Factors such as global warming, dwindling fossil fuel reserves, and energy security concerns combine to indicate that a replacement for the internal combustion engine (ICE) vehicle is needed. Fuel cell vehicles have the potential to address the problems surrounding the ICE vehicle without imposing any significant restrictions on vehicle performance, driving range, or refuelling time. Though there are currently some obstacles to overcome before attaining the widespread commercialization of fuel cell vehicles, such as improvements in fuel cell and battery durability, development of a hydrogen infrastructure, and reduction of high costs, the fundamental concept of the fuel cell vehicle is strong: it is efficient, emits zero harmful emissions, and the hydrogen fuel can be produced from various renewable sources. Therefore, research on fuel cell vehicle design is imperative in order to improve vehicle performance and durability, increase efficiency, and reduce costs. This thesis makes a number of key contributions to the advancement of fuel cell vehicle design within two main research areas: powertrain design and DC/DC converters. With regards to powertrain design, this research presents a novel fuel cell-battery-ultracapacitor topology which shows reduced mass and cost, and increased efficiency, over other promising topologies found in the literature. A detailed vehicle simulator created in MATLAB/Simulink is used to perform a comprehensive parametric study on different fuel cell vehicle types, resulting in general conclusions for optimal topologies, as well as component types and sizes, for fuel cell vehicles. Next, a general analytical method to optimize the novel battery-ultracapacitor energy storage system based on maximizing efficiency, and minimizing cost and mass, is developed. With regards to DC/DC converters, it is important to design efficient and light-weight converters for use in fuel cell and other electric vehicles to improve overall vehicle fuel economy. Thus, this research presents a novel soft-switching method, the capacitor-switched regenerative snubber, for the high-power DC/DC boost converters commonly used in fuel cell vehicles. This circuit is shown to increase the efficiency and reduce the overall mass of the DC/DC boost converter.

Fuel cells are electrochemical devices being developed for a variety of consumer applications including homes and vehicles. Before customers will accept this technology fuel cells must demonstrate suitable durability and reliability. One of the most important parts of a fuel cell stack is the polymer electrolyte membrane (PEM). This layer is responsible for conducting protons from anode to cathode and acting as a gas barrier, while operating in a harsh electrochemical environment. In order to develop better and more durable membranes researchers must understand the linkage between the causes of degradation, such as specific material properties and operational conditions. One significant mode of degradation of the electrolyte membrane is through chemical degradation caused by the crossover of reactant gases leading to the formation of peroxide and ultimately radical species. These radicals are able to attack vulnerable groups in the polymer structure of the membrane. The result is membrane thinning, increased gas crossover, fluoride ion release, and voltage degradation. Considerable experimental work has been done to understand these mechanisms, although there has been no attempt to model the connection between the causes of degradation and the physical effects of degradation on the electrolyte membrane. Such a model can be used as a valuable tool when evaluating different degradation mechanisms, developing stronger materials, and enable estimation of the influence of fuel cell operation and system design on degradation. This work presents the development and application of a dynamic semi-mechanistic chemical degradation model for a reinforced membrane in a polymer electrolyte membrane fuel cell. The model was developed using single cell testing with Gore™ PRIMEA® series 5510 catalyst coated membranes under open circuit voltage (OCV) conditions. Such conditions are useful for accelerated testing since they are believed to enhance chemical degradation in membranes since reactant gas partial pressures are at their maximum. It was found that the electrolyte layer closer to the cathode catalyst preferentially degraded. Furthermore, cumulative fluoride release curves for the anode and cathode began to reach plateaus at similar times. The developed model proposes that as the cathode electrolyte layer is degraded, fluoride release slows due to a lack of reactants since the inert reinforcement layer creates a barrier between the cathode and anode electrolyte layers. It is also believed that all fluoride release originates at the degradation site at the cathode. By fitting key parameters, the fluoride release trends were simulated. The proposed model links material properties such as the membrane gas permeability, membrane thickness, and membrane reactivity, as well as operating parameters such as hydrogen partial pressure and relative humidity to fluoride release, thickness change, and crossover. Further investigation into degradation at OCV operation and different relative humidity conditions showed that initial hydrogen crossover measurements were a good indicator of degradation rate over long testing times. The proposed semi-mechanistic model was able to best model the results when using a second order dependence on the hydrogen crossover term. In all cases there was some discrepancy between the model and experimental data after long times. This was attributed to the onset and contribution of anode side degradation. The effect of drawing current on fluoride release was also investigated. Experimental results showed that with increasing current density the fluoride release rate decreased. Using the developed semi-mechanistic model it was proposed that a decrease in hydrogen crossover was primarily responsible for the reduction in chemical degradation of the membrane. A macro-homogeneous model of the anode catalyst layer was used to show that a reduction in hydrogen concentration through the catalyst layer when a current is drawn is a possible reason for the reduction in degradation. Finally the model was applied to three different dynamic drive cycles. The model was able to show that over different drive cycles, the fuel cell will experience different degradation rates. Thus the developed model can be used as a potential tool to evaluate degradation in systems.

The purpose of this paper is to identify the current status of fuel cell technology and to establish whether said technology is mature enough to be implemented into the Swedish Armed Forces. The question to be answered in this paper is as follows: Can hydrogen gas and fuel cells be used as an alternative source of energy within the Swedish Armed Forces? This paper is based on theoretical studies and reports from prior research done on fuel cells. By studying these facts a predictive answer has been obtained. The answer I have come to, is that the maturity of fuel cell technology is currently inadequate for the Swedish Armed Forces to implement, especially considering its harsh working conditions.

Small combined heat and power generators have the potential to reduce energy consumption and greenhouse gas emissions of residential buildings. Recently, much attention has been given to these units. To date, the majority of studies in this field have concentrated on the steady operational performance of a specific generator type, and the available computer models have largely been theoretical in nature. <br /><br /> The main goal of this study was to evaluate the performance of the latest combined heat and power generators, when integrated into Canadian residential homes. A fair comparison of four 1 kW (electrical) units was made. The combined heat and power units studied were based on PEM fuel cell, solid oxide fuel cell, Stirling Engine, and internal combustion engine energy converters. <br /><br /> This study utilized recent test data in an attempt to evaluate the most efficient method of integrating the combined heat and power units into residential houses. Start-up, shut down, and load change transients were incorporated into the simulations. The impact of load variations due to building thermal envelope differences and varying building heating system equipment was evaluated. The simulations were evaluated using TRNSYS software. The building heat demands were determined with eQuest hourly building simulation software. <br /><br /> All of the combined heat and power units under study were capable of providing a net annual benefit with respect to global energy and greenhouse gas emissions. The fuel cells offer the highest integrated performance, followed closely by the internal combustion engine and lastly the Stirling engine. Annual global energy savings up to 20%, and greenhouse gas savings up to 5. 5 tonnes per year can be achieved compared to the best conventional high efficiency appliances. <br /><br /> Heat demand influences performance greatly. As the thermal output of the generator unit approaches half of the average building thermal demand, the system design becomes critical. The system design is also critical when integrating with a forced air furnace. Only the PEM fuel cell unit produces clear global energy and emissions benefits when operating in the summertime.

In its present form, polymer electrolyte membrane fuel cell (PEMFC) technology requires some method of humidification to ensure that high performance and long life of the fuel cell membrane is maintained. External humidification utilizing ‘gas to gas’ membrane based planar humidifiers is one method of humidifying fuel cell reactant gases. This type of humidification offers the benefit of recycling heat and moisture from the fuel cell exhaust, and returning it to the reactants entering the fuel cell. In designing a planar membrane based fuel cell humidifier the two important areas to be considered are: - humidifier channel and plate design; and - humidifier membrane selection. In this work a humidifier design procedure was developed based on prototype humidifier testing. This design procedure involves selection of design parameters based on a dimensionless parameter which describes the ratio of gas residence time, and water diffusion time from the membrane surface. Humidifiers of different flow channel geometries were created with a rapid prototyping technique. These humidifier units were tested at different operating conditions in an attempt to validate the design equations involving a design parameter which is the ratio between the residence times of gas in the humidifier over the diffusion time of water from the surface of the membrane into the channel. This parameter offers a good starting point for humidifier design, the target value of this parameter was found to be between 2.0 and 4.0, with a desired value of 3.0. A fuel cell stack humidifier design procedure and suggestions are presented based this parameter. The design also considers designing a humidifier on limited volume constraints in which the humidifier would have to fit into the fuel cell system. A membrane selection procedure was developed based on design criteria requirements developed during this work for the fuel cell humidifier. This criterion includes high water permeation, low air permeation, good mechanical strength, robust handling, and long lifetime under various operating conditions. . Specific values for membrane selection included a water flux of greater than 14 kg m-2 h-1 in a water permeation test, less than 3 cm3 min-1 cm-2 kPa-1 air permeation when the membrane was dry, and a lifetime of at least 1500 hours of operation without performance degradation. Sixty membranes from various sources were screened for candidacy for use in the humidifier application. Membranes which passed the initial screenings were tested for durability at high and moderate temperature conditions. These membranes were operated until failure, at which time analysis was completed to determine the failure modes of the membrane. Mitigation strategies were proposed when applicable. Recommendations were made for membrane materials for the proposed operating requirements. Suggested membranes materials included those based on UHMWPE and inorganic additives, as well as homogenous membranes based on Nylon 6,6, PEEK, and PFSA.

Factors such as global warming, dwindling fossil fuel reserves, and energy security concerns combine to indicate that a replacement for the internal combustion engine (ICE) vehicle is needed. Fuel cell vehicles have the potential to address the problems surrounding the ICE vehicle without imposing any significant restrictions on vehicle performance, driving range, or refuelling time. Though there are currently some obstacles to overcome before attaining the widespread commercialization of fuel cell vehicles, such as improvements in fuel cell and battery durability, development of a hydrogen infrastructure, and reduction of high costs, the fundamental concept of the fuel cell vehicle is strong: it is efficient, emits zero harmful emissions, and the hydrogen fuel can be produced from various renewable sources. Therefore, research on fuel cell vehicle design is imperative in order to improve vehicle performance and durability, increase efficiency, and reduce costs. This thesis makes a number of key contributions to the advancement of fuel cell vehicle design within two main research areas: powertrain design and DC/DC converters. With regards to powertrain design, this research presents a novel fuel cell-battery-ultracapacitor topology which shows reduced mass and cost, and increased efficiency, over other promising topologies found in the literature. A detailed vehicle simulator created in MATLAB/Simulink is used to perform a comprehensive parametric study on different fuel cell vehicle types, resulting in general conclusions for optimal topologies, as well as component types and sizes, for fuel cell vehicles. Next, a general analytical method to optimize the novel battery-ultracapacitor energy storage system based on maximizing efficiency, and minimizing cost and mass, is developed. With regards to DC/DC converters, it is important to design efficient and light-weight converters for use in fuel cell and other electric vehicles to improve overall vehicle fuel economy. Thus, this research presents a novel soft-switching method, the capacitor-switched regenerative snubber, for the high-power DC/DC boost converters commonly used in fuel cell vehicles. This circuit is shown to increase the efficiency and reduce the overall mass of the DC/DC boost converter.

Fuel cells are electrochemical devices being developed for a variety of consumer applications including homes and vehicles. Before customers will accept this technology fuel cells must demonstrate suitable durability and reliability. One of the most important parts of a fuel cell stack is the polymer electrolyte membrane (PEM). This layer is responsible for conducting protons from anode to cathode and acting as a gas barrier, while operating in a harsh electrochemical environment. In order to develop better and more durable membranes researchers must understand the linkage between the causes of degradation, such as specific material properties and operational conditions. One significant mode of degradation of the electrolyte membrane is through chemical degradation caused by the crossover of reactant gases leading to the formation of peroxide and ultimately radical species. These radicals are able to attack vulnerable groups in the polymer structure of the membrane. The result is membrane thinning, increased gas crossover, fluoride ion release, and voltage degradation. Considerable experimental work has been done to understand these mechanisms, although there has been no attempt to model the connection between the causes of degradation and the physical effects of degradation on the electrolyte membrane. Such a model can be used as a valuable tool when evaluating different degradation mechanisms, developing stronger materials, and enable estimation of the influence of fuel cell operation and system design on degradation. This work presents the development and application of a dynamic semi-mechanistic chemical degradation model for a reinforced membrane in a polymer electrolyte membrane fuel cell. The model was developed using single cell testing with Gore™ PRIMEA® series 5510 catalyst coated membranes under open circuit voltage (OCV) conditions. Such conditions are useful for accelerated testing since they are believed to enhance chemical degradation in membranes since reactant gas partial pressures are at their maximum. It was found that the electrolyte layer closer to the cathode catalyst preferentially degraded. Furthermore, cumulative fluoride release curves for the anode and cathode began to reach plateaus at similar times. The developed model proposes that as the cathode electrolyte layer is degraded, fluoride release slows due to a lack of reactants since the inert reinforcement layer creates a barrier between the cathode and anode electrolyte layers. It is also believed that all fluoride release originates at the degradation site at the cathode. By fitting key parameters, the fluoride release trends were simulated. The proposed model links material properties such as the membrane gas permeability, membrane thickness, and membrane reactivity, as well as operating parameters such as hydrogen partial pressure and relative humidity to fluoride release, thickness change, and crossover. Further investigation into degradation at OCV operation and different relative humidity conditions showed that initial hydrogen crossover measurements were a good indicator of degradation rate over long testing times. The proposed semi-mechanistic model was able to best model the results when using a second order dependence on the hydrogen crossover term. In all cases there was some discrepancy between the model and experimental data after long times. This was attributed to the onset and contribution of anode side degradation. The effect of drawing current on fluoride release was also investigated. Experimental results showed that with increasing current density the fluoride release rate decreased. Using the developed semi-mechanistic model it was proposed that a decrease in hydrogen crossover was primarily responsible for the reduction in chemical degradation of the membrane. A macro-homogeneous model of the anode catalyst layer was used to show that a reduction in hydrogen concentration through the catalyst layer when a current is drawn is a possible reason for the reduction in degradation. Finally the model was applied to three different dynamic drive cycles. The model was able to show that over different drive cycles, the fuel cell will experience different degradation rates. Thus the developed model can be used as a potential tool to evaluate degradation in systems.

Humidity sensors are one of the most widely used sensors in commercial and industrial applications for environmental monitoring and controlling. Although related technology have been studied intensively, humidity sensing in harsh environments still remains a challenge. The inability of current humidity sensors to operate in high temperature environments is generally due to the degradation of the sensing films caused by high temperature, high humidity level, and/or contamination. Our goal is the design and fabrication of a humidity sensor that is capable of working under high temperatures and in a condensing environment. The targeted application of this sensor is in the polymer electrolyte membrane (PEM) fuel cell, where humidity control is crucial for performance optimization. In this work, ordered macroporous silicon is thoroughly studied as a humidity sensing layer. In addition to the advantages of traditional porous silicon for gas sensing (high resistance to high temperature and good compatibility with current IC fabrication process), the ordered macroporous silicon used in these experiment has uniform pore size, pore shape and distribution. All the vertical aligned pores can be opened to the environment at both ends, which can significantly increase the efficiency of gas diffusion and adsorption. Moreover, this special structure opens the door to uniform surface modifications for sensing enhancement. Both ordered macroporous silicon based heterostructure and self-supporting membrane are fabricated and investigated as a humidity sensor. Heterostructure sensors with different thin film surface coatings including bare Si, thermally grown SiO2, atom layer deposited ZnO, HfO2, and Ta2O5 are characterized. Post micro-fabrication is achieved on this ordered porous structure without affecting the material and its sensing properties. It has been proven that the ordered macroporous silicon with Ta2O5 surface coating shows the best sensing property due to its ultra-hydrophilic surface. The sensor shows high sensitivity, fast response times, small hysteresis, and extraordinary stability and repeatability under high temperatures and in condensing environment. It demonstrates great potential and advantages over existing commercial humidity sensors in the fuel cell application field. In addition to ordered macroporous silicon, well aligned 1D ZnO nanorods/nanowires -another widely used nanostructure in gas sensing- is also investigated as humidity sensing materials. Both vertically and laterally aligned nanorods/nanowires are fabricated and tested against humidity changes. The sensors shows increasing resistance to increasing relative humidity, which is contrary to most published works so far. Possible mechanisms have been proposed in this thesis and future work has been suggested for further study. To the best of our knowledge, this work is the first to use ordered macroporous silicon and well aligned 1D ZnO nanorods/nanowires for humidity sensing.

The durability and performance of commercially available polymer electrolyte membrane fuel cell (PEMFC) technology depends heavily on adequate humidification of the membrane electrode assembly (MEA). Early generation automotive fuel cell stacks will likely rely on an external humidification process based on gas-to-gas membrane planar humidifiers to humidify the inlet cathode stream. The membrane-based humidifier systems allow the reactants to receive recycled heat and moisture from the cathode outlet stream. The objective of this thesis is to develop a flexible, computer-based simulation tool that can be used to aid in the design of these planar humidifier systems. The simulation is based on fundamental mass transfer concepts and experimental membrane behaviour based on literature results. It was determined that the mass transfer resistance through the membrane is several orders of magnitude higher than the resistance contributed by the gas diffusion media (GDM) and thus the mass transfer resistance through the GDM are not considered. An important point to note is that the Schroeder’s Paradox observed in perfluorosulfonic acid (PFSA) membranes implies that membranes in contact with liquid water will exhibit higher mass transfer than membranes in contact with saturated water vapour despite the fact that the water activity in both situations are unity. Initial simulations for which no liquid water was present resulted in a humidifier water transfer rate less than half the rate observed experimentally. Thus it was hypothesized that condensed liquid water was present on the wet-side of the humidifier membrane and as such this work assumes a fraction of the membrane surface is covered by liquid water while the rest of the membrane is exposed to gaseous water concentrations comparable to the bulk channel stream above the GDM. For typical operating conditions the outlet wet-side stream retains 92% of the inlet water content and as such it was hypothesized that constant fractional liquid water coverage across the membrane could be assumed. Later simulations confirmed the validity of this hypothesis. Six models of water coverage estimation were derived using least squares and factorial design methods. The models were compared however no single method was determined to be superior for all situations as the methods exhibit similar sums of squared error.

Proton exchange membrane fuel cell (PEMFC) has been considered as one of the most promising energy conversion devices for the future in automotive applications. One of the major technical challenges for the commercialization of PEMFC is the effective start-up from subzero temperatures, often referred to as “cold start”. The major problem of PEMFC cold start is that the product water freezes when the temperature inside the PEMFC is lower than the freezing point. If the catalyst layer (CL) is fully occupied by ice before the cell temperature rises above the freezing point, the electrochemical reaction may stop due to the blockage of the reaction sites. However, only a few of the previous PEMFC studies paid attention to cold start. Hence, understanding the ice formation mechanisms and optimizing the design and operational strategies for PEMFC cold start are critically important. In this research, an experimental setup for the cold start testing with simultaneous measurement of current and temperature distributions is designed and built; a one-dimensional (1D) analytical model for quick estimate of purging durations before the cold start processes is formulated; and a comprehensive three-dimensional (3D) PEMFC cold start model is developed. The unique feature of the cold start experiment is the inclusion of the simultaneous measurement of current and temperature distributions. Since most of the previous numerical models are limited to either 1D or two-dimensional (2D) or 3D but only considering a section of the entire cell due to computational requirement, the measured distribution data are critically important to better understand the PEMFC cold start characteristics. With a full set of conservation equations, the 3D model comprehensively accounts for the various transport phenomena during the cold start processes. The unique feature of this model is the inclusion of: (i) the water freezing in the membrane electrolyte and its effects on the membrane conductivity; (ii) the non-equilibrium mass transfer between the water in the ionomer and the water (vapour, liquid and ice) in the pore region of the CL; and (iii) both the water freezing and melting in the CL and gas diffusion layer (GDL). This model therefore provides the fundamental framework for the future top-down multi-dimensional multiphase modelling of PEMFC. The experimental and numerical results elaborate the ice formation mechanisms and other important transport phenomena during the PEMFC cold start processes. The effects of the various cell designs, operating conditions and external heating methods on the cold start performance are studied. Independent tests are carried out to identify and optimize the important design and operational parameters.