Le travail présenté est le fruit de 15 ans de recherche, à compter de l'obtention de ma thèse, sur l'étude et la mise en œuvre de méthodes électrochimiques à échelons de potentiel destinées à l'électroanalyse et à la détermination de mécanismes réactionnels. <br />Dans le manuscrit, sont développés principalement, mes travaux relatifs aux réactions électrochimiques simples en régime transitoire ou stationnaire. Les points originaux et les applications de ces travaux se résument par catégorie comme suit.<br /><br />CONTROLE DU COURANT PAR LA DIFFUSION<br /><br />Electrode plane<br /><br /> Traitement unifié des méthodes mono et multi-impulsionnelles dans le cas des réactions électrochimiques réversibles. La recherche d'équivalents mathémati-ques à des solutions sous forme de séries conduit à des formules d'analyse simples. Ceci est particulièrement important pour la voltamétrie à signaux carrés (SWV) et la voltamétrie impulsionnelle différentielle (DPV) qui sont des techniques analytiques performantes.<br /> Etude de la voltamétrie à escalier de potentiel en mode différentiel. L'expression du courant s'adapte à la voltamétrie à balayage linéaire. <br /> Introduction de la voltamétrie impulsionnelle normale (NPV) en mode différentiel qui supprime l'effet de déplétion sur l'électrode non-renouvelée (goutte de mercure ou électrode solide) et permet l'emploi d'impulsions de courte durée. <br /> Présentation dans un but pédagogique d'un traitement simplifié de la polarographie impulsionnelle différentielle (DPP) basé sur le concept de la couche de diffusion.<br />Electrode sphérique<br /><br /> Traitement des méthodes mono et multi-impulsionnelles sur l'électrode à goutte de mercure pour des réactions réversibles avec ou sans formation d'amalgame. <br /> Etablissement d'une solution pour toute voltamétrie en l'absence d'amalgamation. <br /> Présentation d'une solution avec une correction de sphéricité au deuxième ordre qui s'applique sans restriction à toutes les polarographies mono-impulsionnelles. <br /> Etude de la SWV et de la NPV en cas d'amalgamation.<br /><br />Applications :<br /><br /> Caractérisation de la réversibilité et du nombre d'électrons de la réaction électrochimique.<br /> Détermination des coefficients de diffusion.<br /> Optimisation des paramètres expérimentaux en électroanalyse. <br /> Séparation des réponses interférentes par le choix du motif de polarisation et utilisation des expressions littérales pour la déconvolution des réponses.<br /> Prise en compte de la sphéricité de l'électrode à goutte de mercure en électroanalyse.<br /> Description du courant stationnaire sur microélectrode.<br /><br />CONTROLE DU COURANT PAR LA DIFFUSION ET PAR LE TRANSFERT DE CHARGE<br /><br /> Analyse des courbes irréversibles en DPP, SWV et DPV. L'expression du courant en DPP a été établie dans le cadre du modèle de l'électrode plane. L'effet de la sphéricité de la goutte de mercure est donné par une formule empirique.<br /> Introduction des balayages inverses en SWV.<br /> Analyse de la SWV effectuée avec des balayages dans le sens négatif et dans le sens positif. Pour le courant de pic obtenu avec un balayage négatif (Ox initialement présent en solution) des formules empiriques sont proposées à la fois pour l'électrode plane et sphérique.<br /><br />Applications<br /><br /> Détermination des paramètres cinétiques d'une réaction électrochimique irréversible à partir de la largeur et de la position des pics cathodique et anodique obtenus en SWV lors des balayages négatif et positif.<br /> Optimisation des paramètres expérimentaux en électroanalyse (amplitude des impulsions en DPP et en SWV, rapport des temps de polarisation en DPP et en DPV).<br /><br />COURANT STATIONNAIRE SOUS CONVECTION FORCEE <br /><br /> Analyse des voltammogrammes en SWV ou en DPV sur électrode à disque tournant quelle que soit la vitesse de transfert de charge.<br /><br />Applications<br /><br /> Détermination aisée du coefficient de transfert de charge à partir de la hauteur ou de la largeur des courbes différentielles irréversibles.<br /> Détermination de faibles concentrations (de l'ordre de 10-7 M) avec des électrodes solides. <br /><br /> Mes autres travaux, concernant des réactions électrochimiques avec des complications chimiques et de surface sont brièvement commentés dans le manuscrit.

Eine Reihe 3-(p-X-phenyl)-Thiophenmonomeren (X = -H, -CH3, -OCH3, -COCH3, -COOC2H5, -NO2) wurde elektrochemisch polymerisiert, um Filme zu erhalten, die umkehrbar reduziert und oxidiert werden konnten (n-und p-dotiert wurden). Die Oxidationspotentiale der Monomere und die formalen Potentiale der n und p-Dotierprozesse der Polymere wurden mit Resonanz- und induktiven Effekten der Substituenten (Hammett konstanten) am Phenylring sowie semiempirisch errechneten Bildungswärmen der Monomereradikalkationen korreliert. Außerdem wurden die Oxidationspotentiale mit den Ionisierungspotentialen der Monomere verglichen, die über die Dichtefunktionialtheorie (DFT) errechnet wurden, die der Energie für das Erzeugen der Radikalkationen entsprechen. Um theoretische Grundlagen für die Einstufen-Bildung regioregulär -konjungierter Oligo- und Polythiophene zu erhalten, wurden die elektronischen Zustände von 3-Phenylthiophen-Derivaten anhand von Molekülorbitalberechnungen auf Grundlage der Dichtefunktionaltheorie mit Becke’s Drei-Parameter-Funktion (B3LYP), sowie mit den Basissätzen 6-31G(d) und 3-21G(d) erklärt. Die Reaktivität der Verknüpfung von mono- und oligo-3-Phenylthiophenen wurde von den berechneten ungepaarten Elektronenspindichten der entsprechenden Radikal-Anionen abgeleitet. Die Ionisierungspotentiale, die den Energien zur Erzeugung der Radikal-Anionen während der Oxidation entsprechen, wurden abgeschätzt. Die aus den 3-Phenylthiophenen entstandenen regioselektiven Hauptprodukte können gut durch die Größe der Spindichten erklärt werden. Da die Verknüpfungsreaktion an der zwei-Position des Thiophnrings (C-2) sterisch durch die Phenylgruppe und den Thiophenring gehindert ist, startet die Initiierung der 3-Phenylthiophene über die Bildung eines Kopf-Schwanz-Dimers. Folglich spielt das Kopf-Schwanz-Dimer eine wichtige Rolle bei den Wachstumsreaktionen der 3-Phenylthiophene. Die Ursache dafür liegt darin, dass das Kopf-Schwanz-Dimer in 5-Position die höchste Spin-Dichte besitzt und die Wahrscheinlichkeit einer Kopf-Kopf-Verknüpfung aufgrund der sterischen Hinderung zwischen dem Thiophenring und der Phenylgruppe gering ist. Polymerfilme von 3-Phenylthiophenderivaten, die durch elektrochemische Polymerisation synthetisiert wurden, sind in situ und ex situ durch Resonanz-Raman-Spektroskopie bei verschiedenen Anregungswellenlängen, sowie durch in situ und ex situ UV-Vis Spektroskopie analysiert wurden. Die Entwicklung der in situ UV-Vis-Spektren der Polymer von 3-Phenylthiophene nach der Dotierung wird durch ähnliche Eigenschaften gekennzeichnet, wie für viele Polythiophene mit einem hohen Grad der Konjugation beobachtet. Während der schrittweisen Oxidation der Poly-3-phenylthiophen Filme verringert sich die Intensität der Absorption wegen des Überganges bei 450-566 nm und ein neues ausgedehntes Absorptionsband, das auf (bi)polaron Zustände bezogen wird erscheint bei ungefähr 730-890 nm. Andererseits wird während der Oxidation (p-Dotierung) des Poly3-phenylthiophen Filmes eine blau/hypsochrome Verschiebung für beide Absorptionsbänder beobachtet . Es wird durch die Tatsache erklärt, dass ein Polymer eine Verteilung der Kettenlängen enthält und die längste Polymer kette (dessen Absorption bei niedriger Energie auftritt), bei niedrigeren Potentialen zu oxidieren beginnt. Die elektrochemischen Bandlücken der Derivate von 3-Phenylthiophen sind durch zyklische Voltametrie gemessen worden. Der Effekt der Substituenten auf den Oxidations-/Reduktions- potentiale wird besprochen. Bei Bandlücken, die durch zyklische Voltammetrie erhalten wurden, hat sich herausgestellt, dass sie im Allgemeinen höher liegen als optische Bandlücken. Erste Resultate der in situ Resonanz-Raman-Spektroskopie, von dem elektrochemisch erzeugten Polymerderivate von 3-Phenylthiophen Filmen auf einer Platinelektrode, in einer organischen Elektrolytlösung, werden berichtet. Beobachtete Raman Banden werden zugewiesen; gegründet auf diesen Resultaten werden die zuvor angenommenen molekularen Strukturen diskutiert. / A series of 3-(p-X-phenyl) thiophene monomers (X= –H, –CH3, –OCH3, –COCH3, –COOC2H5, –NO2) was electrochemically polymerized to furnish polymer films that could be reversibly reduced and oxidized (n- and p-doped). The oxidation potentials of the monomers and formal potentials of the n- and p-doping processes of polymers were correlated with resonance and inductive effects (Hammett constants) of the substituents on the phenyl ring as well as the semiempirically calculated heats of formation of the monomer radical cations. Moreover, the oxidation potentials of the monomers were correlated with the ionization potentials of the monomers calculated via density functional theory (DFT), which correspond to the energies for generating radical cations during oxidative processes. For obtaining a theoretical basis for the one-step formation of regioregular –conjugated oligo-and polythiophenes, the electronic states of 3-phenylthiophene derivatives were elucidated by molecular orbital calculations using density functional theory with the Becke-type three parameters functional (B3LYP), the 6-31G(d), and 3-21G(d) basis sets. The reactivity for coupling reaction of mono- and oligo-3-phenylthiophenes are inferred from the calculated unpaired electron spin densities of the respective radical cations, and the ionization potentials which correspond to the energies for generating radical cations during oxidative processes were estimated. The major regioselective products of the oligomerization of 3-phenylthiophene can be well understood in terms of the magnitude of spin densities. Since the steric hindrance between the phenyl group and thiophene ring interferes with the coupling reaction occurring between 2-postions (C–2) of thiophene rings, the initiating reaction of 3-phenylthiophene is generaton of a head-to-tail (HT) dimer. Thus, the head-to-tail (HT) dimer plays an important role in the propagation reactions of 3-phenylthiophene. This originates from the highest spin density at the 5- position of the HT dimer and low probability of the HH coupling due to the steric hindrance between thiophene ring and phenyl group. Polymer films of the 3-phenylthiophene derivatives prepared by electrochemical polymerization were analyzed, in situ and ex situ, with resonance Raman spectroscopy using several excitation wavelengths as well as in situ and ex situ UV-Vis-spectroscopy. The evolution of the in situ UV-Vis-spectra of poly 3-phenylthiophene derivatives upon doping is characterized by similar features as observed for many polythiophenes with high degree of conjugation. During stepwise oxidation of the poly-3-phenylthiophene films the intensity of the absorption due to the transition around 450–566 nm decreases and a new broad absorption band related to (bi)polaron states appears around 730-890 nm. On the other hand, during the oxidation (p-doping) of the poly-3-phenylthiophene films a blue/hypsochromic shift is observed for both absorption bands. It is explained by the fact that a polymer contains a distribution of chain lengths, and the longest polymer chains (the absorption of which occurs at lower energies) start to oxidize at lower potentials. The electrochemical bandgaps of 3-phenylthiophene derivatives have been measured by cyclic voltammetry. The effect of substituents on the oxidation / reduction potentials is discussed. Bandgaps obtained by cyclic voltammetry have been found to be in general higher than optical bandgaps. Preliminary results of in situ resonance Raman spectroscopy of electrochemically generated poly-3-phenylthiophene derivatives films on a platinum electrode exposed to an organic electrolyte solution are reported. Observed Raman bands are assigned; based on these results previously suggested molecular structures are discussed.

Thesis (M.S.)--Mississippi State University. Department of Chemistry. / Title from title screen. Includes bibliographical references.

In the search for alternative energy technologies, low temperature fuel cells continue to feature as technologies with the most promise for mass commercialization. Among the low temperature fuel cells, alkaline and proton exchange membrane fuel cells are the most popular. Alkaline fuel cells have typically been used for water generation as well as auxiliary power for space shuttles. Their bulkiness however makes them undesirable for other applications, especially in automobiles, where there is a great demand for alternative technologies to internal combustion engines. Proton exchange membrane fuel cells on the other hand possess numerous qualities including their compact size, high efficiency and versatility. Their mass implementation has however been delayed, because of cost among other reasons. Most of this cost is owed to the Pt/C catalyst that accounts for about half of the price of the PEM Fuel Cell. This catalyst is used to drive the sluggish oxygen reduction reaction that occurs at the cathode of the PEM Fuel Cell. To overcome this obstacle, which is to make PEM Fuel Cell technology more affordable, reducing the amount Pt has traditionally been the approach. Another approach has been to find new ideal catalyst-support combinations that increase the intrinsic activity of the supported material. One more strategy has been to find lower cost alternative materials to Pt through synthetic and kinetic manipulations to rival or exceed the current oxygen reduction reaction activity benchmark. To this end, Palladium has garnered significant interest as a monometallic entity. Its manipulation through synthetic chemistry to achieve different morphologies - which favor select lattice planes - in turn promotes the oxygen reduction reaction to different degrees. In bimetallic or, in more recent times multimetallic frameworks, geometric and ligand effects can be used to form ideal compositions and morphologies that are synergistic for improved oxygen reduction reaction kinetics. In this dissertation, we have explored three different approaches to make contributions to the catalysis and electrocatalysis body of literature. In the first instance, we look at the influence of ligand effects through the active incorporation of a PVP capping agent on the stability of ~3nm Pt NPs. Washed (no capping agent) and unwashed (with capping agent) batches of NPs were evaluated via cyclic voltammogram analyses to evaluate differences there might be between them. It was found that the current density measurements for unwashed particle batches were higher. This increase in current density was attributed to the monodentate and bidentate ligand bonding from the PVP, which increased as a function of cycle number and plateaued when the PVP was completely decomposed. The complete decomposition of PVP during the CV experiment was estimated to occur around 200 cycles. The remaining portion of the dissertation explores the electrocatalytic properties of Palladium based NPs. The first instance, a monometallic study of Palladium cubes and dendrites was aimed at building on a recent publication on the enhanced ORR activity that was achieved with a PdPt bimetallic dendrite morphology. In our work, we sought to isolate the dendritic morphology properties of the monometallic Pd composition in order to understand what advantages could be achieved via this morphology. Pd cubes were used as a comparison, since they could be generated through the combination of a similar set of reagents simply by switching the order of addition. It was found that while there was no significant variation in the ORR activity as a function of morphology / shape, there was an interesting interaction between hydrogen and the palladium NPs in the hydrogen oxidation region that varied as a function of shape. This led to further sorption and ethylene hydrogenation studies, which suggested that, the interaction between hydrogen and Pd depended on the environment. Within the electrochemical environment, the ECSA measured, suggested that hydrogen was being reversibly absorbed into the sub-surface octahedral sites of Pd. The higher ECSA for Pd cubes corroborated with higher sorption for Pd cubes as well. However ethylene hydrogenation showed that the fringes of the Pd dendrites provided additional sites for reaction, which in turn translated to higher conversion. Furthermore, through a Koutecky-Levich analysis, it was found out that the Pd dendrites while exhibiting slightly lower activity, favored the 4-electron oxygen reduction process more than the Pd cubes. In the last part of this dissertation we explored the electrocatalytic properties of Pd-based bimetallic NPs under different morphologies including nanocages and sub-10nm alloys. With the inclusion of Ag, it was found out, through Koutecky-Levich analysis that the 4-electron process was better observed under alkaline conditions using a 0.1M NaOH(aq) electrolyte solution instead of a 0.1M HClO4 (aq) for acidic media testing. It was found that, for PdAg nanocage morphologies, where the Pd galvanically replaced the Ag to form cages, the four-electron process was suited to thinner Pd shells. Indeed the average electron numbers measured for Ag nanocubes coated with a 6nm shell was in agreement, within reason of literature values for bulk Ag. However, since the binding energy that both metals have for OH is so close, the potential for contributions to the ORR kinetics in alkaline media by Pd is a potential consideration.

Dissertation submitted in partial compliance with the requirements of the Masters Degree in Technology: Chemistry, in the Faculty of Applied Sciences at the Durban University of Technology, 2008. / In this work, a holistic approach to validate analytical methods was assessed by virtue of Monte Carlo simulations. This approach involves a statement of the methodsâ s scope (i.e. analytes, matrices and concentration levels) and requisites (internal or external); selection of the methodâ s (fit-for-purpose) features; pre-validation and validation of the intermediate accuracy and its assessment by means of Monte Carlo simulations. Validation of the other methodâ s features and a validity statement in terms of a â fit-for-purposeâ decision making, harmonized validation-control-uncertainty statistics and short-term routine work with the aim of proposing virtually â ready-to-useâ methods. The protocol could be transferred to other methods. The main aim is to harmonize the work to be done by research teams and routine laboratories assuming that different aims, strategies and practical viewpoints exist. As a result, the recommended protocol should be seen as a starting point. It is necessary to propose definitive (harmonized) protocols that must be established by international normalisation/accreditation entities. The Quality Assurance (Method verification and Internal Quality Control, IQC) limits, as well as sample uncertainty were estimated consistently with the validated accuracy statistics i.e. E U (E) and RSDi + U (RSDi). Two case studies were used to assess Monte Carlo simulation as a tool for method validation in analytical laboratories, the first involves an indirect polarographic method for determining nitrate in waste water and the second involves a direct determination of heavy metals in sea water by differential pulse anodic stripping voltammetry, as an example of the application of the protocol. In this sense the uncertainty obtained could be used for decision making purposes as it is very tempting to use uncertainty as a commercial argument and in this work it has been shown that the smaller the uncertainty, the better the measurement of the instrument or the laboratoryâ s reputation.

The electrochemical investigation of nickel, copper and silver thin films interfaced with yttria stabilized zirconia (YSZ) solid electrolyte was accomplished to determine their response to polarization in dilute oxygen environments at 350 °C and assess their viability for electrochemical promotion of catalysis (EPOC). Polycrystalline YSZ (8 mol % Y2O3-ZrO2) pellets were synthesized in the lab and films deposited onto them using evaporative physical vapor deposition (PVD). The critical thickness of copper, silver and nickel thin films were foundusing in-situ resistance measurements. Following this, 50 and 100 nm copper and nickel films were studied using solid electrolyte cyclic voltammetry (SECV) to determine their response to polarization. Given that silver thin films at such thicknesses are thermally unstable, a film of 800 nm was used in this study. The materials were found to respond to polarization in different ways, forming oxides according to Wagner and Mott-Cabrera oxidation models.

The thin-layer flow-cell incorporated an array of 32 gold strip electrodes in a serial configuration opposite a platinum counter electrode. The cell body was made of Macor glass ceramic. A photolithographic procedure for etching the Macor and a simple method of applying a gold ink was devised. Resistive feedback current-to-voltage converters independently controlled the potential difference between the electrodes of the array and the common counter electrode. A microcomputer and a customized high speed data acquisition interface recorded the current response of each electrode. An expression for the faradaic response of a single electrode within a rectangular flow channel was modified to predict the behavior of the multi-electrode flow-cell. The quinone/hydroquinone redox system was used to evaluate the performance of the detector. Summing the signals from the array when all electrodes were held at the same potential improved the signal-to-noise ratio. Hydrodynamic curves were reconstructed from the currents measured at each electrode when a ramp potential profile was applied to the array.

SYNTHESIS, CHARACTERIZATION, AND ELECTRICAL PROPERTIES OF DIAZOPHENYLENE AND DIAZODIPHENYLENE BRIDGED Co, Ni, Cu, Ce, AND Er PHTHALOCYANINE POLYMERS Alkan, Cemil M. Sc., Department of Polymer Science and Technology Supervisor: Prof.Dr. Leyla Aras Co- Supervisor: Prof.Dr. G&uuml / ng&ouml / r G&uuml / nd&uuml / z September 2004, 112 pages In this research, diazophenylene and diazodiphenylene bridged metal-phthalocyanine polymers were produced from diazonium salt of diaminophenylene/bensidin and pre-synthesized tetraamino metal phthalocyanines. Tetraamino metal phthalocyanine complexes of Co, Ni, Cu, Ce, and Er were obtained by reducing tetranitro metal phthalocyanine complexes synthesized from 3-nitrophthalic anhydride, urea, metal salt, and ammonium molybdate catalyst. Complexes and polymers were characterized by Fourier Transform Infrared Radiation (FTIR) and UV-Visible spectroscopies. X-Ray analysis showed that there were short range orientations in the polymers. Thermal analysis of the complexes and the polymers were done by differential scanning calorimetry and thermal gravimetric analysis at a heating rate of 10&amp / #61616 / Cmin&amp / #61485 / 1 under nitrogen atmosphere. Ash analysis was performed to determine the metal content of the polymers. Viscosity and ebullioscopy measurements of the soluble part of the polymers were carried out in THF at 25&amp / #61616 / C. Scanning electron microscopy were used for morphology investigations of the polymers. Four probe conductivity measurements showed that electrical conductivity of the polymers increased according to the metallic conductivity of the metal at the center of the phthalocyanine units. When doped with iodine, the polymer samples showed 104 fold increase in their conductivities. Current-Voltage (I-V) measurements showed that the polymers were optically sensitive and semiconductors. Electrochemical analysis of the soluble part of the polymers were determined in tributylamine perchlorite+dichloromethane mixture utilizing cyclic voltammetry (CV).

In the recent years, environmental pollution becomes a health threatening issue for human beings. Technological developments introduce industrial wastes and heavy metals, and developments in agriculture introduce pesticides into the world that we live. All these toxic wastes accumulate in drinking water and food consumed by humans. Therefore, detection of toxic wastes in all kinds of environmental samples, and development of new detection techniques become an important issue. In this study, development of a protein-based biosensor for detection of heavy metals in environmental samples, by expressing genetically modified glutathione S-transferase (GST-(His)6) protein in E.Coli BL21 (DE3) expression system, was designed. Recombinant GST proteins was expressed in E.Coli BL21 (DE3) expression system and purified with Glutathione Sepharose 4B affinity column and Ni-NTA spin kit. GST activities were determined using the GST substrate 1-chloro-2,4-dinitrobenzene (CDNB). Protein expression was tested by SDS-PAGE and Western blot analysis. Product formation linearly increased up to 1 mM CDNB, 1 mM GSH, 1.7 &micro / g proteins in 0.05 M, pH 6.9 phosphate buffer in the final volume of 1.0 ml at 25&amp / #9702 / C. The Vmax and Km values for GST-(His)6 towards CDNB and GSH were calculated with Lineweaver-Burk as CDNB Vmax / 22.88 &micro / mol/min/mg, Km / 4.29 mM,and as GSH Vmax / 6.42 &micro / mol/min/mg, 24.45 &micro / mol/min/mg, Km / 3.69 mM, respectively. Biosensor working electrode was prepared by immobilizing the GST-(His)6 by 1-(3-dimethylaminopropyl)-3-ethyl-carbodiimide hydrochloride (EDC) coupling on the gold surface. Electrode preparation was confirmed by cyclic voltammetry measurements. The biosensor was inserted as the working electrode in the constructed three(four)-electrode flow cell. The conformational change resulting from the binding of the metal ions to the recombinant protein causing a capacitance change proportional to the concentration of the metal ions was determined. After the working electrode is standardized and calibrated, the heavy metal concentration in water samples was measured. The GST-(His)6 biosensor has a large operational range between 1 fM and 10 mM and a storage stability of approximately 2 weeks. The GST-(His)6 biosensor is very sensitive to, Cu+2&gt / Cd+2&gt / Zn+2&gt / Hg+2 metal ions, at low concentrations.

Thesis (Ph. D) -- University of Western Sydney, Nepean, 1999. / A thesis presented for the degree of Doctor of Philosophy, Centre for Electrochemical Research and Analytical Technology, University of Western Sydney, Nepean. Includes bibliographical references.