Symposium Organizers
Artur Braun Empa – Swiss Federal Laboratories for
Materials Testing and Research
Paul Gannon Montana State University
Sossina Haile California Institute of Technology
RobertA. Robinson Australian Nuclear Science and Technology Organisation (ANSTO)
Symposium Support
Australian Nuclear Science and Technology Organization (ANSTO)
AXPO Holding AG
EMPA, Laboratory for High Performance Ceramics
Montana State University, Chemical &
Biological Engineering
J1/K3: Joint Session: Solid-State Proton Conductors
Session Chairs
Sossina Haile
Truls Norby
Wednesday PM, April 27, 2011
Room 2010 (Moscone West)
9:30 AM - **J1.1/K3.1
Role of Protonic Defects in the Photocatalytic Properties of Oxides.
Truls Norby 1
1 Department of Chemistry, University of Oslo, Oslo Norway
Show AbstractTiO2 is a favourite photocatalytic oxide, with an appropriate bandgap to capture UV light and split water into hydrogen and oxygen or form hydroxide radicals and peroxide species that can disinfect drinking water and make self-cleaning surfaces. However, the detailed understanding of the structure and chemistry of surfaces of TiO2 and other photocatalytic oxides is poor, and consequently, reproducibility and stability remain problematic, and improvement of performance dominated by trial and error. Catalytic properties of oxide surfaces are often assigned to oxygen vacancies as active sites. In this talk, the defect chemistry of TiO2 is revisited and extended by new experiments and computational results. The high temperature bulk equilibrium defect chemistry can be extrapolated to lower temperatures and aqueous conditions and would be expected to apply to surface layers. From this we can safely predict that protonic defects will dominate and that they will be charge compensated by cation vacancies. Moreover, associates of the two will be important and possibly rule the chemistry and structure of the surfaces, the formation of hydrous titanate nanostructures, and the photocatalytic properties of TiO2 and other oxides.
10:00 AM - J1.2/K3.2
Proton Mobility in SiO2 Thin Films and Impact of Hydrogen and Humidity on the Resistive Switching Effect.
Stefan Tappertzhofen 1 , Marek Hempel 1 , Ilia Valov 1 2 , Rainer Waser 1 2
1 Institute of Electronic Materials, RWTH Aachen University, Aachen Germany, 2 Institute of Solid State Research, FZ Juelich, Juelich Germany
Show AbstractRecently, SiO2 based Electrochemical Metallization (ECM) cells were intensively studied as a promising candidate for CMOS compatible non-volatile memory devices. The simple structure of ECM cells consists of a material ensuring a metal ion transport sandwiched between an inert (bottom) electrode and an electrochemically active working (top) electrode. As working electrode typically Ag or Cu are used. The transition between a high resistive (OFF) and low resistive (ON) state of the ECM cell constituting the logical 0 state and 1 state is determined by the process of formation and rupture of a metal filament controlled by the applied voltage. Despite that silicon dioxide is a typical insulator due to the reduced diffusion length (thin film thickness of 30 nm) it is believed to act as a transport layer for metal ions supplied by an oxidation process at the working electrode. However, in this case a counter charge is necessarily needed in order to introduce an oxidized metal ion into the electrolyte. It is not sufficient to apply a positive voltage to the active electrode (Ag or Cu) in order to inject metal ions into the material. At the counter electrode (inert metal) another charge must enter (or leave) the oxide. This charge may be electrons which reduce the oxide, protons/water being reduced or reactions of impurities.In this work we report about the investigations on the proton mobility in amorphous SiO2 thin films focused on the impact of hydrogen and humidity on the resistive switching effect. The transport of hydrogen has been studied by Tof-SIMS and impedance spectroscopy. Additionally, SiO2 thin film membranes mechanically fixed on a carrier substrate and sandwiched between a top and bottom electrode have been fabricated for experiments under chemical potential gradient of hydrogen. The switching behavior was analyzed by current-voltage measurements performed at different ambient conditions. The results led to an expansion of the defect model proposed in the literature.
10:15 AM - J1.3/K3.3
Proton Conducting Zeolites for In-situ Monitoring of DeNOx-SCR.
Ulrich Simon 1 , Thomas Simons 1
1 , RWTH Aachen, Aachen Germany
Show AbstractZeolites are microporous aluminosilicates, which found numerous technical applications in different fields. H-form zeolites, where protons serve as charge compensating cations inside the polyanionic alumosilicate lattice, were found to be proton conductors at elevated temperature and, based on this, serve as NH3-sensor materials [1]. While the proton transport in the solvent free zeolite can be described by means of classical hopping models, a Grotthus-like and a vehicle-like transport was indentified in the presence of NH3, depending on the concentration and temperature range, respectively. At the same time such zeolites are applied as catalysts for DeNOx-SCR (selective catalytic reduction of NOx with NH3), which is of great relevance in exhaust gas after treatment of lean burn diesel engines as well as in NOx producing technical plants [2]. In the study presented here H-form zeolites serve as a proton conducting NH3 sensor and SCR catalysts at the same time, thus allowing in-situ monitoring of the NOx conversion with NH3. Therefore zeolite H-ZSM-5, which was deposited as a thick film on inter digital electrodes on a actively heated sensor chip, was first loaded with NH3 up to its full storage capacity followed by application of NO and NO2 into the surrounding gas phase in a temperature range from 150 – 500 K. The proton conductivity was measured using impedance spectroscopy while loading the catalyst with NH3 as well as during catalytic conversion. Thus, in-situ measurements of the onset temperature and kinetics of NOx conversion become feasible. The results obtained in our study will be discussed in the context of previous studies on the gas sensing properties [2], of the proposed transport models [3] and of very recent studies on the temperature programmed desorption (TPD) of NH3 [4].1.M. E. Franke, U. Simon, R. Moos, A. Knezevic, R Müller, C. Plog, Phys. Chem. Chem. Phys., 2003, 5, 51952. D. J. Kubinski, J. H. Visser, Sens. Actuat. B, 2008, 130 4253. L. Rodriguez-Gonzalez, E. Rodriguez-Castellon, A. Jimenez-Lopez, U. Simon, Solid State Ionics, 2008, 179, 19684. L. Rodriguez-Gonzalez, U. Simon, Meas. Sci. Technol., 2010, 21, 027003
10:30 AM - **J1.4/K3.4
Permeative Gas Transport in Proton Conducting Perovskites.
Ryan O'Hayre 1 , Michael Sanders 1 , Jianhua Tong 1 , Huayang Zhu 2 , Robert Kee 2
1 Metallurgical and Materials Engineering, Colorado School of Mines, Golden, Colorado, United States, 2 Mechanical Engineering, Colorado School of Mines, Golden, Colorado, United States
Show AbstractOne of the more interesting and yet understudied characteristics of proton conducting ceramics is their propensity to exhibit multi-species conduction behavior—specifically the simultaneous occurrence of proton, oxygen vacancy and electronic (electron or hole) conductivity. An often overlooked extension of multi-species transport is the prediction of steam permeation (i.e., the chemical transport of water across a fully dense perovskite membrane), a phenomena that could yield new scientific insights as well as commercial applications. Most research performed to-date on proton conducting ceramic materials has focused on conductivity measurements. This presentation will focus on the gas permeation properties of these materials instead. Unlike conductivity measurements, permeation experiments do not require the charge compensation or electric driving force supplied by electrodes. Permeation is electrode-less and therefore charge balance must be conserved internally during transport. This requirement necessitates multi-species transport coupling and accentuates minority carrier species, whereas conductivity measurements accentuate the majority carrier species. A further important feature of this permeation approach is that the various ionic transport species of interest in the system (namely O2- and H+) can be studied directly and separately using isotopically labeled tracers (such as 18O and 2H). This presentation will focus in particular on two of the potentially most significant practical repercussions of coupled multi-species transport in perovskite systems: 1) High temperature steady-state steam transport in these ceramic materials via multi-species diffusion 2) The intriguing possibility of controlled “uphill transport” in these ceramic systems, achieved by exploiting the transport cross-terms that occur during coupled multi-component diffusion.Our recent results in these areas and potential applications for these intriguing gas permeation phenomena will be discussed.AcknowlegmentsThis work is partially supported by the National Science Foundation MRSEC program under Grant No. DMR-0820518 at the Colorado School of Mines.
11:30 AM - J1.5/K3.5
1H-NMR Measurements on Proton Mobility in Nano-crystalline YSZ.
Judith Hinterberg 1 , Alina Adams 4 , Bernhard Bluemich 4 , Martin Wilkening 3 , Paul Heitjans 3 , Sangtae Kim 2 , Zuhair Munir 2 , Roger De Souza 1 , Manfred Martin 1
1 IPC, RWTH Aachen, Aachen Germany, 4 Institute of Macromolecular Chemistry, RWTH Aachen University, Aachen Germany, 3 Institute of Physical Chemistry and Electrochemistry, Leibniz University of Hannover , Hannover Germany, 2 Department of Chemical Engineering and Materials Science, University of California, Davis, California, United States
Show AbstractWe report Nuclear Magnetic Resonance (NMR) results on water saturated, dense, nano-crystalline YSZ samples (9.5 mol% yttria doped zirconia) which exhibits proton conductivity at temperatures as low as room temperature.[1] Static NMR as well as magic angle spinning NMR spectra show two distinct signals. Their temperature dependent behaviour and their linewidths suggest that one can be attributed to (free) water adsorbed on the surface of the sample and the other one to mobile protons within the sample. This interpretation is supported by comparison with measurements on a single crystalline sample. For the nano-crystalline samples motional narrowing is observed for the signal originating from protons inside. For these protons, the analysis of temperature and field dependent T1 relaxation measurements points towards diffusion in a confined two-dimensional geometry. We attribute this two-dimensional motion to protons that are mobile within the grain boundaries of nano-crystalline YSZ.[1]S. Kim, U. Anselmi-Tamburini, H. J.Park, M. Martin, Z. A. Munir, Adv. Mater., 2008, 20, 556-559
11:45 AM - **J1.6/K3.6
NMR Studies of Local Structure, Cation Ordering and Protonic Conduction in Perovskites.
Lucienne Buannic 2 , Frederic Blanc 1 2 , Derek Middlemiss 1 , Clare Grey 1 2
2 Chemistry, Stony Brook University, Stony Brook, New York, United States, 1 Chemistry, Cambridge University, Cambridge United Kingdom
Show AbstractThis talk will illustrate the use of high field, multinuclear NMR spectroscopy to investigate the nature of the defects in materials for solid-state electrolytes. In particular, we focus on electrolytes that operate via protonic conduction in solid oxide fuel cells. For example, BaZrO3 or BaSnO3 can be doped with Y3+ or Sc3+ to create oxygen vacancies. These vacancies can be filled with H2O, the water molecules dissociating to form mobile ions that contribute to the long-range ionic transport in these systems. NMR experiments are used to examine the local structure, the locations of the vacancies and how this affects protonic/oxygen ion motion in these systems. NMR studies of the host B cations (Zr, Sn) can be used to quantify (particularly in the case of Sn) the ratio of 5:6 fold cations, and thus indirectly, the location of the vacancy. NMR studies of the dopants (Sc, Y) can be used to investigate vacancy trapping. The location of the dopant ion is often ambiguous, and we show that 89Y can be used to investigate cation doping on the A vs. B site of the perovskite, the former reducing the number of oxygen vacancies and thus the number of protons, following hydration. Finally, 17O NMR experiments are shown to be extremely sensitive to the nature of the B cation directly bound to the oxygen site, different resonances being observed for the B-O-B’ sites on cation doping. Chemical shift calculations, performed by using the CASTEP code, reveal that oxygen ions in axial and equatorial positions relative to a vacancy (i.e., in a O(axial)B(O(eq))-vac local environment, where vac = oxygen vacancy) can be distinguished. The implications of these results for protonic conduction will be discussed along with strategies to examine these materials under environments that are closer to those in operating fuel cell devices.
12:15 PM - J1.7/K3.7
Proton Transport Across the Grain Boundaries in Yttrium-doped Barium Zirconates under Applied DC Bias.
Fumitada Iguchi 1 2 , Chien-Ting Chen 1 , Hiroo Yugami 2 , Sangtae Kim 1
1 Department of Chemical Engineering and Materials Science, University of California, Davis, California, United States, 2 Graduate school of engineering, Tohoku University, Sendai Japan
Show AbstractPerovskite-type proton conductors based on barium zirconate, especially yttrium-doped barium zirconate (BZY), are promising candidates as electrolytes of intermediate-temperature solid oxide fuel cells (IT-SOFC), because of their high bulk conductivity in the temperature region of 400oC – 700oC. However, the overall protonic conductivity of BZY is still considerably low due to the high resistance at the grain boundaries.. It is this reason that is currently limiting the full development of BZY as an electrolyte of IT-SOFC. Therefore, a strong emphasis has been placed on elucidating the origin of the blocking effect and improving grain boundary resistance. It has recently been speculated that such high grain-boundary resistance in BZY is due to space-charge effects, meaning that protons deplete at the grain boundaries to form potential barriers which block the proton transport across the grain boundaries. We previously clarified the relationship between potential barrier height and dopant concentration based on space-charge concept. However, direct experimental evidence of the space-charge effect in BZY has not been reported to date. In this contribution, we will present our results of electrochemical impedance spectroscopy (EIS) studies on BZY under applied DC bias. The BZY specimens with relatively large grain sizes (> 2 micrometers) suitable for such experiments were prepared by optimizing sintering temperature and time, e.g. 1800oC for 30h. We will discuss the space-charge effects in BZY based on the dc-bias dependent grain boundary resistance measured from the BZY samples with different dopant concentrations and different thicknesses.
12:30 PM - J1.8/K3.8
Energy Barriers for Proton Migration at Σ3 (111)/[1-10] Barium Zirconate Tilt Grain Boundary.
Dae-Hee Kim 1 , Byung-Kook Kim 2 , Yeong-Cheol Kim 1
1 Department of Materials Engineering, Korea University of Technology and Education, Cheonan, Chungnam, Korea (the Republic of), 2 High Temperature Energy Materials Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractSince the practical proton conductors are polycrystalline, and therefore protons should migrate across grain boundaries, there has been a big demand for the energy barrier calculation about the grain boundaries of barium zirconate. Proton migration at Σ3 (111)/[1-10] tilt grain boundary in barium zirconate was investigated using density functional theory, since the tilt grain boundary was one of the commonly observed grain boundaries experimentally. An optimum Σ3 (111)/[1-10] tilt grain boundary including barium and oxygen atoms at the interface was constructed, and its grain boundary energy was 0.03 eV/Å2. The proton behavior in the grain was similar to that in the bulk barium zirconate with energy barriers in the range of 0.17-0.21 eV. However, energy barriers for proton migration in the range of 1.06-1.30 eV were required to migrate across the grain boundary.
12:45 PM - J1.9/K3.9
Influence of Trivalent Cation on Proton Concentration in BaZrO3 by First Principles Calculations.
Katsuhiro Nakano 1 , Masato Yoshiya 1 2 , Hideyuki Yasuda 1 , Akihide Kuwabara 2
1 Adaptive Machine Systems, Osaka University, Osaka Japan, 2 , Japan Fine Ceramics Center, Nagoya Japan
Show AbstractTrivalent cation-doped BaZrO3 is a protonic conductor, a prime candidate for an electrolyte of the low-temperature solid oxide fuel cell (SOFC). The BaZrO3 has perovskite structure denoted as ABO3, in which A site and B site are occupied by divalent Ba and tetravalent Zr, respectively. The oxygen vacancies are formed to compensate charge when trivalent cations are substituted for Zr atoms at B sites in BaZrO3. Then, H2O molecules are decomposed to substitute OH- for an oxygen vacancy and H+ loosely adhere to a nearby oxygen under wet condition. Yttrium-doped BaZrO3 has been known to have the highest conductivity among trivalent cation-doped BaZrO3 thus far. However, it is still unclear how to further improve the conductivity of trivalent cation-doped BaZrO3 due to lack of quantitative knowledge as to how properties of trivalent cations influence production and conduction of protons. In order to produce protons, oxygen vacancies in BaZrO3 are essentially needed. In order to produce oxygen vacancies, substitution trivalent cations for Zr atoms at B sites in BaZrO3 are essentially needed. However, for these two processes, it is practically difficult to partition the effects of trivalent oxide doping on these two processes separately only by experiments. To overcome this difficulty, theoretical calculations, which can divide their two processes and to analyze underlying physics governing each two process on the atomic level, were employed. In this study, to reveal correlation between trivalent cations and proton concentration, which follows oxygen vacancies formation, first principles calculations have been carried out. The probability of a neutral defect complex creation that involves formation of oxygen vacancies in cubic perovskite supercells containing 320 atoms, repeated four times along each axis, was calculated from formation energy including configurational entropy term for all the possible configurations of defect complexes within the supercell on the basis of statistical mechanics. Then, energy barrier to absorb decomposed H2O molecules was evaluated. To appropriately evaluate the energy barrier, stable protons sites in BaZrO3 were determined in prior. Proton concentration was calculated by summing the probability of the defect complex creation and that of absorption of decomposed H2O molecules. Influence of trivalent cation species for proton concentration will be explored in terms of ionic radius, density of electrons, and so on.
J2: Defects, Confinement, Transport I
Session Chairs
Wednesday PM, April 27, 2011
Room 2012 (Moscone West)
2:30 PM - J2.1
Defect Chemistry of Grain Boundaries in Proton-conducting Solid Oxides.
Roger De Souza 1 , Sangtae Kim 2 , Zuhair Munir 2 , Manfred Martin 1
1 Institute of Physical Chemistry, RWTH Aachen University, Aachen Germany, 2 Dept of Chemical Engineering and Materials Science, University of California-Davis,, Davis, California, United States
Show AbstractThe defect chemistry of charged grain boundaries in an acceptor-doped oxide in equilibrium with a water-containing atmosphere is examined theoretically. The formation of charged grain boundaries and attendant space-charge zones is considered to be governed by the thermodynamic driving energies for the redistribution of oxygen vacancies and hydroxide ions between bulk and grain-boundary core. A one-dimensional continuum treatment, based on the abrupt core|space-charge model, is used to predict the space-charge potential and defect concentrations in the grain-boundary core as a function of water partial pressure and temperature for various values of the two thermodynamic driving energies. The results are discussed with respect to experimental data in the literature for acceptor-doped perovskite oxides (e.g. BaZrO3) and fluorite oxides (e.g. CeO2).
2:45 PM - J2.2
Proton Formation and Diffusion in Amorphous SiNx:H.
Hendrik Dekkers 1 , Victor Prajapati 2 , Sven Van Elshocht 1 , Eric Vancoille 1
1 FPS, imec, Leuven Belgium, 2 SSET, imec, Leuven Belgium
Show AbstractRelease of bonded hydrogen from amorphous silicon nitride (SiNx:H) changes the properties of those films, giving them an additional functionality when used in semiconductor devices. For example, defects and surfaces of devices or substrates on which SiNx:H is deposited can be passivated by hydrogen diffusing from the film. Also material strain in those devices can be induced from the stress formed by chemical reactions in the SiNx:H film, causing the release hydrogen. In this work we investigate the role of proton formation and diffusion in those processes, induced by thermal treatment and ultra violet (UV) illumination.High density SiNx:H films can be used as a source of hydrogen passivation for defected material like low quality silicon substrates for solar cells [1]. We show that hydrogen is mainly released in protonic form and that diffusion might happen via hopping to nitrogen lone-pair orbitals. Density functional theory (DFT) computations demonstrate that the hopping mechanism of protons requires activation energy of 1.7 eV. This value corresponds to the ones estimated from observed diffusion profiles, using deuterium to distinguish the diffusing atoms.In contrast, low density SiNx:H releases large quantities of hydrogen during thermal treatment. In those layers the release of protons has to compete with the direct formation of molecular hydrogen [2] by breaking of Si-H and N-H bonds and cross linking of Si and N. This process induces a high tensile stress (up to 2.1 GPa) and is typically used for electron mobility enhancement in n-type CMOS transistors. Annealing experiments demonstrate the distribution of the activation energy (Ea) conform the amorphous nature of the films. Average activation energy of 2.2 eV, with a 1σ of 0.5 eV is obtained which is within the range of DFT transition state computations. Illumination of the sample with UV light enhances the last reaction significantly. Release of hydrogen far below the deposition temperature of SiNx:H films is clearly observed in Fourier transformed infra red (FTIR) spectroscopy. Careful analysis of the FTIR data reveals the release of N-H and Si-H beyond the penetration depth of UV light with wavelength of 172 nm. Moreover, the N-H bonds are also removed in N-rich SiNx:H where Si-H bonds are lacking. This indicates that holes, formed by band gap excitation from UV illumination, are trapped by the nitrogen lone-pair orbitals and are breaking N-H bonds, forming protons. A model is proposed for hydrogen release and stress formation deep in the SiNx:H involving diffusing protons. Possibilities to use UV light to induce low temperature proton (deuteron) diffusion in both low and high density SiNx:H are further explored experimentally by using deuterium. [1] M. Sheoran, et al. Appl. Phys. Lett. 92, 172107 (2008).[2] H.F.W. Dekkers, et al. Appl. Phys. Lett. 89, 221914 (2006).
3:00 PM - **J2.3
Superfast Proton Transport in Plasma-polymerized Proton Exchange Fuel Cell Membranes.
Vanessa Peterson 1 , Cormac Corr 2 , Gordon Kearley 1 , Roderick Boswell 2 , Zunbeltz Izaola 3
1 The Bragg Institute, ANSTO, Lucas Heights, New South Wales, Australia, 2 Plasma Research Laboratory , Australian National University, Canberra, Australian Capital Territory, Australia, 3 Berlin Neutron Scattering Center, Helmholtz Zentrum Berlin fuer Materialien und Energie, Berlin Germany
Show AbstractFuel cells that use hydrogen and air to produce electricity are among the key enabling technologies for the transition to a hydrogen-based economy, with proton exchange membrane (PEM) fuel cells a potential future power source for zero-emission vehicles. The amount of electricity produced by a fuel-cell is directly proportional to the transport of protons across the PEM. The leading performance PEM, developed by DuPont, is the sulfonated tetrafluoroethylene copolymer, Nafion®. Herein we report proton transport within a PEM, produced via plasma-polymerization of trifluoromethanesulfonic acid and styrene, which is significantly faster than reported in Nafion® and achieved by a new mechanism. In the plasma-polymerized membranes, the styrene constitutes the backbone of the polymer matrix and the proton conductive functions are derived from the trifluoromethanesulfonic acid. The plasma-polymerization method has the additional advantage that the ease of thickness control during the deposition process affords miniaturization, a feature that revolutionized the microelectronics industry. The process results in strong adhesion on electrodes and conformal coatings and the degree of (controllable) cross-linking enables the adjustment of mechanical properties such as chemical and thermal stability. This has led to increased degradation resistance and significant reduction in methanol permeability and improved performance of these membranes for direct-methanol fuel-cell applications through reduced fuel-crossover. We examined proton motions in Nafion® and the plasma-produced PEM using quasielastic neutron scattering to directly measure the self-diffusion of the protons in the water added to the PEMs. We find two types of diffusing protons in the plasma produced PEM, one of which (ca one-third) diffuses significantly faster than those in Nafion®, with the remaining protons moving in an identical way to those in the Nafion®. We find the fast-moving proton population to be moving via a transport mechanism that is significantly different to the slower population. Information associated with the geometry of motions can be gained through analysis of the motions as a function of Q (neutron scattering vector). We find a Q-dependency of the fast-moving proton population significantly different to the slower moving population, and describe this using a Chudley-Elliott jump-diffusion model with a jump length approximately 2.9 Å.
3:30 PM - J2.4
Fundamentals of Hydrogen and Hydride Formation at Defects in Palladium: First-principles Prediction and Inelastic Neutron Scattering Measurements.
Dallas Trinkle 1 , Hyunsu Ju 2 , Brent Heuser 2
1 Materials Science and Engineering, Univ. Illinois, Urbana-Champaign, Urbana, Illinois, United States, 2 Nuclear, Plasma, and Radiological Engineering, Univ. Illinois, Urbana-Champaign, Urbana, Illinois, United States
Show AbstractPalladium has a high hydrogen solubility and diffusivity. H can be stored both in octahedral sites and in dislocation cores, which act as nanoscale H traps--forming Cottrell atmospheres that are metal-hydride-like at low temperatures. The formation of a Cottrell atmosphere can be measured in situ with inelastic neutron scattering. Ab initio density-functional theory computes the potential energy for a hydrogen in the core of a partial dislocation and with volumetric strains. We model changes in the hydrogen potential from neighboring Pd vibrations to predict the vibrational density of states for hydrogen from 0K to room temperature. The predicted inelastic neutron scattering intensity compare with new measurements, which show a shoulder at 0K from the core and hydride formation, widening of the peak at 200K from spreading of the Cottrell atmosphere, and a shift in the peak at 300K as the atmosphere dissolves.
3:45 PM - J2: D-C-T I
BREAK
Symposium Organizers
Artur Braun Empa – Swiss Federal Laboratories for
Materials Testing and Research
Paul Gannon Montana State University
Sossina Haile California Institute of Technology
RobertA. Robinson Australian Nuclear Science and Technology Organisation (ANSTO)
Symposium Support
Australian Nuclear Science and Technology Organization (ANSTO)
AXPO Holding AG
EMPA, Laboratory for High Performance Ceramics
Montana State University, Chemical &
Biological Engineering
J4: Defects, Confinement, Transport III
Session Chairs
Thursday AM, April 28, 2011
Room 2012 (Moscone West)
9:15 AM - **J4.1
Dynamics of Water and Protons Confined in Perfluorinated Membranes and Surfactants.
Sandrine Lyonnard 1 , M. Marechal 1 , Q. Berrod 1 , Armel Guillermo 1 , Gerard Gebel 1 , B. Frick 2 , J. Ollivier 2
1 Laboratorie des Polymeres Conducteurs Ioniques, INAC/SPrAM-CEA-Grenoble, Structures et Proprietes d'Architectures Moleculaires, UMR 5819 (CEA-CNRS-UJF), Grenoble France, 2 , Institut Laue Langevin, Grenoble France
Show AbstractPerfluorinated ionomers, the reference membranes for PEM fuel cells, combine in one macromolecule the hydrophilic character of terminal SO3H functional groups and the hydrophobicity of the polymer backbone. This leads to an hydrophilic/hydrophobic nanoseparation in the presence of water. The confinement of water within the hydrophilic interconnected nanodomains and the interaction with the acidic functional groups plays a central role in the proton conduction mechanism. In order to study the structure/transport relationship, we have investigated by Quasi-elastic Neutron Scattering and Molecular Dynamics Simulations the dynamical behaviour of water confined in different systems: perfluorinated membranes (Nafion® [1], aged Nafion®, and short side chain AquivionTM) and surfactants [2]. The latter mimic the physico-chemical properties of the real systems and offer the advantage to self-assemble in well defined organized phases.QENS studies were performed on both time-of-flight and backscattering spectrometers at the ILL (Grenoble, France). The quasielastic spectra are discussed on the basis of a sophisticated model for confined motion [3]. This unique diffusion model based on Gaussian statistics takes into account both localized translational motions and long-range diffusion. Comparison of the diffusion mechanisms and parameters (diffusion coefficients, confinement sizes and characteristic times) obtained in the various systems as a function of their hydration bring new insight on the complex molecular scenario for proton motion under confinement. [1] J-C. Perrin, S. Lyonnard and F. Volino; Quasielastic neutron scattering study of water dynamics in hydrated nafion membranes, Journal of Physical Chemistry C, 111 (2007), 3393-3404.[2] S. Lyonnard, Q. Berrod, B-A. Brüning, G. Gebel, H. Ftouni, J. Ollivier and B. Frick; Perfluorinated surfactants as model charged systems for understanding the effect of confinement on proton transport and water mobility in fuel cells membranes. A study by QENS. Europhys. J. Special Topics 189 (1) (2010), 205-216.[3] F. Volino, J-C. Perrin and S. Lyonnard; Gaussian model for localized translational motion : application to incoherent neutron scattering, Journal of Physical Chemistry B, 110 (2006), 11217-11223.
9:45 AM - J4.2
Probing the Effects of Pressure-induced Strain and Imperfections on the Proton Transport Properties of Ceramic Proton Conductors.
Qianli Chen 1 2 , Artur Braun 1 , Stuart Holdsworth 3 , Vladimir Pomjakushin 4 , Zhi Liu 5 , Simon Clark 5 , Edvinas Navickas 1 6 , Jan Embs 4 7 , Thierry Straessle 4 , Nikolai Bagdassarov 8 , Thomas Graule 1 9
1 Laboratory for High Performance Ceramics, Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf Switzerland, 2 Department of Physics, ETH Zurich, Zurich Switzerland, 3 Mechanics for Modelling and Simulation, Empa, Dübendorf Switzerland, 4 Laboratory for Neutron Scattering, Paul Scherrer Institut, Villigen Switzerland, 5 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 6 , Kaunas University of Technology, Kaunas Lithuania, 7 , Saarland University, Saarbrücken Germany, 8 Institute for Geosciences, Goethe University Frankfurt, Frankfurt/Main Germany, 9 Institute of Ceramic, Glass- and Construction Material, TU Bergakademie Freiberg, Freiberg Germany
Show AbstractProton conductors are promising solid electrolyte materials for ceramic fuel cells operating at intermediate temperature. Our study focuses on the mechanisms of proton conductivity of perovskite yttrium-doped barium zirconates and cerates. In-situ electrochemical impedance spectroscopy was used to study the effect of lattice volume and compressive strain on the proton conductivity by applying the hydrostatic pressure up to 2 GPa. At high temperature, the activation energy of the bulk conductivity increases upon pressure up to 40%, confirming a previously suggested correlation between the lattice volume and proton diffusivity in the crystal lattice. Compressing the lattice decreases proton conductivity, indicating that the protons need "space" to move freely in the lattice. We are probing the proton diffusion in the atomic scale by quasielastic neutron scattering under high pressure. Also, the chemical interactions of the protons with the lattice are studied with synchrotron techniques, at ambient and high pressure.
10:00 AM - J4.3
Local Structure, Hydrogen-bonding, and Proton Dynamics in Proton-conducting Oxides: Insight from Spectroscopy.
Maths Karlsson 1 2 3
1 , European Spallation Source, Lund Sweden, 2 Applied Physics, Chalmers University of Technology, Goeteborg Sweden, 3 Chemical and Biological Engineering , Chalmers University of Technology, Goeteborg Sweden
Show AbstractSystematic development of materials with sufficiently high proton conductivities for efficient use as electrolytes in fuel cells operating in the intermediate temperature range (~200—500 °C) depends on a better understanding of key fundamental properties of the most promising classes of compounds, but such knowledge is often lacking. We have approached this problem by experimental investigations of the chemistry and physics of the structure-dynamics relationship underpinning hydrogen-bonding interactions and the mechanistic aspects of proton transport in proton-conducting oxides. The primary tools to this end have been the use of vibrational spectroscopy (Raman, infrared, and neutron) [1—4], neutron diffraction [5], and quasielastic neutron scattering [6—8], drawing in complementary information from atomistic modeling [1,6,7].Most recently, we have investigated the proton dynamics in a few different types of proton-conducting perovskite-type oxides [6—8]. We find that the characteristics of the proton motions (e.g. time-scale, activation energy, and spatial geometry) are different amongst the different materials, and we can correlate these dynamical differences to local structural features, as affected by the type and the concentration of dopant atoms, for example. This presentation will highlight these dynamical studies, especially of the hydrated perovskites In-, Sc-, and Y-doped BaZrO3, but also recent neutron spin-echo [7] results of the lanthanum tungstate La6WO12; a proton-conducting oxide which is receiving growing interest [9].1. M. Karlsson et al., Phys. Rev. B 72 (2005) 0943032. M. Karlsson et al., Phys. Rev. B 77 (2008) 1043023. M. Karlsson et al., Chem. Mater. 20 (2008) 34804. M. Karlsson et al., J. Phys. Chem. C 114 (2010) 61775. I. Ahmed et al., J. Alloys and Compds 450 (2008) 1036. M. Karlsson et al., Solid State Ionics 180 (2009) 227. M. Karlsson et al., Chem. Mater. 22 (2010) 7408. M. Karlsson et al., J. Phys. Chem. C 114 (2010) 32929. Anna Magrasó et al., Dalton Trans. (2009) 10273
10:15 AM - J4.4
Mixed Proton and Electron-hole Conduction in Cerium Phosphates.
Hannah Ray 1 2 , Lutgard De Jonghe 1 2
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThe microstructures and mixed proton and electron-hole conducting properties of cerium orthophosphate and cerium metaphosphate are compared. Materials with mixed proton and electron-hole conduction are useful for fuel cell electrode materials, permeation membranes, or sensors. Proton conduction has already been demonstrated in rare earth phosphates (REPO4). When aliovalently doped REPO4 materials are exposed to water vapor or hydrogen gas, protons are incorporated into the structure as charge-compensating defects. When the rare earth cations in the material can exist in multiple valence states, then p-type electronic conduction becomes possible via the transfer of the oxidized state from cation to cation. Various electrochemical techniques including ac impedance measurements of the total conductivity in various atmospheres, permeation measurements, and transference number measurements, can be used to monitor the identity of the dominant carrier in these materials.In this work, the influences of different synthesis techniques and metal to phosphorus ratios on the microstructure, proton content, and conduction properties of cerium phosphate materials are explored.
10:30 AM - **J4.5
Proton Behavior in Perovskite Ceramics and Applications of These Ceramics.
Hugo Schmidt 1 , Chih-Long Tsai 1
1 Department of Physics, Montana State University, Bozeman, Montana, United States
Show Abstract Protons can fit into the perovskite structure because the O-O distance is approximately that of ice. However, to achieve charge balance, -2e charge must be added for every two protons added. O2- ions provide charge -2e, but interstitial O2- ions have high energy, so we need O2- vacancies, for instance by doping barium cerate with yttrium (BCY) to obtain 1 O2- vacancy per 2 Y ions. It is known that proton concentration and conductivity can be increased by exposing BCY to steam molecules, which dissociate into 2 protons and an O2- ion. From our impedance spectroscopy measurements and solid oxide fuel cell (SOFC) work, we find that exposure to H2 on the anode side can add protons. This requires addition of O2- ions on the cathode side from O2 in air. Alternatively, electrons could be added because BCY is a weak electronic semiconductor. BCY is known to be a hole conductor, and this conductivity decreases upon exposure to steam or H2. From our analysis of V(i) curves for SOFCs with BCY electrolyte, at low H2 concentration, increasing this concentration decreases electronic conductivity somewhat, consistent with adding electrons and reducing hole carrier concentration. At higher H2 concentrations, electronic conductivity remains constant.Proton transfer in perovskites such as BCY should be similar to that in usual H-bonded crystals. Such transfer consists of two steps, both required for dc conductivity. One is intrabond proton transfer. The other is a proton jump from one H-bond to an adjacent bond, equivalent to rotation of an O-H unit about the O ion. The main difference from usual H-bonded crystals is that the adjacent O-O pair most likely has no proton between the O ions, so that the Pauling ice rule precluding 2 protons in one bond is not much of a restriction in perovskites because the proton concentration is typically below 0.2 per formula unit. Another difference is that, though protonic semiconductor activation energies are high, in the 0.5 to 1 eV range, the high operating temperatures of SOFCs, 600 to 900 oC, give useful amounts of power per unit area, or in the electrolysis mode, useful amounts of H2 out for steam and electric power input. Two applications for proton-conducting perovskite ceramics are SOFCs and hydrogen separation membranes (HSMs). For SOFCs, we have modeled the V(i) behavior with almost no adjustable parameters, and have succeeded in coming close to the Nernst open circuit potential as well as fitting the V(i) curves for a variety of H2/O2 partial pressure combinations. For HSMs, unlike for SOFCs, an electronic conductivity comparable to the protonic conductivity is desirable, to avoid using a cermet which may develop cracks because of differential thermal expansion.In conclusion, many oxides and fluorides have O-O or F-F separations in the H bonding range and will provide a stimulating playground for further basic and applied research on proton incorporation and dynamics in solids.
11:00 AM - J4: D-C-T III
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