Electrochemical capacitors (ECs) have drawn much attention owing to their fast charging/discharging rate, and long lifetime up to millions of cycles. Applications of EC range from large scale transportation to miniaturized electronics. The research reported herein explores the development of an economical process for the synthesis of high performance electrode material for high power ECs. A two stage synthesis process which consists of electroplating of molybdenum oxide followed by thermal nitridation was developed. X-ray diffraction and X-ray photoelectron spectroscopy revealed the material to be Mo oxide with nitrogen substitution, Moz(O,N). In a three electrode system, the Moz(O,N) electrodes showed capacitance as high as 16 mF/cm2. Symmetric EC cells achieved state of the art time constant of 100 ms. Ultrahigh power ECs were demonstrated for the first time using Moδ(O,N) electrodes and SiWA-H3PO4-PVA electrolyte, achieving with 10 ms time constant one of the lowest time constants reported for EC.

abstract: This dissertation describes the synthesis and study of porous nanocarbon and further treatment by introducing nitrogen and oxygen groups on nanocarbon, which can be used as electrodes for energy storage (supercapacitor). Electron microscopy is used to make nanoscale characterization. ZnO nanowires are used as the template of the porous nanocarbon, and nitrogen doping and oxidation treatment can help further increase the capacitive performance of the nanocarbon. The first part of this thesis focuses on the synthesis of ZnO nanowires. Uniform ZnO nanowires with ~30 nm in width are produced at 1100℃ in a tube furnace with flowing gases (N2: 500 sccm; O2: 15 sccm). The temperature control is one of the most important parameters for making thin and ultra-long ZnO nanowires. The second part of the thesis is about the synthesis of nanocarbons. Ultrapure ethanol is used as the carbon source to make carbonaceous deposition on ZnO nanowires. The thickness of the nanocarbons can be controlled by reaction temperature and reaction time. When the reaction time was controlled around 1h, the carbonaceous materials coating the ZnO nanowires become very thin. Then by flowing (1000 sccm) hydrogen at 750℃ through the reaction tube the ZnO nanowires are removed due to reduction and evaporation. Electrochemical evaluation of the produced nanocarbons shows that the nanocarbons possess very high specific surface area (>1400 m2/g) and a capacitance as high as 180 F/g at 10A/g in 6M KOH). The third part of the thesis is the treatment of the as-synthesized nanocarbons to further increase capacitance. NH3 was used as the nitrogen source to react with nanocarbons at 700℃ to incorporate nitrogen group. Nitric acid (HNO3) is used as the oxidant to introduce oxygen groups. After proper nitrogen doping, the nitrogen doped nanocarbons can show high specific capacitance of 260 F/g at 1A/g in 6M KOH. After further oxidation treatment, the capacitance of the oxidized N-doped nanocarbons increased to 320 F/g at 1A/g in 6M KOH. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2020

This master thesis deals with designing of a recuperative converter system and auxiliary circuits that extend the life of the automotive battery by using supercapacitor as a source of power when starting a car using the start-stop function. The microcontroller is used to measure important circuit values and control the output current of the converter.

No description available.

No description available.

A demanda crescente por meios de armazenar eficientemente energia elétrica tem incentivado a busca de materiais que melhorem o desempenho específico de dispositivos armazenadores de carga elétrica. Dentre os materiais a base de carbono, destaca-se o grafeno e seus derivados como tendo grande potencial para aumentar o desempenho de tais. Nesse trabalho, estudam-se duas abordagens para a imobilização de grafeno sobre condutores metálicos e o efeito que essas tem na eletroquímica dos sistemas. De maneira geral, evitou-se a utilização de polímeros como aglutinantes na construção de eletrodos, visto que esses podem interferir negativamente na eletroquímica do sistema (além de não serem condutores elétricos, não têm nenhum benefício em relação a aumento de capacitância do eletrodo). As metodologias estudadas podem ser separadas em duas categorias, sendo essas a de eletrodos obtidos por deposição eletroforética de derivados de grafeno e imobilização de grafeno sobre condutores metálicos pelo uso de camadas orgânicas, que servem de ponto de ancoragem para os derivados de grafeno. Os eletrodos foram então caracterizados eletroquimicamente, visando principalmente seu uso em capacitores eletroquímicos. Dentre as técnicas utilizadas para tal, destacam-se o uso de voltametria cíclica e espectroscopia de impedância eletroquímica, além de técnicas não eletroquímicas como espectroscopia Raman, microscopia eletrônica de varredura, microscopia de força atômica e microbalança de cristal de quartzo. De modo geral, pode-se observar que a deposição eletroforética é uma maneira simples de obter eletrodos modificados, e apresenta alta reprodutibilidade. O fato de não possuírem outros compostos químicos que não o grafeno, além de serem altamente rugosos, mostrou que esses eletrodos tem desempenho capacitivo muito bom, sendo o método de obtenção do grafeno e a maneira escolhida para deposição diretamente responsáveis pela morfologia obtida. A construção de eletrodos pela ancoragem de grafeno foi feita com base na (eletro)química de sais de diazônio, que se mostrou bastante promissora quanto a capacidade de se obter uma ligação química estável entre as folhas de grafeno e o metal. A alta reatividade dos sais de diazônio, no entanto, se mostrou danosa a eletroquímica do grafeno, sendo que tais eletrodos não apresentaram nenhuma característica que justificasse seu uso em capacitores eletroquímicos. Assim, os avanços e desafios restantes em relação a essas abordagens na construção capacitores eletroquímicos com alto desempenho específico encontram-se aqui detalhados. / The increasing demand for efficient electrical energy storage devices has pushed research towards materials with potential to increase the specific performance of such devices. Among the carbon-based materials, one that has been heavily studied as a potential candidate to accomplish such feat is graphene and its chemical derivatives. In this work, two methodologies to accomplish graphene immobilization over metallic current collectors are approached, as well as the effects that such approaches have on the electrochemistry of the resulting electrodes. As a general guideline, the usage of polymeric binders as ways of keeping good mechanical stability are avoided, due to their tendency to negatively impact the system\'s electrochemistry (not only they\'re normally electrical in sulators, they also don\'t usually possess any intrinsic electroactivity that could enhance the electrode\'s capacitance). The methodologies in study can be separated into two categories, namely, electrophoretic deposition and usage of organic molecules as anchoring points to attach graphene sheets to the surface. Such electrodes were characterized by a number of electrochemical technics, most prominently cyclic voltammetry and electrochemical impedance spectroscopy in the group of electrochemical technics, and Raman spectroscopy, atomic force microscopy, scanning electron microscopy and quartz crystal microbalance in the group of non-electrochemical technics. Electrophoretic deposition of graphene is proved to be a very straightforward and reproducible way to obtain modified electrodes. Since no chemical compound other than the graphene derivatives are necessary, and that the final electrodes have very rough surfaces, such electrodes have very high capacitance, and those characteristics are direct consequence of the chosen method. Anchoring graphene derivatives on the surface of metallic conductors by the (electro)-chemistry of diazonium salts is shown to be a promising method to achieve strongly bound graphene sheets to a surface. The high reactivity of diazonium salts, though, hampers the electrochemical activity of graphene, and no electrodes suitable to be used in electrochemical capacitors were obtained. In summary, the advances and remaining challenges towards the use of such methodologies in the construction of electrochemical capacitors are presented here.

We design a facile approach to investigate the role benzene derivatives play in the capacitance enhancement of graphene-based supercapacitors. The main reason is attributed to the pseudocapacitance of the aromatic molecules rather than the former one. Meanwhile, we find that the para and ortho substituted benzene derivatives contribute much more than the meta substituted ones. In addition, we fabricate an all-solid-state flexible MSC based on metal-reduced GO. The as-fabricated MSC shows high areal capacitance and excellent reliability, which makes it a promising energy storage candidate for wearable electronics. Based on the work of MSC, we achieve a flexible ac line-filter that is not only competitive against commercial product but also suitable for mass production. Meanwhile, we produce a three-dimensional graphene/polydimethylsiloxane composite that gives a thermal resistance as small as 14 mm2K/W, which is comparable to commercial products. What’s more, a convenient transient program that saves much time is developed to measure the thermal resistance.

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No. of bitstreams: 1 klem_ms_me_bauru.pdf: 4012228 bytes, checksum: f1af56b8b0b9f5e19934e197b4755874 (MD5) Previous issue date: 2017-09-27 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Realizou-se primeiramente neste trabalho o estudo de um supercapacitor padrão utilizando coletores de aço inox e eletrodos de grafite Aquadag®. Este dispositivo apresentou uma capacitância máxima de 22 F/g, e seu espectro de impedância foi modelado por um circuito do tipo R(C(RW))(RC)(RC). Com este dispositivo foi possível testar os métodos de produção dos supercapacitores, e identificar as características desejáveis no supercapacitor impresso. Foram testadas duas técnicas de impressão distintas visando o preparo de eletrodos e coletores de corrente impressos em papel para aplicação em supercapacitores. O material ativo utilizado nos eletrodos foi basicamente o PEDOT:PSS, com a adição de óxido de grafeno, grafite aquadag® e nanotubos de carbono de paredes múltiplas (MWNT) para a formação compósitos condutores. Foram realizadas caracterizações morfológicas e elétricas nas superfícies dos eletrodos impressos em papel filtro, vegetal e sulfite. Os eletrodos produzidos por serigrafia utilizando o compósito de PEDOT:PSS com MWNT impressos em papel filtro apresentaram os menores resultados de resistência de folha (17 Ω/sqr), sendo assim utilizados na produção dos supercapacitores. O supercapacitor impresso em papel apresentou um bom comportamento capacitivo através de medidas de espectroscopia de impedância e voltametria cíclica. A curva de impedância foi modelada através de um circuito do tipo R(RC)(C(RQ))(RC), evidenciando uma alta capacitância de dupla camada. Foi encontrada uma capacitância específica máxima de 20,3 F/g.para uma corrente de carga/descarga de 1 mA, e uma resistência equivalente em série de 60 Ω. Estes valores levaram a densidades de energia e potência de 3,1 Wh/kg e 420 W/kg, respectivamente. Realizaram-se também simulações e ajustes a partir das análises em corrente contínua, usando um circuito equivalente RC paralelo com uma resistência em série. Através destes ajustes foi possível extrair parâmetros de grande importância na utilização prática dos supercapacitores. / In this study, we first produced a standard supercapacitor using stainless steel collectors and Aquadag® graphite electrodes. The device exhibited a maximum capacitance of 22 F/g, and an R(C(RW))(RC)(RC) circuit modeled its impedance spectrum. With this device was possible to test the production methods of supercapacitors, and identify its desirable characteristics. Two different printing techniques were tested to produce electrodes/current collectors. The active material used in the electrodes was PEDOT: PSS, with addition of graphene oxide, Aquadag® graphite and multi-walled carbon nanotubes (MWNT), in order to obtain conductive composites. Morphological and electrical characterizations were performed over the surfaces of printed electrodes onto filter, vegetable and bond paper. The electrode produced by screen-printing using the PEDOT: PSS/MWNT composite printed onto filter paper exhibited low sheet resistance (17 Ω /sqr), being used in the production of supercapacitors. Printed supercapacitor showed good capacitive behavior through impedance spectroscopy and cyclic voltammetry measurements. An R(RC)(C(RQ)(RC) circuit modeled the impedance spectrum, evidencing a high double layer capacitance. A maximum specific capacitance of 20.3 F / g was found for a charge/discharge current of 1 mA, and an equivalent series resistance of 60 Ω. These values led to energy and power densities of 3.1 Wh / kg and 420 W / kg, respectively. Simulations and curve fitting were also performed from DC analyzes, using a parallel RC circuit coupled with a series resistance, obtaining important parameters for the practical use of supercapacitors. / FAPESP: 2015/18091-8

A demanda crescente por meios de armazenar eficientemente energia elétrica tem incentivado a busca de materiais que melhorem o desempenho específico de dispositivos armazenadores de carga elétrica. Dentre os materiais a base de carbono, destaca-se o grafeno e seus derivados como tendo grande potencial para aumentar o desempenho de tais. Nesse trabalho, estudam-se duas abordagens para a imobilização de grafeno sobre condutores metálicos e o efeito que essas tem na eletroquímica dos sistemas. De maneira geral, evitou-se a utilização de polímeros como aglutinantes na construção de eletrodos, visto que esses podem interferir negativamente na eletroquímica do sistema (além de não serem condutores elétricos, não têm nenhum benefício em relação a aumento de capacitância do eletrodo). As metodologias estudadas podem ser separadas em duas categorias, sendo essas a de eletrodos obtidos por deposição eletroforética de derivados de grafeno e imobilização de grafeno sobre condutores metálicos pelo uso de camadas orgânicas, que servem de ponto de ancoragem para os derivados de grafeno. Os eletrodos foram então caracterizados eletroquimicamente, visando principalmente seu uso em capacitores eletroquímicos. Dentre as técnicas utilizadas para tal, destacam-se o uso de voltametria cíclica e espectroscopia de impedância eletroquímica, além de técnicas não eletroquímicas como espectroscopia Raman, microscopia eletrônica de varredura, microscopia de força atômica e microbalança de cristal de quartzo. De modo geral, pode-se observar que a deposição eletroforética é uma maneira simples de obter eletrodos modificados, e apresenta alta reprodutibilidade. O fato de não possuírem outros compostos químicos que não o grafeno, além de serem altamente rugosos, mostrou que esses eletrodos tem desempenho capacitivo muito bom, sendo o método de obtenção do grafeno e a maneira escolhida para deposição diretamente responsáveis pela morfologia obtida. A construção de eletrodos pela ancoragem de grafeno foi feita com base na (eletro)química de sais de diazônio, que se mostrou bastante promissora quanto a capacidade de se obter uma ligação química estável entre as folhas de grafeno e o metal. A alta reatividade dos sais de diazônio, no entanto, se mostrou danosa a eletroquímica do grafeno, sendo que tais eletrodos não apresentaram nenhuma característica que justificasse seu uso em capacitores eletroquímicos. Assim, os avanços e desafios restantes em relação a essas abordagens na construção capacitores eletroquímicos com alto desempenho específico encontram-se aqui detalhados. / The increasing demand for efficient electrical energy storage devices has pushed research towards materials with potential to increase the specific performance of such devices. Among the carbon-based materials, one that has been heavily studied as a potential candidate to accomplish such feat is graphene and its chemical derivatives. In this work, two methodologies to accomplish graphene immobilization over metallic current collectors are approached, as well as the effects that such approaches have on the electrochemistry of the resulting electrodes. As a general guideline, the usage of polymeric binders as ways of keeping good mechanical stability are avoided, due to their tendency to negatively impact the system\'s electrochemistry (not only they\'re normally electrical in sulators, they also don\'t usually possess any intrinsic electroactivity that could enhance the electrode\'s capacitance). The methodologies in study can be separated into two categories, namely, electrophoretic deposition and usage of organic molecules as anchoring points to attach graphene sheets to the surface. Such electrodes were characterized by a number of electrochemical technics, most prominently cyclic voltammetry and electrochemical impedance spectroscopy in the group of electrochemical technics, and Raman spectroscopy, atomic force microscopy, scanning electron microscopy and quartz crystal microbalance in the group of non-electrochemical technics. Electrophoretic deposition of graphene is proved to be a very straightforward and reproducible way to obtain modified electrodes. Since no chemical compound other than the graphene derivatives are necessary, and that the final electrodes have very rough surfaces, such electrodes have very high capacitance, and those characteristics are direct consequence of the chosen method. Anchoring graphene derivatives on the surface of metallic conductors by the (electro)-chemistry of diazonium salts is shown to be a promising method to achieve strongly bound graphene sheets to a surface. The high reactivity of diazonium salts, though, hampers the electrochemical activity of graphene, and no electrodes suitable to be used in electrochemical capacitors were obtained. In summary, the advances and remaining challenges towards the use of such methodologies in the construction of electrochemical capacitors are presented here.

The rapid development of microelectronics has equally rapidly increased the demand for miniaturized energy storage devices. On-chip micro-supercapacitors (MSCs), as promising power candidates, possess great potential to complement or replace electrolytic capacitors (ECs) and microbatteries (MBs) in various applications. Recently, planar two-dimensional (2D) MSCs, composed of isolated thin-film microelectrodes with extremely short ionic diffusion path and free of separator on a single substrate, have become particularly attractive because they can be directly integrated with microelectronic devices on the same side of a flexible substrate to act as a standalone microsized power source. However, the areal capacities and energy densities of the 2D MSCs are commonly limited by the low voltage window and the thin layer of the electrode materials. Obviously, integrating more active material into cleverly designed three-dimensional (3D) electrode architectures will effectively increase the areal performance within a limited footprint area in spite of some loss of flexibility and cycling stability. However, it is still a big challenge to effciently and cost-effectively fabricate on-chip MSCs with high electro-chemical performance and abundant electrode structures. Here, three types of MSCs including graphene-based 2D planar MSCs, on-chip 3D interdigital MSCs and self-assembled 3D tubular MSCs were fabricated, respectively. The fabrication process, electrode materials structure and morphology, electrochemical performance, mechanical properties, integration process and difficulty, and practical application of these 2D and 3D devices are studied in detail.