ELECTROCHEMICAL DEVICE FOR FORMING pH GRADIENT

Abstract

To provide a membrane-less electrochemical device to form a pH gradient in a bulk liquid supply flow with low energy consumption, promoting efficient carbon dioxide extraction from seawater or promoting efficient storing of carbon dioxide in seawater, a system comprising the device, and a method of operating the system.SOLUTION: The membrane-less electrochemical device comprises a unit of inputting a fluid supply flow to a membrane-less electrochemical cell, a first electrode, and a second electrode. The first electrode includes a first redox active substance configured to perform a proton coupled oxidation reaction with a first segment of the fluid supply flow. The second electrode includes a second redox active substance configured to perform a proton coupled reduction reaction with a second segment of the fluid supply flow. The first segment and the second segment of the fluid supply flow are separated from each other. A first efflux flow includes the first segment and has a first pH. A second efflux flow includes the second segment and has a second pH different from the first pH.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure generally relates to systems for forming pH gradients within fluid flows and methods of operating the same.

Background Art

[0002] The world's oceans absorb carbon dioxide (CO2) from the atmosphere as part of the carbon cycle. As atmospheric carbon dioxide levels increase, the amount of CO2 absorbed by the oceans also increases. When carbon dioxide dissolves in seawater, it reacts to create carbonic acid. Carbonic acid then releases hydrogen ions (H + ) to form carbonate (CO3 -2 ) and bicarbonate (HCO3 - ) ions. The pH of seawater, which determines the relative fractions of dissolved carbon dioxide, carbonate ions, and bicarbonate ions, is typically about 8.3. This means that most of the total carbon dissolved in seawater is in the form of bicarbonate ions. The accumulation of these reactions over time increases the acidity of the seawater in the oceans, adversely affecting the lives of marine plants and animals. Removing carbon dioxide from the oceans helps to restore the pH balance of the seawater in the oceans in addition to providing the capacity for the oceans to remove further carbon dioxide from the atmosphere. Furthermore, the removed carbon dioxide can be sequestered and / or otherwise used in various industries such as building materials (e.g., concrete), household chemical substances (e.g., polymers, potash), fuels (e.g., liquid hydrocarbons), carbon materials (e.g., graphene, nanotubes, etc.), and aquaculture.

[0003] One method for capturing carbon dioxide from ocean water involves first increasing the acidity of the water to release dissolved bicarbonate and carbonate ions as carbon dioxide, and then increasing the alkalinity to restore the pH. Another method for increasing the alkalinity of ocean water involves mixing acidified water with a fine suspension of calcium carbonate, for example, while releasing the based water into the ocean, thereby converting the calcium carbonate to calcium bicarbonate. Limestone or other carbonate-rich minerals may be added instead of various grades of calcium carbonate. The cations in these reactions do not have to be calcium; magnesium carbonate-rich minerals may be used. Both methods can be achieved using bipolar membrane electrodialysis, which can generate acidifying and alkaline flows. However, the generation of high concentrations of hydronium ions ("protons") in close proximity to high concentrations of hydroxide ions inside the bipolar membrane generates only the minimum energy necessary to form a pH gradient in bulk seawater, which is inefficient for carbon dioxide extraction. Embodiments are disclosed that aim to generate a pH gradient in a bulk liquid feed stream with low energy consumption, thereby facilitating the efficient extraction of carbon dioxide from or storage in seawater. [Overview of the Initiative]

[0004] The embodiments described herein are intended for a membrane-free electrochemical device. The device comprises a fluid supply flow input to a membrane-free electrochemical device, a first electrode, and a second electrode. The first electrode contains a first redox active material configured to undergo a proton-conjugated oxidation reaction with a first portion of the fluid supply flow, and the second electrode contains a second redox active material configured to undergo a proton-conjugated reduction reaction with a second portion of the fluid supply flow. The first and second portions of the supply flow are separated. The device further comprises a first effluent flow comprising a first portion having a first pH, and a second effluent flow comprising a second portion having a second pH. The second pH is different from the first pH.

[0005] Other embodiments relate to a system. The system comprises a fluid supply flow, a membrane-free electrochemical device, an energy source, a first vessel, a second vessel, and a switching valve. The membrane-free electrochemical device comprises a first electrode, a second electrode, a first effluent flow, and a second effluent flow. The first electrode contains a first redox active material configured to undergo a proton-conjugated oxidation reaction with a first portion of the fluid supply flow in response to a first potential, and the second electrode contains a second redox active material configured to undergo a proton-conjugated reduction reaction with a second portion of the fluid supply flow in response to a first potential. The first and second portions are separated from each other. The first effluent flow comprises a first portion and has a first pH, and the second effluent flow comprises a second portion and has a second pH different from the first pH. The energy source is configured to apply a first potential and a second reverse potential between the first and second electrodes. The first container is configured to receive an outflow material having a first pH, and the second container is configured to receive an outflow material having a second pH. A switching valve is connected to the first and second outflow materials and to the first and second containers.

[0006] Further embodiments relate to a method. This method involves introducing a fluid feed stream into a membrane-free electrochemical device. The device comprises a first electrode containing a first redox active material and configured to undergo a proton-conjugated oxidation reaction when in contact with a first portion of the fluid feed stream. The device also comprises a second electrode containing a second redox active material and configured to undergo a proton-conjugated reduction reaction when in contact with a second portion of the fluid feed stream. This method includes guiding the first portion of the fluid feed stream into contact with the first electrode, guiding the second portion of the fluid feed stream into contact with the second electrode, and applying potentials to the first and second electrodes. In response to the application of potentials, the first redox active material on the first electrode in contact with the first portion of the fluid feed stream is oxidized, and the second redox active material on the second electrode in contact with the second portion of the fluid feed stream is reduced. In a first outflow flow having a first pH, a first portion of the fluid supply flow is removed from the electrochemical device, and in a second outflow flow having a second pH different from the first pH, a second portion of the fluid supply flow is removed from the electrochemical device.

[0007] The above summary is not intended to describe each of the disclosed embodiments or all practices of this disclosure. The drawings and the following detailed description illustrate exemplary embodiments more specifically. [Brief explanation of the drawing]

[0008] The following discussion refers to the following figures, and the same reference numbers can be used to identify similar / identical components in multiple figures. However, the use of numbers to refer to components in a given figure is not intended to limit components in other figures labeled with the same number. The drawings are not necessarily to scale. [Figure 1] This is a block diagram of a system comprising a membrane-free electrochemical device for capturing target molecules or solutes using a pH gradient, according to a specific embodiment. [Figure 2] This is a schematic diagram of a layered, membrane-free electrochemical cell according to a specific embodiment. [Figure 3] This is a block diagram of a system comprising a flow-through membrane-free electrochemical cell according to a specific embodiment. [Figure 4] This is a schematic diagram of a flow-through, membrane-free electrochemical cell according to a specific embodiment. [Figure 5] This is a flowchart of the method according to a specific embodiment. [Figure 6] This is a flowchart of the method according to a specific embodiment. [Modes for carrying out the invention]

[0009] Fluid flow control can be used to guide different parts of a fluid flow without using physical barriers such as membranes. For example, fluid flow can be controlled to prevent or minimize mixing between different parts of the fluid flow. This can be achieved by controlling the laminar flow of the fluid and / or by guiding different parts of the flow along a predetermined direction. By controlling separate parts of a fluid flow (e.g., aqueous flow) without mixing the two parts, separation and capture of materials in the fluid flow becomes possible when combined with electrolysis. For example, target components such as molecules or solutes in a fluid flow can be captured by acidifying a portion of the fluid flow to release target molecules or solutes.

[0010] Creating a pH gradient in the fluid flow at two separate electrodes rather than a boundary within a bipolar membrane, and independently maintaining the separation of the acidic portion of the flow, i.e., without a membrane or physical barrier, reduces the energy and cost required to perform and maintain separation. The absence of a membrane also reduces the number of components in the electrochemical device or cell, thereby lowering manufacturing costs. The absence of a membrane also allows the use of electrochemical cells with a wider range of pH values ​​(i.e., electrolytes), enabling the use of a wider variety of (e.g., less expensive) materials. For example, electrochemical devices using input fluid flows (i.e., electrolytes) with extremely high or low pH values ​​may avoid the need for materials designed to withstand corrosion. Furthermore, removing membranes from electrochemical separation cells eliminates issues related to durability, fouling, and resilience of components in the electrolyte. Membrane-free systems also open up a design paradigm where at least some of the components of the electrochemical cell are designed to be inexpensive and / or disposable, or otherwise replaceable periodically or at predetermined intervals. Various systems involving membrane-free electrochemical cells that generate pH gradients will be further described herein.

[0011] Referring to Figure 1, a system 150 is shown that utilizes a membrane-free electrochemical cell 100 to separate components from an input fluid flow 102 by generating a pH gradient in the fluid flow. The fluid flow (e.g., aqueous flow) flows into a membrane-free electrochemical cell having two electrodes, each containing a redox active material. The input flow 102 contains at least one target molecule or solute that can be captured as a result of operating the membrane-free electrochemical cell. The term “membrane-free electrochemical cell” as used herein refers to an electrochemical cell that does not have a membrane positioned between two electrodes, or other non-porous or ion-selective barrier. For example, in certain embodiments, the membrane-free electrochemical cell may have a mesh or porous separator inserted between the electrodes. The electrodes of the electrochemical cell 100 are coupled to an energy source 104 that applies a potential between the electrodes by supplying voltage to the first electrode via coupling 106A and to the second electrode via coupling 106B.

[0012] When a potential is applied between the electrodes, the redox active material of the first electrode undergoes a first proton-conjugated Faraday reaction with an electrolyte (e.g., water), and the redox active material of the second electrode undergoes a second proton-conjugated Faraday reaction with an electrolyte (e.g., water), resulting in the generation of a hydroxide ion or the absorption of a hydronium ion near the first electrode, and then the generation of a hydronium ion or the absorption of a hydroxide ion near the second electrode. Furthermore, the first and second redox-conjugated reactions can also move ions that are neither hydroxide ions nor hydronium ions, such as sodium ions or chloride ions, (for example, simultaneously). As a result, the first portion of the input flow near the first electrode has a different pH value than the second portion of the input flow near the second electrode, creating a pH gradient within the membrane-free electrochemical cell. The pH gradient is relative to the incoming pH of the feed flow 102, but exemplary gradient values ​​may range from approximately 1 to 2 pH units, or approximately 2 to 4 pH units, or approximately 4 to 6 pH units. The pH gradient does not need to be centered on the incoming pH of the feed flow. For example, a feed flow with pH 8 could have two output flows, one at pH 5 and the other at pH 9.

[0013] To prevent mixing and neutralization of the pH gradient, the first and second portions are kept separate within a membrane-free electrochemical cell through controlled and / or induced fluid flows, as further described below. The first acidic portion of the input flow is removed from the membrane-free electrochemical cell as flow 110, and the second alkaline portion of the input flow is removed from the membrane-free electrochemical cell as flow 112. The terms “acidic” and “alkaline” are defined with respect to the initial input pH of the input flow 102 when used herein. A first pH measuring device 108A is paired with flow 110, and a second pH measuring device 108B is paired with flow 112. In certain embodiments, a single pH measuring device is configured to measure the pH of each of the outflow flows 110 and 112.

[0014] The effluent flows 110 and 112 are discharged into separate storage containers to prevent the flows from being neutralized. In certain embodiments, the first effluent flow 110 is diverted to container 118, and the second effluent flow 112 is diverted to container 120. Although containers 118 and 120 are referred to as storage containers, they may also represent discharges from the system or subsequent processing stages. For example, in certain embodiments, at least one of the containers (e.g., 118 containing acidic effluent) contains reactants that further react with the acidic effluent to separate target molecules or solutes from the effluent flow 110.

[0015] Since electrolytes undergo Faraday reactions with each electrode, electrochemical cells are sometimes operated by applying a reverse potential between the electrodes. The reverse potential can be applied as needed or according to a predetermined schedule. The reverse potential has the effect of circulating the redox active material on the first and second electrodes to restore it to the state it was in before the forward potential was applied. When a reverse potential is applied, the electrodes exchange reactions with the electrolyte so that a hydroxide ion is absorbed or a hydronium ion is generated near the first electrode, and then a hydronium ion is absorbed or a hydroxide ion is generated near the second electrode.

[0016] The first and second portions of the input flow still create a pH gradient and remain separated in the membrane-free electrochemical cell, but the pH gradient is reversed. Therefore, if the effluent flow 110 has a lower pH value when the first potential is applied, the effluent flow 110 will have a higher pH value when the reverse potential is applied. Similarly, if the effluent flow 112 has a higher pH value when the first potential is applied, the effluent flow 112 will have a lower pH value when the reverse potential is applied.

[0017] Since the pH value of each effluent changes based on the applied potential, the switching valve 114 is paired with both effluents 110 and 112. For example, when a first potential is applied and effluent 110 has a lower pH, flow 110 is diverted to container 118 through path 116A. However, when a reverse potential is applied, effluent 110 has a higher pH, and the switching valve is activated to divert effluent 110 to container 120 through path 116B. Similarly, when a first potential is applied and effluent 112 has a higher pH, flow 112 is diverted to container 120 through path 116B. However, when a reverse potential is applied, effluent 112 has a lower pH, and the switching valve is activated to divert effluent 112 to container 118 through path 116A to prevent the effluent from being neutralized in containers 118 and 120. In order to create and maintain a pH gradient in a membrane-free electrochemical cell, the first and second parts of the input flow are kept separate, as will be discussed in more detail below.

[0018] In certain embodiments, system 150 may be used to separate carbon dioxide from seawater. In such embodiments, the input stream 102 is seawater containing, among other things, bicarbonate and carbonate ions as dissolved electrolytes. The acidified seawater, exiting cell 100 and induced into storage container 118, contains a higher concentration of carbon dioxide according to the carbon dioxide / bicarbonate / carbonate ion equilibrium. Carbon dioxide can be removed from this acidified seawater by many methods, including vacuum or thermal evaporation. In other embodiments, the acidified seawater is induced into a mixing tank (e.g., container 118 or another optional container) equipped with a stirring mechanism to which a carbon-containing base material (e.g., a carbon-rich mineral such as calcium carbonate, containing bicarbonates and carbon dioxide such as NaHCO3) is optionally added. The reactants react with the seawater to produce gaseous CO2, reducing the acidity. In some embodiments, the carbon-containing base material is formed by the reaction of external seawater with a higher pH stream 112.

[0019] In alternative embodiments, the base material reacts with the acidified flow to neutralize the acid, and as a result, the neutralized effluent can be discharged (e.g., returned to the ocean), while other alkaline effluents are used for carbon capture. In these embodiments, a wider variety of base materials can be used, including carbonic acid / bicarbonate, silicic acid, hydroxides and oxides, or minerals rich in these components. The basic solution / effluent can be discharged into the ocean, where the solution / effluent increases in alkalinity, causing the ocean to take up CO2 from the atmosphere. In other embodiments, the basic effluent can take up CO2 by being exposed to or in contact with a more concentrated flow of CO2, such as fumes from power generation or ship exhaust, or CO2 captured from the air through direct air capture.

[0020] There is no need to physically separate the isolated target molecule or solute (here, for example, carbon dioxide) from the effluent stream. The target component can be reacted with a chemical reagent to convert the target molecule or solute into a different, milder form. For example, if the target molecule is carbon dioxide and calcium carbonate is introduced into and reacts with an acidified stream, calcium carbonate reacts with the dissolved carbon dioxide according to the equation CaCO3 + H2CO3 → Ca(HCO3)2. Thus, the separation of the target molecule or solute can be considered as the removal of components in the target molecule or solute from one or more effluent streams.

[0021] In certain other embodiments, system 150 can be used to desalinate seawater or other electrolyte solutions. This is achieved by selecting a redox pair such as bismuth / bismuth oxychloride (Bi / BiOCl) where the redox cycle moves both protons (or hydroxides) and salt ions together (e.g., simultaneously). In this case, one effluent stream is desalinated while the other effluent stream is concentrated in salt. The desalinated stream may be a stream with a lower pH or a stream with a higher pH. Conversely, the concentrated stream may be a stream with a higher pH or a stream with a lower pH.

[0022] Figure 2 shows a particular embodiment of a membrane-free electrochemical cell, referred to herein as a layered membrane-free electrochemical cell 200. The layered cell 200 comprises a first electrode 202 containing a first redox active material 206, and a second electrode 204 positioned opposite the first electrode and containing a second redox active material 208. The first electrode 202 and the second electrode 204 may also be composed entirely of their respective redox active materials 206, 208. In this case, 206, 208 should be understood as electrodes of the layered membrane-free electrochemical cell 200. In a particular embodiment, the first and second redox active materials 206, 208 are materials constituting the same redox pair, such as Bi / BiOCl or benzoquinone / hydroquinone. In other embodiments, the first and second redox active materials 206, 208 may be the same or different. The redox active materials 206 and 208 may also be at least one of quinones, phenazines, pyrazines, quinoxalines, or derivatives thereof. The redox active materials may also be at least one of ionomers and polymers, at least one of which comprises at least one of quinones, phenazines, pyrazines, quinoxalines, and derivatives thereof. The redox active materials 206 and 208 are selected based on several factors, including ease of production, relative abundance and availability, cost price, redox reaction rate, oxygen stability in any of the redox states, water stability in any of the redox states, and chemical compatibility with the pH of the input flow 210 or any of the solutes dissolved therein.

[0023] In certain embodiments, the redox active materials 206, 208 are coated on the electrodes 202, 204 as shown in FIG. 2. However, in alternative embodiments, the redox active materials 206, 208 are organic molecules grafted onto and / or within the electrodes 202, 204. For example, one or both of the electrodes 202, 204 may include the redox active materials 206, 208 and at least one of a conductive material, a binder, and a conductive binder. The electrodes 202, 204 are positioned opposite each other with a gap therebetween. The gap is determined by one or more of the laminar flow characteristics of the liquid within the layered cell 200, the velocities of the input and output flows, the reaction rate of the electrodes, and the presence or absence of the intervening porous separator 222. If the intervening porous separator 222 is present, it may be flat or may have an integral flow path. Pressure may be applied to the intervening porous separator 222 from an external pressurization to the layered cell 200, and the pressure may be induced through the first and second electrodes 202, 204. The electrodes 202, 204 themselves may also be flat or may have an integral flow path.

[0024] In the layered membrane-free electrochemical cell 200, the input fluid flow, indicated by arrow 210, flows into the cell 200 substantially parallel to the first and second electrodes 202, 204, and as a result, the input fluid flow 210 contacts the main surface and the opposing surface of each of the electrodes 202, 204, as shown in Figure 2. Thus, the laminar flow of the input flow 210 can be considered as layers or portions flowing in the same direction, indicated by arrow 210. For example, the first portion 212 or laminar flow may be close to the first electrode 202, and the second portion 214 or laminar flow may be close to the second electrode 206. When a potential is applied between electrodes 202, 204, the redox active materials 206, 208 of the electrodes undergo a proton-conjugated Faraday reaction with the electrolytes close to the electrodes 202, 204. For example, a hydroxide ion may be absorbed or a hydronium ion may be generated near the first electrode 202, thereby increasing the acidity of the first portion 212, and a hydronium ion may be absorbed or a hydroxide ion may be generated near the second electrode 204, thereby increasing the alkalinity of the second portion 214.

[0025] The laminar flow in both the first and second portions is controlled to minimize or reduce mixing between the acidic first portion 212 adjacent to the first electrode 202 and the alkaline second portion 214 adjacent to the second electrode 204, and to maintain those portions as the separate portions flow through the cell 200. For example, the flow may be controlled by one or more pumps positioned at the input or output of the laminar membrane-free electrochemical cell 200. Furthermore, if present, integrated flow channels in one or both of the electrodes 202, 204 help increase the electrode surface area for the redox reaction, in addition to inducing laminar flow in the first and second portions 212, 214.

[0026] As the first and second portions 212 and 214 exit the layered membrane-free electrochemical cell 200, they are separated by a physical barrier 220 (e.g., an impermeable wall) to maintain the separation of different pH flows. As shown, the first effluent flow 216 has a lower pH, and the second effluent flow 218 has a higher pH. The effluent flows can then be separated with respect to the system 150 as described above.

[0027] Figure 3 shows various embodiments of a system 350 utilizing a membrane-free electrochemical cell, referred to herein as a flow-through membrane-free electrochemical cell 300. The flow-through cell 300 comprises a first permeable electrode 302 containing a first redox active material and a second permeable electrode 304 containing a second redox active material positioned opposite the first electrode 302, with the input supply flow flowing through the respective electrodes 302 and 304. As described above, electrodes 302 and 304 may contain the same redox active material together with one or more conductive materials, binders, and conductive binders. Also as described above, the redox active material may be coated onto the electrodes or grafted onto or inside the electrodes.

[0028] In the flow-through membrane-free electrochemical cell 300, the input fluid flow indicated by arrow 310 flows into the cell 300 in a first direction and is then split orthogonally through the opposing electrodes 302 and 304, as shown in Figure 3. Although the input is shown as two opposing flows, a single input flow may also be used. Similar to the layered membrane-free electrochemical cell described above, when a potential is applied between the electrodes, the redox active material of electrodes 302 and 304 undergoes a proton-conjugated Faraday reaction with the electrolyte adjacent to electrodes 302 and 304. For example, a hydroxide ion is absorbed or a hydronium ion is generated adjacent to the first electrode 302, thereby increasing the acidity of the first portion 312, and a hydronium ion is absorbed or a hydroxide ion is generated adjacent to the second electrode 304, thereby increasing the alkalinity of the second portion 314.

[0029] The flow through the first and second electrodes 302, 304, respectively, is controlled to keep the acidic first portion 312 adjacent to the first electrode 302 separate from the alkaline second portion 314 adjacent to the second electrode 304, as the separate portions exit the cell 300 through separate opposing paths 316, 318. The flow may be controlled, for example, by one or more pumps positioned at one or more input or output sections of the flow-through membrane-free electrochemical cell 300. The separate paths 316, 318 maintain the separation of different pH flows; for example, the first effluent flow 316 may have a lower pH, and the second effluent flow 318 may have a higher pH. As described above, the walls of the flow-through cell 300 may also be equipped with flow channels and / or intervening porous separators. The flow-through electrochemical cell 300 is shown as part of a separation system 350.

[0030] The separation system 350 connects the first and second electrodes 302 and 304 to an energy source 306 that supplies voltage to the first electrode 306A and the second electrode 306B, thereby applying a potential between the electrodes 302 and 304. As described above, the energy source 306 is configured to apply a first potential and a reverse potential to the cell 300. The first pH measuring device 308A is paired with the effluent flow 316, and the second pH measuring device 308B is paired with the effluent flow 318. In certain embodiments, a single pH measuring device is configured to measure the pH of each of the effluent flows 316 and 318.

[0031] The effluent flows 316 and 318 are discharged into separate storage containers to prevent the flows from being neutralized. In certain embodiments, the first effluent flow 316 is diverted to container 322 via path 326, and the second effluent flow 318 is diverted to container 324 via path 328. Although containers 322 and 324 are referred to as storage containers, they may also represent discharges from the system or subsequent processing stages. For example, in certain embodiments, at least one of the containers (e.g., 322 containing acidic effluent) contains reactants that further react with the acidic effluent to separate target molecules or solutes from the effluent flow 316. As described above, the switching valve 320 controls the output of the effluent flows 316 and 318 based on the potential applied between electrodes to switch the effluent flows carried by paths 326 and 328. In other embodiments, the acidified seawater is introduced into a mixing tank optionally equipped with a stirring mechanism to which one or more reactants (e.g., calcium carbonate) are added and react with the seawater, thereby reducing the acidity of the effluent.

[0032] Figure 4 shows an alternative embodiment of the flow-through membrane-free electrochemical cell 400. Cell 400 is similar to that in Figure 3, except for the positioning of the first and second permeable or porous electrodes. While the porous electrodes can be positioned in various configurations, in the flow-through cell 400, electrodes 402 and 404 are positioned at angles converging toward each other rather than facing each other. The first electrode 402 extends from the first wall 422 of cell 400 toward the internal impermeable wall 420, and the second electrode 404 extends from the second wall 424 of cell 400 toward wall 420. When a potential is applied to the first and second electrodes 402 and 404, hydronium ions are generated near the electrode where a hydroxide ion is absorbed or a proton-conjugated oxidation reaction occurs, and hydronium ions are generated near the electrode where a hydronium ion is absorbed or a proton-conjugated reduction reaction occurs.

[0033] There is no non-porous membrane or physical barrier at the input of the supply flow. However, as described above, the walls 422, 424 of the flow-through cell 400 may also be provided with a channel adjacent to the input and / or electrodes 402, 404, and / or an interposed porous separator to assist in guiding the flow through the cell 400. After the first portion 412 of the supply flow 410 has passed through the first electrode 402, it is separated by the wall 420 from the second portion 414 that passes through the second electrode 404. The outflow flows 416, 418 can then be stored, processed, and / or discharged as described above.

[0034] A method for creating a pH gradient using the above-described membrane-free electrochemical cell is shown in Figures 5 and 6. Figure 5 shows the first half of the cyclic operation of the membrane-free electrochemical cell. This method includes providing a feed stream to the membrane-free electrochemical cell 502. The feed stream may be aqueous and contains at least one target molecule or solute to be separated from the stream. A potential is applied between the first and second electrodes 504. For example, the first electrode is charged as the anode and the second electrode is charged as the cathode. The first portion of the feed stream is guided to contact the first electrode (as described above in various embodiments of the membrane-free electrochemical cell) to drive a proton-conjugated oxidation reaction with the redox active material of the first electrode in the first portion of the feed stream 506. The oxidation reaction increases the acidity of the first portion of the feed stream, thereby decreasing the pH value of the first portion in close proximity to the first electrode. The second portion of the feed stream is guided to contact the second electrode (as described above in various embodiments of membrane-free electrochemical cells) to drive a proton-conjugated reduction reaction with the redox active material of the second electrode.508 The reduction reaction increases the alkalinity of the second portion of the feed stream, thereby raising the pH value of the second portion adjacent to the second electrode. Thus, the potential applied between the electrodes creates a pH gradient within the feed stream in the electrochemical cell.

[0035] Next, the acidic and alkaline portions of the feed stream at the opposing electrodes are removed separately from the membrane-free electrochemical cell. The first portion of the feed stream is removed in a first effluent stream having a first pH 510, and the second portion of the feed stream is removed in a second effluent stream having a second pH 512. As described above, the first and second pH values ​​are different. For example, the first pH is lower (i.e., more acidic) than the feed stream and the second pH, and similarly, the second pH is higher (i.e., more alkaline) than the feed stream and the first pH. As described in more detail above, the first and second effluent streams may be stored separately and / or further processed to capture or utilize target components.

[0036] The Faraday reaction at the electrodes in a membrane-free electrochemical cell imposes a charge capacity limit on the redox active material at the electrodes, causing the potential applied between the electrodes to periodically reverse direction. Here, "periodically" may refer to reversing the potential occasionally as needed, or to reversing the potential according to a set schedule. The duration and potential of the reversal do not need to be equal to those during the operation where the forward and reversed directions are not present. Figure 6 shows the second half-cycle operation, complementing the half-cycle shown in Figure 5.

[0037] The method in Figure 6 involves operating a membrane-free electrochemical cell as described in Figure 5 to generate a pH gradient in the feed stream 602. However, the potential applied between the first and second electrodes is reversed so that the first electrode is charged as the cathode and the second electrode is charged as the anode 604. The first portion of the feed stream is still guided to contact the first electrode (as described above in various embodiments), but in this half-cycle, it drives a proton-conjugated reduction reaction with the redox active material of the first electrode, thereby raising the pH and alkalinity of the first portion of the feed stream adjacent to the first electrode to approximately the second pH value described above in relation to Figure 5 606. The second portion of the feed stream is guided to contact the second electrode (as described above in various embodiments) to drive a proton-conjugated oxidation reaction with the redox active material of the second electrode, thereby increasing the acidity of the second portion of the feed stream and lowering the pH value of the second portion adjacent to the second electrode to approximately the first pH value described above in relation to Figure 5.608 Thus, the potential applied between the electrodes creates a pH gradient in the feed stream in a membrane-free electrochemical cell that is opposite to the method in Figure 5.

[0038] Next, the acidic and alkaline portions, separated by opposing electrodes, are removed separately from the membrane-free electrochemical cell. However, in the reverse half-cycle, the first portion of the feed flow is removed in the first effluent flow having a second pH, and the second portion of the feed flow is removed in the second effluent flow having a first pH. To maintain the separation of effluent flows having different pH values, a switching valve is paired with the effluent flow downstream from the membrane-free electrochemical cell. During the reverse half-cycle operation of the electrochemical cell, the switching valve is activated to switch the effluent flows so that they are delivered to a storage container with the same or nearly the same pH.610 For example, if the first effluent flow is stored in the first storage tank during the half-cycle in Figure 5, the second effluent flow is diverted to be stored in the first storage tank during the reverse half-cycle in Figure 6 in order to maintain flows with similar pH values ​​together. In certain embodiments, one or both of the stored effluent flows are further processed by further reacting the flow to capture target molecules or solutes.612 For example, in order to capture carbon dioxide from effluent, low-pH effluent may be reacted with carbon dioxide-rich minerals as described above.

[0039] As described above, various embodiments of membrane-free electrochemical cells can be used to create pH gradients that can be used to separate and / or capture target molecules or solute components. Without a membrane, the electrochemical cell becomes more durable and can generate pH gradients while consuming less energy. These membrane-free electrochemical cells can be used, for example, to remove carbon dioxide from seawater or for desalination.

[0040] In all cases described herein, the redox active material on an electrode should be understood to include not only the oxidized state of one redox pair, but also any intermediate charge state of the redox pair, whether completely reduced or completely oxidized. For example, an electrode coated with bismuth and bismuth oxychloride in a 1:1 molar ratio is considered to be in a 50 percent charge state and should be considered, for the purposes of the present invention, to be coated with one type of redox active material. As another example, an electrode coated with a polymer containing a redox-active quinone moiety is considered to contain one type of redox active material, regardless of whether all quinone moieties on the polymer are in their reduced state, oxidized state, or any combination thereof. Two electrodes having different charge states of the same redox pair are understood to contain the same redox active material.

[0041] Unless otherwise indicated, all numbers used in this specification and the claims to represent feature sizes, quantities, and physical properties should be understood in all cases to be modified by the term “approximately.” Therefore, unless otherwise indicated, the numerical parameters described in the foregoing specification and the appended claims are approximations that may vary depending on the desired properties that a person skilled in the art would seek to obtain using the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (for example, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5), as well as any range within that range.

[0042] The foregoing description is provided for illustrative and explanatory purposes only. It is not intended to be exhaustive or to strictly limit the embodiments to the disclosed forms. Nor is it intended to limit the embodiments to aqueous inks or water-containing inks. Many modifications and variations are possible in light of the above teachings. Any or all features of the disclosed embodiments can be applied individually or in any combination and are not intended to be limiting, but are merely illustrative. The scope of the present invention is not intended to be limited to these “modes for carrying out the invention,” but rather to be determined by the “claims” appended herein.

Claims

1. 1. A membrane-less electrochemical device, comprising: a fluid feed stream input to the membraneless electrochemical device; a first electrode including a first redox active material configured to undergo a proton-coupled oxidation reaction with a first portion of the fluid feed stream; a second electrode including a second redox active material configured to undergo a proton-coupled reduction reaction with a second portion of the fluid feed stream, the first portion and the second portion being separated; a first effluent stream comprising said first portion and having a first pH, said first pH being a pH value of said first effluent stream; a second effluent stream comprising the second portion and having a second pH different from the first pH, the second pH being a pH value of the second effluent stream; a first vessel configured to receive an effluent stream having the first pH; a second vessel configured to receive an effluent stream having the second pH; a diverter valve connected to the first and second effluent streams and to the first and second vessels; A membrane-free electrochemical device comprising:

2. 10. The membraneless electrochemical device of claim 1 , wherein at least one of the first and second redox active materials is coated on at least one of the first or second electrodes.

3. 10. The membraneless electrochemical device of claim 1 , wherein at least one of the first and second redox active materials is a polymer grafted to at least one of the first or second electrodes.

4. 10. The membraneless electrochemical device of claim 1 , wherein the first redox active material and the second redox active material are the same.

5. 2. The membraneless electrochemical device of claim 1 , wherein at least one of the first and second redox active materials is at least one of a quinone, a phenazine, a pyrazine, a quinoxaline, and derivatives thereof, or at least one of the first and second redox active materials is at least one of an ionomer and a polymer, and at least one of the ionomer and polymer comprises at least one of a quinone, a phenazine, a pyrazine, a quinoxaline, and derivatives thereof.

6. 10. The membraneless electrochemical device of claim 1, wherein each of the first and second electrodes comprises at least one of a conductive material, a binder, and a conductive binder.

7. 2. The membraneless electrochemical device of claim 1 , wherein the fluid feed stream flows parallel to a first surface of the first electrode and a first surface of the second electrode, the first surfaces facing each other and separated by a gap of a predetermined distance.

8. 2. The membraneless electrochemical device of claim 1, wherein the first and second electrodes are porous and positioned opposite one another, the first portion of the fluid feed stream flowing through the first electrode and the second portion of the fluid feed stream flowing through the second electrode.

9. The membraneless electrochemical device of claim 1 , wherein the first and second electrodes are porous.

10. 2. The membrane-less electrochemical device of claim 1, wherein the first and second electrodes are coupled to an energy source, the energy source configured to drive a proton-coupled oxidation reaction with the first redox active material and a proton-coupled reduction reaction with the second redox active material when a potential is applied between the first and second electrodes, and wherein when the potential applied between the first and second electrodes is reversed, driving a proton-coupled reduction reaction with the first redox active material and a proton-coupled reduction reaction with the second redox active material causes the first effluent stream to have the second pH, the second pH being a pH value of the second effluent stream before the potential applied between the first and second electrodes was reversed, and the second effluent stream has the first pH, the first pH being a pH value of the first effluent stream before the potential applied between the first and second electrodes was reversed.

11. The membrane-less electrochemical device of claim 1 , wherein the fluid feed stream comprises a target component.

12. 12. The membrane-less electrochemical device of claim 11 , wherein the target component is carbon dioxide.

13. The membrane-less electrochemical device of claim 11 , wherein the target component is a salt.

14. 1. A system comprising: A fluid feed stream; and 1. A membrane-less electrochemical device, comprising: a first electrode including a first redox active material configured to undergo a proton-coupled oxidation reaction with a first portion of the fluid feed stream in response to a first potential between the first electrode and a second electrode; a second electrode including a second redox active material configured to undergo a proton-coupled reduction reaction with a second portion of the fluid feed stream in response to the first potential, the second electrode being separated from the first portion; a first effluent stream comprising the first portion and having a first pH, the first pH being a pH value of the first effluent stream; and a second effluent stream comprising said second portion and having a second pH different from said first pH, said second pH being a pH value of said second effluent stream; A membrane-free electrochemical device comprising: an energy source configured to apply the first potential and a second opposing potential between the first and second electrodes; a first vessel configured to receive an effluent stream having the first pH; a second vessel configured to receive an effluent stream having the second pH; a diverter valve coupled to the first and second effluent streams and the first and second vessels; A system comprising:

15. 15. The system of claim 14, wherein the first container comprises a base material configured to react with an effluent stream having a first pH to increase the pH of the effluent stream to a third pH before the effluent stream is discharged.

16. 15. The system of claim 14, wherein the fluid feed stream includes a target molecule or solute, and the first container includes a base material configured to react with the effluent stream having the first pH to separate the target molecule or solute before the effluent stream is discharged.

17. 15. The system of claim 14, wherein the second effluent stream is treated to absorb and capture carbon dioxide by reacting the second effluent stream with carbon dioxide.

18. 15. The system of claim 14, wherein the switching valve is configured to direct the first effluent stream to the first container and the second effluent stream to the second container when the energy source applies the first potential between the first and second electrodes, and to direct the second effluent stream to the first container and the first effluent stream to the second container when the energy source applies the second reverse potential between the first and second electrodes.

19. 15. The system of claim 14, wherein the fluid feed stream flows parallel to a first surface of the first electrode in the membrane-less electrochemical device and parallel to a first surface of the second electrode in the membrane-less electrochemical device, the first surfaces facing each other and separated by a gap of a predetermined distance.

20. 15. The system of claim 14, wherein the first and second electrodes of the membrane-less electrochemical device are porous, and the first portion of the fluid feed stream flows through the first electrode and the second portion of the fluid feed stream flows through the second electrode.

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