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Ion, Mihaela Florentina. "Proton transport in proton exchange membrane fuel cells /." free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p3164514.
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Liu, Ping. "Composite proton exchange membranes for fuel cells." Diss., Connect to online resource - MSU authorized users, 2006.
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Ergun, Dilek. "High Temperature Proton Exchange Membrane Fuel Cells." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12610803/index.pdf.
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It is desirable to increase the operation temperature of proton exchange membrane fuel cells above 100oC due to fast electrode kinetics, high tolerance to fuel impurities and simple thermal and water management.
In this studythe objective is to develop a high temperature proton exchange membrane fuel cell. Phosphoric acid doped polybenzimidazole membrane was chosen as the electrolyte material. Polybenzimidazole was synthesized with different molecular weights (18700-118500) by changing the synthesis conditions such as reaction time (18-24h) and temperature (185-200oC). The formation of polybenzimidazole was confirmed by FTIR, H-NMR and elemental analysis. The synthesized polymers were used to prepare homogeneous membranes which have good mechanical strength and high thermal stability. Phosphoric acid doped membranes were used to prepare membrane electrode assemblies. Dry hydrogen and oxygen gases were fed to the anode and cathode sides of the cell respectively, at a flow rate of 0.1 slpm for fuel cell tests. It was achieved to operate the single cell up to 160oC. The observed maximum power output was increased considerably from 0.015 W/cm2 to 0.061 W/cm2 at 150oC when the binder of the catalyst was changed from polybenzimidazole to polybenzimidazole and polyvinylidene fluoride mixture. The power outputs of 0.032 W/cm2 and 0.063 W/cm2 were obtained when the fuel cell operating temperatures changed as 125oC and 160oC respectively. The single cell test presents 0.035 W/cm2 and 0.070 W/cm2 with membrane thicknesses of 100 µ
m and 70 µ
m respectively. So it can be concluded that thinner membranes give better performances at higher temperatures.
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Oyarce, Alejandro. "Electrode degradation in proton exchange membrane fuel cells." Doctoral thesis, KTH, Tillämpad elektrokemi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-133437.
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The topic of this thesis is the degradation of fuel cell electrodes in proton exchange membrane fuel cells (PEMFCs). In particular, the degradation associated with localized fuel starvation, which is often encountered during start-ups and shut-downs (SUs/SDs) of PEMFCs. At SU/SD, O2 and H2 usually coexist in the anode compartment. This situation forces the opposite electrode, i.e. the cathode, to very high potentials, resulting in the corrosion of the carbon supporting the catalyst, referred to as carbon corrosion. The aim of this thesis has been to develop methods, materials and strategies to address the issues associated to carbon corrosion in PEMFC.The extent of catalyst degradation is commonly evaluated determining the electrochemically active surface area (ECSA) of fuel cell electrode. Therefore, it was considered important to study the effect of RH, temperature and type of accelerated degradation test (ADT) on the ECSA. Low RH decreases the ECSA of the electrode, attributed to re-structuring the ionomer and loss of contact with the catalyst.In the search for more durable supports, we evaluated different accelerated degradation tests (ADTs) for carbon corrosion. Potentiostatic holds at 1.2 V vs. RHE were found to be too mild. Potentiostatic holds at 1.4 V vs. RHE were found to induce a large degree of reversibility, also attributed to ionomer re-structuring. Triangle-wave potential cycling was found to irreversibly degrade the electrode within a reasonable amount of time, closely simulating SU/SD conditions.Corrosion of carbon-based supports not only degrades the catalyst by lowering the ECSA, but also has a profound effect on the electrode morphology. Decreased electrode porosity, increased agglomerate size and ionomer enrichment all contribute to the degradation of the mass-transport properties of the cathode. Graphitized carbon fibers were found to be 5 times more corrosion resistant than conventional carbons, primarily attributed to their lower surface area. Furthermore, fibers were found to better maintain the integrity of the electrode morphology, generally showing less degradation of the mass-transport losses. Different system strategies for shut-down were evaluated. Not doing anything to the fuel cell during shut-downs is detrimental for the fuel cell. O2 consumption with a load and H2 purge of the cathode were found to give around 100 times lower degradation rates compared to not doing anything and almost 10 times lower degradation rate than a simple air purge of the anode. Finally, in-situ measurements of contact resistance showed that the contact resistance between GDL and BPP is highly dynamic and changes with operating conditions.Denna doktorsavhandling behandlar degraderingen av polymerelektrolytbränslecellselektroder. polymerelektrolytbränslecellselektroder. Den handlar särskilt om nedbrytningen av elektroden kopplad till en degraderingsmekanism som heter ”localized fuel starvation” oftast närvarande vid uppstart och nedstängning av bränslecellen. Vid start och stopp kan syrgas och vätgas förekomma samtidigt i anoden. Detta leder till väldigt höga elektrodpotentialer i katoden. Resultatet av detta är att kolbaserade katalysatorbärare korroderar och att bränslecellens livslängd förkortas. Målet med avhandlingen har varit att utveckla metoder, material och strategier för att både öka förståelsen av denna degraderingsmekanism och för att maximera katalysatorbärarens livslängd.Ett vanligt tillvägagångsätt för att bestämma graden av katalysatorns degradering är genom mätning av den elektrokemiskt aktiva ytan hos bränslecellselektroderna. I denna avhandling har dessutom effekten av temperatur och relativ fukthalt studerats. Låga fukthalter minskar den aktiva ytan hos elektroden, vilket sannolikt orsakas av en omstrukturering av jonomeren och av kontaktförlust mellan jonomer och katalysator.Olika accelererade degraderingstester för kolkorrosion har använts. Potentiostatiska tester vid 1.2 V mot RHE visade sig vara för milda. Potentiostatiska tester vid 1.4 V mot RHE visade sig däremot medföra en hög grad av reversibilitet, som också den tros vara orsakad av en omstrukturering av jonomeren. Cykling av elektrodpotentialen degraderade istället elektroden irreversibelt, inom rimlig tid och kunde väldigt nära simulera förhållandena vid uppstart och nedstängning.Korrosionen av katalysatorbäraren medför degradering av katalysatorn och har också en stor inverkan på elektrodens morfologi. En minskad elektrodporositet, en ökad agglomeratstorlek och en anrikning av jonomeren gör att elektrodens masstransportegenskaper försämras. Grafitiska kolfibrer visade sig vara mer resistenta mot kolkorrosion än konventionella kol, främst p.g.a. deras låga ytarea. Grafitiska kolfibrer visade också en förmåga att bättre bibehålla elektrodens morfologi efter accelererade tester, vilket resulterade i lägre masstransportförluster.Olika systemstrategier för nedstängning jämfördes. Att inte göra något under nedstängning är mycket skadligt för bränslecellen. Förbrukning av syre med en last och spolning av katoden med vätgas visade 100 gånger lägre degraderingshastighet av bränslecellsprestanda jämfört med att inte göra något alls och 10 gånger lägre degraderingshastighet jämfört med spolning av anoden med luft. In-situ kontaktresistansmätningar visade att kontaktresistansen mellan bipolära plattor och GDL är dynamisk och kan ändras beroende på driftförhållandena.
QC 20131104
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Shi, Jinjun. "Composite Membranes for Proton Exchange Membrane Fuel Cells." Wright State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=wright1214964058.
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DeLashmutt, Timothy E. "Modeling a proton exchange membrane fuel cell stack." Ohio : Ohio University, 2008. http://www.ohiolink.edu/etd/view.cgi?ohiou1227224687.
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Xiao, Zhiyong. "Monolithic integration of proton exchange membrane microfuel cells /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?ECED%202008%20XIAO.
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Hattenberger, Mariska. "Composite proton exchange membranes for intermediate temperature fuel cells." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/6194/.
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Intermediate temperature (IT) proton exchange membrane fuel cells (PEMFCs) offer a future that does not rely on the burning of fossil fuels, but dictate durable and high performance component materials. At operating conditions of 120 °C and 50 % relative humidity (RH), composite proton exchange membranes (PEMs) offer increased performance due to enhanced water uptake and retention resulting from the hydrophilic filler material. This project aimed to relate measured data for composite PEMs with literature data on Nafion-graphene oxide (GO) PEMs. In order to achieve this, the membrane casting method was optimised and GO was synthesised in-house. A range of membranes were tested using a calibrated and optimised high temperature test stand. In-situ and ex-situ testing was carried out between 80°C and 120°C, and between 25 and 95 % RH. In contrast with some published data, this study found inconsistent trends between water uptake, ion exchange capacity, membrane resistance and single cell performance. Overall it was found that recast and composite membranes had higher in-plane resistance than Nafion 212, but that composite membranes with low filler loading had comparable in-situ performance to the commercial membrane. Further single cell optimisation is likely to result in further advances for composite PEMs.
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Einsla, Brian Russel. "High Temperature Polymers for Proton Exchange Membrane Fuel Cells." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/27320.
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Novel proton exchange membranes (PEMs) were investigated that show potential for operating at higher temperatures in both direct methanol (DMFC) and H2/air PEM fuel cells. The need for thermally stable polymers immediately suggests the possibility of heterocyclic polymers bearing appropriate ion conducting sites. Accordingly, monomers and random disulfonated poly(arylene ether) copolymers containing either naphthalimide, benzoxazole or benzimidazole moieties were synthesized via direct copolymerization. The ion exchange capacity (IEC) was varied by simply changing the ratio of disulfonated monomer to nonsulfonated monomer in the copolymerization step. Water uptake and proton conductivity of cast membranes increased with IEC. The water uptake of these heterocyclic copolymers was lower than that of comparable disulfonated poly(arylene ether) systems, which is a desirable improvement for PEMs. Membrane electrode assemblies were prepared and the initial fuel cell performance of the disulfonated polyimide and polybenzoxazole (PBO) copolymers was very promising at 80 C compared to the state-of-the-art PEM (Nafion®); nevertheless these membranes became brittle under operating conditions. Several series of poly(arylene ether)s based on disodium-3,3â -disulfonate-4,4â -dichlorodiphenylsulfone (S-DCDPS) and a benzimidazole-containing bisphenol were synthesized and afforded copolymers with enhanced stability. Selected properties of these membranes were compared to separately prepared miscible blends of disulfonated poly(arylene ether sulfone) copolymers and polybenzimidazole (PBI). Complexation of the sulfonic acid groups with the PBI structure reduced water swelling and proton conductivity.
The enhanced proton conductivity of Nafion® membranes has been proposed to be due to the aggregation of the highly acidic side-chain sulfonic acid sites to form ion channels. A series of side-chain sulfonated poly(arylene ether sulfone) copolymers based on methoxyhydroquinone was synthesized in order to investigate this possible advantage and to couple this with the excellent hydrolytic stability of poly(arylene ether)s. The methoxy groups were deprotected to afford reactive phenolic sites and nucleophilic substitution reactions with functional aryl sulfonates were used to prepare simple aryl or highly acidic fluorinated sulfonated copolymers. The proton conductivity and water sorption of the resulting copolymers increased with the ion exchange capacity, but changing the acidity of the sulfonic acid had no apparent effect.Ph. D.
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Marani, Debora. "Development of hybrid proton-conducting polymers for proton exchange membrane fuel cells." Aix-Marseille 1, 2006. http://www.theses.fr/2006AIX11002.
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Le développement d'électrolytes polymères de nouvelle génération est un pré requis essentiel pour la commercialisation à grande échelle des piles à combustibles à membrane polymérique. Ces conducteurs protoniques doivent présenter une bonne stabilité morphologique, hydrolytique, mécanique et une conductivité appropriée à une température supérieure à 100°C à basse humidité relative. Dans ce travail, diverses stratégies sont explorées pour la synthèse de polymères conducteurs hybrides organiques-inorganiques nanocomposites à partir de polymères thermoplastiques aromatiques. L'emploi de matériaux hybrides permet d'exploiter l'effet synergique dû à la présence simultanée d'une composante organique polymérique et d'une partie inorganique à base de silicium. Ces effets synergétiques s'expliquent par la possibilité de moduler et de contrôler la séparation entre les parties hydrophile et hydrophobe, dont dépendent fortement les propriétés de l'électrolyte polymère. Des matériaux hybrides de classe I à base de poly-éther-éther-kétone (PEEK) ont été synthétisés ainsi que plusieurs exemples de matériaux hybrides de classe II à base de PEEK et de poly-phényl-sulfone (PPSU) sulfonatés (SPEEK et SPPSU) et contenant comme partie inorganique des atomes de silicium diversement fonctionnalisés. La caractérisation des matériaux comporte l'analyse structurale, l'étude des propriétés physicochimiques et le comportement électrochimique. Des résultats très positifs ont été obtenus principalement avec deux des systèmes étudiés : un mélange de polymères à base de SPEEK et SPPSU silicié et un polymère interconnecté à base de PEEK sulfonaté et silicié (SOSiPEEK)
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Choi, Pyoungho. "Investigation of thermodynamic and transport properties of proton-exchange membranes in fuel cell applications." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0430104-094215/.
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Zhang, Jingxin. "Investigation of CO tolerance in proton exchange membrane fuel cells." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0708104-193007/.
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Lee, Heon Joong Choe Song-Yul. "Modeling and analysis of a PEM fuel cell system for a quadruped robot." Auburn, Ala, 2009. http://hdl.handle.net/10415/1786.
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Kwan, Siu Ming. "Zeolite-based micro fuel cells /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?CBME%202008%20KWAN.
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Parikh, Harshil R. "Modeling and analysis of proton exchange membrane fuel cell." Ohio : Ohio University, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1088438486.
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Maasdorp, Lynndle Caroline. "Temperature proton exchange membrane fuel cells in a serpentine design." Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_1316_1307961639.
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The aim of my work is to model a segment of a unit cell of a fuel cell stack using numerical methods which is classified as computational fluid dynamics and implementing the work in a commercial computational fluid dynamics package, FLUENT. The focus of my work is to study the thermal distribution within this segment. The results of the work aid in a better understanding of the fuel cell operation in this temperature range. At the time of my investigation experimental results were unavailable for validation and therefore my results are compared to previously published results published. The outcome of the results corresponds to this, where the current flux density increases with the increasing of operating temperature and fixed operating voltage and the temperature variation across the fuel cell at varying operating voltages. It is in the anticipation of determining actual and or unique material input parameters that this work is done and at which point this studies results would contribute to the understanding high temperature PEM fuel cell thermal behaviour, significantly.
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Pasricha, Sandip. "Modeling and Transient Degradation of Proton Exchange Membrane Fuel Cells." Thesis, Montana State University, 2006. http://etd.lib.montana.edu/etd/2006/pasricha/PasrichaS0506.pdf.
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This thesis presents a model based approach to describe proton exchange membrane (PEM) fuel cell degradation with time. This degradation study involves analysis of voltage and current profiles of PEM membranes under transient load conditions. The data is collected from 80 membranes in an Independence1000 1000W PEM system over the life span of the membrane. The thesis also presents PEM fuel cell models developed and validated on a 500W SR-12 commercial PEM stack. Several static models from the literature are reviewed in terms of physical effects, parameterized for identification, and compared using measured data from the commercial PEM stack. The dynamic model is obtained by extending static current voltage profiles to include temperature dependence, and by dynamically modeling the temperature of the membrane. After inspecting all these models a simplified model is used for analyzing PEM fuel cell degradation and changes in physical phenomena in fuel cell observed over a period of time.
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Dong, Daxuan. "Polyphenylene Sulfonic Acids As Proton Exchange Membranes For Fuel Cells." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1332355539.
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Choi, Jonghyun. "Nanofiber Network Composite Membranes for Proton Exchange Membrane Fuel Cells." Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1260461818.
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Ahn, Jong-Woo. "Design and analysis of air and coolant control for a polymer electrolyte membrane fuel cell." Auburn, Ala., 2007. http://repo.lib.auburn.edu/07M%20Theses/AHN_JONGWOO_52.pdf.
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Christian, Joel B. "Tungsten fuel cell catalysts." Diss., Online access via UMI:, 2007.
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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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Bai, He. "High temperature proton-exchange and fuel processing membranes for fuel cells and other applications." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1204732417.
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Primucci, Mauricio. "Experimental characterization and diagonosis tools for proton exchange membrane fuel cells." Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/96767.
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A fuel cell is a device that gives electric power directly from electrochemical reduction and oxidation reactions. PEM fuel cells
present some properties that make them appropriate for portable and transport applications: high efficiency, no emissions,
solid electrolyte, low operating temperatures and high power density. However, some technical problems can be improved,
durability of the materials and the appropriate control of the operating conditions. One important aspect of the operating
conditions is the water management. The right water content is needed in the electrolyte and catalyst layers to maximize the
efficiency of the PEMFC by minimizing the voltage losses. Water content in the fuel cell is given basically by the generation of
the water in the cathode due to the reaction, the humidity of the inlet gases and the transport trough the membrane.
This thesis studies, proposes and compares different experimental characterisation methods aimed to provide performance
indicators of the PEMFC water state.
A systematic use of Electrochemical Impedance Spectroscopy technique is presented and its results are studied in order to
analyse the influence of different operating conditions over the PEMFC response. The variables under analysis include: load
current, pressure temperature and gas relative humidity. All these variables are considered with inlet gases feeding: H2/O2
and H2/Air.
A set of relevant characteristics from the EIS response has been considered. Several equivalent circuits has been analysed
and those that have the best fitting with the experimental EIS data are selected.
When air is used as oxidant, a simple equivalent circuit with a resistance and a Warburg element is proposed. When Oxygen
is used as oxidant, a more complex equivalent circuit is needed. A detailed sensitive analysis is performed indicating those
parameters that best capture the influence of the operating conditions.
A new experimental characterisation technique, based on the inlet gases humidification interruption is proposed. This
dynamic technique combines the information extracted from EIS and the temporal response in order to study the water
transport and storage effects in the PEMFC. Two advantages of this proposed technique is the simple hardware configuration
used and the relative low impact on the fuel cell response, making attractive the humidification interruption as an in-situ
technique.
Three different sets of performance indicators are proposed as diagnosis tool.
Relevant Characteristics from the EIS response, if properly monitored, can give a diagnostic of the fuel cell internal state. After
an analysis, the chosen ones are: low and high frequency resistances (RLF and RHF) and the frequency of the maximum
phase. These RC are helpful to determine if the PEMFC with the current operating conditions is well humidified. If the zone
defined by RLF decrease, RHF slight increase and the frequency of the maximum phase increase is minimal, the cathode is
optimally humidified.
Equivalent Circuit are used in order to give a physical interpretation. The selected parameters as performance indicators are:
membrane resistance, Rm, time constant and resistance of diffusion process (using Warburg elements: Tw and Rw). In this
case, the humidification of the fuel cell is optimum if the zone where Rw and Tw decrease and Rm has slow increase is
minimal.
Model Based performance indicators are proposed: Rm, effective diffusion coefficient, Deff and effective active area, Aeff. The
optimal humidification occurs when the zone where Deff is stationary and Rm has not changed significantly, is minimal. The
parameter Aeff involved in this last diagnosis procedure can be detached from the humidification interruption test and be
used to estimate the effective active area and then is also helpful to compare the PEMFC performance in different operating
conditions.Una pila de combustible es un dispositivo que da energía eléctrica a partir de reacciones electroquímicas de reducción y oxidación. Las pilas del tipo PEMFC presentan propiedades que las hacen adecuadas para aplicaciones de transporte: alta eficiencia, cero emisiones, electrolito sólido, bajas temperaturas de operación y alta densidad de potencia. Sin embargo, algunos problemas técnicos deben ser estudiados: la durabilidad de los materiales y la correcta selección de las condiciones de funcionamiento. Una de las más importantes es la gestión del agua. Un balance adecuado del agua en la pila es necesario para maximizar la eficiencia de la PEMFC reduciendo al mínimo las pérdidas de tensión. El contenido de agua en la PEMFC viene dado por su generación en el cátodo debido a la reacción, la humedad de los gases de entrada y el transporte de agua a través de la membrana. La tesis estudia, propone y compara los diferentes métodos de caracterización experimental con el objetivo de obtener indicadores del estado del agua en la PEMFC. Se realiza un uso sistemático de la técnica “espectroscopía de impedancia electroquímica (EIS)” y el análisis de la influencia de las diferentes condiciones de operación sobre la respuesta de la PEMFC. Las variables estudiadas son: corriente de carga, presión de los gases, temperatura, humedad relativa y también la alimentación de los gases de entrada: H2/O2 y H2/aire. Se presenta un conjunto de características relevantes de la respuesta del EIS y se usan para dar valores iniciales a los circuitos equivalentes. Se estudian diferentes configuraciones de circuitos equivalentes y se seleccionan aquellos que tienen la mejor conexión con los datos experimentales. Se realiza un análisis de sensibilidad de los parámetros de los circuitos equivalentes con respecto a las diferentes condiciones de operación, para encontrar aquellos que sean útiles para representar estas variaciones. Se propone una nueva técnica experimental de caracterización, basada en la interrupción de la humidificación de los gases de entrada. Esta técnica combina la información de la respuesta temporal con la frecuencial (EIS) y es útil para analizar la influencia del agua en la respuesta de la PEMFC. Algunas ventajas de esta técnica son: la fácil implementación física y el bajo impacto sobre la respuesta de la PEMFC, lo cual convierte esta técnica en candidata para ser utilizada “In-situ”. Se proponen tres conjuntos de indicadores de comportamiento de la pila como herramientas de diagnosis. En primer lugar, se presentan las “Características Relevantes” de la respuesta de la EIS que dan un diagnóstico del estado interno de la PEMFC. De entre ellas se selecciona como indicadas: las resistencias de baja y alta frecuencia (RLF y RHF) y la frecuencia del máximo de fase. Estas características sirven para determinar la correcta humidificación de la pila en las condiciones actuales de operación. El cátodo está correctamente humidificado si la respuesta de las características, muestran que la zona definida por RLF bajando, RHF subiendo ligeramente y la frecuencia de la máxima fase está subiendo, es mínima. En segundo lugar, se usan los “Circuitos Equivalentes” para dar una interpretación física a los indicadores. Los parámetros seleccionados son: la resistencia de la membrana, Rm, la resistencia y la constante de tiempo de la difusión (Rw y Tw). En este caso, la humidificación correcta del cátodo ocurre cuando la zona donde Rw y Tw bajan y Rm sube ligeramente, es mínima. Por ultimo, se proponen indicadores de comportamiento utilizando un modelo: Rm, coeficiente de difusión efectivo, Deff y el área activa efectiva, Aeff. La humidificación óptima del cátodo ocurre cuando la zona donde Deff es estable y Rm no cambia significativamente, es mínima. El parámetro Aeff es útil para estimar el área activa efectiva aun cuando no se realice una interrupción de humidificación y para comparar la respuesta de la PEMFC bajo diferentes condiciones de operacion
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Alayyaf, Abdulmajeed A. "Synthesis of Two Monomers for Proton Exchange Membrane Fuel Cells (PEMFCs)." Digital Commons @ East Tennessee State University, 2016. https://dc.etsu.edu/etd/3015.
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The overall goal of this research is to synthesize two different monomers for proton exchange membrane (PEM) Fuel Cells. Such monomers are proposed to be polymerized to improve the efficiency and compatibility of electrodes and electrolytes in PEM fuel cells.
The first target is to synthesize 4-diazonium-3-fluoro PFSI zwitterionic monomer. Three steps were carried out in the lab. First one was the ammonolysis of 3-fluoro-4-nitrobenzenesulfonyl chloride. Second reaction was the bromination of Nafion monomer. The next coupling reaction, between brominated Nafion monomer and the 3-fluoro-4-nitrobenzenesulfonamide, was failed. The obstacles involve the harsh reaction condition and troublesome purification procedure.
The second target is to synthesize 5-nitro-1, 3-benzenedisulfonamide. According to the literature, this synthesis was also designed as three steps: 1)nitration of sodium 1, 3-benzenedisulfonate salt; 2)chlorination of sodium 5-nitro-1, 3-benzenedisulfonate salt; and 3)ammonolysis of 5- nitro-1, 3- benzenedisulfonyl chloride. This monomer is expected to be copolymerized for membrane electrolyte in PEM fuel cells.
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Singer, Simcha Lev. "Low platinum loading electrospun electrodes for proton exchange membrane fuel cells." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/38280.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (p. 104-106).
An experimental study was performed to evaluate the utility of electrospun carbon nanofiber supports for sputtered platinum catalyst in proton exchange membrane fuel cells. The performance of the sputtered nanofiber supports was similar to that of sputtered commercial gas diffusion layers in single cell fuel cell tests. However, sputtered platinum electrodes performed significantly worse than commercial thin film electrodes due to high activation and concentration voltage losses. Cyclic voltammetry and rotating disc electrode experiments were performed in order to evaluate the influence of platinum loading and particle size on the electrochemical active area and oxygen reduction performance of the sputtered platinum. Active area per weight catalyst decreased with sputtering time, and the oxygen reduction activity slightly increases with increasing sputtering time. Both of these effects are thought to be due to increasing platinum particle size as sputtering time is increased.
by Simcha Lev Singer.
S.M.
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Tian, Feng. "Theoretical Studies on Electrode Reactions in Proton Exchange Membrane Fuel Cells." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1291339549.
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Cheddie, Denver Faron. "Computational modeling of intermediate temperature proton exchange membrane (PEM) fuel cells." FIU Digital Commons, 2006. http://digitalcommons.fiu.edu/etd/2124.
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A two-phase three-dimensional computational model of an intermediate temperature (120 - 190 ˚C) proton exchange membrane (PEM) fuel cell is presented. This represents the first attempt to model PEM fuel cells employing intermediate temperature membranes, in this case, phosphoric acid doped polybenzimidazole (PBI). To date, mathematical modeling of PEM fuel cells has been restricted to low temperature operation, especially to those employing Nafion® membranes; while research on PBI as an intermediate temperature membrane has been solely at the experimental level. This work is an advancement in the state of the art of both these fields of research. With a growing trend toward higher temperature operation of PEM fuel cells, mathematical modeling of such systems is necessary to help hasten the development of the technology and highlight areas where research should be focused.
This mathematical model accounted for all the major transport and polarization processes occurring inside the fuel cell, including the two phase phenomenon of gas dissolution in the polymer electrolyte. Results were presented for polarization performance, flux distributions, concentration variations in both the gaseous and aqueous phases, and temperature variations for various heat management strategies. The model predictions matched well with published experimental data, and were self-consistent.
The major finding of this research was that, due to the transport limitations imposed by the use of phosphoric acid as a doping agent, namely low solubility and diffusivity of dissolved gases and anion adsorption onto catalyst sites, the catalyst utilization is very low (~1 - 2 %). Significant cost savings were predicted with the use of advanced catalyst deposition techniques that would greatly reduce the eventual thickness of the catalyst layer, and subsequently improve catalyst utilization. The model also predicted that an increase in power output in the order of 50% is expected if alternative doping agents to phosphoric acid can be found, which afford better transport properties of dissolved gases, reduced anion adsorption onto catalyst sites, and which maintain stability and conductive properties at elevated temperatures.
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Rezaei, Niya Seyed Mohammad. "Process modeling of impedance characteristics of proton exchange membrane fuel cells." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/53653.
Full textAbstract:
The impedance characteristics of proton exchange membrane (PEM) fuel cells are studied and analyzed in this thesis. The modeling approaches presented in literature are thoroughly reviewed and categorized as the measurement-modeling and process-modeling approaches. In the former category, a hypothetical equivalent circuit which has the impedance characteristics similar to measured impedances is presented. Since the equivalent circuit is not directly resulted from the physical and chemical properties of the PEM fuel cells, the majority of the measurement-modeling approaches lead to dubious conclusions. In the process-modeling approach, on the other hand, the governing equations of the fuel cell must analytically be solved to determine and the impedance. However, a few process-modeling approaches presented in literature have shown to be indirectly based on the same assumptions as the measurement-modeling approach, and hence, those can also lead to similar conclusions. Therefore, these process-modeling approaches are referred to as the semi-process models here.
In this thesis, the first complete process model for PEM fuel cells is presented which is not based on the above-mentioned assumptions. For each source of the losses in the fuel cell (i.e., the ohmic, activation and concentration overpotentials), a process model and equivalent circuit are obtained and compared against the impedance measurements reported in literature. The complete model (obtained by combining the models of the three losses) is then verified against the impedances measured in different operating conditions. Using the verified model, the measured Nyquist plots of the PEM fuel cells reported in literature are categorized. As a result, the dominant physical and chemical parameters controlling various arcs of the Nyquist plot are determined. Finally, the sensitivity analysis of the impedance characteristics of fuel cells is conducted using the verified model. As a result of this analysis, a minimum change in the operating conditions which results in statistically different Nyquist plots are determined.
Finally, as an application of the model presented here, the impedance of the cell in the anode and cathode starvation modes are studied. It is shown that the anode starvation cannot be recognized from the impedance measurements, as predicted by the model.Applied Science, Faculty of
Engineering, School of (Okanagan)
Graduate
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SANTORO, THAIS A. de B. "Estudo tecnologico de celulas a combustivel experimentais a membrana polimerica trocadora de protons." reponame:Repositório Institucional do IPEN, 2004. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11174.
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Made available in DSpace on 2014-10-09T12:49:10Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:00:37Z (GMT). No. of bitstreams: 1 09831.pdf: 4253435 bytes, checksum: c758abc7c04ca544bdc0f231316160f0 (MD5)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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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.
Full textAbstract:
Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2007.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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Rodgers, Steven Francis. "Simulation of PEM fuel cells: validation of model and incorporation of humidity dynamics." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2010. http://scholarsmine.mst.edu/thesis/pdf/Rodgers_09007dcc807d8717.pdf.
Full textAbstract:
Thesis (M.S.)--Missouri University of Science and Technology, 2010.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed July 29, 2010) Includes bibliographical references (p. 64-67).
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Pan, Jingjing. "Poly[4(5)-vinylimidazole]/polyvinylidene fluoride composites as proton exchange membranes /." Online version of thesis, 2009. http://hdl.handle.net/1850/10285.
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Shan, Yuyao Choe Song-Yul. "Dynamic modeling of polymer electrolyte membrane fuel cell stack with 1D and 2D CFD techniques." Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Summer/Theses/SHAN_YUYAO_58.pdf.
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Joseph, Krishna Sathyamurthy. "Hybrid direct methanol fuel cells." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44777.
Full textAbstract:
A new type of fuel cell that combines the advantages of a proton exchange membrane fuel cells and anion exchange membrane fuel cells operated with methanol is demonstrated. Two configurations: one with a high pH anode and low pH cathode (anode hybrid fuel cell (AHFC)),and another with a high pH cathode and a low pH anode (cathode hybrid fuel cell (CHFC)) have been studied in this work. The principle of operation of the hybrid fuel cells were explained. The two different hybrid cell configurations were used in order to study the effect of the electrode fabrication on fuel cell performance. Further, the ionomer content and properties such as the ion exchange capacity and molecular weight were optimized for the best performance. A comparison of the different ionomers with similar properties is carried out in order to obtain the best possible ionomer for the fuel cell. An initial voltage drop was observed at low current density in the AHFC, this was attributed to the alkaline anode and the effect of the ionomers with the new cationic groups were studied on this voltage drop was studied. These ionomers with the different cationic groups were studied in the CHFC design as well. Finally, the use of non platinum catalyst cathode with the CHFC design was also demonstrated for the first time.
36
Chedester, R. Clint. "Transport phenomena in microchannels and proton exchange membrane assemblies of fuel cells." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/17825.
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Yazaydin, Ahmet Ozgur. "Investigations Of New Horizons On H2/o2 Proton Exchange Membrane Fuel Cells." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/1054402/index.pdf.
Full textAbstract:
Proton exchange membrane fuel cells are electrochemical devices which
convert the chemical energy of hydrogen into electrical energy with a high
efficiency. They are compact and produce a powerful electric current relative to their
size. Different from the batteries they do not need to be recharged. They operate as
long as the fuel is supplied. Fuel cells, therefore, are considered as one of the most
promising options to replace the conventional power generating systems in the
future.
In this study five PEMFCsnamely EAE1, AOY001, AOY002, AOY003 and AOY004 were manufactured with different methods and in different structures. A test station was built to make the performance tests. Performances of the PEMFCs were compared by comparing the voltage-current (V-i) diagrams obtained during the initial tests at 25 º
C of fuel cell and gas humidification temperatures. AOY001 showed the best performance among all PEMFCs with a current density of 77.5 mA/cm2 at 0.5 V and it was chosen for further parametric studies where the effect of different flow rates of H2 and O2 gases, gas humidification and fuel cell temperatures on the performance were investigated. It was found that increasing fuel cell and gas humidification temperatures increased the performance. Excess flow rate of reactant gases had an adverse effect on the performance. On the other hand increasing the ratio of flow rate of oxygen to hydrogen had a positive but limited effect. AOY001 delivered a maximum current density of 183 mA/cm2 at 0.5 V. The highest power obtained was 4.75 W
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Yurdakul, Ahmet Ozgur. "Acid Doped Polybenzimidazole Membranes For High Temperature Proton Exchange Membrane Fuel Cells." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/2/12608506/index.pdf.
Full textAbstract:
Acid Doped Polybenzimidazole Membranes for High Temperature
Proton Exchange Membrane Fuel Cells
Author: Ahmet Özgü
r Yurdakul One of the most popular candidates for high temperature PEMFC&rsquo
s is phosphoric acid doped polybenzimidazole (PBI) membrane due to its thermal and mechanical stability. In this study, high molecular weight PBI was synthesized by using PPA polymerization. The stirring rate of reaction solution was optimized to obtain high molecular weight. The inherent viscosity of polymer was measured at four points in 96 percent sulphuric acid solution at 30 degree centigrade by using an Ubbelohde viscometer. The highest average molecular weight was found as approximately 120,000 using the Mark-Houwink equation. The polymer was dissolved in N,N-dimethylacetamide at 70 degree centigrade with an ultrasonic stirrer. The membranes cast from this solution were doped with phosphoric acid solutions at different concentrations. The doping levels of the membranes were 6, 8, 10 and 11 moles phosphoric acid/PBI repeat unit. The mechanical strength of the acid doped membranes measured by tensile tests were found as 23, 16, 12 and 11 MPa, respectively. Conductivity measurements were made using the four probe technique. The membranes were placed in a conductivity cell and measurements were taken in humidity chamber with temperature and pressure control. The conductivity of membranes was measured at 110, 130 and 150 degree centigrade in both dry air and water vapor. The highest conductivity was 0.12 S/cm at 150 degree centigrade and 33 percent relative humidity for the membrane doped with 11 moles of H3PO4. The measurements showed that conductivity increased with increasing doping and humidity. Moreover, membranes had acceptable conductivity levels in dry air.
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Blanco, Mauricio. "Study of selected water management strategies for proton exchange membrane fuel cells." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/36643.
Full textAbstract:
Proton exchange membrane fuel cells (PEMFC) are a promising energy conversion alternative for a number of applications including automotive, small power generation, and micro applications. However, many issues, such as poor water management and voltage instability, still have to be addressed in order to remove technical barriers to commercialization. In this work, water management issues in PEM fuel cells were investigated in detail with the purpose of developing approaches to reduce the negative effect of liquid water inside the fuel cell.
The performance of the PEM fuel cell deteriorates when operated at low humidity to dry conditions. It was demonstrated that the use of perforated sheets as water barrier layers improved the operational life of the fuel cell significantly (>3x) compared to a fuel cell with no additional layers. These sheets increase the water content in the cathode catalyst layer and membrane, via back-diffusion to the anode. In addition, these perforated sheets were also used as a diagnostic tool in order to further investigate the role of cathode and anode MPLs. It was shown that the cathode MPL decreases the water saturation in the catalyst layer and improves water removal via the cathode GDL. It was also shown that the anode MPL plays a role in reducing voltage stability at high flow rates and flooding conditions. Perforated sheets were further explored for use as an engineered gas diffusion layer. This type of approach has the advantage that it can be tailored to specific parameters and conditions.
Finally, a new flow field design, used on the cathode side, in which the active area can be modified, is presented and proven to improve the cell voltage and power stability at low power levels. This method increases the effective flow rate inside the flow field by decreasing the active area, resulting in the removal of liquid water and improving the gas diffusion to the cathode catalyst layer. This novel design can also be used to improve cell-to-cell water and gas distribution in fuel cell stacks.
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Zhang, Xiao. "Preparation and characterization of proton exchange membranes for direct methanol fuel cells." Doctoral thesis, Universitat Rovira i Virgili, 2005. http://hdl.handle.net/10803/8525.
Full textAbstract:
Due to the petroleum crisis and its consequent emission problems, fuel cells gain an important place in the application of alternative energy. They are a kind of electrochemical device that converts chemical energy directly into electrical energy. The Direct Methanol Fuel Cells (DMFC) use polymer membranes as the electrolyte; the polymer membranes are capable of conducting hydrogen protons. The fuel cell system is still expensive and the proton exchange membrane has contributed significantly the high cost. At present, perfluorosulfonic acid membranes (PFSA) (e.g. Nafion®, by DuPont) have been widely investigated. However they showed high methanol crossover and high swelling that lead low cell efficiency. The main goal of the thesis is to prepare novel proton exchange membranes to apply in the DMFC. PEG and PA membranes compuestas fueron preparadas. Derivados del ácido fosfórico y lignosulfonados (LS) fueron incluidos en la estructura de la PA para actuar como agentes transportadores de protones. El mecanismo de la conductividad de protón es "hopping". Ellos mostraron el más baja del transporte de metanol.
Se obtuvieron también membranas híbridas de LS, preparadas mediante la mezcla de los dos polímeros, LS y PSU, siguiendo el método de precipitación en inmersión. Las propiedades electroquímicas de las membranas de LS fueron caracterizadas. Las membranas de LS alcanzaron conductividades de protón aceptables (10-20 mS/cm) con capacidad de intercambio iónico muy baja (IEC) (60 veces más baja que Nafion). "Membrane electrode assemblies" (MEAs) fueron preparadas y sus rendimientos de celda fueron medidos en una celda individual directa de metanol (DMFC).
LS membrana is the highlight point of this thesis. It demonstrated the first that LS is a good proton exchange material although it is a waste from the paper industry. It also proved that porous membrane can be used in the DMFC with acceptable proton conductivity and low methanol permeability, which is a totally new way from the existing literatures.
The results have been published on international journals and have been presented on international conferences:
1. X. Zhang, A. Glüsen, R. Garcia-Valls, Porous Lignosulfonate membrane for direct methanol fuel cells, accepted by Journal of Membrane Science, 2005
2. X. Zhang, J. Benavente, R. Garcia Valls, Lignin-based Membranes for Electrolyte Transference, Journal of Power Sources, 145 (2005) 292
3. X. Zhang, L. Pitol Filho, C. Torras, R. Garcia Valls, Experimental and Computational Study of Proton and Methanol Permeability through Composite Membranes, Journal of Power Sources, 145 (2005) 223
4. J. Benavente, X. Zhang, R. Garcia Valls, Modification of Polysulfone Membranes with Polyethylene Glycol and Lignosulfate: Electrical Characterization by Impedance Spectroscopy Measurements, Journal of Colloid and Interface Science, 285 (2005) 273-280
5. X. Zhang, R. Garcia-Valls, Proton transport membrane containing lignin compound for direct methanol fuel cells (Poster), 5th Ibero American Congress on Membrane Science and Technology, 2005, Valencia- Spain
6. X. Zhang, J. Benavente and R. Garcia-Valls, Lignin-based membranes for electrolyte transference (Oral presentation), Fuel Cell Science & Technology, Oct. 2004, Munich- Germany.
7. X. Zhang, R. Garcia-Valls, New membranes for Proton Transport in DMFC (Poster), Euromembrane Sep. 2004, ISBN: 3-930400-65-0, p. 64, Hamburg- Germany,
8. X. Zhang, R. Garcia-Valls, Lignosulfonate Application in Proton Transport Membrane (Oral presentation), 2nd World Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection, May. 2004, Rome- Italy
9. X. Zhang, R. Garcia-Valls, Proton Selective Composite Membrane for Direct Methanol Fuel Cell (Oral presentation), 5th NYM (Network Young Membrains) Oct. 2003, ISBN: 84-688-3132-8, p. 199, Barcelona, Spain
10. X. Zhang, R. Garcia-Valls, A. Jiménez-López, E. Rodríguez-Castellón and J. Benavente, Electrical and Chemical Surface Characterization of Lignosulfate/Polysulfone Membranes for Fuel Cells Application, International Conference on "New Proton Conducting Membranes and Electrodes for PEM FCs", Oct. 2005, Assisi, Italy.
Debido a la crisis de petróleo y a los problemas de emisión, las pilas de combustible adquieren un lugar importante en la aplicación de la energía alternativa. Son una clase de dispositivo electroquímico que convierte la energía química directamente en energía eléctrica. Las celdas de combustible de metanol (DMFC) usan membranas de polímero como el electrolito; las membranas de polímero son capaces de transportar protones de hidrógeno. El sistema de la celda de combustible todavía es costoso y las membranas de intercambio de protón han contribuido significativamente para el costo elevado.
Actualmente, las membranas de ácido perfluorosulfonico (PFSA) (por ejemplo, Nafion ®, de DuPont) ten sido investigadas extensamente. Sin embargo mostraron alto paso de metanol e alto "swelling" lo que lleva a una eficiencia de celda baja.
El objetivo principal de la tesis es preparar membranas de intercambio de protón nuevas para la aplicación en DMFC. Membranas compuestas de PEG y de PA fueron preparadas. Derivados del ácido fosfórico y lignosulfonados (LS) fueron incluidos en la estructura de la PA para actuar como agentes transportadores de protones. El mecanismo de conductividad de protón es "hopping". Ellos mostraron el transporte de metanol más bajo.
Se obtuvieron también membranas híbridas de LS, preparadas mediante la mezcla de los dos polímeros, LS y PSU, siguiendo el método de precipitación en inmersión. Las propiedades electroquímicas de las membranas de LS fueron determinadas. Las membranas de LS alcanzaron conductividades de protón aceptables (10-20 mS/cm) con capacidad de intercambio iónico muy baja (IEC) (60 veces más baja que Nafion). "Membrane electrode assemblies" (MEAs) fueron preparadas y sus rendimientos de celda fueron medidos en una celda individual directa de metanol (DMFC).
Las membranas de LS son el punto principal de esta tesis. Primero se demostró que LS es un material de intercambio de protón muy bueno aunque sea un residuo de la industria de papel. También se probó que membranas porosas pueden ser usadas en DMFC con una conductancia de protón aceptable y baja permeabilidad de metanol, lo que es una manera totalmente nueva comparada a la literatura existente.
Los resultados han sido divulgados en revistas internacionales y han sido presentados en conferencias internacionales:
1. X. Zhang, A. Glüsen, R. Garcia-Valls, Porous Lignosulfonate membrane for direct methanol fuel cells, accepted by Journal of Membrane Science, 2005
2. X. Zhang, J. Benavente, R. Garcia Valls, Lignin-based Membranes for Electrolyte Transference, Journal of Power Sources, 145 (2005) 292
3. X. Zhang, L. Pitol Filho, C. Torras, R. Garcia Valls, Experimental and Computational Study of Proton and Methanol Permeability through Composite Membranes, Journal of Power Sources, 145 (2005) 223
4. J. Benavente, X. Zhang, R. Garcia Valls, Modification of Polysulfone Membranes with Polyethylene Glycol and Lignosulfate: Electrical Characterization by Impedance Spectroscopy Measurements, Journal of Colloid and Interface Science, 285 (2005) 273-280
5. X. Zhang, R. Garcia-Valls, Proton transport membrane containing lignin compound for direct methanol fuel cells (Poster), 5th Ibero American Congress on Membrane Science and Technology, 2005, Valencia- Spain
6. X. Zhang, J. Benavente and R. Garcia-Valls, Lignin-based membranes for electrolyte transference (Oral presentation), Fuel Cell Science & Technology, Oct. 2004, Munich- Germany.
7. X. Zhang, R. Garcia-Valls, New membranes for Proton Transport in DMFC (Poster), Euromembrane Sep. 2004, ISBN: 3-930400-65-0, p. 64, Hamburg- Germany,
8. X. Zhang, R. Garcia-Valls, Lignosulfonate Application in Proton Transport Membrane (Oral presentation), 2nd World Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection, May. 2004, Rome- Italy
9. X. Zhang, R. Garcia-Valls, Proton Selective Composite Membrane for Direct Methanol Fuel Cell (Oral presentation), 5th NYM (Network Young Membrains) Oct. 2003, ISBN: 84-688-3132-8, p. 199, Barcelona, Spain
10. X. Zhang, R. Garcia-Valls, A. Jiménez-López, E. Rodríguez-Castellón and J. Benavente, Electrical and Chemical Surface Characterization of Lignosulfate/Polysulfone Membranes for Fuel Cells Application, International Conference on "New Proton Conducting Membranes and Electrodes for PEM FCs", Oct. 2005, Assisi, Italy La tesis tuvo la cooperación del Forschungszentrum Jülich, Alemania y la doctoranda esta solicitando el titulo de Doctorado Europeo.
41
Rodrigues, Aida. "The effects of carbon monoxide contamination on proton-exchange membrane fuel cells." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq22388.pdf.
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Ous, Talal. "A fundamental study into the performance of proton exchange membrane fuel cells." Thesis, City University London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440687.
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Abaoud, Hassan Abdulaziz. "Studies on proton exchange membrane fuel cells with low platinum loading electrodes." Thesis, Cranfield University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422711.
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Ndzuzo, Linathi. "Platinum based catalysts for the cathode of proton exchange membrane fuel cells." University of the Western Cape, 2018. http://hdl.handle.net/11394/6749.
Full textAbstract:
>Magister Scientiae - MScOxygen reduction reaction (ORR) is carried out in the cathode of the proton exchange membrane fuel cell (PEMFC) and it is known for its sluggish kinetics and the existence of two-pathway mechanism, related with the production of water and hydrogen peroxide. Nowadays, the design of novel cathode catalysts that are able to generate both high oxygen reduction currents and water as main product is a challenge since it causes an enhancement in the performance of PEMFC. Generally, these catalysts are composed of platinum nanoparticles, bearing in mind its high activity towards the ORR. However, the use of platinum means an increase in the total cost of PEMFCs due to its scarcity and high cost. This topic has been the motivation for a wide research in the field of PEMFCs during the last several years, being the main goal to design efficient and low cost catalysts for the cathode of PEMFCs. In this Master thesis project, platinum-palladium (Pt-Pd) catalysts supported on carbon black (CB), carbon nanofibers (CNF) and carbon xerogels (CX) were synthesised using methanol (MeOH), formaldehyde (FMY), n-propanol (nPrOH), ethanol (EtOH) and ascorbic acid (AA). The as-prepared materials were physically characterised by energy dispersive X-ray (EDS), X-ray diffraction (XRD) and transmission electronic microscopy (TEM), in order to determine its composition and morphological characteristics. The catalytic activity towards ORR was assessed by means of electrochemical techniques as rotating disc electrode (RDE) and cyclic voltammetry (CV).
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Hill, Melinda Lou. "Polymeric and Polymer/Inorganic Composite Membranes for Proton Exchange Membrane Fuel Cells." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/37597.
Full textAbstract:
Several types of novel proton exchange membranes which could be used for both direct methanol fuel cells (DMFCs) and hydrogen/air fuel cells were investigated in this work. One of the main challenges for DMFC membranes is high methanol crossover. Nafion, the current perfluorosulfonic acid copolymer benchmark membrane for both DMFCs and hydrogen/air fuel cells, shows very high methanol crossover. Directly copolymerized disulfonated poly(arylene ether sulfone)s copolymers doped with zirconium phosphates and phenyl phosphonates were synthesized and showed a significant reduction in methanol permeability. These copolymer/inorganic nanocomposite hybrid membranes show lower water uptake and conductivity than Nafion and neat poly(arylene ether sulfone)s copolymers, but in some cases have similar or even slightly improved DMFC performance due to the lower methanol permeability. These membranes also show advantages for high temperature applications because of the reinforcing effect of the filler, which helps to maintain the modulus of the membrane, allowing the membrane to maintain proton conductivity even above the hydrated glass transition temperature (Tg) of the copolymer. Sulfonated zirconium phenyl phosphonate additives were also synthesized, and membranes incorporating these materials and disulfonated poly(arylene ether sulfone)s showed promising proton conductivity over a wide range of relative humidities. Single-Tg polymer blend membranes were studied, which incorporated disulfonated poly(arylene ether sulfone) with varied amounts of polybenzimidazole. The polybenzimidazole served to decrease the water uptake and methanol permeability of the membranes, resulting in promising DMFC and hydrogen/air fuel cell performance.Ph. D.
46
Todd, Devin Garret Zech. "Novel transport layer characterization and synthesis for proton exchange membrane fuel cells." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/56235.
Full textAbstract:
Fuel cells are a promising energy conversion technology compatible with developing renewably sourced primary energy distribution. Proton exchange membrane (PEM) fuel cells are particularly suitable for automotive and portable applications. The present thesis advances novel PEM fuel cell porous transport layer (PTL) characterization and materials research. These layers link macro and nano scales by mediating energy and mass transport between reactant distribution channels and catalyst layers. Contemporary commercial PTLs are limited in selection. Moreover, typical characterization methods ignore essential material anisotropy. Herein, a novel transport layer synthesis concept is introduced. By adapting electrospinning technology, structures with engineered morphology are created. PTLs are produced with fibre diameters from 0.2 to 1.6 µm, and are characterized experimentally ex-situ and in-situ. Electrospun PTLs are shown to deliver 85% of equivalent commercial PTL current densities. Furthermore, the state-of-the-art for electronic resistance measurement of PTLs is improved, with rigorous attention given to the anisotropy of the fibre-based media. Novel method and apparatus provide this information as a function of mechanical strain. PTL in-plane resistivities are a unique contribution, where for commercial materials 4.5x10-⁴ to 1.5x10-⁴ Ω∙m are observed for strains from 0.0 to -0.5 m∙m-¹. Finally, electrospun PTLs are developed to investigate the effect of within-plane anisotropy upon fuel cell performance. Electrospun layers are produced with progressively greater fibre alignment to effect anisotropy. This anisotropy is visualized via microscopy, and quantified using the aforementioned electronic resistivity methods. In-situ results with electrospun PTLs, of anisotropy ratios from 1 to 6, suggest greater performance with average fibre alignment perpendicular to gas distribution channels. The present thesis’ contributions strengthen development of a PTL structure-property-performance relationship. With integration into a cell-level relationship, this can empower rational PEM fuel cell design.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
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Redmond, Erin Leigh. "Cathode durability in PEM fuel cells." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50330.
Full textAbstract:
Proton exchange membrane (PEM) fuel cells are competitive with other emerging technologies that are being considered for automotive transportation. Commercialization of PEM fuel cells would decrease emissions of criteria pollutants and greenhouse gases and reduce US dependence on foreign oil. However, many challenges exist that prevent this technology from being realized, including power requirements, durability, on-board fuel storage, fuel distribution, and cost. This dissertation focuses on fuel-cell durability, or more specifically catalyst stability.
New techniques to comprehensively observe and pin-point degradation mechanisms are needed to identify stable catalysts. In this text, an in operando method to measure changes in catalyst particle size at the cathode of a PEM fuel cell is demonstrated. The pair distribution function analysis of X-ray diffraction patterns, generated from an operating fuel cell exposed to accelerated degradation conditions, was used to observe the growth of catalyst particles. The stability of Pt/C and PtCo/C electrodes, with different initial particle sizes, was monitored over 3000 potential cycles. The increase in particle size was fit to a linear trend as a function of cycle number for symmetric linear sweeps of potential. The most stable electrocatalyst was found to be alloyed PtCo with a larger initial particle size.
A better understanding of oxide growth kinetics and its role in platinum dissolution is needed to develop a comprehensive fuel-cell performance model. There is an ongoing debate present in the current literature regarding which oxide species are involved in the oxide growth mechanism. This dissertation discusses the results of in operando X-ray absorption spectroscopy studies, where it was found that PtO2 is present at longer hold times. A new method to quantify EXAFS data is presented, and the extent of oxidation is directly compared to electrochemical data. This comparison indicated that PtO2 was formed at the expense of an initial oxide species, and these steps were included in a proposed mechanism for platinum oxidation.
Simulations of platinum oxidation in literature have yet to fully replicate an experimental cyclic voltammogram. A modified Butler-Volmer rate equation is presented in this thesis. The effect of including an extra parameter, χ, in the rate equations was explored. It was found that while the χ-parameter allowed the cathodic peak width to be decoupled from the Tafel slope for the platinum-oxide reduction, its inclusion could not address all observed experimental characteristics. Exploration of this concept concluded that current is not a function of only potential and coverage. To that end, a heterogeneous oxide layer was introduced. In this model, place-exchanged PtO2 structures of varying energy states are formed through a single transition state. This treatment allowed, for the first time, the simulation of the correct current-potential behavior under varying scan rates and upper potential limits.
Particle size plays a critical role in catalysts stability. The properties of nanoparticles can differ significantly from bulk values, yet few tools exist to measure these values at the nanoscale. Surface stress and surface energy are diagnostic criterion that can be used to differentiate nano from bulk properties. The pair distribution function technique was used to measure lattice strain and particle size of platinum nanoparticles supported on carbon. The effect of adsorbates on surface stress was examined and compared to previous literature studies. Furthermore, a methodology for measuring the surface energy of supported platinum nanoparticles has been developed.
While the results of this work are significant, many more challenges need to be addressed before fuel-cell vehicles are marketed. Recommendations for future work in the field of catalyst durability are addressed.
48
Isikel, Lale. "Design and characterization of nonwoven fabrics for gas diffusion layer in polymer electrolyte membrane fuel cell." Auburn, Ala., 2007. http://repo.lib.auburn.edu/2007%20Spring%20Theses/ISIKEL_LALE_21.pdf.
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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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