Process and apparatus for capturing co 2

Abstract

A process for capturing carbon dioxide is described. The process comprises electrolysing a solution of at least one electroactive species, at least one electrolyte, and at least one non-aqueous solvent in electrochemical cells to sequentially reduce and oxidise the electroactive species allowing the adsorption and release of carbon dioxide. The process may be operated continuously and may be utilised to capture CO2 from ambient air.

Description

Process and apparatus for capturing CO2Cross-reference to related applications

[0001] This application claims priority to Australian provisional application no. 2023903525, filed on 2 November 2023, the entire disclosure of which is hereby incorporated by reference.Field of the disclosure

[0002] The present disclosure relates to a process for capturing carbon dioxide comprising electrolysing a solution of at least one electroactive species, at least one electrolyte, and at least one non-aqueous solvent in electrochemical cells to sequentially reduce and oxidise the electroactive species allowing the adsorption and release of carbon dioxide. The process may be operated continuously and may be utilised to capture CO2 from ambient air. The disclosure also relates to a zero-gap flow cell in which the process may be performed.Background of the disclosure

[0003] There has been an effort to mitigate climate change by the reduction / removal of carbon dioxide emissions. To this effect, Direct Air Capture (DAC) has been widely researched for its potential to remove large volumes of CO2 from the atmosphere. In contrast to other forms of carbon dioxide removal, which are limited in scale due to their large land-use footprints, DAC can capture equivalent volumes of CO2 using a much smaller fraction of land.

[0004] However, the process typically requires large quantities of energy to power adsorption and desorption mechanisms, owing to the dilute nature of CO2 in the air and the energy required to concentrate and extract CO2. In particular, desorbing CO2 from an absorbent material often comprises the largest energy expenditure. Therefore, while DAC may not suffer from the same land-use limitations as other forms of carbon dioxide removal, its energy consumption could serve as a limiting factor.

[0005] There are already a variety of adsorption and desorption mechanisms currently employed throughout the DAC industry ranging from the utilization of aqueous hydroxide solutions, lime carbonation, amine-based solvents and sorbents, Metal- Organic Frameworks (MOFs), and electrochemical systems that utilize amines,disulfides, bipyridines, and quinones. Methods that employ temperature and / or pressure swings to selectively adsorb and desorb CO2 typically involve strong chemisorption bonds between an adsorbent material and CO2 molecules, which consequently requires a more energy-intensive desorption step to liberate captured CO2.

[0006] In contrast, electrochemical systems capitalize on a weaker chemisorption interaction, which consequently enables a low-energy adsorption and desorption step. More specifically, conventional temperature and / or pressure swing systems reportedly use between 230 and 800 thermal kJ per mole of CO2 captured. In contrast, electrochemical systems have reported thermodynamic minimums ranging from 21 to 90 kJ per mole of CO2 captured.

[0007] The stark difference in energy consumption can be attributed not only to the aforementioned weaker interaction with CO2 but also to the process’ simplicity. In temperature and / or pressure swing systems, heat and / or vacuums are applied over large adsorbent materials, which often contain a significant mass and volume of nonactive substrates and coatings. These non-active materials increase a system’s thermal mass, and since energy is applied to non-active materials, energy is wasted. Moreover, these systems are also inefficient as electricity must be converted into heat or pressure, which introduces further energy losses.

[0008] Alternatively, electrochemical systems may apply just enough electrical potential to oscillate redox-active molecules between oxidation states to facilitate adsorption and desorption.

[0009] For these reasons, interest in electrochemical systems for carbon dioxide capture has increased.

[0010] Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and / or combined with other pieces of prior art by a skilled person in the art.Summary of the disclosure

[0011] In one aspect the present disclosure provides an electrochemical process for capturing CO2 comprising the steps of: a) electrolysing a solution comprising CO2, at least one electroactive species, at least one electrolyte, and at least one non-aqueous solvent in a first electrochemical cell under conditions effective to reduce the at least one electroactive species and form a solution comprising reduced electroactive species CO2 adducts; b) electrolysing the solution comprising the reduced electroactive species CO2 adducts in a second electrochemical cell under conditions effective to oxidise the reduced electroactive species thereby releasing CO2 and regenerating the at least one electroactive species; wherein both the first and second electrochemical cells comprise electrodes at least partially immersed in solution.

[0012] In embodiments of the process, both the first and second electrochemical cells comprise cathodic and anodic half-cells, the half-cells being separated by anion exchange membrane, wherein the solution comprising reduced electroactive species CO2 adducts is formed in the cathodic half-cell of the first electrochemical cell and a solution comprising oxidised species is formed from reduced species in the anodic halfcell of the first electrochemical cell; and wherein the reduced electroactive species CO2 adducts are oxidised in the anodic half-cell of the second electrochemical cell to regenerate the at least one electroactive species and the oxidised species are reduced in the cathodic half-cell of the second electrochemical cell to regenerate the reduced species.

[0013] In embodiments of the process, at least one of the first or the second electrochemical cells is a zero-gap electrochemical flow cell.

[0014] In embodiments of the process, the reduced / oxidised species comprises ferrocene / ferrocenium.

[0015] In embodiments, the process further comprises the step of separating released CO2 from the solution of the at least one regenerated electroactive species.

[0016] In embodiments of the process, prior to step a) a solution comprising the at least one electroactive species is contacted with at least one feed gas comprising CO2.

[0017] In embodiments of the process, prior to step b) the solution comprising the reduced electroactive species CO2 adducts is contacted with at least one feed gas comprising CO2.

[0018] In embodiments of the process, the solution comprising regenerated at least one electroactive species formed in step b) is recycled to the first electrochemical cell and contacted with at least one feed gas comprising CO2 either prior to entering the first electrochemical cell or within the first electrochemical cell.

[0019] In embodiments of the process, any two or more of the feed gases comprising CO2 comprise the same feed gas composition.

[0020] In embodiments of the process, any two or more of the feed gases comprising CO2 comprise different feed gas compositions.

[0021] In embodiments of the process, any one or more of the feed gas comprising CO2 comprises ambient air.

[0022] In embodiments, the at least one electroactive species comprise one or more of quinone, pyridine, bipyridine, such as 1 ,4-bipyridine, pyrazine, and phenazine. The electroactive species also includes molecules comprising any one or more of these molecules as substructures within a larger molecule.

[0023] In embodiments, the quinones comprise one or more of benzoquinone, hydroquinone, phenanthraquinone, napthoquinone and anthraquinone.

[0024] In embodiments, the process comprises two or more electroactive species, such as two or more quinones, or mixtures of two or more of quinone, pyridine, bipyridine, pyrazine, and phenazine.

[0025] In embodiments of the process, the at least one electrolyte comprises one or more ammonium salts, alkali metal salts, or trifluoromethanesulfonyl imide salts.

[0026] In embodiments of the process, the at least one electrolyte comprises one or more tetraalkylammonium salts.

[0027] In embodiments of the process, the at least one electrolyte comprises one or more tetraalkylammonium tetrafluoroborate salts, alkali metal (trifluoromethansulfonyl)imide salts, and tetraalkylammonium hexafluorophosphate salts.

[0028] In embodiments of the process, the at least one electrolyte comprises one or more of lithium (trifluoromethanesulfonyl)imide ammonium perchlorate, ammonium nitrate, ammonium sulfate, ammonium fluoride, ammonium bromide, ammonium acetate, ammonium phosphate, tetraethylammonium tetrafluoroborate, triethyl(methyl)tetrafluoroborate and tetrabutylammonium hexafluorophosphate.

[0029] In embodiments of the process, the concentration of electrolyte is from about 0.05 M to about 5 M, or from about 0.1 M to about 2 M, or from about 0.1 M to about 1 M.

[0030] In embodiments of the process, the at least one non-aqueous solvent comprises a solvent with a boiling point of at least about 80°C, or at least about 100°C, or at least about 120°C, or at least about 140°C, or at least about 160°C, or at least about 180°C, or at least about 200°C, or at least about 220°C.

[0031] In embodiments of the process, the at least one non-aqueous solvent comprises a solvent with a dielectric constant of at least about 30.

[0032] In embodiments of the process, the at least one solvent comprises one or more of acetonitrile, tetrahydrofuran, diethyl carbonate, y-butyrolactone, dimethylformamide, ethylene carbonate, propylene carbonate, dimethyl sulfoxide, N,N-dimethylacetamide and dichloromethane.

[0033] In embodiments of the process, the electrochemical cell is a parallel plate electrochemical cell.

[0034] In embodiments of the process, the electrodes comprise one or more of graphite, graphite foil, carbon paper, carbon / graphitic felt, aluminium, stainless-steel, platinum foil, and platinum mesh-covered stainless-steel.

[0035] In embodiments of the process, the electrolysis is conducted at a temperature of about 20 °C or higher.

[0036] In embodiments of the process, the potential difference across the first electrochemical cell is from about 0.5 V to about 3.0 V.

[0037] In embodiments of the process, the potential difference across the second electrochemical cell is from about -0.5 V to about -3.0 V.

[0038] In embodiments of the process, the anion exchange membrane comprises cellulose, polymer or polymer composite.

[0039] In embodiments, the polymer comprises one or more of polyether ketone, polysulfone and polytetrafluoroethylene.

[0040] In another aspect, the present disclosure provides a zero-gap electrochemical flow cell comprising an anode, a cathode, an anion exchange membrane disposed between the anode and cathode, and a cell body comprising at least two cell body elements configured to define an internal flow field and encapsulate the anode, cathode, and anion exchange membrane, each element further comprising inlet and outlet ports configured to supply and remove a first liquid to and from the anode, and supply and remove a second liquid to and from the cathode, each cell body element adapted to hold the first electrode, the second electrode and the anion exchange membrane in place between the cell body elements, wherein the electrochemical flow cell is further characterised by one or more of the following features:(a) the cell body elements comprise a material substantially resistant to non-aqueous solvents;(b) an inter-electrode distance between the first and second electrode from about 25 to about 200 pm, preferably from about 50 to about 100 pm;(c) substantially circular or ovular fluoroelastomer gaskets arranged between the first electrode and the anion exchange membrane, and the second electrode and the anion exchange membrane; and(d) an anion exchange membrane comprising one or more of cellulose, polymer or polymer composite.

[0041] In embodiments, an internal surface of at least one of the cell body elements comprises one or more protrusions with a flow face configured to increase turbulence of liquid flow within the internal flow field.

[0042] In some embodiments, the one or more protrusions comprise a first region and a second region, said first region and second region are of different size, and the one or more protrusions are arranged in the internal flow field such that liquid flow is directed by the flow face from the first region towards the second region to increase turbulence of the liquid flow.

[0043] In some embodiments, one or more protrusions comprise a first region and a second region, said first region and second region are of different height, and the one or more protrusions are arranged in the internal flow field such that liquid flow is directed by the flow face from the first region towards the second region to increase turbulence of the liquid flow.

[0044] In some embodiments, the first region and the second region have a ratio of size and / or height from about 1 :2 to about 1 :4.

[0045] In some embodiments, the flow face of the one or more protrusions comprises a curved region.

[0046] In some embodiments, the one or more protrusions comprise a plurality of protrusions, said plurality of protrusions being arranged such that at least one pair of adjacent protrusions are arranged in different orientations.

[0047] In some embodiments, the flow face of the at least one pair of adjacent protrusions are rotated about 180°.

[0048] In some embodiments, the one or more protrusions comprise a plurality of protrusions, said plurality of protrusions being arranged such that at least one pair of adjacent protrusions are on opposite surfaces of the flow field.

[0049] In some embodiments, one or more protrusions extend from the internal surface to occupy at least 50% of the internal flow field, or at least 60% of the internal flow field, or at least 70% of the internal flow field.

[0050] In embodiments, the first liquid comprises a non-aqueous solvent, at least one electroactive species, at least one electrolyte, and CO2.

[0051] In embodiments, the second liquid comprises a non-aqueous solvent, reduced electroactive species CO2 adducts, and at least one electrolyte.

[0052] In embodiments, the first electrode and the second electrode comprise one or more of graphite, graphite foil, carbon paper, carbon / graphitic felt, aluminium, stainless- steel, platinum foil, and platinum mesh-covered stainless-steel.

[0053] In embodiments, the cell body elements comprise metal or polymer.

[0054] In embodiments, the cell body elements comprise one or more of polypropylene, polyether ether ketone, polylactic acid, acrylonitrile butadiene styrene, and polyethylene terephthalate.

[0055] In a preferred embodiment, the cell body elements comprise polypropylene.

[0056] In embodiments, the anion exchange membrane comprises one or more of polyether ketone, polysulfone and polytetrafluoroethylene.

[0057] In embodiments, the non-aqueous solvent comprises one or more of acetonitrile, tetrahydrofuran, diethyl carbonate, y-butyrolactone, dimethylformamide, ethylene carbonate, propylene carbonate, dimethyl sulfoxide, N,N-dimethylacetamide and dichloromethane.

[0058] In embodiments, the gaskets are O-rings.

[0059] In embodiments, each cell body element is adapted to hold the first electrode, the second electrode and the anion exchange membrane in place by a series of fasteners on each cell body element.

[0060] In some embodiments, the series of fasteners comprise a continuously curved pattern of fasteners.

[0061] In embodiments, the fasteners may be selected from one or more rivets, screws, bolts, nuts, threaded rods, carriage bolts and pins.

[0062] In another aspect, the present disclosure provides a zero-gap electrochemical flow cell as described by any one of the disclosed embodiments for use in CO2 capture, redox-flow batteries, energy storage, hydrogen generation, CO2 reduction and electrochemical mineral refinement.

[0063] In a preferred embodiment, the present disclosure provides a zero-gap electrochemical flow cell as described by any one of the herein disclosed embodiments for use in CO2 capture or CO2 reduction.

[0064] In another aspect, the present disclosure provides a method of fabricating a zero-gap flow cell comprising the step of one or more of 3D printing, injection moulding or CNC milling the cell body elements.

[0065] In another aspect, the present disclosure provides a process of CO2 capture using a zero-gap electrochemical flow cell as described in any one of the herein disclosed embodiments.

[0066] In embodiments, advantages of the presently described electrochemical processes of capturing CO2 include one or more of the following:• they may be used for direct air capture;• they may be run as continuous processes;• they may be energy efficient in operation.

[0067] In embodiments, advantages of the presently described zero-gap flow cell include one or more of the following:• low cost;• scalable;• liquid-tight in the presence of harsh organic solvents;• provide a low resistance flow cell due to the short inter-electrode distance.

[0068] The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended for the purpose of exemplification only.Functionally-equ i valent processes are clearly within the scope of the disclosure as described herein.

[0069] Further aspects of the present disclosure and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.Brief description of the drawings

[0070] Figure 1 is a flowsheet of a process for the capture of CO2 according to one embodiment of the present disclosure.

[0071] Figure 2 is a flowsheet of a process for the capture of CO2 according to another embodiment of the present disclosure.

[0072] Figure 3 is a flowsheet of a process for the capture of CO2 according to another embodiment of the present disclosure.

[0073] Figure 4 is a flowsheet of a process for the capture of CO2 according to another embodiment of the present disclosure.

[0074] Figure 5 is a flowsheet of a process for the capture of CO2 according to another embodiment of the present disclosure.

[0075] Figure 6 is a flowsheet of a process for the capture of CO2 according to another embodiment of the present disclosure.

[0076] Figure 7 is a flowsheet of a process for the capture of CO2 according to another embodiment of the present disclosure.

[0077] Figure 8 is a schematic of one element of a cell body of a partially disassembled zero-gap electrochemical flow cell according to one embodiment of the present disclosure.

[0078] Figure 9 is a top view of a partially disassembled zero-gap electrochemical flow cell with one cell body element removed according to one embodiment of the present disclosure.

[0079] Figure 10 is a side view of a zero-gap electrochemical flow cell according to one embodiment of the present disclosure.

[0080] Figure 11 is a cyclic voltammogram of a quinone dissolved in 80:20 MeCN:ethanol with 0.5 M TBAPFe measured in 100% N2 and in 100% CO2. The trace with a current of about -3 mA at -1 .95 V corresponds to the measurement in N2, and the trace with a current of -4 mA at -1 .95 V corresponds to the measurement in CO2.

[0081] Figure 12 is a A) CV of pyrazine performed at 200 mV / s scan rate; B) CV of 4,4 bipyridine performed at 100 mV / s; C) CV of phenazine performed at 100 mV / s; D) CV of benzoquinone performed at 100 mV / s; E) CV of 2,3,5,6-tetrachloro-p-benzoquinone performed at 100 mV / s scan rate. All measurements were performed with 0.1 M TBAPFe / MeCN solution in 100% N2 environment.

[0082] Figure 13 is a A) CV of phenazine performed at 100 mV / s scan rate in 100% CO2 environment; B) CV of 4,4 bipyridine performed at 100 mV / s in 100% CO2 environment.

[0083] Figure 14 is the chronopotentiometry performed in ambient air with a 0.25 M LITFSI / DMSO solution with a 23.6 mM ferrocene counter-species with A) 11 .8 mM pyrazine; B) 23.6 mM 4,4 bipyridine; C) 11 .8 mM phenazine; D) 11 .8 mM benzoquinone; and E) 11 .8 mM 3,5,6-tetrachloro-p-benzoquinone.

[0084] Figure 15 is the coulombic efficiency after cycling performed in ambient air with a 0.25 M LITFSI / DMSO solution with a 23.6 mM ferrocene counter-species with A) 11 .8 mM pyrazine; B) 23.6 mM 4,4 bipyridine; C) 11 .8 mM phenazine; D) 11 .8 mM benzoquinone; and E) 11 .8 mM 3,5,6-tetrachloro-p-benzoquinone.

[0085] Figure 16 is a cross-sectional side view of one element of the zero-gap electrochemical flow cell according to one embodiment of the present disclosure. The region labelled A is shown in expanded view (15:1 scale) and shows the arrangement of protrusions in adjacent tracks of the flow field.

[0086] Figure 17 is a top view of a partially disassembled zero-gap electrochemical flow cell according to one embodiment of the present disclosure containing protrusions with one cell body element removed.Detailed description of the embodiments

[0087] It will be understood that the disclosure defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the disclosure.Definitions

[0088] For purposes of interpreting this specification, terms used in the singular will also include the plural and vice versa.

[0089] As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps.

[0090] "About" as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20% or ±10%, in some instances ±5%, in some instances ±1%, and in some instances ±0.1% from the specified value, as such variations are appropriate to perform the disclosed processes.

[0091] Ranges: throughout this disclosure, various aspects of the disclosure can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosure. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1 , 2, 2.7, 3, 4, 5, 5.3, and 6. This applies regardless of the breadth of the range.

[0092] “And / or” means “and” and “or”.

[0093] The present disclosure relates to an electrochemical process for capturing CO2 comprising the steps of:a) electrolysing a solution comprising CO2, at least one electroactive species, at least one electrolyte, and at least one non-aqueous solvent in a first electrochemical cell under conditions effective to reduce the at least one electroactive species and form a solution comprising reduced electroactive species CO2 adducts; then b) electrolysing the solution comprising the reduced electroactive species CO2 adducts in a second electrochemical cell under conditions effective to oxidise the reduced electroactive species thereby releasing CO2 and regenerating the at least one electroactive species; wherein both the first and second electrochemical cells comprise electrodes at least partially immersed in solution.

[0094] In embodiments, both the first and second electrochemical cells comprise cathodic and anodic half-cells, the half-cells being separated by anion exchange membrane, wherein the solution comprising reduced electroactive species CO2 adducts is formed in the cathodic half-cell of the first electrochemical cell and a solution comprising oxidised species is formed from reduced species in the anodic half-cell of the first electrochemical cell; and wherein the reduced electroactive species CO2 adducts are oxidised in the anodic half-cell of the second electrochemical cell to regenerate the at least one electroactive species and the oxidised species are reduced in the cathodic half-cell of the second electrochemical cell to regenerate the reduced species.

[0095] The regenerated solution comprising the at least one electroactive species in the anodic half-cell of the second electrochemical cell and the solution comprising the regenerated reduced species in the cathodic half-cell of the second electrochemical cell may be cycled back to the cathodic half-cell and the anionic half-cell of the first electrochemical cell respectively, allowing the process to operate continuously.

[0096] In embodiments of the process, at least one of the first or the second electrochemical cells may be a zero-gap electrochemical flow cell. In some embodiments, at least one of the first or the second electrochemical cells may be a zero-gap electrochemical flow cell according to any one or more of the herein disclosed embodiments.

[0097] In embodiments of the process, the reduced / oxidised species comprises ferrocene / ferrocenium.

[0098] The process may further comprise the step of separating released CO2 from the solution of the at least one regenerated electroactive species.

[0099] In embodiments, prior to step a) a solution comprising the at least one electroactive species is contacted with at least one feed gas comprising CO2.

[0100] In embodiments, prior to step b) the solution comprising the reduced electroactive species CO2 adducts is contacted with at least one feed gas comprising CO2.

[0101] The addition of a feed gas comprising CO2 prior to step b) saturates the solution comprising the electroactive species-CO2 adducts by maximising the amount of gaseous CO2 dissolved in the solution. Upon oxidation in the second electrolyser to regenerate the free electroactive species and release the CO2 from the electroactive species-CO2 adducts, the released CO2 is not able to be solubilised in the solution. Advantageously, this leads to the released CO2 being forced into the headspace, thus enabling removal from the process.

[0102] In embodiments, the regenerated at least one electroactive species formed in step b) is contacted with at least one feed gas comprising CO2 and the resulting solution fed to the first electrochemical cell.

[0103] The present disclosure relates to a further electrochemical process for capturing CO2 comprising the steps of: a) electrolysing a solution comprising CO2, at least one electroactive species, one or more electrolytes and at least one non-aqueous solvent in a first electrochemical cell under conditions effective to reduce the at least one electroactive species and form a solution comprising reduced electroactive species CO2 adducts; then b) contacting the solution comprising the reduced electroactive species CO2 adducts with at least one feed gas comprising CO2 and electrolysing the solution comprising the reduced electroactive species CO2 adducts in a second electrochemical cell under conditions effective to oxidise the reduced electroactive species thereby releasing CO2 and regenerating the at least one electroactive species;wherein both the first and second electrochemical cells comprise electrodes at least partially immersed in solution.

[0104] The process may further require the step of separating released CO2 from the solution of the at least one regenerated electroactive species.

[0105] The processes of the present disclosure may be operated continuously, or in batch mode.Feed gases comprising CO2

[0106] The feed gases comprising CO2 of the present disclosure may comprise the same feed gas composition.

[0107] The feed gases comprising CO2 of the present disclosure may comprise different feed gas compositions.

[0108] The feed gases comprising CO2 may comprise ambient air. Other feed gas sources may comprise effluent gases from coal, or natural gas-fired power plants, concrete production or burning biofuels. Other feed gas sources comprising CO2 are contemplated.

[0109] The feed gas may comprise more than one gas, for example a feed gas may further comprise nitrogen, oxygen, methane, hydrogen, argon, xenon, neon, helium and the like.

[0110] Ambient air as used herein refers to atmospheric air in its natural state. Ambient air typically consists of about 78% nitrogen, 21% oxygen and the remaining 1% a combination of carbon dioxide, helium, methane, argon and hydrogen.

[0111] Any of the feed gases may be used at atmospheric pressure or may be compressed for use in a process of the present disclosure.

[0112] According to one or more embodiments the feed gas comprising CO2 may have a particular concentration. In some embodiments, the CO2 concentration may be from 10 ppm to 1000 ppm. In some embodiments the concentration may be from 0.5% to 15% by volume. Other concentrations of CO2 are envisaged.Electroactive species

[0113] In embodiments, the at least one electroactive species comprise one or more of quinone, pyridine, bipyridine, such as 1 ,4-bipyridine, pyrazine, and phenazine. The electroactive species also includes molecules comprising any one or more of these molecules as substructures within a larger molecule.

[0114] The term “quinone” refers to a class of cyclic organic compound containing two carbonyl groups, either adjacent or separated by a vinylene group (-CH=CH-).

[0115] In embodiments, the quinones comprise one or more of benzoquinone, hydroquinone, phenanthraquinone, napthoquinone and anthraquinone. Other suitable quinones known in the art are contemplated.

[0116] In embodiments, the process comprises two or more electroactive species, such as two or more quinones, or mixtures of two or more of quinone, pyridine, bipyridine, pyrazine, and phenazine.

[0117] In some embodiments, at least two electroactive species may be preferred as increasing the number of electroactive species in solution may increase the concentration of electroactive species-CO2 adducts formed during reduction in the first electrolyser, thus allowing the capture of more CO2. Solutions saturated by one electroactive species may still allow further different electroactive species to be solubilised.Electrolytes

[0118] The electrolytes may comprise one or more ammonium salts, alkali metal salts, or trifluoromethanesulfonyl imide salts. Other electrolytes known in the art are contemplated.

[0119] The electrolytes may comprise one or more tetraalkylammonium salts.

[0120] The electrolytes may comprise one or more tetraalkylammonium tetrafluoroborate salts, alkali metal (trifluoromethanesulfonyl)imide salts and tetraalkylammonium hexafluorophosphate salts.

[0121] Preferably, the at least one electrolyte comprises one or more of lithium (trifluoromethanesulfonyl)imide, ammonium perchlorate, ammonium nitrate, ammoniumsulfate, ammonium fluoride, ammonium bromide, ammonium acetate, ammonium phosphate, tetraethylammonium tetrafluoroborate, triethyl(methyl)tetrafluoroborate and tetrabutylammonium hexafluorophosphate.

[0122] In embodiments, the concentration of electrolyte may be from about 0.05M to about 5M, or from about 0.1 M to about 2M, or from about 0.1 M to about 1 M.Solvents

[0123] Preferably, the solvent or solvent mixture has a high boiling point to minimise solvent loss during the CO2 capture process. Preferably, the boiling point of a solvent or solvent mixture is at least about 80 °C.

[0124] The solvent may comprise a solvent with a dielectric constant of at least about 30.

[0125] The solvent may comprise one or more of acetonitrile, tetrahydrofuran, diethyl carbonate, y-butyrolactone, dimethylformamide, ethylene carbonate, propylene carbonate dimethyl sulfoxide, N,N-dimethylacetamide and dichloromethane. Preferably, the solvent comprises one or more of acetonitrile and propylene carbonate. Other solvents known in the art are contemplated.

[0126] The solvents may be selected to maximise the solubility of one or more of the selected electroactive species to increase the amount of CO2 captured.Electrochemical cell

[0127] In embodiments of the presently disclosed process the electrochemical cell may be a parallel plate electrochemical cell.

[0128] In embodiments the electrochemical cells comprise cathodic and anodic halfcells, the half-cells being separated by anion exchange membrane.

[0129] In embodiments, the anion exchange membrane comprises cellulose, polymer or polymer composite.

[0130] In embodiments, the polymer comprises one or more of polyether ketone, polysulfone and polytetrafluoroethylene.

[0131] The electrolyses of solution may be conducted at a temperature of about 20 °C or higher.

[0132] The potential difference across the first electrochemical cell may be from about 0.5 V to about 3.0 V.

[0133] The potential difference across the second electrochemical cell may be from about -0.5 V to about -3.0 V.

[0134] The electrode used in the first or second electrochemical cell may comprise graphite, graphite foil, carbon paper, carbon / graphitic felt, aluminium, stainless-steel, platinum foil and platinum mesh-covered stainless-steel. Preferably the electrode used in the first or second electrochemical cell comprises graphite foil, carbon / graphitic felt or platinum foil.Zero-gap electrochemical flow cell

[0135] In another aspect, the present disclosure provides a zero-gap electrochemical flow cell comprising an anode, a cathode, an anion exchange membrane disposed between the anode and cathode, and a cell body comprising at least two cell body elements configured to define an internal flow field and encapsulate the anode, cathode, and anion exchange membrane, each element further comprising inlet and outlet ports configured to supply and remove a first liquid to and from the anode, and supply and remove a second liquid to and from the cathode, each cell body element adapted to hold the first electrode, the second electrode and the anion exchange membrane in place between the at least two cell body elements, wherein the electrochemical flow cell is further characterised by one or more of the following features:(a) the cell body elements comprise a material substantially resistant to non-aqueous solvents;(b) an inter-electrode distance between the first and second electrode of between about 25 to about 200 pm, preferably between about 50 to about 100 pm;(c) substantially circular or ovular fluoroelastomer gaskets arranged between the first electrode and the anion exchange membrane, and the second electrode and the anion exchange membrane; and(d) an anion exchange membrane comprising one or more of cellulose, polymer or polymer composite.

[0136] In embodiments, an internal surface of at least one of the cell body elements may comprise one or more protrusions with a flow face configured to increase turbulence of liquid flow within the internal flow field.

[0137] In embodiments, one or more protrusions may comprise a first region and a second region, said first region and second region are of different size, and the one or more protrusions are arranged in the internal flow field such that liquid flow is directed by the flow face from the first region towards the second region to increase turbulence of the liquid flow.

[0138] In embodiments, one or more protrusions may comprise a first region and a second region, said first region and second region are of different height, and the one or more protrusions are arranged in the internal flow field such that liquid flow is directed by the flow face from the first region towards the second region to increase turbulence of the liquid flow.

[0139] In embodiments, the first region and the second region may have a ratio of size and / or height from about 1 :2 to about 1 :4.

[0140] In embodiments, the flow face of the one or more protrusions may comprise a curved region.

[0141] In embodiments, one or more protrusions may comprise a plurality of protrusions, said plurality of protrusions being arranged such that at least one pair of adjacent protrusions are arranged in different orientations.

[0142] In embodiments, the flow face of the at least one pair of adjacent protrusions may be rotated about 180°.

[0143] In embodiments, the one or more protrusions may comprise a plurality of protrusions, said plurality of protrusions being arranged such that at least one pair of adjacent protrusions are on opposite surfaces of the flow field.

[0144] In embodiments, one or more protrusions may extend from the internal surface to occupy at least 50% of the internal flow field, or at least 60% of the internal flow field, or at least 70% of the internal flow field.

[0145] The first liquid may comprise a non-aqueous solvent, at least one electroactive species, at least one electrolyte and CO2.

[0146] The second liquid may comprise a non-aqueous solvent, reduced electroactive species CO2 adducts and at least one electrolyte.

[0147] The first electrode and the second electrode may comprise one or more of graphite, graphite foil, carbon paper, carbon / graphitic felt, aluminium, stainless-steel, platinum foil, and platinum mesh-covered stainless-steel.

[0148] The cell body elements may comprise metal or polymer. Other suitable materials are contemplated.

[0149] The cell body elements may comprise one or more of polypropylene, polyether ether ketone, polylactic acid, acrylonitrile butadiene styrene and polyethylene terephthalate. Other suitable polymers are contemplated.

[0150] Preferably, the cell body elements comprise polypropylene.

[0151] The anion exchange membrane may comprise one or more of polyether ketone, polysulfone and polytetrafluoroethylene. Other suitable anion exchange membranes known in the art are contemplated.

[0152] The non-aqueous solvent may comprise one or more of acetonitrile, tetrahydrofuran, diethyl carbonate, y-butyrolactone, dimethylformamide, ethylene carbonate, propylene carbonate, dimethyl sulfoxide, A / ,A / -dimethylacetamide and dichloromethane. Other suitable non-aqueous solvents are contemplated.

[0153] The gaskets may comprise O-rings. The gasket provides a substantial seal which minimises the amount of liquid leaking from the zero-gap electrochemical flow cell. Other gaskets known in the art are contemplated.

[0154] In embodiments, each cell body element may be adapted to hold the first electrode, the second electrode and the anion exchange membrane in place by a seriesof fasteners on each cell body element. Preferably, the series of fasteners comprise a continuously curved pattern of fasteners.

[0155] The fasteners may be selected from one or more rivets, screws, bolts, nuts, threaded rods, carriage bolts and pins. These fasteners are listed non-exclusively and suitable fasteners known in the art are contemplated.

[0156] The zero-gap electrochemical flow cell as described by any one of the disclosed embodiments may be used for CO2 capture, redox-flow batteries, energy storage, hydrogen generation, CO2 reduction and electrochemical mineral refinement. Other suitable uses for a zero-gap electrochemical flow cell known in the art are contemplated.

[0157] Preferably, the zero-gap electrochemical flow cell as described by any one of the disclosed embodiments may be used in CO2 capture or CO2 reduction.

[0158] The present disclosure provides a method of fabricating a zero-gap flow cell which may comprise one or more of 3D printing, injection moulding or CNC milling the cell body elements. Other suitable fabrication techniques are contemplated.

[0159] The present disclosure provides a process of CO2 capture using a zero-gap electrochemical flow cell as described by any one of the above embodiments.

[0160] While the following discussion of Figures 1 to 7 specifically mentions quinones, no such limitation is intended, and other electroactive species, as disclosed herein, may be utilised.

[0161] Figure 1 illustrates one embodiment of a process for capturing CO2 according to the present disclosure. A solution comprising one or more quinones, one or more electrolytes, one or more solvents, and CO2 is fed through line (1 ) to a first electrolytic cell (2), wherein a potential is applied to reduce the quinones and adduct CO2 dissolved in solution and / or in the atmosphere surrounding the solution. The solution comprising the reduced quinone adducts is then fed through line (3) to a second electrolytic cell (4), where a potential is applied oxidising the reduced quinone CO2 adducts and releasing the CO2. The released CO2 is removed through line (5) and the solution comprising quinones removed through line (6).

[0162] Figure 2 illustrates another embodiment of a process for capturing CO2 according to the present disclosure. A solution comprising one or more quinones, one or more electrolytes, one or more solvents, and CO2 is fed through line (1 ) to a first electrolytic cell (2) wherein a potential is applied to reduce the quinones and adduct CO2 dissolved in solution and / or in the atmosphere surrounding the solution. The solution is then fed through line (3) to a vessel (4) where a feed gas comprising CO2 is fed through line (5) to the vessel (4) increasing the amount of CO2 dissolved in the solution and present in the headspace. The solution comprising the reduced quinone adducts and CO2 is then fed through line (6) to a second electrolytic cell (7) where a potential is applied oxidising the reduced quinone CO2 adducts and releasing the CO2. The released CO2 is removed through line (8) and the solution comprising quinones removed through line (9).

[0163] Figure 3 illustrates another embodiment of a process for capturing CO2 according to the present disclosure. A solution comprising at least one or more quinones, one or more electrolytes, one or more solvents, and CO2 is fed through line (1 ) to a first electrolytic cell (2). A potential is applied to reduce the quinones and adduct CO2 dissolved in solution and / or in the atmosphere surrounding the solution. The solution comprising the reduced quinone adducts is then fed through line (3) to a vessel (4), where a feed gas comprising CO2 is fed through line (5) to the vessel (4) increasing the amount of CO2 dissolved in the solution and present in the headspace. The solution is fed through line (6) to a second electrolytic cell (7) where a potential is applied oxidising the reduced quinone CO2 adducts and releasing the CO2. The solution is then fed through line (8) to a second vessel (9) and the released CO2 is removed through line (10) and the solution comprising quinones removed through line (11 ).

[0164] Figure 4 illustrates another embodiment of a process for capturing CO2 according to the present disclosure. A solution comprising at least one or more quinones, one or more electrolytes, and one or more solvents is fed through line (1 ) to a first electrolytic cell (2). Separately, a feed gas comprising CO2 is fed through line (7) to the first electrolytic cell. A potential is applied to reduce the quinones and adduct CO2 dissolved in solution and / or in the atmosphere surrounding the solution. The solution comprising the reduced quinone adducts is then fed through line (3) to a second electrolytic cell (4), where a second feed gas comprising CO2 is fed through line (8) to the second electrolytic cell, increasing the concentration of CO2. A potential is appliedoxidising the reduced quinone CO2 adducts and releasing the CO2. The released CO2 is removed through line (5) and the solution comprising quinones removed through line (6) and recycled to the first electrolytic cell (2), allowing the process to operate continuously.

[0165] Figure 5 illustrates another embodiment of a process for capturing CO2 according to the present disclosure. A solution comprising at least one or more quinones, one or more electrolytes, one or more solvents, and CO2 is contained in vessel (1 ) and fed through line (2) to a first electrolytic cell (3). A potential is applied to reduce the quinones and adduct CO2 dissolved in solution and / or in the atmosphere surrounding the solution. The solution comprising the reduced quinone adducts is then fed through line (4) to a second vessel (5), where a feed gas comprising CO2 is fed through line (6) to the second vessel (5) to increase the concentration of CO2 dissolved in the solution and present in the headspace. The solution is fed through line (7) to a second electrolytic cell (8) where a potential is applied oxidising the reduced quinone CO2 adducts and releasing the CO2. The solution is then fed through line (9) to a third vessel (10) and the released CO2 is removed through line (1 1 ). The solution comprising the regenerated quinones is removed through line (12) and fed back to the first vessel (1 ), where separately a feed gas comprising CO2 is fed through line (13) to the first vessel (1 ). The process can operate continuously and the feed gas source comprising CO2 may be from the same source, or from different sources.

[0166] Figure 6 illustrates another embodiment of a process for capturing CO2 according to the present disclosure. A solution comprising CC is fed through line (1 ) to half cell (A) of first electrolytic cell (2), which contains one or more quinones, one or more electrolytes, and one or more solvents. An oxidisable species is present in half cell (B) along with electrolyte and solvent. The half cells are separated by membrane (3). A potential is applied to reduce the quinones and adduct CO2 dissolved in solution and / or in the atmosphere surrounding the solution in half cell (A). The solution comprising the reduced quinone adducts is then fed through line (4) to half cell (C) of second electrolyser (5), where a potential is applied oxidising the reduced quinone CO2 adducts and releasing the CO2. Half cells (C) and (D) are separated by membrane (3). The released CO2 is removed through line (6) and the solution comprising quinones removed through line (7) and recycled to half cell (A). The oxidisable species in half cell (B) is oxidised and fed through line (8) to half cell (D) where it is reduced and thereduced solution then removed through line (9) and recycled to half cell (B). The process may operate continuously.

[0167] Figure 7 illustrates another embodiment of a process for capturing CO2 according to the present disclosure. A solution comprising CC is fed through line (1 ) to half cell (A) of first electrolytic cell (2), which contains one or more quinones, one or more electrolytes, and one or more solvents. An oxidisable species is present in half cell (B) along with electrolyte and solvent. The half cells are separated by membrane (3). A potential is applied to reduce the quinones and adduct CO2 dissolved in solution and / or in the atmosphere surrounding the solution in half cell (A). The solution comprising the reduced quinone adducts is then fed through line (4) to vessel (E) where a feed gas comprising CO2 is fed through line (10) to vessel (E) to increase the concentration of CO2 dissolved in the solution and present in the headspace. The solution is then fed from vessel (E) through line (11) to half cell (C) of second electrolyser (5), where a potential is applied oxidising the reduced quinone CO2 adducts and releasing the CO2. Half cells (C) and (D) are separated by membrane (3). The released CO2 is removed through line (6) and the solution comprising quinones removed through line (7) and recycled to half cell (A). The oxidisable species in half cell (B) is oxidised and fed through line (8) to half cell (D) where it is reduced and the reduced solution then removed through line (9) and recycled to half cell (B). The process may operate continuously.

[0168] While the following discussion of Figures 8 to 10, 16 and 17 specifically mentions certain features of the zero-gap electrochemical flow cells, no such limitations are intended, and other features, as disclosed herein, may be utilised.

[0169] Figures 8 is a perspective view, of one element (100) of a cell body of a zerogap electrochemical flow cell according to the present disclosure. In this embodiment the zero-gap electrochemical flow cell comprises multiple substantially planar elements, one such element is shown. The element (100) comprises an input (101 ) and output (102) configured to supply and remove liquids to and from the cell. The element further comprises continuously curved cut outs (103) which are configured to accept bolt fasteners and a further cut out configured to accept an O-ring gasket (104). In the centre of the element there is a flow field (105) in which the liquid is supplied to and removed from during cell operation.

[0170] Figure 9 is a top view photograph of a partially disassembled zero-gap electrochemical flow cell according to one embodiment of the present disclosure, with one cell body element removed and not shown. The cell body element (200) comprises an input (201 ) and output (202) and includes bolt fasteners (203) arranged in a continuously curved / substantially circular arrangement around the centre of the cell body element. O-ring gaskets (204) are placed in the cut outs. An electrode felt (205) sits on top of the flow field (not visible) and is in contact with a current collector (206) which connects the electrode (205) to an external circuit. An anion exchange membrane (207) is placed on top of the electrode (205) covering the electrode.

[0171] Figure 10 is a side view schematic of one embodiment of an assembled zerogap electrochemical flow cell (300) according to the present disclosure. The zero-gap electrochemical flow cell (300) comprises two cell body elements (303) that are connected by a series of fasteners (not shown) with an anion exchange membrane (306) arranged between the two cell body elements (not drawn to scale). Each cell body element comprises an inlet (301 ) and outlet (302) to supply and remove liquids from the internals of the cell during operation.

[0172] Figure 16 is a cross-sectional side view of one embodiment of a zero-gap electrochemical flow cell according to the present disclosure. This figure shows protrusions in the flow field and a section of the flow field labelled A is shown in expanded view. The dotted lines define the protrusions in the flow field in adjacent tracks. Liquid is directed through the flow field from left to right of Figure 16, hitting the curved surface (flow face) of each protrusion thereby facilitating mixing. The protrusions are shown with two regions of different size and height, which helps direct the liquid flow over the flow field. Adjacent protrusions (not shown in the expanded view) have the flow face in the same direction and are arranged such that the protrusions alternate between the top and bottom of the flow field.

[0173] Figure 17 is a top view of one element (400) of a cell body of a zero-gap electrochemical flow cell according to one embodiment of the present disclosure. In this embodiment, the serpentine flow field (401 ) comprises a plurality of protrusions (403 & 404) which are configured to facilitate mixing of a liquid flow through the flow field. In use, a liquid flow enters the flow field via an input aperture (402) and collides with each of the protrusions before leaving the flow field via an output aperture (405). Protrusions (403 & 404) consist of a curved surface which defines a flow face that operates on theincoming liquid. Each flow face in the same track faces the same direction relative to the oncoming liquid flow. Adjacent protrusions are oriented on different surfaces of the flow field, for example as shown with lower protrusions (403) and upper protrusions (404). The lower and upper protrusions are rotated 180° relative to one another, such that the flow faces are in the same direction, but the liquid flow is directed in opposite directions relative to the flow field.Certain embodiments

[0174] Embodiment 1 : A zero-gap electrochemical flow cell comprising an anode, a cathode, an anion exchange membrane disposed between the anode and cathode, and a cell body comprising at least two cell body elements configured to define an internal flow field and encapsulate the anode, cathode, and anion exchange membrane, each element further comprising inlet and outlet ports configured to supply and remove a first liquid to and from the anode, and supply and remove a second liquid to and from the cathode, each cell body element adapted to hold the first electrode, the second electrode and the anion exchange membrane in place between the at least two cell body elements.

[0175] Embodiment 2: The zero-gap electrochemical flow cell according to embodiment 1 , wherein an internal surface of at least one of the cell body elements comprises one or more protrusions with a flow face configured to increase turbulence of liquid flow within the internal flow field.

[0176] Embodiment 3: The zero-gap electrochemical flow cell according to embodiment 2, wherein one or more protrusions comprise a first region and a second region, said first region and second region are of different size, and the one or more protrusions are arranged in the internal flow field such that liquid flow is directed by the flow face from the first region towards the second region to increase turbulence of the liquid flow.

[0177] Embodiment 4: The zero-gap electrochemical flow cell according to embodiment 2 or embodiment 3, wherein one or more protrusions comprise a first region and a second region, said first region and second region are of different height, and the one or more protrusions are arranged in the internal flow field such that liquidflow is directed by the flow face from the first region towards the second region to increase turbulence of the liquid flow.

[0178] Embodiment 5: The zero-gap electrochemical flow cell according to embodiment 3 or embodiment 4, wherein the first region and the second region have a ratio of size and / or height from about 1 :2 to about 1 :4.

[0179] Embodiment 6: The zero-gap electrochemical flow cell according to any one of embodiments 2 to 5, wherein the flow face of the one or more protrusions comprises a curved region.

[0180] Embodiment 7: The zero-gap electrochemical flow cell according to any one of embodiments 2 to 6, wherein the one or more protrusions comprise a plurality of protrusions, said plurality of protrusions being arranged such that at least one pair of adjacent protrusions are arranged in different orientations.

[0181] Embodiment 8: The zero-gap electrochemical flow cell according to embodiment 7, wherein the flow face of the at least one pair of adjacent protrusions are rotated about 180°.

[0182] Embodiment 9: The zero-gap electrochemical flow cell according to any one of embodiments 2 to 8, wherein the one or more protrusions comprise a plurality of protrusions, said plurality of protrusions being arranged such that at least one pair of adjacent protrusions are on opposite surfaces of the flow field.

[0183] Embodiment 10: The zero-gap electrochemical flow cell according to any one of embodiments 2 to 9, wherein one or more protrusions extend from the internal surface to occupy at least 50% of the internal flow field, or at least 60% of the internal flow field, or at least 70% of the internal flow field.

[0184] Embodiment 11 : The zero-gap electrochemical flow cell according to any one of the preceding embodiments, wherein the cell body elements comprise a material substantially resistant to non-aqueous solvents.

[0185] Embodiment 12: The zero-gap electrochemical flow cell according to any one of the preceding embodiments, wherein the first liquid comprises a non-aqueous solvent, at least one electroactive species, at least one electrolyte and CO2.

[0186] Embodiment 13: The zero-gap electrochemical flow cell according to any one of the preceding embodiments, wherein the second liquid comprises a non-aqueous solvent, reduced electroactive species CO2 adducts and at least one electrolyte.

[0187] Embodiment 14: The zero-gap electrochemical flow cell according to any one of the preceding embodiments, wherein the electrochemical flow cell further comprises an inter-electrode distance between the first and second electrode from about 25 to about 200 pm, preferably from about 50 to about 100 pm.

[0188] Embodiment 15: The zero-gap electrochemical flow cell according to any one of the preceding embodiments, wherein the electrochemical flow cell further comprises substantially circular or ovular fluoroelastomer gaskets arranged between the first electrode and the anion exchange membrane, and the second electrode and the anion exchange membrane.

[0189] Embodiment 16: The zero-gap electrochemical flow cell according to any one of the preceding embodiments, wherein the anion exchange membrane comprises one or more of cellulose, polymer, or polymer composite.

[0190] Embodiment 17: The zero-gap electrochemical flow cell according to any one of the preceding embodiments, wherein the first electrode and the second electrode comprises one or more of graphite, graphite foil, carbon paper, carbon / graphitic felt, aluminium, stainless-steel, platinum foil, and platinum mesh-covered stainless-steel.

[0191] Embodiment 18: The zero-gap electrochemical flow cell according to any one of the preceding embodiments, wherein the cell body elements comprise metal or polymer.

[0192] Embodiment 19: The zero-gap electrochemical flow cell according to any one of the preceding embodiments, wherein the cell body elements comprise one or more of polypropylene, polyether ether ketone, polylactic acid, acrylonitrile butadiene styrene and polyethylene terephthalate.

[0193] Embodiment 20: The zero-gap electrochemical flow cell according to embodiment 19, wherein the cell body elements comprise polypropylene.

[0194] Embodiment 21 : The zero-gap electrochemical flow cell according to any one of the preceding embodiments, wherein the anion exchange membrane comprises one or more of polyether ketone, polysulfone and polytetrafluoroethylene.

[0195] Embodiment 22: The zero-gap electrochemical flow cell according to any one of the preceding embodiments, wherein the non-aqueous solvent comprises one or more of acetonitrile, tetrahydrofuran, diethyl carbonate, y-butyrolactone, dimethylformamide, ethylene carbonate, propylene carbonate, dimethyl sulfoxide, N,N- dimethylacetamide and dichloromethane.

[0196] Embodiment 23: The zero-gap electrochemical flow cell according to any one of embodiments 15 to 22, wherein the gaskets are O-rings.

[0197] Embodiment 24: The zero-gap electrochemical flow cell according to any one of the preceding embodiments, wherein each cell body element is adapted to hold the first electrode, the second electrode and the anion exchange membrane in place by a series of fasteners on each cell body element.

[0198] Embodiment 25: The zero-gap electrochemical flow cell according to embodiment 24, wherein the series of fasteners comprise a continuously curved pattern of fasteners.

[0199] Embodiment 26: The zero-gap electrochemical flow cell according to embodiment 24 or embodiment 25, wherein fasteners are selected from one or more rivets, screws, bolts, nuts, threaded bolts, carriage bolts and pins.

[0200] Embodiment 27: A zero-gap electrochemical flow cell according to any one of the preceding embodiments for use in CO2 capture, redox-flow batteries, energy storage, hydrogen generation, CO2 reduction or electrochemical mineral refinement.

[0201] Embodiment 28: The use according to embodiment 27, wherein the zero-gap electrochemical flow cell is used in CO2 capture or CO2 reduction.

[0202] Embodiment 29: A method of fabricating a zero-gap flow cell according to any one of embodiments 1 to 26 comprising the step of one or more of 3D printing, injection moulding, or CNC milling the cell body elements.

[0203] Embodiment 30: A process of CO2 capture using a zero-gap electrochemical flow cell according to any one of embodiments 1 to 26.ExamplesMaterials and equipment

[0204] Benzoquinone, hydroquinone, anthraquinone, phenanthraquinone, pyrazine, tetrabutylammonium hexafluorophosphate (TBAPFe), ferrocene, acetonitrile (MeCN), and ethanol were purchased from Sigma Aldrich, phenazine was purchased from Fluka, 4,4-bipyridine was purchased from Alfa Aesar, 2,3,5,6-tetrachloro-p-benzoquinone was purchased from Merck, dimethyl sulfoxide was purchased from Ajax Finechem, lithium bis((trifluoromethyl)sulfonyl)imide (LITFSI) was purchased from Ambeed.

[0205] The electrochemical cell comprising two half-cells separated by an anion exchange membrane was designed in Fusion 360 (Autodesk) and printed with a polypropylene filament (from Fiberology) using Prusa Slicer and a Prusa Mini + Printer. The anion exchange membrane was a Fumasep® FAA-3-PK-75 membrane and was purchased from commercial sources (Fuel Cell Store). Viton O-rings were purchased from Hydraulic Seals Solutions. CT GF020 graphite felt was purchased from Fuel Cell Store.MethodsCyclic voltammetry (CV)

[0206] Cyclic voltammograms were obtained using an EC Epsilon potentiostat / galvanostat in a glass electrochemical cell with 0.1 M KOH / H2O electrolyte solution, 1 mm diameter glassy carbon working electrode, an Ag / Ag+quasi reference electrode, and a platinum counter electrode, standardized to the ferrocene redox couple: Fc / Fc+. The electrolyte solution was purged with Argon or CO2 for 30 min prior to the measurement depending on which gaseous environment was being studied. Data were analyzed and plotted using SciDavis software package.Chronopotentiometry (CP)

[0207] CP were obtained using an EC Epsilon potentiostat / galvanostat in a 3D printed flow cell with a 0.25 M LITFSI in DMSO electrolyte solution, graphite felt working andcounter electrodes. Chronopotentiometry measurements were performed in ambient air to simulate Direct Air Capture conditions. Data were analyzed and plotted using Graph Pad Prism software package.3D Printing of redox-flow cell

[0208] CAD models were designed in Fusion 360. Models were sliced using Prusa Slicer. 3D printing was performed using Fiberology Polypropylene filament.Example 1 : CO2 capture process

[0209] In an exemplary process of the present disclosure, the electrolysis of hydroquinone (HQ) in a 0.5 M TBAPFe acetonitrile (MeCN) solution was examined. In a continuous flow electrolysis cell with no anion exchange membrane, this system can capture CO2 directly from the air with a theoretical minimum value of 37.1 kJ per mole of CO2.

[0210] Importantly, the system can be adapted to work either in batch operation, or continuous operation, with two electrolysis cells respectively adsorbing or desorbing CO2 from the quinone.

[0211] In batch operation, gas comprising CO2 is pumped into a MeCN bubbler, which saturates the gas with solvent to limit evaporation within the system, which assists in maintaining consistent quinone and electrolyte concentrations.

[0212] In batch operation, the system oscillates between adsorption and desorption in each flow cell, but continuous flow operation is possible, as shown schematically in Figures 4 and 5.Example 2: CO2 capture process

[0213] In a first vessel, ambient air is pumped from an air compressor or an air cylinder into a first vessel containing phenanthraquinone (PAQ) dissolved in a 0.5 M TBAPFe MeCN solution where the CO2 in ambient air is also dissolved in the MeCN. The solution is pumped from the first vessel through a parallel plate electrochemical cell, where the phenanthraquinone in solution is electrochemically reduced via controlled potential electrolysis (CPE) to react with dissolved CO2. Then, the PAQ / CO2 adducts are pumped to a second vessel where ambient air is purged through the solution toreach MeCN’s maximum CO2 solubility limit. The second vessel may be uncapped, which allows N2, O2, H2O, and other air constituents to escape. The solution is then pumped through a second parallel plate electrochemical cell, which oxidizes the reduced PAQ via CPE to desorb CO2. Since the MeCN has already reached its CO2 solubility limit in the second vessel, the desorbed CO2 will bubble out of solution into the headspace of a third vessel where it is captured. The regenerated solution is then pumped back to the first vessel where the process can be repeated. This process can operate continuously.

[0214] Processes using parallel plate electrochemical cells comprising two half-cells and an anion exchange membrane were preferred to avoid side reactions between the reduced species and the oxidized species during operation.

[0215] Systems were tested with different concentrations of ethanol (EtOH) in the MeCN solution, and it was found that the reductive potentials increased with the addition of ethanol. The greatest increase in reductive potential occurred with a 20% ethanol, 80% MeCN concentration.Example 3: Cyclic voltammetry

[0216] Using a quinone solution with 0.5 M TBAPFe in 80% MeCN, 20% ethanol (v / v) cyclic voltammetry was performed in pure N2 and CO2 to elucidate the electrochemical behavior of the solution in a flow cell. To perform CV, flow of the solution had to be halted, which enabled measurement of the processes. As shown in Figure 11, the dissolved quinones show a characteristic one-stage two-electron redox process in the presence of concentrated CO2, and two-separate one-electron redox processes under inert gaseous conditions.Example 4: CO2 capture process

[0217] Phenanthrenequinone (PAQ) in MeCN was dissolved near PAQ’s solubility limit, approximately 2.8 mg / mL in MeCN. Hydroquinone (HQ) was also examined, as it is nearly 25 times more soluble per mL in MeCN. Additionally, HQ’s lower molecular weight enables the capture of over 50 times as many moles of CO2 in an equivalent volume of solvent.

[0218] Controlled potential electrolysis enabled testing of several independent variables: reduction potential, absorption time, oxidation potential, desorption time, volume of solvent, electrolyte concentration, solvent flow rate, and gas pressure during adsorption.

[0219] Experimentally, it was found that the greatest concentration of CO2 was absorbed at +1 .4 V and the greatest concentration was desorbed at -1 .4V.Example 5: CO2 capture process with alternate electroactive species

[0220] Similar CO2 capture processes may be performed in parallel plate electrochemical cells comprising two half-cells and an anion exchange membrane, wherein one half-cell solution (25 mL in volume) comprises approximately 0.0006 mol of ferrocene in 0.25 M LITFSI, and the other half-cell contains 0.0006 mol of either bipyridine, pyrazine, or phenazine in 0.25 M LITSFI.Example 6: CV measurements of electroactive species

[0221] Using a solution containing each of pyrazine, 4,4-bipyridine, phenazine, benzoquinone and 2,3,5,6-tetrachloro-p-benzoquinone with 0.1 M TBAPFe in MeCN, cyclic voltammetry was performed in pure N2 to elucidate the electrochemical behavior of the electroactive species. As shown in Figure 12, the redox-active sp2nitrogenbased molecules all electrochemically reduce at more negative potentials than the quinone molecules.

[0222] From Figure 12C, it is evident that in an inert environment, phenazine undergoes two separate one-electron redox processes. However, in Figure 13A, which shows the CV of phenazine in a 100% CO2 gaseous environment, it is observed that the reversible two-step redox process condenses into a single reversible two-electron reduction. This behavior is similar to the electrochemical behaviour of quinones, which typically undergo two one-electron reductions in the absence of CO2 and a single two- electron reduction in the presence of CO2.Example 7: Chronopotentiometry measurements of electroactive species

[0223] Beyond cyclic voltammetry, galvanostatic measurements such as chronopotentiometry allows the examination of the process’ reversibility and calculates the actual energy consumed by the process relative to the theoretical minimums. Fromchronopotentiometry, the coulombic efficiency can be calculated, which is often tested because inefficiencies detected in early cycling can be indicative of a system’s future lifetime.

[0224] For these measurements, the first adsorption step was performed with 8 mA of current for 90 seconds and the desorption step with -4 mA of current for 180 seconds. After this first cycle, the minimum potential exhibited on the adsorption step and the maximum seen on the desorption step was found, and these values used as voltage cutoffs for future cycling. For every cycle afterwards, the potential limits were set using those initial minimums and maximums, oscillated between adsorption and desorption until the cell reached those potential limits, and coulombic efficiency calculated for each cycle.

[0225] Since the process functionally operates like a redox flow battery, the coulombic efficiency was calculated by dividing the charge in each desorption step by the charge passed during the adsorption step. Coulombic efficiency is a commonly used metric in electrochemistry, and it allows the direct comparison of the reversibility of a system with others in the art.

[0226] As shown in Figure 14, the combination of phenazine and ferrocene provided 100% coulombic efficiency during over 15 cycles, lasting more than 34,000 seconds.Example 8: Coulombic efficiency measurements of electroactive species

[0227] The results in Figure 15 show the wide range of coulombic efficiencies exhibited by the tested electroactive molecules. Each molecule was tested for at least 10 cycles over more than 15,000 seconds, but because certain molecules hit voltage cutoffs at differing times, the number of cycles performed on each molecule varies. Due to the lack of degradation exhibited by phenazine in its initial round of testing, the same solution was cycled for approximately twice as long as the other molecules to see if its coulombic efficiency would drop, which it did not.Example 9: Flow field modification

[0228] Computational fluid dynamics (CFD) simulations were performed using Ansys Fluent software to simulate liquid flow through specifically designed 3D printed flow cells. Specifically, the geometry of the flow field was modified to improve the interactionbetween the solution and the electrode, which sits on top of the flow field. Initial CFD simulations of the unmodified flow field showed that the solution’s velocity vectors linearly followed the path of the flow field with minimal mixing along the z-axis. The most turbulent portions of the unmodified flow field were at the end of each linear section.

[0229] To improve mixing of the solution, protrusions were added to the flow field and simulated (Figure 16). It was found that the addition of protrusions on the edge of the flow field could stimulate turbulent mixing zones. In these areas, solution would hit the protrusion and cause solution mixing which improved the interaction between the flow field and the electrode surface. Overall, this enhanced solution mixing and promoted movement of the solution to the electrode’s surface, thereby improving process efficiency.

Claims

CLAIMS1 . An electrochemical process for capturing CO2 comprising the steps of: a) electrolysing a solution comprising CO2, at least one electroactive species, at least one electrolyte, and at least one non-aqueous solvent in a first electrochemical cell under conditions effective to reduce the at least one electroactive species and form a solution comprising reduced electroactive species CO2 adducts; b) electrolysing the solution comprising the reduced electroactive species CO2 adducts in a second electrochemical cell under conditions effective to oxidise the reduced electroactive species thereby releasing CO2 and regenerating the at least one electroactive species; wherein both the first and second electrochemical cells comprise electrodes at least partially immersed in solution.

2. The process according to claim 1 , wherein both the first and second electrochemical cells comprise cathodic and anodic half-cells, the half-cells being separated by anion exchange membrane, wherein the solution comprising reduced electroactive species CO2 adducts is formed in the cathodic half-cell of the first electrochemical cell and a solution comprising oxidised species is formed from reduced species in the anodic half-cell of the first electrochemical cell; and wherein the reduced electroactive species CO2 adducts are oxidised in the anodic half-cell of the second electrochemical cell to regenerate the at least one electroactive species and the oxidised species are reduced in the cathodic halfcell of the second electrochemical cell to regenerate the reduced species.

3. The process according to claim 1 or claim 2, wherein at least one of the first and second electrochemical cells comprises a zero-gap electrochemical flow cell.

4. The process according to claim 3, wherein the zero-gap electrochemical flow cell comprises an anode, a cathode, an anion exchange membrane disposed between the anode and cathode, and a cell body comprising at least two cell body elements configured to define an internal flow field and encapsulate the anode, cathode, and anion exchange membrane, each element furthercomprising inlet and outlet ports configured to supply and remove a first liquid to and from the anode, and supply and remove a second liquid to and from the cathode, each cell body element adapted to hold the first electrode, the second electrode and the anion exchange membrane in place between the at least two cell body elements.

5. The process according to claim 4, wherein an internal surface of at least one of the cell body elements comprises one or more protrusions with a flow face configured to increase turbulence of liquid flow within the internal flow field.

6. The process according to claim 5, wherein one or more protrusions include at least one of the following:(a) the one or more protrusions comprise a first region and a second region, said first region and second region are of different size, and the one or more protrusions are arranged in the internal flow field such that liquid flow is directed by the flow face from the first region towards the second region to increase turbulence of the liquid flow;(b) the one or more protrusions comprise a first region and a second region, said first region and second region are of different height, and the one or more protrusions are arranged in the internal flow field such that liquid flow is directed by the flow face from the first region towards the second region to increase turbulence of the liquid flow;(c) the flow face of one or more protrusions comprises a curved region;(d) the one or more protrusions comprise a plurality of protrusions, said plurality of protrusions being arranged such that at least one pair of adjacent protrusions are arranged in different orientations;(e) the flow face of the at least one pair of adjacent protrusions are rotated about 180°;(f) the one or more protrusions comprise a plurality of protrusions, said plurality of protrusions being arranged such that at least one pair of adjacent protrusions are on opposite surfaces of the flow field;(g) the one or more extrusions extend from the internal surface to occupy at least 50% of the internal flow field.

7. The process according to any one of claims 2 to 6, wherein the reduced / oxidised species comprises ferrocene / ferrocenium.

8. The process according to any one of claims 1 to 7, wherein the process further comprises the step of separating released CO2 from the solution of the at least one regenerated electroactive species.

9. The process according to any one of claims 1 to 8, wherein prior to step a) a solution comprising the at least one electroactive species is contacted with at least one feed gas comprising CO2.

10. The process according to any one of claims 1 to 9, wherein prior to step b) the solution comprising the reduced electroactive species CO2 adducts is contacted with at least one feed gas comprising CO2.11 . The process according to any one of claims 1 to 10, wherein the solution comprising regenerated at least one electroactive species formed in step b) is recycled to the first electrochemical cell and contacted with at least one feed gas comprising CO2 either prior to entering the first electrochemical cell or within the first electrochemical cell.

12. The process according to any one of claims 9 to 11 , wherein any two or more of the feed gases comprising CO2 comprise the same feed gas composition.

13. The process according to any one of claims 9 to 11 , wherein any two or more of the feed gases comprising CO2 comprise different feed gas compositions.

14. The process according to any one of claims 9 to 13, wherein any one or more of the feed gas comprising CO2 comprises ambient air.

15. The process according to any one of claims 1 to 14, wherein the at least one electroactive species comprises one or more of quinone, pyridine, bipyridine, such as 1 ,4-bipyridine, pyrazine, and phenazine, or larger molecules comprising one or more of these species as substructures therein.

16. The process according to claim 15, wherein the process comprises two or more electroactive species, such as two or more quinones, or mixtures of two or more of quinone, pyridine, bipyridine, pyrazine, and phenazine.

17. The process according to claim 15 or claim 16, wherein the quinones comprise one or more of benzoquinone, hydroquinone, phenanthraquinone, napthoquinone and anthraquinone.

18. The process according to any one of claims 1 to 17, wherein the at least one electrolyte comprises one or more ammonium salts, alkali metal salts, or trifluoromethanesulfonyl imide salts.

19. The process according to claim 18, wherein the at least one electrolyte comprises one or more tetraalkylammonium salts.

20. The process according to claim 18 or claim 19, wherein the at least one electrolyte comprises one or more tetraalkylammonium tetrafluoroborate salts, alkali metal (trifluoromethanesulfonyl)imide salts, and tetraalkylammonium hexafluorophosphate salts.21 . The process according to any one of claims 18 to 20, wherein the at least one electrolyte comprises one or more of lithium (trifluoromethanesulfonyl)imide ammonium perchlorate, ammonium nitrate, ammonium sulfate, ammonium fluoride, ammonium bromide, ammonium acetate, ammonium phosphate, tetraethylammonium tetrafluoroborate, triethyl(methyl)tetrafluoroborate and tetrabutylammonium hexafluorophosphate.

22. The process according to any one of claims 1 to 21 , wherein the concentration of electrolyte is from about 0.05 M to about 5 M, or from about 0.1 M to about 2 M, or from about 0.1 M to about 1 M.

23. The process according to any one of claims 1 to 22, wherein the at least one solvent comprises one or more of acetonitrile, tetrahydrofuran, diethyl carbonate, y-butyrolactone, dimethylformamide, ethylene carbonate, propylene carbonate, dimethyl sulfoxide, N,N-dimethylacetamide and dichloromethane.

24. The process according to any one of claims 1 to 23, wherein the at least one non-aqueous solvent comprises a solvent with a boiling point of at least about 80°C.

25. The process according to any one of claims 1 to 24, wherein the at least one non-aqueous solvent comprises a solvent with a boiling point of at least about 160°C.

26. The process according to any one of claims 1 to 25, wherein the at least one non-aqueous solvent comprises a solvent with a dielectric constant of at least about 30.

27. The process according to any one of claims 1 to 26, wherein the electrochemical cell is a parallel plate electrochemical cell.

28. The process according to any one of claims 1 to 27, wherein the electrodes comprise one or more of graphite, graphite foil, carbon paper, carbon / graphitic felt, aluminium, stainless-steel, platinum foil, and platinum mesh-covered stainless-steel.

29. The process according to any one of claims 1 to 28, wherein electrolysis is conducted at a temperature of about 20 °C or higher.

30. The process according to any one of claims 1 to 29, wherein the potential difference across the first electrochemical cell is from about 0.5 V to about 3.0 V.31 . The process according to any one of claims 1 to 30, wherein the potential difference across the second electrochemical cell is from about -0.5 V to about -3.0 V.

32. The process according to any one of claims 2 to 31 , wherein the anion exchange membrane comprises cellulose, polymer, or polymer ceramic composite.

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