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| 2. |
- Pehlivan, Ilknur Bayrak, et al.
(author)
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Electrochromic Devices with Polymer Electrolytes Functionalized by SiO2 and In2O3:Sn Nanoparticles : Rapid Coloring/Bleaching Dynamics and Strong Near-Infrared Absorption
- 2014
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In: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 126, s. 241-247
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Journal article (peer-reviewed)abstract
- 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.
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| 3. |
- Araujo, Rafael B., et al.
(author)
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High-entropy alloy catalysts : Fundamental aspects, promises towards electrochemical NH3 production, and lessons to learn from deep neural networks
- 2023
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In: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 105
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Journal article (peer-reviewed)abstract
- A computational approach to judiciously predict high-entropy alloys (HEAs) as an efficient and sustainable material class for the electrochemical reduction of nitrogen is here presented. The approach employs density functional theory (DFT), adsorption energies of N atoms and N2 molecules as descriptors of the catalytic activity and deep neural networks. A probabilistic approach to quantifying the activity of HEA catalysts for nitrogen reduction reaction (NRR) is described, where catalyst elements and concentration are optimized to increase the probability of specific atomic arrangements on the surfaces. The approach provides key features for the effective filtering of HEA candidates without the need for time-consuming calculations. The relationships between activity and selectivity, which correlate with the averaged valence electron concentration and averaged electronegativity of the reference HEA catalyst, are analyzed in terms of sufficient interaction for sustained reactions and, at the same time, for the release of the active site. As a result, a complete list of 3000 HEAs consisting of quinary components of the elements Mo, Cr, Mn, Fe, Co, Ni, Cu, and Zn are reported together with their metrics to rank them from the most likely to the least likely active catalysts for NRR in gas diffusion electrodes, or for the case where non-aqueous electrolytes are utilized to suppress the competing hydrogen evolution reaction. Moreover, the energetic landscape of the electrochemical NRR transformations are computed and compared to the case of Fe. The study also analyses and discusses how the results would translate to liquid-solid reactions in aqueous electrochemical cells, further affected by changes in properties upon hydroxylation, oxygen, hydrogen, and water coverages.
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| 4. |
- Atak, Gamze, et al.
(author)
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Cycling durability and potentiostatic rejuvenation of electrochromic tungsten oxide thin films : Effect of silica nanoparticles in LiClO4-Propylene carbonate electrolytes
- 2023
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In: Solar Energy Materials and Solar Cells. - : Elsevier. - 0927-0248 .- 1879-3398. ; 250
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Journal article (peer-reviewed)abstract
- Electrochromic (EC) technology allows control of the transmission of visible light and solar radiation through thin-film devices. When applied to “smart” windows, EC technology can significantly diminish energy use for cooling and air conditioning of buildings and simultaneously provide good indoor comfort for the buildings’ occupants through reduced glare. EC “smart” windows are available on the market, but it is nevertheless important that their degradation under operating conditions be better understood and, ideally, prevented. In the present work, we investigated EC properties, voltammetric cycling durability, and potentiostatic rejuvenation of sputter-deposited WO3 thin films immersed in LiClO4–propylene carbonate electrolytes containing up to 3.0 wt% of ∼7-nm-diameter SiO2 nanoparticles. Adding about 1 wt% SiO2 led to a significant improvement in cycling durability in the commonly used potential range of 2.0–4.0 V vs. Li/Li+. Furthermore, X-ray photoemission spectroscopy indicated that O–Si bonds were associated with enhanced durability in the presence of SiO2 nanoparticles.
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| 5. |
- Atak, Gamze, et al.
(author)
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Durability studies of annealed electrochromic tungsten oxide films
- 2021
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In: EMRS Fall Meeting 2021.
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Conference paper (other academic/artistic)abstract
- In electrochromic (EC) applications, annealing is a crucial parameter not only for an individual layer but also for a full device. For the fabrication of a complete EC device, indium tin oxide (ITO) is often preferred as a transparent conductor layer. ITO films with high transparency and low electrical resistance are usually obtained by sputtering at high substrate temperatures. Consequently, the effect of high temperature on the EC layers can be very significant during sputtering of the ITO top layer for EC devices consisting of five sputtered layers on a single substrate. The role of annealing of a single layer of WO3 may also be important for EC performance. In the present work, we studied the effects of annealing on the durability of WO3 films. Thin films of WO3 were deposited by reactive DC magnetron sputtering in a mixture of Ar and O2 gases using an oxygen to argon ratio of 0.15. The total gas pressure was set to 4.0 Pa, and the sputtering power was 200 W. The WO3 films were deposited onto (i) unheated glass plates, (ii) such plates pre-coated with transparent and electrically conducting ITO with a sheet resistance of 60 Ω/square, and (iii) glass plates pre-coated with fluorine-doped tin oxide (FTO) with a sheet resistance of 14 Ω/square. Film thicknesses were 300±10 nm. After deposition of the films, the samples were annealed at 150, 300, 450, and 600 °C in ambient air for one h using a heating rate of 10 °C min-1. Cyclic voltammetry (CV) was performed for up to 500 cycles between 2.0 and 4.0 V vs. Li/Li+ at a scan rate of 20 mV s–1. Annealing at temperatures at and above 300 °C resulted in deteriorated electrochromic properties of the WO3 films i.e., a decreased transmittance variation. Charge density and coloration efficiency changes during extended electrochemical cycling were also observed as a function of cycle number and annealing temperature. It was found that the maximum optical transmittance modulation at a wavelength of 528 nm after 500 CV cycles was 69.3% for the film annealed at 150 °C.
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| 6. |
- Atak, Gamze, et al.
(author)
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Electrochromic performance of WO3 films with different ITO layers
- 2019
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In: EMRS Spring Meeting 2019..
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Conference paper (other academic/artistic)abstract
- Electrochromic (EC) materials are able to change their optical properties such as transmission, absorption and reflection reversibly by application of an external voltage. EC metal oxides are divided into two groups: cathodic (coloring under ion insertion) and anodic (coloring under ion extraction). Tungsten oxide (WO3) is a well-known cathodic EC material and has been intensively studied in the last 30 years. EC materials and devices have been developed as an alternative to passive coating materials for light and heat management. Conventionally, an EC device is a construction with five-layers: transparent conducting oxide (TCO)/cathodic EC/ion conducting layer (liquid, gel or solid)/anodic EC/TCO, either all on one substrate or positioned between two substrates in a laminated configuration. Indium-tin oxide (ITO) coated substrates are used as a TCO electrode in EC applications due to their high conductivity and transparency.In this study, we deposited WO3 films onto ITO coated glass substrates with different sheet resistances (15, 30, 60 and 1000 Ω/□) by using DC magnetron sputtering technique. Optical and structural properties of ITO films were investigated. For durability studies, cyclic voltammetry data was recorded for up to 500 cycles between 2.0 and 4.0 V versus Li/Li+ at a scan rate of 20 mV s−1. Chronoamperometry measurements of the WO3 films were also performed. We measured the inserted and extracted charges as well as bleaching and coloring times of WO3 films with different ITO layer properties. Generally, ITO with low resistivity is preferred for the electrochemical measurements while absorption is low in the near-infrared region for ITO with higher resistivity. In this study, it is observed that the ITO with 60 Ω/□ sheet resistance is very suitable for optical and electrochromic measurements.
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| 7. |
- Atak, Gamze, et al.
(author)
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Electrochromic tungsten oxide films prepared by sputtering : Optimizing cycling durability by judicious choice of deposition parameters
- 2021
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In: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 367
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Journal article (peer-reviewed)abstract
- Thin films of W oxide were prepared by reactive DC magnetron sputtering (5 cm-diameter W target), and their electrochromic (EC) properties were investigated in an electrolyte of LiClO4 in propylene carbonate. The purpose of the study was to elucidate the role of critical deposition parameters-oxygen/argon gas flow ratio for the sputter plasma Gamma, total pressure in the sputter plasma p(tot) , and sputtering power P-s - on the EC performance with foci on electrochemical cycling durability and optical modulation range Delta T. Specifically, we used 0.15 <= Gamma <= 0.90, 5 <= p(tot) <= 30 mTorr, and 200 <= P-s <= 400 W and studied cycling durability for up to 500 voltammetric cycles in the range 2.0-4.0 V vs. Li/Li+ together with optical properties at a wavelength of 528 nm. Most significantly, we discovered that a judicious choice of deposition parameters could yield films with superior cycling durability. Thus a similar to 300 nm-thick film prepared at Gamma = 0.90, p(tot) = 10 mTorr, and P-s = 200 W showed Delta T approximate to 65% after an initial "training" during similar to 100 voltammetric cycles; higher values of p(tot), on the other hand, yielded films whose Delta Ts degraded by similar to 10% during the cycling, and a lower value of p(tot) led to dark films with only marginal electrochromism. Hence our work delineates a pathway towards W oxide films with excellent durability of the EC properties.
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| 8. |
- Atak, Gamze, et al.
(author)
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Electrochromism of nitrogen-doped tungsten oxide thin films
- 2020
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In: Materials Today. - : Elsevier BV. - 2214-7853. ; 33:6, s. 2434-2439
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Journal article (peer-reviewed)abstract
- Tungsten-oxide-based thin films were prepared by reactive DC magnetron sputtering in the presence ofoxygen and nitrogen. Nitrogen contents up to 12 at.% were documented by Rutherford backscattering spectrometry and time-of-flight elastic recoil detection analysis. Optical and electrochemical measurements showed that films with up to 4 at.% of nitrogen were as transparent as undoped tungsten oxide films and displayed enhanced electrochromic properties manifested in an increase in the coloration efficiency by as much as 20%.
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| 9. |
- Atak, Gamze, et al.
(author)
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Nitrogen doped W oxide films for electrochromic applications
- 2019
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In: EMRS Spring Meeting 2019.
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Conference paper (peer-reviewed)abstract
- Electrochromic (EC) materials are able to change their optical properties such as transmission, absorption and reflection reversibly by application of an external voltage. EC metal oxides are divided into two groups: cathodic (coloring under ion insertion) and anodic (coloring under ion extraction). W oxide is a well-known cathodic EC material and its color changes from transparent to dark blue when ions are inserted.A desirable electrochromic material must have and maintain a high optical modulation, high coloration efficiency, fast coloration/bleaching switching kinetics and a stable charge/ discharge reversibility. In this study, W oxide films with different nitrogen levels were deposited by using reactive DC sputtering onto glass and ITO coated glass in Ar+O2+N2 atmosphere. For all films, the total gas pressure was set to 4.0 Pa, the Ar flow rate was kept at 50 ml/min, and the O2+N2 flow rate was kept at 7.5 ml/min. The optical, structural and electrochromic properties of undoped and N-doped W oxide films were investigated. The optical studies revealed that the average optical transmittance and band gap decreased (from 3.43 to 3.08 eV) due to N doping. It is shown that a small amount of nitrogen has promising effects on the EC performance (i.e. charge/discharge reversibility, optical modulation, coloration efficiency) of the WO3 films. It is observed that CE values increased by increasing N2 flow rate and its maximum value was 33.8 cm2/C. The maximum ΔT at 537 nm was 73.6% for an optimized N doped W oxide film.
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| 10. |
- Atak, Gamze, et al.
(author)
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The role of oxygen to argon gas flow ratio on the durability of sputter-deposited electrochromic tungsten oxide films
- 2021
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In: EMRS Fall Meeting 2021.
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Conference paper (other academic/artistic)abstract
- Materials that are able to vary their transparency and coloration reversibly when they are subjected to an electrical current or voltage are referred to as “electrochromic” (EC). High optical transmittance modulation and long service lifetime are apparent requirements for EC materials used in smart windows technology. An extended service lifetime is provided by the long-term durability of the materials. One important aspect of durability is the ability to sustain charge transport between the EC film and electrolyte, or between the two EC films in a device, for many hundreds or thousands of cycles without any significant changes in the performance such as optical modulation and inserted-extracted charge. The purpose of this study is to clarify the effects of the oxygen-argon gas flow ratio during sputter deposition on the durability of WO3 films. In this study, the oxygen to argon gas-flow ratio was modulated by setting the O2 flow rate to 7.5, 15.0, 22.5, and 45.0 ml min-1 and using a fixed Ar flow rate of 50 ml min-1. Thus, the oxygen to argon gas-flow ratio was varied from 0.15 to 0.90. The pressure in the sputter plasma was set as 30 mTorr and the sputter power was maintained at 200 W. For durability studies, cyclic voltammetry data were recorded for up to 500 cycles between 2.0 and 4.0 V versus Li/Li+ at a scan rate of 20 mV s-1. High oxygen to argon gas ratio was found to have a positive effect on the EC properties of the films. When the long-term performance of the films was examined, it was seen that all the samples displayed a slow decline of the colored-state transmittance due to ion accumulation in the host material. After 500 color-bleach cycles, the maximum optical transmittance modulation between colored and bleached states at a wavelength of 528 nm was 63.6% when the oxygen to argon gas-flow ratio was 0.90.
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