| 1. |
- 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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| 2. |
- 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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| 3. |
- Niklasson, Gunnar A., Professor, 1953-, et al.
(författare)
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Durability of electrochromic films : Aging kinetics and rejuvenation
- 2017
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Ingår i: ECS Transactions. - : Electrochemical Society. ; , s. 1659-1669
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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.
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| 4. |
- Qu, Hui-Ying, et al.
(författare)
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Electrochemical Rejuvenation of Anodically Coloring Electrochromic Nickel Oxide Thin Films
- 2017
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; :9, s. 42420-42424
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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.
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| 5. |
- Barrios, David, et al.
(författare)
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Determination of the optical constants of the active layer of a suspended particle device smart window with multilayer structure at the clear and dark states, with and without applied voltage.
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Smart windows based on suspended particle devices (SPDs) are able to switch optically from dark to clear visual appearance when applying an AC electrical signal. This effect is due to light absorbing nanoparticles that get aligned by the applied voltage. The sandwich structure of a SPD consist of several layers and includes two outer glass substrates, each one covered on its inwards-facing side with a transparent conducting thin layer surrounding the centrally positioned SPD active layer. A knowledge of the optical constants of each layer—i.e., the complex refractive index, including its real and imaginary (absorption and scattering) parts—is a key in the design of the visual appearance of the SPD window and is a useful tool to determine the optimum thickness of the active layer.
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| 6. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
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Bifunctional solar electrocatalytic water splitting using CIGS solar modules and WO3-based electrolyzers
- 2019
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Ingår i: EMRS Spring Meeting 2019.
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Konferensbidrag (refereegranskat)abstract
- Using energy from the sun to produce a fuel and finally obtaining only water as an exhaust is a promising future technology for renewable energy and environmental sustainability. Solar driven water splitting is a method to produce hydrogen from solar energy. Coupling a solar cell with an electrolyzer is the approach with highest technological readiness. CuInxGa1-xSe2 (CIGS) is here a promising solar cell material for water splitting because it is possible to tune the band gap between 1.0 and 1.7 eV by changing the ratio between Ga and In, thus enabling maximum power point matching with an electrolyzer. Tungsten oxide is known as a photocatalytic material and mainly used for the oxygen evolution reaction in a water splitting process. However, WO3 films also show electrochromic activity together with hydrogen evolution. This result is interesting because it shows that WO3 films can be used as bifunctional materials for both hydrogen and oxygen evolution in water splitting, and provide additional functionalities to the system. In this study, WO3 films coated at different sputtering conditions on Ni foam and indium tin oxide substrates were investigated in the potential range of the hydrogen evolution reaction. The best overpotential of 164 mV vs. RHE at 10 mA/cm2 was obtained for WO3 films on Ni foam in 0.5 M H2SO4. The lowest potential needed for 10 mA/cm2 was measured 1.768 V for the electrolyzers consisting WO3 films on Ni foam as the cathode and non-coated Ni foam as the anode. Optimum solar-to-hydrogen (STH) efficiency of the CIGS solar cell modules and the electrolyzers was examined for different band gaps of the CIGS modules and sputtering conditions of WO3 films. Operation points of the combined system were calculated from the intersection of the voltage-current density curves for the CIGS modules and the electrolyzers. The results showed that the detailed sputtering conditions were not very critical to obtain high STH efficiency, indicating that the system could be robust and easily manufactured. The best-matched band gap of the CIGS was 1.19 eV and the highest STH efficiency of the CIGS driven WO3-based electrolyzers was 12.98 %.
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| 7. |
- Granqvist, Claes Göran, 1946-, et al.
(författare)
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Electrochromics on a roll : Web-coating and lamination for smart windows
- 2018
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Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 336, s. 133-138
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Tidskriftsartikel (refereegranskat)abstract
- Electrochromic devices can vary the throughput of solar energy and visible light in glazing for buildings, which are then able to combine improved energy efficiency with enhanced indoor comfort and convenience. The technology can be implemented in different ways; here the focus is on web-coated devices which can be delivered, on a roll or in the form of large sheets, as foil for glass lamination. The present paper introduces the technology, discusses web-coating versus in-line glass coating, mentions lamination, and touches on possibilities to combine electrochromism with other functionalities such as thermochromic control of solar energy transmittance. The purpose of the paper is to give a tutorial overview of a technology that is currently introduced in buildings.
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| 8. |
- Granqvist, Claes-Göran, 1946-, et al.
(författare)
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Solar energy materials for thermal applications : A primer
- 2018
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier. - 0927-0248 .- 1879-3398. ; 180, s. 213-226
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Tidskriftsartikel (refereegranskat)abstract
- Solar energy materials have properties that are tailored to the characteristics of the electromagnetic radiation in our natural surroundings, specifically its spectral distribution, angle of incidence and intensity. This tailoring can be made with regard to solar irradiation, thermal emission, atmospheric absorption, visible light, photosynthetic efficiency and more. Solar energy materials can be of many kinds, e.g., metallic, semiconducting, dielectric, glassy, polymeric, gaseous, etc. In particular, thin surface coatings of solar energy materials may exhibit the desired properties in their own right or may yield such properties when backed by an appropriate substrate. This article surveys a number of topics related to thermal applications such as solar thermal converters, transparent thermal insulators, devices for radiative cooling by exposure to the clear sky, and windows and glass facades with static or dynamic properties. The purpose of the present paper is to provide a bird's eye view over a wide class of materials of rising importance rather than giving detailed accounts of highly specialized topics.
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| 9. |
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| 10. |
- Kish, L. B., et al.
(författare)
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Facts and myths about zero-point thermal noise, and information entropy versus thermal entropy
- 2017
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Ingår i: 2017 International Conference on Noise and Fluctuations (ICNF). - New York : IEEE. - 9781509027606 - 9781509027613
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Konferensbidrag (refereegranskat)abstract
- In this talk, we are briefly surveying our recent results [1-3] about two very popular yet often misunderstood concepts in physical informatics: (i) The existence of Johnson noise at near to absolute zero temperature has been debated many times yet it is generally accepted [1]. We point out the fundamental problems [2] with the particular approach the related quantum theories [4] of Fluctuation-Dissipation Theorem are using. Then we prove that the existence of zero-point noise would allow the construction of a perpetual motion machine [1]. Finally, we cite early works pointing out that the observed “zeropoint” noise in experiments [7] with phase-sensitive linear amplifiers is an amplifier-noise [5,6] due to the uncertainty principle, and it does not exist in the resistor in an objective way, independently from the measurement [1,2]. Thus a correct derivation of the Fluctuation-Dissipation Theorem must include [1] the type of experimental setup used for the measurement. (ii) The general opinion is that information entropy and thermal entropy are interchangeable. This belief triggered Brillouin's negentropy principle of information [8], and Landauer's claimed principle [9] about energy dissipation during information erasure that has been debated on many occasions [10-19]. Here we show the newest and perhaps the simplest arguments [3] proving that the two types of entropies are apples and oranges and are not interchangeable.
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| 11. |
- Qiu, Zhen, et al.
(författare)
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An Electrochemical Impedance Study of Alkaline Water Splitting Using Fe Doped NiO Nanosheets
- 2021
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Ingår i: Physchem. - : MDPI AG. - 2673-7167. ; 1:1, s. 69-81
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Tidskriftsartikel (refereegranskat)abstract
- Mixed nickel-iron (Ni-Fe) compounds have recently emerged as promising non-precious electrocatalysts for alkaline water splitting. The understanding of the charge-transfer mechanism involved in the multi-step Faradic reaction, however, is still limited for the overall electrochemical process. In this paper, electrochemical impedance spectroscopy (EIS) measurements of Fe incorporated Ni oxide nanosheets were used to study the reaction kinetics for both hydrogen (HER) and oxygen (OER) evolution reactions in alkaline media. Our results showed that Fe incorporation improves the catalytic property of NiO nanosheets because of the lower reaction resistance and faster intermediate transformations. Detailed EIS modeling enables a separation of the surface coverage relaxation from the charge transfer resistance, with an inductive behavior observed in the low-frequency range for HER, holding important information on the dominating reaction mechanism. For OER, the good agreement between the EIS experimental results and a model with an inductance loop indicated that similar inductive behavior would be determining the EIS response at very low frequencies. The physical significance of the elementary steps gives insight into the governing reaction mechanisms involved in the electron and hole charge transfer, as well as the inherent properties of catalysts and their surface coverage relaxation.
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| 12. |
- Qiu, Zhen, et al.
(författare)
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Controlled crystal growth orientation and surface charge effects in self-assembled nickel oxide nanoflakes and their activity for the oxygen evolution reaction
- 2017
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Ingår i: International journal of hydrogen energy. - : Elsevier. - 0360-3199 .- 1879-3487. ; 42:47, s. 28397-28407
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 13. |
- Sorar, Idris, et al.
(författare)
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Electrochromism in Ni Oxide Thin Films Made by Advanced Gas Deposition and Sputtering : A Comparative Study Demonstrating the Significance of Surface Effects
- 2020
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 167:11
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Tidskriftsartikel (refereegranskat)abstract
- Films of electrochromic Ni oxide, with thickness in the ∼100–1000-nm range, were prepared by reactive advanced gas deposition (AGD) and, for comparison, also by reactive DC magnetron sputtering (MS). Voltammetric cycling was performed in an electrolyte of lithium perchlorate in propylene carbonate in the voltage range 2.0–4.1 V vs Li/Li+, and concurrent optical transmittance modulation was studied at a wavelength of 530 nm. For the thickest films, the optical modulation range was as large as ∼54% and the maximum transmittance was ∼82% for deposition by AGD, whereas the corresponding numbers were ∼45% and ∼87% for MS. Rutherford backscattering spectrometry together with measurements of film thickness demonstrated that the porosity of 400–500-nm-thick films made by AGD and MS were ∼84% and ∼45%, respectively. The charge exchange per mass unit was as high as 48–67 C g–1 for samples made by AGD. The corresponding number was much lower for MS, namely 13–18 C g–1. These results lend convincing support to the view that the electrochromism of Ni-oxide-based films in Li-ion-conducting electrolytes is dominated by surface effects.
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| 14. |
- Triana, Carlos A, et al.
(författare)
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Modeling of Electronic Properties of Amorphous Oxides
- 2018
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Ingår i: Encyclopedia of Interfacial Chemistry. - : Elsevier. - 9780128097397 - 9780128098943 ; , s. 319-331
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Bokkapitel (refereegranskat)abstract
- Amorphous transition metal oxides (aTMOs) are used as multifunctional materials in many technological applications. A detailed understanding of the electronic density of states is a necessary prerequisite for modeling their functional properties. The electronic properties, however, are structure-dependent making the description of the electronic structure of disordered and amorphous materials challenging. Here we present a scheme based on obtaining atomic model structures from simulations of experimental X-ray-Absorption spectra, together with first principles electronic structure calculations. This approach provides a self-consistent framework to assess fundamental electronic processes in aTMOs and can be applied to the study of disordered and amorphous materials in general.
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| 15. |
- Österlund, Lars, 1967-, et al.
(författare)
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Spectrally selective nanocoatings with synergistically enhanced photocatalytic and solar light modulation properties
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Spectrally selective nanocoatings that exhibit synergistically enhanced solar light modulation, luminous transmittance and catalytic properties can be made by combining dielectric film stacks with complementary optical and structural properties. Here we show two case studies:1)TiO2/VO2 luminous transparent bilayers that exhibits enhanced near-infrared light absorption and heats the TiO2 film by up to ~ 30°C resulting in ~ 2-fold increase of the photocatalytic reaction rate. The TiO2/VO2 bilayer stack exhibits anti-reflective properties, and enhanced solar light modulation (∼ 9%) compared to VO2, and ∼ 20 times% increased solar absorptance compared to TiO2. In addition the TiO2 chemically protects the VO2 layer avoiding oxidation to vanadium pentoxide. 2)TiO2/TiAlN solar absorber bilayers that yield an almost ~ 10-fold enhancement of the quantum yield for acetaldehyde removal (on par with state-of-the-art, heterojunction photocatalysts), and an associated temperature rise ~120 °C.
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