Laboratoire Interfaces et Systèmes Électrochimiques

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Bode plots, corrected for Ohmic resistance, logarithmic plots of the imaginary component of the impedance, and effective capacitance plots are shown to be useful complements to the more traditionally used complex-plane and Bode representations for electrochemical impedance data. The graphical methods are illustrated by synthetic data and by experimental data associated with corrosion in saline environments. Bode plots are shown, in particular, to be confounded by the influence of electrolyte resistance. The plots proposed here provide useful guides to model development for both reactive and blocking systems. The logarithmic plots of the imaginary component of the impedance and effective capacitance plots are useful for all impedance data, and the correction for Ohmic resistance in Bode plots is useful when the solution resistance is not negligible.

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pletely different initial values than the equil ibrium values corresponding to the former pulse. 4. By anodic dissolution of a three-valent metal, proceeding in two steps which were dealt with above, intermediate ion concentrations higher than a critical value cannot be obtained.

Abstract To use water as the source of electrons for proton or CO 2 reduction within electrocatalytic devices, catalysts are required for facilitating the proton‐coupled multi‐electron oxygen evolution reaction (OER, 2 H 2 O→O 2 +4 H + +4 e − ). These catalysts, ideally based on cheap and earth abundant metals, have to display high activity at low overpotential and good stability and selectivity. While numerous examples of Co, Mn, and Ni catalysts were recently reported for water oxidation, only few examples were reported using copper, despite promising efficiencies. A rationally designed nanostructured copper/copper oxide electrocatalyst for OER is presented. This material derives from conductive copper foam passivated by a copper oxide layer and further nanostructured by electrodeposition of CuO nanoparticles. The generated electrodes are highly efficient for catalyzing selective water oxidation to dioxygen with an overpotential of 290 mV at 10 mA cm −2 in 1 m NaOH solution.

High-density amorphous water is studied by neutron scattering in a Q range extending to 16 Å−1. The low density form of amorphous water is also analyzed and compared with previous results. There are very important differences in the composite pair correlation functions of the two forms of amorphous ice, in particular beyond the first nearest-neighbors distance. We conclude that the hydrogen bond network is strongly deformed in a manner analogous to that found in water at high temperature. This is in contrast with the behavior of the pair correlation function of low-density amorphous water, which is closer to that of supercooled water.

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Ferrofluids are colloidal solutions of iron oxide magnetic nanoparticles in either a polar or no polar liquid. We present here two biological applications using maghemite (γFe2O3) ferrofluids: magnetic cell sorting and magnetocytolysis. The first application employs magnetic particles binding a biological effector, which is capable to recognize the target cells specifically. These cells become magnetic and can be sorted in a gradient of magnetic field. We describe first the various steps of the synthesis of a biocompatible ferrofluid and the grafting an effector protein onto the particles. We then describe the use of particles carrying annexin V in the separation and quantification of damaged erythrocytes in blood samples. This very sensitive technique can be used to follow the erythrocytes ageing of normal blood samples during their storage under blood bank conditions or to detect the membrane modifications that are associated with some pathologies such as malaria or Alzheimer's disease. The dependence of the magnetic susceptibility versus the frequency is a way to transform magnetic energy into thermal energy. Magnetocytolysis is the destruction of cells, carrying magnetic particles, through the action of an alternating magnetic field (about 1 MHz). We present here preliminary experiments with macrophages, which demonstrate the method's feasibility and the formation of the non-specific interactions between the cells and the magnetic particles.

When an intermediate species is involved in an electrochemical reaction and is adsorbed on the metal surface, the coverage most often depends on the potential. In this case, impendance measurements allow for the overall reaction to be split into elementary processes on the basis of different relaxation times. Theoretical models are given and checked by experiment for the dissolution of iron, the cupri-cuproloride reduction on an inert electrode and the reversible transition from active to passive state of iron.

International audience

International audience

Electrochemical noise (EN) can be used in situ to investigate corrosion processes and to detect and monitor the corrosion of metallic materials. EN data are largely influenced by the measurement mode, the surface area of the working electrodes, the electrolyte resistance, and the symmetry of the electrode system. Herein, the advantages and limitations of electrochemical kinetics, equivalent circuit, and shot noise methods for quantifying corrosion rates with EN are discussed.

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We report a protocol that allowed us to fabricate nanoparticle aggregates from anionically coated 7 nm iron oxide nanocrystals and cationic-neutral block copolymers. The control of electrostatics resulted in the elaboration of spherical clusters or of highly persistent nanostructured rods, with lengths between 1 and 50 µm (see figure). The rods were shown to be superparamagnetic.

Here, we report a new synthetic route for spherical small copper nanoparticles (CuNPs) with size ranging from 3.5 nm to 11 nm and with an unprecedented associated monodispersity (<10%). This synthesis is based on the reduction of an organometallic precursor (CuCl(PPh3)3) by tert-butylamine borane in the presence of dodecylamine (DDA) at a moderate temperature (50 to 100 °C). Because of their narrow size distribution, the CuNPs form long-range 2D organizations (several μm(2)). The wide range of CuNPs sizes is obtained by controlling the reaction temperature and DDA-to-copper phosphine salt ratio during the synthesis process. The addition of oleic acid (OA) after the synthesis stabilizes the CuNPs (no coalescence) for several weeks under a nitrogen atmosphere. The nature and the reactivity of the ligands were studied by IR and UV-visible spectroscopy. We thus show that just after synthesis the nanoparticles are coated by phosphine and DDA. After adding OA, a clear exchange between phosphine and OA is evidenced. This exchange is possible thanks to an acid-base reaction between the free alkylamine in excess in the solution and OA. OA is then adsorbed on the NPs surface in the form of carboxylate. Furthermore, the use of oleylamine (OYA) instead of DDA as the capping agent allows one to obtain other NP shapes (nanorods, triangles and nanodisks). We get evidence that OYA allows the selective adsorption of chloride ions derived from the copper precursor on the different crystallographic faces during the growth of CuNPs that induces the formation of anisotropic shapes such nanorods or triangles.

We measured single-molecule conductances for three different redox systems self-assembled onto gold by the STMBJ method and compared them with electrochemical heterogeneous rate constants determined by ultrafast voltammetry. It was observed that fast systems indeed give higher conductance. Monotonous dependency of conductance on potential reveals that large molecular fluctuations prevent the molecular redox levels to lie in between the Fermi levels of the electrodes in the nanogap configuration. Electronic coupling factors for both experimental approaches were therefore evaluated based on the superexchange mechanism theory. The results suggest that coupling is surprisingly on the same order of magnitude or even larger in conductance measurements whereas electron transfer occurs on larger distances than in transient electrochemistry.

International audience

International audience

This paper presents a high-sensitive planar microwave sensor based on the metamaterial technology, integrated with a microfluidic channel to be used for liquid sensing in a variety of biomedical applications. The sensor design comprises three cells of circular complementary split ring resonators (CSRRs) engraved on the ground plane of a dielectric substrate in a cascaded configuration. The sensing cells are excited with a time-varying electric field coupled from a planar microstrip-line (MTL) etched on the bottom side of the substrate. The proposed design of multiple coupled resonators would enhance the electric field intensity over a larger sensing region through the inter-resonator coupling, thus improving the overall sensitivity for detecting liquid samples of high permittivity and dielectric losses. The sensor exhibits a reject (band stop) filter behaviour with multiple resonances in the centimeter-wave band 1 - 6 GHz when loaded symmetrically with liquid samples. The sensor is fabricated on an FR4 dielectric substrate with a biocompatible microfluidic channel aligned appropriately over the sensing area to enable consistent and intact sensing of the liquid samples. The CSSR-sensor is numerically modeled and compared in performance to the single-cell CSRR for detecting small variations in the dielectric properties. The sensitivity, reliability, and repeatability of the proposed sensor are practically demonstrated by the in-lab measurements for different liquid samples using a Vector Network Analyzer (VNA) setup where distinctive resonant features (amplitude and frequency) are extracted from multiple resonance modes in the reflection and transmission responses. A high sensitivity is also demonstrated for monitoring glucose level variations in synthetic blood samples of concentrations (70 - 150 mg/dL) which are clinically-relevant to diabetes conditions. Beside its impressive capability in detecting small dielectric variations, the developed sensor features other favorable attributes including compact size, simple fabrication, affordable cost, non-ionizing nature, and minimal health risk or impact. Such key advantages could potentially promote the proposed sensor for integration with other microwave components in an embedded device for non-invasive monitoring of blood glucose for diabetes.

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