uu.seUppsala universitets publikasjoner
Endre søk
Begrens søket
345678 251 - 300 of 395
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 251.
    Niklasson, Gunnar A
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes G
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochromics for Smart Windows: Thin Films of Tungsten Oxide and Nickel Oxide, and Devices Based on These2007Inngår i: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 17, nr 2, s. 127-156Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Electrochromic (EC) materials are able to change their optical properties, reversibly and persistently, by the application of an electrical voltage. These materials can be integrated in multilayer devices capable of modulating the optical transmittance between widely separated extrema. We first review the recent literature on inorganic EC materials and point out that today's research is focused on tungsten oxide ( colouring under charge insertion) and nickel oxide ( colouring under charge extraction). The properties of thin films of these materials are then discussed in detail with foci on recent results from two comprehensive investigations in the authors' laboratory. A logical exposition is obtained by covering, in sequence, structural features, thin film deposition ( by sputtering), electronic band structure, and ion diffusion. A novel conceptual model is given for structural characteristics of amorphous W oxide films, based on notions of defects in the ideal amorphous state. It is also shown that the conduction band density of states is obtainable from simple electrochemical chronopotentiometry. Ion intercalation causes the charge-compensating electrons to enter localized states, implying that the optical absorption underlying the electrochromism can be described as ensuing from transitions between occupied and empty localized conduction band states. A fully quantitative theory of such transitions is not available, but the optical absorption can be modeled more phenomenologically as due to a superposition of transitions between different charge states of the W ions (6+, 5+, and 4+). The Ni oxide films were found to have a porous structure comprised of small grains. The data are consistent with EC coloration being a surface phenomenon, most likely confined to the outer parts of the grains. Initial electrochemical cycling was found to transform hydrated Ni oxide into hydroxide and oxy-hydroxide phases on the grain surfaces. Electrochromism in thus stabilized films is consistent with reversible changes between Ni hydroxide and oxy-hydroxide, in accordance with the Bode reaction scheme. An extension of this model is put forward to account for changes of NiO to Ni2O3. It was demonstrated that electrochromism is associated solely with proton transfer. Data on chemical diffusion coefficients are interpreted for polycrystalline W oxide and Ni oxide in terms of the lattice gas model with interaction. The later part of this review is of a more technological and applications oriented character and is based on the fact that EC devices with large optical modulation can be accomplished essentially by connecting W-oxide-based and Ni-oxide-based films through a layer serving as a pure ion conductor. Specifically, we treat methods to enhance the bleached-state transmittance by mixing the Ni oxide with other oxides characterized by wide band gaps, and we also discuss pre-assembly charge insertion and extraction by facile gas treatments of the films, as well as practical device manufacturing and device testing. Here the emphasis is on novel flexible polyester-foil-based devices. The final part deals with applications with emphasis on architectural "smart'' windows capable of achieving improved indoor comfort jointly with significant energy savings due to lowered demands for space cooling. Eyewear applications are touched upon as well.

  • 252.
    Niklasson, Gunnar A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Lansåker, Pia C.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Teknisk-naturvetenskapliga fakulteten.
    Li, Shu-Yi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Granqvist, Claes G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Plasmonic thin films for application to inproved chromogenic windows2015Inngår i: INERA Conference: Book of Abstracts / [ed] Nesheva, D; Chamati, H; Genova, J; Gesheva, K; Ivanova, T; Szekeres, A, 2015, artikkel-id 012003Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Nanocomposites consisting of noble metal nanoparticles in a transparent matrix exhibit plasmonic absorption in the visible wavelength range. On the other hand conducting oxide nanoparticles display a localized plasma absorption in the near infrared. These 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 insertion/extraction induced by an external voltage. Thermochromic nanocomposites are predicted to exhibit a much improved energy efficiency, as compared to thermochromics thin films. Plasmonic thermochromics 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.

     

    In order to model and optimize chromogenic devices, a good theoretical understanding of plasmonic effects is necessary. The optical properties of nanocomposites are commonly described by effective medium theories. They describe the effective dielectric function of the composite using as input the dielectric functions of the constituents and their respective volume fractions. However, theoretical modelling by effective medium theories is not straightforward since the effective dielectric function is also sensitively dependent on the actual microgeometry of the composite. These structural effects can be described by the so-called spectral density function. In this paper we describe recent work on three topics related to energy efficient chromogenic window coatings: (1) The performance limits of plasmonic electrochromic coatings, (2) the performance of thermochromics nanocomposites and (3) a study of the optical properties of ultrathin silver films by the spectral density formalism.

  • 253.
    Niklasson, Gunnar A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Li, Shu-Yi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Thermochromic vanadium oxide thin films: Electronic and optical properties2014Inngår i: INERA Workshop: Transition Metal Oxides as Functional Layers in Smart windows and Water Splitting Devices / Parallel session of the 18th International School on Condensed Matter Physics / [ed] Kostadinka Gesheva, Institute of Physics Publishing (IOPP), 2014, s. 012001-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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 oC. 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 be less than 0.5 . 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.

  • 254.
    Niklasson, Gunnar A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Malmgren, Sara
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi.
    Green, Sara
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Backholm, Jonas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Determination of electronic structure by impedance spectroscopy2010Inngår i: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 356, nr 11-17, s. 705-709Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a novel method, based on electrochemical intercalation and impedance spectroscopy, to determine the electronic density of states of disordered transition metal oxides. Specifically, we have determined the "electrochemical density of states" of tungsten and iridium oxide thin films over energy ranges as wide as 1-2 eV. Our experimental results show a number of qualitative features exhibited by state-of-the-art band structure computations. Differences in details are probably due to the disordered, porous and sometimes amorphous nature of our films. The results suggest that the impedance spectroscopy method can be used to obtain the density of states only if the conduction band states are localized. The electrochemical density of states is often smaller than the computed one due to kinetic effects, i.e. very slow relaxations of the charge carriers. Nevertheless, our sensitive method opens new vistas for studying the electronic structure of disordered materials.

  • 255.
    Niklasson, Gunnar A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Malmgren, Sara
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Green, Sara
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Ageing of electrochromic tungsten oxide thin films studied by impedance spectroscopy.2016Inngår i: / [ed] M. Labardi and E. Tombari, Pisa, 2016, s. O-89-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Tungsten oxide is the most widely used cathodic electrochromic material for smart window applications and a major challenge is to ensure the durability over a service life of more than 20 years. Hence, the degradation under operating conditions must be better understood and preferably prevented. Recent progress in this field includes studies of the power-law kinetics of the degradation process [1] as well as the possibility to rejuvenate degraded films, thereby restoring them to their initial state [2]. In this paper we use impedance spectroscopy to investigate electrochemical ageing of sputter deposited tungsten oxide thin films. Impedance spectroscopy measurements were carried out in a Li+-containing electrolyte, from the open circuit potential at about 3.2V vs. Li down to (1) 2.2 V, which is in the reversible intercalation range; (2) 1.5 V and (3) 1.0 V; at these latter voltages Li intercalation has been found to be irreversible. Subsequently, measurements were carried out for increasing voltages up to the starting point at 3.2 V vs. Li. The intercalated charge capacity was unaffected when potentials below 2.0 V were avoided, while it decreased drastically on the return path from 1.5 V and 1.0 V vs. Li. We interpret this ageing behaviour as an effect of trapping of Li ions irreversibly in the film. Secondly, after the films had been subjected to the low potentials known to induce degradation, the charge transfer resistance in the usual operating range above 2.0 V vs. Li showed a marked increase. This is interpreted as a signature of the development of a solid-electrolyte interface. In conclusion, our measurements suggest that the development of the solid-electrolyte interface may be responsible for the slow degradation observed under normal operating conditions, while Li ion trapping is mainly responsible for severe degradation at potentials significantly below 2.0 V vs. Li.

     

    [1] R.-T. Wen, C. G. Granqvist, and G. A. Niklasson: Cyclic voltammetry on sputter-deposited films of electrochromic Ni oxide: Power-law decay of the charge density exchange. Appl. Phys. Lett. 105  163502 (2014)

     

    [2] R.-T. Wen, G.A. Niklasson and C.G. Granqvist: Eliminating degradation and uncovering ion-trapping dynamics in electrochromic WO3 thin films. Nature Materials 14  996-1002 (2015)

  • 256.
    Niklasson, Gunnar A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Nettelblad, Bo
    SAAB Electronic Defense Systems, Göteborg.
    Dielectric Properties of Water-Containing Porous Materials: Low Frequency Response of Sandstones2013Inngår i: ISEMA 2013: Proceedings of the 10th International Conference on Electromagnetic Wave Interaction with Water and Moist Substances / [ed] Klaus Kupfer and Norman Wagner, Weimar, Germany: MFPA Weimar , 2013, s. 195-202Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We present results of dielectric spectroscopy measurements on natural sandstones, where the pores were impregnated with water solutions of different conductivity. The measurements were fitted to an equivalent circuit containing a high-frequency Maxwell-Wagner relaxation and a low frequency response due to ion conduction and relaxation in the electrochemical double layer at the interfaces between the solid grains and the water. We propose a novel expression for the low frequency response based on a transmission line model. We also study in detail the shape of the Maxwell-Wagner relaxation in samples of porous polypropylene impregnated with transformer oil.

  • 257.
    Niklasson, Gunnar A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Maria H.
    Musikinstitutet Betel, Bromma Folkhögskola.
    Non-Gaussian distributions of melodic intervals in music: The Lévy-stable approximation2015Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 112, nr 4, artikkel-id 40003Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The analysis of structural patterns in music is of interest in order to increase ourfundamental understanding of music, as well as for devising algorithms for computer-generatedmusic, so called algorithmic composition. Musical melodies can be analyzed in terms of a “music walk” between the pitches of successive tones in a notescript, in analogy with the “random walk”model commonly used in physics. We find that the distribution of melodic intervals between tones can be approximated with a L´evy-stable distribution. Since music also exibits self-affine scaling,we propose that the “music walk” should be modelled as a L´evy motion. We find that the L´evy motion model captures basic structural patterns in classical as well as in folk music.

  • 258.
    Niklasson, Gunnar A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Sara
    Lundellska Skolan, Uppsala.
    Determination of scattering and absorption coefficients from experimental data: Application to sunscreen lotions2013Inngår i: Optics & Photonics in Sweden 2013, 2013Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Materials with pronounced light scattering are of large interest in a variety of scientific and technical disciplines. Their optical properties can to a good approximation be described by two-flux (Kubelka-Munk) theory [1]. This theory considers one light beam propagating in the forward direction and one beam propagating in the backward direction in the material. The optical properties of the material are described by phenomenological scattering (S) and absorption (K) coefficients. Additional parameters are the internal reflection coefficients for diffuse light at the interfaces and the reflection coefficient for incident collimated light at the front interface. The large amount of parameters makes it difficult to invert experimental measurements of transmittance (T) and reflectance (R) in order to obtain the parameters S and K characterizing the material [2,3]. We propose a method to partially overcome this problem in special cases by invoking physically realistic approximations for the reflection coefficients. 

    We consider viscous emulsions or polymeric materials positioned between two transparent substrates separated by a spacer. Many organic and polymeric materials have refractive indices sufficiently close to those of glass and quartz substrates so that reflections between the material and the glass can be neglected. The reflection coefficient of the substrate for collimated light is known from its refractive index. Measurements of R and T in a region of weak scattering and absorption allow us to put quite stringent limits on the internal reflection coefficients for diffuse light. In this way good approximative values for S and K can be obtained.

    We apply this method to spectrophotometric measurements on two commercial sunscreen lotions. A drop of lotion was applied on a quartz substrate and a second quartz plate was put on top. The quartz plates were separated by aluminium foil of thickness 11 mm, except in the area covered by the lotion. Measurements of total R and T were taken by a Perkin-Elmer lambda-900 spectrophotometer equipped with an integrating sphere, in the wavelength range 250-800 nm. The samples were completely diffuse scattering and measurements in a low scattering region indicated a preferential forward scattering. The absorption coefficient was found to be low in the visible region and increased very much in the ultraviolet (UV). The scattering coefficient increased towards shorter wavelengths in the visible but exhibited differing behaviours in the UV. A sunscreen containing TiO2 particles exhibited a very low UV scattering together with higher scattering in the visible range, see fig. 1.

      

    Fig. 1. Scattering (S) and absorption (K) coefficients for a sunscreen containing a mix of chemical pigments and TiO

    [1] P. Kubelka, J. Opt. Soc. Am. 38 (1948) 448.

    [2] R. Levinson, P. Berdahl and H. Akbari, Solar Energy Mater. Solar Cells, 89  (2005) 319.

    [3] D. Barrios, R. Vergaz, J.M. Sanchez-Pena, C.G. Granqvist and G.A. Niklasson, Solar Energy Mater. Solar Cells, 111 (2013) 115.

  • 259.
    Niklasson, Gunnar A
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Fasta tillståndets fysik.
    Norling, A K
    Berggren, L
    Charge transport Between Localized states in Lithium-intercalated Amorphous Tungsten Oxide2006Konferansepaper (Annet vitenskapelig)
  • 260.
    Niklasson, Gunnar A
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Norling, AnnaKarin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Berggren, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Charge transport between localized states in lithium-intercalated amorphous tungsten oxide2007Inngår i: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 353, nr 47-51, s. 4376-4379Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 261.
    Niklasson, Gunnar A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Norling, Anna-Karin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Possnert, Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Jonfysik.
    Berggren, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Optical properties of amorphous tungsten oxide films: Effect of stoichiometry2008Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 100, nr 8, s. 082023-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 262.
    Niklasson, Gunnar A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wen, Rui-Tao
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Arvizu, Miguel A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Malmgren, Sara
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Pehlivan, Esat
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Morales-Luna, Michael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochemical degradation and rejuvenation of electrochromic tungsten oxide thin films2016Konferansepaper (Fagfellevurdert)
    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.

  • 263.
    Niklasson, Gunnar A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wen, Rui-Tao
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochromic oxides: Electrochemical density of states, degradation kinetics and rejuvenation of degraded films2015Konferansepaper (Fagfellevurdert)
    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.

     

  • 264.
    Niklasson, Gunnar A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wen, Rui-Tao
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Materials Processing Center, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
    Qu, Hui-Ying
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. 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 universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Durability of electrochromic films: Aging kinetics and rejuvenation2017Inngår i: ECS Transactions, Electrochemical Society, 2017, Vol. 77, s. 1659-1669Konferansepaper (Fagfellevurdert)
    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.

  • 265.
    Niklasson, Gunnar A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wiebel, Sabine
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Strömme, Maria
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper.
    Hjort, Klas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    van Veldhuizen, Elbert Jan
    Uppsala universitet, The Svedberg-laboratoriet.
    Nilsson, Leif
    Uppsala universitet, The Svedberg-laboratoriet.
    Westerberg, Lars
    Uppsala universitet, The Svedberg-laboratoriet.
    Surface conduction in porous polycarbonate membranes1998Rapport (Annet vitenskapelig)
  • 266.
    Niklasson, Gunnar
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Abatte, Leif
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Karlstads Universitet.
    Rojas González, Edgar Alonso
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Arvizu, Miguel A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Qu, Hui-Ying
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochemical rejuvenation of Tungsten oxide electrochromic thin films: Evidence from impedance spectroscopy2018Inngår i: 13th International Meeting on Electrochromism, IME-13: Book of Abstracts, 2018, s. 11-, artikkel-id IN-3Konferansepaper (Fagfellevurdert)
    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).

     

  • 267.
    Niklasson, Gunnar
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Boström, T. K.
    Tuncer, E.
    Spectral density analysis of the optical properties of Ni-Al2O3 nanocomposite films2011Inngår i: Proceedings of SPIE, Vol. 8168, nr 8168-27, s. 27-Artikkel i tidsskrift (Fagfellevurdert)
  • 268.
    Niklasson, Gunnar
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Granqvist, Claes Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochromic and thermochromic oxide materials2018Inngår i: Towards Oxide-Based Electronics: Spring Meeting 2018 MP1308 TO-BE COST Action, 2018, s. 31-Konferansepaper (Annet vitenskapelig)
    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.

  • 269.
    Niklasson, Gunnar
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Lansåker, Pia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Li, Shu-Yi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Granqvist, C.-G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Plasmonic Thin Films for Application in Improved Chromogenic Windows2016Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 682, nr 012003, s. 1-9Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 270.
    Niklasson, Gunnar
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Li, S.- Y.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, C.-G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Thermochromic Vanadium Oxide Thin Films: Electronic and Optical Properties2014Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 559, nr 012001, s. 012001/1-012001/8Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 271.
    Niklasson, Gunnar
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Norling, A. K.
    Possnert, G.
    Berggren, L.
    Optical properties of amorphous tungsten oxide films: Effect of stoichiometry2008Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 100, nr 8, s. 082023-Artikkel i tidsskrift (Fagfellevurdert)
  • 272.
    Niklasson, Gunnar
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Qiu, Zhen
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Bayrak Pehlivan, Ilknur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Edvinsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Impedance spectroscopy of water splitting reactions on nanostructured metal-based catalysts2019Inngår i: Functional Materials and Nanotechnologies (FM&NT 2018), Institute of Physics Publishing (IOPP), 2019, artikkel-id 012005Konferansepaper (Fagfellevurdert)
    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.

  • 273. Nsimama, P. D.
    et al.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Samiji, M. E.
    Mbise, G. W.
    Wennerberg, Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Plasma emission monitoring (PEM) controlled DC reactive sputtered ZnO:Al thin films2012Inngår i: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 86, nr 12, s. 1939-1944Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 274. Nsimama, P D
    et al.
    Samiji, M E
    Mbise, G W
    Niklasson, Gunnar A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wennerberg, J
    Edoff, M
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Performance comparison of Cu(In,Ga)Se2 solar cells fabricated using RF and DC sputtered ZnO:Al transparent conducting oxides2008Inngår i: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 5, nr 2, s. 612-615Artikkel i tidsskrift (Fagfellevurdert)
  • 275. Nsimama, P. D.
    et al.
    Samiji, M. E.
    Mbise, G. W.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wennerberg, J.
    Structural, optical and electrical properties of DC reactively sputtered ZnO:Al films prepared using a plasma emission monitoring control system2007Konferansepaper (Fagfellevurdert)
  • 276. Nsimama, P. D.
    et al.
    Samiji, M. E.
    Mbise, G. W.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wennerberg, J.
    Edoff, M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Performance comparison of Cu(In,Ga) Se2 solar cells fabricated using RF and DC sputtered ZnO:Al transparent conducting oxides2007Konferansepaper (Fagfellevurdert)
  • 277.
    Pehlivan, E.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Georén, P.
    von Kraemer, S.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, C.-G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochemical impedance spectroscopy of nickel oxide thin films2010Konferansepaper (Fagfellevurdert)
  • 278.
    Pehlivan, E
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Georén, P.
    von Kraemer, S.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, C.-G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Impedance Behavior of WO3 and NiO in Different Electrolytes2010Inngår i: Abstracts for IME-9 Conference, 2010Konferansepaper (Fagfellevurdert)
  • 279.
    Pehlivan, Esat
    et al.
    ChromoGenics AB.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Impedance spectroscopy on electrochromic tungsten and nickel oxide films as a function of applied potential.2012Inngår i: BDS 2012. Broadband Dielectric Spectroscopy and its Applications, Leipzig, September 3-7, 2012., 2012, s. 92-Konferansepaper (Fagfellevurdert)
  • 280.
    Pehlivan, Esat
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Fractal Dimensions of Niobium Oxide Films Probed by Protons and Lithium Ions2006Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 100, nr 5, s. 053506-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 281.
    Pehlivan, Esat
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Fasta tillståndets fysik.
    Azens, Andris
    Gustavsson, Greger
    A Novel Nb2O5 / Polymer Electrolyte / NiOxVy Electrochromic Device2006Konferansepaper (Annet vitenskapelig)
  • 282.
    Pehlivan, Esat
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Georén, Peter
    Ageing of electrochromic WO3 coatings characterized by electrochemical impedance spectroscopy2010Inngår i: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 207, nr 7, s. 1772-1776Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 283.
    Pehlivan, Esat
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Georen, Peter
    Characterization of Ageing of Electrochromic WO3 Coatings by Electrochemical Impedance Spectroscopy2009Inngår i: Advances in Transparent Electronics: From Materials to Device, 2009Konferansepaper (Fagfellevurdert)
  • 284.
    Pehlivan, Esat
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Georen, Peter
    von Kraemer, Sophie
    Impedance spectroscopy of aged electrochromic WO3 thin films2009Inngår i: 6th International Discussion Meeting on Relaxations in Complex Systems: New Results, Directions and Opportunities, 2009Konferansepaper (Fagfellevurdert)
  • 285.
    Pehlivan, Ilknur Bayrak
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Marsal, R.
    Pehlivan, Esat
    Runnerstrom, E. L.
    Milliron, D. J.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochromic Devices with Polymer Electrolytes Functionalized by SiO2 and In2O3:Sn Nanoparticles: Rapid Coloring/Bleaching Dynamics and Strong Near-Infrared Absorption2014Inngår i: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 126, s. 241-247Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 286.
    Pehlivan, Ilknur Bayrak
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Marsal, Roser
    Georén, Peter
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Ionic relaxation in polyethyleneimine-lithium bis(trifluoromethylsulfonyl) imide polymer electrolytes2010Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, nr 7, s. 074102-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 287.
    Pehlivan, Ilknur Bayrak
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Marsal, Roser
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Georén, Peter
    PEI-LiTFSI electrolytes for electrochromic devices: Characterization by differential scanning calorimetry and viscosity measurements2010Inngår i: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 94, nr 12, s. 2399-2404Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 288.
    Qiu, Zhen
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Ma, Yue
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Edström, Kristina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Edvinsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Controlled crystal growth orientation and surface charge effects in self-assembled nickel oxide nanoflakes and their activity for the oxygen evolution reaction2017Inngår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 42, nr 47, s. 28397-28407Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 289.
    Qiu, Zhen
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Ma, Yue
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi. Northwestern Polytechnical University.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Edvinsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Oorganisk kemi. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    An electrochemical impedance study of alkaline water splitting using nickel (iron) oxides nanosheetsInngår i: Artikkel i tidsskrift (Fagfellevurdert)
  • 290.
    Qiu, Zhen
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Edvinsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Investigating the influence of iron on nickel oxide nanosheets for enhancedoverall water splitting through in-situ Raman and impedance spectroscopy.2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

      Mixed iron-nickel-based systems with tuned microstructure have recently emerged as promising non-noble electrocatalysts for alkaline water splitting. The understanding of interfacial reaction induced charge-transfer mechanisms and active phases, however, is still limited in overall water splitting. Herein, we report a detailed investigation of active surface phases and mechanisms during both the oxygen evolution (OER) and hydrogen evolution (HER) reactions in an alkaline electrolyte through in-situ Raman and impedance spectroscopy. The frequency response of electrical behavior is interpreted by a full theoretical equivalent circuit model and is related to the Raman spectra.

      The results show that the reaction resistance exhibits a strong dependence on applied bias and electrode materials in natural correlation with the reaction rate under both OER and HER process. The presence of iron (Fe) results in a less inductive feature observed in HER impedance spectroscopy, which is associated with the coverage relaxation of involved adsorbed intermediates. By in-situ Raman spectroscopy, it is clear to see that the main function of Ni and Fe sites are dependent on the applied energy. When the Femi level shifts to more negative potentials, the hydroxyl groups are prone to adsorb on Fe3+ sites to form Fe oxyhydroxides, whereas the hydrogen groups show the tendency to adsorb (or migrate) to Ni sites, which accelerates water reduction and thus enhances HER activity. Moreover, the presence of Fe promotes the formation of high Ni valency (γ-NiOOH), leading to an improved OER catalytic performance. Our findings provide insights into the active phases formed in-situ under both the HER and OER reactions and are expected to be valuable for design strategies for efficient and earth-abundant Ni-Fe based catalytic systems.

  • 291.
    Qiu, Zhen
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Edvinsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Oorganisk kemi. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Investigating the influence of iron on nickel oxide nanosheets for enhanced overall water splitting through in-situ Raman and impedance spectroscopy2019Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Mixed iron-nickel-based systems with tuned microstructure have recently emerged as promising non-noble electrocatalysts for alkaline water splitting. The understanding of interfacial reaction induced charge-transfer mechanisms and active phases, however, is still limited in overall water splitting. Herein, we report a detailed investigation of active surface phases and mechanisms during both the oxygen evolution (OER) and hydrogen evolution (HER) reactions in an alkaline electrolyte through in-situ Raman and impedance spectroscopy. The frequency response of electrical behavior is interpreted by a full theoretical equivalent circuit model and is related to the Raman spectra.

      The results show that the reaction resistance exhibits a strong dependence on applied bias and electrode materials in natural correlation with the reaction rate under both OER and HER process. The presence of iron (Fe) results in a less inductive feature observed in HER impedance spectroscopy, which is associated with the coverage relaxation of involved adsorbed intermediates. By in-situ Raman spectroscopy, it is clear to see that the main function of nickel (Ni) and Fe sites are dependent on the applied energy. When the Femi level shifts to more negative potentials, the hydroxyl groups are prone to adsorb on Fe3+ sites to form Fe oxyhydroxides, whereas the hydrogen groups show the tendency to adsorb (or migrate) to Ni sites, which accelerates water reduction and thus enhances HER activity. Moreover, the presence of Fe promotes the formation of high Ni valency (γ-NiOOH), leading to an improved OER catalytic performance. Our findings provide insights into the active phases formed in-situ under both the HER and OER reactions and are expected to be valuable for design strategies for efficient and earth-abundant Ni-Fe based catalytic systems.

  • 292.
    Qiu, Zhen
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Tai, Cheuk-Wai
    Stockholm Univ, Dept Mat & Environm Chem, SE-10691 Stockholm, Sweden.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Edvinsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Direct observation of active catalyst surface phases and the effect of dynamic self-optimization in NiFe-layered double hydroxides for alkaline water splitting2019Inngår i: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 12, nr 2, s. 572-581Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 293.
    Qu, Hui-Yang
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Arvizu, MA
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, G A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Degradation and rejuvenation in electrochromic nickel oxide films2017Inngår i: Abstracts, 2017Konferansepaper (Fagfellevurdert)
  • 294.
    Qu, Huiying
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Arvizu, Miguel A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Degradation and rejuvenation in electrochromic nickel oxide films2017Konferansepaper (Fagfellevurdert)
    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.

  • 295.
    Qu, Hui-Ying
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. 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 universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Arvizu, Miguel A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Qiu, Zhen
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Cindemir, Umut
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochemical Rejuvenation of Anodically Coloring Electrochromic Nickel Oxide Thin Films2017Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, nr 9, s. 42420-42424Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 296.
    Qu, Hui-Ying
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. 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 universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Qiu, Zhen
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Österlund, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Cation/Anion-based electrochemical degradation and rejuvenation of electrochromic nickel oxide films2018Inngår i: ChemElectroChem, ISSN 2196-0216, Vol. 5, nr 22, s. 3548-3556Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 297.
    Qu, Hui-Ying
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Rojas González, Edgar Alonso
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Enhanced durability of Tungsten oxide electrochromic films: Processes occurring at the Indium-Tin oxide substrate2018Inngår i: 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, s. 215-, artikkel-id PS1-25Konferansepaper (Fagfellevurdert)
    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.

  • 298.
    Qu, Hui-Ying
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Rojas-González, Edgar Alonso
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Potentiostatically pretreated electrochromic tungsten oxide films with enhanced durability: Electrochemical processes at interfaces of indium–tin oxide2019Inngår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 682, s. 163-168Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 299.
    Rojas Gonzalez, Edgar
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Simultaneous electrochemical and color impedance measurements of electrochromic systems in transmittance mode: Background noise determination and test measurement on WO3.2019Konferansepaper (Fagfellevurdert)
  • 300.
    Rojas González, Edgar Alonso
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper.
    Setup for simultaneous electrochemical and color impedance measurements of electrochromic films: Theory, assessment, and test measurement2019Inngår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 90, nr 8, artikkel-id 085103Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Combined frequency-resolved techniques are suitable to study electrochromic (EC) materials. We present an experimental setup for simultaneous electrochemical and color impedance studies of EC systems in transmission mode and estimate its frequency-dependent uncertainty by measuring the background noise. We define the frequency-dependent variables that are relevant to the combined measurement scheme, and a special emphasis is given to the complex optical capacitance and the complex differential coloration efficiency, which provide the relation between the electrical and optical responses. Results of a test measurement on amorphous WO3 with LED light sources of peak wavelengths of 470, 530, and 810 nm are shown and discussed. In this case, the amplitude of the complex differential coloration efficiency presented a monotonous increase down to about 0.3 Hz and was close to a constant value for lower frequencies. We study the effect of the excitation voltage amplitude on the linearity of the electrical and optical responses for the case of amorphous WO3 at 2.6 V vs Li/Li+, where a trade-off should be made between the signal-to-noise ratio (SNR) of the optical signal and the linearity of the system. For the studied case, it was possible to increase the upper accessible frequency of the combined techniques (defined in this work as the upper threshold of the frequency region for which the SNR of the optical signal is greater than 5) from 11.2 Hz to 125.9 Hz while remaining in the linear regime with a tolerance of less than 5%. (C) 2019 Author(s).

    Fulltekst tilgjengelig fra 2020-09-01 11:13
345678 251 - 300 of 395
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf