Synthesis and Characterization of Carbon Nanotubes and Hybrid Carbon Nanostructures grown on flexible electrodes for Supercapacitor Applications
[eng] Nowadays, Nanotechnology is having an impact on practically every aspect of human life. It is a transformative technology that has influenced and will continue on electronics, computers, medicine, catalysis, energy, and transportation. It has changed the way materials are used in the future, i...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2022 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/185842 |
| Acceso en línea: | https://hdl.handle.net/2445/185842 http://hdl.handle.net/10803/674294 |
| Access Level: | acceso abierto |
| Palabra clave: | Nanotubs Nanoestructures Compostos de carboni Elèctrodes de carboni Nanotubes Nanostructures Carbon compounds Carbon electrodes |
| Sumario: | [eng] Nowadays, Nanotechnology is having an impact on practically every aspect of human life. It is a transformative technology that has influenced and will continue on electronics, computers, medicine, catalysis, energy, and transportation. It has changed the way materials are used in the future, improving their durability and reactivity. We have a lot of opportunities to make things smaller, lighter, and stronger. Carbon materials are one of the main materials that scientists have intensively studied their properties during the last three decades for their remarkable properties, which are still being investigated and new properties and applications being discovered till this moment. Carbon nanotubes (CNTs) and graphene are the main investigated and most important carbon materials since their discovery. The first discovery of CNTs was in 1991 by Dr. Sumio Iijima where they were multi-walled carbon nanotubes (MWCNTs) as he could produce them in his laboratory under stable conditions. Two years later, the same scientist could discover the first single-wall CNTs (SWCNTs). A decade later, the revolution of graphene started when Prof. Andre Geim and Prof. Constantine Novoselv could obtain a single layer of graphene by separating the graphite fragments repeatedly until they obtained a layer of carbon of one atom thick. Indeed, since the technology for producing CNTs and graphene on an industrial scale has been progressed, they can be found in a numerous number of applications, such as reinforcing polymers, acting as scaffolds for the artificial tissue growth, using them in many sensor devices such as electrical, optical, and biological, manufacturing the components of next-generation battery electrodes and supercapacitors. CNTs and graphene are ideal supporters for other materials especially when they are combined together with high capacitance materials. Researchers and companies all around the world are devoting significant efforts to developing electrodes with three-dimensional design at the nanoscale and a high specific surface area. This thesis focuses on the optimization of CNTs synthesis parameters using different methodologies to obtain the CNTs on conductive and flexible substrates and without substrate to use them as electrodes for supercapacitors. The CNTs have been studied separately, combined with graphene nanowalls (GNWs), and combined with MnO2 in order to increase the capacitance as much as possible. All the methodologies of CNTs and GNWs synthesis are CVD-related processes. The studied technologies also offer a diversity of production methods of nanomaterials, which open other future developments of flexible electrodes for supercapacitors and batteries, sensors, photo and electrocatalysis, and other developments like biosensors for smart wear. CHAPTER 1-INTRODUCTION: This chapter covers some basic principles of nanoscience and nanotechnology. Carbon materials take the rest of the chapter starting from carbon allotropes, explaining in detail concepts about carbon nanotubes, their properties, synthesis techniques, growth mechanism, and the catalyst and precursor gases effect on the growth. Then, graphene history and concepts are explained briefly in addition to its structure and thermal and mechanical properties. CHAPTER 2 – CHARACTERIZATION TECHNIQUES: The characterization techniques used during this thesis are described in detail in this chapter. Different spectroscopic, electrical and electrochemical measurements were carried out to characterize the carbon materials we synthesized, as well as their application as electrodes for supercapacitor devices. In this chapter, also there are the descriptions of electronic microscopies and surface analysis techniques used for the compositional, structural and morphological characterization of samples. CHAPTER 3 – EXPERIMENTAL CONCEPTS AND SETUPS: This chapter is the core for the ability to imagine how the work of synthesis material was carried out. It covers in detail the vacuum system concepts and the possible gas resources inside vacuum chambers, plasma concepts and the related processes of physical vapor deposition (PVD) and chemical vapor deposition (CVD). The three reactors that we used to synthesize the carbon materials are explained. In particular, their parts (working principle, pumps, vacuum gauges, etc…) and the importance of each part for a successful and safe use of the chambers. Finally, an atmospheric plasma technique for the synthesis of metal nanoparticles was explained as well. CHAPTER 4 – SYNTHESIS OF CARBON-BASED COMPOSITES ON HIGHLY FLEXIBLE PAPYEX® SUBSTRATE: In this chapter, the optimization of the growth parameters of vertically aligned CNTs (VACNTs) and their GNWs composite on Papyex® graphite substrate using plasma enhanced CVD (PECVD) and inductively coupled plasma CVD (ICP-CVD) is presented in view to use them as electrodes for supercapacitors. The parameters were optimized one by one including the sample’s plasma functionalization. The samples were characterized using different microscopic, spectroscopic and X-ray techniques. The electrochemical properties of the CNTs and hybrid carbon structures were investigated before and after the electro-deposition of MnO2. CHAPTER 5 – SYNTHESIS OF CARBON-BASED COMPOSITES DIRECTLY ON FLEXIBLE SS310 ALLOYS: In this chapter, we studied the growth of CNTs directly on SS310 stainless steel alloys using the catalyst particles present on the substrate itself in a single continuous process using PECVD. The optimization of the process parameters was carried out through Box-Wilson experimental design. The obtained CNTs were decorated with GNWs flakes in order to increase their specific surface area. The morphology and properties of CNTs and CNTs-GNWs composite were characterized by different microscopic and spectroscopic techniques. Manganese dioxide was deposited on the obtained structure and their electrochemical properties studied. CHAPTER 6 – SYNTHESIS OF CARBON NANOTUBES AND METAL OXIDE NANOPARTICLES AT ATMOSPHERIC PRESSURE: This is the last chapter of results, which will present a different technique for the growth of CNTs. The CNTs synthesis was done without substrate using floating catalyst CVD (FC-CVD). This technique allows the continuous (scalable) synthesis of CNTs at atmospheric pressure in a free-oxygen environment inside a tubular furnace reactor. Another technique for the synthesis of metal oxide nanoparticles is presented in this chapter called plasma-liquid interaction. Through this technique, different metal oxides were synthesized but we used only the NiO2. Through these techniques we could obtain a hybrid structure of CNTs and NiO2 nanoparticles. Both were characterized by microscopic and spectroscopic techniques to finally use them for electrochemical applications. The most of this work was carried out during a short stay at Ulster University - Northern Ireland. CONCLUSIONS: The exposition of results and discussion has been completed by a list of conclusions derived from the main results and achievements of the thesis. |
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