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  • 301.
    Jeschull, Fabian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Maibach, Julia
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    On the Electrochemical Properties and Interphase Composition of Graphite: PVdF-HFP Electrodes in Dependence of Binder Content2017In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 164, no 7, p. A1765-A1772Article in journal (Refereed)
    Abstract [en]

    Poly(vinylidene-difluoride) (PVdF) based polymers constitute the most commonly used binders for lithium-ion battery electrodes. In scientific studies, the binder content often exceeds commercially meaningful amounts. At the same time, the battery electrode performance can in various ways be coupled to its binder content, partly due to its influence on the surface properties. For example, an optimum binder content of around 5 wt% has been reported. In this study, graphite: PVdF-HFP electrodes containing 2.5, 5 and 10 wt% of PVdF-HFP are investigated, and their electrochemical behavior are put into context of the electrode-electrolyte interphase of the different formulations. Although the electrodes display similar electrochemical behavior, the SEI layer composition and thickness, analyzed by photoelectron spectroscopy, vary notably depending on binder content. It was found that a binder content of 5 wt% maintained the best cycling stability and also exhibited a thinner SEI layer with a larger fraction of inorganic components. In contrast to higher binder contents, where the binder covers most of the surface, larger parts of the active material are exposed directly to the electrolyte with binder contents of 2.5-5 wt%. The formation of a thinner, yet protective, SEI layer is beneficial for cycling performance of the graphite electrode. (C) 2017 The Electrochemical Society. All rights reserved.

  • 302.
    Jeschull, Fabian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Maibach, Julia
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Félix Duarte, Roberto
    Helmholtz Zentrum Berlin für Materialien und Energie.
    Wohlfahrt-Mehrens, Margret
    Zentrum für Sonnenenergie- und Wasserstoff-Forschung (ZSW).
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Memm, Michaela
    Zentrum für Sonnenenergie- und Wasserstoff-Forschung (ZSW).
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Analysis of the solid-electrolyte interphase of water-processed graphite electrodes by photoelectron spectroscopyManuscript (preprint) (Other academic)
    Abstract
  • 303.
    Jeschull, Fabian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Maibach, Julia
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Félix, R.
    Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin, Germany.
    Wohlfahrt-Mehrens, M.
    Zentrum für Solarenergie- und Wasserstoff-Forschung (ZSW), Lise-Meitner-Straße 24, 89081 Ulm, Germany.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Memm, M.
    Zentrum für Solarenergie- und Wasserstoff-Forschung (ZSW), Lise-Meitner-Straße 24, 89081 Ulm, Germany.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Solid Electrolyte Interphase (SEI) of Water-Processed Graphite Electrodes Examined in a 65 mAh Full Cell Configuration2018In: ACS Applied Energy Materials, ISSN 2574-0962, Vol. 1, no 10, p. 5176-5188Article in journal (Refereed)
    Abstract [en]

    Electrode binders, such as sodium carboxymethyl cellulose (CMC-Na), styrene–butadiene rubber (SBR) and poly(sodium acrylate) (PAA-Na) are commonly applied binder materials for the manufacture of electrodes from aqueous slurries. Their processability in water has considerable advantages over slurries based on N-methylpyrrolidone (NMP) considering toxicity, environment and production costs. In this study, water-processed graphite electrodes containing either CMC-Na:SBR, PAA-Na, or CMC-Na:PAA-Na as binders have been prepared on a pilot scale, cycled in graphite||LiFePO4 Li-ion battery cells and analyzed post-mortem with respect to the binder impact on the SEI composition, using in-house (1486.6 eV) and synchrotron-based (2300 eV) photoelectron spectroscopy (PES). The estimated SEI layer thickness was smaller than 11 nm for all samples and decreased in the order: PAA-Na > CMC-Na:SBR > CMC-Na:PAA-Na. The SEI thickness correlates with the surface concentration of CMC-Na, for example, the CMC-Na:PAA-Na mixture showed signs of polymer depletion of the PAA-Na component. The SEI layer components are largely comparable to those formed on a conventional graphite:poly(vinylidene difluoride) (PVdF) electrode. However, the SEI is complemented, by notable amounts of carboxylates and alkoxides, whose formation is favored in water-based negative electrodes. Additionally, more electrolyte salt degradation is observed in formulations comprising PAA-Na. The choice of the binder for the negative electrode had little impact on the surface layer formed on the LiFePO4 positive electrode, except for different contents of sodium salt deposits, as a result of ion migration from the counter electrode.

  • 304. Jia, Ning
    et al.
    Li, Shu-Ming
    Ma, Ming-Guo
    Sun, Run-Cang
    Zhu, Jie-Fang
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hydrothermal fabrication, characterization, and biological activity of cellulose/CaCO3 bionanocomposites2012In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 88, no 1, p. 179-184Article in journal (Refereed)
    Abstract [en]

    Bionanocomposites with the combination of natural polymers and inorganic nanoparticles may induce unique properties and exhibit promising functions for different applications. Herein, we report a hydrothermal route to the preparation of cellulose/CaCO3 bionanocomposites using the cellulose solution. Ca(NO3)(2)center dot 4H(2)O and Na2SiO3 center dot 9H(2)O. The cellulose solution was previously prepared by the dissolution of microcrystalline cellulose in NaOH-urea aqueous solution. The urea also acts as the CO32- source for the synthesis of CaCO3. The influences of several reaction parameters, such as the heating time, the heating temperature, and the types of additives on the products were investigated by X-ray powder diffraction, Fourier transform infrared spectrometry, scanning electron microscopy, thermogravimetric analysis, and differential thermal analysis. The experimental results demonstrated that the hydrothermal conditions had an effect on the morphology of the bionanocomposites. Cytotoxicity experiments indicated that the cellulose/CaCO3 bionanocomposites had good biocompatibility, so that the bionanocomposites could be ideal candidate for practical biomedical applications.

  • 305.
    Jin, Rui
    et al.
    Shanghai Univ, Res Ctr Nanosci & Nanotechnol, Shanghai 200111, Peoples R China..
    Fu, Lixin
    Shanghai Univ, Res Ctr Nanosci & Nanotechnol, Shanghai 200111, Peoples R China..
    Zhou, Hualan
    Univ Shanghai Sci & Technol, Sch Med Instrument & Food Engn, Shanghai 200093, Peoples R China..
    Wang, Zhuyi
    Shanghai Univ, Res Ctr Nanosci & Nanotechnol, Shanghai 200111, Peoples R China..
    Qiu, Zhengfu
    Shanghai Univ, Res Ctr Nanosci & Nanotechnol, Shanghai 200111, Peoples R China..
    Shi, Liyi
    Shanghai Univ, Res Ctr Nanosci & Nanotechnol, Shanghai 200111, Peoples R China..
    Zhu, Jie-Fang
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Yuan, Shuai
    Shanghai Univ, Res Ctr Nanosci & Nanotechnol, Shanghai 200111, Peoples R China..
    High Li+ Ionic Flux Separator Enhancing Cycling Stability of Lithium Metal Anode2018In: ACS SUSTAINABLE CHEMISTRY & ENGINEERING, E-ISSN 2168-0485, Vol. 6, no 3, p. 2961-2968Article in journal (Refereed)
    Abstract [en]

    The metallic lithium anode provides unparalleled opportunities for rechargeable batteries with very high energy density. A main problem hindering the development of cells using metallic lithium anodes stems from the electrochemical instability of the interface between metallic lithium and organic liquid electrolytes. This paper reports an approach rationally designing the surface characteristic of separator for stable, dendrite-free operation of lithium-metal batteries. A unique polymer multilayer PEI(PAA/PEO)(3) was fabricated on the microporous polyethylene (PE) separator by a simple layer-by-layer (LbL) assembly process, which maintains the pore structure and thickness of PE separator but remarkably enhances the ionic conductivity (from 0.36 mS cm(-1) to 0.45 mS cm(-1)) and Li+ transference number (from 0.37 to 0.48), as well as stabilizes lithium metal anodes against the reaction with liquid electrolytes during storage and repeated charge/discharge cycles, which is responsible for restraining the electrode polarization and the formation of lithium dendrites, and therefore endows lithium metal batteries with long-term cycling at high columbic efficiency and excellent rate capability, as well as the improved safety.

  • 306.
    Jo, Jae Hyeon
    et al.
    Sejong Univ, Dept Nano Technol & Adv Mat Engn, Seoul, South Korea; Sejong Univ, Sejong Battery Inst, Seoul, South Korea.
    Choi, Ji Ung
    Sejong Univ, Dept Nano Technol & Adv Mat Engn, Seoul, South Korea; Sejong Univ, Sejong Battery Inst, Seoul, South Korea.
    Park, Yun Ji
    Sejong Univ, Dept Nano Technol & Adv Mat Engn, Seoul, South Korea; Sejong Univ, Sejong Battery Inst, Seoul, South Korea.
    Zhu, Jie-Fang
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Yashiro, Hitoshi
    Iwate Univ, Dept Chem & Biol Sci, Morioka, Iwate, Japan.
    Myung, Seung-Taek
    Sejong Univ, Dept Nano Technol & Adv Mat Engn, Seoul, South Korea; Sejong Univ, Sejong Battery Inst, Seoul, South Korea.
    New Insight into Ethylenediaminetetraacetic Acid Tetrasodium Salt as a Sacrificing Sodium Ion Source for Sodium-Deficient Cathode Materials for Full Cells2019In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, no 6, p. 5957-5965Article in journal (Refereed)
    Abstract [en]

    Sacrificing sodium supply sources is needed for sodium-deficient cathode materials to achieve commercialization of sodium-ion full cells using sodium-ion intercalation anode materials. Herein, the potential of ethylenediaminetetraacetic acid tetrasodium salt (EDTA-4Na) as a sacrificing sodium supply source was investigated by intimately blending it with sodium-deficient P2-type Na0.67[Al0.05Mn0.95]O2. The EDTA-4Na/Na0.67[Al0.05Mn0.95]O2 composite electrode unexpectedly exhibited an improved charge capacity of 177 mA h (g-oxide)−1 compared with the low charge capacity of 83 mA h (g-oxide)−1 for bare Na0.67[Al0.05Mn0.95]O2. The reversible capacity of an EDTA-4Na/Na0.67[Al0.05Mn0.95]O2//hard carbon full-cell system increased to 152 mA h (g-oxide)−1 at the first discharge with a Coulombic efficiency of 89%, whereas the Na0.67[Al0.05Mn0.95]O2 without EDTA-4Na delivered a discharge capacity 51 mA h g–1 because of the small charge capacity. The EDTA-4Na sacrificed itself to generate Na+ ions via oxidative decomposition by releasing four sodium ions and producing C3N as a decomposition resultant on charge. It is thought that the slight increase in discharge capacity is associated with the electroconducting nature of the C3N deposits formed on the surface of the Na0.67[Al0.05Mn0.95]O2 electrode. We elucidated the reaction mechanism and sacrificial activity of EDTA-4Na, and our findings suggest that the addition of EDTA-4Na is beneficial as an additional source of Na+ ions that contribute to the charge capacity.

  • 307.
    Johansson, David
    et al.
    Insplor AB, Medicinaregatan 8A, S-41390 Gothenburg, Sweden..
    Andersson, Jenny
    Insplor AB, Medicinaregatan 8A, S-41390 Gothenburg, Sweden..
    Wickman, Bjorn
    Chalmers Univ Technol, Dept Phys, Kemivagen 9, S-41296 Gothenburg, Sweden..
    Björefors, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Sobkowiak, Adam
    Uppsala Univ, Angstrom Lab, Dept Chem, Lagerhyddsvagen 1, S-75121 Uppsala, Sweden..
    Kasemo, Bengt
    Chalmers Univ Technol, Dept Phys, Kemivagen 9, S-41296 Gothenburg, Sweden..
    Nanoplasmonic Sensing of Pb-acid and Li-ion Batteries2016In: Sensors And Electronic Instrumentation Advances (SEIA) / [ed] Yurish, SY Malayeri, AD, INT FREQUENCY SENSOR ASSOC-IFSA , 2016, p. 57-59Conference paper (Refereed)
    Abstract [en]

    The increasing sophistication and performance of batteries are connected with more complex chemical and physical battery processes and increase the need of more direct and informative measurements, both in the R&D phase and for monitoring and control during operation of vehicles. Todays potentiometric based measurement sensors are not sufficiently accurate for optimal battery sensing. To avoid the built in wide safety margins new, more informative monitoring signals are therefore desired or needed. In this study the optical technology NanoPlasmonic Sensing (NPS) has been used to in-situ monitor the charge and discharge processes of lead-acid and Li-ion batteries. The optical signals were found to correlate well with charging/discharging of both battery technologies.

  • 308.
    Johansson, Malin B
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Philippe, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Banerjee, Amitava
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cameau, Mathis
    Zhu, Huimin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Johansson, Erik M. J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Cesium bismuth iodide, CsxBiyIz, solar cell compounds from systematic molar ratio variationManuscript (preprint) (Other academic)
  • 309.
    Johansson, Patrik
    et al.
    Chalmers Univ. of Technol., Gothenburg, Sweden.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Polymer Electrolytes (ISPE 2016)2017In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 247, p. 564-568Article in journal (Refereed)
  • 310.
    Johnson, C.S
    et al.
    Argonne National Laboratory US.
    Vaughey, J.T
    Argonne National Laboratory US.
    Thackeray, M.M
    Argonne National Laboratory.
    Sarakonsri, T
    Hackney, S.A
    Fransson, L
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Thomas, John Oswald
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry. strukturkemi.
    Electrochemistry and in situ X-ray diffraction of InSb in lithium batteries2000In: Electrochemistry Communications, Vol. 2, p. 595-Article in journal (Refereed)
  • 311.
    Johnson, William B.
    et al.
    W. L. Gore & Associates.
    Worrell, Wayne L.
    University of Pennsylvania.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Malmgren, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Sundaram, S K
    Alfred University.
    Solid-State Devices: Impedance Response of Electrochromic Materials and Devices2018In: IMPEDANCE SPECTROSCOPY: Theory, Experiment, and Applications / [ed] Evgenij Barsoukov and J. Ross Macdonald, Hoboken,: John Wiley & Sons, 2018, 3rd, p. 247-291Chapter in book (Refereed)
  • 312.
    Jolla, Kullgren
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Lu, ZS.
    Yang, ZX
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Sulfidation and Sulfur Recovery from SO2 over Ceria2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 31, p. 17499-17504Article in journal (Refereed)
    Abstract [en]

    Sulfidation, sulfation and sulfur recovery of ceria(111) and ceria(110) surfaces are studied usingDensity Functional Theory(DFT) calculations. Under reducing atmosphere SO2 adsorption leadsto stable surface sulfate species on the (110) surface and sulfides on the (111) surface. A mechanismfor sulfur recovery from SO2 is also presented. In this mechanism SO2 reacts with a surface sulfideto form a thio-sulfite species. This thio-sulfite species is subsequently reduced by an oxygen vacancyto form a monodentate S2O structure. This structure can then be desorbed as S2 (g).

  • 313.
    Kadas, Krisztina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Andersson, Matilda
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Holmström, Erik
    Wende, Heiko
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Urbonaite, Sigita
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Butorin, Sergei M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Nikitenko, Sergey
    Kvashnina, Kristina O.
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Structural properties of amorphous metal carbides: Theory and experiment2012In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, no 12, p. 4720-4728Article in journal (Refereed)
    Abstract [en]

    By means of theoretical modeling and experimental synthesis and characterization, we investigate the structural properties of amorphous Zr-Si-C. Two chemical compositions are selected: Zr0.31Si0.29C0.40 and Zr0.60Si0.33C0.07. Amorphous structures are generated in the theoretical part of our work by the stochastic quenching (SQ) method, and detailed comparison is made regarding the structure and density of the experimentally synthesized films. These films are analyzed experimentally using X-ray absorption spectroscopy, transmission electron microscopy and X-ray diffraction. Our results demonstrate a remarkable agreement between theory and experiment concerning bond distances and atomic coordination of this complex amorphous metal carbide. The demonstrated power of the SQ method opens up avenues for theoretical predictions of amorphous materials in general.

  • 314. Kaleva, G. M.
    et al.
    Politova, E. D.
    Ivanov, Sergey A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mosunov, A. V.
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Puri, Anil Kumar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Preparation, electrical conductivity, and magnetic susceptibility of (Ba1-x Bi (x) )(Mn0.5+x/2Nb0.5-x/2)O-32013In: Inorganic Materials (Neorganicheskie materialy), ISSN 0020-1685, E-ISSN 1608-3172, Vol. 49, no 5, p. 513-516Article in journal (Refereed)
    Abstract [en]

    (Ba1 - x Bi (x) )(Mn0.5 + x/2Nb0.5 - x/2)O-3 perovskite solid solutions have been prepared by solid-state reactions and their physicochemical properties have been investigated. We have studied the influence of bismuth substitution for barium cations on the phase composition of the samples. Their magnetic susceptibility and electrical conductivity have been measured as functions of temperature. The composition dependence of the antiferromagnetic ordering temperature is presented.

  • 315. Kan, Erjun
    et al.
    Li, Ming
    Hu, Shuanglin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Xiao, Chuanyun
    Xiang, Hongjun
    Deng, Kaiming
    Two-Dimensional Hexagonal Transition-Metal Oxide for Spintronics2013In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 7, p. 1120-1125Article in journal (Refereed)
    Abstract [en]

    Two-dimensional materials have been the hot subject of studies due to their great potential in applications. However, their applications in spintronics have been blocked by the difficulty in producing ordered spin structures in 2D structures. Here we demonstrated that the ultrathin films of recently experimentally realized wurtzite MnO can automatically transform into a stable graphitic structure with ordered spin arrangement via density functional calculation, and the stability of graphitic structure can be enhanced by external strain. Moreover, the antiferromagnetic ordering of graphitic MnO single layer can be switched into half-metallic ferromagnetism by small hole-doping, and the estimated Curie temperature is higher than 300 K. Thus, our results highlight a promising way toward 2D magnetic materials.

  • 316.
    Kasemaegi, Heiki
    et al.
    Univ Tartu, Inst Technol, Tartu, Estonia..
    Ollikainen, Madis
    Univ Tartu, Inst Technol, Tartu, Estonia..
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Aabloo, Alvo
    Univ Tartu, Inst Technol, Tartu, Estonia..
    Molecular Dynamics Modelling of Block-Copolymer Electrolytes with High t(+) Values2015In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 175, p. 47-54Article in journal (Refereed)
    Abstract [en]

    Molecular Dynamics simulations of the BAB type triblock copolymer lithium poly[(4-styrenesulfonyl) (trifluoromethylenesulfonyl) imide)]-block-poly(ethylene oxide)-block-lithium poly[(4-stryrenesylfonyl) (trifluoromethanesulfonyl) imide] (P(STFSILi)-b-PEO-b-P(STFSILi)) were carried out for different simulation temperatures and B-block lengths. By covalently binding the anion to the polymer backbone, it is immobilised and the cation transference number thereby raised significantly. It was found that the Li-ion diffusion decreases exponentially with growth of the B-block length. The poly(ethylene oxide) matrix dissolves Li-ions already during the equilibration stage of the simulation, and no Li-ion diffusion pathways were identified along the STFSI branches, which significantly influence the transport properties of the material.

  • 317.
    Kebede, Getachew
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Water in and on ionic materials: Structure, energetics, and vibrations2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Many chemical and physical phenomena in nature, in industrial processes, and in our daily lives take place at water/solid interfaces. The aim of this thesis is to further our knowledge of such processes at a molecular level. Here theoretical calculations can provide new insights about molecular bonding, structure and dynamics and how these respond to the perturbations from the surroundings. Coalculations can also yield for example vibrational spectra to be directly compared with experimental ones and help in the interpretation. This thesis describes the results of quantum-mechanical and quantum-dynamical studies of water properties on ionic surfaces [NaCl(001), MgO(001) and CaO(001)] and in ionic hydrates [e.g Na2CO3∙10H2O, MgSO4∙11H2O, Al(NO3)3∙9H2O] with especial emphases on surface and interface systems. In particular, calculations of binding energies, OH stretching frequencies, in situ electric field, dipole moments and intra/intermolecular OH distances were performed and analyzed to probe the strength of the water–environment interplay and to disentangle the components of the perturbation. Furthermore, validation of a range of dispersion-inclusive DFT methods for binding energies of interface water and structure and vibrational properties of water in condensed systems also constitutes part of the thesis.

    Two correlations among the investigated properties were established and extensively explored: (i) OH stretching frequency vs. H-bond distance to characterize the H-bond strength and patterns on the surfaces and (ii) OH stretching frequency vs. local electric field to understand the effect of the water/hydroxide environment on the calculated gas-to-bound OH frequency shift behaviour. It was found that both the intact and dissociated water molecules on MgO(001) and CaO(001) follow essentially the same frequency-distance correlations. However, if the frequency is instead correlated against the in situ electric field from the environment, water and hydroxide ion follow different “frequency vs. field” curves. Both water and hydroxide curves, however, can be described by the same model, namely by an electrostatic dipole model presented in the thesis. The gas-to-surface frequency shifts can be traced back to the competition between the signs and magnitudes of the permanent and induced dipole derivatives along the stretching coordinate. Furthermore, the “frequency vs. field” model offers useful insights into the frequency shifts of various surface H-bond motifs on the H2O/MgO interface induced by the adsorption of multilayer cold water.

    List of papers
    1. Comparing van der Waals DFT methods for water on NaCl(001) and MgO(001)
    Open this publication in new window or tab >>Comparing van der Waals DFT methods for water on NaCl(001) and MgO(001)
    Show others...
    2017 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, article id 064703Article in journal (Other (popular science, discussion, etc.)) Published
    National Category
    Theoretical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-315592 (URN)10.1063/1.4971790 (DOI)000394577400037 ()28201901 (PubMedID)
    Funder
    Swedish Research CouncilSwedish National Infrastructure for Computing (SNIC)
    Available from: 2017-02-15 Created: 2017-02-15 Last updated: 2019-02-19Bibliographically approved
    2. Fifty Shades of Water: Benchmarking DFT Functionals against Experimental Data for Ionic Crystalline Hydrates
    Open this publication in new window or tab >>Fifty Shades of Water: Benchmarking DFT Functionals against Experimental Data for Ionic Crystalline Hydrates
    Show others...
    2019 (English)In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 15, no 1, p. 584-594Article in journal (Refereed) Published
    Abstract [en]

    We propose that crystalline ionic hydrates constitute a valuable resource for benchmarking theoretical methods for aqueous ionic systems. Many such structures are known from the experimental literature, and they contain a large variety of water–water and ion–water structural motifs. Here we have collected a data set (CRYSTALWATER50) of 50 structurally unique "in-crystal" water molecules, involved in close to 100 nonequivalent O–H···O hydrogen bonds. A dozen well-known DFT functionals were benchmarked with respect to their ability to describe these experimental structures and their OH vibrational frequencies. We find that the PBE, RPBE-D3, and optPBE-vdW methods give the best H-bond distances and that anharmonic OH frequencies generated from B3LYP//optPBE-vdW energy scans outperform the other methods, i.e., here we performed B3LYP energy scans along the OH stretching coordinate while the rest of the structure was kept fixed at the optPBE-vdW-optimized positions.

    National Category
    Theoretical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-347222 (URN)10.1021/acs.jctc.8b00423 (DOI)000455558200051 ()30380849 (PubMedID)
    Funder
    Swedish Research CouncileSSENCE - An eScience Collaboration
    Note

    Title in thesis list of papers: Fifty shades of water: Benchmarking DFT functionals against diffraction and spectroscopic data for crystalline hydrates

    Available from: 2018-03-27 Created: 2018-03-27 Last updated: 2019-02-19Bibliographically approved
    3. Hydrogen-Bond Relations for Surface OH Species
    Open this publication in new window or tab >>Hydrogen-Bond Relations for Surface OH Species
    Show others...
    2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 9, p. 4849-4858Article, book review (Refereed) Published
    Abstract [en]

    This paper concerns thin water films and their hydrogen-bond patterns on ionic surfaces. As far as we are aware, this is the first time H-bond correlations for surface water and hydroxide species are presented in the literature while hydrogen-bond relations in the solid state have been scrutinized for at least five decades. Our data set, which was derived using density functional theory, consists of 116 unique surface OH groups–intact water molecules as well as hydroxides–on MgO(001), CaO(001) and NaCl(001), covering the whole range from strong to weak to no H-bonds. The intact surface water molecules are found to always be redshifted with respect to the gas-phase water OH vibrational frequency, whereas the surface hydroxide groups are either redshifted (OsH) or blueshifted (OHf) compared to the gas-phase OH frequency. The surface H-bond relations are compared with the traditional relations for bulk crystals. We find that the “ν(OH) vs R(H···O)” correlation curve for surface water does not coincide with the solid state curve: it is redshifted by about 200 cm–1 or more. The intact water molecules and hydroxide groups on the ionic surfaces essentially follow the same H-bond correlation curve.

    Place, publisher, year, edition, pages
    Uppsala: , 2018
    National Category
    Physical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-347220 (URN)10.1021/acs.jpcc.7b10981 (DOI)000427331300013 ()
    Funder
    Swedish Research Council
    Available from: 2018-03-27 Created: 2018-03-27 Last updated: 2019-02-19Bibliographically approved
    4. Red-shifting and blue-shifting OH groups on metal oxide surfaces: towards a unified picture
    Open this publication in new window or tab >>Red-shifting and blue-shifting OH groups on metal oxide surfaces: towards a unified picture
    2018 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 18, p. 12678-12687Article in journal (Refereed) Published
    Abstract [en]

    We analyse the OH vibrational signatures of water molecules and hydroxide ions on thin water films on MgO(001) and CaO(001), using DFT-generated anharmonic potential energy surfaces. We find that the OH stretching frequencies of intact water molecules on the surface are always downshifted with respect to the gas-phase species while the OH– groups are either upshifted or downshifted. Despite these differences, the main characteristics of the frequency shifts for all three types of surface OH groups (OHw, OsH and OHf) can be accounted for by one unified expression involving the in situ electric field from the surrounding environment, and the molecular properties of the vibrating species (H2O or OH–). The origin behind the different red- and blueshift behaviour can be traced back to the fact that the molecular dipole moment of a gas-phase water molecule increases when an OH bond is stretched, but the opposite is true for the hydroxide ion. We propose that familiarity with the relations presented here will help surface scientists in the interpretation of vibrational OH spectra for thin water films on ionic crystal surfaces.

    National Category
    Physical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-347218 (URN)10.1039/C8CP00741A (DOI)000431825300035 ()29697122 (PubMedID)
    Funder
    eSSENCE - An eScience CollaborationSwedish Research Council
    Available from: 2018-03-27 Created: 2018-03-27 Last updated: 2019-01-08Bibliographically approved
    5. OH vibration at the water / MgO(001) interface
    Open this publication in new window or tab >>OH vibration at the water / MgO(001) interface
    (English)Manuscript (preprint) (Other academic)
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-348133 (URN)
    Available from: 2018-04-10 Created: 2018-04-10 Last updated: 2018-04-11
  • 318.
    Kebede, Getachew G.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Spångberg, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Mitev, Pavlin D.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Comparing van der Waals DFT methods for water on NaCl(001) and MgO(001)2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, article id 064703Article in journal (Other (popular science, discussion, etc.))
  • 319.
    Kebede, Getachew
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Mitev, Pavlin D.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Briels, Wim
    Computational Biophysics, University of Twente, Enschede, The Netherlands; Forschungszentrum Jülich, Jülich, Germany..
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Red-shifting and blue-shifting OH groups on metal oxide surfaces: towards a unified picture2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 18, p. 12678-12687Article in journal (Refereed)
    Abstract [en]

    We analyse the OH vibrational signatures of water molecules and hydroxide ions on thin water films on MgO(001) and CaO(001), using DFT-generated anharmonic potential energy surfaces. We find that the OH stretching frequencies of intact water molecules on the surface are always downshifted with respect to the gas-phase species while the OH– groups are either upshifted or downshifted. Despite these differences, the main characteristics of the frequency shifts for all three types of surface OH groups (OHw, OsH and OHf) can be accounted for by one unified expression involving the in situ electric field from the surrounding environment, and the molecular properties of the vibrating species (H2O or OH–). The origin behind the different red- and blueshift behaviour can be traced back to the fact that the molecular dipole moment of a gas-phase water molecule increases when an OH bond is stretched, but the opposite is true for the hydroxide ion. We propose that familiarity with the relations presented here will help surface scientists in the interpretation of vibrational OH spectra for thin water films on ionic crystal surfaces.

  • 320.
    Kebede, Getachew
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Mitev, Pavlin D.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Fifty Shades of Water: Benchmarking DFT Functionals against Experimental Data for Ionic Crystalline Hydrates2019In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 15, no 1, p. 584-594Article in journal (Refereed)
    Abstract [en]

    We propose that crystalline ionic hydrates constitute a valuable resource for benchmarking theoretical methods for aqueous ionic systems. Many such structures are known from the experimental literature, and they contain a large variety of water–water and ion–water structural motifs. Here we have collected a data set (CRYSTALWATER50) of 50 structurally unique "in-crystal" water molecules, involved in close to 100 nonequivalent O–H···O hydrogen bonds. A dozen well-known DFT functionals were benchmarked with respect to their ability to describe these experimental structures and their OH vibrational frequencies. We find that the PBE, RPBE-D3, and optPBE-vdW methods give the best H-bond distances and that anharmonic OH frequencies generated from B3LYP//optPBE-vdW energy scans outperform the other methods, i.e., here we performed B3LYP energy scans along the OH stretching coordinate while the rest of the structure was kept fixed at the optPBE-vdW-optimized positions.

  • 321.
    Kebede, Getachew
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Mitev, Pavlin D.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Kullgren, Jolla
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hydrogen-Bond Relations for Surface OH Species2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 9, p. 4849-4858Article, book review (Refereed)
    Abstract [en]

    This paper concerns thin water films and their hydrogen-bond patterns on ionic surfaces. As far as we are aware, this is the first time H-bond correlations for surface water and hydroxide species are presented in the literature while hydrogen-bond relations in the solid state have been scrutinized for at least five decades. Our data set, which was derived using density functional theory, consists of 116 unique surface OH groups–intact water molecules as well as hydroxides–on MgO(001), CaO(001) and NaCl(001), covering the whole range from strong to weak to no H-bonds. The intact surface water molecules are found to always be redshifted with respect to the gas-phase water OH vibrational frequency, whereas the surface hydroxide groups are either redshifted (OsH) or blueshifted (OHf) compared to the gas-phase OH frequency. The surface H-bond relations are compared with the traditional relations for bulk crystals. We find that the “ν(OH) vs R(H···O)” correlation curve for surface water does not coincide with the solid state curve: it is redshifted by about 200 cm–1 or more. The intact water molecules and hydroxide groups on the ionic surfaces essentially follow the same H-bond correlation curve.

  • 322.
    Kebede, Getachew
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Mitev, Pavlin D.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    OH2017Conference paper (Other academic)
  • 323.
    Kettner, Miroslav
    et al.
    Charles Univ Prague, Fac Math & Phys, Dept Surface & Plasma Sci, V Holesovickach 2, Prague 18000 8, Czech Republic;Friedrich Alexander Univ Erlangen Nurnberg, Chair Interface Res & Catalysis, Egerlandstr 3, D-91058 Erlangen, Germany.
    Duchon, Tomas
    Charles Univ Prague, Fac Math & Phys, Dept Surface & Plasma Sci, V Holesovickach 2, Prague 18000 8, Czech Republic;Forschungszentrum Julich, Peter Grunberg Inst 6, D-52425 Julich, Germany.
    Wolf, Matthew J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Univ Bath, Dept Phys, Bath BA2 7AY, Avon, England.
    Kullgren, Jolla
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Senanayake, Sanjaya D.
    Brookhaven Natl Lab, Dept Chem, Upton, NY 11973 USA.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Veltruska, Katerina
    Charles Univ Prague, Fac Math & Phys, Dept Surface & Plasma Sci, V Holesovickach 2, Prague 18000 8, Czech Republic.
    Nehasil, Vaclav
    Charles Univ Prague, Fac Math & Phys, Dept Surface & Plasma Sci, V Holesovickach 2, Prague 18000 8, Czech Republic.
    Anion-mediated electronic effects in reducible oxides: Tuning the valence band of ceria via fluorine doping2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, no 4, article id 044701Article in journal (Refereed)
    Abstract [en]

    Combining experimental spectroscopy and hybrid density functional theory calculations, we show that the incorporation of fluoride ions into a prototypical reducible oxide surface, namely, ceria(111), can induce a variety of nontrivial changes to the local electronic structure, beyond the expected increase in the number of Ce3+ ions. Our resonant photoemission spectroscopy results reveal new states above, within, and below the valence band, which are unique to the presence of fluoride ions at the surface. With the help of hybrid density functional calculations, we show that the different states arise from fluoride ions in different atomic layers in the near surface region. In particular, we identify a structure in which a fluoride ion substitutes for an oxygen ion at the surface, with a second fluoride ion on top of a surface Ce4+ ion giving rise to F 2p states which overlap the top of the O 2p band. The nature of this adsorbate F--Ce4+ resonant enhancement feature suggests that this bond is at least partially covalent. Our results demonstrate the versatility of anion doping as a potential means of tuning the valence band electronic structure of ceria.

  • 324.
    Kettner, Miroslav
    et al.
    Charles Univ Prague, Dept Surface & Plasma Sci, Prague, Czech Republic..
    Duchon, Tomas
    Charles Univ Prague, Dept Surface & Plasma Sci, Prague, Czech Republic..
    Wolf, Matthew
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Kullgren, Jolla
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Kus, Peter
    Charles Univ Prague, Dept Surface & Plasma Sci, Prague, Czech Republic..
    Sevcikova, Klara
    Charles Univ Prague, Dept Surface & Plasma Sci, Prague, Czech Republic.;Elettra Sincrotrone Trieste, Trieste, Italy..
    Rafaj, Zdenek
    Charles Univ Prague, Dept Surface & Plasma Sci, Prague, Czech Republic..
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Nehasil, Vaclav
    Charles Univ Prague, Dept Surface & Plasma Sci, Prague, Czech Republic..
    Modification of valence band of ceria via anion doping with fluorine2017In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 254Article in journal (Other academic)
  • 325.
    Kim, Byung-Hyun
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Wolf, Matthew J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Kullgren, Jolla
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Multiscale modelling of CeO2 nano-interfaces2017Conference paper (Other academic)
  • 326.
    Kim, Byung-Hyun
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Korea Inst Energy Res, Platform Technol Lab, Daejeon, South Korea.
    Kullgren, Jolla
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Wolf, Matthew J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Multiscale Modeling of Agglomerated Ceria Nanoparticles: Interface Stability and Oxygen Vacancy Formation2019In: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 7, article id 203Article in journal (Refereed)
    Abstract [en]

    The interface formation and its effect on redox processes in agglomerated ceria nanoparticles (NPs) have been investigated using a multiscale simulation approach with standard density functional theory (DFT), the self-consistent-charge density functional tight binding (SCC-DFTB) method, and a DFT-parameterized reactive force-field (ReaxFF). In particular, we have modeled Ce40O80 NP pairs, using SCC-DFTB and DFT, and longer chains and networks formed by Ce40O80 or Ce132O264 NPs, using ReaxFF molecular dynamics simulations. We find that the most stable {111}/{111} interface structure is coherent whereas the stable {100}/{100} structures can be either coherent or incoherent. The formation of {111}/{111} interfaces is found to have only a very small effect on the oxygen vacancy formation energy, E-vac. The opposite holds true for {100}/{100} interfaces, which exhibit significantly lower E-vac values than the bare surfaces, despite the fact that the interface formation eliminates reactive {100} facets. Our results pave the way for an increased understanding of ceria NP agglomeration.

  • 327.
    Kim, Byung-Hyun
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Korea Inst Energy Res, R&D Platform Ctr, Daejeon 34129, South Korea;Korea Inst Sci & Technol, Computat Sci Res Ctr, Seoul 02792, South Korea.
    Park, Mina
    Korea Inst Sci & Technol, Computat Sci Res Ctr, Seoul 02792, South Korea.
    Kim, Gyubong
    Korea Inst Sci & Technol, Computat Sci Res Ctr, Seoul 02792, South Korea.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Choi, Heon-Jin
    Yonsei Univ, Dept Mat Sci & Engn, 262 Seongsanno, Seoul 120749, South Korea.
    Lee, Kwang-Ryeol
    Korea Inst Sci & Technol, Computat Sci Res Ctr, Seoul 02792, South Korea.
    Indirect-to-Direct Band Gap Transition of Si Nanosheets: Effect of Biaxial Strain2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 27, p. 15297-15303Article in journal (Refereed)
    Abstract [en]

    The effect of biaxial strain on the band structure of two-dimensional silicon nanosheets (Si NSs) with (111), (110), and (001) exposed surfaces was investigated by means of density functional theory calculations. For all the considered Si NSs, an indirect-to-direct band gap transition occurs as the lateral dimensions of Si NSs increase; that is, increasing lateral biaxial strain from compressive to tensile always enhances the direct band gap characteristics. Further analysis revealed the mechanism of the transition which is caused by preferential shifts of the conduction band edge at a specific k-point because of their bond characteristics. Our results explain a photoluminescence result of the (111) Si NSs [U. Kim et al., ACS Nano 2011,.5, 2176-2181] in terms of the plausible tensile strain imposed in the unoxidized inner layer by surface oxidation.

  • 328.
    Kitz, Paul G.
    et al.
    Paul Scherrer Inst, Electrochem Lab, CH-5232 Villigen, Switzerland.
    Lacey, Matthew
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Novak, Petr
    Paul Scherrer Inst, Electrochem Lab, CH-5232 Villigen, Switzerland.
    Berg, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Paul Scherrer Inst, Electrochem Lab, CH-5232 Villigen, Switzerland.
    Operando EQCM-D with Simultaneous in Situ EIS: New Insights into Interphase Formation in Li Ion Batteries2019In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 91, no 3, p. 2296-2303Article in journal (Refereed)
    Abstract [en]

    An operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) with simultaneous in situ electrochemical impedance spectroscopy (EIS) has been developed and applied to study the solid electrolyte interphase (SEI) formation on copper current collectors in Li-ion batteries. The findings are backed by EIS simulations and complementary analytical techniques, such as online electrochemical mass spectrometry (OEMS) and X-ray photoelectron spectroscopy (XPS). The evolution of mass and the mechanical properties of the SEI are directly correlated to the electrode impedance. Electrolyte reduction at the anode carbon active material initiates dissolution, diffusion, and deposition of reaction side products throughout the cell and increases electrolyte viscosity and the ohmic cell resistance as a result. On Cu the reduction of CuOx and HF occurs at >1.5 V and forms an initial LiF-rich interphase while electrolyte solvent reduction at <0.8 V vs Li+/Li adds a second, less rigid layer on top. Both the shear storage modulus and viscosity of the SEI generally increase upon cycling but-along with the SEI Li+ diffusion coefficient-also respond reversibly to electrode potential, likely as a result of Li+/EC interfacial concentration changes. Combined EIS-EQCM-D provides unique prospects for further studies of the highly dynamic structure-function relationships of electrode interphases in Li ion batteries.

  • 329.
    Kjell, Maria Hellqvist
    et al.
    Applied Electrochemistry, KTH.
    Malmgren, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Ciosek, Katarzyna
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Behm, Marten
    Applied Electrochemistry KTH.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Lindbergh, Goran
    Applied Electrochemistry KTH.
    Comparing aging of graphite/LiFePO4 cells at 22 degrees C and 55 degrees C - Electrochemical and photoelectron spectroscopy studies2013In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 243, p. 290-298Article in journal (Refereed)
    Abstract [en]

    Accelerated aging at elevated temperature is commonly used to test lithium-ion battery lifetime, but the effect of an elevated temperature is still not well understood. If aging at elevated temperature would only be faster, but in all other respects equivalent to aging at ambient temperature, cells aged to end-of-life (EOL) at different temperatures would be very similar. The present study compares graphite/LiFePO4-based cells either cycle- or calendar-aged to EOL at 22 degrees C and 55 degrees C. Cells cycled at the two temperatures show differences in electrochemical impedance spectra as well as in X-ray photoelectron spectroscopy (XPS) spectra. These results show that lithium-ion cell aging is a complex set of processes. At elevated temperature, the aging is accelerated in process-specific ways. Furthermore, the XPS results of cycle-aged samples indicate increased deposition of oxygenated LiPF6 decomposition products in both the negative and positive electrode/electrolyte interfaces. The decomposition seems more pronounced at elevated temperature, and largely accelerated by cycling, which could contribute to the observed cell impedance increase.

  • 330.
    Klett, Matilda
    et al.
    Applied Electrochemistry, KTH.
    Eriksson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Groot, Jens
    AB Volvo.
    Svens, Pontus
    Scania CV AB.
    Högström, Katarzyna Ciosek
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Lindstrom, Rakel Wreland
    Applied Electrochemistry KTH.
    Berg, Helena
    Libergreen.
    Gustafsson, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Lindbergh, Goran
    Applied Electrochemistry KTH.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Non-uniform aging of cycled commercial LiFePO4//graphite cylindrical cells revealed by post-mortem analysis2014In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 257, p. 126-137Article in journal (Refereed)
    Abstract [en]

    Aging of power-optimized commercial 2.3 Ah cylindrical LiFePO4//graphite cells to be used in hybrid electric vehicle is investigated and compared for three different aging procedures; (i) using a simulated hybrid electric vehicle cycle within a narrow SOC-range, (ii) using a constant-current cycle over a 100% SOC-range, and (iii) stored during three years at 22 degrees C. Postmortem analysis of the cells is performed after full-cell electrochemical characterization and discharge. EIS and capacity measurements are made on different parts of the disassembled cells. Material characterization includes SEM, EDX, HAXPES/XPS and XRD. The most remarkable result is that both cycled cells displayed highly uneven aging primarily of the graphite electrodes, showing large differences between the central parts of the jellyroll compared to the outer parts. The aging variations are identified as differences in capacity and impedance of the graphite electrode, associated with different SEI characteristics. Loss of cyclable lithium is mirrored by a varying degree of lithiation in the positive electrode and electrode slippage. The spatial variation in negative electrode degradation and utilization observed is most likely connected to gradients in temperature and pressure, that can give rise to current density and potential distributions within the jellyroll during cycling.

  • 331. Knaup, Jan M.
    et al.
    Frauenheim, Thomas
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Ramanathan, Shriram
    Focus on Functional Oxides Preface2014In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 8, no 6, p. 451-452Article in journal (Other academic)
  • 332. Kocak, Tayfun
    et al.
    Jeschull, Fabian
    Valvo, Mario
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Liivat, Anti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Turan, Servet
    Alternative binders for lithium iron silicate (Li2FeSiO4) cathodes2016Conference paper (Refereed)
  • 333.
    Kotronia, Antonia
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Investigation of novel, redox-active organic materials for lithium-ion and lithium-oxygen batteries2016Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis encompasses the successful synthesis, characterization (NMR, IR, TGA) and electrochemical testing of novel, potentially redox-active organic materials. These were destined as electrodes for Li-organic cells and/or as catalysts for Li–O2 cells.

    The electrochemical performance of the dilithiated and tetralithiated salts of 2,5-dialkylamide hydroquinones (with ethyl, isopropyl or benzyl as the alkyl group) and of a partially lithiated polymer with a backbone of alternating 2,5-dicarbonylhydroquinone and 1,4-benzyl diaminophenylene units was evaluated. The small organicsalts exhibited redox-activity around 1.0 V vs Li/Li+ (the terephthaloyl redox system) and 2.8 V vs Li/Li+ (the quinone redox system). These values drifted depending on lithiation degree and alkyl substituent. Redox irreversibility featured these materials which decomposed and dissolved. The polymer exhibited multiple redox-activity in the region of 2.5-3.6 V vs Li/Li+, which was however also irreversible.

    Further on, the small organic salts were tested as to their impact on the dischargeproduct (Li2O2) yield in Li-O2 cells. Discharge profiles of cells with and without the inclusion of the salts were contrasted to each other; the former having a jagged appearance, indicative of side-reactions. The O2 electrode was studied by XRD todetect the formed products and the amount of Li2O2 present was quantified throug htitration and UV-vis spectroscopy. Organic salt inclusion was found to negatively affect the Li2O2 formation and also attack the Li-electrode.

  • 334.
    Kotronia, Antonia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Asfaw, Habtom Desta
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    CaS- and MgS-assisted graphitization of porous carbons for energy storage applications2017Conference paper (Other academic)
  • 335.
    Krishna Ammothum Kandy, Akshay
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Kullgren, Jolla
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Can water affect the shape of CeO2 nanopartiles?2017Conference paper (Other academic)
  • 336.
    Kristiansen, Paw
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Dahbi, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Gustafsson, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Newby, D.
    Smith, K.E.
    Duda, L.-C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    X-ray absorption spectroscopy and resonant inelastic scattering study of the first lithiation cycle of the Li-ion battery cathodeLi(2-x)MnSiO42014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 8, p. 3846-3852Article in journal (Refereed)
  • 337.
    Kristiansen, P.T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Dahbi, M
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Gustafsson, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Newby, D.
    Smith, Kevin E.
    Boston University.
    Duda, Laurent-Claudius
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    X-ray absorption spectroscopy and resonant inelastic scattering study of the first lithiation cycle of the Li-ion battery cathode Li-2-xMnSiO42014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, ISSN 1463-9076, Vol. 16, no 8, p. 3846-3852Article in journal (Refereed)
  • 338.
    Krsmanovic, Dejana
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Fraunhofer ICT.
    Development of a property forecast tool for flexible compositions of Li-ion batteries, including raw material availability and price forming2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In today's world full of rigorous government measures regarding the fuel economyand a large EV and smart device market emerging from it, batteries represent apioneering technology used as storage for renewable energies such as wind and solar.More precisely, the Li-ion family of batteries has experienced an exponential growthin sales. Having high energy density, these batteries are also well suited for mobiledevices such as wearables, smartphones, tablets, cameras, notebooks and electricvehicles.[1] However, the technology has not completely matured yet and there is stilla lot of space for improvements and new discoveries. This thesis considers thecomposition of lithium-ion batteries together with the global distribution andeconomical aspects of materials used. The components of Li-ion cells of different cellformats (e.g. 18650, 21700) were investigated together with their physical andchemical properties. Through this process, an interactive tool for calculating costs,cell parameters and quantity of active materials was developed. The main purpose ofthe tool was to enable a user to input data such as thicknesses of electrodes, togetherwith the capacity of the cell and output how much material is needed for suchelectrodes and what energy density is achieved. These parameters, such as the massof active material, were linked to a cost calculator, determining the costs of a singlecell. The calculator is useful for further research purposes on Li-ion batteries, as theinput variables can be modified in according to the user's preferences, whereas costdetermination is useful for sales planning and battery manufacturing.

  • 339.
    Kullgren, J.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Wolf, Matthew J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Castleton, C. W. M.
    Mitev, Pavlin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Briels, W. J.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Oxygen Vacancies versus Fluorine at CeO2(111): A Case of Mistaken Identity?2014In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 112, no 15, p. 156102-Article in journal (Refereed)
    Abstract [en]

    We propose a resolution to the puzzle presented by the surface defects observed with STM at the (111) surface facet of CeO2 single crystals. In the seminal paper of Esch et al. [Science 309, 752 (2005)] they were identified with oxygen vacancies, but the observed behavior of these defects is inconsistent with the results of density functional theory (DFT) studies of oxygen vacancies in the literature. We resolve these inconsistencies via DFT calculations of the properties of both oxygen vacancies and fluorine impurities at CeO2(111), the latter having recently been shown to exist in high concentrations in single crystals from a widely used commercial source of such samples. We find that the simulated filled-state STM images of surface-layer oxygen vacancies and fluorine impurities are essentially identical, which would render problematic their experimental distinction by such images alone. However, we find that our theoretical results for the most stable location, mobility, and tendency to cluster, of fluorine impurities are consistent with experimental observations, in contrast to those for oxygen vacancies. Based on these results, we propose that the surface defects observed in STM experiments on CeO2 single crystals reported heretofore were not oxygen vacancies, but fluorine impurities. Since the similarity of the simulated STM images of the two defects is due primarily to the relative energies of the 2p states of oxygen and fluorine ions, this confusion might also occur for other oxides which have been either doped or contaminated with fluorine.

  • 340.
    Kullgren, Jolla
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Oxygen Vacancy Chemistry in Ceria2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Cerium(IV) oxide (CeO2), ceria, is an active metal oxide used in solid oxide fuel cells and for the purification of exhaust gases in vehicle emissions control. Behind these technically important applications of ceria lies one overriding feature, namely ceria's exceptional reduction-oxidation properties. These are enabled by the duality of the cerium ion which easily toggles between Ce4+ and Ce3+. Here the cerium 4f electrons and oxygen vacancies (missing oxygen ions in the structure) are key players. In this thesis, the nature of ceria's f electrons and oxygen vacancies are in focus, and examined with theoretical calculations.

    It is shown that for single oxygen vacancies at ceria surfaces, the intimate coupling between geometrical structure and electron localisation gives a multitude of almost degenerate local energy mimima. With many vacancies, the situation becomes even more complex, and not even state-of-the-art quantum-mechanical calculations manage to predict the experimentally observed phenomenon of vacancy clustering. Instead, an alternative set of computer experiments managed to produce stable vacancy chains and trimers consistent with experimental findings from the literature and revealed a new general principle for surface vacancy clustering.

    The rich surface chemistry of ceria involves not only oxygen vacancies but also other active oxygen species such as superoxide ions (O2). Experiments have shown that nanocrystalline ceria demonstrates an unusually large oxygen storage capacity (OSC) and an appreciable low-temperature redox activity, which have been ascribed to superoxide species. A mechanism explaining these phenomena is presented.

    The ceria surface is also known to interact with SOx molecules, which is relevant both in the context of sulfur poisoning of ceria-based catalysts and sulfur recovery from them. In this thesis, the sulfur species and key mechanisms involved are identified.

    List of papers
    1. Tuning LDA+U for electron localization and structure at oxygen vacancies in ceria
    Open this publication in new window or tab >>Tuning LDA+U for electron localization and structure at oxygen vacancies in ceria
    2007 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 127, no 24, p. 244704-244704-11Article in journal (Refereed) Published
    Abstract [en]

    We examine the real space structure and the electronic structure (particularly Ce4f electron localization) of oxygen vacancies in CeO2 (ceria) as a function of U in density functional theory studies with the rotationally invariant forms of the LDA+U and GGA+U functionals. The four nearest neighbor Ce ions always relax outwards, with those not carrying localized Ce4f charge moving furthest. Several quantification schemes show that the charge starts to become localized at U~3 eV and that the degree of localization reaches a maximum at ~6 eV for LDA+U or at ~5.5 eV for GGA+U. For higher U it decreases rapidly as charge is transferred onto second neighbor O ions and beyond. The localization is never into atomic corelike states; at maximum localization about 80-90% of the Ce4f charge is located on the two nearest neighboring Ce ions. However, if we look at the total atomic charge we find that the two ions only make a net gain of (0.2-0.4)e each, so localization is actually very incomplete, with localization of Ce4f electrons coming at the expense of moving other electrons off the Ce ions. We have also revisited some properties of defect-free ceria and find that with LDA+U the crystal structure is actually best described with U=3-4 eV, while the experimental band structure is obtained with U=7-8 eV. (For GGA+U the lattice parameters worsen for U>0 eV, but the band structure is similar to LDA+U.) The best overall choice is U~6 eV with LDA+U and ~5.5 eV for GGA+U, since the localization is most important, but a consistent choice for both CeO2 and Ce2O3, with and without vacancies, is hard to find.

    Keywords
    Other nonmetals, Point defects and defect clusters, Density functional theory, local density approximation, gradient and other corrections
    National Category
    Chemical Sciences
    Identifiers
    urn:nbn:se:uu:diva-12806 (URN)10.1063/1.2800015 (DOI)000251987800030 ()
    Available from: 2008-01-15 Created: 2008-01-15 Last updated: 2019-02-19Bibliographically approved
    2. B3LYP calculations of cerium oxides
    Open this publication in new window or tab >>B3LYP calculations of cerium oxides
    Show others...
    2010 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 132, no 5, p. 054110-Article in journal (Refereed) Published
    Abstract [en]

    In this paper we evaluate the performance of density functional theory with the B3LYP functional for calculations on ceria (CeO2) and cerium sesquioxide (Ce2O3). We demonstrate that B3LYP is able to describe CeO2 and Ce2O3 reasonably well. When compared to other functionals, B3LYP performs slightly better than the hybrid functional PBE0 for the electronic properties but slightly worse for the structural properties, although neither performs as well as LDA+U(U = 6 eV) or PBE+U(U = 5 eV). We also make an extensive comparison of atomic basis sets suitable for periodic calculations of these cerium oxides. Here we conclude that there is currently only one type of cerium basis set available in the literature that is able to give a reasonable description of the electronic structure of both CeO2 and Ce2O3. These basis sets are based on a 28 electron effective core potential (ECP) and 30 electrons are attributed to the valence space of cerium. Basis sets based on 46 electron ECPs fail for these materials

    Place, publisher, year, edition, pages
    American Institute of Physics, 2010
    National Category
    Inorganic Chemistry
    Research subject
    Chemistry with specialization in Inorganic Chemistry
    Identifiers
    urn:nbn:se:uu:diva-121560 (URN)10.1063/1.3253795 (DOI)000274319900011 ()
    Available from: 2010-03-25 Created: 2010-03-25 Last updated: 2019-02-19Bibliographically approved
    3. Many Competing Ceria (110) Oxygen Vacancy Structures: From Small to Large Supercells
    Open this publication in new window or tab >>Many Competing Ceria (110) Oxygen Vacancy Structures: From Small to Large Supercells
    2012 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 4, p. 044705-Article in journal (Refereed) Published
    Abstract [en]

    We present periodic "DFT+U" studies of single oxygen vacancies on the CeO2(110) surface using a number of different supercells, finding a range of different local minimum structures for the vacancy and its two accompanying Ce(III) ions. We find three different geometrical structures in combination with a variety of different Ce(III) localization patterns, several of which have not been studied before. The desired trapping of electrons was achieved in a two-stage optimization procedure. We find that the surface oxygen nearest to the vacancy either moves within the plane towards the vacancy, or rises out of the surface into either a symmetric or an unsymmetric bridge structure. Results are shown in seven slab geometry supercells, p(2 x 1), p(2 x 2), p(2 x 3), p(3 x 2), p(2 x 4), p(4 x 2), and p(3 x 3), and indicate that the choice of supercell can affect the results qualitatively and quantitatively. An unsymmetric bridge structure with one nearest and one next-nearest neighbour Ce(III) ion (a combination of localizations not previously found) is the ground state in all (but one) of the supercells studied here, and the relative stability of other structures depends strongly on supercell size. Within any one supercell the formation energies of the different vacancy structures differ by up to 0.5 eV, but the same structure can vary by up to similar to 1 eV between supercells. Furthermore, finite size scaling suggests that the remaining errors (compared to still larger supercells) can also be similar to 1 eV for some vacancy structures.

    Keywords
    DFT, Ceria, (110), Vacancies, Supercell approximation
    National Category
    Materials Chemistry
    Identifiers
    urn:nbn:se:uu:diva-167996 (URN)10.1063/1.4723867 (DOI)000307611500053 ()
    Available from: 2012-02-03 Created: 2012-02-03 Last updated: 2019-02-19Bibliographically approved
    4. Oxygen Vacancy Clustering at the Ceria(111) surface
    Open this publication in new window or tab >>Oxygen Vacancy Clustering at the Ceria(111) surface
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Oxygen vacancy clustering at the ceria(111) surface have been studied with both force-field and density function theory methods. Two of the methods predict that stable clusters of surface oxygen vacancies should form on these surface, as seen in numerous experimental studies. We propose that vacancy clustering of both surface and sub-surface vacancies follow the simple principle of sharing their Ce(III) neighbors. For surface oxygen vacancies this leads to compact clusters separated by one surface lattice constant. On the other hand for sub-surface this leads to sparse clusters separated by two surface lattice constants.

    National Category
    Materials Chemistry
    Identifiers
    urn:nbn:se:uu:diva-168002 (URN)
    Available from: 2012-02-03 Created: 2012-02-03 Last updated: 2014-07-25
    5. Supercharged Low-Temperature Oxygen Storage Capacity of Ceria at the Nanoscale
    Open this publication in new window or tab >>Supercharged Low-Temperature Oxygen Storage Capacity of Ceria at the Nanoscale
    2013 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 4, p. 604-608Article in journal (Refereed) Published
    Abstract [en]

    We provide an explanation for the experimental finding of a dramatically enhancedlow-temperature oxygen storage capacity for small ceria nanoparticles. At low temperature, small octahedral ceria nanoparticles will be understoichiometric at both oxidizing and reducing conditions without showing explicit oxygen vacancies. Instead, rather than becoming stoichiometric at oxidizing conditions, such particles are stabilized through oxygen adsorption forming superoxo (O-2(-)) ions and become in this way supercharged with oxygen. Thesupercharging effect is size-dependent and largest for small nanoparticles where it gives a direct increase in the oxygen storage capacity and simultaneously provides a source of active oxygenspecies at low temperatures.

    National Category
    Materials Chemistry
    Identifiers
    urn:nbn:se:uu:diva-168004 (URN)10.1021/jz3020524 (DOI)000315432000010 ()
    Available from: 2012-02-03 Created: 2012-02-03 Last updated: 2019-02-19Bibliographically approved
    6. SOx on ceria from adsorbed SO2
    Open this publication in new window or tab >>SOx on ceria from adsorbed SO2
    Show others...
    2011 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 18, p. 184703-Article in journal (Refereed) Published
    Abstract [en]

    Results from first-principles calculations present a rather clear picture of the interaction of SO2 with unreduced and partially reduced (111) and (110) surfaces of ceria. The Ce3+/Ce4+ redox couple, together with many oxidation states of S, give rise to a multitude of SOx species, with oxidation states from + III to + VI. SO2 adsorbs either as a molecule or attaches via its S-atom to one or two surface oxygens to form sulfite (SO32-) and sulfate (SO42-) species, forming new S-O bonds but never any S-Ce bonds. Molecular adsorption is found on the (111) surface. SO32- structures are found on both the (111) and (110) surfaces of both stoichiometric and partially reduced ceria. SO42-structures are observed on the (110) surface together with the formation of two reduced Ce3+ surface cations. SO2 can also partially heal the ceria oxygen vacancies by weakening a S-O bond, when significant electron transfer from the surface (Ce4f) into the lowest unoccupied molecular orbital of the SO2 adsorbate takes place and oxidizes the surface Ce3+ cations. Furthermore, we propose a mechanism that could lead to monodentate sulfate formation at the (111) surface.

    National Category
    Chemical Sciences Inorganic Chemistry
    Research subject
    Chemistry with specialization in Inorganic Chemistry
    Identifiers
    urn:nbn:se:uu:diva-154547 (URN)10.1063/1.3566998 (DOI)000290589900035 ()
    Available from: 2011-06-07 Created: 2011-06-07 Last updated: 2019-02-19Bibliographically approved
    7. Sulfidation of ceria surfaces from sulfur and sulfur diffusion
    Open this publication in new window or tab >>Sulfidation of ceria surfaces from sulfur and sulfur diffusion
    2012 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 15, p. 8417-8425Article in journal (Refereed) Published
    Abstract [en]

    Even very low levels of sulfur contaminants can degrade the catalytic performance of cerium oxide. Here, the interaction of atomic sulfur with the ceria (111) and (110) surfaces has been studied using first-principles methods. Two sulfoxy species are identified: oxido-sulfate(2-) species (SO2-) on both the CeO2 (111) and (110) surfaces and hyposulfite (SO22-) on the (110) surface. Sulfide (S2-) is formed when a surface or a subsurface oxygen atoms is replaced by sulfur. These sulfide species are most stable at the surface. Furthermore, sulfite (SO32-) structures are found when sulfur is made to replaces one Ce in the ceria (111) and (110) surfaces. The calculated sulfur diffusion barriers are larger than 1.4 eV for both surfaces and thus sulfur is essentially immobile, providing a possible explanation for the sulfidation phenomena of the ceria-based catalysis. Thus we find three different species from interaction of S with Ceria which are all, due to their strong binding, capable of poisoning the surface, reduced or unreduced. Our results suggest that under reducing conditions, sulfur is likely to be found in the (111) surface (replacing oxygen) but on the (110) surface (as SO22-).

    National Category
    Materials Chemistry
    Identifiers
    urn:nbn:se:uu:diva-167999 (URN)10.1021/jp2092913 (DOI)000302924900010 ()
    Available from: 2012-02-03 Created: 2012-02-03 Last updated: 2019-02-19Bibliographically approved
    8. Sulfidation and Sulfur Recovery from SO2 over Ceria
    Open this publication in new window or tab >>Sulfidation and Sulfur Recovery from SO2 over Ceria
    2014 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 31, p. 17499-17504Article in journal (Refereed) Published
    Abstract [en]

    Sulfidation, sulfation and sulfur recovery of ceria(111) and ceria(110) surfaces are studied usingDensity Functional Theory(DFT) calculations. Under reducing atmosphere SO2 adsorption leadsto stable surface sulfate species on the (110) surface and sulfides on the (111) surface. A mechanismfor sulfur recovery from SO2 is also presented. In this mechanism SO2 reacts with a surface sulfideto form a thio-sulfite species. This thio-sulfite species is subsequently reduced by an oxygen vacancyto form a monodentate S2O structure. This structure can then be desorbed as S2 (g).

    National Category
    Materials Chemistry
    Identifiers
    urn:nbn:se:uu:diva-168001 (URN)10.1021/jp4094673 (DOI)000340222300036 ()
    Available from: 2012-02-03 Created: 2012-02-03 Last updated: 2019-02-19Bibliographically approved
  • 341.
    Kullgren, Jolla
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Castleton, Christopher
    School of Science and Technology, Nottingham Trent University.
    Mitev, Pavlin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Briels, Wim
    Computational Biophysics, University of Twente.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Oxygen Vacancy Clustering at the Ceria(111) surfaceManuscript (preprint) (Other academic)
    Abstract [en]

    Oxygen vacancy clustering at the ceria(111) surface have been studied with both force-field and density function theory methods. Two of the methods predict that stable clusters of surface oxygen vacancies should form on these surface, as seen in numerous experimental studies. We propose that vacancy clustering of both surface and sub-surface vacancies follow the simple principle of sharing their Ce(III) neighbors. For surface oxygen vacancies this leads to compact clusters separated by one surface lattice constant. On the other hand for sub-surface this leads to sparse clusters separated by two surface lattice constants.

  • 342.
    Kullgren, Jolla
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Ceria chemistry at the nanoscale: effect of the environment2013In: Solar Hydrogen And Nanotechnology Viii / [ed] Yosuke Kanai and David Prendergast, 2013, p. 88220D-Conference paper (Refereed)
    Abstract [en]

    We use theoretical simulations to study how oxidative and humid environments affect the chemical composition, shape and structure of ceria nanoparticles. Based on our calculations, we predict that small stoichiometric ceria nanoparticles will have a very limited stability range when exposed to these environments. Instead, we find that reduced ceria nanoparticles are stabilized without changing their inherent shape through the adsorption of oxygen molecules in the form of superoxo species and water in the form of hydroxo species. Based on our results, we propose a redox-cycle for meta-stable ceria nanoparticles without the formation of explicit oxygen vacancies, which is important for understanding the low-temperature oxygen chemistry of ceria at the nanoscale.

  • 343.
    Kullgren, Jolla
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Reactive oxygen species in stoichiometric ceria: Bulk and low-index surfaces2014In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 8, no 6, p. 600-604Article in journal (Refereed)
    Abstract [en]

    We have calculated the stabilities of some reactive oxygen species (ROS) in stoichiometric bulk ceria and at the low-index (111) and (110)-surfaces, both in vacuum and in the presence of additional O-2 molecules. We find that the formation of intrinsic ROS, here oxygen superoxides (O-2(-)) and peroxides (O-2(2-)), is always endothermic at vacuum conditions and that the superoxide formation always leads to a higher formation energy than the peroxide formation. In the presence of additional O-2 molecules, intrinsic peroxide formation becomes exothermic at the (110)-surface in conjunction with the formation of extrinsic superoxide ions from adsorbed O-2 molecules. This coexistence of intrinsic and extrinsic ROS species is anticipated to be stable at low temperatures, and can be important for understanding the ROS chemistry for nanoceria used in low-temperature applications. [GRAPHICS] Oxygen-assisted reduction of the ceria(110) surface. 

  • 344.
    Kullgren, Jolla
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Supercharged Low-Temperature Oxygen Storage Capacity of Ceria at the Nanoscale2013In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 4, p. 604-608Article in journal (Refereed)
    Abstract [en]

    We provide an explanation for the experimental finding of a dramatically enhancedlow-temperature oxygen storage capacity for small ceria nanoparticles. At low temperature, small octahedral ceria nanoparticles will be understoichiometric at both oxidizing and reducing conditions without showing explicit oxygen vacancies. Instead, rather than becoming stoichiometric at oxidizing conditions, such particles are stabilized through oxygen adsorption forming superoxo (O-2(-)) ions and become in this way supercharged with oxygen. Thesupercharging effect is size-dependent and largest for small nanoparticles where it gives a direct increase in the oxygen storage capacity and simultaneously provides a source of active oxygenspecies at low temperatures.

  • 345.
    Kullgren, Jolla
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Castleton, Christopher
    School of Science and Technology, Nottingham Trent University.
    Many Competing Ceria (110) Oxygen Vacancy Structures: From Small to Large Supercells2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 4, p. 044705-Article in journal (Refereed)
    Abstract [en]

    We present periodic "DFT+U" studies of single oxygen vacancies on the CeO2(110) surface using a number of different supercells, finding a range of different local minimum structures for the vacancy and its two accompanying Ce(III) ions. We find three different geometrical structures in combination with a variety of different Ce(III) localization patterns, several of which have not been studied before. The desired trapping of electrons was achieved in a two-stage optimization procedure. We find that the surface oxygen nearest to the vacancy either moves within the plane towards the vacancy, or rises out of the surface into either a symmetric or an unsymmetric bridge structure. Results are shown in seven slab geometry supercells, p(2 x 1), p(2 x 2), p(2 x 3), p(3 x 2), p(2 x 4), p(4 x 2), and p(3 x 3), and indicate that the choice of supercell can affect the results qualitatively and quantitatively. An unsymmetric bridge structure with one nearest and one next-nearest neighbour Ce(III) ion (a combination of localizations not previously found) is the ground state in all (but one) of the supercells studied here, and the relative stability of other structures depends strongly on supercell size. Within any one supercell the formation energies of the different vacancy structures differ by up to 0.5 eV, but the same structure can vary by up to similar to 1 eV between supercells. Furthermore, finite size scaling suggests that the remaining errors (compared to still larger supercells) can also be similar to 1 eV for some vacancy structures.

  • 346.
    Kullgren, Jolla
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Kim, Byung-Hyun
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    SCC-DFTB simulations of ceria surfaces and nanoparticles2017Conference paper (Other academic)
    Abstract [en]

    First principles modelling, using e.g. the density functional theory (DFT), has become a valuable tool in materials research. However, today’s computer resources limit the size and time scales that can be studied with such techniques, thereby hindering the full utilization of computational chemistry for large-scale systems in practice. Thus, new developments of reliable approximate and/or parameterized methods are needed.

    One promising approximate method, conceptually similar to the DFT, is the self-consistent charge density functional based tight binding method (SCC-DFTB). SCC-DFTB calculations are parameterized against DFT data (see illustration in Figure 1) and are at least two orders of magnitude faster than a standard semi-local DFT calculation. However, to obtain an accuracy comparable to DFT for complex oxides is a task that has proven to be a challenge.

    In this talk, I will present our SCC-DFTB parameterization effort for the technologically important reducible oxide CeO2.1 I will discuss the strategy we have developed for the parameterization and the special complication that follows with reducible oxides. Furthermore, I will demonstrate the applicability of the generated parameters and show results from validation by comparing to data obtained from DFT calculations for CeO2. I will show results for oxygen vacancy formation in various ceria structures of different dimensionality, ranging from 0D (nano) to 3D (bulk) and for oxygen adsorption on ceria nanoparticles and preliminary results regarding ceria nanoparticle agglomeration.

  • 347.
    Kullgren, Jolla
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Wolf, Matthew J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Koehler, Christof
    Univ Bremen, Bremen Ctr Computat Mat Sci, POB 330440, D-28334 Bremen, Germany..
    Aradi, Balint
    Univ Bremen, Bremen Ctr Computat Mat Sci, POB 330440, D-28334 Bremen, Germany..
    Frauenheim, Thomas
    Univ Bremen, Bremen Ctr Computat Mat Sci, POB 330440, D-28334 Bremen, Germany..
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Self-Consistent-Charge Density-Functional Tight-Binding (SCC-DFTB) Parameters for Ceria in 0D to 3D2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 8, p. 4593-4607Article in journal (Refereed)
    Abstract [en]

    Reducible oxides such as CeO2 are challenging to describe with standard density-functional theory (DFT) due to the mixed valence states of the cations; they often require the use of non-standard correction schemes, and/or more computationally expensive methods. This adds a new layer of complexity when it comes to the generation of Slater-Koster tables and the corresponding repulsive potentials for self-consistent density-functional based tight-binding (SCC-DFTB) calculations of such materials. In this work, we provide guidelines for how to set up a parametrization scheme for mixed valence oxides within the SCC-DFTB framework, with a focus on reproducing structural and electronic properties as well as redox reaction energies calculated using a reference DFT method. This parametrization procedure was here used to generate parameters for Ce-O systems, with Ce in its +III or +IV formal oxidation states. The generated parameter set is validated by comparison with DFT calculations for various ceria (CeO2) and reduced ceria (CeO2-x) systems of different dimensionalities ranging from 0D (nanoparticles) to 3D (bulk). As oxygen vacancy defects in ceria are of crucial importance to many technological applications, special focus is directed toward the capability of describing such defects accurately.

  • 348.
    Kullgren, Jolla
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Wolf, Matthew J.
    Mitev, Pavlin D.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Briels, Wim J.
    Computational Biophysics, University of Twente, Box 217, 7500 AE Enschede, The Netherlands, Forschungszentrum Jülich, ICS 3, D-52425 Jülich, Germany.
    Defect cluster at the CeO2(111) surface: A combined DFT and Monte-Carlo study2017Conference paper (Other academic)
  • 349.
    Kullgren, Jolla
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Wolf, Matthew J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Mitev, Pavlin D.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Briels, Wim J.
    Univ Twente, Computat Biophys, Box 217, NL-7500 AE Enschede, Netherlands.;Forschungszentrum Julich, ICS 3, D-52425 Julich, Germany..
    DFT-based Monte Carlo Simulations of Impurity Clustering at CeO2(111)2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 28, p. 15127-15134Article in journal (Refereed)
    Abstract [en]

    The interplay between energetics and entropy in determining defect distributions at ceria(111) is studied using a combination of DFT+U and lattice Monte Carlo simulations. Our main example is fluorine impurities, although we also present preliminary results for surface hydroxyl groups. A simple classical force-field model was constructed from a training set of DFT+U data for all symmetrically inequivalent (F-)(n)(Ce3+)(n) nearest-neighbor clusters with n = 2 or 3. Our fitted model reproduces the DFT energies well. We find that for an impurity concentration of 15% at 600 K, straight and hooked linear fluorine clusters are surprisingly abundant, with similarities to experimental STM images from the literature. We also find that with increasing temperature the fluorine cluster sizes show a transition from being governed by an attractive potential to being governed by a repulsive potential as a consequence of the increasing importance of the entropy of the Ce3+ ions. The distributions of surface hydroxyl groups are noticeably different.

  • 350.
    Kvarned, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    PILCs for trapping phosphorus in a heavy duty engine exhaust system: An experimental evaluation of the phosphorus sorption capability of different clay materials2016Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In order to fulfil the requirements in the EURO VI standard, regulating emissions from heavy duty vehicles, the exhaust aftertreatment system needs to maintain its efficiency for at least seven years or 700 000 km. In diesel applications the diesel oxidation catalyst (DOC) is located closest to the engine and is thus the most vulnerable to poisoning contaminants, such as phosphorus originating from fuel and oil additives, which deactivates the catalyst.

    An idea to reduce the impact from phosphorus impurities (recently patented by Scania CV) is to place a low-cost sacrificial substrate, consisting of one or more pillared clay mineral (PILC) with high affinity for phosphorus, upstream the aftertreatment system in order to protect and thus increase the lifetime of the catalytic components which contain platinum group metals.

    In this work one commercially available and four custom made PILCs, comprising of two conventional type PILCs and two of the type porous clay heterostructures (PCH), were evaluated. The PILCs were exposed to a phosphorus-containing gaseous mixture using a lab-scale experimental setup in order to determine their phosphorus sorption potential.

    The PILC materials exhibit potential to function as sacrificial substrates for phosphorus in the intended application. It was indicated to be a correlation between increasing iron content (wt%) and increasing phosphorus sorption capability. The most promising material was the custom made Al,Fe-pillared saponite, which was up to twice as effective in trapping phosphorus as the DOC. The commercial sample, the Al-pillared montmorillonite, was only about as efficient as the DOC.

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