Canada
Colloidal crystal templating methods are among the “hottest” areas in materials science today. Three-dimensional macroporous ordered structures (“opals” and “inverse opals”) can be produced by these methods on a large scale. Although a principal area of research for materials with opal and inverse opal morphologies is that of photonic crystals, a few investigations have examined the possibility of using these structures as gas sensors, catalysts and battery electrodes.Specifically, there are several potential advantages of lithium-ion battery electrodes, based on inverse opal structures. High electrode-electrolyte interfacial surface area and easier access to the bulk of electrode, as well as reduced lithium diffusion length allow for the use of batteries at higher discharge rates . Highly open hierarchical structures also provide better mechanical stability to volume swings during battery cycling.The theoretical capacity of silicon for lithium insertion at room temperature is 3579mAh/g (Li15Si4 phase) . For comparison, the theoretical capacity of graphite, the material of choice in modern state-of-the-art lithium-ion batteries, is only 372mAh/g. This makes silicon one of the most promising anode materials despite its relatively low electronic conductivity and lithium diffusion rates.In this study, opal films (10–40 μm thick) of monodisperse silica nanospheres were fabricated by the evaporation induced self-assembly method . These templates were uniformly infiltrated with amorphous silicon via chemical vapor deposition, with subsequent removal of the silica template . The structural/electrochemical property relationships of silicon inverse colloidal crystal films have been investigated and compared to traditional negative electrode materials, so as to outline the main benefits of the inverse opal hierarchical structure. Electrochemical cycling of silicon inverse opal films demonstrated their good cycling ability, high lithium insertion capacity approaching the theoretical value and excellent coulombic efficiency. Electron microscopy studies confirmed that the open hierarchical structure is maintained during lithium insertion-deinsertion and revealed interesting morphological changes occurring in the system during cycling.References:1. J. S. Sakamoto, B. Dunn, J. Mater. Chem., 2002, 12, 28592. M. N.Obrovac, L. Christensen, El-Chem. Solid-State Lett., 2004, 7, A933. P. Jiang, J. F. Bertone, K. S. Hwang, V. L. Colvin, Chem. Mater., 1999, 11, 21324. A. Blanco, E. Chomski, S. Grabtchak, M. Ibisate, S. John, S. W. Leonard, C. Lopez, F. Messeguer, H. Miguez, J. P. Mondia, G. A, Ozin, O. Toader, H. M. van Driel, Nature, 2000, 405, 437
10:45 AM - AA7.5/BB8.5
Preparation and Characterization of ALD TiN Thin Films on Lithium Titanate Spinel (Li4Ti5O12) for Lithium Ion Battery Applications.
Mark Snyder 1 , Boris Ravdel 4 , Joseph DiCarlo 4 , M. Wheeler 1 , Carl Tripp 2 3 , William DeSisto 1 3 Show Abstract
1 Chemical & Biological Engineering, University of Maine, Orono, Maine, United States, 4 , Lithion Corp., Pawcatuck, Connecticut, United States, 2 Chemistry, University of Maine, Orono, Maine, United States, 3 Laboratory for Surface Science & Technology (LASST), University of Maine, Orono, Maine, United States
Lithium titanate spinel (Li4Ti5O12) has received an increasing level of attention over the last five years as a nanopowder lithium-ion battery anode. Nanopowder electrodes may provide a higher energy density than currently available. Applying a thin film that is both conducting and chemically inert to harmful reactions with the solvent/electrolyte may enhance battery cycle life. We are investigating thin TiN films on Li4Ti5O12 prepared by atomic layer deposition (ALD) and have characterized their properties, including their influence, on Li-ion battery performance. ALD consists of sequential deposition of self-terminating, surface layer half-reactions (an “A step” and “B step”) and has the potential to uniformly coat irregular surfaces like nanoparticles. To gain a basic understanding of the mechanism of thin film formation on a powder surface, modification of a silica powder surface with TiCl4 (step A) and NH3 (step B) to form a TiN thin film has been performed and characterized in situ with FTIR. Six layers were deposited at 400 C. IR spectra of a TiClx-terminated surface after step A, and an NH-terminated surface after step B were obtained. Insight was gained on causes of incomplete surface film coverage. ALD thin films have been deposited on Li4Ti5O12 as well. Thin films of 200 to 1000 layers were deposited at temperatures from 400 to 600 C. A 200-layer film deposited at 500 C had an estimated thickness of 6 nm on a particle of about 50 nm in length. Nitrogen analysis and transmission electron microscopy were used to verify the presence of nitrogen and formation of a thin film, respectively, on Li4Ti5O12. Modifying the powder with an ALD thin film coating produced a powder that maintained charge longer with shorter transient periods during cyclic voltammetry. It also held a more consistent charge capacity over varying discharge rates in coin cell testing than unmodified Li4Ti5O12. Furthermore, the surface of the spinel nanopowder has been studied under vacuum and at varying temperatures with diffuse reflectance infrared Fourier transform spectroscopy revealing surface hydroxyls, carbonates and water. Several probe molecules have been used to determine the presence of acid/base sites and explore potential methods of bonding with thin film precursors. Pyridine bonded with the surface at Lewis acid sites. No evidence of Brönsted acid sites were observed. Hexamethyldisilazane formed Ti-O-Si bonds. Both of these reactions proceeded at room temperature and 400 C.
11:30 AM - **AA7.6/BB8.6
Nanostructured Catalysts for Portable Fuel Cells Applications.
Vincenzo Antonucci 1 , Vincenzo Baglio 1 , Alessandra Di Blasi 1 , Alessandro Stassi 1 , Claudia D'Urso 1 , Antonino Arico' 1 Show Abstract
1 Energy and Transport, CNR-ITAE, Messina Italy
Stationary and automotive fuel cells (FC) devices are expected to play an important role for the sustainable energy generation in the next years. Significant interest is also addressed to small portable fuel cells that possibly will find market application before large-size FC systems. The potential market for portable fuel cell systems deals with remote and micro-distributed electrical energy generation including mobile phones, lap-top computers, energy supply for weather stations, medical devices, auxiliary power units (APU) etc. The main advantages of such systems rely on the high energy density of liquid fuels such as methanol and ethanol, long-life-time, easy recycle and low emission of pollutants in the environment. The CNR-ITAE Istitute is involved in European and National projects with the aim to develop nanostructured catalyst for portable direct methanol and ethanol fuel cells. The target for DMFC/DEFC devices for portable application is to work at relatively low temperatures and atmospheric pressure with high efficiency and performance. The effective operation at this low temperature is particularly challenging and requires innovation in different aspects of materials and system development. In particular to address the poor reaction kinetics at the anode, high surface area catalysts composed of nanosised noble metal particles need to be developed and investigated for operation at low temperatures starting from sub-ambient to 60 °C. Although, one of the main drawback of DMFC systems i.e. the methanol cross-over through the membrane is strongly depressed by the decrease of the operating temperature, this constraint affects the cathode performance even at low temperature by causing a mixed potential and poisoning of the cathode surface. Accordingly, it is strongly necessary to develop methanol /ethanol tolerant cathode catalysts with suitable activity at low temperature. Also in this case, a proper catalytic activity for achieving portable fuel cells performance targets is assured by noble metal catalyst properly modified with transition metals capable of reducing the adsorption of alcohols on the cathode surface. The activity presented in this communication deals with both anode and cathode catalysts synthesised by a low–temperature colloidal route characterised by high concentration of metallic phase on carbon black and particle size smaller than 3 nm. The structure and morphology of the catalysts has been investigated and these properties have been correlated with the electrochemical activity and tolerance to methanol poisoning.
12:00 PM - AA7.7/BB8.7
Synthesis of Bimetallic and Trimetallic Alloy Nanoparticles as Catalysts in Fuel Cells.
Peter Njoki 1 , Jin Luo 1 , Bilal Khan 1 , Suprav Mishra 1 , Ravishanker Sujakumar 1 , Chuan-Jian Zhong 1 Show Abstract
1 Chemistry, State Univ. of New York at Binghamton, Binghamton, New York, United States
12:15 PM - AA7.8/BB8.8
Passive Air Breathing Fuel Cells For Portable Applications: What are the Limits to Cathode Performance?
Ryan O'Hayre 1 2 , Tibor Fabian 2 , Shawn Litster 2 , Fritz Prinz 2 , Juan Santiago 2 Show Abstract
1 Metallurgical and Materials Engineering, Colorado School of Mines, Golden, Colorado, United States, 2 Mechanical Engineering, Stanford University, Stanford, California, United States
12:30 PM - AA7.9/BB8.9
Direct-Write Microfabrication of Single-Chamber Solid Oxide Fuel Cells with Interdigitated Electrodes.
Melanie Kuhn 1 , Teko Napporn 2 , Michel Meunier 2 , Daniel Therriault 1 , Srikar Vengallatore 3 Show Abstract
1 Department of Mechanical Engineering, Ecole Polytechnique de Montreal, Montreal, Quebec, Canada, 2 Department of Engineering Physics, Ecole Polytechnique de Montreal, Montreal, Quebec, Canada, 3 Department of Mechanical Engineering, McGill University, Montreal, Quebec, Canada
Miniaturized single-chamber solid-oxide fuel cells (SC-SOFC) are a promising class of devices for portable power generation required in the operation of distributed networks of microelectromechanical systems (MEMS) in harsh environments. The single-face configuration, which consists of interdigitated (comb-like) array of electrodes on an yttria-stabilized zirconia (YSZ) electrolyte substrate, is of particular interest because of the ease of high-temperature microfluidic packaging and integration with MEMS. The primary design consideration for this configuration is the minimization of electrode widths and inter-electrode spacings to dimensions on the order of a few micrometers. This is necessary to minimize polarization resistance and increase fuel cell efficiency. Achieving these geometries using standard microfabrication methods is difficult because of the thickness, porosity, and complex chemistries of the electrodes. Here, we report the development of an innovative and rapid method for manufacturing SC-SOFCs with interdigitated electrodes using robot-controlled direct-writing. The main steps consist of: (i) formation of inks (or suspensions) using anode (NiO-YSZ) and cathode (lanthanum strontium manganite) powders, (ii) pressure-driven extrusion of inks through a micronozzle using a robot-controlled platform, and (iii) sequential sintering to form the fuel cell. The first-generation SC-SOFC device, with electrode widths of 130 μm and inter-electrode spacing of 300 μm, has been manufactured using direct-write microfabrication. The electrodes have been extensively characterized using electron microscopy and x-ray diffraction to assess porosity and to confirm phase identity. The primary process parameters in this approach are the particle size and size distribution, rheological properties of the suspension, extrusion pressure, nozzle size, stage velocity, and sintering conditions. As the first step in the development of detailed process-structure-performance correlations for the fuel cells, we have studied the effects of extrusion pressure (in the range 30-40 bar) and stage velocity (in the range 0.2-2.0 mm/s) on the geometry and size of electrodes, for fixed suspension viscosity and nozzle diameter. An optimal combination of speed and pressure has been identified and catalogued in the form of process maps. Similarly, the particle size distribution of the anode and cathode powders is found to have a significant effect on the microstructure, especially porosity, of the sintered electrodes. The implications of these results for the design of the next generation of SC-SOFC, with reduced electrode dimensions and improved electrochemical performance, will be discussed.
12:45 PM - AA7.10/BB8.10
Materials and Design Study for Micromachined Solid Oxide Fuel Cells Membranes.
Samuel Rey-Mermet 1 , Paul Muralt 1 Show Abstract
1 STI-IMX-LC, Ecole Polytechnique Fédérale de Lausanne, Lausanne Switzerland
In this work we studied materials design and processes for the realization of a micro SOFC entirely based on silicon MEMS technology. As electrolyte materials, ceria doped gadolinia Ce0.8Gd0.2O2-x (CGO) and zirconia stabilized with yttria Zr 0.92Y0.08O2-x (YSZ) were investigated in the form of 0.2 to 2 μm thick films deposited by reactive magnetron sputtering. X-rays diffraction patterns and scanning electron microscopy show that both types of films exhibit a crystalline columnar structure. Predominant texture are are (111) for CGO and (101) for YSZ. The ionic conductivities measured by DC and AC techniques matched well with the literature values. For the CGO thin films, the conductivity of the film perpendicular to the substrate was slightly smaller (1.8 S/m at 700°C in air) than the conductivity in the plane of the film (2 S/m at 700°C in air) proving that there was no short through the grain boundaries. The activation energies for ionic conduction were measured as 0.51-0.58 eV for CGO films and are thus slightly smaller than the bulk ceramics values. The ionic conductivity of the YSZ thin film in reducing conditions at 500°C amounts to 35 S/m in reducing atmosphere at 900°C, with an activation energy of 0.21 eV. Stress analysis made by curvature measurements show that a thermal treatment of the CGO films reduces the compressive stress after deposition. This heat treatment reorganizes or removes the oxygen vacancies in the film leading to a change of the strain. Free standing 200 nm thick CGO membranes of 500 μm diameter were realized. These membranes are too fragile for application in real conditions. A supporting nickel grid was developed giving mechanical stability up to at least 550°C. The electrochemically deposited nickel grid is applied on the anode side and serves as a current collector at the same time. With this design, it is possible to fabricate 1 μm thin free standing membranes with a diameter of 5 mm. The grid is composed of hexagonal cells with a diagonal of 100 μm and a line width of 10 μm. The anode is made of porous Ni-CGO co-sputtered by reactive magnetron sputtering using a nickel and a CGO target. The anode has a total conductivity of 5000 S/cm in argon atmosphere. The cathode of cobalt doped lanthanum perovskite La0.32Sr0.68CoO3 (LSC) is also deposited by reactive magnetron sputtering. A dense and thin LSC film covers the entire cell surface and has a conductivity of 80 S/cm at 600°C in air. A platinum current collector mesh is also deposited on the LSC to increase the electronic conductivity of the cathode. In this work we realized large, mechanically stable fuel cell membranes and developed materials by sputtering with sufficient properties for applications.
AA8: Fuel Cells: PEM-FCs
Wednesday PM, November 29, 2006
Republic B (Sheraton)
2:30 PM - **AA8.1
Hybrid Proton Conducting Polymeric Electrolytes for Intermediate Temperature PEMFCs.
Silvia Licoccia 1 Show Abstract
1 Chemical Science and Technology, University of Rome Tor Vergata, Rome Italy
To successfully perform in Polymer Electrolyte Membrane Fuel Cells (PEMFCs), the electrolytes must meet several requirements, most important among them high proton conductivity, high hydrolytic stability, high oxidative resistance, good mechanical properties and, possibly, low cost. New generation electrolytes should maintain such performances above 100 °C to increase CO tolerance, enhance fuel oxidation kinetics, ease thermal balance. Furthermore, for automotive application, operating a FC vehicle at ambient temperature above 20 °C requires either a large radiator, a solution certainly not ideal for most car manufactures, or an increase the operation T above 100 °C.Significant research efforts are devoted to the achievement of the above mentioned goals and two main topics have been identified: understanding the mechanisms of functioning of Nafion, the most widely accept standard for PEMFCs, and sulfonation and/or modification of different polymers.In our laboratory attention has been focused on the development of composite Nafion-based membranes to obtain systems capable to perform at T > 100 °C and on possible modifications that can be introduced in sulfonated arylene main chain polymers, in particular polyetheretherchetone (PEEK) and polyphenylsulfone (PPSU). Both these latter polymers show rather large conductivity when sulfonated, but their mechanical, morphological and solubility properties progressively deteriorate with the degree of sulfonation (DS) because acid groups directly linked to the aromatic hydrophobic backbones cannot assemble in phase separated domains as well as perfluorinated systems with more hydrophobic flexible side chains.Different strategies are under investigation to increase the operation temperature of Nafion and to implement the properties of SPEEK with high DS: i)preparation of Class I hybrids, where components are bound by weak interactions, using as fillers ceramic oxides, inorganic proton conductors or functionalized organically modified silanes (ormosils).ii)preparation of organic/inorganic Class II hybrid systems where -Si-O-Si-units link two polymeric chains, and the inorganic part would offer thermal and mechanical stability and the organic component flexibility and processability. The combination of the two features could contribute to sharpen the border between the hydrophobic and hydrophilic regions, thus modulating the requirements of high conductivity and low permeability.iii)preparation of polymer blends to combine the positive features of different polymeric materials. Membranes deriving from these different approaches were successfully prepared by casting. Their structure, fuel permeability, and electrochemical performances were investigated by means of several techniques including 1-H and 29-Si NMR, ATR/FTIR, FE-SEM and EIS and tested in a prototype fuel cell.
3:00 PM - AA8.2
New High Temperature Polymer Electrolyte Membranes and their Fuel Cell Performance.
Nora Gourdoupi 1 , Maria Daletou 2 3 , Maria Geormezi 2 3 , Joannis Kallitsis 2 3 , Stelios Neophytides 3 Show Abstract
1 Advent Technologies S.A., Patras Science Park, Patras Greece, 2 Department of Chemistry, University of Patras, Patras Greece, 3 , Institute of Chemical Engineering and High Temperature Chemical Processes, Patras Greece
Polymer electrolyte membrane fuel cells are the most promising renewable power generators for zero-emissions vehicles and portable applications. PEMFCs that operate at high temperatures (>120 oC) show certain advantages which relate to increased tolerance of the anode to carbon monoxide (>0.1 CO at 150 oC), enhancement of reaction rate, electrochemical performance relatively independent of humidity, simplification of the system. Membrane electrode assembly (MEA) is the heart of a PEM fuel cell and consists of a proton exchange membrane, catalyst layers and gas diffusion layers. Concerning the membrane, the properties that should be met in order to be used as an electrolyte are the following: good mechanical properties, high thermal, chemical and oxidative stability, high doping ability with strong acids, high proton conductivity, low electronic conductivity, low gas permeability and low cost.Polybenzimidazole (PBI) doped with H3PO4 is the state of the art high temperature polymer electrolyte. Although it exhibits high thermal stability, high ionic conductivity and high fuel cell performance, its low oxidative stability is a critical disadvantage for its long term performance. Our approach to the development of new polymer membranes include the synthesis of new aromatic polyethers containing polar units in the main chain and the preparation of PBI based and PBI-free blends. Aromatic polyethers are chosen due to their good mechanical properties and high thermal stability while the insertion of polar pyridine is done with the view of having sites that can interact with phosphoric acid resulting thus in highly conductive materials. Characterization of the prepared polymers with conventional techniques showed that they fulfill all the prerequisites in order to be used as high temperature electrolytes.In addition, membrane electrode assemblies were prepared with the new materials and were further tested in 2x2 and 5x5 cm2 single cells. The conductivity of the polymer membranes as well as the different MEAs performance were tested by means of AC impedance. It is shown that upon current application, water is dragged through the membrane while the conductivity of the H3PO4 doped membranes strongly depends on the partial pressure of steam and on the applied potential. Conductivities in the range of 10 -2 S/cm were obtained while the single cell performance is comparable and in some cases better to that reported for the PBI-membranes.
3:15 PM - AA8.3
New Polybenzimidazole-based Membranes for Fuel Cells.
Eliana Quartarone 1 , Arianna Carollo 1 , Federico Belotti 1 , Piercarlo Mustarelli 1 , Aldo Magistris 1 , Corrado Tomasi 3 , Luigi Garlaschelli 2 , Pierpaolo Righetti 2 Show Abstract
1 Dept. of Physical Chemistry, University of Pavia, Pavia Italy, 3 , IENI-CNR, Pavia Italy, 2 Dept. of Organic Chemistry, University of Pavia, Pavia Italy
3:30 PM - AA8.4
Fuel Crossover and Fuel Cell Performance of Layer-by-Layer Assembled Proton Exchange Membranes.
J. Ashcraft 1 , Avni Argun 1 , Paula Hammond 1 Show Abstract
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
Recent research has shown layer-by-layer (LBL) assembly to be a robust technique for the fabrication of proton exchange membranes with tunable properties. In this work, multilayer systems of poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) assembled at different numbers of bilayer pairs and several pH values are characterized with respect to z-plane ionic conductivity and gas permeation. By altering the pH of assembly conditions, the relative amounts of each polymer deposited in the film are controlled, which impacts many bulk properties of the film. A 30 bilayer film assembled at pH=2.5 is shown to effectively block the permeation of nitrogen through a LBL membrane. Hydrogen crossover can be minimized by tuning the pH of film assembly and film thickness. Also, we report a maximum ionic conductivity of 3.8 x 10-4 S/cm for a PEO/PAA film at 100% RH. These films will then be tested as the proton exchange membrane in commercial fuel cell hardware to determine the optimal film assembly conditions for fuel cell operation. The PEO/PAA films, along with multilayer films of Nafion® and linear poly(ethylene imine) (LPEI) will be investigated as thin coatings on commercial Nafion® membranes. Barrier layers of PEO/PAA and Nafion/LPEI have the potential to reduce fuel crossover and membrane degradation while minimally impacting the overall fuel cell performance.
3:45 PM - AA8.5
Proton Conducting Hybrid Phosphosilicate Membranes for Medium Temperature H2/O2 Fuel Cells.
Martin Mika 1 , Marketa Masinova 1 , Martin Paidar 1 , Karel Bouzek 1 , Bretislav Klapste 2 , Jiri Vondrak 2 Show Abstract
1 Department of Glass and Ceramics, Institute of Chemical Technology Prague, Prague Czech Republic, 2 Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic, Rez near Prague Czech Republic
A limited supply and high costs of crude oil force the main car producers to focus more on the development of alternative engines and fuels for their future vehicles. One of the promising solutions can be a car powered by affordable hydrogen fuel cells. In these fuel cells a suitable membrane represents a critical component. For transportation applications a membrane must exhibit sufficiently high proton conductivity and tolerate a wide range of operating conditions including low humidity and intermediate temperatures up to 130°C. Currently, the low operating temperatures of available proton conducting polymer membranes and their humidity requirements add high complexity to the fuel cell system that impacts its cost and durability. Therefore, our recent research has been focused on the development of improved membranes with better performance at lower cost.Our membranes are based on hybrid inorganic-organic phosphosilicate polymers. The backbone of the membrane is the polydimethylsiloxane polymer with phosphorus heteroatoms. Generally, polysiloxanes (silicones) possess high temperature stability and chemical durability as the result of their -Si-O-Si- bonds having high bonding energy and stabilizing the organic groups bonded to Si atoms. The synthesis of our membranes is based on the reactions of dimethyldichlorosilane and tetraethoxysilane in liquid or molten orthophosphoric acid. The developed preparation procedure ensures a high concentration of hydroxyl groups in the polymer that facilitate fast proton migration at low humidity. The prepared polymers were thoroughly characterized with analytical tools, including optical and electron microscopy (SEM-EDS), differential thermal analysis-thermal gravimetric analysis, infrared and Raman spectroscopy, and nuclear magnetic resonance. The temperature dependence of the proton conductivity was measured using electrochemical impedance spectroscopy. The recorded impedance data were fitted with an equivalent circuit and from its parameters the proton conductivity was calculated. In a dry atmosphere the conductivity was about 0.02 S/cm at 130°C. We tested our membranes in a commercial H2/O2 fuel cell operating in the temperature range from 22 to 130°C using dry H2 and O2 gases. We employed standard electrodes made of carbon paper with Pt/C catalyst. The surface area of the electrodes was 5 cm2. The performance of the fuel cell significantly improved as the temperature increased; the maximum of power density increased and moved to higher current densities and the absolute value of the slope of the voltage/current characteristic decreased. In our paper we report and discuss the observed effects of composition and preparation conditions on the measured properties of our membranes and on their performance in the H2/O2 fuel cell at elevated temperatures using dry reactant streams.
4:30 PM - AA8.6
Spatial and Temporal Mapping of Water Content across Nafion Membranes under Wetting and Drying Conditions.
Ziheng Zhang 1 , Bruce Balcom 1 , Andrew Marble 1 2 Show Abstract
1 MRI Centre, Department of Physics, University of New Brunswick, Fredericton, New Brunswick, Canada, 2 Department of Electrical and Computer Engineering, University of New Brunswick, Fredericton, New Brunswick, Canada
4:45 PM - AA8.7
State of Water in Nafion 117 Proton Exchange Membranes Studied by Dielectric Relaxation Spectroscopy.
Georgios Polizos 1 , Zijie Lu 1 , Digby Macdonald 1 , Evangelos Manias 1 Show Abstract
1 Materials Science & Engineering, Penn State University, University Park, Pennsylvania, United States
5:15 PM - AA8.9
Ten Fold Catalytic Activity Enhancement in Pt/C by Doping Single Wall Carbon Nanotubes for DAFC.
Jayasri Narayanamoorthy 1 , Yuan Xu 1 , Jaewu Choi 1 Show Abstract
1 Electrical and Computer Engineering, Wayne State University, Detroit, Michigan, United States
5:30 PM - AA8.10
Mediated Biocatalytic Cathode Operating on Gas-Phase Oxygen for Fuel Cells.
Nicholas Hudak 1 , Scott Calabrese Barton 2 Show Abstract
1 Chemical Engineering, Columbia University, New York, New York, United States, 2 Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States
A mediated biocatalytic cathode comprising an osmium-based redox polymer and the oxygen-reducing enzyme laccase  can operate on gas-phase oxygen as part of a membrane-electrode assembly in a hydrogen fuel cell. When the cathode initially contains a small amount of buffer solution and is supplied with a humidified oxygen stream, the fuel cell produces 1 mA/cm2 at 0.8 V and 25°C for 5 hours or longer. Such bio-cathodes are typically tested by providing convective flow of oxygen-saturated buffer solution through the electrode. This flow increases current density but requires stirring or pumping, creating a parasitic power loss. The use of gas-phase oxygen instead of oxygen-saturated solution at the cathode is a step towards an air-breathing biocatalytic electrode, which would operate passively by using ambient air. As in conventional fuel cells, water management is crucial in such an air-breathing biocatalytic cathode. Water loss by diffusion to the anode or evaporation to the oxygen stream must be balanced with water production by the fuel cell to maintain the optimum level of hydration. The enzyme and mediator are dependent on water for catalytic activity and electron transport, respectively. When the cathode is initially saturated with buffer solution and supplied with a dry oxygen stream, current density is low because the electrode is flooded. At a constant potential of 0.8 volts, the cell steadily increases to 1.2 mA/cm2 over two hours as water evaporates and oxygen diffusion into the electrode increases. After this maximum is reached, continued drying out of the cathode adversely affects the enzyme and mediator and results in a steady decrease in current density over the following 8 hours. Use of a humidified oxygen stream significantly slows down this rate of decrease. The performance of the cell over time will be studied as a function of humidification conditions, cell temperature, and cathode catalyst composition. Cell polarization and impedance spectroscopy will be used to characterize hydration, electron transport, and oxygen transport in the cathode. In addition, hydrophobic phases will be incorporated into the carbon support to facilitate gas transport into and throughout the cathode. References:  S. C. Barton, H.-H. Kim, G. Binyamin, Y. Zhang, and A. Heller, Journal of Physical Chemistry B 2001, 105, 11917-11921.  N. S. Hudak, and S. C. Barton, Journal of the Electrochemical Society 2005, 152, (5), A876-A881.
5:45 PM - AA8.11
Investigation of the Structural Evolution and Ionic Characterization of Monolithic Phosphosilicate Gels by Concurrent Brillouin and Raman Scattering.
Arthur Feldman 1 , Liping Huang 1 , John Kieffer 1 Show Abstract
1 Materials Science & Engineering, University of Michigan, Ann Arbor, Michigan, United States
Phosphosilicate glasses are a promising material for the design of medium temperature, low humidity proton exchange membranes in fuel cells due to their relatively good conductivity and environmental robustness. However, these materials have not yet achieved the high conductivities seen in polymeric exchange membranes such as Nafion. In order to better elucidate the proton transport mechanisms in these gels we have employed a combination of light scattering techniques coupled with impedance spectroscopy. The structural development of the gels is monitored using concurrent Brillouin and Raman scattering. The latter is used to track the development of the structural units themselves and the former to gauge the connectivity between these structural units. The conductivity of the final product, as determined from impedance spectroscopy, can then be correlated to multi-scale structural information provided by the light scattering. We present the results for a series of phosphosilicate compositions and examine the relationship between the molar ratios of the phosphate and silica precursors and their application performance, both in terms of mechanical rigidity and proton conductivity.
AA9: Poster Session: Solid State Ionics
Wednesday PM, November 29, 2006
Exhibition Hall D (Hynes)
9:00 PM - AA9.1
Gas Sensing Properties of Nanostructured BiCoO3 Prepared by Solution-polymerization Method using Polyvinyl Alcohol and Sucrose.
Carlos Michel 1 , Martinez Alma 1 , Gloria Santillan 1 , Arturo Chavez 1 Show Abstract
1 Department of Physics, Universidad de Guadalajara, Guadalajara, Jalisco, Mexico
Ceramic oxides with the perovskite structure (ABO3) such as: La1-xSrxCoO3, LaFeO3 and SrFexCo1-xO3 have been successfully tested as gas sensor materials, the application of these sensors includes the detection of methanol vapor, hydrocarbons in exhaust gas outlets in combustion engines, detection of oxygen at various partial pressures, etc. Many other possible combinations of rare earth elements, alkali metals and transition metals in the perovskite structure may expand the range of electrical and gas sensing properties of these oxides; these combinations may result from the aliovalent doping with alkali metals and/or by the partial replacement of the B site by another transition metal.For cobalt-perovskites, aliovalent doping produces a mixed-valence state in cobalt: Co2+ and Co3+, which improves the catalytical and transport properties. In this work, polycrystalline samples of BiCoO3 were prepared by three different synthesis methods: solid state reaction method, solution method and solution-polymerization method using polyvinyl alcohol and sucrose. In the ceramic method, Bi(NO3)35H2O and Co(OH)2, were used as reagents; by solution method Bi(NO3)35H2O and Co(NO3)26H2O were dissolved in water containing citric acid in a low concentration. The solution polymerization (SP) route involved the preparation of a mixture of polyvinyl alcohol and sucrose in a 1:1 ratio, then this solution was mixed with an aqueous solution containing stoichiometric amounts of Bi(NO3)35H2O and Co(NO3)26H2O. The precursor materials obtained at low temperature, from each route, were calcined at 600oC for 4 hours, the powders were analyzed by X-ray powder diffraction indicating that BiCoO3 was the main phase. All the powders were observed by SEM, however, a nanostructured powder was formed only by SP method, this material was also observed by TEM in bright field mode. The average particle size of the latter was approximately 30 nm, and selected area electron diffraction was used to confirm its crystallinity. DC electrical conductivity measurements were performed in air, O2 and CO2, from room temperature to 700oC, on thick films prepared by the screen printing technique. BiCoO3 shows a p-type semiconductor behaviour, and high O2 and CO2 sensitivities at approximately 420oC. On the other hand, whereas nanostructured perovskites with composition Sm1-xAxCoO3 (A = Sr, Ba) respond with an increment (or decrement) of few ohms to a change in gas type, nanostructured BiCoO3 thick-films yield a higher change in electrical resistance of three orders of magnitude; also shorter recovery times and faster response to gases, compared to samarium cobaltites, were registered.
9:00 PM - AA9.11
High Contrast Electrochromism and Surface Characterization of Ionic Self-Assembled Multilayer Nanocomposites.
Vaibhav Jain 1 , Randy Heflin 2 , Reza Montazami 2 Show Abstract
1 Macromolecular Science and Engineering, Virginia Tech, Blacksburg, Virginia, United States, 2 Physics, Virginia Tech, Blacksburg, Virginia, United States
9:00 PM - AA9.12
Novel Green Organic Electrochromic Anode for High Contrast Smart Window.
Xiangxing Kong 1 , Chunye Xu 1 , Minoru Taya 1 Show Abstract
1 Department of Mechanical Engineering, University of Washington, Seattle, Washington, United States
9:00 PM - AA9.13
Effect Of Water On the IR Properties of Mg2+ Intercalated Electrochromic Nb2O5 Thin Films.
Gargi Agarwal 1 , G. Reddy 1 Show Abstract
1 Physics, Indian Institute of Technology Delhi, New Delhi India
9:00 PM - AA9.14
Influence of Stoichiometry of V2O5 Thin Films on the Electrochemical Properties.
M. Sahana 1 , C. Sudakar 1 , R. Baird 2 , G. Auner 2 , G. Lawes 1 , K. Padmanabhan 1 , Vaman Naik 3 , R. Naik 1 Show Abstract
1 Department of Physics and Astronomy, Wayne State University, Detroit, Michigan, United States, 2 Department Electrical and Computer Engineering, Wayne State University, Detroit, Michigan, United States, 3 Department of Natural Sciences, U Michigan-Dearborn, Dearborn, Michigan, United States
9:00 PM - AA9.15
Light-Emitting Devices from Solid-State Ionic Complexes.
Jason Slinker 1 , Leonard Soltzberg 2 , Ji-Seon Kim 3 , Hector Abruna 4 , George Malliaras 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Chemistry, Simmons College, Boston, Massachusetts, United States, 3 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom,