Academic literature on the topic 'Electric double layer capacitors'

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 68-72).<br>In capacitive deionization (CDI), salt water is passed through two polarized electrodes, whereby salt is adsorbed onto the electrode surface and removed from the water stream. This approach has received renewed interest for water desalination due to the development of new high-surface area, carbon-based nanomaterials. However, there is limited understanding as to how electrode geometry, surface properties, and capacitance affect ion capture. In this work, we experimentally investigated various standard carbon-based electrode materials, including activated carbon and carbon cloths, as well as microfabricated silicon structures for CDI. Electrochemical characterization through cyclic voltammetry was used to determine the electrochemical properties of each material. The capacitance values of the carbon materials tested were 40 F/g for 2000 m2 /g carbon cloth, 32 F/g for 1000 m2 /g carbon cloth, and 25 F/g for activated carbon. In addition, we constructed two iterations of flow test channels to perform parametric studies on ion capture. The first flow cell utilized a commercial conductivity probe to measure salt concentration after charging the electrodes without flow. We showed that the ion capture on both the carbon cloth and activated carbon electrodes were proportional to the applied voltage, however two orders of magnitude smaller than what is expected from the electrode charge. We addressed a significant experimental limitation in the second flow cell by integrating conductivity sensors into the flow channel to measure effluent salt concentration during electrode charging. We found that the salt adsorption increased from 33.1 pmol/g in the first flow cell to 63.5 pmol/g in the redesigned flow for an applied potential of 1.2 V. Future directions will focus on controlling electrode geometry and chemistry to help elucidate transport mechanisms and provide insight into the design of optimal materials for capacitive deionization.<br>by Batya A. Fellman.<br>S.M.

Doutoramento em Ciência e Engenharia de Materiais<br>O presente estudo teve como objetivo principal a elaboração e caracterização de hétero-estruturas hibridas tridimensionais (3D) de nanotubos de carbono alinhados verticalmente e revestidos com óxido de manganês para aplicações em condensadores eletroquímicos como elétrodos livres de aditivos. Numa primeira fase, foram desenvolvidas metodologias para o crescimento de nanotubos de carbono puro e para nanotubos de carbono dopados com azoto, em substratos isoladores e metálicos, por deposição química em fase de vapor. Foi dada especial atenção ao crescimento direto de nanotubos de carbono alinhados verticalmente no substrato metálico (Inconel®600) e sua aplicação em elétrodos livres de aditivos à base de carbono. Posteriormente, foi desenvolvido um processo inovador para a deposição de óxido de manganês (Mn3O4) por deposição por camada atómica para o revestimento de nanoestruturas, como os nanotubos de carbono, para a elaboração de heteroestruturas. Estas foram devidamente caracterizadas como materiais para aplicações em eléctrodos. A eficiência electroquímica dos eléctrodos atinge um máximo para o nanocompósito de nanotubos de carbono puro/óxido de manganês revestidos com 600 ciclos por deposição por camada atómica e apresenta uma capacitância de 78.68 mF cm-2 a 5 mV s-1. Este resultado pode ser atribuído ao efeito cooperativo entre os componentes do nanocompósito e uma utilização eficaz dos materiais ativos. Provou-se que um material nanocompósito que englobe a capacitância da dupla camada elétrica, bem como a estrutura condutora dos nanotubos de carbono e a pseudocapacitância dos óxidos metálicos é de grande interesse devido ao seu mecanismo duplo de armazenamento de carga e as vantagens de cada mecanismo são exploradas nestes novos dipositivos híbridos. Este trabalho foi realizado na Universidade de Aveiro e na Universidade de Humboldt (Berlim), beneficiando das infraestruturas adequadas à execução do trabalho experimental de ambas as instituições e das competências complementares das equipas de investigação associadas. Devido à natureza multidisciplinar da área de investigação onde este doutoramento se insere, a colaboração com outras instituições internacionais valorizaram a discussão dos resultados obtidos e fundamentaram os novos materiais desenvolvidos<br>The purpose of this work was the elaboration and characterization of hybrid three-dimensional (3D) arrays of vertically aligned carbon nanotubes coated with manganese oxide heterostructures for application as binder-free electrodes in electrochemical capacitors. In the first stage, methodologies to grow pure and nitrogen doped vertically aligned carbon nanotubes arrays on nonmetallic and metallic substrates by thermal chemical vapor deposition have been developed. Particular attention was devoted to obtain vertically aligned carbon nanotubes arrays grown directly on metallic conductive substrates (Inconel®600) and their application in binderfree carbon-based electrodes. Subsequently, as one of the main points of this work, a novel manganese oxide (Mn3O4) atomic layer deposition process has been developed for coating nanostructures, such as carbon nanotubes, for the elaboration of heterostructures which were further used and characterized as electrodes materials. The electrochemical performance of the electrodes reaches a maximum for the pure carbon nanotubes/manganese oxide nanocomposite coated with 600 ALD cycles exhibiting a specific capacitance of 78.68 mF cm-2 at 5 mV s-1. This result could be attributed to the synergetic effect between the components in the nanocomposite and an effective utilization of the active materials. Therefore it was demonstrated that a nanocomposite material comprising electric double layer capacitance together with the conductive framework of the carbon nanotubes and pseudocapacitive metal oxides is of great interest due to its dual charge storage mechanism and the advantages of each mechanism are exploited in these new hybrid devices. This work was carried out at University of Aveiro and at Humboldt-Universität zu Berlin due to complementary avaivable expertises and equipments, and also benefits of several international collaborations due to the multidisciplinar nature of the research field.

Today’s society is currently performing an exit from fossilfuel energy sources. The change to sustainable alternativesrequires inexpensive and environmentally friendly energy storagedevices. However, most current devices contain expensive,rare or toxic materials. These materials must be replaced bylow-cost, abundant, nontoxic components.In this thesis, I suggest the production of paper-based electricdouble-layer capacitors (EDLCs) to meet the demand oflow-cost energy storage devices that provide high power density.To fulfill the requirements of sustainable and environmentallyfriendly devices, production of EDLCs that consist of paper,graphite and saltwater is proposed. Paper can be used as aseparator between the electrodes and as a substrate for theelectrodes. Graphite is suited for use as an active material in theelectrodes, and saltwater can be employed as an electrolyte.Westudied and developed different methods for the productionof nanographite and graphene from graphite. Composites containingthese materials and similar advanced carbon materialshave been tested as electrode materials in EDLCs. I suggest theuse of cellulose nanofibers (CNFs) or microfibrillated cellulose(MFC) as a binder in the electrodes. In addition to improvedmechanical stability, the nanocellulose improved the stabilityof graphite dispersions and the electrical performance of theelectrodes. The influence of the cellulose quality on the electricalproperties of the electrodes and EDLCs was investigated.The results showed that the finest nanocellulose quality is notthe best choice for EDLC electrodes; MFC is recommended forthis application instead. The results also demonstrated thatthe capacitance of EDLCs can be increased if the electrodemasses are adjusted according to the size of the electrolyte ions.Moreover, we investigated the issue of high contact resistancesat the interface between porous carbon electrodes and metalcurrent collectors. To reduce the contact resistance, graphitefoil can be used as a current collector instead of metal foils.Using the suggested low-cost materials, production methodsand conceptual improvements, it is possible to reduce the material costs by more than 90% in comparison with commercialunits. This confirms that paper-based EDLCs are apromising alternative to conventional EDLCs. Our findings andadditional research can be expected to substantially supportthe design and commercialization of sustainable EDLCs andother green energy technologies.<br>I dagens samhälle pågår en omställning från användning avfossila energikällor till förnybara alternativ. Denna förändringkräver miljövänliga och kostnadseffektiva elektriska energilagringsenheterför att möjliggöra en kontinuerlig energileverans.Dagens energilagringsenheter innehåller ofta dyra, sällsyntaeller giftiga material som behöver bytas ut för att nå hållbaralösningar.I denna avhandling föreslås att tillverka pappersbaseradesuperkondensatorer som möter kraven för kostnadseffektivaelektriska energilagrare med hög effekttäthet. För att nå kravenpå miljömässigt hållbara enheter föreslås användning avendast papper, grafit och saltvatten. Papper kan användas somseparator mellan elektroder likväl som substrat vid elektrodbestrykning.Grafit kan användas som aktivt elektrodmaterialoch saltvatten fungerar som elektrolyt. Olika metoder har härutvecklats för att producera nanografit och grafen från grafit.Dessa material har tillsammans med liknande, kommersiellt tillgängliga,avancerade kolmaterial testats i elektrodkompositerför superkondensatorer. Som bindemedel i dessa kompositerföreslås nanofibrillerad eller mikrofibrillerad cellulosa. Jaghar demonstrerat att nanocellulosa ökar dispersionsstabilitetensamt förbättrar den mekaniska stabiliteten och dom elektriskaegenskaperna i elektroderna. Hur cellulosans kvalitet påverkarelektroderna har undersökts och visar att den finaste kvaliteteninte är det bästa valet för superkondensatorer, istället rekommenderasmikrofibrillerad cellulosa. Utöver detta demonstrerasmöjligheten att öka superkondensatorernas kapacitans genomatt balansera elektrodernas massa med hänsyn till jonernasstorlek i elektrolyten. I avhandlingen diskuteras även svårigheternamed hög kontaktresistans i gränssnittet mellan porösakolstrukturer och metallfolie och hur detta kan undvikas omgrafitfolie används som kontakt.Genom att använda de material, produktionstekniker ochkonceptförbättringar som föreslås i avhandlingen är det möjligtatt reducera materialkostnaderna med mer än 90% i jämförelsemed kommersiella superkondensatorer. Detta bekräftar att pappersbaserade superkondensatorer är ett lovande alternativoch våra resultat tillsammans med vidare utveckling harstor potential att stödja övergången till miljömässigt hållbarasuperkondensatorer och annan grön energiteknik.<br><p>Vid tidpunkten för disputationen var följande delarbeten opublicerade: delarbete 6 inskickat.</p><p>At the time of the doctoral defence the following papers were unpublished: paper 6 submitted.</p>

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.<br>Includes bibliographical references (p. 223-227).<br>This thesis documents the work on the modeling of double layer capacitors (DLCs) and the validation of the modeling procedure. Several experiments were conducted to subject the device under test to a variety of charging/discharging profile and temperatures in an effort to simulate the various conditions such a device might encounter in an automotive type application. High and low current charging profiles were performed for both charge/discharge and charge/hold/discharge type experiments. Low temperature ([approx.] -25 ⁰C), room temperature ([approx.] 21 ⁰C), and high temperature experiments ([approx.] 50 ⁰C) were performed for the investigation of temperature effects on these devices. The derived DLC model was used in PSpice® and Matlab® simulations to determine how accurately the model could predict the performance of the device. The nonlinear characteristics of the device were also investigated and the nonlinear modeling information presented as an addition to the basic DLC model. Device variation was explored for a small sample of these devices in an effort to gain insight on the range of tolerances for modern devices. This work also presents an extensive look into the variety of electrochemical capacitor devices under investigation and in use today. An explanation of these devices and their distributed resistances and capacitance is included. This thesis gives a detailed look into the experimental setups and testing procedures used to test the devices, the simulations for the comparison, and presents the results of the comparison. Finally, this thesis documents the conclusion that this simple model procedure adequately predicts the performance of the device under these various performance profiles.<br>by David Allen New.<br>S.M.