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  • 201.
    Eriksson, Susanna K
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Hahlin, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kahk, Juhan Matthias
    Villar-Garcia, Ignacio J
    Webb, Matthew J
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Grennberg, Helena
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Yakimova, Rositza
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hagfeldt, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Siegbahn, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Edwards, Mårten O M
    Karlsson, Patrik G
    Backlund, Klas
    Ahlund, John
    Payne, David J
    A versatile photoelectron spectrometer for pressures up to 30 mbar2014In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 85, no 7, p. 075119-Article in journal (Refereed)
    Abstract [en]

    High-pressure photoelectron spectroscopy is a rapidly developing technique with applications in a wide range of fields ranging from fundamental surface science and catalysis to energy materials, environmental science, and biology. At present the majority of the high-pressure photoelectron spectrometers are situated at synchrotron end stations, but recently a small number of laboratory-based setups have also emerged. In this paper we discuss the design and performance of a new laboratory based high pressure photoelectron spectrometer equipped with an Al Kα X-ray anode and a hemispherical electron energy analyzer combined with a differentially pumped electrostatic lens. The instrument is demonstrated to be capable of measuring core level spectra at pressures up to 30 mbar. Moreover, valence band spectra of a silver sample as well as a carbon-coated surface (graphene) recorded under a 2 mbar nitrogen atmosphere are presented, demonstrating the versatility of this laboratory-based spectrometer.

  • 202.
    Eriksson, Therese
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Mindemark, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Yue, Ma
    Northwestern Polytech Univ, Ctr Nano Energy Mat, Sch Mat Sci & Engn, Youyi West Rd 127, Xian, Shaanxi, Peoples R China.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Effects of nanoparticle addition to poly(epsilon-caprolactone) electrolytes: Crystallinity, conductivity and ambient temperature battery cycling2019In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 300, p. 489-496Article in journal (Refereed)
    Abstract [en]

    It has previously been shown that nanoparticle additives can, in a simple way, significantly improve the ionic conductivity in solid polymer electrolyte systems with the semi-crystalline poly(ethylene oxide) (PEO) as a host material. It has been suggested that the improved ionic conductivity is a result of reduced degree of crystallinity and additional conductivity mechanisms occurring in the material. In this work, this principle is applied to another semi-crystalline polymer host: poly(epsilon-caprolactone) (PCL). This is a polymer with comparable properties (T-g, T-m, etc.) as PEO, and constitute a promising material for use in solid polymer electrolytes for lithium ion batteries. 15 wt% of the respective nanoparticles TiO2, Al2O3 and h-BN have been added to the PCL-LiTFSI solid polymer electrolyte in an attempt to increase the conductivity and achieve stable room temperature cyclability. The crystallinity, ionic conductivity and electrochemical properties were investigated by differential scanning calorimetry, electrochemical impedance spectroscopy and galvanostatic cycling of cells. The results showed that with an addition of 15 wt% Al2O3, the degree of crystallinity is reduced to 6-7% and the ionic conductivity increased to 6-7 x 10(-6) S cm(-1) at room temperature, allowing successful cycling of cells at 30 degrees C, while h-BN did not contribute to similar improvements. The effect of nanoparticles, however, differ significantly from previous observations in PEO systems, which could be explained by different surface-polymer interactions or the degree of ordering in the amorphous phases of the materials.

  • 203.
    Eriksson, Therese
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Mindemark, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Yue, Ma
    School of Materials Science and Engineering, Center for Nano Energy materials, Northwestern Polytechnical University, Youyi west road 127, Xi'an, China.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Nanoparticle Additives in Poly(ε-Caprolactone)-Based Solid PolymerElectrolytes; Towards Lower Crystallinity and Higher Ionic Conductivity.2018Conference paper (Refereed)
  • 204.
    Etman, Ahmed
    et al.
    Stockholm University.
    Inge, Ken
    Stockholm University.
    Jiaru, Xu
    Peking University.
    Younesi, Reza
    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.
    Sun, Junliang
    Stockholm University, Peking University.
    A Water Based Synthesis of Ultrathin Hydrated Vanadium Pentoxide Nanosheets for Lithium Battery Application: Free Standing Electrodes or Conventionally Casted Electrodes?2017In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 252, p. 254-260Article in journal (Refereed)
    Abstract [en]

    Abstract: Ultrathin hydrated vanadium pentoxide (V2O5·nH2O) nanosheets are fabricated via a water based exfoliation technique. The exfoliation process involves reflux of the precursor, 1:4 mixture of VO2 and V2O5, in water at 80 °C for 24 h. Operando and ex situ X-ray diffraction (XRD) studies are conducted to follow the structural changes during the exfoliation process. The chemical and thermal analyses suggest that the molecular formula of the nanosheet is H 0.2 V 1.8 V V 0.2 IV O 5 ⋅ 0.5 H 2 O . The V2O5·nH2O nanosheets are mixed with 10% of multi-walled carbon nanotube (MW-CNT) to form a composite material assigned as (VOx-CNT). Free standing electrodes (FSE) and conventionally casted electrodes (CCE) of VOx-CNT are fabricated and then tested as a positive electrode material for lithium batteries. The FSE shows reversible capacities of 300 and 97 mAhg-1 at current densities of 10 and 200 mAhg-1, respectively. This is better than earlier reports for free-standing electrodes. The CCE delivers discharge capacities of 175 and 93 mAhg-1 at current densities of 10 and 200 mAhg-1, respectively.

  • 205.
    Etman, Ahmed S.
    et al.
    Stockholms Universitet.
    Asfaw, Habtom D.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Yuan, Ning
    Stockholm University and SLU.
    Li, Jian
    Peking University, China.
    Zhou, Zhengyang
    Peking University.
    Peng, Fei
    Stockholm University.
    Persson, Ingmar
    Swedish University of Agricultural Sciences.
    Zou, Xiaodong
    Stockholm University.
    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.
    Sun, Junliang
    Stockholm University and Peking University.
    A one-step water based strategy for synthesizing hydrated vanadium pentoxide nanosheets from VO2(B) as free-standing electrodes for lithium battery applications2016In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 4, no 46, p. 17988-18001Article in journal (Refereed)
    Abstract [en]

    The synthesis of two dimensional (2D) materials from transition metal oxides, chalcogenides, and carbides mostly involve multiple exfoliation steps in which hazardous solvents and reagents are used. In this study, hydrated vanadium pentoxide (V2O5[middle dot]nH2O) nanosheets with a thickness of a few nanometers were prepared via a facile environmentally friendly water based exfoliation technique. The exfoliation process involved refluxing the precursor, vanadium dioxide (VO2(B)), in water for a few days at 60 [degree]C. The proposed exfoliation mechanism is based on the intercalation/insertion of water molecules into the VO2(B) crystals and the subsequent cleavage of the covalent bonds holding the layers of VO2(B) together. The thermal and chemical analyses showed that the approximate chemical composition of the nanosheets is H0.4V2O5[middle dot]0.55H2O, and the percentage of VV content to that of VIV in the nanosheets is about 80(3)% to 20(3)%. The exfoliated aqueous suspension of the V2O5[middle dot]0.55H2O nanosheets was successfully deposited onto multi-walled carbon nanotube (MW-CNT) paper to form free-standing electrodes with a thickness of the V2O5[middle dot]0.55H2O layer ranging between 45 and 4 [small mu ]m. A series of electrochemical tests were conducted on the electrodes to determine the cyclability and rate capability of lithium insertion into V2O5[middle dot]0.55H2O nanosheets. The electrodes with the thinnest active material coating ([similar]4 [small mu ]m) delivered gravimetric capacities of up to 480 and 280 mA h g-1 when cycled at current densities of 10 and 200 mA g-1, respectively.

  • 206.
    Etman, Ahmed S.
    et al.
    Berzelii Center EXSELENT on Porous Materials, Department of Material and Environmental Chemistry (MMK), Stockholm University, Sweden.
    Inge, Andrew Kentaro
    Berzelii Center EXSELENT on Porous Materials, Department of Material and Environmental Chemistry (MMK), Stockholm University, Sweden.
    Jiaru, Xu
    College of Chemistry and Molecular Engineering, Peking University, China.
    Younesi, Reza
    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.
    Sun, Junliang
    Berzelii Center EXSELENT on Porous Materials, Department of Material and Environmental Chemistry (MMK), Stockholm University, Sweden; College of Chemistry and Molecular Engineering, Peking University, China.
    Simple and Green Method for Fabricating V2O5·nH2O Nanosheets for Lithium Battery Application2017Conference paper (Other academic)
    Abstract [en]

    During the last few years, the synthesis of inorganic two dimensional (2D) materials tremendously increased, due to their promising surface area1,2. However, the synthesis of these 2D materials can significantly influence our environment, by the use of harmful chemicals and severe reaction conditions3,4.

    Herein, we report on a simple and green strategy for fabricating hydrated vanadium pentoxide (V2O5.nH2O) nanosheets from commercially available vanadium oxides precursors via water based exfoliation technique. Operando and ex situ X-ray diffraction (XRD) studies were conducted to track the structural changes during the exfoliation process. The vanadium oxidation states and the water content of the material were determined by X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA), respectively. Electron microscopy and atomic force microscopy (AFM) showed that the V2O5.nH2O is composed of a few nanometer thick nanosheets. A composite material of the V2O5∙nH2O nanosheets and multi-walled carbon nanotube (MW-CNT) were fabricated and then tested as a free standing electrodes (FSE) and conventionally casted electrodes (CCE) for lithium battery. Both electrodes showed promising capacities and rate capabilities for lithium-ion intercalation.

    References:

    (1) Nicolosi, V.; Chhowalla, M.; Kanatzidis, M. G.; Strano, M. S.; Coleman, J. N. Liquid Exfoliation of Layered Materials. Science (80-. ). 2013, 340 (6139), 1226419.

    (2) Etman, A. S.; Asfaw, H. D.; Yuan, N.; Li, J.; Zhou, Z.; Peng, F.; Persson, I.; Zou, X.; Gustafsson, T.; Edström, K.; Sun, J. A One-Step Water Based Strategy for Synthesizing Hydrated Vanadium Pentoxide Nanosheets from VO2 (B) as Free-Standing Electrodes for Lithium Battery Applications. J. Mater. Chem. A 2016, 4 (46), 17988–18001.

    (3) Wei, Q.; Liu, J.; Feng, W.; Sheng, J.; Tian, X.; He, L.; An, Q.; Mai, L. Hydrated Vanadium Pentoxide with Superior Sodium Storage Capacity. J. Mater. Chem. A 2015, 3, 8070–8075.

    (4) Zhou, K.-G.; Mao, N.-N.; Wang, H.-X.; Peng, Y.; Zhang, H.-L. A Mixed-Solvent Strategy for Efficient Exfoliation of Inorganic Graphene Analogues. Angew. Chem. Int. Ed. Engl. 2011, 50 (46), 10839–10842.

  • 207.
    Etman, Ahmed S
    et al.
    Stockholm University.
    Wang, Ligang
    Peking University.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Nyholm, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Sun, Junliang
    Stockholm University.
    Molybdenum Oxide Nanosheets with Tunable Plasmonic Resonance: Aqueous Exfoliation Synthesis and Charge Storage Applications2018In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 29, no 4, article id 1806699Article in journal (Refereed)
    Abstract [en]

    Herein, a simple aqueous-exfoliation strategy is introduced for the fabrication of a series of MoO3−x nanosheets (where x stands for oxygen vacancies) using two commercial molybdenum oxide precursors, MoO2 and MoO3. The nanosheets offer a localized surface plasmon resonance (LSPR) effect which is dependent on the structure and local environment of the nanosheets. The LSPR can be efficiently tuned by changing the weight ratio between the molybdenum oxide precursor(s) and/or by solar light irradiation using a low-energy UV lamp (36 W). For the pristine MoO3−x nanosheets, the highest LSPR signal is obtained for nanosheets prepared using 80% MoO2. On the contrary, after solar light irradiation, the nanosheets prepared using pure MoO3 offer the highest LSPR response. The nanosheets also show an outstanding rate capability when used as binder-free supercapacitor electrodes in an acidified Na2SO4 electrolyte. The electrodes exhibit discharge capacities of 110 and 75 C g−1 at a scan rate of 20 and 1000 mV s−1, respectively. The MoO3−x nanosheets can likewise be used as a negative electrode material for lithium-ion batteries. The efficient eco-friendly synthesis and the ability to tune the photochemical and electrochemical properties of the nanosheets make this approach interesting to many energy-related research fields.

  • 208. Etman, Ahmed
    et al.
    Sun, Junliang
    Younesi, Reza
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    V2O5·nH2O nanosheets and multi-walled carbon nanotube composite as a negative electrode for sodium-ion batteries2019In: Journal of Energy Chemistry, ISSN 2095-4956, Vol. 30, p. 145-151Article in journal (Refereed)
    Abstract [en]

    Two dimensional (2D) transition metal oxides and chalcogenides demonstrate a promising performance in sodium-ion batteries (SIBs) application. In this study, we investigated the use of a composite of freeze dried V2O5 center dot nH(2)O nanosheets and multi-walled carbon nanotube (MWCNT) as a negative electrode material for SIBs. Cyclic voltammetry (CV) results indicated that a reversible sodium-ion insertion/deinsertion into the composite electrode can be obtained in the potential window of 0.1-2.5 V vs. Na+/Na. The composite electrodes delivered sodium storage capacities of 140 and 45 mAh g(-1) under applied current densities of 20 and 100 mA g(-1), respectively. The pause test during constant current measurement showed a raise in the open circuit potential (OCP) of about 0.46 V, and a charge capacity loss of similar to 10%. These values are comparable with those reported for hard carbon electrodes. For comparison, electrodes of freeze dried V2O5 center dot nH(2)O nanosheets were prepared and tested for SIBs application. The results showed that the MWCNT plays a significant role in the electrochemical performance of the composite material. 

  • 209.
    Etman, Ahmed
    et al.
    Stockholm University.
    Wang, Ligang
    Peking University.
    Nyholm, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Sun, Junliang
    Stockholm University, Peking University.
    One-pot Synthesis of MoO3-x Nanosheets for Supercapacitor Applications2018Conference paper (Other academic)
    Abstract [en]

    Molybdenum oxide nanosheets are interesting materials for energy storage, catalysis, and gas sensor applications.1 However, they are traditionally prepared via a variety of approaches which require the use of high temperature or organic solvents.2,3 Herein, we report the synthesis of MoO3-x nanosheets (where x denotes oxygen vacancy) via a one-step water based exfoliation strategy using bulk molybdenum oxides precursors.4 Scanning and transmission electron microscopy show that the MoO3-x has a typical nanosheet morphology with a few nanometer thickness. The MoO3-x nanosheets display localized surface plasmon resonance (LSPR), which can be enhanced by modifying the morphology and the amount of oxygen vacancies (x) using chemical and/or photochemical treatments.

    The aqueous suspension of the MoO3-x nanosheets was drop-cast onto carbon paper and this material was then used as binder free electrodes for supercapacitor applications. The electrodes showed promising performance regarding capacitance and rate capability in acidified sodium sulphate solutions. The facile green synthesis of MoO3-x nanosheets coupled with their significant photochemical and electrochemical properties pave the way for the use of the nanosheets in a variety of applications.

    References:

    (1)        de Castro, I. A.; Datta, R. S.; Ou, J. Z.; Castellanos-Gomez, A.; Sriram, S.; Daeneke, T.; Kalantar-zadeh, K. Molybdenum Oxides - From Fundamentals to Functionality. Adv. Mater. 2017, 29 (40), 1701619.

    (2)        Xiao, X.; Song, H.; Lin, S.; Zhou, Y.; Zhan, X.; Hu, Z.; Zhang, Q.; Sun, J.; Yang, B.; Li, T.; Jiao, L.; Zhou, J.; Tang, J.; Gogotsi, Y. Scalable Salt-Templated Synthesis of Two-Dimensional Transition Metal Oxides. Nat. Commun. 2016, 7, 11296.

    (3)        Alsaif, M. M. Y. A.; Field, M. R.; Daeneke, T.; Chrimes, A. F.; Zhang, W.; Carey, B. J.; Berean, K. J.; Walia, S.; van Embden, J.; Zhang, B.; Latham, K.; Kalantar-zadeh, K.; Ou, J. Z. Exfoliation Solvent Dependent Plasmon Resonances in Two-Dimensional Sub-Stoichiometric Molybdenum Oxide Nanoflakes. ACS Appl. Mater. Interfaces 2016, 8 (5), 3482–3493.

    (4)      Etman A. S.; Abdelhamid H. N.; Yuan Y.; Wang L.; Zou X.; Sun J. Facile Water Based Strategy for Synthesizing MoO3-x Nanosheets: Efficient Visible Light Photocatalyst for Dye Degradation. ACS Omega. in Press.

  • 210.
    Fang, Hailiang
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Li, Jiheng
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. Univ Sci & Technol Beijing, State Key Lab Adv Met & Mat, Beijing, Peoples R China.
    Shafeie, Samrand
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Cedervall, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Ekström, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gómez, Cesar Pay
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Bednarcik, Jozef
    Deutsch Elektronen Synchrotron DESY, Notkestr 85, D-22603 Hamburg, Germany.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Insights into phase transitions and magnetism of MnBi crystals synthesized from self-flux2019In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 781, p. 308-314Article in journal (Refereed)
    Abstract [en]

    To effectively synthesize high purity ferromagnetic low temperature phase (LTP) MnBi with optimal microstructure is still a challenge that needs to be overcome for the system to reach its full potential. Here, the phase transitions and magnetic properties of MnBi crystals are reported. The phase transition between the low and high temperature structure of MnBi was systematically investigated at different heating/cooling rates using in situ synchrotron radiation X-ray diffraction. The material crystallizes in a layered hexagonal structure giving a platelike microstructure. The magnetic characterization of the crystals reveal that the saturation magnetization varies from 645 kA/m at 50 K to 546 kA/m at 300 K. Magnetization measurements also show that the sample upon heating becomes non-magnetic and transforms to the high temperature phase (HTP) at similar to 640 K, and that it regains ferromagnetic properties and transforms back to the LTP at similar to 610 K upon subsequent cooling.

  • 211.
    Farhat, Douaa
    et al.
    Univ Francois Rabelais Tours, France..
    Ghamouss, Fouad
    Univ Francois Rabelais Tours, France..
    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.
    Lemordant, Daniel
    Univ Francois Rabelais Tours, France..
    Adiponitrile-Lithium Bis(trimethylsulfonyl)imide Solutions as Alkyl Carbonate-free Electrolytes for Li4Ti5O12 (LTO)/LiNi1/3Co1/3Mn1/3O2 (NMC) Li-Ion Batteries2017In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 18, no 10, p. 1333-1344Article in journal (Refereed)
    Abstract [en]

    Recently, dinitriles (NC(CH2)(n)CN) and especially adiponitrile (ADN, n = 4) have attracted attention as safe electrolyte solvents owing to their chemical stability, high boiling points, high flash points, and low vapor pressure. The good solvation properties of ADN toward lithium salts and its high electrochemical stability (approximate to 6 V vs. Li/Li+) make it suitable for safer Li-ions cells without performance loss. In this study, ADN is used as a single electrolyte solvent with lithium bis(trimethylsulfonyl) imide (LiTFSI). This electrolyte allows the use of aluminium collectors as almost no corrosion occurs at voltages up to 4.2 V. The physicochemical properties of the ADN-LiTFSI electrolyte, such as salt dissolution, conductivity, and viscosity, were determined. The cycling performances of batteries using Li4Ti5O12 (LTO) as the anode and LiNi1/3Co1/3Mn1/3O2 (NMC) as the cathode were determined. The results indicate that LTO/NMC batteries exhibit excellent rate capabilities with a columbic efficiency close to 100 %. As an example, cells were able to reach a capacity of 165 mAhg(-1) at 0.1C and a capacity retention of more than 98% after 200 cycles at 0.5 C. In addition, electrodes analyses by SEM, X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy after cycling confirming minimal surface changes of the electrodes in the studied battery system.

  • 212.
    Farhat, Douaa
    et al.
    Univ Francois Rabelais Tours, UFR Sci & Tech, Lab PCM2E, EA 6296, Parc Grandmont, F-37200 Tours, France.
    Maibach, Julia
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Eriksson, Henrik
    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.
    Lemordant, Daniel
    Univ Francois Rabelais Tours, UFR Sci & Tech, Lab PCM2E, EA 6296, Parc Grandmont, F-37200 Tours, France.
    Ghamouss, Fouad
    Univ Francois Rabelais Tours, UFR Sci & Tech, Lab PCM2E, EA 6296, Parc Grandmont, F-37200 Tours, France.
    Towards high-voltage Li-ion batteries: Reversible cycling of graphite anodes and Li-ion batteries in adiponitrile-based electrolytes2018In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 281, p. 299-311Article in journal (Refereed)
    Abstract [en]

    Due to their low vapor pressure and their promising electrochemical and thermal stability, N C- (CH2)n-C N dinitriles are proposed as an electrolyte solvent for Li-ion batteries. Adiponitrile (ADN) has substantial advantages, especially for applications requiring high potential cathodes, because it has high electrochemical/thermal stability (up to 6 V vs. Li/Li+, > 120 degrees C). However, to obtain very high voltage batteries, ADN electrolytes must also passivate the anode of the battery. In this work, reversible cycling of graphite in adiponitrile was successfully achieved by adding a few percent of fluoroethylene carbonate allowing the realization of Graphite/NMC Li-ion battery. The battery of specific capacity of 135 mAhh.g(-1) showed a cycling stability for more than 40 cycles. The composition of the solid electrolyte interphase (SEI) was determined as a function of the FEC concentration as well as the state of charge of the graphite anode using hard X-ray photoelectron spectroscopy (HAXPES) and XPS. With FEC, the SEI layer is thinner and depends on the SOC of the anode, but does not depend on the FEC concentration. SEM characterizations clearly showed that the surface of the anode is completely covered by the SEI layer, regardless of the concentration of FEC. Indeed, 2% of FEC is sufficient to suppress the reduction of adiponitrile which is explained by a specific adsorption of FEC on the graphite anode.

  • 213. Feng, Feng
    et al.
    Hu, Shuanglin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Guo, Yuqiao
    Zhao, Jiyin
    Chan, Ngai Yui
    Fei, Linfeng
    Yan, Wensheng
    Ning, Wei
    Yang, Jinlong
    Wang, Yu
    Xiea, Yi
    Wu, Changzheng
    Room-temperature large magnetic-dielectric coupling in new phase anatase VTiO42013In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 49, no 89, p. 10462-10464Article in journal (Refereed)
    Abstract [en]

    The synthetic new-phase VTiO4, as a new solid solution structure of anatase type, brings a large magnetodielectric ratio (Delta epsilon/epsilon(0)) of 7.2% at 300 K, representing a new simple-oxide structural catalogue exhibiting a room-temperature large magnetic-dielectric effect.

  • 214. Feng, Jun
    et al.
    Peng, Lele
    Wu, Changzheng
    Sun, Xu
    Hu, Shuanglin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Lin, Chenwen
    Dai, Jun
    Yang, Jinlong
    Xie, Yi
    Giant Moisture Responsiveness of VS2 Ultrathin Nanosheets for Novel Touchless Positioning Interface2012In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 24, no 15, p. 1969-1974Article in journal (Refereed)
    Abstract [en]

    Utilizing a thin film of VS2 ultrathin nanosheets with giant and fast moisture responsiveness, a brand-new model of moisture-based positioning interface is put forward here, by which not only the 2D position information of finger tips can be acquired, but also the relative height can be detected as the third dimensionality, representing a promising platform for advanced man-machine interactive systems.

  • 215.
    Flores, Eibar
    et al.
    Paul Scherrer Inst, Electrochem Lab, Energy & Environm Res Div, Villigen, Switzerland.
    Novak, Petr
    Paul Scherrer Inst, Electrochem Lab, Energy & Environm Res Div, Villigen, Switzerland.
    Jämstorp, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Paul Scherrer Inst, Electrochem Lab, Energy & Environm Res Div, Villigen, Switzerland.
    In situ and Operando Raman Spectroscopy of Layered Transition Metal Oxides for Li-ion Battery Cathodes2018In: FRONTIERS IN ENERGY RESEARCH, ISSN 2296-598X, Vol. 6, article id 82Article in journal (Refereed)
    Abstract [en]

    In situ and operando Raman spectroscopy is proposed to provide unique means for deeper fundamental understanding and further development of layered transition metal LiMO2 (M = Ni, Co, Mn) oxides suitable for Li-ion battery applications. We compare several spectro-electrochemical cell designs and suggest key experimental parameters for obtaining optimum electrochemical performance and spectral quality. Studies of the most practically relevant LiMO2 compositions are exemplified with particular focus on two experimental approaches: (1) lateral and axial Raman mapping of the electrode's (near-) surface to monitor inhomogeneous electrode reactions and (2) time-dependent single-particle spectra during cycling to analyze the LixMO2 lattice dynamics as a function of lithium content. Raman Spectroscopy is claimed to provide a unique real-time probe of the M-O bonds, which are at the heart of the electrochemistry of LiMO2 oxides and govern their stability. We highlight the need for further fundamental understanding of the relationships between the spectroscopic response and oxide lattice structure with particular emphasis on the development of a theoretical framework linking the position and intensity of the Raman bands to the local LixMO2 lattice con figuration. The use of complementary experimental techniques and model systems for validation also deserve further attention. Several novel LiMO2 compositions are currently being explored, especially containing dopings and coatings, and Raman spectroscopy could offer a highly dynamic and convenient tool to guide the formulation of high specific charge and long cycle life LiMO2 oxides for next-generation Li-ion battery cathodes.

  • 216.
    Flores, Eibar
    et al.
    Paul Scherrer Inst, Electrochem Lab, Villigen, Switzerland.
    Vonrüti, Nathalie
    Univ Bern, Dept Chem & Biochem, Bern, Switzerland.
    Novák, Petr
    Paul Scherrer Inst, Electrochem Lab, Villigen, Switzerland.
    Aschauer, Ulrich
    Univ Bern, Dept Chem & Biochem, Bern, Switzerland.
    Berg, Erik Jämstorp
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Paul Scherrer Inst, Electrochem Lab, Villigen, Switzerland.
    Elucidation of LixNi0.8Co0.15Al0.05O2 Redox Chemistry by Operando Raman Spectroscopy2018In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 30, no 14, p. 4694-4703Article in journal (Refereed)
    Abstract [en]

    The local structure evolution of LixNi0.8Co0.15Al0.05O2 (NCA) is linked to its electrochemical response during cycling (and overcharge) by operando Raman spectroscopy with findings supported by complementary techniques, such as online electrochemical mass spectrometry (OEMS) and density functional theory (DFT) phonon calculations. The vibrational motion of lattice oxygens is observed to be highly dependent on the local LixMO2 lattice environment, e.g. M—O bonding strength/length and state of lithiation x. All vibrational modes generally harden upon delithiation due to M—O bond character (ionic → covalent) evolution (disregarding an early bond softening due to Li+ vacancy formation) and evidence the important influence of the local structural lattice configuration on the electrochemical response of NCA. Although the intensities of all Raman active bands generally increase upon delithiation, a major inflection point at x = 0.2 marks the onset of a partly irreversible fundamental transition within NCA that is most likely related to electron removal from MO bonding states and partial oxidation of oxygen sublattice, which is also indicated by the observed concomitant O2 release from the particle surface. Operando Raman spectroscopy with higher time resolution provides unique possibilities for detailed studies of how chemical parameters (Li+ vacancy formation, transition metal cation concentration, and lattice doping, etc.) may govern the onset and nature of processes (such as bond character evolution and stability) that define the performance of the LixMO2 class of oxides. The further insights thus gained can be exploited to guide the development of next-generation layered cathodes for Li-ion batteries operating stably at higher voltages and capacities.

  • 217.
    Franco, Alejandro A.
    et al.
    Univ Picardie Jules Verne, CNRS, LRCS, Hub Energie,UMR 7314, 15 Rue Baudelocque, F-80039 Amiens 1, France;CNRS, Reseau Stockage Electrochim Energie RS2E, Hub Energie, FR 3459, 15 Rue Baudelocque, F-80039 Amiens 1, France;CNRS, ALISTORE European Res Inst, Hub Energie, FR 3104, 15 Rue Baudelocque, F-80039 Amiens 1, France;Inst Univ France, 103 Blvd St Michel, F-75005 Paris, France.
    Rucci, Alexis
    Univ Picardie Jules Verne, CNRS, LRCS, Hub Energie,UMR 7314, 15 Rue Baudelocque, F-80039 Amiens 1, France;CNRS, Reseau Stockage Electrochim Energie RS2E, Hub Energie, FR 3459, 15 Rue Baudelocque, F-80039 Amiens 1, France.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. CNRS, ALISTORE European Res Inst, Hub Energie, FR 3104, 15 Rue Baudelocque, F-80039 Amiens 1, France.
    Frayret, Christine
    Univ Picardie Jules Verne, CNRS, LRCS, Hub Energie,UMR 7314, 15 Rue Baudelocque, F-80039 Amiens 1, France;CNRS, Reseau Stockage Electrochim Energie RS2E, Hub Energie, FR 3459, 15 Rue Baudelocque, F-80039 Amiens 1, France;CNRS, ALISTORE European Res Inst, Hub Energie, FR 3104, 15 Rue Baudelocque, F-80039 Amiens 1, France.
    Gaberscek, Miran
    CNRS, ALISTORE European Res Inst, Hub Energie, FR 3104, 15 Rue Baudelocque, F-80039 Amiens 1, France;Natl Inst Chem, Dept Mat Chem, Hajdrihova 19, SI-1000 Ljubljana, Slovenia.
    Jankowski, Piotr
    CNRS, ALISTORE European Res Inst, Hub Energie, FR 3104, 15 Rue Baudelocque, F-80039 Amiens 1, France;Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden;Warsaw Univ Technol, Fac Chem, Noakowskiego 3, PL-00664 Warsaw, Poland.
    Johansson, Patrik
    CNRS, ALISTORE European Res Inst, Hub Energie, FR 3104, 15 Rue Baudelocque, F-80039 Amiens 1, France;Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden.
    Boosting Rechargeable Batteries R&D by Multiscale Modeling: Myth or Reality?2019In: Chemical Reviews, ISSN 0009-2665, E-ISSN 1520-6890, Vol. 119, no 7, p. 4569-4627Article, review/survey (Refereed)
    Abstract [en]

    This review addresses concepts, approaches, tools, and outcomes of multiscale modeling used to design and optimize the current and next generation rechargeable battery cells. Different kinds of multiscale models are discussed and demystified with a particular emphasis on methodological aspects. The outcome is compared both to results of other modeling strategies as well as to the vast pool of experimental data available. Finally, the main challenges remaining and future developments are discussed.

  • 218.
    Fredriksson, Wendy
    et al.
    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.
    XPS study of duplex stainless steel as a possible current collector in a Li-ion battery2012In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 79, p. 82-94Article in journal (Refereed)
    Abstract [en]

    The surface chemistry and corrosion property of a duplex LDX 2101 steel that had been cycled in a Li-ion battery with a 1 M LiPF6 in EC/DMC 1:1 electrolyte was studied. The results are compared to those of steel stored for the same length of time. Cyclic voltammetry was used to sweep the steel between 0 V and 5 V and the different reduction products were identified with SEM, XRD and XPS. A conversion reaction occurred during the cathodic sweep between 2.0 and 1.5 V where chromium and iron oxides were reduced forming Li2O and metal. At 0.5 V vs. Li+/Li a Solid Electrolyte Interface (SEI) was irreversibly formed predominantly during the first cycle. During the oxidation sweep the typical stainless steel passive layer of chromium and iron oxides/hydroxides formed at 2.5 V vs. Li/Li+. Li2O also decomposed at this potential. Simultaneously metal fluorides are formed. The XPS revealed a thicker SEI containing organic and inorganic species on the cycled electrode than on the stored. The stored sample showed chemical formation of CrF3 on the surface. Depth profiling of the cycled electrode by Ar+ etching showed a thick layer of CrF3 and a thin layer of FeF3. We conclude that the level of corrosion of this duplex steel is acceptable in the 3–4.5 V vs. Li+/Li region. However, in a Li-ion battery it is too reactive at low potentials to be considered as a replacement for copper as an anode current collector. We also observe that the PF6 anion from the electrolyte salt plays an important role in the formation of metal fluorides which is a fact generally neglected in the discussion of conversion reactions of metal-oxide anodes for Li-ion batteries. For stainless steel to be considered as current collectors for Li-ion batteries optimisation of alloy compositions need to be made to reduce corrosion occurring during cycling in organic solvents.

  • 219.
    Fredriksson, Wendy
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Olsson, Claes
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
    XPS analysis of manganese in stainless steel passive films on 1.4432 and the lean duplex 1.41622010In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 52, no 7, p. 2505-2510Article in journal (Refereed)
    Abstract [en]

    Passive films were compared on two stainless steels: the recent lean duplex EN 1.4162 and EN 1.4432 (316L). For alloys with significant amount of manganese and nickel, the Mn 2p(3/2) peak will overlap with the Ni-LMM. To resolve this overlap, Ni 2p(3/2) to Ni-LMM intensity ratios were recorded on 1.4432, compensated for overlayer thickness, and then used to fix the Ni-LMM intensities in the Mn 2p spectra on the duplex material. Manganese was found in oxidation states II and V/VI: its film content was not dependent on the bulk composition. (C) 2010 Elsevier Ltd. All rights reserved.

  • 220.
    Fredriksson, Wendy
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Malmgren, Sara
    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.
    Gorgoi, Mihaela
    Helmholtz Zentrum Berlin Germany.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Full depth profile of passive films on 316L stainless steel based on high resolution HAXPES in combination with ARXPS2012In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 258, no 15, p. 5790-5797Article in journal (Refereed)
    Abstract [en]

    Depth profiles of the passive films on stainless steel were based on analysis with the non-destructive hard X-ray photoelectron spectroscopy (HAXPES) technique in combination with the angular resolved X-ray photoelectron spectroscopy (ARXPS). The analysis depth with ARXPS is within the passive film thickness, while the HAXPES technique uses higher excitation energies (between 2 and 12 keV) also non-destructively probing the chemical content underneath the film. Depth profiles were done within and underneath the passive film of 316L polarized in acidic solution. The passive film thickness was estimated to 2.6 nm for a sample that was polarized at 0.6 V and the main component in the passive film is, as expected, chromium. From the high resolution HAXPES spectra we suggest chromium in three different oxidation states present. Also for iron three oxides were detected. Gradients of chromium and iron concentrations and oxidation states within the film and an enrichment of nickel within a 0.5 nm layer directly underneath the passive film are some of the results discussed. 

  • 221.
    Fredriksson, Wendy
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Petrini, Daniel
    Erasteel Kloster AB, Box 100, Söderfors SE-815 82, Sweden.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Björefors, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Nyholm, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Corrosion Resistances and Passivation of Powder Metallurgical and Conventionally Cast 316L and 2205 Stainless Steels2013In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 67, p. 268-280Article in journal (Refereed)
    Abstract [en]

    The corrosion resistances and passivation of austenitic 316L and duplex 2205 powder metallurgical (P/M) steels, produced by employing gas atomizing and hot isostatic pressing (HIP), have been compared with those of their conventional cast and forged counterparts. The P/M 316L steel is shown to have a significantly higher pitting corrosion resistance than the conventional 316L steel in 0.5 M HCl. Since the chemical composition and the total amount of inclusions were analogous for the two steels, the effect is ascribed to the finer grained microstructure for the P/M 316L steel yielding a better passive layer. This is supported by photoelectron spectroscopy data demonstrating differences between the thickness and composition of the passive layers for the two 316 L steels. Differences in the passivation process were also found for the different steels as three mixed potentials were observed in the polarization curves for the P/M and conventional 316L steels whereas only one mixed potential at about +0.7 V vs. Ag/AgCl was observed for the two duplex steels in 0.5 M HCl. The results indicate that discussions of the shapes of polarization curves and mixed potentials should be based on the anodic and cathodic partial currents, including the reduction of oxygen. HIP:ed P/M steels are clearly well-suited for applications requiring high pitting corrosion resistances.

  • 222.
    Freitag, Marina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Uppsala Univ, Dept Chem, Angstrom Lab, Box 523, SE-75120 Uppsala, Sweden.;Ecole Polytech Fed Lausanne, Inst Chem Sci & Engn, Lab Photomol Sci, CH-1015 Lausanne, Switzerland..
    Giordano, Fabrizio
    Ecole Polytech Fed Lausanne, Inst Chem Sci & Engn, Lab Photon & Interfaces, CH-1015 Lausanne, Switzerland..
    Yang, Wenxing
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Pazoki, Meysam
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hao, Yan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Zietz, Burkhard
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Graetzel, Michael
    Ecole Polytech Fed Lausanne, Inst Chem Sci & Engn, Lab Photon & Interfaces, CH-1015 Lausanne, Switzerland..
    Hagfeldt, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Ecole Polytech Fed Lausanne, Inst Chem Sci & Engn, Lab Photomol Sci, CH-1015 Lausanne, Switzerland..
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Copper Phenanthroline as a Fast and High-Performance Redox Mediator for Dye-Sensitized Solar Cells2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 18, p. 9595-9603Article in journal (Refereed)
    Abstract [en]

    The most commonly used redox mediators in dye-sensitized solar cells (DSCs), iodide/triiodide and cobalt trisbipyridine ([Co(bpy)(3)](2+/3+)), were successfully replaced by bis (2,9-dimethy1-1,10-phenanthroline) copp er (I/H) ([Cu(dmp)(2)](1+/2+)). The use of the copper complex based electrolyte led to an exceptionally high photovoltaic performance of 8.3% for LEG4-sensitized TiO2 solar cells, with a remarkably high open-circuit potential of above 1.0 V at 1000 W m(-2) under AM1.5G conditions. The copper complex based redox electrolyte has higher diffusion coefficients and is considerably faster in dye regeneration than comparable cobalt trisbipyridine based electrolytes. A driving force for dye regeneration of only 0.2 eV is sufficient to obtain unit yield, pointing to new possibilities for improvement in DSC efficiencies. The interaction of the excited dye with components of the electrolyte was monitored using steady-state emission measurements and time-correlated single-photon counting (TC-SPC). Our results indicate bimolecular reductive quenching of the excited LEG4 dye by the [Cu(dmp)(2)](2+) complex through a dynamic mechanism. Excited-state dye molecules can readily undergo bimolecular electron transfer with a suitable donor molecule. In DSCs this process can occur when the excited dye is unable to inject electrons into the TiO2. With a high electrolyte concentration the excited dye can be intercepted with an electron from the electrolyte resulting in the reduced state of the dye. Quenching of the reduced dye by the electrolyte competes with electron injection and results in a lower photocurrent. Quenching of excited LEG4 by complexes of [Cu(dmp)(2)](+), [Co(bpy)(3)](2+), and [Co(bpy)(3)](3+) followed a static mechanism, due ground-state dye-quencher binding. Inhibition of unwanted quenching processes by structural modifications may open ways to further increase the overall efficiency.

  • 223.
    Fu, Lian-Hua
    et al.
    Beijing Forestry Univ, Coll Mat Sci & Technol, Beijing Key Lab Lignocellulos Chem, Beijing 100083, Peoples R China..
    Liu, Yan-Jun
    Beijing Forestry Univ, Coll Mat Sci & Technol, Beijing Key Lab Lignocellulos Chem, Beijing 100083, Peoples R China..
    Ma, Ming-Guo
    Beijing Forestry Univ, Coll Mat Sci & Technol, Beijing Key Lab Lignocellulos Chem, Beijing 100083, Peoples R China..
    Zhang, Xue-Ming
    Beijing Forestry Univ, Coll Mat Sci & Technol, Beijing Key Lab Lignocellulos Chem, Beijing 100083, Peoples R China..
    Xue, Zhi-Min
    Beijing Forestry Univ, Coll Mat Sci & Technol, Beijing Key Lab Lignocellulos Chem, Beijing 100083, Peoples R China..
    Zhu, Jie-Fang
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Microwave-Assisted Hydrothermal Synthesis of Cellulose/Hydroxyapatite Nanocomposites2016In: Polymers, ISSN 2073-4360, E-ISSN 2073-4360, Vol. 8, no 9, article id 316Article in journal (Refereed)
    Abstract [en]

    In this paper, we report a facile, rapid, and green strategy for the synthesis of cellulose/hydroxyapatite (HA) nanocomposites using an inorganic phosphorus source (sodium dihydrogen phosphate dihydrate (NaH(2)PO(4)2H(2)O)), or organic phosphorus sources (adenosine 5-triphosphate disodium salt (ATP), creatine phosphate disodium salt tetrahydrate (CP), or D-fructose 1,6-bisphosphate trisodium salt octahydrate (FBP)) through the microwave-assisted hydrothermal method. The effects of the phosphorus sources, heating time, and heating temperature on the phase, size, and morphology of the products were systematically investigated. The experimental results revealed that the phosphate sources played a critical role on the phase, size, and morphology of the minerals in the nanocomposites. For example, the pure HA was obtained by using NaH(2)PO(4)2H(2)O as phosphorus source, while all the ATP, CP, and FBP led to the byproduct, calcite. The HA nanostructures with various morphologies (including nanorods, pseudo-cubic, pseudo-spherical, and nano-spherical particles) were obtained by varying the phosphorus sources or adjusting the reaction parameters. In addition, this strategy is surfactant-free, avoiding the post-treatment procedure and cost for the surfactant removal from the product. We believe that this work can be a guidance for the green synthesis of cellulose/HA nanocomposites in the future.

  • 224. Gao, Feng
    et al.
    Nishihara, Sadafumi
    Brant, William
    Younesi, Reza
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Towards Beyond Li-Ion Battery Technologies2017Conference paper (Other academic)
  • 225.
    Gebresenbut, Girma
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Andersson, Mikael Svante
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Beran, Pr™emysl
    Manuel, Pascal
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Gomez, Cesar Pay
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Long range ordered magnetic and atomic structures of the quasicrystal approximant in the Tb-Au-Si system2014In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, no 32, p. 322202-Article in journal (Refereed)
    Abstract [en]

    The atomic and magnetic structure of the 1/1 Tb(14)Au(70)Si(16) quasicrystal approximant has been solved by combining x-ray and neutron diffraction data. The atomic structure is classified as a Tsai-type 1/1 approximant with certain structural deviations from the prototype structures; there are additional atomic positions in the so-called cubic interstices as well as in the cluster centers. The magnetic property and neutron diffraction measurements indicate the magnetic structure to be ferrimagnetic-like below 9 K in contrast to the related Gd(14)Au(70)Si(16) structure that is reported to be purely ferromagnetic.

  • 226.
    Gebresenbut, Girma H.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Andersson, Mikael S.
    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.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Gomez, Cesar Pay
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Tailoring Magnetic Behavior in the Tb-Au-Si Quasicrystal Approximant System2016In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 55, no 5, p. 2001-2008Article in journal (Refereed)
    Abstract [en]

    A novel synthesis method, "arc-melting-self-flux", has been developed and a series of five Tsai-type 1/1 approximant crystals in the Tb-Au-Si system have been synthesized. The synthesis method, by employing a temperature program which oscillates near the melting and nucleation points of the approximants, has provided high-quality and large single crystals in comparison to those obtained from the standard arc-melting-annealing and self-flux methods. The atomic structures of the approximants have been determined from single-crystal X-ray diffraction data and described using concentric atomic clusters with icosahedral symmetry. The compounds are nearly isostructural with subtle variations; two types of atomic clusters which mainly vary at their cluster centers are observed. One type contains a Tb site at the center, and the other contains a disordered tetrahedron decorated with Au/Si mixed sites. Both cluster types can be found coexisting in the approximants. The compounds have different average weighted ratios of central Tb to disordered tetrahedron in the bulk material. Furthermore, a strategy for chemically tuning magnetic behavior is presented. Magnetic property measurements on the approximants revealed that the magnetic transition temperature (T-c) decreases as the occupancy of the central Tb site increases. T-c decreased from 11.5 K for 0% occupancy of the central Tb to 8 K for 100% occupancy. Enhanced magneto crystalline anisotropy is observed for the approximants with higher central Tb occupancy in comparison to their low central Tb occupancy counterparts. Hence, the previously reported "ferrimagnetic-like" magnetic structure model remains valid.

  • 227.
    Gebresenbut, Girma Hailu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Andersson, Mikael
    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.
    Qureshi, Navid
    Institut Laue Langevin, 6 rue Jules Horowitz, Boîıte Postale 156, F-38042 Grenoble, France.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Pay Gómez, Cesar
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Single crystal growth, structure determination and magnetic behavior of RE-Au-Si quasicrystal approximants (RE = Ho and Tb)Manuscript (preprint) (Other academic)
  • 228.
    Gebresenbut, Girma Hailu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Tamura, Ryuji
    Eklof, Daniel
    Gomez, Cesar Pay
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Syntheses optimization, structural and thermoelectric properties of 1/1 Tsai-type quasicrystal approximants in RE-Au-SM systems (RE = Yb, Gd and SM = Si, Ge)2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 13, p. 135402-Article in journal (Refereed)
    Abstract [en]

    Yb-Cd (Tsai-type) quasicrystals constitute the largest icosahedral quasicrystal family where Yb can be replaced by other rare earth elements (RE) and Cd by pairs of p- and d-block elements. YbCd6 is a prototype 1/1 Tsai-type approximant phase which has a similar local structure to the Yb-Cd quasicrystal. In this study, the syntheses of Yb15.78Au65.22Ge19.00, Gd14.34Au67.16Ge18.5 and Gd14.19Au69.87Si15.94 Tsai-type 1/1 quasicrystal approximants are optimized using the self-flux technique. The crystal structures of the compounds are refined by collecting single crystal x-ray diffraction data. The structural refinements indicated that the compounds are essentially isostructural with some differences at their cluster centers. The basic polyhedral cluster unit in all the three compounds can be described by concentric shells of icosahedra symmetry and of disordered tetrahedra and/or a rare earth atom at the cluster center. Furthermore, the thermoelectric properties of the compounds are probed and their dimensionless figures of merit are calculated at different temperatures. A significant difference is observed in their thermoelectric properties, which could arise due to the slight difference in their crystal structure and chemical composition, as we move from Ge to Si and/or Gd to Yb. Therefore, this study shows the systematic effect of the chemical substitution of structurally similar materials on their thermoelectric properties.

  • 229.
    Gerz, Isabelle
    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.
    Mindemark, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Oligomer electrolytes for light-emitting electrochemical cells: Experimental and computational insights2018Conference paper (Refereed)
  • 230. Grazioli, Davide
    et al.
    Verners, Osvalds
    Zadin, Vahur
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Simone, Angelo
    Electrochemical-mechanical modeling of solid polymer electrolytes: Impact of mechanical stresses on Li-ion battery performance2019In: Elsevier IFAC Publications / IFAC Proceedings series, ISSN 1474-6670, Vol. 296, p. 1122-1141Article in journal (Refereed)
    Abstract [en]

    We analyze the effects of mechanical stresses arising in a solid polymer electrolyte (SPE) on the electrochemical performance of the electrolyte component of a lithium ion battery. The SPE is modeled with a coupled ionic conduction-deformation model that allows to investigate the effect of mechanical stresses induced by the redistribution of ions. The analytical solution is determined for a uniform planar cell operating under galvanostatic conditions with and without externally induced deformations. The roles of the polymer stiffness, internally-induced stresses, and thickness of the SPE layer are investigated. The results show that the predictions of the coupled model can strongly deviate from those obtained with an electrochemical model—up to +38% in terms of electrostatic potentialdifference across the electrolyte layer—depending on the combination of material properties and geometrical features. The predicted stress level in the SPE is considerable as it exceeds the threshold experimentally detected for irreversible deformation or fracture to occur in cells not subjected to external loading. We show that stresses induced by external solicitations can reduce the concentration gradient of ions across the electrolyte thickness and prevent salt depletion at the electrode-electrolyte interface.

  • 231. Grazioli, Davide
    et al.
    Zadin, Vahur
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Simone, Angelo
    Electrochemical-mechanical modeling of solid polymer electrolytes: Stress development and non-uniform electric current density in trench geometry microbatteries2019In: Elsevier IFAC Publications / IFAC Proceedings series, ISSN 1474-6670, Vol. 296, p. 1142-1162Article in journal (Refereed)
    Abstract [en]

    We study the effect of mechanical stresses arising in solid polymer electrolytes (SPEs) on the electrochemical performance of lithium-ion (Li-ion) solid-state batteries. Time-dependent finite element analyses of interdigitated plate cells during a discharge process are performed with a constitutive model that couples ionic conduction within the SPE with its deformation field. Due to the coupled nature of the processes taking place in the SPE, the non-uniform ionic concentration profiles that develop during the discharge process induce stresses and deformations within the SPE; at the same time the mechanical loads applied to the cell affect the charge conduction path. Results of a parametric study show that stresses induced by ionic redistribution favor ionic transport and enhance cell conductivity—up to a 15% increase compared to the solution obtained with a purely electrochemical model. We observe that, when the contribution of the mechanical stresses is included in the simulations, the localization of the electric current density at the top of the electrode plates is more pronounced compared to the purely electrochemical model. This suggests that electrode utilization, a limiting factor for the design of three-dimensional battery architectures, depends on the stress field that develops in the SPE. The stress level is indeed significant, and mechanical failure of the polymer might occur during service.

  • 232.
    Gyoeroek, Michael
    et al.
    Univ Innsbruck, Inst Ion Phys & Appl Phys, Technikerstr 25, A-6020 Innsbruck, Austria.
    Kaiser, Alexander
    Univ Innsbruck, Inst Ion Phys & Appl Phys, Technikerstr 25, A-6020 Innsbruck, Austria.
    Sukuba, Ivan
    Comenius Univ, Dept Nucl Phys & Biophys, Fac Math Phys & Informat, SK-84248 Bratislava, Slovakia.
    Urban, Jan
    Comenius Univ, Dept Nucl Phys & Biophys, Fac Math Phys & Informat, SK-84248 Bratislava, Slovakia.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Probst, Michael
    Univ Innsbruck, Inst Ion Phys & Appl Phys, Technikerstr 25, A-6020 Innsbruck, Austria. ; VISTEC, Wangchan 20210, Rayong, Thailand.
    Surface binding energies of beryllium/tungsten alloys2016In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 472, p. 76-81Article in journal (Refereed)
    Abstract [en]

    Binding energies of beryllium and tungsten atoms on surfaces of the alloys Be2W and Be12W were obtained from density functional theory calculations. Values of 4.08–5.63 eV for beryllium and 6.81–10.04 eV for tungsten were obtained. An analytical force field agrees for beryllium, but its tungsten surface atoms are too strongly bound. The surface binding energies of Be and W on Be12W surfaces is slightly smaller than on the pure Be and W surfaces, respectively. For higher tungsten content, i.e. for Be2W, the situation is more complicated. For some surfaces of this alloy the surface binding energies are enhanced while for others they are diminished, compared to the pure metal surfaces. The dependency of the cohesive energy on the mole fraction follows a linear relationship.

  • 233.
    Gómez, Cesar Pay
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Takakura, Hiroyuki
    Division of Applied Physics, Graduate School of Engeneering, Hokkaido University, Sapporo, 060-8628, JAPAN.
    Yamamoto, Akiji
    National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki, 305-0044, JAPAN.
    Tsai, An Pang
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, JAPAN.
    ANALYSIS OF STRUCTURE AD CHEMICAL ORDER I A TERNARY Yb12Mg52Cd36 QUASICRYSTAL2010In: Philosophical Magazine, Sapporo, 2010Conference paper (Refereed)
    Abstract [en]

    The atomic structure of the ternary Yb12Mg52Cd36 quasicrystal has been refined from single crystal X-ray data. The ternary quasicrystal is related to the binary i-Yb16Cd84 parent phase,[1, 2] and suffers from chemical disorder mainly due to mixing between Mg and Cd. Studies on related ternary approximants however indicate that this chemical disorder is only partial, and that there are strong selection rules in several ternary systems that govern the choice of a particular atom at a specific site. The purpose of this work is thus to elucidate the chemical order between the constituent elements in the ternary Yb12Mg52Cd36 quasicrystal and its relation to ternary approximants in other REMg-Cd (RE=Rare Earth) systems. The structure refinements performed on the Yb12Mg52Cd36 quasicrystal clearly indicate that it is composed of similar atomic clusters as the binary i-Yb16Cd84 phase and that there is a strong selection rule that mainly determines the chemical order at the cluster level. Similar observations have also been made in related ternary approximant phases. The structure refinement is the first of its kind performed on a ternary Yb-Cd-related quasicrystal, and the results indicate that the structures and chemical order of ternary quasicrystals can be understood by extracting and combining information from structure refinements on both quasicrystals and related approximants.

  • 234.
    Gómez, Cesar Pay
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Tsai, An Pang
    Crystal chemistry and chemical order in ternary quasicrystals and approximants2014In: Comptes rendus. Physique, ISSN 1631-0705, E-ISSN 1878-1535, Vol. 15, no 1, p. 30-39Article in journal (Refereed)
    Abstract [en]

    In this work we review our current understanding of structure, stability and formation of icosahedral quasicrystals and approximants. The work has special emphasis on Cd–Yb type phases, but several concepts are generalized to other families of icosahedral quasicrystals and approximants. The paper handles topics such as chemical order and site preference at the cluster level for ternary phases, valence electron concentration and its influence on formation and composition, fundamental building blocks and cluster linkages, and the similarities and differences between different families of icosahedral quasicrystals and approximants.

  • 235.
    Hall, Markus
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Probing ion movement in conjugated polymers2019Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Electronic conduction in conjugated polymers can be increased through electrochemical doping. This is utilised in light-emitting electrochemical cells and allows for a less demanding manufacturing process compared to the related organic light-emitting diode. The doping process requires ion transport into the conjugated polymer and has yet to be quantified for an electrolyte-free conjugated polymer.

    In this project the ion movement of lithium trifluoromethanesulfonate in poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) has been studied with several electrochemical techniques: cyclic voltammetry, galvanostatic cycling, staircase potentiostatic electrochemical impedance spectroscopy and staircase potentiostatic chronoamperometry. The measurements have been performed on a dry system of spin-coated MEH-PPV films with lithium trifluoromethanesulfonate dissolved in a copolymer of poly(epsilon-caprolactone) and poly(trimethylene carbonate), PCL–PTMC, as a solid electrolyte.

    Infrared spectroscopy (FTIR) showed evidence of ion association of lithium trifluoromethanesulfonate dissolved in MEH-PPV. The electrochemical analyses confirmed the possibility to insert trifluoromethanesulfonate anions into electrolyte-free MEH-PPV; extraction of the ions was also possible, albeit with limited reversibility. Insertion of lithium ions was not observed. Adding the ion transporter trimethylolpropane ethoxylate (TMPE-OH) was seen to increase the reversibility of the process. The results also indicated different ion mobilities in doped and undoped MEH-PPV. Doping of an MEH-PPV film was shown to change the behaviour of the film from capacitive to faradaic behaviour. MEH-PPV did also show indications of two different levels of p-doping, one above 3.3 V vs. Li+/Li and the other above 3.7 V, with over-oxidation occurring at potentials over 4.1 V.

    The full text will be freely available from 2021-01-31 23:59
  • 236. He, Minglong
    et al.
    Fic, Krzysztof
    Poznan Univ Tech, Inst Chem & Tech Electrochem, PL-60695 Poznan, Poland.
    Frackowiak, Elzbieta
    Poznan Univ Tech, Inst Chem & Tech Electrochem, PL-60695 Poznan, Poland.
    Novak, Petr
    Paul Scherrer Inst, Electrochem Lab, CH-5232 Villigen, Switzerland.
    Jämstorp, 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.
    Towards more Durable Electrochemical Capacitors by Elucidating the Ageing Mechanisms under Different Testing Procedures2019In: CHEMELECTROCHEM, ISSN 2196-0216, Vol. 6, no 2, p. 566-573Article in journal (Refereed)
    Abstract [en]

    Electrical double-layer capacitors (EDLCs) commonly denoted supercapacitors are rechargeable energy storage devices with excellent power and energy delivery metrics intermediate to conventional capacitors and batteries. High-voltage aqueous electrolyte based EDLCs are particularly attractive due to their high-power capability, facile production, and environmental advantages. EDLCs should last for thousands of cycles and evaluation of future cell chemistries require long-term and costly galvanostatic cycling. Voltage holding tests have been proposed to shorten evaluation time by accelerating cell degradation processes. Whether voltage holding can replace cycling completely remains undemonstrated. In this work, a systematic investigation of the influence of testing procedure on cell performance is presented. The state-of-the-art post-mortem and operando experimental techniques are implemented to elucidate ageing mechanisms and kinetics inside EDLC cells under different testing procedures. Carbon corrosion occurring on the positively polarized electrode leads to the lower active surface area and higher oxygen content. On the contrary, an increase of surface area and micropore volume are observed on the negatively polarized electrode. Repeated galvanostatic cycles at U<1.6 V appears to facilitate the depletion of oxygen species on the positively polarized electrode in comparison with voltage holding, which indicates a more complex degradation mechanism during cycling. Caution is advised when comparing results from different test procedures.

  • 237.
    Hedman, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Characterization of reaction products in sodium-oxygen batteries: An electrolyte concentration study2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis, the discharge products formed at the cathode and the performance and cell chemistry of sodium-oxygen batteries have been studied. This was carried out using different NaOTf salt concentrations. The influence of different salt concentrations on sodium-oxygen batteries was investigated since it has been shown that increasing the salt concentration beyond conventional concentrations could result in advantages such as increased stability of the electrolytes towards decomposition, higher thermal stability and lower volatility. An increase in salt concentration has also been shown to influence the electrochemical potential window. The solubility of NaOTf was investigated in two different solvents, DME and diglyme. NaOTf was found to be more soluble in DME compared to diglyme but due to the volatile nature of DME, three different concentrations of NaOTf were prepared with diglyme as solvent. Experimentation involved discharging the batteries to either maximum or limited capacity. The discharge products were examined and characterized using XRD and SEM. The main discharge product was identified as sodium superoxide although sodium peroxide dihydrate was also identified in one battery. A trend of higher capacity and voltage plateaus with higher salt concentration was also found. The influence of trace amounts of water was suggested as one explanation as it works as a catalyst, promoting sodium superoxide cube growth due to improved transportation of superoxide. Another or contributing explanation could be a possible change in donor number with increased salt concentration, resulting in higher solubility and longer lifetime of superoxide, promoting the growth of sodium superoxide cubes.

  • 238.
    Hedman, Jonas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Morat, Julia
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Johansson, David
    Langhammer, Elin
    Björefors, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Uppsala University.
    Nanoplasmonics for online monitoring of lithium-ion batteries2017Conference paper (Other academic)
  • 239.
    Hedman, Jonas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Morát, Julia
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Johansson, David
    Langhammer, Elin
    Björefors, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Nanoplasmonics for online monitoring of lithium-ion batteries2018Conference paper (Other academic)
  • 240.
    Hellqvist Kjell, Maria
    et al.
    Kungliga tekniska högskolan.
    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, Mårten
    Kungliga tekniska högskolan.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Lindbergh, Göran
    Kungliga tekniska högskolan.
    Comparing Aging of MCMB Graphite/LiFePO4 cells at 22°C and 55°C. Electrochemical and Photoelectron Spectroscopy Studies.Manuscript (preprint) (Other academic)
  • 241.
    Hellström, Matti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Chemistry and Physics of Cu and H2O on ZnO Surfaces: Electron Transfer, Surface Triangles, and Theory2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis discusses the chemistry and physics of Cu and H2O on ZnO surfaces, based primarily on results from quantum chemical calculations. The underlying context is heterogeneous catalysis, where Cu/ZnO-mixtures are used in the industrial synthesis of methanol and in the water gas shift reaction. Electron transfer between small Cu clusters and ZnO is central to this thesis, as are the design and use of models that can describe realistic and very large-scale ZnO surface structures while still retaining the electronic nature of the system. Method and model enhancements as well as tests and validations constitute a large part of this thesis.

    The thesis demonstrates that the charges of small Cu clusters, adsorbed on the non-polar ZnO(10-10) surface, depend on whether the Cu clusters contain an even or odd number of atoms, and whether water is present (water can induce electron transfer from Cu to ZnO). On the polar Zn-terminated ZnO(0001) surface, Cu becomes negatively charged, which causes it to attract positively charged subsurface defects and to wet the ZnO(0001) surface at elevated temperatures.

    When a Cu cluster on a ZnO surface becomes positively charged, this happens because it donates an electron to the ZnO conduction band. Hence, it is necessary to use a method which describes the ZnO band gap correctly, and we show that a hybrid density functional, which includes a fraction of Hartree-Fock exchange, fulfills this requirement. When the ZnO conduction band becomes populated by electrons from Cu, band-filling occurs, which affects the adsorption energy. The band-filling correction is presented as a means to extrapolate the calculated adsorption energy under periodic boundary conditions to the zero coverage (isolated adsorbate, infinite supercell) limit.

    A part of this thesis concerns the parameterization of the computationally very efficient SCC-DFTB method (density functional based tight binding with self-consistent charges), in a multi-scale modeling approach. Our findings suggest that the SCC-DFTB method satisfactorily describes the interaction between ZnO surfaces and water, as well as the stabilities of different surface reconstructions (such as triangularly and hexagonally shaped pits) at the polar ZnO(0001) and ZnO(000-1) surfaces.

     

    List of papers
    1. Cu dimer formation mechanism on the ZnO(10(1)over-bar0) surface
    Open this publication in new window or tab >>Cu dimer formation mechanism on the ZnO(10(1)over-bar0) surface
    2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 23, p. 235302-Article in journal (Refereed) Published
    Abstract [en]

    The formation of Cu dimers on the ZnO(10 (1) over bar0) surface has been studied using hybrid density functional theory. Depending on the adsorption site, Cu atoms are found to adsorb with either oxidation state 0 or +1. In the latter case, the Cu atom has donated an electron to the ZnO conduction band. The two modes of adsorption display similar stability at low coverages, while at higher coverages the neutral species is more stable. Single Cu atoms diffuse across the ZnO(10 (1) over bar0) surface with small barriers of migration (0.3-0.4 eV) along ZnO[1 (2) over bar 10], repeatedly switching their oxidation states, while the barrier along ZnO[0001] is significantly higher (>1.5 eV). The formation of a Cu dimer from two adsorbed Cu atoms is energetically favorable with two competing structures of similar stability, both being charge neutral. The minimum energy paths for Cu atom diffusion and dimer formation are characterized by at least one of the two Cu atoms being in oxidation state 0.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-191772 (URN)10.1103/PhysRevB.86.235302 (DOI)000311806300007 ()
    Available from: 2013-01-15 Created: 2013-01-14 Last updated: 2019-02-19Bibliographically approved
    2. Small Cu Clusters Adsorbed on ZnO(10(1)over-bar0) Show Even-Odd Alternations in Stability and Charge Transfer
    Open this publication in new window or tab >>Small Cu Clusters Adsorbed on ZnO(10(1)over-bar0) Show Even-Odd Alternations in Stability and Charge Transfer
    2014 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 12, p. 6480-6490Article in journal (Refereed) Published
    Abstract [en]

    Using hybrid density functional theory, we investigate structural and electronic properties of small Cu-n clusters (with n <= 9) adsorbed on the nonpolar ZnO(10 (1) over bar0) surface. The Cu clusters grow in a planar fashion up to a size of six atoms, after which the clusters take on a polyhedral shape. We find even odd alternations with respect to both duster stability (for n = 1-6) and cluster charge, as a function of the number of atoms. Even-numbered dusters are always charge-neutral, while odd-numbered clusters can become positively charged by donation of an electron to the ZnO conduction band, which can be traced back to the fact that the ionization energies of odd-numbered gas-phase Cu dusters are lower than for even-numbered ones. The most stable adsorbed odd-numbered clusters are neutral and planar for n <= 3 and positively charged and polyhedral for n >= 7. For n = 5, both neutral planar and positively charged polyhedral configurations are similarly stable.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-224359 (URN)10.1021/jp412694y (DOI)000333578300057 ()
    Available from: 2014-05-12 Created: 2014-05-09 Last updated: 2019-02-19Bibliographically approved
    3. Water-Induced Oxidation and Dissociation of Small Cu Clusters on ZnO(101̅0)
    Open this publication in new window or tab >>Water-Induced Oxidation and Dissociation of Small Cu Clusters on ZnO(101̅0)
    2015 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 3, p. 1382-1390Article in journal (Refereed) Published
    Abstract [en]

    The interaction between water molecules and small Cu clusters (up to a size of four atoms) adsorbed on the nonpolar ZnO(10 (1) over bar0) surface has been studied using hybrid density functional theory. We find that the water molecules can give rise to different scenarios: (i) In contrast to water adsorption on the clean ZnO(10 (1) over bar0) surface, which occurs molecularly, the first water molecule often preferentially dissociates upon adsorption on the Cu cluster, which may be a key step in the watergas shift reaction. (ii) While the adsorption of the first water molecule on the adsorbed Cu clusters is always more favorable than the adsorption on the bare ZnO surface, the opposite is true for the second molecule. (iii) As a water molecule adsorbs on the adsorbed Cu atom, it induces charge transfer between the Cu and the ZnO, so that an electron from the Cu atom populates the ZnO conduction band (giving an oxidized Cu species). (iv) Water molecule adsorption on the adsorbed Cu trimer results in a spontaneous dissociation of the Cu trimer into an adsorbed dimer and an adsorbed atom, after which the water molecule adsorbs on the atom, again resulting in the Cu-ZnO charge transfer. We also show that the use of a hybrid density functional gives qualitatively different results as compared to a semilocal density functional for this system, and we explain this in terms of the underestimation of the ZnO band gap obtained with the semilocal functional.

    National Category
    Theoretical Chemistry Physical Chemistry Materials Chemistry
    Identifiers
    urn:nbn:se:uu:diva-236298 (URN)10.1021/jp509501z (DOI)000348491900013 ()
    Available from: 2014-11-17 Created: 2014-11-17 Last updated: 2019-02-19Bibliographically approved
    4. Cu wets the polar ZnO(0001)-Zn surface because of interaction with subsurface defects
    Open this publication in new window or tab >>Cu wets the polar ZnO(0001)-Zn surface because of interaction with subsurface defects
    Show others...
    (English)Article in journal (Refereed) Submitted
    National Category
    Materials Chemistry Theoretical Chemistry Inorganic Chemistry Physical Chemistry Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-236300 (URN)
    Available from: 2014-11-20 Created: 2014-11-17 Last updated: 2015-01-14
    5. Band-Filling Correction Method for Accurate Adsorption Energy Calculations: A Cu/ZnO Case Study
    Open this publication in new window or tab >>Band-Filling Correction Method for Accurate Adsorption Energy Calculations: A Cu/ZnO Case Study
    2013 (English)In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 9, no 11, p. 4673-4678Article in journal (Refereed) Published
    Abstract [en]

    We present a simple method, the “band-filling correction”, to calculate accurate adsorption energies (Eads) in the low coverage limit from finite-size supercell slab calculations using DFT. We show that it is necessary to use such a correction if charge transfer takes place between the adsorbate and the substrate, resulting in the substrate bands either filling up or becoming depleted. With this correction scheme, we calculate Eads of an isolated Cu atom adsorbed on the ZnO(101̅0) surface. Without the correction, the calculated Eads is highly coverage-dependent, even for surface supercells that would typically be considered very large (in the range from 1 nm × 1 nm to 2.5 nm × 2.5 nm). The correction scheme works very well for semilocal functionals, where the corrected Eads is converged within 0.01 eV for all coverages. The correction scheme also works well for hybrid functionals if a large supercell is used and the exact exchange interaction is screened.

    Place, publisher, year, edition, pages
    Columbus, Ohio: American Chemical Society (ACS), 2013
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-213142 (URN)10.1021/ct400645v (DOI)000327044500001 ()
    Available from: 2013-12-18 Created: 2013-12-18 Last updated: 2019-02-19Bibliographically approved
    6. An SCC-DFTB Repulsive Potential for Various ZnO Polymorphs and the ZnO-Water System
    Open this publication in new window or tab >>An SCC-DFTB Repulsive Potential for Various ZnO Polymorphs and the ZnO-Water System
    Show others...
    2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 33, p. 17004-17015Article in journal (Refereed) Published
    Abstract [en]

    We have developed an efficient scheme for the generation of accurate repulsive potentials for self-consistent charge density-functional-based tight-binding calculations, which involves energy-volume scans of bulk polymorphs with different coordination numbers. The scheme was used to generate an optimized parameter set for various ZnO polymorphs. The new potential was subsequently tested for ZnO bulk, surface, and nanowire systems as well as for water adsorption on the low-index wurtzite (10 (1) over bar0) and (11 (2) over bar0) surfaces. By comparison to results obtained at the density functional level of theory, we show that the newly generated repulsive potential is highly transferable and capable of capturing most of the relevant chemistry of ZnO and the ZnO/water interface.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-208368 (URN)10.1021/jp404095x (DOI)000323593100028 ()
    Available from: 2013-09-30 Created: 2013-09-30 Last updated: 2019-02-19Bibliographically approved
    7. Large-scale SCC-DFTB calculations of reconstructed polar ZnO surfaces
    Open this publication in new window or tab >>Large-scale SCC-DFTB calculations of reconstructed polar ZnO surfaces
    Show others...
    2014 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 628, p. 50-61Article in journal (Refereed) Published
    Abstract [en]

    We present a theoretical study of a range of surface defects for the most abundant polar ZnO(0001)/(000 (1) over bar) surfaces using a tight binding approach with self-consistent charges (SCC-DFTB). We find that a combination of triangular pits at the Zn-terminated surface and a strongly ordered hexagonal defect pattern at the O-terminated surface constitutes a very stable reconstruction, in excellent agreement with experimental findings. On the whole, the SCC-DFTB method describes the polar surfaces of ZnO very well, and at a low computational cost which allows for the investigation of larger - and more realistic - surface structures compared to previous studies. Such large-scale calculations show that, at the Zn-terminated surface, the reconstruction results in a high density of one-layer deep triangular pit-like defects and surface vacancies which allow for a high configurational freedom and a vast variety of defect motifs. We also present extensive tests of the performance of the SCC-DFTB method in comparison with DFT results.

    Keywords
    ZnO, Polar surfaces, SCC-DFTB, DFT
    National Category
    Condensed Matter Physics Chemical Sciences
    Identifiers
    urn:nbn:se:uu:diva-230913 (URN)10.1016/j.susc.2014.05.001 (DOI)000340221200008 ()
    Available from: 2014-09-05 Created: 2014-09-01 Last updated: 2019-02-19Bibliographically approved
  • 242.
    Hellström, Matti
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Beinik, Igor
    Aarhus Univ, Interdisciplinary Nanosci Ctr iNANO, Aarhus, Denmark..
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Lauritsen, Jeppe V.
    Aarhus Univ, Interdisciplinary Nanosci Ctr iNANO, Aarhus, Denmark..
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Subsurface hydrogen bonds at the polar Zn-terminated ZnO(0001) surface2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 94, no 24, article id 245433Article in journal (Refereed)
    Abstract [en]

    The role of hydrogen and other defects in the stabilization of polar oxide interfaces is a matter of significant fundamental and practical interest. Using experimental (scanning tunneling microscopy, x-ray photoelectron spectroscopy) and theoretical (density functional theory) surface science techniques, we find that the polar Zn-terminated ZnO(0001) surface becomes excessively Zn deficient during high-temperature annealing (780 K) in ultrahigh vacuum (UHV). The Zn vacancies align themselves into rows parallel to the [10 (1) over bar 10] direction, and the remaining surface Zn ions alternately occupy wurtzite (hcp) and zinc-blende (fcc) lattice positions, giving a characteristic "striped" c(root 12 x root 12) R30 degrees surface morphology with three types of rows: wurtzite Zn, zinc-blende Zn, and Zn vacancies. Interstitial H plays a central role in such a reconstruction, as it helps to compensate the excessive Zn deficiency. We propose a model in which hydrogen occupies positions in half of the vacancy rows to form hydroxide ions that can participate in hydrogen bonds in the O subsurface layer as a result of the mixed wurtzite/zinc-blende stacking.

  • 243.
    Hellström, Matti
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Jorner, Kjell
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Bryngelsson, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Huber, Stefan E.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Kullgren, Jolla
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Frauenheim, Thomas
    Broqvist, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    An SCC-DFTB Repulsive Potential for Various ZnO Polymorphs and the ZnO-Water System2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 33, p. 17004-17015Article in journal (Refereed)
    Abstract [en]

    We have developed an efficient scheme for the generation of accurate repulsive potentials for self-consistent charge density-functional-based tight-binding calculations, which involves energy-volume scans of bulk polymorphs with different coordination numbers. The scheme was used to generate an optimized parameter set for various ZnO polymorphs. The new potential was subsequently tested for ZnO bulk, surface, and nanowire systems as well as for water adsorption on the low-index wurtzite (10 (1) over bar0) and (11 (2) over bar0) surfaces. By comparison to results obtained at the density functional level of theory, we show that the newly generated repulsive potential is highly transferable and capable of capturing most of the relevant chemistry of ZnO and the ZnO/water interface.

  • 244.
    Hellström, Matti
    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.
    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.
    Water-Induced Oxidation and Dissociation of Small Cu Clusters on ZnO(101̅0)2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 3, p. 1382-1390Article in journal (Refereed)
    Abstract [en]

    The interaction between water molecules and small Cu clusters (up to a size of four atoms) adsorbed on the nonpolar ZnO(10 (1) over bar0) surface has been studied using hybrid density functional theory. We find that the water molecules can give rise to different scenarios: (i) In contrast to water adsorption on the clean ZnO(10 (1) over bar0) surface, which occurs molecularly, the first water molecule often preferentially dissociates upon adsorption on the Cu cluster, which may be a key step in the watergas shift reaction. (ii) While the adsorption of the first water molecule on the adsorbed Cu clusters is always more favorable than the adsorption on the bare ZnO surface, the opposite is true for the second molecule. (iii) As a water molecule adsorbs on the adsorbed Cu atom, it induces charge transfer between the Cu and the ZnO, so that an electron from the Cu atom populates the ZnO conduction band (giving an oxidized Cu species). (iv) Water molecule adsorption on the adsorbed Cu trimer results in a spontaneous dissociation of the Cu trimer into an adsorbed dimer and an adsorbed atom, after which the water molecule adsorbs on the atom, again resulting in the Cu-ZnO charge transfer. We also show that the use of a hybrid density functional gives qualitatively different results as compared to a semilocal density functional for this system, and we explain this in terms of the underestimation of the ZnO band gap obtained with the semilocal functional.

  • 245.
    Hellström, Matti
    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.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Uppsala Univ, Dept Chem Angstrom, SE-75121 Uppsala, Sweden..
    Treatment of Delocalized Electron Transfer in Periodic and Embedded Cluster DFT Calculations: The Case of Cu on ZnO (10(1)over-bar0)2015In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 36, no 32, p. 2394-2405Article in journal (Refereed)
    Abstract [en]

    We assess the consequences of the interface model-embedded-cluster or periodic-slab model-on the ability of DFT calculations to describe charge transfer (CT) in a particularly challenging case where periodic-slab calculations indicate a delocalized charge-transfer state. Our example is Cu atom adsorption on ZnO(10 (1) over bar0), and in fact the periodic slab calculations indicate three types of CT depending on the adsorption site: full CT, partial CT, and no CT. Interestingly, when full CT occurs in the periodic calculations, the calculated Cu atom adsorption energy depends on the underlying ZnO substrate supercell size, since when the electron enters the ZnO it delocalizes over as many atoms as possible. In the embedded-cluster calculations, the electron transferred to the ZnO delocalizes over the entire cluster region, and as a result the calculated Cu atom adsorption energy does not agree with the value obtained using a large periodic supercell, but instead to the adsorption energy obtained for a periodic supercell of roughly the same size as the embedded cluster. Different density functionals (of GGA and hybrid types) and basis sets (local atom-centered and plane-waves) were assessed, and we show that embedded clusters can be used to model Cu adsorption on ZnO(10 (1) over bar0), as long as care is taken to account for the effects of CT.

  • 246.
    Hellström, Matti
    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.
    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.
    Band-Filling Correction Method for Accurate Adsorption Energy Calculations: A Cu/ZnO Case Study2013In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 9, no 11, p. 4673-4678Article in journal (Refereed)
    Abstract [en]

    We present a simple method, the “band-filling correction”, to calculate accurate adsorption energies (Eads) in the low coverage limit from finite-size supercell slab calculations using DFT. We show that it is necessary to use such a correction if charge transfer takes place between the adsorbate and the substrate, resulting in the substrate bands either filling up or becoming depleted. With this correction scheme, we calculate Eads of an isolated Cu atom adsorbed on the ZnO(101̅0) surface. Without the correction, the calculated Eads is highly coverage-dependent, even for surface supercells that would typically be considered very large (in the range from 1 nm × 1 nm to 2.5 nm × 2.5 nm). The correction scheme works very well for semilocal functionals, where the corrected Eads is converged within 0.01 eV for all coverages. The correction scheme also works well for hybrid functionals if a large supercell is used and the exact exchange interaction is screened.

  • 247.
    Hellström, Matti
    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.
    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.
    Cu dimer formation mechanism on the ZnO(10(1)over-bar0) surface2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 23, p. 235302-Article in journal (Refereed)
    Abstract [en]

    The formation of Cu dimers on the ZnO(10 (1) over bar0) surface has been studied using hybrid density functional theory. Depending on the adsorption site, Cu atoms are found to adsorb with either oxidation state 0 or +1. In the latter case, the Cu atom has donated an electron to the ZnO conduction band. The two modes of adsorption display similar stability at low coverages, while at higher coverages the neutral species is more stable. Single Cu atoms diffuse across the ZnO(10 (1) over bar0) surface with small barriers of migration (0.3-0.4 eV) along ZnO[1 (2) over bar 10], repeatedly switching their oxidation states, while the barrier along ZnO[0001] is significantly higher (>1.5 eV). The formation of a Cu dimer from two adsorbed Cu atoms is energetically favorable with two competing structures of similar stability, both being charge neutral. The minimum energy paths for Cu atom diffusion and dimer formation are characterized by at least one of the two Cu atoms being in oxidation state 0.

  • 248.
    Hellström, Matti
    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.
    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.
    Small Cu Clusters Adsorbed on ZnO(10(1)over-bar0) Show Even-Odd Alternations in Stability and Charge Transfer2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 12, p. 6480-6490Article in journal (Refereed)
    Abstract [en]

    Using hybrid density functional theory, we investigate structural and electronic properties of small Cu-n clusters (with n <= 9) adsorbed on the nonpolar ZnO(10 (1) over bar0) surface. The Cu clusters grow in a planar fashion up to a size of six atoms, after which the clusters take on a polyhedral shape. We find even odd alternations with respect to both duster stability (for n = 1-6) and cluster charge, as a function of the number of atoms. Even-numbered dusters are always charge-neutral, while odd-numbered clusters can become positively charged by donation of an electron to the ZnO conduction band, which can be traced back to the fact that the ionization energies of odd-numbered gas-phase Cu dusters are lower than for even-numbered ones. The most stable adsorbed odd-numbered clusters are neutral and planar for n <= 3 and positively charged and polyhedral for n >= 7. For n = 5, both neutral planar and positively charged polyhedral configurations are similarly stable.

  • 249.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    DFT-based multi-scale modelling of materials and nanoparticles2017Conference paper (Other academic)
    Abstract [en]

    Redox-active metal oxide surfaces and interfaces ‒ such as electrodes, catalysts, and sensors ‒ play crucial roles in our society and in the development of new materials and greener technologies. In the scientific literature, a full arsenal of experimental methods are being used to help to characterize such materials interfaces. Simultaneously, the (ever-increasing) theoretical materials studies in the literature provide structural and mechanistic information at a detail that is difficult to beat by experiments – but are the models accurate enough? There are at least two major challenges in materials modelling: (i) how to build structural models that capture the complexity and imperfections of the real systems, and (ii) how to find good enough interaction models (say a DFT functional [1] or a force-field). Here mimicking the interactions and chemical properties of materials without explicit electrons present is a formidable task, especially when the transfer of electrons is closely coupled to the material's functionality, as is the case for redox-active metal oxides.

    I will discuss some of our efforts in the development of a multiscale modelling approach for surfaces and interfaces of metal oxides (e.g. CeO2, ZnO, MgO) – with and without interacting molecules (e.g. O2 and water).

    In summary, we combine a range of theoretical methods including DFT [2], tight-binding-DFT [3], and reactive force-field simulations [4] in a consistent multi-scale approach to examine the properties of oxide nanosystems. We generate images and spectra to make direct comparisons with the experimental counterparts (e.g. IRRAS spectra [5]), but we also generate properties that cannot be measured by experiments such as the water dipole moment enhancement on a surface (often much larger [1] than in liquid water!). I will also inform about the European Materials Modelling Council (https://emmc.info/), and our efforts to promote the use and quality of materials modelling in industry; the EMMC is open to everyone interested.

     

    References

    [1] G. G. Kebede, D. Spångberg, P. D. Mitev, P. Broqvist, K. Hermansson, "Comparing van der Waals DFT methods for water on NaCl(001) and MgO(001), The Journal of Chemical Physics 146, 064703 (2017).

     [2] M. Hellström, D. Spångberg, K. Hermansson, "Treatment of Delocalized Electron Transfer in Periodic and Embedded Cluster DFT Calculations: The Case of Cu on ZnO (10-10)", Journal of Computational Chemistry 36, 2394 (2015).

     [3] J. Kullgren, M. J. Wolf, K. Hermansson, Ch. Köhler, B. Aradi,Th. Frauenheim, and P. Broqvist, "Self-Consistent-Charge Density-Functional Tight-Binding (SCC-DFTB) Parameters for Ceria in 0D to 3D". J. Phys. Chem. C  121, 4593−4607 (2017).

     [4] P. Broqvist, J. Kullgren, M. J. Wolf, A. C. T. van Duin, K. Hermansson, "A ReaxFF force-field for ceria bulk, surfaces and nanoparticles", J. Phys. Chem. C 119, 13598 (2015).

     [5] S. Hu, Z. Wang, A. Mattsson, L. Österlund, K. Hermansson, "Simulation of IRRAS Spectra for Molecules on Oxide Surfaces: CO on TiO2(110)", J. Phys. Chem. C 119, 5403 (2015).

  • 250.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hydrogen bonds – on the move2017Conference paper (Other academic)
    Abstract [en]

    Hydrogen bonds are quite special bonds: they are strong enough to significantly modify a molecule’s properties and hold it in place in a structure, yet weak enough to be distorted or broken fairly easily by an external stimulus, an incoming reactant or a by-passing molecule. Thus, its place between the strong normal chemical bonds and the weakest van der Waals interactions makes the H-bond a very versatile and useful actor – as demonstrated by nature in numerous examples from Biology to Materials Science.

    This functional diversity is a unique and important feature, and an opportunity, but also a challenge since no controlled use of the remarkable properties of H-bonds can be achieved without a thorough understanding of their multi-functionality. Here computational approaches at a range of time and length scales can be of immense help as they provide results of unmatched detail, as well as the needed atomic-level understanding ‒ if the computational models and methods are accurate and realistic enough. Many such efforts can be found in the literature.*)  At the same time, new powerful experimental characterization techniques emerge and new infrastructures are under development in Europe. The interplay between experiment and theory is becoming even more compelling as the dimensions of experimental and computational targets approach each other. **)

     

    *)  Some published [1,2,3] and unpublished examples of our own efforts here for H-bonded systems (solutions, solids, surfaces) will also be mentioned.

    *) Here I will also inform about new European initiatives on this topic such as the European Materials Modelling Council.

     

     

    References

     

    [1] The vibrating hydroxide ion in water  (Perspectives article), K. Hermansson, Ph.A. Bopp, D. Spångberg, Lj. Pejov, I. Bako, P. D. Mitev; Chemical Physics Letters 514, (2011), 1.

    [2] H-bond and Electric Field Correlations for Water in Highly Hydrated Crystals (invited), A. Sen, P. Mitev, A. Eriksson, K. Hermansson, Int. J. Quantum Chemistry 116, (2016), 57.

    [3] Comparing van der Waals DFT methods for water on NaCl(001) and MgO(001), G. G. Kebede, D. Spångberg, P.D. Mitev, P. Broqvist, and K.Hermansson, J. Chem. Phys. 146, (2017), 064703.

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