Co2 electrolysis system

Abstract

A method of reducing CO2 captured within a CO2-amine complex in an electrolyser to form a carbon compound is provided. Also provided is a system for the electrolysis of CO2 contained in a CO2-amine complex. The method and system provide an alternative pathway to existing technologies to provide an energy and / or carbon efficient scheme for carbon based chemical production while also being capable of being integrated in existing CO2 capture systems.

Description

"CO2 electrolysis system"Technical Field

[0001] The present disclosure relates to a method of reducing CO2 to form a carbon compound, particularly a method of reducing CO2 in an electrolyser, more particularly reducing CO2 captured within a CCh-amine complex in an electrolyser. The present disclosure also relates to a novel system for CO2 electrolysis, particularly a system for electrolysis of CO2 contained in a CCh-amine complex.Background

[0002] The consumption of fossil fuels in the past decades has caused increasing levels of atmospheric carbon dioxide (CO2), contributing to an increase in the greenhouse effect and a number of environmental problems.

[0003] Carbon capture, utilisation and storage is considered an effective strategy to reduce global CO2 emissions and convert CChinto value-added chemicals.Industrialised CO2 capture and utilisation processes usually employ aqueous alkanolamine solutions as a CO2 capture agent owing to their high CO2 capture capacity, good technology compatibility, and economic considerations. However, a series of steps (separation, purification, and compression) are required to process the CO2- saturated solution to obtain high-purity CO2 gas, making the process energy -intensive and reducing the positive impact of the carbon capture process.

[0004] The electrochemical reduction of CO2, interchangeably referred to as CO2 electrolysis, offers a significant opportunity to convert waste CO2 gases into industrial feedstocks. State-of-the-art CO2 electrolysis requires the use of high-purity CChgas and faces serious technological challenges. First, the production and transportation of high- purity CO2 gas involves a range of complicated and energy-consuming steps including CO2 thermal-separation, purification, and compression, thereby making the use of high- purity CChgas impractical and relatively expensive. Second, the CO2 utilizationefficiency of conventional gas CO2 electrolysis is relatively low meaning that the unreacted CO2 gas mixes with reaction products and complicates product separation.

[0005] Therefore, it would be advantageous to develop alternative CO2 electrolysis technology and methods that can address the aforementioned problems and provide a viable alternative to the utilisation of waste CO2 gases.Summary

[0006] In one broad aspect, the present disclosure provides a system and method for converting amine-captured CO2 streams into industrial feedstocks. In another broad aspect, the present disclosure provides a system for converting amine-captured CO2 streams into industrial feedstocks. In another broad aspect, the present disclosure provides a method for converting amine-captured CO2 streams into industrial feedstocks. Advatageously, the methods and systems described herein provide an alternative pathway to existing technologies to provide an energy and / or carbon efficient scheme for carbon based chemical production. A further advantage of various aspects and embodiments described herein is that they may be integrated in existing CO2 capture systems thereby allowing for increased energy and carbon efficiency for less capital expenditure.

[0007] In a first aspect, the present disclosure provides a method of reducing carbon dioxide (CO2) to a carbon compound in an electrolyzer comprising: providing a first electrolyte comprising a CCh-amine complex to a cathodic compartment comprising a cathode and a cathode current collector, said cathode comprising a cathode transition metal catalyst; providing a second electrolyte to an anodic compartment comprising an anode; applying a current across the anode and the cathode to reduce at least a portion of the CO2 contained within the CCh-amine complex to form the carbon compound; and recovering the carbon compound and a CCh-depleted amine solution.

[0008] In embodiments, the amine is selected to form a zwitterionic carbamate following exposure to a carbon dioxide source, preferably wherein the amine is piperazine. In embodiments, the amine is piperazine.

[0009] In embodiments, the cathode transition metal catalyst is a single-atom transition metal catalyst.

[0010] In embodiments, the cathode transition metal catalyst is a nickel single-atom catalyst.

[0011] In embodiments, a mass loading of the transition metal catalyst on the cathode (mg / cm2) is between about 1 to about 10, or between about 2 to about 6.

[0012] In embodiments, the carbon compound comprises carbon monoxide.

[0013] In embodiments, the first electrolyte is continuously fed to the cathodic compartment.

[0014] In embodiments, the amine-CCh complex is obtained from contacting an amine capture solution with a source of carbon dioxide. Preferably the source of carbon dioxide is a flue gas.

[0015] In embodiments, at least a portion of the CO2 depleted amine solution is recycled. Preferably at least a portion of the CO2 depleted amine solution is recycled as at least a portion of the amine capture solution.

[0016] In embodiments, the reduction of CO2 is performed at a temperature (°C) of between about 20 to about 80, or between about 20 to about 50.

[0017] In embodiments, the method further comprising separating at least a portion of the carbon compound from the carbon compound and the CCh-depleted amine solution to produce a carbon compound-enriched gas stream.

[0018] In embodiments, the applying a current across the anode and the cathode reduces water at the cathode to form hydrogen (H2).

[0019] In embodiments, the method further comprising reacting at least a portion of the carbon compound and hydrogen to form a hydrocarbon.

[0020] In embodiments, the current applied (mA / cm2) is between about 10 to about 500, or between about 50 to about 200.

[0021] In a second aspect, the present disclosure provides a method of reducing carbon dioxide (CO2) to carbon monoxide (CO) in an electrolyzer comprising: providing a first electrolyte comprising a CO2-diamine complex to a cathodic compartment comprising a cathode and a cathode current collector, said cathode comprising a cathode transition metal catalyst; providing a second electrolyte comprising potassium hydroxide to an anodic compartment comprising an anode and a current collector, said anode comprising a transition metal foam anode catalyst; applying a current across the anode and the cathode to reduce at least a portion of the CO2 contained within the CCh-amine complex to form CO; and recovering the CO and a CO2-depleted amine solution.

[0022] In embodiments, the CO2-diamine complex is a CO2-piperazine complex.

[0023] In embodiments, the CO2-piperazine complex is formed by exposure of a CO2- containing flue gas to a piperazine aqueous solution.

[0024] In embodiments, the cathode transition metal catalyst is a nickel single-atom catalyst.

[0025] In a third aspect, the present disclosure provides a system for carbon dioxide reduction comprising: an electroylzer comprising:a cathodic compartment comprising a cathode and a cathode current collector, said cathode comprising a transition metal catalyst, and configured to receive a first electrolyte comprising a CCh-amine complex; an anodic compartment comprising an anode, and configured to receive a second electrolyte; a power supply connected to apply a potential difference between the anode and the cathode; and a means for recovering a carbon dioxide reduction product configured to be in communication with the cathodic compartment.

[0026] In embodiments, the system further comprising an ion permeable membrane separating the anodic compartment and the cathodic compartment.

[0027] In embodiments, the ion permeable membrane is an anion exchange membrane, preferably a zero-gap anion exchange membrane.

[0028] In embodiments, the cathodic compartment comprises a liquid outlet configured to recover a CCh-depleted amine solution.

[0029] In embodiments, the amine is selected to form a zwitterionic carbamate upon contact with a carbon dioxide source. In embodiments, the amine the amine is piperazine.

[0030] In embodiments, the cathode transition metal catalyst is a single-atom catalyst, preferably a nickel single-atom catalyst.

[0031] In a fourth aspect, the present disclosure provides a method of screening an amine for use in an electrochemical CO2 reduction comprising: determining a CO2 capture activity of the amine; and determining an electrolysis activity of the formed CCh-amine complex, wherein the CO2 capture activity is calculated by multiplying an amine mass normalized CO2 capture capacity of the amine and a CO2 absorption rate of the amine,wherein electrolysis activity is based on the Gibbs free energy of a carbamate formed by the CCh-amine complex.

[0032] In embodiments, the screened amine is used for the CO2 reduction performed using the method or system described herein.Brief Description of Drawings

[0033] Preferred embodiments of the present disclosure will be further described and illustrated, by way of example only, with reference to the accompanying drawings in which:

[0034] Figure l is a block flow diagram of an embodiment of the system and method described herein;

[0035] Figure 2 shows the CO2 mass loading various amines based on a 1.5 M concentration in aqueous solution;

[0036] Figure 3 shows literature reported values for the CO2 adsorption rate for a variety of amines;

[0037] Figure 4 shows the carbamate formation energy calculated via DFT for a variety of amines;

[0038] Figure 5 (a) shows the relationship between the CO2 capture activity, defined by the multiplying of CO2 absorption rate and amine mass normalized CO2 capture capacity, and the electrolysis activity, defined by the Gibbs free energy of amine carbamate (dashed volcano plot shown for guidance only), and (b) structures of a variety of amines including primary, secondary, tertiary, and di / multi amines;

[0039] Figure 6 shows the calculated theoretical overpotentials of the hydrogen evolution reaction and CO2RR for a range of metal SACs with geometrical coordination inserted;

[0040] Figure 7 shows in-situ ATR-FTIR spectra of Ni SACs during the reduction reaction in the 1.5 M PZ-captured CO2 solution under electrocatalytic applied potential from 0 to -2.5 V vs. RHE. The magnified spectra from 1200 to 800 cm-1, 1600 to 1200 cm-1, 2000 to 1600 cm-1, and 3000 to 2000 cm-1, where the 100% CO2 loading implies that the CO2 loading capacity is 1.05 mol CCF / mol PZ;

[0041] Figure 8 shows the H-cell configuration from the (a) front and (b) top;

[0042] Figure 9 shows the FEco of Ni SACs in the electrolysis of 1.5 M amine- captured CO2 solutions;

[0043] Figure 10 shows the zero-gap CO2 electrolyzer components, cathode catalyst layer, anion-exchange membrane (Fumasep FAA-3-50), anode catalyst layer (Ni foam), and the end plates, respectively. The working electrode area is 5 cm2;

[0044] Figure 11 shows chronoamperometry test of the 1.5 M PZ-CO2 solution without CO2 purging at the voltage of 2.0 V; and the CO2 loading capacities before and after the electrolysis reaction; and

[0045] Figure 12 shows the carbon efficiency and energy efficiency of the CO2-PZ reduction scheme along with cycling numbers.Description of EmbodimentsGeneral terms

[0046] With regards to the definitions provided herein, unless stated otherwise, or implicit from context, the defined terms and phrases include the provided meanings. Unless explicitly stated otherwise, or apparent from context, the terms and phrases below do not exclude the meaning that the term or phrase has acquired by a person skilled in the relevant art. The definitions are provided to aid in describing particular embodiments, and are not intended to limit the claimed invention, because the scope of the invention is limited only by the claims. Furthermore, unless otherwise required bycontext, singular terms shall include pluralities and plural terms shall include the singular.

[0047] All publications discussed and / or referenced herein are incorporated herein in their entirety.

[0048] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present disclosure. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.

[0049] Throughout this disclosure, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition of matter, group of steps or group of compositions of matter shall be taken to encompass one and a plurality (i.e., one or more) of those steps, compositions of matter, groups of steps or groups of compositions of matter. Thus, as used herein, the singular forms “a”, “an” and “the” include plural aspects unless the context clearly dictates otherwise. For example, reference to “a” includes a single as well as two or more; reference to “an” includes a single as well as two or more; reference to “the” includes a single as well as two or more and so forth.

[0050] Those skilled in the art will appreciate that the disclosure herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the disclosure includes all such variations and modifications. The disclosure also includes all of the examples, steps, features, methods, compositions, processes, referred to or indicated in this specification, individually or collectively, and any and all combinations or any two or more of said steps or features.

[0051] The term “and / or”, e.g., “X and / or Y” shall be understood to mean either “X and Y” or “X or Y” and shall be taken to provide explicit support for both meanings or for either meaning.

[0052] As used herein, the phrase “at least one of’, when used with a list of items, means different combinations of one or more of the listed items may be used and only one of the items in the list may be needed. The item may be a particular object, thing, or category. In other words, “at least one of’ means any combination of items or number of items may be used from the list, but not all of the items in the list may be required. In some cases, “at least one of item A, item B, and item C” may mean, for example and without limitation, two of item A, one of item B, and ten of item C; four of item B and seven of item C; or some other suitable combination.

[0053] As used herein, the term “about”, unless stated to the contrary, typically refers to + / - 10%, for example + / - 5%, of the designated value.

[0054] Throughout the present specification, various aspects and components of the invention can be presented in a range format. The range format is included for convenience and should not be interpreted as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range, unless specifically indicated. For example, description of a range such as from 1 to 5 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 5, from 3 to 5 etc., as well as individual and partial numbers within the recited range, for example, 1, 1.5, 2, 2.2, 3, 4, 4.6, and 5, unless where integers are required or implicit from context. This applies regardless of the breadth of the disclosed range. Where specific values are required, these will be indicated in the specification.

[0055] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a statedelement, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0056] In the following description, reference is made to the accompanying drawings which form a part hereof, and which is shown, by way of illustration, several embodiments. It is understood that other embodiments may be utilised and structural changes or adaptions to one or more methods or processes, may be made without departing from the scope of the present disclosure.Method and system

[0057] In an aspect of the present disclosure, there is provided a method of reducing carbon dioxide (CO2) to a carbon compound in an electrolyzer comprising: providing a first electrolyte comprising a CCh-amine complex to a cathodic compartment comprising a cathode and a cathode current collector, said cathode comprising a cathode transition metal catalyst; providing a second electrolyte to an anodic compartment comprising an anode; applying a current across the anode and the cathode to reduce at least a portion of the CO2 contained within the CCh-amine complex to form the carbon compound; and recovering the carbon compound and a CCh-depleted amine solution.

[0058] In another aspect of the present disclosure, there is provided a system for carbon dioxide reduction comprising: an electroylzer comprising: a cathodic compartment comprising a cathode and a current collector, said cathode comprising a cathode transition metal catalyst, and configured to receive a first electrolyte comprising a CCh-amine complex; an anodic compartment comprising an anode, and configured to receive a second electrolyte; a power supply connected to apply a potential difference between the anode and the cathode; anda means for recovering a carbon dioxide reduction product configured to be in communication with the cathodic compartment.

[0059] In another aspect of the present disclosure, there is provided a method of reducing carbon dioxide (CO2) to a carbon compound in an electrolyzer comprising: providing a first electrolyte comprising a CCh-amine complex to a cathodic compartment comprising a cathode and a cathode current collector, said cathode comprising a cathode transition metal catalyst; providing a second electrolyte to an anodic compartment comprising an anode; applying a current across the anode and the cathode to reduce at least a portion of the CO2 contained within the CCh-amine complex to form the carbon compound; and recovering the carbon compound and a CCh-depleted amine solution, wherein the cathode transition metal catalyst is, or comprises, Ni.

[0060] In another aspect of the present disclosure, there is provided a method of reducing carbon dioxide (CO2) to a carbon compound in an electrolyzer comprising: providing a first electrolyte comprising a CCh-amine complex to a cathodic compartment comprising a cathode and a cathode current collector, said cathode comprising a cathode transition metal catalyst; providing a second electrolyte to an anodic compartment comprising an anode; applying a current across the anode and the cathode to reduce at least a portion of the CO2 contained within the CCh-amine complex to form the carbon compound; and recovering the carbon compound and a CCh-depleted amine solution, wherein the cathode transition metal catalyst is a nickel single atom catalyst.

[0061] In another aspect of the present disclosure, there is provided a system for carbon dioxide reduction comprising: an electroylzer comprising:a cathodic compartment comprising a cathode and a current collector, said cathode comprising a cathode transition metal catalyst, and configured to receive a first electrolyte comprising a CCh-amine complex; an anodic compartment comprising an anode and configured to receive a second electrolyte; a power supply connected to apply a potential difference between the anode and the cathode; and a means for recovering a carbon dioxide reduction product configured to be in communication with the cathodic compartment, wherein the cathode transition metal catalyst is, or comprises, Ni.

[0062] In another aspect of the present disclosure, there is provided a system for carbon dioxide reduction comprising: an electroylzer comprising: a cathodic compartment comprising a cathode and a current collector, said cathode comprising a cathode transition metal catalyst, and configured to receive a first electrolyte comprising a CCh-amine complex; an anodic compartment comprising an anode and configured to receive a second electrolyte; a power supply connected to apply a potential difference between the anode and the cathode; and a means for recovering a carbon dioxide reduction product configured to be in communication with the cathodic compartment, wherein the cathode transition metal catalyst is a nickel single atom catalyst.

[0063] With reference to Figure 1, according to embodiments of the present disclosure there is provided a method and a system for the reduction of CO2. With reference to Figure 1, according to embodiments of the present disclosure there is provided a system for the reduction of CO2. With reference to Figure 1, according to embodiments of the present disclosure there is provided a method for the reduction of CO2.

[0064] The system (100) comprises an electrolyser (110) comprising a cathodic compartment (111) comprising a cathode (113) and an anodic compartment (112) comprising an anode (114), the cathodic compartment is configured to receive a first electrolyte (SI) via a cathodic compartment inlet (117) and to recover a carbon compound and a CCh-depleted amine solution (S2) from the cathodic compartment (111) via a cathodic compartment outlet (118). The anodic compartment is configured to receive a second electrolyte (S6) via an anodic compartment inlet (119a) and to recover the second electrolyte and anode reaction products (S7) via an anodic compartment outlet (119b). Optionally, the cathodic compartment and anodic compartment are separated by an ion membrane (115), and a power supply (116) configured to be connected via electrical leads (116a, 116b) to both the cathode and anode to apply a potential difference between said anode (114) and cathode (113). The system further comprises a means for recovering a carbon dioxide reduction product, referred to herein as a carbon compound, (120) configured to be in communication with the cathodic compartment (111) of the electrolyser (110).

[0065] The system described herein is able to be integrated and / or retrofitted into existing carbon capture systems. In embodiments, the system further comprises a CO2 absorption system (130) configured to be in communication with the cathodic compartment. In embodiments, the CO2 absorption unit (130) is configured to be in communication with the cathodic compartment inlet (117). In embodiments, the CO2 absorption system (130) is configured to be in communication with the cathodic compartment outlet (118).

[0066] With reference to Figure 1, according to embodiments of the present disclosure, the method comprises providing a first electrolyte comprising a CCh-amine complex (SI) to a cathodic compartment (111) comprising a cathode (113) via a cathodic compartment inlet (117), applying a potential between the anode and the cathode to induce current flow and reduce at least a portion of the CO2 contained within the CCh-amine complex to form a carbon compound, and recovering the carbon compound and a CCh-depleted amine solution (S2) from the cathodic compartment (110) via a cathodic compartment outlet (118).

[0067] In embodiments, at least a portion of the carbon compound is separated (120) from the carbon compound and CCh-depleted amine solution recovered from the cathodic compartment (111) to obtain a stream comprising at least a portion of the carbon compound (S4) and a stream comprising the CCh-depleted amine solution (S3). At least a portion of the stream comprising the CCh-depleted amine solution (S3) is recycled to a CO2 absorption system (130) as at least a portion of an amine capture solution. The CO2 absorption unit (130) is fed with a CO2 containing feed (S8), preferably a flue gas. In the CO2 absorption unit (130) at least a portion of the CO2 fed reacts with the amine capture solution to form a CCh-amine complex and is recovered as a CCh-amine complex solution (S10). Optionally, the CO2-amine complex solution (S10) may be further treated (150) before being utilised as at least a portion of the first electrolyte (SI).

[0068] In another aspect of the present disclosure, there is provided a method of reducing carbon dioxide (CO2) to carbon monoxide (CO) in an electrolyzer comprising: providing a first electrolyte comprising a CO2-diamine complex to a cathodic compartment comprising a cathode and a cathode current collector, said cathode comprising a cathode transition metal catalyst; providing a second electrolyte comprising potassium hydroxide to an anodic compartment comprising an anode and a current collector, said anode comprising a transition metal foam anode catalyst; applying a current across the anode and the cathode to reduce at least a portion of the CO2 contained within the CCh-amine complex to form CO; and recovering the CO and a CO2-depleted amine solution.

[0069] In another aspect of the present disclosure, there is provided a method of reducing carbon dioxide (CO2) to carbon monoxide (CO) in an electrolyzer comprising: providing a first electrolyte comprising a CO2-diamine complex to a cathodic compartment comprising a cathode and a cathode current collector, said cathode comprising a cathode transition metal catalyst;providing a second electrolyte comprising potassium hydroxide to an anodic compartment comprising an anode and a current collector, said anode comprising a transition metal foam anode catalyst; applying a current across the anode and the cathode to reduce at least a portion of the CO2 contained within the CCh-amine complex to form CO; and recovering the CO and a CO2-depleted amine solution, wherein the cathode transition metal catalyst is, or comprises, Ni.

[0070] In another aspect of the present disclosure, there is provided a method of reducing carbon dioxide (CO2) to carbon monoxide (CO) in an electrolyzer comprising: providing a first electrolyte comprising a CO2-diamine complex to a cathodic compartment comprising a cathode and a cathode current collector, said cathode comprising a cathode transition metal catalyst; providing a second electrolyte comprising potassium hydroxide to an anodic compartment comprising an anode and a current collector, said anode comprising a transition metal foam anode catalyst; applying a current across the anode and the cathode to reduce at least a portion of the CO2 contained within the CCh-amine complex to form CO; and recovering the CO and a CO2-depleted amine solution, wherein the cathode transition metal catalyst is a nickel single atom catalyst.First electrolyte

[0071] In embodiments, the first electrolyte comprises a CO2-amine complex. In embodiments, the first electrolyte is an aqueous solution comprising the CO2-amine complex. It will be understood that, as used herein, the term CO2-amine complex refers to any one or more chemical species formed by the chemical reaction or complexation of an amine molecule and CO2. That is, the CO2 may not be in ‘free form’ and may exist as one or more complexes or adducts with the amine. Throughout the present disclosure reference to the use of the term amine, unless otherwise specified, includes both amine that is complexed and not complexed with carbon dioxide. It will also be appreciated that the first electrolyte may, and likely will, comprise further carbonspecies which can be reduced at the cathode including, but not limited to, carbonate and bicarbonate species as well as the first electrolyte also comprising dissolved CO2.

[0072] In embodiments, the concentration of the amine (M) in the first electrolyte is about, or greater than about: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. In embodiments, the concentration of the amine (M) in the first electrolyte is less than about: 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1. In embodiments, the concentration of the amine (M) in the first electrolyte may be in a range provided by any two of these upper and / or lower values, for example between about 0.1 and about 20, between about 1 and about 5, or between about 1 and about 4.

[0073] In embodiments, the CO2 loading in the first electrolyte (mol of CO2 / mol of amine) is about, or greater than about: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, or 5. In embodiments, the CO2 loading in the first electrolyte (mol of CO2 / mol of amine) is less than about: 5, 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1. In embodiments, the CO2 loading in the first electrolyte (mol of CO2 / mol of amine) may be in a range provided by any two of these upper and / or lower values, for example between about 0.1 and about 5, or between about 0.1 and about 2.

[0074] In embodiments, the first electrolyte is continuously fed to the cathodic compartment.

[0075] In embodiments, the first electrolyte is provided to the cathodic compartment at a flow rate (in mL / min) of about, or greater than about: 10, 20, 30, 40, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 700 750, 800, 850, 900, 950 or 1000. In embodiments, the first electrolyte is provided to the cathodic compartment at a flow rate (in mL / min) of less than about: 1000, 950, 900, 850, 800, 750, 700, 650, 600, 550, 500, 450, 400, 350, 300, 250, 200, 150, 100, 50, 40, 30, 20, or 10. In embodiments the first electrolyte is provided to the cathodic compartment at a flow rate (in mL / min) which may be in a range provided by any two or more of the upper and / or loweramounts, for example the first electrolyte is provided to the cathodic compartment at a flow rate (in mL / min) of between about 10 to about 1000.

[0076] It will be appreciated by a person of skill in the art that the particular flow rate selected will be based upon the size of the cell in use and other, related, operational considerations. In embodiments, when the general system step-up is as described in the Examples under “Continuous electrochemical testing using Ni SAC and CO2-PZ solution” and depicted in Figure 10, the first electrolyte is provided to the cathodic compartment at a flow rate (in mL / min) of about, or greater than about: 10, 20, 30, 40, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 700 750, 800, 850, 900, 950 or 1000. In embodiments, the first electrolyte is provided to the cathodic compartment at a flow rate (in mL / min) of less than about: 1000, 950, 900, 850, 800, 750, 700, 650, 600, 550, 500, 450, 400, 350, 300, 250, 200, 150, 100, 50, 40, 30, 20, or 10. In embodiments the first electrolyte is provided to the cathodic compartment at a flow rate (in mL / min ) which may be in a range provided by any two or more of the upper and / or lower amounts, for example the first electrolyte is provided to the cathodic compartment at a flow rate ( in mL / min) of between about 10 to about 1000. The arrangement shown in Figure 10 was for a 5 cm2liquid-fed electrolyser. Adjustments based on the information provided herein could be made by a person of skill in the art to tailor flow rate to the particular arrangement being used.Amine

[0077] In embodiments, the first electrolyte comprises an amine wherein at least a portion of the amine is complexed with carbon dioxide. Preferred amines are selected for not only for their CO2 capture performance but also favourable electrolysis reaction kinetics, both of which are heavily dependent on the physicochemical properties of the amines. It has been surprisingly found that the effectiveness of amines for CCh-amine complex based reduction of CO2 is, in part, dependent on the CO2 capture capability of the amine and the electrolysis activity of amine-captured CO2 solutions. Without wishing to be bound by theory, it is believed that these are determined by the aminemass normalized CO2 capture capacity, CO2 absorption rate, and the Gibbs free energy of the carbamate formed in the reaction between CO2 and the amine.

[0078] In embodiments, the amine is selected from ethanolamine (MEA), propylamine (PLA), 2-amino-2-methyl-l -propanol (AMP), 3 -amino- 1 -propanol (3A1P), n-butylamine (BTA), diethylamine (DELA), morpholine (MP), piperidine (PD), (2-methoxyethyl)methylamine (MOMELA), triethylamine (TREA), piperazine (PZ), 1,4-diaminobutane (DABT), ethylenediamine (EDA), N,N- Dimethylethylenediamine (DMEDA), N1 -methylpropane- 1,3 -diamine (N-MEPDA), diethylenetriamine (DETA), tetraethylenepentamine (TEPTA), 1,3-diaminopropane (DAPP), and combinations thereof.

[0079] In embodiments, the amine comprises at least 2 amine groups. In embodiments, the amine comprises at least two amine groups independently selected from a primary amine group, a secondary amine group, a tertiary amine group, and combinations thereof.

[0080] In embodiments, the amine is selected from one or more diamines. In embodiments, in the amine, the at least 2 amine groups are separated by no more than 3 carbon atoms, preferably by no more than 2 carbon atoms.

[0081] In embodiments, the amine is selected from one or more heterocyclic diamines.

[0082] In embodiments, the amine is selected for its ability to form a zwitterionic carbamate following exposure to a carbon dioxide source.

[0083] Diamines typically have a higher CO2 capture capacity relative to monoamines of similar molecular weight owing to the ratio of amine groups to CO2 molecules (2: 1). Advantageously, the reaction between diamines molecules and CO2 molecules tends to form zwitterion species, which can be easily adsorbed on the cathode surface due to strong electrode-electrolyte interaction.

[0084] In embodiments, the amine is a heterocyclic diamine capable of forming a zwitterionic carbamate following exposure to a carbon dioxide source.

[0085] In embodiments, the amine is selected from piperazine, 1,4-diaminobutane, ethylenediamine, N,N-Dimethylethylenediamine, N 1 -methylpropane- 1 ,3 -diamine, diethylenetriamine, tetraethylenepentamine, 1,3 -di aminopropane, and combinations thereof.

[0086] In embodiments, the amine is selected from piperazine, 1,4-diaminobutane, ethylenediamine, diethylenetriamine, 1,3 -di aminopropane, and combinations thereof.

[0087] In embodiments, the amine is piperazine.Cathodic compartment

[0088] It will be understood that the cathodic compartment is any suitable container made of one or more suitable material to house a cathode and to contain the first electrolyte and reaction products formed at the cathode. In embodiments, the cathodic compartment comprises a cathode. In embodiments, the cathodic compartment comprises a cathode current collector.

[0089] In embodiments, the cathodic compartment comprises at least one outlet configured to facilitate recovery of a mixture comprising the carbon compound and the CCh-depleted amine solution.

[0090] In embodiments, the cathodic compartment comprises a liquid outlet configured to facilitate recovery of a CCb-depleted amine solution.

[0091] In embodiments, the cathodic compartment comprises a gas outlet configured to recover a gas component comprising the carbon compound. In embodiments, the cathodic compartment comprises a gas outlet configured to recover a gas component comprising at least a portion of the carbon compound.Cathode

[0092] In embodiments, the cathode comprises a cathode transition metal catalyst.

[0093] In embodiments, the cathode transition metal catalyst is selected from Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ag, Zn, Bi, and combinations thereof. In embodiments, the cathode transition metal catalyst is selected from Fe, Co, Ni, and combinations thereof. In embodiments, the cathode transition metal catalyst is selected from Co, Ni, and combinations thereof. In some embodiments, the cathode transition metal catalyst is, or comprises, Co. In some embodiments, the cathode transition metal catalyst is, or comprises, Fe.

[0094] In some embodiments, the cathode transition metal catalyst is, or comprises, Ni.

[0095] In embodiments, the cathode transition metal catalyst is a single atom catalyst. In preferred embodiments, the cathode transition metal catalyst is a nickel single atom catalyst. It will be appreciated that a single-atom catalyst (SAC) refers to a type of catalyst wherein the cathode transition metal catalyst atoms are individually dispersed on a support material. Advantageously, the catalyst cost of transition metal single-atom catalysts is lower than alternatives, for example the use of non-metal single atom catalysts due to high metal mass loading including but not limited to metal additive catalysts, metal film catalysts, or noble metal catalysts.

[0096] In embodiments, the mass loading of the cathode transition metal catalyst on the cathode (mg / cm2) is about, or greater than about: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. In embodiments, the mass loading of the cathode transition metal catalyst on the cathode (mg / cm2) is less than about: 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1. In embodiments, the mass loading of the cathode transition metal catalyst on the cathode (mg / cm2) may be in a concentration rangeprovided by any two of these upper and / or lower values, for example between about 0.1 and about 20, or between about 1 and about 10, or between about 2 to about 6.Cathode current collector

[0097] In embodiments, the cathode current collector serves as a support material for the cathode transition metal catalyst.

[0098] In embodiments, the cathode current collector serves as a support material for a single-atom catalyst.

[0099] In embodiments, the cathode current collector may be selected from any suitable material. In embodiments, the cathode current collector comprises one or more carbon-based materials including graphene, carbon nanotubes, carbon fibres, carbon nanofibers, metal oxides, and nitrogen doped carbon-based materials. In embodiments, the carbon current collector comprises a carbon-based material. In embodiments, the cathode current collector is a carbon fibre current collector.

[0100] In embodiments, the cathode transition metal catalyst is a nickel single atom catalyst and the carbon current collector comprises a carbon-based material.CC -amine complex formation

[0101] In embodiments, the CCh-amine complex in the first electrolyte is obtained from contacting an amine capture solution with a source of carbon dioxide. In embodiments, the source of carbon dioxide is a flue gas. In embodiments, the amine capture solution comprises a diamine. In embodiments, the amine capture solution is an aqueous amine capture solution. In embodiments, the amine capture solution is an aqueous diamine capture solution. In embodiments, the amine capture solution comprises a piperazine.

[0102] In embodiments, the CCh-amine complex is a CCh-diamine complex. In embodiments, the CCh-amine complex is a CCh-piperazine complex. In embodiments,the CCh-piperazine complex is obtained from contacting a CCh-containing flue gas with a piperazine aqueous solution.

[0103] In embodiments, a CCh-depleted amine solution is recovered from the cathodic compartment. In embodiments, at least a portion of the CCh-depleted amine solution is recycled. In embodiments, at least a portion of the CCh-depleted amine solution is recycled as at least a portion of the amine capture solution. The CO2- depleted amine solution comprises amine regenerated from the reduction of the CO2 contained in the CCh-amine complex from the first electrolyte.

[0104] In embodiments, the CCh-depleted amine solution is recycled. In embodiments, the CCh-depleted amine solution is recycled as the amine capture solution.Anodic compartment

[0105] It will be understood that the anodic compartment may be any suitable container made of one or more suitable materials to house an anode and to contain the second electrolyte and reaction products formed at the anode. In embodiments, the anodic compartment comprises an anode. In embodiments, the anodic compartment comprises a current collector.

[0106] In embodiments, the anodic compartment further comprises an inlet configured to receive the second electrolyte.

[0107] In embodiments, the anodic compartment further comprises at least one outlet to facilitate recovery of a product mixture comprising second electrolyte and a portion of reaction products formed at the anode.Anode

[0108] The anode may be selected from any suitable anode material to allow the electrolyser to operate at the desired potential and / or current. In embodiments, the anode comprises an anode catalyst.

[0109] In embodiments, the anode catalyst is a transition metal catalyst.

[0110] In embodiments, the transition metal catalyst is a transition metal foam catalyst. Advantageously, transition metal foam catalysts allow the anode catalyst to serve not only as the catalyst but also function as a gas diffusion electrode and / or current collector.

[0111] In embodiments, the anode is selected from a pure Ni foam anode, a Ni-Fe layered double hydroxide (LDH) supported on Ni foam anode, a Ni-Mo oxides supported on Ni foam anode, a Ni-Ru supported on Ni foam anode , a Ir and / or IrCb supported on titanium foam anode.

[0112] In embodiments, the anode is a transition metal catalyst supported on a carbon current collector. In embodiments, the anode is selected from the group consisting of IrCh supported on carbon paper, RuCh supported on carbon paper, and Ir-Ru oxides supported on carbon paper.Second electrolyte

[0113] The person skilled in the art would appreciate that the anode and the second electrolyte may be selected from any suitable combination to ensure stable operation of the electrolyser at the desired potential and / or current.

[0114] In embodiments, the second electrolyte is an acidic aqueous solution. In embodiments, the second electrolyte is selected from aqueous solutions of H2SO4, HC1, H3PO4, and combinations thereof. In embodiments, the pH of the second electrolyte is between about 1 to about 4.

[0115] In embodiments, the second electrolyte is a basic aqueous solution. In embodiments, the second electrolyte is selected from aqueous solutions of LiOH, NaOH, KOH, and combinations thereof. In embodiments, the pH of the second electrolyte is between about 9 to about 14.

[0116] In embodiments, the second electrolyte is continuously fed to the anodic compartment.

[0117] In embodiments, the second electrolyte is provided to the anodic compartment at a flow rate (in mL / min) of about, or greater than about: 10, 20, 30, 40, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 700 750, 800, 850, 900, 950 or 1000. In embodiments, the second electrolyte is provided to the anodic compartment at a flow rate (in mL / min) of less than about: 1000, 950, 900, 850, 800, 750, 700, 650, 600, 550, 500, 450, 400, 350, 300, 250, 200, 150, 100, 50, 40, 30, 20, or 10. In embodiments the second electrolyte is provided to the anodic compartment at a flow rate (in mL / min) which may be in a range provided by any two or more of the upper and / or lower amounts, for example the second electrolyte is provided to the anodic compartment at a flow rate (in mL / min) of between about 10 to about 1000.Membrane

[0118] In embodiments, the electrolyser further comprises a membrane separating the cathodic compartment and the anodic compartment. The membrane may be selected from any membrane suitable to allow for ionic communication between the cathodic compartment and the anodic compartment of the electrolyser.

[0119] In embodiments, the membrane is an ion permeable membrane. In embodiments, the membrane is an anion exchange membrane. In embodiments, the membrane is a zero-gap anion exchange membrane.

[0120] In embodiments, the membrane is a proton exchange membrane.

[0121] In embodiments, the thickness of the membrane (in pm) is about, or greater than about 1, 2, 3, 4, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 300, 400, or 500. In embodiments, the thickness of the membrane (in gm) is less than about 500, 400, 300, 200, 190, 180, 170, 160, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 5, 4, 3, 2, or 1. In embodiments, the thickness of the membrane (in gm) may be in a range provided by any two or more of the upper and / or lower amounts, for example, between about 1 and about 500, or between about 30 to about 100.Current and potential

[0122] In embodiments, the current applied between the anode and the cathode per unit area of cathode (mA / cm2) is about, or greater than about 1, 5, 10, 20, 30, 40, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 700 750, 800, 850, 900, 950 or 1000. In embodiments, the current applied between the anode and the cathode per unit area of cathode (mA / cm2) is less than about 1000, 950, 900, 850, 800, 750, 700, 650, 600, 550, 500, 450, 400, 350, 300, 250, 200, 150, 100, 50, 40, 30, 20, or 10. In embodiments, the current applied between the anode and the cathode per unit area of cathode (mA / cm2) may be in a range provided by any two or more of the upper and / or lower amounts, for example the current applied between the anode and the cathode per unit area of cathode (mA / cm2) is between about 1 to about 1000, or between about 10 to about 500, between about 50 to about 200. In embodiments, the current applied between the anode and the cathode per unit area of cathode (mA / cm2) is between about 1 to about 200, or between about 10 to about 200, or between about 10 to about 100.

[0123] In embodiments, the potential difference applied between the anode and the cathode (V) is about, or greater than about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, or 5. In embodiments, the potential difference applied between the anode and the cathode (V) is less than about 5, 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1. In embodiments, the potential difference applied between the anode and the cathode (V) may be in a range provided by any two or more of the upper and / or lower amounts, for example the potential difference applied between the anode and the cathode (V) isbetween about 0.1 to about 5, or between about 2 to about 4. In embodiments, the potential difference applied between the anode and the cathode (V) is about 3.Temperature

[0124] In embodiments, the reduction of carbon dioxide is performed at a temperature (in °C) of about, or greater than about 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95. In embodiments, the reduction of carbon dioxide is performed at a temperature (in °C) of less than about 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 0. In embodiments, the reduction of carbon dioxide is performed at a temperature (in °C) which may be in a range provided by any two or more of the upper and / or lower amounts, for example, the reduction of carbon dioxide is performed at a temperature (in °C) of between about 0 to about 100, or between about 20 to about 80, or between about 20 to about 50.Reaction products

[0125] It will be understood that reference to the reduction of CO2, unless otherwise indicated, relates to the reduction of CO2 contained within the CCh-amine complex in the first electrolyte to produce at least one carbon compound. A CCh-depleted amine solution comprising at least a portion of regenerated amine may also be produced. At least a portion of the CCh-depleted amine solution can be recycled and contacted with a source of carbon dioxide to form a reusable CCh-amine complex.

[0126] In embodiments, the carbon compound is selected from formic acid, carbon monoxide, methanol, methane, ethane, acetylene, ethylene, ethanol, propanol, and combinations thereof.

[0127] In embodiments, the carbon compound is carbon monoxide.

[0128] In embodiments, the at least one carbon compound is a gas and can be recovered from the cathodic compartment without further separation from the CO2- depleted amine solution.

[0129] In embodiments, the at least one carbon compound is a liquid and can be recovered from the cathodic compartment as a mixture with the CCh-depleted amine solution. The mixture can then be subjected to further processing to separate at least a portion of the at least one carbon compound from the CCh-depleted amine solution.

[0130] It will be appreciated by the person of skill in the art that the contacting of the amine capture solution with the CO2 source will likely result in further species other than the CCh-amine complex being present in the first electrolyte. The CO2 source itself will likely have a range of carbon-containing species entrained therein in addition to CO2 itself. The capture or dissolution of these various species within the amine capture solution may result in a variety of dissolved and / or captured and / or complexed species within the first electrolyte which provide a secondary carbon source which can undergo reduction at the cathode. Reduction of one or more of these secondary carbon sources may produce a desired carbon compound being obtained at the cathode in addition to that obtained from reduction of the CO2 contained, or directly participating, in the CCh-amine complex. Reduction of all such sources, as components within the CCh-amine complex first electrolyte, are considered to be within the scope of the present invention.

[0131] In embodiments, the first electrolyte comprises a secondary carbon source. In embodiments, the secondary carbon source undergoes reduction at the cathode. In embodiments, the secondary carbon source is selected from CO2, bicarbonate, carbonate, and combinations thereof. In embodiments, the reduction of the secondary carbon source produces one or more further carbon compounds. The one or more further carbon compounds formed from the reduction of the secondary carbon source may be the same or different from the carbon compound formed from the reduction of CO2 within the CCh-amine complex.

[0132] In embodiments, at least one carbon compound is formed from the reduction of CO2, and potentially related CO2 dissolution and breakdown species, at the cathode. In embodiments, at least one carbon compound is formed from the reduction of CO2 contained within a CCh-amine complex at the cathode.

[0133] In embodiments, the one or more further carbon compounds is selected from formic acid, ethane, acetylene, methanol, methane, ethylene, ethanol, propanol, and combinations thereof.

[0134] In embodiments, water reduction occurs at the cathode to form hydrogen (H2).

[0135] In embodiments, the method comprises recovering a carbon compound and a CO2-depleted amine solution from the cathodic compartment. In embodiments, the method further comprises recovering hydrogen (H2) from the cathodic compartment. In embodiments, the method comprises recovering a carbon compound, H2, and a CO2- depleted amine solution from the cathodic compartment.

[0136] In embodiments, the method further comprises separating at least a portion of the carbon compound from the carbon compound and the CCh-depleted amine solution recovered from the cathodic compartment, to produce a product stream comprising a carbon compound.

[0137] In embodiments, the method further comprises separating at least a portion of the carbon compound and at least a portion of the H2 from the carbon compound, H2, and the CCh-depleted amine solution recovered from the cathodic compartment, to produce a stream comprising a carbon compound and H2. In embodiments, the carbon compound and H2 stream comprises carbon monoxide and H2.

[0138] In embodiments, the method further comprises reacting at least a portion of the carbon compound and hydrogen to form a further carbon based compound. In embodiments, the method further comprises reacting at least a portion of the carbon compound and hydrogen to form a hydrocarbon.Power supply

[0139] In embodiments, the power supply is configured to be in electrical communication with the cathode. In embodiments, the power supply is configured to be in electrical communication with the anode. In embodiments, the power supply is configured to be in electrical communication with the cathode and the anode.

[0140] In embodiments, the power supply is provided with energy from a renewable energy source. In embodiments, the renewable energy source is selected from wind, solar, bioenergy, geothermal, hydropower, and combinations thereof. In embodiments, the renewable energy source is selected from wind, bioenergy, solar, and combinations thereof.Use

[0141] In embodiments, the system described herein is used to perform the method described herein.Amine screening method

[0142] In another aspect of the present disclosure, there is provided a method of screening an amine for use in an electrochemical CO2 reduction comprising: determining a CO2 capture activity of the amine; and determining an electrolysis activity of the formed CCh-amine complex, wherein the CO2 capture activity is calculated by multiplying a amine mass normalized CO2 capture capacity of the amine and a CO2 absorption rate of the amine, wherein electrolysis activity is based on the Gibbs free energy of a carbamate formed by the CCh-amine complex.

[0143] In embodiments, the amine screened is used when the CO2 reduction is performed by the method as described herein.ExamplesAmine screening

[0144] Amine absorbent screening criteria for traditional CO2 scrubbing technology are not necessarily compatible with the electrolysis method and system described herein. Amine absorbents for CO2 scrubbing require thermal regeneration, demanding properties, including but not limited to, heat of absorption and thermal stability. These attributes do not necessarily translate to those required for the electrochemical regeneration of amine and the reduction of carbon dioxide.

[0145] A range of amine absorbents covering four main categories: primary, secondary, tertiary, and di / multi amines were screened. Without being bound by theory, it is believed that it is a combination of amine mass normalized CO2 capture capacity, CO2 absorption rate, and carbamate formation energy properties that allow for the identification of amines that are preferable to be used in the method and system described herein.

[0146] For the CO2 capture step, amine mass normalized CO2 capture capacity dictates the CO2 cyclic amount per unit mass of amine in solution. This value offers a measure of an amine absorbent's capability for industrial use. Figure 2 shows the amine mass normalized CO2 capture capacity for a selection of primary, secondary, tertiary, and di / multi amines. Higher amine mass normalized capacity implies an increased amount of CO2 the amine can capture with identical energy input. Among these amine absorbents, diamines usually exhibit higher amine mass normalized capacity than mono / multi amines owing to a balance between molecular weight and the number of amine groups.

[0147] The CO2 absorption rate evaluates the reaction rate between amine absorbents and CO2 gases, see Figure 3. Faster amine CO2 reaction kinetics indicates CO2 gas can be removed quickly, delivering high processing efficiency.

[0148] The CO2 capture activity is obtained by multiplying the amine mass normalized CO2 capture capacity and CO2 absorption rate.

[0149] Regarding the reduction of CO2 contained in the CCh-amine complex, the carbamate formation energy was used to evaluate the electrolysis performance, see Figure 4. Carbamate formation energy was measured and tested as a parameter of interest as the electrochemical cleavage of the C-N bond is a reverse process of the C- N bond formation step. Higher carbamate formation energy implies higher stability of the amine carbamate, making its reduction difficult. Lower carbamate formation energy leads to its potential hydrolysis to bicarbonate. A moderate carbamate formation energy is required to enable quicker carbamate reduction reaction kinetics.

[0150] Figure 5 shows the relationship between the CO2 capture activity and the electrolysis activity. Amines exhibit a volcano shape distribution based on the described screening principle. Those amines approaching the apex of the volcano, for example piperazine, 1,4-diaminobutane, ethylenediamine, N,N- Dimethylethylenediamine, Nl-methylpropane-l,3-diamine, di ethylenetriamine, tetraethylenepentamine, 1,3 -diaminopropane , are considered to be better candidates for higher efficiency CO2 electrolysis.Catalyst identification

[0151] Based on the amine screening described above, PZ was identified as a suitable amine for use in the method described herein. DFT calculations were used to determine the theoretical overpotential of CO2 reduction reaction (CO2RR) and its competitive hydrogen evolution reaction (HER) over a series of metal SACs (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Ag). As shown in Figure 6, most of these metal SACs are calculated with high CO2 reduction overpotential (> 1.0 eV) except for Co SACs and Ni SACs with relatively lower energy barrier (< 1.0 eV). Compared to Co SACs, Ni SACs also exhibit considerably higher HER overpotential (> 2.0 eV), manifesting Ni SACs could be a suitable catalyst to be used in conjunction with PZ.

[0152] In-situ ATR-FTIR spectra of Ni SACs during the reduction reaction in the 1.5 M PZ-captured CO2 solution under electrocatalytic applied potential from 0 to -2.5 V vs. RHE. The magnified spectra from 1200 to 800 cm-1, 1600 to 1200 cm-1, 2000 to 1600 cm-1, and 3000 to 2000 cm-1 are depicted in (a-d). Here the 100% CO2 loading implies that the CO2 loading capacity is 1.05 mol CCh / mol PZ. The peak intensity ratio of H+PZCOO“ (1288.6 cm-1) to PZ (1155.2 cm-1) at the Ni SACs surface indicated that the previous symmetric O=C=O stretching at 1289.98 cm-1for H+PZCOO“ splits into two asymmetric stretching at two spectra at 1221.2 and 1288.6 cm, see Figure 7, and suggests that H+PZCOO“ are likely critical species in the electrolysis of CO2 from CO2- PZ complexes.

[0153] The CO2RR performance of the Ni SACs in reducing other amine-captured CO2 solutions was evaluated. Of these amine solutions, only CO and H2 were detected as products, and FEco is the top level for reducing PZ-captured CO2 solutions compared with others at identical current density ranges. This again suggests the carbamate formation energy is a reasonable metric for evaluating this scheme. The superior capture / reduction kinetics observed endow PZ with improved performance over the other amine solutions, consolidating the amine screening principle and the excellence of PZ as a CO2 absorbent.Preparation of amine solutions and PZ solutions with CO2 loadings

[0154] 1.5 M amine aqueous solutions were prepared by adding 0.3 M of the amine into a glass beaker followed by 200 mL deionized water (DI water). The 200 mL 1.5 M amine aqueous solutions were stirred for 1 hour. Pure CO2 gas with a controlled flow rate of ~50 mL / min was bubbled into the amine solution for approximately 150 minutes until fully saturated. After the bubbling, the pH value of the CCF-saturated amine solutions were tested to be ~7.5, implying the full saturation of CO2. Industrial grade N2 (99.9%) with a flow rate of 20 seem was bubbled through the solution for 1-2 hours to remove dissolved CO2, and the pH value of the solution was tested to be ~7.9.

[0155] 3 M piperazine aqueous solutions were prepared by adding 51.682 g of PZ (0.6 M) into a glass beaker with 200 mL of deionised water. All the preparations were operated at room temperature (293.15 K) unless otherwise noted. Pure CO2 gases were continuously bubbled into the solutions until the pH values of the after-bubbled solutions reached ~8.0.Preparation of catalysts

[0156] Metal single-atom catalysts (SACs) were prepared by the solid pyrolysis method.

[0157] Nickel (II) nitrate hexahydrate (Ni(NC>3)2 6H2O) was added into a glass bottle with oxygen-removed Dl-water to prepare a nickel nitrate solution with a molar concentration of 0.08519 mol / L. Then, 0.40 g of ethylenediaminetetraacetic acid (EDTA) and 2 g of urea were added into a glass beaker followed by adding 40 mL DI water. Subsequently, 1200 pL of as-prepared nickel nitrate solution was transferred to the solution and the mixed solution was stirred in a water bath at 80 °C for 3 hours.After the evaporation of the water, the precursor was obtained and then transferred to a crucible. The precursor was calcinated at a tube furnace under a high-purity N2 atmosphere at 900 °C for 3 hours with a ramp rate of 5 °C / min. Lastly, the Ni single atoms (Ni SAs) were obtained by grinding the calcined sample.

[0158] For the preparation of the Fe SACs, Iron (III) nitrate nonahydrate (Fe(NO3)3'9H2O) was added into a glass bottle with oxygen-removed Dl-water to prepare to a solution with a molar concentration of 0.08519 mol L-L 0.40 g of EDTA, 2 g of urea, and 400 pL of as-prepared Iron (III) nitrate nonahydrate solution was added into a glass beaker with 40 mL DI water. After the evaporation of water content, the metal precursors were calcined and subjected to grinding as described above.

[0159] For the preparation of the Co SACs, Cobalt (II) nitrate hexahydrate (Co(NO3)26H2O) was added into a glass bottle with oxygen-removed Dl-water to prepare to a solution with a molar concentration of 0.08519 mol L-L 0.40 g of EDTA,2 g of urea, and 1200 pL of as-prepared Cobalt (II) nitrate hexahydrate solution was added into a glass beaker with 40 mL DI water. After the evaporation of water content, the metal precursors were calcined and subjected to grinding as described above.

[0160] The SACs were dissolved in a Nafion solution (Nafion 3% and IPA 97%) to form a homogeneous catalyst ink after sonication at ice bath. For the preparation of the working electrode, the as-prepared catalyst ink was deposited into carbon paper (Troy paper 090, 5% PTFE content, 1 >< 2 cm2) with a catalyst loading amount of 4 mg / cm2.Electrochemical testing using Ni SAC

[0161] The electrochemical performances of the as-prepared catalysts in CCh-amine complex solutions were tested in a H-cell. The Ni SACs were dissolved in a Nafion solution (Nafion 3% and IPA 97%) to form a homogeneous catalyst ink after sonication at ice bath. For the preparation of the working electrode, the as-prepared catalyst ink was deposited into carbon paper (Troy paper 090, 5% PTFE content, 1 x 2 cm2) with a catalyst loading amount of 4 mg / cm2. Ag / AgCl electrode and Pt wire were employed as reference and counter electrode, respectively. Proton-exchange membrane (Nafion 117) is used as the separator. During the electrochemical test, the H-cell with separate two chambers (50 mL) was sealed, and the gaseous products were transferred by a glass needle to GC for gas detection and analysis. The inlet / out switching valves can be both opened to bubble CO2 gases to connect a gas bag or closed to seal the cathode chamber, while for the normal tests (a series of amine-captured CO2 solutions at different loading), the volume of the catholyte is controlled with 50 mL then the headspace of the cell can be determined (80 mL). Subsequently, switch off the valves (Figure 8) and start the electrochemical tests using chronopotentiometry and / or chronoamperometry for a short time (3 mins) to make sure the produced gases will not affect the pressure. Finally, stop the electrochemical tests and use a precise gas syringe to take 1 mL of gas for analysis via gas chromatography (GC). All the electrochemical tests are operated at room temperature (293.15 K) and pressure (100.3 KPa).

[0162] Based on the aforementioned analysis, the FEco can be calculated and the FEco values for Ni SACs in the electrolysis of amine-captured CO2 solutions are shown in Figure 9.

[0163] Table 1 shows the FEco and FEH in the electrolysis of 1.5 M PZ-captured CO2 systems at three CO2 loading capacities.Table 1 : FEco and FEH in the electrolysis of 1.5 M PZ-captured CO2 systems at three CO2 loading capacities

[0164] Table 2 shows the FE and the CO selectivity in the electrolysis of 1.5 M mono amine-captured CO2 systems with 100% CO2 loading.Table 2: FE and the CO selectivity in the electrolysis of 1.5 M mono amine-captured CO2 systems with 100% CO2 loading.

[0165] Table 3 shows the FE and the CO selectivity in the electrolysis of 1.5 M di / multi amine-captured CO2 systems with 100% CO2 loading.Table 3: FE and the CO selectivity in the electrolysis of 1.5 M di / multi amine-captured CO2 systems with 100% CO2 loading.Continuous electrochemical testing using Ni SAC and CO2-PZ solution

[0166] A zero-gap CO2 electrolyzer was used (Dioxide Materials) with a serpentine cathode and anode flow plates. The membrane electrode assembly was assembled with the use of Ni SACs supported on carbon paper as the cathode gas diffusion electrode (GDL), Ni foam as the anode GDL, and anion-exchange membrane (Fumasep FAA-3- 50) as the separator. The setup is shown in Figure 10.

[0167] 3 M PZ-loaded CO2 aqueous solution and 2 M KOH solution as the cathode and anode electrolyte respectively with a constant flow rate. The generated syngas were directly collected by gas bag through a separate pipeline. Successful operation of the AEM electrolyzer was achieved and the current density was found to be 100 mA / cm2at the potential of 3 V. Without CO2 backup, the electrolysis of PZ-captured solutions can be operated for 26 hours, and the CO2 loading capacity was reduced from 1.03 mol CCh / mol PZ to 0.8 mol CCb / mol PZ (Figure 11). Of the produced -642.6 mL ofsyngas, the FEco and FEH2 are determined to be -37.8% and -43.3% respectively. The overall carbon efficiency and energy efficiency are 75.6% and 25.1%, respectively.

[0168] To verify the repeatability and scale-up ability of the method described herein, the electrochemical regenerated PZ solutions were bubbled with CO2 gases and reelectrolyzed for continuous producing syngas. The system can be operated for more than 10 cycles. The carbon / energy and electrochemical amine regeneration efficiencies and the FEco of each cycle are depicted in Figure 12 and the relatively high-efficiency values for over ten cycles confirm the high feasibility of this method and system described herein.

[0169] It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. A method of reducing carbon dioxide (CO2) to a carbon compound in an electrolyzer comprising: providing a first electrolyte comprising a CCh-amine complex to a cathodic compartment comprising a cathode and a cathode current collector, said cathode comprising a cathode transition metal catalyst; providing a second electrolyte to an anodic compartment comprising an anode; applying a current across the anode and the cathode to reduce at least a portion of the CO2 contained within the CCh-amine complex to form the carbon compound; and recovering the carbon compound and a CCh-depleted amine solution.

2. The method of claim 1, wherein the amine of the CCh-amine complex is selected to form a zwitterionic carbamate following exposure to a carbon dioxide source.

3. The method of claim 1 or claim 2, wherein the cathode transition metal catalyst is a single-atom transition metal catalyst.

4. The method of any one of the preceding claims, wherein a mass loading of the transition metal catalyst on the cathode (mg / cm2) is between about 1 to about 10, or between about 2 to about 6.

5. The method of any one of the preceding claims, wherein the carbon compound comprises carbon monoxide.

6. The method of any one of the preceding claims, wherein the first electrolyte is continuously fed to the cathodic compartment.

7. The method of any one of the preceding claims, wherein the amine-CCh complex is obtained from contacting an amine capture solution with a source of carbon dioxide, preferably a flue gas.

8. The method of claim 7, wherein at least a portion of the CO2 depleted amine solution is recycled, preferably as at least a portion of the amine capture solution.

9. The method of any one of the preceding claims, wherein the reduction of CO2 is performed at a temperature (°C) of between about 20 to about 80, or between about 20 to about 50.

10. The method of any one of the preceding claims, further comprising separating at least a portion of the carbon compound from the carbon compound and the CO2- depleted amine solution to produce a carbon compound-enriched gas stream.

11. The method of any one of the preceding claims, wherein the applying a current across the anode and the cathode reduces water at the cathode to form hydrogen (H2).

12. The method of claim 11, further comprising reacting at least a portion of the carbon compound and hydrogen to form a hydrocarbon.

13. The method of any one of the preceding claims, wherein the amine of the CO2- amine complex, and amine capture solution, is piperazine.

14. The method of any one of the preceding claims, wherein the cathode transition metal catalyst is a nickel single-atom catalyst.

15. A method of reducing carbon dioxide (CO2) to carbon monoxide (CO) in an electrolyzer comprising: providing a first electrolyte comprising a CO2-diamine complex to a cathodic compartment comprising a cathode and a cathode current collector, said cathode comprising a cathode transition metal catalyst; providing a second electrolyte comprising potassium hydroxide to an anodic compartment comprising an anode and a current collector, said anode comprising a transition metal foam anode catalyst;applying a current across the anode and the cathode to reduce at least a portion of the CO2 contained within the CCh-amine complex to form CO; and recovering the CO and a CO2-depleted amine solution.

16. The method of claim 15, wherein the C02-diamine complex is a CO2-piperazine complex.

17. The method of claim 16, wherein the CO2-piperazine complex is formed by exposure of a CO2-containing flue gas to a piperazine aqueous solution.

18. The method of any one of claims 15 to 17, wherein the cathode transition metal catalyst is a nickel single-atom catalyst.

19. A system for carbon dioxide reduction comprising: an electroylzer comprising: a cathodic compartment comprising a cathode and a current collector, said cathode comprising a transition metal catalyst, and configured to receive a first electrolyte comprising a CCh-amine complex; an anodic compartment comprising an anode, and configured to receive a second electrolyte; a power supply connected to apply a potential difference between the anode and the cathode; and a means for recovering a carbon dioxide reduction product configured to be in communication with the cathodic compartment.

20. The system of claim 19, further comprising an ion permeable membrane separating the anodic compartment and the cathodic compartment.

21. The system of claim 20, wherein the ion permeable membrane is an anion exchange membrane, preferably a zero-gap anion exchange membrane.

22. The system of any one of claim 19 to claim 21, wherein the cathodic compartment comprises a liquid outlet configured to recover a CCh-depleted amine solution.

23. The system of any one of claim 19 to claim 22, wherein the amine is selected to form a zwitterionic carbamate upon contacting with a carbon dioxide source, preferably wherein the amine is piperazine.

24. The system of any one of claim 19 to claim 23, wherein the cathode transition metal catalyst is a single-atom catalyst, preferably a nickel single-atom catalyst.

25. A method of screening an amine for use in an electrochemical CO2 reduction comprising: determining a CO2 capture activity of the amine; and determining an electrolysis activity of the formed CCh-amine complex, wherein the CO2 capture activity is calculated by multiplying an amine mass normalized CO2 capture capacity of the amine and a CO2 absorption rate of the amine, wherein electrolysis activity is based on the Gibbs free energy of a carbamate formed by the CCh-amine complex.

26. The method of claim 25, wherein the screened amine is used for the CO2 reduction performed by the method of any one of claims 1 to 18.

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