| 1. |
- Arvizu, Miguel A, et al.
(författare)
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Electrochromism in sputter-deposited W-Ti oxide films : Durability enhancement due to Ti
- 2014
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 125, s. 184-189
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of W-Ti oxide were prepared by reactive DC magnetron sputtering and were characterized by Rutherford bathcattering spectrometry, X-ray diffraction, scanning electron microscopy and atomic force microscopy. The electrochromic properties were studied by cyclic voltammetry in an electrolyte of lithium perchlorate in propylene carbonate and by optical transmittance measurements. The addition of Ti significantly promoted the amorphous nature of the films and stabilized their electrochemical cycling performance and dynamic range for electrochromism. (C) 2014 Elsevier B.V. All rights reserved.
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| 2. |
- Arvizu, Miguel A, et al.
(författare)
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Electrochemical pretreatment of electrochromic WO3 films gives greatly improved cycling durability
- 2018
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 653, s. 1-3
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Tidskriftsartikel (refereegranskat)abstract
- Electrochromic WO3 thin films have important applications in devices such as smart windows for energy-efficient buildings. Long-term electrochemical cycling durability of these films is essential and challenging. Here we investigate reactively sputter-deposited WO3 films, backed by indium-tin oxide layers and immersed in electrolytes of LiClO4 in propylene carbonate, and demonstrate unprecedented electrochemical cycling durability after straight-forward electrochemical pretreatments by the application of a voltage of 6 V vs. Li/Li+ for several hours.
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| 3. |
- Arvizu, Miguel A., et al.
(författare)
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Electrochromic dc sputtered W1-x-y Moy Tix O3 thin films: : Optical properties and durability.
- 2016
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Konferensbidrag (refereegranskat)abstract
- The key component in an electrochromic (EC) device is its primary EC thin film. The outstanding intrinsic ECproperties of tungsten oxide (WO3) make this material the best option available for the cathodic layer in an ECdevice. Nevertheless much research remains in order to optimize WO3 with regard to optical properties, durability,etc. It is well known that addition of titanium (Ti) into the matrix of WO3 increases significantly the resistance of the film to electrochemical cycling both under norma loperation and during accelerated aging in extended voltage ranges [1]. On the other hand, using molybdenum (Mo) as an additive in small concentrations helps to improve the color rendering by shifting th eposition of the maximum of the coloration band to higher energies [2]. The present work reports our recent investigations on thin films of mixed oxides with a focus on ways to optimize tungsten oxide thin films regarding both their durability and color by the addition of Ti and Mo. The films were deposited by reactive DC cosputtering from Mo and W-Ti alloy targets. Cyclic voltammetry, in a three-electrode system consisting of the film and lithium foils, was performed in a solution 1 MLiClO4 in propylene carbonate (Li–PC) as electrolyte. Insitu and ex-situ optical characterization was done for the EC films, and the transmittance switching and coloration efficiency were determined. Durability was studied by analyzing how the charge density evolved and how rapidly the transmittance modulation deteriorated during cycling for the different concentrations of Mo and Ti .References[1] M.A. Arvizu, C.A. Triana, B.I. Stefanov, C.G.Granqvist , G.A. Niklasson, “Electrochromism in SputterdepositedW-Ti Oxide Films: Durability Enhancement dueto Ti”, Solar Energy Materials & Solar Cells 125 (2014)184-189 (and references therein).[2] M.A. Arvizu, C.G. Granqvist and G.A. Niklasson,“Electrochromism in sputter deposited W1–yMoyO3 thinfilms”, Journal of Physics: Conference Series 682 (2016)012005 (and references therein).
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| 4. |
- Arvizu, Miguel A, et al.
(författare)
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Electrochromic W(1-x-y)Ti(x)lo(y)O(3) Thin Films Made by Sputter Deposition : Large Optical Modulation, Good Cycling Durability, and Approximate Color Neutrality
- 2017
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 29:5, s. 2246-2253
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Tidskriftsartikel (refereegranskat)abstract
- Tungsten oxide thin films are used in electrochromic devices such as variable-transmittance "smart windows" for energy efficient buildings with good indoor comfort. Two long-standing issues for WO3 thin films are their limited durability under electrochemical cycling and their blue color in transmission. Here, we show that both of these problems can be significantly alleviated by additions of titanium and molybdenum. We found that similar to 300 nm-thick films of sputter deposited W1-x-yTixMoyO3 are able to combine a midluminous transmittance modulation of 0.4 similar to 70% with good color neutrality and durability under extended electrochemical cycling. The Ti content should be similar to 10 at. % in order to achieve durability without impairing transmittance modulation significantly, and the Mo content preferably should be no larger than 6 at. % in order to maintain durability. Hence, our results give clear guidelines for making three-component mixed-oxide thin films that are suitable for electrochromic "smart windows".
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| 5. |
- Arvizu, Miguel A., et al.
(författare)
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Electrochromism in DC sputtered W1-yMoyO3 thin films
- 2015
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Ingår i: INERA Conference 2015. - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- Electrochromic (EC) properties of tungsten–molybdenum oxide (W1–yMoyO3) thin films were investigated. The films were deposited on indium tin oxide covered glass by reactive DC sputtering from tungsten and molybdenum targets. Elemental compositions of the W1–yMoyO3 films were determined by Rutherford back scattering. Voltammetric cycling was performed in an electrolyte of 1 M LiClO4 in propylene carbonate. The increase in molybdenum content in the EC films caused both a shift towards higher energies and a quenching of the value of the maximum of the coloration band, as compared with WO3 EC films. Durability was also diminished for W1–yMoyO3 EC films.
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| 6. |
- Arvizu, Miguel A, et al.
(författare)
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Influence of Thermal Annealings in Argon on the Structural and Thermochromic Properties of MoO3 Thin Films
- 2017
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Ingår i: International journal of thermophysics. - : Springer Science and Business Media LLC. - 0195-928X .- 1572-9567. ; 38:4
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Tidskriftsartikel (refereegranskat)abstract
- The effect of thermal annealing in an inert atmosphere (argon) on the structural and thermochromic properties of MoO3 thin films was investigated. MoO3 thin films were deposited by thermal evaporation in vacuum of MoO3 powders. X-ray diffraction patterns of the films showed the presence of the monoclinic Magneli phase Mo9O26 for annealing temperatures above 250 degrees C. Absorbance spectra of the films annealed in argon indicated that their thermochromic response increases with the annealing temperature in the analyzed range (23 degrees C-300 degrees C), a result opposite to the case of thermal annealings in air, for which case the thermochromic response shows a maximum value around 200 degrees C-225 degrees C and decreases for higher temperatures. These results are explained in terms of a higher density of oxygen vacancies formed upon thermal treatments in inert atmospheres.
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| 7. |
- Arvizu, Miguel A, et al.
(författare)
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Rejuvenation of degraded electrochromic MoO3 thin films made by DC magnetron sputtering : Preliminary results
- 2016
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Ingår i: Journal of Physics: Conference Series. - : Institute of Physics Publishing (IOPP).
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Konferensbidrag (refereegranskat)abstract
- Molybdenum oxide thin films were deposited by reactive DC magnetron sputtering and were subjected to voltammetric cycling in an electrolyte comprised of lithium perchlorate in propylene carbonate. The films were heavily degraded during 20 voltammetric cycles in an extended voltage range. The films were subsequently rejuvenated by use of potentiostatic treatments under different voltages during 20 hours. Optical changes were recorded during the electrochemical degradation and ensuing rejuvenation.
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| 8. |
- Baloukas, Bill, et al.
(författare)
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Galvanostatic Rejuvenation of Electrochromic WO3 Thin Films : Ion Trapping and Detrapping Observed by Optical Measurements and by Time-of-Flight Secondary Ion Mass Spectrometry
- 2017
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 9:20, s. 16996-17002
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Tidskriftsartikel (refereegranskat)abstract
- Electrochromic (EC) smart windows are able to decrease our energy footprint while enhancing indoor comfort and convenience. However, the limited durability of these windows, as well as their cost, result in hampered market introduction. Here, we investigate thin films of the most widely studied EC material, WO3. Specifically, we combine optical measurements (using spectrophotometry in conjunction with variable-angle spectroscopic ellipsometry) with time-of-flight secondary ion mass spectrometry and atomic force microscopy. Data were taken on films in their as-deposited state, after immersion in a Li-ion-conducting electrolyte, after severe degradation by harsh voltammetric cycling and after galvanostatic rejuvenation to regain the original EC performance. Unambiguous evidence was found for the trapping and detrapping of Li ions in the films, along with a thickness increase or decrease during degradation and rejuvenation, respectively. It was discovered that (i) the trapped ions exhibited a depth gradient; (ii) following the rejuvenation procedure, a small fraction of the Li ions remained trapped in the film and gave rise to a weak short-wavelength residual absorption; and (iii) the surface roughness of the film was larger in the degraded state than in its virgin and rejuvenated states. These data provide important insights into the degradation mechanisms of EC devices and into means of achieving improved durability.
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| 9. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
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Impedance Spectroscopy Modeling of Nickel–Molybdenum Alloys on Porous and Flat Substrates for Applications in Water Splitting
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:39, s. 23890-23897
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen production by splitting water using electrocatalysts powered by renewable energy from solar or wind plants is one promising alternative to produce a carbon-free and sustainable fuel. Earth-abundant and nonprecious metals are, here, of interest as a replacement for scarce and expensive platinum group catalysts. Ni–Mo is a promising alternative to Pt, but the type of the substrate could ultimately affect both the initial growth conditions and the final charge transfer in the system as a whole with resistive junctions formed in the heterojunction interface. In this study, we investigated the effect of different substrates on the hydrogen evolution reaction (HER) of Ni–Mo electrocatalysts. Ni–Mo catalysts (30 atom % Ni, 70 atom % Mo) were sputtered on various substrates with different porosities and conductivities. There was no apparent morphological difference at the surface of the catalytic films sputtered on the different substrates, and the substrates were classified from microporous to flat. The electrochemical characterization was carried out with linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in the frequency range 0.7 Hz–100 kHz. LSV measurements were carried out at direct current (DC) potentials between 200 and −400 mV vs the reversible hydrogen electrode (RHE) in 1 M NaOH encompassing the HER. The lowest overpotentials for HER were obtained for films on the nickel foam at all current densities (−157 mV vs RHE @ 10 mA cm–2), and the overpotentials increased in the order of nickel foil, carbon cloth, fluorine-doped tin oxide, and indium tin oxide glass. EIS data were fitted with two equivalent circuit models and compared for different DC potentials and different substrate morphologies and conductivities. By critical evaluation of the data from the models, the influence of the substrates on the reaction kinetics was analyzed in the high- and low-frequency regions. In the high-frequency region, a strong substrate dependence was seen and interpreted with a Schottky-type barrier, which can be rationalized as being due to a potential barrier in the material heterojunctions or a resistive substrate–film oxide/hydroxide. The results highlight the importance of substrates, the total charge transfer properties in electrocatalysis, and the relevance of different circuit components in EIS and underpin the necessity to incorporate high-conductivity, chemically inert, and work-function-matched substrate–catalysts in the catalyst system.
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| 10. |
- Gesheva, Kostadinka, et al.
(författare)
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Optical, structural and electrochromic properties of sputter deposited W-Mo oxide thin films
- 2016
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Ingår i: INERA CONFERENCE. - : Institute of Physics Publishing (IOPP).
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Konferensbidrag (refereegranskat)abstract
- Thin metal oxide films were investigated by a series of characterization techniques including impedance spectroscopy, spectroscopic ellipsometry, Raman spectroscopy, and Atomic Force Microscopy. Thin film deposition by reactive DC magnetron sputtering was performed at the Ångström Laboratory. W and Mo targets (5 cm diameter) and various oxygen gas flows were employed to prepare samples with different properties, whereas the gas pressure was kept constant at about 30 mTorr. The substrates were 5×5 cm2 plates of unheated glass pre-coated with ITO having a resistance of 40 ohm/sq. Film thicknesses were around 300nm as determined by surface profilometry. Newly acquired equipment was used to study optical spectra, optoelectronic properties, and film structure. Films of WO3 and of mixed W–Mo oxide with three compositions showed coloring and bleaching under the application of a small voltage. Cyclic voltammograms were recorded with a scan rate of 5 mV s–1. Ellipsometric data for the optical constants show dependence on the amount of MoOx in the chemical composition. Single MoOx film, and the mixed one with only 8% MoOx have the highest value of refractive index, and similar dispersion in the visible spectral range. Raman spectra displayed strong lines at wavenumbers between 780 cm–1 and 950 cm–1 related to stretching vibrations of WO3, and MoO3. AFM gave evidence for domains of different composition in mixed W-Mo oxide films.
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