Orientador: Fernando Luis Fertonani / Banca: Clóvis Augusto Ribeiro / Banca: Vera Aparecida Oliveira Tiera / Banca: Lucildes Pita Mercuri / Banca: Paulo Rogério Pinto Rodrigues / Resumo: Os metais nobres Pt, Rh e Ir e suas ligas apresentam diversas aplicações tecnológicas. O Hg pode ser considerado o principal contaminante dos metais nobres e suas ligas binárias e terciárias, por apresentar alta reatividade e uma ação corrosiva sobre os mesmo. Devido a isso, o objetivo deste trabalho foi estudar as reações em estado sólido das ligas Pt-6% Rh e Pt-10% Ir na presença e ausência de Hg, empregando técnicnas eletroquímicas e termogravimétricas. O preparo dos sistemas para os estudos eletroquímicos e de termogravimetria (TG/DTG) constituiu em fazer eletrodeposições de Hg no substrato metálico, com o auxílio de voltametria cíclica, gerando um filme de Hg e compostos intermetálicos sobre a superfície da lâmina. A partir desses resultados, foi possível evidenciar o ataque efetivo do mercúrio sobre o substrato, e a formação de compostos intermetálicos (PtHg, PtHg2, RhHg2 e PtHg4), que foram caracterizados com o auxílio das seguintes técnicas de análise de superfície: microanálise por EDX, mapeamento dos elementos, obtenção de imagens de MEV e difratometria de raios X (XRD). Estas análises de superfície revelaram também, uma distribuição homogênea do Hg, e a presença de um filme de intermetálicos sobre a superfície do substrato. A comparação entre os sistemas Pt-10% Ir-Hg e Pt-6% Rh-Hg sugere uma menor reatividade do substrato de Ir quando são empregadas as mesmas condições experimentais / Abstract: The noble metals Pt, Rh and Ir and its alloys have many technological applications. Mercury can be considered a major contaminant of noble metals and their binary and tertiary alloys due to high reactivity and a corrosive action on the same. Because of this, the objective was to study the solid state reactions of the alloys Pt-6% Rh and Pt-10% Ir in the presence and absence of mercury, using electrochemical and thermogravimmetry techniques. The preparation of systems for electrochemical and thermogravimmetry (TG/DTG) studies consisted to make electrodepositions of mercury in the metallic substrate, using cyclic voltammetry techniques to generate a film of mercury and intermetallic compounds. From these studies, it was possible to show the actual attack of mercury on the substrate, and the formation of intermetallic compounds (PtHg, PtHg2, RhHg2 and PtHg4), which were characterized using these analysis of surface techniques: EDX microanalysis, mapping of the elements, scanning electronic microscopy and X-ray diffraction (XRD).These analysis also revealed a homogeneous distribution of mercury, and the presence of an film of intermetallic compounds on the surface of the substrate. The comparison between the systems Pt-10% Ir-Hg and Pt-6% Rh-Hg suggesting a lower reactivity of Ir are used when the same experimental conditions / Doutor

The oxygen evolution reaction (OER) is kinetically slow and hence a significant efficiency loss in electricity-driven water electrolysis. Understanding the relationships between architecture, composition, and activity in high-performing catalyst systems are critical for the development of better catalysts. This dissertation discusses areas both fundamental and applied that seek to better understand how to accurately measure catalyst activity as well as ways to design higher performing catalysts. Chapter I introduces the work that has been done in the field to date. Chapter II compares various methods of determining the electrochemically active surface area of a film. It further discusses how pulsed and continuous electrodepostition techniques effect film morphology and behavior, and shows that using a simple electrodeposition can create high loading films with architectures that outperform those deposited onto inert substrates. The reversibility of the films, a measure of the films transport efficiency, is introduced and shown to correlate strongly with performance. Chapter III uses high energy x-ray scattering to probe the nanocrystalline domains of the largely amorphous NiFe oxyhydroxide catalysts, and shows that significant similarities in the local structure are not responsible for the change in performance for the films synthesized under different conditions. Bond lengths for oxidized and reduced catalysts are determined, and show no significant phase segregation occurs. Chapter IV seeks to optimize the deposition conditions introduced in Chapter II and to provide a physical representation of how tuning each of the parameters affects film morphology. The deposition current density is shown to be the most important factor affecting film performance at a given loading. Chapter V highlights the different design considerations for films being used in a photoelectrochemical cell, and how in situ techniques can provide information that may otherwise be unobtainable. Chapter VI serves as a summary and provides future directions. This dissertation contains previously published coauthored material.

Graphite and graphene electrodes are used to study two electrochemical processes: the decoration of these electrodes with Au metallic nanoparticles through the use of electrodeposition, and electrowetting, the potential-dependent change in hydrophobicity of a surface. Electrodeposition provides a useful route to electrode functionalisation, in particular to combine the enhanced properties of metallic nanoparticles with the advantageous features of carbon materials. A combination of cyclic voltammetry, chronoamperometry, and both ex situ and in situ atomic force microscopy are used to deduce the mechanism of Au electrodeposition on graphite and graphene. Notably, the mechanism of Au nanoparticle formation cannot be deduced from simple voltammetry alone, and the spontaneous formation of Au within the timescale of the electrodeposition experiment is confirmed. Electrowetting is a uniquely responsive method to manipulate the wetting properties of an electrode. However, a dielectric coating is commonly required to protect the surface from electrolysis, which in turn further increases the potentials needed to perform electrowetting. In contrast to this, here it is shown that bare graphite and graphene electrodes support electrowetting without the disadvantages of a dielectric coating, allowing an unprecedented combination of performance and efficiency. Furthermore, the ideal behaviour this system demonstrates is implemented as a platform to study electrowetting itself. The influence of electrolyte composition, surface defects and electrode-blocking dielectric-like films are investigated to determine the factors that impede electrowetting, a key step to understanding the phenomenon that is normally hindered by the use of the dielectric.

nÃo hà / O desenvolvimento de revestimentos metÃlicos cada vez mais resistentes à corrosÃo e ao desgaste mecÃnico tem originado inÃmeros estudos na Ãrea de eletrodeposiÃÃo. Com intuito de se obter ligas metÃlicas com boas propriedades mecÃnicas, associadas a uma elevada resistÃncia à corrosÃo, à que os revestimentos de Zn-Mn tÃm sido bastante abordados nos Ãltimos anos, tendo em vista que estes oferecem melhores caracterÃsticas anticorrosivas quando comparados com revestimentos de zinco metÃlico, usualmente utilizados na indÃstria convencional. Neste trabalho, objetivou-se a obtenÃÃo e caracterizaÃÃo das ligas de Zn-Mn eletrodepositadas sobre eletrodos de platina e cobre metÃlico a partir de soluÃÃes a base de sais de sulfato dos metais em questÃo. Estudou-se a liga de Zn-Mn com utilizaÃÃo de voltametria cÃclica e linear, como tambÃm de cronoamperometria, onde nesta etapa todas as amostras foram obtidas em banho sem agitaÃÃo, à temperatura ambiente, 25ÂC, em diferentes densidades de corrente. Analisou-se tambÃm a estrutura fÃsica e morfolÃgica das ligas obtidas com uso de tÃcnicas como Microscopia EletrÃnica de Varredura (MEV) e Energia Dispersiva de Raios-X (EDX), variando-se parÃmetros como: densidade de corrente aplicada, pH da soluÃÃo eletrolÃtica, temperatura de deposiÃÃo e concentraÃÃo dos reagentes presentes no eletrÃlito. Para anÃlise da estrutura quÃmica das espÃcies formadas na liga em questÃo, utilizou-se a tÃcnica de DifraÃÃo de Raios-X (DRX) nas amostras obtidas em eletrodo de cobre. A partir dos resultados obtidos por meio das anÃlises voltamÃtricas, pÃde-se determinar os potenciais de reduÃÃo e oxidaÃÃo para a liga Zn-Mn onde estes ocorreram isoladamente para o zinco e para o manganÃs. Para as anÃlises de MEV e EDX observou-se que o manganÃs na liga apresenta-se na forma de oxido e o zinco na forma de metal isolado. Para as anÃlises de DRX, pÃde-se determinar as fases em que as espÃcies de Zn-Mn apresentam-se na liga, assim como tambÃm espÃcies de zinco e manganÃs isoladas. Os melhores resultados foram obtidos quando se aplicou uma densidade de corrente de 10 mA.cm-2, pH 6,0, temperatura ambiente e proporÃÃo de 1:1 entre o zinco e o manganÃs no eletrÃlito. / The development of alloys that are resistant to corrosion and good wear resistance led to several studies on the electrodeposition field. With the intention of carry out alloys with good mechanic properties, associated to a high corrosion resistance, Zn-Mn alloys have been frequently studied in the last years, once they offer better anticorrosive characteristics when compared to metallic zinc films, usually used in the conventional industry. This work aimed obtain and characterize Zn-Mn alloy electrodeposited on platinum electrode and metallic cooper from solutions composed by sulfate salts from the metals previously mentioned. Zn-Mn alloys were studied by using of cyclic and linear voltammetry, and also chronoamperommetry, in which all samples were obtained in bath without agitation, room temperature, 25 C, on different current densities. The physical and morphological structure of the alloys that have been obtained were analyzed by using technique such as scanning electronic microscopy (SEM) and X-ray dispersive energy (XDE), varying parameters such as: current density applied, pH, deposition temperature and reagents concentration in the bath. In order to analyze the chemical structure of the species formed on the alloy mentioned, a x-ray diffraction (XRD) technique was used with the samples obtained in cooper electrode. From the results obtained through voltammetric analyses, it is possible to determine the potential of reduction and oxidation of Zn-Mn alloy, which occurred separately to zinc and manganese. It was possible to observe that the manganese in the alloy appears as the oxide and the zinc as an isolated metal. Through XRD analysis, it was possible to determine the phases in which the Zn-Mn species appears in the alloy, and also isolated zinc and manganese. The best results were obtained when was applied 10mA.cm-2 current density; pH 6,0; room temperature and 1:1 proportion of zinc and manganese in the electrolytic bath.

There are very few studies that have investigated directly the effect of an oxide film on tin whisker growth, since the cracked oxide theory was proposed by Tu in 1994. The current work has investigated the effect of using an electrochemically formed oxide and both a molybdate conversion coating and a tungstate conversion coating on tin whisker growth from Sn-Cu electrodeposits on Cu, and compared it with that from a native air-formed oxide. X-ray photoelectron spectroscopy (XPS) has been used to investigate the effect of coating parameters on the thickness and composition of the oxide film. The XPS studies show that the oxide film formed using either of the conversion coating baths was significantly thicker than that produced from the potassium bicarbonate-potassium carbonate bath. Initial observations suggest that both the tungstate-based conversion coatings and the molybdate-based conversion coatings significantly reduced whisker growth by over 80 %, compared with a native air-formed oxide, and provide improved whisker mitigation compared with the electrochemically formed oxides. The current work has also investigated the potential of using a dual-layer system, comprised of both an electrochemically formed oxide bottom layer and an acrylic conformal coating top layer, for the mitigation of tin whisker growth. The electrochemically formed oxide used in the dual-layer system was produced at 2 V vs. Ag/AgCl while passing a charge of 60 mC cm-2 and the thickness of the conformal coating was aimed to be between ~5 μm to ~6 μm. This thickness was chosen to enable the study of whisker growth on a shorter time scale and to study the effect the electrochemically formed oxide had when used in conjunction. Initial observations showed that the dual-layer system provided improved whisker mitigation compared with both the electrochemically formed oxides and acrylic conformal coatings when used singularly. As part of the self-healing work, nanocapsules filled with the reactive agent were needed to be synthesised and the compatibility of them with different solvents needed to be studied. Capsules filled with the reactive agent were successfully synthesised, however, it was found that the capsules agglomerated and the size of the capsules, in some instances, were too large to be incorporated into a thin conformal coating. Regardless, the capsules were still analysed to check the compatibility with different solvents, to identify a suitable conformal coating mixture that would not dissolve the polymer shell of the capsules. It was observed that the capsules were stable in three out of the five solvents that were analysed, them being isopropanol (IPA), butanone and methylcyclohexane.

Present state-of-the-art hydrogen sensors are limited by a number of defects such as poisoning effects, slow response, and/or the range of concentrations that can be detected. Thus, hydrogen sensors are currently under investigation. In the search for the ultimate sensor, a variety of materials have been employed as the sensing layer. One of these materials is palladium. Palladium is widely used for hydrogen sensing due to its high selectivity and property of spontaneously absorbing hydrogen. Thin and thick film palladium hydrogen sensors have been reported, as well as palladium nanostructures. Specifically, palladium nanowires for hydrogen sensing have had improved results relative to other types of sensors; these have been reported with a response time down to 75ms and do not suffer from poisoning effects. Additionally, the fabrication of these nanostructures via electrodeposition is simple and cost efficient. For this reason, palladium nanostructures were chosen as the front-end for a novel hydrogen sensor. The nanostructures were to be employed as the sensing front-end of a Surface Acoustic Wave (SAW) sensor. It was theorized that the response time would be vastly improved if these were used as opposed to a thin or thick palladium film due to the decreased hydrogen diffusion distance, which is a result of the structures being one-dimensional. Because it was theorized that the dimensions of the nanostructures play an integral role in the response time to hydrogen, control of the morphology was required. This control was achieved by varying the plating variables in the electrodeposition experiments. The plating variables investigated were deposition potential, time, and counter-electrode area. The dimensions of the resulting nanostructures were measured via Scanning Electron Microscopy (SEM) and correlated to the conditions of the electrodeposition experiments. Nanowires under 40nm were successfully fabricated.

There are substantial advances in Additive Manufacturing (AM) technologies. The simplest and advantageous technique of AM in terms of cost and scaling of the substrate is Fused Deposition Modeling(FDM). Currently, integration of electronics to a 3D printed structure is done manually after fabrication of the structure. To print electronic circuits directly on a 3D printed structure, copper electroplating process has been studied in this work. To electroplate on the 3D printed insulating substrate, various materials were studied to make substrate conductive. By using conductive Polylactic Acid (PLA) filaments, a compatible substrate for electroplating was printed. Electroplating was proved to be advantageous in terms of uniform distribution as well as fast deposition rate when performed laterally. The conductive levels of the electrodeposited layers on 3D printed conductive substrates were studied at different voltages in different configurations. Furthermore, the textures of the electroplated layer were studied using Scanning Electron Microscopy(SEM) method. The resistance of samples was measured using four-point probe resistance setup. The Morphology and roughness of the samples were studied by an optical profilometer system. In addition, the adhesion strength of the electrodeposited copper on conductive PLA material was tested by a peel test using scotch tape. Thickness and conductivity calculations were performed for uniformly deposited samples. Further study is required for optimizing electroplating process to be used for in situ metallizations of a 3D printed structure.

La technologie de piles à combustible PEM (Proton Exchange Membrane) voit encore sa commercialisation limitée du fait de son coût élevé. L'un des éléments les plus coûteux est le catalyseur, constitué de platine, métal noble, représentant 25 % du coût global. L'étude mise en place dans le cadre de cette thèse s'oriente vers l'amélioration de l'utilisation de cet élément. La voie de nanostructuration s'avère d'un intérêt majeur afin de maintenir des tailles de structure proposant des propriétés électrocatalytiques intéressantes. De plus, l'élaboration électrochimique de catalyseurs présente l'avantage majeur de remplir l'une des conditions nécessaires en pile à combustible : le contact électronique. La réunion des deux précédents points nous a permis de mettre en place un procédé d'élaboration électrochimique de nanostructures, ensuite charactérisées par méthodes électrochimiques et physiques afin d'évaluer et de comprendre leurs propriétés catalytiques.

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Multilayered iron electrodeposits composed of alternating layers of coarse-grained iron (grain size: 1.87 μm; (110) texture; hardness: 177 VHN) and fine-grained iron (grain size: 132 nm; (211) texture; hardness: 502 VHN), with layer thicknesses ranging from ~0.2-7 μm were successfully synthesized. The average hardness of the multilayered electrodeposits increased from 234 VHN to 408 VHN with decreasing layer thickness, consistent with a Hall-Petch type behaviour. In three-point bending tests, they failed in a macroscopically brittle manner although local ductility was observed in certain layers. Fractography analysis has shown that strain incompatibility between alternating layers contributes to the brittle nature of these materials. This study has demonstrated the possibility of applying a multilayered structure design to tailor the microstructure and mechanical properties of electrodeposited iron.