CA2444390C

CA2444390C - Charge barrier flow-through capacitor

Info

Publication number: CA2444390C
Application number: CA002444390A
Authority: CA
Inventors: Marc D. Andelman
Original assignee: Biosource Inc USA
Current assignee: Voltea Ltd
Priority date: 2001-04-18
Filing date: 2001-04-18
Publication date: 2007-07-03
Anticipated expiration: 2021-04-18
Also published as: WO2002086195A1; CN100489160C; IL158319A0; CN100518910C; IL158319A; CA2444390A1; CN1505700A; CN1788831A

Abstract

Flow-through capacitors (15) are provided with one or more charge barrier layers (3). Ions trapped in the pore volume of flow-through capacitors (15) cause inefficiencies as these ions are expelled during the charge cycle into the purification path. A charge barrier layer (3) holds these pore volume ions to one side of a desired flow stream, thereby increasing the efficiency with which the flow-through capacitor (15) purifies or concentrates ions.

Description

CHARGE BARRIER FLOW-THROUGH CAPACITOR
Field of the Invention The invention relates to a flow-through capacitor for deionizing or decontaminating a fluid.

Background of the Invention The invention relates to flow-through capacitors for deionizing solutions, e.g., aqueous solutions, with improved operation at concentrated solutions, including such applications as low energy desalination of seawater.

Technologies to deionize water include electrodeionization and flow-through capacitors. The term electrodeionization, including electrodialysis and continuous electrodeionization, has traditionally referred to a process or device that uses electrodes to transform electronic current to ionic current by oxidation-reduction reactions in anolyte and catholyte compartments located at the anodes and cathodes. Traditionally, the ionic current has been used for deionization in ion-depleting compartments, and neither the anolyte chambers, the catholyte chambers nor the oxidation-reduction products have participated in the deionization process. In order to avoid contamination and to allow multiple depletion compartments between electrodes, the ion-concentrating and ion-depleting compartments were generally separated from the anolyte and catholyte compartments. To minimize oxidation-reduction product formation at the electrodes, electrodeionization devices typically comprised multiple layers of ion-concentrating and ion-depleting compartments, bracketed between pairs of end electrodes.

One disadvantage of prior art systems is the energy loss resulting from using multiple compartment layers la between electrodes, thereby creating an electrical resistance. This is generally true of prior art electrodeionization devices and is one characteristic that differentiates them from flow-through capacitors.
Flow-through capacitors differ in a number of other ways from electrodeionization as well. One difference is that flow-through capacitors purify water without oxidation-reduction reactions. The electrodes electrostatically adsorb and desorb contaminants, so that the electrode (anode and cathode) compartments participate directly in deionization and are located within one or both of the ion-depleting and ion-concentrating compartments. The anolyte and catholyte are partly or largely contained within a porous electrode. Electronic current is generally not transmuted by an oxidation-reduction reaction. Instead, charge is transferred by electrostatic adsorption.
However, flow-through capacitors of the prior art become energy inefficient and impractical at high ion or contaminant concentrations. The reason for this is due to the pore volume in the electrodes. Dissolved counterion salts present in the pore volume adsorb onto the electrodes, whereas, pore volume coion salts are expelled from the electrodes. This has a doubly deleterious effect. Counterions occupy capacitance within the electrode. This amount of charge-holding capacitance is therefore unavailable for purification of ions from the feed water purification stream. Coions expelled from the electrodes enter the feed water purification stream and contaminate it with additional ions. This effect becomes worse with increased concentration. The flow-through capacitor is typically regenerated into liquid of the feed concentration. When purifying a concentrated liquid, ions are passively brought over into the pores prior to application of a voltage or electric current. Once voltage is applied, these ions are simultaneously adsorbed and expelled during the purification process. Purification can only

2 occur when an excess of feed ions, over and above the pore volume ions, are adsorbed by the electrodes. This puts an upper practical limit on the economy of the flow-through capacitor, typically, in the range of approximately 2500 to 6000 parts per million (ppm). The flow-through capacitor of the prior art requires both slower flow rates and higher energy usage. Beyond 6000 ppm, energy usage required is typically more than 1 joule per coulomb of dissolved ions, making prior art flow-through capacitors too energy intensive to be practical. Deionizing seawater, which has ion concentrations of approximately 35,000 ppm, becomes impractical to deionize due to energy inefficiency caused by these pore volume losses. Pore volume losses occur at all concentrations but get worse at higher concentrations.

Another way to describe pore volume losses is that they cause diminished ionic efficiency. Ionic efficiency is defined as the ratio of coulombs of ions purified to coulombs of electrons utilized.

Thus, a need exists to improve the ionic and energy efficiency of flow-through capacitors, particularly when treating solutions with ion concentrations in excess of 2500 ppm. A further need exists for a flow-through capacitor to purify solutions with an energy usage of less than 1 joule per coulomb of purified ionic charge. Ionic efficiency is the coulombs of ionic charge purified per coulombs of electrons used, and should be 50% or more.
Sturanary of the Invention According to the present invention, there is provided a flow-through capacitor comprising: (a) a plurality of electrodes comprising an electrode material having a surface area for electrostatic adsorption of feed

3 ions; (b) a pore structure in one or more of said plurality of electrodes, whereby said electrode is a porous electrode having a pore volume; and (c) a first charge barrier material different from said electrode material, located adjacent to said electrode.

Also according to the present invention, there is provided a flow-through capacitor comprising: (a) a plurality of electrodes; and (b) a first charge barrier located between two of said plurality of electrodes, wherein the charge barrier is an electrically-conductive membrane with a low resistance-capacitance (RC) time constant material, and wherein the capacitance of the charge barrier is less than 20 farads/gram.

According to the present invention, there is further provided a flow-through capacitor comprising: (a) a plurality of electrodes; and (b) a first charge barrier located between two of said plurality of electrodes, wherein the charge barrier is electrically connected to a first power supply, and at least one of the plurality of electrodes is electrically connected to a second power supply.

According to the present invention, there is further provided a flow-through capacitor comprising: (a) a plurality of electrodes; and (b) a first charge barrier located between two of said plurality of electrodes, wherein the flow-through capacitor comprises a series resistance of less than 50 ohm cm2.

According to the present invention, there is further provided a flow-through capacitor comprising: (a) a plurality of electrodes; and (b) a first charge barrier located between two of said plurality of electrodes, wherein

4 the flow-through capacitor has a series resistance to leakage ratio of greater than 100.

According to the present invention, there is further provided a flow-through capacitor comprising: (a) a plurality of electrodes; and (b) a first charge barrier located between two of said plurality of electrodes, wherein the electrodes within a cell of the flow-through capacitor are ionically insulated and connected electrically in series.

According to the present invention, there is further provided a flow-through capacitor having an ionic efficiency, said flow-through capacitor comprising: (a) a plurality of electrodes comprising an electrode material having a surface area for electrostatic adsorption of ions;

(b) a pore volume in one or more of said plurality of electrodes comprising pore volume loss; and (c) means for enhancing the ionic efficiency of said flow-through capacitor by compensating for said pore volume loss.

According to the present invention, there is further provided a flow-through capacitor comprising: (a) a plurality of electrodes comprising an electrode material having a surface area for electrostatic adsorption of ions;
(b) a pore volume in one or more of said plurality of electrodes, whereby said pore volume adsorbs and expels pore volume ions; and (c) means for reducing said adsorption and expulsion of pore volume ions.

According to the present invention, there is further provided a flow-through capacitor comprising: (a) a plurality of electrodes comprising an electrode material having a surface area for electrostatic adsorption of feed ions; (b) a pore volume in one or more of said plurality of

5 electrodes, whereby said pore volume contains pore ions; and c) means for providing an excess of feed ions to pore volume ions.

It has been discovered that a charge barrier placed adjacent to an electrode of a flow-through capacitor can compensate for the pore volume losses caused by adsorption and expulsion of pore volume ions.

Using the charge barrier flow-through capacitor of the invention, purification of water, including a seawater concentrated solution, e.g., 35,000 ppm NaCl, has been observed at an energy level of less than 1 joules per coulomb ions purified, for example, 0.5 joules per coulomb ions purified, with an ionic efficiency of over 90%.

As used herein, the term "charge barrier" refers to a layer of material which is permeable or semipermeable and is capable of holding an electric charge. Pore ions are retained, or trapped, on the side of the charge barrier towards which the like-charged ion, or coion, migrates.

This charge barrier material may be a laminate which has a conductive low resistance-capacitance (RC) time constant, an electrode material, or may be a permselective, i.e., semipermeable, membrane, for example, a cation or anion permselective material, such as a cation exchange or anion exchange membrane. The charge barrier may have a single polarity, two polarities, or may be bipolar. Generally, a charge barrier functions by forming a concentrated layer of ions. The effect of forming a concentrated layer of ions is what balances out, or compensates for, the losses ordinarily associated with pore volume ions. This effect allows a large increase in ionic efficiency, which in turn allows energy efficient purification of concentrated fluids.

6 Description of the Drawings Fig. 1 is a generalized, schematic view of a flow-through capacitor of an embodiment of the invention, illustrating the placement of charge barrier layers, electrodes, an optional current collector, and a flow channel spacer.

Fig. 2 is a generalized, schematic view of a flow-through capacitor of an embodiment of the invention, containing charge barriers of the same polarity as the adjacent or underlying electrode, together with a representation of the ions being purified or concentrated, and displaying the direction of ion migration in the electric field.

Fig. 3 represents the flow-through capacitor of Fig. 2 in the discharge cycle, illustrating the release of concentrated ions into a flow channel located between the charge barrier layers.

Fig. 4 is a generalized, schematic view of a flow-through capacitor of an embodiment of the invention, containing charge barrier layers of opposite polarity to that of the adjacent or underlying electrodes, together with representations of ions being purified or concentrated, and displaying the direction of ionic migration in the electric field.

Fig. 5 is a generalized view of the discharge cycle of the flow-through capacitor of Fig. 4, which illustrates how a centrally-located flow channel is purified by virtue of ionic migration through the charge barrier layers towards the electrodes.

6a Fig. 6 is a generalized, schematic view of a stacked-layer, flow-through capacitor of an embodiment of the invention.

Fig. 7 is a generally schematic view of a dual-flow channel, flow-through capacitor of an embodiment of the invention, with a sealing agent to isolate simultaneously purified and concentrated fluid streams.

Fig. 8A is a generalized, top schematic view of the flow-through capacitor of an embodiment of the invention with transverse flow channels;

Fig. 8B is a front, cross-sectional, generalized schematic view of the flow-through capacitor of an embodiment of the invention with transverse flow channels;

Fig. 8C is a top sectional view of the flow-through capacitor of an embodiment of the invention showing a charge barrier and a flow spacer;

Fig. 8D is a side sectional, generalized schematic view of the flow-through capacitor of an embodiment of the invention with transverse flow channels;

Fig. 9 shows a graph of the data generated from the flow-through capacitor of an embodiment of the invention when operated in cycles and is represented by charging and discharging in polarities according to the sequence depicted by Figs. 2, 3, 4, and 5;

Fig. 10 is a generalized schematic diagram of the flow-through capacitor of an embodiment of the invention showing the attachment of conductive charge barriers to a separate DC power supply; and 6b Fig. 11 is a schematic view of a flow-through capacitor system of an embodiment of the invention.
Detailed Description The charge barrier flow-through capacitor of the invention, the anolyte and catholyte chambers may be integral with ion-depletion or concentrating chambers, or they may be separate chambers. The electrodes in flow-through capacitors are spaced apart or are separated by a spacer. The spacer may be any ion-permeable, electronically-nonconductive material, including membranes and porous and nonporous materials (see U.S. Patent No. 5,748,437, issued May 5, 1998). The spacer may define a flow channel (see U.S. Patent No. 5,547,581, issued August 20, 1996), or may be of a double-layer spacer material with the flow channel between the layers (as in U.S. Patent No. 5,748,437). Purification and concentration may take place in either the spacers, the electrodes, or both, depending upon the geometry of the flow channel. For example, in a flow-through capacitor utilizing a double-space layer as described above, the ion-depleting, purification, or concentration compartment may be located between the spacer layers. U.S. Patent No. 5,192,432, issued March 9, 1993, describes use of a porous electrode material. In this case, ion depletion or ion concentration would occur directly in the electrodes themselves, in order to affect purification or concentration of a fluid. In both cases, however, the electrodes are directly involved in the purification process. The electrodes are used to adsorb or release a charge, and generally, do not transfer electronic to ionic current by oxidation-reduction reactions common to electrodeionization technologies. In either case, no more than a single, 6c separately-compartmentalized, concentrating or ion-depleting layer is required between each set of electrodes.

Therefore, one advantage the flow-through capacitor has over deionization is that less 6d energy is wasted by oxidation-reduction reactions and there is less internal resistance.
In the flow-through capacitor of the present invention, the charge barrier may have just one layer or the charge barrier may have two or more layers. Ion selective membranes may also be used to select for particular species of ions of interest. Where the charge barrier is a permselective membrane, it may be any membrane, e.g., a nonwoven, a woven, or a semipermeable sheet material. Examples of materials for use as charge barriers are available commercially, e.g., Raipore 1010 and 1030, Tokuyama Soda Neosepta CM-1 and AM-1,(NEOSEPTA is a registered trademark of Tokuyama Corporation of Mikage-cho Tokuyama City, Yamaguchi Prefecture Japan) and Selemnion brand anion and cation exchange membranes. These membranes may be supported by a web or may be manufactured, cast, or attached integrally to the electrode material. Bipolar membranes may also be used.
Where the charge barrier material is a low resistance-capacitance (RC) time constant material, this material may be an ionically-permeable, conductive, porous, or nonporous sheet material, for example, conductive membranes, conductive polymer sheet materials, carbon fibrous materials, either in a nonwoven or woven, e.g., woven cloth form, activated carbon cloths, nanotubes, carbon or graphite tissue, aerogel, metal mesh or fibers, perforated graphite or metal foil, activated carbon, and carbon black sheet materials, including carbons held together with a polytetrafluoroethylene (PTFE) binder. These conductive materials may also be derivatized with the same ionically charged groups common to anion and cation exchange membranes.
An example of these low RC time constant, conductive charge barrier material is a low surface area, low capacitance, carbon black bound with PTFE. For example, materials with a capacitance of less than 20 farads/gram or 30 farads/cm2 (as measured in concentrated sulfuric

7 acid) may be used. A non-electrically conductive, ion-permeable spacer may be placed between the electrode and the charge barrier material in order to facilitate formation of a reverse electric field. In this case, the charge barrier material may have integral leads, or, may have its own current ion-permeable collector with leads. These leads may be hooked up in parallel with the electrode leads or may be powered by a separate power supply. Optionally, the separate power supply may be set to a voltage that is higher than the power supply connected to the electrodes.

In this way, the charge barrier materials contain a higher voltage than the electrode materials. One advantage of a discrete power supply is that the charge barrier materials may remain permanently charged, or may be charged to a higher voltage than the electrode materials, thereby enhancing the reverse electric field. It is this reverse electric field which forms a charge barrier to pore volume ions, thereby increasing ionic efficiency of the flow-through capacitor. Alternatively, the same power supply may be used for both the electrodes and the charge barrier. Optionally, a resistor may be added to the electrode lead circuits.

Any electrode of utility in prior art flow-through capacitors may be used as the underlying electrode material.
For example, small particle size carbons have lower series resistance. Carbon particles of less than 10 microns, for example, 1 micron or less, may be formed into an electrode sheet with PTFE or other binders and calendered or extruded into sheet electrodes of less than 0.02 inches thick with low series resistance, less than 40 ohm cm2, where cm2 is the spacer area.

8 The charge barrier material may preferably be combined with the electrode. In this way, the electrode itself offers structure and strength, so that a thin, weak charge barrier may be used. For example, a thin coating of a charge barrier ion exchange material may be applied directly onto the electrode. Alternatively, the charge barrier material may be directly infiltrated into the electrode, especially if the electrode is porous or provided with holes as in U.S. Patent No. 6,214,204. A preferred embodiment is to provide a carbon electrode with a secondary pore structure that is larger than the primary surface area pores. These large secondary pores may be coated with or infiltrated with an anion or cation exchange material.

Since the electrodes provide strength, the ion exchange groups on the charge barrier material may be supported on a hydrogel, for example polyacrylamide or polysaccharide material. Suitable ion exchange membrane formulations and ionic groups may include, for example, perfluorinated films, NAFIONETM, carboxylate or sulfonate polymers, perfluorinated sulfonic acid, a mixture of styrene and divinylbenzene, olefins and polyolefins, or any polymer derivatized with various ionic groups, including sulfonyl halide, amine, diamine, aminated polysulfone, carboxyl, sulfate, nitrate, phosphate, chelating agent, ethylenediaminetetraacetic acid (EDTA), cyanide, imine, polyethyleneimine, amide, polysulfone, or any other fixed ionic group may be used as the charge barrier material. See also, Thomas A. Davis et al, A First Course In Ion Permeable Membranes (The Electrochemical Consultancy, Hants, England, 1997).

A particularly preferred embodiment of the present invention is to combine the charge barrier within the structure of the electrode. Any electrode material that has

9 through holes, or which has a porous structure, may be used.
The porous structure may include a combination of pore sizes, for example, macropores, micron-sized pores or larger, combined with meso or micro pores in order to improve conductivity of ions into the electrode and accessibility of the surface area. The charge barrier material may be infiltrated into this pore structure in order to form a combined electrode-charge barrier material that may be used as spaced-apart electrodes or with any flow spacer.

9a Fig. 1 shows a generalized drawing of a charge barrier flow-through capacitor, with electrode 2, charge barrier 3, spacer 4, and optionally, current collector 1.
An electrode 2 is prepared from a high capacitance material, preferably with a capacitance of over 1 farad per gram or 1 farad per cubic centimeter (as measured in concentrated sulfuric acid). The charge barrier 3 may be a permselective membrane of either polarity and either the same polarity as each other or an opposite polarity.
The charge barrier 3 may also be a bipolar membrane. The charge barrier 3 may also be prepared from an electrode material with a lower RC time constant than the underlying electrode 2, and either laminated during manufacture directly upon and integral to electrode 2, or simply laid together separately. For the best results, the electrode material should have an RC time constant that is at least twice as high as the RC time constant of the charge barrier 3. In order to improve performance of the charge barrier 3, the capacitance of the underlying electrode may be reduced or resistance of the underlying electrode 2 may be increased relative to the charge barrier 3 material. Ideally, the electrode 2 RC time constant may be manipulated by increasing capacitance more than by increasing resistance, in order to have a low series resistance, highly energy efficient capacitor.
So that the charge barrier 3 may have a lower RC time constant than the underlying electrode 2, either resistance or capacitance of the charge barrier 3 may be decreased relative to the electrode 2. However, changing either value will suffice to alter the RC time constant.
During charge of such a laminated electrode 2, with the lower RC time constant material facing outward to the flow channel spacer, the outer low RC time constant electrode 2 charges up first. This creates an inverse electric field localized within the electrode 2 of the opposite direction to the electric field between the anode and cathode electrodes 2. This inverse field holds pore volume ions trapped within the electrode 2.

In order to maintain charge neutrality, counterions migrate into the electrode 2 where they form a concentrated solution with the trapped coions, thereby increasing ionic efficiency. Spacer 4 may be prepared from any material which defines a flow channel, or it may be simply a space between the anode and cathode pairs of electrodes 2 that is ionically permeable and electron insulating, with flow channel 5 defined by the spacer 4, within the spacer 4, or in the layers between the spacer 4 and the electrode 2. This flow channel 5 may be formed by grooves or ribs embossed into either the spacer 4 or electrode 2. Alternatively, the spacer 4 may be an open netting, filter, particulate, or screen-printed material of any geometry that serves to space apart the electrode 2 layers and allow flow paths S. The spacer 4 may be a doubled-up layer of material with a flow path 5 between the layers. It is desirable that the flow spacer 4 be thin, e.g., under 0.01 inches thick.
Further, it is desirable that doubled-up charge permselective membranes or membranes and flow spacer combinations be thin, e.g., under 0.02 inches thick, and preferably, less than 0.01 inch thick. If the charge barrier 3 is a permselective membrane, the polarities may be the same, either negative or positive, or there may be one of each polarity, i.e., one negative and one positive. In order to limit series resistance, the electrodes 2 should also be thin, such as under 0.06 inch thick, for example, 0.02 inch thick or less. Spacing between layers should also be thin, such as under 0.06 inch, for example, 0.01 inches or less. It is important to limit leakage, because this bleeds off the charge responsible for maintaining a charge barrier.
Leakage resistance of over 100 ohm cm2 is preferred, such as over 1000 ohm cmZ, and series resistance of under 50 ohm cm2 is preferred, as measured by recording the instantaneous current upon application of 1 volt to a cell equilibrated with 0.1 M NaCl. The cm2 in the ohm cm 2 above refers to the electrode 2 facing area, which is the same as the spacer 4 area. The ratio of leakage resistance to series resistance should be in excess of 100, such as, for example, in excess of 300.

Electrode 2 materials may be selected for nonfouling characteristics. For example, activated carbon tends to absorb organics and many ions passively. Carbon blacks, which may be selected for use, show less tendency to adsorb passively a foulant that is causing a problem with activated carbon electrodes 2. Carbon black may also be derivatized with fluorine groups in order to make it less passively adsorptive. However, for treatment of polyaromatic hydrocarbons, trihalomethane, and other organics, the passive absorptive behavior may be selected for in electrode 2. These electrode 2 materials may be electrochemically destroyed once they are adsorbed passively. To facilitate passive adsorption, it may be advantageous to provide flow pores through the current collector 1 and electrode 2 so that nonionic species may be exposed to the electrodes 2 by convective flow there through. Charge barrier 3 material may also be a permselective membrane, such as a cation, anion, or ion-specific membrane material.

Flow-through capacitors of the invention may be electrically connected in series as separate, electrically-insulated cells. These cells may be built within the same flat stacked layer or within a spirally-wound layer, flow-through capacitor. For example, individual cells containing multiple electrode pairs and other layers may be provided with an ionically-insulating component on the end of the electrode 2 stack. This ionically-insulating component may be electrically conductive so as to form an electrical series connection from one capacitive layer to the next, on opposing sides of this ionically-insulating layer. A number of cells may be rolled up in concentric spirals in order to form an electrical series, connected, flow-through capacitor with parallel fluid flow between the layers. A cell is any arrangement of layers that includes parallel pairs of 12a electrodes 2 with the same voltage. By stacking cells in series, the voltage is additive across the stack and is therefore increased in order to take advantage of less expensive, higher voltage, lower amperage power. For example, a 480 to 600 volt stack is ideal for use with power received directly from transmission lines, without the need for transformers to step down the voltage.
Fig. 2 represents a flow-through capacitor of the invention incorporating electrode 2 and charge barrier 3.
In this case, the charge barrier 3 either has a lower RC
time constant material than does electrode 2, or the charge barrier 3 is a permselective membrane of the same polarity as the adjacent electrode 2. Upon applying voltage, anions and cations are expelled from the anodes and cathodes, respectively. The ion movement is shown in Fig. 2 by the horizontal or bent arrows. These ions are repelled by and trapped, against charge barrier 3, which, if made from a low RC time constant material, has like polarities in the form of electric charges, or, in the case of a permselective membrane, has like polarities in the form of bound charges to that of the adjacent electrode 2. Ions from the flow channel 5, e.g., a central flow channel, migrate through the permselective membrane to balance the charge of these trapped ions. As a result, a concentrated solution of ions forms in the compartments surrounding electrode 2. Ions are depleted from the flow channel 5, allowing purified water to exit the flow channel 5. Counterions already present in the pore volume electrostatically adsorb on their respective electrodes 2. Although, this takes up an adsorption site, the concentrated solution formed by the trapped ions and by the charge-balancing ions make up for any loss of adsorption capacity.
In essence, the charge barrier 3 forms an inverse electric field which keeps coions inside the electrode 2.
In order to balance charge, counterions migrate into the electrode chamber where they form a concentrated solution, thereby, allowing a flow-through capacitor of improved ionic efficiency, e.g., such as 30 to 99%.
Fig. 3 represents the flow-through capacitor of Fig. 2 after it is discharged. Desorbed ions, together with ions that had concentrated in the electrodes 2, are discharged as a concentrate. A flow channel 5 may be formed from a spacer component (not shown). Spacer 4 may be formed from flow patterns directly embossed into the electrode 2 or from a separate flow channel 5 forming spacer 4 (shown in Fig. 1), such as, without limitation, an open netting material, screen-printed protrusions or ribs, or a nonwoven filter material.
Spacer 4 may be incorporated into one or more flow channels S. Flow channel 5 may exist as two types, i.e., between the charge barrier 3 layers or between the electrodes 2 and charge barriers 3, or both types of flow channels 5 may exist at the same time, with each type isolated from the other type. Two simultaneous types of flow channels 5 allow for simultaneous purification and concentration.
Fig. 4 represents a flow-through capacitor with a double permselective membrane adjacent to the electrode 2, whereby the adjacent membranes are of opposite polarity to the electrode 2. This may be accomplished electronically, merely by reversing the polarity of the capacitor in Fig. 2, for example, if operating the capacitor with alternating polarity charge cycles. In the capacitor of Fig. 4, ions concentrate into the space between the membranes during application of a voltage. Flow channels 5 may be incorporated centrally, or two-sided, or both side and central. A
concentrate is released from the central flow channel 5 during application of a voltage. If the side and central flow channels 5 are isolated by a gasket or sealing agent, then purified water may be retrieved from the side flow channels 5 at the same time that concentrated water is retrieved from the central flow channel 5.

In Fig. 5, purified water is collected from the central flow channel 5. This mechanism is due to the fact that the discharging capacitor of Fig. 4, with opposite- charged permselective membranes adjacent to the electrodes 2, is analogous to the charging capacitor of Fig. 2, with like-charged permselective electrodes 2 adjacent to the electrodes 2. When the capacitor of Fig. 4 is discharged, an interesting observation may be made, discharging counterions become trapped between the electrode 2 and the membranes, where they draw ions from the central channel into the side channels in order to maintain electroneutrality. If isolated side flow channels 5 were also provided, concentrated fluid may simultaneously be retrieved.
By incorporating a separate flow channel 5 shown in Figs. 2 and 4, the flow-through capacitor purifies and concentrates simultaneously. The flow-through capacitor of the invention may also have a central flow channel 5 composed of opposite or like-polarity permselective membranes. In the case of opposite-polarity membranes, the flow-through capacitor may be cycled with alternating-charge polarities. This situation is represented by the charge polarity shown in Fig. 4, followed by the discharge cycle shown in Fig. 5, followed by the polarity shown in Fig. 2 (the reverse of Fig. 4), followed by a discharge cycle. This situation creates two purification cycles in a row, followed by two concentration cycles in a row. Therefore, the flow-through capacitor of the invention may extend artificially the length of time the cell spends purifying. Depending upon the orientation of the membranes, purification or concentration can occur either upon a voltage rise or a voltage decrease. This differs markedly from flow-through capacitors of the prior art, which exhibit purification upon application of voltage of either polarity, as opposed to a change in voltage, for example, from negative towards zero.

Fig. 6 shows a stacked-layer capacitor of the invention. Material layers are arranged around a central flow hole 8. Material layers may be discs, squares, or polygons consisting of electrodes 2, charge barriers 3 materials (either lower RC time constant electrode 2 material or permselective membranes of the same or opposite polarities). Optionally, spacer 4 forms a central flow path 8. The spacer 4 may be prepared from, for example, any open netting, nonwoven cloth, loosely applied particle material, screen-printed protrusions, or ribs.
Fig. 7 shows a layer capacitor of the invention modified so as to allow multiple flow paths S. Charge barriers 3 are prepared with permselective membranes.
Permselective membrane 3 are sealed to electrode 2 in order to form two alternating flow paths. One flow path 24 flows between pairs of permselective membranes and out flow holes 26. The other flow path 25 flows between electrode 2 and one charge barrier 3, and then out through separate flow holes 27. This capacitor has two discrete outlets formed by the seals 9 but does not require inlets to be separately sealed. Optionally, the inlets may be separately sealed in order to allow backwashing. The seal 9 may be accomplished by using, for example, a washer, gasket, glue, or resin material that seals layers together. Optionally, the electrode 2 may have an enlarged central hole 10 so that a seal need only be made between two charge barriers 3, rather than between a charge barrier 3 and an electrode 2. The layers of charge barriers 3 and electrodes 2 may be repeated within a particular cell any number of times.
Typically, where the electrode 2 is an end electrode, it may be single-sided; whereas, where the electrode 2 is internal, it may be double-sided, such as on either side of a current collector 1 within the same cell.
Figs. 8A, 8B, 8C and 8D represent a flow-through capacitor of the invention comprised of parallel rectangular layers of electrodes 2, a spacer 4, e.g., a flow spacer to allow an electronically-insulated flow channel 5, located between an electrode 2 and a seal 9, e.g., a gasket seal to form two sets of isolated, manifolded flow channels S. The charge barrier 3 may function as, or together with, the seal 9 gasket. A flow slot 10 may be cut into one end of charge barrier 3.
This forms a manifold flow channel 23 between two layers of charge barrier 3. A spacer 4, shown in the inset, may be placed between the charge barrier layers 3 in order to form a flow channel S. Containment plate 11 is part of a cartridge holder that holds the entire flow-through capacitor cartridge formed of the layers of charge barrier 3. A second set of flow channels 5, transverse to the above flow channels 5, is formed between electrode 2 and charge barrier 3. These flow channels 5 may be formed from another set of spacers (not shown) located in this space or may be formed from a textured pattern embossed directly into either the electrode 2 or charge barrier 3. A flow channel 5 may be formed from a netting, a ribbed particulate, a microprotrusion, or a diamond-shaped pattern, e.g., a protruding or embossed pattern to form a flow channel 5.
Any of the layers may contain a flow channel 5 or may be textured, or have openings, pores, or spacers to form a flow channel 5. The flow pattern may, for example, consist of 0.001 inch deep grooves in a pattern of 0.005 inch diamonds embossed in a 0.01 inch thick electrode 2.
These transverse flow channels 5 are likewise manifolded together into common inlets and outlets. In this way, simultaneously-concentrated and purified fluid streams may be fed into or collected from the flow-through capacitor.
Fig. 9 shows a graph of the data obtained from a capacitor charged in the sequence demonstrated by charging as shown in Fig. 2, discharging as shown in Fig. 3, with the polarity of electrode 2 set so as to charge as shown in Fig. 4, and followed by discharging as in Fig. 5. Note how in this case, purification occurs upon a voltage rise, and concentration occurs upon a voltage decrease.
Fig. 10 represents an arrangement of layers of charge barriers 3 in the flow-through capacitor of the invention where the charge barrier 3 is a conductive material having a lower RC time constant than the electrode 2. The ratio of RC time constants of charge barrier 3 to electrode 2 should be more than a factor of two, and preferably, more than 4, such as, for example,

10.
Electrode 2 is connected by lead 12 to DC power source 13. The lead 12 may be integral with the electrode 2 or may be attached to a separate current collector layer (not shown), in which case the electrode 2 may be on both sides of the current collector. A spacer 4, such as an ionically-conductive, electrically-insulating spacer or a flow spacer separates the electrode 2 from the conductive, low RC time constant charge barrier 3. A separate power source 14 connects through its lead 12 to the charge barrier 3 in order to charge the charge barrier 3 to a higher, varying, or constant voltage than the underlying electrode 2. By "underlying" is meant in the direction of migration of cation 6 and anion 7. The anion 7 is held inside the chamber containing left, negative electrode 2 and spacer 4. This causes a cation 6 to migrate through the charge barrier layer 3, where it forms a concentrated solution in conjunction with anion 7. The opposite occurs on the other side of the flow-through capacitor.
Fig. 11 represents a stack of flow-through capacitors 15 with separate purification and concentration streams. Flow-through capacitors 15 are fluidly and electrically connected with leads 12 in series. The DC power source 13 provides the voltage and selected constant or variable current to the capacitor 15 stack. The controller, logic, and switching instrument 20 provides alternating-polarity charge cycles and discharge cycles. Conductivity controller 22 monitors the outlet fluid concentration of purification stream 18 to provide data with which to operate logic instrument 20, and valve component 16, which switch fluid streams in order to separate waste stream 17 and purification stream 18. Optionally, the hold-up tank 21 regulates the flow in case purification stream 18 is variable or intermittent. Optionally, a component 19 may be placed upstream of the capacitors 15 to pretreat the water.
A component 19, may be any technology known to treat water, for example, a component for reverse osmosis, micro or ultra filtration, carbon filtration, flocculation, electrowinning, or addition of chemicals. For example, it may be desirable to add chemicals that will presterilize the water, which chemicals may be further reduced or oxidized to a salt form by further chemical addition, then removed later in their salt form from the flow-through capacitor 15. A
pretreatment component 19 may also be used for a post treatment, by placing it downstream of the flow-through capacitor in the outlet purification stream 18.

The flow-through capacitors of the invention may be utilized in any system configuration common to ion exchange, electrodialysis, or reverse osmosis, or flow-through capacitors, including bleed and feed, batch, or continuous processes.

Examples Example 1 The flow-through capacitor of Fig. 10 is prepared using electrodes composed of 95% carbon black and 5% of a polymer PTFE or similar polymer. Charge barriers are composed of permselective membranes. In the capacitor of Fig. 10, a cation exchange membrane, such as RaiporeTM 1010 membrane with fixed benzyl sulfonic acid groups, is placed touching and adjacent to the negative electrode. An anion exchange membrane, in this case, a RaiporeTM 1030 membrane with fixed phenyl tetramethyl ammonium groups, is placed touching and adjacent to the positive electrode. A 0.003 inch thick filtration netting is placed between the two oppositely-charged permselective membranes and to form the flow path. The capacitor is charged at constant current, up to a voltage limit of 1 volt. Seawater flowing between the membranes is purified to 12%. In order to reach a purity of 99%, several capacitors are used in series or stages with series flow to reduce the salinity to 6000 ppm. An additional flow-through capacitor, e.g., a reverse osmosis series stage may be used to further reduce the remaining salinity to 250 ppm.
Example 2 The flow-through capacitor of Example 1 is used at a flow rate of less than 1 ml/minute/gram of carbon, for example, 0.1 ml/minute/gram of carbon, to achieve greater than 90% purification of a 35,000 ppm salt solution.
Example 3 The flow-through capacitor of Example 1 is coupled through an inductor in order to recover energy during discharge. This energy is used to charge a second capacitor during its purification cycle. Maximum charging voltage of both capacitors is kept below 0.7 volts, in order to minimize energy usage. Capacitors may be charged either at constant voltage, constant current, or at constantly increasing voltage, or constantly increasing current.
Optionally, capacitors may be charged in series in order to increase the voltage for maximum energy recovery and power supply efficiency.

Example 4 The flow-through capacitor of Fig. il is made by using activated carbon black as the electrodes. A low RC
time constant material, such as carbon fibers, nanotube mesh, or low capacitance activated carbon cloth aerogel is used as a charge barrier material. Water with 5000 ppm minerals and salts is passed through this device at a flow rate of less than 20 ml/minute per gram of carbon, with the flow rate adjusted downwards in order to achieve 95%
purification. The flow rate may be further decreased into the charge cycle in order to maintain the desired 20a level of purification for a longer period of time. Once the level of purification drops below 80%, the capacitor is discharged through an energy-recovery circuit. That energy is added to the energy from the DC power source and used to charge another capacitor which purifies while the first capacitor is releasing a concentrated stream of contaminants.
Example 5 The flow-through capacitor of Example 4 may be powered by a fuel cell.
Example 6 A flow-through capacitor is made utilizing low surface area carbon black, in the range between 300 and 900 Brunauer Emmett Teller method (BET), selected for being less likely to passively adsorb contaminants and therefore foul the flow path. The charge barrier materials are NEOSEPTA . The flow arrangement is a dual-flow channel device as shown in Figs. 7 and 8A, 8B, 8C, and 8D. One flow channel is formed between and by spacing apart the two charge barrier materials. A pair of side flow channels is located on either side of the central flow channel. These side flow channels are also formed by placing a spacer between the electrodes and the charge barrier materials. A membrane that selectively allows anions to migrate through it (anion permselective, because it has bound positively-charged ionic groups), is initially placed on the side of the negative electrode, with a flow spacer in between. The membrane that selectively allows cations to migrate through it (cation permselective, because it has bound negatively-charged ionic groups). During this charge cycle, purified water is retrieved from the outlet of the central flow channel.
Simultaneously, concentrated water is retrieved from the electrode facing side flow channels.
The same flow-through capacitor may subsequently be discharged. A concentrated solution is recovered from the central flow channel. The capacitor may be repeatedly run in this polarity sequence. Alternatively, the polarity may be reversed. Reversing the polarity places the permselective membranes adjacent to the oppositely-charged electrodes. This means that a concentrated stream is recovered during the charge cycle from the central flow channel. Simultaneously, a purified stream may be recovered from the side flow channels. Subsequently, the flow-through capacitor may be discharged. During the discharge cycle,, a purified liquid is recovered from the central flow stream, and a concentrated liquid is recovered from the side flow channels.

Example 7 A flow-through capacitor is made utilizing one micron small particle size activated carbon powder electrodes bound together with 5% PTFE binder. The charge barrier material is a conductive polymer coating 0.001 inch thick. Ten of the charge barriers are connected in a 7-volt series bank of capacitors.
Seawater of 35,000 ppm is treated to 500 ppm at an energy usage of 0.7 joules per coulomb. 70% of the energy is recovered during discharge of the capacitors using inductive coils to recharge a second bank of capacitors in series.
Example 8 In a flow-through capacitor using edge plane graphite with a surface area of 500 square meters per gram for electrodes, an anion and a cation exchange membrane are used as charge barriers. An additional pair of bipolar membranes is placed between the cation or anion membranes and the electrodes. Flow spacers are placed between all the above layers, or merely between the cation and anion exchange membranes. The resulting cell may be used in any application of bipolar membrane electrodialysis, but without oxidation reduction reactions at the electrodes, for example, recovery of organic acids, proteins, or biological molecules from fermentation broths. Another application is the recovery of SO2 or NO3 from stack gas.
Example 9 A flow-through capacitor is made using an electrode composed of a high-capacitance electrode material, such as high-surface-area carbon cloth, or edge plane graphite, or carbon black particles bound together with fibrillated PTFE. Membranes selective for transmigration of cations and anions, respectively, are placed touching the electrodes. A central flow channel is formed by any spacing component, including biplanar filtration netting under 0.01 inches thick, screen-printed protrusions or ribs, or membranes textured with premanufactured flow channels in a diamond pattern. The initial charge sequence is at constant current selected for low I
squared R energy losses, where "I" is amps and "R" is electrical series resistance. A top charging voltage of 0.6 volts is selected to minimize the amount of energy required to purify a given amount of ions. The charge cycles are carried out as follows:

During the first charge cycle, the electrodes are of the same polarity as the fixed charge inside the membranes. Coions expelled from the pore volume of the electrodes are trapped against the membranes. This causes an amount of counterions in the central flow channel to migrate through the membranes, where they form a concentrated solution in the electrode layer. This counteracts the losses ordinarily caused by adsorption and expulsion of dissolved pore volume salts. Therefore, the ionic efficiency, as measured by coulombs of ionic charge purified divided by coulombs of electronic charge utilized, is greater than 30%. In this case, for 35,000 ppm salts, ionic efficiency is 85%, and the energy utilized is 0.35 joules per coulomb of charge.
The next cycle is a discharge cycle in which concentrated waste is released into a feed stream fed into the central flow channel and recovered from the outlet. The next cycle, after discharge, is a reverse polarity charge. Here, the bound charge on the membranes is opposite to the electronic charge on the electrodes. Ions are driven from the electrode across to the adjacent membrane, but cannot migrate through the second membrane.
Therefore, a concentrated solution forms in the central flow channel and is released through the outlet. Upon discharge from this polarity, ions migrate from the central flow channel back into the electrode chambers, thereby purifying the feed stream. The subsequent cycle goes back to the beginning. These cycles can be repeated as many times as desired. An example of data from the above is shown in Fig. 9. Fig. 9 shows the underlying usefulness of the charge cycle in Example 7. Note that two purification cycles occur in a row. Likewise, two concentration cycles occur in a row. This doubling up of purification or concentration artificially extends the length of time the capacitor is performing a particular purification or concentration cycle.

Example 10 The flow-through capacitor of Fig. 11 is used to make ultrapure water of, e.g., 18 megaohms cm. The water may be pretreated using one or more of a microfilitration unit, a water softener, and followed by a reverse osmosis unit. The water may be post treated using, e.g., a polishing bed of deionization resin. The flow-through capacitor removes some or all of the dissolved solids from the deionization bed, thereby prolonging the lifetime of the deionization bed.

Example 11 The flow-through capacitor of Fig. 11 may be used to post-treat seawater which has been previously treated by reverse osmosis. The salinity of the seawater is initially reduced by reverse osmosis from 35,000 ppm to 10,000 ppm.
Subsequently, treatment with the flow-through capacitor further reduced the salt concentration to 250 ppm. The combined use of reverse osmosis and the flow-through capacitor desalinated seawater for 15 kw 24a hours per thousand gallons, which is a 30% energy savings compared to using reverse osmosis alone.
Example 12 The flow-through capacitor of the invention may be used to purify seawater to 500 ppm.
Example 13 Individual flow-through capacitor cells are made with the following sequence of layers: current collector layers, such as using 0.005 inch thick graphite foil; an electrode layer of any capacitance material, for example, carbon microparticle containing sheet material; a pair of charge barrier layers consisting of carbon cloth or of an anion and a cation exchange membrane bracketing a central flow netting spacer of .005 inch thick polypropylene; a second electrode layer needed to form a pair; and a second current collector layer. The current collectors are ionically insulating but electronically conductive.
Therefore, if a number n of the above sequence of layers are stacked up as flat sheets, or rolled in concentric spirals, they will form a series-connected, flow-through capacitor with single-sided capacitive electrodes facing outwardly from the current collector. The current collector forms the ionically-nonconductive boundary between cells and establishes an electrical series connection. If the electrode is conductive enough not to require a current collector, then a thin sheet of plastic may be used as long as series leads are connected between cells. The electrode does not need to be single-sided.
Any number of double-sided electrodes connected electrically in parallel may exist within particular cells. Each cell may be made with the same capacitance by matching the construction of each cell. Flow in the spiral cell may be alongside the layers.
Example 14 Activated carbon particles in the 0.2 to 5 micron diameter range, conductive ceramic, aerogel, carbon black, carbon fibers, or nanotubes with a BET of between 300 and 2000, are mixed together with 5% PTFE binder, ion exchange resins as a charge barrier, and carboxymethylcellulose as a plasticizer, and calendered into a 0.01 thick sheet. These are made separately in anion, cation, and bipolar versions. Any ion exchange resin known to be used in ion exchange or electrodialysis membranes may be used. Ion exchange groups include any strong or weak acid or base, for example, sulfonic acid or amine groups.
Ionic group support material includes any material used in ion exchange or membranes, including fluorinated polymers, divinylbenzene, or styrene polymers, or any other kind of polymer, zeolite, or ceramic material. The geometry of construction will be known to those of skill in the art, including, but not limited to those described in the U.S.
Patent Nos. 5,192,432, 5,415,768, 5,538,611, 5,547,581, 5,620,597, 5,748,437, 5,779,891, and 6,127,474. The electrodes may be spaced apart or provided with a flow spacer and an optional current collector in order to form a charge barrier flow-through capacitor. The advantage of this example is that the charge barrier material is evenly distributed throughout the electrode layers, thereby eliminating extra charge barrier layers, the cost due to these extra parts, and allowing the electrodes to be spaced closer together, less than 0.02 inches, for example, which cuts resistance and increases flow rate of purification.
Monolithic or sintered carbon electrodes may also be used, for example, electrodes with honeycomb holes incorporated into the structure may have these holes filled in with ion exchange resin to effect a combined charge barrier electrode material.

Claims

CLAIMS:

1. A flow-through capacitor comprising:

(a) a plurality of electrodes comprising an electrode material having a surface area for electrostatic adsorption of feed ions;

(b) a pore structure in one or more of said plurality of electrodes, whereby said electrode is a porous electrode having a pore volume; and (c) a first charge barrier material different from said electrode material, located adjacent to said electrode.

2. The flow-through capacitor of claim 1, wherein the charge barrier material is characterized by low resistance-capacitance.

3. The flow-through capacitor of claim 1 or 2, wherein at least one of the electrodes is an anode and at least one of the electrodes is a cathode.

4. The flow-through capacitor of claim 1, 2 or 3, wherein the charge barrier material comprises a first semipermeable membrane.

5. The flow-through capacitor of claim 4, wherein said flow-through capacitor further comprises a second charge barrier material semipermeable membrane, said first membrane being a cation exchange membrane and said second membrane being an anion exchange membrane.

6. The flow-through capacitor of claim 5, wherein the anion exchange membrane is proximal to an anode, and the cation exchange membrane is proximal to a cathode.

7. The flow-through capacitor of claim 6, wherein the locations of the anion and cation exchange membranes relative to the electrodes are reversed by reversal of voltage polarity on the electrodes.

8. The flow-through capacitor of claim 5, 6 or 7, wherein the electrode is operated in the charge cycles of opposite polarity, separated by discharge cycles.

9. The flow-through capacitor of any one of claims 1 to 8, further comprising a flow channel.

10. The flow-through capacitor of claim 9, wherein the flow channel is formed by a spacer.

11. The flow-through capacitor of claim 9, wherein the flow channel is located between one of the electrodes and the first charge barrier material.

12. The flow-through capacitor of claim 11, further comprising a second charge barrier material and further comprising a flow channel located between the first and second charge barrier materials.

13. The flow-through capacitor of claim 2, wherein the charge barrier material is an electrically-conductive membrane with a low resistance-capacitance (RC) time constant.

14. The flow-through capacitor of claim 13, wherein the capacitance of the charge barrier material is less than 20 farads/gram.

15. The flow-through capacitor of any one of claims 1 to 14, wherein the charge barrier material is electrically connected to a first power supply, and at least one of the plurality of electrodes is electrically connected to a second power supply.

16. The flow-through capacitor of any one of claims 1 to 15, wherein the charge barrier material has a voltage and one or more electrodes of said plurality of electrodes has a voltage, the charge barrier voltage being greater than the electrode voltage.

17. The flow-through capacitor of claim 4, further comprising a second charge barrier material membrane, wherein the charge barrier membranes are identically-charged semipermeable membranes, selected from the group consisting of cation exchange membranes and anion exchange membranes.

18. The flow-through capacitor of any one of claims 1 to 17, wherein the flow-through capacitor comprises a series resistance of less than 50 ohm cm2.

19. The flow-through capacitor of any one of claims 1 to 18, wherein the flow-through capacitor has a series resistance to leakage ratio of greater than 100.

20. The flow-through capacitor of any one of claims 1 to 8, wherein the electrodes within a cell of the capacitor are ionically insulated and connected electrically in series.

21. The flow-through capacitor of claim 20, further comprising a flow path adjacent to each of the electrodes.

22. A system comprising the flow-through capacitor of any one of claims 1 to 21 and a valve.

23. The system of claim 22, comprising a means for allowing fluid in said system to bypass a flow-through capacitor in said system.

24. The system of claim 22, comprising a means for directing fluid in said system from said flow-through capacitor to a second flow-through capacitor in said system.

25. The system of claim 22, 23 or 24, further comprising a means for monitoring the concentration of ions in a fluid in said system.

26. The system of any one of claims 22 to 25, further comprising a means for controlling the concentration of ions in a fluid in said system.

27. A flow-through capacitor comprising:
(a) a plurality of electrodes; and (b) a first charge barrier located between two of said plurality of electrodes, wherein the charge barrier is an electrically-conductive membrane with a low resistance-capacitance (RC) time constant material, and wherein the capacitance of the charge barrier is less than 20 farads/gram.

28. A flow-through capacitor comprising:
(a) a plurality of electrodes; and (b) a first charge barrier located between two of said plurality of electrodes, wherein the charge barrier is electrically connected to a first power supply, and at least one of the plurality of electrodes is electrically connected to a second power supply.

29. A flow-through capacitor comprising:
(a) a plurality of electrodes; and (b) a first charge barrier located between two of said plurality of electrodes, wherein the flow-through capacitor comprises a series resistance of less than 50 ohm cm2.

30. A flow-through capacitor comprising:
(a) a plurality of electrodes; and (b) a first charge barrier located between two of said plurality of electrodes, wherein the flow-through capacitor has a series resistance to leakage ratio of greater than 100.

31. A flow-through capacitor comprising:
(a) a plurality of electrodes; and (b) a first charge barrier located between two of said plurality of electrodes, wherein the electrodes within a cell of the flow-through capacitor are ionically insulated and connected electrically in series.

32. The flow-through capacitor of claim 31, further comprising a flow path adjacent to each of the electrodes.

33. The flow-through capacitor of claim 1, wherein said first charge barrier material is a laminate coating on said electrode material.

34. The flow-through capacitor of claim 33, wherein said laminate coating is an ion exchange material.

35. The flow-through capacitor of claim 33, wherein said laminate coating is characterized by a low-resistance capacitance (RC) time constant.

36. The flow-through capacitor of claim 1, wherein said first charge barrier material is a conductive polymer sheet material.

37. The flow-through capacitor of claim 1, wherein said first charge barrier material is material selected from the group consisting of a fibrous material, a woven material, and a mesh material.

38. The flow-through capacitor of claim 1, wherein said first charge barrier material is an aerogel.

39. The flow-through capacitor of claim 1, wherein said first charge barrier material is a hydrogel.

40. The flow-through capacitor of claim 1, wherein said first charge barrier material is selected from the group consisting of a carbon powder material and a graphite material.

41. The flow-through capacitor of claim 1, wherein said first charge barrier material infiltrates said at least a portion of said pore volume of said electrode to form a combined electrode charge barrier material composite.

42. The flow-through capacitor of claim 1, wherein said flow-through capacitor comprises a plurality of ion-depleting and ion-concentrating compartments.

43. The flow-through capacitor of claim 1, wherein said first charge barrier material is an ion-exchange resin.

44. The flow-through capacitor of claim 1, wherein said first charge barrier material is evenly distributed throughout said electrode material of one or more of said plurality of electrodes.

45. The flow-through capacitor of claim 1, wherein said charge barrier material comprises one or more bipolar membranes.

46. The flow-through capacitor of claim 1, wherein said flow-through capacitor has an ionic efficiency of at least 30%.

47. The flow-through capacitor of claim 1, wherein said flow-through capacitor has an ionic efficiency of at least 70%.

48. The flow-through capacitor of claim 1, wherein said adjacent charge barrier material is within the pore structure of the electrode.

49. The flow-through capacitor of claim 1, wherein said adjacent charge barrier material is infiltrated into the pore structure of the electrode.

50. The flow-through capacitor of claim 1, wherein said adjacent charge barrier material is a coating layer.

51. The flow-through capacitor of claim 1, wherein said adjacent charge barrier material is a membrane layer.

52. The flow-through capacitor of claim 1, where said adjacent charge barrier material is infiltrated into the pore structure of said porous electrode, said charge barrier material selected from the group consisting of an ion exchange polymer and a hydrogel.

53. The flow-through capacitor of claim 1, where said adjacent charge barrier material is a coating blocking the pore volume of said porous electrode, said charge barrier material selected from the group consisting of an ion exchange polymer and a hydrogel.

54. The flow-through capacitor of claim 1, wherein said pore volume contains pore ions and said electrode has a ratio of feed ions to pore ions, and wherein said first charge barrier material increases the ratio of feed ions to pore ions in said electrode.

55. The flow-through capacitor of claim 1, wherein said flow-through capacitor has an energy usage of less than 1 joule per coulomb of ionic charge purified.

56. The flow-through capacitor of claim 1, wherein said flow-through capacitor has an energy usage of less than 0.5 joule per coulomb of ionic charge purified.

57. The flow-through capacitor of claim 1, wherein said flow-through capacitor has an ionic efficiency of greater than 50% in the presence of a feed stream having an ionic concentration of at least 2500 parts per million.

58. The flow-through capacitor of claim 57, wherein said feed stream has an ionic concentration of at least 6000 parts per million.

59. The flow-through capacitor of claim 3 comprising a first electric field that is between said anode and cathode, and further comprising a second electric field that is within said electrode and inverse to said first electric field.

60. A flow-through capacitor having an ionic efficiency, said flow-through capacitor comprising:
(a) a plurality of electrodes comprising an electrode material having a surface area for electrostatic adsorption of ions;

(b) a pore volume in one or more of said plurality of electrodes comprising pore volume loss; and (c) means for enhancing the ionic efficiency of said flow-through capacitor by compensating for said pore volume loss.

61. A flow-through capacitor comprising:

(a) a plurality of electrodes comprising an electrode material having a surface area for electrostatic adsorption of ions;

(b) a pore volume in one or more of said plurality of electrodes, whereby said pore volume adsorbs and expels pore volume ions; and (c) means for reducing said adsorption and expulsion of pore volume ions.

62. A flow-through capacitor comprising:

(a) a plurality of electrodes comprising an electrode material having a surface area for electrostatic adsorption of feed ions;

(b) a pore volume in one or more of said plurality of electrodes, whereby said pore volume contains pore ions; and (c) means for providing an excess of feed ions to pore volume ions.

63. The flow-through capacitor of claim 62, further comprising a feed stream having a flow rate, and means for altering said flow rate.

64. The flow-through capacitor of claim 62, further comprising a source of voltage to said flow-through capacitor, and a means for altering said voltage.

65. The flow-through capacitor of claim 62, further comprising a means for recovering energy from said flow-through capacitor.

66. The flow-through capacitor of claim 62, wherein said flow-through capacitor has a polarity and further comprises means for reversing said polarity.