M. Tech. (Engineering, Electrical, Department Applied Electronics and Electronic Communication, Faculty of Engineering and Technology) -- Vaal University of Technology / This dissertation presents the design and development of a remote monitoring system (RMS) for polymer electrolyte membrane fuel cells (PEMFC) to facilitate their efficient operation. The RMS consists of a data acquisition system built around the PIC 16F874 microcontroller that communicates with a personal computer (PC) by use of the RS232 serial communication standard, using a simple wired connection between the two. The design also consists of a human machine interface (HMI) developed in Visual Basic 6.0 to provide a platform for display of the monitored parameters in real time. The first objective was to establish performance variables and past studies on PEM fuel cells revealed that variables that affect the system's performance include: fuel and oxidant input pressure and mass flow rates as well as operation temperature and stack hydration. The next objective was to design and develop a data acquisition system (DAS) that could accurately measure the performance variables and convey the data to a PC. This consisted of sensors whose outputs were input into two microcontrollers that were programmed to process the data received and transfer it to the PC. A HMI was developed that provided graphical display of the data as well as options for storage and reviewing the data. The developed system was then tested on a 150Watt PEM fuel cell stack and the data acquisition system was found to reliably capture the fuel cell variables. The HMI provided a real-time display of the data, with alarms indicating when set minimums were exceeded and all data acquired was saved as a Microsoft Excel file. Some recommendations for improved system performance are suggested. / Vaal University of Technology -- National Research Foundations

Proton exchange membrane (PEM) fuel cells are an eco-friendly power source that has great potential to reduce our oil dependence for our stationary and transportation applications. In order to make PEM fuel cells an economically viable option, further effort is needed to improve proton conduction under wide operating conditions and reduce the cost of production. Design and synthesis of novel membranes that have superior characteristics require a fundamental molecular-level understanding of the relationship between the polymer chemistry, water content and proton conduction. The performance of a fuel cell is influenced by the electrochemical and molecular/proton transport processes that occur at the catalytic sites in the electrode/electrolyte interface. Therefore, understanding the molecular-level details of proton transport and structure of the multi-phase interfaces is critical. This work is subdivided into two main tasks. The first task is to model membrane/water vapor interfaces and to study their morphology and the transport properties of water and hydronium ions. Classical molecular dynamics simulation is used as the modeling tool for the characterization of the interface. The second task is to model proton transport through the aqueous domains of PEM. Such a model is inherently challenging since proton transport occurs through a combination of structural and vehicular diffusions that are associated with disparate time scales. Toward this end, we have developed and implemented a new reactive molecular dynamics algorithm to model the structural diffusion of proton that involves breaking and forming of covalent bonds. The proton transport through aqueous channels in PEM is governed by acidity and confinement. Therefore, systems in which the acidity and confinement can be independently varied, including bulk water, aqueous hydrochloric acid solutions and water confined in carbon nanotubes are also examined in addition to the application in PEM. We have developed an understanding of how acidity and confinement independently impact proton transport. The correlation between the two components of charge diffusion and their contribution to the total charge diffusion has also been explored for a basic understanding of the proton transport mechanisms. These studies will eventually help us establish the correlation between the morphology of the membrane and proton conduction.

In this work characterisation methods and fuel cell hardwarewere developed for studying the components of the polymerelectrolyte fuel cell (PEFC). Humidifiers and other componentswere tested in order to develop reproducible and reliableexperimental techniques. A set-up for testing larger cells andstacks was developed. A new type of polymer electrolyte membrane fuel cell wasdeveloped for laboratory investigations. Current collectormaterial and gas flow channels can easily be modified in thisconstruction. The electrode potentials can be measured at thegas backing layers, thereby allowing measurement of contactresistances. The use of a reference electrode is alsopossible. Contact resistances were studied in situ as a function oftime, clamping pressure, gas pressure and current density.Ex-situ measurements were used to validate the in-situ contactresistance measurements. The validity and error sources of theapplied in-situ measurement methods with reference electrodesand potential probes were studied using both computersimulations and experiments. An in-house membrane electrode assembly (MEA) productionline was developed. In-house produced MEAs were utilised inboth membrane degradation and mass transport studies. The durability testing of PVDF based membranes membranes wasstudied both by fuel cell experiments and ex-situ testing.Raman spectra were measured for used membranes. A current distribution measurement method was developed. Theeffect of inlet humidification and gas composition at thecathode side was studied. In addition, two different flow fieldgeometries were studied. The results of current distributionmeasurements were used to validate a PEFC model. Methods for characterising gas diffusion layer (GDL)performance by fuel cell testing and ex-situ measurements weredeveloped. The performance of GDL materials was tested withvarying cell compression and cathode humidity. Porosity, poresize distribution and contact angle were determined. Electricalcontact resistance, thermal impedance and gas permeabilitieswere measured at different compression levels. Development work on a stack with stainless steel net wascarried out as well as characterisation studies of differentstack components. Thermal impedances and flow fieldpermeability were measured. Mass transport limitations in the cathodes were studied byvarying the electrode thickness, partial pressure and humidityof oxygen. <b>Keywords:</b>polymer electrolyte membrane fuel cell (PEFC),contact resistance, clamping pressure, stainless steel,membrane degradation, current distribution, gas diffusionlayer, stack, thermal impedance, permeability.

This project is aimed at developing and demonstrating highly conductive, lightweight, and low-cost thermoplastic blends to be used as flow field bipolar plates for polymer electrolyte membrane (PEM) fuel cells. <br><br> The research is focused on designing, prototyping, and testing carbon-filled thermoplastic composites with high electrical conductivity, as well as suitable mechanical and process properties. <br><br> The impact of different types of fillers on the composite blend properties was evaluated, as well as the synergetic effect of mixtures of fill types within a thermoplastic polymer matrix. A number of blends were produced by varying the filler percentages. Composites with loadings up to 65% by weight of graphite, conductive carbon black, and carbon fibers were investigated. Research results show that three-filler composites exhibit better performance than single or two-filler composites. <br><br> Injection and compression molding of the conductive carbon filled polypropylene blend was used to fabricate the bipolar plates. A Thermal Gravimetric Analysis (TGA) was used to determine the actual filler loading of composites. A Scanning Electron Microscope (SEM) technique was use as an effective way to view the microstructure of composite for properties such as edge effects, porosity, and fiber alignment. Density and mechanical properties of conductive thermoplastic composites were also investigated. During this study, it was found that 1:1:1 SG-4012/VCB/CF composites showed better performance than other blends. The highest conductivity, 1900 S/m in in-plane and 156 S/m in through plane conductivity, is obtained with the 65% composite. Mechanical properties such as tensile modulus, tensile strength, flexural modulus and flexural strength for 65% 1:1:1 SG-4012/VCB/CF composite were found to be 584. 3 MPa, 9. 50 MPa, 6. 82 GPa and 47. 7 MPa, respectively, and these mechanical properties were found to meet minimum mechanical property requirements for bipolar plates. The highest density for bipolar plate developed in this project is 1. 33 g/cm³ and is far less than that of graphite bipolar plate. <br><br> A novel technique for metal insert bipolar plate construction was also developed for this project. With a copper sheet insert, the in-plane conductivity of bipolar plate was found to be significantly improved. The performance of composite and copper sheet insert bipolar plates was investigated in a single cell fuel cell. All the composites bipolar plates showed lower performance than the graphite bipolar plate on current-voltage (I-V) polarization curve testing. Although the copper sheet insert bipolar plates were very conductive in in-plane conductivity, there was little improvement in single cell performance compared with the composite bipolar plates. <br><br> This work also investigated the factors affecting bipolar plate resistance measurement, which is important for fuel cell bipolar plate design and material selection. Bipolar plate surface area (S) and surface area over thickness (S/T) ratio was showed to have significant effects on the significance of interfacial contact resistances. At high S/T ratio, the contact resistance was found to be most significant for thermoplastic blends. Other factors such as thickness, material properties, surface geometry and clamping pressure were also found to affect the bipolar plate resistance measurements significantly.

This project is aimed at developing and demonstrating highly conductive, lightweight, and low-cost thermoplastic blends to be used as flow field bipolar plates for polymer electrolyte membrane (PEM) fuel cells. <br><br> The research is focused on designing, prototyping, and testing carbon-filled thermoplastic composites with high electrical conductivity, as well as suitable mechanical and process properties. <br><br> The impact of different types of fillers on the composite blend properties was evaluated, as well as the synergetic effect of mixtures of fill types within a thermoplastic polymer matrix. A number of blends were produced by varying the filler percentages. Composites with loadings up to 65% by weight of graphite, conductive carbon black, and carbon fibers were investigated. Research results show that three-filler composites exhibit better performance than single or two-filler composites. <br><br> Injection and compression molding of the conductive carbon filled polypropylene blend was used to fabricate the bipolar plates. A Thermal Gravimetric Analysis (TGA) was used to determine the actual filler loading of composites. A Scanning Electron Microscope (SEM) technique was use as an effective way to view the microstructure of composite for properties such as edge effects, porosity, and fiber alignment. Density and mechanical properties of conductive thermoplastic composites were also investigated. During this study, it was found that 1:1:1 SG-4012/VCB/CF composites showed better performance than other blends. The highest conductivity, 1900 S/m in in-plane and 156 S/m in through plane conductivity, is obtained with the 65% composite. Mechanical properties such as tensile modulus, tensile strength, flexural modulus and flexural strength for 65% 1:1:1 SG-4012/VCB/CF composite were found to be 584. 3 MPa, 9. 50 MPa, 6. 82 GPa and 47. 7 MPa, respectively, and these mechanical properties were found to meet minimum mechanical property requirements for bipolar plates. The highest density for bipolar plate developed in this project is 1. 33 g/cm³ and is far less than that of graphite bipolar plate. <br><br> A novel technique for metal insert bipolar plate construction was also developed for this project. With a copper sheet insert, the in-plane conductivity of bipolar plate was found to be significantly improved. The performance of composite and copper sheet insert bipolar plates was investigated in a single cell fuel cell. All the composites bipolar plates showed lower performance than the graphite bipolar plate on current-voltage (I-V) polarization curve testing. Although the copper sheet insert bipolar plates were very conductive in in-plane conductivity, there was little improvement in single cell performance compared with the composite bipolar plates. <br><br> This work also investigated the factors affecting bipolar plate resistance measurement, which is important for fuel cell bipolar plate design and material selection. Bipolar plate surface area (S) and surface area over thickness (S/T) ratio was showed to have significant effects on the significance of interfacial contact resistances. At high S/T ratio, the contact resistance was found to be most significant for thermoplastic blends. Other factors such as thickness, material properties, surface geometry and clamping pressure were also found to affect the bipolar plate resistance measurements significantly.

Polymer electrolyte membrane fuel cells (PEMFCs) have the potential to play a major role as energy generators for transportation and portable applications. One of the current barriers to their commercialization is the cost of the components and manufacturing, specifically the bipolar plates. One approach to preparing PEMFCs for commercialization is to develop new bipolar plate materials, related to mass production of fuel cells. Thermoplastic/carbon filler composites with low filler loading have a major advantage in that they can be produced by a conventional low-cost injection molding technique. In addition, the materials used are inexpensive, easy to shape, and lightweight. An optimal bipolar plate must possess high surface and bulk electronic conductivity, sufficient mechanical integrity, low permeability, and corrosion resistance. However, it is difficult to achieve high electrical conductivity from a low-cost thermoplastic composite with low conductive filler loading. Concerns over electrical conductivity improvement and the injection processability of composites have brought forth the idea of producing a polypropylene/three-carbon-filler composite for bipolar plate application. The thesis addresses the development of synergistic effects of filler combinations, investigating composite conductive materials and using composite bipolar plate testing in PEMFCs. One significant effect of conductive network formation is the synergetic effects of different carbon filler sizes, shapes, and multiple filler ratios on the electrical conductivity of bipolar plate materials. A polypropylene resin combined with low-cost conductive fillers (graphite, conductive carbon black, and carbon fibers with 55 wt% of filler loading) compose the main composite for all investigations in this research. Numerous composite formulations, based on single-, two-, and three-filler systems, have been created to investigate the characteristics and synergistic effects of multiple fillers on composite conductivity. Electrical conductivity measurements corresponding to PEMFC performance and processing characteristics were investigated. Experimental work also involved other ex-situ testing for the physical requirements of commercial bipolar plates. All combinations of fillers were found to have a significant synergistic effect that increased the composite electrical conductivity. Carbon black was found to have the highest influence on the increase of electrical conductivity compared to the other fillers. The use of conjugated conducting polymers such as polypyrrole (PPy) to help the composite blends gain desirable conductivities was also studied. Electrical conductivity was significantly improved conductivity by enriching the conducting paths on the interfaces between fillers and the PP matrix with PPy. The conductive network was found to have a linkage of carbon fibers following the respective size distributions of fibers. The combination of Fortafil and Asbury carbon fiber mixture ameliorated the structure of conductive paths, especially in the through-plane direction. However, using small fibers such as carbon nanofibers did not significantly improve in electrical conductivity. The useful characteristics of an individual filler and filler supportive functions were combined to create a novel formula that significantly improved electrical conductivity. Other properties, such as mechanical and rheological ones, demonstrate the potential to use the composites in bipolar plate applications. This research contributes a direction for further improvement of marketable thermoplastic bipolar plate composite materials.

It is desirable to increase the operation temperature of proton exchange membrane fuel cells above 100oC due to fast electrode kinetics, high tolerance to fuel impurities and simple thermal and water management. In this study / the objective is to develop a high temperature proton exchange membrane fuel cell. Phosphoric acid doped polybenzimidazole membrane was chosen as the electrolyte material. Polybenzimidazole was synthesized with different molecular weights (18700-118500) by changing the synthesis conditions such as reaction time (18-24h) and temperature (185-200oC). The formation of polybenzimidazole was confirmed by FTIR, H-NMR and elemental analysis. The synthesized polymers were used to prepare homogeneous membranes which have good mechanical strength and high thermal stability. Phosphoric acid doped membranes were used to prepare membrane electrode assemblies. Dry hydrogen and oxygen gases were fed to the anode and cathode sides of the cell respectively, at a flow rate of 0.1 slpm for fuel cell tests. It was achieved to operate the single cell up to 160oC. The observed maximum power output was increased considerably from 0.015 W/cm2 to 0.061 W/cm2 at 150oC when the binder of the catalyst was changed from polybenzimidazole to polybenzimidazole and polyvinylidene fluoride mixture. The power outputs of 0.032 W/cm2 and 0.063 W/cm2 were obtained when the fuel cell operating temperatures changed as 125oC and 160oC respectively. The single cell test presents 0.035 W/cm2 and 0.070 W/cm2 with membrane thicknesses of 100 &micro / m and 70 &micro / m respectively. So it can be concluded that thinner membranes give better performances at higher temperatures.

<p>In this work characterisation methods and fuel cell hardwarewere developed for studying the components of the polymerelectrolyte fuel cell (PEFC). Humidifiers and other componentswere tested in order to develop reproducible and reliableexperimental techniques. A set-up for testing larger cells andstacks was developed.</p><p>A new type of polymer electrolyte membrane fuel cell wasdeveloped for laboratory investigations. Current collectormaterial and gas flow channels can easily be modified in thisconstruction. The electrode potentials can be measured at thegas backing layers, thereby allowing measurement of contactresistances. The use of a reference electrode is alsopossible.</p><p>Contact resistances were studied in situ as a function oftime, clamping pressure, gas pressure and current density.Ex-situ measurements were used to validate the in-situ contactresistance measurements. The validity and error sources of theapplied in-situ measurement methods with reference electrodesand potential probes were studied using both computersimulations and experiments.</p><p>An in-house membrane electrode assembly (MEA) productionline was developed. In-house produced MEAs were utilised inboth membrane degradation and mass transport studies.</p><p>The durability testing of PVDF based membranes membranes wasstudied both by fuel cell experiments and ex-situ testing.Raman spectra were measured for used membranes.</p><p>A current distribution measurement method was developed. Theeffect of inlet humidification and gas composition at thecathode side was studied. In addition, two different flow fieldgeometries were studied. The results of current distributionmeasurements were used to validate a PEFC model.</p><p>Methods for characterising gas diffusion layer (GDL)performance by fuel cell testing and ex-situ measurements weredeveloped. The performance of GDL materials was tested withvarying cell compression and cathode humidity. Porosity, poresize distribution and contact angle were determined. Electricalcontact resistance, thermal impedance and gas permeabilitieswere measured at different compression levels.</p><p>Development work on a stack with stainless steel net wascarried out as well as characterisation studies of differentstack components. Thermal impedances and flow fieldpermeability were measured.</p><p>Mass transport limitations in the cathodes were studied byvarying the electrode thickness, partial pressure and humidityof oxygen.</p><p><b>Keywords:</b>polymer electrolyte membrane fuel cell (PEFC),contact resistance, clamping pressure, stainless steel,membrane degradation, current distribution, gas diffusionlayer, stack, thermal impedance, permeability.</p>

Polymer electrolyte membrane fuel cells (PEMFCs) have the potential to play a major role as energy generators for transportation and portable applications. One of the current barriers to their commercialization is the cost of the components and manufacturing, specifically the bipolar plates. One approach to preparing PEMFCs for commercialization is to develop new bipolar plate materials, related to mass production of fuel cells. Thermoplastic/carbon filler composites with low filler loading have a major advantage in that they can be produced by a conventional low-cost injection molding technique. In addition, the materials used are inexpensive, easy to shape, and lightweight. An optimal bipolar plate must possess high surface and bulk electronic conductivity, sufficient mechanical integrity, low permeability, and corrosion resistance. However, it is difficult to achieve high electrical conductivity from a low-cost thermoplastic composite with low conductive filler loading. Concerns over electrical conductivity improvement and the injection processability of composites have brought forth the idea of producing a polypropylene/three-carbon-filler composite for bipolar plate application. The thesis addresses the development of synergistic effects of filler combinations, investigating composite conductive materials and using composite bipolar plate testing in PEMFCs. One significant effect of conductive network formation is the synergetic effects of different carbon filler sizes, shapes, and multiple filler ratios on the electrical conductivity of bipolar plate materials. A polypropylene resin combined with low-cost conductive fillers (graphite, conductive carbon black, and carbon fibers with 55 wt% of filler loading) compose the main composite for all investigations in this research. Numerous composite formulations, based on single-, two-, and three-filler systems, have been created to investigate the characteristics and synergistic effects of multiple fillers on composite conductivity. Electrical conductivity measurements corresponding to PEMFC performance and processing characteristics were investigated. Experimental work also involved other ex-situ testing for the physical requirements of commercial bipolar plates. All combinations of fillers were found to have a significant synergistic effect that increased the composite electrical conductivity. Carbon black was found to have the highest influence on the increase of electrical conductivity compared to the other fillers. The use of conjugated conducting polymers such as polypyrrole (PPy) to help the composite blends gain desirable conductivities was also studied. Electrical conductivity was significantly improved conductivity by enriching the conducting paths on the interfaces between fillers and the PP matrix with PPy. The conductive network was found to have a linkage of carbon fibers following the respective size distributions of fibers. The combination of Fortafil and Asbury carbon fiber mixture ameliorated the structure of conductive paths, especially in the through-plane direction. However, using small fibers such as carbon nanofibers did not significantly improve in electrical conductivity. The useful characteristics of an individual filler and filler supportive functions were combined to create a novel formula that significantly improved electrical conductivity. Other properties, such as mechanical and rheological ones, demonstrate the potential to use the composites in bipolar plate applications. This research contributes a direction for further improvement of marketable thermoplastic bipolar plate composite materials.

The work present in this thesis report introduces a novel non-destructive technique for experimentally measuring through thickness hygro-thermal strain of Nafion membranes though digital image correlation. An Optical Coherence Tomography (OCT) system was used to acquire images of a Nafion-TiO2 (titanium dioxide powder) composite membranes in a fuel cell like device. The proposed technique, commonly known as optical coherence elastography (OCE) makes use of the normalized correlation algorithm to calculate strain between two successive scans of different relative humidity step values. Different normalized correlation parameters were compared to measured results of PDMS-TiO2 phantoms in order to analyze accuracy. The effect of TiO2 on Nafion membranbes mechanical properties was further analysed by comparing the swelling behaviour of membranes with different concentrations. It has been found that Nafion undergoes approximately 25 – 30% more strain on the land section than on the channel section, regardless gas diffusion electrode (GDE) layer presence. Furthermore, it was shown that the overall strain on the material decrease by approximately 10% when GDE layers are present. Overall this work demonstrated how OCE is a viable technique for measuring through thickness strain distribution in Nafion composite membranes and has the potential to be implemented for non-destructive in situ measurements. / Graduate / 0548 / kellerv@uvic.ca