Sylvie Sanchez

Cathodic Deposition of Copper Selenide Films on Tin Oxide in Sulfate Solutions

The reactions accompanying the electrodeposition of binary copper selenium compounds from cupric sulfate and selenious acid solutions were studied by voltammetry. The deposits were chemically analyzed and the formed phases were identified by X-ray diffractometry. The deposit composition is determined by the fluxes of the Cu(II) and Se(IV) species arriving at the electrode in a relatively narrow potential range, from [minus]0.5 to [minus]0.8 V vs. MSE. For the more negative values of potential, only Cu[sub 2]Se is obtained as a solid but nonadherent compound. If there is a selenium excess, it is reduced to soluble selenide species. A model gives the distribution of the formed products as a function of the solution concentration and applied potential.

Electrodeposition of indium selenide In2Se3

Indium selenide has been prepared by electrodeposition from indium sulphate and selenious acid solutions at 22 and 82°C. The deposits were analysed chemically and the films were characterised by anodic stripping, X-ray diffractometry and optical measurements. The reactions occurring during the process were studied. The formation of In2Se3 occurs via a reduction of Se(IV) into Se(-II), which then reacts with the In3+ ions to give In2Se3. Deposits prepared at 82°C have a better crystallinity than those obtained at 22°C. Optical characterisation of the electrodeposited In2Se3 gives a band gap energy of 1.58 eV. Voltammograms under illumination with the deposits as electrode material show a strong anodic photocurrent characteristic of an n-type semiconductor. Annealing at 390°C under an argon atmosphere increases the photocurrent.

Americium chemical properties in molten LiCl-KCl eutectic at 743 K

Abstract The chemical and electrochemical properties of americium chlorides have been studied in the fused LiCl–KCl eutectic at 743 K using a tungsten working electrode and a pO 2− indicator electrode. The standard potential of Am (III)/Am (II) and Am (II)/Am redox couples were determined using cyclic voltammetry. Titration of Am (III) chlorocomplex by O 2− demonstrated the existence of the soluble americium species AmO + and the precipitation of AmOCl and Am 2 O 3 . The electrochemical behaviour of AmO + was then studied by cyclic voltammetry. All these data allowed us to draw the potential–pO 2− diagram which summarises the properties of americium species in the melt.

Copper diffusion in solid copper sulfide electrode

The electrochemical behavior of a copper sulfide electrode (Cu 1.95 S) in a sulfate bath containing Cu 2+ ions is studied by cyclic voltammetry and impedance spectroscopy techniques. Cyclic voltammetry shows that several cathodic reductions occur at the copper sulfide electrode, one of which involves the copper vacancies as electroactive species. The reaction pathway at the equilibrium potential is established and a diffusion step of the copper vacancies in the copper sulfide electrode is shown. The impedance spectroscopy leads us to determine a diffusion coefficient of the copper vacancies close to 10 -10 cm 2 s -1 .

Temperature dependence and effect of oxide anion on the americium chemistry in the molten LiCl-KCl eutectic

Summary The chemical properties of americium chlorides have been studied in the fused eutectic LiCl-KCl as a function of temperature ranging from 743K to 943K. Titration of Am(III) chlorocomplex by O2- demonstrated the existence of soluble AmO+ species as well as the precipitation of AmOCl and Am2O3 solid compounds. The corresponding solubility products of AmOCl and Am2O3 have been determined. Calculated Am(II) disproportionation equilibrium constant indicates that the stability of Am(II) chlorocomplex increases with the increase of temperature.

Influence of the Composition on the Copper Diffusion in Copper Sulfides Study by Impedance Spectroscopy

Diffusion of copper in copper sulfides, Cu 2-x S is studied as a function of by means of electrochemical impedance spectroscopy (EIS) at room temperature. Copper sulfide compositions were determined from electromotive force determinations in the Cu|Cu 2+ aq|Cu 2-x S galvanic cell. The same cell was used to change the x value by imposing a potential different of the equilibrium one. Experimental EIS determinations relate diffusion coefficients and concentrations of diffusing species. The experimental data are discussed accordingly.

Molten salt electrosynthesis of ZnSe

Abstract High temperature molten salt electrosynthesis is a promising method for preparing thin layers of metallic or composite compounds. In this case no post heat treatment (modifying the interface composition) is needed. In this work, we report the electrowinning of ZnSe which is performant for realizing diode lasers and solar cells. Thin films containing up to 90% well crystallized ZnSe with Se/Zn around 1.1 and a grain size equal to 1 μm was obtained in the molten mixture NaClCaCl2 fused at 550°C. Optical properties are currently studied.

Electrochemical behaviour of indium ions in molten equimolar CaCl2-NaCl mixture at 550°C

The stability of indium chloride and oxide as well as the electrochemical behaviour of indium ions have been studied in the equimolar CaCl2–NaCl melt at 550 ∘C by X-ray diffraction (XRD) and different electrochemical techniques, using molybdenum and tungsten wires as working electrodes. Voltammetric and chronopotentiometric studies showed signals attributed to the presence of three oxidation states of indium, i.e. 0, i and iii. The standard potential of the redox couples, as well as the solubility products of indium oxides have been determined, showing that In(iii) ions are completely reduced to monovalent indium by the indium metal according to the reaction: In (Ш) + 2 In ↔ 3 In () and that In2O is a strong oxide donor according to the reaction: In2O(s)→ 2 In() + O2- These results have allowed the construction of E-pO2− equilibrium diagrams summarising the properties of In–O compounds. The electrodeposition of indium was uncomplicated at Mo and W electrodes. Very good adherence of liquid indium to the electrode materials was observed, with the formation of Na–In alloys at highly reducing potentials, and there was no evidence of indium dissolution into the melt. Moreover, the voltammograms corresponding to the electrochemical In(iii)/In(i) exchange were well defined. The two electrochemical steps were found to be quasi-reversible, and the values of the kinetic parameters, ko and α, for both reactions, as well as the diffusion coefficients, DIn(III) and DIn(I) were calculated.

Electrochemical oxidation of a metal involving two successive charge transfer steps with adsorbed intermediate species. II—Theoretical expressions for electrochemical impedance spectra

Abstract The theoretical expression for the electrochemical impedance of anodic oxidation of a metal in which two successive charge transfer steps occur and involving two adsorbed species has been established. An equivalent electrical circuit has been given and the relationships between electrical and kinetic parameters were used for clearly discussing the dependence of the shapes of the impedance spectra upon potential and relative values of kinetic parameters. In particular, the appearance of an inductive effect or a negative polarization relativistic is strongly correlated with relative values of kinetic parameters and especially those of desorption steps.