Showing papers on "Electrochromism published in 1994"

Generalized synthesis of periodic surfactant/inorganic composite materials

Abstract: THE recent synthesis of silica-based mesoporous materials1,2 by the cooperative assembly of periodic inorganic and surfactant-based structures has attracted great interest because it extends the range of molecular-sieve materials into the very-large-pore regime. If the synthetic approach can be generalized to transition-metal oxide mesostructures, the resulting nanocomposite materials might find applications in electrochromic or solid-electrolyte devices3,4, as high-surface-area redox catalysts5 and as substrates for biochemical separations. We have proposed recently6 that the matching of charge density at the surfactant/inorganic interfaces governs the assembly process; such co-organization of organic and inorganic phases is thought to be a key aspect of biomineralization7. Here we report a generalized approach to the synthesis of periodic mesophases of metal oxides and cationic or anionic surfactants under a range of pH conditions. We suggest that the assembly process is controlled by electrostatic complementarity between the inorganic ions in solution, the charged surfactant head groups and—when these charges both have the same sign—inorganic counterions. We identify a number of different general strategies for obtaining a variety of ordered composite materials.

Preparation and Photoelectrochemical Characterization of Thin SnO2 Nanocrystalline Semiconductor Films and Their Sensitization with Bis(2,2'-bipyridine)(2,2'-bipyridine-4,4'-dicarboxylic acid)ruthenium(II) Complex

Abstract: Thin, transparent films of SnO 2 semiconductor have been prepared from 30-A-diameter colloids. Scanning electron microscopy and X-ray powder diffraction studies indicate a three-dimensional network of SnO 2 nanocrystallites of particle diameter ≤50 A. These thin nanocrystalline films exhibit reversible electrochromic effects. The electron trapping process in SnO 2 particles has been investigated by both spectroelectrochemical and laser flash photolysis techniques. These electrodes are photoelectrochemically active in the UV region with incident photon-to-photocurrent conversion efficiency of 20% at 280 nm. The photocurrent increases with increasing film thickness but attains a limiting value at thickness greater than 0.75 μm

Fast Electrochromic Switching with Nanocrystalline Oxide Semiconductor Films

Abstract: Forward biasing of transparent nanocryst. TiO2 (anatase) films in lithium ion-contg. org. electrolytes leads to rapid and reversible coloration due to electron accumulation and Li+ intercalation in the anatase lattice. Absorption of >90% light throughout the visible and near IR can be switched on an off with a few seconds. The nanocryst. morphol. of the film plays role in enhancing the electrochromic process.

Synthesis and Properties of Novel Water-Soluble Conducting Polyaniline Copolymers

Abstract: The chemical polymerization of aniline and sodium diphenylamine-4-sulfonate produces poly(aniline-co-N-(4-sulfophenyl)aniline) (PAPSA), copolymers which have high molecular weights and are recovered as a dark green powder. The PAPSA copolymers have a monomer composition like the composition in the reaction mixture. They have conductivities which range between the conductivities of the poly(N-(4-sulfophenyl)aniline) homopolymer (0.0035 S/cm) and polyaniline (5.2 S/cm). While the homopolymer poly(N-(4-sulfophenyl)aniline) is 10 3 times less conductive than polyaniline, it is still 10 6 times more conductive than other polyanilline polymers with sulfonate groups. The conductivity and the ESR signal both decrease with the phenylsulfonic acid content in the copolymer

Preparation and Electrochromic Properties of RF-Sputtered NiOx Films Prepared in Ar/O2/H2 Atmosphere

Abstract: The preparation of electrochromic nickel oxide ( NiOx ) films, which are colorless in an as-deposited state, has been carried out in Ar/O2/H2 mixed gas by the rf-sputtering method. Highly transparent films of as-deposited nickel oxide could be prepared in the sputtering atmosphere consisting of Ar:O2:H2=50:10:40. From IR and XPS measurements, the as-deposited films were found to be hydrated and to have the component of Ni(OH)2. When these films were electrochemically colored, NiOOH was known to remain in the films. The coloration efficiency of the films at the wavelength of 633 nm was nearly independent of hydrogen content in sputtering atmosphere up to 40%, but it depended on sputtering pressure. The maximum value of coloration efficiency was 36 cm2/C for films prepared at hydrogen content of 40% and total pressure of 8 Pa.

Complementary surface confined polymer electrochromic materials, systems, and methods of fabrication therefor

Abstract: An electrochromic device (100) with electrode surface confined complementary polymer electrochromic materials. The electrochromic material (20), able to change from a substantially colorless to a colored state upon oxidation, is surface confined onto one of the electrodes (25), which is on a glass substrate (30). For transmissive electrochromic devices, (25) is preferably transparent electrode such as ITO. For reflective electrochromic devices, (25) is preferably a Pt coating. The electrochromic material (20), and the electrochromic material (35) able to change from a substantially colorless state to a colored state upon reduction are physically separate from one another but ionically connected by means of an electrolyte. The two glass substrates (30) are placed together, with gaskets (45) keeping the respective glass substrates (30), with their respective electrochromic materials (20) and (35) apart.

Chromic materials. Part 1.—Liquid-crystalline behaviour and electrochromism in bis(octakis-n-alkylphthalocyaninato)lutetium(III) complexes

Abstract: Novel bis(phthalocyaninato)lutetium(III) complexes substituted with long n-alkyl chains have been synthesized. These complexes, 1a–c, show three kinds of discotic mesophase (Dhd, Dob.d, and DL). Also 1a–c display the three primary colours (red, green, blue) of electrochromism in their solutions. The solutions of oxidized species of 1a–c are nearly red, although those of conventional bis(phthalocyaninato)lutetium(III) complexes are orange.

Electrochromic devices with improved processability and methods of preparing the same

Abstract: Electrochromic devices and processes for preparing the same are provided which do not require a separate process step of ion intercalation by employing an electrochromically-inert reducing or oxidizing additive in the electrochemically active material or the electrolyte of the electrochromic devices.

Sulfonated polyaniline films as cation insertion electrodes for battery applications. Part 1.—Structural and electrochemical characterization

Abstract: Sulfonated polyaniline (SPAN) was synthesized by sulfonation of polyaniline (PANI) base with fuming sulfuric acid. Thin films were cast from polymer solutions in basic media. The polymer films were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible–near-infrared spectroscopy, scanning electron microscopy (SEM) and cyclic voltammetry. XPS in combination with FTIR showed that the preparation procedure led to ca. 47% sulfonation of an otherwise unchanged polyaniline backbone. The NIR spectra of SPAN films showed a polaron band at higher energies than with polyaniline. This is in agreement with the lower conductivity of SPAN as compared with polyaniline. SEM micrographs of the SPAN films showed a compact globular morphology. Electrodes modified with thin SPAN films exhibited two redox steps, both in aqueous and in non-aqueous electrolytes. The specific charge stored in SPAN films was found to be ca. 37 A h kg–1 in aqueous solution (only the first redox step) and ca. 68 A h kg–1 in non-aqueous media (both redox steps). A practical SPAN–Li battery could have 50% more specific energy than a PANI–Li battery. The optical spectra of SPAN films exhibited bands at 310, 450 and 750 nm, the intensities of which changed during the redox process. The absorption coefficients of SPAN (emeraldine base state) solutions had values of a= 410 at 313 nm and a= 239 at 563 nm. The suitability of SPAN for use as a cation-insertion material for battery and electrochromic applications is discussed.

Electrochromic and photoelectrochromic behavior of thin WO[sub 3] films prepared from quantum size colloidal particles

Abstract: Thin films of WO[sub 3] are cast from quantum size colloids onto an optically transparent electrode. These thin particulate films are found to exhibit reversible electrochromic and photoelectrochromic effects. A blue coloration of the WO[sub 3] particulate film is seen when electrons are injected into the conduction band of WO[sub 3] by electrochemical or UV-excitation methods. The onset potential of the electrochromic effect is dependent on the pH and corresponds to the flat band potential of WO[sub 3]. Spectroelectrochemical and microwave absorption experiments suggest that trapped electrons are the major species responsible for the blue coloration of the WO[sub 3] particulate film. 34 refs., 9 figs.

Tungsten Oxide‐Prussian Blue Electrochromic System Based on a Proton‐Conducting Polymer Electrolyte

Abstract: A new solid-state electrochromic system is presented. It is transparent and is comprised of a tungsten oxide and Prussian blue (PB) thin film couple in combination with a proton-conducting, solid polymer electrolyte. This electrochromic system exhibits rapid and deep optical switching; characteristics of a complementary configuration, both electrochromic films color and bleach in phase. Complementary electrochromic cells with the tungsten oxide-PB couple have previously been based on Li[sup +] or K[sup +]-conducting electrolytes. A repetitively cycling cell has not previously been reported with a proton-conducting solid polymer electrolyte. The devices were operated at low applied voltages, +1.2 V to darken and [minus]0.6 V to bleach. Repeated reduction and oxidation of the current system over 20,000 cycles has been demonstrated, indicating a large number of switchings without great degradation or irreversible side reactions. The sustained, high overall coloration efficiency of the devices suggests the insertion/extraction of protons into and out of both WO[sub 3] and PB films. The effects of cell size and operating temperature on the switching response are discussed.

Electrode for display devices

Abstract: Display devices incorporating an improved working electrode are disclosed The devices comprise a transparent outer layer, a first electrode having a reflective surface facing the transparent layer, an electrochromic material located between the reflective surface and the outer transparent layer, an electrolyte in contact with the electrochromic material and a second electrode located behind the first electrode The first electrode is ion-permeable, allowing ions to pass through and contact the electrochromic material in order to alter the optical properties of the material The electrochromic material is preferably a conductive polymer such, as polyaniline The display devices are capable of changing reflectance and/or color by the application of an electric potential to the electrodes

Redox Cyclability of a Self‐Doped Polyaniline

Abstract: Poly(4-anilino-1-butanesulfonic acid) sodium salt was synthesized from the electrochemical oxidation of 4-anilino-1-butanesulfonic acid sodium salt, which was readily obtained from aniline and 1,4-butane sultone. The resulting water-soluble polymer has shown much higher redox cyclability than unsubstituted polyaniline, which was demonstrated by an in situ spectroelectrochemical and a cyclic voltammetric study

A Comparative Study of the Electrochemical Properties of Dip‐Coated, Spun, and Langmuir‐Blodgett Films of Polyaniline

Abstract: The electrochemistry of polyaniline (PANi), which has been chemically synthesized and processed in a variety of ways into thin films, has been studied, and a comparison to those properties observed in thin electrochemically grown PANi films made. In this work, PANi via solution processing has been formed into thin films using dip coating, spin coating, and the Langmuir‐Blodgett (LB) technique on indium tin oxide electrodes to facilitate both cyclic voltammetry and spectroelectrochemical analysis. We find that the LB technique yields films which display the most defined voltammetric properties, although in all cases electroactivity is observed. Effects due to the residual solvent contained in the films are seen. This has enabled us to comment on the role played by the solvent molecules within the PANi matrix. Further, in the case of LP‐PANi, the ultrathin films, ca. 60 A thick, as well as exhibiting excellent electrochemistry are found to be deposited in the fully oxidized, pernigraniline form of PANi, as confirmed by rest potential measurements, UV/visible and Fourier‐transform infrared spectroscopy. From our results it is quite feasible to suggest that large scale electrochromic displays could be fabricated using PANi as the active material.

Growth of In2 O 3 Thin Films by Atomic Layer Epitaxy

Abstract: Simultaneously occurring transparency and electrical conductivity give rise to numerous thin film applications for indium oxide doped with tin (ITO), e.g., as transparent electrodes in flat panel displays and electrochromic windows, as active and passive components in photovoltaic devices, and as long wavelength IR radiation reflecting heat mirror layers in energy saving windows. Indium oxide thin films were deposited by atomic layer epitaxy technique at 400 and 500 C using InCl[sub 3] and water as reactants. The films were characterized by means of X-ray diffraction, Rutherford backscattering spectrometry, nuclear reaction analysis, scanning electron microscopy, and by optical and electrical measurements. The highest deposition rate obtained was only 0.27 [angstrom]/cycle. The films were polycrystalline In[sub 2]O[sub 3] having the [100] direction as the most pronounced orientation. The resistivities of the highly transparent films were in the order of 3 [times] 10[sup [minus]3] [Omega]-cm.

Electrochemical and Structural Properties of SnO2 and Sb : SnO2 Transparent Electrodes with Mixed Electronically Conductive and Ion‐Storage Characteristics

Abstract: Sb:SnO2 films (body resistance 1.2 X 10-2 (Omega) cm) which were deposited by dip-coating technique via the sol-gel route using SnCl4(DOT)5H2O and SbCl3 precursors have been found to exhibit mixed electronic conductivity and ion-storage characteristics. The Li+ and H+ ion (de)insertion properties of the films were determined from the cyclic voltammetric (CV) measurements from solvents containing LiClO4 (0.1 M) in acetonitrile or water, LiOH (0.1 M) and HClO4 (0.001 - 0.01 M). The particle grain size of Sb:SnO2 and SnO2 films has been determined from the XRD measurements and was found to be larger for undoped (55 - 71 angstroms) than for the Sb doped films (46 - 58 angstroms). The Sb:SnO2 films exhibit effective charges per film thickness (Q(deint)/d) in the range 0.01 - 0.02 mC/cm2nm and outrange by about 3 times the Q/d values obtained for undoped films. Combining the CV results with the in-situ spectroelectrochemical measurements it was concluded that the intercalation process of Li+ ions in Sb:SnO2 films is governed by the layer charging of the inner grain surfaces which overwhelms the underlaying redox changes involving the Sn4+ ions. The performance of the transmissive electrochromic device made of WO3/H3PO4-polyvinyl alcohol (PVA)/Sb:SnO2 was tested and the results presented and discussed.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Characterization of Nonstoichiometric Nickel Oxide Thin‐Film Electrodes

Abstract: Thin-film nonstoichiometric nickel oxide is an interesting intercalation electrode with unique electrochemical and optical properties which can be successfully used for improved electrochromic displays and windows of relevant technological interest. However, the correlation between the intercalation process of lithium and the modifications of the physical properties of the host oxide are not yet fully understood. We attempt here to demonstrate that these modifications may be interpreted conveniently on the basis of a small polaron model. The results confirm that a model of this type can account for the observed electrochemical and electrochromic response of the nickel oxide electrode as a function of the injected charge, Q Li

Electrochromic Properties of Molybdenum Trioxide Thin Films Prepared by Chemical Vapor Deposition

Abstract: Electrochromic tungsten trioxide thin films were prepared by a photochemical vapor deposition. The source material was tungsten carbonyl. A 6 W low pressure mercury lamp was used as a light source. Amorphous tungsten trioxide thin films were obtained at a substrate temperature of 200 C. The UV radiation enhances the oxidation of tungsten, in addition to the acceleration of the deposition of the films. Reduction and oxidation of the films in a 0.3M LiClO[sub 4] propylene carbonate solution resulted in desirable changes in optimal absorption. The bleaching time was short compared to the amorphous CVD film. Coulometry indicated that the coloration efficiency was 222 cm[sup 2]/C.

Kinetic Study of Lithium Electroinsertion in Titanium Oxide Thin Films

Abstract: The electrochromic reaction of titanium oxide films prepared by RF sputtering was studied. Chronopotentiometric experiments associated with transmittance measurements in LiClO[sub 4]/propylene carbonate solutions were carried out for several film thicknesses. The reaction kinetics is controlled by lithium ion diffusion into the titanium oxide matrix. The diffusion equations have been solved for the appropriate finite boundary conditions, and from these analyses l[sup 2]/D values are obtained. Combining these data with coulometric titration data, one can conclude that the diffusion phenomenon is only produced in a part of the film. The l parameter was calculated and a value of 11 nm was obtained, coinciding with the thickness of the accumulation space charge layer for n-type TiO[sub 2]. Consequently, Li[sup +] diffusion process only occurs in this region. 20 refs., 10 figs., 1 tab.