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1.	Arvizu, Miguel A, et al. (författare) Electrochromism in sputter-deposited W-Ti oxide films : Durability enhancement due to Ti 2014 Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 125, s. 184-189 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.
2.	Arvizu, Miguel A, et al. (författare) Electrochemical pretreatment of electrochromic WO3 films gives greatly improved cycling durability 2018 Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 653, s. 1-3 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.
3.	Arvizu, Miguel A., et al. (författare) Electrochromic dc sputtered W1-x-y Moy Tix O3 thin films: : Optical properties and durability. 2016 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).
4.	Arvizu, Miguel A, et al. (författare) 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 Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 29:5, s. 2246-2253 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".
5.	Arvizu, Miguel A., et al. (författare) Electrochromism in DC sputtered W1-yMoyO3 thin films 2015 Ingår i: INERA Conference 2015. - : Institute of Physics (IOP). 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.
6.	Arvizu, Miguel A, et al. (författare) Influence of Thermal Annealings in Argon on the Structural and Thermochromic Properties of MoO3 Thin Films 2017 Ingår i: International journal of thermophysics. - : Springer Science and Business Media LLC. - 0195-928X .- 1572-9567. ; 38:4 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.
7.	Arvizu, Miguel A, et al. (författare) Rejuvenation of degraded electrochromic MoO3 thin films made by DC magnetron sputtering : Preliminary results 2016 Ingår i: Journal of Physics: Conference Series. - : Institute of Physics Publishing (IOPP). 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.
8.	Baloukas, Bill, et al. (författare) 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 Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 9:20, s. 16996-17002 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.
9.	Bayrak Pehlivan, Ilknur, et al. (författare) Impedance Spectroscopy Modeling of Nickel–Molybdenum Alloys on Porous and Flat Substrates for Applications in Water Splitting 2019 Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:39, s. 23890-23897 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.
10.	Gesheva, Kostadinka, et al. (författare) Optical, structural and electrochromic properties of sputter deposited W-Mo oxide thin films 2016 Ingår i: INERA CONFERENCE. - : Institute of Physics Publishing (IOPP). 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.
11.	Granqvist, Claes G., 1946-, et al. (författare) Advances in electrochromic device technology : Multiple roads towards superior durability 2019 Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 357, s. 619-625 Tidskriftsartikel (refereegranskat)abstract Most electrochromic (EC) devices must have a service lifetime of many years, and this is particularly so for “smart windows” in buildings with good energy efficiency and indoor comfort. The central part of oxide-based EC devices contains thin films based on W oxide and Ni oxide together with an interposed electrolyte. Depending on operating conditions, these films may show degradation at a slower or faster pace, and means to prevent or reverse this phenomenon, or as a minimum allow reliable lifetime prediction, have been sought ever since the beginnings of EC technology. Here we survey recent endeavors related to EC films of W oxide and Ni oxide and show that (i) electrochemical pretreatment of films in a liquid electrolyte can significantly improve durability, (ii) electrochemical posttreatment in a liquid electrolyte can rejuvenate degraded films, (iii) mixed oxides can have better durability and optical performance than corresponding pure oxides, and (iv) lifetime prediction is possible.
12.	Granqvist, Claes Göran, 1946-, et al. (författare) Electrochromic materials and devices for energy efficiency and human comfort in buildings : A critical review 2018 Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 259, s. 1170-1182 Forskningsöversikt (refereegranskat)abstract Electrochromic (EC) materials can be integrated in thin-film devices and used for modulating optical transmittance. The technology has recently been implemented in large-area glazing (windows and glass facades) in order to create buildings which combine energy efficiency with good indoor comfort. This critical review describes the basics of EC technology, provides a case study related to EC foils for glass lamination, and discusses a number of future aspects. Ample literature references are given with the object of providing an easy entrance to the burgeoning research field of electrochromics.
13.	Morales-Luna, Michael, et al. (författare) Electrochromic properties of W1-x-yNixTiyO3 thin films made by DC magnetron sputtering 2016 Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 615, s. 292-299 Tidskriftsartikel (refereegranskat)abstract We investigated the electrochromic properties of tungsten-nickel-titanium oxide (W1-x-yNixTiyO3) thin films. Special emphasis was put on W0.83-xNixTi0.17O3 since this composition gave the highest electrochemical durability. The films were deposited onto indium-tin oxide coated glass by reactive DC magnetron sputtering, and cyclic voltammetry as well as optical transmittance measurements were performed in an electrolyte of 1 M LiClO4 in propylene carbonate. The potential window was chosen so as to cause rapid degradation of the samples. Elemental compositions were obtained by Rutherford backscattering spectroscopy and structural information by X-ray diffraction. We verified that the titanium additive improved the electrochemical durability of tungsten-oxide-based films and also documented that a further addition of nickel was unable to enhance the EC performance to any significant degree.
14.	Morales-Luna, Michael, et al. (författare) Sputter deposited W1-x-yNixTiyO3 thin films : Electrochromic properties and durability 2016 Ingår i: INERA Conference. - : Institute of Physics (IOP). Konferensbidrag (refereegranskat)abstract Previous research demonstrated that a small amount of nickel enhances the coloration efficiency of tungsten-nickel oxide electrochromic (EC) thin films with respect to that of pure tungsten oxide (WO3) films. Furthermore the incorporation of titanium gives an improvement in the durability of tungsten-titanium oxide EC thin films. In this work we investigated the EC performance of tungsten-nickel-titanium oxide (W1-x-yNixTiyO3) EC thin films with emphasis on durability. The films were deposited on indium tin oxide covered glass by reactive dc sputtering from tungsten, tungsten-titanium alloy and nickel targets. Cyclic voltammetry was performed using 1 M LiClO4 in propylene carbonate as electrolyte. The voltage window was chosen to induce fast degradation of the samples within 80 cycles. Elemental compositions were obtained by Rutherford Backscattering Spectroscopy.
15.	Niklasson, Gunnar A., Professor, 1953-, et al. (författare) Durability of electrochromic films : Aging kinetics and rejuvenation 2017 Ingår i: ECS Transactions. - : Electrochemical Society. ; , s. 1659-1669 Konferensbidrag (refereegranskat)abstract 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.
16.	Niklasson, Gunnar A., 1953-, et al. (författare) Electrochemical degradation and rejuvenation of electrochromic tungsten oxide thin films 2016 Konferensbidrag (refereegranskat)abstract 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.
17.	Qu, Huiying, et al. (författare) Degradation and rejuvenation in electrochromic nickel oxide films 2017 Konferensbidrag (refereegranskat)abstract 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.
18.	Qu, Hui-Ying, et al. (författare) Electrochemical Rejuvenation of Anodically Coloring Electrochromic Nickel Oxide Thin Films 2017 Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; :9, s. 42420-42424 Tidskriftsartikel (refereegranskat)abstract 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.
19.	Wen, Ruitao, et al. (författare) Electrochromics for energy efficient buildings : Towards long-term durability and materials rejuvenation 2016 Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 290, s. 135-139 Tidskriftsartikel (refereegranskat)abstract Electrochromic devices such as "smart windows" for energy efficient windows must be durable enough for many years of practical use. Typical devices employ films based on W oxide and Ni oxide, and this paper surveys recent progress on durability-related issues for these materials. In the case of W oxide, we discuss the beneficial effects of Ti addition, and we describe recent and unexpected progress concerning galvanostatic rejuvenation of aged W oxide films. For Ni oxide, we report how charge exchange declination during extended voltammetric cycling can be modeled in terms of a power law.
20.	Wen, Rui-Tao, et al. (författare) Ion Trapping and Detrapping in Amorphous Tungsten Oxide Thin Films Observed by Real-Time Electro-Optical Monitoring 2016 Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 28:13, s. 4670-4676 Tidskriftsartikel (refereegranskat)abstract Several technologies for energy saving and storage rely on ion exchange between electrodes and electrolytes. In amorphous electrode materials, a detailed knowledge of Li-ion intercalation is hampered by limited information about the structure and transport properties of the materials. Amorphous tungsten oxide is the most studied electrochromic material and suffers from ion trapping-induced degradation of charge capacity and optical modulation span upon extensive electrochemical cycling. In this paper, we investigate trapping and detrapping processes in connection with performance degradation and specifically use real-time electro-optical monitoring to identify different trap energy ranges pertinent to the ion-intercalated system. Evidence of three kinds of traps that degrade electrochromic tungsten oxide during ion intercalation is presented: (i) shallow traps that erode the colored state, (ii) deep traps that lower the bleached-state transmittance, and (iii) irreversible traps. Importantly, Li-ion detrapping from shallow and deep traps takes place by different processes: continuous Li-ion extraction is possible from shallow traps, whereas a certain release time must be exceeded for detrapping from deep traps. Our notions for ion trapping and detrapping, presented here, may serve as a starting point for discussing ion intercalation in various amorphous materials of interest for energy-related applications.
21.	Wen, Rui-Tao, et al. (författare) Progress in Electrochromics: Towards Long-Term Durability and Materials Rejuvenation for Oxide-Based Thin Films 2015 Ingår i: ECS Transactions. - : Electrochemical Society. - 1938-5862 .- 1938-6737. ; , s. 9-16 Konferensbidrag (refereegranskat)abstract Most electrochromic devices, such as “smart windows” for energy efficient glazings, must be durable enough for many years of service life. Typical constructions use films based on thin films of W oxide and Nioxide, and this paper summarizes progress on durability-related issues for these materials. For W oxide, we describe recent and unexpected progress on galvanostatic rejuvenation of aged W oxide films, and we also discuss the beneficial effects of Ti addition. For Ni oxide, we report how charge exchange declination during extended voltammetric cycling can be modeled in terms of a power law and also demonstrate how modest additions of Ir can dramatically extend the cycling durability.
22.	Arvizu, Miguel A, et al. (författare) Electrochromic WO3 thin films attain unprecedented durability by potentiostatic pretreatment 2019 Ingår i: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 7:6, s. 2908-2918 Tidskriftsartikel (refereegranskat)abstract Electrochromic windows and glass facades are able to impart energy efficiency jointly with indoor comfort and convenience. Long-term durability is essential for practical implementation of this technology and has recently attracted broad interest. Here we show that a simple potentiostatic pretreatment of sputterdeposited thin films of amorphous WO3-the most widely studied electrochromic material-can yield unprecedented durability for charge exchange and optical modulation under harsh electrochemical cycling in a Li-ion-conducting electrolyte and effectively evades harmful trapping of Li. The pretreatment consisted of applying a voltage of 6.0 V vs. Li/Li+ for several hours to a film backed by a transparent conducting In2O3: Sn layer. Associated compositional and structural modifications were probed by several techniques, and improved durability was associated with elemental intermixing at the WO3/ITO and ITO/glass boundaries as well as with carbonaceous solid-electrolyte interfacial layers on the WO3 films. Our work provides important new insights into long-term durability of ion-exchange-based devices.
23.	Arvizu, Miguel. A., et al. (författare) Electrochromism in Sputter Deposited W1-yMoyO3 Thin Films 2016 Ingår i: Journal of Physics, Conference Series. - 1742-6588 .- 1742-6596. ; :012005, s. 1-6 Tidskriftsartikel (refereegranskat)
24.	Arvizu, Miguel, et al. (författare) Galvanostatic ion de-trapping rejuvenates oxide thin films 2015 Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 7:48, s. 26387-26390 Tidskriftsartikel (refereegranskat)abstract Ion trapping under charge insertion-extraction is well-known to degrade the electrochemical performance of oxides. Galvano-static treatment was recently shown capable to rejuvenate the oxide, but the detailed mechanism remained uncertain. Here we report on amorphous electrochromic (EC) WO3 thin films prepared by sputtering and electrochemically cycled in a lithium-containing electrolyte under conditions leading to severe loss of charge exchange capacity and optical modulation span. Time-of-flight elastic recoil detection analysis (ToF-ERDA) documented pronounced Li+ trapping associated with the degradation of the EC properties and, importantly, that Li+ detrapping, caused by a weak constant current drawn through the film for some time, could recover the original EC performance. Thus, ToF-ERDA provided direct and unambiguous evidence for Li+ detrapping.
25.	Boyadjiev, Stefan I., et al. (författare) Study of the electrochromic properties of MAPLE and PLD deposited WO3 thin films 2017 Konferensbidrag (refereegranskat)abstract Tungsten trioxide (WO3) thin films were grown by matrix assisted pulsed laser evaporation (MAPLE) and pulsed laser deposition (PLD), and their properties were investigated for electrochromic applications. The structure, morphology and optical properties of these MAPLE and PLD grown from monoclinic WO3 nano-sized particles WO3 thin films were also studied. A KrF* excimer (λ=248 nm, ζFWHM=25 ns) laser source was used in all experiments. The films were studied by atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXRD) and Fourier transform infrared spectroscopy (FTIR). Cyclic voltammetry measurements were also performed in glove box with Ar atmosphere towards Li electrode, and the coloring and bleaching states were investigated. The morpho-structural investigations disclosed the synthesis of single-phase monoclinic WO3 films consisting of crystalline nano-grains embedded in an amorphous matrix. All thin films showed good electrochromic properties - strong coloration and fast and full bleaching. The effect was observed for many cycles, the strong coloration and full bleaching being preserved. These results are promising for future application of MAPLE and PLD deposited WO3 thin films in the development of electrochromic devices.
26.	Niklasson, Gunnar, 1953-, et al. (författare) Electrochemical rejuvenation of Tungsten oxide electrochromic thin films : Evidence from impedance spectroscopy 2018 Ingår i: 13th International Meeting on Electrochromism, IME-13. ; , s. 11- Konferensbidrag (refereegranskat)abstract 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).
27.	Qu, Hui-Ying, et al. (författare) Degradation and rejuvenation in electrochromic nickel oxide films 2017 Ingår i: Hybrid & Organic Photovoltaics. Konferensbidrag (refereegranskat)
28.	Wen, Ruitao, et al. (författare) Electrochromics for energy efficient buildings : Towards long-term durability and materials rejuvenation 2015 Ingår i: Surface and Coating Technology. - : Elsevier. - 0257-8972. ; 278, s. 121-125 Tidskriftsartikel (refereegranskat)abstract Electrochromic devices such as “smart windows” for energy efficient windows must be durable enough for many years of practical use. Typical devices employ films based on W oxide and Ni oxide, and this paper surveys recent progress on durability-related issues for these materials. In the case of W oxide, we discuss the beneficial effects of Ti addition, and we describe recent and unexpected progress concerning galvanostatic rejuvenation of aged W oxide films. For Ni oxide, we report how charge exchange declination during extended voltammetric cycling can be modeled in terms of a power law.

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