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1
BONIZZONI, SIMONE. "Anion Conducting Polymers for Fuel Cell and Electrolyzer." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2022. http://hdl.handle.net/10281/382284.
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The hydrogen, as energy vector, is considering one promising green, sustainable, low-cost alternative to hydrocarbon fuels. In the circular hydrogen economy, the fuel cell technologies play a crucial role of the energy conversion and, in particular, Anion Exchange Membrane Fuel Cell are retained to be very promising for the high-power delivery, the short waiting time before providing energy, the low working temperature.
My PhD is focus on synthesis and characterization of anionic conducting polymer for fuel cell and electrolyzer applications.
The first part of activities is focused on the study of new chemical modifications of polyfluorinated (Aquivion®), aliphatic polyketones, polystyrene polymer matrix to address the main drawbacks of the chemical and electrochemical stability and also the high cost. The synthesis methods involve the organic chemistry procedure for examples Pall-Knorr reaction, Baeyer-Villiger oxidation, methylation process.
The physical-chemical characterization part is aimed to the better understand the properties of the functionalized polymer matrix. The polymer structure is investigated by spectroscopes technique for example FTIR and solid-state NMR while, the thermal properties and their stability are determined by TGA and DSC measurements. For the promising work of Aquivion® modification, I also performed accelerated ageing treatment for testing the chemical and electrochemical stability and I used them in for water Electrolyzer application.
The functionalized polymers show interesting and promising properties for fuel cell and electrolyzer applications and, in particular, modified Aquivion® membranes show excellent stability in alkaline environmental and archive 130 mA cm-2 at 80°C. The results of Aquivion® modification are published on two international journals and the polyketones functionalization work is undergoing publication.<br>The hydrogen, as energy vector, is considering one promising green, sustainable, low-cost alternative to hydrocarbon fuels. In the circular hydrogen economy, the fuel cell technologies play a crucial role of the energy conversion and, in particular, Anion Exchange Membrane Fuel Cell are retained to be very promising for the high-power delivery, the short waiting time before providing energy, the low working temperature.
My PhD is focus on synthesis and characterization of anionic conducting polymer for fuel cell and electrolyzer applications.
The first part of activities is focused on the study of new chemical modifications of polyfluorinated (Aquivion®), aliphatic polyketones, polystyrene polymer matrix to address the main drawbacks of the chemical and electrochemical stability and also the high cost. The synthesis methods involve the organic chemistry procedure for examples Pall-Knorr reaction, Baeyer-Villiger oxidation, methylation process.
The physical-chemical characterization part is aimed to the better understand the properties of the functionalized polymer matrix. The polymer structure is investigated by spectroscopes technique for example FTIR and solid-state NMR while, the thermal properties and their stability are determined by TGA and DSC measurements. For the promising work of Aquivion® modification, I also performed accelerated ageing treatment for testing the chemical and electrochemical stability and I used them in for water Electrolyzer application.
The functionalized polymers show interesting and promising properties for fuel cell and electrolyzer applications and, in particular, modified Aquivion® membranes show excellent stability in alkaline environmental and archive 130 mA cm-2 at 80°C. The results of Aquivion® modification are published on two international journals and the polyketones functionalization work is undergoing publication.
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Rossi, Gianmarco. "modeling of proton exchange membrane water electrolyzer for green hydrogen production from solar energy." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
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Hydrogen is considered one of the means by which to store energy coming from renewable and intermittent power sources. With the growing capacity of renewable energy sources, a storage system is required to not waste energy. PEM electrolysis provides a sustainable solution for the production of hydrogen and is well suited to couple with energy sources such as solar and wind.
This work reports the development of simulation software to estimate the performance of a proton exchange membrane electrolyzer working at atmospheric or low pressure conditions connected to a solar energy source. The electrolyzer is defined from a validated reference semi-empirical model, which allows for simulating the electrochemical, thermal and H2 output flow behaviours with enough precision for engineering applications. An algorithm for a fitting procedure to characterize commercial products, and functions for power modulation have been implemented. A series of simulations have been carried on, starting from real photovoltaic data of input power, and the output values have been discussed, with particular attention to output flow rate, thermal behaviour and the cooling demand in order to preserve the operation of the electrolyzer.
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Sundin, Camilla. "Environmental Assessment of Electrolyzers for Hydrogen Gas Production." Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-260069.
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Hydrogen has the potential to become an important energy carrier in the future with many areas of applications, as a clean fuel for transportation, heating, power generation in places where electricity use is not fit, etc. Already today hydrogen plays a key role in numerous industries such as petroleum refineries and chemical industries. There are different production methods for hydrogen. Today, natural gas reforming is the most commonly used. With the growing importance of green production paths, hydrogen production by electrolysis is expected to grow. Two main electrolyzer technologies are used today; alkaline and polymer electrolyte membrane electrolyzer. High-temperature electrolyzers are also interesting techniques, where solid oxide is under development and molten carbonate electrolyzers is researched. In this thesis, a comparative life cycle analysis was performed on the alkaline and molten carbonate electrolyzer. Due to inaccurate inventory data for the molten carbonate electrolyzer, those results are excluded from the published thesis. The environmental performance of the alkaline electrolyzer technology was compared to that of the solid oxide and the polymer electrolyte membrane electrolyzers. The system boundaries were set as cradle to gate. Thereby, the life cycle steps included in the study are raw material extraction, electrolyzer manufacturing, hydrogen production, and transports in between these steps. The functional unit was chosen as 100 kg produced hydrogen gas. The results show that the polymer electrolyte membrane electrolyzer has the lowest environmental impact out of the compared technologies. It is also determined that the lifetime and the current density of the electrolyzers have significant impact on their environmental performance. Moreover, it is established that electricity for hydrogen production has the highest environmental impact out of the electrolyzers life cycle steps. Therefore, it is important to make sure that the electricity used for hydrogen production derives from renewable sources.<br>Vätgas har potential att spela en viktig roll som energibärare i framtiden med många användningsområden, såsom ett rent bränsle för transporter, uppvärmning, kraftförsörjning där elproduktion inte är lämpligt, med mera. Redan idag är vätgas ett viktigt inslag i flera industrier, där ibland raffinaderier och kemiska industrier. Det finns flera metoder för att producera vätgas, där reformering av naturgas är den största produktionsmetoden idag. I framtiden spås vätgasproduktion med elektrolys bli allt viktigare, då hållbara produktionsprocesser prioriteras allt mer. Idag används främst två elektrolysörtekniker, alkalisk och polymerelektrolyt. Utöver dessa är högtemperaturelektrolysörer också intressanta tekniker, där fastoxidelektrolysören är under utveckling och smältkarbonatelektrolysören är på forskningsstadium. I det här examensarbetet har en jämförande livscykelanalys utförts på alkalisk- och smältkarbonatelektrolysören. På grund av felaktiga indata för smältkarbonatelektrolysören har dessa resultat uteslutits från den publika rapporten. Miljöpåverkan från den alkaliska elektrolysören har sedan jämförts med miljöpåverkan från fastoxid- och polymerelektrolytelektrolysörerna. Systemgränserna sattes till vagga till grind. De livscykelsteg som inkluderats i studien är därmed råmaterialutvinning, elektrolysörtillverkning, vätgasproduktion och transporter mellan dessa steg. Den funktionella enheten valdes till 100 kg producerad vätgas. Resultaten visar att polymerelektrolytteknologin har den lägsta miljöpåverkan utav de tekniker som jämförts. Resultaten påvisar också att livstiden och strömtätheten för de olika teknikerna har signifikant påverkan på teknikernas miljöpåverkan. Dessutom fastslås att elektriciteten för vätgasproduktion har högst miljöpåverkan utav de studerade livscykelstegen. Därför är det viktigt att elektriciteten som används för vätgasproduktionen kommer ifrån förnybara källor.
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Coetzee, Morné Pieter. "Upscaling of a sulphur dioxide depolarized electrolyzer / Coetzee, M.P." Thesis, North-West University, 2012. http://hdl.handle.net/10394/7001.
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In the last couple of years there has been a great need for finding alternative, cleaner burning fuel sources. This search has led to the development of various hydrogen technologies. The reason for this is that when burnt, hydrogen gas only forms water and oxygen as products. One of the methods used in the production of hydrogen gas is that of the electrolysis of sulphur dioxide which is facilitated by a sulphur dioxide depolarized electrolyzer. The electrolysis of sulphur dioxide has the advantage of requiring lower cell voltages in the electrolysis process when compared to the electrolysis of water.
This type of electrolyzer unfortunately suffers from low hydrogen gas production volumes. It was thought that by linearly increasing the reactions active area of the electrolyzer, the production volumes can be increased. A linearly upscaled 100cm2 cell was designed by using computer aided design software, such as SolidWorks, Cambridge Engineering Selector, EES and ANSYS. The cell was then constructed and tested to determine the effects of linearly upscaling. The results of the 100cm2 cell were compared to the results of a similar 25cm2 cell and results obtained from the literature. The 100cm2 cell exhibited very poor performance when compared to the other cells. The 100cm2 cell showed lower hydrogen production volumes at higher energy inputs than the 25cm2 cell and an 86cm2 stack assembly. It was concluded that creating stack assemblies with cells with smaller active areas would be much more efficient than linearly upscaling the active area of the cells.<br>Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012.
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Hýbl, Jiří. "Nové typy membrán pro elektrolyzér vodík - kyslík." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2010. http://www.nusl.cz/ntk/nusl-218372.
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This work deals with the production of hydrogen and oxygen by electrolysis. Aims of this thesis are to measure different types of membranes and choose the best for use in elektrolyzer for hydrogen and oxygen production. Properties of membranes were tested in the laboratory electrolyzer in the short and long operation. The emerging gases from elektrolyzer were also tested on a gas chromatograph to determine the purity of produced hydrogen. At the same time are also tested different concentrations of KOH elektrolyte and the effect of concentrations on efficiency of electrolyzer.
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Yodwong, Burin. "Contribution to the development of a high-power low-voltage DC-DC converter for proton exchange membrane electrolyzer applications." Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0064.
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Cette thèse de doctorat a été réalisée dans le cadre d’un accord de cotutelle entre l’Université de Lorraine, IUT de Longwy, laboratoire GREEN et Renewable Energy Research Centre (RERC), King Mongkut’s University of Technology North Bangkok, Thaïlande. Par ailleurs, cette thèse s’inscrit dans le cadre du programme de bourses Franco-Thaï 2019 soutenu par l’ambassade de France en Thaïlande et Campus France. L’objectif principal de cette thèse est de développer un convertisseur DC-DC dévolteur basse tension haute puissance et un algorithme de contrôle non linéaire pour des applications d’électrolyseurs PEM. Tout d’abord, les technologies d’électrolyseurs et les topologies de convertisseurs DC-DC pour des systèmes de production d’hydrogène reposant sur le processus d’électrolyse de l’eau ont été étudiées avec attention. De plus, une étude bibliographique des modèles d’électrolyseurs PEM a été réalisée pour analyser les comportements statiques et dynamiques de ces derniers. Dans ce travail, la technologie d’électrolyseur PEM a été considérée en raison de ses avantages principaux tels que sa densité de courant élevée, sa réponse rapide aux sollicitations dynamiques, et sa large plage de fonctionnement. De là, cette technologie est particulièrement bien adaptée pour être couplée avec des sources d’énergies renouvelables. Cependant, les électrolyseurs peuvent être vus comme des charges électrochimiques basse tension fort courant exigeant en conséquence un convertisseur DC-DC dévolteur adapté. Après avoir effectué une analyse bibliographique sur les convertisseurs DC-DC les plus utilisés et les topologies candidates pour cette application, un convertisseur buck entrelacé trois niveaux (communément appelé three-level interleaved buck converter (TLIBC)) a été choisi dû à ses caractéristiques principales. En effet, cette topologie est caractérisée par une ondulation de courant de sortie faible, une conversion en tension faible, et une disponibilité en cas de défaillances électriques. Dans un second temps, un émulateur d’électrolyseur PEM a été conçu et implémenté en s’appuyant sur les comportements statiques et dynamiques d’un électrolyseur PEM commercial. Cet émulateur a été utilisé avec le convertisseur buck entrelacé trois niveaux pour éviter toute condition de fonctionnement critique qui pourrait endommager un électrolyseur physique pendant les phases d’expérimentation. Enfin, pour assurer d’excellentes performances du système, un contrôle non-linéaire mode glissant (communément appelé sliding-mode control (SMC)) amélioré a été conçu pour le convertisseur étudié. Le choix de ce contrôleur est motivé par ses bénéfices en termes de réponse dynamique et robustesse contre les incertitudes de paramètres du système. Ensuite, le convertisseur piloté par le contrôle non-linéaire mode glissant a été testé en simulation et expérimentalement. Les résultats obtenus à la fois en simulation et en pratique ont démontré la robustesse du contrôleur proposé dans la gestion du courant de sortie (i.e. réglage du débit d’hydrogène) qui suit avec précision une référence donnée avec une faible ondulation de courant de sortie, tout en garantissant l’équilibre des tensions des deux condensateurs d’entrée en conditions de fonctionnements dynamiques et d’incertitudes des paramètres<br>This Ph.D. work has been carried out within the framework of a cotutelle agreement between the Group of Research in Electrical Engineering of Nancy (GREEN), Université de Lorraine, IUT de Longwy section, France, and Renewable Energy Research Centre (RERC), Thai French innovation institute, Faculty of technical education, King Mongkut's University of Technology North Bangkok, Thailand. Besides, this Ph.D. comes within the scope of the 2019 Franco-Thai Scholarship Program supported by the French Embassy in Thailand and Campus France. The major goal of this Ph.D. work is to develop a high-power low voltage step-down DC-DC converter and a non-linear control algorithm for PEM electrolyzer applications. First, the electrolyzer technologies and power electronics topologies for hydrogen production systems relying on water electrolysis process have been thoroughly studied. Besides, a literature review of PEM electrolyzer models has been carried out to investigate static and dynamic behaviors. In this work, PEM electrolyzer technology has been considered due to their main advantages such as high current densities, fast dynamic responses, and large partial load range. Hence, this technology is perfectly fit to be coupled with renewable energy sources. However, PEM electrolyzers are low-voltage high-current electrochemical loads requiring the use of a suitable step-down DC-DC converter. After reviewing the most used topologies and topologies candidates for this application, a three-level interleaved buck converter (TLIBC) has been chosen because of their main benefits. Indeed, the main features of the TLIBC are low output current ripple, low step-down conversion ratio gain, and availability in case of electrical failures. Second, a PEM electrolyzer emulator has been designed and implemented based on the static and dynamic behavior of a commercial PEM electrolyzer. This emulator has been used with the TLIBC to avoid critical operating conditions that may damage a real electrolyzer during experimental tests. Finally, to ensure excellent performance of the system, a non-linear improved sliding-mode control (SMC) has been designed for the TLIBC. The choice of this controller has been motivated by its major benefits such as fast dynamic response and robustness against parameters uncertainties. Then, the TLIBC driven by the improved SMC has been tested in simulation and experimentally. Both obtained simulation and experimental results have demonstrated the robustness of proposed control laws in managing the output inductor current (i.e., hydrogen flow rate) that precisely follows its reference with very low current ripple, while guaranteeing the balance of both input capacitors voltages with respect to the dynamic operating condition and uncertainty parameters
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Panda, Ronit Kumar. "Développement d'un simulateur d'électrolyse alcalin avec membrane polymère échangeuse d'anions." Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALI041.
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Cette thèse décrit la modélisation des performances AEMWE (chap 1) et ses dégradations (chap 2). Les modèles sont développés dans le code MePHYSTO développé au CEA dans la plateforme Matlab/Simulink. Le modèle de performance a été développé grâce aux caractérisations électrochimiques réalisées au CEA au cours du projet. Les phénomènes électrochimiques essentiels sont bien capturés, notamment l'effet de concentration en KOH et l'effet de couverture de bulles, et les courbes de polarisation sont correctement simulées.Concernant les dégradations, ces travaux s'appuient sur les résultats expérimentaux obtenus au CEA au cours du projet. Les résultats expérimentaux ont apporté plusieurs idées : les dégradations comportent à la fois des parties réversibles et irréversibles qui évoluent différemment. En effet, les dégradations réversibles augmentent avec le temps tandis que les parties irréversibles diminuent. Nous avons supposé que la partie réversible provenait de la présence des bulles dans l'anode qui la dénoie partiellement. Concernant la partie irréversible, plusieurs phénomènes interviennent. Nous avons quantifié les différentes contributions de ces dégradations grâce au modèle électrochimique que nous avons développé et aux courbes de polarisation fournies. Dans un premier temps, la dégradation du catalyseur est quantifiée via l'estimation du facteur de rugosité au début des courbes de polarisation. Dans un deuxième temps, l’évolution de la surtension d’échange d’ions entre l'électrolyte et le ionomère est quantifiée en ajustant le modèle à l’aide des courbes de polarisation. Ensuite, les dégradations associées au transport de masse sont analysées en détail. Nous avons supposé qu'elles sont induites par la perte de mouillabilité qui augmente la présence des bulles à l'anode et réduit ainsi les performances. Ceci est cohérent avec l’augmentation des dégradations réversibles que nous associons à la présence des bulles. L'évolution de l'angle de contact du PTL qui caractérise cette perte de mouillabilité est calculée selon une approche originale. Nous développons une méthode basée sur des simulations de l'écoulement dans la géométrie réelle du PTL à l'aide d'images tomographiques 3D et du code GeoDict. Les propriétés d'écoulement (perméabilité et pression capillaire) et l'angle de contact sont extraits de ces simulations et sont utilisés dans le code MePHYSTO pour calculer les performances à différents moments du vieillissement avec une bonne précision<br>This report describes the modelling AEMWE performances (chap 1) and degradations (chap 2). The models are developed in the MePHYSTO code developed at CEA in the Matlab/Simulink platform. The performance model has been developed thanks to the electrochemical characterization performed at CEA during the project. The essential electrochemical phenomena are captured including KOH concentration effect and bubble coverage effect and the IV curves are correctly simulated.Regarding the degradation, the work is based on the experimental results obtained at CEA during the project. The experimental results provided several ideas: the degradations include both reversible and irreversible parts that evolve differently. Indeed, the reversible degradations increases with time while irreversible parts decreases. We assumed the reversible part comes from the anode bubble coverage. Regarding the irreversible part, several phenomena are involved. We quantified the different contributions of these degradations thanks to the electrochemical model we developed, and the IV curves provided. First, the catalyst degradation is quantified via the estimation of the roughness factor at the beginning of the IV curves. Secondly, the ion-exchange over-potential evolution is quantified by fitting the model using the IV curves. Then, the degradations associated to the mass transport are analyzed in detail. We assumed that they are induced by the loss of wettability that increases the anode bubble coverage and thus, reduces the performances. This is coherent with the increase of the reversible degradations we associate to the bubble coverage. The evolution of the sinter contact angle that characterized this loss of wettability is calculated using an original approach. We develop a method based on simulations of the flow in the real geometry of the sinter using tomographic 3D picture and the GeoDict code. The flow properties (permeability and capillary pressure) and the contact angle are extracted from these simulations and are used in the MePHYSTO code to calculate the performances at different aged times with a good accuracy
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Petrik, Leslie F. "Pt Nanophase supported catalysts and electrode systems for water electrolysis." Thesis, University of the Western Cape, 2008. http://hdl.handle.net/11394/2743.
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Doctor Scientiae - DSc<br>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.<br>South Africa
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Dedigama, I. U. "Diagnostics and modeling of polymer electrolyte membrane water electrolysers." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1426127/.
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Proton exchange membrane water electrolyser (PEMWE) technology can be used to produce hydrogen from renewable energy sources; the technology is therefore a promising component in future national power and transportation fuel systems. The main challenges faced by the technology include prohibitive materials costs, maximising efficiency and ensuring suitable longevity. Therefore, research is needed to understand the internal operation of the systems so that cell design can be optimised to obtain maximum performance and longevity. PEMWE is a low temperature electrolysis system that consists of cell components such as end plates, current collectors, bipolar plates, gas diffusion layers (GDLs) and membrane electrode assemblies (MEAs). Cell performance is strongly reliant on the materials and designs of each of the components. Three cell designs were used to study different aspects of PEMWE operation: commercial cell, optically transparent cell and combined optical and current mapping cell. Polarisation measurements performed on a commercially available lab-scale test cell at ambient conditions illustrated an increase in mass transport limitations with increasing water flow rate which was confirmed using electrochemical impedance spectroscopy (EIS) measurements. A transparent cell was constructed to allow optical access to the flow channels. Measurements made on the cell showed a transition from bubbly to slug flow that affects mass transport limitations and consequently the electrochemical performance. Thermal imaging measurements supported a mass and energy balance of the system. Finally, a combined transparent and current mapping cell was constructed using PCB technology that indicated higher current densities closer to the exit of the channel. Optical measurements showed that this increase in current was associated with larger bubbles and a transition to slug flow which led to enhanced mass transport of water to the electrode surface. A model developed for the system showed that the cell potential is dominated by the anode activation overpotential. Experimental data obtained at similar conditions with the commercially available lab-scale test cell agreed well with the model and the fitted parameters were in close proximity with values published in literature.
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Guenot, Benoit. "Etude de matériaux catalytiques pour la conversion électrochimique de l'énergie Clean hydrogen generation from the electrocatalytic oxidation of methanol inside a proton exchange membrane electrolysis cell (PEMEC): effect of methanol concentration and working temperature Electrochemical reforming of Dimethoxymethane in a Proton Exchange Membrane Electrolysis Cell: a way to generate clean hydrogen for low temperature fuel cells." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2017. http://www.theses.fr/2017ENCM0004.
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L’hydrogène est un vecteur énergétique prometteur réalisant une très bonne synergie avec l’exploitation des sources d’énergie intermittentes telles que le solaire ou l’éolien. Le développement de ses moyens de production et de conversion électrochimique représente un enjeu majeur dans le contexte de transition énergétique dans lequel nous vivons aujourd’hui. Les piles à combustible et les électrolyseurs utilisant la technologie PEM (Membrane Echangeuse de Protons) sont des systèmes électrochimiques de conversion de l’énergie matures tandis que les systèmes réversibles capables de remplir ces deux fonctions – les piles à combustible régénératrices unitaires – sont encore à l’état de développement. Leur principal verrou technologique est la conception d’une électrode bifonctionnelle à oxygène. Les matériaux catalytiques mis en œuvre dans ces systèmes sont principalement des métaux nobles et il convient d’en réduire autant que possible la charge massique dans les électrodes pour diminuer le coût des systèmes. Trois aspects complémentaires ont été développés lors de ces travaux de thèse. D’une part, des oxydes d’iridium et de ruthénium ont été élaborés par voie hydrothermale afin de catalyser la génération d’oxygène en fonctionnement électrolyseur. D’autre part, des catalyseurs à base de platine supportés sur des matériaux non carbonés, en particulier le nitrure de titane, ont été synthétisés par des voies colloïdales, afin de catalyser la réduction de l’oxygène en fonctionnement pile à combustible. L’association de ces matériaux est une première étape vers la conception d’une électrode bifonctionnelle à oxygène. Le troisième point se concentre sur la production de l’hydrogène et propose une alternative à l’oxydation de l’eau. L’oxydation électrochimique de composés organiques tels que le méthanol ou le diméthoxyméthane à l’aide de catalyseurs à base de platine et de ruthénium métallique permet la production d’hydrogène de grande pureté avec une consommation d’énergie électrique moindre par rapport à l’électrolyse de l’eau<br>Hydrogen is a promising energy vector, particularly for energy storage from intermittent energy sources such as solar or wind. The development of its production methods and its electrochemical conversion represents a major challenge in the context of energy transition in which we live nowadays. Fuel cells and electrolyzers using PEM technology (Proton Exchange Membrane) are mature electrochemical energy conversion systems, while reversible systems capable of performing both functions – unitized regenerative fuel cells – are still in the early stage of development. Their main technological bottleneck is the design of a bifunctional oxygen electrode. The catalytic materials used in these systems are mainly noble metals and it is necessary to reduce as much as possible their loading in the electrodes to decrease the system cost. Three complementary aspects have been developed during this thesis. On the one hand, iridium and ruthenium oxides have been prepared by hydrothermal treatment in order to catalyze the oxygen evolution under electrolyzer operation. On the other hand, platinum-based catalysts supported on non-carbonaceous materials, especially titanium nitride, have been synthesized by colloidal routes, in order to catalyze the oxygen reduction under fuel cell operation. The combination of these materials is the first step towards the design of a bifunctional oxygen electrode. The third topic focuses on the production of hydrogen and proposes an alternative to the oxidation of water. The electrochemical oxidation of organic compounds such as methanol or dimethoxymethane using platinum and ruthenium based catalysts allows producing clean hydrogen with a lower electrical energy consumption compared to the electrolysis of water
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Hegge, Friedemann [Verfasser], Stefan [Akademischer Betreuer] Glunz, and Simon [Akademischer Betreuer] Thiele. "Morphology analysis and development of electrodes for polymer electrolyte membrane water electrolyzers and fuel cells." Freiburg : Universität, 2020. http://d-nb.info/1218464089/34.
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Xu, Chenxi. "Development of membranes for low and intermediate temperature polymer electrolyte membrane fuel cell." Thesis, University of Newcastle upon Tyne, 2013. http://hdl.handle.net/10443/2123.
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Proton exchange membrane fuel cells (PEMFCs) are promising electrochemical energy ® conversion devices, which are based on high cost materials such as Nafion membranes. The high cost and limited availability of noble metals such as Pt hinder the commercialisation of PEMFCs. The research described in this thesis focused on the development of composite materials and functionalised polymer membranes for intermediate temperature PEMFCs that o operate in the temperature range of 120 to 200 C. A higher operating temperature would enhance the kinetics of the cell compared to a perfluorinated polymer membrane based cell and provide a greater opportunity to use non-noble metal electrocatalysts. Inorganic–organic composite electrolyte membranes were fabricated from Cs substituted heteropolyacids (CsHPAs) and polybenzimidazole (PBI) for application in intermediate temperature hydrogen fuel cells. Four caesium salts of heteropolyacid, (CsHPMoO X3-X1240 (CsPOMo), CsHPWO(CsPOW), CsHSiMoO(CsSiOMo) and CsHX3-X1240 X4-X1240 X4- SiWO(CsSiOW)) and an ionic liquid heteropolyacid were used to form composite X1240 , membranes with PBI. The membranes were characterised by using SEM, FTIR and XRD. The CsHPA powders were nano-size as shown in the XRD and SEM data. The CsHPA/PBI composite membranes, loaded with HPO had high conductivity, greater than that of a 34 phosphoric acid loaded PBI membrane. Cs substituted heteropolyacid salt showed better enhancement of conductivity than that provided from ionic liquid heteropolyacid salt. The conductivity increased with an increase in the percentage of powder in the composite. The 30% -1 CsPOMo/PBI/HPO exhibited a conductivity of 0.12 S cm under anhydrous conditions 34 although its mechanical strength was the poorest, but still promising with a value of 40 MPa. The performance of the hydrogen fuel cell with composite membranes was better than that with a phosphoric acid-doped PBI membrane under the same conditions. The CsPOMo gave -2 the best power density, of around 0.6 W cm with oxygen at atmospheric pressure. A novel method was used to prepare poly (ethylene oxide)/graphite oxide (PEO/GO) composite membrane aimed for low temperature polymer electrolyte membrane fuel cells without any chemical modification. The membrane thickness was 80 µm with the GO content was 0.5 wt. %. SEM images showed that the PEO/GO membrane was a condensed composite material without structure defects. Small angle XRD for the resultant membrane results showed that the d-spacing reflection (001) of GO in PEO matrix was shifted from2θ=11º to 4.5 º as the PEO molecules intercalated into the GO layers during the membrane -1 preparation process. FTIR tests showed that the vibration near 1700 cm was attributed to the -COOH groups. The ionic conductivity of this PEO/GO membrane increased from 0.086 S -1 -1 cm at 25 ºC to 0.134 S cm at 60 ºC and 100% relative humidity. The DC electrical resistance of this membrane was higher than 20 MΩ at room temperature and 100% relative humidity. Polarisation curves in a single cell with this membrane gave a maximum power -2 density of 53 mW cm at temperature around 60 ºC, although an optimised catalyst layer composition was not used. Polybenzimidazole/graphite oxide (GO /PBI), sulphonated graphite oxide/PBI and ionic liquid GO/PBI composite membranes were prepared for high temperature polymer electrolyte membrane fuel cells. The membranes were loaded with phosphoric acid to provide suitable proton conductivity. The PBI/GO and PBI/SGO membranes were characterised by XRD which showed that the d-spacing reflection (001) of SGO in PBI matrix was shifted from 2θ=11º, meaning that the PBI molecules were intercalated into the SGO layers during the membrane preparation. A low acid loading reduced the free acid in the membranes which avoided water loss and thus conductivity loss. The ionic conductivities of the GO /PBI and -1 -1 SGO/PBI and ILGO/PBI membranes, with low acid loading, were 0.027 S cm , 0.052 S cm -1 and 0.025 S cm at 175 ºC and 0% humidity. Fuel cell performance with SGO/PBI -2 membranes gave a maximum power density of 600 mW cm at 175 ºC. A quaternary ammonium PBI was synthesised as a membrane for applications in intermediate temperature (100-200°C) hydrogen fuel cells. The QPBI membrane was loaded with phosphoric acid (PA) to provide suitable proton conductivity and compared to that of a similar PA loading of the pristine PBI membrane. The resulting membrane material was characterised in terms of composition, structure and morphology by NMR, FTIR, SEM, and −1 EDX. The proton conductivity of the membrane was 0.051 S cm at 150 °C and a PA acid loading of 3.5 PRU (amount of HPO per repeat unit of polymer QPBI). The fuel cell 34 -2 performance with the membrane gave a peak power density of 440 mW cm and 240 mW −2 cm at 175 °C using oxygen and air, respectively. Inorganic–organic composite electrolyte membranes were fabricated from CsHPMoO X3-X1240 CsPOMo and quaternary diazabicyclo-octane polysulfone (QDPSU using a polytetrafluoroethylene (PTFE) porous polymer matrix for applications in intermediate temperature (100-200°C) hydrogen fuel cells. The CsPOMo/QDPSU/PTFE composite membrane was made proton conducting using a relatively low phosphoric acid loading to provide the membrane conductivity without compromising the mechanical strength to a great extent. A casting method was used to build a thin and robust composite membrane. The resulting membrane materials were characterised in terms of composition, structure and morphology by EDX, FTIR and SEM. The proton conductivity of the membrane was 0.04 S -1 cm with a PA loading of 1.8 PRU (amount of HPO per repeat unit of polymer QDPSU). 34 -2 The fuel cell performance with the membrane gave a peak power density of 240 mW cm , at 150 °C and atmospheric pressure. A composite material for phosphoric acid (PA) loaded membrane was prepared using a porous polytetrafluoroethylene (PTFE) thin film. N, N-Dimethylhexadecylamine partially - quaternised poly (vinyl benzyl chloride) (qPVBzCl ) was synthesised as the substrate for the - phosphoric acid loaded polymer membrane. The qPVBzCl was filled into the interconnected - pores of a PTFE thin film to prepare the PTFE/qPVBzCl membrane. A SEM data indicated - that the pores were filled with the qPVBzCl . The PA loading was calculated to be on average 4.67~5.12 per repeat unit. TGA results showed that the composite membrane’s was stable at intermediate temperatures of 100°C to 200 °C. The composite membrane’s tensile stress was 56.23 MPa, and Young’s Modulus was 0.25GPa. The fractured elongation was 23%. The - conductivity of the composite membrane after PA addition (PTFE/qPVBzCl /HPO) 34 -1 -1 increased from 0.085 S cm to 0.1 S cm from 105°C to 180 °C. The peak power density of the H/O fuel cell, at 175 °C under low humidity conditions (<1%), with the22 PTFE/qPVBzCl /HPO 34 membranes was 360 mW cm.
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Sengul, Erce. "Preparation And Performance Of Membrane Electrode Assemblies With Nafion And Alternative Polymer Electrolyte Membranes." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/2/12608734/index.pdf.
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Hydrogen and oxygen or air polymer electrolyte membrane fuel cell is one of the most promising electrical energy conversion devices for a sustainable future due to its high efficiency and zero emission. Membrane electrode assembly (MEA), in
which electrochemical reactions occur, is stated to be the heart of the fuel cell. The aim of this study was to develop methods for preparation of MEA with alternative polymer electrolyte membranes and compare their performances with the conventional Nafion®<br>membrane. The alternative membranes were sulphonated polyether-etherketone (SPEEK), composite, blend with sulphonated polyethersulphone
(SPES), and polybenzimidazole (PBI). Several powder type MEA preparation techniques were employed by using Nafion®<br>membrane. These were GDL Spraying, Membrane Spraying, and Decal methods. GDL Spraying and Decal were determined as the most efficient and proper MEA preparation methods. These methods were tried to improve further by changing
catalyst loading, introducing pore forming agents, and treating membrane and GDL. The highest performance, which was 0.53 W/cm2, for Nafion®<br>membrane was obtained at 70 0C cell temperature. In comparison, it was about 0.68 W/cm2 for a commercial MEA at the same temperature. MEA prepared with SPEEK membrane resulted in lower performance. Moreover, it was found that SPEEK membrane was not suitable for high temperature operation. It was stable up to 80 0C under the cell operating conditions. However, with the blend of 10 wt% SPES to SPEEK, the operating temperature was raised up to 90 0C without any membrane deformation.
The highest power outputs were 0.29 W/cm2 (at 70 0C) and 0.27 W/cm2 (at 80 0C) for SPEEK and SPEEK-PES blend membrane based MEAs. The highest temperature, which was 150 0C, was attained with PBI based MEA during fuel cell
tests.
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Treptow, Florian. "Polyaniline as electrolyte in polymer electrolyte membrane fuel cells." Thesis, Loughborough University, 2005. https://dspace.lboro.ac.uk/2134/11086.
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The applications of polyaniline (PAni) for use as electrolyte in Polymer-Electrolyte-Membrane Fuel Cells (PEMFC) were investigated. P Ani was dissolved in N-methyl pyrrolidone (NMP), cast as Emeraldine Base membranes (EB) and then doped with halide acids. The proton conductivity was measured according to Hittorf. The chloride ion distribution within the membrane was evaluated using energy-dispersive-X-ray analysis (EDX) and photometric analysers and the diffusion coefficient was calculated. The specific resistance was determined using conventional 4-point measurement. Halide doped membranes were found to be proton conducting, however, during cell operation halide removal occurred causing a rapid decline in the cell performance. The maximum power density achieved was O.3m W·cm-2 for a 70J.1m thick membrane saturate with chloride between 3,5 and 4,5mgchloride per gPAni. Composite membranes with phosphotungstic acid (PWA), antimonic acid (AA) and zirconium phosphate (ZP) were developed and also tested in a standard measuring fuel cell. While membranes produced via ion exchange (ZP) showed the same result like halide doped ones, AA composite membranes showed a stable voltage and current results. The highest measured outcome of 373.3mW·cm-2 was found with a PWA membrane, produced through dispersing 3g of phosphotungstic acid in 300ml of a 1% polyanilinelNMP solution. It was also observed, that the higher power density was obtained from the fuel cell which uses the lower-loaded membrane. It is clear that a positive effect on the cell performance is given by the addition of phosphotungstic acid to the polyaniline membrane. Therefore, the saturation of PW A have to be taken into account to not lower the power density.
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Borah, Deepjyoti Verfasser], Werner [Akademischer Betreuer] [Lehnert, and Lorenz [Akademischer Betreuer] Singheiser. "Two-phase flow in porous transport layers of polymer electrolyte membrane electrolysers / Deepjyoti Borah ; Werner Lehnert, Lorenz Singheiser." Aachen : Universitätsbibliothek der RWTH Aachen, 2021. http://d-nb.info/1241891540/34.
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Savignac, Julie. "Impact des interactions membrane/électrolyte sur la diffusion de sucres à travers des membranes échangeuses d'ions." Phd thesis, Université Paul Sabatier - Toulouse III, 2010. http://tel.archives-ouvertes.fr/tel-00581794.
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Des travaux récents ont montré que le transfert d'espèces neutres à travers différents types de membranes est modifié selon la composition ionique. En présence de sels, le flux de soluté est augmenté, ce qui peut conduire à une dégradation des performances des procédés. Ce travail présente les résultats d'une étude expérimentale dans laquelle les flux de diffusion de sucre dans différentes matrices ioniques, eau et électrolytes, ont été déterminés à travers des membranes échangeuses d'ions. Une procédure spécifique a été mise au point pour déterminer l'impact des différentes interactions sur les flux de solutés. Les résultats montrent que, dans les conditions étudiées, la modification du transfert de matière est due principalement aux interactions entre le matériau membranaire et la solution. Une corrélation a été établie entre l'échelle d'hydratation des contre-ions de la membrane et le flux de soluté.
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Fuoco, Alessio. "Computational and experimental studies on membrane-solute interactions in desalination systems using ion-exchange membranes." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30132/document.
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Des études antérieures ont mis en évidence que le transfert de solutés neutres à travers des membranes est influencé par la présence d'ions en solution. Ainsi, la connaissance des interactions multiples à l'échelle nanométrique, entre le polymère, l'eau et les solutés (ions, espèces organiques) constituent un verrou pour l'amélioration des performances des procédés membranaires. Dans cette étude une approche multi-échelle fondamentale est proposée, combinant des outils théoriques et expérimentaux, afin d'obtenir les paramètres microscopiques et macroscopiques caractérisant les interactions étudiées pour différentes compositions ioniques. Plus précisément, il s'agit de comprendre comment les ions affectent le transfert d'un soluté organique. Dans un premier temps, certaines propriétés caractérisant l'hydratation des ions sont calculées et comparées aux flux de diffusions de sucres à travers des membranes de Nanofiltration et échangeuses d'ions obtenus pour différentes compositions ioniques. Dans un deuxième temps, des systèmes constitués d'une membrane échangeuse de cations (CMX) équilibrée avec différents cations ainsi que le glucose hydraté sont modélisés en utilisant une approche combinée Mécanique Quantique/ Mécanique Moléculaire. Cette approche a permis d'étudier la solubilité du sucre dans la matrice polymère ainsi que les interactions polymère-polymère comme l'énergie de cohésion. Enfin, l'influence des ions sur les caractéristiques physiques de la membrane CMX est étudiée en utilisant diverses méthodes expérimentales comme la détermination des angles de contacts et des spectres IR ou la mesure de la température de solidification par DSC. Les propriétés vibrationnelles sont également calculées dans le cadre de la théorie de la fonctionnelle de la densité (DFT). L'ensemble de ces données sont comparées avec les grandeurs de transport afin de valider les mécanismes moléculaires proposés. Ce travail montre que la nature des contre-ions de la membrane modifie l'énergie de cohésion entre les fragments de la membrane. Ainsi, l'énergie de cohésion influe sur la diffusion des composés organiques neutres à travers les membranes<br>Previous works have shown that the transfer of neutral solutes through membranes is influenced by the presence of ions in solution. In the framework of process intensification, the knowledge of the molecular mechanisms involved is of fundamental importance to increase and predict the process performances. The aim of this Thesis is to use a combined quantum/molecular computational approach and experimental methodologies to better understand how ions can affect the solute flux. In the first part of the work, some properties of ions in solution are computed and compared with sugar fluxes through membranes for nanofiltration and electrodialysis. In the following, systems composed of Cation-exchange membrane equilibrated by different counter-ion and hydrated glucose are examined by Quantum Mechanics/Molecular Mechanics. This is done mainly to investigate the sugar solubility in the polymer matrix and diffusion related interactions like polymer chain-chain cohesion energy. In the last part, contact angle, differential scanning calorimetry and Infra-Red spectra are measured to characterize the physical properties of the membrane and possible influence of the counter-ion on cation exchange membrane. This work shows that the nature of the counter-ions modifies the cohesion energy between the membrane polymer fragments. In its turn, the cohesion energy affects the diffusion of neutral organic compounds through the membranes
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Sivertsen, Edvard. "Membrane Separation of Anions in Concentrated Electrolytes." Doctoral thesis, Norwegian University of Science and Technology, Department of Chemical Engineering, 2001. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-2100.
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Zhou, Zhen. "Development of polymer electrolyte membranes for fuel cells to be operated at high temperature and low humidity." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/22559.
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Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2007.<br>Committee Chair: Wong, C.P.; Committee Co-Chair: Liu, Meilin; Committee Member: Barefield, Kent; Committee Member: Collard, David; Committee Member: Fahrni, Christoph.
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Pehlivan-Davis, Sebnem. "Polymer Electrolyte Membrane (PEM) fuel cell seals durability." Thesis, Loughborough University, 2016. https://dspace.lboro.ac.uk/2134/21749.
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Polymer electrolyte membrane fuel cell (PEMFC) stacks require sealing around the perimeter of the cells to prevent the gases inside the cell from leaking. Elastomeric materials are commonly used for this purpose. The overall performance and durability of the fuel cell is heavily dependent on the long-term stability of the gasket. In this study, the degradation of three elastomeric gasket materials (silicone rubber, commercial EPDM and a developed EPDM 2 compound) in an accelerated ageing environment was investigated. The change in properties and structure of a silicone rubber gasket caused by use in a real fuel cell was studied and compared to the changes in the same silicone rubber gasket material brought about by accelerated aging. The accelerated aging conditions were chosen to relate to the PEM fuel cell environment, but with more extreme conditions of elevated temperature (140°C) and greater acidity. Three accelerated ageing media were used. The first one was dilute sulphuric acid solution with the pH values of 1, 2 and 4. Secondly, Nafion® membrane suspended in water was used for accelerated ageing at a pH 3 to 4. Finally, diluted trifluoroacetic acid (TFA) solution of pH 3.3 was chosen. Weight change and the tensile properties of the aged gasket samples were measured. In addition, compression set behaviour of the elastomeric seal materials was investigated in order to evaluate their potential sealing performance in PEM fuel cells. The results showed that acid hydrolysis was the most likely mechanism of silicone rubber degradation and that similar degradation occurred under both real fuel cell and accelerated aging conditions. The effect of TFA solution on silicone rubber was more aggressive than sulphuric acid and Nafion® solutions with the same acidity (pH value) suggesting that TFA accelerated the acid hydrolysis of silicone rubber. In addition, acid ageing in all three acidic solutions caused visible surface damage and a significant decrease in tensile strength of the silicone rubber material, but did not significantly affect the EPDM materials. EPDM 2 compound had a desirable (low) compression set value which was similar to silicone rubber and much better than the commercial EPDM. It also showed a very good performance in the fuel cell test rig conforming that it a potential replacement for silicone rubber in PEMFCs.
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Verma, Atul. "Transients in Polymer Electrolyte Membrane (PEM) Fuel Cells." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/64247.
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The need for energy efficient, clean and quiet, energy conversion devices for mobile and stationary applications has presented proton exchange membrane (PEM) fuel cells as a potential energy source. The use of PEM fuel cells for automotive and other transient applications, where there are rapid changes in load, presents a need for better understanding of transient behavior. In particular at low humidity operations; one of the factors critical to the performance and durability of fuel cell systems is water transport in various fuel cell layers, including water absorption in membrane. An essential aspect to optimization of transient behavior of fuel cells is a fundamental understanding of response of fuel cell system to dynamic changes in load and operating parameters. This forms the first objective of the dissertation. An insight in to the time scales associated with various transport phenomena will be discussed in detail. In the second component on the study, the effects of membrane properties on the dynamic behavior of the fuel cells are analyzed with focus on membrane dry-out for low humidity operations. The mechanical behavior of the membrane is directly related to the changes in humidity levels in membrane and is explored as a part third objective of the dissertation. Numerical studies addressing this objective will be presented. Finally, porous media undergoing physical deposition (or erosion) are common in many applications, including electrochemical systems such as fuel cells (for example, electrodes, catalyst layer s, etc.) and batteries. The transport properties of these porous media are a function of the deposition and the change in the porous structures with time. A dynamic fractal model is introduced to describe such structures undergoing deposition and, in turn, to evaluate the changes in their physical properties as a function of the deposition.<br>Ph. D.
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Inaba, Minoru. "Electrochemical Reactions on Polymer Electrolyte Membrane/Electrode Composites." Kyoto University, 1994. http://hdl.handle.net/2433/74664.
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De, Beer Chris. "Condition monitoring of polymer electrolyte membrane fuel cells." Doctoral thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13264.
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Includes bibliographical references.<br>As the global demand for energy continues to grow new technologies and systems must be developed to supply the market. This includes renewable energy generation, storage and conversion systems. The primary storage technology in use today in the portable electronics, the automotive sector and to a lesser extent power networks is battery based systems. To overcome some of the limitations inherent in batteries, fuel cell based power generators and converters have been developed. Fuel cells act as electrochemical energy converters that convert a fuel source such as natural gas directly into electrical power without any secondary phases. For systems running on Hydrogen generated via renewable or natural sources, the input/output cycle becomes completely sustainable. Out of the different fuel cell types available and under development, the Proton Exchange Membrane or Polymer Electrolyte Membrane (PEM) fuel cell has emerged as the technology of choice, and currently owns more than 80% of the commercial fuel cell market. This has spurred further research in the field to increase performance and life expectancy of the cell materials. A promising development in the form of High Temperature PEM (HT-PEM) fuel cells has recently emerged and addresses some of the shortcomings of the low temperature counterparts. A critical field of research is the condition monitoring strategies and technologies for the electrochemical device that ties in with the power conditioning sub-systems. This thesis presents the development of condition monitoring systems by conducting detailed studies on the fault/degradation mechanisms prevalent in the cell materials for the purpose of detection, classification and implementation of possible mitigation strategies. Specific consideration is given to the detailed analysis of the fault mechanisms in HT-PEM fuel cells that are not yet fully understood and commercialized. In particular, electrochemical equivalent circuit models and reduced order semi- empirical models are developed to facilitate fault detection. Based on these models, mitigation strategies for specific faults are proposed and experimentally verified. New systems and methods are developed for rapid online impedance signature mapping that provide a basis for early fault prediction that can increase system performance and life expectancy. The findings in this research provide valuable insight into the effect that most prevalent faults have on the internal electrochemistry and the impact on electrical performance. From the experimental results, a semi-empirical electrochemical model is developed to assist with life time estimation and system optimization. The model is integrated with a real time emulator platform that can reproduce single cell voltage levels at the high output currents and transient characteristics. A detailed analysis is conducted on CO poisoning and the resulting effects on key equivalent circuit parameters that enable quantification of the fault condition. It is shown that the catalyst at the higher operating temperature is still susceptible to a certain degree of semi-permanent degradation. To mitigate these effects, a new active current control strategy is proposed to enforce electro-oxidation of the CO to recover the lost active area that delivered superior results compared to current pulsing strategies. New rapid online detection strategies are proposed by using small voltage transients in an operational HT-PEM fuel cell. The method makes use of the discrete S-transform that overcomes some of the limits in other signal processing methods used in fuel cell diagnostics. To enable detailed parameter calculation, a population based incremental learning algorithm is implemented in the developed method. A new condition monitoring system is developed that makes use of Optimized Broadband Impedance Spectroscopy. The hardware is designed to accommodate both single cell and stack level implementation. It is shown that the proposed system is able to deliver measurements under extreme non-linear conditions that can occur in PEM fuel cells in a fraction of the time associated with normal EIS based systems.
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Puthiyapura, Vinod Kumar. "Development of anode catalysts for proton exchange membrane water electrolyser." Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2446.
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The proton exchange membrane water electrolyser (PEMWE) is a promising technology for the production of hydrogen from water. The oxygen evolution reaction (OER) has a high over potential cf. with the hydrogen evolution reaction and is one of the main reasons for the high energy demand of the electrolyser. RuO₂ and IrO₂ are the most active catalyst for OER, but are costly, making the electrolyser system expensive. In general, it is important to use stable, active and cheap catalysts in order to make a cost efficient electrolyser system. Supporting the active catalyst on a high surface area conducting support material is one of the approaches to reduce the precious metal loading on the electrode. Antimony tin oxide (ATO) and indium tin oxide (ITO) were studied as possible support materials for IrO₂ in the PEMWE anode prepared by the Adams method. The effect of the support material on the surface area, electronic conductivity, particle size and agglomeration were investigated. The IrO₂ showed highest conductivity (4.9 S cm-¹) and surface area (112 m2 g-¹) and decreased with the decrease in the IrO₂ loading. Using the catalysts in the membrane electrode assemblies (MEA) with Nafion®-115 membranes, at 80°C showed that the catalyst with better dispersion and conductivity gave better performance. The unsupported IrO₂ and 90% IrO₂ supported on ATO and ITO showed the best performance among all the catalysts tested, achieving a cell voltage of 1.73 V at 1 A cm-². A lower IrO₂ loading decreased the conductivity and surface area. The IrO₂ particle size and bulk conductivity of the supported catalyst significantly influenced the MEA performance. Overall, it is important to maintain a conductive network of IrO₂ on the non-conducting support to maintain the bulk conductivity and thus reduce the Ohmic potential drop. Although RuO₂ is the most active catalyst for OER, it lacks stability on long term operation. RuxNb1-xO₂ and IrxNb1-xO₂ catalysts were synthesized and characterized, to try to develop stable electrodes for PEMWE. However the Adams method of catalyst synthesis formed a sodium–niobium complex making it unsuitable for preparation of Nb based catalysts. In both Adams and hydrolysis methods of synthesis, the addition of Nb ₂O₅ decreased the anodic charge and electronic conductivity of the catalyst due to the dilution of the active RuO₂. The RuO₂ catalyst showed the best performance in MEA evaluation compared to the bimetallic catalyst (1.62 V and 1.75 V @1 A cm-² for RuO₂(A) and RuO₂(H) respectively). A higher stability for bimetallic catalyst compared to the monometallic catalysts was obtained from the continuous CV cycling and MEA stability test.
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Gao, Hongrong. "Stabilisation des Membranes Perfluorosulfoniques par Réticulation et Développement de Membranes Composites Inorganique-organique. Application aux Piles à Combustible à Moyenne Température." Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20236.
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Ce travail décrit le développement de membranes réticulées et de membranes composites inorganique-organique basées sur des polymères perfluorosulfoniques (PFSA) à chaîne longue (LSC) et courte (SSC) et à faible masse équivalente, pour application dans une pile à combustible fonctionnant à moyenne température et à faible humidité relative. Des membranes (LSC-PFSA) réticulées par des groupements sulfonimide ont été préparées à partir de membranes fonctionnalisées par des groupements fluorure de sulfonyle. Les membranes réticulées de type SSC-PFSA ont été préparées à partir d'un polymère à chaînes 2-bromo-1,1,2,2-tetrafluoroéthoxy pendantes et réticulables, par traitement thermique pour former des ponts perfluoro. Les membranes préparées ont été caractérisées par spectroscopies IR, Raman, RMN et XPS, par MEB-EDX et ATG. Les membranes de LSC-PFSA et SSC-PFSA réticulées présentent une stabilité dimensionnelle accrue et une meilleure performance en pile à combustible hydrogène-oxygène jusqu'à 110°C que celles des membranes de PFSA non modifiées. Une procédure d'échange ionique/précipitation a été utilisée pour la préparation de systèmes composites à partir de membranes de LSC-PFSA et SSC-PFSA. Plusieurs techniques ont été utilisées pour caractériser les matériaux préparés. Les membranes de type SSC-PFSA-ZrP présentent une morphologie distincte, et différente de celle des membranes LSC-PFSA-ZrP. En pile à combustible, ces membranes composites autorisent une température de fonctionnement plus élevée et une humidité relative plus faible, que les membranes non modifiées<br>The objective of this research was to develop cross-linked and composite inorganic-organic membranes based on long and short side chain (LSC, SSC) perfluorosulfonic acid (PFSA) polymers with low equivalent weight/high ion exchange capacity for operation at medium temperature and low relative humidity in proton exchange membrane fuel cells. Covalently cross-linked LSC-PFSA membranes were prepared from sulfonyl fluoride form membranes by reaction with an ammonium base followed by thermal processing to give cross-linking through sulfonimide groups. Covalently cross-linked SSC-PFSA membranes were prepared by formation of perfluoro-cross-links under thermal treatment of solution cast polymers containing cross-linkable 2-bromo-1,1,2,2-tetrafluoroethoxy side chains. Evidence for cross-linking was provided by IR, Raman, NMR and XPS spectroscopies, SEM-EDX, tensile testing and TGA. Cross-linked LSC and SSC-PFSA membranes have increased dimensional stability and improved performance in a single hydrogen-oxygen cell fuel up to 110°C compared with the corresponding non-cross-linked membranes. Composite PFSA-zirconium phosphate membranes, based on LSC and SSC PFSA (or cross-linked PFSA) membranes were prepared using an ion exchange/precipitation procedure. The physical properties of LSC-PFSA-ZrP and SSC-PFSA-ZrP have been compared and the morphology of the composite membranes shown to differ in SSC and LSC membranes. Composite membranes enabled fuel cell operation at higher temperature/lower RH than non-composite PFSA. Preliminary results indicated that association of cross-linking and composite membrane formation is a clear future perspective of this work
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Chen, Cheng. "Membrane degradation studies in PEMFCs." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29712.
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Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2010.<br>Committee Chair: Fuller, Thomas; Committee Member: Beckham, Haskell; Committee Member: Hess, Dennis; Committee Member: Koros, William; Committee Member: Meredith, Carson. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Fanapi, Nolubabalo Hopelorant. "Durability studies of membrane electrode assemblies for high temperature polymer electrolyte membrane fuel cells." University of the Western Cape, 2011. http://hdl.handle.net/11394/5416.
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>Magister Scientiae - MSc<br>Polymer electrolyte membrane fuel cells (PEMFCs) among other fuel cells are considered the best candidate for commercialization of portable and transportation applications because of their high energy conversion and low pollutant emission. Recently, there has been significant interest in high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), due to certain advantages such as simplified system and better tolerance to CO poisoning. Cost, durability and the reliability are delaying the commercialization of PEM fuel cell technology. Above all durability is the most critical issue and it influences the other two issues. The main objective of this work is to study the durability of membrane electrode assemblies (MEAs) for HT-PEMFC. In this study the investigation of commercial MEAs was done by evaluating their performance through polarization studies on a single cell, including using pure hydrogen and hydrogen containing various concentrations of CO as fuel, and to study
the performance of the MEAs at various operating temperatures. The durability of the MEAs was evaluated by carrying out long term studies with a fixed load, temperature cycling and open circuit voltage degradation.
Among the parameters studied, significant loss in the performance of the MEAs was noted during temperature cycling. The effect of temperature cycling on the performance of the cell showed that the performance decreases with increasing no. of cycles. This could be due to leaching of acid from the cell or loss of electrochemically active surface area caused by Pt particle size growth. For example at 160°C, a performance loss of 3.5% was obtained after the first cycle, but after the fourth cycle a huge loss of 80.8% was obtained. The in-house MEAs with Pt-based binary catalysts as anodes were studied for CO tolerance, performance and durability. A comparison of polarization curves between commercial and in-house MEAs illustrated that commercial MEA gave better performance, obtaining 0.52 A/cm² at 0.5V and temperature of 160°C, with in-house giving 0.39A/cm² using same parameters as commercial. The CO tolerance of both commercial and in-house MEA was found to be similar. In order to increase the CO tolerance of the in-house MEAs, Pt based binary catalysts were employed as anodesand the performance was investigated In-house MEAs with Pt/C and Pt-based binary catalysts were compared and a better performance was observed for Pt/C than Pt-alloy catalysts with Pt-Co/C showing comparable performance. At 0.5 V the performance obtained was 0.39 A/cm2 for Pt/C, and 0.34A/cm²,0.28A/cm²,0.27A/cm² and 0.16A/cm² were obtained for Pt-Co/C, Pt-Fe/C, Pt-Cu/C and Pt-Ni respectively. When the binary catalysts were tested for CO tolerance, Pt-Co showed no significant loss in
performance when hydrogen containing CO was used as anode fuel. Scanning electron
microscopy (SEM) revealed delamination between the electrodes and membrane of the tested and untested MEA's. Membrane thinning was noted and carbon corrosion was observed from the tested micro-porous layer between the gas diffusion layer (GDL) and catalyst layer (CL).
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Barron, Olivia. "Gas diffusion electrodes for high temperature polymer electrolyte membrane fuel cells membrane electrode assemblies." University of the Western Cape, 2014. http://hdl.handle.net/11394/4323.
Full textAbstract:
Philosophiae Doctor - PhD<br>The need for simplified polymer electrolyte membrane fuel cell (PEMFCs) systems, which do not require extensive fuel processing, has led to increased study in the field of high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) applications. Although these HT-PEMFCs can operate with less complex systems, they are not without their own challenges; challenges which are introduced due to their higher operation temperature. This study aims to address two of the main challenges associated with HT-PEMFCs; the need for alternative catalyst layer (CL) ionomers and the prevention of excess phosphoric acid (PA) leaching into the CL. The first part of the study involves the evaluation of suitable proton conducting materials for use in the CL of high temperature membrane electrode assemblies (HT-MEAs), with the final part of the study focusing on development of a novel MEA architecture comprising an acid controlling region. The feasibility of the materials in HT-MEAs was evaluated by comparison to standard MEA configurations.
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Kolstad, Aleksander. "Membrane processes relevant for the polymer electrolyte fuel cell." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for kjemi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22427.
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Research in the Proton Exchange Membrane Fuel Cell (PEMFC) is important toget an efficient fuel cell that can be used as an energy carrier, for example in thetransport sector. Understanding the different phenomena and variations in temperature,heat and other quantities is critical. Non-equilibrium thermodynamics is usedto establish a 1-dimensional model for transport processes in a Nafion membranesystem consisting of heat and mass transport, and for a PEM fuel cell with heat andtransport of mass and charge.The Nafion membrane in part 2 is coated with a Sigracet layer of either GDL10AAwithout Teflon or with GDL10BA with 5 % Teflon. Outside of these layers is liquidwater. The absorption enthalpy between liquid water and the Sigracet layer hasbeen found by combining experimental data with the established simulation model.For GDL10AA without Teflon this absorption enthalpy ranges from -460 J/mol to-3380 J/mol for mean temperatures of 30 oC and 75 oC respectively. For GDL10BAwith Teflon this absorption enthalpy ranges from 1150 J/mol to 7850 J/mol for meantemperatures of 30 oC and 75 oC respectively. The heat capacity value of water for Sigracet GDL10AA and GDL10BA was found to be 10 J/K mol and 223 J/Kmol respectively. The effect on the absorption enthalpy and the sign and value ofthe water flux by changing the temperature and material properties is studied. Thisstudy has found that the heat conductivities play a minor role when it comes totransport of water compared to the diffusion constant of the Nafion membrane andthe Sigracet layers.A simulation model is established for the PEM Fuel Cell in part 3. Only variationsin quantities along one dimension is considered. Non-equilibrium thermodynamics isused to properly describe heat and transport of mass and charge. The system has aNafion membrane coated with a Sigracet layer of GDL10AA without Teflon at bothends. Outside of these layers are water vapor with hydrogen at one side and oxygenat the other. Case studies such as the reversible limit is studied in detail to confirmthe accuracy and validity of the simulation model. Profiles of temperature, chemicalcomposition, water content, measurable heat flux, electrical potential and entropyproduction are found by use of the simulation model for various current densities.A polarization curve by plotting the cell potential for different current densities isfound. Additionally study and a sensitivity analysis for the PEM fuel cell are carriedout to fully understand transport processes and the effects from material properties.
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Al-Musa, Abdullah Abdulaziz. "Partial oxidation of propene using solid electrolyte membrane reactors." Thesis, Loughborough University, 2002. https://dspace.lboro.ac.uk/2134/6915.
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This study investigates the efficiency of a calcia stabilised zirconia (CaSZ) solid electrolyte as an oxygen ion conductor. The study also examines the behaviour of the oxygen species conducted by the solid electrolyte compared to species provided in the gas phase for partial oxidation of hydrocarbons. In this work, an electrochemical cell of the form Air, AgHCaSZ//Ag, Carrier gas was used to investigate the electrochemical efficiency and stability of the solid electrolyte CaSZ conducting of oxygen ions under atmospheric pressure conditions at 500 degrees C by applying a range of electrical potentials from I to 16 volts across the electrochemical cell. Due to the applied potential oxygen anions are transferred across the solid electrolyte from the cathode side of the cell to the anode side. It was found that the employed electrolyte is approximately a 100% purely ionic conductor of oxygen ions in the range of electrical voltage applied from I to 10 volts. Above that range the cell started to degrade and loose its ionic efficiency. It was possible to generate gas mixtures containing trace quantities of oxygen. The viscosity of these gas mixtures as a function of oxygen concentration was determined using an established flow perturbation technique (Flux Response Technology). Partial oxidation of propene was used to investigate the difference between the oxygen species produced electrochemically via electrical potential application across the electrochemical cell Air, AgHCaSZ//Ag, Propene, Ar and oxygen provided in the gaseous state co-fed with propene over silver electrode under atmospheric pressure and 450 degrees C and 500 degrees C. It was found that the method of electrochemical provision of oxygen caused the silver catalyst to be more selective to 1,5-hexadeine, whereas the gaseous oxygen provision produced acrolein as the major product. Carbon dioxide formation was not affected by the method of oxygen provision. The Ag electrode was compared to an Au-rich Ag alloy electrode for propene partial oxidation using electrochemical provision. It was found that 1,5-hexadiene was the major product over both electrodes, but the Au-rich alloy was more selective for acrolein than the Ag electrode. This might be due to the gold serving as a separator between Ag particles which hinder the back-spill over of oxygen and allow desorption of molecular oxygen in the gas phase, which then re-adsorb molecularly on silver sites producing acrolein. The effect of the sequence of the method of oxygen provision on the partial oxidation of propene was tested using the electrochemical cell Y-BiMoHAg//CaSZ//Ag at 450 degrees C and atmospheric pressure. A sharp decrease in acrolein selectivity was found when oxygen was provided in the gas phase after treatment with electrochemical oxygen, while no significant effect was noticed when the electrochemical oxygen was used after treatment with gaseous oxygen. This large decrease in acrolein selectivity might be attributed to the severe reduction of the catalyst, which is probably caused by high electrical potential application. A temperature increase from 450 to 500 degrees C seemed to suppress the formation of acrolein for both methods of oxygen provision and enhance the 1,5-hexadiene formation.
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Tumuluri, Uma. "Nonlinear State Estimation in Polymer Electrolyte Membrane Fuel Cells." Cleveland State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=csu1231961499.
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Balogun, Emmanuel O. "Comparative analysis of Polymer Electrolyte Membrane (PEM) fuel cells." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29764.
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Per-Fluoro-Sulphonic-Acid (PFSA) ionomers have been singled out as the preferable ionomers for making the Polymer Electrolyte Membrane Fuel Cells (PEMFC) membranes owing to their extensive intrinsic chemical stability and super sulfonic acid strength which is core to the PEMFC proton conductivity. This thesis presents a deeper analysis into these PFSA ionomer membrane electrode assemblies (MEA), presenting an electrochemical-analytical comparative analysis of the two basic types, which are the Long-Side-Chain (LSC) Nafion® and the ShortSide-Chain (SSC) Aquivion® ionomer MEA with emphasis on performance and durability which are currently not well understood. In particular, electrochemical circuit models and semiempirical models were employed to enable distinguishable comparative analysis. Also, in this thesis, we present a further probe into the effect of ionomer ink making processes, critically investigating the effect of the High Share Dispersion (HSD) process on both the Nafion® and Aquivion® ionomer membrane electrode assembly (MEA). The findings in this research provides a valuable insight into the performance and durability of PFSA ionomer membrane under various application criteria. The effect of operating parameters and accelerated stress testing (AST) on the PFSA ionomers was determined using electrochemical impedance spectroscopy (EIS) and electronic circuit model (ECM) analysis. The result of this study, shows that the ionomer ink making process for Nafion® and Aquivion® MEAs are not transferrable. Analysis of the PEMFC performance upon application of the high shear dispersion (HSD) process showed that Nafion® MEA had a 10.47% increase in voltage while the Aquivion® MEA had a 2.53% decrease in voltage at current density of 1.14A/cm2 . Also, upon accelerated stress testing, the Nafion® showed a 10.49% increase in its voltage while the Aquivion® on the other hand had a 7.16% decrease in voltage at 0.66A/cm2 . Thus indicating the HSD process enhances the performance of the Nafion® MEA and inhibits the performance of the Aquivion® MEA.
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Mamlouk, Mohamed. "Investigation of high temperature polymer electrolyte membrane fuel cells." Thesis, University of Newcastle upon Tyne, 2008. http://hdl.handle.net/10443/3973.
Full textAbstract:
the major issues limiting the introduction of polymer electrolyte membrane fuel cells (PEMFC) is the low temperature of operation which makes platinum-based anode catalysts susceptible to poisoning by trace amounts of CO, typically present in reformed fuel. In order to alleviate the problem of CO poisoning and improve the power density of the cell, operating at temperature above 100°C is preferred. Nafion® type perfluorosulphonated polymers have been typically used for PEMFC but cannot function at temperatures above 100°C. In addition, higher temperatures will enable more effective cooling of the cell stacks and provide a means for combined electrical and heat energy generation. The solution to improved PEMFCs technology is to develop a new polymer electrolyte membrane which exhibits stability and high conductivity in the absence of liquid water. A HighTemperature PEMFC based on a Phosphoric acid (H3P04) doped Polybenzimidazole poly[2,2- (m-phenylene)-5,5 bibenzimidazole] (PBI) membrane has been developed and demonstrated as an alternative to Nafion® for operation at temperatures up to 200°C. PBI membranes, when doped with phosphoric acid, do not rely on hydration for conductivity; a significantly lower water content of the membrane, compared to Nafion, is required for proton transport. The resulting system improvements include; high CO tolerance, simple thermal and water management, excellent oxidative and thermal stability, and good proton conductivity at elevated temperatures. Two issues associated with phosphoric acid in the PBI based fuel cell are the lower activity of the electrocatalysts and the potential loss of the acid into the fuel cell gas/vapour exhaust streams. The limited oxygen permeability and slow oxygen reduction kinetics in phosphoric acid is a major limitation for the performance ofPBI based PEMFCs. The kinetics of oxygen reduction in PBVH3P04 has been studied in electrochemical single electrode cells. Several Membrane Electrode Assemblies (MEAs) have been manufactured to allow optimisation of the electrode performance. Various electrochemical techniques such as chronoamperometry, polarisation curves and Frequency Response Analysis (FRA) were used to study and separate the effects of the various phenomena taking place at the electrode surface: IR losses, mass transport and kinetics. A new Electrode structure utilizing PTFE has been developed allowing higher oxygen permeability and therefore enhanced performance of 0.55 W cm-2 with oxygen and 0.27 W cm-2 with air (atm) at temperature as low as 120 ·C. The Platinum loading was reduced to 0.4 mgpt cm-2 at the cathode and 0.2 mgpt cm-2 at the anode. Further reduction of cathode platinum loading to 0.2 mgPI cm-2 was achieved without dramatic drop in the performance by utilising Pt based binary alloy catalyst (Pt-Co/C). A simplified thin film steady-state, isothermal, one dimensional model of a proton exchange membrane fuel cell (PEMFC), with a polybenzimidazole (PBD membrane, was developed. The electrode kinetics were represented by the Butler-Volmer equation, mass transport was described by the multi-component Stefan Maxwell equations and Fick's law, and the ionic and electronic resistances described by Ohm's law. The model incorporated the effects of temperature and pressure on the open circuit potential, the exchange current density and diffusion coefficients, together with the effect of water on the acid concentration and ionic conductivity. The polarisation curves predicted by the model were validated against experimental data for a PEMFC which included the effect of temperature and oxygen/air pressure on cell performance. An additional problem which faces the introduction ofPEMFC technology is that of supplying or storing hydrogen for cell operation, especially for vehicular applications. Consequently the use of alternative fuels such as methanol and ethanol is of interest, especially if this can be used directly in the fuel cell, without reformation to hydrogen. A limitation of the direct use of alcohol is the lower activity of oxidation in comparison to hydrogen, and hence to improve activity and power output higher temperatures of operation are preferable. The performance of a high temperature direct methanol fuel cell (DMFC) using PBI based electrode assemblies was investigated. The performance of the system was limited by poor methanol oxidation kinetics in a phosphoric acid environment and consequently power performance was inferior to that achieved with low temperature DMFCs based on Nafion membranes.
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Aksakal, Ziya Can Şeker Erol. "Hydrogen production from water using solar cells powerd nafion membrane electrolyzers/." [s.l.]: [s.n.], 2007. http://library.iyte.edu.tr/tezlerengelli/master/enerjimuh/T000633.pdf.
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Bühler, Melanie [Verfasser], Stefan [Akademischer Betreuer] Glunz, and Simon [Akademischer Betreuer] Thiele. "Development of novel electrode concepts for proton exchange membrane water electrolyzers." Freiburg : Universität, 2019. http://d-nb.info/1208148044/34.
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Prifti, Helen Chemical Sciences & Engineering Faculty of Engineering UNSW. "Electrolyte and membrane studies of the novel vanadium bromide redox flow cell." Awarded by:University of New South Wales. Chemical Sciences & Engineering, 2008. http://handle.unsw.edu.au/1959.4/41478.
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The novel Vanadium Bromide (V/Br) redox flow cell employs a V (III)/V (II) couple in the negative half-cell and a Br/Br2 couple in the positive half-cell, with hydrobromic acid and hydrochloric acid as the supporting electrolyte. This study evaluated the chemical and electrochemical properties of the electrolytes and assessed experimental and commercial membranes for use in the V/Br flow cell. A number of techniques were employed to characterise the composition of the V/Br flow cell electrolytes. During charge, the conductivity of the positive half-cell electrolyte increased, whilst the density and viscosity increased. The reverse was observed for the negative half-cell. The UV-visible spectra of the electrolytes showed characteristic peak wavelengths of the vanadium oxidation states and provided and insight into the halogenated species forming during the operation of the V/Br flow cell. The electrochemical properties of the electrolytes were also examined using cyclic voltammetry. NMR studies examined the relationships between the 35CI and 79Br nuclei in the presence of halide and paramagnetic vanadium ions. It was established that the SOC and performance of the V/Br flow cell can be measured by changes in slllectral chemical shifts and line widths. Small-scale cycling experiments were conducted to evaluate the performance of ion exchange membranes in the V/Br redox flow cell. Of the membranes evaluated, a number were not suitable for use due to high membrane resistances or low chemical stability. The perfluorinated Nafion?? and Gore Select?? ion exchange membranes proved to be the most chemically inert and showed low resistances. The Gore Select?? membranes did however exhibit blistering during extended cycling. The chemical stability and cycling performance of the HiporeTM microporous separator showed promise for future studies to optimise the selectivity and ion exchange capacity of the membrane. Tests of membrane ion exchange capacity, diffusivity and conductivity mirrored the properties displayed in the cell cycling experiments. Results suggested that the structural characteristics of the membrane (including functionality and crosslinking) greatly influenced membrane properties and performance. Tests of long term stability showed a negative change in membrane properties. These changes did not however reflect measured changes during cell cycling experiments.
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Zhou, Zhilian DeSimone Joseph M. "Novel polymer electrolyte membranes for fuel cell applications." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2006. http://dc.lib.unc.edu/u?/etd,580.
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Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2006.<br>Title from electronic title page (viewed Oct. 10, 2007). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry." Discipline: Chemistry; Department/School: Chemistry.
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Michaels, W. C. "Microheterogeneous solid polymer electrolyte (SPE) membranes for electrocatalysis." Thesis, Stellenbosch : Stellenbosch University, 2002. http://hdl.handle.net/10019.1/52934.
Full textAbstract:
Dissertation (Ph.D.)--Stellenbosch University, 2002.<br>ENGLISH ABSTRACT: The deposition of platinum catalyst on cation-exchange membranes was achieved by
a counter diffusion deposition method known as the Takenaka- Torikai method. The
morphology of the platinum catalyst on the membranes were controlled by varying
the conditions of the platinum deposition process, such as, temperature, type of
reducing agent and concentration of the platinic acid solution. The effect of the
sonication of platinic acid solution and the pre-treatment of membranes on the
morphology of a platinum catalyst was also investigated.
Platinum loading on cation-exchange membranes was determined by UV
spectrophotometric and gravimetric analyses. Suitable conditions for the quantitative
determination of the platinum loading on membranes by UV spectrophotometric
analysis was established through the development of a protocol.
Membranes were characterised using different techniques such as, Atomic
Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Infrared
spectrometry (IR), Dielectric analysis (DEA) and Brunauer Emmett Teller adsorption
(BET).
The roughness profile of a platinum catalyst embedded on a membrane was
explored by various statistical methods. The statistical analysis of various data sets for
a surface of a platinum-containing membrane was investigated using the Hurst
exponent.
The effect of surface modification of membranes on the deposition process, as
well as the morphology of the platinum catalyst, was investigated. Membranes were
modified with ethylene diamine (EDA) and cetyltrimethylammonium bromide
surfactant. Modification of membranes with cetyltrimethylammonium bromide
surfactant resulted in a unique textured platinum catalyst.
The electrochemical "switching" phenomenon was investigated for EDAmodified
membranes and EDA-modified membranes embedded with platinum
catalyst. The "switching" phenomenon was observed in i-V cyclic curves, which were
obtained by galvanodynamie measurements.
The application of electro catalytic membrane systems in the anodic oxidation
of water was investigated by electrochemical techniques such as galvanostatic and
cyclic voltammetric measurements.<br>AFRIKAANSE OPSOMMING: Die deponering van 'n platinum katalis op katioon-uitruil membrane is suksesvol
gedoen d.m.v. die Takenaka-Torikai metode. Die morfologie van die platinum katalis
op die membrane is gekontrolleer deur variasie van die kondisies van die platinum
deponeringsproses, bv. temperatuur, tipe reduseermiddel gebruik en konsentrasie van
die platiensuuroplossing, asook die ultrasonifikasie van die platiensuuroplossing en
voorafbehandeling van die membrane.
UV spektrofotometriese asook gravimetriese analitiese metodes is gebruik om
die platinumlading op katioon-uitruil membrane te bepaal. Geskikte kondisies vir die
kwantitatiewe bepaling van die platinumlading op membrane d.m.v. UV
spektrofotometriese analise is ontwikkel deur die skep van 'n protokol.
Membrane is gekarakteriseer d.m.v. die volgende tegnieke: Atoomkrag Mikroskopie,
Skanderingselektron Mikroskopie, Infrarooi Spektrometrie, di-elektriese analise en
Brunauer Emmett Teller adsorpsie.
Die skurtheidsprofiel van 'n platinum katalis op 'n membraan is ondersoek
deur gebruik te maak van verskeie statistiese metodes. Statistiese analises van
verskeie data stelsels van 'n platinum-bevattende membraan is ondersoek deur
gebruik te maak van die Hurst eksponent.
\
Die effek van oppervlakmodifikasie op membrane sowel as die
deponeringsproses en morfologie van die platinum katalis is ondersoek deur die
modifikasie van membrane met etileen diamien (EDA) en setieltrimetielammonium
bromied as versepingsmiddel
Die elektrochemiese omswaai van EDA-gemodifiseerde membrane sowel as
gemodifiseerde platinum bevattende membrane is ondersoek d.m.v. galvanodinamiese
metings.
Die gebruik van elektro-katalitiese membraansisteme in die anodiese oksidasie
van water is ondersoek deur gebruik te maak van elektrochemiese tegnieke, bv.
galvanostatiese en sikliese voltammetriese metings.
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Harry, Katherine Joann. "Lithium dendrite growth through solid polymer electrolyte membranes." Thesis, University of California, Berkeley, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10150902.
Full textAbstract:
<p> The next generation of rechargeable batteries must have significantly improved gravimetric and volumetric energy densities while maintaining a long cycle life and a low risk of catastrophic failure. Replacing the conventional graphite anode in a lithium ion battery with lithium foil increases the theoretical energy density of the battery by more than 40%. Furthermore, there is significant interest within the scientific community on new cathode chemistries, like sulfur and air, that presume the use of a lithium metal anode to achieve theoretical energy densities as high as 5217 W˙h/kg. However, lithium metal is highly unstable toward traditional liquid electrolytes like ethylene carbonate and dimethyl carbonate. The solid electrolyte interphase that forms between lithium metal and these liquid electrolytes is brittle which causes a highly irregular current distribution at the anode, resulting in the formation of lithium metal protrusions. Ionic current concentrates at these protrusions leading to the formation of lithium dendrites that propagate through the electrolyte as the battery is charged, causing it to fail by short-circuit. The rapid release of energy during this short-circuit event can result in catastrophic cell failure. </p><p> Polymer electrolytes are promising alternatives to traditional liquid electrolytes because they form a stable, elastomeric interface with lithium metal. Additionally, polymer electrolytes are significantly less flammable than their liquid electrolyte counterparts. The prototypical polymer electrolyte is poly(ethylene oxide). Unfortunately, when lithium anodes are used with a poly(ethylene oxide) electrolyte, lithium dendrites still form and cause premature battery failure. Theoretically, an electrolyte with a shear modulus twice that of lithium metal could eliminate the formation of lithium dendrites entirely. While a shear modulus of this magnitude is difficult to achieve with polymer electrolytes, we can greatly enhance the modulus of our electrolytes by covalently bonding the rubbery poly(ethylene oxide) to a glassy polystyrene chain. The block copolymer phase separates into a lamellar morphology yielding co-continuous nanoscale domains of poly(ethylene oxide), for ionic conduction, and polystyrene, for mechanical rigidity. On the macroscale, the electrolyte membrane is a tough free-standing film, while on the nanoscale, ions are transported through the liquid-like poly(ethylene oxide) domains. </p><p> Little is known about the formation of lithium dendrites from stiff polymer electrolyte membranes given the experimental challenges associated with imaging lithium metal. The objective of this dissertation is to strengthen our understanding of the influence of the electrolyte modulus on the formation and growth of lithium dendrites from lithium metal anodes. This understanding will help us design electrolytes that have the potential to more fully suppress the formation of dendrites yielding high energy density batteries that operate safely and have a long cycle life. </p><p> Synchrotron hard X-ray microtomography was used to non-destructively image the interior of lithium-polymer-lithium symmetric cells cycled to various stages of life. These experiments showed that in the early stages of lithium dendrite development, the bulk of the dendritic structure was inside of the lithium electrode. Furthermore, impurity particles were found at the base of the lithium dendrites. The portion of the lithium dendrite protruding into the electrolyte increased as the cell approached the end of life. This imaging technique allowed for the first glimpse at the portion of lithium dendrites that resides inside of the lithium electrode. </p><p> After finding a robust technique to study the formation and growth of lithium dendrites, a series of experiments were performed to elucidate the influence of the electrolyte’s modulus on the formation of lithium dendrites. Typically, electrochemical cells using a polystyrene – block¬ – poly(ethylene oxide) copolymer electrolyte are operated at 90 °C which is above the melting point of poly(ethylene oxide) and below the glass transition temperature of polystyrene. In these experiments, the formation of dendrites in cells operated at temperatures ranging from 90 °C to 120 °C were compared. The glass transition temperature of polystyrene (107 °C) is included in this range resulting in a large change in electrolyte modulus over a relatively small temperature window. The X-ray microtomography experiments showed that as the polymer electrolyte shifted from a glassy state to a rubbery state, the portion of the lithium dendrite buried inside of the lithium metal electrode decreased. These images coupled with electrochemical characterization and rheological measurements shed light on the factors that influence dendrite growth through electrolytes with viscoelastic mechanical properties. (Abstract shortened by ProQuest.)</p>
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Qu, Cheng. "Novel Polymer Electrolyte Membranes for Nickel-Zinc Battery." University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1384534927.
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Jia, Nengyou. "Electrochemistry of proton-exchange-membrane electrolyte fuel cell (PEMFC) electrodes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0019/MQ54898.pdf.
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Brunello, Giuseppe. "Computational modeling of materials in polymer electrolyte membrane fuel cells." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/48937.
Full textAbstract:
Fuel cells have the potential to change the energy paradigm by allowing more efficient use of energy. In particular, Polymer Electrolyte Membrane Fuel Cells (PEMFC) are interesting because they are low temperature devices. However, there are still numerous challenges limiting their widespread use including operating temperature, types of permissible fuels and optimal use of expensive catalysts. The first two problems are related mainly to the ionomer electrolyte, which largely determines the operating temperature and fuel type. While new ionomer membranes have been proposed to address some of these issues, there is still a lack of fundamental knowledge to guide ionomer design for PEMFC.
This work is a computational study of the effect of temperature and water content on sulfonated poly(ether ether ketone) and the effect of acidity on sulfonated polystyrene to better understand how ionomer material properties differ. In particular we found that increased water content preferentially solvates the sulfonate groups and improves water and hydronium transport. However, we found that increasing an ionomer’s acid strength causes similar effects to increasing the water content.
Finally, we used Density Functional Theory (DFT) to study platinum nano-clusters as used in PEMFCs. We developed a model using the atom’s coordination number to quickly compute the energy of a cluster and therefore predict which platinum atoms are most loosely held. Our model correctly predicted the energy of various clusters compared to DFT. Also, we studied the interaction between the various moieties of the electrolyte including the catalyst particle and developed a force field.
The coordination model can be used in a molecular dynamics simulation of the three phase region of a PEMFC to generate unbiased initial clusters. The force field developed can be used to describe the interaction between this generated cluster and the electrolyte.
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Ohkubo, Takahiro, Koh Kidena, and Akihiro Ohira. "Time-dependent diffusion coefficient of proton in polymer electrolyte membrane." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-192269.
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We investigated the time-dependent self-diffusion coefficients of water, D(T eff), in polymer electrolyte membranes at 278 K. TheD(T eff) was measured from T eff=0.7 to 100 ms by field gradient NMR techniques. The results showed that the self-diffusion coefficients of water were dependent on T eff less than 2 ms due to restricted diffusion, and were constant beyond 3 ms. The tortuosity and surface-to-volume ratio related to water diffusion were also estimated from D(T eff). The obtained values revealed the existence of large-scale restricted geometry compared with well-known nanometer-sized domain in polymer electrolyte membranes.
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Ohkubo, Takahiro, Koh Kidena, and Akihiro Ohira. "Time-dependent diffusion coefficient of proton in polymer electrolyte membrane." Diffusion fundamentals 10 (2009) 21, S. 1-3, 2009. https://ul.qucosa.de/id/qucosa%3A14112.
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We investigated the time-dependent self-diffusion coefficients of water, D(T eff), in polymer electrolyte membranes at 278 K. TheD(T eff) was measured from T eff=0.7 to 100 ms by field gradient NMR techniques. The results showed that the self-diffusion coefficients of water were dependent on T eff less than 2 ms due to restricted diffusion, and were constant beyond 3 ms. The tortuosity and surface-to-volume ratio related to water diffusion were also estimated from D(T eff). The obtained values revealed the existence of large-scale restricted geometry compared with well-known nanometer-sized domain in polymer electrolyte membranes.
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Zhu, Huizhen. "Applications of polyamidoamine dendrimers in polymer electrolyte membrane fuel cells." Thesis, [Tuscaloosa, Ala. : University of Alabama Libraries], 2009. http://purl.lib.ua.edu/2188.
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Budiarto, Thomas [Verfasser], Jens-Uwe [Akademischer Betreuer] Repke, Jens-Uwe [Gutachter] Repke, and Peter [Gutachter] Strasser. "Modeling process dynamics in membrane-electrolyte-assemblies of chloralkali electrolyzers considering steric and hydration effects / Thomas Budiarto ; Gutachter: Jens-Uwe Repke, Peter Strasser ; Betreuer: Jens-Uwe Repke." Berlin : Technische Universität Berlin, 2021. http://d-nb.info/1230468374/34.
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Sutherland, Richard Daniel. "Performance of different proton exchange membrane water electrolyser components / cRichard Daniel Sutherland." Thesis, North-West University, 2012. http://hdl.handle.net/10394/9214.
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Water electrolysis is one of the first methods used to generate hydrogen and is thus not considered to be a new technology. With advances in proton exchange membrane technology and the global tendency to implement renewable energy, the technology of water electrolysis by implementation of proton exchange membrane as solid electrolyte has developed into a major field of research over the last decade. To gain an understanding of different components of the electrolyser it is best to conduct a performance analysis based on hydrogen production rates and polarisation curves. The study aim was to compare the technologies of membrane electrode assembly with gas diffusion electrode and the proton exchange membranes of Nafion® and polybenzimidazole in a commercial water electrolyser. To determine which of the components are best suited for the process a laboratory scale electrolyser was to be used to replicate the commercially scaled performance. The effect of feed water contaminants on electrolyser performance was also investigated by introducing iron and magnesium salt solutions and aqueous methanol solutions in the feed reservoir. Components to be tested included different PEM types as well as the base component on which the electrocatalyst layer is applied. The proton exchange membranes compared were standard Nafion® N117 and polybenzimidazole meta-sulfone sulfonated polyphenyl sulfone (PBI-sPSU). A laboratory scale electrolyser from Giner Electrochemical Systems was utilised where different components were tested and compared with one another. Experimental results with commercial membrane electrode assemblies and gas diffusion electrodes demonstrated the influence of temperature on electrolyser performance for the proton exchange membranes, where energy efficiency increased with temperature. The effect of pressure was insignificant over the selected pressure range. Comparison of membrane electrode assembly and gas diffusion electrode technologies showed enhanced performance from MEA technology, this was most likely due to superior electrocatalyst contact with the PEM. Results of synthesised Nafion® N117 and PBI-sPSU MEA showed increased performance for PBI-sPSU, but it was found to be more susceptible to damage under severe conditions. The effect of metal cations in the supply reservoir exhibited reduced energy efficiencies and increased specific energy consumption for the test duration. Treatment with sulphuric acid was found to partially restore membrane electrode assembly performance, though it is believed that permanent damage was inflicted on the membrane electrode assembly electrocatalyst. Use of aqueous methanol solutions were found to increase electrolyser performance. It was also found that aqueous methanol electrolysis occurs at lower current densities, whereas a combination of aqueous methanol and water electrolysis occurred at higher current densities depending on the concentration of methanol.<br>Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013.
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Wauters, Cary N. "Electrolytic membrane recovery of bromine from waste gas-phase hydrogen bromide streams using a molten salt electrolyte." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/10131.
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Marczynski, Elaine Sirlei. "Avaliação de membranas hidrocarbônicas não fluoradas para uso como eletrólito em célula a combustível tipo DEFC." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2013. http://hdl.handle.net/10183/103831.
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Membranas hidrocarbônicas não fluoradas têm sido desenvolvidas para uso em substituição as membranas fluoradas (Nafion®) em células a combustível de eletrólito polimérico (PEMFC), ou em temperaturas superiores a 80 °C, ou em células com adição direta de álcool. Este trabalho teve como objetivo avaliar o desempenho de membranas hidrocarbônicas catiônicas, desenvolvidas para uso em célula a combustível alimentada com etanol (DEFC), e de camadas de difusão gasosa (GDL – Gas Difusion Layer) e eletrodos (GDE – Gas Difusion electrode) preparados para uso com as mesmas. Duas membranas hidrocarbônicas (E-750 e P-730) da empresa FuMATech®/GR foram avaliadas quanto à capacidade de troca iônica e grau de inchamento em água/etanol, quanto a composição química, morfologia, comportamento térmico e visoelástico e condutividade por impedância. As GDLs foram preparadas a partir de uma emulsão aquosa de Teflon® e pó de carbono Vulcan XC-72R®, com e sem agente emulsificante (resina sulfonada), dispersa em ambas as faces do tecido de carbono pelo método de aspersão. Os GDEs foram preparados pela deposição de emulsão catalítica de diferentes eletrocatalisadores sobre as respectivas GDLs do ânodo e catodo. Os GDEs anódico e catódico foram preparados com 1 mg.cm-2 do eletrocatalisador de PtSn/C 20% (75:15) e de Pt/C (20:80), respectivamente, e caracterizados por MEV-EDS. As características fisico-químicas das membranas hidrocarbônicas foram similares às apresentadas pela membrana Nafion®. O desempenho do protótipo de célula unitária DEFC com as membranas FuMATech® foi inferior ao obtido com a membrana Nafion® usando-se GDE comercial. Por outro lado, ensaios com a membrana Nafion® utilizando-se os eletrodos preparados neste trabalho e eletrodos comerciais apresentaram valores de potencial similares.<br>Non-fluorinated hydrocarbon cationic membranes have been developed for use instead of Nafion® in Polymer Electrolyte Membrane Fuel Cells (PEMFCs), or at higher temperatures than 80 ºC, or in fuel cells fed with alcohol. The aim of this work was to evaluate the performance of commercial non-fluorinated hydrocarbon cationic membranes with potential use in direct ethanol fuel cell (DEFC), and also evaluate the Gas Difusion Layer (GDL) and Gas Difusion electrode (GDE) prepared for use with them. Two hydrocarbon membranes (E-750 and P-730) produced by FuMATech®/GR were analyzed according to their ion exchange capacity, water uptake in water/alcohol solution, morphology, chemical composition, thermal and viscoelastic behaviour, and conductivity by impedance. The GDLs were prepared by spraying an aqueous emulsion of Vulcan carbon/Teflon®, with and without emulsifier agent (sulfonated hydrocarbon resin), in both sides of a carbon fabric. The electrodes were prepared by the respective deposition of the electrocatalysts emulsions on the cathode and anode GDLs. The anodic and cathodic GDEs were prepared with 1 mg.cm-2 of the electrocatalyst of PtSn/C 20% (75:15) and of Pt/C (20:80), respectively, which were characterized by SEM-EDS. The physicochemical properties of the hydrocarbon membranes were similar to the Nafion® membrane ones. The potential values obtained in a DEFC prototype unit cell with FuMATech® membranes were lower than those with Nafion-117 membrane. On the other hand, the performance of the DEFC prototype with Nafion-117 membrane was the same if used GDEs commercial or here prepared.
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Benjaminsen, Bjørn Eirik. "Nanoflow of Protons and Water in Polymer Electrolyte Membranes." Thesis, Norges Teknisk-Naturvitenskaplige Universitet, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-20835.
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This master thesis studies the applicability of continuum mean-field theories such as the Poisson-Nernst-Planck equations and the Stokes equation. In particular, we investigate electro-osmotic flow of water and protons in infinite cylindrical nano-scale pores with a uniform surface charge density, representing pores in polymer electrolyte membranes. The impact of different modifications to the continuum theory is explored. Including finite-size ions in the Poisson-Boltzmann equation and spatially dependent profiles for permittivity and viscosity, values are found for the water drag coefficient and the pore conductivity. For surface charge densities sigma_s = -0.1 to sigma_s = -0.5 C m^-2, values of 2-5 are found for the water drag coefficient, compared to 7.5 to 22 for the unmodified equations. Similarly, values for the pore conductivity range from $5.5$-30 S m^-1 when including the modifications, compared to 13-100 S m^-1 for the unmodified equations. A final modification to the Poisson-Boltzmann equations is made by including a field dependent explicit model for the permittivity. This model yields a permittivity profile comparable to predictions based on microscopic simulations, but with a lower permittivity near the wall. The proton concentration exhibits pronounced saturation effects near the wall.