This work focused on the study of self-discharge mechanisms of carbon electrochemical capacitor electrodes in 1.0 M H2SO4 electrolyte. Electrochemical capacitors have an increasingly important role in the future of energy storage for specific applications due to their high cycle lives, high power capabilities and the ability to use environmentally friendly materials. Remediation of the occurrence of self-discharge – the loss of charge over time when left in open-circuit configuration – must take place before electrochemical capacitors can be used more widely as this diminished potential results in a reduction of stored energy. By examining the now poorly understood causes and mechanisms of self-discharge, beneficial modifications to the electrochemical capacitors systems can be made, improving device performance. Three-electrode electrochemical set-ups were used to separate self-discharge mechanisms on the negative and positive electrodes. Various electrode and electrolyte reactions were investigated in relation to self-discharge, including Fe-contamination reaction, electrolyte decomposition, oxygen-reduction, carbon oxidation, and carbon surface group development. All experiments were conducted on porous carbon electrodes. It was determined that Fe-contamination increased self-discharge on both carbon electrodes at concentrations >10-3 M, and that previously developed planar kinetic models applied to these porous systems. Electrolyte decomposition did not result in increased self-discharge on either electrode. Electrolyte oxygen content must be minimized as oxygen is believed to undergo reduction to hydrogen peroxide on the negative-electrode, resulting in an increase in self-discharge. The carbon electrodes used in this work must be cycled prior to energy storage as the capacitance varies greatly with continued cycling, and the lack of cycling results in increased self-discharge. Additionally, interest in the carbon electrode’s surface functionalities resulted in the standardization of the Boehm titration.

Philosophiae Doctor - PhD / Tuberculosis (TB) is an infectious disease with adverse effect on a global scale. The disease is one of the major causes of death in sub-Saharan Africa. Nearly 70% of TB-infected persons are co-infected by the human immunodeficiency virus (HIV). About 50% of TB/HIV patients are smear negative and up to 28% are sputum scarce, which is a significant problem in South Africa since sputum smear microscopy is the most widely used diagnostic test for TB. The detection of Mycobacterium tuberculosis (MTB) and resistance to the TB drug rifampicin (RIF) are the basis of the GeneXpert MTB/RIF protocol. The GeneXpert MTB/RIF is an automated nucleic acid amplification technique for detecting the DNA that originates from MTB. However, low sensitivity and low concentrations of MTB for DNA amplification are a serious issue associated with the protocol. Therefore, other TB diagnostic methods, such as the ones involving biochemical markers of TB, are becoming very important. / 2020-08-31

The present study presents the current status of research into the production of active carbons from environmental applications using waste newspaper. A number of studies have been performed to investigate the pyrolysis of waste paper ash to carbon gel.Although several studies report the production of carbon from waste tyre, bamboo, coconut shell, this study is first of its kind that for the first time, the waste newspapers have been used as a raw material for supercapacitor electrodes. A cheap raw material, and a simple method of preparation make this carbon gel more economically attractive. By carbonizing a waste paper a new carbon-carbon composite as electrode material was prepared through RF gel. The surface morphology and electrochemical characteristics of the carbon composite were investigated by Scanning Electron Microscopy, Cyclic Voltammetry, Electrochemical impedance spectroscopy and galvanostatic charge-discharge cycle tests with various current densities. The SEM study reveals that the connectivity between the grains increases during cycling thus enhances the cyclic stasitity. The CV’s suggests that there is simultaneous redox and capacitive behavior and these behaviors are highly reversible even after 8 lakh cycles. The reversibility was still maintained even in the range – 3 V to + 3 V. The charge/discharge cycle tests reveal the cycle stasitity and delivered more then 8 lakh cycles at 100 mA/cm2. The maximum specific capacitance of 300 F/g was obtained at 150 mA/cm2 current density. These results imply that this newspaper based carbon gel be used as potential candidate for supercapacitors.

Prussian blue (PB) nanoparticles were synthesized from FeCl3.6H2O, K4[Fe(CN)6].3H2O, and from Fe(NO3)3.9H2O and K4[Fe(CN)6].3H2O, and then characterized by Fourier transform infrared (FT-IR), Ultraviolet-visible spectroscopy, X-ray diffraction (XRD), Energy dispersive spectroscopy (EDS), Scanning electron microscopy (SEM), Raman spectroscopy and thermogravimetric analysis. Graphene oxide and carbon nanotubes were also synthesized and characterized. PB nanoparticles, carbon nanotubes (CNT), graphene oxide (GO) and cetyltrimethylammonium bromide (CTAB) were sequentially deposited onto glassy carbon electrode surface to form chemically modified electrode for the detection of hydrogen peroxide (H2O2) and dopamine. The following electrodes were fabricated, GC-PB, GC-MWCNT, GCGO, GC-CTAB, GC-MWCNT-PB, GC-GO-PB and GC-CTAB-PB. Cyclic and Square wave voltammetric techniques were used to measure the hydrogen peroxide detectability of the electrodes at pH ranges of (3 - 7.4) in 0.1M phosphate buffer solution, in the absence or presence of 25 μL of H2O2. The GC-CNT-PB, GC-GO-PB,GC-CTAB-PB electrodes showed a good response for the detection of hydrogen peroxide in both acidic and neutral media while the GCPB electrode only showed good response in acidic media.

<p>In this thesis, I present the electrochemical studies of three dendrimeric polypropylene imine (PPI) nanomaterials and their applications as a platform in the development of a novel label free DNA nanobiosensor based on electrochemical impedance spectroscopy. Cyclic voltammetry (CV), differentia pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivities of the nanomaterials on glassy carbon electrode (GCE) as the working electrode.</p>

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<p>In this thesis, I present the electrochemical studies of three dendrimeric polypropylene imine (PPI) nanomaterials and their applications as a platform in the development of a novel label free DNA nanobiosensor based on electrochemical impedance spectroscopy. Cyclic voltammetry (CV), differentia pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivities of the nanomaterials on glassy carbon electrode (GCE) as the working electrode.</p>

Philosophiae Doctor - PhD / In this thesis, I present the electrochemical studies of three dendrimeric polypropylene imine (PPI) nanomaterials and their applications as a platform in the development of a novel label free DNA nanobiosensor based on electrochemical impedance spectroscopy. Cyclic voltammetry (CV), differentia pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivities of the nanomaterials on glassy carbon electrode (GCE) as the working electrode. / South Africa

This master thesis deals with supercapacitors based on electrical double layer and proper carbon electrodes for this type of supercapacitors. In theoretical part of work is described theory of supercapacitors, energy storage principles and their properties. In the next part are described carbon materials, their properties and electrochemical methods of measurements that we used. In the experimental part is described preparation of electrodes, results and conclusion.

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