WO2022226589A1

WO2022226589A1 - Electrochemical capture of carbon dioxide and production of carbonate mineral

Info

Publication number: WO2022226589A1
Application number: PCT/AU2022/050385
Authority: WO
Inventors: Chong-Yong Lee; Gordon George Wallace
Original assignee: University Of Wollongong
Priority date: 2021-04-28
Filing date: 2022-04-27
Publication date: 2022-11-03

Abstract

Disclosed is an electrochemical cell, system and method for capturing carbon dioxide. In an example the electrochemical mineral carbonation cell comprises a gas permeable cathode and carbon dioxide gas is able to pass into an outer surface of and at least partially through the gas permeable cathode to react with a liquid catholyte. A voltage difference is able to be applied between the gas permeable cathode and an anode. A membrane is positioned between the gas permeable cathode and the anode. The liquid catholyte is positioned between the gas permeable cathode and the membrane and the liquid catholyte includes mineral ions, for example sodium, potassium, lithium or calcium ions, a liquid anolyte is positioned between the anode and the membrane. In operation of the cell, the liquid catholyte flows along an inner surface of the gas permeable cathode, and a carbonate mineral, for example sodium carbonate, potassium carbonate, lithium carbonate or calcium carbonate, is produced at or near the inner surface of the gas permeable cathode and is at least partially transported away from the inner surface of the gas permeable cathode by the liquid catholyte flow.

Description

ELECTROCHEMICAL CAPTURE OF CARBON DIOXIDE AND PRODUCTION OF CARBONATE MINERAL

TECHNICAL FIELD

[001] The embodiments described herein broadly relate to electrochemical mineral carbonation cells and the electrochemical capture of carbon dioxide, and particularly to electrochemical capture of carbon dioxide and production of carbonate mineral. Example embodiments relate to electrochemical cells and electrochemical systems including electrochemical cells for capturing carbon dioxide, and to methods of electrochemically capturing carbon dioxide using electrochemical cells.

BACKGROUND

[002] Carbon dioxide gas (C0₂(g)) is accepted to have a major influence on climate, and production of CO2 needs to be reduced and existing CO2 needs to be removed from the environment. Although it may be possible to phase out use of carbon based fossil fuels for the power and transportation industries, using renewable energy sources, other industries such as construction using steel/cement production, air transport, etc., do not have suitable alternatives for carbon based fossil fuels. Also, due to net global deforestation and growing demand for carbon as a resource, CO2 will otherwise continue to be emitted and accumulate in the environment. Thus, technologies for CO2 capture and utilization are required and are critically important.

[003] The transition from a fossil-fuel driven economy to a carbon-neutral clean energy economy requires the development of low-cost carbon dioxide (CO2) capture (also referred to as “carbon capture”) and storage technologies. Current commercially available carbon capture technologies are expensive, typically ranging from US$60 to several hundred dollars to capture 1 metric ton of CO2. It is expected the deployment of carbon capture and storage systems will only start to be economically significant with operational costs below about US$20 to US$30 per metric ton of CO2. [004] The use of widely available and abundant minerals as carbon capture agents offers an opportunity in developing low-cost carbon capture technology. For example, a known and more established amine- scrubbing carbon capture technology using a relatively costly capture agent, amine and it derivatives such as monoethanolamine (MEA), is approximately ten times more expensive than calcium based carbon capture agents, such as calcium chloride and calcium hydroxide. The use of amine organic-based carbon capture agents also involves costly regeneration processes, expensive infrastructure, and suffers from oxidative and thermal degradation. In contrast, carbonate minerals are stable and abundant forms of inorganic material.

[005] The sluggish kinetics that determine the rate of mineral carbonation processes is a problem that needs to be overcome. CO2 has inherently low solubility in aqueous solution, therefore limiting the quantity of dissolved CO2 either in the form of carbonate or bicarbonate ions able to participate in the mineral carbonation process, and hence lowering the efficiency of the overall process. Costly and energy intensive high pressurise facilities are often needed to enhance the CO2 solubility in a mineral carbonation reactor. Developing a more efficient approach to increase or maximise the concentration of available CO2 and associated carbonate ions is highly desirable.

[006] An electrochemical cell produces one or more chemical materials over sustained periods of time, typically for use outside of the electrochemical cell. The chemical materials may be in the form of gases, liquids and/or solids. In the electrochemical reaction for mineral carbonation or CO2 mineralisation, currently known processes involve direct injection of gaseous CO2 into an aqueous electrolyte. Since the CO2 solubility in aqueous solution is low (0.033 M at ambient atmosphere), the kinetics of the CO2 mineralisation is a rate limiting factor and is another problem that needs to be overcome.

[007] Additionally, the cost of a regeneration process for the carbon capture agent that is used plays a significant part in the economics of carbon capture technology. In presently known calcium-looping carbon capture technology, high temperature calcium regeneration significantly adds to the overall cost for this type of carbon capture technology. Reducing the cost of a regeneration process for the carbon capture agent that is used is another problem that needs to be addressed.

[008] Thus, new or improved electrochemical cells and/or electrochemical systems for the capture of carbon dioxide are needed. New or improved methods for the electrochemical capture of carbon dioxide using electrochemical cells or electrochemical systems are also needed.

[009] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

SUMMARY

[010] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify all of the key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[Oil] In one aspect, there is provided an electrochemical cell for the electrochemical capture of carbon dioxide. In another aspect, there is provided an electrochemical cell for the electrochemical capture of carbon dioxide and the production of carbonate mineral. In another aspect, there is provided an electrochemical system including at least one electrochemical cell, for the electrochemical capture of carbon dioxide and/or the production of carbonate mineral. In another aspect, there is provided a method of electrochemically capturing carbon dioxide and/or the production of carbonate mineral using an electrochemical cell. In another example, the electrochemical cell is an electrochemical flow cell.

[012] In another aspect, there is provided an electrochemical mineral carbonation cell for capturing carbon dioxide, the electrochemical cell comprising a gas permeable cathode, wherein carbon dioxide gas is able to pass into an outer surface of and at least partially through the gas permeable cathode to react with a liquid catholyte. An anode is provided, wherein a voltage difference is able to be applied between the gas permeable cathode and the anode. A membrane is positioned between the gas permeable cathode and the anode. The liquid catholyte is positioned between the gas permeable cathode and the membrane, the liquid catholyte including mineral ions, for example preferably calcium ions, sodium ions, potassium ions, and/or lithium ions, either individually or in any combination. A liquid anolyte is positioned between the anode and the membrane. In operation, the liquid catholyte flows along an inner surface of the gas permeable cathode and a carbonate mineral is produced at or near the inner surface of the gas permeable cathode and is at least partially transported away from the inner surface of the gas permeable cathode by the liquid catholyte flow.

[013] In one example, in operation, the liquid catholyte flows along an inner surface of the gas permeable cathode and a carbonate mineral is produced by being precipitated at the inner surface of the gas permeable cathode and the carbonate mineral is at least partially transported away from the inner surface of the gas permeable cathode by the liquid catholyte flow. In further examples, the carbonate mineral may be produced by being precipitated on the inner surface of the gas permeable cathode, and the carbonate mineral may be at least partially removed (from the inner surface of the gas permeable cathode) and transported away from the inner surface of the gas permeable cathode by the liquid catholyte flow. The carbonate mineral that is produced by being precipitated at or on the inner surface of the gas permeable cathode is insoluble or substantially insoluble in the liquid catholyte. In these examples, an example carbonate mineral that is produced by being precipitated is calcium carbonate.

[014] In another example, in operation, the liquid catholyte flows along an inner surface of the gas permeable cathode and a carbonate mineral is produced in solution in the liquid catholyte at the inner surface of the gas permeable cathode and the carbonate mineral is at least partially transported away from the inner surface of the gas permeable cathode by the liquid catholyte flow. The carbonate mineral that is produced in solution in the liquid catholyte at the inner surface of the gas permeable cathode is soluble or substantially soluble in the liquid catholyte. The soluble carbonate mineral can be produced in an aqueous form. In these examples, example carbonate minerals that are produced in solution in the liquid catholyte are sodium carbonate, potassium carbonate, or lithium carbonate.

[015] In other optional examples, the mineral ions can be, or can include, magnesium ions, strontium ions, and/or barium ions. In these optional examples, the produced carbonate minerals can be magnesium carbonate, strontium carbonate or barium carbonate.

[016] In another aspect, there is provided an electrochemical system for capturing carbon dioxide, the electrochemical system comprising a stack of a plurality of electrochemical cells. At least one, or each, electrochemical mineral carbonation cell comprises a gas permeable cathode, an anode, a membrane positioned between the gas permeable cathode and the anode. A carbon dioxide gas source introduces carbon dioxide gas into an outer surface of and at least partially through the gas permeable cathode. A power supply applies a voltage difference between the gas permeable cathode and the anode. A liquid catholyte source supplies a liquid catholyte as a liquid catholyte flow between the gas permeable cathode and the membrane, the liquid catholyte including mineral ions, for example preferably calcium ions, sodium ions, potassium ions and/or lithium ions. An anolyte source supplies a liquid anolyte between the anode and the membrane. In operation, the liquid catholyte flows along an inner surface of the gas permeable cathode, and carbonate mineral is produced at or near the inner surface of the gas permeable cathode and is at least partially transported away from the inner surface of the gas permeable cathode by the liquid catholyte flow. The carbonate mineral formed, and whether the carbonate mineral that is produced precipitates out of solution or remains in solution, depends on the mineral ions used, for example the carbonate mineral can be calcium carbonate, sodium carbonate, potassium carbonate and/or lithium carbonate. Typically, in an aqueous catholyte (which could be at or around room temperature for example, but could be at other temperatures), calcium carbonate is insoluble or substantially insoluble and is produced as a precipitate, whereas sodium carbonate, potassium carbonate and lithium carbonate are soluble or substantially soluble and are produced in solution without forming a precipitate. [017] For the example of some carbonate minerals, for example calcium carbonate that is insoluble or substantially insoluble in a preferred liquid catholyte, the liquid catholyte flows along the inner surface of the gas permeable cathode, and the carbonate mineral is produced by being precipitated on the inner surface of the gas permeable cathode and the carbonate mineral is at least partially removed and transported away from the inner surface of the gas permeable cathode by the liquid catholyte flow.

[018] In another aspect, there is provided a method of operating an electrochemical mineral carbonation cell to capture carbon dioxide and produce carbonate mineral. In various examples, the carbonate mineral is in the form of calcium carbonate, sodium carbonate, potassium carbonate or lithium carbonate, which are stable inorganic materials that can permanently store carbon dioxide. The method including introducing carbon dioxide gas into the outer surface of the gas permeable cathode and allowing the carbon dioxide gas to pass at least partially through the gas permeable cathode to react with the liquid catholyte including mineral ions. The method also includes applying a voltage difference between the anode and the gas permeable cathode, and flowing the liquid catholyte along the inner surface of the gas permeable cathode.

[019] In some examples, soluble carbonate mineral, for example sodium carbonate, potassium carbonate or lithium carbonate, is formed at the inner surface of the gas permeable cathode, and is at least partially transported away from the inner surface of the gas permeable cathode by the flowing liquid catholyte (i.e. by the liquid catholyte flow). In other examples, carbonate mineral precipitate, for example calcium carbonate precipitate, is formed on the inner surface of the gas permeable cathode, and is at least partially removed (from the inner surface of the gas permeable cathode) and transported away from the inner surface of the gas permeable cathode by the flowing liquid catholyte (i.e. by the liquid catholyte flow).

[020] In other examples, the carbonate mineral is in the form of sodium carbonate, potassium carbonate or lithium carbonate, which have high solubility in the liquid electrolyte (i.e. liquid catholyte) and can permanently store carbon dioxide. An example method also includes introducing carbon dioxide gas into the outer surface of the gas permeable cathode and allowing the carbon dioxide gas to pass at least partially through the gas permeable cathode to react with the liquid catholyte including mineral ions. The method also includes applying a voltage difference between the anode and the gas permeable cathode, and flowing the liquid catholyte along the inner surface of the gas permeable cathode. The produced carbonate mineral that is soluble or substantially soluble, for example sodium carbonate, potassium carbonate or lithium carbonate, is formed at, or on, the inner surface of the gas permeable cathode, and is transported away from the inner surface of the gas permeable cathode by the flowing liquid catholyte (i.e. by the liquid catholyte flow).

[021] In another aspect, in examples where calcium ions, sodium ions, potassium ions, or lithium ions are utilised, there is provided a method to regenerate the form of calcium carbonate, sodium carbonate, potassium carbonate, or lithium carbonate to the capture agent or sorbent which is calcium ions, sodium ions, potassium ions, or lithium ions such as calcium chloride, sodium chloride, potassium chloride, or lithium chloride and release the carbon dioxide. The carbon dioxide is stored, and regenerated calcium ions, sodium ions, potassium ions, or lithium ions are reused to participate in the electrochemical carbon capture process. The regeneration method including a chemical reaction between calcium carbonate, sodium carbonate, potassium carbonate, or lithium carbonate and hydrochloric acid to form a mineral chloride (e.g. calcium chloride, sodium chloride, potassium chloride, or lithium chloride), water and carbon dioxide. The source of hydrochloric acid can be fully or partially derived from the anodic process within the same electrochemical cell, such as chloride oxidation, or externally from, for example, industry plants with hydrochloric acid emitted as a waste, or externally outsource chemical reagent.

[022] In another aspect, there is provided a method and system of regenerating carbonate mineral in an electrochemical mineral carbonation cell to capture carbon dioxide. Carbon dioxide gas is introduced into an outer surface of a gas permeable cathode, and the carbon dioxide gas is allowed to pass at least partially through the gas permeable cathode to react with a liquid catholyte including mineral ions, for example calcium ions, sodium ions, and/or potassium ions, either individually or in any combination. The liquid catholyte is positioned between an inner surface of the gas permeable cathode and a membrane, the membrane positioned between the gas permeable cathode and an anode, and a liquid anolyte positioned between the anode and the membrane. A voltage difference is applied between the anode and the gas permeable cathode. The liquid catholyte flows along the inner surface of the gas permeable cathode. The liquid anolyte flows along an inner surface of the anode. Carbonate minerals such as calcium carbonate, sodium carbonate, potassium carbonate and/or lithium carbonate are produced or formed, as precipitated material or soluble material, at, near or on the inner surface of the gas permeable cathode. The carbonate mineral is at least partially transported away from the inner surface of the gas permeable cathode by the flowing liquid catholyte (i.e. by the liquid catholyte flow). Optionally, although preferably, the mineral ions are regenerated in the liquid catholyte by reacting at least some of the carbonate mineral that has been transported with hydrochloric acid or chlorine gas to form mineral chloride in solution in water. The hydrochloric acid can be produced at the anode. Preferably, the regeneration also includes storing released CO2 gas when forming the mineral chloride in solution in water.

BRIEF DESCRIPTION OF THE FIGURES

[023] Example embodiments will now be described solely by way of non-limiting examples and with reference to the accompanying figures. Various example embodiments will be apparent from the following description, given by way of example only, of at least one preferred but non-limiting embodiment, described in connection with the accompanying figures.

[024] Figure 1 illustrates an example electrochemical mineral carbonation cell with a gas permeable cathode to produce carbonate mineral.

[025] Figure 2 illustrates example processes occurring at or in the vicinity of the gas- phase, solid-phase and liquid-phase interface of the example electrochemical mineral carbonation cell illustrated in Figure 1.

[026] Figure 3 illustrates another example electrochemical mineral carbonation cell with a gas permeable cathode to produce carbonate mineral. In this example electrochemical cell, the anode is a gas permeable anode, and a produced gas, for example hydrogen gas, can be transferred from a cathodic compartment to an anodic compartment.

[027] Figure 4 illustrates a flowchart of an example electrochemical process of the production of a carbonate mineral from aqueous mineral ions in the presence of CO2.

[028] Figure 5 illustrates a flowchart of an example electrochemical process of the production of calcium carbonate from aqueous calcium ions in the presence of CO2.

[029] Figure 6 is a schematic diagram showing electrochemically generated carbonate mineral accumulating on the surface of a gas permeable cathode in a static liquid electrolyte (i.e. catholyte).

[030] Figure 7 is a schematic diagram showing electrochemically generated carbonate mineral not accumulating on the surface of a gas permeable cathode in an electrolyte flow (i.e. a catholyte flow) (contrasted to Figure 6).

[031] Figure 8 is a schematic diagram showing electrochemically generated carbonate mineral not accumulating on the surface of a gas permeable cathode in an alternating electrolyte flow (i.e. an alternating catholyte flow) (contrasted to Figure 6).

[032] Figure 9 illustrates an example stack of electrochemical mineral carbonation cells including multiple electrochemical cell units to capture carbon dioxide as carbonate mineral. Each electrochemical cell includes a gas permeable cathode. The configuration represents individually independent and separable electrochemical cells.

[033] Figure 10 illustrates another example stack of electrochemical mineral carbonation cells including multiple electrochemical cell units to capture carbon dioxide as carbonate mineral. Each electrochemical cell includes a gas permeable cathode. The configuration represents an integrated stack configuration including each cathodic or anodic compartment sharing the same current collector. [034] Figure 11 illustrates another example stack of electrochemical mineral carbonation cells including multiple electrochemical cell units to capture carbon dioxide as carbonate mineral. The configuration represents an integrated stack configuration including each cathodic or anodic compartment sharing the same current collector. Each electrochemical cell includes a gas permeable cathode. The anodic compartment of each electrochemical cell also includes a gas permeable anode.

[035] Figure 12 illustrates an example electrochemical system including a stack of electrochemical mineral carbonation cells with gas permeable cathodes and associated example components to capture carbon dioxide as carbonate mineral, and mineral-sorbent regeneration process.

[036] Figure 13 illustrates part of an example electrochemical system including a stack of electrochemical mineral carbonation cells with gas permeable cathodes (to capture carbon dioxide as carbonate mineral) and gas permeable anodes (where hydrogen oxidation reaction is taking place that used to produce acid at anode, which the acid is employable to regenerate CO2.

[037] Figure 14 shows a representative SEM image of calcium carbonate produced and collected from an example electrochemical mineral carbonation cell including a gas permeable cathode.

[038] Figure 15 shows representative XRD and Raman spectroscopies confirming the formation of high purity calcium carbonate from an example electrochemical mineral carbonation cell including a gas permeable cathode.

[039] Figure 16 shows representative Raman spectrum confirming the formation of lithium carbonate from an example electrochemical mineral carbonation cell including a gas permeable cathode. DETAILED DESCRIPTION

[040] The following modes, features or aspects, given by way of example only, are described in order to provide a more precise understanding of the subject matter of a preferred embodiment or embodiments.

[041] Embodiments relate to electrochemical cells and electrochemical systems for the electrochemical capture of carbon dioxide, and for the production of a carbonate mineral, preferably for the production of sodium carbonate, potassium carbonate, lithium carbonate or calcium carbonate, and to methods of electrochemically capturing carbon dioxide and preferably to the production of carbonate mineral using an electrochemical cell. Preferably, the electrochemical cell is an electrochemical flow cell, meaning that liquid electrolyte in the electrochemical cell is flowing or moving past one or more electrodes in the electrochemical cell.

[042] As used herein, reference to a “gas permeable cathode”, or a “gas permeable anode” or a “gas permeable electrode”, is to be read as not needing to be made of a single material or continuous materials providing both gas permeability and acting as a conductor. A gas permeable cathode/anode/electrode can be formed of separate components or separate layers that are joined together, such as providing a laminate structure, or positioned adjacent each other, or provided as a contiguous layered structure. For example, a gas permeable cathode/anode/electrode can be provided as a gas diffusion electrode (GDE), or as a layered structure which includes separate conducting and non conducting layers, such as including a non-conducting polymeric gas permeable membrane provided as a layer of the gas permeable cathode/anode/electrode with a separate conducting layer provided.

[043] As used herein, reference to the electrolyte, preferably a liquid electrolyte, can refer to both or either of a catholyte, for example in a cathode compartment, and/or a anolyte, for example in an anode compartment, if distinct cathode and anode compartments with distinct catholyte and anolyte are utilised. [044] As used herein, reference to CO2 gas is to be read as a reference to pure CO2 gas or any gas mixture containing CO2 gas at any level of concentration and with any combination of other gas or gases. It should be understood that reference to a flow of CO2 gas is to be read as a reference to a flow of pure gas or gas mixture including CO2 gas at some level of greater than 0 % up to 100% by volume. Thus, reference to CO2 gas includes but is not limited to ambient air, compressed air, industry waste gas containing CO2, pure CO2, and intentional or unintentional prepared gas mixtures containing CO2.

[045] As used herein, the terms "carbonate mineral" and "mineral carbonate" are intended to have the same meaning and are therefore interchangeable terms.

[046] As used herein, embodiments of an electrochemical cell that (directly or indirectly) produce a carbonate mineral (for example as a product, or by-product) may also be referred to as an "electrochemical mineral carbonation cell". The one or more type of carbonate mineral produced in these embodiments may be soluble or insoluble.

[047] Embodiments also relate to methods to capture CO2, to produce carbonate mineral, and for regeneration of a carbon dioxide (CO2) capture agent or sorbent. A flow of CO2 gas, or a gas mixture containing CO2 gas, preferably a continuous flow of gas, is introduced through a gas permeable cathode, which may include a catalyst layer, to participate in electrochemical-driven carbonate mineral (for example sodium carbonate Na₂C0₃, potassium carbonate K2CO3, lithium carbonate L^CCE or calcium carbonate CaCCE) formation.

[048] Example embodiments relate to efficient processes including introducing gaseous CO2 (or a gaseous mixture including CO2) via a gas permeable cathode, for example a gas diffusion electrode (GDE) which can be provided with a catalyst, for example as a catalyst layer, or for example a gas permeable membrane with an integrated conductive catalyst, so as to interact with the catalyst and with liquid-phase mineral ions within an electrolyte, and to thereby produce carbonate mineral, either in solution or as precipitated carbonate mineral. In one form, the operating electrochemical system includes a stack of integrated electrochemical cells. In operation, the process produces, and optionally collects, soluble or precipitated carbonate mineral, preferably continuously, and preferably additionally the regeneration of the CO2 capture agent or sorbent, being liquid- phase mineral ions within the electrolyte. In various examples, the mineral ions are calcium ions, sodium ions, potassium ions, lithium ions, magnesium ions, strontium ions and/or barium ions. In various examples, the carbonate mineral is calcium carbonate (when calcium ions are utilised), sodium carbonate (when sodium ions are utilised), potassium carbonate (when potassium ions are utilised), lithium carbonate (when lithium ions are utilised), magnesium carbonate (when magnesium ions are utilised), strontium carbonate (when strontium ions are utilised) and/or barium carbonate (when barium ions are utilised). In one preferred example, the mineral ions are calcium ions and the carbonate mineral is calcium carbonate. In another preferred example, the mineral ions are sodium ions and the carbonate mineral is sodium carbonate. In another preferred example, the mineral ions are potassium ions and the carbonate mineral is potassium carbonate. In another preferred example, the mineral ions are lithium ions and the carbonate mineral is lithium carbonate.

[049] In the electrochemical reaction for mineral carbonation or CO2 mineralisation, currently known processes involve direct injection of gaseous CO2 into an aqueous electrolyte. Since the CO2 solubility in aqueous solution is low (0.033 M at ambient atmosphere), the kinetics of the CO2 mineralisation is a rate limiting step. In contrast, embodiments of the present invention use a gas permeable cathode as the cathode in an electrochemical cell. The gas permeable cathode can be, for example, a gas diffusion electrode (GDE), most preferably provided with a catalyst or catalyst layer, or a non- conductive polymeric gas permeable membrane provided with an integrated conductive catalyst or a conductive catalyst layer. In one example, the gas permeable cathode can include a cathodic catalyst layer that is conductive. In another example, the gas permeable cathode can include a cathodic catalyst layer that is provided on or adjacent a separate conductive material layer, for example a conductive material (e.g. a metal) that is deposited on or positioned adjacent a non-conductive polymeric gas permeable membrane of the gas permeable cathode. Example non-conductive polymeric gas permeable membrane materials include polytetrafluoroethylene (PTFE), polyethylene (PE) and polypropylene (PP). [050] In operation, the gas permeable cathode is in contact with an electrolyte containing mineral ions, preferably though not necessarily containing calcium ions, sodium ions, potassium ions, and/or lithium ions which provides an excellent solid-liquid interface so that CO2 gas, supplied either as pure CO2 gas or as a gaseous mixture including CO2 gas, can be introduced to participate in the mineral carbonation reaction by passing through the gas permeable cathode to interact with the electrolyte. The flow of CO2 gas through the gas permeable cathode offers an improved and continuous supply pathway of the reactant (CO2 gas) for the mineral carbonation process. The improved mass transfer of reactants and/or products, preferably including an efficient process in removing the produced carbonate mineral, is important in significantly improving overall process efficiency and reducing overall operational cost. It should be noted that the gas permeable cathode can also be provided with a catalyst, for example as a catalyst layer, in contact with the electrolyte.

[051] Reducing the cost of a regeneration process for the carbon capture agent or sorbent that is used is another problem that needs to be overcome. The inventors have also developed an integrated electrochemical process for mineral ions regeneration, for example calcium, sodium, potassium or lithium ions regeneration, at room temperature to reduce the cost of the regeneration process for the carbon capture agent or sorbent (e.g. as calcium ions, sodium ions, potassium ions or lithium ions in the electrolyte).

[052] In another embodiment there is provided a method including the steps of introducing CO2 gas, or a gas mixture containing CO2 gas, through or via the gas permeable cathode, for example being a gas diffusion electrode (GDE) provided with a catalyst layer, or a gas permeable membrane provided with an integrated conductive catalyst, to an electrolyte-cathode interface, so as to participate in the formation of carbonate mineral. It should be noted that reference to CO2 gas passing into and through the gas permeable cathode means the CO2 gas need not enter and completely exit the other side of the gas permeable cathode. For example, it may be that the solid-liquid-gas interface region of the gas permeable cathode, where electrochemical reactions occur, is at least partly inside of the gas permeable cathode, rather than wholly adjacent and external to the gas permeable cathode. Hence, any reference to CO2 gas passing into and through the gas permeable cathode means the CO2 gas passes into and at least partially through (i.e. internal to) the gas permeable cathode.

[053] A gas permeable cathode/anode/electrode can be provided as a gas diffusion electrode (GDE) or as a layered structure which includes a non-conducting gas permeable membrane as a non-conductive layer and one or more separate conductive layers. A gas permeable cathode (or a gas permeable anode) could be formed by, for example:

(1) Depositing or positioning a conformal conductive catalyst layer on or adjacent a non-conductive gas permeable membrane, typically a non- conductive polymeric gas permeable membrane, such as a porous PFTE membrane.

(2) Depositing or positioning a conductive (current collector) layer on a non- conductive gas permeable membrane, typically a non-conductive polymeric gas permeable membrane, such as a porous PFTE membrane, and depositing or positioning a catalyst layer on or adjacent the conductive layer.

(3) Using a gas diffusion electrode (GDE), which is conductive by itself.

A catalyst layer and a conductive layer, if separate layers are used, are gas permeable layers. A support structure layer (if utilised) may not be the same composition or permeability as a gas permeable membrane layer (if used). A support structure layer for a catalyst layer and/or a conductive layer would not be needed if the conducting material used (i.e. conductive layer) was itself porous to gases, for example a metal mesh. [054] Figure 1 illustrates a configuration of an example electrochemical cell 100. In the preferred embodiment, as illustrated, the electrochemical cell 100 is an electrochemical flow cell, meaning the electrolyte flows past an electrode in the electrochemical cell. An input supply or flow of CO2 gas 105, or a mixture including CO2 gas, during operation continuously passes into a surface (the outer surface, or a first surface) of and at least partially through a gas permeable cathode 110, for example being a gas diffusion electrode (GDE) preferably provided with a cathodic catalyst, e.g. as a cathodic catalyst layer, or being a gas permeable membrane provided with a conducting layer including a cathodic catalyst. That is, the outer surface of gas permeable cathode 110 faces the input supply of CO2 gas 105, or a mixture including CO2 gas. Gas permeable cathode 110 is preferably liquid-impermeable so as to contain liquid electrolyte, i.e. liquid catholyte, although liquid electrolyte can penetrate gas permeable cathode 110 to a certain extent which may improve liquid-gas phase electrochemical interaction. Examples of gas permeable membrane materials include polytetrafluoroethylene (PTFE), polyethylene (PE) and polypropylene (PP).

[055] Gas permeable cathode 110 includes a cathodic catalyst layer 120, i.e. a catalyst layer or a first catalyst, that faces and contacts liquid electrolyte, i.e. liquid catholyte 130, at a solid-liquid-gas interface layer 125. Cathodic catalyst layer 120 can be provided as part of gas permeable cathode 110 by conventional means, for example by being deposited on the surface of or joined to another layer, such as a non-conductive polymeric gas permeable membrane (if the catalyst is itself conductive or part of a conductive mixture) or a conductive support layer provided on the non-conductive polymeric gas permeable membrane, in which cases the cathodic catalyst layer 120 is provided as an integrated layer of overall gas permeable cathode 110. Liquid catholyte 130 contains mineral ions, which in particular examples are calcium ions, sodium ions, potassium ions or lithium ions.

[056] A membrane 140, which can be a separator, is positioned between gas permeable cathode 110 and anode 160 and provides electrochemical cell 100 with an anodic compartment 165 separated from a cathodic compartment 135 by membrane 140. A liquid anolyte 150 is provided to flow adjacent to anode 160 and between membrane 140 and anode 160, in anodic compartment 165. Liquid catholyte 130 is provided to flow adjacent to gas permeable cathode 110 and between membrane 140 and gas permeable cathode 110, in cathodic compartment 135. Preferably, though not necessarily, liquid anolyte 150 is provided to flow adjacent to anode 160 and between membrane 140 and anode 160, in anodic compartment 165. Thus, in operation, liquid anolyte 150 flows along an inner surface of anode 160 as a liquid catholyte flow. Membrane 140 separates liquid catholyte 130 and liquid anolyte 150 into distinct regions or compartments. Collectively, liquid catholyte 130 and liquid anolyte 150 provide the liquid electrolyte of the electrochemical cell 100. Anode 160 is also preferably provided with an anodic catalyst that can be provided as part of anode 160 by convention means, for example by being deposited as an anodic catalyst layer on the surface of anode 160 facing anolyte 150 or by being provided as an integrated layer of anode 160. In one example, the liquid anolyte flow rate is variable, and can be reversible in direction. In another example, a flow direction of the liquid anolyte flow can be in the same direction as the liquid catholyte flow. In another example, the liquid anolyte flow is in the opposite direction to the liquid catholyte flow.

[057] Catholyte 130 containing mineral ions flows into electrochemical cell 100 as illustrated as a catholyte flow, preferably during operation catholyte 130 continuously flows into electrochemical cell 100. Catholyte 130 flows along the surface (the inner surface, or a second surface) of gas permeable cathode 110 that faces catholyte 130 and that is preferably provided with cathodic catalyst layer 120. Carbonate mineral (i.e. produced or generated carbonate mineral, either in solution or as a precipitate, e.g. such as calcium carbonate if calcium ions are utilised) flows out of, i.e. is washed out of or is transported away, electrochemical cell 100 as part of an exit flow 170 of catholyte 130. Preferably, during operation, carbonate mineral, with catholyte 130, continuously flows out of electrochemical flow cell 100 as exit flow 170 of catholyte 130 and carbonate mineral. In some examples, the carbonate mineral may not be a precipitate. That is, the carbonate mineral remains in solution in the catholyte. Liquid anolyte 150 flows along the surface (the inner surface) of anode 160 that faces liquid anolyte 150 and that is preferably provided with an anodic catalyst layer. Liquid anolyte 150 flows out of anodic compartment 165 as at least part of an anodic compartment exit flow 175.

[058] An output flow 180 of any excess or unreacted CO2 gas 105, or excess mixture including CO2 gas, or any gases generated from electrochemical reactions with products such as hydrogen, passes out of electrochemical flow cell 100, preferably continuously during operation, and may be recirculated as input supply of CO2 gas 105, or a mixture including CO2 gas. An electrical supply 190 is used to provide a desired voltage difference (i.e. voltage potential) between gas permeable cathode 110 and anode 160, or a desired current flow through gas permeable cathode 110.

[059] Electrochemical cell 100 includes an anodic compartment 165 separated from a cathodic compartment 135 by membrane 140, preferably being an anion exchange membrane, a cation exchange membrane, an ion selective membrane or a bipolar membrane. Input CO2 gas 105, or a mixture including CO2 gas, is introduced into gas chamber 115 that faces the outer surface of gas permeable cathode 110, and output flow 180 of CO2 gas 105, or a mixture including CO2 gas, exits from gas chamber 115 or could be recirculated within gas chamber 115. Anode 160 can be a gas permeable anode, e.g. a gas diffusion electrode, or can be a gas impermeable electrode, e.g. a solid metallic electrode.

[060] Figure 2 illustrates an example of at least some electrochemical processes occurring at or in the vicinity of the gas-phase and liquid-phase interface of the electrochemical flow cell 100 illustrated in Figure 1. Solid-liquid-gas interface 125 is the interface of the solid gas permeable cathode 110 / solid cathodic catalyst layer 120, liquid catholyte 130 and CO2 gas 105 having passed into gas permeable cathode 110. Occurring at solid-liquid-gas interface 125 is an electrocatalytic reduction process that generates OH and reacts with Ca²⁺ in the electrolyte. Carbonate is formed from the CO2 gas being continuously supplied at least partially through gas permeable cathode 110 to chemically precipitate as solid carbonate mineral (CaC0₃(s)) on the inner surface of gas permeable cathode 110 (the surface of gas permeable cathode 110 facing the liquid catholyte 130). CO2 gas is transported or held in a gas chamber or a gas supply to be introduced to gas permeable cathode 110. CO2 gas moves into and at least partially through gas permeable cathode 110 to interface 125 where it undergoes an electrochemical reaction. Catholyte 130 is transported or held in a liquid catholyte chamber 135 or a liquid catholyte region to be introduced to gas permeable cathode 110 at interface 125. Gas permeable cathode 110 is liquid impermeable so as to confine liquid catholyte 130 to the liquid catholyte chamber 130 or the liquid catholyte region.

[061] The electrochemical cell may optionally be enclosed in a liquid-impermeable and gas-impermeable external housing (not illustrated). The external housing may incorporate liquid conduit(s) that form inlet(s) and outlet(s) to allow for the ingress and egress of liquid electrolyte(s). The liquid conduits may be connected to or in fluid communication with a liquid storage system(s), preferably an external liquid storage system that contains the liquid electrolyte(s). That is, optionally, at least one external liquid conduit is in fluid communication with an external liquid storage system for externally storing the liquid electrolyte(s). The cathode and the anode are connected to an external electrical circuit, e.g. a power supply, by a first electrical connection and a second electrical connection, respectively. The first electrical connection or the second electrical connection or the external electrical circuit itself, may penetrate the external housing without compromising its gas- and liquid-impermeable nature. The external electrical circuit can supply electrical energy to the cell.

[062] Figure 3 illustrates a configuration of another example electrochemical cell 300. In the preferred embodiment, as illustrated, the electrochemical cell 300 is an electrochemical flow cell, meaning the electrolyte flows past an electrode in the electrochemical cell. An input supply or flow of CO2 gas 305, or a mixture including CO2 gas, during operation continuously passes into a surface (the outer surface, or a first surface) of and at least partially through a gas permeable cathode 310, for example being a gas diffusion electrode (GDE) preferably provided with a cathodic catalyst, e.g. as a cathodic catalyst layer, or being a gas permeable membrane provided with a conducting layer including a cathodic catalyst. That is, the outer surface of gas permeable cathode 310 faces the input supply of CO2 gas 305, or a mixture including CO2 gas. Gas permeable cathode 310 is preferably liquid-impermeable so as to contain liquid electrolyte, i.e. liquid catholyte, although liquid electrolyte can penetrate gas permeable cathode 310 to a certain extent which may improve liquid-gas phase electrochemical interaction. Examples of gas permeable membrane materials include polytetrafluoroethylene (PTFE), polyethylene (PE) and polypropylene (PP).

[063] Gas permeable cathode 310 includes a cathodic catalyst layer 320, i.e. a catalyst layer or a first catalyst, that faces and contacts liquid electrolyte, i.e. liquid catholyte 330, at a solid-liquid-gas interface layer 325. Cathodic catalyst layer 320 can be provided as part of gas permeable cathode 310 by conventional means, for example by being deposited on the surface of or joined to another layer, such as a non-conductive polymeric gas permeable membrane (if the catalyst is itself conductive or part of a conductive mixture) or a conductive support layer provided on the non-conductive polymeric gas permeable membrane, in which cases the cathodic catalyst layer 320 is provided as an integrated layer of overall gas permeable cathode 310. Liquid catholyte 330 contains mineral ions, which in a particular example are calcium ions. [064] A membrane 340, which can be a separator, is positioned between gas permeable cathode 310 and gas permeable anode 360 and provides electrochemical cell 300 with an anodic compartment 365 separated from a cathodic compartment 335 by membrane 340. A liquid anolyte 350 is provided to flow adjacent to gas permeable anode 360 and between membrane 340 and gas permeable anode 360, in anodic compartment 365. Liquid catholyte 330 is provided to flow adjacent to gas permeable cathode 310 and between membrane 340 and gas permeable cathode 310, in cathodic compartment 335. Preferably, though not necessarily, liquid anolyte 350 is provided to flow adjacent to gas permeable anode 360 and between membrane 340 and gas permeable anode 360, in anodic compartment 365. Thus, in operation, liquid anolyte 350 flows along an inner surface of gas permeable anode 360 as a liquid catholyte flow. Membrane 340 separates liquid catholyte 330 and liquid anolyte 350 into distinct regions or compartments. Collectively, liquid catholyte 330 and liquid anolyte 350 provide the liquid electrolyte of the electrochemical cell 300. Gas permeable anode 360 is also preferably provided with an anodic catalyst that can be provided as part of gas permeable anode 360 by conventional means, for example by being deposited as an anodic catalyst layer on the surface of gas permeable anode 360 facing anolyte 350 or by being provided as an integrated layer of gas permeable anode 360. In one example, the liquid anolyte flow rate is variable, and can be reversible in direction. In another example, a flow direction of the liquid anolyte flow can be in the same direction as the liquid catholyte flow. In another example, the liquid anolyte flow is in the opposite direction to the liquid catholyte flow.

[065] Catholyte 330 containing mineral ions flows into electrochemical cell 300 as illustrated as a catholyte flow, preferably during operation catholyte 330 continuously flows into electrochemical cell 300. Catholyte 330 flows along the surface (the inner surface, or a second surface) of gas permeable cathode 310 that faces catholyte 330 and that is preferably provided with cathodic catalyst layer 320. Carbonate mineral (i.e. produced or generated carbonate mineral, such as: sodium carbonate if sodium ions are utilised, potassium carbonate if potassium ions are utilised, or lithium carbonate if lithium ions are utilised) flows out of, i.e. is washed out of or is transported away, electrochemical cell 300 as part of an exit flow 370 of catholyte 330. Preferably, during operation, carbonate mineral, with catholyte 330, continuously flows out of electrochemical flow cell 300 as exit flow 370 of catholyte 330 and carbonate mineral. The carbonate mineral may be in solution with catholyte. That is, the carbonate mineral may be soluble, or partially soluble with the catholyte. Liquid anolyte 350 flows along the surface (the inner surface) of gas permeable anode 360 that faces liquid anolyte 350 and that is preferably provided with an anodic catalyst layer. Liquid anolyte 350 flows out of anodic compartment 365 as at least part of an anodic compartment exit flow 375.

[066] An output gas flow 380 of any excess or unreacted CO2 gas 305, or excess mixture including CO2 gas, or any gases generated from electrochemical reactions with products such as hydrogen, passes out of electrochemical flow cell 300, preferably continuously during operation, and may be recirculated as input supply of CO2 gas 305, or a gas mixture including CO2 gas. For example, a flow of gas 385, such as hydrogen gas for example, can be directed to from cathode gas chamber 315 to an anode gas chamber so that flow of gas 385 is passed through the gas permeable anode 360 to react with the liquid anolyte. An electrical supply 390 is used to provide a desired voltage difference (i.e. voltage potential) between gas permeable cathode 310 and gas permeable anode 360, or a desired current flow through gas permeable cathode 310 and/or gas permeable anode 360.

[067] Electrochemical cell 300 includes an anodic compartment 365 separated from a cathodic compartment 335 by membrane 340, preferably being an anion exchange membrane, a cation exchange membrane, an ion selective membrane or a bipolar membrane. Input CO2 gas 305, or a mixture including CO2 gas, is introduced into cathode gas chamber 315 that faces the outer surface of gas permeable cathode 310, and output flow 380 of CO2 gas 305, or a mixture including CO2 gas, exits from cathode gas chamber 315 or could be recirculated within cathode gas chamber 315. Gas permeable anode 360 can be a gas diffusion electrode.

[068] Figure 4 shows a flowchart of an example method 400 including the electrochemical induction of carbonate mineral from aqueous mineral ions (M) in the presence of CO2 gas continuously introduced into a gas permeable cathode, for example a gas diffusion electrode with a catalyst layer, or a non-conducting polymeric gas permeable membrane with an integrated conductive catalyst layer (i.e. a cathodic catalyst layer), or a non-conducting polymeric gas permeable membrane with a conductive layer and a cathodic catalyst layer. Preferably, the mineral ions (M) are or comprise: calcium ions, sodium ions, potassium ions, and/or lithium ions. Method 400 includes the steps of:

(1) Introducing mineral ions (M) in an aqueous catholyte.

(2) Producing bicarbonate and/or carbonate ions in the aqueous catholyte, which is obtained from CO₂ gas being continuously supplied at least partially through the gas permeable cathode, the CO₂ gas having reacted with the aqueous catholyte. Depending on the pH, the ions could be HCO₃ or CO₃ ² or it mixture when CO₂ reacts with water.

(3) Producing OH ions in the aqueous catholyte, which is induced by the electrochemical reaction.

(4) Reacting mineral ions (M) and HCO₃ (or CO₃ ² and its mixture) ions and OH ions in the aqueous catholyte.

(5) Resultant generation of carbonate mineral and H2O. The carbonate mineral may be in solution with the catholyte or a solid precipitate.

[069] Figure 5 shows a flowchart of another example method 500 including the electrochemical induction of calcium carbonate from aqueous calcium ions in the presence of CO2 gas continuously introduced into a gas permeable cathode, for example a gas diffusion electrode with a catalyst layer, or a non-conducting polymeric gas permeable membrane with an integrated conductive catalyst layer (i.e. a cathodic catalyst layer), or a non-conducting polymeric gas permeable membrane with a conductive layer and a cathodic catalyst layer. Method 300 includes the steps of:

(1) Introducing Ca²⁺ ions in an aqueous catholyte.

(3) Producing OH ions in the aqueous catholyte, which is induced by the electrochemical reaction. (4) Reacting Ca²⁺ ions and HCO3 (or CO3² and its mixture) ions and OH ions in the aqueous catholyte.

(5) Resultant precipitation of solid CaC0₃ and H2O. [070] One side of the gas permeable cathode is in contact with the electrolyte containing a liquid-phase mineral, preferably calcium ions, sodium ions, potassium ions, and/or lithium ions. The electrolyte containing a liquid-phase mineral can be any type of electrolyte that contains one or more minerals, such as for example calcium, sodium, potassium, lithium, magnesium, strontium and/or barium.

[071] The electrolyte containing a liquid -phase mineral is preferably continuously flowing, i.e. there is a continuous flow of electrolyte past the gas permeable cathode, and fresh electrolyte or injection of electrolyte containing minerals, such as calcium chloride, can be introduced into an electrolyte chamber. The electrolyte containing a liquid-phase mineral can include mineral ions, and/or other additive(s), preferably with one or more functionalities, such as:

(1) enhancing electrolyte conductivity via the introduction of supporting electrolytes, such as sodium chloride and/or potassium chloride,

(2) enhancing carbon capture via introduction of additional capture agent(s) or sorbent(s), such as amine and its derivatives,

(3) handling any other pre-existing cations or anions present during recovery and extraction processes of mineral ions from their original sources.

[072] The outer surface or side of gas permeable cathode 110, 310 allows introduction of CO2 gas, or a gas mixture including CO2 gas, preferably under continuous flow of gas, to the gas permeable membrane. The CO2 gas is passed at least partially through the solid- phase gas permeable cathode 110, 310 which is in contact with the liquid-phase electrolyte (i.e. liquid-phase catholyte 130, 330). The CO2 gas either remains as gas-phase CO2 or is converted to dissolved forms, such as carbonate and bicarbonate ions, within the electrolyte matrix containing one or more types of minerals.

[073] Under sufficient applied voltage between gas permeable cathode 110, 310 and anode 160, 360, from voltage supply 190, 390 (i.e. power supply to apply a voltage differential), one or several electrocatalytic reductive reactions, such as water reduction, proton reduction, and/or O2 reduction, occur at gas permeable cathode 110, 310 inducing the formation of hydroxide ions. The electrolyte includes mineral ions, for example calcium ions, sodium ions, potassium ions, and/or lithium ions, together with dissolved carbonate and/or bicarbonate derived from CO2 gas introduced via gas permeable cathode 110, 310, and then electrochemically reacts inducing hydroxide ions to form a carbonate mineral, for example calcium carbonate, sodium carbonate, potassium carbonate, and/or lithium carbonate. The occurrence of a particular reaction, as well as the route in inducing hydroxide formation, depends on factors such as the type and performance of the catalysts, applied voltage potentials, current densities, and concentration of the minerals and other ions in the electrolyte.

[074] Thus, in some embodiments there is provided an electrochemical mineral carbonation cell 100, 300 for capturing carbon dioxide 105, 305, the electrochemical cell 100, 300 comprising a gas permeable cathode 110, 310 wherein carbon dioxide gas 105, 305 is able to pass into an outer surface of and at least partially through the gas permeable cathode 110, 310 to react with a liquid catholyte 130, 330. An anode 160, 360 is provided, wherein a voltage difference is able to be applied between the gas permeable cathode 110, 310 and the anode 160, 360. A membrane 140, 340 is positioned between the gas permeable cathode 110, 310 and the anode 160, 360. The liquid catholyte 130, 330 is positioned between the gas permeable cathode 110, 310 and the membrane 140, 340, the liquid catholyte including mineral ions. A liquid anolyte 150, 350 is positioned between the anode 160, 360 and the membrane 140, 340. In operation, the liquid catholyte 130, 330 flows along an inner surface of the gas permeable cathode 110, 310 and carbonate mineral is produced (for example upon reaction between electrochemically generated hydroxide and carbon dioxide) at, near or on the inner surface of the gas permeable cathode 110, 310 and is at least partially transported away from the inner surface of the gas permeable cathode 110, 310 by the liquid catholyte flow 130, 330.

[075] In some examples, there may be one or more carbonate minerals produced in the electrochemical cell that are/is soluble or substantially soluble in the liquid catholyte. Examples may include: sodium carbonate, potassium carbonate and/or lithium carbonate. The mineral ions being used may be or may comprise sodium ions, potassium ions, and/or lithium ions. Utilising sodium ions produces sodium carbonate. Utilising potassium ions produces potassium carbonate. Utilising lithium ions produces lithium carbonate.

[076] In some examples, there may be additionally or alternatively one or more carbonate minerals produced in the electrochemical cell by being precipitated on the inner surface of the gas permeable cathode. The carbonate mineral may at least be partially removed and transported away from the inner surface of the gas permeable cathode by the liquid catholyte flow. Such carbonate mineral may include, for example, calcium carbonate. The mineral ions being used may be or may comprise calcium ions. Utilising calcium ions produces calcium carbonate.

[077] In other examples, during operation the carbon dioxide gas continuously passes at least partially through the gas permeable cathode 110, 310 and carbonate mineral is continuously produced at or near, or precipitated on, the inner surface of the gas permeable cathode 110, 310 and is continuously transported away from the inner surface of the gas permeable cathode 110,310 by continuous liquid catholyte flow 130, 330.

[078] In another example, the gas permeable cathode 110, 310 is a gas diffusion electrode provided with a cathodic catalyst layer 120, 320. In other examples, the gas permeable cathode 110, 310 comprises a conductive cathodic catalyst layer, or the gas permeable cathode 110, 310 is a gas permeable membrane, preferably a non-conductive polymeric gas permeable membrane, provided with a conductive cathodic catalyst layer, or the gas permeable cathode 110, 310 is a gas permeable membrane, preferably a non- conductive polymeric gas permeable membrane, provided with a cathodic catalyst layer provided on a conductive layer that is deposited on, or positioned adjacent to, the gas permeable membrane. In another example, the cathodic catalyst is provided as a cathodic catalyst layer 120, 320 at the inner surface of the gas permeable cathode 110, 310. In another example, the cathodic catalyst layer is formed of or includes a hydrogen evolution catalyst. In another example, the cathodic catalyst layer is formed of or includes an oxygen reduction catalyst. In another example, the cathodic catalyst layer is formed of or includes a bi-functional catalyst or a multifunctional catalyst. In another example, the cathodic catalyst layer is formed of or includes one or more metals selected from the group of noble metals (e.g. Pt, Ag), earth-abundant metals (e.g. Ni, Co, Mo), alloys thereof, metal phosphines, or other non-metallic catalysts. In another example, the cathodic catalyst layer is formed of or includes a hydrophobic material. In another example, the cathodic catalyst layer is formed of or includes a hydrophilic material.

[079] In another example, the anode 160, 360 includes an anodic catalyst, preferably as an anodic catalyst layer. In another example, the anodic catalyst layer is formed of or includes an oxygen evolution catalyst. In another example, the anodic catalyst layer is formed of or includes a hydrogen oxidation catalyst. In another example, the anodic catalyst layer is formed of or includes a chlorine evolution catalyst. In another example, the gas permeable cathode 110, 310 includes a carbon protective layer.

[080] In another example, a flow rate of the liquid catholyte flow is variable, preferably when the carbonate mineral is insoluble. In another example, the liquid catholyte flow alternates between flowing in a first direction and flowing in a second direction past the inner surface of the gas permeable cathode.

[081] In another example, the carbon dioxide gas 105, 305 is selected from the group of: pure carbon dioxide gas, substantially pure carbon dioxide gas, a gas mixture including carbon dioxide gas, ambient air, compressed air, industry waste gas including carbon dioxide, and a prepared gas mixture including carbon dioxide gas.

[082] In another example, mineral containing liquid catholyte 130, 330 has an acidic to alkaline pH. In another example, mineral containing liquid catholyte 130, 330 is at or about neutral pH. In other specific examples, the liquid catholyte (with for example 0.5 M NaCl and with DI water) may be, for example, about pH 5.0, about pH 5.5, about pH 6.0, about pH 6.5, about pH 7.0, about pH 7.5, about pH 8.0, about pH 8.5, or about pH 9.0, or from about pH 5.0 to about pH 9.0, or from about pH 5.0 to about pH 8.0, or from about pH 6.0 to about pH 8.0. With CO2 purging, the liquid catholyte becomes more acidic, for example about pH 5.0. In another example, the liquid anolyte 150, 350 is an electrolyte containing various concentration of proton and hydroxide ions, and the membrane 140, 340 is an ion exchange or ion selective membrane. In another example, the liquid anolyte 150, 350 is an alkaline electrolyte and the membrane 140, 340 is an anion exchange, cation exchange or bipolar membrane. In another example, the liquid anolyte 150, 350 is an acidic electrolyte and the membrane 140, 340 is a cation exchange, anion exchange or a bipolar membrane. In another example, the liquid anolyte 150, 350 includes sodium chloride and has neutral pH and the membrane 140, 340 is a cation exchange, anion exchange, or a bipolar membrane. The selection of type of membrane is dependent on both the catholyte and anolyte, and the ions preferred to be transferred.

[083] In another example, there is provided an electrochemical system for capturing carbon dioxide that includes at least one electrochemical cell as described herein. The electrochemical system includes a carbon dioxide gas source to supply the carbon dioxide gas 105, 305, and a power supply 190, 390 to apply the voltage difference between the gas permeable cathode 110, 310 and the anode 160, 360. A liquid catholyte source supplies the liquid catholyte 130, 330, and an anolyte source supplies the liquid anolyte 150, 350. A separation unit removes the carbonate mineral from the liquid catholyte flow.

[084] In another embodiment there is provided a method of operating the electrochemical mineral carbonation cell 100, 300 to capture carbon dioxide and produce carbonate mineral. The method including introducing carbon dioxide gas into the outer surface of the gas permeable cathode 110, 310 and allowing the carbon dioxide gas 105, 305 to pass at least partially through the gas permeable cathode 110, 310 to react with the liquid catholyte 130, 330 including mineral ions. The liquid catholyte 130, 330 is positioned between an inner surface of the gas permeable cathode 110, 310 and the membrane 140, 340, and the membrane 140, 340 is positioned between the gas permeable cathode 110, 310 and the anode 160, 360. The liquid anolyte 150, 350 is positioned between the anode 160, 360 and the membrane 140, 340. The method also includes applying a voltage difference between the anode 160, 360 and the gas permeable cathode 110, 310, and flowing the liquid catholyte 130, 330 along the inner surface of the gas permeable cathode 110, 310. In one example, carbonate mineral precipitate is formed (for example upon reaction between electrochemically generated hydroxide and carbon dioxide) on the inner surface of the gas permeable cathode 110, 310, and is at least partially removed and transported away from the inner surface of the gas permeable cathode 110, 310 by the flowing liquid catholyte 130, 330. In another example, carbonate mineral is produced in solution at or near the inner surface of the gas permeable cathode 110, 310, and is at least partially transported away from the inner surface of the gas permeable cathode 110, 310 by the flowing liquid catholyte 130, 330.

[085] In another example, the method further includes continuously circulating the liquid catholyte into and out of the electrochemical cell 100, 300. In another example, the method further includes continuously circulating the liquid anolyte into and out of the electrochemical cell 100, 300. In another example, the method further includes continuously introducing carbon dioxide gas into the outer surface of the gas permeable cathode 110, 310, and continuously removing and transporting away the carbonate mineral precipitate from the inner surface of the gas permeable cathode 110, 310 by the continuously flowing liquid catholyte 130, 330. In another example, the method further includes continuously introducing carbon dioxide gas into the outer surface of the gas permeable cathode 110, 310, and continuously transporting away the carbonate mineral produced at or near the inner surface of the gas permeable cathode 110, 310 by the continuously flowing liquid catholyte 130, 330.

[086] In another example, the method further includes a reductive catalytic process that generates localized alkalinity at the surface of the gas permeable cathode. In another example, the method further includes that the carbonate mineral precipitate is removed from the flowing liquid catholyte and is collected. In another example, the method further includes that the carbonate mineral in solution is removed from the flowing liquid catholyte and is collected. In another example, the method further includes that a rate of carbonate mineral formation is changed by altering the applied voltage difference and/or by altering a current density through the gas permeable cathode.

[087] In another example, the method operates at ambient air temperature and ambient air pressure. In another example, hydroxide ions are formed by an electro-catalytic reaction, the hydroxide ions reacting with the mineral ions in the liquid catholyte and reacting with bicarbonate formed from the carbon dioxide gas.

[088] In another example, the method includes regenerating the capture agent or sorbent, for example which are mineral ions being calcium ions, sodium ions, potassium ions or lithium ions, in the liquid catholyte. [089] Another example includes regenerating the mineral ions in the liquid catholyte by: (1) Reacting the carbonate mineral that has been collected with hydrochloric acid to form mineral chloride, CO2 and water. CO2 is stored as chemical feedstock with resale value. This endothermic process is as follow (M representing a mineral ion which may be divalent or monovalent): MCO3 (s) + 2HC1 (aq) MCI2 (aq) + CO2 (g) + H2O (aq), M2CO3 (s) + 2HC1 (aq) 2MC1 + C0₂ + H₂0, or MHCO3 (aq) + HC1 (aq) MCI (aq) + C0₂(g) + H2O (aq). In another example, the source of HC1 can be obtained fully or partially from anodic process within the electrochemical cell such as hydrogen oxidation, as following: H2(g) 2H⁺+ 2e (aq). Chloride from cathodic compartment is migrated through anion exchange membrane to the anodic compartment to form HC1: H⁺ + Cl HC1. Another process is chloride oxidation at the anode, where chlorine gas then react with water to form hydrochloric acid and hypochlorous acid, as following: Ck(g) + H2O (aq) HC1 (aq) + HOC1 (aq). Hypochlorous acid is further transform to HC1 under light illumination, as following: 2HOC1 (aq) 2HC1 (aq) + 02(g). In another example, when dilute HC1 is employed at the anode, an electrochemical reaction in the presence of ¾ gas and chloride ions (supply across membrane from cathodic compartment) facilitates the formation of concentrated HC1. In another example, chlorine gas at the anode can be reacted with the hydrogen generated at the cathode to form hydrochloric acid. In addition, hydrochloric acid can be an external outsourced chemical reagent or obtained from industry plants that emitted it as a waste.

(2) Reacting calcium carbonate that has been collected with chlorine gas to form calcium chloride, CO2 and hypochlorous acid, as following: 2Ch (g) + CaCC (s) + H2O

(aq) CaCh (aq) + C0₂ (g) + 2HOC1 (aq).

(3) Heating the calcium carbonate that has been collected to produce CaO and converting the CaO to calcium ions. [090] In another example, the method includes regenerating the capture agent or sorbent, for example which is calcium ions in the liquid catholyte. Another example includes regenerating the calcium ions in the liquid catholyte by: (1) Reacting the calcium carbonate that has been collected with hydrochloric acid to form calcium chloride, CO2 and water. CO2 is stored as chemical feedstock with resale value. This endothermic process is as follow: CaC0₃ (s) + 2HC1 (aq) CaCh (aq) + CO2 (g) + H2O (aq), where 2 moles of HC1 is needed to regenerate 1 mole of CaCh In another example, the source of HC1 can be obtained fully or partially from anodic process within the electrochemical cell such as chloride oxidation, as following: 2CT (aq) Cb (g) + 2e . Chlorine gas then react with water to form hydrochloric acid and hypochlorous acid, as following: Ch(g) + H2O (aq) HC1 (aq) + HOC1 (aq). Hypochlorous acid is further transform to HC1 under light illumination, as following: 2HOC1 (aq) 2HC1 (aq) + O2 (g). In another example, when dilute HC1 is employed at the anode, an electrochemical reaction in the presence of ¾ gas and chloride ions (supply across membrane from cathodic compartment) facilitates the formation of concentrated HC1. In another example, chlorine gas at the anode can be reacted with the hydrogen generated at the cathode to form hydrochloric acid. In addition, hydrochloric acid can be an external outsourced chemical reagent or obtained from industry plants that emitted it as a waste.

(2) Reacting calcium carbonate that has been collected with chlorine gas to form calcium chloride, CO2 and hypochlorous acid, as following: 2Ch (g) + CaCC (s) + H2O (aq) CaCh (aq) + C0₂ (g) + 2HOC1 (aq).

(3) Heating the calcium carbonate that has been collected to produce CaO and converting the CaO to calcium ions.

[091] Passing CO2 gas through a gas permeable cathode allows improved and efficient interaction between the catalyst, the electrolyte and the CO2 gas. A first side (i.e. an outer side or an outer surface) of the solid gas permeable cathode allows continuous introduction of CO2 gas, or a gaseous mixture containing CO2 gas, as the gas is preferably under continuous flow. The CO2 gas, or gas mixture, is flown through the gas permeable cathode which on a second side (i.e. an inner side or an inner surface) is coated or impregnated with the catalyst (or one or more catalysts) and is in contact with liquid- phase electrolyte. The electrolyte preferably contains mineral ions. The CO2 gas, or a gaseous mixture containing CO2 gas, either remains in gas phase or dissolves in forms such as carbonate and bicarbonate ions in the electrolyte matrix. [092] Due to the hydroxide ions forming on the gas permeable cathode, the reaction, for example when using calcium ion being Ca²⁺ + HCO3- + OH CaC0₃ + H2O, takes place in close proximity to, or adjacent to, or at, or near, or on, the gas permeable cathode and the produced carbonate mineral, for example when using calcium ions being deposited solid CaC0₃, would otherwise cover the gas permeable cathode reducing its efficiency. This is mitigated, or avoided, by using a flow system where the liquid electrolyte, or at least the liquid catholyte, flows past or flows along, for example continuously flows past, or continuously flows along, the gas permeable cathode to, in the case of a carbonate mineral that is produced as a precipitate such as calcium carbonate, transport away, remove, scrub or wash off the deposited solid carbonate mineral, for example CaCC . In the case of a carbonate mineral that is produced in solution, still due to the hydroxide ions forming on the gas permeable cathode, the reaction takes place in close proximity to, or adjacent to, or at, or near, or on, the gas permeable cathode and the produced carbonate mineral, for example when using sodium ions, potassium ions or lithium ions, would otherwise concentrate in solution near the gas permeable cathode reducing its efficiency. This is similarly mitigated, or avoided, by using a flow system where the liquid electrolyte, or at least the liquid catholyte, flows past or flows along, for example continuously flows past, or continuously flows along, the gas permeable cathode to, in the case of a carbonate mineral that is produced in solution, such as sodium carbonate, potassium carbonate or lithium carbonate, transport away, remove, flush or wash away the carbonate mineral in solution.

[093] The method of introducing CO2 gas via the gas permeable cathode is efficient and sensitive. The conversion to calcium carbonate occurs under several examined conditions, including from using a 100 % high purity CO2 gas, to using a gas mixture including CO2 as low as 1 % by volume (mixed with inert gas such as Argon), to using atmospheric ambient air of 0.04 % CO2 by volume. In the latter case using ambient air, the presence of O2 is found to have a positive impact in increasing current densities due to an oxygen reduction reaction also contributing to hydroxide ion generation. Control experiments demonstrated that when the purging of CO2 gas through the gas permeable cathode is stopped this results in the discontinuance of carbonate mineral formation, confirming the source of carbonate ions. [094] Under the preferable condition of continuous electrolyte flow at the gas permeable cathode, the formed carbonate mineral is continuously removed from the surface of the gas permeable cathode facing the continuous electrolyte flow, and the removed carbonate mineral is collected at a catholic reservoir. This is achieved by utilising one or more of the following factors:

(1) Altering flow parameters of a liquid electrolyte pump, such having uni- or bi direction flow of liquid electrolyte, either under a constant flow rate or a variable flow rate.

(2) Providing electrochemical cells with a specific design of the cathodic electrolyte compartment (i.e. catholyte compartment). Preferably, the electrochemical cell design includes a selected spacing and volume of the cathodic electrolyte compartment, incorporating cathodic electrolyte inlets and outlets that improve the electrolyte flow and the collection of the carbonate mineral.

(3) Providing an in-built mechanical brushing system within the cathodic electrolyte compartment that enables the cleaning and removal of carbonate mineral from the cathode surface.

(4) Introducing externally assisted forces, preferably by placing the electrochemical cell under vibration or ultrasonic ation, to facilitate the collection and removal of carbonate mineral, whilst also enhancing the kinetics of the processes.

(5) Providing a periodic cleaning of the cathode to obtain a refreshed cathode surface by using a chemical treatment, preferably by using hydrochloric acid to dissolve any carbonate mineral remaining deposited on the cathode surface.

[095] Figure 6 is a schematic diagram showing electrochemically generated carbonate mineral 410 accumulating over time on or at an inner surface 125, 325 of gas permeable cathode 110, 310. Using a static electrolyte (non-flowing) as illustrated, carbonate mineral 410 accumulates on the inner surface 125, 325 of gas permeable cathode 110, 310, resulting in a mass transfer issue, which lowers the process efficiency and reduces the quantity of produced carbonate mineral. [096] Figure 7 is a schematic diagram showing electrochemically generated carbonate mineral 510 being removed and transported away over time from an inner surface 125, 325 of gas permeable cathode 110, 310. Using a flow of electrolyte 520 (i.e. the electrolyte is flowing past the gas permeable cathode 110, 310) in the direction as illustrated, carbonate mineral 510 does not accumulate on or at the inner surface 125, 325 of gas permeable cathode 110, 310, which improves the process efficiency and increases the quantity of produced carbonate mineral. The flow of electrolyte 520 provides an effective force to remove or wash away electrochemically generated carbonate mineral 510 from the inner surface 125, 325 of gas permeable cathode 110, 310 (contrasted to Figure 4). The removed carbonate mineral 510, for example solid carbonate mineral, can be transported away and subsequently collected.

[097] Figure 8 is a schematic diagram showing electrochemically generated carbonate mineral 510 being removed from an inner surface 125, 325 of a gas permeable cathode 110, 310. Using alternating flows of electrolyte 520 (i.e. the electrolyte is flowing past the gas permeable cathode 110, 310) in the alternating directions as illustrated, carbonate mineral 510 does not accumulate on or concentrate at the inner surface 125, 325 of gas permeable cathode 110, 310, which improves the process efficiency and increases the quantity of produced carbonate mineral. The alternating flows of electrolyte 520 provides an effective force to remove or wash away electrochemically generated carbonate mineral 510 from the inner surface 125, 325 of gas permeable cathode 110, 310 (contrasted to Figure 4). The alternating flows of electrolyte 520 alternates between flowing in a first direction and flowing in a second direction past the inner surface 125, 325 of gas permeable cathode 110, 310. Alternating the direction of flow of electrolyte 520, and/or flow rates, can enhance the mass transfer of carbonate mineral. The removed carbonate mineral 510, for example solid carbonate mineral, can be transported away and subsequently collected.

[098] To maintain long-term performance of the gas permeable cathode, either to avoid electrode fouling as a result of deposition or concentration of carbonate mineral, or to enhance catalyst physical and chemical stability, or to optimise the gas-liquid-solid interface, the gas permeable cathode can be constructed or modified, preferably in any one or more the following ways: (1) Using a catalyst. For example, by applying a coating, preferably as a thin layer, of catalyst made of metallic, organic, inorganic or its hybrid materials, preferably by but not limited to air brushing, spray coating, electrodeposition, atomic layer deposition, chemical bathing or chemical vapour deposition.

(2) Introduction of a carbon protective layer, for example in particular to maintain electrode hydrophobicity when the gas permeable cathode is in contact with the electrolyte thereby ensuring an excellent gas-solid-liquid interface.

(3) Incorporation of a hydrophobic material (for example PTFE), a hydrophilic material (for example the Nafion^® membrane supplied by the Chemours company, which is a sulfonated tetrafluoroethylene based fluoropolymer- copolymer membrane), or a mixture containing a hydrophobic material or a hydrophilic material, during catalyst preparation that acts as a binder, and thereby improves the efficiency of channels for gas diffusion within the gas permeable cathode.

[099] The collection of carbonate mineral in the catholyte reservoir includes a separation system, for example a filter system, to separate carbonate mineral from the liquid electrolyte (i.e. from the catholyte). In one example, the separation system preferably uses a gravimetric process of carbonate mineral sedimentation (i.e. a gravimetric separation system), and/or uses a filter or filtering membrane. Other separation systems that are known to the skilled person can be used for different types of carbonate minerals, for example if the carbonate mineral remains in solution.

[0100] In the output flow 180, 380 of CO2 gas, or mixture containing CO2 gas, under electrocatalytic conditions, depending on the employed catalyst(s) and the input flow of CO2 gas 105, 305, or mixture containing CO2 gas, either in the metallic, bimetallic or molecular form, products such as hydrogen can be part of the output flow 180, 380 of CO2 gas, or mixture containing CO2 gas, and can be collected or separated. [0101] In a preferred embodiment, the electrochemical cell 100, 300 includes an anodic compartment 165, 365 separated from a cathodic compartment 135, 335 by membrane 140, 340, preferably being an anion exchange membrane, a cation exchange membrane, an ion selective membrane or a bipolar membrane. The pH of the electrolytes in the anodic compartment 165, 365 (i.e. the pH of the anolyte) and in the cathodic compartment 135, 335 (i.e. the pH of the catholyte) ranges from 1 to 14. Anode 160, 360 can be a gas permeable anode, e.g. a gas diffusion electrode, or can be a gas impermeable electrode, e.g. a solid metallic electrode.

[0102] In one example embodiment, the gas permeable cathode has a catalyst layer, with the catalyst layer in contact with mineral containing electrolyte (initially neutral pH), coupled to the anode in an alkaline electrolyte separated by an anion exchange membrane. In this configuration, the OH ions migrate to the gas permeable cathode and the pH of the unbuffered catholyte could change to become slightly alkaline.

[0103] In another example embodiment, the gas permeable cathode has a catalyst layer, with the catalyst layer in contact with mineral containing electrolyte at neutral pH, coupled to the anode in an acidic electrolyte separated by a cation exchange membrane. In this configuration, pH of the catholyte remains neutral. If dilute HC1 is employed at the anode, an electrochemical reaction in the presence of ¾ and chloride ions can facilitate the formation of concentrated HC1.

[0104] In another example embodiment, the gas permeable cathode has a catalyst layer, with the catalyst layer in contact with mineral containing electrolyte at neutral pH, coupled to the anode in an electrolyte containing sodium chloride at neutral pH separated by an ion-selective membrane. In this configuration, chlorine gas is generated at the anode, as well as dissolved HC1 and HOC1. The pH of the anolyte becomes acidic, and the pH of the catholyte remains near neutral.

[0105] In another example embodiment there is provided a stack of a plurality of electrochemical cells, the stack being configurable with multiple electrochemical cells, for example of alternate voltage polarities. Electrochemical cells in the stack can be connected in series or parallel depending on the preferable electrical configuration.

[0106] Figure 9 illustrates an example configuration of a stack 700 of a plurality of electrochemical cells including multiple electrochemical cell units to produce carbonate mineral. The configuration represents individually independent and separable electrochemical cells. An electrochemical cell is repeated in the stack 700 and each electrochemical cell includes a gas permeable cathode 710, catholyte 730 that includes mineral ions and in which carbonate mineral is produced, membrane 740 separating catholyte 730 and anolyte 750. Catholyte 730 is provided as a continuous flow and anolyte 750 is provided as a continuous flow. A voltage difference is applied across anode 760, which is supplied with a relative positive electric potential, and cathode 710, which is supplied with a relative negative electric potential. Catholyte exit flow 770 contains the produced carbonate mineral, and preferably catholyte flow 770 is continuous during operation of the stack 700 of a plurality of electrochemical cells. In this example, the multiple cathodes 710 of each cell can share a common electrical current collector.

[0107] In this example configuration, multiple individual separable electrochemical cells are assembled into a stack of electrochemical cells. An individual electrochemical cell contains stand-alone cathodic and anodic compartments and is independent from another cell. This stack configuration offers an advantage of ease of maintenance where any faulty cell can be individually repaired or replaced, however a higher material cost involved.

[0108] Figure 10 illustrates an example configuration of a stack 800 of a plurality of electrochemical cells including multiple electrochemical cell units to produce carbonate mineral. The configuration represents an integrated stack configuration including each cathodic or anodic compartment sharing the same current collector. An electrochemical cell includes a gas permeable cathode 810, where a cathode shares a current collector with patterned gas channels at both a front side and a back side, with each side in contact with the gas permeable cathode 810. Anodes 860 share a current collector. A voltage difference is applied across anodes 860, which are supplied with a relative positive electric potential, and cathodes 810, which are supplied with a relative negative electric potential. Catholyte exit flow 870 contains the produced carbonate mineral, and preferably catholyte flow 870 is continuous during operation of the stack 800 of a plurality of electrochemical cells.

[0109] In this example configuration, for reduced material cost, the cathode and anode are configurable with a shared cathodic current collector plate, and a shared anodic current collector plate, respectively. In this case, the gas flow current collector at the cathode is patterned at both front and back sides, whereby both sides of the current collector are in contact with two gas permeable cathodes. The flow of CO2 gas therefore shares the same common gas channel, hence having the same inlet gas flow and outlet gas flow for two electrochemical cells. Likewise, the anodes share the same current collector for two electrochemical cells.

[0110] Figure 11 illustrates an example configuration of a stack 900 of a plurality of electrochemical cells including multiple electrochemical cell units to produce carbonate mineral. The configuration represents an integrated stack configuration including each cathodic or anodic compartment sharing the same current collector. An electrochemical cell includes a gas permeable cathode 910, where a cathode shares a current collector with patterned gas channels at both a front side and a back side, with each side in contact with the gas permeable cathode 910. An electrochemical cell also includes a gas permeable anode 960, where an anode shares a current collector with patterned gas channels at both a front side and a back side, with each side in contact with the gas permeable anode 960. A voltage difference is applied across anodes 960, which are supplied with a relative positive electric potential, and cathodes 910, which are supplied with a relative negative electric potential. Catholyte exit flow 970 contains the produced carbonate mineral, and preferably catholyte flow 970 is continuous during operation of the stack 900 of a plurality of electrochemical cells.

[0111] In this example configuration, which is the same as that illustrated in Figure 8 except the anodes are gas permeable anodes, a shared anodic compartment with patterned current collector plate is employed. A desired gas is introduced at the anodic compartments of two electrochemical cells sharing the same common gas channels.

[0112] In all of the above configurations, there is preferably a continuous flow of catholyte and anolyte. Preferably, the catholyte at the cathode for each individual cell is connected in parallel, having separate individual outlet channel facilitates for the collection of carbonate mineral, and for maintenance of a cell. At the anodes, it is optional if the anolyte flow is separated (connected in parallel channels) or is continuous (connected in series channels) for the stack of cells. [0113] Cost efficient regeneration of the carbon capture agent or sorbent is an important part of the overall economics of carbon capture technology. Preferably, when mineral ions (such as calcium ions, sodium ions, potassium ions and/or lithium ions for example) are used the regeneration process involves the recovery of mineral chloride (such as calcium chloride, sodium chloride, potassium chloride and/or lithium chloride for example) as a precursor electrolyte medium used to capture CO2 in the form of carbonate mineral (such as calcium carbonate, sodium carbonate, potassium carbonate and/or lithium carbonate for example). In an example regeneration process, calcium carbonate, sodium carbonate, potassium carbonate, or lithium carbonate is reacted with hydrochloric acid to form calcium chloride, sodium carbonate, potassium carbonate or lithium carbonate respectively, as well as form CO2 and water. The released CO2 is captured and stored, and potentially used as a chemical feedstock or a commodity product with resale value. Mineral chloride and the associated electrolyte is reused for electrochemical CO2 capture.

[0114] In one example, as described previously, concentrated hydrochloric acid is collected from an anodic reaction. In another example, hydrochloric acid or chlorine gas is produced at the anode (within the same electrochemical cell) using a chloride oxidation reaction at the anode. In another example, hydrogen at the cathode or external hydrogen is supplied to anode generates hydrochloric acid through hydrogen oxidation reaction. Chloride ions can be transferred from cathodic to anodic compartment through an anion exchange membrane. In another example, as described previously, chloride oxidation occurs to generate chlorine, and chlorine is dissolved to form hydrochloric acid and hypochlorous acid. Hypochlorous acid is further reduced to hydrochloric acid by light illumination. Alternatively, chlorine gas can be reacted with the hydrogen generated at the cathode to form hydrochloric acid. In another example, chlorine gas can react directly with CaC0₃ to form CaC In an alternative economic regeneration, calcium carbonate is heated to form calcium oxide, releasing CO2. Calcium oxide is then reacted with hydrochloric acid to form calcium chloride, CO2 and water.

[0115] Figure 12 illustrates an example electrochemical system 1000 including a stack 1010 of electrochemical cells, and associated example components to electrochemically capture CO2 in the form of carbonate mineral, optionally including regeneration of mineral ions.

[0116] Preferably, the CO2 capture system 1000 comprises of a stack 1010 of a plurality of electrochemical cells, a power supply 1020 to supply a voltage differential to the cathodes/anodes of stack 1010, and containing tanks such as mineral tank 1030, chloride tank 1040, dilute hydrochloric acid tank (not shown). A carbon dioxide gas source 1060 supplies carbon dioxide gas to a gas valve and/or gas flow meter 1070, where the carbon dioxide gas (or a gas mixture containing carbon dioxide gas) is supplied to stack of a plurality of electrochemical cells 1010. Optionally, a hydrogen gas source and/or a carbon feedstock source 1080 supplies hydrogen gas and/or carbon feedstock to the stack 1010 of a plurality of electrochemical cells. Excess or unreacted carbon dioxide gas (or a gas mixture containing carbon dioxide gas) is reintroduced through gas line 1090 to be re input to stack 1010. Pumps 1100 are used to draw material from tanks 1030, 1040 to supply materials, if desired, to stack 1010. Separation unit 1110 (for example a filtration unit if the carbonate mineral is a solid precipitate) removes carbonate mineral from catholyte that can be held in carbonate mineral storage unit 1120. Optionally, regeneration unit 1050 uses hydrochloric acid and carbonate mineral from carbonate mineral storage unit 1120 for mineral ions regeneration supplied along pipe 1130 to mineral tank 1030. Any produced carbon dioxide can be stored in carbon dioxide tank 1140.

[0117] CO2 capture system 1000 thus provides two important aspects:

(1) A system and method for carbon capture and storage, that is CO2 stored as a carbonate mineral, such as calcium carbonate, sodium carbonate, potassium carbonate or lithium carbonate.

(2) A system and method for regenerative carbon capture, that is a carbonate mineral, such as calcium carbonate, sodium carbonate, potassium carbonate or lithium carbonate, can be regenerated to form mineral ions to again capture CO2. For example, by forming calcium ions via forming calcium chloride, and the released CO2 can be captured, and may be sold. The chemical reagent for mineral ion (e.g. calcium ion) regeneration (e.g. HC1) can be obtained from the anodic products, thereby making a closed system of regeneration possible. Alternatively, some CO2 emission plants generate HC1 which could be utilised for regeneration.

[0118] Thus, there is provided a method and system 1000 of regenerating carbonate mineral in an electrochemical mineral carbonation cell (such as calcium carbonate, sodium carbonate, potassium carbonate and/or lithium carbonate), preferably using a stack of a plurality of electrochemical cells 1010, to capture carbon dioxide. System 1000 includes carbon capture agent or sorbent source sub-system 1210, carbon capture sub system 1220, and regeneration sub-system 1230.

[0119] As previously described, carbon dioxide gas is introduced into an outer surface of the gas permeable cathode, and the carbon dioxide gas is allowed to pass at least partially through the gas permeable cathode to react with a liquid catholyte including mineral ions. The liquid catholyte is positioned between an inner surface of the gas permeable cathode and a membrane, the membrane positioned between the gas permeable cathode and an anode, and a liquid anolyte positioned between the anode and the membrane. A voltage difference is applied between the anode and the gas permeable cathode. The liquid catholyte flows along the inner surface of the gas permeable cathode. The liquid anolyte flows along an inner surface of the anode. Carbonate mineral is produced (for example upon reaction between electrochemically generated hydroxide and carbon dioxide). Carbonate mineral may be a precipitate formed on the inner surface of the gas permeable cathode. Additionally or alternatively, the carbonate mineral may be in an aqueous form. That is, the carbonate mineral is in solution in the catholyte, with the carbonate mineral soluble or partially soluble in the catholyte. The carbonate mineral is at least partially transported away from the inner surface of the gas permeable cathode by the flowing liquid catholyte.

[0120] The mineral ions are regenerated in the liquid catholyte by reacting at least some of the removed carbonate mineral with hydrochloric acid or chlorine gas to form mineral chloride in solution in water. The hydrochloric acid or the chlorine gas is produced at the anode. Preferably, the regeneration also includes storing released CO2 gas when forming the mineral chloride in solution in water. [0121] Thus, in an example embodiment there is provided an electrochemical system 1000 for capturing carbon dioxide, the electrochemical system 1000 comprising a stack 1010 of a plurality of electrochemical cells. At least one, or each, electrochemical mineral carbonation cell comprises a gas permeable cathode, an anode, a membrane positioned between the gas permeable cathode and the anode. A carbon dioxide gas source 1060 introduces carbon dioxide gas into an outer surface of and at least partially through the gas permeable cathode. A power supply 1020 applies a voltage difference between the gas permeable cathode and the anode. A liquid catholyte source 1030 supplies a liquid catholyte as a liquid catholyte flow between the gas permeable cathode and the membrane, the liquid catholyte including mineral ions. An anolyte source 1040 supplies a liquid anolyte between the anode and the membrane. In operation, the liquid catholyte flows along an inner surface of the gas permeable cathode, and carbonate mineral is produced (for example upon reaction between electrochemically generated hydroxide and carbon dioxide) at or near, or on, the inner surface of the gas permeable cathode and is at least partially transported away from the inner surface of the gas permeable cathode by the liquid catholyte flow. The carbonate mineral may be precipitated on the inner surface of the gas permeable cathode and is at least partially removed and transported away from the inner surface of the gas permeable cathode by the liquid catholyte flow.

[0122] A separation unit 1110 removes the carbonate mineral from the liquid catholyte flow. A liquid electrolyte pump 1100 forces the liquid catholyte flow between the gas permeable cathode and the membrane. In one example, the liquid electrolyte pump 1100 forces an alternating bi-directional flow of the liquid electrolyte. In one example, the liquid electrolyte pump 1100 provides a constant flow rate of the liquid electrolyte. In one example, the liquid electrolyte pump 1100 provides a variable flow rate of the liquid electrolyte.

[0123] In one example, at least one of the electrochemical cells is subjected to vibration and/or ultrasonication. In another example, the separation unit 1110 is a gravimetric separation unit. In another example, the separation unit 1110 includes a filter or is a filter unit. [0124] Figure 13 illustrates another example electrochemical system 1300. The electrochemical system comprises an electrochemical cell 1310 containing any features as described with reference to any of the previously described embodiments of electrochemical cells, but additionally or alternatively may comprise other features that will be described with reference to Figure 13.

[0125] In some examples, the electrochemical cell 1310 of Figure 13 can be configured to regenerate carbon dioxide after the electrochemical capture of carbon dioxide. This can be done through carbonation and/or acidification.

[0126] The regeneration of carbon dioxide through carbonation may be described as follows. The electrochemical cell 1310 receives a gas stream 1315 containing carbon dioxide. The carbon dioxide gas is captured by the electrochemical cell 1310 by reacting with the hydroxide ions contained in the catholyte 1320 (that is, the cation containing electrolyte) to generate carbonate mineral, thus resulting in the electrochemical capture of carbon dioxide. The carbonate mineral produced from the electrochemical capture reaction of carbon dioxide gas in the cathodic compartment may be stored in a reservoir 1325 to be set aside for the regeneration of carbon dioxide gas. Preferably, it is pure carbon dioxide gas that is regenerated.

Carbon dioxide gas may be additionally or alternatively regenerated through acidification as follows. Hydrogen gas from the cathodic compartment or externally supplied can be passed into the anolyte 1330 for a hydrogen oxidation reaction that results in the concentrating of protons. For example, in producing hydrochloric acid, chloride can be transferred from the cathodic compartment through an anion exchange membrane. In the carbon dioxide regeneration process, the acid reservoir is then reacted with the carbonate and bicarbonate mineral to form carbon dioxide, water and mineral ions. Cation-based mineral ions can be reused for carbon dioxide capture process. FURTHER EXAMPLES

[0127] The following further examples provide a more detailed discussion of particular embodiments. The further examples are intended to be merely illustrative and not limiting to the scope of the present invention.

[0128] The capability of the described electrochemical cells to operate efficiently over a broad range of CO2 levels in a gas mixture to generate carbonate mineral is reflected in the below examples.

Example 1:

[0129] Figure 14 shows a representative SEM image of a sample of solid calcium carbonate produced and collected from an example electrochemical cell having a gas permeable cathode. Figure 15 shows representative XRD and Raman spectroscopies confirming the formation of high purity calcium carbonate from the example electrochemical cell having a gas permeable cathode.

[0130] The sample of solid calcium carbonate was produced from an example electrochemical cell having a gas permeable cathode, constructed and operated as follows. The gas permeable cathode was constructed of a gas diffusion electrode, (Sigracet 39 BC™), deposited with 2 mg cm ² 10 wt % Pt on carbon black as a cathode catalyst containing Nafion dispersion as a binder. Sigracet 39 BC™ is a non-woven carbon paper gas diffusion media with a Microporous Layer (MPL) that has been PTFE treated to 5%. It has a total thickness of 325 pm (microns). The anode material is a nickel foam coated with a layer of nickel-iron layered double hydroxide catalyst prepared by hydrothermal method. The gas permeable cathode and NiFe-LDH anode were assembled in a two-electrode full cell system as depicted in Figure 1. The catholyte was 0.2 M CaCl₂.2H₂0 with 4 M NaCl as a supporting electrolyte, while the anolyte was 1 M KOH, supplied from two separate electrolyte reservoirs each with a volume of 15 ml. Both compartments were separated by an anion exchange membrane (Fumasep FAB-PK-130). Prior to applying voltage, both catholyte and anolyte were circulated at a flow rate of 17.5 ml min ¹ using a peristaltic pump (BT100-2J, Thermoline). The CO2 gas (> 99.99 % purity) was introduced into the outer layer of the gas diffusion electrode at the cathodic chamber at a flow rate of 40 mL min ¹. All the experiments were performed at room temperature at ambient atmosphere. In one instance, the applied fixed voltage of 2.0 V resulted in current densities of ~ 70 mA cm ². In another instance, the applied fixed voltage of 3.0 V resulted in current densities of ~ 40 mA cm ². Within 10 min, the white calcium carbonate precipitation appears within the flow catholyte from the electrochemical cell to the catholyte reservoir, and the catholyte gradually became cloudy over the time due to accumulation of calcium carbonate. It was found complete calcium carbonate mineralisation was achieved in about 30 mins, and this was verified by water hardness indicator paper not detecting calcium ions in the catholyte. Applying an alternate flow of catholyte enabled more efficient removal of calcium carbonate (reducing calcium carbonate deposition on the cathode). Increasing catholyte flow rate would have a similar impact and improve removal of calcium carbonate. The precipitated calcium carbonate was washed and centrifuged several times with deionised water, before being dried naturally in air.

[0131] It was found the rate of calcium carbonate precipitation was significantly dependant on the applied current or voltage. For example, a current density of 100 mA cm ² accelerates the calcium carbonate formation by completing carbonation in less than 20 min. Depending on the applied catalysts, electrolytes and the desirable current densities, the operation voltages of each individual cell was varied, for example, between about 1.5 V to about 6 V. Typically, the minimal current density of about 20 mA cm ² was required to initiate sufficient amount of hydroxide ions, that reacts to form calcium carbonate. The applied voltage and hence generated current densities also depends on the cell configuration with respect to geometry. For example, distance between gas permeable cathode and anode was about 1 cm for the above experiment. A shorter distance between cathode and anode will reduce the cell resistance, hence reducing the applied voltage.

[0132] The electrochemical formation of calcium carbonate was also examined across different volume percentages of CO2 gas (100 % to 1 %). This was achieved by introducing different volumes of CO2 and inert Ar gases by using gas flow controllers/meters. The sensitivity of the gas permeable cathode was demonstrated where the gas mixture containing as low as 1 % CO2 by volume capable of forming calcium carbonate. The introduction of ambient air and compressed air to the cathodic chamber also allowed the formation of calcium carbonate. This is noteworthy as when using air containing 21 % oxygen by volume, the enhancement of current densities was evident (compared to pure CO2 or a mixture of COi/Ar gas) due to the oxygen reduction reaction. This experimental result highlights the distinct advantage of a gas permeable cathode that offers an excellent interface between the CO2 gas, catalyst and mineral containing ions such as calcium ions to interact and facilitate formation of calcium carbonate.

[0133] Further experimental examination of example cathode related materials was as follows. Sputtered Pt was found less catalytically efficient in comparison to the nanostmctured 10 wt % Pt on carbon black. It was found the amount of loaded nanostmctured 10 wt % Pt on carbon black is important in enhancing the catalytic current densities. For example, approximately doubling of current density was obtained when 2 mg cm ² Pt was loaded on the Sigarect 39 BC™ gas permeable cathode, instead of a loading of lmg cm ² Pt. The higher current density resulting in faster mineral carbonation rate. Potential catalysts for the cathodic reaction are preferably, but not limited to, platinum, nickel, nickel phosphine, nickel chalcogenide, cobalt, cobalt phosphine, cobalt chalcogenide and metal alloys (such as PtNi).. Apart from the employed carbon paper- based gas diffusion electrode, hydrophobic polymeric membranes made of polytetrafluoroethylene and polyethylene can serve as a gas permeable membrane. The catalyst can be deposited directly on the membrane or between a layer of conductor applied on the membrane.

[0134] Further experimental examination of example anode related materials was as follow. Anode materials using a dimensional stable anode consist of mixed Ru-TiC coated on Ti mesh allowed chloride oxidation reaction (e.g. 0.6 M NaCl), and the cell was assembled using a Nafion cation exchange membrane. In this configuration, it was found the concentration of NaCl in both anodic (as media for chloride oxidation) and cathodic (as supporting electrolyte) compartments has a great impact on the carbonation rate. This is due to increasing NaCl concentration (e.g. increased from 0.6 M NaCl to 3M NaCl) reducing the overall cell resistance, as well as enhancing the kinetics for chloride oxidation. Potential catalysts for the anodic reaction include, depending on the employed electrolytes: an alkaline solution (e.g. KOH), preferably but not limited to NiFe, Ni, Co, and metal alloys; an acidic solution (e.g. HC1), preferably but not limited to Pt, IrC , RuC ; or a neutral solution (e.g. NaCl) for chlorine generation, preferably but not limited to a range of dimensional stable electrodes containing mixed metal oxides such as Ti02:Ru02, or T1O2: IrC , or Ti02:Ru02:Ir02.

[0135] All the experiments were performed at the laboratory temperature (21°C ± 2) and at the atmospheric pressure. As the solubility of CO2 in water decreases as the temperature increases, and kinetics of the catalytic reaction decreases if lower temperature is employed, therefore ambient temperature is a preferable operating condition. The gas permeable cathode offers an excellent interface to introduce CO2 gas and overcome solubility issue, hence a costly pressurisation system is not a requirement for efficient calcium carbonate formation. Therefore, ambient pressure is a preferable operating condition.

Example 2:

[0136] Soluble potassium and sodium carbonate were produced from an example electrochemical cell having a gas permeable cathode, constructed and operated as follows. The gas permeable cathode comprised a gas diffusion electrode, (Sigracet 39 BC™), deposited with 2 mg cm ² 10 wt % Pt on carbon black as a cathode catalyst containing Nafion dispersion as a binder. The anode material is a nickel foam coated with a layer of nickel-iron layered double hydroxide catalyst prepared using a hydrothermal method. The gas permeable cathode and NiFe-LDH anode were assembled in a two- electrode full cell system as depicted in Figure 1. The catholyte was 4 M NaCl or KC1, while the anolyte was 1 M KOH, supplied from two separate electrolyte reservoirs each with a volume of 15 ml. Both compartments were separated by an anion exchange membrane (Fumasep FAB-PK-130) or a nafion membrane (Nafion™ 117). Prior to applying voltage, both catholyte and anolyte were circulated at a flow rate of 17.5 ml min ¹ using a peristaltic pump (BT100-2J, Thermo line). The CO2 gas (> 99.99 % purity) or mixed CO2 with N2 gas or compressed air was introduced into the outer layer of the gas diffusion electrode at the cathodic chamber at a flow rate of 40 mL min ¹. All experiments were performed at room temperature at ambient atmosphere. The applied voltage between 1.5 V to 2.5 V resulting in current densities of 50 to 150 mA cm ². The carbonate formation was verified by titration with HC1 resulting in released of CO2. [0137] In another configuration, the Pt/C coated gas permeable electrode that served as a cathode as described above, was also used as an anode. The assembly of the two- electrode full cell was as shown in Figure 3. The flowed catholyte was 4 M NaCl, and the flowed anolyte was 1M NaCl or diluted HC1 (e.g. 0.1 M). The anolyte and catholyte was separated by an anion exchange membrane (Fumasep FAB -PK- 130) that promotes transfer of chloride ions and inhibits proton cross-over. Under an applied voltage, the hydrogen generated at the cathode or from an external source would be passed through the gas permeable anode to allow hydrogen oxidation process occurs at the cathode. This subsequently concentrating the acid. At the cathodic compartment, a stream of CO2 containing gas (high purity CO2, mixed CO2 with N2 gas or compressed air) passed through the gas permeable cathode produced sodium carbonate. When sodium carbonate or sodium bicarbonate reacted with hydrochloric acid generated at anode, regeneration of carbon dioxide is achieved.

Example 3:

[0138] The lithium carbonate (soluble at room temperature) was produced from an example electrochemical cell having a gas permeable cathode, constructed and operated as follows. The gas permeable cathode was constructed of a gas diffusion electrode, (Sigracet 39 BC™), deposited with 2 mg cm ² of 10 wt % Pt on carbon black as a cathode catalyst containing Nafion dispersion as a binder. The anode material was a dimensionally stable (DSA) anode consists of IrC -TiC coated on titanium electrode. The gas permeable cathode, and DSA anode were assembled in a two-electrode full cell system as depicted in Figure 1. The flow through catholyte reservoir was comprised of 0.5 M L1CI2 and 0.5 M NaCl, and the flow through anolyte reservoir was 4 M NaCl. At the cathodic compartment, a stream of CO2 containing gas such as high purity CO2 passed through the gas permeable cathode. Under the applied fixed current (e.g. 100 mA cm ²) for 30 min, lithium carbonate was produced. Taking advantage of lower solubility at higher temperature, lithium carbonate was readily separated and crystallined from sodium chloride at around 80°C to 90°C. Figure 16 shows example of Raman Spectra of the produced lithium carbonate in compared to that obtained from commercially available lithium carbonate sample. Example 4:

[0139] A closed-loop CO2 capture system can be implemented using the as described electrochemical cell CO2 capture system for utilisation in CO2 gas emitted industrial processes, such as coal based power generation, cement production, steel production, and hydrogen production plants to capture emitted CO2 with a concentration range between about 10 % to about 30 % CO2 by volume. The captured CO2 can be stored via the calcium regeneration strategy, and the calcium capture agent or sorbent can be reused for subsequent electrochemical CO2 mineral carbonation.

Example 5:

[0140] The as described electrochemical cell CO2 capture system is capable of handling a very low level of CO2, including utilising ambient air as an input gas feedstock. Hence, the described CO2 capture system and method can act as a standalone, or component part, of direct air carbon capture technology.

Example 6:

[0141] The as described electrochemical cell CO2 capture system can be utilised to produce precipitated calcium carbonate for a wide range of applications, including for example as building and construction material, as a filler in paper, in plastics, in paints and coatings, and in personal heath and food production. For example, the as described electrochemical cell CO2 capture system and methods can be coupled to an existing cement production plant to directly capture CO2 for conversion to building materials. As part of the circular economy, calcium ions are extracted from the building and construction waste to recycle into calcium carbonate. High purity CO2 and calcium ions are applicable in this method to generate high purity calcium carbonate for use in applications that require high purity calcium carbonate.

Example 7:

[0142] Hard water is a common water problem found in the domestic and industry, particularly for countries/states with water supply of water hardness classified as hard water (e.g. dissolved hardness minerals of 7 to 10.5 grains per gallon) and very hard water (e.g. dissolved hardness minerals above 10.5 grains per gallon). The most common hardness causing minerals are calcium and magnesium which are dissolved in a water supply. The as described electrochemical cell CO2 capture system can be utilised to treat the water hardness by removing the dissolved minerals such as calcium and magnesium ions. A CO2 source can be obtained from, for example, ambient air or a gas cylinder. This method offers a new strategy to the common approach of chemical treatment such as the use of water softeners, and a small quantity of sodium chloride may need to be added to improve the water electrical conductivity.

Example 8:

[0143] Oceans are the largest reservoir of carbon on earth. A large portion of anthropogenic CO2 dissolves in the seawater and is converted in equilibrium between hydrogen carbonate and carbonate ions. The inventors have found that an in-situ CO2 storage process depends on the applied current density from CO2 electrolysis, in which higher current promotes the generation of hydroxide ions and hence calcification. In this example, the electrochemical flow cell as previously described in figure 1 is utilised, with an exception that a three-electrode configuration was employed. In this configuration, the cathode is a working electrode, the anode is a counter electrode, and with an addition of a Ag/AgCl reference electrode located at the cathodic compartment. The reported potential is converted to the Reversible Hydrogen Electrode (RHE). The inventors examined seawater as the electrolyte and observed calcium carbonate in the calcite phase is readily formed using a gas diffusion electrode (GDE) as the gas permeable cathode with a Ag based cathodic catalyst.

[0144] Deposition of calcite on the cathode surface is mitigated by using the gas-phase CO2 electrochemical flow cell as previously described. This configuration not only overcomes the low solubility of CO2 in aqueous electrolytes, but also allows the collection of precipitated insoluble calcite in parallel with electroreduction of some portion of the input CO2.

[0145] Seawater electrolyte was circulated through the electrochemical flow cell and was in direct contact with a Ag catalyst provided as a surface layer on the gas permeable cathode (i.e. using a GDE), and CO2 was passed through the outside surface (back-side) of the GDE. Calcification occurred as a result of interaction between calcium ions present in the seawater electrolyte, the dissolved CO2 (in the form of HCO3 ) and hydroxide ions due to the increase in localised pH on the catalyst surface. The use of higher electrocatalytic current density promoted the calcification process since the pH change was accelerated. The continuous flows in the electrochemical flow cell allowed the collection of calcite in an external electrolyte reservoir, rather than accumulation on the catalyst surface at the cathode, thereby importantly ensuring the electrocatalyst remains active.

[0146] Example experiments employed the nano particulate Ag as a model catalyst. Ag was deposited as a catalyst on the gas permeable layer (acting as the cathode) Sigracet 39 BC™ (Ag-GDL) by air brushing about 100 nm Ag dispersion containing Nafion^® (a membrane supplied by the Chemours company, which is a sulfonated tetrafluoroethylene based fluoropolymer-copolymer membrane, or also a proton-conductive polymer film), and was employed as a working cathode.

[0147] It was found that increasing applied potentials from -0.8 V to -1.4 V vs. RHE for 1 hour electrolysis resulted in increased accumulation of calcite collected from the seawater reservoir. This can be explained by the higher current densities resulting from the larger applied potentials, which promotes the formation of hydroxide and hence the calcification process. At low applied potential with relatively low current densities (about _2

10 mAcm ) no resulting precipitation was observed. Purging Ar, instead of CO2, no calcite was formed, confirming the supplied CO2 as a source of the calcification reaction.

[0148] In these examples it has been demonstrated that an electrochemical flow cell configuration using a gas permeable cathode and that enables circulation, i.e. flow, of the electrolyte allows calcite formed to be collected, instead of being deposited on the cathode surface.

[0149] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. [0150] Optional embodiments may also be said to broadly consist in the parts, elements and features referred to or indicated herein, individually or collectively, in any or all combinations of two or more of the parts, elements or features, and wherein specific integers are mentioned herein which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

[0151] Although a preferred embodiment has been described in detail, it should be understood that many modifications, changes, substitutions or alterations will be apparent to those skilled in the art without departing from the scope of the present invention.

Claims

The claims defining the invention are as follows:

1. An electrochemical mineral carbonation cell for capturing carbon dioxide, the electrochemical cell comprising: a gas permeable cathode, wherein carbon dioxide gas is able to pass into an outer surface of and at least partially through the gas permeable cathode to react with a liquid catholyte; an anode, wherein a voltage difference is able to be applied between the gas permeable cathode and the anode; a membrane positioned between the gas permeable cathode and the anode; the liquid catholyte positioned between the gas permeable cathode and the membrane, the liquid catholyte including mineral ions; and a liquid anolyte positioned between the anode and the membrane; wherein, in operation, the liquid catholyte flows along an inner surface of the gas permeable cathode, and wherein a carbonate mineral is produced at or near the inner surface of the gas permeable cathode, and the carbonate mineral is at least partially transported away from the inner surface of the gas permeable cathode by the liquid catholyte flow.

2. The electrochemical cell of claim 1, wherein the carbonate mineral is soluble or substantially soluble in the liquid catholyte.

3. The electrochemical cell of claim 1 or 2, wherein the mineral ions are or comprise sodium ions, potassium ions, and/or lithium ions.

4. The electrochemical cell of any one of claims 1 to 3, wherein the carbonate mineral is or comprises sodium carbonate, potassium carbonate, and/or lithium carbonate.

5. The electrochemical cell of claim 1, wherein the carbonate mineral is produced by being precipitated on the inner surface of the gas permeable cathode, and the carbonate mineral is at least partially removed and transported away from the inner surface of the gas permeable cathode by the liquid catholyte flow.

6. The electrochemical cell of claim 5, wherein the mineral ions are or comprise calcium ions.

7. The electrochemical cell of claim 5 or 6, wherein the carbonate mineral is or comprises calcium carbonate.

8. The electrochemical cell of any one of claims 1 to 4, wherein during operation the carbon dioxide gas continuously passes at least partially through the gas permeable cathode, and the carbonate mineral is continuously produced in solution at the inner surface of the gas permeable cathode and is continuously transported away from the inner surface of the gas permeable cathode by continuous liquid catholyte flow.

9. The electrochemical cell of any one of claims 1 or 5 to 7, wherein during operation the carbon dioxide gas continuously passes at least partially through the gas permeable cathode, and the carbonate mineral is continuously precipitated on the inner surface of the gas permeable cathode and is continuously removed and transported away from the inner surface of the gas permeable cathode by continuous liquid catholyte flow.

10. The electrochemical cell of claim 8 or 9, wherein the gas permeable cathode is associated with a gas chamber able to transport gas generated from a reaction between carbon dioxide gas and the liquid catholyte.

11. The electrochemical cell of any one of claims 1 to 10, wherein the gas permeable cathode is a gas diffusion electrode provided with an integrated catalyst or a cathodic catalyst layer, preferably wherein the gas permeable cathode comprises: a conductive cathodic catalyst layer, or a non-conductive polymeric gas permeable membrane and a conductive cathodic catalyst layer, or a non-conductive polymeric gas permeable membrane, a conductive layer provided on or adjacent the non-conductive polymeric gas permeable membrane, and a cathodic catalyst layer provided on or adjacent the conductive layer.

12. The electrochemical cell of claim 11, wherein the cathodic catalyst layer is positioned at the inner surface of the gas permeable cathode.

13. The electrochemical cell of any one of claims 1 to 12, wherein the anode includes an anodic catalyst layer.

14. The electrochemical cell of any one of claims 1 to 13, wherein a flow rate of the liquid catholyte flow is variable, preferably when the carbonate mineral is insoluble.

15. The electrochemical cell of any one of claims 1 to 14, wherein the liquid catholyte flow alternates between flowing in a first direction and flowing in a second direction past the inner surface of the gas permeable cathode.

16. The electrochemical cell of any one of claims 1 to 15, wherein, in operation, the liquid anolyte flows along an inner surface of the anode as a liquid anolyte flow, preferably wherein, in operation: the liquid anolyte flow rate is variable, the liquid anolyte flow is in the same direction as the liquid catholyte flow, or the liquid anolyte flow is in an opposite direction to the liquid catholyte flow.

17. The electrochemical cell of any one of claims 1 to 16, wherein the carbon dioxide gas is selected from the group of: pure carbon dioxide gas, substantially pure carbon dioxide gas, a gas mixture including carbon dioxide gas, ambient air, compressed air, industry waste gas including carbon dioxide, and a prepared gas mixture including carbon dioxide gas.

18. The electrochemical cell of any one of claims 1 to 17, wherein the liquid catholyte has an acidic to alkaline pH.

19. The electrochemical cell of any one of claims 1 to 18, wherein: the liquid anolyte is or includes one of: an alkaline electrolyte, an acidic electrolyte, or sodium chloride and has neutral pH, and the membrane is an anion exchange membrane, a cation exchange membrane, or a bipolar membrane.

20. An electrochemical system for capturing carbon dioxide, the electrochemical system comprising: at least one electrochemical cell according to any one of claims 1 to 19; a carbon dioxide gas source to supply the carbon dioxide gas; a power supply to apply the voltage difference between the gas permeable cathode and the anode; a liquid catholyte source to supply the liquid catholyte; a liquid anolyte source to supply the liquid anolyte; and a separation unit to remove the carbonate mineral from the liquid catholyte flow.

21. An electrochemical system for capturing carbon dioxide, the electrochemical system comprising: a stack of a plurality of electrochemical cells, at least one, or each, electrochemical mineral carbonation cell comprising: a gas permeable cathode; an anode; a membrane positioned between the gas permeable cathode and the anode; a carbon dioxide gas source to introduce carbon dioxide gas into an outer surface of and at least partially through the gas permeable cathode; a power supply to apply a voltage difference between the gas permeable cathode and the anode; a liquid catholyte source to supply a liquid catholyte as a liquid catholyte flow between the gas permeable cathode and the membrane, the liquid catholyte including mineral ions; and a liquid anolyte source to supply a liquid anolyte between the anode and the membrane; wherein, in operation, the liquid catholyte flows along an inner surface of the gas permeable cathode, and wherein carbonate mineral is produced at or near the inner surface of the gas permeable cathode and is at least partially transported away from the inner surface of the gas permeable cathode by the liquid catholyte flow.

22. The electrochemical system of claim -21, further comprising a separation unit to remove the carbonate mineral from the liquid catholyte flow.

23. The electrochemical system of claim 21 or 22, further comprising a liquid electrolyte pump to force the liquid catholyte flow between the gas permeable cathode and the membrane, preferably wherein: the liquid electrolyte pump forces an alternating bi-directional flow of the liquid catholyte, and/or the liquid electrolyte pump provides a constant or a variable flow rate of the liquid catholyte.

24. A method of operating an electrochemical mineral carbonation cell to capture carbon dioxide and produce carbonate mineral, the method comprising the steps of: introducing carbon dioxide gas into an outer surface of a gas permeable cathode, and allowing the carbon dioxide gas to pass at least partially through the gas permeable cathode to react with a liquid catholyte including mineral ions, the liquid catholyte positioned between an inner surface of the gas permeable cathode and a membrane, the membrane positioned between the gas permeable cathode and an anode, and a liquid anolyte positioned between the anode and the membrane; applying a voltage difference between the anode and the gas permeable cathode; flowing the liquid catholyte along the inner surface of the gas permeable cathode; producing carbonate mineral at or on the inner surface of the gas permeable cathode; and at least partially transporting away the carbonate mineral from the inner surface of the gas permeable cathode by the flowing liquid catholyte.

25. The method of operating the electrochemical cell of claim 26, further comprising continuously introducing carbon dioxide gas into the outer surface of the gas permeable cathode, and continuously transporting away the carbonate mineral from the inner surface of the gas permeable cathode by the continuously flowing liquid catholyte.

26. The method of operating the electrochemical cell of any one of claims 24 or 25, wherein a reductive catalytic process generates localized alkalinity at the surface of the gas permeable cathode.

27. The method of operating the electrochemical cell of any one of claims 24 to 26, wherein the carbonate mineral is removed from the flowing liquid catholyte and is collected.

28. The method of operating the electrochemical cell of any one of claims 24 to 27, wherein a rate of carbonate mineral formation is changed by altering the applied voltage difference and/or by altering a current density through the gas permeable cathode.

29. The method of operating the electrochemical cell of any one of claims 24 to 28, wherein the method operates at ambient air temperature and/or ambient air pressure.

30. The method of operating the electrochemical cell of any one of claims 24 to 29, wherein hydroxide ions are formed by an electro -catalytic reaction, the hydroxide ions reacting with the mineral ions in the liquid catholyte and reacting with bicarbonate formed from the carbon dioxide gas.

31. The method of operating the electrochemical cell of any one of claims 24 to 30, further comprising regenerating the mineral ions in the liquid catholyte.

32. The method of operating the electrochemical cell of any one of claims 24 to 31, wherein the mineral ions are calcium, sodium, potassium and/or lithium ions, and further comprising regenerating the mineral ions in the liquid catholyte by: reacting carbonate mineral that has been collected with hydrochloric acid to form mineral chloride in solution in water, and storing the released carbon dioxide;

33. The method of operating of the electrochemical cell of claim 32, further comprising: producing hydrochloric acid at the anodic compartment, preferably by using hydrogen gas generated at the gas permeable cathode or externally supplied, for a hydrogen oxidation reaction to generate protons.

34. A method of regenerating carbonate mineral in an electrochemical mineral carbonation cell to capture carbon dioxide, the method comprising the steps of: introducing carbon dioxide gas into an outer surface of a gas permeable cathode, and allowing the carbon dioxide gas to pass at least partially through the gas permeable cathode to react with a liquid catholyte including mineral ions, the liquid catholyte positioned between an inner surface of the gas permeable cathode and a membrane, the membrane positioned between the gas permeable cathode and an anode, and a liquid anolyte positioned between the anode and the membrane; applying a voltage difference between the anode and the gas permeable cathode; flowing the liquid catholyte along the inner surface of the gas permeable cathode; flowing the liquid anolyte along an inner surface of the anode; producing carbonate mineral at or on the inner surface of the gas permeable cathode; at least partially transporting away the carbonate mineral from the inner surface of the gas permeable cathode by the flowing liquid catholyte; and, regenerating the mineral ions in the liquid catholyte by reacting at least some of the removed carbonate mineral with hydrochloric acid or chlorine gas to form mineral chloride in solution in water.

35. The method of claim 34, wherein the mineral ions are or comprise: calcium ions, sodium ions, potassium ions, and/or lithium ions.

36. The method of claim 34 or 35, wherein the hydrochloric acid is produced at the anode.

37. The method of any one of claims 34 to 36, wherein, the regenerating step includes storing released carbon dioxide gas when forming the mineral chloride in solution in water.