Philosophiae Doctor - PhD / The need for clean, non-toxic drinking water supplies, free of pollutants and metal contamination is vital in impoverished areas and the developing world alike. With this in mind, the development of accurate, inexpensive, portable and simple devices for remote sensing applications is therefore pivotal for early detection and the prevention of illnesses. Over the last two decades, adsorptive stripping voltammetry (AdSV) has emerged as a superior detection method over common analytical techniques due to its low-cost instrumentation, unskilled labour and ability to detect a wide range of analytes. / 2020-08-31

L’objectif de ce travail était de démontrer la possibilité de coupler sur un même catalyseur, la fonction de stockage et réduction des NOx (sur le baryum) avec un effet électrochimique reposant sur un système micropile. Ce système micropile est composé de nanoparticules catalytiques (Pt et Rh) déposés sur conducteur ionique par les ions O2- (YSZ) en contact avec un support conducteur électronique (SiC dopé) de façon à pouvoir générer, sous mélanges réactionnels, une force électromotrice capable de réduire électrochimiquement une partie des NOx sur le Pt et d’oxyder le CO, les hydrocarbures imbrûlés et H2 sur le Rh. L’effet micropile a été observé sur un catalyseur Pt/Ba (matériau de stockage)/YSZ/Rh enduit dans les canaux d’un filtre à particule en carbure de silicium dopé, en condition essence pauvre à 400°C et en condition Diesel à plus basse température (300°C). Une augmentation de la conversion des NOx d’environ 10% a été observé sur les catalyseurs micropile. L’effet électrochimique a été détecté par une surproduction de CO2, en milieu riche (très peu ou pas de O2) provenant de la réaction d’oxydation électrochimique du CO (produit par vaporeformage) en réagissant avec les ions O2- provenant de YSZ. De plus, des tests catalytiques ont montré que YSZ peut être utilisée comme matériau de stockage des NOx. En effet, un traitement réducteur préalable augmente fortement sa capacité de stockage des NOx / The main objective of this study was to demonstrate the coupling between NOx storage/reduction process on barium, with an electrochemical reduction of NOx (micro fuel cell effect) on the same catalyst. The micro fuel cell effect is ensured by a an electromotive force (potential) which is created between catalytic nanoparticules (Pt and Rh) in contact with an ionic conductor (YSZ) and an electronic conductor (doped SiC). The micro fuel cell effect was observed, during the regeneration phase of the catalysts (rich period), on a Pt/Ba/doped α-SiC-YSZ/Rh monolithic system under lean-burn gasoline conditions at 400°C with an enhancement of about 10 % of the NOx conversion over a complete cycle lean/rich. This electrochemical effect was characterized by the electrochemical oxidation of CO (produced by steam reforming) into CO2 by using O2- ions coming from YSZ. Under Diesel conditions, the micro fuel cell system was found to work at low temperature especially at 300°C. In the second part of the work, a new generation of NOx Storage and reduction catalyst was developed consisting only of noble metals (Pt and/or Rh) deposited on YSZ support (Ba free catalyst). The catalytic measurements revealed that YSZ can be used as a NOx storage material in lean burn conditions (Gasoline and Diesel) especially when it was previously reduced under hydrogen. The storage mechanism would take place on the oxygen vacancies created by the removal of O-2 ions from the YSZ structure

This thesis addresses simulation of electrochemical experiments, with an emphasis on processes of diffusional mass transport to electrode surface. Following system has been studied: • Applying theoretical modeling and experimentation is shown that even significant surface roughness produced by deliberate polishing or scratching is not sufficient to be distinguished in cyclic voltammetry experiments conducted under the usual conditions. In stripping voltammetry experiment the shape of the voltammograms strongly depends on the model of the electron transfer but is not always sensitive to the precise model of the electrode surface; the conditions under which this is the case are identified, and generic roughness effects on stripping voltammetry are quantified. Electrode roughness can have a significant effect on the stripping of the metals from the solid electrode especially in respect of the voltammetric waveshape. • We first consider two different models of electrodes covered with electroinactive layers: the electrode is covered with a uniform layer and the layer contains pinholes. Both models are simulated and then compared to identify conditions under which they can be distinguished. Next we propose generic model to predict the influence of electroactive layer on the cyclic voltammetric. The conditions under which deviation from the behavior of a planar electrode are predicted. • We first consider one electron, one proton and next two electron, two proton reduction of surface bound species. Two mechanisms of reaction are considered: stepwise and concerted. Voltammetry studied under the three regimes of protons mass transport: infinitely fast (fully buffered solution), infinitely slow (infinitely high surface coverage of electrode) and intermediate case of finite rate of diffusional mass transport to electrode surface. Types of voltammograms observed in each case are presented and discussed. • Theory of chronoamperometry on disc and ring-recessed microelectrodes and their arrays is reported. Three and four different regimes of transient current versus time can be observed at microelectrode arrays of disc and ring electrodes, accordingly. A generic, accurate and easy to use method of experimental chronoamperometric data analysis is proposed. It is shown that the method can be applied to the simultaneous measurement of D and nC in solution. • The fabrication, characterization, and use of arrays of ring-recessed disk generator-colector microelectrodes are reported. Experiments and simulations relating to time- of-flight experiments in which material electrogenerated at a disk is diffusionally transported to the ring are reported. We further study voltammetry of electrochemically active species which undergoes first and second order chemical reactions. Current transients are found to be sensitive to the diffusion coefficient of both the reduced and oxidised species as well as to the rate of the chemical reaction and its mechanism.

Imidazolium-based ionic liquids are very popular for different applications because of their low viscosity and melting point. However, the hydrogen atom at the C2 position of the imidazolium cation can easily be deprotonated by a base, resulting in a reactive carbene. If an inert ionic liquid is needed, it is necessary to introduce an unreactive alkyl or aryl group at the C2 position to prevent deprotonation. Tunable aryl alkyl ionic liquids (TAAILs) were first introduced by our group in 2009 and are characterized by a phenyl group at the N1 position, which offers the possibility to fine-tune the physicochemical properties by using different electron-donating or -withdrawing substituents. In this work, we present a new series of TAAILs where the C2 position is blocked by a methyl, propyl or phenyl group. For each of the blocking groups, the phenyl and three different phenyl derivatives (2-Me, 4-OMe, 2,4-F₂) are compared with respect to melting point, viscosity, conductivity and electrochemical window. In addition, the differences between blocked and unblocked TAAILs with regard to their electrochemical reduction potentials are investigated by quantum chemical methods.