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Heterogeneous nanostructures such as coaxial nanotubes, nanowires and nanorods have been of growing interest due to their potential for high energy-conversion efficiencies and charge/discharge rates in solar cell, energy storage and fuel cell applications. Their superior properties at nanoscale as well as their high surface area, fast charge transport along large interfacial contact areas, and short charge diffusion lengths have made them attractive components for next generation high efficiency energy-conversion devices. The primary focus of this work was to understand the doping mechanism of TiO2 nanotube exclusively with strontium as an alkaline earth metal to shine light on the relation between the observed enhancement in photocatalytic properties of doped TiO2 nanotubes and its structural and electronic characteristics. The mechanism of Sr incorporation into the TiO2 nanotube structure with the hypothesis of possibility of phase segregation has been explored in low concentrations as a dopant and in very high concentrations by processing of SrTiO3 nanotube arrays. Detailed experimental examination of the bulk and surface of the Sr-doped nanotubes has been performed to understand the effect of dopant on electronic structure and optical properties of the TiO2 nanotubes. Moreover, in order to minimize the polarizations associated with the ionic/electronic charge transport in the electrolyte and anode of solid oxide fuel cells (SOFCs), a new platform is developed using vertically oriented metal oxide nanotube arrays. This novel platform, which is made of coaxial oxide nanotubes on silicon substrates, has the potential to simultaneously lower the operating temperature and production cost leading to significant enhancement in the performance of micro-SOFCs.

The focus of this work is to investigate transport phenomena in recently developed microscale fuel cell designs using computational fluid dynamics (CFD). Two microscale fuel cell systems are considered in this work: the membraneless microfluidic fuel cell and a planar array of integrated fuel cells. A concise electrochemical model of the key reactions and appropriate boundary conditions are presented in conjunction with the development of a threedimensional CFD model of a membraneless microfluidic fuel cell that accounts for the coupled flow, species transport and reaction kinetics. Numerical simulations show that the fuel cell is diffusion limited, and the system performances of several microchannel and electrode geometries are compared. A tapered-electrode design is proposed, which results in a fuel utilization of over 50 %. A computational heat transfer analysis of an array of distributed fuel cells on the bottom wall of a horizontal enclosure is also presented. The fuel cells are modelled as flush-mounted sources with prescribed heat flux boundary conditions. The optimum heat transfer rates and the onset of thermal instability are found to be governed by the length and spacing of the sources and the width-to-height aspect ratio of the enclosure. The transition from a conduction-dominated to a convectiondominated regime occurs over a range of Rayleigh numbers. Smaller source lengths result in higher heat transfer rates due to dramatic changes in Rayleigh-Bénard cell structures following transition.

A good understanding of the various mass and heat transport, and electrochemical re-action processes is required for design strategies that lead to increased performance of proton exchange membrane (PEM) fuel cells. Traditionally, attempts at understand¬ing how these processes interact has been through mathematical modeling where efforts have focussed on understanding the cathode. The interaction between mass transport, membrane hydration and the effects of heat generation and transfer com¬plicates our understanding of relevant processes, hampering the effort to improve fuel cell performance. To further our basic understanding of how the power density of a PEM fuel cell can be increased, and, thereby, decrease the cost of a complete fuel cell system, a comprehensive performance model of a PEM fuel cell has been formulated and investigated. This model explicitly examines the anode as well as the cathode, and includes the effects of energy transfer as temperature control is critical to PEM cells. The results of this model suggest that humidification of the cathode gas stream may be reduced at high operating currents, the temperature peak across a single cell increases as operating temperature decreases, and the gas backing has a significant effect on mass transport at typical operating potentials, especially with air operation.

A systematic study of formic acid electrooxidation on polycrystalline palladium is presented. The study begins with a discussion on the oxide growth process on platinum and palladium. CO electrooxidation under controlled mass transport is studied in order to elucidate the manner in which Pd interacts with CO, a proposed poisoning species in formic acid oxidation. The mechanism of formic acid oxidation is studied using various potentiodynamic techniques, including dynamic electrochemical impedance spectroscopy, which provides impedance measurements during a voltammogram. Through kinetic analysis, a model for the oxidation was developed. The impedance measurements support both the dc measurements as well as the results of the oxidation model. It was determined that CO formation was slow on Pd within the time scale of the experiments. The chief cause of surface deactivate was then determined to be the Pd surface interaction with the (bi)sulfate adsorption in the double layer region. / Graduate

<p>The direct methanol fuel cell or DMFC is emerging as a promising alternative energy source for many applications. Developed and developing countries, through research, are fast seeking a cheap and stable supply of energy for an ever-increasing number of energy-consuming portable devices. The research focus is to have DMFCs meeet this need at an affordable cost is problematic. There are means and ways of making this a reality as the DMFC is found to be complementary to secondary batteries when used as a trickle charger, full charger, or in some other hybrid fuel cell combination. The core functioning component is a catalyst containing MEA, where when pure platinum is used, carbon monoxide is the thermodynamic sink and poisons by preventing further reactions at catalytic sites decreasing the life span of the catalyst if the CO is not removed. Research has shown that the bi-functional mechanism of a platinum-ruthenium catalyst is best because methanol dehydrogenates best on platinumand water dehydrogenation is best facilitated on ruthenium. It is also evident that the addition of other metals to that of PtRu/C can make the catalyst more effective and effective and increase the life span even further. In addition to this, my research has attempted to reduce catalyst cost for DMFCs by developing a low-cost manufacturing technique for catalysts, identify potential non-noblel, less expensive metallic systems to form binary, ternary and quarternary catalysts.</p>