Lithium-ion batteries (LIBs) are widely applied in a variety of applications such as mobile phones, laptop chargers, and electric vehicles. Thanks to a high energy density of about 120 to 220 Wh kg-1, LIBs are used for a long time, however, the present technology is unable to satisfy the increasing energy storage requirements. Therefore, increasing the energy density of LIBs to improve the performance is very important. Because of that the specific capacity and operation voltage of the anode and cathode materials determine the energy density, improving these two parameters is the key point. This can be achieved in two ways, one being the optimization of the electrode materials of existing LIBs, both cathode and anode, the other is the development of new battery systems to replace LIBs, potassium-ion batteries (KIBs) and sodium-ion batteries (NIBs) are examples of such new systems. In any case, the selection of the electrode materials is crucial. With a rapid development of two-dimensional (2D) materials, leading directly to an increase interest in exploring 2D materials in order to serve as possible electrode materials, based on their unique 2D structures, large conductivity, and most importantly, wide specific surface area. Among them lays graphene-like carbon-nitride materials with lightweight properties. These materials have collected spotlights in multiple fields that are concerned with energy harvesting and storage. The metallic monolayer C6N3 is a very recently discovered member in this family, which is chemically, mechanically, dynamically, and thermodynamically stable through the first-principal calculations. In this work, we investigate the monolayer C6N3 performance as a potential and promising foundation for the anode material of LIBs/NIBs/KIBs. According to our theoretical investigation, the metallic monolayer C6N3 should be an effective anode material for the LIBs/NIBs/KIBs, which combines high specific capacity and low average open-circuit voltage.

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The compressive creep behaviour of a high purity silicon nitride ceramic with and without the addition of Ba was studied at 1400°C. Two distinct creep stages were observed during high temperature deformation of these materials. The stress exponents for creep of the two materials indicate that they have different creep mechanisms during the second stage of creep. Cavitation during creep was determined by measuring the density change before and after creep using a water­-displacement method. The Ba doped material exhibited an obvious density decrease, indicating cavitation during creep, whereas the undoped material exhibited no cavitation. This is consistent with TEM observations. The microstructure of the materials, especially the amorphous grain-boundary phase was investigated for both as-sintered and crept specimans by means of transmission electron microscopy (TEM). Statistical analysis of a number of grain-­boundary films indicates that the film thickness is confined to a narrow range (standard deviation less than 0.15 nm) in the as-sintered materials. The average film thickness depends on film chemistry, increasing from 1.0 nm to 1.4 nm when Ba is added. The standard deviation of the film thickness of a given material after creep, however, is considerably larger than before (0.30 nm ~ 0.59 nm). This suggests that the grain-boundary glass phase is redistributed during creep. Viscous flow of the glass phase is proposed as die mechanism responsible for the first stage of creep. The data are compared with a model for viscous creep, yielding good correlation. / Thesis / Master of Engineering (ME)

A series of niobium-containing nitride and carbides were prepared by a temperature-programmed synthesis method. The catalysts synthesized comprised a monometallic niobium oxynitride and a new bimetallic oxycarbide supported system, Nb-Mo-O-C/Al₂O₃ (Mo/Nb = 1.2; 1.6; 2.0). In the case of the niobium oxynitride, the progress of formation was analyzed by interrupting the synthesis at various stages. The effect of the heating rate on product properties was also investigated. The solid intermediates and the final niobium oxynitride were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental analysis (CHNS), and gas adsorption techniques. The solid state transformation occurred directly from Nb₂O₅ to NbN_xO_y without any suboxide intermediates. The bimetallic supported oxycarbide materials were also characterized by X-ray diffraction (XRD), gas adsorption techniques, X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS). It was found that the electronic properties of the oxycarbide were modified by the interaction with the Al₂O₃ support, and that most of the oxygen atoms were associated with the niobium rather than the molybdenum atom. All of the niobium-containing catalysts were tested in a three-phase trickle-bed reactor for the simultaneous hydrodenitrogenation (HDN) of quinoline and hydrodesulfurization (HDS) of dibenzothiophene. The niobium oxynitride presented low HDS activity and moderate HDN activity, whereas the supported bimetallic oxycarbide was found to be highly active for both, HDN and HDS, demonstrating higher activities than the commercial sulfided Ni-Mo/Al₂O₃ when compared on the basis of active sites. In addition to these studies a comprehensive investigation of the HDN reaction mechanism was carried out over bulk unsupported Mo₂C, NbC, NbMo₂-O-C, and compared with the mechanism over a sulfide catalyst, MoS₂/SiO₂. For this purpose, a comparison of the HDN rate of a series of isomeric amines was performed, and the reaction occurred mainly through a β-elimination mechanism for all catalysts. Temperature programmed desorption of ethylamine was used to investigate the acid properties of the catalytic surfaces, and a good agreement between the specific rate of reaction and the number of Brønsted acid-sites was obtained. Infrared spectroscopy showed that the amines interacted with acidic centers to form adsorbed quartenary ammonium species. The deamination reaction over the carbide and sulfide catalysts probably occurs by a concerted push-pull mechanism involving basic sulfur species and Brønsted-acidic centers. In order to obtain more insight into the mechanism a study of the pyridine HDN network was carried out.All of the catalysts showed the same activity trend: the reactivity of n-pentylamine was high, while those of piperidine and pyridine were relatively low. The carbide catalysts showed higher selectivity towards HDN products than the sulfide catalyst at the same conversion levels. The higher selectivity was related to the higher ratio (r = k₂/k₁) between the rate constants of the two consecutive reactions, hydrogenation of pyridine (k₁) and ring opening of piperidine (k₂). The order of activity of the carbides and sulfide differed considerably depending on the substrate. However, for the pyridine reaction network the similarity in product distribution suggested that a similar surface composition, a carbosulfide, was attained during the reaction. / Ph. D.