京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第17887号 / 工博第3796号 / 新制||工||1581(附属図書館) / 30707 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 酒井 明, 教授 邑瀬 邦明 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第17888号 / 工博第3797号 / 新制||工||1581(附属図書館) / 30708 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 酒井 明, 教授 邑瀬 邦明 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18983号 / 工博第4025号 / 新制||工||1620(附属図書館) / 31934 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 宇田 哲也, 教授 白井 泰治 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20368号 / 工博第4305号 / 新制||工||1667(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 乾 晴行, 教授 邑瀬 邦明 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第21881号 / エネ博第382号 / 新制||エネ||74(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー応用科学専攻 / (主査)教授 馬渕 守, 教授 宅田 裕彦, 教授 土井 俊哉 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

To capture the underlying chemistry and physics of a system on electronic structure platform, it is necessary to accurately describe the intermolecular interactions such as repulsion, polarization, hydrogen bonding, and van der Waals interactions. Among these interactions, van der Waals (dispersion) interactions are weak in nature as compare to covalent bonds and hydrogen bonding, but it is physically and chemically very important in accurately predicting condensed phase properties such as Vapor liquid equilibria. This presents a significant challenge in modeling VLE using a first principles approach. However, recent developments in dispersion corrected (DFT-D3) and nonlocal density functionals can model dispersion interactions with reasonable accuracy. Here, we will present some of results that quantify efficacy of recent density functionals in predicting phase equilibria of molecular systems via first principle Monte Carlo (FPMC) simulations. Our aim is to assess the performance of several density functional by determining VLE, critical properties, dimer potential energy curves, vibrational spectra, and structural properties. The functional used in our study includes PBE-D3, BLYP-D3, rVV10, PBE0- D3, and M062X-D3. In addition, we have used the second order Møller-Plesset perturbation theory (MP2) method for computing density of argon at single temperature. The organic compounds considered for this study involves argon, CO2, SO2, and various hydroflurocarbons (R14, R134a, CF3H, CF2H2, CFH3) molecules. Additionally, the development of new materials, ionic liquids, and modification of industrial processes are an ongoing effort by researchers to efficiently capture acidic gases. Our ability to model these sorption processes using a first principles approach can have significant impact in speeding up the discovery process. In our work, we have predicted CO2 solubility in triethyl(butyl)phosphonium ionic liquid via FPMC simulations. Our results reveal the infrared spectra, structural and transport properties for pure ionic liquid and its mixture with CO2 through ab initio molecular dynamics simulations.

This dissertation undertakes theoretical research into the adsorption, pattern formation, and reactions of atoms, molecules, and layered materials on catalyst surfaces. These investigations are carried out from first-principles calculations of electronic and geometric structures using density functional theory (DFT) for predictions and simulations at the atomic scale. The results should be useful for further study of the catalytic activities of materials and for engineering functional nanostructures. The first part of the dissertation focuses on systematic first-principles simulations of the energetic pathways of CO oxidation on the Cu2O(100) surface. These simulations show CO to oxidize spontaneously on the O-terminated Cu2O(100) surface by consuming surface oxygen atoms. The O-vacancy on Cu2O(100) then is subsequently healed by dissociative adsorption of atmospheric O2 molecules. The second part discusses the pattern formation of hydrogen on two and three layers of Co film grown on the Cu(111) surface. It is found that increasing the pressure of H2 changes the hydrogen structure from 2H-(2 × 2) to H-p(1 × 1) through an intermediate structure of 6H-(3 × 3). The third part compares the results of different ways of introducing van der Waals (vdW) interactions into DFT simulations of the adsorption and pattern formation of various molecules on certain substrates. Examinations of the physisorption of five nucleobases on iii graphene and of n-alkane on Pt(111) demonstrate the importance of taking vdW interactions into account, and of doing so in a way that is best suited to the particular system in question. More importantly, as the adsorption of 1,4 diaminebenzene molecules on Au(111) shows inclusion of vdW interactions is crucial for accurate simulation of the pattern formation. The final part carries out first-principles calculations of the geometric and electronic structure of the Moir´e pattern of a single layer of Molybdenum disulfide (MoS2 ) on Cu(111). The results reveal three possible stacking types. They also demonstrate that the MoS2 layer to be chemisorbed, albeit weakly, and that, while Cu surface atoms are vertically disordered, the layer itself is not strongly buckled.

The main objective of this work is to gain basis for rational design of catalysts used in fuel cells for conversion of chemical energy stored in hydrogen molecules into electric energy, as well as photo-catalysts used for hydrogen production from water under solar irradiation. This objective is achieved by applying the first principles computational approach to reveal relationship among compositions of materials under consideration, their electronic structure and catalytic activity. A major part of the work is focused on electro-catalysts for hydrogen fuel cells. Platinum (Pt) is widely used in the electrodes of fuel cells due to its good catalytic properties. However, Pt is an expensive and scarce element, its catalytic activity is not optimal and also it suffers from CO poisoning at anode. Therefore the search for new catalytic materials is needed for large scale implementation of fuel cells. The main direction of search of more efficient electro-catalysts is based in the design in which an active element monoatomic layer (AE) is deposited on a metal substrate (MS) made of a cost-effective material. Two goals are achieved by doing this: on the one hand, the cost of the catalytic system is reduced by reducing the amount of the AE in the system and on the other hand the catalytic properties of the AE can be tuned through its interactions with the MS. In the first part of this work the Pd-based alloys and layered structures have been studied as promising electro-catalysts for the ORR on the fuel cell cathodes, more precisely Pd-Co alloys and Pd/M/Pd (M=Co,Fe). There exists a robust model linking the activity of a surface toward ORR to computable thermodynamic properties of the system and further to the binding energies iv of the ORR intermediates on the catalyst surface. A more challenging task is to find how to tune these binding energies through modification of the surface electronic structure that can be achieved by varying the surface composition and/or morphology. To resolve this challenge, the electronic structure, binding energies of intermediates and the ORR free energies have been calculated within the density functional theory (DFT) approximation. The results presented in this work show that in contrast to the widely accepted notion, the strain exerted by a substrate on AE hardly affects the surface activity toward ORR, while the hybridization of the electronic states of the AE-and MS-electronic states is the key factor controlling the catalytic properties of these systems. Next it is shown that the catalytic activity of the promising anode electrocatalysts, such as Pt/M, M=Au, Ru and Pd, is also determined by the AE-MS hybridization with a minor effect of the strain. Furthermore, we have shown that, if AE is weakly bound to the substrate (as it is for Pt/Au), surface reconstruction occurs. This leads to the breaking of the relation between the electronic structure of the clean surface and the reactivity of the sytem. Other kind of promising ORR catalysts is designed in the form of Ru nanoparticles modified by chalcogens. In this work, I present the results obtained for small Ru clusters and flat Ru facets modified with chalcogens (S, Se and Te). The O and OH binding energies are chosen as descriptors of the ORR. The results on the two systems are compared, concluding that large clusters with relative large flat facets have higher catalytic activity due to the absence of low coordinated and thus high reactive Ru atoms. Regarding the problem of the hydrogen production via photo-catalytic splitting of water, one of the challenges is tuning the band gap of the photo-anodes to optimal levels. Graphitic carbon nitride (g-C3N4) is a promising material to be used as a photo-anode, however, a v reduction of the band gap width by rational doping of the material would improve the efficiency significantly. This issue is addressed in the last chapter of this work. Two problems are considered: a) the stability of the doped system and b) the band gap width. To address the first problem the ab-initio thermodynamics approach has been used, finding that the substitution of C and N with the doping agent (B, C, N, O, Si and P) is thermodynamically preferred over the interstitial addition of dopant to the g-C3N4 structure. However, due to high kinetic energy barriers for the detachment of C and N atoms, involved in the substitution doping, the interstitial addition found to be kinetically more favorable. Since the density functional theory fails to reproduce the band gap of semiconductors correctly, the GW approximation was used to study the band gap of the system. The results indicate that the g-C3N4 system maintain its semiconductor character if doped with B, O and P under certain conditions, while reducing the band gap.

Due to recent advances in computational hardware and code accessibility, state-of-the-art calculations are currently employed to investigate materials at the nanoscale with varying levels of accuracy. As such, this dissertation highlights a series of materials ranging from one-dimensional wires, to reactive surfaces, to bulk crystals. Initial characterizations for all considered materials are carried out using density functional theory where additional approximations are utilized to obtain more complex quantities. For Millon's salt, first-principles calculations confirm a quasi-one-dimensional description where the metallic backbone influences electronic properties while hydrogen-bonding between ligands results in structural stability. We show that valence band dispersion can be controlled via strain or ligand substitution, pointing to tunable hole-carrier possibilities. Optical properties are also addressed with respect to experimental and theoretical findings. Our focus then shifts to titanium dioxide, a popular and promising photocatalyst. Specific nitrogen doping on the anatase (001) surface introduces intra gap states accessible for photoactivation in the visible. The additional presence of a fluorine dopant or oxygen vacancy enhances the density of these particular states available for transitions. Titanium dioxide also has experimentally displayed involvement in carbon dioxide reduction mechanisms. From first-principles calculations, anatase (001) surfaces containing an oxygen vacancy exhibit an increased potential for carbon dioxide to undergo reduction due to an exposed titanium atom in comparison to the pristine case. Other binding configurations on both types of surfaces suggest the existence of alternative conversion pathways. As a recently realized plasmonic material, titanium nitride proves advantageous in relation to more traditional materials, e.g., gold or silver; one of the main factors stems from its tunable permittivity. We investigate this aspect by theoretically incorporating defects into titanium nitride, which introduces a systematic approach to control plasmonic activity over a broad frequency range. Finally, lifetimes of hot-electrons, originating from plasmonic decay, for instance, possess finite lifetimes in titanium nitride, as well as in other similar materials, that are described by electron-electron interactions through the electron self-energy. Average lifetimes resemble those obtained with a free electron gas model while details of the band structure influence lifetime behavior. Calculations exploring factors affecting these lifetimes are presented.

No description available.