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1
Parackal, Bhavana. "An Investigation of Low Temperature Direct Propane Fuel Cells". Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/35896.
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This research is directed toward the investigation of a low temperature direct propane fuel cell (DPFC). Modeling included a parametric study of a direct propane fuel cell using computational fluid dynamics (CFD), specifically FreeFem++ software. Polarization curves predicted by the CFD model were used to understand fuel cell performance. The predictions obtained from the computational fluid dynamics mathematical model for the fuel cell were compared with experimental results. The computational work identified some critical parameters (exchange current density, pressure, temperature) for improving the overall performance of the fuel cell. The model predictions clearly highlighted the role of catalysts in significantly enhancing the overall performance of a DPFC. Experiments were performed using commercial Nafion-Pt based membrane electrode assemblies (MEAs) to obtain a basis for comparison. It is the first report in the literature that a Pt-Ru (Platinum-Ruthenium) MEA was used in the investigation of a DPFC. Also, it was the first study that fed liquid water continuously to a DPFC by using interdigitated flow field (IDFF) at the anode to humidify the dry propane feed gas. During the experiments oscillations were observed at very low current densities i.e. in nA/cm2, which is a rare case and not reported in the literature to date. This observation has raised serious concerns about the existence of absolute open-circuit cell potential difference for a DPFC. The cycling behaviour observed with DPFC indicated the presence of a continuous degradation-regeneration process of the catalyst surface near open-circuit potential. The experimental work further evaluated the performance of fuel cell by measurement of polarization curves.
2
Khakdaman, Hamidreza. "A Two Dimensional Model of a Direct Propane Fuel Cell with an Interdigitated Flow Field". Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/22732.
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Increasing environmental concerns as well as diminishing fossil fuel reserves call for a new generation of energy conversion technologies. Fuel cells, which convert the chemical energy of a fuel directly to electrical energy, have been identified as one of the leading alternative energy conversion technologies. Fuel cells are more efficient than conventional heat engines with minimal pollutant emissions and superior scalability. Proton Exchange Membrane Fuel Cells (PEMFCs) which produce electricity from hydrogen have been widely investigated for transportation and stationary applications.
The focus of this study is on the Direct Propane Fuel Cell (DPFC), which belongs to the PEMFC family, but consumes propane instead of hydrogen as feedstock. A drawback associated with DPFCs is that the propane reaction rate is much slower than that of hydrogen. Two ideas were suggested to overcome this issue: (i) operating at high temperatures (150-230oC), and (ii) keeping the propane partial pressure at the maximum possible value. An electrolyte material composed of zirconium phosphate (ZrP) and polytetrafluoroethylene (PTFE) was suggested because it is an acceptable proton conductor at high temperatures. In order to keep the propane partial pressure at the maximum value, interdigitated flow-fields were chosen to distribute propane through the anode catalyst layer.
In order to evaluate the performance of a DPFC which operates at high temperature and uses interdigitated flow-fields, a computational approach was chosen. Computational Fluid Dynamics (CFD) was used to create two 2-D mathematical models for DPFCs based on differential conservation equations. Two different approaches were investigated to model species transport in the electrolyte phase of the anode and cathode catalyst layers and the membrane layer. In the first approach, the migration phenomenon was assumed to be the only mechanism of proton transport. However, both migration and diffusion phenomena were considered as mechanisms of species transport in the second approach. Therefore, Ohm's law was used in the first approach and concentrated solution theory (Generalized Stefan-Maxwell equations) was used for the second one. Both models are isothermal.
The models were solved numerically by implementing the partial differential equations and the boundary conditions in FreeFEM++ software which is based on Finite Element Methods. Programming in the C++ language was performed and the existing library of C++ classes and tools in FreeFEM++ were used. The final model contained 60 pages of original code, written specifically for this thesis.
The models were used to predict the performance of a DPFC with different operating conditions and equipment design parameters. The results showed that using a specific combination of interdigitated flow-fields, ZrP-PTFE electrolyte having a proton conductivity of 0.05 S/cm, and operating at 230oC and 1 atm produced a performance (polarization curve) that was (a) far superior to anything in the DPFC published literature, and (b) competitive with the performance of direct methanol fuel cells. In addition, it was equivalent to that of hydrogen fuel cells at low current densities (30 mA/cm2).
3
Psofogiannakis, George. "A mathematical model for a direct propane phosphoric acid fuel cell". Thesis, University of Ottawa (Canada), 2003. http://hdl.handle.net/10393/26424.
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In direct hydrocarbon fuel cells, a hydrocarbon fuel is oxidised in the anode electrode. This thesis presents a mathematical model to predict the performance of a unit cell that utilises propane as the fuel, oxygen as the oxidant, phosphoric acid as the electrolyte, and platinum as the catalyst, supported on porous carbon electrodes. The phenomena considered include the electrochemical reactions of propane oxidation and oxygen reduction on platinum, the diffusion of the gases in gas-filled electrode pores, the dissolution and diffusion of dissolved gases in liquid-filled electrode pores as well as ionic conduction of protons. The model was based on the multi-layered physical structure of a modern unit fuel cell.
The model was first applied to a phosphoric acid fuel cell cathode electrode.
Subsequently, the model was applied to a direct propane-oxygen cell. (Abstract shortened by UMI.)
4
Vafaeyan, Shadi. "A Density Functional Theory of a Nickel-based Anode Catalyst for Application in a Direct Propane Fuel Cell". Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23316.
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The maximum theoretical energy efficiency of fuel cells is much larger than those of the steam-power-turbine cycles that are currently used for generating electrical power. Similarly, direct hydrocarbon fuel cells, DHFCs, can theoretically be much more efficient than hydrogen fuel cells. Unfortunately the current densities (overall reaction rates) of DHFCs are substantially smaller than those of hydrogen fuel cells. The problem is that the exchange current density (catalytic reaction rate) is orders of magnitude smaller for DHFCs. Other work at the University of Ottawa has been directed toward the development of polymer electrolytes for DHFCs that operate above the boiling point of water, making corrosion rates much slower so that precious metal catalysts are not required. Propane (liquefied petroleum gas, LPG) was the hydrocarbon chosen for this research partly because infrastructure for its transportation and storage in rural areas already exists. In this work nickel based catalysts, an inexpensive replacement for the platinum based catalysts used in conventional fuel cells, were examined using density functional theory, DFT. The heats of propane adsorption for 3d metals, when plotted as a function of the number of 3d electrons in the metal atom, had the shape of a volcano plot, with the value for nickel being the peak value of the volcano plot. Also the C-H bond of the central carbon atom was longer for propane adsorbed on nickel than when adsorbed on any of the other metals, suggesting that the species adsorbed on nickel was less likely to desorb than those on other metals. The selectivity of the propyl radical reaction was examined. It was found that propyl radicals
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Sultan, Jassim. "Direct methanol fuel cells /". Internet access available to MUN users only, 2003. http://collections.mun.ca/u?/theses,162066.
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Joseph, Krishna Sathyamurthy. "Hybrid direct methanol fuel cells". Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44777.
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A new type of fuel cell that combines the advantages of a proton exchange membrane fuel cells and anion exchange membrane fuel cells operated with methanol is demonstrated. Two configurations: one with a high pH anode and low pH cathode (anode hybrid fuel cell (AHFC)),and another with a high pH cathode and a low pH anode (cathode hybrid fuel cell (CHFC)) have been studied in this work. The principle of operation of the hybrid fuel cells were explained. The two different hybrid cell configurations were used in order to study the effect of the electrode fabrication on fuel cell performance. Further, the ionomer content and properties such as the ion exchange capacity and molecular weight were optimized for the best performance. A comparison of the different ionomers with similar properties is carried out in order to obtain the best possible ionomer for the fuel cell. An initial voltage drop was observed at low current density in the AHFC, this was attributed to the alkaline anode and the effect of the ionomers with the new cationic groups were studied on this voltage drop was studied. These ionomers with the different cationic groups were studied in the CHFC design as well. Finally, the use of non platinum catalyst cathode with the CHFC design was also demonstrated for the first time.
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Kim, Hyea. "High energy density direct methanol fuel cells". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37106.
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The goal of this dissertation was to create a new class of DMFC targeted at high energy density and low loss for small electronic devices. In order for the DMFC to efficiently use all its fuel, with a minimum of balance of plant, a low-loss proton exchange membrane was required. Moderate conductivity and ultra low methanol permeability were needed. Fuel loss is the dominant loss mechanism for low power systems. By replacing the polymer membrane with an inorganic glass membrane, the methanol permeability was reduced, leading to low fuel loss. In order to achieve steady state performance, a compliant, chemically stable electrode structure was investigated. An anode electrode structure to minimize the fuel loss was studied, so as to further increase the fuel cell efficiency. Inorganic proton conducting membranes and electrodes have been made through a sol-gel process. To achieve higher voltage and power, multiple fuel cells can be connected in series in a stack. For the limited volume allowed for the small electronic devices, a noble, compact DMFC stack was designed. Using an ADMFC with a traditional DMFC including PEM, twice higher voltage was achieved by sharing one methanol fuel tank. Since the current ADMFC technology is not as mature as the traditional DMFCs with PEM, the improvement was accomplished to achieve higher performance from ADMFC. The ultimate goal of this study was to develop a DMFC system with high energy density, high energy efficiency, longer-life and lower-cost for low power systems.
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Yu, Eileen Hao. "Development of direct methanol alkaline fuel cells". Thesis, University of Newcastle Upon Tyne, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289171.
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Pereira, Joana Patrícia Carvalho. "Passive direct ethanol fuel cells: modeling studies". Master's thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/11407.
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Mestrado em Engenharia do AmbienteO presente trabalho teve como objetivo o estudo de modelação de uma célula de combustível com injeção direta e passiva de etanol operando em condições ambientais. Este estudo foi desenvolvido tendo em conta a importância crescente dos sistemas com alimentação direta e passiva de etanol como solução para as aplicações portáteis. No decurso deste trabalho, foi desenvolvido um modelo matemático para a célula passiva, em estado estacionário e a uma dimensão, incorporando o transporte de calor e massa bem como as reações eletroquímicas que ocorrem no ânodo e no cátodo da célula de combustível. Este modelo simplificado pode ser rapidamente implementado usando métodos numéricos simples existentes no Excel, e reproduz de modo satisfatório os dados experimentais obtidos. Neste trabalho, foi também desenvolvida uma instalação laboratorial para determinação experimental das curvas de polarização e de potência da célula. Para esse fim, foi concebida e construída uma célula com uma área ativa de 25 cm2. Um estudo experimental detalhado para a célula passiva operando sob condições ambientais é apresentado nesta tese. As previsões do modelo foram comparadas com os resultados experimentais e verificou-se uma grande concordância entre ambos. Deste modo, o funcionamento da célula de combustível com injeção direta e passiva de etanol foi explicado à luz das previsões do modelo para o atravessamento de metanol e de água através da membrana. O efeito das condições de operação (tais como a concentração de etanol na alimentação ao ânodo e a densidade de corrente), bem como de parâmetros de configuração (materiais que constituem as camadas de difusão e espessura da membrana polimérica), no desempenho da célula foi estudado detalhadamente, e as previsões do modelo reproduziram satisfatoriamente os resultados obtidos. Dada a escassa informação existente sobre este tema na literatura atual, os resultados obtidos neste estudo são de elevado interesse e apresentam grande importância para o futuro desenvolvimento de células de combustível com injeção direta e passiva de etanol.
Bearing in mind that the passive feed Direct Ethanol Fuel Cell (DEFC) systems emerge as a solution for portable applications, the main objective of this thesis was the modelling study of a passive feed DEFC working under ambient conditions. A steady state, one dimensional and non-isothermal model was developed, accounting for coupled heat and mass transfer processes along with the electrochemical reactions occurring in the fuel cell. This simplified model was rapidly implemented using simple numerical tools as Excel, and reproduced with satisfactory accuracy the experimental data. An experimental set-up was implemented in order to determine the cell polarization and power density curves. For the experimental studies, an “inhouse” passive feed DEFC with an active area of 25 cm2 was designed, and a detailed experimental characterization of the cell working under ambient conditions was performed. The model predictions were compared with the experimental results, and a very successful accuracy was found. Therefore, the experimental results could be explained under the light of the model predictions concerning both ethanol and water crossover. Moreover, the effect of operating conditions (ethanol feed concentration and current density) and design parameters (anode diffusion layer material and thickness, anode catalyst loading and membrane thickness) on the fuel cell performance was intensively investigated. The model proved to predict accurately the trends of the effect of the different parameters on both ethanol and water crossover, and subsequently on the cell performance. Given the lack of information concerning this issue in the actual literature, the results achieved in this work provide very interesting and useful information for the future development of passive DEFCs.
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Ye, Qiang. "Spontaneous hydrogen evolution in direct methanol fuel cells /". View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?MECH%202005%20YEQ.
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Hacquard, Alexandre. "Improving and Understanding Direct Methanol Fuel Cell (DMFC) Performance". Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-050505-151501/.
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Ertan, Salih. "Preparation And Characterization Of Carbon Supported Platinum Nanocatalysts With Different Surfactants For C1 To C3 Alcohol Oxidations". Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613623/index.pdf.
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In this thesis, carbon supported platinum nanoparticles have been prepared by using PtCl4 as a starting material and 1-octanethiol, 1-decanethiol, 1-dodecanethiol and 1-hexadecanethiol as surfactants for methanol, ethanol and 2-propanol oxidation reactions. The structure, particle sizes and surface morphologies of the platinum were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). XRD and TEM results indicate that all prepared catalysts have a face centered cubic structure and are homogeneously dispersed on the carbon support with a narrow size distribution (2.0 to 1.3 nm). X-ray photoelectron spectra of the catalysts were examined and it was found that platinum has two different oxidation state, Pt (0) and Pt (IV), oxygen and sulfur compounds are H2Oads and OHads, bounded and unbounded thiols. The electrochemical and electrocatalytic properties of those catalysts were investigated towards C1 to C3 alcohol oxidations by cyclic voltammetry (CV) and chronoamperometry (CA). The highest electrocatalytic activity was obtained from catalyst I which was prepared with 1-octanethiol. This may be attributed to decrease in the ratio of bounded to unbounded thiol species and increase in Pt (0)/Pt (IV), H2Oads/OHads ratios, electrochemical surface area, CO tolerance and percent platinum utility.
13
Wu, Pin-Han. "Pre-stretched Recast Nafion for Direct Methanol Fuel Cells". Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1212685669.
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Chan, Yeuk Him. "A self-regulated passive fuel-feed system for passive direct methanol fuel cells /". View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?MECH%202008%20CHAN.
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Troughton, Gavin L. "Anodes for the direct methanol fuel cell". Thesis, University of Newcastle Upon Tyne, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335195.
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Saunders, Gary J. "Reactions of hydrocarbons in zirconia fuel cells". Thesis, University of Birmingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288890.
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Garnica, Rodríguez Jairo Ivan. "Polyaniline-silica-nafion composite membranes for direct methanol fuel cells /". [St. Lucia, Qld.], 2005. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe18986.pdf.
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Pan, Yining. "Immobilized Viologen Polymer for Use in Direct Carbohydrate Fuel Cells". BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3524.
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Glucose and other carbohydrates are some of the most abundant renewable energy sources in the world. The oxidation of carbohydrates in a fuel cell allows their chemical energy to be converted directly into electrical energy. Viologen has been indentified and shows promising ability as an electron-transfer catalyst or mediator for carbohydrate oxidation in an alkaline carbohydrate fuel cell. Building on the previous results, the objective of this work was to develop an immobilization chemistry of viologen onto an electrode and to investigate the catalytic activity for carbohydrate oxidation in direct carbohydrate fuel cells.The immobilization was achieved by electropolymerizing a novel viologen monomer onto an electrode surface. The novel viologen monomer, which functions as a monosubstituted viologen, was synthesized and isolated in-house. Gold-plated nickel wire and graphite disks were used as the substrates for the electropolymerization. SEM, EDAX, XPS and water-contact-angle measurement were used to verify the formation of the coating on the gold and graphite surfaces. The catalytic activity of the immobilized viologen on graphite disk surface was examined using a fuel-cell-like device. The test was operated within the desired pH range for an operating fuel cell; it was found that the immobilized viologen polymer has a low catalytic activity toward oxidizing carbohydrates. In addition, the electrochemical properties of the novel viologen monomer were investigated by the method of cyclic voltammetry, as well as for that of two aminoviologens synthesized in-house. Redox potentials, diffusion coefficients, and heterogeneous electron-transfer rate constants were determined.
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Matsuoka, Koji. "Studies on direct alcohol fuel cells using anion-exchange membrane". 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/144928.
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Kyoto University (京都大学)0048
新制・課程博士
博士(工学)
甲第11583号
工博第2529号
新制||工||1344(附属図書館)
23226
UT51-2005-D332
京都大学大学院工学研究科物質ｴﾈﾙｷﾞｰ化学専攻
(主査)教授 小久見 善八, 教授 垣内 隆, 教授 田中 功
学位規則第4条第1項該当
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Suzuki, Shohei. "Studies on Direct Ammonia Fuel Cells Employing Anion Exchange Membranes". 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215557.
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Cooper, Richard John. "Flow and reaction in solid oxide fuel cells". Thesis, University of Birmingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367622.
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Wong, Chung Wai. "Experimental investigations of the anode flow fields of micro direct methanol fuel cells /". View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?MECH%202005%20WONG.
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Liang, Zhenxing. "Preparation of high-durability membrane and electrode assemblies for direct methanol fuel cells /". View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?MECH%202008%20LIANG.
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Sprague, Isaac Benjamin. "Characterization of a microfluidic based direct-methanol fuel cell". Online access for everyone, 2008. http://www.dissertations.wsu.edu/Thesis/Summer2008/I_Sprague_072208.pdf.
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Xu, Chao. "Transport phenomena of methanol and water in liquid feed direct methanol fuel cells /". View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?MECH%202008%20XU.
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Felipe, Alfonso Martínez. "Preparation and characterisation of new materials for electrolytes used in Direct Methanol Fuel Cells". Available from the University of Aberdeen Library and Historic Collections Digital Resources. Restricted: contains 3rd party material and therfore cannot be made available electronically, 2009. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=59378.
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Baldwin, Zachary D. "Characterization of Anode Conditions and Limitations in Direct Carbon Fuel Cells". Cleveland, Ohio : Case Western Reserve University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1248203858.
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Thesis (M.S.)--Case Western Reserve University, 2009Title from PDF (viewed on 19 August 2009) Department of Mechanical and Aerospace Engineering Includes abstract Includes bibliographical references Available online via the OhioLINK ETD Center
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Hansen, Dane C. "Homogeneous Viologens for Use as Catalysts in Direct Carbohydrate Fuel Cells". BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3647.
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Deriving electrical energy from glucose and other carbohydrates under mild conditions is an important research objective because these biomolecules are abundant, renewable, and can provide 12 to 24 electrons per molecule, yielding substantial electrical power. It was previously observed that disubstituted viologens, salts of N,N'-disubstituted 4,4'-bipyridine, are able to oxidize glucose under alkaline conditions. Building on that initial result, the objective of this work was to understand and quantify the effectiveness and utility of viologens as catalysts for use in direct carbohydrate fuel cells.The extent that viologens oxidize carbohydrates, the conditions under which that oxidation occurs, and the mechanism for the oxidation were examined using oxygen-uptake and other methods. Viologens were found to catalytically oxidize carbohydrates extensively in alkaline solution. Viologens were also found to react with the enediol form of the carbohydrate, initiating carbohydrate oxidation with subsequent reduction of the viologen. If the viologen/carbohydrate ratio is low, electron transfer from the carbohydrate to the viologen becomes limiting and the carbohydrates undergoing oxidation rearrange into unreactive intermediates such as carboxylic acids and alcohols. At high catalyst ratios, excess viologen more rapidly oxidizes the carbohydrate and minimizes formation of unreactive intermediates. We also found that viologen polymers were more efficient than an equivalent concentration of monomers, suggesting that the higher localized concentration in polymeric viologen acts to efficiently oxidize carbohydrates and simulates high viologen/carbohydrate ratios.Monoalkyl viologens, aminoviologens, indigo carmine, and methylene blue were investigated by the method of cyclic voltammetry to inform their use as catalysts in the oxidation of carbohydrates. Redox potentials, diffusion coefficients, and heterogeneous electron-transfer rate constants were determined. Stability in alkaline solution and aqueous solubility were also examined in a semi-quantitative fashion. A comparison between the catalysts was made and viologens were found to be superior based on the examined parameters.The catalytic oxidation of carbohydrates by viologen was also examined using a fuel cell-like device. For the conditions in which a test cell was operated, oxidation efficiencies of up to 33% were observed, compared to previously reported values from about 2.5% to 80%. Anode polarization curves were obtained and used to determine the behavior of the viologen-controlled anode as a function of pH, viologen and carbohydrate concentration, and carbohydrate identity. pH was found to have a stronger effect on the performance at the anode for carbohydrates with a higher number of carbons than those with a lower number.
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Knox, Daniel. "Performance Characteristics of PBI-based High Temperature Direct Methanol Fuel Cells". Digital WPI, 2012. https://digitalcommons.wpi.edu/etd-theses/956.
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"This thesis investigates the effect of temperature, methanol concentration, and oxidant type on the performance of a Direct Methanol Fuel Cell (DMFC) using two versions of a commercially available polybenzimidazole (PBI)-based membrane electrode assembly (MEA): the Celtec®-P 1000 MEA of original thickness and double thickness. The PBI-based MEA’s were tested under the vapor-phase methanol concentrations of 1M, 2M, 3M, 5M, 7.5M, and 10M, temperatures of 160-180°C, and oxidants of oxygen and air. It was found that performance increased with temperature and that oxygen outperformed air as methanol concentrations increased. The double thickness PBI-based MEA, was more resistant to methanol crossover and performed better with increasing methanol concentrations. Thus, these commercial MEAs may be suitable for developing higher temperature DMFCs."
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Schrauth, Anthony J. "Design of high-ionic conductivity electrodes for direct methanol fuel cells". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67596.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 175-178).
Carbon-supported porous electrodes are used in low-temperature fuel cells to provide maximum catalyst surface area, while taking up little volume and using minimum catalyst material. In Direct Methanol Fuel Cells (DMFCs), however, much of the catalyst included in the anode is significantly under-utilized, while a small fraction of the catalyst facilitates the bulk of the oxidation reaction. In this thesis, the porous carbon electrode used as the anode in a DMFC is analyzed using Axiomatic Design theory. The imbalance of catalyst utilization in these electrodes is determined to be a result of coupled design, in which large amounts of catalyst can compromise ionic resistance and fuel transport within the electrode. This design flaw is confirmed experimentally using cyclic voltammetry and impedance spectroscopy. Tests of standard electrodes show that they have a maximum Nafion content of about 30% Nafion by weight and that excessive catalyst loading eventually results in less available catalyst, not more. An alternative design is proposed to alleviate the coupling between functions by applying micron-scale structure to the nano-porous electrode. The proposed design introduces ionically conductive channels through the thickness of the porous electrode to greatly reduce ionic resistance to catalyst particles far from the ion exchange membrane without compromising access to catalyst particles near the membrane accessible for fuel delivery and product removal. The influence of the proposed design on ionic conductivity is analyzed using a twodimensional analog of the transmission line model for porous electrodes. The model suggests that ionic resistance can be decreased by up to 87 % with the addition of ionically conductive posts. Structured electrodes with 75 pm diameter posts spaced 175 tm apart are shown in electrochemical impedance spectroscopy experiments to perform notably better than standard cells. The structured cells show a 6 % increase in available catalyst area and a 46 % decrease in ionic resistance. Peak cell power is estimated to increase by 4 % as a result of the best electrode tested while an electrode with ideal geometry could increase peak cell power by 9 %. Even greater benefits could be realized if, as predicted, structured cells can keep ionic resistance constant while catalyst loading is increased.
by Anthony J. Schrauth.
Ph.D.
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Kavanagh, R. J. "A computational study of anode electrocatalysis in direct ethanol fuel cells". Thesis, Queen's University Belfast, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678702.
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Density Functional Theory calculations are employed in the investigation of the ethanol oxidation reaction (EOR) at the anode of Direct Ethanol Fuel Cells (DEFC), with a view to mechanistic understanding of the reaction pathways, determination of the factors governing the onset potential of activity and selectivity towards C02, and ultimately the design of an optimal electrocatalyst in these regards. The lowest energy pathway of ethanol decomposition on platinum is identified and it is found that the reaction kinetics do not significantly vary with catalyst morphology. The aqueous medium is found to somewhat facilitate all reaction pathways. Surface hydroxyl is found to oxidise ethanol to acetaldehyde. Surface atomic oxygen is found to selectively oxidise adsorbed carbon monoxide to carbon dioxide. The onset potentials of surface hydroxyl and atomic oxygen on platinum are calculated to be in good agreement with experimental data. It is determined that onset potentials of < 0.1 V vs. SHE will result in inactive hydroxyls, while an onset potential of < 0.2 V results in inactive surface atomic oxygen, providing a target for catalyst optimisation. Onset of EOR is found to occur at potentials between 0.4 V and 0.5 V earlier on a range of platinum tin catalysts than on platinum, and Pt3Sn is found to be kinetically the best example of such a catalyst These findings are in good agreement with experimental observations. The addition of rhodium to platinum is found to result in a hydroxyl onset potential below the 0.1 V threshold for activity, and the near-optimal onset potential of surface atomic oxygen, resulting in excellent selectivity towards C02. However, the stability of the hydroxyl species delays the formation of atomic oxygen and so delays the onset of ethanol oxidation activity to an unacceptably high degree. This effect is believed to be general to metallic systems.
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DeLuca, Nicholas William Elabd Yossef A. "Nafion® blend membranes for the direct methanol fuel cell /". Philadelphia, Pa. : Drexel University, 2008. http://hdl.handle.net/1860/2710.
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Chen, Rong. "Coupled electrochemical and heat/mass transport characteristics in passive direct methanol fuel cells /". View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?MECH%202007%20CHEN.
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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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Argyropoulos, Panagiotis. "Performance and modelling of the direct methanol fuel cell (DMFC)". Thesis, University of Newcastle Upon Tyne, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247913.
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Gubner, Andreas. "Modelling of high temperature fuel cells : the thermal, chemical, electrochemical and fluidmechanical behaviour of solid oxide fuel cells operating with internal reforming of methane". Thesis, University of Portsmouth, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336474.
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Since only little is known in the field of Solid Oxide Fuel Cell (SOFC) operation about internal reforming of methane at present, the aim of this thesis study is to conduct a detailed investigation delivering the basis for further experimental and theoretical work. Also information is required if the concept of internal reforming has technical development potential. The thesis is arranged into two major parts being a thermodynamic investigation and an application of a suitable kinetic model. Pure methane tends to decompose at the high operation temperatures of the SOFC (about 950°C) thus forming solid carbon. Therefore it is necessary to include a fuel preparation process delivering H2 and CO that can be utilized by the SOFC. The fuel processing can either be carried out by steam reforming or partial oxidation. It is shown by a thermodynamic investigation that fuel processing by partial oxidation yields a fuel gas of inferior quality than fuel processing by steam reforming. The kinetic part contains the application of a model describing the chemical and electrochemical conversion occuring in the SOFC as detailed as possible at present. This model is used to investigate the thermal behaviour of an SOFC process referring to technical operation parameters. It is shown that internal reforming has technical development potential although a lot of care must be paid to the heat management. Particular operation conditions might exist where the highly endothermic steam reforming process could cause a breakdown of the complete fuel cell process due to its enormous local cooling effect.
37
Zhang, Haifeng. "Reduction of methanol crossover in direct methanol fuel cells by an integrated anode structure and composite electrolyte membrane /". View abstract or full-text, 2010. http://library.ust.hk/cgi/db/thesis.pl?CBME%202010%20ZHANG.
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Zhang, Xiao. "Preparation and characterization of proton exchange membranes for direct methanol fuel cells". Doctoral thesis, Universitat Rovira i Virgili, 2005. http://hdl.handle.net/10803/8525.
Texto completoResumen
Due to the petroleum crisis and its consequent emission problems, fuel cells gain an important place in the application of alternative energy. They are a kind of electrochemical device that converts chemical energy directly into electrical energy. The Direct Methanol Fuel Cells (DMFC) use polymer membranes as the electrolyte; the polymer membranes are capable of conducting hydrogen protons. The fuel cell system is still expensive and the proton exchange membrane has contributed significantly the high cost. At present, perfluorosulfonic acid membranes (PFSA) (e.g. Nafion®, by DuPont) have been widely investigated. However they showed high methanol crossover and high swelling that lead low cell efficiency. The main goal of the thesis is to prepare novel proton exchange membranes to apply in the DMFC. PEG and PA membranes compuestas fueron preparadas. Derivados del ácido fosfórico y lignosulfonados (LS) fueron incluidos en la estructura de la PA para actuar como agentes transportadores de protones. El mecanismo de la conductividad de protón es "hopping". Ellos mostraron el más baja del transporte de metanol.
Se obtuvieron también membranas híbridas de LS, preparadas mediante la mezcla de los dos polímeros, LS y PSU, siguiendo el método de precipitación en inmersión. Las propiedades electroquímicas de las membranas de LS fueron caracterizadas. Las membranas de LS alcanzaron conductividades de protón aceptables (10-20 mS/cm) con capacidad de intercambio iónico muy baja (IEC) (60 veces más baja que Nafion). "Membrane electrode assemblies" (MEAs) fueron preparadas y sus rendimientos de celda fueron medidos en una celda individual directa de metanol (DMFC).
LS membrana is the highlight point of this thesis. It demonstrated the first that LS is a good proton exchange material although it is a waste from the paper industry. It also proved that porous membrane can be used in the DMFC with acceptable proton conductivity and low methanol permeability, which is a totally new way from the existing literatures.
The results have been published on international journals and have been presented on international conferences:
1. X. Zhang, A. Glüsen, R. Garcia-Valls, Porous Lignosulfonate membrane for direct methanol fuel cells, accepted by Journal of Membrane Science, 2005
2. X. Zhang, J. Benavente, R. Garcia Valls, Lignin-based Membranes for Electrolyte Transference, Journal of Power Sources, 145 (2005) 292
3. X. Zhang, L. Pitol Filho, C. Torras, R. Garcia Valls, Experimental and Computational Study of Proton and Methanol Permeability through Composite Membranes, Journal of Power Sources, 145 (2005) 223
4. J. Benavente, X. Zhang, R. Garcia Valls, Modification of Polysulfone Membranes with Polyethylene Glycol and Lignosulfate: Electrical Characterization by Impedance Spectroscopy Measurements, Journal of Colloid and Interface Science, 285 (2005) 273-280
5. X. Zhang, R. Garcia-Valls, Proton transport membrane containing lignin compound for direct methanol fuel cells (Poster), 5th Ibero American Congress on Membrane Science and Technology, 2005, Valencia- Spain
6. X. Zhang, J. Benavente and R. Garcia-Valls, Lignin-based membranes for electrolyte transference (Oral presentation), Fuel Cell Science & Technology, Oct. 2004, Munich- Germany.
7. X. Zhang, R. Garcia-Valls, New membranes for Proton Transport in DMFC (Poster), Euromembrane Sep. 2004, ISBN: 3-930400-65-0, p. 64, Hamburg- Germany,
8. X. Zhang, R. Garcia-Valls, Lignosulfonate Application in Proton Transport Membrane (Oral presentation), 2nd World Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection, May. 2004, Rome- Italy
9. X. Zhang, R. Garcia-Valls, Proton Selective Composite Membrane for Direct Methanol Fuel Cell (Oral presentation), 5th NYM (Network Young Membrains) Oct. 2003, ISBN: 84-688-3132-8, p. 199, Barcelona, Spain
10. X. Zhang, R. Garcia-Valls, A. Jiménez-López, E. Rodríguez-Castellón and J. Benavente, Electrical and Chemical Surface Characterization of Lignosulfate/Polysulfone Membranes for Fuel Cells Application, International Conference on "New Proton Conducting Membranes and Electrodes for PEM FCs", Oct. 2005, Assisi, Italy.
Debido a la crisis de petróleo y a los problemas de emisión, las pilas de combustible adquieren un lugar importante en la aplicación de la energía alternativa. Son una clase de dispositivo electroquímico que convierte la energía química directamente en energía eléctrica. Las celdas de combustible de metanol (DMFC) usan membranas de polímero como el electrolito; las membranas de polímero son capaces de transportar protones de hidrógeno. El sistema de la celda de combustible todavía es costoso y las membranas de intercambio de protón han contribuido significativamente para el costo elevado.
Actualmente, las membranas de ácido perfluorosulfonico (PFSA) (por ejemplo, Nafion ®, de DuPont) ten sido investigadas extensamente. Sin embargo mostraron alto paso de metanol e alto "swelling" lo que lleva a una eficiencia de celda baja.
El objetivo principal de la tesis es preparar membranas de intercambio de protón nuevas para la aplicación en DMFC. Membranas compuestas de PEG y de PA fueron preparadas. Derivados del ácido fosfórico y lignosulfonados (LS) fueron incluidos en la estructura de la PA para actuar como agentes transportadores de protones. El mecanismo de conductividad de protón es "hopping". Ellos mostraron el transporte de metanol más bajo.
Se obtuvieron también membranas híbridas de LS, preparadas mediante la mezcla de los dos polímeros, LS y PSU, siguiendo el método de precipitación en inmersión. Las propiedades electroquímicas de las membranas de LS fueron determinadas. Las membranas de LS alcanzaron conductividades de protón aceptables (10-20 mS/cm) con capacidad de intercambio iónico muy baja (IEC) (60 veces más baja que Nafion). "Membrane electrode assemblies" (MEAs) fueron preparadas y sus rendimientos de celda fueron medidos en una celda individual directa de metanol (DMFC).
Las membranas de LS son el punto principal de esta tesis. Primero se demostró que LS es un material de intercambio de protón muy bueno aunque sea un residuo de la industria de papel. También se probó que membranas porosas pueden ser usadas en DMFC con una conductancia de protón aceptable y baja permeabilidad de metanol, lo que es una manera totalmente nueva comparada a la literatura existente.
Los resultados han sido divulgados en revistas internacionales y han sido presentados en conferencias internacionales:
1. X. Zhang, A. Glüsen, R. Garcia-Valls, Porous Lignosulfonate membrane for direct methanol fuel cells, accepted by Journal of Membrane Science, 2005
2. X. Zhang, J. Benavente, R. Garcia Valls, Lignin-based Membranes for Electrolyte Transference, Journal of Power Sources, 145 (2005) 292
3. X. Zhang, L. Pitol Filho, C. Torras, R. Garcia Valls, Experimental and Computational Study of Proton and Methanol Permeability through Composite Membranes, Journal of Power Sources, 145 (2005) 223
4. J. Benavente, X. Zhang, R. Garcia Valls, Modification of Polysulfone Membranes with Polyethylene Glycol and Lignosulfate: Electrical Characterization by Impedance Spectroscopy Measurements, Journal of Colloid and Interface Science, 285 (2005) 273-280
5. X. Zhang, R. Garcia-Valls, Proton transport membrane containing lignin compound for direct methanol fuel cells (Poster), 5th Ibero American Congress on Membrane Science and Technology, 2005, Valencia- Spain
6. X. Zhang, J. Benavente and R. Garcia-Valls, Lignin-based membranes for electrolyte transference (Oral presentation), Fuel Cell Science & Technology, Oct. 2004, Munich- Germany.
7. X. Zhang, R. Garcia-Valls, New membranes for Proton Transport in DMFC (Poster), Euromembrane Sep. 2004, ISBN: 3-930400-65-0, p. 64, Hamburg- Germany,
8. X. Zhang, R. Garcia-Valls, Lignosulfonate Application in Proton Transport Membrane (Oral presentation), 2nd World Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection, May. 2004, Rome- Italy
9. X. Zhang, R. Garcia-Valls, Proton Selective Composite Membrane for Direct Methanol Fuel Cell (Oral presentation), 5th NYM (Network Young Membrains) Oct. 2003, ISBN: 84-688-3132-8, p. 199, Barcelona, Spain
10. X. Zhang, R. Garcia-Valls, A. Jiménez-López, E. Rodríguez-Castellón and J. Benavente, Electrical and Chemical Surface Characterization of Lignosulfate/Polysulfone Membranes for Fuel Cells Application, International Conference on "New Proton Conducting Membranes and Electrodes for PEM FCs", Oct. 2005, Assisi, Italy La tesis tuvo la cooperación del Forschungszentrum Jülich, Alemania y la doctoranda esta solicitando el titulo de Doctorado Europeo.
39
Breitwieser, Matthias [Verfasser] y Roland [Akademischer Betreuer] Zengerle. "Direct membrane deposition as novel fabrication technique for high performance fuel cells". Freiburg : Universität, 2017. http://d-nb.info/1142738566/34.
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Breitwieser, Matthias, Riko Moroni, Jonathan Schock, Michael Schulz, Burkhard Schillinger, Franz Pfeiffer, Roland Zengerle y Simon Thiele. "Water management in novel direct membrane deposition fuel cells under low humidification". Elsevier, 2016. https://publish.fid-move.qucosa.de/id/qucosa%3A72518.
Texto completoResumen
Polymer electrolyte membrane fuel cells (PEMFCs) fabricated by direct membrane deposition (DMD) were shown to work even at dry conditions without significant deterioration of the membrane resistance. Here, in situ neutron radiography is used to investigate the water management in those fuel cells to uncover the phenomena that lead to the robust operation under low humidification. A constant level of humidification within the membrane electrode assembly (MEA) of a DMD fuel cell is observed even under dry anode operation and 15% relative humidity on the cathode side. This proves a pronounced back diffusion of generated water from the cathode side to the anode side through the thin deposited membrane layer. Over the entire range of polarization curves a very high similarity of the water evolution in anode and cathode flow fields is found in spite of different humidification levels. It is shown that the power density of directly deposited membranes in contrast to a 50 μm thick N-112 membrane is only marginally affected by dry operation conditions. Water profiles in through-plane direction of the MEA reveal that the water content in the DMD fuel cell remains steady even at high current densities. This is in contrast to the N-112 reference fuel cell which shows a strong increase in membrane resistance and a reduced MEA water content with raising current densities. Thus this new MEA fabrication technique has a promising perspective, since dry operation conditions are highly requested in order to reduce fuel cell system costs.
41
Mollá, Romano Sergio. "Application of Nanofibres in Polymer Composite Membranes for Direct Methanol Fuel Cells". Doctoral thesis, Universitat Politècnica de València, 2015. http://hdl.handle.net/10251/58611.
Texto completoResumen
[EN] Direct methanol fuel cells are feasible devices for efficient electrochemical power generation if some issues can be solved regarding both electrodes and membranes. The research carried out in this Ph.D. thesis has particularly focused on the concerns associated with the membranes.
Nafion is the most standard fuel cell membrane material due to its high proton conductivity and exceptional chemical and mechanical stability. However, it suffers from a considerably high methanol permeability and a limited operating temperature (< 80 ºC). The first aspect was addressed with the use of PVA nanofibres and the second one replacing Nafion with SPEEK-based polymers.
Composite membranes of Nafion with PVA nanofibres, surface functionalised with sulfonic acid groups, exhibited lower methanol permeabilities due to the intrinsic barrier property of PVA, although proton conductivity was also affected as a result of the non-conducting behaviour of the bulk PVA phase. Remarkably, the nanofibres provided strong mechanical reinforcement which enabled the preparation of low thickness membranes (< 20 micrometres) with reduced ohmic losses, thus counteracting their lower proton conductivities.
SPEEK-based membranes were examined for DMFC operation within the intermediate temperature range of 80-140 ºC, in which sluggish electrochemical reactions at the electrodes are accelerated and proton conductivity activated.
SPEEK was blended and crosslinked with PVA and PVB polymers for avoiding its dissolution in hot water conditions. SPEEK-PVA compositions showed practical proton conductivities and SPEEK-PVB blends presented very low methanol permeabilities.
Nanocomposite membranes composed of SPEEK-30%PVB nanofibres embedded in a SPEEK-35%PVA matrix were prepared and characterised. A nanocomposite membrane crosslinked at 120 ºC revealed promising results for DMFCs operating at intermediate temperatures.
Electrospinning is concluded to be a suitable technique for obtaining polymer nanofibre mats intended for advanced composite membranes with improved characteristics and fuel cell performances.[ES] Las pilas de combustible de metanol directo son dispositivos factibles para la generación electroquímica eficiente de energía eléctrica si se pueden solucionar algunas cuestiones relacionadas tanto con los electrodos como las membranas. La investigación llevada a cabo en esta tesis doctoral se ha centrado particularmente en los problemas asociados con las membranas. Nafion es el material de membrana más común para pilas de combustible debido a su alta conductividad protónica y excepcional estabilidad química y mecánica. Sin embargo, padece una considerablemente alta permeabilidad al metanol y una limitada temperatura de operación (< 80 ºC). El primer aspecto se abordó con el uso de nanofibras de PVA y el segundo reemplazando Nafion con polímeros basados en SPEEK. Membranas compuestas de Nafion con nanofibras de PVA, funcionalizadas en su superficie con grupos ácidos sulfónicos, exhibieron menores permeabilidades al metanol debido a la propiedad barrera intrínseca del PVA, aunque la conductividad protónica también se vio afectada como resultado del comportamiento global no conductor de la fase de PVA. Remarcablemente, las nanofibras proporcionaron un refuerzo mecánico fuerte que permitió la preparación de membranas de bajo espesor (< 20 micrómetros) con unas pérdidas óhmicas reducidas, así contrarrestando sus menores conductividades protónicas. Se examinaron membranas basadas en SPEEK para la operación de pilas de combustible de metanol directo dentro del rango intermedio de temperaturas entre 80-140 ºC, en el que las lentas reacciones electroquímicas en los electrodos se aceleran y la conductividad protónica se activa. El SPEEK se combinó y entrecruzó con los polímeros de PVA y PVB para evitar su disolución en condiciones de agua caliente. Las composiciones de SPEEK-PVA mostraron conductividades protónicas funcionales y las mezclas de SPEEK-PVB presentaron permeabilidades al metanol muy bajas. Se prepararon y caracterizaron membranas nanocompuestas constituidas por nanofibras de SPEEK-30%PVB embebidas en una matriz de SPEEK-35%PVA. Una membrana nanocompuesta entrecruzada a 120 ºC reveló resultados prometedores para pilas de combustible de metanol directo operando a temperaturas intermedias. Se puede concluir que la electrohilatura es una técnica apropiada para la obtención de mallas de nanofibras poliméricas destinadas a membranas compuestas avanzadas con características y rendimientos en pilas de combustible mejorados.
[CAT] Les piles de combustible de metanol directe són dispositius factibles per a la generació electroquímica eficient d'energia elèctrica si es poden solucionar algunes qüestions relacionades tant amb els elèctrodes com les membranes. La investigació duta a terme en esta tesi doctoral s'ha centrat particularment en els problemes associats amb les membranes. Nafion és el material de membrana més comú per a piles de combustible a causa de la seua alta conductivitat protònica i excepcional estabilitat química i mecànica. No obstant això, patix una considerablement alta permeabilitat al metanol i una limitada temperatura d'operació (< 80 ºC). El primer aspecte es va abordar amb l'ús de nanofibres de PVA i el segon reemplaçant Nafion amb polímers basats en SPEEK. Membranes compostes de Nafion amb nanofibres de PVA, funcionalizades en la seua superfície amb grups àcids sulfónics, van exhibir menors permeabilitats al metanol a causa de la propietat barrera intrínseca del PVA, encara que la conductivitat protònica també es va veure afectada com resultat del comportament global no conductor de la fase de PVA. Remarcablement, les nanofibres van proporcionar un reforç mecànic fort que va permetre la preparació de membranes de baixa grossària (< 20 micròmetres) amb unes pèrdues òhmiques reduïdes, així contrarestant les seues menors conductivitats protòniques. Es van examinar membranes basades en SPEEK per a l'operació de piles de combustible de metanol directe dins del rang intermedi de temperatures entre 80-140 ºC, en el que les lentes reaccions electroquímiques en els elèctrodes s'acceleren i la conductivitat protònica s'activa. El SPEEK es va combinar i va entrecreuar amb els polímers de PVA i PVB per a evitar la seua dissolució en condicions d'aigua calenta. Les composicions de SPEEK-PVA van mostrar conductivitats protòniques funcionals i les mescles de SPEEK-PVB van presentar permeabilitats al metanol molt baixes. Es van preparar i caracteritzar membranes nanocompostes constituïdes per nanofibres de SPEEK-30%PVB embegudes en una matriu de SPEEK-35%PVA. Una membrana nanocomposta entrecreuada a 120 ºC va revelar resultats prometedors per a piles de combustible de metanol directe operand a temperatures intermèdies. Es pot concloure que l'electrofilatura és una tècnica apropiada per a l'obtenció de malles de nanofibres polimériques destinades a membranes compostes avançades amb característiques i rendiments en piles de combustible millorats.
Mollá Romano, S. (2015). Application of Nanofibres in Polymer Composite Membranes for Direct Methanol Fuel Cells [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/58611
TESIS
Premiado
42
Yang, Weiwei. "Mathematical modeling of two-phase mass transport in liquid-feed direct methanol fuel cells /". View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?MECH%202009%20YANG.
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Mohamed, Rushanah. "Synthesis and characterisation of proton conducting membranes for direct methanol fuel cell (DMFC) applications". Thesis, University of the Western Cape, 2005. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_6787_1194349066.
Texto completoResumen
For a direct methanol fuel cell (DMFC), the proton exchange membrane must conduct protons and be a good methanol barrier. In addition to the high methanol permeability achieved by these membranes, they are very expensive and contribute greatly to theoverall cost of fuel cell set up. The high cost of the DMFC components is one of the main issues preventing its commercialization. The main objective of this study was thus to produce highly proton conductive membranes that are cheap to manufacture and have low methanol permeability.
44
Celik, Caglar. "Carbon Supported And Surfactant Stabilized Metal Nanoparticle Catalysts For Direct Methanol Fuel Cells". Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606368/index.pdf.
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ABSTRACT
CARBON SUPPORTED AND SURFACTANT STABILIZED METAL NANOPARTICLE CATALYSTS FOR DIRECT METHANOL FUEL CELLS
Çelik, Ç
aglar M.S., Department of Chemistry Supervisor: Assoc. Prof. Dr. Gü
lsü
n Gö
kagaç
August 2005, 72 pages Carbon supported surfactant, such as 1-decanethiol and octadecanethiol, stabilized platinum and platinum/ruthenium species have been prepared recently. In this thesis, for the first time, 1-hexanethiol has been used as an organic stabilizer for the preparation of carbon supported platinum and platinum/ruthenium nanoparticle catalysts. These new catalysts were employed for methanol oxidation reaction, which were used for direct methanol fuel cells. Cyclic voltammetry, X-ray photoelectron spectroscopy and transmission electron microscopy have been used in order to determine the nature of the catalysts. The effect of temperature and time on catalytic activity of catalysts were examined and the maximum catalytic activity was observed for carbon supported 1-hexanethiol stabilized platinum nanoparticle catalyst (with 1:1 thiol/platinum molar ratio) which was heated up at 200oC for 5 hours. The particle size of platinum nanoparticles was determined to be ~ 10 nm in diameter. The size and distribution of metal nanoparticles on carbon support, the Pt/Ru surface composition, the relative amount of Pt(0), Pt(II) and Pt(IV) and the removal of organic surfactant molecules around the metal nanoparticles were found to be important in determining the catalytic activity of electrodes towards methanol oxidation reaction. A significant decrease in catalytic activity was observed for carbon supported 1-hexanethiol stabilized Pt75Ru25 and Pt97Ru3 (with 1:1 thiol/PtRu molar ratio) with respect to carbon supported 1-hexanethiol stabilized Pt (with 1:1 thiol/platinum molar ratio). This result might be due to unremoved stabilizer shell around platinum/ruthenium nanoparticles and increase in amount of Pt(II) and Pt(IV) compared to Pt(0) where the methanol oxidation occured.
45
Al-Othman, Amani Lutfi. "Composite Zirconium Phosphate/PTFE Polymer Membranes for Application in Direct Hydrocarbon Fuel Cells". Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/22804.
Texto completoResumen
Higher temperature (~ 200°C) operation for proton exchange membrane (PEM) fuel cells would have several advantages including enhanced electrochemical kinetics, useful heat recovery, and improved catalyst tolerance for contaminants. Conventional perfluorosulfonic acid membranes (PFSA), such as Nafion show a dramatic decrease in proton conductivity at temperatures above 80°C. For this reason, there has been an increasing effort toward the development of stable, higher temperature membranes with acceptable proton conductivity. This work is directed toward the development of Nafion free membranes for direct hydrocarbon PEM fuel cells containing zirconium phosphate as the proton conductor component. Hence, composite membranes composed of zirconium-phosphate (ZrP), a solid proton conductor, which was precipitated within the voids of a porous polytetraflouroethylene (PTFE) support were synthesized. Amorphous-like zirconium phosphate (ZrP) powder was synthesized in this work. ZrP was prepared by precipitation at room temperature via reaction of ZrOCl2 with H3PO4 aqueous solutions. The proton conduction properties of ZrP powder were studied under the processing conditions found in direct hydrocarbon fuel cell. Our experimental results showed that the ZrP powder processed at 200°C possess a proton conductivity that is greater by one order of magnitude than the oven-dried samples at 70°C. Thereby, it was possible to avoid the normal decrease in conductivity with increasing temperature by having sufficient water in the vapor phase. This thesis reports the first synthesis of composite ZrP/PTFE/Glycerol (GLY) membranes. Glycerol (GLY) was introduced into the pores of PTFE with the ZrP proton conductive material using the successive wetting/drying technique. These membranes had reasonable values of proton conductivities (0.045 S cm-1), approaching that of Nafion (0.1 S cm-1) at room temperature. Samples of these composite membranes were processed at the inlet conditions of a propane fuel cell, at 200°C. Experimental results showed that the proton conductivity remained almost unchanged. This thesis also describes and reports the first synthesis of sulphur “S” or silicon, Si–modified zirconium phosphate (ZrP), porous polytetrafluoethylene (PTFE) and, glycerol (GLY) composite membranes. It was aimed at the substitution of a minor amount of phosphorus “P” in the ZrP by (S or Si) in the ZrP to modify the proton conduction properties. The modification was performed by adding a certain amount of silicic acid or sulphuric acid into phosphoric acid then proceeding with the precipitation in situ. A high proton conductivity, of 0.073 S cm-1,i.e. 73% of that of Nafion, was observed for the Si–ZrP/PTFE/GLY composite membrane.
46
Birgersson, Erik. "Mathematical Modeling of Transport Phenomena in Polymer Electrolyte and Direct Methanol Fuel Cells". Doctoral thesis, KTH, Mechanics, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3692.
Texto completoResumen
This thesis deals with modeling of two types of fuel cells:the polymer electrolyte fuel cell (PEFC) and the directmethanol fuel cell (DMFC), for which we address four majorissues: a) mass transport limitations; b) water management(PEFC); c) gas management (DMFC); d) thermal management.
Four models have been derived and studied for the PEFC,focusing on the cathode. The first exploits the slenderness ofthe cathode for a two-dimensional geometry, leading to areduced model, where several nondimensional parameters capturethe behavior of the cathode. The model was extended to threedimensions, where four di.erent flow distributors were studiedfor the cathode. A quantitative comparison shows that theinterdigitated channels can sustain the highest currentdensities. These two models, comprising isothermal gasphaseflow, limit the studies to (a). Returning to a two-dimensionalgeometry of the PEFC, the liquid phase was introduced via aseparate flow model approach for the cathode. In addition toconservation of mass, momentum and species, the model wasextended to consider simultaneous charge and heat transfer forthe whole cell. Di.erent thermal, flow fields, and hydrodynamicconditions were studied, addressing (a), (b) and (d). A scaleanalysis allowed for predictions of the cell performance priorto any computations. Good agreement between experiments with asegmented cell and the model was obtained.
A liquid-phase model, comprising conservation of mass,momentum and species, was derived and analyzed for the anode ofthe DMFC. The impact of hydrodynamic, electrochemical andgeometrical features on the fuel cell performance were studied,mainly focusing on (a). The slenderness of the anode allows theuse of a narrow-gap approximation, leading to a reduced model,with benefits such as reduced computational cost andunderstanding of the physical trends prior to any numericalcomputations. Adding the gas-phase via a multiphase mixtureapproach, the gas management (c) could also be studied.Experiments with a cell, equipped with a transparent end plate,allowed for visualization of the flow in the anode, as well asvalidation of the two-phase model. Good agreement betweenexperiments and the model was achieved.
Keywords:Fuel cell; DMFC; PEFC; one-phase; two-phase;model; visual cell; segmented cell; scale analysis; asymptoticanalysis.
47
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.
Texto completoResumen
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
48
Oseghale, Charles Ijogbemeye. "Gold copper based catalysts in the development of direct formic acid fuel cells". Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/20827/.
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There is a growing awareness of the need for fundamental and applied research in energy storage and conversion due to the global climate issue with energy sources, environmental and human health challenges. In this work, development of a new synthesis route for catalysts, physicochemical and electrochemical research is reported for direct formic acid fuel cells. The synthesis method is based on the sodium borohydride reduction of (Pd2+, Cu2+, Au3+) precursor, stabilised by polyvinylpyrrolidone for the preparation of a highly stable catalysts with, well-controlled particle size distribution. The surface and bulk properties of the catalysts were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), and electrochemically by cyclic voltammetry and chronoamperometry. The results obtained for Pd-C showed that a uniform XRD estimated the size distribution in a narrow particle size range with an average size of 1.4 ± 0.11 nm. Electrochemical studies for formic acid electrooxidation reveals that Pd-CH3BO3 + NH4F(21wt.%) presents superior catalytic activity (over 44 %) than that of the Pd-CPVP(43.5wt.%) synthesis route. For an equivalent electrode paste, Pd-CPVP(43.5wt.%) exhibited a greater electrochemical surface area (ECSA) than Pd-CPVP(43.5wt.%) but achieved a lower utilisation of palladium. The electrooxidation of the catalyst shows three times higher activity for formic acid oxidation than commercial gold nanoparticles dispersed on the carbon support. The enhanced catalytic performance is attributed to the electronic synergistic effect of copper and the specific gold structure promoting oxidation of adsorbed intermediate species. Overall, these findings have significant implications for practical direct formic acid fuel cells (DFAFCs) technology by the controlled Au-shell Cu-core anode catalysts application. Overall, palladium catalysts demonstrated better electrocatalytic activities for formic oxidation than Au and gold copper catalysts. This work is part of the initial stages of the effort to develop a low-cost gold-catalyst for DFAFCs technology.
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Rosenthal, Neal Stephen. "An Exploration of the Promises and Limitations of Passive Direct Methanol Fuel Cells". Digital WPI, 2011. https://digitalcommons.wpi.edu/etd-theses/1011.
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"While Direct Methanol Fuel Cells (DMFC) have a promising future as a long-lasting and environmentally friendly energy source, the use of balance of plant (BOP) equipment, such as pumps, fans, and compressors, create a complex system that can significantly reduce plant efficiency and increase cost. As an alternative, passive DMFCs have been designed and studied due to their ability to run under ambient conditions without any BOP equipment. However, before they become a feasible energy source, more must be understood about their promise and limitations. In this thesis, performance of a self-designed and constructed passive DMFC was investigated. In addition, an analytical mathematical model was developed in order to gain a better understanding of the limitations of the passive DMFC. The model was compared with literature's data to ensure reliability. Passive DMFCs, consisting of one to twelve Membrane Electrode Assemblies (MEAs) were designed, constructed and tested. The smaller scale fuel cell was optimized using different setups and elaborately tested using a variety of fuels, most notably methanol chafing gel, to determine an optimal performance curve. The larger fuel cells were further used to test for long-term performance and practical feasibility. The compact four-cell units could run for at least 24 hours and can provide performance akin to an AA battery. A larger 12-cell fuel cell was also designed and built to test feasibility as a convenient power supply for camping equipment and other portable electronics, and was tested with neat methanol and methanol gel. In all fuel cell prototypes, polarization plots were obtained, along with open circuit voltage (OCV) plots and long-term performance plots. While it is currently not possible to differentiate which methanol fuel source is the best option without a more thorough investigation, methanol gel has shown great potential as a readily available commercial fuel. The three largest restrictions in passive DMFC performance are 1) slow mass transfer of fuel to the anode, 2) slow kinetics of methanol and oxygen electrodes, and 3) methanol crossover. The developed model correctly predicts the effect of methanol crossover and the resulting crossover current on OCV as well as on performance of the fuel cell over the entire voltage-current range. Further, the model correctly predicts the effect of increasing methanol feed concentration on reduced OCV but increased limiting current density. The effect of the proton exchange membrane thickness is also well explained. Finally, the model describes the significant power losses from larger overpotentials, as well as crossover current, and the resulting significant heat generated and low efficiency. Overall, PDMFCs show great promise for potential application provided the cost can be reduced significantly."
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Ma, Jia. "Development of Cost-Effective Membrane-Electrode-Assembly (MEA) for Direct Borohydride Fuel Cells". The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1326302289.
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