ABSTRACT KIM, HYUNGJOO. Functionalized Buckypapers for Supercapacitor Electrodes: Effect of Intrinsic Chemical Interactions on Electrochemical Performance. (Under the direction of Dr. Philip D Bradford). Carbon nanotubes (CNTs) and their composites have been widely applied to many fields due to their unique electrical and mechanical properties. In the field of energy storage devices, they have been recognized as promising materials to develop supercapacitor electrodes with outstanding electrochemical performance such as high power density, fast charge/discharge time, low level of heating, safety and long cycle life. Ternary composites, consisting of CNT, conductive polymer (CP) and metal (oxide), have been actively studied to develop supercapacitor electrodes because improved electrochemical performance can be achieved as compared to binary composite or pristine forms. Many researches demonstrated that this improved performance was induced by synergistic effects among the three components in the composite. However, in most of reported researches, all three materials were simply mixed to induce this synergistic effect. To further improve electrochemical performance of ternary composite- based supercapacitors, three different strategies to further improve and understand these synergistic effects were utilized in this study. The first method studied was the introduction of epoxide functional groups on the buckypaper. Raman, XPS and FT-IR were used to analyze the structure of functionalized buckypaper, indicating that epoxide functional groups were well formed on the surface of buckypaper. In addition, to further investigate advantages of epoxide functionalized buckypaper (EBP) as a supercapacitor electrode, key factors affecting electrochemical performance were also studied. According to the result, EBP exhibited wider surface area, higher surface energy and enhanced electrical conductivity when compared with purified pristine buckypaper (PPBP). Hence, EBP showed higher electrochemical performance than PPBP. Specific capacitances of EBP were calculated based on Galvanostatic Charge/Discharge (GCD) curve, resulting in 41.12 F/g, about 3time higher than that of PPBP (15.94 F/g). Second, chemical interactions among all three different components in the composites were intentionally formed. In this study, both hydrogen bond and metal bonding formations were generated to develop chemically connected composite-based supercapacitor electrode. For instance, hydrogen bond was formed between oxygen in EBP and amine in CPs. On the other hand, silver nanoparticles (AgNPs) were bind with nitrogen in CPs (Polypyrrole and Polyaniline) due to tis high affinity toward AgNP. In addition, nickel oxide nanoparticles (NiO) were also applied and chemically interacted with carboxylic acid in CP (Poly(meta-anthranilic acid)). These interactions were clarified by XPS, Raman and FT-IR. Furthermore, their effect on electrochemical performance was also determined, revealing that electrochemical performance was improved when compared with control groups with no chemical interactions. This phenomenon can be explained by chemical interactions since they enhanced both charge-transfer efficiency and electrical conductivity. At last, crystalline CP was applied in the prepared composite. Among CPs selected to develop a supercapacitor electrode in this research, aniline could be polymerized with EBP because epoxide functional groups were acted as oxidants and involved in polymerization. Therefore, epitaxial growth phenomenon could be occurred, resulting in crystalline polyaniline formation. Due to this crystalline nature, more organized and better packed polyaniline structure was constructed and accordingly high electrical conductivity was obtained leading to improved electrochemical performance. © Copyright 2018 by Hyungjoo Kim All Rights Reserved Functionalized Buckypapers for Supercapacitor Electrodes: Effect of Intrinsic Chemical Interactions on Electrochemical Performance by Hyungjoo Kim A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Fiber and Polymer Science Raleigh, North Carolina 2018 APPROVED BY: _______________________________ _______________________________ Philip D Bradford Yuntian Zhu Committee Chair _______________________________ _______________________________ Xiangwu Zhang Wei Gao BIOGRAPHY Hyungjoo Kim was born in Seoul and grew up in Daejeon, Republic of Korea. He studied advanced organic materials & textile system engineering as an undergrad at Chungnam National University and became interested in organic/inorganic materials. After obtaining his B.E in 2012, he continued to pursue M.E in advanced organic materials and textile system engineering at Chungnam National University. His research topic was design and synthesis of organic/inorganic materials. Through that research, he acquired the ability to develop new organic/inorganic materials and analyze their optical/electrochemical properties. After he graduated in 2014, he decided to apply for Ph.D. programs and started his research at North Carolina State University in August 2015. During his Ph.D. training, his research was focused on organic/inorganic composites, especially functionalized carbon nanotube/conductive polymer/metal (oxide) based composites, to develop energy storage materials with excellent electrochemical performance. After a successful dissertation defense, he will be obtaining a Ph.D. in Fiber and Polymer Science. ii ACKNOWLEDGMENTS I would like to sincerely thank my advisor, Dr. Philip Bradford and lab advisor, Dr. Yuntian Zhu for giving me an opportunity to start my graduate career. In addition, due to your guidance, I learned about research ethics, hard work and how to develop at a scientific researcher. Also, I would like to thank to my advisory committee members- Dr. Xiangwu Zhang and Dr. Wei Gao. I would also like to say thank to my lab mates (Haotian Deng and Xiaotian Fang) since you help me a lot though out my time in the lab. At last, I would like to thank my parents and sister for their love, encouragement and support. I really want to say “I love you”. iii TABLE OF CONTENTS LIST OF SCHEMES ............................................................................................................... vii LIST OF TABLES ................................................................................................................. viii LIST OF FIGURES ................................................................................................................. ix Chapter 1: Introduction and Motivation ............................................................................... 1 Chapter 2: Literature Review ................................................................................................. 4 2.1 Advantages of Supercapacitor ............................................................................................ 5 2.2 Different Types in Supercapacitors ..................................................................................... 6 2.3 Separators......................................................................................................................... 10 2.4 Electrolyte ........................................................................................................................ 10 2.4.1 Comparison between Aqueous and Organic Electrolytes.............................................. 11 2.5 Electrode Materials........................................................................................................... 11 2.5.1 Carbon Materials ......................................................................................................... 13 2.5.1.1 Activated Carbon ...................................................................................................... 14 2.5.1.2 Carbon Nanotubes .................................................................................................... 16 2.5.1.2.1 Functionalized Carbon Nanotube ......................................................................... 18 2.5.1.3 Carbon Aerogels ....................................................................................................... 20 2.5.1.4 Templated Carbons ................................................................................................... 22 2.5.2 Conductive Polymers ................................................................................................... 24 2.5.2.1 Polyaniline .............................................................................................................. 26 2.5.2.2 Polypyrrole ............................................................................................................. 28 2.5.2.3 Polythiophene ......................................................................................................... 29 2.5.3 Noble Metal (Silver) .................................................................................................... 30 2.5.4 Metal Oxides ............................................................................................................... 31 2.6 Composite ........................................................................................................................ 32 2.6.1 Carbon-Conductive Polymer Based Composite ............................................................ 33 2.6.2 Carbon-Metal Oxide Based Composite .......................................................................