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<p> Cathodic electrodeposition method has been developed for the fabrication of manganese oxide films for application in electrochemical supercapacitors (ES). The manganese oxide films prepared from KMn04 and NaMn04 aqueous solution showed an increasing deposition yield with the deposition time. The deposition rate decreases with increasing the concentration of deposition precursor. The obtained films were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD), thermogravimetric and differential thermal analysis (TGA/DTA). The SEM observations revealed uniform films of highly porous nanostructure on different substrates. The capacitive behavior of the deposits was investigated by cyclic voltammetry and chronopotentiometry method in 0.1M NaS04 aqueous solutions. As prepared deposits exhibited pseudocapacitive behavior in the potential window of 0-1.0 V versus SCE with excellent cyclability. A maximum specific capacitance (SC) of 353 Fig was obtained for the 45 μg/cm2 film deposited from KMn04 solution on stainless steel foil, at a scan rate of 2 m V /s in the 0.1 M Na2S04 solution. It was found that the SC decreased with increasing deposit thickness and scan rate. No significant effect was obtained on the films prepared from 20 mM KMn04 on stainless steel after heat treatment at various temperatures. The capacitance of as-prepared electrode did not change by changing the electrolyte from Na2S04 to K2S04 solutions. However, higher capacitance values were observed by using electrolyte with higher concentration. Different structures of manganese oxides were obtained when different deposition precursors were used. No significant difference in capacitive behavior was found between the films prepared from different deposition precursor. However it was concluded that conductivity of the film is key in determining the performance of the electrodes. The effect of substrates on the electrochemical behavior has also been investigated by using stainless steel and nickel foils. </p> / Thesis / Master of Applied Science (MASc)

The characteristic polarization response of a ferroelectric material to an applied electric field enables a binary state device in the form of a thin film ferroelectric capacitor that can be used to store digital information. In a high density memory the capacitor is placed on the top of a poly-silicon plug which is connected to the drain of a transistor. Such a configuration poses constraints on the processing conditions of the ferroelectric capacitor in addition to the already existing reliability issues of a ferroelectric capacitor. The current research is an attempt to integrate the ferroelectric capacitor directly into a high density memory structure. Pb_1.1Zr_0.53Ti_0.47O₃ (PZT) and SrBi₂Ta₂O₉ (SBT) are two most promising materials for ferroelectric memory applications. PZT has excellent ferroelectric properties with wide operating temperature range. However, PZT exhibits a considerable loss of switchable polarization with cumulative switching cycles. This phenomenon is known as fatigue and is one of the critical problems affecting the life time of ferroelectric memories. In this research, Ir based electrodes are shown to improve fatigue characteristics of PZT based capacitors not only by enhancing a homogenous growth of perovskite phase of PZT but also by lowering the entrapment of oxygen vacancies at the interface. These Ir electrodes also acted as diffusion barriers for silicon, oxygen and lead. Additionally, Ir electrodes were found to be chemically stable at the processing temperatures of PZT capacitors. These features of Ir based electrodes could help in realization of a practical PZT based high density non volatile random access memories. SBT is an another promising ferroelectric material for ferroelectric memory applications. While SBT has a fatigue free nature, it has a very high processing temperature (>800 °C). Such a high processing temperature limits the choice of electrodes that could be used to integrate the ferroelectric capacitor into the high density memory structure. In this research, an attempt is made to lower the processing temperature and suitable electrodes are chosen accordingly, to enable the integration of SBT based capacitors into high density memories. Lowering the processing temperature was obtained by growing a-b oriented SBT crystallites rather than c-axis oriented crystallites. Additionally, reliability (degradation) and yield of SBT thin film capacitors was found to be correlated to the amount of segregated bismuth oxide in the films. Elimination of secondary phase bismuth oxide was found to result in dramatic improvement in the reproducibility of SBT thin films with a processing temperature close to 750 °C. PtRh based electrodes were found to be quite suitable for integrating SBT capacitors into high density memory structures. These electrodes could withstand a processing temperature of 750 °C while preventing the interdiffusion of silicon, oxygen and bismuth. A solid solution of SBT and Bi₃TiNbO₉ (BTN) is made which reduced the processing temperature of the capacitor material from 750 °C to 650 °C while retaining the excellent fatigue and retention characteristics of SBT. / Ph. D.

Le travail de thèse présenté dans ce mémoire, est consacré à l'étude des interactions interfaciales entre une espèce active électrochimiquement (l'étain) et une matrice (le borophosphate) capable d'absorber les variations volumiques dues à la formation électrochimique des diverses compositions Li-Sn (« buffer »). L'objectif de cette étude est de comprendre la nature des réactions ayant lieu avec l'introduction du Li dans le matériau composite. Pour cela, nous avons réalisé une étude détaillée d'un composite de référence mis au point dans des études précédentes Sn-0,4 BPO4 ; nous avons évalué l'influence du type de matrice et de la voie de synthèse sur son comportement global. Le matériau composite a pu être décrit comme possédant une interface vitreuse contenant de l'étain oxydé (SnII) qui lui donne la structuration suivante : Elément actif Sn0(1-w)/SnIIwBxPyOz/BPO4 Phase support Interphase. Des études in situ operando complémentaires en diffraction des rayons X et spectrométrie Mößbauer ont permis d'analyser le comportement électrochimique du matériau composite : un premier processus correspond à l'extrusion d'une petite partie d'étain métallique de la zone interfaciale qui augmente la conductivité électronique du composite ; il est suivi par une réorganisation de l'interface avec extrusion de tout le contenu en étain et la formation des premières compositions Li-Sn. Enfin, le cyclage galvanostatique se poursuit grâce à la formation de plusieurs compositions Li-Sn riches en étain (Li2Sn5 et LiSn) et puis enrichies en lithium (Li13Sn5 et Li7Sn2). / The Phd work, presented in this manuscript, is devoted to the study of the interface interactions between an electroactive species (tin) and a matrix (borophosphate). The latter has a buffer role and is thus able to absorb the volume variations taking place during the Li-Sn electrochemical reaction.The aim of this study is to understand the nature of the reactions occurring during lithium introduction in the composite. In order to do that, a detailed study of a previously studied reference composite (Sn-0,4 BPO4) has been undertaken. The effect of some modified matrixes as well as the synthesis route has also been evaluated. The composite material can be described as having a glassy interface containing some oxidized tin (SnII) which leads to the following global structure: Active element Sn0(1-w)/SnIIwBxPyOz/BPO4 Buffering phase Interphase. A complementary in situ operando study (X-ray diffraction and Mößbauer spectroscopy) gave the possibility to analyze the electrochemical behavior of the material. A first process corresponds to a small tin extrusion from the interfacial zone. This contributes to the increase of the electrical conductivity of the composite material which is followed by the interphase reorganization with the extrusion of the whole tin content. Li-Sn reactions take place then, with the galvanostatic cycling going on between the tin rich compositions (Li2Sn5 and LiSn) and the lithium rich ones (Li13Sn5 and Li7Sn2).

Neste trabalho, avaliou-se as propriedades eletrocatalíticas de eletrodos de óxidos do tipo ânodos dimensionalmente estáveis, ADEs, em meio de NaCl e sua aplicação na oxidação do etanol. Para isso, vários fatores foram investigados, como a mudança de óxido modulador, a mudança do método de preparação dos eletrodos e a mudança do pH do meio reacional. Os eletrodos de composição Ti/MxS(1-x)O2 (onde M = Ru e Ir, S = Ti e Sn com x = 0,3; 0,5 e 0,7) foram preparados pelo método da decomposição térmica variando os precursores: (i) precursores poliméricos, DPP e (ii) precursores inorgânicos (cloretos) dissolvidos em isopropanol, DPI/ISO. Os eletrólitos de suporte foram NaCl 3,0 mol dm-3 e NaCl 3,0 mol dm-3 acidificado com HCl 0,01 mol dm-3. Existe um problema quando se trabalha com cloreto de estanho na confecção de eletrodos de óxidos. O cloreto de estanho, em meio ácido, oxida de cloreto de estanho(II) para cloreto de estanho(IV), que é volátil à temperatura utilizada no tratamento térmico (T = 450 ºC). Análises de MEV e EDX foram realizadas para avaliar se a mudança do método de preparação dos eletrodos contribuiu para inibir a volatilização do estanho. Os resultados mostraram que todos os eletrodos investigados apresentam boa concordância das porcentagens atômicas nominais e experimentais, provando que ambos os métodos de preparação dos eletrodos são eficientes para a fixação do estanho na matriz eletródica. Foram realizadas investigações eletroquímicas na ausência e presença do etanol, cujos resultados mostraram que os eletrodos preparados por DPP com SnO2 apresentam as melhores propriedades catalíticas para a produção de agentes oxidantes e para a oxidação do etanol em meio de NaCl. Eletrólises a corrente constante foram realizadas para 4 composições de eletrodos Ti/Ru0,5Ti0,5O2, Ti/Ru0,7Sn0,3O2, Ti/Ir0,5Ti0,5O2 e Ti/Ir0,3Sn0,7O2, todos preparados por DPP. Aplicou-se duas densidades de corrente diferentes: 25 mA cm-2 e 75 mA cm-2. Os resultados obtidos mostraram que a alteração da corrente aplicada nas eletrólises muda o mecanismo de oxidação do etanol, tornando-o diferente para baixas densidades de corrente (25 mA cm-2) e para altas densidades de corrente (75 mA cm-2). Em ambas densidades de corrente, tem-se o ácido acético como produto majoritário, e observa-se também a quebra da ligação C-C formando CO2, resultado que não havia sido observado por outros autores em eletrólises de etanol com ADEs. Porém, à 25 mA cm-2 observa-se a formação de acetaldeído, produto que não é observado a 75 mA cm-2. Neste caso, a densidade de corrente mais alta pode favorecer a oxidação dos produtos orgânicos formados durante o tempo de eletrólise. Testes realizados em ausência de cloreto mostraram que não ocorre a formação de CO2. Portanto, a presença de oxidantes (cloro/hipoclorito) favorece a quebra da ligação C-C com formação de CO2 como produto de oxidação do etanol. / In this work, it was investigated the electrocatalytic properties of oxides electrodes denominated dimensionally stable anodes, DSA®, in NaCl medium, applying them for ethanol oxidation. For this propose, many experimental parameters nave been investigated: the modulator oxide, changes in the preparation method of the electrode and pH changes of the solution. Electrodes with nominal composition Ti/MxS(1-x)02 (where M = Ru and Ir, S = Ti and Sn, x = 0.3; 0.5 and 0.7) were prepared by thermal decomposition changing the precursors solution; (i) polymeric precursors (DPP) and (ii) inorganic precursors (Chloride) dissolved in isopropanol (DPI/ISO). The support electrolytes were 3.0 mol dm-3 NaCl and 3.0 mol dm-3 NaCl acidified with 0.01 mol dm-3 HCl. There is a problem when one prepares oxides electrodes using tin chloride. The tin chloride, in acid medium, suffers oxidation from Sn (II) to Sn (IV), the latter one volatilize at the higher temperatures used to prepare the electrode (450° C). SEM and EDX analyses were used to evaluate if the changes introduced in the preparation method contributed to inhibit the tin volatilization. The results obtained for all electrodes showed a good agreement of nominal and experimental compositions, proving that both preparation methods are efficient to fix tin in the coating. It was performed electrochemical investigation in the presence and absence of ethanol, the experimental results for DPP electrodes containing Sn02 show better catalytic properties for oxidation species production and also for ethanol oxidation. Electrolyses at constant current were performed with four nominal electrode compositions: Ti/Ru0.5Ti0.5O2, Ti/Ru0.7Sn0.3O2, Ti/Ir0.5Ti0.5O2 e Ti/Ir0.3Sn0.7O2, all of them was prepared through DPP method. It has been applied two different current densities: 25 mA cm-2 and 75 mA cm-2. Both current densities showed acetic acid as main oxidation product, it was also observed the C-C bond break forming C02, this has not been reported before for ethanol oxidation using DSA®. However, at 25 mA cm-2 acetaldehyde is formed, whereas, it was not observed at 75 mA cm-2. In this case, the high current density might favor the oxidation of intermediate products formed during the electrolysis. Experiments performed in the absence of chloride did not show the formation of CO2, Therefore, the presence of oxidizing species (chlorine and hypochlorite) favors the cleavage of C-C and formation of C02 as oxidation product of ethanol.

Les travaux de cette thèse portent sur l'élaboration de capteurs électrochimiques pour la détection de micropolluants mis sous surveillance par la Directive Cadre sur l'Eau (DCE/200/60/CE) tels que Ni(II) et Pb(II). Actuellement, le contrôle des eaux est effectué par prélèvements cependant les méthodes d'analyses sont longues et coûteuses et les seuils de concentration très faibles imposés par la loi, nécessitent d’avoir recourt à d’autres types d’équipements, tels que les capteurs électrochimiques. L'amélioration indispensable de leur sensibilité et de leur sélectivité peut être atteinte par le choix du matériau d'électrode et de sa fonctionnalisation de surface. Ces capteurs ont pour objectif, à terme, d’analyser la qualité des eaux sur site en continu ou semi-continu. Dans le cas de l'étude de la sélectivité, les sels de diazonium ont été choisis pour le greffage des fonctions benzamides oximes, complexantes du Ni(II). Cette molécule n'ayant jamais été étudiée électro-chimiquement, son domaine d'électro-activité et les mécanismes d'oxydation ont été étudiés. Les électrodes greffées ont permis la détection électrochimique et montrent une sélectivité pour le Ni(II), en présence d'interférents comme Pb(II) et Cu(II). Cette étude a prouvé que les amines aromatiques et aliphatiques peuvent être greffées par oxydation en milieux aqueux. Les électrodes ainsi fonctionnalisées ont montré que la mobilité des fonctions complexantes, via la structure et la longueur du squelette carboné, influence la limite de détection des capteurs, les chaînes aliphatiques complexant particulièrement bien les cations métalliques. Enfin, l’influence de différentes formes allotropiques du carbone, utilisées en tant que phases actives d’électrodes sérigraphiées, a été étudié. Des électrodes composées de différentes formes allotropiques de carbones ont été fonctionnalisées par des sels de diazonium et utilisées pour la détection du Pb(II). Les résultats montrent que certains matériaux carbonés, comme les nanotubes de carbone, améliorent les propriétés électro-catalytiques des capteurs. / This work is focused on the elaboration of electrochemical sensors for Ni(II) and Pb(II) micropollutants detection, targeted by the Water Framework Directive (WFD 2000/60/CE). Currently, water supervision is carried out by sampling and analytical equipments, however these methods are too long and too expensive, the very low concentration limits imposed by laws, needed to be reached using other kind of equipments such as electrochemical sensors. The sensitivity and selectivity of these sensors can be improved by the choice of the electrode materials and their surface functionalization. The aim of these sensors is to make possible the water quality analysis on site, continuously or semi-continuously. The selectivity was reached by grafting diazonium salts composed of benzamide oxime functions, complexing Ni(II). The electro-activity area and the oxidation mechanisms of this molecule were investigated. It is to be underlined that the electrochemical behavior of this molecule has never been studied in the litterature. The grafted electrodes were used for the electrochemical detection, and they turned out to be selective for Ni(II) detection in the presence of both Pb(II) and Cu(II). To improve the sensitivity of these sensors, the mobility of the complexing function is important. This study shows the possibility to graft aliphatic and aromatic amines via oxidation reactions in aqueous media. These electrodes revealed better analytical performances for the sensors grafted by aliphatic amines through the mobility of the carbon chains complexing metallic cations. Finally, the influence of the different allotropic kind of carbons, used as screen printing electrodes, were compared. These electrodes, functionalized with diazonium salts and used for the detection of the Pb (II) showed that some carbonaceous materials such as carbon nanotubes, improve the electro-catalytic properties of the sensors.

In this research various techniques were used to study surface groups on carbon electrodes, including the spectroscopic techniques UV-Vis-NIR, FTIR, PAS, XPS and XAS, as well as the Boehm titration. The methods determined to give the best insight to the surface functionalities on the carbon were XPS, XAS and the Boehm titration. The Boehm titration methodology was standardized before use. An in situ method of examining surface groups using spectroscopy during electrochemistry was attempted. Spectroelectrochemistry is a useful way to gain information on how electrochemistry affects electrodes during experimentation; however, it was unsuccessful for the carbon used and remains to be developed. Polymerization of the copolymer of PANI and PPy as a potential electrode material for ECs was achieved by electrochemical cycling and was studied through spectroelectrochemical measurements. Overall, the research completed included the initial stages to studying electrodes for electrochemical capacitors using analytical, non-electrochemistry techniques in conjunction with electrochemistry.

Neuro-engineering is an emerging multi-disciplinary domain which investigates the electrophysiological activities of the nervous system. It provides procedures and techniques to explore, analyze and characterize the functions of the different components comprising the nervous system. Neuro-engineering is not limited to research applications; it is employed in developing unconventional therapeutic techniques for treating different neurological disorders and restoring lost sensory or motor functions. Microelectrodes are principal elements in functional electric stimulation (FES) systems used in electrophysiological procedures. They are used in establishing an interface with the individual neurons or in clusters to record activities and communications, as well as modulate neuron behaviour through stimulation. Microelectrode technologies progressed through several modifications and innovations to improve their functionality and usability. However, conventional electrode technologies are open to further development, and advancement in microelectrodes technology will progressively meliorate the neuro-interfacing and electrotherapeutic techniques. This research introduced design methodology and fabrication processes for intra-cortical microelectrodes capable of befitting a wide range of design requirements and applications. The design process was employed in developing and implementing an ensemble of intra-cortical microelectrodes customized for different neuro-interfacing applications. The proposed designs presented several innovations and novelties. The research addressed practical considerations including assembly and interconnection to external circuitry. The research was concluded by exhibiting the Waterloo Array which is a high channel count flexible 3-D neuro-interfacing array. Finally, the dissertation was concluded by demonstrating the characterization, in vitro and acute in vivo testing results of the Waterloo Array. The implemented electrodes were tested and benchmarked against commercial equivalents and the results manifested improvement in the electrode performance compared to conventional electrodes. Electrode testing and evaluation were conducted in the Krembil Neuroscience Centre Research Lab (Toronto Western Hospital), and the Neurosciences & Mental Health Research Institute (the Sick Kids hospital). The research results and outcomes are currently being employed in developing chronic intra-cortical and electrocorticography (ECoG) electrode arrays for the epilepsy research and rodents nervous system investigations. The introduced electrode technologies will be used to develop customized designs for the clinical research labs collaborating with CIRFE Lab.