L'état d'hydratation des électrolytes polymères pour piles à combustibles de type PEMFC et donc, la conductivité protonique de ce type d'électrolytes, est le point crucial pour comprendre et expliquer les performances électrochimiques de ce type de système. Le fonctionnement de la pile (création, absorption, diffusion, migration et désorption d'eau) conduit à une forte hétérogénéité de l'état d'hydratation du matériau polymère et donc de sa conductivité.La conductivité protonique des membranes actuellement utilisées comme électrolyte est le fait de la structure du matériau, des mécanismes de diffusion de l'eau et du proton, et des interactions eau-polymère au sein de la membrane. Nous nous sommes intéressés à ces problèmes et avons étudié les mécanismes d'hydratation et de diffusion par les techniques de spectroscopies vibrationnelles Infra-Rouge et Raman.Ce travail démontrera, entre autres, l'apport particulièrement intéressant des spectroscopies vibrationnelles in-situ pour la résolution de la problématique de la distribution de l'eau au sein de la membrane et son influence sur les performances de la pile. Nous proposons ici une étude de deux polymères perfluorosulfonés, le Nafion et l'Aquivion.Les propriétés d'absorption d'eau, de diffusion d'eau et de transport du proton dans ces deux membranes sont étudiées dans diverses conditions d'hydratation : dans les conditions d'équilibre, sous gradient d'activité chimique de l'eau (mesure in situ) et sous l'effet d'un champ électrique (mesure in situ et operando dans une pile en fonctionnement). La spectroscopie Infra-Rouge est utilisée pour étudier les changements structuraux des polymères ainsi que l'état de confinement de l'eau au cours de l'hydratation des membranes soumises à différentes valeurs de pression partielle d'eau et de température. Elle permet également d'étudier les interactions entre l'eau et les différents groupements chimiques présents dans la structure du polymère. L'ensemble des résultats est utilisé pour proposer des mécanismes d'absorption de l'eau ainsi que de dissociation des groupements acides de la membrane. La micro-spectroscopie Raman confocale, grâce à sa résolution spatiale micrométrique, permet de sonder l'épaisseur de la membrane et de déterminer le gradient d'eau transverse. Une cellule micro-fluidique a été développée pour l'étude des phénomènes de transport diffusif. Cette technique est actuellement la seule permettant de calculer les coefficients de diffusion équivalente à partir des gradients de concentration d'eau interne.Une pile à combustible spécialement adaptée aux mesures Raman, nous a permis, pour la première fois avec cette technique, de déterminer la distribution de l'eau à travers l'épaisseur de la membrane dans le système électrochimique en fonctionnement. Les informations ainsi obtenues sont des données primordiales pour comprendre, expliquer et prévoir l'impact de la distribution de l'eau au sein du cœur de pile sur les performances globales de ce système. / The water content of polymer electrolytes for Proton Exchange Membrane Fuel Cells and, thus, their proton conductivity, is the key issue to understand and to explain the electrochemical performances of the PEMFC electrochemical device. The fuel cell operation (creation, absorption, diffusion, migration and desorption of water) leads the hydration state of the membrane strongly heterogeneous. The proton conductivity of state-of-art polymer electrolytes results from the material structure, the water and proton diffusion mechanisms and the interactions between water and the polymer phase within the membrane. This work deals with these issues and uses vibrational spectroscopy techniques (Infra-Red and Raman) to study hydration and diffusion phenomena. Among others, this work shows the contribution of in-situ vibrational spectroscopies to the understanding of the water management issue and relationships between the water distribution throughout the membrane and the fuel cell electrochemical performances. Two perfluorosulfonated polymers, Nafion and Aquivion, are investigated.The water absorption and diffusion properties of these two membranes are studied under several hydration conditions: at the equilibrium, under external gradient of the water chemical activity and under the effect of an electric gradient (in-situ and operando measurements with the working fuel cell).Infrared spectroscopy is used to study structural modifications of the polymer phase occurring during the hydration process as well as the confinement state of water sorbed within the membrane. The last is submitted to different water vapor pressures and temperatures. This spectroscopy also allows to study interactions between water and the different chemical groups belonging to the polymer structure. Results are used to describe water absorption as well as the proton dissociation mechanism involving the sulfonic groups.Confocal Raman Micro-spectroscopy allows, by the spatial resolution at the micrometric scale, to probe the thickness of the membrane and to measure the inner, through-plane, water gradient. A micro-fluidic cell has been developed for the study of diffusion transport phenomena. This method is currently the only one by which equivalent diffusion coefficients can be calculated from internal water concentration gradients.A fuel cell especially designed for Raman measurements allowed us, for the first time by means of this technique, to determine the water distribution through the thickness of the membrane working in the electrochemical device. The new insights so obtained are essential for understanding, explaining and predicting the effects of the heterogeneous water distribution throughout the fuel cell heart on the electrochemical behavior.

DMagister Scientiae - MSc / The proton exchange membrane is one key component of direct methanol fuel cells, which has double functions of conducting protons, separating fuels and oxidant. At present, the performance and price of sulfonic acid proton exchange membrane used in direct methanol fuel cells are deeply concerned. In order to reduce membrane 's cost and improve performance of Nafion membrane, three different kinds of membranes have been studied in this thesis. These membranes are SPEEK membranes, SPEEK/ZP composite membranes and Nafion/ZP composite membranes. / South Africa

Poly(vinyl alcohol) (PVA)-based membranes have gathered significant interest because of their film forming ability and low cost. These films are usually crosslinked to provide a macromolecular network with high dimensional stability. PVA can be modified by introduction of sulfonic acid groups (sPVA) contributing to increase its proton conductivity. In addition, the preparation of hybrid organic-inorganic composite membranes by the addition of graphene oxide (GO) as nano-filler not only reinforces the matrix but also decreases the permeability of solvents. All this has motivated the use of these materials for the preparation of proton exchange membranes (PEMs) for direct methanol fuel cell (DMFC) applications. Contribution I presents the chemical schemes followed for the bi-sulfonation of the PVA, the synthesis of GO and the preparation of PVA/GO and sPVA/GO composite membranes. In addition, a structural, morphological, thermal, and mechanical characterization of the starting materials and the composite membranes were performed. Finally, in order to evaluate the suitability of the prepared PEMs in fuel cells, the prot cond. was evaluated at room temperature. The results showed that the addition of GO (1 wt.%) into the sPVA matrix, 30sPVA/GO membrane, enhance by 89% the prot cond. compared to its homologue membrane, 30sPVA, free-standing of GO. In Contribution II, the proton conductive properties of the previously prepared membranes were investigated as a function of the structural (bi-sulfonation) and morphological (crosslinking and addition of GO) modifications. The bi-sulfonated membrane reinforced with GO, 30sPVA/GO, stands out over the rest. The addition of GO improves considerably its prot cond. (20.96 mS/cm at 90 °C) and its maximum power density (Pmax) in the H2-O2 fuel cell test (13.9 mW/cm2 at 25 ºC). In Contribution III was studied the effect of a new variable, the sufonation of the GO (sGO), on the functional properties of the composites PVA/sGO and sPVA/sGO for DMFC applications. In addition, the results were compared to that obtained for the previously described PVA/GO and sPVA/GO composites. The results conclude that, contrary to expectations, the multiple sulfonation of the 30sPVA/sGO composite strongly reduces the prot cond. (5.22 mS/cm at 50 °C) compared to its homologue 30sPVA/GO (8.42 mS/cm at 50 °C), despite its higher values of ion exchange capacity (IEC). Finally, the 30PVA/sGO composite (1.85 mW/cm2) shows a significant improvement of the DMFC performance (50 °C, 4M methanol solution) compared to the 30sPVA/GO composite (1.00 mW/cm2). The Layer-by-Layer (LbL) assembly method was used in Contribution IV for the preparation of composite membranes assembled via hydrogen bonding interactions. To do this, GO/PVA and GO/sPVA bilayers were deposited on the surface of 15PVA and 15sPVA substrate membranes, respectively. The composites were denoted as 15PVA(GO/PVA)n and 15sPVA(GO/sPVA)n where n is the number of deposited bilayers, in our case n ranges between 1 and 3. Finally, the potential of the composite membranes for DMFC applications were evaluated, showing the best performance the 15sPVA(GO/sPVA)1 composite. Finally, the Contribution V was focused on the preparation of composite membranes by LbL Assembly method, but in this case the assembly forces were electrostatic interactions. The GO was dispersed in a poly(allyl amine hydrochloride) solution (GO-PAH) in order to obtain a positively charged solution. The composites were assembled by alternate deposition of GO-PAH and sPVA layers on the surface of 15PVA and 15sPVA substrates, obtaining as a result the composites 15PVA(GO-PAH/sPVA)n and 15sPVA(GO-PAH/sPVA)n. The best value of prot cond. (8.26 mS/cm at 90 °C) was obtained for the 15PVA(GO-PAH/sPVA)1 composite, almost twice that the value obtained for its homologue sulfonated composite 15sPVA(GO-PAH/sPVA)1 (4.96 mS/cm a 90 °C). / Membranas constituidas básicamente por alcohol polivinílico (PVA) han despertado un gran interés debido a su bajo coste y su fácil procesado para conformarlas en forma de films. Estos films frecuentemente son sometidos a entrecruzamiento para disponer de una red macromolecular con una elevada estabilidad dimensional. La modificación del PVA por introducción de grupos sulfónicos (sPVA) cambia la estructura del polímero contribuyendo a aumentar su conductividad protónica. Además, la preparación de membranas híbridas orgánico-inorgánicas (composites) mediante la adición de óxido de grafeno (GO) refuerza la matriz, a la vez que disminuye su permeabilidad frente a disolventes. Todo ello ha motivado el uso de estos materiales para la preparación de membranas de intercambio protónico (PEMs) empleadas en pilas de combustible de metanol (DMFCs). En la Contribución I se presentan los esquemas químicos conducentes a la bi-sulfonación del PVA, la síntesis del GO y la preparación de las membranas composite PVA/GO y sPVA/GO. Además, se realizó la caracterización estructural, morfológica, térmica y mecánica de cada uno de los materiales de partida y de los composite. Finalmente, con el fin de evaluar su idoneidad como PEMs en pilas de combustible, se evaluó su cond. prot a temperatura ambiente. Los resultados obtenidos mostraron que la adición de GO (1 wt.%) como nano-carga a la matriz de sPVA genera un composite, 30sPVA/GO, cuya cond. prot supera en un 89 % a la de su membrana homóloga sin carga, 30sPVA. La Contribución II trata de explorar las propiedades conductoras de las membranas preparadas previamente en función de la modificación estructural (bi-sulfonación) y la morfológica (reticulación y adición de GO). La membrana bi-sulfonada y reforzada con GO, 30sPVA/GO, destaca sobre el resto. La adición de GO mejora considerablemente tanto la cond. prot (20.96 mS/cm a 90 ºC) como la densidad de potencia máxima (Pmax) en pila de combustible de hidrógeno (13.9 mW/cm2 a temperatura ambiente). En la Contribución III se estudió el efecto de una nueva variable, la sulfonación del GO (sGO), sobre las propiedades funcionales de los composites PVA/sGO y sPVA/sGO en aplicaciones de DMFC. Además, se llevó a cabo un estudio comparativo con los composite PVA/GO y sPVA/GO previamente descritos. Los resultados concluyeron que, en contra a lo esperado, la múltiple sulfonación de la membrana 30sPVA/sGO reduce fuertemente su cond. prot (5.22 mS/cm a 50 ºC) en comparación con su homóloga 30sPVA/GO (8.42 mS/cm a 50 ºC), aun mostrando valores superiores de IEC. Finalmente, el rendimiento de la composite 30PVA/sGO (1.85 mW/cm2) en una DMFC (50 ºC, disolución de metanol 4M) mostró una mejora significativa en comparación con la composite 30sPVA/GO (1.00 mW/cm2). El método de LbL assembly se empleó en la Contribución IV para la preparación de composites ensamblados mediante enlaces por puente de hidrógeno. Para ello, se llevó a cabo la deposición de bicapas de GO/PVA y GO/sPVA sobre los substratos 15PVA y 15sPVA, respectivamente. Los composites se codificaron como 15PVA(GO/PVA)n y 15sPVA(GO/sPVA)n siendo n el número de bicapas depositadas, en nuestro caso n varía entre 1 y 3. Por último, se evaluó su potencial para aplicaciones en DMFC, presentando el mejor comportamiento el composite 15sPVA(GO/sPVA)1. Finalmente, la Contribución V va dedicada a la fabricación de composites mediante el método de LbL Assembly, pero en este caso a través de interacciones electrostáticas. El GO se dispersó en una disolución de hidrocloruro de polialilamina (GO-PAH), con el fin de dotarlo de carga positiva. El ensamblaje se realizó por deposición alterna de capas de GO-PAH y sPVA, obteniéndose los composites 15PVA(GO-PAH/sPVA)n y 15sPVA(GO-PAH/sPVA)n. El mejor valor de cond. prot (8.26 mS/cm a 90 ºC) se obtuvo para el composite 15PVA(GO-PAH/sPVA)1, siendo casi el doble que el obtenido para su homólogo s / Membranes constituïdes a base PVA han despertat un gran interès a causa del seu baix cost i el seu fàcil processament per conformar-les en forma de films. Aquests films freqüentment són sotmesos a entrecreuament per disposar d'una xarxa macromolecular amb una elevada estabilitat dimensional. La modificació del PVA per introducció de grups sulfònics (sPVA) canvia l'estructura del polímer contribuint a augmentar la seua conductivitat protònica. A més, la preparació de membranes híbrides orgànic-inorgànics (composites) mitjançant addició d'òxid de grafè (GO) reforça la matriu, alhora que disminueix la seua permeabilitat enfront de dissolvents. Tot això ha motivat l'ús d'aquestos materials per a la preparació de membranes d'intercanvi protònic (PEMs) emprades en piles de combustible de metanol (DMFCs). En la Contribució I es presenten els esquemes químics conduents a la bi-sulfonació del PVA, la síntesi del GO i la preparació de les membranes composite PVA/GO i sPVA/GO. A més, es va realitzar la caracterització estructural, morfològica, tèrmica i mecànica de cada un dels materials de partida i de les membranes composite. Finalment, per tal d'avaluar la seua idoneïtat com a PEMs en piles de combustible, es va mesurar la seua cond. prot a temperatura ambient. Els resultats obtinguts van mostrar que l¿addició de GO (1 wt.%) com a nano-càrrega en la matriu de sPVA genera un composite, 30sPVA/GO, amb una cond. prot que supera en un 89% a la de la seua membrana homòloga sense càrrega, 30sPVA. La Contribució II tracta d'explorar les propietats conductores de les membranes composite preparades prèviament en funció de la modificació estructural (bi-sulfonació) i morfològica (reticulació i addició de GO). La membrana bi-sulfonada i reforçada amb GO, 30sPVA/GO, destaca sobre la resta. L'addició de GO millora considerablement tant la cond. prot (20.96 mS/cm a 90 ºC) com la densitat de potència màxima (Pmax) a la pila de combustible d'hidrogen (13.9 mW/cm2 a temperatura ambient). En la Contribució III es va estudiar l'efecte d'una nova variable, la sulfonació del GO (sGO), sobre les propietats funcionals dels composites PVA/sGO i sPVA/sGO per aplicacions en DMFC. A més, es va dur a terme un estudi comparatiu amb els composites PVA/GO i sPVA/GO prèviament descrits. Els resultats van concloure que en contra del que s'esperava, la múltiple sulfonació de la membrana 30sPVA/sGO redueix fortament la seua cond. prot (5.22 mS/cm a 50 ºC) en comparació amb la seua homòloga 30sPVA/GO (8.42 mS/cm a 50 ºC), tot i que mostra valors superiors de IEC. Finalment, el rendiment de la membrana 30PVA/sGO (1.85 mW/cm2) en una DMFC (50 ºC, dissolució de metanol 4M) va mostrar una millora significativa en comparació amb la membrana 30sPVA/GO (1.00 mW/cm2). El mètode de LBL assembly es va emprar en la Contribució IV per a la preparació de composites acoblats mitjançant enllaços per pont d'hidrogen. Amb aquest fi, es va dur a terme la deposició de bicapes de GO/PVA i GO/sPVA sobre els substrats 15PVA i 15sPVA, respectivament. Els composites es van codificar com a 15PVA(GO/PVA)n i 15sPVA(GO/sPVA)n on n és el nombre de bicapes dipositades, en el nostre cas n varia entre 1 i 3. Finalment, es va avaluar el seu potencial per a aplicacions en DMFC, presentant el millor comportament el composite 15sPVA(GO/sPVA)1. Finalment, la Contribució V va dedicada a la fabricació de composites mitjançant el mètode de LBL Assembly, però en aquest cas acoblats a través d'interaccions electrostàtiques. El GO es va dispersar en una dissolució de hidroclorur de polialilamina (GO-PAH), per tal de dotar-lo de càrrega positiva. L'acoblament es va realitzar per deposició alterna de capes de GO-PAH i sPVA, obtenint-se els composites 15PVA(GO-PAH/sPVA)n i 15sPVA(GO-PAH/sPVA)n. El millor valor de cond. prot (8.26 mS/cm a 90 ºC) es va obtenir per al composite 15PVA(GO-PAH/sPVA)1, sent gairebé el doble que l'obtingut / Sánchez Ballester, SC. (2017). Synthesis and characterization of new polymer electrolytes to use in fuel cells fed with bio-alcohols [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86198 / TESIS

No description available.

This thesis presents analyses of hydrogen-bonded materials using solid-state nuclear magnetic resonance (NMR) spectroscopy. Proton dynamics were investigated in two classes of phosphate-based proton conductors: phosphate solid acids and tin pyrophosphates. These materials have the potential to be used as solid state proton conductors in fuel cells. Proton dynamics in phosphate solid acids were probed based on the attenuation of homonuclear dipolar coupling with increasing temperature. These studies showed that homonuclear dipolar recoupling NMR techniques can be employed in complex multi-spin systems. Additionally, two pathways for proton hopping in monoclinic RbH2PO4, a sample with two proton environments, were identified and quantified for the first time using a combination of dipolar recoupling and proton exchange NMR methods. Tin pyrophosphates, another class of solid-state proton conductor with analogous phosphate tetrahedral structure, were studied. Proton dynamics had to be analyzed via exchange-based NMR techniques as a result of low proton concentration in these materials. Proton mobility in tin pyrophosphate was found to increase with increased protonation. Furthermore, hydrogen bonding was investigated as a coordination mode in silicone boronic acid (SiBA) elastomers, potential materials for contact lens manufacture. As in the phosphate-based proton conductors, hydrogen bonding played an important role in the structure of the SiBA elastomers as one of the mechanisms through which these materials crosslink. In addition to hydrogen bonding, covalent bonding between boronic acids was found to occur at three- and four-coordinate boron centers. The purpose of this study was to determine the influence of boronic acid loading and packing density on crosslinking in SiBA elastomers. Boron coordination environments were investigated by 11B quadrupolar lineshape analysis. The incidence of four-coordinate dative bonding, a predictor of the stress-strain response in these materials, increased with boronic acid loading but was most heavily influenced by boronic acid packing density. / Thesis / Doctor of Philosophy (PhD) / Hydrogen bonds are intermolecular interactions that are significant in many structural (low crystal density in ice) and dynamic (enzymatic processes occurring under biological conditions) processes that are necessary to maintain life. In this thesis, solid-state nuclear magnetic resonance (NMR) spectroscopy is used to explore proton dynamics of hydrogen-bonded networks in various materials. Advanced NMR experiments that probe homo- and heteronuclear dipolar coupling interactions revealed possible pathways for proton transport in phosphate-based proton conducting materials. This study provided a better understanding of ion conducting mechanisms that can be used in intermediate-temperature fuel cell applications. Additionally, solid-state NMR was used in the identification of hydrogen bonding and other coordination modes in silicone boronate acids (SiBA), a class of elastomers with potential applications as contact lens. Boron coordination in SiBA elastomers was dependent on both boronic acid loading and boronic acid packing density.

Made available in DSpace on 2017-07-21T20:43:50Z (GMT). No. of bitstreams: 1 Ana K.pdf: 5354849 bytes, checksum: 5d4ba75f894ea071a739c12aebbddbe2 (MD5) Previous issue date: 2016-08-09 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Solid oxide fuel cells (SOFC) are devices that convert chemical energy directly into electricity and have shown a good alternative due to its high efficiency (more than 70%) have only components solid and clean energy. Among the biggest advantages are high reliability and low emission reducing the impact on the greenhouse effect. A SOFC comprises an electrolyte and two electrodes, the cathode and the anode, and must provide substantial conductivity, above 0.1 S.cm-1. The ceramics which have excellent electrical properties are compounds based on the structure of the perovskite (ABO3), and some of these have proton and ion conduction. The objective of this study was the synthesis of a perovskite with BaCe0,2Zr0,7Y0,1O3-δcomposition and obtain a dense compound for use as an electrolyte in SOFC. The ceramic compound this composition has enhanced electrical properties, as it has proton conduction. The powders were synthesized by the modified Pechini method, and various processing routes were tested until they found the ideal containing two calcinations, a 350°C for 4 hours and another 900°C for 12 hours. After obtaining the powder were tested two types of grinds, one in vibratory mill for 6 hours and another at high energy mill for 1 hour in order to refine the particle BCZY27 and improve densification of the sample after sintering. It also used the zinc oxide, 2% and 4 mol%, as a dopant assist densification. The characterization of the post was made by X and scanning electron microscopy with EDS rays. The results showed that, as the temperature was 900C possible to obtain the desired phase containing second phases. The sintering was done at 1300°C, 1400°C and 1600°C together with milling in a vibration mill and Spex mill, with the aim of testing the best composition in each. The characterization of the sintered samples was made by X-ray diffraction, scanning electron microscopy, EDS, dilatometry, porosity and density. Impedance spectroscopy were also made to the atmospheric air and humid air at temperatures from 200 to 600°C with intervals of approximately 25°C the samples possessed apparent porosity of less than 5%. The samples sintered at 1400°C with the addition of 4 mol% of ZnO, proved to be good for the application as an electrolyte because reached full enough electrical conductivity to be used. / As células a combustível de óxido sólido (CaCOS) são dispositivos que convertem energia química diretamente em elétrica e têm se mostrado uma boa alternativa devido a sua alta eficiência (acima de 70%), ter apenas componentes no estado sólido e produzir energia limpa. Entre as maiores vantagens estão a alta confiabilidade e a baixa emissão de gases diminuindo o impacto sobre o efeito estufa. Uma CaCOS é constituída por um eletrólito e dois eletrodos, o catodo e o anodo, e deve apresentar condutividade elétrica considerável, acima de 0,1 S.cm-1. As cerâmicas que apresentam propriedades elétricas são compostos baseados na estrutura da perovskita (ABO3), sendo que algumas dessas apresentam condução protônica e iônica. Assim, o objetivo deste trabalho foi estudar a síntese de uma perovskita com composição BaCe0,2Zr0,7Y0,1O3-δe obter um composto denso para utilização como eletrólito em CaCOS. O composto cerâmico com esta composição possui propriedades elétricas otimizadas, pois apresenta condução protônica. Os pós foram sintetizados pelo método Pechini modificado e foram testadas diversas rotas de processamento até que se considerou a ideal contendo duas calcinações, uma de 350°C por 4 horas e a outra de 900°C por 12 horas. Após a obtenção do pó, foram testados dois tipos de moagens, uma em moinho vibratório por 6 horas e outra em moinho de alta energia por 1 hora, com a finalidade de refinar as partículas de BCZY27 e melhorar a densificação da amostra após a sinterização. Foi utilizado também o óxido de zinco, a 2% e 4% em mol, como dopante auxiliar de densificação. A caracterização dos pós foi feita por difração de raios X e microscopia eletrônica de varredura com EDS. Os resultados mostraram que, a partir da temperatura de 900ºC foi possível obter a fase desejada contendo segundas fases. As sinterizações foram feitas em 1300°C, 1400°C e 1600°C em conjunto com as moagens em moinho vibratório e moinho Spex, com o objetivo de testar a melhor composição em cada uma delas. A caracterização das amostras sinterizadas foi feita por difração de raios X, microscopia eletrônica de varredura, EDS, dilatometria, porosidade e densidade aparente. Foram feitas também medidas de espectroscopia de impedância ao ar atmosférico e ao ar úmido em temperaturas de 200 até 600°C com intervalos aproximados de 25°C das amostras que possuíram porosidade aparente inferior a 5%. As amostras sinterizadas a 1400°C, com a adição de 4% mol de ZnO, se mostraram boas para a aplicação como eletrólito, pois atingiram a condutividade elétrica total suficiente para sua utilização.

<p>In this study novel composite electrodes were developed, in which the catalytic components were deposited in nanoparticulate form. The efficiency of the nanophase catalysts and membrane electrodes were tested in an important electrocatalytic process, namely hydrogen production by water electrolysis, for renewable energy systems. The activity of electrocatalytic nanostructured electrodes for hydrogen production by water electrolysis were compared with that of more conventional electrodes. Development of the methodology of preparing nanophase materials in a rapid, efficient and simple manner was investigated for potential application at industrial scale. Comparisons with industry standards were performed and electrodes with incorporated nanophases were characterized and evaluated for activity and durability.</p>

<p>In this study novel composite electrodes were developed, in which the catalytic components were deposited in nanoparticulate form. The efficiency of the nanophase catalysts and membrane electrodes were tested in an important electrocatalytic process, namely hydrogen production by water electrolysis, for renewable energy systems. The activity of electrocatalytic nanostructured electrodes for hydrogen production by water electrolysis were compared with that of more conventional electrodes. Development of the methodology of preparing nanophase materials in a rapid, efficient and simple manner was investigated for potential application at industrial scale. Comparisons with industry standards were performed and electrodes with incorporated nanophases were characterized and evaluated for activity and durability.</p>

Face aux demandes croissantes en énergie, la tendance mondiale est au développement des énergies non émettrices de gaz à effets de serre. Dans ce contexte, plusieurs technologies de piles à combustibles utilisant l’hydrogène ont été développées. Le souhait d’abaisser les températures de fonctionnement des SOFC a conduit à s’intéresser au concept des piles PCFC dont la conduction ionique de l’électrolyte est assurée par l’hydrogène au lieu des anions oxydes. Les composés pyrochlores A₂B₂O₇ sont des candidats prometteurs comme matériaux d’électrolyte de PCFC.Il s’avère toutefois indispensable de comprendre les mécanismes de diffusion de l’hydrogène dans ces matériaux avant d’orienter les recherches vers la mise au point d’un matériau électrolyte performant. Dans ce travail, une approche multi-échelle est employée pour étudier l’impact de microstructure sur les propriétés de conduction protonique du matériau modèle La₂Zr₂O₇ dopé Sr. Pour ce faire, plusieurs voies de synthèse ont été utilisées afin d’obtenir des morphologies de poudres différentes.A l’échelle nanométrique, les études structurales menées par diffraction des rayons X puis des études par spectroscopie Raman et spectroscopie de pertes d’énergie des électrons (EELS) ont montré que la structure basse température étaient une structure pyrochlore désordonnée. Cette dernière s’ordonne lors de recuit thermique.Les techniques d’analyses par faisceau d’ions ont permis de sonder à l’échelle micrométrique les profils de concentration en hydrogène des matériaux préalablement hydratés. La quantité d’hydrogène incorporé dépend de la densification de la pastille.Les mesures par spectroscopie d’impédance ont permis d’obtenir des informations à l’échelle macroscopique du comportement électrique des matériaux. Une conductivité protonique a été mise en évidence sous atmosphère humide. Cette conductivité est fortement dépendante non seulement de la méthode d’élaboration des matériaux mais aussi des procédés de densification utilisés. / Due to the increase of energy demand and environmental issues of fossil energy, many researches are moving towards green energy. In this context, several technologies using hydrogen have been developed. To reduce the working temperature of SOFC fuel cell, the concept of PCFC is emerging. The ionic conductivity is due to hydrogen instead of oxide anions. The A₂B₂O₇ compounds are promising candidates as electrolyte materials for PCFC. However, it appears necessary to understand the hydrogen diffusion mechanisms in these materials before to investigate news materials with best properties. In this work, a multi-scale approach is performed to study the impact of microstructure on proton-conducting properties in Sr doped La₂Zr₂O₇ as model material. Several synthetic routes have been used to obtain powders with different morphologies.At the nanometric scale, studies by X-ray diffraction, then by Raman spectroscopy and electron energy loss spectroscopy (EELS) have shown that the low temperature structure were disordered a pyrochlore structure. The latter is ordered during thermal annealing. At the micrometric scale, ion beam techniques allowed us to get the hydrogen concentration profiles on the previously hydrated materials. The amount of incorporated hydrogen depends on the densification processes. At the macroscopic scale, impedance spectroscopy measurements were used to obtain information on the electrical behavior of materials. Evidence of proton conductivity has been demonstrated in wet atmosphere. This conductivity is highly dependent not only on the sample preparation but also on processes densification used.

Polymer electrolyte membrane fuel cells (PEMFCs) are one of the most promising clean technologies under development. However, the main obstacles for commercialising PEMFCs are largely attributed to the technical limitations and cost of current PEM materials such as Nafion. Novel poly(2,5-benzimidazole) (ABPBI)/POSS based polymer composite electrolyte membranes with excellent mechanical and conductivity properties were developed in this project including (I) ABPBI, polybenzimidazole (PBI) and their copolymers were synthesised by solution polymerisation and their chemical structures were confirmed by FTIR and elemental analysis. ABPBI/ActaAmmonium POSS (ABPBI/AM) and ABPBI/TriSilanolPhenyl POSS (ABPBI/SO) composites were also synthesised in situ. High quality polymer and composite membranes were fabricated by a direct cast method; and (II) The mechanical and thermal properties, microstructure and morphology, water and H3PO4 absorbility and proton conductivity of phosphoric acid doped and undoped ABPBI and ABPBI/POSS composite membranes were investigated. SEM/TEM micrographs showed that a uniform dispersion of POSS nano particles in ABPBI polymer matrix was achieved. The best performances on both mechanical properties and proton conductivities were obtained from the ABPBI/AM composite membrane with 3 wt% of POSS (ABPBI/3AM). It was found that both the water and H3PO4 uptakes were increased significantly with the addition of POSS due to formation of hydrogen bonds between the POSS and H2O/H3PO4, which played a critical role in the improvement of the conductivity of the composite membranes at temperatures over 100oC. ABPBI/3AM membranes with H3PO4 uptake above 117% showed best proton conductivities at both hydrous and anhydrous conditions from room temperature to 160oC, which is comparable with the conductivity of commercial Nafion 117 at 20oC in water-saturated condition, indicating that these composite membranes could be excellent candidates as a polymer electrolyte membrane for high temperature applications. A new mechanism for illustrating the improved proton conductivity of composite membranes was also developed.