Chemical Vapor Deposition (CVD)

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Background and General Motivation

The increasing demand for a reliable and sustainable source of energy for technological growth and development has facilitated a simultaneous increase in funding energy- related research. The increasing world population and advancement in technology has also created an increase in the global demand for energy use ranging from small scale domestic applications (in terms of personal use) to large scale industrial applications for transportation and manufacturing purposes. However, in a bid to create sufficient energy to meet the sky-rocketing demand, the diverse routes taken in the production of energy also constitutes a great threat to life and the universe at large. Some of these routes include, the energy generated from thermal power stations via combustion of coal, hydroelectric power stations using dams and most recently, nuclear reactors among others.
These pose issues of global warming and environmental pollution, on one hand, and the toxic waste from energy generation on the other, are of important concern to many countries today. The depletion of natural resources like crude oil, coal and natural gas reserves which are the most common sources of fuel for energy generation today has resulted in the need to develop a sustainable and reliable form of energy for the future. Renewable energy sources are energy resources which can be easily and quickly restored by a natural process. This has led to an increasing interest in renewable energy-based research for generating a much cleaner and safer energy generation/conversion systems.
Furthermore, if the main goal is to ensure a readily available energy source to meet the demand, there is also a need to build reliable and efficient energy storage systems to preserve the excess generated power (from these renewable energy sources) for use when required for specific applications. Such storage systems must possess high energy and high power densities in order to provide a robust storage capacity along with an instantaneous/rapid delivery capability respectively. This will provide a reliable system which is able to fit into present day ubiquitous technology where energy is needed at different instances to power complex assemblies such as portable electronic gadgets, hybrid electric vehicles, speed trains etc.
Some of the common energy storage devices in use today are batteries and conventional capacitors which are characterized with low power density and energy density respectively. Thus, an efficient high performance, low cost and environmentally safe all-in-one energy storage system which combines the properties of the batteries and capacitors is required. Electrochemical Capacitors (ECs) are emerging technologies with a bright as well as promising future to complement and possibly replace batteries and conventional capacitors for energy storage [1,2]. However, the performance of these technologies is related to their constitutive material characteristics. In order to optimize them for suitable specific energy storage applications, there is a need to analyze their individual properties to meet the increasing consumption rate. It is worth stating that the lifetime of storage systems should be comparable to the requirements presented by these emerging technologies.
Furthermore, the long term goal is to develop a system which is easily compatible with individual energy conversion systems like fuel cells, solar cells, windmills, etc. in order to easily collect excess generated energy and store it for later use. Electrochemical capacitors (ECs), Supercapacitors (SCs) or Ultracapacitors (UCs) are commonly used to classify a category of energy storage devices that are closely linked with rapid storage and release of energy [3]. In comparison with conventional capacitors, the specific energies of SCs are much higher while their corresponding power densities are much greater than most batteries [3,4]. Thus, with the appropriate structural model, there is a promising trend to obtain hybrid structures with a combination of both conventional capacitors and batteries which exists as a stand-alone storage unit.
Their highly reversible charge-storage capability also makes them the ideal candidate for much desirable long term applications which fits perfectly into the fast growing technological advancements in the energy industry [3–6]. SCs are broadly divided into two main types based on their mode of energy storage and associated material components, namely; The EDLCs store energy by charge separation which is similar to the charge storage mechanism in a basic capacitor. However, the magnitude of charge stored in the EDLCs is very much higher due to the surface area of the active electrode material and the distance over which charge separation occurs [1]. The ions within the electrolyte which are responsible for charge movement between the electrode and electrolyte interface involves very fast processes as compared to batteries [4]. This explains the reason for their dynamic charge propagation (short-term pulse) which is useful in emerging technological applications (like hybrid electric vehicles, emergency doors of aircraft etc.) where an initial high specific power is required.
Carbon is the only material used for fabricating EDLCs and this has been extensively studied by researchers [4,7]. This has led to the discovery of numerous forms of carbon depending on the synthesis route used. Some of the important forms of carbon suitable for electrochemical studies include activated carbon [8–10], graphene [11,12], carbon nanotubes [13,14], onion-like carbons [15], activated carbon fibers (ACF) [16], etc. These different forms of carbon mentioned are also associated with a broad range of selective properties which make them suitable for energy storage applications. Some of these properties include; high surface area, controllable pore size, high conductivity, good corrosion resistance, high temperature stability, relatively low cost due to its abundance in nature and its compatibility with other material matrix to form composites [2,4,11,17–19].

Table of Contents :

• Declaration
• Dedication
• Acknowledgements
• Table of Contents
• List of figures
• List of Equations
• List of Tables
• List of Abbreviations and Symbols
• CHAPTER INTRODUCTION
  • 1.1 Background and General Motivation
  • 1.2 Aim and Objectives
  • 1.3 Scope and Outline of thesis
  • 1.4 References
• CHAPTER LITERATURE REVIEW
  • 2.1 Charge storage – Basic design
  • 2.2 Electrochemical capacitors: Principle of energy storage
    • 2.2.1 Electric Double Layer Capacitors (EDLCs)
    • 2.2.2 Pseudocapacitors (PCs or Redox Electrochemical Capacitor)
    • 2.2.3 Hybrid Electrochemical Capacitors and Composite materials
  • 2.3 Electrolytes
  • 2.4 Advantages, application and challenges arising from the use of ECs
  • 2.5 Fabrication of electrodes for electrochemical capacitors
  • 2.6 Electrochemical testing of the electrode material
  • 2.7 Evaluation of electrode material
    • 2.7.1 Cyclic Voltammetry (CV)
    • 2.7.2 Chronopotentiometry (CP) or Galvanostatic Charge/Discharge (GCD)
    • 2.7.3 Electrochemical Impedance Spectroscopy (EIS)
  • 2.8 References
• CHAPTER EXPERIMENTAL PROCEDURE AND CHARACTERIZATION TECHNIQUES
  • 3.1 Chemical Vapor Deposition (CVD)
  • 3.2 Solvothermal Chemical Growth (SCG)
    • 3.2.1 Solvent-assisted chemical growth of metal-layered double hydroxides
    • 3.2.2 Exfoliation-assisted chemical growth of metal hydroxides-graphene composites
  • 3.3 Materials characterization
    • 3.3.1 Morphological studies
    • 3.3.2 Structural and Qualitative Phase studies
    • 3.3.3 Gas Adsorption Analysis
    • 3.3.4 Raman Analysis
    • 3.3.5 Fourier Transform Infra-red Resonance (FTIR) Spectroscopy
    • 3.3.6 Thermal Gravimetric Analysis
    • 3.3.7 Electrochemical Analysis
  • 3.4 References
• CHAPTER RESULTS AND DISCUSSION
  • 4.1 Incorporation of graphene into the main matrix of NiAl layered double hydroxides and NiAl double hydroxide microspheres
    • 4.1.1 Introduction
    • 4.1.2 Result and discussion
    • 4.1.3 Publication 1: Solvothermal synthesis of NiAl double hydroxide microspheres on a nickel foam-graphene as an electrode material for pseudo-capacitors
    • 4.1.4 Concluding Remarks
    • 4.1.5 References
  • 4.2 Enhancement of the electrochemical properties of P3HT:PCBM polymer-blend electrodes using NiAl layered double hydroxide-graphene composites
    • 4.2.1 Introduction
    • 4.2.2 Result and discussion
    • 4.2.3 Publication 2: P3HT:PCBM/nickel-aluminum layered double hydroxide-graphene foam composites for supercapacitor electrodes
    • 4.2.4 Concluding Remarks
    • 4.2.5 References
  • 4.3 In-situ growth of simonkolleite-graphene foam composites for pseudocapacitor electrodes
    • 4.3.1 Introduction
    • 4.3.2 Results and discussion
    • 4.3.3 Publication 3: Simonkolleite-graphene foam composites and their superior electrochemical performance
    • 4.3.4 Concluding Remarks
    • 4.3.5 References

• CHAPTER  GENERAL CONCLUSIONS
• CHAPTER FUTURE WORK

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