One of the major limiting factors in fuel cell production is the time and effort that are required in the ink coating process of the Nafion film that is at the heart of what makes a fuel cell work. The principle reason that this issued has not been tackled by the industry at large is the inherent difficulties that arise. First and foremost is the rapid and extensive expansion of the material upon contact with the liquid ink causing the Nafion film to wrinkle while being processed. In the drive to help mitigate this issue it must be understood by what conditions and severity that wrinkling occurs. The method chosen to detect this was to develop a laser profile scanner to record and output the severity of any wrinkles present in the film. This thesis showcases and explains the laser scanning system designed specifically for this problem and material. / Mechanical Engineering / text

Cette thèse propose une approche de modélisation de la dégradation chimique par attaque radicalaire de la membrane dans les piles à combustibles à membrane électrolyte polymère, ainsi que à son impact sur la dégradation de la performance électrochimique. La membrane considérée dans cette étude est de type perfluorosulfonique, avec une structure dépen-dant fortement de son humidification et conditionnant les propriétés de transport. Afin d'étudier la dégradation de la membrane, il faut dans un premier temps établir un modèle de transport, qui sera utilisé aussi bien dans le modèle de dégradation que par les modèles de performance de cellule déjà existants. Une fois ce modèle établi, nous nous focalisons sur la partie dégradation chimique. Après une compréhension globale des phénomènes physico-chimiques se déroulant lors de la dégradation, une mise en équation détaillée est nécessaire. Même les concepts utilisés sont relativement simples, le besoin de nombreux paramètres nous a contraint à simplifier le modèle sur certains points, notamment le mécanisme de dégradation chimique, tant la complexité du phénomène est un frein à la paramétrisa-tion du modèle. Ce modèle, avec ses simplifications et ses hypothèses, est ensuite validé, aussi bien d'un point de vue performance que d'un point de vue dégradation. Il est pour finir exploité dans différents cas de figures, allant de l'utilisation ininterrompue à courant constant (test purement utilisé en laboratoire) à un cyclage plus représentatif de conditions de fonctionnement réelles. / This thesis proposes a modeling approach of the chemical degradation by radcals attack of the mem-brane in polymer electrolyte membrane fuel cells, as well as its impact on the electrochemical per-formance degradation. The work considers a perfluorosulfonated acid type membrane. Its structure is strongly influenced by humidification, which also impacts the transport properties of mass and charge within the membrane. In order to study the degradation of the membrane, we first established a multi-species transport model for protons, water, and dissolved gases, radicals and ions. We then included detailed chemical reaction mechanisms of hydrogen peroxide formation, hydrogen peroxide decompo-sition, and radical attack of the membrane. Finally, a feedback between degradation, structure, and performance was established. Parameters were identified and the model was validated using literature experimental data both under performance and degradation aspects. The model was then exploited under different conditions, from pure laboratory conditions (constant current kept over a long time) to working conditions which are more representative of the use of a PEMFC for stationary applications (performance cycles).

A 3,4-metilenodioximetanfetamina (MDMA) é a principal substância psicoativa comercializada ilegalmente em comprimidos de ecstasy. O MDMA é uma droga de ação psicotrópica e uso proscrito, conforme lista F (grupo F2) da ANVISA, pois apresenta propriedades alucinógenas e estimulantes e seu uso/abuso pode gerar uma série de danos à saúde dos usuários. O desenvolvimento de eletrodos quimicamente modificados (EQMs) na eletroanalítica tem por finalidade a obtenção de sistemas de detecção mais sensíveis e seletivos para o analito de interesse. Também, considera-se necessário desenvolver novas técnicas e métodos para a detecção de compostos em amostras de interesse forense, a fim de obter ferramentas para auxiliar os cientistas forenses no combate ao comércio ilícito de substâncias. Conforme problemática exposta, este trabalho teve por finalidade o desenvolvimento de eletrodos quimicamente modificados utilizando como modificadores da superfície eletródica de carbono vítreo o Nafion e Nafion/CB[7], utilizando deposição por drop coating e spin coating para a detecção de MDMA através das técnicas de voltametria cíclica e onda quadrada. Conforme o sistema empregado, os melhores EQMs desenvolvidos foram de Nafion (1,5% v/v) e Nafion (1,5% v/v)/CB[7] (10,0 µg.mL-1). Os EQMs desenvolvidos apresentaram limite de detecção e quantificação na faixa de traços e menores que aqueles reportados em outros trabalhos da literatura. Considerando a aplicação dos EQMs para a detecção de MDMA em amostras de ecstasy, verificaram-se as respostas voltamétricas de outras substâncias: cafeína, metanfetamina, teobromina, lidocaína, cloridrato de procaína, (±)-metanfetamina e cloridrato de cocaína. Nas condições experimentais empregadas, observou-se que as substâncias estudadas não atuam como falsos positivos para o MDMA. Paralelamente, obtiveram-se onze lotes de comprimidos de ecstasy (apreendidos e cedidos pela Polícia técnico-científica de Ribeirão Preto-SP) e realizaram-se análises qualitativas e quantitativas nos mesmos, utilizando técnicas colorimétricas (Marquis, Ácido sulfúrico, Simon e Simon com acetona) e cromatográficas (CG-EM E CLAE-EM). Considerando o melhor EQM desenvolvido, quantificaram-se 11 lotes de ecstasy pela técnica voltamétrica e cromatográfica, dentre os lotes estudados, dois não continham MDMA, um apresentou uma mistura de MDMA e cafeína e os demais continham MDMA. A concentração de MDMA presente nos lotes variou de 0 até 61 % em massa. A detecção de MDMA em ecstasy pelo método voltamétrico desenvolvido se mostrou viável e sensível para o analito de interesse. / The 3,4-methylenedioxymethamphetamine (MDMA) is the main psychoactive component of ecstasy tablets, that have an illicit trade. MDMA has been an illicit psychotropic drug, and it has a prohibited use (group F2, in ANVISAs F list), because of its hallucinogenic and stimulating effects, and the use/abuse can poses serials health risks. The development of chemically modified electrodes (CME) in electroanalytical methods aims to get more sensitive and selective systems to detect the analytes. In this context, it is necessary to develop new techniques and methodologies to the detection of illicit samples; it provides more tools to help the forensic scientists to combat the illicit drug trade. So, this work focused in the development of chemically modified electrodes (CMEs) with modifications on the glassy carbon surface by drop coating and spin coating using Nafion and Nafion/CB[7] solutions. The CMEs were tested using cyclic, and square wave voltammetry to detect MDMA. Considering the employed system, the best CMEs were made by Nafion (1.5% v/v), and Nafion (1.5% v/v)/CB[7] (10.0 µg.mL-1) thin films. It was possible to observe better sensitivities for these sensors, in comparison to other MDMA studies reported in the literature. The specificity of the proposed sensors was checked in relation to other drugs: caffeine, methamphetamine, theobromine, lidocaine, procaine hydrochloride, and cocaine hydrochloride. These drugs do not interfere in this voltammetric method. Additionally, we studied eleven lots of ecstasy samples, allowed by the Scientific Police - Ribeirão Preto-SP, and we provide qualitative and quantitative studies using colorimetric techniques (Marquis, Sulfuric acid, Simon, and Simon with acetone), and chromatografic techniques (GC-MS and HPLC-MS). The MDMA quantification in real samples was obtained by high performance liquid chromatography with a mass spectrophotometer, and we compared with the voltammetric technique, using the developed CME. Between the analyzed lots, two of them didnt present in their composition, one lot had a mix of caffeine and MDMA, and another presented MDMA. The MDMAs concentration in lots had a large variation, with 0 to 61 % w/w. The MDMAs voltammetric detection in ecstasy lots was viable. And, it is also possible to apply this methodology to analyze MDMA traces.

Neste trabalho foi estudado o efeito dos parâmetros de síntese na resposta de polarização de híbridos Nafion-SiO2 como eletrólitos em células a combustível poliméricas (PEMFC) em elevadas temperaturas (até 130 °C). A fase inorgânica foi adicionada à matriz polimérica com o objetivo de aumentar a retenção de água na membrana em elevadas temperaturas (acima de 100 °C); melhorar as propriedades mecânicas do Nafion e favorecer cineticamente as reações eletródicas. As membranas foram preparadas a partir da incorporação in-situ de sílica em membranas comerciais de Nafion por rota sol-gel acompanhada de catálise ácida. Os parâmetros de síntese, tais como: concentração do catalisador ácido, natureza do solvente, temperatura e tempo de reação e concentração do precursor de silício (Tetraetil-Ortosilicato TEOS) foram avaliados em função do grau de incorporação e resposta de polarização. Os híbridos Nafion-SiO2 foram física e quimicamente caracterizados por gravimetria, termogravimetria (TG), microscopia eletrônica de varredura e espectroscopia de energia dispersiva de raios X (MEV-EDX), espectroscopia de impedância eletroquímica (EIS) e espalhamento de raios X em baixos ângulos (SAXS). Por fim, os híbridos sintetizados foram avaliados diretamente como eletrólitos em células PEM unitárias alimentadas com hidrogênio (H2) e oxigênio (O2) no intervalo de temperatura de 80 ºC a 130 ºC e a 130 ºC em condições de umidade relativa reduzida (75 e 50%). Resumidamente, o desempenho dos híbridos se mostrou fortemente dependente dos parâmetros de síntese, principalmente, o tipo de álcool utilizado e concentração inicial de TEOS. / In this work, the effect of sol-gel synthesis parameters on the preparation and polarization response of Nafion-SiO2 hybrids as electrolytes for proton exchange membrane fuel cells (PEMFC) operating at high temperatures (130 oC) was evaluated. The inorganic phase was incorporated in a Nafion matrix with the following purposes: to improve the Nafion water uptake at high temperatures (> 100 oC); to increase the mechanical strength of Nafion and; to accelerate the electrode reactions. The hybrids were prepared by an in-situ incorporation of silica into commercial Nafion membranes using an acid-catalyzed sol-gel route. The effects of synthesis parameters, such as catalyst concentration, sol-gel solvent, temperature and time of both hydrolysis and condensation reactions, and silicon precursor concentration (Tetraethylorthosilicate TEOS), were evaluated as a function on the incorporation degree and polarization response. Nafion-SiO2 hybrids were characterized by gravimetry, thermogravimetric analysis (TGA), scanning electron microscopy and X-ray dispersive energy (SEM-EDS), electrochemical impedance spectroscopy (EIS), and X-ray small angle scattering (SAXS). The hybrids were tested as electrolyte in single H2/O2 fuel cells in the temperature range of 80 130 oC and at 130 oC and reduced relative humidity (75% and 50%). Summarily, the hybrid performance showed to be strongly dependent on the synthesis parameters, mainly, the type of alcohol and the TEOS concentration.

The thermally regenerative fuel cell (TRFC) concept that is analyzed is a polymer electrolyte membrane fuel cell (PEMFC), powered by the electro-oxidation of H2 and the electro-reduction of propiophenone. The main products of this fuel cell should be 1-phenyl-1-propanol and electricity. The 1-phenyl-1-propanol should then be converted back to propiophenone, while hydrogen is regenerated by using waste heat and a metal catalyst (Pd/SiO2). The first objective was to find a compatible polymer that would work as either an ionomer/binding agent and as a membrane in the membrane electrode assembly (MEA) of the TRFC. This was achieved by checking the compatibility of each polymer with 1-phenyl-1-propanol and propiophenone (the alcohol-ketone pair). Catalyst coated gas diffusion layers or catalyst coated membranes were made to test the stability of the polymers in the catalyst bed when exposed to the alcohol-ketone pair. If the polymer was compatible with the alcohol-ketone pair, MEAs were constructed using this polymer. The second objective was to test these MEAs inside a H2/propiophenone fuel cell that would prove the concept of our envisioned TRFC. It was found that the only polymer that was stable in the alcohol-ketone pair was mPBI (m-phenylene polybenzimidazole). The mPBI had to be doped with H3PO4 to enable H+ conductivity. Unfortunately, some H3PO4 leached out of the H3PO4-doped mPBI when in the presence of the alcohol-ketone pair. MEAs that were created using H3PO4-doped mPBI were found to work for H2/air and H2/propiophenone fed PEMFCs. The best performance achieved with the H2/propiophenone powered fuel cell was 6.23 μW/cm2. Unfortunately, the presence of the 1-phenyl-1-propanol product could not be proved by EIS or CV on the fuel cell, or by GC-FID of the cathode effluent. Other unknown products were seen in the GC-FID spectrum of the cathode effluent. Therefore, it is possible that the propiophenone did reduce at the cathode but it produced an unknown product. In conclusion, the viability of the proposed TRFC system was not verified. H3PO4 leaching from the MEA makes it impossible to use H3PO4-doped mPBI as the electrolyte in the final version of the MEA in the TRFC system. / Thesis (Master, Chemistry) -- Queen's University, 2013-04-12 17:16:37.724

Além da necessidade do desenvolvimento de novos eletrocatalisadores para aplicação em células à combustível, há também a necessidade da diminuição do crossover, que compromete a eficiência da reação de oxidação do combustível. Sendo assim, foi realizada neste trabalho a dopagem das membranas de Nafion® 117 com nanopartículas de \'PT\' e \'PT\'/\'RU\', em duas concentrações diferentes de platina, pelo método de absorção-redução. Os resultados de Absorção Atômica e a coloração das amostras comprovaram a absorção da solução de precursores metálicos pela membrana. Os dados de FTIR-ATR e DRX mostraram que houve a formação de nanopartículas. Pelos testes em células unitárias (PEMFC, DMFC e DEFC), observou-se que tanto a PEMFC como a DEFC apresentaram uma melhora na eficiência. Apesar de ter havido um ganho significativo de densidade de potência, de até 50%, com membranas dopadas, não foi possível eliminar o crossover. Entretanto, no caso da DEFC, encontrou-se uma alta porcentagem de produtos oxidados com dois átomos de carbono na saída do cátodo. Os principais produtos formados foram acetaldeído e ácido acético, sendo que o ácido acético foi o produto majoritário. Também foram detectados traços de ácido fórmico comprovando que houve, em menor escala, a quebra da ligação C-C. Além disso, os resultados mostraram que a dopagem das membranas de Nafion® parece ter conferido uma melhora na durabilidade das amostras, já que estas, quando comparadas à membrana sem partículas metálicas, alcançaram maiores densidades de correntes. Finalmente, a dopagem da membrana e a elevação de temperatura provocaram um melhor desempenho nas DEFCs testadas. / Beyond the necessity of the development of new electrocatalysts for fuel cell application, there is also the necessity of diminishing of the crossover that compromises the oxidation efficiency of the fuel. So, in this work was carried out the doping of the Nafion® 117 membranes with \'PT\' and \'PT\'/\'RU\' nanoparticles in two different platinum concentrations by using the absorption-reduction method. The Atomic Absorption results and the color of the samples proved that the absorption of the metallic precursor solutions by the membrane happened. FTIR-ATR and XRD data showed the formation of nanoparticles. It was observed that in unitary fuel cells (PEMFC, DMFC and DEFC) tests the PEMFC and DEFC showed an improvement in the efficiency. Although a significant increase in the power density, up to 50 % by using doped membranes, it was not possible to eliminate the crossover. However, in the case of the DEFC, a high percentage of oxidized products with two carbon atoms was found in the cathode exit. The main formed products were acetaldehyde and acetic acid, being the acetic acid the majority product. Traces of formic was also detected demonstrating that, in lesser scale, the break of the C-C bond is feasible. Moreover, the results showed that the durability of the doped Nafion® membranes is higher than the membrane without metallic particles, since bigger current densities were reached in the former case. Finally, the membrane doping and the temperature rise led the DEFC to the best performance.

Direct methanol fuel cell (DMFC) is considered as a highly promising power source. It is based on polymer electrolytes membrane (PEM) fuel cell technology. It posses a number of advantages such as a liquid fuel, quick refueling, low cost of methanol and the compact cell, design making it suitable for various potential applications including stationary and portable applications. DMFCs are also environmentally friendly. Although carbon dioxide is produced, there is no production of sulfur or nitrogen oxides. The development of commercial DMFCs has nevertheless been hindered by some important issues. The most important are the low power density caused by the slow electrochemical methanol oxidation at the anode and methanol crossover through PEM, which is responsible for inhibiting the activity of the cathode catalyst as well. With the eventual goal of improving the overall performance of the DMFC, this study has been concerned with an investigation of the issues and effect of various parameters on its performance. First of all, the electrode preparation methodology and the effect of the catalyst were investigated. The most efficient membrane electrode assembly (MEA) was prepared with Pt/Ru black at anode and Pt black cathode on either side of a Nafion 117 membrane. Performance was however limited by current oscillations observed at low cell voltage and high current density attributed to carbon dioxide removal. Consequently, the effect of flow rate was investigated. Higher flow rates eliminated these oscillations. Then attention was focused on the management of the two-phase flow that occurs in the diffusion layer of the electrode as well as in the anode bipolar plate flow channels. Removal of carbon dioxide formed during methanol oxidation was thus found to be an important issue in DMFC. There is a competition between methanol diffusion to the catalyst layer and CO2 removal in the opposite direction. The two fluxes needed to be balanced in order to optimize performance. To accomplish this, the ratio of hydrophilic and hydrophobic pores respectively formed in the catalytic layer by Nafion and PTFE (Teflon) was altered. It also had an effect on crossover. The effect of a barrier layer was investigated to reduce crossover. Finally, zirconia and silica nano-composite membranes were tested instead of Nafion and found to reduce crossover. Developing a good understanding of what happens on the catalyst surface is important to develop a strategy on how improve DMFC performance. Thus is why a dynamic model based on a simplified mechanism for methanol electro-oxidation reaction was developed. It shows, amongst other insights, how the intermediate species coverage evolves with time. The mechanism was however too simple to provide an idea of which poisoning species are formed on the catalyst surface. A more exhaustive mechanism is thus being developed using Reaction Route analysis.

Direct methanol fuel cell (DMFC) is considered as a highly promising power source. It is based on polymer electrolytes membrane (PEM) fuel cell technology. It posses a number of advantages such as a liquid fuel, quick refueling, low cost of methanol and the compact cell, design making it suitable for various potential applications including stationary and portable applications. DMFCs are also environmentally friendly. Although carbon dioxide is produced, there is no production of sulfur or nitrogen oxides. The development of commercial DMFCs has nevertheless been hindered by some important issues. The most important are the low power density caused by the slow electrochemical methanol oxidation at the anode and methanol crossover through PEM, which is responsible for inhibiting the activity of the cathode catalyst as well. With the eventual goal of improving the overall performance of the DMFC, this study has been concerned with an investigation of the issues and effect of various parameters on its performance. First of all, the electrode preparation methodology and the effect of the catalyst were investigated. The most efficient membrane electrode assembly (MEA) was prepared with Pt/Ru black at anode and Pt black cathode on either side of a Nafion 117 membrane. Performance was however limited by current oscillations observed at low cell voltage and high current density attributed to carbon dioxide removal. Consequently, the effect of flow rate was investigated. Higher flow rates eliminated these oscillations. Then attention was focused on the management of the two-phase flow that occurs in the diffusion layer of the electrode as well as in the anode bipolar plate flow channels. Removal of carbon dioxide formed during methanol oxidation was thus found to be an important issue in DMFC. There is a competition between methanol diffusion to the catalyst layer and CO2 removal in the opposite direction. The two fluxes needed to be balanced in order to optimize performance. To accomplish this, the ratio of hydrophilic and hydrophobic pores respectively formed in the catalytic layer by Nafion and PTFE (Teflon) was altered. It also had an effect on crossover. The effect of a barrier layer was investigated to reduce crossover. Finally, zirconia and silica nano-composite membranes were tested instead of Nafion and found to reduce crossover. Developing a good understanding of what happens on the catalyst surface is important to develop a strategy on how improve DMFC performance. Thus is why a dynamic model based on a simplified mechanism for methanol electro-oxidation reaction was developed. It shows, amongst other insights, how the intermediate species coverage evolves with time. The mechanism was however too simple to provide an idea of which poisoning species are formed on the catalyst surface. A more exhaustive mechanism is thus being developed using Reaction Route analysis.

For fuel cells to become commercially viable in a wider range of applications, the amount of catalyst must be reduced. One crucial area of the fuel cell assembly is the anode and cathode; these layers allow fuel and exhaust gases to diffuse, provide conduction paths for both protons and electrons, and house sites for electrocataytic reactions. Despite their multi-functionality and importance, these layers have received little attention in the way of engineering design. While Nafion and catalyst loading has been studied, the electrode layer is still considered a two-dimensional structure. By understanding the current electrode limitations, available materials, and interactions at the sites reaction sites, an intelligent, deliberate design of the anode and cathode layer can be undertaken. A three-dimensional, fibrous mat of continuous, networked proton-conducting fibers can decrease mass diffusion limitations while maintaining proton conductivity. Nafion can be formed into these types of fibers via the fabrication technique of electrospinning. By forcing a solution of Nafion, solvent, and carrier polymer through a small nozzle under high electric voltage, the polymer can be extruded into fibers with nanometer-scale diameters. The ability to control the fiber morphology lies with solution, environmental and equipment properties. In order to successfully fabricate Nafion nanofibers, we looked to both existing methodologies as well as mathematical models to try to predict behavior and fabricate our own nanofibers. Once fabricated, these mats are assembled in a membrane-electrode assembly and tested with both methanol and hydrogen as fuel, with performance compared against known data for conventional MEAs. We have been able to successfully electrospin Nafion® nanofibers continuously, creating fiber mats with fiber diameters near 400nm as verified by SEM. These mats were tested in a direct methanol fuel cell (DMFC) application as cathodes, and showed improved performance with a dilute methanol feed compared to conventional MEAs with equivalent Nafion and catalyst loading. An MEA fabricated with twin electrospun electrodes was compared against an equivalent conventional MEA, showing the same performance enhancement using a dilute methanol fuel.

Direct methanol fuel cells (DMFCs) are considered a clean source of electrical power for future energy demand, creating a potential to reduce our dependency on fossil fuels. Despite their advantages, including high energy density, efficiency and easy handling and distribution of fuel, the commercialization of DMFCs has suffered from some drawbacks, including methanol crossover and contamination of the system. Metal cation contaminants (such as Ni, Co, etc) introduced through the degradation of fuel cell components (bipolar plate and electro-catalyst layer) can significantly affect the Nafion-membrane properties and overall fuel cell performance. In the current study, a systematic approach is taken to characterize and identify the mechanism of the effect of metal solution contaminants on the activities of electro-catalysts of DMFCs. Cyclic voltammetry and rotating disk electrode (RDE) techniques were utilized in order to characterize the effect of various concentrations (i.e., 2x10-x M (x=1-7)) of six metal solution contaminants (i.e., Co, Ni and Zn with sulfate and nitrate as counter-anions) on the voltammetric properties and electro-catalytic activity of polycrystalline Pt during methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). The results showed a decrease in the MOR and ORR activities of Pt as the concentration of metal solution increased. The effect of counter-anion on the Pt activity was further investigated. The results showed that a combined effect of counter-anions and metal cations may be responsible for the decrease in the electro-catalytic activity of Pt. The effect of metal solution contaminants on the Nafion-ionomer of anode electro-catalysts was investigated using Nafion-coated Pt electrode. Voltammetric properties and MOR activities of Nafion-coated and bare Pt electrodes in the presence of Ni solution contaminants were characterized using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The overall results showed a significant negative effect of Ni solution contaminants on the electro-catalytic activity of bare Pt electrode as compared to the Nafion-coated Pt electrode. Based on the results, it appears that Nafion-ionomer film may interact with metal cations (through its sulfonate groups) and repel them away from the Pt active sites, partially inhibiting the negative effect of metal cations on the Pt activity of Nafion-coated Pt electrode. The effect of metal solution contaminants on the carbon-supported platinum nanoparticle (Pt/C) with various Nafion-ionomer distributions and contents (i.e., Nafion-incorporated Pt/C and Nafion-coated Pt/C electrodes) was further investigated. Cyclic voltammetry and EIS techniques were employed to characterize the effect of Ni solution contaminants on the voltammetric properties and MOR activities of Nafion-incorporated and Nafion-coated Pt/C electrodes. The overall results showed a stronger negative effect of Ni solution contaminants on the electro-catalytic activity of Nafion-incorporated Pt/C electrodes as compared to the Nafion-coated Pt/C electrodes. This further confirms previous observations showing the sulfonate groups of Nafion-ionomer film may attract the Ni metal cations, localize them away from the Pt active sites, and subsequently suppress the negative effect of cations on the activity of Nafion-coated Pt/C electrodes.