O uso do cianeto em processos de eletrodeposição proporciona à prática industrial risco ambiental e ocupacional. Com isso, estudos têm buscado alternativas para a substituição desse agente nocivo. O Instituto de Pesquisas Tecnológicas (IPT) desenvolveu um banho de cobre alcalino sem cianeto, que utilizou como substituinte o HEDP (1-hidroxietano-1,1-difosfônico). Para a recuperação desse ácido a eletrodiálise foi avaliada, que consiste no uso de um sistema de membranas trocadoras de íons (MTI) e de corrente elétrica como força motriz. Meios oxidantes, corrosivos e com materiais orgânicos favorecem a degradação da membrana, inibindo sua capacidade em separação. Alternativas de manutenção têm sido estudadas para o aumento da vida útil das membranas, como o uso de agentes de limpeza. O estudo do envelhecimento proporciona a avaliação de um material em condições específicas, a fim de monitorar alterações em função do tempo de contato com o meio. O presente estudo propõe o envelhecimento de membranas aniônicas comerciais em soluções diluídas, provenientes do banho sintético de cobre à base de HEDP. Como objeto de estudo, foram selecionadas duas membranas, sendo uma heterogênea e uma membrana homogênea. Essas foram envelhecidas em três concentrações distintas (CuHEDP 1%, 5%, 10% v/v), por 400h de contato, sob agitação. As possíveis modificações estruturais foram avaliadas por meio de técnicas como a microscopia eletrônica de varredura acoplada à espectroscopia de energia dispersiva de raios-X (MEV-EDS), a análise termogravimétrica (TGA) e espectroscopia por infravermelho com transformada de Fourier (FTIR-ATR). As propriedades intrínsecas das membranas estão diretamente relacionadas ao seu caráter seletivo e morfológico. Para avaliar tais propriedades, foram utilizados ensaios cronopotenciométricos e a titulação potenciométrica. As propriedades investigadas foram o grau de inchamento, a capacidade de troca, a resistência elétrica, a densidade de corrente limite e a permeseletividade. Paralelamente, submeteu-se a membrana heterogênea ao envelhecimento em um sistema de eletrodiálise por 400h, monitorando-se as alterações em sua densidade de corrente e resistência elétrica a cada 100h de ensaio. Em adição, realizou-se a avaliação de agentes de limpeza de caráter ácido e básico, em concentrações distintas. O agente que atingiu melhor desempenho em remover a incorporação iônica foi aplicado às membranas envelhecidas em 100h de envelhecimento. Em seguida, essas foram reavaliadas a partir de ensaios eletroquímicos. Observou-se que houve interação entre os íons em solução e as membranas estudadas, que proporcionaram alterações em sua estrutura e propriedades, porém sem causar modificações que indicassem o descarte para ambas membranas. / The use of cyanide in electrodeposition processes provides industrial practice environmental and occupational risk. Thereby, studies have looked for alternatives for the substitution of this noxious agent. The Institute of Technological Research (ITR) developed an alkaline copper bath cyanide-free, which used HEDP (1-hydroxyethane- 1,1-diphosphonic) as a substitute. For the recovery of this acid the electrodialysis was evaluated, which consists of the use of an ion-exchange membrane (IEM) system and electric current as the driving force. Oxidizing, corrosive and organic materials favor membrane degradation, inhibiting their separation ability. Maintenance alternatives have been studied to increase the shelf life of membranes, such as the use of cleaning agents. The ageing study provides the evaluation of a material under specific conditions, in order to monitor changes as a function of the time of contact with the medium. The present study proposes the ageing of commercial anionic membranes in dilute solutions from the synthetic copper bath with HEDP. The purpose of the study was selected two membranes, being a heterogeneous and homogeneous membrane. These were aged in three distinct concentrations (CuHEDP 1%, 5%, 10% v/v) for 400 hours of contact, under stirring. The possible structural modifications were evaluated by techniques such as scanning electron microscopy coupled to X-ray dispersive energy spectroscopy (SEM-EDS), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR-ATR). The intrinsic properties of the membranes are directly related to their selective and morphological character. To evaluate such properties, chronopotentiometric assays and potentiometric titration were used. The investigated properties were swelling degree, ion-exchange capacity, electrical resistance, current density, and permselectivity. In parallel, the heterogeneous membrane was subjected to ageing in an electrodialysis system for 400h, monitoring the changes in its current density and electrical resistance every 100h of the test. In addition, acid and basic cleaning agents were evaluated in different concentrations. The agent that achieved the best performance in removing the ionic incorporation was applied to the membranes aged in 100h of ageing. These were then reevaluated from electrochemical tests. It was observed that there was interaction between the ions in solution and the membranes studied, which provided alterations in its structure and properties, but without provide modifications that indicated the need of disposal for both membranes.

Fuel cells are electrochemical devices that rely on the transport of reactants (oxygen and hydrogen) and products (water and heat). These transport processes are coupled with electrochemistry and further complicated by phase change, porous media (gas diffusion electrodes) and a complex geometry. This thesis presents a three dimensional, non-isothermal computational model of a proton exchange membrane fuel cell (PEMFC). The model was developed to improve fundamental understanding of transport phenomena in PEMFCs and to investigate the impact of various operation parameters on performance. The model, which was implemented into a Computational Fluid Dynamics code, accounts for all major transport phenomena, including: water and proton transport through the membrane; electrochemical reaction; transport of electrons; transport and phase change of water in the gas diffusion electrodes; temperature variation; diffusion of multi-component gas mixtures in the electrodes; pressure gradients; multi-component convective heat and mass transport in the gas flow channels. Simulations employing the single-phase version of the model are performed for a straight channel section of a complete cell including the anode and cathode flow channels. Base case simulations are presented and analyzed with a focus on the physical insight, and fundamental understanding afforded by the availability of detailed distributions of reactant concentrations, current densities, temperature and water fluxes. The results are consistent with available experimental observations and show that significant temperature gradients exist within the cell, with temperature differences of several degrees Kelvin within the membrane-electrode-assembly. The three-dimensional nature of the transport processes is particularly pronounced under the collector plates land area, and has a major impact on the current distribution and predicted limiting current density. A parametric study with the single-phase computational model is also presented to investigate the effect of various operating, geometric and material parameters, including temperature, pressure, stoichiometric flow ratio, porosity and thickness of the gas diffusion layers, and the ratio between the channel with and the land area. The two-phase version of the computational model is used for a domain including a cooling channel adjacent to the cell. Simulations are performed over a range of current densities. The analysis reveals a complex interplay between several competing phase change mechanisms in the gas diffusion electrodes. Results show that the liquid water saturation is below 0.1 inside both anode and cathode gas diffusion layers. For the anode side, saturation increases with increasing current density, whereas at the cathode side saturation reaches a maximum at an intermediate current density (≈ 1.1Amp/cm2) and decreases thereafter. The simulation show that a variety of flow regimes for liquid water and vapour are present at different locations in the cell, and these depend further on current density. The PEMFC model presented in this thesis has a number of novel features that enhance the physical realism of the simulations and provide insight, particularly in heat and water management. The model should serve as a good foundation for future development of a computationally based design and optimization method. / Graduate

This research focuses on new rapid prototype development techniques for Proton Exchange Membrane (PEM) fuel cell gas delivery plates. The study addresses several key issues in the design, analysis and manufacturing of fuel cell plates. The approach combines theoretical modeling, experimental study, physical plate making process, and virtual prototyping to form a new scheme for the rapid prototype development of fuel cell plates. The research extends the newly introduced screen-printing layer deposition manufacturing technique to complete the entire cycle of rapid plate development. A number of key issues on plate materials and the layer deposition process are addressed. The study has identified the cause of the problem with the poster-ink based screen-print ink material, explored various alternative composite ink materials, and narrowed down to the promising “conductive polymer ∼ epoxy ∼ graphite power” composite. A new, concurrent approach for developing new composite materials through various experiments and material tests has been introduced, and demonstrated through the development of one particular ink composite with promising results. In this research, the method for virtual prototyping fuel cell gas delivery plate using advanced CAD/CAE commercial software is introduced. The method allows a “virtual prototype” of the fuel cell plate to be constructed and the performance of the plate to be evaluated through various analyses as “virtual prototype tests.” These include the prediction of fuel cell performance through the CFD calculation on the average oxygen concentration; as well as the assessments of the maximum stress and undesirable temperature variation on the printed fuel cell plate through finite element analysis. Design optimization is conducted using the virtual prototypes to improve the design of the flow field and the plate. Three disciplinary models are simulated and their results are subject to disciplinary optimizations. Global design optimization is carried out using multiple objective optimization, combining the functional performance measures from three disciplinary models. This multi-disciplinary optimization integrates performance considerations of PEM fuel cell plate, and provides guidelines to the plate development. The research contributes to a new approach for the rapid development of fuel cell plates with a great potential to be applied to other mechanical parts. The study also extends the methodology of computational design and rapid prototyping. / Graduate

O uso do cianeto em processos de eletrodeposição proporciona à prática industrial risco ambiental e ocupacional. Com isso, estudos têm buscado alternativas para a substituição desse agente nocivo. O Instituto de Pesquisas Tecnológicas (IPT) desenvolveu um banho de cobre alcalino sem cianeto, que utilizou como substituinte o HEDP (1-hidroxietano-1,1-difosfônico). Para a recuperação desse ácido a eletrodiálise foi avaliada, que consiste no uso de um sistema de membranas trocadoras de íons (MTI) e de corrente elétrica como força motriz. Meios oxidantes, corrosivos e com materiais orgânicos favorecem a degradação da membrana, inibindo sua capacidade em separação. Alternativas de manutenção têm sido estudadas para o aumento da vida útil das membranas, como o uso de agentes de limpeza. O estudo do envelhecimento proporciona a avaliação de um material em condições específicas, a fim de monitorar alterações em função do tempo de contato com o meio. O presente estudo propõe o envelhecimento de membranas aniônicas comerciais em soluções diluídas, provenientes do banho sintético de cobre à base de HEDP. Como objeto de estudo, foram selecionadas duas membranas, sendo uma heterogênea e uma membrana homogênea. Essas foram envelhecidas em três concentrações distintas (CuHEDP 1%, 5%, 10% v/v), por 400h de contato, sob agitação. As possíveis modificações estruturais foram avaliadas por meio de técnicas como a microscopia eletrônica de varredura acoplada à espectroscopia de energia dispersiva de raios-X (MEV-EDS), a análise termogravimétrica (TGA) e espectroscopia por infravermelho com transformada de Fourier (FTIR-ATR). As propriedades intrínsecas das membranas estão diretamente relacionadas ao seu caráter seletivo e morfológico. Para avaliar tais propriedades, foram utilizados ensaios cronopotenciométricos e a titulação potenciométrica. As propriedades investigadas foram o grau de inchamento, a capacidade de troca, a resistência elétrica, a densidade de corrente limite e a permeseletividade. Paralelamente, submeteu-se a membrana heterogênea ao envelhecimento em um sistema de eletrodiálise por 400h, monitorando-se as alterações em sua densidade de corrente e resistência elétrica a cada 100h de ensaio. Em adição, realizou-se a avaliação de agentes de limpeza de caráter ácido e básico, em concentrações distintas. O agente que atingiu melhor desempenho em remover a incorporação iônica foi aplicado às membranas envelhecidas em 100h de envelhecimento. Em seguida, essas foram reavaliadas a partir de ensaios eletroquímicos. Observou-se que houve interação entre os íons em solução e as membranas estudadas, que proporcionaram alterações em sua estrutura e propriedades, porém sem causar modificações que indicassem o descarte para ambas membranas. / The use of cyanide in electrodeposition processes provides industrial practice environmental and occupational risk. Thereby, studies have looked for alternatives for the substitution of this noxious agent. The Institute of Technological Research (ITR) developed an alkaline copper bath cyanide-free, which used HEDP (1-hydroxyethane- 1,1-diphosphonic) as a substitute. For the recovery of this acid the electrodialysis was evaluated, which consists of the use of an ion-exchange membrane (IEM) system and electric current as the driving force. Oxidizing, corrosive and organic materials favor membrane degradation, inhibiting their separation ability. Maintenance alternatives have been studied to increase the shelf life of membranes, such as the use of cleaning agents. The ageing study provides the evaluation of a material under specific conditions, in order to monitor changes as a function of the time of contact with the medium. The present study proposes the ageing of commercial anionic membranes in dilute solutions from the synthetic copper bath with HEDP. The purpose of the study was selected two membranes, being a heterogeneous and homogeneous membrane. These were aged in three distinct concentrations (CuHEDP 1%, 5%, 10% v/v) for 400 hours of contact, under stirring. The possible structural modifications were evaluated by techniques such as scanning electron microscopy coupled to X-ray dispersive energy spectroscopy (SEM-EDS), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR-ATR). The intrinsic properties of the membranes are directly related to their selective and morphological character. To evaluate such properties, chronopotentiometric assays and potentiometric titration were used. The investigated properties were swelling degree, ion-exchange capacity, electrical resistance, current density, and permselectivity. In parallel, the heterogeneous membrane was subjected to ageing in an electrodialysis system for 400h, monitoring the changes in its current density and electrical resistance every 100h of the test. In addition, acid and basic cleaning agents were evaluated in different concentrations. The agent that achieved the best performance in removing the ionic incorporation was applied to the membranes aged in 100h of ageing. These were then reevaluated from electrochemical tests. It was observed that there was interaction between the ions in solution and the membranes studied, which provided alterations in its structure and properties, but without provide modifications that indicated the need of disposal for both membranes.

Proton exchange membrane (PEM) fuel cells are at the forefront among different types of fuel cells and are likely to be important power sources in the near future. PEM is a key component of the PEM fuel cells. The objective of this research is to investigate the fundamental aspects of PEM in terms of thermodynamics and proton transport in the membrane, so that the new proton conducting materials may be developed based on the detailed understanding. Since the proton conductivity increases dramatically with the amount of water in PEM, it is important to maintain a high humidification during the fuel cell operation. Therefore, the water uptake characteristics of the membrane are very important in developing fuel cell systems. Thermodynamic models are developed to describe sorption in proton-exchange membranes (PEMs), which can predict the complete isotherm as well as provide a plausible explanation for the long unresolved phenomenon termed Schroeder¡¯s paradox, namely the difference between the amounts sorbed from a liquid solvent versus from its saturated vapor. The sorption isotherm is a result of equilibrium established in the polymer-solvent system when the swelling pressure due to the uptake of solvent is balanced by the surface and elastic deformation pressures that restrain further stretching of the polymer network. The transport of protons in PEMs is intriguing. It requires knowledge of the PEM structure, water sorption thermodynamics in PEM, proton distribution in PEM, interactions between the protons and PEM, and proton transport in aqueous solution. Even proton conduction in water is anomalous that has received considerable attention for over a century because of its paramount importance in chemical, biological, and electrochemical systems. A pore transport model is proposed to describe proton diffusion at various hydration levels within Nafion¢ÃƒÂ§ by incorporating structural effect upon water uptake and various proton transport mechanisms, namely proton hopping on pore surface, Grotthuss diffusion in pore bulk, and ordinary mass diffusion of hydronium ions. A comprehensive random walk basis that relates the molecular details of proton transfer to the continuum diffusion coefficients has been applied to provide the transport details in the molecular scale within the pores of PEM. The proton conductivity in contact with water vapor is accurately predicted as a function of relative humidity without any fitted parameters. This theoretical model is quite insightful and provides design variables for developing high proton conducting PEMs. The proton transport model has been extended to the nanocomposite membranes being designed for higher temperature operation which are prepared via modification of polymer (host membrane) by the incorporation of inorganics such as SiO2 and ZrO2. The operation of fuel cells at high temperature provides many advantages, especially for CO poisoning. A proton transport model is proposed to describe proton diffusion in nanocomposite Nafion¢ÃƒÂ§/(ZrO2/SO42-) membranes. This model adequately accounts for the acidity, surface acid density, particle size, and the amount of loading of the inorganics. The higher proton conductivity of the composite membrane compared with that of Nafion is observed experimentally and also predicted by the model. Finally, some applications of PEM fuel cells are considered including direct methanol fuel cells, palladium barrier anode, and water electrolysis in regenerative fuel cells.

Thesis (Ph. D.)--Michigan State University. Dept. of Chemistry, 2006. / Title from PDF t.p. (viewed on June 19, 2009) Includes bibliographical references (p. 148-154). Also issued in print.

Thesis (Ph. D.)--Worcester Polytechnic Institute. / Keywords: kinetic modeling; electrocatalysis; CO tolerance; PEM fuel cells. Includes bibliographical references.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Thermodynamics; Fuel Cell; Proton-exchange membranes; Proton Transport. Includes bibliographical references.

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