Rechargeable lithium ion batteries are common materials in everyday applications. The most frequently used cathode material, LiCoO2, provides high energy density and stable charge/discharge performance. However, LiCoO2 is toxic and relatively expensive, therefore, other alternatives are being sought after in the development of battery materials, such as LiMn0.33Ni0.33Co0.33O2 (identified commonly as 333 compound). The 333 compound is now popular due to its comparable performance with LiCoO2, lower price, enhanced stability, and more environmentally friendly characteristics. In addition, Li1.2Mn0.54Ni0.13Co0.13O2 (HENMC) is still on the stage of testing and it attracts wide attention due to its higher rechargeable capacity and thermal stability. However, there are still challenges confronted: cycle stability and low rate capability. In order to verify all the roles played by different elements shown in NMC materials and explore the corresponding performance with different formula units, compositional analysis is needed. ICP-MS (inductively coupled plasma mass spectrometry) can provide bulk compositional information and has been used in recent work, giving a general idea of the composition of NMC materials. However, compositional inhomogeneity analysis has usually been neglected in these studies. Therefore, the objective of this work was to explore this variation in composition locally with higher spatial resolution, at the NMC particle level. This work was carried out through the use of scanning electron microscopy – energy dispersive spectroscopy (SEM-EDS) and Auger electron spectroscopy (AES). Furthermore, nano-scale quantitative analysis was done with transmission electron microscopy – energy dispersive spectroscopy (TEM-EDS). Moreover, an optimal approach and procedure of compositional analysis by using EDS and AES was explored with proper standards and operation conditions to provide consistent and stable results. The optimal quantification method was applied to investigate the compositions of 333 compound before and after ball milling and HENMC specimen before and after cycling. The results support the structural changes and in turn the electrochemical performance of the battery material. In the 333 compound, the electrochemical performance of the battery was deteriorated due to ball milling, during which Zr was introduced and particles were more compact. In HENMC, during cycling, the Mn distribution was homogeneous at the beginning, then inhomogeneous and homogeneous again, supporting the hypothesis of the transformation of phases: formation of spinel phase and potential SEI layer. In-depth structural analysis of different NMC materials has been reported previously by other groups. However, the structural effects due to cycling, within particles still needs investigation. Therefore, X-ray diffraction (XRD) was used to investigate the bulk material crystalline structure. Local nano-scale level structural variations amongst different isolated primary particles were investigated by the electron diffraction pattern based on TEM. The 333 compound and HENMC cycling was examined before and after cycling. After cycling, in the 333 compound, the O1 phase domains with P-3m1 space group appear inside the O3 phase with R-3m lattice. With more cycling, more domains appear. For HENMC, the original pristine samples exhibit the rhombohedral and monoclinic phases. After cycling, more and more spinel phase appear. Finally, after 100 cycles, we observe evidence of the potential solid electrolyte interphase (SEI) formation. In all, all the results above support the phase changes of 333 compound and HENMC. More investigations are needed to understand the degradation process of both compounds. / Thesis / Master of Materials Science and Engineering (MMatSE)

<p> This report deals with the design of an electrode system which utilizes the double dis- charge technique to achieve a Uniform discharge between two continuous electrodes with the intent of using this electrode system as the excitation unit for a TEA CO2 laser. The particular electrode configuration dealt with in this report involves a continous cathode and a similar continuous anode which has a set of rounded tip, rod, preionization electrodes set into holes in it. Also included in this report is a preliminary measure of the gain of the resultant double discharge TEA CO2 laser. </p> / Thesis / Master of Science (MSc)

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<p> This thesis demonstrates two concepts, one a viable fabrication process for an FeCr alloy supported solid oxide fuel cell (SOFC), and second, the use of CozMn04 (spinel)as the cathode material. Ni/YSZ and YSZ layers were used as anode and electrolyte respectively. The fabrication process consisted of tape casting of iron and chromium oxide powders for the support, dip coating of NiO-YSZ-Fe30 4-Crz03-C and YSZ as anode and electrolyte respectively, synthesis of CozMn04 from Co304 and MnOz as the , cathode material and finally screen printing of the CozMn04 cathode. The support, the anode, and the electrolyte were co-fired at 1350°C in air for 10 hours, then CozMn04 was screen printed and the cell was again fired at 1250°C for 4 hours in air. The complete cell was reduced in pure Hz at 950°C for 10 hours to convert the major part of support into Fe-Cr alloy, leaving approximately 20% unreduced FeCrz04. </p> <p> The fully fabricated cell was tested at 820°C using 7% Hz, 93% Nz as the fuel and air as the oxidant. The Co2MnO4 cathode which reduced to MnO + Co during the final processing stage was recovered in-situ at the start of the test. Pt mesh was used for current collection. The power density was in the range of 80-120 mW/cm2. </p> / Thesis / Master of Applied Science (MASc)

This research was conducted to achieve four objectives. The first objective was to develop an analytic model to predict the expected luminance distribution through the shadow mask structure on a color CRT display system. The model incorporates functions to describe the unique features of a color CRT, that is, the discrete sampling imposed by the shadow mask/ phosphor-dot arrangement as well as the electron beam phase relationships. The model also includes a flexible beam profile which allows the user to specify the desired shape of the beam profile, that is, whether the profile is described with a Gaussian, leptokurtic, or platykurtic distribution. This objective was fully satisfied with a computer program written in Lightspeed C which runs efficiently on Macintosh computers. The second objective was to determine detection thresholds for various levels of misconvergence of the three electron guns. When the three guns are properly registered, the luminance profiles converge and one perceives a color combination rather than the separate red, green, and blue luminances. Misconvergence is perceived by a change in the overall color or by color fringes, for example, a red edge to a yellow line. Past research has shown that threshold detection of misconvergence occurs when the primary beams are misconverged by 1 to 2 visual arcminutes of separation. This finding was replicated in this research for the two-color beam combinations which have previously been investigated, as well as for a white pixel, which involves all three guns. The third objective was to demonstrate the effect of misconvergence on the performance of a visual task and on subjective estimates of image quality. While subjective quality and threshold detection have previously been investigated for some color combinations, the three tasks (i.e., threshold detection, visual task performance, and subjective estimates) have not been systematically combined within the same data set for a variety of misconvergence conditions. This research provides such a composite data set. The subjective quality estimates were significantly correlated with the threshold detection data. In other words, as misconvergence of the display image increased, the probability of detection of misconvergence increased and the subjective quality rating decreased. However, the selected visual task (a short reading task with average reading time of 6.5 s) was not significantly affected by very large levels of misconvergence. Rather than conclude that the levels of misconvergence used in this research do not affect reading task performance, a more comprehensive visual task (e.g., a longer editing task, a random search task, or a map reading task) should be evaluated. The final objective was to evaluate the ability of selected image quality metrics which are computed from the model to predict threshold detection, subjective quality ratings, or visual task performance. The three metrics computed in this model (MTF Area, MTFA, and SQRI) are all based upon the modulation transfer function (MTF) of the display. These three computed metrics were for all practical purposes constant across the range of misconvergence. While this result was unexpected, it does suggest (1) that a model based only on luminance may be deficient because of the omission of chromaticity, and (2) that MTF-based metrics may not be an appropriate representation because misconvergence does not change the display’s ability to transmit information, but is a phase shift along the shadow mask. As summarized, this research successfully met three of the stated objectives. Further, it points toward future research opportunities to further this type of modelling effort and to successfully develop image quality metrics for color displays. / Ph. D.

A transient model of the cathode catalyst layer of a proton exchange membrane fuel cell is presented. The catalyst layer structure can be described as a superposition of the polymer membrane, the backing layer, and some additional platinum particles. The model, which incorporates some of the features of the pseudo-homogeneous models currently present in the literature, considers the kinetics of the electrochemical reaction taking place at the platinum surface, the proton transport through the polymer agglomerates, and the oxygen and water transport within the pores as well as the membrane material of the catalyst layer. Due to the lower porosity of this region and the higher liquid water content, the catalyst layer can be current limiting in the fuel cell. Furthermore, since the cost of the catalyst material is critical, it is important to have a model predicting the effective utilization of this catalyst layer as well as one, which gives insights into how it might be improved. Equations are presented for the mass conservation of reactants and products, the electrical and ionic currents, and the conservation of energy. A discussion of a number of the closure relations such as the Butler-Volmer equation employed is included as is a discussion of the initial and boundary conditions applied. The mathematical model is solved using a finite elements approach developed at the I.U.S.T.I. / Master of Science

The typical catalyst layer structure for proton exchange membrane (PEM) fuel cells has changed little over the last two decades. A new electrode design with improved control over factors such as ionic and electrical pathways, porosity, and catalyst placement, could allow the application of less expensive catalyst alternatives. In this work, a novel electrode design based on ionomer-coated carbon nanofibers is proposed and studied. Governing equations for this design were established, and a mathematical model was created and solved using MATLAB to predict the performance of the new electrode design. A parametric study was performed to identify the design variables that had the most significant effect on performance. The best performing catalyst layer design studied with this model produces a current density of 1.1 A cm-2 at 600 mV which is better than state-of-the-art cathode designs. The results offer insight into the performance of ionomer-coated carbon nanofiber catalyst layers and can guide the fabrication and testing of these promising catalyst layer structures. / Master of Science / Proton exchange membrane (PEM) fuel cells have the potential to replace traditional energy conversion systems in many applications, however their widespread adoption is currently limited by their high cost and insufficient durability. PEM fuel cells are expensive because they require the use of platinum as a catalyst. Currently, less expensive non-platinum catalysts, must be used in much higher amounts in the catalyst layer to achieve similar electrochemical activity, creating very thick catalyst layers. Traditional fuel cell catalyst layer structures are designed to be thin and perform poorly when thick enough to accommodate non-platinum catalysts. This work proposes a novel catalyst layer design based on ionomer-coated carbon nanofibers that can allow for thicker catalyst layers and much higher catalyst loadings. A mathematical model was developed for the novel catalyst layer based on first principles. The model was solved using MATLAB to predict the performance of the new catalyst layer design. A parametric study was performed to identify the critical design variables and their effect on catalyst layer performance. The best performing catalyst layer design studied with this model produced a current density of 1.1 A cm-2 at 600mV, which is better than state-of-the-art fuel cell designs. This work is meant to offer insight into the performance of an ionomer-coated nanofiber catalyst layer and to guide future research in the fabrication of high performance fuel cells based on this novel catalyst layer architecture.