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Nomnqa, Myalelo Vuyisa. "Simulation and optimisation of a high temperature polymer electrolyte membrane fuel cell stack for combined heat and power". Thesis, Cape Peninsula University of Technology, 2011. http://hdl.handle.net/20.500.11838/880.
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Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2011High temperature polymer electrolyte membrane fuel cells (PEMFC) operating between 120-180 oC are currently of much research attention. The acid doped polybenzimidazole (PBI) membranes electrolyte are known for their tolerance to relatively high levels of carbon monoxide impurity in the feed. Most fuel cell modelling are theoretical in nature and are solved in commercial CFD platforms such as Fluent. The models require a lot of time to solve and are not simple enough to be used in complex systems such as CHP systems. This study therefore, focussed on developing a simple but yet accurate model of a high temperature PEMFC for a CHP system. A zero dimensional model for a single cell was developed and implemented in Engineering Equations Solver (EES) environment to express the cell voltage as a function of current density among others. Experimental results obtained from literature were used to validate and improve on the model. The validated models were employed for the simulation of the stack performance to investigate the effects of temperature, pressure, anode stoichiometry and the level of CO impurity in the synthesis gas, on the cell potential and overall performance. Good agreement was obtained from the simulation results and experimental data. The results showed that increasing temperature (up to 180oC) and acid doping level have positive effects on the cell performance. The results also show that the cell can operate with a reformate gas containing up to 2% CO without significant loss of cell voltage at elevated temperatures. The single cell model was extended to a 1 kWe high temperature PEMFC stack and micro-CHP system. The stacks model was validated with experimental data obtained from a test station. The model was used to investigate the performance of PEMFC and CHP system by using uncertainty propagation. The highest combined cogeneration system efficiency of 87.3% is obtained with the corresponding electrical and thermal efficiencies are 41.3% and 46 % respectively. The proposed fuel processing subsystem provides an adequate rate of CH4 conversion and acceptable CO-level, making it appropriate for integration with an HT PEMFC stack. In the steam methane reformer 97% of CH4 conversion is achieved and the water gas shift reactors achieve about 98% removal of CO.
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Radhakrishnan, Arjun. "Thermal conductivity measurement of gas diffusion layer used in PEMFC /". Online version of thesis, 2009. http://hdl.handle.net/1850/10839.
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Alan, Dunlavy Choe Song-Yul. "Dynamic modeling of two-phase heat and vapor transfer characteristics in a gas-to-gas membrane humidifier for use in automotive PEM fuel cells". Auburn, Ala., 2009. http://hdl.handle.net/10415/1951.
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Nomnqa, Myalelo Vuyisa. "Design of a domestic high temperature proton exchange membrane fuel cell cogeneration system : modelling and optimisation". Thesis, Cape Peninsula University of Technology, 2017. http://hdl.handle.net/20.500.11838/2574.
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Thesis (DTech (Chemical Engineering))--Cape Peninsula University of Technology, 2017.Fuel cells are among power generation technologies that have been proven to reduce greenhouse gas emissions. They have the potential of being one of the most widely used technologies of the 21st century, replacing conventional technologies such as gas turbines in stationary power supplies, internal combustion engines in transport applications and the lithium-ion battery in portable power applications. This research project concentrates on the performance analysis of a micro-cogeneration system based on a high temperatureproton exchange membrane (HT-PEM) fuel cell through modelling and parametric analysis. A model of a 1kWe micro-cogeneration system that consists of a HT-PEM fuel cell, a methane steam reformer (MSR) reactor, a water-gas-shift (WGS) reactor, heat exchangers and an inverter was developed. The model is coded/implemented in gPROMS Model Builder, an equation oriented modelling platform. The models predictions for the HTPEM fuel cell, MSR and WGS, and the whole system were validated against experimental and numerical results from literature. The validation showed that the HT-PEM fuel cell model was able to predict the performance of a 1kWe fuel cell stack with an error of less than 6.4%. The system model is rstly used in a thermodynamic analysis of the fuel processor for a methane steam reforming process and investigated in terms of carbon monoxide produced. The combustor fuel and equivalence ratios were shown to be critical decision variables to be considered in order to keep the carbon monoxide from the fuel processor at acceptable levels for the fuel cell stack.
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Ntsendwana, Bulelwa. "Advanced low temperature metal hydride materials for low temperature proton exchange membrane fuel cell application". Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_8494_1307431585.
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Energy is one of the basic needs of human beings and is extremely crucial for continued development of human life. Our work, leisure and our economic, social and physical welfare all depend on the sufficient, uninterrupted supply of energy. Therefore, it is essential to provide adequate and affordable energy for improving human welfare and raising living standards. Global concern over environmental climate change linked to fossil fuel consumption has increased pressure to generate power from renewable sources [1]. Although substantial advances in renewable energy technologies have been made, significant challenges remain in developing integrated renewable energy systems due primarily to mismatch between load demand and source capabilities [2]. The output from renewable energy sources such as photo-voltaic, wind, tidal, and micro-hydro fluctuate on an hourly, daily, and seasonal basis. As a result, these devices are not well suited for directly powering loads that require a uniform and uninterrupted supply of input energy.
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McGee, Seán. "Thermal energy management and chemical reaction investigation of micro-proton exchange membrane fuel cell and fuel cell system using finite element modelling". Thesis, KTH, Kraft- och värmeteknologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-173001.
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Fuel cell systems are becoming more commonplace as a power generation method and are being researched, developed, and explored for commercial use, including portable fuel cells that appear in laptops, phones, and of course, chargers. This thesis examines a model constructed on inspiration from the myFC PowerTrekk, a portable fuel cell charger, using COMSOL Multiphysics, a finite element analysis software. As an educational tool and in the form of zero-dimensional, two-dimensional, and three-dimensional models, an investigation was completed into the geometric construction, air conditions and compositions, and product materials with a best case scenario completed that summarizes the results identified. On the basis of the results of this research, it can be concluded that polyoximetylen and high-density polyethylene were considered as possible materials for the majority of the product, though a more thorough investigation is needed. Air flow of above 10 m/s, air water vapour mass fraction below 50% and initial temperature between 308K and 298K was considered in this best scenario. Suggestions on future expansions to this project are also given in the conclusion.
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Tichagwa, Anesu. "Micro combined heat and power management for a residential system". Master's thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/16914.
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Fuel cell technology has reached commercialisation of fuel cells in application areas such as residential power systems, automobile engines and driving of industrial manufacturing processes. This thesis gives an overview of the current state of fuel cell-based technology research and development, introduces a μCHP system sizing strategy and proposes methods of improving on the implementation of residential fuel cell-based μCHP technology. The three methods of controlling residential μCHP systems discussed in this thesis project are heat-led, electricity-led and cost-minimizing control. Simulations of a typical HT PEMFC -based residential μCHP unit are conducted using these control strategies. A model of a residential μCHP system is formulated upon which these simulated tests are conducted. From these simulations, equations to model the costs of running a fuel-cell based μCHP system are proposed. Having developed equations to quantify the running costs of the proposed μCHP system a method for determining the ideal size of a μCHP system is developed. A sizing technique based on industrial CHP sizing practices is developed in which the running costs and capital costs of the residential μCHP system are utilised to determine the optimal size of the system. Residential thermal and electrical load profile data of a typical Danish household are used. Having simulated the system a practical implementation of the power electronics interface between the fuel cell and household grid is done. Two topologies are proposed for the power electronics interface a three-stage topology and a two-stage topology. The efficiencies of the overall systems of both topologies are determined. The system is connected to the grid so the output of each system is phase-shifted and DC injection, harmonic distortion, voltage range and frequency range are determined for both systems to determine compliance with grid standards. Deviations between simulated results and experimental results are recorded and discussed and relevant conclusions are drawn from these.
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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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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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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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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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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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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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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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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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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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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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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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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
23
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.
25
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.
27
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.
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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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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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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.
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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.
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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.
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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.
33
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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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.
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>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).
38
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.
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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.
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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.
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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
40
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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Adigoppula, Vinay Kumar. "A study on Nafion® nanocomposite membranes for proton exchange membrane fuel cells". Thesis, Wichita State University, 2011. http://hdl.handle.net/10057/3940.
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With a rise in demand for electricity and depletion of fossil fuel levels, researchers are looking for an alternative resource to generate power, one which is more environmentally friendly. Fuel cells are one of the best alternatives presently available and are considered by many to be the most promising energy sources with efficiencies of up to 60%. Presently, the cost associated with the usage of fuel cells available in the market is quite high. Researchers are trying to bring down costs associated with their usage and improve efficiency. PEM fuel cells are one of the most promising types of fuel cells. Researchers are currently trying to improve its efficiency by improving its electrolyte. Nafion® is one of the main electrolyte used in PEM fuel cells as it acts as proton conductor. Graphene has an exceptionally high surface area to volume ratio and excellent strength. Current research is focused on integrating graphene in PEM fuel cell electrolytes to improve performance. In this study, graphene is added to Nafion® in varying weight percentages to study the performance of the fuel cell given these changes. The graphene weight percentage is varied by 1, 2, 3, and 4. The fuel cell was operated and it was observed that with the addition of graphene there is an improvement in voltage, proton conductivity, and electron conductivity of the PEM fuel cell. The improvement of proton conductivity and electron conductivity followed a linear path with the increase in graphene weight percentage in the Nafion®. Physical properties of the Nafion® membrane with additional graphene were measured and found out that dielectric constant and thermal conductivity also improved linearly with an increase in graphene weight percentage.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering.
43
Snyder, Loren E. "A feasibility study of internal evaporative cooling for proton exchange membrane fuel cells". Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/3115.
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An investigation was conducted to determine the feasibility of using the technique of ultrasonic nebulization of water into the anode gas stream for evaporative cooling of a Proton Exchange Membrane (PEM) fuel cell. The basic concept of this form of internal evaporative cooling of the PEM fuel cell is to introduce finely atomized liquid water into the anode gas stream, so that the finely atomized liquid water adsorbs onto the anode and then moves to the cathode via electro-osmotic drag, where this water then evaporates into the relatively dry cathode gas stream, carrying with it the waste thermal energy generated within the fuel cell. The thermal and electrical performance of a 50 cm2 PEM fuel cell utilizing this technique was compared to the performance obtained with conventional water management. Both techniques were compared over a range of humidification chamber temperatures for both the anode and cathode gas streams so as to determine the robustness of the proposed method. The proposed method produced only meager levels of evaporative cooling (at best 2 watts, for which a minimum of 30 watts was required for adequate cooling), but the average cell voltage increased considerably (as much as a 10% gain), and the technique increased the fault tolerance of the fuel cell (the Nafion membrane did not dry out even if cell temperature went well in excess of 70° C despite both anode and cathode humidification temperatures of 55° C). An interesting phenomena was also observed wherein the fuel cell voltage oscillated regularly with a period of tens of seconds, and that the amplitude of this oscillation corresponded inversely with the level of humidification received by the fuel cell.
44
Alrweg, Mohmad Salem. "Investigation into the performance and acoustical characteristics of proton exchange membrane fuel cells". Thesis, Manchester Metropolitan University, 2017. http://e-space.mmu.ac.uk/621246/.
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Over the last three decades, much research has been conducted into developing fuel cells (FCs) owing to their high efficiency and environmental friendly operation. Among different types of FCs, proton exchange membrane fuel cells (PEMFCs) are popular for stationary and mobile applications. They have a high-energy density, low operating temperatures, quick start-up times and zero emissions. However, their low reliability and unacceptable high costs limit their wider adoption in the above-mentioned applications. Lack of understanding and complexity of FC operations, mechanical failure, and the lack of root cause analysis and prevention techniques are obstacles that stand in the way of improving such low durability and reliability. The aim of this PhD work is first to derive a realistic model that represents the complex operations of a single PEMFC and experimentally verify the effectiveness of the developed model. Second, to gain a clear understanding of PEMFCs' failure modes and effects analysis. Third, to assess the detectability of commonly used monitoring techniques and explore the acoustical characteristics of PEMFCs under normal and faulty conditions. Power parameters are directly affecting the operating conditions of PEMFC and hence are expected to carry useful information about their conditions. Unfortunately, those measurements are intrusive and they do not detect faults at the early stages of onset. However, PEMFCs are dynamic chemical systems that involve phase transitions and thus are acoustically active. Chemical changes during interactions are usually accompanied by a transfer of energy and part of energy may be converted to an acoustic emission (AE). Although, AE techniques are widely adopted for monitoring chemical and electrochemical systems, no rigorous work has undertaken to characterise the acoustical behaviour of PEMFCs. Therefore, the nature and source of AE in PEMFCs are identified and effect of load variations on them are experimentally investigated as part of this study. It is anticipated the work presented in this thesis will open the door for more studies to build non-intrusive robust diagnostic systems, which will contribute to enhance the reliability of PEMFCs.
45
Gupta, Gaurav. "Bimetallic Platinum-Chromium Nanoparticles as electrocatalysts for proton exchange membrane fuel cells (PEMFCs)". Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5527/.
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Polymer electrolyte membrane fuel cells (PEMFCs) are envisioned to replace internal combustion engines (ICEs) as vehicle power sources and to compete with conventional technologies in backup power systems, residential combined heat and power (CHP) devices and consumer electronics. However, the commercial viability is still hindered due to the cost and durability that are significantly related to the precious metal catalysts used in these cells. In the current work, two different methods towards reducing the precious metal content by the use of transition metal (Cr) with Pt as electrocatalysts for PEMFCs are reported. The commercial Pt/C catalysts layer consists of three components i.e. Pt, carbon support and Nafion ionomer. The Nafion ionomer binder does not penetrate through the microporous carbon support and thus limits the triple phase boundary region (catalytic reaction takes place at triple phase boundary), which in turn leaves a significant amount of Pt being inactive or not utilised. In the first part of this work, Nafion- stabilised Pt-Cr alloys are synthesised using a novel wet chemical synthesis. The aim of this work is to improve the triple phase boundary region with the introduction of Nafion during the synthesis and alloying with Cr that can enhance the catalytic activity. Thus, in turn improving the utilisation of the catalyst and also reducing the amount of Pt loading.
46
Carrère, Pierre. "Modelling and numerical simulation of water transfer in Proton Exchange Membrane Fuel Cells". Thesis, Toulouse, INPT, 2019. http://www.theses.fr/2019INPT0123.
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La gestion de l’eau dans les piles à combustible à membrane d’échange de proton (PEMFC) est une problématique principale pour assurer leur efficacité et leur durabilité. La couche de diffusion côté cathode est considérée comme l’un des composants critiques concernant cette problématique. Dans ce contexte, l’objectif principal de la thèse est d’améliorer la compréhension des mécanismes intervenants dans la formation et le transport de l’eau dans la couche dediffusion côté cathode. Pour ce faire, un modèle en réseau de pores d’injection mixte liquidevapeur (MIPNM) est développé. Ce nouveau modèle permet de simuler la formation et le transport de l’eau dans la couche de diffusion côté cathode sur une plus large gamme de conditions de fonctionnement de la pile (température, densité de courant et humidité relative dans le canal) qu’avec les modèles des travaux précédents. Différents régimes de formation et de transport del’eau sont identifiés et décrits. Dans une seconde partie, le travail de thèse se focalise sur l’impact du traitement hydrophobe de la couche de diffusion. Les couches de diffusion actuellement commercialisées sont rendues hydrophobes en déposant une couche de polytétrafluoroéthylène (PTFE) sur les fibres de carbones hydrophiles. Il a été observé que le revêtement peut être non uniforme sur des couches de diffusion neuves et que le revêtement peut se dégrader au cours dufonctionnement de la pile. L’impact de ces deux phénomènes sur la distribution de l’eau liquide et sur l’accès du gaz réactif jusqu’à la couche catalytique est étudié en utilisant le modèle MIPNM pour des réseaux à mouillabilité mixte. Dans une troisième partie, un travail visant à l’amélioration de l’efficacité des piles est réalisé. Le but est d’optimiser l’accès du gaz réactif jusqu’à la couche catalytique en modifiant la microstructure des couches de diffusion. Ce travail est réalisé en couplant le modèle en réseau de pore avec un algorithme génétique. En complément, la modification des propriétés de mouillabilité des couches de diffusion est étudiée dans le but d’améliorer l’accès du gaz réactif. Enfin, un modèle 1D de tout l’assemblage anode-cathode est développé pour prendre en compte à la fois les conditions de fonctionnement à la cathode et à l’anode. Ce modèle 1D est couplé au MIPNM afin d’évaluer l’impact des conditions de fonctionnement côté anode sur la distribution d’eau liquide dans la couche de diffusion côté cathodeWater management is considered as a key issue in order to improve Proton Exchange Membrane Fuel Cells efficiency and durability. One of the critical components regarding this issue is the athode Gas Diffusion Layer (GDL). In this context, the main goal of the PhD work is to improve the understanding of the mechanisms responsible for the liquid water formation and transport in the cathode GDL. To this end, a Mixed liquid-vapour Injection Pore Network Model (MIPNM) is developed. This new model enables one to simulate the liquid water formation and transport in the cathode GDL for a larger range of operating conditions (temperature, current density and channel relative humidity) than in previous works. Different regimes of water formation and transport are identified and described. In a second part, the PhD work focus on the impact of the GDL hydrophobic treatment. Currently commercialized GDLs are rendered hydrophobic by coating Polytetrafluoroethylene (PTFE) onto the hydrophilic carbon fibres. It has been reported that the coating can be nonuniform on fresh GDLs and also that the coating can be altered during the operation of the fuel cell. The impact of these two phenomena on the liquid water distribution and on the reactant gas access to the catalyst layer is studied using the MIPNM for mixed wettability networks. In a third part, a work aiming at the improvement of PEMFC efficiency is developed. The goal is to optimise the reactant gas access to the catalyst layer by modifying the microstructure of GDLs. This is performed by coupling the PNM with a genetic algorithm. In a complementary study, the improvement of the reactant gas access is studied through modifications of the GDL wettability properties. Finally, a 1D model of the whole anode-cathode assembly is developed so as to take into account both anode and cathode operating conditions. This 1D model is coupled with the MIPNM in order to assess the impact of the anode operating conditions on the liquid water distribution in the cathode GDL
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Wang, Hang. "Synthesis and Characterization of Multiblock Copolymers for Proton Exchange Membrane Fuel Cells (PEMFC)". Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/26026.
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Nanophase-separated hydrophilic-hydrophobic multiblock copolymers are promising proton exchange membrane (PEM) materials due to their ability to form various morphological structures which enhance transport.
Four arylene chlorides monomers (2,5-Dichlorobenzophenone and its derivatives) were first successfully synthesized from aluminum chloride-catalyzed, Friedel-Crafts acylation of benzene and various aromatic compounds with 2,5-dichlorobenzoyl chloride. These monomers were then polymerized via Ni (0)-catalyzed coupling reaction to form various high molecular weight substituted poly(2,5-benzophenone)s. Great care must be taken to achieve anhydrous and inert conditions during the reaction.
A series of poly(2,5-benzophenone) activated aryl fluoride telechelic oligomers with different block molecular weights were then successfully synthesized by Ni (0)- catalyzed coupling of 2,5-dichloro-benzophenone and the end-capping agent 4-chloro-4'-fluorobenzophenone or 4-chlorophenly-4â -fluorophenyl sulfone. The molecular weights of these oligomers were readily controlled by altering the amount of end-capping agent. These telechelic oligomers (hydrophobic) were then copolymerized with phenoxide terminated disulfonated poly (arylene ether sulfone)s (hydrophilic) by nucleophilic aromatic substitution to form novel hydrophilic-hydrophobic multiblock copolymers.
A series of novel multiblock copolymers with number average block lengths ranging from 3,000 to 10,000 g/mol were successfully synthesized. Two separate Tgs were observed via DSC in the transparent multiblock copolymer films when each block length was longer than 6,000 g/mol (6k). Tapping mode atomic force microscopy (AFM) also showed clear nanophase separation between the hydrophilic and hydrophobic domains and the influence of block length, as one increased from 6k to 10k. Transparent and creasable films were solvent-cast and exhibited good proton conductivity and low water uptake.
These PAES-PBP multiblock copolymers also showed much less relative humidity (RH) dependence than random sulfonated aromatic copolymers BPSH 35 in proton conductivity, with values that were almost the same as Nafion with decreasing RHs. This phenomenon lies in the fact that this multiblock copolymer possesses a unique co-continuous nanophase separated morphology, as confirmed by AFM and DSC data. Since this unique co-continuous morphology (interconnected channels and networks) dramatically facilitates the proton transport (increase the diffusion coefficient of water), improved proton conductivity under partially hydrated conditions becomes feasible. These multiblock copolymers are therefore considered to be very promising candidates for high temperature proton exchange membranes in fuel cells.Ph. D.
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Siroma, Zyun. "Studies on local reactions and degradation mechanisms of proton exchange membrane fuel cells". 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/136371.
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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.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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Sombatmankhong, Korakot. "The development and characterisation of microfabricated polymer electrolyte membrane fuel cells". Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610026.
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