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1
Park, Gu-Gon. "Studies on the performance enhancement of polymer electrolyte fuel cells." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136358.
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Liu, Chen. "Structural Studies of Pt-Based Electrocatalysts for Polymer Electrolyte Fuel Cells." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263807.
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付記する学位プログラム名: 京都大学大学院思修館京都大学
新制・課程博士
博士(総合学術)
甲第23346号
総総博第19号
京都大学大学院総合生存学館総合生存学専攻
(主査)教授 寶 馨, 教授 内本 喜晴, 特定教授 橋本 道雄
学位規則第4条第1項該当
Doctor of Philosophy
Kyoto University
DFAM
3
Choo, Hyun-Suk. "Fundamental Studies on Oxidation of Graphite for Polymer Electrolyte Fuel Cells." 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/124501.
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Ma, Yulin. "The Fundamental Studies of Polybenzimidazole/Phosphoric Acid Polymer Electrolyte for Fuel Cells." Case Western Reserve University School of Graduate Studies / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=case1089835902.
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Miyazaki, Kohei. "Studies on anode catalysts using gold nanoparticles for polymer electrolyte fuel cells." 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/136301.
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Kinumoto, Taro. "Fundamental studies on durability and performance improvement of polymer electrolyte fuel cells." 京都大学 (Kyoto University), 2006. http://hdl.handle.net/2433/144023.
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Kyoto University (京都大学)0048
新制・課程博士
博士(工学)
甲第12337号
工博第2666号
新制||工||1377(附属図書館)
24173
UT51-2006-J329
京都大学大学院工学研究科物質エネルギー化学専攻
(主査)教授 小久見 善八, 教授 江口 浩一, 教授 田中 功
学位規則第4条第1項該当
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Takeuchi, Norimitsu. "Studies on Oxidative Degradation of Carbon Support of Electrocatalysts for Polymer Electrolyte Fuel Cells." Kyoto University, 2017. http://hdl.handle.net/2433/225965.
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Fujiwara, Naoko. "Studies on Electrochemical Oxidation of Organic Compounds for Direct Polymer Electrolyte Fuel Cells." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/124566.
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Fanapi, Nolubabalo Hopelorant. "Durability studies of membrane electrode assemblies for high temperature polymer electrolyte membrane fuel cells." University of the Western Cape, 2011. http://hdl.handle.net/11394/5416.
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>Magister Scientiae - MScPolymer electrolyte membrane fuel cells (PEMFCs) among other fuel cells are considered the best candidate for commercialization of portable and transportation applications because of their high energy conversion and low pollutant emission. Recently, there has been significant interest in high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), due to certain advantages such as simplified system and better tolerance to CO poisoning. Cost, durability and the reliability are delaying the commercialization of PEM fuel cell technology. Above all durability is the most critical issue and it influences the other two issues. The main objective of this work is to study the durability of membrane electrode assemblies (MEAs) for HT-PEMFC. In this study the investigation of commercial MEAs was done by evaluating their performance through polarization studies on a single cell, including using pure hydrogen and hydrogen containing various concentrations of CO as fuel, and to study the performance of the MEAs at various operating temperatures. The durability of the MEAs was evaluated by carrying out long term studies with a fixed load, temperature cycling and open circuit voltage degradation. Among the parameters studied, significant loss in the performance of the MEAs was noted during temperature cycling. The effect of temperature cycling on the performance of the cell showed that the performance decreases with increasing no. of cycles. This could be due to leaching of acid from the cell or loss of electrochemically active surface area caused by Pt particle size growth. For example at 160°C, a performance loss of 3.5% was obtained after the first cycle, but after the fourth cycle a huge loss of 80.8% was obtained. The in-house MEAs with Pt-based binary catalysts as anodes were studied for CO tolerance, performance and durability. A comparison of polarization curves between commercial and in-house MEAs illustrated that commercial MEA gave better performance, obtaining 0.52 A/cm² at 0.5V and temperature of 160°C, with in-house giving 0.39A/cm² using same parameters as commercial. The CO tolerance of both commercial and in-house MEA was found to be similar. In order to increase the CO tolerance of the in-house MEAs, Pt based binary catalysts were employed as anodesand the performance was investigated In-house MEAs with Pt/C and Pt-based binary catalysts were compared and a better performance was observed for Pt/C than Pt-alloy catalysts with Pt-Co/C showing comparable performance. At 0.5 V the performance obtained was 0.39 A/cm2 for Pt/C, and 0.34A/cm²,0.28A/cm²,0.27A/cm² and 0.16A/cm² were obtained for Pt-Co/C, Pt-Fe/C, Pt-Cu/C and Pt-Ni respectively. When the binary catalysts were tested for CO tolerance, Pt-Co showed no significant loss in performance when hydrogen containing CO was used as anode fuel. Scanning electron microscopy (SEM) revealed delamination between the electrodes and membrane of the tested and untested MEA's. Membrane thinning was noted and carbon corrosion was observed from the tested micro-porous layer between the gas diffusion layer (GDL) and catalyst layer (CL).
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Aoki, Hiroyoshi. "Studies on Electronic and Local Structure of Pt based Cathode Catalysts for Polymer Electrolyte Fuel Cells." Kyoto University, 2011. http://hdl.handle.net/2433/142305.
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Kyoto University (京都大学)0048
新制・課程博士
博士(人間・環境学)
甲第16177号
人博第560号
新制||人||134(附属図書館)
22||人博||560(吉田南総合図書館)
28756
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 内本 喜晴, 教授 杉山 雅人, 教授 田部 勢津久, 准教授 福塚 友和
学位規則第4条第1項該当
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Aaron, Douglas Scott. "Transport in fuel cells: electrochemical impedance spectroscopy and neutron imaging studies." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34699.
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Current environmental and energy sustainability trends have instigated considerable interest in alternative energy technologies that exhibit reduced dependence on fossil fuels. The advantages of such a direction are two-fold: reduced greenhouse gas emissions (notably CO2) and improved energy sustainability. Fuel cells are recognized as a potential technology that achieves both of these goals. However, improvements to fuel cell power density and stability must be realized to make them economically competitive with traditional, fossil-based technologies. The work in this dissertation is largely focused on the use of analytical tools for the study of transport processes in three fuel cell systems toward improvement of fuel cell performance.
Polymer electrolyte membrane fuel cells (PEMFCs) are fueled by hydrogen and oxygen to generate electrical current. Microbial fuel cells (MFCs) use bacteria to degrade carbon compounds, such as those found in wastewaters, and simultaneously generate an electric current. Enzyme fuel cells (EFCs) operate similarly to PEMFCs but replace precious metal catalysts, such as platinum, with biologically-derived enzymes. The use of enzymes also allows EFCs to utilize simple carbon compounds as fuel. The operation of all three fuel cell systems involves different modes of ion and electron transport and can be affected negatively by transport limitations. Electrochemical impedance spectroscopy (EIS) was used in this work to study the distribution of transport resistances in all three fuel cell systems. The results of EIS were used to better understand the transport resistances that limited fuel cell power output. By using this technique, experimental conditions (including operating conditions, construction, and materials) were identified to develop fuel cells with greater power output and longevity. In addition to EIS, neutron imaging was employed to quantify the distribution of water in PEMFCs and EFCs. Water content is an integral aspect of providing optimal power output from both fuel cell systems. Neutron imaging contributed to developing an explanation for the loss of water observed in an operating EFC despite conditions designed to mitigate water loss. The findings of this dissertation contribute to the improvement of fuel cell technology in an effort to make these energy devices more economically viable.
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Anderson, Jordan. "Electrochemical Studies of Nanoscale Composite Materials as Electrodes in Direct Alcohol Fuel Cells." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5104.
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Polymer electrolyte membrane fuel cells (PEMFCs) have recently acquired much attention as alternatives to combustion engines for power conversion. The primary interest in fuel cell technology is the possibility of 60% power conversion efficiency as compared to the 30% maximum theoretical efficiency limited to combustion engines and turbines. Although originally conceived to work with hydrogen as a fuel, difficulties relating to hydrogen storage have prompted much effort in using other fuels. Small organic molecules such as alcohols and formic acid have shown promise as alternatives to hydrogen in PEMFCs due to their higher stability at ambient conditions. The drawbacks for using these fuels in PEMFCs are related to their incomplete oxidation mechanisms, which lead to the production of carbon monoxide (CO). When carbon monoxide is released in fuel cells it binds strongly to the platinum anode thus limiting the adsorption and subsequent oxidation of more fuel. In order to promote the complete oxidation of fuels and limit poisoning due to CO, various metal and metal oxide catalysts have been used. Motivated by promising results seen in fuel cell catalysis, this research project is focused on the design and fabrication of novel platinum-composite catalysts for the electrooxidation of methanol, ethanol and formic acid. Various Pt-composites were fabricated including Pt-Au, Pt-Ru, Pt-Pd and Pt-CeO2 catalysts. Electrochemical techniques were used to determine the catalytic ability of each novel composite toward the electrooxidation of methanol, ethanol and formic acid. This study indicates that the novel composites all have higher catalytic ability than bare Pt electrodes. The increase in catalytic ability is mostly attributed to the increase in CO poison tolerance and promotion of the complete oxidation mechanism of methanol, ethanol and formic acid. Formulations including bi- and tri-composite catalysts were fabricated and in many cases show the highest catalytic oxidation, suggesting tertiary catalytic effects. The combination of bi-metallic composites with ceria also showed highly increased catalytic oxidation ability. The following dissertation expounds on the relationship between composite material and the electrooxidation of methanol, ethanol and formic acid. The full electrochemical and material characterization of each composite electrode is provided.Ph.D.
Doctorate
Chemistry
Sciences
Chemistry
13
Treptow, Florian. "Polyaniline as electrolyte in polymer electrolyte membrane fuel cells." Thesis, Loughborough University, 2005. https://dspace.lboro.ac.uk/2134/11086.
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The applications of polyaniline (PAni) for use as electrolyte in Polymer-Electrolyte-Membrane Fuel Cells (PEMFC) were investigated. P Ani was dissolved in N-methyl pyrrolidone (NMP), cast as Emeraldine Base membranes (EB) and then doped with halide acids. The proton conductivity was measured according to Hittorf. The chloride ion distribution within the membrane was evaluated using energy-dispersive-X-ray analysis (EDX) and photometric analysers and the diffusion coefficient was calculated. The specific resistance was determined using conventional 4-point measurement. Halide doped membranes were found to be proton conducting, however, during cell operation halide removal occurred causing a rapid decline in the cell performance. The maximum power density achieved was O.3m W·cm-2 for a 70J.1m thick membrane saturate with chloride between 3,5 and 4,5mgchloride per gPAni. Composite membranes with phosphotungstic acid (PWA), antimonic acid (AA) and zirconium phosphate (ZP) were developed and also tested in a standard measuring fuel cell. While membranes produced via ion exchange (ZP) showed the same result like halide doped ones, AA composite membranes showed a stable voltage and current results. The highest measured outcome of 373.3mW·cm-2 was found with a PWA membrane, produced through dispersing 3g of phosphotungstic acid in 300ml of a 1% polyanilinelNMP solution. It was also observed, that the higher power density was obtained from the fuel cell which uses the lower-loaded membrane. It is clear that a positive effect on the cell performance is given by the addition of phosphotungstic acid to the polyaniline membrane. Therefore, the saturation of PW A have to be taken into account to not lower the power density.
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Buche, Silvain. "Polymer electrolyte fuel cell diagnostics." Thesis, University of Bath, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285318.
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Feser, Joseph P. "Convective flow through polymer electrolyte fuel cells." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 1.77 Mb., 93 p, 2005. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1428199.
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Wesselmark, Maria. "Electrochemical Reactions in Polymer Electrolyte Fuel Cells." Doctoral thesis, KTH, Tillämpad elektrokemi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-25267.
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The polymer electrolyte fuel cell converts the chemical energy in a fuel, e.g. hydrogen or methanol, and oxygen into electrical energy. The high efficiency and the possibility to use fuel from renewable sources make them attractive as energy converters in future sustainable energy systems. Great progress has been made in the development of the PEFC during the last decade, but still improved lifetime as well as lowered cost is needed before a broad commercialization can be considered. The electrodes play an important role in this since the cost of platinum used as catalyst constitutes a large part of the total cost for the fuel cell. A large part of the degradation in performance can also be related to the degradation of the porous electrode and a decreased electrochemically active Pt surface. In this thesis, different fuel cell reactions, catalysts and support materials are investigated with the aim to investigate the possibility to improve the activity, stability and utilisation of platinum in the fuel cell electrodes. An exchange current density, i0, of 770 mA cm-2Pt was determined for the hydrogen oxidation reaction in the fuel cell with the model electrodes. This is higher than previously found in literature and implies that the kinetic losses on the anode are very small. The anode loading could therefore be reduced without imposing too high potential losses if good mass transport of hydrogen is ensured. It was also shown that the electrochemically active surface area, activity and stability of the electrode can be affected by the support material. An increased activity was observed at higher potentials for Pt deposited on tungsten oxide, which was related to the postponed oxide formation for Pt on WOx. An improved stability was seen for Pt deposited on tungsten oxide and on iridium oxide. A better Pt stability was also observed for Pt on a low surface non-graphitised support compared to a high surface graphitised support. Pt deposited on titanium and tungsten oxide, displayed an enhanced electrochemically active surface area in the cyclic voltammograms, which was explained by the good proton conductivity of the metal oxides. CO-stripping was shown to provide the most reliable measure of the electrochemically active surface area of the electrode in the fuel cell. It was also shown to be a useful tool in characterization of the degradation of the electrodes. In the study of oxidation of small organic compounds, the reaction was shown to be affected by the off transport of reactants and by the addition of chloride impurities. Pt and PtRu were affected differently, which enabled extraction of information about the reaction mechanisms and rate determining steps. The polymer electrolyte fuel cell converts the chemical energy in a fuel, e.g. hydrogen or methanol, and oxygen into electrical energy. The high efficiency and the possibility to use fuel from renewable sources make them attractive as energy converters in future sustainable energy systems. Great progress has been made in the development of the PEFC during the last decade, but still improved lifetime as well as lowered cost is needed before a broad commercialization can be considered. The electrodes play an important role in this since the cost of platinum used as catalyst constitutes a large part of the total cost for the fuel cell. A large part of the degradation in performance can also be related to the degradation of the porous electrode and a decreased electrochemically active Pt surface. In this thesis, different fuel cell reactions, catalysts and support materials are investigated with the aim to investigate the possibility to improve the activity, stability and utilisation of platinum in the fuel cell electrodes. An exchange current density, i0, of 770 mA cm-2Pt was determined for the hydrogen oxidation reaction in the fuel cell with the model electrodes. This is higher than previously found in literature and implies that the kinetic losses on the anode are very small. The anode loading could therefore be reduced without imposing too high potential losses if good mass transport of hydrogen is ensured. It was also shown that the electrochemically active surface area, activity and stability of the electrode can be affected by the support material. An increased activity was observed at higher potentials for Pt deposited on tungsten oxide, which was related to the postponed oxide formation for Pt on WOx. An improved stability was seen for Pt deposited on tungsten oxide and on iridium oxide. A better Pt stability was also observed for Pt on a low surface non-graphitised support compared to a high surface graphitised support. Pt deposited on titanium and tungsten oxide, displayed an enhanced electrochemically active surface area in the cyclic voltammograms, which was explained by the good proton conductivity of the metal oxides. CO-stripping was shown to provide the most reliable measure of the electrochemically active surface area of the electrode in the fuel cell. It was also shown to be a useful tool in characterization of the degradation of the electrodes. In the study of oxidation of small organic compounds, the reaction was shown to be affected by the off transport of reactants and by the addition of chloride impurities. Pt and PtRu were affected differently, which enabled extraction of information about the reaction mechanisms and rate determining steps.Polymerelektrolytbränslecellen omvandlar den kemiska energin i ett bränsle, exv. vätgas eller metanol, och syrgas till elektrisk energi. Den höga verkningsgraden samt möjligheten att använda bränsle från förnyelsebara källor gör dem attraktiva som energiomvandlare i framtida hållbara energisystem. En enorm utveckling har skett under det senaste årtiondet men för att kunna introducera polymerelektrolytbränslecellen på marknaden i en större skala måste livstiden öka och kostnaden minska. Elektroderna har en central del i detta då den platina som används som katalysator står för en stor del av kostnaden för bränslecellen. En stor del av prestandaförsämringen med tiden hos bränslecellen kan också relateras till en degradering av den porösa elektroden och en minskad elektrokemiskt aktiv platinayta. I denna avhandling studeras olika bränslecellsreaktioner samt olika katalysatorer och supportmaterial med målet att undersöka möjligheten att förbättra platinakatalysatorns aktivitet, stabilitet och utnyttjandegrad i bränslecellselektroder. Utbytesströmtätheten, i0, för vätgasoxidationen i bränslecell bestämdes till 770 mA cm-2Pt genom försök med modellelektroderna. Denna var högre än vad som framkommit tidigare i litteratur, vilket visar att de kinetiska förlusterna på anoden är mycket små. Katalysatormängden på anoden borde därför kunna minskas utan några större potentialförluster så länge masstransporten av vätgas är tillräcklig. Den elektrokemiskt aktiva ytan, aktiviteten och stabiliteten hos elektroden visade sig kunna påverkas av supportmaterialet. Platina deponerad på volfram oxid hade en högre aktivitet vid höga potentialer vilket relaterades till den förskjutna oxidbildningen på ytan. Elektroder med platina på volframoxid och iridiumoxid var mer stabila än elektroder med platina på kol. Det var även platina på ett icke grafitiserat kol med låg yta jämfört med platina på grafitiserade kol med en hög yta. Platina på metalloxidskikt av volfram och titan visade en högre elektrokemiskt aktiv yta i de cykliska voltamogrammen än platina på kol, vilket förklarades med att båda metalloxiderna har en bra protonledningsförmåga. CO-stripping gav det säkraste måttet på den elektrokemiskt aktiva ytan i en elektrod i bränslecell. CO-stripping visade sig även vara användbart för karaktärisering av degraderingen av en elektrod. Oxidationen av små organiska föreningar påverkades av borttransporten av intermediärer samt av kloridföroreningar. Pt aoch PtRu påverkades olika vilket gjorde det möjligt att få fram information om reaktionsmekanismer och hastighetsbestämmande steg.
QC 20101014
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Matian, Mardit. "Heat transfer in polymer electrolyte fuel cells." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/6215.
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A three dimensional computational fluid dynamics (CFD) model of a polymer electrolyte membrane fuel cell (PEMFC) stack has been developed in order to study heat transfer in single-cell and two-cell stacks. In order to simplify the computational model, the electrochemical and water transport aspects of fuel cell operation were decoupled from those of heat transfer; the PEMFC fuel cell membrane electrode assembly (MEA), which comprises the electrode and electrolyte functional layers, was substituted with an electrically heated-plate to simulate the heat generated by an MEA. A fuel cell stack was manufactured and instrumented with calibrated thermocouples to measure the temperature distribution. The effect of reactant gas flow rate and cell thermal power density on the temperature distribution within the stack was studied with a view to validating the CFD model over a broad range of operating conditions. Also, in order to study the effects of natural and forced convection on the temperature distribution in the stack, an infra-red imaging camera was used. The predicted temperature distribution showed good agreement with the experiment over a wide range of gas flow rates, both in terms of local temperature distribution and overall energy balance. Results show that increasing the number of cells in a stack from one to two causes in a larger temperature variation, and therefore heat management in the stack becomes increasingly critical. The validated computational model was used as a modelling framework to design and test different cooling plates for stacks in order to overcome this issue. As a result, the bipolar plate in the two-cell stack was replaced with an air-cooled cooling plate in order to minimise temperature variation and to improve overall stack performance.
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Fedock, John Andrew. "Low temperature polymer electrolyte fuel cell performance degradation." [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002565.
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Tingelöf, Thomas. "Polymer Electrolyte Fuel Cells in Reformate Power Generators." Doctoral thesis, KTH, Skolan för kemivetenskap (CHE), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-26938.
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The topic of this thesis is the generation of electricity from hydrocarbon fuels via polymer electrolyte fuel cells (PEFC). The aim has been to develop methods and hardware for experimental evaluation of process parameters and design variables in PEFC reformate cells and stacks. Reformate fuel cell systems have the potential to offer a way for utilizing fuels efficiently with low global and local emissions. Reforming of hydrocarbon fuels may also provide a way around the famous “chicken or egg” dilemma of hydrogen vehicles and infrastructure. In this thesis current distribution measurements are introduced as a tool for investigating the current distribution in a PEFC with Pt/C or PtRu/C anode catalyst as function of reformate fuel gas composition. It is shown that CO may induce a strong transient behavior, with respect to current density, on both Pt/C and PtRu/C catalysts, depending on mode of operation. Analysis of the exhaust fuel gas showed that the oxygen in the air bleed most likely reacts close to the anode inlet, but this is not visible in the measured current density plots. The time dependence of the CO poisoning reactions is studied more closely in a commercial fuel cell stack. The development of a test fuel cell system, called multisinglecell, that can multiply the capacity of a conventional test station is reported. The setup is successfully demonstrated with initial screening of the corrosion resistance of different stainless steel grades and coatings. Most of the iron originating from a stainless steel sample accumulates in the MEA and GDLs. These results were validated with a similar measurement in a commercial fuel cell stack. The experimental validation of a 3D FEM computer endplate model, which can accurately predict pressure distribution within any type of fuel cell at any temperature, is described. The model could reliably predict trends in changes in the compression pressure distribution. The PBI fuel cell competes with the PEFC in small-scale power applications. A high temperature break-in procedure for PBI fuel cells is developed, which can rapidly and reproducibly ensure stable cell behavior.QC 20101130
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Verma, Atul. "Transients in Polymer Electrolyte Membrane (PEM) Fuel Cells." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/64247.
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The need for energy efficient, clean and quiet, energy conversion devices for mobile and stationary applications has presented proton exchange membrane (PEM) fuel cells as a potential energy source. The use of PEM fuel cells for automotive and other transient applications, where there are rapid changes in load, presents a need for better understanding of transient behavior. In particular at low humidity operations; one of the factors critical to the performance and durability of fuel cell systems is water transport in various fuel cell layers, including water absorption in membrane. An essential aspect to optimization of transient behavior of fuel cells is a fundamental understanding of response of fuel cell system to dynamic changes in load and operating parameters. This forms the first objective of the dissertation. An insight in to the time scales associated with various transport phenomena will be discussed in detail. In the second component on the study, the effects of membrane properties on the dynamic behavior of the fuel cells are analyzed with focus on membrane dry-out for low humidity operations. The mechanical behavior of the membrane is directly related to the changes in humidity levels in membrane and is explored as a part third objective of the dissertation. Numerical studies addressing this objective will be presented. Finally, porous media undergoing physical deposition (or erosion) are common in many applications, including electrochemical systems such as fuel cells (for example, electrodes, catalyst layer s, etc.) and batteries. The transport properties of these porous media are a function of the deposition and the change in the porous structures with time. A dynamic fractal model is introduced to describe such structures undergoing deposition and, in turn, to evaluate the changes in their physical properties as a function of the deposition.Ph. D.
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Chivengwa, Tapiwa. "Microchannel flow fields for polymer electrolyte fuel cells." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/13674.
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Fuel cell technology represents an efficient and relatively quiet way of generating electricity. Among the various types of fuel cells, the polymer electrolyte fuel cell (PEFC) is the leading candidate for portable, automotive and more recently stationary applications. One of the key challenges affecting both the performance and durability of low temperature PEFCs is water management. Various water management strategies in PEFCs have been employed to date ranging from manipulation of operating conditions, fuel cell component design and flow field design to name a few. The optimisation of the flow field design for water removal has primarily focused on the use of flow channels which are in the minichannel range. This study investigated the use of a microchannel flow field design (channel hydraulic diameters of less than or equal to 200 ìm) for a low temperature PEFC. Specifically it focused on the effect of using a microchannel design on overall fuel cell performance, pressure drop and the cell voltage behaviour over time. In addition the effect of different operating conditions was also investigated. The overall aim was to develop a more comprehensive understanding of the use of a microchannel based flow field system with specific focus on water management. Fuel cell testing of two different flow field designs, namely a microchannel design and a more conventional commercial minichannel design, was performed in a single cell set up. Two operating conditions, cathode flow rate and cell compression, were varied and the effect on overall fuel cell performance and limiting current was investigated. Several diagnostic measurements including polarization curve, high frequency resistance, electrochemical impedance spectroscopy, pressure drop co-efficient and cell voltage monitoring were conducted to understand the water management behaviour and trends in the two different aforementioned flow field designs.
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De, Beer Chris. "Condition monitoring of polymer electrolyte membrane fuel cells." Doctoral thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13264.
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Includes bibliographical references.As the global demand for energy continues to grow new technologies and systems must be developed to supply the market. This includes renewable energy generation, storage and conversion systems. The primary storage technology in use today in the portable electronics, the automotive sector and to a lesser extent power networks is battery based systems. To overcome some of the limitations inherent in batteries, fuel cell based power generators and converters have been developed. Fuel cells act as electrochemical energy converters that convert a fuel source such as natural gas directly into electrical power without any secondary phases. For systems running on Hydrogen generated via renewable or natural sources, the input/output cycle becomes completely sustainable. Out of the different fuel cell types available and under development, the Proton Exchange Membrane or Polymer Electrolyte Membrane (PEM) fuel cell has emerged as the technology of choice, and currently owns more than 80% of the commercial fuel cell market. This has spurred further research in the field to increase performance and life expectancy of the cell materials. A promising development in the form of High Temperature PEM (HT-PEM) fuel cells has recently emerged and addresses some of the shortcomings of the low temperature counterparts. A critical field of research is the condition monitoring strategies and technologies for the electrochemical device that ties in with the power conditioning sub-systems. This thesis presents the development of condition monitoring systems by conducting detailed studies on the fault/degradation mechanisms prevalent in the cell materials for the purpose of detection, classification and implementation of possible mitigation strategies. Specific consideration is given to the detailed analysis of the fault mechanisms in HT-PEM fuel cells that are not yet fully understood and commercialized. In particular, electrochemical equivalent circuit models and reduced order semi- empirical models are developed to facilitate fault detection. Based on these models, mitigation strategies for specific faults are proposed and experimentally verified. New systems and methods are developed for rapid online impedance signature mapping that provide a basis for early fault prediction that can increase system performance and life expectancy. The findings in this research provide valuable insight into the effect that most prevalent faults have on the internal electrochemistry and the impact on electrical performance. From the experimental results, a semi-empirical electrochemical model is developed to assist with life time estimation and system optimization. The model is integrated with a real time emulator platform that can reproduce single cell voltage levels at the high output currents and transient characteristics. A detailed analysis is conducted on CO poisoning and the resulting effects on key equivalent circuit parameters that enable quantification of the fault condition. It is shown that the catalyst at the higher operating temperature is still susceptible to a certain degree of semi-permanent degradation. To mitigate these effects, a new active current control strategy is proposed to enforce electro-oxidation of the CO to recover the lost active area that delivered superior results compared to current pulsing strategies. New rapid online detection strategies are proposed by using small voltage transients in an operational HT-PEM fuel cell. The method makes use of the discrete S-transform that overcomes some of the limits in other signal processing methods used in fuel cell diagnostics. To enable detailed parameter calculation, a population based incremental learning algorithm is implemented in the developed method. A new condition monitoring system is developed that makes use of Optimized Broadband Impedance Spectroscopy. The hardware is designed to accommodate both single cell and stack level implementation. It is shown that the proposed system is able to deliver measurements under extreme non-linear conditions that can occur in PEM fuel cells in a fraction of the time associated with normal EIS based systems.
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Branco, Carolina Musse. "Multilayer membranes for intermediate temperature polymer electrolyte fuel cells." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7717/.
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IT-PEFC operating at 120°C and not the usual 80°C has many advantages, such as faster chemical reactions. If the gas humidification is reduced, simpler and lighter humidifiers can be used, leading to a reduction in the fuel cell total cost. However, at this condition the current commercial membrane Nafion is not able to hold water and perform satisfactorily. Therefore, in this study the application of multilayer membranes for IT-PEFC was investigated. These membranes were divided into two groups, a first with external layers of Nafion and an inner layer of sulphonated polyindene, and a second with external layers of Nafion and an inner layer of graphene oxide. The membrane preparation method was also investigated. The multilayer membranes were prepared by hot pressing and solution casting. As a result, cast multilayer membranes showed better performance and proton conductivity than hot pressed. Delamination and low interface interaction were the main drawbacks for hot pressed membranes. Cast multilayer sulphonated polyindene membranes showed higher performance than Nafion at 120°C and 20% of relative humidity. In the meantime, cast graphene oxide multilayer membranes showed higher water uptake and open circuit voltage than Nafion.
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Tumuluri, Uma. "Nonlinear State Estimation in Polymer Electrolyte Membrane Fuel Cells." Cleveland State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=csu1231961499.
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Balogun, Emmanuel O. "Comparative analysis of Polymer Electrolyte Membrane (PEM) fuel cells." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29764.
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Per-Fluoro-Sulphonic-Acid (PFSA) ionomers have been singled out as the preferable ionomers for making the Polymer Electrolyte Membrane Fuel Cells (PEMFC) membranes owing to their extensive intrinsic chemical stability and super sulfonic acid strength which is core to the PEMFC proton conductivity. This thesis presents a deeper analysis into these PFSA ionomer membrane electrode assemblies (MEA), presenting an electrochemical-analytical comparative analysis of the two basic types, which are the Long-Side-Chain (LSC) Nafion® and the ShortSide-Chain (SSC) Aquivion® ionomer MEA with emphasis on performance and durability which are currently not well understood. In particular, electrochemical circuit models and semiempirical models were employed to enable distinguishable comparative analysis. Also, in this thesis, we present a further probe into the effect of ionomer ink making processes, critically investigating the effect of the High Share Dispersion (HSD) process on both the Nafion® and Aquivion® ionomer membrane electrode assembly (MEA). The findings in this research provides a valuable insight into the performance and durability of PFSA ionomer membrane under various application criteria. The effect of operating parameters and accelerated stress testing (AST) on the PFSA ionomers was determined using electrochemical impedance spectroscopy (EIS) and electronic circuit model (ECM) analysis. The result of this study, shows that the ionomer ink making process for Nafion® and Aquivion® MEAs are not transferrable. Analysis of the PEMFC performance upon application of the high shear dispersion (HSD) process showed that Nafion® MEA had a 10.47% increase in voltage while the Aquivion® MEA had a 2.53% decrease in voltage at current density of 1.14A/cm2 . Also, upon accelerated stress testing, the Nafion® showed a 10.49% increase in its voltage while the Aquivion® on the other hand had a 7.16% decrease in voltage at 0.66A/cm2 . Thus indicating the HSD process enhances the performance of the Nafion® MEA and inhibits the performance of the Aquivion® MEA.
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Mamlouk, Mohamed. "Investigation of high temperature polymer electrolyte membrane fuel cells." Thesis, University of Newcastle upon Tyne, 2008. http://hdl.handle.net/10443/3973.
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the major issues limiting the introduction of polymer electrolyte membrane fuel cells (PEMFC) is the low temperature of operation which makes platinum-based anode catalysts susceptible to poisoning by trace amounts of CO, typically present in reformed fuel. In order to alleviate the problem of CO poisoning and improve the power density of the cell, operating at temperature above 100°C is preferred. Nafion® type perfluorosulphonated polymers have been typically used for PEMFC but cannot function at temperatures above 100°C. In addition, higher temperatures will enable more effective cooling of the cell stacks and provide a means for combined electrical and heat energy generation. The solution to improved PEMFCs technology is to develop a new polymer electrolyte membrane which exhibits stability and high conductivity in the absence of liquid water. A HighTemperature PEMFC based on a Phosphoric acid (H3P04) doped Polybenzimidazole poly[2,2- (m-phenylene)-5,5 bibenzimidazole] (PBI) membrane has been developed and demonstrated as an alternative to Nafion® for operation at temperatures up to 200°C. PBI membranes, when doped with phosphoric acid, do not rely on hydration for conductivity; a significantly lower water content of the membrane, compared to Nafion, is required for proton transport. The resulting system improvements include; high CO tolerance, simple thermal and water management, excellent oxidative and thermal stability, and good proton conductivity at elevated temperatures. Two issues associated with phosphoric acid in the PBI based fuel cell are the lower activity of the electrocatalysts and the potential loss of the acid into the fuel cell gas/vapour exhaust streams. The limited oxygen permeability and slow oxygen reduction kinetics in phosphoric acid is a major limitation for the performance ofPBI based PEMFCs. The kinetics of oxygen reduction in PBVH3P04 has been studied in electrochemical single electrode cells. Several Membrane Electrode Assemblies (MEAs) have been manufactured to allow optimisation of the electrode performance. Various electrochemical techniques such as chronoamperometry, polarisation curves and Frequency Response Analysis (FRA) were used to study and separate the effects of the various phenomena taking place at the electrode surface: IR losses, mass transport and kinetics. A new Electrode structure utilizing PTFE has been developed allowing higher oxygen permeability and therefore enhanced performance of 0.55 W cm-2 with oxygen and 0.27 W cm-2 with air (atm) at temperature as low as 120 ·C. The Platinum loading was reduced to 0.4 mgpt cm-2 at the cathode and 0.2 mgpt cm-2 at the anode. Further reduction of cathode platinum loading to 0.2 mgPI cm-2 was achieved without dramatic drop in the performance by utilising Pt based binary alloy catalyst (Pt-Co/C). A simplified thin film steady-state, isothermal, one dimensional model of a proton exchange membrane fuel cell (PEMFC), with a polybenzimidazole (PBD membrane, was developed. The electrode kinetics were represented by the Butler-Volmer equation, mass transport was described by the multi-component Stefan Maxwell equations and Fick's law, and the ionic and electronic resistances described by Ohm's law. The model incorporated the effects of temperature and pressure on the open circuit potential, the exchange current density and diffusion coefficients, together with the effect of water on the acid concentration and ionic conductivity. The polarisation curves predicted by the model were validated against experimental data for a PEMFC which included the effect of temperature and oxygen/air pressure on cell performance. An additional problem which faces the introduction ofPEMFC technology is that of supplying or storing hydrogen for cell operation, especially for vehicular applications. Consequently the use of alternative fuels such as methanol and ethanol is of interest, especially if this can be used directly in the fuel cell, without reformation to hydrogen. A limitation of the direct use of alcohol is the lower activity of oxidation in comparison to hydrogen, and hence to improve activity and power output higher temperatures of operation are preferable. The performance of a high temperature direct methanol fuel cell (DMFC) using PBI based electrode assemblies was investigated. The performance of the system was limited by poor methanol oxidation kinetics in a phosphoric acid environment and consequently power performance was inferior to that achieved with low temperature DMFCs based on Nafion membranes.
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Pehlivan-Davis, Sebnem. "Polymer Electrolyte Membrane (PEM) fuel cell seals durability." Thesis, Loughborough University, 2016. https://dspace.lboro.ac.uk/2134/21749.
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Polymer electrolyte membrane fuel cell (PEMFC) stacks require sealing around the perimeter of the cells to prevent the gases inside the cell from leaking. Elastomeric materials are commonly used for this purpose. The overall performance and durability of the fuel cell is heavily dependent on the long-term stability of the gasket. In this study, the degradation of three elastomeric gasket materials (silicone rubber, commercial EPDM and a developed EPDM 2 compound) in an accelerated ageing environment was investigated. The change in properties and structure of a silicone rubber gasket caused by use in a real fuel cell was studied and compared to the changes in the same silicone rubber gasket material brought about by accelerated aging. The accelerated aging conditions were chosen to relate to the PEM fuel cell environment, but with more extreme conditions of elevated temperature (140°C) and greater acidity. Three accelerated ageing media were used. The first one was dilute sulphuric acid solution with the pH values of 1, 2 and 4. Secondly, Nafion® membrane suspended in water was used for accelerated ageing at a pH 3 to 4. Finally, diluted trifluoroacetic acid (TFA) solution of pH 3.3 was chosen. Weight change and the tensile properties of the aged gasket samples were measured. In addition, compression set behaviour of the elastomeric seal materials was investigated in order to evaluate their potential sealing performance in PEM fuel cells. The results showed that acid hydrolysis was the most likely mechanism of silicone rubber degradation and that similar degradation occurred under both real fuel cell and accelerated aging conditions. The effect of TFA solution on silicone rubber was more aggressive than sulphuric acid and Nafion® solutions with the same acidity (pH value) suggesting that TFA accelerated the acid hydrolysis of silicone rubber. In addition, acid ageing in all three acidic solutions caused visible surface damage and a significant decrease in tensile strength of the silicone rubber material, but did not significantly affect the EPDM materials. EPDM 2 compound had a desirable (low) compression set value which was similar to silicone rubber and much better than the commercial EPDM. It also showed a very good performance in the fuel cell test rig conforming that it a potential replacement for silicone rubber in PEMFCs.
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Brunello, Giuseppe. "Computational modeling of materials in polymer electrolyte membrane fuel cells." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/48937.
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Fuel cells have the potential to change the energy paradigm by allowing more efficient use of energy. In particular, Polymer Electrolyte Membrane Fuel Cells (PEMFC) are interesting because they are low temperature devices. However, there are still numerous challenges limiting their widespread use including operating temperature, types of permissible fuels and optimal use of expensive catalysts. The first two problems are related mainly to the ionomer electrolyte, which largely determines the operating temperature and fuel type. While new ionomer membranes have been proposed to address some of these issues, there is still a lack of fundamental knowledge to guide ionomer design for PEMFC.
This work is a computational study of the effect of temperature and water content on sulfonated poly(ether ether ketone) and the effect of acidity on sulfonated polystyrene to better understand how ionomer material properties differ. In particular we found that increased water content preferentially solvates the sulfonate groups and improves water and hydronium transport. However, we found that increasing an ionomer’s acid strength causes similar effects to increasing the water content.
Finally, we used Density Functional Theory (DFT) to study platinum nano-clusters as used in PEMFCs. We developed a model using the atom’s coordination number to quickly compute the energy of a cluster and therefore predict which platinum atoms are most loosely held. Our model correctly predicted the energy of various clusters compared to DFT. Also, we studied the interaction between the various moieties of the electrolyte including the catalyst particle and developed a force field.
The coordination model can be used in a molecular dynamics simulation of the three phase region of a PEMFC to generate unbiased initial clusters. The force field developed can be used to describe the interaction between this generated cluster and the electrolyte.
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Pilditch, Stephen Robert. "Modelling high temperature phosphoric acid doped polymer electrolyte fuel cells." Thesis, University of Newcastle Upon Tyne, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.519580.
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El-Kharouf, Ahmad. "Understanding GDL properties and performance in polymer electrolyte fuel cells." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5211/.
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The Gas Diffusion Layer (GDL) has the important role of transporting the reactants into, and products out of the cell. This study aims to provide insights for understanding the relationship between GDL properties and the performance of PEFCs. Ex-situ characterisation techniques were employed to study the mechanical, physical and electrical properties of the GDL. The relationship between the various properties of GDL was investigated and discussed in this work. The study shows that characteristics such as GDL thickness, bulk density, PTFE and MPL content, porosity, hydrophobicity, permeability and electrical conductivity are closely connected. The effect of compression on the cathode GDL performance in PEFC membrane electrode assembly (MEA) is discussed using Polarisation (IV) curve and electrochemical Impedance Spectroscopy (EIS). Compression affects the electrical and mass transport properties of the GDL and therefore needs to be optimised. The results show that there is an optimum compression point, at which; a minimum contact resistance and optimum water transport are achieved. The optimum compression level is dependent on the GDL properties. The optimum compression ratio varies for the different GDLs according to the difference in the material properties. At optimum compression, the performance of the different GDL materials was compared to understand the effect of the GDL properties on the performance. GDL characteristics such as structure, thickness, bulk density, PTFE loading, and MPL presence have a direct effect on the MEA performance and need to be optimized for the different PEFC applications.
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Epting, William K. "Characterizing Electrode-Level Oxygen Transport in Polymer Electrolyte Fuel Cells." Research Showcase @ CMU, 2015. http://repository.cmu.edu/dissertations/623.
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Polymer electrolyte fuel cells (PEFCs) are a promising technology for environmentally friendly automobiles, among other applications. However, performance losses due to oxygen transport hindrances in the PEFC’s cathode continue to be an issue in widespread commercialization. This dissertation focuses on the transport of oxygen through the thickness of the PEFC cathode, and the effect of the cathode’s microstructure on that transport. In order to react in the cathode, oxygen travels from gas flow channels down through a diffusion medium, through the pores of a catalyst layer, and finally, into and through the ionomer covering the catalyst particles. Transport resistances throughout this path lead to oxygen starvation at some of the catalyst particles. Due to these transport resistances, much of the platinum is underutilized when the fuel cell is operating at appreciable currents. This dissertation aims to characterize the transport resistance in each of these phases. We study (1) oxygen transport throughout the diffusion medium using a commercial electrochemical microsensor at multiple points, (2) oxygen transport through the entire diffusion medium using a thin film oxygen microsensor at one point, (3) transport through the catalyst layer pores using a device that allows oxygen microsensors to contact the side of the catalyst layer at multiple points, (4) the effect of the catalyst layer’s microstructure on oxygen transport using x-ray computed tomography, and (5) transport into and through ionomer-covered catalyst agglomerates using ex-situ experiments. We go on to discuss the application of similar methods to solid oxide fuel cells. Using the methods developed in this work, we determine that the two dominant oxygen transport resistances are the diffusion medium, and a “local” resistance at the interface of the platinum catalyst and the ionomer binder that has previously generated some controversy in the field. The oxygen transport resistance of the diffusion medium in this work (defined as the ratio of the drop in concentration across a component to the flux through it) is 65 s/m, with about 2/3 of that coming from its microporous layer. This value can rise to double or more in the case of liquid water condensation in the diffusion medium’s pores. We find that the oxygen transport resistance in the catalyst layer’s pores is an order of magnitude less than that of the diffusion medium. That value, too, can change depending on liquid water flooding. In previous works, the “local” oxygen transport resistance at the level of the platinum catalyst and ionomer binder was of unclear origin. We have determined that it arises at the Pt|ionomer interface – it does not originate from the ionomer|gas interface, nor is it due to nanoscale confinement effects. In our investigation of the catalyst layer’s morphology, we find that a popular approach to modelling PEFC performance – the agglomerate model – changes significantly when one incorporates a realistic distribution of agglomerate sizes instead of assuming a uniform agglomerate size. This effect, however, is small compared to the oxygen transport resistance of the diffusion medium oxygen resistance and the Pt|ionomer interfacial oxygen resistance.
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Zhu, Huizhen. "Applications of polyamidoamine dendrimers in polymer electrolyte membrane fuel cells." Thesis, [Tuscaloosa, Ala. : University of Alabama Libraries], 2009. http://purl.lib.ua.edu/2188.
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Alcock, Hannah Jane. "High throughput studies of polymer electrolytes for battery and fuel cell applications." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/79788/.
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New methods for the high-throughput characterisation of polymer electrolytes have been developed. Polymer electrolytes for use in lithium ion batteries have been prepared in a novel systematic manner that involves parallel preparation and subsequent high-throughput conductivity measurements of up to 64 individual compositions in a multi-electrode cell. The method of casting the polymer electrolytes directly onto the substrate also allows high-throughput characterisation by x-ray diffraction. The technique was applied specifically to a ternary system of PVdF-HFP, LiTFSI and PC. By preparing a vast array of samples across the composition range, it was found that the conductivity reached a maximum value when the weight fraction composition was 0.45/0.45/0.1 of PVdF-HFP/LiTFSI/PC with completely free standing samples. The trend of increasing conductivity tended towards the maximum liquid conductivity of LiTFSI/PC. Due to limitations of this method with highly conductive polymer electrolytes, a second novel alternative polymer synthesis, preparation and measurement technique was developed for proton conducting polymers for fuel cell applications. In addition a second multi-electrode cell was designed and constructed specifically allowing AC Impedance measurements to be taken whilst allowing the polymer electrolytes to be subjected to temperature and relative humidity effects. The multi-electrode cell was calibrated using commercially available Nafion samples before being used with synthesised samples. PEEK was sulfonated to SPEEK using varying temperatures and reaction times to obtain many samples with differing DS values. The conductivity of the samples was measured in situ using an in-plane 4 electrode impedance measurement, over a range of environmental conditions. It was found that water loss caused significant conductivity decay under PEMFC conditions for Nafion but not for SPEEK samples. SPEEK with a DS of 75 % was found to have the maximum SPEEK equilibration conductivity of 0.177 S cm-1, a value comparable to that of commercial membranes. By blending this sample with a lower DS SPEEK, high conductivity values could be maintained at temperatures of 105 °C and 75 % relative humidity with maintained mechanical integrity. When an inorganic additive (Zr(HPO4)2) was introduced into the blended samples, the conductivity was enhanced further due to increased water retention within the phosphate structure.
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Leahy, Scott B. "Active Flow Control of Lab-Scale Solid Polymer Electrolyte Fuel Cells." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5188.
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The effects of actively pulsing reactant flow rates into solid polymer electrolyte fuel cells were investigated in this thesis. First, work was conducted to determine the magnitude of voltage response to pulsed reactant flow on a direct hydrogen proton exchange membrane (PEM) cell. The effects of pulsed reactant flow into a direct methanol fuel cell (DMFC) were then considered.
The PEM work showed substantially greater response to pulsed air flow than to pulsed fuel flow. It was found that several parameters affect the magnitude of cell response to active flow control (AFC). Increasing current load, increasing the magnitude of flow oscillation, decreasing the frequency of oscillation, and decreasing the average level of excess reactant supplied were found to maximize both the level of voltage oscillations and the decrease in cell power from steady state performance. Greater response to pulsed oxidant flow is believed to have been observed due to effects brought about by changes in membrane humidity.
In contrast, pulsed fuel flow showed the greatest response in the study of DMFC technology. In this case, time averaged cell voltage was found to increase as the time averaged fuel flow rate was reduced. The increase in average cell power is the result of a reduction in methanol crossover; sustainable increases of up to 6% in power output were measured. The parameters found to effect the increase in cell power observed include the frequency of oscillation and the time-averaged NOSfuel. Pulsed air flow on the DMFC did not show any such rise in voltage, supporting the hypothesis that a reduction in methanol crossover is the phenomenon which brings about enhanced performance.
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Thompson, Scott Damon 1976. "Electrodeposition of platinum-based catalysts for polymer electrolyte membrane fuel cells." Monash University, School of Physics and Materials Engineering, 2003. http://arrow.monash.edu.au/hdl/1959.1/5668.
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Yau, Tak Cheung. "A study of water crossover in polymer electrolyte membrane fuel cells." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/30755.
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Water crossover between anode and cathode of polymer electrolyte membrane fuel cells has been studied together with fuel cell performance at steady state. The parameters considered included temperature, pressure, inlet humidity and the presence of a cathode microporous layer. In general water crossover was found to be increasingly toward the anode side with increasing current density up to a certain point beyond which a plateau was observed. Larger cathode-to-anode inlet humidity gradient, lower temperature and higher cathode pressure enhanced water crossover to the anode, due to a higher downstream humidity at the cathode catalyst layer.
The presence of a cathode microporous layer enhanced water crossover to the anode only when the cathode inlet humidity was low. It was proposed that this layer imposed a larger diffusion barrier between the cathode channel and the membrane interface whose effects diminished at high relative humidity. The zero crossover rate under zero humidity gradients with no load regardless of the presence of the cathode microporous layer suggested that capillary action was not a contributing factor for the action of the layer.
In addition, the quantitative data obtained by the water crossover measurement equipment were found to be useful in model validation and parameter estimations. The data could pinpoint inadequacies in models, as well as providing estimated parameters that were more consistent with changes in the oxygen concentration and fitted better to both the current density and water crossover data given a certain voltage.
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Rama, Pratap. "On the mechanisms of electrochemical transport in Polymer Electrolyte Fuel Cells." Thesis, Loughborough University, 2010. https://dspace.lboro.ac.uk/2134/5978.
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The Polymer Electrolyte Fuel Cell (PEFC) is well-poised to play a key role in the portfolio of future energy technologies for civil and military applications. Principally, the PEFC converts part of the chemical energy released during hydrogenoxidation and oxygen-reduction into electrical energy, generating water a bi-product. It is potentially a zero-emissions technology which can operate silently due to the absence of any moving parts, has quick start-up characteristics and can achieve high thermodynamic efficiency. In order to ensure that the PEFC emerges as a viable option for all applications, it is necessary to ensure that the technology is reliable, capable of delivering performance and cost-effective throughout its life-cycle. To achieve these objectives, a better fundamental understanding of the mechanisms of electrochemical transport in the PEFC is required than is presently available. The literature identifies that multi-component electrochemical transport within the PEFC plays a central role in fuel cell operation and longevity. Water transport is one of these. It is well-understood that excessive amounts of water within the porous electrodes of the cell can cause flooding, which impedes the supply of reactant gases. It is also well-understood that insufficient water can cause the polymer electrolyte membrane (PEM) to dehydrate, thereby reducing its proton conductivity. Both of these processes can undermine cell performance. Repetitive hydration cycles are also known to precipitate degradation mechanisms which can undermine reliability. However, the mechanisms of multi-component and potentially two-phase transport across the PEFC as a multi-layered assembly which includes the porous electrodes and the PEM are not understood as well: the mechanisms of contaminant transport, fuel crossover and liquid water infiltration particularly through the PEM are important examples. The modelling literature demonstrates that electrochemical transport in the PEFC is treated either through the use of dilute solution theory or concentrated solution theory. The modelling literature also demonstrates a wide spectrum in the application of modelling assumptions and the formulation of electrochemical equations to simulate transport in the different layers of the PEFC. This thesis describes research aimed at reconciling the different modelling approaches and philosophies in the literature by developing and applying a unified mechanistic electrochemical treatment to describe multi-component, two-phase transport across the layers of the PEFC. The approach adopted here is first to construct a multi-component zerodimensional model for multi-component input gases which is merged with a multilayer PEFC model to correctly predict the boundary conditions in the gas channels based on the cross-flow of components through the cell. The model is validated using data from the open literature and applied to understand contaminant crossover from anode to cathode. The second step is to develop a unified mechanistic electrochemical treatment to describe multi-component transport across the layers of the PEFC: the general transport equation. This is central to the contribution of this thesis. It is theoretically validated by deriving the key transport equations used in the benchmark fuel cell modelling literature. It is then implemented with the multi-component input model developed previously and validated using data from the open literature. The model is subsequently applied to understand fuel crossover characteristics in the cell. The third and final step is to further-develop the application of the general transport equation to account for two-phase transport across the layers of the PEFC. The resulting model is validated against three different sets of data from the open literature and subsequently applied to understand the effects of PEM thickness, anode gas humidification, cell compression and PEM structural reinforcement on liquid infiltration and two-phase transport across the PEM. It is demonstrated that the general transport equation developed in this thesis establishes a backbone understanding of the modelling and simulation of transport across the layers of the PEFC. The study successfully reconciles the different modelling philosophies in the fuel cell literature. The progressive validation and application of the general transport equation demonstrates the potential to enhance the scientific understanding of factors affecting PEFC performance and demonstrates its value as a tool for computationally-based cell design, optimisation and diagnostics.
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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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Cruz-Manzo, Samuel. "Electrochemical mechanisms of the impedance spectrum in polymer electrolyte fuel cells." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12316.
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Electrochemical impedance spectroscopy (EIS) is a powerful technique that can be applied in-situ to deconvolute the various loss mechanisms in the polymer electrolyte fuel cell (PEFC) that occur at different rates. The frequency response of a PEFC that results from EIS is in essence characterised by energy dissipating and energy storing elements of the cell. It can be represented by an equivalent circuit that is composed of resistors and capacitors respectively. By understanding the arrangement and magnitude of the electrical components in the equivalent electrical circuit, it is possible to generate a deeper understanding of how and where the electrical energy that is generated due to the redox reaction is being dissipated and retained within the real physical system. Although the use of equivalent circuits is often an adequate approach, some electrochemical processes are not adequately described by electrical components. In which case, it is necessary to adopt a more rigorous approach of describing processes through the use of differential equations to describe the physics of the electrochemical system at the frequency domain. Studies in the literature have attempted to construct mathematical models to describe the impedance response of the cathode catalyst layer (CCL) based on conservation equations describing the electrochemical and diffusion processes. However this has resulted in a complicated mathematical analysis which in turn results in complicated solutions. The resulting equations cannot be easily validated against real-world EIS measurements and only analytical results have been reported. In this thesis a mathematical model to describe the impedance response of the CCL has been developed. This model is derived from fundamental electrochemical theory describing the physics of the CCL. The mathematical treatment is simplified by taking into account some considerations based on the EIS theory. The resulting model can be easily applied to real-world EIS measurements of PEFCs and presents parameters commonly known in the electrochemical area. The scientific contribution of this doctoral thesis is mainly divided in two sections: Modelling and Application. The first step of the modelling section develops an equation describing charge conservation in the CCL and together with Ohm s Law equation accounting for ionic conduction, predicts the impedance response of the CCL at low currents. The second step includes the change of oxygen concentration during the oxygen reduction reaction (ORR) into the equation accounting for CCL low current operation. The study of mass transport in the CCL is very complex; the literature has treated it with simplifications and approximations. The finite diffusion distance for oxygen to reach the reaction sites in the CCL forms a complicated network of multi-phase parallel and serial paths and can change in dimension at different operating conditions (flooding, drying). In the mathematical treatment of this doctoral thesis the finite diffusion distance and surface concentration of oxygen in the CCL are considered to be independent of the thickness of the CCL. EIS reflects only bulk measurements based on the total CCL thickness. Even though this results in an over-simplification for the oxygen diffusion in the total CCL, this approach simplifies the mathematical treatment to predict the impedance response of the CCL at high current operation, and as result it can be successfully validated against real-world EIS measurements. In the application section the model is applied with real-world EIS measurements of PEFCs. First the model is applied with EIS measurements presenting inductive effects at high frequencies. The model reveals mechanisms masked at high frequencies of the impedance spectrum by inductance effects. The results demonstrate that the practice of using the real part of the Nyquist plot where the imaginary part is equal to zero to quantify the ohmic resistance in PEFCs can be subject to an erroneous interpretation due to inductive effects at high frequencies. Secondly the model is applied to cathode impedance data obtained through a three-electrode configuration in the measurement system and gives an insight into the mechanisms represented at low frequencies of the impedance complex-plot. The model predicts that the low frequency semicircle in PEFC measurements is attributed to low equilibrium oxygen concentration in the CCL-gas diffusion layer (GDL) interface and low diffusivity of oxygen through the CCL. In addition the model is applied with simultaneous EIS measurements in an Open-Cathode PEFC stack. The factors that limit the performance of the PEFC stack are evaluated with simultaneous EIS measurements and the model. The results show that the change in impedance response of individual cells within the stack is attributed to oxygen limitations, degradation in membrane electrode assemblies (MEAs) and temperature distribution. This EIS knowledge enables an assessment of the state of health in operational fuel cell stacks. In the last section of the application section, the mathematical model translated in the time domain via reverse Laplace Transform predicts the current distribution through the CCL. This provides information to improve the performance of the CCL as well as determine the uptake of product water in the membrane. Finally the conclusions and future work are presented. This doctoral thesis has established a backbone understanding of how the electrochemical and diffusion mechanisms relate to the electrochemical impedance spectra of PEFCs. The goal of a future work is to develop this EIS knowledge into a real-time EIS system for non-intrusive diagnostics of degradation in operational PEFCs. This implies a modification of the model to consider oxygen transport through the CCL thickness as part of a multi-species mixture using mass transport theory including concentrated solution theory to fuel cell engineering.
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Mansor, N. B. "Development of catalysts and catalyst supports for polymer electrolyte fuel cells." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1460064/.
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Polymer Electrolyte Membrane fuel cells (PEMFC) are clean and efficient electrochemical energy converters that can be adapted to a wide range of domestic and automotive applications. However, large-scale commercialisation is hindered by issues of cost and durability relating to the catalyst layer. This work aims to address the need for cheaper and durable catalysts through the development of novel catalyst and catalyst support. The initial aim of this work is to investigate the potential application of Pd-based alloy catalyst in PEMFC. Pd is about 42% cheaper than Pt and 50 times more abundant on earth. Previous studies have shown that there is a correlation between electronic structure and catalytic activity of Pd binary alloys, and therefore it is possible to design a highly efficient Pd-based alloy catalyst. In this work, Pd-based catalyst was synthesised and characterized electrochemically in ex-situ and in-situ configurations to determine their activity and durability. It was found that Pd-based catalyst could potentially replace Pt as a low-cost anode catalyst. The second part of this work investigated the potential application of graphitic carbon nitride materials as catalyst support. Carbon black is the most widely used catalyst support for state-of-the-art PEMFCs even though it is known to undergo carbon corrosion during operation. Graphitic carbon nitride could offer enhanced durability and activity due to their graphitic structure and intrinsic catalytic properties. In addition, graphitic carbon nitride is low-cost, fairly simple to synthesise and highly tunable. In this work, various graphitic carbon nitride materials were prepared and characterised using accelerated carbon corrosion protocol. They were found to be more electrochemically stable compared to conventional carbon black. Superior methanol oxidation activity is also observed for graphitic carbon nitride supported Pt catalysts on the basis of the catalyst electrochemical surface area. However further work is needed to optimise the deposition and utilisation of metal catalyst on graphitic carbon nitride materials.
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Worsdale, Matthew Clive. "Ab-initio investigation into catalyst supports for polymer electrolyte fuel cells." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/413850/.
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One of the most promising families of catalyst support materials from the point of view of durability in the PEFC are metal oxides. SnO2 can only corrode, in a strong acid, at potentials ! 1.4V, progressing through surface hydroxide formation. The bulk stability is backed up by simulated potential cycling, with minimal ESCA loss at 1.6V. The conductivity of pure SnO2, which forms the rutile crystal structure, is very small compared to C but can increase by orders of magnitude with formation of certain intrinsic defects which create electron donor levels in the band gap (which, at 3.6 eV, classes the undoped oxide as a wide band gap semiconductor). The ab-initio study evaluates the potential of extrinsic dopants to increase conductivity through adding n-type charge carriers to the system, investigating the influence of Ta on the thermodynamic stability and electronic properties through DFT calculations. Particular focus has been given to Ta, as TaO2 also forms with the rutile structure. This allows investigation of the full range of Ta doping concentration from an isolated defect to alloy by including it as a substitutional defect. A cluster expansion parameterised in terms of binary occupation variable that equal Sn or Ta is used to calculate the orderings (distributions of Ta:Sn atoms over the lattice at fixed concentration). It is found that alloys are stabilized thermodynamically by lattice distortions, with the creation of donor levels near the conduction band minimum (CBM) that with the relaxation of the lattice turn into states lying deep in the band gap that are calculated to give inadequate donation of electrons to the conduction band. This is indicative of collaborating Jahn-Teller active (JT) distortion modes of the disordered crystallite oxide which is shown through analysis of the spin density. The results suggest that alloying of metals in oxide systems is not a feasible approach to increasing conductivity with thermodynamic stability due to JT effects. The second part of this thesis explores the potential of hydrogen defects, which have been shown to form at interstitial and host oxygen sites under laboratory conditions. The same methodology is followed to establish the efficacy of hydrogen as an electron donor and its relation to other defects in SnO2. Much theoretical work has been devoted to the study of hydrogen in n-type semiconductors and experimental work supports that hydrogen can be expected to act as a conventional n-type donor in SnO2. It is found that interstitial H not only makes SnO2 metallic as recorded by the electronic structure, but further that the defect can bring about a large downward shift in the effective band gap. This also raises the possibility of activating Ta-induced deep donor levels.
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Benson, Paul Alan. "Analysis of low-pressure evaporatively cooled polymer electrolyte membrane fuel cells." Thesis, Loughborough University, 2004. https://dspace.lboro.ac.uk/2134/34098.
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The polymer electrolyte membrane fuel cell is being proposed for a number of power generation systems. With regard to replacing conventional technologies, they offer many advantages including quiet operation with low emissions. However, the key issue for the success of fuel cell system will be a superior operational efficiency. The associated subsystems for controlling fuel cell stack thermal and water management contribute significantly to the reduction in stack weight and volume and increase the associated operational parasitic losses. In this thesis a novel fuel cell operational method has been proposed which utilises a combined humidification and cooling mechanism based on the direct injection of liquid water to the cathode flow-field. Several analyses were performed to investigate critical issues for the workable concept of such an EC, or evaporatively cooled, fuel cell system.
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Cai, Bin, Sebastian Henning, Juan Herranz, Thomas J. Schmidt, and Alexander Eychmüller. "Nanostructuring noble metals as unsupported electrocatalysts for polymer electrolyte fuel cells." Wiley-VCH, 2018. https://tud.qucosa.de/id/qucosa%3A31155.
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Two major challenges that impede fuel cell technology breakthrough are the insufficient activity of the electrocatalysts for the oxygen reduction reaction and their degradation during operation, caused by the potential-induced corrosion of their carbon-support upon fuel cell operation. Unsupported electrocatalysts derived from tailored noble-metal nanostructures are superior to the conventional carbon-supported Pt nanoparticle catalysts and address these barriers by fine-tuning the surface composition and eliminating the support. Herein, recent efforts and achievements in the design, synthesis and characterization of unsupported electrocatalysts are reviewed, paying special attention to noble-metal aerogels, nano/meso-structured thin films and template-derived metal nanoarchitectures. Their electrocatalytic performances for oxygen reduction are compared and discussed, and examples of successful catalyst transfer to polymer electrolyte fuel cells are highlighted. This report aims to demonstrate the potential and challenges of implementing unsupported catalysts in fuel cells, thereby providing a perspective on the further development of these materials.
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Kienitz, Brian L. "The Effects of Cationic Contamination on Polymer Electrolyte Membrane Fuel Cells." Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1228255795.
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Kamarajugadda, Sai K. "Advanced Models for Predicting Performance of Polymer Electrolyte Membrane Fuel Cells." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1323758118.
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Gao, Xiao. "Elucidation of Ionomer/Electrode Interfacial Phenomena in Polymer Electrolyte Fuel Cells." Kyoto University, 2020. http://hdl.handle.net/2433/254528.
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Kyoto University (京都大学)0048
新制・課程博士
博士(人間・環境学)
甲第22708号
人博第958号
新制||人||227(附属図書館)
2020||人博||958(吉田南総合図書館)
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 内本 喜晴, 教授 高木 紀明, 教授 中村 敏浩
学位規則第4条第1項該当
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Davies, Damian Patrick. "Development and optimisation of solid polymer electrolyte fuel cell systems." Thesis, De Montfort University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391234.
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Jennings, Paul Christopher. "Computational studies of mono- and bimetallic nanoclusters for potential polymer electrolyte fuel cell applications." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5324/.
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A problem with the Polymer Electrolyte Fuel Cell (PEFC) is the expensive platinum (Pt) electrocatalyst. This thesis aims to investigate alloying of Pt with cheaper metals that not only reduce the overall cost but also alter the electronic properties to improve reaction kinetics. A Genetic Algorithm (GA) coupled with Density Functional Theory (DFT) approach has been used to perform structural searches on small Pt clusters doped with early transition metals (M). It is found that varying spin can have significant effects on the minimum energy structures of pure Pt clusters, while doping with early transition metals leads to spin quenching. DFT studies have been performed to predict potential Pt-based alloy nanoparticles that will result in weaker Pt–O interactions. This is achieved by investigating nanoalloys that lead to filling of the Pt d-band. Early transition metals are found to be promising, where donation of electron density from M to Pt results in additional filling of the Pt d-band. The surfaces of pure Pt clusters are found to distort, facilitating fast oxygen dissociation. It is found that the strong Pt-M interactions, which lead to filling of the d-band, can lead to Pt clusters becoming more structurally rigid, which inhibits oxygen dissociation. A search has been performed to find the best compromise for a system that retains flexibility of the Pt surface, to allow fast dissociation while also allowing M to Pt electron donation, leading to filling of the Pt d-band.
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Jalani, Nikhil H. "Development of nanocomposite polymer electrolyte membranes for higher temperature PEM fuel cells." Link to electronic dissertation, 2006. https://www.wpi.edu/ETD-db/ETD-catalog/view%5Fetd?URN=etd-032706-165027.
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Marshall, Josiah. "Synthesis of the Diazonium Zwitterionic Polymer/Monomer for Use as the Electrolyte in Polymer Electrolyte Membrane (PEM) Fuel Cells." Digital Commons @ East Tennessee State University, 2021. https://dc.etsu.edu/etd/3968.
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My research goals are to synthesize new zwitterionic perfluorosulfonimide (PFSI) monomer/polymers. They are expected to replace traditionally used perfluorosulfonic acid (PFSA) polymers as the electrolyte in PEM fuel cells. For the PFSI monomer preparation, we designed a nine-step synthesis route. Thus far, I have successfully completed the synthesis of 4- (2-bromotetrafluoroethoxy)-benzenesulfonyl amide, 4-acetoxybenzenesulfonic acid sodium salt, and 4-chlorosulfonyl phenyl acetate. The coupling reaction of 4-(2-bromotetrafluoroethoxy)- benzenesulfonyl amide with 4-chlorosulfonyl phenyl acetate, was troublesome due to slow reaction kinetics and byproducts. Additionally, I did a methodology study for the homopolymerziation of the perfluoro 3(oxapent-4-ene) sulfonyl fluoride monomer. We compared the weight average molecular weight (Mw) of different reaction conditions. The best Mw was achieved when the polymerization was carried out for five days at 100 °C and150 psi with 2 wt % initiator and 5 g of monomer. All the compounds were characterized by melting point, GC-MS, GPC, FT-IR, and 13C/1H/19F NMR.