A more energy efficient and sustainable method of desalinating water is needed due to increasing water shortages and contamination of current freshwater sources. Capacitive deionization (CDI), a new emerging technology, is a type of electric desalination that uses an applied voltage to pull the salt ions out of the salty solution and store the ions in porous carbon electrodes. CDI uses less applied energy than more commonly used methods of desalination like reverse osmosis and multi-flash distillation and has the added advantage of energy recovery. This report details experiments conducted to analyze the effect of different separation distances between the electrodes on salt ion adsorption for a high concentration solution under various flow rates and a 1 V voltage potential difference. The testing was performed in the Multiscale Thermal-Fluids Laboratory at The University of Texas at Austin using a uniquely fabricated CDI cell. Voltage, elapsed time, and electrical conductivity measurements were taken during the testing. Electrical conductivity was used to signify salinity of the solution. Two different separation distances were created by placing either one 2mm mesh between the electrodes or by using two 2 mm meshes between the electrodes. The results did not agree with the expectation that the one-mesh tests would adsorb twice the amount of salt ions as the two-mesh tests because of the differences in the electric field between the two types of tests. This is believed to be due to the high concentration tested. Future testing should include repeating these tests to verify the results and performing the tests for lower concentrations to see if they followed the expectation. / text

In this thesis, two different experimental approaches to capacitive deionization (CDI) process are presented. In the first approach, transient system characteristics were analyzed to find three different operating points, first based on minimum outlet concentration, second based on maximum average adsorption rate and third based on maximum adsorption efficiency. These three operating points were compared in long term desalination tests. In addition, the effects of inlet stream salinity and CDI system size have been characterized to assess the feasibility of a commercial CDI system operating at brackish water salinity levels. In the second approach, the physical phenomena occurring inside a capacitive deionization system were studied by laser-induced fluorescence visualization of a “pseudo-porous” CDI microstructure. A model CDI cell was fabricated on a silicon-on-insulator (SOI) substrate and charged fluorophores were used to visualize the simultaneous electro migration of oppositely charged ions and to obtain in situ concentration measurements. / text

Water scarcity is set to become a big challenge in the 21st century and more efficient desalinationtechnologies will be needed in the future. In this project, one desalination method called capacitivedeionization (CDI) is explored and we used a model called the ELC model to simulate CDI withComsol. The goal of this project focuses on evaluating the performance of CDI and how changingdifferent operational parameters of the process affects other aspects of desalination. Some examplesare power consumption, desalination rate and water usage. With the gathered information, the process of CDI can be optimized in some way. Even though our project simulates a specific model ofCDI, the hope is to have come to general conclusions regarding CDI so that the results can be usedfor other models. If the correlations between parameters are known, it will be easier to calibrate anysetup of CDI. The gathered data is exported, stored, processed, and plotted using Matlab functionsintegrated with Comsol. The results consist of two sets, the first for constant voltage and the secondfor constant current. Both have results on how desalination rate and energy efficiency are related toparameters such as internal voltage intervals controlling how long the desalination cycle is running,external voltage, and inflow salt concentration in the water. The key conclusions drawn are as thefollowing for constant voltage. High external voltages are effective in increasing both desalinationrate and energy efficiency but will degrade the CDI electrodes. The internal voltage span should bepretty long with high max internal voltage and the minimum internal voltage the same as the external voltage. The energy efficiency increase with lower salt concentrations in the inflow water up toa point. The best setup for the desalination rate is at quite a high maximum internal voltage withvaried low minimum internal voltage. For constant current, low current is generally efficient, whilethe maximum external voltage depends on the current. Avoid a high current with a low externalvoltage. By relating all these parameters, we get more insights into what an energy-efficient and fastadsorbing CDI setup looks like.

Carbon based materials, including porous carbons and carbon layer composites, are finding increased usage in latest environmental and energy related research. Among porous carbon materials, hierarchical porous carbons with multi-modal porosity are proving out to be an effective solution for applications where the traditional activated carbons fail. Thus, there has been a lot of recent interest in developing low-cost, facile, easy to scale-up, synthesis techniques for producing such multi-modal porous carbons. This dissertation offers two novel synthesis techniques: (i) ice templating integrated with hard templating, and (ii) salt templating coupled with hard templating, for producing such hierarchically porous carbons. The techniques offer tight control and tunability of porosity (macro- meso- and microscale) in terms of both size and extent. The synthesized multi-modal porous carbons are shown to be an effective solution for three important environment related applications – (i) Carbon dioxide capture using amine supported hierarchical porous carbons, (ii) Reduction in irreversible fouling of membranes used for wastewater reuse through a deposition of a layer of hierarchical porous carbons on the membrane surface, (iii) Electrode materials for electrosorptive applications. Finally, because of their tunability, the synthesized multi-modal porous carbons serve as excellent model systems for understanding the effect of different types of porosity on the performance of porous carbons for these applications. Also, recently, there has been a lot of interest in developing protective layer coatings for preventing photo-corrosion of semiconductor structures (in particular Cu2O) used for photoelectrochemical water splitting. Most of the developed protective strategies to date involve the use of metals or co-catalyst in the protective layer. Thus there is a big need for developing low-cost, facile and easy to scale protective coating strategies. Based on the expertise gained in synthesizing porous carbon materials, and owing to our group’s interest in developing suitable photoelectrode materials, this dissertation also proposes a novel carbon-Cu2O composite comprising of a carbon layer coated Cu2O nanowire array structure as a high performance and stable photoelectrode material for photoelectrochemical water splitting.

Carbon has been used electrochemically in various forms for water treatment and the carbon aerogel is one of them. Carbon Aerogels (CA) are used as electrodes due to their high surface capacity and high electrical conductivity. They are also known as Carbon Nanofoams (CNF). CA electrodes attract oppositely charged ions that are nearby. This concept is known as Capacitive De-Ionization (CDI). The use of CA in CDI for water purification is well documented, but not much work has been done on regeneration of CA electrodes. Once saturated, these electrodes lose their ability to adsorb additional ions and it must be restored by regeneration. If they cannot be regenerated, they would need to be replaced, which would greatly increase the cost of the treatment they are expensive. The goal of this study is to obtain data to define optimal regeneration conditions and to develop predictive capability by examining desorption behavior of adsorbed ions on CA electrodes. This study focuses on desorption of adsorbed ions and regeneration of CA. Various experiments were conducted to explore the effects on regeneration of CA of shorting of electrodes, change of polarity of electrodes, flow speed of water over CA electrodes, and temperature of regeneration water. The optimal combination of experimental variables was identified and was used for remaining experiments that tested the effect of size, charge and mass of adsorbed ions on regeneration of CA. Also, the effect of thickness of CA and its pore size on regeneration of CA was studied. Results indicated that application of reverse potential for the first few minutes of the total regeneration time provided the greatest regeneration. Longer application of reverse potential did not result in higher regeneration. The regeneration behavior when no potential applied with and without shorting was as expected. Application of reverse potential with variable temperature or variable flow speed of water over CA surfaces provided results that were different from the ones that were obtained with no potential being applied with or without shorting of electrodes.

The shortage of clean water has become a significant global problem, and capacitive deionization (CDI) is a technology that can be used to help relieve the problem. A Ćuk converter system that can recover energy from CDI cells is described. This converter transfers energy between two CDI cells when a cell is in its desorption period, allowing energy that would otherwise be lost to be recovered and improving overall system efficiency. In order to control the states of the MOSFET switches in the converter, a self boost charge pump is used. In this way, the microcontroller can control system duty cycle and optimize energy efficiency. A design method of reducing ripple losses caused by passive elements is presented. Several sensor circuits and their design methods that can minimize power losses are shown. The influence of initial voltage drop and voltage ramp time is also examined. This Ćuk converter system is tested using a dummy cell and a real CDI cell. The converter system shows promising performance experimentally.

Made available in DSpace on 2016-06-02T19:56:57Z (GMT). No. of bitstreams: 1 6597.pdf: 4764954 bytes, checksum: 5414abc6292e5e2fc5ec8124840f6a6b (MD5) Previous issue date: 2015-02-20 / Universidade Federal de Sao Carlos / In this work, different commercial carbon materials that could be used as electrodes for capacitive deionization were investigated: carbon cloth, carbon foam, carbon felt, carbon fiber, carbon veil and activated carbon powder (AC). The materials were characterized by scanning electron microscopy (SEM), surface resistivity, wettability and cyclic voltammetry (CV). The performance in terms of electrosorption of NaCl was evaluated for different cell potentials. The AC electrode showed the best capacity of removing ions, and presented good values of charge efficiency (QE) and specific energy consumption (η) and, thusly, it was chosen to be modified using different techniques in an attempt to improve its characteristics aiming better results of electrosorption. Part of the strategies was the addition of carbon black and sodium chloride in order to improve the electrode conductivity and its macroporosity, respectively. A factorial experimental design was used to evaluate the effect of the AC mass, NA, mass of sodium chloride used in the electrode preparation and also the cell potential, on the capacity of removing ions (R), QE and η. The variables that showed the greatest effect on the CDI process was the cell potential and the AC mass (that create different thickness for the electrode). In spite of increasing the electrode conductivity, the NA did not show any improvement on the electrosorption of the electrode. Afterwards, an individual analysis showed that the use of sodium chloride to increase electrode macroporisity improved the capacity of the electrode to remove ions but just for the thickest electrode. However, it was verified that the increase of the thickness did not implied in a linear increase of the ion removal capacity. This behavior may be attributed to the non-uniform distribution of the electric field on the porous film. Thusly, even the thicker electrode showing a better capacity of removing ions, a great part of its mass was not being used for electrosorption. Additionally, the increase of the thickness led to a decrease on desorption. Those results indicate that the electrode thickness must be optimized. Another strategy to improve the electrode wettability and capacitance was the deposition of silica and alumina. It was observed an improvement on the wettability of the electrode, however those electrodes voltammograms showed an increase on the resistivity and as result, besides not presenting any improvement on the capacity of electrosorption, there was still a reduction of the ion removal kinect. Finally, the last strategy used to improve the AC electrode was the addition of the conducting polymer polypyrrole aiming to improve the electrode capacity of removing ions through the pseudo capacitance effect. The addition of polypyrrole increased the total of ions removed from solution, however, in all the cases, the values of QE and η were worse than those observed for the AC electrode. Due to the polypyrrole characteristics, the drying temperature used to prepare the electrode was reduced from 130°C to 80°C and when this temperature was reduced, it was verified that this variable had a strong effect on improving the capacity of removing ions and the energy efficiency of the AC electrode. / Neste trabalho foi realizado o estudo de diferentes materiais de carbono disponíveis comercialmente e que poderiam ser utilizados como eletrodos para deionização capacitiva. Dentre eles estão o tecido de carvão ativado, espuma de carbono, feltro de carbono, fibra de carbono, véu de carbono e pó de carvão ativado (CA). Esses materiais foram caracterizados por microscopia eletrônica de varredura, resistividade superficial, molhabilidade e voltametria cíclica. O desempenho dos diferentes eletrodos em termos da eletrossorção de cloreto de sódio foi avaliado para diferentes potenciais de célula. O material que apresentou melhor capacidade de remoção de íons e ao mesmo tempo apresentando bons valores de eficiência de carga (QE) e consumo energético específico (η) foi o eletrodo preparado usando pó carvão ativado. Desta forma, este material foi selecionado para estudos posteriores em que diferentes estratégias de modificação deste eletrodo foram avaliadas para tentar otimizar suas características visando melhores resultados de eletrossorção. Dentre essas estratégias, adicionou-se negro de acetileno e cloreto de sódio na preparação do eletrodo visando melhorar sua condutividade e aumentar sua macroporosidade, respectivamente. Um planejamento fatorial de experimentos foi utilizado a fim de verificar o efeito da massa de CA, negro de acetileno e cloreto de sódio usadas na preparação do eletrodo e também do potencial de célula sobre as variáveis dependentes remoção total de íons (R), QE e η. Observou-se nesta etapa que as variáveis que tiveram o maior efeito no processo de deionização capacitiva foram o potencial de célula e a massa do eletrodo (que por sua vez determina a sua espessura). Constatou-se que a adição de negro de acetileno ao eletrodo, apesar de aumentar a condutividade (como já era esperado), causava uma diminuição da área superficial específica através do entupimento de poros e como consequência, não verificou-se melhoria da eletrossorção, algo que seria esperado pela melhoria da condutividade do eletrodo. Posteriormente, foi realizada uma análise individual do efeito da macroporosidade e da espessura de eletrodo. Os resultados mostraram que o aumento da macroporosidade decorrente do uso de NaCl durante a preparação do eletrodo levou a um aumento da capacidade de eletrossorção somente para o eletrodo mais espesso, porém, na análise da influência do aumento da espessura do eletrodo, verificou-se que não houve um aumento linear na quantidade de íons removidos da solução em função do aumento da espessura, o que pode ser atribuído à nãouniformidade do campo elétrico no filme poroso. Desta forma, apesar do filme mais espesso ter capacidade de remover mais íons, uma grande parte da massa de CA utilizada estava inativa. Adicionalmente, o aumento da espessura levou a uma diminuição da cinética de dessorção. Estes resultados indicam que a espessura do eletrodo deve ser otimizada. Uma outra estratégia analisada para tentar melhorar a molhabilidade e a capacidade de eletrossorção do eletrodo de CA foi a deposição de sílica e alumina. Observouse que houve realmente uma melhoria da molhabilidade, mas por outro lado, os voltamogramas destes eletrodos mostraram um aumento de sua resistividade e como consequência, além de não se verificar uma melhoria na capacidade de eletrossorção, houve ainda uma piora da cinética do processo. Finalmente, a última estratégia utilizada para melhorar o eletrodo de CA foi a adição do polímero condutor polipirrol visando melhorar sua capacidade de remoção de íons através da introdução de pseudocapacitância. A adição de polipirrol causou um leve aumento no total de íons removidos da solução, porém, em todos os casos, os valores de QE e η foram piores do aqueles observados para o eletrodo de CA. Devido às característicos do polipirrol, a temperatura de secagem do eletrodo teve que ser reduzida de 130°C para 80°C e quando se reduziu esta temperatura verificou-se que esta variável desempenhava um papel importante na melhoria da capacidade de remoção de íons e da eficiência energética do eletrodo de CA.

No description available.

Capacitive deionization based on electrosorption has become a viable process for brackish water desalination. In this study, activated biochar was employed as low-cost and alternative carbon-based electrodes substituting activated carbon with comparable adsorption capacity. Effects of different activation temperatures of the biochar were studied by physical characterization (i.e. SEM, TEM, elemental analysis, and Raman spectroscopy) and electrochemical characterization (i.e. cyclic voltammetry and galvanostatic charge/discharge measurement) based on the electrical double layer theory. The highest specific capacitance obtained (118.50 F g-1) was from activated biochar electrode treated at 800°C. The removal capacity was investigated by AAS and conductivity measurements. Several limitations associated with them were identified to improve the measurements. The removal capacity of biochar electrode is ~ 2 mg g-1 with significant results for both one-sided and two-sided t-test. In summary, activated biochar can be used as a cheap-alternative electrode material for desalination based on capacitive deionization.

Clean, drinkable water is nowadays taken for granted in most developed coun-tries. However, over two billion people in the world do not have access to drink-ing water. In an attempt to combat this, capacitive deionization (CDI) hasgained increased attention in recent years. CDI is an emergent method of de-salination through separation of ionic species in aqueous solutions. The perfor-mance of CDI is dependent on materials used and how the device is constructed.This paper investigates key metrics relating the efficiency and applicability oftwo different CDI materials, activated carbon (Zorflex FM10 Chemivron) andCobalt Prussian Blue Analogue (referred to as the active material), in regardsto the electrodes used. These metrics include energy consumption, energy re-covery and Faradaic efficiency. The results were gathered from building a circuitwith the CDI cell as the capacitor and switching the polarity of the cell when adefined threshold of the voltage (1.5 V) was reached. The energy consumptionof the activated carbon (0.450 kWh/m3) was found to be less than that of theactive material (1.45 kWh/m3). The energy recovery was found to be roughlyequal for both materials, 80.6 % for the activated carbon and 79.5 % for theactive material. Finally, the activated carbon had a Faradaic efficiency of 0.75while the active material had 1.8.