The experimental test and analysis of the direct methanol fuel cell (DMFC), which is made with a newly developed heterogeneous composite carbon fiber unipolar/bipolar plate, is performed in our lab. The work from the making of carbon fiber unipolar plate to the design of single-cell DMFC is also included in this study. The experimental work of various control parameters, such as methanol concentration, operating temperature, and the air flow rate, is also conducted in this thesis. The formation of carbon dioxide in anode is inspected during experiment. From a series of experimental test, we have understood the characteristics of DMFC better. The experimental result and experience can also provide the references of the application and development of DMFC in the future. According to our experiment, we find that the assembling of the new-type unipolar/bipolar plate doesn¡¦t need to use the large compressing force to reduce the contact resistance like those of the traditional unipolar/bipolar plates. The structure of the DMFC stack made with the new carbon fiber unipolar/bipolar plate is simple and weight light. However, the experimental results still show that the factors that affect the performance of the DMFC fuel cell are similar to those with the conventional unipolar/bipolar plates. For example, increasing the reactive temperature of fuel, proper methanol concentration, and proper content of catalyst all can effectively improve the power density of a DMFC. The structure of the methanol mixture directly stored in the flow channel of the anode is simple. However, the design exists the problems of the crossover of methanol, the stripping of the anode electrode, and the removal of the carbon dioxide. Special attention is needed to overcome and improve those problems in making DMFC stacks. Or the performance of the cell will decline after long period operation.

<p>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.</p><p>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.</p><p>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.</p><p>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.</p><p>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.</p><p>Keywords: direct methanol fuel cell, fuel cell, DMFC, anode,model</p>

Direct Methanol Fuel Cells (DMFC) provide an exciting alternative to current energy storage technologies for powering small portable electronic devices. For applications with sufficiently long durations of continuous operation, DMFC’s offer higher energy density, the ability to be refueled instead of recharged, and easier fuel handling and storage than devices that operate with hydrogen. At present, materials and manufacturing challenges impede performance and have prevented the entry of these devices to the marketplace. Higher-performing, cost-effective materials and efficient manufacturing processes are needed to enable the commercialization of DMFC. In a DMFC, the methanol-rich fuel stream and the oxidant are isolated from one another by a proton-conducting and electrically insulating membrane. Catalysts in the electrodes on either side of the Membrane Electrode Assembly (MEA) promote the two simultaneous half-reactions which allow the chemical energy carried in the fuel and oxidant to be converted directly into electricity. The goal of this research effort is to develop a continuous manufacturing process for the fabrication of effective DMFC MEAs. Based on the geometry of the electrode and materials used in the MEA, we propose a roll-to-roll process in which electrodes are coated onto a suitable substrate and subsequently assembled to form a MEA. Appropriate coating methods for electrode fabrication were identified by evaluating the requirements of continuous manufacturing processes; an appropriate set of these processes was then reduced to practice on a custom-designed flexible test bed designed explicitly for this project. After establishing baseline capabilities for several candidate methods, a spraying process was selected and a continuous manufacturing process concept was proposed. Finally, key control parameters of the spraying process were identified and their influence tested on actual MEAs to define optimal operating conditions. / text

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</style><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal" / mso-tstyle-rowband-size:0 / mso-tstyle-colband-size:0 / mso-style-noshow:yes / mso-style-priority:99 / mso-style-qformat:yes / mso-style-parent:"" / mso-padding-alt:0in 5.4pt 0in 5.4pt / mso-para-margin-top:0in / mso-para-margin-right:0in / mso-para-margin-bottom:10.0pt / mso-para-margin-left:0in / line-height:115% / mso-pagination:widow-orphan / font-size:11.0pt / font-family:"Calibri","sans-serif" / mso-ascii-font-family:Calibri / mso-ascii-theme-font:minor-latin / mso-fareast-font-family:"Times New Roman" / mso-fareast-theme-font:minor-fareast / mso-hansi-font-family:Calibri / mso-hansi-theme-font:minor-latin / mso-bidi-font-family:"Times New Roman" / mso-bidi-theme-font:minor-bidi / } </style> <![endif]--><span style="font-size: 12pt / font-family: &quot / Times New Roman&quot / ,&quot / serif&quot / ">The objective of this study was thus to prepare highly proton condictivity membranes that are cheap to manufacture and have low methanol permeability. &nbsp / &nbsp / </span></p>

<p>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.</p>

Philosophiae Doctor - PhD / 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. / South Africa

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

>Magister Scientiae - MSc / Fuel cells are widely considered to be efficient and non-polluting power source offering much higher energy density. This study is aimed at developing oxygen reduction reactions (ORR) catalysts with reduced platinum (Pt) loading. In order to achieve this aim, monometallic Pd and Pt nanostructured catalysts were electrodeposited on a substrate (carbon paper) by surface limited redox replacement using electrochemical atomic layer deposition (ECALD) technique. Pd:Pt bimetallic nanocatalysts were also deposited on carbon paper. Pd:Pt ratios were (1:1, 2.1 and 3:1). The prepared mono and bimetallic catalysts were characterized using electrochemical methods for the ORR in acid electrolyte. The electrochemical characterization of these catalysts includes: Cyclic Voltammetry (CV) and linear sweep voltammetry (LSV). The physical characterization includes: scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) for Morphology and elemental composition, respectively. The deposition of copper (Cu) on carbon paper was done by applying a potential of -0.05 V at 60s, 90s and 120s. 8x cycles of Pt or Pd showed better electrochemical activity towards hydrogen oxidation reaction. Multiples of eight were used in this work to deposit Pt: Pd binary catalyst. Cyclic voltammetry showed high electroactive surface area for Pt24Pd24/Carbon-paper while LSV showed high current density and positive onset potential. HRSEM also displayed small particle size compared to other Pt:Pd ratios.

As the world begins to focus more and more on new and more effective means of energy production, fuel cells become increasingly more popular. While different fuel cells are already found in industry today, the direct methanol fuel cell (DMFC) is becoming an increasingly more probable means for portable power production. In such applications a passive air breathing direct methanol fuel cell would be ideal. However, successful use of the passive DMFC in such applications requires that the fuel cell be capable of operating at various temperatures and relative humidities. A passive air breathing direct methanol fuel cell was developed and manufactured for this study. This work studied the effects of varying relative humidity and temperature over a probable range of operating conditions for small scale portable power applications on the performance of the fuel cell, both in relation to power production and fuel consumption. Potentiostatic, electrochemical impedance spectroscopy, and polarization tests were performed in order to characterize the performance of the fuel cell. Additionally, a one dimensional steady state isothermal mass transport model was developed to provide insight to the behavior of the fuel cell. The experimental data and model results show that increasing the fuel cell temperature and decreasing the ambient relative humidity increases the current production capabilities of the fuel cell. Further, the experimental data suggests that the major problem hindering current production in passive air breathing direct methanol fuel cells is flooding of the cathode diffusion layer. / Master of Science

The demand for higher efficiency and cleaner power sources increases daily. The Direct Methanol Fuel Cells (DMFC) is one of those power sources that produces reliable electrical energy at high efficiencies and very low pollution levels. Remote telecommunication sites need power sources that can deliver reliable power. This dissertation informs the reader about the working principles of the DMFC and the materials it consists of. A good amount of theoretical background is also given on the DMFC, especially on the Membrane Electrode Assembly (MEA). Different membranes as well as their properties are discussed. Results from other researchers on DMFCs are also captured. A DMFC stack including a test rig, was built. The DMFC stack consisted of five single DMFC cells. Each cell contained an MEA, Gas Diffusion Layers (GDLS), highly corrosive resistant metal support grids, bipolar flow field plates and end plates. The DMFC stack was operated and tested in a test rig. The test rig held the air blower which supplied the cathode with the required oxidant (air), and the methanol solution tank plus its liquid pump. The liquid pump circulated the methanol solution through the anode side of the stack. It was observed that the DMFC is very susceptible to corrosion, especially if the methanol solution becomes conductive owing to solubility of C02 in it. Methanol itself is a corrosive substance. However the results obtained from the experiments clearly indicate that the DMFC can be implemented as an electrical power source for telecommunications.