Studies on Electrocatalysts for Oxygen Electrochemistry, Hydrogen Evolution, and Carbon Dioxide Conversion and Their Applications

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Title
Studies on Electrocatalysts for Oxygen Electrochemistry, Hydrogen Evolution, and Carbon Dioxide Conversion and Their Applications
Author
Kim, Changmin
Advisor
Kim, Guntae
Issue Date
2020-02
Publisher
Graduate School of UNIST
Abstract
Global energy demand and consumption of humankind have increased significantly over the industrial period and continue to increase steadily. A stable retention of energy resources has become a critical issue in terms of economic, industrial, technical, military and national competitiveness. Fossil fuels have been used extensively throughout the world owing to the miniaturization of combustion energy converters together with their high technological maturity. Accordingly, atmospheric carbon dioxide (CO2) has increased from 278 to 412 parts per million (ppm) over a century and has critically impacted on environmental issues and climate changes. Human beings are now faced irreversible energy requirements and environmental issues, and thus finding new energy sources and energy conversion devices for clean and efficient energy storage and generation is becoming an important challenge. Metal-air batteries have been regarded as prime alternatives for energy storage and conversion devices from their far higher specific energy than that of lithium-ion batteries. However, many complications related to metal anodes (e.g., self-corrosion, rechargeability, etc.), electrolytes (e.g., solution resistance, short-circuit, sluggish ion transfer of separators, etc.), and catalysts (e.g., activities, asymmetrical redox trends, corrosions, durability, high-cost, etc.) should be addressed for the development and implementation of metal-air batteries. Hydrogen (H2), a clean energy source, is widely viewed as a promising alternative energy source to finite fossil fuels, but it has been pointed out that H2 is mainly produced by a hydrocarbon thermolysis (e.g., steam methane reforming) releasing a significant amount of CO2. Alkaline water electrolysis has been known as the green H2 production technology from its nature of no CO2 emissions. However, its energy-intensive electrolysis processes require the development of efficient hydrogen and oxygen evolution catalysts. To reduce carbon footprint, considerable research has been focused on a carbon capture, utilization and storage/sequestration (CCUS) technology to recycle CO2 as a resource to produce high value-added carbon compounds, such as methanol, organic materials, and plastics. So far, however, the economic feasibility of the existing conversion technologies is still inadequate due to sluggish CO2 conversion. Thus, the development of efficient CO2 utilizing electrochemical cells and active electrocatalysts is required.   This dissertation focuses on the studies of electrocatalysts for oxygen electrochemistry, hydrogen evolution, and carbon dioxide conversion applicable to metal-air batteries, alkaline water electrolysis, and metal-CO2 cells. This dissertation discovers the active electrocatalysts and the promising electrochemical cells with the detailed discussions organized by material characterizations, electrochemical analyses, mechanism analyses, thermodynamic studies, computational studies, and efficiency calculations. This dissertation starts with brief backgrounds of electrocatalysis, metal-air batteries, alkaline water electrolysis, and CO2 conversion technology in Chapter 1. And the detailed experimental techniques for electrochemical analyses for half-cell and full-cell configurations will be covered in Chapter 2. The rest of chapters will cover the studies of electrocatalysts for oxygen electrochemistry, hydrogen evolution, and carbon dioxide conversion and their applications. The chapters are categorized as follows: Chapter 3 discovers new composite catalysts consisting of nanorod type perovskites and edge-iodinated graphene nanoplatelets for efficient bifunctional catalysts toward oxygen reduction reaction and oxygen evolution reaction, with the application on hybrid Li-air batteries. Chapter 4 discovers new binder-free electrodes prepared by structuring polypyrrole-assisted cobalt oxide anchored carbon fiber for efficient bifunctional catalysts toward oxygen reduction reaction and oxygen evolution reaction, with the application on seawater batteries. Chapter 5 discovers new heterostructure electrocatalysts consisting of perovskite oxides and transition metal dichalcogenides for efficient overall water electrolysis. During overall water splitting operation, the catalysts performed excellent performance and durable stability for a long-term. Chapter 6 discovers new hybrid Na-CO2 electrochemical cells that producing electric energy and hydrogen by efficiently consuming CO2 from the nature of spontaneous CO2 dissolution in an aqueous solution with a long-term stable operation. Chapter 7 discovers new aqueous Zn/Al-CO2 electrochemical cells that utilize CO2 as a useful resource to produce electricity and hydrogen gas using Zn and Al metals, which are abundant, low-cost, and environmentally friendly. The proposed systems presented the best performance among metal-CO2 systems reported so far.
Description
Department of Energy Engineering (Energy Engineering)
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