Ludovic Legrand

Experimental investigations on iron corrosion products formed in bicarbonate/carbonate-containing solutions at 90°C

The influence of initial oxygen level and bicarbonate content on iron corrosion was examined during the early stages of a storage at 90°C. The nature of corrosion products formed on iron surface was investigated through FTIR, Raman spectrometry and scanning electron microscopy. It has been shown that high bicarbonate content (1 M) promotes the formation of siderite whatever the initial oxygen level. Decreasing the bicarbonate content (from 0.1 to 0.001 M) will favour the formation of FeII(OH−)x(HCO3−/CO32−)y species with increasing x values and decreasing y values. FeII(OH−)x(HCO3−/CO32−)y species may suffer a series of transformations into green rust GR1(CO3) (intermediate species), FeII(OH−)n(HCO3−/CO32−)m gel-like precipitate, magnetite or lepidocrocite depending on the initial oxygen level.

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

Abstract 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 Mossbauer 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) 2 Fe (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.

A Raman and infrared study of a new carbonate green rust obtained by electrochemical way

The occurrence of a new carbonate green rust (GR) obtained by electrochemical oxidation of iron in bicarbonate/carbonate solutions has been evidenced by infrared spectroscopy, Raman microprobe and coulometric titration. The Fe2+/Fe3+ ratio is 1 that corresponds to an iron oxidation state of 2.5. Under wet and dry aerial oxidation conditions, the 1/1 carbonate GR is significantly more stable than the 2/1 carbonate GR, reported in the literature by now. The ultimate oxidation product is ferrihydrite. From coulometric investigations, the mechanism of formation was found to involve both an oxidation of iron to Fe(II) complexes and a solution oxidation of Fe(II) to Fe(III) prior to the precipitation of 1/1 carbonate GR.

Study of oxidation products formed on iron in solutions containing bicarbonate/carbonate

Abstract Oxidation layers formed on iron in deaerated bicarbonate/carbonate solutions at potentials in the active range were investigated through electrochemical techniques, FTIR and scanning electron microscopy. Three oxidation products have been obtained, siderite, am-FeOOH with adsorbed carbonate or bicarbonate ions and green rust GR1(CO 3 ). It has been shown that the formation of either compound was strongly dependent on the concentration, temperature and pH of solutions.

Electrochemical deposition of thin films of green rusts 1 and 2 on inert gold substrate

Abstract Green rusts are layered Fe(II)–Fe(III) hydroxy-salts that play an important role in iron corrosion, soil chemistry, and environmental engineering. Successful electrochemical depositions of thin layers of green rusts incorporating anions such as carbonate or chloride (GRs1) or sulphate (GR2) on gold substrate are presented. As far as we know, it is the first time that such synthesis has been reported. The thin layers of green rusts were characterized by ex situ methods such as XRD, SEM, EDS and FTIR. This new way of synthesis allowed us to get green rust particles with sizes significantly larger than those obtained from the ways reported until now.

Ion–ion interactions and lithium stability in a crosslinked PEO containing lithium salts

Abstract The electrochemical properties of a solid polymer electrolyte prepared by chemical crosslinking of PEO 2000 and containing LiAsF 6 or LiCF 3 SO 3 were investigated for electrochemical window, lithium stability and lithium/electrolyte interface stability. FTIR spectroscopy of the salt anion (AsF 6 − and CF 3 SO 3 − ) was also used to determine the nature and the extent of ion pairing and ion aggregation in these crosslinked electrolytes. The lithium corrosion appears as a diffusion limited process as the coulombic efficiency of a lithium deposit decreases with the square root of the contact time of lithium with the crosslinked PEO. Impedance parameters are consistent with an increase of the passivating layer upon storage. Their values strongly differ with the salt anion.

Sulfone-based electrolytes for aluminum electrodeposition

Abstract We developed new electrolytes for aluminum deposition based on AlCl3/dialkylsulfones (XSO2) mixtures usable in the 40–150 °C temperatures range along the melting point of the sulfone choosen. NMR study of these electrolytes showed that they contain AlCl4−, Al(XSO2)33+ and 1: 1 molecular adducts AlCl3-XSO2 ; this latter Al species is formed at the expense of Al(XSO2)33+, especially in diethylsulfone and dipropylsulfone-based electrolytes. The Al species responsible for aluminum deposition has been shown to be Al(XSO2)33+. Al deposits formed from AlCl 3 XSO 2 , electrolytes exhibit fine grain size, relatively smooth surface aspect and high purity. High deposition rates (> 50 μm h−) and thick Al deposits with thickness up to a few hundreds micrometers were obtained from AlCl3/dimethylsulfone at 130 °C.

Design of metal organic framework–enzyme based bioelectrodes as a novel and highly sensitive biosensing platform

Nanocomposites combining the mesoporous iron(iii) trimesate MIL-100(Fe) (MIL: Matériaux Institut Lavoisier) and platinum nanoparticles (Pt-NPs) have been used as immobilization matrices of glucose oxidase (GOx). Due to the physico-chemical properties of Pt-NPs (electroactivity) and MIL-100(Fe) (high specific surface area and pore volume, biocompatibility), the resulting GOx-MIL-100(Fe)-PtNP bioelectrode exhibits excellent electrocatalytic performances for glucose detection. This novel glucose biosensor presents a high sensitivity of 71 mA M-1 cm-2 under optimum conditions and a low limit of detection of 5 μM with low response time (<5 s). In contrast, substitution of iron by chromium or aluminum in MIL-100 leads to a much lower sensitivity and higher response time values, suggesting that the iron centres of MIL-100(Fe) may be involved in a synergistic effect which indeed enhances the catalytic oxidation of glucose and biosensor activity. Thus, this work extends the scope of MOF nanoparticles with engineered cores and surface to the field of highly sensitive, durable glucose biosensors.

Behaviour of aluminium as anode in dimethylsulfone-based electrolytes

Abstract Electrochemical behaviour of aluminium has been investigated in dimethylsulfone in presence of AlCl 3 and LiCl salts in the temperature range of 80–160°C. Electrochemically active aluminium can be cathodically deposited and anodically stripped from LiAl 2 Cl 7 /DMSO 2 electrolyte. High efficiencies ( > 90%) have been obtained during cycling of aluminium in this medium. Comparison with other systems has been done.

Electroanalytical and Kinetic Investigations on the Carbonate Green Rust-Fe(III) Redox System

Electrochemical measurements were associated with Fourier transform infrared spectroscopy, Raman microprobe, scanning electron microscopy and X-ray diffraction to study the behavior of carbonate green rust/Fe(III) redox system, in carbonate solutions. Carbonate green rust undergoes a reversible oxidation, leading to the transformation of Fe(II) present in its structure into Fe(III). This oxidation does not involve a dissolution/precipitation mechanism, but a solid-state transformation. Two oxidized products have been detected. Fe(III) 1 and Fe(III) 2 . Fe(III) 1 is the first ferric product resulting from the oxidation of carbonate green rust; it undergoes a structural rearrangement that leads to its gradual conversion into a more stable product. Fe(III) 2 . The kinetics of the Fe(III) 1 -to-Fe(III) 2 transformation were investigated. It allowed us to explain the evolution of the potential during the oxidation by air of a carbonate green rust suspension.