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This thesis describes the application of macro, micro, ultra-microelectrodes and microelectrode arrays to the measurement of trace concentrations of nickel and cobalt in sediment and natural waters by adsorptive cathodic stripping voltammetric methods. In addition the measurement of tin by adsorptive cathodic stripping voltammetry in sediment and natural waters is discussed. Also, the application of macroelectrodes and microelectrode arrays to the measurement of lead, cadmium and zinc in sediment and natural waters by anodic stripping voltammetry is considered. In all cases the determination of the six metals was optimised by investigating the influence of various significant parameters, such as in-situ mercury plating, complexing agent concentration, scan rate, pulse height, accumulation time and potential, buffer concentration and pH. The results obtained for these investigations are discussed in this thesis / Doctor of Philosophy (PhD)

In this study it was proposed to investigate the use of 3D metal oxides (specifically titanium oxides) as potential electrode materials for lithium ion batteries. Three different approaches were taken: mesoporous materials to increase the surface area and improve the capacity; nanocrystalline materials to increase the surface area and to investigate any changes that may occur using nanocrystals; and microporous materials that are more open, allowing rapid diffusion of lithium and higher capacities. Of the three categories of materials studies, mesoporous TiO2 was the least promising with low reversible capacities (20 mAh??g-1) due to densification resulting in a loss of surface area. In nanocrystalline rutile an irreversible phase change occurred upon initial intercalation, however after this intercalation occurred reversibly in a single phase mechanism giving capacities of 100 mAh??g-1. A trend in intercalation potential was observed with crystallite size that was related to the ability of the structure to relax and accept lithium. Doping of rutile yielded no real improvement. Brookite gave only low capacities from a single phase intercalation mechanism. TiO2 films produced by a novel electrochemical technique showed that while amorphous films give greater capacities, more crystalline (anatase) films give greater reversibility. Overall, microporous titanosilicates showed the most promise with sitinakite giving a reversible capacity of 80 mAh??g-1 after twenty cycles or double this when dried. The intercalation was found to occur by two steps that generate large changes in crystallite size explaining the capacity fade witnessed. While doping did not improve the performance, cation exchange has proven beneficial. The remaining titanosilicates did not perform as well as sitinakite, however a trend was observed in the intercalation potentials with the wavenumber of the Ti-O Raman stretch. This was due to the covalent nature of the bonding. Upon reduction an electron is added to the bond meaning the energy of the bond determines intercalation potential. Overall, most promise was shown by the microporous titanosilicates. The capacities of sitinakite after drying, are comparable to those of the "zero strain" material Li4Ti5O12. Investigation of the titanosilicates and their ion-exchanged derivatives is a promising path for new lithium-ion battery electrode materials.

The work presented in this thesis is concerned with electrodes modified with carbon nanotubes. Carbon nanotubes have been characterised with special emphasis on the oxygenated species generated from cutting in acid mixtures. Several different techniques have been used for the analysis, especially infrared spectroscopy (IR) in combination with X-ray spectroscopy (XPS) analysis and transmission electron microscopy (TEM) in combination with atomic force microscopy (AFM). TEM analyses were used to reveal the morphological differences between various nanotube cutting times. The lengths of the nanotube were found to decrease with increasing cutting time. Electrochemical measurements were performed on carbon nanotube modified electrodes using nanotubes of different cutting time. The peak separation of ferricyanide redox reaction was found to depend strongly on the length of nanotube and also on the orientation of nanotube at the interface. Whilst at the randomly dispersed, the peak separation showed a decrease with decreasing nanotube length, vertically aligned nanotubes showed no dependence of the peak separation on the nanotube length. Electrochemical results together with spectroscopy measurements show that the highly electroactive edge planes were located on the carbon nanotubes and the oxygenated species in the ends of the nanotubes from cutting in acid mixtures were responsible for the good electrochemical properties. Bamboo-shaped carbon nanotube is a morphological variation of multi-walled carbon nanotubes where the graphite planes are formed at an angle to the axis of the tube. Glassy carbon electrodes modified with bambootype carbon nanotubes showed greater electrochemical signal compared with electrodes modified with singlewalled carbon nanotubes due to the edge planes of graphite located at regular intervals along the walls of the bamboo-shaped carbon nanotube, thus confirming the importance of the ends of nanotube in controlling the kinetics of electron transfer events. Effect of nanotube orientation was studied using ferrocenemethylamine attached to randomly dispersed and vertically aligned nanotubes. The electron transfer kinetics was found to depend strongly on the orientation of the nanotube with the electron transfer at the randomly dispersed slower than vertically aligned. Results were addressed using the analogy that the ends of the nanotubes are like the ends of the tubes can be described as edge-plane-like whilst the tube walls are basal-plane-like. Difference in electron transfer kinetics suggested that the electron transfer in nanotubes could occur via two different pathways: through the edge plane-like opening of the nanotube or by hopping across the walls of the nanotube. Triton X-100 was used to dialyse the acid cut nanotubes. XPS analysis of dialysed nanotubes was compared with non-dialysed nanotubes. A reduced concentration of sulfate ions was found in the dialysesd sample. Nitrate ion (407 eV) was removed after dialysis. Amino groups (400 ev) and protonated amino-group (402 eV) both seemed to be removed slowly by dialysis. Theses ions could be ascribed to residual ions trapped inside nanotubes from cutting in acid mixtures. The electrochemical response of ferrocenemethylamine was also studied. The electron transfer rate constants were rate constants were higher at dialysed nanotube assembly than non-dialysed, which was attributed to doping effect incurred from cutting. Electron transfer between nanotube and gold electrode surface was studied by attaching nanotubes to linker length of 6, 8, and 11 carbons. The results were exploited to rationalise the role of the chemical structure of the nanotubes in facilitating electron transfer from the redox species to the electrode surface that was otherwise suppressed without the presence of nanotubes. The observed redox activity was a consequence of resonant electron transfer from the LUMO of the acceptor to the HOMO of the donor under the influence of an applied voltage, assuming the nanotube modified electrode behaves similarly to the metal-molecule-metal junction mode.

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<p>The performance of negative electrodes based on Si nanoparticles for Li-ion batteries has been investigated. Electrodes consisted of Si nanoparticles, carbon black and Na-CMC. The investigation covered electrode production parameters such as pre-treatment of the Si-powder, different emulsifiers and cycling with two different electrolytes. Testing of the electrodes’ performance was done electrochemically with two different galvanostatic approaches: constant charge rate and stepped-up charge rate. Electrodes’ morphology, stability and surface chemistry were also evaluated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thickness measurements and X-ray photoelectron spectroscopy (XPS).</p><p> </p><p>High electrode capacities were achieved though strong variation depending on electrode thickness has been found. For the best performing electrodes the capacity exceeded 1600 mAh/g with slight fading after 10-15 cycles. The difference in performance could not be assigned to the different production parameters, but had a clear correlation to the thickness of the electrode and the different electrolytes used. Propylene carbonate based electrolyte gives a lower coulombic efficiency and lower capacity retention than an ethylene carbonate-diethyl carbonate based electrolyte. The electrodes could not store any capacity at cycling rates higher than 2C, but were not damaged by cycling rates up to 50C. SEM micrographs revealed that a solid electrolyte interface (SEI) was formed on the electrodes during cycling and their surface analysis by XPS suggested that the SEI was formed by decomposition of electrolyte components.</p>

Thesis (M.S.)--Oregon Graduate Center, 1972.

M.S. / Chemistry / The present investigation concerns itself with the study of the pressure dependence of hydrogen adsorption on a platinum electrode in acid media. The specific intent of this work is to find whether additional hydrogen adsorbs onto a platinum electrode when the system pressure is increased. Through this means it is possible to prove or disprove the assumption usually made that hydrogen forms a monolayer on a platinum electrode at one atmosphere pressure. Secondary aspects of this study are the effects of diffusion of hydrogen atoms into the electrode bulk, and the desorption and diffusion of hydrogen molecules into the solution layer surrounding the electrode.

<p>The objective of this research was to develop highly efficient and yet effective MnO2 electrode materials for supercapacitors applications. Most attention had focussed on MnO2 as a candidate for pseudo-capacitor, due to the low cost of the raw material and the fact that manganese is more environmental friendly than any other transition metal oxide system. The surface area and pore distribution of MnO2 can be controlled by adjusting the reaction time. The MnO2 synthesised under optimum conditions display high capacitance, and exhibit good cycle profile. This work investigates the ways in which different morphological structures and pore sizes can affect the effective capacitance. Various -MnO2 were successfully synthesised under low temperature conditions of 70 oC and hydrothermal conditions at 120 oC. The reaction time was varied from 1 to 6 hours to optimise the conditions. KMnO4 was reduced by MnCl.H2O under low temperature, whereas MnSO4.4H2O, (NH4)2S2O8 and (NH4)2SO4 were co-precipitated under hydrothermal conditions in a taflon autoclave to synthesise various -MnO2 nano-structures.</p>

The performance of negative electrodes based on Si nanoparticles for Li-ion batteries has been investigated. Electrodes consisted of Si nanoparticles, carbon black and Na-CMC. The investigation covered electrode production parameters such as pre-treatment of the Si-powder, different emulsifiers and cycling with two different electrolytes. Testing of the electrodes’ performance was done electrochemically with two different galvanostatic approaches: constant charge rate and stepped-up charge rate. Electrodes’ morphology, stability and surface chemistry were also evaluated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thickness measurements and X-ray photoelectron spectroscopy (XPS).   High electrode capacities were achieved though strong variation depending on electrode thickness has been found. For the best performing electrodes the capacity exceeded 1600 mAh/g with slight fading after 10-15 cycles. The difference in performance could not be assigned to the different production parameters, but had a clear correlation to the thickness of the electrode and the different electrolytes used. Propylene carbonate based electrolyte gives a lower coulombic efficiency and lower capacity retention than an ethylene carbonate-diethyl carbonate based electrolyte. The electrodes could not store any capacity at cycling rates higher than 2C, but were not damaged by cycling rates up to 50C. SEM micrographs revealed that a solid electrolyte interface (SEI) was formed on the electrodes during cycling and their surface analysis by XPS suggested that the SEI was formed by decomposition of electrolyte components.