Academic literature on the topic 'Electrode capacitive'

Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2009.<br>Committee Chair: Degertekin, F. Levent; Committee Member: Benkeser, Paul; Committee Member: Berhelot, Yves; Committee Member: Brand, Oliver; Committee Member: Hesketh, Peter. Part of the SMARTech Electronic Thesis and Dissertation Collection.

La compréhension de la formation et de la charge de la double couche électrique (EDL) des matériaux d'électrodes capacitives est cruciale pour développer les systèmes de stockage électrochimique de l'énergie de forte puissance, y compris en recharge. Cependant, les études expérimentales de la cinétique de charge des électrodes de carbone poreux, matériaux de choix pour les électrodes de supercondensateurs, posent d'importants défis en raison de la dynamique rapide des ions. Ce sont ces défis que nous proposons de relever dans ce travail. Dans un premier temps, nous nous sommes concentrés sur des carbones poreux de type CDC, c'est-à-dire des carbones dérivés de carbures (CDCs), et les avons caractérisés dans des électrolytes aqueux de différentes concentrations. En utilisant une micro-électrode à cavité, nous avons pu observer la déplétion de l'électrolyte lors de polarisations sous fortes surtensions, et avons analysé systématiquement son impact sur la cinétique de charge. Les résultats ont montré qu'une faible concentration d'électrolyte (10-3 M), une surtension élevée (&gt; 200 mV) et une petite taille de pores de carbone (0,6 nm) exacerbent les gradients de concentration dans l'électrolyte, entraînant un transport ionique retardé. Dans un deuxième temps, nous avons étudié le mécanisme de stockage de charge dans un matériau de type oxyde de graphène réduit (rGO), toujours dans des électrolytes aqueux neutres. Les résultats de caractérisations électrochimiques operando par microbalance à quartz (EQCM) ont dépeint un mécanisme d'adsorption cationique en deux étapes : une adsorption de cations hydratés à faible surtension cathodique, suivie d'un mécanisme de déshydratation cationique pour des surtensions plus élevées (&gt;200 mV). Notablement, une augmentation significative de la capacitance a été observée en raison de la déshydratation des cations, corrélée à une augmentation des interactions cation-rGO provenant de la charge de surface négative (potentiel zêta) du rGO. Ces résultats soulignent le rôle critique des interactions ion-électrode et de la désolvatation des cations dans les mécanismes de stockage de charge. Dans la dernière partie de cette thèse, nous avons caractérisé des matériaux de type réseaux métallo-organiques (MOFs) conducteurs lamellaires comme matériaux d'électrode. Des mesures par EQCM ont montré que le mécanisme de stockage de la charge dans ces MOFs en électrolyte non aqueux est dominé par l'adsorption des cations. Lorsque des cations de petites tailles sont utilisés (type tetraethylammonium), la capacité s'en trouve augmentée, tandis que l'utilisation de cations plus volumineux (tetrabutyl, hexyl) conduisent à une saturation des pores des électrodes MOF, entraînant une dynamique de charge plus lente avec une hystérésis, entraînant un déplacement important des molécules de solvant. Les résultats de cette thèse ont permis de développer notre compréhension de du transport et de l'adsorption ionique dans les milieux confinés, et du rôle de la dynamique des solvants, posant les bases pour concevoir des matériaux optimisés pour le stockage de l'énergie capacitive<br>Understanding the formation and structure of the electrical double layer (EDL) in state-of-the-art capacitive electrode materials is crucial for preparing the next-generation of fast charging and high-power energy storage systems. However, experimental investigations of the charging kinetics of porous carbon electrodes, the materials of choice for electrochemical capacitors, pose significant challenges due to rapid ion dynamics; this is the challenge we want to address in this work. This thesis starts with a focus on carbide-derived porous carbon (CDC), employing chronoamperometry in electrolytes of varying concentrations. Using a cavity micro-electrode setup, we were able to observe electrolyte depletion and we systematically analyzed its impacts on charging the kinetics. Results indicated that for low electrolyte concentration (10-3 M), high overpotential (&gt; 200 mV), and small carbon pore size (0.6 nm) exacerbated electrolyte depletion, slowing down ion transportation. Then, we further investigated the charge storage mechanism in reduced graphene oxide (rGO) electrodes in near-neutral aqueous electrolytes. Operando EQCM results depicted a two-step cation adsorption mechanism with i) initial hydrated cation adsorption at low overpotential followed by cation dehydration for higher overvoltage(&gt;200 mV). Notably, a significant increase in capacitance was observed due to cation dehydration, with the degree of enhancement correlating with non-electrostatic cation-rGO interactions due the negative charge of the rGO surface (zeta potential). These findings underscore the critical role of ion-electrode interactions and cation desolvation in modulating the charge storage mechanisms and capacitance. In a last part, we used conductive layered metal-organic frameworks (MOFs) as electrode materials. These MOFs revealed a cation-dominated charge storage mechanism in non-aqueous electrolytes via EQCM measurements. The use of small size cations (tetraethylammonium) resulted in improved capacity, while larger cations (butyl, hexyl ammonium) saturated MOF electrode pores, leading to asymmetric and sluggish charging dynamics, forcing solvent molecules to participate in the charge storage mechanism under nanopore confinement. The discoveries of this thesis significantly advance our understanding of ion electrosorption, ion transportation, and the role of solvent dynamics in confined pores, thus guiding the design of materials with improved performance for capacitive energy storage devices

Biochar, a by-product of biomass pyrolysis, was investigated as a carbon-based electrode material for a water treatment method based on electrostatic adsorption/desorption of ions in electric double layers (EDLs) formed on the charged electrodes (capacitive deionization, CDI). Surface area, porous structure, and functional groups of biochar were developed, and corresponding effects on EDL capacitive performance were studied. A novel method was explored to tailor the micro- and meso-porous structures of activated biochar by exploiting the interaction between pre-carbonization drying conditions and carbonization temperature (475–1000 C) in a thermo-chemical process (KOH chemical activation). The mechanism of porosity development was investigated; results suggest that the conversion of KOH to K₂CO₃ under different drying conditions has a major role in tailoring the structure. The resultant surface area, micro- and meso-pore volumes were: 488–2670 m² g-¹, 0.04–0.72 cm³ g-¹, and 0.05–1.70 cm³ g-¹, respectively. Tailored biochar samples were investigated using physico-chemical surface characterization and electrochemical methods. For electrochemical testing, activated biochar was sprayed onto Ni mesh current collectors using Nafion® as binder. The majorly microporous activated biochar showed promising capacitances between 220 and 245 F g-¹ when 0.1 mol L-¹ NaCl/NaOH was used as the electrolyte. Addition of mesoporous structure resulted in significantly reduced electrode resistance (up to 80%) and improved capacitive behaviour due to enhanced ion transport within the pores. CDI of NaCl and ZnCl₂ solutions was investigated in a batch-mode unit through the use of tailored biochar electrodes. For NaCl removal, all samples showed promising capacity (up to 5.13 mg NaCl g-¹) and durability through four consecutive cycles. In contrast, in the case of ZnCl₂, the microporous sample showed a considerable drop in removal capacity (>75%) from cycle 1 to 4, whereas the combined micro- and mesoporous sample exhibited relatively small electrosorption capacity. Interestingly, the sample with mostly mesoporous structure has shown the highest removal capacity (1.15 mg ZnCl₂ g-¹) and durability for Zn²⁺ removal. These results emphasize the importance of tailoring the porous structure of biochar as a function of the specific size of adsorbate ions to improve the CDI performance.<br>Applied Science, Faculty of<br>Chemical and Biological Engineering, Department of<br>Graduate

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 147-151).<br>Spot defects are a leading source of failure in the fabrication of integrated circuits (ICs). Thus, the IC industry inspects for defects at multiple stages of IC fabrication, especially the fabrication of IC photomasks. However, existing non-invasive imaging methods cannot image a modern photomask in a reasonable time-frame. Electroquasistatic (EQS) sensors are arrays of electrode pairs that capacitively couple to targets they sweep over. Utilizing high measurement frequencies and a number of parallel scanning electrode pairs, EQS sensors have been suggested as a potential high speed alternative for defect detection in IC fabrication. This thesis continues the investigation into EQS sensors for high speed imaging by exploring EQS sensors driven with high excitation frequencies. We develop electrode arrays that can be driven with high excitation frequencies and construct high frequency EQS sensors by attaching them to high frequency drive electronics. We also fabricate a test fixture for positioning these sensors relative to and sweeping them across targets on a conductive base. As the sensors sweep across targets, their impedance is measured from 1 - 500 MHz using an impedance analyzer and is later converted into the capacitance between the sensor's electrode array and the target. Capacitance changes are produced by a variable air gap and by a dielectric step, confirming these sensors can detect changes in a target's geometric and material properties with high excitation frequencies. Finally, we present concepts for a high speed measurement system which utilizes these sensors.<br>by Tyler Thomas Hamer.<br>S.M.<br>S.M. Massachusetts Institute of Technology, Department of Mechanical Engineering

Nanosatellites, such as Cubesats, are a rapidly growing sector of the space industry. Their popularity stems from their low development cost, short development cycle, and the widespread availability of COTS subsystems. Budget-conscious spacecraft designers are working to expand the range of missions that can be accomplished with nanosatellites, and a key area of development fueling this expansion is the creation of micropropulsion systems. One such system, originally developed at the Australian National University (ANU), is an electrothermal plasma thruster known as Pocket Rocket (PR). This device heats neutral propellant gas by exposing it to a Capacitively Coupled Plasma (CCP), then expels the heated gas to produce thrust. Significant work has gone towards understanding how PR creates and sustains a plasma and how this plasma heats the neutral gas. However, no research has been published on varying in the device's geometry. This thesis aims to observe how the size of the RF electrode affects PR operation, and to determine if it can be adjusted to improve performance. To this end, a thruster has been built which allows the geometry of the RF electrode to be easily varied. Measurements of the plasma density at the exit of this thruster with different sizes of electrode were then used to validate a Computational Fluid Dynamics (CFD) model capable of approximately reproducing experimental measurements from both this study and from the ANU team. From this CFD, the number of argon ions in the thruster was found for each geometry, since collisions between argon ions and neutrals are primarily responsible for the heating observed in the thruster. A geometry using a 10.5 mm electrode was observed to produce a 23% increase in the quantity of ions produced compared to the baseline 5 mm electrode size, and a 3.5 mm electrode appears to produce 88% more ions.

Face aux problèmes de réchauffement climatique, trouver des ressources énergétiques propres et durables pour remplacer les combustibles fossiles conventionnels est d'une importance capitale. L'énergie osmotique demeure une ressource énergétique inexploitée avec un potentiel significatif. Dans ce travail, nous parvenons à une conversion efficace de l'énergie osmotique en électricité grâce à un processus de mélange bien contrôlé utilisant un système d'électrodialyse inverse capacitif (CRED). Il est démontré qu'un écart substantiel de densité de puissance existe entre le système CRED et la valeur maximale théorique, principalement en raison de l'efficacité de conversion faible du flux ionique-électronique dans les électrodes capacitifs. Pour pallier cette limitation, nous proposons la stratégie de boosting pour optimiser le régime de fonctionnement du système CRED. Des expériences et des modélisations confirment une amélioration de la performance énergétique du système CRED. Pour avancer vers des applications réelles, nous évaluons les performances du système CRED sous des solutions composées de mélanges ioniques complexes. Contrairement à la chute significative de la densité de puissance observée dans les systèmes RED classiques, le système CRED ne présente qu'une légère diminution lorsqu'il est soumis à des solutions avec un mélange d'ions divalents. Ce phénomène est attribué au renversement périodique des solutions dans les compartiments, qui atténue l'effet d'empoisonnement de la membrane. Ce résultat est ensuite validé par des tests à long terme avec des solutions réelles. Pour généraliser le système CRED dans un spectre plus large, nous proposons une cellule de gradient de pH avec des électrodes de MnO2 à pseudo-capacité. Elle utilise l'énergie osmotique établie dans un processus de capture de CO2 basé sur un électrolyte et vise à réduire le coût global du processus de capture de carbone. La cellule de gradient de pH présente une augmentation inattendue de la densité de puissance sous la stratégie de boosting. Cela est dû à la contribution de tension supplémentaire des électrodes en raison du changement de couverture fractionnelle lié aux réactions d'oxydoréduction. Cependant, elle reste dans le cadre du régime capacitif et est bien décrite par une modélisation CRED adaptée<br>Given the global warming issues, finding clean and sustainable energy resources to replace conventional fossil fuels is of paramount importance. Osmotic energy remains an untapped energy resource with significant potential. In this work, we achieve efficient conversion of osmotic energy into electricity through a well-controlled mixing process using a capacitive reverse electrodialysis (CRED) system. It is demonstrated that a substantial power density gap exists between the CRED system and the theoretical maximum value, primarily due to the low ionic-electronic flux conversion efficiency in capacitive electrodes. To address this limitation, we propose the boosting strategy to optimize the working regime of the CRED system. Both experiments and modeling confirm an enhanced energy performance of the CRED system. To advance towards real-world applications, we assess the performance of the CRED system under solutions composed of complex ion mixing. In contrast to the significant power density drop observed in classic RED systems, the CRED system exhibits only a minor decrease when subjected to solutions with divalent ion mixing. This phenomenon is attributed to the periodic water chamber reversal, which mitigates the membrane poisoning effect. This result is further validated through long-term testing with real-world solutions. To generalize the CRED system into a broader spectrum, we propose a pH gradient cell with MnO2 electrodes of pseudo capacitance. It uses the osmotic energy established within an electrolyte based CO2 capturing process and aims to reduce the overall cost of carbon capturing process. The pH gradient cell presents unexpected power density increase under boosting strategy. This is due to the additional electrode voltage contribution due to fractional coverage change related to redox reactions. However, it stays in the framework of capacitive regime and remains well described by an adapted CRED modeling

>Magister Scientiae - MSc<br>Membrane Capacitive Deionisation (MCDI) is a technology used to desalinate water where a potential is applied to an electrode made of carbonaceous materials resulting in ion adsorption. Processes and materials for the production of electrodes to be applied in Membrane Capacitive Deionisation processes were investigated. The optimal electrode composition and synthesis approached was determined through analysis of the salt removal capacity and the rate at which the electrodes absorb and desorb ions. To determine the conductivity of these electrodes, the four point probe method was used. Contact angle measurements were performed to determine the hydrophilic nature of the electrodes. N2 adsorption was done in order to determine the surface area of carbonaceous materials as well as electrodes fabricated in this study. Scanning electron microscopy was utilised to investigate the morphology. Electrodes were produced with a range of research variables; (i) three different methods; slurry infiltration by calendaring, infiltration ink dropwise and spray-coating, (ii) electrodes with two different active material/binder ratios and a constant conductive additive ratio were produced in order to find the optimum, (iii) two different commercially available activated carbon materials were used in this study (YP50F and YP80F), (iv) two different commercially available electrode substrates were utilised (JNT45 and SGDL), (v) different slurry mixing times were investigated showing the importance of mixing, and (vi) samples were treated at three different temperatures to establish the optimal drying conditions. Through optimization of the various parameters, the maximum adsorption capacity of the electrode was incrementally increased by 36 %, from 16 mg·g-1 at the start of the thesis to 25 mg·g-1 at the end of the study.

Pour lutter efficacement contre le réchauffement climatique, il est nécessaire d'augmenter la production d'énergies propres et renouvelables. L'énergie solaire, l'énergie éolienne, l’hydroélectrique et l'énergie marémotrice sont des technologies matures. L'augmentation de la production d'énergie renouvelable nécessite l'utilisation de sources d'énergie peu ou pas exploitées, comme l’énergie bleue. Cette forme d’énergie correspond à l’énergie générée lors du mélange d'eau douce et d'eau salée. Cependant, les procédés actuels d’extraction d'énergie à partir de gradients de sel restent inefficaces, principalement parce que les membranes sélectives commerciales sont peu performantes comme le cas de l’électrodialyse inverse ou l’Osmose à pression retardée qui ne sont toujours pas économiquement rentable. Les espoirs de membranes non sélectives dotées de canaux nanofluidiques chargés qui ont été conçus pour réduire la résistance interne de la cellule semblent être vains. Une nouvelle solution est proposée qui consiste à augmenter le potentiel de circuit ouvert de la membrane en y attachant des électrodes capacitives avec des groupements fonctionnels chargés négativement qui permet l’adsorption des ions, essentiellement les ions positifs. Une telle configuration nous permet de doubler le potentiel du circuit ouvert de la cellule sans trop modifier la résistance ohmique globale et donc de multiplier par 4 la puissance brute potentiellement récupérable.Après une étude approfondie réalisée dans le but de caractériser le procédé et une optimisation de la consommation énergique due aux pertes de charge, nous présentons un dispositif de quelques centimètres carrés avec une seule membrane récoltant une densité de puissance nette de 2 Watts par mètre carré de membrane (densité de puissance potentielle nette estimée à 5.4 W.m-2, ce qui rend le système économiquement viable<br>To effectively combat global warming, it is necessary to increase the production of clean, renewable energy. Solar, wind power, hydroelectric dams and tidal power plants are mature technologies. Increasing the production of this energy requires the use of energy sources that are little or not exploited like the blue energy which is the a less-known source with enormous potential that can be generated directly from the mixing of fresh and salt water. However, current processes for energy harvesting from salt gradients remain inefficient mainly because commercial selective membranes have poor performance as in the reverse electrodialysis or in the pressure retarded osmosis and still not economically viable. Hopes for nonselective membranes with charged nanofluidic channels which have been designed to reduce the internal resistance of the cell seem to be in vain. Here we present a novel solution that involves increasing the open circuit potential of the membrane by attaching tailored capacitive layers with negatively charged functional groups on the surface that adsorb ions, mainly the positive ones. Such a configuration allows us to double the potential of the open circuit of the cell without modifying too much the global ohmic resistance and thus to multiply by 4 the potentially recoverable power.After a thorough study carried out in order to characterize the process and an optimization of the energy consumption caused by the hydraulic pressure drop, we display a device of a few squared centimeters with only one membrane harvesting a net power density of 2 Watts per square meter of the membrane (estimated net potential power density 5.4 W.m−2 ) which makes the system economically viable