Master´s thesis is focused on development of electrodes used in alcaline accumulators, by using new kinds of materials and compounds. Basic possitive eletrode was made of nickel, on this electrode were applied new layers of Ni(OH)2 by using the method called electrodeposition. For electrodeposition was used solution with Ni(NO3)2 in diverse concentrations. Later on, this material was enriched with aluminium admixtures to increase stability of alfa modification in Ni(OH)2. These concentrations were measured and analysed in diagrams. For measurement was used device Biologic. The diagrams were commented with recommendations for production use in accumulators.

Master’s thesis is deals with the effect of carbon additives on the positive electrode in the NiCd batteries. It examines whether the positive electrode material enrichment of carbon additives to achieve improved internal parameters of conductivity and better contact with the electrode materials in a discharged. Galvanostatic cycling and electro-chemical impedance spectroscopy (EIS) are used for evaluation of graphite aditives.

This dissertation is focused on the study of selected additives and their effect on positive and negative electrodes of Ni-Zn secondary cells. The first group of additives consists of the inorganic compounds that reduce zinc oxide solubility and thus prevents shape changes of the zinc electrode. The second group contains organic additives that have the beneficial effect of dendrite growth prevention. All additives were examined in relationship to their compatibility with the positive electrode and to their effect on the zinc electrode dendrites inhibition, hydrogen evolution and corrosion inhibition. Moreover, the study of decomposition kinetics of supersaturated zincate solution with the first group of additives was performed. Finally, a short study of pulse regime charging mode with regard to dendrites inhibition was performed and evaluated.

No description available.

Nesta tese de doutorado foram desenvolvidos e caracterizados nanomateriais eletroativos, explorando estratégias de estabilização e os efeitos sinérgicos em nanomateriais multifuncionais baseados em alfa-hidróxido de níquel, com potencial aplicação nas mais essências e urgentes áreas de atuação científica e tecnológicas, como por exemplo na conversão e armazenamento de energia, e sensores amperométricos. Nesse sentido, foram desenvolvidos nanopartículas (NPs) de alfa-hidróxidos de níquel (α-Ni(OH)2) estabilizados pela formação de nanocompósitos com óxido de grafeno (GO), denominados de α-Ni(OH)2@GO. Analogamente, foram preparados NPs de sais de hidróxido duplo de níquel e cobalto (α- NiCo(OH)2), estabilizados pela incorporação cátions Co2+ na estrutura do α-Ni(OH)2, e o correspondente nanocompósito com óxido de grafeno reduzido (rGO) denominado de α- NiCo(OH)2@rGO. De modo geral, os nanocompósitos exibiram alta capacidade de carga em elevadas densidades de corrente, alta capacidade de retenção de carga e elevada estabilidade como consequência da interação sinergística de seus componentes, com potencial aplicação em dispositivos de armazenamento de energia de alto desempenho, como por exemplo em supercapacitores híbridos. Por outro lado, um dos principais desafios no campo da conversão de energia, concentra-se no desenvolvimento de eletrocatalisadores eficientes e robustos para impulsionar a cinética intrinsecamente lenta da reação de evolução de oxigênio (OER), que envolve etapas de transferência de elétrons acopladas a de prótons. Para isso, foram preparados nanocompósitos ternários baseados em NPs de αNi(OH)2 de diferentes tamanhos, octacarboxiftalocianina de ferro (FeOCPc) e rGO (α-NiFeOCPc@rGO). As NPs de α- Ni@rGO-K maiores e mais cristalinas e seus respectivos nanocompósitos mostraram propriedades eletrocatalíticas superiores para a OER quando comparados com os respectivos derivados de α-Ni(OH)2-Na, indicando a relevância do tamanho do nanocristal de α-Ni(OH)2 na estrutura do nanocompósito e consequente efeitos sinérgicos nas propriedades eletroquímicas e eletrocatalíticas dos nanocompósitos ternários. Além disso, foram desenvolvidos eletrodos modificados com NPs de hidróxido duplo lamelar de NiCe (α-NiCe) como sensores de alta sensibilidade, e de fundamental importância para detecção e quantificação de prednisona, uma droga proibida pelo Comitê Olímpico Internacional (COI). Em resumo, a incorporação de 20% em mols de íons Ce(III/IV) em nanopartículas de α- Ni(OH)2 aumentou a estabilidade deste material na fase alfa, conferindo melhores propriedades eletrocatalíticas responsáveis pela rápida oxidação da prednisona e de seus subprodutos de degradação, permitindo a preparação de sensores amperométricos com elevada sensibilidade e baixo limite de detecção (LOD) em comparação aos eletrodos modificados já reportando na literatura. Em suma, as estratégias no design de nanomateriais foram exploradas com sucesso para gerar novos nanomateriais e nanocompósitos com propriedades eletrocatalíticas e de armazenamento de carga aprimoradas, com potencial de aplicação em sensores e supercapacitores híbridos. / In this doctoral thesis, nanomaterials design strategies were explored in order to improve the stability of alpha-nickel hydroxide nanoparticles while developing synergistic effects, generating multifunctional electrochemically active nanomaterials and nanocomposites with potential application in amperometric sensors and energy conversion and storage devices. In this context, the α-Ni(OH)2 NPs were stabilized by generating double hydroxide salts, by interaction with octacarboxyphthalocyanine molecules and graphene oxide (GO) generating hybrid and nanocomposite materials, for example α-Ni(OH)2@GO. Nickel hydroxide NPs was stabilized by incorporation of Co2+ cation to produce α-NixCoy(OH)2 double hydroxide salts and the corresponding nanocomposite with reduced graphene oxide (rGO) designated - NiCo(OH)2@rGO. In this way, nanocomposites with potential application in high performance energy storage devices such as hybrid supercapacitors were produced, since exhibited large charge capacities at high current densities and great stability as a consequence of the synergistic interaction of their componentes. One of the main challenges in the field of energy conversion, the development of efficient and robust electrocatalysts to boost the intrinsically slow multielectronic multiprotonic transfer kinetics of the oxygen evolution reaction (OER) was also addressed using ternary nanocomposites based on α-Ni(OH)2 NPs, iron octacarboxyphthalocyanine (FeOCPc) and rGO (α-NiFeOCPc@rGO). The more crystalline - Ni@rGO-K NPs and their respective nanocomposites showed superior electrocatalytic properties when compared to the respective α-Ni(OH)2-Na derivatives, indicating the relevance of the α-Ni(OH)2 nanocrystal size and synergistic effects on their electrochemical and electrocatalytic properties. In addition, amperometric sensors based on NiCe layered doublehydroxide NPs (α-NiCe) were developed for determination of prednisone, a drug forbidden by the International Olympic Committee (IOC). The incorporation of 20 m% of Ce3+/4+ ions in α- Ni(OH)2 nanoparticles increased its stability in the alpha phase, conferring improved electrocatalytic properties responsible for the rapid oxidation of prednisone and its degradation byproducts, responsible for the higher sensitivity and lower detection limits (LOD) than similar devices reported in the literature. In short, nanomaterials design strategies were successfully explored to generated new nanomaterials and nanocomposites with enhanced electrocatalytic and charge storage properties with potential application in sensors and hybrid supercapacitors.

Commercial alkaline accumulators with positive electrode based on nickel hydroxide generally comprise beta modification of the active material at present due to its excellent stabilization of performance during electrochemical cycling. This dissertation refers to a research work accomplished by author, which has been aimed to utilization of alpha nickel hydroxide in alkaline batteries including exploration of possibilities to attain its stability in strong alkali medium of the electrolyte. I have focused my effort to elucidate reasons for its transformation tendency and to find way of their suppression.

Orientador: Lauro Tatsuo Kubota / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-27T17:12:32Z (GMT). No. of bitstreams: 1 Giordano_GabrielaFurlan_M.pdf: 2251330 bytes, checksum: a6853decc37a3f82817a0457cc141778 (MD5) Previous issue date: 2015 / Resumo: Este trabalho teve como objetivo desenvolver um sistema eletroquímico capaz de detectar e quantificar etanol presente em amostras de vinho de cana-de-açúcar. Três métodos de modificação de eletrodo de níquel foram estudados visando à obtenção das espécies Ni(OH)2/NiOOH. Um dos métodos consistiu no condicionamento eletroquímico em NaOH, o outro, na oxidação química em persulfato de amônio e tratamento térmico e o terceiro, na deposição eletroquímica de Ni(OH)2 dopados com Co2+ e Cd2+, a partir de solução contendo os nitratos desses metais. Esse último apresentou resultados com maior repetibilidade de preparação e resposta. As técnicas SEM-FEG e XPS foram empregadas, a fim de caracterizar morfologicamente o Ni(OH)2 obtido e permitir determinações qualitativas e quantitativas sobre a composição química da superfície, respectivamente. Para a aplicação nas amostras empregou-se a técnica de extração por difusão gasosa através de uma membrana hidrofóbica. Assim, um módulo de extração foi construído no qual uma membrana de PTFE separou a solução de etanol - a ser analisada - de uma solução receptora de NaOH 100,0 mmol L-1, na qual o sistema eletroquímico foi acoplado. As condições aplicadas ao sistema foram otimizadas de modo a resultar em menores desvios das medidas analíticas. O vapor de etanol recolhido na solução de NaOH foi analisado utilizando o eletrodo de trabalho desenvolvido e foi possível monitorar soluções de etanol no intervalo 2,0 a 20,0% v/v. A concentração de etanol foi determinada em amostras de vinho de cana-de-açúcar por dois métodos diferentes: interpolação em curva analítica preparada em meio salino com condutividade similar às amostras e adição de padrão. Os resultados obtidos foram estatisticamente equivalentes em comparação com a técnica de FTIR, considerando nível de confiança de 95% / Abstract: This work describes the development of an electrochemical system to detect and quantify ethanol on fermentation broths. Three methods were studied to modify the electrode surface in order to obtain Ni(OH)2/NiOOH species: i) electrochemical cycling in NaOH solution; ii) chemical oxidation on ammonium persulfate and heat treatment; and, iii) electrochemical deposition of nickel, cobalt and cadmium from a solution containing the respective nitrates and application of cathodic current. The latter one showed good repeatability, therefore, an analytical curve was obtained by cyclic voltammetry technique and the analytical sensitivity was 1.2 ìA L mmol-1. Scanning electron microscopy and X-ray photoelectron spectroscopy were employed to characterize the structures formed and allow qualitative and quantitative determination about the surface chemical composition. In order to provide selectivity to electrochemical determination of ethanol on complex samples, the electrochemical system was coupled to gas diffusion extraction through hydrophobic membrane. Thus, an extraction module was constructed in which a PTFE membrane separated the ethanol donor solution, standard or sample, from receptor solution, the electrolyte used on electrochemical analyses (100.0 mmol L-1 NaOH). The conditions applied to the system were optimized to yield repeatability on analytical measurements. In this platform, it was possible to monitor ethanol solutions in the range of 2.0 up to 20.0% v/v. Samples of fermentation broth were analyzed by two methods: direct interpolation on saline analytical curve with conductivity similar to samples and standard addition. The results were in agreement with respect to those obtained by FTIR method at 95% confidence level / Mestrado / Quimica Analitica / Mestra em Química

This dissertation work deals with analysis of nickel hydroxide phases, their oxidation compounds, their stability and degradation mechanisms of electrochemically more active alpha phase on standard beta phase. The active material was prepared by both methods, electrodeposition and chemical precipitation. Main analysis method was Electrochemical Quartz Crystal Microbalance in combination with common analytical methods (cyclic voltammetry, potenciometry) can resolute between alpha and beta phases and quantitatively describe differences in main reaction by monitoring mass changes in the active material. Poor stability of the ?-Ni(OH)2 were improved by adding cations with valence two three and four into the structure instead of Ni atoms. The most important role plays cobalt and its hydroxide. Totally new way is to use titanium in combination with other cations. In electrolyte the most significant addition is LiOH, which has beneficial influent on cycle ability, stability in strong alkaline medium and cycle life.

The aim of my diploma thesis was to explore the influence of manganese ions put into nickel nitrate structure. The attention was focused mainly on the stabilization of nickel nitrate a modification, which could not change into b modification. The theoretical part of my thesis focused on applied materials, kinds of acumulators, basic parameters of acumulators and the description of chosen methods of measurement employed. It contained the electrodeposition, the impedance spectroscopy and the cyclic voltammetry. The task of the experimental part was to measure the effect of manganese ions put into potassium hydroxide structure. Proportions of Ni (nickel nitrate) : Mn (manganese nitrate) 10:0, 7:3, 5:5, 6:1 and 6:4 were blended for the measurement. By means of the electrodeposition, there was a thin layer of nickel hydroxide with an admixture of manganese ions from nickel nitrate and manganese nitrate dilution put on the nickel plate. After the spread of the thin layer on the nickel plate, the measurement by the method of cyclic voltammetry followed. The next task consisted in trying to add KOH (potassium hydroxide) anionic and cationic surfactant into the dilution.

The interconversion of α- and β-Ni(OH)₂ was studied using cyclic voltammetry and dynamic electrochemical impedance (dEIS). Holding experiments were done at 0.5 V, 0.6 V, 0.8 V and 1.0 V while subsequent cathodic holds were applied in selected experiments at -0.1, -0.2, -0.25 V. The number of thickness of Ni(OH)₂ formed increased with increasing anodic potential. After α-Ni(OH)₂ was formed (< 0.5 V), it was easily reduced by sweeping down to -0.15 V. However, sweeping further (> 0.5 V) resulted in its "irreversible" conversion to β-Ni(OH)₂. Since β-Ni(OH)₂ was not reduced by sweeping to -0.15 V, the current, capacitance and the conductance at the α-Ni(OH)₂ peak (at 0.2 V) decreased as a result. However, β-Ni(OH)₂ was shown to be reducible during potential holds at -0.2 V or lower. In contrast, holding at -0.1 V only resulted in partial reduction. Eventually, a link was established between the reduction of β-Ni(OH)₂ and hydrogen evolution. The relatively slow reduction of the β-Ni(OH)₂ to metallic nickel appears to inhibit the capacitance increase at -0.15 V which occurs when the potential is kept under 0.5 V. The retention of a low capacitance while β-Ni(OH)₂ persists suggests a blocking mechanism. A concerted adsorption-desorption step which generates adsorbed hydrogen prior to hydrogen evolution was proposed. An exponential increase in current and capacitance occurred during the potential hold at -0.2 V. The capacitance increase suggests a reversal of the blocking (low capacitance at -0.15 V) caused by the persistence of β-Ni(OH)₂. Additionally, the exponential current decay during the hold at -0.2 V was significantly slower than the conversion of α- to β-Ni(OH)₂ at 0.8 V. This further demonstrates the possibility of a slow step involving surface blocking during the reduction of β-Ni(OH)₂. These observations provide new information on the mechanism and kinetics of the interconversion of α-Ni(OH)₂ into β-Ni(OH)₂ and the interaction of the latter in the hydrogen evolution reaction. / Graduate