Fabrication of films of hydrogen uranyl phosphate tetrahydrate and their use as solid electrolytes in electrochromic displays
TL;DR: In this paper, it was shown that the high proton conductivity of hydrogen uranyl phosphate tetrahydrate HUO 2 PO 4 ·4H 2 O (HUP) is sufficient to enable an HUP/H x WO 3 electrochromic cell to function as fast as a cell with an acidic solution electrolyte.
Abstract: We have found that the high proton conductivity of hydrogen uranyl phosphate tetrahydrate HUO 2 PO 4 ·4H 2 O (HUP) is sufficient to enable an HUP/H x WO 3 electrochromic cell to function as fast as a cell with an acidic solution electrolyte. Switching times down to 0.3 s were found. The fabrication procedure to obtain the stable and uniform films of HUP required has been optimized, and dense sintered films up to 6 cm in diameter have been produced.
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TL;DR: In this article, inorganic and organic electrochromic materials are discussed in the context of developing a film-based optical shutter for a window application, which allows regulation of conductive and radiative heat transfer rates, with variable optical attenuation.
Abstract: Numerous inorganic and organic electrochromic materials are discussed in the context of developing a film-based optical shutter for a window application. It is possible electronically to alter a window's transmission and reflection properties by use of electrochromic thin films. This allows regulation of conductive and radiative heat transfer rates, with variable optical attenuation. As a result, an aperture can be optically and thermally managed, reducing space heating and cooling loads. The properties of transition metal oxides, such as WO 3 , MoO 3 , Ir 2 O 3 and V 2 O 5 are detailed. Organic systems such as heptyl viologen and polytungsten anion are reviewed. Also, intercalated structures are discussed. Various designs of working devices are outlined with emphasis on solid-state configurations. From this quantification, materials and devices with appropriate deposition techniques for window applications are detailed.
548 citations
TL;DR: In this paper, the development, history, theoretical basis, and experimental performance of solid-state hydrogen detectors under flow-through conditions available to date such as pyroelectric, piezoelectric, fiber optic, and electrochemical devices are reviewed.
Abstract: This paper reviews the development, history, theoretical basis, and experimental performance of solid‐state hydrogen detectors under flow‐through conditions available to date such as pyroelectric, piezoelectric, fiber optic, and electrochemical devices. Semiconductor hydrogen detectors will only be reviewed briefly, as excellent reviews on this subject already exist. In view of the fact that almost all the devices that will be discussed later in this paper use Pd as a hydrogen trap, we devote a subsection to examining the role of palladium as a catalyst as well as some of the characteristics of the Pd‐H2 system. Non‐solid‐state hydrogen sensors, such as the flame ionization detector are not the object of this review. A useful feature of this review is a comparison of operating characteristics of each device in a general table in Sec. VII. In that section a general discussion is presented, including a critical comparison of the capabilities and parameters of various solid‐state hydrogen sensors in the form of a table showing data collected from the literature. The Pd‐fiber optic sensor is the most sensitive optical device operating at room temperature. The Pd‐photopyroelectric sensor appears to be most economical and second best in sensitivity at room temperature; it has the best potential for high signal‐to‐noise operation at the widest temperature range, down to cryogenic temperatures. The Pd‐field effect transistor devices exhibit the second highest sensitivity at elevated temperatures.
218 citations
TL;DR: In this paper, a two-part in-depth review is given of the electrochromic behaviour of thin films of transition metal oxides. But the authors focus on the method and details of film deposition or growth, which determine film stoichiometry and morphology and in turn strongly influence electro chromic behaviour.
Abstract: Thin films of a number of transition metal oxides, when employed as electrodes in the appropriate electrochemical cells, exhibit electrochromism by a reversible ion-insertion mechanism. These oxides may be divided into two groups, those which colour cathodically by a reduction process, and those which colour anodically by an oxidation process. At present the former class is known to contain the oxides of W, Mo, V, Nb and Ti, whereas those of Ir, Rh, Ni and Co are contained in the latter class. A two-part in-depth review is given of the electrochromic behaviour of thin films of these oxides. This part of the paper considers cathodically coloured oxides, with anodically coloured oxides the subject of the second part. Special attention is given to tunstic oxides as the most studied example and as a model for the behaviour of other members of its class. Significant advances in the understanding and development of electrochromic displays are highlighted. Fabrication and performance of display electrode and complete display cells based on these materials is described and compared, suggestion put forward regarding the most promising electrochromic material/electrolyte combinations for further study. Emphasis is placed on the method and details of film deposition or growth which determine film stoichiometry (including moisture content) and morphology and in turn strongly influence electrochromic behaviour.
176 citations
TL;DR: In this paper, the authors review designs and properties of ECDs, giving special emphasis to transparent devices, i.e., smart windows, and classify them according to the type of electrolyte or ion conductor: liquid, solid inorganic in bulk or thin-film form, or solid organic (polymer).
Abstract: An electrochromic device (ECD) has in its center an electrolyte or ion conductor, which is in contact with films that provide optical modulation, ion storage, and (transparent) electrical conduction. We review designs and properties of ECDs, giving special emphasis to transparent devices, i.e. smart windows. The ECDs are categorized according to the type of electrolyte or ion conductor: liquid, solid inorganic in bulk- or thin-film form, or solid organic (polymer). The electrochromic film is W oxide; this material is used in the majority of all studied ECDs.
148 citations
TL;DR: In this article, the principles, physical configuration and the materials employed to make the solid state electrochromic (EC) devices are described and the merits of sol-gel method to deposit coatings for this application are discussed.
Abstract: Solid state electrochromic (EC) devices are composed of multiple thin film layers in which each coating performs specific optical and electrical functions. This review describes the principles, physical configuration and the materials employed to make the EC devices. The merits of sol-gel method to deposit coatings for this application are discussed. Sol-gel activities to date for making these devices and coatings are summarized.
98 citations
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TL;DR: In this article, it was shown that the layered hydrate HUO2PO4 is a rapid proton conductor with a room temperature conductivity of 4 × 10−3ohm−1cm−1.
Abstract: We have found that the layered hydrate HUO2PO4. 4H2O is a rapid proton conductor. The room temperature conductivity of 4 × 10−3ohm−1cm−1 is higher than that of Na+ in β alumina. The activation energy is 30± 3 kJ mol−1. The material is insoluble, and presses into transluscent discs suitable for solid electrolyte applications.
136 citations
TL;DR: In this paper, a Grotthus-type mechanism of conduction is proposed which involves intermolecular transfer steps (hopping) and inter-parallel transfer steps in comparable numbers, the former facilitated by the high concentration of H 3 O + ions in the structure, and the latter most likely facilitated by high H-bond vacancies.
Abstract: We have found that hydrogen uranyl phosphate tetrahydrate HUO 2 PO 4 ·4H 2 O has a high proton conductivity. The ac conductivity was 0.4 ohm −1 m −1 at 290°K measured parallel to the faces of sintered disks of the compound. The activation energy was found to be 31 ± 3 kJ mole −1 . The values of conductivity were between 3 and 10 times lower when measured perpendicular to the disk faces due to preferred orientation of the plate-like crystals. Both the powder and sintered disks are stable in air and insoluble in phosphoric acid solution of pH 2.5. Experiments are described which enable possible grain boundary contributions to the conductivity to be determined in such hydrates. The extrinsic grain boundary contribution to the conductivity was found to be small from experiments in which the pH in a solution cell was varied. The abnormally high bulk H + conductivity thus inferred is attributed primarily to the high concentration of H + , which exists as H 3 O + in the interlamellar hydrogen-bonded network. A Grotthus-type mechanism of conduction is proposed which involves intermolecular transfer steps (hopping) and intramolecular transfer steps, in comparable numbers, the former facilitated by the high concentration of H 3 O + ions in the structure, and the latter most likely facilitated by the high concentration of H-bond vacancies.
132 citations
TL;DR: In this paper, the main features of a passive thin-film display cell based on the electrochemically reversible formation of a tungsten bronze according to the reaction are considered, where a critical requirement of these cells is that Dτ(qCm/Q)2 ≈ 1, where the symbols are, in order, the M+ diffusion coefficient, the required device response time, the electronic charge, the maximum practical volume concentration of M in the WO3 film and lastly the area colouring charge.
Abstract: The main features of a passive thin film display cell based on the electrochemically reversible formation of a tungsten bronze according to the reaction
(colourless) WO3 + xM+ + xe− ⇌ MxWO3(blue)
where 0 < x < 1 are considered. Chemical analysis of an electrochemically coloured WO3 film has confirmed the presence of M. It is shown that a critical requirement of these cells is that Dτ(qCm/Q)2 ≈ 1, where the symbols are, in order, the M+ diffusion coefficient, the required device response time, the electronic charge, the maximum practical volume concentration of M in the WO3 film and lastly the area colouring charge. Typical energy requirements might be about 10 mJ cm−2 per complete cycle in a favourable case.
Ionic injection overpotentials and ionic diffusion both appear to play a significant role in determining cell currents. Preliminary diffusion coefficient results for Li+ in r.f. sputtered WO3 films are reported, and their predicted dependence of film structure is discussed. The optical absorption of coloured WO3 films is presented, and it is interpreted as being predominantly due to free-electron intraband transitions.
116 citations
TL;DR: In this article, a model is proposed in which the electrocoloration process is attributed to the formation of a ‘tungsten-blue’ phase following cathodic reduction by active hydrogen.
Abstract: Studies of electrochromism in evaporated and chemically prepared tungsten-oxide films have shown that electrocoloration takes place only in films containing H2O. A model is proposed in which the electrocoloration process is attributed to the formation of a ‘tungsten-blue’ phase following cathodic reduction by active hydrogen.
100 citations