Symposium Organizers
Enrico Traversa University of Rome Tor Vergata
Timothy Armstrong Carpenter Technology Corporation
Koichi Eguchi Kyoto University
M. Rosa Palacin Institut de Ciencia de Materials de Barcelona (CSIC)
S1: Micro SOFCs: From Materials to Devices
Session Chairs
Tim Armstrong
Enrico Traversa
Monday PM, December 01, 2008
Back Bay A (Sheraton)
9:30 AM - **S1.1
Investigation of Cathode Behavior of Model Thin Film SrTi1-xFexO3-δ Mixed Ionic-Electronic Conducting Electrodes.
Harry Tuller 1 , WooChul Jung 1
1 Materials Science & Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractThe defect structure, transport properties and band structure of the perovskite solid solution SrTi1-xFexO3-δ(STF) have recently been refined and reported1. Of particular interest is the ability to systematically increase both the electronic and ionic conductivity, over orders of magnitude, by increase of the Fe fraction on the Ti site. This suggests that STF may serve as a model cathode material, given the ability to systematically vary levels of mixed ionic-electronic conductivity in the system by control of x. STF cathodes, with compositions x = 0.05 to 1, prepared as dense films by pulsed layer deposition (PLD) were therefore investigated by electrochemical impedance spectroscopy (EIS) as a function of electrode geometry, temperature and oxygen partial pressure. The STF cathode was observed to exhibit typical mixed ionic-electronic behavior with the electrode reaction occurring over the full electrode surface area rather than being limited to the triple phase boundary. The electrode impedance was observed to be independent of electrode thickness and inversely proportional to the square of the electrode diameter pointing to surface exchange limited kinetics. Furthermore, a GDC interlayer was found to have no effect on the electrode impedance. Values for the surface exchange coefficient, κ, were calculated and found to be comparable in magnitude to those exhibited by other popular mixed ionic-electronic conductors such as (La,Sr)(Co,Fe)O3, thereby, confirming the suitability of STF as a model mixed conducting cathode material. The observed trends are discussed in relation to the known defect and transport properties of STF._____1. A. Rothschild, W. Menesklou, H. L. Tuller, and E. Ivers-Tiffee, Chem. Mater., 18, 3651 (2006).
10:00 AM - S1.2
Local Electronic Structure and Surface Chemistry of Solid Oxide Fuel Cell Cathodes.
Bilge Yildiz 1 , Burc Misirlioglu 1 , Richard Schalek 2 , Balasubramaniam Kavaipatti 3 , Paul Salvador 3
1 Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Center for Nanoscale Systems, Harvard University, Cambridge, Massachusetts, United States, 3 Materials Science and Engineering, Carnegie Mellon University, Pittsburgh,, Pennsylvania, United States
Show AbstractSurface structure has a major role on the electrocatalytic activity of the solid oxide fuel cell (SOFC) cathodes. We are investigating the correlations of the crystallographic structure, cation composition, and lattice strain to the electronic structure, defect chemistry, and electronic and ionic transport characteristics of cathode surfaces. The understanding and tailoring of the activity at the “inhomogeneities” on the surfaces, namely grain boundaries and surface segregates, is important for our research.We are employing variable tempearture Scanning Tunneling Microscopy and Spectroscopy (STM/STS) to probe the localized topological and electronic properties at the nanoscale confined features and inhomogeneities on the cathode surfaces. We correlate the surface structure and electronic properties found by STM/STS to electrocatalytic activity using electrochemical characterization and Auger electron nano-spectroscopy. Our prototype cathode structures include the epitaxial single crystal and textured polycrystalline dense thin-films in the presence of nano-scale grain boundaries. The dense thin film cathode samples consisted of 10-200 nm thick La0.7Sr0.3MnO3 (LSM) and La0.7Sr0.3CoO3 (LSC) on single crystal yttria stabilized zirconia and 0.7% Nb-SrTiO3 substrates.We found that an in-plane retexturing of the dense thin film cathodes in the form of small rectangular islands has occurred upon electrochemical treatment at 300 mA/cm2 and 800C. The restructuring can be related to the preferential stabilization of an in-plane crystallographic epitaxy domain that LSM and LSC can form on the YSZ upon high-temperature treatment. Furthermore, we observed that fine segregate particles of few-nm size exist on the surfaces of the 100nm LSM film. These fine segregates can be related to the cation enrichment that we identified upon depth profiling with Auger Electron Spectroscopy.We found that the Fermi-level tunneling conductance of the surfaces exhibited thickness dependence. The thin 10-50 nm LSM films have zero near-Fermi level tunneling conductance with an electronic band-gap of 1.5-2.2 V, while the thick 100 nm LSM displays a large spread in the number of surface sites with dI/dV greater than zero. We expect that the 100 nm thick LSM have higher activity due to more available electronic states to exchange electrons with oxygen on its surface. Non-zero tunneling conductance on the 100nm-LSM film can be a consequence of more favorable relaxation of the local and overall strain states. Electrochemical activity of these electrodes ranked consistently with the findings from the STM/STS analysis. Increasing the temperature upto 680K have shown a spread of band-gap values on the surface, with a fixed conduction band lower level and varying valance band and Fermi level, with a more semiconductor-like behavior at 680K and 10-8 bar. We will continue to probe the evolution of spatially localized surface structure and electronic behavior on SOFC cathodes upto 1100K.
10:15 AM - S1.3
In situ Characterization of Equilibrium Strontium Surface Segregation in Epitaxial La0.7Sr0.3MnO3 at Solid Oxide Fuel Cell Conditions.
Tim Fister 1 , Matthew Highland 1 , Marie-Ingrid Richard 1 , Dillon Fong 1 , Jeffrey Eastman 1 , Peter Baldo 1 , Paul Fuoss 1 , Kavaipatti Balasubramaniam 2 , Joanna Meador 2 , Paul Salvador 2
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractLa1-xSrxMnO3 (LSMO) is a widely used cathode material in solid oxide fuel cells (SOFCs) because of its excellent catalytic properties, good electronic conductivity, and chemical stability at high temperatures. In each case, the relevant properties depend on the interplay between the strontium concentration, the manganese charge state, and oxygen nonstoichiometry. Surface composition is particularly important in controlling both the catalytic and transport properties of LSMO thin films and heterostructures, but previous studies have only probed nonequilibrium states far from typical SOFC operating conditions. We employ in situ synchrotron measurements of total reflection x-ray fluorescence to monitor the behavior of (001)-oriented La0.7Sr0.3MnO3 thin film surfaces under a wide range of temperatures (25-900°C) and oxygen partial pressures (pO2 = 0.15-150 Torr). The strontium surface concentration is observed to increase with decreasing pO2 at all measured temperatures, suggesting that the surface oxygen vacancy concentration plays a significant role in controlling the degree of segregation; in contrast, La0.7Sr0.3MnO3 film thickness and epitaxial strain state display little impact on segregation behavior. Interestingly, the enthalpy of segregation becomes less exothermic with increasing pO2, varying from -9.5 to -2.0 kJ/mol over the range of measured conditions. We also observe that the surface strontium enrichment persists in LaMnO3-capped LSMO thin films, suggesting that the segregation occurs during the growth process, possibly driven by the requirement of providing charge compensation of the polar LaMnO3 surface. Using these results, we discuss the impact of surface polarity and point defect chemistry on the performance of solid oxide fuel cells.This work is supported by the U.S. Department of Energy (DOE) Strategic Energy Conversion Alliance (SECA) program, and at Argonne by DOE under contract DE-AC02-06CH11357.
10:30 AM - S1.4
Application of Nanoscaled LSC Thin Film Cathodes in SOFCs: FEM Modelling and Experimental Verification.
Jan Hayd 1 , Ellen Ivers-Tiffee 1 , Bernd Rueger 1 , Uwe Guntow 2
1 Institute of Materials for Electrical Engineering (IWE) , Universität Karlsruhe (TH), Karlsruhe Germany, 2 , Fraunhofer-Institut für Silicatforschung, Würzburg Germany
Show Abstract10:45 AM - S1.5
Oxygen Exchange Kinetics of Epitaxial PrBaCo2O5+x and LaBaCo2O5+x Thin Films.
Xuening Jiang 1 , Shuangyan Wang 1 , Guntae Kim 1 , Jian Liu 2 , M. Liu 2 , Wenquan Gong 1 , Chonglin Chen 2 , Allan Jacobson 1
1 Chemistry, University of Houston, Houston, Texas, United States, 2 Physics, University of Texas at San Antonio, San Antonio, Texas, United States
Show AbstractReducing the operating temperature of solid oxide fuel cells from 1000 oC to intermediate temperatures (IT, 500-700 oC) has been a research focus in recent years. At ITs, cathode polarization of conventional (La,Sr)MnO3 becomes prohibitively large, therefore, cathode materials with faster oxygen transport and exchange kinetics are desired. Oxygen-deficient double perovskite with mixed oxygen ionic-electronic conductivities are promising cathode materials for use with ceria based electrolytes. In our work, we prepared dense epitaxial PrBaCo2O5+x (PBCO) and LaBaCo2O5+x (LBCO) thin films on SrTiO3 (STO) and LaAlO3 (LAO) single crystalline substrates by Pulsed Laser Deposition (PLD). The rocking curve measurements indicated an excellent epitaxial nature for these films. The oxygen exchange kinetics of PBCO and LBCO thin films have been determined by electrical conductivity relaxation (ECR). Surface oxygen exchange coefficients and/or bulk oxygen diffusion coefficients were obtained by fitting the ECR profiles. The results for PBCO and LBCO thin films will be compared.
11:00 AM - S1:mSOFCs
BREAK
11:30 AM - **S1.6
Micro-Solid Oxide Fuel Cells: From Thin Films to Power Delivering Membranes.
Jennifer L.M. Rupp 1 , Anja Bieberle-Huetter 1 , Anna Evans 1 , Henning Galinski 1 , Ashley Harvey 1 , Thomas Ryll 1 , Barbara Scherrer 1 , Rene Tolke 1 , Ludwig Gauckler 1
1 Nonmetallic Inorganic Materials, ETH Zurich, Zurich Switzerland
Show Abstract12:00 PM - S1.7
Deposition of a Proton Conductive Oxide Thin Film on a Porous Stainless Steel Substrate using Liquid Delivery MOCVD.
Kiyoshi Uchiyama 1 , Hiroyuki Sakairi 1 , Hiroshi Ichise 1 , Gakuko Lin 1 , Tadashi Shiosaki 1 , Hiroki Ikeda 2 , Katsu Yanagimoto 2 , Akira Nakayama 3 4 , Yoji Yamada 3
1 School of Materials Science, Nara Institute of Science and Technology, Ikoma, Nara, Japan, 2 , Sanyo Special Steel, Himeji Japan, 3 , Ion Engineering Research Institute, Hirakata Japan, 4 , Osaka Scienece & Technology Center, Osaka Japan
Show AbstractSolid oxide fuel cells (SOFCs) are considered to be one of the solutions for future alternative energy sources of automobiles and home electricity. However, one of the issues for enlarging their applications is reducing their operating temperatures. Generally, they need about 800°C for and it is too high to use general metallic materials, i.e. stainless steel, as their components. As a result, device costs of SOFCs become too expensive to use for consumer applications. In 2004, one solution for reducing operating temperatures was proposed by Toyota Motor Corp. In their new SOFC, they adopted a proton conductive oxide, i.e. doped-BaCeO3, as an electrolyte which operates as low as 500°C. In addition, this kind of SOFCs brings other benefit. In this configuration, the water vapor is generated in the air side and no mixing of the water and hydrogen occurred in a fuel gas. This makes an SOFC device structure much simpler and reducing a device cost. However, this proton conductive type SOFC still has some issues for realizing actual SOFC applications. One of the issues is reducing the electrolyte resistibility. The proton conductive material has about 10-2-10-4S/cm and it is said at least 10-1S/cm is required for the SOFCs. The second issue is what kind of materials are suitable as an electrode. In the Toyota’s SOFC, they used 100μm-thick Pd as a bottom electrode. They needed 100μm thickness for Pd because it also acts as a supporting material of the MEA (Membrane Electrode Assembly) itself. However, the use of 100μm-thick Pd results in higher SOFC costs. In order to solve these issues, we proposed a new MEA structure with proton conductive thin films on a porous stainless steel substrate. A proton conductive films as thin as 200nm brings a lower resistibility of the electrolyte and the use of porous stainless steel as a substrate also solves cost issues. However, it was quite difficult to deposit such kind of thinner oxide films on the porous stainless steels. Sol-gel and sputtering could not fabricate fine films and only MOCVD could fabricate dense and defect-less oxide thin films. The films do not show leaky properties for gases at all. In this paper, we will describe the deposition conditions and film properties in detail. Acknowledgements: This work was supported by the Japan Science and Technology Agency (JST) and the Foundation for NAIST. We also thank to ADEKA Corp. for providing MOCVD precursors.
12:15 PM - S1.8
Microstructure and Electrochemical Properties of Epitaxial Samarium Doped Ceria (SDC)-SrTiO3 (STO) Buffered-MgO Films by Pulsed Laser Deposition.
Simone Sanna 1 2 , Vincenzo Esposito 1 , Silvia Licoccia 1 , Giuseppe Balestrino 2 , Enrico Traversa 1
1 NAST Center & Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata, Rome Italy, 2 INFM – CNR Coherentia and Dipartimento di Ingegneria Meccanica, Università di Roma Tor Vergata, Rome Italy
Show AbstractSolid oxide fuel cells (SOFCs) can be miniaturized for portable applications (micro-SOFCs) leading to energy power density 4-times larger then the state-of-the-art batteries. This needs the reduction of the operative temperature and therefore the development of materials in thin-film form. Samarium oxide doped ceria (SDC) has much interest as electrolyte for IT-SOFCs due to its high-ionic conductivity compared to other conventional materials such as yttria stabilized zirconia (YSZ). In the relevant literature, many works are reported about gadolinium doped ceria (GDC) and SDC grown by pulsed laser deposition (PLD) on several perovskite substrates such as SrTiO3 (STO) providing a good lattice match for the fluorite structure of ceria. However, STO substrates are not stable at high temperatures and might show electronic conduction at temperatures above 300 °C.In this work, samarium oxide 20%-doped ceria, and STO thin films were grown by pulsed-laser deposition (PLD) on single crystal (001) MgO substrates. The STO thin film was used as buffer layer to provide the proper crystalline match to grow epitaxial SDC fluorite on the (001) MgO. The prepared thin films were analyzed by X-ray diffraction (XRD). Microstructures and geometrical features of the SDC/STO on (001) MgO layered system were observed by Field Emission Scanning Electron Microscopy (FE-SEM). SDC film thickness was around 250 nm and it resulted (001) mono-oriented and grain-boundary-free. Finger-type Au electrodes were deposited on the SDC surface at a distance of about 2 mm. Electrochemical impedance spectroscopy (EIS) measurements showed large ionic conductivity and no interfacial blocking effects. Ionic and electronic conductivity were separated by varying the oxygen partial pressure (pO2) in the 10-25 to 1 atm range at several temperatures (400-700 °C). SDC/STO films on (100) MgO showed dominant ionic conductivity up to pO2 ≈10-15 atm with ionic conductivity around 5 10-2 S cm-1 at 600 °C. The very low electronic conductivity demonstrated the lack of electronic contribution given by the STO buffer layer.
12:30 PM - S1.9
Sol-gel and PLD Preparation of Lanthanum Gallate-based Mixed Ionic-electronic Conducting Oxides.
Natalia Golubko 2 , Galina Kaleva 2 , Yuliana Roginskaya 2 , Sergey Kabanov 2 , Alexander Avetisov 2 , Gunnar Suchaneck 1 , Ekaterina Politova 2
2 , L.Y.Karpov Institute of Physical Chemistry, Moscow Russian Federation, 1 Solid State Electronics Lab, TU Dresden, Dresden Germany
Show Abstract12:45 PM - S1.10
Enhanced Oxide Ion Conductivity at (Y2O3)x(ZrO2)1-x /SrTiO3 Ultra Thin-Film Epitaxial Heterostructures.
Javier Garcia-Barriocanal 1 , Alberto Rivera-Calzada 1 , Maria Varela 3 , Zouhair Sefrioui 1 , Enrique Iborra 2 , Carlos Leon 1 , Steve Pennycook 3 , Jacobo Santamaria 1
1 Dpto. Fisica Aplicada III, Universidad Complutense Madrid, Madrid Spain, 3 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Escuela Técnica Superior de Ingenieros de Telecomunicaciones, Universidad Politécnica de Madrid, Madrid Spain
Show AbstractIt has been recently reported a systematic increase of the oxide ion conductivity in thin films of yttria stabilized zirconia (Y2O3)x(ZrO2)1-x (YSZ) when decreasing their thickness below 60 nm down to 15nm [1]. These results could be explained by assuming that the oxide ion conductivity is several orders of magnitude higher at the interface between the substrate and the YSZ thin film than for bulk YSZ. In order to test this attractive scenario of a highly oxygen conducting interfacial plane, we have grown heterostructures where ultra thin YSZ layers (with 8 %mol nominal yttria content) of thickness down to 1 nm, were sandwiched between two layers of insulating SrTiO3 (STO) 10 nm thick. Also, superlattices were grown alternating the same thickness of YSZ and STO as in the trilayers. YSZ and STO layers were grown on STO (100) substrates in a high pressure (3 mbar) pure oxygen RF sputtering system. High pressure and high substrate temperature (900 °C) ensures a slow (1 nm/min) and highly thermalized growth of complex oxides providing excellent epitaxial properties [2, 3]. The structural characterization by XRD and STEM has evidenced the high quality of our epitaxial heterostructures, and that the interfaces between YSZ and STO layers are continuous and atomically flat over long lateral distances (a few microns). Lateral electrical conductivity measurements show an enhanced oxygen conductivity in ultra thin film heterostructures, which for 1 nm thick YSZ layers is found to be as high as 0.014 S/cm at 357 K (about eight orders of magnitude higher than that of bulk YSZ), with a substantial decrease of the activation energy for the dc ionic conductivity from 1.1 eV down to 0.64 eV. EELS analysis is consistent with a partial occupancy and high disorder in the interface oxygen plane between YSZ and STO layers, which would yield a large number of interfacial oxygen vacancies and simultaneously give rise to a decrease in the activation energy for oxygen migration. Thus, our results demonstrate that the observed high oxygen conductivity in ultra thin layers is a genuine interface process, and that the design of suitable heterogeneous interfaces in epitaxial heterostructures might have important implications in the search of artificial nanostructures with high ionic conductivity for application in solid oxide fuel cells or other technological devices.[1] I. Kosacki, C. M. Rouleau, P. F. Becher, J. Bentley, and D. H. Lowndes, Solid State Ionics 176, 1319 (2005).[2] M. Varela, W. Grogger, D. Arias, Z. Sefrioui, C. León, C. Ballesteros, K. M. Krishnan, and J. Santamaría, Phys. Rev. Lett. 86, 5156 (2001).[3] V. Peña, Z. Sefrioui, D. Arias, C. Leon, J. Santamaria, J. L. Martinez, S. G. E. te Velthuis, and A. Hoffmann, Phys. Rev. Lett. 94, 57002 (2005).
S2: Modelling and Fundamental Studies
Session Chairs
Monday PM, December 01, 2008
Back Bay A (Sheraton)
2:30 PM - **S2.1
Solid State NMR Studies of Lanthanum Gallate Solid Electrolytes: Ion Mobility and Trapped Defects.
Frederic Blanc 1 , John Palumbo 1 , Clare Grey 1
1 Chemistry, Stony Brook University, Stony Brook , New York, United States
Show AbstractNew materials with improved ionic conductivity at moderate temperatures, and hence materials with higher numbers of mobile oxygen-ion vacancies O2- (the charge carriers), are required in order to lower the operating temperature of a solid oxide fuel cell (SOFC). Often dopant ions Mn+ are substituted for higher valent ions, M(n+1)+ or M(n+2)+ in order to create these vacancies. Typically, the dopant sits on a normal crystallographic site, so it is not straighforward to distinguish between the mobility near the dopant and near the normal site using diffraction techniques. To date, the electrolyte of choice for SOFC is yttrium stabilized zirconia (YSZ). However, lanthanum gallate compounds are under consideration for their lower operating temperature and better ionic conductivities. Lanthanum gallate, LaGaO3, adopts the perovskite structure ABO3 and can accommodate a wide range of dopants on both the A and B sites to induce vacancies. In particular, the combination of Sr2+ doping on the La3+ (A) site and Mg2+ doping on the Ga3+ (B) site (thereafter named LSGM) has been shown to result in the highest increase in ionic conductivity in the series, the conductivity for La0.9Sr0.1Ga0.9Mg0.1O2.9 (0.1 S.cm-1 at 800 °C) being approximately an order of magnitude higher at similar temperatures than that achieved with only either Mg2+ or Sr2+ doping (T. Ishihara et al. J. Am. Chem. Soc. 1994, 116, 3801-3803 and Solid State Ionics 1995, 79, 147-151). Clearly the vacancies cannot be observed directly by Nuclear Magnetic Resoance (NMR) spectroscopy. However, it is possible to identify the cation sites with lower coordination environments than those of the bulk. We, therefore, use a combination of different NMR experiments involving various nuclei such as 139La, 69/71Ga, 25Mg and 17O NMR to examine the local structures in these materials. 69/71Ga is a relatively straightforward (I = 3/2) nucleus to study by NMR and like 27Al, its chemical shift correlates with coordination number (T. J. Bastow et al. Solid State Ionics 2004, 175, 129-133 and D. Massiot et al. Solid State NMR 1995, 4, 241-248) and lineshapes analysis which will give insight into the presence of vacancies. These experiments are performed in parallel with 25Mg NMR. This (I = 5/2) nucleus has a quadrupole moment that is similar to that of 27Al, its disadvantages being its low natural abundance (10 %) and its low gyromagnetic ratio. Nonetheless, a series of recent experiments have identified the chemical shift ranges for this nucleus and have shown that typical quadrupole coupling constants are not prohibitive. Multiple Quantum Magic Angle Spinning (MQMAS, L. Frydman and J.S. Harwood J. Am. Chem. Soc. 1995, 117, 5367-5368 and A. Medek et al. J. Am. Chem. Soc. 1995, 117, 12779-12787) and Satellite Transition Magic Angle Spinning (STMAS, S.E. Ashbrook and S. Wimperis P. Nucl. Mag. Res. 2004, 45, 53-108) NMR will be used, where necessary, to help separate the signals from the different coordinate environments. 17O Magic Angle Spinning (MAS) NMR (including MQMAS and others techniques) on 17O-enriched samples are used to identify the Ga-O-Ga and Ga-O-Mg environments and probe the mobility.
3:00 PM - S2.2
Influence of the Chemical Strain Effect on the Lattice Parameter of Ce0.8Gd0.2O1.9.
Anna Kossoy 1 , Isai Feldman 2 , Roman Korobko 1 , Ellen Wachtel 2 , Joachim Maier 3 , Igor Lubomirsky 1
1 Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot Israel, 2 Department of Chemical Research Support, Weizmann Institute of Science, Rehovot Israel, 3 , Max Planck Institute for Solid State Research, Stuttgart Germany
Show AbstractStrong deviation from linear elasticity observed in thin films of Ce0.8Gd0.2O1.9 is attributed to the association/dissociation of point defects, presumably aliovalent ions and oxygen vacancies (so-called “chemical stain effect”). We investigated the kinetics and the magnitude of the chemical strain effect in substrate-supported and self-supported films of Ce0.8Gd0.2O1.9. The direct measurements of stress and strain in the substrate-supported films indicate that the “apparent” elastic modulus of these films is more than ten times lower than that measured in bulk ceramics, which matches our previous data obtained with self-supported films. By monitoring the rate of the chemical strain effect in substrate-supported and in self-supported films, it was found that the activation energy of the defect reaction responsible for the chemical strain effect is about 1 eV. In addition, on the basis of temperature-dependent XRD measurements, it was concluded that the complexes of the aliovalent ions and oxygen vacancies completely dissociate above 300 °C. From these data and from the strain-temperature dependence, it was determined that the formation of the aliovalent ion - oxygen vacancy complex is accompanied by volume increase (i.e. the volume effect of the complex formation is positive).Our findings may explain large discrepancies in the literature data on the lattice parameter of Ce0.8Gd0.2O1.9. Since, the time necessary to establish the defect equilibrium at room temperature is of the order of a few months, the “observable” lattice parameter may differ by a few tenths of a percent depending on the sample prehistory and preparation route.
3:15 PM - S2.3
First-Principles Study of ZrO2 – In2O3 Heterointerface Structure and Properties.
Hakim Iddir 1 , Peter Zapol 1 , Fong Dillon 1 , Paul Fuoss 1 , Jeffrey Eastman 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractOxide heterostructures of ZrO2 and In2O3 have potential for producing novel mixed conduction properties, since they exhibit ionic and electronic types of conductivity, respectively. Since these oxides exhibit poor solid miscibility and good epitaxial match, they can form nanostructured materials, which would be of interest for a wide range of applications, including solid oxide fuel cells. A first-principles study of ZrO2 – In2O3(001) interfaces is performed to identify the stable configurations under different oxygen and electron chemical potentials. Two different interfaces, each sharing a common oxygen plane, are considered for the (001) orientation: (1) a flat interface with two types of In atoms (8b and 24d) present at the interface, and (2) a buckled interface with one type of In atom (24d). We present results on the atomic and electronic structure of different interfaces as a function of oxygen partial pressure. Theoretical studies of oxygen vacancy diffusion at the interface have also been carried out, providing insight into the effects of interfacial proximity on optical and conduction properties. The results are compared with those from synchrotron x-ray scattering and transport measurements on sputter-deposited ZrO2 – In2O3 heterostructures. Finally, we discuss the impact of Y and Sn dopants in ZrO2 and In2O3, respectively, on interfacial segregation behavior and electrical transport. This work is supported by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357.
3:30 PM - S2.4
Examination of the LaFeO3 (010) Surface using Density Functional Theory and Thermodynamics.
Chan-Woo Lee 1 , Eric Wachsman 1 , Simon Phillpot 1 , Ram Devanathan 2 , Susan Sinnott 1
1 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractElectronic structure and thermodynamic calculations are combined to understand the stability of the LaFeO3 (010) surface, which is the base material of La1-xSrx CoyFe1-yO3 (LSCF), a potential candidate for solid oxide fuel cell (SOFC) cathodes. In particular, classical thermodynamics are combined with density functional theory calculations to predict a surface phase diagram of the LaFeO3 (010) plane of varying terminations. Specifically, the LaO3 -, LaO2 -, LaO -, La -, FeO3 -, FeO2 -, FeO - and Fe - terminations are considered. Preliminary calculations indicate that the FeO2 - and LaO2 - terminated surfaces are stable under typical operating conditions for SOFCs: PO2 ≈ 0.21 atm and T ≈ 900 – 1300 K. In addition, charge compensation mechanisms of the (010) plane with varying PO2 and T are investigated. The mechanisms of molecular oxygen adsorption and dissociation on the various terminations with and without intrinsic and extrinsic defects, are also examined.
3:45 PM - S2.5
Ab initio Thermokinetic Modeling of Defect Chemistry, Oxygen Transport, and Surface Oxygen Reduction Reactions for (La,Sr)MnO3 for Solid Oxide Fuel Cells.
Yueh-Lin Lee 1 , Dane Morgan 1
1 Materials Science Program, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractPerovskite (La,Sr)MnO3 (LSM) is the primary cathode catalyst used in commercial solid oxide fuel cells (SOFC). Essential to its use in SOFCs is the oxygen reduction reaction (ORR) on the surface and oxygen ion transport during operation. Ab initio based thermokinetic models are being developed to investigate bulk LSM defect chemistry, bulk vs. surface diffusivity, and surface ORR to understand the reaction mechanisms and rate-limiting steps. The bulk defect reaction energies and interactions have been calculated using density functional theory (DFT) for a wide range of defect species (e.g., antisites and vacancies). Our defect reaction results show that Sr and La antisite defects are unstable but that Mn antisites are quite low energy, and vacancy formation on the Mn sublattice is much easier than for the La sublattice. Defect interaction results reveal that the defects in this system are highly non-ideal, with nearest-neighbor repulsion and attraction energies as large as 1-2 eV. This suggests that non-ideal defect interactions will play a significant role in LSM defect behavior both thermodynamically (e.g. nonstoichiometry vs P (O2)) and kinetically (e.g. ionic transport), especially at low temperatures. We have explore the most stable {100} LSM surfaces, where vacancies are found to be stabilized by well over 1 eV compared to bulk, implying an enormous increase in vacancy content in near surface layers compared to bulk. Preliminary results using the an ideal solution defect model have demonstrated that near-surface transport can be ~106 times faster than the bulk, mediated by the higher vacancy content. The key energy terms that must be determined to model the surface ORR are the oxygen adsorption, O2 dissociation, surface vacancy, and oxygen hopping energies. These are difficult to determine experimentally and have been calculated directly by ab initio methods. Ab initio ORR energetics are being incorporated into the surface model to determine rates of LSM surface ORR processes vs. oxygen partial pressure and temperature.
4:30 PM - S2.6
First-principles and CALPHAD Thermodynamic Modeling of Defects in La1-xSrxCoO3-δ.
James Saal 1 , Mei Yang 1 , Venkateswara Rao Manga 1 , Zi-Kui Liu 1
1 Materials Science and Engineering, Penn State University, University Park, Pennsylvania, United States
Show AbstractThe perovskite La1-xSrxCoO3-δ (LSCO) has a unique range of properties that are strongly dependent on the temperature, oxygen partial pressure, and strontium content, which makes LSCO an important material in a range of applications, including fuel cells and gas sensors. To fully exploit the properties of LSCO, a comprehensive and quantitative description of its defects is necessary. Typically, thermodynamic models for the defects in ionic systems evaluate the parameters of the Gibbs free energy by fitting to experimental measurements of the defect concentrations. Such an approach reproduces the defect quantities but is not always capable of uniquely describing the thermodynamic properties of the material. We overcome this difficulty by incorporating first-principles calculations of LSCO. This allows the model to predict not only measurable quantities, such as the oxygen vacancy concentration δ, but also properties that are difficult to determine experimentally, such as the concentration of the valences of cobalt. The resulting model is able to describe the material as a function of temperature, oxygen partial pressure, and strontium content.This technology development has been supported in part by the U.S. Department of Energy under Contract No. DE-FC26-98FT40343. The Government reserves for itself and others acting on its behalf a royalty-free, nonexclusive, irrevocable, worldwide license for Governmental purposes to publish, distribute, translate, duplicate, exhibit and perform this copyrighted paper.
4:45 PM - S2.7
Computing Electrochemical Impedance of Solid Electrolyte from Fluctuations.
Eunseok Lee 1 , Wei Cai 1 , Fritz Prinz 1 2
1 Mechanical Engineering, Stanford University, Stanford, California, United States, 2 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractWe present a new method for computing the electrochemical impedance of solid electrolyte from kinetic Monte Carlo (kMC) simulations of the ionic diffusion. Using the fluctuation-dissipation theorem, the impedance at overall frequency can be obtained from the correlation function of microscopic current fluctuations through a single equilibrium simulation. In the conventional approach, the impedance at a given frequency has been obtained by a non-equilibrium kMC simulation subjected to an AC voltage at this frequency. Our fast method enables us to obtain the overall impedance and infer the governing mechanisms of ionic diffusion by decomposition of the impedances of materials into the impedances of basic chemical reactions. The effects of doping concentration and the doping distribution to the ionic diffusion in yttria-stabilized zirconia (YSZ) are discussed.
5:00 PM - S2.8
Thermodynamics and Kinetics of Conversion Reaction Cathodes from First Principles.
Robert Doe 1 , Kristin Persson 1 , Gerbrand Ceder 1
1 Dept. of Materials Science & Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show Abstract5:15 PM - S2.9
DFT-based Design of Orthosilicate-based Cathode Materials for Li Ion Batteries.
Anti Liivat 1 , Kinson Kam 1 , John Thomas 1
1 Materials Chemistry, Uppala University, Uppsala Sweden
Show AbstractSeveral lithium-rich materials with tetrahedrally or tetragonally coordinated ions are known to be good Li-ion conductors and have been studied as cathode materials for lithium ion batteries for almost three decades [1]. They typically contain the polyanion AO4n-, with covalent A-O bonds (for A=Al, Si, Ge and P), or involve redox-active Transition Metal (TM) atoms (for A=V, Ti, Cr and Mn). The structural stability of the polyanion matrix allows for a wide range of different cation compositions, with polymorphs having vacancy- or interstitialcy-driven Li-ion conductivity. Furthermore, these structures could give rise to dramatically improved energy density, if multi-electron redox-active TMs (such as Mn, V, Cr) could be embedded in the materials, and if the otherwise rather poor electron conductivity could be improved.It is known that the TM-ion redox potential varies with crystal structure; e.g., it is ca. 2.9 V for Fe in LiFeP2O7, but 3.5 V for Fe in LiFePO4. The redox potential also varies with the induction effect, originating from the covalency of the A-O bonds in the AO4n- polyanion [2]. Here, we used Density Functional Theory (DFT) to study the substitution of SiO44- polyanions in Li2MSiO4 (M=Fe, Mn) [3-6] with AO4n-, A=V,Ti, for the purpose of:i) lowering of the redox-potential for M=Mn systems; ii) enhancing electron transfer between the TM-ion and the polyanion;iii) introducing redox-active polyanions; especially in vanadate.Our calculations show that such substitutions lead to significant changes in the electronic structure and intercalation potentials of the host system. For example, in Li2FeVO4, besides a ca. 10% increase in unit-cell size, no major structural distortions could be observed. The delithiation starts with the oxidization of V4+ in VO44- to V5+ at a potential of 2.2 V, followed by the complete delithiation of the Li2FeVO4 host structure to FeVO4, with the Fe2+/Fe3+ oxidation occurring in the voltage range 3.1-3.5 V. Models involving the co-doping of Mn into Fe-sites are also investigated for systems containing VO44- and/or other polyanions. Furthermore, the insights from these calculations have been used in synthesis of such electrode materials. References1. A. D. Robertson, A. R. West and A. G. Ritchie, Solid State Ionics, 1, 104 (1997).2. A. K. Padhi, K. S. Nanjundaswamy, C. Masquelier, S. Okada, and J. B. Goodenough, J. Electrochem. Soc., 144, 1609 (1997). 3. A. Nytén, A. Abouimrane, M. Armand, T. Gustafsson, and J. O. Thomas. Electrochem. Commun., 7, 156 (2005).4. P. Larsson, R. Ahuja, A. Nytén, and J. O. Thomas, Electrochem. Commun., 8, 797 (2006).5. A. Nytén, S. Kamali, L. Häggström, T. Gustafsson, and J. O. Thomas. J. Mater. Chem., 16, 2266 (2006).6. A. Kokalj, R. Dominko, G. Mali, A. Meden, M. Gaberscek, and J. Jamnik. Chem. Mater., 19, 3633 (2007).
5:30 PM - S2.10
Polyatomic Anions as Mobile Species in Solid Electrolytes.
Stefan Adams 1 , Yongkai Zhou 1 , R. Prasada Rao 1 , Arkady Neiman 2 , Doreen Edwards 3
1 Mater. Science and Eng. , Nat. University of Singapore, Singapore Singapore, 2 Chemical Department, Ural State University, Ekaterinburg Russian Federation, 3 Inamori School of Engineering , Alfred University, Alfred, New York, United States
Show AbstractIon transport in solids has been observed for a limited number of structure types typically containing low-valent mobile ions. In contrast scandium tungstate has been reported as the prototype of a class of trivalent cation conductors. Here we reinvestigate ion transport in scandium (and related trivalent cation) tungstates to clarify the mobile species and the ion transport mechanism. Structural and electrochemical properties are monitored over an extended temperature range by Rietveld analysis of non-ambient XRD, impedance spectroscopy and electrolysis experiments. Results are interpreted with the help of molecular dynamics (MD) simulations and bond valence (BV) ion transport pathway modeling. XRD data for 11 – 1300 K were used to fine-tune a force-field. MD simulations this force-field qualitatively reproduce the structure variation, especially the negative thermal expansion and the pressure-dependant phase transition to a monoclinic phase. Isothermal-isobaric MD simulations as well as constant volume MD simulations for fully ordered, initially defect-free Sc2(WO4)3 structure models containing 1224 atoms show that ion transport starts with a high energy Frenkel defect creation, where an entire WO42- group hops into a neighboring interstitial site leaving a vacancy behind. This triggers a chain of WO42- hops, which due to the limited size of the structure models ends in translation copies of the initially created vacancy. Thereby the activation energy for diffusion in the simulation significantly exceeds the experimentally observed value of 45kJ/mol for T > 1100K. In reality defects are probably created during sample preparation, i.e. the defect concentration is fixed extrinsically throughout the temperature range studied. The increase of activation energy to 65kJ/mol for T<800K may then be tentatively ascribed to defect association. This is consistent with further MD simulations, where a WO42- defect is built into the initial model, leading to a close match of the simulated and experimental activation energies as well as absolute conductivities. No matter whether a Sc3+ and WO42- is introduced, no Sc3+ migration is observed in the simulations. Further evidence that anions rather than the previously assumed trivalent cations cause the ion transport stems from Tubandt-type electrolysis experiments, which show mass transfer from the anode pellet to the cathode pellet. Our earlier BV analyses of pathways for Sc3+, O2- or WO42- ions in time averaged structure models suggested that low energy diffusion pathways exist only for WO42-. Using series of instantaneous structure models from the MD simulations, a BV analysis of the transport pathway dynamics was achieved. WO42- hops between equilibrium sites closely follow the instantaneous diffusion pathways, except for the high energy defect creation. The individual tungstate transport step combines features of an intersticialcy mechanism with a unique rotation of the polyatomic anion.
5:45 PM - S2.11
Point Defect Mediated Cation Transport in MgAl2O4.
Samuel Murphy 1 , Blas Uberuaga 2 , Kurt Sickafus 2 , Roger Smith 3 , Robin Grimes 1
1 Materials, Imperial College London, London United Kingdom, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 Mathematical Sciences, Loughborough University, Loughborough United Kingdom
Show AbstractThe mechanisms by which Mg2+ and Al3+ ions are transported through the MgAl2O4 spinel lattice are investigated using atomic scale computer simulation. Both vacancy and interstitial cation processes are considered. Stable vacancies can be generated on either the magnesium or aluminium sublattices but the Mg2+ and Al3+ cation interstitials are most stable when incorporated into a split interstitial configuration along with another Mg2+ ion, centred about a vacant Mg2+ site. There are three principle factors which can affect transport of cation species in spinel, these are: (i) the concentration and hence availability of the mediating point defect, (ii) the activation energy for the isolated jump process and (iii) the diffusion prefactor, D0. The prefactor contains information such as the number of equivalent pathways, jump distances and the attempt frequency. Combining all of this information allows us to determinate the preferred mechanisms for cation transport in spinel. Our calculations have demonstrated the importance of considering the affects that antisite defects may have on both the availability of transport mediating point defects as well as the migration pathways themselves. We have also demonstrated that, in the case of spinel, the concentration and activation energies are the dominant factors in determining how cations diffuse.
S3: Poster Session: Batteries
Session Chairs
Tim Armstrong
Toshiaki Matsui
Rosa Palacin
Enrico Traversa
Tuesday AM, December 02, 2008
Exhibition Hall D (Hynes)
9:00 PM - S3.1
Silicon Cobalt Graphite Composite as the Anode Materials of Lithium Ion Secondary Batteries.
Jian Hong 1 , Stanley Whittingham 1
1 , State University of New York at Binghamton, Binghamton, New York, United States
Show Abstract Silicon is an attractive candidate for high-energy anode material for Li-ion batteries. Although the introduction of transition metal as buffer media could release some of the stain during the lithium ion intercalation and extraction into the silicon host, the extreme large volume change between the de-lithiated and fully lithiated states of silicon makes this kind of material unsuitable for industrial application at the current stage. The strain may be released by creating nano-composite materials such as silicon particles embedded completely and uniformly in the carbonaceous matrix. In this work, high-energy ball milling and carbon coating route to such structure are investigated.Si-Co-graphite composites were synthesized from nano-silicon, cobalt and graphite powders in a high-energy milling machine followed by heat treatment in N2 atmosphere. The products were characterized by x-ray diffraction (XRD) and scanning electron microscopy. The electrochemical properties were tested in 1M LiPF6 in EC/EMC (1:1) liquid electrolyte. The XRD data indicates diamond structure of the nano-silicon powder and poor crystallinity of the composite material. The initial cycle of the composite has large irreversible capacity, which may come from the formation of solid electrolyte interface (SEI). In the following cycles, the reversible capacity increased initially and then continuously decreased. After 50 cycles, the composite electrode has a reversible capacity of 350 mAh/g, which is half of initial one (~700 mAh/g). Possible reason for the degradation of cycle life is a poor attachment between the graphite matrix and silicon active material. The SEM image of the electrode after 50 cycles revealed cracks on the surface of about 0.5 mm width. Future effort will be focused on the improvement of the bonding strength between the nano-silicon and carbon matrix and on elimination of first-cycle irreversible capacity. This work is supported by the US Department of Energy, Office of FreedomCAR and Fuel Partnership through the BATT program at Lawrence Berkeley National Laboratory.
9:00 PM - S3.10
New Polymeric Electrolytes with Titanium Oxide as Inert Fillers Prepared by Sol-gel Technique.
Liliana Hechavarria 1 , Narcizo Mendoza 1 , Hailin Hu 1 , Jose Campos 1
1 Centro de Investigacion en Energia, Universidad Nacional Autonoma de Mexico, Temixco, Morelos, Mexico
Show AbstractTransparent and conductive polymeric gels have been prepared from polyethylen glycol (PEG), polyethylene oxide (PEO) or Pluronic F127 by incorporating titanium isopropoxide into the polymer matrixes with sol-gel method. The presence of titanium oxide compound and its interaction with the polymers were confirmed by FT-IR. Optical transmittance spectra of the polymeric gels were studied as a function of titanium isopropoxide percentage, as well as the molecular weight of each polymer. For the dye-sensitized solar cell (DSSC) or photoelectrochromic cell (PEC) application purpose, LiI was added into the polymeric gels to form polymeric gel electrolytes. The electrical conductivity of each electrolyte was measured by electrochemical impedance spectroscopy at a temperature interval from 0 to 80 C. To keep the transparency of the electrolytes, it is important to avoid the reduction of iodine by controlling the electrolyte preparation conditions. The increase of the electrical conductivity in the resulting polymeric gel electrolytes can be explained by a higher microscopic disorder or larger space between polymeric chains created by the titanium oxide compound in the original polymers, that leads to a faster ion transport.
9:00 PM - S3.11
Component Diffusion in the Miscible Polymer Blend of PEGDME and PMMA Doped with LiTFSI Measured by Multinuclear PFG NMR.
Yan Meng 1 , Luis Smith 1
1 Carlson School of Chemistry and Biochemistry, Clark University, Worcester, Massachusetts, United States
Show AbstractThe blending of miscible or compatible polymers based on available polymers is an attractive and economic alternative in the development of new materials rather than designing and synthesizing completely new polymers because of the energy, materials and time savings. When a miscible polymer blend in the solid state is formed by a rigid solid polymer and a liquid polymer, it can have relatively good mechanical strength, and at the same time the liquid component in it still has high mobility. Such a property can be utilized to develop solid polymer electrolytes with good performance for secondary lithium batteries. It has been reported that poly (vinyl methyl ether)/polystyrene (PVME/PS, 50/50 wt.) with PVME being a liquid at the temperature of measurement exhibits almost the same Li+ conductivity with that in pure liquid PVME [1]. To further explore the possibility of this kind of polymer blends being a good lithium electrolyte, some important questions urgently need to be answered. Specifically, while the liquid polymer is the carrier of Li+, what is the effect of the addition of lithium salts on the self-diffusion of the liquid polymer? How do the apparent self-diffusion coefficients (ADC) of Li+, TFSI- and PEGDME in the polymer blend change as a function of salt concentration and temperature? How does the ADC value of the liquid polymer change after it is blended with the other rigid polymer? In this work, these studies were done on the liquid polymer of poly (ethylene oxide), which has been the most representative and widely studied polymer for lithium polymer electrolytes. A novel solid state polymer electrolyte is prepared by doping poly (ethylene glycol) dimethyl ether / poly(methyl methacrylate) (PEGDME/PMMA, 40/60 wt.) with LiN(CF3SO2)2 (LiTFSI) at different concentrations. The effect of the addition of LiN(CF3SO2)2 (LiTFSI) at different concentrations on the self-diffusion of PEGDME is observed using Li7, F19 and H1 pulsed field gradient (PFG) NMR experiments at different temperature. The apparent self-diffusion coefficients (ADC) of Li+, TFSI- and PEGDME were measured, and were found to be in the range of 10e-9 to 10e-8 cm2/s at 60 degree C. For PEGDME in the same polymer blend without the lithium salt, ADC values of an order of magnitude greater were observed and are comparable with pure liquid PEGDME. The results show that the addition of lithium salts slows down the self-diffusion of PEGDME, but does not substantially limit diffusion, making this blend an interesting electrolyte candidate. [1] D. Cangialosi, A. Alegria, J. Colmenero. Macromolecules, 41, 1565-1569 (2008).
9:00 PM - S3.12
Atomistic Studies of Ionic Diffusion in Lithium Aluminosilicate.
Alexander Chroneos 1 2 , Hartmut Bracht 2 , Robin Grimes 1 , Andre Schirmeisen 3 , Bernhard Roling 4
1 Department of Materials, Imperial College London, London United Kingdom, 2 Institut für Materialphysik and Collaborative Research Centre (SFB 458), Westfälische Wilhelms-Universität Münster, Münster Germany, 3 Centre for Nanotechnology (CeNTech) and Collaborative Research Centre (SFB 458), Westfälische Wilhelms-Universität Münster, Münster Germany, 4 Fachbereich Chemie, Philipps-Universität Marburg, Marburg Germany
Show AbstractLithium aluminosilicate (LiAlSiO4) is a highly conductive solid electrolyte material and is technologically important due to its potential application in microlithium batteries. Importantly, crystalline LiAlSiO4 exhibits one-dimensional superionic conductivity as the lithium ions are transported in structural channels. In a recent study [Schirmeisen et al. Phys. Rev. Lett. 98, 225901 (2007)] it was determined that in a nanostructured LiAlSiO4 glass ceramic, the interfacial regions between the glass matrix and the embedded crystallites exhibit ionic conductivity that is orders of magnitude higher than that of the glass or the crystallites. In the present study, we use density functional theory calculations to predict the migration energy barriers for Li+ transport in LiAlSiO4. Atomistic simulation based in pair potentials is used to identify the mechanisms for the increased ionic conductivity observed at the interfaces between the glass and crystalline LiAlSiO4.
9:00 PM - S3.14
Synthesis of Mesoporous Manganese Oxide with a High Surface Area.
Akira Endo 1 , Bao Wang Lu 1 , Takao Ohmori 1 , Keigo Matsuda 2
1 Research Institute for Innovation in Sustainable Chemistry, National Institute of Advance Industrial Science and Techology (AIST), Tsukuba, Ibaraki, Japan, 2 Department of Chemistry and Chemical Engineering, Yamagata University, Yamagata, Yamagata, Japan
Show Abstract9:00 PM - S3.15
Transmission Electron Microscopy Observation of Li Extraction/insertion Behaviors in Li1.2Mn0.4Fe0.4O2 Positive Electrode Material for Li-ion Battery.
Jun Kikkawa 1 , Tomoki Akita 1 , Mitsuharu Tabuchi 1 , Masahiro Shikano 1 , Kuniaki Tatsumi 1 , Masanori Kohyama 1
1 Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka, Japan
Show AbstractThe electrochemical performance of Li-ion batteries depends on the extraction/insertion behaviors of Li ions in positive electrode materials during charge/discharge. Clarifying the distribution of Li ions in positive electrode materials at the nanometer or atomic scales is a crucial issue. Especially, real-space observations of the behaviors of Li ions are strongly demanded. In this study, we have achieved the ‘Li mapping’ of lithiated transition-metal oxides with spatial resolutions of about 1–2 nm, by using a spectrum imaging scheme based on scanning transmission electron microscopy-electron energy-loss spectroscopy (STEM-EELS). The ‘Li mapping’ scheme was applied to Li1.2Mn0.4Fe0.4O2 (Li2MnO3–LiFeO2 system) as a high-capacity 3V-class positive electrode material at each stage of the first charge-discharge cycle. Each Li1.2Mn0.4Fe0.4O2 (synthesized using MnCl2 and Fe(NO3)3 as manganese and iron sources) particle was found to be comprised of both Li2MnO3-like and α-LiFeO2-like nanodomains on a common oxygen sub-lattice of the cubic close-packed structure. The Li ions are firstly extracted from α-LiFeO2-like nanodomains and subsequently extracted from the whole region during charging to 4.5 V at 60 degree C. Both nanodomains are really activated, which is different from inactive bulks of α-LiFeO2 and Li2MnO3. We have also observed that Li ions are inserted into both nanodomains after the discharge to 2.0 V. The results have provided a design concept of novel positive electrode materials forming nanodomains even though each pure phase is inactive. The present ‘Li mapping’ technique will bring great advances of the science and technology of Li-ion batteries. [This work was financially supported by R&D project for Li batteries (“Li-EAD” project) by METI and NEDO, Japan]
9:00 PM - S3.16
Structural and Electrochemical Studies of Chemical Solution Derived xLiMn2O3-(1-x)Li[Mn0.5Ni0.5]O2 Cathodes.
Naba Karan 1 , Dillip Pradhan 1 , Jose Saavedra-Arias 1 , Reji Thomas 1 , Ram Katiyar 1
1 Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractRecently, layered LiMn0.5Ni0.5O2 has drawn attention as an alternate cathode material for secondary lithium-ion batteries due to its lower cost, better stability at high voltages and improved thermal safety characteristics compared with LiCoO2. It has been reported recently that the electrochemical properties of layered lithium–manganese–nickel electrodes are enhanced by the addition of excess lithium, typically 10–15%. The effect of lithium content in LiMn0.5Ni0.5O2,or more precisely, in Li1+y[Mn0.5Ni0.5]1−yO2, is of particular interest because, unlike LiCoO2 or LiNiO2, LiNi0.5Mn0.5O2 can accommodate considerable amount of lithium in the transition metal sites without disturbing the overall rhombohedral structure (R-3m) of the material. Since the lithium layer is fully occupied by 1Li in the layered structure of Li1+y[Mn0.5Ni0.5]1−yO2, the excess lithium yLi resides in the transition metal layer to form cation ordering with Mn ions, resulting in local Li2MnO3-like domains. Such compounds can also be reformulated in the two-component notation as xLi2MnO3-(1-x)LiMn0.5Ni0.5O2. The addition of Li2MnO3 to this system is thought to structurally stabilize the overall electrode while providing diffusion pathways for lithium cations. The structures of mixed xLi2MnO3-(1-x)LiMn0.5Ni0.5O2 are extremely complex and the cation distribution and ordering is highly dependent on the synthesis methods, which has profound influence on the electrochemical behavior. In the present work, xLiMn2O3-(1-x)Li[Mn0.5Ni0.5]O2 bulk cathodes (x=0.0–0.4) were synthesized using a cost effective solution technique. The structural properties and oxidation state of Mn and Ni were investigated using X-ray diffraction, Raman Spectroscopy and X-ray photoelectron spectroscopy. The electrochemical measurements of the synthesized cathodes were performed in a two-electrode coin-cell configuration (CR2032), using liquid electrolyte [1M LiPF6 in (1EC:1DMC by volume)] and Li-metal as anode. The major peaks in the XRD patterns of the synthesized xLiMn2O3-(1-x)Li[Mn0.5Ni0.5]O2 cathode materials could be indexed to R-3m symmetry, which characterizes layered LiCoO2. Weak peaks that are characteristic of cation ordering in the transition metal layer, as in the case of LiMn2O3, were present between 20-25o. They could be indexed to the [020] and [110] lattice planes of a LiMn2O3 like unit cell with C2/m symmetry.The first charge and discharge capacity for the composition 0.4LiMn2O3-0.6Li[Mn0.5Ni0.5]O2 were 399 and 225 mAh/g, respectively correspond to a coulombic efficiency of 56%. However, the coulombic efficiency considerably increased to 78% in the 2nd cycle. The effect of LiMn2O3 fraction on the charge and discharge capacity along with the effect of annealing conditions upon electrochemical properties will be presented and discussed in conjunction with local structure of the as prepared and electrochemically cycled electrode materials using ex-situ Raman spectroscopy.
9:00 PM - S3.17
Size Control and Mechanistic Study of LiFePO4 in the Polyol Process.
Wang Hay Kan 1 , Christian Maunders 2 , Shri prakash Badi 1 , Brian L. Ellis 1 , Gianluigi Botton 2 , Linda Nazar 1
1 Chemistry, University of Waterloo, Waterloo, Ontario, Canada, 2 Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada
Show AbstractOlivine lithium metal phosphates, including LiFePO4, are amongst the most promising cathode materials for lithium ion rechargeable batteries. We have investigated the polyol method as a route to prepare nanocrystallites of LiMPO4 (M = Fe, Mn), in order to understand size dependent solid solution behavior. Nanocrystallites of varying dimensions were synthesized through the manipulation of experimental parameters such as reaction time, choice of solvent, and reagent concentration. We found that phase pure samples could be isolated in remarkably short reaction times. Characterization by XRD revealed that the coherence length in the long [200] direction (SG:Pnma) was as low as 12 nm under optimized reaction conditions, which was consistent with our TEM measurements. Longer reaction times or increased concentrations resulted in the formation of substantially larger, and more anisotropic nanocrystallites. High resolution electron loss spectroscopy studies (HREELS) conducted in the TEM revealed the existence of Fe3+ defects on the surface, and also within the bulk of nanocrystallites which can be explained by nucleation and growth mechanisms that will be discussed. The solid solution behavior of the nanocrystallites were examined by a combination of Mössbauer, electrical conductivity and variable temperature XRD studies, which showed that the transition temperature decreases with decreasing particle size, for both the Fe and Mn olivines, although the activation energy for small polaron hopping is relatively size independent.
9:00 PM - S3.18
Crystal Structure and Lithium Diffusion in Copper Doped LiFePO4.
Shailesh Upreti 1 , Natalya Chernova 1 , M. Whittingham 1 , Olga Yakubovich 2 , J. Cabana 3 , Clare Grey 3 , Janice Musfeldt 4
1 Chemistry and Materials, Binghamton University, Binghamton, New York, United States, 2 Geology, Moscow State University, Moscow, Moscow, Russian Federation, 3 Chemistry , SUNY Stony Brook, Stony Brook, New York, United States, 4 Chemistry , University of Tennessee, Knoxville, Tennessee, United States
Show AbstractModern LiFePO4 technology for lithium ion batteries is already in commercial growth owing to the excellent electrochemical performance, high-rate capability and structural stability of this cathode material. However, the two main functional characteristics of LiFePO4 – electronic and ionic conductivity – still remain a subject of controversy. The material behaves like an electronic insulator, but its band structure is not clear. The delithiation of LiFePO4 proceeds as a two-phase reaction, making the determination of the Li diffusion coefficient impossible by means of standard impedance techniques. In nature, lithium-deficient olivine phosphates are stabilized by divalent ions, such as Mg2+ or Ca2+, on the Fe sites of the structure. This inspires us to produce a series of doped olivine phosphates and study their structure and electrochemical behavior.In this work, Cu-substituted LiFePO4 obtained under high-pressure, high-temperature hydrothermal conditions (4000C, 1000 atm) is reported. Dark brown single crystals of composition Li0.95[(Fe2+)0.61(Fe3+)0.10Cu0.24Li0.05]PO4 were successfully grown. A remarkably high level of Cu-substitution is achieved compared to those reported earlier. A systematic single crystal x-ray examination revealed Pnma space group with unit cell dimensions a = 10.226(2) Å, b = 6.012(1) Å, c = 4.682(1) Å and V = 287.8(1) Å3. In order to ascertain the presence of Li ions and/or holes at the transition metal sites, a detailed solid-state Li NMR study is in progress. Temperature dependent magnetic studies confirm the oxidation states expected from the composition and show an antiferromagnetic behavior below 49.5 K with magnetic moments aligned along [010]. Optical properties are being examined with the goal of confirming that Fe2+/Fe3+ charge transfer is responsible for the dark color, and to determine the electronic band structure and vibrational properties.The compound delivers a discharge capacity of 100 mAhg-1 when cycled between 2 and 4.5 V at a current density of 0.1 mAcm-2; this capacity is sustained at higher current rates. A 3.4 V plateau is observed at the charge curve, indicating that Li removal occurs mostly as a two-phase reaction. Upon chemical delithiation in Br2, the single crystal structure is preserved, which allows us to conduct comprehensive structural characterization. In situ and ex situ chemical delithiation studies using single-crystal x-ray diffraction are attempted with the goal of estimating Li diffusion rate. The results will be discussed in comparison with LiFePO4. This work is supported by the US Department of Energy, Office of FreedomCAR and Vehicle Technologies through the BATT program
9:00 PM - S3.19
Morphology and Electrochemistry of Hydrothermally Synthesized Na2FePO4F.
Linda Nazar 1 , Brian Ellis 1 , Emilyne Nicolas 1
1 , University of Waterloo, Waterloo, Ontario, Canada
Show Abstract Among the many positive electrode materials being studied for rechargeable lithium batteries, iron phosphates in particular, are promising electrode materials due to their minimal environmental impact and low cost of the raw materials. We have recently reported on a new iron fluorophosphate, Na2FePO4F,(1) which like other iron phosphates, has a low inherent electrical conductivity.(2) To produce Na2FePO4F that exhibits close to theoretical capacity at high rates, the crystallites must be coated with a conductive material, and most importantly, the particle size must be minimized to reduce the transport path length. We report here a novel synthetic method based on hydrothermal synthesis in the presence of carbon-containing additives, which results in nanocrystallite, single-phase Na2FePO4F. The morphology of the end product can be controlled by the manipulation of the concentration of precursors, hydrothermal pressure and the nature of the additive. Control of these factors results in crystallites with an average size of less than 300nm and a narrow particle size distribution. The effects of morphology and particle size on electrochemical performance will be described. Temperature-dependent Mössbauer spectroscopy measurements show that the compound, when partially oxidized, undergoes a transition into a regime of rapid electron hopping. The onset of this phenomenon occurs at a lower temperature than that for LiFePO4,(3) suggesting a lower activation energy for electron hopping in the bulk phase of the material. References1. Ellis, B.; Makahnouk, W. R. M.; Makimura, Y.; Toghill, K.; Nazar, L.F. Nat. Mat. 2007, 6, 749.2. Chung, S-. Y.; Bloking, J. T.; Chiang, Y-. M. Nat. Mat. 2002, 1, 123.3. Ellis, B.; Perry, L. K.; Ryan, D. H.; Nazar, L. F. J. Am. Chem. Soc. 2006, 128, 11416.
9:00 PM - S3.2
Growth, Characterization of Silicon Nanostructures and their Application as an Anode Material for Rechargeable Lithium Batteries.
Sri Lakshmi Katar 1 2 , Deepak Varshney 1 3 , Gerardo Morell 1 3
1 Institute of Functional nanomaterials, University of Puerto Rico, San Juan, Puerto Rico, United States, 2 Chemistry, University of Puerto Rico, San Juan, Puerto Rico, United States, 3 Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractSilicon nanowires were selectively grown by vapor liquid solid method (VLS) by simply placing a mixture of silica and graphite powder in a flowing nitrogen gas environment on substrates(Cu,Si,Quartz,Mo). The obtained silcon nanostructures is characterized by X ray Diffraction , Scanning electron microscopy (SEM), Energy dispersive x ray análisis (EDAX) Raman spectroscopy, and Transmission electron microscopy(TEM). The electrochemcial properties are studied by cyclic voltammetry, and charge discharge measurements.
9:00 PM - S3.21
Surface Modification of LiCoO2 for Improvement of Cycle Life Performance at High Voltage.
Jae Won Lee 1 , Sun Min Park 1
1 , Korea Inst. Ceramic Eng. & Tech., Seoul Korea (the Republic of)
Show AbstractA transition metal oxide was coated on the surface of LiCoO2 to improve the cycle life performance and increase the energy capacity. The metal oxide was coated via sol-gel process. SEM, TEM analysis were applied to observe the surface of the orginal and the metal-oxide coated LiCoO2. The change in crystal structure after the coating was estimated through XRD analysis. The charge and discharge characteristics and cycle life performance were measured and compared before and after the coating and the difference was discussed.
9:00 PM - S3.22
Orientation Dependence of Microstructure and Electrochemical Properties of LiCoO2 Cathode Films Deposited on Single-Crystalline La2/3-xLi3xTiO3.
Kengo Goto 1 , Kyosuke Kishida 1 , Yuji Yamaguchi 1 , Norihiko Okamoto 1 , Katsushi Tanaka 1 , Haruyuki Inui 1 , Yasutoshi Iriyama 2 , Zempachi Ogumi 3
1 Department of Materials Science and Engineering, Kyoto University, Kyoto Japan, 2 Department of Materials Science & Chemical Engineering, Shizuoka University, Hamamatsu Japan, 3 Department of Energy and Hydrocarbon Chemistry, Kyoto University, Kyoto Japan
Show AbstractSolid state lithium-ion conductors have received a considerable amount of attentions as solid electrolytes for all solid-state lithium rechargeable batteries. In the case of the all solid-state batteries especially with a crystalline solid electrolyte, the solid / solid interface between the electrode and electrolyte are considered to have significant influences on the battery performance such as resistivity and mechanical stability upon charging and discharging. Recently, we have studied influences of microstructures of the solid electrolyte / solid cathode interfaces on the electrochemical properties using model assemblies with a perovskite-based lithium lanthanum titanate (LLT: La2/3-xLi3xTiO3) solid electrolyte and a LiCoO2 cathode with a layered rock-salt type rhombohedral structure. We have revealed the orientation relationship between the LLT and LiCoO2 and effects of the lattice defects on the battery performance. These preliminary results suggest the resistivity as well as the mechanical stability of the interface can be controlled partly by the geometrical configuration of the Li layers in the LiCoO2 crystal against the interface plane. In order to elucidate the influences of the geometrical configuration of the layered structure of the LiCoO2 on the battery performance, we have prepared single-crystalline LLT by a unidirectional solidification process and investigated the variation of the microstructure and electrochemical properties of the LiCoO2 thin films deposited by PLD as a function of the surface orientation of the LLT solid electrolyte. The LiCoO2 thin-film cathode consisting of differently oriented fine domains is epitaxially grown on the LLT with the orientation relationships: {111}LLT//(0001) LiCoO2 and <110>LLT//<11-20>LiCoO2 irrespective of the surface plane of the LLT. When the interface is parallel to the (110) of the LLT, all domains of the LiCoO2 is grown so that the layered structure are aligned perpendicular to the interface. In contrast, when the interface is parallel to the (112) of the LLT, the layered structure LiCoO2 are mostly inclined about 20° from the interface. Reflecting such a geometrical difference in the oriented growth of the LiCoO2, the interface resistivity is about one-lower for the former case. Details of the microstructure observations as well as the electrochemical property measurements will be presented.
9:00 PM - S3.23
Effects of Incident Laser Energy on Transport in Printed Microbattery and Supercapacitor Electrodes.
Christina Peabody 1 , Ashwin Atre 2 , Jonathan Scholl 2 , Craig Arnold 1
1 Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States, 2 Chemical Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractLaser direct-write printing has been shown to be a successful method of producing thick-film patterns of complex electrode materials for energy storage devices. However, in prior work, the effects of the incident laser have been minimized in order to preserve the pre-existing properties of these materials. In this paper, we demonstrate that incident laser irradiation of electrochemically active materials can have a significant effect on the energy storage and power delivery performance by modifying the electrode material during the transfer process. The influence of incident laser energy during deposition is studied and exploited in order to modify and optimize electrochemical properties. At low transfer energy densities, the material maintains its structural, morphological, and electrochemical properties in comparison to control samples. However, higher energy density produces noticeable changes to the morphology, structure, and electrochemistry leading to modifications in the transport properties. Implications of this process for cell fabrication on low temperature substrates and integration with existing devices will be discussed in the context of hydrous ruthenium oxide supercapacitor and lithium-ion battery systems.
9:00 PM - S3.3
Preparation and Characterization of Porous SnO2-CNT Thin Films as Anodes for Li-ion Batteries.
Abirami Dhanabalan 1 , Yan Yu 1 , Chunlei Wang 1
1 Mechanical & Materials Engineering, Florida International University, Miami, Florida, United States
Show AbstractTin-based composites, such as MxSny alloy, (M= Fe, Ni, Mn, and Co), amorphous tin composite oxide (ATCO) and nanosized SnO2 are able to store Li via alloy formation through electrochemical means resulting in capacities substantially higher than those of the carbonaceous materials. (Theoretically, 781mAh/g for SnO2 vs. 372 mAh/g for graphite). The internal stresses arising from the volume changes would eventually lead to material failure by mechanical disintegration, and poor cycling performance in applications. Many efforts have been made to prevent the aggregation of the tin nano particles and compensating for the expansion of the reactants, so as to preserve the electrical pathway. Tubular or porous or hollow structure tin-based oxides have been also proposed to “buffer” the large volume change during the repetitive charging and discharging of the battery. It has been demonstrated that carbon nanotubes (CNTs) have a much lower resistance than activated carbon, and highest reversible capacity of any carbon material used in lithium-ion batteries. Thus, it is desirable to develop simple and highly efficient ways to prepare SnO2/CNT composites which not only preserve the structure of the CNTs but also provide good practicality. Here, we fabricated SnO2-CNT thin film electrodes for Li-ion batteries using Electrostatic Spray Deposition [ESD] technique. In order to compare the effectiveness of different content, 10wt%, 20wt%, 30wt%, and 40wt% CNT were added to 0.005M Sn(OAC)4 glycol solutions. The deposition was carried out in three different substrate temperatures, 250°C, 300°C, and 350°C. The as-deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray absorption spectroscopy (XAS), and Raman scattering. The as-deposited thin films were assembled as a working electrode, with lithium metal as both counter electrode and reference electrode in 1 M LiPF6 EC/DMC(1:1,V/V) electrolyte solution in an argon-filled glove box. The electrochemical performance was tested at different current densities in the voltage range of 0.01–3.0 V on a NEWARE battery tester. The samples which delivered the optimum electrochemical performance will be discussed in detail. Acknowledgement: This work was supported by USA Air Force (No.FA9550-05-1-0232)
9:00 PM - S3.4
Fabrication of Nano-structured Tin-oxide Electrode based on Cu Nano Current Collector for Li-ion Batteries.
Xiangping Chen 1 2 , Huanan Duan 2 , Boquan Li 2 , Jianyu Liang 2
1 , South China University of Technology, Guangzhou, Guangdong, China, 2 , Worcester Polytechnic Institute, Worcester, Massachusetts, United States
Show Abstract9:00 PM - S3.5
Micro/Nano Hierarchical Porous Tin Oxide Thin Film as Anode for Li-ion Batteries.
Yan Yu 1 , Varun Penmatsa 1 , Abirami Dhanabalan 1 , Chunlei Wang 1
1 Department of Mechanical and Materials Engineering, Florida International University,, Miami, Florida, United States
Show AbstractSn-based composites have been projected as promising anode materials for lithium secondary batteries due to their huge lithium storage capacity.[1] However, the practical implementation of tin-based composites is hampered by the large capacity loss at first cycle and poor capacity retention resulting from large volume change during the lithium insertion/extraction process.[2] One of the most promising ways is to fabricate nanoscale Sn-based materials with high porosity. Materials with highly porous structures can be benefitial to electrolyte accessibility and ionic transport. In addition, nanosizing is an effective way to get higher surface area and shorter Li-ion diffusion length,[2] which leads to a substantial improvement of rate capability. In this work, we fabricated micro/nano hierarchically porous amorphous SnO2 thin-films as anodes for Li-ion batteries by Electrostatic Spray Deposition (ESD) technique.[3] With 0.005M C16H30O4Sn in glycol (HOCH2CH2OH) as precursor solution, SnO2 films were deposited on heated nickel foil disks. All as-deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The SEM image of an as-deposited SnO2 thin film for deposited for 2h at 300 degree C in air. The thin film is constructed with microsized pores (diameter 1~2 μm) and nanosized pores (diameter 100~200 nm) interconnected hierarchical porous structure. The wall of porous structure was constructed with aggregated nanoparticles (diameter 100~200nm) and nanorods. An electrochemical test cell was assembled in an argon-filled glovebox using the as-deposited SnO2 thin film on Ni foil as the working electrode, a lithium metal foil as the counter/reference electrode, and 1 M solution of LiPF6 in a 1:1 v/v mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) as the electrolyte. The cell was charged and discharged galvanostatically between 0.01V to 2 V using a battery tester. The correlation between deposition temperature, porosity, thickness and electrochemical performance of SnO2 thin film electrodes will be presented in details at the meeting. References:[1] Y. Idota, T. Kubota, A. Matsufuji, Y. Maekawa, T. Miyasaka, Science 276, 1395 (1997)[2] O. Mao, R. L. Turner, I. A. Courtney, B. D. Fredericksen, M. I. Buckett, L. J.Krause, J. R. Dahn, Electrochem. Solid-State Lett., 2, 3 (1999).[3] C. H. Chen, E. M. Kelder, P. J. J. M. van der Put, J. Schoonman, J. Mater. Chem. 6, 765 (1996).AcknowlegementsThis work is financially supported by Airforce (No. FA9550-05-1-0232) USA
9:00 PM - S3.6
Investigation of Graphites at High Potentials with Synchrotron-Based In Situ XRD.
Wolfgang Markle 1 , Dietrich Goers 2 , Michael Spahr 2 , Petr Novak 1
1 Electrochemistry Laboratory, Paul Scherrer Institut, CH-5232 Villigen PSI Switzerland, 2 , TIMCAL Ltd., CH-6743 Bodio TI Switzerland
Show Abstract9:00 PM - S3.7
Structural and Electrochemical Characterization of Layered Lithium Nitridometallates.
Bach Stephane 1 , Pereira-Ramos Jean Pierre 2
1 , National Education, Thiais France, 2 , CNRS, Thiais France
Show Abstract9:00 PM - S3.8
Determination of the Structural Parameters Governing Copper Displacement Phenomena in Cu-V-O System.
Patrick Rozier 1 , Mickael Dolle 1 , Mathieu Morcrette 2 , Christine Surcin 2 , Jean-Marie Tarascon 2
1 , CEMES/CNRS, Toulouse France, 2 , LRCS, Amiens France
Show Abstract
Symposium Organizers
Enrico Traversa University of Rome Tor Vergata
Timothy Armstrong Carpenter Technology Corporation
Koichi Eguchi Kyoto University
M. Rosa Palacin Institut de Ciencia de Materials de Barcelona (CSIC)
S4: Innovative Concepts for Energy Storage
Session Chairs
Rosa Palacin
Enrico Traversa
Tuesday AM, December 02, 2008
Back Bay A (Sheraton)
9:30 AM - **S4.1
Lithium Metal Semi-Fuel Cells: A New Generation of High Energy Density Batteries.
Steven Visco 1 2 , Eugene Nimon 1 , Lutgard De Jonghe 1 2
1 , PolyPlus Battery Company, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show Abstract10:00 AM - **S4.2
Charge Storage Mechanism in Carbon Sub-nanometer Pores and its Consequences for Electrical Double Layer Capacitors.
Patrice Simon 1 , Yury Gogotsi 2
1 CIRIMAT-Materials Science, Universite Paul Sabatier, Toulouse France, 2 Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractElectrochemical Double Layer Capacitors, also known as supercapacitors, are energy storage devices similar to batteries that store the charge electrostatically through reversible ion adsorption onto high-surface area carbon materials. As a consequence, they can achieve higher power performances than batteries, with lower energy density. Such performance make then suitable for many applications where high power is needed up to few seconds, such as in power electronics (Unit Power Saving and power buffer) [1].Carbon-based capacitors, store the energy through reversible ion adsorption on high specific surface area (SSA) carbons at the carbon / electrolyte interface. This surface storage explains the high power capability of these systems. However, as a consequence of the reversible electrostatic surface charging, these systems suffer from limited energy density. Today’s EDLC research is largely focused on increasing their energy performance and temperature limit [2].We have used Carbide-Derived Carbons (CDCs) as model material to study the influence of pore size onto the capacitance. CDCs were obtained from chlorination of TiC particles at temperature ranging from 400°C up to 1000°C. These materials offer the unique advantage of perfectly controlling pore size, depending on the chlorination temperature and time. CDCs with controlled pore size between 0.6 and 1.1 nm have been prepared and tested firstly in ACN+NEt4BF4 electrolyte [3,4]. We recently demonstrated that, defying the conventional wisdom stating that pores larger than the size of solvated ion (>2nm) were needed to optimize the charge storage, sub-nanometer pores (<1nm) lead to huge capacitance increase. This was possible thanks to the distortion of the ion solvation shell, alloying ions to come closer to the carbon surface [3]. In this presentation, we will discuss results obtained in two different electrolytes: ACN + 1M NEt4BF4 and a solvent-free electrolyte (EMI,TFIS ionic liquid) [4,5]. These results confirmed that ions must be desolvated for entering micropores, and that the optimum pore size needed to maximize the capacitance is close to the ion size, ruling out the way charge storage is traditionally described in EDLC materials, with ions adsorbed on both pore walls. Recasting the theory of double layers in electrochemistry to take into account solvation effects could lead to a better understanding of charge storage in electrochemical capacitors and more generally of ion transport in sub-nanopores.References[1] R. Kötz, M. Carlen Press, Electrochim. Acta, 2000, 45, 15-16, 2483-2498.[2] A. G. Pandolfo, A.F. Hollemkamp, J. Power Sources 2006, 157, 11-27.[3] J. Chmiola, G. Yushin, Y. Gogotsi, C. Portet, P. Simon, P.L. Taberna, Science, 313 (2006) 1760-1763.[4] J. Chmiola, C. Largeot, P.-L. Taberna, P. Simon, Y. Gogotsi, Ang. Chem., 47 (2008) 3392-3395.[5]C. Largeot, C. Portet, J. Chmiola, P.-L. Taberna, Y. Gogotsi, P. Simon, J. Amer. Chem. Soc 130 (9), 2730 -2731 (2008).
10:30 AM - **S4.3
Research Advances in the Development of Nanostructured Free-Standing Electrodes for Energy Applications.
Mohamed Mohamedi 1
1 Énergie, Matériaux et Télécommunications, INRS-EMT Univ, Varennes, Quebec, Canada
Show AbstractS5: Battery Materials: Electrolytes and Systems
Session Chairs
Christian Masquelier
Rosa Palacin
Tuesday PM, December 02, 2008
Back Bay A (Sheraton)
11:30 AM - **S5.1
All-solid-state Lithium Rechargeable Batteries with Sulfide Glass-based Solid Electrolytes.
Masahiro Tatsumisago 1 , Akitoshi Hayashi 1
1 Department of Applied Chemistry, Osaka Prefecture University, Sakai, Osaka Japan
Show Abstract12:00 PM - S5.2
Ion Transport and Stability of Polymer Electrolytes for Lithium Batteries based on Polysiloxanes and Polyphosphazenes.
Yunus Karatas 1 , Miriam Kunze 2 , Raphael Stolina 1 , Romek Mueller 1 , Marika Burjanadze 1 , Hellmut Eckert 2 , Monika Schoenhoff 2 , Hans Wiemhofer 1
1 Institute of Inorganic and Analytical Chemistry, and SFB 458, University of Münster, Münster Germany, 2 Institute of Physical Chemistry, and SFB 458, University of Münster, Münster Germany
Show Abstract12:15 PM - S5.3
Preparation and Characterization of Lithium Ion Conducting Li2S-P2S5 Glass-ceramic Electrolytes.
Keiichi Minami 1 , Akitoshi Hayashi 1 , Masahiro Tatsumisago 1
1 Department of Applied Chemistry, Osaka Prefecture University, Sakai, Osaka Japan
Show Abstract12:30 PM - S5.4
Nanostructured Composites for Li-S Batteries.
Xiulei Ji 1 , Kyu Tae Lee 1 , Linda Nazar 1
1 , University of Waterloo, Waterloo, Ontario, Canada
Show AbstractSafe, low-cost, high energy density and long-lasting rechargeable batteries are in high demand to address pressing environmental needs. Lithium-ion batteries (LIBs) used in today’s portable electronic devices operate on the basis of topotactic intercalation reactions: reversible uptake of Li ions and electrons in a solid accompanied by minimal change to the structure. They typically use a lithium transition metal oxide or phosphate as a positive electrode.[1] Because the reaction is topotactic at both electrodes, the charge storage capability is inherently limited. Cost effective lithium-sulfur (Li-S) cells are considered to be promising candidates to replace conventional LIBs.[2] Above all, the energy density of the Li-S battery can approach nearly the highest values possible (on a weight (2500 Wh/kg) or volume (2800 Wh/l) basis) of any known combinations of materials, assuming a complete conversion of elemental sulfur to Li2S. However, the many characteristics presented by Li-S cells, including low capacity, poor reversibility, and solubility of the intermediate species, have presented challenges for over a decade.[3] In particular, to enable a reversible electrochemical reaction at high current rates, the highly insulating sulfur mass must maintain intimate contact with a conductive matrix. Here, we report a novel approach to this problem which utilizes mesoporous carbon materials to generate periodically ordered carbon/sulfur nanoarchitectures. Such mesoporous carbons with high surface area, large pore volume, long range ordered nanoporous structure and good electrical conductivity have important potential applications in electrochemical devices, such as batteries and low temperature fuel cells.[4,5] We have developed simple strategies to incorporate the sulfur within a variety of mesoporous carbon structures, that produce highly ordered nanocomposites containing up to 70 wt% sulfur, and which exhibit reversible capacities up to 1200 mAh/g. We will discuss our methods to inhibit dissolution of soluble polysulfide anions, which reduces loss of active mass from the cathode and enables excellent cyclability of the cell. References1. Kang, K.; Meng, Y.S.; Breger, J.; Grey, C.P.; Ceder, G. Science, 2006, 311, 977.2. M.Y. Chu, US Patent US05814420 1998.3. Cheon, S.E.; Ko, K.S.; Cho, J.H.; Kim, S.W.; Chin, E.Y.; Kimd, H.T. Journal of The Electrochemical Society, 2003,150, A800.4. Ryoo, R.; Joo, S. H.; Jun, S. J. Phys. Chem. B, 1999, 103, 7743. 5. Ji, X.; Herle, P.S.; Rho, Y.H.; Nazar, L.F. Chem. Mater. 2007, 19, 374.
12:45 PM - S5.5
Transport in Polyiodide Networks of a Self-Assembled Lithium Iodide Battery.
William Yourey 1 , L. Weinstein 1 , G. Amatucci 1
1 Materials Science and Engineering, Rutgers, The State University of New Jersey, North Brunswick, New Jersey, United States
Show AbstractAs MEMS devices for biomedical and other applications continue to develop and decrease in dimensions, the demand for power supplies with the appropriate size and energy density continues to grow. Although energy density is an important factor, one of the most crucial factors is the ability to fabricate cells in a variety of shapes so to enable the greatest design flexibility when fabricating a device. Recently our group has introduced an electrochemically self formed battery to grant a path towards the greatest flexibility. In short, a nanocomposite of an alkali halide such as lithium iodide is placed between current collectors and polarized thereby creating a lithium anode and polyiodide cathode in-situ. As with primary lithium-iodine cells the transport within the cathode is a complex mechanism involving the Li+, I-, and e- all within the polyiodide network. After our recent work on in-situ EIS evaluation of the technology, we have launched on an effort to greater understand the limiting transport mechanisms in the positive electrode as a function of polyiodide network development.An in-depth characterization study was performed on the LiI-I2-PVP-H20 at various molar ratios to understand the structural and conductivity changes that take place during formation of the cellA combination of AC impedance and DC polarization studies were used for the impedance characterization in conjunction with blocking electrode methodology for separating the conductivity into its electronic and ionic portions. Also, FTIR and Raman were used to structurally characterize the samples for both the polyiodide formation and the interaction between the polyiodides and polyvinylpyrrolidone (PVP). Being non conjugated, PVP was chosen as it does not intrinsically contribute to the conductivity of the composite but does induce the formation of polyiodide species. As different molar ratio composites are prepared, the concentration of different polyiodide species (I3-, I5-, In-) within the composite change and affect the overall conductivity. A 3-dimensional plot of composite conductivity reveals a high electronic conductivity ridge for samples containing either LiI anhydrous or monohydrate at a constant I2 to PVP ratio. These 3-dimensional plots also allow us to correlate represent in an ex-situ format the electronic and ionic conductivity of the cathode/electrolyte at various depths of discharge
S6/PP5: Joint Session: Solid State Ionics for Energy
Session Chairs
Miguel Alario-Franco
Silvia Licoccia
Tuesday PM, December 02, 2008
Back Bay C (Sheraton)
2:30 PM - **S6.1/PP5.1
Lithium Metal Phosphates for Energy Storage.
Linda Nazar 1 , Brian Ellis 1 , Jack Kan 1 , Shriprakesh B Badi 1
1 , University of Waterloo, Waterloo, Ontario, Canada
Show AbstractNanomaterials have the potential to significantly change the capacity and power delivery of energy storage systems. Amongst the most promising devices are Li-ion rechargeable batteries, where next-generation electrode materials could enable their implementation in hybrid electric vehicles and as reservoirs for intermittent energy sources such as solar energy, in order to address growing environmental concerns. Nanosized olivine LiFePO4 for example, amongst other lithium metal phosphates, has attracted much attention as a potential candidate for this aim. While conventional factors such as reduced path length for transport could also be at heart, claims have been made that in nanocrystallites of LiFePO4, reduced strain energy between the end members of the redox couple and/or increased solid solution regimes may be responsible for their enhanced electrochemical performance. Little unequivocal quantification of “nano” effects has been provided, however, owing to the difficulty of measuring them. This presentation will discuss these factors in a range of lithium metal phosphate nanocrystallites, including LiMPO4 (M = Fe, Mn); Na2FePO4F; Li2FePO4F; and some of their “doped” analogues. A broad range of techniques, including x-ray/neutron diffraction, conductivity, TEM/HREELS and Mössbauer measurements are used to probe differences in the temperature for the transition to the solid solution regime; the activation energy for small polaron hopping; and the stability of Li vacancies in bulk vs nanocrystallite materials.
3:00 PM - S6.2/PP5.2
First-principles Studies of Phase Stability of LiFePO4 in Aqueous Solutions.
Gerbrand Ceder 1 , Lei Wang 1 , Kristin Persson 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractOlivine structure LiFePO4 has emerged as a promising high-rate cathode material in Li-ion batteries. In recent years much research effect has been devoted to the synthesis of this material in low temperature solution environments.[1, 2] The searching for optimum aqueous solution conditions where the precipitation of LiFePO4 is thermodynamically favored over other competing products is of great interest to the practical synthesis. Meanwhile, the effort of controlling the particle morphology for LiFePO4 in solution environment [3] is also important because the lithium diffusion for this material is believed to be one-dimensional in the olivine structure. We have developed a thermodynamic formalism to study the stability of metals and oxides in aqueous solutions. In this work, we demonstrate the methodology in LiFePO4 and investigate the thermodynamic equilibria between solid phases and aqueous ions in solutions. The stability of bulk LiFePO4 in aqueous solution is presented in the calculated Pourbaix diagram, which shows the phase equilibria as a function of potential and pH value of the solution. Previously, we studied the equilibrium particle morphology of LiFePO4 using the calculated surface energies for clean surfaces.[4] In this work, we consider the appearance of different adsorbates, e.g. H, OH, H2O, on the surfaces of LiFePO4 and investigate the change of surface energies and equilibrium particle shape in different solution conditions. By taking into account the surface absorption reactions, we are able to study the stability of LiFePO4 surfaces in aqueous solutions. And the corresponding modification of equilibrium morphology will be discussed in the calculated Pourbaix diagram for finite-size LiFePO4.Our results provide useful insights into the synthesis of LiFePO4 in solution environments and the change of particle morphology in different solution conditions.Reference: [1]J. J. Chen and M. S. Whittingham, Electrochem. Commun. 8, 855 (2006).[2]C. Delacourt, P. Poizot, S. Levasseur, and C. Masquelier, Electrochemical and Solid State Letters 9, A352 (2006).[3]K. Dokko, S. Koizumi, and K. Kanamura, Chemistry Letters 35, 338 (2006).[4]L. Wang, F. Zhou, Y. S. Meng, and G. Ceder, Phys. Rev. B 76, 165435 (2007).
3:15 PM - S6.3/PP5.3
Ion-Exchange and Subsequent Li-Insertion Chemistry of a New Family of Iron Phosphate Compounds Exhibiting Channeled Structures.
Gregory Becht 1 , John Vaughey 2 , Robin Britt 3 , Cassandra Eagle 3 , Shiou-Jyh Hwu 1
1 Department of Chemistry, Clemson University, Clemson, South Carolina, United States, 2 Chemical Sciences and Engineering, Argonne National Laboratory, Argonne, Illinois, United States, 3 Department of Chemistry, Appalachian State University, Boone, North Carolina, United States
Show AbstractSince the demonstration of the reversible extraction of lithium from LiFePO4 (triphylite), an enormous amount of effort has been devoted to the identification of other lithium insertion compounds that can be used as cathodes for secondary lithium battery devices. Among iron-containing polyanion-based compounds include the NASICON-type Li3Fe2(PO4)3 as well as pyrophosphates LiFeP2O7 and Fe4(P2O7)3. While the olivine-type LiFePO4 has maintained prominence, it has some inherent shortcomings, including one-dimensional Li+-ion transport and a two phase redox reaction. Thus, electrochemical extraction was reportedly limited to ca. 0.6 Li/formula unit, which is equivalent to the specific capacity of 100-110 mAh/g. The discovery of new open-framework solids that technically exhibit pathways for facile Li+ transport, extended charge/discharge capacity, and structure stability upon electrochemical cycling is especially critical for the development of large-capacity systems required in technologies such as plug-in hybrid electric vehicles.A newly devised synthetic approach, combining high-temperature solid-state and low- temperature solution methods, has allowed the discovery of new lithium iron phosphate compounds that otherwise cannot be synthesized directly through conventional solid-state methods. By employing molten salt methods, we have isolated several new iron phosphate compounds containing large alkali metal cations in layered and channeled structures. These new solids were subject to ion-exchange and reduction insertion with Li+ cations. The parent structure used in the ion-exchange reported here was Cs9-xKxFe7(PO4)10. The electropositive cations, Cs+ and K+, reside in two interconnected orthogonal channels. Consequently, the direct ion exchange on single crystals was proven possible under mild hydrothermal conditions in 1M nitrate solutions, and it has revealed remarkable ion exchange properties with all of the monovalent alkali metal cations. Employing a n-BuLi/hexane solution, the ion-exchanged Fe(III) compound Li9Fe7(PO4)10 can be further lithiated to a reduced Fe(II) phosphate phase Li16Fe7(PO4)10 at room temperature. In this presentation, we will discuss the synthesis, structure and electrochemical properties of these newly synthesized iron phosphate compounds. We will also discuss the use of large electropositive cations as a template for the synthesis of new open-framework compounds and offer insight into the synthesis of new Fe(III)-containing phosphate compounds having structural versatility and extended capacity.
3:30 PM - **S6.4/PP5.4
New Mechanisms of Li Insertion/extraction in LiFePO4.
Christian Masquelier 1 , Pierre Gibot 1 , Montse Casas Cabanas 1 , Lydia Laffont-Dantras 1 , Stéphane Levasseur 2 , Philippe Carlach 2 , Stéphane Hamelet 1 , Jean-Marie Tarascon 1
1 LRCS, Chemistry Dept., Université Picardie Jules Verne, Amiens France, 2 , UMICORE Research, Olen Belgium
Show AbstractLiFePO4 is now recognized (and used) as a new electrode material for Li-ion batteries as it represents a low cost and non toxic material that exhibits high specific capacity and stability upon cycling. Li ions can be reversibly removed from the structure, leading to the formation of FePO4 in a two-phase process with a theoretical specific capacity of 170 mAhg-1 [1]. Its main drawback is its low electrical conductivity and effective approaches such as the use of LiFePO4/carbon composites [2-3] or the minimization of particle sizes [4] have been proposed to overcome this limitation.Downsizing LiFePO4 particles to the nanometric scale indeed translates in an improved electrochemical activity against lithium as the electrode/electrolyte contact area is increased, which yields higher cycling rates, and the mean path lengths for both electrons and lithium cations are minimized, allowing the use of low electronic and/or ionic conducting materials. The crystal chemistry and electrochemical behavior of various nanometric “LiFePO4” powders prepared by direct precipitation in water [5] will be presented. We report on the discovery, probed by insitu X-Ray diffraction, of a full solid solution process during Li+ extraction / insertion at room temperature for triphylite nanopowders that contain significant amounts of defects on the Li and Fe octahedral crystallographic sites, as deduced from Rietveld analysis of powder neutron diffraction data [6]. The possibility of having single phase extraction/insertion mechanisms (e.g., a sloping voltage curve) presents some intrinsic advantages with respect to applications such as an easier and cheaper monitoring state of charge of the battery as compared to a flat constant voltage curve.References[1]. A.K. Padhi, K.S. Nanjundaswamy, J.B. Goodenough, J. Electrochem. Soc., 144(4) 1188-1194 (1997).[2]. H. Huang, S.C. Yin, L.F. Nazar, Electrochem. Solid-State Lett., 4(10), A170-A172 (2001).[3]. N. Ravet, J.B. Goodenough, S. Besner, M. Simoneau, P. Hovington, M. Armand, Abstract #127, 196th ECS meeting, Honolulu, 17-22 October 1999.[4]. C. Delacourt, P. Poizot, S. Levasseur, C. Masquelier, Electrochem. Solid-State Lett., 9(7), A352-A355 (2006).[5] Delacourt, C., Poizot, P., Masquelier, C., Crystalline nanometric LiFePO4, World Patent, CNRS-UMICORE, #WO 2007/0051 (2007)[6]. P. Gibot, M. Casas-Cabanas, L. Laffont, S. Levasseur, P. Carlach, S. Hamelet, J.M., C. Masquelier, Nature Materials, in press, (2008)
4:00 PM - S6/PP5:SSI
BREAK
4:30 PM - **S6.5/PP5.5
Designing The Next Generation of Proton Conductors.
Sossina Haile 1 , Calum Chisholm 1 2 , Eric Toberer 1
1 Materials Science / Chemical Engineering, California Institute of Technology, Pasadena, California, United States, 2 , Superprotonic, Inc., Pasadena, California, United States
Show AbstractSolid acids, or acid salts, are a class of proton conducting electrolytes with stoichiometries MHXO4, M3H(XO4)2 (M = Cs, Rb, NH4; X = S, Se), and MH2X’O4 (X’ = P, As). Many of these compounds undergo a remarkable phase transition at which the proton conductivity jumps by three to four orders of magnitude to a “superprotonic” state with conductivity in the range of 10-3-10-1 Ω-1 cm-1. These high levels of conductivity are a result of rapid librations of the tetrahedral oxyanion groups ( ~ 1012 Hz) in combination with a high rate of proton transfer between tetrahedral groups (~ 109 Hz). A curious feature of these materials is the apparent restriction of superprotonic behavior to compounds in which the M cation is either an alkali metal or the ammonia ion. In this work we explore the possibility of extending superprotonic solid acids to compounds based on alkaline earth metals, with particular emphasis on derivatives of Ba3(PO3)2. Through a combination of X-ray powder diffraction, 1H NMR spectroscopy, thermal gravimetric analysis, energy dispersive chemical analysis, and conductivity measurements, we show that it is possible to partially substitute K + H for Ba, and create crystal-chemical analogs to the known superprotonic conductors MH3(SeO4)2. While the conductivities of the alkaline earth phosphate materials are lower than those of the alkali selenates, this new class of proton conductors displays key advantages for practical applications, including chemical stability in reducing atmospheres and insolubility in water.
5:00 PM - **S6.6/PP5.6
Composite Effects of Pyrophosphate Matrices on the Proton Conductivity for CsH5(PO4)2 Electrolytes at Intermediate Temperatures.
Toshiaki Matsui 1 , Hiroki Muroyama 1 , Ryuji Kikuchi 1 , Koichi Eguchi 1
1 Department of Energy & Hydrocarbon Chemistry, Graduate school of Engineering, Kyoto University, Kyoto Japan
Show Abstract5:30 PM - **S6.7/PP5.7
Ionic Conduction in the Solid-state, the Influence of Defect-defect Interactions.
Paul Madden 1 , Dario Marrocchelli 1
1 School of Chemistry, University of Edinburgh, Edinburgh United Kingdom
Show AbstractAt the simplest level, ionic conduction in the crystalline state is due to the hopping of vacancies and interstitials. However, when such defects are introduced by aliovalent doping the ionic conductivity often does not increase with the defect concentration, as might be expected from this simple picture. A good example is the case of yttria-stabilized zirconia, which is often used as an oxide ion conductor in solid-oxide fuel cells. Here, the conductivity decreases with increasing yttria content for doping levels beyond about 10%. Several factors could contribute to this effect – trapping of vacancies by spatial fluctuations in the dopant cation concentration, interactions between the vacancies causing the formation of low mobility clusters…….To distinguish between these effects by purely experimental means is very difficult, the interactions may have weak consequences in diffraction or thermochemistry but even if such structural effects are detected there is no direct way of linking them to the conduction mechanism. Here we describe computer simulation studies on transition metal oxide mixtures carried out with polarisable interaction potentials parameterized from ab initio electronic structure calculations. The calculations reproduce extremely well the experimental data for the conductivity and also the structural information obtained by analysis of the total (Bragg and diffuse) neutron scattering. By introducing a third cation, such as Nb5+ and varying the composition, such experiments have been performed on a range of samples with the same vacancy concentration, which enables the different influences on the conductivity to be traced. The simulations may be interrogated at the atomic level to clarify the important influences on the ionic conduction mechanism.
Symposium Organizers
Enrico Traversa University of Rome Tor Vergata
Timothy Armstrong Carpenter Technology Corporation
Koichi Eguchi Kyoto University
M. Rosa Palacin Institut de Ciencia de Materials de Barcelona (CSIC)
S7/T6: Joint Session: Solid State Ionics for Mobile Energy
Session Chairs
Jennifer Rupp
Enrico Traversa
Wednesday AM, December 03, 2008
Back Bay A (Sheraton)
9:30 AM - **S7.1/T6.1
Functional Impact of Nafion-Metal Oxide Composite Membranes in Proton Exchange Membrane Fuel Cells: The Elevated Temperature Operating Window.
Andrew Bocarsly 1 , Paul Majsztrik 1 , Jay Benziger 2
1 Department of Chemistry, Princeton University, Princeton, New Jersey, United States, 2 Chemical Engineering, Princeton University, Princeton, New Jersey, United States
Show Abstract Present day proton exchange membrane (PEM) fuel cells (FC) are subject to poisoning by the presence of trace amounts of CO in the hydrogen fuel stream, water management limitations and difficulty in dumping waste heat. One solution to this problem is the implementation of a PEMFC that operates at an elevated temperature regime (i.e. from 120-150°C). However, Nafion®, the primary proton exchange membrane material available, undergoes changes above ~90°C that lead to extensive degradation of fuel cell output parameters. We have found however, that the use of a composite membrane formed from the addition of a metal oxide to a Nafion matrix allows for reproducible, stable cell operation up to ~145°C. Addition of a metal oxide component also provides improved performance under conditions of low humidity in the 60-80°C operation range. Metal oxide/Nafion composite membranes can be synthesized by the direct addition of metal oxide particles to a Nafion recasting suspension followed by solvent evaporation. Metal oxide content of 3-20% by weight leads to a mechanically and thermally robust composite membrane. The nature of the metal oxide and the recasting solvent is critical to the operation of the membrane. A model is put forward to account for the observed cell improvement involving a specific chemical interaction between the Nafion sulfonate groups and coordinately unsaturated sites on the metal oxide surface. Extensive interfacial interaction can lead to the leaching of metal ions from the oxide particle. This process degrades membrane performance in a fuel cell. On the other hand, if the interfacial interaction is extremely weak, no benefit is observed. Metal oxide-Nafion systems that show a catalytic chemical interaction using thermal gravimetric analysis are found to also provide a robust fuel cell response. Chemical modification of the metal oxide surface can be used to vary the polymer-inorganic interaction, thereby optimizing the observed PEM performance. Elevated temperature cells running above 135°C show enhanced carbon monoxide tolerance and good water management properties. An unexpected benefit of introducing a metal oxide phase is improved membrane mechanical parameters. The viscoelastic response of the PEM membrane is found to directly couple to the electrochemical output of the fuel cell. The composite membranes under consideration here have mechanical stability and improved elastic relaxation properties, providing an improved electrochemical response under conditions where the cell humidity, thermal content, or electrical power is varying.
10:00 AM - S7.2/T6.2
Influence of Titania Morphology on the Electrochemical Properties of Composite Polymer Electrolyte Membranes.
Debora Marani 1 2 , Chavalit Trakanprapai 1 , Silvia Licoccia 1 , Enrico Traversa 1 , Masaru Miyayama 2
1 NAST Center & Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma “Tor Vergata”, Roma Italy, 2 Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo Japan
Show AbstractOne of the key topics in membrane electrolyte research is the need to develop inexpensive polymeric electrolyte membranes (PEMs) for operation under increased temperature (120-130 °C) and low humidity level (20-50 % of RH) with limited methanol permeability. An effective strategy to achieve high temperature and low humidity operation conditions deals with the development of electrolytes containing dispersed hygroscopic oxides. Several ceramic compounds, such as titania, silica, and zirconia, have been already evaluated, and encouraging results have been obtained.In this work, the influence of titania morphology on the electrochemical properties of 58% degree of sulfonation S-PEEK-based composites was investigated. Inorganic fillers were anatase powders having two different morphologies, mesoporous and nanometric. PEEK sulfonation reaction was carried out in concentrated H2SO4. The sulfonation degree was determined by titration and by H1 NMR, obtaining results in agreement. Mesoporous titania powders were obtained using a non-ionic surfactant assisted procedure: titanium alkoxide as metal precursor (Ti(OR)4) and non-ionic surfactant as templating agent (polyoxyethylene (18) tridecyl ether, C13EO18) were used. The obtained products were calcined at 350°C for 6 hours. Nanometric titania powders were synthesized using a sol-gel procedure, starting from Ti(OiPr)4. The obtained xerogels were calcined at 450°C for 4 hours. The powders were characterized using X-ray diffraction (XRD) analysis, specific surface area (B.E.T.) measurements, and scanning electron microscopy (SEM) observations. Composite membranes with different titania content, ranging from 1.33 up to 10 wt.%, were prepared by casting and characterized in terms of thermal stability, ion exchange, water uptake, and proton conductivity.The comparison between the two different morphologies showed significant differences in their effect both on water absorption and electrochemical properties. From the electrochemical characterization, the nanometric composites clearly showed a superior electrochemical performance, showing a higher enhancement in proton conductivity values. This observed effect could be associated to the larger number of water-adsorbing acidic sites on the nanometric surface, despite of its lower specific surface area (83 m2/g and 147 m2/g for nanometric and mesoporous titania powders, respectively). Further investigations to better understand this point are in progress.
10:15 AM - S7.3/T6.3
Highly Conductive Polyelectrolyte Multilayers for Electrochemical Devices.
Avni Argun 1 , James Ashcraft 1 , Paula Hammond 1
1 Department of Chemical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractThe increasing focus on clean and sustainable energy sources has led to an interest in electrochemical energy devices such as batteries, fuel cells, and dye-sensitized solar cells. At the core of these devices is an electrolyte which facilitates charge transport between electrodes. Polymeric ionic conductors offer high mechanical strength and fabrication flexibility compared to traditional electrolytes, as well as better physical separation of electrodes. Although the desired properties of solid-state polymer electrolytes depend on the device application, fast ion conduction is essential to reduce electrical resistance and power losses. Furthermore, it would be desirable to utilize approaches that are cost effective and environmentally friendly. Layer-by-layer (LBL) assembly is a versatile thin-film fabrication technique which consists of the repeated, sequential immersion of a substrate into aqueous solutions of complementary functionalized materials.
[1] This approach presents strong advantages as it allows the incorporation of many different functional materials within a single film at a full range of compositions with exceptional homogeneity. In one example, we have developed LBL films by pairing a sulfonated poly(2,6-dimethyl 1,4-phenylene oxide) (sPPO) with poly(diallyl dimethyl ammonium chloride) (PDAC) to obtain ionic conductivity values of 35.2 mS/cm at 25°C and 98% relative humidity. These multilayer films exhibit low liquid methanol permeability and have high chemical stability to provide a direct application as proton-exchange membranes in direct methanol fuel cells (DMFCs). We have demonstrated that simply coating traditional fuel cell membranes with 3 to 5 bilayers of these LBL films improves the power output of DMFCs by over 50% at 25°C.
[2] We are currently developing standalone LBL films peeled off from a low surface energy template as a way of eliminating the need for a substrate.
[1] Lutkenhaus, J. L.; Hammond, P. T., Electrochemically Enabled Polyelectrolyte Multilayer Devices: From Fuel Cells to Sensors. Soft Matter 2007, 3, 804-816.
[2] Argun, A. A.; Ashcraft, J. N.; Hammond, P. T.,
Highly Conductive, Methanol Resistant Polyelectrolyte Multilayers. Advanced Materials
2008,
20, 1539-1543.
10:30 AM - S7.4/T6.4
Titanium Body-Centered-Cubic (BCC) Alloys as Anodes for Lithium Ion Batteries.
Ruigang Zhang 1 , Shailesh Upreti 1 , M. Stanley Whittingham 1
1 , Binghamton University, Binghamton, New York, United States
Show AbstractTitanium BCC alloys with many interstitial insertion sites are one of the state-of-the-art hydrogen storage materials and have been shown to react rapidly with large amounts of hydrogen. Their electrochemical discharge capacity can reach near 1000 mAh/g when using as nickel-hydrogen battery anode. Due to the similarity between hydrogen and lithium, it is interesting to study whether this kind of alloy can be used as the anode in lithium ion batteries. A series of titanium BCC alloys were prepared by arc melting method and their crystal structures were studied by powder X-ray diffraction. Before reaction with lithium, these alloys were treated by various processes including ball milling of various duration, with and without various coatings; annealing at different temperature, and applying hydrogen decrepitation reaction to produce alloy fine particles by reaction with hydrogen gas. Another alloy preparation method — high-energy mechanical ball milling — was also studied. All of the alloys produced by the above processes were tested electrochemically. Experimental results indicate that BCC alloys could improve their lithium intercalation-deintercalation capacity from zero to near 100 mAh/g after the hydrogen decrepitation process. From this initial study, we can conclude that titanium BCC hydrogen storage materials may be considered as lithium ion battery anode. Optimization of synthesis and hydrogen decrepitation conditions, detailed electrochemical studies and determination of structural changes after hosting lithium are underway. We thank Robert Huggins for some initial discussions on these alloys. This work is supported by the US Department of Energy, Office of FreedomCAR and Fuel Partnership, through the BATT program at Lawrence Berkeley National Laboratory.
10:45 AM - S7.5/T6.5
Thermogalvanic Cells for Small-Scale Energy Harvesting and Storage.
Nicholas Hudak 1 , Glenn Amatucci 1
1 Department of Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States
Show AbstractFor many applications, the nodes in a wireless sensor network must be cubic-millimeter sized and have a long lifetime. The amount of energy that can be stored in a sensor node is determined by its size. A cubic-millimeter-sized node with a battery as the sole power source has a severely limited lifetime. Alternatively, energy harvesting devices may be used to recharge the battery or to directly power the sensor and communication components, thus allowing for small nodes with unlimited lifetime. Small-scale energy harvesting devices based on thermoelectric, vibration, and radiofrequency power conversion have been considered for this purpose. An alternative type of thermal energy harvesting, based on thermogalvanic cells, accomplishes both energy harvesting and energy storage in the same device. This multi-functionality is an important space-saving advantage because it eliminates the need for an interface between the energy harvester and the battery. A thermogalvanic cell (or non-isothermal cell) is an electrochemical cell in which the two electrodes are at different temperatures. In symmetric thermogalvanic cells (those with compositionally identical electrodes), the temperature gradient produces a proportional voltage output. The dV/dT values of thermogalvanic cells are typically ~1 mV/K or higher, which is four to five times higher than those of the best thermoelectric materials. A cell with symmetric, single-phase intercalation electrodes can undergo a charge-discharge cycle when supplied with oscillating heat flow. We have demonstrated symmetric LixTiS2 cells operating near room temperature with a temperature difference between the electrodes ranging from 1 K to 10 K. The dV/dT values are dependent on electrode composition (x in LixTiS2) and are around 1 mV/K for 0.4 < x < 0.8. There is also a slight dependence on electrolyte concentration and electrolyte anion. Unlike thermoelectric Seebeck coefficients, these thermogalvanic dV/dT values are closely related to both the entropy of lithium intercalation into LixTiS2 and the thermal diffusion potential of the electrolyte solutions. The former is a function of many parameters including the site energy, related to the overall Madelung energy of the host. A greater understanding of these effects will aid in the selection of materials for battery-type thermogalvanic cells, and results for a range of electrode-electrolyte combinations will be presented.
11:30 AM - S7.6/T6.6
Structural Optimization by TOhoku University Mixed-Basis Orbitals ab Initio Computation Method (TOMBO): Case Study of Hydrides and Molecules.
Ryoji Sahara 1 , Masaya Iwamoto 1 , Osamu Kikegawa 1 , Bahramy Saeed 1 , Ryunosuke Note 1 , Hiroshi Mizuseki 1 , Marcel Sluiter 2 , Yoshiyuki Kawazoe 1
1 , Institute for Materials Research, Sendai Japan, 2 , Dept of MSE, 3ME, TU Delft, Delft Netherlands
Show Abstract To realize applicable hydrogen storage materials, fundamental understanding for hydrides is an important task. While, it is well-known that it is impossible to treat some properties such as XPS spectra and hyperfine structure within pseudopotential approaches. An all-electron method can overcome these limitations. It tends to be slower than a pseudopotential method which deals with valence eigenstates only. Mixed-basis method, in which the electronic eigenstates are expressed in terms of truncated atomic eigenfunctions augmented with plane waves, can be expected to be conceptually and computationally advantageous compared to other full-potential all-electron methods. Although the development of scheme has been attempted, it is not sufficient yet. Our laboratory has developed original program code TOMBO (TOhoku university Mixed-Basis Orbitals ab initio computation method) [2, 3]. In the present study, we deal, for the first time, with structural optimization for twenty molecules including hydrides by TOMBO to testify the effect of the method for light elements including hydrogen compared with “conventional” approaches. The bond lengths and bond angles are compared with the results obtained by VASP [3], Gaussian[4] and experimental values. Present results reproduce experimental values well. That is, the difference between the calculation and experimental data are within 1\% in the typical case. In our presentation, to introduce an advantage of mixed basis method, we also show the results for other molecules and discuss relationship between optimized structures and calculation condition, such as cut-off energy, unit cell and so on.[1] http://www-lab.imr.edu/~marcel/index.html[2] K. Ohno, K. Esfarjani, and Y. Kawazoe, Computational Materials Science, Solid State Sciences 129, (Springer Verlag, Berlin, 1999).[3] http://cms.mpi.univie.ac.at/vasp/vasp/vasp.html[4] Gaussian 03, Revision D.01, M. J. Frisch et al..
11:45 AM - S7.7/T6.7
Synthesis of High Surface Area Pt-Ru Alloys for Electrocatalytic Oxidation of Methanol.
A. Anumol 1 , Aditi Halder 1 , Ravishankar Narayanan 1
1 Materials Research Centre, Indian Institute of Science, Bangalore India
Show AbstractPt alloys are attracting a considerable amount of attention for the last few years as anode catalysts for direct methanol fuel cells (DMFCs) and CO-tolerant proton exchange membrane (PEM) fuel cells. Bi-functional theory invoked for the methanol oxidation in fuel cell mainly rely on the fact that Pt activates the C-H bonds of methanol having the by-product Pt-CO while Ru activates water to produce hydroxyl ion at lower potential and accelerates oxidation of surface-adsorbed CO to CO2. We are reporting a new method of synthesis of Pt-Ru alloys in organic medium. The nanoalloys formed are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX). Microstructural studies have been carried out using high resolution transmission electron microscopy (TEM). Cyclic voltammeter (CV) studies have been carried out to verify the electrocatalytic behaviour towards the methanol oxidation.
12:00 PM - S7.8/T6.8
Self-Filling Small-Scale Electrochemical Cells by Dual Laser Beam Processing.
John Brehm 1 , Alberto Pique 2 , Craig Arnold 1
1 Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States, 2 , Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractThe fabrication of small-scale energy storage components for microdevices is necessary to meet growing demands in these emerging technologies. Successful microbatteries and ultracapacitors electrodes have previously been fabricated, but the completed electrochemical cells typically require assembly or additional processing. One particular complication is the addition of a controlled amount of liquid electrolyte to activate the device. In this work, we present results on a dual-beam laser processing technique that is able to complete the required fabrication including forming electrodes and electrolyte filling in a single processing step. We focus on the system of hydrous ruthenium oxide electrode material with liquid sulfuric acid electrolyte. Electrode and electrolyte material is deposited by laser direct write and the cells are fabricated in a planar geometry. Results show high capacity (>200 mF/cm2) and material utilization with linear discharge behavior. The implications of this technique are discussed in the context of improving the efficiency of these small energy storage devices as well as enabling direct integration on existing microdevices.
12:15 PM - S7.9/T6.9
Solid Oxide Fuel Cell System for Air-independent Applications.
Louis Carreiro 1 , Alan Burke 1
1 Code 8231, Naval Undersea Warfare Center, Newport, Rhode Island, United States
Show AbstractThe U.S. Navy’s need for an unmanned undersea vehicle (UUV) power source with extended mission capability has prompted the development of a solid oxide fuel cell (SOFC) system designed for air-independent operation. To this end, a 30-cell SOFC stack with balance of plant (BoP) was tested under closed anode-loop operation using a high-temperature blower to recycle hot anode exhaust gases generated by the fuel cell. The exhaust was passed through a steam reformer, which converted S-8 (synthetic diesel fuel) to a hydrogen/methane-rich gas stream. A carbon dioxide sorbent bed was employed to prevent fuel dilution by accumulation of carbon dioxide, as well as to provide additional heating for the steam reformer. Over 1 kilowatt of power was generated by the stack with only S-8 and pure oxygen supplied to the stack. The following were achieved simultaneously: greater than 90% oxygen utilization, 75% S-8 utilization, water neutral operation and over 50% efficiency based on the electricity generated versus the lower heating value of S-8.
12:30 PM - S7.10/T6.10
Modeling of the Cycle Life of a Lithium-polymer Battery.
Chee Burm Shin 1 , Ui Seong Kim 1 , Won Jin Jeon 1
1 Chemical Engineering, Ajou University, Suwon Korea (the Republic of)
Show AbstractS8: Cathodes for SOFCs
Session Chairs
Wednesday PM, December 03, 2008
Back Bay A (Sheraton)
2:30 PM - **S8.1
Materials for ITSOFC Cathodes.
John Kilner 1
1 Department of Materials, Imperial College, London United Kingdom
Show AbstractThere is much interest in developing new cathodes for SOFC’s operating in the intermediate temperature range below 700○C. Materials that have been studied include the very interesting oxygen excess materials in the Ruddlesdon–Popper series ABO3(AO)n, such as La2NiO4+δ, and perovskites with ordered A cations in the series AA’B2O5+δ, such as GdBaCo2O5+δ. Details will be given of oxygen isotopic exchange measurements to measure the oxygen transport in these new mixed conducting materials, and, in particular, data from thin film measurements on the anisotropy in the oxygen diffusion coefficient in La2NiO4+δ will be examined and compared to theoretical predictions from atomistic simulations. Finally the relationship between the kinetics of oxygen exchange and their performance of these materials as SOFC cathodes will be examined.
3:00 PM - S8.2
The Remarkable Properties of (Ba0.5Sr0.5)(Co0.8Fe0.2)O3-δ: A Highly Active SOFC Cathode Material.
Jianhua Tong 1 , Justin Ho 1 , Zongping Shao 1 2 , Wei Lai 1 3 , Sossina Haile 1
1 Materials Science / Chemical Engineering, California Institute of Technology, Pasadena, California, United States, 2 College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing, Jiangsu, China, 3 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe compound (Ba0.5Sr0.5)(Co0.8Fe0.2)O3-δ or BSCF has attracted considerable attention since 2004 when it was demonstrated to be a highly active cathode material for solid oxide fuel cells in both dual-chamber (i.e., conventional) and single-chamber configurations [1]. While the exceptional electrochemical activity of BSCF for oxygen electro-reduction at moderate temperatures (in the 500 to 700°C range) has now been confirmed in several laboratories, with fuel cell power output as high as 1.3 W/cm2 at just 600°C reported by G.Y. Meng [2], the fundamental materials parameters governing the electroreduction process are not accurately known. In particular, the few literature values available for the oxygen vacancy concentration, diffusion coefficient, and surface exchange coefficient differ significantly. Here we report the vacancy diffusion and surface exchange coefficients obtained from oxygen flux data collected in in such a way to enable extraction of both of these parameters from a single set of measurements, avoiding discrepancies that can result from combining data from different samples with inevitable slight differences in stoichiometry (especially surface stoichiometry). Vacancy concentration, obtained by conventional thermal analysis methods, is also reported here.[1] Z.P. Shao, S.M. Haile, Nature, 2004, 431, 170-173.[2] G.Y. Meng, C.R. Jiang, J.J. Ma, Q.L. Ma, X.Q Liu, Journal of Power Sources, 2007, 173,189-193.
3:15 PM - S8.3
A study of the electrochemical properties of Ba0.5Sr0.5Co0.8Fe0.2O3-δ.
Monica Burriel 1 , Christian Niedrig 1 , Stefan Wagner 1 , Wolfgang Menesklou 1 , Ellen Ivers-Tiffee 1
1 , Institut fuer Werkstoffe der Elektrotechnik IWE, Universitaet Karlsruhe (TH), Karlsruhe Germany
Show Abstract3:30 PM - S8.4
New Cathode Candidates to IT-SOFCs, the Oxygen Deficient (Bi0.15Sr0.85-xAx)Co1-yFeyO3-d Perovskites.
Annika Eriksson 1 , Christopher Knee 2 , Sten-G. Eriksson 1 , Gunnar Svensson 3 , Peter Svedlindh 4
1 Chemical and Biological Engineering, Environmental Inorganic Chemistry, Chalmers Univeristy of Technology, Gothenburg Sweden, 2 Dept. of Chemistry, The University of Gothenburg, Gothenburg Sweden, 3 Dept. of Structual Chemistry, Stockholm University, Stockholm Sweden, 4 Dept. of Engineering science, Uppsala University, Uppsala Sweden
Show AbstractExploring new materials are of high importance for the next generation of high performance cathodes in solid oxide fuel cells (SOFCs). The present traditional cathodes are operating at high temperatures (800-1000°C) and have material compatibility challenges to overcome which give rise to high running costs. [1] A new mixed ionic and electronic conducting (MIEC) cathode material with promising property is the reported oxide perovskite structured (Ba0.5Sr0.5)1-xSmxCo0.8Fe0.2O3-d [2]. The results of this oxygen deficient perovskite inspired us to study similar series of Co and Fe containing perovskites, the A and B substituted solid solution series (Bi0.15Sr0.85-xAx)Co1-yFeyO3-d, where Ax is Ca0.17 or Ba0.286 and 0.0 < y < 1.0.Here we present two studies based on neutron powder diffraction (NPD), high resolution microscopy/electron diffraction (HREM/ED), thermogravimetrical (TGA), conductivity/resistivity and magnetic susceptibility measurements.A complicated series of different perovskite structures appeared as the degree of Fe content increased. Weak diffraction peaks or diffuse scattering resolved from NPD and HREM/ED for the as-prepared samples with; x = 0.1 Fe content resulted in a P 4/mmm supercell, a = b ≈ ap and c ≈ 2ap; x = 0.2-0.6 a disordered simple cubic unit cell P m3m a ≈ ap and x = 0.8-1.0 pseudo-cubic P 4/mmm, a,b ≈ ap, c≈ap unit cell with increased tetragonality vs. the amount of Fe. By increased Fe addition in these systems, short range ordering was detectable by diffuse scattering, indicating the local ordering of Co-O and Fe-O coordination. Upon oxygen annealing of the Sr/Ca as-prepared samples resulted in contracted simple cubic unit cells and the diffuse scattering disappeared. However in the Ba samples most of the magnetic intensity remained, indicating a more stable Co/Fe magnetic ordering. Detailed magnetisation results revealed spin glass behaviour for the x = 0.1, 0.25 and 1.0 Sr/Ca-oxygen annealed samples, in contrast to the antiferromagnetically ordered ground state of the as-prepared materials. [3] TGA/DSC results show that these materials show good redox properties in the IT-SOFC range and conductivity data indicate comparable or better conductivity to similar systems reported in the literature and are therefore promising new cathode candidate for (MIEC) solid oxide cathode.[1] Z. Shao and S.M Halle, Nature 431 (2004) 170[2] S. Li, Z Lü, X. Huang, B. Wie and W. Su, Solid State Ionics, 178 (2007) 417[3] A. K. Eriksson et al., corrected proof in J. Solid State Chem. 2008
3:45 PM - S8.5
Composite Cathodes on Barium Cerate Proton Conducting Electrolyte for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs).
Emiliana Fabbri 1 , Silvia Licoccia 1 , Enrico Traversa 1 , Eric Wachsman 2
1 NAST Center & Department of Chemical Science and Technology, University of Rome Tor Vergata , Rome Italy, 2 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractSignificant efforts have being recently oriented towards the development of materials for intermediate temperature (IT, 400–700°C) solid oxide fuel cells (SOFCs). Proton conductor perovskites offer several advantages as IT electrolyte materials: no dilution of the fuel with water vapor, the possibility of internal reforming of hydrocarbon fuel without CO2 generation, and high conductivity at intermediate temperature because of low activation energy for proton transport.The reduction of SOFC operating temperature causes large overpotential at the electrode–electrolyte interface. In particular, the cathode plays a critical role in establishing intermediate operating temperature because the oxygen reduction kinetics are several orders of magnitude slower than the kinetics related to the fuel oxidation. Cathode overpotential can be reduced using composite electrodes, due to the increased triple phase boundary (TPB) length.Reports about composite electrode materials for IT-SOFC based on a proton conductor electrolyte are scarce. Therefore, the development of a performing cathode is crucial to make IT-SOFCs based on proton conductors competitive with the more established SOFCs using an oxygen-ion conductor electrolyte.This work reports the investigation of composite cathodes for proton conductor electrolyte made of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) as the O2-/e- mixed conductor phase, combined with BaCe0.9Yb0.1O3-δ (10YbBC) proton conductor phase. 10YbBC was chosen as proton conductor phase because it has shown good mixed ionic-electronic conduction under high pO2 atmosphere, a condition that is particularly interesting since it corresponds to the operating conditions in fuel cell cathode. Microstructural and electrochemical parameters have been studied to optimize the composite cathode performance. Hence, the area specific resistance (ASR) was studied as a function of cathode composition, sintering temperature, particle size, and oxygen partial pressure. The optimized composite cathode has achieved lower ASR than the commonly used LSCF cathode, as well as than platinum electrode.
4:30 PM - **S8.6
Deconvolution of SOFC Cathode Polarization Mechanism.
Eric Wachsman 1
1 Florida Institute for Sustainable Energy, University of Florida, Gainesville, Florida, United States
Show AbstractFuel cells offer great promise as a clean and efficient process for directly converting chemical energy to electricity while providing significant environmental benefits. Among the different fuel cell technologies, solid oxide fuel cells (SOFCs) are unique in their ability to operate both within the current fossil fuel based energy infrastructure and as part of a future proposed hydrogen fuel infrastructure. Unfortunately, SOFC cost and reliability are limited by high operating temperature requirements. With the current state of the art SOFCs, performance at lower temperature is limited by cathode polarization.In order to understand the various mechanistic contributions to cathode polarization and apply this knowledge to development of lower-polarization/lower-temperature SOFC cathodes, we have embarked on a multi-faceted, multi-disciplinary approach to deconvolute the various contributions to SOFC cathode polarization. This approach includes FIB/SEM to quantify the cathode microstructure (in terms of tortuosity and porosity for gas diffusion, solid-phase surface area for gas adsorption/surface diffusion, and triple phase boundaries for the charge transfer reaction) and heterogeneous catalysis techniques (temperature programmed desorption and reaction) and O-isotope exchange to evaluate the O2 reduction mechanism at the gas-solid reaction interface. These results are then combined (and contrasted) with the more conventional electrochemical polarization techniques (impedance spectroscopy and I-V behavior) to try and elucidate each of the mechanisms as a function of material and microstructure. The progress to date on this investigation will be presented.
5:00 PM - S8.7
A Comparison of Electrochemical Performance of Double Perovskite REBaCo2O5+x Cathodes in Symmetrical Solid Oxide Fuel Cells.
W. Gong 1 , Manoj Yadav 1 , Allan Jacobson 1
1 Chemistry, University of Houston, Houston, Texas, United States
Show AbstractThe ordered vacancies in the oxygen-deficient double perovskites REBaCo2O5+x (RE = La, Pr, Nd, Sm, Eu) could greatly enhance the diffusivity of oxide ions in the bulk of these materials and possibly supply surface defect sites with enhanced reactivity towards molecular oxygen. Some materials in this family of RBCO compounds, such as PrBaCo2O5+x, (PBCO), have already demonstrated high electronic conductivity, rapid oxygen ion diffusion and surface exchange kinetics. Therefore, the family of RBCO compounds were synthesized and evaluated as promising cathode materials for low and intermediate temperature solid oxide fuel cells (SOFCs) based on gadolinium doped ceria (CGO) and doped lanthanum gallate (LSGM) electrolytes. The electrochemical performance of symmetrical cells (RBCO/CGO and RBCO/LSGM composite cathodes on the CGO and LSGM electrolytes, respectively) was evaluated by using AC impedance spectroscopy. The area specific resistance (ASR) performance was measured as a function of temperature as well as oxygen partial pressure.
5:15 PM - S8.8
LnBaCo2O5+δ Double Perovskites as Cathodes for Solid Oxide Fuel Cells.
Jung-Hyun Kim 1 , Arumugam Manthiram 1
1 Materials Science and Engineering, The University of Texas at Austin, Austin, Texas, United States
Show AbstractThe solid oxide fuel cell (SOFC) technology is confronted with slow oxygen reduction kinetics with the conventional cathode materials at the intermediate operating temperatures of 500 – 800 °C. In this regard, the mixed ionic-electronic conducting (MIEC) properties of the double perovskite oxides LnBaCo2O5+δ have become appealing recently. A few groups have reported the fast surface exchange kinetics of the LnBaCo2O5+δ oxides (Ln = Pr and Gd) using 18O/16O isotope exchange depth profile (IEPD) and their possible application as cathodes for SOFC. This presentation will focus first on a systematic investigation of the influence of the Ln3+ ions on the high temperature properties of the LnBaCo2O5+δ (Ln = La, Nd, Sm, Gd, and Y) oxides and an exploration of their use as cathodes for intermediate temperature SOFC. The oxygen content (5+δ), thermal expansion coefficient (TEC), and electrical conductivity decrease with decreasing size of the Ln3+ ions from Ln = La to Y. Single cell SOFC performance tests show that the catalytic activity for the oxygen reduction reaction (ORR) decreases with decreasing size of the Ln3+ ions from Ln = La to Gd. In addition, oxygen permeability through the LnBaCo2O5+δ membranes decreases from Ln = La to Sm. These results suggest that lanthanide ions with an intermediate size offer a tradeoff between catalytic activity and TEC. The presentation will then focus on the modification of the LnBaCo2O5+δ compositions to tune the properties and performance parameters further for SOFC application. For example, NdBaCo2O5+δ exhibits good performance in SOFC, but with a high TEC (19.1 x 10-6 K-1). Interestingly, the substitution of Ni for Co is found to lower the TEC to 16.9 x 10-6 K-1 while still maintaining high catalytic activity at x = 0.4 in NdBaCo2-xNixO5+δ. Similarly, GdBaCo2O5+δ exhibits chemical instability with the electrolyte materials such as GDC and LSGM at high temperatures of 1100 °C. Substitution of Sr for Ba is found to improve the chemical stability of the GdBa1-xSrxCo2O5+δ cathodes with improved catalytic activity. However, unlike the Ni substitution, the GdBa1-xSrxCo2O5+δ system exhibits a structural change from orthorhombic (x = 0) to tetragonal (x = 0.2 - 0.6) with increasing TEC values. The difference in the ionic radii between (Ba1-xSrx)2+ and Gd3+ also plays a dominant role in determining the oxygen content value in the GdBa1-xSrxCo2O5+δ system.
5:30 PM - S8.9
Morphology of Sr-doped LaMnO3 Nanoparticles on Single Crystal (100) YSZ.
Leta Woo 1 2 , Raymond Gorte 2 , Robert Glass 1 , Art Nelson 1 , Christine Orme 1
1 Chemistry, Materials, Earth and Life Sciences, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractThe interaction between nanoparticles of strontium-doped lanthanum manganite (LSM) and single crystal (100) yttria-stabilized zirconia (YSZ) was investigated using atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM)/energy-dispersive x-ray spectroscopy (EDS). Nanoparticles of LSM (La0.85Sr0.15MnO3) were deposited directly onto single crystal (100) YSZ substrates using an ultrasonic spray nozzle. Samples were then annealed from 850°C to 1250°C, and AFM results showed that nanoparticles gradually decreased in height and eventually disappeared completely. Subsequent reduction in H2/H2O at 700°C resulted in the reappearance of individual discernable nanoparticles. Studies were carried out on identical regions of the sample allowing the same nanoparticles to be characterized at different temperatures. XPS results confirmed the formation of a thin layer of LSM with increasing temperature. SEM/EDS was used to analyze the composition of the nanoparticles that reappeared in the sample reduced in H2/H2O at 700°C and showed evidence of the presence of lanthanum. The analysis suggests that the LSM morphology changes from particles to a film at temperatures that are usually used to process LSM/YSZ cathodes (~1200°C). The reappearance of discrete particles under reducing conditions at 700°C may indicate that nanoporosity at the LSM/YSZ interface plays a role in the observed activation behavior of LSM cathodes, where performance improves after the initial application of cathodic current. The processing temperatures of LSM/YSZ cathodes (~1200°C) result in a thin film that initially limits the diffusion of oxygen ions and lowers performance. Cathodic polarization then results in reducing conditions at the LSM/YSZ interface and creates porosity that allows oxygen to reach the LSM/YSZ interface improving performance. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Support for this work was provided by the U.S. Department of Energy's Hydrogen Fuel Initiative (grant DE-FG02-05ER15721).
5:45 PM - S8.10
In Situ Synchrotron X-ray Studies of Model Perovskite Thin-Film Solid Oxide Fuel Cell Cathodes.
Kee-Chul Chang 1 , Brian Ingram 2 , Bilge Yildiz 3 , Balasubramaniam Kavaipatti 4 , Paul Salvador 4 , Daniel Hennessy 1 , Hoydoo You 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractThe solid oxide fuel cell (SOFC) has advantages of high efficiency and fuel-flexibility but is not yet economically competitive enough to gain widespread acceptance. One of the areas of improvement for SOFCs is the cathode performance, which requires a more fundamental understanding of the mechanism and kinetics of the oxygen reduction reaction at the cathode.We are attempting to elucidate what happens on the cathode surface during heating and under applied potential by using dense epitaxial thin-films of La0.7Sr0.3MnO3 (LSM) or La0.7Sr0.3CoO3 (LSC) electrodes on single crystal yttria-stabilized zirconia electrolytes. Although industrial SOFC use porous electrodes, electrochemical reactions in such systems are complex, so we hope to gain better understanding by controlling the reaction pathways with our film structure. For our in situ studies, grazing incidence x-rays were used for surface sensitive characterization on the thin-film electrodes, heated up to temperatures between 700 to 1000°C in atmospheric pressure. The applied potential on the electrode was controlled using a half cell setup. Chemical state changes were monitored with X-ray absorption near edge spectroscopy (XANES) and the cation concentration depth profile was obtained by a combination of X-ray reflectivity and fluorescence by varying the incidence angle of the X-rays.We find that for LSC, the edge energy in the Co K edge XANES changes as the sample is heated up to high temperature, implying a change in the Co chemical state. But the XANES does not change further with applied potential even with decreasing electrode resistance.We also found evidence of Sr surface segregation at room temperature, which was especially prominent for the LSM but is also present in LSC. This is especially significant for LSM (110) oriented films grown on YSZ (111) and the X-ray fluorescence results combined with atomic force microscopy reveals that the Sr segregation is concentrated on particles, which increase in number on the surface after annealing. At high temperature, the surface Sr is reincorporated into the surface and the reincorporation rate seems to have a weak dependence on the applied potential. These results suggest that role of cation segregation may be important for understanding the cathode activity for these Sr doped perovskite thin film electrodes.
S9: Poster Session: Solid State Ionics
Session Chairs
Tim Armstrong
Toshiaki Matsui
Rosa Palacin
Enrico Traversa
Thursday AM, December 04, 2008
Exhibition Hall D (Hynes)
9:00 PM - S9.1
Phase Transformation in Titania Nanocrystals by the Oriented Attachment Mechanism: The Role of pH Medium.
Caue Ribeiro 1 , Cristiano Barrado 2 , Emerson Camargo 2 , Elson Longo 3 , Edson Leite 2
1 , Embrapa Instrumentação Agropecuária, Sao Carlos, SP, Brazil, 2 Chemistry, Universidade Federal de Sao Carlos, Sao Carlos, Sao Paulo, Brazil, 3 Chemistry, Universidade Estadual Paulista, Araraquara, Sao Paulo, Brazil
Show AbstractNanoparticle growth mechanisms have received much attention in recent years, especially in view of the importance of controling nanostructural sizes and morphologies. In-depth investigations into classical nanoparticle coarsening processes (Ostwald ripening, OR) have demonstrated the importance of proper control in this stage of the synthesis so that the desired nanostructures can be obtained. However, the Oriented Attachment (OA) mechanism has been highlighted as a common step in nanocrystal growth, even in systems with high solubility (when OR is expected). The influence of this mechanism on the anisotropy of oxide nanocrystals has been investigated, and a wide range of distinct nanostructures are reportedly formed through this mechanism. However, although the role of this mechanism in nanoparticle morphology is well understood, investigations into other implications are still incipient. One of these aspects is the mechanism's influence in phase control, an important variable, particularly in systems with many polymorphs, and one that is frequently disregarded. The role of the growth mechanism in phase control can be understood in terms of its influence on the total distribution of the facets, which can be attained by tailoring anisotropic structures (since the OA mechanism is related to this aspect). Its influence is interpreted as the modification of the Area/Volume relation in the formed particles, favoring phase transformation or not according to the crystallographic planes exposed after the event. However, the surface energy of each plane is strongly influenced by the presence of counterions in the medium. As an example, in the synthesis of TiO2 nanoparticles, it has been shown that the presence of common ions in the synthesis environment, such as Cl- or organic chains from the precursors, can alter phase stability. In order to obtain a representative system for TiO2 with minimal interferences, we have developed a clean synthesis using metallic Ti and hydrogen peroxide as precursors, crystallized in a conventional hydrothermal apparatus. This system can offer some insights concerning the influence of surface energy in the OA mechanism and its importance for adequate phase control of nanoparticles during synthesis. The results revealed the evolution of the crystal morphology dictated by the conditions of pH, which shows a strong dependence on the surface conditions, i.e., surface energy. The occurrence of the OA mechanism as an important way to modify the morphology and, hence, the distribution of surface energy, confirmed that the mechanism can accelerate some phase transitions, albeit with interference of the pH medium in terms of how the mechanism affects the final particle morphology and direction of crystalline growth. Finally, the importance of the mechanism was also apparent in an extremely basic condition, indicating a possible correlation with the formation of hydrogen titanate nanostructures.
9:00 PM - S9.10
Development and Study of Au-(Y2O3)x(ZrO2)y Nanocomposites Films for All-Optical Harsh Environment Chemical Sensing Applications.
Phillip Rogers 1 , Michael Carpenter 1
1 College of Nanoscale Science and Engineering, University at Albany, Albany, New York, United States
Show AbstractThe development of novel harsh environment compatible chemical sensing technologies is of critical need for optimal control of future zero emission power plants and low emission jet turbine engines as current sensor technologies cannot withstand these environments. As an alternative sensing technology gold nanoparticle embedded yttria-stabilized zirconia (Au-YSZ) nanocomposite films have been deposited on optically transparent sapphire substrates. The Au nanoparticle surface plasmon resonance (SPR) band was monitored as concentrations of O2, H2, and NO2 in N2, were varied and flowed over Au-YSZ films at elevated temperatures (~500 °C). Detectable changes in the SPR band were observed for all of the test gases as long as the temperature was greater than ~350 °C. Extensive O2/H2 and O2/NO2 titration experiments were performed and will be discussed in terms of reactions occurring between exposure gases, Au nanoparticles and YSZ, which result in charge transfer to and from the Au nanoparticles upon concentration changes in gas exposure environment. Because the peak position of the SPR band relies closely on the number of driven oscillating free electrons per gold nanoparticle, we were able to monitor electrochemical charge transfer to and from Au nanoparticles to diffusing oxygen ions by monitoring the optical properties of the Au-YSZ nanocomposite thin film, specifically the peak position of the SPR band. We have developed an electrochemical model which agrees with the experimental data obtained for both H2/O2 and NO2/O2 titration experiments and a direct relation was observed for the change in the equilibrium ratios, pH21/4pO2-1/8 and pO2-1/8pNO2-1/4, contributing to oxygen ion diffusion into and out of the YSZ matrix, and the change in the square of the SPR band peak position. Free electron theory states that this change in the square of the SPR band peak position is directly proportional to the change in conduction electrons available per Au nanoparticle, thus our observations agree with the expected trend for charge transfer versus the redox gas mixture. Future experiments are focused on the layer-by-layer deposition of colloidal Au nanoparticles within the YSZ matrix. Colloidal Au offers the benefits of a greater degree of size control and narrower size distributions. With greater control of the Au nanoparticle sizes we intend to investigate the fundamental interactions between exposure chemicals and Au nanoparticles in harsh environments.
9:00 PM - S9.11
Defect State Dampening of the Au Nanoparticle SPR Band in Au-YSZ Nanocomposites in Harsh Environments.
Phillip Rogers 1 , Michael Carpenter 1
1 College of Nanoscale Science and Engineering, University at Albany, Albany, New York, United States
Show AbstractThe optical signature of Au nanoparticles within an yttria-stabilized zirconia matrix has been demonstrated as an optical beacon for changes in emission gas concentrations within harsh environments. Characteristic of these optical signals is an increased dampening of the surface plasmon resonance (SPR) band of the Au nanoparticles at 500 °C under increasing O2 concentrations in N2. It has been proposed that this broadening in the SPR band is due to adsorbate induced dampening of the SPR band, which was initially observed using gas aggregation techniques on Ag nanoparticles, and can be observed at elevated temperatures by simply changing the gas environment of Au-YSZ films. We have developed a model to describe the changes we see in the SPR band broadening based on adsorbate induced dampening theory for metallic nanoparticles. The model agrees with experimental results within a factor of three and shows promise in furthering the understanding of the optical properties possessed by noble metal nanoparticles embedded in a metal oxide matrix. Future experiments will be focused on the more precisely measuring the electronic defect states for the Au-YSZ material set and in varying the doping profile of Y2O3 in Au-YSZ nanocomposite thin films by kinetic demixing. Y2O3 concentration gradient profiles across the nanocomposite thin film will offer a fast method for manufacturing optical arrays where the oxygen ion vacancy concentration is different from one point of the film to another allowing for the parallel data acquiring of optical absorption data for films possessing different average oxygen ion vacancy concentrations, which will effect the broadening observed.
9:00 PM - S9.12
Polyaniline-Silica Aerogel Composites.
Dylan Boday 1 , Douglas Loy 1
1 Materials Science & Engineering, University of Arizona, Tucson, Arizona, United States
Show AbstractAerogels are extremely high surface area, low density materials with numerous applications including thermal insulators, radiation detectors, cometary dust particle traps, and adsorbents. However, their low density also makes them extremely fragile and almost impossible to machine or process without breaking. This has lead to the development of aerogel composites with enhanced mechanical properties through the addition of polymers or surface modifiers. Polyaniline is a conjugated polymer that can be formed as nanofibers and has been successfully applied as anti-corrosive coatings and the active component in sensors. In this study we have, for the first time, integrated polyaniline nanofibers into silica aerogels. The composites are formed by introducing the pre-formed polyaniline nanofibers into the sol-gel polymerization. The point at which the polyaniline is introduced into the polymerization can have profound effects on the morphology of the composites. The resulting gels are processed using supercritical carbon dioxide-solvent exchange and drying to afford black aerogels. Our results show that the incorporation of the polyaniline nano-fibers increases the strength of the silica aerogel tenfold over that of silica aerogels without polyaniline fibers. The mechanical properties of the composites are dramatically affected by the concentration of the polyaniline incorporated into the silica aerogel, with the strongest composites containing ~9 wt% of polyaniline. We have also been studying the electrical conductivity of the composite aerogels as a function of polyaniline content, composite morphology and chemical doping. The high surface area of aerogels coupled with the improvement in mechanical properties and doping dependent electrical conductivity make these new materials attractive candidates for sensors and electrodes.
9:00 PM - S9.13
The Effects of Partial Crystallinity on the Hydrogen Permeation Properties in Amorphous Metallic Systems.
Kyle Brinkman 1 , Elise Fox 1 , Thad Adams 1
1 Materials Science and Technology Directorate, Savannah River National Laboratory (SRNL), Aiken, South Carolina, United States
Show AbstractIt is recognized that hydrogen separation membranes are a key component of the emerging hydrogen economy. A potentially exciting material for membrane separations are bulk metallic glass materials due to their low cost, high elastic toughness and resistance to hydrogen embrittlement as compared to crystalline Pd-based membrane systems. However, at elevated temperatures and extended operation times structural changes including partial crystallinity may appear in these amorphous metallic systems. A systematic evaluation of the impact of partial crystallinity/devitrification on the diffusion and solubility behavior in multi-component Metallic Glass materials would provide great insight into the potential of these materials for hydrogen applications. This study will report on the impact of hydrogen on the thermodynamics and kinetics of phase evolution during crystallization obtained by thermal annealing under different gas environments. This structural data will be related to diffusion, solubility, and ultimately the hydrogen permeation properties of commercially available Zr and Fe/Co based Metallic Glass materials.
9:00 PM - S9.14
Directing the Morphology of Polyaniline Composites via in Situ Polymerization Assisted by Block Polyelectrolyte.
Chi-Yang Chao 1 , I-Chun Hsieh 1
1 Materials Science and Engineering, National Taiwan University , Taipei Taiwan
Show AbstractIn this study, polyaniline (PANi) composites were prepared from in situ polymerization of aniline monomers dispersed in block polyelectrolyte aqueous solution. The block polyelectrolyte, poly(styrene-block-sulfonated hydroxystyrene) (PS-b-sPHS), with various molecular weights and compositions were synthesized through anionic polymerization and sequential analogous chemistry. The pendant sulfonic acids of sPHS segment had strong interaction with aniline monomers and the composites exhibited special morphologies including nanoparticles, nanorods, nanotubes, hierarchical aggregation of short nanorods, hallow spheres as well as networks. These morphologies were found to associate with the structures of the block polyelectrolyte micelles formed in the solution. By controlling the concentrations of aniline and of the block polyelectrolyte in the solution as well as the chemical composition of the block polyelectrolyte, the morphologies of the composite could be manipulated. The morphologies and sizes of the composites were also found to strongly relate to the polymerization time, which enable us to study the mechanism of the formation of the PANi composites. Some of the PANi composites, containing only small amount of PANi, exhibit high electric conductivity in the range of several S/cm without extra doping since sulfonic acids also served as doping reagents. The conductivity was found to be a complexed function of the morphology of the composite and the composition of the block polyelectrolyte.
9:00 PM - S9.2
Laser Sintering of Titanium Oxide for Low Temperature Processing of Photoelectrochemical Cells.
Elena Krieger 1 2 , Guodan Wei 1 2 , Nan Yao 1 2 , Craig Arnold 1 2
1 Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States, 2 Princeton Institute for Science and Technology of Materials, Princeton University, Princeton, New Jersey, United States
Show Abstract9:00 PM - S9.3
Synthesis of Novel Zr- or Ti-based Porous Mixed Oxides through the Wall Ion Exchange Method.
Shunsuke Hori 1 , Insuhk Suh 1 , Toshihiro Tanaka 1 , Masakazu Iwamoto 1
1 Chemical Resources Laboratory, Tokyo institute of Technology, Yokohama Japan
Show Abstract1. Introduction We have reported that sulfate anions in hexagonally mesostructured zirconium sulfate-surfactant micelle materials (ZS) were readily exchanged for oxyanions of P, As, or Se in aqueous solutions1, 2) and that the P-exchanged ones showed hexagonally ordered pore systems and high surface areas (> 400 m2g-1) upon calcination.1) This new preparation method of mesostructured or mesoporous materials is named the Wall Ion Exchange (WIE) method. In the present study we applied the method to several transition metal oxyanions on ZS and titanium oxysulfate-surfactant micelle mesostructured materials (TS) and various porous mixed metal oxides could be prepared.2. Experimental The parent materials ZS and TS were synthesized by the reported manners. Their chemical compositions were Zr(HSO4)(C19H42N)0.5(OH)3.5.2H2O and TiO(HSO4)0.7(OH)1.9(C19H42N)0.6.H2O. The ion-exchange was carried out in an aqueous solution of K2CrO4, (NH4)6Mo7O24, (NH4)10W12O41, NH4VO3, KMnO4, NH4[NbO(C2O4)2(H2O)2] or NaReO4. The pH value of the solution was adjusted by adding an aqueous ammonia or HCl solution. The parent material was dropped into the solution, shaken at 303 K and 120 rpm for 24 h, filtered, and dried at 353 K for 12 h. The resulting Metal-ZS or -TS were heated at 673 K for 2 h in air. 3. Results and Discussion The introductions of metal oxyanions were observed in the wide range of pH of the solutions but most of their hexagonal structures were destroyed upon the calcination. When the WIE treatment was carried out in the pH range of mono oxyanions we could obtain the corresponding porous materials. The obtained porous/nonporous materials could be divided into three groups from the viewpoint of surface area. The wall densities are dependent on the specific gravities of components and therefore we used the surface areas per unit volume for comparison. High surface areas above 1,000 m2cm-3 were observed on Cr-, P-, W-, and Mo-ZS and Cr-TS. Medium surface areas of 999-50 m2cm-3 were on V-, Mn-ZS and Mo- and W-TS. Low surface areas below 50 m2cm-3 were on Re-, and Nb-ZS. It should be noted that the values of Cr-ZS (2300 m2 cm-3), Cr-TS (2000), and P-ZS (1960) were comparable to that of silica MCM-41 (2200). The materials of the first group possessed the hexagonal array of pores. The pore diameters, however, were all 0.8-0.9 nm which were smaller than that of P-ZS (1.66 nm) or silica MCM-41 (2.2). This was due to the increment of the wall thickness of Metal-ZS which was approximately 1.7-2.1 nm. The values were much thicker than that of silica MCM-41 (1.0-1.1 nm). It follows that the WIE method is the very new and widely-usable preparation method of porous mixed metal oxides. 1) P. Wu and M, Iwamoto, Chem. Lett., 1213 (1998). P. Wu, M. Iwamoto et al., Chem. Mater., 17, 3921 (2005).2) M. Iwamoto, H. Kitagawa and Y. Watanabe, Chem. Lett., 814 (2002). H. Takada, Y. Watanabe and M. Iwamoto, Chem. Lett., 62 (2004).
9:00 PM - S9.4
Modeling of Ionic Transport through Functionalized Nanopores.
Petr Kral 1 , Boyang Wang 1
1 Department of Chemistry M/C 111, University of Illinois at Chicago, Chicago, Illinois, United States
Show Abstract9:00 PM - S9.5
Preparation of Nanosuperionic Materials by Ball-Milling.
Georges Denes 1 , M. Cecilia Madamba 1 , Abdualhafed Muntasar 1 , Alena Peroutka 1
1 Chemistry and Biochemistry, Concordia University, Montreal, Quebec, Canada
Show AbstractThe best fluoride-ion conductors were, for a long time the MF2 (M = Ca, Sr, Ba and Pb) compounds that have the fluorite-type structure, with β-PbF2 having the highest performance from far. The superior performance of the fluorite-type materials has been explained by the presence of a large number of empty F8 cubes (half of them, the other half being occupied in its center by a M2+ cation) that can be used as interstitial sites for a Frenkel defect type of conduction. However, Dénès has shown that this mechanism does not explain why β-PbF2 has a conductivity that is much higher than that of BaF2, since the F8 cubes of BaF2 are large enough to take a fluoride ion without local strain, when the F8 cube of β-PbF2 requires local distortion and should therefore be less efficient. Furthermore, new materials, most containing divalent tin prepared in the last two decades, have a fluoride ion conductivity much higher than any other fluoride known before, and can therefore be labeled superionics. This is the case of the MSnF4 materials (M = Ba & Pb), the conductivity of which is three orders of magnitude higher than that of the corresponding MF2, and also of disordered systems such as PbSn4F10 and the Pb1-xSnxF2 solid solution. Furthermore, new materials, the conductivity of which has not been measured yet, have been prepared in our laboratory, such as Pb2SnF6, CaSn2F6 and the Ca1-xSnxF2 solid solution. In a new development of this work, nanocrystalline disordered phases of many of the materials containing tin(II) and either lead(II) or Ba have been prepared and studied. They were obtained by mild ball-milling, for a very short time (1-5 minutes for all the PbSnF4 phases, up to 40 minutes for BaSnF4). The order-disorder transition has been studied by X-ray diffraction, and 119Sn Mössbauer spectroscopy was used to investigate the tin electronic structure and eliminate the possibility of electronic conduction. All materials studied so far by electrical methods have a fluoride ion transport number equal to 0.99 or higher.
9:00 PM - S9.6
NASICON-like Phases in InPO4-Na3PO4-Li3PO4 Quasiternary System.
Anna Potapova 1 , Irina Smirnova 1 , Felix Spiridonov 2 , Andrey Novoselov 1 , Sergey Stefanovich 2 , Galina Zimina 1
1 Department of Chemistry and Chemical Engineering for Rare and Dispersed Elements, Lomonosov Moscow State Academy of Fine Chemical Technology, Moscow Russian Federation, 2 Department of Chemistry, Lomonosov Moscow State University, Moscow Russian Federation
Show Abstract9:00 PM - S9.7
Proton Conductivity of PAA-KDP Composites.
Dmitry Zakharyevich 1 , Vladimir Burmistrov 1
1 Condensed Matter Physics, Chelyabinsk State University, Chelyabinsk Russian Federation
Show Abstract9:00 PM - S9.8
Influence of Alkaline Earth Oxide Coatings on the Oxygen Exchange Kinetics of Sr(Ti1-xFex)O3-δ.
Stefan Wagner 1 , Wolfgang Menesklou 1 , Christos Argirusis 2 , Guenter Borchardt 2 , Ellen Ivers-Tiffee 1
1 , Institut fuer Werkstoffe der Elektrotechnik IWE, Universitaet Karlsruhe (TH), Karlsruhe Germany, 2 , Institut fuer Metallurgie, Technische Universitaet Clausthal, Clausthal-Zellerfeld Germany
Show Abstract9:00 PM - S9.9
Sensing Behavior in Diesel Exhaust of Impedancemetric NOx Gas Sensor Based On Porous YSZ/Dense Electrode Interface.
Leta Woo 1 3 , Robert Glass 1 , Robert Novak 2 , Jaco Visser 2 , Erica Murray 2 , Raymond Gorte 3
1 , Lawrence Livermore National Laboratory, Livermore, California, United States, 3 Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 , Ford Motor Company, Dearborn, Michigan, United States
Show Abstract
Symposium Organizers
Enrico Traversa University of Rome Tor Vergata
Timothy Armstrong Carpenter Technology Corporation
Koichi Eguchi Kyoto University
M. Rosa Palacin Institut de Ciencia de Materials de Barcelona (CSIC)
S10: Solid Oxide Fuel Cells I
Session Chairs
John Kilner
Eric Wachsman
Thursday AM, December 04, 2008
Back Bay A (Sheraton)
9:30 AM - **S10.1
Microstructural Evolution and Performance in Impregnated Oxide SOFC Electrodes.
John T.S. Irvine 1 , Gael Corre 1 , Guntae Kim 2 , Ray Gorte 2 , John Vohs 2
1 Chemistry, St Andrews University, St Andrews United Kingdom, 2 Chemical and Biomolecular Engineering,, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractFuel cells will undoubtedly find widespread use in this new millennium in the conversion of chemical to electrical energy, as they offer very high efficiencies and have unique scalability in electricity generation applications. The solid oxide fuel cell (SOFC) offers certain advantages over lower temperature fuel cells, notably its ability to utilise CO as a fuel rather than being poisoned and the availability of high-grade exhaust heat for combined heat and power or combined cycle gas turbine applications. Although cost is clearly the most important barrier to widespread SOFC implementation, perhaps the most important technical barriers currently being addressed relate to the electrodes, particularly the fuel electrode or anode. In terms of mitigating global warming, the ability of the SOFC to utilise commonly available fuels at high efficiency, promises an effective and early reduction in carbon dioxide emissions and hence is one of the lead new technologies to improve the environment. In the longer the ability to utilise waste derived fuels such as biogas will be of critical importance. We have recently demonstrated that it is possible toachieve a very high performance with an electrode made from 45 wt % La0.8Sr0.2Cr0.5Mn0.5O3(LSCM), 0.5 wt % Pd, and 5 wt % ceria infiltrated into a porous YSZ scaffold.In this composite electrode,LSCM provides electronic conductivity, YSZ provides ionic conductivity, and the Pd–ceria mixture enhances the catalytic activity for fuel oxidation. An SOFC with this fuel–electrode composition exhibited maximum power densities at 1073 K of 1.1 and 0.71 W/cm2 in humidified (3% H2O) H2 and CH4, respectively, even though the cell had a relatively thick, 60 micron YSZ electrolyte. The composite electrode was also stable to oxidation and reduction cycles,showing conductivity under both oxidizing and reducing conditions.Performance in hydrogen improved markedly on increasing temperature from 700 to 800oC and then less significantly on increasing to 900oC. These changes correlated closely with an evolution in microstructure from the smooth coating that initially formed on synthesis in oxidising conditions to yield a structure rich in triple phase boundaries with small, approaching nanoscale, LSCM particles forming on the YSZ scaffold at 800oC. On reoxidation at 800oC the nanoparticles merged again yielding a smooth coating once more.The underlying chemistry and materials science will be discussed and its implications for design of high efficiency SOFC fuel electrodes working in variable fuels and lower temperature presented.
10:00 AM - S10.2
Analysis of Electrochemical Performance of Single Step Co-fired Solid Oxide Fuel Cell (SOFC) using Polarization Model and Impedance Spectroscopy.
Kyung Joong Yoon 1 , Srikanth Gopalan 1 , Uday Pal 1
1 Manufacturing Engineering, Boston University, Brookline, Massachusetts, United States
Show AbstractAnode-supported planar solid oxide fuel cell (SOFC) fabricated by a single step co-firing process comprised of a porous Ni + yittria-stabilized zirconia (YSZ) anode support, a porous and fine-grained Ni + YSZ anode active layer, a dense YSZ electrolyte, a porous and fine-grained Ca-doped LaMnO3 (LCM) + YSZ composite cathode active layer, and a porous LCM cathode current collector layer. The fabricated cell was tested between 700~800°C with humidified hydrogen (97% H2+3% H2O) as fuel and air as oxidant. The experimentally measured cell performance was fitted into a polarization model, and the cell parameters including the area specific ohmic resistance, exchange current density, anodic limiting current density, cathodic limiting current density, effective binary diffusivity of hydrogen and water vapor in the anode, and that of oxygen and nitrogen in the cathode were obtained. The polarization resistances of the cell calculated using the cell parameters obtained from the polarization model were compared with the corresponding values measured using impedance spectroscopy. They showed good agreement within 3% indicating the validity and accuracy of the parameters obtained from the polarization modeling. The effect of current density and temperature on various polarization losses and their contributions to the cell resistance was studied, and the performance of the co-fired cell was analyzed in detail using the polarization modeling results.
10:15 AM - S10.3
Performance of Solid Oxide Electrolysis Cells using ScSZ Electrolytes.
Miguel Laguna-Bercero 1 , Stephen Skinner 1 , John Kilner 1
1 Department of Materials, Imperial College, London United Kingdom
Show AbstractOne of the major issues in hydrogen economy is the production of clean hydrogen. In order to achieve zero-emission hydrogen production the hydrogen must be produced from non H-C source, like the electrolysis of water [1]. In this field, high temperature electrolysis offers significant power, and hence cost, savings over conventional low temperature electrolysers. Nuclear power, renewable energy and high temperature industrial processes could be used to supply the heat and power needed for electrolysis.To date there have been relatively few investigations of ceramic electrolysers with the majority of studies focussing on the low temperature polymer based systems. Most of the ceramic electrolysers studied have been based on the high temperature yttria stabilised zirconia (YSZ) system [2]. Working with intermediate temperature electrolysers has potentially significant engineering advantages, such as the easily sealing between the materials. Another advantage is the possibility of use waste heat from power stations to produce hydrogen.Zirconia doped with scandia and ceria (10Sc1CeSZ) has been tested as an electrolyte in solid oxide electrolysis cells (SOECs) for hydrogen production at intermediate temperatures. At 700 °C, the conductivity of the 10Sc1CeSZ is 0.057 S/cm and the ASR at OCV is 0.27 Ω/cm2. The electrolysis tests using Pt electrodes showed that the oxygen ion conduction in the electrolyte produces high current outputs when operating as a SOEC (-420 mA/cm2 at 1.5V). Those preliminary results demonstrate the suitability of 10Sc1CeSZ as an electrolyte for SOECs. Our work is now focused in developing the electrodes. Semi-cells of Ni-YSZ/10Sc1CeSZ are been tested with different anodes in SOEC mode, like Pt, LSM-YSZ and Ni2AlO4+δ. Results of these measurements with different electrodes are presented and discussed in this paper.[1] E. Erdle et al., Proceedings of the Third International Workshop Vol. 2 High Temperature Technology and its Applications. Konstanz, federal Republic of Germany, 1986, p. 727-736 [2] M. Mogensen et al., 7th Solid Oxide Fuel Cell Forum Proceedings, Lucerne, Switzerland (2006), P0301.
10:30 AM - S10.4
Degradation Mechanisms in Solid Oxide Electrolysis Anodes: Cr Poisoning and Cation Interdiffusion.
Vivek Sharma 1 , Bilge Yildiz 1
1 Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractHigh temperature steam electrolysis is one of the most efficient processes for Hydrogen generation from water with no CO2 emissions using electricity and heat from nuclear or concentrated solar plants. Solid Oxide Electrolytic Cells (SOECs) are the proposed technology being researched and developed for this purpose. Over a long period of operation of the cells, various sources for degradation in the cells’ electrochemical performance prevail, and hence the cell resistance increases and the process becomes inefficient. Our research is aimed at identifying the mechanisms for the loss in the electrochemical performance of the cell, particularly of the oxygen electrode, namely the anode. We are performing post-mortem analysis of the anode materials from SOEC stacks that were subject to demonstration tests over 2000 hours. We are focusing on two mechanisms of degradation: 1) on the diffusion and reaction of chromium from the stainless steel interconnects onto the bond layer (cobaltite) and electrode (manganite) surface, 2) inter-diffusion of electrode and composite cations dissociating the anode composition. Chromium penetrates into the electrode microstructure through vapor-phase or solid state transport and reacts with the electrode material to form secondary and inactive phases which block the active sites. We have employed Raman Spectroscopy and identified the secondary phases that include mainly Cr2O3, LaCrO3, La2O3 and Co3O4, which have much lower conductivity than the original perovskite structure. We used scanning Auger Electron Nano-spectroscopy (AES) to study the local variations in the air electrode and the bond layer microchemistry and microstructure on a nano-to-micron scale. Presence of chromium was clearly observed in the cobaltite bond layer, particularly in the middle region of the cross section of the bond layer. The manganite and manganite/zirconia composite electrode layers did not contain chromium. The bond layer exhibited an A-site segregation on the surface and significant local variation of chemical constituents across the grain. Using high-resolution characterization, we are studying the high-resolution distribution of the chromium-containing phases on the surfaces, and the interdiffusion and dissociation of electrode constituents across the grains. In our approach, we are combining focused ion beam techniques for selective specimen preparation, and Electron Energy Loss Spectroscopy coupled with Transmission Electron Microscopy for chemical and structural analysis. This investigation will be particularly important for the identification of chemical stability at the grain boundaries between the electrode and electrolyte particles in the electrode microstructure.
10:45 AM - S10.5
Probing Phases and Strains Generated by Cr-contaminants inside of SOFC Electrodes using HEWAXS Technique.
Di-Jia Liu 1 , Jon Almer 2
1 Chemical Sciences & Engineering Div, Argonne National Lab, Argonne, Illinois, United States, 2 X-ray Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractFuel flexibility and high quality process heat make the solid oxide fuel cell (SOFC) attractive energy conversion device for future electric power generation. SOFC stack with a planar configuration is generally constructed by overlaying thin layers of solid oxide electrodes with individual cells connected by high temperature ferritic stainless steel. Although with an excellent potential to achieve high energy densities, such design is also vulnerable to the contamination by the reactive contaminants such as volatile chromium oxides generated from the metallic interconnect during the SOFC operation, a phenomenon often known as Cr-poisoning. Although various studies have shown Cr accumulation inside of the cathode, the understanding on the nature of chromium species, their distributions and the root cause to SOFC degradation is limited due to the constraint of the conventional characterization techniques. We reported here the first experimental demonstration on 3-D phase and concentration distributions of Cr-contaminants, as well as the structural properties such as porosity and strains altered by the formation of Cr-compounds, in a deactivated SOFC using a high-energy wide-angle X-ray scattering (HEWAXS) technique with micron probing beam resolution. A SOFC consisting of a Ni/YSZ anode, a YSZ electrolyte, and a LSM/YSZ active cathode was tested with direct contact to an E-Brite® interconnect at 800C using humidified air at the cathode and H2/N2 mixture at the anode. The cell was found deactivated after 100 hour on-stream. A cross-section of the sample was subsequently cut and probed at the directions both parallel and orthogonal to the SOFC plane by the micro-focused x-ray with the beam dimension of 2μmx50μm. We not only unambiguously identified MnCr2O4 and Cr2O3 as two main phases between the metallic interconnect and YSZ electrolyte, but also found their concentrations were strongly correlated to the cathode compositions at different layer depths. The accumulation of Cr species also led to substantial reduction of electrode porosity and generated significant lattice distortion and deviatoric strain between the electrode catalyst and the ion conductor. The investigation sheds new light on the Cr poisoning mechanism in SOFC.The work was supported by U. S. Department of Energy. Use of the Advanced Photon Source is supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.
11:30 AM - **S10.6
Tailoring Chemically Stable Perovskite-Type High Temperature Protonic Conductors.
Elisabetta Di Bartolomeo 1 , Emiliana Fabbri 1 , Alessandra D'Epifanio 1 , Laure Chevallier 1 , Milan Zunic 1 , Silvia Licoccia 1 , Enrico Traversa 1
1 , University of Rome Tor Vergata, Rome Italy
Show Abstract12:00 PM - S10.7
High Performance Intermediate Temperature SOFC Based on Doped Barium Cerate Thin Film Electrolyte.
Yeong Yoo 1 , Nguon Lim 1
1 ICPET, National Research Council Canada, Ottawa, Ontario, Canada
Show AbstractThe high performance anode supported single cells for a variety of applications such as direct utilization of ammonia as fuel and high temperature steam electrolysis as a reversible SOFC, comprising of BSCF (Ba0.5Sr0.5Co0.8Fe0.2O3-δ)//BCZY (Ba0.98Ce0.6Zr0.2Y0.2O3-δ)//NiO-BCZY have been fabricated by wet colloidal spray and co-firing for depositing 10-15 µm thin film electrolytes. The detailed characterization of BSCF, including electrical conductivities of sintered specimen as a function of temperature has been conducted to investigate the possibility to utilize BSCF as cathode for proton conducting electrolyte based cells. The electrochemical performance of single cells was characterized at the temperature 600-700 °C under humid 50-75% H2 in N2 (3% H2O) as well as cracked ammonia as the fuel gas and air as the oxidant gas at a gas flow rate of 10-100 mL min-1. The open circuit voltages were around 1.05-1.13 V at 600 °C indicating little gas leakage through the electrolyte. Maximum power density of 420-490 mW/cm2 was obtained at 600 °C under air as the oxidant gas and humid 75% H2 in N2 (3% H2O) as the fuel gas at gas flow rates of 100 and 10-100 mL min-1, respectively. Alternative cathodes of LSCM (La0.8Sr0.2Cr0.5Mn0.5O3-δ) and PSN (Pr1.4Sr0.6Ni1.0O4+δ) on BCZY (10-15 µm) // NiO-BCZY have been fabricated by wet colloidal spray for investigating the compatibility and stability of candidate cathodes on barium cerate based electrolytes. In addition, the electrochemical performance of single cells under fuel cell and electrolysis modes were characterized at the temperature 600-700 °C. The area specific resistance of an anode supported button cell of BSCF // BCZY // NiO-BCZY in fuel cell mode was about 0.46 Ω cm2 and in the electrolysis mode was 0.26 Ω cm2 at 600 °C, indicating an efficient reversible SOFC. The measured hydrogen evolution rate at the fuel electrode under the current density 1050 mA cm-2 at 600 °C was 7.1 cc min-1 cm-2, resulting in a current efficiency of around 97% to produce hydrogen.
12:30 PM - S10.9
EXAFS Study of Local Distortions in the Fluorite Lattice of CeO2 and Ce0.8Gd0.2O1.9
Anna Kossoy 1 , Anatoly Frenkel 2 , Igor Lubomirsky 1
1 Materials and Interfaces, Weizmann Institute of Science, Rehovot Israel, 2 Physics, Yeshiva University, New York, New York, United States
Show AbstractTo understand the deviation from linear elasticity and anomalies in time-temperature evolution of the unit cells of CeO2 and Ce0.8Gd0.2O1.9 thin films 1,2, we have investigated the local environment of cations in thin films and powders by LIII EXAFS and LI, LIII XANES. The EXAFS data indicate that the local distances between the neighboring cations are smaller than that calculated on the basis of the unit cell size measured by XRD. The Ce and Gd LIII edge XANES measurements show that “white line” intensity of 2p-5d transition differs between films and powders. Since 5d band in these compounds is nominally empty, such difference indicates changes in the band width rather than the occupancy of the 5-d orbital of Ce and Gd. Combined, the observed XANES, EXAFS, XRD and elastic properties data can be explained by assuming that the fluorite lattice of CeO2 and Ce0.8Gd0.2O1.91,2 undergoes local distortions along face and body diagonals (110 and 111 directions) and the fluorite symmetry observed by XRD is a result of averaging of locally distorted regions (domains) with lower symmetry. These distortions are similar to those observed in oxygen deficient phases of CeO2 Therefore, one can expect that similar effects can be observed in other ceria-based alloys and, possibly, in other fluorite structures.1 A. Kossoy et al. Adv. Funct. Mater. 2007, 17, 2393–23982 A. Kossoy at al. “Influence of point defect reactions on the lattice parameter of doped ceria” submitted to publication
12:45 PM - S10.10
Degradation of Ni-YSZ Anodes of Solid Oxide fuel Cells in Phosphorous-Containing Syngas.
Mingjia Zhi 1 , Nianqiang Wu 1
1 Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia, United States
Show Abstract Solid oxide fuel cells (SOFCs) have greater fuel feasibility compared with other types of fuel cells. Direct utilization of coal derived syngas in SOFC for power generation could bring many benefits such as increased energy efficiency and clean energy production. However, Coal derived syngas contains a lot of trace impurities such as P, As and Zn. The Ni/Yttria-stabilized zirconia (YSZ) anode of SOFC operated in the syngas is subject to severe degradation due to the attack by these impurities. Therefore, it is necessary to study the fundamental degradation mechanism of the SOFC anode operated in the coal derived syngas. In our experiments, traditional Ni-YSZ/YSZ/Ni-YSZ half cells are fabricated in order to evaluate the effects of the phosphorous impurity on the performance of the Ni-YSZ cermet anode of SOFC. The poisoning effects of the phosphorous impurity are evaluated in the coal syngas (30.6% H2, 30% CO, 11.8% CO2, and 27.6% H2O) containing various PH3 concentrations (5ppm to 10ppm) at in the temperature range from 750oC to 900oC. AC electrochemical impedance spectrum (EIS) and DC Tafel plots are collected for performance evaluation. Thermodynamics calculations are incorporated with the post experimental micro-analytical methods such as scanning electron microscopy (SEM), X-ray photoelectron spectrum (XPS) and X-ray diffraction (XRD) to elucidate the degradation mechanism of Ni-YSZ anode. Our results have shown that both the charge transfer and mass transfer resistances increase with the exposure time. Nickel and zirconia oxide react with P to form secondary phases, leading to the blockage of the mass transport channels and the loss of electrocatalytic activity of the Ni-YSZ anode.
S11: Solid Oxide Fuel Cells II
Session Chairs
Elisabetta Di Bartolomeo
Toshiaki Matsui
Thursday PM, December 04, 2008
Back Bay A (Sheraton)
2:45 PM - S11.2
Electrical Performance of Calcium doped Lanthanum Ferrite for use in Single-Step Co-fired Solid Oxide Fuel Cells (SOFCs).
Peter Zink 1 , Srikanth Gopalan 1 , Uday Pal 1
1 Manufacturing Engineering, Boston University, Brookline, Massachusetts, United States
Show AbstractIn the single-step SOFC co-firing process YSZ electrolytes with sintering aid densify at a temperature of ~1300°C. Electrodes employed in the single-step co-fired SOFC must therefore sinter with the right microstructure at ~1300°C. Calcium-doped lanthanum ferrite, La0.8Ca0.2FeO3±δ (LCF-20) was identified in earlier studies as a possible stable cathode material for the single-step co-fired SOFC. LCF-20 is also expected to be a more stable cathode material than LSCF (strontium and cobalt doped lanthanum ferrite). Four-probe conductivity tests yielded ~93 S/cm at 800°C and showed an increase in conductivity as pO2 increases, characteristic of p-type conduction. LCF has a higher electrical conductivity compared to LSCF and LCM+YSZ cathode materials. Oxygen ion conductivity of LCF-20 obtained from permeability measurements is higher than that of YSZ and LSF-20. Therefore LCF has excellent mixed conducting properties to serve as a catalytically active cathode material for co-fired solid oxide fuel cells operating at intermediate temperatures. Electrochemical Impedance Spectroscopy (EIS) measurements were made on symmetrical cells fabricated with YSZ electrolyte and the electrode materials. A gadolium doped ceria (GDC) barrier layer was employed to prevent LCF/YSZ reaction. Comparison of LCF/GDC/YSZ/GDC/LCF EIS data to LCM+YSZ/YSZ/LCM+YSZ EIS data gathered using identical test conditions and electrode microstructures shows that LCF has a measured polarization resistance (Rp) of approximately half that seen in LCM+YSZ. Variations in cathode thickness and porosity show the best performance with a cathode of a critical thickness and finer porosity. Slight stoichiometric deviations in LCF result in the formation of a Ca-Fe-O liquid phase during electrode sintering at around 1220 C. The liquid phase migrates into and through the GDC layer. EDX line scans show the second phase to be rich in Ca and Fe. Thicker GDC layers seem to prevent the liquid phase from reaching the electrolyte/GDC interface. Structural analysis with TEM will be performed.The properties and the effect of the Ca-Fe-O phase on the cathodic performance of the cell are being investigated; however, preliminary results indicate that minor amounts of the Ca-Fe-O phase will not interfere with the electrochemical performance of the LCF cathode. The high temperature instability in LCF has been observed in other studies, but has not been studied specifically in the literature.
3:15 PM - S11.4
Doped Apatite Type Lanthanum Silicates: Structure and Property Characterization.
Tamara Kharlamova 1 , Svetlana Pavlova 1 , Vladislav Sadykov 1 , Tamara Krieger 1 , Lubsan Batuev 1 , Olga Lapina 1 , Dzalil Khabibulin 1 , Marina Chaikina 2 , Nikolai Uvarov 2 , Yurii Pavlukhin 2 , Christos Argirusis 3
1 , Boreskov Institute of Catalysis, Novosibirsk Russian Federation, 2 , Institute of Solid State Chemistry and Mechanochemistry, Novosibirsk Russian Federation, 3 , Clausthal University of Technology, Clausthal-Zellerfeld Germany
Show AbstractApatite type lanthanum silicates (ATLS) attract an interest as a new class of solid electrolytes with oxygen ion conductivity, possessing some peculiarities of transport properties in comparison with perovskite and fluorite type systems. Thus, the ion conductivity is determined by the interstitial oxygen migration instead of the oxygen atoms jumps into vacancies, which results in a higher conductivity at intermediate temperatures and a lower activation energy. The present paper is devoted to the study of structural features and transport properties of Fe- and Al-doped ATLS. The structure of samples with different stoichiometry prepared via mechanochemical activation followed by calcination at high temperatures (1200-1450 C) was studied with XRD, TEM, IR, UV–Vis electron, Mossbauer, 29Si and 27Al MAS NMR spectroscopy. The transport properties were characterized using impedance spectroscopy and oxygen isotope exchange study. The effects of doping on phase composition, structure and conductivity were considered, taking into account the substitution limit, dopant coordination and apatite stoichiometry. Some new data concerning the role of oxygen excess and cation vacancies were obtained. Doping was shown to improve transport properties in comparison with undoped lanthanum silicate due to the presence of an oxygen excess. The cation vacancies appear to favor formation of the additional interstitial oxygen due to the association of two [SiO4]4- groups, which is confirmed by IR and 29Si MAS NMR spectroscopy. Oxygen-ion motion involving the cooperative displacements of the silicate substructure similar to Grotthuss mechanism of H+ motion in water solution via fluctuations in the solvation shell of the hydrated ions was considered to explain the results obtained.This work was supported by the European Commission 6th Framework Programme within MATSILC Project.
3:30 PM - S11.5
Transport Through Electrophoretically Deposited CuMn1.8O4 Spinel Coatings on Crofer Interconnects.
Wenhua Huang 2 3 , Srikanth Gopalan 1 2 , Uday Pal 1 2 , Soumendra Basu 1 2
2 Department of Manufacturing Engineering, Boston University, Brookline, Massachusetts, United States, 3 , Nanodynamics Energy Inc., Buffalo, New York, United States, 1 Division of Materials Science and Engineering, Boston University, Brookline, Massachusetts, United States
Show AbstractDense and well-adhered Mn-Cu spinel oxide coatings are successfully deposited on Crofer 22 APU stainless steel substrates by a cost effective electrophoretic deposition technique. Coated and uncoated Crofer substrates were oxidized for 120 hours in air at 800°C and 750°C. X-ray diffraction analysis and electron probe microanalysis showed the presence of Cr2O3 and MnCr2O4 in the thermally grown oxide scales. The uncoated stainless steel substrates exhibited parabolic oxidation kinetics, with kg values of 6.67X10-14 gm2/cm4-s and 3.64X10-15 gm2/cm4-s at 800°C and 750°C, respectively. A diffusion model was developed to understand the functional form of oxidation kinetics in the presence of a coating. It was assumed that only a scale formed between the coating and the substrate by inward diffusion of O2- through the coating and combined O2- and Cr3+ diffusion through the oxide. The model shows that the coated stainless steel substrates should exhibit para-linear oxidation kinetics. The effective diffusivities in the coating and in the thermally grown oxide scale were calculated to be 2X10-15 cm2/s and 2.5X10-16 cm2/s respectively, at 800°C and 5X10-16 cm2/s and 1.6X10-17 cm2/s respectively, at 750°C. Area specific resistances (ASR) of coated and uncoated samples were measured in a temperature range of 600°C to 800°C with 50°C increments. The as-processed coated sample showed only 4.6 mΩ cm2 ASR at 800°C. The ASR values of thermally cycled samples at 800°C did not show a significant difference compared to the isothermally oxidized sample for the same total oxidation time, suggesting good adherence of the coatings. The ASR of coated Crofer 22 APU is expected to be around 3.8x10-2Ωcm2 after being exposed to air at 800oC for 50000 hours, making these EPD CuMn1.8O4 coatings excellent candidates for interconnect applications for SOFCs operated at 800°C or lower.
3:45 PM - S11.6
Synthesis and Activity of Co-doped Barium Cerium Zirconate for Hydrogen Reforming and Purification.
Aravind Suresh 1 2 , Joysurya Basu 1 , Benjamin Wilhite 1 2 , Barry Carter 1
1 Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States, 2 Connecticut Global Fuel Cell Center (CGFCC), University of Connecticut, Storrs, Connecticut, United States
Show AbstractHydrogen is an enticing potential energy-carrier of the future – available from various (local) energy sources and promising high efficiencies (relative to current fuel-specific power systems) when used in energy conversion devices like Fuel Cells. Reforming of high-energy-density liquid fuels (e. g. alcohols) in the presence of a catalyst is currently the most convenient way of generating Hydrogen. Efficiency of Hydrogen generation is strongly dependent on the structure and chemistry of the catalyst, temperature of operation and chemical composition of the feed mixture. In the reforming process, however, Hydrogen is accompanied by several other reaction products that may degrade the catalyst or reduce the efficiency of the system. To counter this we propose to design an electro-ceramic membrane with dual functionalities:-Catalytic activity for reforming of liquid fuels.-Pathway for Hydrogen purification by Mixed Proton-Electron Conductivity.Cobalt doped Barium Cerium Zirconate has been chosen as the potential material. Cobalt doped powder of the above mentioned material was produced in the oxalate chemistry route almost at ambient temperature starting with nitrate salts of the chosen metals as precursors. The powder was washed and calcined at several higher temperatures before using it to test catalytic activity/conductivity. Structure and chemistry of the powder was characterized at each step with XRD and TEM. As synthesized powder is amorphous and gradually transforms into several crystalline phases with high-temperature calcination. Initially in the crystalline mixture presence of Barium Cerate, Barium Zirconate and Barium Cobaltate could be observed and after very high temperature calcinations the mixture evolves into the as desired Barium Cerium Zirconate phase. Unavailability of phase diagrams makes it difficult to understand the phase transformation behavior of the powder. Catalytic activity of the material w.r.t Methanol oxidation was tested at different O2/fuel ratios over a temperature range of 400 to 600 deg C. Promising Hydrogen yields and Methanol conversions were obtained along with presence of CO, CO2 and trace of CH4. We plan to map out conductivity of the material (at 400 to 600 deg C) under different environments using AC Impedance Spectroscopy. We also plan to conduct Hydrogen permeation experiments on the material. Results from these three tests would indicate if the chosen material is suitable for achieving the dual functionalities mentioned above.
S12: PEM Fuel Cells
Session Chairs
Andrew Bocarsly
Mohamed Mohamedi
Thursday PM, December 04, 2008
Back Bay A (Sheraton)
4:30 PM - **S12.1
Design and Development of High-Performance Hybrid Inorganic-Organic Fuel Cell Membranes.
Christel Laberty 1 , Ozlem Sel 1 , Karine Valle 2 , Frank Perreira 2 , Clement Sanchez 1
1 , LCMCP/UPMC, Paris France, 2 , CEA, Tours France
Show Abstract5:00 PM - S12.2
SPEEK-based Composite Membranes for Direct Methanol Fuel Cell DMFCs.
Barbara Mecheri 1 , Alessandra D'Epifanio 1 2 , Fang Chen 1 , Enrico Traversa 1 , Lorenzo Pisani 3 , Christoph Weise 2 , Steve Greenbaum 2 , Silvia Licoccia 1
1 , univesità di Roma Tor Vergata, Roma Italy, 2 , Hunter College of the City University of New York, New York, New York, United States, 3 , CRS4 Parco Scientifico e Tecnologico, POLARIS, Pula , CA, Italy
Show AbstractDirect methanol fuel cells (DMFCs) have attracted considerable attention as candidates for portable power sources, because they offer the advantages of high efficiency, simple design and nearly zero emissions to environment.Functionalized polyether ether ketone (PEEK) is widely investigated as a promising electrolyte for DMFCs. PEEK is a low cost polymer with good thermal stability and mechanical properties that can be made conductive by sulfonation (SPEEK), the degree of sulfonation (DS) being a key parameter that greatly affects the properties of the SPEEK membranes.Extensive efforts have been devoted to tune the performance of this kind of polymer using protons conducting additives like silica, zirconium phosphate, heteropolyacids, (HPAs) and various metal oxides.In this work SPEEK-based composite membranes comprising particles of hydrated tin oxide (SnO2 nH2O) have been prepared at two different oxide content, i.e. 23wt.% and 50wt.%. Despite of the high inorganic loading, the membranes are still plastic and robust.The proton transport characteristics were investigated by measuring conductivity as a function of RH. Conductivity increased with RH for the unfilled SPEEK membrane and for the composite membranes, the conductivity of the composite membranes being higher than that of the corresponding reference membrane at all RH values. The higher conductivity values for the composite membranes suggested the involvement of hydrated tin oxide in the proton conduction mechanism. Moreover, the lower water uptake values determined for the composite membranes with respect to the unfilled SPEEK samples, resulted in enhanced hydrolytic stability for the composites.To understand the SnO2nH2O effect on the proton transport properties of the SPEEK-based membrane, we employed an analytical model that predicts the membrane conductivity as a function of its hydration level and porous structure. Comparison of the model results with the experimental proton conductivity values demonstrated that the tin oxide phase provides additional paths between the water clusters for proton transport, these resulting in reduced tortuosity and enhanced proton conductivity.Pulse-field-gradient spin-echo NMR (PFGSE-NMR) technique was employed in this work to obtain a direct measurement of water self-diffusion coefficient in unfilled and filled SPEEK based membranes as a function of temperature and RH. Differences were observed between unfilled SPEEK and the composites at the same RH values, including deviations from the normal correlation between water diffusivity and proton conductivity, particularly in the case of composites.The presence of the oxide led also to a decrease in the methanol permeability of the membrane exhibiting good performance in a direct methanol fuel cell at 100°C.
5:15 PM - S12.3
Structure and Transport in Polymer Electrolyte Membranes for Fuel Cell Application.
Nitash Balsara 1 2 3 , Moon Jeong Park 1 2
1 Chemical Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractFuel cells have the potential to provide power for a wide variety of applications ranging from electronic devices to transportation vehicles. Cells operating with H2 and air as inputs and electric power and H2O as the only outputs are of particular interest due to their ability to produce power without degrading the environment. Polymer electrolyte membranes (PEMs), with hydrophilic, proton conducting channels embedded in a structurally sound hydrophobic matrix, play a central role in the operation of polymer-electrolyte fuel cells. Proton conductivity is closely coupled to the presence of contiguous hydrated channels within the membrane. The current state-of-the-art PEM, Nafion®, a perfluorosulfonic acid polymer, exhibits sufficient proton conductivity (0.1 S/cm) for applications below 80 °C. However, significantly lower conductivities are obtained at and above 80 °C due to the loss of water. Here, we establish a new systematic methodology for controlling the water retention of polymer electrolyte membranes. We show that block copolymer membranes with well-defined hydrophilic channels in the 2 to 5 nm range remain moist in a relatively dry environment (relative humidity = 50%) up to temperatures as high as 90 °C. This retention of water leads to an increase in the overall conductivity with increasing temperature. Simple calculations suggest that capillary condensation is important at these length scales. The morphology of the hydrated membranes is determined by a combination of in-situ neutron scattering and cryogenic electron microscopy.
5:30 PM - S12.4
Hybrid Membranes Based on Aromatic Polymers Blends for Fuel Cells Applications.
Catia de Bonis 1 , Barbara Mecheri 1 , Alessandra D'Epifanio 1 , Maria Luisa Di Vona 1 , Marcella Trombetta 2 , Enrico Traversa 1 , Silvia Licoccia 1
1 , Univesità di Roma Tor Vergata, Rome Italy, 2 , CIR-Centro Interdisciplinare di Ricerca, Università “Campus Bio-Medico”, Rome Italy
Show AbstractAromatic high performance polymers, such as polyetheretherketone (PEEK) and polyphenylsulfone (PPSU), represent an interesting alternative to Nafion to be used in proton exchange membrane fuel cells (PEMFCs). These polymers have good chemical and mechanical resistance, high thermo-oxidative stability and exhibit large conductivity if sulfonated, but show strong swelling for high sulfonation degrees (DS) [1]. Several approaches can be followed to improve the membrane properties, including the preparation of blend systems where sulfonated polyetheretherketone (SPEEK) represents the major component. Moreover, the use of an hybrid organic-inorganic polymer as second component of blend, allows further control of the ratio between hydrophilic and hydrophobic domains leading to a much finer tailoring of the membrane characteristics [2]. In this work, we present hybrid electrolytes based on blends of SPEEK with silylated and sulfonated polyphenylsulfone (SPhSiPPSU) or silylated and sulfonated polyetheretherketone (SPhSiPEEK), at different sulfonation degrees. SPEEK was prepared by reaction of PEEK with concentrated sulfuric acid and the hybrid organic-inorganic polymers SPhSiPPSU and SPhSiPEEK were synthesized according to procedures specifically designed on the basis of the desired structures. The chemical structure of the functionalized polymers were investigated by NMR and ATR/FT-IR spectroscopy.SPEEK-based blend membranes containing different amounts of hybrid polymer were prepared by casting technique, using N,N-dimethylacetamide as solvent. The physico-chemical and the proton-conducting properties of the membranes were investigated by differential scanning calorimetry, solvent uptake measurements and electrochemical impedance spectroscopy. Moreover, fuel cell tests at T ≥ 80 °C were carried out to evaluate the suitability of the blend membranes for direct methanol fuel cell (DMFC) applications.The interaction between the two physically cross-linked polymers led to improvement of the blend membranes properties with respect to pure SPEEK membrane, in terms of solvent uptake, proton conductivity and electrochemical performance. The proton conductivity values of blend systems were always higher than those of a reference membrane, indicating that the interaction between the two sulfonated polymers gave a real contribution to the proton transport. Moreover, the blends showed reduced methanol permeability with respect to pure SPEEK, as indicated by both methanol uptake measurements and open circuit voltage values recorded in the DMFC station. All these features identify the prepared blend membranes as promising electrolytes for fuel cells operating at intermediate temperature.[1] J. A. Kerres, Development of ionomer membranes for fuel cells, J. Membr. Sci., 2001, 185, 3-27[2] S. Licoccia et al., SPPSU-based hybrid proton conducting polymeric electrolytes for intermediate temperature PEMFCs, J. Power Sources, 2007, 167, 79-83
S13: Poster Session: Fuel Cells
Session Chairs
Tim Armstrong
Toshiaki Matsui
Rosa Palacin
Enrico Traversa
Friday AM, December 05, 2008
Exhibition Hall D (Hynes)
9:00 PM - S13.1
Low-Temperature Hydrothermal Synthesis of Nanocrystalline BaCeO3-based Proton Conductors.
Sanjit Bhowmick 1 , Joysurya Basu 1 , C. Carter 1
1 Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States
Show AbstractDoped barium cerate is an attractive candidate for solid-oxide fuel cells and other solid-state ionic devices due to its high protonic conductivity in reduced-temperature operating conditions. Unfortunately, recent studies indicate that barium cerate is thermodynamically unstable in the presence of carbon dioxide. In the present work, the ionic conductivity and chemical stability of barium cerate with added Co have been investigated. Nanoparticles of barium cerate were prepared by a low-temperature wet-chemistry route. The calcined powder has been characterized by X-ray diffraction to determine the phases present. Cobalt was added as a catalyst in two ways. In one case, Co was doped in barium cerate, and in another case, nanoparticles of Co were incorporated on the surface of barium cerate by dewetting technique to obtain ‘nano-on-nano’ structure; i.e., Co nanoparticles on barium cerate nanocubes. The morphology and chemistry of such nanocubes were determined by Z-contrast imaging and XEDS in the TEM. The distribution of Co was determined by analytical mapping. In situ dewetting experiments of sputter-coated cobalt films inside the TEM were carried out to investigate the parameters that control the size and position of the Co nanoparticles on the barium cerate surface. Implication concerning the reactivity with CO2 at different temperatures will be discussed.
9:00 PM - S13.10
Synthesis and Characterization of Polybenzimidazole Derivatives for Mid-Temperature Polymer Electrolyte Fuel Cells.
Hiroki Ohmori 1 , Masahiro Yoshizawa-Fujita 1 , Yuko Takeoka 1 , Masahiro Rikukawa 1
1 Materials and Life Science, Sophia University, Tokyo Japan
Show AbstractThe Mid-temperature polymer electrolyte fuel cells (MT-PEFCs) that operate above 120 °C without humidification have been considered to provide many advantages including fast electrode kinetics, high tolerance to fuel impurities, and simplified system designs. Phosphoric acid (PA) doped polybenzimidazoles (PBI) are attractive candidates for MT-PEFCs because of their excellent thermal stability and high proton conductivity above 120 °C. However, the performance of PA-doped PBIs seriously decreases below 120 °C. In order to improve the low temperature performance, poly[2,2-(2,6-pyridine)-5,5- bibenzimidazole] (PyPBI), which includes pyridine rings instead of benzene rings, was synthesized. The increase in basicity of polymer is expected to promote high PA doping level and high proton conductivity. PyPBI was synthesized by the reaction of 3,3-diaminobenzidine and 2,6-pyridinedicarboxylic acid. The reduced viscosity (ηred) of PyPBI was measured with sulfuric acid solution at a concentration of 0.2 g dL-1 at 30 °C. N,N’-Dimethylacetamide solution of PyPBI was cast onto glass plates and was dried at 80 °C for 24 h in order to obtain free-standing films. PyPBI/H3PO4 complexes were prepared by immersing PyPBI membranes into phosphoric acid/methanol solution with various concentrations for 72 h. The proton conductivity of PA-doped polymers was estimated by the complex impedance method. The fuel cell performance was measured by using dry hydrogen and dry air gases.The structure of PyPBI was confirmed by FT-IR and elemental analysis, and the ηred of PyPBI was 1.09 dL g-1. The formation of PyPBI/H3PO4 was also confirmed by FT-IR measurements. The NH2+ stretching band was observed in the range from 2000 to 3600 cm-1 due to the interaction between H3PO4 and imidazole groups. Two absorption bands of HPO42- and H2PO4- for PyPBI/H3PO4 appeared at 950 and 1100 cm-1, respectively. The adsorption level of H3PO4 for PyPBI/H3PO4 membranes was higher than that of PBI/H3PO4 membrane and increased with H3PO4 concentration The thermal stability of PyPBI/H3PO4 complexes was investigated by using TG-DTA. The TG curve of complexes exhibited a weight loss at about 140 °C due to the dehydration of phosphoric acid. The TG-DTA analyses clearly indicated that PyPBI/H3PO4 complexes were thermally stable as polymer electrolytes for MT-PEFC applications. The conductivity of PyPBI/H3PO4 complexes (3.76 mol unit-1) increased with temperature and was higher than that of PBI/H3PO4 complex (2.15 mol unit-1). The proton transport of PyPBI/H3PO4 is assumed to occur according to the Grotthus mechanism, which involves an exchange of protons between H3PO4 and HPO42- or H2PO4-. PEFC performance of PyPBI /H3PO4 complex (3.76 mol unit-1) was higher than that of PBI/H3PO4 complex (2.52 mol unit-1) and as 0.854 V and 21.5 mW cm-2 for open circuit voltage and maximum power density at 40 °C.
9:00 PM - S13.11
Synthesis and Evaluation of Polymer Electrolytes based on Poly(phenylene) Block Copolymers. –Effect of Hydrophobic Unit Length and Ratio.-
Azusa Osawa 1 , Masahiro Fujita 1 , Yuko Takeoka 1 , Masahiro Rikukawa 1
1 Department of Materials and Life Science , Sophia University, Tokyo Japan
Show AbstractSulfonated poly(4-phenoxybenzoyl-1,4-phenylene)s (S-PPBP)s show high proton conductivity and high chemical stability. It is difficult to control the sulfonation level of S-PPBP and to maintain its mechanical properties under humidified conditions. In this study, hydrophobic units, poly(benzoyl-1,4-phenylene) (PBP), were introduced into S-PPBP in order to overcome such drawbacks. Poly(4-phenoxybenzoyl-1,4-phenylene-co-benzoyl-1,4-phenylene) block copolymers were synthesized from Cl-terminated 2,5-dichlorobenzophenone oligomer (Cl-PBP) and 2,5-dichloro-4’-phenoxybenzophene (DPBP) by Ni(0) coupling reaction. The number of repeating unit of Cl-PBP was calculated to be 15 and 43 by GPC measurements. In this study, three kinds of copolymers, PPBP-PBP15, PPBP-PBP43(1:1), and PPBP-PBP43(1:2), were synthesized (The numbers and (1:1) denotes PBP lengths and the unit ratio of PPBP and PBP). S-PPBP-PBPs were obtained by reacting PPBP-PBP with H2SO4 for 24 hours. Sulfonated homopolymer , S-PPBP, was also synthesized for comparison. Structures of oligomers and polymers were confirmed by means of NMR, FT-IR, and elemental analysis. The weight-average molecular weights of S-PPBP-PBP15, S-PPBP-PBP43(1:1), and S-PPBP-PBP43(1:2) measured by GPC were 103,820, 145,000, and 87,000, respectively. The decomposition temperatures of S-PPBP-PBPs was about 210 °C, which was enough thermal stability as polymer electrolyte membranes for fuel cell applications. The onset decomposition temperatures were independent of the unit length and unit ratio, suggesting that this temperature were attributable to the elimination of sulfonate groups. The water uptakes of S-PPBP-PBPs were lower than those of S-PPBP. The ion exchange capacities of S-PPBP-PBP15, S-PPBP-PBP43(1:1), S-PPBP-PBP 43(1:2), and S-PPBP were estimated as 2.37, 2.64, 2.76, and 2.49 meq g-1 by back titration. S-PPBP-PBP15 showed higher proton conductivity, as compared with that of S-PPBP especially in the range of 30 - 50 %RH at 80 °C in spite of the lower water uptake ability. These results would be based on the formation of fast proton-transport channels.
9:00 PM - S13.12
Synthesis and Characterization of IEC-controlled Poly(phenylene) Derivatives.
Satoshi Takahashi 1 , Masahiro Yoshizawa-Fujita 1 , Yuko Takeoka 1 , Masahiro Rikukawa 1
1 , Sophia University, Tokyo Japan
Show AbstractSulfonated poly(4-phenoxybenzoyl-1,4-phenylene) (S-PPBP) exhibits high thermal stability and high proton conductivity. S-PPBP has been synthesized by the sulfonation of poly(4-phenoxybenzoyl-1,4-phenylene) (PPBP) with sulfonating reagents such as concentrated sulfuric acid and it is hard to control the ion exchange capacity (IEC) of S-PPBP because the post-sulfonation progresses in a heterogeneous reaction, and the degradation of polymer main chain occurs by sulfonating reagents. Copolymers of sulfonated monomer, 4-[4-(2,5-dichlorobenzoyl)phenoxy] acid 2,2-dimethylpropyl ester (NS-DPBP), and non-sulfonated monomer, 2,5-dichloro-4’-phenoxybenzophenone (DPBP), were synthesized in order to control IEC of S-PPBPs.NS-DPBP and DPBP were copolymerized with various feed molar ratios. The IECs of S-PPBP were determined by elemental analysis and back titration agreed. It was capable to accurately control the IEC of S-PPBP. The weight-average molecular weights of S-PPBP that was synthesized in this study were over 200,000. Water uptakes, proton conductivities, swelling ratio, and radical stability of S-PPBP membranes were evaluated. Water uptakes and proton conductivities of S-PPBP membranes increased with increasing IEC. The water uptake of S-PPBP membrane (IEC 2.87 meq./g) was 85 wt. % under 100%RH at 25 °C, and its proton conductivity reached 0.2 S/cm under 90%RH at 80 °C. The changes of length in the thickness direction of S-PPBP membranes also increased with increasing IEC after immersion in water at 80 °C for 2 h, whereas the changes of length in the in-plane direction was relatively small. S-PPBP membranes showed anisotropic swelling behavior. The radical stability of S-PPBP membranes was investigated by immersing in Fenton reagent. The weight loss of S-PPBP membranes after immersing in Fenton reagent increased with IEC, and S-PPBP membranes (IEC 2.87 meq./g), that had the highest IEC in this study dissolved completely in Fenton reagent.
9:00 PM - S13.13
Triazole-based PEM Fuel Cells Operated in a Wide Temperature Range (25~150°C) with Dry H2 and O2.
Min Kyu Song 1 , Huiping Li 1 2 , Xiaobing Zhu 1 , Meilin Liu 1
1 School of Materials Science & Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Chemical Engineering, Zhengzhou University, Zhengzhou, Henan, China
Show AbstractWhile proton exchange membrane (PEM) fuel cells are considered the primary candidates for automotive applications as well as the promising replacements for rechargeable batteries for certain portable devices, many challenges still remain. Most of the difficulties are associated with the need for humidification of conventional PEMs (e.g., Nafion), which limits the maximum operation temperature of fuel cells below the boiling point of water under atmospheric pressure (i.e., 100°C). The limited operation temperature (typically 60~80°C) requires very expensive platinum catalysts, which can be readily poisoned by even trace amounts of CO[1]. Also, a hydrated membrane can suffer from degradation induced by freeze/thaw cycles (e.g. fuel cell vehicles in winter season)[2]. Thus, the development of PEMs functional in a wide temperature range without the need for humidification is highly desired to overcome the problems associated with CO poisoning and water management. Recently, it has been demonstrated that triazole can promote proton motion through anhydrous PEMs[3-5]. Our group has successfully developed a novel membrane based on 1H-1,2,4-triazole grafted polysiloxane, reinforced with ePTFE and doped with 40wt.% of phosphoric acid. The novel membranes exhibited not only high proton conductivity under anhydrous conditions but also good thermal stability and mechanical strength. Here we report the performances of PEM fuel cells based on these novel membranes at a wide range of temperatures (25~150°C) without external humidification. Both membrane resistances and interfacial polarization resistances of triazole-based electrodes were determined using impedance spectroscopy. Results indicate that the proton conductivities have little dependence on operation temperature, showed good performance at temperatures above 100°C and at room temperature without external humidification. The new PEM will dramatically simplify the fuel cell systems, with great potential for fuel cell vehicles. The performance can be further enhanced by reducing the membrane thickness and optimizing the electrode composition and microstructure.[1] Q. Li, R. He, J. O. Jensen, N. J. Bjerrum, Chem. Mater. 2003, 15, 2.[2] S. Kim, M. M. Mench, J. Power Sources 2007, 174, 1.[3] S. Li, Z. Zhou, Y. Zhang, M. Liu, Chem. Mater. 2005, 17, 24.[4] Z. Zhou, S. Li, Y. Zhang, M. Liu, W. Li, J. Am. Chem. Soc. 2005, 127, 31.[5] R. Subbaraman, H. Ghassemi, T. A. Zawodzinski, J. Am. Chem. Soc. 2007, 129, 8.
9:00 PM - S13.15
Preparation and Characterization of Phosphonium-based Ionic Liquid/hydroxide Composites.
Atsushi Itani 1 , Masahiro Yoshizawa-Fujita 1 , Yuko Takeoka 1 , Masahiro Rikukawa 1
1 Materials and Life Sciences, Sophia University, Tokyo Japan
Show AbstractIt is well known that ionic liquids (ILs) have excellent properties such as negligible vapor pressure, non-flammability, and high ionic conductivity. ILs have been studied as neoteric solvents for organic reactions and as electrolyte materials for battery applications. There is no report about hydroxide ion-conductive ILs because typical ILs (e.g. ILs composed of imidazolium cation) are low alkaline resistance. In this study, phosphonium-based ILs are used as a matrix of hydroxide ion-conductors, and the thermal behavior, viscosity, and ionic conductivity of composites are investigated. Triethylpentylphosphonium bis(trifluoromethylsulfonyl)amide ([P2225][NTf2]) (Nippon Chemical Industrial) was used as received. Potassium hydroxide (KOH) was dissolved in ethanol and was purified by filtration. The composites were prepared by mixing [P2225][NTf2] and KOH solution with various ratios at 120 °C for 24 h. The structure of composites was confirmed by means of 1H NMR. The ionic conductivity was measured by the complex-impedance method, and the viscosity was measured by using a microviscometer (Anton Paar, AMVn). The 1H NMR spectra of composites did not show notable changes. The composites were thermally stable up to 410 °C, which was equal to that of the pristine IL. These results reveal that phosphonium-based ILs are high alkaline resistance. The composites showed almost the same ionic conductivity in the range from 0 to 23 mol% of KOH mole fraction. Since the addition of salts into ILs results in an increase in viscosity, their ionic conductivities decrease. In order to study the relationship between ionic conductivity and viscosity, the viscosity of composites was measured. Although the viscosity of composites increased with increasing molar fraction of KOH, the ionic conductivity maintained almost the same value in the range of KOH content 0 and 23 mol%. It is unusual tendency as compared with that of typical ILs, suggesting that [P2225][NTf2]-KOH composites have a different ion conductive mechanism. Further details of the mechanism will be studied by means of pfg-NMR technique.
9:00 PM - S13.16
Fundamental Studies of the Electronic Transfer Properties of Tailored Carbon Fibers Substrate as Nanoparticles Catalyst Support for Direct Methanol Fuel Cell Reactions.
Zehira Hamoudi 1 , Brahim Aissa 1 , My Ali El Khakani 1 , Mohamed Mohamedi 1
1 Énergie, Matériaux et Télécommunications, INRS-EMT Univ, Varennes, Quebec, Canada
Show Abstract9:00 PM - S13.2
Acceleration of Electrochemical Reaction in SOFC Electrodes by A Novel Nanoparticles Processing.
Kazuyoshi Sato 1 , Satoshi Ohara 1 , Hiroya Abe 1
1 , Osaka University, Ibaraki Japan
Show AbstractRecent nano technology offers a variety of nanoparticles. For practical applications, the morphology of nanoparticles such as size, shape and arrangement must precisely be controlled. In the present study, we demonstrated a novel synthesis and integration technology of nanocrystalline composite particles with well controlled morphology for electrodes of solid oxide fuel cells (SOFCs). The nanocomposite provided significant enlargement of electrochemically active sites in the electrodes, resulting in accelerated electrochemical reaction kinetics even at lower operation temperature.
9:00 PM - S13.3
Design and Characterization of LSM-ScCeSZ Nanocomposite as MIEC Material for SOFC Cathode and Oxygen-separation Membranes.
Vladislav Sadykov 1 , Vitalii Muzykantov 1 , Tamara Kharlamova 1 , Lubsan Batuev 1 , Galina Alikina 1 , Andrei Boronin 1 , Tamara Krieger 1 , Arcady Ishchenko 1 , Oleg Bobrenok 2 , Nikolai Uvarov 3 , Alevtina Smirnova 4 , Oleksandr Vasylyev 5
1 , Boreskov Institute of catalysis, Novosibirsk Russian Federation, 2 , Institute of Thermophysics, Novosibirsk Russian Federation, 3 , Institute of Solid State Chemistry, Novosibirsk Russian Federation, 4 , University of Connecticut, Storrs, Connecticut, United States, 5 , Institute of Problems of Materials Sciences, Kyiv Ukraine
Show Abstract9:00 PM - S13.4
The Thickness Dependence of Oxygen Permeability in Sol-Gel Derived Ce0.8Gd0.2O2-δ-CoFe2O4 Thin Films on Porous Ceramic Substrates: A Sputtered “Blocking” Layer for Thickness Control.
Kyle Brinkman 1 2 , Takashi Iijima 2 , Hitoshi Takamura 3
1 Materials Science and Technology Directorate, Savannah River National Laboratory, Aiken, South Carolina, United States, 2 Research Institute of Instrumentation Frontier (RIIF), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan, 3 Department of Materials Science, Graduate School of Engineering, Tohoku Univ., Sendai Japan
Show AbstractMixed conductive oxides are a topic of interest for applications in oxygen separation membranes as well as use in producing hydrogen fuel through the partial oxidation of methane. The oxygen flux through the membrane is governed both by the oxygen ionic conductivity as well as the material’s electronic conductivity; composite membranes like Ce0.8Gd0.2O2-δ(CGO)-CoFe2O4 (CFO)use gadolinium doped ceria oxides as the ionic conducting material combined with cobalt iron spinel as an electronic conductor. Microstructural modifications have been shown to influence the flux of these composite membranes with nanocrystalline thin films on porous substrates displaying enhanced flux as compared to bulk ceramic specimens1. However, extensive investigations into separating the impact of reduced grain size versus reduced membrane thickness on the material transport and permeation properties has not been explored to a large extent. In this study we employ ~ 50 nm sputtered CeO2 layers on the surface of porous CGO ceramic substrates which serve as solution “blocking” layers during the thin film fabrication process facilitating the control of film thickness. These solution “blocking” layers allow gas flow but impede large amount of solution leakage into the porous substrate during the fabrication process. Films with thickness of ~ 2 and 4 microns were prepared by depositing 40 and 95 separate sol-gel layers respectively. Dense ceramic membranes of 1mm thickness were prepared from the same sol-gel based solution for comparison of bulk and nanocrystalline properties. Oxygen flux measurements indicated that the permeation increased with decreasing membrane thickness; thin film membrane with thickness on the micron level showed flux values an order of magnitude greater (0.03 μmol/cm2 s) at 800oC as compared to 1mm thick bulk ceramic membranes (0.003 μmol/cm2). Observed differences in permeation will be related to processing induced microstructural features and membrane thickness.
9:00 PM - S13.6
Improvement of Oxide Ionic Conductivity of M0.25Ce0.75O1.875 (M=Dy, Gd) Specimen by a Control of its Nano-inhomogeneity.
Hirokazu Suga 1 4 , Toshiyuki Mori 1 , Fei Ye 1 , Ding Rong Ou 1 , Toshiyuki Nishimura 2 , John Drennan 3 , Hidehiko Kobayashi 4
1 Fuel Cell Materials Center, National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 4 Graduate School of Science and Engineering, Saitama University, Saitama, Saitama, Japan, 2 Nano-Ceramics Center, National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 3 Centre for Microscopy and Microanalysis, The University of Queensland, Brisbane, Queensland, Australia
Show Abstract9:00 PM - S13.7
Oxygen Ion Diffusion In Pure And Doped Bi2O3.
Sakis Kotsantonis 1 , John Kilner 1
1 Materials, Imperial College London, London United Kingdom
Show AbstractThe high oxide ion conductivity of bismuth oxide was initially discovered by Takahashi et al. [1]. They showed that the high temperature face centered cubic (fcc) phase of bismuth (δ- Bi2O3) has the highest oxide ion conductivity of all oxide ion conductors known so far. Here we report oxygen transport experiments on pure Bi2O3 and doped Bi2O3 based materials exhibiting the δ-phase (Bi12.5RE1.5ReO24.5 where RE=rare earth element) and also the rhombohedral β- phase (Bi0.775La0.225O1.5). The 18O/16O Isotope Exchange Depth Profile technique (IEDP) was applied to determine the surface exchange coefficient and bulk oxygen tracer diffusion coefficient. The isotope concentration profiles were obtained by secondary ion mass spectrometry (SIMS). Initial experiments indicated that exchange of oxygen with dry gas was very slow similar to the slow surface kinetics found by Vannier et al [2] and Fouletier et al [3] for the BIMEVOX type materials, so exchanges have been performed with H218O which enhances the surface reaction kinetics enabling the extraction of diffusion profiles.1.T. Takahashi, H. Iwahara, and Y. Nagai, High oxide ion conduction in sintered Bi2O3 containing SrO, CaO or La2O3. Journal of Applied Electrochemistry, 1972. V2(2): p. 97-104.2.R.N. Vannier, S.J. Skinner, R.J. Chater, J.A. Kilner, and G. Mairesse, Oxygen transfer in BIMEVOX materials. Solid State Ionics, 2003. 160(1-2): p. 85-92.3.M. Guillodo, J.M. Bassat, J. Fouletier, L. Dessemond, and P. Del Gallo, Oxygen diffusion coefficient and oxygen exchange coefficient of BIMEVOX.10 (ME=Cu, Co) ceramic membranes. Solid State Ionics, 2003. 164(1-2): p. 87-96.
9:00 PM - S13.8
Viscoelastic Behaviours of Fused Seals Composed of Glass and Alloy for Micro-SOFC Stacking.
Masahiko Matsumiya 1 , Seiichi Suda 1 , Koichi Kawahara 1 , Kaori Jono 1
1 Materials Research and Development Laboratory, Japan Fine Ceramics Center, Nagoya Japan
Show AbstractIt is necessary for micro-SOFC stacking to develop steadily interfaces functioning both gas-tight seals and conduction paths. We fabricated the insulating and the conductive sheets, which mainly consist of glass-precursor sealing materials and binary metallic alloys, respectively. This glass sealing material is characterized by two kinds of amorphous spherical particles Na2O-SiO2 and small amount of SiO2 acting as a filler. In addition, this conducting sheet consisting of Ag-Si eutectic alloy is good wettability on the fused glass seals.In order to obtain the optimum fusion condition, we investigate the viscoelastic behaviours of fused glass and alloy seals by dynamic-mode TMA. In the case of the fused glass seal, the storage modulus around 460-520C decreases with temperature and the corresponding loss modulus increases with temperature. This viscoelasticity peak is corresponding to the glass transition point because this peak designates the frequency dependence. Moreover, the storage modulus gradually decreases and the corresponding loss factor: tanδ increases at approximately 550-600C, which is the softening point of this fused glass seal. Furthermore, both storage and loss moduli drastically decrease at 770C, which is the melting point of the fused glass seal. In the case of the alloy seal, both storage and loss moduli drastically decrease at 850C, which is corresponding to the eutectic point of Ag-Si alloy. According to the viscoelastic results for fused glass and alloy seals, the optimum fused temperature region is 770-850C. For the practical use of fused glass and alloy seals, we also investigate the viscoelastic behaviours of these seals in diluted hydrogen atmosphere.
9:00 PM - S13.9
Characterizing State Of Water in Fuel Cell Membranes Using NMR T1 Relaxation.
David Lee 1 , Alan Benesi 1 , Harry Allcock 1 , Digby Macdonald 2
1 Chemistry , The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractWater plays an important role in the performance of a polymer fuel cell membrane. It is accepted that phase separated channels of liquid water are formed when Nafion® is hydrated. This allows protons to conduct within these water channels, which imparts high proton conductivity to Nafion. However, the presence of another state of water has been suggested. These are water molecules that bind strongly to the sulfonic acid groups and have ice-like characteristics. These tightly bound water molecules, similar to those found in Zeolites, are hard to remove and can exist even at high temperatures. It is possible that these ice-like water molecules can be utilized in a high temperature fuel cell that can operate at above 100 °C at ambient pressures.In this study, we seek to characterize the different states of water in fuel cell membranes and establish a relationship between the state of water and ionic conductivity. Deuterium NMR T1 relaxation of fuel cell membranes hydrated with 2H2O was employed to characterize the different states of water. 2H NMR is particularly advantageous because the 2H quadrupolar interaction is so large that other interactions can be neglected. This allows direct measurement of the 2H2O reorientational motion without making assumptions. The 2H T1 relaxation of solid water is 4 – 8 ms depending on magnetic field because the molecular motion frequency of solid water is comparable to the Larmor frequency of the spectrometers. The 2H T1 relaxation of liquid water is 400 ms but does not have magnetic field dependence because the molecular motion of liquid water is much faster compared to the Larmor frequency.We have observed that the 2H T1 value of Nafion increases with hydration level. As the observed T1 value is an average, the increasing T1 value indicates that there are different states of water, and that the distribution of solid water and liquid water changes with hydration level. At low hydration levels, most of the water molecules are used to solvate the sulfonic acid groups. Therefore the T1 value is lower because the water molecules have a more solid-like character. As Nafion absorbs more water, the T1 value increases because there are higher populations of water that are unbound and exist as liquid water. We also report a new phenomenon that the T1 values of all samples increase with magnetic field which indicates that solid water is present at all hydration levels even at room temperature. We can evaluate the ratio of solid water and liquid water using the T1 values obtained. In conclusion, we have demonstrated that the measurement of T1 relaxation is a direct and quatitative method for the characterization of different states of water in fuel cell membranes.
Symposium Organizers
Enrico Traversa University of Rome Tor Vergata
Timothy Armstrong Carpenter Technology Corporation
Koichi Eguchi Kyoto University
M. Rosa Palacin Institut de Ciencia de Materials de Barcelona (CSIC)
S14: Battery Materials: Electrodes
Session Chairs
Friday AM, December 05, 2008
Back Bay A (Sheraton)
9:30 AM - **S14.1
Solid State Electrochemistry of Mesoporous Materials: Electrodes for Energy Storage and Conversion.
Linda Nazar 1 , Xiulei Ji 1 , Kyu-Tae Lee 1 , SiHyoung Oh 1
1 , University of Waterloo, Waterloo, Ontario, Canada
Show AbstractMesoporous materials with high surface area and highly ordered structures are attracting growing attention for their potential applications in the area of hydrogen storage, fuel cells and as electrodes and supercapacitors in electrochemical energy storage. Following the report of Ryoo et al. of CMK-1 in 1999, many porous carbon materials have been synthesized as the inverse replicas of “mesoporous” silicates. The silicate structures are formed by growth of soluble silica, templated by either short-chain ionic surfactants to form the MCM-41 and MCM-48 class of materials; or longer chain tri-block copolymer surfactants to form large-pore silicates first reported by Stucky et al, such as the SBA-15 and SBA-16 silicates. Carbon precursors impregnated within the hollow cavity of the silicate serve as the sources for the amorphous porous carbon replica structures formed after removal of the silica scaffold. Alternatively, porous metal oxides, or metal phosphates can be formed as the inverse replicas by impregnation of suitable inorganic precursors. In this presentation, a brief overview of developments in the field will be presented, followed by highlights from our own recent work in the area. Methods to increase the conductivity of mesoporous carbons through the generation of partially graphitized carbons with nanopore dimensions on the order of 3-5 nm will be discussed. We have employed these as electrically conductive scaffolds to encapsulate active electrode materials, leading to the design of structured composites where both components play a role in controlling the electrochemical performance. These include active materials that involve topotactic and non-topotactic reactions, and especially those that uptake lithium ions (and electrons) by “conversion reactions”. Very high capacities are achievable with such chemistry, although an unacceptably high degree of hysteresis is usually seen between oxidation and reduction. A key issue is to restrict the active material particle size to nanodimensions to ensure a high degree of reversibility of the reaction. In the nanostructured materials described here, the graphitic carbon framework serves as both a restrictive containment of the active material contained within the porous structure, and as an “inner electrode” that acts as an electron and ion delivery system. We have also uncovered simple methods to induce high, homogeneous loading of the framework with nanocrystallites tunable from 1 – 4 nm, that can be well anchored to the carbon support by tweaking the hydrophobic/hydrophilic nature of the surface. The utilization of the porous framework as a host for such catalysts that are active as the gas diffusion electrode in fuel cell systems; and as supercapacitors will be presented.
10:00 AM - S14.2
A Synchrotron-based PES study of Li2(Fe,Mn)SiO4 During Electrochemical Lithium Deintercalation.
David Ensling 1 , Torbjörn Gustafsson 1 , Josh Thomas 1
1 Angstrom Advanced Battery Centre, Department of Materials Chemistry , Uppsala University, Uppsala Sweden
Show AbstractWith its theoretical capacity of ~170 mAh/g, the iron-silicate based material Li2FeSiO4 is seen as a low-cost, environmentally friendly alternative to LiFePO4 as cathode in Li-ion batteries for EV/HEV and other large-battery applications [1]. Although it has only a rela-tively low voltage of 2.8V, partial substitution of Fe typically by Mn (to give Li2(Fe,Mn)SiO4) could facilitate the “>1 electron reaction”: Li+2(Fe2+1-yMn2+y)SiO4 → Li+1-x,(Fe3+1-yMn4+y)SiO4 + (1+x)Li+ + (1+x)e-. For example, the theoretical capacity would increase from 170 to 255 mAh/g for y=0.5 to give a potential plateau at 4.3-4.5 V vs. Li+/Li0. High-performance cathode materials development demands a careful investigation of the stability issues involved. Surface-sensitive photoelectron spectroscopy methods like SXPS and SXAS are appropriate tools to characterize the chemical and electronic structure of such cathode surfaces. Chemical analysis of the SEI surface phases for a new battery material yields information about their formation and stability which is highly relevant to its subsequent area of application [2,3].Fundamental information can also be derived relating to delithiation and lithium re-insertion mechanisms during cycling. It is an open question as to if and how Fe, Mn and O states are involved in these processes. Stability limits can be governed by the contribution from oxygen; little data is yet available for this new Li2Fe1-yMySiO4 systems, however. Li2FeSiO4 was prepared by the solid-state reaction of Li2SiO3 with FeC2O4∙2H2O [1]. The chemistry of the electrolyte/electrode interface and changes in the electronic structure of the cathode have been studied by in situ electrochemical delithiation and subsequent reintercalation. These experiments have been carried out at the synchrotron facility BESSY II in Berlin in a specially designed glass cell under Ar atmosphere. The cell is directly connected to the Solid Liquid Analysis System (SoLiAS) [4], which facilitates a contamination-free transfer of the treated samples from the electrochemical cell to the UHV analysis. Changes in the electronic structure during delithiation of Li2FeSiO4 cathodes have been investigated by SXPS and SXAS. Unique insights are obtained into the surface chemistry and changes in the electronic properties of the Li2FeSiO4 and Li2(Fe,Mn)SiO4 electrode materials during the electrochemical deintercalation reaction. Detailed information on the oxidation states of the transition metal ions can be deduced. References1. A. Nytén, M. Stjerndahl, H. Rensmo et al., J. Mater. Chem., 16, 3483 (2006).2. K. Edström, T. Gustafsson, J.O. Thomas, Electrochim. Acta, 50, 397 (2004).3. M. Herstedt, M. Stjerndahl, A. Nytén et al., Electrochem. and Solid State Letters, 6, A202 (2003). 4. T. Mayer, M. Lebedev, R. Hunger, W. Jaegermann, Appl. Surf. Sci., 252, 1 (2005).
10:15 AM - S14.3
The Electrospinning Synthesis of Vanadium Oxide Nanofibers for Rechargeable Lithium Battery.
Chunmei Ban 1 , Natalya Chernova 1 , M. Stanley Whittingham 1
1 Chemistry, Binghamton University, Binghamton, New York, United States
Show AbstractThe investigation of nano-scale materials is facing a challenge of synthesis method. Not only sizes of materials have to be controlled, but also desirable structures of materials need to be obtained for some specific application, such as lithium insertion/extraction in rechargeable lithium battery. Hydrothermal technique has been proved highly successful in the formation of open structures suitable for the lithium intercalation. Electrospinning is a promising technique, which has been widely used in the synthesis of polymer nanofibers. In order to control morphology of hydrothermal product, a methodology including hydrothermal and electrospinning technique was employed here to improve the electrochemical properties for lithium ion battery. By using hydrothermal treatment on electrospun composite nanofibers, single-crystal vanadium oxide nanofibers with layered structure have been formed. FTIR and X-ray power diffraction show the presence of δ-phase V4O10 in the vanadium oxide nanofibers. The electrochemical behavior of the vanadium oxide nanofibers was determined in a lithium cell at different current density for 50 cycles. It was found that the discharge capacities exceed 350 mAh/g for the first cycles and maintain a capacity in the range of 250-300 mAh/g for the following cycles, which exceeds that of bulk vanadium oxide. Interestingly, several vanadium phosphate compounds synthesized by similar technique do not reveal fiber-like morphology. Differences in reaction pathways in oxide and phosphate syntheses will be discussed. This work is supported by the National Science Foundation through grant DMR-0705657.
10:30 AM - S14.4
In-Situ Imaging of Nanocrystal Formation in Olivine-Type LiFePO4.
Sung-Yoon Chung 1 2
1 Materials Sci. & Eng., Inha University, Incheon Korea (the Republic of), 2 , Nalphates, Wilmington, Delaware, United States
Show AbstractThe control of the nucleation and growth behavior of crystals from solutions or melts in inorganic compounds is scientifically and technologically of great importance for fabricating crystalline particles of optimum size and shape as well as with a narrow size distribution. To describe the crystallization process, a number of theoretical investigations on crystal nucleation and growth have been documented systematically. Because nucleation and subsequent growth usually occur very rapidly in many cases, most of the experimental observations have been of select systems that show relatively slow phase transition kinetics, such as colloidal crystals, proteins, and large organic molecules, largely at moderate temperatures at a micron or submicron scale. By contrast, synthesis processes at high temperatures are, in general, associated with obtaining the thermodynamically stable crystals of inorganic compounds with a complex crystal structure and multiple components. Although still challenging, a high-temperature, real-time observation of the crystallization of such compounds is therefore necessary, as it could provide us with unique phenomenological information, enabling new development for the efficient fabrication of such crystals. Here, we show the formation of metal phosphate nanocrystals at a high temperature using high-resolution transmission electron microscopy (HRTEM), of which new developments allow one to determine the structural variation in real time in a variety of nanoscale materials. Lithium iron phosphate (LiFePO4) was selected as a multi-component model system for this atomic-level in situ observation. Since the report of the impressive lithium intercalation reaction in LiFePO4 [S.-Y. Chung et al., Nature Mater., 1, 123 (2002)], a great deal of attention has been paid to the phosphate as an alternative cathode material in lithium-ion batteries due to its outstanding thermochemical stability and environmental benignity. In particular, the crystal size is known to be one of the most significant parameters among many other factors that determine the electrochemical cycling performance of LiFePO4. Thus, our present study will be able to suggest practical approaches to the effective synthesis of metal phosphate nanocrystals, as well as to elucidate the fundamental mechanism for nucleation and growth during crystallization of complex inorganic materials. More details for atomic-scale probing of crystallization and resulting nanocrystal formation in LiFePO4 will be presented.
10:45 AM - S14.5
Evidence of Structural Changes Occurring in the Positive Electrode of Nickel Batteries upon Charge/discharge Processes.
Montse Casas-Cabanas 1 , Jesus Canales-Vazquez 1 , Juan Rodriguez-Carvajal 2 , M. Rosa Palacin 1
1 , Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Bellaterra, Barcelona, Spain, 2 , Institut Max Von Laue-Paul Langevin, Grenoble France
Show AbstractNickel based batteries using nickel hydroxide as the active material in the positive electrode have been extensively used since the publication of the first patents more than one hundred years ago. This type of batteries still represent an important part of the rechargeable battery market and are have regained interest in the last years for HEV applications. Different technologies have been developed using a range of negative electrode materials such as either Ni/H2 or Ni/MH, but the positive electrode material remains unchanged, i.e. layered brucite type β-Ni(OH)2 in the discharged state and β-NiOOH in the charged state. β-Ni(OH)2 crystallizes in a brucite type structure (space group P-3m1, a=3.126 Å and c= 4.593 Å (1)). However, the complete structural characterisation of β-NiOOH had not been achieved to date due to its poor crystallinity, which in turn is a sine quanon reason for good electrochemical performances. Nevertheless, there has been a general agreement considering that no major modifications take place in the brucite structure upon oxidation (2,3). In other words, it was assumed that no relevant structural changes occur in the nickel positive electrode under working conditions, with the exception of an irreversible microstructural transformation that produces a mosaic texture during the first oxidation of β-Ni(OH)2 as proposed from low resolution TEM studies (4). This process involves the formation of several slightly misoriented domains within each crystallite caused by the relaxation of the microstrains that appear when half the hydrogen atoms from the hydroxide are extracted.In order to carry out a complete study of the structural and microstructural evolution of the positive active material upon battery operation, pure phases were chemically prepared mimicking the electrochemical processes occurring upon battery charge/discharge. The results of X-ray and neutron diffraction studies combined with high resolution transmission electron microscopy (HRTEM) indicate that, contrary to what was believed, nickel battery positive electrode material undergoes a structural modification upon operation that results from a shearing of the layers (5). With the simultaneous consideration of structural and microstructural models in the Rietveld refinements, we have been able to determine the crystal structure of β-NiOOH, which will also be presented. References1. C. Greaves and M.A. Thomas Acta Crystall. B-Stru. 42, 51 (1986).2. P. Oliva, J. Leonardi, J.F. Laurent, C. Delmas , J. J. Braconnier, M. Figlarz, F. Fievet and A. Guibert J. Power Sources 8, 229 (1982).3. J. McBreen, Modern Aspects of Electrochemistry (ed. White, R. E., Bockris J. O'M. & Conway, B. E.), p: 29-63, Plenum Press, New York (1990).4. A. Delahaye-Vidal, B.Beaudoin, and M. Figlarz React. Solid. 2, 223 (1986).5. M. Casas-Cabanas, J. Canales-Vázquez, J. Rodríguez-Carvajal and M.R. Palacín, J. Amer. Chem. Soc., 129, 58 (2007).
11:30 AM - **S14.6
On the Very High Li-Conductivity in La/Li Titanates: The Influence of the Microstructure.
Miguel Alario-Franco 1 , Susana Garcia-Martín 1 , Ainhoa Morata-Orrantia 1 , Juan Rodriguez-Carvajal 2 , Ulises Amador 3
1 Quimica Inorganica I, Facultad de Quimica. Universidad Complutense, Madrid Spain, 2 Diffraction Group, ILL, Grenoble France, 3 Departamento de Quimica, Universidad San Pablo-CEU, 28668 Boadilla del Monte, Madrid, Spain. Spain
Show Abstract12:00 PM - S14.7
Multifunctional Carbon Nanofoams for Energy Storage Applications.
Justin Lytle 1 , Jennifer Dysart 1 , Megan Bourg 1 , Jeffrey Long 1 , Debra Rolison 1
1 Surface Chemistry, Naval Research Laboratory, Washington, District of Columbia, United States
Show Abstract12:15 PM - S14.8
Enhanced Potential of Amorphous Electrode Materials: Case Study of RuO2.
Olga Delmer 1 , Palani Balaya 1 2 , Lorenz Kienle 1 , Joachim Maier 1
1 , Max-Planck-Institute, Stuttgart Germany, 2 , National University of Singapore, Singapore Singapore
Show AbstractA basic technique to store electrical energy lies in the possibility to store lithium electrochemically. Here we investigate Li-storage in amorphous matter.Metastable amorphous phases have higher Gibbs free energy of formation as compared to their crystalline counterparts. This feature is quantitatively studied through the measurement of open cell voltage (OCV) of a reversible model cell. The measurements show that the kinetically stable amorphicity can play a beneficial role in significantly enhancing the cell voltage. Present work investigates the OCV of amorphous paracrystalline and crystalline phase of RuO2. The amorphous phase occurrs in Li cells with RuO2 cathodes after a deep discharge/charge cycle. The amorphicity has been confirmed by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). We observed excess potential of 0.6 V during the intercalation reaction for the amorphous RuO2 in comparison with the potentials of crystalline RuO2 of 100 nm and 10 µm sizes. This excess potential can be quantitatively interpreted as being essentially the free melting enthalpy of RuO2 at operation temperature. Additionally, more details about thermodynamics, Li+ diffusion, the electrochemical amorphisation and recrystallisation processes of RuO2 during the cell operation were studied in the crystalline, paracrystalline and amorphous cases.
12:30 PM - S14.9
Crystal – chemistry as a Tool for Properties Enhancement in the Field of Materials for Energy Storage: Displacement Process in (Ag, Cu)-V-O Bronzes.
Mickael Dolle 1 , Patrick Rozier 1 , Christine Surcin 2 , Mathieu Morcrette 2 , Jean-Marie Tarascon 2 , Jean Galy 1
1 , CEMES/CNRS, Toulouse France, 2 , LRCS, Amiens France
Show AbstractTo answer the need for increasing demand in term of energy storage, breakthrough research directions have to be followed. In this field, the discovery of the specific two modes reactivity versus lithium of Cu7/3V4O11 [P. Rozier, C. Satto and J. Galy Solid State Sciences, 2 (6), 595-606, 2000], which associates conventional intercalation process and displacement, opens the way for new classes of materials to be used as positive electrode active materials for lithium batteries.The aim of this presentation is to report the full study of the structural parameters governing the existence, efficiency and reversibility of the displacement process in Ag, Cu and mixed Ag/Cu vanadium oxide bronzes. Conventional solid state routes have been used to isolate the limit of the different homogeneity domains. The structure of the different observed phases has been determined using Single Crystal X Ray diffraction, while a careful study of electronic density distribution allowed determining the mobility / reactivity of copper and silver ions within the V-O based host network. Using in situ XRD experiments upon cycling, the electrochemical behaviour has been correlated to structural parameters evolution and it has enabled to check the importance of structural considerations. It will then be demonstrated that even though the dimensionality of the V-O host network is an important parameter, the mobility of the guest ions (silver, copper) appears as the most crucial parameter to ensure efficient combination of displacement and insertion reactions. General rules will then be given allowing to predict the expected electrochemical properties on the basis of crystal chemistry concepts.
12:45 PM - S14.10
Annealing Effect on Hydrothermal Synthesized Vanadium Oxide (V2O5) Nanobelts and its Electrochemical Capacitance
Eugene Khoo 1 , JinMing Wang 1 , Pooi See Lee 1 , Jan Ma 1
1 School of materials science and engineering, Nanyang Technological University, Singapore Singapore
Show AbstractNanostructured transition metal oxides based supercapacitor electrode has the advantages of short diffusion length and high surface areas which enhances the ion storage performance. In this work, single crystal vanadium oxide (V2O5) nanobelts have been formed through hydrothermal process. The nanobelts are densely formed with a width ~ 150-300nm and thickness ~10-50nm. The nanobelts were air-annealed at different temperatures (100oC-500oC) for 2 hours to investigate the annealing effect on the oxide and its electrochemical capacitance. Phase transition was found to occur upon annealing leading to formation of tetragonal V2O5 at 500oC from X-Ray Diffraction (XRD) analysis. Transmission Electron Microscopy (TEM) shows significant surface roughening for 500oC annealed nanobelts. The single crystalline nanobelt samples were subjected to cyclic voltammetry (CV) studies in 1M LiClO4 in propylene carbonate (PC) electrolyte between ±1V for scan rate ranging from 5mV/s to 1000mV/s. The 500oC annealed V2O5 nanobelts showed improved capacitance of 220F/g at 5mV/s compared to 142 F/g for samples without annealing. At scan rate of 1000mV/s, the annealed nanobelts maintained a capacitance of 93F/g. The enhancement in capacitance for the annealed samples is attributed to water evaporation (evident from Differential Scanning Calorimetry (DSC)) hence improving the mass effectiveness of V2O5 during the energy storage. In addition, the morphological change of the nanobelts (surface roughening) accounts for the increased interfaces and pathways for ion insertion/extraction.