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  • 251.
    Niklasson, Gunnar A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Norling, AnnaKarin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Berggren, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Charge transport between localized states in lithium-intercalated amorphous tungsten oxide2007In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 353, no 47-51, p. 4376-4379Article in journal (Refereed)
    Abstract [en]

    We report on electron transport in amorphous tungsten oxide films, prepared by dc magnetron sputtering and subsequently electrochemically intercalated with lithium. The ion–electron intercalation process allows us to change the position of the Fermi level in a controlled way and to determine the density-of-states in the conduction band. We present a new method to determine the localization length of the electron states in disordered materials. The method is based on measurements of the electronic density-of-states together with electrical resistance in the variable range hopping regime. We find that the electronic states of amorphous tungsten oxide are localized up to about 1.3 eV into the conduction band, where an insulator-metal transition occurs. The localization length was determined on the insulating side of the transition and the estimated scaling exponent is consistent with the scaling theory of localization.

  • 252.
    Niklasson, Gunnar A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Norling, Anna-Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Ion Physics.
    Berggren, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Optical properties of amorphous tungsten oxide films: Effect of stoichiometry2008In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 100, no 8, p. 082023-Article in journal (Refereed)
    Abstract [en]

    The optical properties of sputter deposited amorphous tungsten oxide films have been measured in-situ during slow electrochemical cycling in a lithium containing electrolyte. Amorphous films exhibit coloration under Li insertion and bleaching under Li extraction. Substoichiometric films show almost reversible optical changes already in the first electrochemical cycle and are completely reversible thereafter. Tungsten oxide films sputtered in a large excess of oxygen were found to be slightly overstoichiometric, as determined by Rutherford Backscattering Spectrometry. They exhibit irreversible charge transfer and coloration in the first cycle. Thereafter they cannot be completely bleached and exhibit transmittance contrast between coloured and partially bleached states. The irreversible colouration of the stoichiometric films is associated with a feature at 2.6 to 2.9 eV vs. Li in electrochemical measurements. Possible chemical reactions giving rise to this behaviour are discussed.

  • 253.
    Niklasson, Gunnar A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wen, Rui-Tao
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Arvizu, Miguel A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Malmgren, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Pehlivan, Esat
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Morales-Luna, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochemical degradation and rejuvenation of electrochromic tungsten oxide thin films2016Conference paper (Refereed)
    Abstract [en]

    Tungsten oxide is the most widely used cathodic electrochromic material for smart window applications. One of the main challenges for smart window technology is to ensure the durability of the electrochromic devices over a service life of more than 20 years. Hence, in order to facilitate large-scale practical application of electrochromic materials, their degradation under operating conditions must be better understood and preferably prevented. In this paper we address these issues by three different approaches. First we show that the electrochemical ageing of electrochromic tungsten oxide, under stressed conditions, can be described by stretched exponential kinetics. The goal of such accelerated ageing studies is eventually to be able to predict service life using this empirical relationship. Secondly, we report on a recently discovered rejuvenation processes for restoring aged coatings to their initial state. During severe ageing of the coatings, Li ions are trapped in the film, and subsequently these ions can be released by application of a high electrochemical potential for a few hours. We estimate activation energies for the release process from chronoamperometric measurements during rejuvenation. Thirdly we address the issue of the growth of a solid-electrolyte interface. Impedance spectroscopy measurements on tungsten oxide films were used to obtain the interfacial charge transfer resistance. After the films had been subjected to low potentials known to induce degradation, the charge transfer resistance in the usual operating range showed a marked increase. This is interpreted as a signature of the development of a solid-electrolyte interface. A similar increase of the charge transfer resistance has been observed in electrochromic devices subjected to accelerated aging at an elevated temperature of 80oC for a thousand cycles.

  • 254.
    Niklasson, Gunnar A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wen, Rui-Tao
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromic oxides: Electrochemical density of states, degradation kinetics and rejuvenation of degraded films2015Conference paper (Refereed)
    Abstract [en]

    Electrochromic (EC) materials change their optical properties upon the application of a voltage signal. EC devices are of interest for energy efficient smart windows, as well as for a number of niche applications. An EC device can be viewed as a thin-film electrical battery whose charging state is manifested by optical absorption. The central part of the device comprises EC thin films based on amorphous tungsten oxide (WO3) and nano-crystalline nickel oxide (NiOx) joined by a layer of polymer electrolyte. This three-layer arrangement is positioned between transparent and electrically conducting thin films of indium tin oxide (In2O3:Sn; ITO) backed by polyester foils. Applying a voltage between the ITO films induces transport of ions between the WO3 and NiO films, together with charge compensating electron transport through the outer circuit. Insertion of ions and electrons in WO3 and extraction of them from NiO lead to enhanced optical absorption. In this paper we report novel developments regarding the electronic density of states (DOS), the ageing kinetics and the rejuvenation of aged EC materials.

     

    The optical absorption in EC oxides is due to electronic transitions between localized states close to the band edges. In order to model the optical absorption it is necessary to have a good understanding of the electronic DOS. We have found that it is possible to derive an effective DOS from electrochemical measurements, in particular from measurements of quasi-steady-state potential curves, during the ion/electron insertion process. The obtained “electrochemical DOS” exhibits good agreement with state-of-the-art density functional calculations of the DOS for a number of amorphous and nano-crystalline oxides.

     

    EC devices are prone to slowly degrade under repeated electrochemical cycling and a thorough understanding of the kinetics of this degradation is necessary in order to estimate the lifetime of smart window products. The ageing is often ascribed to irreversible incorporation of ions at the film surfaces or inside the film. We present results which show that the degradation displays dispersive kinetics and the chemical reaction behind the process can be modelled by using a rate constant with power-law time dependence. Results obtained for WO3 and NiO thin films show both similarities and differences.

     

    We have very recently found that rejuvenation of previously degraded WO3 films is possible. Films with heavily degraded charge capacity and optical switching were subjected to a galvanostatic treatment for a certain time. After subjecting the film to a small current for a number of hours, it regained its initial charge capacity and optical properties. The rejuvenation is ascribed to de-trapping of ions from deep traps, induced by a high electrochemical potential over the film.

     

    The optical absorption and switching as well as the durability of EC material are key issues for the successful commercial development of smart windows. The results presented here pave the way for an increased understanding of the optical switching as well as of the degradation kinetics. The possibility of rejuvenating degraded films is highly exciting, and further studies are necessary in order to develop this idea into a practical process.

     

  • 255.
    Niklasson, Gunnar A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wen, Rui-Tao
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Materials Processing Center, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
    Qu, Hui-Ying
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, China.
    Arvizu, Miguel A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Durability of electrochromic films: Aging kinetics and rejuvenation2017In: ECS Transactions, Electrochemical Society, 2017, Vol. 77, p. 1659-1669Conference paper (Refereed)
    Abstract [en]

    A major challenge for energy-efficient smart window technology is to ensure the durability of electrochromic (EC) devices over aservice life of more than 20 years. In this paper, we report recent results from a fundamental study of the aging kinetics of EC tungsten oxide and nickel oxide thin films and describe electrochemical rejuvenation mechanisms that are able to restore the films to their initial state. The aging kinetics displays an approximate power-law decrease of the charge capacity as a function of cycle number. This decay of charge capacity can be understood in terms of models built on so-called dispersive chemical kinetics. Tungsten oxide and nickel oxide EC films can be rejuvenated by applying a high electrochemical potential or a small constant current. Trapped ions in the bulk or at the surface of the films can be released by these procedures.

  • 256.
    Niklasson, Gunnar A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wiebel, Sabine
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    van Veldhuizen, Elbert Jan
    Uppsala University, The Svedberg Laboratory.
    Nilsson, Leif
    Uppsala University, The Svedberg Laboratory.
    Westerberg, Lars
    Uppsala University, The Svedberg Laboratory.
    Surface conduction in porous polycarbonate membranes1998Report (Other academic)
  • 257.
    Niklasson, Gunnar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Abatte, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Karlstads Universitet.
    Rojas González, Edgar Alonso
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Arvizu, Miguel A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Qu, Hui-Ying
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochemical rejuvenation of Tungsten oxide electrochromic thin films: Evidence from impedance spectroscopy2018In: 13th International Meeting on Electrochromism, IME-13: Book of Abstracts, 2018, p. 11-, article id IN-3Conference paper (Refereed)
    Abstract [en]

    A major challenge for energy-efficient smart window technology is to ensure the durability of electrochromic (EC) devices capable of render a service life significantly higher than 20 years. The development of more durable EC materials would also make it possible to increase the transmittance contrast between bleached and colored states without the risk of limiting service life. Recently, it has been shown that degraded EC coatings can be restored to their initial state by electrochemical rejuvenation treatments.1,2 In addition, it was found that tungsten oxide EC films could gain vastly improved durability after extended electrochemical treatments at high applied potentials.3 In this paper we present an attempt to unravel the complex mechanisms behind high potential rejuvenation and durability-enhancing treatments. We study EC amorphous tungsten oxide, which is the most commonly used EC oxide. It is used in most commercial device designs, often in combination with a nickel oxide-based complementary EC layer.

    Amorphous tungsten oxide thin films were deposited by sputtering onto conducting indium-tin oxide (ITO) coated glass substrates. Ion intercalation and diffusion in the films were studied by electrochemical impedance spectroscopy measurements in the frequency range 10 mHz-10 kHz and for potentials between 2.0 and 3.3 V vs. Li/Li+, using the film as working electrode in a Li+ containing electrolyte. Measurements were carried out for as-deposited EC tungsten oxide films, degraded and rejuvenated films as well as durability-enhanced WOx films. The impedance data were in good agreement with a Randles-type equivalent circuit containing an anomalous diffusion element.4 In this study we focus on changes at the electrolyte/EC film and EC film/ITO interfaces during degradation and after different electrochemical treatments.

    The most notable changes were associated with the high frequency and charge transfer resistances. The high frequency resistance increased significantly during degradation as well as extended rejuvenation treatments; a similar effect was observed in durability-enhanced WOx films. This might indicate compositional or chemical changes in the ITO backing or at the film/ITO interface. The charge transfer resistance associated with the electrolyte/film interface also increased after treatments, but in addition exhibited a strong potential dependence. The appearance of a second high-frequency process after rejuvenation is considered to be more interesting. Possible explanations include an additional adsorption step preceding ion intercalation into the EC film, or alternatively the appearance of a solid-electrolyte interphase layer of the type commonly observed in Li-ion batteries.

    Ion diffusion coefficients were not significantly different for rejuvenated EC films as compared to the as-deposited ones. On the other hand degraded films exhibited a completely different impedance response, which could be interpreted as being due to parasitic chemical reactions in the system.

    An increased understanding of ageing and rejuvenation processes will facilitate the search for more durable EC materials and preliminary results suggest that interfacial characteristics may influence durability. Eventually, improved EC coatings will be important for large-scale practical application of electrochromic materials, for example in smart windows.

     

     

    References

    [1]     R.-T. Wen, C.G. Granqvist, G.A. Niklasson, Nature Mater., 14, 996 (2015).

    [2]     H.-Y. Qu, D. Primetzhofer, M.A. Arvizu, Z. Qiu, U. Cindemir, C.G. Granqvist, G.A. Niklasson, ACS Appl. Mater. Interf., 9, 42420 (2017).

    [3]     M.A. Arvizu, H.-Y. Qu, G.A. Niklasson, C.G. Granqvist, Thin Solid Films, 653, 1 (2018).

    [4]     S. Malmgren, S.V. Green, G.A. Niklasson, Electrochim. Acta, 247, 252 (2017).

     

  • 258.
    Niklasson, Gunnar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Boström, T. K.
    Tuncer, E.
    Spectral density analysis of the optical properties of Ni-Al2O3 nanocomposite films2011In: Proceedings of SPIE, Vol. 8168, no 8168-27, p. 27-Article in journal (Refereed)
  • 259.
    Niklasson, Gunnar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromic and thermochromic oxide materials2018In: Towards Oxide-Based Electronics: Spring Meeting 2018 MP1308 TO-BE COST Action, 2018, p. 31-Conference paper (Other academic)
    Abstract [en]

    Electrochromic (EC) and thermochromic (TC) oxides have important applications in devices for modulating optical properties. EC thin films change their optical transmittance of visible and solar radiation under electrically stimulated insertion/extraction of ions. A typical device sustains ion transport between two EC oxide films via an electrolyte; one film (typically W-oxide-based) darkens under ion insertion and the other film (typically Ni-oxide-based) darkens under ion extraction. The film/electrolyte/film three-layer construction is positioned between transparent electrical conductors which normally are oxide-based films. The main application of these devices is in “smart” windows and glass facades for energy efficient buildings. Future developments include multi-component oxides with optimized optical properties and superior electrochemical durability. TC oxides have qualitatively different optical properties when their temperature is below/above a “critical” value τc. The most widely used TC materials are based on VO2; thin films are infrared transmitting/reflecting at low/high temperature while the luminous transmittance remains moderately high. Corresponding nanoparticle composites are transparent/near-infrared absorbing at low/high temperature. TC thin films and nanoparticles can be used in windows which admit solar energy preferentially when there is a heating demand in the building. Future developments include multicomponent VO2-based materials with additions for adjusting τc to near room temperature and to decrease the luminous absorptance, integration of these materials in multilayer constructions and nanoparticle composites, and implementation of oxidation-protecting coatings. Multi-functional devices—e.g., with EC and TC properties—yield interesting future scenarios.

  • 260.
    Niklasson, Gunnar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lansåker, Pia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Li, Shu-Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Plasmonic Thin Films for Application in Improved Chromogenic Windows2016In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 682, no 012003, p. 1-9Article in journal (Refereed)
    Abstract [en]

    Nanocomposites consisting of noble metal nanoparticles in a transparent matrix exhibit plasmonic absorption in the visible wavelength range, and conducting oxide nanoparticles display a localized plasma absorption in the near infrared. The optical properties of nanocomposites are commonly modelled by effective medium theories, which describe the effective dielectric function of the composite using as input the dielectric functions of the constituents and their respective volume fractions. Plasmonic effects can be exploited in the design of energy-efficient windows in order to obtain improved performance. Electrochromic coatings that switch in the near infrared make use of the modulation of the plasma absorption of oxide nanoparticles due to charge density modulation induced by an external voltage. Plasmonic thermochromic switching in the near infrared has the potential to be significantly larger than in the case of a thin film. Very thin noble metal films are an interesting alternative to conducting oxides as transparent contacts to electrochromic devices. However, in this latter case plasmonic effects are to be avoided rather than exploited.

  • 261.
    Niklasson, Gunnar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Li, S.- Y.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Thermochromic Vanadium Oxide Thin Films: Electronic and Optical Properties2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 559, no 012001, p. 012001/1-012001/8Article in journal (Refereed)
    Abstract [en]

    ABSTRACT: Vanadium dioxide, VO2, is a widely studied thermochromic material with potential applications in energy efficient window technology. It undergoes a first-order metal-to- insulator transition, accompanied by a crystal structure transformation from monoclinic to tetragonal rutile, at a critical temperature of 68 °C. Below this temperature, VO2 is semiconducting and infrared transmitting whereas it is metallic and infrared reflecting above the transition temperature. However, in order to achieve significant thermochromic switching, the luminous transmittance of thin films will typically be less than 50%. Here we report on recent research to improve the luminous transmittance as well as the transmittance change at the transition temperature. We systematically evaluate the effect of antireflection coatings, doping with Mg and the performance of coatings comprising thermochromic nanoparticles in a transparent matrix. The last option is shown to give the best performance and holds great promise for practical applications.

    Full-text · Article · Nov 2014 · Journal of Physics Conference Series

  • 262.
    Niklasson, Gunnar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Norling, A. K.
    Possnert, G.
    Berggren, L.
    Optical properties of amorphous tungsten oxide films: Effect of stoichiometry2008In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 100, no 8, p. 082023-Article in journal (Refereed)
  • 263.
    Niklasson, Gunnar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Qiu, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Bayrak Pehlivan, Ilknur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Impedance spectroscopy of water splitting reactions on nanostructured metal-based catalysts2019In: Functional Materials and Nanotechnologies (FM&NT 2018), Institute of Physics Publishing (IOPP), 2019, article id 012005Conference paper (Refereed)
    Abstract [en]

    Hydrogen production by water splitting using nanomaterials as electrocatalysts is a promising route enabling replacement of fossil fuels by renewable energy sources. In particular, the development of inexpensive non-noble metal-based catalysts is necessary in order to replace currently used expensive Pt-based catalysts. We report a detailed impedance spectroscopy study of Ni-Mo and Ni-Fe based electrocatalytic materials deposited onto porous and compact substrates with different conductivities. The results were interpreted by a critical comparison with equivalent circuit models. The reaction resistance displays a strong dependence on potential and a lower substrate dependence. The impedance behaviour can also provide information on the dominating reaction mechanism. An optimized Ni-Fe based catalyst showed very promising properties for applications in water electrolysis.

  • 264. Nsimama, P. D.
    et al.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Samiji, M. E.
    Mbise, G. W.
    Wennerberg, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Plasma emission monitoring (PEM) controlled DC reactive sputtered ZnO:Al thin films2012In: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 86, no 12, p. 1939-1944Article in journal (Refereed)
    Abstract [en]

    High deposition rate ZnO:Al films have been produced at room temperature by reactive DC sputtering using a plasma emission monitoring (PEM) control system. We have investigated the relationship between structural, optical and electrical properties of the ZnO:Al films. Crystal structures of the films have been studied by X-ray diffraction. Optimum ZnO:Al films, with 17-40 Omega/square sheet resistance range and transmittance approaching 88% in the visible region, exhibited a hexagonal ZnO structure with preferential (002) orientation and crystallite sizes of about 27 nm. Resistive transparent films displayed a more random orientation showing peaks at (100) and (102) orientations. Dark "metallic" films were shown to consist of mainly zinc. The optimal ZnO:Al film has been determined from a figure of merit based on power losses due to absorption and series resistance in the ZnO:Al films. It is highly transparent, with low resistance, pronounced (002) peak and large crystallite size. (C) 2012 Elsevier Ltd. All rights reserved.

  • 265. Nsimama, P D
    et al.
    Samiji, M E
    Mbise, G W
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wennerberg, J
    Edoff, M
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Performance comparison of Cu(In,Ga)Se2 solar cells fabricated using RF and DC sputtered ZnO:Al transparent conducting oxides2008In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 5, no 2, p. 612-615Article in journal (Refereed)
  • 266. Nsimama, P. D.
    et al.
    Samiji, M. E.
    Mbise, G. W.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wennerberg, J.
    Structural, optical and electrical properties of DC reactively sputtered ZnO:Al films prepared using a plasma emission monitoring control system2007Conference paper (Refereed)
  • 267. Nsimama, P. D.
    et al.
    Samiji, M. E.
    Mbise, G. W.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wennerberg, J.
    Edoff, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Performance comparison of Cu(In,Ga) Se2 solar cells fabricated using RF and DC sputtered ZnO:Al transparent conducting oxides2007Conference paper (Refereed)
  • 268.
    Pehlivan, E.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Georén, P.
    von Kraemer, S.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochemical impedance spectroscopy of nickel oxide thin films2010Conference paper (Refereed)
  • 269.
    Pehlivan, E
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Georén, P.
    von Kraemer, S.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Impedance Behavior of WO3 and NiO in Different Electrolytes2010In: Abstracts for IME-9 Conference, 2010Conference paper (Refereed)
  • 270.
    Pehlivan, Esat
    et al.
    ChromoGenics AB.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Impedance spectroscopy on electrochromic tungsten and nickel oxide films as a function of applied potential.2012In: BDS 2012. Broadband Dielectric Spectroscopy and its Applications, Leipzig, September 3-7, 2012., 2012, p. 92-Conference paper (Refereed)
  • 271.
    Pehlivan, Esat
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Fractal Dimensions of Niobium Oxide Films Probed by Protons and Lithium Ions2006In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 100, no 5, p. 053506-Article in journal (Refereed)
    Abstract [en]

    Cyclic voltammetry (CV) and atomic force microscopy (AFM) were used to determine fractal surface dimensions of sputter deposited niobium pentoxide films. Peak currents were determined by CV measurements. Power spectral densities obtained from AFM measurements of the films were used for calculating length scale dependent root mean square roughness. In order to compare the effect of Li and H ion intercalation at the fractal surfaces, LiClO4 based as well as propionic acid electrolytes were used. The CV measurements gave a fractal dimension of 2.36 when the films were intercalated by Li ions and 1.70 when the films were intercalated by protons. AFM measurements showed that the former value corresponds to the fractal surface roughness of the films, while the latter value is close to the dimensionality of the distribution of hillocks on the surface. We conclude that the protons are preferentially intercalated at such sites.

  • 272.
    Pehlivan, Esat
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Fasta tillståndets fysik.
    Azens, Andris
    Gustavsson, Greger
    A Novel Nb2O5 / Polymer Electrolyte / NiOxVy Electrochromic Device2006Conference paper (Other academic)
  • 273.
    Pehlivan, Esat
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Georén, Peter
    Ageing of electrochromic WO3 coatings characterized by electrochemical impedance spectroscopy2010In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 207, no 7, p. 1772-1776Article in journal (Refereed)
    Abstract [en]

    We have developed a method for characterization of ageing of electrochromic materials by electrochemical impedance spectroscopy (EIS). Electrochromic WO3 thin films have been electrochemically cycled in propionic acid electrolyte and probed by EIS and optical measurements. A very small amount of optical degradation was observed in both the bleached and coloured states. The samples exhibited a few hundred times higher impedance in the bleached state than in the coloured state. It was observed that, in the bleached state, impedance values at low frequencies increased significantly with increasing number of cycles.

  • 274.
    Pehlivan, Esat
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Georen, Peter
    Characterization of Ageing of Electrochromic WO3 Coatings by Electrochemical Impedance Spectroscopy2009In: Advances in Transparent Electronics: From Materials to Device, 2009Conference paper (Refereed)
  • 275.
    Pehlivan, Esat
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Georen, Peter
    von Kraemer, Sophie
    Impedance spectroscopy of aged electrochromic WO3 thin films2009In: 6th International Discussion Meeting on Relaxations in Complex Systems: New Results, Directions and Opportunities, 2009Conference paper (Refereed)
  • 276.
    Pehlivan, Ilknur Bayrak
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Marsal, R.
    Pehlivan, Esat
    Runnerstrom, E. L.
    Milliron, D. J.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromic Devices with Polymer Electrolytes Functionalized by SiO2 and In2O3:Sn Nanoparticles: Rapid Coloring/Bleaching Dynamics and Strong Near-Infrared Absorption2014In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 126, p. 241-247Article in journal (Refereed)
    Abstract [en]

    We studied the optical properties and coloring/bleaching dynamics of electrochromic devices based on tungsten oxide and nickel oxide and incorporating polymer electrolytes functionalized by adding about one percent of nanoparticles of SiO2 (fumed silica) or In2O3:Sn. SiO2 improved the coloring/bleaching dynamics and In2O3:Sn quenched the near-infrared transmittance. Both of these effects can be important in electrochromic smart windows, and our results point at the advantage of a polymer laminated construction over a monolithic one.

  • 277.
    Pehlivan, Ilknur Bayrak
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Marsal, Roser
    Georén, Peter
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ionic relaxation in polyethyleneimine-lithium bis(trifluoromethylsulfonyl) imide polymer electrolytes2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 7, p. 074102-Article in journal (Refereed)
    Abstract [en]

    Polymer electrolytes containing polyethyleneimine and different concentrations of lithium bis(trifluoromethylsulfonyl) imide were investigated by impedance spectroscopy at different temperatures. Two equivalent circuit models were compared for the bulk impedance response. The first one includes a conductive Havriliak-Negami (HN) element which represents ionic conductivity and ion pair relaxation in a single process, and the second model includes a dielectric HN element, which represents ion pair relaxation, in parallel with ion conductivity. Comparison of the two circuit models showed that the quality of the fit was similar and in some cases better for the conductive model. The experimental data follow the Barton-Nakajima-Namikawa relation, which relates the ion conductivity and the parameters of the relaxation. This indicates that ion conductivity and ion pair relaxation are two parts of the same process and should be described by the conductive model.

  • 278.
    Pehlivan, Ilknur Bayrak
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Marsal, Roser
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Georén, Peter
    PEI-LiTFSI electrolytes for electrochromic devices: Characterization by differential scanning calorimetry and viscosity measurements2010In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 94, no 12, p. 2399-2404Article in journal (Refereed)
    Abstract [en]

    Polymer electrolytes containing poly(ethylene imine) (PEI) and lithium bis(trifluoromethylsulfonyl) imide (LiTFSI) can serve as model electrolytes for electrochromic devices. Such electrolytes were characterized by differential scanning calorimetry, conductivity, and viscosity measurements. The glass transition temperature (T-g) and viscosity of the PEI-LiTESI electrolytes have minima at a [N]:[Li] ratio of 100:1. Both T-g and viscosity increased at high salt concentrations. The temperature dependences of ionic conductivity and viscosity followed an Arrhenius equation with parameters depending only weakly on the salt concentration. The fluid behavior of the electrolytes could be reconciled with the Bingham plastic model with parameters being functions of salt concentration.

  • 279.
    Qiu, Zhen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ma, Yue
    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.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Controlled crystal growth orientation and surface charge effects in self-assembled nickel oxide nanoflakes and their activity for the oxygen evolution reaction2017In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 42, no 47, p. 28397-28407Article in journal (Refereed)
    Abstract [en]

    Although sustainable hydrogen production from solar energy is a promising route for the future, the cost of the necessary photovoltaic and photoelectrochemical devices as well as a lack of detailed understanding and control of catalyst interfaces in nanomaterials with high catalytic activity are the largest impediments to commercial implementation. Here, we report how a higher catalytic efficiency can be achieved by utilizing an earth-abundant Nickel oxide (NiO) catalyst via an improved control of the crystalline growth orientation and self-assembly. The relationship between the surface charge and the morphology of the nano-catalysts is investigated using a hydrothermal method where the pH is utilized to control both the crystal growth direction and crystallization of Ni(OH)2 and eventually in NiO, where the self-assembly properties of nanoflakes (NFs) into hierarchical flower-like nickel oxide NFs depend on balancing of forces during synthesis. The surface charge ofthe NiO at different pH values was measured with electrophoretic dynamic light scattering (EDLS) and is known to be closely related to that of Ni(OH)2 and is here utilized to control the relative change in the surface charge in the precursor solution. By preparing NiO NFs under variation of the pH conditions of the precursor Ni(OH)2 system, the surface energies of exposed lattice planes of the growing nanostructures can be altered and an enhanced crystal growth orientation in a different direction can be controlled. Specifically, the [111] and [220] growth orientation in cubic NiO can be favored or suppressed with respect to the [200] direction. Benefiting from the large surface area provided by the mesoporous NiO NFs, the catalyst electrode exhibits high activity toward the oxygen evolution reactions in alkaline electrolyte. The NiO nanostructure synthesized at pH 10 displays oxygen evolution reaction (OER) overpotential of 0.29 V and 0.35 V versus the reversible hydrogen electrode (RHE) at 1 mA cm2 and 10 mA cm2 current density, respectively. This is compared to commercial NiO with more than 0.15 V additional overpotential and the same or lower overpotential compared to RuO2 and IrO2 at alkaline conditions. The results show that the OER catalytic activity can be drastically increased by a detailed control of the crystal growth orientation and the self-assembly behavior where the active surface charge around the point of zero charge during synthesis of the metal hydroxides/oxides is introduced as an important design principle for producing efficient electrocatalysts.

  • 280.
    Qiu, Zhen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ma, Yue
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Northwestern Polytechnical University.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    An electrochemical impedance study of alkaline water splitting using nickel (iron) oxides nanosheetsIn: Article in journal (Refereed)
  • 281.
    Qiu, Zhen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Tai, Cheuk-Wai
    Stockholm Univ, Dept Mat & Environm Chem, SE-10691 Stockholm, Sweden.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Direct observation of active catalyst surface phases and the effect of dynamic self-optimization in NiFe-layered double hydroxides for alkaline water splitting2019In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 12, no 2, p. 572-581Article in journal (Refereed)
    Abstract [en]

    Earth-abundant transition metal-based compounds are of high interest as catalysts for sustainable hydrogen fuel generation. The realization of effective electrolysis of water, however, is still limited by the requirement of a high sustainable driving potential above thermodynamic requirements. Here, we report dynamically self-optimized (DSO) NiFe layered double hydroxide (LDH) nanosheets with promising bi-functional performance. Compared with pristine NiFe LDH, DSO NiFe LDH exhibits much lower overpotential for the hydrogen evolution reaction (HER), even outperforming platinum. Under 1 M KOH aqueous electrolyte, the bi-functional DSO catalysts show an overpotential of 184 and -59 mV without iR compensation for oxygen evolution reaction (OER) and HER at 10 mA cm(-2). The material system operates at 1.48 V and 1.29 V to reach 10 and 1 mA cm(-2) in two-electrode measurements, corresponding to 83% and 95% electricity-to-fuel conversion efficiency with respect to the lower heating value of hydrogen. The material is seen to dynamically reform the active phase of the surface layer during HER and OER, where the pristine and activated catalysts are analyzed with ex situ XPS, SAED and EELS as well as with in situ Raman spectro-electrochemistry. The results show transformation into different active interfacial species during OER and HER, revealing a synergistic interplay between iron and nickel in facilitating water electrolysis.

  • 282.
    Qu, Hui-Yang
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Arvizu, MA
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, G A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Degradation and rejuvenation in electrochromic nickel oxide films2017In: Abstracts, 2017Conference paper (Refereed)
  • 283.
    Qu, Huiying
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Arvizu, Miguel A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Degradation and rejuvenation in electrochromic nickel oxide films2017Conference paper (Refereed)
    Abstract [en]

    Because of the rapidly increasing energy consumption and the associated global environmental problems, it is necessary and urgent to develop renewable energy solutions.  In addition, materials that lead to more efficient use of energy are of high importance. Electrochromic (EC) materials can be part of the solution to the problem of energy efficiency in the built environment. EC materials have the ability to change their optical properties upon the application of a small electrical signal. They have great potential for energy-efficient buildings, low-power display devices and the photoelectrochromic devices which combine EC and the nanostructured TiO2 based solar cells.

    Nickel oxide is one of the most widely used anodic EC materials, which can also be used as the ion storage layer of EC devices. However, from the view of application, the poor cycling durability of nickel oxide limits the life of EC devices. Moreover, although it has been 30 years since it was found, the underlying coloration mechanism is still not understood. Thus, improving the EC performance of nickel oxide is as important as clarifying its coloration mechanism.

    Recently we have studied the ageing process of the nickel oxide film when cycling in different ranges (2-4 V, 1.7-4 V and 2-4.3 V vs. Li/Li+). The film decays faster as we expand the potential range. This can be quantified by the reducing optical modulation from the transmission spectra as well as the decreasing charge capacity calculated from cyclic voltammetry curves. However, the aged film can be rejuvenated and regain its initial highly reversible EC performance when the trapped Li+ ions are removed by an electrical stimulus. Moreover, this rejuvenation process can be repeated many times. In order to optimize our results, several electrochemical techniques including potentiostatic and galvanostatic methods with different experimental parameters have been applied. Results show that when potentiostatic technique is applied, 4.1V is high enough to extract the trapped Li+ ions to regain the initial EC performance, but it needs a long time (20 h) to run. However, only 20 min is needed using galvanostatic treatment. The potential can go up to 4.7 V at the end of the process, which provides a larger potential difference to the trapped Li+ ions in a short time, without affecting the structure and the performance of the films. Raman, X-ray diffraction, Rutherford Backscattering Spectrometry and Elastic Recoil Detection Analysis measurements have also been used to understand the degradation and rejuvenation processes. The discovery of a rejuvenation process in nickel oxide is of interest for the long-time durability for practical EC devices and may also have implications for other energy research fields such as batteries and supercapacitors.

  • 284.
    Qu, Hui-Ying
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Harbin Institute of Technology, School of Chemistry and Chemical Engineering, MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage.
    Primetzhofer, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Arvizu, Miguel A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Qiu, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Cindemir, Umut
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochemical Rejuvenation of Anodically Coloring Electrochromic Nickel Oxide Thin Films2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, no 9, p. 42420-42424Article in journal (Refereed)
    Abstract [en]

    Nickel oxide thin films are of major importance as anodically coloring components in electrochromic smart windows with applications in energy-efficient buildings. However, the optical performance of these films degrades upon extended electrochemical cycling, which has hampered their implementation. Here, we use a potentiostatic treatment to rejuvenate degraded nickel oxide thin films immersed in electrolytes of LiClO4 in propylene carbonate. Time-of-flight elastic recoil detection analysis provided unambiguous evidence that both Li+ ions and chlorine-based ions participate in the rejuvenation process. Our work provides new perspectives for developing ion-exchange-based devices embodying nickel oxide.

  • 285.
    Qu, Hui-Ying
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Harbin Inst Technol, Sch Chem & Chem Engn, MIIT Key Lab Crit Mat Technol New Energy Convers, Harbin 150001, Heilongjiang, Peoples R China.
    Primetzhofer, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Qiu, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Cation/Anion-based electrochemical degradation and rejuvenation of electrochromic nickel oxide films2018In: ChemElectroChem, ISSN 2196-0216, Vol. 5, no 22, p. 3548-3556Article in journal (Refereed)
    Abstract [en]

    Ni oxide thin films are widely used in electrochromic (EC) devices with variable throughput of visible light and solarenergy. However, the mechanisms underlying the optical modulation – and its degradation under extended operationand subsequent rejuvenation – are poorly understood especially for Li+-conducting electrolytes. Here, we report a comprehensive study of the EC properties of sputter-deposited Ni oxide films immersed in an electrolyte of LiClO4 in propylene carbonate. Cyclic voltammetry and optical transmittance measurements were used to document degradation and subsequent potentiostatic rejuvenation. X-ray diffraction did not show evidence for accompanying changes in crystallinity, whereas vibrational spectroscopy indicated that degraded films had carbonaceous surface layers. Time-of-flight elastic recoil detection analysis demonstrated that both Li+ and Cl-based ions participate in the electrochromism and its degradation and rejuvenation. A major result was that degradation is associated with a reduced difference in the concentrations of Li+ and Cl based ions in the nickel oxide during extended electrochemical cycling, and rejuvenation of degraded films is achieved by removal of Li+ ions and accumulation of Cl-based anions to regain their initial concentration difference. Our work provides new insights into the use of ion-exchange-based devices incorporating nickel oxide.

  • 286.
    Qu, Hui-Ying
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Rojas González, Edgar Alonso
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Enhanced durability of Tungsten oxide electrochromic films: Processes occurring at the Indium-Tin oxide substrate2018In: IS-TCMs: 7^th International Symposium on Transparent Conductive Materials and 4^th E-MRS & MRS-J Bilateral Symposium on Advanced Oxides and Wide Bandgap Semiconductors,, 2018, p. 215-, article id PS1-25Conference paper (Refereed)
    Abstract [en]

    Durability is a key issue for ensuring widespread and successful use of electrochromic(EC) films in energy-efficient smart windows and also for other devices such as lithium-ionbatteries and supercapacitors. Recent results showed [1] that the durability of EC WO3 thinfilms can be greatly improved by a facile electrochemical treatment at high potentials. Glass coated with In2O3:Sn (ITO) was then used as the substrate, and here we present evidence that changes in the properties of the ITO substrate is connected with the improved durability.We deposited a ~300-nm-thick WO3 film on ITO-coated glass with a sheet resistance of 60 Ω/sq and then applied 6 V vs. Li/Li+ to pretreat the WO3 thin film for 24 h in an electrolyte of LiClO4 in propylene carbonate. After the pretreatment, the durability of the WO3 thin film was excellent even after harsh electrochemical cycling in the 1.5–4 V vs. Li/Li+ range. Scanning electron microscopy showed that the thickness of the ITO layer became smaller after the pretreatment. X-ray photoelectron spectroscopy (XPS) depth profile measurements (Fig. 1) demonstrated that the concentration of In and Sn decreased significantly after pretreatment. In addition, the depth profile indicates a significant intermixing of W and In, which even seems to extend into the underlying glass. Supplementary impedance spectroscopy measurements showed that the high-frequency resistance (mainly due to the ITO) increased significantly after the pretreatment.

    We also studied the behavior of ITO films with a sheet resistance of 60 Ω/sq by cyclic voltammetry. XPS measurements verified a strong decrease of In and Sn contents as well asITO thickness when the upper potential exceeded 6 V vs. Li/Li+. We propose that these interactions between WO3 and the ITO substrate, as well as physical changes in the ITO, have a positive effect on the durability of the EC WO3 thin film. This discovery may be of interest for ITO-based electronic devices as well as for designing long-time-durable EC devices.

  • 287.
    Qu, Hui-Ying
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Rojas González, Edgar Alonso
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Potentiostatically pretreated electrochromic tungsten oxide films with enhanced durability: Electrochemical processes at interfaces of indium–tin oxide2019In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 682, p. 163-168Article in journal (Refereed)
    Abstract [en]

    Recent work has shown that electrochromic WO3 films, backed by In2O3:Sn (ITO) and immersed in a lithium-ion-conducting electrolyte, can attain unprecedented electrochemical cycling durability after potentiostatic pretreatment at high voltage. Here we demonstrate that this intriguing feature is associated with changes in the properties of the ITO film. Specifically, we studied thin films of ITO and WO3/ITO immersed in an electrolyte of LiClO4 in propylene carbonate at potentials up to 6.0 V vs. Li/Li+ by cyclic voltammetry and impedance spectroscopy and present evidence that electrochemical reactions occur under these conditions. X-ray photoemission spectroscopy indicated that the ITO film was partly dissolved at high voltages and that the dissolution reaction promoted diffusion of In and Sn into the WO3 film.

  • 288.
    Rojas González, Edgar Alonso
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Qu, Hui-Ying
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochemical impedance spectroscopy analysis of Indium-Tin oxide films at high applied potentials2018In: IS-TCMs: 7^th International Symposium on Transparent Conductive Materials and 4^th E-MRS & MRS-J Bilateral Symposium on Advanced Oxides and Wide Bandgap Semiconductors, Chania Crete Grekland, 2018, p. 223-, article id PS1-33Conference paper (Refereed)
    Abstract [en]

    Indium-tin oxide (ITO) coated substrates are readily used as transparent conductors in energy-related applications like photovoltaics and smart window technology. Recently, it has been reported that electrochemical treatments at high applied voltages can enhance the durability of electrochromic (EC) films [1], and in addition rejuvenate already degraded films [2]. However, the EC electrode consists of an EC film on a transparent conductor, usually ITO, and changes in the ITO film may affect the durability and rejuvenation properties of the system. In a Li+-containing electrolyte, the safe potential range of ITO is 2-4 V vs. Li/Li+. At low potentials below 2 V vs. Li/Li+ Li compounds will form and result in a color change of ITO [3]. However, the behavior of ITO in Li+-containing electrolyte at high potentials up to 6 V vs. Li/Li+ is to our knowledge virtually unknown.   

    In this work, ITO coated glass substrates with nominal sheet resistance of 60 Ω/sq, and 15 Ω/sq, having thicknesses of 50 nm, and 150 nm, respectively were used as working electrodes (WE) in a three-electrode electrochemical cell. Lithium foils were used both as counter and reference electrodes in an electrolyte consisting of 1 M LiClO4 dissolved in propylene carbonate.

    A potentiostatic pretreatment at 6 V vs Li/Li+ during 24 h was applied on the WE. The current during the pretreatment showed an initial rapid decrease followed by a plateau, after which it decreased ~2 orders of magnitude. The width of the plateau for the 15 Ω/sq film was ~3 times longer than for the 60  Ω/sq film, which correlates to their thickness ratio. Cyclic voltammetry between 3.5 V and 6 V vs. Li/Li+ showed a significant current response only for potentials above 5 V for an as-deposited sample, and very little activity for a pretreated WE. The latter result indicates that the film had been stabilized by the pre-treatment.

    Electrochemical impedance spectroscopy (EIS) spectra were measured at pseudo equilibrium potentials from 3.5 V vs. Li/Li+, and up to 6 V vs. Li/Li+. The spectra were modeled and fitted in terms of equivalent circuits. The spectra for potentials below 5 V were dominated by a blocking electrode response, whereas for higher voltages a low-frequency response was identified as being due to an electrochemical reaction which becomes more intense as the potential is increased. In addition the high frequency series resistance, mainly due to the ITO, is increased at high voltages and after pretreatment. Supplementary investigations by Scanning electron microscopy and X-ray photoelectron spectroscopy gave evidence for a smaller film thickness and a significantly decreased In content in films exposed to treatments at high potentials.

    A better understanding of the effects of high applied potentials on transparent conductors like ITO will help to unravel mechanisms of durability enhancement and rejuvenation, and may provide guidelines for designing new procedures to enhance the durability of EC systems for energy-efficient smart windows.

     

    1. M.A. Arvizu, H.-Y Qu, G.A. Niklasson and C.G. Granqvist, Thin Solid Films 653 (2018) 1-3.

    2. R.-T. Wen, G.A. Niklasson and C.G. Granqvist, Nature Materials, 14 (2015) 996-1001.

    3. P.M.M.C. Bressers and E.A. Meulenkamp, J. Electrochem. Soc. 145 (1998) 2225-2230.

  • 289.
    Skorodumova, Natalia V.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Jonsson, A.K.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Herranen, Merja
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Strömme, M
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Niklasson, G A
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Simak, S. I.
    Random conductivity of delta-Bi2O3 films2005In: Applied Physics Letters, Vol. 86, p. 241910 1-3Article in journal (Refereed)
    Abstract [en]

    The experimental investigation of the cubic -Bi2O3 phase grown on a (110) Au substrate at low temperature has disclosed a chaotic character of the conductivity at low voltage and temperature. Based on first-principles calculations, we show that the conductivity of this oxide strongly depends on the distribution of oxygen ions and that oxygen migration is able to cause a momentary switch of the conduction mechanism.

  • 290.
    Smulko, J
    et al.
    Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Gdansk, Polen.
    Kotarski, M
    Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Gdansk, Polen.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kish, L B
    Dept of Electrical Engineering, Texas A&M University, College Station, USA.
    Fluctuation-enhanced gas sensing in practice2011Conference paper (Refereed)
    Abstract [en]

    The technique of fluctuation-enhanced sensing (FES) in resistive gas sensors was proposed a few years ago. The method improves the selectivity and sensitivity of gas detection. This was confirmed in numerous laboratory experiments. Some of the latest results obtained for practical applications of the FES method are presented (toxic gases detection; problems of detection repeatability; detection of essential oils intensity during aromatherapy, biological agent detection). Additionally, a new prototype nanoparticle gas sensor was introduced with an additional potential of gas detection using noise induced by UV irradiations.

  • 291. Sorar, I.
    et al.
    Pehlivan, E.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromism of DC Magnetron-Sputtered TiO2: Role of Film Thickness2014In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 318, p. 24-27Article in journal (Refereed)
  • 292.
    Sorar, Idris
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Pehlivan, Esat
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. ChromoGenics AB.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromic properties of TiO2 thin films deposited by DC magnetron sputtering: The effect of total gas pressure and oxygen gas flow rate.2012In: IME-10. Tenth International meeting on Electrochromism, Holland, MI USA, August 12-16, 2012., 2012, p. 40-Conference paper (Refereed)
  • 293.
    Sorar, Idris
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Pehlivan, Esat
    ChromoGenics AB, Uppsala.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromism of DC magnetron sputtered TiO2: Role of film thickness2014In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 318, p. 24-27Article in journal (Refereed)
    Abstract [en]

    Titanium dioxide films were prepared by reactive DC magnetron sputtering and the role of the film thick-ness d on the electrochromism was analyzed for 100 < d < 400 nm. The best properties were obtainedfor the thickest films, which yielded a mid-luminous transmittance modulation of 58% and a corre-sponding coloration efficiency of 26.3 cm2/C. The films were amorphous according to X-ray diffractionmeasurements and showed traces of adsorbed water as revealed by infrared spectroscopy.

  • 294.
    Sorar, Idris
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Pehlivan, Esat
    ChromoGenics AB.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromism of DC magnetron sputtered TiO2 thin films: Role of deposition parameters2013In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 115, p. 172-180Article in journal (Refereed)
    Abstract [en]

    We performed a comprehensive study on the electrochromism in TiO2 thin films made by reactive DC magnetron sputtering and elucidated the roles of sputter gas pressure p, O-2/Ar gas ratio gamma and substrate temperature tau(s). Good mid-luminous optical modulation taken to be similar to 50% in similar to 200-nm-thick films was obtained under charge exchange in a Li+ electrolyte for p > 15 mTorr and tau(s) < 100 degrees C, whereas gamma was less important. The deposition rate dropped for increasing p, and hence p approximate to 15 mTorr was optimal. These films were X-ray amorphous and contained some water. The coloration efficiency eta was 25 cm(2)/C, which exceeds data on eta in most prior studies on sputter deposited TiO2 and verifies that such films can display the same values of eta as those of TiO2 films made by several chemical techniques.

  • 295.
    Sotelo, Juan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. University of Technology, Sydney, Australia.
    Ederth, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Optical properties of polycrystalline metallic films2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, p. 195106-Article in journal (Refereed)
    Abstract [en]

    We extend the Mayadas and Shatkes’s approach @Phys. Rev. B 1, 1382 ~1970!# to study the optical propertiesof polycrystalline metal thick films in the visible and far infrared range of the spectrum. We show that in thisrange grain boundary scattering can account for the experimentally observed lowering of the film reflectivity asthe mean size of its constituent grains decreases.

  • 296.
    Stefanov, Bozhidar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnar, Niklasson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Quantitative relation between photocatalytic activity and degree of〈001〉orientation for anatase TiO2 thin films2015In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 33, p. 17369-17375Article in journal (Refereed)
    Abstract [en]

    We demonstrate a quantitative relation between exposed crystal surfaces and photocatalytic activity of nanocrystalline anatase TiO2. Thin films with controlled amount of 〈001〉 preferential orientation were prepared by reactive DC magnetron sputtering in Ar/O2 atmosphere with the partial O2 pressure as control parameter. The samples were characterized with X-ray diffraction, transmission electron microscopy and atomic force microscopy, from which the degree of preferential 〈001〉 orientation and exposed facets were determined by an extension of the March–Dollase model. Photocatalytic degradation of methylene blue dye shows that the photocatalytic reaction rate increases approximately with the square of the fraction of 〈001〉 oriented surfaces, with about eight times higher rate on the {001} surfaces, than on {101}, thus quantifying the effect of crystal facet abundancy on the photocatalytic activity of anatase TiO2.

  • 297.
    Stefanov, Bozhidar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gas-phase photocatalytic activity of sputter-deposited anatase TiO2 films: Effect of <001> preferential orientation, surface temperature and humidity2016In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 335, p. 187-196Article in journal (Refereed)
    Abstract [en]

    We present a systematic in situ study of the environmental reaction conditions on the photocatalytic activity of sputter deposited anatase TiO2 films with controlled amounts of preferential <001> orientation. In particular, the effects of relative humidity (RH) and substrate temperature ( ) are investigated. It is found that {001} facets, which are present in higher abundance on highly oriented samples, exhibit an order of magnitude higher reactivity for gas-phase photocatalytic oxidation of the indoor air pollutant acetaldehyde (CH3CHO) than {101} facets do, and a functional dependence of the reaction rate on facet orientation is determined. It is proposed that water adsorbed on the film contributes with two counteracting effects on the photocatalytic activity: (i) It provides hole acceptors to complete the photo-induced redox cycle and subsequent OH– radical formation for pollutant degradation, and (ii) it creates a diffusion barrier between the catalyst interface and pollutant molecules adsorbed in the water layer. As a consequence, increasing  at high RH has the beneficial effect of removing excess water and reducing the diffusion barrier, thereby improving the photocatalytic activity. A comparison is also made with a commercial anatase TiO2 film, with less developed surface crystallinity and random facet distribution, where the improvement is even more pronounced. Films with a higher degree of orientation exhibit much more stable performance over a range of operating conditions, which suggests that it is possible to tune the effects of water and exposed facet orientation to achieve optimum activity and making TiO2 films amenable to a larger (RH, ) parameter space for practical applications.

  • 298.
    Strömme, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Azens, A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Purans, A.
    Li intercalation in transparent Ti-Ce oxide films: Energetics and ion dynamics1997In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 81, no 9, p. 6432-6437Article in journal (Refereed)
    Abstract [en]

    Films of Ti dioxide, mixed Ti–Ce oxide, and Ce dioxide were produced by reactive dc magnetron sputtering.Electrochemical lithiation was probed by chronopotentiometry, cyclic voltammetry together with optical transmittance recording, and impedance spectroscopy. Evidence was found for inserted electrons being accommodated in Ce4f states; this contention was supported by preliminary results from x-rayabsorption fine-structure spectroscopy. These electrons do not produce luminous electrochromism. The variation of the chemical diffusion coefficient of Li, with film composition and Li content, was also studied.

  • 299.
    Strömme, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Gutarra, A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Impedance spectroscopy on lithiated Ti oxide and Ti oxyfluoride thin films1996In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 79, p. 3749-Article in journal (Refereed)
    Abstract [en]

    Films of Ti oxide and Ti oxyfluoride were produced by reactive magnetron sputtering of Ti in Ar+O2(+CF4). Compositional and structuralanalyses were accomplished by Rutherford backscattering spectrometry, x‐ray diffraction(XRD), infrared absorption spectrometry, and atomic force microscopy(AFM).Electrochemical characterization of films immersed in a Li conducting electrolyte was performed with cyclic voltammetry and coulometric titration. Detailed impedance spectra were recorded for the 2×105–1×10−3 Hz range. The impedance responses of pure and fluorinated Ti oxide films in the lithium containing electrolyte differed significantly even if their structures, according to AFM and XRD, were very similar. One main difference was the size of the charge transfer resistance, presumably connected to the Li ion injection from the electrolyte into the film. A modest fluorination lowered this resistance by about two orders of magnitude. The voltammetric and the impedance responses, as well as the magnitude of the chemical diffusion coefficient, of the fluorinated Ti oxide film were strikingly similar to the response of WO3films. This similarity does not occur for the pure Ti oxide films, where a process, believed to be the Li ion injection, could be identified with the main features of the frequency‐dependent impedance. Underlying this charge transfer mechanism, however, a process represented by a constant phase element seems to be operating. This latter process may have its origin in Li diffusion into the film.

  • 300.
    Strömme, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Isidorsson, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Impedance studies on Li insertion electrodes of Sn oxide and oxyfluoride1996In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 80, no 1, p. 233-241Article in journal (Refereed)
    Abstract [en]

    Films of Sn oxide and oxyfluoride were made by reactive rf magnetron sputtering onto ITO‐coated glass. We analyzed the composition by Rutherford backscattering spectrometry, the structure by x‐ray diffraction, and the surfacetopography by atomic force microscopy. Li intercalation from a liquid electrolyte was more facile in the oxide than in the oxyfluoride, as found from cyclic voltammetry. Impedance spectra were taken for a wide range of frequencies and polarizing voltages. Nyqvist diagrams were interpreted from a circuit model with elements representing Li insertion at the electrolyte/film interface and electron insertion at the film/ITO interface. The data were consistent with a fractal surface of the Sn oxide film, with a dimension in excellent agreement with measures obtained through several independent techniques. The chemical diffusion coefficient was ∼10−13 cm2/s and slightly decreasing with increasing potential for all films.

345678 251 - 300 of 378
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