Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 206-221). Available also in a digital version from Dissertation Abstracts.

This study presents the development, calibration, characterization, and use of new instrumentation for in situ measurements of electron-beam-induced surface voltage. The instrument capabilities allow for measurements of a full range of insulating materials that are of concern to NASA spacecraft charging experts. These measurements are made using moveable capacitive sensor electrodes that can be swept across the sample using an in vacu stepper motor. Testing has shown a voltage range of more than ±30 kV with a low-voltage resolution of 0.2 V. The movable sensors allow for a radial measurement of surface voltage with spatial resolution as low as 1.5 mm. The instrumentation has response time of ~7 s from the time the beam is shut off until the probe is in position to take data and uses computer automation to stabilize the system and acquire data over the period of several days or longer. Three types of measurements have been made on two prototypical polymeric spacecraft materials, Low-density Polyethylene (LDPE) and polyimide (KaptonTM HN), to illustrate the research capabilities of the new system. Surface voltage measurements were made periodically during the charging process using a pulsed electron beam and subsequently as the surface voltage discharged to a grounded substrate; these were used to obtain information about the material’s electron yields and bulk resistivity. The spatial profile of the voltage across the sample surface was also measured by sweeping the electrode across the surface. Subsequent measurements monitored the time evolution of the magnitude and spatial charge distribution as charge dispersed radially across the sample surface. The results of these measurements are present and compared to literature values validating the instrument’s effectiveness.

Thermal analysis methods have ben used for many years for material characterization. In recent years, thermal methods have been coupled to other methods of chemical analysis to obtain more complete material characterization. This study looks at thermal decomposition of polymer samples as well as coal samples in atmospheres of nitrogen and air. The thermal analysis instrument used was coupled to a Gas Chromatograph (GC) and a Fourier Transform Infrared Spectrometer (FTIR) so that the gaseous products evolved during thermal decomposition could be analyzed. The results obtained show that the coupled techniques of TG -GC and TG-FTIR can show pyrolysis and combustion of different materials.

Abstract The electrocatalysis of oxygen plays a significant role in several electrochemical energy storage and conversion systems including metal−air batteries, fuel cells, electrocatalytic and photocatalytic water splitting. The sluggish kinetics and complex reaction mechanism of this cathodic oxygen reduction reaction (ORR) affect the performance and practical application of such renewable energy technologies. To address this limiting factor, a suitable electrocatalyst is required for ORR. In general, platinum or highly dispersed Pt-based nanoparticles on carbon black are considered as the best ORR catalyst. But platinum being very scarce and expensive tends to increase the cost. Moreover, platinum-based catalysts are prone to several serious problems, including declining activity, the fuel-crossover, and poisoning effects. This has initiated overwhelming research attention towards the development of low cost ORR catalysts. Jasinski et al. pioneered in reporting that a N4-chelate complex with a transition metal could be used for electrochemical oxygen reduction. Subsequently many nonprecious ORR catalysts have been investigated so far to replace platinum which include transition metal chalcogenides, nitrogen-doped carbon nanotubes or graphene, carbon nitride, and metal-N4 chelate macrocycles (M-N4-macrocycles). However, most of these current catalysts exhibited insufficient activity and low stability in corrosive environment of fuel cells. Thus, new strategies to develop catalysts which can meet the combined requirements of low cost, high catalytic activity and long-term durability still remains a challenge. Recently our group has reported synthesis of heteroatom doped porous carbon through chemical activation of simple monomers. The facile synthetic route, high surface areas with abundant micropores, inherent presence of heteroatoms and tunable structure/composition at the molecular level make them potential for high-performance ORR electrocatalysts. To increase the catalytic performance in both acidic and basic media, it is important to incorporate or coordinate the doped heteroatom centers with 3d transition metals such as iron or cobalt. Herein, two different synthetic strategies will be presented to synthesize transition metal-based heteroatom doped porous carbon as ORR catalyst. In the first approach, iron (III) thiocyanate as iron salts was pyrolyzed with benzimidazole to introduce sulfur along with nitrogen and iron in the porous carbon. Another synthetic approach involved hydrothermal synthesis of cobalt oxide on the surface of benzimidazole derived porous carbon. ORR can proceed via either one step four-electron reduction pathway producing water or two step two-electron reduction pathway producing HO2-, OH- and H2O2. Both of these synthesized catalysts favored 4e- reduction pathway which is energetically efficient and do not produce corrosive byproducts. The electrochemical performance of the synthesized catalyst will be analyzed by cyclic voltammetry, linear sweep voltammetry and amperometric i-t technique and compared with commercially available 20 wt% Pt based carbon in both acidic and basic media. The effect of pore size, nitrogen content, bonding configurations of nitrogen and sulfur, influence of cobalt and iron on ORR performance will also be discussed.

Thesis (Ph. D.)--Drexel University, 2006. / Includes abstract and vita. Includes bibliographical references (leaves 149-158).

Recently, the rate of corrosion of copper water pipes in Bowling Green, Kentucky has unexpectedly accelerated. The specific reasons for this are unknown. Our aim is to elucidate the factors enhancing the corrosion and help understand the primary mechanisms of action. This will help in combating and reducing future corrosion incidents leading to pipe failure, thus reducing losses experienced when these pipes are replaced. This study seeks to explore the characteristics and factors involved. The scanning electron microscopy was used to obtain elemental composition, and images of both inside and outside of the corroded pipes. Strikingly, corrosion primarily occurred on the outside of the pipes, not inside. X-ray crystallography also was used to examine the pipes. The results showed that the interior of the pipes mostly consisted of SiO2, CuO2, CaCO3 while the exterior consisted of Cu2(OH)2CO3, Fe2Al2O4, CaCO3, SiO2 and Cu2O. There was no clear single factor for the corrosion observed. For further studies, we plan to long temporal experiments. The results from the study will help in minimizing the costs to the city in Bowling Green, Kentucky.

Perovskites-photovoltaic cells are a type of photovoltaic cells which include a chemical compound having perovskite structure, most often a hybrid organic-inorganic lead or a tin halide, in its light-converting active layer. The efficiency of photovoltaic cells used in these materials is increasing constantly since the beginning of the new millennium. It went from 3.8% in 2009 [6] to 22.1% [7] in early 2016 [8].Up until today, this is the fastest development in the history of the photovoltaic history. To this day, some stability problems unfortunately still remain unsolved. However, this technology still exhibits a significant margin to improve performance and low production costs. This means that perovskite cells have become commercially attractive, and start-up companies already announce modules on the market by 2019. This study concluded that the addition of halogenated bidentate additives such as 1,8 Diiodooctane (DIO) not only influenced the performances of perovskite solar cells but also their stability over time. By fine elemental analysis, it was concluded that the addition of chlorine in the solution did not imply the substitution of iodide by chlorine in the structure. Chlorine is therefore believed to play a role in getting rid of the excess of methylamine, thus helping stabilizing the cell and enhancing its performance. As requested by the industry, this work demonstrated the feasibility of replacing the electron transport layer (ETL) of TiO2 by a materials obtained by liquid low-temperature process (<150°C).

It is imperative to develop alternative battery technologies based on naturally abundant elements, with competitive performance as lithium-ion batteries. Sodium has a natural abundance 1000 times more than lithium with both lithium and sodium-ion batteries having similar chemistry. Sodium-ion batteries are potentially an alternative that can achieve such competitive performance, given that electrode and electrolyte materials of high rate and long-term electrochemical performance are being developed. This thesis investigates the rate capability and long-term performance of bulk bismuth electrodes containing varying carbon content. The electrodes were cycled in cells with glyme-based electrolytes: diglyme and tetraglyme. Scanning electron microscopy and energy dispersive spectroscopy showed the morphology and elemental mapping of pristine and cycled bismuth electrodes. The result demonstrates the evolving porosity as the electrode cycled. The galvanostatic cycling of half-cells showed two plateaus each for sodiation and desodiation. Also, two peaks are seen in cyclic voltammetry suggesting a two-phase reaction. When cycled between -0.6 to 0.6 V in a symmetrical cell, the bismuth electrode showed an appreciable rate capability at a current rate of 770  mA/g in diglyme. In tetraglyme, it showed a poor rate capability, even at a current rate of 308 mA/g. The rate performance in a full cell cycled between 0.1 to 3.2 V also showed a good rate capability at a current rate of 770  mA/g in diglyme. Tetraglyme showed poor rate capability at the same current rate. The capacity retention was higher in the symmetrical cells, with 79 % and 78 % capacity retention relative to the initial charge capacity after 100 cycles for diglyme and tetraglyme. At the same current rate and more than 70 cycles, the full cells showed capacity retention of 58 % in diglyme and 44.8 % in tetraglyme. The capacity retention varied slightly for the two different electrode composites.  The superior performance in the symmetrical cell is due to the narrow voltage window.  Evaluating the stability of the solid electrolyte interphase via galvanostatic cycling suggests some stability issues. The full cells showed growing resistance with an increasing number of cycles.

Metal-organic frameworks are porous materials resulting from the coordination of a metal ion (the Lewis acid) and organic polydentated ligands. In the case of the MOFs, the SBU (Secondary Building Unit) is defined by taking the active groups of the ligands involved in coordination and the metal ion as a block. The remaining part of the organic ligand is therefore called simply a linker, so that MOFs can also be defined, in a supra-molecular view, as a material composed of SBUs and linkers combined together to form regular, periodic and porous structures. The possible textures and the possible combinations are virtually infinite, depending especially on the properties ofthe linkers, much more than of the metal ions involved, in order to design the pore size, the pore dimensionality and the catalytic properties. It gives this class of nano-materials a very interesting perspective in the most various applications, by allowing to ”tune” each relevant chemical or physical parameter concerning porous materials and their applications in nanotechnology.

Finding materials based on non-rare earth metals is vital for the global transition to a more sustainable economy. Discovering useful properties in common metal oxides is a promising avenue for new materials. In this work we have investigated the properties of Ru(x)CoMo(1-x) to evaluate the feasibility of its use as an electrocatalyst for the oxygen evolution reaction (OER). Herein, the plasma spray deposition on FTO and glass is reported as a method for production of low Ru content-CoMo oxide. The material showed a good performance in an alkaline electrolyte for OER, with no loss on stability and overpotentials to achieve a current density of 10 mA cm-2 of 528, 483, 455, 439 mV for 0, 10, 20, and 30 At% of Ru, respectively. The final material is shown to be composed entirely of Co and Mo oxides, as well as Ru which is present in the crystal structure of these metal oxides as observed using optical characterization techniques, XRD, Raman and SEM. With the aim of maximising performance and decreasing the amount of Ru used, we find a Ru content of 20 At% is most optimal for OER in alkaline. We find therefore Ru(0.2)(CoMo)(0.8) to be an effective electrocatalyst for OER in alkaline, while examples from literature outperforms it in other applications, it is still a good basis for further work and development.