A half cell of an electrochromic (EC) device has been used to determine theelectrochromic response of a nickel oxide film in nine different electrolytes. Six of thenine electrolytes were 0.1 M non-aqueous salts dissolved in equal weight % ofpropylene carbonate and ethylene carbonate. Three of them were lithium-based andthree of them tetrabutylammonium (TBA)-based. The last three electrolytes wereproton-based aqueous solutions of 1 M KOH, 0.1 M propionic acid and 0.1 Mphosphoric acid, respectively. The electrolytes were subjected to electrochemical measurements of cyclicvoltammetry and square wave voltammetry, both with simultaneous in-situ opticaltransmittance measurements in the visible region. Ex-situ optical measurements wereperformed in the UV-VIS-NIR (300-2500 nm) range and IR-spectroscopymeasurements in the 600 – 4000 cm-1range.To determine the performance of the nickel oxide films, the coloration efficiency (CE)is used as a figure of merit. The desired value is to achieve a high optical modulationwith as little amount of charge inserted/extracted as possible.The results show that neither lithium nor TBA has a significant impact on theelectrochromic (EC) response, compared with the protonic electrolytes. Anargument can be made that the intercalation of neither cation (lithium or TBA) is thereason behind the electrochromic behaviour of the nickel oxide. In KOH it is ratherthe OH- that transfer to the surface and attracts protons (H+) from the bulk nickeloxide that enhances the EC response. In both propionic and phosphoric acid, it is thereversible intercalation of protons (H+) into the porous nickel oxide that gives theelectrochromic response.

Thesis (MS)--Montana State University--Bozeman, 2009. / Typescript. Chairperson, Graduate Committee: Stephen W. Sofie. Includes bibliographical references (leaves 98-103).

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This study reports on an electrochemical capacitive properties of nickel tetraaminophthalocyanine (NiTAPc), nickel tetraaminophthalocyanine incorporated with Nickel oxide (NiTAPc-NiO) and nickel oxide incorporated with multi-walled carbon nanotubes (NiO-MWCNT), using three different techniques known as successive ionic layer adsorption reaction (SILAR), electrodeposition and dip-dry. This study also reports on the effect of undoped polymer of poly-pyrrole on NiTAPc. The physical properties of the synthesised materials were investigated using SEM and EDX and the electrochemical properties were investigated using cyclic voltammetry (CV), charge-discharge (CD) and electrochemical impedance spectroscopy (EIS). The supercapacitive properties of NiTAPc film on nickel foam showed a maximum specific capacitance of 416.0 Fg-1, a maximum power density of 15.50x103 WKg-1 and a maximum specific energy of 66.0 WhKg-1. The NiO-MWCNT film on nickel foam gave a maximum specific capacitance of 1034.0 Fg-1, a maximum power density of 10.41x103 WKg-1 and a maximum specific energy of 132.0 WhKg-1. The NiTAPc-NiOE film on nickel foam was found to possess a maximum specific capacitance of 1117.0 Fg-1, a maximum power density of 20.48x103 WKg-1 and a maximum specific energy of 119.0 WhKg-1. The NiTAPc-NiOE-S film on nickel foam gave a maximum specific capacitance of 1279.0 Fg-1, a maximum power density of 26.96x103 WKg-1 and a maximum specific energy of 114.0 WhKg-1. Finally, the NiO mixed with an oxidant (NiOS-ox) film on nickel foam gave a maximum specific capacitance of 1403.0 Fg-1, power density of 14.44x103 WKg-1 and a maximum specific energy of 147.0 WhKg<sdup>-1. In addition, the electrodes were found to be very stable even after repetitive cycling. These electrodes have clearly proved that they may be suitable for use as potential supercapacitors. Further research is necessary to fully explore their supercapacitive behaviour in single cell (2-electrode)systems. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Chemistry / unrestricted

In this study, the carbon electrode of supercapacitor was fabricated by using mesocarbon microbeads. For finding the optimal processing parameters of carbon electrode, the effects of specific surface area of activated carbon, the amount of carbon black and binder, and various electrolytes on the capacitative properties of supercapacitor are investigated. To fabricate the composite electrode of supercapacitor, NiO and WO3 thin films were deposited respectively on the carbon electrode by electron beam evaporation. The influences of various scan rates of cyclic voltammograms (CV) on the characteristic of capacitance are studied. The charge-discharge efficiency and life time of the composite electrode are also discussed. Experimental results reveal that the optimum carbon electrode can be obtained using mesocarbon microbeads with high specific surface area (2685 m2/g) and larger pore volume (0.6 cm3/g) and adding 10 wt.% carbon black and 2wt.% binder. The specific capacitances of carbon electrodes in 1 M KOH and 1 M Et4NBF4 are 230.8 F/g and 221.5 F/g, respectively. Besides, the XRD and SEM results showed that NiO and WO3 thin films on composite electrode are sheet-liked crystal structure and stone-liked amorphous structure, respectively. The composite electrode exhibits better capacitance properties than those of carbon electrode at high scan rate by CV analysis. It reveals the promotion of the capacitative property of supercapacitor at higher power density and the improving of the decay property in capacitance at high scan rate. Finally, in the test of charge-discharge efficiency and life time, the charge-discharge efficiency is near 100% after 5000 cycles and it still retains good adhesion between electrode material and substrate.

Fundamental studies on the mechanisms and kinetics of reduction of dense synthetic nickel oxide have been carried out in H2-N2 and H2-H2O mixtures. The influences of temperature, hydrogen partial pressure, and hydrogen-steam ratio on the reduction process were systematically investigated. The kinetics of the reduction process were followed metallographically by measuring the advance of the nickel product layer. The microstructures of the reduction products and their changes during heating were characterized using a high resolution scanning electron microscopy. In H2-N2 mixtures and H2-H2O mixtures with low steam content, it was found that the initial reduction rates were first order with respect to hydrogen partial pressure. In both sets of mixtures, it was found that the progress of NiO reduction was not a monotonic function of temperature. A minimum rate of advancement of NiO reduction was observed in the temperature range 700oC – 800oC depending on the hydrogen partial pressures and reduction time. A number of distinctly different nickel product microstructures, originating at the Ni-NiO interface were observed under various reduction conditions, namely coarse fibrous nickel with fissures, fine porous nickel-planar interface, large porous nickel-irregular interface and dense nickel product layer. The microstructures of reduction product were found to change with temperature and time. It was found that heating the coarse fibrous nickel structure resulted in a re-crystallization, grain growth and densification of nickel product. When the heat treatments were carried out on the porous nickel structures, the number of pores decreases with increasing temperature and time, which was accompanied by the increase in the pore sizes. The microstructures and kinetics of the reduction of nickel oxide were found to be a function of temperature, gas composition and reaction time. The study provides strong evidence for a link between the reduction kinetics and the changes in the reduction product microstructures. Mechanisms and kinetics of the reduction of nickel oxide have been discussed by considering reduction conditions, information on the structures and elementary processes involving in the reduction process.

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At the heart of all power electronic systems lies the semiconductor, responsible for passing large amounts of current at negligible power losses in the on-state, while instantaneously switching to withstand high voltages in the off-state. For decades silicon (Si) has dominated nearly all aspects of electronic systems including power. As importunity for efficiency at higher power and fast switching speeds grows, the environments with which these systems are being tasked to operate in has also increased in rigor. This has placed semiconductors at the forefront of innovation as novel materials are being explored in hopes of meeting the demands for the future of power electronics. This exploration of novel materials for power electronics has come to fruition as the performance limits of narrow bandgap (EG) materials such as Si (1.1 eV) have been reached. The EG is a key measure of a materials ability to operate at high voltages and within high temperature environments. This is due to the direct relationship of the EG to the critical field strength which enables increased performance beyond that of narrow band gap materials such as Si and gallium arsenide. Wide bandgap (WBG) materials such as silicon carbide (SiC) and gallium nitride (GaN) with EG 3.3 eV and 3.4 eV, respectively, have emerged within the power electronics field to offer increased breakdown voltages (VBR) at lower on-resistances. However, ultrawide bandgap (UWBG) devices possess greater potential with superior performance limits in comparison to SiC and GaN. Ga2O3 (4.8 eV) is the only UWBG semiconductor with melt-growth capabilities that has already demonstrated research grade wafers up to 6" in diameter. Ga2O3 is also advantaged by the ability to grow thick, lowly-doped homoepitaxial drift regions from methods such as halide vapor phase epitaxy (HVPE) and metal organic chemical vapor deposition (MOCVD). This makes Ga2O3 a prime candidate for vertical power rectifiers as thick, high quality drift regions are a necessity for high voltage devices such as the PN diode, junction barrier Schottky (JBS) diode, merged-PiN-Schottky (MPS) diode, and Schottky barrier diode (SBD). However, Ga2O3 exhibits a lack of p-type conductive that arises from an absence of dispersion within the valence band maximum. This has caused researchers to abandon the idea of homojunction devices that Si, SiC, and GaN devices benefit from; shifting to a heterojunction approach where NiO (3.7 eV) provides the source of p-type conductivity. This complicates fabrication and device characterization particularly for the Ga2O3 JBS diode where an etched Ga2O3-NiO heterojunction has thus far been unreported throughout the literature. This work investigates the numerous individual aspects that comprise an etched Ga2O3 heterojunction device which include the etching method, post etch damage removal and its impact on electrical performance, and ohmic and Schottky contacts critical for a JBS diode; all culminating in the demonstration of a JBS and MPS diodes. We also report our investigations into co-doping of Ga2O3 that yield degenerately doped epitaxial layers with record mobility (μ) values. While not directly correlated with Ga2O3-NiO heterojunction devices, this study lays the ground work for semi-insulating Ga2O3 depletion into unintentionally doped (UID) n-type Ga2O3. / Doctor of Philosophy / Power semiconductor devices reside at the center of many critical infrastructures that power modern society. These systems include but are not limited to; telecommunications, power supplies, motor drives, and electric trains. The semiconductors embedded within these systems are tasked with passing large amounts of current at negligible power losses in the on-state, while simultaneously withstanding high voltages in the off-state. For decades, the ground breaking discoveries and engineering feats produced by scientist and engineers have propelled the field of power electronics forward. As importunity for efficiency at higher power and fast switching speeds grows, the environments with which these systems are being tasked to operate in has also increased in rigour. These demands cannot be met with traditional silicon (Si) based devices as the material properties have been pushed to their performance limits. This has led to emerging and novel wide and ultrawide bandgap semiconductors such as silicon carbide (SiC), gallium nitride (GaN), and gallium oxide (Ga2O3) becoming a greater presence within the field of high power electronics. Ga2O3 in particular has seen a recent surge in interest within the power electronics communities due to the prospect of meeting the aforementioned demands, aided by a number of advantageous material and electrical properties. Ga2O3 is unlike any other wide or ultrawide bandgap material in that high quality Ga2O3 films known as epitaxial layers can be deposited atop native meltgrown Ga2O3 substrates. This reduces any mismatch or undesirable boundaries between the substrate and epitaxial layers that could otherwise impact device performance. This makes Ga2O3 a prime candidate for vertical power rectifiers, or switches such as a PN diode, junction barrier Schottky (JBS) diode or Schottky barrier diode (SBD). However, there has been no realization of p-type conductivity, or positively charged mobile carriers, within Ga2O3. This makes devices such as the PN and JBS diode difficult, as they rely on both n- and p-type conductivity. Without a source of p-type conductivity, Ga2O3 will be limited to unipolar devices that lack superior breakdown voltages and robustness. This work explores Ga2O3 heterojunction diodes, specifically the JBS diode, where nickel oxide (NiO) is used as the source of p-type conductivity. The need for a heterojunction introduces a host of issues that are otherwise not seen within bipolar semiconductors such as Si, SiC, and GaN. Our work details the analysis of the individual aspects that comprise a Ga2O3 heterojunction barrier Schottky diode including the etching process, etch damage removal, NiO sputtering, and contact formation. Our efforts have provided insight into unexplored areas within the Ga2O3 literature, leading to the first demonstration of a Ga2O3 merged- PiN-Schottky (MPS) diode; a more robust JBS diode capable of handling surge current. This work serves to further Ga2O3 as a viable semiconductor for the future of high power vertical rectifiers.