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.

Several disadvantages in general unipolar/bipolar plates are that cost is expensive, weight is heavy and the volume is large. The high compressing pressure is also necessary to reduce the contact resistance in making up a fuel cell stack. Therefore, it is difficult in making use general unipolar/bipolar plates to portable fuel cells. With a new heterogeneous carbon fiber bipolar plate, pumpless and air-breathing design and in cooperating with a special MEA, a portable fuel cell stacks developed in our lab have made portable applications to be possible. The structure of the DMFC stack made with the new carbon fiber bipolar plate is much more simple and weight-light than the other designs. The three portable DMFC stacks flat type, cylinder type (I), and cylinder type (II) are developed in series in our lab. The methanol solution can be stored directly in the flow channel of the anode, and does not need the extra auxiliary equipment, so it easy to apply to the portable fuel cell. The developed portable DMFC of cylinder type (II), weight is only 20g, volume is 30cm3, and the fuel stored capacity is 7.5ml. In the flat type DMFC, In anode Pt-Ru loading 3 mg/cm2, and cathode Pt loading 1 mg/cm2, methanol concentration 3 M, pumpless, air-breathing, and room temperature, the largest of output power density of the fuel cell can reach 5.27 mW/cm2, and the total power can reach 71 mW. The weight of DMFC of cylinder type (II) is far lower than DMFC of flat type in addition, so its power density 1.33mW/g is about 1.68 times of flat type 0.79 mW/g.

In this thesis heterogeneous bipolar plates are applied to pure hydrogen PEMFC (called HFC) stacks. The experimental methods are adopted to study the performance and characteristics of the cell under certain operational conditions. In order to obtain the permeability of carbon fiber bipolar plates the pressure drops and flow rates are measured on the two sides of the carbon fiber bunch. A test device has been developed to separate the gas of the two sides so that the gas can only flow through the gaps between carbon fibers. Additionally, the gas pressures on the flow channel and the output voltage of each cell in several locations are measured to help us to understand their relationships. The flow characteristics of the gas reactants in these carbon fiber bipolar plates can also be understood from these measurements. A bipolar plate with the parallel or serpentine flow channel can be formed by properly arranging the carbon fiber bunches. However, if the oxidizer is air and only single inlet and outlet in cathode chamber are designed, the oxidizer can always not be supplied sufficiently in high power density. The experimental studies display that the output voltages of cells in the midstream or downstream are far below the output voltage in the upstream. The voltage of cells in the upstream is the highest, the next one is in the downstream, and the lowest one is located in the midstream due to accumulating of nitrogen. The insufficiency of oxidizer occurs more seriously in the parallel flow channel than that in serpentine flow channel in single inlet and outlet design. The distribution of current is not uniform especially near midstream, although this phenomenon can be improved by increasing the air inlet pressure. However, the problems are hard to solve in large MEA if we just increase the inlet pressure. Another strategy is needed to solve this problem. In order to solve the insufficient supply of air in single inlet and outlet design, multiple inlets and outlets are designed. In this design multiple entries can supply enough fresh air driven by fan, and multiple exits can exhaust inert gas by exhausting fan to avoid accumulating in a reactive chamber so that the performance of stack can be improved dramatically.

In this thesis the experimental method is used to study the characteristics of a DMFC when a heterogeneous carbon fiber bipolar plate is applied to it. The first main study is about the effect of the different structures of the carbon fiber bunch on the fuel cell performance. Additionally, a high temperature hot-pressing process is performed to change the inner molecular structure so that the hydrogen ion can be blocked to avoid the lateral migration between two adjacent cells. Finally, the two techniques are applied to make our new portable DMFC stack. The bipolar plates with the sawtooth or non-sawtooth carbon fiber bunches have been used in making our DMFC stack. The experimental results display that the performances of the two structures both are better than the traditional graphite bipolar plate. However, the performance of DMFC with the sawtooth bipolar plate is much better than that without sawtooth, especially in high current density. When carbon fiber bunches with sawtooth use at anode and cathode of bipolar plates, the performance can be enhanced and its power density 27.6% higher than that without sawtooth. During our study we also found that part of hydrogen ions can laterally migrate to its adjacent cathode and do not directly cross to its opposite cathode, when the banded type MEA are used to multiple cell stack. Therefore, the performance cannot be performed well due to this type ion transfer. In order to block the lateral migration, the narrow area of the membrane between two adjacent electrodes is pressed with a high temperature hot-pressing device. After a short time hot-press between two adjacent electrodes, the hydrogenion migration phenomenon reduced, and the performance had been improved about 10% higher than that without hot-press. Finally, a double layer 2x6-cell flat type DMFC is made. This 12-cell stack is composed of each electrode area 0.5x5cm2, two sheets of membrane for 6-cell using Nafion 117, the anode catalyst Pt-Ru loading 4mg/cm2, and cathode catalyst Pt loading 4mg/cm2, the methanol concentration 3M, air-breathing, and operating in room temperature. The output power of the cell can reach an average power density 8.0mW/cm2 and total power 240mW with our handmade stack. If the performance of each fuel cell is more uniform, we expect that total power can reach 480 mW. The power level should be satisfied for any kind mobile phone.

Abstract Ammonia is one of valuable chemicals which are commonly used in various industrial factors. It is also a typical pollutant, and has a long-term impact on human health for toxicity characteristics. This study was to investigate the performance, product selectivity and kinetics in oxidation of ammonia solution in WAO process over Cu/ACF catalyst. The operation parameters in continuous WAO process were performed as follows: initial concentration of ammonia in ranging from 200 ppm to 1000 ppm, pH at 12, velocity of influent at below 3.0 ml/min, temperature ranging from 443K to 463K and pressure at 3.0 MPa. In the experiments of catalyst selection, we decided to use 5% Cu/ACF catalyst for its high conversion and selectivity in oxidation of ammonia. A conversion of 95.42% in oxidation of ammonia was achieved under 463K and the product selectivity of N2 was raised from 53% to 85%. We found that Cu/ACF and ACF catalysts both had the good conversion and selectivity in oxidation of ammonia in WAO process. In the long-term test of catalyst stability, Cu/ACF had a bad stability after 48 hours reaction in WAO process. The tests such as XRD, SEM and EA were also determined. The kinetics of WAO over Cu/ACF catalyst in oxidation of ammonia using Power-Rate Law was presented. The apparent reaction order and activated energy were obtained.

In this work the conditions for which a (0,90,90,0,0,90)s BMI-carbon fiber laminate will initiate transverse microcracking are determined for the fabrication of a cryogenic fuel tank for use in a Reusable Launch Vehicle (RLV). This is accomplished using a quadratic interaction criterion failure analysis on the total stress state at possible launch conditions. There are three major sources of stress, that is, thermal residual stress, internal pressure stress, and applied load stress, that are evaluated at the launch stage to determine the total stress state. To assess the accuracy of the analysis the well known X-33 cryogenic fuel tank failure was analyzed as an example. The results of the X-33 example show that the analysis accurately portrays the failure of the X-33 and provides evidence that the analysis can be used to provide reliable conditions for the initiation of microcracking. The final result of this study is a range of launch conditions that can be used without the initiation of microcracking and a limiting range of conditions that cause complete microcracking throughout the laminate.

The performance characteristics of pure hydrogen PEMFC (called HFC) stacks made with heterogeneous carbon fiber bipolar plates are studied in this thesis. In addition, the problem that the heterogeneous carbon fiber bipolar plate leaks in the high gas pressure is also solved in this studies so that the new plate can be used to the high current power sources. Because of the gas leakage of the first generation stack at high inlet gas pressure, the fuel supply is insufficient in the high current density. A 4-cell PEMFC stack made with this new bipolar plate is built with weight 370 g and volume 385 cm3 without a fan. The total power out of the 4-cell stack is about 30 W at room temperature. The specific power and volumetric power densities are 81 mW/g and 78 mW/cm3, respectively. The average power density is about 160 mW/cm2, but the power density of a single-cell can reach a value about 220 mW/cm2. The insufficient fuel supply cause that the power density of 4-cell PEMFC stack is lower than single cell, so it is necessary to solve the gas leakage at high pressure. Our experiment found that gas leakage occurs in heterogeneous bipolar plates can be relate to the insufficient or improper hot-pressing temperature, time and pressure while we are making the carbon fiber bunches. So the processes in making new carbon fiber bunches include water expansion, uniform glue adding, high hot-pressing pressure, and using proper temperature and enough solidification time. The airtight of the second generation of heterogeneous carbon fiber bipolar plates improves obviously with the new processes. No leakage occurs for gas pressure under 1atm. We expect that this design can be used to high inlet pressure. It is also quite suitable for various high-power electrical sources.

The effects of the structure of new carbon fiber bunch heterogeneous unipolar plates on the performance of PEMFC are studied in this thesis. Internal structure of carbon fiber bunches can be modified by embedding different thickness or number of copper plates in the glue bonding area to increase the air permeability of carbon fiber bunches in its soft end. We can add different thickness or amount of coppers at the middle of bonding area, making the carbon fiber bunches soft side to form parallel to the longitudinal fiber bunch with a small flow channel. We can also make a trench at the appropriate place of the soft side of the carbon fiber bunches to form an extra air passage. In order to make the above flow channel, a new process for making the carbon fiber bunches is developed also. This process will be easier to produce a variety of different structures of carbon fiber bunch. Finally, several different experiments are performed to help us to understand the effect of the carbon fiber bunch structure on the performance and find out the best structure of the carbon fiber bunches. The carbon fiber bunch structures of the test cells on the anode side are all the same, but the carbon fiber bunch structures of on cathode side are all different. Experiments show that there are two structures among all test structures displayed better gas permeability. The first one is two 0.2 mm copper plates embedded within both sides of the glue ends of a cathode carbon fiber bunch, so that a small longitudinal flow channel are formed in soft end of the cathode carbon fiber bunch. When the HFC operates at room temperature and by air-breathing, the highest performance of the HFC can reach a value of 185 mW/cm2. The second one is a 0.2 mm copper plate embedded in the center of the glue end of a carbon fiber bunch, and then three 2 mm wide serrated slots are cut on the soft end of the carbon fiber bunch. The highest performance of the HFC can reach a value of 190 mW/cm2. The highest performance of the HFC with no copper plate and no slot structure can only reach a value 160 mW/cm2. The second design can increase the no structure cell performance 18.8%. Therefore, the internal structures of carbon fiber bunches are significant to affect on the fuel cell performance, and its internal design must be considered.

In this paper a proton exchange membrane fuel cell (called PEMFC) stack was developed to power or charge 3C products without any voltage transformer. PEMFC stacks made with traditional bipolar plates to generate a high voltage are usually by accumulating multiple single fuel cells together. The design with traditional heavy and large bipolar plates is inconvenient for 3C products to generate a high voltage in a finite volume. To solve this problem, a heterogeneous carbon fiber bunch unipolar plate is adopted to replace traditional bipolar plates, and a special membrane electrode assembly (called MEA) with multiple sets of banded electrodes is used to replace a traditional MEA that is made with only a set electrodes. With this new design, the fuel cell voltage can easily increase in a layer. The designed stack can provide multiple voltages and currents by proper series and/or parallel connections. The variable voltage 16-cell fuel cell is composed of 4-layer 4-banded type MEAs and 5 heterogeneous carbon fiber bunch bipolar plates. The 16-cell stack is divided into 4 sets. Each set of 4 series connection cell is arranged in a line in 4 different layers. The 4-cell sets can connect by series/parallel on the two ends of the stack. The total volume of the 16-cell stack is 385cm3 and its weight is 365g. The new design can power or charge certain 3C products directly. If 2 sets of 4-cell fuel cells are connected in series, the stack can provide 2A at 3.6V. With the above 2 sets of 2*4-cell connected in parallel, the stack can provide 3.5A at 3.6V. If the 4 sets of 4-cell are all connected in series, the stack can provide 1.8 A at 7.2V. These voltages and currents derived from these stacks can power or charge a mobile phone, a photo camera and a video camera directly. If a higher voltage or current are needed, two or more 16-cell stacks can be connected in series XI or parallel. Then notebooks or any other 3C products in which higher power are needed can be driven.

<p>The exploitation of sandwich structures as a means toachieve high specific strength and stiffness is relatively new.Therefore, the knowledge of its damage tolerance is limitedcompared to other structural concepts such as truss bars andmonocoque plate solutions.</p><p>Several aspects of the damage tolerance of sandwichstructures are investigated. The influence of impact velocityonresidual strength is investigated. Sandwich panels withfaces of glass fiber reinforced vinylester are impacted bothwith very high velocity and quasi static. The residual strengthafter impact is found to be similar for both cases of impactvelocity.</p><p>Curved sandwich beams subjected to opening bending momentare studied. Faceñcore debonds of varying size areintroduced between the compressively loaded face sheet and thecore. Finite element analysis in combination with a pointstress criterion is utilized to predict the residual strengthof the beams. It is shown that it is possible to predict thefailure load of the beams with face-core debond.</p><p>Using fractography the governing mode of failure ofcompressively NCF-carbon is characterized. Sandwich panelssubjected to compression after impact are shown to fail byplastic micro buckling.</p><p>The residual compressive strength after impact of sandwichpanels is investigated. Sandwich panels with face sheets ofnon-crimp fabric (NCF) carbon are subjected to different typesof impact damages. Predictions of residual strength are madeusing the Budiansky, Soutis, Fleck (BSF) model. The residualstrength is tested, and the results are compared topredictions. Predictions and tests correlate well, and indicatethat the residual strength is dependent on damage size and notthe size of the damaged panel.</p><p>A study of the properties of a selection of fiberreinforcements commonly used in sandwich panels is conducted.The reinforcements are combined with two types of core materialand three types of matrix. Also the influence of laminatethickness is tested. Each combination materials is tested inuni-axial compression, compressive strength after impact andenergy absorption during quasi static indentation. Thespecimens which are tested for residual strength are eithersubjected to quasi-static or dynamic impact of comparableenergy level. Prediction of the residual strength is made andcorrelates reasonably whith the test results. The tests showthat if weight is taken into account the preferred choice offiber reinforcement is carbon.</p>