Cette étude concerne l’élaboration et la caractérisation de membranes composites de piles àcombustible PEMFC. Ces nouveaux composites associent un ionomère commercial leNafion® à des charges acides minérales qui sont des acides phosphoantimoniques. Descharges mono et triacides, H1 et H3, ont été utilisées à des taux massiques compris entre 5 et20%. Outre, leur contribution à la conduction protonique et à l’hydratation, les 2 chargesaméliorent sensiblement, même à faible taux, la tenue thermomécanique des membranes. Cerenforcement permet de diminuer l’épaisseur des membranes et donc la chute ohmique. Lestests en pile, réalisés dans une large gamme d’hydratation des gaz et de température,démontrent l’apport incontestable des charges, les membranes composites étant sensiblementplus performantes dès lors que la température de fonctionnement atteint ou dépasse 80°C. / This study deals with the elaboration and characterization of composite membranes intendedto be used in PEMFC. These new composites combine a commercial ionomer, Nafion®, withinorganic acidic fillers that are phosphatoantimonic acids. Mono and triacid fillers, H1 and H3, have been used at 5 to 20wt% contents. Besides, their contribution to proton conductionand hydration, both fillers markedly improve, even at low content, the thermomechanicalperformances of the membranes. This reinforcement allows the thickness and, therefore, theohmic drop to be decreased. The MEA tests, performed in a wide range of gas humidificationand temperature, indisputably demonstrate the benefic effect of the fillers; Compositemembranes performing significantly better as soon as the operating temperature reaches orexceed 80°C.

Ces travaux de thèse portent sur l'optimisation des méthodes de fabrication des assemblages membrane électrodes des Piles à Membrane Echangeuse de Protons (PEMFC, Proton Exchange Membrane Fuel Cell). Ils ont pour objectif d'optimiser le dépôt des couches catalytiques sur la membrane par une méthode de transfert. Le procédé a été utilisé pour fabriquer d'une part des assemblages à membrane Nafion® pour les piles à combustible à membrane fonctionnant à 80 °C (PEMFC) et d'autre part des assemblages à membrane polybenzimidazole dopée en acide phosphorique pour les PEMFC à haute température (160 °C). Au cours de cette étude, la détermination précise de la quantité de platine a été rendue possible par des mesures non destructives en fluorescence X. Nous avons développé également une méthode originale de fabrication de suspensions de blendes Nafion-PBI qui ont été incorporées dans les électrodes des assemblages à membrane PBI. L'effet de la composition, des épaisseurs et du mode de préparation des électrodes sur les performances des assemblages a été discuté. Les assemblages membrane électrodes à membrane PBI ont été caractérisés par des mesures en polarisation et en spectroscopie d'impédance (EIS). La détermination de surface active d'électrode a été réalisée par des mesures en voltammétrie cyclique in-situ (CV). La mise au point du procédé de fabrication des électrodes par transfert de couches actives sur membrane a permis d'obtenir des informations importantes sur les conditions de préparation des électrodes. Les performances des assemblages à membrane Nafion® sont supérieures à celles obtenues sur des assemblages de référence avec des électrodes supportées sur couche de diffusion (GDE). Il a été possible de réaliser pour la première fois des assemblages avec un dépôt sur des membranes polybenzimidazole déjà dopées en acide, les premiers résultats obtenus sont extrêmement encourageants. Le procédé de transfert des couches catalytiques pourrait être adapté pour réaliser des dépôts sur d'autres variétés de membranes dopées ou non dopées en acide. / This work concerns the optimization of the fabrication processes of membrane electrode assemblies for the Proton Exchange Membrane Fuel Cell (PEMFC). The objective is to carry out the deposition of catalyst layers onto the membranes by a transfer process. The optimization of the catalyst layer compositions and its morphology is crucial for this process. Assemblies with Nafion® membranes for PEMFC working at 80 °C and phosphoric acid doped polybenzimidazole membranes for HTPEMFC (160 °C) have been prepared by this method. X-ray fluorescence spectrometry, due to its non destructive nature, was applied for precise analysis of platinum loading on the electrodes. In this work, a new method was also developed for the preparation of Nafion-PBI blend suspensions that have been incorporated in the electrodes of the PBI membrane electrodes assemblies. The PBI membrane electrode assemblies have been characterized by polarization measurements and electrochemical impedance spectroscopy (EIS). The in situ PEM Fuel Cell electrochemical surface area (ECSA) has been determined by cyclic voltammétrie measurements. The performances of Nafion membrane assemblies are higher than those obtained on reference assemblies, with gas diffusion layer supported electrodes. Promising results have been obtained on the assemblies performed for the first time with acid doped PBI membranes. The transfer process of the catalyst layer can also be used on other types of membrane.

Dans cette thèse, les membranes perfluorosulfoniques (PFSA) et les polymères aromatiques sulfonés (SAP) sont étudiés en vue d'une meilleure compréhension de leurs propriétés thermodynamiques, d'hydratation, mècaniques et électriques.Concernant les PFSA: 1) Préparation de membranes Nafion ayant diverses morphologies et structures (amorphe, semi-cristalline, stratifiée) et relation avec les propriétés, comme la transition vitreuse, la fusion, la conductivité protonique. 2) Divers traitements de recuit ont été appliqués et analysés par une nouvelle méthode quantitative appelé INCA (Ionomère nc analyse), utilisant aussi des agents de recuit spéciaux. Concernant les SAP: 1) Synthèse in situ de polymères réticulés et clarification du mécanisme. 2) Optimisation du degré de reticulation en vue de la meilleure conductivité protonique. 3) Obtention d'ionomères conducteurs cationiques par échange de cations du SPEEK et détermination des propriétés de ces nouveaux ionomères. / In this thesis, perfluorosulfonic acid membranes (PFSA) and sulfonated aromatic polymers (SAP) are studied to better understandtheir thermodynamic, hydration, mechanical and electrical properties. The following main points were addressed:Regarding PFSA:1) Nafion membranes with various morphology and microstructure (amorphous, semi-crystalline, layered) were prepared and the relation to the properties, such as glass and melting transitions, and proton conductivity, was established.2) Various annealing treatments were performed and analyzed by the quantitative INCA (Ionomer nc Analysis) method using also special annealing agents. Regarding SAP:1) The in situ synthesis of cross-linked polymers was studied and the mechanism was clarified. 2) The degree of cross-linking was optimized for best proton conductivity.3) Cation-conducting ionomers were obtained by cation exchange of SPEEK and the properties of these new ionomers were determined.

O Nafion é um ionômero constituído por uma matriz de politetrafluoroetileno (PTFE) contendo ramificações laterais terminadas em grupos sulfônicos. Neste trabalho, a membrana na forma ácida e nas formas salinas (Li+, Na+, K+, Rb+ e Cs+) foram analisadas, via espectroscopia vibracional e análise térmica. Para proceder à análise vibracional, dividiu-se o ionômero em três grupos, cada qual pertencente a um grupo pontual distinto: o grupo sultanato (C3v) ; o grupo éter (C2v) e a matriz fluorocarbônica D(14π/15). O grupo sulfonato apresenta modos vibracionais de estiramento simétrico (1060 cm-1) e de estiramento degenerado (na região de 1300 cm-1). O Nafion apresenta dois grupos éter, os quais deram origem no espectro a duas bandas: uma em 984 e outra na região de 970 cm-1. Verificou-se que apenas a banda em 970 cm-1 sofre uma influência mais direta do ambiente iônico. A atribuição das bandas da matriz polimérica foi feita considerando-se que a cadeia de PTFE apresenta estrutura helicoidal (157) . Nesta estrutura são previstas a existência de quatro espécies de simetria que apresentam atividade nos espectro Raman e infravermelho. No Raman são ativos os modos de espécie A1, E1 e E2 e no infravermelho são ativos os modos de espécie A2 e E1. A análise térmica dividiu-se em: termogravimetria e calorimetria exploratória diferencial. A termogravimetria mostrou que a membrana na forma ácida apresenta um padrão de decomposição distinto das membranas nas formas salinas. A calorimetria exploratória diferencial mostrou que a membrana na forma ácida apresenta três eventos endotérmicos: em 134ºC, em 250ºC e o último em 325ºC. Na membrana nas formas salinas apenas o primeiro pico endotérmico é bastante evidente, o segundo pico é pouco pronunciado e o terceiro está completamente ausente. / Nafion is an ionomer that consists of a polytetrafluoroethylene (PTFE) backbone with side chains terminated with a sulfonate group. In this work, Nafion in acid and saline forms (Li+, Na+, K+, Rb+ e Cs+) forms were investigated by vibrational spectroscopy, thermogravimetry and differential scanning calorimetry. To proceed to the vibrational analysis the ionômero was splitted into three regions and which one has its own symmetry group. Sulfonate group (C3v), ether group (C2v) and the polymeric matrix D(14π/15). The sulfonate group presents two modes: the symmetric stretching (1060 cm-1) and the degenerated stretching (around 1300 cm-1). Nafion has two ether groups which originated two bands: one in 984 and the other in 970 cm-1. We verify that only the band in 970 cm-1 is affected by the ionic ambient. The assignment of the polymeric band was made considering that the PTFE has helicoidal structure (157). In this structure four symmetry species are predicted. In Raman spectra the following species are active: A1, E1 and E2 and the infrared are active the species: A2 and E1. Thermal analysis consisted of thermogravimetry and differential scanning calorimetry. Thermogravimetry shows that water content is dependent of cation change. Thermogravimetry also shows that the membrane in the acid and saline forms have different mechanisms of decomposition. Differential scanning calorimetry of Nafion-H shows three endothermic peaks: the first in 134ºC, the second in 250ºC and the last in 325ºC. Nafion saline forms shows only the first peak.

O alto custo da produção de hidrogênio puro para ser usado como combustível para uma reação de oxidação de hidrogênio (ROH) em células a combustível faz com que seja atrativo o uso de hidrogênio gerado através da reforma de combustíveis fóssil. Entretanto, o hidrogênio gerado por reforma de outros combustíveis possui contaminantes como CO, que por se adsorver fortemente sobre a superfície do eletrodo de platina, prejudica em muito o processo de oxidação do hidrogênio. Assim o estudo de novos catalisadores mais resistentes a essa contaminação e de outros mecanismos que contribuam para um melhor desempenha de uma célula a combustível do tipo PEMFC, se faz necessário. Esse presente trabalho tem como objetivo o estudo dos catalisadores PtMo/C - 80:20, PtMoO2/C, PtMoO3/C, que foram sintetizados, e PtMoPtRu/C, PtMoPt3Fe/C e PtMoPt3FePtRu/C que foram obtidos através da mistura do PtMo/C - 80:20 sintetizado com os PtRu/C e PtFe/C que são comerciais, através da realização de curvas de polarização no estado estacionário, voltametrias cíclicas e degradação eletroquímica acelerada. Também foi avaliada a eficiência da membrana de Aquivion®, com relação ao cruzamento de subprodutos da degradação dos eletrodos, através de curvas de polarização no estado estacionário, voltametrias cíclicas e variação de temperatura de operação da célula PEMFC. O método usado para a síntese dos eletrocatalisadores se mostrou eficiente na obtenção dos catalisadores, obtendo-se os catalisadores com proporção bem próxima da desejada. Os resultados mostraram uma grande estabilidade química dos catalisadores mistos sendo o PtMoPt3FePtRu/C o mais estável e o PtMoPtRu/C o catalisador mais ativo para uma ROH. Os experimentos com a membrana de Aquivion® mostraram que essa é capaz de diminuir o cruzamento de subprodutos da degradação dos eletrodos. / The high cost of pure hydrogen production to be used as fuel for a hydrogen oxidation reaction (HOR) in fuel cells makes it attractive to use hydrogen generated by reforming of fossil fuels. However, the hydrogen generated by reforming other fuels has contaminants such as CO, which adsorb strongly on the surface of the platinum electrode, affect much the hydrogen oxidation process. Thus the study of new catalysts more resistant to such contamination and other mechanisms that contribute to a better performs of a fuel cell of the PEMFC type, it is necessary. This present study aims to study of catalysts PtMo/C - 80:20 PtMoO2/C, PtMoO3/C, which were synthesized and PtMoPtRu/C, PtMoPt3Fe/C and PtMoPt3FePtRu/C which were obtained by mixing the PtMo/C - 80:20 synthesized with PtRu/C and PtFe/C which are commercial, by performing polarization curves at steady state, cyclic voltammetry and electrochemical degradation accelerated. It also evaluated the efficiency of Aquivion® membrane with respect to the cross-products of degradation of the electrodes by means of polarization curves at steady state, cyclic voltammetry and operating temperature range of the cell PEMFC. The method used for the synthesis of electrocatalysts proved efficient in obtaining the catalysts, the catalysts obtaining very near to the desired proportion. The results showed a great chemical stability of the mixed catalyst being PtMoPt3FePtRu/C more stable and PtMoPtRu/C as catalyst more active for HOR. Experiments with Aquivion® membrane have shown that this can reduce the cross-products of degradation of the electrodes.

O alto custo da produção de hidrogênio puro para ser usado como combustível para uma reação de oxidação de hidrogênio (ROH) em células a combustível faz com que seja atrativo o uso de hidrogênio gerado através da reforma de combustíveis fóssil. Entretanto, o hidrogênio gerado por reforma de outros combustíveis possui contaminantes como CO, que por se adsorver fortemente sobre a superfície do eletrodo de platina, prejudica em muito o processo de oxidação do hidrogênio. Assim o estudo de novos catalisadores mais resistentes a essa contaminação e de outros mecanismos que contribuam para um melhor desempenha de uma célula a combustível do tipo PEMFC, se faz necessário. Esse presente trabalho tem como objetivo o estudo dos catalisadores PtMo/C - 80:20, PtMoO2/C, PtMoO3/C, que foram sintetizados, e PtMoPtRu/C, PtMoPt3Fe/C e PtMoPt3FePtRu/C que foram obtidos através da mistura do PtMo/C - 80:20 sintetizado com os PtRu/C e PtFe/C que são comerciais, através da realização de curvas de polarização no estado estacionário, voltametrias cíclicas e degradação eletroquímica acelerada. Também foi avaliada a eficiência da membrana de Aquivion®, com relação ao cruzamento de subprodutos da degradação dos eletrodos, através de curvas de polarização no estado estacionário, voltametrias cíclicas e variação de temperatura de operação da célula PEMFC. O método usado para a síntese dos eletrocatalisadores se mostrou eficiente na obtenção dos catalisadores, obtendo-se os catalisadores com proporção bem próxima da desejada. Os resultados mostraram uma grande estabilidade química dos catalisadores mistos sendo o PtMoPt3FePtRu/C o mais estável e o PtMoPtRu/C o catalisador mais ativo para uma ROH. Os experimentos com a membrana de Aquivion® mostraram que essa é capaz de diminuir o cruzamento de subprodutos da degradação dos eletrodos. / The high cost of pure hydrogen production to be used as fuel for a hydrogen oxidation reaction (HOR) in fuel cells makes it attractive to use hydrogen generated by reforming of fossil fuels. However, the hydrogen generated by reforming other fuels has contaminants such as CO, which adsorb strongly on the surface of the platinum electrode, affect much the hydrogen oxidation process. Thus the study of new catalysts more resistant to such contamination and other mechanisms that contribute to a better performs of a fuel cell of the PEMFC type, it is necessary. This present study aims to study of catalysts PtMo/C - 80:20 PtMoO2/C, PtMoO3/C, which were synthesized and PtMoPtRu/C, PtMoPt3Fe/C and PtMoPt3FePtRu/C which were obtained by mixing the PtMo/C - 80:20 synthesized with PtRu/C and PtFe/C which are commercial, by performing polarization curves at steady state, cyclic voltammetry and electrochemical degradation accelerated. It also evaluated the efficiency of Aquivion® membrane with respect to the cross-products of degradation of the electrodes by means of polarization curves at steady state, cyclic voltammetry and operating temperature range of the cell PEMFC. The method used for the synthesis of electrocatalysts proved efficient in obtaining the catalysts, the catalysts obtaining very near to the desired proportion. The results showed a great chemical stability of the mixed catalyst being PtMoPt3FePtRu/C more stable and PtMoPtRu/C as catalyst more active for HOR. Experiments with Aquivion® membrane have shown that this can reduce the cross-products of degradation of the electrodes.

O Nafion é um ionômero constituído por uma matriz de politetrafluoroetileno (PTFE) contendo ramificações laterais terminadas em grupos sulfônicos. Neste trabalho, a membrana na forma ácida e nas formas salinas (Li+, Na+, K+, Rb+ e Cs+) foram analisadas, via espectroscopia vibracional e análise térmica. Para proceder à análise vibracional, dividiu-se o ionômero em três grupos, cada qual pertencente a um grupo pontual distinto: o grupo sultanato (C3v) ; o grupo éter (C2v) e a matriz fluorocarbônica D(14π/15). O grupo sulfonato apresenta modos vibracionais de estiramento simétrico (1060 cm-1) e de estiramento degenerado (na região de 1300 cm-1). O Nafion apresenta dois grupos éter, os quais deram origem no espectro a duas bandas: uma em 984 e outra na região de 970 cm-1. Verificou-se que apenas a banda em 970 cm-1 sofre uma influência mais direta do ambiente iônico. A atribuição das bandas da matriz polimérica foi feita considerando-se que a cadeia de PTFE apresenta estrutura helicoidal (157) . Nesta estrutura são previstas a existência de quatro espécies de simetria que apresentam atividade nos espectro Raman e infravermelho. No Raman são ativos os modos de espécie A1, E1 e E2 e no infravermelho são ativos os modos de espécie A2 e E1. A análise térmica dividiu-se em: termogravimetria e calorimetria exploratória diferencial. A termogravimetria mostrou que a membrana na forma ácida apresenta um padrão de decomposição distinto das membranas nas formas salinas. A calorimetria exploratória diferencial mostrou que a membrana na forma ácida apresenta três eventos endotérmicos: em 134ºC, em 250ºC e o último em 325ºC. Na membrana nas formas salinas apenas o primeiro pico endotérmico é bastante evidente, o segundo pico é pouco pronunciado e o terceiro está completamente ausente. / Nafion is an ionomer that consists of a polytetrafluoroethylene (PTFE) backbone with side chains terminated with a sulfonate group. In this work, Nafion in acid and saline forms (Li+, Na+, K+, Rb+ e Cs+) forms were investigated by vibrational spectroscopy, thermogravimetry and differential scanning calorimetry. To proceed to the vibrational analysis the ionômero was splitted into three regions and which one has its own symmetry group. Sulfonate group (C3v), ether group (C2v) and the polymeric matrix D(14π/15). The sulfonate group presents two modes: the symmetric stretching (1060 cm-1) and the degenerated stretching (around 1300 cm-1). Nafion has two ether groups which originated two bands: one in 984 and the other in 970 cm-1. We verify that only the band in 970 cm-1 is affected by the ionic ambient. The assignment of the polymeric band was made considering that the PTFE has helicoidal structure (157). In this structure four symmetry species are predicted. In Raman spectra the following species are active: A1, E1 and E2 and the infrared are active the species: A2 and E1. Thermal analysis consisted of thermogravimetry and differential scanning calorimetry. Thermogravimetry shows that water content is dependent of cation change. Thermogravimetry also shows that the membrane in the acid and saline forms have different mechanisms of decomposition. Differential scanning calorimetry of Nafion-H shows three endothermic peaks: the first in 134ºC, the second in 250ºC and the last in 325ºC. Nafion saline forms shows only the first peak.

In light of the world‟s growing demand for energy that is environmentally friendly and sustainable, energy sources such as hydrogen have been considered potential contenders. Hydrogen, which can be used for energy storage, can be produced efficiently by the membrane based Hybrid Sulfur (HyS) thermo-chemical process consisting of a decomposition and an electrolysis step. During the HyS electrolysis step, SO2 and H2O are converted to H2 and H2SO4, which implies that the proton exchange membranes (PEMs) to be used for this process should have a high proton conductivity, limited SO2 cross-over and good H2SO4 stability. In order to find alternatives to the costly and high-temperature unstable Nafion®, the aim of this study was to evaluate the H2SO4 stability of various novel membranes. To structure the study, the novel PEM materials were grouped according to the PBI-type base component within the blend membranes, resulting in three groups comprising non-PBI based membranes, PBIOO based membranes and F6-PBI based membranes. Nafion®212 was included as reference PEM. By repeating the H2SO4 treatment with three different Nafion®212 samples, the obtained Nafion® data was also used to determine the experimental and analytical error margins for the study. The stability of all membranes was determined by submerging the membrane samples in 80 wt% H2SO4 at 80 °C for 120 hours. To determine the influence of the acid on the membranes, all samples were characterised before and after the H2SO4 treatment and compared in terms of their acid stability. Physical characterisation of the PEMs included the evaluation of weight and thickness changes, while IEC, SEM-EDX, FTIR and TGA were used to elucidate possible chemical changes due to the H2SO4 treatment. According to the Nafion®212 data, which had been obtained in triplicate for each of the analytical techniques, the experimental error of both the analytical and H2SO4 treatment remained below 10 %, except for the SEM-EDX sulfur-content where significantly larger errors were observed. In spite of the high error margins of the SEM-EDX data (S-content), its results, combined with the results from the other analytical techniques, resulted in a better understanding (both physical and chemical) of the effect the H2SO4 had on the membrane. This further facilitated the evaluation and comparison of the various blended PEM materials in terms of their H2SO4 stability, and the subsequent relation obtained between the observed stability and the chemical constitution and cross-linking of the membranes. After the 80 wt% H2SO4 treatment, significant weight losses were reported for the non-PBI based and PBIOO based membrane groups in comparison with the minimal changes noted for the F6-PBI based group and Nafion®212. Furthermore, significant thickness changes were reported for most of the PBIOO based membranes. The small weight and thickness changes observed for the F6-PBI confirmed the improved stability of this group of membranes in an H2SO4 environment, most likely due to the protective role of the partially fluorinated basic polymer and the known strength of the C-F bonds present. The results showed a clear correlation between the H2SO4 stability and the specific polymers present in the PEM blends investigated. Specific effects found included sulfonation, salt formation, hydrolysis and the accompanied dissolution of membrane fragments. Significant physical changes, for example ascribed to sulfonation of the concerned polymers, were supported by increased IEC measurements and peak intensities of the FTIR spectra, corresponding to the additional –SO3H groups present, while a variation in TGA signals served to further support the altered membrane composition and structure due to the H2SO4 treatment. In the case of dissolution, the corresponding chemical changes (analytical techniques) were supported by the decreased peak intensities of FTIR spectra, IEC measurements and TGA signals associated with degradation of the polymer backbone. It was shown that the stability of the blended membranes depended on the composition (blend components) of the membrane and the effective cross-linking (interaction) between the blend components. For all three groups examined, it became apparent that blend components sFS and sPSU were, for example, more stable than sPEEK and that ionical cross-linking seemed more effective than covalent cross-linking of blend components. When considering all membranes tested, the non-PBI based blend membranes consisting of (s)PSU and PFS copolymers in the presence of fluorinated cross-linkers and the PBIOO-sPSU blended membranes including most of the F6-PBI based membranes showed sufficient stability to be recommended for SO2 electrolysis. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

In light of the world‟s growing demand for energy that is environmentally friendly and sustainable, energy sources such as hydrogen have been considered potential contenders. Hydrogen, which can be used for energy storage, can be produced efficiently by the membrane based Hybrid Sulfur (HyS) thermo-chemical process consisting of a decomposition and an electrolysis step. During the HyS electrolysis step, SO2 and H2O are converted to H2 and H2SO4, which implies that the proton exchange membranes (PEMs) to be used for this process should have a high proton conductivity, limited SO2 cross-over and good H2SO4 stability. In order to find alternatives to the costly and high-temperature unstable Nafion®, the aim of this study was to evaluate the H2SO4 stability of various novel membranes. To structure the study, the novel PEM materials were grouped according to the PBI-type base component within the blend membranes, resulting in three groups comprising non-PBI based membranes, PBIOO based membranes and F6-PBI based membranes. Nafion®212 was included as reference PEM. By repeating the H2SO4 treatment with three different Nafion®212 samples, the obtained Nafion® data was also used to determine the experimental and analytical error margins for the study. The stability of all membranes was determined by submerging the membrane samples in 80 wt% H2SO4 at 80 °C for 120 hours. To determine the influence of the acid on the membranes, all samples were characterised before and after the H2SO4 treatment and compared in terms of their acid stability. Physical characterisation of the PEMs included the evaluation of weight and thickness changes, while IEC, SEM-EDX, FTIR and TGA were used to elucidate possible chemical changes due to the H2SO4 treatment. According to the Nafion®212 data, which had been obtained in triplicate for each of the analytical techniques, the experimental error of both the analytical and H2SO4 treatment remained below 10 %, except for the SEM-EDX sulfur-content where significantly larger errors were observed. In spite of the high error margins of the SEM-EDX data (S-content), its results, combined with the results from the other analytical techniques, resulted in a better understanding (both physical and chemical) of the effect the H2SO4 had on the membrane. This further facilitated the evaluation and comparison of the various blended PEM materials in terms of their H2SO4 stability, and the subsequent relation obtained between the observed stability and the chemical constitution and cross-linking of the membranes. After the 80 wt% H2SO4 treatment, significant weight losses were reported for the non-PBI based and PBIOO based membrane groups in comparison with the minimal changes noted for the F6-PBI based group and Nafion®212. Furthermore, significant thickness changes were reported for most of the PBIOO based membranes. The small weight and thickness changes observed for the F6-PBI confirmed the improved stability of this group of membranes in an H2SO4 environment, most likely due to the protective role of the partially fluorinated basic polymer and the known strength of the C-F bonds present. The results showed a clear correlation between the H2SO4 stability and the specific polymers present in the PEM blends investigated. Specific effects found included sulfonation, salt formation, hydrolysis and the accompanied dissolution of membrane fragments. Significant physical changes, for example ascribed to sulfonation of the concerned polymers, were supported by increased IEC measurements and peak intensities of the FTIR spectra, corresponding to the additional –SO3H groups present, while a variation in TGA signals served to further support the altered membrane composition and structure due to the H2SO4 treatment. In the case of dissolution, the corresponding chemical changes (analytical techniques) were supported by the decreased peak intensities of FTIR spectra, IEC measurements and TGA signals associated with degradation of the polymer backbone. It was shown that the stability of the blended membranes depended on the composition (blend components) of the membrane and the effective cross-linking (interaction) between the blend components. For all three groups examined, it became apparent that blend components sFS and sPSU were, for example, more stable than sPEEK and that ionical cross-linking seemed more effective than covalent cross-linking of blend components. When considering all membranes tested, the non-PBI based blend membranes consisting of (s)PSU and PFS copolymers in the presence of fluorinated cross-linkers and the PBIOO-sPSU blended membranes including most of the F6-PBI based membranes showed sufficient stability to be recommended for SO2 electrolysis. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

Le polymère Nafion est l'électrolyte de référence de la pile à combustible. Lorsqu'il est hydraté, il présente une conductivité élevée (10^-2 S.cm^-1). Néanmoins cette conductivité chute à faible taux d'hydratation. L'ajout d'un composé hygroscopique dans la membrane, tel le phosphate de zirconium (ZrP), a été proposé dans la littérature pour répondre à ce problème. <br /><br />La conductivité est le fait de la structure du matériau, des mécanismes de diffusion du proton, et des interactions eau-polymère au sein de la membrane. Nous nous sommes intéressés à cette dernière partie du problème. Nous avons étudié les mécanismes d'hydratation à l'échelle moléculaire pour les membranes Nafion puis Nafion-ZrP par technique de spectrométrie infrarouge. Cette technique peut être couplée à une étude par dynamique moléculaire que nous avons initié sur le polymère Nafion. Les spectres infrarouges du Nafion et du Nafion-ZrP ont été mesurés sur toute la gamme d'hydratation.<br /><br />Les résultats obtenus font état de 5 mécanismes d'hydratation successifs pour la membrane Nafion. L'ionisation des groupes sulfoniques SO_3H est très rapide en début d'hydratation. Elle est suivie d'un éloignement des protons H^+ par rapport aux groupes sulfonates SO_3^- dont ils sont issus et d'une réorganisation du réseau de liaisons H autour de ces groupes ioniques. Enfin une eau de type « bulk » apparaît vers 40% d'hydratation. Nous avons ainsi une "photographie" de la membrane à chaque taux d'hydratation. L'ajout d'un composé inorganique ZrP n'influe pas sur les mécanismes d'hydratation. <br /><br />D'après la comparaison entre nos mécanismes et la courbe de conductivité, il est nécessaire de dissocier tous les groupes sulfoniques pour atteindre une diffusion optimale du proton, probablement assurée par le mécanisme de Grotthuss.