The maximum theoretical energy efficiency of fuel cells is much larger than those of the steam-power-turbine cycles that are currently used for generating electrical power. Similarly, direct hydrocarbon fuel cells, DHFCs, can theoretically be much more efficient than hydrogen fuel cells. Unfortunately the current densities (overall reaction rates) of DHFCs are substantially smaller than those of hydrogen fuel cells. The problem is that the exchange current density (catalytic reaction rate) is orders of magnitude smaller for DHFCs. Other work at the University of Ottawa has been directed toward the development of polymer electrolytes for DHFCs that operate above the boiling point of water, making corrosion rates much slower so that precious metal catalysts are not required. Propane (liquefied petroleum gas, LPG) was the hydrocarbon chosen for this research partly because infrastructure for its transportation and storage in rural areas already exists. In this work nickel based catalysts, an inexpensive replacement for the platinum based catalysts used in conventional fuel cells, were examined using density functional theory, DFT. The heats of propane adsorption for 3d metals, when plotted as a function of the number of 3d electrons in the metal atom, had the shape of a volcano plot, with the value for nickel being the peak value of the volcano plot. Also the C-H bond of the central carbon atom was longer for propane adsorbed on nickel than when adsorbed on any of the other metals, suggesting that the species adsorbed on nickel was less likely to desorb than those on other metals. The selectivity of the propyl radical reaction was examined. It was found that propyl radicals

The shift to strong hybrid and electrified vehicle architectures engenders controversy and brings about many unanswered questions. It is unclear whether developed markets will have the infrastructure in place to support and successfully implement them. To date, limited effort has been made to comprehend if the energy and transportation solutions that work well for one city or geographic region may extend broadly. A region's capacity to supply a fleet of EVs, or plug-in hybrid vehicles with the required charging infrastructure, does not necessarily make such vehicle architectures an optimal solution. In this study, a mix of technologies ranging from HEV to PHEV and EREV through to Battery Electric Vehicles were analyzed and set in three Canadian Provinces and 3 U.S. Regions for the year 2020. Government agency developed environmental software tools were used to estimate greenhouse gas emissions and energy use. Projected vehicle technology shares were employed to estimate regional environmental implications. Alternative vehicle technologies and fuels are recommended for each region based on local power generation schemes. / UOIT

A molten carbonate fuel cell (MCFC) is an electro-chemical energy conversion technology that runs on natural gas and employs a molten salt electrolyte. In order to keep the electrolyte in this state, the cell must be kept at a temperature above 500 C, eliminating the need for precious metals as the catalyst. There has been only a limited amount of research on modelling the transport processes inside this device, mainly due to its limited ability for mobile applications. In this thesis, three one-dimensional models of a MCFC are presented based on different types of diffusion and convection. Comparisons between models are performed so as to assess their validity. Regarding ion transport, it is shown that there exists a limiting case for ion migration across the cathode that depends on the conductivity for the liquid potential. Finally, an optimization of the diffusivity across the cathode is carried out in an attempt to increase the cell performance and its longevity. / UOIT

The goal of this research project was to characterize the physical and electrochemical properties of a commercially available fuel cell-based breath alcohol sensor. Characteristics of the existing sensor were compared with state of the art power generating fuel cells with the goal of understanding the factors that limit performance, lifetime and cost effectiveness of the sensors. This will guide the development of the next generation of breath alcohol sensors. The average lifetime of the current sensor falls short of the industry standards. In particular, sensors operating in dry conditions experience more rapid loss of sensitivity and failure. Two primary causes of degradation were investigated in this study. Loss of proton conductivity as a result of membrane dehydration was shown to be reversible by rehydrating the membrane in humid conditions. Loss of electrochemically active surface area of Pt is irreversible and seems to be caused by a change in sensor morphology after long-term exposure to dry conditions. / UOIT

Molten carbonate fuel cells (MCFCs) have become an attractive emerging technology for stationary co-generation of heat and power. From a technical perspective, dynamic operation has a significant effect on the fuel cell life cycle and, hence, economic viability of the device. The scope of this thesis is to present an improved understanding of the system behaviour at transient operation that can be used to design a more robust control system in order to overcome the cost and the operating lifetime issues. Hence, a comprehensive multi-component multidimensional transient mathematical model is developed based on the conservation laws of mass, momentum, species, energy and electric charges coupled through the reaction kinetics. In essence, this model is a set of partial differential equations that are discretized and solved using the finite-volume based commercial software, ANSYS FLUENT 12.0.1. The model is validated with two sets of experimental results, available in open literature, and good agreements are obtained. The validated model is further engaged in an extensive study. First, the MCFC behaviour at high current densities or oxidant utilization, when the mass transfer becomes dominant, is investigated using peroxide and superoxide reaction mechanisms. In brief, both mechanisms predicted the linear region of the polarization curve accurately. However, none of these mechanisms showed a downward bent in the polarization curve. A positive exponent for the carbon-dioxide mole fraction is probably essential in obtaining the downward bent (“knee”) at high current densities which is in contrast to what has been reported in the literature to date. Next, a sinusoidal impedance approach is used to examine the dynamic response of the unit cell to inlet perturbations at various impedance frequencies. This analysis is further used to determine the phase shifts and time scales of the major dynamic processes within the fuel cell. Furthermore, numerical simulation is utilized in order to investigate the underlying electrochemical and transport phenomena without performing costly experiments. Results showed that the electrochemical reactions and the charge transport process occur under a millisecond. The mass transport process showed a comparatively larger time scale. The energy transport process is the slowest process in the cell and takes about an hour to reach its steady state condition. Furthermore, the developed mathematical model is utilized as a predictive tool to provide a three-dimensional demonstration of the transient physical and chemical processes at system startiv up. The local distribution of field variables and quantities are presented. The results show that increasing the electrode thickness provides a higher reaction rate, but may lead to larger ohmic loss which is not desirable. The reversible heat generation and consumption mechanisms of the cathode and anode are dominant in the first 10 s while the heat conduction from the solid materials to the gas phase is not considerable. The activation and ohmic heating have the same impact within the anode and cathode because of their similar electric conductivity and voltage loss. Increasing the thermal conductivity of the cathode material will facilitate the process of heat transport throughout the cell. This can also be accomplished by lowering the effects of heat conduction by means of a cathode material with a smaller thickness. In addition, a thermodynamic model is utilized to examine energy efficiency, exergy efficiency and entropy generation of a MCFC. By changing the operating temperature from 883 K to 963 K, the energy efficiency of the unit cell varies from 42.8 % to 50.5 % while the exergy efficiency remains in the range of 26.8% to 36.3%. Both efficiencies initially rise at lower current densities up to the point that they attain their maximum values and ultimately decrease with the increase of current density. With the increase of pressure, both energy and exergy efficiencies of the cell increase. An increase in this anode/cathode flow ratio lessens the energy and exergy efficiencies of the unit cell. Higher operating pressure and temperature decrease the unit cell entropy generation. / UOIT

This thesis is concerned with the thermodynamic analyses of ion and proton-conducting solid oxide fuel cells (SOFC) fed with ammonia and urea as fuels. A multi-level approach was used to determine the feasibility and the performance of the fuel cells. First, the cell-level thermodynamics were examined to capture the effect of various operating parameters on the cell voltage under open-circuit conditions. Second, electrochemical studies were conducted to characterize the cell-level performance under closed-circuit conditions. Third, the fuel cells were individually integrated in a combined-cycle power generation system and parametric studies were performed to assess the overall performance as well as the thermal and exergy efficiencies. The findings of this study showed that the overall performance and efficiency of the ammonia fed SOFC is superior in comparison to that of the urea fed counterpart. In particular, the ammonia fed system combined with proton-conducting SOFC achieved a thermal efficiency as high as 85% and exergy efficiency as high as 75%. The respective efficiencies of the ammonia fed system combined with ion-conducting SOFC were lower by 5-10%. However, the urea fed system combined with ion or proton-conducting SOFC demonstrated much lower performance and efficiencies due to higher thermodynamic irreversibilities. / UOIT

The reduction of manufacturing costs and the facilitation of direct-oxidation of hydrocarbon fuels have been identified as means of promoting the commercialization of the solid oxide fuel cell, a technology that offers both environmental and fuel conservation benefits compared to conventional energy conversion technologies. This research was conducted with the aim of realizing the production of direct-oxidation anodes using atmospheric plasma spraying, which has been identified as a fabrication technique that has the potential to reduce the manufacturing costs of solid oxide fuel cells. This thesis details the rationale behind the selection of the anode compositions (BaO-Ni-YSZ, CeO2-Ni-YSZ, and Sn-Ni-YSZ) and the specifics of the specialized fabrication strategy (SPS-SPPS) that was devised with the aim of realizing microstructures similar to those where the secondary phases (BaO, CeO2, and Sn) coat the surfaces of the primary Ni and YSZ phases. Results of XRD, SEM and EDS analyses are presented.

The reduction of manufacturing costs and the facilitation of direct-oxidation of hydrocarbon fuels have been identified as means of promoting the commercialization of the solid oxide fuel cell, a technology that offers both environmental and fuel conservation benefits compared to conventional energy conversion technologies. This research was conducted with the aim of realizing the production of direct-oxidation anodes using atmospheric plasma spraying, which has been identified as a fabrication technique that has the potential to reduce the manufacturing costs of solid oxide fuel cells. This thesis details the rationale behind the selection of the anode compositions (BaO-Ni-YSZ, CeO2-Ni-YSZ, and Sn-Ni-YSZ) and the specifics of the specialized fabrication strategy (SPS-SPPS) that was devised with the aim of realizing microstructures similar to those where the secondary phases (BaO, CeO2, and Sn) coat the surfaces of the primary Ni and YSZ phases. Results of XRD, SEM and EDS analyses are presented.

Reactive spray deposition technology (RSDT) is a method of depositing films or producing nanopowders through combustion of metal-organic compounds dissolved in a solvent. This technology produces powders of controllable size and quality by changing process parameters to control the stoichiometry of the final product. This results in a low-cost, continuous production method suitable for producing a wide range of fuel cell related catalyst films or powders. In this work, the system is modified for direct deposition of both unsupported and carbon supported layers on proton exchange membrane (PEM) fuel cells. The cell performance is investigated for platinum loadings of less than 0.15 mg/cm² using a heterogeneous bi-layer consisting of a layer of unsupported platinum followed by a composite layer of Nafion®, carbon and platinum. Comparison to more traditional composite cathode architectures is made at loadings of 0.12 and 0.05 mg platinum/cm². The composition and phase of the platinum catalyst is confirmed by XPS and XRD analysis while the particle size is analyzed by TEM microscopy. Cell voltages of 0.60 V at 1 A/cm² using H₂/O₂ at a loading of 0.053 mg platinum/cm² have been achieved.

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