The EChemPen: A Guiding Hand To Learn Electrochemical Surface Modifications

The Electrochemical Pen (EChemPen) was developed as an attractive tool for learning electrochemistry. The fabrication, principle, and operation of the EChemPen are simple and can be easily performed by students in practical classes. It is based on a regular fountain pen principle, where the electrolytic solution is dispensed at a tip to locally modify a conductive surface by triggering a localized electrochemical reaction. Three simple model reactions were chosen to demonstrate the versatility of the EChemPen for teaching various electrochemical processes. We describe first the reversible writing/erasing of metal letters, then the electrodeposition of a black conducting polymer “ink”, and finally the colorful writings that can be generated by titanium anodization and that can be controlled by the applied potential. These entertaining and didactic experiments are adapted for teaching undergraduate students that start to study electrochemistry by means of surface modification reactions

Local enhancement of hydrogen production by the hydrolysis of Mg17Al12 with Mg “model” material

The effect of galvanic coupling on the corrosion behavior of Mg and Mg17Al12 in Mg-Al alloys was studied by Scanning ElectroChemical Microscopy (SECM). The effect of galvanic coupling between Mg and Mg17Al12 was investigated using a “model” Mg+Mg17Al12 material with a controlled microstructure to evaluate the hydrogen evolution at a micrometric scale. SECM maps revealed that galvanic coupling between Mg and Mg17Al12 accelerates the corrosion rate (formation of a thicker passive layer) of both components. Mg17Al12 acts controversially to a conventional cathode in galvanic system since hydrogen production by its hydrolysis reaction was found to increase due to the electron transfer with the anode (Mg).Fil: Al Bacha, S.. Lebanese University, Faculty Of Sciences Ii; Líbano. Universite de Bordeaux; Francia. Université Paris-Saclay; FranciaFil: Farias, Eliana Desiree. Universite de Bordeaux; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Garrigue, Patrick. Universite de Bordeaux; FranciaFil: Zakhour, Mirvat. Lebanese University, Faculty Of Sciences Ii; LíbanoFil: Nakhl, Michel. Lebanese University, Faculty Of Sciences Ii; LíbanoFil: Bobet, Jean Louis. Universite de Bordeaux; FranciaFil: Zigah, Dodzi. Universite de Bordeaux; Francia. Université de Poitiers; Franci

Analyse de surfaces par imagerie électronique

Le développement de dispositifs électroniques de taille de plus en plus petite a obligé le monde scientifique à se doter d'outils pouvant analyser à l'échelle microscopique la réactivité d'une surface. C'est ainsi qu'est né le SECM (Scanning ElectroChemical Microscopy) ou microscopie électrochimique à balayage. Cette technique, dérivée des microscopies à champ proche (STM, AFM), permet d'observer de façon locale une surface en s'appuyant sur les propriétés des ultramicroélectrodes (UME). L'UME et la surface à analyser sont placées dans une solution électrolytique contenant un médiateur rédox. Le SECM fournit alors un véritable "pinceau" chimique qui va sonder la surface. La première partie de ces travaux a été consacrée à l'étude de surfaces de carbone conductrices et de surfaces de silicium isolantes, fonctionnalisées par une molécule rédox (ferrocène), stable à l'état oxydé et à l'état réduit. Nous avons ensuite étudié des systèmes plus complexes. Nous avons suivi pas à pas, à l'aide du SECM, la conception d'un édifice biocatalytique sur une surface conductrice et sur une surface isolante. Dans la dernière partie de cette thèse, nous nous sommes intéressés aux interfaces électrode/liquides ioniques. Les liquides ioniques sont des sels liquides à température ambiante qui sont de plus en plus utilisé en chimie comme substituant aux solvants classiques. A l'aide d'un modèle théorique, nous avons utilisé le SECM en conditions transitoires afin de déterminer de façon originale la valeur des coefficients de diffusion de molécules organiques dans ce type de solvant.With the progressive decrease in the size of electronic devices, scientists were obliged to develop tools capable of analyzing surface reactivity on microscopic level. This marked the birth of SECM (Scanning ElectroChemical Microscopy). This technique, derived from scan probe microscopy (STM, AFM) makes it possible the study a local area based on ultramicroelectrodes properties (UME). The UME and the surface to be analyzed are placed in an electrolyte solution containing a redox mediator. The SECM provides a real "brush" chemical that will probe the surface. The first part of this work focused on the study of conducting and insulating surfaces, composed of carbon and silicon respectively, which were functionalized by a stable redox molecule (ferrocene), at an oxidized and reduced state. We then studied more complex systems. We used the SECM method to fellow the biocatalytic formation on a conducting and an insulated surface. In the last part of this thesis, we studied the electrode/ionic liquid interfaces. Ionic liquids are salt liquids at room temperature, mostly used in chemistry as a substitute for conventional solvents. With a theoretical model, we used SECM in transient conditions, to determine the diffusion coefficients of organic molecules in this type of solvent.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Optimized preparation and scanning electrochemical microscopy analysis in feedback mode of glucose oxidase layers grafted onto conducting carbon surfaces.

International audienceAn optimized immobilization procedure based on the electroreduction of aryldiazonium salt followed by covalent attachment of a cross-linked hydrogel was used to graft glucose oxidase on a carbon surface. Scanning electrochemical microscopy (SECM) and cyclic voltammetry were used to follow the construction steps of the modified electrode. By adjusting the compactness of the layer through the electrografting reaction, the penetration of the mediator through the layer can be controlled to allow the monitoring of the enzymatic activity by both cyclic voltammetry and SECM in feedback mode. The enzymatic activity of the film is finally characterized by SECM

Diffusion of Molecules in Ionic Liquids/Organic Solvent Mixtures. Example of the Reversible Reduction of O to Superoxide

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Charge Transfer between Electroactive Species Immobilized on Carbon Surfaces by Aryl Diazonium Reduction. SECM Investigations

International audienceElectron transfers in modified polyaryl multilayers containing redox active molecules (ferrocenyl moieties) have been investigated by scanning electrochemical microscopy (SECM) in feedback mode. The modified surfaces were prepared by the electro-reduction of aryl diazonium salts that provides anchoring layers for the immobilization of the electroactive groups. Two types of anchoring films were prepared, the first with aminophenyl and the second with phenylcarboxylic acid groups, allowing us to vary the oxidation level of the electroactive film. Determination of the apparent electron transfer rates between the modified surface and a series of redox mediators displaying increasing standard potentials permits the analysis of different processes involved in the charge transfer, namely, the permeation of the organic molecules (the mediator) and the conduction mechanism. In addition to the first oxidation of the immobilized molecules by the mediator at the solution−film interface, the global oxidation kinetics involves the conduction by charge transfer between grafted ferrocenes and the reverse charge transfer reaction from the film to mediator. This last step that is required to maintain the charge balance could become a kinetic limit for the highest driving force. For the most oxidizing mediator, analyses also suggest that the aromatic layer participates in the charge transfer

Wireless Electronic Light Emission: An Introduction to Bipolar Electrochemistry

International audienceElectrochemistry is taught in most undergraduate chemistry programs. Although this topic is important for students due to its broad interest in industry (energy, diagnostics, car industry, etc.), they often find it difficult, because it is based on a combination of various physical concepts such as electric fields, interfacial processes or charge and mass transports. Among electrochemical concepts, bipolar electrochemistry is of special interest and might be easier to teach due to a very simple general setup. In this case, an oxidation and a reduction reactions occur at the two ends of a single conductive object exposed to an electric field in solution. Such an object is therefore called a bipolar electrode. The nature of the electrochemical reactions and their amplitude can be tuned by playing with the electric field. The fundamental concepts of bipolar electrochemistry are introduced here with a series of basic experiments designed to be carried out in a standard teaching laboratory. These simple and affordable experiments illustrate the key-parameters driving electrochemical reactions at a bipolar electrode. Their influence can be readily visualized using a cheap, commercially available light emitting diode (LED) acting as the bipolar electrode, which illuminates when the current generated by the electrochemical reactions flows through it. The concept of bipolar electrochemistry with eye-catching experiments enables a good introduction to genera

Synthesis and immobilization of Ag(0) nanoparticles on diazonium modified electrodes: SECM and cyclic voltammetry studies of the modified interfaces.

International audienceA versatile method was used to prepare modified surfaces on which metallic silver nanoparticles are immobilized on an organic layer. The preparation method takes advantage, on one hand, of the activated reactivity of some alkyl halides with Ag-Pd alloys to produce metallic silver nanoparticles and, on the other hand, of the facile production of an anchoring polyphenyl acetate layer by the electrografting of substituted diazonium salts on carbon surfaces. Transport properties inside such modified layers were investigated by cyclic voltammetry, scanning electrochemical microscopy (SECM) in feedback mode, and conducting AFM imaging for characterizing the presence and nature of the conducting pathways. The modification of the blocking properties of the surface (or its conductivity) was found to vary to a large extent on the solvents used for surface examination (H(2)O, CH(2)Cl(2), and DMF)

Original Dual Microelectrode: Writing and Reading a local click reaction with Scanning Electrochemical Microscopy

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