abstract: This dissertation describes fundamental studies of hollow carbon nanostructures, which may be used as electrodes for practical energy storage applications such as batteries or supercapacitors. Electron microscopy is heavily utilized for the nanoscale characterization. To control the morphology of hollow carbon nanostructures, ZnO nanowires serve as sacrificial templates. The first part of this dissertation focuses on the optimization of synthesis parameters and the scale-up production of ZnO nanowires by vapor transport method. Uniform ZnO nanowires with 40 nm width can be produced by using 1100 °C reaction temperature and 20 sccm oxygen flow rate, which are the two most important parameters. The use of ethanol as carbon source with or without water steam provides uniform carbonaceous deposition on ZnO nanowire templates. The amount of as-deposited carbonaceous material can be controlled by reaction temperature and reaction time. Due to the catalytic property of ZnO surface, the thicknesses of carbonaceous layers are typically in nanometers. Different methods to remove the ZnO templates are explored, of which hydrogen reduction at temperatures higher than 700 °C is most efficient. The ZnO templates can also be removed under ethanol environment, but the temperatures need to be higher than 850 °C for practical use. Characterizations of hollow carbon nanofibers show that the hollow carbon nanostructures have a high specific surface area (>1100 m2/g) with the presence of mesopores (~3.5 nm). The initial data on energy storage as electrodes of electrochemical double layer capacitors show that high specific capacitance (> 220 F/g) can be obtained, which is related to the high surface area and unique porous hollow structure with a thin wall. / Dissertation/Thesis / Doctoral Dissertation Physics 2016

Submitted by Diogo Oliveira (diogo_dpo@hotmail.com) on 2018-09-11T19:27:30Z No. of bitstreams: 4 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertação - Diogo Padilha Oliveira.pdf: 2087027 bytes, checksum: dce925c5d03b977ea55d48f64a89b36c (MD5) Carta de Encaminhamento para Autodepósito.pdf: 1300274 bytes, checksum: bc86221770e14a2d384060440c52b343 (MD5) Ata de Defesa Pública.pdf: 1062842 bytes, checksum: 30613942cf00a0bcfda46d50a69d6af4 (MD5) / Approved for entry into archive by PPGCEM Ciência e Engenharia de Materiais (ppgcem@ufam.edu.br) on 2018-09-11T19:42:20Z (GMT) No. of bitstreams: 4 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertação - Diogo Padilha Oliveira.pdf: 2087027 bytes, checksum: dce925c5d03b977ea55d48f64a89b36c (MD5) Carta de Encaminhamento para Autodepósito.pdf: 1300274 bytes, checksum: bc86221770e14a2d384060440c52b343 (MD5) Ata de Defesa Pública.pdf: 1062842 bytes, checksum: 30613942cf00a0bcfda46d50a69d6af4 (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2018-09-12T13:44:19Z (GMT) No. of bitstreams: 4 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertação - Diogo Padilha Oliveira.pdf: 2087027 bytes, checksum: dce925c5d03b977ea55d48f64a89b36c (MD5) Carta de Encaminhamento para Autodepósito.pdf: 1300274 bytes, checksum: bc86221770e14a2d384060440c52b343 (MD5) Ata de Defesa Pública.pdf: 1062842 bytes, checksum: 30613942cf00a0bcfda46d50a69d6af4 (MD5) / Made available in DSpace on 2018-09-12T13:44:19Z (GMT). No. of bitstreams: 4 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertação - Diogo Padilha Oliveira.pdf: 2087027 bytes, checksum: dce925c5d03b977ea55d48f64a89b36c (MD5) Carta de Encaminhamento para Autodepósito.pdf: 1300274 bytes, checksum: bc86221770e14a2d384060440c52b343 (MD5) Ata de Defesa Pública.pdf: 1062842 bytes, checksum: 30613942cf00a0bcfda46d50a69d6af4 (MD5) Previous issue date: 2018-02-26 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The materials research for high efficiency in energy storage has grown in recent years. Different phases of NiS for application in supercapacitors have been synthesized at different temperatures by hydrothermal method, which is a simple and low cost way. In this work different phases of NiS in powdered carbon were obtained, and their evaluation was made for use in supercapacitors. The material obtained showed better electrochemical properties in the condition synthesis 2 mmol of Na2 S · 9H2O, 1 mmol of Ni (NO3) 2 · 6H2O and 10% by weight of Vulcan carbon at 160 ° C, with a specific capacitance value of 685,66 F g-1. The NiS / Carbon was able to provide a good power density, 327.87 W kg-1, with an energy density of 15.24 Wh kg -1 and 26.10% of capacitance retention after 1000 cycles. The low values of energy density and capacitance retention can be justified by the material amorphous morphology, which has a direct influence on the interaction of the electrode with the electrolyte. Due to these results, the obtained NiS / Carbon is a material with potential use for the application in electrochemical capacitors. / A pesquisa por materiais com alta eficiência em armazenamento de energia tem crescido muito nos últimos anos. Diferentes fases de NiS para aplicação em supercapacitores têm sido sintetizadas em diferentes temperaturas através do método hidrotermal, que tem como principais vantagens ser simples e de baixo custo. Neste trabalho foram obtidas diferentes fases de NiS em carbono em pó, e foi feita sua avaliação para a utilização em supercapacitores. O material obtido apresentou melhores propriedades eletroquímicas na condição de síntese 2 mmol de Na2S·9H2O, 1 mmol de Ni(NO3)2·6H2O e 10% em peso de carbono Vulcan a 160 °C, alcançando valor de capacitância específica de 685,66 F g-1. O NiS/Carbono conseguiu fornecer uma boa densidade de potência, 327,87 W kg-1, com uma densidade de energia de 15,24 Wh kg-1, obtendo 26,10 % de retenção da capacitância em 1000 ciclos. Os baixos valores de densidade de energia e de retenção da capacitância podem ser justificados pela morfologia amorfa deste material, que tem influência direta na interação do eletrodo com o eletrólito. Devido a esses resultados, o NiS/Carbono obtido é um material com potencial uso para a aplicação em capacitores eletroquímicos.

Over the last century, almost all of the carbon materials developed for the energy industry are derived from fossil fuels. The growing global concerns about energy needs, fossil fuels consumption, and the related environmental issues have motived scientists to find new, green and sustainable energy resources such as the wind, solar and biomass energy. Essentially, biomass-derived materials can be utilized in energy storage and conversion devices such as Li-ion batteries, fuel cells, and supercapacitors. Among the biomass resources, lignin is a high volume byproduct from the pulp and paper industry and is currently burned to generate electricity and steam. The pulp and paper industry has been searching for high value-added uses of lignin to improve its overall process economics. The importance of manufacturing valuable materials from lignin is, discussed in Chapter 2, demonstrating the need for a facile, green and scalable approach to synthesize bio-char and porous carbon for use in Li-ion batteries. From this context, lignin is first carbonized in water at 300 °C and 103 bar to produce bio-char, which is then graphitized using a metal nitrate catalyst at 900-1100 °C in an inert gas at 1 bar. Graphitization effectiveness of three different catalysts, iron, cobalt and manganese nitrates was examined. The obtained materials were analyzed for morphology, thermal stability, surface properties, and electrical conductivity. Both annealing temperature and the catalyst affects the degree of graphitization. High-quality graphitization is obtained by using Mn(NO3)2 at 900 °C or Co(NO3)2 catalysts at 1100 °C. Research on various energy storage materials for supercapacitors has grown rapidly in the recent years. Various advanced materials have been shown as a promising candidate for future’s high-energy supercapacitor electrodes. For a material in a supercapacitor electrode to be considered, it must show promising results for its specific power and energy density, electrical conductivity, surface properties, durability, surface area and pore-size distribution in order to design and develop high-performance supercapacitor devices. The industrial applications of supercapacitors have not been satisfied due to the low energy density (the commercially available supercapacitors have between 5 to 10 times less energy density than that of batteries) and moderate charge-discharge rate of supercapacitor electrode. Thus, chapter 3 was aimed to design and synthesize nitrogen-doped carbon materials that show the characteristic of high-energy and high-power density supercapacitor electrodes with a long cycle life. With this aim, organosol lignin was successfully converted into N-doped carbon materials using a two-step conversion process. The nitrogen content in the carbon was up to 5.6 wt.%. The synthesize materials exhibit high surface area up to 2957 m2/g with micro/meso porosity and a sheet-like structure. The N-doped carbon produced at 850 oC exhibited a high capacitance value of 440 F g-1 at a 1 mV s-1 scan rate and demonstrated excellent cyclic stability over 30,000 cycles in 1 M KOH. In addition, the NC-850 delivers a high energy density of 15.3 W h kg-1 and power density of 55.1 W kg−1 at 1 mV s-1. Therefore, this study suggests that N-doped carbon materials synthesized from a pulp and paper byproduct, lignin, are promising environmentally-sustainable candidates for supercapacitor applications. Challenges for commercialization of fuel cells include high operation cost, inadequate operational stability, and poisoning by H2O2. To address the challenge, costly Pt-based catalysts are needed in order to facilitate the oxygen reduction reaction (ORR) at the cathode and the hydrogen oxidation reaction (HOR) at the anode. In chapter 4, alternative metal-free ORR catalyst materials derived from lignin are studied in order to simultaneously enhance the catalytic activity, lessen the Pt dependency and reduce the excessive costs associated. Calcium sulfonate lignin was successfully converted into sulfur self-doped carbons via in-situ hydrothermal carbonization and followed by post-annealing treatment. The sulfur content in the as-prepared porous carbons is up to 3.2 wt.%. The resulting materials displayed high surface areas (up to 660 m2 g-1) with micro/meso porosity and graphitic/amorphous carbon structure. The as-prepared sulfur self-doped electrode materials (SC-850) were tested as a potential cathodic material for ORR. The number of electrons transferred per molecule was measured to be ~ 3.4 at 0.8 V, which approaches the optimum 4 electron pathway. Additionally, S-doped materials were also applied as a supercapacitor electrode material. The SC-850 electrode exhibited a high specific and volumetric capacitance values of 225 F g-1 and 300 F cm-3 at a scan rate of 0.5 A g-1. The SC-850 electrode also exhibited consistent response over 10,000 cycles at harsh conditions. It was shown that the metal-free SC-850 is a promising electrode material for supercapacitors and ORR applications. All of the studies presented in this dissertation involve the development and application of carbon-based materials derived from lignin and its application towards the Li-ion batteries, supercapacitor, and fuel cell. Insight into the applicability of lignin-derived carbon materials towards electrochemical applications is made readily available, supplemented by detailed physical, chemical and electrochemical characterization, to examine the specific factors influencing the Li-ion batteries, supercapacitor, and electrocatalysis of fuel cell activity.

Cette thèse s’inscrit dans le cadre de conception d’une stratégie de gestion de l’énergie dans un système hybride de génération d'énergie électrique composé d’une pile à combustible (PC) et un module de supercondensateurs (SC). La source hybride fournit une puissance maximale de 1,2 kW et sa conception implique des décisions concernant la sélection de l’architecture du système hybride ainsi que le choix de la topologie et le dimensionnement d’une unité de convertisseurs. La stratégie de gestion vise à satisfaire la demande d’énergie électrique de la charge et favoriser la consommation énergétique efficiente ; sa performance est évaluée en développant un simulateur qui comprend la dynamique des éléments mis en jeu : deux sources et l’unité de convertisseurs. Le générateur hybride est supposé alimenter un profil de consommation correspondant à un véhicule électrique, de ce fait un cycle standard de conduite en ville en échelle est demandé lors des simulations, ce qui permet d’évaluer la performance du générateur hybride et plus spécifiquement de la stratégie de gestion énergétique.Dans une première étape de cette thèse, un simulateur intégral a été construit avec des librairies de Simscape. Le simulateur est constitué des blocs de différents domaines, contenant des modèles fondamentaux des composants du système. Le block de pile à combustible modèle la dynamique d’un système BAHIA® (400 W - 1100 W, 0 A - 70 A nominale) et le block de supercondensateur modèle les cycles charge-décharge d’un module Maxwell de 400 F et 16 V. Un onduleur de tension pont complet avec convertisseur élévateur conditionne l’énergie délivrée par la pile à combustible et un convertisseur bidirectionnel (buck-boost) est connecté au module de supercondensateurs afin de conditionner les cycles de charge-décharge. L’unité des convertisseurs a été dimensionné, puis, un modèle moyen de petits signaux a été formulé afin de décrire la dynamique de ces dispositifs. Les différents composants ont été intégrés dans l’environnement Simulink. Dans une deuxième étape, la stratégie de gestion énergétique a été conçue en considérant les caractéristiques et performances des sources ; le résultat est une stratégie de trois niveaux hiérarchiques, dont l’aspect principal es la définition des lois de commande locales et globale. Dans une troisième étape, le système complet est évalué en termes du niveau d’utilisation des sources, du domaine d’opération de la pile à combustible, et de l’accomplissement des objectifs des commandes locales et global, qui engagent notamment le SOC des supercondensateurs et la régulation de la tension du générateur hybride. / Energy generation from fossil fuels combustion is predicted to have severe future impacts in the world’s economy and ecology. Fuel cells and supercapacitors are an alternative power source, environmentally friendly.This dissertation presents a regulation architecture developed to coordinate a hybrid renewable source for typical solicitations of electric vehicles in a scaled operating range of 1 kW. The hybrid system is composed of a Polymer Electrolyte Membrane (PEM) fuel cell module, a supercapacitors bank and their respective power conditioning units. In order to optimize the overall operation, the proposed strategy is organized into three hierarchical levels, and the power demand for each energy source is determined in real time with a basis on a frequency distribution and a cutoff frequency, defined in accordance with the dynamical capabilities of the sources.Even if numerous researches have been reported on the subject, few studies have taken into account the proper dynamics of each source in order to optimize the global performance of the hybrid power supply.The goal of this work is to implement a complete simulator integrating not only dynamical models of each energy source, but also dynamical models of the power conditioning units. The control strategy consists of nested loops, arranged in three functional levels of hierarchy. The central idea is to find the optimal set point for each energy source, according to their own physical properties. Contrary to the existing control strategies, this strategy dynamically calculates the appropriate power demand for each energy source. Due to the complexity of the system, cascade control loops are proposed, organized into blocks, according to the system functionality and dynamics.A functional simulation is obtained, where the system ensures the adequate supercapacitor state of charge and soft current demands to keep the fuel cell working in its safe operating region. Thus, lower fuel consumption and rapid response to load demands are guaranteed to improve efficiency.Results demonstrate that the control strategy allows the regulation of the DC bus voltage under UDDS and ECE-15 driving cycles as load profiles. The fuel cell works within its maximum efficiency region, without falling in the degradation zone. In addition, the supercapacitor state of charge remains within the recommended range.

This thesis deals with comprehensive study and design of recovery system of a road vehicle powered by human power. It contains an overview of different types of heat recovery devices, their characteristics, advantages, disadvantages and applicability in the construction of such a vehicle.

Battery storage devices have been widely utilized for different applications. However, for high power applications, battery storage systems come with several challenges, such as the thermal issue, low power density, low life span and high cost. Compared with batteries, supercapacitors have a lower energy density but their power density is very high, and they offer higher cyclic life and efficiency even during fast charge and discharge processes. In this dissertation, new techniques for the control and energy management of the hybrid battery-supercapacitor storage system are developed to improve the performance of the system in terms of efficiency, power quality and reliability. To evaluate the findings of this dissertation, a laboratory-scale DC microgrid system is designed and implemented. The developed microgrid utilizes a hybrid lead-acid battery and supercapacitor energy storage system and is loaded under various grid conditions. The developed microgrid has also real-time monitoring, control and energy management capabilities. A new control scheme and real-time energy management algorithm for an actively controlled hybrid DC microgrid is developed to reduce the adverse impacts of pulsed power loads. The developed control scheme is an adaptive current-voltage controller that is based on the moving average measurement technique and an adaptive proportional compensator. Unlike conventional energy control methods, the developed controller has the advantages of controlling both current and voltage of the system. This development is experimentally tested and verified. The results show significant improvements achieved in terms of enhancing the system efficiency, reducing the AC grid voltage drop and mitigating frequency fluctuation. Moreover, a novel event-based protection scheme for a multi-terminal DC power system has been developed and evaluated. In this technique, fault identification and classifications are performed based on the current derivative method and employing an artificial inductive line impedance. The developed scheme does not require high speed communication and synchronization and it transfers much less data when compared with the traditional method such as the differential protection approach. Moreover, this scheme utilizes less measurement equipment since only the DC bus data is required.

This thesis deals with comprehensive study and design of recovery system of a road vehicle powered by human power. It contains an overview of different types of heat recovery devices, their characteristics, advantages, disadvantages and applicability in the construction of such a vehicle.

Master’s thesis deals with the design concept of DC/DC convertor usable for a backup source with supercapacitors. The paper describes the theoretical knowledge of supercapacitors technology, principle of basic DC/DC convertors and their use in electrical energy storage systems. The thesis contains a description of the designed backup power system and its properties, which has been measured.

This work deals with the issues of using conducting polymers for supercapacitor electrodes and optimizing the technological process for their production. The work focuses on optimizing the amount of polymer used in order to achieve the most capacity. The methodology consists of creating an appropriate experimental electrode and subsequent measuring its associated capacity with BioLogic. This approach leads to creating charts which show the dependencies of capacity on the amount of polymer used.

This master thesis deals with supercapacitors based on electrical double layer and proper carbon electrodes for this type of supercapacitors. In theoretical part of work is described theory of supercapacitors, energy storage principles and their properties. In the next part are described carbon materials, their properties and electrochemical methods of measurements that we used. In the experimental part is described preparation of electrodes, results and conclusion.