Attractive forces in microporous carbon electrodes for capacitive deionization

Biesheuvel, P.M.; Porada, S.; Levi, Mikhael D.; Bazant, Martin Z.

doi:10.1007/s10008-014-2383-5

Cited by 264 publications

(253 citation statements)

References 94 publications

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Section: Saturation Of the Potential Rise At High Base Potentialmentioning

confidence: 86%

“…In particular, an accurate modeling of the experimental results, which was developed for CDI [40], predicts also in this case two plateaus at ±80 mV for the potential rise. It is worth noting that there is a thermodynamical relation [18] between the desalination charge efficiency of the above-mentioned models [40] and the potential rise of CAPMIX, that holds in equilibrium conditions. The apparent discrepancy that we observe between the capacitive deionization experiments and our CAPMIX potential rises should lead to the conclusion that the latter are not obtained in equilibrium conditions; indeed, they are measured on time scales that are shorter than that of the CDI experiments.…”

Section: Saturation Of the Potential Rise At High Base Potentialmentioning

confidence: 86%

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Modification of the surface of activated carbon electrodes for capacitive mixing energy extraction from salinity differences

Marino

Misuri

Jiménez

et al. 2014

Journal of Colloid and Interface Science

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The "capacitive mixing" (CAPMIX) is one of the techniques aimed at the extraction of energy from the salinity difference between sea and rivers. It is based on the rise of the voltage between two electrodes, taking place when the salt concentration of the solution in which they are dipped is changed. We study the rise of the potential of activated carbon electrodes in NaCl solutions, as a function of their charging state. We evaluate the effect of the modification of the materials obtained by adsorption of charged molecules. We observe a displacement of the potential at which the potential rise vanishes, as predicted by the electric double layer theories. Moreover, we observe a saturation of the potential rise at high charging states, to a value that is nearly independent of the analyzed material. This saturation represents the most relevant element that determines the performances of the CAPMIX cell under study; we attribute it to a kinetic effect.

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Section: Saturation Of the Potential Rise At High Base Potentialmentioning

confidence: 86%

Section: Saturation Of the Potential Rise At High Base Potentialmentioning

confidence: 86%

Modification of the surface of activated carbon electrodes for capacitive mixing energy extraction from salinity differences

Marino

Misuri

Jiménez

et al. 2014

Journal of Colloid and Interface Science

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“…Therefore, the electrosorption capacity is determined by the volume (porosity) of the micropores and the energy barrier. The microporosity-based electrosorption theory is critical in analyzing energy consumption during CDI.z E-mail: kkarthikeyan@wisc.edu Although significant progress has been made recently in the development of diverse electrode materials, 13,[19][20][21][22][23][24][25][26][27] theoretical models, [16][17][18] water treatment and desalination devices, 28-30 only very few studies address the issue of energy consumption during CDI. The role of electrode materials in electrosorption and energy consumption is not completely understood and, more importantly, the impact of operational conditions on energy consumption has not been rigorously evaluated when nanoscale porous electrode is applied.…”

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confidence: 99%

Energy Consumption and Recovery in Capacitive Deionization Using Nanoporous Activated Carbon Electrodes

Han

Karthikeyan

Gregory

2015

J. Electrochem. Soc.

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Capacitive deionization (CDI) is an emerging desalination technology which utilizes porous electrodes to remove ions in water by electrosorption. Similar to electric capacitors, energy is stored and released during charging and discharging cycles, respectively. In this study, a nanoporous activated carbon coupled flow-through CDI device was used to evaluate energy consumption and recovery under various operational conditions by charging and discharging the cell at a constant current, respectively. Results indicated that the charging/discharging current, salt concentration and water flow rate were major factors impacting electrosorption and energy consumption, by changing the structure of the electrical double layer (EDL) and how ion transport occurs between the interface and bulk solution. A porosity-based EDL theory was applied to explain the experimental observations. Between 30 and 45% of the energy consumed during charging could be recovered depending on operational conditions, although thermodynamically more than 98% of the total energy should be recoverable. Results indicated that overpotential and faradaic reactions induced irreversible energy are the major reasons for gaps in observed energy losses. Energy consumption for reducing the salinity of brackish water from 32.7 to 5.5 mM by our device could be as low as 0.85 kWh/m 3 under most optimized conditions (dependent on materials used and cell configuration). The energy consumption can be dramatically reduced by employing more electron-conductive and Faradaic-resistant electrode materials. Increasing demand for freshwater is driving the need for energyefficient and cost-effective technologies to generate potable water from unconventional sources such as brackish water.1 Due to its simplicity and reliability, capacitive deionization (CDI) has attracted a growing interest for water desalination.1-7 Capacitive deionization utilizes highly porous electrodes to remove charged ions in water by electrosorption (Figure 1). During charging, an electric voltage is applied and ions are driven to oppositely charged electrodes by electrostatic force and entrapped at the electrode-water interface by the formation of an electric double layer (EDL). After removing the ions, the electric voltage is removed or reversed to discharge and regenerate the electrodes. Ions return to solution and the concentrated brine is discarded. Desalination is realized by means of consecutive charging/discharging cycles to separate influent water into freshwater and brine (concentrate) streams.Energy consumption is a major factor driving the synthesis of new CDI electrode materials. Energy-efficient CDI devices are required for up-scaling the process and for broader adoption of this technology for potable or agricultural water treatment. An important feature of CDI is that part of the energy consumed during charging can be recovered during discharging, a process similar to charge/discharge in electric capacitors.6,8 CDI could become more cost competitive compared with well-established desa...

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“…The attractive excess chemical potential μ for each ion in the micropores has been shown to be inversely proportional to the micropore total ion concentration. 27 In addition, the accumulated charge in the capacitive mixing operation cycle is believed to be constant and, therefore, for the differentiation of ϕ with respect to log[N a + ] macro , the terms μ and ϕ st can be excluded and the derivative reaches its maximal value as follows:…”

Section: Resultsmentioning

confidence: 99%

Anion-Exclusion Carbon Electrodes for Energy Storage and Conversion by Capacitive Mixing

Shapira

Cohen

Avraham

et al. 2017

J. Electrochem. Soc.

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Capacitive mixing is a newly emerging technique for the production of renewable energy from the controlled mixing of river water and seawater. Energy extraction is provided by the potential rise in electrodes held in a fixed charge, as a response to the concentration change. Therefore, electrodes that exhibit high potential variation as a response to concentration change (negative rise for the cation-capturing electrode and vice versa) are highly desirable. In this work, electrodes that can accommodate mostly cations within their porous structure are discussed. In accordance to the modified Donnan (mD) model of the electrical double layer, it is expected that such electrodes will display the highest potential change as a response to concentration change (while being held with a fixed charge). Using appropriate selective activated carbon electrodes, high potential rise, around 50 mV, was observed as a response to concentration change, when the concentration of NaCl solutions was changed from 1M to 10 −1 M and from 10 −1 M to 10 −2 M. Such a capability of potential rise of selective electrodes can serve as a good basis for energy extraction by capacitive mixing. The energy that dissipates due to the mixing of two solutions with different salt concentrations, such as seawater and river water, can be, in fact, partially harvested by controlled mixing. The upper limit of energy that can be obtained from mixing two ideal solutions with different concentrations is given by the Gibbs free energy of mixing. 1For example, the maximum energy that can be obtained from mixing 1 Liter of seawater and 1 Liter of river water is about 2 kJ. There are several methods for energy extraction by controlled mixing of seawater and river water, including pressure-retarded osmosis (PRO), 2 reversed electro-dialysis (RED) 3,4 and vapor-pressure difference utilization.5 Recently, energy extraction from salinity difference by swelling and shrinking of hydrogels has been suggested. 6 However, to the best of our knowledge, these methods have to be proven as commercially viable.Capacitive mixing 7-15 (CAPMIX), first proposed by Brogioly, 16 is a membrane-free technique. In general, the energy extraction is based on potential differences developed as a result of double-layer (i.e., electrostatic) interactions between high-surface-area electrodes through which solutions of different NaCl concentrations flow. In principle, the exchange between two bulk solutions with different salinities that are in contact with two charged high-surface-area electrodes leads to changes in their capacitance and, consequently, in the potential of the electrochemical cell utilizing them:where V [V] is the electrodes-potential difference [i.e., the sum, in absolute values, of the electrical double layer (EDL)-related potentials of both the cation-and the anion-capturing electrodes], Q [C] is the total charge of the electrodes (equal but with opposite signs) and C [F] is the change in capacitance resulting from the mixing. A decrease in cell potential (for a cell with...

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Attractive forces in microporous carbon electrodes for capacitive deionization

Cited by 264 publications

References 94 publications

Modification of the surface of activated carbon electrodes for capacitive mixing energy extraction from salinity differences

Modification of the surface of activated carbon electrodes for capacitive mixing energy extraction from salinity differences

Energy Consumption and Recovery in Capacitive Deionization Using Nanoporous Activated Carbon Electrodes

Anion-Exclusion Carbon Electrodes for Energy Storage and Conversion by Capacitive Mixing

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