Use of waste glycerol as fuel in microbial fuel cells (MFCs) would result in the production of valuable metabolites and electricity, to the benefit of biodiesel operations. In this research, the effect of salt and other compounds found in waste glycerol from biodiesel production on the metabolism and performance of three cultures (Escherichia coli W3110, Propionibacterium freudenreichii ssp. shermanii and mixed culture AR2), used as anodic catalysts in an MFC was studied. MFC experiments were performed in parallel with serum bottle fermentations to allow for comparison of glycerol consumption and metabolite yield. The effect of salt content on the performance of all three cultures was positive in most cases and negligible in others. Using waste glycerol with an increased concentration of other compounds (other than salt) only reduced the performance of AR2, however an inhibitory effect on the rate of glycerol consumption was observed with both AR2 and P. freudenreichii ssp. shermanii. For all strains, the rate of glycerol consumption was slower in MFCs than in fermentations as a result of the electrochemical environment; the yield of various metabolites also differed.

The goal of current research is probing the relationship between catalyst features and the fuel cell performance with a range of in-depth structural analysis. The study investigated different catalyst systems including core-shell structured catalyst, catalysts with unique carbon-transition metal oxide supports. PtRu catalysts nanoparticles with unique core-shell structure, one of the most practical catalysts in PEMFC technology, have been successfully obtained with the evidence from the characterization results. It is found that the enhanced CO oxidation may be achieved through the interactions between the Pt shell and Ru core atoms, which can modify the electronic structure of the Pt surface by the presence of subsurface Ru atoms or by disrupting the Pt surface arrangement. Furthermore, the possibility of presence of the compressive strain within the Pt rich shell is proved by the lattice measurements, which could significantly affect the catalytic activity. Pt catalysts supported on complex oxide and carbon support were studied to investigate the relationship between the catalyst and its support. Observations from STEM images and HAADF and energy dispersive X-ray spectrometry demonstrate the preferential distribution of Pt nanoparticles on the hybrid supports, which include Nb2O3 / C, Ta2O5 / C, (Nb2O3+TiOx) / C, (Ta2O5+TiOx) / C, and (WO3+TiOx)/C). Such evidence indicates the interaction between the catalyst and support is based on the presence of an interconnected oxide network over the carbon support and the presence of Pt strongly connected to the oxide network. In addition, using electron energy loss spectroscopy (EELS), the electronic structure of the catalyst support under various conditions was also studied to provide further evidence of the strong metal support interaction effect. / Thesis / Doctor of Philosophy (PhD)

Multifunctional material systems are systems that contain individual materials or components which are capable of performing multiple functions. The combination of functions into single entities allows for system-level benefits that are not possible through the optimization of subsystems independently. Benefits enabled through multifunctional designs include increased system efficiency through mass and or volume savings as well as part count reductions. Fiber reinforced polymer (FRP) composite materials are lightweight, high-strength materials that can be tailored to achieve a unique set of properties. These characteristics make composites ideal materials for multifunctional designs. The current research focuses on the production, optimization, and characterization of a multifunctional fuel cell system. This product combines fuel cell technology with composite materials technology to achieve a design that produces electrical power while also providing specific load carrying capability. The study investigates new system designs and new processing techniques, including vacuum assisted resin transfer molding (VARTM) and pultrusion. A metric which allows for the characterization of multifunctional fuel cell systems is developed and applied to three fuel cell designs. This metric uses Frostig's Higher Order Theory to analyze the mechanical behavior of the cells while the electrical performance of each device is based on its specific power output. For the cells investigated here, multifunctional efficiencies between 22% and 69% are achieved. The multifunctional efficiency is highly dependent on the transverse pressure applied to the fuel cell components, as this pressure determines ohmic resistances, mass transfer properties, and sealing abilities of the systems. The mechanical pressures at the GDL/Polar Plate interface of a model fuel cell system are explored via experiments with pressure-sensitive film as well as FEA studies, and an optimum structural pressure of approximately 200 psi is identified. Additionally, the effects that concentrated, bending loads have on the electrochemical performance of a model multifunctional cell are explored. The results indicate that one must give generous consideration to the out of plane loads which the fuel cell system will be subjected to (both inherent, structural loads resulting from processing conditions and external, applied loads encountered during operation) in order to achieve optimal multifunctional efficiency. / Ph. D.

The catalyst layer of a proton exchange membrane (PEM) fuel cell is a mixture of polymer, carbon, and platinum. The characteristics of the catalyst layer play a critical role in determining the performance of the PEM fuel cell. This research investigates the role of catalyst layer composition using a Central Composite Design (CCD) experiment with two factors which are Nafion content and carbon loading while the platinum catalyst surface area is held constant. For each catalyst layer composition, polarization curves are measured to evaluate cell performance at common operating conditions, Electrochemical Impedance Spectroscopy (EIS), and Cyclic Voltammetry (CV) are then applied to investigate the cause of the observed variations in performance. The results show that both Nafion and carbon content significantly affect MEA performance. The ohmic resistance and active catalyst area of the cell do not correlate with catalyst layer composition, and observed variations in the cell resistance and active catalyst area produced changes in performance that were not significant relative to compositions of catalyst layers. / Master of Science

A multifunctional structural polymer electrolyte membrane (PEM) fuel cell was designed, developed and manufactured. The structural fuel cell was designed to represent the rear rib section of an aircraft wing. Custom membrane electrode assemblies (MEA s) were manufactured in house. Each MEA had an active area of 25cm2.The platinum loading on each electrode (anode and cathode) was 0.5mg/cm2. Sandwiched between the electrodes was a Nafion 212 electrolyte membrane. Additional components of the structural fuel included metallic bipolar plates and end plates. Initially all the components were manufactured from aluminium in order for the structural fuel cell to closely represent an aircraft wing rib. However due to corrosion problems the bipolar plate had to be manufactured from marine grade 361L stainless steel with a protective coating system. A number of different protective coating systems were tried with wood nickel strike, followed by a 5μm intermediate coat of silver and a 2μm gold top coat being the most successful. Full fuel cell experimental setup was developed which included balance of plant, data acquisition and control unit, and a mechanical loading assembly. Loads were applied to the structural fuel cells tip to achieve a static deflection of ±7mm and dynamic deflections of ±3mm, ±5mm, and ±7mm. Static and dynamic torsion induced 1° to 5° of twist to the structural fuel cell tip. Polarisation curves were produced for each load case. Finite element analysis was used to determine the structural fuel cell displacement, and stress/strain over the range of mechanical loads. The structural fuel cells peak power performance dropped 3.9% from 5.5 watts to 5.3 watts during static bending and 2% from 6.2 watts to 6.1 watts during static torsion. During dynamic bending (2000 cycles) the structural fuel cell peak power performance dropped 11% from 6.7 watts to 6 watts (3mm deflection at 190N), 23% from 6.3 watts to 4.8 watts (5mm deflection at 270N), and 41% from 7.2 watts to 5 watts (7mm deflection at 350N). During dynamic torsion (2000 cycles) the structural fuel cell peak power performance dropped 16% from 6 watts to 5.1 watt (3° of torsional loading), and 30% from 6.4 watts to 4.3 watts (5° of torsional loading). The simulated (finite element modelling) displacement of -6.6mm (At maximum bending load of 364.95N) was within 9% of the actual measured displacement of -7.2mm at 364.95N. Furthermore the majority of the simulated strain values were within 10% of the actual measured strain for the structural fuel cell.

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

Essa dissertação dedica-se ao estudo de instabilidades cinéticas em células a combustível de membrana trocadora de prótons (PEMFC, do inglês proton exchange membrane fuel cell). As PEMFC apresentam baixíssima perda por polarização quando operadas com H2. Contudo, quando o processo de produção de H2 se dá por reforma catalítica de hidrocarbonetos, CO está presente em níveis inaceitáveis para PEMFC equipada com ânodo de Pt/C. Dentre as propostas para superar esse problema, ligas bimetálicas de Pt têm se mostrado uma alternativa promissora para tornar a célula mais tolerante à CO. Além disso, é plausível que um comportamento dinâmico surja nesse tipo de sistema eletroquímico, devido à interação de fatores como transferência de massa, corrente, potencial do eletrodo e a presença de um veneno catalítico, nesse sistema o CO, que pode ser uma impureza do H2 ou um intermediário de reação (em células a combustível alimentadas diretamente com metanol, ácido fórmico ou etanol). Uma das motivações em se estudar tais instabilidades cinéticas é que uma célula a combustível operando em regime oscilatório pode resultar em um desempenho superior, uma vez que a limpeza auto-organizada da superfície previne que o ânodo seja completamente envenenado por CO. Nesse contexto, estudou-se a emergência de instabilidades cinéticas em PEMFC operando com ânodo de Pd-Pt/C ou Pd/C durante a oxidação de H2 e H2/CO, assim como em célula a combustível a metanol direto (DMFC, do inglês direct methanol fuel cell) com ânodo de Pt black. Os resultados indicaram que oscilações de potencial surgem na PEMFC durante a oxidação H2/CO sobre Pd-Pt/C assim como sobre Pd/C. Acoplando as medidas de potencial com espectrometria de massas on line na saída do ânodo, investigou-se o consumo de CO e a produção de CO2 durante as oscilações. Observou-se que as oscilações de potencial levam a variações na fração molar de CO e CO2. Adicionalmente, identificou-se oscilações de potencial em DMFC, fenômeno até então não relatado na literatura. / This dissertation deals with kinetic instabilities in proton exchange membrane fuel cells (PEMFC). PEMFCs show very small polarization losses when operating with pure H2. However, when the H2 production takes place by catalytic reforming of hydrocarbons, CO is present in the fuel stream at unacceptable levels for PEMFC equipped with a Pt/C anode. Among the possibilities to overcome this problem, bimetallic Pt alloys have proven to be a promising alternative to increase CO tolerance. Furthermore, it is plausible that a dynamic behavior emerge in such electrochemical system due to the interaction of factors like mass transfer, current, potential, and the presence of a catalyst poison, for this system CO which can be a H2 impurity or a reaction intermediate (in direct methanol/formic acid/ethanol fuel cells). One of the motivations for studying kinetic instabilities is that a fuel cell operating under oscillatory regime might result in higher performance, because the self-organized cleaning of the surface prevents the anode to be completely poisoned by CO. In this context, kinetic instabilities were studied in PEMFC operating with Pt-Pd/C or Pd/C anode during the oxidation of H2 and H2/CO mixture, as well as in direct methanol fuel cell (DMFC) with Pt black anode. It was observed the emergency of potential oscillations during the H2/CO oxidation on both catalysts, Pt-Pd/C and Pd/C. By coupling the potential measurements with on line Mass Spectrometry in the anode outlet it was investigated a variation in the concentration of CO and CO2 during oscillatory dynamic. It was found that the potential oscillations lead to variations in the molar fraction of CO and CO2. Additionally, it was observed potential oscillations in DMFC, phenomenon not previously reported in the literature.

This thesis focuses on developing support materials for direct methanol fuel cell (DMFC) catalysts. The approach involves using graphene based materials including reduced graphene oxide (rGO), reduced graphene oxide-activated carbon (rGO-AC) hybrid and reduced graphene oxide-silicon carbide (rGO-SiC) hybrid as a support for Pt and Pt-Ru nanoparticles. Pt/rGO and Pt-Ru/rGO catalysts were synthesized by three chemical reduction methods: (1) modified polyol, (2) ethylene glycol (EG) reduction and (3) mixed reducing agents (EG + NaBH4) methods. The synthesized catalysts were characterized by physical and electrochemical techniques. The results demonstrated that Pt/rGO-3 and Pt-Ru/rGO-3 catalyst synthesized with Method-3 exhibit higher electrochemical active surface area (ECSA) than the other rGO supported and Vulcan supported commercial electrocatalysts. In addition, Pt/rGO-3 and Pt-Ru/rGO-3 catalysts showed better oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) activities, respectively. The DMFC tests under different cell temperature (30, 50 and 70°C) and methanol concentration (1, 2 and 4 M) conditions further demonstrated the higher catalytic activity of the catalysts. The peak power density obtained with Pt/rGO-3 cathode and Pt-Ru/rGO-3 anode catalysts at 70°C with 1 M methanol was 63.3 mW/cm2 which is about 59 % higher than that of commercial Pt/C and Pt-Ru/C catalysts. The enhanced performance was attributed to the highly accessible and uniformly dispersed nanoparticles on rGO support with large surface area and high conductivity. Pt/rGO-AC (reduced graphene oxide-activated carbon) and Pt-Ru/rGO-AC catalysts were synthesized with various rGO:AC support ratios by using biomass derived AC. The results showed that the catalysts with content of 20 wt. % AC support (Pt/rGO-AC20 and Pt-Ru/rGO-AC20) exhibited higher ECSA, better catalytic activity and stability among all the tested catalysts. With 1 M methanol and 70°C cell temperature, the MEA with Pt/rGO-AC20 cathode and Pt-Ru/rGO-AC anode catalysts gave 19.3 % higher peak power density (75.5 mW/cm2), than that of Pt/rGO-3 and Pt-Ru/rGO-3 catalysts. The better DMFC performance was due to the incorporation of AC particles into rGO structure which builds electron-conductive paths between rGO sheets, facilitates the transport of reactant and products and provides higher specific surface area for the uniform distribution of nanoparticles. Pt/rGO-SiC catalysts were synthesized with variable silicon carbide (SiC) content in the hybrid support. Pt/rGO-SiC10 (10 wt. % of SiC support) catalyst showed higher ECSA and better catalytic activity compared to the Pt/SiC, Pt/rGO-3 and Pt/rGO-SiC20 catalysts. In addition, the Pt/rGO-SiC10 gave 14.2 % higher DMFC performance than the Pt/rGO-3 catalyst in terms of power density. The high performance can be attributed to the insertion of the SiC nanoparticles into rGO structure that improves the conductivity and stability of the catalyst by playing a spacer role between rGO layers. In summary, the overall results showed that the catalytic performance of the catalysts followed the trend in terms of support material: rGO-AC20 > rGO-SiC10 > rGO > Vulcan. The study demonstrated that the novel rGO-AC and rGO-SiC hybrids are promising catalyst supports for direct methanol fuel cell applications.

Une pile à combustible microbiennes (PCM) est un dispositif capable de produire de l’énergie électrique à partir d’énergie chimique grâce à l’activité catalytique des bactéries en présence de combustibles organiques. Ces travaux de thèse ont eu pour objectif la synthèse des nouveaux matériaux d’anode et de cathode qui pourraient constituer des alternatives aux matériaux à base de platine. Coté anode, nous avons synthétisé des matériaux par précipitation chimique sur du graphite en poudre à partir de mélanges contenant des ions ferreux et sulfures. Les caractérisations physicochimiques ont montré la formation de composés soufrés (mackinawite, polysulfures et soufre élémentaire) qui se transforment en produits soufrés plus oxydés en présence d’air. La formation de vivianite a été confirmée dans le cas d’un excès d’ions ferreux par rapport aux ions sulfures. Les analyses électrochimiques montrent que ces matériaux ont un comportement réversible avec des densités de courant d’oxydation élevées à bas potentiel. Coté cathode, nous avons choisi la synthèse par voie électrochimique d’un film de MnOx sur substrat d’acier inoxydable. Les caractérisations physicochimiques ont démontré la formation de la birnessite. Les analyses électrochimiques montrent que la réduction de ce matériau conduit à des courants cathodiques significatifs mais avec une réversibilité limitée, même en présence d’air. La réalisation de prototypes de PCM dans lesquels l’anode à base de composés soufrés est immergée dans une solution de terreau et la cathode à base de MnOx est au contact de l’air, a permis d’obtenir des puissances instantanées maximales de l’ordre de 12 W.m-3 et 1,8 W.m-2, et des densités de courant de l’ordre de 25 A.m-3 et 3,8 A.m-2. Un travail d’optimisation du fonctionnement de PCM a été réalisé. Ainsi, l’augmentation de la conductivité de la solution anodique et la diminution de quantité de sédiment dans la solution de terreau a permis d’améliorer la réponse électrochimique du matériau anodique et d’obtenir des puissances instantanées maximales de l’ordre de 17,5 W.m-3 et 2,7 W.m-2, et des densités de courant de l’ordre de 60 A.m-3 et 9,2 A.m-2. Le facteur limitant reste toujours le comportement électrochimique du film de MnOx. / A microbial fuel cell (MFC) is a device allowing the production of electric power from chemical energy thanks to the catalytic activity of bacteria in presence of organic fuel. These works aimed the synthesis of new anode and cathode materials which could be an alternative to platinum materials. On the anode side, we synthesized the materials by chemical precipitation on powder graphite from mixtures containing ferrous and sulfide ions. Physicochemical characterizations showed the formation of sulfur compounds (mackinawite, polysulfide and elementary sulfur) which transform into sulfur products more oxidized in presence of air. Formation of vivianite was confirmed in the case of an excess of ferrous ions in relation to sulfide ions. Electrochemical analysis shows that these materials have a reversible behavior with high current densities at low voltage. On the cathode side, we chose electrochemical synthesis of an MnOx film on stainless steel substrate. Physicochemical characterizations showed birnessite formation. Electrochemical analysis show that the reduction of this material Leeds to significative cathodic currents but with a limited reversibility, even in presence of air. The realization of MFC prototypes in which the sulfur compounds-based anode is submerged in compost solution and the MnOx-based cathode is in contact with air, allowed the getting of maximum instantaneous powers on the order of 12 W.m-3 and 1,8 W.m-2, and current densities on the order of 25 A.m-3 et 3,8 A.m-2. An optimization work of the MFC functioning has been done. So, the conductivity increase of the anodic solution and the decrease of sediment quantity in the compost solution allowed the improvement of the electrochemical response of the anodic material and to obtain maximal instantaneous powers on the order of 17,5 W.m-3 and 2,7 W.m-2, and current densities on the order of 60 A.m-3 et 9,2 A.m-2. The limiting factor remains the electrochemical behavior of the MnOx film.

Tese de doutoramento. Engenharia Química e Biológica. Universidade do Porto. Faculdade de Engenharia. 2011