Water plays an important role in the operation of Fuel Cell. It determines where the electrochemical reactions should or should not occur. The purpose of this study is to investigate the transport characteristics of vapor through all components of an electrode and how they are related to the cell performance. In the transmit experiment of cell produce water which prove the level of water steam transmission characteristics has relative relations with the measurements of water transport in fuel cell. In a sum, the electrode with higher water steam transmission characteristics, the measurement of water transport will also be higher. From cell performance measure experiment, we can found that water steam transmission characteristics have the opposite relation with the concentration loss¡]mass transfer behavior¡^. As cell working on high current density, water will not clog easily under the great quality transmit electrode. Further, catalyst layer that has enough concentration would not cause the cell performance dismiss with the follow up reactions and it represents that cell performs batter with mass transfer. According to the experiment, PTFE in MPL with smaller amount has better performance to fuel cell. What the differences between the presentation of water as liquid state or gaseous state when it transmits in electrode? We can discover the rate of gaseous state water is faster compared to liquid state water when transmitting through MEA in a simple experiment. We assume that gaseous state of water is the first type within the electrode.

An investigation was performed to demonstrate system design for the delivery of water required for evaporative cooling of a proton exchange membrane fuel cell (PEMFC). The water delivery system uses spray nozzles capable of injecting water directly and uniformly to the nickel metal foam flow-field (element for distributing the reactant gases over the surface of the electrodes) on the anode side from which water can migrate to the cathode side of the cell via electroosmotic drag. For an effective overall cooling, water distribution over the surface of the nickel foam has to be uniform to avoid creation of hotspots within the cell. A prototype PEMFC structure was constructed modeled after a 35 kW electrical output PEMFC stack. Water was sprayed on the nickel metal foam flow-field using two types of nozzle spray, giving conical fog type flow and flat fan type flow. A detailed investigation of the distribution pattern of water over the surface of the nickel metal flow field was conducted. The motive behind the investigation was to determine if design parameters such as type of water flow from nozzles, vertical location of the water nozzles above the flowfield, area of the nozzles, or operating variables such as reactant gas flow had any effect on water distribution over the surface of the Ni-metal foam flow field. It was found that the design parameters (types of flow, area and location of the nozzle) had a direct impact on the distribution of water in the nickel metal foam. However, the operating variable, reactant gas flow, showed no effect on the water distribution pattern in the Ni-foam.

Abstract The objectives of the thesis are to study and research the function of the fuel cell¡¦s bipolar plate which is vital to the Proton Exchange Membrane fuel cell¡Aand to create a new bipolar plate composed of nonhomogeneous plate and conductive object which conductive object are put through light weight plastic plate in consideration of low cost¡Bmini size¡Blight weight and high efficiency¡Atogether with a series of test for its capability. Of the same section area¡Athe electric resistance of carbon fiber used in this experiment is lower than traditional graphite bipolar plate.According to related literature¡Athe resistant of the graphite bipolar plateis lower than the ones made of other materials or composite material.The carbon fiber is a suitable conductive object for bipolar plate consequently. Without leakage¡Athe material are stand the differential pressure up to 0.5 kg/cm2 through the leakage/pressure tests.It is good enough in most of practical application.The strength of bipolar plate to resist the differential pressure is related to the plate strength and the strength of bond¡Ainterface between bond and plate or bond and carbon fiber.The proper bond is very important in this case. The efficiency of fuel cell decreases rapidly in line with the increase of loading during the efficiency test of fuel cell and sudden drop portion situates at Ohm resistance domain.Other papers describe about the main factor of Ohm resistance domain is resistance loss¡Aparameter include conductive coefficient¡Barea of conductive material¡Blength of conductive material.The most different of experiment compare with previous is the area of conductive material.Therefore the area of conductive fiber in bipolar plate influences the efficiency of fuel cell a lot. Through the research¡Athe availability of the new bipolar plate composed of nonhomogeneous plate and conductive object is proven and the cause of its defect in efficiency is identified for improvement in practical application.

Abstract The experimental tests and analysis of single fuel cell unit are performance in this research, and the electrolyte in MEA(membrane and electrode assembly) we used Nafion 112.Accroding to change several design factors and operation conditions, we can find out how important the factors affect the PEMFC power output. The experimental conditions in this study are various of type of fasten torque, flow channels, oxidizers, catalyst type and loading in cathode side, materials of electron collector, inlet gas pressure and humidification of membrane. The results can provide us references to assemble a fuel cell stack in future. PEMFC can start quickly at low temperature and achieves stable output voltage. When the 4 N-m torque is applied to fasten the reaction chamber, the contact resistance between the electrode and electron collector reaches a minimum value. The results show that when the area ratio(Af /At)is 58.41%, we can have better ratio between channel areas and contact area, and the output can be larger. We found that increasing the loading of catalyst in the cathode, the power output rises up clearly, but the loading also has a limitation. By using gold to be the electron collector, the result shows that it has better performance than using graphite, but the price is also much higher. Our experiments display that use oxygen to be oxidizer can have better performance than use air. When we heated membrane in the water at 80¢J, it can resupply the water in the membrane, remain enough humidification of membrane can be clearly helpful to the PEMFC power output, because humidification can keep the proton conductivity of the membrane in good condition. And we also found while the hot press pressure at 160atm, the performance can be better than using other pressure. Key words : PEMFC¡BMEA¡BFlow area ratio

Producing more reaction regions on the PEMFC cathode using cavities with micro structures can be used to add more reaction points on the electrode. The original ladder type cavity is limited by the laser diffraction in its manufacture. The flat electrode has its performance improved for 58%. The energy density is increased from 462 mW/cm2 to 720mW/cm2. Pressure required in the micro-structure imprinting is reduced, so as the fuel transportation blocked by mold releasing. The total catalyst amount is cut from 0.5mg/cm2 to 0.25mg/cm2. No obvious performance drop can be found. This shows that most of the reactions happen in the region between catalyst layer and micro hole layer. Limited by the pattern of micro-structure, the electrospray does not perform as expected. In the future, this issue should be considered in making micro-structure.

This thesis discusses the effect of initial particle size and alloying of Pt nanocatalysts on the degradation of Proton Exchange Membrane Fuel Cells (PEMFC). Platinum nanocatalysts with initial particle sizes of 2.2nm, 3.2nm, 5.0nm, 6.7nm and 11.3nm were studied, before and after potential cycling. The two smallest initial particle sizes show significant degradation, while the remainder of the samples show negligible degradation after 10,000 cycles. Among the possible degradation mechanisms operating, the results show that dissolution and re-precipitation is insignificant among all the samples. On the other hand, modified electrochemical Ostwald ripening (MEOR) is the main cause for particle growth and degradation of the Pt nanocatalysts. Moreover, MEOR could also assist the coalescence of particles. Thus, controlling the Pt dissolution rate is the key factor to prevent degradation. In the case of Pt₃Co nanocatalysts, both MEOR as well as dissolution & reprecipitation play an irrelevant role in degradation. However, particle migration and coalescence seems to be more severe in Pt₃Co nanoparticles than for Pt nanoparticles. / text

Hydrogen fuel cells have held out the promise of clean, sustainable power generation for decades, but have failed to deliver on that potential. Inefficiencies in research and development work can be overcome to increase the rate of new knowledge acquisition in this field. A number of medical and engineering disciplines utilise a wide variety of statistical tools in their research to achieve this same end, but there has been little adoption of such statistical approaches within the fuel cell research community. This research undertakes a design of experiments (DoE) approach to the analysis of multiply-covarying (M-ANOVAR) factors by using historic data, and direct experimental work, on a wide variety of polymer electrolyte membrane fuel cells (PEMFCs) cathode gas diffusion media (GDM) and dual layered catalyst structures. This research developed a gradient of polarisation regions' approach; a method for making robust numerical comparisons between large numbers of samples based on polarisation curves, while still measuring the more usual peak power of the PEMFC. The assessment of polarisation gradients was completed in a statistically robust fashion that enabled the creation of regression models of GDMs for multiple input and multiple output data sets. Having established the multivariate method; a set of possibly co-varying factors, a DoE approach was used to assess GDM selection, dual layered catalyst structures and degradation of membrane electrode assembly (MEA) performance over time. Degradation studies monopolise resources to be monopolised for protracted periods. M-ANOVAR allows the addition of other factors in the study, and the total efficiency of the degradation experiment is increased. A 20% reduction in the number of samples to be tested was achieved in the case study presented in this thesis (compared to the usual one factor at a time (OFAT) approach). This research highlights the flexibility and efficiency of DoE approaches to PEMFC degradation experimentation. This research is unique in that it creates catalyst ink formulations where the variation in catalyst loading in each sub-layer of the catalyst layer (CL) was achieved by having a different concentration of the catalyst material on the carbon supports. The final M-ANOVAR analysis indicates a simple average of the individual responses was appropriate for the experiments undertaken. It was shown that low concentration dual layer catalysts on paper GDMs have improved performance compared to paper GDMs with uniform, single layer catalysts: Demonstrating reduced platinum concentrations to achieve equivalent open cell performance. The time to peak power during testing (how long after starting the test it takes to achieve the maximum performance in the cell) was strongly impacted by GDM selection. Furthermore, there was a strong suggestion that previously published results crediting a change in performance due to a single layer, or multi-layered catalyst structures may, in fact, have been due to the selection of GDM used in the experiment instead.

In this work, a micro-model of the catalyst layer of polymer electrolyte membrane fuel cell (PEMFC) was developed. The micro-model includes the transport phenomena and the reaction kinetics within a three dimensional micro-structure representing a sample of PEMFC catalyst layer. Proper physical boundary conditions have been described on the surfaces of the sample as well as on the interfaces between the regions through which all constituents are solved in a coupled manner. A four-phase micro-structure of CL was reconstructed, the platinum particles were resolved in the computational grid generation and the governing equations were solved within platinum region. A body-fitted computational mesh was generated for the reconstructed micro-structure of CL. The number of computational cells were optimized based on how close to an analytical sphere the magnitude of the surface area of a sphere can be captured after generating the computational cells. The interfaces with important physical phenomena were more refined than the rest of the interfaces, specially the electrochemically active reaction surface. The computational mesh was checked for a grid independent numerical solution. The Knudsen effects was included by calculating the characteristic length in the pore region. Four different cases of including Knudsen effects were studied. Also, a comparison was made between solution with and without Knudsen effects. A physical model of oxygen dissolution was developed, the oxygen dissolution at the interface between pore and ionomer was treated as an superficial phenomenon. The performance curves were produced and provided for the reconstructed micro-structure along with the distribution of field variables. A length study of the reconstructed micro-structure was conducted such that the results from the micro-modeling can capture the trend in variable distributions observed in the macro-modeling of CL or experiments. A platinum loading study was preformed and the anomalous phenomena of dramatic increase in oxygen transport resistance observed in some experimental works was explained by isolating the ionomer region of the CL micro-structure and numerically calculating the shape factor for diffusive transport. It was found that the increase in oxygen transport resistance is due to the increase in diffusion pathway and decrease in the transport surface area. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2013-03-06 15:55:21.564

Liquid water management in the cathode of polymer electrolyte membrane fuel cells (PEMFC) is crucial to efficient transport of gases and to maintaining electrochemical activity in the catalyst layer. Cracks and interfacial voids are typical of catalyst layers in operating cells, and are thought to affect water management and other transport properties such as gas diffusion and conductivity. This thesis investigates the effect of such morphological imperfections on liquid water transport using a combination of numerical techniques. Both the catalyst layer and microporous layer parts of the cathode are considered. The layers are first numerically reconstructed using data from advanced microscopy, and cracks, perforations and interfacial voids are created. Lattice Boltzmann simulations of the dynamics liquid water imbibition process are performed to study the effect of characterizing features of the cracks and interfacial voids such as aperture area, degree of protrusion, and tortuosity. The resulting liquid water distributions were then input into a pore scale model to characterize the effect of the morphological features on other transport properties, such as effective diffusivities and conductivities. Larger crack apertures were found to increase liquid water uptake, and elongated cracks allowed for faster breakthrough at lower saturation levels. A notable observation is that short and large interfacial cracks have a higher liquid water uptake potential due to the lower effective capillary pressures. It was also found that elongated cracks aligned with the pressure gradient provide preferential pathway, and a capillary pressure increase that favours liquid water transport towards the membrane and mitigates flooding. The effective diffusivity increased for all crack protrusion depths, even for the wet catalyst layer, likely due to low liquid water saturation. The geometry with the most elongated crack showed a significant increase in gas diffusion under wet conditions, indicating that enhanced gas transport is achievable when liquid water removal is effective. Protonic and electrical conductivities decreased for all crack shapes due to higher contact resistance. / Graduate / 0548 / vlosier@uvic.ca

In this thesis, a portable PEMFC stack, which can directly power or charge 3C products, will be developed. The stack is developed for portable applications, so the structure of the stack is simplified as possible as we can. The PEMFC stack is made with 32 carbon fiber bunches for current collectors and two 8-cell banded-type MEAs which are made with 8 sets of electrodes on a piece of membrane. The stack can develop a high voltage by serially connecting 8 cell or 16 cell outside of the reaction chamber. The resistance of each carbon bunch assembling with carbon cloth is measured before they are assembled into the stack. Under assembly pressure 3 bar, the total resistance is about 8.7m£[ or 11m£[¡Ecm2. The resistance is about one half of that graphite plate assembling with carbon cloth. Without being compressed greatly in diffusion layer, the fluid can easily flow through the gaps between carbon fiber and within diffusion layers, and then the reactive region will react more uniformly. In addition, the connecting wires are assembled to a wire collecting board, so that the stack is look more neat, and it easier assemble or dissemble. In this thesis, the volume of the developed 16-cell hydrogen fuel cell stack is about 9.6 cm*6.3 cm*2.2 cm. The total electrode area is 50 cm2 (16-cell¡Ñ3.15 cm2 per cell). When the stack is operating at room temperature and air-breathing, an 8-cell stack in series connection can generate 3.7V voltage. Its power at voltage 3.7V is about 3.6W. It can directly power PDAs, mobile phones or digital cameras. A 16-cell stack in series connection can generate 7.2V voltage. Its power at this voltage can offer 7W. The 16-cell stack can directly power digital single-lens reflex cameras. If two or more of this stack are connected in series, it will be able to power a notebook or other more power products.