A spray deposition manufacturing route has been developed for the fabrication of carbon nano-structured and micro-structured energy storage devices in a thin film format, with controlled film thickness, homogeneous film surface morphology and high electrochemical performance for both supercapacitors and lithium ion battery anodes. Three types of low cost commercially available carbon materials (graphite, activated carbon and carbon black) have been investigated, and electrodes characterised in terms of surface morphology, surface chemistry, microstructure and electrochemical properties. By using ball milling, CO₂ activation and adding suitable carbon conductive additives, nano-graphite-based film electrodes (one meter long and ~ 3 µm thickness) have been fabricated, with excellent ion transport and low electrical resistance (< 1.8 Ω). Specific capacitance of 110 F/g at a scan rate of 100 mV/s in 1 M H₂SO₄ was achieved. The high rate performance of activated carbon-based electrodes ( ~2 µm thickness) has been enhanced by reducing the contact resistance of electrode/current collector interface and building a well-interconnected and hierachical meso/macro-porous structure. A specific capacitance of over 120 F/g at a scan rate of 600 mV/s or 20 A/g current density in 1 M H₂SO₄ was achieved. The performance of carbon black-based electrodes (~4 µm thickness) in different electrolytes has been studied in both two- and three-electrode cells. High specific capacitances of 260 F/g at 1 A/g was achieved in 6 M KOH, together with energy and power densities of 21 kW/kg and 18 Wh/kg in 1 M Na₂SO₄. Finally, graphite-based electrodes for rechargeable lithium-ion batteries have also been fabricated with controlled film thickness from ~ 900 nm to ~ 40 µm and 98% capacity retention of 371 mA/g after 20 cycles. Spray deposition has been demonstrated to have the potential for scalability in the manufacture of carbon-based thin film electrodes with competitive properties.

This dissertation describes photocoulometric and AC impedance studies of dye-modified electrodes. The photocoulometric technique allowed photoelectrochemical phenomena to be observed without mass transport effects. These measurements confirmed the photoconductive properties of monomeric silicon phthalocyanine dye. They also showed that the photo-assisted oxidation of hydroquinone to benzoquinone at n-tin oxide electrodes modified with this dye involved a cation dye intermediate with a lifetime of between 0.05 and 350 ns, with the rate limiting step being charge transport through the dye film or charge transfer across the interface between the dye and the substrate. AC impedance studies included Mott-Schottky measurements and faradaic impedance experiments on tin oxide and gold metallized plastic optically transparent electrodes. They also examined the substrates modified with monomeric silicon phthalocyanine and chloro-gallium phthalocyanine. The Mott-Schottky measurement procedure was free of systematic errors that affected other published work, and the results of these measurements were consistent with those found by independent methods. The faradaic impedance technique was applied to dye-modified electrodes for the first time. These studies found evidence for an adsorption or electrodeposition process in the oxidation of hydroquinone at these electrodes, and gave exchange current densities that were consistent with the values that were found by other methods.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Electrogenerated chemiluminescence (ECL) of new, highly fluorescent molecules was studied. Six novel, highly fluorescent, green emitters were synthesized by incorporating an acceptor group like 2,1,3-Benzothiadiazole between different donor groups. The structural effects on the electrochemical, spectroscopic, and ECL behavior are shown in detail. Stable electrochemistry and high PL quantum yield were observed. Most of the ECL was visible by the naked eye. Well-known, fluorescent, polyaromatic hydrocarbons (PAH), like 9,10-diphenylanthracene derivatives, pyrene, and anthracene were incorporated between two bulky fluorene derivative groups. The fluorene substitutions block the active positions of the PAH cores, permitting the formation of stable radical ions upon electrochemical oxidation or reduction. Such a tailoring led to increase electrochemical reversibility and tuning of the ECL wavelength. Fluorene-based DPA (FDF) is characterized by a highly efficient and stable blue-cyan color. Another interesting type of molecules was star-shaped structures. The effects of structure on the electrochemistry and spectroscopy of a series of star-shaped, rigid molecules was examined. T1-T4 is composed of oligofluorene arms with truxene as a central core basically there were weak donor and weak acceptors. The ECL quantum efficiency was near 80% for the long-arm T4. One of the interesting goals in ECL is to find ECL emitters in aqueous media. Organic nanoparticles (ONPs) were chosen to achieve this goal. An organic nanoparticle (ONPs) is still challenging area in nanoscience. The key factor of such a challenge comes from the difficulty to control the size and shape of the prepared nanoparticles. ONPs of common hydrocarbon ECL emitters like rubrene and 9,10-diphenylanthracene (DPA) were prepared in aqueous solution using a reprecipitation method. ECL of rubrene NPs was observed when tripropylamine (TPrA) was used as a coreactant, and weaker ECL of DPA NPs was observed when the oxalate ion was used as a coreactant. The ECL of ONPs in aqueous media may open a new field in ECL, allowing the exploration of more phenomena in organic nanoscience. Organic nanoparticle ECL (especially if one able to make small size to be diffused easily) has potential application as a tag for the analysis of biologically interesting molecules. / text

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