Dissertations / Theses: 'Direct methanol fuel cells'

1

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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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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3

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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4

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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6

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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7

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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8

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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9

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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10

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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11

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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12

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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13

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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14

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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15

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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16

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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17

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 CeltecÂ®-P 1000 MEA of original thickness and double thickness. The PBI-based MEAâ€™s were tested under the vapor-phase methanol concentrations of 1M, 2M, 3M, 5M, 7.5M, and 10M, temperatures of 160-180Â°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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18

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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19

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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20

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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21

Dawson, Craig. "Materials for direct methanol fuel cells: inhibition of methanol crossover using novel membrane electrode assemblies." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/materials-for-direct-methanol-fuel-cells-inhibition-of-methanol-crossover-using-novel-membrane-electrode-assemblies(843284c4-3620-4cac-9118-06671d7bb420).html.

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This thesis focuses on developing an alternative system for membrane electrode assembly (MEA) formation to use with a direct methanol fuel cell (DMFC). The approach involves incorporating inorganic fillers with an industry standard Nafion polymer as part of a methanol resistant composite barrier layer at the anode/membrane interface of MEA featuring Nafion 117 membranes. This procedure is used to reduce the fuel cell losses related to the crossover of un-oxidised methanol through the membrane and prevent its subsequent reaction at the cathode. The inorganic filler used within this study was mordenite that has Si/Al ratio of 5 and by incorporating this into the barrier layer a superior DMFC performance has been achieved in comparison to a standard MEA featuring a Nafion 117 membrane. The voltage, current density and power density used as a measure of DMFC performance under a range of methanol molarities (1M-4M) and cell temperatures (40°C-70°C) have been taken for both the novel and standard MEA. Linear sweep voltammetry (LSV) and AC impedance spectroscopy (ACIS) were used to give some insight into what was occurring within the MEA with regards to methanol crossover current and the proton conductivity within the DMFC. To obtain the best possible DMFC performance a range of mordenite loadings from 0wt%1.0wt% were utilised and an optimum loading of 0.5wt% was reached. MEA which featured mordenite that had undergone ion exchange into a protonated form (from the sodium form) and had a silane functional group (glycidoxypropyltrimethoxysilane) grafted onto the surface, gave DMFC performances that were as much as 50% better than the standard. The highest power density obtained with this MEA was 43.6mW/cm-2 compared to the 35mW/cm-2 obtained using the standard. Values obtained for the methanol crossover current and proton conductivity under working DMFC operating conditions showed that this novel MEA had as much as 16% lower methanol permeability compared to the standard combined with comparable proton conductivity when using a 1M methanol feed. The durability of a novel MEA featuring the 0.5wt% functionalised H-mordenite composite barrier layer was tested in the DMFC and compared to a standard MEA at a constant current of 50mA/cm-2 over 100 hours. The cell potential fell by 0.1mV/h in comparison to a 0.23mV/h loss observed with the standard. The work reported within this study aims to show that by incorporating a thin Nafion/mordenite composite layer at the anode/membrane interface within an MEA will result in improvements in DMFC performance. The development of this technology has led to the application for a patent due to the potential for the commercial development of DMFC using this novel approach.

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22

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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23

Nordlund, Joakim. "The Anode in the Direct Methanol Fuel Cell." Doctoral thesis, KTH, Chemical Engineering and Technology, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3676.

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The direct methanol fuel cell (DMFC) is a very promisingpower source for low power applications. High power and energydensity, low emissions, operation at or near ambientconditions, fast and convenient refuelling and a potentiallyrenewable fuel source are some of the features that makes thefuel cell very promising. However, there are a few problemsthat have to be overcome if we are to see DMFCs in our everydaylife. One of the drawbacks is the low performance of the DMFCanode. In order to make a better anode, knowledge about whatlimits the performance is of vital importance. With theknowledge about the limitations of the anode, the flow field,gas diffusion layer and the morphology of the electrode can bemodified for optimum performance.

The aim of this thesis is to elucidate the limiting factorsof the DMFC anode. A secondary goal is to create a model of theperformance, which also has a low computational cost so that itcan be used as a sub model in more complex system models. Toreach the primary goal, to elucidate the limiting factors, amodel has to be set up that describes the most importantphysical principles occurring in the anode.

In addition, experiments have to be performed to validatethe model. To reach the secondary goal, the model has to bereduced to a minimum. A visual DMFC has been developed alongwith a methodology to extract two-phase data. This has provento be a very important part of the understanding of thelimiting factors. Models have been developed from a detailedmodel of the active layer to a two-phase model including theentire three-dimensional anode.

The results in the thesis show that the microstructure inthe active layer does not limit the performance. Thelimitations are rather caused by the slow oxidation kineticsand, at concentrations lower than 2 M of methanol, the masstransport resistance to and inside the active layer. Theresults also show that the mass transfer of methanol to theactive layer is improved if gas phase is present, especiallyfor higher temperatures since the gas phase then contains moremethanol.

It is concluded that the mass transport resistance lower theperformance of a porous DMFC anode at the methanolconcentrations used today. It is also concluded that masstransfer may be improved by making sure that there is gas phasepresent, which can be done by choosing flow distributor and gasdiffusion layer well.

Keywords: direct methanol fuel cell, fuel cell, DMFC, anode,model

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24

Hogarth, Martin P. "The development of the direct methanol fuel cell." Thesis, University of Newcastle Upon Tyne, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295055.

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25

Allen, Ruth Gleave. "New anodes for the direct methanol fuel cell." Thesis, University of Newcastle Upon Tyne, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413008.

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26

Dickinson, Angus John. "Development of a direct methanol fuel cell system." Thesis, University of Newcastle Upon Tyne, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324802.

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27

Lee, Jeong Kyu. "Direct Methanol Fuel Cell Membranes from Polymer Blends." Case Western Reserve University School of Graduate Studies / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=case1134316195.

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28

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.

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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.

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29

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.

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[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

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30

Naidoo, Sivapregasen. "Synthesis of multi-metallic catalysts for fuel cell applications." Thesis, University of the Western Cape, 2008. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_6275_1241512064.

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The direct methanol fuel cell or DMFC is emerging as a promising alternative energy source for many applications. Developed and developing countries, through research, are fast seeking a cheap and stable supply of energy for an ever-increasing number of energy-consuming portable devices. The research focus is to have DMFCs meeet this need at an affordable cost is problematic. There are means and ways of making this a reality as the DMFC is found to be complementary to secondary batteries when used as a trickle charger, full charger, or in some other hybrid fuel cell combination. The core functioning component is a catalyst containing MEA, where when pure platinum is used, carbon monoxide is the thermodynamic sink and poisons by preventing further reactions at catalytic sites decreasing the life span of the catalyst if the CO is not removed. Research has shown that the bi-functional mechanism of a platinum-ruthenium catalyst is best because methanol dehydrogenates best on platinumand water dehydrogenation is best facilitated on ruthenium. It is also evident that the addition of other metals to that of PtRu/C can make the catalyst more effective and effective and increase the life span even further. In addition to this, my research has attempted to reduce catalyst cost for DMFCs by developing a low-cost manufacturing technique for catalysts, identify potential non-noblel, less expensive metallic systems to form binary, ternary and quarternary catalysts.

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Prakash, Shruti. "The development and fabrication of miniaturized direct methanol fuel cells and thin-film lithium ion battery hybrid system for portable applications." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28279.

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Thesis (M. S.)--Chemical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Kohl, Paul; Committee Member: Fuller, Tom; Committee Member: Gray, Gary; Committee Member: Liu, Meilin; Committee Member: Meredith, Carson; Committee Member: Rincon-Mora, Gabriel.

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32

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.

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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.

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33

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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34

Li, Xiao. "Development of composite membranes for direct methanol fuel cell." Thesis, University of Manchester, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.556263.

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35

Özdinçer, Baki. "Novel support materials for direct methanol fuel cell catalysts." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/novel-support-materials-for-direct-methanol-fuel-cell-catalysts(f7dfe29a-a593-44a6-a9e3-e9e8f5b8b2a2).html.

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This thesis focuses on developing support materials for direct methanol fuel cell (DMFC) catalysts. The approach involves using graphene based materials including reduced graphene oxide (rGO), reduced graphene oxide-activated carbon (rGO-AC) hybrid and reduced graphene oxide-silicon carbide (rGO-SiC) hybrid as a support for Pt and Pt-Ru nanoparticles. Pt/rGO and Pt-Ru/rGO catalysts were synthesized by three chemical reduction methods: (1) modified polyol, (2) ethylene glycol (EG) reduction and (3) mixed reducing agents (EG + NaBH4) methods. The synthesized catalysts were characterized by physical and electrochemical techniques. The results demonstrated that Pt/rGO-3 and Pt-Ru/rGO-3 catalyst synthesized with Method-3 exhibit higher electrochemical active surface area (ECSA) than the other rGO supported and Vulcan supported commercial electrocatalysts. In addition, Pt/rGO-3 and Pt-Ru/rGO-3 catalysts showed better oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) activities, respectively. The DMFC tests under different cell temperature (30, 50 and 70Â°C) and methanol concentration (1, 2 and 4 M) conditions further demonstrated the higher catalytic activity of the catalysts. The peak power density obtained with Pt/rGO-3 cathode and Pt-Ru/rGO-3 anode catalysts at 70Â°C with 1 M methanol was 63.3 mW/cm2 which is about 59 % higher than that of commercial Pt/C and Pt-Ru/C catalysts. The enhanced performance was attributed to the highly accessible and uniformly dispersed nanoparticles on rGO support with large surface area and high conductivity. Pt/rGO-AC (reduced graphene oxide-activated carbon) and Pt-Ru/rGO-AC catalysts were synthesized with various rGO:AC support ratios by using biomass derived AC. The results showed that the catalysts with content of 20 wt. % AC support (Pt/rGO-AC20 and Pt-Ru/rGO-AC20) exhibited higher ECSA, better catalytic activity and stability among all the tested catalysts. With 1 M methanol and 70Â°C cell temperature, the MEA with Pt/rGO-AC20 cathode and Pt-Ru/rGO-AC anode catalysts gave 19.3 % higher peak power density (75.5 mW/cm2), than that of Pt/rGO-3 and Pt-Ru/rGO-3 catalysts. The better DMFC performance was due to the incorporation of AC particles into rGO structure which builds electron-conductive paths between rGO sheets, facilitates the transport of reactant and products and provides higher specific surface area for the uniform distribution of nanoparticles. Pt/rGO-SiC catalysts were synthesized with variable silicon carbide (SiC) content in the hybrid support. Pt/rGO-SiC10 (10 wt. % of SiC support) catalyst showed higher ECSA and better catalytic activity compared to the Pt/SiC, Pt/rGO-3 and Pt/rGO-SiC20 catalysts. In addition, the Pt/rGO-SiC10 gave 14.2 % higher DMFC performance than the Pt/rGO-3 catalyst in terms of power density. The high performance can be attributed to the insertion of the SiC nanoparticles into rGO structure that improves the conductivity and stability of the catalyst by playing a spacer role between rGO layers. In summary, the overall results showed that the catalytic performance of the catalysts followed the trend in terms of support material: rGO-AC20 > rGO-SiC10 > rGO > Vulcan. The study demonstrated that the novel rGO-AC and rGO-SiC hybrids are promising catalyst supports for direct methanol fuel cell applications.

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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.

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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.

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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 Ç
elik, 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.

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38

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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39

Jackson, Colleen. "Preparation and characterisation of Pt-Ru/C catalysts for direct methanol fuel cells." Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/24322.

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The direct methanol fuel cell (DMFC) is identified as a promising fuel cell for portable and micro fuel cell applications. One of the major benefits is that methanol is an energy dense, inexpensively manufactured, easily stored and transported, liquid fuel (Hamann et al., 2007). However, the DMFC's current efficiency and power density is much lower than theoretically possible. This inefficiency is predominantly due to the crossover of methanol from the anode to the cathode, Ru dissolution and Ru crossover from the anode to the cathode. In addition, the DMFC has a high manufacturing cost due to expensive catalyst costs and other materials. Catalyst expenses are further increased by catalyst loading due to low activity at the anode of the DMFC (Zhang, 2008). Hence, with increasing activity and stability of the Pt-Ru/C catalyst, catalyst expenditure will decrease due to a decrease in catalyst loading. In addition, performance will increase due to a reduction in ruthenium dissolution and crossover. Therefore, increasing the activity and stability of the Pt-Ru/C catalyst is paramount to improving the current DMFC performance and viability as an alternative energy conversion device. Pt-Ru/C catalyst synthesis method, precursors, reduction time and temperature play a role in the activity for methanol electro-oxidation and stability since these conditions affect structure, morphology and dispersivity of the catalyst (Wang et al., 2005). Metal organic chemical deposition methods have shown promise in improving performance of electro-catalysts (Garcia & Goto, 2003). However, it is necessary to optimise deposition conditions such as deposition time and temperature for Pt(acac)₂ and Ru(acac)₃ precursors. This study focuses on a methodical approach to optimizing the chemical deposition synthesis method for Pt-Ru/C produced from Pt(acac)₂ and Ru(acac)₃ precursors. Organo-metallic chemical vapour deposition (OMCVD) involved the precursor's vapourisation before deposition and a newly developed method which involved the precursors melting before deposition. An investigation was conducted on the effects of precursor's phase before deposition. The second investigation was that of the furnace operating temperature, followed by an exploration of the furnace operating time influence on methanol electro-oxidation, CO tolerance and catalyst stability. Lastly, the exploration of the Pt:Ru metal ratio influence was completed. It was found that the catalyst produced via the liquid phase precursor displayed traits of a high oxide content. This led to an increased activity for methanol electro-oxidation, CO tolerance and catalyst stability despite the OMCVD catalyst producing smaller particles with a higher electrochemically active surface area (ECSA).

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Piet, Marvin. "Synthesis and characterization of cathode catalysts for use in direct methanol fuels cells." Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_3065_1307691154.

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In this work a modified polyol method was developed to synthesize in-house catalysts. The method was modified for maximum delivery of product and proved to be quick and efficient as well as cost effective. The series of IH catalysts were characterized using techniques such as UV-vis and FT-IR spectroscopy, TEM, XRD, ICP and CV.

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Luo, Hongze. "Polymer/nano-organic composite proton exchange membranes for direct methanol fuel cell application." Thesis, University of the Western Cape, 2005. http://etd.uwc.ac.za/index.php?module=etd&amp.

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The proton exchange membrane is one key component of direct methanol fuel cells, which has double functions of conducting protons, separating fuels and oxidant. At present, the performance and price of sulfonic acid proton exchange membrane used in direct methanol fuel cells are deeply concerned. In order to reduce membrane 's cost and improve performance of Nafion membrane, three different kinds of membranes have been studied in this thesis. These membranes are SPEEK membranes, SPEEK/ZP composite membranes and Nafion/ZP composite membranes.

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Luo, Hongze. "Proton conducting polymer composite membrane development for Direct Methanol Fuel Cell applications." Thesis, University of Western Cape, 2008. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_1362_1262901908.

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The objective of this study was thus to prepare highly proton condictivity membranes that are cheap to manufacture and have low methanol permeability.

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Kothandaraman, R. "Studies On Direct Methanol And Direct Borohydride Fuel Cells." Thesis, 2006. http://hdl.handle.net/2005/415.

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A fuel cell is an electrochemical power source with advantages of both the combustion engine and the battery. Like a combustion engine, a fuel cell will run as long as it is provided fuel; and like a battery, fuel cells convert chemical energy directly to electrical energy. As an electrochemical power source, fuel cells are not subjected to the Carnot limitations of combustion (heat) engines. Fuel cells bear similarity to batteries, with which they share the electrochemical nature of the power generation process and to the engines that, unlike batteries, will work continuously consuming a fuel of some sort. A fuel cell operates quietly and efficiently and, when hydrogen is used as a fuel, it generates only power and water. Thus, a fuel cell is a so called ‘zero-emission engine’. In the past, several fuel cell concepts have been tested in the laboratory but the systems that are being potentially considered for commercial developments are: (i) Alkaline Fuel Cells (AFCs), (ii) Phosphoric Acid Fuel Cells (PAFCs), (iii) Polymer Electrolyte Fuel Cells (PEFCs), (iv) Solid Polymer Electrolyte Direct Methanol Fuel Cells (SPE-DMFCs), (v) Molten Carbonate Fuel Cells (MCFCs) and (vi) Solid Oxide Fuel Cells (SOFCs). Among the aforesaid systems, PEFCs that employ hydrogen as fuel are considered attractive power systems for quick start-up and ambient temperature operations. Ironically, however, hydrogen as fuel is not available freely in the nature. Accordingly, it has to be generated from a readily available hydrogen carrying fuel such as natural gas, which needs to be reformed. But, such a process leads to generation of hydrogen contaminated with carbon monoxide, which even at minuscule level is detrimental to the fuel cell performance. Pure hydrogen can be generated through water electrolysis but hydrogen thus generated needs to be stored as compressed/liquefied gas, which is cost-intensive. Therefore, certain hydrogen carrying organic fuels such as methanol, ethanol, propanol, ethylene glycol and diethyl ether have been considered for fueling PEFCs directly. Among these, methanol with hydrogen content of about 12.8 wt.% (specific energy = 6.1kWh kg-1) is the most attractive organic liquid. PEFCs using methanol directly as fuel are referred to as SPE-DMFCs. But SPE-DMFCs suffer from methanol crossover across the polymer electrolyte membrane, which affects the cathode performance and hence the fuel cell during its operation. SPE-DMFCs also have inherent limitations of low open-circuit-potential and low electrochemical-activity. An obvious solution to the aforesaid problems is to explore other promising hydrogen carrying fuels such as sodium borohydride (specific energy = 12kWh kg-1), which has a capacity value of 5.67Ah g-1 and a hydrogen content of about 11wt.%. Such fuel cells are called direct borohydride fuel cells (DBFCs). This thesis is directed to studies on SPE-DMFCs and DBFCs

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Schökel, Alexander. "Ruthenium dissolution in direct methanol fuel cells." Phd thesis, 2015. http://tuprints.ulb.tu-darmstadt.de/4454/1/PhD%20thesis_Alexander%20Sch%C3%B6kel.pdf.

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The lifetime of a direct methanol fuel cell (DMFC) is mostly determined by the degradation of its active component, the membrane electrode assembly (MEA). Besides degradation of the proton conducting membrane, the aging of the electrodes and especially the catalysts therein is the major limiting factor. One of the catalyst degradation mechanisms is ruthenium dissolution. This work is the first extensive study on the dissolution, migration and deposition of ruthenium in a DMFC single cell during early operation, i.e. between first start-up of the cell till approx. 100 h of operation. To analyze the dissolution process it is necessary to track the trace amounts of ruthenium being dissolved and transported through the MEA. For this task x-ray fluorescence spectroscopy (XRF), x-ray absorption spectroscopy (XAS), inductively coupled plasma mass spectrometry (ICP-MS) and cyclic voltammetry (CV) were used. The characterization of the catalysts itself was carried out by x-ray powder diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). Fuel cell tests were explicitly not including any extreme operation conditions, such as fuel starvation or accelerated aging protocols. Each DMFC test was run at one specific potential for the duration of the test. After operation the cells were disassembled, the MEA removed, dried and cathode and anode catalysts removed from the membrane to be analyzed separately. Two different MEA fabrication techniques, wet spray coating and dry decal transfer, were used to produce MEAs. The fabrication techniques are compared in respect to their influence on ruthenium dissolution. It is shown, that the crystalline fraction of the commercial platinum-ruthenium on carbon anode catalyst and platinum on carbon cathode catalyst does not change under the operation conditions investigated. The mean lattice parameters of the platinum and platinum-ruthenium catalysts are 3.916 and 3.866, respectively, as determined by XRD measurements. Both values are in good agreement with the lattice parameters reported in literature. Also the XPS measurements do not show any significant change in the catalyst composition after operation in the DMFC. XAS measurements gave evidence that a transfer of ruthenium already takes place during fabrication of the MEA. While XAS could only be used for qualitative analysis of the samples, XRF and complementary ICP-MS analyses provided quantitative measurements for the migrated ruthenium. Even though it was expected that the wet spray coating technique causes a higher amount of ruthenium to migrate onto the cathode side, the Ru transfer of both techniques in the order of 0.02 wt%. It is important to note, that this transfer happened during fabrication and before the MEA was even assembled inside a DMFC. After cell assembly and start of DMFC operation a fast dissolution process transfers an additional 0.2 wt% ruthenium onto the cathode side. Here the fabrication technique seems to influence the ruthenium crossover. The sprayed MEAs show a significantly higher Ru transfer of about 0.3 wt% during the first 2 h of operation. Over the next 100 h of cell operation of the decal MEAs at open circuit conditions another 0.3 wt% ruthenium are transferred by a presumably slower process. It can be assumed that 4 there are two sources of ruthenium feeding these two processes. Highly soluble ruthenium species like hydroxides could by the source for the fast dissolution process, while the slower process is fed by harder to dissolve oxides. ICP-MS analyses of different solvents after leaching experiments using the platinum-ruthenium catalyst show that both water and methanol can dissolve low amounts of ruthenium from the catalyst. In contrast formic acid, which is also present in DMFCs as a product of an incomplete methanol oxidation side reaction, has the capability to dissolve significant amounts of ruthenium and even to attack platinum. Consequently, formation of formic acid inside the DMFC and ruthenium dissolution may be closely correlated.

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45

Tung, Shih-ping, and 董士平. "Phosphor-silicate Glass for Direct Methanol Fuel Cells." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/eu3xm2.

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博士
國立臺灣科技大學
化學工程系
94
In this study, three stages of research are preformed here. In the first part, an accelerated sol-gel process with water/vapor management was developed to synthesize phosphor-silicate glass membranes for shortening the gelation time and enhancing their proton conductivities. The gelation time needed is shortened from 1~6 months in the literature’s report [Materials Letters, 42, 2000, 225] to about 3 days successfully in the developed process. The gelation reactions in the sol-gel process for the synthesis of SiO2-P2O5 glass membranes were investigated by in-situ FTIR spectroscopy. Types of water involving free/hydrogen bonded/strong hydrogen bonded water and hydroxyl group in the synthesized SiO2-P2O5 glass membranes were determined by TGA and in-situ FTIR. A SiO2-P2O5 glass membrane with a methanol permeability of 2.1 x 10-9 cm2/s and high proton conductivity (9.45x10-3 S/cm) was obtained by the developed process. In the second part of this study, a series of inorganic proton conductive membranes based on hydrated phosphor-silicate glass [xP2O5-(100-x)SiO2, x=10, 20, 30, 40 and 50, molar ratio] synthesized by an accelerated sol-gel process with water/vapor management are investigated. The phosphor-silicate glass membranes with high P2O5 content can be synthesized successfully in a short time (~3 days) by the developed process. Due to the formation of the P2O5 and SiO2 network structure, the hydrated phosphor-silicate glass membranes show good thermal stability. Two or three kinds of pore sizes existing in the synthesized glass membranes were observed. Increasing the content of the P2O5 of the glass membrane leads to decrease its major pore size and increase its porosity. However, it was observed that the pore size of the glass membrane becomes larger while its P2O5 content is higher than 40%. The conductivity and the methanol permeability increase with the increasing the content of the P2O5, and interestingly, a maximum selectivity (the ratio of the conductivity to permeability) occurs at the 30P2O570SiO2 glass membrane. The glass membranes shows slightly lower conductivity but much higher selectivity compared with the Nafion 117 membrane. The effect of the P2O5 content on the properties of the glass membrane is also characterized and discussed. At the last part, the characteristics of the Nafion/hydrated phosphor-silicate hybrid membranes for direct methanol fuel cells (DMFCs) were investigated. The effect of the ratio of the hydrated phosphor-silicate to Nafion on the morphology, thermal and chemical stabilities, crystalline structure, proton conductivity, and methanol permeability of the hybrid membrane were studied. The thermal and chemical stability as well as methanol impermeability of the hybrid membrane are relatively better than those of the Nafion 117 membrane. The hybrid membranes show higher proton conductivity than the hydrated phosphor-silicate glass membranes but slightly lower than the Nafion 117 membrane. It was found that the crystalline structure of the hybrid membranes is changed with the content of the SiO2-P2O5 particles. The direct methanol fuel cell composed of the hybrid membrane shows a maximum power density of about 13.42 mW cm-2 at the condition of 20 oC air breathing and 2 M methanol feed solution. The single cell of the hybrid membrane also shows a higher open circuit voltage than that of the Nafion 117 membrane, indicating the methanol crossover of the hybrid membranes is less than compared to that of the Nafion.

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46

Dixon, Ditty. "Spatially resolved studies in direct methanol fuel cells." Phd thesis, 2012. https://tuprints.ulb.tu-darmstadt.de/3025/1/Dixon_ditty_thesis.pdf.

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The thesis mainly focuses on the spatially resolved characterization of a direct methanol fuel cell. Initially spatially resolved analyses were carried out on an end of life (5000 hrs operated) stack membrane electrode assembly (MEA) using various techniques, like X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive X-ray (EDX) mapping and X-ray absorption spectroscopy (XAS). The fate of the Ru in the direct methanol fuel cell (DMFC) with ageing is carefully analyzed in these studies. It was found that the large oxidized ruthenium fraction in the anode catalyst plays a significant role in particle growth and ruthenium dissolution. Ru was also found in the form of precipitates in the Nafion membrane preferentially at the methanol outlet regions. Ex-situ studies were preceded by in-situ spatially resolved XAS studies. For these, in-situ cells for spatially resolved DMFC studies are developed and optimized. The relative OH and CO coverages on both the anode and cathode were followed using the  XANES technique at different regions of a DMFC during operation at several current levels in dependence on the oxygen flow. For the first time, a very strong “cross-talk” between the anode and cathode is seen with the anode dictating at high O2 flow rate the OH coverage on the cathode. The fuel starvation studies on the single DMFC cell revealed a non-uniform degradation pattern with a high degradation at the methanol inlet and low degradation at methanol outlet. Finally, shape-selected Pt nanoparticles were synthesized using different surfactants like tetradecyltrimethylammonium bromide (TTAB) and polyvinylpyrrolidone (PVP) and tested fuel cell performance. These shape-selected Pt nanoparticles were characterized by TEM and their electrocatalytical activity tested by cyclic voltammetry. High potential cycling of the shape-selected particles revealed a preferential degradation of Pt (100) facets over Pt (110). The TEM analysis of the cycled samples showed predominantly shape-selected particles with very few spherical particles. Finally, supported shape-selected particles showed excellent fuel performance even with low Pt loading. Tuning of the shape of Pt nanoparticles is expected to increase the Pt utilization, i.e. Pt loading can be reduced in the MEA. Further higher durability is expected for the shape-selected particles than the commercial catalyst. Thus by tuning the shape of the Pt nanoparticles, cost reduction and increased durability can be achieved.

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47

Hsu, Chun Ting, and 許鈞婷. "Manufacturing electrodes for direct methanol alkaline fuel cells." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/f4rrp5.

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48

Yo, Chia-Min, and 游嘉旻. "Titanium nitride-based electrodes for direct methanol fuel cells." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/32176577955935153532.

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碩士
國立中興大學
化學工程學系所
103
TiN is a transition metal compound which has inert nature, high electrical conductivity and corrosion resistance. In this study, platinum and palladium nanoparticles were successfully deposited on titanium nitride（TiN）and their electrocatalytic activities for methanol oxidation were investigated. The morphology of TiN was inspected by scanning electron microscope. The study include two parts, in part Ι, Pt nanoparticles supported on TiN were investigated as anode electrocatalytic materials for direct methanol fuel cells. The morphology and composition of the Pt/TiN were characterized by scanning electron microscopy, atomic force microscope, X-ray diffraction, and energy dispersive X-ray spectroscopy. The Pt/TiN showed a sharp hydrogen desorption peak at about -0.2 V vs. Ag/AgCl in a solution of 0.5 M H2SO4. In comparison with Vulcan XC-72-Pt modified glassy carbon electrode（Vulcan XC-72-Pt/GCE）, the Pt/TiN exhibited a high value of electrochemically active surface area（ECSA）and an excellent electrocatalytic activity for methanol electrooxidation reaction. The electrocatalytic properties of Pt/TiN for methanol electrooxidation were investigated by cyclic voltammetry in 2 M CH3OH + 1 M H2SO4 solution. The Pt/TiN showed a higher If/Ib value and a better stability than Vulcan XC-72-Pt/GCE. In partⅡ, Pd nanoparticles supported on TiN were investigated as anode electrocatalytic materials for direct methanol fuel cells in alkaline media. The morphology and composition of the Pd/TiN were characterized by scanning electron microscopy, atomic force microscope, X-ray diffraction, and energy dispersive X-ray spectroscopy.Cyclic voltammetry and chronoamperometry tests demonstrated that the Pd/TiN showed higher activity and stability for the methanol oxidation reaction in alkaline media than the Vulcan XC-72-Pd /GCE did.

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49

Hsu, Wei-Lun, and 徐偉倫. "Sensor-less concentration control for direct methanol fuel cells." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/4n9w3u.

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碩士
國立臺北科技大學
電機工程系研究所
97
In recent years, energy shortage becomes a serious problem. Many kinds of renewable energy are taken into consideration as alternatives. Among many new energy solutions, the hydrogen energy is perhaps the most ideal candidate. As a renewable, its by-product is the water and a little carbon dioxide. Among fuel cells, the direct methanol fuel cell (DMFC) is much emphasized for low power applications for example, 3C-products. The main issue of this thesis focuses on the power source management system and an effective method for maintaining methanol concentration, namely Voltage Double-Check Concentration Control (VDC3), will be proposed. VDC3 can decide the feeding timing of pure methanol to maintain the methanol concentration in a suitable range. The change of output voltage is affected by the loading current. An impermanent overshoot or undershoot phenomenon of output voltage is found when the load changes from low to high or high to low, respectively. The proposed decision maker VDC3 is developed according to these phenomena. Compared to the existed algorithm in the literature designed for constant load, this research proposes a sensor-less control algorithm for varied load. It considers the features of transient response caused by loading change. The proposed algorithm can judge whether the methanol concentration is insufficient and inject pure methanol at correct timing to maintain the methanol concentration in a suitable range.

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50

Liu, Tao-Chun, and 劉陶鈞. "Flexible Mini-Direct Methanol Fuel Cell." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/2h6sgp.

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