Electrochemical Behaviour Of Iron Research Articles

Electrochemical Behavior of Iron and Several Iron Complexes in Hydrophobic Room Temperature Molten Salts

Electrochemical Behavior of Iron and Several Iron Complexes in Hydrophobic Room Temperature Molten Salts

Electrochemical behavior of iron(III) complexes with aminohydroxamic acids

The electrochemical reduction of various aminohydroxamate complexes of iron(III), such as alanine-, serine-, lysine-, histidine- and glutamo-γ-hydroxamate, has been investigated in aqueous solution by cyclic voltammetry on hanging mercury drop electrodes to determine the mechanism involved in the electron transfer processes. In all the studied cases the iron(III) complexes, with the exception of histidinehydroxamate, have been found to undergo reversible reductions followed by irreversible chemical reactions (EC mechanism). Rate constants for the irreversible dissociation of iron(II) complexes were calculated. The typical quasi-reversible pattern for the reduction of histidinehydroxamate was attributed to the different coordination mode. The observed differences in redox potentials between the investigated complexes suggest that the electronic effect of the substituent on the carbonyl group, involved in the coordination to the iron center, may modify the donor properties of the oxygen atoms of the hydroxamate moiety. The potentials determined at physiological pH are in the range of biological reducing agents, which makes these compounds potential siderophore models.

Comparison of the influence of nitrate ions on the electrochemical behaviour of iron and carbon steels in sulphate solutions

The effect of nitrate ions on the electrochemical behaviour of iron (ferrite) and two carbon steels (martensite and pearlite) in sulphate solutions of different pH values was investigated by cyclic voltammetry polarization and electrochemical impedance spectroscopy. The pitting inhibiting effect of nitrate ions on ferrite in sulphate media is pH dependent. Nitrate ions were unable to inhibit the pitting on ferrite in neutral sulphate solutions, but did effectively protect passivated ferrite from pitting in acidic sulphate solutions. No pitting occurred on the surface of the martensite and pearlite specimens in sulphate solutions regardless of the pH of the solutions. At the open-circuit corrosion potentials, the three materials underwent general corrosion. The impedance spectra for the three materials measured in neutral sulphate solutions containing nitrates and chlorides at the corrosion potentials all showed a capacitive loop, while in acidic sulphate solutions their impedance spectra were greatly reduced in size and displayed at least a low frequency impedance loop (inductive or capacitive loop) besides the well-known high frequency capacitive loop. The variation of the impedance behaviour with pH is explained.

Electrochemical behaviour of iron(III) salen and poly(iron–salen). Application to the electrocatalytic reduction of hydrogen peroxide and oxygen

The electropolymerisation of the iron(III) salen complex is reported, as well as the electrochemical behaviour of the monomer. High scan rate cyclic voltammetry allows us to calculate the lifetime of the cation radical generated during oxidation. Although the films are more difficult to prepare than several other poly(metal–salen) films (e.g. with nickel or copper), poly(iron–salen) can be well characterised by electrochemistry, either in organic or aqueous medium. The efficiency of the films towards the catalytic electroreduction of hydrogen peroxide and oxygen has been tested, and a different kinetic behaviour has been observed for both substrates, with a much greater efficiency in the case of oxygen.

Electrochemical formation of a new Fe(II)Fe(III) hydroxy-carbonate green rust: characterisation and morphology

Electrochemical behaviour of iron in deaerated 0.2 M carbonate/bicarbonate solution pH 9.6 and T=25°C was investigated. Oxidation of iron leads to the formation of green rust as intermediate product and ferrihydrite as ultimate product. Characterisation of green rust was done through FTIR, TEM, XRD and Mössbauer spectroscopy. Results point out differences in the structure and morphology, such as size of hexagonal crystal lattice, parameter c and Fe(II)/Fe(III) ratio, between our electrochemically formed GR and GR1(CO 3 2−) obtained by oxidation of Fe(OH) 2. Co-precipitation of Fe(II) and Fe(III) species during the electrochemical procedure leads to a new GR. We propose the following chemical formula for this GR, [Fe (II) 2Fe (III) 2(OH) 8] 2+·[CO 3] 2−. However, the possibility that incorporation of both CO 3 2− and Cl − ions could occur is not ruled out.

The Passivity of Iron in the Presence of Ethylenediaminetetraacetic Acid I. General Electrochemical Behavior

The effect of EDTA (ethylenediaminetetraacetic acid, added as ) on the electrochemical behavior of iron and on the semiconducting properties of passive films formed on this metal in borate buffer solution (pH 8.4) was studied. Electrochemical studies, including potentiodynamic and galvanostatic reduction experiments and capacitance measurements coupled with Mott‐Schottky analysis, were carried out over the entire passive range in borate buffer solutions in the presence and absence of 0.01 M EDTA. Passive films formed in the presence of EDTA were thinner and showed higher donor concentrations. EDTA present in the borate buffer solution effectively inhibited the formation of the Fe(III) outer layer, thereby rendering the defective inner layer to direct examination. The barrier layer is found to be an n‐type semiconductor, which is consistent with the oxide being a defective magnetite in which the principal defects are oxygen vacancies and cation interstitials. EDTA effectively competes with chloride ion for adsorption into oxygen vacancies at the barrier layer/solution interface, thereby suggesting that the chelating agent might be an effective inhibitor of passivity breakdown. © 2000 The Electrochemical Society. All rights reserved.

Passivation of iron in solutions containing borate using rotating ring-disc measurements

The electrochemical behavior of iron in neutral solutions of perchlorate and low borate concentrations was investigated using cyclic voltammetry and the rotating ring-disc electrode techniques. In solutions containing just perchlorate, iron passivation was observed at potentials higher than the potential of an anodic peak corresponding to the active range at which the dissolution of Fe2+ and Fe3+ species was detected. When borate is added to the solution, this anodic peak decreased as well as the amount of the active soluble species. The increase of pH, keeping the borate and perchlorate concentrations constant, was found to be less effective at promoting iron passivation than the increase of borate concentration. The results demonstrated that the interaction between borate ion and the electrode surface occurs by chemical adsorption according to the Langmuir isotherm.

Electrochemical behaviour of iron in neutral solutions of acetate and benzoate anions

The electrochemical behaviour of iron in pH 6 aqueous solutions of benzoate and acetate anions mixed in varying concentrations and constant ionic strength was investigated. For that purpose cyclic voltammetric experiments were carried out at a disc electrode either static and/or rotating. A high surface coverage is observed in the presence of benzoate anions, thus favouring the establishment of a passive state. The overall process is discussed in terms of a three-dimensional film, the growth mechanism of which is under diffusion and migration control. It was also observed that the addition of chloride ions to the mixed electrolyte solutions containing increasing benzoate concentration shifts the breakdown potential and the repassivation potential toward more positive values.

The Electrochemical Behavior of Iron(III) Incorporated in Zeolite Y-Modified Electrode and the Catalytic Oxidation of Ascorbic Acid

A new method is developed for the catalytic oxidation of ascorbic acid (AA) at a graphite-zeolite-modified electrode doped with iron(III) (Fe3+Y/ZCME), in which iron(III) exchanged in zeolite Y can act as catalyst to oxidize AA. First, the electrochemical behavior of iron(III) incorporated in the zeolite Y-modified electrode was studied. The results illustrate that diffusion controls the ferric/ferrous redox process at the Fe3+Y/ZCME. The anodic current of this process increases with the supporting electrolyte concentration of non-size-excluded cation and was suppressed when using size-excluded cation. Second, the catalytic oxidation of AA was explored at Fe3+Y/ZCME. With constant potential amperometric measurements optimal conditions for AA determination were obtained. The working potential was 0.55 V (vs. SCE); the supporting electrolyte was 0.1 M KNO3Or 0.05 M Na2HPO4-KH2PO4buffer solution (pH 6.8). The response current exhibits a linear relationship with the concentration of AA over the range of 1.58×10–6–2.15×10–2 M. When samples of urine, and fruit were analyzed with Fe3+Y/ZCME, we obtained AA recovery of 98–102%, and a relative standard deviation lower than 3%. Meanwhile, interferences from other ions and organic substances were examined.

The Electrochemical Behavior of Iron(III) Incorporated in Zeolite Y-Modified Electrode and the Catalytic Oxidation of Ascorbic Acid

The Electrochemical Behavior of Iron(III) Incorporated in Zeolite Y-Modified Electrode and the Catalytic Oxidation of Ascorbic Acid

Electrochemical Behaviour of Iron in NaOH 0.01 mol/L Solutions Containing Variable Amounts of Silicate

Repetitive voltammetric cycling of iron in NaOH solutions containing variable silicate concentrations between 10 ppm and 1500 ppm, shows different behaviour for the first scan when compared to the following ones in all studied solutions. This difference indicates a modification on the film formation process. A transition in the i/E profile between 10 ppm and 100 ppm of silicate was observed allowing considerations about silicate incorporation to be formulated.

Electrochemical Behavior of Iron(III)/Iron(II) Couple in Dimethylformamide

The electrochemical behavior of the iron(III)/iron(II) couple was investigated in both complexing (Cl−) and noncomplexing (ClO−4) media in dimethylformamide (DMF), and the results were compared with the results obtained in aqueous solutions. The diffusion coefficients for iron(III) and iron(II) in DMF are larger in complexing medium than in noncomplexing medium, contrary to the results obtained in aqueous solutions. The heterogeneous electron transfer rate constants for the iron(III)/iron(II) couple obtained in DMF were found to be smaller in DMF solution as a result of the specific adsorption of DMF. The formal potential of the Fe(III)/Fe(II) couple in DMF is about 0.2 V less positive in noncomplexing medium as a result of the greater stabilization of iron(III) by the strongly cation-solvating DMF. The formal potential of the same couple in complexing medium (Cl−) was found to be 0.5 V less positive due to a combination of solvation and complexation effects. Cyclic voltammetric investigations show a quasi-reversible electron transfer without any coupled chemical reaction.

Electrochemical behaviour of iron and copper in a culture solution for Spirulina platensis

Cyclic voltammograms of iron and copper electrodes were run in sodium hydroxide, carbonate–bicarbonate buffer and culture media for Spirulina platensis at 30°C. Potentiostatic steady state polarisation curves for both electrode surfaces in these electrolytes were performed in the presence and the absence of S. platensis at fixed temperature. Corrosion potential and corrosion current density values of iron and copper were obtained graphically from these curves. In all cases, the largest corrosion current density corresponded to the maximum biogenerated-oxygen concentrations, that is, illuminated culture media containing S. platensis. Corrosion potentials of iron electrodes shifted to positive values for increasing corrosion rates, whereas constant corrosion potentials were obtained for copper electrodes independently of the electrolyte.

Effect of sulfate and chloride ions on the electrochemical behavior of iron in aqueous phosphate solutions

The electrochemical behavior of iron in aqueous phosphate solutions (0.005–0.1M) of pH∼8 at room temperature was investigated with an emphasis on the effect of chloride and /or sulfate ions on the initiation of the localized attack. Electrochemical techniques were complemented by SEM microscopy, FTIR, X-ray fluorescence analysis and ICP measurements. It has been shown that phosphate ions are very effective inhibitors against localized attack, and in the presence of sulfate ions still show an effect very similar to that of phosphate ions in the active–passive dissolution peak region.

Solvent effects on the electrochemical behavior of iron(III) Schiff base complex

Electrochemical reduction of FeIIILCl where L is a Schiff base has been investigated in various aprotic solvents. From a plot of the half wave potential E1/2 for the reduction of these complexes vs. E1/2 for the oxidation of ferrocene, the solvent–solute interactions were studied: the E1/2 variation is found to be a function of Lewis-type acceptor–donor interactions. The diffusion coefficients D in the different solvents were also been determined by linear sweep voltammetry. The variation of D is discussed in terms of viscosity and dielectric constant.

Electrochemical behaviour of iron and iron oxide thin films in alkaline (1 m KOH) aqueous solution: a voltammetry study for cathodic instability of coating/metal interface

The electrochemical behaviour of thin film metallic iron and the iron oxides in 1 m KOH anaerobic aqueous solution was studied by cyclic voltammetry technique. The material studied was of thin film (50 nm) iron supported on a glass substrate, and the oxide thermally formed on the iron film. The voltammetry of thin film iron on glass was similar to that of low carbon steel and gave a convenient means for preparing specimens for obtaining information relevant to the degradation of structural steel. In this report, the formation of various types of oxides on the iron surface are identified, and the electrochemical stability of the oxides and their relevance to the cathodic disbonding of organic coating from cathodically protected steel pipelines are discussed.

Substituent effects on the electrochemical behaviour of iron(II) in Schiff bases derived from ferrocene and their cyclopalladated compounds

Abstract Cyclic voltammetries of ferrocenylimines [(η 5 − C 5 H 5 ) Fe ∗(η 5 − C 5 H 4 )− C ( R 1 )= N − R 2 ∗] ( 1–3 ) and [(η 5 − C 5 H 5 ) Fe ∗(η 5 − C 5 H 4 )−( CH 2 ) n − N = CH ( C 6 H 5−x R 3 x )∗] (4, 5), and bis(ferrocenyl)imine [(η 5 − C 5 H 5 ) Fe ∗(η 5 − C 5 H 4 )−( CH 2 ) n − N = C ( R 4 ) (η 5 − C 5 H 4 ) Fe (η 5 − C 5 H 5 ] ( 6 ) are reported. The comparison of the half-wave potentials ( E 1 2 ) shows that the liability of iron(II) to undergo oxidation is highly dependent on the nature of the substituents. For their mono- and dinuclear cyclopalladated compounds, and , the E 1 2 values reveal that the formation of a σ(Pd(sp2, ferrocene)) bond favours the oxidation of the ferrocenyl moiety, while for compounds with a σ(PdC(sp2, phenyl)) bond the trend is the opposite.

The Electrochemical Behavior of Iron in Acetate Solutions Containing Perchlorate

Iron dissolution in acetate media, pH = 5, containing perchlorate in the range of 10- 3 M to 0.1 M was studied. Tests on disk and ring disk electrodes using cyclie voltammetry were conducted. The presence of perchlorate increases the iron dissolution rate which is influenced by hydrodynamic conditions. The acetate inhibits the deleterious effect of perchlorate.

Electrochemical Behavior of Iron in Alkaline Solution in the Presence of Silicate and Sulphate

Electrochemical Behavior of Iron in Alkaline Solution in the Presence of Silicate and Sulphate

Use of in situ Mössbauer spectroscopy for electrochemical reactions involving57Fe

An electrochemical cell and relevant electrodes have been carried out in order to study in situ various electrochemical reactions involving iron using57Fe Mossbauer resonance. The electrochemical behaviour of iron in strongly alkaline solution (KOH 5N) in the potential range (−1200<E<−200 mV) has been examined. The introduction of sulfide ions in this electrolyte leads to the formation of a new phase, the mackinawite FeS. Optimized electrochemical conditions for growing a FeS deposit on an iron electrode have been specified.