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No presente trabalho foi proposta a construção de eletrodos de níquel e algumas ligas (Sn, Ru), assim como de materiais nanoestruturados, para a determinação de etanol em amostras de bebidas e medicamentos. Para isto, foram utilizadas técnicas como a voltametria cíclica, a cronoamperometria, a espectroscopia de impedância eletroquímica, a microscopia de força atômica e a microscopia de transmissão. O eletrodo da liga Ni-Sn foi preparado por eletrodeposição, utilizando um banho de Watts contendo 6,25 g de NiCl2.6H2O e 0,5 g de SnCl2.2H2O em 25 mL de solução aquosa. Os depósitos foram modificados com RuO2, utilizando uma solução RuCl3 0,1 M. O eletrodo da liga foi deixado na solução em banho de ultrasson e posteriormente aquecido a 400ºC em forno em presença de oxigênio, para a decomposição térmica. O Ni nanoestruturado foi preparado a partir de uma solução contendo 1,8 g NiCl2.6H2O dissolvido em 30 mL etanol, adicionando uma mistura de 3,5 g de Zn em pó e 10 mL de aminoetanol, em agitação. A separação do pó preto foi feita com uma placa magnética. Para a confecção do eletrodo foi adicionada uma alíquota 10 mL da solução contendo o pó, náfion e etanol, na superfície do eletrodo de grafite pirolítico. Os perfis voltamétricos foram analisados em meio de hidróxido de sódio 0,5 M, podendo-se assim observar as reações de oxi-redução característica do Ni, da liga Ni-Sn, da liga modificada com RuO2 e da nanoestrutura. Foi utilizado intervalo de potencial de 100 a 700 mV com velocidade de 50 mVs-1. As medidas de impedância eletroquímica foram realizadas em sistemas com etanol com o intuito único de demonstrar a presença de um loop indutivo, que pode ser associado à transformação óxido superior/óxido inferior na superfície do eletrodo. Este loop foi observado para os eletrodos de Ni e liga, não sendo muito evidente para o eletrodo modificado com RuO2. Foram realizadas medidas de AFM para a caracterização topográfica dos eletrodos, mostrando a diferença entre as superfícies, indicando que o Ni liso foi modificado com o eletrodepósito da liga Ni-Sn e que esta também foi modificada pela deposição do RuO2. A morfologia da nanoestrutura foi observada por microscopia eletrônica de transmissão, podendo observar que se obtiveram estruturas de níquel em escala nanométrica. Os eletrodos foram utilizados na determinação de etanol em meio de NaOH 0,5 mol L-2, com a construção de curvas analíticas pelo método da adição consecutiva de alíquotas de etanol, a partir de uma solução estoque. Após a curva analítica ser levantada, foram feitos os tratamentos estatísticos obtendo-se os valores para os limites de detecção e quantificação. Com o eletrodo Ni nanoestruturado obteve-se o melhor resultado sendo este empregado na determinação de etanol nas amostras de conhaque, cachaça e enxaguante bucal, utilizando a técnica de cronoamperometria. A excelente porcentagem de recuperação obtida mostrou que o efeito da matriz, nestas determinações, é praticamente desprezível, o que está de acordo com o mecanismo da reação de oxidação do etanol sobre Ni, fortemente catalisado pela superfície dos eletrodos em estudo. / This objective of this work is related to the development of nickel and some nickel-alloys electrodes, as well as some nanostructured nickel surfaces, for ethanol determinations in drinks and in pharmacological formulations. For this, some experimental techniques were employed, as cyclic voltammetry, cronoamperometry, electrochemical impedance spectroscopy, atomic force microscopy and transmission microscopy. The Ni-Sn alloy electrode was prepared by electrodeposition from a Watts bath containing 6,25 g NiCl2.6H2O and 0,5 g SnCl2.2H2O and water in order to produce 25 mL of aqueous solution. The electrodeposits were further modified with RuO2 obtained from a 0.1 mol L-1 RuCl3 solution. The Ni-Sn alloy electrode were allowed in the ruthenium solution in ultrasonic bath and further heated to 400 oC in the presence of oxygen, in order to promote the thermal decomposition of ruthenium chloride. The nanostructured Ni surface was obtained from a chemical deposition in a solution composed by 1.8 g NiCl2.6H2O dissolved in 30 mL ethanol and adding 3.5 g of powdered Zn and 10 mL of aminoethanolic solution, under mechanical stirring. The black powder precipitated was separated by a magnetic rod. In order to prepare the electrode, with such powder, a 10 mL aliquot of solution containing the Ni powder, Nafion® and ethanol were dipped in a pirolitic graphite surface and allowed to dry. The voltammetric profiles were analyzed in order to evaluate the oxireduction characteristics of Ni surfaces, as well as the Ni-Sn alloy and the RuO2 modified surfaces and the nanostructured one. A potential window between 100 and 700 mV was scanned at 50 mV s-1, in 0.5 mol L-1 NaOH electrolyte. The electrochemical impedance spectroscopy measurements were performed in electrolytes containing ethanol, in order to observe the presence of an inductive loop, which has been associated to the low/high valences Ni oxides formed during ethanol oxidation on such surfaces. This loop was quite evident in Ni surfaces but not on the surfaces modified with RuO2. AFM measurements were performed in order to obtain the topological characteristics of the surfaces, indicating the eventual alterations associated with the RuO2 modifications. The nanostructures morphology was investigated by transmission microscopy were the nanometric dimensions of Ni phases were evident. The developed electrodes were applied in ethanol determinations in 0.5 mol L-1 NaOH solutions, prepared with Milli-Q water. The successive standard additions were used to obtain an analytical plot. After the analytical plot has been obtained, statistical analyses were performed, in order to determine the detection and quantification limits, as well as the errors involved in such determinations. As the Ni nanostructured electrodes yielded the best results, it was used in the determination of ethanol in samples of cognac, \"aguardente\" (sugar cane distilled drink) and mouthwash liquids, using chronoamperometry. The excellent recoveries percentages obtained showed that the matrix effect, in such determinations, was almost depreciable. This is related with the high catalytic power of Ni surfaces towards the ethanol oxidation reaction.

Adherent Cu films were electrodeposited onto polycrystalline W foils from purged solutions of 0.05 M CuSO4 in H2SO4 supporting electrolyte and 0.025 M CuCO3∙Cu(OH)2 in 0.32 M H3BO3 and corresponding HBF4 supporting electrolyte, both at pH = 1. Films were deposited under constant potential conditions at voltages between -0.6 V and -0.2 V versus Ag/AgCl. All films produced by pulses of 10 s duration were visible to the eye, copper colored, and survived a crude test called "the Scotch tape test", which involves sticking the scotch tape on the sample, then peeling off the tape and observing if the copper film peels off or not. Characterization by scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) and X-ray photon spectroscopy (XPS) confirmed the presence of metallic Cu, with apparent dendritic growth. No sulfur impurity was observable by XPS or EDX. Kinetics measurements indicated that the Cu nucleation process in the sulfuric bath is slower than in the borate bath. In both baths, nucleation kinetics does not correspond to either instantaneous or progressive nucleation. Films deposited from 0.05 M CuSO4/H2SO4 solution at pH > 1 at -0.2 V exhibited poor adhesion and decreased Cu reduction current. In both borate and sulfate baths, small Cu nuclei are observable by SEM upon deposition at higher negative overpotentials, while only large nuclei (~ 1 micron or larger) are observed upon deposition at less negative potentials. Osmium metal has been successfully electrodeposited directly onto p-Si (100) from both Os3+ and Os4+ in both sulfuric and perchloric baths. This electrochemical deposition of osmium metal can provide sufficient amount of osmium which overcome ion beam implantation limitations. The deposited metal can undergo further processing to form osmium silicides, such as Os2Si3, which can be used as optical active materials. The higher osmium concentration results in large deposition currents and more negative peak potential due to larger transfer coefficient. No matter which supporting electrolyte is used, no stripping peak exists in this study. The oxidation ability of anion plays an important role in osmium electrodeposition because it will change the silicon substrate conductivity. In our case, perchloric acid oxidized silicon surface severely. Os4+ seems more favorable for reduction but has a stronger oxidization ability to lower the conductivity. The microscopic images verified osmium is deposited on silicon and forms cluster sizes of < 1 µm to > 10 µm. The Rutherford backscattering spectroscopy (RBS) data indicate osmium can diffuse into the silicon as far as 500 nm and the Si crystal structure is unchanged by the process. This means that the Si does not disassociate and migrate into deposited Os. Osmium is distributed randomly throughout the lattice interstitially. It appears field assisted diffusion can significantly drive the Os into Si (100). This finding is very valuable but needs further study.

Lithium is a very attractive material for batteries. It has low redox potential (-3.04V vs SHE) and high theoretical capacity of 3860 mAh g-1. So, lithium batteries would have high energy density. During charging and discharging of the batteries, the interface between electrode and electrolyte changes as lithium is deposited or dissolved. If the deposition is dendritic, it can short circuit and cause failure of the battery. During dissolution of lithium from the electrode, pits can form on the surface and some part of lithium is detached. It is called dead lithium since it is not electrochemically active. Solid electrolyte and lithium metal interfaces are characterized by high interfacial resistance. The interface between electrode and electrolyte is critical to the safety and performance of lithium batteries. The aim of this research is to understand the evolution of interface between electrode and electrolyte as charging or discharging occurs. Three kinds of interfaces are considered, interface formed between intercalation anode and liquid electrolyte, interface of metal anode and liquid electrolyte and interface between metal anode and solid electrolyte.<br>Stringent performance and operational requirements in electric vehicles can push lithium-ion batteries toward unsafe conditions. Electroplating and possible dendritic growth are a cause for safety concern as well as performance deterioration in such intercalation chemistry-based energy storage systems. There is a need for better understanding of the morphology evolution due to electrodeposition of lithium on graphite anode surface, and the interplay between material properties and operating conditions. In this work, a mesoscale analysis of the underlying multi-modal interactions is presented to study the evolution of morphology due to lithium deposition on typical graphite electrode surfaces. It is found that electrodeposition is a complex interplay between the rate of reduction of Li ion and the intercalation of Li in the graphite anode. The morphology of the electrodeposited film changes from dendritic to mossy structures due to the surface diffusion of lithium on the electrodeposited film.<br>Dendritic deposition on lithium metal anode during charging poses a safety concern. During discharging, formation of dead lithium results in low Coulombic efficiency. In this work, a comprehensive understanding of the interface evolution leading to the formation of dead lithium is presented based on a mechanism-driven probabilistic analysis. Non-dendritic interface morphology is obtained under reaction controlled scenarios. Otherwise, this may evolve into a mossy, dendritic, whisker or needle-like structures with the main characteristic being the propensity for undesirable vertical growth. During discharging, pitted interface may be formed along with bulk dissolution. Surface diffusion is a key determinant controlling the extent of dead lithium formation, including a higher probability of the same when the effect of surface diffusion is comparable to that of ionic diffusion in the electrolyte and interface reaction.<br>One of the biggest advantages of solid electrolyte over liquid electrolyte is its mechanical rigidity which provides resistance to dendritic deposition. The electrodeposition at the interface of solid electrolyte and lithium metal anode will be affected by the nature of the interface formed between solid electrolyte and lithium metal, i.e. coherent, semi-coherent or incoherent depending on the misfit between the two crystal lattices. A coupled energetics and deposition mesoscale model is developed to investigate the nature of deposition and surface roughness of the deposition. The strength of interaction between metal anode surface and solid electrolyte surface at the interface is key in determining the roughness of the morphology during deposition. The energy is localized to region near the interface. With surface diffusion at the interface, the roughness of the interface as well as the energy near the interfacial region decreases.

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<p> The amount of chloride ion incorporated into a copper electrodeposit prepared from an aqueous copper sulphate solution has been determined at low chloride concentrations by the use of radiotracers. It has been found that the electrodeposits have a surface layer which is enriched in chloride ion. Evidence has been obtained that incorporation of chloride is preceded by the formation of cuprous chloride. The incorporation of chloride has been found to be increased by the presence of organic additives in the solution. The polarization during the first 30 seconds of electolysis has been interpreted using the knowledge obtained from the radiotracer work.</p> / Thesis / Doctor of Philosophy (PhD)

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