A. Gorenstein

The Intercalation of Lithium in Nickel Oxide and Its Electrochromic Properties

Under rigorously dry conditions, nickel oxide sputtered samples undergo a reversible lithium intercalation-deintercalation process which is accompanied by a net electrochromic effect. The characteristics of the process have been studied by cyclic voltammetry and by optical transmittance. The use of lithium-intercalated nickel oxide as a new type of counter-electrode in electrochromic windows is also discussed

Electrochromic nickel oxide thin films deposited under different sputtering conditions

Abstract In this work, non stoichiometric nickel oxide (NiO x ) thin films were deposited by r.f. reactive sputtering of a metallic nickel target in an O 2 -Ar atmosphere. A systematic variation of two deposition parameters was done: the oxygen flux (φ) and the r.f. power ( P ). The electrochemical characterization of the films was performed in aqueous electrolyte. The spectral transmittance measurements, as well as the X-ray diffraction analysis were performed ex-situ, while monochromatic transmittance and stress measurements were performed in situ. Samples deposited at low oxygen flux (or high power) are transparent, in contrast to those deposited at high oxygen flux (or low power), which are dark brown. The films were cubic NiO, with preferred orientation in the (111) direction. Lattice parameters increase with increasing oxygen flux during deposition, but decrease with increasing power. For all samples, the ratio O Ni was greater than 1, as determined by Rutherford back-scattering analysis. Also, an important hydrogen content was found in the films. The relationship between optical, electrochemical, mechanical, structural and morphological behaviour of the above mentioned films will be reported and discussed in this work.

Electrochromism of WO3 in acid solutions: An electrochemical, optical and electrogravimetric study

Abstract The electrochromic reaction of a tungsten trioxide electrode prepared by electrochemical deposition was studied. Chronopotentiometric experiments associated with transmittance measurements were carried out for several film thicknesses. The dependence of electrochromic efficiency on the coloration/bleaching current density, the wavelength of the light source and the film thickness were analysed. The mass and structural changes due to the electrochromic reaction were followed using a quartz crystal microbalance and stress experiments respectively. Film formation and dissolution processes for WO 3 in acidic media are also discussed.

An Electrochromic Window Based on Li x WO 3 / ( PEO ) 8LiClO4 / NiO

Electrochromic materials are characterized by reversible but persistent changes of the optical properties when subjected to suitable electrochemical reactions. Electrochromism can be utilized in windows, most conveniently by exploiting all-solid-state multilayer coating backed by glass. The multilayer coating should comprise the following sequence of layers: a transparent and electrically conducting base layer, an electrochromic layer, and electrolyte, a conterelectrode, and a transparent conducting top layer. For window applications, the electrolyte should be transparent, and the conterelectrode must be either optically passive (colorless irrespective of its ionic content) or electrochromic in a sense that is complementary to the electrochromism of the electrochromic layer. The latter condition implies that if the electrochromic layer is cathodic (anodic), the counterelectrode must be anodic (cathodic). This paper reports preliminary data taken on samples with electrochromic layers based on tungsten oxide, WO{sub 3}, and nickel oxide, NiO, and an intermediate solid electrolyte of poly(ethylene oxide) doped with lithium perchlorate, (PEO){sub 8}LiClO{sub 4}, where 8 signifies the number of oxygen heteroatoms per lithium ion.

Electrochromic nickel hydroxide films on transparent/conducting substrates

Abstract Nickel hydroxide films were electrochemically precipitated onto transparent conducting substrates. Electrochromic effects were observed in alkaline solutions. Transmittance can be varied from 72% (clear state) to 33% (dark state) on changing the applied potential. Intermediate transmittance states are also possible. Coloration-bleaching times range from 20 to 40 s and depend on the applied potential. Phase changes and loss of charge with potential cycling are discussed.

Electrochromic NiOxHy, hydrated films: cyclic voltammetry and ac impedance spectroscopy in aqueous electrolyte

Abstract The characteristics of the electrochromic process of sputtered hydrated nickel oxide films have been investigated by cyclic voltainmetry, in situ optical transmittance and ac impedance spectroscopy. The results indicate that the state of coloration of these films is related to the conditions used to drive the electrochromic process, whose kinetics at high positive potentials become controlled by ion diffusion into and from the nickel oxide structure.

Raman and XPS characterization of vanadium oxide thin films deposited by reactive RF sputtering

Abstract In this paper we report on Raman and XPS characterization of vanadium oxide thin films deposited by RF-sputtering. The samples were deposited by using a vanadium target in different oxygen fluxes, so that the stoichiometry (O/V ratio) of the oxide was varied. Several physical parameters of the films indicate a strong structural difference between the sample deposited at lower oxygen flux (1xa0sccxa0m) and those obtained with higher flux (from 1.25 to 9xa0sccxa0m). The increase of O/V ratio corresponds to a lower crystallinity of the thin films as indicated by the initial lowering and the final disappearance of the characteristic Raman mode of V 2 O 5 (crystal) at about 140xa0cm −1 . For the highest flux samples new broad bands develop, typical of amorphous materials, both in polarized as well as in depolarized Raman spectra.

Infrared characterization of electrochromic nickel hydroxide prepared by homogeneous chemical precipitation

Abstract Two different methods for preparing electrochromic nickel hydroxide films are tested: thermal hydrolysis of [Ni(NH 3 ) 6 ] 2+ complex and thermal decomposition of a mixture of urea and NiSO 4 . Both methods lead to adherent and homogeneous films presenting good electrochromic properties. Thermogravimetric analysis shows that Ni(OH) 2 prepared from urea decomposition has intercalated water molecules, while hydroxides prepared from ammonia complexes present s-like structure without hydration. Ex-situ infrared spectroscopy was used to characterize virgin, bleached and colored states of the films under different experimental conditions. IR spectra of the colored state show the diminution of the 3650 cm −1 band related to free OH − stretching vibrations. The disappearance of this band is associated with the oxidation process and also with the physicochemical nature of alkaline cations incorporated in the oxide matrix during the coloration process.

Infrared reflectance spectroscopy of electrochromic NiO x H y films made by reactive dc sputtering

Films of NiO x H y were made by reactive dc magnetron sputtering of Ni followed by electrochemical treatment in KOH. Infrared reflectance spectroscopy with obliquely incident p-polarized light documented a unique topochemical reaction with the bleached state being β-Ni(OH) 2 and the colored state being β-NiOOH. The same technique yielded clear, though not yet fully understood, data on the evolution of electrochromism during potentiodynamic cycling

Radio-frequency reactively sputtered VOx thin films deposited at different oxygen flows

The effect of different oxygen flow rate on the properties of vanadium oxide thin films formed by radio-frequency, reactive sputtering deposition are investigated. The stoichiometry of the as-deposited films was investigated by Rutherford backscattering spectrometry. For high oxygen flows, films were mainly V 2 O 5 while a lower oxide was obtained at the lowest flow. Forward recoil spectrometry indicated a significant hydrogen content in the thin films. X-ray diffraction showed that the films were amorphous. The electrochromism shown by such films upon lithium intercalation was also studied. Samples deposited at high oxygen flow were transparent/yellow, and showed a somewhat complicated electrochromic behavior. Upon lithium insertion up to 25 mC/cm 2 , the films acted as cathodically coloring materials at wavelengths higher than 500 nm and as anodically coloring material at lower wavelengths. For the higher insertion levels, the opposite behavior was observed. Samples deposited at very low O 2 flows showed no electrochromic behavior.