ELECTRO-CHEMICAL REGENERATION SYSTEM AND METHODS OF USING SAME CROSS REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY [0001] The present application claims priority to U.S. provisional patent application no. 63/396,563 filed on August 9, 2022, the entire contents of which are hereby incorporated by reference. TECHNICAL FIELD [0001] The disclosure relates generally to direct air capture of carbon dioxide, and more particularly to systems and methods for regenerating liquid solvents used for direct air capture of carbon dioxide. BACKGROUND [0002] Conventional Direct Air Capture (DAC) methods may use alkaline liquid solvents ⁽⁸⁾ or amine-based solid adsorbents ^(9–11) to capture carbon dioxide (CO2). Captured CO2 is typically liberated from the capture media using thermal energy, simultaneously producing a stream of high-purity CO2, and regenerating the capture media. The energy distribution for conventional DAC methods may be approximately 80% thermal and 20% electrical energy ⁽¹²⁾ . Regeneration of alkaline capture liquids from post-capture solutions may require high-quality heat (e.g.900 °C) supplied by calciner units. Since calciner units are typically powered by fossil fuels and consume significant amounts of energy, the associated CO2 emissions are high, estimated at 0.3 – 0.5 tonnes of CO2 emitted per tonne CO2 captured ⁽¹³⁾ . SUMMARY [0003] The high carbon footprint of conventional DAC methods may be mitigated by alternative DAC systems, including regeneration methods, which may be free of thermal energy reliance. [0004] In one aspect, the disclosure describes a system comprising: a reactor comprising a first electrode, a second electrode, and a common electrode; wherein: in a first mode of operation a voltage is applied to the first electrode and the common electrode to convert: an electrolyte and water (H2O) to an alkaline capture solvent and an reagent; in a second mode of operation, the common electrode and the second electrode convert: the reagent to an acid.

1 CAN_DMS: \1000584587\2 [0005] In another aspect, the disclosure describes a method of operating a electrochemical regeneration system having reactor comprising a first electrode, a second electrode, and a common electrode, the method comprising: in a first mode of operation, applying a voltage to the first electrode and the common electrode to convert: an electrolyte and water (H2O) to an alkaline capture solvent and an reagent; in a second mode of operation, converting: the reagent to an acid. [0006] In a further aspect, the disclosure describes a method for reducing and oxidizing at a common electrode of a reactor of an electrochemical regeneration system, the reactor comprising a first electrode, a second electrode, and a common electrode, the method comprising: alternating between: a) applying a voltage to the first electrode and common electrode to oxidize a halide ion at the common electrode to form a diatomic halogen, and reduce an alkali halide or alkaline earth halide at the first electrode to form an alkali hydroxide or alkaline earth hydroxide; and b) reducing the diatomic halogen at the common electrode to form the halide ion, and oxidizing hydrogen to form hydrogen ions at the second electrode in the fuel cell. [0007] In a further aspect, the disclosure describes a system comprising: a reactor comprising a first electrode, a second electrode, and a common electrode; wherein: in a first mode of operation a voltage is applied to the first electrode and the common electrode to convert: an electrolyte and water (H ₂ O) to an alkaline capture solvent and an reagent; in a second mode of operation, the common electrode and the second electrode convert: the reagent to an acid; an air contactor, the air contactor configured to mix the alkaline capture solvent from the reactor with air, the air comprising CO2, to form at least one metal carbonate; a CO2 liberator, the CO2 liberator configured to convert: the metal carbonate from the air contactor and the acid from the reactor into CO2(g), H2O(l), and the electrolyte; and wherein the reactor is configured to received the electrolyte from the CO2 liberator. [0008] In a further aspect, the disclosure describes a method comprising: providing a reactor comprising a first electrode, a second electrode, and a common electrode; an air contactor, and a CO2 liberator; in a first mode of operation, applying a voltage to the first electrode and the common electrode to convert: an electrolyte and water (H2O) to an alkaline capture solvent and an reagent; in a second mode of operation, converting: the reagent to an acid; mixing the alkaline capture solvent

2 CAN_DMS: \1000584587\2 produced in the first mode of operation with air, the air comprising CO2, to form at least one metal carbonate; converting the at least one metal carbonate and the acid produced in the second mode of operation to CO2(g), H2O(l), and the electrolyte; and providing the electrolyte to the reactor. [0009] Embodiments may include combinations of the above features. [0010] Further details of these and other aspects of the subject matter of this application will be apparent from the detailed description included below and the drawings. DESCRIPTION OF THE DRAWINGS [0011] Reference is now made to the accompanying drawings, in which: [0012] FIG.1 shows a schematic view of a direct air capture (DAC) system for carbon dioxide. The illustrated DAC system includes (A) an air contactor, (B) a CO ₂ liberator, and (C) an electrochemical regeneration system with Alternating Electrocatalysis (AE). [0013] FIG.2A is a schematic view of an example regeneration systems for capture solvents of the direct air capture system shown in FIG.1. FIG.2A illustrates an example electrochemical regeneration system comprising an electrolyser-fuel cell combination in a two-reactor configuration. [0014] FIG.2B and 2C illustrate an example tri-electrode reactor of a regeneration system in an electrolysis mode and fuel cell mode respectively. [0015] FIG.2D illustrates electrolyser power and electrolyser voltage at selected current densities for the two-reactor electrolyser-fuel cell combination of FIG.2A; and electrolyser power and electrolyser voltage for the electrolyser-fuel cell combination of FIGs.2B and 2C, operating in the electrolysis mode shown in FIG.2B. [0016] FIG.2E illustrates maximum fuel cell power at selected current densities for the two-reactor electrolyser-fuel cell combination of FIG.2A; and maximum fuel cell power at selected current densities for the electrolyser-fuel cell combination of FIG.2B and 2C, operating in the fuel cell mode of shown in FIG.2C. [0017] FIG.2F is an example current density graph demonstrating system stability for an example regeneration system for the electrolyser-fuel cell combination of

3 CAN_DMS: \1000584587\2 FIGs.2B and 2C. FIG.2F illustrates example current density vs. time data when the example tri-electrode reactor of FIGs.2B an 2C operates in electrolysis mode and fuel cell mode respectively. [0018] FIG.2G and 2H each show a portion of the current densities vs. time 5 data of the electrolyzer and fuel cell for the 100-hour test illustrated in FIG.2F. [0019] FIGs.3A and 3B each illustrate a comparison of thermal and electrochemical methods to regenerate alkaline capture liquids from post-capture solutions. FIG.3A illustrates an example DAC system in which high temperature thermal methods are used for the regeneration of capture liquids. FIG.3B illustrates an 10 example DAC system in which an electricity powered electrochemical post-capture solution regeneration methods is used. [0020] FIG 3C is a total energy expenditure vs. carbon footprint graph comparing example DAC systems with thermal and electrochemical regeneration methods, including tri-electrode reactor, to prior art regeneration systems. 15 [0021] FIG.3D illustrates the theoretical power required for direct air capture of CO ₂ when using different species to generate the CO ₂ liberation solution. [0022] FIG.4A shows a total energy expenditure graph for two example regeneration system for DAC including a two-reactor (four-electrode) configuration shown in FIG.2A and a tri-electrode reactor (AE) shown FIG.2B and FIG.2C. 20 [0023] FIG.4B shows an pie chart graph of energy expenditure by DAC system component. [0024] FIG.5 shows a schematic diagram of an example regeneration system according to this disclosure in an electrolyzer mode and a fuel cell mode. [0025] FIG.6 shows an exploded view of an example tri-electrode reactor. 25 [0026] FIG.7 illustrates a schematic flow chart of an example method for operating an electrochemical regeneration system. [0027] FIG.8 illustrates a schematic flow chart of an example method for operating an electrochemical regeneration system.

4 CAN_DMS: \1000584587\2 [0028] FIG.9 is a schematic diagram of a controller of an example regeneration system; and [0029] FIG.10 shows experimental data in a chart comparing total energy expenditure for tri-electrode reactors using NaCl, NaBr, or NaI, as electrochemical 5 regeneration system input electrolyte. [0030] FIG.11 shows experiments results of tandem electrolyzer-fuel cell performance using different halogen or oxygen intermediates in a two-reactor configuration. [0031] FIG.12 shows a graph of the the stability of the hydrogen-iodine ₁₀ electrolyzer in the two-reactor configuration operating at 100 mA cm ^-2 tested in FIG.11. [0032] FIG.13 shows experimental results of a tandem electrolyzer-fuel cell in a two-reactor configuration shown in FIG.2A illustrating fuel cell polarization curves and power density. [0033] FIG.14 shows experiments result of an electrolyzer-fuel cell in an tri- 15 electrode Alternating Electrocatalysis (AE) configuration using cyclic voltammetry with a range of frequencies. [0034] FIG.15 shows a graph of example electrolyzer current density vs. voltage in AE configuration. [0035] FIG.16 shows an example AE electrolyzer energy loss analysis. 20 [0036] FIG.17 shows an AE fuel cell anode Electrochemical Impedance Spectroscopy (EIS). [0037] FIGs.18A and 18B shows experimental data of fuel cell performance in the alternating electrocatalysis (AE) configuration. [0038] FIGs.19A and 19B shows experimental data of pH of the regenerated 25 LiOH capture liquid and HI acid during AE. [0039] FIG.20 shows regenerated LiOH capture liquid and HI acid at different electrolyte flow rates during AE. [0040] FIG.21 shows images of scanning electron microscopy (SEM) imaging of the common electrode in the alternating electrocatalysis (AE) configuration.

5 CAN_DMS: \1000584587\2 [0041] FIG.22 shows a high pressure ion chromatography analysis of standard sample solution and post electrolysis solution. [0042] FIG.23 shows a process flow diagram for an example 1 kilotonne per year DAC system. [0043] FIG.24 shows images of an experimental demonstration of DAC using AE regenerated solutions. [0044] FIG.25 shows a full cycle demonstration of AE Performance for capture liquid regeneration. [0045] FIG.26 shows a image of the setup of the AE reactor used to demonstrate the results in FIG.25. [0046] FIG.27 shows graphical results of an AE system compatibility test. DETAILED DESCRIPTION [0047] Direct air capture (DAC) of carbon dioxide (CO ₂ ) from the atmosphere is essential to any net-zero emissions scenario. Current DAC methods are heavily reliant on thermal energy inputs, emitting sizeable amounts of CO ₂ in the process and limiting the net environmental impact. Aspects of this disclosure are directed to an electrochemical strategy to regenerate liquid solvents used for DAC, enabling the utilization of low-carbon renewable electricity. One aspect includes a tri-electrode reactor which regenerates capture solvents (e.g. lithium hydroxide (LiOH)) and CO2- liberation solutions (e.g. hydroiodic acid (HI)), from an electrolyte (e.g. lithium iodide (LiI)). Embodiments of the tri-electrode reactor may allow CO2 capture with reduced energy input in comparison to a four electrode electrolyzer-fuel cell combinations, for example the tri-electrode reactor may have an energy input of 6 - 6.5 GJ/t CO2 at an industrially relevant current density of 100 mA/cm ² or 4.9 - 7.8 GJ/t CO2 for 10 - 200 mA/cm ² . In an example, the energy input is 6.4 GJ/t CO2 at an industrially relevant current density of 100 mA/cm ² , which may operate consistently for over 100 hours, and emit less than 30 kg CO2/tCO2 captured. In an example, 11 kg CO2/tCO2 is captured if 100% renewable sources are used.

6 CAN_DMS: \1000584587\2 [0048] The electrochemical process and regeneration systems according to this disclosure may allow for the regeneration of DAC liquid solvents using electrical energy instead of thermal energy. The tri-electrode reactor allows reagents such as a diatomic halogen (e.g. I2) to be generated and reacted into an acid such as halogen acid (e.g. HI) rapidly and efficiently. When powered with renewable electricity, such an advancement may enable energy efficient capture of CO2 at a much lower carbon footprint than conventional DAC systems. [0049] Electrochemical pathways to regenerate liquid capture solvents have been reported based on single cation exchange membrane (CEM) ^{(14, 36)} , double CEM ⁽¹⁶⁾ , and bipolar membrane (BPM) ⁽¹⁷⁾ . Despite recent advances to improve the efficiency of capture liquid regeneration and CO ₂ liberation, the overall energy requirement of electrochemical DAC systems remains high. In contrast, embodiments of the electrochemical regeneration system according to this disclosure may provide a DAC method to simultaneously achieved low energy requirements (< 7 GJ/tCO ₂ ) and low carbon emissions (< 20 kgCO ₂ emitted/tCO ₂ ). [0050] Although terms such as “maximize”, “minimize” and “optimize” may be used in the present disclosure, it should be understood that such term may be used to refer to improvements, tuning and refinements which may not be strictly limited to maximal, minimal or optimal. [0051] The term “connected” or "coupled to" may include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements). [0052] The terms "preferably," "preferred," "prefer," "optionally," "may," and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention. [0053] The term “substantially” as used herein may be applied to modify any quantitative representation which could permissibly vary without resulting in a change in the basic function to which it is related. [0054] Terms such as "up to", "at least", "greater than", "less than", "more than", "or more", and the like, include the number recited and such terms refer to ranges that

7 CAN_DMS: \1000584587\2 can be subsequently broken down into sub-ranges. In the same manner, all ratios recited herein also include all sub-ratios falling within the broader ratio. [0055] The singular forms "a," "an," and "the" include the plural reference unless the context clearly dictates otherwise. The term "and/or" means any one of the items, 5 any combination of the items, or all of the items ,:with which this term is associated. [0056] The term "about" can refer to a variation of ± 5%, ± 10%, ± 20%, or± 25% of the value specified. For example, "about 50" percent can in some embodiments carry a variation from 45 to 55 percent. For integer ranges, the term "about" can include one or two integers greater than and/or less than a recited integer at each end of the 10 range. Unless indicated otherwise herein, the term "about" is intended to include values and ranges proximate to the recited range that are equivalent in terms of the functionality of the composition, or the embodiment. [0057] Tri-electrode reactors described herein may comprise at least three electrodes, one of which is a common electrode to both an “Electrolysis Cell” and “Fuel 15 Cell” of a tri-electrode reactor. The term “Electrolysis Cell” of a tri-electrode reactor refers a portion of the electrochemical regeneration systems described herein in which a first electrode and the common electrode of the tri-electrode reactor perform electrolysis using electrical energy. Similarly, operating in an “Electrolysis mode” (also referred to herein as a “first mode”) for the tri-electrode reactor refers to performing 20 electrolysis with the first electrode and the common electrode of the tri-electrode reactor, i.e. a reaction in which reduction occurs on the first electrode and oxidation occurs on the common electrode. The term “Fuel Cell” of a tri-electrode reactor refers to a portion of the electrochemical regeneration systems described herein in which a second electrode and the common electrode of the tri-electrode reactor uses chemical 25 energy of a fuel (e.g. hydrogen) and an oxidizing agent (referred to herein as a reagent), e.g. a halogen, to provide electricity. Similarly, operating in an “Fuel Cell mode” (also referred to herein as a “second mode”) for the tri-electrode reactor refers to using chemical energy of the fuel (e.g. hydrogen) and the oxidizing agent (e.g. the halogen) to provide electricity with the second electrode and the common electrode of 30 the tri-electrode reactor, i.e. a reaction in which reduction occurs on the common electrode 44 and oxidation occurs on the second electrode 48.

8 CAN_DMS: \1000584587\2 [0058] The term “common electrode” refers to an electrode that may alternate between operating as either an anode or cathode in a tri-electrode reactor of this disclosure. The common electrode may switch between operating as an anode or cathode in the first and second modes of operation. [0059] The term “Alternating Electrocatalysis” (AE) refers to alternating between the electrolysis mode of operation and the fuel cell mode of operation. AE is also referred to in this disclosure as the “Alternating Voltage Strategy”, “Alternating Voltage Methods”. [0060] Aspects of various embodiments are described through reference to the drawings. [0061] FIG.1 shows a schematic view of a direct air capture (DAC) system 1 for carbon dioxide. The illustrated DAC system 1 includes (A) an Air Contactor 20, (B) a CO ₂ Liberator 30, and (C) an Electrochemical Regeneration System 40 for AE. Electrochemical regeneration system 40 may regenerate liquid solvents used for capture of CO ₂ from air 2 using exclusively electrical energy. Air contactor 20 may receive atmospheric air driven into contact with an alkaline capture solvent 21. Air contactor 20 may be configured to mix M(OH), where M is an alkali metal or an alkaline earth metal, from electrochemical regeneration system 40 with air 2, the air comprising CO ₂ , to form at least one metal carbonate. In the illustrated example of FIG.1, alkaline capture solvent 21, e.g. aqueous LiOH, is contacted with air comprising carbon dioxide to form lithium carbonate (Li2CO3) and water (H2O) according to the reaction CO2 + 2LiOH → Li2CO3 + H2O to provide air contactor output 22. LiOH may also react with carbon dioxide to form lithium bicarbonate (LiHCO3) according to the reaction CO2(g) + LiOH(aq) → LiHCO3(aq) which may also provide air contactor output 22. In another example, alkaline capture solvent 21 may be NaOH, the at least one metal carbonate is at least one of NaHCO3(aq) and Na2CO3(aq), and the at least one metal carbonate is formed according to at least one of the reactions: CO2(g) + NaOH(aq) → NaHCO3(aq), and CO2(g) + 2NaOH(aq) → Na2CO3(aq) + H2O(l).

9 CAN_DMS: \1000584587\2 Other example alkaline capture solvents may be used in other embodiments. For example, the at least one metal carbonate may be Li2CO3 and/or LiHCO3 formed according to at least one of the reactions: CO2(g) + LiOH(aq) → LiHCO3(aq), and →Li2CO3 ^{+ H2O(l)} , In at least one metal carbonate may be K2CO3 and/or KHCO3 formed to at one of the reactions: CO2(g) + KOH(aq) → KHCO3(aq), and CO _2(g) + 2KOH _(aq) →K ₂ CO ₃ ^{+ H2O(l).} [0062] Air contactor 20 may output clean air 3 having a reduced CO ₂ content in comparison to air 2 input into air contactor 20. Air contactor 20 may be any known air contactor suitable for contacting air with an alkaline capture solvent such as a liquid- based packed slab air-contactor developed by Carbon Engineering Ltd. which is described in Holmes et al. “An air–liquid contactor for large-scale capture of CO ₂ from air”, Phil. Trans. R. Soc. A(2012)370, 4380–4403doi:10.1098/rsta.2012.0137, the entire contents of which are hereby incorporated by reference. Other non-limiting examples of suitable air contactors may have commonalities with existing gas separation technologies and large-scale cooling towers which may have the capacity to drive large volumes of ambient air through the alkaline capture solvent. [0063] Continuing the example, output 22 from air contactor 20 is sent to the CO2 liberator which is configured to convert the metal carbonate in output 22 from the air contactor 20 and aqueous halogen acid 31 (i.e. a hydrogen halide HX) from regeneration system 40 into CO2(g), H2O(l), and MX, where M is an alkali metal or an alkaline earth metal and X is a halogen. In the illustrated example, the metal carbonate is Li2CO3 which is neutralized with a halogen acid 31, e.g. hydrogen Iodide (HI), in CO2 liberator 30 to produce a gaseous stream 4 of pure CO2 and aqueous electrolyte 32. In the illustrated example, aqueous electrolyte 32 is LiI which is produced by the reaction Li2CO3 + 2HI → CO2 + 2LiI + H2O in CO2 liberator 30. CO2 liberator may comprise at least two liquid inlets to receive output 22 from air contactor 20 and aqueous halogen acid 31 from regeneration system 40; a liquid outlet for aqueous electrolyte 32, and a gas outlet for gaseous stream 4. CO2 liberator may comprise a motor driven impeller and baffles (not shown) for improved mixing. Example CO2 liberators are described in

10 CAN_DMS: \1000584587\2 Torotwa, I.; Ji, C. A Study of the Mixing Performance of Different Impeller Designs in Stirred Vessels Using Computational Fluid Dynamics. Designs 2018, 2, 10. https://doi.org/10.3390/designs2010010, the entire contents of which are hereby incorporated by reference. [0064] In an embodiment, carbonates and/or bi-carbonates ((bi)carbonates) from air contactor 20 may be extracted from output 22. Extracted (bi)carbonates may be pelletized and stored for release via the CO2 liberator 30 at a later time. Storing the (bi)carbonates may be feasible as the salts are chemically stable. (Bi)carbonates may be extracted with a crystallizer 23, e.g. a crystallization tower, receiving (bi)carbonates from output 22. Liquid output from crystallizer 23 may be sent back to air contactor 20 for additional CO ₂ capture. Of the example alkali carbonates evaluated, Li ₂ CO ₃ may have the lowest solubility in aqueous solutions with salt precipitation taking place at concentrations exceeding 0.18 M ⁽²¹⁾ . Carbonates, such as Li ₂ CO ₃ , may precipitate and be collected from a post-capture solution of outlet 22 via phase separation and injected into the CO ₂ liberator 30. By concentrating high-purity carbonates, e.g. Li ₂ CO ₃ , and acid in the CO ₂ liberator may be used exclusively for CO ₂ regeneration while no energy is wasted neutralizing metal hydroxides, e.g. LiOH. [0065] Electrochemical regeneration system 40 may receive aqueous electrolyte 32, e.g. spent LiI electrolyte, from CO ₂ Liberator 30 and electrochemically regenerate the electrolyte back into the alkaline capture solvent 21 (e.g. LiOH) and aqueous halogen acid 31 (e.g. HI) according to the general overall reaction MX + H2O → MOH +HX where MX is a alkali halide or an alkaline earth halide, MOH is a alkali metal hydroxide or alkaline earth hydroxide, and HX is a hydrogen halide. As shown in the example of FIG.1, aqueous electrolyte 32 may be regenerated according to the reaction LiI + H2O → LiOH + HI. Energy source 5, may be a renewable energy source, used to provide electrochemical regeneration system 40 with electricity. [0066] FIG.2A is a schematic view of example electrochemical regeneration system(s) 40 of the direct air capture system shown in FIG.1; and FIGs.2B and 2C are another example electrochemical regeneration system(s) 41 of the direct air capture system shown in FIG.1. In an aspect, regeneration system 40 may comprises an electrolyser-fuel cell combination. FIG.2A, illustrates an example regeneration system comprising a first electrode 42, a second electrode 43, and electrolysis anode 47 and

11 CAN_DMS: \1000584587\2 fuel cell cathode 48. A first ion-exchange membrane 46 may separate the first electrode 42 and electrolysis anode 47; and a second ion-exchange membrane 46’ may separate the second electrode 43 and fuel cell cathode 48. To electrochemically regenerate alkaline capture solvent from the spent electrolyte 32 received from the CO2 liberator 30, the metal cation may be separated from the anion by migrating across electrolyser (cation) exchange membrane 46 (See Fig.2A, and FIG.2C). Alkali metals may be favorable for use in regeneration systems according to this disclosure due to their singular positive charge in ionic form and high current selectivity within cation exchange membranes, which may minimize the total current density and input electricity required to power the electromigration. [0067] Electrolyte anion(s) may dictate the electrolyser anodic reaction and the fuel cell cathodic reaction of electrochemical regeneration system(s) according to this disclose, such as the systems shown in Fig.2A ; FIGs.2B, and 2C. In some embodiments, the electrolyser anodic reaction and fuel cell cathodic reaction may be preferred to proceed with minimal overpotential to minimize the net energy input to regeneration system 40. The oxygen (O ₂ ) evolution reaction, one of the most common anodic reactions, is a four-electron process and has much slower kinetics than the oxidation of halides, which are two-electron processes ⁽²²⁾ . Experiments using regeneration system 40 were performed with water, and chloride (Cl-), bromide (Br-), or iodide (I-) anions and found that the oxidation of I- exhibited the lowest overpotential (See FIG.10). Amongst halogens, iodine (I2) may be the safest chemical to use in regeneration system 40 due to its non-corrosive nature and low volatility ^{(23, 24)} . Taken together, LiI may be an ideal intermediate electrolyte for the electrochemical regeneration of capture solvents. [0068] Continuing the example of FIG.2A, in the electrolyser, regeneration system 40 may convert the metal halide electrolyte, e.g. LiI, into the alkaline capture solvent and halogen, e.g. a LiOH capture solvent and I2 molecule (See. e.g. Fig.2A; and electrolyser mode of operation show in FIG.2B . The halogen (I2) may be regenerated into halogen acid (e.g. HI) – a process which typically takes place via thermocatalytic hydrogenation at elevated temperature and pressure ⁽²⁵⁾ . In contrast, because regeneration system 40 comprises a fuel cell coupled with an electrolyser, regeneration system 40 may electrochemically hydrogenate the halogen molecule (e.g.

12 CAN_DMS: \1000584587\2 I2). Hydrogen (H2) evolved at the electrolyser cathode may be oxidized at the fuel cell anode, generating electrical energy in the process to offset the energy required for electrolysis. Both H2 reactions have very fast kinetics, minimizing the net energy input ^{(26, 27)} . [0069] The electrochemical regeneration strategy shown in FIG.2A uses a four- electrode configuration (i.e., a dedicated electrolyzer and dedicated fuel cell with no common electrode) which may also be referred to as a two-reactor configuration. The electrolyser was tested at current densities between 10 and 200 mA/cm ² shown in FIG. 2D illustrating the cell voltage increasing substantially with current density. At 200 mA/cm ² , for the two-reactor configuration, the cell voltage reached 2.09 V and with a corresponding power input of 418 mW/cm ² – which may be correlated to a CO ₂ capture energy. Some of the evolved halogen molecule (I ₂ ) may accumulate on the anode, lowering the ionic conductivity of regeneration system 40, and increasing the voltage further over time. Halogen ion (e.g. I-) present in the electrolyte and halogen (I ₂ ) produced from the electrolyser may react chemically to form polyiodides (e.g., I ₃ - or I ₅ -) ^{(28, 29)} . This will enhance I ₂ solubility and dilute the halogen on route to the fuel cell, resulting in significant mass transport losses In an example, for the four electrode configuration shown in FIG.2A (i.e. the two-reactor configuration), a constant electrolyser current, providing a constant I ₂ production rate, was applied and the fuel cell current was varied to identify the maximum fuel cell power output (i.e. the product of current and voltage). The complete data set for the two-reactor configuration of FIG.2A with the values at maximum power output is shown in FIGs.2D and 2E. As shown in FIG.2D, at 100 mA/cm ² , the maximum fuel cell power is low for the two-reactor configuration, <10 mW/cm ² , due to I2 mass transport limitations. At 100 mA cm ^-2 , the electrolyzer in the example two-reactor configuration required a cell voltage of -1.68 V, compared to -1.36 V for AE. The power required by the electrolyzer was likewise reduced: 168 mW cm ^-2 for the two-reactor configuration at 100 mA cm ^-2 vs.136 mW cm ^-2 for AE at the same current. It was observed that if the distance between the electrolysis anode 47 and the fuel cell cathode 48 was increased slightly, > 1cm, then the I2 became even more dilute, and the maximum power output of the fuel cell was reduced further. Additionally, in the four-electrode configuration shown in FIG.2A, halogen, e.g. Cl2, Br2, or I2, (illustrated as I2), must travel from the electrolysis anode 47

13 CAN_DMS: \1000584587\2 via a connector to reach the fuel cell cathode 48. Transfer of halogen between electrolysis anode 47 to the fuel cell cathode 48 may be slow, reducing the efficiency of the regeneration system and fuel cell power output which may contrast with a tri- electrode reactor design, described below. However, each of the electrolysis cell and fuel cell may be operated concurrently and do not require alternating voltage to operate. In example tri-electrode reactor 41, the (diatomic) halogen does not need to travel between electrodes because the halogen is produced at common electrode 44 in the electrolysis cell mode of operation and is reduced at common electrode 44 in the fuel call mode of operation without transportation which may improve electrically and chemical efficiency and performance of regeneration system 40. Tri-electrode reactor 41 may utilize an alternating voltage strategy for operation where common electrode 44 acts as the anode in electrolysis mode and as a cathode in fuel cell mode. Alternating between the electrolysis mode of operation and the fuel cell mode of operation is referred to in this disclosure as the “Alternating Voltage Strategy”, “Alternating Voltage Methods”, or “Alternating Electrocatalysis” (“AE”). [0070] FIGs.2B and 2C illustrate an example tri-electrode reactor 41 of regeneration system 40 which may address the challenges of halogen (I ₂ ) product retention and certain other inefficiencies of the four-electrode configuration described above with respect to FIG.2A. Implementations of alternating currents in organic electrosynthesis have facilitated a unique reaction environment to encourage the reaction of short-lived electrogenerated intermediates ⁽³¹⁾ . Elsewhere, secondary zinc-air batteries have used tri-electrode designs to tailor the reaction environment specific to the necessary air reaction (O2 evolution or O2 reduction) and achieve high energy density and long-term stability ^{(32, 33)} . [0071] Tri-electrode reactor 41 may comprise a first electrode 42, a second electrode 43, and a common electrode 44. In tri-electrode reactor 41, two of the three electrodes are active at any time. Depending on the pair of active electrodes, tri- electrode reactor 41 could act either as an electrolyser (as shown in FIG.2B) or as a fuel cell (as shown in Fig.2C). Common electrode 44 may be a single element and may be used as an anode when regeneration system 40 is in an electrolyser mode of operation, or as a cathode when regeneration system 40 is in a fuel cell mode of operation. Tri-electrode reactor 41 may comprise a first membrane 46 separating the

14 CAN_DMS: \1000584587\2 first electrode 42 and the common electrode 44; and a second membrane 46’ separating the second electrode 42 and the common electrode 44. In an embodiment, first membrane 46 and second membrane 46’ may be cation selective. A controller 50 (shown in FIG.1) may be in communication with an electrical energy source 5 and configured to alternate between a first mode of operation and a second mode of operation. In the first mode of operation, illustrated FIG.2B, regeneration system 40, and tri-electrode reactor 41, may perform electrolysis causing electrical energy source 5 to apply a voltage to first electrode 42 and common electrode 44 to produce alkaline capture solvent 21 and reagent (e.g. halogen) according to the following overall general reaction: nMX _2/n + 2H ₂ O → nM(OH) _2/n + X ₂ + H ₂ , where: MX is an alkali halide or an alkaline earth halide, M(OH) is a alkali metal hydroxide or alkaline earth hydroxide, and X is a halogen produced at the common electrode, n = 2 when MX is alkali halide; or n=1 when MX is an alkaline earth halide; In the second mode of operation, illustrated FIG.2C, regeneration system 40, and tri- electrode reactor 41, may operate as a fuel cell where a voltage is applied to common electrode 44 and second electrode 43 to produce halogen acid 31 according to the following overall general reaction: 2X + H2 → 2HX, where: HX is a hydrogen halide the X is a reagent at the common electrode. [0072] By alternating tri-electrode reactor 41 between electrolyser and fuel cell modes of operation, the reagent (e.g. I2) accumulated on the common electrode during electrolyser operation may be readily available for conversion into halogen acid (e.g. HI) when tri-electrode reactor 41 is switched into fuel cell mode (shown in FIG.2C). Common electrode 44 may be hot-pressed to improve ionic conductivity. In an embodiment, ion-exchange membranes 46, 46’ may be catalyst coated membrane(s); and first electrode 42 and second electrode 43 may each be a gas diffusion electrode

15 CAN_DMS: \1000584587\2 optimized for H2 evolution and H2 oxidation ^{(34, 35)} . In an embodiment, common electrode 44 may be optimized for halogen evolution and oxidation. [0073] Controller 50 may cause tri-electrode reactor 41 to alternate between the electrolyser mode and the fuel cell mode of operation. The tri-electrode reactors were tested at several different frequencies between 0.2 and 2 Hz and it was found that 0.5-1 Hz, or about 1 Hz, may be a desirable frequency for cycling between the two operational modes (i.e. electrolyser mode and the fuel cell mode of operation) for this test example reactor. At lower frequencies the reagent halogen (e.g. I2) grew large and the fraction of halogen (I2) reacted was decreased, whereas at higher frequencies than 1 Hz there was no visible improvement with respect to the key performance metrics. [0074] Tri-electrode reactors according to this disclosure may provide several key advantages over the traditional four electrode reactor configuration described above with respect to FIG.2A, as the electrolyser and fuel cell of the tri-electrode reactor both operated more efficiently. In FIG.2D, electrolyser voltages may be comparably much lower for tri-electrode reactor 41 which may be due to reduced bubble buildup on common electrode 44. In an example, at 100 mA/cm ² the dedicated system shown in FIG.2A required a cell voltage of 1.68 V whereas as shown in FIG.2D the tri-electrode reactor needed only 1.36 V. The reduced voltages in turn reduced the power input for the tri-electrode reactor in electrolyser mode: 168 mW/cm ² for the dedicated electrolyser at 100 mA/cm ² in comparison to 136 mW/cm ² in the tri-electrode setup at the same current as shown in FIG.2D. A higher fuel cell power output for tri-electrode reactor 41 compared to the four-electrode configuration was shown, see FIG.2E. In the example, at 100 mA/cm ² , tri-electrode reactor 41 recovered 13.7 mW/cm ² of power whereas the four-electrode configuration recovered only 7.3 mW/cm ² . As shown in FIG.2F, an example current density graph for example regeneration system including tri-electrode reactor 41 is illustrated wherein tri-electrode reactor 41 was operated continuously for over 100 hours. During the 100-hour test, -1.36 V was applied during the electrolyzer mode which maintained a current density of 100 mA/cm ² . Within each cycle, fuel cell operation was evaluated at two different applied voltages. The fuel cell was first operated at 0.27 V to yield the maximum power output and then operated at 0 V to reduce any remaining I2. Throughout the 100-hour test experiment, the current density during fuel cell mode was maintained at 80 and 90 mA/cm ² , respectively. FIGs.2G and

16 CAN_DMS: \1000584587\2 2H each shows the current density of the electrolyzer and fuel cells for portions of the 100-hour test illustrated in FIG.2F. [0075] FIG.3A and 3B show a comparison of thermal and electrochemical methods to regenerate post-capture solutions. FIG.3A illustrates an example DAC system in which high temperature thermal methods are used for the regeneration of alkaline capture liquids. As shown, MxOH is an alkaline capture solvent which reacts with CO2 in the air in stream to form a carbonate and/or bi-carbonate compound, MxCO3. Heat may then be used to liberate CO2 from the carbonate and/or bi-carbonate compound forming a spend metal oxide MxO which needs to be regenerated. As shown in FIG.3A, conventional DAC methods may use alkaline liquid solvents ⁸ or amine-based solid adsorbents ⁹ to capture CO ₂ . Captured CO ₂ may be liberated from the capture liquid using thermal energy, simultaneously producing a stream of high- purity CO ₂ , and regenerating the capture liquid. Since these conventional DAC units are powered by fossil fuels and consume significant amounts of energy, the associated CO ₂ emissions may be as high as 0.5 tonnes of CO ₂ emitted per tonne captured. The electrochemical regeneration of post-capture solutions could eliminate thermal energy requirements and provide a low-carbon route to DAC, powered by renewable electricity, see FIG.3B. FIG 3B illustrates an example DAC system in which an electricity powered electrochemical post-capture solution regeneration method is used. As shown, alkaline capture solvent MxOH is mixed with air to reactor with CO2 and form carbonate and/or bi-carbonate compound, MxCO3. An acid HA, may then be used to liberate CO2 from the carbonate and/or bi-carbonate compound forming a spent metallic acid MxA which needs to be regenerated. FIG.3C compares total energy expenditure of DAC system 1 comprising a tri-electrode reactor 41 to others DAC technologies reported in literature. Several electrochemical methods have demonstrated a low carbon footprint but high energy expenditure whereas conventional thermal-powered DAC methods may have low energy expenditures but high carbon footprints. As shown, alternating electrocatalysis (AE) method utilizing a tri-electrode reactor according to this disclosure may provide an electrochemical pathway to DAC systems simultaneously achieving a low carbon footprint (e.g. less than 20 kg CO2 / tCO2) and low energy expenditure (e.g. <7 GJ/tCO2). FIG.3D compares the theoretical power required for direct air capture of CO2 when using different species to generate the CO2

17 CAN_DMS: \1000584587\2 liberation solution. As shown in FIG.3D, O2, Cl2, Br2, and I2, were evaluated to determine theoretical power at 100 mA cm ^-2 , and the net energy expenditure, to generate CO2 liberation solution using a combined electrolyser and fuel cell. [0076] FIG.4A shows a total energy expenditure graph for an example regeneration system including the four-electrode reactor (shown in FIG.2A ) and a tri- electrode reactor 41 in an example DAC system and FIG.4B shows a pie chart illustrating energy expenditure of each component of the DAC system using a tri- electrode reactor 41 In FIG.4A , the electrolyser energy inputs and the fuel cell energy outputs at the different current densities were calculated to determine energy expenditure per tonne of CO ₂ captured from the air when using tri-electrode 41 in a regeneration system 40 for electrochemical solvent regeneration. The tri-electrode reactor 41 configuration demonstrated a significant reduction in energy when compared to the four-electrode configuration. In the illustrated example, the tri-electrode reactor configuration for electrochemical regeneration of the capture solvents demonstrated a modest energy requirement, 6.26 GJ/tonne at 100 mA/cm ² . The energy requirement increased slightly with current density as all reaction over-potentials increased. As shown in FIG.4B, the detailed energy breakdown illustrates that electrolysis energy was the dominant energy input, accounting for >95% of the energy inputs at 100 mA/cm ² while the fuel cell was able to recover 9% of the total energy input. The energy requirement is comparable to conventional DAC methods powered predominantly by thermal energy. [0077] A wide range of salts may be used in DAC systems according to this disclosure. In the example shown in FIG.2, lithium is a metallic cation to form metal hydroxides that may be provided to air contactor 20; and iodine is a halogen group anion used to form a halogen acid that may be provided to CO2 liberator 30. In some embodiments, a metallic cation, capable of forming metal hydroxides, may be any one of: Li ⁺ , Na ⁺ , K ⁺ , Be ²⁺ , Mg ²⁺ , Ca ²⁺ ; and halogen group anions may be any one of: F-, Cl-, Br-, and I-. The concentration of the salt solution may be determined by the solubility limit of the salt to provide a highly concentrated solution to improve reaction kinetics without causing precipitation. [0078] Example reactions that occur in a regeneration system 40, i.e. in tri- electrode reactor 41, are shown below for various metallic cations and halogen group

18 CAN_DMS: \1000584587\2 anions. In an example the metallic cation may be sodium; the halogen group anion may be chlorine; and the reactions in the electrolysis and fuel cell respectively may include: Electrolysis Cell Anode (CER) 2Cl- → Cl ₂ + 2e- Cathode (HER) 2H2O + 2e- → H2 +2OH-; 2Na ⁺ + 2OH- → 2NaOH Overall Reaction 2NaCl + 2H2O → 2NaOH + Cl2 + H2 Fuel Cell Anode (HOR) H2 → 2H ⁺ + 2e- Cathode (CRR) Cl2 + 2e- → 2Cl- Overall Reaction H2 + Cl2 → 2HCl [0079] In another example the metallic cation may be sodium; the halogen group anion may be bromine; and the reactions in the electrolysis cell and fuel cell of regeneration system 40 respectively may include: Electrolysis Mode Anode (BER) 2Br- → Br ₂ + 2e- Cathode (HER) 2H2O + 2e- → H2 +2OH-; 2Na ⁺ + 2OH- → 2NaOH Overall Reaction 2NaBr + 2H2O → 2NaOH + Br2 + H2 Fuel Cell Mode Anode (HOR) H2 → 2H ⁺ + 2e- Cathode (BRR) Br ₂ + 2e- → 2Br- Overall Reaction H2 + Br2 → 2HBr [0080] In another example the metallic cation may be sodium; the halogen group anion may be Iodine; and the reactions in the electrolysis and fuel cell of regeneration system 40 respectively may include:

19 CAN_DMS: \1000584587\2 Electrolysis Mode Anode (IER)^ 2I-^→^I2^+ 2e-^ Cathode (HER)^ 2H ₂ O + 2e-^→^H ₂ ^+2OH-;^2Na ⁺ ^+^2OH-^→^2NaOH Overall Reaction^ 2NaI^+ 2H ₂ O^→^2NaOH^+^I ₂ ^+^H ₂ ^ Fuel Cell Mode Anode (HOR)^ H ₂ ^→^2H ⁺ ^+^2e-^ Cathode (IRR)^ I ₂ ^+^2e-^→^2I-^ Overall R _eaction^ ^{H2^+^I2^→^2HI^} [0081] In another example the metallic cation may be lithium; the halogen group anion may be Iodine; and the reactions in the electrolysis and fuel cell of regeneration system 40 respectively may include: Electrolysis Mode Anode (IER)^ 2I-^→^I2^+ 2e-^ Cathode (HER)^ 2H2O + 2e-^→^H2^+2OH-;^2Li ⁺ ^+^2OH-^→^2LiOH Overall Reaction^ 2LiI^+ 2H2O^→^2LiOH^+^I2^+^H2^ Fuel Cell Mode Anode (HOR)^ H2^→^2H ⁺ ^+^2e-^

20 CAN_DMS: \1000584587\2 Cathode (IRR)^ I ₂ ^+^2e-^→^2I-^ Overall R _eaction^ ^{H2^+^I2^→^2HI^} [0082] In another example the metallic cation may be potassium; the halogen group anion may be Iodine; and the reactions in the electrolysis and fuel cell of regeneration system 40 respectively may include: Electrolysis Mode Anode (IER)^ 2I-^→^I2^+ 2e-^ Cathode (HER)^ 2H2O + 2e-^→^H2^+2OH-;^2K ⁺ ^+^2OH-^→^2KOH Overall Reaction^ 2KI^+ 2H2O^→^2KOH^+^I2^+^H2^ Fuel Cell Mode Anode (HOR)^ H2^→^2H ⁺ ^+^2e-^ Cathode (IRR)^ I2^+^2e-^→^2I-^ Overall R _eaction^ ^{H2^+^I2^→^2HI^} [0083] In another example the metallic cation may be magnesium; the halogen group anion may be chloride; and the reactions in the electrolysis and fuel cell of regeneration system 40 respectively may include: Electrolysis Mode Anode (IER)^ 2Cl-^→^Cl2^+ 2e-^ Cathode (HER)^ 2H2O + 2e-^→^H2^+2OH-;^Mg ²⁺ ^+^2OH-^→^Mg(OH)2

21 CAN_DMS: \1000584587\2 Overall Reaction^ MgCl ₂ ^+ 2H ₂ O^→^Mg(OH) ₂ ^+^Cl ₂ ^+^H ₂ ^ Fuel Cell Mode Anode (HOR)^ H ₂ ^→^2H ⁺ ^+^2e-^ Cathode (IRR)^ Cl ₂ ^+^2e-^→^2Cl-^ Overall R _eaction^ ^{H2^+^Cl2^→^2HCl^} [0084] ALTERNATING VOLTAGE SYSTEM AND METHODS [0085] Alternating voltage strategy, also referred to as Alternating Electrocatalysis (AE) herein, i.e. alternating between the first mode of operation (an electrolysis mode) and a second mode of operation (a fuel cell mode), in tri-electrode reactor 41, may minimize mass transport losses in comparison to a combined electrolyser-fuel cell reactor. The mass transport losses in the combined electrolyser- fuel cell reactor may be in the fuel cell compartment of the reactor and/or due to mass transport losses throughout the reactor. A limiting factor for optimal fuel cell performance may be the availability of diatomic halogen, e.g. Cl ₂ , Br ₂ , or I ₂ , to be electrochemically reduced into ions, e.g. Cl-, Br-, or I- ions, to form halogen acid solutions, e.g. acidic HCl, HBr, or HI solutions. Voltage switches, i.e. switching between the first mode of operation and the second mode of operation, in the tri-electrode reactors may occur in set intervals. [0086] In an embodiment, alternating between the first mode of operation and the second mode of operation occurs at a time interval. In an example, the time interval may be selected to optimize performance of the tri-electrode reactor based on the scale of the system to enable at least one of: (1) sufficient diatomic halogen (e.g. Cl ₂ , Br ₂ , or I ₂ ) to build up on the common electrode during the first mode (electrolysis mode) so that there would not be mass transfer limitations during the fuel cell mode; (2) the product metal hydroxide from electrolysis and halogen acid from fuel cell modes of the tri- electrode reactor, to have approximately a 1:1 molar ratio; (3) maximize current density

22 CAN_DMS: \1000584587\2 output when in the second mode (fuel cell mode); and/or (4) maximum fuel cell power output. As described above, electrolysis mode may refer to a mode of operation in which reduction occurs on the first electrode 42 and oxidation occurs on the common electrode 44; and the Fuel cell mode may refer when reduction occurs on the common electrode 44 and oxidation occurs on the second electrode 48. In an example, if the electrolysis compartment operates at 100 mA/cm ² , and the fuel cell outputs 50 mA/cm ² , then the alternating voltage time interval may be set up as 0.5 second for electrolysis and 1 seconds for fuel cell modes of operation. In another example, if the electrolysis compartment operates at 100 mA/cm ² for 1 second, the fuel cell may be operated at 80 mA/cm ² for 1 second followed by a continuous fuel cell mode at 90 mA/cm ² for 0.22 second. In another embodiment, alternating between the first mode of operation and the second mode of operation may occur at a time interval of approximately 1 second or less. In another embodiment, the time interval may be in a range of 0.1 to 5 seconds. In another embodiment, the time interval may be greater than 5 seconds. [0087] In an embodiment, alternating between the first mode of operation to the second mode of operation of the tri-electrode reactor may occur when a concentration of diatomic halogen X (e.g. Cl ₂ , Br ₂ , I ₂ ) at the common electrode exceeds a first threshold value governed by first equation: ^^ _^^^^௧ = ூ∗^ ଽ^ସ଼ହ ∗ ⁽ ^^ _^^௧ + ^^ _^^௧ ⁾ [ ^^ ^^ ^^] , and of operation to the first mode of operation when the concentration of X at the common electrode is below a second threshold value governed by second equation: ^^ _^^^^^ௗ = ூ∗^ ଽ^ସ଼ହ ∗ ( ^^ _^^௧ )[ ^^ ^^ ^^], M _first is the first threshold, Msecond is the second threshold, ^^ is the operating current in the unit of [A], ^^ is the reaction area of the electrolyzer in the unit of [m ² ], 96485 is the Faraday constant in units of [C mol ^-1 ]

23 CAN_DMS: \1000584587\2 ^^ _^^௧ is the activation time, and ^^ _^^௧ is the alternating time interval in the unit of [s]. [0089] In an embodiment, the activation time is a time period in which a tri- electrode reactor is initially operated in the first mode (electrolysis mode) to provide sufficient halogen and hydrogen for the fuel cell to operation. In example, the activation time may be in a range of less than 200 seconds, 200 – 500 seconds, or greater than 500 seconds. [0090] EXAMPLE REGENERATION SYSTEM AND TRI-ELECTRODE REACTOR [0091] FIG.5 shows a schematic diagram of an example regeneration system according to this disclosure. Example regeneration system 40 comprises tri-electrode reactor 41. Example regeneration System 40 comprises a controller 50, electrical source 51. In an embodiment, regeneration system 40 may comprise electrolysis mode potentiostat 52, and/or fuel cell mode potentiostat 53. In an example, potentiostat 52, 53 may be Metrohm Autolab/ PGSTAT204. Controller 50 may be configured to conduct the alternating voltage strategy described herein to tri-electrode reactor 41. In an example, a controller 50 (e.g. an arduino controller) may alternative between the electrolysis operation mode and fuel cell operation mode. For example, tri-electrode reactor 41 may operated in electrolysis mode at a constant voltage mode for one second and then switch to fuel cell mode operates at a constant voltage mode for another second. Hydrogen (H2) 57 evolved at the electrolyser cathode may be oxidized at the fuel cell anode, generating electrical energy in the process to offset the energy required for electrolysis. Experimental data was recorded by NOVA Autolab software with an interval of 0.1s (A total of 10 data points can be recorded in one second). Tri- electrode reactor 41 may provide a high concentration of alkaline capture solution 54 (e.g. NaOH, LiOH, or KOH) and produce a high concentration of halogen acid solution 55 (e.g. HBr, HCl, or HI) at the same time to act as an acidic release solution in a CO2 Liberator. Water 56 and spent electrolyte 32 (i.e. metal halides such as NaBr, NaCl, or LiI) may be supplied to tri-electrode reactor 41. [0092] FIG.6 shows an exploded view of an example tri-electrode reactor 41. Tri-electrode reactor 41 may include opposing end plates 49, 49’, a first electrode 42, a

24 CAN_DMS: \1000584587\2 second electrode 43, and a common electrode 44. In some embodiments, electrode 42, 43 may comprise materials and/or arrangements to provide features including: electrical conductivity; porous structure to maximize gas diffusion; increased reaction area (surface area on electrode), minimize reaction overpotentials, maximize stability, and/or maximize chemical resistance. In an embodiment, common electrode 44 may be tolerant to highly acidic conditions and alternating voltage; and electrode 42 is configured for chemical stability in alkaline conditions; and electrode 43 is hydrophobic. Membrane 46 may be coated electrode 42. In an example, first electrode 42 is a 3- layer N115 (Iridium Ruthenium Oxide (IrRuOx)/ Platinum Black (PTB)) or a N115 (PtB) catalyst coated membrane; common electrode 44 is titanium fiber felt coated with an Ir- Mixed Metal Oxide (MMO) commercial catalyst, e.g. an iridium oxide titanium felt electrode; and second electrode 43 is 0.5 mg/cm260% platinum on vulcan - carbon cloth electrode. Polytetrafluoroethylene (PTFE) may be sprayed on one face of the Ir- MMO commercial catalyst. A membrane 46’ may be positioned between common electrode 44 and second electrode 43. In an example, membrane 46’ may be a cation exchange membrane N117. A common current connector 39, e.g. a titanium middle channel, may be positioned adjacent the common electrode 44. The components of tri- electrode reactor 41 may be assembled and then hot pressed and/or bolted together. [0093] FIG.7, a schematic diagram illustrating a method 1000 of operating an electrochemical regeneration system. [0094] At 1002, method 1000 comprises providing an electrochemical regeneration system comprising a tri-electrode reactor having a having first electrode, a second electrode, and a common electrode according to this disclosure. [0095] At 1004, in a first mode of operation, the method comprises applying a voltage to the first electrode and the common electrode to convert: an electrolyte and water (H2O) into an alkaline capture solvent and an reagent. In an embodiment, in the first mode of operation, the method comprises converting: nMX2/n + 2H2O → nM(OH)2/n + X2 + H2, wherein the first electrode is a first cathode, the common electrode is a first anode and an oxidation reaction at the common electrode is: 2X- → X2 + 2e-,

25 CAN_DMS: \1000584587\2 [0096] At 1006, in a second mode of operation, the method comprises converting the reagent into an acid. In an embodiment, in the second mode of operation, the method comprises converting: X2 + H2 → 2HX, wherein the second electrode is a second anode and the common electrode is a second cathode and a reduction reaction at the common electrode is: X2 + 2e- → 2X- where: the electrolyte (MX), i.e. the metal halide, is alkali halide or an alkaline earth halide, the alkaline capture solvent (M(OH)), is a alkali metal hydroxide or alkaline earth hydroxide, and the reagent (X) is a halogen produced at the common electrode in the first mode of operation and is a reagent at the common electrode, n = 2 when MX is alkali halide; or n=1 when MX is an alkaline earth halide, X- is a halide ion of the halogen X _, the acid (HX), i.e. the halogen acid, is a hydrogen halide. [0097] Method 1000 may comprise alternating between block 1004 and 1006 according to alternating voltage methods described herein. [0098] In an embodiment, the method comprises mixing the nM(OH)2/n (i.e. alkaline capture solvent) produced in the first mode of operation with air, e.g. in an air contactor, to form at least one metal carbonate due to the alkaline capture solvent reacting the carbon dioxide in the air. The at least one metal carbonate and the HX (i.e. hydrogen halide/ halogen acid) produced in the second mode of operation may be mixed, e.g. in a CO2 liberation, to provide CO2(g), H2O(l), and MX. The MX may then be sent to the electrochemical regeneration system for regeneration. [0099] In an embodiment, the at least one metal carbonate is at least one of NaHCO3(aq) and Na2CO3(aq), and the at least one metal carbonate is formed according to at least one of the reactions: CO2(g) + NaOH(aq) → NaHCO3(aq), and CO2(g) + 2NaOH(aq) → Na2CO3(aq) + H2O(l).

26 CAN_DMS: \1000584587\2 [0100] In another embodiment, the at least one metal carbonate is Li2CO3 formed according to the reaction: CO2(g) + 2LiOH(aq) →Li2CO3 + H2O(l). [0101] In another embodiment, the at least one metal carbonate is K2CO3 formed according to the reaction: CO2(g) + 2KOH(aq) →K2CO3 + H2O(l). [0102] In an embodiment, MX is NaCl, M(OH) is NaOH, X is Cl2, HX is HCl, and the overall reaction of the first mode of operation is: 2NaCl + 2H2O → 2NaOH + Cl2 + H2, and the overall reaction of the second mode of operation is: H2 + Cl2 → 2HCl. [0103] In another embodiment, MX is NaBr, M(OH) is NaOH, X is Br2, HX is HBr, the overall reaction of the first mode of operation is: 2NaBr + 2H2O → 2NaOH + Br ₂ + H ₂ , and the overall reaction of the second mode of operation is: H ₂ + Br ₂ → 2HBr. [0104] In another embodiment, MX is NaI, M(OH) is NaOH, X is I ₂ , HX is HI, the overall reaction of the first mode of operation is: 2NaI + 2H ₂ O → 2NaOH + I ₂ + H ₂ , and the overall reaction of the fuel cell is: H ₂ + I ₂ → 2HI. [0105] In another embodiment, MX is LiI, M(OH) is LiOH, X is I ₂ , HX is HI, the overall reaction of the first mode of operation is: 2LiI + 2H ₂ O → 2LiOH + I ₂ + H ₂ , and the overall reaction of the fuel cell is: H ₂ + I ₂ → 2HI. [0106] In another embodiment, MX is KI, M(OH) is KOH, X is I ₂ , HX is HI, the overall reaction of the first mode of operation is: 2KI + 2H ₂ O → 2KOH + I ₂ + H ₂ , and the overall reaction of the fuel cell is: H ₂ + I ₂ → 2HI. [0107] FIG.8, a schematic diagram illustrating a method 1100 of reducing and oxidizing at a common electrode of an electrochemical regeneration system. [0108] At 1102, method 1100 comprises providing an electrochemical regeneration system comprising a tri-electrode reactor having a having first electrode, a second electrode, and a common electrode. The common electrode may be separated from the first electrode by a first membrane, and the common electrode may be separated from the second electrode by a second membrane. The first and second membranes may be cation selective. [0109] At 1104, method 1100 comprises applying a voltage to the first electrode and common electrode to oxidize a halide ion at the common electrode to form a

27 CAN_DMS: \1000584587\2 diatomic halogen, and reduce an alkali halide or alkaline earth halide at the first electrode to form an alkali hydroxide or alkaline earth hydroxide. [0110] At 1106, method 1100 comprises reducing the diatomic halogen at the common electrode to form the halide ion, and oxidizing hydrogen to form hydrogen ions 5 at the second electrode in the fuel cell. [0111] Method 1100 may comprise alternating between block 1104 and 1106 according to alternating voltage methods described in this disclosure. [0112] In an embodiment, the halide ion is chloride ion; the diatomic halogen is chlorine; alkali halide or alkaline earth halide is sodium; and alkali hydroxide or alkaline 10 earth hydroxide is sodium hydroxide. [0113] In another embodiment, the halide ion is bromide ion; the diatomic halogen is bromine; alkali halide or alkaline earth halide is sodium; and alkali hydroxide or alkaline earth hydroxide is sodium hydroxide. [0114] In another embodiment, the halide ion is iodide ion; the diatomic halogen 15 is iodine; alkali halide or alkaline earth halide is sodium; and alkali hydroxide or alkaline earth hydroxide is sodium hydroxide. [0115] In another embodiment, the halide ion is iodide ion; the diatomic halogen is iodine; alkali halide or alkaline earth halide is lithium; and alkali hydroxide or alkaline earth hydroxide is lithium hydroxide MX is LiI. 20 [0116] In another embodiment, the halide ion is iodide ion; the diatomic halogen is iodine; alkali halide or alkaline earth halide is potassium; and alkali hydroxide or alkaline earth hydroxide is potassium hydroxide MX is KI. [0117] CONTROLLER [0118] FIG.9 shows a generalized schematic view of example system 2000 for 25 controlling a regeneration system for alkaline capture solvents of a direct air capture system. System 2000 may comprise controller 2001, described herein. Controller 2001 includes a processor 2002 configured to implement processor readable instructions that, when executed, configure the processor 2002 to conduct operations described herein. The processor 2002 may be a microprocessor or microcontroller, a digital signal 30 processing (DSP) processor, an integrated circuit, a field programmable gate array

28 CAN_DMS: \1000584587\2 (FPGA), a reconfigurable processor, a programmable read-only memory (PROM), or combinations thereof. Controller 2001 may include a communication interface 2004 to communicate with other computing or sensor devices, to access or connect to network resources, or to perform other computing applications by connecting to a network (or 5 multiple networks) capable of carrying data. In some examples, the communication interface 2004 may include one or more busses, interconnects, wires, circuits, and/or any other connection and/or control circuit, or combination thereof. The communication interface 2004 may provide an interface for communicating data between the system 2000 and a display 2015. 10 [0119] Controller 2001 may also comprise connections for communicating with any component of a tri-electrode reactor 41, air contactor 2007 and/or CO ₂ Liberator 2008 according to this disclosure to transmit setpoint(s) or receive data such as flow, valve position, concentration, and pressure data/values, among other data. [0120] Controller 2001 may comprise a sensor 2010 connection(s) for 15 monitoring current and/or voltage of the electrode of the tri-electrode reactor. [0121] Controller 2001 may be coupled to a data system 2014 for storing system data and/or may be configured to communicate with cloud services such as iCloud, Dropbox, Google clouds, or any other digital data servers. Data system 2014 may also comprises a universal asynchronous receiver-transmitter (UART) to allow 20 communication with other devices, e.g. a smartphone or a computer, for transmitting data for analysis and/or storage. UART may include or be coupled to a wireless transceiver for wireless communication with such other devices, e.g., by way of infra- red, Bluetooth, Wi-Fi, or the like. Network 2500 may include any wired or wireless communication path, such as an electrical circuit. In some embodiments, the network 25 2500 may include one or more busses, interconnects, wires, circuits, and/or any other connection and/or control circuit, or a combination thereof. In some embodiments, the network 2500 may include a wired or a wireless wide area network (WAN), local area network (LAN), a combination thereof, or the like. In some embodiments, the network 2500 may include a Bluetooth® network, a Bluetooth® low energy network, a short- 30 range communication network, or the like.

29 CAN_DMS: \1000584587\2 [0122] Controller 2001 may include memory 2006. The memory 2006 may include one or a combination of computer memory, such as static random-access memory (SRAM), random-access memory (RAM), read-only memory (ROM), electro- optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like. [0123] The memory 2006 may store an application 2012 including processor readable instructions for conducting operations described herein. In some examples, the application 2012 may include operations for controlling a regeneration system for regenerating alkaline capture solvent according to any one of the methods described herein. [0124] Controller 2001 may also be coupled to power source(s) 2005 to control power to the tri-electrode reactors described herein. [0125] In an embodiment, application 2012 may include operations for applying a voltage from a power source to a first electrode and the common electrode of tri- electrode reactor 2009 in a first mode of operation a to convert: an electrolyte and water (H ₂ O) into an alkaline capture solvent and an reagent. In an embodiment, in the first mode of operation the conversion is: nMX _2/n + 2H ₂ O → nM(OH) _2/n + X ₂ + H ₂ , where: the electrolyte (MX) is alkali halide or an alkaline earth halide, the alkaline capture solvent (M(OH)) is a alkali metal hydroxide or alkaline earth hydroxide, and the reagent (X) is a halogen produced at the common electrode, n = 2 when MX is alkali halide; or n=1 when MX is an alkaline earth halide. [0126] Application 2012 may also include operations for stopping application of power from the power source in a second mode of operation to allow the common electrode and the second electrode to convert the reagent to an acid. In an embodiment, the conversion of the reagent to the acid is: X2 + H2 → 2HX, where:

30 CAN_DMS: \1000584587\2 the acid (HX) is a hydrogen halide. [0127] In an embodiment, application 2012 may include operations for alternating between the first mode of operation and the second mode of operation according to the alternating voltage strategy described herein. [0128] EXAMPLES [0129] Example 1 [0130] Performance comparison for a four-electrode regeneration system (combined electrolysis cell/fuel cell system shown in FIG.2A) was compared with a tri- electrode reactor using NaBr as the alkaline capture solvent. As shown in Table 1, the tri-electrode reactor required less energy than the four-electrode system. These sets of experiment were conducted with 3M NaBr as input chemical. At low current density (10 mA cm ^-2 ), the system net energy required is very close because the energy regenerated through by the fuel cell is very low and the electrolysis system dominates the energy consumption. At higher current density (50, 100, 150, 200 mA cm ^-2 ), the fuel cell recovered more energy. Thus, the net energy difference between four-electrode system and three-electrode system increased with current density. The tri-electrode system improved the fuel cell performance by minimizing the halogen (e.g. Cl ₂ , Br ₂ , or I ₂ ) mass transport losses. Table 1. Performance comparison for four-electrode system VS three-electrode system using NaBr as alkaline capture solvent Current Density Net Energy Required [GJ/t CO2] [mA cm ^-2 ] Four-electrode system Three-electrode system [0131] Example 2 [0132] The purpose of this experiment was to study the power consumption performance of the electrolysis operation mode under different current densities. A 1 cm ² electrolysis system was operated under a constant voltage in a range of 2.1 V to 2.75 V. A 1 cm ² fuel cell system was operated under a constant voltage of 0.8 V. These experiments operated at room temperature and ambient pressure. Deionized water was

31 CAN_DMS: \1000584587\2 used as the catholyte and 3M NaCl was used as the anolyte. As a result, the average NaCl electrolysis power consumption is in a range of 0.052 to 0.578 W/cm ² between 10 to 200 mA/cm ² electrolysis system current density. [0133] Example 3 [0134] The purpose of this experiment was to study the power regeneration performance of the fuel cell operation mode under different voltages. A 1 cm ² electrolysis system operated under a constant voltage of 2.3V. A 1 cm ² fuel cell system operated under a constant voltage in a range of 0.2 to 1.2 V. This experiment operates at room temperature and ambient pressure. Deionized water was used as the catholyte and 3M NaCl was used as the anolyte. As a result, the average NaCl fuel cell power regeneration is in a range of 0.02 to 0.062 W/cm ² between 0.2 to 1.2 V fuel cell system voltage. [0135] Example 4 [0136] The purpose of this experiment was to study the electrolysis system and the fuel cell system operation for NaBr anolyte with different operating voltages. A 1 cm ² electrolysis system operated under a constant voltage in a range of 1.4 V to 2.4 V. A 1 cm ² fuel cell system operated under a constant voltage in a range of 0.2 to 0.8 V. This experiment operated at room temperature and ambient pressure. Deionized water was used as the catholyte and 6M NaBr was used as the anolyte. As a result, the average NaBr electrolysis power consumption is in a range of 0.022 to 0.490 W/cm ² between 10 to 200 mA/cm ² electrolysis system current density. Additionally, the average NaBr fuel cell power regeneration is in a range of 0.016 to 0.045 W/cm ² between 0.2 to 0.8 V fuel cell system voltage. [0137] Example 5 [0138] FIG.10 illustrates experiments results of a comparison of total energy expenditure vs. current density for NaCl, NaBr, and NaI as alkaline capture solvents in a tri-electrode reactor. The same concentration of alkaline capture solvent was used for each test. NaI showed the lowest energy expenditure at each current density: 4.93 – 7.82 GJ/tCO2 Cap (elec); and 6.14 GJ/tCO2 at 100 mA/cm ² . [0139] Example 6

32 CAN_DMS: \1000584587\2 [0140] FIG.11 illustrates experiments results of tandem electrolyzer-fuel cell performance using different halogen or oxygen intermediates in a two-reactor configuration, e.g. the configuration shown in FIG.2A. Graph A shows electrolyzer voltage using different halogen or oxygen intermediates at 100 mA cm ^-2 current densities with 1.5 M Li2SO4, 3 M LiCl, 3 M LiBr, and 3 M LiI electrolyte, comparing with voltages of the theoretical model shown in Table 2 below. Graph B shows the corresponding fuel cell polarization curve for the Hydrogen-oxygen fuel cell; Graph C shows the corresponding fuel cell polarization curve for Hydrogen-chlorine fuel cell, Graph D shows the corresponding fuel cell polarization curve for Hydrogen-bromine fuel cell, and Graph E shows the corresponding fuel cell polarization curve for Hydrogen- iodine fuel cell, when connected to the electrolyzer tested in Graph A. Table 2. Theoretical electrolyzer power model analysis. Product ^^ ^{^} ^^ _ோ^ௗ / ^^ _ை௫ ^^ _^^^^ Electrolyzer power @100mA species (V) (V) (V) cm ^-2 (mW cm ^-2 ) Cathode reaction H ₂ 0 -0.77 Anode reaction O2 1.23 1.11 1.88 188 Cl ₂ 1.36 1.32 2.09 209 Br2 1.07 1.03 1.80 180 I2 0.54 0.45 1.22 122 [0141] As noted above with respect to FIG.11, preliminary tandem electrolyzer- fuel cell experiments were conducted with water, chloride (Cl-), bromide (Br-), or iodide (I-) anions and found that the oxidation of I- exhibited the lowest overpotential, agreeing

33 CAN_DMS: \1000584587\2 with theory as shown in Table 2 and FIG.11. I2 has additional advantages owing to its low volatility, mitigating the interference with captured gas phase CO2 stream. ^23,24 However, other reports of electrocatalytic I- oxidation (e.g., in redox flow batteries) have demonstrated that continuous operation forms dense I2 layers, which impose large charge transfer resistances and diminish the energy efficiency attainable with iodine chemistry. ^25–27 [0142] FIG.12 shows a graph of the the stability of the hydrogen-iodine electrolyzer in the two-reactor configuration operating at 100 mA cm ^-2 tested in FIG.11 above. Some of the evolved I2 accumulated on the anode, lowering the ionic conductivity of the system, and further increasing the voltage over time. [0143] Example 7 [0144] FIG.13 shows experimental results of a tandem electrolyzer-fuel cell in a two-reactor configuration shown in FIG.2A illustrating fuel cell polarization curves and power density when the electrolyzer was operating at (A) 10 mA cm-2, (B) 50 mA cm-2, (C) 100 mA cm-2, (D) 150 mA cm-2, (E) 200 mA cm-2 with 3 M LiI as the electrolyte. [0145] Both half-reactions of the fuel cell (i.e., I ₂ reduction and H ₂ oxidation) have reactant availability impacted by the electrolyzer I ₂ /H ₂ production rate. Therefore, at a constant electrolyzer current, the fuel cell current was varied as shown in FIG.13 to identify the maximum fuel cell power output (i.e., product of current and voltage) – see also FIG.2E. The continuous fuel cell power output (7.3 mW cm ^-2 at 100 mA cm ^-2 ) was much lower than expected (>20 mW cm ^-2 . At peak power output, the fuel cell voltage was close to the expected value, but the current was low (See Table 2, Figure 13). The I- present in the electrolyte and I2 produced from the electrolyzer react chemically to form polyiodides. ^31,32 In the reducing environment of the fuel cell cathode, these polyiodides (e.g., I3- or I5-) behave similarly to I2 and can be electrochemically reduced directly into I-. ^32,33 The low fuel cell current suggested that the local I2/polyiodide concentration at the fuel cell cathode was limiting. It was concluded that conventional electrochemical approaches with independent electrolyzers and fuel cells (two-reactor systems) cannot realize energy-efficient regeneration. I2 film formation in the electrolyzer and a lack of the local availability of the iodine redox intermediate in the fuel cell fundamentally limit the efficiency and stability of continuous operation.

34 CAN_DMS: \1000584587\2 [0146] Example 8 [0147] FIG.14 shows experiments result of an electrolyzer-fuel cell in an tri- electrode AE configuration using cyclic voltammetry with a range of frequencies between 0.005 and 1 Hz with 3 M LiI electrolyzer anolyte at 100 mA cm-2 steady state electrolyzer current density. Graph (A) shows a 0.005 Hz cyclic fuel current density plot. Graph (B) shows a 0.05 Hz cyclic fuel current density plot. Graph (C) shows a 0.5 Hz fuel current density plot. Graph (D) shows 1 Hz cyclic fuel current density plot. Graph (E) shows a fuel cell power output at different frequencies. [0148] As shown in FIG.14, at lower frequencies, the I2 accumulated during oxidation was not fully recovered during reduction. It was found that frequencies higher than 0.5 Hz were sufficient to avoid excessive I ₂ filming and diffusion. Frequencies 0.5 Hz and above yielded comparable fuel cell power outputs as shown in Group E of FIG. 14. [0149] AE outperformed the two-reactor configuration as the electrolyzer and fuel cell both operated more efficiently. Unlike the two-reactor configuration, the AE electrolyzer was operated in potentiostatic mode to limit the voltage which the electrodes were exposed to while they were switched off (See FIG.5 for layout of the example AE electrolyzer). Linear interpolation was used to determine the electrolyzer voltage required to achieve the same time-averaged current densities as the two- reactor configuration which are illustrated in FIG.15 that shows a graph of example Electrolyzer current density vs. voltage in AE configuration. The AE electrolyzer voltages were lower due to reduced film accumulation on the anode. [0150] Example 9 [0151] Voltage distribution of the AE electrolyzer operating at 100 mA cm ^-2 was analyzed. FIG.16 shows an example AE electrolyzer energy loss analysis. Nyquist plots and fitting curves (dashed lines; equivalent circuits shown in inset) in pH 13.1 LiOH electrolyzer catholyte and 3M LiI electrolyzer anolyte with an Electrochemical Impedance Spectroscopy (EIS) frequency range of 0.1 MHz to 100 mHz and 5 mV amplitude shown at Graph (A) an cathode voltage of -1.08 V vs. Ag (s)/AgCl (aq, 3M). Graph (B) shows an anode voltage of 0.33 V vs. Ag (s)/AgCl (aq, 3M). Graph (C) shows a full cell voltage of -1.52 V. Graph (D) shows a voltage breakdown of the

35 CAN_DMS: \1000584587\2 electrolyzer (combined voltage of -1.52 V). To provide sufficient time to make the EIS measurements, the half-cell and full-cell voltage measurements were made on an electrolyzer operated 200 s continuously at 100 mA cm ^-2 . The AE electrolyzer operating at the same current density exhibits a lower overall voltage (-1.36 V), due to a reduced Nernst loss on the electrolyzer anode and an overpotential reduction on the electrolyzer cathode through pulsed electrolysis. [0152] Nernst losses are the dominant source of voltage loss in the electrolyzer. Operating in the AE configuration, instead of the two-reactor configuration, significantly reduces I2 filming, limits the I2 concentration on the electrolyzer anode, and reduces the Nernst loss. [0153] FIG.17 shows an AE fuel cell anode EIS. Nyquist plots and fitting curves (dashed lines; equivalent circuits shown in inset) during ex-situ measurements with an EIS frequency range of 0.1 MHz to 100 mHz and 5 mV amplitude at an anode voltage at -0.4 V vs. Ag (s)/AgCl (aq, 3M). The fuel cell anode was installed in a flow cell with 3 M LiI electrolyte to measure the electrode capacitance. [0154] FIGs.18A and 18B show fuel cell performance in the alternating electrocatalysis (AE) configuration. The fuel cell polarization curves and power density when the electrolyzer was operating at (A) 8.3 mA cm-2, (B) 15 mA cm-2, (C) 28 mA cm-2, (D) 48 mA cm-2, (E) 63 mA cm-2, (F) 86 mA cm-2, (G) 127 mA cm-2, (H) 156 mA cm-2, (I) 182 mA cm-2, (J) 209 mA cm-2, (K) Interpolated polarization curves at intermediate current densities: 10, 50, 100, 150, 200 mA cm-2. Interpolation performed using linear regression on experimental data shown in Graphs (A) to (J). [0155] The fuel cell current was much higher for AE than in the two-reactor configuration at a given voltage due to improved I2 availability on the electrode surface. AE also yielded much higher fuel cell power outputs for all I2/H2 production rates. [0156] Example 10 [0157] pH measurements of the effluent were takes to confirm that an AE electrolyzer and fuel cell can generate sufficiently alkaline and acidic solutions, respectively.

36 CAN_DMS: \1000584587\2 [0158] FIGs.19A and 19B shows pH of the regenerated LiOH capture liquid and HI acid during AE. Graph (A) is a pH calibration of LiOH solution at various concentrations. Graph (B) is a pH calibration of HI solution at various concentrations in 3 M LiI supporting electrolyte. Graph (C) shows current density behavior during pH measurement experiment (10 mL of DI water electrolyzer catholyte, 50 mL of 3 M LiI electrolyzer anolyte, 10 mL min-1 electrolyzer catholyte flow rate, 10 mL min-1 electrolyzer anolyte flow rate). Graph (D) shows Electrolyzer catholyte pH and OH- concentration. Graph (E) shows electrolyzer anolyte pH and OH- concentration. Graph (F) shows current efficiency in the electrolyzer. Graph (G) shows current efficiency in the fuel cell. [0159] As shown in Graphs (D) and (E) of FIG.19B, after 34 min of operation, the regenerated LiOH capture liquid reached a pH of 13.1 and the HI acid reached a pH of 1.1. Since the pH change of the electrolytes was governed by electromigration through the membranes, the electrolytes reached similar pH values irrespective of the electrolyte flow rates and shown in FIG.20. FIG.20 illustrates regenerated LiOH capture liquid and HI acid at different electrolyte flow rates during AE. The same flow rate was used for the electrolyzer catholyte and the electrolyzer anolyte. AE was performed with electrolyzer operation at -1.36 V for 1 s, fuel cell operation at 0.27 V for 1 s, and fuel cell operation at 0 V for 0.5 s. (A) Electrolyzer catholyte pH. (B) Electrolyzer anolyte pH. [0160] Example 11 [0161] FIG.21 shows images of scanning electron microscopy (SEM) imaging of the common electrode in the alternating electrocatalysis configuration. Image (A) is Pre-experiment. Image (B) is Post-experiment. After operating the AE continuously for 100 hours with stable electrochemical performance, Image (B) shows no apparent change in electrode morphology. [0162] During the experiment, -1.36 V was applied during electrolyzer mode, which maintained an average current density of 107 mA cm ^-2 . Within each cycle, the fuel cell operated at two-step voltages - initially at 0.27 V to yield the maximum power and then at 0 V to reduce any remaining I2. Throughout the 100-hour test experiment, the average current density during fuel cell mode was maintained at 51 mA cm ^-2 during

37 CAN_DMS: \1000584587\2 the 0.27 V step and 110 mA cm ^-2 during the 0-V step. Analysis of the regenerated LiI electrolyte indicated that this system did not over-oxidize the I2 into IO3- or IO4- as shown in FIG.22. Specifically, FIG.22 shows a high pressure ion chromatography analysis of standard sample solution and post electrolysis solution: 0.02mM I- solution; 0.02mM IO3- solution; 0.02mM IO4- solution; 1/150000 dilution post-electrolysis electrolyzer anolyte solution; and 1/5000 dilution post-electrolysis electrolyzer catholyte solution. [0163] Example 12 [0164] FIG.23 shows a process flow diagram for an example 1 kilotonne per year DAC system. In an integrated DAC system based on AE regeneration system, atmospheric air may be driven into contact with LiOH, the alkaline capture liquid, forming solid Li ₂ CO ₃ . The Li ₂ CO ₃ precipitates may be neutralized with HI acid in the CO ₂ liberator to produce a gaseous stream of pure CO ₂ and aqueous LiI. Experiments confirm that ~98% of the CO ₂ captured by a LiOH capture liquid can be recovered in the CO ₂ liberator. The LiI electrolyte generated in the CO ₂ liberator is then used as the input for AE, where it is regenerated into capture liquid and acid for neutralization [0165] Since the electrolyzer and fuel cell operate with the same electrical charge and Faradaic efficiency, the OH- generated on the electrolyzer cathode (i.e., for the capture solution) equals to the H+ generated on the fuel cell cathode (i.e., for the CO2 liberator solution). Within the CO2 liberator solution, Li2CO3 neutralization increases the pH while fuel cell operation simultaneously decreases the pH, both at equal rates (since the CO2 capture rate is coupled to the OH- regeneration rate). In an integrated system based on the cycling approach, the pH of the CO2 liberator solution will thus remain constant. An acidic starting electrolyte facilitates an environment for efficient release of CO2 even though it introduces an additional voltage penalty for electrolysis. [0166] Example 13 [0167] Testing of AE-regenerated capture liquid was done to show the capture liquid can capture CO2 from the air and release high purity CO2 when neutralized with the AE-produced HI.

38 CAN_DMS: \1000584587\2 [0168] FIG.24 shows images of an experimental demonstration of DAC using AE regenerated solutions. Image (A) shows bubbling air through capture solution generated by AE. Image (B) shows Li2CO3 salt precipitation. Image (C) shows solid and liquid separation to obtain Li2CO3 precipitates. Image (D) shows neutralization of Li2CO3 with HI (CO2 liberator efficiency: 98 ± 2 %). [0169] In scaled operation, the neutralization of Li2CO3 to CO2 in the CO2 liberator will eventually saturate the electrolyzer anolyte with CO2 and introduce carbonic species into the electrolyte. Carbonic species can also be present in the electrolyzer catholyte, at levels below the Li2CO3 solubility limit, as a result of recirculation through the air contactor. To assess the impact on the electrolyzer, a carbon-containing catholyte (Li ₂ CO ₃ ) was employed as the electrolyzer catholyte (in place of water) and carbonic species were introduced to the electrolyzer anolyte via a CO ₂ purge. There were no side reactions detected between the carbonic species and the electrolyte. In this batch demonstration, the AE performance was the same with and without carbon-containing species in the electrolytes. FIG.25 shows a full cycle demonstration of AE Performance for capture liquid regeneration. Cycle 1 shown in Graph (A) is during the first cycle of the AE operation, the electrolyzer catholyte and anolyte were filled with water and LiI, respectively. At the end of the first cycle, the electrolyzer catholyte was removed and exposed to air to form Li ₂ CO ₃ . Graph (B) shows Cycle 2 where the Li2CO3 precipitates were extracted and put in the electrolyzer anolyte to start the second cycle of AE operation. During this second cycle, the electrolyzer anolyte was held under an atmosphere of pure CO2. [0170] FIG.26 shows a image of the setup of the AE reactor used to demonstrate the results in FIG.25. The electrolyzer catholyte is recirculated from a reservoir into the cell. The LiI electrolyzer anolyte (fuel cell catholyte) is recirculated from a reservoir into the cell. Both reservoirs are equipped with a pH probe. [0171] Example 14 [0172] FIG.27 shows graphical results of an AE system compatibility test. The performance of alkaline capture liquid regeneration using 3M LiI (squares) and 3M NaI (circles) electrolyzer anolyte (electrolyzer voltage of -1.36V). The LiI electrolyzer had an average current density of 104.3 mA cm-2, and the NaI electrolyzer had an average

39 CAN_DMS: \1000584587\2 current density of 99.1 mA cm-2. This work has demonstrated that AE can be used to efficiently regenerate inorganic alkaline capture liquids for DAC. [0173] Alternate embodiments [0174] The above description is meant to be exemplary only, and one skilled in 5 the relevant arts will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. The present disclosure may be embodied in other specific forms without departing from the subject matter of the claims. The present disclosure is intended to cover and embrace all suitable changes in technology. Modifications which fall within the scope of the present 10 invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims. Also, the scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole. 15 [0175] As can be understood, the detailed embodiments described above and illustrated are intended to be examples only. The invention is defined by the appended claims. [0176] The claims are not intended to include, and should not be interpreted to include, means-plus- or step-plus-function limitations, unless such a limitation is 20 explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively. [0177] All documents disclosed herein are incorporated by reference in their entirety. [0178] REFERENCES 25 1. L. Joppa, A. Luers, E. Willmott, S. J. Friedmann, S. P. Hamburg, R. Broze, Microsoft’s million-tonne CO2-removal purchase — lessons for net zero. Nature.597, 629–632 (2021). 2. H. L. van Soest, M. G. J. den Elzen, D. P. van Vuuren, Net-zero emission targets for major emitting countries consistent with the Paris Agreement. Nat Commun. 30 12, 2140 (2021).

40 CAN_DMS: \1000584587\2 3. N. Höhne, M. J. Gidden, M. den Elzen, F. Hans, C. Fyson, A. Geiges, M. L. Jeffery, S. Gonzales-Zuñiga, S. Mooldijk, W. Hare, J. Rogelj, Wave of net zero emission targets opens window to meeting the Paris Agreement. Nat. Clim. Chang.11, 820–822 (2021). 5 4. International Energy Agency (IEA), “Net Zero by 2050 - A Roadmap for the Global Energy Sector” (2021), p.224. 5. S. J. Davis, N. S. Lewis, M. Shaner, S. Aggarwal, D. Arent, I. L. Azevedo, S. M. Benson, T. Bradley, J. Brouwer, Y.-M. Chiang, C. T. M. Clack, A. Cohen, S. Doig, J. Edmonds, P. Fennell, C. B. Field, B. Hannegan, B.-M. Hodge, M. I. Hoffert, E. Ingersoll, 10 P. Jaramillo, K. S. Lackner, K. J. Mach, M. Mastrandrea, J. Ogden, P. F. Peterson, D. L. Sanchez, D. Sperling, J. Stagner, J. E. Trancik, C.-J. Yang, K. Caldeira, Net-zero emissions energy systems. Science.360, eaas9793 (2018). 6. K. S. Lackner, S. Brennan, J. M. Matter, A.-H. A. Park, A. Wright, B. van der Zwaan, The urgency of the development of CO2 capture from ambient air. Proceedings 15 of the National Academy of Sciences.109, 13156–13162 (2012). 7. G. Realmonte, L. Drouet, A. Gambhir, J. Glynn, A. Hawkes, A. C. Köberle, M. Tavoni, An inter-model assessment of the role of direct air capture in deep mitigation pathways. Nat Commun.10, 3277 (2019). 8. J. K. Stolaroff, D. W. Keith, G. V. Lowry, Carbon Dioxide Capture from 20 Atmospheric Air Using Sodium Hydroxide Spray. Environ. Sci. Technol.42, 2728–2735 (2008). 9. C. Gebald, J. A. Wurzbacher, P. Tingaut, T. Zimmermann, A. Steinfeld, Amine- Based Nanofibrillated Cellulose As Adsorbent for CO 2 Capture from Air. Environ. Sci. Technol.45, 9101–9108 (2011). 25 10. J.-T. Anyanwu, Y. Wang, R. T. Yang, Amine-Grafted Silica Gels for CO 2 Capture Including Direct Air Capture. Ind. Eng. Chem. Res.59, 7072–7079 (2020). 11. D. R. Kumar, C. Rosu, A. R. Sujan, M. A. Sakwa-Novak, E. W. Ping, C. W. Jones, ACS Sustainable Chem. Eng., in press, doi:10.1021/acssuschemeng.0c03706. 12. N. McQueen, P. Psarras, H. Pilorgé, S. Liguori, J. He, M. Yuan, C. M. Woodall, 30 K. Kian, L. Pierpoint, J. Jurewicz, J. M. Lucas, R. Jacobson, N. Deich, J. Wilcox, Cost Analysis of Direct Air Capture and Sequestration Coupled to Low-Carbon Thermal Energy in the United States. Environ. Sci. Technol.54, 7542–7551 (2020).

41 CAN_DMS: \1000584587\2 13. D. W. Keith, G. Holmes, D. St. Angelo, K. Heidel, A Process for Capturing CO2 from the Atmosphere. Joule.2, 1573–1594 (2018). 14. S. Stucki, Coupled CO2 recovery from the atmosphere and water electrolysis: Feasibility of a new process for hydrogen storage. International Journal of Hydrogen 5 Energy.20, 653–663 (1995). 15. A. Iizuka, K. Hashimoto, H. Nagasawa, K. Kumagai, Y. Yanagisawa, A. Yamasaki, Carbon dioxide recovery from carbonate solutions using bipolar membrane electrodialysis. Separation and Purification Technology.101, 49–59 (2012). 16. Q. Shu, L. Legrand, P. Kuntke, M. Tedesco, H. V. M. Hamelers, Electrochemical 10 Regeneration of Spent Alkaline Absorbent from Direct Air Capture. Environ. Sci. Technol.54, 8990–8998 (2020). 17. M. D. Eisaman, L. Alvarado, D. Larner, P. Wang, B. Garg, K. A. Littau, CO ₂ separation using bipolar membrane electrodialysis. Energy Environ. Sci.4, 1319–1328 (2011). 15 18. F. Sabatino, M. Mehta, A. Grimm, M. Gazzani, F. Gallucci, G. J. Kramer, M. van Sint Annaland, Evaluation of a Direct Air Capture Process Combining Wet Scrubbing and Bipolar Membrane Electrodialysis. Ind. Eng. Chem. Res.59, 7007–7020 (2020). 19. J. Wohland, D. Witthaut, C.-F. Schleussner, Negative Emission Potential of Direct Air Capture Powered by Renewable Excess Electricity in Europe. Earth’s Future. 20 6, 1380–1384 (2018). 20. M. Fasihi, O. Efimova, C. Breyer, Techno-economic assessment of CO2 direct air capture plants. Journal of Cleaner Production.224, 957–980 (2019). 21. D. R. Lide, G. Baysinger, L. I. Berger, R. N. Goldberg, H. V. Kehiaian, K. Kuchitsu, G. Rosenblatt, D. L. Roth, D. Zwillinger, CRC Handbook of Chemistry and 25 Physics (CRC Press, Boca Raton, FL, ed.85th, 2005; http://hbcponline.com/faces/contents/ContentsSearch.xhtml). 22. J. G. Vos, A. Venugopal, W. A. Smith, M. T. M. Koper, Competition and selectivity during parallel evolution of bromine, chlorine and oxygen on IrOx electrodes. Journal of Catalysis.389, 99–110 (2020). 30 23. A. Jameson, E. Gyenge, Halogens as Positive Electrode Active Species for Flow Batteries and Regenerative Fuel Cells. Electrochem. Energ. Rev.3, 431–465 (2020). 24. K. T. Cho, M. C. Tucker, A. Z. Weber, A Review of Hydrogen/Halogen Flow Cells. Energy Technol.4, 655–678 (2016).

42 CAN_DMS: \1000584587\2 25. W. Yang, M. R. Grochowski, A. Sen, Selective Reduction of Biomass by Hydriodic Acid and Its In Situ Regeneration from Iodine by Metal/Hydrogen. ChemSusChem.5, 1218–1222 (2012). 26. Z. W. Seh, J. Kibsgaard, C. F. Dickens, I. Chorkendorff, J. K. Nørskov, T. F. 5 Jaramillo, Combining theory and experiment in electrocatalysis: Insights into materials design. Science.355, eaad4998 (2017). 27. K. C. Neyerlin, W. Gu, J. Jorne, H. A. Gasteiger, Study of the Exchange Current Density for the Hydrogen Oxidation and Evolution Reactions. Journal of The Electrochemical Society.154, B631 (2007). 10 28. In Chemistry of the Elements (Elsevier, 1997; https://linkinghub.elsevier.com/retrieve/pii/B97807506336595 00237), pp.789–887. 29. J. Ma, M. Liu, Y. He, J. Zhang, Iodine Redox Chemistry in Rechargeable Batteries. Angew. Chem. Int. Ed.60, 12636–12647 (2021). 30. L. Su, A. F. Badel, C. Cao, J. J. Hinricher, F. R. Brushett, Toward an 15 Inexpensive Aqueous Polysulfide–Polyiodide Redox Flow Battery. Ind. Eng. Chem. Res.56, 9783–9792 (2017). 31. S. Rodrigo, D. Gunasekera, J. P. Mahajan, L. Luo, Alternating current electrolysis for organic synthesis. Current Opinion in Electrochemistry.28, 100712 (2021). 20 32. A. Loh, Selection of oxygen reduction catalysts for secondary tri-electrode zinc– air batteries. Scientific Reports, 16 (2022). 33. Y. Li, M. Gong, Y. Liang, J. Feng, J.-E. Kim, H. Wang, G. Hong, B. Zhang, H. Dai, Advanced zinc-air batteries based on high-performance hybrid electrocatalysts. Nat Commun.4, 1805 (2013). 25 34. D. Hart, F. Lehner, S. Jones, J. Lewis, The Fuel Cell Industry Review 2019 (2019), (available at www.FuelCellIndustryReview.com). 35. K. Ayers, N. Danilovic, R. Ouimet, M. Carmo, B. Pivovar, M. Bornstein, Perspectives on Low-Temperature Electrolysis and Potential for Renewable Hydrogen at Scale. Annu. Rev. Chem. Biomol. Eng.10, 219–239 (2019). 30 36. S. Kim, M. Choi, J. S. Kang, H. Joo, B. H. Park, Y.-E. Sung, J. Yoon, Electrochemical recovery of LiOH from used CO2 adsorbents. Catalysis Today.359, 83–89 (2021).

43 CAN_DMS: \1000584587\2 37. S. Baker, J. K. Stolaroff, G. Peridas, S. H. Pang, H. M. Goldstein, F. R. Lucci, W. Li, E. W. Slessarev, J. Pett-Ridge, F. J. Ryerson, J. L. Wagoner, W. Kirkendall, R. D. Aines, D. L. Sanchez, B. Cabiyo, J. Baker, S. McCoy, S. Uden, R. Runnebaum, J. Wilcox, P. C. Psarras, H. Pilorgé, N. McQueen, D. Maynard, C. McCormick, “Getting to 5 Neutral” (LLNL-TR-796100, Lawrence Livermore National Laboratory, 2020). 38. M. Erans, E. S. Sanz-Pérez, D. P. Hanak, Z. Clulow, D. M. Reiner, G. A. Mutch, Direct air capture: process technology, techno-economic and socio-political challenges. Energy Environ. Sci.15, 1360–1405 (2022). 10 39. N. McQueen, K. V. Gomes, C. McCormick, K. Blumanthal, M. Pisciotta, J. Wilcox, A review of direct air capture (DAC): scaling up commercial technologies and innovating for the future. Prog. Energy.3, 032001 (2021). 15 40. N. McQueen, M. J. Desmond, R. H. Socolow, P. Psarras, J. Wilcox, Natural Gas vs. Electricity for Solvent-Based Direct Air Capture. Front. Clim.2, 618644 (2021).

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