Symposium Organizers
Nelson Bell Sandia National Laboratories
Yet-Ming Chiang Massachusetts Institute of Technology
Sossina M. Haile California Institute of Technology
Matthew M. Seabaugh NexTech Materials, Ltd.
JJ1: Nanoionics for SOFCs - Transport and Characterization
Session Chairs
Tuesday PM, April 10, 2007
Room 3022 (Moscone West)
9:30 AM - **JJ1.1
Ionic Nanowires: Using Mesoporous Nanoarchitectures to Optimize Electrical Transport at 600°C.
Debra Rolison 1 , Christel Laberty-Robert 1 2 , Christopher Chervin 1 , Katherine Pettigrew 1 , Jeffrey Long 1 , Rhonda Stroud 3
1 Surface Chemistry Branch, Naval Research Laboratory, Washington, District of Columbia, United States, 2 , Université Pierre-et-Marie-Curie, Paris 6, Paris France, 3 Materials and Sensors Branch, Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractFuel cells are rate-critical applications that require facile transport of reactant and charge carriers for high performance [1]. Aerogels and ambigels, which are sol–gel-derived ultraporous nanoarchitectures, unite high surface area for heterogeneous reactions with a continuous, porous network for rapid diffusional flux of molecules. Response times to gas-phase analytes are >10 times faster than those of the same chemistry expressed in a xerogel [2,3]. The impedance of oxide nanoarchitectures of relevance and at temperatures of relevance to intermediate-temperature solid-oxide fuel cells markedly decreases with respect to that of the same material expressed as crystalline nanoparticles. Ceria ambigels exhibit higher oxygen-ion conductivity and more rapid spectral response to changes in the partial pressure of oxygen relative to nanocrystalline CeO2 [4]. We also find that these pore–solid nanoarchitectures impose electrical pathways that yield macroscopic diffusion lengths for oxygen-ion transport at 600°C. Gadolinium-doped ceria aerogels exhibit a diffusion transport path for oxygen ions that at 0.5-millimeters in length spans the ceramic monolith. The bonded transport pathways inherent to the bicontinuous pore-solid networks of these nanoarchitectures are key to imparting these optimal electrical responses. [1] D.R. Rolison, Science 299 (2003) 1698. [2] N. Leventis, I. Elder, D.R. Rolison, M.L. Anderson, C.I. Merzbacher, Chem. Mater. 11 (1999) 2837. [3] J.M. Wallace, J.K. Rice, J.J. Pietron, R.M. Stroud, J.W. Long, D.R. Rolison, Nano Lett. 3 (2003) 1463. [4] C. Laberty-Robert, J.W. Long, E.M. Lucas, K.A. Pettigrew, R.M. Stroud, and D.R. Rolison, Chem. Mater. 18 (2006) 50.
10:00 AM - JJ1.2
Synthesis, Characterization and Electrical property of Rich Three-dimensional Nanostructures of CeO2 Nanowires
Jong Lee 1 , Christoph Mitterbauer 1 , Nigel Browning 1 , Sangtae Kim 1
1 Chemical Engineering and Materials Science, University of California, Davis, Davis, California, United States
Show AbstractCerium dioxide (CeO2) is a fluorite structured nonstoichiomeric oxide with a greater structural tolerance to reduction. Its electrical property as well as oxygen storage capacity has been a center of attention for decades because of the potential for various applications such as exhaust catalysts, oxygen sensors, and, in particular, a solid electrolyte (SE) for solid oxide fuel cells (SOFCs) when doped. In recent years, the electrical conductivity of nanostructured CeO2 has been of particular interest. The initial hypothesis for possible enhanced conductivity is based on the assumption that the large surface/interface area in the nanomaterials may serve as fast conduction pathways leading to high conductivity. Hence the preparations as well as the electrical behavior of CeO2 in the forms of nanocrystalline (the crystallite size < 50 nm) thin films (2-dimensional) and ceramics (3-dimensional) have been extensively explored. Unlike other oxide conductors, however, little attention has been paid to synthesis of one-dimensional (1-D) nanostructured (e.g. nanowires) CeO2 and thus to their electrical properties although they can serve as ideal model systems to study the size effects on their physical properties. In this contribution, we report a synthesis of variety of 3-D nanostructures (e.g. nanobundles and stars) of CeO2 nanowires about 20 nm thick and tens of μm long, and detailed structural analysis. We also discuss the electrical conductivity of CeO2 nanobundles measured at elevated temperatures.
10:15 AM - JJ1.3
Manipulation of the Grain Boundary Resistivity of Gadolinium Doped Ceria: Alteration of the Space Charge Potential.
Hugo Avila Paredes 1 , Chien Ting Chen 1 , Sangtae Kim 1
1 Chemical Eng. and Materials Science, University of California, Davis, Davis, California, United States
Show AbstractRecently, the goal of reducing the operation temperature of solid oxide fuel cells (SOFCs) to a 500 – 700 degrees Celsius range has become of particular interest because of the advantage of eliminating the constraint of the type of materials used to constituting the SOFC system. In this context, doped ceria is one of the best candidates to be used as an electrolyte in SOFC systems since it is characterized by a higher conductivity in the temperature range of interest, compared to yttria stabilized zirconia, the most commonly used electrolyte in conventional SOFCs.Lowering the operation temperature however may have a significant effect on the contribution of the grain boundary resistance to the overall electrolyte resistance to oxygen ion diffusion, which is usually not considered at conventional operation temperatures. One of the crucial factors contributing to the grain boundary resistance is the space charge potential: the grain boundary core of ceria is reported to be positively charged, such that oxygen vacancies are depleted in the space charge layers. This causes a blocking effect for oxygen ion conduction across grain boundaries. It is known that at low dopant concentrations, the space charge potential dominates the grain boundary resistance. In the present contribution, we demonstrate that it is possible to reduce the positive core charge in the grain boundaries of 1% Gd doped ceria by the introduction of small amounts of different transition metals (TMs: Co, Fe, Cu, Mn) since they almost exclusively segregate to the grain boundaries but leave the bulk electrical properties mainly unchanged. We also discuss the effect of the concentration of the different TMs on 1% Gd doped ceria and present the results obtained for highly doped ceria.
10:30 AM - JJ1.4
Quantitative Analysis of Space Charge Effects in Sm Doped Ceria as Measured by Impedance Spectroscopy.
Wei Lai 1 , Sossina Haile
1 Materials Science Department, California Institute of Technology, Pasadena, California, United States
Show Abstract11:15 AM - **JJ1.5
Can Nano Technology Play a Role in Solid Oxide Fuel Cells?
Eric Wachsman 1
1 UF-DOE High Temperature Electrochemistry Center, University of Florida, Gainesville, Florida, United States
Show AbstractSolid oxide fuel cells (SOFCs) offer great promise as a clean and efficient process for directly converting chemical energy to electricity while providing significant environmental benefits. They are essentially pollution free and have three times the efficiency of an internal combustion engine. SOFCs are unique in that they not only operate on hydrogen, but can also operate on fuels such as natural gas and gasoline. Thus, they have the ability to operate within both the current fossil fuel based energy infrastructure and the future proposed hydrogen fuel infrastructure. Nano technology is purported to hold the answer to our energy needs. However, the role of nanostructured ceramics in SOFCs is not clear. At typical SOFC operating temperatures (700-1000°C) most materials cannot maintain a nanostructure. Therefore, the key for the utilization of nanostructured ceramics in SOFCs is to reduce the operating temperature. However, this dramatically reduces the SOFC performance. The opportunities and tradeoffs for employing nanostructured ceramics in SOFCs will be described.
11:45 AM - JJ1.6
Dynamic Pathway Models for ion Transport in Nanostructured Heterolayers.
Stefan Adams 1 , Esther Tan 1
1 Materials Science and Engineering, National University of Singapore, Singapore Singapore
Show Abstract12:00 PM - JJ1.7
In-situ High-resolution Ion Scattering Studies on Oxygen Defect Chemistry and Migration Kinetics Across Nanoscale Oxide Hetero-interfaces.
Chia-Lin Chang 1 , V. Shutthanandan 2 , Subhash Singhal 2 , Shriram Ramanathan 1
1 Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show Abstract12:15 PM - JJ1.8
Use of Oxygen-Plasma-Assisted MBE to Achieve Optimum Conductivity in Highly Oriented [Ce1-x Smx]O2-x Thin Films
Z. Yu 1 , O. Marina 2 , C. Wang 2 , Laxmikant Saraf 2 , M. Engelhard 2 , V. Shutthanandan 2 , P. Nachimuthu 2 , D. McCready 2 , S. Thevuthasan 2
1 Department of Chemistry, Nanjing Normal University, Nanjing 210097 China, 2 Environmental Molecular Sciences Lab, Pacific Northwest National Laboratory, Richland , Washington, United States
Show AbstractIt is known that grain boundary orientation plays significant role in determining the final conductivity of the electrolyte layer used in solid oxide fuel cells (SOFC). In order to perform an effective development of such electrolyte layers, one needs to achieve a fine control over the tuning of grain boundary density. oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE) is an excellent technique to grow high quality oriented electrolyte films such as [Ce1-x Smx]O2-x which are known to possess high ionic conductivity in SOFC at relatively lower operating temperatures. In this study, we have used (OPA-MBE) to grow highly oriented [Ce1-x Smx]O2-x films on single crystal c-plane Al2O3 to study conductivity as a function of Sm-concentration. These films were grown at an oxygen partial pressure of ~2.0×10–5 Torr and at a substrate temperature of 650 0C in a dual-chamber ultrahigh vacuum (UHV) system equipped with an electron cyclotron resonance (ECR) oxygen plasma source. Several microstructural, morphological and surface characterizations were performed along with impedance spectra measurement over the frequency range of 1 MHz to 1 Hz in air for the temperature range of 300-900 0C by conventional d.c four-gold-probes (Van der Pauw) method. We have observed that dominant (111) orientation in these films were maintained up to 10 atom% dopant concentration. The highest conductivity of 0.04 S.cm-1 at 600 0C is observed with 5 atom% (~11 cation%) samaria dopant concentration. We believe that a loss of orientation enhancing the grain boundary scattering is mainly responsible for decreased conductivity. We conclude our discussion by focusing on [Ce1-x Smx]O2-x system for its novel ion conducting properties for future intermediate temperature SOFC’s.
12:30 PM - **JJ1.9
Structure Studies of Nanostructured Energy Related Materials.
Simon Billinge 1
1 Dept. of Physics & Astronomy, Michigan State University, East Lansing, Michigan, United States
Show AbstractA diverse array of complex materials and structures are driving the nanotechnology revolutions. This is especially evident in systems for energy production, storage and conversion.To understand and design these materials, it is essential to perform high precision structural characterization at the nanoscale. Often, even sub-Angstrom changes in inter-atomic bond lengths have profound consequences for the chemistry and functionality of these structure-sensitive materials. Crystallographic methods are the gold standard for atomic structure determination, however a broad and growing class of materials and/or nanophase morphologies do not yield to a crystallographic analysis. The scattering is diffuse and Bragg-peaks become broad and overlapped. This is "the nanostructureproblem" which currently has no robust solution. I will discuss alternative, more broadly applicable, methods which are emerging for these nanostructure problems. I will also describe current examples where we have applied scattering methods, in particular the atomic pair distribution function, to energy related materials.
JJ2: Solid Oxide Fuel Cells
Session Chairs
Tuesday PM, April 10, 2007
Room 3022 (Moscone West)
2:30 PM - **JJ2.1
Formation of Nanometer-Scale Electro-Catalyst Particlesin Novel Solid Oxide Fuel Cell Anodes
Scott Barnett 1
1 Materials Science, Northwestern University, Evanston, Illinois, United States
Show AbstractThis talk will describe novel solid oxide fuel cell (SOFC) anodes that contain a nano-scale electro-catalyst phase. Motivations for replacing conventional Ni-YSZ anodes with these oxide anodes will be discussed, particularly novel energy applications involving hydrocarbon fuels. A new method for forming nanometer-sized catalyst particles within SOFC anodes will be described. One example is a composite anode consisting of La0.8Sr0.2Cr0.82Ru0.18O3-δ (LSCrRu) and Ce0.9Gd0.1O1.95 (GDC). Electrical testing in H2 fuel of SOFCs with these anodes showed a factor of ~3 decrease in anode polarization resistance during the first ~50h of cell operation, with cell power density reaching 0.5 W/cm2 at 800oC (limited mainly by electrolyte resistance). Electron microscope observations showed this change was due to the precipitation of 1-3nm diameter Ru particles on the chromite particle surfaces. Life tests beyond the initial performance improvement (~50 - 300 h) showed stable anode polarization resistance and no obvious coarsening of the Ru nano-clusters. This general approach allows one to introduce nanometer-sized catalyst particles in SOFC anodes after high-temperature firing steps are completed, without the need for additional processing steps.
3:15 PM - JJ2.3
Impedance Studies of Thin-film, Patterned and Nanostructured Sr-doped LaMnO3 on Yttria-stabilized Zirconia for Probing Oxygen Reduction Kinetics
Gerardo Jose La O 1 , Yang Shao-Horn 1
1 , MIT, Cambridge, Massachusetts, United States
Show AbstractHigh temperature or solid oxide fuel cells (SOFCs) have been identified as having large potential for stationary and possibly mobile power applications with enhanced system efficiency, low noise and minimal environmental impact. Sr-doped LaMnO3 (LSM) and Yttria-stabilized Zirconia (YSZ) are the conventional cathode and electrolyte materials used for these systems as they have shown excellent performance and lifetime. Nonetheless, the precise molecular mechanisms that occur during oxygen reduction reaction (ORR) at the cathode/electrolyte interface are still unclear and have been a roadblock for further enhancement of SOFC performance, especially at reduced temperatures. In this study, LSM is fabricated by thin-film sputtering techniques and patterned via photolithography to obtain precise microelectrode (dimensions 50-200μm) and microstructures (240nm thickness and 20-70nm columnar grain widths). These microelectrodes are then tested using electrochemical impedance spectroscopy (EIS) to identify the various transport/reaction steps occurring at the LSM/YSZ interface. Initial EIS results have shown at least four distinct processes occurring during ORR, namely, (i) a surface chemical reaction on LSM, (ii) bulk/three-phase boundary (TPB) charge transfer process, (iii) surface diffusion on LSM and (iv) electrolyte ionic transport. The overall limiting reaction was found to originate from the bulk/TPB charge transfer process below 700°C and shifted to surface chemical reactions above this temperature. Moreover, using the patterned electrodes, ORR current contributions from the bulk and TPB incorporation pathways were estimated by correlating microelectrode size to the EIS data. This novel microelectrode technique, although in the early stages, has shown good potential to deconvolute coupled reaction/transport processes and provide a clearer understanding of the molecular mechanisms that occur during ORR.
3:30 PM - JJ2.4
Solid Oxide Fuel Cell with Nanostructured Fuel Electrode.
Syed Ansar 1 , Zeynep Ilhan 1
1 , German Aerospace Center, Stuttgart Germany
Show AbstractNanostructured YSZ+Ni anodes (fuel electrode) for solid oxide fuel cell (SOFC) were developed by plasma spraying. Influence of processing parameters was correlated with deposit microstructure and properties. Anodes with well distributed finely porous nanoscale microtructure were produced by controlling plasma enthalpy and velocity. These anodes exhibited high gas permeability, suitable high temperature electronic conductivity, enhanced triple phase boundaries and catalytic activity. Electrochemical performance of optimized nanostructured anode was compared with conventional NiO+YSZ and Ni-C+YSZ anodes by testing full cells at 800°C. 9.5 mol% YSZ electrolyte and LSM cathode were deposited onto these anodes for electrochemical testing in static and dynamic conditions. Impedance spectroscopy measurements were performed to collect data on polarization resistance and catalytic behavior of anode layers. It was established that enlarged reaction zone, provided by high specific surface area of nanostructured anodes, and finely porous microstructure, led to lower activation and concentration polarizations and enhanced cell performance by more than 60% compared to conventional cells.
3:45 PM - JJ2.5
Nanoscale Gd-doped CeO2 Buffer Layer for a High Performance Solid Oxide Fuel.
Cornelia Endler 1 , Andre Weber 1 , Ellen Ivers-Tiffee 1 , Uwe Guntow 2
1 , Institut fuer Werkstoffe der Elektrotechnik, Karlsruhe Germany, 2 , Fraunhofer-Institut fuer Silicatforschung (ISC), Wuerzburg Germany
Show Abstract4:30 PM - **JJ2.6
Interface Engineering for Solid Oxide Fuel Cells:Potential of Nanoscaled Interface Layers.
Ellen Ivers-Tiffee 1
1 Institut fuer Werkstoffe der Elektrotechnik , Universitaet Karlsruhe, Karlsruhe Germany
Show AbstractThe solid oxide fuel cell is an efficient alternative for future energy conversion, contributing to a sustainable future. However, the system’s efficiency and performance is limited by losses resulting from reaction kinetics and charge transport processes. The reaction kinetic of the cathode is controlled by gas diffusion, adsorption and dissociation of oxygen molecules, surface transport, charge transfer processes and the incorporation of oxygen ions from the cathode material into the ionic conducting electrolyte. In SOFC-technology, there are 3 types of porous gas-diffusion cathodes. Each shows a different characteristic in the reaction kinetic:1. Single phase, electronic conducting cathode: Electrochemical reaction takes place solely at the three phase boundary of the cathode and electrolyte material and the oxidant gas. Due to insufficient power density, this configuration is only of minor technical relevance. 2. Composite cathode, consisting of an ionic conductor and an electronic conductor: The 2 materials interpenetrate each other, resulting in an expansion of the electrochemically active zone into the cathodic volume. Because of the high power density of this structure, state-of-the-art SOFCs use composite cathodes. 3. Single phase, mixed ionic and electronic conducting (MIEC) cathode: Due to an additional ionic conductivity of some metal oxide perovskite materials, the electrochemical active site can be increased to the total cathodic surface. By applying this type of electrode as a thin film layer, the already high performance of the material can be improved significantly. Ohmic losses resulting from the moderate ionic conductivity are reduced, while still having a large electrochemically active surface.Nanostructured functional layers were introduced in the SOFC technology in 1999 by the application of Metal-Organic-Deposition (MOD) method [1]. In this paper, nanostructured MOD thin films of the perovskite material Lanthanum-Strontium-Cobaltate (LSC) are used for fundamental research on transport mechanisms within this MIEC material. 1st tests have already revealed an outstandingly high performance of such thin films: An ASRCathode of 85 mΩ.cm2 at a temperature of 600 °C was measured. This does not represent the full potential of nanostructured SOFC cathodes, even though it is the lowest value ever reported.This new technology also shows great potential for real world applications such as auxiliary power unit (APU) systems. Due to the high performance and the possible combination of nano layers with different coefficients of thermal expansion, start up times can be shortened and operation temperatures can be lowered. This has the advantage that lower grade and less expensive materials for insulation and sealing can be applied. Such systems include airplane, automotive and ship APUs as well as portable systems in the (sub) kW range. [1]D. Herbstritt, A. Weber, E. Ivers-Tiffée, The Electrochemical Society, PV 99-19, 972-980, (1999)
5:00 PM - JJ2.7
Doped Nanocrystalline Pt-promoted Ceria-Zirconia as Anode Catalysts for IT SOFC: Synthesis and Properties
Vladislav Sadykov 1 , Natalia Mezentseva 1 , Galina Alikina 1 , Anton Lukashevich 1 , Vitalii Muzykantov 1 , Lubsan Batuev 1 , Andrei Boronin 1 , Egor Pazhetnov 1 , Eugenii Paukshtis 1 , Alevtina Smirnova 2 , Oleksandr Vasylyev 3 , John Irvine 4 , Oleg Bobrenok 5
1 , Boreskov Institute of catalysis, Novosibirsk Russian Federation, 2 Global Fuel Cell Center, University of Connecticut, Storrs, Connecticut, United States, 3 , Institute of Materials Science Problems , Kyiv Ukraine, 4 , University of St Andrews, Fife United Kingdom, 5 , Institute of Thermophysics SB RAS, Novosibirsk Russian Federation
Show AbstractNanocrystalline doped CeO2 or ceria-zirconia with supported precious metals are promising as active components of catalysts for transformation of hydrocarbons into syngas via partial oxidation (PO) and steam reforming (SR). Their supporting on cermet anodes of IT SOFC is considered now as a promising approach to enhance performance and suppress coking when operating on stoichiometric methane/steam feeds. Both lattice oxygen mobility and precious metal dispersion appear to be controlling factors for these additives application as cermet anode dopants. While pure ceria-zirconia is unstable in hydrothermal conditions due to segregation of Ce- or Zr-enriched phases, its doping by Me3+ cations stabilizes fluorite-like solid solution and prevents sintering. This work present results of systematic studies of the surface properties and lattice oxygen mobility and reactivity of nanocrystalline ceria-zirconia (Ce:Zr=1:1) system doped by rare-earths cations (Gd, Sm, La, Pr, dopant content up to 30 at.%) prepared via modified Pechini route as related to catalysis of anode reactions in IT SOFC. Pt (1.4 wt.%) was supported via the incipient wetness impregnation with H2PtCl6 solution. Surface features were characterized by XPS and FTIRS of adsorbed CO, while oxygen mobility and reactivity were estimated by using oxygen isotope exchange, CH4 TPR and methane steam reforming. For oxidized samples, both small Pto clusters and cationic Pt forms (Pt+, Pt2+ and even Pt4+ state for Pr-doped samples) were revealed indicating strong Pt-support interaction with preferable Pt location on Lewis acid sites and in vicinity of domain boundaries. For samples doped with the most basic Sm and La cations, a partial incorporation of Pt into the surface layer or Pt decoration by LnOx species takes place. The lattice oxygen mobility tends to decline with the dopant content due to preferential formation of dopant-anion vacancy complex defects while increasing with the density of domain boundaries especially those decorated by Pr3+/4+ or Ptn+ cations forming mixed ionic-electronic conducting chains. In general, the lattice oxygen mobility tends to increase with the dopant size due to expansion of the fluorite-like lattice decreasing the activation energy for the oxygen migration. The rate of samples reduction by CH4 as well as the specific activity in methane PO and SR are mainly determined by the surface concentration of Pt2+ species as precursors of small reactive Pto clusters. The lattice oxygen mobility was shown to prevent coking even in realistic stoichiometric methane-steam feeds both for nanocrystalline active components and cermet Ni-YSZ anodes promoted by up to 10 wt.% of these catalysts. Stable and efficient performance in the 600-800 C range is thus achieved. This work is in part supported by NATO SFP 980878 and Integration Project 95 of SB RAS –NaN Ukraine.
5:15 PM - JJ2.8
La0.9Sr0.1Ga0.8Mg0.2O3-δ Nanopowders Prepared by Glycine-Nitrate Combustion Process for Solid Oxide Fuel Cell Electrolyte
Bangwu Liu 1 , Yue Zhang 1 , Ruiping Gao 2 , Kexin Chen 2
1 Department of Materials Physics, University of Science and Technology Beijing, Beijing China, 2 , Natinal Natural Science Foundation of China, Beijing China
Show Abstract5:30 PM - **JJ2.9
Role of Kinetics in the Measurement of Properties Under Thermodynamically Equilibrated Conditions.
Anil Virkar 1
1 Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah, United States
Show AbstractTransport in many oxides is very sluggish at low temperatures. Slow transport kinetics makes it difficult to accurately measure phase equilibria and properties. Approaches are needed to accelerate kinetics to achieve equilibrium in a reasonable time. Many oxides,MOy±δ , exhibit nonstoichiometry,δ , which is a function of temperature, T , and oxygen partial pressure, po2, δ=δ(T, po2). This deviation manifests as point defects (vacancies and interstitials), and electronic defects (electrons and holes). Properties of oxides such as ionic and electronic conductivities, chemical diffusion coefficient, thermoelectric power, chemical expansion, etc. depend on concentrations and mobilities of defects. Upon change of environment, sample tends to absorb or expel oxygen, with kinetics governed by chemical diffusion coefficient, Do . For a sample thickness 2d , equilibration time required is tCeq ~d2/Do. For a 2d = 2 mm, equilibration time in excess of days is common, and equilibration does not occur in a typical experiment. For measurement of ‘true’ properties, kinetics must be enhanced, which can be achieved by using porous samples with grain size ~microns. This expedites kinetics by six orders magnitude, and facilitates measurement of properties under equilibrated conditions. Experimental results will be presented on measurements of thermoelectric power on oxides (Gd-doped CeO2 and Y-doped BaZrO3), using porous and dense samples. Under equilibrated conditions, thermoelectric power is same on porous and dense samples. Kinetics of equilibration was over two orders of magnitude faster in porous samples. This suggests thermoelectric power on oxides should be measured on porous instead of dense samples.Another example is measurement of chemical diffusion coefficient and surface exchange coefficient on mixed ionic electronic conducting (MIEC) oxides (Sr-doped LaCoO3). Samples with porous surface layers allow accurate measurement of transport parameters. Slow kinetics of transport also prevents accurate measurement of phase equilibria. Many ceramic solid solutions stable at high temperatures are only stable kinetically at lower temperatures. Determination of true phase equilibria requires that kinetics of transport be accelerated. This can be achieved by enhancing solid state transport through defect chemistry, or by using molten salts to provide alternate path for transport. The TiO2-SnO2 system will be described as a case study.
Symposium Organizers
Nelson Bell Sandia National Laboratories
Yet-Ming Chiang Massachusetts Institute of Technology
Sossina M. Haile California Institute of Technology
Matthew M. Seabaugh NexTech Materials, Ltd.
JJ3: Thermoelectrics and Batteries
Session Chairs
Wednesday AM, April 11, 2007
Room 3022 (Moscone West)
9:30 AM - **JJ3.1
Self-Assembled Nanometer Lamellae of Thermoelectric PbTe and Sb2Te3 with Epitaxy-like Interfaces.
G. Jeffrey Snyder 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractRemarkably high thermoelectric figure of merit (zT > 2) has been achieved in thin film, epitaxial superlattices or “quantum well” materials with feature sizes of several to tens of nanometers using (Bi,Sb)2Te3 and Pb(Te,Se) based systems. However, improved performance over bulk processed material has yet to be reported because of the difficulty of the thin film processing and the complications with fabricating devices out of thin film thermoelectric material. We have found that such epitaxial superlattice like structures can be formed and their feature sizes controlled with bulk processing. Utilizing the decomposition of metastable Pb2Sb6Te11 into PbTe and Sb2Te3, a layered (lamellar) microstructure of PbTe and Sb2Te3 is produced that can be controlled by the temperature and time of the decomposition process. Average lamellar spacings of as small as 180 nm are observed, corresponding to a PbTe layer thickness of 40 nm. Adjacent PbTe and Sb2Te3 lamellae are crystallographically oriented indicating high quality epitaxy-like interfaces.
10:00 AM - **JJ3.2
Oxides for Direct Thermal-to-electric Energy Conversion.
Xiao-Dong Zhou 1 , Larry Pederson 1
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractMaterials research focused on energy conversion is driven by the recognition of limited fossil energy sources and continuously increasing consumption, which raises the energy shortage as one of the most challenging problems facing humanity in the next few decades. Thermoelectric devices produce electricity from temperature differentials. During this process, the non-uniform distribution of charge carriers leads to an electrical and chemical potential difference across a material. To fully enable this technology, high efficiency thermoelectric p- and n-type materials that are stable at high temperature are required. Ideal thermoelectric (TE) materials must simultaneously possess high electrical conductivity (σ), low thermal conductivity (κ), and a large Seebeck coefficient (S). Oxides have not received much attention for TE applications until very recently, primarily because of their modest figure of merit, (S2σT/κ) or ZT, where S usually can be high but both σ and κ are low. To illustrate this, I will provide a background on energy conversion research and then describe the electrical/thermal transport in both p type and n type oxides, with emphasis on the role of size and crystal structure on these properties.
11:00 AM - **JJ3.3
Nanocomposites: Opening The Door to New Concepts in Energy Storage.
F. Badway 1 , W. Tong 1 , N. Pereira 1 , L. Weinstein 1 , P. Barpanda 1 , W. Yourey 1 , J. Al-Sharab 1 , F. Cosandey 1 , A. Skrzypczak 1 , I. Plitz 1 , J. Gural 1 , Glenn Amatucci 1
1 , Rutgers University, North Brunswick, New Jersey, United States
Show AbstractElectrochemical energy storage in the form of state of the art battery technologies such as the ubiquitous Li-ion battery is largely governed and limited by a myriad of charge transport issues. These challenges are manifested in both electronic and ionic aspects. Ionic transport includes diffusion between electrodes via liquid or solid state electrolytes, diffusion through interfaces which form on electrodes as byproducts of reactions with the electrolyte, and complex diffusion within and between the domains of the electroactive material. The latter can exist as distributed intercalation processes or through two phase boundaries which develop during the redox process. Electronic transport includes electronic conduction within the electrode material which in many cases changes as a function of depth of discharge, tunneling relatively insulative solid state electrolyte interfaces to a conductive additive, and finally percolation of the electron to the current collector which is often covered in a semiconducting or thin insulative oxide. Nanomaterials and nanocomposites have opened the door to the utilization of materials and more importantly energy storage mechanisms not deemed practical or even possible a decade ago. In almost all cases, this has been due to improved transport, either electronic or ionic. In this paper we take a look at a few of these which we have developed in our laboratories. We will specifically relate the nanoenabling aspects of transport to the delivery of (1) high power, (2) storage of a high degree of energy per volume and weight, and (3) the development of unique approaches for the fabrication of microbatteries. In each case we will discuss not only the aspect of transport that has enabled each property and/or mechanism but will also put in context relative to practicality and the possible deleterious aspects of the adoption of nanomaterials in electrochemical energy storage systems. Stress will be given to the fact that only in a very few circumstances can nanomaterials be adopted blindly, the entire chemical system and in many cases engineering must be developed in parallel to realize the true potential of nano in electrochemical energy storage.
11:30 AM - JJ3.4
Embedded Nanostructured Cathodes of Defective Lithium Manganospinels For MicroBattery Applications
Arul Chakkaravarthi Arjunan 1 , Rajiv Singh 1 , Deepika Singh 2
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 , Sinmat Inc., Gainesville, Florida, United States
Show Abstract11:45 AM - JJ3.5
Metal Oxide Nanoparticles for Improved Lithium Ion Battery Technologies
Anne Dillon 1 , Se-Hee Lee 1 , Rohit Deshpande 1 , Philip Parilla 1 , Erin Whitney 1 , Kim Jones 1 , A. Mahan 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractLithium-ion batteries are the current power sources of choice for portable electronics. Although such batteries are commercially successful, they are not keeping pace with the rapid advances in computing technologies. Also, further improvement of performance and simultaneous reduction in cost as well as material toxicity could allow for the deployment of lithium-ion batteries in hybrid electric vehicles. Hot-wire chemical vapor deposition has been employed as an economically scalable method for the deposition of crystalline metal oxide nanoparticles at high density(1). Under optimal synthesis conditions, only crystalline nanostructures with a smallest dimension of ~ 10 - 50 nm are observed with extensive transmission electron microscopy analyses. The crystalline phases of the nanoparticles have been probed with Raman spectroscopy, as well as, electron and x-ray diffraction. Recently the incorporation of crystalline molybdenum oxide nanoparticles into porous films has led to profound advancements in state-of-the–art negative electrodes (anodes) in lithium-ion batteries. A surprisingly high and reversible capacity of ~ 600 mAh/g has been observed. Furthermore, the nanoparticle materials exhibit a high rate capability due to the reduced solid state Li-ion diffusion length. Coating the nanoparticle films with an elastic solid polymer electrolyte mitigates structural mechanical problems associated with volume changes accompanied by lithium insertion and increases the durability. Investigations to employ alternate metal oxides to improve the positive electrode (cathode) materials are underway. The synthesis of these novel nanostructured materials and their potential for improving lithium-ion battery technologies will be discussed in detail.(1)S.-H. Lee, R. Deshpande, P. A. Parilla, K. M. Jones, B. To, A. H. Mahan, and A. C. Dillon, Adv. Mat. 18 (2006) 763.
12:15 PM - JJ3.7
Size-Dependent Lithium Miscibility Gap In Lithium Iron Phosphate.
Nonglak Meethong 1 , Hsiao-Ying Huang 1 , W. Craig Carter 1 , Yet-Ming Chiang 1
1 , MIT, Cambridge, Massachusetts, United States
Show Abstract12:30 PM - JJ3.8
Modelling The Observed Particle-Size Dependent Phase Stability In LiFePO4: Gibbs-Thomson Or Coherency Stresses?
Hsaio-Ying Huang 1 , Nonglak Meethong 1 , Yet-Ming Chiang 1 , W. Craig Carter 1
1 , MIT, Cambridge, Massachusetts, United States
Show Abstract12:45 PM - JJ3.9
NASICON-like Phases in InPO4-Na3PO4 Quasibinary System.
Anna Potapova 1 , Irina Smirnova 1 , Felix Spiridonov 2 , Andrey Novoselov 1 , Sergey Stefanovich 2 , Galina Zimina 1
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
Show AbstractJJ4: Batteries and Solid Oxide Fuel Cells
Session Chairs
Wednesday PM, April 11, 2007
Room 3022 (Moscone West)
2:30 PM - **JJ4.1
Hierarchically Organized Ceramics for Li Storage: Novel Wiring Concepts for Fast Kinetics.
Janez Jamnik 1
1 , National Institute of Chemistry, Ljubljanan Slovenia
Show AbstractOne of the primary aims in battery research is to achieve moderate rate performance when utilizing insulating materials with high intrinsic capacity or very high rates when using moderately conducting materials. In principle, this can be achieved by introducing hierarchically organized mixed conducting wiring matrix into the bulk active material. One possibility is to prepare a material with hierarchically organized pores internally coated by carbon or contacted by nanowires, thus providing ionic and electronic contacts from the inner side of the material. This strategy is demonstrated on the example of LiFePO4 where the whole architecture can be made in a single synthesis step. During the heat tretment of initial mixture, an appropriate organic additive is decomposed simultaneously into gases and solid carbon. The former create interconnected pores with wide distribution of pore sizes. The carbon is deposited on the walls of emerging pores as a continuous nanometer-thick film that is permeable for Li ions in the perpenicular direction and electronically conductive in the lateral direction. The preparation and microstrucctural characterization has been studied in detail using XRD, thermal analysis, EXAFS/XANES, Moessbauer spectroscopy, SEM, TEM with electtron diffraction and Raman spectroscopy. The transport properties of carbon coatings have been further checked on model architectures prepared on well-defined titania particles. Furthermore, the stabilizing effect of carbon on the microstructure has been elucidated. The kinetics of Li storage was examined using in situ X-ray diffraction during charge-discarge cycles combined with impedance spectroscopy. To distinguish between the transport steps along the mixed-conductive wiring networks and the nearly insulating bulk we varied the extensive electrode parameters. We identified two different transport mechanisms, one typical for the low and the other for the high current densities. The so-called core-shell model of the biphasic system has been critically examined. Possible structural changes in the system are discussed in view of a non-trivial size effect. Finally, the generality of the findings is tested on a completely new family of active host materials with even lower intrinsic conductivity, but potentially high capacities – the silicates.
3:00 PM - JJ4.2
Metal Oxide Nanowires as Li Battery Electrodes
Yi Cui 1 , Candace Chan 1
1 , Stanford University, Stanford, California, United States
Show AbstractNanostructured materials can potentially increase Li battery energy and power density due to their large surface area and short Li ion diffusion distance. Here we report the synthesis and Li intercalation in metal oxide nanowire materials. With V2O5 nanowires as a model system, we found that transformation of V2O5 into the ω-Li3V2O5 phase depends strongly on the size of nanowires. Transformation can take place within 10 seconds in thin nanowires, suggesting a Li diffusion constant 3 orders of magnitude faster than in bulk materials, resulting in a significant increase in battery power density. For the first time, complete delithiation of ω-Li3V2O5 back to the single-crystalline, pristine V2O5 nanowires was observed, indicating a 30% higher energy density. These new observations are attributed to the ability of facile strain relaxation and phase transformation at the nanoscale. In addition, efficient electronic transport can be maintained to charge a Li3V2O5 nanowire within less than 5 seconds. These exciting nano-size effects can be exploited to fabricate high performance Li-batteries for applications in electric and hybrid electric vehicles.
3:15 PM - JJ4.3
Freestanding Mesoporous Quasi-Single-Crystalline Co3O4 Nanowire Arrays and Their Use as Negative Electrode for Lithium Ion Battery.
Yanguang Li 1 , Bing Tan 1 , Yiying Wu 1
1 Chemistry, The Ohio State University, Columbus, Ohio, United States
Show Abstract Co3O4 is a technologically important material with applications in Li-ion batteries, gas sensing, and electrochromic devices. Nanostructured Co3O4 is particularly attractive due to the high surface area and enhanced electrochemical reactivity. For most demonstrated applications of Co3O4, electric signals need to either be applied to or be extracted from the active materials. In the case of Li-ion batteries, this is normally achieved by mixing nanostructured Co3O4 with carbon and polymer binders and compressing them into pellets. This risks negating the benefits associated with the reduced particle size and introduces supplementary, undesirable interfaces. For these reasons, the direct growth of Co3O4 nanowires on various substrates, especially on conducting substrates, is an important issue for their applications. Here we report a facile template-free method for the large-area growth of freestanding hollow Co3O4 nanowire arrays on a variety of substrates including transparent conducting glass, Si wafer, and copper foil 1. More interestingly, these nanowires have the combined properties of mesoporosity and quasi-singlecrystallinity. With their high surface area and crystallinity, and their direct growth on conductive substrate, these Co3O4 nanowire arrays are excellent candidate for various applications, and their direct use as negative electrode for Li-ion battery was demonstrated.1. Li, Y., Tan, B., Wu, Y. J. Am. Chem. Soc. 2006, 128, 14258-14259
3:30 PM - JJ4.4
Molecular Dynamics Simulations Of Li Ion Diffusion In Rapid Transport Paths In Nanostructured Vanadia Cathodes.
Stephen Garofalini 1 , Weiqun Li 1
1 , Rutgers University, Piscataway, New Jersey, United States
Show AbstractMolecular dynamics (MD) computer simulations using a charge transfer model have been used to study Li migration in a nanocrystalline vanadia cathode in a solid state oxide thin film battery. Previous simulations have shown that Li transport into the cathode crystal is effected by the orientation of this layered crystal at the interface, with the largest activation barriers to diffusion in the [001] direction. Experiments show that this slowest diffusion direction is perpendicular to the interface, thus inhibiting diffusion into the cathode. However, molecular dynamics simulations show rapid diffusion paths in nanocrystalline vanadia that would offset the natural orientation of these crystals at the cathode/electrolyte interface. These rapid diffusion paths involve a thin amorphous vanadia film between the nanocrystals of vanadia and could be processed using controlled depositions and annealing.
3:45 PM - JJ4.5
Nanostructured Electrode Materials for High Energy Density Thermal Batteries
Ming Au 1
1 , Savannah River National Laboratory, Aiken, South Carolina, United States
Show Abstract5:00 PM - JJ4.7
Processing and Structural Characterization of Nanoscaled La1-xSrxCoO3 (LSC) Thin Film Cathodes.
Christoph Peters 1 , Irene Netsch 1 , Holger Goetz 1 , Uwe Guntow 2 , Andre Weber 1 , Ellen Ivers-Tiffee 1
1 Institute of Materials for Electrical Engineering, University of Karlsruhe, Karlsruhe Germany, 2 , Fraunhofer Institute for Silcate Research (ISC), Würzburg Germany
Show Abstract5:15 PM - JJ4.8
Effects of Coarsening on the Microstructure of Solid Oxide Fuel Cell Electrodes.
Hsun-Yi Chen 1 , Roberto Mendoza 1 2 , James Wilson 2 , Worawarit Kobsiriphat 2 , Hon Hiller 3 , Dean Miller 3 , Peter Voorhees 2 , Stuart Adler 4 , Scott Barnett 2 , Katsuyo Thornton 1
1 Material Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Material Science and Engineering, Northwestern University, Evanston, Illinois, United States, 3 , Argonne National Laboratory, Argonne, Illinois, United States, 4 Chemical Engineering, University of Washington, Seattle, Washington, United States
Show AbstractThe microstructure of a solid oxide fuel cell anode evolves during operation, as it coarsening to reduce the surface energy. Coarsening degrades the efficiency of solid oxide fuel cells (SOFCs) because the electrochemically active regions such as the three-phase boundaries decrease in size. Therefore, a detailed understanding is required in order to control the coarsening effects and to increase the SOFC efficiency and lifetime. We perform simulations of the evolution of anodes in SOFCs using a phase-field model. Experimentally obtained three-dimensional reconstructions of SOFC electrodes provide the initial microstructural data. The cell efficiency is highly dependent on the triple phase boundaries, which are the anode reaction zone. The tortuosity determines the effective diffusion coefficients. The evolution of these parameters is examined systematically to characterize the effect of coarsening on SOFC efficiency.
5:30 PM - **JJ4.9
Synthesis Routes to Nanostructured Solid Oxide Electrolytes.
Martha Mecartney 1
1 The Henry Samueli School of Engineering, University of California-Irvine, Irvine, California, United States
Show AbstractThe goal of this research is to effectively study how changing the grain size of oxide electrolytes to a nanocrystalline grain size will influence the ionic conductivity. The challenges of fabricating dense single phase solid oxide electrolytes with a nanocrystalline grain size will be examined. Different synthesis routes will be presented, from sol-gel solution chemistry approaches to chemical vapor deposition for the successful fabrication of thin film nanocrystalline yttria stabilized zirconia. In order to minimize interfacial electrode effects and to compare conductivity data on nanocrystalline electrolytes with the extensive data on large grain electrolytes, it would be preferable to fabricate dense bulk materials with a range of grain sizes down to the nanocrystalline range. However, these materials are often difficult to synthesize in bulk while retaining a nanocrystalline grain size. Research using cryo-milling and a two step sintering process in order to make bulk yttria stabilized zirconia with a nanocrystalline grain size will be presented. Traditional yttria stabilized materials, fabricated with a range of grain sizes in bulk, will be compared to a newer class of lanthanum silicate apatite electrolytes. The vacancy diffusion mechanism for oxygen ions in yttria stabilized zirconia can be contrasted with a proposed interstitial diffusion mechanism for oxygen ions in lanthanum silicate apatite. The role of grain boundaries on limiting oxygen ion transport for these two systems will be discussed.
Symposium Organizers
Nelson Bell Sandia National Laboratories
Yet-Ming Chiang Massachusetts Institute of Technology
Sossina M. Haile California Institute of Technology
Matthew M. Seabaugh NexTech Materials, Ltd.
Thursday AM, April 12, 2007
Room 3022 (Moscone West)
9:30 AM - **JJ5.1
Low Temperature Synthesis for Novel Nano-Ceramics Fabrication Routes of Oxide Protonics Materials.
Shu Yamaguchi 1 , Rinlee Cervera 1 , Yukiko Oyama 1 , Kiyoshi Kobayashi 2
1 Department of Materials Science, School of Engineering, University of Tokyo, Tokyo Japan, 2 Nanoionics Materials Group, NIMS, Tokyo Japan
Show AbstractThe authors report a novel low-temperature synthetic method via various soft-chemical routes, in order to overcome problems in the survey and fabrication of oxide protonics materials, such as significant inhomogeneity, loss of protonic defects, or even the dissociation of oxide protonic phase due to increased instability of protonic defects or dissolved water at elevated temperatures, caused by relatively high temperatures necessary for conventional ceramic processing. A good example of the low temperature synthesis principle is a sol-gel synthesis of high temperature proton conducting perovskite oxides, Y- and Sc-doped BaZrO3 and relating double perovskite phase that can only be exist at low temperatures. The authors have employed all-alkoxide method to synthesize a complex alkoxide sol with common alkyl group via alcoholysis reaction, followed by a uniform hydrolysis after gelation process. One of the most important issues found in the low temperature synthesis is the activation of chemical dopant by the incorporation into the host crystal necessary for protonic defect introduction. By a careful design of hydrolysis reaction, dopant of Y or Sc is accommodated into crystal at low temperatures, which results in full protonation and creation of mobile protons at low temperatures. Nano-ceramics powders synthesized have their average grain size of typically about several nm, and are processed by a low temperature sintering process at ultra high pressure to obtain nanosize-grained bulk materials below the dehydration temperature. Unique features of those bulk materials in electrochemical properties will be presented and discussed with the emphasis of the advantages of the low temperature synthesis over conventional ceramic one. Also, a spin-coating technique has been developed to fabricate thin films using the sol as a precursor. In addition, recent results will be presented to demonstrate the applicability of the present principle for lanthanum-germanate and silicate with apatite structure, fluorite CeO2 heavily doped with protons.
10:00 AM - **JJ5.2
Ceramic Microreactors Based on Mesoporous Ru/SiC and Ru/SiCN Monoliths for the Production of Hydrogen: Ammonia Decomposition and Propane Steam Reforming.
Paul Kenis 1 , Michael Mitchell 1 , J. Christian 1
1 , University of Illinois - Urbana Champaign, Urbana, Illinois, United States
Show Abstract11:00 AM - JJ5.3
Precursors Effect on the Synthesis of Tailor-Made Ceramic Nanoparticle Morphology and Phase.
Bernadette Hernandez-Sanchez 1 , Timothy Boyle 1 , Luke Brewer 1
1 Advanced Materials Laboratory, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractThe synthetic design of various nanoarchitectures and control over the final phase of ceramics nanomaterials is of considerable interest for a number of energy applications. With nanoparticle synthesis, many variables can play a role in the final materials properties, however; one variable such as the metal precursor can play a dramatic role on designing tailor-made ceramic materials. Through our exploration of novel synthetic routes to tailor-made ceramic nanoparticles, we have observed that there are two roles the precursor plays. The precursors explored include: metal alkoxides, metal amides,and metal alkyls. These precursors all have characteristics that make them suitable for nanoparticle synthesis such as: high solubility, high volatility, and low decomposition temperatures. All are important to the design of nanomaterials synthetic routes because many use solvents to thermally decompose the precursors into the final materials or stabilize the crystals. Two arguements can be made from the synthesis of ceramic nanopaticles. The first is the Precursor Structure Argument (PSA) where the precursor plays a role in the final morphology of the nanomaterials. The second observation indicates that the precursor decomposition pathway (PDP) has an influence on the final affects the final phase of the material. These two arguments have been profered for the generation of Ge nano dots and wires, CaOx nano dots and wires, tin oxides and hydroxides, and CdE (E = S, Se, Te) nanomaterials. A Complete overview of synthesis and characteriaation will be presented.This work supported by the Department of Energy, Office of Basic Energy Sciences and the United States Department of Energy under contract number DE-AC04-94AL85000. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the United States Department of Energy.
11:15 AM - JJ5.4
The Role of Immiscible Additives on the Evolution of Microstructure and Morphology of Metal Oxides.
Thorsten Enz 1 , Hermann Sieger 1 , Ralf Theissmann 2 , Claudia Fasel 3 , Horst Hahn 1 2
1 Joint Research Laboratory Nanomaterials, TU Darmstadt and Forschungszentrum Karlsruhe GmbH, Darmstadt Germany, 2 Institute for Nanotechnology, Forschungszentrum Karlsruhe GmbH, Karlsruhe Germany, 3 Institute of Materials Science, TU Darmstadt, Darmstadt Germany
Show AbstractThe tremendous impact of nanocrystalline materials in science and engineering is based on many improved or even novel properties compared to bulk materials due to smaller grain sizes and higher surface and interface areas respectively. However there is a huge driving force for thermally induced grain growth and sintering processes. This is a serious issue in high temperature applications of catalysts and gas sensing devices whose performance is often related to grain size and accessibility of surface area.The addition of a second phase can significantly improve the thermal stability by reducing the grain boundary mobility or cutting off diffusion pathways. In this study the influence of MgO on grain growth and surface area evolution of Sm2O3 is investigated. Like other rare earth oxides Sm2O3 is a selective catalyst for the oxidative coupling of methane to higher hydrocarbons at temperatures from 700 to 800°C. MgO is known to be an effective grain growth inhibitor.Samples of different compositions have been synthesized by spray drying of aqueous metal carboxylate gels prepared by a citrate technique. Hollow spheres are obtained with diameters in the micrometer range and thin shells of roughly 100nm thickness as evidenced by high resolution scanning electron microscopy (HRSEM). Metal cation ratios and carbon, nitrogen, and oxygen concentrations are determined by inductively coupled-plasma atomic emission spectroscopy (ICP-AES) and combustion analysis respectively. Structural properties are investigated by X-ray diffraction (XRD) and fourier transform-infrared spectroscopy (FT-IR). Thermal decomposition and crystallisation behavior of the initially amorphous samples are determined by means of simultaneous thermal analysis (STA) and high temperature-X-ray diffraction (HT-XRD). Transmission electron microscopy (TEM) imaging and electron energy loss spectroscopy (EELS) mapping are applied to reveal the spatial element distribution after crystallisation. The evolution of surface area against temperature is probed by nitrogen adsorption. The value of the stabilizing effect of MgO strongly depends on the volume fraction and has its origin in a very fine segregation of both oxides on the nanometer scale. As a result of this study it is possible to predict microstructure and morphology as a function of composition and thermal treatment.
11:30 AM - JJ5.5
Structure and Polarity of ZnO Nanopillars
Jacek Jasinski 1 , Daqing Zhang 2 , Jenny Parra 2 , Vanvilai Katkanant 2 , Valerie Leppert 1
1 School of Engineering, University of Califronia, Merced, Merced, California, United States, 2 Department of Physics, California State University, Fresno, Fresno, California, United States
Show AbstractWurtzite ZnO with its unique combination of properties is an attractive energy material. Due to its wide energy band gap of 3.37 eV and strong exciton binging energy of 60 meV, which enables efficient exciton emission at room temperature under low excitation energy, ZnO has been recognized as a promising photonic material in the blue–UV region, and has been widely used for light emitting diodes and lasers. Another active, energy-related area of ZnO applications includes photovoltaic devices. Recent reports have demonstrated that ZnO has great potential for use as an electrode for dye-sensitized solar cells. Moreover, it is being used in hybrid organic/inorganic solar cells, where the organic component (polymer) serves as a light absorber and hole conductor, and ZnO is used as the electron transporter. Finally, due to its strong piezoelectricity, ZnO also has a number of applications as a functional material, enabling the conversion of mechanical vibration into an electric signal or vice versa. Many of these applications are possible or enhanced due to the use of nanostructured ZnO, which can be produced in various forms including nanopillars, nanobelts, nanowires or nanohelices.Here, in this paper, we report on the structure and growth polarity of wurtzite ZnO nanopillars, synthesized by chemical vapor deposition. Their chemical composition and crystal structure were verified by chemical mapping and electron diffraction, respectively. Nanopillars were determined to be narrow hexagonal columns, grown along the c-direction, with their {1-100}-type side-walls in the width range of 65-70 nm. Their tips had the form of a truncated hexagonal pyramid, with top surface terminated at the (0001) plane and the side-walls at the {1-101}-type planes. Nanoplliars were found to grow along the (0001), Zn-polarity. This was confirmed by both convergent beam electron diffraction and channeling-enhanced electron energy loss spectroscopy methods. The present study is the first attempt to our knowledge of using the latter method for polarity determination of a nanostructure.
11:45 AM - JJ5.6
Self-catalyzed TiO2-δ Nanowire Growth and their Visible-light Photoluminescence Characteristics.
Nguyen Thi Quynh Hoa 1 , Sueng-Hee Kang 1 , Soon-Gil Yoon 1 , Eui-Tae Kim 1
1 Nano Science & Technology, Chungnam National University, Daejeon Korea (the Republic of)
Show AbstractTiO2 materials have been widely studied as promising materials for solar cells, photocatalysis, gas sensors, and biomaterials because of their high photocatalytic reactivity, good chemical stability, nontoxicity, and favorable electrical and optical properties. For solar cell applications, however, wide bandgap energy (~3.0-3.2 eV) of TiO2 limits solar light conversion efficiency to as low as ~2-3%. To enhance the efficiency in the visible light range, studies on dye sensitization or doping have been intensively performed. An alternative approach can be utilizing oxygen vacancies at various shallow level energies in TiO2 bandgap, which can lead visible-light luminescence. The effect of oxygen vacancies can be maximized by applying TiO2 nanostructures with large specific surface area. In this presentation, we introduce high-efficient visible-light photoluminescence (PL) characteristics of TiO2-δ nanowires grown by metalorganic chemical vapor deposition (MOCVD). Most TiO2 nanowires or nanotubes have been synthesized through nanoparticle-based growth or chemical-solution methods such as sol-gel. Few research results have been reported 1-dimensional TiO2 nanostructures grown by CVD even though CVD process is compatible with Si technology and has been effectively used to fabricate various high-quality nanowire and nanotube materials. Here we report growth and optical characteristics of TiO2-δ nanowire (ribbon) semiconductors fabricated by MOCVD. Especially, we introduce self-catalyzed (Au-free) growth of TiO2-δ nanowires. TiO2 nanowire (ribbon) semiconductors were fabricated onto various substrates using (C11H19O2)2(C3H7O)2Ti as a Ti metalorganic source. The Ti source was bubbled in the range of 180-210 oC with gas flow of 150 sccm. The growth temperature and pressure were varied in the ranges of 430-670 oC and 0.7-100 Torr, respectively. For formation of TiO2-δ nanowires, one of the most important growth factors was growth environment condition. TiO2 nanowires could be grown under oxygen-deficient growth environment while TiO2 thin films were formed with supplying enough O2. Under oxygen-deficient growth conditions, some Ti metals or Ti very-rich seeds seemed to be act as a catalyst for nanowire growth. The nanowires grown at 510 oC had mixed nanocrystallines of anatase and rutile. Importantly, TiO2-δ nanowires showed high-efficient PL in visible-light wavelength regime (~450-750 nm) while TiO2 thin films had a very poor PL efficiency. Our systematic annealing studies under various environments indicated that the origin of the PL emissions can be attributed to oxygen vacancies at various shallow level energies. These results demonstrate one of the ways to exploit large specific surface area of TiO2 nanowires for solar cell, photocatalyst, and gas and bio sensors applications. We will further discuss the growth mechanism and optical characteristics of self-catalyzed TiO2-δ nanowires grown by MOCVD.
12:00 PM - JJ5.7
Nanofiber Based Er(III) Metal Pyrochlore Oxides : Synthesis and Characterization.
Ruofeng Wang 1 , Edward Bender 2 3 , Mohannad Aljarrah 1 , Edward Evans 1 , Rex Ramsier 2 3 4
1 Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, Ohio, United States, 2 Department of Physics, The University of Akron, Akron, Ohio, United States, 3 Department of Chemistry, The University of Akron, Akron, Ohio, United States, 4 The Institute for Teaching and Learning, The University of Akron, Akron, Ohio, United States
Show AbstractA series of nanofiber based erbium metal pyrochlore oxides (e.g., Er2Ti2O7) have been synthesized by electrospinning mixtures of polymers, metal-containing materials, and either erbia particles or erbium acetate. These electrospun nanofibers were subsequently annealed at temperatures of 850, 950, 1050, and 1150 oC to remove the organics and leave behind the metal oxides. The crystal structure and optical properties of the nanofiber pyrochlores were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transformation IR (FTIR) spectroscopy. Different crystal structures were formed by controlling the annealing conditions. XPS data are compared with near-IR spectra to better understand the effects of the different metal oxide matrices on the Er (III) thermally-excited selective optical emission process. Finally, the relevance of this work to thermophotovoltaics (TPV) and other applications is discussed.
12:15 PM - JJ5.8
Nanocrystalline Eu3+ doped M3Al2O6 (M = Ba, Ca and Sr) red phosphors prepared by Sucrose-PVA-metal ion complex route.
Alp Manavbasi 1 , Palkin Zed 1 , Jeffrey LaCombe 1
1 Materials Science & Engineering, University of Nevada Reno, Reno, Nevada, United States
Show AbstractNanocrystalline (<100 nm) red emitting Eu3+- doped M3Al2O6(M = Ba, Ca and Sr) phosphors were prepared by an aqueous Sucrose-PVA-metal ion complex route. The aqueous sucrose-PVA solution includes 20 mol% PVA, and the method is based on the dehydration of a transparent metal ion-sucrose-PVA solution to a highly viscous liquid and then precursor formation by heating at 250 °C. The phase formation depending on the calcination temperature was investigated by x-ray diffraction techniques. The photoluminescence (PL) and PL excitation characteristics have been investigated. PL excitation studies revealed that all samples have broad charge transfer bands centered around 269 nm and other lines attributed to the characteristic f-f transitions of Eu3+ ions.The PL spectra of Ba3Al2O6:Eu3+ and Sr3Al2O6:Eu3+ have comparable emission intensity in the 5D0 → 7F1 and 5D0 → 7F2 bands. However, Ca3Al2O6:Eu3+ has the highest emission intensity from the red 5D0 → 7F2 transition at 614 nm. Additional optical properties of nanocrystalline europium doped host lattices, M3Al2O6 (M = Ba, Ca and Sr), will be presented in addition to the morphological characterization by SEM, and particles size distributions from photon correlation spectroscopy analysis.
12:30 PM - JJ5.9
Creating Dense, Constrained Ce0.9Gd0.1O1.95 Films at Low Temperature for SOFC Applications.
Jason Nicholas 1 , Lutgard De Jonghe 1
1 Materials Science and Engineering Department, University of California at Berkeley, Berkeley, California, United States
Show AbstractJJ6: Dielectrics and Photoelectrochemical Systems
Session Chairs
Thursday PM, April 12, 2007
Room 3022 (Moscone West)
2:30 PM - **JJ6.1
Nonlinear Current-Voltage Behavior and Giant Dielectric Response in Multifunctional Calcium Copper Titanate.
Sung-Yoon Chung 1
1 Department of Materials Sci. & Eng., Inha University, Incheon Korea (the Republic of)
Show AbstractOwing to their unique electrical properties, perovskite-type oxides have been used for various applications in electronic devices. Recently, CaCu3Ti4O12 has become of interest since the discovery of its giant dielectric property with a relative permittivity in the order of 100,000. One of its notable physical features is that there is neither a ferroelectric phase transition nor a change in the structural long-range order with variation of temperature. Such a high dielectric constant remains unchanged over a wide range of temperatures, although it abruptly decreases to less than 100 below ~100 K. A number of theoretical studies and experimental observations have been reported in efforts to elucidate this remarkable dielectric property. Along with an internal barrier-layer capacitor model, several possible morphologies have been proposed to explain the giant dielectric phenomena.By using microcontact current-voltage (I-V) measurements and Kelvin probe force microscopy, we have also recently shown that a large potential barrier intrinsically exists at the grain boundaries in addition to the intriguing dielectric response. Such a potential barrier serves as an obstacle to the current flow through the conductive bulk grains in a polycrystalline specimen, and thereby resulting in enormous nonlinearity between the current and the applied voltage. In this presentation, we show that selective doping with 3d-metal cations has a critical impact on the extinction of an electrostatic barrier at grain boundaries. As a result, a huge change in the relative permittivity by three orders of magnitude as well as a different behavior in the I-V characteristics can be observed, providing compelling evidence for the extrinsic origin of the giant dielectricity in CaCu3Ti4O12. Another intriguing finding in CaCu3Ti4O12 in addition to the peculiar grain boundary phenomena is that its crystal lattice is inherently bent at a nanometer scale. A direct comparison between experimentally obtained and simulated images of high-resolution electron microscopy (HREM) is presented to demonstrate the nanoscale lattice bending and resultant lattice distortion. Our discussion of the overall experimental results features various potential applications for CaCu3Ti4O12, including efficient switching devices, low-voltage varistors, gas sensors and high-permittivity dielectrics.
3:00 PM - JJ6.2
Non-reducible BaTiO3-based Dielectric Ceramic Powder for X7R Ceramic Capacitors with Ni-electrode Synthesized by Sol-gel Method.
Jia Deng 1
1 Materials Physics, University of science and technology Beijing, Beijing China
Show Abstract3:15 PM - JJ6.3
High Permittivity and High Dielectric Strength Nanocomposites viaSurface Modification of BaTiO3 with Functional Phosphonic Acids.
Philseok Kim 1 , Simon Jones 1 , Peter Hotchkiss 1 , Joshua Haddock 2 , Bernard Kippelen 2 , Seth Marder 1 , Joseph Perry 1
1 School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractPolymer/ceramic nanocomposites are of significant current interest in which high permittivity (εr) metal oxide nanoparticles such as BaTiO3 (BT) and lead magnesium niobate–lead titanate (PMN-PT) are incorporated into a polymer host(1,2). We have shown that phosphonic acid ligands can effectively yield robust surface modification on BT nanoparticles and related perovskite nanoparticles when compared to analogous trimethoxysilanes, carboxylic acids, and sulfonic acids(3). The binding of phosphonic acid to the surface of BT nanoparticles has been found to be mainly of a tridentate form by FT-IR and 31P MAS SS-NMR. Surface modification of BT nanoparticles with phosphonic acids of tailored functionality allowed effective dispersion of BT nanoparticles in selected polymer hosts such as polycarbonate and poly(vinylidene-co-hexafluoropropylene). Homogeneous nanocomposite thin films can be readily obtained from the dispersions by simple solution processing, which reflects the effectiveness of phosphonic acid ligand shell making the nanoparticles compatible with the surrounding polymer hosts and preventing the agglomeration of nanoparticles. The nanocomposites based on high εr host materials showed a remarkable combination of high εr (up to 48) and high dielectric strength (>200 V/μm) with relatively low dielectric loss (<7 %) at 1 MHz, suitable for energy storage or peak load leveling applications(4). We attribute these results to the improved film quality due to the surface modification and to the effective passivation of ionizable surface hydroxyl groups on the nanoparticle interfaces that eliminates charge sources and migration pathways. We also found that the phosphonic acid ligands contribute very little to the dielectric loss up to 1 MHz. Further optimization of the dielectric nanoparticles and the host materials system offers a path to yet higher εr and dielectric strength.1.S. Ramesh, B. A. Shutzberg, C. Huang, J. Gao, E. P. Giannelis, IEEE Trans. Adv. Packag. 2003, 26, 17.2.Y. Bai, Z.-Y. Cheng, V. Bharti, H. S. Xu, Q. M. Zhang, Applied Physics Letters 2000, 76, 3804.3.P. Kim, S. C. Jones, P. J. Hotchkiss, J. N. Haddock, B. Kippelen, S. R. Marder, J. W. Perry, PMSE Preprint 2006, 94, 10.4.J. P. Calame, Journal of Applied Physics 2006, 99, 084101.
3:30 PM - JJ6.4
Fabrication of Multilayer Ultrathin PLZT Capacitors by Chemical Solution Deposition.
Geoff Brennecka 1 , Bruce Tuttle 1 , Luke Brewer 1 , Bonnie McKenzie 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractContinued miniaturization of integrated microsystems as well as the development of novel and advanced energy generation and conversion technologies must be accompanied by comparable advances in capacitive energy storage. The three factors which determine volumetric capacitance are the dielectric constant (K), thickness, and active area of the dielectric layer. Traditionally, capacitor technologies have essentially sacrificed one of these three factors for the optimization of the other two. However, by developing ultrathin high-K dielectrics and integrating them into multilayer structures, we have utilized advances in all three factors to realize signficant improvements in capacitance density. Using spin-coating methods, multilayer capacitors have been fabricated with high dielectric constants (>1000) and individual dielectric layer thicknesses of 50nm and below. This results in capacitor structures in excess of 2μF/mm2 which can be further scaled using a Sandia-developed appliqué process. Discussion will focus on the materials issues in the fabrication of PLZT-based high-K multilayer capacitors, including processing issues and the increased importance of the electrode/dielectric interface(s) in retaining a high dielectric constant at the nanoscale. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.
4:15 PM - JJ6.5
Influence of Dipolar Fields on the Photochemical Reactivity of Thin Titania Films on BaTiO3 Substrates.
Nina Burbure 1 , Paul Salvador 1 , Gregory Rohrer 1
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractThis study is motivated by the idea that the efficiency of hydrogen generation by metal oxide photocatalysts might be improved by creating spatially distinct sites for oxidation and reduction. In this work, dipolar fields from BaTiO3 substrates were used to create preferential sites for silver reduction on TiO2 thin film surfaces. Atomic Force Microscopy revealed that reaction products formed on the TiO2 surface in patterns consistent with the domain structure of the ferroelectric substrate. As the film thickness was increased, the titania more effectively screened the ferroelectric field and the pattern of reaction products was obscured. It is concluded that dipolar fields from the ferroelectric substrate influence charge carrier transport in the film and spatially localize the reaction products.
4:30 PM - JJ6.6
The Ferrocatalytic Effect on the Photochemical Activity of SrXBa1-XTiO3.
Abhilasha Bhardwaj 1 , Gregory Rohrer 1
1 Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractThe efficiency of particulate water photolysis catalysts is impractically low due to the recombination of intermediate species. The back reaction can occur easily if the oxidation and reduction sites on the surface of the catalyst are not far enough apart. It is hypothesized that increasing the separation of the sites of the two half reactions could significantly increase the efficiency of the process. The present work compares the photochemical reactivities of ferroelectric and nonferroelectric materials (SrXBa1-XTiO3, 0.0≤ x ≤1.0) with similar composition and structure. The reactivities are compared by observing the color change of the methylene blue dye on reacting with the surface of ceramic sample pellets after fixed time of UV light exposure. The polarization in the ferroelectric material enhances the charge separation relative to the nonferroelectric material and this should increase the separation between the sites of reduction and oxidation. However, a peak in the reactivity is observed at the ferroelectric to non-ferroelectric transition. This enhanced reactivity can be attributed to the peak in the dielectric constant and the subsequent enlargement of the space charge region at the phase boundary.
4:45 PM - JJ6.7
Luminescence of Flame-made, Nanosized Y2O3:Eu3+ Particles.
Adrian Camenzind 1 , Reto Strobel 1 , Frank Krumeich 2 , Sotiris E. Pratsinis 1
1 Particle Technology Laboratory, Mechanical & Process Engineering, ETH Zurich, CH-8092 Zurich Switzerland, 2 Laboratory of Inorganic Chemistry, Chemical and Applied Biosciences, ETH Zurich, CH-8092 Zurich Switzerland
Show Abstract5:00 PM - JJ6.8
Metastability Limits of Anatase and Rutile TiO2 Nanocrystals Under Pressure.
Varghese Swamy 1 , Leonid Dubrovinsky 2 , Barry Muddle 1
1 Materials Engineering, Monash University, Clayton Campus, Victoria, Australia, 2 Bayerisches Geoinstitut, University of Bayreuth, Bayreuth, Bavaria, Germany
Show AbstractPhase stability and phase transitions of nanoscale materials are of great fundamental and technological significance. Phase transitions of nanocrystals have been suggested as simpler models for understanding the kinetics and microscopic mechanisms of solid-solid transitions in bulk materials. The phase transitions of nanomaterials may also lead to the formation of new, useful materials.We have investigated pressure-induced phase transition behaviors of anatase and rutile TiO2 nanocrystals. TiO2 is one of the most versatile technological materials and a prototypical system in the study of phase transitions at the bulk and nanoscale. The present study compares pressure-driven phase transitions in size-controlled anatase and rutile nanocrystals observed using angle-dispersive synchrotron x-ray diffraction (XRD) and Raman spectroscopy in diamond-anvil cells to pressures up to 50 GPa.Our XRD and Raman results as well as other published data on anatase nanocrystals demonstrate that in the nanocrystalline form the anatase structure displays enhanced metastability to very high pressures that is particle size-dependent. Particle size also determines the crystal structure of the post-anatase phase: pressure-induced amorphization at the very small size regime (<10 nm), anatase-baddeleyite transition at an intermediate size regime, and anatase-α-PbO2 transition for the largest nanoparticles to bulk material. The pressure-amorphized small nanoparticles also show a low density amorphous (LDA) – high density amorphous (HDA) polyamorphic transition upon pressure cycling. The pressure-induced phase transitions of rutile TiO2 nanocrystals have not received similar attention (most likely due to the difficulty of obtaining size-controlled nanocrystals with very small crystallite sizes). We have synthesized a series of size-controlled rutile nanocrystals using the hydrothermal method and investigated the high-pressure phase transitions at ambient temperature using synchrotron XRD (at the 16-IDB HP-CAT beamline of the Advanced Photon Source, Chicago) and Raman spectroscopy. The results suggest an overall similarity in phase transitions between anatase and rutile, but there are distinct differences in the details. The combined XRD and Raman results will be presented in an effort to understand the phase transition behaviors and their underlying reasons.
5:15 PM - JJ6.9
Electrochemical Micromachining of Patterned Aluminum Films by Porous-type Anodization.
Dmitri Brevnov 1 , Plamen Atanassov 1 , Larry Mosley 2
1 Chem & Nuclear Engineering, University of New Mexico, Albuquerque, New Mexico, United States, 2 , Intel Corporation, Santa Clara, California, United States
Show AbstractPorous-type anodization of patterned Al films and subsequent chemical etching of porous Al2O3 can be considered as a sub-category of electrochemical micromachining (EMM). This method results in metallic pillars separated by micro-grooves, whose dimensions are defined by the design of anodization masks and a degree of anisotropy of porous-type anodization. The pillars have a trapezoidal shape with concave slopes due to undercutting, which results from the lateral pore growth under the anodization mask. Regardless of undercutting, porous-type anodization shows a higher degree of anisotropy than mostly isotropic wet chemical etching and allows for more accurate shape control of 3-D metallic microstructures. Being technologically advantageous to mostly isotropic wet chemical etching and offering a lower cost of ownership than plasma etching, porous-type anodization of patterned Al represents a compromise between these two methods. Consequently, porous-type anodization may constitute an inexpensive and scalable to large geometric areas platform for micro-structuring of Al substrates and may be considered as an economical alternative to plasma etching. EMM of patterned Al films can be utilized in a wide number of applications including miniature power sources and energy storage devices.
5:30 PM - JJ6.10
Anodization of Sputtered Titanium Films
Deepak Dhawan 1 , Suresh Bhagrava 1 , Wojtek Wlodarski 1 , Kourosh Kalantar-zadeh 1
1 Electrical and Computer Engineering, RMIT University, Melbourne, Victoria, Australia
Show AbstractThe anodic formation of nanoporous Ti (and TiOx) by anodization of RF sputtered titanium thin films was investigated. A solution of 1M (NH4)2SO4 (ammonium sulphate) electrolytes containing 0.5wt% (NH4)F (ammonium fluoride) was used in the anodization process. Different nano and micro structures were obtained by anodization in this electrolyte. It was observed that the magnitude of the different applied voltage have significant role in the formation of different surface morphologies with various nano/micro structures. A 2 to 10V dc voltage was employed in the process. The anodized titanium thin films were characterised using scanning electron microscopy and x-ray diffraction techniques.Micro and nano porous thin films have received considerable attention in recent years due to their high potential for commercial and technological applications. These materials have utilization in optical, electrical, and micromechanical devices. One approach is to use these materials as the template for the fabrication of nanostructures. These nano-structures are promising, especially for the preparation of large surface to volume area with high aspect ratios, which are difficult to form by lithographic processes when dimensions approach features of less than 100nm. Metals which can be used for the formation of the self organised porous structures include: Al, Si, W, Nb, Ti and Ta. Such nano porous materials show specific structure which give them unique functional properties that can be employed in the fabrication of electronics and optical devices as well as application in chemical and biochemical engineering. Among these materials, titanium, along with its oxide form, TiOx, has a unique place due to its gas sensing properties, self-cleaning abilities, controllable wetability, photo and thermal catalysis and use in solar cells.In lower voltages such as 2V we observed pores dimensions of approximately 200 nm and gap sizes of approximately 300nm. However voltages larger than 5V pores were formed in crystallites with a shape of hatched eggs of less than 200nm. This time the pore diameters were less than 100nm. Such a method has a promising result in obtaining the porous structures.
JJ7: Poster Session
Session Chairs
Friday AM, April 13, 2007
Salon Level (Marriott)
9:00 PM - JJ7.1
Preparation and Characterization of GC/Pt/CeO2 Electrodes by Occlusion Deposition Technique. Electrochemistry Impedance Spectroscopy Characterization (EIS).
Christian Campos 1 , Carlos Cabrera 1
1 Chemistry, University of Puerto Rico, San Juan, Puerto Rico, United States
Show Abstract9:00 PM - JJ7.10
Thermoelectric Properties of NaCo2O4 Single Crystal in Magnetic Field
Min Wook Oh 1 , Bong Seo Kim 1 , Su Dong Park 1 , Hee Woong Lee 2
1 Electric and Magnetic Devices Research Group, Korea Electrotechnology Research Institute(KERI), Changwon, Gyeongnam, Korea (the Republic of), 2 Advanced Materials and Application Research Laboratory, Korea Electrotechnology Research Institute(KERI), Changwon, Gyeongnam, Korea (the Republic of)
Show Abstract9:00 PM - JJ7.11
Tin-Substituted Lithium Manganese Oxide Thin Films as a Cathode for Lithium Batteries.
Dong Wook Shin 1 2 , Ji-Won Choi 1 , Yong Soo Cho 2 , Seok-Jin Yoon 1
1 , Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 , Yonsei University, Seoul Korea (the Republic of)
Show AbstractThe influences of the unknown substitution of Sn in lithium manganese oxide thin films being used as a cathode have been studied to improve ultimately the physical and electrical performance of thin film lithium batteries. The thin films corresponding to LiSnx/2Mn2-xO4 (x<0.1) were prepared on Pt/Ti/SiO2/Si(100) substrates by the solution deposition method utilizing tin(II) acetate, lithium acetylacetonate and manganese(III) acetylacetonate as precursors. The annealing temperature was fixed at 750oC. Within the range of the substitution (x<0.1), no distinguishable second phase was observed but the lattice constant calculated in the XRD patterns tends to increase with increasing the Sn substitution. Surface morphology observed by SEM and AFM was found to be affected by Sn with the clear evidence of changes in grain size and surface roughness depending on the content of Sn. The results on microstructure observation were correlated to the improved electrochemical characteristics, such as discharge capacity and cyclability, of the thin film cathodes. For example, a higher cyclic efficiency obtained for the Sn-substituted samples was believed to be associated with the suppression of unwanted phase transition and the enhancement of the physical characteristics of the thin films.
9:00 PM - JJ7.12
Study of CVD ZrC Process for TRISO Coated Fuel Particle by using Computational Simulation and Actual Experiment.
Jun Gyu Kim 1 , Jin Hyung Jun 1 , Doo Jin Choi 1 , Young Woo Lee 2 , Ji Yeon Park 2
1 Department of Ceramic Engineering, Yonsei University , Seoul Korea (the Republic of), 2 Functional Materials, Korea Atomic Energy Research Institute, Daejon Korea (the Republic of)
Show AbstractTRISO coated fuel particle is one of the most important materials for hydrogen production using HTGR (High Temperature Gas-cooled Reactors). It is composed of three isotropic layers: inner pyrolytic carbon (IPyC), silicon carbide (SiC), outer pyrolytic carbon (OPyC) layers for retaining fission products within the fuel particle. The SiC layer is a critical and essential layer in TRISO coated fuel particles since it is a protective layer against diffusion of metallic and gaseous fission products and provides mechanical strength for the fuel particle. However, SiC has critical disadvantage that it loses mechanical integrity by thermal dissociation and phase change. As a result, capturing ability of SiC layer for fission production such as cesium is degraded at high temperature. In order to solve the problem, the ZrC layer instead of SiC layer for TRISO coated fuel particles has been proposed. ZrC has a high melting point of 3400°c and high temperature stability. In addition, ZrC layer has higher resistance to chemical attack by fission product than SiC layer does. In this study, we carried out computational simulation before real experiment with input gas velocity, temperature profile and pressure in the reaction chamber by using thermodynamic simulation (SOLGASMIX-PV program) and process simulation (Fluent 6.0 computer program). With the simulation results, we deposited the ZrC layers on the different type substrates such as graphite substrate and SiC/graphite substrate through CVD process in a horizontal hot wall tube furnace. For ZrC deposition, we used SiC films deposited at 1200°c since the SiC films have different microstructure with a variation of deposition temperature of 1200~1400°c. The SiC film deposited at 1200°c have stratified structure with small grain and high corrosion resistance plane. In addition, the properties of ZrC/graphite and ZrC/SiC/graphite samples were compared to those of SiC/graphite substrate. We studied chemical and mechanical characteristics of the samples. In order to investigate the phase and preferred orientation of deposited ZrC layers, XRD method was conducted. The microstructures and thickness of deposited ZrC layers on each different substrate were examined using SEM and EDS. Chemical composition of ZrC/SiC/graphite, ZrC/Graphite and SiC/graphite were analyzed by XPS. Hardness and elastic modulus of those samples were also analyzed by nano indentation method. The surface morphologies of ZrC/Graphite were domed-top structure but surface of ZrC/SiC/graphite has spherical granular structure. The ZrC/SiC/graphite and ZrC/graphite showed better mechanical properties such as hardness and elastic modulus than SiC/graphite substrate. The ZrC layer, which has improved mechanical properties and less reactivity with fission products, will contribute to fabrication of TRISO coated fuel particle with high stability.
9:00 PM - JJ7.13
Hydrothermal Synthesis and Semiconducting Behavior of Doped Ceria Nano-particles for Solar Cells
Jong Won Lee 1 , Nam-Gyu Park 2 , Yong Soo Cho 1
1 Department of Materials Science and Engineering, Yonsei University , Seoul Korea (the Republic of), 2 Materials Science and Technology Division, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractCeria nano-powders have been intensively investigated due to practical applications as grinding media mainly for the chemical-mechanical planarization (CMP) process. The utilization of nano-ceria to solar cell systems was very selectively studied as a potential replacement of titania. Ceria was recently discovered to have distinct semiconducting nature only when the particle size is substantially small, namely less than a few tens of nanometer. This work covers the effects of unknown dopants, such as Li+1, Ca2+, La3+, and Zr4+, primarily on the electrical behavior of the synthesized ceria. Nano-scaled particles of ceria-based materials were synthesized in hydrothermal conditions below 220oC. X-ray diffraction patterns of doped cerium oxide powder showed no secondary phase up to 10 mol% addition levels, but corresponding peaks shifted largely depending on the doping level. The optical band gap was measured as ~ 2.9 eV for undoped CeO2 and < 2.8 eV for doped CeO2. These values are lower than the reported band gap of 3.2 eV for bulk CeO2. This inconsistency related to the quantum size effect is thought to come from oxygen vacancies and defects on the powder surface. This work intends to demonstrate the possibility of utilizing the nano-powders for the solar cell applications by optimizing semiconducting behavior through the choice of desirable type and content of dopants. Performance evaluations of subsequent cells, including I-V, impedance parameters and energy conversion efficiency, are to be correlated with such mentioned powder characteristics.
9:00 PM - JJ7.14
Photo-patternable Nanoporous Titania Thin Films Templated by Block Copolymers
Ho-Cheol Kim 1 , Oun-Ho Park 1 , Joy Cheng 1 , Hyun Suk Kim 1 , Philip Rice 1 , Teya Topuria 1 , Leslie Krupp 1 , Robert Miller 1
1 , IBM Almaden Research Center, San Jose, California, United States
Show AbstractNanostructured metal oxides have received increasing attention due to their attractive optical and electrical characteristics such as high refractive index and semiconductivity. Among them, of great interest is nanoporous titania which shows promising optoelectrical properties for the applications including photovoltaic cells, photocatalysts, and optical waveguide devices. Numerous researchers have synthesized nanostructured titania using various structure-directing agents such as diblock copolymers or triblock copolymers (e.g. Pluronics, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)). However, most of synthetic procedures require highly acidic condition to reduce the condensation rate during self-assembly and careful environment control to obtained desired nanostructures because of the increased reactivity and high sensitivity to moisture of typical titania precursors such as alkoxides or chlorides. An alternative way to suppress the titania precursors reactivity is their chemical modification using chelating agents. The modified titania precursor can be converted into oligomeric titanate species using simple sol-gel reaction. The chelated oligomeric titanate provides not only excellent stability during self-assembly, which is essential to the formation of well defined morphology templated by the block copolymers, but also the photosensitivity for imaging patterns using conventional optical lithography. In the present work, we report a method to create photo-patternable nanoporous titania thin films using coassembly of polystyrene and poly(ethylene oxide) diblock copolymers (PS-b-PEO) and a chemically modified oligomeric titanate (OT). With this approach, average pore size and porosity were determined by the molecular weight and loading level of the block copolymers. Crystal structure of nanoporous titania was generated upon heat-treatment condition. Optically defined patterns of nanohybrid films were successfully fabricated by UV exposure followed by wet developing process. Subsequent heat treatment generated the patterned titania with a hierarchical pore structure (i.e. nano-sized pores within micron-sized features). The patterned nanoporous titania films could potentially be used for applications including photovoltaic cells, optics, and photocatalysts.
9:00 PM - JJ7.15
Developing Nanostructured Cathode of Thin Film SOFC and its Characteristics.
Jongsik Yoon 1 , Roy Araujo 1 , Haiyan Wang 1 , Nicolas Grunbaum 2 , Laura Baque 2 , Adriana Serquis 2 , Xinghang Zhang 3
1 Eelctrical Engineering, Texas A&M University, College Station, Texas, United States, 2 , Centro Atómico Bariloche, 8400 S. C. de Bariloche Argentina, 3 Department of Mechanical Engineering, Texas A&M University, College Station, Texas, United States
Show Abstract9:00 PM - JJ7.16
Nanostructured Ceramic Thin Films for Photocatalytic Applications
Yixin Zhao 1 2 , Xiaofeng Qiu 1 2 , Clemens Burda 1 2
1 Center for Chemical Dynamics and Nanomaterials Research, Case Western Reserve University, Cleveland, Ohio, United States, 2 Department of Chemistry, Case Western Reserve University, Cleveland, Ohio, United States
Show Abstract9:00 PM - JJ7.18
Impedance Spectroscopy Modeling of LSGM-based Composite Electrolyte for Intermediate Temperature Solid Oxide Fuel Cells.
Kuo-Chuang Chiu 1
1 , Industrial Technology Research Institute, Chutung, Hsinchu Taiwan
Show Abstract9:00 PM - JJ7.2
Preparation and Characterization of Large Surface Area Electrodes from Diamond Nanoparticles by Electrophoretic Deposition Method.
Lyda La Torre Riveros 1 , Carlos Cabrera 1
1 Chemistry, University of Puerto Rico, San Juan, Puerto Rico, United States
Show Abstract9:00 PM - JJ7.20
Hydrothermal Synthesis of Structure and Shape Controlled Manganese Oxide Octahedral Molecular Sieve (OMS) Nanomaterials
Weina Li 1 , Jikang Yuan 1 , Xi Chen 1 , Xiong-Fei Shen 1 , Sinue Gomez-Mower 2 , Lin-ping Xu 2 , Shantakumar Sithambaram 1 , Mark Aindow 1 , Steven Suib 1 2 , Yun-shuang Ding 2 , Chun-hu Chen 2
1 Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States, 2 Chemistry Deparment, University of Connecticut, Storrs, Connecticut, United States
Show Abstract Highly uniform single crystal Na-OMS-2, pyrolusite, and g-MnO2 nano-structures with an interesting three dimensional urchin-like morphology have been successfully prepared using a hydrothermal method based on a mild and direct reaction between sodium dichromate and manganese sulfate. The crystal phases, shapes and tunnel sizes of the manganese dioxide nano-structures can be tailored. Reaction temperature, concentrations of the reactants, and acidity of the solution play important roles in controlling the synthesis of these manganese dioxides. Field emission scanning electron microscope (FESEM) and transmission electron microscopy (TEM) studies showed that the nano-materials obtained were constructed of self-assembled nano-rods. The X-ray diffraction (XRD) and TEM results indicated that the constituent manganese dioxide particles are single crystalline materials. EDXS and magnetic studies imply that chromium cations may be incorporated into the framework and/or tunnels of the manganese dioxides. A mechanism for the growth of manganese dioxides with urchin-like architectures was proposed.
9:00 PM - JJ7.21
New plug-in Ceramics for the Ionics.
Dmitry Zakharyevich 1 , Vladimir Burmistrov 1 , Alexandr Popov 1
1 Dept. of Condensed Matter Physics, Chelyabinsk State University, Chelyabinsk Russian Federation
Show Abstract9:00 PM - JJ7.22
Transparent Oxide Films with Carbon Nanotubes.
Monica Jung de Andrade 1 2 , Marcio Dias Lima 1 2 , Viera Skakalova 1 , Carlos Perez Bergmann 2 , Siegmar Roth 1
1 Von Klitzing Department, Max-Planck Institute for Solid State Research, Stuttgart Germany, 2 Materials Engineering Dept. , Federal University of Rio Grande do Sul, Porto Alegre Brazil
Show Abstract9:00 PM - JJ7.23
Synthesis and Photoelectrochemical Properties of Nitrogen-incorporated ZnO Films.
Kwang-Soon Ahn 1 , Yanfa Yan 1 , Se-Hee Lee 1 , Todd Deutsch 1 , John Turner 1 , Mowafak Al-Jassim 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show Abstract9:00 PM - JJ7.4
Thermoelectric Characteristics and Nanowire Formation Behavior of the n-type Bi2Te3 and the p-type (Bi,Sb)2Te3 Processed by Electrodeposition
Tae-Jin Yoon 1 , Min-Young Kim 1 , Jin-Sang Kim 2 , Tae-Sung Oh 1
1 Materials Science and Engineering, Hongik University, Seoul Korea (the Republic of), 2 Center for Thin Film Processing, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractRecently, thermoelectric energy conversion efficiencies of low dimensional structures have been predicted to be improved significantly compared with bulk thermoelectric materials due to the quantum confinement effects. Among low dimensional thermoelectric structures, 1D nanowires are more attractive than 2D superlattices because higher figure-of-merit is predicted and processing is easier with adapting a template for growth and structural support of nanowire array. Bi2Te3-based alloys exhibit the highest ZT near room temperature and can be good candidates for thermoelectric nanowires. While various processing techniques can be used for nanowire fabrication, electrodeposition has several advantages such as rapid and inexpensive process and easy controllability for the composition and the microstructure by changing the electrodeposition parameters. In this study, n-type Bi2Te3 and p-type (Bi,Sb)2Te3 were electrodeposited with variations of the current density and the solution compositions, and their thermoelectric characteristics were characterized for nanowire applications. While power factor of the n-type Bi2Te3 was remarkably improved about 5 times to 33x10-4 W/K2-m by hydrogen annealing at 450C for 4 hours, power factor of the p-type (Bi,Sb)2Te3 was degraded with hydrogen annealing. The n-type Bi2Te3 and p-type (Bi,Sb)2Te3 nanowire composites were processed by electrodeposition into the Al2O3 templates. Nanowire formation behavior was characterized with variation of the electrodeposition current density and the solution concentration.Acknowledgement: This work was supported by Center for Nanostructured Materials Technology under 21st Century Frontier R&D Programs of Ministry of Science and Technology, Korea.
9:00 PM - JJ7.5
Alkaline Earth Titanate (AETiO3) Perovskite Nanoparticles Synthesized from Structurally Characterized Single-Source Alkoxides.
Bernadette Hernandez-Sanchez 1 , Timothy Boyle 1 , Bruce Tuttle 1 , Luke Brewer 1
1 Advanced Materials Laboratory, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractAlkaline earth titanate (AETiO3) perovskite nanoparticles are of interest for thier tunable dielectric and ferroelectric applications. To produce tNew produce large-scale quantities of these nanomaterials, we have developed new synthetic strategies to control the AETiO3) nanoparticle composition, crystallinity, and morphology through the carefully constructed metal alkoxides. The utility of single-source precursors has been studied extensively for sol-gel processing, but not as rigorously for nanoparticle synthesis. A series of alkaline earth modified titanium neo-pentoxide (OCH2CCMe3, ONep) derivatives were synthesized through the alcoholysis reaction of [Ti(μ-ONep)(ONep)3]2 and the respective alkaline earth neo-pentoxide (AE(OR)2), where AE = Ca, Sr, and Ba. For each AE cation, the following mixed cation species were identified by single-crystal X-ray diffraction as: (py)2AE[Ti(μ-ONep)2(ONep)3]2. These single-source compounds were used to synthesize nanoparticles of AETiO3 using solution precipitation (methyl-imidazole:water) and solvothermal (benzyl alcohol) routes. For comparison, stoichiometeric mixtures of the individual precursors were processed under identical conditions. The nanoparticles (5 – 50 nm) synthesized varied in phase from carbonates to perovskites based on the cation and the synthetic conditions used. Based on the comparison of routes, stoichiometric mixtures were better in generating single phase AETiO3 from the MeIm/H2O route after calcination; whereas, through solovothermal synthesis routes, single-source and stoichiometric mixtures both gave favorable crystalline results for Sr and Ba. The dielectric properties of these materials along with thier full characterization will be presented. This work supported by the Department of Energy, Office of Basic Energy Sciences and the United States Department of Energy under contract number DE-AC04-94AL85000. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the United States Department of Energy.
9:00 PM - JJ7.6
Synthesis and Luminescent Properties of Nano-crystalline Ba2YAlO5:Eu3+ Red Phosphors.
Case Egan 1 , Alp Manavbasi 1 , Jefferey LaCombe 1
1 Materials Science & Engineering, University of Nevada, Reno, Reno, Nevada, United States
Show AbstractA new red phosphor Ba2YAlO5: Eu3+ with crystallite size of <60 nm was synthesized by the simple polyvinyl alcohol (PVA) method. Photoluminescence (PL) and PL excitation studies revealed that Ba2YAlO5 doped with trivalent europium ions emit strongly in the orange and red light regions under excitation at 254 nm. These characteristic emissions are ascribed to the transitions from the 5D0 excited level to 7FJ (J = 0, 1, 2, 3) ground states of Eu3+ ions. The PL excitation studies revealed the well-formed charge transfer band between 210 and 300 nm with other characteristic absorption lines of Eu3+ ions. The structural properties of the samples were determined by x-ray diffraction depending on the heat treating temperatures. Scanning electron microscopy analysis showed that nano- scale individual phosphor particles are irregularly rounded and formed loosely connected larger particles. The crystallite size of phosphors was increased to 50 nm from 28 nm when the heat treating temperature increased from 1000 to 1200 °C for 5 mol% Eu3+ doped samples and the emission intensities at the dominant peaks relatively increased.
9:00 PM - JJ7.7
Properties and Consolidation of Nanostructured Ce0.8Gd0.2O2-δ with Addition of Fe2O3 by Pulsed Current Activated Sintering.
In-Jin Shon 1 , Dong Ki Kim 1 , In Kyoon Jeong 1 , Hyun kuk Park 1 , In Yong Ko 1
1 Advanced Materials, Chonbuk University, JeonJu, Jeonbuk, Korea (the Republic of)
Show Abstract9:00 PM - JJ7.8
Zirconia Nanopowders and Nanostructured Ceramics for Different Application.
Tatjana Konstantinova 1 , Victor Varyukhin 1 , Igor Danilenko 1
1 , Donetsk Institute of Physics & Engineering, Donetsk Ukraine
Show Abstract9:00 PM - JJ7.9
Thermal Oxidation of Zr/Y Metal Films to Cubic YSZ Thin Films used as the Solid Electrolyte in the Fuel Cell.
Yang-Ming Lu 1 , Ping-Han Hsieh 2 , Kuan-Zong Fung 3
1 , National Formosa University, Yunlin Taiwan, 2 , Kun Shan University, Tainan Taiwan, 3 , National Cheng Kung University, Tainan Taiwan
Show Abstract
Symposium Organizers
Nelson Bell Sandia National Laboratories
Yet-Ming Chiang Massachusetts Institute of Technology
Sossina M. Haile California Institute of Technology
Matthew M. Seabaugh NexTech Materials, Ltd.
JJ8: Solid Oxide Fuel Cells
Session Chairs
Friday AM, April 13, 2007
Room 3022 (Moscone West)
9:15 AM - JJ8.1
Effect of Micro-patterned Electrodes in Co-planar Type Single Chamber Solid Oxide Fuel Cell.
Sung-Jin Ahn 1 , Jooho Moon 1 , Jong-Ho Lee 2 , Joosun Kim 2
1 Department of Materials Science and Engineering, Yonsei University, Seoul Korea (the Republic of), 2 Nano-Materials Research Center, KIST, Seoul Korea (the Republic of)
Show Abstract9:45 AM - JJ8.3
Slow Crack Growth Analyses of Oxygen Transport Ceramic Membranes.
Jing Zhang 1 , Nagendra Nagabhushana 2 3 , Thangamani Nithyanantham 3 , Sukumar Bandhopadhyay 3
1 Mechanical Engineering, University of Alaska Fairbanks, Fairbanks, Alaska, United States, 2 , Praxair Inc., Tonawanda, New York, United States, 3 Mining and Geological Engineering, University of Alaska Fairbanks, Fairbanks, Alaska, United States
Show AbstractPerovskite-type oxides are promising materials with potential use as dense membranes for oxygen separations. We report slow crack growth (SCG) studies of La0.2Sr0.8Fe0.8Cr0.2O3-δ(LSFCO) perovskite membranes as Oxygen Transport Membranes (OTM). Two sample batches of perovskite were tested to investigate the effect of temperature, specific chemical environments, and loading rate on flexure strengths, using four-point bending tests. The first batch was examined at room temperature in air. The second batch was soaked in a N2/air atmosphere at 1000 oC for 1 hour prior to application of load. Loading rates varied from 0.00005 mm/s to 0.01 mm/s. Flexure data indicates that the examined OTM material showed little susceptibility to SCG at room temperature in air. However, the sample is susceptible to SCG in a N2/air environment at 1000 oC. Also, the experiments demonstrate flexure-strength rate dependency, with strength increasing with the loading rate. The observed phenomena are explained by the decomposition and microstructural transitions in the perovskite. The results provide important information about OTM mechanical degradation, which is valuable for future OTM design applications.
10:00 AM - **JJ8.4
Solid Solution in Cubic Perovskite Between La0.6Ba0.4ScO3-d and BaZrO3, and its Hydration and Proton Conductive Properties.
Tetsuya Uda 1 , Koichi Suehiro 1 , Susumu Imashuku 1 , Yasuhiro Awakura 1
1 Department of Materials Science and Engineering, University of Kyoto, Kyoto Japan
Show AbstractWe found the existence of complete solid solution between La0.6Ba0.4ScO3-d and BaZrO3 at 1600°C which is typical sintering temperature for these oxides. The solid solution has cubic perovskite structure. Assuming lanthanum and barium occupy only A site and scandium and zirconium occupy only B site in the cubic perovskite structure, the general formula can be written as La1-xBaxSc1-yZryO3-d where x and y are substituted ratio at each site for lanthanum and scandium with barium or zirconium, respectively. d is number of oxygen vacancy per unit cell, which is equal to 1/2(x-y) in principle. In humid atmosphere, water in gas phase dissolves into such oxides by reacting the oxygen vacancy and the lattice oxygen. The reaction is H2O(gas) + Vo + Oo ->2OHo. Then, the perovskite oxides show proton conduction. One end member of this solid solution is BaSc1-yZryO3-d which corresponds to that at x=1( this compound is stable when y is larger than 0.42), and another end member is La0.6Ba0.4ScO3-d which corresponds to that at x =0.4 and y=0. Both end members are known as a high protonic conductor. According to literature and this study, the protonic conductivities of bulk of both compounds are almost same at 300°C (about 3x10-4 S/cm). But, the difference is in the activation energy of proton migration. The activation energy of proton conduction in La0.6Ba0.4ScO3-d is much larger than that of BaSc1-yZryO3-d, in other word, La0.6Ba0.4ScO3-d has larger pre-exponential term than that of BaSc1-yZryO3-d. Therefore, the proton conductivity of La0.6Ba0.4ScO3-dis expected to be higher than that of BaSc1-yZryO3-d at higher temperature than 300°C. However, the dehydration reaction starts in the hydrated La0.6Ba0.4ScO3-d just above 300°C. On the other hand, water in BaSc1-yZryO3-d remains up to higher temperature. Consequently, the proton conductivity of BaSc1-yZryO3-d is higher than that of La0.6Ba0.4ScO3-d at higher temperature. Therefore, our interest is in the intermediate properties of the discovered solid solution. Now we are carrying out a thermogravimetry and AC conductivity measurement in various humid conditions as a function of temperature. With these measurements, we can evaluate the concentration of proton as a function of temperature and the partial pressure of water, the Gibbs energy change of hydration, the parameters of proton migration (the activation energy and the attempt frequency) in various composition in the solid solution. In this talk, first of all, we will focus on the established partial phase diagrams of the LaO1.5-BaO-ScO1.5 ternary system and of the LaO1.5-BaO-ScO1.5-ZrO2 quaternary system at 1600°C. Then, we will introduce the above mentioned proton migration properties as a function of composition, and expect to discuss a critical element or an optimal composition to increase the dehydration temperature, the basicity of lattice oxygen and the proton conductivity.
10:30 AM - JJ8.5
The Proton-conduction Properties of Nano- and Micro-Crystalline Barium Zirconante.
Heejung Park 1 , Umberto Anselmi-Tamburini 1 , Zuhair Munir 1 , Sangtae Kim 1
1 Chemical engineering and Materials science, University of California, Davis, Davis, California, United States
Show AbstractHigh protonic conductivity has been reported for various perovskite-type oxides such as cerates. Such proton conducting oxides can possibly be used as solid electrolytes for solid oxide fuel cells at intermediate temperatures, namely < 700 oC. However, only a few materials satisfy both high protonic conductivity and thermodynamic stability required for applications. Consequently the search for stable materials with high protonic conductivity continues. Chemically stable polycrystalline conductors such as BaZrO3-based ceramics have very high overall protonic conductivity at 300 – 600 oC. However, the measured overall conductivity is still markedly lower than that of the corresponding single crystal. This strongly implies, on the one hand, that the protonic resistance for grain-to-grain transfer in these materials is significantly high. On the other hand, this suggests that one may be able to modify the overall conductivity by optimizing the grain boundary properties. Therefore detailed knowledge of the interfacial properties and their contributions to the overall conductivity is essential. Whereas control parameters for concentrations and mobilities in the bulk are relatively well understood, little is known about them at the grain boundary. In view of a large interface to volume ratio, the grain boundary contribution to overall protonic conduction in doped BaZrO3 becomes significant as the grain size decreases.In this presentation, we report the electrical property of grain boundary of 16 mol% Y-doped BaZrO3 dense ceramics with the grain size of ~70 nanometer. The results will be compared with those measured from the ceramics with the grain size of ~1 micrometer.
Friday PM, April 13, 2007
Room 3022 (Moscone West)
11:15 AM - **JJ9.1
Electronic Structure Investigation of MAX-phases by Soft X-ray Emission Spectroscopy.
Martin Magnuson 1
1 , Department of Physics, Uppsala Sweden
Show AbstractThe electronic structures of epitaxially grown films of so-called MAX-phases were investigated by soft X-ray emission spectroscopy. These nanolaminated carbide and nitide compounds represent a class of layered materials with a combination of properties from both metals and ceramics. The bulk-sensitive soft X-ray emission technique is shown to be particularly useful for detecting detailed electronic structure information about internal monolayers and interfaces. A weak covalent Ti-Al bond is manifested by a pronounced shoulder in the Ti L-emission of Ti3AlC2, Ti2AlC and Ti2AlN. When Al is replaced by Si or Ge, the shoulder disappears. Furthermore, the spectral shapes of Al, Si and Ge in the MAX-phases are strongly modified in comparison to the corresponding pure elements. The measured X-ray emission spectra are compared and interpreted with ab initio density-functional theory including core-to-valence dipole matrix elements. The calculated results are found to yield consistent spectral functions to the experimental data. By varying the constituting elements, a change of the electron population is achieved causing a change of covalent bonding between the laminated layers, which enables control of the macroscopic properties of the material.
11:45 AM - JJ9.2
Hydrogen Purification using Ultra-thin Palladium Films supported on Porous Anodic Alumina Membranes.
Alexander Kirchner 1 , Ian Brown 1 , Mark Bowden 1 , Tim Kemmitt 1
1 Hydrogen & Distributed Energy, MacDiarmid Institute / Industrial Research, Lower Hutt New Zealand
Show Abstract12:00 PM - JJ9.3
Iron-Phosphate/Platinum/Carbon Nanocomposites for the Enhanced Electrocatalytic Stability.
Chunjoong Kim 1 , Byungjoo Lee 1 , Yejun Park 1 , Byungwoo Park 1
1 Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractDespite significant progress in PEMFC research and engineering nowadays, there are still prohibitive issues for the wide-range commercialization, such as the low efficiency of cathode for oxygen-reduction reaction, the loss of Pt activity by a long-term operation, etc. To resolve these, nanostructured Pt-based catalysts and electrodes have been intensively investigated. FePO
4-Pt/C nanocomposites were synthesized by a hydrothermal process, and their catalytic properties and stabilities were examined. The phosphate-Pt nanocomposites exhibited the similar electrocatalytic properties to Pt/C without any initial degradation, and also showed the enhanced long-term stabilities and decreased Pt dissolution compared with the Pt/C catalysts. The well-dispersed FePO
4 nanoparticles exhibited an important role preserving the Pt surface activities, by preventing both the agglomeration and dissolution of Pt. [1] P. J. Bouwman, W. Dmowski, J. Stanley, G. B. Cotten, and K. E. Swider-Lyons,
J. Electrochem. Soc. 151, A1989 (2004). [2] B. Lee, C. Kim, Y. Park, T.-G. Kim, and B. Park,
Electrochem. Solid-State Lett. 9, E27 (2006). Corresponding Author: Byungwoo Park:
[email protected]12:15 PM - JJ9.4
The Effects of Metal-Phosphate Coating on Ru Dissolution in PtRu Thin-Film Electrodes.
Byungjoo Lee 1 , Chunjoong Kim 1 , Yejun Park 1 , Yuhong Oh 1 , Byungwoo Park 1
1 Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractThe direct methanol fuel cell (DMFC) has been a subject of intense study due to the high energy density, easy handling of liquid, and low operating temperature. Platinum-ruthenium alloy is generally accepted as the most promising catalysts for methanol oxidation. However, Ru dissolution from PtRu anode may occur during the operation of DMFC due to the intrinsic instability of the PtRu catalysts. We report the possible ability of metal phosphates to promote CO oxidation and the effective transfer of protons during methanol oxidation. Also, metal phosphates are coated on PtRu thin-film electrodes to investigate the nanostructural effects on Ru dissolution. Moreover, the thickness effect of the metal-phosphate layer on the electrochemical properties will be discussed. [1] P. Piela, C. Eickes, E. Brosha, F. Garzon, and P. Zelenay,
J. Electrochem. Soc. 151, A2053 (2004). [2] B. Lee, C. Kim, Y. Park, T.-G. Kim, and B. Park,
Electrochem. Solid-State Lett. 9, E27 (2006). Corresponding Author: Byungwoo Park:
[email protected]12:30 PM - JJ9.5
Macroporous Silicon as Fuel Cell Proton Exchange Membranes.
Jeffrey Clarkson 1 , Timothy Reissman 2 , Ethan Israel 2 , Philippe Fauchet 1 , Ephrahim Garcia 2
1 Materials Science, University of Rochester, Rochester, New York, United States, 2 Mechanical and Aerospace Engineering, Cornell University, Ithaca, New York, United States
Show AbstractInvestigation of alternative materials that can be used in proton exchange membranes (PEM) will play a key role for improving the performance of future fuel cells. In this study, we report on the use of macroporous silicon (MPS) as a free standing ion transport membrane for direct methanol fuel cells (DMFCs). The material is comprised of an ordered matrix of pores up to 300 um in length with diameters ranging from 1 to3 um. At this scale, it is believed that electro-chemical effects play a critical role in ion transport through the membrane. Positive ions in the liquid form an electric double layer (EDL) near the pore walls in accordance with the Boltzmann relationship. Normally, the EDL is small enough to assume that the majority of the bulk fluid is electro-neutral, but in capillaries on the order of one micron, the EDL becomes significant. This has been investigated experimentally by modulating an EDL within a pore with various ionic concentrations, which in turn affected the output voltage of a DMFC. In addition to this, pore diameter and membrane thickness is expected to influence the overall fuel cell performance. Membrane design to increase hydrogen ion transport, decrease methanol fuel crossover, and ultimately optimize the power output of the cell will also be discussed.
12:45 PM - JJ9.6
Hydrogen Sorption Properties and the Microstructure of the Mg-Al-X System.
David Mitlin 1 , Julian Haagsma 1 , Erik Luber 1 , Colin Ophus 1 , Reza Mohammadi 1 , Zonghoon Lee 1 , Ulrich Dahmen 2 , Velimir Radmilovic 2
1 Chemical and Materials Engineering and National Institute for Nanotechnology, University of Alberta and NRC, Edmonton, Alberta, Canada, 2 NCEM, Lawrence Berkeley National Laboratory, University of California, Berkeley, California, United States
Show AbstractWe have explored the Mg-Al-X (where X is a series of catalytic additions) system for its hydrogen storage properties. In doing so, we employed two approaches: We co-sputtered 1.5 micron thin films of various compositions and co-high-energy-milled mixed powders. We then tested the materials’ hydrogen sorption kinetics and thermodynamics, and analyzed the as-synthesized, hydrided, and the post-sorption cycled microstructures using TEM and x-ray diffraction. The results in both cases were fairly consistent. Hydrogen sorption kinetics are optimized within a certain composition range corresponding to a microstructure consisting of a mixture of amorphous and nanocrytalline Mg-Al phases. There is also some preliminary evidence that such a microstructure actually results in less negative heat of hydride formation. Ternary and quaternary alloy additions not only act catalytically active phases, but also stabilize the favorable microstructure against repeated absorption-desorption cycling.