Une technique experimentale pour l'etude de la surtension cathodique des metaux par la methode directe: Application aux metaux du groupe Fe---Co---Ni

Detailed analysis of the experimental conditions for obtaining polarization curves by the direct method has led to modifications in the usual technique applied to study of cathodic overvoltage.

An experimental installation; suitable for a more rigorous control of the various factors involved in the electrodeposition, is described. Special attention has been paid to the construction of the electrolytic cell; several modifications to the cell proposed by Piontelli in 1954 are suggested.

Electrical measurements are galvanostatic, with recording of the cathode potential as a function of time; the amount of electricity passed per unit surface area is taken into account quantitatively.

The technique has been applied to cathodic deposition of the metals of the group Fe---Co---Ni, at low current densities (0·4–120 μA/cm²), from 0·1 M aqueous chloride solution.

The results show that certain causes of errors leading to non-reproductibility of the polarization curves can be avoided. In particular, the influence on overvoltage of the change in the structure of the surface with time, is clearly demonstrated.     

Comportement electrochimique de l'uranium,du fer et du vanadium,dans l'acide orthophosphorique et dans le melange H3 PO4 5M—HF 1M. Etude cinetique de la reduction de l'uranium (VI) par le fer (II)

The electrochemical behaviour of uranium, iron and vanadium in 0,1 M–10 M phosphoric acid solutions, has been investigated by polarography, cyclic voltammetry and controlled-potential electrolyses. In concentrated phosphoric acid solutions (|H₃ PO₄| > 3 M), uranium (VI) can be reduced by iron (II). Kinetic measurements of the reduction in 5 M H₃PO₄ and 5 M H₃PO₄—1 M HF mixtures have been carried out.     

Etude du mecanisme et de la cinetique de la reduction des ions uranyles dans des solutions d'acide phosphorique

The electrochemical reduction of uranyl ions in 0,1-9 M phosphoric acid has been investigated by polarography, cyclic voltammetry, chronopotentiometriy and potentiostatic coulometry.In concentrated phosphoric acid solutions (H₃PO₄ < 1 M), an adsorption pre-wave appears in addition to the main wave of diffusion. The electrochemical reaction involves a single electron. Kinetic usually corresponds to a quasi-reversible system, but it evolves according to the variation of U(VI) and H₃PO₄ concentrations. So, when the concentration of U(VI) increases and/or that of H₃PO₄ reduces, the system becomes reversible.     

Comportement electrochimique et reactivite du systeme Ag(II)/Ag(I)-bipyridine dans le carbonate de propylene—III. Etude du mecanisme et de la cinetique de la reaction d'oxydation catalytique de la bipyridine

The electrochemical behaviour of the Ag(II)/Ag(I)-bipyridine system has been investigated in solutions containing bipyridine in excess with respect to the Ag⁺-bipy: 1–2 stoichiometry. The nature of the coupled chemical reaction indicates a chemical catalysis of an electrochemical reaction. The rate constant of the reaction of destruction of the intermediate complex (k₂ = 1.8 × 10^?3s^?1) has been calculated from measurements performed during electrolysis of Ag^I(bipy)⁺₂-bipy solutions.     

Interpretation des courbes de polarisation cathodique du cuivre dans les solutions chlorurees acides desaerees: etude simultanee de la corrosion du cuivre et de la reduction des ions H+

During cathodic polarization of copper in deaerated acidic chloride solutions, two simultaneous processes occur: the dissolution of the metal and the reduction of the H⁺ ions. One can explain the steady state curves lg I = f(E) by means of the theory of adsorbed species. Each interpretation differs according to the nature of the adsorbed species (Cu H⁺_ads for the first one, Cu H_ads for the second one). They are made up of three consecutive reactions involving a rate determining step (R.D.S.) and another step during which the desorption of the adsorbed species brings out the two simultaneous experimental phenomena.     

Comportement electrochimique et reactivite du systeme Ag(II)-Ag(I)-bipyridine dans le carbonate de propylene

The electrochemical behaviour of silver(I)- and silver(II)-bipyridyl complexes has been investigated using voltammetry, cyclic voltammetry and coulometry in propylene carbonate. In unbuffered non-acidic medium, when the stoichiometry of the solutions is C_L/C_Ag = 2, the Ag^I(bipy)⁺ concentration is low; the preponderant species is Ag^I(bipy)₂⁺. Under such conditions, the Ag^II(bipy)₂²⁺/Ag^I(bipy)₂⁺ couple hs a reversible behaviour and is one of the must powerful oxidants used in the solvent (E^′° = 0.790 V vsE_Fc^′° + _Fc). As a function of the acidity level of the solutions, one observes the oxidation of either Ag^I(bipy)⁺ or Ag⁺ in the presence of the protonated ligand to complexed Ag(II). The silver(II) species produced oxidizes water and the excess of ligand (C_L/C_Ag > 2).     

Reduction electrochimique de sels de fer(III) et de leurs complexes chlores en solution dans le, N, N-dimethylformamide

The Fe(III) electrochemical reduction, Fe³⁺ + e^? → Fe²⁺ was studied, for the first step, in DMF with or without Cl^? ions. The results obtained with anhydrous and hydrated salts are compared and show the fast ligand water—DMF exchange when the salts are solubilized. Without Cl^? ions, Fe(III) shows two equilibrated solvation states. When Cl^? ions exist in the solutions, the species reduced at the electrode are generally more complexed than those existing in the bulk of the solution.     

Etude, par voie electrochimique, de l''influence du fer (II) sur la reduction de cetones en solution dans le N, N-dimethylformamide (DMF)

The electrochemical reduction, in DMF, of a series of aromatic ketones has been studied in the presence of iron salts. With these ketones, the first reduction peak of the ketone is always preceeded by another peak which appears at a less negative potential. This peak is attributed to a fast chemical reaction between Fe(II) and the anion radical of the ketone, which shifts the electrochemical peak potential. With fluorenone, several species are formed corresponding to 1/1, 3/4, 1/2, 1/4 iron/ketone ratios. For the other ketones, the 1/1 species is mainly formed.     

Determination potentiometrique des constantes de stabilite des complexes entre l'argent(I) et quelques heterocycles azotes en milieu neutre et acide dans le carbonate de propylene

The formation of AgL⁺_n (n = 1–4) (L = pyridine), AgL′⁺ and AgL′₂⁺ [L′ = 2,2′ bipyridine, 2,2′ biquinoline, 2-(2-pyridyl)benzimidazole] complexes has been studied using potentiometry with a silver electrode. The acidity constants of the ligands have been measured potentiometrically with the hydrogen electrode. The silver distribution between the Ag⁺ and AgL_n⁺ species has been computed by means of the so obtained β_n. In acidic medium, the metallic complexes are destroyed by the ligand protonation.     

Comportement electrochimique et reactivite du systeme Ag(II)/Ag(I)-bipyridine dans le carbonate de propylene—IV. Etude du mecanisme de l'oxydation catalytique de la methyl-4 pyridine et de la dimethyl-2,6 pyridine

The reactivity of the Ag(II)/Ag(I)-bipyridine system towards substituted pyridines L (L = 4-Mepy, 2,6-diMepy) has been investigated during electrolysis of the Ag^I(bipy)⁺ complex in various medium conditions. This study, using voltammetry, coulometry and EPR points out the influence of the substrate geometry upon the catalytic oxidation mechanism. The processes, involving mixed complexes of silver(II) Ag^II(bipy)L²⁺_n (n = 1,2), are relevant of a chemical catalysis of electrochemical oxidations.     

Essais d'insertion dans le graphite d'halogenures de titane(IV): Structure et proprietes du compose lamellaire graphite-tetrafluorure de titane

Syntheses of lamellar compounds were attempted by heating mixtures of graphite and halides of titanium(lV), TiCl₄ and TiF₄ in chlorine atmosphere confined in sealed tubes.The whole liquid range of TiCl₄ was explored without observing any reaction. Thus Croft's result [4] about the non-intercalation of this compound was confirmed.In case of TiF₄, a synthesis was obtained at 300°C. Differential thermal analysis (DTA, see Fig. 1) and X-ray powder diffraction show clearly that TiF₄ is intercalated into the lattice of graphite.DTA: Fig. 1(c, d and e) are the curves for the intercalated compound: 1(c and d) are obtained under dry argon, 1(e) under air. No indications of physical transformation of pure TiF₄ (Fig. 1a) are observed.An X-ray pattern of a product obtained at 25 atm of chlorine is given in Table 1: the strong band for pure graphite is split in two lines around 3 and 3.7 Å. Elemental analysis gives a certain range of non stoichiometry from C₁₉ to C₂₄,TiF₄ for the product made under chlorine at a pressure larger than 5 atm. In all cases, no chlorine has been found in the compound.Assuming a 3rd stage layer structure and atomic configuration of TiF₄ as shown in Fig. 2. the relative intensities of X-rays diffraction lines were calculated for C₁₅ to C₂₇TiF₄. The results are shown in Fig. 3 for the 00l diffraction lines: 001 reflexion has a minimum for C₂₁ TiF₄ and as we have never seen this reflexion, we assume that this is the ideal stoichiometry. Table 2 compares the observed and calculated intensities for C₂₁TiF₄. Agreement is quite good.Synthesis carried out under pressure of chlorine lower than 5 atm gave disordered products. Table 3 compares the obtained X-ray pattern for a product made at 1 atm of chlorine and the pattern calculated on the following assumptions: 4th stage, stoichiometry of C₂₈TiF₄. The pattern of TiOF₂ is also present in the table. Agreement is not very good, and moreover the pattern of products depends on the pressure of chlorine as shown on Fig. 4 for the 004 and 005 reflexions. We have had then to introduce a “pseudo-stage” n + x (formula (2) in appendix).On Fig. 5 the inverse of this pseudo-stage is plotted vs the Cl₂ pressure. A stable domain of 3rd stage is observed between 5 and 19 atm. Below 5 atm higher stages and disordered products are obtained.Figures 6 and 7 relate to a thermal stability study of the C₂₁ TiF₄ product. Figure 6 is a thermolysis curve made under dry argon (a) and under vacuum (10 ²torr) (b). Figure 7 is a thermolysis curve made in a diffraction high temperature chamber under vacuum (10^?5 torr): $\text{1}\text{(n + x)}$ is plotted vs temperature. In all cases the product gives higher stages and disordered products.     

Etude cinetique des etapes initiales de l'electrocristallisation de quelques metaux bivalents (Cu,Cd Pb)— I. Mise en evidence de la participation des anions par les methodes de double impulsion

Galvanostatic and potentiostatic double pulse methods allowed shorttime range (70 ns–100 μs) kinetic measurements, when the contribution of the fast step M/M(I) to the total current was preponderant. The kinetics of the interfacial exchange processes appeared to be during the first instants, independent of the concentration of metal ions in solution, but essentially a function of the nature of the supporting electrolyte anion and even, in the case of the CIO^?4 anion, of its concentration. Analysis of double pulse potentiostatic transients I (√t, which were linear up to values of t between 25 and 100 μs, depending on the systems studied, confirmed the anionic contribution of interfacial exchanges and revealed the essential part played by the anion adsorbability.     

Reduction electrochimique comparee de Mg2+ et du cryptate (221, Mg)2+ dans le carbonate de propylene

A comparison is made between the electroreduction of magnesium (II) and of magnesium (II) cryptate. The bielectronic polarographic reduction of the cryptate is more cathodic but faster than the reduction of the solvated Mg²⁺, at the half wave potential.     

Etude potentiometrique de la stabilite de complexes Ag(I)-pyridines substituees et de complexes mixtes Ag(I)-bipyridine-pyridines substituees dans le carbonate de propylene

The formation of Ag^IL⁺_n (L = substituted pyridines, n = 1,2) and Ag^I(bipy)L⁺ (bipy = 2,2 bipyridine) complexes has been investigated using potentiometry in propylene carbonate. This study, required by the investigation of the reactivity of Ag(II)/Ag(I)-bipyridine system towards pyridine-type substrates, allows the determination of the nature and distribution of the species in solutions containing Ag⁺ ions and both types of ligands; bipyridine and substituted pyridines.     

Comportement electrochimique et reactivite dy systeme Ag(II)/Ag(I)-bipyridine dans le carbonate de propylene—II. Etude du couple carbonate de propylene—II. Etude du couple AgII(bipy)2+/AgI(bipy)+

Due to the reactivity expected in the presence of an excess Ag⁺ with respect to the 1–2 stoichiometry (Ag-bipy), the electrochemical behaviour of the Ag(II)/Ag(I)-bipyridine system has been investigated using voltammetry and coulometry. The change in the current-potential curves has been rationalized taking into account an equilibrium between different species of Ag(I) in neutral or acidic media. Changes of the solution nature (ratio C_bipy/C_Ag) or pH actually led to the formation of reactive species.     

ETude cinetique des systemes Cd---Cd(II) et Fe(II)---Fe(II) en milieu aqueux par trace d'oscillogrammes lineaires au moyen de la methode de double impulsion potentiostatique

The principle and construction of a quadratic function generator are described. The voltage output, supplying the oscilloscope time-base, gives a linear i(√t) oscillogram and allows the transfer cd i_a to be read on the oscilloscope screen.

The kinetic parameters of the Cd---Cd(II0 and Fe(II)---fe(III) sytsems are determined in this way. In these two examples, the second Fick equation is solved numerically in order to establish the validity of the formula used to calculate T₀, the time corresponding to the cd i_a.

Zusammenfassung

Man beschreibt die Einstellung von einem Quadratischfunktiongenerator. Wenn die Klemmenspannung dieses Generators mit der Zeitablenkung des Oszillographes angeschaltet wird, erreicht man ein lineares Oszillogramm i(√t); die Durchtrittstromdichte i_a wird sofort auf dem Oszilloskopschrim gelesen.

Mann kann mit dieser Methode die elektrolytischen Konstanten der Reaktionen Cd---Cd(II) und Fe(II)---Fe(III) bestimmen. Jedenfalls integriert man die Zweite Diffusion differentialgleichung zahlenmässig und so, kann man die Richtigkeit der die Zeit gebenden Formel, welcher Zeit die Ordinate i_a auf die Linie i(√t) entspricht, bestätigen.     

Electrochimie dans la cryolithe fondue—I influence de la teneur en fluorures et en alumine sur le potentiel du systeme A1(III+)/A1(0)

The influence of additions of NaF and AlF₃ on the potential of an aluminium electrode has been studied in molten cryolite. The redox system Al(III+)/Al(0) is reversible, and the value K = 0,03 (ionic fractions) for the dissociation equilibrium (AlF^3?₆ ? AlF^?₄ + 2F^?) has been deduced from potentiometric measurements. Dissolution of Al₂O₃ probably leads to AlOF^2?₃ species.     

Comportement electrochimique d''oxocarbones et d''aci-reductones en relation avec le transfert d''electrons dans les processus biologiques—IV: incidence des equilibres d''hydratation, de dimerisation et de dismutation sur la reversibilite du couple ninhydrine/derive dihydro

This voltammetric and potentiometric study concerns the reduction pre-waves of ninhydrin 1, the one electron cathodic and anodic waves of the pinacol reduction product 3 and the anodic (two electron) of the dihydro derivative, aci-reductone 2.

The rate of the electronic transfer depends on the disproportionation and dimerisation reactions of the semiquinone radical 1^·. In dilute solution, the redox system 1/2 is reversible; the value of ^′° (+ 30 mV) stands between those of the dehydro ascorbic acid/ascorbic acid and the rhodizonic acid/tetrahydroxyquinone systems previously studied. This value explains the catalytic action of the system 1/2 in the oxydation of thiol.     

Mécanisme de la réduction électrochimique en milieu non aqueux de materiaux cathodiques utilises dans les piles au lithium. V. Utilisation des hexacyanoferrates de fer (II et III) comme materiaux cathodiques reversibles

Résumé On présente les résultats obtenus concernant la réduction électrochimique dans le mélange solvant 80% en volume de 1,2-diméthoxyéthane-20% en volume de carbonate de propylène rendu conducteur par LiClO₄ 1M, d'électrodes membranaires constituées d'hexacyanoferrates der fer (II) et (III). Les hexacyanoferrates étudiés ont pour formule approximative: (a) KFE^IIFe ₃ ^III [Fe^II(CN)₆]₃, (b) Fe ₃ ^III [Fe^II(CN)₆]₃, et (c) KFe^III [Fe^II(CN)₆]. Leur réduction électrochimique s'effectue vers 3 V par rapport au système Li⁺/Li avec un rendement voisin de 90%. On montre, par voltampérométrie, que cette réduction est reversible et qu'il est meme possible d'oxyder partiellement les trois hexacyanoferrates.Des cycles de charge-décharge effectués sur des électrodes membranaires des différents produits confirment la réversibilité des divers systèmes électrochimiques engagés. Ainsi, pour des décharges du produit (a) jusqu'à 2.5 V et des charges jusqu'à 4V le rendement électrochimique évolue de 94% au premier cycle à 50% au 300 ème cycle. On interprète ces résultats, en supposant que le Fe(III) contenu dans les composés est susceptible de se réduire à l'état (II) sans destruction de la structure cristalline avec probablement insertion de cations Li⁺ en provenance de l'électrolyte selon: Fe _cristal ³⁺ + Li⁺+eFe²⁺Li _cristal ⁺ . Il est donc possible d'utiliser ces hexacyanoferrates comme matières actives dans des générateurs secondaires à électrolyte non aqueux et notamment à électrode négative de lithium.

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The results of the electrochemical reduction of membrane electrodes of Fe(II) and Fe(III) hexacyanoferrates in 80 vol% 1,2-dimethoxyethane, 20 vol% propylene carbonate with 1M LiClO₄ are presented. The hexacyanoferrates studied were of the following formula: (a) KFe^IIFe^III[Fe^II(CN)₆]₃, (b) Fe ₄ ^III [Fe^II(CN)₆]₃, and (c) KFe_III [Fe^II(CN)₆]. Reduction occurred at about 3V with 90% efficiency. It is shown by voltammetry that this reduction is reversible and that it is possible to partially oxidize the three hexacyanoferrates. The charge-discharge cycles carried out on the electrode membranes of different composition confirmed this reversibility for various electrochemical systems. For (a), the cycle: discharge at 2.5 V and charge at 4 V gave an efficiency ranging from 94% on the first cycle to 50% on the 300th. These results are interpreted by supposing that the Fe(III) is easily reduced to Fe(II) without the destruction of the crystalline net, but with the probable insertion of Li⁺ cations from the solutions: Fe _crystal ³⁺ + Li⁺ + eFe²⁺Li^crystal/+. It is possible to use these hexacyanoferrates as active constituents in secondary cells with non-aqueous electrolytes, particularly with a negative lithium electrode.