ELECTROCHEMICAL CELL WITH FLUIDICALLY CONTROLLED CHARGE CARRIERS AND RELATED DEVICES, SYSTEMS, AND TECHNIQUES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This patent application claims the benefit of and priority to U.S. Provisional Patent Application No. 63/427,554, filed on Nov. 23, 2022, which is herein incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

[0002]The present disclosure relates to electrochemical processes and, more particularly, to electrochemical processes involving the simultaneous splitting of water or salts and the manipulation of electrolyte chemistry.

BACKGROUND

[0003]With greater availability of intermittent renewable energy sources, such as solar and wind energy, the price of such energy is dropping. This development strongly favors low capital-intensive electrochemical installations that can afford to sit idle during times of limited energy supply. However, current electrochemical devices are too costly to idle for any significant stretch of time. Also, adding the complexities of direct air capture, liquid synthesis, and reliance on intermittent power supply for operating puts further pressure on reducing the total cost of such installations.

SUMMARY

[0004]One example embodiment provides an electrochemical device. The electrochemical device includes a plurality of one or more electrochemical cells that contain a volume with its size in one direction (width) much smaller than in the other two directions (height and length) and an electric field pointing in the direction of the short dimension (width) containing a liquid electrolyte. With this example electrochemical device, pressure gradients in the direction of the electric field are actively controlled to maintain low flow speeds in the direction of or opposite to the direction of the electric field that are comparable to the speed of ions moving relative to the electrolyte under the influence of the electric field present. Also, with this example electrochemical device, the flow speed of the electrolyte is controlled such that the combined speed of liquid electrolyte and ionic drift of selected ions in the electric field is, according to the choice of the operator, either sped up, slowed down, stopped, or reversed.

[0005]In some cases, flow continuity is maintained by feeding liquid electrolyte into certain regions of the electrolyte volume (the input) of an electrochemical cell and removing electrolyte from the same or other regions of the electrolyte volume (the output). In some such cases, the chemical composition of the input electrolytes to an individual cell and output electrolytes to an individual cell are not all the same. In some such instances: the corresponding inputs to each cell are of the same chemical composition as in all other cells; and all corresponding outputs are the same as in all other cells. In some other such instances, for some streams, outputs from one cell are routed to inputs to another cell.

[0006]In some cases, some regions of the electrolyte volume are separated by permeable barriers. In some such cases, the permeable barriers are comprised of one or more of the following: a non-woven textile; a woven textile; a knitted textile; a flat or pleated, perforated inert membrane with perforation holes of regular or irregular shape, with sizes in the range from 0.5 μm to 1 mm, and preferably in the range between 10-100 μm, and for which the aspect ratio between hole diameter and membrane thickness is between 0.01:1 to 100:1; a monolith-like structure of substantially straight channels across the monolith and aligned with the electric field in the electrochemical cell; a macroporous material with connected open pores; a microporous material with connected open pores; a permeable nano-porous membrane that does not exhibit ion selectivity; a permeable nano-porous membrane that does exhibit ion selectivity; and an aerogel-like membrane with high permeability for the electrolyte in the electrochemical cell. In some such instances, a circulation flow is maintained within the regions of the electrochemical cells that are delineated by barriers or the cathodic end or the anodic end of the cell; and the flow speeds in the circulation flow are substantially larger than the controlled flow in the electric field direction. In some such instances, the average pressure of the cross-circulation flow in a region of the electrochemical cell (flow channel), the pressure differentials within this flow, and the addition or withdrawal of fluid can be independently controlled by the operator. In some such instances, the circulation flow enters and leaves the electrochemical cell; and some or all means of pressure control, differential pressure control, addition and withdrawal of fluid, and chemical adjustments to the fluid are effectuated outside of the electrochemical cell.

[0007]In some cases, the electrochemical device further includes sensors configured to provide feedback for the control system. In some such cases, pressure sensors; differential pressure sensors; fluid flow or fluid speed sensors; temperature sensors; chemical sensors, like pH sensors, oxygen sensors, carbon dioxide sensors, hydrogen sensors, sensors sensitive to specific ions including carbonates or bicarbonates; optical sensors; colorimetric sensors; and acoustic sensors.

[0008]In some cases, flows on the opposite sides of a permeable barrier are controlled in a manner as to minimize variations in the pressure differential across the permeable barrier as a function of the position on the locations of the permeable barrier. In some such cases, the pressure gradients introduced by the circulation flow in directions orthogonal to the electric field are smaller than, comparable to, or larger than the controlled pressure drop or drops across the permeable barrier or barriers. In some instances, average pressures in the regions of the electrochemical cells that are delineated by barriers, or the anodic end, or the cathodic end of the cells are controlled in a manner such that the pressure drop across each barrier produces the desired hydrodynamic flow velocity component aligned with the electric field.

[0009]In some cases, the separation among electrochemical cells is provided by bipolar membranes, permeable or impermeable electrodes, or permeable or impermeable electrically inert walls and a solid or permeable electrode embedded into the region that is adjacent to the separating wall and the first permeable barrier or where a permeable electrode also functions as the first permeable barrier that is adjacent to the end permeable or impermeable wall of an electrochemical cell.

[0010]In some cases, at least some of the electrochemical cells are fluidically coupled. In some cases, at least some of the electrochemical cells are electrically coupled. In some cases, all or some electrochemical cells are electrically connected in series. In some cases, all or some electrochemical cells are electrically connected in parallel. In some cases, at least some electrochemical cells are electrically isolated from each other.

[0011]In some cases, pressure control systems control cross-circulation flow and trans-barrier flow individually in each cell. In some cases, pressure control systems for cross-circulation are acting simultaneously on multiple electrochemical cells. In some cases, pressure control systems for trans-barrier flows are acting simultaneously on multiple electrochemical cells.

[0012]In some cases, control systems are comprised of: subsystems that act on individual electrochemical cells; and subsystems that act on clusters of electrochemical cells. In some cases, at least some aspects of the control system rely on stabilizing physical effects. In some cases, at least some aspects of the control system rely on sensor feedback and algorithmic control from electronic processors.

[0013]In some cases, all or some of the electrolytes in the electrochemical cells are aqueous salt solutions. In some such cases, the salts in the aqueous solution are mixtures of hydroxides, carbonates, and bicarbonates. In some such instances, the cations in the aqueous solution comprise at least one of sodium ions and potassium ions.

[0014]In some cases, the inputs and outputs to electrochemical cells differ in at least one of pH and salinity. In some such cases, the electrochemical device further includes one or more electrochemical cells of substantially identical geometry, each electrochemical cell incorporating one input stream and two output streams, with one output leaving from the cathodic region at high pH (e.g., greater than about 12), one output leaving from the anodic region with a low pH (e.g., in the range of about 7-11), and the input into the electrochemical cell of an intermediate pH (e.g., in the range of about 9 to 14).

[0015]In some cases, one barrier separating the cathodic region from the anodic region of each electrochemical cell and the input stream is added to the anodic compartment. In some cases, one barrier separating the cathodic region from the anodic region of each electrochemical cell and the input stream is added to the cathodic region. In some cases, two barriers separating each electrochemical cell into three regions and the input stream is added to the center region. In some cases, the electrochemical cells comprise an anode and a cathode and operate as electrolyzers. In some such instances, one or both electrodes also perform the function of one of the permeable barriers; and the output stream leaving the cell near such a dual-function electrode is extracted between the end wall and the electrode. In some such instances, both electrodes of a cell act as a barrier; and the input stream enters the cell between the two electrodes. In some cases, one or both electrodes also perform the function of the end wall of the electrochemical cell. In some cases, one or both electrodes are embedded into the first region adjacent to the cell.

[0016]In some cases, cross-circulation in all regions of the electrochemical cells is maintained; and the cross-circulation speed is greater than (e.g., 100-10,000 times faster than) the controlled crossflow speeds aligned with the electric field. In some cases, the electrochemical cells produce hydrogen at the cathodes and oxygen at the anodes. In some such cases, the gases produced at the anode or cathode are substantially outgassed from the cross-circulation stream outside of the electrochemical cells. In some such instances, the salt composition is substantially a mixture of hydroxide, carbonate, or bicarbonate.

[0017]In some cases, for cells with an anolyte compartment and a catholyte compartment: the liquid inputs are: substantially a bicarbonate/carbonate solution with balancing cations of pH greater than 8 and less than 14 (anolyte); and substantially a hydroxide solution with balancing cations with pH greater than 12 (catholyte). Also, the liquid outputs are: substantially a bicarbonate/carbonate solution with balancing cations with a pH that is lower than that of the anolyte input but greater than 8 and less than 12; and substantially a hydroxide solution with balancing cations with pH greater than that of the catholyte input and greater than 12. In some such cases, the cations in both anolyte and catholyte streams are predominantly potassium at a concentration between 0.1-10 M. In some other such cases, the cations in both anolyte and catholyte streams are predominantly sodium at a concentration between 0.1-10 M. In some cases, the gaseous output streams are: a substantially pure hydrogen stream; and a stream with majority oxygen.

[0018]In some cases, the electrochemical device further includes cells with an anolyte compartment and a catholyte compartment for which the liquid inputs are both substantially a potassium hydroxide solution with a concentration between 0.1-20 M. In some cases, the electrochemical device further includes a first gaseous output stream which is substantially pure hydrogen; and a second gaseous output stream with a majority content of oxygen.

[0019]The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been selected principally for readability and instructional purposes and not to limit the scope of the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 illustrates a schematic of an example electrochemical cell.

[0021]FIG. 2 illustrates an electrochemical cell configured with a flow distribution described in relation to FIG. 1, in accordance with an embodiment of the present disclosure.

[0022]FIG. 3 illustrates a top view of a flow distribution frame configured in accordance with an embodiment of the present disclosure.

[0023]FIG. 4 illustrates an electrochemical cell with two flow channels where the pressure of the anolyte is greater than the catholyte, thereby establishing a crossflow from anolyte to catholyte (i.e., a cationic-biased crossflow), in accordance with an embodiment of the present disclosure.

[0024]FIG. 5 illustrates an electrochemical cell with a third, interstitial flow, in accordance with an embodiment of the present disclosure.

[0025]FIG. 6 illustrates an electrochemical cell configured in accordance with an embodiment of the present disclosure.

[0026]FIG. 7 illustrates an electrochemical cell configured in accordance with an embodiment of the present disclosure.

[0027]FIG. 8 illustrates that multiple cells can be connected electrically and fluidically to form an electrochemical system or stack, in accordance with an embodiment of the present disclosure.

[0028]FIG. 9 illustrates a system configured with flow and pressure controls, in accordance with an embodiment of the present disclosure.

[0029]FIG. 10 is a graph illustrating pressure drops over a barrier along a flow in the catholyte and anolyte channels from inlets to outlets, in accordance with an embodiment of the present disclosure.

[0030]FIG. 11 illustrates a decoupled multi-control system configured in accordance with an embodiment of the present disclosure.

[0031]FIG. 12 illustrates a schematic of an electrochemical stack, visualized schematically as only one call, employed in a direct air capture setting, in accordance with an embodiment of the present disclosure.

[0032]These and other features of the present embodiments will be understood better by reading the following detailed description, taken together with the figures herein described. The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing.

DETAILED DESCRIPTION

[0033]An electrochemical cell with fluidically controlled charge carriers and related systems and techniques are disclosed. In accordance with some embodiments, the disclosed electrochemical cell may be configured to suppress fluidic mixing while controlling fluid flow in the direction of the electric field at rates that are comparable to the speed of electromigration, contrary to existing approaches that use ion-selective membranes to manipulate electromigration. To such ends, the disclosed electrochemical cell may employ, in accordance with some embodiments, a low-cost, permeable barrier and may be configured to be operated with a control scheme that allows for variable modulation of the type of charge carrier crossing the barrier. In particular, the disclosed electrochemical cell can modulate, in a controlled manner, the contribution of the different charge carriers to the electric current through the cell by superimposing a fluid flow through individual sections of the cell that substantially align with the direction of the electric field, in accordance with some embodiments. These flows may be controlled, in accordance with some embodiments, by manipulating pressures in the electrochemical cell. Therefore, the disclosed electrochemical cell may be configured, in accordance with some embodiments, to use fluid flows to choose whether cations or anions travel between the electrodes. Additionally, the modulation of charge carriers allows for targeted manipulation of anolyte and catholyte chemistry, which has additional utility described herein. Numerous configurations and variations will be apparent in light of this disclosure.

General Overview

[0034]Controlling charge carriers in a water-splitting or other electrochemical cell can be achieved by using an ion-exchange membrane between the electrodes and their respective electrolyte media. In these existing approaches, electric current is manipulated by selectively changing the mobility of either (A) anions via an anionic exchange membrane or (B) cations via a cationic exchange membrane. Although these ionic exchange membranes also serve to keep produced gases—hydrogen (H₂) and oxygen (O₂)—separate and, in some applications, manipulate the chemistry of the anolyte and catholyte, they are limited to their respective single modalities and are costly and prone to degradation.

[0035]As will be appreciated in light of this disclosure, electrochemical cells can maintain density gradients along the electric field direction via electromigration of different species. Such chemical gradients can be obliterated, though, by fluid dynamic mixing of the electrolyte. If such mixing can be suppressed, however, it is possible to use electric fields to separate various ionic species.

[0036]Thus, and in accordance with some embodiments, an electrochemical cell with fluidically controlled charge carriers and related systems and techniques are disclosed. In accordance with some embodiments, the disclosed electrochemical cell may be configured to suppress fluidic mixing while controlling fluid flow in the direction of the electric field at rates that are comparable to the speed of electromigration, contrary to existing approaches that use ion-selective membranes to manipulate electromigration. To such ends, the disclosed electrochemical cell may employ, in accordance with some embodiments, a low-cost, permeable barrier and may be configured to be operated with a control scheme that allows for variable modulation of the type of charge carrier crossing the barrier. In particular, the disclosed electrochemical cell can modulate, in a controlled manner, the contribution of the different charge carriers to the electric current through the cell by superimposing a fluid flow through individual sections of the cell that substantially align with the direction of the electric field, in accordance with some embodiments. These flows may be controlled, in accordance with some embodiments, by manipulating pressures in the electrochemical cell. Therefore, the disclosed electrochemical cell may be configured, in accordance with some embodiments, to use fluid flows to choose whether cations or anions travel between the electrodes. Additionally, the modulation of charge carriers allows for targeted manipulation of anolyte and catholyte chemistry, which has additional utility described herein.

[0037]By way of a non-limiting example, consider an electrochemical cell filled with potassium hydroxide (KOH). Under conventional operation of such a cell, the current normally may be carried solely by hydroxide (OH⁻) ions. However, in consideration of techniques disclosed herein, by flowing electrolyte from the anode at a sufficiently slow speed that matches the transport rate of OH⁻ against the fluid, the electric charge transfer may be accomplished by the motion of cations, which now may carry the electric current instead of the OH, in accordance with some embodiments. As will be appreciated in light of this disclosure, application of techniques disclosed herein may have no (or otherwise minimal) substantive impact on the electrochemical cell (e.g., unless the chemical composition of the fluid entering the cell differs from the one leaving the cell), in accordance with some embodiments.

[0038]As will be appreciated in light of this disclosure, the devices, systems, and techniques disclosed herein may be utilized in any of a wide range of target applications and end-uses. For example, in accordance with some embodiments, the disclosed subject matter may be utilized, in part or in whole, with synthetic fuel production systems and methods such as those disclosed in U.S. patent application Ser. No. 17/535,263, titled “Synthetic Fuel Production System and Related Techniques,” the disclosure of which is herein incorporated by reference in its entirety. More generally, the teachings of the present disclosure may be utilized, in accordance with some embodiments, to simplify water splitting cells and reduce their costs. At least some embodiments disclosed herein may be implemented in scalable, global energy solutions involving, for example, generating hydrogen from electrochemical water splitting, synthesizing alcohols or hydrocarbons from such hydrogen and from non-fossil carbon dioxide (CO₂), and collecting CO₂ from ambient air through direct air capture, among others that will be apparent in light of this disclosure.

[0039]As will be further appreciated in light of this disclosure, techniques and structures disclosed herein may open the door to cost-effective electrochemical cells for water splitting and for cells that combine water splitting with CO₂ production or salt splitting. In accordance with some embodiments, the disclosed electrochemical cell may lack an ion exchange membrane and, thus, may provide a significantly cheaper water-splitting device as compared to existing approaches.

[0047]Also, as used herein, the term “electrolyte” generally may refer to an aqueous solution with dissolved ionic content. The ions may be, for example, dissociated salts or deprotonated acids or, more simply, protons and hydroxide (OH⁻) ions. In accordance with some embodiments, solutions where the cations are any one (or combination) of potassium (K⁺) and sodium (Na⁺) may be of primary interest, but the present disclosure further contemplates other suitable cations, such as ammonium (NH₄⁺), iron (Fe⁺²/Fe⁺³), calcium (Ca⁺²), and magnesium (Mg⁺²), among others. In accordance with some embodiments, solutions where the anions are any one (or combination) of hydroxide (OH⁻), bicarbonate (HCO₃⁻), and carbonate (CO₃⁻²) may be of primary interest, but the present disclosure further contemplates other suitable anions, such as sulfate (SO₄⁻²), phosphate (PO₄⁻³), and acetate (CH₃O₂⁻), among others. Also of note, the electrolyte flowing in contact with the cathodic end is referred to herein as the “catholyte,” whereas the electrolyte flowing in contact with the anodic end is referred to herein as the “anolyte.”

Electrochemical Cell Structure and Operation

[0052]As can be seen from FIG. 1, cell 100 may include an electrode 101 (e.g., a cathode) and an electrode 102 (e.g., an anode). Any of a wide range of conductive materials which is chemically stable in a given environment may serve as electrode(s) 101, 102. Such materials may include, for example, conductive ceramics, various allotropes of carbon, pure metals, and metal alloys. Furthermore, any combination of such materials in the form of sheets, wire meshes, or foams may serve as electrode(s) 101, 102. For neutral-to-alkaline environments, for example, it may be desirable to utilize nickel and nickel-based alloys for electrode(s) 101, 102. Also, as will be appreciated, the materials need not be the same for cathode 101 as for anode 102. The materials utilized (A) can be formed into a permeable surface, allowing for liquid flow through the same, substantially in the same direction as the electric field in cell 100, or (B) can be combined directly with cell separator wall 106 (discussed below). Also, as can be seen from FIG. 1, cell 100 may include one or more cell channels 104, where neighboring channels 104 may be separated by a permeable barrier 103.

[0053]Furthermore, as can be seen from FIG. 1, cell 100 may include a channel spacer/flow guides 105 and a cell separator wall 106. If cell separator wall 106 is made from an electrically insulating material (e.g., such as plastic, ceramic, or glass), it may be desirable to include an electric bridge which allows for an electrical connection to a region outside cell 100. In some designs for which electrodes 101, 102 allow liquid flow across them in the direction of the electric field, either or both of electrodes 101, 102 can perform the function of a permeable barrier 103 between flow channels 104. In this case, the cathodic end or anodic end of cell 100 may be limited on one side by a cell separator wall 106 and on the other side by the permeable electrode 101 and/or 102.

[0054]Permeable barrier 103 of electrochemical cell 100 may be a component that allows for liquid flow that is substantially a function of the differential pressure between the bulk liquids in flow channels 104 on either side of barrier 103. In the simplest case, the flow characteristics of barrier 103 can be explained using a material dependent permeability constant K barrier (ml/cm²/s/Pa). Denoting the liquid flux through barrier 103 by Fl (ml/cm²/s) and the differential pressure over barrier 103 locally by ΔP, a linear relationship between the flux of liquid through barrier 103 and the differential pressure over the same is given by:

$F1=K_{\mathrm{barrier}}\Delta P.$

This type of flux through a given barrier 103 is referred to as the cell “crossflow.” Note that crossflows are substantially parallel to the electric field as depicted in FIG. 1, as opposed to other flows in cell 100, referred to as “circulation flows,” that are perpendicular to the electric field.

[0055]In accordance with some embodiments, examples of permeable barriers 103 which may be utilized in conjunction with the disclosed techniques and structures may be comprised of one or more of the following: a non-woven textile; a woven textile; a knitted textile; a flat or pleated, perforated inert membrane with perforation holes of regular or irregular shape; a naturally porous inert membrane; a monolith-like structure of substantially straight channels across the monolith and aligned with the electric field in the electrochemical cell; a macroporous material with connected open pores; a microporous material with connected open pores; a permeable nanoporous membrane that does not exhibit ion selectivity (e.g., such as graphene or a composite membrane); a permeable nano-porous membrane that does exhibit ion selectivity; or an aerogel-like membrane with high permeability for the electrolyte in the electrochemical cell. The pores/holes in the membrane of any kind may be in the range from 0.01 μm to 1 mm and preferably in the range between 0.1-10 μm. The aspect ratio between hole/pore diameter and membrane thickness may be chosen between 0.01:1 to 100:1. However, any other material layer that provides a well-defined resistance to flow, and for which ion selectivity by itself is insufficient to control the flow, can act as a permeable barrier, in accordance with some embodiments.

[0056]In accordance with some embodiments, spacers/flow guides 105 in flow channels 104 in electrochemical cell 100 may be configured to keep the channel volume approximately constant, independent of fluid dynamic characteristics of the flow in neighboring channels 104 while still allowing for flow both in and orthogonal to the electric field direction. In accordance with some embodiments, possible spacer/flow guide 105 materials may include those substantially inert in the specific chemical environment of electrochemical cell 100. In the case of aqueous alkaline electrolytes, they may include, for example, various species of plastics (e.g., nylon, polypropylene, polyurethane, etc.), ceramics, and glasses. Spacer 105 materials may be formed into meshes, for example, with square, rectangular, round, or diamond-shaped openings.

[0057]As will be appreciated, the present disclosure builds on controlling the differential pressure over a given permeable barrier 103 and, hence, controlling the crossflow through that barrier 103 when electrochemical cell 100 carries an electric current. A crossflow through barrier 103 from the channel closer to anode 102 to the channel closer to cathode 101 will bias the transport of charge carriers across barrier 103 in favor of cations from the anolyte at the expense of anions from the catholyte, referred to as a “cationic-biased flow.” Contrariwise, a crossflow through barrier 103 from the channel closer to cathode 101 to the channel closer to anode 102 will bias the transport of charge carriers across barrier 103 in favor of anions from the catholyte at the expense of cations from the anolyte, referred to as an “anionic-biased flow.”

[0058]The present disclosure discusses several ways of controlling liquid pressures in electrochemical cell 100. Utilizing such controls avoids the need for ion exchange membranes, which are both expensive and prone to degradation.

[0059]As will be appreciated in light of this disclosure, the magnitude of the crossflows required to control the chemistry of cell 100 is a function of both charge concentration in the electrolyte and the applied cell current/current density. Herein, the cationic charge concentration of an electrolyte is denoted by C⁺_electrolyte (C/L). For an electrolyte with several cationic species with individual concentrations [Cat_i] (mol/L) and valences n_i, the positive charge concentration is given by

$C_{\mathrm{anolyte}}^{+}=\sum n_i\left[{\mathrm{Cat}}_i\right]/F,$

where Faraday's constant F=96,485 (C/mol). Charge neutrality implies that

$C_{\mathrm{electrolyte}}^{+}=C_{\mathrm{electrolyte}}^{-},$

where the latter is the concentration of negative charge in the electrolyte similarly defined. The cell current I(A) corresponds to a nominal current density

$i=I/A\left(A/{\mathrm{cm}}^2\right),$

where A is the cross-sectional area of cell 100 (height multiplied by length). Establishing cationic-biased crossflows on the same order of magnitude as i/C⁺_electrolyte (L/cm²/s) or for the entire barrier 103 I/C⁺_electrolyte (L/s) enables the convective flow to carry sufficient current. The entity i/C⁺_electrolyte may be viewed as an order-of-magnitude guide, and modifications may be necessary to adjust for different mobility of different ionic species. Modulating the pressure drop to attain a crossflow to between 0.1-10 times this value may be beneficial to ensure proper transport.

[0060]In addition to the crossflows, cell 100 may be constructed to handle flows perpendicular to the electric field, the direction of which is substantially depicted in FIG. 1 inside each cell channel 104, so-called “circulation flows.” These flows may be approximately equal in adjacent, fluidically coupled channels 104, and significantly faster (e.g., between 100-10,000 times faster) than the crossflows. These circulatory flows can be designed to carry flow out of the electric field region (i.e., out of the volume that is conventionally considered inside electrochemical cell 100) to facilitate mixing, outgassing of product gases, absorption of additional gases into the flow, and other chemical conversions. The circulation flows will carry away produced gases separately from cell 100. The crossflow (or crossflows, if there are more than two flow channels) can be arranged with the purpose of minimizing any gas crossover inside one cell 100.

[0061]The circulation flows may result in pressure gradients inside flow channel 104 in cell 100, and, in many instances, the pressure variations inside a region of flow channel 104 can be substantial if measured relative to the size of the pressure drop one aims for across barrier 103 (i.e., the pressure drop inside cell 103 in the direction of the electric field). Another reason for such pressure changes may be due to gravity if cells 100 are oriented in a way such that moving parallel to barrier 103 can include a vertical component. Crossflows can impact the net electric current density across barrier 103. Therefore, it may be desirable to ensure uniform crossflows across the entirety of barrier 103 (i.e., uniform over the height and the length of barrier 103). In designs that see substantive pressure variations in the circulation flow of cell 100, it may become important to match such pressure changes on both sides of barrier 103, so that the variations across barrier 103, whether they are temporal or spatial, cancel out, resulting in a pressure differential across barrier 103 that is independent of the location on barrier 103. The present disclosure discusses a flow distribution envelope that ensures uniform distribution of liquid circulation flows along the length of cell channel 104 in cell 100. By keeping liquid flow paths from outside cell 100 to injection points inside cell 100 of even length and mutually equal cross-sections, the pressure drop will be substantially identical, thereby ensuring uniform flow distribution to the separate injection points in cell 100.

[0062]FIG. 2 illustrates an electrochemical cell 200 configured with such a flow distribution described above in relation to FIG. 1, in accordance with an embodiment of the present disclosure. Separate flow frames 201 for the anolyte and catholyte are designed to establish a unidirectional circulation flow along the height of channel 202. Establishing such a flow is important to achieve close to identical pressure drops on either side of barrier 203 and, hence, a constant pressure drop across barrier 203. The schematic of FIG. 2 shows one example embodiment of how the example electrochemical cell 100 of FIG. 1 may be reconstructed with one permeable barrier 203 and two flow channels 202 and equipped with circulation flow inlets 204 and outlets 205, in accordance with some embodiments. Also, sealing members 206 may be arranged between flow frames 201 and permeable barrier 203 in such a way to keep the anolyte and the catholyte from leaking out from the channel. It should be noted that some features not called out here in relation to FIG. 2 are otherwise seen and described in relation to FIG. 1, discussed above.

[0063]FIG. 3 illustrates a top view of such a flow distribution frame 300 configured in accordance with an embodiment of the present disclosure. Providing flow paths of approximately equal length from inlets 301 to the bottom of channel 304 will ensure a uniform pressure drop of the flow inside flow frame 300 and, hence, a unidirectional flow from the bottom of cell channel 304. As indicated in FIG. 2, these flow frames 300 allow for bulk anolyte and catholyte flow not just for inlet 301/outlets 302 but also as conduits to neighboring cells 200. That is, two or more cells 200 can be fluidically coupled in the sense that one input stream gets distributed to two or more individual cells 200, and the outputs from two or more individual cells 200 get combined into one output stream. In some embodiments, these flow frames 300 and separators 206 may be made from one or more plastics, such as polyetheretherketone (PEEK), polyetherimide (PEI) such as ULTEM® polyetherimide available from General Electric Co., acrylic, high-density polypropylene (HDPP), and high-density polyethylene (HDPE), among others. Furthermore, in some embodiments, flow frames 300 may be 2.5-dimensional, meaning that one face is substantially (e.g., completely) flat and all forming can be achieved from the other side. This means that frames 300 may be machined through stamping, routing, or milling from stock material or near net shape forms, in addition to the possibility of molded parts. In the depicted embodiment of FIG. 2, frame 300 presents flat faces for gaskets or other sealing members. In other embodiments, grooves can be included for traditional O-ring seals. The embodiment shown in FIG. 3 also includes openings 305 for bolts or set screws for stack assembly. The schematic of FIG. 3 shows an embodiment of a flow frame 300 of a 2.5-dimensional structure, where circulation flow distribution paths 303 from cell inlets 301 to anywhere at the bottom of flow channel 304 are of similar lengths and cross-section and, hence, ensure similar pressure drop for each such path.

[0064]FIG. 4 illustrates an electrochemical cell 200 with two flow channels 202 where the pressure of the anolyte is greater than the catholyte, thereby establishing a crossflow from anolyte to catholyte (i.e., a cationic-biased crossflow), in accordance with an embodiment of the present disclosure. FIG. 5 illustrates an electrochemical cell 500 with a third, interstitial flow, in accordance with an embodiment of the present disclosure. The configurations seen in these figures may allow, in accordance with some embodiments, operation where fluid flows from an anodic compartment to a cathodic compartment and, in the process, a carbonate solution is converted to a bicarbonate solution to be withdrawn at an anode and hydroxide solution to be recovered at a cathode. Furthermore, by adjusting the crossflow, the amount of hydroxide generated may be adjusted, in accordance with some embodiments. Additional details are provided below with respect to control system structure and operation.

[0065]FIG. 6 illustrates an electrochemical cell 600 configured in accordance with an embodiment of the present disclosure. As can be seen, two porous electrodes 601 and 602 may be utilized as the barriers separating (A) anolyte 603 from interstitial flow 605 and (B) catholyte 604 from interstitial flow 605. In that case, the cathodic end of cell 600 may have a solid wall 606, and liquid may flow behind cathode 601, the interstitial electrolytic flow channel 605 may be bounded by cathode 601 and anode 602, and there may be an anodic chamber 603 where fluid is flowing on the backside of anode 602. In this design, liquid may enter into center 605 and be withdrawn from the ends of catholyte flow 604 and anolyte flow 603, like in FIG. 5.

[0066]FIG. 7 illustrates an electrochemical cell 700 configured in accordance with an embodiment of the present disclosure. As can be seen, a hybrid may be provided in which there is an additional barrier 701 creating a channel for an interstitial flow 702 and an intermediate flow 703. The configuration may be: wall 704|hydroxide withdrawal channel/catholyte flow 705|cathode 707|carbonate injection channel/interstitial flow 702|barrier 701|intermediate flow 703|anode 708|bicarbonate extraction chamber/anolyte 706|wall. As will be appreciated in light of this disclosure, such a configuration may minimize (or otherwise reduce) CO₂ spillover to the cathode 701 side of cell 700.

[0067]In certain applications, it may be favorable to introduce a third flow channel 501 as seen in FIG. 5 into cell 500. Establishing two pressure gradients,

$\Delta P_1\left(h\right)=P_{\mathrm{interstitial}}\left(h\right)-P_{\mathrm{catholyte}}\left(h\right),\mathrm{and}$$\Delta P_2\left(h\right)=P_{\mathrm{interstitial}}\left(h\right)-P_{\mathrm{anolyte}}\left(h\right),$

where ΔP₁ need not be equal to ΔP₂, would result in two crossflows. If, as defined, both ΔP₁ and ΔP₂ are positive, then the convective flow from interstitial channel 501 to catholyte channel 502 will bias: (A) transport of positive (cationic) charge carriers from interstitial channel 501 to catholyte channel 502 over negative (anionic) charge carriers from catholyte channel 502 to interstitial channel 501 and (B) transport of negative (anionic) charge carriers from interstitial channel 501 to anolyte channel 503 over positive (cationic) charge carriers from anolyte channel 503 to interstitial channel 501. The rate of withdrawal from interstitial channel 501 could vary from (A) a dead-ended flow, where the entire volume gets distributed to the anolyte and the catholyte to (B) a marginal withdrawal, where interstitial outlet flow 504 is marginally lower than the inlet flow in the same channel.

[0068]FIG. 8 illustrates that multiple cells 802 can be connected electrically and fluidically to form an electrochemical system or stack 800, in accordance with an embodiment of the present disclosure. In addition to one or more copies of identical cells, stack 800 may be equipped with end plates 801 that are sufficiently stiff to distribute even compression over all cells 802 and sealing members 803. This stack 800 may have electrical leads 804 that allow for connection to a power source to energize cells 802 connected in series. Furthermore, stack 800 may have inlets 805 and outlets 806 for the anolyte and catholyte circulation flows. The inlets may be configured on the same side of stack 800, as seen in FIG. 8, or they can be arranged on opposite sides of stack 800. Stacks 800 may be configured to perform electrolysis or salt splitting operations.

Control System Structure and Operation

[0069]FIG. 9 illustrates a system 900 configured with flow and pressure controls, in accordance with an embodiment of the present disclosure. Note that, in FIG. 9, dashed lines indicate an actuator signal 901, whereas dash-dot lines indicate sensor signals 902. Considering FIG. 9, the behavior of such an electrochemical stack 800 can be manipulated or managed by controlling the pressure differentials across barriers 403 in a cell 400. Pressure sensors 903 of various sorts may make it possible to determine actual pressure differentials against those that are desired. Further control can be asserted by measuring outcomes, like chemical compositions, pH, chemical gradients, temperatures, etc. In the following, the control system is discussed in the context of an electrolyzer stack 800 that is (A) designed to produce hydrogen at cathode 401 and oxygen at anode 402 and (B) fed a carbonate/bicarbonate solution at anode 402 at a rate that results in a cationic current that maintains a steep pH gradient across cell 400. The anolyte is at a lower pH than the catholyte, which approaches hydroxide conditions. While a carbonate solution is added to anolyte 904, the operation of stack 800 produces an anolyte that is substantially a bicarbonate solution, but it remains at a pH level at which outgassing of CO₂ does not occur at any appreciable rate. This discussion is illustrative for a wide range of applications and is not intended to limit the scope of the present disclosure.

[0070]In accordance with some embodiments, controller 901 of system 900 may have several objectives. First, controller 901 may be configured to establish a cross-barrier pressure differential that is uniform over the entire area of every permeable barrier 403 in stack 800. This may be done to ensure uniform flow across barrier 403 when cells 400 are in stable operation (quasi-steady-state operation). Second, controller 901 may be configured to ensure that P_anolyte>P_catholyte in both transient and stable operation to prevent backflow from the catholyte to the anolyte. This can be verified by controlling based on the signals from pressure sensors 902 in system 900. Specifically, referring to FIG. 9, such a backflow can be prevented by ensuring that p3>p2 and p4>p1. Transient operation includes start-up and shut-down, as well as when moving from a stable operation point due to set-point changes, external load changes, or sensor noise. Third, controller 901 may be configured to establish crossflows at rates such that cationic (and/or anionic) carriers convectively match the applied current density to each of cells 400 in stack 800. Here, it is assumed that the flow (or pressure drop) set-points are given to controller 901 as a function of the applied electrical current or voltage.

[0071]The above-mentioned first objective for controller 901 may be achieved by implementing a control law that reaches a steady state where (in FIG. 9):

$p3-p2=p4-p1,$

where p3>p2 and p4>p1, assuming all set-points are given by the above-mentioned third objective as:

$\mathrm{flowOverCell}=f\left(A\right)=\left\{\mathrm{p1\_set}-\mathrm{point},\mathrm{p2\_set}-\mathrm{point},\mathrm{p3\_set}-\mathrm{point},\mathrm{p4\_set}-\mathrm{point}\right\}.$

In the steady state:

$p1=\mathrm{p1\_set}-\mathrm{point},$$p2=\mathrm{p2\_set}-\mathrm{point},$$p3=\mathrm{p3\_set}-\mathrm{point},\mathrm{and}$$p4=\mathrm{p4\_set}-\mathrm{point}.$

[0072]FIG. 10 is a graph illustrating pressure drops over barrier 403 along the flow in the catholyte and anolyte channels from inlets 401 and 402 to outlets 403 and 404, in accordance with an embodiment of the present disclosure. Several control strategies, discussed immediately below, can be implemented to achieve this.

[0073]In accordance with some embodiments, a single-input single-output (SISO) architecture may be employed. In this case, both pumps 903 and 904 may be variable in speed, anolyte pump 904 may control p3, and catholyte pump 903 may control p2 to achieve a specified pressure difference between inlets 805 that will produce the desired flow over cell 400. To keep the pressure difference between outlets 806 (p4, p1) equal to that between inlets 805, catholyte and/or anolyte restrictors 905, 906 may be controlled to compensate for the higher flow on the anolyte side. In this case, catholyte restrictor 905 may control p1, and anolyte restrictor 906 may control p4. Another possible variant is to control only one of restrictors 905 or 906 and let it track the other outlet pressure p1 or p4, compensated for the inlet pressure difference. That is, if controlling anolyte restrictor 906,

$\mathrm{p4\_set}-\mathrm{point}=p1+\left(p3-p2\right),$

whereas if controlling catholyte restrictor 905,

$\mathrm{p1\_set}-\mathrm{point}=p4-\left(p3-p2\right).$

[0074]In accordance with some other embodiments, a different SISO architecture may be employed. In this case, both pumps 903 and 904 may be variable in speed, and p1 and p4 may be controlled by changing the static pressure in catholyte reservoir 907 and/or anolyte reservoir 908 by manipulating catholyte check valve 909 and anolyte check valve 910 to change the pressure in the vessels by controlling the flow rate of the outflowing gas. In this setup, pressure may build up in reservoirs 907, 908 as they start to be filled by gas. The upstream pressures, p2 and p3, may be controlled by changing the speeds of pumps 903, 904. As in the case when using restrictors 905, 906, another variant is to control only the static pressure in one of reservoirs 907, 908.

[0075]In accordance with some other embodiments, a multiple-input multiple-output (MIMO) architecture may be employed. In this case, controllers 1101 (see FIG. 11 discussed below) can be implemented, where model predictive control (MPC) may be particularly well-suited for system 900. In an MPC implementation, entire system 900 may be considered when calculating the control signals for actuators 903, 904, 905, 906, 909, and 910. To implement MPC, a dynamic model of system 900 under control may be needed, as well as a cost function (J) that calculates the cost of a given set of inputs/outputs over a pre-defined time horizon:

$J=\sum _{i=1}^N{w_{\mathrm{xi}}\left(r_i-x_i\right)}^2+\sum _{i=1}^N{w}_{\mathrm{ui}}\Delta u_i^2$

$x_{i,\min }\le x_i\le x_{i,\max };\mathrm{and}$$u_{i,\min }\le u_i\le u_{i,\max }.$

In system 900, x and r will both be the same as for the SISO system:

$x=\left\{p1,p2,p3,p4\right\},$$r=\left\{\mathrm{p1\_set}-\mathrm{point},\mathrm{p2\_set}-\mathrm{point},\mathrm{p3\_set}-\mathrm{point},\mathrm{p4\_set}-\mathrm{point}\right\},$

while the weights will be tuning parameters of controller 1101.

[0080]To fulfill the above-mentioned second objective for controller 1101 (P_anolyte>P_catholyte), different approaches can be utilized. For the SISO implementations, well-tuned controller 1101 loops which ensure robust, stable, and fast set-point control, noise rejection, and load rejection may be implemented. Handling of load disturbances may be particularly important in system 900, as the power available to cell 100 may fluctuate with the availability of a given renewable energy source powering system 900. Fluctuating power levels over cell 100 may require controller 1101 to stabilize at a new operating point. Solar and wind-based energy sources may demonstrate high levels of fluctuations, and controller 1101 may be very well tuned to ensure stable operation. In some instances, the SISO approach may not be enough, especially when the control loops are strongly coupled and/or fast transients and/or delays are part of system 900 dynamics, in which case, additional complexity may need to be added.

[0081]In accordance with some embodiments, system 900 may be strongly coupled due to the connection of flow channels 806 and the circular flow of each channel 806. When a simple SISO design is not enough to ensure stable and fast operation, the MIMO structure in FIG. 11 may be implemented.

[0082]FIG. 11 illustrates a decoupled multi-control system 1100 configured in accordance with an embodiment of the present disclosure. In FIG. 11, {r₁, r₂, . . . , r_n} are the set-points, {C₁, C₂, . . . , C_n} are controllers 1101 (e.g., proportional-integral-derivative, or PID, controllers), D is the decoupler, and G_p is the process under control. In decoupled control system 1100, each controller signal first is paired with the measurement to which it is strongest coupled. This is determined by calculating the relative gain array (RGA) of system 900. RGA is utilized to find the best pairing in terms of how coupled the signals are. Once done, the pairing for the different SISO loops may be known according to:

$\left\{u_1,y_1\right\},\left\{u_2,y_2\right\},\dots ,\left\{u_n,y_n\right\}.$

Next, each controller {C₁, C₂, . . . , C_n} may be tuned to desired performance without considering the coupling between the controller loops. Next, the decoupler (D) is designed to minimize the effect of the coupling between controller 1101 loops.

[0083]Another facet to consider is the startup logic of one or several cells 100 connected to an array of solar panels. The control needs to make the decision whether to start a cell stack 900 based on the available power. As the power available from renewable energy sources can fluctuate significantly, it is not enough to consider the data available at a given moment but also the future available power needs to be prognosticated to avoid cycling a cell on/off in such a way that normal, stable operation cannot be reached. Several ways to achieve this can be considered. First, the control may be connected to the internet, and local weather information (e.g., wind strength, cloud coverage, etc.) may be available for use. Second, the time of day may be known and, together with seasonal data, a statistically informed estimation of the available power may be made. Third, images of the sky may be taken, and image analysis may be deployed both to identify the type of clouds (and, therefore, the power loss when they are covering the sun) and how long it may take before they will cover the sun by estimating their speed and direction.

[0084]To ensure a controlled startup/shutdown of stack 800, controller 901 itself may be powered by a battery or another type of energy accumulator, where the power available at any given moment can be measured. This may make it possible to (1) start up stack 800 only when sufficient power for the controls is available and (2) shut down stack 800 before controller 901 runs out of power to avoid stack 800 being powered down mid-operation.

[0085]As system 900 is designed to be connected to an intermittent energy source, a capacitor bank may be installed, in some cases, between the energy source and system 900. This may be done to filter the supplied voltage/current to system 900, which may smoothen out the load disturbances on stack 800.

Example Use Contexts & Applications

[0086]As will be appreciated in light of this disclosure, the electrochemical cell(s) and related systems and techniques disclosed herein may be utilized in any of a wide range of target applications and end-uses. For example, in accordance with some embodiments, the disclosed subject matter may be utilized with a water splitting cell. A water splitting cell has substantially only two output streams—hydrogen gas and oxygen gas. Possible electrolyte chemistries include (but are not limited to) aqueous solutions of potassium hydroxide (KOH) or sodium hydroxide (NaOH). The concentration of the electrolyte can vary from about 0.1-20 M (solubility limit at room temperature). If the water splitting cell is used as a hydrogen generator, it may be desirable to minimize the oxygen content in this product stream. This can be accomplished by establishing a pressure gradient from the catholyte to the anolyte. Such a flow may bias the charge carriers in favor of hydroxide ions across barrier 403. For a given current density (i) of cell 400, typically between 0.01-1 A/cm², the necessary crossflow rates may be on the order of

$i/\left[{\mathrm{OH}}^{-}\right]/F,$

where [OH⁻] is the concentration of hydroxides in solution, and Faraday's constant F=96,485 C/mol.

[0087]Potential barrier 403 materials for use in a water splitting cell include sheets of non-woven plastic fabrics (e.g., polyolefin, polyethylene, polypropylene), microporous filters, etc. With the permeability of such a barrier 403 denoted K_barrier (mL/cm²/s/Pa), the pressure drop across barrier 403 may be on the order of:

$i/\left[{\mathrm{OH}}^{-}\right]/F/K_{\mathrm{barrier}}.$

Such a pressure drop can be established and varied, with any one (or combination) of the methods outlined above, on a timescale that is commensurate with the fluctuation of available power to the water splitting cell. For instance, a renewable energy source will have intermittencies over several time scales (e.g., seconds and below, hours, days, and seasons). An electrolyzer system 900 as disclosed herein connected to such a renewable source, potentially via an interim energy storage element (e.g., a small battery or capacitor bank), can modulate the fluid flows inside stack 800 to match the available power (current density) for stack 800

[0088]In accordance with some embodiments, the disclosed subject matter may be utilized with an acidifier of a carbonate stream from a direct air capture application. As is known, exposing an alkaline solution of potassium hydroxide (KOH) or sodium hydroxide (NaOH), for example, to ambient air may dissolve CO₂ and convert it to carbonate. Subsequent reduction of pH of this solution may cause a shift in equilibrium from carbonate toward bicarbonates and, if reduced even more, toward carbonic acid/dissolved CO₂.

[0089]One existing approach describes methods of using an electrolyzer to acidify a carbon bearing stream to outgas CO₂, regenerate fresh alkaline solution for continued capture of CO₂, and in parallel generate hydrogen. This existing approach discloses use of a cell that has three output gas streams: H₂; O₂; and CO₂. Specifically, the pH of the anode stream is disclosed to be acidic to neutral (e.g., substantially less than 7) to achieve a sufficiently high partial pressure of CO₂. Contrariwise, the subject matter of the present disclosure is different at least in that (A) substantially no CO₂ may be evolved in the cell and (B) the pH in the anode channel may be maintained in the alkaline regime (e.g., greater than 8). Keeping the pH in the alkaline regime not only improves conductivity in the cell but also allows for using less-resilient (e.g., lower cost) anode materials. In another existing approach, a cationic membrane is employed as permeable barrier 103, which constitutes a completely separate system and operation.

[0090]FIG. 12 illustrates a schematic of an electrochemical stack 800, visualized schematically as only one cell, employed in a direct air capture setting, in accordance with an embodiment of the present disclosure. As can be seen in FIG. 12, the central part is electrochemical stack 800, which may comprise one or more cells 400, each of which has two flow channels (anolyte and catholyte) separated by a permeable barrier 403. Electrochemical stack 800 may be operated with cationic-biased flow (e.g., with a crossflow from the anolyte to the catholyte, which biases the charge transport across barrier 403 in favor of cations from the anolyte at the expense of anions from the catholyte). Charge neutrality in the catholyte may be maintained through the production of hydroxides as part of the hydrogen evolution reaction at the cathode. Charge neutrality in the anolyte may be maintained by consumption of hydroxides (acidification) as part of the oxygen evolution reaction at the anode. Operation of electrochemical system 1200 may result in (1) a cathode output stream 1201 that has a higher pH than that of the catholyte input stream 1202 and (2) an anolyte output stream 1203 that has a pH lower than that of the anolyte input stream 1204.

[0091]Catholyte reservoir 1205 and anolyte reservoir 1206 may be configured, in accordance with some embodiments, as vessels holding a certain volume of the liquids that make up the circulation flows in the catholyte and anolyte flow channels in stack 800. Both reservoirs 1205, 1206 may be equipped with a venting port 1207, 1208 that ejects the produced gases—hydrogen (H₂) from the catholyte reservoir 1205 and oxygen (O₂) from anolyte reservoir 1206—that are carried out from electrochemical stack 800 in the respective stream. Catholyte reservoir 1205 may have a further outlet 1209 that allows for withdrawing liquids, including regenerated sorbent to be used in the direct air capture stage. Anolyte reservoir 1206 may be equipped with an inlet port taking in a stream 1210, which may be loaded aqueous sorbent including (or otherwise consisting primarily of) carbonate/bicarbonate solution (CO₃² and HCO₃⁻). The pH of stream 1210 may be, for example, between 10-14. Stream 1211 may be withdrawn from anolyte reservoir 1205 and may include (or otherwise consist primarily of) bicarbonates and carbonates at a pH greater than 8 and less than 12. CO₂-outgasser stage 1213 may extract CO₂ from the incoming stream and return a stream 1212 to anolyte reservoir 1205 at a slightly higher pH, shifting the balance towards carbonate from bicarbonate compared to 1211.

Further Examples

[0092]The following examples pertain to some further embodiments of the disclosure, from which numerous permutations and combinations will be apparent.

[0093]Example 1 is an electrochemical cell having an internal volume configured to contain a liquid electrolyte. A size of the electrochemical cell in a first direction is substantially smaller than in both a second direction and a third direction. The electrochemical cell is configured for alignment of the first direction with a direction of an electric field within the internal volume. Pressure gradients in the first direction are controllable to maintain flow speeds in the direction of or opposite to the direction of the electric field, wherein the flow speeds are comparable to a speed of ions moving relative to the liquid electrolyte under influence of the electric field. A flow speed of the liquid electrolyte is controllable such that a combined speed of the liquid electrolyte and ionic drift of one or more selected ions in the electric field is adjustable.

[0094]Example 2 includes the subject matter of any of Examples 1 and 3-53, wherein: the first direction corresponds with a width of the electrochemical cell; the second direction corresponds with a height of the electrochemical cell; and the third direction corresponds with a length of the electrochemical cell.

[0095]Example 3 includes the subject matter of any of Examples 1-2 and 4-53, wherein in being adjustable, the combined speed of the liquid electrolyte and ionic drift is able to be increased, decreased, stopped, or reversed.

[0096]Example 4 includes the subject matter of any of Examples 1-3 and 5-53, further including at least one permeable barrier disposed within the internal volume.

[0097]Example 5 includes the subject matter of any of Examples 1~4 and 6-53, wherein: the at least one permeable barrier: is disposed in an anodic region of the electrochemical cell; and separates a cathodic region of the electrochemical cell from the anodic region and an input stream of the electrochemical cell.

[0098]Example 6 includes the subject matter of any of Examples 1-5 and 7-53, wherein the at least one permeable barrier: is disposed in a cathodic region of the electrochemical cell; and separates an anodic region of the electrochemical cell from the cathodic region and an input stream of the electrochemical cell.

[0099]Example 7 includes the subject matter of any of Examples 1-6 and 8-53, wherein: the at least one permeable barrier includes two barriers disposed within the interior volume so as to separate the electrochemical cell into three regions; and an input stream of the electrochemical cell is fluidically coupled with a central one of the three regions.

[0100]Example 8 includes the subject matter of any of Examples 1-7 and 9-53, wherein the at least one permeable barrier includes at least one of: a non-woven textile; a woven textile; and a knitted textile.

[0101]Example 9 includes the subject matter of any of Examples 1-8 and 10-53, wherein the at least one permeable barrier includes either: a flat inert membrane having perforation holes formed therein; or a pleated inert membrane having perforation holes formed therein.

[0102]Example 10 includes the subject matter of any of Examples 1-9 and 11-53, wherein the perforation holes are sized within the range of 0.5-1,000 μm.

[0103]Example 11 includes the subject matter of any of Examples 1-10 and 12-53, wherein the perforation holes are sized within the range of 10-100 μm.

[0104]Example 12 includes the subject matter of any of Examples 1-11 and 13-53, wherein an aspect ratio between a size of the perforation holes and a thickness of the inert membrane is in the range of 0.01:1 to 100:1.

[0105]Example 13 includes the subject matter of any of Examples 1-12 and 14-53, wherein the at least one permeable barrier includes a monolith-like structure of substantially straight channels across the structure and aligned with the electric field.

[0106]Example 14 includes the subject matter of any of Examples 1-13 and 15-53, wherein the at least one permeable barrier includes a macroporous material with connected open pores.

[0107]Example 15 includes the subject matter of any of Examples 1-14 and 16-53, wherein the at least one permeable barrier includes a microporous material with connected open pores.

[0108]Example 16 includes the subject matter of any of Examples 1-15 and 17-53, wherein the at least one permeable barrier includes a permeable, nano-porous membrane that does not exhibit ion selectivity.

[0109]Example 17 includes the subject matter of any of Examples 1-16 and 18-53, wherein the at least one permeable barrier includes an aerogel-like membrane with high permeability for the liquid electrolyte.

[0110]Example 18 includes the subject matter of any of Examples 1-17 and 19-53, wherein the electrochemical cell is configured such that flows on opposing sides of the at least one permeable barrier are controllable so as to reduce variations in pressure differential across the at least one permeable barrier as a function of position on locations of the at least one permeable barrier.

[0111]Example 19 includes the subject matter of any of Examples 1-18 and 20-53, wherein the electrochemical cell is configured such that average pressures in regions of the interior volume which are delineated by at least one of (i) the at least one permeable barrier of the electrochemical cell, (ii) a cathodic end of the electrochemical cell, and (iii) an anodic end of the electrochemical cell are controllable such that a pressure drop across the at least one permeable barrier produces a target hydrodynamic flow velocity component aligned with the direction of the electric field.

[0112]Example 20 includes the subject matter of any of Examples 1-19 and 21-53, further including an anode and a cathode.

[0113]Example 21 includes the subject matter of any of Examples 1-20 and 22-53, wherein the electrochemical cell is configured to operate as an electrolyzer.

[0114]Example 22 includes the subject matter of any of Examples 1-21 and 23-53, wherein at least one of the anode and the cathode is configured to function as a permeable barrier.

[0115]Example 23 includes the subject matter of any of Examples 1-22 and 24-53, wherein the electrochemical cell is configured such that an output stream of the electrochemical cell which is proximate to the at least one of the anode and the cathode is extractable between an end wall of the electrochemical cell and the at least one of the anode and the cathode.

[0116]Example 24 includes the subject matter of any of Examples 1-23 and 25-53, wherein both the anode and the cathode are configured to function as permeable barriers.

[0117]Example 25 includes the subject matter of any of Examples 1-24 and 26-53, wherein the electrochemical cell is configured such that an input stream of the electrochemical cell enters the electrochemical cell between the anode and the cathode.

[0118]Example 26 includes the subject matter of any of Examples 1-25 and 27-53, wherein at least one of the anode and the cathode is configured to function as an end wall of the electrochemical cell.

[0119]Example 27 includes the subject matter of any of Examples 1-26 and 28-53, wherein at least one of the anode and the cathode is embedded into a first region adjacent to the electrochemical cell.

[0120]Example 28 includes the subject matter of any of Examples 1-27 and 29-53, wherein the electrochemical cell is configured to maintain a circulation flow within the interior volume which is delineated by at least one of: at least one permeable barrier of the electrochemical cell; a cathodic end of the electrochemical cell; and an anodic end of the electrochemical cell.

[0121]Example 29 includes the subject matter of any of Examples 1-28 and 30-53, wherein flow speeds in the circulation flow are substantially larger than a controlled flow in the direction of the electric field.

[0122]Example 30 includes the subject matter of any of Examples 1-29 and 31-53, wherein an average pressure of the circulation flow in a flow channel of the electrochemical cell is user-controllable.

[0123]Example 31 includes the subject matter of any of Examples 1-30 and 32-53, wherein pressure differentials within the circulation flow in a flow channel of the electrochemical cell is user-controllable.

[0124]Example 32 includes the subject matter of any of Examples 1-31 and 33-53, wherein: the circulation flow enters and leaves the electrochemical cell; and at least one of the following is effectuated external to the electrochemical cell: pressure control; differential pressure control; addition and withdrawal of the liquid electrolyte; and chemical adjustment of the liquid electrolyte.

[0125]Example 33 includes the subject matter of any of Examples 1-32 and 34-53, wherein pressure gradients introduced by the circulation flow in directions orthogonal to the direction of the electric field are less than a controlled pressure drop across a permeable barrier of the electrochemical cell.

[0126]Example 34 includes the subject matter of any of Examples 1-33 and 35-53, wherein pressure gradients introduced by the circulation flow in directions orthogonal to the direction of the electric field are substantially equal to a controlled pressure drop across a permeable barrier of the electrochemical cell.

[0127]Example 35 includes the subject matter of any of Examples 1-34 and 36-53, wherein pressure gradients introduced by the circulation flow in directions orthogonal to the direction of the electric field are greater than a controlled pressure drop across a permeable barrier of the electrochemical cell.

[0128]Example 36 includes the subject matter of any of Examples 1-35 and 37-53, wherein the liquid electrolyte includes an aqueous salt solution.

[0129]Example 37 includes the subject matter of any of Examples 1-36 and 38-53, wherein the aqueous salt solution includes at least one of: sodium ions; and potassium ions.

[0130]Example 38 includes the subject matter of any of Examples 1-37 and 39-53, wherein the liquid electrolyte includes at least one of: a hydroxide; a carbonate; and a bicarbonate.

[0131]Example 39 includes the subject matter of any of Examples 1-38 and 40-53, wherein the liquid electrolyte includes a mixture of hydroxide, carbonate, and bicarbonate.

[0132]Example 40 includes the subject matter of any of Examples 1-39 and 41-53, wherein the liquid electrolyte as input into the internal volume differs in chemical composition as compared to the liquid electrolyte as output by the internal volume.

[0133]Example 41 includes the subject matter of any of Examples 1-40 and 42-53, wherein at least one of: an input of the electrochemical cell is in the range of 9-14; a first output from a cathodic region of the electrochemical cell is in the range of 12 or greater; and a second output from an anodic region of the electrochemical cell is in the range of 7-11.

[0134]Example 42 includes the subject matter of any of Examples 1-41 and 43-53, wherein at least two of: an input of the electrochemical cell is in the range of 9-14; a first output from a cathodic region of the electrochemical cell is in the range of 12 or greater; and a second output from an anodic region of the electrochemical cell is in the range of 7-11.

[0135]Example 43 includes the subject matter of any of Examples 1-42 and 44-53, wherein: an input of the electrochemical cell is in the range of 9-14; a first output from a cathodic region of the electrochemical cell is in the range of 12 or greater; and a second output from an anodic region of the electrochemical cell is in the range of 7-11.

[0136]Example 44 includes the subject matter of any of Examples 1-43 and 45-53, wherein the electrochemical cell is configured such that flow continuity is maintainable by feeding the liquid electrolyte into one or more regions of the internal volume and removing the liquid electrolyte from the same or one or more other regions of the internal volume.

[0137]Example 45 includes the subject matter of any of Examples 1-44 and 46-53, wherein at least one of addition and withdrawal of the liquid electrolyte is user-controllable.

[0138]Example 46 includes the subject matter of any of Examples 1-45 and 47-53, wherein cations in both an anolyte stream and a catholyte stream of the electrochemical cell include potassium at a concentration in the range of 0.1-10 M.

[0139]Example 47 includes the subject matter of any of Examples 1-46 and 48-53, wherein cations in both an anolyte stream and a catholyte stream of the electrochemical cell include sodium at a concentration in the range of 0.1-10 M.

[0140]Example 48 includes the subject matter of any of Examples 1-47 and 49-53, further including an anolyte compartment and a catholyte compartment, each having a liquid input including potassium hydroxide solution having a concentration in the range of 0.1-20 M.

[0141]Example 49 includes the subject matter of any of Examples 1-48 and 50-53, further including an anolyte compartment and a catholyte compartment, wherein at least one liquid input of the electrochemical cell includes at least one of: a bicarbonate/carbonate solution with balancing cations having a pH in the range of 8-14; and a hydroxide solution with balancing cations having a pH in the range of 12 or greater.

[0142]Example 50 includes the subject matter of any of Examples 1-49 and 51-53, wherein at least one liquid output of the electrochemical cell includes at least one of: a bicarbonate/carbonate solution with balancing cations having a pH that is (i) less than that of the at least one liquid input and (ii) in the range of 8-12; and a hydroxide solution with balancing cations having a pH that is (i) greater than that of the at least one liquid input and (ii) in the range of 12 or greater.

[0143]Example 51 includes the subject matter of any of Examples 1-50 and 52-53, wherein the electrochemical cell: further includes a cathode and an anode; and is configured to produce: hydrogen at the cathode; and oxygen at the anode.

[0144]Example 52 includes the subject matter of any of Examples 1-51 and 53, wherein the electrochemical cell is configured to produce a plurality of gaseous output streams including: a first gaseous output stream including substantially pure hydrogen; and a second gaseous output stream including mostly oxygen.

[0145]Example 53 includes the subject matter of any of Examples 1-52, wherein: the electrochemical cell further includes a cathode and an anode; and a gas produced at the cathode or the anode is outgassed from a cross-circulation stream external to the electrochemical cell.

[0146]Example 54 is an electrochemical device including a plurality of an electrochemical cell including the subject matter of any of Examples 1-53 and 55-76.

[0147]Example 55 includes the subject matter of any of Examples 1-54 and 56-76, wherein at least two of the electrochemical cells are of substantially similar or identical geometry.

[0148]Example 56 includes the subject matter of any of Examples 1-55 and 57-76, wherein at least two of the electrochemical cells are fluidically coupled with one another.

[0149]Example 57 includes the subject matter of any of Examples 1-56 and 58-76, wherein an output of at least one electrochemical cell is fluidically coupled with an input of at least one other electrochemical cell.

[0150]Example 58 includes the subject matter of any of Examples 1-57 and 59-76, wherein: an input of the electrochemical device is divided to enter at least two of the plurality of electrochemical cells; and outputs of the at least two of the plurality of electrochemical cells are combinable.

[0151]Example 59 includes the subject matter of any of Examples 1-58 and 60-76, wherein at least two of the electrochemical cells are electrically connected with one another.

[0152]Example 60 includes the subject matter of any of Examples 1-59 and 61-76, wherein the at least two of the electrochemical cells are electrically connected in series.

[0153]Example 61 includes the subject matter of any of Examples 1-60 and 62-76, wherein the at least two of the electrochemical cells are electrically connected in parallel.

[0154]Example 62 includes the subject matter of any of Examples 1-61 and 63-76, wherein at least two of the electrochemical cells are electrically isolated from one another.

[0155]Example 63 includes the subject matter of any of Examples 1-62 and 64-76, wherein inputs to at least two of the electrochemical cells are of the same chemical composition as one another.

[0156]Example 64 includes the subject matter of any of Examples 1-63 and 65-76, wherein outputs of at least two of the electrochemical cells are of the same chemical composition as one another.

[0157]Example 65 includes the subject matter of any of Examples 1-64 and 66-76, wherein inputs and outputs of the plurality of electrochemical cells differ in at least one of: pH; and salinity.

[0158]Example 66 includes the subject matter of any of Examples 1-65 and 67-76, wherein separation among the plurality of electrochemical cells is provided by bipolar membranes.

[0159]Example 67 includes the subject matter of any of Examples 1-66 and 68-76, wherein separation among the plurality of electrochemical cells is provided by permeable electrodes.

[0160]Example 68 includes the subject matter of any of Examples 1-67 and 69-76, wherein separation among the plurality of electrochemical cells is provided by impermeable electrodes.

[0161]Example 69 includes the subject matter of any of Examples 1-68 and 70-76, wherein separation among the plurality of electrochemical cells is provided by permeable, electrically inert walls having a solid or permeable electrode embedded into a region adjacent to the walls and a permeable barrier.

[0162]Example 70 includes the subject matter of any of Examples 1-69 and 71-76, wherein the permeable electrode is configured to function as the permeable barrier that is adjacent to a permeable end wall of at least one of the plurality of electrochemical cells.

[0163]Example 71 includes the subject matter of any of Examples 1-70 and 72-76, wherein the permeable electrode is configured to function as the permeable barrier that is adjacent to an impermeable end wall of at least one of the plurality of electrochemical cells.

[0164]Example 72 includes the subject matter of any of Examples 1-71 and 73-76, wherein separation among the plurality of electrochemical cells is provided by impermeable, electrically inert walls having a solid or permeable electrode embedded into a region adjacent to the walls and a permeable barrier.

[0165]Example 73 includes the subject matter of any of Examples 1-72 and 74-76, wherein the permeable electrode is configured to function as the permeable barrier that is adjacent to a permeable end wall of at least one of the plurality of electrochemical cells.

[0166]Example 74 includes the subject matter of any of Examples 1-73 and 75-76, wherein the permeable electrode is configured to function as the permeable barrier that is adjacent to an impermeable end wall of at least one of the plurality of electrochemical cells.

[0167]Example 75 includes the subject matter of any of Examples 1-74 and 76, wherein: cross-circulation in all regions of the plurality of electrochemical cells is maintained; and a speed of the cross-circulation is greater than a controlled crossflow speed aligned with the direction of the electric field.

[0168]Example 76 includes the subject matter of any of Examples 1-75, wherein the speed of the cross-circulation is in the range of 100-10,000 times faster than the controlled crossflow speed.

[0169]Example 77 is a system including: an electrochemical device including the subject matter of any of Examples 1-76 and 78-94; and a control system configured to control the electrochemical device.

[0170]Example 78 includes the subject matter of any of Examples 1-77 and 79-94, wherein the control system includes a plurality of sub-systems configured to act on the plurality of electrochemical cells at least one of: individually; and in groupings.

[0171]Example 79 includes the subject matter of any of Examples 1-78 and 80-94, wherein the control system is configured to rely, at least partially, on stabilizing physical effects.

[0172]Example 80 includes the subject matter of any of Examples 1-79 and 81-94, wherein the control system is configured to rely, at least partially, on sensor feedback.

[0173]Example 81 includes the subject matter of any of Examples 1-80 and 82-94, wherein the control system is configured to rely, at least partially, on a control signal from a processing element.

[0174]Example 82 includes the subject matter of any of Examples 1-81 and 83-94, further including a sensor configured to provide feedback on operation of the electrochemical device to the control system.

[0175]Example 83 includes the subject matter of any of Examples 1-82 and 84-94, wherein the sensor includes: a pressure sensor; or a differential pressure sensor.

[0176]Example 84 includes the subject matter of any of Examples 1-83 and 85-94, wherein the sensor includes: a fluid flow sensor; or a fluid speed sensor.

[0177]Example 85 includes the subject matter of any of Examples 1-84 and 86-94, wherein the sensor includes a temperature sensor.

[0178]Example 86 includes the subject matter of any of Examples 1-85 and 87-94, wherein the sensor includes a pH sensor.

[0179]Example 87 includes the subject matter of any of Examples 1-86 and 88-94, wherein the sensor includes at least one of: an oxygen sensor; a carbon dioxide sensor; and a hydrogen sensor.

[0180]Example 88 includes the subject matter of any of Examples 1-87 and 89-94, wherein the sensor is sensitive to at least one of: carbonate ions; and bicarbonate ions.

[0181]Example 89 includes the subject matter of any of Examples 1-88 and 90-94, wherein the sensor includes an optical sensor.

[0182]Example 90 includes the subject matter of any of Examples 1-89 and 91-94, wherein the sensor includes a colorimetric sensor.

[0183]Example 91 includes the subject matter of any of Examples 1-90 and 92-94, wherein the sensor includes an acoustic sensor.

[0184]Example 92 is a system including: an electrochemical device including the subject matter of any of Examples 1-91 and 93-94; and a pressure control system configured to control the electrochemical device.

[0185]Example 93 includes the subject matter of any of Examples 1-92 and 94, wherein the pressure control system is configured to control at least one of a cross-circulation flow and a trans-barrier flow individually in each of the plurality of electrochemical cells.

[0186]Example 94 includes the subject matter of any of Examples 1-93, wherein in being configured to control the cross-circulation flow, the pressure control system is configured to act simultaneously on multiple electrochemical cells.

[0187]The foregoing description of example embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed. Many modifications and variations are possible in light of this disclosure. It is intended that the scope of the present disclosure be limited not by this detailed description. Future-filed applications claiming priority to this application may claim the disclosed subject matter in a different manner and generally may include any set of one or more limitations as variously disclosed or otherwise demonstrated herein.