Flow systems and related methods for treating seawater

Abstract

Flow systems and related methods of treating seawater are generally described. For example, a method of removal of chemical products in seawater, resulting from increased atmospheric carbon dioxide levels using pulsed electrolysis using coated conversion-type Bi / G electrodes is described.

Description

FLOW SYSTEMS AND RELATED METHODS FOR TREATING SEAWATER RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 63 / 760,104, filed February 18, 2025, which is hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] Flow systems and related methods for treating seawater are generally described.BACKGROUND

[0003] For electrochemical carbon capture technologies for use in ocean water, numerous challenges persist regarding their long-term resiliency. One major concern is the presence of problematic magnesium (Mg2+) and calcium (Ca2+) ions in ocean water, which can precipitate on the electrode surfaces and compromise performance. Accordingly, improved systems and methods that have improved long-term resiliency and / or reduced precipitation on electrode surfaces in the presence of magnesium and / or calcium ions are needed.SUMMARY

[0004] Flow systems and related methods for treating seawater are generally described. For example, in some embodiments, the flow system comprises an electrochemical cell comprising a first electrode and a second electrode. In certain embodiments, the first electrode comprises bismuth. In accordance with some embodiments, the electrochemical cell is configured to perform pulsed electrolysis and / or is configured to provide an electrochemical pH swing. According to some embodiments, a method comprises treating seawater using a flow system described herein. In some cases, the seawater comprises bicarbonate, and the method comprises converting a portion of the bicarbonate to carbon dioxide and removing a portion of the carbon dioxide from the seawater. The subject matter of the present disclosure involves, in some cases, interrelated products, alternative solutions to a particular problem, and / or a plurality of different uses of one or more systems and / or articles.

[0005] Certain aspects relate to flow systems. In some embodiments, the flow system comprises a first orifice configured to intake untreated seawater comprising bicarbonate; and an electrochemical cell; wherein: the electrochemical cell is configured to perform pulsed 1#14916960vlelectrolysis; the electrochemical cell comprises a first electrode and a second electrode; and the first electrode comprises bismuth.

[0006] In certain embodiments, the flow system comprises an electrochemical cell comprising a first electrode and a second electrode, wherein: the first electrode and the second electrode are coated conversion-type electrodes; the first electrode comprises bismuth; and the electrochemical cell is configured to perform pulsed electrolysis on seawater to mitigate formation of precipitation on a surface of the first electrode and / or the second electrode.

[0007] According to some embodiments, the flow system comprises an electrochemical cell configured to provide an electrochemical pH swing; and a first orifice configured to intake untreated seawater comprising bicarbonate; wherein the electrochemical cell comprises a first electrode and a second electrode, and wherein the first electrode and the second electrode are coated conversion-type electrodes.

[0008] According to certain embodiments, the flow system comprises an electrochemical cell configured to perform pulsed electrolysis; and a first orifice configured to intake seawater comprising bicarbonate; wherein the flow system: (a) has a lifetime of greater than or equal to 50 cycles; and / or (b) has a decrease of less than or equal to 20% in cycling capacity and / or a decrease of less than or equal to 20% in Qacid utilization over the lifetime of the flow system.

[0009] In accordance with certain embodiments, the flow system comprises an electrochemical cell comprising a first electrode and a second electrode, wherein the first electrode comprises bismuth; and a first orifice configured to intake untreated seawater comprising bicarbonate; wherein the flow system: (a) has a lifetime of greater than or equal to 50 cycles; and / or (b) has a decrease of less than or equal to 20% in cycling capacity and / or a decrease of less than or equal to 20% in Qacid utilization over the lifetime of the flow system.

[0010] Certain aspects relate to methods. In some embodiments, the method comprises intaking untreated seawater through a first orifice into a flow system, wherein the untreated seawater comprises bicarbonate; lowering the pH of the untreated seawater using pulsed electrolysis with an electrochemical cell to form treated seawater in which a portion of the bicarbonate has been converted to carbon dioxide; and removing a portion of the carbon dioxide from the treated seawater; wherein the electrochemical cell comprises a first electrode and a second electrode, and wherein the first electrode comprises bismuth.2#14916960vl

[0011] In certain embodiments, the method comprises performing pulsed electrolysis on seawater with an electrochemical cell comprising a first electrode and a second electrode; wherein: the first electrode comprises bismuth; the first electrode and the second electrode are coated conversion-type electrodes; and the pulsed electrolysis mitigates formation of precipitation on a surface of the first electrode and / or the second electrode.

[0012] According to some embodiments, the method comprises intaking untreated seawater through a first orifice into a flow system comprising an electrochemical cell, wherein the untreated seawater comprises bicarbonate; providing an electrochemical pH swing to the untreated seawater with the electrochemical cell; converting a portion of the bicarbonate to carbon dioxide to form treated seawater; and removing a portion of the carbon dioxide from the treated seawater; wherein the electrochemical cell comprises a first electrode and a second electrode, wherein the first electrode and the second electrode are coated conversiontype electrodes.

[0013] According to certain embodiments, the method comprises intaking seawater through a first orifice into a flow system comprising an electrochemical cell, wherein the seawater comprises bicarbonate; lowering the pH of the seawater by pulsed electrolysis to convert a portion of the bicarbonate to carbon dioxide; and removing a portion of the carbon dioxide from the seawater; wherein: (a) the flow system has a lifetime of greater than or equal to 50 cycles; and / or (b) the flow system has a decrease of less than or equal to 20% in cycling capacity and / or a decrease of less than or equal to 20% in Qacid utilization over the lifetime of the flow system.

[0014] In accordance with some embodiments, the method comprises intaking untreated seawater through a first orifice into a flow system, wherein the untreated seawater comprises bicarbonate; lowering the pH of the untreated seawater to form treated seawater in which a portion of the bicarbonate has been converted to carbon dioxide; and removing a portion of the carbon dioxide from the treated seawater; wherein the flow system comprises an electrochemical cell comprising a first electrode and a second electrode, wherein the first electrode comprises bismuth; and wherein: (a) the flow system has a lifetime of greater than or equal to 50 cycles; and / or (b) the flow system has a decrease of less than or equal to 20% in cycling capacity and / or a decrease of less than or equal to 20% in Qacid utilization over the lifetime of the flow system.

[0015] One aspect of the disclosure herein is a method, comprising:3#14916960vla. intaking untreated and impure ocean water seawater containing bicarbonate through a first orifice into a flow system;b. in a first portion of the flow system, lowering the pH of the seawater by pulsed electrolysis using coated conversion-type Bi / G electrodes operating in a pulsed sequence, thereby converting at least some bicarbonate to carbon dioxide;c. removing at least some of the carbon dioxide from the seawater;d. flowing the solution into a second portion of the flow system, and raising the pH of the solution;e. ejecting the solution from the flow system through a second orifice.

[0016] In one embodiment of the disclosed method, the pulsed sequence is of 500 ms to 5 s duration separated by 2 s pauses.

[0017] In one embodiment, the disclosed method further comprises, in the first portion, lowering the pH of the seawater by releasing H+ from a first electrode into the seawater, and in the second portion, at a second electrode capturing H+ thereby raising the pH of the seawater.

[0018] In one embodiment, the disclosed method further comprises:a. intaking seawater containing bicarbonate through the second orifice into the flow system;b. in the second portion of the flow system, lowering the pH of the solution by pulsed electrolysis releasing H+from the second electrode into the input solution using coated conversion-type Bi / G electrodes operating in a pulsed sequence, thereby converting at least some bicarbonate to carbon dioxide; c. removing at least some of the carbon dioxide from the solution;d. flowing the solution into the first portion of the flow system, and at the first electrode capturing H+thereby raising the pH of the solution;e. ejecting the solution from the flow system through the first orifice.

[0019] Other advantages and novel features of the present disclosure will become apparent from the following detailed description of various non-limiting embodiments of the disclosure when considered in conjunction with the accompanying figures. In cases where the present specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification shall control.4#14916960vlBRIEF DESCRIPTION OF THE DRAWINGS

[0020] Non-limiting embodiments of the present disclosure will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale unless otherwise indicated. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the disclosure shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure. In the figures:

[0021] FIG. 1. shows a flow system comprising an electrochemical cell, first orifice, and, optionally, a second orifice, first electrode, and second electrode, in accordance with some embodiments.

[0022] FIGs. 2A-2D show impacts of ocean water species. FIG. 2A shows a schematic of a CO2 capture process with two identical bismuth- silver cells, in accordance with some embodiments. FIG. 2B shows a schematic of a custom single cell setup, in accordance with some embodiments. Planar Bi and Ag electrodes were placed parallel to one another, creating a chamber in which the electrolyte may flow. A tertiary reference electrode and pH probe were inserted for half-cell potential and pH measurements, respectively. FIG. 2C and FIG.2D show time-resolved pH and Bi half-cell potential profiles under various electrolytes. The grey trace refers to NaCl (0.5 M) free of impurities. Simulated seawater (SW) refers to NaCl adjusted to include MgCh (50 mM) and CaCh (10 mM) for a total Cl’ concentration of 0.5 M. The cell was flushed with mildly acidic DI water before use, explaining the initial pH of ~5.

[0023] FIGs. 3A-3C show SEM images of a Bi / graphene (Bi / G) electrode (FIG. 3A), Bi / G coated with PiperlON® resin (surface view) (FIG. 3B), and Bi / G coated with PiperlON® resin (sideview) (FIG. 3C). The inset portrays a change in the morphologies, resembling a layer on top of the Bi / G composite.

[0024] FIGs. 4A-4K show performance and imaging of modified Bi electrodes. FIG. 4A shows resultant pH and half-cell potential profiles of Bi / CB, Bi / G, and coated Bi / G in simulated SW electrolyte. The white datapoints correspond to the times at which in situ images were taken. FIG. 4B, FIG. 4C, FIG. 4D, FIG. 4E, FIG. 4F, and FIG. 4G show in situ imaging of the coated Bi / G surface before, during, and after electrolysis. FIG. 4H shows a representative SEM image of a deposit taken after regeneration. FIG. 41, FIG. 4J, and FIG. 4K show corresponding elemental mapping for Mg, Ca, and Bi, respectively. The5#14916960vlsignal for magnesium completely overwhelmed any signals for Ca and Bi, indicating that it had fully coated the Bi surface.

[0025] FIGs. 5A-5F show pulsed alkalinization of coated Bi / G in simulated SW. FIG. 5A shows a schematic of testing strategy. FIG. 5B shows a diagram of pulsed sequences A, B, C.FIG. 5C and FIG. 5D show charge-normalized half-cell potentials and pH profiles during pulsed alkalinization and concurrent acidification, respectively. The black, dashed line corresponds to the Bi / CB under no pulsing operation. The dotted datapoints correspond to times at which optical images were taken. FIG. 5E shows half-cell potentials for a single pulse. The inset is for sequence B between coated and uncoated Bi / G. FIG. 5F shows in situ imaging of the coated Bi / G interface before electrolysis, during pulsed regeneration, and during acidification.

[0026] FIGs. 6A-6D. show impacts of Mg2+and Ca2+ions. FIG. 6A illustrates the CO2 capture process with two identical bismuth-silver cells, in accordance with some embodiments. FIG. 6B shows a diagram of a single cell setup with the pH probe, tertiary Ag / AgCl reference, and optical setup for in situ imaging of the Bi interface, in accordance with some embodiments. FIG. 6C shows time-resolved Bi half-cell potentials and pH profiles under representative electrolytes. The grey trace refers to NaCl (0.5 M), free of other species. Simulated seawater (black trace) is NaCl spiked with Mg2+(50 mM) and Ca2+(10 mM). The cell was flushed with mildly acidic DI (adjusted with HC1) before testing, explaining the initial pH values of ~5. The black dotted datapoints correspond to times at which optical images were taken. FIG. 6D shows in situ images of the Bi surface during simulated SW operation, demonstrating negligible morphological change.

[0027] FIGs. 7A-7D show the characterization of Bi / CB after Mg2+exposure. FIG. 7A shows oxidative LSV scans taken after reducing Bi / CB samples in NaCl with either 0 or 50 mM Mg2+. Inset: CP voltammograms at -1 mA cm'2prior to the scans. FIG. 7B shows posttesting SEM image of Bi / CB after alkalinization in NaCl only. FIG. 7C shows post-testing SEM and corresponding elemental mapping analyses of Bi and Mg after alkalinization in NaCl + 50 mM Mg2+. All scale bars: 2 pm. FIG. 7D shows XRD spectra of Bi / CB independently tested in electrolytes (pH 7 or 2) with either 0 or 50 mM Mg2+. Each sample was subject to one full operating cycle (alkalinization acidification) prior to characterization.

[0028] FIGs. 8A-8D show an overview of bismuth electrode modifications. FIG. 8A shows a schematic of applied changes, in accordance with some embodiments. FIG. 8B shows a6#14916960vlSEM image of the surface of coated Bi / G. The inset of FIG. 8B zooms into the clear differences in morphology between the ionomer and Bi / G layers. FIG. 8C and FIG.8D show oxidative LSV scans of uncoated and coated Bi / G under various [Mg2+], respectively.

[0029] FIGs. 9A-9C show pulsed alkalinization of coated Bi / G in simulated SW. FIG. 9A shows in situ images during pulsed sequence B, demonstrating negligible surface change. All scale bars: 20 pm. FIG. 9B shows post-testing SEM image of the coated Bi / G surface. FIG.9C shows a cycling test using pulsed sequence B in simulated SW, showcasing stable pH swing performance.

[0030] FIGs. 10A-10D show CO2 removal assessments of coated Bi / G in simulated SW. FIG. 10A shows charge-normalized half-cell potentials, pH, and CO2 extraction profiles during acidification. FIG. 10B shows magnesium tolerance assessment at Mg2+concentrations at 1, 5, 10, 25, and 50 mM. Tests were performed independently for Bi / CB and Bi / G. All alkalinization steps were pulsed using sequence B from FIGs. 5A-5E and FIGs. 9A-9C. FIG. 10C shows stability assessment of coated Bi / G in simulated SW with pulse alkalinization sequence B. The Bi electrode was left untouched throughout the entire experiment. FIG. 10D shows an overview schematic of some of the strategies presented, in accordance with some embodiments.

[0031] FIGs. 11A-11B show images of the custom single cell setup, in accordance with some embodiments. FIG. 11A shows the setup used for flow characterizations, with the Ag / AgCl reference (near cell inlet) and pH probe (near outlet) visible. This cell was sandwiched using stainless steel current collectors. FIG. 11B shows the setup modified for in situ optical imaging, with the camera, objective, and relevant lighting equipment. The stainless steel plate at the silver side was replaced with a transparent acrylic plate (for the camera). A strip of graphite sheet long enough to protrude outside the cell was used as the silver current collector. This did not affect the cell’s flow channel geometry and assembly as all other components (i.e., electrodes, gaskets) were kept the same. A hole was cut out of the Ag counter for the objective opening.DETAILED DESCRIPTION

[0032] Flow systems and related methods for treating seawater are generally described. In some embodiments, the flow system comprises an electrochemical cell comprising a first electrode and a second electrode. In certain embodiments, the first electrode comprises bismuth. For example, in some cases, the first electrode comprises a bismuth-graphene7#14916960vlcomposite. In certain instances, the first electrode comprises a coating comprising an anion-exchange ionomer, such as PiperlON®. In accordance with some embodiments, the electrochemical cell is configured to perform pulsed electrolysis and / or is configured to provide an electrochemical pH swing. In some instances, the flow system comprises a first orifice (e.g., configured to intake seawater) and / or a second orifice (e.g., configured to release treated seawater out of the flow system).

[0033] According to some embodiments, a method comprises treating seawater using a flow system described herein. In some cases, the seawater comprises bicarbonate, and the method comprises converting a portion of the bicarbonate to carbon dioxide and removing a portion of the carbon dioxide from the seawater prior to releasing the seawater from the flow system (e.g., out of a second orifice in the flow system and / or back to the body of water from which the seawater came).

[0034] In accordance with certain embodiments, the seawater that enters the first orifice is untreated seawater that comprises magnesium ions (e.g., greater than or equal to 0.1 mmol / L) and / or calcium ions (e.g., greater than or equal to 0.1 mmol / L). In accordance with some embodiments, the flow systems disclosed herein have improved lifetime, improved efficiency, and / or reduced precipitation (e.g., magnesium and / or calcium) on a surface of one or more electrodes.

[0035] Certain embodiments are related to flow systems. A non-limiting example of a flow system is shown in FIG. 1.

[0036] In some embodiments, the flow system comprises a first orifice. For example, as shown in FIG. 1, in some cases, flow system 100 comprises first orifice 102. According to some embodiments, the first orifice is configured to intake seawater (e.g., any seawater disclosed herein, such as untreated seawater). In certain embodiments, the seawater (e.g., untreated seawater) is water from a body of water with unobstructed fluid connection to an ocean, other than a river or other body of water that continuously flows into the ocean and contains essentially no salt water from the ocean, e.g., seawater includes marshes, estuaries, and other non-ocean bodies, some of which include brackish water. According to certain embodiments, the seawater is water from an ocean and / or sea.

[0037] In accordance with some embodiments, the seawater comprises sodium chloride. For example, in certain cases, the seawater comprises greater than or equal to 0.01 mol / L, greater than or equal to 0.05 mol / L, greater than or equal to 0.1 mol / L, greater than or equal to 0.2 mol / L, greater than or equal to 0.3 mol / L, greater than or equal to 0.4 mol / L, or greater than8#14916960vlor equal to 0.5 mol / L sodium chloride. In certain instances, the seawater comprises less than or equal to 2 mol / L, less than or equal to 1.9 mol / L, less than or equal to 1.8 mol / L, less than or equal to 1.7 mol / L, less than or equal to 1.6 mol / L, less than or equal to 1.5 mol / L, less than or equal to 1.3 mol / L, less than or equal to 1 mol / L, less than or equal to 0.9 mol / L, less than or equal to 0.8 mol / L, or less than or equal to 0.7 mol / L sodium chloride. Combinations of these ranges are also possible (e.g., greater than or equal to 0.01 mol / L and less than or equal to 2 mol / L, greater than or equal to 0.01 mol / L and less than or equal to 0.7 mol / L, or greater than or equal to 0.4 mol / L and less than or equal to 0.7 mol / L).

[0038] In accordance with certain embodiments, the seawater (e.g., untreated seawater) comprises bicarbonate. For example, in some instances, the seawater (e.g., untreated seawater) comprises at least 1 mg / L, at least 10 mg / L, at least 20 mg / L, at least 30 mg / L, at least 40 mg / L, or at least 50 mg / L bicarbonate. In some instances, the untreated seawater comprises less than or equal to 300 mg / L, less than or equal to 250 mg / L, less than or equal to 200 mg / L, less than or equal to 150 mg / L, or less than or equal to 100 mg / L bicarbonate. Combinations of these ranges are also possible (e.g., at least 1 mg / L and less than or equal to 300 mg / L or at least 50 mg / L and less than or equal to 200 mg / L).

[0039] According to some embodiments, the seawater (e.g., the seawater that flows into the first orifice of the flow system) comprises untreated seawater. In certain instances, untreated seawater is seawater that has not been treated in any capacity (e.g., the seawater is taken directly from the body of water). In some instances, untreated seawater is seawater that has not been treated with nanofiltration, ion exchange, and / or reverse osmosis filtration. For example, in certain cases, the untreated seawater is seawater that has been treated with basic filtration steps that do not include nanofiltration, ion exchange, and / or reverse osmosis filtration. In some cases, untreated seawater is seawater that has not been treated with nanofiltration.

[0040] In accordance with some embodiments, untreated seawater is seawater that comprises magnesium ions. For example, in some cases, the untreated seawater comprises greater than or equal to 0.1 mmol / L, greater than or equal to 0.2 mmol / L, greater than or equal to 0.3 mmol / L, greater than or equal to 0.5 mmol / L, greater than or equal to 1 mmol / L, greater than or equal to 2 mmol / L, greater than or equal to 3 mmol / L, greater than or equal to 5 mmol / L, greater than or equal to 10 mmol / L, greater than or equal to 15 mmol / L, greater than or equal to 20 mmol / L, greater than or equal to 25 mmol / L, or greater than or equal to 30 mmol / L magnesium ions. In certain embodiments, the untreated seawater comprises less than or9#14916960vlequal to 200 mmol / L, less than or equal to 175 mmol / L, less than or equal to 150 mmol / L, less than or equal to 125 mmol / L, less than or equal to 100 mmol / L, less than or equal to 90 mmol / L, less than or equal to 80 mmol / L, less than or equal to 70 mmol / L, less than or equal to 65 mmol / L, less than or equal to 60 mmol / L, less than or equal to 55 mmol / L, or less than or equal to 50 mmol / L magnesium ions. Combinations of these ranges are also possible (e.g., greater than or equal to 0.1 mmol / L and less than or equal to 200 mmol / L, greater than or equal to 0.1 mmol / L and less than or equal to 100 mmol / L, or greater than or equal to 30 mmol / L and less than or equal to 70 mmol / L).

[0041] In accordance with some embodiments, untreated seawater is seawater that comprises calcium ions. For example, in some cases, the untreated seawater comprises greater than or equal to 0.1 mmol / L, greater than or equal to 0.2 mmol / L, greater than or equal to 0.3 mmol / L, greater than or equal to 0.5 mmol / L, greater than or equal to 1 mmol / L, greater than or equal to 2 mmol / L, greater than or equal to 3 mmol / L, greater than or equal to 5 mmol / L, greater than or equal to 6 mmol / L, greater than or equal to 7 mmol / L, greater than or equal to 8 mmol / L, greater than or equal to 9 mmol / L, or greater than or equal to 10 mmol / L calcium ions. In certain embodiments, the untreated seawater comprises less than or equal to 20 mmol / L, less than or equal to 17 mmol / L, less than or equal to 15 mmol / L, less than or equal to 14 mmol / L, less than or equal to 13 mmol / L, less than or equal to 12 mmol / L, less than or equal to 11 mmol / L, or less than or equal to 10 mmol / L calcium ions. Combinations of these ranges are also possible (e.g., greater than or equal to 0.1 mmol / L and less than or equal to 20 mmol / L or greater than or equal to 5 mmol / L and less than or equal to 15 mmol / L).

[0042] According to certain embodiments, the flow system comprises an electrochemical cell. For example, as shown in FIG. 1, in some cases, flow system 100 comprises electrochemical cell 101. In some embodiments, the electrochemical cell comprises a first electrode. For example, as shown in FIG. 1, in some cases, electrochemical cell 101 comprises first electrode 104. In certain embodiments, the electrochemical cell comprises a second electrode. For example, as shown in FIG. 1, in some cases, electrochemical cell 101 comprises second electrode 105. According to some embodiments, the electrochemical cell comprises a first electrode and a second electrode. For example, as shown in FIG. 1, in some cases, electrochemical cell 101 comprises first electrode 104 and second electrode 105.

[0043] In accordance with some embodiments, the first electrode is a coated conversion-type electrode. In some instances, the second electrode is a coated conversion-type electrode. In10#14916960vlsome cases, the first electrode and the second electrode are coated conversion-type electrodes.

[0044] According to some embodiments, the flow system comprises one or more additional electrochemical cells (e.g., comprising any embodiments or combinations thereof disclosed herein for an electrochemical cell), such as one, two, three, or more additional electrochemical cells. For example, in some instances, the flow system comprises a first electrochemical cell and a second electrochemical cell. In certain embodiments, the first electrochemical cell and second electrochemical cell are the same. In accordance with some embodiments, the first electrochemical cell and second electrochemical cell are different.

[0045] In accordance with certain embodiments, the first electrode comprises bismuth. In some cases, the first electrode comprises carbon black and / or graphene. For example, in certain cases, the first electrode comprises graphene. In certain instances, the first electrode comprises a bismuth / graphene composite. Without wishing to be bound by theory, it is believed that composites (e.g., a bismuth / graphene composite) with larger and / or more bulbous particles and / or that more effectively cover active materials based on their lattice orientation and / or packing distribution more effectively inhibit magnesium access, in some instances.

[0046] In some embodiments, the first electrode comprises a coating. In some cases, the coating comprises an anion-exchange ionomer. Non-limiting examples of anion-exchange ionomers include PiperlON ®. Without wishing to be bound by theory, it is believed that coatings comprising an anion-exchange ionomer (e.g., PiperlON®) exclude cations such as Mg2+and / or facilitate Cl’ crossover, in some embodiments.

[0047] According to some embodiments, the second electrode comprises Ag, such as AgCl. In some cases, the second electrode comprises bismuth (e.g., any bismuth electrode disclosed herein). In certain instances, the second electrode comprises a faradaic-type electrode, such as a carbon electrode.

[0048] In certain embodiments, the electrochemical cell is configured to provide an electrochemical pH swing. In some embodiments, the electrochemical pH swing changes the pH (e.g., of seawater) by greater than or equal to 1 pH unit, greater than or equal to 2 pH units, greater than or equal to 3 pH units, greater than or equal to 4 pH units, greater than or equal to 5 pH units, greater than or equal to 6 pH units, greater than or equal to 7 pH units, or greater than or equal to 8 pH units. In some instances, the electrochemical pH swing changes the pH (e.g., of seawater) by less than 14 pH units, less than or equal to 13 pH units, less than11#14916960vlor equal to 12 pH units, less than or equal to 11 pH units, less than or equal to 10 pH units, less than or equal to 9 pH units, or less than or equal to 8 pH units.

[0049] In some cases, the electrochemical cell is configured to alternately provide a basic pH and an acidic pH. In accordance with certain embodiments, the acidic pH is greater than or equal to 1, greater than or equal to 2, greater than or equal to 3, greater than or equal to 4, greater than or equal to 5, or greater than or equal to 6. In some embodiments, the acidic pH is less than 7, less than or equal to 6, less than or equal to 5, less than or equal to 4, less than or equal to 3, or less than or equal to 2. Combinations of these ranges are also possible (e.g., greater than or equal to 1 and less than 7). In accordance with some embodiments, the basic pH is greater than 7, greater than or equal to 8, greater than or equal to 9, greater than or equal to 10, greater than or equal to 11, greater than or equal to 12, or greater than or equal to 13. In certain embodiments, the basic pH is less than or equal to 14, less than or equal to 13, less than or equal to 12, less than or equal to 11, less than or equal to 10, less than or equal to 9, or less than or equal to 8. Combinations of these ranges are also possible (e.g., greater than 7 and less than or equal to 14).

[0050] According to certain embodiments, the electrochemical cell is configured to perform pulsed electrolysis (e.g., on seawater, such as untreated seawater). In some instances, the pulsed electrolysis comprises pulsed alkalinization. In certain cases, the pulsed electrolysis mitigates formation of precipitation on a surface of the first electrode and / or the second electrode. Without wishing to be bound by theory, it is believed that the pulsed electrolysis sequence (e.g., current, duration, and / or interval) affects electrode integrity, the effectiveness of acidification, the pH swing performance, cyclability, and / or magnesium hydroxide precipitation on a surface of one or more electrodes, in some instances.

[0051] In some cases, the pulsed electrolysis comprises pulsing at a current (e.g., jpuise) of greater than or equal to 0.01 mA / cm2, greater than or equal to 0.05 mA / cm2, greater than or equal to 0.1 mA / cm2, greater than or equal to 0.125 mA / cm2, greater than or equal to 0.15 mA / cm2, greater than or equal to 0.175 mA / cm2, greater than or equal to 0.2 mA / cm2, greater than or equal to 0.25 mA / cm2, greater than or equal to 0.3 mA / cm2, greater than or equal to 0.35 mA / cm2, greater than or equal to 0.4 mA / cm2, greater than or equal to 0.45 mA / cm2, greater than or equal to 0.5 mA / cm2, greater than or equal to 0.6 mA / cm2, greater than or equal to 0.7 mA / cm2, greater than or equal to 0.8 mA / cm2, greater than or equal to 0.9 mA / cm2, greater than or equal to 1 mA / cm2, greater than or equal to 2 mA / cm2, greater than or equal to 3 mA / cm2, or greater than or equal to 4 mA / cm2. In some embodiments, the12#14916960vlpulsed electrolysis comprises pulsing at a current of less than or equal to 10 mA / cm2, less than or equal to 9.5 mA / cm2, less than or equal to 9 mA / cm2, less than or equal to 8.5 mA / cm2, less than or equal to 8 mA / cm2, less than or equal to 7.5 mA / cm2, less than or equal to 7 mA / cm2, less than or equal to 6.5 mA / cm2, less than or equal to 6 mA / cm2, less than or equal to 5.5 mA / cm2, less than or equal to 5 mA / cm2, less than or equal to 4 mA / cm2, less than or equal to 3 mA / cm2, less than or equal to 2 mA / cm2, less than or equal to 1 mA / cm2, less than or equal to 0.9 mA / cm2, less than or equal to 0.8 mA / cm2, less than or equal to 0.7 mA / cm2, or less than or equal to 0.6 mA / cm2. Combinations of these ranges are also possible (e.g., greater than or equal to 0.01 mA / cm2and less than or equal to 10 mA / cm2, greater than or equal to 0.2 mA / cm2and less than or equal to 1 mA / cm2, or greater than or equal to 0.4 mA / cm2and less than or equal to 0.6 mA / cm2).

[0052] In some embodiments, the pulsed electrolysis comprises pulsing for an average duration (e.g., / pilise) of greater than or equal to 10 milliseconds, greater than or equal to 50 milliseconds, greater than or equal to 100 milliseconds, greater than or equal to 250 milliseconds, greater than or equal to 400 milliseconds, greater than or equal to 500 milliseconds, greater than or equal to 750 milliseconds, greater than or equal to 1 second, greater than or equal to 1.5 seconds, greater than or equal to 2 seconds, greater than or equal to 3 seconds, greater than or equal to 4 seconds, greater than or equal to 5 seconds, greater than or equal to 10 seconds, or greater than or equal to 15 seconds per pulse. In certain cases, the pulsed electrolysis comprises pulsing for an average duration of less than or equal to 200 seconds, less than or equal to 175 seconds, less than or equal to 150 seconds, less than or equal to 125 seconds, less than or equal to 100 seconds, less than or equal to 75 seconds, less than or equal to 50 seconds, less than or equal to 40 seconds, less than or equal to 30 seconds, less than or equal to 20 seconds, less than or equal to 15 seconds, less than or equal to 10 seconds, less than or equal to 9 seconds, less than or equal to 8 seconds, less than or equal to 7 seconds, less than or equal to 6 seconds per pulse. Combinations of these ranges are also possible (e.g., greater than or equal to 10 milliseconds and less than or equal to 200 seconds, greater than or equal to 1 second and less than or equal to 10 seconds, or greater than or equal to 4 seconds and less than or equal to 6 seconds).

[0053] In accordance with some embodiments, the pulsed electrolysis comprises pulsing with an interval (e.g., alkalinization time - talk) between pulses (e.g., between the end of a first pulse and the beginning of a second pulse) of less than or equal to 10 seconds, less than or equal to 9 seconds, less than or equal to 8 seconds, less than or equal to 7 seconds, less13#14916960vlthan or equal to 6 seconds, less than or equal to 5 seconds, less than or equal to 4 seconds, less than or equal to 3 seconds, or less than or equal to 2.5 seconds between pulses. In certain cases, the pulsed electrolysis comprises pulsing with an interval of greater than or equal to 1 second, greater than or equal to 1.5 seconds, greater than or equal to 2 seconds, greater than or equal to 3 seconds, greater than or equal to 4 seconds, greater than or equal to 5 seconds, greater than or equal to 6 seconds, greater than or equal to 7 seconds, greater than or equal to 8 seconds, or greater than or equal to 9 seconds between pulses. Combinations of these ranges are also possible (e.g., less than or equal to 10 seconds and greater than or equal to 1 second, less than or equal to 5 seconds and greater than or equal to 1 second, or less than or equal to 2.5 seconds and greater than or equal to 1.5 seconds). For example, in some cases, the interval (e.g., alkalinization time - talk) between pulses (e.g., between the end of a first pulse and the beginning of a second pulse) is 2 seconds. Without wishing to be bound by theory, it is believed that having a short pulsing interval (e.g., alkalinization time - talk) attenuates Mg(OH)2 nucleation and growth rates, in some cases.

[0054] In certain embodiments, the alkalinization current, ;aik, is greater than or equal to -20 mA cm'2, greater than or equal to -15 mA cm'2, greater than or equal to -10 mA cm'2, greater than or equal to -8 mA cm'2, greater than or equal to -6 mA cm'2. In some cases, the alkalinization current, ;aik, is less than or equal to 10 mA cm'2, less than or equal to 5 mA cm'2, less than or equal to 0 mA cm'2, less than or equal to -2 mA cm'2, or less than or equal to -4 mA cm'2. Combinations of these ranges are also possible (e.g., greater than or equal to -20 mA cm'2and less than or equal to 10 mA cm'2, greater than or equal to -10 mA cm'2and less than or equal to 0 mA cm'2, or greater than or equal to -6 mA cm'2and less than or equal to -4 mA cm'2). For example, in some cases, the alkalinization current, ;aik, is -5 mA cm'2.

[0055] In accordance with some embodiments, the flow system comprises a first portion and a second portion. In some cases, the first portion and second portion are fluidically connected. For example, in certain instances, a fluid (e.g., seawater) flows from the first portion to the second portion. The flow system comprises additional portions, in certain embodiments. In some such instances, the first portion, second portion, and one or more (e.g., all) additional portions are fluidically connected. For example, in some embodiments, a fluid (e.g., seawater) flows from the first portion to the additional portion to the second portion. In certain cases, the first portion is configured to lower the pH of the seawater (e.g., untreated seawater) to form treated seawater (e.g., using pulsed electrolysis and / or by providing an electrochemical pH swing) (e.g., seawater in which a portion of the bicarbonate14#14916960vlhas been converted to carbon dioxide). In some cases, the first portion and / or an additional portion of the flow system is configured to remove a portion of the carbon dioxide from the treated seawater. According to some embodiments, the first portion and / or an additional portion of the flow system is configured to remove a portion of carbon dioxide from treated seawater via gas-phase extraction, vacuum stripping, and / or hollow fiber membrane contactors. In some instances, the second portion of the flow system is configured to raise the pH of the treated seawater (e.g., after the portion of carbon dioxide has been removed) (e.g., using pulsed electrolysis and / or by providing an electrochemical pH swing).

[0056] In certain embodiments, the flow system comprises a second orifice. For example, as shown in FIG. 1, in some cases, flow system 100 comprises second orifice 103. In some cases, the second orifice is configured to release treated seawater out of the flow system. For example, in certain cases, the second orifice is configured to release treated seawater (e.g., seawater comprising reduced levels of carbon dioxide and / or bicarbonate) back to the body of water from which the seawater came (e.g., a sea or ocean).

[0057] In some instances, the flow system has a relatively long lifetime. For example, in some cases, the flow system has a lifetime of greater than or equal to 50 cycles, greater than or equal to 55 cycles, greater than or equal to 60 cycles, greater than or equal to 65 cycles, greater than or equal to 70 cycles, greater than or equal to 75 cycles, greater than or equal to 80 cycles, greater than or equal to 85 cycles, greater than or equal to 90 cycles, greater than or equal to 95 cycles, or greater than or equal to 100 cycles. In certain embodiments, the flow system has a lifetime of less than or equal to 300 cycles, less than or equal to 275 cycles, less than or equal to 250 cycles, less than or equal to 225 cycles, less than or equal to 200 cycles, less than or equal to 175 cycles, less than or equal to 150 cycles, less than or equal to 125 cycles, less than or equal to 110 cycles, or less than or equal to 100 cycles. Combinations of these ranges are also possible (e.g., greater than or equal to 50 cycles and less than or equal to 300 cycles, greater than or equal to 50 cycles and less than or equal to 150 cycles, greater than or equal to 50 cycles and less than or equal to 100 cycles, or greater than or equal to 100 cycles and less than or equal to 200 cycles). In some embodiments, one cycle is one round of reduction (Qregen) and oxidation (Qpuise).

[0058] As used herein, the lifetime of the flow system is the number of cycles in which the flow system achieves a Qacid utilization greater than 65% and / or a cycling capacity greater than 90% (e.g., a Qacid utilization greater than 65% and a cycling capacity greater than 90%) (e.g., any Qacid utilization greater than 65% disclosed herein and / or any cycling capacity15#14916960vlgreater than 90% disclosed herein). In some cases, the lifetime of the flow system is the number of cycles in which the flow system achieves a Qacid utilization greater than 65% and / or a cycling capacity greater than 90% (e.g., a Qacid utilization greater than 65% and a cycling capacity greater than 90%) (e.g., any Qacid utilization greater than 65% disclosed herein and / or any cycling capacity greater than 90% disclosed herein) with no shutdown, cleaning steps (e.g., flushing), and / or additional treatment.

[0059] In certain instances, the flow system has a relatively high Qacid utilization. For example, in accordance with some embodiments, the flow system has a Qacid utilization of greater than 65%, greater than or equal to 67%, greater than or equal to 70%, greater than or equal to 72%, greater than or equal to 75%, greater than or equal to 77%, greater than or equal to 80%, greater than or equal to 82%, greater than or equal to 85%, greater than or equal to 87%, greater than or equal to 90%, greater than or equal to 92%, greater than or equal to 95%, greater than or equal to 97%, or greater than or equal to 99%. In some cases, the flow system has a Qacid utilization of less than or equal to 100%, less than or equal to 99%, less than or equal to 97%, less than or equal to 95%, less than or equal to 93%, less than or equal to 90%, less than or equal to 88%, less than or equal to 85%, less than or equal to 83%, less than or equal to 80%, less than or equal to 78%, less than or equal to 75%, less than or equal to 73%, or less than or equal to 70%. Combinations of these ranges are also possible (e.g., greater than 65% and less than or equal to 100%).

[0060] According to some embodiments, the flow system has a relatively high cycling capacity. For example, in certain embodiments, the flow system has a cycling capacity of greater than 90%, greater than or equal to 91%, greater than or equal to 92%, greater than or equal to 93%, greater than or equal to 94%, greater than or equal to 95%, greater than or equal to 96%, greater than or equal to 97%, greater than or equal to 98%, or greater than or equal to 99%. In accordance with some embodiments, the flow system has a cycling capacity of less than or equal to 100%, less than or equal to 99%, less than or equal to 98%, less than or equal to 97%, less than or equal to 96%, less than or equal to 95%, less than or equal to 94%, less than or equal to 93%, less than or equal to 92%, or less than or equal to 91%. Combinations of these ranges are also possible (e.g., greater than 90% and less than or equal to 100%). Without wishing to be bound by theory, it is believed that when cycling capacity is less than or equal to 90%, the flow system fails after only a few cycles, in certain instances.16#14916960vl

[0061] As used herein, Qacid utilization = (Qacid,PH / Qacid) * 100%. As used herein, cycling capacity = (Qacid / Q k)*100%. As used herein, Qaik is the total charge passed during reduction (e.g., to prime the electrode for use). As used herein, Qacid,PH is the amount of charge passed during oxidation that leads to a bulk and noticeable acidic pH swing, wherein a bulk and noticeable pH swing is defined by the inflection point in which the rate of pH changes drastically. As used herein, Qacid is the total charge passed during oxidation (e.g., to acidify the solution) (e.g., up to +0.4 V vs. Ag / AgCl). Without wishing to be bound by theory, it is believed that Qacid,PH may be greater than Qacid in untreated seawater, as Mg2+and Ca2+may consume the generated protons, in some cases. In some embodiments, Qaik has a cutoff of +0.4 V (e.g., in some cases, Qaik has a cutoff of +0.4 V, or is +0.4 V, when determining lifetime) (e.g., in some cases, Qaik is less than or equal to 0.4 V, such as less than or equal to 0.3 V, less than or equal to 0.2 V, less than or equal to 0.1 V; greater than or equal to 0 V; or combinations of these ranges). Without wishing to be bound by theory, it is believed that higher values of Qaik will compromise energetics and damage the electrode over time, in some cases.

[0062] According to some embodiments, the flow system has a relatively low decrease in cycling capacity and / or Qacid utilization (e.g., cycling capacity and Qacid utilization) over the lifetime of the flow system. For example, in certain cases, the flow system has a decrease of less than or equal to 20%, less than or equal to 18%, less than or equal to 15%, less than or equal to 13%, less than or equal to 10%, less than or equal to 8%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or 0% in the cycling capacity and / or Qacid utilization (e.g., cycling capacity and Qacid utilization) over the lifetime of the flow system. For example, in some instances, the flow system has a decrease of less than or equal to 20% in cycling capacity and / or a decrease of less than or equal to 20% in Qacid utilization over the lifetime of the flow system (e.g., a decrease of less than or equal to 20% in cycling capacity and a decrease of less than or equal to 20% in Qad utilization over the lifetime of the flow system).

[0063] According to some embodiments, the flow system has a relatively low decrease in cycling capacity and / or Qacid utilization (e.g., cycling capacity and Qacid utilization). For example, in certain cases, the flow system has a decrease of less than or equal to 20%, less than or equal to 18%, less than or equal to 15%, less than or equal to 13%, less than or equal to 10%, less than or equal to 8%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or 0% in the cycling capacity and / or Qacid utilization (e.g., cycling capacity and Qacid utilization) over greater than or equal to 50 cycles (e.g., greater than or equal to 60 cycles, greater than or equal to 7017#14916960vlcycles, greater than or equal to 80 cycles, greater than or equal to 90 cycles, or greater than or equal to 100 cycles; less than or equal to 300 cycles, less than or equal to 200 cycles, less than or equal to 150 cycles, or less than or equal to 100 cycles; or combinations thereof). For example, in some instances, the flow system has a decrease of less than or equal to 20% in cycling capacity and / or a decrease of less than or equal to 20% in Qacid utilization over greater than or equal to 50 cycles (e.g., a decrease of less than or equal to 20% in cycling capacity and a decrease of less than or equal to 20% in Qacid utilization over greater than or equal to 50 cycles).

[0064] Certain embodiments are related to methods. In some embodiments, the method comprises intaking seawater (e.g., any seawater disclosed herein, such as untreated seawater) through a first orifice into a flow system (e.g., any flow system disclosed herein).

[0065] In certain embodiments, the method comprises providing an electrochemical pH swing (e.g., any electrochemical pH swing disclosed herein) to the seawater (e.g., any seawater disclosed herein, such as untreated seawater) with an electrochemical cell (e.g., any electrochemical cell disclosed herein). In some embodiments, the method comprises performing pulsed electrolysis (e.g., any pulsed electrolysis disclosed herein) on seawater (e.g., untreated seawater) with an electrochemical cell (e.g., any electrochemical cell disclosed herein). In accordance with some embodiments, the method comprises lowering the pH of the seawater (e.g., untreated seawater) to form treated seawater. For example, the method comprises lowering the pH of the seawater (e.g., untreated seawater) by pulsed electrolysis in some instances. For example, in some cases, the method comprises lowering the pH of the seawater (e.g., untreated seawater) using pulsed electrolysis with an electrochemical cell to form treated seawater.

[0066] In accordance with some embodiments, the method comprises periodic polarity reversal (e.g., during pulsed electrolysis and / or when providing an electrochemical pH swing). Without wishing to be bound by theory, it is believed that periodic polarity reversal increases dynamic fluctuations in local pH from proton release, which reduces precipitation of magnesium hydroxide on a surface of one or more electrodes, in some cases.

[0067] In certain embodiments, the method comprises converting a portion (e.g., at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 75%, at least 90%, at least 98%, or at least 99%; less than or equal to 100%, less than or equal to 90%, less than or equal to 75%, or less than or equal to 50%; or combinations of these ranges; or all) of the bicarbonate in the seawater to carbon dioxide. For example, in some instances, lowering the18#14916960vlpH of the seawater (e.g., untreated seawater) converts a portion (e.g., at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 75%, at least 90%, at least 98%, or at least 99%; less than or equal to 100%, less than or equal to 90%, less than or equal to 75%, or less than or equal to 50%; or combinations of these ranges; or all) of the bicarbonate in the seawater to carbon dioxide.

[0068] In accordance with certain embodiments, the method comprises removing a portion (e.g., at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 75%, at least 90%, at least 98%, or at least 99%; less than or equal to 100%, less than or equal to 90%, less than or equal to 75%, or less than or equal to 50%; or combinations of these ranges; or all) of the carbon dioxide from the treated seawater. According to some embodiments, the method comprises removing a portion (e.g., at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 75%, at least 90%, at least 98%, or at least 99%; less than or equal to 100%, less than or equal to 90%, less than or equal to 75%, or less than or equal to 50%; or combinations of these ranges; or all) of carbon dioxide from treated seawater via gas-phase extraction, vacuum stripping, and / or hollow fiber membrane contactors.

[0069] In certain cases, lowering the pH of the seawater (e.g., untreated seawater) to form treated seawater (e.g., using pulsed electrolysis and / or by providing an electrochemical pH swing) is in a first portion of the flow system. In some cases, the removal of a portion of the carbon dioxide from the treated seawater is in the first portion and / or in an additional portion of the flow system. In some instances, the method comprises flowing the treated seawater into the second portion of the flow system after the portion of carbon dioxide has been removed. In certain instances, the method comprises raising the pH of the treated seawater (e.g., after the portion of carbon dioxide has been removed). For example, in some embodiments, the method comprises raising the pH of the treated seawater (e.g., after the portion of carbon dioxide has been removed) in the second portion of the flow system.

[0070] In some cases, a portion (e.g., at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 75%, at least 90%, at least 98%, or at least 99%; less than or equal to 100%, less than or equal to 90%, less than or equal to 75%, or less than or equal to 50%; or combinations of these ranges; or all) of the treated seawater (e.g., after the portion of carbon dioxide has been removed and / or after the pH has been raised) exits the flow system through the second orifice. For example, in certain cases, a portion (e.g., at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 75%, at least 90%, at least 98%, or at least 99%; less than or equal to 100%, less than or equal to 90%, less than or equal to 75%, or less19#14916960vlthan or equal to 50%; or combinations of these ranges; or all) of the treated seawater (e.g., after the portion of carbon dioxide has been removed and / or after the pH has been raised) exits the flow system through the second orifice and returns to the body of water from which the seawater came (e.g., a sea or ocean).

[0071] The following examples are intended to illustrate certain embodiments of the present invention, but do not exemplify the full scope of the invention.EXAMPLE 1

[0072] For electrochemical carbon capture technologies for use in ocean water, numerous challenges persist regarding their long-term resiliency. One major concern is the presence of problematic magnesium (Mg2+) and calcium (Ca2+) ions in ocean water, which can precipitate on the electrode surfaces and compromise performance. This example examines the impacts of these species on an asymmetric configuration, which consists of electrochemical cells housing bismuth and silver electrodes. An overview of the process, the cell design, and corresponding experimental results are showcased in FIGs. 2A-2D.

[0073] Bismuth essentially dictated the overall performance of this setup, and its resilience to Mg2+and Ca2+was thus the main focus of this example. When electrolyte was sent through the cell, Bi reversibly uptook Cl’ to form bismuth oxychloride and simultaneously released protons (Bi + Cl’ + H2OBiOCl + 2H++ 3e’; E° = 0.16 VSHE) via oxidation. This step acidified the bulk solution which then allowed for the release of CO2 downstream. Once the electrode capacities were exhausted, the polarity was flipped to regenerate BiOClBi via reduction. This alkalinized the bulk to offset the previously acidic stream and enabled cyclical operation, in which the cell polarities and seawater flow were continuously flipped to facilitate acidification and regeneration for pH control and CO2 capture. Meanwhile, silver served as a chloride-reactive counter (AgCl + e’ -> Ag + Cl’; E° = 0.23 VSHE) to complete the electron flow without generating additional H+ / OH’ that may otherwise compromise bulk pH.

[0074] Nevertheless, the alkaline environment during regeneration can also spur the precipitation of Mg(OH)2 and Ca(OH)2 deposits (as well as carbonates if CO2 is not fully extracted from the ocean water influent beforehand). Magnesium, in particular, led to massive losses in Bi performance (FIGs. 2A-2D), evidenced by a near complete disappearance in the pH swing. In FIGs. 2C-2D, Bi was first subject to regeneration (-1 mA cm’2) and subsequent acidification (+1 mA cm’2). In NaCl, Bi demonstrated a strong pH swing between 11.3 and 3.0 during this cycle. When NaCl was replaced with simulated20#14916960vlseawater (SW), the pH flatlined with no significant acidification observed until after 103 min (-72% of the Qacidification passed). It is possible that the scale deposits formed during regeneration were consuming protons before they could diffuse back into the bulk solution.

[0075] This example proposes a framework of strategies to bolster the impurity tolerance of the Bi electrodes against magnesium and calcium ions found in seawater. Current CO2 capture cells assume the use of pre-treated seawater for operation. Developing impurity-resilient electrodes would greatly reduce such costs and improve the versatility of such cells to be employed independently and in a decentralized manner. The first strategy was to explore modifications to the electrodes by 1) verifying the selection of carbon and its impact on Mg2+sorption, and 2) application of a coating to inhibit magnesium transport to the interface. Carbon can capacitively store ions via electrosorption, and its physicochemical properties strongly influence total uptake. The original synthesis procedure used carbon black (CB) as a conductive additive, and this was replaced with graphene (G) for experimental comparisons. From here, the impacts of Bi coating were explored, using a PiperlON® ionomer. This resin acts as an anion-exchange medium to block Mg2+transport while still allowing Cl’ to crossover for the Bi / BiOCl reaction. FIGs. 3A-3C shows representative SEM images of the modified electrodes.

[0076] The Bi / G and PiperION®-coated Bi / G samples were tested under the same flow cell and operating conditions, as shown in FIG. 4A. Compared to the Bi / CB electrode, the Bi / G electrode exhibited performance improvements as the onset of acidification occurred at an earlier timeframe; and the potentials were relatively stable with no upward spikes (a sign of capacity depletion). Such effects were further enhanced with the coated Bi / G electrodes, show-casing improved pH swing performance. Using the same cell, in situ imaging of the coated Bi / G surface before electrolysis and during operation (FIGs. 4B-4G) was conducted. After just 30 min of regeneration, various deposits were randomly distributed on top of the electrode surface; these deposits only grew over time (i.e., 60 min), shown most clearly by the features located in the top-right and bottom-middle of the images. It is worth highlighting how aggressively these deposits adhered to the surface, as they never fully disappeared after formation. Acidification after 90 and 119 min (i.e., pH drops to -4) was insufficient for deposit dissolution. Afterwards, the system was left at rest (i.e., open-circuit potential) and the rough features still remained weakly visible. Subsequent ex situ characterization of the deposits confirmed the presence of Mg(OH)2 fully coating the Bi surface (FIGs. 4H-4K).21#14916960vl

[0077] From here, pulsed electrolysis was explored to ameliorate the issue of scaling and further minimizing losses in pH swings. A comprehensive overview and relevant datasets are displayed in FIGs. 5A-5F. Given that pulsing conditions are largely empirical, an array of sequences was run to analyze changes to the electrode surface (FIG. 5A). A single pulsed cycle was defined by a set amount charge dedicated towards reduction (Qregen) and another set dedicated towards oxidation (Qpuise). The primary condition was that Qregen should be significantly more than Qpuise to ensure adequate regeneration, and a starting condition of Qpuise / (Qpuise + Qregen) = 0.25 was set. Given that regeneration was most relevant to scale formation, the acidification steps were operated without any pulsing ((FIG. 5A).

[0078] Four distinct variables were defined to evaluate Qregen and Qpuise: (1) regeneration current, jred, (2) regeneration time, tred, (3) pulsing current, jpuise, and (4) pulsing time, tpuise. To minimize the otherwise impractical number of testing sequences, several assumptions were used for the initial examinations. First, it was hypothesized that tred should be kept relatively short (2 s) to minimize the extent of Mg(OH)2 nucleation and growth; in turn, ;red must be higher than before to ensure a reasonable Qregen value (otherwise the sequence may become too time intensive). Thus, jred and / red were initially set to -5 mA cm'2and 2 s for all sequences, respectively (FIG. 5B). Using this condition, two general cases for the pulsing step were formulated while maintaining Qpuise is equal across each sequence. The first case utilized a fast and high-magnitude oxidative pulse to invoke drastic and frequent perturbations at the interface; accordingly, sequence A was set to have a pulsing step of +5 mA cm'2for 500 ms. In contrast, the second case was to have a low and slow pulsing bias designed for more moderate environments yet longer z,c<i to ensure substantial time for the precipitates to redissolve and diffuse away (i.e., timescale of dissolution). As a result, Sequences B and C were set to be +0.5 mA cm'2for 5 s and +0.125 mA cm'2for 20 s, respectively.

[0079] Pulsed regeneration of the coated Bi / G samples led to significant improvements in concurrent acidification performance, even under simulated SW. FIGs. 5C-5E portray the pH and Bi half-cell potentials across both regeneration and acidification for a single cycle, normalized by the total charge passed. In the regeneration profiles (FIG. 5C), the voltages across all sequences generally showed no differences in magnitude. The pH values equilibrated at different values, due to the fact that the sequences were operating at a distinct C / L basis. After about 0.5 mAh passed, the voltages attained a pseudo-steady-state; the voltage differences were examined more carefully between each Qregen and Qpuise in FIG. 5E.22#14916960vlAcross A-C, the voltages expectedly spiked up with the onset of each pulse given the oxidative driving force to enable transient Bi BiOCl and proton release. Even though Qpuise was constant across all three sequences, the magnitude of the voltage difference was higher for B and notably C due to more diffusion and ion transport at the interface. This was also dependent on the presence of the coating, as the inset revealed a much higher voltage change for uncoated Bi / G under the same sequence (B). This was attributed to an ion trapping effect, in which the resin could store Cl’ and OH’ during these short timescales before they could fully diffuse into the bulk. This, in turn, affected the microenvironment and would further dampen the local pH shifts at the ionomer surface.

[0080] The acidification results in FIG. 5D showcase that pulsed sequences A and B resulted in the best pH swing performances. Sequences A-B yielded the earliest pH swings (after ~1.0 mAh) even in the simulated SW electrolyte. Surprisingly, Sequence C demonstrated the worst performance even with the longest / pilise and lowest C / L basis, in which the recoverable capacity was markedly worse; furthermore, the pH gradient was noticeably slower in comparison to all other sequences. On this note, it was observed that the test with no pulsing not only exhibited a delayed pH response, but also initially plateaued to a less acidic value (—4.2) before converging with the pH values of A and B (after 2.5 mAh had passed). This may be associated with additional protons being consumed to redissolve the rest of acid-resistant Mg(OH)2 still remaining at the interface, further eliciting the benefits of pulsed operation. Lastly, in situ imaging revealed no macroscopic changes to the surface roughness at any given time, unlike what was observed in FIGs. 4A-4K.

[0081] Overall, this unique and optimized combination of electrode modifications and pulsed operation demonstrated major improvements for a direct ocean capture process. Successful implementation of these strategies would allow for DOC technologies to be much more versatile and highlights its use without the need for ocean water pretreatment.

[0082] EXAMPLE 2

[0083] Electrochemical cells may modulate influent ocean pH to enable removal of dissolved inorganic carbon as gaseous CO2. However, the oceans contain magnesium and calcium impurities that can damage cell components and ultimately undermine performance. An implicit assumption in these technologies is that seawater will be pretreated to remove inorganic foulants, compounding to purification operating costs and design constraints. As a23#14916960vlresult, the development of electrochemical systems capable of withstanding these impure feed streams would not only offer more stable and sustainable technologies, but also broaden implementation. Herein, this example presents a robust framework of strategies for direct use in untreated seawater. The methods limited impurity transport to the electrode surface and alleviated precipitation buildup. Upon optimization, the recovery rates in total pH swing performance were improved from <25 to -70% and system longevity was extended from <5 to at least 100 cycles (-300 hours) of operation.

[0084] As atmospheric CO2 levels continue to rise, the importance of widescale decarbonization in response to everchanging industrial demands and sustainability needs cannot be overstated. One avenue of interest is capture of inorganic carbon from ocean water, known as direct ocean capture (DOC). The oceans function as a major sink for CO2 released into the atmosphere, as they can currently uptake approximately 30% of total anthropogenic emissions. Moreover, volumetric concentrations of dissolved inorganic carbon (DIC) in the ocean (-2 mM) are over 100X that in ambient air, potentially enabling circumvention of energetic losses associated with the CO2 absorption step in direct air capture systems.

[0085] DOC technologies can take advantage of this abundance of DIC in ocean water and induce a swing in bulk pH for CO2 extraction. In brief, carbon dioxide from the atmosphere dissolves into seawater, which then speciates as bicarbonate (HCO3 ) and carbonate (CO32) through the following equilibria:CO2(aq) + H2O HCO3 + H+( 1 )HCO3 «-> CO32+ H+(2)DIC = [CO2(aq)] + [HCO3] + [CO32] (3)

[0086] To reverse this process and enable CO2 removal, acid may be added to the seawater to lower pH and shift DIC equilibrium back towards CO2(aq) for gas-phase extraction downstream (e.g., via vacuum stripping). Once the DIC is extracted, the effluent seawater may be neutralized (via addition of base) and restored to its original alkalinity levels before discharge back into the environment, enabling continuous atmospheric CO2 absorption and oceanic re-equilibration.

[0087] While CO2 capture technologies often rely on energy-intensive pressure, thermal, or auxiliary chemical inputs, electrochemically-mediated configurations may modulate ocean pH using renewable energy and operate under ambient conditions. The electrodes may facilitate redox reactions that directly generate H+ / OH ions in seawater without creating24#14916960vladditional waste, eliminating the need for chemical acid and base inputs. An electrochemical DOC process using asymmetric cells comprised of bismuth (Bi) and silver (Ag) electrodes was recently developed; some advantages included a membrane-free setup, low voltage requirements (~0.6 volts) and steadfast reversibility for continuous CO2 extraction.

[0088] A challenge intrinsic to any ocean-based application is the complex composition of the ocean itself, which contains a wide range of constituents that may compromise electrochemical cell integrity and system stability. Dissolved solids in seawater primarily comprise Na+and Cl’ ions (0.47 to 0.55 mol kg1) but also include magnesium, sulfate, calcium, and an assortment of other species at lower levels (i.e., Sr2+, B(OH)s / B(OH)4’, Br, F’ , etc.). In particular, Mg2+and Ca2+(0.05 and 0.01 mol kg1, respectively) may be detrimental to electrochemical cells, as they can precipitate as scale and damage the electrodes under alkaline conditions. This predicament may require pretreatment of any influent seawater before utilization, imposing additional operational costs and design constraints depending on treatment requirements (i.e., add-on equipment, geographical reliance on existing centralized infrastructure, etc.). As a result, electrochemical systems that can tolerate Mg2+, Ca2+, and other impurities may substantially bolster process resiliency, simplify engineering requirements, and broaden geographical versatility.

[0089] Herein, a framework of strategies is reported to enhance the impurity tolerance and stability of electrochemical DOC technologies. This example is centered on the failures associated with Mg2+and Ca2+in seawater, using an asymmetric Bi-Ag CO2 capture process. Deactivation mechanisms were quantitatively uncovered behind observed performance losses. Using these insights, this example employed an ionomer coating to inhibit Mg2+access to the Bi surface, as well as pulsed electrolysis to mitigate Mg(OH)2 accumulation. Optimization of these approaches increased charge (Q) utilization rates from <25% to -70% in raw synthetic seawater and extended longevity from <5 to at least 100 cycles of operation without additional cleaning measures.

[0090] In this example, the impacts of Mg2+and Ca2+present in untreated seawater were examined on the disclosed asymmetric electrochemical CO2 removal process (FIG. 6A). Briefly, this configuration comprised two identical flow cells comprised of bismuth and silver electrodes. When seawater was sent through Cell 1, bismuth uptook Cl’ and dissociated water to form bismuth oxychloride and simultaneously released H+; the resultant acidified stream could then be sent for CO2 stripping (e.g., via hollow fiber membrane contactors). Silver25#14916960vlchloride served as a Cl-reactive counter that did not generate additional H+ / OH , which could otherwise compromise the pH swing.Bi + Cl’ + H2O BiOCl + 2H++ 3e ; £° = 0.16 VSHE (4)AgCl + e Ag + Cl"; £° = 0.23 VSHE (5)

[0091] After a certain point, the electrode capacities became depleted, and the cell (now designated as Cell 2) was replaced with a fresh cell (now Cell 1) that had been regenerated in the previous cycle of operation. The regeneration of the electrodes in Cell 2 was achieved by flipping the polarity to reduce BiOCl to Bi and oxidize Ag to AgCl, respectively. This regeneration of Bi concurrently produced OH- that alkalized the feed stream (i.e., the DIC-depleted acidic stream) before it was released back into the environment. Overall, this setup enabled cyclical operation in which the cell polarities and electrolyte flow were flipped periodically to facilitate sustained acidification (Bi oxidation) and alkalinization (BiOCl reduction for electrode regeneration) for CO2 removal.

[0092] Bismuth affected the pH and overall performance, and its resilience to seawater was consequently the primary focus of this example. To investigate, a single cell of the asymmetric process was reconfigured (FIG. 6B and FIGs. 11A-11B) to assess the Bi halfcell potentials and bulk pH during each cycle, as well as conduct in situ optical imaging of the Bi / BiOCl interface. A tertiary Ag / AgCl reference was inserted at the cell inlet where it was not subject to the strong pH gradients inside the cell chamber. Relatedly, the effluent pH was monitored across all cycles as the primary metric of performance. For in situ imaging, the camera and objective were positioned at the Ag counter side, and a small hole was created in the Ag electrode to probe the Bi surface on the adjacent side.

[0093] In simulated treated seawater free of Mg2+and Ca2+, bismuth delivered strong pH swing capabilities during both acidification and alkalinization cycles. In short, Bi powders were mixed with a conductive carbon black additive to form a composite (denoted Bi / CB). Cyclic voltammetry (CV) scans demonstrated sharp reductive currents beyond -0.5 VAg / Agci, followed by the onset of BiBiOCl oxidation around -0.15 VAg / Agci. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses confirmed the existence of a dispersed network of nanoparticles corresponding to metallic Bi and Bi oxide structures. The flow cell was assembled and Bi / CB was tested during reduction and oxidation (FIG. 6C), starting with 0.5 M NaCl (light grey trace) to represent purified seawater. Generally, all Bi samples were initially cycled for surface conditioning, reduced (alkalinization) to incur26#14916960vlprecipitation and / or other known failure pathways, and subsequently oxidized (acidification) to evaluate resultant pH swing performance. In NaCl, Bi / CB consistently delivered a pH swing between -11.3 and -3.0 at current densities ( / ) of ±1 mA cm'2(60 minutes each). During alkalinization, the potentials quickly plateaued to approximately -0.6 VAg / Agci; similarly, the potentials stabilized between -0.15 and -0.10 VAg / Agci during acidification, eliciting the low energetics of Bi / BiOCl (-500 mV voltage difference).

[0094] Cell efficacy instantly plummeted once Mg2+and Ca2+ions were introduced, evidenced by a near complete disappearance in pH swing. To simulate untreated seawater (black trace), NaCl was spiked with 50 mM Mg2+(using MgCh) and 10 mM Ca2+(using CaCh) while maintaining a total Cl' concentration of 0.5 M based on known compositions. During alkalinization, the potentials were nearly identical to those of the NaCl trial, but the pH was less alkaline at -9.9 after 60 minutes. In the following acidification step, the potentials depicted a distinct tapering pattern, first lingering at more negative values (-0.36 to -0.30 VAg / Agci) before momentarily rising to -0.15 VAg / Agci. From here, the overpotentials skyrocketed due to the oxidation of less-accessible inner core Bi atoms underneath the Bi / BiOCl phase boundary. Electrolysis was correspondingly terminated after +0.4 VAg / Agci, since more oxidative environments signify Bi depletion and the onset of oxygen evolution. During this period, the pH flatlined (8.7-8.9) with no further reduction observed until 43-minutes into the 55-minute cycle. To account for seawater (SW) matrix effects in the metrics, the bismuth cycling capacity was defined as Qacid (total charge passed during oxidation up to +0.4 VAg / Agci) / Qaik (total charge passed during reduction). Similarly, Qacid utilization was defined as the ratio of charge dedicated towards an acidic pH swing (Qacid,PH) over Qacid; the former term, Qacid,PH, was measured from each dataset at the inflection point in which the rate of pH changes increases drastically. As a reference, the cycling capacity and Qacid utilization in NaCl after one cycle were 95% and 83%, respectively. In simulated SW, the cycling capacity remained relatively high at 92% (despite the increase in overpotentials); however, Qad utilization dropped to 22% with no steady-state acidification. Mg2+and Ca2+had no effect on the silver potentials, suggesting losses were mainly bismuth-related. Lastly, these behaviors were persistent across multiple cycles with zero recovery in Qacid utilization rates.

[0095] No scale precipitation was observed on the Bi / CB interface at any given point of operation. In FIG. 6D, in situ optical images revealed negligible changes in macroscopic surface roughness, irrespective of alkalinization (59-minute) or acidification (119-minute); this detail was in sharp contrast to reports of significant deposition accompanied by new27#14916960vlmorphologies in previous seawater-related electrochemical studies. Even though microscopic Mg(OH)2 and Ca(OH)2 formation was still feasible, a concurrent redox interaction between Mg2+and Bi was postulated, given the tapered shifts in the oxidative potentials. In this regard, supplementary research confirmed Mg2+as the dominant driver behind such losses. The procedures delineated in FIGs. 6A-6D were repeated with NaCl spiked independently with Mg2+or Ca2+. Losses in Qacid utilization were only visible when magnesium was present, even when at concentrations as low as 10 mM; meanwhile, Ca2+had almost no impact on overall performance. On this note, Mg2+was only detrimental during alkalinization. In a separate trial, when Bi / CB was reduced in NaCl and then oxidized in simulated SW, it exhibited a full recovery in pH swing performance.

[0096] Post-characterizations revealed that magnesium adhered strongly to the Bi / CB matrix and competed faradaically with the Bi / BiOCl reaction. Parallel batch cell assessments were performed (FIG. 7A), in which Bi / CB samples were independently reduced in NaCl containing 0 or 50 mM Mg2+. Immediately afterwards, linear sweep voltammetry (LSV) scans were conducted, revealing the BiBiOCl oxidation peak (-0.15 VAg / Agci) in NaCl only, and a second peak (onset potentials of -0.36 to -0.30 VAg / Agci) upon the inclusion of magnesium. This feature occurred prior to the thermodynamic requirement for BiOCl reduction and coincided with the tapered potentials in FIGs. 6A-6D. In turn, the area of the BiOCl peak was diminished, which was only exacerbated at higher Mg2+concentrations. To elucidate this phenomenon, each electrode was soaked in DI water (~4 hours) to dissolve extraneous deposits and the remaining magnesium was inspected. For reference, Bi / CB was first characterized after operation in NaCl only (FIG. 7B), which retained its network of dispersed particles seen previously before use. Conversely, Bi / CB exposed to Mg2+exhibited a distribution of flaky crystals and amorphous clusters (FIG. 7C).Elemental mapping analyses illustrated that magnesium was scattered throughout the electrode matrix, intermixed with bismuth. Given that certain clusters could be residual MgO, the same testing protocols were repeated with the same electrolytes but preadjusted to pH 2 to eliminate Mg(OH)2 accumulation and interference. Even with these highly acidic conditions (and DI rinse), magnesium remained substantially adsorbed to Bi / CB after reduction.Elemental mapping demonstrated far fewer clusters, but also depicted substantial overlaying of both Bi and Mg signals.

[0097] One possibility was the uptake of Mg2+occurred via forming an alloy with bismuth during reduction. A reported mechanism was the formation of MgsBi2 (3Mg2++ 2Bi + 6e"28#14916960vlMgsBi2); magnesium ions diffused toward the interface and subsequently underwent faradaic insertion into the Bi matrix. The precise chemistries remained unclear at this stage due to environmental complexities (i.e., pH swings, high Cf concentrations, Ca2+). Nevertheless, a comparable alloying pathway was plausible given the high affinity of Bi for Mg uptake. Such a reaction did not generate H+ / OH and would explain the diminution in acidification (alongside Mg(0H)2 consumption). In this regard, some non-faradaic Mg2+sorption to the Bi / CB particles was also detected. Fresh electrodes were submerged in the magnesium-spiked NaCl under open-circuit potentials (OCP). Magnesium was still visible on the surface, albeit at weaker intensities and in the absence of any new agglomerates.

[0098] Regardless of the precise phenomena at play, it became imperative to curtail Mg2+access to the Bi / CB electrode. The ensuing combination of microscopic Mg(OH)2 deposition, sorption, and faradaic alloying during alkalinization considerably inhibited electrode capacity. To confirm these losses, all trials were repeated for one full operating cycle (i.e., alkalinizationacidification) in the designated NaCl electrolytes (at either pH 7 or 2) with or without Mg2+. Post-testing XRD analyses (FIG. 7D) revealed an absence of BiOCl after cycling in the presence of Mg2+. Following acidification, BiOCl was the dominant phase; which was confirmed in the NaCl-only cases by their corresponding spectra (notably at 32.4 and 33.1°). Upon magnesium exposure, such features vanished regardless of pH and were replaced by peaks representative of metallic Bi, possibly from oxidative dealloying.Sequentially, several new peaks emerged that may correlate to Mg(OH)2 and / or perhaps pertinent Mg-Bi complexes.

[0099] This example explores two distinct electrode modification procedures to boost magnesium tolerance (FIG. 8A). The first approach was to determine whether the carbon additive affects Mg2+uptake. Carbon can store divalent ions capacitively via electrosorption, which is controlled by its particle size, contact, and other physicochemical properties.Similarly, carbon morphologies may govern ion diffusion and the arrangement of bismuth particles, effectively dictating the active Bi surface area and rate of exposure to Mg2+(and other ions). For comparison, another set of electrodes was synthesized using the same procedures but replacing carbon black with graphene nanoplatelets. The Bi / graphene (Bi / G) composites were comprised of larger, more bulbous particles than in Bi / CB (FIG. 8B). One explanation is that graphene tends to agglomerate and wrap around its active material counterparts, which could possibly inhibit Mg2+access. While this may reduce the microscopic surface area, Bi / G demonstrated performance comparable to Bi / CB; in the29#14916960vlabsence of Mg2+, the potentials and pH profiles of each were nearly indistinguishable from one another.

[0100] The second approach was to apply a protective coating to block bismuth and Mg2+contact at the interface. PiperlON® (an anion-exchange ionomer) was selected for its widespread use in electrochemical applications, its ability to exclude cations (Mg2+) via Donnan exclusion while facilitating Cl’ crossover, and reported longevity. The ionomer was first dropcast onto the Bi / G surface at various amounts (0.3, 0.6, and 0.9 mg cm’2) to attain an optimum mass loading. The addition of PiperlON® led to slightly higher overpotentials (~50 mV) and charge-transfer resistances during alkalinization. However, these metrics were consistent across all mass loadings, and thus 0.6 mg cm’2was selected for all subsequent evaluations. The ionomer formed a smooth layer that fully covered the bulbous Bi / G particles (FIG. 8B) and had no impact on overall performance in NaCl. Although the rate of pH change was slightly delayed (due to the diffusional resistance to H+ / OH’ transport through PiperlON®), the consequent steady-state pH values matched those of the uncoated trials. Finally, the ionomer did not alter the composite roughness, as the electrochemically active surface areas were consistent between the coated and uncoated samples.

[0101] The coated Bi / G electrodes were more resistant to faradaic Bi-Mg effects than were the Bi / CB samples. This was evinced by batch cell characterizations (FIGs. 8C-8D) using the same LSV analyses delineated in FIG. 7A. Briefly, both uncoated and coated Bi / G were first reduced in NaCl spiked with various Mg2+concentrations (0, 50, 100, 200 mM) and immediately analyzed via LSVs. For uncoated Bi / G (FIG. 8C), the Bi / BiOCl redox peak (-0.15 VAg / Agci) was mostly retained when [Mg2+] was set to 50 mM, and the parasitic Bi-Mg affiliated peak (-0.36 to -0.30 VAg / Agci) was not detected. Bi / G likely has fewer surficial Bi atoms available for ion access, due to its relatively larger particle sizes and the tendency of graphene to cover active materials based on its lattice orientation and packing distribution. This was supported by a persistent peak at approximately +0.2 VAg / Agci and onwards, linked to inner core Bi and Bi oxides with restricted Cl’ availability. Regardless, Bi / G alone could not tolerate higher magnesium concentrations (100, 200 mM), in which the Bi-Mg peak strongly resurfaced at the expense of Bi / BiOCl capacity. Post-characterizations of the uncoated sample illustrated extensive deposition of flakelike magnesium crystals all over the surface, mirroring the behaviors witnessed for Bi / CB. Nonetheless, the PiperION®-coated Bi / G (FIG.8D) retained its Bi / BiOCl capacity across all [Mg2+], even when as high as 200 mM. The peak locations were slightly shifted due to the higher charge-transfer resistances;30#14916960vlregardless, the Bi-Mg peak was greatly suppressed, indicating the coating successfully blocked Mg2+transport to the bismuth particles.

[0102] Such enhancements were directly corroborated in the flow cell (FIG. 4A). The uncoated and coated Bi / G electrodes were tested in simulated SW under the same operating conditions (60-minute alkalinization and 60-minute acidification, ±1 mA cm'2) for direct comparisons with Bi / CB. During alkalinization, all electrodes exhibited similar pH profiles (9.7-10.1 at steady-state) with slightly higher overpotentials for the coated sample. In the subsequent acidification step, the tapered potentials characteristic of Bi / CB had largely disappeared for the Bi / G samples; instead, the potential waveforms mirrored the shapes observed previously under NaCl only, stabilizing between approximately -0.15 and -0.05 VAg / AgCi. Furthermore, the coated Bi / G delivered a Qacid utilization rate at 55% (compared to 22% earlier for Bi / CB). For both Bi / G samples, the pH eventually plateaued to a value of 4.3, which was less acidic than in the NaCl only trials (~3.0) in FIGs. 6A-6D.

[0103] The dominant failure mechanism in these trials shifted from faradaic uptake to Mg(OH)2 accumulation. In situ optical imaging was performed for the coated Bi / G sample in simulated SW (FIGs. 4B-4F), unveiling a plethora of macroscopic deposits. Particle nucleation became visible within the first 30 minutes of testing, gradually growing and thickening over time. Near the end of alkalinization (59 minutes), the precipitates were of various sizes and randomly distributed in a nonuniform manner. For the next 60 minutes (acidification), the deposits remained aggressively attached to the surface. As the pH started to fall (90 minutes), some of the smaller deposits began to thin and eventually disappeared by the end of the cycle (119 minutes). The larger deposits (such as the one positioned in the bottom-right of the images) remained mostly intact, indicating sluggish dissolution kinetics even as the pH became acidic (4.3). SEM images of the Mg(OH)2 deposits revealed highly amorphous morphologies (FIGs. 4H-4K) unlike the flakelike crystals seen on Bi / CB. In addition, corresponding elemental mapping analyses revealed heavy magnesium buildup that obscured the presence of surficial bismuth, blocking its access to the electrolyte, from which a lack of alloying behavior can be inferred.

[0104] Overall, the use of graphene and PiperlON® inhibited Mg2+transport to Bi, but magnesium still led to cell deactivation as the dominant failure pathway shifted to Mg(OH)2 growth. Accordingly, the use of pulsed electrolysis was investigated to mitigate this buildup and further recover performance in seawater.31#14916960vl

[0105] Unlike in non-pulsed operation, pulsed electrolysis introduces periodic changes to the otherwise constant bias of a cell. These intentional perturbations involve alternating current and / or voltage (Z-V) waveforms that modulate mass transfer rates to remove impurities and clean the electrode surface. The objective was to analogously employ a pulsed sequence that disrupts Mg(OH)2 scale buildup.

[0106] One major task was to optimize the pulse parameters, downselecting from an otherwise infinite number of pulsing sequence permutations. To address this, an array of sequences was tested on coated Bi / G in simulated SW; a comprehensive overview is showcased in FIGs. 5A-5C, FIG. 5E, FIGs. 9A-9C. Since Mg(OH)2 forms during reduction, the investigations were consolidated to pulsed alkalinization; all subsequent acidification steps were kept consistent (+2 mA cm'2) to effectively compare each pH profile (FIG. 5A).In this disclosure, the polarity of all pulses was reversed (i.e., oxidation) to accelerate collapse of the boundary layer and transiently generate H+. Consequently, each pulsing cycle comprised of a set charge for alkalinization (Qaik) and a set charge for oxidation (Qpuise). Qaik should be higher than Qpuise to provide adequate bismuth regeneration, and thus an empirical governing condition of Qaik / (QPuise + Qaik) = 0.25 or 25% was set.

[0107] Four distinct variables were defined to optimize Qaik and Qpuise: (1) alkalinization current, ;aik, (2) alkalinization time, talk, (3) pulsing current, jpuise, and (4) pulsing time, zpi, ise. Next, several assumptions were set to minimize the number of testing scenarios. First, talk was kept short to attenuate Mg(OH)2 nucleation and growth rates; in turn, jaik was increased to ensure sufficiently high Qaik. As a result, ;aik and talk were set to -5 mA cm'2and 2 seconds for all trials, respectively. Next, the pulse waveforms were simplified into two general cases while keeping Qpuise equal (FIG. 5B). The first case utilized fast, highly oxidative pulses to invoke drastic and frequent perturbations at the interface; in this regard sequence A was set to +5 mA cm'2( / puise) for 500 milliseconds (tpuise) per pulse. In contrast, the second case constituted low and slow pulses to resemble more moderate conditions with longer / pi,ise for scale dissolution and Mg2+back-diffusion into the bulk. Sequence C was appropriately set to +0.125 mA cm'2( / puise) for 20 seconds (rpuise) per pulse. Lastly, sequence B (+0.5 mA cm'2for 5 seconds) was tested as a midpoint between these two scenarios.

[0108] The half-cell potentials and pH profiles were evaluated, normalized by net total Qaik, across all pulsed alkalinization sequences (FIG. 5C). The steady-state pH equilibrated at different values (9.4-10.2), as each sequence operated at a distinct net current density and total testing time. After ~0.5 mAh net Qaik had passed, the potentials attained a32#14916960vlpseudo-steady state. Bi potentials temporarily spiked during each pulse, consistent with transient Bi BiOCl conversion and H+release. The potential differences were lower when PiperlON® was present; this is because the ionomer could behave like a capacitor and trap OH’ in this transitory environment. The uptake of OH’ may further dampen local alkalinity levels and hinder Mg(OH)2 agglomeration.

[0109] Depending on the sequence, pulsed alkalinization resulted in more effective acidification (FIG. 5E). Sequences A and B yielded the best pH swing performances, with onsets as early as 0.86 mAh (71% Qacid utilization rate). Moreover, the subsequent steadystate pH (~3.0) mirrored the values previously observed under magnesium-free conditions. This was markedly different from the case with no pulsing, in which the pH first plateaued to 4.2 before converging to 3.1 at the very end of operation. Such behaviors are consistent with a relative lack of Mg(OH)2 on the Bi interface after pulsed alkalinization, whereas the deposits during operation without pulsing acted as a local buffer and increased bulk pH. This effect was confirmed via in situ imaging (FIG. 9A); with pulsing, the Bi surface remained unchanged at all times, displaying no new morphologies. Meanwhile, sequence C exhibited the worst cycling capacity and pH swing, which took much more Qacid to stabilize. It is possible these losses resulted from self-discharge or passivation (i.e., from Cl ) during the pulses independently of Mg2+, setting a precedent that an extended / pilise is not always the most effective strategy. Overall, the considerable enhancements of the modified electrodes and setup are highlighted when compared to the Bi / CB sample (black, dashed trace), in which the cycling capacity was far lower (68%) and acidification was completely nullified.

[0110] In the remainder of this example, focus was placed on sequence B ( / puise: +0.5 mA cm’2| / pulse: 5 seconds) for more in-depth insights. Despite the promising short-term results of A, its rapid (<1 s) and high-amplitude changes (+10 mA) may have compromised electrode integrity over time (i.e., particle detachment, ionomer cracking). To verify earlier hypotheses, two comparative pulsing sequences were performed with the same net current densities as B, but with either longer taik (D) or higher frequency (E). Neither led to acidification results as effective as B, attesting to the sensitivity of the process to the pulse parameters. For one, high frequency reduction (<1 second) worsened the cycling capacity, due to greater capacitive contributions per step (i.e., double-layer charging). Furthermore, Mg(OH)2 nucleation was a factor; once the deposits grew to a certain size, the pulses were almost useless in their removal.33#14916960vl

[0111] Pulsed alkalinization greatly enhanced the longevity of the Bi electrodes in simulated SW. Post-testing SEM imaging (FIG. 9B) uncovered a rougher Bi / G surface with crystalline particles protruding out of the ionomer coating. Elemental mapping analyses indicated these features were primarily bismuth and that magnesium was largely absent. Bismuth may have broken through the coating during its phase transition into BiOCl, which is over 150% larger in volume than its Bi° counterpart. Crystalline protrusions were likewise visible when the electrodes were pulsed in NaCl. Nevertheless, the overall cyclability in seawater was substantially improved by implementing pulsed sequences over non-pulsed operation. FIG.9C shows the pH and potential profiles of the electrode over 40 cycles. The half-cell potentials were steady and demonstrated negligible change; the cycling capacities and Qacid utilization rates remained at -93% and 68% throughout the entire duration. In contrast, the cycling capacity decayed over time under non-pulsed operation (70% after 10 cycles), and the pH swing became ineffective as it could no longer maintain steady-state acidification. XRD analyses were conducted for each electrode after the cycling tests, confirming desirable BiOCl spectra on the pulsed sample but weak and dampened peaks for the non-pulsed case.

[0112] Finally, CO2 extraction assessments of coated Bi / G were conducted in simulated SW spiked with DIC (-2 mM) to validate the efficacy of the disclosed strategies. Using the same setup, a hollow fiber membrane contactor was installed at the outlet to strip the CO2 from the acidified water fed to the shell side using a N2 sweep passing through the lumens of the fibers. All electrodes were first reduced either via non-pulsed or via pulsed alkalinization to attain a net Qaik of 3 mAh, in accordance with the protocols outlined in FIGs. 5A-5C, FIG.5E, and FIGs. 9A-9C.

[0113] FIG. 10A showcases the Bi potentials, pH, and CO2 concentrations in the sweep stream during subsequent acidification, normalized by Qacid. First, the performance of the coated Bi / G in NaCl was benchmarked under non-pulsed operation (grey trace) to measure the baseline CO2 removal rate without any impurity interference; the total CO2 removed amounted to 0.039 mmol, or 87% removal efficiency. Upon introducing simulated SW, there was a stagnation in the pH swing across all cases, lingering around 8.0. These effects were attributed to the additional buffering capacity of the carbonate species, as well as possible respeciation of scale as CaCCh / MgCO?. Regardless, CO2 was still gradually removed from the SW electrolyte after 1 mAh Qacid had passed. The electrode subject to pulsed alkalinization delivered the highest recovery with a total of 0.016 mmol CO2 extracted, or 40% removal, outperforming the non-pulsed case equivalent (0.007 mmol, or 18%). Both trials still34#14916960vlperformed far better than the Bi / CB sample, in which cycling capacity and CO2 extracted fell to 60% and 8% (0.003 mmol), respectively.

[0114] Magnesium tolerance at variable concentrations was evaluated to emulate different levels of pretreatment requirements (FIG. 10B). Herein, Bi / CB and coated Bi / G were separately tested under pulsed alkalinization conditions in [Mg2+] ranging from 1 mM (i.e., 98% Mg2+removal) to 50 mM (no pretreatment), while keeping Ca2+(10 mM) and DIC compositions constant. In the case of Bi / CB, CO2 removal efficiencies relative to those for Mg2+-free solutions plummeted to 39% at [Mg2+] as low as 10 mM (i.e., 80% Mg2+removal); by 25 mM and higher concentrations, efficiencies were below 10%, and performance was essentially compromised. Coated Bi / G results established a similar tradeoff relationship, but removal efficiencies were much higher (>40%) across all trials. The plateau in the rates between 25 and 50 mM Mg2+exemplified a magnesium saturation effect and suggested that lower levels of pretreatment (i.e., 50%) do not always convey performance improvements (i.e., it may be more effective to bypass pretreatment altogether and directly use raw seawater).

[0115] Lastly, a long-term stability test was conducted with a coated Bi / G electrode and pulsed alkalinization in untreated simulated SW for 100 cycles (-300 hours), which demonstrated unwavering performance levels (FIG. 10C). For one, the Bi potentials remained steadfast throughout the entire operating period, even though no additional cleaning measures were implemented. The corresponding cycling capacities averaged to 93.2%.Likewise, CO2 removal efficiencies stabilized to an average of 41.1%, indicating Mg2+and Ca2+did not directly lead to any performance decay. Moreover, the cell was reassessed in NaCl immediately after the stability test, and the removal efficiency spiked back up to 82% after a single cycle. Overall, Mg2+and Ca2+did not irreversibly damage the modified DOC system. One process design standpoint is to use DIC- stripped seawater effluents during alkalinization to limit additional interference from carbonate buffering capacity. Postcharacterizations once more revealed limited magnesium and calcium on the electrode surface

[0116] Impurity-resilient DOC technologies present a complex, challenging, yet rewarding avenue that could mitigate reduce or eliminate pretreatment measures and greatly advance the versatility of oceanic carbon removal. In this example, the detrimental impacts of Mg2+and Ca2+in seawater on the asymmetric bismuth-silver CO2 capture process were quantitatively examined and several design strategies to successfully recover performance were presented.35#14916960vlThe endeavors are schematically summarized in FIG. 10D, in which magnesium can both faradaically adhere and locally precipitate as Mg(OH)2 on the Bi surface. To counter such phenomena, electrode modifications (i.e., graphene, ionomer coating) were introduced and electrolysis was pulsed to block Mg2+access to the bismuth matrix and minimize scale accumulation. These measures cumulatively increased the Qacid utilization rate from <25 to 70%, enhanced CO2 removal efficiencies from just 8% to 40% directly in untreated seawater, and demonstrated steady operation over 100 cycles while maintaining low Bi voltage requirements of 500 mV.

[0117] Reagents and Materials

[0118] All chemicals were used as received without additional purification. Bismuth, silver, V-methyl-2-pyrrolidone (NMP), polyvinylidene fluoride (PVDF, 10 wt.%), ethanol, sodium chloride, sodium bicarbonate, magnesium chloride hexahydrate, calcium chloride dihydrate, and hydrochloric acid were all obtained from SIGMA- ALDRICH®. Carbon black (Super P) and graphene nanoplatelets were obtained from MSE SUPPLIES® and THERMO FISHER®, respectively. PiperlON® dispersion (5 wt.%) was obtained from Fuel Cell Store.

[0119] Electrode Preparation

[0120] Bismuth electrodes were synthesized by mixing bismuth powder, carbon black, and PVDF at a ratio of 8:1:1 (by weight) in NMP solvent to form a slurry. Before doing so, the bismuth and carbon powders were separately ball milled (600 rpm) for 16 hours to improve surficial contact. The slurry was then cast (via doctor blade method) on top of a graphite sheet (200 pm thickness) and dried overnight in an oven (80° C) before use. The silver counter electrodes were also synthesized using this same procedure. For the Bi / graphene electrodes, the sole modification was replacing carbon black with the graphene nanoplatelets. For the ionomer coating, PiperlON® was first diluted with ethanol (1:2 ratio by volume) and then drop-cast onto the electrode surface at their designated mass loadings. All samples were dried at room temperature for 1 hour before use.

[0121] Electrochemical Experiments

[0122] All electrochemical measurements were recorded using a BIO-LOGIC® SP-150 potentiostat and done under ambient conditions. For the flow-cell tests, the bismuth and silver electrodes were placed on opposite sides of a gasket chamber housing a 0.5 cm x 4.0 cm channel for the flow of electrolyte (2 cm2geometric area) and an interelectrode spacing of 2 mm. The cell was fastened together using stainless-steel current collectors in a typical parallel-plate configuration and placed perpendicular to the ground so that the electrolyte36#14916960vlflowed from the bottom to top. Unless otherwise specified, all electrolytes were sent into the cell at 0.5 mL min1using a peristaltic pump (VWR®). A tertiary Ag / AgCl reference electrode (CH INSTRUMENTS®) was inserted at the cell inlet for three-electrode measurements; similarly, a pH electrode (LE422, METTLER TOLEDO®) was inserted at the cell outlet to monitor all pH swings. All pH data was acquired and analyzed using EDAQ™ ISOPODS™ streaming data recorders. Given that bismuth was the focus of this example, silver electrodes were periodically replaced with fresh samples to account for any charge imbalances and capacity depletion during long-term operation.

[0123] For batch analyses, the bismuth electrodes were tested in a glass H-cell separated by an anion-exchange membrane (FAB-PK-130, Fumasep™). The Bi and Ag / AgCl reference electrodes were sectioned into one compartment of the cell, and a Pt counter was placed into the other. Before testing, the cell was purged with N2 to minimize any gas-induced parasitic reactions (e.g. oxygen reduction). All electrolytes were replenished after each trial for consistent reporting. Unless specified, all linear and cyclic voltammetry scans were swept at 5 mV s’1. All voltages are the raw data without iR compensation; this was due to the fact that the open-circuit potentials are continuously changing (i.e., Bi / BiOCl phase change).

[0124] In situ Optical Imaging Experiments

[0125] To in situ image the Bi surface the same flow cell components were utilized as described above but one of the stainless steel current collectors was replaced with a transparent acrylic backplate (0.5 cm thickness). The Ag counter was pressed against this plate, and a strip of graphite sheet long enough to protrude outside the cell was placed at the electrode edge as the current collector. An opening (4 mm diameter) was cut out of the Ag counter; this was large enough for the camera objective without compromising the silver capacity. A DSLR camera (NIKON® D5600®) and the objective setup (MX-6, Infinity Photo-Optical Company™; 5X N-ACHROPLAN®, ZEISS®) were positioned in front of the opening (~1 cm working distance) to capture images using the timelapse function. An LED array light (LIUCWHA, THORLABS®) was set up near the opening to better illuminate the Bi surface during tests. Finally, videos of the collected images were compiled at a rate of 50 seconds per frame.

[0126] Characterization

[0127] Scanning electron microscopy (SEM) images were performed using a ZEISS® Gemini 450 SEM to post-characterize the electrode surface. Elemental mapping analyses were conducted using high spatial energy dispersive spectroscopy (EDS) with an OXFORD37#14916960vlINSTRUMENTS® AZTEC® 100 EDS detector. The crystal structures of all samples were analyzed by X-ray diffraction (XRD) using a PANALYTICAL® X’Pert PRO XRD. All electrochemical characterizations were analyzed using EC-LAB® software. Effluent bismuth and silver contents were analyzed using inductively coupled plasma - optical emission spectroscopy (ICP-OES, AGILENT® 5100).

[0128] Calculation of bismuth thermodynamic potentials.Bi + C + H2O <-> BiOCl + 2H++ 3e0.16 VSHE

[0129] The standard potential converts to -0.0376 VAg / Agci (saturated KC1). Unless specified, NaCl (0.5 M) was used at an initial pH of 7. The equilibrium potential under these conditions were calculated as following:E = E - 0.0197 V log[0.5] - 0.0394 V [pH 7]E = -0.0376 - 0.0197(-0.301) - 0.0394(7)E = -0.0376 - 0.0197(-0.301) - 0.0394(7)E = -0.307 VAg / Agci (at pH 7)

[0130] For reference, the thermodynamic potentials were also calculated for pH 11 (alkalinization) and pH 3 (acidification) under 0.5 M NaCl.E (pH 11): -0.0376 - 0.0197(-0.301) - 0.0394(pH 11) = -0.465 VAg / AgciE (pH 3): -0.0376 - 0.0197(-0.301) - 0.0394(pH 3) = -0.150 VAg / Agci

[0131] To assess CO2removal rates, the same flow cell was utilized and a hollow fiber membrane contactor (LIQULCEL® MM-0.5xl Series, 3M) was attached right at the cell outlet (before the pH probe). The contactor had an inlet / outlet for a liquid stream, as well as an inlet / outlet for a vacuum running perpendicular to the liquid stream. In the liquid side, the acidified (and alkalinized) SW streams were sent in at 0.5 mL min1. On the vacuum side, the inlet was connected to a N2 tank as a gaseous sweep, which was sent through at 5 mL min1. A CO sensor (CO2 Meter) was attached directly at the outlet to measure CO2 concentrations, and all data was collected via GASLAB® software. The CO2 coming out of the sensor was released into open air. Across all trials and calibrations, the vacuum side inlet was kept plugged in for consistent measurements.38#14916960vl

[0132] All electrolytes were spiked with 2.5 mM NaHCCh to account for the effects of ionic strength (i.e., 0.5 M NaCl) on CO2 speciation, and the fact that bicarbonate is the dominant form of DIC in seawater. For the stability test, the membrane contactor was periodically removed every 15-20 cycles and flushed with DI water to rinse off any residual Mg2+and Ca2+.

[0133] Over time, the Bi / CB potential stabilized and capacity increased due to surface reconstruction and activation. To ensure the most representative results, all samples were thus precycled several times (3-4X, starting with reduction and ending with oxidation) in this manner before use.

[0134] In NaCl, Bi / CB delivered steadfast voltages and an unwavering pH swing across all 5 cycles. In contrast, operation in simulated SW eliminated ability to drive a pH swing. The tapering pattern in the acidification potentials grew with each cycle.

[0135] Calcium had negligible impacts on performance, given that the respective pH and potential profiles were almost identical to those of the NaCl only control. Losses in Bi / CB performance were a function of magnesium concentration, with major delays in pH swing observed at [Mg2+] as low as 10 mM.

[0136] In pH 2, Mg(OH)2 formation was minimal. Nevertheless, a strong presence of magnesium was still observed on the Bi / CB surface. The respective Mg signals were seen all over the surface, even when no new crystals or deposits were visible. The distribution of Mg and Bi signals also appeared to overlap with one another, pointing to a sorption mechanism between the two elements.

[0137] Compared to Bi / CB, the Bi / G particles were significantly larger. It is possible that more carbon (and less bismuth) was resultantly available on the electrochemically active surface. This was suggested by the weaker signal intensities for BiOCl in the Bi / G sample, as well as the sharp peak at 54.8° which overlapped with both graphene nanoplatelets and Bi20s. Despite these observations, it was verified that using graphene did not detract from cell performance.

[0138] The CV results imply Bi / G was relatively less active than Bi / CB, given the lower current magnitudes throughout the scan. Nevertheless, Bi / G still yielded similar levels of acidification as Bi / CB.

[0139] The underlying assumption behind double-layer capacitance measurements is to scan a potential window free of any faradaic contributions. For a conversion-type material like bismuth, faradaic activity was technically feasible at all of the voltages reported in this39#14916960vldisclosure (i.e., -0.6 to +0.4 VAg / Agci), depending on the state of charge. However, datasets indicate the voltages in between this range are transient, inferring minute levels of conversion. As mentioned above, all samples were precharged beforehand to further minimize this effect. Lastly, the slopes of the scan rate- voltage dependence (characteristic to ECSA) were approximately the same across all samples, bolstering the claim that Bi roughness did not change significantly with ionomer addition.

[0140] Without the coating, Bi / G particles were completely covered by the flakelike crystals indicative of magnesium deposition. The XRD spectra demonstrated patterns similar to those shown earlier in FIG. 7D; peaks corresponding to BiOCl (32.4 and 33.1°) disappeared and were replaced by peaks for metallic Bi and bismuth oxides.

[0141] Mg(OH)2 fully coated the surface and completely overpowered the signals for bismuth, as well as other elements. The lack of overlapping signals between Mg and Bi indicated substantially reduced faradaic uptake.

[0142] Sequence D exhibited the longest delay in pH swing onset and the less acidic steadystate values. These losses were attributed to the longer talk, which increased the likelihood of scale accumulation. Sequence E exhibited a slightly lower cycling capacity, possibly due to greater capacitive effects (i.e., double-layer charging contributions) within the short 500-millisecond talk durations.

[0143] Regardless of operating conditions, the profiles indicated extensive regions at the surface in which Mg(OH)2 formation was thermodynamically feasible. These results also pointed to negligible Mg2+mass transfer differences with each pulse (due to the already high bulk concentrations of 50 mM). Since precipitation was limited during pulsing, it was suspected that local oxidation (acidification) was a more dominant driver in recovering performance. While homogenous precipitation was still thermodynamically possible, this was kinetically unlikely given the comparatively short residence time in the cell; in this regard, no scale was visible in the electrolyte at any given point of operation.

[0144] The particle protrusions and increased roughness of the interface correlated strongly to bismuth, while magnesium presence was minimal. One possible loss pathway was increased roughness often leads to more crystallization / nucleation sites. Another was any Bi that breaks through the ionomer becomes exposed and would have access to Mg2+.

[0145] Unlike in coated Bi / G, Bi / CB demonstrated substantial losses in cycling capacity as [Mg2+] increased.40#14916960vl

[0146] While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the functions and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the teachings of the present invention is / are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, and / or methods, if such features, systems, articles, materials, and / or methods are not mutually inconsistent, is included within the scope of the present invention.

[0147] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0148] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to “A and / or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0149] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when41#14916960vlseparating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0150] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0151] Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

[0152] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” and the like are to be understood to be open-ended, i.e., to mean including but not42#14916960vllimited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.43#14916960vl

Claims

CLAIMSWhat is claimed is:

1. A flow system, comprising:a first orifice configured to intake untreated seawater comprising bicarbonate; and an electrochemical cell;wherein:the electrochemical cell is configured to perform pulsed electrolysis;the electrochemical cell comprises a first electrode and a second electrode; and the first electrode comprises bismuth.

2. A method, comprising:intaking untreated seawater through a first orifice into a flow system, wherein the untreated seawater comprises bicarbonate;lowering the pH of the untreated seawater using pulsed electrolysis with an electrochemical cell to form treated seawater in which a portion of the bicarbonate has been converted to carbon dioxide; andremoving a portion of the carbon dioxide from the treated seawater;wherein the electrochemical cell comprises a first electrode and a second electrode, and wherein the first electrode comprises bismuth.

3. A flow system, comprising:an electrochemical cell comprising a first electrode and a second electrode, wherein:the first electrode and the second electrode are coated conversion-type electrodes;the first electrode comprises bismuth; andthe electrochemical cell is configured to perform pulsed electrolysis on seawater to mitigate formation of precipitation on a surface of the first electrode and / or the second electrode.

4. A method, comprising:performing pulsed electrolysis on seawater with an electrochemical cell comprising a first electrode and a second electrode;44#14916960vlwherein:the first electrode comprises bismuth;the first electrode and the second electrode are coated conversion-type electrodes; andthe pulsed electrolysis mitigates formation of precipitation on a surface of the first electrode and / or the second electrode.

5. A flow system, comprising:an electrochemical cell configured to provide an electrochemical pH swing; and a first orifice configured to intake untreated seawater comprising bicarbonate; wherein the electrochemical cell comprises a first electrode and a second electrode, andwherein the first electrode and the second electrode are coated conversion-type electrodes.

6. A method, comprising:intaking untreated seawater through a first orifice into a flow system comprising an electrochemical cell, wherein the untreated seawater comprises bicarbonate;providing an electrochemical pH swing to the untreated seawater with the electrochemical cell;converting a portion of the bicarbonate to carbon dioxide to form treated seawater; andremoving a portion of the carbon dioxide from the treated seawater;wherein the electrochemical cell comprises a first electrode and a second electrode, wherein the first electrode and the second electrode are coated conversion-type electrodes.

7. A flow system, comprising:an electrochemical cell configured to perform pulsed electrolysis; anda first orifice configured to intake seawater comprising bicarbonate;wherein the flow system:(a) has a lifetime of greater than or equal to 50 cycles; and / or45#14916960vl(b) has a decrease of less than or equal to 20% in cycling capacity and / or a decrease of less than or equal to 20% in Qacid utilization over the lifetime of the flow system.

8. A method, comprising:intaking seawater through a first orifice into a flow system comprising an electrochemical cell, wherein the seawater comprises bicarbonate;lowering the pH of the seawater by pulsed electrolysis to convert a portion of the bicarbonate to carbon dioxide; andremoving a portion of the carbon dioxide from the seawater;wherein:(a) the flow system has a lifetime of greater than or equal to 50 cycles; and / or (b) the flow system has a decrease of less than or equal to 20% in cycling capacity and / or a decrease of less than or equal to 20% in Qacid utilization over the lifetime of the flow system.

9. A flow system, comprising:an electrochemical cell comprising a first electrode and a second electrode, wherein the first electrode comprises bismuth; anda first orifice configured to intake untreated seawater comprising bicarbonate; wherein the flow system:(a) has a lifetime of greater than or equal to 50 cycles; and / or (b) has a decrease of less than or equal to 20% in cycling capacity and / or a decrease of less than or equal to 20% in Qacid utilization over the lifetime of the flow system.

10. A method, comprising:intaking untreated seawater through a first orifice into a flow system, wherein the untreated seawater comprises bicarbonate;lowering the pH of the untreated seawater to form treated seawater in which a portion of the bicarbonate has been converted to carbon dioxide; andremoving a portion of the carbon dioxide from the treated seawater;46#14916960vlwherein the flow system comprises an electrochemical cell comprising a first electrode and a second electrode, wherein the first electrode comprises bismuth; and wherein:(a) the flow system has a lifetime of greater than or equal to 50 cycles; and / or (b) the flow system has a decrease of less than or equal to 20% in cycling capacity and / or a decrease of less than or equal to 20% in Qacid utilization over the lifetime of the flow system.

11. The flow system or method of any preceding claim, wherein the flow system comprises a first orifice configured to intake seawater comprising bicarbonate.

12. The flow system or method of any preceding claim, wherein the seawater is untreated seawater.

13. The flow system or method of any preceding claim, wherein the electrochemical cell is configured to perform pulsed electrolysis.

14. The flow system or method of any preceding claim, wherein the electrochemical cell is configured to perform pulsed electrolysis on seawater to mitigate formation of precipitation on a surface of the first electrode and / or the second electrode.

15. The flow system or method of any preceding claim, wherein the electrochemical cell is configured to provide an electrochemical pH swing.

16. The flow system or method of any preceding claim, wherein the electrochemical cell comprises a first electrode and a second electrode, and the first electrode comprises bismuth.

17. The flow system or method of any preceding claim, wherein the electrochemical cell comprises a first electrode and a second electrode, and the first electrode and the second electrode are coated conversion-type electrodes.

18. The flow system or method of any preceding claim, wherein the flow system has a lifetime of greater than or equal to 50 cycles.47#14916960vl19. The flow system or method of any preceding claim, wherein the flow system has a lifetime of less than or equal to 300 cycles.

20. The flow system or method of any preceding claim, wherein the flow system has a decrease of less than or equal to 20% in cycling capacity and / or a decrease of less than or equal to 20% in Qacid utilization over the lifetime of the flow system.

21. The flow system or method of any preceding claim, wherein the flow system has a decrease of less than or equal to 5% in cycling capacity and / or a decrease of less than or equal to 5% in Qacid utilization over the lifetime of the flow system.

22. A method, comprising intaking the seawater through the first orifice into the flow system of any preceding claim.

23. The method of any preceding claim, comprising:lowering the pH of the seawater using pulsed electrolysis with an electrochemical cell to form treated seawater in which a portion of the bicarbonate has been converted to carbon dioxide; andremoving a portion of the carbon dioxide from the treated seawater.

24. The method of claim 23, wherein:the lowering the pH of the seawater to form treated seawater is in a first portion of the flow system, and the method further comprises:flowing the treated seawater into a second portion of the flow system after the portion of carbon dioxide has been removed; andraising the pH of the treated seawater in the second portion of the flow system.

25. The method of any preceding claim, wherein the treated seawater exits the flow system through a second orifice.

26. The method of any preceding claim, comprising providing an electrochemical pH swing to the seawater with the electrochemical cell.48#14916960vl27. The method of any preceding claim, comprising performing pulsed electrolysis on seawater with the electrochemical cell.

28. The flow system or method of any preceding claim, wherein the untreated seawater:(a) has not been treated with nanofdtration; and / or(b) comprises greater than or equal to 0.01 mol / L sodium chloride; and / or(c) comprises greater than or equal to 0.1 mmol / L magnesium ions; and / or(d) comprises greater than or equal to 0.1 mmol / L calcium ions.

29. The flow system or method of any preceding claim, wherein the first electrode comprises graphene and / or carbon black.

30. The flow system or method of any preceding claim, wherein the first electrode comprises a coating comprising an anion-exchange ionomer.

31. The flow system or method of claim 30, wherein the anion-exchange ionomer comprises PiperlON®.

32. The flow system or method of any preceding claim, wherein the second electrode comprises AgCl and / or bismuth.

33. The flow system or method of any preceding claim, wherein the pulsed electrolysis comprises pulsing:(a) at a current of greater than or equal to 0.01 mA / cm2and less than or equal to 10 mA / cm2; and / or(b) for an average duration of greater than or equal to 10 milliseconds and less than or equal to 200 seconds per pulse; and / or(c) with an interval of less than or equal to 10 seconds between pulses.

34. The flow system or method of any preceding claim, wherein the pulsed electrolysis comprises pulsing:(a) at a current of greater than or equal to 0.2 mA / cm2and less than or equal to 1 mA / cm2; and / or49#14916960vl(b) for an average duration of greater than or equal to 1 second and less than or equal to 10 seconds per pulse; and / or(c) with an interval of greater than or equal to 1 second and less than or equal to 5 seconds between pulses.

35. A method, comprising:a. intaking untreated and impure ocean water seawater containing bicarbonate through a first orifice into a flow system;b. in a first portion of the flow system, lowering the pH of the seawater by pulsed electrolysis using coated conversion-type Bi / G electrodes operating in a pulsed sequence, thereby converting at least some bicarbonate to carbon dioxide;c. removing at least some of the carbon dioxide from the seawater; d. flowing the solution into a second portion of the flow system, and raising the pH of the solution; ande. ejecting the solution from the flow system through a second orifice.

36. The method of claim 35, wherein the pulsed sequence is of 500 ms to 5 s duration separated by 2 s pauses.

37. The method of claim 35, further comprising, in the first portion, lowering the pH of the seawater by releasing H+ from a first electrode into the seawater, and in the second portion, at a second electrode capturing H+ thereby raising the pH of the seawater.

38. The method of claim 35, further comprising:f. intaking seawater containing bicarbonate through the second orifice into the flow system;g. in the second portion of the flow system, lowering the pH of the solution by pulsed electrolysis releasing H+from the second electrode into the input solution using coated conversion-type Bi / G electrodes operating in a pulsed sequence, thereby converting at least some bicarbonate to carbon dioxide; and h. removing at least some of the carbon dioxide from the solution;50#14916960vli. flowing the solution into the first portion of the flow system, and at the first electrode capturing H+thereby raising the pH of the solution; j. ejecting the solution from the flow system through the first orifice.

39. The method of claim 38, wherein the pulsed sequence is of 500 ms to 5 s duration separated by 2 s pauses.51#14916960vl

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