Alternating dual-electrolyser systems and methods for direct air capture (DAC) and release of co2

Abstract

An alternating dual-electrolyser system for direct air capture and release of CO2 includes a reduction compartment comprising a cathode of a first electrolyser; an oxidation compartment comprising an anode of a second electrolyser; and an alternating redox compartment separated from the reduction compartment by a first cation exchange membrane of the first electrolyser and from the oxidation compartment by a second cation exchange membrane of the second electrolyser. The redox compartment receives an electrolyte solution comprising an organic redox-active molecule in fluid isolation of the reduction compartment. The redox compartment includes an alternating electrode serving as an anode of the first electrolyser for oxidation of the redox-active molecule in the redox compartment to facilitate regeneration of hydroxide capture solution in the reduction compartment, and as a cathode of the second electrolyser for reduction of the oxidized redox-active molecule to facilitate regeneration of an acidic neutralizing solution in the redox compartment.

Description

TITLE: ALTERNATING DUAL-ELECTROLYSER SYSTEMS AND METHODS FOR DIRECT AIR CAPTURE (DAC) AND RELEASE OF CO2CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of United States Provisional Patent Application No. 63 / 515,620, filed July 26, 2023, which is hereby incorporated herein by reference in its entirety.FIELD

[0002] The teachings disclosed herein relate to direct air capture (DAC) and release of CO2.INTRODUCTION

[0003] The development and scaling of carbon capture, utilization, and storage (CCUS) technologies are needed to mitigate past and present anthropogenic carbon dioxide (CO2) emissions. Direct air capture (DAC) can be used to extract low concentration CO2 (e.g. 412 ppm or 0.0412%) directly from the atmosphere.1-3

[0004] Developed industrial-scale DAC methods rely on alkanolamine or aqueous alkaline absorbents, which require a temperature-swing process to release the captured CO2 and regenerate the sorbents.4-6However, these approaches rely on fossil fuels to produce the necessary heat which can emit significant amounts of CO2.7

[0005] Electrochemical CO2 capture and release methods have garnered significant attention for their potential to employ renewable energy. Two primary electrochemical mechanisms are used for electrochemical CO2 capture and release: direct electro-swing and indirect pH-swing. The direct electro-swing method utilizes organic redox-active compounds such as quinone8-12and bipyridine derivatives15as a CO2 sorbent to achieve low energy consumption.

[0006] However, this method relies on expensive ionic liquids or organic solvents, which are highly sensitive to oxygen (O2) and water vapor. No study has demonstrated a direct electro-swing approach with the IOW-CO2, high-02conditions relevant for DAC. Further material or solvent design is needed to enable DAC feasibility of the direct electro-swing approach. In contrast, the indirect pH-swing strategy using hydroxide absorbents has achieved stable atmospheric CO2 capture and release, albeit with relatively high energy consumption.16-20Recently, CO2 capture or DAC has been achieved with relatively low energy, using a pH-swing approach based on organic redox- active molecules, such as phenazine and pyridinyl derivatives.21-25The electrochemical reduction and oxidation of these organic molecules trigger water dissociation through proton uptake and release. Highly alkaline and acidic solutions are formed in this process for CO2 capture and release, respectively. However, phenazine derivatives are typically sensitive to O2.21-23Pyridinyl derivative is unstable and O2 exposure accelerates its decomposition.25Neutral red, a phenazine derivative, is insensitive to O2 but requires additional hydrotropic agents to increase the solubility of neutral red.24These agents increase the vapour pressure and susceptibility to vaporization, when exposed to a high air flow rate - necessitating replenishment and increasing operating costs.26The energy-efficient electrochemical regeneration of capture absorbents is thus limited by O2 sensitivity and their volatility - especially at DAC conditions where the O2 concentration can exceed that of CO2 by 500-fold and the CO2 concentration in air can be relatively low.SUMMARY

[0007] According to some aspects, DAC systems and methods are disclosed that can facilitate stable and efficient atmospheric CO2 capture and release via a pH-swing mechanism, by reducing loss of the organic redox-active mediator. In the systems and methods of the present disclosure, the hydroxide and the organic redox-active species are separated. This can help eliminate the exposure of the organic redox-active molecule to O2 and high gas flow rates, thereby inhibiting effective loss (e.g. decomposition and / or evaporation) of the organic molecule.

[0008] According to some aspects, a method for operating an alternating dual-electrolyser system for direct air capture (DAC) and release of CO2,includes: (a) supplying a post-capture solution to a reduction compartment of the system, the reduction compartment comprising a cathode of a first electrolyser of the system; (b) supplying an electrolyte solution comprising an organic redox-active molecule to an alternating redox compartment of the system, the redox compartment separated from the reduction compartment by a first cation exchange membrane of the first electrolyser, and the redox compartment comprising an alternating electrode operable alternatingly as an anode of the first electrolyser and as a cathode of a second electrolyser of the system; (c) operating the first electrolyser to oxidize the redox-active molecule in the redox compartment and reduce the post-capture solution in the reduction compartment to produce hydrogen gas and regenerate a hydroxide capture solution for CO2 capture; (d) supplying the hydrogen gas produced in the reduction compartment to an oxidation compartment of the system, the oxidation compartment having an anode of the second electrolyser and separated from the redox compartment by a second cation exchange membrane of the second electrolyser; and (e) operating the second electrolyser to oxidize the hydrogen gas to hydrogen ions in the oxidation compartment and reduce the oxidized redox-active molecule in the redox compartment to regenerate an acidic neutralizing solution for CO2 neutralization and release.

[0009] In some examples, the method further includes repeating (a) to (e) in a plurality of regeneration cycles to repeatedly regenerate the hydroxide capture solution for CO2 capture and the acidic neutralizing solution for CO2 neutralization and release.

[0010] In some examples, the method further includes capturing CO2 with the hydroxide capture solution to produce a post-capture carbonate compound and post-capture solution, supplying the carbonate compound to a neutralization chamber for neutralization and release of the CO2, and supplying the post-capture solution back to the reduction compartment for a subsequent regeneration cycle.

[0011] In some examples, the method further includes supplying the acidic neutralizing solution regenerated in the redox compartment to theneutralization chamber to neutralize and release the CO2 from the carbonate compound and produce the electrolyte solution for supply back to the redox compartment for a subsequent regeneration cycle.

[0012] In some examples, the method further includes supplying the hydroxide capture solution regenerated in the reduction compartment to an air contactor without any of the redox-active molecule.

[0013] In some examples, the organic redox-active molecule is a compound represented by the Formula I:wherein:R1and R2are independently selected from Ci-ioalkyl, Ci-walkenyl, Ci-walkynyl, Ci-ealkyleneCa-iscycloalkyl, Ci-ealkyleneCs-isheterocycloalkyl, C-i-ealkyleneCe- isaryl, Ci-salkyleneCe-isheteroaryl, Cs-iscycloalkyl, Cs-isheterocycloalkyl, Ce- isaryl, Cs-isheteroaryl, C-i-ioalkylenePOs2-and Ci-walkyleneSOs', the aryl, heteroaryl, heterocycloalkyl and cycloalkyl groups are optionally substituted with one or more of halogen or Ci -1 oal ky I , further optionally substituted with one to three P(O)(OR3)2, wherein R3is selected from H or Ci ealkyl .

[0014] According to some aspects, a method for cyclical regeneration of a hydroxide capture solution for direct air capture (DAC) of CO2 and an acidic neutralization solution for neutralization and release of the CO2, includes: (a) operating a first electrolyser to oxidize an organic redox-active molecule in an alternating redox compartment and reduce a post-capture solution in a reduction compartment to regenerate the hydroxide capture solution in the reduction compartment, the reduction compartment separated from the redox compartment by a first cation exchange membrane; and (b) after (a), operating a second electrolyser to oxidize hydrogen in an oxidation compartment and reduce the oxidized redox-active molecule in the redox compartment to regenerate the acidic neutralizing solution in the redox compartment, the redoxcompartment separated from the oxidation compartment by a second cation exchange membrane.

[0015] In some examples, the redox compartment includes an alternating electrode, and (a) includes operating the alternating electrode as an anode of the first electrolyser and (b) includes operating the alternating electrode as a cathode of the second electrolyser.

[0016] According to some aspects, an alternating dual-electrolyser system for direct air capture (DAC) and release of CO2 includes: (a) a reduction compartment comprising a cathode of a first electrolyser for reduction of post- capture solution received in the reduction compartment to produce hydrogen gas and a hydroxide capture solution for supply to an air contactor for CO2 capture; (b) an oxidation compartment for receiving the hydrogen gas produced in the reduction compartment and comprising an anode of a second electrolyser for oxidation of the hydrogen gas to hydrogen ions; and (c) an alternating redox compartment separated from the reduction compartment by a first cation exchange membrane of the first electrolyser and from the oxidation compartment by a second cation exchange membrane of the second electrolyser, the redox compartment for receiving an electrolyte solution comprising an organic redox-active molecule in fluid isolation of the reduction compartment to maintain the redox-active molecule separate from the hydroxide capture solution thereby reducing loss of the redox-active molecule during CO2 capture. The redox compartment has an alternating electrode. The alternating electrode is operable alternatingly as an anode of the first electrolyser for oxidation of the redox-active molecule in the redox compartment to facilitate regeneration of the hydroxide capture solution, and as a cathode of the second electrolyser for reduction of the oxidized redox-active molecule to facilitate regeneration of an acidic neutralizing solution in the redox compartment for supply to a neutralization chamber for CO2 neutralization and release.

[0017] In some examples, the dual-electrolyser system includes a control system having at least one controller configured to cycle operation ofthe dual-electrolyser system between a capture solution mode in which the first electrolyser operates to regenerate the hydroxide capture solution and a neutralizing solution mode in which the second electrolyser operates to regenerate the acidic neutralizing solution.

[0018] In some examples, the hydroxide capture solution is suppliable to 5 the air contactor without any of the redox-active molecule.

[0019] In some examples, the redox-active molecule is a compound represented by the Formula I:I 10 wherein: R1and R2are independently selected from C1-10alkyl, C1-10alkenyl, C1-10alkynyl, C1-6alkyleneC3-15cycloalkyl, C1-6alkyleneC3-15heterocycloalkyl, C1-6alkyleneC6- 15aryl, C1-6alkyleneC6-15heteroaryl, C3-15cycloalkyl, C3-15heterocycloalkyl, C6- 15aryl, C5-15heteroaryl, C1-10alkylenePO32-and C1-10alkyleneSO3-, the aryl, 15 heteroaryl, heterocycloalkyl and cycloalkyl groups are optionally substituted with one or more of halogen or C1-10alkyl, further optionally substituted with one to three P(O)(OR3)2, wherein R3is selected from H or C1-6alkyl.

[0020] According to some aspects, a direct art capture system for CO2 capture and release includes: (a) an air contactor for receiving a hydroxide 20 capture solution for CO2 capture to produce a carbonate compound and post- capture solution; (b) a neutralization chamber for receiving the carbonate compound and an acidic neutralization solution for neutralization and release of CO2 from the carbonate compound to and formation of an electrolyte solution for regeneration of the hydroxide capture solution; (c) an alternating dual- 25 electrolyser system for cyclical regeneration of the hydroxide capture solution and the acidic neutralization solution, the dual-electrolyser system including: (i) a reduction compartment for receiving the post-capture solution and comprising a cathode of a first electrolyser for reduction of the post-capture solution in thereduction compartment to produce hydrogen gas and the hydroxide capture solution for supply to the air contactor; (ii) an oxidation compartment for receiving the hydrogen gas produced in the reduction compartment and comprising an anode of a second electrolyser for oxidation of the hydrogen gas to hydrogen ions; and (iii) an alternating redox compartment separated from the reduction compartment by a first cation exchange membrane of the first electrolyser and from the oxidation compartment by a second cation exchange membrane of the second electrolyser, the redox compartment for receiving the electrolyte solution from the neutralization chamber, the electrolyte solution comprising an organic redox-active molecule in fluid isolation of the reduction compartment to maintain the redox-active molecule separate from the hydroxide capture solution thereby reducing loss of the redox-active molecule during CO2 capture. The redox compartment has an alternating electrode. The alternating electrode operable alternatingly as an anode of the first electrolyser for oxidation of the redox-active molecule in the redox compartment to facilitate regeneration of the hydroxide capture solution in the reduction compartment, and as a cathode of the second electrolyser for reduction of the oxidized redox- active molecule to facilitate regeneration of the acidic neutralizing solution in the redox compartment for supply to the neutralization chamber.

[0021] According to some aspects, an alternating dual-electrolyser system for direct air capture (DAC) and release of CO2 includes: (a) a reduction compartment comprising a cathode of a first electrolyser; (b) an oxidation compartment comprising an anode of a second electrolyser; and (c) an alternating redox compartment separated from the reduction compartment by a first cation exchange membrane of the first electrolyser and from the oxidation compartment by a second cation exchange membrane of the second electrolyser, the redox compartment for receiving an electrolyte solution comprising an organic redox-active molecule in fluid isolation of the reduction compartment, and the redox compartment including an alternating electrode serving as an anode of the first electrolyser for oxidation of the redox-active molecule in the redox compartment to facilitate regeneration of hydroxide capture solution in the reduction compartment, and as a cathode of the secondelectrolyser for reduction of the oxidized redox-active molecule to facilitate regeneration of an acidic neutralizing solution in the redox compartment.

[0022] Other features and advantages of the present disclosure will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the application, are given by way of illustration only and the scope of the claims should not be limited by these embodiments, but should be given the broadest interpretation consistent with the description as a whole.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Certain embodiments of the application will now be described in greater detail with reference to the attached drawings in which:

[0024] Figure 1 (a) is a schematic showing an example direct air capture (DAC) system and method to regenerate DAC solutions and release CO2 using a dual-electrolyser system.

[0025] Figure 1 (b) is a schematic showing two example alternating electrolysers (E1 and E2) of the DAC system utilizing an organic (redox-active) molecule (OM).

[0026] Figure 1 (c) is a schematic showing an example organic redox- active molecule (viologens): methyl-substituted viologen (MV), 1 ,1’- bis(3sulfonatopropyl)-4,4’-bipyridinium (SPRV), 1 , 1 ’-bis(3-phosphonopropyl)- [4,4’-bipyridine]-1 ,1’diium (BPPV) and benzyl-substituted viologen (BV) undergoing oxidation and reduction to store and release ions.

[0027] Figure 2 shows the1H NMR spectra of an example organic redox- active molecule BPPV in DMSO. The peak of DMSO solvent is at 2.6 ppm. The corresponding chemical bonds were labeled, indicating each individual peak in the spectrum.

[0028] Figure 3 shows the1H NMR spectra of an example organic redox- active molecule SPRV in DMSO. The peak of DMSO solvent is at 2.6 ppm. Thecorresponding chemical bonds were labeled, indicating each individual peak in the spectrum.

[0029] Figure 4(a) shows the species concentration (mmol) of CO2 (aq), HCO3; CO32; H+, and OH+present in a neutralization solution.

[0030] Figure 4(b) shows the species concentration (mmol) of CO2 (aq), HCO3; CO32; H+, and OH+present in a capture solution.

[0031] Figure 5 shows a first image (left-a) of the colored immobilization film formation onto a carbon electrode in the dual-electrolyser system, using example organic redox-active molecule BV at 0.1 M in 1 M NaCI aqueous electrolyte, and a second image (right-b) of the original carbon electrode.

[0032] Figure 6(a) shows the results of density functional theory (DFT)- calculated binding energy (eV) of example organic redox-active molecules (viologens with different substituents).

[0033] Figure 6(b) shows the results of cyclic voltammograms of first electron transfer redox pairs of example organic redox-active molecules MV, SPRV and BPPV at 0.02 M in 1 M NaCI aqueous electrolyte (H-cell configuration).

[0034] Figure 6(c) shows the results of reduction and oxidation charge of example organic redox-active molecules MV, SPRV and BPPV at 0.1 M in 1 M NaCI aqueous electrolyte during dual-electrolyser system operation.

[0035] Figure 6(d) shows the summary of the limiting current densities (mA cm'2) of example organic redox-active molecules MV, SPRV and BPPV at 0.1 M in 1 M NaCI aqueous electrolyte in the dual-electrolyser system operation under cycle time of 2, 20, 60, and 120 s.

[0036] Figure 7(a) shows the dual-electrolyser system performance (current density mA cm'2) using example organic redox-active molecule MV at 0.1 M in 1 M NaCI aqueous electrolyte under cycle time of 2 s.

[0037] Figure 7(b) shows the dual-electrolyser system performance (current density mA cm-2) using example organic redox-active molecule MV at 0.1 M in 1 M NaCI aqueous electrolyte under cycle time of 20 s.

[0038] Figure 7(c) shows the dual-electrolyser system performance (current density mA cm-2) using example organic redox-active molecule MV at 0.1 M in 1 M NaCI aqueous electrolyte under cycle time of 60 s.

[0039] Figure 7(d) shows the dual-electrolyser system performance (current density mA cm'2) using example organic redox-active molecule MV at 0.1 M in 1 M NaCI aqueous electrolyte under cycle time of 120 s.

[0040] Figure 8 is a schematic illustrating the limiting oxidation reaction of example organic redox-active molecule MV.

[0041] Figure 9(a) shows the dual-electrolyser system performance (current density mA cm'2) using example organic redox-active molecule SPRV at 0.1 M in 1 M NaCI aqueous electrolyte under cycle time of 2 s.

[0042] Figure 9(b) shows the dual-electrolyser system performance (current density mA cm'2) using example organic redox-active molecule SPRV at 0.1 M in 1 M NaCI aqueous electrolyte under cycle time of 20 s.

[0043] Figure 9(c) shows the dual-electrolyser system performance (current density mA cm'2) using example organic redox-active molecule SPRV at 0.1 M in 1 M NaCI aqueous electrolyte under cycle time of 60 s.

[0044] Figure 9(d) shows the dual-electrolyser system performance (current density mA cm'2) using example organic redox-active molecule SPRV at 0.1 M in 1 M NaCI aqueous electrolyte under cycle time of 120 s.

[0045] Figure 10(a) shows the dual-electrolyser system performance (current density mA cm'2) using example organic redox-active molecule BPPV at 0.1 M in 1 M NaCI aqueous electrolyte under cycle time of 2 s.

[0046] Figure 10(b) shows the dual-electrolyser system performance (current density mA cm'2) using example organic redox-active molecule BPPV at 0.1 M in 1 M NaCI aqueous electrolyte under cycle time of 20 s.

[0047] Figure 10(c) shows the dual-electrolyser system performance (current density mA cm-2) using example organic redox-active molecule BPPV at 0.1 M in 1 M NaCI aqueous electrolyte under cycle time of 60 s.

[0048] Figure 10(d) shows the dual-electrolyser system performance (current density mA cm-2) using example organic redox-active molecule BPPV at 0.1 M in 1 M NaCI aqueous electrolyte under cycle time of 120 s.

[0049] Figure 11 is a schematic illustrating the effective reduction and oxidation reaction of example organic redox-active molecules BPPV and SPRV.

[0050] Figure 12(a) shows the results of the Fourier-transform infrared spectroscopy (FT-IR) analysis of example organic redox-active molecules BPPV, 4,4’-bipyridine, and diethyl(3-bromopropyl)phosphonate.

[0051] Figure 12(b) shows the results of the FT-IR analysis of example organic redox-active molecules SPRV, 4,4’-bipyridine, and 1 ,3’- propanesultone.

[0052] Figure 13(a) shows the results of the high-pressure ion chromatography analysis of 0.5 mM PCs2' standard solution and 0.5 mM example BPPV electrolyte.

[0053] Figure 13(b) shows the results of the high-pressure ion chromatography analysis of 0.5 mM SOs- standard solution and 0.5 mM example SPRV electrolyte.

[0054] Figure 14(a) is a schematic illustrating a neutral overall charge of example organic redox-active molecule SPRV permeating through the sulfonate-functionalized cation exchange membrane.

[0055] Figure 14(b) is a schematic illustrating an overall 2 negatively charged example organic redox-active molecule BPPV repelling by the sulfonate-functionalized cation exchange membrane.

[0056] Figure 15(a) shows the results of the UV-visible spectrophotometry analysis for permeability of example organic redox-active molecule BPPV at concentrations of 5, 10, 20, 40, 50 pmol / L.

[0057] Figure 15(b) shows the calibration line and measured concentrations of example organic redox-active molecule BPPV.

[0058] Figure 15(c) shows the results of the UV-visible spectra of diluted concentrations of example organic redox-active molecule BPPV at receiving compartment after 2, 4, and 6 days.

[0059] Figure 15(d) shows the calibration line estimating the concentration of the example organic redox-active molecule BPPV cross over at receiving compartment after 2, 4, and 6 days.

[0060] Figure 16(a) shows the results of the UV-visible spectrophotometry analysis for permeability of example organic redox-active molecule SRPV at concentrations of 5, 10, 20, 40, 50 pmol / L.

[0061] Figure 16(b) shows the calibration line and measured concentrations of example organic redox-active molecule SPRV.

[0062] Figure 16(c) shows the results of the UV-visible spectra of diluted concentrations of example organic redox-active molecule SPRV at receiving compartment after 2, 4, and 6 days.

[0063] Figure 16(d) shows the calibration line estimating the concentration of the example organic redox-active molecule SPRV cross over at receiving compartment after 2, 4, and 6 days.

[0064] Figure 17(a) shows cyclic voltammograms of two electron transfer redox pairs of example organic redox-active molecule BPPV at 0.02 M in 1 M NaCI aqueous electrolyte (H-cell configuration).

[0065] Figure 17(b) shows cyclic voltammograms of example organic redox-active molecule BPPV at 0.02 M in 1 M NaCI aqueous electrolyte in electrolyte pH values of 2, 3 and 7(H-cell configuration).

[0066] Figure 17(c) shows linear scan voltammetry of the second electrolyser (E2) with various concentrations of example organic redox active molecule BPPV in 1 M example LiCI aqueous electrolyte.

[0067] Figure 18(a) shows the results of the linear scan voltammetry study of the dual-electrolyser system using 0.1 M of example organic redox active molecule BPPV and 1 M LiCI with electrolyte flow channel thickness of 0.5 mm and 1 mm.

[0068] Figure 18(b) shows the results of the linear scan voltammetry study of the dual-electrolyser system using 0.1 M of example organic redox active molecule BPPV with 1 M LiCI and electrolyte flow rate of 10, 20 and 30 ml min'1.

[0069] Figure 18(c) shows the results of the linear scan voltammetry study of the dual-electrolyser system using example electrolyte of 0.2 M organic redox active molecule BPPV with different lithium concentrations and additional solid carbonate.

[0070] Figure 19(a) shows the results of the linear scan voltammetry studies of the dual-electrolyser system using example organic redox active molecule BPPV at 0.1 M and 1 M LiCI with various catalyst binder materials.

[0071] Figure 19(b) shows the results of the linear scan voltammetry studies of the dual-electrolyser system using example organic redox active molecule BPPV at 0.1 M with 1 M LiCI with various catalyst materials.

[0072] Figure 19(c) shows the results of the linear scan voltammetry studies of the dual-electrolyser system using example organic redox active molecule BPPV at 0.1 M with 1 M LiCI and activated porous carbon nanoparticle loaded at various densities.

[0073] Figure 20(a) shows the scanning electron microscopy (SEM) imaging of the bare carbon electrode with the scale bar of 10 pm and 100 pm.

[0074] Figure 20(b) shows the scanning electron microscopy (SEM) imaging of the activated porous carbon nanoparticle coated carbon electrode with the scale bar of 10 pm and 100 pm.

[0075] Figure 21 (a) is a schematic showing operation and measurement for an example dual-electrolyser system.

[0076] Figure 21 (b) shows system voltage of the dual-electrolyser system operation (both electrolysers operated at 40 mA cm'2).

[0077] Figure 21 (c) shows the pH of regenerated capture solution and the current efficiency profile of the first electrolyser of the system.

[0078] Figure 21 (d) shows the pH of the regenerated capture solution and the total amount of CO2 captured from an example stream containing 1 % v / v CO2 and 99% v / v air.

[0079] Figure 21 (e) shows the pH of the neutralization solution and the total amount of CO2 released during operation of the DAC system.

[0080] Figure 22 shows the setup for an example dual-electrolyser system.

[0081] Figure 23 shows theoretical capture solution pH VS experimental pH in example dual-electrolyser system operation.

[0082] Figure 24(a) is a schematic of CO2 capture demonstration setup of an example ultra-diluted (1 % v / v CO2 + 99% v / v air) CO2 capture experiment.

[0083] Figure 24(b) shows CO2 capture rate (seem) monitored by flow meter for about 2.5 hours.

[0084] Figure 25(a) is a schematic of an example CO2 capture setup.

[0085] Figure 25(b) shows CO2 capture rate (ppm) and total amount of CO2 (mmol) captured profile monitored by flow meter for 20 h.

[0086] Figure 26(a) shows1H NMR spectra of capture and neutralization solutions before and after 1 round, 3-hour reaction in DMSO.

[0087] Figure 26(b) show the results of the quantification of example redox active organic molecule BPPV in the capture solution (pH 13.3) after 1 round operation.

[0088] Figure 27 shows cyclic voltammetry of DI water and diluted example redox active organic molecule BPPV solution at room temperature.

[0089] Figure 28(a) shows the summary of the voltage and net energy consumption of an example dual-electrolyser system versus current densities of 10 to 120 mA cm'2.

[0090] Figure 28(b) shows the voltage of the example dual- electrolyser system of fig. 28(a) with current densities of 10 to 120 mA cm'2measured for 300 s.

[0091] Figure 29 shows the voltage of an example dual-electrolyser system during 67 rounds (201 h) of prolonged operation (both electrolysers operated at 40 mA cm'2).

[0092] Figure 30(a) shows1H NMR spectra of example redox active molecule BPPV in DMSO before the prolonged operation of an example dual- electrolyser system.

[0093] Figure 30(b) shows1H NMR spectra of capture solution (pH 13.3) in DMSO after the 201 h prolonged operation of an example dual-electrolyser system.

[0094] Other features and advantages of the present disclosure will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the disclosure, are given by way of illustration only and the scope of the claims should not be limited by these embodiments, but should be given the broadest interpretation consistent with the description as a whole.DETAILED DESCRIPTION

[0095] Unless otherwise indicated, the definitions and embodiments described in this and other sections are intended to be applicable to all embodiments and aspects of the present disclosure herein described for which they are suitable as would be understood by a person skilled in the art.

[0096] The term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and / or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and / or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives.

[0097] Terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.

[0098] As used in this application, the singular forms “a”, “an” and “the” include plural references unless the content clearly dictates otherwise.

[0099] In embodiments comprising an “additional” or “second” component, the second component as used herein is chemically different from the other components or first component. A “third” component is different from the other, first, and second components, and further enumerated or “additional” components are similarly different.

[0100] The term “and / or” as used herein means that the listed items are present, or used, individually or in combination. In effect, this term means that “at least one of” or “one or more” of the listed items is used or present.

[0101] The term “carbonate” or “carbonate compound” as used herein means a compound containing the carbonate group [COs]2-. The terms encompass both carbonate / bicarbonate mixtures and compounds containingsolely the carbonate. The term “bicarbonate” is defined as a compound containing the bicarbonate group [HCOs]'. The carbonate compound of the present disclosure can be a solid or dissolved in a solvent. In some embodiments, the carbonate compound can be precipitated to obtain a solid.

[0102] The term “redox-active species” or “redox-active molecule” as used herein refers to any molecule or compound or a portion thereof (e.g., a molecular or functional moiety of a molecular or compound) that can be oxidized and / or reduced during or upon electrical stimulation (e.g., during or upon application of an electrical potential), or can undergo a Faradaic reaction. For example, a redox species comprises one or more molecular moieties that accept and / or donate one or more electrons depending on its redox state. Thus, the redox species can form part (e.g., a molecular moiety) of a small molecule, a compound, a polymer molecule, or can exist as an individual molecule or compound.

[0103] The term “alkyl” as used herein, whether it is used alone or as part of another group, means straight or branched chain, saturated alkyl groups. The number of carbon atoms that are possible in the referenced alkyl group are indicated by the prefix “Cni-n2”. For example, the term Ci -1 oal kyl means an alkyl group having 1 , 2, 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms. All alkyl groups are optionally fluoro-substitued unless otherwise indicated.

[0104] The term “alkylene”, whether it is used alone or as part of another group, means straight or branched chain, saturated alkylene group, that is, a saturated carbon chain that contains substituents on two of its ends. The number of carbon atoms that are possible in the referenced alkylene group are indicated by the prefix “Cni-n2”. For example, the term C2-6alkylene means an alkylene group having 2, 3, 4, 5 or 6 carbon atoms. All alkylene groups are optionally fluoro-substitued unless otherwise indicated.

[0105] The term “alkenyl” as used herein, whether it is used alone or as part of another group, means straight or branched chain, unsaturated alkyl groups containing at least one double bond. The number of carbon atoms that are possible in the referenced alkylene group are indicated by the prefix “Cni-n2”. For example, the term C2-ealkenyl means an alkenyl group having 2, 3, 4, 5 or 6 carbon atoms and at least one double bond. All alkenyl groups are optionally fluoro-substitued unless otherwise indicated.

[0106] The term “alkynyl” as used herein, whether it is used alone or as part of another group, means straight or branched chain, unsaturated alkynyl groups containing at least one triple bond. The number of carbon atoms that are possible in the referenced alkyl group are indicated by the prefix “Cni-n2”. For example, the term C2-ealkynyl means an alkynyl group having 2, 3, 4, 5 or 6 carbon atoms.

[0107] The term “aryl” as used herein, whether it is used alone or as part of another group, refers to carbocyclic groups containing at least one aromatic ring with 6 to 15 carbon atoms.

[0108] The term “cycloalkyl,” as used herein, whether it is used alone or as part of another group, means a saturated carbocyclic group containing one or more rings. The number of carbon atoms that are possible in the referenced cycloalkyl group are indicated by the numerical prefix “Cni-n2”. For example, the term Cs-wcycloalkyl means a cycloalkyl group having 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms.

[0109] The term “heteroaryl” as used herein, whether it is used alone or as part of another group, refers to cyclic groups containing at least one heteroaromatic ring in which one or more of the atoms are a heteroatom selected from O, S and N. When a heteroaryl group contains the prefix Cni-n2 this prefix indicates the number of carbon atoms in the corresponding carbocyclic group, in which one or more, suitably 1 to 5, of the ring atoms is replaced with a heteroatom as defined above.

[0110] The term “heterocycloalkyl” as used herein, whether it is used alone or as part of another group, refers to cyclic groups containing at least one non-aromatic ring in which one or more of the atoms are a heteroatom selected from O, S and N. Heterocycloalkyl groups are either saturated or unsaturated (i.e. contain one or more double bonds). When a heterocycloalkyl groupcontains the prefix Cni-n2 this prefix indicates the number of carbon atoms in the corresponding carbocyclic group, in which one or more, suitably 1 to 5, of the ring atoms is replaced with a heteroatom as defined above.

[0111] All cyclic groups, including aryl, heteroaryl, cycloalkyl and heterocycloalkyl groups, contain one (i.e. are monocyclic) or more than one ring (i.e. are polycyclic). When a cyclic group contains more than one ring, the rings may be fused, bridged or spirofused.

[0112] The term “benzofused” as used herein refers to a polycyclic group in which a benzene ring is fused with another ring.

[0113] A first ring being “fused” with a second ring means the first ring and the second ring share two adjacent atoms there between.

[0114] A first ring being “bridged” with a second ring means the first ring and the second ring share two non-adjacent atoms there between.

[0115] A first ring being “spirofused” with a second ring means the first ring and the second ring share one atom there between.

[0116] The terms “halo” or “halogen” as used herein, whether it is used alone or as part of another group, refers to a halogen atom and includes fluoro, chloro, bromo and iodo.

[0117] Referring to Figure 1a, an example direct air capture (DAC) system 100 for capture and release of CO2 is shown schematically. In the example illustrated, the direct air capture system 100 includes an air contactor 102 for receiving a hydroxide capture solution for direct air capture of CO2 to produce a carbonate compound and post-capture solution. The DAC system 100 further includes a neutralization chamber (e.g. tank) 104 for receiving the carbonate compound (e.g. through a carbonate compound supply line) and an acidic neutralization solution for neutralization and release of CO2 from the carbonate compound and formation of an electrolyte solution for regeneration of the hydroxide capture solution.

[0118] In the example illustrated, the DAC system 100 further includes an alternating dual-electrolyser system 110 for cyclical regeneration of the hydroxide capture solution and the acidic neutralization solution. In the example illustrated, the dual-electrolyser system 110 includes a reduction (first) compartment 112 for receiving the post-capture solution. In the example illustrated, the reduction compartment 112 receives the post-capture solution from the air contactor 102 (e.g. through a post-capture solution return line). The reduction compartment 112 includes a cathode 114 of a first electrolyser 116 (Electrolyser-1 or E1) for reduction of the post-capture solution in the reduction compartment 112 to produce (i) hydrogen gas H2(g) and (ii) the hydroxide capture solution for supply to the air contactor 102 (e.g. through a capture solution supply line).

[0119] In the example illustrated, the dual-electrolyser system 110 further includes an oxidation (second) compartment 122 for receiving the hydrogen gas produced in the reduction compartment 112 (e.g. through a hydrogen gas supply line). In the example illustrated, the oxidation compartment includes an anode 124 of a second electrolyser 126 (Electrolyser- 2 or E2) for oxidation of the hydrogen gas to hydrogen ions.

[0120] In the example illustrated, the dual-electrolyser system 110 further includes an alternating redox (third) compartment 132 between the reduction compartment 112 and the oxidation compartment 122. In the example illustrated, the redox compartment 132 is separated from the reduction compartment by a first cation exchange membrane 118 of the first electrolyser 116 and from the oxidation compartment 122 by a second cation exchange membrane 128 of the second electrolyser 126. In the example illustrated, redox compartment 132 receives the electrolyte solution from the neutralization chamber 104 (e.g. through an electrolyte solution return line).

[0121] In the example illustrated, the electrolyte solution comprises an organic redox-active molecule (OM). The organic redox-active molecule can undergo reversible oxidation and reduction. The redox-active molecule is kept in fluid isolation of the reduction compartment to maintain the redox-activemolecule separate from the hydroxide capture solution, which is suppliable to the air contactor 102 without any of the redox-active molecule. This can help reduce loss (e.g. decomposition and / or evaporation) of the redox-active molecule during CO2 capture, for example, by reducing exposure to oxygen O2 and high gas flow rates at the air contactor 102.

[0122] In the example illustrated, the redox compartment 132 includes an alternating electrode 134. The organic redox-active molecule can alternate between oxidation and reduction on the alternating electrode (e.g. to undergo oxidation by the first electrolyser and reduction by the second electrolyser). In the example illustrated, the alternating electrode 134 is operable alternatingly as an anode of the first electrolyser 116 for oxidation of the redox-active molecule (from OM to OM+) in the redox compartment 132 to facilitate regeneration of the hydroxide capture solution in the reduction compartment 112, and as a cathode of the second electrolyser 126 for reduction of the oxidized redox-active molecule (from OM+to OM) to facilitate regeneration of the acidic neutralizing solution in the redox compartment 132 for supply to the neutralization chamber 104 (e.g. through a neutralizing solution supply line).

[0123] In some examples, the DAC system 100 can further include a control system 138 including at least one controller (e.g. comprising one or more processors) configured to cycle operation of the dual-electrolyser system 110 between a capture solution mode (see e.g. left in Figure 21a) in which the first electrolyser 116 operates to regenerate the hydroxide capture solution and a neutralizing solution mode (see e.g. right in Figure 21a) in which the second electrolyser 126 operates to regenerate the acidic neutralizing solution.

[0124] In operation, the post-capture solution is supplied to the reduction compartment 112. The electrolyte solution comprising the redox active molecule is supplied to the redox compartment 132. The first electrolyser 116 is operated to oxidize the redox active molecule in the redox compartment 132 and reduce the post-capture solution in the reduction compartment 112 to produce hydrogen and regenerate the hydroxide capture solution. The hydroxide capture solution regenerated in the reduction compartment 112 issupplied to the air contactor 102, without any of the redox active molecule, which remains in fluid isolation of the reduction compartment 112 and hydroxide capture solution throughout the process.

[0125] CO2 is captured at the air contactor 102 by the hydroxide capture solution to produce post-capture carbonate compound and the post-capture solution. The carbonate compound is supplied to the neutralization chamber 104 for neutralization and release of the CO2, and the post-capture solution is supplied to the reduction compartment 112 for a subsequent regeneration cycle.

[0126] The hydrogen gas produced in the reduction compartment 112 is supplied to the oxidation compartment 122. The second electrolyser 126 is operated to oxidize the hydrogen gas to hydrogen ions in the oxidation compartment 122 and reduce the oxidized redox active molecule (OM+) in the redox compartment 132 to regenerate the acidic neutralizing solution.

[0127] The acidic neutralizing solution regenerated in the redox compartment 132 is supplied to the neutralization chamber 104 to neutralize and release the CCte from the carbonate compound and produce the electrolyte solution, which is supplied back to the redox compartment 132 for a subsequent regeneration cycle.

[0128] The above process can be repeated in a plurality of regeneration cycles to repeatedly regenerate the hydroxide capture solution for CO2 capture and the acidic neutralizing solution for CO2 neutralization and release.

[0129] In some embodiments, the redox-active molecule is a compound represented by the Formula I:wherein:R1and R2are independently selected from C1-10alkyl, C1-10alkenyl, C1-10alkynyl, C1-6alkyleneC3-15cycloalkyl, C1-6alkyleneC3-15heterocycloalkyl, C1-6alkyleneC6- 15aryl, C1-6alkyleneC6-15heteroaryl, C3-15cycloalkyl, C3-15heterocycloalkyl, C6- 15aryl, C5-15heteroaryl, C1-10alkylenePO32-and C1-10alkyleneSO3-, the aryl, heteroaryl, heterocycloalkyl and cycloalkyl groups are optionally substituted 5 with one or more of halogen or C1-10alkyl, further optionally substituted with one to three P(O)(OR3)2, wherein R3is selected from H or C1-6alkyl.

[0130] In some embodiments, R1and R2are independently selected from C1-8alkyl, C1-8alkenyl, C1-8alkynyl, C1-6alkyleneC6-15cycloalkyl, C1- 6alkyleneC6-15heterocycloalkyl, C1-6alkyleneC6-15aryl, C1-6alkyleneC6- 10 15heteroaryl, C3-15cycloalkyl, C3-15heterocycloalkyl, C6-15aryl, C5-15heteroaryl, C1- 8alkylenePO32-and C1-8alkyleneSO3-, the aryl, heteroaryl, heterocycloalkyl and cycloalkyl groups are optionally substituted with one or more of halogen or C1- 10alkyl, further optionally substituted with one to three P(O)(OR3)2, wherein R3is selected from H or C1-6alkyl. 15

[0131] In some embodiments, R1and R2are independently selected from C1-6alkyl, C1-6alkyleneC6-15cycloalkyl, C1-6alkyleneC6-15heterocycloalkyl, C1-6alkyleneC6-15aryl, C1-6alkyleneC6-15heteroaryl, C1-6alkylenePO32-and C1- 6alkyleneSO3-, the aryl, heteroaryl, heterocycloalkyl and cycloalkyl groups are optionally substituted with one or more of halogen or C1-10alkyl, further 20 optionally substituted with one to three P(O)(OR3)2, wherein R3is selected from H or C1-6alkyl.

[0132] In some embodiments, R1and R2are independently selected from C1-4alkyl, C1-6alkyleneC6-15aryl, C1-4alkyleneC6-15heteroaryl, C1- 4alkylenePO32-and C1-4alkyleneSO3-, the aryl and heteroaryl are optionally 25 substituted with one or more of halogen or C1-10alkyl or halogen, further optionally substituted with one to three P(O)(OR3)2, wherein R3is selected from H or C1-6alkyl.

[0133] In some embodiments, R1and R2are independently selected from CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CH2CH2CH2CH3, C(CH3)3, 30 CH(CH3)CH2CH3 and CH2CH(CH3)2.

[0134] In some embodiments, R1and R2are independently selected from C1-6alkyleneC6-15aryl, the aryl is optionally substituted with one or more of halogen or C1-6alkyl, further optionally substituted with one to three P(O)(OR3)2, wherein R3is selected from H or C1-4alkyl. Examples of C1-6alkyleneC6-15aryl include but are not limited to C1-4alkylenephenyl, C1-4alkylenenaphthyl, C1- 5 4alkylenephenalenyl, C1-4alkyleneanthryl, C1-4alkylenephenanthryl, C1-4alkylenedihydronaphthyl, C1-4alkyleneindenyl, C1-4alkyleneindanyl and the like. In some embodiments, R1and R2are independently selected from C1- 4alkylenephenyl and C1-4alkylenephenalenyl, the phenyl and phenalenyl are optionally substituted with one C1-4alkyl, further optionally substituted with one 10 P(O)(OH)2.

[0135] In some embodiments, R1and R2are independently selected from C1-4alkyleneC6-15heteroaryl, the heteroaryl is optionally substituted with one or more of halogen or C1-6alkyl, further optionally substituted with one to three P(O)(OR3)2, wherein R3is selected from H or C1-4alkyl. Examples of C1- 15 4alkyleneC6-15heteroaryl include but are not limited to C1-4alkylenepyrazinyl, C1- 4alkylenepyrazolyl, C1-4alkylenepyridazinyl, C1-4alkylenepyridyl, C1- 4alkylenepyrimidinyl, C1-4alkylenetriazinyl, C1-4alkylenebenzimidazolyl, C1- 4alkyleneindazolyl, C1-4alkyleneindolyl, C1-4alkyleneisoindolyl, C1- 4alkylenequinolinyl, C1-4alkyleneisoquinolinyl, C1-4alkylenequinazolinyl, C1- 20 4alkylenequinoxaline and the like. In some embodiments, R1and R2are independently selected from C1-4alkyleneindolyl, the indolyl is optionally substituted with one C1-4alkyl, further optionally substituted with one P(O)(OH)2.

[0136] In some embodiments, R1and R2are independently selected from CH3, C1alkylephenyl, C3alkylenePO32-, C3alkyleneSO3-, 25 C1alkylenephenalenylC1alkylP(O)(OH)2, C2alkyleneindolyl, and C1alkylenephenalenyl .

[0137] In some embodiments, R1and R2are both CH3.

[0138] In some embodiments, R1and R2are both C1alkylenephenyl.

[0139] In some embodiments, R1and R2are both C3alkylenePO32-. 30- 24 -

[0140] In some embodiments, R1and R2are both CsalkyleneSOs'.

[0141] In some embodiments, R1and R2are both CialkylenephenalenylCialkylP(O)(OH)2.

[0142] In some embodiments, R1and R2are both C2alkyleneindolyl.

[0143] In some embodiments, R1and R2are both Cialkylenephenalenyl.

[0144] In some embodiments, the compound represented by the Formula I is selected from:1-7.

[0145] The redox-active molecule can include any molecule that is able to absorb and release anions during the redox reaction. Examples of suitableorganic redox-active molecules include but are not limited to phenazines, such as dimethylphenazine, tetrathiafulvalene, 4-hydroxy-2,2,6,6-tetramethyl- piperdin-1-oxyl, (ferrocenylmethyl)- trimethylammonium and the like. As such, in some embodiments, the organic redox-active molecule is selected from phenazine, tetrathiafulvalene, 4-hydroxy-2,2,6,6-tetramethyl-piperdin-1 -oxyl and (ferrocenylmethyl)- trimethylammonium.

[0146] In some embodiments, the organic redox active molecule can be present in the electrolyte solution at a concentration of about 0.02 M to about 10 M. In some embodiments, the organic redox active molecule can be present in the electrolyte solution at a concentration of about 0.02 M, about 0.1 M, about 0.2 M, about 0.3 M, about 0.4 M, about 0.5 M, about 1 M, about 1 .5 M, about 2 M, about 3 M, about 5 M, about 6 M, about 7 M, about 8 M, about 9 M, or about 10 M and values therebetween. In some embodiments, the organic redox active molecule is present in the electrolyte solution at a concentration of about 0.1 M. In some embodiments, the organic redox active molecule is present in the electrolyte solution at a concentration of about 0.2 M.

[0147] In some embodiments, the binding energy of the organic redox- active molecule to the alternating electrode can be between about -1 to about - 2.5. In some embodiments, the binding energy of the organic redox-active molecule to the alternating electrode can be between about -1.2 to about -2, about -1 .4 to -1 .6, about -1 .4, about -1 .5, about -1 .6, or about -1 .8 and values therebetween.

[0148] In some embodiments, the organic redox active molecule can have a difference in reductive and oxidative peak potentials (Ered-oxi) of about 20 mV to about 150 mV. In some embodiments, the organic redox active molecule can have a difference in reductive and oxidative peak potentials (Ered- oxi) of about 30 mV, about 40 mV, about 50 mV, about 75 mV, about 100 mV, or about 125 mV, and values therebetween.

[0149] In some embodiments, the organic redox active molecule can have a cation exchange membrane permeability of about 1 x 10'8cm2s'1to 10 x 10'12cm2s'1. In some embodiments, the organic redox active molecule canhave a cation exchange membrane permeability of about 1 .5 x 1 O'10cm2s'1to about 8 x 10'10cm2s'1, about 2 x 10'10cm2s'1, about 3 x 10'10cm2s'1, about 4 x 1 O'10cm2s'1, about 5 x 1 O'10cm2s'1, about 6 x 1 O'10cm2s'1, or about 7 x 10'10cm2s'1, and values therebetween. In some embodiments, the organic redox active molecule can have a cation exchange membrane permeability of about 2.63 x 10'10cm2s'1.

[0150] In some embodiments, the electrolyte solution comprises a supporting electrolyte with a cationic portion and an anionic portion. In some embodiments, the organic redox active molecule is dissolved in the solution of the electrolyte at about 80% to about 100%, about 85%, about 90%, about 95%, or about 99%, and values therebetween. The solvent of the electrolyte solution can be any solvent that is non-reactive with the organic redox active molecule and permits the organic redox active molecule to efficiently undergo redox reactions. In some embodiments, the solvent of the electrolyte is selected from aqueous-based, non-aqueous (organic), protic or aprotic, and polar or non- polar solvent. In some embodiments, the aqueous-based solvent is selected from water, and water in admixture with a water-soluble co-solvent. In some embodiments, the protic organic solvent is selected from alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol, t-butanol, n-pentanol, isopentanol, 3-pentanol, neopentyl alcohol, n-hexanol, 2- hexanol, 3-hexanol, 3-methyl-1 -pentanol, 3, 3-dimethyl-1 -butanol, isohexanol, and cyclohexanol. In some embodiments, the polar aprotic solvent is selected from nitrile solvents (e.g., acetonitrile, propionitrile, and butyronitrile), sulfoxide solvents (e.g., dimethyl sulfoxide, ethyl methyl sulfoxide, diethyl sulfoxide, methyl propyl sulfoxide, and ethyl propyl sulfoxide), sulfone solvents (e.g., methyl sulfone, ethyl methyl sulfone, methyl phenyl sulfone, methyl isopropyl sulfone, propyl sulfone, butyl sulfone, tetramethylene sulfone, i.e., sulfolane), amide solvents (e.g., N,N-dimethylformamide, N,N-diethylformamide, acetamide, dimethylacetamide, and N-methylpyrrolidone), ether solvents (e.g., diethyl ether, 1 ,2-dimethoxyethane, 1 ,2-diethoxyethane, 1 ,3-dioxolane, and tetrahydrofuran), carbonate solvents (e.g., propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, fluorocarbonatesolvents, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate), organochloride solvents (e.g., methylene chloride, chloroform, 1 ,1 ,- trichloroethane), ketone solvents (e.g., acetone and 2-butanone), and ester solvents (e.g., 1 ,4-butyrolactone, ethylacetate, methylpropionate, ethylpropionate, and the formates, such as methyl formate and ethyl formate). In some embodiments, the polar inorganic solvent is selected from supercritical carbon dioxide, carbon disulfide, carbon tetrachloride, ammonia, and sulfuryl chloride fluoride. In some embodiments, the non-polar solvent is selected from the liquid hydrocarbons, such as the pentanes, hexanes, heptanes, octanes, pentenes, hexenes, heptenes, octenes, benzene, toluenes, and xylenes. In some embodiments, the solvent may be an ionic liquid, either alone or in admixture with a non-ionic liquid solvent. In some embodiments, the solvent is an aqueous-based solvent. In some embodiments, the aqueous-based solvent is water.

[0151] In some embodiments, the supporting electrolyte comprises a salt compound that contains a cationic portion selected from alkali species in combination with an anionic portion selected from halide, phosphate, perchlorate and sulfate species. In some embodiments, the supporting electrolyte is selected from lithium halides (e.g., LiF, LiCI, LiBr, Lil), sodium halides (e.g., NaF, NaCI, NaBr, Nal), potassium halides (e.g., KF, KCI, KBr, KI), rubidium halides (e.g., RbF, RbCI, RbBr, Rbl), lithium phosphate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, sodium perchlorate, and lithium sulfate. In some embodiments, the supporting electrolyte is selected from lithium halides. In some embodiments, the supporting electrolyte is LiCI.

[0152] In some embodiments, the supporting electrolyte can be present in the electrolyte solution at a concentration of about 0.01 M to about 10 M. In some embodiments, the supporting electrolyte can be present in the electrolyte solution at a concentration of about 0.01 M, about 0.05 M, about 0.1 M, about 0.2 M, about 0.3 M, about 0.4 M, about 0.5 M, about 1 .0 M, about 1 ,5M, about2 M, about 3 M, about 4 M, about 5 M, about 6 M, about 7 M, about 8 M, about 9 M, or about 10 M, and values therebetween. In some embodiments, the supporting electrolyte can be present in the electrolyte solution at a concentration of about 1 M. In some embodiments, the supporting electrolyte can be present in the electrolyte solution at a concentration of about 2 M.

[0153] In some embodiments, the electrolyte solution can have a flow channel thickness of about 0.1 mm to about 5 mm. In some embodiments, the electrolyte solution can have a flow channel thickness of about 0.1 mm to about 2.5 mm, about 0.25 mm, about 0.5 mm, about 1 mm, about 1 .5 mm, or about 2 mm. In some embodiments, the electrolyte solution can have a flow channel thickness of about 0.5 mm.

[0154] In some embodiments, the electrolyte solution can have a flow rate of about 1 ml min'1to about 50 ml min'1. In some embodiments, the electrolyte solution can have a flow rate of about 2 ml min'1to about 40 ml min'1, about 5 ml min'1, about 10 ml min'1, about 25 ml min'1, about 30 ml min'1, or about 35 ml min'1, and values therebetween. In some embodiments, the electrolyte solution can have a flow rate of about 10 ml min'1.

[0155] In some examples, in the first electrolyser, the electrolyte solution comprises a solution of organic redox active molecule (OM) and the supporting electrolyte having a cationic portion and an anionic portion (X+Y'). The electrolyte solution is supplied to the redox compartment and water is supplied to the reduction compartment. Hydrogen evolution reaction (HER) takes place at the cathode, and OM is oxidized to OM+at the anode (Eq. 1). The dissolved Y' are attracted by OM+and X+cross the first cation exchange membrane to produce the hydroxide (XOH) capture solution. The hydroxide capture solution reacts with CO2 to produce X2CO3 and H2O (Eq. 2). The X2CO3 is fed to the neutralization chamber and the post-capture solution comprising H2O is fed to the reduction compartment for regeneration of the hydroxide capture solution (see e.g. Figures 1 (a),(b)).

[0156] In some examples, in the second electrolyser, the electrolyte solution is supplied to the cathode (in the redox compartment) and the hydrogen produced by the first electrolyser is fed to the anode (in the oxidation compartment). OM+is reduced back to OM and hydrogen oxidation reaction (HOR) occurs, leading to the release of Y- and the formation of HY (Eq. 3). The solution containing HY and OM is fed into the neutralization chamber with the X2CO3 to neutralize and release CO2 (Eq. 4 and Fig. 1 a-b).

[0157] In some embodiments, the systems of the present disclosure operate the two electrolysers (E1 and E2) in an alternating fashion. As such, the hydroxide capture solution and hydrogen gas are produced in the reduction compartment, the hydrogen is supplied to the oxidation compartment and then the acidic neutralizing solution is produced for supply to a neutralization chamber for CO2 neutralization and release. The post capture solution is fed to the reduction compartment and the electrolyte solution is supplied to the redox compartment (e.g. from the neutralization chamber). The first and the second electrolysis is then repeated. As such, the first and the second electrolysers are operated sequentially and the hydroxide capture solution and the acidic neutralization solution are regenerated cyclically.

[0158] In the systems of the present disclosure, the first cation exchange membrane separates the reduction and redox compartments in the first electrolyser, and the second cation exchange membrane separates the oxidation and redox compartments in the second electrolyser. The cation exchange membranes permit the passage of cations and generally prevent passage of the organic redox active molecule from the redox compartment (e.g. into the reduction compartment). As such, in some embodiments, the first cation exchange membrane transports cations from the redox compartment to the reduction compartment. In some embodiments, the second cation exchange membrane transports cations from the oxidation compartment to the redox compartment.

[0159] Many types of cation exchange membranes can be used for the systems and methods of the present disclosure. Example membranes include but are not limited to a fluoroethylene, fluoropropylene, a sulfonated tetrafluoroethylene-based fluoropolymer, such as commercially available Nation® membranes (Nation 115, Nation 117, Nation 211 and the like). In some embodiments, the cation exchange membrane comprises a fluorinated polymer backbone. In some embodiments, the fluorinated polymer is functionalized with sulphonic acid moieties.

[0160] In some embodiments, the first cation exchange membrane is Nation 115. In some embodiments, the second cation exchange membrane Nation 115. In some embodiments, the cation exchange membrane is coated with a catalyst.

[0161] In some embodiments, the first cation exchange membrane is coated with the catalyst. The catalyst can be any catalyst known in the art. In some embodiments, the catalyst comprises one or more of Ru, Ni, Co, Fe, Pt and platinum black. In some embodiments, the catalyst comprises platinum black.

[0162] The electrodes of the systems of the present disclosure can be constructed of any electrode materials suitable for the purposes described herein. In some embodiments, the cathode comprises a current collector. Thecurrent corrector may comprise a single material or may comprise a plurality of materials, provided that at least one of the materials is substantially electrically conductive. In some embodiments, the cathode comprises a nickel iron (NiFe) foam current collector.

[0163] In some embodiments, the anode comprises carbon paper electrode. In some embodiments, the anode comprises a catalyst. In some embodiments, the catalyst is Pt.

[0164] In some embodiments, the alternating electrode comprises an electrolyte plate. In some embodiments, the electrolyte plate can be placed generally in the middle of the redox compartment (relative to first and second cation exchange membranes). In some embodiments, the alternating electrode comprises a carbon-based support layer.

[0165] In some embodiments, the alternating electrode further comprises a catalyst binder. In some embodiments, the catalyst binder is selected from a hydrophilic ionomer, a hydrophobic ionomer, a hydrophilic polymer, and a hydrophobic polymer. In some embodiments, the catalyst binder comprises the hydrophilic polymer. In some embodiments, the catalyst binder is present at about 2 wt% to about to about 30 wt%. In some embodiments, the catalyst binder is present at about 5 wt, about 10 wt%, about 15 wt%, or about 20 wt% and values therebetween. The amount of the catalyst binder is not limited and is within the consideration of the person skilled in the art.

[0166] The hydrophilic polymer binder used for the alternating electrode according to the present disclosure is not particularly limited as long as it is a polymer that can be dissolved or dispersed in an aqueous solvent. In some embodiments, the hydrophilic polymer is polyethylene glycol.

[0167] In some embodiments, the carbon-based support layer further comprises a catalyst layer. In some embodiments, the catalyst layer can comprise a catalyst selected from carbon black or activated porous carbon nanoparticles. In some embodiments, the catalyst comprises the activated porous carbon nanoparticles.

[0168] In some embodiments, the carbon black can have a specific surface area of about 50 m2g'1to about 250 m2g'1, about 200 m2g'1, about 210 m2g'1, about 220 m2g'1, or about 230 m2g'1and values therebetween. In some embodiments, the specific area of carbon black can be about 230 m2g'1.

[0169] In some embodiments, the activated porous carbon nanoparticles can have a surface specific area of about 1000 m2g'1to about 1500 m2g'1, about 1100 m2g'1, about 1200 m2g'1, about 1300 m2g'1, or about 1400 m2g'1and values therebetween. In some embodiments, the specific area of the activated porous carbon nanoparticles can be about 1300 m2g'1.

[0170] In some embodiments, the catalyst can be loaded on the carbon- based support layer at a density of about 0.05 mg cm'2to about 5 mg cm'2. In some embodiments, the catalyst can be loaded on the carbon-based support layer at a density of about 0.1 mg cm'2to about 3 mg cm'2, about 0.2 mg cm'2to about 1 mg cm'2, about 0.3 mg cm'2, about 0.4 mg cm'2, about 0.5 mg cm'2, about 0.6 mg cm'2, about 0.7 mg cm'2, about 0.8 mg cm'2, or about 0.9 mg cm'2and values therebetween. In some embodiments, the catalyst can be loaded on the carbon-based support layer at a density of about 0.5 mg cm'2.

[0171] In some embodiments, the systems of the present disclosure can operate the first and second electrolysers in a cycle time of 2 sec to 5 minutes, or more. In some embodiments, the time cycle can be 2 sec, 10 sec, 30 sec, 1 min, 2 min, 3 min, 4 min, or more than 5 minutes and any values therebetween. In some embodiments, the time cycle is 20 sec. The skilled person would appreciate that the time cycle can vary depending on the application and desired parameters.

[0172] In some embodiments, a current density of the systems of the present disclosure resulting from the applied current is substantially maintained at a density of about 10 mA cm'2to about 200 mA cm'2. In some embodiments, the current density can be from about 10 mA cm'2to about 150 mA cm'2, from about 30 mA cm'2to about 100 mA cm'2, about 10 mA cm'2, about 20 mA cm'2, about 30 mA cm'2, about 40 mA cm'2, about 50 mA cm'2, about 60 mA cm'2, about 70 mA cm'2, about 80 mA cm'2, about 90 mA cm'2, about 100 mA cm'2,about 110 mA cm-2, or about 120 mA cm-2and values therebetween. In some embodiments, the current density is about 40 mA cm-2.

[0173] In some embodiments, an average combined voltage of the systems of the present disclosure can be substantially maintained at a voltage of about -2 V to about -0.5 V. In some embodiments, an average voltage of the system can be substantially maintained at a voltage of about -1.5 V to about - 0.8 V, about -1.3 V, about -1.1 V, about 1.0 V, or about 0.9 V, and values therebetween. In some embodiments, the average voltage of the system can be substantially maintained at a voltage of about -1.05 V. In some embodiments, the average voltage of the system can be substantially maintained at a voltage of about -1.15 V.

[0174] In some embodiments, the average combined voltage of the systems of the present disclosure can be substantially maintained for over 60 rounds of the electrolysis. In some embodiments, the average combined voltage of the systems of the present disclosure can be substantially maintained for over 200 hours (over 67 rounds), for over 300 hours (100 rounds), or for over 600 hours (200 rounds) of the electrolysis. The number of rounds can vary depending on the cycle time of the system and is within the consideration of the person skilled in the art.

[0175] In some embodiments, a voltage of the first electrolyser can be substantially maintained at a value of about -0.2 V to about -1.5 V. In some embodiment, a voltage of the first electrolyser can be substantially maintained at a value of about -0.2 V to about -1 .2 V. In some embodiments, the voltage of the first electrolyser can be substantially maintained at the value of about -0.3 V, about -0.4 V, about -0.5 V, about -0.6 V, about -0.7 V, about -0.8 V, or about -0.9 V and values therebetween. In some embodiments, the voltage of the first electrolyser can be substantially maintained at the value of about -0.43 V.

[0176] In some embodiments, a voltage of the second electrolyser can be substantially maintained at a value of about -0.2 V to about -1 .5 V. In some embodiments, a voltage of the second electrolyser can be substantially maintained at a value of about -0.2 V to about -1.2 V. In some embodiments,the voltage of the second electrolyser can be substantially maintained at the value of about -0.3 V, about -0.4 V, about -0.5 V, about -0.6 V, about -0.7 V, about -0.8 V, or about -0.9 V, and values therebetween. In some embodiments, the voltage of the second electrolyser can be substantially maintained at the value of about -0.62 V.

[0177] In some embodiments, the CO2 source gas for capture is from an atmospheric source, e.g., atmospheric air. In some embodiments, the CO2 source gas is an effluent from an industrial source. In some embodiments, the CO2 source gas is a mixture of effluent from an industrial source and atmospheric air. In some embodiments, the CO2 source gas can comprise about 1 % v / v to about 12% v / v CO2. In some embodiments, the CO2 source gas can comprise about 1 % v / v CO2, about 3% v / v CO2, about 5% v / v CO2, about 7% v / v CO2, about 9% v / v CO2, or about 11 % v / v CO2 and values therebetween. In some embodiments, the CO2 source gas comprises about 1 % v / v CO2.

[0178] In some embodiments, the CO2 source gas for capture can have an inlet air flow rate to the air contactor of about 20 seem to about 300 seem. In some embodiments, the CO2 source gas can have an inlet air flow rate of about 30 seem, about 50 seem, about 80 seem, about 100 seem, about 120 seem, about 150 seem, about 200 seem, about 250 seem, or about 300 seem. In some embodiments, the CO2 source gas has an inlet air flow rate of about 150 seem. In some embodiments, the CO2 source gas has an inlet air flow rate of about 50 seem.

[0179] In some embodiments, the capture solution can have an average current efficiency of about 60% to about 99%. In some embodiments, the capture solution can have an average current efficiency of about 70% to about 99%, about 80% to about 99%, about 85%, about 88%, about 90%, about 92%, about 95%, or about 97%, and values therebetween. In some embodiments, the capture solution has the average current efficiency of about 92%. In some embodiment, the capture solution has the average current efficiency of about 90%.

[0180] In some embodiments, the systems of the present disclosure can have a CO2 capture efficiency of about 60% to about 99%. In some embodiments, the systems of the present disclosure can have a CO2 capture efficiency of about 70% to about 99%, about 80% to about 99%, about 85%, about 88%, about 90%, about 92%, about 95%, or about 97%, and values therebetween. In some embodiments, the systems of the present disclosure can have a CO2 capture efficiency of about 96%. In some embodiments, the systems of the present disclosure have a CO2 capture efficiency of about 98%.

[0181] In some embodiments, the systems of the present disclosure can have a CO2 release efficiency of about 60% to about 99%. In some embodiments, the systems of the present disclosure can have a CO2 capture release of about 70% to about 99%, about 80% to about 99%, about 85%, about 88%, about 90%, about 92%, about 95%, or about 97%, and values therebetween. In some embodiments, the systems of the present disclosure have a CO2 release efficiency of about 91 %. In some embodiments, the systems of the present disclosure have a CO2 release efficiency of about 93%.

[0182] In some embodiments, the systems of the present disclosure can have a minimum energy consumption of about 0.1 GJ per tC02 to about 3 GJ per tCO2. In some embodiments, the systems of the present disclosure can have a minimum energy consumption of about 0.5 GJ per tC02, about 0.7 GJ per tCO2, about 0.9 GJ per tC02, about 1.5 GJ per tC02, or about 3 GJ per tCO2. In some embodiments, the systems of the present disclosure can have a minimum energy consumption of about 0.87 GJ per tC02.

[0183] In some embodiments, the systems of the present disclosure can have a DAC energy consumption of about 1 GJ per tC02 to about 10 GJ per tCO2at 10 mA cm-2. In some embodiments, the systems of the present disclosure can have a DAC energy consumption of about 1.5 GJ per tC02, about 2 GJ per tC02, about 3 GJ per tC02, about 4 GJ per tC02, about 5 GJ per tCO2, about 6 GJ per tC02, about 7 GJ per tC02, about 8 GJ per tC02, or about 9 GJ per tC02 at 10 mA cm'2, and values therebetween. In someembodiments, the systems of the present disclosure have a DAC energy consumption of 3.9 GJ per tCCte at 10 mA cm-2.

[0184] In some embodiments, the systems of the present disclosure can be further characterized by mass loss of the organic redox active molecule of less than 10% over more than 200 hours of the system operation. In some embodiments, the mass loss of the organic redox active molecule is less than 9%, less than 8%, less than 7%, less than 6%, or less than 5% over more than 200 hours of the system operation. In some embodiments, the mass loss of the organic redox active molecule is less than 6% over more than 200 hours of the system operation.

[0185] In some embodiments, the reduction, oxidation, and redox compartments are not restricted with regard to shape, material, dimensions, etc. and can be constructed of any suitable materials that are non-reactive and suitable for holding aqueous or non-aqueous (i.e. , organic) liquid solutions. In some embodiments, according to the electrolysis to be conducted, respective conduit means (i.e. lines such as, for example, pipes, conduits, channels, etc.) for reactants and products are provided. There is no restriction in this regard either, and the flow through the individual spaces may be in parallel flows or in countercurrent.

[0186] The capture solution, the acidic neutralizing solution and the electrolyte may be provided either in continuous form or, for example, pulsed form, etc., and for which pumps, valves, etc. may correspondingly be provided as part of the DAC system. The materials of said constituents of the DAC system may be suitably matched here in accordance with desired reactions, reactants, products, electrolytes, etc. Furthermore, at least one power source can also be included. The power source can be any desired source of electrical energy suitable for electrolysis, air flow, fluid pumping, valve operation, sensor / probe operation, control system component (processor) operation, and / or any other functionality required for operation of the DAC system according to the present teachings. In some embodiments, the source of electrical energy can be a renewable source of energy, such as wind, solar, orhydropower. Further apparatus parts such as electrical communication means, such as wires that occur in electrolysis systems may also be provided.EXAMPLESGeneral Experimental Methods and MaterialsCatalysts and chemicals preparation

[0187] All chemicals used were purchased from Sigma Aldrich, including methyl viologen dichloride hydrate (98%), benzyl viologen dichloride (97%), 4,4’-bipyridine (98%), diethyl(3-bromopropyl)phosphonate (95%), bromotrimethylsilane (for synthesis), 1 ,3-propanesultone (98%), lithium chloride (ACS reagent, >99%), lithium carbonate (ACS reagent, >99%), N,N- dimethylformamide (ACS reagent, >99.8%), acetonitrile (anhydrous, >99.8%), dichloromethane (anhydrous, >99.8%), isopropyl alcohol (anhydrous, 99.5%), toluene (anhydrous, >99.8%). All aqueous electrolytes and solutions were prepared using Milli-Q grade deionized water (DI, 18.2MQ).

[0188] A nickel iron (NiFe) foam current collector was purchased from Xiamen Lith Machine Limited. A catalyst-coated membrane (Nation® 115 coated with platinum black, PtB), nation membrane (Nation® 115) hydrophilic carbon electrode (AvCarb MGL 190), hydrophobic platinum on Vulcan electrode (0.5 mg / cm260% platinum on Vulcan - carbon paper electrode) were purchased from the Fuel Cell Store.Electrocatalysis H-cell configuration

[0189] A 10 mL laboratory H-type electrolytic cell was purchased from Tianjin Aida Hengsheng Technology Development Co., Ltd. A working electrode was 1cm x 1cm AvCarb MGL 190, a reference electrode was 3M KCI silver / silver chloride (Ag / AgCI) reference electrode, and a counter electrode is 2cm x 2cm platinum mesh. A Nation® 115 was placed between cathode compartment and anode compartment as the membrane.Dual-electrolyser system configuration

[0190] A laboratory 1 cm2membrane electrode assembly cell was custom made from University of Toronto Machine Shop. The PtB catalyst- coated Nation membrane and the NiFe foam current collector was carefully placed as the electrolyser-1 cathode compartment. A customized common electrolyte plate and AvCarb MGL 190 was placed as the middle layer and acted as the alternating common electrode (electrolyser-1 anode and electrolyser-2 cathode). Another Nation® 115 and hydrophobic platinum on Vulcan electrode was carefully placed as the electrolyser-2 anode compartment. Gaskets with 1 cm x 1cm window were placed to ensure no system liquid leakage.

[0191] In the experiments, the capture solution tank was filled with DI water, while U2CO3 mixed with BPPV and LiCI was supplied to the neutralization solution in the neutralization solution tank at the start of the experiment. Both liquids were pumped into the dual-electrolyser system of the present disclosure from the bottom, exited at the top of the system and recirculated from the reservoirs (10 mL for capture solution and 10 mL for the neutralization solution) to the system in a closed loop. For 67 rounds prolonged testing, the capture solution and neutralization solution were refreshed every 3 hours..

[0192] All electrochemical tests were performed at room temperature (-298K) and atmospheric pressure (~1 atm), using an electrochemical workstation (Autolab PGSTAT302N). During the system operation, two independent electrochemical workstations were applied to the Electrolyser-1 and Electrolyser-2, to perform the chronopotentiometry measurement with pre- set cyclic time, respectively. The alternating configuration was switched using a microcontroller magnetic switch. During the 67 rounds prolonged testing, the system alternated among chronopotentiometry Electrolyser-1 mode (-40 mA, ti=10s) and chronopotentiometry Eletrolyser-2 mode (-40 Ma, t2=10s). Electrochemical data was recorded by NOVA Autolab software every 1s. All voltages reported are full cell voltages without iR compensation.Product analysis

[0193] During the experiment, the pH of the capture solution and neutralization solution were measured using pH meters (OMEGA™ PHH444 portable pH meter with Data Logging Function). The total amount of CO2 released from neutralization solution tank was measured with a flowmeter (Honeywell AWM3150V) in the gas outlet.

[0194] The post-capture solution and post-regeneration solution were quantified using nuclear magnetic resonance spectroscopy (NMR). 1 H NMR spectra of aqueous samples were collected with an internal standard, dimethyl sulfoxide (DMSO), on an Agilent DD2 500 spectrometer using water suppression mode.

[0195] During the H-cell permeability tests, samples in the receiving compartment were analysed using UV-visible spectrophotometry (PerkinElmer FL6500). The UV-vis spectra range was set from 200 to 400nm with a scan rate of 600 nm min'1.Experimental Synthesis and CharacterizationSynthesis of 1 ,1 ’-bis(3-phophonopropyl)-[4,4’-bipyridine]-1 ,1 ’-diium dibromide (BPPV):

[0196] A mixture of 1.36 grams of 4,4’-bipyridine and 5 milliliters of diethyl(3-bromopropyl)phosphonate were introduced into a 20 milliliters solution of dimethylformamide. The reaction took place on a heating plate set at 95°C and was stirred for 72 hours under a nitrogen atmosphere. The resulting slurry was subjected to five cycles of washing with acetonitrile and participated by centrifugal separator. Subsequently, the resulting pink-white solids, 1 ,1’- bis(3-(diethoxyphosphoryl)propyl)-[4,4’-bipyridine]-1 ,1’-diium dibromide, were dried under vacuum condition for 24 hours.

[0197] A mixture of 0.674 grams of 1 ,1’-bis(3- (diethoxyphosphoryl)propyl)-[4,4’-bipyridine]-1 ,T-diium dibromide and 1.32 milliliters of bromotrimethylsilane were added to 12 milliliter solution of dichloromethane. The reaction was carried out at room temperature and stirredfor 24 hours under a nitrogen atmosphere. The resulting orange solution was washed five times with isopropyl alcohol and participated by centrifugal separator. The resulting orange-white solid, BPPV, was then dried under vacuum condition for 24 hours [Fig. 2],Synthesis of 1 ,1 ’-bis[2-sulfonatopropyl]-4,4 ’-bipyridinium (SPRV):

[0198] A mixture of 1.57 grams of 1 ,3’-propanesultone and 1 gram of 4,4’-bipyridine were introduced into a 20 milliliters solution of toluene. The reaction took place on a heating plate set to 110°C and was stirred for 4 hours under a nitrogen atmosphere. The resulting slurry was subjected to five cycles of washing with acetonitrile and participated by centrifugal separator. The resulting white solid, SPRV, was dried under vacuum condition for 24 hours (Fig. 3).BPPV and SPRV permeability experimental details

[0199] The permeability of BPPV and SPRV was measured and quantified across a Nation 115 cation exchange membrane. An H-cell configuration was employed, consisting of a donating compartment with redox- active molecule and a receiving compartment which was periodically assessed.

[0200] In the case of the SPRV evaluation, a solution containing 0.1 M SPRV was introduced to the donating compartment, while the receiving compartment was filled with deionized (DI) water. For BPPV evaluation, a solution containing 0.1 M BPPV was placed on the donating compartment, while the receiving compartment was filled with DI water. The migration of the redox-active molecule was tracked over a period of 6 days.

[0201] To simulate the fluid pumping environment in the dual-electrolysis system configuration, the experiments were placed on a rotating table. Both the donating and receiving compartments initially contained an equal volume of 10 ml solution. Periodic monitoring of the crossover of the redox-active moleculeby taking a 0.5 ml sample from receiving compartment and replenishing it with fresh solution. This withdrawn sample was subsequently diluted and analyzed using UV-visible spectrophotometry to determine the concentration of organic redox-active molecule (viologen).

[0202] The permeability of BPPV and SRPV was estimated using Fick’s 5 Law:

[0203] Where ^^ is the permeability (cm2s-1), ^^^^is the organic redox- active molecule concentration measured at the receiving compartment at different periods, ^^0is the initial concentration of organic redox-active molecule 10 in the donating compartment (0.1 M), ^^0is the initial volume of solution (10 ml), ^^ is the effective membrane surface area (1.13 cm2), ^^ is the thickness of the membrane (0.0127 cm), and Δt is the intervals (s). CO2 capture and release analysis

[0204] Hydroxide solution was used for CO2 capture, and the CO2 is 15 stored as dissolved inorganic carbon (DIC) and exists in three main components: CO2 (aq), bicarbonate (HCO3-), and carbonate (CO32-). The equilibria of carbonate species present in aqueous solution (Eq.5): CO2(aq) + H2O ↔ HCO3−+ H+↔ CO23−+ 2H+(Eq.5)

[0205] The first and second stoichiometric equilibrium constants are K1and K2, respectively, a d d fi d f ll i E 6 E 7 20[HCO−3]

[0206] The K1and K2are 1.543 × 10−6M and 1.437 × 10−9M, indicating the first and second pKa for carbonic acid are 5.81 and 8.84 respectively. When solution pH < 5.81, total DIC is presented as primarily CO2 (aq), and in theintermediate region of 5.81 < pH < 8.84, the total DIC is presented as primarily of HCO3; and when pH > 8.84, the total DIC is presented as primarily of COs2'The sum of the DIC species present in solution (Eq. 8):The total alkalinity (TA) of solution can be defined as (Eq. 9):

[0207] The equilibrium constant for water dissociation is 10-14M2. The concentration of hydroxide and proton can be considered from water dissociation (Eq. 10):H2O [OH-] + [H+] (Eq. 10)

[0208] During the theoretical consideration, the concentration of CO2 (aq), HCO3; and COs2' can be estimated as a function of H+under different pH via the following equations (Eq. 11) - (Eq. 13):

[0209] The concentration of CO2 (aq), HCO3; CO32; H+, and OH' during the CO2 capture and CO2 release in the regeneration solution is illustrated in Fig. 4a-b.Theoretical calculation for CO2 capture:

[0210] 10ml regenerated capture solution was used to capture CO2 and bring the pH down from 13.3 to 10.8, which consumed 1.83 mM of OH'. Based on the DIC and pH consideration, it was considered that all OH' would captureCO2 and form CO32-only due to the post-capture solution pH is 10.8 and the total DIC is presented as primarily of > 99% CO32-(Fig.4b). Using Eq.6 and Eq.7 the DIC was calculated to be 0.91mM. Considering the density of CO2 is 1.815 kg / m3at 20°C and 1 bar condition, ideally, the total amount of 22.20 ml CO2 will be captured through 1 round, 3-hour system operation. 5 Ultra-diluted CO2 capture experiment: Regenerated capture solution was used to capture from 1% v / v CO2and 99% v / v air (Fig. 23). A 10 ml hydroxide capture solution was demonstrated from initial pH of 13.3. The inlet flow rate was set to 50 sccm. The outlet flow rate was monitored by the flow meter. When solution pH less than 11, the CO2 10 capture rate decreases rapidly and reaches to ~ 0 sccm. This is due to the kinetic limitation of low concentration of CO2 and hydroxide to form bicarbonate (CO2(aq) + OH−↔ HCO−3). The experimental result showed that the total CO2 capture amount is 0.89 mmol, which represents that the capture efficiency is 98%. 15 DAC CO2 capture experiment:

[0211] Regenerated capture solution was used to capture from air for 20 hours (Fig.24a-b). A 5 ml hydroxide capture solution was demonstrated. The inlet air flow rate was set to 150 sccm. The outlet flow rate was monitored by the flow meter. The experimental result showed that the total CO2 capture 20 amount is 0.41 mmol. pH vs current calculation:

[0212] Faraday’s law is applied to calculate the production rate in mol s-1of OH- in the capture solution and H+ in the regeneration solution: ^ 14)^^^^+= (Eq.15) 2 ∗ nF

[0213] Where the ^^^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^^1^&^2, represents the applied current density 25 for Electrolyser-1 and Eectrolyser-2. n, is the number of participating electronsper generation of one hydroxide or proton (n=1). F is the Faraday constant (96485 s A mol'1). The hydroxide and proton production rates are divided by 2 due to the alternating reaction. Since the Electrolyser-1 and Electrolyser-2 were operated at the same current density - r0H- = rH+.CO2 release:

[0214] Considering a total of 0.89 mmol CO2 is being captured and converted to 0.89 mmol U2CO3 formation for the post-capture condition, a total of 65.8 mg U2CO3 will precipitate and put into regeneration solution. During regeneration solution production, the produced H+reacts with U2CO3 to produce CO2. During the experiment, it was observed from flow meter that the total amount of 0.83 mmol CO2 was released, which represents the release efficiency of 93%.Minimum energy requirements

[0215] The amount of minimum energy requirements evaluated from cyclic voltammetry (Eq. 16).

[0216] Where £ceUis voltage required of Electrolyser-1 and Electrolyser- 2 systems. The system voltage can be obtained from the setup as shown on Figure 22 where EEHER / HORrepresents difference of experimental cyclic voltammetry oxidation peak and reduction peak, 0.25V and &EVRR / V0Ris 0.06V. WCO2is work required to capture a specific mass of CO2, mC02is the mass of CO2, F is Faraday’s constant, MC02is the molar mass of CO2, n current is the current efficiency of the capture solution regeneration ,90%, T]C02capture is CO2 capture efficiency, 96%, T]C02 REIEASEis CO2 release efficiency, 91 %.Alternating dual-electrolyser system energy consumption calculationU2CO3 as the post-capture solution:

[0217] The energy consumption in GJ of the alternating dual-electrolyser system to capture 1 tonne of CCte was calculated in this section (Eq. 17). The post-capture solution is lithium carbonate as input, which requires two hydroxides to capture one CO2 molecule. Therefore, two electrons need to be provided to regenerate the hydroxide through an electrochemical process. H2O + CO2UHCO3 as the post-capture solution:

[0218] The post-capture solution is lithium bicarbonate as input, which requires two hydroxides to capture one CO2 molecule. Therefore, one electrons need to be provided to regenerate the hydroxide through an electrochemical process. The energy consumption in GJ of the alternating dual-electrolyzer system to capture 1 tonne of CO2was calculated in this section (Eq. 18).Design of the electrocatalytic system using cyclic organic molecule

[0219] To prevent the exposure of the organic redox-active molecule to O2 and high airflow rates, the systems of the present disclosure were designed to effectively separate the hydroxide-based absorbents, which directly contact air, from the organic redox-active species used to facilitate CO2 release (Fig. 1 a). This system uses, for example, the hydroxide capture solution’s high resistance to O2 and the organic molecule’s fast reaction kinetics.

[0220] The system operates two electrolysers in an alternating fashion such that the anode of a first Electrolyser-1 (E1 ) serves as the cathode of a second Electrolyser-2 (E2) (Fig. 1 b). Both electrolysers are equipped withcation exchange membranes (CEMs) to allow cation transport from the anode to the cathode.

[0221] In the capture solution formation process (E1 ), post-capture solution is supplied to the cathode while a common electrolyte, aqueous solution of organic molecule (OM) and lithium chloride (LiCI), is fed to the anode. Hydrogen evolution reaction (HER) takes place at the cathode, whereas OM is oxidized to OM+at the anode. Dissolved chloride ions (Cl’) are attracted by OM+and lithium ions (Li+) cross the CEM to produce lithium hydroxide (LiOH) capture solution. Highly alkaline LiOH capture solution is used for DAC, facilitating the formation of lithium carbonate (U2CO3) salts.

[0222] In the neutralization solution formation process (E2), the common electrolyte serves as a cathode and hydrogen (H2) produced from E1 is fed to the anode. OM+is reduced back to OM and hydrogen oxidation reaction (HOR) occurs, leading to the release of Cl’ and the formation of hydrochloric acid (HCI). The acidic solution containing HCI and OM is fed into a storage reservoir with the post-capture Li2COs salts to neutralize and release CO2.

[0223] A common electrode design (i.e. anode electrode of E1 and cathode electrode of E2) was implemented, to minimize mass transport losses and enhance the availability of OM / OM+during both reactions. This design modification reduces energy consumption and increases the overall efficiency of the system.Comprehensive study and viologen comparison

[0224] An organic mediator undergoes reversible oxidation and reduction to store and release ions and electrons in this aqueous environment. Optimally, the molecule should possess high aqueous solubility to operate at high current density, fast redox kinetics to attain low system energy, a robust molecular structure to achieve low fabrication costs and high durability. Viologen, for example, is widely used in aqueous redox flow batteries, because the 1 , 1 ’-disubstituted-4,4’-bipyridine structure possesses a stable organic radical structure, high aqueous solubility, and desirable electron-acceptingcapability (Fig. 1 c).2728The properties and electrochemical behaviour of viologens can be tuned by incorporating different substituents.2930Therefore, viologen materials were selected for further exploration.

[0225] During operation of the dual-electrolyser system, the viologen alternates on the common electrode between oxidation, during E1 , and reduction, during E2. Previous studies suggest that viologen desorption is the rate-limiting factor during the entire redox cycle.31-33For example, benzyl- substituted viologen (BV) exhibits pronounced interactions with carbon electrode, facilitated by both strong cation-TT stacking force from the bipyridine structure and electrostatic attraction from the hydrophobic substituent - a benzyl ring.3435BV forms a coloured immobilization film on the electrode surface and requires an additional energy barrier to desorb during electrochemical reaction (Fig. 5).36-38Consequently, a viologen molecule with a relatively low binding energy should reduce the energy barrier and enable relatively fast reaction kinetics. It was hypothesized that different substituents could influence the interaction between the viologen molecule and carbon surface.29Density functional theory (DFT) calculations investigated the binding energies of seven viologen molecules with different substituents, including methyl-substituted viologen (MV), 1 ,T-bis(3sulfonatopropyl)-4,4’-bipyridinium (SPRV), 1 ,1 ’-bis(3- phosphonopropyl)-[4,4’-bipyridine]-1 ,1’diium (BPPV), benzyl-substituted viologen (BV), bis(2-phosphono-methyl-4-benzyl)-4,4’-bipyridilium (BNV), 1 ,1 ’- bis(2-(1 h-indol-3-yl)ethyl)-4,4’-bipyridinium (IEV), and (1 H-phenalene-5- yl)methyl-bipyridinium (PMV) (Fig. 6a). The DFT analysis revealed that the MV, SPRV, and BPPV exhibited lower binding energy to the carbon surface than BV (-1 .57 eV) with values of -1 .41 , -1 .45 and -1 .49 eV. Based on these findings, these viologens with relatively low binding energies were experimentally tested.

[0226] Cyclic voltammetry (CV) studies were conducted in a H-cell configuration to assess the electrochemical behaviour of the three substituents (Fig 6b). One electron transfer scans of MV, SPRV, and BPPV were performed under a nitrogen headspace. The CV results indicate that the difference in reductive and oxidative peak potentials (Ered-oxi) for MV, SPRV, and BPPV wereonly 83, 97 and 109mV, respectively. These three molecules had fast kinetics and no immobilization film formed on the electrode surface during the redox reaction.

[0227] Electrostatic interaction plays an effect during the viologens redox reaction near the electrode surface.40’41Here a strategy that utilizing the dipolar structured viologens to effectively achieve reduction and oxidation was proposed.

[0228] The dipolar structured redox intermediate on the common electrode is optimal for high current density reduction or oxidation. The dual- electrolyser system was utilized to test the charge passed (i.e. , the product of current density and time) during one reduction (E2) and one oxidation (E1 ) cycle of MV, SPRV, and BPPV over different cycle times (Fig. 6c), (Fig. 6d).

[0229] MV exhibited an imbalance between reduction and oxidation charge at all cycle times, with oxidation always being the limiting reaction (Fig. 7a-d). MV has high solubility in both dicationic (V2+) and radical (V+) forms. During reduction, the positively-charged 2+ structure is attracted to the negatively-charged electrode and can be reduced from V2+to V+(Fig. 8). However, during oxidation, the positive electric field around the electrode prevents the positively-charged V+from effectively contacting the electrode, thereby limiting the concentration and the reaction rate.

[0230] SPRV and BPPV demonstrated relatively balanced charge and discharge processes with strong charges that steadily grew with increased cycle time (Fig. 9a-d) (Fig. 10a-d). These di-polar viologens possess a positively charged bipyridine structure and negatively charged substituents (Fig. 1 1 ). Fourier-transform infrared spectroscopy (FT-IR) and ion chromatography (IC) results confirmed that both SPRV and BPPV have anion function groups in their dissolved aqueous solution (Fig. 12a-b), (Fig. 13a-b). As shown in FT-IR result, the peak at 1637 cm-1 is for stretching vibrations of the C=C bond, and peaks at 1 180 and 3027 cm-1 are for stretching vibrations of the C-H bond. N-C stretching appears at 1216 cm-1. The peaks at 1508 and 1561 cm-1 are for C=N vibration, while 947 and 1030 cm-1 are the vibrationalpeaks of the phosphoryl group. 1030 cm-1 is the vibrational peak of SO from the sulfonate group. Their zwitterion structure can overcome the electric field repulsion during both reduction and oxidation processes and facilitate high reaction rates in both operational modes. Therefore, it was concluded that the di-polar viologens were optimal for high current density reduction and oxidation in the dual-electrolyser system.Selection among di-polar viologens

[0231] Although SPRV and BPPV both performed well in the system, it was sought to minimize viologen transport through the CEM from the neutralization solution (i.e., anolyte of E1 / catholyte of E2) to the capture solution. A comparative analysis between SPRV and BPPV - two molecules which both possessed di-polar structures (see section “Experimental synthesis and characterization” above) was conducted.42'44SPRV has 2 negatively charged substituents yielding a neutral overall charge (Fig. 14a), whereas BPPV has 4 negatively charged substituents and an overall charge of -2 (Fig. 14b). It was hypothesized that the additional negative charge should make BPPV less susceptible to permeation through the CEM. The permeability of BPPV was measured to be 30 times lower than the permeability of SPRV through a CEM, with values of 2.63 x 10'11and 7.37 x 10'10cm2S'1, respectively (Fig. 15a-d), (Fig. 16a-d), (see section “BPPV and SPRV permeability experimental details” above). The BPPV was identified as a suitable viologen for the system to achieve high current density operation and minimal viologen crossover.Electrochemical screening of BPPV in an H-cell configuration

[0232] To better understand the electrochemical properties of BPPV, a full potential CV scan with BPPV electrolyte, including an extremely negative potential range was conducted: as the reducing potential was increased, the first electron and second transfers started at -0.41 V and -0.86 V versus Ag / AgCI, respectively (Fig. 17a). BPPV4', the product formed after two electron transfers from BPPV2', can cause viologen decomposition and irreversible solid crystallization formation.44 45To avoid the two-electron reduction of BPPV2' toBPPV4-, -0.9 V vs Ag / AgCI (-0.7 V vs RHE) served as the practical limit for the E2 cell voltage.

[0233] CV analyses of BPPV at different pH (Fig. 17b) were performed. The positions of first electron transfer redox pairs remained at same potential across the pH range of 7 to 2 in the aqueous solution. This observation confirms that proton-coupled electron transfer does not occur for BPPV reduction and oxidation reactions. Consequently, it demonstrates that the performance of BPPV is pH-independent within the expected pH range of the common electrolyte in the system.Common electrolyte optimization

[0234] The BPPV was incorporated into the dual-electrolyser system and the chemical concentrations related to the common electrolyte (i.e., neutralization solution) were screened.

[0235] First, a series of linear scan voltammetry (LSV) measurements were conducted to optimize the BPPV concentration for E2 (Fig. 17c). The peak reduction current density increased gradually from -45.4 mA cm-2to -144.5 mA cm'2as the BPPV concentration increased from 0.02 to 0.4 M. The peak current density increased minimally as the BPPV concentration increased above 0.2 M. These results suggest that reaction was not mass transfer limited and further increase in BPPV concentration would not yield improvement in electrokinetic performance.

[0236] Linear scan voltammetry studies of the system using 0.1 M BPPV with 1 M LiCI were conducted using common electrolyte common electrolyte flow channel thickness of 0.5 mm and 1 mm. It was observed that a 0.5 mm channel thickness resulted in a 3-fold increase in current density, compared to a 1 mm thickness, due to lower ohmic resistance between the common electrodes and the counter electrode (Fig. 18a). Further, linear scan voltammetry studies of the system using 0.1 M BPPV with 1 M LiCI were conducted with the common electrolyte flow rate of 10, 20 and 30 ml min'1. It was observed that a flow rate of 10 ml min'1reached a peak reduction currentdensity of -50.3 mA cm-2@ -0.43 V whereas, at 20 ml min-1, the peak current density was -81.2 mA cm-2@ -0.48 V (Fig. 18b). The increased reduction rate can be attributed to increased reactant supply and improved mass transfer via convective effects. Further increasing flow rate to 30 ml min-1did not significantly improve the current density.

[0237] Varying the Li+concentration between 1 , 2, and 3 M LiCI yielded similar E2 current densities (Fig. 18c). This indicates that increasing the Li+concentration did not significantly improve the system performance. It was hypothesized that increased Li+concentration could yield higher current efficiencies for E1 . The performance with U2CO3 added to the electrolyte was also tested, to simulate the carbon content found in real-world DAC systems, and there was no loss in performance (Fig. 18c). Therefore, 0.2 M BPPV in 2 M LiCI was selected, as it was anticipated that this selection will result in a high current efficiency (i.e. , Li+serves as charge carrier during the reaction) in the system operation.Common electrode optimization

[0238] To minimize active site limitations on the common electrode of the dual-electrolyser system of the present disclosure, a high surface area electrode consisting of a nanoporous catalyst layer on top of a carbon-based support layer was designed. Three electrode factors were studied: the catalyst binder, the nanoparticle morphology, and the catalyst loading.

[0239] The electrochemical surface area (ECSA) is impacted by the catalyst binder’s functional group charge density and the binder’s hydrophobicity.46To compare the effectiveness of different binder materials, a hydrophilic ionomer, a hydrophobic ionomer, a hydrophilic polymer, and a hydrophobic polymer were tested (Fig. 19a). The functional groups in ionomer binders create an electrostatic repulsion between the electrode surface and di- cationic bipyridine structure that reduces viologen concentration at the catalyst. Hydrophilic binders increase catalyst surface wetting and catalyst utilization. As a result, the hydrophilic polymer yielded the highest current density and a substantial increase compared to the bare carbon paper.

[0240] To further improve the ECSA, different carbon nanostructures on the carbon-based support layer, including carbon black (Vulcan XC-72), and activated porous carbon nanoparticles were tested (Fig. 19b) (Fig. 20a-b). Previous studies have shown that the specific surface area of carbon black is 230 m2g'1, whereas activated porous carbon nanoparticles are 1300 m2g-1.46 47The activated porous carbon nanoparticles yielded the highest current density of 153.3 mA cm'2.

[0241] Different catalyst loading can impact ECSA (Fig. 19c). Loading densities of 0.2, 0.5, and 1 mg cm'2activated porous carbon nanoparticles were tested. The highest current density occurred at a loading of 0.5 mg cm'2. A thicker catalyst layer, 1 mg cm'2loading density, restricts the diffusion of the viologen to the deeper sections of the electrode, resulting in a trade-off between thickness and activity. 0.5 mg cm'2of activated porous carbon nanoparticles were incorporated with a hydrophilic polymer binder into the common electrode.System performance with DAC Solutions

[0242] Three-hour electrolysis experiment was performed to demonstrate the system performance using BPPV as the redox mediator in the common electrolyte at a current density of 40 mA cm'2(Fig. 21 a), (Fig. 22). The two electrolysers of the system were cycled every 20 s. Throughout the experiment, the average combined voltage was -1.05 V: Electrolyser-1 voltage was -0.43 V, and Electrolyser-2 voltage was -0.62 V (Fig. 21 b).

[0243] During the experiment, the total gas flow rate and pH were measured using a digital flow meter and pH probe, respectively. The pH of the capture solution started at 6.7 and climbed to 13.3 (Fig. 21 c). The average current efficiency in this electrolyser was 92% (Fig. 21 c). The regenerated capture solution is theoretically sufficiently alkaline for further DAC. To test this hypothesis, the regenerated capture solution was used to capture CO2 from a stream containing 1 % v / v CO2 and 99% v / v air (21 % v / v O2) (Fig. 21 d), (Fig. 24a-b). The capture solution experienced a drop in pH from 13.3 to 10.8, indicating that CO2 was reacting with OH' to form COa2'. After flowing 50 seem of mixture (0.5 seem of CO2) for 2.5 h, a total of 0.89 mmol of CO2 was capturedwith this capture solution regenerated via the electrolysis (see section “CO2 capture and release analysis” above). Regenerated capture solution was also used to capture CO2 from air and demonstrate relevance to real-world DAC systems (Fig. 25a-b).

[0244] U2CO3 was transferred into the neutralization solution tank at the start of the experiment. During the experiment, the neutralization solution pH decreased from 6.8 to 2.8, as electrochemically generated protons reacted continuously with U2CO3 to release CO2 gas (Fig. 21 e). The total amount of CO2 released was 0.83 mmol, which represents 93% of the CO2 embodied in the U2CO3 (see section “CO2 capture and release analysis” above). The regenerated neutralization solution was sufficiently acidic for the majority of the CO2 to be liberated.

[0245] NMR analysis was conducted on both the common electrolyte and capture solution after the 3-hour experiment (Fig. 26a-b). The BPPV was a robust choice for this application as no additional molecules, apart from BPPV, were detected in the regenerated neutralization solution. No BPPV was detected in the regenerated capture solution which indicated that there was no detectable crossover of BPPV through the CEM.DAC energy consumption using electrolysis system regeneration

[0246] First, the minimum energy consumption of the system was estimated based on the potential difference in an H-cell CV scan (Fig. 27). This minimum energy consumption was estimated to be 0.87 GJ per tC02 (see Section “minimum energy requirements” above). Dual-electrolyser system at different current densities between 10 and 120 mA cm-2was also performed (Fig. 28a-b). The energy consumption in the electrolysis system was 3.9 GJ per tCO2at 10 mA cm'2(see Section “Alternating dual-electrolyser system energy consumption calculation” above). This energy consumption is competitive with other electrochemical CO2 separation methods for atmospheric CO2 capture.Stability test of alternating dual-electrolyser system

[0247] Stability is a concern for industrial DAC deployment and was a driver in the development of the methods and systems of the present disclosure. Following one 3-hour round of electrolysis, the regenerated capture solution is transported to the air contactor, the capture solution reservoir is emptied and refilled with water, and U2CO3 from the air contactor is supplied to the neutralization solution tank. Over 67 rounds (201 hours) of the electrolysis at 40 mA cm'2, the system maintained an average full-cell voltage of -1.15 ± 0.1V (Fig. 29). Analysis of the neutralization solution before and after this prolonged experiment again confirmed no chemical degradation of BPPV but indicated that 5.7% of the initial BPPV was lost (Fig. 30a-b). This demonstrated a robust and 02-tolerant electrolysis strategy with reasonable organic molecule loss.Conclusions

[0248] In summary, a dual-electrolyser system was developed that utilizes the benefits of hydroxide capture solution’s high resistance to O2 and the fast reaction kinetics of an organic mediator. Amongst various viologen families, those with di-polar structures enabled efficient oxidation and reduction cycles and BPPV resisted viologen crossover through CEMs. The dual- electrolyser system was stable for over 200 hours of operation. When powered, for example, with renewable electricity, this strategy provides a possible approach for industrial DAC deployment.REFERENCE DOCUMENTS1. McQueen N, Gomes KV, McCormick C, Blumanthal K, Pisciotta M, Wilcox J. A review of direct air capture (DAC): Scaling up commercial technologies and innovating for the future. Progress in Energy. 2021 ;3(3).2. Erans M, Sanz-Perez ES, Hanak DP, Clulow Z, Reiner DM, Mutch GA. Direct air capture: process technology, techno-economic and socio-political challenges. Energy Environ Sci. 2022; 15(4): 1360-405.3. Hashimoto K. Global Carbon Dioxide Recycling For Global Sustainable Development by Renewable Energy. 2019. 1-96 p.4. Sabatino F, Grimm A, Gallucci F, van Sint Annaland M, Kramer GJ, Gazzani M. A comparative energy and costs assessment and optimization for direct air capture technologies. Joule [Internet], 2021 ;5(8):2047-76. Available from: https: / / doi.org / 10.1016 / jjoule.2021.05.0235. Keith DW, Holmes G, St. Angelo D, Heidel K. A Process for Capturing CO2 from the Atmosphere. Joule [Internet], 2018;2(8):1573-94. Available from: https: / / doi.Org / 10.1016 / j.joule.2018.05.0066. Deutz S, Bardow A. Life-cycle assessment of an industrial direct air capture process based on temperature-vacuum swing adsorption. Nat Energy [Internet], 2021 ;6(2):203-13. Available from: http: / / dx.doi.org / 10.1038 / s41560- 020-00771-97. Ozkan M, Nayak SP, Ruiz AD, Jiang W. Current status and pillars of direct air capture technologies. iScience [Internet], 2022;25(4): 103990. Available from: https: / / doi.Org / 10.1016 / j.isci.2022.1039908. Simeon F, Stern MC, Diederichsen KM, Liu Y, Herzog HJ, Hatton TA. Electrochemical and Molecular Assessment of Quinones as CO2-Binding Redox Molecules for Carbon Capture. Journal of Physical Chemistry C. 2022; 126(3): 1389-99.9. Gurkan B, Simeon F, Hatton TA. Quinone Reduction in Ionic Liquids for Electrochemical CO2 Separation. ACS Sustain Chem Eng. 2015;3(7): 1394- 405.10. Diederichsen KM, Liu Y, Ozbek N, Seo H, Hatton TA. Toward solvent- free continuous-flow electrochemically mediated carbon capture with high- concentration liquid quinone chemistry. Joule [Internet], 2022;6(1):221-39. Available from: https: / / doi.org / 10.1016 / jjoule.2021 .12.00111. Voskian S, Hatton TA. Faradaic electro-swing reactive adsorption for CO2 capture. Energy Environ Sci. 2019;12(12):3530-47.12. Liu Y, Ye HZ, Diederichsen KM, Van Voorhis T, Hatton TA. Electrochemically mediated carbon dioxide separation with quinone chemistry in salt-concentrated aqueous media. Nat Commun. 2020 Dec 1 ;11 (1 ).13. Ishida H, Ohba T, Yamaguchi T, Ohkubo K. Interaction between CO 2 and Electrochemically Reduced Species of N-propyl-4,4'-bipyridinium Cation. Vol. 23, Chemistry Letters. 1994. p. 905-8.14. Ranjan R, Olson J, Singh P, Lorance ED, Buttry DA, Gould IR. Reversible Electrochemical Trapping of Carbon Dioxide Using 4,4'-Bipyridine That Does Not Require Thermal Activation. Journal of Physical Chemistry Letters. 2015;6(24):4943-6.15. Li X, Zhao X, Liu Y, Hatton TA, Liu Y. Redox-tunable Lewis bases for electrochemical carbon dioxide capture. Nat Energy. 2022;7(11 ): 1065-75.16. Eisaman MD, Alvarado L, Larner D, Wang P, Garg B, Littau KA. CO2 separation using bipolar membrane electrodialysis. Energy Environ Sci. 2011 ;4(4): 1319-28.17. Eisaman MD, Parajuly K, Tuganov A, Eldershaw C, Chang N, Littau KA. CO2 extraction from seawater using bipolar membrane electrodialysis. Energy Environ Sci. 2012;5(6):7346-52.18. Stucki S, Schuler A, Constantinescu M. Coupled CO2 recovery from the atmosphere and water electrolysis: Feasibility of a new process for hydrogen storage. Int J Hydrogen Energy. 1995;20(8):653-63.19. Kim S, Choi M, Kang JS, Joo H, Park BH, Sung YE, et al.Electrochemical recovery of LiOH from used CO2 adsorbents. Catal Today [Internet], 2021 ;359(February 2019):83-9. Available from: https: / / doi.Org / 10.1016 / j.cattod.2019.06.05620. Shu Q, Legrand L, Kuntke P, Tedesco M, Hamelers HVM. Electrochemical Regeneration of Spent Alkaline Absorbent from Direct Air Capture. Environ Sci Technol. 2020;54(14):8990-8.21 . Xie H, Wu Y, Liu T, Wang F, Chen B, Liang B. Low-energy-consumption electrochemical CO2 capture driven by biomimetic phenazine derivatives redox medium. Appl Energy [Internet], 2020;259 (December 2019): 114119. Available from: https: / / doi.Org / 10.1016 / j.apenergy.2019.11411922. Jin S, Wu M, Jing Y, Gordon RG, Aziz MJ. Low energy carbon capture via electrochemically induced pH swing with electrochemical rebalancing. Nat Commun. 2022;13(1 ).23. Jin S, Wu M, Gordon RG, Aziz MJ, Kwabi DG. PH swing cycle for CO2capture electrochemically driven through proton-coupled electron transfer. Energy Environ Sci. 2020; 13(10):3706-22.24. Seo H, Hatton TA. Electrochemical direct air capture of CO2 using neutral red as reversible redox-active material. Nat Commun. 2023; 14(1 ): 1 —1 1.25. Seo H, Rahimi M, Hatton TA. Electrochemical Carbon Dioxide Capture and Release with a Redox-Active Amine. J Am Chem Soc. 2022;144(5):2164- 70.26. Almeida ARRP, Oliveira JASA, Monte MJS. Thermodynamic study of nicotinamide, N-methylnicotinamide and N,N-dimethylnicotinamide: Vapour pressures, phase diagrams, and hydrogen bonds. Journal of ChemicalThermodynamics [Internet], 2015;82:108-15. Available from: http: / / dx.doi.Org / 10.1016 / j .jot.2014.11 .00127. Singh V, Kim S, Kang J, Byon HR. Aqueous organic redox flow batteries. Nano Res. 2019;12(9):1988-2001 .28. Anson CW, Stahl SS. Mediated Fuel Cells: Soluble Redox Mediators and Their Applications to Electrochemical Reduction of 02 and Oxidation of H2, Alcohols, Biomass, and Complex Fuels. Chem Rev. 2020;120(8):3749-86.29. Striepe L, BaumgartnerT. Viologens and Their Application as Functional Materials. Chemistry - A European Journal. 2017;23(67): 16924-40.30. Ding J, Zheng C, Wang L, Lu C, Zhang B, Chen Y, et al. Viologen- inspired functional materials: Synthetic strategies and applications. J Mater Chem A Mater [Internet], 2019;7(41):23337-60. Available from: http: / / dx.doi.Org / 10.1039 / C9TA01724K31. Burgess M, Hernandez-Burgos K, Simpson BH, Lichtenstein T, Avetian S, Nagarjuna G, et al. Scanning Electrochemical Microscopy and Hydrodynamic Voltammetry Investigation of Charge Transfer Mechanisms on Redox Active Polymers. J Electrochem Soc. 2016;163(4):H3006-13.32. Matheson MS, Lee PC, Meisel D, Pelizzetti E. Kinetics of hydrogen production from methyl viologen radicals on colloidal platinum. Journal of Physical Chemistry. 1983;87(3):394-9.33. Yu YX. Binding energy and work function of organic electrode materials phenanthraquinone, pyromellitic dianhydride and their derivatives adsorbed on graphene. ACS Appl Mater Interfaces. 2014;6(18): 16267-75.34. Yu HF, Chen KI, Yeh MH, Ho KC. Effect of trifluoromethyl substituents in benzyl-based viologen on the electrochromic performance: Optical contrast and stability. Solar Energy Materials and Solar Cells. 2019;200(January).35. Feng R, Chen Y, Yang L, Du Q, Zhuo K. Ethyl viologen-functionalized reduced graphene oxide composites for asymmetric ionic liquid-based supercapacitors. Chemical Engineering Journal [Internet],2023;468(May): 143693. Available from: https: / / doi.Org / 10.1016 / j.cej.2O23.14369336. Zhao F, Li Q, Han K, Lian T. Mechanism of Efficient Viologen Radical Generation by Ultrafast Electron Transfer from CdS Quantum Dots. Journal of Physical Chemistry C. 2018;122(30):17136-42.37. Liu X, Neoh KG, Kang ET. Viologen-functionalized conductive surfaces: Physicochemical and electrochemical characteristics, and stability. Langmuir. 2002;18(23):9041-7.38. Carragher U, Breslin CB. Formation of benzyl viologen-containing films at copper and their protective properties. Electrochim Acta [Internet], 2020;342: 136071. Available from: https: / / d0i.0rg / l 0.1016 / j.electacta.2020.13607139. Liu W, Tkatchenko A, Scheffler M. Modeling adsorption and reactions of organic molecules at metal surfaces. Acc Chem Res. 2014;47(11):3369-77.40. Sagara T, Hagi Y, Toyohara M. Binding of Sulfate-Terminated Surfactants with Different Alkyl Chain Lengths to Viologen Sites Covalently Embedded in the Interior of a Self-Assembled Monolayer on a Au Electrode. Langmuir. 2022;38(3):979-86.41. Qiu Z, Liu Z, Lu X, Zhang S, Yan Y, Chi C, et al. Dual Molecules Cooperatively Confined In-Between Edge-oxygen-rich Graphene Sheets as Ultrahigh Rate and Stable Electrodes for Supercapacitors. Small. 2023;2302316:1-11.42. Debruler C, Hu B, Moss J, Luo J, Liu TL. A Sulfonate-Functionalized Viologen Enabling Neutral Cation Exchange, Aqueous Organic Redox Flow Batteries toward Renewable Energy Storage. ACS Energy Lett. 2018;3(3):663- 8.43. Luo J, Hu B, Debruler C, Bi Y, Zhao Y, Yuan B, et al. Unprecedented Capacity and Stability of Ammonium Ferrocyanide Catholyte in pH Neutral Aqueous Redox Flow Batteries. Joule. 2019;3(1 ): 149-63.44. Jin S, Fell EM, Vina-Lopez L, Jing Y, Michalak PW, Gordon RG, et al. Near Neutral pH Redox Flow Battery with Low Permeability and Long-Lifetime Phosphonated Viologen Active Species. Adv Energy Mater. 2020; 10(20): 1-10.45. DeBruler C, Hu B, Moss J, Liu X, Luo J, Sun Y, et al. Designer Two- Electron Storage Viologen Anolyte Materials for Neutral Aqueous Organic Redox Flow Batteries. Chem. 2017;3(6):961-78.46. Cao H, Pan J, Zhu H, Sun Z, Wang B, Zhao J, et al. Interaction Regulation Between Ionomer Binder and Catalyst: Active Triple-Phase Boundary and High Performance Catalyst Layer for Anion Exchange Membrane Fuel Cells. Advanced Science. 2021 ;8(19): 1 — 14.47. https: / / www.us-nano.com / inc / sdetail / 149 [Internet], Available from: https: / / www.us-nano.com / inc / sdetail / 149.

Claims

CLAIMS:1 . A method for operating an alternating dual-electrolyser system for direct air capture (DAC) and release of CO2, comprising: a) supplying a post-capture solution to a reduction compartment of the system, the reduction compartment comprising a cathode of a first electrolyser of the system; b) supplying an electrolyte solution comprising an organic redox- active molecule to an alternating redox compartment of the system, the redox compartment separated from the reduction compartment by a first cation exchange membrane of the first electrolyser, and the redox compartment comprising an alternating electrode operable alternatingly as an anode of the first electrolyser and as a cathode of a second electrolyser of the system; c) operating the first electrolyser to oxidize the redox-active molecule in the redox compartment and reduce the post-capture solution in the reduction compartment to produce hydrogen gas and regenerate a hydroxide capture solution for CO2 capture; d) supplying the hydrogen gas produced in the reduction compartment to an oxidation compartment of the system, the oxidation compartment having an anode of the second electrolyser and separated from the redox compartment by a second cation exchange membrane of the second electrolyser; and e) operating the second electrolyser to oxidize the hydrogen gas to hydrogen ions in the oxidation compartment and reduce the oxidized redox- active molecule in the redox compartment to regenerate an acidic neutralizing solution for CO2 neutralization and release.

2. The method of claim 1 , further comprising repeating (a) to (e) in a plurality of regeneration cycles to repeatedly regenerate the hydroxide capture solution for CO2 capture and the acidic neutralizing solution for CO2 neutralization and release.

3. The method of claim 2, further comprising capturing CO2 with the hydroxide capture solution to produce a post-capture carbonate compound and post-capture solution, supplying the carbonate compound to a neutralization chamber for neutralization and release of the CO2, and supplying the post- capture solution back to the reduction compartment for a subsequent 5 regeneration cycle.

4. The method of claim 3, further comprising supplying the acidic neutralizing solution regenerated in the redox compartment to the neutralization chamber to neutralize and release the CO2 from the carbonate compound and produce the electrolyte solution for supply back to the redox compartment for a 10 subsequent regeneration cycle.

5. The method of claim 4, further comprising supplying the hydroxide capture solution regenerated in the reduction compartment to an air contactor without any of the redox-active molecule.

6. The method of any one of claims 1 to 5, wherein the organic redox-active 15 molecule is a compound represented by the Formula I:I wherein: R1and R2are independently selected from C1-10alkyl, C1-10alkenyl, C1-10alkynyl, 20 C1-6alkyleneC3-15cycloalkyl, C1-6alkyleneC3-15heterocycloalkyl, C1-6alkyleneC6- 15aryl, C1-6alkyleneC6-15heteroaryl, C3-15cycloalkyl, C3-15heterocycloalkyl, C6- 15aryl, C5-15heteroaryl, C1-10alkylenePO32-and C1-10alkyleneSO3-, the aryl, heteroaryl, heterocycloalkyl and cycloalkyl groups are optionally substituted with one or more of halogen or C1-10alkyl, further optionally substituted with one 25 to three P(O)(OR3)2, wherein R3is selected from H or C1-6alkyl.

7. The method of claim 6, wherein R1and R2are independently selected from C1-6alkyl, C1-6alkyleneC6-15cycloalkyl, C1-6alkyleneC6-15heterocycloalkyl, C1-6alkyleneC6-15aryl, C1-6alkyleneC6-15heteroaryl, C1-6alkylenePO32-and C1- 6alkyleneSO3-, the aryl, heteroaryl, heterocycloalkyl and cycloalkyl groups are optionally substituted with one or more of halogen or C1-10alkyl, further 5 optionally substituted with one to three P(O)(OR3)2, wherein R3is selected from H or C1-6alkyl.

8. The method of claim 7, wherein R1and R2are independently selected from C1-4alkyl, C1-6alkyleneC6-15aryl, C1-4alkyleneC6-15heteroaryl, C1- 4alkylenePO32-and C1-4alkyleneSO3-, the aryl and heteroaryl are optionally 10 substituted with one or more of halogen or C1-10alkyl or halogen, further optionally substituted with one to three P(O)(OR3)2, wherein R3is selected from H or C1-6alkyl.

9. The method of claim 8, wherein R1and R2are independently selected from CH3, C1alkylephenyl, C3alkylenePO32-, C3alkyleneSO3-, 15 C1alkylenephenalenylC1alkylP(O)(OH)2, C2alkyleneindolyl, and C1alkylenephenalenyl 10. The method of claim 6, wherein the compound represented by the Formula I is selected from: 20I-2;I-7.

11. The method of any one of claims 1 to 5, wherein the redox-active molecule is selected from phenazine, tetrathiafulvalene, 4-hydroxy-2, 2,6,6- tetramethyl-piperdin-1-oxyl, and (ferrocenylmethyl)- trimethylammonium.

12. A method for cyclical regeneration of a hydroxide capture solution for direct air capture (DAC) of CO2 and an acidic neutralization solution for neutralization and release of the CO2, comprising: a) operating a first electrolyser to oxidize an organic redox-active molecule in an alternating redox compartment and reduce a post-capture solution in a reduction compartment to regenerate the hydroxide capture solution in the reduction compartment, the reduction compartment separated from the redox compartment by a first cation exchange membrane; and b) after (a), operating a second electrolyser to oxidize hydrogen in an oxidation compartment and reduce the oxidized redox-active molecule in the redox compartment to regenerate the acidic neutralizing solution in the redox compartment, the redox compartment separated from the oxidation compartment by a second cation exchange membrane.

13. The method of claim 12, wherein the redox compartment comprises an alternating electrode, and (a) includes operating the alternating electrode as an anode of the first electrolyser and (b) includes operating the alternating electrode as a cathode of the second electrolyser.

14. An alternating dual-electrolyser system for direct air capture (DAC) and release of CO2, the system comprising: a) a reduction compartment comprising a cathode of a first electrolyser for reduction of post-capture solution received in the reduction compartment to produce hydrogen gas and a hydroxide capture solution for supply to an air contactor for CO2 capture; b) an oxidation compartment for receiving the hydrogen gas produced in the reduction compartment and comprising an anode of a second electrolyser for oxidation of the hydrogen gas to hydrogen ions; and c) an alternating redox compartment separated from the reduction compartment by a first cation exchange membrane of the first electrolyser and from the oxidation compartment by a second cation exchange membrane of the second electrolyser, the redox compartment for receiving an electrolyte solution comprising an organic redox-active molecule in fluid isolation of the reduction compartment to maintain the redox-active molecule separate from the hydroxide capture solution thereby reducing loss of the redox-active molecule during CO2 capture, and d) the redox compartment comprising an alternating electrode, the alternating electrode operable alternatingly as an anode of the first electrolyser for oxidation of the redox-active molecule in the redox compartment to facilitate regeneration of the hydroxide capture solution, and as a cathode of the second electrolyser for reduction of the oxidized redox-active molecule to facilitate regeneration of an acidic neutralizing solution in the redox compartment for supply to a neutralization chamber for CO2 neutralization and release.

15. The system of claim 14, further comprising a control system including at least one controller configured to cycle operation of the dual-electrolyser system between a capture solution mode in which the first electrolyser operates to regenerate the hydroxide capture solution and a neutralizing solution mode in which the second electrolyser operates to regenerate the acidic neutralizing solution.

16. The system of any one of claims 14 to 15, wherein the hydroxide capture solution is suppliable to the air contactor without any of the redox-active molecule.

17. The system of any one of claims 14 to 16, wherein the redox-active molecule is a compound represented by the Formula I: 5I wherein: R1and R2are independently selected from C1-10alkyl, C1-10alkenyl, C1-10alkynyl, C1-6alkyleneC3-15cycloalkyl, C1-6alkyleneC3-15heterocycloalkyl, C1-6alkyleneC6- 10 15aryl, C1-6alkyleneC6-15heteroaryl, C3-15cycloalkyl, C3-15heterocycloalkyl, C6- 15aryl, C5-15heteroaryl, C1-10alkylenePO32-and C1-10alkyleneSO3-, the aryl, heteroaryl, heterocycloalkyl and cycloalkyl groups are optionally substituted with one or more of halogen or C1-10alkyl, further optionally substituted with one to three P(O)(OR3)2, wherein R3is selected from H or C1-6alkyl. 15 18. The system of any one of claims 14 to 16, wherein the organic redox- active molecule is selected from phenazine, tetrathiafulvalene, 4-hydroxy- 2,2,6,6-tetramethyl-piperdin-1-oxyl and (ferrocenylmethyl)- trimethylammonium.

19. A direct art capture system for CO2 capture and release, comprising: 20 a) an air contactor for receiving a hydroxide capture solution for CO2 capture to produce a carbonate compound and post-capture solution; b) a neutralization chamber for receiving the carbonate compound and an acidic neutralization solution for neutralization and release of CO2 from the carbonate compound to and formation of an electrolyte solution for 25 regeneration of the hydroxide capture solution;c) an alternating dual-electrolyser system for cyclical regeneration of the hydroxide capture solution and the acidic neutralization solution, the dual- electrolyser system including: i) a reduction compartment for receiving the post-capture solution and comprising a cathode of a first electrolyser for reduction of the post-capture solution in the reduction compartment to produce hydrogen gas and the hydroxide capture solution for supply to the air contactor; ii) an oxidation compartment for receiving the hydrogen gas produced in the reduction compartment and comprising an anode of a second electrolyser for oxidation of the hydrogen gas to hydrogen ions; and iii) an alternating redox compartment separated from the reduction compartment by a first cation exchange membrane of the first electrolyser and from the oxidation compartment by a second cation exchange membrane of the second electrolyser, the redox compartment for receiving the electrolyte solution from the neutralization chamber, the electrolyte solution comprising an organic redox-active molecule in fluid isolation of the reduction compartment to maintain the redox-active molecule separate from the hydroxide capture solution thereby reducing loss of the redox-active molecule during CO2 capture, and iv) the redox compartment comprising an alternating electrode, the alternating electrode operable alternatingly as an anode of the first electrolyser for oxidation of the redox-active molecule in the redox compartment to facilitate regeneration of the hydroxide capture solution in the reduction compartment, and as a cathode of the second electrolyser for reduction of the oxidized redox-active molecule to facilitate regeneration of the acidic neutralizing solution in the redox compartment for supply to the neutralization chamber.

20. An alternating dual-electrolyser system for direct air capture (DAC) and release of CO2, comprising: a) a reduction compartment comprising a cathode of a first electrolyser; b) an oxidation compartment comprising an anode of a second electrolyser; and c) an alternating redox compartment separated from the reduction compartment by a first cation exchange membrane of the first electrolyser and from the oxidation compartment by a second cation exchange membrane of the second electrolyser, the redox compartment for receiving an electrolyte solution comprising an organic redox-active molecule in fluid isolation of the reduction compartment, and the redox compartment including an alternating electrode serving as an anode of the first electrolyser for oxidation of the redox-active molecule in the redox compartment to facilitate regeneration of hydroxide capture solution in the reduction compartment, and as a cathode of the second electrolyser for reduction of the oxidized redox-active molecule to facilitate regeneration of an acidic neutralizing solution in the redox compartment.

Images