Effects of carbon nanomaterials on the performance of symmetric pseudocapacitors

iv Table of Content . vi List of Abbreviations and Symbols . xii List of Tables . xv List of Figures . xvi 1 CHAPTER 1: INTRODUCTION . 1 Global Interest in Renewable Energy . 2 1.1 Energy Storage Systems (ESS) . 5 1.2 Electrochemical Energy Storage Systems (EESs) . 7 1.3 The Objectives / Scope of this Study . 8 1.4 Outline of the Dissertation . 11 1.5 References . 12 2 CHAPTER 2: LITERATURE STUDIES / BACKGROUND . 15 Electrochemical Capacitors (ECs): An Overview . 16 2.1 Historical Background of Electrochemical Capacitors (ECs) . 19 2.2 Basic Principles of Electrochemical Capacitors (ECs) . 20 2.3 2.3.1 Energy Storage in Electrical Double Layer Capacitors (EDLCs) . 23 © University of Pretoria vii 2.3.2 Energy Storage in Pseudocapacitors (PCs) . 25 2.3.3 Energy Storage in Hybrid Capacitors (HCs). 28 2.3.4 Performance of Electrochemical Capacitors (ECs) . 31 Electrode Materials for the ECs . 36 2.4 2.4.1 Carbon Structure and Porous Texture on EDLC Performance . 36 Activated Carbon . 37 a) Graphene and Graphene Oxide . 39 b) Carbon Nanotubes (CNTs) . 43 c) Onion-like Carbons (OLCs) . 47 d) 2.4.2 Transition Metal Oxide (i.e., MnxOy) as Pseudocapacitor Materials . 52 MnO2 . 52 a) Mn3O4 . 55 b) Mn2O3 . 57 c) 2.4. 3 Transition Metallophthalocyanines (i.e., MPc) as Pseudocapacitor Materials . 60 Electrochemical Characterization Techniques for ECs Applications . 63 2.5 2.5. 1 Cyclic Voltammetry (CV) . 63 2.5. 2 Galvanostatic Charge-Discharge (GCD) . 67 2.5. 3 Electrochemical Impedance Spectroscopy (EIS) . 69 Microscopic, Spectroscopic and Thermal Characterization Techniques for 2.6 Energy Storage Electrodes In ECs Application . 74 2.6. 1 Scanning Electron Microscopy (SEM) . 74 © University of Pretoria viii 2.6. 2 Transmission Electron Microscopy (TEM) . 76 2.6. 3 Energy Dispersive X-ray Spectroscopy (EDX) . 77 2.6. 4 X-Ray Diffraction (XRD) . 78 2.6. 5 X-Ray Photoelectron Spectroscopy (XPS) . 79 2.6. 6 Infrared Spectroscopy . 80 2.6. 7 Gas Adsorption Technique . 80 2.6. 8 Raman Spectroscopy. 81 2.6. 9 Thermo-Gravimetric Analysis (TGA). 82 Reference . 83 3 Chapter 3: Experimental Techniques and Methods . 115 Materials and Reagents . 116 3.1 Synthesis of Materials . 117 3.2 3.2.1 Synthesis of Onion-Like Carbon (OLC) . 117 3.2.2 Functionalization of Multiwalled carbon nanotubes (CNT) . 117 3.2.3 Synthesis of Graphene Oxide (GO) . 118 3.2.4 Synthesis of Carbon/Birnessite-MnO2 Nanohybrid . 119 3.2.5 Synthesis of Hausmannite Mn3O4 and Carbon/Hausmannite Mn3O4 Nanohybrid 120 3.2.6 Synthesis of NiTAPc and GO/NiTAPc . 120 Microscopic and Spectroscopic Characterization Equipment . 121 3.3 3.3.1 Scanning Electron Microscopy (SEM) . 121 © University of Pretoria ix 3.3.2 Energy dispersive X-ray spectra (EDX) . 121 3.3.3 Transmission electron microscopy (TEM) . 121 3.3.4 X-ray diffraction (XRD) . 121 3.3. 5 Raman Analysis . 122 3.3. 6 Fourier infrared spectroscopy (FTIR) . 122 3.3. 7 X-ray photoelectron spectroscopy (XPS) . 122 3.3. 8 Nitrogen gas sorption . 122 Electrochemical Characterization Procedure . 124 3.4 3.4.1 Fabrication of Carbon/MnO2 Nanohybrid Electrodes for Electrochemical Capacitors . 124 3.4.2 Electrochemical Procedure . 124 References . 126 4 Chapter 4: Carbon/birnessite-type Manganese Oxide (C/MnO2) Nanohybrids as Pseudocapacitor Materials . 127 Introduction . 128 4.1 Results and Discussion . 131 4.2 4.2.1 SEM and TEM analysis . 131 4.2.2 XRD, Raman, FTIR, EDX, and XPS studies . 133 4.2.3 Cyclic Voltammetric (CV) analysis of various carbon-MnO2 based electrodes on Ni foam. 145 4.2.4 Galvanostatic Charge-Discharge (GCD) analysis of various carbon-MnO2 based electrodes on Ni foam.