Symposium Organizers
Artur Braun Empa – Swiss Federal Laboratories for Materials Testing and Research
Jinghua Guo Lawrence Berkeley National Laboratory
Randall E. Winans Argonne National Laboratory
Helmut Schober Institut Max von Laue - Paul Langevin (ILL)
W1: Solid Oxide Fuel Cells and Electronic Structure of Ceramics
Session Chairs
Mirco Grosse
Adam Hitchcock
Tuesday PM, April 06, 2010
Room 3004 (Moscone West)
9:45 AM - W1.1
Chemistry, Structure and Transport Processes in Solid Oxide Fuel Cell Components Investigated With X-ray and Neutron Methods.
Artur Braun 1 , Selma Erat 1 , Peter Holtappels 1 , Thomas Graule 1 2 , Markus Janousch 3 , Josef Sfeir 7 , Jan Ilavsky 10 , Andrew Allen 9 , Robert Steinberger-Wilckens 6 , Jan Embs 5 , Thierry Straessle 5 , Eberhard Lehmann 4 , Jari Kiviaho 8 , Zhi Liu 11
1 Laboratory for High Performance Ceramics, EMPA, Dübendorf Switzerland, 2 , TU Bergakademie Freiberg, Freiberg Germany, 3 Swiss Light Source, Paul Scherrer Institut, Villigen Switzerland, 7 , Hexis AG, Winterthur Switzerland, 10 Advanced Photon source, Argonne National Laboratory, Argonne, Illinois, United States, 9 , US NIST, Gaithersburg, Maryland, United States, 6 , Forschungszentrum Jülich, Jülich Germany, 5 Laboratory for Neutron Scattering, Paul Scherrer Institut, Villigen Switzerland, 4 SINQ, Paul Scherrer Institut, Villigen Switzerland, 8 , VTT, Espoo Finland, 11 Advanced Light source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThe all-ceramic solid oxide fuel cell is a good example to illustrate the complexity of electrochemical energy conversion devices.A detailed overview is presented about how either component can be subject to in-depth studies with respect to structural properties, chemistry, and functionality.For the anode - the fuel electrode - it is shown how sulfur poisoning and sulfur-anode interaction can be addressed with element specific x-ray absorption spectroscopy. Here in particular S(1s) x-ray absorption near-edge spectra show some unexpected chemistry going on during fuel cell operation.For the ceramic electrolytes we show the example for proton conductors, where quasi elastic neutron scattering is employed to measure the proton diffusivity and thus proton conductivity as a function of temperature. This quantity is compared with electrochemical impedance spectroscopy data.For the cathodes we show a suite of soft x-ray and photoelectron spectroscopy data correlate quantitatively with the electronic conductivity of iron perovskites as a function of temperature and A-site and B-site substitution.[1] A Braun, M. Janousch, J. Sfeir, J. Kiviaho, M. Noponen, F. E. Huggins, M. J. Smith, R. Steinberger-Wilckens, P. Holtappels, T. Graule, Molecular speciation of sulfur in solid oxide fuel cell anodes with x-ray absorption spectroscopy, J. Power Sources 2008,183, 2, 564-570. [2] J. Richter, A. Braun, A.S. Harvey, P. Holtappels, T. Graule, L.J. Gauckler, Valence changes of manganese and praseodymium in Pr(1–x)Sr(x)Mn(1–y)In(y)O(3–δ) perovskites upon cation substitution as determined with XANES and ELNES. Physica B 2008, 403(1) 87-94. [3] A Braun, S. Duval, J.P. Embs, F. Juranyi, P. Ried, P. Holtappels, R. Hempelmann, U. Stimming, Th. Graule. Proton diffusivity in the BaZr0.9Y0.1O3-delta proton conductor. Journal of Applied Electrochemistry, 2009, 39(4), 471-475.[4] O. Haas, U.F. Vogt, C. Soltmann, A. Braun, W.-S. Yoon, X.Q. Yang, T. Graule. The Fe K-edge X-Ray Absorption Characteristics of La1-xSrxFeO3-δ Prepared by Solid State Reaction. Materials Research Bulletin 44 (2009), pp. 1397-1404. [5]A.J. Allen, J. Ilavsky, A. Braun, Multi-Scale Microstructure Characterization of Solid Oxide Fuel Cell Assemblies with Ultra Small-Angle X-Ray Scattering, Advanced Engineering Materials 2009, 11 (6), 495-501.[6] A Braun, X. Zhang, Y. Sun, U. Müller, Z. Liu, S. Erat, M. Ari, H. Grimmer, S.S. Mao, T. Graule, Correlation of high temperature X-ray photoemission valence band spectra and conductivity in strained LaSrFeNi-oxide on SrTiO3(110), Applied Physics Letters, 95, 022107, 2009.
10:00 AM - W1.2
In-situ Studies of Changes in Phonon Spectra Across the Ferroelectric to Paraelectric Phase Transitions in Model Ferroelectrics.
Narayani Choudhury 1 5 , Alexander Kolesnikov 2 , Helmut Schober 3 , Eric Walter 4 , Mark Johnson 3 , Doug Abernathy 2 , M. Lucas 2
1 Dept. of Physics, University of Arkansas, Fayetteville, Arkansas, United States, 5 Solid State Physics Division, Bhabha Atomic Research centre, Mumbai India, 2 Neutron Scattering Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , Institut Laue-Langevin, Grenoble, Cedex, France, 4 , College of William and Mary, Williamsburg, Virginia, United States
Show AbstractFerroelectric materials interconvert electrical and mechanical energies and find key technological applications as piezoelectric transducers and actuators used in ultrasonic devices, medical imaging, and telecommunications. The functional behavior of these materials, including its dielectric, piezoelectric and elastic response is intimately connected to their phonon spectra and lattice dynamics. Detailed ab initio lattice dynamics studies and inelastic neutron scattering (INS) measurements of model perovskite ferroelectrics [1] revealed that distinct bonding characteristics in the ferroelectric (FE) and paraelectric (PE) phases give rise to spectacular vibrational signatures. These studies [1] have also illustrated the important role of vibrational spectroscopy in novel materials design. Here we report, INS measurements and ab initio lattice dynamics calculations for studies of the in-situ changes in vibrational spectra across the FE-FE and FE-PE phase transitions in PbTiO3 and BaTiO3. There are radical changes in material behavior across the FE-PE transition and such studies are of interest to understand the microscopic correlations between vibrational spectra and functional properties. While both PbTiO3 and BaTiO3 are ferroelectric, SrTiO3 is a quantum paraelectric. The ferroelectric phase in SrTiO3 is suppressed even as T→0 K by zero-point fluctuations. Intrinsic differences in the bonding in BaTiO3, PbTiO3 and SrTiO3 give rise to their vastly different phase diagrams and FE behaviors [1,2]. These in turn give rise to interesting manifestations in their PDOS, which is the key quantity that determines various thermodynamic properties. Time-of-flight INS measurements of the PDOS as a function of temperature have been carried out using the HRMECS spectrometer at the Intense Pulsed Neutron Source, Argonne National Lab., the ARCS spectrometer at the Spallation Neutron Source, Oak Ridge National Lab. and at the Institut Laue Langevin to characterize the changes in PDOS across the FE-FE and FE-PE phase transitions of PbTiO3 and BaTiO3. Changes in phonon spectra across the antiferrodistortive transition of SrTiO3 have also been studied. The experiments have been analyzed using accurate density functional perturbation theory calculations. Theoretical lattice dynamics studies have been employed to derive the phonon and neutron weighted spectra, infrared reflectivity spectra and thermodynamic properties like the specific heat and equation of state. The observed specific heat of PbTiO3 exhibits a sharp discontinuity across the first order FE to PE phase transition; inclusion of excess entropy and latent heat terms are required to help explain this complex thermodynamic behavior. The integration of theory and experiments provides a fundamental atomic level understanding of material behavior in these systems.[1] N. Choudhury et al., Phys. Rev. B 77, 134111 (2008). [2] R.E. Cohen, Nature 358, 156 (1992).
10:15 AM - W1.3
Dynamics of Nanocage-based Materials Revealed by Neutron Scattering Experiments and First Principle Powder Averaged Lattice Dynamics Calculations.
Michael Koza 1 2 , Andreas Leithe-Jasper 2 , Yuri Grin 2 , Hannu Mutka 1 , Romain Viennois 3 , Zenji Hiroi 4 , Peter Franz 6 , Didier Ravot 3 , Mark Johnson 1 , Martin Rotter 5
1 , Institut Laue Langevin, Grenoble France, 2 CPfS, Max Planck Institut, Dresden Germany, 3 LPMC, Univeriste de Montpellier II, Montpellier France, 4 ISSP, University of Tokyo, Tokyo Japan, 6 , University of Vienna, Vienna Austria, 5 Physics Department, University of Oxford, Oxford United Kingdom
Show AbstractThe direct conversion of waste heat into electrical power in thermoelectric devices is believed to contribute substentially to future power supply and sustainable energy management. Nanocage-based crystalline structures like filled skutterudite systems XFe4Sb12 (X = Ca, Cs, Ba, La, Ce, Yb, Nd, ...) and clathrate materials like BaGe and BaSi have attracted some scientific interest as they are sought to be excellent thermoelectric materials. Their applicability for an efficient conversion of thermal into electrical energy is based on the opportunity of tuning appreciably the heat transport through the sample leaving the electron transport rather uneffected. For example, by a progressive filling of the voids in a Co4Sb12 skutterudite with guest atoms, e.g., La or Ce, the thermal conductivity drops by two orders of magnitude when the filling ratio is about 50 % [1]. Since glasses display a reduced thermal conductivity as compared with their crystalline counterparts it has been deduced that the mechanisms in nanocage structures and glasses might be the same, furthermore controlled by the specific phonon modes associated with the guest atoms, believed to be independent rattling modes in the cages of the host structure. The introduced nanocage-based materials are therefore termed 'electron crystals and phonon glasses'[2].A comprehensive description of the basic physical principles underlying the low thermal conductivity is required to enable an ad hoc design of thermoelectric devices. Our approach towards the understanding of this effect is based on neutron scattering experiments assisted by different computer simulation and calculation tools, like ab initio lattice dynamics. Neutron scattering is a powerful experimental technique since the kinematic properties of the neutron probe matches perfectly the energy and momentum scales of phonons, i.e., the very carriers of heat energy. Characteristic finger prints of the guest-dynamics in filled nanocage structures can be studied in detail.We will give some examples of our work on filled skutterudite and clathrate structures and pyrochlore osmates XOs2O6 (X = K, Rb, Cs) [3,4]. From an academic point of view, pyrochlore osmates seem to be excellent candidates for unravelling the mystery of ‘rattling’ dynamics in nanocage structures. We will present a new approach based on ab initio lattice dynamics calculations towards the interpretation of experimental data particularly dedicated to polycrystalline systems.[1] G.P. Meisner, D.T. Morelli, S. Hu, J. Yang, and C. Uher, Phys. Rev. Lett. 80, 3551, (1998).[2] B.C. Sales, D. Mandrus, B.C. Chakoumakos, V. Keppens, and J.R. Thompson, Phys. Rev. B. 56, 15081, (1997).[3] M.M. Koza, M.R. Johnson, R. Viennois, H. Mutka, L. Girard and D. Ravot, Nature Materials 7, 805, (2008)[4] H. Mutka, M.M. Koza, M.R. Johnson, Z. Hiroi, J.-I. Yamaura and Y. Nagao, Phys. Rev. B 78, 104307, (2008)
10:30 AM - **W1.4
Energy Research at Paul Scherrer Institute’s Large-scale Facilities.
Joel Mesot 1
1 , Paul Scherrer Institute, Villigen Switzerland
Show AbstractBeside running three large scale facilities (muon, neutron, synchtrotron) one of the main research focus at the Paul Scherrer Institute (PSI) is on energy sciences. In order to make best use of this unique constellation at PSI, dedicated beamlines (BL) have been developed in the past 10 years to investigate problems related to energy and environmental issues. In this talk I shall review the latest developments obtained at the Neutron- and x-ray micro radiography BL (fuel cells); in situ XAS BL (catalysts), VUV-spectroscopy BL (chemical reactions) and in-situ diffraction studies (micro- and nano-size materials).
11:00 AM - W1: SOFC I
BREAK
11:30 AM - W1.5
Performance Improvement of Solid Oxide Fuel Cell Using Platinum Modification.
Xubin Pan 1 , Iliana Medina-Ramirez 2 , Jinbo Liu 3
1 Environmental Engineering, Texas A&M University - Kingsville, Kingsville, Texas, United States, 2 Chemistry, Universidad Autonoma de Aguascalientes, Aguascalientes Mexico, 3 Chemistry, Texas A & M University – Kingsville, Kingsville, Texas, United States
Show AbstractFuel cells are green energy sources that spontaneously convert chemical energy into electricity, releasing heat and water when reduction oxidation reactions occur. One class called solid oxide fuel cells (SOFC) are devices drawing significant attention. Studies on SOFC cathode materials are critical to improve the performance of SOFC device due to its complexity of reducing oxygen. The lanthanum strontium cobalt iron oxide (LaxSr1-xCoyFe1-yO3, LSCF) displays high catalytic activity for O2 reduction reaction (ORR), high ionic and electronic conductivity at an intermediate temperature. Platinum modification on LSCF induces its band gap energy decrease, which allows rapid electron transfer from valance to conduction band, consequently ORR is advanced. In this study, CeO2 based materials were used as the electrolyte because LSCF cathode shows poor compatibility with traditionally used yttria stabilized zirconia (YZS).Sol-Gel method followed by Pt modification was used to improve fuel cell performance and to achieve high specific surface area of LSCF and Pt-LSCF. The kinetics of SOFC was evaluated using redox rate (exchange current density, io). The DC polarization was conducted to identify io when overpotentials (η) of -0.7 - +0.7 V were applied and temperatures varied from 400 to 700 °C with an interval of 50 °C. 3-electrode cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were implemented. EIS was performed to establish resistance-free i/η relationship, when the frequency varies from 0.05-106 Hz. Comparison indicates the Pt modification significantly improves io at identical operating conditions. It can be seen the specific area resistance from EIS and io were reached at ca. 0.30 Ω×cm2 and 250 mA/cm2 for LSCF and 0.12 Ω×cm2 and 565 mA/cm2 for Pt-LSCF at 700°C, respectively. Nanostructural characterization was implemented using high resolution transmission/scanning electron microscopy (HRTEM/SEM), X-ray powder diffraction (XRD) and wavelength dispersive spectroscopy (WDS). TEM/SEM images depict that the diameter of cathode materials is approximately 20-50 nm to enlarge its surface area (5.6 m2/g), which allows the rapid gas diffusion and instantaneous chemisorption of O2. TEM morphology showed that highly crystalline and mono-dispersive LSCF and Pt-LSCF nanoparticles. XRD results indicate that the nanoparticles are well aligned with standard LSCF perovsike and Pt cubic. Crystallite size obtained from Scherer equation corresponds with the TEM/SEM measured size. Elemental mapping from WDS shows that all elements (La, Sr, Co, Fe and Pt) distribute uniformly.
11:45 AM - W1.6
Electronic and Crystallographic Structure of LaSrFeNi-oxides: Potential Cathode Materials for Solid Oxide Fuel Cells.
Selma Erat 1 2 , Artur Braun 1 , Alejandro Ovalle 1 , Cinthia Piamonteze 3 , Zhi Liu 4 , Ludwig Gauckler 2 , Thomas Graule 1 5
1 , Empa, - Swiss Federal Laboratories for Materials Testing & Research, Dubendorf Switzerland, 2 Department for Nonmetallic Inorganic Materials, ETH-Zurich, Zurich Switzerland, 3 Swiss Light Source, Paul Scherrer Institute, Villigen Switzerland, 4 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 5 , Technische Universität Freiberg, Freiberg Germany
Show AbstractSolid oxide fuel cells (SOFCs) are electrochemical devices which produce electricity directly from oxidizing a fuel. SOFCs have three main parts; anode, cathode and electrolyte. We work on LaSrFeNi-oxides as a potential cathode material for intermediate temperature SOFCs. The electrical conductivity of LSF-Ni oxides which show semiconducting behavior at elevated temperatures and metallic like behavior at high temperatures explained in terms of changes in crystallographic structure monitored by temperature dependent neutron diffraction, in microstructure and in electronic structure, as well. In order to investigate the electronic structure, we used X-ray absorption spectroscopy technique and supported with the theoretical calculation depending on Ligand Field Atomic Multiplet Theory. We get very good agreement between experimental results and theoretically calculated results. For example, La0.5Sr0.5Fe0.75Ni0.25O3 which has higher conductivity has 50% Fe3+ and 50% Fe4+, both in high spin state with 10Dq=1.85 eV. In addition to that, the hybridization between Fe/Ni 3d and O 2p orbitals is stronger than La1-xSrxFe-oxides which make the Ni containing samples more conducting. The transport properties of the Ni containing samples can be explained by two different mechanisms: electron hole hopping via superexchange unit Fe3+-O-Fe4+ and charge transfer from O 2p to Ni 3d.
12:00 PM - **W1.7
Strong Correlation in Transport Properties Between Holes/Protons and B-site Multivalent Cations in Perovskite Oxides for SOFC Materials by XAS and RPES/RIXS.
Take0 Kikuchi 1 , Mao Tamaru 1 , Tohru Higuchi 2 , Jinghua Guo 3 , Shu Yamaguchi 1
1 Dept. of Materials Science, University of Tokyo, Tokyo Japan, 2 Dept. of Appl. Phys., Tokyo University of Science, Tokyo Japan, 3 ALS, Laurence Berkeley National Lab., Berkeley, California, United States
Show AbstractA strong correlation in electrical transport properties between holes/protons and B-site multivalent cation in perovskite oxides were found in acceptor- and donor-doped BaPrO3 and BaZr1-xPrxO3 systems. In case of BaPrO3, auto-ionization which corresponds to the electron transfer from O2- to Pr4+ to form O-(hole) and Pr3+(electrons) pairs, is favored. Such strongly correlated electron-hole pair is observed by soft X-ray absorption spectroscopy (XAS) and Raman inelastic X-ray scattering (RIXS) measurements and the charge transfer from Pr4f0-O2p6 to Pr4f1-O2p5 is identified. The electrical transport properties are examined by both the electrical conductivity and thermoelectric power measurements, showing a possible small polaron hopping for both electrons and holes with similar estimated mobility of 10-3~10-4 cm2V-1s-1. Due to a strong correlation with the interaction energy of ≈2.2 eV, a strange correlated migration of holes and electrons that cannot carry net charge is estimated. Recent report on a careful examination of partial electronic conductivity for CeO2 systems exhibits similar situation of strongly correlated carrier formation by the auto-ionization. A possible extension of auto-ionization and relating electronic band structure for proton/electrons on transition metal cation will be discussed.
W2: Solid Oxide Fuel Cells and Solid State Ionics
Session Chairs
Peter Chupas
Shu Yamaguchi
Tuesday PM, April 06, 2010
Room 3004 (Moscone West)
2:30 PM - W2.1
Dynamic Instability at the Origin of Oxygen Ion Conduction in Solid Oxides at Ambient Temperature.
Helmut Schober 1 , Werner Paulus 2 , Mark Johnson 1 , Stefan Eibl 2 , Monica Ceretti 2 , Carlo Lamberti 3 , Marie Plazanet 1 , Ollivier Hernandez 2
1 Science Division, Institut Laue Langevin, Grenoble France, 2 Sciences Chimiques de Rennes, CNRS-Universite de Rennes1, Rennes France, 3 , University of Turin, Turin Italy
Show AbstractThe conduction of ions in solids is of paramount importance for many technological devices like solid oxide fuel cells. It is inherent to solids that ions are trapped within potential wells. Their transport thus has to be activated at the price of elevated temperatures, a condition that is often incompatible with technological requirements. While atomic vibrations have the potential of assisting the diffusion process little is known about the exact conditions that have to be reunited to trigger such a process. Here we show that dynamic instability is responsible for the large ion conduction in SrFeO2.5 with Brownmillerite-type structure. Using ab-initio molecular dynamics calculations we observe the migration of oxygen ions away from the original lattice positions into the vacancy channels of the Brownmillerite structure. The escape of the oxygen ion is rendered possible by the destabilization of a shallow potential well due to low-lying vibrational modes, the existence of which is confirmed by neutron spectroscopy. Analyzing the lattice dynamics as a function of structural parameters it is possible to identify the structural subtleties responsible for the instability. It is found that in the isostructural compound CaFeO2.5 fast oxygen ion diffusion is absent at low temperatures. The origin of this behaviour lies with the slightly different iron-oxygen distances rendering the potentials better defined and less amenable to dynamical destabilization. The here-introduced concept of dynamical instability is not restricted to the discussed class of materials but may be applied to any system that features ion conduction at low temperatures.W.Paulus, H.Schober, S.Eibl, M.Johnson,T. Berthier, O.Hernandez, M.Ceretti,M.Plazanet, K.Conder, and Carlo Lamberti, JACS (2008)
2:45 PM - **W2.2
Hard X-rays: A Tool for Mapping Energy Materials in Space and Time.
Henning Poulsen 1 , Poul Norby 1
1 Risoe National Laboratory for Sustainable Energy, Technical University of Denmark, Roskilde Denmark
Show AbstractDuring the last decade our group has developed of a number of methods for comprehensive 4D (space and time-resolved) studies at the micron scale using x-rays in the 35-200 keV. These include - 3DXRD microscopy: enabling studies of the dynamics (orientation, morphology) of several hundred of grains simultaneosusly- plastic strain tomography: mapping the deformation field- stress mapping: in crystalline as well as amorphous materials- fast time-resolved diffractionThese status of these methods will be presented and initiatives towards generalising the concepts to the nano-scale presented.The prospect of using the hard x-rays for in situ studies of materials for energy technology is illustrated with case stories from a set of applications: - studies of strain and oxidation kinetics in fuel cells and oxygen permeable membranes- studies of grain dynamics in superconducting tapes- studies of polymer composites for wind turbines
3:15 PM - W2.3
Correlation of Structure and Conductivity of Proton Conducting Ceramics.
Qianli Chen 1 2 , A. Braun 1 , A. Ovalle 1 , A. Cervellino 3 , J. Embs 3 4 , T. Straessle 3 , W. Stolte 5 , O. Safonova 6 , S. Duval 1 , W. Haeussler 7 8 , P. Holtappels 1 , V. Pomjakushin 3 , N. Bagdassarov 9 , T. Graule 1 10
1 Laboratory for High Performance Ceramics, EMPA - Swiss Federal Laboratories for Materials Testing and Research, Duebendorf Switzerland, 2 Department of Physics, ETH Zurich, Zurich Switzerland, 3 Laboratory for Neutron Scattering, ETH Zurich & Paul Scherrer Institut, Villigen Switzerland, 4 , Saarland University, Saarbruecken Germany, 5 , Advanced Light Source, Berkeley, California, United States, 6 Swiss Norwegian Beamlines, ESRF, Grenoble France, 7 Physics Department, TU Munich, Garching Germany, 8 , FRM-II, Garching Germany, 9 Institute of Geoscience, University of Frankfurt, Frankfurt Germany, 10 , TU Bergakademie Freiberg, Freiberg Germany
Show AbstractProton conductors are promising solid electrolyte materials for ceramic fuel cells at intermediate working temperature. Our study focuses on the molecular mechanisms of proton conductivity of peroskite yttrium doped barium zirconates and cerates, extensively with synchrotron and neutron radiation at large scale facilities. Our recent results in Y-resonant X-ray diffractograms of BaZr0.9Y0.1O2.95 (BZY10) reveal that Y atoms are organized in a superstructure. Comparison with neutron diffraction superstructure reflections in protonated/deuterated BZY10 suggests that both superstructures are linked, and that protons move in the landscape imposed by the Y. The onset temperature of lateral proton diffusion coincides with its thermal lattice expansion, which exhibits a contraction for protonated BZY10 at about T = 648 K, suggesting a correlation of toughening of the lattice and proton conductivity. The chemical shift in the Y L1-shell x-ray absorption spectra reveals a reduction from Y3+ towards Y2+ upon protonation. The Y K-edge spectra reveal a charge transfer, which vanishes at high temperatures, possibly suggesting a thermally unstable H-Y bond. We have previously found that the activation energy of proton conductivity decreases linearly with the lattice parameter, indicating that the protons need "space" to move freely in the lattice.
3:30 PM - **W2.4
Characterizing Solid Oxide Fuel Cells During Electrochemical Operation Using Ambient Pressure XPS.
Michael Grass 2 , Farid El Gabaly 1 , Anthony McDaniel 1 , Kevin McCarty 1 , Hendrik Bluhm 2 , Roger Farrow 1 , Zahid Hussain 2 , Zhi Liu 2
2 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 1 , Sandia National Laboratories, Livermore, California, United States
Show AbstractElectrochemical systems for energy applications are hampered by lack of fundamental measurements and understanding of ion transport and interfacial charge transfer mechanisms. Electrochemical devices based on the conduction of O2- anions through a solid electrolyte, such as a solid oxide fuel cell (SOFC) or electrolyzer (SOEC), have great potential for both clean, efficient power generation and efficient production of fuels such as hydrogen or synthesis gas. The essential physical phenomena that govern reaction and charge transfer across material interfaces are poorly understood. The ability to directly observe changes in chemical composition and elemental oxidation state at surfaces and interfaces under electrochemically active conditions will provide insight into such processes. Here, we report in situ measurements of Ni and Pt patterned thin films (300nm) electrodes in solid-oxide electrochemical cells using ambient pressure X-ray photoelectron spectroscopy (APXPS, beamlines 9.3.2 and 11.0.2 of the Advanced Light Source, Lawrence Berkeley National Laboratory). This novel setup provides quantitative information about the elemental surface composition, local surface potential of electrolyte and electrodes, and changes in elemental oxidation state as a result of electrochemical and thermochemical activity occurring under relevant operating conditions: typically 0.25 Torr of hydrogen and 0.25 Torr of water, T=1023K, and under applied bias potential. A new endstation at ALS beamline 9.3.2 allows us to map electrochemically driven surface phenomena with 20 micron resolution.
4:00 PM - W2: SOFC II
BREAK
4:30 PM - **W2.5
Anomalous Ultrasmall-angle X-ray Scattering Studies of Electrochemical Interface Evolution in Solid Oxide Fuel Cells in Response to Service Life and Fuel Sulfur Content.
Andrew Allen 1 , Jan Ilavsky 2 , Pete Jemian 2 , Artur Braun 3
1 Ceramics Division, NIST, Gaithersburg, Maryland, United States, 2 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States, 3 Laboratory for High Performance Materials, EMPA, Dubendorf Switzerland
Show AbstractThe use of small-angle X-ray and neutron scattering (SAXS and SANS) methods has become widespread for quantifying nanoscale features in heterogeneous materials of all types. The primary parameters obtained are the mean size, the total surface area and, with absolute intensity calibration, the volume fraction size distribution. With the development of ultrasmall-angle scattering (USAXS and USANS) methods (that exploit crystal diffraction optics to extend the measurements to smaller scattering angles and correspondingly larger sizes), these microstructural parameters can now be determined over a contiguous length scale from nanometers to micrometers. At a 3rd generation synchrotron facility, the USAXS technique can cover much of this scale range within a single measurement, using a beam size (hence spatial resolution) down to a few micrometers in one dimension. This makes the method ideally suited to studying advanced energy materials, which frequently contain hierarchical void structures over many length scales, several co-existing solid phases, and microstructural gradients or interfaces. All of these aspects must be well characterized in order to establish the processing – microstructure – property relationships that govern performance. We have employed the USAXS technique to study a solid oxide fuel cell (SOFC) system.In the SOFC context, it is important to distinguish among the different electrochemically-active solid components and their associated void morphologies close to the electrolyte – electrode interfaces. To do this, USAXS measurements must be made at each sample position using several X-ray energies just below the X-ray absorption edge for a selected atomic species in the system. The “anomalous” variation of X-ray scattering contrast with energy can then be used to distinguish those aspects of the microstructure associated with the phase containing the selected atom. For truly multi-component systems such as SOFC’s, correlated anomalous USAXS measurements are needed at two or more widely separated absorption edges. This paper will illustrate these points through anomalous USAXS studies of a SOFC system (previously measured to obtain a basic microstructure characterization [1]) to obtain the electrochemically-active interface response to service life in the presence or absence of sulfur within the fuel. [1] A.J. Allen, J. Ilavsky and A. Braun; "Multi-scale microstructure characterization of solid oxide fuel cell assemblies with ultrasmall-angle X-ray scattering," Adv. Eng. Mater., 11, 495-501 (2009).
5:00 PM - W2.6
Neutron Diffraction Study of NiO/LiCoO2 Electrodes for Innovative Fuel Cell Development.
Roberto Coppola 1 , Paul Henry 3 , Angelo Moreno 2 , Juan Rodiguez-Carvajal 3 , Elisabetta Simonetti 2
1 FISNUC, ENEA, Roma Italy, 3 , ILL, Grenoble France, 2 IDROCOMB, ENEA-Casaccia, Rome Italy
Show AbstractThis contribution presents the results of a neutron diffraction study carried out on Ni-NiO 30% electrodes coated with LiMg 0.05 Co 0.95 O2 cobaltite deposited on the substrate by complex sol-gel process. The neutron diffraction measurements were carried out at the D20 diffractometer at the High Flux reactor of the Institut Max von Laue – Paul Langevin. The catalytic layer being only a few microns in thickness, the diffracting volume of the cobaltite phase was optimised by stacking 40 small rectangular pieces cut from the original electrode. A pure cobaltite sample was used as a reference for identifying in the complete electrode the diffraction peaks of the catalytic layer. Both an as-received sample and an electrode tested 100 h at 650 °C were measured. The adopted technique provides useful and accurate information on the crystallographic phases present the in the as-received electrode, where a cobaltite volume fraction of the order of 0.01 is estimated; after 100 h at 650°C in the cell the initial crystallographic structure is completely changed but traces of hexagonal phase are still detectable.
5:15 PM - W2.7
Total Reflection Inelastic X-ray Scattering; A Direct Probe of Defect Chemistry in Thin Films.
Tim Fister 1 , Dillon Fong 1 , Jeffrey Eastman 1 , Hakim Iddir 1 , Peter Zapol 1 , Hui Du 2 , Paul Salvador 2 , Paul Fuoss 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractAt the high temperatures associated with many growth techniques and thin film devices, the mobility of ionic defects can lead to strong property gradients near the surface that influence, and are influenced by, chemical and electrical boundary conditions. To study equilibrium changes in composition, valence, and electronic structure near the surface and into the bulk, we present a new approach, total reflection inelastic x-ray scattering (TRIXS). TRIXS uses highly penetrating hard x-rays (10 keV) to create an in situ alternative to traditional sub-keV spectroscopies that are generally limited to use under vacuum conditions. We demonstrate the feasibility of this new approach by characterizing a 10-nm-thick film of La0.6Sr0.4CoO3-δ (LSCO) grown epitaxially onto a (100) SrTiO3 substrate. LSCO is a prototypical mixed conductor and an important candidate material for application in intermediate-temperature solid oxide fuel cells. By comparing data acquired under total x-ray reflection and penetrating conditions, we are able to separate the oxygen K-edge spectra from a LSCO thin film from that of the underlying SrTiO3 substrate. Working at high temperature, we examine the relationship between the oxygen K-edge and the cobalt 3d final states under controlled oxygen partial pressure conditions, and make a direct measurement of the interplay between oxygen vacancy concentration and cobalt valence state. We also will describe how using a higher energy probe than comparable soft x-ray absorption measurements provides the ability to easily access dipole-forbidden final states, using the dramatic evolution of hybridized lanthanum f-electron states with momentum transfer as an example.This work is supported by the U.S. Department of Energy (DOE) Solid State Energy Conversion Alliance (SECA) program, and at Argonne by DOE under contract DE-AC02-06CH11357
5:30 PM - W2.8
3D Chemical Imaging of Solid Oxide Fuel Cells Revealed by Synchrotron X-ray Fluorescence (sub)Microtomography.
Pierre Bleuet 1 , Peter Cloetens 2 , Gerard Delette 3 , Patrice Gergaud 1 , Olivier Sicardy 3 , Remi Tucoulou 2 , Julie Villanova 3
1 , CEA, LETI, MINATEC, Grenoble France, 2 , European Synchrotron Radiation Facility, Grenoble France, 3 , CEA, LITEN, Grenoble France
Show AbstractSOFCs are interesting power source alternatives that convert chemical energy into electrical energy at high temperatures. From the chemical point of view they are made of ceramic materials containing major and minor elements, including oxygen, nickel, zirconium, lanthanum, strontium, manganese, yttrium, cerium or gadolinium. This complex arrangement is based on a mesoscopic scale structure. To image and measure the distributions of all these elements at the very same time and in a non destructive way, we use x-ray fluorescence tomography based on a 3rd generation synchrotron source.In fluorescence tomography, a pencil, focused (or collimated) beam is produced and a sample, usually few hundred times bigger than the beam, is raster scanned along a particular axis while being rotated, so that a 1st generation of medical scanner geometry is faked. Eventually this scanning scheme can be repeated several times at several altitudes and this 3-axes motion allows 3D imaging. All along the scan, fluorescence spectra are recorded using an energy-dispersive detector placed at 90 degrees with respect to the beam. After appropriate peak fitting, so-called fluorescence sinograms can be built that serve as an input for 2D, or 3D, elemental reconstruction. Although the technique was limited to the micrometer scale until a few years back, x-ray optics progresses have recently been performed that now allows reaching 100nm resolution in the 15-30keV x-ray regime. Extension to depth-resolved crystalline imaging has also been proved, which could be of great interest for SOFCs. Experiments on SOFCs have been performed at the ESRF beamline ID22NI. Fluorescence tomography has been applied to SOFCs imaging, revealing features that cannot be observed by any other technique, including more conventional x-ray tomography or electron imaging that have also both been carried out. The principle of the method will be discussed as well as its limitations.
5:45 PM - W2.9
In-situ Electrochemical Polarization Experiments for Two-terminal Type Gapless Cu2S Atomic Switch Using Hard X-ray PES.
Takashi Tsuchiya 1 , Shogo Miyoshi 1 , Yoshiyuki Yamashita 3 , Kauya Terabe 2 , Shu Yamaguchi 1
1 Dept. of Materials Eng., University of Tokyo, Tokyo Japan, 3 SPring-8, National Inst. of Materials Science, Sayo Japan, 2 Nano System Functionality Center, National Inst. of Materials Science, Tsukuba Japan
Show AbstractAn attempt to in-situ electrochemical polarization measurements has been made to analyze the local nonstoichiometry modulation of Cu2S in the neighboring region of the blocking electrode, in order to verify the nonstoichiometry-induced carrier modfication model for gapless-type two-An attempt to in-situ electrochemical polarization measurements has been made to observe the local nonstoichiometry modulation of Cu2S in the neighboring region of the blocking electrode, in order to verify the nonstoichiometry-induced carrier modfication model for gapless-type two-probe atomic switch using Cu2S. An asymmetric Hebb-Wagner type electrochemical cell, of which construction is expressed as Cu (Reversible electrode)/Cu2S/Pt (Blocking electrode), is used for the experiment at BL-15XU in SPring-8 facility. A marked band bending was observed just below the critical applied potential for the metallic Cu precipitation in addition to a chemical shift of both Cu2p and S1s orbital. In contrast, in-situ measurement using coulometric titration cell composed of Cu/RbCu4Cl3I2/Cu2S have shown none of such broadening while a non-linear chemical shift is observed. The comparison of these PES data suggest a possible reason for the band bending as the steep band bending by the nonstoichiometry modulation because of the supersaturation. Further attempt to oxide atomic switch system will be presented and discussed.
Symposium Organizers
Artur Braun Empa – Swiss Federal Laboratories for Materials Testing and Research
Jinghua Guo Lawrence Berkeley National Laboratory
Randall E. Winans Argonne National Laboratory
Helmut Schober Institut Max von Laue - Paul Langevin (ILL)
W3: H2 Storage and Hydrogen in Solids I
Session Chairs
Qianli Chen
Helmut Schober
Wednesday AM, April 07, 2010
Room 3004 (Moscone West)
9:30 AM - W3.1
Synchrotron Powder Diffraction Simplified: Introducing the High-resolution Diffractometer 11-BM at the Advanced Photon Source.
Matthew Suchomel 1 , Lynn Ribaud 1 , Robert Von Dreele 1 , Brian Toby 1
1 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractSynchrotrons have revolutionized powder diffraction. They make possible the rapid collection of data with tremendous resolution and a superb signal to noise ratio. The high penetration and wide Q range afforded by high energy light sources like the Advanced Photon Source (APS) even allow synchrotrons to make inroads into territory that previously demanded neutron scattering techniques. Despite all these advances, still relatively few researchers utilize synchrotrons for their powder diffraction experiments.To help address this, the 11-BM synchrotron powder diffractometer at the APS provides users with world-class data via a convenient mail-in service or through on-site experiments. This instrument offers resolution unmatched in North America (ΔQ/Q ~ 2×10-4). With both vertical and horizontal beam focusing capabilities and a detection system consisting of twelve perfect crystal analyzers, the diffractometer can collect a superb pattern suitable for Rietveld analysis in one hour or less. Users of the unique 11-BM rapid access mail-in program typically receive their high-resolution data via email within two weeks of sample receipt at the APS.This presentation will introduce potential users to 11-BM and its associated mail-in program. The performance and capabilities of the current instrument will be discussed. Currently the instrument is equipped with a robotic arm for automated sample changes, and features several sample environments. This presentation will walk would-be users though the simple steps required to submit their own samples via the 11-BM mail-in program and describe the additional options available to on-site users. Examples from previous work by 11-BM users and beamline staff will demonstrate how your research can benefit from high-resolution synchrotron powder diffraction.More information about 11-BM and its mail-in program can also be found on online at http://11bm.xor.aps.anl.gov.
9:45 AM - **W3.2
Combined Gravimetric and Neutron Powder Diffraction Studies of Hydrogen Storage Materials.
Bill David 1 2 , Martin Jones 2 1 , Peter Edwards 2
1 ISIS Facility, STFC, Chilton United Kingdom, 2 Inorganic Chemistry Laboratory, University of Oxford, Oxford United Kingdom
Show AbstractOne of the greatest technological hurdles preventing the widespread development of the hydrogen economy is the lack of a viable hydrogen storage medium for transportation. The storage of hydrogen gas in solids has the potential to address this key requirement - such a store should possess a high capacity (with a system capacity ideally in excess of 5wt% hydrogen), a low desorption temperature of around 120°C, and a complete reversibility of the absorption/desorption cycle. These factors are intimately linked to the crystal structure of any solid state storage material, so that a full structural description coupled with an in-depth investigation of the physical-chemical properties of the absorption/desorption process are necessary to fully understand, and hence properly optimize, the mechanism of hydrogenation and dehydrogenation. To undertake these studies, we have designed and commissioned apparatus that allows neutron diffraction studies to be performed simultaneously with thermogravimetric analysis. In this presentation, we describe experiments performed with this apparatus, the Intelligent Gravimetric Analyzer in conjunction with Neutron diffraction (IGAn). This work was undertaken as a joint project between the Rutherford Appleton Laboratory, Chilton, Didcot (UK) and Hiden Isochema Ltd. The IGAn comprises a microbalance housed in a stainless steel vessel that can be used on neutron powder diffractometers at ISIS. The IGAn thus combines two techniques, neutron powder diffraction and gravimetric analysis, that are among the most important for characterization of hydrogen storage solids. Taken simultaneously, these two techniques give valuable information on both the structural changes and the mechanism and kinetics of hydrogenation and dehydrogenation of solid state hydrogen stores. Various case-studies, including the lithium amide/ lithium imide system, will be described that have been performed on the GEM and HRPD diffractometers at the ISIS pulsed neutron source, Rutherford Appleton Laboratory, UK.
10:15 AM - W3.3
Quaternary Ammonium Borohydride Adsorption in Mesoporous Silicate MCM-48.
Michael Wolverton 1 2 , Luke Daemen 1 , Monika Hartl 1 , Abhijit Bhattacharyya 2
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Applied Science, University of Arkansas at Little Rock, Little Rock, Arkansas, United States
Show AbstractInorganic borohydrides have a high gravimetric hydrogen density but release H2 only under energetically unfavorable conditions. Surface chemistry may help in lowering thermodynamic barriers, but inclusion of inorganic borohydrides in porous silica materials has proved hitherto difficult or impossible. We show that borohydrides with a large organic cation are readily adsorbed inside mesoporous silicates, particularly after surface treatment. Thermal analysis reveals that the decomposition thermodynamics of tetraalkylammonium borohydrides are substantially affected by inclusion in MCM-48. Inelastic neutron scattering (INS) data show that the compounds adsorb on the silica surface. Evidence of pore loading is supplemented by DSC/TGA, XRD, FTIR, and BET isotherm measurements. Mass spectrometry shows significant hydrogen release at lower temperature from adsorbed borohydrides in comparison with the bulk borohydrides. INS data measured for partially decomposed samples indicates that the decomposition of the cation and anion is likely simultaneous. Additionally, these data confirm the formation of Si-H bonds on the silica surface upon decomposition of adsorbed tetramethylammonium borohydride.
10:30 AM - W3.4
NaBX4-MgX2 Composites (X: D,H) Investigated by in situ Neutron Diffraction.
Daphiny Pottmaier 1 , Sebastiano Garroni 2 , Michella Brunelli 3 , Alberto Castellero 1 , Enric Menendez 4 , Gavin Vaughan 5 , Maria Baro 2 , Marcello Baricco 1
1 Chimica IFM, Universita di Torino, Turin Italy, 2 Fisica, Universidad Autonoma de Barcelona, Barcelona Spain, 3 D20, Institut Laue-Langevin, Grenoble France, 4 Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, Dresden Germany, 5 ID11, European Synchrotron Radiation Facility, Grenoble France
Show AbstractComplex hydrides (e.g.NaBH4) combined with metal hydrides (e.g.MgH2) is considered a primary class of solid state hydrogen storage materials, the so-called Reactive Hydride Composite (RHC). In spite of drawbacks such as unfavourable thermodynamics and poor kinetics in the dehydrogenation reaction of single hydrides, enhancements may occur in RHCs by nanostructuring of reactant phases and formation of more stable product phases (e.g.MgB2) which lower overall reaction enthalpy and allows reversibility. One potential system is based on ball milling NaBH4 and MgH2 together in a 2:1 molar ratio which can store considerable amounts of hydrogen by weight (up to 7.8wt%). The corresponding desorption reaction 2NaBX4+MgX2 -> MgB2+2NaX+4X2 is assessed by means of in-situ neutron diffraction with different combinations of hydrogen and deuterium on X position. Desorption reaction is established to begin at temperatures as low as 250°C due to joint effects of nanostructured MgX2 and its destabilization by NaBX4. Moreover, successive MgB2 formation along with NaBH4 dehydrogenation is shown to proceed at temperatures higher than 350°C. Due to high scattering of hydrogen element, a direct correlation with H/D desorption reactions is found by the study of the background profile of neutron diffraction patterns in function of temperature. Combined use of hydrogen and deuterium analysed by neutron radiation added insights in the reaction mechanism of this system.
10:45 AM - W3.5
Neutron Scattering and First Principles to Characterize Cu/Mg Destabilized Hydrogen Storage Materials.
Maria Braga 1 , Monika Hartl 1 , Michael Wolverton 1 , Hongwu Xu 1 , Yusheng Zhao 1 , Luke Daemen 1
1 , LANSCE-LC, LANL, Los Alamos, New Mexico, United States
Show AbstractThe pioneering work of Reilly and Wiswall (Inorg. Chem., 1967) on hydrogen storage in Cu2Mg provides the first clear example of destabilization. CuMg2 was reversibly hydrogenated to 3/2MgH2 + 1/2Cu2Mg with an equilibrium pressure of 1 bar at 240 °C. This temperature is ~ 40 °C lower than T(1 bar) for pure MgH2. Nevertheless, since CuMg2 does not form a hydride, the referred work was set aside until very recently. The current search for an on-board hydrogen storage material led to a point where only a system of up to 4 elements will cover all specifications, and this with difficulty. A destabilization strategy then becomes a viable, attractive solution.CuMg2 has an orthorhombic crystal structure (Fddd). However CuLixMg2-x (x = 0.08) has a hexagonal crystal structure (P6222), just like NiMg2 -a compound known for its hydrogen storage properties. NiMg2 absorbs up to 3.6 wt% of hydrogen, at 1 bar and 282 °C (555 K). In spite of the fact that the percentage of H2 absorbed by NiMg2 is enough to propitiate practical applications, the temperature at which the alloy desorbs hydrogen is much too high for current applications. Still, the alloy can be found in practical applications when added to other elements/alloys. A comparison between the phase diagrams of the systems Cu-Mg and Ni-Mg shows that these binary systems form compounds with similar stoichiometry. NiMg2 is formed by peritectic reaction of the elements at 759 °C (1032 K) and CuMg2 at 568 °C (841 K) by congruent melting. The presence of Li lowers even further the melting point of CuMg2. Since the energy of formation of the hydride is related to that of the primary alloy, it was hypothesized that CuLixMg2-x might also be a hydrogen storage material similar to NiMg2. Presumably, its advantage would be that it would release hydrogen at a lower temperature (possibly close to room temperature).Preliminary studies at the Los Alamos Neutron Scattering Center showed that CuLixMg2-x might absorb approximately 5.3 wt% H for an equilibrium pressure of approx. 27 bar at 200 °C. DSC experiments show that a considerable amount of hydrogen can be released at T < 100 °C. If these results are confirmed, this will mean that, not only CuLixMg2-x absorbs a considerable amount of hydrogen, but also will probably release it at a temperature in the range of 50 to 200 °C, where applications are easier to develop. Hence it should be possible to use this alloy with fuel cells or in batteries. It was also observed that a sample containing CuMg2 could release hydrogen at 180 °C ≤ T ≤ 205 °C, probably meaning that the presence of CuLixMg2-x will make MgH2 to release hydrogen at an even lower temperature. In this work we have characterized Cu-Li-Mg (Li, B, Al, Ti) hydrogen storage systems and its thermodynamic properties by means of neutron scattering, first principles calculations, and other complementary techniques.
11:00 AM - W3: Hydrogen I
BREAK
11:30 AM - W3.6
High-intensity Neutron Total Scattering Instrument (NOVA) for Structural Studies of Hydrogen Storage Materials at J-PARC.
Toshiya Otomo 1 , Kentaro Suzuya 2 , Masakatsu Misawa 1 , Naokatsu Kaneko 1 , Hidetoshi Ohshita 1 , Toshiharu Fukunaga 3 , Keiji Itoh 3 , Kazuhiro Mori 3 , Masaaki Sugiyama 3 , Yasuo Kameda 4 , Toshio Yamaguchi 5 , Koji Yoshida 5 , Yukinobu Kawakita 6 , Kenji Maruyama 7 , Shinichi Shamoto 2 , Shinichi Takata 2 , Setsuo Satoh 1 , Suguru Muto 1 , Junichi Suzuki 1 , Takashi Kamiyama 1 , Susumu Ikeda 1 , Yoshiji Yasu 1 , Kazuo Nakayoshi 1 , Hiroshi Sendai 1 , Shinichi Itoh 1
1 Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, Japan, 2 , Japan Atomic Energy Agency, Tokai, Ibaraki, Japan, 3 Research Reactor Institute, Kyoto University, Kumatori, Osaka, Japan, 4 Faculty of Science, Yamagata University, Yamagata, Yamagata, Japan, 5 Faculty of Science, Fukuoka University, Fukuoka, Fukuoka, Japan, 6 Faculty of Science, Kyushu University, Fukuoka, Fukuoka, Japan, 7 Faculty of Science, Niigata University, Niigata, Niigata, Japan
Show AbstractStructure analysis with the atomic Pair Distribution Function (PDF) is now widely used for materials research. Pulsed neutron sources are unique for total scattering measurement to obtain PDF since they provide short-wavelength neutrons effectively, which is important to measure reliable high-Q diffraction data. High-intensity total scattering instrument (NOVA) is a new total diffractometer for disordered materials installed at J-PARC. By utilizing a broadband width of neutron wavelength, it will cover a wide Q-range (0.01 Å-1 < Q < 100 Å-1). NOVA will also be used as a very intense powder diffractometer since its Q-resolution is about 0.35 % at back scattering detectors. These features provide high quality diffraction pattern in absolute scale with reasonable resolution for PDF analysis as well as Rietveld refinement. Also, with the low Q data, larger scale structure and/or fluctuations will be observed. Typical measurement time is expected to be several minutes for full Q-range measurement. Based on these features of NOVA, studies of hydrogen storage mechanism will be intensively focused. In-situ measurements of hydrogen absorbing/desorbing process are planned to understand local structural changes in hydrogen storage materials. NOVA started its commissioning in the end of May 2009. Since then, measurements of diamond powder, silica glass and so on were made and static structure factors, S(Q), were obtained in absolute values successfully. In this talk, the performance expected from these commissioning will be presented. Concepts and ideas for structural studies of hydrogen storage materials will be also presented such as detector arrangements and an inelastic measurement option. This research is supported by NEDO (New Energy and Industrial Technology Department Organization) under "Advanced Fundamental Research Project on Hydrogen Storage Materials"
11:45 AM - W3.7
Structure and Hydrogen Storage Properties of Lithium Amidoborane-Ammonia Borane Complex.
Guotao Wu 1 , Chengzhang Wu 1 , Ping Chen 1
1 , Dalian Institute of Chemical Physics, Dalian, Liaoning, China
Show AbstractThe crystal structure of Lithium Amidoborane-Ammonia Borane complex(LiABAB)was then solved using the combined direct space simulated annealing method and first-principles calculations. LiABAB is of the monoclinic structure (space group P21/c)with lattice constants a = 7.0536(9)Å, b = 14.8127(20)Å, c = 5.1315(7)Å, beta= 97.491(5)°. LiABAB can released 2 equiv. H2 below 100 °C. Additional 3 equiv. H2 can be released if the temperature further increases to 228 °C.The dehydrogenation of LiABAB leaded to the formation of BN, Li3BN2 and LiBH4.
12:00 PM - **W3.8
Energy Materials Research Using Neutron Scattering: An Australian Perspective.
Robert Robinson 1
1 Bragg Institute, Australian Nuclear Science & Technology Organisation, Menai, New South Wales, Australia
Show AbstractIn 2006, two major new research facilities started up in Australia: the Australian Synchrotron (a third-generation 3-GeV machine) and the OPAL Research Reactor (a 20-MW medium-flux reactor). Approximately ten beam lines are now operating, or are under construction, at each facility, with energy materials a focus at both. In my talk, I will focus on the work performed at the OPAL reactor, on a range of energy materials including: hydrogen storage, clathrates, batteries and materials for nuclear power applications.
12:30 PM - W3.9
Ex-situ and in-situ Neutron Radiography Investigations of the Hydrogen Uptake of Nuclear Fuel Cladding Materials During Steam Oxidation at 1000°C and Above.
Mirco Grosse 1 , Eberhard Lehmann 2
1 Institute for Material Research, Karlsruhe Institute of Technology, Karlsruhe Germany, 2 Department of Spallation Neutron Source, Paul Scherrer Institute , Villigen Switzerland
Show AbstractThe most important accident management measure to terminate a severe accident transient in a Light Water Reactor (LWR) is the injection of water to cool down the uncovered degraded core. The combination of hot fuel rods and steam results in a strong exothermic oxidation reaction connected with a sharp increase in temperature, hydrogen production and fission product release. Free protons (hydrogen) are produced in the steam oxidation reaction. They can recombine to H2 gas and be released or they can diffuse through the growing oxide layer and be absorbed by the β-Zr phase. Whereas the released hydrogen gives the risk of a hydrogen detonation in the reactor environment, the absorbed hydrogen results in a shift of the time scale of the hydrogen release and in a reduction of toughness. The results of neutron radiography investigations will be presented in this paper. At first, the method will be introduced and the calibration of the method is described. A linear dependence of the total macroscopic neutron cross section in respect to the hydrogen to zirconium atomic ratio was found, It can be explained by a theoretical interpretation. The results of ex-situ experiments at small cladding segments from separate tests and with samples withdrawn from large scale severe accident simulation tests will be given. The dependence on temperature and time will be discussed for various Zr-Sn and Zr-Nb alloys commonly applied for fuel rod claddings. For compact oxide layers at Zr-Sn alloys the hydrogen concentration reaches a maximal value after short time. Then it decreases with time according to a power of -1/4 dependence. A theoretical model describing this behaviour has been developed and is presented in the paper. A different time dependence of the hydrogen concentration was found for the Zr-Nb alloys. The oxide layer morphology has a strong influence on the. Hydrogen uptake. A crack structure is formed due to the tetragonal to monoclinic phase transformation (known as “breakaway effect”) at temperatures of around 1000°C and results in an about one order of magnitude higher hydrogen concentration in the remaining metal. The mechanism of the “hydrogen pump effect” of open cracks in the oxide will be explained.A reaction furnace with a windows transparent for neutrons was constructed and commissioned in 2008. The first in-situ investigations give information about the first stage of the hydrogen uptake and about details of the processes occurring during the breakaway effect.
12:45 PM - W3.10
Regeneration of AlH3 Studied With Raman and Infrared Spectroscopy.
David Lacina 1 , Yusuf Celebi 1 , James Wegrzyn 1 , Jason Graetz 1
1 Energy Sciences and Technology, Brookhaven National Lab, Upton, New York, United States
Show AbstractAluminum hydride compounds are known to exhibit a 10% by weight hydrogen storage capacity that makes them suited for technologies that require hydrogen as a fuel, such as PEM fuel cells. The current challenge associated with this material is how to regenerate the hydride from the spent fuel and H2 gas. We employ a two-step process to regenerate the hydride compound which first requires the formation of a stable aluminum hydride adduct using a tertiary amine. This is followed by a second step consisting of adduct separation and hydride recovery.The alane amines that are formed by this two-step process tend to decompose at high temperature (> 150°C), where the AlH3 is unstable and favors decomposition into aluminum and H2 gas. An additional step involving transamination is required to create a less stable adduct that is easier to separate. For this purpose, triethylamine (TEA) was used to replace the amine in the alane amine adduct to form a less stable adduct that can be separated into AlH3 and TEA by heating to 75°C under a nitrogen sweep (J. H. Murib et al., U.S. patent 3,642,853, 1972.). The conceptual regeneration procedure for AlH3 is shown below:Al* + NR3 + 3/2H2 → AlH3-NR3 + TEA → AlH3-TEA + NR3↑ → AlH3 + TEA↑ The first step in the regeneration of AlH3 involves the formation of an alane amine (AlH3-NR3) from spent fuel. We present results which show that adducts of AlH3 can be formed by hydrogenation of catalyzed aluminum, by adding 2 mol% titanium, in a liquid solvent at low pressures using one of several different tertiary amines. An important part of developing and understanding new materials requires some structural knowledge. Raman and infrared spectroscopy was performed on the products of these reactions to better understand the structure of the alane amines that are formed, as well as the reactions that take place during hydrogenation. Many of the alane amines created in the regeneration process can be formed as either solids, with poorly known structures, or alane containing liquids depending upon the tertiary amine, solvent, and formation conditions employed. A vibrational analysis of the regeneration products performed with Raman and infrared spectroscopy is presented and will help clarify the molecular and vibrational structures of these alane amine adducts.
W4: H2 Storage and Hydrogen in Solids II
Session Chairs
Wednesday PM, April 07, 2010
Room 3004 (Moscone West)
2:30 PM - W4.1
Nanostructured Metal Hydrides for Hydrogen Storage Studied by in situ Synchrotron and Neutron Diffraction.
Volodymyr Yartys 1 2 , Roman Denys 1 , Jan Petter Maehlen 1 , Colin Webb 3 , Evan Gray 3 , Tomas Blach 3 , Andrey Poletaev 1 2 , Jan Ketil Solberg 2 , Olivier Isnard 4
1 , IFE, Kjeller Norway, 2 , NTNU, Trondheim Norway, 3 , Griffith University, Brisbane, Queensland, Australia, 4 , CNRS, Grenoble France
Show AbstractRecent R&D on hydrogen storage have resulted in a new method, “hybrid” H storage, yielding improved by up to 50 % overall H storage system efficiency. In this work we have focused on metal hydrogen systems where one can significantly increase hydrogen storage capacity of the MH on application of high H2 pressures. H storage capacities of the MH suitable for such systems are highly pressure-dependent, when pressures increase to a few hundred bar. High equilibrium hydrogen pressures result in low hydrogenation enthalpies, assisting in achieving high rates of heat exchange during the H loading. Kinetics and mechanism of the phase-structural transformations were studied at the D1B, ILL by in situ PND studies of metal-hydrogen interaction at D2 pressures reaching 1000 bar. High pressures, were generated by use of multistage, heat-based deuterium intensifier. The systems studied included Al-modified Laves-type C15 ZrFe2-xAlx intermetallics with x = 0.02; 0.04 and 0.20. SR XRD measurements showed that Al substitution for Fe leads to a slight expansion of the unit cells. Deuteration showed a very fast kinetics of H/D exchange and resulted in increase of the unit cells volumes reaching 23.5 % for ZrFe1.98 Al0.02D2.9(1). D content, hystheresis of H uptake and release, unit cell expansion and stability of the hydrides systematically change with Al content. D atoms exclusively occupy the Zr2Fe2 tetrahedra. Observed interatomic distances, Zr-D = 2.01-2.07; (Fe,Al)-D=1.75 Å, do not ruled out a possibility of occupancy of the Al-substituted sites. Magnetic moments of Fe slightly increase from the alloy (RT; 1.9 mB) to the corresponding deuteride (RT; 2.2 mB).A different, complementary approach to the development of H storage systems is based on the hydrides of light elements, first of all the Mg-based ones. Time resolved in situ synchrotron X-ray diffraction (SR XRD; 20-400°C; 0-50 bar H2) studied were performed at the SNBL, ESRF. Reactive ball milling in hydrogen (HRBM) allowed synthesis of the nanostructured hydrides of: (a) Mg metal; (b) eutectic alloy Mg8Mm20Ni; Mg+Mg2Ni+MmMg12; (c) LaMg12; (d) Mg-C; (e) Mg-V and Mg-V-C. The experimental parameters (PH2, T, energy of milling, ball / sample ratio and balls size), significantly influence rate of hydrogenation. The studies confirmed (a) a completeness of hydrogenation of Mg into MgH2; (b) indicated a partial transformation of the originally formed beta-MgH2 into a metastable gamma-MgH2 (a ratio beta/gamma was 3/1); (c) yielded the crystallite size for the main hydrogenation product, beta-MgH2, as close to 10 nm. The materials containing hydride-forming additives (Mg8Mm20Ni and V-containing composites) showed decreased temperatures of hydrogen vacuum desorption and fast subsequent rates of rehydrogenation. Influence of the additives to Mg on the structure and hydrogen absorption / desorption properties and cycle behaviour of the composites will be discussed.
2:45 PM - W4.2
Magnetic State in Iron Hydride Under Pressure Studied by X-ray Magnetic Circular Dichroism at the Fe K-edge.
Naoki Ishimatsu 1 , Yasuharu Matsushima 1 , Hiroshi Maruyama 1 , Takao Tsumuraya 2 , Tamio Oguchi 2 , Kenichi Takemura 3 , Takahiro Matsuoka 4 , Masaichiro Mizumaki 4 , Naomi Kawamura 4
1 , Grad. Sch. of Sci, Hiroshima Univ., Higashi-Hiroshima Japan, 2 , ADSM, Hiroshima Univ., Higashi-Hiroshima Japan, 3 , NIMS, Tsukuba Japan, 4 , JASRI/SPring-8,, Kouto, Sayo Japan
Show AbstractSince the discovery of iron hydride (FeH) [1,2], the effects of hydrogenation on crystal structure and magnetic property in FeH have attracted great interest. FeH can be synthesized by a reaction of Fe metal with hydrogen fluid under 3.5 GPa. Hydrogenation gives rise to a structural transition from bcc-Fe to double-hcp (dhcp) FeH accompanied with a large lattice expansion [3]. Furthermore, FeH is a ferromagnet [2], so that the transition markedly contrasts with the ferromagnetic bcc-Fe→nonmagnetic hcp-Fe transition appearing at 14 GPa by use of a standard pressure transition medium. To understand the stability of ferromagnetic state in FeH, modification in the electronic structure due to the hydrogenation is an important issue. Here we report pressure dependence of the magnetic state in FeH up to 27 GPa, which was determined by X-ray magnetic circular dichroism (XMCD) at the Fe K-edge. In this study, hydrogen effect on the magnetic state was also investigated. XMCD is a spectroscopic technique using the synchrotron radiation, which provides the element-selective and orbital-specific information about ferromagnetic sample. The XMCD experiments were carried out using the helicity-modulation method on the beamline 39XU at SPring-8. A tiny foil of Fe was loaded into a diamond-anvil cell together with hydrogen fluids. The measurement was done at room temperature.In the pressure range of 3.3 GP〈P〈3.8 GPa, a drastic change in the XMCD spectrum was observed, so that the transition from bcc-Fe to dhcp-FeH occurs within the narrow pressure range. The residual XMCD signal observed at P≥3.8 GPa indicates that FeH remains ferromagnetic state. The XMCD profile of FeH is characterized by a large negative peak near the absorption edge, and it is clearly different from a dispersion-type profile of bcc-Fe. The observed change in XMCD is related to the hydrogen effect on the electronic structure. The XMCD profile for FeH is probably ascribed to the 3d electronic state classified as strong ferromagnetism. On the other hand, the 3d electronic state in bcc-Fe is classified as weak ferromagnetism. When the pressure increases more up to 27 GPa, the integrated intensity is gradually reduced to about 1/5 of that at 3.8 GPa. Critical pressure Pc, where the ferromagnetic state disappears, is estimated to be Pc~29.5 GPa by extrapolation from the pressure variation. Therefore, the ferromagnetic state in FeH is more stable under pressure than that in pure Fe. It is successfully demonstrated that the hydrogenation induces the strong influence on the electronic- and magnetic states in FeH. [1] V.E. Antonov et al., Sov. Phys. Dokl. 25, 490 (1980)[2] V.E. Antonov, J. Alloys Compd., 330-332, 110 (2002)[3] J.V. Badding et al., Science, 253 421 (1991)
3:00 PM - W4.3
Kinetics Study of Methane Hydrates in Dynamic-DAC.
Jing-Yin Chen 1 , Choong-Shik Yoo 1
1 , Institute for Shock Physics and Department of Chemistry, Washington State University, Pullman, Washington, United States
Show AbstractUnderstanding the high-pressure kinetics associated with the formation of methane hydrates is critical to the practical use of the most abundant nature energy resource. In this study, we have studied, for the first time, the kinetics of the formation and phase transitions of methane hydrates under high pressures over a large range of compression rates and pressures, using dynamic-Diamond Anvil Cell (d-DAC) coupled with a high-speed camera and a confocal micro-Raman spectroscopy. At slow compression rates (< 0.1 GPa/s) and below ~1.0 GPa, methane hydrates are formed by forming water clathrates and concurrently capturing methane gas molecules. On the other hand, at high compression rates (>1 GPa/s) and beyond 1 GPa, water molecules solidify, instead, because of a relatively slow rate of hydrate formation and a fast solidification of water. We observed a large pressure hysteresis in both the formation and the decomposition processes of methane hydrates, which likely arises from high (meta) stability of methane hydrates.Below 10 GPa, methane hydrates exist in three polymorphs, sI, sII, and sH, with characteristic Raman spectra and visual appearance. The sI and sII phases of methane hydrates have similar crystalline textures and optical transparencies, yet the sH phase has a substantially darker “dirty-look” texture. We have examined the dynamics of the sI-sII transition over the compression rates of 0.0008-0.1 GPa/s and pressures of 0.6-1.5 GPa and of the sII-sH transition over the compression rates 0.002-0.9 GPa/s and pressures of 1.8-2.4 GPa. The results indicate a similar dynamics governing the forward and backward transitions between sI and sII phases, but very different ones between sII and sH phase transitions. That is, the sII-to-sH transition occurs substantially faster than the reverse process. In this talk, we will discuss about chemical mechanisms of the formation and phase transitions of methane hydrates, following a brief description of dynamic-DAC.
3:15 PM - W4.4
Ammonia Borane and a New Ammonia Borane-hydrogen Compound at High Pressure.
Yu Lin 1 , Vadym Drozd 2 , Jiuhua Chen 2 , Luke Daemen 3 , Ho-kwang Mao 4 , Wendy Mao 1 5
1 Geological and Environmental Sciences, Stanford University, Stanford, California, United States, 2 , Mechanical and Materials Engineering, Florida International University, Miami, Florida, United States, 3 , Los Alamos Neutron Science Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 4 , Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, United States, 5 , Photon Science, SLAC National Accelerator Laboratory, Menlo Park, California, United States
Show AbstractAmmonia borane (AB), NH3BH3, is a novel hydrogen storage material with its high gravimetric and volumetric hydrogen density compared to other candidates. High pressure studies can improve our understanding of structural relationships in hydrogen storage materials and provide guidance for designing improved storage materials. We investigated the effect of pressure on the bonding in AB using Raman spectroscopy up to 22.3 GPa in a diamond anvil cell. Two new transitions were observed at approximately 5 and 12 GPa. Vibrational frequencies for the modes of the NH3 proton donor group exhibited negative pressure dependence, which is consistent with the behavior of conventional hydrogen bonds, while the vibrational frequencies of the BH3 proton acceptor group showed positive pressure dependence. The observed behavior of these stretching modes supports the presence of dihydrogen bonding at high pressure. The observation that BH3 and NH3 bending modes showed an increase in spectral complexity with increasing pressure together with a discontinuity in dν/dP also suggests rotational disorder in this molecule. We also studied AB in the presence of excess hydrogen (H2) pressure and discovered a novel solid phase, AB(H2)x, where x ~ 1.3 - 2. The new AB-H2 compound can store an estimated 8 - 12 wt% molecular H2 in addition to the chemically bonded H2 in AB. This phase formed slowly at 6.2 GPa, but the reaction rate could be enhanced by crushing the AB sample to increase its contact area with H2. X-ray diffraction of the new phase indicates that it has a different crystal structure from pure AB at the equivalent pressure. The compound has two Raman H2 vibron peaks from the absorbed H2 in the new phase: one at frequency 70 cm-1 below the free H2 vibron, and the other at higher frequency overlapping with the free H2 vibron at 6 GPa and becoming visible above 8.8 GPa. The splitting of the N-H and B-H stretching modes, as well as the distinct H2 vibrons suggest a strong molecular bonding between AB and H2, and the structural complexity of this new compound. Storage of significant amounts of additional molecular H2 in AB increases the already high hydrogen content of AB. The complex reaction kinetics, bonding variations, and slow reaction rate give hope for designing alternative chemical paths to synthesize and retain the new compound for practical hydrogen storage application.
3:30 PM - W4:Hydrogen II
BREAK
W5: PEM Fuel Cells and Electrocatalysis
Session Chairs
Wednesday PM, April 07, 2010
Room 3004 (Moscone West)
4:00 PM - **W5.1
Neutron Imaging Methods for the Investigation of Energy Related Materials (Fuel Cells, Battery, Hydrogen Storage and Nuclear Fuel).
Eberhard Lehmann 1 , Pierre Boillat 1
1 NUM, Paul Scherrer Institut, Villigen Switzerland
Show AbstractNovel approaches will play an important role in the world-wide energy supply and consumption. Among the favorite concepts for mobility and local electricity production the electro-chemistry concepts of fuel cells and of improved batteries will raise importance. In this context, also the storage of hydrogen as an energy carrier will get a higher level of consideration. Although some of the mentioned devices and techniques are already in use, the improvement of their performance and reliability is an important issue to introduce them on economic level in competition to other concepts. This talk is focused on the non-invasive investigation of components and materials for fuel cells, batteries and potential hydrogen storage devices. The applied method is neutron imaging which is developed and practiced on high performance level at Paul Scherrer Institute, Switzerland, at the spallation neutron source SINQ. Neutron imaging can provide structural information of samples and systems in two dimensions (radiography) and three dimensions (tomography) and is able to study time-dependent phenomena in a quasi-real time regime. It is the advantage of neutron imaging methods to enable a high contrast to light elements like hydrogen and lithium while the transmission of structural materials like Al, C or even steel is given for thick layers. Therefore, it is an ultimate approach to investigate Polymer Electrolyte Membrane Fuel Cells (PEM-FC) in respect to its water distribution in the membrane region. Different membrane materials are under investigation and the performance is tested under realistic operational conditions while the water distribution is observed.In the case of battery research two major questions are of importance: how the gas production is related to loading/discharging cycles; is there a migration of ions visible during battery operation. Studies in this respect have just started. Different material combinations will be under evaluation. The storage of hydrogen will become more importance when fuel cells and other hydrogen related energy processes will be introduced on broad scale. Not only the gas storage under pressure or low temperature is than an option but the bonding on metals and other chemicals which deliver hydrogen on demand. Materials like zirconium have a high affinity to hydrogen and might be used as storage devices. With the help of neutron imaging methods it is relatively easy to determine the hydrogen uptake and loss under realistic conditions in assemblies of different size. The talk will describe the methods principle, show the layout of the used facilities and gives examples of latest investigations.
4:30 PM - W5.2
Origin of Enhanced Oxygen Reduction Activity on Dealloyed PtCu3 Thin Films.
Ruizhi Yang 1 , Mike Toney 1
1 , Stanford University, Menlo Park, California, United States
Show AbstractThe oxygen reduction activity of the electrochemically dealloyed PtCu3 thin film was studied in 0.1 M HClO4 using a rotating disk electrode (RDE) method. The dealloyed sample showed a ~2.4 fold gain in the specific activity over pure Pt thin film sample. A thick Pt enriched surface layer and Cu depleted interior (bulk ratio of alloying components is different from PtCu3) were shown to be formed in the dealloyed PtCu3 film by synchrotron-based anomalous X-ray diffraction (AXRD). The lattice constant of Pt enriched surface layer is smaller than that of pure Pt and thus induce the compressive lattice strain in the thick surface layer, which is shown to dominate the enhanced catalytic activity of the dealloyed Pt-Cu thin film.
4:45 PM - W5.3
Surface Structure and Electrochemistry of Model Electrocatalysts.
Alexander Brownrigg 1 , Christopher Lucas 1 , Paul Thompson 1 , Michael Cormack 1 , Michael Darlington 1 , Voja Stamenkovic 2 , Dusan Strmcnik 2 , Nenad Markovic 2
1 Oliver Lodge Laboratory, University of Liverpool, Liverpool United Kingdom, 2 Material Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractSince the early days of modern surface science, the main goal in the electrochemical community has been to find correlations between the microscopic structures formed by surface atoms and adsorbates and the macroscopic kinetic rates of a particular electrochemical reaction. The establishment of such relationships, previously only developed for catalysts under ultrahigh vacuum (UHV) conditions, has been broadened to embrace electrochemical interfaces. In early work, determination of the surface structures in an electrochemical environment was derived from ex situ UHV analysis of emersed surfaces. The application of in situ surface sensitive probes, most notably synchrotron based surface x-ray scattering (SXS) and scanning tunneling microscopy (STM) has overcome the “emersion gap” and provided information on potential-dependent surface structures at a level of sophistication that is on a par with (or, even, in advance of) that obtained for surfaces in UHV. In this talk we will describe the application of the synchrotron SXS technique for exploring surface atomic structure in an electrochemical environment in order to understand processes relevant to the development of new materials for energy applications [1]. The focus will not just be on the determination of the atomic structure at the electrochemical interface but will also describe the use of SXS in potentiodynamic measurements where the aim is to correlate, directly, the electrochemical reactivity with atomic-scale structural changes at the electrode surface. Results will be presented for both extended low-index single crystal surfaces and stepped electrode surfaces. The stepped surfaces enable a correlation between reactions on flat terraces to those occurring at well-defined steps. Measurements of various potential-dependent reactions, for example, the oxidation of carbon monoxide and the oxygen reduction reaction (ORR) will be discussed.
5:00 PM - **W5.4
Chemical Mapping of Fuel Cell Membrane Electrode Assemblies by Soft X-ray Spectromicroscopy.
Adam Hitchcock 1 , Dmitri Bessarabov 2
1 BIMR, McMaster University, Hamilton, Ontario, Canada, 2 , Automotive fuel Cell Cooperation, Burnaby, British Columbia, Canada
Show AbstractSoft X-ray scanning transmission X-ray microscopy (STXM) is a synchrotron based technique which provides speciation through near-edge X-ray absorption spectroscopy, and quantitative chemical and orientation mapping at 30 nm spatial resolution [1]. It was applied at the C 1s, N 1s, O 1s, Co 2p and F 1s edges to the membrane electrode assemblies (MEAs) of hydrogen-based polymer electrolyte membrane (PEM) fuel cell before and after being subjected to a specific drive cycle simulating the operation of a fuel cell vehicle (FCV). The catalyst coated membranes (CCMs) were extracted from the MEAs and 100 or 300 nm thick microscopy samples of CCM cross-sections were prepared at various positions along the CCM using embedding and ultramicrotomy. Post-mortem studies of CCM samples were carried out to determine the degree of Pt dissolution in the membrane. STXM results were complemented by SEM and TEM imaging and X-ray fluorescence analysis (EDX). All STXM measurements were made at beamline 5.3.2 of the Advanced Light Source (Berkeley, CA).This study provided information on: (1) morphology and chemistry of platinum particles in the membrane, (2) chemical differences between the beginning-of- life (BOL) and end-of-life (EOL) samples, (3) evaluating STXM versus EDX in TEM and SEM as a probe of the distribution of Co across the CCM, (4) porosity of the CCM.It was demonstrated that STXM is a useful technique for studies of MEA components of a fuel cell. STXM can map Co in the cathode and membrane to low levels (~100 ppm). Detailed, spatially resolved spectroscopy at multiple core level edges gave insights into the chemical changes that occur in association with component degradation of fuel cells through automotive operation. Several different approaches to mapping porosity were explored.Research funded by AFCC and NSERC.[1] H. Ade and A.P. Hitchcock, Polymer 49 (2008) 643
5:30 PM - W5.5
Activation of O2 by Gold Nanoparticles? In situ Ambient-pressure X-ray Photoelectron Spectroscopy Study.
Peng Jiang 1 , Soeren Porsgaard 2 , Ferenc Borondics 3 , Mariana Koeber 1 , Alfonso Caballero 1 , Hendrik Bluhm 3 , Flemming Besenbacher 2 , Miquel Salmeron 1
1 Materials Sciences Division, Lawrence Berkeley National Lab, Berkeley, California, United States, 2 Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Aarhus Denmark, 3 Chemical Sciences Division, Lawrence Berkeley National Lab, Berkeley, California, United States
Show AbstractThe interaction of O2 with gold foil and gold nanoparticles grown by vapor deposition on TiO2(110) was studied by in situ ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). No spontaneous dissociation of O2 was observed either on Au foil or on Au nanoparticles up to one atmosphere of O2. X-ray irradiation, however, is very effective in promoting gold oxidation on both surfaces in the presence of O2. These results help reconcile recent conflicting experimental observations regarding the activation of molecular oxygen on Au nanoparticles, which is at the core of their catalytic performance in oxidation reactions.
5:45 PM - W5.6
In-situ Investigations of Pt DENs Using EXAFS During CO Stripping and Oxygen Reduction.
Michael Weir 1 , Sue Myers 1 , Richard Crooks 1 , Anatoly Frenkel 2
1 Chemistry & Biochemistry, Univ. of Texas @ Austin, Austin, Texas, United States, 2 , Yeshiva University, New York, New York, United States
Show AbstractWe have recently used extended x-ray absorbance-fine structure (EXAFS) as a tool to probe the in-situ behavior of small (< 3nm) Pt nanoparticles. The ability to transition from ex-situ to in-situ characterization methods is particularly important for these small particles because such a large portion of their component atoms are on the surface (> 50%). Therefore, they are more sensitive to surface induced structural changes. We have designed a cell which allows us to perform traditional 3-electrode electrochemistry and still measure the nanoparticles using EXAFS. These measurements allow us to correlate previous electrochemical results with ex-situ characterization. So far, we have investigated the behavior of Pt dendrimer-encapsulated nanoparticles (DENs) during CO stripping and the oxygen reduction reaction (ORR).The dendrimer-encapsulation technique is a templating method that allows synthesis of mono- and bi- metallic nanoparticles on the 1-2 nm scale (40-240 atoms). The size of these nanoparticles, particularly with the protective dendrimer, reduces the availability of analytical techniques. EXAFS is well-suited for our system, as the x-rays are unaffected by the dendrimer. Also, the coordination numbers obtained from a first-shell fitting analysis can be used to determine particle diameter in this size regime.The CO stripping process involves the electrochemically induced adsorption and removal of a single monolayer of CO onto a Pt surface. The amount of current passed during the removal is used to determine the electrochemically active surface area of the Pt. Because CO is a strongly binding ligand, and known to anneal and/or agglomerate larger particles, we have been concerned that the CO stripping process would cause changes in the size and structure of the DENs, invalidating any comparison between previous characterization work and the electrochemical data. Accordingly, we have used EXAFS to probe the structure of these Pt DENs during the CO stripping process. The reducing potential used to adsorb the CO layer is shown to further reduce the Pt nanoparticles, while the CO has no significant effect on the state of these particles. That is, the dendrimer is able to prevent agglomeration of our Pt nanoparticles during the CO stripping process.The oxygen reduction reaction is another electrochemical reaction which we have previously studied ex-situ. Here we expect to answer the questions of whether the Pt DENs change over the time needed to measure their catalytic ability and whether any transformation is potential dependent. Initial results indicate an irreversible change under catalytic conditions. Regardless of the final conclusions, we have demonstrated the ability to detect structural changes in Pt DENs during electrochemical reactions.
W6: Poster Session
Session Chairs
Thursday AM, April 08, 2010
Salon Level (Marriott)
9:00 PM - W6.1
In situ XRD Investigation of Tin Oxide/Multiwalled Carbon Nanotubes Composite Anode for Li-ion Battery.
Abirami Dhanabalan 1 , Kevin Bechtold 1 , Chunlei Wang 1
1 MME, Florida International University, Miami, Florida, United States
Show AbstractAmorphous tin composite oxide (ATCO) has gained much attraction due to their high theoretical capacity compared to the commonly used graphite anodes. In this work, porous tin oxide/ multiwalled carbon nanotubes (MWCNTs) has been suggested to reduce the drawbacks such as the stress associated with huge volume change during Li-ion insertion / desertion and poor conductivity of tin oxide based electrodes. The samples were prepared using Electrostatic Spray Deposition technique (ESD). Currently the mechanism of operation of these anodes at the micro structural level is not yet fully understood. In order to investigate the correlation between the micro structural changes and electrochemical property, in situ X-ray Diffraction was used. As prepared tin oxide / MWCNTs was used as the anode in 1M lithium bis(perfluoroethylsulfonyl)imide in ethylene carbonate and diethyl carbonate (EC-DEC, 1:1 v/v) electrolyte versus Lithium (counter and reference electrode) in a specially designed test cell. In situ XRD measurements were carried out using XRD D-5000 with Cu-Kα radiation. The sequence of Li-ion insertion mechanism and the micro structural changes were studied during the charge-discharge cycle. The results were compared with pure tin oxide and pure CNT electrodes prepared using the same method.
9:00 PM - W6.10
Real-time and Direct Observation of Hydrogen Absorption Dynamics for Pd Nanoparticles.
Daiju Matsumura 1 , Yuka Okajima 1 , Yasuo Nishihata 1 , Jun'ichiro Mizuki 1
1 , Japan Atomic Energy Agency, Hyogo Japan
Show AbstractPalladium is known to show high performance for the hydrogen storage because of the small activation barrier for the surface adsorption and the exothermal reaction for the inner absorption. Although it has been established that the H atoms are absorbed into the octahedral vacancies of Pd fcc lattice, the dynamic mechanisms of the hydrogen storage process which consists of the surface adsorption and following inner absorption have not been well understood yet, especially for the case of Pd metal fine particles which sometimes show unique properties of the gas-solid interaction.Pd metal fine particles show the different interaction with hydrogen from the bulk Pd. There is a significant phase boundary between the low-concentrate phase (interstitial phase) and the high-concentrate phase (hydride phase) as for the bulk Pd. On the other hand, the Pd metal fine particles show smooth change between interstitial and hydride phases.In order to understand the size effect of the Pd particles concerning the dynamical hydrogen storage process including surface adsorption and inner absorption, we have observed the Pd K-edge x-ray absorption fine structure (XAFS) spectra with dispersive optics from the viewpoint of the dynamical change of atomic and electronic structures during reaction between Pd particles and H2 gases.XAFS spectra were observed at BL14B1 of SPring-8 by dispersive mode. Laue configuration with Si(422) reflection plane was adopted for bend crystal polychromator. The transmitted x rays were observed by CCD camera (640 x 480, 12 bits) with Gd2O2S(Tb) phosphor. The local structural transformation of Pd nanoparticles on Al2O3 during H2 dosing was investigated at 273-373 K by 50-200 Hz rate (each 20-5 ms) with the real-time-resolved mode. No data accumulation by the repetition of the reaction was operated. Although XAFS technique does not indicate the contribution of the electron scattering from light H atoms, absorbed H atoms in the Pd lattice elongate the interatomic distance of Pd-Pd bondings. Therefore, we can observe the atomic structure dynamics of Pd nanoparitcles even at the high frame rate.Under the hydrogen atmosphere, Pd particles showed large expansion of the Pd-Pd interatomic distance from 2.73 to 2.83 A. The expansion of the Pd particles was completed during only 10 ms under the H2 pressure of 700 kPa. It was revealed that Pd lattice is directly changed to the hydride phase in short time. We did not observe any intermediate state between bare Pd particles and hydride phase. In the pressure dependent study, the Pd-Pd interatomic distance is elongated as the hydrogen pressure increases from 10 to 700 kPa, which indicates that wide range of the hydrogen pressure creates different H-include Pd particles. This is the first direct observation of lattice expansion of the Pd nanoparticle under the several pressures of H2 gases with the high frame rate of over 100 Hz.
9:00 PM - W6.11
Cobalt Chemical State Determination in LiCoO2 Cathode Material Using X-ray Photoelectron Spectroscopy (XPS).
Tae Kyong John Kim 1 , Jonggeol Kim 1
1 , LG Chem, Daejeon Korea (the Republic of)
Show AbstractLiCoO2 is a widely used cathode material for Li-ion batteries. Much attention has been devoted to studying the bulk properties of the compound as such properties indubitably play an important role in determining the battery performance. However, to attain a complete understanding of LiCoO2 and its effect on battery performance, it is essential to have a solid grasp of LiCoO2 surface chemistry. Studying the surface chemistry would entail investigation of the changes in Co chemical state with the changes in battery operating conditions. X-ray Photoelectron Spectroscopy (XPS) is a technique that nicely meets such a need where the probe depth of 10 nm ensures that the surface region is analyzed. A methodology for Co chemical state characterization using XPS is presented noting the difficulties that arise when differentiating the different chemical states of Co. As well, precautions that must be heeded for the characterization process will also be addressed. A brief example will be shown where the methodology has been applied for a cathode that has undergone a typical battery cycling process.
9:00 PM - W6.12
Photoemission Study of Au-Schottky Barrier Formation on GaYbN Using Synchrotron Radiation.
Stephen McHale 1 , John McClory 1 , James Petrosky 1 , Peter Dowben 2 , Yaroslav Losovyj 3 2
1 Engineering Physics, Air Force Institute of Technology, Wright Patterson AFB, Ohio, United States, 2 Physics and Astronomy, University of Nebraska, Lincoln, Nebraska, United States, 3 Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana, United States
Show AbstractAu-GaYbN Schottky barrier formation is observed using Au evaporation on multiple concentrations of GaxYb1-xN thin films deposited on (111) Si substrates. Low Energy Electron Diffraction was performed to verify the integrity of the Au deposition. Energy dependent, synchrotron generated photoemission spectroscopy ranging from 15 to 26 eV under UHV conditions clearly determines a valence band shift of up to 0.5 eV.Semiconductor devices require contacts to make interconnections. In order to reduce resistance and to aid in exterior bonding, these contacts are most often formed from various metals. The choice of metals is largely dependent upon the metal-semiconductor interface structure and the carrier energy. The workfunction difference between the metal and semiconductor presents a potential barrier that forms a barrier to carrier flow, known as the Schottky barrier. Thus, to build better devices, it is vital to fully understand effects of material interfaces. The formation of the Schottky barrier in wide band gap materials has piqued researchers’ interest to optimize carrier efficiencies. The wide band gap of GaN, of about 3.5 eV, makes GaN devices an attractive option to meet highpower and high speed applications, to include high speed communication platforms or fast sensing systems. In this paper, we report experimental results for Au overlayers on several concentrations of the alloy GaxYb1−xN.Two spectroscopic techniques, UV photoemission spectroscopy (UPS) and Low Energy ElectronDiffraction (LEED), were used to explore the structure and carrier energy in this study. The experiment was performed at the Louisiana State University (LSU) Center for Advanced Microstructures and Devices (CAMD) using the 3m normal incidence monochromator (NIM) beamline, where res-olution is possible below 10 meV. All surfaces were prepared in a stainless-steel preparation chamber with base pressures ≈ 10−10 torr. Au deposition was made by exposing the sample to a stream of Au atoms emerging from an evaporator consisting of an Au bead suspended in a coil of W wire. The coverage in monolayers, where one monolayer is defined to be one Au atom per surface atom, was deposited at a rate of 4.0 ± 1.0 monolayer/hour. The deposition rate was monitored byLEED diffraction pattern identification, where prior research at the same facility provided a bench-mark for comparison. Reference spectra were taken from Au evaporated onto a Mo substrate, which was attached to the same mounting plate as our semiconductor sample, and the mounting plate was grounded to the analyzer. After accounting for surface charging effects common to insulators, the valence bandshifts towards the Fermi edge, as expected. Analyses of UPS spectra for GaYbN with different Au coverages, taken at multiple energies within 15 to 26 eV under UHV conditions yielded a GaYbN valence band shift of up to 0.5 eV. This band bending represents an equivalent Schottky barrier formation.
9:00 PM - W6.2
Study of the Electronic Structure of AlH3 Using Soft X-ray Emission and Absorption Spectroscopy.
Yukiharu Takeda 1 , Tetsuo Okane 1 , Shin-ichi Fujimori 1 , Akira Yasui 1 , Yuji Saitoh 1 , Hiroshi Yamagami 1 2 , Hiroyuki Saitoh 1 , Akihiko Machida 1 , Katsutoshi Aoki 1 , Takayuki Muro 3 , Yukako Kato 3 , Toyohiko Kinoshita 3
1 Synchrotron Radiation Research Center, Japan Atomic Energy Agency, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 Japan, 2 Department of Physics, Kyoto Sangyo University, Motoyama,Kamigamo,Kita-Ku,Kyoto 603-8555 Japan, 3 , Japan Synchrotron Radiation Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 Japan
Show AbstractAluminum hydride AlH3 qualifies as a candidate for a hydrogen storage material because of its large gravimetric and volumetric hydrogen contents. In order to understand the mechanism of the hydrogenation-dehydrogenation of AlH3, it is very important to grasp the electronic structure. Theoretical researches of AlH3 have been performed extensively so far. However, there is no experimental report on the electronic structure of AlH3. In the present study, we have performed synchrotron-radiation-excited soft x-ray emission spectroscopy (XES) and x-ray absorption spectroscopy (XAS) experiments and revealed the electronic structure of α-AlH3 synthesized under high pressures. The Al 3p partial density of states (PDOS) of the valence and conduction bands can be observed by the XES and XAS at the Al 1s edge, respectively. In order to investigate the change in the electronic structure accompanied with hydrogenation, we have also measured Al metal. From the comparison between AlH3 and Al metal, we have found clear differences in the Al 3p PDOS. In addition, we will discuss the electronic structure in comparison with the theoretical PDOS obtained by band-structure calculation in the local-density approximation.
9:00 PM - W6.3
Electronic Structure of La(Fe0.88Si0.12)13.
Nozomu Kamakura 1 , Tetsuo Okane 1 , Yukiharu Takeda 1 , Shin-ichi Fujimori 1 , Yuji Saitoh 1 , Hiroshi Yamagami 1 2 , Atsushi Fujimori 1 3 , Asaya Fujita 4 , Shun Fujieda 5 , Kazuaki Fukamichi 5
1 Synchrotron Radiation Research Center, Japan Atomic Energy Agency, Hyogo Japan, 2 Department of Physics, Kyoto Sangyo University, Kyoto Japan, 3 Department of Physics, University of Tokyo, Tokyo Japan, 4 Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai Japan, 5 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan
Show AbstractLa(FexSi1-x)13 compounds show a magnetic-field-induced metamagnetic transition above the Curie temperature TC of the first order ferromagnetic-paramagnetic transition in the concentration range 0.86 ≤ x ≤ 0.90. In the metamagnetic and ferromagnetic transitions of the La(FexSi1-x)13 compounds, the onset of the magnetic moment brings about significant volume expansion. La(FexSi1-x)13 compounds are known to absorb hydrogen. Hydrogen absorption in the La(FexSi1-x)13 compounds also causes lattice expansion and modifies the magnetic properties. The lattice expansion by the hydrogen adsorption results in the increase of the Curie temperature TC up to room temperature. Thus, the magnetic transition that can be controlled around room temperature by the hydrogen absorption enables one to apply La(FexSi1-x)13 compounds to large magnetostrictive materials and magnetic refrigerant materials using magnetocaloric effect. The magnetic properties of La(FexSi1-x)13 compounds are considered to be derived by the itinerant Fe 3d electrons. In this context, the volume expansion originates from the magnetic moment induced by the exchange splitting of the 3d band. Thus, the knowledge of the electronic states is important for understanding a variety of the magnetic properties in La(FexSi1-x)13 compounds. Here, the electronic states of La(FexSi1-x)13 with x = 0.88 have been investigated by the valence-band and core-level photoemission spectroscopy using synchrotron soft x-rays. The valence-band photoemission spectrum for the ferromagnetic state of the La(Fe0.88Si0.12)13 compound shows the main peak at ~1 eV binding energy. The feature of the valence-band is consistent with the band calculation which indicates the electronic states formed by the exchange split Fe 3d band near the Fermi level. The Fe 2p core-level photoemission spectrum showing an asymmetric line shape indicates the itinerant character of the Fe 3d electrons. The Fe 3s core-level photoemission spectrum of the ferromagnetic state shows a satellite structure at ~ 4 eV higher binding energy side of the main peak. The spectral splitting in the 3s core level which is attributed to the 3s-3d exchange interaction is known to reflect the local magnetic moment. The features of the Fe core-level photoemission spectra indicate that the Fe 3d electrons are itinerant and derive the magnetic properties of the La(Fe0.88Si0.12)13 compound. The Fe 3d states associated with a variety of the magnetic properties of the La(FexSi1-x)13 compounds will be discussed.
9:00 PM - W6.4
In situ X-ray Diffraction Studies of Functional Metal-organic Framework Materials.
Gregory Halder 1 , Karena Chapman 2 , Peter Chupas 2 , John Schlueter 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 X-ray Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractThe accurate elucidation of the often complex structure-function relationships in functional porous materials, such as metal-organic frameworks (MOFs), presents a crucial step in their advancement toward becoming industrially important energy materials. This requires the development of in situ structural techniques, such as X-ray diffraction, to precisely monitor the structural response of materials under the conditions (e.g., industrially relevant temperatures, pressures, and chemical environments) in which they perform their targeted functions. These studies promise an unparalleled insight of the synergies between structure and function, including major structural changes (e.g., phase transformations) and other more elusive structural variants, such as those associated with host-guest interactions. Here, we present pressure- and temperature-dependent in situ structural studies carried out at the 1-BM beamline at the Advanced Photon Source (Argonne National Laboratory) on a range of functional MOF materials.
9:00 PM - W6.5
Structural Characterization of PdCu Oxygen Reduction Reaction Catalysts by EXAFS.
Sue Myers 1 , Richard Crooks 1 , Michael Weir 1 , Wenjie Tang 1 , Graeme Henkelman 1 , Anatoly Frenkel 2
1 Chemistry, University of Texas at Austin, Austin, Texas, United States, 2 Physics, Yeshiva University, New York, New York, United States
Show AbstractThe dendrimer templating method for nanoparticle synthesis can be used to produce very well-defined, size monodisperse particles < 2 nm in diameter. This is significant for two reasons. 1) Particles in this size regime can show interesting physical and catalytic properties. 2) The small size of the particles is accessible to first principles calculations of the nanoparticle. However, the size of the particles (40 – 250 atoms) can make characterization of these materials challenging. We have synthesized PdCu dendrimer encapsulated nanoparticles (DENs) containing an average of ~64 atoms with varying ratios of the two metals. Structural characterization of the materials by EXAFS indicates alloying of the two metals. The bimetallic material has been found to show enhanced catalytic activity for the oxygen reduction reaction (ORR) relative to the monometallic material. These results are compared to DFT calculations of PdCu model systems of a comparable size.
9:00 PM - W6.6
NEXAFS and RIXS Study of Four Fundamental Manganese Oxides.
Sanjukta Choudhury 1 , Gap Soo Chang 1 , Alexander Moewes 1
1 Physics and Engineering physics, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
Show AbstractL2, 3 near-edge X-ray absorption fine structure (NEXAFS) and resonant inelastic X-rayscattering (RIXS) spectra are recorded for Mn (II), Mn (III), Mn (IV), and mixture ofMn (II) and Mn (III) valence states from MnO, Mn2O3, MnO2, and Mn3O4, respectively.A systematic blue shift is observed in Mn L2, 3 NEXAFS absorption edge as theMn-valence increases, where O 1s NEXAFS absorption edge show a red shift with theincrease of Mn-valence, which can be used as a potential probe of Mn-valence. RIXSspectra probe the low-lying electronic excited states through the d-d excitation and chargetransfer excitation. Resonant emissions are observed fundamentally different for selectiveexcitation energies and necessarily different for different oxides. Experimentally obtainedNEXAFS and RIXS spectra are simulated using atomic multiplet calculations with anoctahedral crystal field superimposed; we reproduce both energy positions and intensityvariations of d-d excitations relative to the elastic peak. Charge transfer features arefound more prominent in higher Mn-valence oxides, which is indicative of the increase ofdegree of covalency.
9:00 PM - W6.8
Clathrates Compounds Under Extreme Conditions.
Jose Flores Livas 1 , R. Debord 1 , S. Le Floch 1 , S. Pailhes 1 , Alfonso San Miguel 1
1 Laboratoire de Physique de la Matière Condensée et Nanostectures, Université Claude Bernard Lyon 1 and CNRS, Lyon, Rhône Alpes, France
Show AbstractGroup-IV clathrate materials are extended Si, Ge, and Sn cagelike solids with sp3-hybridized networks [1]. Clathrates exhibit metallic, superconducting, semiconducting, or insulating behavior depending upon the occupation fraction and substitution of the metal atom in the cage and on the substitution in the group-IV framework [2]. The study of clathrates opens a field of designing new materials with a wide variety of properties. In the field of thermoelectricity where the challenge is to have high electrical conductivity and low thermal conductivity, clathrates appear to be ideal candidates because of the cage-like crystal structures in which the spaces are filled with atoms that can rattle around and scatter phonons. We investigate new approaches to design novel magnetic materials system on a basis of the silicon clathrate with polyhedral cage structure, where d- block elements are introduced. Type-I clathrate samples having stoicheiometry Ba8Si46-xMx (M=Mn, Ni, Co) were prepared under high-pressure and high temperature conditions. We presented results on the synthesis and physical properties of Ba8Si46-xMx (M=Mn, Ni, Co) host-substituted type-I silicon clathrates studied by X-ray diffraction, Raman spectroscopy, elastic and inelastic neutron scattering as well as through magnetotransport measurements.[1] “High-pressure properties of group IV clathrates” San Miguel, Alfonso et al, High Pressure Research Vol. 25, No. 3, (2005), 159–185[2] “Superconducting group-IV semiconductors”, Blase, Xavier et al, Nature Materials (2009) DOI: 10.1038/NMAT2425.
9:00 PM - W6.9
Development of an Energy Domain 57Fe Mossbauer Spectrometer Using Synchrotron Radiation and Its Application to Ultra High-pressure Study on Metal Hydrides.
Takaya Mitsui 1 , Naohisa Hirao 2
1 , Japan Atomic Energy Agency, Sayo-cho, Hyogo, Japan, 2 , Japan Synchrotron Radiation Research Institute, Sayo-cho, Hyogo, Japan
Show AbstractAn energy domain 57Fe Mössbauer spectrometer using synchrotron radiation (SR) with a diamond anvil cell (DAC) has been developed for ultrahigh-pressure experiments. The optical system consists of a single-line pure nuclear Bragg reflection from an oscillating 57FeBO3 single crystal near the Néel temperature and an X-ray focusing device. The developed spectrometer can deliver the Doppler-shifted single-line 57Fe-Mössbauer radiation with a narrow bandwidth of neV order from a broadband SR source. The focused incident X-rays make it easy to measure a small specimen in the DAC. The design and performance of the SR 57Fe-Mössbauer spectrometer will be presented, which include the study on metal hydrides under high hydrogen pressures in the giga-pascal range.
Symposium Organizers
Artur Braun Empa – Swiss Federal Laboratories for Materials Testing and Research
Jinghua Guo Lawrence Berkeley National Laboratory
Randall E. Winans Argonne National Laboratory
Helmut Schober Institut Max von Laue - Paul Langevin (ILL)
W7: Batteries and Photosynthesis
Session Chairs
Thursday AM, April 08, 2010
Room 3004 (Moscone West)
9:15 AM - W7.1
Effect of Processing Conditions on Physical and Electrochemical Characteristics of Disordered Carbon Li-ion Negative Electrodes.
John Camardese 1 , Adam Timmons 2
1 Natural Sciences, Lawrence Technological University, Southfield, Michigan, United States, 2 Electrochemical Energy Research Lab, General Motors Global Research and Development, Warren, Michigan, United States
Show AbstractGraphite is commonly used as the active material in the negative electrode of a lithium-ion cell. Graphite has a maximum lithium storage capacity of one lithium atom per six carbon atoms. It has been shown that by creating disorder by milling natural flake graphite samples the maximum lithium storage capacity can be increased. This increase can be as much as three times that of graphite but at the cost of an increased irreversible capacity [1], similar to that observed for synthetic and highly disordered graphite made from petroleum coke fired at moderate temperatures [2,3]. It is also well known that irreversible capacity is diminished by preventing oxygen from accessing oxygen-sensitive active-material powders during electrode and cell fabrication. Absent in the literature is a systematic comparison using identical cell conditions of disordered carbon reversible and irreversible capacities as a function of active material milling time, milling atmosphere and electrode coating atmosphere. Samples of natural flake graphite were milled using a SPEX 8000D mill for different times ranging from 10 to 1270 minutes in three different atmospheres: air, argon and argon mixed with 5% hydrogen. Electrodes were coated in air using the materials milled in all three atmospheres. Also, electrodes were coated in argon using the materials milled in the argon and argon with 5% hydrogen atmospheres. Coin-type half cells were assembled in argon from each electrode and cycled for at least 50 lithium insertion / removal cycles. Results showing changes in the physical and electrochemical characteristics with milling time and milling/coating atmosphere will be presented. It was discovered that the changes in materials properties, through characterizations including pair distribution function analysis from conventional and synchrotron X-ray diffraction measurements, offer a plausible explanation for the observed electrochemical results.[1] F. Disma, L. Aymard, L. Dupont and J.-M. Tarascon, J. Electrochem. Soc., 143, 3959 (1996).[2] J. R. Dahn, A. K. Sleigh, H. Shi, J. N. Reimers, Q. Zhong and B. M. Way, Electrochim. Acta, 38, 1179 (1993).[3] D. A. Stevens and J. R. Dahn, J. Electrochem. Soc., 148, A803 (2001).
9:30 AM - W7.2
Nano-imaging and 3D Tomography of Energy Materials Using Full-field Hard X-ray Transmission Microscopy at SSRL.
Joy Andrews 1 , Piero Pianetta 1 , Florian Meirer 2 , Yijin Liu 1 , Jordi Cabana 3 , Vincent Battaglia 3 , Jia Zhu 4 , Yi Cui 4
1 SSRL, SLAC National Accelerator Laboratory, Menlo Park, California, United States, 2 Technical Institute, Atomic Institute of the Austrian Universities, Vienna Austria, 3 Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 Dept. of Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractThe state-of-the-art full-field transmission x-ray microscope (TXM) at the 54-pole wiggler end station on beam line 6-2 of the Stanford Synchrotron Radiation Lightsource (SSRL) is being used to image a variety of samples, including several with use in energy applications. With capability for imaging over the full 5-14 keV energy range with resolution better than 30 nm, it is possible to obtain high-resolution 2D and 3D data, as well as spectroscopic images above and below the absorption edge of an element of interest. This will be used to characterize NiO used as a high energy density electrode in lithium ion batteries. Nanoscale porosity and tortuosity of graphite electrodes were also studied, with 3D tomography in Zernike phase contrast. 3D tomography was also collected on PbSe nanowires with potential applications for energy harvesting or other nanoelectronics. 2D and 3D images of the wires, synthesized using a central nanowire template via vapor-liquid-solid branching, revealed orthogonal branches. The TXM data will be useful in optimizing these materials for use in energy applications.
9:45 AM - W7.3
In-situ Ambient-pressure XPS Observation of Reversible Charge Storage on Ni Battery Electrodes.
Farid El Gabaly 1 , Anthony McDaniel 1 , Michael Grass 2 1 , Zhi Liu 2 , Roger Farrrow 1 , Kevin McCarty 1 , Hendrik Bluhm 2
1 , Sandia National Laboratories, Livermore, California, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThe most realistic pathway for quickly transitioning the transportation sector from fossil fuels to renewable energy is using electric vehicles. Secondary (rechargeable) battery technology will power these vehicles. Nickel metal-hydride batteries are currently the best candidate for use in electric cars [1]. The key element of a high-performance secondary battery is its electrode materials. The Ni electrode is widely used in battery technology, such as Ni/Cd, Ni/Zn, Ni/Fe, Ni/H2, and Ni/metal-hydride (MH) cells. Although the attractive properties of this electrode have led to many investigations, a number of aspects of its operation, including how the energy-storing Ni phases are created and consumed during charging and discharging, are not yet fully understood [2].We report the use of ambient-pressure X-ray Photoelectron Spectroscopy [3] (APXPS, Beamlines 11.0.2 and 9.3.2 at the Advanced Light Source, Lawrence Berkeley National Laboratory) to characterize Ni hydroxide phases produced by in-situ electrochemistry. In the reported experiments, a Ni (metal) electrode was hydroxidized by being exposed to H2O/H2 under electrochemical bias. The induced phase change was reversible and has been followed in real time with APXPS. The created phase, identified by the Ni2p core level (NiOOH, the phase used in commercial Ni/MH batteries) can store chemical energy –so once the potential is removed from the electrode (i.e., the charging step ends), the electrode will start its reduction back to Ni metal (discharge), presenting the typical discharge potential of a battery. The measured discharge potential plateau agrees with the thermodynamic potential of NiOOH phase with respect to Ni metal. Our planar geometry has allowed us to observe as well the direction of the discharging ‘front’ (hydroxide/metal interphase), revealing important hydroxide phase change kinetic information.The combination of APXPS and in-situ electrochemistry that this work presents emphasizes the power to understand relevant materials processes by combining detailed chemical and electrical information. This study opens the door to the investigation of more complex battery systems using in-situ synchrotron XPS.This research was supported by the U. S. Department of Energy under Contract No.DE-AC04-94AL85000 (Sandia) and DE-AC02-05CH11231 (LBNL).[1] S. R. Ovshinsky et al., “A Nickel Metal Hydride Battery for Electric Vehicles”, Science 260 (1993) 176[2] R.A. Huggins, “Advanced Batteries”, Springer New York, 2009[3] D.F. Ogletree, H. Bluhm, G. Lebedev, C.S. Fadley, Z. Hussain, M. Salmeron, Rev. Sci. Instrum. 73 (2002) 3872.
10:00 AM - W7.4
Layered Mixed Transition Metal Oxide Materials for Li-ion Battery Cathodes.
Thomas Conry 1 , Marca Doeff 1
1 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractLayered transition metal oxide materials have been used as cathodes for rechargeable Li-ion batteries for decades. The most common commercially used material is LiCoO2, introduced by Sony in 1991, though other systems have been widely studied in an effort to increase the performance and safety of devices. Mixed transition metal oxides containing nickel, manganese, and cobalt (NMCs) in various proportions have emerged as encouraging candidates to replace LiCoO2, with much recent focus on the LiNi0.33Co0.33Mn0.33O2 and LiNi0.4Co0.2Mn0.4O2 formulations. It is desirable to decrease the Co content in these systems for cost and environmental concerns, without unduly sacrificing performance, as the Co adds structural stability and improves rate capability. This can be achieved both by increasing the relative stoichiometries of the Ni and Mn or by substituting another transition metal, such as Al, at the Co site. In this investigation, the LiNi0.45Co0.1-xAlxMn0.45O2 (0≤x≤0.1) system is explored. The effect of Al-substitution on practical capacity, rate capability, and cycling stability of the material are discussed through electrochemical measurements. X-ray absorption spectroscopy (XAS) and x-ray diffraction are used to determine the oxidation identities of the components at various points during cycling, and to resolve the electronic and structural consequences of the Al-substitution.
10:15 AM - **W7.5
In situ X-ray Absorption Spectroscopic Study of LiNi0.4Co0.15Mn0.4Al0.05O2 Cathode Material.
Elton Cairns 1 2 , Aniruddha Deb 3
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Chemical Engineering, University of California at Berkeley, Berkeley , California, United States, 3 Chemistry, The University of Michigan, Ann Arbor, Michigan, United States
Show AbstractAfter the recent upsurge of interest in the layered LiNi1/3Co1/3Mn1/3O2 system for use as a cathode material for rechargeable lithium batteries, we have studied the charge compensation mechanism and structural perturbations occurring during cycling of the this type of novel layered system of LiNi0.4Co0.15Mn0.4Al0.05O2, to investigate the effect on the system on Al doping and reducing the Co concentration. In situ X-ray absorption spectroscopy (XAS) measurements were performed utilizing a novel in situ electrochemical cell, specifically designed for long-term X-ray experiments. The cell was cycled at a moderate rate through a typical Li-ion battery operating voltage range (2.8–4.7 V). XAS measurements were performed at different states of charge (SOC) during cycling, at the Ni, Co, and the Mn edges, revealing details about the response of the cathode to Li insertion and extraction processes. Extended X-ray absorption fine structure region of the spectra revealed the changes of bond distance and coordination number of Ni, Co, and Mn absorbers as a function of the SOC of the material. We found that the oxidation states of the transition metals in the system are Ni2+, Co3+, and Mn4+ in the fully discharged condition. During charging the Ni2+ is oxidized to Ni4+ through an intermediate stage of Ni3+, Co3+ is oxidized towards Co4+. The EXAFS measurements results recorded during cycling will be discussed.
10:45 AM - W7.6
Application of Hard and Soft X-ray Spectroscopy and Scattering in Lithium Ion Battery Research.
Artur Braun 2 1 , Pieter Glatzel 3 4 , Uwe Bergmann 3 , Hongxin Wang 3 4 , Stephen Cramer 3 4 , Elton Cairns 2 5
2 Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 1 Laboratory for High Performance Ceramics, EMPA, Dübendorf Switzerland, 3 Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 Applied Physics, UC Davis, Davis, California, United States, 5 Chemical Engineering, UC Berkeley, Berkeley, California, United States
Show AbstractWe provide a detailed overview of synchrotron x-ray studies for lithium ion battery cathodes, i.e. lithium manganese oxide.The presentation includes in-situ XANES, EXAFS, XRD and ASAXS results of a battery cell during charging and discharging.Ex-situ studies include K-beta and soft x-ray photoemission studies in order to differentiate between the Mn oxidation state on the surface and in the bulk, and in order to make a depth profile of a charged cathode with respect to the Mn oxidation state.Finally a suite of Li NEXAFS spectra of Li battery components and reference materials is presented, include a comparison with x-ray Raman data.
11:00 AM - W7: Batteries
BREAK
11:30 AM - **W7.7
Synchrotron Spectroscopy of Nanoclusters in Metalloenzymes.
Stephen Cramer 1 2
1 Applied Science, University of California, Davis, California, United States, 2 Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractOver the past 30 years, synchrotron spectroscopy has evolved from a few basic techniques (EXAFS and photoemission) to a wide range of methods including x-ray MCD, resonant inelastic x-ray scattering, and even nuclear resonance spectroscopies. Many of the techniques that have been applied to metalloenzymes such as hydrogenase and nitrogenase are transferable to complex materials problems. I will illustrate the application of these techniques and draw analogies to materials science issues. Prospects for the future on 4th generation free electron laser sources will be discussed, and comparisons made with what might be available from seeded FELs and "ultimate storage rings".
12:00 PM - W7.8
Ex-situ Electronic Behavior of Haematite Film Under Operating Condition in a Photoelectrochemical (PEC) Cell Studied by O K Edge and Fe-L Edge Soft X-ray Spectroscopy.
Debajeet Bora 1 2 , Selma Erat 1 3 , Artur Braun 1 , Ariffin Ahmad 4 5 , Edwin Constable 2 , Thomas Graule 1
1 Lab for High Performance Ceramics, EMPA-Dubendorf, Dubendorf, Zurich, Switzerland, 2 Department of Chemistry, Universitat Basel, Basel Switzerland, 3 Department of Non Metallic Materials, ETH Zurich, Zurich Switzerland, 4 Department of Physics, Humboldt University, Berlin Germany, 5 BESSYII,GmbH, Helmholtz Centre for Material and Energy, Berlin Germany
Show AbstractPhotoelectrochemical splitting of water over semiconductors is an effective method for converting solar energy into clean and renewable hydrogen fuel. Since the first reported water splitting over TiO2 photo electrode (oxygen evolution connected to a platinum counter electrode for hydrogen evolution), a number of other semiconductor materials have been developed for this purpose. Iron oxide (alpha-Fe2O3 or hematite) photoanode has received considerable attention on account of its abundance, stability and environmental compatibility, as well as its suitable band gap and valence band edge position. In order to fully understand the electronic behaviour of haematite film under operating condition in a PEC cell, we performed an ex-situ spectroscopic investigation by O K edge and Fe L edge soft x-ray absorption spectroscopy. The O k edge NEXAFS spectra arise from the hybridization between O 2p and Fe 3d states as well as Fe 4p states ,showing that later are also important for the bonding interaction of oxides . For the same, nanocrystalline (alpha-Fe2O3) haematite films were choronoamperometrically cycled under different electrochemical condition and variation in shape ,position and intensity of the O K edge and Fe L edge NEXAFS spectra have been analyzed in terms of electronic structure. In this study, nanocrystalline (alpha-Fe2O3) haematite films were prepared via dip coating of bare FTO substrate in iron oleate complex precursor solution and corresponding post annealing technique. The synthesized films were further characterized by UV-VIS spectroscopy, XRD and Scanning electron microscopy. From XRD result it was found there is only one strong peak due to haematite, namely the (110) reflection (in hexagonal coordinates).FESEM further signifies the highly porous architecture of the films with a thickness of 630 nm. The photoactivity of the films was studied by measuring short circuit photocurrent in 1 M KOH as an electrolyte in a three electrode cappuccino cell. The photocurrent density for the same was found to be around550 µA/cm2. The spectra of the different cycled samples show more differences, in particular a well separated eg/t2g doublet at the pre-edge with different band intensity ratios in comparison to the pristine electrode.
12:15 PM - W7.9
X-ray Emission and Absorption Spectroscopy of the Water-splitting Catalysts in Natural and Artificial Systems.
Junko Yano 1 , Jan Kern 1 , Vittal Yachandra 1 , Uwe Bergmann 2
1 Physical Biosciences Division, Lawrence Berkeley National Lab., Berkeley, California, United States, 2 , SLAC National Accelerator Laboratory, Menlo Park, California, United States
Show AbstractPhotosynthetic water oxidation in nature has four oxidation steps operating in cyclic fashion resulting from the successive absorption of 4-photons. Experimental evidence shows that a Mn4Ca cluster is involved in storing oxidizing equivalents, successively binding two substrate water molecules, abstracting protons, using the oxidizing equivalents to oxidize the water, to form an O-O bond and eventually release O2. The goal of understanding the fundamental factors that control this complex four-electron, four-proton reaction is one of science’s grand challenges, because research progress in this area is essential for the development of efficient artificial photosynthetic machines to convert sunlight into stored chemical energy on an enormous scale. The structure of the Mn4Ca cluster in the dark state (S1 state) is emerging from X-ray diffraction(1,2) and X-ray spectroscopy studies(3), but much less is known about the structural changes in the Mn4Ca cluster through the catalytic cycle, which are critical for understanding the mechanism of oxygen evolution. The intermediate S-states of the oxygen evolving complex, S0 through S3, have been studied to varying degrees using biochemical and spectroscopic techniques(4). Based on these studies, there are many proposed mechanisms for the photosynthetic water oxidation reaction and the formation of the O-O bond(5). Recent studies of X-ray absorption/emission spectroscopy have revealed several important aspects regarding the geometric and electronic structure of the Mn4Ca cluster. Single crystal X-ray absorption spectroscopy of Photosystem II single crystals was used to evaluate the Mn cluster geometry based on the published crystallographic data. Additionally, Resonant Inelastic X-ray scattering (RIXS) method and X-ray Kβ emission spectroscopy were applied to address the electronic structural changes of the Mn4Ca cluster during the catalytic cycle. The mechanism of the photosynthetic water-splitting reaction in natural and artificial systems compatible with these results will be discussed.References1. Ferreira, K. N. et al. (2004) Science 303, 1831-1838.2. Loll, B. et al. (2005) Nature 438, 1040-1044.3. Yano, J. et al. (2006) Science 314, 821-825.4. Pushkar, Y. et al. (2008) Proc. Natl. Acad. Sci. U. S. A. 105, 1879-1884.5. McEvoy, J. P. & Brudvig, G. W. (2006) Chem. Rev. 106, 4455-4483.
12:30 PM - W7.10
Nuclear Resonance Vibrational Spectroscopy Monitoring H and C Related Vibrations.
Hongxin Wang 1 2 , Yisong Guo 1 , Saeed Kamali 1 , Stephen Cramer 1 2
1 Applied Science, University of California, Davis, California, United States, 2 , Lawrence Berkeley National Lab, Berkeley, California, United States
Show AbstractSynchrotron radiation based nuclear resonance vibrational spectroscopy (NRVS) measures 57Fe specific Fe-X vibrations, such as the iron-hydrogen and iron-carbon, inside various iron complexes and iron containing enzymes. In this study, we have measured several iron complexes, and provided a site specific X-ray spectroscopic probe on light elements which are associated with 57Fe, such as Fe-H and Fe-C inside various molecules.The application of NRVS on energy related enzymatic systems in nature, such as hydrogenase, has also been discussed.
12:45 PM - W7.11
Characterization of Dye Attachment to TiO2 and to Buffer Layers in Dye Sensitized Solar Cells.
Jonathan Bakke 1 , Thomas Brennan 1 , Chad Miller 2 , Dennis Nordlund 2 , Michael Toney 2 , Stacey Bent 1
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 , Stanford Synchrotron Radiation Lightsource (SSRL), Menlo Park, California, United States
Show AbstractAs concerns about climate change and energy security mount, next generation photovoltaics with a lower cost-per-Watt performance are expected to make the economics of solar energy more favorable. One such technology is the dye-sensitized solar cell (DSSC) in which a monolayer of ruthenium-based dye molecules is adsorbed on nanoporous TiO2. The function of the dye is to absorb photons, which create an e-/h+ pair in the dye; TiO2 transports the generated electrons to a transparent anode. A newer type of DSSC that uses a solid state (ss-DSSC), organic hole transporter has attracted recent attention. Despite the desirability of the solid state design, these cells suffer in performance due to a high charge recombination rate at the interface of the TiO2 and dye.To reduce charge recombination, we modify the interface by inserting a thin buffer layer between the dye and the TiO2. These “anti-recombination” layers must be very thin (< 2 nm) to allow the dye to inject electrons into the TiO2. Buffer layers that we have investigated include various oxides such as Al2O3 grown by atomic layer deposition (ALD) as well as self-assembled monolayers (SAMs) consisting of short phosphonic acids such as aminomethyl phosphonic acid and p-aminobenzyl phosphonic acid. Despite the importance of the dye-surface interface, little is known about the dye molecular structure on the surface. In this work, we investigate the bonding of the dye at the surface of TiO2 and at the surface of the inserted buffer layers using synchrotron techniques, including X-ray reflectivity (XRR) and near-edge X-ray absorption fine structure (NEXAFS). We first study the dye adsorption to atomically flat ALD TiO2 to mimic the surface of the DSSC. Using XRR, we determine the thickness of the dye and the interface roughness with the TiO2. From this information, we can make estimates as to the conformation and packing of the dye on the surface. Furthermore, angle-resolved NEXAFS at the N1s and C1s edge of the dye molecules allows us to study the orientation of the π* and σ* orbitals in the dye molecules on TiO2. To determine the conformation, it has been particularly useful to probe the sulfur atom orbitals of the dye, since these do not react with the TiO2 and are located on the exposed side of the dye.We also investigate using XRR and NEXAFS the effect of the interfacial buffer layers on the bonding of the dye to the surface. Different ALD oxides could cause changes in the packing or number of active sites at the surface and in the case of phosphonic acids, the dye must bond to the tail group of the SAM rather than the TiO2. Both these can create differences in bonding. Our XRR data show that the bonding of the dyes to ALD oxides is similar to that of TiO2. The information on dye/surface structure gained from the XRR and NEXAFS results will be correlated with electrical data obtained from working ss-DSSCs using the same interfacial buffer layers.
W8: Solar Cells
Session Chairs
Farid El Gabaly
Selma Erat
Thursday PM, April 08, 2010
Room 3004 (Moscone West)
2:30 PM - W8.1
Impact of Heat Treatments on Interfaces and Contacts in CdTe Thin-film Solar Cells Studied by Soft X-ray Emission Spectroscopy.
Sujitra Pookpanratana 1 , Xiangxin Liu 2 , Lothar Weinhardt 3 , Marcus Baer 4 , Monika Blum 1 3 , Yufeng Zhang 1 , Fatima Khan 1 , Alvin Compaan 2 , Clemens Heske 1
1 Chemistry, University of Nevada, Las Vegas, Las Vegas, Nevada, United States, 2 Physics and Astronomy, The University of Toledo, Toledo, Ohio, United States, 3 Experimentelle Physik II, University of Wuerzburg, Wuerzburg Germany, 4 Solar Energy Research, Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Berlin Germany
Show AbstractCdTe-based solar cells have reached efficiencies of up to 16.5% on the laboratory scale [1], and the manufacturing costs of CdTe modules are reported below $1/W
p [2]. For CdTe-based solar cells, it is necessary to perform a CdCl
2 activation (
i.e., annealing) step of the CdTe/CdS layer stack to make highly efficient devices. Futhermore, numerous studies (
e.g., [3,4]) have reported on diffusion processes at different interfaces in CdTe-based solar cells. Using synchrotron-based soft x-ray emission spectroscopy (XES), we recently confirmed that the CdCl
2 activation induces migration of S across the CdTe/CdS interface [5]. Here, we report on the characterization of a deliberately designed sample series to further clarify the effect of the CdCl
2 and contact heat treatments.
Various CdTe/CdS/SnO2:F/glass samples with a combination of either Cu, Au, Au/Cu or “no” contact deposited were investigated by XES. XES is the technique of choice for such studies since it can probe buried layers (e.g., S atoms buried below 15 – 50 nm of Cu and/or Au), and has been shown to be very sensitive in distinguishing different chemical environments in other solar cell materials [6,7]. The CdTe and CdS thin films were deposited by R.F. magnetron sputtering. Half of the samples were activated by a CdCl2 treatment at 390°C for 30 minutes in dry air. From the entire sample set, three quarters of the samples were coated with the contact metals, and again half of these were heat-treated for the contact formation step (at 150°C in air for 45 minutes). With this sample matrix, it is now possible to discern the impacts of the various heat treatments on the chemical properties of the different interfaces in the sample. All samples were packed and sealed in dry N2 (at Toledo), and shipped to the Advanced Light Source in Berkeley, CA, for transfer into ultra-high vacuum (without air exposure) and XES characterization (Beamline 8.0.1 in the SXF endstation). The S L2,3 XES spectra show a significant increase in the signal intensity after CdCl2 activation, as expected. In comparison, samples with both a CdCl2 activation and a subsequent contact formation step show a less intense S emission. We also observe an additional sulfate contribution in the S L2,3 XES spectra when the contact heat treatment is performed. These findings will be discussed together with results obtained from the characterization of the CdTe/CdS interface made accessible by using a suitable lift-off technique.
1.X. Wu et al., Conf. Proceedings, 17th EPVSEC, Munich, (2001) 995.
2.http://investor.firstsolar.com/phoenix.zhtml?c=201491&p=irol-newsArticle&ID=1259614
3.N. Nakayama et al., Jap. J. Appl. Phys. 19, (1980) 703.
4.D. Grecu et al., J. Appl. Phys. 88, (2000) 2490.
5.X. Liu et al., Proc. 34th IEEE PVSC, Philadelphia, (2009) in press.
6.C. Heske et al., Appl. Phys. Lett. 74, (1999) 1451.
7.L. Weinhardt et al., Appl. Phys. Lett. 82, (2003) 571.
2:45 PM - **W8.2
Using Soft X-rays to Look Into Interfaces of Photoelectrochemical Devices.
Clemens Heske 1
1 Chemistry, University of Nevada, Las Vegas, Las Vegas, Nevada, United States
Show AbstractThe electronic and chemical structure of interfaces is of central importance for understanding and tailoring of materials, chemical processes, and electronic as well as photoelectrochemical devices. Over the past few decades, significant experimental (and theoretical) insights into electronic and chemical structures of well-defined model surfaces have been gained by a variety of approaches, and properties of interfaces have been inferred. However, very little is known about interfaces that are not “well-behaved” – for example, interfaces that are buried and exhibit intermixing processes, impurities, and/or degradation effects. The purpose of this talk is to demonstrate how a tool chest of soft x-ray spectroscopies (in particular using high-brilliance synchrotron radiation) is uniquely suited to address such questions. In the talk, materials for photoelectrochemical water splitting will be discussed, and it will be shown how soft x-rays can be utilized to shed light on the electronic and chemical properties of the surfaces and interfaces involved.
3:15 PM - W8.3
XANES Studies on Eu-doped Fluorozirconate Based Glass Ceramics.
Bastian Henke 1 2 , Patrick Keil 3 , Christian Passlick 2 , Marie-Christin Wiegand 4 , Jacqueline Johnson 5 , Stefan Schweizer 1 2
1 , Fraunhofer Center for Silicon Photovoltaics, Halle (Saale) Germany, 2 Centre for Innovation Competence SiLi-nano(R), Martin Luther University of Halle-Wittenberg, Halle (Saale) Germany, 3 Department of Interface Chemistry and Surface Engineering, Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf Germany, 4 Department of Physics, Faculty of Science, University of Paderborn, Paderborn Germany, 5 Department of Materials Science and Engineering, University of Tennessee Space Institute, Tullahoma, Tennessee, United States
Show AbstractA class of fluorobromo- (FBZ) and fluorochlorozirconate (FCZ) glass ceramics has been developed for ionizing radiation detection and photovoltaic applications. The composition of these materials is derived from a standard ZBLAN glass - a fluoride glass, made from Zr, Ba, La, Al, and Na fluorides. Several synthesis routes have been derived to maintain Zr in the 4+ state where the addition of a small amount of YF3 or InF3 plays a key role in the glass production process. The glasses under investigation were additionally doped with Br or Cl ions by partial substitution of the fluorides BaF2 and NaF for BaX2 and NaX (X = Br, Cl), respectively. This enabled precipitation of BaX2 nanocrystals within the glass upon appropriate annealing.For ionizing radiation detection, Eu is added to the glass for optical activation. Depending on the structural phase of the BaX2, the glass-ceramic material can act either as a scintillator (able to convert ionizing radiation to visible light), or as a storage phosphor (able to convert the radiation into stable electron-hole pairs, which can be released at a later time with a scanning laser beam). For photovoltaic applications, the solar cell efficiency in the ultraviolet spectral range can be significantly increased by applying a transparent Eu-doped glass-ceramic top layer, which down-converts the incident ultraviolet photons to photons of a wavelength in the visible, which is more effectively absorbed by the solar cell.For luminescence from these materials, the critical component is the Eu2+, in particular the Eu2+ present in the BaX2 nanocrystals. However, there is always a significant amount of Eu3+ in the glass which reduces the performance of these systems as both scintillators and storage phosphors. X-ray absorption near edge structure (XANES) measurements showed that one source was found to be in the as-bought EuF2, in which Eu2+ is oxidized to Eu3+ before and/or during glass melting. In such a complex system, the addition of each new chemical and each change in processing affects the material properties and so must be systematically investigated. In this work we investigate the influence of adding YF3 or InF3 and remelting on the Eu2+ to Eu3+ ratio.
3:30 PM - W8.4
Soft X-ray Investigation of the Solid-phase Crystallization of Amorphous Silicon – Impact on the Chemical Structure of the Deeply Buried Si/ZnO Interface.
Marcus Baer 1 , Maurizio Roczen 1 , Regan Wilks 1 , Mark Wimmer 1 , Dominic Gerlach 1 , Florian Ruske 1 , Klaus Lips 1 , Bernd Rech 1 , Monika Blum 2 , Lothar Weinhardt 2 , Sujitra Pookpanratana 3 , Stefan Krause 3 , Yufeng Zhang 3 , Clemens Heske 3
1 Solar Energy Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin Germany, 2 Physikalisches Institut, Universität Würzburg, Würzburg Germany, 3 Department of Chemistry, University of Nevada, Las Vegas, Las Vegas, Nevada, United States
Show AbstractPolycrystalline silicon (poly-Si) is a promising candidate absorber material for low-cost, high efficiency thin-film solar cells. A rather simple way to obtain poly-Si at relatively low process temperatures is solid-phase crystallization (SPC) of hydrogenated amorphous silicon (a-Si:H). Solar cell minimodules (94cm2) based on poly-Si prepared by the SPC process have already demonstrated efficiencies of up to 10.4% by utilizing a complex point contact design.[1] If this contact structure could be replaced by a transparent conducting oxide (TCO), the manufacturing process would be greatly simplified and an easy series interconnection scheme using laser scribing would become possible; both would aid large-scale mass production needed for commercialization. In addition, by texturing the TCO one could easily improve the light trapping. For these reasons, an Al/p+-Si/p-Si/n+-Si/ZnO:Al/glass structure was recently suggested as a potential solar cell concept.[2] This design, however, involves a high-temperature annealing step (SPC at 600°C), which could induce chemical interaction/diffusion processes across the Si/ZnO interface.We will report the results of our synchrotron-based soft x-ray spectroscopic investigation of the deeply buried n+-Si/ZnO:Al interface before and after SPC. For this experiment, 50 nm phosphorus-doped a-Si:H was deposited by plasma-enhanced chemical vapor deposition (PECVD) on 900 nm rf-sputtered ZnO:Al. After deposition, one sample underwent SPC at 600°C for 72 h. In order to shed light on the impact of the SPC on the chemical structure at the formed n+-Si/ZnO:Al interface, we conducted soft x-ray emission (XES) measurements at the Si L2,3 and O K edge using the SXF spectrometer of Beamline 8.0 at the Advanced Light Source (Lawrence Berkeley National Laboratory). To eliminate the influence of SiO2 that is natively formed at silicon surfaces upon air-exposure, the measurements were conducted before and after an HF-dip. As expected, we find the formation of SiO2 on the surface of the investigated n+-Si/ZnO:Al before and after SPC. Using a combination of different sample treatments, variable measurement geometry, and selected XES emission lines of different information depths, we were also able to identify an SPC-induced formation of O-Si bonds at the Si/ZnO interface. In addition, we find enhanced Zn incorporation in the Si after SPC. A complementary investigation of the chemical interface structure by x-ray photoelectron spectroscopy is currently ongoing.[1] M.J. Keevers, T.L. Young, U. Schubert, and M.A. Green, Proc. 22nd European Photovoltaic Solar Energy Conference, 3-7 September 2007, Milan, Italy, 1783.[2] C. Becker, F. Ruske, T. Sontheimer, B. Gorka, U. Bloeck, S. Gall, and B. Rech, J. Appl. Phys. 106, 084506 (2009).
3:45 PM - W8: Solar
BREAK
4:15 PM - W8.5
Identification of the Structure of Optically Active Defects in Chalcogen Doped Silicon.
Bonna Newman 1 , Joseph Sullivan 1 , Mark Winkler 2 , Meng-Ju Sher 2 , Matthew Marcus 3 , Sirine Fakra 3 , Eric Mazur 2 , Tonio Buonassisi 1
1 , MIT, Cambridge, Massachusetts, United States, 2 , Harvard, Cambridge, Massachusetts, United States, 3 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractPulsed laser irradiation is used to dope silicon with chalcogens in concentrations up to 1% atomic, 4-5 orders of magnitude greater than room temperature equilibrium solubility. This silicon-based material demonstrates unique properties such as enhanced broadband absorption that extends to the infrared regime and below the band gap of elemental silicon [1]. “Black silicon” as this material is called, is being explored for use in solar cells, LEDs, and photodetectors. However, the mechanism for enhanced absorption has not yet been clearly identified.We use synchrotron-based extended x-ray absorption fine structure (EXAFS) to probe the chemical state of the chalcogen dopant atoms in the silicon matrix. High concentrations of selenium atoms are implanted using femtosecond laser irradiation of a crystalline silicon wafer coated with a 70 nm elemental Se film. After irradiation, Se is incorporated up to 1 atomic % in a layer extending 200 nm from the surface. These samples absorb over 90% of incident photons with wavelengths between 300 and 2300 nm. After thermal annealing, the infrared absorption of these samples decreases to nearly that of pure silicon; a sample annealed at 950°C for 30 minutes demonstrates only ~10% infrared absorption.We find that the Se chemical state, measured by EXAFS, is directly correlated with the average infrared absorption from 1100 to 2300 nm. Theoretical fitting of the EXAFS spectrum from a highly infrared absorbing sample reveals that the selenium is arranged in clusters of two or more atoms. In contrast, the EXAFS spectrum from the annealed sample (which does not absorb significantly in the infrared wavelengths) is no longer consistent with a structure of clustered selenium atoms. Work is currently underway to identify the exact chemical structure and develop a 3D molecular model of the optically active state. The relationship of the selenium molecular structure and resulting bulk properties of absorption will be explained in the context of temperature processing. [1] J. E. Carey, C. H. Crouch, M. Shen, and E. Mazur, Optical Letters 30, 1773, (2005)
4:30 PM - W8.6
WAXS and XAFS Studies of Local Structure in Amorphous Transparent Conductors.
Brandon Reese 1 2 , J. Leisch 2 , P. Parilla 2 , T. Gennett 2 , J. Perkins 2 , D. Ginley 2 , D. Miracle 3
1 Electrical, Computer, and Energy Engineering, University of Colorado at Boulder, Boulder, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States, 3 Materials and Manufacturing Directorate, Air Force Research Laboratory, Dayton, Ohio, United States
Show AbstractTransparent conducting oxides (TCO’s) are critical materials for photovoltaics and organic light-emitting diodes. Traditional TCO’s, such as indium tin oxide, are crystalline materials that lend themselves to analysis by traditional laboratory X-ray diffraction techniques. Recently, a new class of amorphous TCO’s has emerged, typified by indium zinc oxide (IZO). It has been observed that these materials can exhibit drastic changes in conductivity of ~7 orders of magnitude by varying the oxygen partial pressure during deposition or by using a relatively low temperature thermal annealing process. We hope to learn what changes in the local atomic structure are producing the drastic changes observed in the electrical conductivity of these materials.We are using two synchrotron radiation techniques in a complementary fashion to characterize these materials. The first is X-ray absorption Fine Structure (XAFS) analysis. The second is the Pair Distribution Function (PDF) analysis. The PDF is obtained from wide-angle scattering (WAXS). Both XAFS and WAXS are particularly well suited to amorphous materials, because neither method relies on the analysis of the Bragg scattering peaks. We are analyzing thin film samples of both insulating and conducting IZO. The IZO thin films were grown by sputtering onto <100>-Si substrates with a 20nm thick SiOx thermal oxide layer. The substrate was chosen to minimize the background signal during the data collection. The XAFS data was collected from BL4-1 at the Stanford Synchrotron Radiation Laboratory (SSRL). The WAXS data was collected from BL7-2 at SSRL. The XAFS data is being analyzed using the program SIXPack and to a lesser extent the HORAE package. From the XAFS data we have learned that both conducting and insulating IZO films look nearly identical when the indium site is probed. Preliminary results indicate that the first shell (oxygen) is at a radius of 2.15 Å, and the second shell (In or Zn) is at a radius of 3.36 Å. The XAFS Debye-Waller factor for these two shells is 0.008 and 0.015, respectively. However, when the zinc site is probed the first shell is nearly identical but the second shell exhibits significant differences. We are in the process of analyzing the WAXS data to find any correlation to the effect seen in the XAFS data.Another round of beam time is planned for the end of January. We will be using BL10-2 for the next round and will access to significantly higher X-ray energies for the WAXS experiments. This will probe a higher Q-range, which will significantly decrease the uncertainty in the interatomic distances.
4:45 PM - W8.7
Local Melting of Metal-Silicide Precipitates in a Silicon Matrix Upon Cooling.
D. Fenning 1 , B. Newman 1 , M. Bertoni 1 , S. Bernardis 1 , S. Hudelson 2 , S. Fakra 3 , M. Marcus 3 , T. Buonassisi 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , 1366 Technologies, North Lexington, Massachusetts, United States, 3 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractMetallic impurities in silicon are detrimental to the performance of silicon photovoltaic devices. The high temperature processing involved in the manufacturing of such solar cells can significantly change the distribution of metal impurities. In particular, for many metallic interstitial solutes in silicon, the binary system exhibits a phenomenon known as retrograde solubility, where the maximum solidus concentration occurs at a temperature higher than the eutectic temperature. This retrograde solubility can lead to supersaturated conditions during cooling above the eutectic temperature. Using synchrotron-based data collected with an ambient-controlled, high temperature sample stage to perform in-situ¬ micro X-ray absorption (µ-XAS), we present experimental evidence for the precipitation of liquid metal-silicide droplets in a solid silicon matrix during cooling. We observe the formation of liquid droplets from a solid phase solution of metal impurities in silicon when saturated samples are cooled, but remain at temperatures above the binary eutectic. In this study, silicon wafers are intentionally contaminated with metal impurity defects at temperatures above the binary eutectic and quenched to room temperature to maintain a supersaturated solution. Micro X-ray absorption measurements were performed on these samples as they are quickly reheated to temperatures above the eutectic temperature and then cooled down in an in-situ microscope stage. These measurements confirm a local solid-to-liquid phase transition upon cooling while remaining above the eutectic temperature, followed by a liquid-to-solid transition after dropping below the eutectic temperature. Comparison of samples prepared with different initial concentrations of metal impurities verifies a proposed formation pathway for metal-Si systems. From this model, we predict similar phenomena in other binary systems in silicon and germanium, semiconductors highly relevant to the photovoltaic industry.
5:00 PM - W8.8
Photon-in/Photon-out Soft-X-ray Spectroscopy: An Emerging Probe for Renewable Energy Science.
Jinghua Guo 1
1 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractSolar energy can be converted to electricity and chemical fuels for energy use and storage. However, the cost and conversion efficiency have been the biggest challenge for potential use of solar energy. There are the emerging technologies of using semiconductors for light harvestingassemblies; and charge transfer processes to solar cells. It could provide a significant contribution to our electrical and chemical resources if efficient and inexpensive systems utilizing readily available materials could be devised for the conversion process.This presentation will shade some light on synchrotron radiation based soft-x-ray spectroscopy study of nanostructured materials. Soft-x-ray absorption probes the local unoccupied electronic structure (conduction band); soft-x-ray emission probes the occupied electronic structure (valence band); and the addition of resonant inelastic soft-x-ray scattering (Raman spectroscopy with soft x-rays) can tell the energy levels that reflect the chemical and physical properties of semiconductors. The experimental studies suggest that in-situ photon-in/photon-out soft-x-ray spectroscopy becomes an emerging tool for investigating the surface and interface science.(1) The examples show quantum size effects on the exciton and band-gap energies of semiconductor nanocrystals (Hematite nanoarrays). Such finding strongly suggests that such designed nanomaterials could meet the bandgap requirement for the photocatalytic oxidation of water without an applied bias.(2) The storage of hydrogen in a both safe and compact manner is of great importance for, for example, hydrogen powered vehicles. We have explored in-situ photon-in/photon-out soft-X-ray spectroscopy to study the molecular adsorption of H2 on SWNTs under ambient pressures. The spectral changes with the increasing gas pressures provide the strong evidences for the tube-wall structure deformation and possibly a fraction of charge transfer due to the gas collision.
Symposium Organizers
Artur Braun Empa – Swiss Federal Laboratories for Materials Testing and Research
Jinghua Guo Lawrence Berkeley National Laboratory
Randall E. Winans Argonne National Laboratory
Helmut Schober Institut Max von Laue - Paul Langevin (ILL)
W9: Catalysis
Session Chairs
Debajeet Bora
Randall Winans
Friday AM, April 09, 2010
Room 3004 (Moscone West)
9:30 AM - W9.1
Biomass Dynamic Studies Using Synchrotron Infrared Light.
Alejandro Cruz Gonzalez 1 2 , Chenlin Li 2 3 , Lan Sun 2 3 , Joanna Chen 2 , Seema Singh 2 3 , Blake Simmons 2 3
1 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Deconstruction, Joint BioEnergy Institute, Emeryville, California, United States, 3 , Sandia National Laboratories, Livermore, California, United States
Show AbstractIonic liquids are a new class of non-volatile solvents exhibiting excellent solvating properties and have shown great promise for lignocellulosic biomass pretreatment with easy recovery of cellulose by rapid precipitation with anti-solvents. However, to date, molecular level understanding of ionic liquid pretreatment on lignin and hemicellulose and its impact on different biomasses is lacking. The aim of this research is to develop a fundamental understanding of ionic liquid pretreatment by monitoring the compositional changes during the pretreatment process. IR microscopy based on molecular vibrational spectroscopy is a label-free imaging technique capable of real-time and noninvasive examination of plant cell wall structures with chemical selectivity. In this research, we employ synchrotron IR imaging at the ALS to study the chemical composition of bioenergy crops and impact of ionic liquid pretreatment on these biomasses to identify signatures for predicting deconstructionability and understand pretreatment dynamics by monitoring morphological and compositional evolution during deconstruction.
9:45 AM - **W9.2
In-situ Microscopy and Spectroscopy for Structural and Catalytic Studies.
Miquel Salmeron 1 2
1 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Materials Science & Engineering, UC Berkeley, Berkeley, California, United States
Show AbstractIn my laboratory we have developed and applied microscopy and spectroscopy techniques for in situ studies of the surfaces in the presence of gases. These include Scanning Tunneling Microscopy (STM) in a reactor chamber at high pressure (1 atm), and in situ x-ray spectroscopies, including high pressure x-ray absorption (XAS) at atm pressures and X-ray photoelectron spectroscopy (HP-XPS) at several Torr. We have applied these techniques to the study of surfaces of metals and oxides, and also nanoparticles (NP). I will illustrate the capabilities of these techniques with examples, including the unique structure of surface layers of CO and NO on Rh(111) in equilibrium with gas phase, the surface phase diagram of PdOx and O2, and the restructuring of Pt crystals in the presence of CO. In the case of nanoparticles I will also show the application of XAS and HP-XPS to studies of the structure and reactivity of Au NP for CO oxidation, and of Co NP CO for methanation. Finally, HP-XPS revealed structural modifications of core-shell Rh-Pd and Rh-Pt alloy nanoparticles during oxidative and reducing conditions.
10:15 AM - W9.3
Pressure-dependent Restructuring of Bimetallic Nanoparticle Catalysts.
Feng Tao 1 2 , Miquel Salmeron 1 2 , Gabor Somorjai 1 2
1 Department of Chemistry, University of California at Berkeley, Berkeley, California, United States, 2 Materials Science Division, Lawrence Berkeley National Lab, Berkeley, California, United States
Show AbstractWe have demonstrated that core-shell structured RhxPd1-x nanoparticles can be restructured in depth under reaction conditions with Torr pressure range by using techniques of in-situ studies. Recently, we found the restructuring is pressure-dependent. There is a pressure threshold for significant restructuring of RhxPd1-x nanoparticles. Although surface of the nanoparticles was expected to be covered with a full layer of reactant molecules and/or their dissociated species at pressures lower than the pressure threshold, no significant restructuring was observed at low pressures. The pressure-dependent restructuring will be presented and interpretation will be discussed.
10:30 AM - W9: Catalysis
BREAK
11:00 AM - **W9.4
Catalysts Designed at the Subnanometer to the Nanometer Scale for Bond-selective Reactions.
Stefan Vajda 1 2 6 , Sungsik Lee 1 , Byeongdu Lee 3 , Marcel Di Vece 6 1 , Soenke Seifert 3 , Randall Winans 3 , Jeffrey Elam 4 , Michael Pellin 5 , Stephanie Mucherie 1 , Christopher Marshall 1 , Yu Lei 7 1 , Randall Meyer 7 , Xiaoming Wang 6 , Gary Haller 6 , Lisa Pfefferle 6 , Alexandra Fraile Rodriguez 9 , Kristian Sell 8 , Armin Kleibert 8 9 , Ingo Barke 8 , Viola von Oeynhausen 8 , Karl-Heinz Meiwes-Broer 8 , Detre Teschner 10 , Robert Schloegl 10
1 Chemical Sciences and Engineering Division , Argonne National Laboratory, Argonne, Illinois, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 6 Department of Chemical Engineering, Yale University, New Haven, Connecticut, United States, 3 X-ray Sciences Division, Argonne National Laboratory, Argonne, Illinois, United States, 4 Energy Systems Division, Argonne National Laboratory, Argonne, Illinois, United States, 5 Materials Sciences Division, Argonne National Laboratory, Argonne, Illinois, United States, 7 Department of Chemical Engineering, University of Illinois at Chicago, Chicago, Illinois, United States, 9 Swiss Light Source, Paul-Scherrer Institut, Villigen Switzerland, 8 Institute for Physics, University Rostock, Rostock Germany, 10 Department of Inorganic Chemistry, Fritz-Haber-Institut, Berlin Germany
Show AbstractThe elucidation of the size/composition/shape/structure and function correlation, the effect of support along with the determination of the nature of the catalytic particles under reaction conditions are instrumental for addressing fundamental aspects of catalysis on the way to the design of new classes of catalytic materials. Uniform particles on technologically relevant supports are prerequisites for such studies(1), making size-selected clusters of few atoms to several nm in size as ideal model systems. Our experimental studies are based on 1) chemically uniform support fabrication, 2) size-selected cluster deposition, 3) electron microscopy of nanoclusters, and 4) in situ synchrotron X-ray characterization of clusters under working conditions, combined with mass spectroscopy analysis of the reaction products. This contribution focuses on the following reactions: 1) Partial oxidation of propene on alumina supported Ag nanoparticles and sub-nanometer sized clusters. Scanning electron microscopy is used to image the nanoparticles before and after the catalytic reaction. Grazing incidence X-ray scattering reveals a change in the shape of the catalysts upon the inlet of the reactants at room temperature and its further evolution with temperature.(2) The size-dependent activity and selectivity of Ag nanocatalysts will be discussed and compared with the performance of Ag3 clusters(3) and stabilized Au6-10 clusters.(4) 2) Activation of propane and cyclohexane on Pt-based catalysts. First, we will discuss the catalytic activity and selectivity of size-preselected subnanometer clusters in the oxidative dehydrogenation of propane.(5) Next, results on the dehydrogenation of cyclohexane on subnanometer clusters will be presented.(6) The performance of the sub-nanometer catalysts will be compared with the activity of their nanometer sized counterparts produced by impregnation of carbon nanotubes.(7) Grazing incidence X-ray scattering and X-ray absorption are employed to monitor the size and oxidation state of the catalysts during reaction.1. A.T. Bell, Science 299, 1688 (2003)2. S. Vajda et al, J. Chem. Phys., 131, 121104 (2009), Communication3. Y. Lei et al, to be submitted4. S. Lee et al, Angew. Chemie. Int. Ed. 48, 1467 (2009)5. S. Vajda et al., Nat. Mater. 8, 213 (2009)6. S. Lee et al, to be submitted7. M. Di Vece et al., to be submitted
11:30 AM - W9.5
Troubleshooting Synthesis of Nanoporous Palladium and Alloys With Small-angle Neutron and X-ray Scattering.
Markus Ong 1 , David Robinson 1 , Michael Kent 2 , Rex Hjelm 3 , Jaclyn Murton 2 , Jacob Urquidi 4 , Benjamin Jacobs 1 , Mary Langham 1 , Stephen Fares 1
1 Energy Nanomaterials, Sandia National Laboratories, Livermore, California, United States, 2 Bioenergy and Defense Technology, Sandia National Laboratories, Albuquerque, New Mexico, United States, 3 Lujan Neutron Science Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 4 Department of Physics, New Mexico State University, Las Cruces, New Mexico, United States
Show AbstractNanoporous palladium and palladium alloy powders are of potential value for hydrogen isotope storage applications with improved kinetics. We have synthesized these in a scalable fashion by chemical reduction of palladium salts in a concentrated aqueous surfactant. Particles produced by this method are on the order of microns in diameter and are perforated by 3 nm pores. As determined by electron microscopy and tomography and small-angle X-ray scattering, pore density and order are a strong function of palladium content; other metals such as platinum, rhodium, and palladium alloys produce more uniform pores. Small-angle neutron scattering was used as a diagnostic tool to determine the structure of the templating surfactants and the effects of the presence of various salts and metal species during the course of reaction. This revealed that the surfactant is less ordered than expected even in the absence of palladium and has led to new synthetic approaches.
11:45 AM - **W9.6
Neutron Scattering Studies of Materials for Energy Applications.
Alan Hurd 1
1 Lujan Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractNeutrons provide unique advantages to researchers investigating materials for energy storage, transmission, and creation. Although there are never enough neutrons for this inherently low flux technique, new capabilities for investigating increasingly complex materials are available through user facilities across the world. At the Lujan Center at LANSCE, new results have been obtained in studies of hydrogen storage, extraction from geological strata, materials for nuclear fuels and vessels, thin-film structures for solar collection, battery electrode materials, and complex electronic materials such as thermoelectrics and superconductors. These topics will be surveyed to illustrate the advantages of neutron scattering with a mention of future capabilities.
12:15 PM - W9.7
Fundamental Insights into Metal Catalysed Carbon-carbon Bond Forming Reactions by Synchrotron Radiation Techniques.
Vijay Kanuru 1 , Georgios Kyriakou 1 , Anthoula Papageorgiou 1 , Simon Humphrey 1 , Simon Beaumont 1 , David Watson 1 , Minthco Tikhov 1 , Richard Lambert 1 , Jonathan Burton 2 , David Jefferson 1
1 Department of Chemistry, University of Cambridge, Cambridge United Kingdom, 2 Department of Chemistry, University of Oxford, Oxford United Kingdom
Show AbstractMetal catalysed carbon-carbon(C-C) bond forming reactions (e.g. Sonogashira coupling) are of paramount importance in many applications. They represent an important strategy in synthetic organic chemistry, yet the fundamental mechanism remains controversial for more than a decade, despite the number of attempts to resolve the issue. The key question is whether the catalysis occurs heterogeneously at the surface of transition metal nanoparticles (Pd, Rh, Au…) or whether it occurs homogeneously, induced by transition metal complexes in solution, derived from the metal nanoparticles (NPs). This reflects the limitations of the experimental methodologies that have been employed thus far. In this study we have followed a dual approach in order to address this problem. Firstly by studying Sonogashira coupling catalyzed by rhodium nano clusters as a function of reaction variables such as particle size and extent of metal leaching. Secondly by investigating the same reaction on Au (111) surface under ultra high vacuum conditions where any possibility of homogenous catalysis is totally excluded, thus providing an unambiguous test. Using rhodium nanoparticles in solution we show that over a wide range of conditions essentially all the observed catalytic activity can be ascribed to the Rh particles with a negligible contribution from Rh species in solution. Moreover, we find a clear particle size effect—bigger particles are more effective than small ones, the opposite of what is usually reported. This dependence of particle size reinforces our principal conclusion, namely that the catalytic reaction is heterogeneous. We may rationalize this behavior in terms of steric effects: both reactants may be readily accommodated on a single facet of a large NP, but not on a small NP. Moreover, in the case of small NPs, there is a higher probability of adsorption at a facet edge, where bond-breaking may lead to molecular decomposition. Sonogashira coupling on Au (111) has been studied by TPR, synchrotron XPS and NEXAFS and STM. The reaction follows first order kinetics and the cross coupling product diphenylacetylene desorbs at ~300K following adsorption of iodobenzene and phenylacetylene on Au (111) at 90K. Synchrotron XPS shows that the scission of C-I bond of iodobenzene occurs at ~266K. At 90K sub monolayer coverage, iodobenzene is tilted ~33.40 with respect to the surface whereas in phenylacetylene the ring is slightly inclined toward the surface with the acetylenic group is appreciably tilted away (~45.40). Neither cross coupling nor homo coupling between phenylacetylene and Iodobenzene was observed on roughened argon-sputtered Au(111) surface demonstrating that these coupling reactions are highly sensitive to the details of the surface structure, consistent with particle size effects found with the NP catalysts. Our results provide the first unambiguous demonstration that this chemistry does indeed occur heterogeneously.
12:30 PM - **W9.8
An Eye on the Inside of Zeolite Materials: New Insights in Molecular Diffusion Barriers, Mesoporosity and Bronsted Acidity.
Bert Weckhuysen 1
1 Chemistry, Utrecht University, Utrecht Netherlands
Show AbstractA novel methodology has been developed to study individual zeolite crystals in a space- and time-resolved manner at the micron- and nanoscale. First, the intergrowth structure of the zeolite crystals is elucidated in great detail. For this purpose, a template burning method has been developed with confocal fluorescence microscopy, whereas the pore orientation of the individual building blocks can be assessed with Electron Back-Scattering Diffraction and Focused Ion Beam milling. By analyzing a large set of various morphological distinct large H-ZSM-5 crystals a unifying view on the intergrowth structure of these materials could be obtained. Furthermore, by using TEM lamelling, electron diffraction studies in combination with AFM and XPS, it was possible to reveal outer and inner surface molecular diffusion boundaries affecting the overall performance of the crystals. In a second step, UV-Vis, synchrotron IR and fluorescence microscopy has been employed to map the formation of reaction products and the absorption spectra obtained allow for a kinetic analysis of the reaction products formed. In a third step, 3-D maps of the reactant and product molecules within the crystal are visualized with Coherent Anti-Stokes Raman Scattering (CARS) and confocal fluorescence microscopy. Finally, in situ Scanning Transmission X-ray Microscopy has been used to reveal spatial heterogeneities at the nanoscale. We have shown the capabilities of this multi-technique approach by using the styrene oligomerization as probe reaction for mapping Brønsted acidity in H-ZSM-5 crystals. Furthermore, we have extended this methodology to study the effect of mesoporosity in H-ZSM-5 crystals on their reactivity in the oligomerisation of styrene as well as in the methanol-to-hydrocarbon, revealing interesting coke formation patterns.
W10: Porous Media and Disordered Systems
Session Chairs
Friday PM, April 09, 2010
Room 3004 (Moscone West)
2:30 PM - W10.1
Understanding the Correlation Between Pore Structure and Electronic Properties in Nanoporous Materials.
Anthony van Buuren 1 , Juergen Biener 1 , Jonathan Lee 1 , Trevor Willey 1 , Sergei Kucheyev 1 , Joerg Weissmueller 2 , Arne Wittstock 3 , Marcus Baeumer 3 , Jan Ilavsky 4 , Alex Hamza 1
1 Physics and Life Sciences, LLNL, Livermore, California, United States, 2 , Forschungszentrum Karlsruhe, Inst Nanotechnol, Karlsruhe Germany, 3 , Inst Angew & Phys Chem,, Germany, Bremen Germany, 4 Advanced Photon Source, Argonne National Laboratory, Argonne , Illinois, United States
Show AbstractUnderstanding how the pore structure and electronic properties evolve as the surface chemistry is manipulated is one of the fundamental questions in designing new porous materials for energy storage. In many cases unique properties are observed in nanoporous materials as the surface chemistry and density are manipulated. For example, charge-transfer induced changes of the surface stress can trigger macroscopic and reversible strain effects in nanoporous carbon in electrochemical environments. How porous materials react under such conditions has been examined in-situ with a combination of small-angle x-ray scattering (SAXS), x-ray adsorption (XAS) and high resolution synchrotron-radiation-computed tomography (SRCT). Unexpected changes in the pore structure and electronic properties of carbon and metal oxide aerogels are observed as a function of change in both density and surface environment. We find that in low density nanoporous materials the correlation range (or distance between ligaments) scales inversely with density until a critical value is reached below which the density decreases with no corresponding change in correlation range. X-ray and neutron scattering results show that bellow the critical density the nanoporous structure remain constant and the decreased density is obtained by the formation of large ~ 1000nm voids. This critical structure may prove to be a key in understanding the minimum density possible in nanoporous materials. Although a great amount of study has been devoted to the physical properties of porous structures, it is not clear whether the theoretical models developed to date can be extended to nanoscopic length scales. Input from both SAXS and SRCT have been used to generate microstructural models of the foams for analysis with finite-element modeling in order to understand the critical density. We have also used XAS and SAXS to determine how the electronic and pore structure of nanoporous materials change when exposed to various gases. We correlate these results to changes in the surface stress determined by measuring macroscopic volume changes. Using these tools, we will address correlations between surface electronic structures, pore structure and compare these findings with macroscopically measurable properties such as capacity.
2:45 PM - **W10.2
Using the Pair-Distribution-Function Approach to Study Materials in-situ.
Peter Chupas 1 , Karena Chapman 1
1 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractMaterials scientists have recognized the utility and benefit of producing-nanoscale materials as a means to enhance their functionality (for example in battery materials). A perpetual challenge that continues to hinder our understanding of why certain physical properties (eg. catalytic behavior) change dramatically for many materials as their particle sizes are reduced into the nano length-scale, is the lack of good methods to characterize structure with atomic resolution. This is particularly true with respect to understanding the structure of nano-materials under the conditions which they operate. We have been developing capabilities that allow the atomic-resolution structure of nano-materials to be probed in-situ using the Pair-Distribution-Function (PDF) method. The Pair-Distribution-Function (PDF) method utilizes high-energy X-rays to recover structural information of disordered materials and is particularly advantageous in studying local structure (<2nm). This talk will cover our recent work using the PDF method to study chemical reactions in-situ, specifically targeting observing the structural changes that occur to catalytic materials under operation conditions.
3:15 PM - W10.3
Determination of the Shape and Dimensions of Interconnected Nanoparticle Aggregate Structures in Phase-segregated Microstructures.
Charles Capozzi 1 , Runqing Ou 1 , C. Aaron Parker 1 , Rosario Gerhardt 1 , Jan Ilavsky 2 , Lyle Levine 3 , Gabrielle Long 2
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 X-Ray Division, Advanced Photon Source, Argonne National Labs, Argonne, Illinois, United States, 3 , National Institute for Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractUSAXS and stereology measurements were used to determine the dimensions of nanoparticle aggregate structures in polymer-matrix composite systems that form percolating phase-segregated networks. The samples investigated contained polymethylmethacrylate (PMMA) as the matrix phase and indium tin oxide (ITO) or carbon black (CB) nanoparticles as the filler phase. These specimens have been shown to percolate at compositions with <0.5 vol% filler.1-4 USAXS imaging2 and transmission optical microscopy1,3,4 were previously used to demonstrate the presence of the percolating networks in the opaque CB-filled PMMA composites and the transparent ITO-filled PMMA composites, respectively. In this paper, we report on the analysis of ultra-small angle x-ray scattering intensity curves (USAXS) used for determining the diameter of the filler aggregate-wire structures. Percolation does not occur until the nanoparticles aggregate into 3-dimensionally interconnected micron sized wires. Therefore, the unified rod model was applied to model the USAXS scattering data below and near the percolation threshold. The USAXS information was combined with stereological measurements of the edge lengths of the deformed PMMA particles to estimate the volume fraction of fillers necessary to promote percolating networks in these materials. Additionally, it is shown that at compositions above the percolation threshold, a transition from interconnected 1-D wires into interconnected 2-D sheets occurs. ________________*To whom correspondence should be addressed:
[email protected]**This work was funded by NSF under DMR-06042111. R. Ou, S. Gupta, C.A. Parker and R.A. Gerhardt, “Fabrication and Electrical Conductivity of PMMA/CB composites: Comparison between an ordered carbon black-nanowire segregated structure and a randomly dispersed carbon black nanostructure” J. Phys.Chem. B 110[45], 22362-22370(2006). 2.L.E. Levine, G.G. Long, R.A. Gerhardt, R. Ou, J. Ilavsky and C.A. Parker, “Self-Assembly of Carbon Black into Nanowires that Form an Interconnected 3-Dimensional Micro-network,” Applied Phys. Lett 90, 014101(2007).3.C.J. Capozzi and R.A. Gerhardt, “Novel Percolation Mechanism in PMMA matrix composites containing segregated ITO nanowire networks,” Adv .Functional Matls. 17, 2515-2521(2007).4. C.J. Capozzi, Zhi Li, R.A. Gerhardt and R.J. Samuels, “Impedance Spectroscopy and Optical Properties of polymethylmethacrylate/indium tin oxide Nanocomposites with 3-dimensional Voronoi Microstructures, j. Applied Physics 104(11), 114902/1-114902/10 (2008).
3:30 PM - W10.4
Pressure-induced Pore Modification and Amorphization in a Metal-organic Framework.
Karena Chapman 1 , Gregory Halder 2 , Peter Chupas 1
1 X-ray Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Material Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractPorous materials are a cornerstone of modern chemical industry involved in storage, separations, and catalysis spanning petroleum cracking to waste sequestration. Metal-organic frameworks (MOFs), an emerging class of crystalline solid, hold promise as the next generation of porous materials. Their more diverse, expanded components allow unsurpassed porosities, internal surface areas, and structural and chemical versatility. These characteristics, which make nanoporous MOFs so apt for advanced applications, also impact correlated physical properties that must be thoroughly understood before MOFs can supersede current materials technologies. The highly porous (i.e., low density) MOF structures are extremely flexible/compressible, with considerable sensitivity to applied force. With the functional properties of MOFs often being disproportionately responsive to subtle structural changes, MOF functionalities are likely to be strongly pressure dependent. Pressure-induced changes in pore geometry will strongly affect sorption selectivity, sorption capacity, and access to binding sites. As such, exploring the pressure-dependence of MOF functionality is pivotal to the realization of new MOF-based technologies.Here we investigate the impact of modest, industrially accessible pressures (~1 GPa) on the structure and porosity of Zn(2-methylimidazole)2 (ZIF-8), a MOF now sold as a high-surface-area catalyst. Using synchrotron-based in-situ powder diffraction, the framework was found to be highly compressible with an irreversible transition to a nanoporous amorphous phase at extremely low pressure. Importantly, this pressure-modification is effective at lower pressures than in zeolites and, as such, is easily scalable and industrially relevant.
3:45 PM - W10.5
Correlating Small Angle Scattering Spectra to Electrical Resistivity Changes in a Nickel-base Superalloy.
Ricky Whelchel 1 , V. Kumar S.K. Kelekanjeri 1 , Rosario Gerhardt 1 , Jan Ilavsky 3 , Ken Littrell 2
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 X-Ray Operations, Argonne National Laboratory, Argonne, Illinois, United States, 2 HFIR, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractWaspaloy is an age-hardenable nickel-base superalloy utilized in hot section components of gas turbine engines. Waspaloy possesses excellent high temperature mechanical properties, as a result of the formation of γ’ precipitate phases, via heat treatment. However, the nanosized γ’ precipitates are known to evolve upon long term in-service thermal exposure, thus creating the need for accurate non-destructive evaluation techniques that could be used to track the evolving microstructure. Small angle scattering (SAS) is being used as a method to quantify the precipitate size population and thus provide a link between the non-destructive resistivity measurements and the precipitate size populations present in the alloys. The microstructure of the samples are also characterized via SEM and AFM for comparison.Waspaloy samples were aged at 725, 800, and 875°C for times ranging from 0.5 to 263.5hr, after a common solution treatment at 1145°C. Modeling of ultra small angle X-ray scattering (USAXS) and small angle neutron scattering (SANS) data acquired were performed to obtain the γ’ particle size distributions (PSD’s). The analysis of the SAS spectra revealed bimodal distributions of precipitates in some cases. Examination of the primary precipitate population as a function of time at each aging temperature showed the expected t1/3 temporal power law associated with coarsening.The PSD’s were used to create an empirical figure of merit of electron scattering intended to correlate electrical resistivity changes with the evolving precipitate microstructure induced via heat treatment. This figure of merit has two terms: one involving electron scattering from precipitates (ηg) and another involving electron scattering from solute atoms (ηc). Due to the nature of the precipitation process, ηg is the dominant term at short aging times when the precipitates are small and closely spaced. Conversely, at long aging times, ηc is the dominant term due to significant precipitate phase solute removal.The figure of merit was found to show a direct correlation with the electrical resistivity measurements, suggesting that the proposed figure of merit is a good indicator of the effects of precipitation on the electrical properties in Waspaloy. Since both electrical and mechanical properties in precipitation hardened materials are dependent on the precipitate microstructure, it is believed that the proposed figure of merit could be used to correlate mechanical and electrical properties in age hardened Waspaloy. Such a correlation would have implications towards non-destructive testing and lifetime prediction in gas turbine engine components. This work was funded by the U.S. Department of Energy under DE-FG-02-03-ER 46035.