Valérie Albin

Design and characterization of chemically modified electrodes with iron(III) porphyrinic-based polymers: study of their reactivity toward nitrites and nitric oxide in aqueous solution

Abstract This study gives new examples of iron porphyrin film electrodes prepared either by electrochemical polymerization or by incorporation in pre-electropolymerized pyrrole derivatives. It shows also the different kinds of interactions between nitric oxide, nitrites and the supported iron porphyrins in acidic and neutral aqueous solutions. It gives clear indications, by cyclic voltammetry and UV-visible spectrophotometry of the formation of the suggested iron-nitrosyl intermediate, [Fe(III)(NO)]+, in supported films.

Electrochemical deposition of Co3O4 thin layers in order to protect the nickel-based molten carbonate fuel cell cathode

Abstract In order to protect the state-of-the-art nickel cathode used in the molten carbonate fuel cell, electrochemical potentiostatic deposition, a cheap and low-temperature technique, has been used to produce a cobalt oxide coating. This process was optimised on nickel substrates, analysing thoroughly the effect of the imposed potential, electrolyte composition, pH, electrolysis duration and the pre-oxidation of the substrate. Thin and homogeneous cobalt oxide layers were elaborated, in particular, in nitrate media at pH 7.4 on a nickel substrate previously oxidised. The structure and morphology of the deposits were characterised either directly or after an annealing treatment, by X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy. A cubic Co3O4 structure was identified, which is in agreement with the results obtained by cyclic voltammetry.

Thermodynamic and electrochemical behavior of nickel in molten Li2CO3-Na2CO3 modified by addition of calcium carbonate

Abstract The thermodynamic and electrochemical behavior of nickel species are investigated in Li+Na carbonate eutectic containing different amounts of calcium carbonate. NiO dissolution is predicted theoretically, and its solubility is determined experimentally by an electrochemical technique under P (CO 2 )=1 atm. The addition of calcium increases the melt basicity and reduces the NiO solubility significantly. Chemical insertion and electrochemical intercalation of alkali ions (mostly Li + ) in the NiO lattice are analyzed in Li+Na and Li+Na+Ca carbonate melts under P (CO 2 )=0.1 atm+ P (O 2 )=0.9 atm and P (CO 2 )=0.3 atm+ P (O 2 )=0.14 atm by potentiometry, voltammetry and SEM spectroscopy.

Nickel tetrasulfonated phthalocyanine based platinum microelectrode array for nitric oxide oxidation

We report in this paper on the electrochemical formation of nickel tetrasulfonated phthalocyanine (NiTSPc) based films on bulk Pt disk microelectrodes (diameter d = 50 μm) and thin-film Pt microdisk (diameter d = 10 μm) arrays for the realisation of Pt based nitric oxide sensors. Our results show that, despite the simultaneous formation of platinum oxides, NiTSPc deposited film offers an interesting alternative to elaborate new electrode configuration.

New conducting polymers: preparation and spectroscopic properties of zinc-porphyrin and anthraquinone-coated electrodes

Abstract This study concerns some aspects of the electrochemical design and characterization of zinc porphyrins and anthraquinone-based polymers. The electron-formation of the films on the electrode surface is achieved by cyclic voltammetry in organic solvents such as acetonitrile. Film deposition is based on the electrochemical oxidative polymerization of the pyrrole-substituted phenyl groups attached on the porphyrin or anthraquinone molecules. The redox characteristics of the polymer films are studied by cyclic voltammetry and spectrophotometry, and are compared to those of the starting monomers. Attempts to find a correlation between the composition of the conducting polymers and the electrochemical and spectroscopic properties of the zinc porphyrin are discussed.

First electrochemical evidence of existence of an oxomanganese(V) porphyrin intermediate in the reaction of manganese(III) porphyrin and hydrogen peroxide as a model of enzyme mimetics

Abstract We report in this study on the first electrochemical evidence of existence of an oxomanganese(V) porphyrin complex, formed upon the reaction of the manganese meso -tetrakis-(2,3,5,6-tetrafluoro- N , N , N -trimethyl-4-aniliniumyl) porphyrin (noted Mn(TF 4 TMPA) with hydrogen peroxide in 50 mM borate buffer aqueous solution (pH 10.5) at 0 °C. The obtained results bring a clear insight into the previously reported and suggested formation of such an intermediate during the electroassisted reaction of manganese porphyrins or Schiff bases and molecular oxygen in various conditions, as enzyme mimetic.

Structural and Electrical Properties of Gadolinia-doped Ceria Mixed with Alkali Earth Carbonates for SOFC Applications

The properties of composite materials based on mixtures of gadolinium-doped ceria (GDC) and Li(2)CO(3)-K(2)CO(3) are analyzed as potential SOFC electrolytes. In a temperature range higher than 500 degrees C, their ionic conductivity is significantly higher than for single GDC. Discontinuities were found in the conductivity Arrhenius diagram (sigma vs. 1/T) around the melting point of the carbonate mixture (490 degrees C), showing, at least partially, the contribution of molten carbonates. At this stage, precise mechanisms are still under analysis.

Screening and Properties of New Materials for MCFC Application

In the past years, the molten carbonate fuel cell development has been very fast, with about 50 demonstration systems installed in the United-States, Japan, Korea, Germany, Spain and proximately France. Nevertheless, an important research effort is essential in order to obtain reliable systems with higher lifetime, performance and cheap materials. Although the scientific and technological University teams or Institutes dedicated to this task are not so abundant, some serious advances can be observed concerning the search of new materials. The control and improvement of the molten carbonate eutectic and matrix are important topics involving a good knowledge of solution chemistry, oxoacidity concept and physicochemical properties (evaporation, wettability, stability). Li2CO3/K2CO3 and Li2CO3/Na2CO3 are the commonly used electrolytes, but the presence of additives increasing their basicity is necessary. The dissolution and corrosion of the state-of-the art cathode, LixNi1-xO, requires either its replacement by new materials (mixtures of Co-Ni and Fe oxides, perovskite) or the presence of stabilizing dopants. The use of protective coatings is also a very attractive solution because of the fast expansion of the thin layer technology. This aspect will be developed thoroughly because it is also of particular interest for the protection of the stainless steels used as bipolar plates or current collectors. Ni-Al presents a better stability and performance with respect to the classical Ni-Cr anode. Fig. 1 shows a SEM/EDS cross section analysis of the NiAl anode after immersion in the molten carbonate electrolyte. The thickness and composition of the corrosion layer were determined. The corrosion layer of about 10 μm is mainly constituted by a protective LiAlO2 film.