This thesis describes modulated methods using both voltammetric and microfluidic perturbations to study mechanisms of electrolysis reactions. The initial chapters provide an overview of applications and research development in the fields of micro-engineering and electrochemistry, including microfabrication methodology, electrochemical detection techniques and analysis methods. Some typical electrochemical reactions have been studied for different kinds of industrial applications. Also hydrodynamic modulation methods have been investigated. The result chapters begin in Chapter 3 with detailed investigation of various electrochemical reactions by using cyclic voltammetry (CV) and large amplitude Fourier transformed alternating current voltammetry (FTACV) under microfluidic conditions. Single electron transfer reactions with different kinetics were studied first by using potassium ferrocyanide and ferrocenecarboxylic acid (FCA). Dual electron transfer reactions with different pathways were investigated by using 2,5-dihydroxybenzoic acid for one step oxidation and N,N,N',N'-tetramethyl-para-phenylene-diamine (TMPD) for two consecutive one-electron step oxidation. An irreversible reaction was explored by using borohydride solution. Examples of homogeneous reaction mechanisms were studied by using the combinations of Fe(CN)64-/L-cysteine or TMPD/ascorbic acid. The current response of all the electrolysis reactions except single electron transfer reactions was first reported under microfluidic conditions with FTACV, which has shown sensitive with the change of volume flow rates and the substrate concentrations when homogeneous reactions are involved. The linear relationships between peak current and volume flow rates or substrate concentrations can be obtained in every harmonic component. In chapter 4, the modulated technique was applied to microfluidic hydrodynamic systems. A range of electrolysis mechanisms including single electron transfer reactions, dual electron transfer reactions, irreversible reaction and homogeneous reactions were studied under hydrodynamic modulated conditions. The system showed rapid response with the change of volume flow rates during one measurement. The linear relationships between peak current and flow rates, as well as substrate concentrations, can be obtained simultaneously in one scan, which reveals a promising approach to get more information in a short-time measurement. Chapter 5 demonstrated a new protocol by forcing an oscillation of the electrochemical active solution flowing. Analysis of transition time and its effect on limiting current are presented to begin exploration of this new tool for supporting researchers on understanding redox mechanisms. A short simulated study was carried out to help better understand the mechanism under different hydrodynamic conditions.

Vita. / Digitized by Kansas Correctional Industries

No description available.

In electrochemical sensing, the miniaturisation of electrodes leads to enhanced characteristics, including higher signal-to-noise ratio and lower detection limits and sensitivity to external convection due to more efficient mass transport. In recent years, this has generated considerable interest in both the manufacturing and characterisation of nanoelectrodes. However, the high-volume, commercial fabrication of integratable, low cost nanoelectrodes remains a challenge. This work presents a nanoelectrode architecture that can be manufactured using established and well-characterised microfabrication methods. Vertical ring electrodes are fabricated at hole edges using thin film deposition and microlithography techniques. A metal layer of nanometre thickness is sandwiched between two insulators on a substrate followed by the etching of micron scale holes through the stack of layers. This leads to the exposure of a metal nanoband around the hole perimeter and thus a nanoelectrode with the area defined by the hole perimeter and the deposited metal layer thickness. This work first reports a simulation study, which investigates the in uence of design parameters such as band and insulator thicknesses and hole size on the diffusive current. The results show a relative independence of the current to the band thickness and a linear dependence on the hole perimeter with a steady state current comparable to that of a microelectrode. For example, a nanoband electrode with a band thickness of 50nm produces up to approximately half of the limiting current measured on a planar microsquare electrode and a 25 nm electrode produces 88% of the current of a 50 nm electrode. This information contributed to the development of a process for the fabrication of arrays of platinum nanoband electrodes in microsquare holes on a silicon substrate with control over the critical geometric parameters. Electrodes with band thicknesses of 5 nm to 50 nm and a range of square side lengths have been fabricated for experimental validation. Their performance has been compared to microsquare electrode arrays, and was shown to give a similar response to established microdisc and square electrodes. An analysis procedure has been developed and inherent nanoelectrode behaviour and effects have been investigated. The relative importance of a range of nanoeffects on the electrodes has been assessed, indicating a contribution of migration to mass transfer. It has been demonstrated that these nanoband electrodes can be used to detect rapid processes such as the measurement of large electrochemical rate constants, unlike microsquare array electrodes.

This thesis reports the development of acid-operating microbial fuel cells (MFCs) for the investigation of elevated electrical conductivity and resulting enhanced bioelectricity generation. This project describes the use of extremophile microorganisms as the biological material in MFCs, for the investigation of low internal resistance biological fuel cells. In particular, this thesis focuses on BPV (biological photovoltaic) cells, a type of MFC that utilises autotrophic biological material, which relies on oxygenic photosynthesis and hence simply requires water as the electron donor (unlike traditional MFCs, which are dependent of an organic substrate feed). Novel reactor designs based on acidophilic and metallotolerant microorganisms, studied using electrochemical techniques, are reported for the first time. The novel strategy consists in the adoption of very low pH and elevated heavy metal concentration levels for biological fuel cell operation, which is possible due to the choice of suitable extremophile microorganisms that are able to thrive under such severe physicochemical conditions. In order to support the analysis of the subject MFCs, a series of electrochemical and fluorescence techniques were employed. Chapter 3 reports the study of standard BPV cells, focusing on classic cell configuration and choice of biological material. BPV cells based on the standard prokaryotic and eukaryotic strains Synechococcus elongatus and Chlorella vulgaris, respectively, were built and electrochemically characterised by means of polarisation curves and continuous power output monitorisation. Subsequently, a study on the potential conditioning of BPV cells was conducted using Pulse Amplitude Modulation (PAM) Fluorimetry; it is the first documented observation of short-term electrolytic potential conditioning effects on photosynthetic efficiency and associated parameters. The work in chapters 4 and 5 explores the extent to which acidophiles may be used as the biological material in MFCs. A search to find a set of naturally-occurring, metallotolerant acidophiles is undertaken throughout the Rio Tinto ecosystem, selected for its unique extreme physicochemical nature and reported extremophile presence. Chapter 4 informs about the physicochemical characterisation of the chosen sampling points, describing the evolution of pH, electrical conductivity, heavy metal concentration, ferric/ferrous ion balance and dissolved oxygen throughout a natural year, in order to identify the sites with the hardest physicochemical conditions. Finally, chapter 5 investigates the presence of living microorganisms in the sampled sites, enabling the identification of the best location for the purpose of this study. A tailored sediment cell was built and tested in situ (for the first time in an extremophilic environment), and compared to the electrical performance of a novel BPV cell based on commercially-available photosynthetic acidophile Dunaliella acidophila.

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.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

The sea as a dynamic conducting medium interacts continually with the earth' s magnetic field. The physical principles underlying this interaction are reviewed. These results are applied to the particular problem of towed electrodes at the sea surface. Data using this method are then shown to be sensitive to stability oscillations especially in lower latitudes. Finally, some features of the water velocity around the Panama Basin are investigated from towed electrode measurements. / Graduation date: 1970

Thesis (Ph. D.)--Ohio State University, 2006. / Full text release at OhioLINK's ETD Center delayed at author's request

This document describes research conducted during 2009-2010 in the Kerman Group laboratory at the University of Toronto Scarborough to investigate the application of electrochemical techniques for the detection of acetylcholinesterase inhibitors in aqueous samples. Two main projects were completed and are discussed herein. The first project demonstrated that the new unmodified, nanostructured gold disposable electrochemical printed (DEP) chips produced by BioDevice Technology can compete with surface-modified electrode configurations to detect trace concentrations of insecticides. This was achieved through the measurement of acetylcholinesterase-catalyzed production of thiocholine after incubation of the enzyme with low concentrations of paraoxon (10 ppb) and carbofuran (8 ppb). The second project featured the novel application of a glassy carbon (GC) electrode to monitor the changes in availability of Thioflavin T (ThT) for oxidation at the electrode surface, which is non-linearly modulated by the presence of acetylcholinesterase and the enzyme’s pre-treatment with trace concentrations of paraoxon and carbachol.