Density functional theory has been used to investigate cathode materials for rechargeable batteries, carbon nanotube interactions with catalyst particles and transition metal catalyzed hydrogen release in magnesium hydride nanoclusters. An effort has been made to the understand structural and electrochemical properties of lithium iron silicate (Li2FeSiO4) and its manganese-doped analogue. Starting from the X-ray measurements, the crystal structure of Li2FeSiO4 was refined, and several metastable phases of partially delithiated Li2FeSiO4 were identified. There are signs that manganese doping leads to structural instability and that lithium extraction beyond 50% capacity only occurs at impractically high potentials in the new material. The chemical interaction energies of single-walled carbon nanotubes and nanoclusters were calculated. It is found that the interaction needs to be strong enough to compete with the energy gained by detaching the nanotubes and forming closed ends with carbon caps. This represents a new criterion for determining catalyst metal suitability. The stability of isolated carbon nanotube fragments were also studied, and it is argued that chirality selection during growth is best achieved by exploiting the much wider energy span of open-ended carbon nanotube fragments. Magnesium hydride nanoclusters were doped with transition metals Ti, V, Fe, and Ni. The resulting changes in hydrogen desorption energies from the surface were calculated, and the associated changes in the cluster structures reveal that the transition metals not only lower the desorption energy of hydrogen, but also seem to work as proposed in the gateway hypothesis of transition metal catalysis.

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.

Interfacial polarization resistances limit the performance of many thin film solid-state devices, especially at low temperatures. To improve performance, a fundamental understanding of the electrode kinetics that govern interfacial reaction rates must be developed. The goal of this work is to determine site-specific reaction mechanisms and the relative significance of various reactions in order to quantify optimum structural parameters within the cathode microstructure. Key parameters include the length of triple phase boundary (TPB), the quantity of exposed electrolyte/electrode surface, and the ratio of electrolyte to electrode material. These parameters, when studied in a specific system, can be incorporated into broader models, which will encompass the specific conductivity of each component to develop an optimized three-dimensional network. The emphasis of this work is the systematic control and manipulation of potential cathodic reaction sites in order to develop an understanding of the relative importance of specific reaction sites. Since the physical dimensions of reaction sites are relatively small, an approach has been developed that utilizes micro-fabrication (similar to that used in integrated-circuit fabrication) to produce small and highly controlled microstructures. Investigations were made into the nature and reactivity of Triple Phase Boundaries (hereafter TPB) through the use of patterned platinum electrodes since only the TPBs are active in these electrodes. After the processing details of micro-fabrication were established for the platinum electrodes, patterned Mixed-Ionic/Electronic Conducting (MIEC) electrodes were fabricated and studied using impedance spectroscopy to determine the contributions from the MIEC surface versus the TPB. Systematically changing the geometry of the MIEC electrodes (thickness and line width) allowed for the determination of the effect of ambipolar transport within the MIEC on the activity of MIEC surfaces versus the TPB. This information is critical to rational design of functionally graded electrodes (with optimal particle size, shape, porosity and conductivity). In addition to experimental studies, representative patterned electrode samples were made available for collaborative studies with surface scientists at other institutions to provide additional techniques (such as Raman Spectroscopy) on the carefully designed and controlled cathode surfaces.

Nitroxide polymer brushes grafted on silica nanoparticles as binder-free cathode for organic radical battery have been investigated. Scanning electron microscopy, transmission electron microscopy, infrared spectroscopy and electron spin resonance confirm that the nitroxide polymer brushes are successfully grafted onto silica nanoparticles via surface-initiated atom transfer radical polymerization. The thermogravimetric analysis results indicate that the onset decomposition temperature of these nitroxide polymer brushes is found to be ca. 201 ◦C. The grafting density of the nitroxide polymer brushes grafted on silica nanoparticles is 0.74¡V1.01 chains nm−2. The results of the electrochemical quartz crystal microbalance indicate that the non-crosslinking nitroxide polymer brushes prevent the polymer from dissolving into organic electrolytes. Furthermore, the electrochemical results show that the discharge capacity of the polymer brushes is 84.9¡V111.1 mAh g−1 at 10 C and the cells with the nitroxide polymer brush electrodes have a very good cycle-life performance of 96.3% retention after 300 cycles.

The electrochemical behavior of a poly(2,2,6,6-tetramethylpiperidin- 1-oxyl-4-yl methacrylate) (PTMA) cathode in organic radical batteries with lithium bis(trifluoromethylsulfonyl)imide in N-butyl-N-methyl- pyrrolidinium bis(trifluoromethylsulfonyl)imide (LiTFSI/BMPTFSI) ionic liquid electrolytes is investigated. The ionic liquid electrolytes containing a high concentration of the LiTFSI salt have a high polarity, preventing the dissolution of the polyvinylidene fluoride (PVdF) binder and PTMA in the electrolytes. The results of cyclic voltammetry and AC impedance indicate that an increase in the LiTFSI concentration results in a decrease in the impedance of the lithium electrode, which affects the C-rate performance of batteries. The discharge capacity of the PTMA composite electrode in a 0.6 m LiTFSI/BMPTFSI electrolyte is 92.9 mAh g−1 at 1 C; its C-rate performance exhibits a capacity retention, 100 C/1 C, of 88.3%. Moreover, the battery with the 0.6-m LiTFSI/BMPTFSI electrolyte has very good cycle-life performance.

To minimize the size of the electronic ballast, a half-bridge load- resonant inverter with a cascading Rosen-type piezoelectric transformer (PT) is designed for cold cathode fluorescent lamps (CCFLs). The electrical characteristics of the PT are investigated to obtain a higher voltage gain by adapting the load impedance to the interposed network. The circuit parameters are selected under the considerations of (1) the minimum inductor size, (2) the higher circuit efficiency, (3) the rated current of the PT, and (4) the stable lamp operation. The electronic ballasts are designed for operating the lamp at the rated lamp power and with dimming control by asymmetrical pulse-width-modulation (APWM),respectively. Laboratory circuits are assembled and, experimental tests are carried out to validate the theoretical analyse

For a back-light module with multiple cold cathode fluorescent lamps (CCFLs) in mid-size or large size liquid crystal displays, a balance scheme must be included to have approximately equal currents among the lamps and hence to output equal brightness. In this thesis, a half-bridge inverter is adopted to drive multiple step-up transformers with the same turn ratio, in which the primary windings of the transformers are connected in series whereas the second windings drive CCFLs in parallel. Due to the series connection of the transformer sets, the current going through the primary windings is identical, so that the lamp currents from second windings tend to be equal. A driver circuit with the proposed scheme is designed for 8 U-type cold cathode fluorescent lamps in a 32-inch backlight module. The simulation and experimental results demonstrate the effectiveness of the balance scheme, even for the lamps operating at low current.

<p>Fuel cells are promising candidates for converting chemical energy into electrical energy. The Molten Carbonate Fuel Cell (MCFC) is a high temperature fuel cell that produces electrical energy from a variety of fuels containing hydrogen, hydrocarbons and carbon monoxide. Since the waste heat has a high temperature it can also be used leading to a high overall efficiency.</p><p>Material degradation and the cost of the components are the problems for the commercialisation of MCFC. Although there are companies around the world starting to commercialise MCFC some further cost reduction is needed before MCFC can be fully introduced at the market.</p><p>In this work, alternative materials for three different components of MCFC have been investigated. The alternative materials should have a lower cost compared to the state-of-the-art materials but also meet the life-time goal of MCFC, which is around 5 years. The nickel dissolution of the cathode is a problem and a cathode with lower solubility is needed. The dissolution of nickel for three alternative cathode materials was investigated, where one of the materials had a lower solubility than the state-of-the-art nickel oxide. This material was also tested in a cell and the electrochemical performance was found to be comparable with nickel oxide and is an interesting candidate.</p><p>An inexpensive anode current collector material is also desired. For the anode current collector, the contact resistance should be low and it should have good corrosion properties. The two alternative materials tested had low contact resistance, but some chromium enrichment was seen at the grain boundaries. This can lead to a decreased mechanical stability of the material. In the wet-seal area, the stainless steel used as bipolar/separator plate should be coated. An alternative process to coat the stainless steel, that is less expensive, was evaluated. This process can be a suitable process, but today, when the coating process is done manually there seems to be a problem with the adherence.</p><p>This work has been a part of the IRMATECH project, which was financed by the European Commission, where the partners have been universities, research institutes and companies around Europe.</p>

Thesis (Ph. D.)--University of California, San Diego, 2003. / Vita. Includes bibliographical references (leaves 371-389).

This study was undertaken to understand the effect of applied pressure on the performance of the lithium sulfur cathode. Compressible carbon based cathodes and novel nickel based cathodes were fabricated. For each cathode, pore volume and void volume were quantified and void fraction was calculated, compression under 0 to 2MPa was measured, and lithium-sulfur cells were assembled and cycled at pressures between 0 and 1MPa. The cathodes studied had void fractions in the range of 0.45 to 0.90. Specific discharge capacities between 200 and 1100 mAh/g under 1MPa were observed in carbon-based cathodes. Nickel-based cathodes showed increased specific discharge capacity of up to 1300 mAh/g, with no degradation of performance under pressure. The high correlation of specific discharge capacity and void fraction, in conjunction with previous work, strongly suggest that the performance of lithium-sulfur cathodes is highly dependent on properties that influence ionic mass transport in the cathode.