A. Hugot-Le Goff

Electrochromic Reactions in Manganese Oxides I . Raman Analysis

Like nickel oxide, manganese oxide is a widely studied material in the primary batteries field. The reactions taking place during voltametric cycling of manganese oxides can be determined using in situ Raman spectroscopy. The main difficulty for the oxide identification is to obtain relevant Raman reference spectra because of the many possible compounds and, for some of these compounds, of their instability in the laser beam. As a consequence, several modifications of different tetra-, tri- and divalent manganese oxides and oxyhydroxides were carefully studied. The electrochromic behavior of three types of manganese oxides, two prepared by thermal oxidations and the other by electrochemical deposition, were then compared. The presence of nonstoichiometry in the pristine material was necessary to obtain a reversible electrochromic effect. The reaction during electrochromic cycling is more complicated than a simple passage from MnO[sub 2] to MnOOH.

Sensitization of TiO2 by Polypyridine Dyes Role of the Electron Donor

Dye-sensitized photoelectrochemical cells (DSSC) are characterized by electrochemical impedance spectroscopy (EIS) and Raman spectroscopy during their polarization. Cells realized with a dye recently synthesized in one of our laboratories, containing two terpyridyl (terpy) ligands, are compared with cells using commercial dyes (Ru535 and Ru620) containing isothiocyanates and either bipyridyl (bpy) or terpy ligands. Here, two points are emphasized, first, the role of the functional group (carboxylate or phosphonate) which ensures the linkage to TiO 2 and, second, the role of the redox couple (I /I - 3 ) present in the electrolyte which can react with the dye D to give unwanted intermediate species. Two species, each of them giving a characteristic Raman band in the low wavenumber range, are characterized by Raman spectroscopy. The first of these species is triiodide; the nature of the second one, which directly implies the oxidized form of dye, D + , is discussed. During the DSSC functioning, EIS allows one to discriminate three potential ranges, the photocurrent plateau, the recombination range, and the direct current range when the voltage decreases from anodic to cathodic. The second intermediate exists only in the photocurrent plateau, while I - 3 exists also in the recombination range. These results do not depend on the nature (bpy or terpy) of the ligand.

Electrochromic properties of TiO2 anatase thin films prepared by a dipping sol–gel method

Abstract Electrochromic TiO 2 anatase thin films on ITO were prepared by the sol–gel dipping method using a solution of titanium tetraisopropoxide, diethanolamine and ethanol. The films were transparent in the visible range and can be colored in a solution of LiClO 4 in propylene carbonate. The transmittances of the colored films were found to be strongly dependent on the Li + inserted charge. Combining the experimental data obtained from in situ Raman and in situ transmittance spectra with the data from chronoamperometic measurements, it was demonstrated that the fully colorated state of the TiO 2 anatase films is Li 0.5 TiO 2 with a crystalline structure of Imma space group symmetry. In the Raman spectra this coloration state exhibits five characteristic bands at 176, 224, 316, 531 and 629 cm −1 .

Electrochromic Behavior of Nickel Oxide Electrodes I . Identification of the Colored State Using Quartz Crystal Microbalance

In the present paper the quartz crystal microbalance is used as a sensitive detector of mass changes taking place during an electrochromic process. Electrochemical and electrochromic characteristics of nickel oxide electrodes strongly depend on the preparation method of the samples. Three different types of materials are studied and their electrogravimetric responses compared: hydroxide film prepared by cathodic deposition from a Ni 2+ -containing solution; porous and stoichiometric nickel oxide films formed by anodic oxidation of a nickel electrode in a concentrated H 2 SO 4 solution; and nonstoichiometric NiO(OH) x films prepared by electron-beam evaporation. A formula describing the colored film is proposed, taking into account the effect of hydrated alkaline cation (Li + ; K + ) incorporation

Electrochromic Behavior of Nickel Oxide Electrodes II . Identification of the Bleached State by Raman Spectroscopy and Nuclear Reactions

Three different types of nickel oxide electrochromic films are colored and bleached in 1M KOH solution: porous NiO prepared by anodic oxidation of nickel, NiO(OH) x obtained by reactive evaporation, and Ni(OH) 2 cathodically deposited. Their crystallographic and chemical identification in the colored and bleached states after one cycle and after long time performance testing is obtained by Raman spectroscopy. Nuclear reaction analysis is also performed

Electrochromism in anodic WO3 films I: Preparation and physicochemical properties of films in the virgin and coloured states

WO3 films grown by anodic oxidation have been studied by different optical and structural techniques. Their growth kinetics have been investigated by multichannel optical analysis; a very fast initial growth step must be responsible for their particular (hexagonal) crystallographic structure. Reflection high energy electron diffraction and Raman spectroscopy allowed us to follow the structural changes related to the coloration of the oxide by different intercalated ions: H+, Na+ and above all Li+. In fact, no changes in WO3 composition (stoichiometry) or in the crystalline order can be detected: the main effect is a profound chemical perturbation of the lattice leading to the formation of W=O in place of the initial WO bonds.

Use of Raman Spectroscopy and Rotating Split Ring Disk Electrode for Identification of Surface Layers on Iron in 1M NaOH

In situ Raman spectroscopy and rotating split‐ring disk electrode were used to identify products formed on iron in at 22°C at various peaks of cyclic voltammograms. The peak at the most active potential of the cathodic reverse sweep has been ascribed to the reduction of to Fe2+ species: this peak suggested that started to form at the first peak of anodic sweep and that it built up at nobler potentials. The Raman spectroscopy has revealed the formation of in the wide range of potentials, of and/or at peak III of anodic sweep, and of after prolonged polarization at a potential of 0.27 V (SCE). Rapid cycling or long exposure resulted in the formation of and . It is suggested that the passivating film on iron in is composed of an inner layer and of an outer layer containing other products.

In‐Situ Raman Spectroscopy Combined with X‐Ray Photoelectron Spectroscopy and Nuclear Microanalysis for Studies of Anodic Corrosion Film Formation on Fe‐Cr Single Crystals

Detection et interpretation des spectres Raman des films passifs et transpassifs formes sur des monocristaux Fe-Cr en milieu 1M de KOH

In Situ Raman Study of the Corrosion of Zinc‐Coated Steel in the Presence of Chloride I . Characterization and Stability of Zinc Corrosion Products

The different corrosion products formed on zinc specimens (pure or industrially electrodeposited) during exposure to solutions containing two concentrations of chloride were identified by Raman spectroscopy ; the crystallographic nature of these products was checked by x-ray diffraction and their morphology was described by scanning electron microscopy. The conditions of formation of hydroxycarbonates and hydroxychlorides were described, as well as the influence of pH on the growth of the different modifications of Zn(OH) 2 . The cathodic or anodic nature of the mechanisms leading to the stabilization of the different products was particularly emphasized.

Raman spectroscopy and XPS investigations of anodic corrosion films formed on FeMo alloys in alkaline solutions

Abstract Raman spectroscopy and X-ray photo-electron spectroscopy have been used to study anodic films formed on iron-molybdenum (Fe Mo) alloys. It is shown that the composition of the passive film formed after oxidation/reduction cycles (ORC) in 1 M KOH depends upon the anodic reversal potential and the sweep rate of the ORC. Finally it is concluded that the growth of the ferric outer layer (amorphous a-FeOOH able to crystallize in α-FeOOH or γ-FeOOH after a certain number of cycles) is related to the reduction of the magnetite (Fe3O4) inner layer that provides a source of iron ions.