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Yakdi N.,CNRS Laboratory Interfaces & Systems Electrochemistry | Huet F.,CNRS Laboratory Interfaces & Systems Electrochemistry | Ngo K.,CNRS Laboratory Interfaces & Systems Electrochemistry
Electrochimica Acta | Year: 2015

Over the last few years, particle sizing techniques in multiphase flows based on optical technologies emerged as standard tools but the main disadvantage of these techniques is their dependence on the visibility of the measurement volume and on the focal distance. Thus, it is important to promote alternative techniques for particle sizing, and, moreover, able to work in hostile environment. This paper presents a single-particle sizing technique at a millimeter scale based on the measurement of the variation of the electrolyte resistance (ER) due to the passage of an insulating sphere between two electrodes immerged in a conductive solution. A theoretical model was proposed to determine the influence of the electrode size, the interelectrode distance, the size and the position of the sphere, on the electrolyte resistance. Experimental variations of ER due to the passage of spheres and measured by using a home-made electronic device are also presented in this paper. The excellent agreement obtained between the theoretical and experimental results allows validation of both model and experimental measurements. In addition, the technique was shown to be able to perform accurate measurements of the velocity of a ball falling in a liquid. © 2015 Elsevier Ltd.

Joiret S.,CNRS Laboratory Interfaces & Systems Electrochemistry | Pillier F.,CNRS Laboratory Interfaces & Systems Electrochemistry | Lemarchand A.,CNRS Laboratory of Theoretical Physics and Condensed Matter
Journal of Physical Chemistry C | Year: 2014

To propose a picture of plaster hydration at a submicrometric scale, we have developed a kinetic Monte Carlo simulation model of gypsum crystal growth. Raman spectroscopy is used to check the model and to assign physical values to the parameters. Special focus is put on the effects of increasing plaster-to-water ratio and using citric acid as an additive. The hypothesis about the autocatalytic growth of gypsum needles during the first stage of the reaction is confirmed by the correct simulation of the induction period preceding the fast growth regime. The aspect ratio of gypsum needles, defined as the ratio of needle length and width, emerges as a relevant parameter to control both dynamics and material structure. Addition of citric acid is known to produce compact gypsum crystals instead of long needles. The choice of a small aspect ratio is sufficient for the simulations to reproduce the effects of citric acid, including the slowing down of the reaction without recourse to fitting parameters. The kinetic Monte Carlo simulation model proved to be a predictive tool that could assist the rational development of novel additives and reagent treatments with the aim of producing materials with predefined properties. © 2014 American Chemical Society.

Fakhry A.,CNRS Laboratory Interfaces & Systems Electrochemistry | Cachet H.,CNRS Laboratory Interfaces & Systems Electrochemistry | Debiemme-Chouvy C.,CNRS Laboratory Interfaces & Systems Electrochemistry
Electrochimica Acta | Year: 2015

In the presence of a high concentration of weak-acid anions, such as monohydrogenophosphate which confer to a pyrrole aqueous solution a pH around 9, an ultra thin non-conductive overoxidized polypyrrole film is deposited on the electrode under an anodic polarization. In the same experimental conditions, after addition of perchlorate anions (C > 0.5 mM) in the pyrrole solution the electrooxidation of the monomers leads to the synthesis of a superhydrophilic nanostructured conductive polypyrrole film (network of nanofibers or oriented nanowires, 50-120 nm in diameter). The aim of the present paper is to confirm the mechanism that we have previously proposed and so to explain the spontaneous nanostructuration of the electrogenerated polypyrrole films. We have assumed that this templateless formation of nanostructures is notably due to the oxidation of water with production of hydroxyl radicals and nanobubbles of dioxygen. Due to the fact that pyrrole polymerization is associated to the release of protons, we have first verified that the electrode/solution interfacial pH is compatible with the water oxidation potential. For this purpose, during the monomer oxidation the interfacial pH variation has been monitored using a pH electrode having a flat glass membrane which was covered with a Pt grid used as the working electrode. Secondly, the presence of dioxygen nanobubbles has been indirectly confirmed by rotating the working electrode. Indeed rotation of the electrode allows eliminating the nanobubbles present inside the polypyrrole film. For the highest rotation speed tested (94 rad s-1), a very thin overoxidized film was electrogenerated. Our results are in good agreement with the fact that the nanobubbles protect the PPy film against the action of the hydroxyl radicals which react with the polypyrrole film leading to its overoxidation. © 2015 Elsevier Ltd. All rights reserved.

Fakhry A.,CNRS Laboratory Interfaces & Systems Electrochemistry | Pillier F.,CNRS Laboratory Interfaces & Systems Electrochemistry | Debiemme-Chouvy C.,CNRS Laboratory Interfaces & Systems Electrochemistry
Journal of Materials Chemistry A | Year: 2014

Different superhydrophilic polypyrrole nanostructures can be electrosynthezised in the presence of anions of weak acid (monohydrogenophosphate) and non-acidic anions (perchlorate) without the need for templates. Actually the type of nanostructures formed depends both on the concentration of anions at the electrode and on the interfacial pH. Depending on the anion composition of the pyrrole aqueous solution the film electrogenerated under a given applied potential is either a very thin membrane (10-20 nm) consisting of overoxidized polypyrrole or a tridimensional film with oriented nanowire array or a network of more or less interconnected nanofibers. The formation of such nanostructures is explained by a side reaction which is water oxidation. Since this reaction is pH-dependent, the pH of the pyrrole solution is one of the key parameter for the synthesis of such nanostructures. The reaction mechanism is discussed and compared to those proposed in the literature for nanofiber network electrosynthesis. Actually in the monomer solution, the role of the anions of weak acid is twofold. On the one hand they allow to limit the decrease of the interfacial pH during pyrrole oxidation and on the other hand to decrease the interfacial anion concentration, so that water oxidation takes place with formation of hydroxyl radicals and dioxygen nanobubbles. This journal is © the Partner Organisations 2014.

Faure M.,CNRS Laboratory Interfaces & Systems Electrochemistry | Sotta B.,CNRS Developmental Biology Laboratory | Gamby J.,CNRS Laboratory Interfaces & Systems Electrochemistry
Biosensors and Bioelectronics | Year: 2014

Real time monitoring of electrolyte resistance changes during hydrolysis of 4-nitrophenylphosphate (pNPP) by alkaline phosphatase (ALP) bound on paramagnetic-beads was performed into a small dielectric channel. The reaction kinetic fit with a non-competitive substrate-inhibition equation. Michaelis-Menten apparent constant, KMapp, was determined as 0.33±0.06mM and the maximum apparent rate, Vmaxapp as 98±5pMs-1. The detection limits were 15fM for ALP and 0.75mM for pNPP. © 2014 Elsevier B.V.

Monnier J.,CNRS East Paris Institute of Chemistry and Materials Science | Chen H.,CNRS East Paris Institute of Chemistry and Materials Science | Joiret S.,Paris-Sorbonne University | Joiret S.,CNRS Laboratory Interfaces & Systems Electrochemistry | And 2 more authors.
Journal of Power Sources | Year: 2014

To improve the performances of Nickel-Metal Hydride batteries, an important step is the understanding of the corrosion processes that take place in the electrode material. In particular, the present study focuses for the first time on the model (La, Mg)2Ni7 system. The calendar corrosion in 8.7 M KOH medium was investigated from 6 h to 16 weeks immersion. By a unique combination of structural and elemental characterisations, the corrosion products are evidenced in those systems. In particular, we demonstrate that Ni and Mg combine in a pseudo-binary hydroxide Mg1-xNi x(OH)2 whereas La corrodes into nanoporous La(OH) 3 needles with inner hollow nanochannels. © 2014 Elsevier B.V. All rights reserved.

Alexander C.L.,University of Florida | Tribollet B.,CNRS Laboratory Interfaces & Systems Electrochemistry | Orazem M.E.,University of Florida
Electrochimica Acta | Year: 2016

Finite-element simulations were performed to determine the influence of a radial distribution of capacitance on the impedance of ideally polarized disk electrodes. The characteristic length associated with this form of distribution was found to be the period of the distribution. This work showed that while a capacitance distribution causes frequency dispersion, this effect is seen only at frequencies that are much higher than those associated with the disk-geometry-induced frequency dispersion. Thus, a constant-phase-element associated with a surface distribution of time constants cannot be attributed to a distribution of capacitance. © 2015 Elsevier Ltd. All rights reserved.

Lugaresi O.,University of Milan | Perales-Rondon J.V.,University of Alicante | Minguzzi A.,University of Milan | Solla-Gullon J.,University of Alicante | And 3 more authors.
Applied Catalysis B: Environmental | Year: 2015

Electrochemical abatement of volatile polychlorinated organic compounds for environmental applications represents a very attractive and feasible alternative for working at mild reaction conditions and reduced costs. We present herein the synthesis of three different sized Ag nanoparticles (NPs) and their electrocatalytic performance in the degradation of a model pollutant (trichloromethane, CHCl3) in aqueous media. Two different methodologies are used: A conventional study based on voltammetry and chronoamperometry and a novel screening approach based on the micropipette delivery/substrate collection (MD/SC) mode of the scanning electrochemical microscopy (SECM). This new approach allows to dose any reactant, in this case CHCl3, even if the latter cannot be electrogenerated. Moreover, we introduce here a novel platform for studying nanomaterials by reducing the current collector background contribution using disposable screen-printed array electrodes. The performance ranking obtained by the SECM for the three different samples of Ag NPs synthesized is validated by its comparison with the results obtained by chronoamperometry, which demonstrates the feasibility and the good sensitivity of SECM in electrocatalysts screening for the CHCl3 reduction reaction. In addition, SECM allows to analyze simultaneously a large number of catalysts in one single experiment under constant experimental conditions. We suggest the proper size range and the presence of abundant superficial defective sites, such as steps or kinks, as the main reasons for Ag NPs C1 exhibiting the best overall catalytic performance in trichloromethane electrochemical reduction. © 2014 Elsevier B.V.

Cachet H.,CNRS Laboratory Interfaces & Systems Electrochemistry | Sutter E.M.M.,CNRS Laboratory Interfaces & Systems Electrochemistry
Journal of Physical Chemistry C | Year: 2015

The electronic properties of a TiO2-nanotube (NT) array used as a photoelectrode for water oxidation at neutral and basic pH were characterized by combining complementary measurement techniques: transient photocurrents, stationary photocurrent-voltage curves, photo-electrochemical impedance spectroscopy (PEIS), and intensity-modulated photocurrent spectroscopy (IMPS). Transient measurements point out the slow chemical modification of the TiO2 surface when going from dark to light, essentially around neutral pH. After this transient period, a new stationary state of the TiO2 surface is established, allowing small amplitude perturbation techniques (PEIS and IMPS) to be applied to obtain information on transfer and recombination kinetics and on surface states contribution. The relevant information was obtained via theoretical models for the PEIS and IMPS responses, involving physical parameters with values extracted by nonlinear least-squares fitting. The main conclusions taken from our experiments include the following: (i) Under ultraviolet light illumination, the surface chemistry of TiO2 was found relatively stable at basic pH but strongly modified (hydroxylation) at neutral pH. (ii) Hole transfer to solution species takes place preferentially via the valence band. (iii) Recombination is mainly a surface process. (iv) Rate constants for charge transfer and recombination were determined as a function of the applied potential in agreement with the stationary photocurrent-voltage curve. © 2015 American Chemical Society.

Ngaboyamahina E.,CNRS Laboratory Interfaces & Systems Electrochemistry | Debiemme-Chouvy C.,CNRS Laboratory Interfaces & Systems Electrochemistry | Pailleret A.,CNRS Laboratory Interfaces & Systems Electrochemistry | Sutter E.M.M.,CNRS Laboratory Interfaces & Systems Electrochemistry
Journal of Physical Chemistry C | Year: 2014

Using highly ordered TiO2 nanotube arrays as the substrate for electropolymerization provides a high surface area for polymer deposit and vertical pathways for electron transport. The challenge is to deposit the polymer on the inner and outer walls of the tubes and to avoid the sealing of the tubes at the mouth. Ideally, this situation could be reached by filling the tubes from the bottom. We demonstrate here that by using pulsed methods (light pulses, potential pulses), the deposition rate can be controlled, leading to a better monomer supply within the nanotubular matrix. The parameters to apply for the deposition are greatly dependent on the nature of the anion in the electrolyte, which determines the rate and the location of the polymer growth at the electrolytic solution/semiconductor interface. © 2014 American Chemical Society.

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