Metal Oxides in Energy Technologies

Yuping Wu, Ghenadii Korotcenkov

• Publisher: Elsevier
• Year: 2018
• Print ISBN: 9780128104156
• eBook ISBN: 9780128104163
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Metal Oxides in Energy Technologies provides, for the first time, a look at the wide range of energy applications of metal oxides. Topics covered include metal oxides materials and their applications in batteries, supercapacitors, fuel cells, solar cells, supercapacitors, and much more. The book is written by an experienced author of over 240 papers in peer-reviewed journals who was also been recognized as one of Thomson Reuter's "World's Most Influential Scientific Minds in 2015. This book presents a unique work that is ideal for academic researchers and engineers.- Presents an authoritative overview on metal oxides in energy technologies as written by an expert author who has published extensively in the area- Offers up-to-date coverage of a large, rapidly growing and complex literature- Focuses on applications, making it an ideal resource for those who want to apply this knowledge in industry

1

Introduction: Energy technologies and their role in our life

Yuping Wu⁎; Teunis van Ree^{† ⁎} State Key Laboratory of Materials-Oriented Chemical Engineering, School of Energy Science and Engineering, Institute for Electrochemical Energy Storage, Nanjing Tech University, Nanjing, People's Republic of China
^† Department of Chemistry, University of Venda, Thohoyandou, South Africa

Abstract

Metal oxides are well-known materials. Their application for energy technologies has also been well used. However, their wide applications are expected recently due to the energy and environment problems. In this chapter, a short introduction to preparation methods of metal oxides and their possible use in energy generation, energy storage, energy conversion, and the energy and environment is given. Further detailed knowledge will be given in the following chapters.

Keywords

Batteries; Biodiesel; Energy conversion; Energy harvesting; Energy technology; Metal oxides; Lithium-ion battery; Fuel cells; Nuclear energy; Solar cells; Supercapacitors; Superconductivity

Acknowledgment

Financial support from the National Materials Genome Project (2016YFB0700600), China National Fund for Distinguished Youth Scientists (51026004), and NSFC (U1601214, 51502137, and 21603103) is gratefully acknowledged.

Metal oxides have long been acknowledged and well used in many applications during the development of humankind though they were not well recognized at first. For example, China has long been famous for ceramics production technologies. Later, with the development of modern chemistry originating from the western countries, metal oxides become a highly topical subject. Their components, structures, preparation methods, characterization and so on have been well investigated. Meanwhile, the demand for energy has become a problem due to rapid economic development. New energy technologies have become important in sustainable human development, with metal oxides playing a dominant role.

1.1 Preparation methods of metal oxides and energy technologies

Metal oxides have a wide range of applications, and they can be prepared by a wide variety of methods, such as the following:

• • High-temperature solid-state (ceramic) method. A simple method in which the solid precursors are mixed intimately and then reacted at a high temperature [1].
• • Hydrothermal method. A solution of the precursor is heated in an autoclave to produce a crystalline product [2, 3].
• • Templating method. Organic materials especially polymers such as polystyrene are used to form a template with a distinct morphology and then a metal oxide is deposited into the empty space to form a porous material after the removal of the template [4, 5].
• • Sol-gel method. A sol is formed by the precursors, usually by means of hydrolysis and condensation reactions. After the sol polymerizes to form a gel, the gel is dried and heated to form the nanomaterial. In some cases, carriers such as organic complex can be added [6, 7].
• • Electrodeposition. A suspension of metal ions and insoluble particles is deposited electrochemically on an inert cathode surface [8, 9].
• • Chemical vapor deposition. The low-deposition temperature combined with a high-deposition rate produces a solid membrane with controllable composition and crystallinity [10, 11].
• • Chemical precipitation. An insoluble metal oxide is formed by chemical reaction between different solutions [12, 13].

Of course, morphology or shapes of the prepared metal oxides can also be tailored. They can be used for a wide range of applications [14]. However, one of their most important applications is in energy technologies including energy production, storage, conversion, and emission control (Fig. 1.1).

Fig. 1.1 Applications of metal oxides in energy technologies.

Metal oxides are widely applied in energy storage technologies, because they generally are able to generate charge carriers when energy is applied. They are especially useful electrode materials, leading to significant performance improvements, because a wide variety of oxidation states is possible for redox charge transfer. Metal oxides are also used as catalysts, for example, for hydrocarbon reforming reactions, in which a substance such as ceria is an outstanding catalyst and is resistant to carbon deposition. In this book, we introduce their applications as electrode materials for energy generation, conversion, and storage in a wide range of applications, such as solar cells, fuel cells, combustion, and nuclear reactors; batteries and supercapacitors; for hydrogen and biodiesel production [15]. Of course, many metal oxides such as catalysts perform very well in emission control, such as spinels (e.g., ZnAl₂O₄ and CuFe₂O₄), perovskites (such as SrTiO₃ and MgTiO₃), transition metal oxides (TMOs) (e.g., Mn, Cu, Co, Ti, Zr, and Ce oxides), and mixed metal oxides (MOXs) (such as MnO_x-CeO₂, CoO_x-CeO₂, CuO-CeO₂, and Ce_0.5Pr_0.5O₂) [16].

1.2 Energy generation

Metal oxide catalysts and electrode materials have become essential parts of our society to avoid energy and environmental crises via green energy generation, and degrading environmental organic pollutants [17]. Solar cells, fuel cells, and other developing energy conversion technologies are gradually becoming more useful in terms of efficiency, cost, and long-term stability.

1.2.1 Solar cells

A solar cell converts sunlight directly into electricity. Light shining on a solar panel generates current and voltage to produce electric power. This process requires a material in which the absorption of light excites an electron to a higher energy state, followed by transport of this high-energy electron from the solar cell into an external circuit. The electron drives work in the external circuit and returns to the solar cell. Although many materials and processes can provide photovoltaic energy conversion, most photovoltaic energy conversion is done in practice using semiconductors such as metal oxides and organic perovskites in the form of a p-n junction. Solar energy is not only clean, renewable, and plentiful, and an attractive addition or alternative to fossil fuels, but it can also help to relieve concerns about the environment [18] and energy security [19].

Solar water splitting (WS) in photocatalytic and photoelectrochemical systems is based on common semiconductor materials, especially metal oxides such as TiO₂, WO₃, BiVO₄, α-Fe₂O₃, and Cu₂O though sulfides are also useful. It is still necessary to improve the efficiency for solar WS, indicating a direction of future research trends.

1.2.2 Fuel cells

Fuel cells have high energy-conversion efficiencies and produce clean emissions, pointing to another promising trend in electric power generation. In fuel cells, chemical energy stored in a fuel, combined with oxygen in the air, is converted directly to electrical power by electrochemical reactions at very high theoretical and practical efficiencies compared to conventional internal combustion engines.

A basic fuel cell consists of three components: an anode, a cathode, and an electrolyte. In the fuel cell, the fuel and oxygen are oxidized and reduced, respectively, with electrons transferred from the anode to the cathode via the external circuit, whereas cations or oxygen anions are transported between the anode and the cathode through the electrolytes. Metal oxides such as cerium oxide have been introduced recently as anode materials, resulting in substantial performance improvement. However, several di...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of contributors
• About the Series Editor
• About the author
• Preface to the series
• Preface
• 1: Introduction: Energy technologies and their role in our life
• 2: Metal oxides in fuel cells
• 3: Metal oxide-based thermoelectric materials
• 4: Mixed oxides in nuclear fuels
• 5: Piezoelectric energy harvesting systems with metal oxides
• 6: Metal oxides in batteries
• 7: Metal oxides in supercapacitors
• 8: Metal oxide semiconductors for solar water splitting
• 9: Metal oxides for hydrogen storage
• 10: Requirements for efficient metal oxide photocatalysts for CO2 reduction
• 11: Metal oxide catalysts for biodiesel production
• 12: Solar-driven fuel production by metal-oxide thermochemical cycles
• 13: Metal oxides in energy-saving smart windows
• 14: Metal oxide-based superconductors in AC power transportation and transformation
• 15: Metal oxides for emission control
• Index