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Biology is a good source of analogies for engineering design. One approach of retrieving biological analogies is to perform keyword searches on natural-language sources such as books, journals, etc. A challenge in retrieving information from natural-language sources is the potential requirement to process a large number of search results. This thesis describes two methods on improving the relevancy of the search results. The first method is inserting metadata such as part- of-speech, word sense and lexicographical data for each word in a natural-language. The second method is categorizing the search results, using WordNet relationships and Wikipedia structures as ontologies. Although this research is still exploratory, initial qualitative observations demonstrate successful identification and separation of biological phenomena relevant to either desired functions or desired qualities. The benefits of embedding metadata are demonstrated through a case study on the redesign of a fuel cell bipolar plate. A prototype was constructed with ability to passively prevent prolonged catastrophic flooding.

Biology is a good source of analogies for engineering design. One approach of retrieving biological analogies is to perform keyword searches on natural-language sources such as books, journals, etc. A challenge in retrieving information from natural-language sources is the potential requirement to process a large number of search results. This thesis describes two methods on improving the relevancy of the search results. The first method is inserting metadata such as part- of-speech, word sense and lexicographical data for each word in a natural-language. The second method is categorizing the search results, using WordNet relationships and Wikipedia structures as ontologies. Although this research is still exploratory, initial qualitative observations demonstrate successful identification and separation of biological phenomena relevant to either desired functions or desired qualities. The benefits of embedding metadata are demonstrated through a case study on the redesign of a fuel cell bipolar plate. A prototype was constructed with ability to passively prevent prolonged catastrophic flooding.

Fuel cell, as an alternative green power source for automobiles and portable electronics, has attracted worldwide attention due to its desirable properties such as high energy density and low greenhouse gas emission. Despite great progress in the past decades, several challenges still remain as obstacles for the large-scale commercialization. Among them, the high cost of Pt-based electrode material is considered as a major barrier, while the life span or stability of electrode catalysts is another concern since the electrocatalysts can be easily poisoned during the fuel cell operation. In order to overcome these issues, nanostructured carbon materials, especially carbon nanotubes (CNTs), are studied as catalyst support. In addition, recent research also suggests that the coupling of a second metal element with Pt can effectively protect the electrocatalysts from being poisoned and thus improve their long-term durability. The objective of the present work was to demonstrate an efficient synthetic method for the preparation of CNTs supported binary PtM (M=Ru, Sn) electrocatalysts. In this project, a polymer wrapping technique along with an in-situ polyol reduction strategy was adopted to decorate well-dispersed binary PtM nanoparticles on the surface of modified-CNTs. The unique nanostructures as well as the excellent catalytic activities of the as-prepared nanohybirds were investigated through a diversity of physiochemical and electrochemical characterization techniques. This fabrication method provided a simple and convenient route to assemble Pt-based catalyst on carbon substrates, which is useful for the further development of high-performance fuel cell catalysts.

The microbial fuel cell (MFC) is an innovative renewable energy technology that also serves to treat wastewater through the bacteria-driven oxidation of organic substrates. The liquid anolyte contains the organic substrate to be oxidized, while the catholyte contains the substance to be reduced. In a dual-chamber MFC, the catholyte typically contains dissolved oxygen or another easily reducible compound (e.g., ferricyanide) in an aqueous solution, while in a single-chamber MFC, gaseous airborne oxygen reacts directly at the cathode. A single-chamber air-cathode microbial fuel cell was operated using an acetate substrate and a 0.2 mg/cm2 platinum catalyst cathode in the initial stages of the project. The platinum catalyst was airbrushed onto a carbon paper cathode and hot-pressed onto a Nafion 117 membrane. After the platinum runs were completed, the MFC was disassembled, cleaned and reassembled with a new non-precious nitrogen-doped carbon composite catalyst replacing the platinum. Two MFCs were operated at different loading levels (1.0 mg/cm2 and 2.0 mg/cm2) of the new catalyst. The cell was configured to operate in a fed-batch and upflow modes. Preliminary experiments were conducted using two non-precious catalysts synthesized with different nitrogen precursors, polyaniline and ethylenediamine (EDA). These experiments showed the ethylenediamine-based-catalyst exhibited higher catalytic activity for oxygen reduction (ORR) with a half-wave potential of 0.57 V versus 0.43 V for the polyaniline catalyst. These values were lower than the expected half-wave potential of 0.65 – 0.70 V. Consequently, the catalyst based on EDA was used in all subsequent experiments. SEM images revealed that this catalyst has a fluffy, bulbous, highly porous structure, while EDAX and XRD both detected the presence of residual iron and cobalt from the preparation procedure. Nitrogen (3.57 wt %) and oxygen (4.87 wt %) were also detected from the EDAX analysis. Operation with a hydraulic residence time (HRT) of 24 hours and feed COD concentration of 6.44 g COD/L-day was found to produce the highest power density of 141.7 ± 2.4 mW/m2 from the experiments conducted on the platinum catalyst. A subsequent run at a 12 hour HRT and 3.22 g COD/L-day feed produced only 104.4 ± 5.2 mW/m2. When the cell operation was reverted to the original high HRT and high feed COD concentration, the original current was not recovered and in fact remained virtually unchanged from the level attained at the lower HRT and COD feed level (105.7 ± 2.7 mW/m2). It was suspected that the decreased acetate concentration in the second phase, and the biomass accumulation in the replicate third phase were the cause of the decreased currents. Overall, the COD removal in each phase was high, between 87 – 95% although only a maximum of 4.24% was due to electricity generation. A significant portion of the COD removal during operation at high HRT and feed concentration was due to methane generation (30-50%), while the effect of oxygen leakage from the cathode into the anode compartment was estimated to account for a flux of up to 3.08 g COD/L-day, leading to significant biomass accumulation within the cell. Upon replacement of the platinum catalyst with the non-precious catalyst at the cathode, the current and power densities generated in the 1.0 mg/cm2 and 2.0 mg/cm2 cells rose by 50.5% and 205%, respectively, to 213.2 ± 13.9 mW/m2 and 431.8 ± 23.6 mW/m2. Importantly, the current generated in these cells was found to be exactly proportional to the catalyst loading level. The COD removal in these runs amounted to 79.6% and 92.2% of acetate, comparable to that achieved with the platinum catalyst. The coulombic efficiency increased as a result of the improved current densities to 6.71% and 12.18%, respectively. The improved performance with the non-precious catalyst demonstrates that it is a potentially attractive replacement for the conventional platinum as the catalyst for energy production. The proportionality between the generated current density and the catalyst loading also suggests that operation at higher catalyst loading levels will lead to further improvement in performance.

The microbial fuel cell (MFC) is an innovative renewable energy technology that also serves to treat wastewater through the bacteria-driven oxidation of organic substrates. The liquid anolyte contains the organic substrate to be oxidized, while the catholyte contains the substance to be reduced. In a dual-chamber MFC, the catholyte typically contains dissolved oxygen or another easily reducible compound (e.g., ferricyanide) in an aqueous solution, while in a single-chamber MFC, gaseous airborne oxygen reacts directly at the cathode. A single-chamber air-cathode microbial fuel cell was operated using an acetate substrate and a 0.2 mg/cm2 platinum catalyst cathode in the initial stages of the project. The platinum catalyst was airbrushed onto a carbon paper cathode and hot-pressed onto a Nafion 117 membrane. After the platinum runs were completed, the MFC was disassembled, cleaned and reassembled with a new non-precious nitrogen-doped carbon composite catalyst replacing the platinum. Two MFCs were operated at different loading levels (1.0 mg/cm2 and 2.0 mg/cm2) of the new catalyst. The cell was configured to operate in a fed-batch and upflow modes. Preliminary experiments were conducted using two non-precious catalysts synthesized with different nitrogen precursors, polyaniline and ethylenediamine (EDA). These experiments showed the ethylenediamine-based-catalyst exhibited higher catalytic activity for oxygen reduction (ORR) with a half-wave potential of 0.57 V versus 0.43 V for the polyaniline catalyst. These values were lower than the expected half-wave potential of 0.65 – 0.70 V. Consequently, the catalyst based on EDA was used in all subsequent experiments. SEM images revealed that this catalyst has a fluffy, bulbous, highly porous structure, while EDAX and XRD both detected the presence of residual iron and cobalt from the preparation procedure. Nitrogen (3.57 wt %) and oxygen (4.87 wt %) were also detected from the EDAX analysis. Operation with a hydraulic residence time (HRT) of 24 hours and feed COD concentration of 6.44 g COD/L-day was found to produce the highest power density of 141.7 ± 2.4 mW/m2 from the experiments conducted on the platinum catalyst. A subsequent run at a 12 hour HRT and 3.22 g COD/L-day feed produced only 104.4 ± 5.2 mW/m2. When the cell operation was reverted to the original high HRT and high feed COD concentration, the original current was not recovered and in fact remained virtually unchanged from the level attained at the lower HRT and COD feed level (105.7 ± 2.7 mW/m2). It was suspected that the decreased acetate concentration in the second phase, and the biomass accumulation in the replicate third phase were the cause of the decreased currents. Overall, the COD removal in each phase was high, between 87 – 95% although only a maximum of 4.24% was due to electricity generation. A significant portion of the COD removal during operation at high HRT and feed concentration was due to methane generation (30-50%), while the effect of oxygen leakage from the cathode into the anode compartment was estimated to account for a flux of up to 3.08 g COD/L-day, leading to significant biomass accumulation within the cell. Upon replacement of the platinum catalyst with the non-precious catalyst at the cathode, the current and power densities generated in the 1.0 mg/cm2 and 2.0 mg/cm2 cells rose by 50.5% and 205%, respectively, to 213.2 ± 13.9 mW/m2 and 431.8 ± 23.6 mW/m2. Importantly, the current generated in these cells was found to be exactly proportional to the catalyst loading level. The COD removal in these runs amounted to 79.6% and 92.2% of acetate, comparable to that achieved with the platinum catalyst. The coulombic efficiency increased as a result of the improved current densities to 6.71% and 12.18%, respectively. The improved performance with the non-precious catalyst demonstrates that it is a potentially attractive replacement for the conventional platinum as the catalyst for energy production. The proportionality between the generated current density and the catalyst loading also suggests that operation at higher catalyst loading levels will lead to further improvement in performance.

Bipolar plates used in a PEM fuel cell must have high electric conductivity, good mechanical and chemical stability, low gas permeability, and low cost. For portable applications, lightweight and low volume should also be considered. Our laboratory has developed a new heterogeneous composite bipolar plate. Which has many advantages, such as low contact resistance, good chemical stability, low cost, lightweight and high performance. Since automation is the key to low cost, this research is to develop the automatic fabrication process of the new plate. The process involves mainly the making of carbon fiber bunches by sticking the central portion of the carbon fiber together with glue but leaving both ends free. Secondly, use injection molding to form the plastic main body with all the carbon fiber bunches. In order to shorten the developing time, we divide the process into four parts: (1) the unfolding of carbon fiber (2) the automation of gluing (3) harden and cutting to sizes (4) Injection molding of bipolar plates. This thesis has completed the study of the first three parts of the manufacturing processes. We have compared the contact resistances between our product and the previously handmade ones and found that the results are satisfactory.

Rapidly rising fossil fuel costs along with increased environmental awareness has encouraged the development of alternative energy sources. Such sources include fuel cells, wind, solar and ocean tide power. Among them, fuel cells have received increased interest in the recent years. This is mainly due to their high efficiency, modularity, and simple construction. However, due to their low output voltage and wide variation from no load to full load, a power electronics converter is required to interface the fuel cell with its loads. This dissertation focuses on developing a set of considerations that will assist designers of the power electronics converter in the design and optimization of the system. These design considerations are obtained analytically and verified experimentally and allow obtaining an efficient and stable fuel cell – power converter system. In addition to the design guidelines this dissertation presents new power converter topologies that do not require the use of transformers to achieve a large voltage gain. Further a new modular fuel cell power converter system that divides the fuel cell stack to optimize power generation is proposed. It is shown by means of mathematical analysis and experimental prototypes that the proposed solutions contribute to the reduction of size and cost of the power converter as well to increase the efficiency of the system.

The electrochemical performance of a polymer electrolyte membrane fuel cell is known to be dominated by the cathode processes comprising the various reaction and transport steps in the overall oxygen electro-reduction to water occurring in the catalyst layer (CL). This thesis is concerned with one such transport process – oxygen transport in ionomer phase of the CL – and the synthesis/characterization of platinum catalyst on an alternative support – carbon nanotubes (CNT). Specifically, the objectives of the thesis are: (i) exploration of methods for determining the effective permeability of oxygen in the ionomer phase of the carbon-ionomer composite representing the PEMFC catalyst layer (ii) synthesis of Pt/CNT catalysts and characterization thereof. An electrochemical method for determination of oxygen permeability in Nafion and Nafion-carbon composite films was explored. Since the method is suitable for dense films, mathematical model for data analysis had to be modified to allow treatment of porous films. Applying the modified model to the porous Nafion film, the oxygen permeation in the Nafion phase was found to agree with the literature data for oxygen permeation in Nafion membranes. However, no relationship between the effective permeability and ionomer content was found. Two methods for synthesis of Pt/CNT catalysts were studied – the precipitation method and the colloidal/ethylene glycol method. Functionalization of CNTs was found to be critical to obtaining any significant amount of Pt deposition on CNT. The precipitation method did not yield reproducible results. Pt/CNT catalysts of desired properties were synthesized via the colloidal/EG method. It was found that a high pH of 8.5 to 10.5 resulted in smallest Pt particle size. The Pt particles size was determined to range 2-4 nm. The synthesized Pt/CNT catalysts were also tested in a fuel cell environment. Steady-state polarization curves in humidified H2/Air system were obtained that demonstrated performance comparable to commercial electrodes in that cell potential of greater than 0.6 V at current density of 800 mA/cm2 electrode area and a limiting current density of 1200 mA/cm2 electrode area were observed. / Thesis (Master, Chemical Engineering) -- Queen's University, 2009-01-13 14:46:53.853

Solid Oxide Fuel Cells (SOFC) as the heat source for a heat engine power cycle can greatly increase the overall efficiency. The maximum efficiency is limited in at least the following ways. All thermal heat engine power cycles are limited by the Carnot efficiency which is a function of the hot and cold reservoirs the cycle operates between. Another irreversibility that limits the maximum efficiency of a fossil fuel cycle is the combustion reaction. In a boiler or combustion chamber, the chemical reaction of combustion happens spontaneously, meaning that the reaction happens without being used to generate power. A fuel cell decreases this irreversibility because it generates work as the combustion reaction happens. A SOFC can do this without an expensive catalyst due to the higher operating temperature. The power generated by the fuel cell can be added to the power generated by the thermal power cycle operating from the exhaust of the SOFC. The total work generated would be more than the system would have generated from just the heat engine resulting in a higher overall efficiency for the cycle. A SOFC and a recovery power cycle was simulated in Engineering Equation Solver (EES) to solve for ideal operating conditions. The fuel cell and gas turbine system had a net power output of 136 MW and had an efficiency of 60.84%, assuming the fuel cell had an 85% fuel utilization.