M. Tech. (Engineering Department Applied Electronics and Electronic Communication, Faculty of Engineering) Vaal University of Technology / This study presents the design of a proton exchange membrane fuel cell stack that can be used to replace conventional sources of electrical energy in an uninterruptible power supply system, specifically for use in the telecommunications industry. One of the major concerns regarding the widespread commercialization of fuel cells is the high cost associated with fuel cell components and their manufacturing. A fuel cell design is presented in which existing, low-cost, technologies are used in the manufacture of cell components. For example, printed circuit boards are used in the manufacturing of bipolar flow plates to significantly reduce the cost of fuel cells. The first objective was to design, construct and test a single fuel cell and small fuel cell stack in order to evaluate the use of printed circuit boards in bipolar plate manufacturing. Since the use of copper in a fuel cell environment was found to reduce the lifetime of the cells, the bipolar plates were coated with a protective layer of nickel and chrome. These coatings proved to increase the lifetime of the cells significantly. Power outputs of more than 4 W per cell were achieved. The second objective was to analyze a small fuel cell stack in order to obtain a model for predicting the performance of larger stacks. A mathematical model was developed which was then used to design an electronic circuit equivalent of a fuel cell stack. Both models were adapted to predict the performance of a fuel cell stack containing any number of cells. The models were proven to be able to accurately predict the performance of a fuel cell stack by comparing simulated results with practical performance data. Finally, the circuit equivalent of a fuel cell stack was used to evaluate the capability of a switch mode boost converter to maintain a constant voltage when driven by a fuel cell stack, even under varying load conditions. Simulation results showed the ability of the boost converter to maintain a constant output voltage. The use of supercapacitors as a replacement for batteries as a secondary energy source was also evaluated.

Poisoning of the catalyst seems to be one of the most serious problems preventing a widespread commercialization of fuel cell technology. This thesis focuses on the effect of CO poisoning and hydrogen dilution by nitrogen on performance of fuel cells with low platinum content. Catalysts were deposited by magnetron sputtering directly on membrane etched by plasma. Alloys with different platinum-ruthenium ratio were used to mitigate the CO poisoning. We found that presence of nitrogen has almost negligible effect on the fuel cell performance. On the other hand, CO, even in small concentrations, caused a significant drop in power density. PtRu with atomic ratio 2:1 and 1:1 showed the best CO tolerance.

A energia é o combustível do crescimento e um requisito essencial para o desenvolvimento sócio-econômico. No entanto, o atual modelo de produção baseado em combustíveis fósseis é considerado ameaçador para o homem e a natureza. Desta forma, as preocupações relacionadas às atividades antrópicas e os seus efeitos no meio ambiente são traduzidos pela implementação de padrões mais rígidos de controle ambiental e pela mobilização da sociedade em favor das tecnologias energéticas menos impactantes. Diante desse cenário, a Célula a Combustível de Membrana Trocadora de Prótons - PEMFC tem sido reconhecida como a resposta para a premente necessidade de energia limpa e eficiente. Em relação aos sistemas convencionais de geração de energia, suas vantagens durante o uso a configuram como candidata ideal para diversas aplicações, em especial as móveis. Entretanto, embora o foco de diversas avaliações ambientais em sistemas de energia seja voltado para a etapa da sua utilização, os estágios relacionados à produção do sistema e destinação final devem ser considerados já que estes também apresentam impactos. No caso da PEMFC, nas fases anteriores e posteriores ao uso, os aspectos relacionados aos catalisadores de platina apontam cargas ambientais que não podem ser negligenciadas. Neste sentido, a Avaliação do Ciclo de Vida tem sido utilizada para entender e questionar os riscos e oportunidades que acompanham um determinado produto, a partir de uma visão sistêmica das suas relações com o meio ambiente. É precisamente nesse contexto que o presente trabalho pretende dar sua maior contribuição, a partir de um estudo exploratório almeja-se prover uma análise ambiental dessa tecnologia na etapa pós-uso do conjunto eletrodo membrana, nomeadamente em relação aos catalisadores de platina, sob o enfoque da Avaliação do Ciclo de Vida - ACV. Para atingir tal propósito, são apresentadas e discutidas as relações entre energia, meio ambiente e desenvolvimento, bem como a tecnologia de Células a Combustível e os atuais estudos sobre ACV da PEMFC. As contribuições das questões levantadas foram utilizadas para o desenvolvimento de um método de recuperação dos catalisadores da PEMFC e, especialmente, para a sua posterior avaliação ambiental. Dentre os resultados significativos destaca-se a importância da ACV como ferramenta útil para compreender o peso das questões ambientais relacionadas à platina e, para subsidiar as estratégias relacionadas ao desenvolvimento, consolidação e inovação da PEMFC. / The energy is the fuel of growth and an essential requirement for the socioeconomic development. However, the current production model is based on fossil fuels, considered as threat to man and nature. As for, the relating to the human activities and their effects on the environment, they are handled by the implementation of a more rigid model of environmental control and the mobilization of the society in favor of technologies with less energy impact. In view of this scenario, the Proton Exchange Membrane Fuel Cell - PEMFC has been recognized as a key for the vital need of a clean and efficient energy. Considering the conventional power generation system, their advantages during usage configure its application as an ideal option for several utilities, especially in the mobile sector. Even though, the focus on several environmental evaluations in energy systems is referred back to the initial stage of it use, the employment relating to production of the system and to final destination should be considered, since these also present impacts. In the case of PEMFC, their previous and subsequent phases of use are issues related to the platinum catalysts, which indicates an environmental importance that cannot be overlooked. In this sense, the Life Cycle Assessment has been used to understand and to question the risks and opportunities that are associated to certain product, starting from a systemic concept of their relationships with the environment. It is precisely in this context that the present research intends to present its major contribution, starting from an exploratory study towards the its objectives to provide an environmental analysis of such technology linked to post stage of powder-use of the membrane electrode assembly - MEA, concerning the platinum catalysts, on the subject of Life Cycle Assessment - LCA. To attain such aim, the relationships between energy, environment and development are presented and discussed, as well as, the Fuel Cell technology and the current studies on LCA of PEMFC. Several questions raised up on this issues have conthbuted in the development of a method of recuperating the PEMFC catalysts and, particularly, for its subsequent environmental evaluation. Among significant results are the importance of LCA, out lined as useful tool for perceiving the weight of environmental matters concerning the platinum and its subsidy strategies relating to the development, consolidation and to the innovation of PEMFC.

A energia é o combustível do crescimento e um requisito essencial para o desenvolvimento sócio-econômico. No entanto, o atual modelo de produção baseado em combustíveis fósseis é considerado ameaçador para o homem e a natureza. Desta forma, as preocupações relacionadas às atividades antrópicas e os seus efeitos no meio ambiente são traduzidos pela implementação de padrões mais rígidos de controle ambiental e pela mobilização da sociedade em favor das tecnologias energéticas menos impactantes. Diante desse cenário, a Célula a Combustível de Membrana Trocadora de Prótons - PEMFC tem sido reconhecida como a resposta para a premente necessidade de energia limpa e eficiente. Em relação aos sistemas convencionais de geração de energia, suas vantagens durante o uso a configuram como candidata ideal para diversas aplicações, em especial as móveis. Entretanto, embora o foco de diversas avaliações ambientais em sistemas de energia seja voltado para a etapa da sua utilização, os estágios relacionados à produção do sistema e destinação final devem ser considerados já que estes também apresentam impactos. No caso da PEMFC, nas fases anteriores e posteriores ao uso, os aspectos relacionados aos catalisadores de platina apontam cargas ambientais que não podem ser negligenciadas. Neste sentido, a Avaliação do Ciclo de Vida tem sido utilizada para entender e questionar os riscos e oportunidades que acompanham um determinado produto, a partir de uma visão sistêmica das suas relações com o meio ambiente. É precisamente nesse contexto que o presente trabalho pretende dar sua maior contribuição, a partir de um estudo exploratório almeja-se prover uma análise ambiental dessa tecnologia na etapa pós-uso do conjunto eletrodo membrana, nomeadamente em relação aos catalisadores de platina, sob o enfoque da Avaliação do Ciclo de Vida - ACV. Para atingir tal propósito, são apresentadas e discutidas as relações entre energia, meio ambiente e desenvolvimento, bem como a tecnologia de Células a Combustível e os atuais estudos sobre ACV da PEMFC. As contribuições das questões levantadas foram utilizadas para o desenvolvimento de um método de recuperação dos catalisadores da PEMFC e, especialmente, para a sua posterior avaliação ambiental. Dentre os resultados significativos destaca-se a importância da ACV como ferramenta útil para compreender o peso das questões ambientais relacionadas à platina e, para subsidiar as estratégias relacionadas ao desenvolvimento, consolidação e inovação da PEMFC. / The energy is the fuel of growth and an essential requirement for the socioeconomic development. However, the current production model is based on fossil fuels, considered as threat to man and nature. As for, the relating to the human activities and their effects on the environment, they are handled by the implementation of a more rigid model of environmental control and the mobilization of the society in favor of technologies with less energy impact. In view of this scenario, the Proton Exchange Membrane Fuel Cell - PEMFC has been recognized as a key for the vital need of a clean and efficient energy. Considering the conventional power generation system, their advantages during usage configure its application as an ideal option for several utilities, especially in the mobile sector. Even though, the focus on several environmental evaluations in energy systems is referred back to the initial stage of it use, the employment relating to production of the system and to final destination should be considered, since these also present impacts. In the case of PEMFC, their previous and subsequent phases of use are issues related to the platinum catalysts, which indicates an environmental importance that cannot be overlooked. In this sense, the Life Cycle Assessment has been used to understand and to question the risks and opportunities that are associated to certain product, starting from a systemic concept of their relationships with the environment. It is precisely in this context that the present research intends to present its major contribution, starting from an exploratory study towards the its objectives to provide an environmental analysis of such technology linked to post stage of powder-use of the membrane electrode assembly - MEA, concerning the platinum catalysts, on the subject of Life Cycle Assessment - LCA. To attain such aim, the relationships between energy, environment and development are presented and discussed, as well as, the Fuel Cell technology and the current studies on LCA of PEMFC. Several questions raised up on this issues have conthbuted in the development of a method of recuperating the PEMFC catalysts and, particularly, for its subsequent environmental evaluation. Among significant results are the importance of LCA, out lined as useful tool for perceiving the weight of environmental matters concerning the platinum and its subsidy strategies relating to the development, consolidation and to the innovation of PEMFC.

The overall goal of this research is to synthesize two different monomers for proton exchange membrane (PEM) Fuel Cells. Such monomers are proposed to be polymerized to improve the efficiency and compatibility of electrodes and electrolytes in PEM fuel cells. The first target is to synthesize 4-diazonium-3-fluoro PFSI zwitterionic monomer. Three steps were carried out in the lab. First one was the ammonolysis of 3-fluoro-4-nitrobenzenesulfonyl chloride. Second reaction was the bromination of Nafion monomer. The next coupling reaction, between brominated Nafion monomer and the 3-fluoro-4-nitrobenzenesulfonamide, was failed. The obstacles involve the harsh reaction condition and troublesome purification procedure. The second target is to synthesize 5-nitro-1, 3-benzenedisulfonamide. According to the literature, this synthesis was also designed as three steps: 1)nitration of sodium 1, 3-benzenedisulfonate salt; 2)chlorination of sodium 5-nitro-1, 3-benzenedisulfonate salt; and 3)ammonolysis of 5- nitro-1, 3- benzenedisulfonyl chloride. This monomer is expected to be copolymerized for membrane electrolyte in PEM fuel cells.

A novel method based on pulse current electrodeposition (PCE) employing four different waveforms was developed and utilized for fabricating membrane-electrode assemblies (MEAs) with low platinum loading for use in low-temperature proton exchange membrane fuel cells. It was found that both peak deposition current density and duty cycle control the nucleation rate and the growth of platinum crystallites. Based on the combination of parameters used in this study, the optimum conditions for PCE were found to be a peak deposition current density of 400 mA cm-2, a duty cycle of 4%, and a pulse generated and delivered in the microsecond range utilizing a ramp-down waveform. MEAs prepared by PCE using the ramp-down waveform show performance comparable with commercial MEAs that employ ten times the loading of platinum catalyst. The thickness of the pulse electrodeposited catalyst layer is about 5-7 µm, which is ten times thinner than that of commercial state-of-the-art electrodes. MEAs prepared by PCE outperformed commercial MEAs when subjected to a series of steady-state and transient lifetime tests. In steady-state lifetime tests, the average cell voltage over a 3000-h period at a constant current density of 619 mA cm-2 for the in-house and the state-of-the-art MEAs were 564 mV and 505 mV, respectively. In addition, the influence of substrate and carbon powder type, hydrophobic polymer content in the gas diffusion layer, microporous layer loading, and the through-plane gas permeability of different gas diffusion layers on fuel cell performance were investigated and optimized. Finally, two mathematical models based on the microhardness model developed by Molina et al. [J. Molina, B. A. Hoyos, Electrochim. Acta, 54 (2009) 1784-1790] and Milchev [A. Milchev, “Electrocrystallization: Fundamentals of Nucleation And Growth” 2002, Kluwer Academic Publishers, 189-215] were refined and further developed, one based on pure diffusion control and another based on joint diffusion, ohmic and charge transfer control developed by Milchev [A. Milchev, J. Electroanal. Chem., 312 (1991) 267-275 & A. Milchev, Electrochim. Acta, 37 (12) (1992) 2229-2232]. Experimental results validated the above models and a strong correlation between the microhardness and the particle size of the deposited layer was established.

A novel method based on pulse current electrodeposition (PCE) employing four different waveforms was developed and utilized for fabricating membrane-electrode assemblies (MEAs) with low platinum loading for use in low-temperature proton exchange membrane fuel cells. It was found that both peak deposition current density and duty cycle control the nucleation rate and the growth of platinum crystallites. Based on the combination of parameters used in this study, the optimum conditions for PCE were found to be a peak deposition current density of 400 mA cm-2, a duty cycle of 4%, and a pulse generated and delivered in the microsecond range utilizing a ramp-down waveform. MEAs prepared by PCE using the ramp-down waveform show performance comparable with commercial MEAs that employ ten times the loading of platinum catalyst. The thickness of the pulse electrodeposited catalyst layer is about 5-7 µm, which is ten times thinner than that of commercial state-of-the-art electrodes. MEAs prepared by PCE outperformed commercial MEAs when subjected to a series of steady-state and transient lifetime tests. In steady-state lifetime tests, the average cell voltage over a 3000-h period at a constant current density of 619 mA cm-2 for the in-house and the state-of-the-art MEAs were 564 mV and 505 mV, respectively. In addition, the influence of substrate and carbon powder type, hydrophobic polymer content in the gas diffusion layer, microporous layer loading, and the through-plane gas permeability of different gas diffusion layers on fuel cell performance were investigated and optimized. Finally, two mathematical models based on the microhardness model developed by Molina et al. [J. Molina, B. A. Hoyos, Electrochim. Acta, 54 (2009) 1784-1790] and Milchev [A. Milchev, “Electrocrystallization: Fundamentals of Nucleation And Growth” 2002, Kluwer Academic Publishers, 189-215] were refined and further developed, one based on pure diffusion control and another based on joint diffusion, ohmic and charge transfer control developed by Milchev [A. Milchev, J. Electroanal. Chem., 312 (1991) 267-275 & A. Milchev, Electrochim. Acta, 37 (12) (1992) 2229-2232]. Experimental results validated the above models and a strong correlation between the microhardness and the particle size of the deposited layer was established.

Intensive research on development of alternative low cost, high temperature membranes for proton exchange membrane (PEM) fuel cells is going on because of the well-known limitations of industry standard perfluoro-sulfonic acid (PFSA) membranes. To overcome these limitations such as the decrease in performance at high temperatures (&gt / 80 0C) and high cost, non-fluorinated aromatic hydrocarbon based polymers are attractive. The objective of this study is to develop alternative membranes that possess comparable properties with PFSA membranes at a lower cost. For this purpose post-sulfonation studies of commercially available engineering thermoplastics, polyether-ether ketone (PEEK) and polyether-sulfone (PES), were performed by using suitable sulfonating agents and conditions. Post sulfonated polymers were characterized with proton nuclear magnetic resonance spectroscopy (H+-NMR), sulfur elemental analysis and titration to calculate the degree of sulfonation (DS) values and with TGA and DSC for thermal stability and glass transition temperature (Tg). Chemical stabilities were evaluated by hydrogen v peroxide tests. Proton conductivities of sulfonated PEEK (SPEEK) measured by electrochemical impedance spectroscopy (EIS) were observed to increase linearly with degree of sulfonation (DS). However, above a certain DS SPEEK loses its mechanical stability significantly with excessive swelling which leads to deteriorations in mechanical stability. Therefore, DS of 50-70% were used for the fabrication of composite membranes. To improve mechanical stability, SPEEK polymers were blended with more stable polymers, polyether-sulfone (PES) or in its sulfonated form (SPES) or with polybenzimidazole (PBI). In addition, the composite approach, which involves the incorporation of various inorganic fillers such as zeolite beta, TiO2, montmorrilonite (MMT), heteropolyacids (HPA), was used for further improvement of proton conductivity. Among the composite membranes 20% TPA/SPEEK (DS=68) composites conductivity value exceeded that of Nafion&lsquo / s at room temperature. Effects of various parameters during the fabrication process such as the filler type and loading, DS of sulfonated polymer, casting solvents, and thermal and chemical treatment were also investigated and optimized. Various blend/composite membranes were fabricated with solvent casting method, and characterized for their proton conductivity, chemical/thermal stability and for evaluating their voltage/current performance at various temperatures in a single cell setup. Chemically and thermo-hydrolytically stable composite/blend membranes such as 25% tungstophosphoric acid (TPA)/PBI(5%)/SPEEK (DS=68) with good single cell performances at 800C were developed (~450 mA/cm2 at 0.5 V). The performance of the hydrolytically stable composite/blend membrane prepared with SPEEK (DS=59) / 5% PBI / and 10% TiO2 increased appreciably when the temperature was raised from 80 0C to 90 0C while the performance of Nafion decreases sharply after 80 0C. Methanol permeability studies were also performed for investigating the potential of fabricated blend/composite membranes for direct methanol fuel cell (DMFC) use. Selectivities (conductivity/methanol permeability) vi greater than Nafion 112 (S=7.3x107) for DMFC were observed for composite/blend membranes such as 10% TiO2/10% PES blend with SPEEK (DS=68) with a selectivity of 9.3x107. The factors that affect proton conductivity measurements were investigated and equivalent circuit analysis was performed with results obtained by electrochemical impedance spectroscopy (EIS). The choice of the conductivity cell (electrodes, cell geometry) and the method (2-probe vs 4-probe) were shown to affect the conductivity analysis. A systematic development and characterization route was established and it was shown that by optimizing proton conductivity and thermal/chemical stability with blending/composite approaches it is possible to produce novel high performance proton exchange membranes for fuel cell applications.

The need for sustainable energy use has motivated the exploration of renewable alternative fuels and fuel conversion technology on a global scale. Fuel cells, which convert chemical energy directly into electrical energy with high efficiency and low emissions, provide a promising strategy for achieving energy sustainability. The current progress in fuel cell commercialization is mainly in portable and stationary applications, but fuel cell technology for transportation applications, which make up a substantial portion of the global energy market, have seen little commercial success. Proton exchange membrane fuel cells (PEMFCs) have high potential for addressing the future energy needs of the transportation energy sector. However, one of the prevailing limitations of the PEMFC is the availability of high-performance, cost-effective electrolyte materials. These materials may be realized in the near future by developing multi-functional polymer blends targeted at specific performance capabilities. Due to the near-infinite possibilities of polymer combinations and processing techniques high-throughput polymer characterization techniques are necessary to effectively and systematically screen for optimal materials and relevant structure-property relationships. In this work, a high-throughput mass transport assay (HT-MTA) has been developed to characterize water flux and permeability at multiple sample locations in parallel. The functionality of HT-MTA was evaluated using standard Nafion® films and a model semi-interpenetrated polymer network with commercial polyvinylidine fluoride as the host matrix for a proprietary polyelectrolyte supplied by Arkema, Inc. To further demonstrate the utility of HT-MTA, the instrument was incorporated into the lab's current high-throughput characterization toolset and used to investigate the mechanisms and effects of rapid free radical degradation of Nafion® membranes based on various concentrations of hydrogen peroxide and iron(II) sulfate in solution. The results have been used suggest the effects of these regent components on preferential degradation pathways and will prove to be useful in later simulating the membrane performance during in-situ fuel cell lifetime which is both time-intensive and costly. The high-throughput toolset was also used to develop a novel optimized blend consisting of polyetherimide (PEI), a low-cost high performance resin, and sulfonated PEI (S-PEI) made using a relatively mild post sulfonation reaction with trimethylsilyl chlorosulfonate. The effects of blend composition and thermal annealing on film performance were evaluated and the polymer system was shown to have optimal performance properties that should prove to be useful in other high-performance applications where mechanical strength is critical. In general, this work shows promising results for efficiently developing advanced polymer materials using high-throughput screening techniques.

A new type of fuel cell that combines the advantages of a proton exchange membrane fuel cells and anion exchange membrane fuel cells operated with methanol is demonstrated. Two configurations: one with a high pH anode and low pH cathode (anode hybrid fuel cell (AHFC)),and another with a high pH cathode and a low pH anode (cathode hybrid fuel cell (CHFC)) have been studied in this work. The principle of operation of the hybrid fuel cells were explained. The two different hybrid cell configurations were used in order to study the effect of the electrode fabrication on fuel cell performance. Further, the ionomer content and properties such as the ion exchange capacity and molecular weight were optimized for the best performance. A comparison of the different ionomers with similar properties is carried out in order to obtain the best possible ionomer for the fuel cell. An initial voltage drop was observed at low current density in the AHFC, this was attributed to the alkaline anode and the effect of the ionomers with the new cationic groups were studied on this voltage drop was studied. These ionomers with the different cationic groups were studied in the CHFC design as well. Finally, the use of non platinum catalyst cathode with the CHFC design was also demonstrated for the first time.