Synthesis of matrices-supported metal nanoparticles and catalysis applications /by Byunghoon Yoon.

Thesis (Ph. D.)--University of Idaho, December 2006

A Novel Methodology for Estimating Technology Value and Importance of Factors in Market-Based Approach

Technology valuation methods are classified into income-based, cost-based, and market-based approaches depending on the perspective of valuing technology. The market approach evaluates the value of technology by referring to cases in which similar technologies have been traded before. In this study, we use prior technology transaction data to estimate the technology value based on the market approach and to identify influential factors to the estimated value. To this end, we adopt a multivariate k-nearest neighbor (MKNN) regression model to accommodate mixed-type input variables aiming at estimating multivariate technology values, selecting influencing factors, and the relative importance of the selected factors. In addition, we can optimize the number of transaction cases k in k-NN regression. Our proposed regression model outperforms an embedding model with cosine similarity in predicting multivariate response variables. In addition, we illustrate how to select and assess the influential factors based on the real-life dataset

Atomistic investigation of doping effects on electrocatalytic properties of cobalt oxides for water oxidation

The development of high-performance oxygen evolution reaction (OER) catalysts is crucial to achieve the clean production of hydrogen via water splitting. Recently, Co-based oxides have been intensively investigated as some of the most efficient and cost-effective OER catalysts. In particular, compositional tuning of Co-based oxides via doping or substitution is shown to significantly affect their catalytic activity. Nevertheless, the origin of this enhanced catalytic activity and the reaction mechanism occurring at catalytic active sites remain controversial. Theoretical investigations are performed on the electrocatalytic properties of pristine and transition metal (Fe, Ni, and Mn)-substituted Co oxides using first-principle calculations. A comprehensive evaluation of the doping effects is conducted by considering various oxygen local environments in the crystal structure, which helps elucidate the mechanism behind the doping-induced enhancement of Co-based catalysts. It is demonstrated that the local distortion induced by dopant cations remarkably facilitates the catalysis at a specific site by modulating the hydrogen bonding. In particular, the presence of Jahn-Teller-active Fe(IV) is shown to result in a substantial reduction in the overpotential at the initially inactive catalysis site without compromising the activity of the pristine active sites, supporting previous experimental observations of exceptional OER performance for Fe-containing Co oxides.

Anionic Redox Activity Regulated by Transition Metal in Lithium‐Rich Layered Oxides

The anionic redox activity in lithium-rich layered oxides has the potential to boost the energy density of lithium-ion batteries. Although it is widely accepted that the anionic redox activity stems from the orphaned oxygen energy level, its regulation and structural stabilization, which are essential for practical employment, remain still elusive, requiring an improved fundamental understanding. Herein, the oxygen redox activity for a wide range of 3dtransition-metal-based Li(2)TMO(3)compounds is investigated and the intrinsic competition between the cationic and anionic redox reaction is unveiled. It is demonstrated that the energy level of the orphaned oxygen state (and, correspondingly, the activity) is delicately governed by the type and number of neighboring transition metals owing to the pi-type interactions between Li-O-Li and Mt(2g)states. Based on these findings, a simple model that can be used to estimate the anionic redox activity of various lithium-rich layered oxides is proposed. The model explains the recently reported significantly different oxygen redox voltages or inactivity in lithium-rich materials despite the commonly observed Li-O-Li states with presumably unhybridized character. The discovery of hidden factors that rule the anionic redox in lithium-rich cathode materials will aid in enabling controlled cumulative cationic and anionic redox reactions.

Native defects in Li10GeP2S12 and their effect on lithium diffusion

Defects in crystals alter the intrinsic nature of pristine materials including their electronic/crystalline structure and charge-transport characteristics. The ionic transport properties of solid-state ionic conductors, in particular, are profoundly affected by their defect structure. Nevertheless, a fundamental understanding of the defect structure of one of the most extensively studied lithium superionic conductors, Li10GeP2S12, remains elusive because of the complexity of the structure; the effects of defects on lithium diffusion and the potential to control defects by varying synthetic conditions also remain unknown. Herein, we report, for the first time, a comprehensive first-principles study on native defects in Li10GeP2S12 and their effect on lithium diffusion. We provide the complete defect profile of Li10GeP2S12 and identify major defects that are easily formed regardless of the chemical environment while the presence of path-blocking defects is sensitively dependent on the synthetic conditions. Moreover, using ab initio molecular dynamics simulation, it is demonstrated that the major defects in Li10GeP2S12 significantly alter the diffusion process. The defects generally facilitate lithium diffusion in Li10GeP2S12 by enhancing the charge carrier concentration and flattening the site energy landscape. This work delivers a comprehensive picture of the defect chemistry and structural insights for fast lithium diffusion of Li10GeP2S12-type conductors.

Native Defects in Li10GeP2S12 and Their Effect on Lithium Diffusion

Defects in crystals alter the intrinsic nature of pristine materials including their electronic/crystalline structure and charge-transport characteristics. The ionic transport properties of solid-state ionic conductors, in particular, are profoundly affected by their defect structure. Nevertheless, a fundamental understanding of the defect structure of one of the most extensively studied lithium superionic conductors, Li10GeP2S12, remains elusive because of the complexity of the structure; the effects of defects on lithium diffusion and the potential to control defects by varying synthetic conditions also remain unknown. Herein, we report, for the first time, a comprehensive first-principles study on native defects in Li10GeP2S12 and their effect on lithium diffusion. We provide the complete defect profile of Li10GeP2S12 and identify major defects that are easily formed regardless of the chemical environment while the presence of path-blocking defects is sensitively dependent on the synthetic conditions. Moreover, using ab initio molecular dynamics simulation, it is demonstrated that the major defects in Li10GeP2S12 significantly alter the diffusion process. The defects generally facilitate lithium diffusion in Li10GeP2S12 by enhancing the charge carrier concentration and flattening the site energy landscape. This work delivers a comprehensive picture of the defect chemistry and structural insights for fast lithium diffusion of Li10GeP2S12-type conductors. © 2018 American Chemical Societ

Anionic Redox Activity Regulated by Transition Metal in Lithium-Rich Layered Oxides

The anionic redox activity in lithium-rich layered oxides has the potential to boost the energy density of lithium-ion batteries. Although it is widely accepted that the anionic redox activity stems from the orphaned oxygen energy level, its regulation and structural stabilization, which are essential for practical employment, remain still elusive, requiring an improved fundamental understanding. Herein, the oxygen redox activity for a wide range of 3dtransition-metal-based Li(2)TMO(3)compounds is investigated and the intrinsic competition between the cationic and anionic redox reaction is unveiled. It is demonstrated that the energy level of the orphaned oxygen state (and, correspondingly, the activity) is delicately governed by the type and number of neighboring transition metals owing to the pi-type interactions between Li-O-Li and Mt(2g)states. Based on these findings, a simple model that can be used to estimate the anionic redox activity of various lithium-rich layered oxides is proposed. The model explains the recently reported significantly different oxygen redox voltages or inactivity in lithium-rich materials despite the commonly observed Li-O-Li states with presumably unhybridized character. The discovery of hidden factors that rule the anionic redox in lithium-rich cathode materials will aid in enabling controlled cumulative cationic and anionic redox reactions.

Using First-Principles Calculations for the Advancement of Materials for Rechargeable Batteries

Rechargeable batteries have been regarded as leading candidates for energy storage systems to satisfy soaring energy demands and ensure efficient energy use, and intensive efforts have thus been focused on enhancing their energy densities and power capabilities. First-principles calculations based on quantum mechanics have played an important role in obtaining a fundamental understanding of battery materials, thus providing insights for material design. In this feature article, the theoretical approaches used to determine key battery properties, such as the voltage, phase stability, and ion-diffusion kinetics, are reviewed. Moreover, the recent contribution of first-principles calculations to the interpretation of complicated experimental characterization measurements on battery materials, such as those obtained using X-ray absorption spectroscopy, electron energy-loss spectroscopy, nuclear magnetic resonance spectroscopy, and transmission electron microscopy, are introduced. Finally, perspectives are provided on the research direction of first-principles calculations for the development of advanced batteries, including the further development of theories that can accurately describe the dissolved species, amorphous phases, and surface reactions that are integral to the operation of future battery systems beyond Li-ion batteries.