Les phénomènes de corrosion localisée observés sur les matériaux passifs, largement utilisés dans l’industrie et le transport, résultent de la présence d’hétérogénéités microstructurales et de l’effet des sollicitations mécaniques et thermomécaniques. C’est pourquoi la caractérisation et la compréhension des processus réactionnels nécessitent l’utilisation de techniques d’investigation locales. La microscopie électrochimique à balayage (SECM), technique récente, a été utilisée dans différentes situations. Dans un premier temps, des essais permettant de visualiser les sites d’amorçage des piqûres ont été réalisées sur un acier inoxydable en situation de corrosion. Les modifications de réactivité de surface induites par des déformations élastiques et plastiques ont ensuite été étudiées sur ce même matériau. Une corrélation a notamment pu être établie entre la répartition des déformations et la répartition de la constante cinétique apparente en fond d’entaille sur une éprouvette pré-entaillée.Enfin, sur des alliages d’aluminium soudés par FSW (Friction Stir Welding), des situations de couplage galvanique à différentes échelles ont été révélées à l’échelle microscopique du fait de la présence des composés intermétalliques et à l’échelle de la structure dans le cas d’une soudure de deux alliages d’aluminium différents. / Localized corrosion phenomena observed on passive materials, used in industry and transport, areresulting from the presence of microstructural heterogeneities and the effect of mechanical andthermomechanical stresses. The characterization and the understanding of reaction processes requirethe use of local electrochemical techniques. The scanning electrochemical microscopy (SECM), newpowerful local technique was used in different situations. First, in order to detect pitting corrosionareas, measurements were performed on a stainless steel in corrosion situation. Then, changes insurface reactivity induced by elastic and plastic deformations were measured on the same material. Ina notch root, correlation between the distribution of deformation and the distribution of the apparentelectrochemical rate constant has been established. Finally, on aluminum alloy welded by FSW(Friction Stir Welding), situations of galvanic coupling at different scales have been shown at themicroscopic scale, because of the presence of intermetallic compounds and at the scale of the structurewhen two different aluminum alloys are welded.

Ce manuscrit décrit les travaux menés pour le développement et l'utilisation du microscope électrochimique (SECM) pour l'étude des surfaces fonctionnelles. Cette microscopie à sonde locale, utilisant les propriétés des ultramicroélectrodes (UMEs), permet l'analyse de la réactivité chimique à la surface d'un échantillon. Le but de ces travaux est alors l'analyse de surfaces fonctionnalisées par une couche organique. Dans un premier temps, nous avons développé la méthodologie du SECM par l'utilisation de sonde redox spécifique. D'abord, cela nous a permis de déterminer la distance entre l'électrode-sonde et la surface grâce à un médiateur redox irréversible comme les polyaromatiques. Ensuite, nous avons pu observer des propriétés physico-chimiques d'une surface, notamment afin de différencier les différents modes de transport électronique au travers une couche organique, grâce à l'utilisation des catéchols ou des dendrimères redox. Nous avons également commencé le développement d'un nouveau mode d'utilisation du SECM : le SECM transitoire. Dans un deuxième temps, nous avons utilisé le SECM afin d'analyser trois surfaces fonctionnalisées. La première surface est un substrat d'or fonctionnalisé par des calixarènes. La deuxième est une surface de verre sur laquelle il a été déposée des nanoparticules photosensibles, appelées « quantum rods ». Et la dernière est un substrat de silicium modifié par un récepteur anthracène. Finalement, la dernière étude qui a été menée concerne l'écriture et la lecture d'une monocouche organique grâce à la sonde du SECM. Ces modifications localisées de la couche organique sont alors de la taille de l'UME, soit de l'ordre du micromètre. Dans notre cas nous avons choisi la modification de monocouche organique auto-assemblée (SAM) sur un substrat d'or grâce à la réaction de couplage de Huisgen. En plus, de l'amélioration de nos conditions de fonctionnalisation, nous avons pu mettre en évidence un phénomène de propagation catalytique en surface grâce à un complexe spécial de cuivre (II) contenant une fonction éthynyle. / This manuscript describes the work done for the development and use of electrochemical microscope (SECM) for the investigations of functional surfaces. This local probe microscopy, using the properties of ultramicroelectrodes (UMEs), permits the analysis of chemical reactivity on the sample’s surface. The aim of this work is then analyzing surfaces functionalized with an organic layer. Initially, we have developed the SECM methodology by using specific redox probes. First, it allowed us to determine the absolute distance between the electrode and the surface, thanks to an irreversible redox mediator such as polyaromatic. Then, we could observe the physicochemical surface properties, in particular to differentiate the electronic transfer modes through an organic layer, by using catechols or redox dendrimers. We have also started the development of a new mode of SECM: transient SECM. Secondly, we used the SECM to analyze three functionalized surfaces. The first surface is a gold substrate functionalized by calixarenes. The second is a glass side on which it was deposed photosensitive nanoparticles, called "quantum rods" and the last sample is a substrate of silicon modified by anthracene receptors. Finally, the last study concerns the writing and reading on an organic monolayer with the SECM probe. These localized changes of the organic layer are about the size of the UME, of the order of a micrometer. In our case, we chose the modification of self-assembled organic monolayer (SAM) on a gold substrate by the Huisgen coupling reaction. In addition to the improvement of our conditions of functionalization, we were able to demonstrate a phenomenon of surface catalytic propagation due to a special complex of copper (II) containing ethynyl functions.

L’électrochimie devient incontournable dans les nouvelles technologies de stockage et de conversion de l’énergie. La réaction de dégagement de dihydrogène constitue aujourd’hui une réaction à fort intérêt sociétal qui est au cœur des nouvelles technologies permettant l’élaboration de systèmes pour la conversion de l’énergie. Cependant, des problématiques liées à l’utilisation de certains métaux nobles (le platine notamment) en tant que catalyseurs restent encore à résoudre. Ce travail de thèse s’inscrit dans les thématiques scientifiques de l’équipe de Recherche et d’Innovation en Electrochimie pour l’Energie (ERIEE) qui s’intéresse depuis plusieurs années à la substitution de ces métaux nobles par l’utilisation de catalyseurs moléculaires constitués de composés organiques contenant des métaux de transition comme centre électro-actif pour application dans les électrolyseurs industriels. Ce travail de thèse se focalise sur l’étude d’une famille de complexes moléculaires à base de métaux de transition (Co ou Fe), les clathrochélates, caractérisés par différentes structures chimiques. Le choix des ligands de ces complexes ainsi que l’étude des processus de fonctionnalisation sur des substrats ad hoc, sont des éléments déterminants dans l’appréhension des performances électro-catalytiques obtenues.Ces électro-catalyseurs ont été étudiés à la fois en solution (phase homogène) et fonctionnalisés à la surface d’électrodes solides. Leurs propriétés physico-chimiques ainsi que leurs performances électro-catalytiques vis-à-vis de la réaction de dégagement d’hydrogène, ont été caractérisés de façon systématique.La microscopie électrochimique à balayage (SECM) a notamment permis d'effectuer une caractérisation à l’échelle locale des propriétés électro-catalytiques des électrodes modifiées. / Electrochemistry is becoming a major field in new energy storage and conversion technologies. Nowadays, the hydrogen evolution reaction (HER) is a reaction of great societal interest, which is at the heart of new technologies enabling the development of systems for the conversion of energy. However, some issues related to the use of noble metals (platinum, in particular) as catalysts have not been solved yet. This thesis is part of the scientific approach of the Research and Innovation in Electrochemistry for Energy (ERIEE) research group which has been interested for several years in the substitution of these noble metals by the use of transition metal based electro-catalysts. These molecules consist of organic compounds containing transition metals as an electro-active center for application in industrial electrolysers. This thesis focuses on the study of a family of molecular complexes based on transition metals (Co or Fe), the so-called clathrochelates, characterized by different chemical structures. The choice of the ligands constituting these complexes as well as the study of their functionalization processes on ad hoc substrates, constitute key elements in the apprehension of the resulting electro-catalytic performances.These electro-catalysts were studied both in solution (homogeneous phase) and functionalized at the surface of solid electrodes. Their physico-chemical properties as well as their electrocatalytic turnover for the hydrogen evolution reaction, have been systematically characterized.In particular, scanning electrochemical microscopy (SECM) allowed for the characterization of the electrocatalytic properties of modified electrodes at the local scale.

This dissertation focuses on developing new methods using the scanning electrochemical microscope (SECM) to produce chemical concentration maps of different chemical species on various surfaces. Reactive oxygen species (ROS) and transition metal ion maps were generated, indicating the presence or absence of relative types of chemical species on the surface. Imaging of both species was based on a modified scanning UME tip and monitoring the change in the tip impedance. 4-Nitrobenzenediazonium tetrafluoroborate was used as the main modifier, and resultant nitrophenyl groups on the modified electrodes were electrochemically converted to aniline to yield the two types of modified electrodes. In the presence of ROS, a permanent change in the impedance accompanies reaction of the surface layer with the ROS, and this change can be used to map the localized reactive species. The spot scanning method was introduced over continuous scanning to enhance the sensitivity. This enhanced method generated a more effective method to map ROS compared to the diAC/dxmajor image in the continuous scanning method. Images obtained by this sacrificial method show that alternating current SECM (AC-SECM) can be used to map ROS on a surface. The capacitive change gives direct indication of the concentration of these highly reactive species. Transition metal ions showed a partially reversible adsorption with aniline-modified electrodes. Localized concentrations of buffered copper and nickel divalent cations were generated by pumping through a micro-capillary embedded in a substrate. Copper and nickel ions on these substrates were mapped successfully. A solution of calcium ions was used as the negative control. Biased nickel, copper, and lead wire-embedded substrates were line scanned to validate these results. An aniline-modified electrode was placed away from the metal wire and the time taken for metal ions to reach the electrode tip was measured after a voltage pulse. These data were compared with calculated diffusion times. Both systems were optimized using the medium pH, scan rates, and tip potentials. AC-SECM coupled with modified electrodes showed the capability of mapping both ROS and some transition metal ions semi-quantitatively.

Ce travail de thèse a été consacré à la mise au point d'une nouvelle microscopie électrochimique à force atomique (AFM-SECM) à haute résolution, totalement innovante, désignée par l'acronyme MT/AFM-SECM pour « Mediator Tethered–AFM/SECM », et pour laquelle le médiateur rédox ferrocène (Fc) est lié à la micro-électrode sonde combinée par le biais de chaînes flexibles polyéthylène glycol (PEG). Il a été établi que les têtes ferrocènes ainsi attachées à l'extrémité de la pointe-sonde AFM-SECM sont capables de sonder la réactivité locale d'un substrat. Il a de plus été démontré que les pointes AFM-SECM Fc-PEGylées peuvent être utilisées en imagerie en mode tapping, permettant l'acquisition simultanée d'un courant de feedback électrochimique et de la topographie du substrat, et ce avec une résolution latérale et verticale de l'ordre du nanomètre. Ce nouveau type de microscopie SECM, devrait trouver de nombreuses applications en partie parce qu'il permet d'obtenir une résolution SECM de l'ordre du nanomètre, dictée par la longueur des chaînes PEG, sans avoir à utiliser des sondes nanométriques. Cette nouvelle microscopie présente donc une résolution suffisante pour permettre de localiser des macromolécules individuelles, en particulier des molécules d'enzyme rédox, sur une surface. Mais de plus, parce qu'elle est libre des contraintes diffusionnelles de la SECM « classique », la microscopie MT/AFM-SECM devrait, en principe, permettre également de caractériser le fonctionnement cinétique de ces enzymes, molécule d'enzyme par molécule d'enzyme.

Les techniques électrochimiques locales comme la microscopie électrochimique à balayage (SECM) permettent, au moyen d'une ultramicroélectrode utilisée comme sonde locale, de caractériser la topographie ou la réactivité locale de la surface d'un substrat. Cependant, il faut noter que la SECM a largement été utilisée dans des conditions stationnaires. L'objectif de ce travail a été de développer la technique SECM en mode courant alternatif (ac-SECM) tant d'un point de vue expérimental que théorique. Le mode ac- SECM a tout d'abord été utilisé pour caractériser un processus électrochimique simple (le ferri/ferrocyanure en solution aqueuse) afin de calibrer la contribution spécifique du transport de matière entre la sonde et le substrat et les processus se déroulant au niveau du substrat. Dans une seconde étape, cette nouvelle approche a été utilisée pour la caractérisation des processus d'adsorption lors de la réaction de dégagement d'hydrogène (HER) dans une solution d'acide sulfurique. Il a été montré que cette technique permet l'analyse quantitative des processus d'adsorption, et les mesures de la capacité différentielle en fonctionde la fréquence ont pu ête obtenus. La constante de temps pour la relaxation de l'hydrogène adsorbé est d'environ 2 Hz, et l'analyse du diagramme de Nyquist permet une évaluation directe de la charge impliquée. En outre, la comparaison des impédances électrochimique traditionnelles et des résultats de ac-SECM obtenus simultanément permet la caractérisation des processus qui se produisent à la surface et en solution.

Hot microelectrodes are very small electrodes (usually 1 100 µm in diameter), which have a surface temperature much higher than the temperature in the bulk solution. In this work, the heating is achieved by applying an alternating potential of very high frequency (100 MHz 2 GHz) and of high amplitude (up to 2.8 Vrms) to the microelectrode. As a result, very fast (on the order of milliseconds) changes in the temperature of the electrolyte solution surrounding the electrode can be achieved. Due to the size of the heated microelectrodes, the hot zone in solution is small. Therefore, the solution can be easily overheated and temperatures above the boiling point can be reached.<p> The purpose of this research was to investigate and understand the phenomena occurring at ac polarized microelectrodes and to propose new applications of these electrodes. Using both steady-state and fast-scan (10 V/s) cyclic voltammetry measurements, mass transport of redox species has been studied at ac heated microelectrodes. It has been established that the convection at hot-disk microelectrodes is driven primarily by the electrothermal flow of an electrolyte solution. In addition, other effects such as ac dielectrophoresis and Soret (nonisothermal) diffusion are also observed. Numerical simulations have been employed to predict the distribution of temperature in the hot zone, the direction and magnitude of the electrothermal force and the solution flow rate, as well as the voltammetric response of hot-disk microelectrodes. The results of the simulations agree well with the experimental observations. Theoretical findings of this PhD work are very important for the understanding of the fundamentals of high temperature electrochemistry, particularly mass transport. The proposed explanation of the convection mechanism is most likely applicable not only to ac polarized microelectrodes, but also to the microwave heated microelectrodes, since the only difference between these two heating methods is in the way of delivering electrical energy (wired vs. wireless). The results of the studies of Soret diffusion indicate that it contributes significantly to mass transfer of redox species at hot microelectrodes. Taking into account that the magnitude of the Soret effect has been considered negligible by other electrochemists, the results obtained in this work prove the opposite and show that Soret diffusion affects both the faradaic current and the half-wave potential of the redox reaction. Therefore, the Soret effect can not be ignored if working with hot microelectrodes.<p> Hot microelectrodes can have a number of interesting applications. The results of the initial investigations indicate that these electrodes can be successfully used in the arrangement for Scanning Electrochemical Microscopy (such a novel technique is termed Hot-Tip SECM). In addition, the observed dielectrophoretic and electrothermal convection effects can enhance the performance of the electrochemical sensors based on hot microelectrodes. This can lead to the improvement of the detection limits of many biologically important analytes, such as proteins, bacteria and viruses.

Hot microelectrodes are very small electrodes (usually 1 100 µm in diameter), which have a surface temperature much higher than the temperature in the bulk solution. In this work, the heating is achieved by applying an alternating potential of very high frequency (100 MHz 2 GHz) and of high amplitude (up to 2.8 Vrms) to the microelectrode. As a result, very fast (on the order of milliseconds) changes in the temperature of the electrolyte solution surrounding the electrode can be achieved. Due to the size of the heated microelectrodes, the hot zone in solution is small. Therefore, the solution can be easily overheated and temperatures above the boiling point can be reached.<p> The purpose of this research was to investigate and understand the phenomena occurring at ac polarized microelectrodes and to propose new applications of these electrodes. Using both steady-state and fast-scan (10 V/s) cyclic voltammetry measurements, mass transport of redox species has been studied at ac heated microelectrodes. It has been established that the convection at hot-disk microelectrodes is driven primarily by the electrothermal flow of an electrolyte solution. In addition, other effects such as ac dielectrophoresis and Soret (nonisothermal) diffusion are also observed. Numerical simulations have been employed to predict the distribution of temperature in the hot zone, the direction and magnitude of the electrothermal force and the solution flow rate, as well as the voltammetric response of hot-disk microelectrodes. The results of the simulations agree well with the experimental observations. Theoretical findings of this PhD work are very important for the understanding of the fundamentals of high temperature electrochemistry, particularly mass transport. The proposed explanation of the convection mechanism is most likely applicable not only to ac polarized microelectrodes, but also to the microwave heated microelectrodes, since the only difference between these two heating methods is in the way of delivering electrical energy (wired vs. wireless). The results of the studies of Soret diffusion indicate that it contributes significantly to mass transfer of redox species at hot microelectrodes. Taking into account that the magnitude of the Soret effect has been considered negligible by other electrochemists, the results obtained in this work prove the opposite and show that Soret diffusion affects both the faradaic current and the half-wave potential of the redox reaction. Therefore, the Soret effect can not be ignored if working with hot microelectrodes.<p> Hot microelectrodes can have a number of interesting applications. The results of the initial investigations indicate that these electrodes can be successfully used in the arrangement for Scanning Electrochemical Microscopy (such a novel technique is termed Hot-Tip SECM). In addition, the observed dielectrophoretic and electrothermal convection effects can enhance the performance of the electrochemical sensors based on hot microelectrodes. This can lead to the improvement of the detection limits of many biologically important analytes, such as proteins, bacteria and viruses.

This thesis focuses on in-situ studies at the solid-liquid interface by combining scanning electrochemical microscopy (SECM) with gold and platinum mercury amalgam microelectrodes. It is shown that stripping voltammetry experiments at imaging amalgam microelectrodes provide laterally resolved insight on the electrochemistry of biogeochemically relevant processes. SECM provides information on electroactive surface processes with high spatial resolution, and offers the opportunity to study heterogeneous electron-transfer reactions. Thereby, chemical species of interest, such as metal ions, can be electrochemically detected at mercury amalgam electrodes. Platinum and gold mercury amalgam microelectrodes were developed for the detection of biogeochemically relevant analytes such as manganese and iron during SECM imaging experiments at the mineral/water interface establishing the fundamental basis of SECM imaging with amalgam microelectrodes. SECM experiments were performed for the quantitative determination of Mn2+ during the dissolution of microstructured manganese carbonate (rhodochrosite) precipitates at mildly acidic conditions. SECM images along with spatially resolved quantitative data on the Mn2+ concentration were obtained. This measurement concept was then extended to the investigation of the corrosion behavior of diamond-like carbon (DLC) protected zinc selenide (ZnSe) waveguides applied in mid-infrared attenuated total reflectance spectroscopy at strongly oxidizing conditions. The corrosion behavior of DLC coated and uncoated ZnSe crystals was studied obtaining laterally resolved information on the oxidative degradation of ZnSe at defects of the DLC layer utilizing SECM in combination with square wave anodic stripping voltammetry (SWASV) at gold amalgam microelectrodes. Thereby, insight on the corrosion behavior of ZnSe and concentration profiles of Zn2+ at oxidizing conditions was obtained. These results corroborate the utility of SECM imaging with amalgam microelectrodes for addressing relevant analytical questions. Finally, the developed amalgam microelectrodes were applied for SECM studies of iron-reducing proteins separated from Shewanella microbes in native polyacrylamide gels. After calibration of Pt/Hg microelectrodes in bulk solution for the targeted analytes (iron and sulfur species), SECM approach curves recorded above the native gel enabled positioning of the amalgam electrode in close proximity above protein bands with suspected iron-reducing activity. This technique enabled the (semi)quantitative determination of the anaerobic respiratory activity associated with microbial proteins/protein complexes responsible for the reductive dissolution of manganese and iron oxides above microbial protein bands separated in a native gel matrix.

In this dissertation I describe a model system to characterize the response of an oral bacterial pathogen, Aggregatibacter actinomycetemcomitans to the metabolic byproducts of a representative member of the oral flora, Streptococcus gordonii. A. actinomycetemcomitans is a causative agent of periodontal infections in humans. To cause infection, A. actinomycetemcomitans must overcome numerous challenges, including the host immune system and toxic metabolite production from other microbes. The most numerically dominant flora in the oral cavity are oral streptococci, which are well known for their ability to produce copious amounts of lactic acid and H₂O₂. By studying the response to H₂O₂ and lactic acid in pure and co-cultures, I have demonstrated that A. actinomycetemcomitans responds to these metabolites by several novel mechanisms that both enhance its survival in the presence of the host immune system and in the presence of the model oral streptococci S. gordonii. These studies have demonstrated that metabolites produced by normal flora can impact the survival of a single species in vivo as much as previously known virulence factors have done. In addition, I present a new method for measuring metabolite production in an attached cell population. This method is a novel application of scanning electrochemical microscopy (SECM) and I used this technique to study H₂O₂ production in the three dimensional space surrounding a multispecies biofilm in real time. In a related study I present the use of SECM to discover a novel redox chemistry phenomenon in the opportunistic pathogen Pseudomonas aeruginosa. / text