Junichi Nagai

Electrochromism of 3d transition metal oxides

Abstract Thin films of 3d transition metal oxides, TiO x , MnO x , CrO x , CoO x and NiO x , were prepared by electron-beam evaporation. These films showed electrochromic behavior in a non-aqueous electrolyte such as 1M LiClO 4 /γ-butylolactone. Structural, electrochromic and electrochemical properties were studied. Among these 3d metal oxides, NiO x and TiO x films were found to be most promising for ion storage oxides in terms of cyclic stability. Particularly, it was found that the NiO x film was an excellent anode with the highest coloration effciency of the films studied.

Electrochromic devices for transmissive and reflective light control

Abstract Fundamental properties of a transmissive electrochromic device are described. The device consists of a semisolid electrolyte and a WO3 film sandwiched by a pair of transparent conductive glass sheets. The transmittance of the device can be arbitrarily controlled within the range from 80% to 10%. The response time was found to be greatly dependent on the device size. The lifetime for repetitive operations is more than 105 cycles. Reasonably good durability has been determined. This device is capable of controlling the reflectance of a mirror, with the reflective layer coated on the either surface of the outer glass sheet. Details of this reflective device are also described. The reflectance of the mirror of the size of 25 cm × 6.5 cm can be changed from 72% to 20% within 4 s at 1.5 VDC. This device is suitable as an antidazzling mirror for motor cars.

Characterization of evaporated nickel oxide and its application to electrochromic glazing

Abstract In this work, optical and electrochemical properties of electrochromic NiOx films and their application to electrochromic glazing are studied. Quartz crystal microbalance (QCM) study reveals that OH− insertion/extraction occurs during coloration and bleach reaction of NiOx film in an organic electrolyte. This process is also confirmed by reflectance measurement by FTIR. Electrochromic glazing consisting of WO3/PEO-based Li+ electrolyte/NiOx system shows promising solar control properties. The possibility towards NIR-reflectance control using WO3 is exemplified.

Kinetic Study of LixWO3 Electrochromism

Coloring/bleaching processes of LixWO3 electrochromism were examined in terms of emf, chronoamperometry, voltammetry and ac impedance measurements. The current-potential relation was found to be ohmic in the short time region and expressed by i=(Eapp-emf (x))/R. Satisfactory fittings were obtained for chronoamperometry and voltammetry measurements on the basis of the assumption of diffusion-limited process with above i-E relation. Diffusion coefficient was estimated to be about 5×10-10 cm2/sec. It was elucidated from the detailed analysis of impedance that R was given by the summation of the resistances of solution, electrode, charge transfer and material transfer. Since it was found that the WO3 film was regarded as a large condenser with a serially connected resistor, color/bleach processes were understood as charging/discharging processes of WO3 film.

Transmissive electrochromic device

Abstract This paper describes the fundamental properties of a transmissive electrochromic device. The device is comprised of a semi-solid electrolyte and a WO3 film sandwiched by a pair of electroconductive sheet glasses. The transmittance of the device can be arbitrarily controlled within the range from 80% to 10%. The response time was found to be greatly dependent on the size of the device and the applied dc voltage. The lifetime for repetitive operation is more than 105 cycles. The devices have fairly good durability against outdoor conditions. Based on a kinetic study of the tungsten bronze and an equivalent circuit analysis, the effects of the rate determining factors are discussed.

Electrochromic Devices For Transmissive And Reflective Light Control

Fundamental properties of the transmissive electrochromic device are described. The device comprises of a semi-solid electrolyte and a WO3 film sandwiched by a pair of transparent electroconductive sheet glasses. The transmittance of the device can be arbitrarily controlled within the range from 80% to 10%. The response time was found to be greatly depended on the size. The life time for the repetitive operations is more than 105 cycles. Fairly good durability against the outdoor conditions has been clarified. This device is capable of controlling reflectance of mirror when a reflective layer is coated on the either surface of outer glass. Outline of this reflective device is also described. The reflectance of the mirror of the size of 25cm x 6.5cm can be changed from 72% to 20% within 4sec at 1.5VDC. This device is suitable for anti-dazzling mirror of motor cars.

Transmissive Electrochromic Device

This paper describes the fundamental properties of the transmissive electrochromic device. The device comprises of a semi-solid electrolyte and a WO3 film sandwiched by a pair of electroconductive sheet glasses. The transmittance of the device can be arbitrarily controlled within the range from 80% to 10%. The response time was found to be greatly dependent on the size of device and the applied DC voltage. The life time for the repetitive operations is more than 105 cycles. The devices have fairly good durability against the outdoor conditions. Based on the kinetic study on tungsten bronze and the analysis of equivalent circuit, the effects of the rate determining factors are discussed.

Transport of Li+ Ions In Amorphous Tungsten Oxide Films

Coloring / bleaching processes of LixWO3 electrochrothismwere examined by means of emf, chronoamperometry, voltammetry and ac impedance measurements. Current-potential relation was found to be ohmic in the short time region and expressed by i=(Eapp-emf(x))/ R. Satisfactory fittings were obtained for chronoamperometry and voltammetry measurements on the basis of the assumption of diffusion-limited process with above i-E relation. It was elucidated from the detailed analysis of impedance that R was given by the summation of the resistances of solution, electrode, charge transfer and material transfer. It was newly found that diffusion coefficients for several WO3 films were in the range of 1.5 X 10-9 to 3 x 10-12 cm2,sec at 20°C and they were strongly dependent on water content in the electrolyte solution.

Electrochromism in amorphous lithium tungsten oxide films

Abstract A small ac-signal impedance analysis was utilized to characterize the surface property of an ITO electrode and Li transport in an Li x WO 3 electrode. The as-deposited ITO film has a surface layer with extremely high carrier density, which could be easily removed by mechanical polishing. Based on the kinetic model of Li x WO 3 , the diffusion coefficient of Li transport was obtained. It depends on the various deposition conditions of WO 3 films and the composition of the electrolyte used. The response of Li x WO 3 film showed a gradual decrease and reached a certain equilibrium after repeated cycling (more than 10 4 times). The examination of such a degradation phenomenon leads to the conclusion that there are two active sites in the WO 3 structure, which are available for the Li ion; one for coloration ( x Li + + WO 3 + x e − ↔ Li x WO 3 ), and the other for an ion exchange reaction expressed by WO-H+Li + ↔ WO-Li+H + . The mechanism of these phenomena are further discussed. Impedance analysis has been proved to be very sensitive and applicable enough to the quantitative characterization of ITO and Li x WO 3 electrodes involved in the electrochromic device.

Advances in research and applications of electrochromic smart windows

Abstract Electrochromic smart window can change its transmittance electronically by use of electrochromic films. Fundamental properties of electrochromic materials are discussed. The guiding principle of the working devices is detailed in the context of materials science and device technology.