CN114600285A

CN114600285A - Electrochemically mediated gas capture including from low concentration streams

Info

Publication number: CN114600285A
Application number: CN202080074936.2A
Authority: CN
Inventors: 萨哈格·沃斯基昂; 特雷弗·艾伦·哈顿
Original assignee: Massachusetts Institute of Technology
Current assignee: Massachusetts Institute of Technology
Priority date: 2019-08-28
Filing date: 2020-08-27
Publication date: 2022-06-07
Also published as: MX2022002468A; CA3152518A1; JP2022546697A; EP4021618A1; EP4021618A4; AU2020335875A1; KR20220052984A; IL290765A

Abstract

Methods, apparatus and systems related to electrochemical separation of a target gas from a gas mixture are provided. In some cases, a target gas, such as carbon dioxide, is captured and optionally released (e.g., by bonding with an electroactive species in a reduced state) using an electrochemical cell. Some embodiments are particularly useful for selectively capturing a target gas while reacting little or no with oxygen that may be present in the gas mixture. Some such embodiments may be used in applications involving separation from gas mixtures having relatively low concentrations of target gases, such as direct air capture and aerated air treatment.

Description

Electrochemically mediated gas capture including from low concentration streams

RELATED APPLICATIONS

This application is a continuation-in-part application No. 16/659,398 of U.S. patent application No. 10/21, filed 2019, entitled "electrochemical media gates Capture, incorporated from Low communication Streams," and is also a continuation-in-part application No. PCT/US2019/057224 of international patent application No. PCT/US2019, filed 2019, 21, 8/28, each according to 35 u.s.c. 119(e) claiming priority of U.S. provisional application No. 62/892,962, filed 2019, 28, 8/28, entitled "electrochemical media Capture from Low communication Streams," which is hereby incorporated by reference in its entirety for all purposes.

Technical Field

Methods, apparatus, and systems relating to electrochemical separation of a target gas from a gas mixture are generally described.

Background

Efforts are made to remove target substances from gas mixtures. For example, over the past two decades, efforts have been made to suppress anthropogenic carbon dioxide (CO)₂) And emissions to alleviate global warming. Many processes have been carried out, such as conventional thermal processes to handle carbon dioxide capture at different stages of its production: captured after combustion in a power plant, or concentrated from the atmosphere, then pressurized and stored in geological formations, or converted to be commercially usefulThe chemical compound of (1). Other potential applications of target gas removal include removing target gas directly from air or from ventilated air (ventilated air). Improved apparatuses, methods, and/or systems are desired.

Disclosure of Invention

Methods, apparatus and systems related to electrochemical separation of a target gas from a gas mixture are provided. In some cases, a target gas, such as carbon dioxide, is captured and optionally released (e.g., by bonding with an electroactive species in a reduced state) using an electrochemical cell. Some embodiments are particularly useful for selectively capturing a target gas while reacting little or no with oxygen that may be present in the gas mixture. Some such embodiments may be used in applications involving separation from gas mixtures having relatively low concentrations of target gases, such as direct air capture and aerated air treatment. In some cases, the subject matter of the present disclosure relates to associated products, alternative solutions to specific problems, and/or a number of different uses for one or more systems and/or articles.

In one aspect, an electrochemical cell is described. In some embodiments, an electrochemical cell includes a negative electrode comprising a first electroactive species; a positive electrode; and a separator between the negative electrode and the positive electrode, the separator capable of containing a conductive liquid, wherein the first electroactive species has an oxidized state and at least one reduced state in which the species is capable of bonding with a target gas but, for the at least one reduced state, with oxygen (O) at least one temperature₂) The reaction of (2) is thermodynamically unfavorable. In some embodiments, the first electroactive species has at least one reduced state in which the species is capable of bonding with a target gas, but for which oxygen (O) is reacted at least one temperature greater than or equal to 223K and less than or equal to 573K₂) The reaction of (a) is thermodynamically unfavorable. In some embodiments, the first electroactive species has at least one reduced state in which the species is capable of bonding with a target gas, but is directed toThe at least one reduced state is reacted with oxygen (O) at least one temperature greater than or equal to 223K and less than or equal to 373K₂) The reaction of (2) is thermodynamically unfavorable.

In some embodiments, an electrochemical cell comprises: a negative electrode comprising a first electroactive species immobilized on the negative electrode; and a positive electrode; wherein the first electroactive species has an oxidized state and at least one reduced state in which the species is capable of bonding with a target gas but for which oxygen (O) is associated at least one temperature₂) The reaction of (a) is thermodynamically unfavorable. In some embodiments, the first electroactive species has at least one reduced state in which the species is capable of bonding with a target gas, but for which oxygen (O) is reacted at least one temperature greater than or equal to 223K and less than or equal to 573K₂) The reaction of (a) is thermodynamically unfavorable. In some embodiments, the first electroactive species has at least one reduced state in which the species is capable of bonding with a target gas, but for which oxygen (O) is reacted at least one temperature greater than or equal to 223K and less than or equal to 373K₂) The reaction of (2) is thermodynamically unfavorable.

In another aspect, a gas separation system is described. In some embodiments, the gas separation system comprises a plurality of electrochemical cells in fluid communication with a gas inlet and a gas outlet, wherein the gas separation system is configured to have a gas flow rate of 0.003kg or greater at or equal to 0.001L/sec and less than or equal to 500L/sec_{Target gas}/(kg_Bedt_b) In kg, wherein_BedIs the bed weight and t_bIs the breakthrough time of the gas separation system.

In another aspect, a method of at least partial gas separation is described. In some embodiments, the method comprises applying a potential difference across the electrochemical cell; exposing a gas mixture comprising a target gas to an electrochemical cell; and in applyingRemoving an amount of a target gas from a gas mixture during and/or after a first potential difference, wherein any oxygen (O) present in the gas mixture₂) Is less than or equal to 0.1% by volume is removed from the gas mixture.

In some embodiments, the method comprises applying a first potential difference across the electrochemical cell; exposing a first quantity of an input gas mixture comprising a target gas to an electrochemical cell; bonding at least a portion of the target gas with an electroactive species of the electrochemical cell during and/or after applying the first potential difference to produce a first treated gas mixture having a lower amount of the target gas than the first gas mixture; applying a second potential difference across the electrochemical cell; and releasing some or all of the target gas bonded to the electroactive species to produce a second treated gas mixture; wherein during and/or after the releasing, the method further comprises flowing a second gas through the electrochemical cell to remove at least a portion or all of the released target gas from the electrochemical cell, and/or applying a vacuum condition to the electrochemical cell to remove at least a portion or all of the released target gas from the electrochemical cell.

Other advantages and novel features of the invention will become apparent from the following detailed description of various non-limiting embodiments of the invention when considered in conjunction with the drawings. In the event that the present specification and a document incorporated by reference include conflicting and/or inconsistent disclosure, the present specification shall control.

Drawings

Some non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, which are schematic and are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated is typically represented by a single numeral. For purposes of clarity, not every component may be labeled in every drawing, nor may every component of every embodiment of the invention be shown, unless illustration is necessary to allow those of ordinary skill in the art to understand the invention. In the figure:

fig. 1A shows a schematic side view of an exemplary electrochemical cell including a negative electrode and a positive electrode, according to one or more embodiments;

fig. 1B shows a schematic side view of an exemplary electrochemical cell including a negative electrode, a positive electrode, and a separator, according to one or more embodiments;

fig. 2 shows an exploded schematic view of an exemplary electrochemical cell according to one or more embodiments;

fig. 3A shows an exploded schematic view of an electrochemical cell operating in a charging mode according to one or more embodiments;

fig. 3B shows an exploded schematic view of an exemplary electrochemical cell operating in a discharge mode according to one or more embodiments;

FIG. 4 shows a schematic diagram of an exemplary gas separation system in accordance with one or more embodiments;

fig. 5A shows a schematic diagram of an exemplary system for performing a gas separation process in accordance with one or more embodiments;

fig. 5B shows a schematic diagram of an exemplary system including a flow field for performing a gas separation process in accordance with one or more embodiments;

fig. 5C-5E show schematic side views of exemplary flow field channel patterns according to one or more embodiments;

FIG. 6 shows a schematic diagram of an exemplary gas separation system in accordance with one or more embodiments;

fig. 7A shows a schematic diagram of an exemplary system for performing a gas separation process in accordance with one or more embodiments;

FIG. 7B shows a schematic diagram of an exemplary system for performing a gas separation process in accordance with one or more embodiments;

figures 8A-8B show schematic diagrams of a method for flowing a gas through a bed of an electrochemical device, according to one or more embodiments;

fig. 9 shows electrochemical data listed for a plurality of quinones and oxygen in accordance with one or more embodiments.

Fig. 10A shows a schematic diagram of an exemplary system including a plurality of electrochemical cells performing a gas separation process in accordance with one or more embodiments;

fig. 10B shows a schematic diagram of an exemplary system for performing a gas separation process, including a plurality of electrochemical cells electrically connected in parallel, according to one or more embodiments;

fig. 10C shows a schematic diagram of an exemplary system for performing a gas separation process, including a plurality of electrochemical cells electrically connected in series, according to one or more embodiments;

fig. 11 shows a schematic diagram of an exemplary system for performing a gas separation process, including a plurality of electrochemical cells electrically connected in series and one or more electrically conductive materials between the electrochemical cells, in accordance with one or more embodiments;

FIGS. 12A to 12D show 2-chloro-9, 10-anthraquinone (AQ-Cl) (FIG. 12A), ester derivatives of 9, 10-anthraquinone (AQ-COO-C)₃H₇) (FIG. 12B), 9, 10-Anthraquinone (AQ) (FIG. 12C) and ether derivatives of 9, 10-anthraquinone (AQ-O-C)₃H₇) (FIG. 12D) in the presence of hydrogen atom₂(left) or CO₂0.1M [ n-Bu ] in (right) saturated DMF₄N]PF₆Cyclic voltammetry in solution;

FIGS. 13A-13B show p-Benzoquinone (BQ) (FIG. 13A) and p-naphthoquinone (p-NQ) (FIG. 13B) in N-positions₂Or CO₂0.1M [ n-Bu ] in saturated DMF₄N]PF₆Cyclic voltammetry in solution of (a);

FIG. 14 shows CO at increased concentrations for naphthoquinone (p-NQ)₂Gas saturation (with N)₂Equilibrium) of 0.1M [ n-Bu ] in DMF₄N]PF₆Cyclic voltammetry in solution of (a);

FIG. 15 shows that 5mM vs. naphthoquinone (p-NQ) is at 20% CO₂Saturation (with N)₂Equilibrium) of 0.1M [ n-Bu ] in DMF₄N]PF₆Cyclic voltammetry at different scan rates in solution; and

FIGS. 16A to 16B show the conversion of 9, 10-Phenanthrenequinone (PQ) (FIG. 16A) and o-naphthoquinone (o-NQ) (FIG. 16B) in N₂Or CO₂0.1M [ n-Bu ] in saturated DMF₄N]PF₆Cyclic voltammetry in solution.

Detailed description of the preferred embodiments

Methods, apparatuses, and systems related to electrochemical separation of a target gas from a gas mixture are provided. In some cases, the target gas, such as carbon dioxide, is captured and optionally released (e.g., by bonding with an electroactive species in a reduced state) using an electrochemical cell. Some embodiments are particularly useful for selectively capturing a target gas while reacting little or no with oxygen that may be present in the gas mixture. Some such embodiments may be used in applications involving separation from gas mixtures having relatively low concentrations of target gases, such as direct air capture and aerated air treatment. Certain such embodiments are less energy intensive or less costly than certain prior art techniques (e.g., thermal or pressure swing target gas separation).

In some aspects, methods of at least partially separating a gas mixture are generally described, as well as electrochemical cells and gas separation systems that may be used for such applications. Certain aspects relate to applying a potential difference across an electrochemical cell and containing a target gas (e.g., CO)₂) Is exposed to the electrochemical cell (e.g., low concentration mixtures such as ambient air, vented air). Electrochemical cells may include electrodes that contain certain electroactive species (e.g., certain optionally substituted quinones or polymer derivatives thereof) that can attain a state generated by an electrochemical potential that is reactive with a target gas but not with a potentially interfering species (e.g., oxygen). Reactions between the electroactive species and oxygen can be reduced or avoided by careful selection of the electroactive species (e.g., selecting an electroactive species having a reduced state that is capable of bonding with the target gas, for which the reaction with oxygen is thermodynamically unfavorable). Certain other aspects relate to methods of gas flow during capture and release processes, and to methods of capturing target gases with high productivity even at low concentration gas mixturesA gas separation system.

Target gas capture including from low concentration target gas streams can be valuable, but difficult to perform inexpensively without the use of energy intensive methods. The existing conventional methods and systems have a number of disadvantages, including high energy requirements and waste. Furthermore, conventional thermal methods of capturing target gases (e.g., carbon dioxide) often fail to meet the increasingly stringent efficiency and capacity standards set by regulatory agencies.

As a specific example with respect to carbon dioxide gas removal, although the goal of most such applications is high CO from industrial, power generation, and other such point sources₂A stream of concentration (3% to 15%), but it may be desirable to remove CO from an enclosed space₂For the purpose of ventilation in buildings and cabins, or cabin environment control systems on board spacecraft and submarines, where the maximum CO allowed in the habitable space₂The concentration was 5,000ppm (or 0.5%). However, in such applications, the CO is low₂The concentration presents challenges, which may be due to low driving force and the addition of CO₂In addition to the large amount of other substances present in the air. Such concerns are also prevalent with CO proceeding from the atmosphere at concentrations of about 400ppm₂May be worth considering as a long-term mitigation strategy.

In particular, with respect to electrochemical CO₂Capture (although related to other target gases), O₂Can be at the target CO₂Plays an important role in electrochemically mediated separations, particularly with relatively high oxygen concentrations and/or relatively low CO₂Concentration of a gas mixture (e.g., aerated air applications, direct air capture applications, etc.). May be suitable for use with CO when in a reduced state₂Certain electroactive species that react may also be able to react with O₂And (4) reacting. As a non-limiting example, quinones typically undergo two consecutive one-electron reductions in an aprotic electrolyte solution (e.g., a conducting liquid), and both reduction states have been observed with CO₂Effectively complexing. It has been found in the context of the present disclosure that standard reduction of quinones is activatedThe potential is to identify CO for electrochemistry₂Important parameters for the isolation of suitable redox-active molecules. Dissolved O in aprotic electrolyte solution₂Single electron reduction of gases to produce stable superoxide ions (O)₂ ^-) It may be an effective nucleophile. Superoxide ions undergo nucleophilic addition to a carbonyl atom bonded to an electron-withdrawing leaving group (such as anhydrides and esters). Previous studies have shown that superoxide ion pairs CO in aprotic electrolyte solutions₂Has reactivity and generates an anionic free radical intermediate CO₄ ^-·Which subsequently form peroxydicarbonate C₂O₆ ^2-. Furthermore, it has been observed in the context of the present disclosure that the use of common alkyl carbonate electrolytes, such as propylene carbonate and ethylene carbonate, is not recommended when superoxide ions are generated in any electrochemical process. Thus, for O₂Standard reduction potentials for one-electron reduction are helpful to identify for electrochemical CO₂Important parameters for the isolation of suitable redox-active molecules. In addition, chemical oxidation of electrochemically reduced (activated) electrodes by oxygen molecules can create a charge imbalance in the electrochemical cell. In some cases, this charge imbalance may render the target gas trapping electrode inactive against the target gas.

Certain methods and electrochemical cells have been developed that take advantage of these insights and are generally described herein. In some cases, the methods and electrochemical cells and systems involve an Electro-Swing Adsorption (ESA) process that can, in some cases, remove a target gas from a gas mixture while removing little or no oxygen present.

In some aspects, electrochemical cells are described. Fig. 1A depicts a schematic of an exemplary electrochemical cell 100, which includes a negative electrode 110 and a positive electrode 120. In some cases, electrochemical cells are adapted to react with a target gas from a gas mixture in any of a variety of applications including: a target gas mixture (e.g., ambient air, ventilation air, etc.) having a relatively low concentration of a target gas is at least partially separated. As used herein, the term "electrochemical cell" refers to a device in which redox half-reactions occur at a negative electrode and a positive electrode. The term "electrochemical cell" is intended to include devices that meet these criteria even though the performance of the cell may arguably be characterized by more pseudocapacitive than faradaic, and thus may also be referred to as a type of capacitor.

As described above, in some embodiments, an electrochemical cell includes a negative electrode. As used herein, the negative electrode of an electrochemical cell refers to the electrode into which electrons are injected during charging. For example, referring to fig. 1A, when electrochemical cell 100 is charged (e.g., by application of an electrical potential from an external power source), electrons travel through an external circuit (not shown) and into negative electrode 110. Thus, in some cases, the species associated with the negative electrode may be reduced to a reduced state (a state of increased electron number) during the charging process of the electrochemical cell.

The electrochemical cell can also include a positive electrode. As used herein, the positive electrode of an electrochemical cell refers to the electrode from which electrons are removed during charging. For example, referring again to fig. 1A, when electrochemical cell 100 is charged (e.g., by application of an electrical potential from an external power source), electrons pass from positive electrode 120 and enter an external circuit (not shown). Thus, in some cases, the species associated with the positive electrode can oxidize to an oxidation state (state of reduced electron count) during charging of the electrochemical cell.

In some embodiments, the negative electrode comprises a first electroactive species. As used herein, an electroactive species generally refers to an agent (e.g., a chemical entity) that undergoes oxidation or reduction upon exposure to an electrical potential in an electrochemical cell. It is to be understood that when the electrode comprises an electroactive species, the electroactive species can be located at the surface of the electrode, in at least a portion of the interior of the electrode (e.g., in the pores of the electrode), or both. For example, in some embodiments, the negative electrode 110 in fig. 1 comprises a first electroactive species. The first electroactive species may be on the surface of the negative electrode 110 or near the surface of the negative electrode 110, the first electroactive species may be internal to at least a portion of the negative electrode 110, or a combination of both.

In some embodiments, the first electroactive species is immobilized on the negative electrode. Such embodiments may be distinguished from embodiments of other systems in which electroactive species may be freely transported from one electrode to another by, for example, advection. As generally understood, a substance immobilized on an electrode (e.g., a negative electrode) is a substance that is not free to diffuse away from or separate from the electrode under a given set of conditions. The electroactive species may be immobilized on the electrode in a variety of ways. For example, in some cases, an electroactive species can be immobilized on an electrode by bonding (e.g., by covalent bonds, ionic bonds, and/or intramolecular interactions such as electrostatic forces, van der waals forces, hydrogen bonds, etc.) to the electrode surface or to a substance or material attached to the electrode. In some embodiments, the electroactive species can be immobilized on the electrode by adsorption to the electrode. In some cases, the electroactive species may be immobilized on the electrode by polymerization to the electrode. In some cases, the electroactive species can be immobilized on the electrode by being included in a composition (e.g., coating, composite layer, etc.) applied to or deposited on the electrode. In some cases, an electroactive species (e.g., a polymeric electroactive material or a molecular electroactive material) infiltrates a pad of microfibers or nanofibers or carbon nanotubes such that the electroactive material is immobilized relative to the pad. The mat can provide enhanced surface area enhancement for electrolyte and gas pathways, as well as an extended network for conductivity. In some embodiments, the electroactive species is part of a gel composition associated with the electrode (e.g., as a layer deposited on the electrode, as a composition that penetrates into the pores of the electrode, or as a composition that at least partially encapsulates a component of the electrode (e.g., fibers or nanotubes of the electrode)). Such electroactive species-containing gels (e.g., hydrogels, ionic gels, organogels, etc.) can be prepared prior to association with the electrode (e.g., applied as a coating to form a layer), or the gels can be prepared by contacting (e.g., by coating or immersion) the electrode with a gel precursor (e.g., a prepolymer solution containing an electroactive species) in the presence of the electrode, and then the gel formation can be initiated (e.g., by crosslinking via introduction of a crosslinking agent, free radical initiator, heating, and/or irradiation with electromagnetic radiation (e.g., ultraviolet radiation)).

In some embodiments described in more detail below, the negative electrode comprises an electroactive composite layer comprising an immobilized polymer composite of an electroactive material and an additional material (e.g., a carbonaceous material). For example, in some embodiments, the electroactive composite layer comprises a composite of a polymer comprising the first electroactive species (e.g., a redox active polymer having a reduction potential in the range described below) and Carbon Nanotubes (CNTs).

The first electroactive species may have an oxidized state (having fewer electrons than the reduced state) and at least one reduced state (having more electrons than the oxidized state). As a non-limiting example, if the first electroactive species is benzoquinone, the neutral benzoquinone will be considered in the oxidized state, the semiquinone (the product of adding one electron to the neutral benzoquinone) will be considered in one reduced state, and the benzoquinone dianion (the product of adding one electron to the neutral benzoquinone) will be considered in another reduced state.

In some embodiments, the first electroactive species has at least one reduced state in which the species is capable of reacting with a target gas (e.g., CO)₂) And (4) bonding. A substance capable of bonding with a target gas generally refers to the ability of the substance to undergo a bonding reaction with the target gas to a sufficiently significant extent and at a sufficiently significant rate for a useful gas separation process to occur. For example, the substance capable of bonding with the target gas may have a molecular weight of 10 or more at room temperature (23 ℃)¹M^-1Greater than or equal to 10²M^-1And/or up to 10³M^-1Or a higher binding constant to the target gas. The species capable of bonding with the target gas may be capable of bonding with the target gas on a timescale on the order of minutes, seconds, milliseconds, or as low as microseconds or less. The substance may be capable of being at least one temperature (e.g., greater than or equal to223K and less than or equal to 573K, e.g., 298K). In some embodiments, the species is capable of bonding with the target gas at a first temperature, but bonding with the target gas at a second temperature is thermodynamically and/or kinetically unfavorable. Such temperature dependence can be based on the temperature dependence of the gibbs free energy change between the substance (e.g., reduced quinone) and the target gas (e.g., carbon dioxide). With the knowledge and guidance of the present disclosure, one of ordinary skill in the art will be able to select an appropriate temperature to promote bonding between the species in its at least one reduced state and the target gas.

In some embodiments, the first electroactive species has an oxidation state in which it is capable of releasing the bound target gas. The first electroactive species may be selected such that, in at least one reduced state, it has a strong affinity for the intended target gas for its intended particular application. For example, in CO₂In some embodiments of the target gas, the first electroactive species selected can have a value of 10¹To 10³M^-1Binding constant to carbon dioxide. In some embodiments, the selected electroactive species may have a 10¹To 10³M^-1With different target gases. It has been observed that some quinones may be used as suitable electroactive species. In some embodiments, in CO₂Optionally substituted quinone can be reduced to its semiquinone or dianion (e.g., in a single step or multiple steps), then reacted with CO₂Binding to form a complex. Can also be used in the reduction with CO₂Other electroactive species that form covalent bonds to form carboxylate moieties.

In some embodiments, the first electroactive species has at least one reduced state in which the species is capable of bonding with a target gas, but for which there is at least one temperature (e.g., 298K): at which temperature the substance reacts with oxygen (O)₂) The reaction of (a) is thermodynamically unfavorable. In some cases, the first electroactive species has an activity ofAt least one reduced state in which the species is capable of bonding with a target gas, but for which there is at least one temperature (e.g., 298K): at which temperature the substance reacts with oxygen (O)₂) The reaction of (a) is kinetically unfavorable because the rate constant of the reaction is too low for the reaction to occur on a time scale commensurate with gas capture (e.g., microseconds, milliseconds, seconds, or minutes). As noted above, the ability of an electroactive species to react with a target gas but not with oxygen (at least in a thermodynamically and/or kinetically favorable manner) may be useful in: in certain applications where a relatively large amount of oxygen is present in the gas mixture to be separated, or when the target gas is present in a relatively low amount (thus, if oxygen is present, it must compete with oxygen for the reaction in the case of at least one reduced state). In some embodiments, the first electroactive species has at least one reduced state in which the species is capable of bonding with a target gas, but for which the species is associated with oxygen (O)₂) The reaction of the reaction is thermodynamically unfavorable at least one temperature within the following range: greater than or equal to 223K, greater than or equal to 248K, greater than or equal to 273K, greater than or equal to 298K, and/or up to 323K, up to 348K, up to 373K, up to 398K, up to 423K, up to 448K, up to 473K, up to 498K, up to 523K, up to 548K, up to 573K, or higher. In some embodiments, the first electroactive species has at least one reduced state in which the species is capable of bonding with a target gas, but for which the species is associated with oxygen (O)₂) The reaction of the reaction is thermodynamically unfavorable at a temperature of 298K. It is to be understood that as used herein, a reaction that is thermodynamically unfavorable at a given temperature means having a positive change in gibbs free energy (ag) at that temperature_rxn) The reaction of (1). For example, the reaction between the species in at least one reduced state and oxygen may have greater than 0kcal/mol, greater than or equal to +0.1kcal/mol, greater than or equal to +0.5kcal/mol, greater than or equal to, at least one temperature within the following rangesA change in Gibbs free energy (AG) of +1kcal/mol, greater than or equal to +2kcal/mol, greater than or equal to +3kcal/mol, greater than or equal to +5kcal/mol, and/or up to +8kcal/mol, up to +10kcal/mol, up to +20kcal/mol, or higher_rxn): greater than or equal to 223K, greater than or equal to 248K, greater than or equal to 273K, greater than or equal to 298K, and/or up to 323K, up to 348K, up to 373K, up to 398K, up to 423K, up to 448K, up to 473K, up to 498K, up to 523K, up to 548K, up to 573K, or higher. In some embodiments, the reaction between the species in the at least one reduced state and oxygen has a gibbs free energy change (ag) of greater than 0kcal/mol, greater than or equal to +0.1kcal/mol, greater than or equal to +0.5kcal/mol, greater than or equal to +1kcal/mol, greater than or equal to +2kcal/mol, greater than or equal to +3kcal/mol, greater than or equal to +5kcal/mol, and/or up to +8kcal/mol, up to +10kcal/mol, up to +20kcal/mol, or more at a temperature of 298K (ag)_rxn)。

In the context of the present disclosure, it has been found that some electroactive species capable of bonding with a target gas may still be reactive to oxygen or its reduction products (e.g., superoxide ion, peroxide dianion, etc.). In some such cases, reactivity with oxygen or its reduction products is detrimental to the gas separation process. For example, reactivity with oxygen may reduce the efficiency of capturing the target gas, or superoxide ions or peroxide ions may have deleterious reactivity with components of the electrochemical cell (e.g., electroactive species, target gas, separator, conductive liquid (when present), etc.). However, it has been found in the context of the present disclosure that some particular electroactive species may have at least one reduced state capable of bonding with a target gas, but for which reduced state oxygen (O) is associated₂) The reaction of (a) is thermodynamically and/or kinetically unfavorable. Examples and selection criteria for some such electroactive species are described in more detail below.

In some embodiments, the standard reduction potential ratio for generating at least one reduced state of the first electroactive species in the conducting liquid is for oxygen (O)₂) And superoxideSubstance ion (O)₂ ^-) The standard reduction potential correction of interconversion between. Having such a standard reduction potential may help the species in at least one reduced state to be able to bond with the target gas while also being thermodynamically unfavorable for the reaction with oxygen. As an example, in a conductive liquid of 0.1M n-tetrabutylammonium hexafluorophosphate in Dimethylformamide (DMF) at room temperature, (O) is₂/O₂ ^-) The redox couple may have a standard reduction potential of-1.35V relative to a given reference. Thus, any suitable electroactive species having a standard reduction potential more positive than-1.35V (for a given reference) in the conductive liquid at room temperature will be referred to as having a standard reduction potential more positive than for oxygen (O)₂) With superoxide ion (O)₂ ^-) At least one reduction state corrected for the standard reduction potential of the interconversion between. In some embodiments, the standard reduction potential ratio in the conducting liquid for interconversion between the oxidized state and the at least one reduced state of the first electroactive species is for superoxide (O)₂ ^2-) With peroxides (O)₂ ^2-) The standard reduction potential correction of interconversion.

One of ordinary skill in the art, with the benefit of this disclosure, will be able to determine the standard reduction potential of an electroactive species in a given conductive liquid. For example, one of ordinary skill in the art can measure the standard reduction potential using cyclic voltammetry, linear sweep voltammetry, or any other suitable electrochemical technique. In some cases where, for example, cyclic voltammetry waves are irreversible to the electroactive species, the standard reduction potential may be approximately determined using any suitable technique known to those of ordinary skill in the art, such as peak potential. The standard reduction potential may depend on the temperature at which the measurement is made. In some embodiments, the standard reduction potential is measured at any of the temperatures described above, e.g., at 298K.

In some embodiments, the standard reduction potential for producing at least one reduced state of the first electroactive species in the conductive liquid is at least 5mV, at least 10mV, at least 20mV, at least 50mV, at least 100mV, at least 200mV, at least 400mV, or more than that for oxygenGas (O)₂) With superoxide ion (O)₂ ^-) The standard reduction potential correction of interconversion between. As an example, if the interconversion of oxygen and superoxide ions in the conducting liquid is-1.35V relative to a given reference, and the standard reduction potential of the electroactive species used to produce the reduced state of said species is-1.00V relative to the given reference, the standard reduction potential ratio of the electroactive species used to produce the reduced state is for oxygen (O)₂) With superoxide ion (O)₂ ^-) The standard reduction potential for interconversion between the two is corrected by 350 mV. In some embodiments, the standard reduction potential ratio for generating at least one reduced state of the first electroactive species in the conducting liquid is for oxygen (O)₂) And superoxide ion (O)₂ ^-) The standard reduction potential for interconversion therebetween is just less than or equal to 1V, less than or equal to 900mV, less than or equal to 800mV, less than or equal to 600mV, or less than or equal to 500 mV.

In some embodiments, the standard reduction potential ratio for generating at least one reduced state of the first electroactive species in the conducting liquid is for the superoxide ion (O)₂ ^-) With peroxide dianion (O)₂ ^2-) The standard reduction potential for interconversion between is positive by at least 5mV, at least 10mV, at least 20mV, at least 50mV, at least 100mV, at least 200mV, at least 400mV, or more. In some embodiments, the standard reduction potential ratio for generating at least one reduced state of the first electroactive species in the conducting liquid is for the superoxide ion (O)₂ ^-) With peroxide dianion (O)₂ ^2-) The standard reduction potential for interconversion therebetween is just less than or equal to 1V, less than or equal to 900mV, less than or equal to 800mV, less than or equal to 600mV, or less than or equal to 500 mV.

The first electroactive species may be in any suitable form, provided that it meets at least one of the criteria claimed herein. In some embodiments, the first electroactive species is or comprises a molecular species. For example, the first electroactive species may be or comprise an organic molecule. The first electroactive species may include one or more functional groups capable of binding with the target gas and gas mixture (e.g., when the electroactive species is in a reduced state). The functional group may include, for example, a carbonyl group. In some embodiments, the first electroactive species is part of a polymer, such as a redox-active polymer. The first electroactive species may be part of a polymer material immobilized on the negative electrode. For example, referring to fig. 1A, the first electroactive species may be a portion of a polymeric material immobilized on the negative electrode 110 of the electrochemical cell 100.

In some embodiments, the first electroactive species is or comprises an optionally substituted quinone (i.e., the quinone can comprise functional groups and/or other moieties or bonds bonded to the main structure of the quinone). In some cases, the first electroactive species is or comprises a redox-active polymer comprising an optionally substituted quinone. The choice of substituent (e.g., functional group) on the optionally substituted quinone can depend on any of a variety of factors, including but not limited to its effect on the standard reduction potential of the optionally substituted quinone. The skilled artisan, with the benefit of this disclosure, will understand how to determine which substituents or group of substituents on an optionally substituted quinone are suitable for use in a first electroactive species based on, for example, synthetic feasibility and the resulting standard reduction potential. Exemplary functional groups that can functionalize the optionally substituted quinone include, but are not limited to, halogen (e.g., chlorine, bromine, iodine), hydroxyl, carboxylate/carboxylic acid, sulfonate/sulfonic acid, alkylsulfonate/alkylsulfonic acid, phosphonate/phosphonic acid, alkylphosphonate/alkylphosphonic acid, acyl (e.g., acetyl, ethyl ester, etc.), amino, amido, quaternary ammonium (e.g., tetraalkylamino), branched or unbranched alkyl (e.g., C1 to C18 alkyl), heteroalkyl, alkoxy, glycoloxy (glycoxy), polyalkyleneglycoloxy (e.g., polyethyleneglycoloxy), imino, polyimino, branched or unbranched alkenyl, branched or unbranched alkynyl, aryl, heteroaryl, heterocyclyl, nitro, nitrile, thio, and/or carbonyl, any of which is optionally substituted.

The optionally substituted quinone of the first electroactive species may comprise one or more of the structures selected from formulae (IA) and (IB):

wherein R is¹、R²、R³And R⁴May be the same or different, and may be hydrogen, halogen (e.g., chlorine, bromine, iodine), hydroxyl, carboxylate/carboxylic acid, sulfonate/sulfonic acid, alkylsulfonate/alkylsulfonic acid, phosphonate/phosphonic acid, alkylphosphonate/alkylphosphonic acid, acyl (e.g., acetyl, ethyl ester, etc.), amino, amido, quaternary ammonium (e.g., tetraalkylamino), branched or unbranched alkyl (e.g., C1 to C18 alkyl), heteroalkyl, alkoxy, dialdoxoxy, polyalkyleneglycoloxy (e.g., polyethyleneglycoloxy), imino, polyimino, branched or unbranched alkenyl, branched or unbranched alkynyl, aryl, heteroaryl, heterocyclyl, nitro, nitrile, thio, and/or carbonyl, any of which is optionally substituted, and/or R¹To R⁴Any two adjacent groups of (a) may be linked together to form an optionally substituted ring.

In some embodiments, the optionally substituted quinone is or comprises an optionally substituted naphthoquinone. In certain instances, the optionally substituted quinone is or comprises an optionally substituted anthraquinone. In some embodiments, the optionally substituted quinone is or comprises an optionally substituted phenanthrenequinone (also referred to as an optionally substituted phenanthrenedione). The substituent (e.g., functional group) may be any of those listed above.

In some embodiments, the electroactive species is or comprises one or more of: phenanthrenequinone ester (PQ-ester), iodophenanthrenequinone (PQ-I), diiodophenanthrenequinone (PQ-I)₂) Phenanthrenequinone (PQ), o-naphthoquinone (o-NQ), and dimethyl-p-naphthoquinone (p-NQ-Me)₂) P-naphthoquinone (p-NQ), di-tert-butyl benzoquinone (TBQ), and Benzoquinone (BQ) having the following structures:

wherein R is⁵Is optionally substituted branched or unbranched C1 to C18 alkyl (e.g. alkylMethyl, ethyl, propyl, butyl, etc.).

In some cases, other regioisomers (regio-isomers) of the above non-limiting examples of electroactive species are also suitable (e.g., having substituents at different positions of the quinone).

As described above, the first electroactive species may be part of a redox-active polymer. In some cases, any of the optionally substituted quinones described herein can be part of a redox-active polymer. In some such cases, at least a portion of the redox-active polymer comprises a backbone and one or more of an optionally substituted quinone covalently bonded to the backbone. Backbone generally refers to the longest series of covalently bonded atoms that together form a continuous chain of polymer molecules. In certain other instances, the optionally substituted quinones described herein may be part of the backbone of a redox-active polymer.

The electroactive species (e.g., the first electroactive species) can include a crosslinked polymeric material. For example, in some embodiments, the electroactive species comprises or is incorporated into a hydrogel, an ionic gel, an organogel, or a combination thereof. Such crosslinked polymeric materials are generally known in the art, and in some cases may comprise an electroactive species described herein as part of a three-dimensional structure (e.g., via covalent bonds). However, in some embodiments, the electroactive species is incorporated into the crosslinked polymeric material by adsorption (e.g., physisorption and/or chemisorption). In some embodiments, the electroactive species comprises an extended network. For example, the electroactive species may comprise a Metal Organic Framework (MOF) or a Covalent Organic Framework (COF). In some embodiments, the electroactive species comprises a functionalized carbonaceous material. For example, the electroactive species can include functionalized graphene, functionalized carbon nanotubes, functionalized carbon nanoribbons, edge-functionalized graphite, or a combination thereof.

In some embodiments, the separator is between the negative electrode and the positive electrode. For example, referring to fig. 1B, the separator 130 is between the negative electrode 110 and the positive electrode 120. The separator may serve as a protective layer that may prevent the respective electrochemical reactions at the electrodes from interfering with each other. The separator may also help electrically isolate the negative and positive electrodes from each other and/or from other components within the electrochemical cell to prevent short circuits. One of ordinary skill will be able to select an appropriate spacer with the benefit of this disclosure. The separator may include a porous structure. In some cases, the separator is or comprises a porous solid material. In some embodiments, the separator is or comprises a membrane. The membrane of the spacer may be made of a suitable material. For example, the film of the separator may be or comprise a plastic film. Some non-limiting examples of the plastic film include polyamide, polyolefin resin, polyester resin, polyurethane resin, or acrylic resin containing lithium carbonate, or potassium hydroxide, or sodium peroxide-potassium dispersed therein. The material for the separator may include a cellulose film, a polymer material, or a polymer-ceramic composite. Additional examples of spacers include polyvinylidene fluoride (PVDF) spacers, PVDF-alumina spacers, or Celgard.

In some embodiments, the electrochemical cell includes one or more separators that comprise or are capable of comprising an electrically conductive liquid (e.g., an ionic liquid). As an example, referring to fig. 1B, the separator 130 of the electrochemical cell 100 can contain or be capable of containing a conductive liquid. The conductive liquid generally refers to a liquid having a relatively high conductivity at room temperature (23 ℃). The conductive liquid can have a sufficiently high conductivity to facilitate an electrochemical reaction in an electrochemical circuit involving the negative electrode and the positive electrode. The conductive liquid is generally ionically conductive because it facilitates the transport of ions. However, conductive liquids typically have relatively low electronic conductivity (e.g., conductivity due to charge movement, e.g., by electrons or holes) to prevent shorting of the electrochemical cell.

In some cases, the separator containing the conductive liquid is at least partially (or completely) impregnated with the conductive liquid. For example, the separator may absorb an amount of the conductive liquid while being immersed, coated, dipped or otherwise associated with the conductive liquid. In some such cases where the separator is porous, some or all of the pores of the separator (within the interior of the separator and/or near the surface of the separator) may become at least partially filled with the conductive liquid. In some embodiments, the separator is saturated with the conductive liquid. A conductive liquid saturated separator generally refers to a separator that contains the maximum amount of conductive liquid that can be contained within the separator volume at room temperature (23 ℃) and ambient pressure. In some embodiments, the electrochemical cell can be configured such that no conductive liquid is present in the separator, but the separator can contain the conductive liquid when it is placed into operation to perform a gas separation process. One way in which the separator can contain a conductive liquid is by having a relatively high porosity and/or containing a material that can absorb and/or be wetted by the conductive liquid.

In some embodiments, the conductive liquid comprises an ionic liquid, such as a room temperature ionic liquid ("RTIL"). The RTIL electrolyte may have low volatility (i.e., room temperature vapor pressure less than 10 a)^-5Pa, e.g. 10^-10Pa to 10^-5Pa) to reduce the risk of drying of the electrode and to allow the gas to flow through the electrode without significant evaporation losses or entrainment losses. In some embodiments, the ionic liquid constitutes substantially all (e.g., at least 80 vol.%, at least 90 vol.%, at least 95 vol.%, at least 98 vol.%, at least 99 vol.%, at least 99.9 vol.%) of the electrically conductive liquid.

The ionic liquid may comprise an anionic component and a cationic component. The anion of the ionic liquid may include, but is not limited to: halide, sulfate, sulfonate, carbonate, bicarbonate, phosphate, nitrate, acetate, PF₆ ^-、BF₄ ^-Triflate, perfluorobutylsulfonate, bis (trifluoromethanesulfonyl) amide, trifluoroacetate, heptafluorobutyrate, haloaluminate, triazolidine (triazolide), and amino acid derivatives (e.g., proline with protons removed at the nitrogen). The cations of the ionic liquid may include, without limitation: imidazole

Pyridine, and their use

Pyrrolidine, and a salt thereof

Phosphorus, phosphorus

Ammonium, sulfonium, thiazole

Pyrazoline, pyrazoline

(pyrazolium), piperidine

Triazole, and mixtures thereof

Pyrazoline, pyrazoline

、

Azole

Guanidine, and their use in the treatment of diabetes

And dialkyl morpholine

. In some embodiments, the room temperature ionic liquid comprises an imidazole

As the cationic component. As an example, in some embodiments, the room temperature ionic liquid packageContaining 1-butyl-3-methylimidazole

("Bmim") as the cationic component. In some embodiments, the room temperature ionic liquid comprises bis (trifluoromethylsulfonyl) imide ("TF)₂N ") as an anionic component. In some embodiments, the room temperature ionic liquid comprises 1-butyl-3-methylimidazole represented by formula (IIA) below

Bis (trifluoromethylsulfonyl) imide ([ Bmim)][TF₂ N])：

In some embodiments, the room temperature ionic liquid comprises 1-butyl-3-methylimidazole represented by the following formula (IIB)

Tetrafluoroborate (BF)₄)([Bmim][BF₄])：

In some embodiments, the conductive liquid comprises a low volatility electrolyte solution. For example, the conductive liquid may include a liquid solvent having a relatively high boiling point and an ionic species (e.g., dissolved supporting electrolyte ions) dissolved therein. The liquid solvent having a relatively high boiling point may be non-aqueous. For example, the liquid solvent may include N, N-Dimethylformamide (DMF) and the like.

The positive electrode is turned on, and in some embodiments, the positive electrode comprises a second electroactive species. The second electroactive species may be a different composition than the first electroactive species of the negative electrode, although in some embodiments, the second electroactive species is the same as the first electroactive species. In some embodiments, the positive electrode includes an electroactive layer (sometimes referred to as a complementary electroactive layer) that includes a second electroactive species. The complementary electroactive layer may be in the form of a composite material and thus may be a complementary electroactive composite layer. In operation, the second electroactive species may serve as an electron source for reducing the first electroactive species present in the negative electrode. Also, the second electroactive species may act as an electron trap (sink for electron) during oxidation of the first electroactive species. In this manner, the electroactive layer of the positive electrode can be described as "complementary. The second electroactive species may include, for example, a redox-active polymer. In some embodiments, the redox-active polymer is or comprises a polymer comprising ferrocene (e.g., as a moiety bonded to a polymer backbone). In some embodiments, the second electroactive species comprises a metallocene (e.g., ferrocene). In some such cases, the second electroactive species comprises a redox-active polymer comprising a metallocene. As a non-limiting embodiment, the redox-active polymer includes polyvinylferrocene. As another example, the second electroactive species may include a polymer comprising thiophene. In some such cases, the second electroactive species comprises poly (3- (4-fluorophenyl) thiophene). In some embodiments, the second electroactive species comprises phenothiazine. As another example, in some embodiments, the second electroactive species comprises a (2, 2, 6, 6-tetramethylpiperidin-1-yl) oxy group (referred to as "TEMPO") or a derivative thereof (e.g., comprising an optional substituent). In some cases, the second electroactive species comprises a faradaic redox species: which has a standard reduction potential of at least 0.5 volts (V), at least 0.6V, at least 0.8V, and/or up to 1.0V, up to 1.5V, or higher, positive than the first reduction potential of the first electroactive species.

As with the primary electroactive composite layer of the negative electrode, the complementary electroactive composite layer of the positive electrode can include an immobilized polymer composite of an electroactive species and another material (e.g., a carbonaceous material). Some examples of carbonaceous materials include carbon nanotubes (e.g., single-walled carbon nanotubes, multi-walled carbon nanotubes), carbon black, ketjen black (ketjen black), carbon black Super P, or graphene. Other materials are also possible. In some cases, the second electroactive species can be immobilized on the positive electrode by being included in a composition (e.g., coating, composite layer, etc.) applied to or deposited on the positive electrode. In some cases, the second electroactive species (e.g., a polymeric electroactive material or a molecular electroactive material) infiltrates a mat of microfibers, nanofibers, or carbon nanotubes associated with the positive electrode such that the second electroactive species is immobilized relative to the mat of the positive electrode. The second electroactive species may also be part of a gel associated with the positive electrode in the same or similar manner as described above with respect to the first electroactive species.

According to one or more embodiments, the electroactive composite layer of the positive electrode can have a particular weight ratio of electroactive material to carbonaceous material. The weight ratio may be selected to promote a high electron current per mass of electroactive material. In some embodiments, the weight ratio of the mass of electroactive material to the mass of carbonaceous material for the complementary electroactive composite layer may be 1 to 2 to 1. In some embodiments, it may be 1 to 1. Other ratios are also possible.

In some cases, one or more electrodes of an electrochemical cell include an electroactive composite layer. For example, in some embodiments, the negative electrode includes an electroactive composite layer (e.g., a primary electroactive composite layer). Referring again to fig. 1B, according to certain embodiments, the negative electrode 110 includes a composite electroactive composite layer 114 facing the positive electrode 120. In some cases, the positive electrode includes an electroactive composite layer (e.g., a complementary electroactive composite layer). For example, in fig. 1B, the negative electrode 120 includes an electroactive composite layer 124 facing the negative electrode 110. The electroactive composite layer of the positive electrode can also be referred to as a complementary electroactive composite layer because the electroactive material therein serves as an electron sink or source of electrons for the electroactive material of the negative electrode. In some cases, the electroactive composite layer of an electrode (e.g., negative electrode, positive electrode) extends through the entire thickness dimension of the electrode. For example, the electroactive composite layer may be inserted through the entire thickness of the electrode. However, in some embodiments, the electroactive composite layer of the electrode does not extend through the entire thickness dimension of the electrode. In some such cases, the electroactive composite layer is inserted through some, but not all, of the thickness of the electrode. In some cases, the electroactive composite layer is a coating on the surface of another component of the electrode (e.g., a current collector, a gas permeable layer, etc.).

In some embodiments, the electroactive species of the electrode (e.g., a first electroactive species of the negative electrode, a second electroactive species of the positive electrode) is part of an electroactive composite layer. For example, in fig. 1B, the electroactive composite layer 114 includes a first electroactive species described herein, according to some embodiments. Similarly, in some embodiments, the electroactive composite layer 124 includes a second electroactive species (e.g., polyvinylferrocene).

The electroactive composite layer of the negative electrode may also comprise a carbonaceous material in addition to the electroactive species. Some examples of suitable materials include, but are not limited to, carbon nanotubes (e.g., single-walled carbon nanotubes, multi-walled carbon nanotubes), carbon black, ketjen black, carbon black Super P, graphene, or combinations thereof. Other examples also include immobilizing and/or coating an electroactive species (e.g., in polymer or molecular form or otherwise) into/onto a mat of microfibers, nanofibers, or carbon nanotubes by intercalation, grafting, Chemical Vapor Deposition (CVD), or other means.

According to one or more embodiments, the electroactive composite layer of the negative electrode may have a specific weight ratio of electroactive species to carbonaceous material. The weight ratio may be selected to promote a high electron current per mass of electroactive material. In some embodiments, the weight ratio of the mass of electroactive material to the mass of carbonaceous material may be 1 to 10. In some embodiments, it may be 1 to 3. Other ratios are also possible.

The negative electrode may also include a gas permeable layer. The gas permeable layer (which may also be referred to as a substrate layer) may be proximate to the electroactive composite layer and face outward with respect to the electrochemical cell. In some embodiments, the gas permeable layer is in contact with the first electroactive species. In some such cases, the gas permeable layer is in direct contact with the first electroactive species, while in other such cases, the gas permeable layer is in indirect contact with the first electroactive species. It will be understood that when a portion (e.g., a layer) is "on" or "in contact with" another portion, it can be directly on the other portion, or intervening portions (e.g., layers) can also be present (in which case the one portion is understood to be "indirectly on" or "in indirect contact with" the other portion). One portion "directly on," in "direct contact with" another portion means that there are no intervening portions. It will also be understood that when an element is referred to as being "on" or "in contact with" another element, it can cover all or a portion of the other element. In some embodiments, the gas permeable layer is in contact (e.g., direct contact or indirect contact) with the electroactive composite layer of the negative electrode.

The gas flow may diffuse through the gas permeable layer to contact the electroactive composite layer. The gas permeable layer may comprise an electrically conductive solid material and serve as a current collector within the cell.

The gas permeable layer may comprise a porous material. In some embodiments, the gas permeable layer has a porosity of, for example, greater than or equal to 60%, greater than or equal to 70%, greater than or equal to 75%, greater than or equal to 80%, or greater. In some embodiments, the gas permeable layer has a porosity of less than or equal to 85%, less than or equal to 90%, or higher. Combinations of these ranges are possible. For example, in some embodiments, the gas permeable layer of the negative electrode has a porosity greater than or equal to 60% and less than or equal to 90%. Other porosities are also possible. Some examples of suitable materials for the gas permeable layer include, but are not limited to, carbon paper (treated, TEFLON treated, or untreated), carbon cloth, and non-woven carbon mats. Other materials may also be used.

While in some embodiments the electrochemical cell includes a single negative electrode, in other embodiments the electrochemical cell includes more than one negative electrode. For example, in some embodiments, the negative electrode described herein is a first negative electrode, and the electrochemical cell comprises a second negative electrode. The positive electrode may be between the first negative electrode and the second negative electrode. The second negative electrode may further comprise a first electroactive species. The second negative electrode may be identical to the first negative electrode in configuration and composition. In some embodiments, the electrochemical cell comprises greater than or equal to 1 negative electrode, greater than or equal to 2 negative electrodes, greater than or equal to 3 negative electrodes, greater than or equal to 5 negative electrodes, greater than or equal to 10 negative electrodes, and/or up to 15 negative electrodes, up to 20 negative electrodes, up to 50 negative electrodes, or more.

While in some embodiments the electrochemical cell includes a single separator (e.g., between the negative electrode and the positive electrode), in other embodiments the electrochemical cell includes more than one separator. For example, in some embodiments, the separator described herein is a first separator, and the electrochemical cell comprises a second separator. In some embodiments, where a second negative electrode is present, the second separator may be between the positive electrode and the second negative electrode. The second separator may be identical to the first separator in configuration and composition. In some cases, the second separator can contain (e.g., be saturated with) a conductive liquid. In some embodiments, the electrochemical cell comprises greater than or equal to 1 separator, greater than or equal to 2 separators, greater than or equal to 3 separators, greater than or equal to 5 separators, greater than or equal to 10 separators, and/or up to 15 separators, up to 20 separators, up to 50 separators, or more. In some cases, each separator is between a respective negative electrode and positive electrode.

In some embodiments of electrochemical cells in which the positive electrode has negative electrodes (e.g., a first negative electrode and a second negative electrode) on either side thereof, the positive electrode comprises a second electroactive species facing each negative electrode. In some such embodiments, the positive electrode includes two complementary electroactive composite layers each facing one of the negative electrodes.

The positive electrode can also include a substrate layer positioned adjacent to or between the one or more electroactive composite layers. The substrate layer may be in direct contact or indirect contact with one or more electroactive composite layers. The base layer of the positive electrode may comprise the same or different material as the base layer of the negative electrode (when present). For example, the substrate layer may comprise a material such as carbon paper (treated, TEFLON treated, or untreated), carbon cloth, or a non-woven carbon mat. In some embodiments, the substrate may comprise a mat comprising, for example, carbon nanotubes, microfibers, nanofibers, or a combination thereof. Other materials are also possible. The base layer of the positive electrode may comprise a conductive material and serve as a current collector within the cell. In some embodiments, the substrate comprises a metal and/or metal alloy. For example, the substrate may include a metal and/or metal alloy foil (e.g., having a relatively small thickness of less than or equal to 200 microns, less than or equal to 100 microns, less than or equal to 10 microns, and/or as low as 1 micron or less). Some examples of suitable foils may include, but are not limited to, aluminum foil, titanium foil. As a specific example, in some embodiments, the positive electrode includes a substrate between a first complementary electroactive composite layer facing the first negative electrode and a second complementary electroactive composite layer facing the second negative electrode. In this case, if a line extending away from the electroactive composite layer body may intersect a particular electrode (e.g., a negative electrode) without passing through the substrate, the electroactive composite layer of the positive electrode may face the electrode. One object (e.g., an electroactive composite layer) may face another object when the object is in contact with the other object, or when one or more intervening materials are located between the surface and the other object. For example, two objects facing each other may be in contact or may include one or more intervening materials (e.g., spacers) between them.

Fig. 2 depicts an example of an electrochemical cell according to some, but not necessarily all, embodiments and having one or more of the above-described components. Electrochemical cell 100 includes a positive electrode 120 between two negative electrodes 110. The separator 130 separates the positive electrode 120 and the negative electrode 110. Each negative electrode 110 includes: an optional gas permeable layer 112 positioned away from the center of the cell 100; and an optional primary electroactive composite layer 114 facing the positive electrode 120. In some embodiments, the positive electrode 120 includes a base layer 122 and two complementary electroactive composite layers 124 thereon. The different components of the electrochemical cell 100 may have certain characteristics described throughout this disclosure, for example, including the electrode materials (e.g., electroactive species) described above. The configuration of the negative electrode 110 with both faces facing outward, as shown for example in fig. 2, provides the advantage of doubling the gas absorption area exposed to the gas in some cases.

According to one or more embodiments, the target gas comprises a nucleophilic molecule. According to one or more embodiments, the target gas may include an aprotic acidic gas. According to one or more embodiments, the target gas comprises a gas capable of forming a complex with the electroactive species of the negative electrode when the electroactive species is in its reduced state (e.g., by bonding with the species in its reduced state). According to one or more embodiments, the target gas comprises carbon dioxide (CO)₂). According to one or more embodiments, the target gas comprises sulfur dioxide (SO)₂). According to one or more embodiments, the target gas comprises Borane (BR)₃) Wherein each R may be the same or different and is a suitable substituent (e.g., hydrogen, alkyl, aryl, etc., each optionally substituted). In some embodiments, the target gas comprises one species (one type of molecule). In some embodiments, the target gas includes more than one species (e.g., a first type of molecule and a second, different type of molecule). The potential window over which capture and release occur may depend on the particular target gas of the embodiment, and thus the enrichment and removal of the target gas may be controlled by applying an appropriate potential difference applied across the electrochemical cell.

In some embodiments, the gas mixture (e.g., input gas mixture) to be at least partially separated from the gas mixture by exposure to the electrochemical cell is ambient air (e.g., air from the surrounding environment, such as outdoor air). Ambient air generally refers to air that exists in an open location, such as outdoors. In some such cases, electrochemical cells are used for direct air capture. The systems and methods described herein may be useful techniques for removing a target gas, such as carbon dioxide, directly from ambient air (e.g., to reduce greenhouse gas levels) without the need for pre-concentration of the target gas. In some cases, certain aspects of the present disclosure may make the systems and methods described herein particularly useful for direct air capture (e.g., capable of bonding with a target gas while thermodynamically unfavorable for reaction with a major component of ambient air, such as oxygen).

In some embodiments, the concentration of the target gas in the gas mixture is relatively low. One such case may be when the gas mixture is ambient air. In some embodiments, the concentration of the target gas in the gas mixture prior to exposure to the electrochemical cell is less than or equal to 500ppm, less than or equal to 450ppm, less than or equal to 400ppm, less than or equal to 350ppm, less than or equal to 300ppm, less than or equal to 200ppm, or less. In some embodiments, the concentration of the target gas in the gas mixture is as low as 100ppm, as low as 50ppm, as low as 10ppm, or less. Combinations of these ranges are possible. For example, in some embodiments, the concentration of the target gas in the gas mixture is less than or equal to 500ppm and as low as 10 ppm. In some embodiments where the target gas is carbon dioxide, the concentration of carbon dioxide in the gas mixture is less than or equal to 500ppm, less than or equal to 450ppm, less than or equal to 350ppm, or less prior to exposure to the electrochemical cell. In some embodiments, the concentration of carbon dioxide in the gas mixture is greater than or equal to 300ppm, greater than or equal to 350ppm, or higher prior to exposure to the electrochemical cell. Combinations of these ranges are possible. For example, in some embodiments, the concentration of carbon dioxide in the gas mixture prior to exposure to the electrochemical cell is greater than or equal to 300ppm and less than or equal to 400ppm, or greater than or equal to 300ppm and less than or equal to 500 ppm.

In some embodiments, the gas mixture (e.g., input gas mixture) to be at least partially separated from the gas mixture by exposure to the electrochemical cell is vented air. The ventilation air may be air of an enclosed or at least partially enclosed location (e.g., air circulating in an enclosed location). Some examples of locations in which a gas mixture (e.g., ventilation air) may be located include, but are not limited to, sealed buildings, partially ventilated locations, compartments, manned submersibles, airplanes, and the like.

The target gas concentration in the ventilation air may be higher than ambient air, but lower than the typical concentration of industrial processes. In some embodiments, the concentration of the target gas in the gas mixture prior to exposure to the electrochemical cell is less than or equal to 5,000ppm, less than or equal to 4,000ppm, less than or equal to 2,000ppm, less than or equal to 1,000ppm or less. In some embodiments, the concentration of the target gas in the gas mixture (e.g., when it is ventilation air/air in an enclosed space) is as low as 1,000ppm, as low as 800ppm, as low as 500ppm, as low as 200ppm, as low as 100ppm, as low as 10ppm, or less. Combinations of these ranges are possible. For example, in some embodiments, the concentration of the target gas in the gas mixture is less than or equal to 5,000ppm and as low as 500 ppm. In some embodiments wherein the target gas is carbon dioxide, the concentration of carbon dioxide in the gas mixture is less than or equal to 5,000ppm, less than or equal to 4,000ppm, less than or equal to 2,000ppm, less than or equal to 1000ppm, less than or equal to 500ppm, or less prior to exposure to the electrochemical cell. In some embodiments, the concentration of carbon dioxide in the gas mixture prior to exposure to the electrochemical cell is greater than or equal to 10ppm, greater than or equal to 100ppm, greater than or equal to 300ppm, greater than or equal to 500ppm, greater than or equal to 1,000ppm, greater than or equal to 2,000ppm, or higher. Combinations of these ranges are possible. For example, in some embodiments, the concentration of carbon dioxide in the gas mixture prior to exposure to the electrochemical cell is greater than or equal to 500ppm and less than or equal to 5,000ppm, or greater than or equal to 10ppm and less than or equal to 5,000 ppm.

In some embodiments, the gas mixture comprises oxygen (O)₂). In some such embodiments, including those in which the gas mixture comprises ambient air or ventilation air, or even a high purity oxygen mixture. In some, but not necessarily all instancesIn embodiments, the gas mixture has a relatively high concentration of oxygen (e.g., prior to exposure to the electrochemical cell). Certain aspects of the systems and methods described herein (e.g., selection of particular electroactive species, methods of treating gases in the system, etc.) may facilitate the ability to capture a target gas in a gas mixture (where oxygen is present) without harmful interference. In some embodiments, oxygen is present in the gas mixture (e.g., prior to exposure to the electrochemical cell) at a concentration of: greater than or equal to 0 vol%, greater than or equal to 0.1 vol%, greater than or equal to 1 vol%, greater than or equal to 2 vol%, greater than or equal to 5 vol%, greater than or equal to 10 vol%, greater than or equal to 20 vol%, greater than or equal to 50 vol%, greater than or equal to 75 vol%, greater than or equal to 90 vol%, greater than or equal to 95 vol%, greater than or equal to 99 vol%, greater than or equal to 99.9 vol%, greater than or equal to 99.99 vol%, or higher. In some embodiments, the oxygen is present in the gas mixture at a concentration of: less than or equal to substantially 100 vol%, less than or equal to 99.9999 vol%, less than or equal to 99.999 vol%, less than or equal to 99.99 vol%, less than or equal to 99.9 vol%, less than or equal to 99 vol%, less than or equal to 95 vol%, less than or equal to 90 vol%, less than or equal to 75 vol%, less than or equal to 50 vol%, less than or equal to 25 vol%, less than or equal to 21 vol%, less than or equal to 10 vol%, less than or equal to 5 vol%, less than or equal to 2 vol%, or less. Combinations of these ranges are possible. For example, in some embodiments, oxygen is present in the gas mixture at a concentration of: greater than or equal to 0% and less than or equal to substantially 100% by volume (e.g., for high O applications)₂A combustion process), greater than or equal to 0 vol% and less than or equal to 50 vol%, greater than or equal to 0 vol% and less than or equal to 21 vol% (e.g., during incomplete combustion), and greater than or equal to 10 vol% and less than or equal to 25 vol% (e.g., for a ventilation air or direct air capture process).

In some embodiments, the gas mixture subjected to at least partial gas separation comprises water vapor. For example, the gas mixture may include water vapor, as the gas mixture is or includes ambient air or ventilation air. In some cases, the gas mixture (e.g., prior to exposure to the electrochemical cell) has a relatively high relative humidity. For example, in some embodiments, the gas mixture has a relative humidity greater than or equal to 0%, greater than or equal to 5%, greater than or equal to 10%, greater than or equal to 25%, greater than or equal to 50%, greater than or equal to 75%, greater than or equal to 90%, or higher at least one temperature in the range of-50 ℃ to 100 ℃. In some embodiments, the gas mixture has a relative humidity of less than or equal to 100%, less than or equal to 95%, less than or equal to 90%, less than or equal to 75%, less than or equal to 50%, less than or equal to 25%, less than or equal to 10%, or less at least one temperature in the range of-50 ℃ to 100 ℃.

The gas mixture that undergoes at least partial separation by exposure to the electrochemical cell (e.g., the input gas mixture) may have any of a variety of pressures when exposed to the electrochemical cell. For example, the gas mixture may have the following total pressure (e.g., in a gas separation system): greater than or equal to 0.1 bar, greater than or equal to 0.2 bar, greater than or equal to 0.5 bar, greater than or equal to 1 bar, greater than or equal to 2 bar, and/or up to 5 bar, up to 8 bar, up to 10 bar, or higher. The gas mixture may have any of these pressure values while containing the target gas and oxygen in any of the above concentration ranges.

In accordance with one or more embodiments, the electrochemical cells generally described herein may be operated to at least partially separate a gas mixture. In some embodiments, the gas mixture is a gas stream. In some embodiments, the gas mixture is air in a ventilation structure, and in some cases, the air is ambient air (e.g., in direct air capture embodiments). However, the gas mixture is not limited to such an embodiment. For example, in some embodiments, the gas mixture is a gas from an industrial process (e.g., a flue gas). In some embodiments, an electrochemical cell can be operated to perform a gas separation process involving a gas mixture. For example, the electrochemical cell may be operated to remove a portion of the target gas from the gas mixture. In some such cases, operation of the electrochemical cell involves exposing the gas mixture to the electrochemical cell. The gas mixture may be exposed to the electrochemical cell such that the target gas bonds with the first electroactive species to produce a treated gas mixture having a lower amount of the target gas than the gas mixture initially exposed to the electrochemical cell (sometimes referred to as the "input gas mixture").

The process of at least partially separating the target gas from the gas mixture may comprise applying a potential difference across the electrochemical cell. One of ordinary skill, with the benefit of this disclosure, will understand how to apply an electrical potential across an electrochemical cell. One way of applying the electrical potential is to connect the negative and positive electrodes to a suitable power source capable of polarizing the negative and positive electrodes. In some embodiments, the power supply is a dc voltage to the system. Some non-limiting examples include batteries, power grids, regenerative power sources (e.g., wind generators, photovoltaic cells, tidal power generators), generators, and the like. The power source may include one or more of such power sources (e.g., batteries and photovoltaic cells).

In some embodiments, the process further comprises exposing the electrochemical cell to a gas mixture. The potential difference may be applied during at least a portion of the time that the gas mixture is exposed to the electrochemical cell. However, some embodiments include applying a potential difference prior to exposing the gas mixture to the electrochemical cell. In other words, in some embodiments, the step of exposing the gas pressure to the electrochemical cell occurs during the step of applying a potential difference across the electrochemical cell and/or after applying a potential difference across the cell. In some embodiments, exposing the gas mixture to the electrochemical cell includes exposing the gas mixture to a target gas (e.g., CO)₂) Is introduced into the electrochemical cell to bond the target gas with the first electroactive species to produce a treated gas mixture (e.g., a treated gas stream).

According to some embodiments, applying a positive voltage to the electrochemical cell during the charging mode causes a redox half-reaction at the negative electrode, wherein the electroactive species is reduced. As discussed herein, the electroactive species of the negative electrode is selected for its following characteristics: to a target gas (e.g., CO) when it is in a reduced state relative to when it is in an oxidized state₂) Has higher affinity. By reducing the electroactive species and passing a gas mixture (e.g., ventilation air, ambient air, industrial gas flow) across the face of the negative electrode, a target gas (e.g., CO)₂) May be bonded to the electroactive species. In this manner, the target gas may be removed from the gas mixture to provide a treated gas mixture (e.g., including a smaller amount of the target gas than the gas mixture).

As a non-limiting example, in some embodiments in which the electroactive species of the negative electrode is an optionally substituted quinone, the electroactive species may be reduced to at least one of its reduced states according to reaction (1) below:

again as a non-limiting example, in some embodiments in which the electroactive species is reduced in the presence of a target gas comprising carbon dioxide, the following reaction (2) occurs:

according to some embodiments, when the first electroactive species (e.g., an optionally substituted quinone) is reduced at the negative electrode, the second electroactive species (e.g., a redox-active polymer, such as polyvinylferrocene) is oxidized at the positive electrode. During the charging mode, oxidation of the second electroactive species provides an electron source for driving reduction of the first electroactive species.

Again as a non-limiting example, in some embodiments in which the electroactive species of the positive electrode comprises polyvinylferrocene, the second electroactive species may be oxidized according to reaction (3) below:

although each of reactions (1) to (3) is shown to occur in one direction, some reversibility may be exhibited. As will be appreciated by those of ordinary skill in the art, similar reactions may occur with the use of different substances.

In some embodiments, the second electroactive species comprises an intercalation compound. For example, the second electroactive species may comprise a metal ion intercalating compound. One exemplary class of intercalation compounds includes metal oxides. The intercalation compounds may include intercalation compounds of alkali metal ions, such as lithium and/or sodium ions. In some embodiments, the intercalation compound includes an alkali metal ion transition metal oxide (e.g., lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and/or lithium oxides comprising cobalt, manganese, and/or nickel). In some embodiments, the intercalation compound comprises an alkali metal transition metal polyoxoanion (polyoxanion), for example, a lithium transition metal phosphate. One example of a suitable lithium transition metal phosphate for the positive electrode is lithium iron phosphate (LiFePO)₄). In some embodiments, during the charging mode, as an alkali metal ion intercalation compound (e.g., LiFePO)₄) Oxidation of the form of the second electroactive species provides an electron source for driving reduction of the first electroactive species while releasing alkali metal ions (e.g., lithium ions) that can shuttle through the electrolyte (e.g., on or within the separator (when present)) toward the negative electrode to maintain charge balance and complete the electrochemical circuit. Conversely, during discharge mode, the reduction of the second electroactive species in the form of an alkali metal ion intercalation compound provides a trap for electrons from the oxidation of the first electroactive species, while alkali metal ions (e.g., lithium ions) can shuttle from a region proximate to the negative electrode toward the positive electrode through the electrolyte (e.g., on or at the separator (when present))Internal), alkali metal ions can intercalate into the intercalation compound and maintain charge balance in the positive electrode.

According to one or more embodiments, upon charging the electrochemical cell by applying a potential difference across the positive electrode and the negative electrode, electrons flow from a portion of the second electroactive species on the positive electrode (e.g., a ferrocene (Fc) cell in a pVFc-CNT composite) to the negative electrode through an external circuit, thereby oxidizing the second electroactive species (e.g., by oxidizing ferrocene to ferrocene

(Fc⁺) (as shown in reaction (3)). At the negative electrode, a first electroactive species (e.g., an optionally substituted quinone unit in a CNT composite) is present in a target gas (e.g., CO)₂) (which diffuses into the negative electrode) in the presence of a reducing agent (e.g., to the semiquinone or dianionic form of the optionally substituted quinone). The electroactive species in its reduced state (e.g., the divalent anion of an optionally substituted quinone) is readily covalently bonded to CO₂Binding, as shown in equation (2), forms a complex.

The potential difference applied across the electrochemical cell during the charging mode may have a particular voltage. The potential difference applied across the electrochemical cell may depend, for example, on a standard reduction potential for generating at least one reduced state of the first electroactive species, and a standard reduction potential for interconversion between a reduced state and an oxidized state of the second electroactive species (when present). In some embodiments, the potential difference is at least 0V, at least 0.1V, at least 0.2V, at least 0.5V, at least 0.8V, at least 1.0V, at least 1.5V, or higher. In some embodiments, the potential difference is less than or equal to 2.0V, less than or equal to 1.5V, less than or equal to 1.0V, less than or equal to 0.5V, or lower. Combinations of these voltages are also possible. For example, in some embodiments, the potential difference applied across the electrochemical cell is at least 0.5V and less than or equal to 2.0V. Other values are also possible.

Fig. 3A shows an exploded view of an exemplary electrochemical cell 100a operating in a charging mode, according to one or more embodiments. The components of electrochemical cell 100a may be similar to those described for electrochemical cell 100 described herein with respect to fig. 2. As shown in fig. 3A, according to some embodiments, a potential difference is applied across electrochemical cell 100a using power source 140a and wiring 150 a. According to certain embodiments, this results in a flow of electrons 160a in the external circuit 150a, directing the electrons toward the primary electrically active composite layer 114a of each negative electrode 110 a. In some embodiments, a redox half-cell reaction occurs at the electroactive composite layer 114a to reduce the first electroactive species immobilized in the layer 114 a. According to certain embodiments, in its reduced state, the electroactive species exhibits an increased affinity for a target gas (not shown) in the gas mixture. The target gas of the gas flow may permeate the gas permeable layer 112a of the negative electrode to bond with the reducing material of the composite layer 114 a.

In some embodiments, a relatively large amount of the target gas is removed from the gas mixture during the processes described herein. In some cases, removal of relatively large amounts of target gases may be beneficial for any of a variety of applications, such as for environmental reasons capturing gases that may be harmful if released into the atmosphere. As an example, in some embodiments, the target gas includes carbon dioxide, and removing a relatively large amount of carbon dioxide from the gas mixture may be beneficial to limit the greenhouse gas impact of a process (e.g., an industrial process or a transportation process) or even reduce the amount of carbon dioxide in a room or atmosphere (whether for thermodynamic reasons of heating and air conditioning processes or for environmental reasons).

In some embodiments, the amount of target gas in the treated gas mixture (e.g., the gas mixture from which an amount of target gas is removed upon exposure to the electrochemical cell) is less than or equal to 50%, less than or equal to 25%, less than or equal to 10%, less than or equal to 5%, less than or equal to 2%, less than or equal to 1%, less than or equal to 0.5%, less than or equal to 0.1%, or less of the amount (in volume percent) of the target gas in the original gas mixture prior to treatment (e.g., the amount of target in the gas mixture prior to exposure to the electrochemical cell). In some embodiments, the amount of target gas in the treated gas mixture is greater than or equal to 0.001%, greater than 0.005%, greater than or equal to 0.01%, greater than or equal to 0.05%, greater than or equal to 0.1%, greater than or equal to 0.5%, greater than or equal to 1%, greater than or equal to 2%, greater than or equal to 5%, or more of the amount (in volume percent) of the target gas in the original gas mixture prior to treatment.

In some embodiments, the amount of target gas in the treated gas mixture (e.g., the gas mixture from which an amount of target gas is removed upon exposure to the electrochemical cell) is less than or equal to 50%, less than or equal to 25%, less than or equal to 10%, less than or equal to 5%, less than or equal to 2%, less than or equal to 1%, less than or equal to 0.5%, less than or equal to 0.1%, or less of the amount (in mole percent) of the target gas in the original gas mixture prior to separation (e.g., the amount of target in the gas mixture prior to exposure to the electrochemical cell). In some embodiments, the amount of target gas and treated gas mixture is greater than or equal to 0.001%, greater than 0.005%, greater than or equal to 0.01%, greater than or equal to 0.05%, greater than or equal to 0.1%, greater than or equal to 0.5%, greater than or equal to 1%, greater than or equal to 2%, greater than or equal to 5%, or more of the amount (in mole percent) of the target gas in the original gas mixture prior to treatment.

In some embodiments, the methods described herein can be used to remove an amount of a target gas from a gas mixture (e.g., during and/or after application of an electrical potential across an electrochemical cell) while removing a relatively small amount of any oxygen (O) that may be present in the gas mixture₂). In some such cases, this is beneficial because reactivity with oxygen may be detrimental to the performance of the systems and methods (e.g., reduced capture efficiency, damage to components of the electrochemical cell, etc.). Any of the many features described herein, alone or in combination, can contribute to the ability to remove an amount of a target gas from a gas mixture while removing a relatively small amount of any oxygen that may be present in the gas mixture. For example,the use of a first electroactive species in the negative electrode having a reduced state where the species is capable of bonding with the target gas, but for which the reactivity with oxygen is thermodynamically unfavorable, may allow for the removal of relatively large amounts of the target gas, allowing for little or no removal of oxygen.

One non-limiting way in which the target gas may be removed with little or no oxygen removal from the gas mixture is by applying a potential across the electrochemical cell during at least a portion of operation. For example, it has been found in the context of the present disclosure that a potential (e.g., a first potential) sufficient to reduce a first electroactive species to at least one reduced state in which the species is capable of reacting with a target gas may be applied across an electrochemical cell, but the potential is insufficient to achieve such a state: in which state the substance (or the electrode itself) is capable of reacting with oxygen (e.g., to form superoxide ions or superoxide dianions). Judicious selection of the first electroactive species may allow such an electrical potential to be applied, while some conventional electroactive species may not. The potential applied across the electrochemical cell can be such that the electrode potential at the negative electrode is positive (e.g., greater than or equal to 10mV, greater than or equal to 50mV, greater than or equal to 100mV, greater than or equal to 200mV, greater than or equal to 5mV, and/or up to 1V or more) relative to a standard reduction potential for interconversion of oxygen with superoxide ions, or superoxide ions with peroxide ions.

In some embodiments, an amount of a target gas (e.g., CO)₂) Is removed from the gas mixture during and/or after the application of the potential difference, and less than or equal to 0.1%, less than or equal to 0.05%, less than or equal to 0.001%, and or as low as 0.0001%, as low as 0.00001% or less (by volume%) of any oxygen present in the gas mixture is removed from the gas mixture. In some embodiments, an amount of the target gas is removed from the gas mixture during and/or after application of the potential difference, and no oxygen is removed from the gas mixture (e.g.,during the removal of the target gas). These ranges of oxygen removal in the gas mixture can be achievable even when oxygen is present in the gas mixture in relatively high amounts (e.g., greater than or equal to 0 vol%, greater than or equal to 1 vol%, greater than or equal to 5 vol%, greater than or equal to 10 vol%, greater than or equal to 21 vol%, greater than or equal to 50 vol%, and/or up to 75 vol%, up to 90 vol%, up to 99 vol%, essentially 100 vol%, or higher).

In some, but not necessarily all, instances when oxygen is present in the gas mixture, an amount of oxygen is removed from the gas mixture during at least a portion of the time that an amount of the target gas is removed from the gas mixture (e.g., during and/or after the application of the electrochemical potential). In some such embodiments, the ratio of the amount of target gas removed to the amount of oxygen removed is greater than or equal to relatively high. The ratio may be relatively high in the following cases: in such cases, the electroactive species in at least one reduced state formed during and/or after application of a potential across the electrodes is in contact with the target gas (e.g., CO)₂) The reaction between them is thermodynamically more favorable than the reaction of the substance with oxygen. In some embodiments, the ratio of the amount of target gas removed to the amount of oxygen removed is greater than or equal to 10: 1, greater than or equal to 100: 1, greater than or equal to 1,000: 1, greater than or equal to 10,000: 1, and/or up to 100,000: 1, up to 1,000,000, up to 10,000,000: 1, up to 100,000: 1, up to 1,000,000,000: 1, or higher.

In some embodiments, a positive electrode (e.g., positive electrode 120a in fig. 3A) is used as an electron source during operation in a charging mode. In fig. 3A, according to certain embodiments, a corresponding redox half-cell reaction occurs at the complementary electroactive composite layer 124a of the positive electrode 120a to oxidize its electroactive species. The oxidation reaction can release electrons from a complementary electroactive species (e.g., polyvinylferrocene). These electronic reaction products may then travel through the base layer 122a and/or the external wiring 150a to complete the circuit, according to some embodiments. According to certain embodiments, the separator 130a separates the positive electrode 120a and the negative electrode 110 a.

According to one or more embodiments, the operation of the electrochemical cell further comprises: a second potential difference is applied across the electrochemical cell to release the target gas bonded to the first electroactive species. In some embodiments, releasing the target gas produces a product or treated gas mixture (e.g., a target gas-rich gas mixture, such as a target gas-rich gas stream) having a higher concentration of the target gas than the original gas mixture exposed to the electrochemical cell. According to some embodiments, after operating the electrochemical cell in the charging mode, during which the target gas bonds with the first electroactive species of the negative electrode, for a period of time, operation may be switched to the discharging mode. During operation in the discharge mode, the applied voltage is switched to provide a flow of electrons in a direction opposite to the flow of electrons during the charge mode. When operating in a discharge mode, a negative voltage may be applied across the electrochemical cell. In the discharge mode, a redox half-reaction occurs at the negative electrode, wherein the first electroactive species of the negative electrode is oxidized. During operation in the discharge mode, the target gas may be released from the electroactive species bonded thereto in the negative electrode.

According to some embodiments, wherein the electroactive species of the negative electrode is an optionally substituted quinone, the electroactive species is oxidized during the discharge mode according to reaction (4) below:

according to some embodiments, in which the electroactive species is oxidized after bonding with the target gas comprising carbon dioxide, the following reaction (5) may occur:

according to some embodiments, when a first electroactive species (e.g., comprising an optionally substituted quinone) is oxidized at the negative electrode, a second electroactive species (e.g., polyvinylferrocene) is reduced as the positive electrode. During the discharge mode, the reduction of the second electroactive species acts as an electron trap.

According to some embodiments, wherein the electroactive species of the positive electrode comprises polyvinylferrocene, the second electroactive species is reduced according to reaction (6) below:

although each of reactions (4) to (6) is shown to occur in one direction, some reversibility may be exhibited. Similar reactions may occur with the use of different substances, as will be appreciated by one of ordinary skill in the art, given the benefit of this disclosure.

According to some such embodiments, the electroactive species of the negative electrode is oxidized by discharging the electrochemical cell when the polarization of the external circuit is changed to allow electrons to flow in the opposite direction compared to the charging process. According to certain embodiments, the quinone is optionally substituted with CO₂The covalent bond formed between the molecules is broken (as shown in reaction (5)), thereby allowing CO to be generated₂Gas is released to diffuse out of the negative electrode, and electrons flowing to the positive electrode will Fc⁺The unit is reduced to Fc (as shown in reaction (6)). According to some such embodiments, polyvinylferrocene may be used as an electron source for the reduction of the optionally substituted quinone or as an electron trap for the oxidation of the carbon dioxide adduct of the optionally substituted quinone.

During the discharge mode, the potential difference across the electrochemical cell may have a particular voltage. For example, in some embodiments, the potential difference may be less than 0V, less than or equal to-0.5V, less than or equal to-1.0V, or less than or equal to-1.5V. In some embodiments, the potential difference may be at least-2.0V, at least-1.5V, at least-1.0V, or at least-0.5V. Combinations of these voltages are also possible, for example at least-2.0V and less than or equal to-0.5V. Other values are also possible.

Fig. 3B illustrates an exploded view of an exemplary electrochemical cell 100B operating in a discharge mode according to one or more embodiments. According to certain embodiments, the components of electrochemical cell 100b are the same as those of cell 100a of fig. 3A. However, according to certain embodiments, the voltage applied by the power source 140b has been changed to produce a potential difference that reverses the direction of electron flow 160b through the external wiring 150b relative to the direction of electron flow 160a in fig. 3A. According to some embodiments, in the discharge mode, a redox half-cell reaction occurs at the electroactive composite layer 114b of the negative electrode 110b to oxidize the first electroactive species immobilized in the layer 114 b. In some embodiments, the first electroactive species exhibits a reduced affinity for the target gas in its oxidized state, resulting in release of the target gas from the electroactive material. The released target gas may exit through the gas permeable layer 112b and may be directed toward further processing, sequestration, or other desired destination. Meanwhile, in some embodiments, the positive electrode 120b functions as an electron trap during operation in the discharge mode. According to some embodiments, a half-cell reaction occurs at the complementary electroactive composite layer 124b of the positive electrode 120b to reduce the second electroactive species. In some embodiments, during the reduction reaction, electrons that have traveled through the wiring 150b and the base layer 122b bond with the complementary electroactive species, completing the circuit. According to some, but not necessarily all, embodiments, the separator 130b separates the positive electrode 120b from the negative electrode 110 b.

According to one or more embodiments, one or more electrochemical cells as described herein may be incorporated into a gas separation system. According to any of the embodiments described herein, the gas separation system may comprise a plurality of electrochemical cells in fluid communication with the gas inlet and the gas outlet.

The gas separation system may include an external circuit connecting the negative electrode (or first and second negative electrodes (when both are present)) and the positive electrode of each electrochemical cell to a power supply configured to apply a potential difference across the negative and positive electrodes of each electrochemical cell.

Fig. 4 illustrates a schematic diagram of an exemplary gas separation system 400 in accordance with one or more embodiments. According to certain embodiments, the system 400 includes a housing 460 having an inlet 470 and an outlet 480. Located within the housing is an electrochemical cell 405. Although only one battery 405 is shown in fig. 4 for clarity, it will be readily understood that a plurality of batteries 405 may be located in the enclosure 460. According to some embodiments, a power source 440, which may be located inside or outside the enclosure 460, is connected to the battery 405. According to certain embodiments, the negative electrode 410 is connected to the power source 440 through a wire 450a, and the positive electrode is connected through a wire 450 b. When a voltage is applied to operate the battery in a charging mode, a gas mixture (e.g., a flow of gas, such as ventilation air or ambient air) to be at least partially separated is delivered through inlet 470, as described elsewhere herein. In some embodiments, the gas mixture includes a target gas designed to be at least partially removed by the system 400. The gas mixture then passes close to the cell 405, in particular close to the negative electrode 410. In some embodiments, the first electroactive species in at least one of its reduced states in the negative electrode 410 bonds with the target gas, removing at least a portion of the target gas from the gas mixture. According to certain embodiments, optional second negative electrode 410, second separator 420, and corresponding wiring 450a are shown in dashed lines. While the embodiments shown in fig. 4 and other figures include an optional cover, it should be understood that the electrochemical cell may be located in a variety of environments, such as in-line in a conduit, or otherwise without a cover.

Fig. 5A shows a schematic diagram of an exemplary system for performing a gas separation process during a charging mode, according to one or more embodiments. In fig. 5A, according to certain embodiments, a potential difference is applied across each electrochemical cell such that each electrochemical cell operates in a charging mode. According to certain embodiments, in the charging mode, a redox reaction (e.g., reduction) of the first electroactive species in the negative electrode 510 increases the affinity between the electroactive species and the target gas 590. A gas mixture 575 containing a target gas 590 is introduced into the system and passed adjacent the negative electrode 510. According to certain embodiments, the increased affinity causes the target gas (e.g., CO)₂) And an electroactive materialAnd (5) material bonding. In this manner, at least a portion of the target gas is separated from gas mixture 575 to produce treated gas mixture 585.

In some embodiments, the gas separation system includes a plurality of electrochemical cells, and the flow field is between at least some (e.g., some or all) of the plurality of electrochemical cells. As an illustrative example, fig. 5B shows a schematic diagram of an exemplary system according to one or more embodiments that includes a flow field 511 separating electrochemical cells 500, which electrochemical cells 500 perform a gas separation process during a charging mode. It will be appreciated that when the first object is between the second object and the third object, it may be between the first object and the entirety of the second object, or between the first object and a portion of the second object. In some embodiments, the flow field between two adjacent electrochemical cells is directly adjacent to each adjacent electrochemical cell such that there are no intervening structures/layers between the flow field and the electrochemical cell. However, in some embodiments, the flow field between two adjacent electrochemical cells is indirectly adjacent to one or both cells such that there are one or more intermediate structures/layers, such as electrically conductive solids.

A flow field generally refers to a solid structure configured to define a path through which a fluid may flow. In some cases, the flow field includes a solid article that defines apertures or channels for fluid flow while allowing fluid exposure to adjacent structures. Suitable materials for the solid article of the flow field include, but are not limited to, polymeric materials (e.g., plastics), metal/metal alloys, graphite, composite materials (e.g., graphite-polymer composites). In some embodiments, the flow field comprises a solid article comprising one or more surfaces having patterned channels. The channel pattern can be selected to effectively distribute fluid (e.g., gas) across one or more dimensions of the flow field. Suitable channel patterns include, but are not limited to, serpentine, parallel, and interdigitated. Fig. 5C, 5D, and 5E show schematic side view illustrations of faces of a flow field 511a having a serpentine pattern, a flow field 511b having a parallel pattern, and a flow field 511C having an interdigitated pattern, each having a direction of fluid flow as indicated by the arrows, according to certain embodiments. The flow field channel pattern may be formed, for example, by etching, cutting, stamping, molding, grinding, or additive manufacturing. In some embodiments, the flow field comprises a porous solid. For example, the flow field may comprise carbon fiber paper, felt, or cloth, or metal foam.

In fig. 5B, gas 590 from the fluid mixture 575 is distributed along a face region of the electrode 510 via the flow field 511 (e.g., via channels not shown). It has been recognized in the context of the present disclosure that the flow field may help distribute the gas mixture relatively uniformly over the electrode and may help control the duration of gas exposure to the electrode (e.g., to promote effective capture of the target gas). By utilizing a larger percentage of the electrode area (e.g., including electroactive species in at least one reduced state) to bind the target gas, a relatively uniform distribution of the gas may improve efficiency. In some embodiments, during at least a portion of the charging process, the flow of the gas mixture across the negative electrode face area in the system is within 50%, within 25%, within 15%, within 10%, within 5%, within 2%, within 1%, or less of the average flow across the entire negative electrode face area during the charging process.

According to certain embodiments, the system 400 shown in fig. 4 may also be operated in a discharge mode by varying the voltage applied from the power source 440 to cause a flow of electrons in a direction opposite to the flow in the charge mode. This change causes a different redox reaction to occur at the negative electrode 410, for example, a redox reaction in which the first electroactive species of the negative electrode is oxidized. Such a change in the oxidation state of the electroactive species may cause the target gas to be released from the electroactive species to produce a treated gas mixture having a higher amount of the target gas than the original gas mixture (e.g., the input gas mixture). The treated gas mixture may exit through outlet 480 or an alternative outlet (not shown).

In some, but not necessarily all, embodiments, because operation in the discharge mode causes the target gas material to be released, simultaneous introduction of gas streams through inlet 470 that will undergo at least partial gas separation will have the opposite effect. Thus, during operation in the discharge mode, the inlet 470 is closed, or a different flow (e.g., waste stream) is redirected to the inlet. However, in certain embodiments, a second portion of the gas mixture to be subjected to at least partial gas separation is introduced via inlet 470 while operation in discharge mode occurs.

According to some, but not necessarily all, embodiments, a gas separation system includes a first electrochemical cell stack and a second electrochemical cell stack. Each of the first and second sets may include one or more electrochemical cells as described throughout this disclosure. The first and second sets may be operated in parallel in an alternating manner such that one battery operates in a charging mode and captures a target gas (e.g., CO) from a gas mixture₂) While the other battery pack operates in a discharge mode and releases the target gas (e.g., CO)₂). The system may include a separate cover for each of the electrochemical cells. The system may further comprise conduits and valves arranged to direct the fluid in a desired manner. At a given time, the gas separation system may allow for continuous or semi-continuous separation of a gas mixture (e.g., a gas stream) with the gas mixture directed to the stack operating in a charge/capture mode, while a separate target gas-rich treated mixture is produced by an additional stack operating in a discharge/release mode. Further, additional electrochemical cell stacks may be added in parallel or in series, as desired for the application.

An example of one embodiment of such a gas separation system is shown in fig. 6. In gas separation system 600, a first electrochemical cell stack 605a is located in a first enclosure 660a and a second electrochemical cell stack 605b is located in a second enclosure 660 b. A conduit connects the gas inlet 670 with the

mask inlets

672a and 672 b. The valve 684 may be arranged to direct fluid to either of the

groups

605a and 605b, depending on which group is currently operating in the charging mode.

In operation, containing a target gas (e.g., CO)₂) Is/are as followsThe gas stream may be introduced to the gas separation system 600 through an inlet 670. According to certain embodiments, when first cell stack 605a is operating in a charging/capture mode, valve 684 may be arranged to direct a flow to be proximate to first cell stack 605a where the target gas may bond with the electroactive species in cell 605a to produce a treated gas mixture (treated gas mixture having a reduced concentration of the target gas) that then exits enclosure 660a through outlet 673 a. An additional valve 686a downstream of the housing outlet 673a may be arranged to direct the treated gas flow through the treated gas outlet 680.

When the first battery 605a is operating in a charging mode, the second battery 605b may be operating in a discharging mode, wherein previously accumulated target gas is released from the electroactive material of the second battery 605 b. In the embodiment shown, the valve 684 is arranged to isolate the gas mixture from the battery 605b operating in the discharge mode. The release of the target gas from the stack 605b produces a target gas-rich gas mixture that subsequently exits the enclosure 660b through outlet 673 b. The valve 686b may be arranged to separate the target gas rich gas mixture from the treated stream outlet 680 and direct the target gas rich stream to a waste outlet 682b where it may be further treated, stored, etc.

After operating for a period of time in the manner described above, the modes of the

batteries

605a and 605b may be interchanged. The first cell set 605b is then operated in a discharge mode to release the accumulated target gas from its electrodes. During this period, the valve 684 is rearranged to isolate the process stream from the first battery stack 605 a. During this period, valve 686a is rearranged to direct the target-rich stream toward waste outlet 682 a.

At the same time, the operation of the second battery pack 605b is reversed such that they operate in a charging mode to capture the target gas and produce a treated stream. An inlet valve 684 is arranged to direct the process gas mixture from the system inlet 670 to the second stack 605b via the second shield inlet 672b by a conduit. Outlet valve 686b is rearranged to direct the treated gas mixture to outlet 680.

In this manner, according to certain embodiments,

different battery packs

605a and 605b may be cycled through the modes while together providing continuous or semi-continuous separation of the gas streams containing the target gases. While the particular embodiment shown in fig. 6 shows one particular arrangement of system components (e.g., valves, conduits, inlets and outlets), it will be appreciated that different configurations may be provided to still meet the goal of providing a continuous operation with separate streams of treated and target-rich gas.

Fig. 7A shows a schematic diagram of an exemplary system similar to the system of fig. 6, which performs a gas separation process in which a first cell stack 705a operates in a charging mode and a second cell stack 705b operates in a discharging mode, according to one or more embodiments. In the charging mode, the applied voltage causes a redox reaction (e.g., reduction) of the electroactive species in the negative electrode 710a, which increases the affinity between the first electroactive species and the target gas 790. A gas stream 575 containing a target gas 590 is introduced into the cell stack 705a and passed adjacent the negative electrode 510 a. The increased affinity causes the target gas (e.g., CO)₂)790 are bonded to the electroactive material. In this manner, at least a portion of the target gas is separated from the gas stream 775 to produce a treated gas stream 785.

According to certain embodiments, in the discharge mode, the second applied voltage causes a flow of electrons in a direction opposite to the flow of electrons during the charge mode, causing a second redox reaction (e.g., oxidation) of the first electroactive species in the negative electrode 710b, which reduces the affinity between the electroactive species and the target gas 790. The released target gas 790 enters the target gas-rich gas mixture 787.

FIG. 7B shows a schematic diagram of an exemplary system similar to that of FIG. 6, which performs a gas separation process in which the mode of operation shown and described in FIG. 7A is reversed. In fig. 7B, the voltage applied across the first cell set 705a has changed and the cell 705a operates in a discharge mode to release the stored target gas 790 from the negative electrode 710a to produce a target gas-rich gas mixture, according to certain embodiments. At the same time, the voltage applied across second battery pack 705b has also changed, causing them to operate in a charging mode. The target gas 790 of the process stream 775 bonds with the negative electrode 710b to produce a processed stream 785.

As described above, the gas separation system may include a plurality of electrochemical cells electrically connected in parallel or in series. Persons of ordinary skill in the art, with the benefit of this disclosure, will generally understand how to electrically connect electrochemical cells to form an electrical circuit. Such connection may be achieved by establishing a conductive path for electrons to flow between the electrodes of the electrochemical cell (in other words, establishing electrical coupling between the electrodes). In some cases, the conductive pathway may be established by one or more conductive solid materials (e.g., conductive metals, alloys, polymers, composites, carbonaceous materials, or combinations thereof). For example, the conductive pathway may be established by routing the electrodes of the electrochemical cell. The electrochemical cell may have any of the above configurations. For example, in some embodiments, some or all of the electrochemical cells in the system have a single negative electrode (e.g., comprising a first electroactive species), a single positive electrode (e.g., comprising a second electroactive species), and an optional separator between the first positive electrode and the second positive electrode. Fig. 10A shows a schematic diagram of an arrangement of electrochemical cells 1100 in one such system 1000, wherein each electrochemical cell 1100 sequentially includes a negative electrode 1010, an optional separator 1020, and a positive electrode 1030, according to certain embodiments. A gas mixture 1075 containing a target gas can be introduced into the system such that the gas mixture 1075 passes proximate to the negative electrode 1010 of the first electrochemical cell 110 and the adjacent positive electrode 1030 of the second electrochemical cell 1100. Although fig. 10A shows three electrochemical cells 1100, it is to be understood that any of a number of suitable number of electrochemical cells (e.g., electrically connected in parallel or series) may be employed in a gas separation system, depending on the requirements of a particular application as desired.

In other embodiments, the electrochemical cells of some or all of the gas separation systems include a positive electrode (e.g., comprising a second electroactive species), a first negative electrode (e.g., comprising a first electroactive species), a second negative electrode (e.g., comprising a first electroactive species), a first separator between the first negative electrode and the positive electrode, and a second separator between the positive electrode and the second negative electrode. Examples of such electrochemical cells are shown in fig. 1B and 2.

Fig. 10B illustrates a schematic diagram of a configuration in which a plurality of electrochemical cells 1100 in the system 1000 are electrically connected in parallel, according to some embodiments. In a parallel configuration, each negative electrode 1010 is electrically coupled to a first terminal (e.g., of a power source) and each positive electrode 1030 is electrically coupled to a second terminal (e.g., of the power source). For example, in fig. 10B, according to certain embodiments, each negative electrode 1010 is electrically coupled to a first terminal of a power source through wiring 115, and each positive electrode 1030 is electrically coupled to a second terminal of the power source through wiring 116.

Fig. 10C shows a schematic of a configuration in which a plurality of electrochemical cells 11000 are electrically connected in series in a system 1000, according to some embodiments. In a series configuration, the positive electrode of a first electrochemical cell of the system is electrically connected with the negative electrode of a second electrochemical cell. For example, in fig. 10B, according to certain embodiments, the negative electrode 1010 of the first electrochemical cell 1100a is electrically connected to the positive electrode 1030 of the second electrochemical cell 1100B by a wire 1017, and the negative electrode 1010 of the second electrochemical cell 1100B is electrically connected to the positive electrode 1030 of the third electrochemical cell 1100c by a wire 1018. Further, according to certain embodiments, the positive electrode 1030 of the first electrochemical cell 1100a is electrically coupled to a first terminal of a power source via wiring 114 and the negative electrode 1030 of the third electrochemical cell 1100a is electrically coupled to a second terminal of the power source via wiring 119.

It has been determined in the context of the present disclosure that certain configurations of gas separation systems comprising a plurality of electrochemical cells electrically connected in series can facilitate relatively efficient charge transport and/or gas transport. For example, in some embodiments, the conductive material between electrochemical cells may establish a conductive path rather than using external wiring. For example, a gas separation system may include a first electrochemical cell and a second electrochemical cell electrically connected in series, where the electrical connection is established through one or more electrically conductive materials between the first electrochemical cell and the second electrochemical cell. Any of a variety of suitable electrically conductive materials may be located between the electrochemical cells to establish an electrical connection between, for example, the negative electrode of a first electrochemical cell and the positive electrode of a second electrochemical cell. For example, the conductive material may be a conductive solid. The conductive solid may include, for example, a metal and/or metal alloy (e.g., steel, silver metal/alloy, copper metal/alloy, aluminum metal/alloy, titanium metal/alloy, nickel metal/alloy). In some embodiments, the conductive solid comprises a carbonaceous material (e.g., graphite, single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon black, carbon mats (e.g., carbon nanotube mats), ketjen black, carbon black Super P, graphene, etc.). In some embodiments, the carbonaceous material is a porous carbonaceous material as described elsewhere herein. In some embodiments, the conductive solid comprises a composite of the conductive solid and a binder resin. In some embodiments, the conductive solid between electrochemical cells comprises a conductive polymer material.

In some, but not necessarily all, embodiments, the electrically conductive material between the electrochemical cells comprises bipolar plates. It should be understood that in the context of the present disclosure, the plate need not be flat. Bipolar plates are known to those skilled in the art and are commonly used in fields other than gas separation, such as fuel cells. The bipolar plate may be configured to separate a fluid (e.g., gas) contacting the positive electrode from a fluid contacting the negative electrode. The bipolar plates may comprise an electrically conductive solid, such as steel, titanium, or graphite.

In some embodiments, at least some of the plurality of electrochemical cells (e.g., connected in series) are separated by a flow field. As described above, positioning of the flow field between adjacent electrochemical cells may promote beneficial gas distribution and relatively efficient interaction (e.g., for bonding) between the gas and the electrodes. In some embodiments, a bipolar plate as described above includes a flow field (e.g., by etching fluid channels in one or both faces of the plate), however, in other embodiments a different flow field is used instead of or in addition to a bipolar plate containing a flow field.

Fig. 11 shows a schematic diagram of an exemplary gas separation system 1000, the gas separation system 1000 including electrochemical cells 1100 electrically connected in series by one or more conductive materials between the cells, according to certain embodiments. In fig. 11, the system 1000 includes an electrically conductive solid material in the form of a bipolar plate 1012 and ribs (rib) 1014. The ribs in the gas separation system may be made of any of the above-described electrically conductive solid materials. In the embodiment shown in fig. 11, a first electrochemical cell 1100a is separated from a second electrochemical cell 1100b by a bipolar plate 1012 and ribs 1014. The bipolar plate 1012 and the ribs 1014 may be directly adjacent to the negative electrode 1010 of the first electrochemical cell 1100a and the positive electrode 1030 of the second electrochemical cell 1100b, thereby establishing a series-connected conductive path. Other electrochemical cells in the system may be similarly electrically connected. Although bipolar plates and ribs are shown in fig. 11, such depiction is non-limiting and other configurations (e.g., no bipolar plates, no ribs, etc.) are possible. Fig. 11 also illustrates an optional flow field 1011 separating the electrochemical cells 1100 according to certain embodiments. In some embodiments, one or more components (e.g., conductive solids, such as ribs) may establish channels between the negative and positive electrodes of adjacent electrochemical cells. For example, the ribs 1014 in fig. 11 may have dimensions such that: the dimensions are such that the channels 1013 establish pathways for gases (e.g., gas mixtures) to flow between the electrochemical cells 1011 and interact with the electrodes. For example, according to certain embodiments, the gas mixture 1075 may pass through the channels 1013, through the flow field 1011, and between the first electrochemical cell 1100a and the second electrochemical cell 1100 b.

The flow of current in some embodiments described above may encounter less resistance than other configurations. For example, in some embodiments in which electrochemical cells are connected in series by conductive material between at least some of the electrochemical cell stacks (stacks), current may flow in a direction perpendicular to the stacks. Fig. 11 shows one such example, where current may flow in a direction x perpendicular to the electrochemical cell 1100, while the gas mixture 1075 may flow in a direction parallel to the electrochemical cell 1100. In fig. 11, the path through which the current travels is relatively short and is determined by the thickness of the bipolar plate 1012 and the ribs 1014. In some embodiments, the thickness of the one or more conductive solids between electrochemical cells is less than or equal to 10mm, less than or equal to 5mm, less than or equal to 2mm, less than or equal to 1mm, and/or as low as 0.5mm, as low as 0.2mm, as low as 0.1mm, or lower. In contrast, in embodiments where the electrochemical cells are electrically connected in parallel or in series by external wiring, the current must flow through up to the full height and/or length of the electrode (e.g., the current collector of the electrode) and through an electrode tab (electrode tab) to reach the external wiring. Such height and/or length can be, for example, at least 1cm, at least 2cm, at least 5cm, at least 10cm, and/or up to 20cm, up to 50cm, up to 100cm, or higher. In such embodiments, the greater distance traveled by the current typically results in a greater overall cell resistance, which may reduce charge transport and/or energy efficiency for the methods of at least partial gas separation described herein.

The electrochemical cells, systems, and methods described herein can be implemented in a variety of applications. The number of electrochemical cells or batteries may be scaled according to the requirements of a particular desired application. In some embodiments, the systems and methods described herein may be used to remove CO from ambient air and enclosed spaces such as enclosed buildings, compartments-reducing the heating cost of the incoming air for ventilation-and submarines and space pods₂Where CO is present₂The increase in levels can be catastrophic. In embodiments involving the power industry, they may be used to capture varying concentrations of post-combustion carbon dioxide. In some embodiments, the systems and methods are suitable for separating a target gas from an industrial flue gas. In addition, they can be used to capture sulfur dioxide and other gases from flue gases. In embodiments involving the oil and gas industry, the disclosed systems and methods may be used to capture carbon dioxide and other gases from different processes and transfer them for downstream compression and/or processing. The disclosed systems and methods may be used to capture carbon dioxide from natural gas combusted for heating greenhouses in mild and cold climates, and then transfer the captured carbon dioxide to the greenhouse for plants in the greenhouseThe plant is used for photosynthesis, namely, feeding the plant.

In some embodiments, the gas separation systems described herein can capture a target gas with relatively high productivity. The productivity of a gas separation system to capture a target gas from a gas mixture at a given gas flow rate through the gas separation system generally refers to the ratio: target gas captured during a gas capture process (measured by mass and referred to herein as kg)_{Target gas}) Divided by the mass of the bed of the gas separation system (referred to herein as the kg bed) and the breakthrough time (referred to as t)_b) The product of (a). A bed of a gas separation system generally refers to an absorbent material of the gas separation system, such as a layer of electroactive species (e.g., a primary electroactive composite layer) of an electrochemical cell as described herein. One of ordinary skill in the art will appreciate that the breakthrough time of a gas separation system generally refers to the time required for an electrode to reach saturation or the outlet target gas concentration to begin to increase as the gas mixture flows through the system during the capture process. Where it is desired that the gas separation system be performed with high efficiency, a relatively high productivity may be desired, even when the gas separation system is relatively small (e.g., total volume less than or equal to 1,000 cubic feet (ft)³) Less than or equal to 500 cubic feet, less than or equal to 200 cubic feet, less than or equal to 100 cubic feet, less than or equal to 50 cubic feet, less than or equal to 25 cubic feet, less than or equal to 10 cubic feet, and/or as low as 5 cubic feet, as low as 2 cubic feet, as low as 1 cubic foot, as low as 0.1 cubic feet, or less). Some such small gas separation systems may be particularly useful for aeration systems or systems for direct air capture. One or more of the features described herein can contribute to a gas separation system having relatively high productivity, such as the use of particular electroactive species, the use of porous electrodes, and the use of electrochemical cells having a first negative electrode, a second negative electrode, and a positive electrode between the first negative electrode and the second negative electrode).

In some embodiments, the gas separation system is configured to have a gas flow rate of greater than or equal to 0.001L/sec and less than or equal to 500L/secGreater than or equal to 0.003kg_{Target gas}/(kg_Bedt_b) 0.005kg or more_{Target gas}/(kg_Bedt_b) 0.01kg or more_{Target gas}/(kg_Bedt_b) 0.02kg or more_{Target gas}/(kg_Bedt_b) 0.03kg or more_{Target gas}/(kg_Bedt_b) Or larger for capturing target gases (e.g. CO)₂) The productivity of (c). In some embodiments, the gas separation system is configured to have less than or equal to 0.05kg at a gas flow rate greater than or equal to 0.001L/sec and less than or equal to 500L/sec_{Target gas}/(kg_Bedt_b) Less than or equal to 0.04kg_{Target gas}/(kg_Bedt_b) Less than or equal to 0.03kg_{Target gas}/(kg_Bedt_b) Less than or equal to 0.02kg_{Target gas}/(kg_{Bed with adjustable mattress}t_b) Less than or equal to 0.015kg_{Target gas}/(kg_{Bed with adjustable mattress}t_b) Or smaller for capturing target gases (e.g., CO)₂) The productivity of (c). In some cases, due to the contributions of certain features described herein, a gas separation system can have these ranges of productivity even in the case of a gas mixture containing a relatively low concentration of a target gas and or in the case of a gas mixture containing a potentially interfering gas, such as oxygen. It should be understood that while the gas separation system may be configured to achieve the above-described productivity when operating within the noted flow rate range, in some cases, the gas separation system may operate at flow rates other than the indicated flow rate, provided that the indicated productivity is achieved with such same configuration (e.g., electrochemical cell type, size, arrangement). In some embodiments, the flow rate described herein refers to the flow rate of the gas stream per negative electrode face area. For example, in some embodiments, the flux described herein refers to flow per 100cm²The negative electrode of (2). In this case, the negative electrode face region may be the sum of the face regions of the plurality of negative electrodes in the plurality of electrochemical cells, the plurality of electrochemical cell stacks in the system. In some embodiments of the present invention, the substrate is,the flow rates described herein refer to the flow rates of gas flow per electrochemical cell stack in the system. For example, in some embodiments, the flow rates described herein refer to the flow rate of the gas stream for every 10 electrochemical cells in the system.

In accordance with one or more embodiments, a gas mixture (e.g., a gas stream, such as an input gas stream) is introduced to a gas separation system at a particular flow rate. In some embodiments, the flow rate is greater than or equal to 0.001L/sec, greater than or equal to 0.005L/sec, greater than or equal to 0.01, greater than or equal to 0.05L/sec, greater than or equal to 0.1L/sec, greater than or equal to 0.5L/sec, greater than or equal to 1L/sec, greater than or equal to 5L/sec, greater than or equal to 10L/sec, greater than or equal to 50L/sec, greater than or equal to 100L/sec, or greater. In some embodiments, the flow rate of the gas mixture (e.g., gas stream, e.g., input gas stream) is less than or equal to 500L/sec, less than or equal to 400L/sec, less than or equal to 300L/sec, less than or equal to 200L/sec, less than or equal to 100L/sec, less than or equal to 50L/sec, less than or equal to 10L/sec, less than or equal to 1L/sec, less than or equal to 0.5L/sec, less than or equal to 0.1L/sec, or less. Combinations of these ranges are possible. For example, in some embodiments, the flow rate is greater than or equal to 0.001L/sec and less than or equal to 500L/sec. As noted above, in some embodiments, these flow rates are per 100cm²The flow rate of (c). In some embodiments, these flow rates are flow rates per 10 electrochemical cells in the system.

Certain aspects described herein relate to methods of capturing and releasing a target gas. For example, certain embodiments include capturing a target gas by applying a first potential difference across an electrochemical cell (e.g., electrochemical cell 100) and exposing a first quantity of an input gas mixture comprising the target gas to the electrochemical cell. The first quantity of input gas mixture may be exposed by flowing the first quantity of input gas mixture as a gas stream through an electrochemical cell (or a gas separation system including a plurality of electrochemical cells), such as shown in fig. 5-7B. In some embodiments, during and/or after application of the first potential difference, a portion of the target gas bonds with an electroactive species of the electrochemical cell to produce a first treated gas mixture. For example, the target gas (e.g., carbon dioxide) may bond with the first electroactive species of the negative electrode of the electrochemical cell when the first electroactive species is in at least one of its reduced states generated by applying an electrical potential across the electrochemical cell. The bonding of the target gas to the electroactive species may result in the treated gas mixture having a lower amount of target gas (as described above with respect to the range of amounts of target gas removed) compared to the first gas mixture. Fig. 8A through 8B and example 2 below describe an exemplary method of flowing an input gas mixture and a second gas. It should be understood that additional gases may be flowed in addition to the input gas mixture and the second gas (e.g., a third gas, a fourth gas, a fifth gas, etc.). The additional gas may flow through the electrochemical system before and/or after the second gas flows.

In some cases, a second potential difference is applied across the electrochemical cell after at least a portion of the target gas bonds with the electroactive species. The second potential difference may be different from the first potential difference. In some embodiments, applying the second potential difference generates a step of releasing part or all of the target gas bonded to the electroactive species to generate a second treated gas mixture. The second treated gas mixture may have a higher amount of the target gas than the input gas mixture. For example, the target gas may be present in the second treated gas mixture in an amount such that its volume percentage is 10% higher, 20% higher, 50% higher, 100% higher, 200% higher, 1000% higher, and/or up to 2,000% higher, 5,000% higher, 10,000% higher, or higher than the first amount of the gas mixture.

In some embodiments, during and/or after the release of the target gas from the electroactive species, the method further comprises flowing a second gas through the electrochemical cell to remove at least a portion or all of the released target gas from the electrochemical cell. In some embodiments, the second gas is different from the input gas mixture. For example, the second gas may be an inert gas. In other cases, the second gas is a substantially pure gas of the target gas (e.g., greater than or equal to 99.9% pure,Greater than 99.99%, greater than or equal to 99.999%, greater than 99.9999%, or higher). For example, the second gas may be substantially pure CO₂. As another example, the second gas may include steam.

One exemplary situation where a second gas is passed through an electrochemical cell to remove at least some or all of the released target gas from the electrochemical cell may be beneficial is when the amount of target gas captured is greater than the bed volume of the electrochemical cell. In some such cases, more than one bed volume of the target gas bonds with the first electroactive species. For example, in some cases, the volume of target gas captured by the electrochemical cell is equal to at least 1.5 times, at least 2 times, at least 3 times, at least 5 times, at least 10 times, at least 20 times, or more the bed volume of the electrochemical cell. In some such cases where the volume of target gas captured is greater than the bed volume of the electrochemical cell, more than one bed volume of target gas is released from the first electroactive species. In these cases, the release of the trapped target gas may result in the gas pressure of the electrochemical cell being greater than the ambient gas pressure. In some such cases, the released target gas will then flow out of the electrochemical cell, under the force of the resulting pressure differential with the ambient atmosphere, until about 1 bed volume of target gas remains. To remove the remaining released target gas, a second gas may be flowed through the electrochemical cell. In some cases, a substantially pure target gas (e.g., CO) is allowed to flow₂) To remove the remaining target gas. In other cases, an inert gas (e.g., nitrogen, N)₂) Flows through the electrochemical cell to remove the remaining released target gas.

Another situation where a second gas flow through the electrochemical cell to remove at least some or all of the released target gas from the electrochemical cell may be beneficial is when the amount of captured target gas is less than or equal to the bed volume of the electrochemical cell. For example, in some cases, the volume of target gas captured by the electrochemical cell is less than or equal to 1.0 times, less than or equal to 0.8 times, less than or equal to 0.5 times, less than or equal to 0.3 times, and/or less than the bed volume of the electrochemical cellTo 0.2 times, as low as 0.1 times, as low as 0.01 times, or less. In some such cases, the pressure inside the bed of the electrochemical cell will be less than or equal to ambient pressure. In these cases, it may be advantageous to flow a second gas through the electrochemical cell to provide the force required to remove the released target gas from the electrochemical cell. In some such cases, the second gas is a carrier gas. The carrier gas may be any suitable gas that can transport the target gas without reacting with the target gas or the electrochemical cell assembly. The carrier gas can be easily separated from the target gas by any of a variety of techniques that are less costly or energy intensive as the initial separation of the target gas from the gas mixture. For example, the target gas and carrier gas may be separable by condensation or flash separation techniques. The carrier gas may flow through the electrochemical cell during and/or after the step of releasing the target gas. In some cases, the carrier gas is an inert gas. In some cases, the carrier gas is a substantially pure target gas (e.g., substantially pure CO)₂). In some cases, the carrier gas comprises steam. In some embodiments, the second gas (e.g., carrier gas) is a second portion of the input gas mixture. For example, in a venting application, an amount of target gas may be removed from the venting air during application of a first potential across the electrochemical cell, and then more venting air may be flowed through the electrochemical cell during and/or after release of the target gas to remove the released target gas.

In some embodiments, during and/or after the step of releasing the target gas, the method further comprises applying vacuum conditions to the electrochemical cell to remove at least a portion or all of the released target gas from the electrochemical cell. One of ordinary skill, with the benefit of this disclosure, will appreciate suitable techniques and equipment for applying vacuum conditions to an electrochemical cell. For example, a vacuum pump may be fluidly connected to the gas outlet of the electrochemical cell. The vacuum pump may be operated to create a negative pressure differential between the electrochemical cell bed and the downstream location. Such vacuum conditions may provide a force sufficient to cause the target gas released during the above-described releasing step to flow out of the electrochemical cell. Vacuum conditions can be applied such that the pressure inside the electrochemical cell during and/or after the release of the target gas is less than or equal to 2000 torr, less than or equal to 1500 torr, less than or equal to 1200 torr, less than or equal to 1000 torr, less than or equal to 900 torr, less than or equal to 800 torr, less than or equal to 760 torr, less than or equal to 700 torr, less than or equal to 500 torr, less than or equal to 100 torr, less than or equal to 50 torr, less than or equal to 10 torr, and/or as low as 5 torr, as low as 1 torr, as low as 0.5 torr, as low as 0.1 torr, or less. The vacuum condition may be applied such that the pressure inside the electrochemical cell during and/or after release of the target gas is less than the pressure of the environment surrounding the gas separation system including the electrochemical cell. Such an environment may be an environmental condition on earth at sea level such that the vacuum condition establishes a pressure of less than or equal to 760 torr, less than or equal to 100 torr, less than or equal to 10 torr, etc. inside the electrochemical cell during and/or after release of the target gas. However, the environment surrounding the gas separation system may be pressurized, for example in some cases where the gas separation system is in a pressurized structure such as a spacecraft (which may be pressurized to 1.2 times atmospheric pressure at sea level). In some such pressurized environments, the vacuum condition establishes a pressure within the electrochemical cell, e.g., 2000 torr, less than 1000 torr, etc., during and/or after release of the target gas.

In releasing a target gas (e.g., CO) from an electrochemical cell₂) In some embodiments, the released target gas may be treated in any of a variety of ways. For example, the released target gas may be vented from the electrochemical cell (and gas separation system) at the same partial pressure established at the initial release. The released target gas may then be expelled into the ambient environment as an exhaust gas, or may be directed (e.g., by flowing) for further downstream processing. In some embodiments, the released target gas may be incorporated into a target gas having a relatively high partial pressure (e.g., greater than or equal to 10 bar, greater than or equal to 20 bar, greater than or equal to 50 bar, greater than or equal to 75 bar, greater than or equal to 100 bar, and/or up to 110 bar, up to 120 bar, up to 150 bar, orHigher) fluid mixtures (e.g., gas mixtures). In some embodiments, the partial pressure of the resulting fluid mixture is more supercritical (e.g., greater than 130 bar for carbon dioxide). In some cases, incorporation into the fluid mixture may be achieved by combining the released target gas with the fluid mixture already containing the target gas (thereby increasing the partial pressure of the target gas). In some embodiments, the target gas is incorporated into a fluid mixture having a relatively high partial pressure of the target gas by compressing the released target gas. Persons of ordinary skill in the art, with the benefit of this disclosure, will understand how to compress the released target gas (e.g., CO) exhausted from an electrochemical cell₂) For example, using standard compressor equipment and techniques.

In some embodiments, the negative electrode or a portion thereof (e.g., an electroactive composite layer of the negative electrode, when present) has the ability to absorb a target gas (e.g., CO)₂) Of the specific capacity of the battery. For example, in some embodiments, the negative electrode or portion thereof (e.g., electroactive composite layer of the negative electrode (when present)) has at least 0.01mol/m²At least 0.02mol/m²At least 0.05mol/m²Or greater absorbent capacity. In some embodiments, the negative electrode or portion thereof (e.g., electroactive composite layer of the negative electrode, when present) has less than or equal to 0.1mol/m²Less than or equal to 0.08mol/m²Less than or equal to 0.5mol/m²Less than or equal to 0.03mol/m²Or a smaller absorbent capacity. Combinations of these ranges are possible. For example, in some embodiments, the negative electrode or portion thereof (e.g., electroactive composite layer of the negative electrode (when present)) has at least 0.01mol/m²And less than or equal to 0.1mol/m²Or at least 0.01mol/m²And less than or equal to 0.03mol/m²The absorption capacity of (2).

In some embodiments, the negative electrode or a portion thereof (e.g., an electroactive composite layer of the negative electrode, when present) is capable of absorbing a target gas (e.g., CO) at a particular rate₂). For example, in some embodiments, the negative electrode or a portion thereof (e.g., the electrical activity of the negative electrode)The composite layer (when present)) has at least 0.0001mol/m²At least 0.0002 mol/m/sec²At least 0.0005 mol/m/sec²A rate of absorption capacity per second, or greater. In some embodiments, the negative electrode or portion thereof (e.g., electroactive composite layer of the negative electrode, when present) has less than or equal to 0.001mol/m²Per second, less than or equal to 0.0008mol/m²Second, less than or equal to 0.0005mol/m²A rate of absorption capacity per second, or less. In some embodiments, the electroactive composite layer has at least 0.0001mol/m²Second and less than or equal to 0.0005mol/m²Rate of absorption capacity per second. Other rates of absorption capacity are also possible.

In some embodiments, the electroactive composite layer of the negative electrode can have a specific surface area exposed to the gas mixture, for example, greater than or equal to 5cm²Greater than or equal to 8cm²Greater than or equal to 10cm²And/or up to 10cm²Up to 20cm²Up to 50cm²Up to 1m²Or larger. Other values are also possible.

In some embodiments, at least a portion or all of the electrodes described herein (e.g., negative electrode, positive electrode) comprise a porous material. The porous electrode may be made of any suitable material and/or may include any suitable shape or size. In one non-limiting embodiment, the electrode comprises a porous carbonaceous material. The term carbonaceous material is given in the art in its usual meaning and refers to an electrically conductive carbon or graphite containing material. Non-limiting examples of carbonaceous materials include carbon nanotubes, carbon fibers (e.g., carbon nanofibers), and/or graphite. In some such embodiments, the electrodes may be made in part of a carbonaceous material, or a carbonaceous material may be deposited on an underlying material. The underlying material typically comprises an electrically conductive material such as a metal and/or metal alloy solid (e.g., steel, copper, aluminum, etc.). Other non-limiting examples of conductive materials are described herein.

In some embodiments, the electrodes (e.g., negative electrode, positive electrode) are porous. The porosity of an electrode may be measured as a percentage or fraction of the void space in the electrode. The percent porosity of the electrode can be measured using techniques known to those of ordinary skill in the art, such as using volume/density methods, water saturation methods, water evaporation methods, mercury intrusion porosimetry, and nitrogen adsorption methods. In some embodiments, the electrode is at least 10% porous, at least 20% porous, at least 30% porous, at least 40% porous, at least 50% porous, at least 60% porous, at least 70% porous, or more. In some embodiments, the electrode is at most 90% porous, at most 85% porous, at most 80% porous, at most 70% porous, at most 50% porous, at most 30% porous, at most 20% porous, at most 10% porous, or less. Combinations of these ranges are possible. For example, the electrode may be at least 10% porous and at most 90% porous. The pores may be open pores (e.g., at least a portion of the pores are open to the outer surface of the electrode and/or other pores). In some cases, only a portion of the electrode is porous. For example, in some cases, only a single surface of the electrode is porous. As another example, in some cases, the outer surface of the electrode is porous while the inner core of the electrode is substantially non-porous (e.g., less than or equal to 20%, less than or equal to 10% porous, less than or equal to 5% porous, less than or equal to 1% or less). In a specific embodiment, the entire electrode is substantially porous.

In some embodiments, the electrochemical cell has a particular cycle time. The cycle time of an electrochemical cell generally refers to the period of time during which a charge mode and a discharge mode are performed. The cycle time may be at least 60 seconds, at least 100 seconds, at least 300 seconds, at least 500 seconds, at least 1000 seconds, or longer. In some embodiments, the cycle time is less than or equal to 3600 seconds, less than or equal to 2400 seconds, less than or equal to 1800 seconds, or less. Combinations of these ranges are possible. For example, in some embodiments, the cycle time is at least 60 seconds and less than or equal to 3600 seconds, or at least 300 seconds and less than or equal to 1800 seconds.

According to some implementations, the electrochemical cell and its components have a particular thickness, depending on the desired application (e.g., gas separation of ventilator air, direct air capture, etc.). In some embodiments, the electrochemical cell has a thickness of at least 10 μm, at least 20 μm, at least 50 μm, at least 100 μm, at least 200 μm, at least 300 μm, at least 500 μm, or more. In some embodiments, the electrochemical cell has a thickness of less than or equal to 750 μm, less than or equal to 600 μm, less than or equal to 500 μm, less than or equal to 300 μm, or less. Combinations of these ranges are possible. For example, in some embodiments, the electrochemical cell has a thickness of at least 200 μm and less than or equal to 750 μm. In some embodiments, the electrochemical cell has a thickness of at least 10 μm and less than or equal to 750 μm.

In some embodiments, the negative or positive electrode has a thickness of at least 0.5 μm, at least 1 μm, at least 2 μm, at least 5 μm, at least 10 μm, at least 20 μm, at least 50 μm, at least 75 μm, at least 100 μm, or more. In some embodiments, the negative or positive electrode has a thickness of less than or equal to 200 μm, less than or equal to 150 μm, less than or equal to 100 μm, or less. Combinations of these ranges are possible. For example, in some embodiments, the negative or positive electrode has a thickness of at least 50 μm and less than or equal to 200 μm. In some embodiments, the negative or positive electrode has a thickness of at least 0.5 μm and less than or equal to 200 μm in some embodiments.

In some embodiments, the electroactive composite layer of the negative or positive electrode has a thickness of at least 10nm, at least 20nm, at least 40nm, at least 0.1 μm, at least 0.2 μm, at least 0.5 μm, at least 1 μm, at least 2 μm, at least 5 μm, at least 10 μm, at least 50 μm, at least 100 μm, or more. In some embodiments, the electroactive composite layer of the negative or positive electrode has a thickness of less than or equal to 200 μm, less than or equal to one hundred 50 μm, less than or equal to one hundred microns, less than or equal to 50 μm, less than or equal to 20 μm, less than or equal to 10 μm, less than or equal to 5 μm, less than or equal to 2 μm, less than or equal to 1 μm, less than or equal to 0.5 μm, less than or equal to 0.2 μm, less than or equal to 0.1 μm, or less. Combinations of these ranges are possible. For example, in some embodiments, the electroactive composite layer of the negative or positive electrode has a thickness greater than or equal to 10 μm and less than or equal to 200 μm. In some embodiments, the electroactive composite layer of the negative or positive electrode has a thickness greater than or equal to 10nm and less than or equal to 100nm, or greater than or equal to 50nm and less than or equal to 500 nm.

The various components of the system, such as electrodes (e.g., negative electrodes, positive electrodes), power sources, electrolytes, separators, containers, circuits, insulating materials, etc., can be fabricated by one of ordinary skill in the art from any of a variety of components. The assembly may be molded, machined, extruded, pressed, isopressed (isopress), infiltrated, coated, or formed by any other suitable technique in the green or fired state. Techniques for forming the system components herein are readily known to those of ordinary skill in the art.

The electrodes (e.g., negative electrode, positive electrode) described herein can have any suitable size or shape. Some non-limiting examples of shapes include sheets, cubes, cylinders, hollow tubes, spheres, and the like. The electrodes may be of any suitable size depending on the application for which they are used (e.g., separation of gas from ventilation air, direct air capture, etc.). Additionally, an electrode may include a means of connecting the electrode to another electrode, a power source, and/or another electrical device.

The various electrical components of the system may be in electrical communication with at least one other electrical component through the means for connecting. The means for connecting may be any material that allows electrical flow to occur between the first component and the second component. One non-limiting example of a means for connecting two electrical components is a wire comprising a conductive material (e.g., copper, silver, etc.). In some cases, the system may also include an electrical connector between two or more components (e.g., a lead and an electrode). In some cases, wires, electrical connectors, or other means for connecting may be selected such that the resistance of the material is low. In some cases, the resistance may be substantially less than the resistance of the electrodes, electrolyte, and/or other components of the system.

U.S. provisional application No. 62/892,962 entitled "Electrochemical media Carbon Capture from Low communication Streams" filed on 28.8.2019, U.S. patent application No. 15/335,258 entitled "Electrochemical Process for Gas Separation" filed on 26.10.21.2019, U.S. patent application No. 16/659,398 entitled "Electrochemical media Capture, incorporation from Low communication Streams" filed on 21.10.2019, and international patent application No. 2019/PCT 057224 entitled "Electrochemical media Capture, incorporation from Low communication Streams" filed on 21.10.2019 are each incorporated herein by reference in its entirety for all purposes.

The following examples are intended to illustrate certain embodiments of the invention, but do not exemplify the full scope of the invention.

Example 1

This example describes experiments, embodiments and non-limiting theories regarding the effect of the electrochemistry and reactivity of oxygen on the electrochemical separation of a target gas from a gas mixture, and the methods described herein. The materials and parameter values described in this example are non-limiting and are by way of example only.

In electrochemical processes, superoxide ions can be reduced by heterogeneous single electrons on the electrode surface or by redox-active molecules with dissolved O₂A homogeneous single electron transfer reaction. It has been reported that O is present in DMF electrolyte solution₂Quasi-reversible electron transfer was shown to form superoxide ions at a half-wave potential of-1.35V (0.87V versus Standard Calomel Electrode (SCE) reference electrode). In order to limit or prevent the production of superoxide by heterogeneous reduction on the electrode surface, it has been found in the context of the present disclosure that the half-wave reduction potential of the activated quinone should in some cases be more positive than the half-wave potential at which superoxide ions are formed. In addition, the reduced quinone can be reacted with O₂Homogeneous one-electron transfer reaction occurs if the half-wave reduction potential ratio O of quinone₂The half-wave reduction potential of (a) is more negative. Formation of superoxide ion follows

Or

And (4) reacting. In the case of weakly complexing (complexing) quinones, it has been determined that the electrode potential should be sufficiently negative to form a complex for use with CO in some cases₂The dianion quinone required for carboxylation, whereas in the case of strongly complex quinones the formation of the semiquinone is sufficient to promote CO₂And (4) compounding. In the case of weakly associative (associative) quinones, from divalent anionic quinones to O₂The equilibrium constant for electron transfer of (a) can be calculated using:

in the case of strongly associative quinones, from semiquinones to O₂The equilibrium constant for electron transfer of (a) can be calculated using:

wherein the content of the first and second substances,

and

a formula-weighted standard reduction potential for the first and second electron transfer to the quinone, respectively, and

is O₂The formula for reduction measures the standard reduction potential. Cyclic voltammetry is performed to measure or approximately determine the standard reduction potential of various quinones. Tables 1 and 2 summarize the equilibrium constants measured and determined for various quinones. Calculated DBQ semiquinone from this example withO₂Equilibrium constant (K) of_{Reaction of}＝49.0M^-1) And the experimental value (K) reported previously_{Reaction of}＝43.8±3.8M^-1) Similarly.

TABLE 1 divalent anions of weakly complexing quinones with O₂The equilibrium reaction of (1).

TABLE 2 semiquinones and O of strongly complex quinones₂The equilibrium reaction of (1).

Based on the reaction constant, none of the weakly associated quinones are suitable for being at O under the measurement conditions₂Performing electrochemical CO in the presence of₂Separated because of the divalent anion quinone to O₂Is advantageous and will generate superoxide ions in the system. Determination that several strongly associative quinones are suitable at O₂Performing electrochemical CO in the presence of₂Separation: PQ-ester (phenanthrenequinone ethyl ester), PQ-I, PQ-I₂、PQ、o-NQ、p-NQ-Me₂p-NQ, TBQ and BQ. The various quinone structures measured in this example are at N₂And CO₂The peak potentials of the following reduction waves are summarized in fig. 9. FIG. 9 shows the various quinones shown in scheme 1 at a scan rate of 100 mV/sec over N₂(for each quinone, the upper circular symbol connected by a line) or CO₂(for each quinone, lower circle symbol) saturated anhydrous 0.1M n-tetrabutylammonium hexafluorophosphate ([ n-Bu)₄N]PF₆) Tabulated cyclic voltammetry results for a 20mM solution in Dimethylformamide (DMF) electrolyte. The filled circle symbols represent the half-wave potential of a first electron transfer from the quinone to the semiquinone (right symbols) and a second electron transfer from the semiquinone (left symbols) that occurs at more negative electrode potentials. Half-wave potentials can be used to approximately determine the standard reduction potential for the conversion.

Scheme 1. Structure and name of quinone molecule measured in this example.

The larger negative electrode potential and the two reduction waves required for carboxylation of weakly complex quinones in some cases prevent them from acting as CO₂Use of a complexing agent in isolation. This is not the case for some strongly complex quinones which exhibit sufficient redox properties for use in removing oxygen from gas mixtures, especially those containing O₂To efficiently separate CO from a gas mixture of₂. During the complexing step, these compounds can be electrochemically activated to form semiquinones with electrode potentials of-0.87V to-1.07V, which in this case are more positive than-1.35V to form undesirable superoxide anions at the electrode, as desired.

These experimental results indicate that suitable electroactive species having at least one functional group capable of reacting with an exemplary target gas (CO) can be identified₂) A reduced state bonded but not reactive with oxygen. This example also demonstrates an exemplary manner of making such a determination for a given candidate electroactive species.

Example 2

This example describes the capture and release of an exemplary target gas (e.g., CO)₂) And embodiments described herein including methods for aeration and direct air capture applications, and non-limiting theory. The materials and parameter values described in this example are non-limiting and are by way of example only.

The apparatus of this example can be used for a variety of carbon capture applications (low concentration or CO-rich) on a variety of possible scales₂Streams and compositions of). These applications can be classified as targeted for CO removal₂Application and object of (1) to CO upgrading₂For downstream sequestration or processing applications.

When CO is present₂When recovery is not important

In these applications, unlike in Direct Air Capture (DAC), the same is trueReleased CO₂Are generally discarded because their volume is small compared to the total gas volume being processed. Therefore, this mode of operation is mainly on feed concentrations < 1% CO₂(10,000ppm) is significant, which is advantageous for aeration applications. Here, CO₂Is removed from the input gas mixture ("feed stream") and the bed of the electrochemical cell is saturated. Then pure CO is added₂Released into the same inlet stream which is used to purge the bed during the release period to regenerate the bed. The captured energy may also be less important in this mode, as the bed must be regenerated at a much lower frequency (about 10 to 50 times per day) than in the other modes. Furthermore, the energy cost of convection of inlet air via the fan is comparable to captured energy. Thus, full bed activation and full bed regeneration may be performed prior to adsorption. This will increase the energy capture to about 120 kJ/mol. Fig. 8A shows a schematic diagram of one non-limiting example of a method of flowing an input gas mixture and other gases (e.g., a second gas) under these conditions.

Aeration (feed concentration: 1,000ppm CO)₂To 5,000ppm CO₂)

Removal of metabolized CO from buildings and other structures₂More recently, attention has been directed to improving the efficiency of HVAC (Heating, ventilation, and air conditioning) systems by reducing the amount of heat required for the incoming air. Indoor CO in human living quarters₂The concentration was maintained below 5,000ppm by continuously replacing the indoor air with fresh outdoor air up to 10 times a day. The moderate temperatures required to replace the air (whether cooling or heating) often result in excessive energy consumption for typical residential and commercial buildings. However, it has been realized that if CO is removed from the air₂Indoor air can be recirculated for longer periods of time with intermittent replacement of much smaller volumes.

While Volatile Organic Compounds (VOCs) and other indoor air contaminants present at concentrations of < 100ppm are removed by physical filtration and occasional moisture removal, they can be captured directly from the recirculated air by the electrochemical cell and gas separation system described hereinObtaining CO₂. CO depletion of feed air after capture₂And is used to purge the bed upon release, with the outlet stream of the bed being diverted to the outside. Constant current release at high current can achieve high regeneration rates of the bed, although not fully produced.

The bed volume required for each person can be calculated by scaling the manufactured device. At about 22 mol/day, human CO₂The rate of formation and bed saturation period of about 0.5 hours, i.e. regeneration frequency of about 50/day, per person the electrochemical cell bed required is 0.8X 10^-2m³To 1X 10^-2m³(8L to 10L). This can be easily integrated into existing HVAC systems where 7.5L/sec. people are considered¹And a difference between indoor and outdoor temperatures of 25 c, a reduction in energy consumption of up to 60% can be expected. Heating or cooling at this aeration rate would require > 150W, whereas the electrochemical process described herein, at a human rate of 250. mu. moL/sec, would require about 30W at 120 kJ/moL. By reducing the total air replacement requirement to 20% of the specified value, the total energy consumption should not exceed 60W.

The electrochemical cell and gas separation systems and methods described herein may also be used for cabin ventilation, in which case the mode of operation is very similar to indoor ventilation, with smaller beds and more frequent regeneration. In addition thereto, an electrochemical aeration unit may be installed therein for removing CO₂Are the only possible venting mechanisms on spacecraft and space stations. Current NASA demand for International Space Stations (ISS) requires removal of about 4 kg/day of CO₂. Current Pressure Swing Adsorption (PSA) or Temperature Swing Adsorption (TSA) systems operate at 300W. In this case, the bed can be regenerated by passing pure CO with the inlet valve closed₂Release into the vacuum of the space. More recently, however, the "zero waste" policy for NASA has been considered for CO to be captured₂The valuation has generated interest in other useful compounds and oxygen. In this case, the electrochemical system described herein must be used to recover CO₂And (4) operating in a mode.

CO₂Is important

For CO in this mode of operation₂One possible use of capture is to capture CO₂Increasing the concentration from a low inlet concentration to nearly pure CO₂For downstream sequestration or valuation. CO by the electrochemical methods described herein₂Capture proceeds in this mode in a similar manner as before. For cases where high feed concentration and capture energetics are important, adsorption can be carried out by activating the half bed followed by constant potential capture. However, full bed activation can also be performed when the inlet concentration is very low and it is desired to disconnect the power supply.

However, pure CO₂In the presence of pure CO₂Stream flushing after bed with inlet seal just prior to breakthrough to remove CO lean₂A gas column. Then by using pure N₂Flushing to remove final CO₂A column, as shown in fig. 6. During the rinsing step (before and after release, respectively), pure CO₂And N₂Is very high to achieve Re > 2000, which ensures plug flow with a sharp front. This minimizes mixing at the gas column interface, which allows for a sharp transition from one gas to another at the outlet. Fig. 8B shows a schematic diagram of one non-limiting example of a method of flowing an input gas mixture and other gases (e.g., a second gas) under these conditions.

The water content in exhaust gases and room air can have negative effects on electrochemical cells, including decomposition of electrolyte Ionic Liquids (IL), and by CO₂Competing with the reduced quinone to reduce the electrode capacity. In some cases, this can be avoided by using hydrophobic ILs that repel the wet electrode from water. Hydrophobic IL's typically have highly fluorinated cations and anions, such as bis [ (trifluoromethyl) sulfonyl ] s]Imide [ Tf ]₂N^-]This further increases CO₂Solubility in IL and possibly enhance its transport through the electrode.

Direct Air Capture (DAC) (e.g., feed concentration: 300ppm CO₂To 400ppm CO₂)

As interest in carbon-negative technologies as offsetting carbon footprints grows, DAC becomes important. However, most existing adsorbent materials considered or under development for DACs require thermal regeneration; i.e. processes associated with energy loss of the adsorbent and other matrix materials used.

100% CO recovery from binary gas mixtures at 100% purity₂The thermodynamic minimum work of is given by:

wherein R is the gas constant, T is the temperature, and y is the CO in the binary mixture₂Mole fraction of (c). The above equation shows that the minimum work of separation is with CO₂The concentration decrease increased significantly at 400ppm (atmospheric CO)₂Average value of the concentration) reaches a value of about 22 kJ/mol. But the charge-discharge electrochemistry of the quinone has a minimum V-Q work greater than that. Thus, the energy required for DAC using the electrochemical methods described herein is coupled with the inlet CO₂The concentration is irrelevant.

The capture process may be performed by half-bed or full-bed activation. However, given the energy economy of DAC technology, it is suggested in some cases to capture at a constant potential after half-bed activation. The release process may follow the scheme described in FIG. 8B to allow recovery of pure CO₂. The regeneration frequency of the beds in the DAC (even for small beds at reasonable inlet flow rates) is very small and the capture time can be on the order of days.

While the electrochemical systems and methods described herein have been determined to allow the DAC to be at about 45kJ/mol, which is lower than many thermal regeneration systems (55kJ/mol to 130kJ/mol), additional expense may result when running a fan to force convection of air through the electrochemical cell. The electrochemical devices described herein have been manufactured and found to have a pressure drop of no greater than 100Pa at a flow rate of 1L/min to 2L/min. However, in some cases a greater pressure differential may be required to allow for physical filtration of dust and other air contaminants.

Example 3

This example describes experiments, embodiments and non-limiting theories regarding the electrochemically mediated reactivity of certain electroactive species with a target gas. The materials and parameter values described in this example are non-limiting and are by way of example only.

To demonstrate the reactivity of the non-limiting example electroactive species with carbon dioxide, cyclic voltammetry experiments were performed with the optionally substituted quinones described above in the presence of carbon dioxide and in an inert nitrogen atmosphere. Cyclic voltammetry of weakly complex quinones was also performed.

Cyclic voltammetry measurements Using Versastudio with from Princeton Applied Research^TMThe software Parstat 3000-A potentiostat was performed using a standard three-electrode cell. Electrochemical measurements were performed in glass cells, maintaining the temperature of the solution at a defined temperature. Platinum working electrodes were purchased from BASi. A platinum wire was used as the counter electrode and a leak-free Ag/AgCl reference electrode was used. Ferrocene was used as internal standard. Using 0.1M [ n-BU ] in DMF₄N]PF₆An electrolyte. The solution was carefully purged with nitrogen for 30 minutes with gentle stirring and a nitrogen atmosphere was maintained during the electrochemical experiment.

Weak complex quinones

The five weakly complexing quinones mentioned in example 1 are classified on the basis of their reactivity with carbon dioxide in the electrochemical reduction. Based on it with CO₂The weak complex quinone is tetrachlorop-benzoquinone (BQ-Cl)₄) 2, 7-dichlorobenzoquinone (BQ-Cl)₂) 2-3-dichloro-p-naphthoquinone (p-NQ-Cl)₂) 2-chloro-9, 10-anthraquinone (AQ-Cl), 9, 10-anthraquinone 2-propionate (AQ-COO-C)₃H₇) And 9, 10-anthraquinone butylamide derivative (AQ-CONH-C)₄H₉). FIG. 12a shows AQ-C1 at N₂(left) and CO₂(right) cyclic voltammogram at a scan rate of 100 mV/sec under atmosphere. The results for AQ-Cl represent the other four designated weak complex quinones. When the electrolyte solution is passed through CO₂At saturation, neither the cathodic nor the anodic wave of the first electron transferThere is a change observed (at a more positive potential), but the cathodic wave of the second electron transfer is shifted positively, and the oxidation wave exhibits a characteristic indicative of irreversible behavior at the scan rate employed. In FIG. 12A, at N₂AQ-Cl exhibits two reversible single electron transfer processes under atmosphere, where the process is relative to ferrocene

Ferrocene (Fc)⁺/Fc), the first half-wave potential is at-1.26V and the second half-wave potential is at-2.00V. When CO is present₂When introduced into the solution, no change was observed in the cathodic peak current and position of the first electron transfer, but a positive shift of the second cathodic wave indicated that CO had occurred₂Reduction addition to AQ-C1 dianion. The dianion is believed to be associated with CO₂By means of oxygen anions with CO₂Nucleophilic addition reactions between electropositive carbon atoms of the molecule.

CO₂The value of the association constant of the complex with the divalent anion of the weakly complex quinone depends on the ratio of CO₂The positive shift in the half-wave potential of the second electron transfer when introduced into the solution is calculated using the formula:

wherein F is the Faraday constant, R is the ideal gas constant, T is the temperature, and is obtained by reacting CO₂Shifting of half-wave potential upon introduction into the system, [ CO ]₂]Is dissolved CO₂The concentration of (c). The calculated value ranges from BQ-Cl₄6 x 10 of¹M^-1To 2.32X 10 of AQ-Cl³M^-1。

BQ-Cl₂、BQ-Cl₄And p-NQ-Cl₂CO of₂Variation of the association constant oxygen anion due to electron-withdrawing substituents on the quinoid ring structureResonance and inductive stabilization effects of the daughter. Greater stabilization of the oxyanion reduces its CO-contribution₂Nucleophilic reactivity of addition and reduction of CO₂The association constant. For example, p-NQ-Cl₂Relative to BQ-Cl₂CO of divalent anions₂The decrease in binding constant is believed to be primarily due to resonance stabilization by electron delocalization within the aromatic phenyl groups fused to the quinone ring structure, consistent with the effect of resonance stabilization on the basicity of the aromatic oxide anion observed in the phenol and 1-naphthol molecules. In dilute aqueous solution, phenol (phenolate pk)_b3.11) to 1-naphthol (naphtholate pK)_b3.66) is more basic. In organic solvents, the strength of the oxyanion, a lewis base, is reflected in its hydrogen bonding and capacity. And BQ-Cl₂In contrast, BQ-Cl₄Measured lower CO₂The binding constant is believed to be primarily due to the electron withdrawing properties of the chloro side groups; by replacing BQ-Cl by two chlorine atoms₂Two hydrogen atoms of (A) to give the divalent anion BQ-C1₄More stabilize and reduce the anion pair CO₂Nucleophilicity of (c).

The fusion of the aromatic phenyl group with the quinone ring shows that the influence on the resonance stabilization of the oxyanion is smaller than the influence on the resonance stabilization of the oxyanion by the connection of the electron-withdrawing group to the quinone ring structure. Thus, replacement of an electron withdrawing group with a fused aromatic phenyl group increases CO₂Association constants, e.g. AQ-Cl, AQ-CONH-C, anthraquinone derivatives₄H₉And AQ-COO-C₃H₇As shown, these derivatives are classified as weakly complex quinones because of the CO₂The addition does not affect the reduction and oxidation waves of the first electron transfer while the half-wave electron transfer is shifted forward.

₂Electrochemistry of strong complex quinones in the presence of CO

CO₂To CO₂The addition of strongly interacting quinones results in cyclic voltammetric waves that are significantly different from those discussed for the weakly complex quinones above. The 11 quinones mentioned in example 1 are classified as strong complex quinones: BQ, p-NQ, AQ-O-C₃H₇、o-NQ、PQ、DBQ、TBQ、p-NQ-Me₂PQ-I and PQ-I₂. The first six compounds are discussed below because these quinones exhibit unique cyclic voltammograms over the complete range of interactions.

Anthraquinone derivative AQ-COO-C₃H₇Showing the strongest CO in the group of weakly complex quinones₂The association constant. The electron withdrawing nature of the carbonyl (C ═ O) group of the ester substituent reduces the lewis basicity of the oxyanion, which is believed to limit its interaction with CO₂The association constant of (c). Replacement of the ester group with any electron donating substituent is believed to result in CO₂The association constant increases. Two anthraquinone derivatives AQ-COO-C with opposite induction effects₃H₇And AQ-O-C₃H₇Compared to the electrochemical behavior of the unsubstituted anthraquinone molecule AQ, wherein the hydrogen substituent induction effect is between that of the ester and ether groups.

FIGS. 12B to 12D show AQ-COO-C, respectively₃H₇AQ and AQ-O-C₃H₇In the warp of N₂(left) saturated and in CO₂(right) cyclic voltammetry data at a scan rate of 100 mV/sec in DMF electrolyte saturated in atmosphere. AQ-COO-C₃H₇AQ and AQ-O-C₃H₇The cyclic voltammogram of (A) is shown at N₂The next two single electron transfer waves, which are about 0.7V apart. When the electrolyte solution is CO-treated, as with other weak complex quinones₂When saturated, AQ-COO-C₃H₇The peak current and position of the first reduction wave of (2) are not changed, but the second reduction wave is shifted forward (fig. 12B). In both cases of hydrogen and ether substituents, CO is expected₂All the association constants are stronger than that of CO in the case of ester group₂Association constants, therefore for AQ and AQ-O-C₃H₇(FIGS. 12C and 12D, respectively), a large positive shift of the second reduction wave is observed. The positive shift of the second (more negative) reduction wave is accompanied by an increase in the first cathodic current. In the case of AQ (FIG. 12C), the second reduction wave is only shoulder shaped (shoulder), whereas in AQ-O-C₃H₇(FIG. 12D) was not observed. The first cathodic peak current of AQ increases from 56 μ A to 70 μ A, whereas AQ-O-C₃H₇Of the heartThe peak current increased from 56vA to 83 μ a. In AQ and AQ-O-C₃H₇Only one oxidation wave is observed in the voltammogram of (A), wherein CO is present₂The current of the lower oxidation wave is higher than that of N₂The current of the oxidation wave of (1). The increase in current in the first oxidation wave is believed to correspond to quinone-CO₂Oxidation of the monoadduct, which releases CO₂And regenerating the semiquinone, which is immediately oxidized to the neutral quinone species. Since the energy of the electrode potential to oxidize the mono-adduct is sufficient to further oxidize the semiquinone thus produced, two simultaneous oxidation processes occur.

Quinones with electron donating substituents are expected to have stronger CO₂The association constant. CO based on their molecular structure, the oxyanions of BQ and p-NQ₂The association constant should be higher than AQ and AQ-O-C₃H₇Both of oxygen anions of CO₂The association constant. The basicity of the p-NQ oxyanion is expected to be between that of BQ and AQ oxyanions, according to the previously described resonance stabilization concept and its effect on the basicity of the aromatic oxyanions. In the absence of a fused aromatic phenyl ring, the BQ oxyanion is the strongest lewis base among the three quinones.

FIGS. 13A-13B show quinone concentrations at 100 mV/sec using 4mM (left) and 20mM (right) quinone concentrations over N₂Or CO₂0.1M [ n-Bu ] in saturated DMF₄N]PF₆Cyclic voltammetry of p-Benzoquinone (BQ) (fig. 13A) and p-naphthoquinone (p-NQ) (fig. 13B) solutions in (B). Under nitrogen, two well separated electrochemical waves were observed for the BQ and p-NQ solutions. In CO₂In the presence of these quinones, they show: the peak current for the first electron transfer is significantly increased due to two consecutive electron transfers at the reduction potential; and the disappearance of the reduction wave of the second electron transfer, which is probably due to the rapid disproportionation of the semiquinone (production of the monoadduct dianion and the neutral quinone).

At a BQ concentration of 4mM, CO₂The presence of (c) increases the peak current of the first electron transfer from 24.5 μ a to 36.0 μ a, i.e. by about 47%. For 20mM BQ, the current increase reached 54%. Similarly, at 4mMp-NQ, the peak current increased from 22.6vATo 30.3 μ a, or about a 34% increase; whereas at 20mM p-NQ, the peak current increased from 77.6. mu.A to 135.5. mu.A, or about 75%. This indicates that the formation of the monoadduct dianion of BQ and p-NQ depends on the concentration of its semiquinone within the boundary layer at the surface of the electrode.

FIGS. 13A-13B show voltammograms of BQ and p-NQ, which show the results from quinone derived from the dianion with CO₂The electron capture of the interacting products results in two oxidation waves corresponding to two different oxidation mechanisms at two oxidation potentials. These are indicated by downward arrows in fig. 13A to 13B. The first oxidation wave is due to CO₂The single adduct, while the second oxidation wave, which occurs at a small negative potential, is due to the oxidation process of the double adduct. In the case of BQ, the anodic peak current of the single adduct was observed at-0.83V, while the anodic peak current of the double adduct was observed at-0.32V. In the case of p-NQ, the anodic peak current for the mono-adduct oxidation process was observed at-1.01V, while the anodic peak current for the bis-adduct was observed at-0.50V.

₂Mechanistic analysis of naphthoquinone electrochemistry and subsequent CO addition

Deeper mechanistic analysis of p-NQ to more fully understand electrochemically induced reductive CO₂The mechanism of addition. This was done by studying the CO concentration increase of p-NQ₂(with N)₂Equilibrium) is determined. FIG. 14 shows the use of a glassy carbon working electrode at a scan rate of 500mV sec with increasing CO concentration₂Gas saturation (with N)₂Equilibrium) of 0.1M [ n-Bu ] in DMF₄N]PF₆Cyclic voltammetry of a solution of 5mM to naphthoquinone (p-NQ). CV in FIG. 14 is shown at very low CO₂At concentration, there is a clear tendency for new peaks to appear and other peaks to diminish. The following discussion will continually refer to fig. 14 and explain the main features observed through thermodynamic and kinetic phenomena.

The first major observation of CV from FIG. 14 is in CO₂In the presence of two reducing substances, semiquinone NQ^·-And quinol dianionIonic NQ^2-Is very different. Generating NQ^·-Intensity of the first reduced cathodic peak with CO₂The increase in concentration decreased only slightly, indicating CO₂Relatively weak equilibrium.

The semiquinone monoadduct resulting from this equilibrium has an electron density obtained in the first reduction wave (the conjugation moving from the conjugation of the naphthoquinone aromatic ring to the newly added carboxylate moiety, which is separated from the conjugation of the rest of the molecule by the newly formed sigma bond). This results in a relative neutralization of the aromatic ring, which can now acquire a second electron at the more positive potential, i.e. the first reduction potential or tens of mV thereof, as shown in fig. 14 for 100% CO₂CV and fig. 13B. This is believed to be primarily because the reduction of the quinone at the electrode interface occurs by electron transfer from the electrode to the aromatic conjugated system.

At low concentration of CO₂Lower, i.e. 0.5% CO in FIG. 14₂CV and 1.0% CO₂In CV, the forward reaction rate in the semiquinone monoadduct formation reaction is relatively slow, and the cathodic peak between the first and second reduction waves occurs closer to the second reduction wave. With CO₂At 20% CO₂CV and 100% CO₂In CV, the peak moves more positively and is at 100% CO₂In the case of (2), the peak merges with the cathode peak of the first reduction wave, causing the peak position to shift due to the convolution effect. This peak is believed to be caused primarily by kinetic effects: such as NQ in the first reduction wave near the electrodes^·-Formation of the CO in the electrode diffusion layer₂React to form a semiquinone bis adduct, which in turn can accept a second electron at a more positive reduction potential. However, during the negative (cathode) scan of the CV, the glassy carbon electrode acquires an increasingly negative potential and thus an increasingly large overpotential η, where η ═ E_{Application of}-E_BalancingAnd E_BalancingObtained from the nernst expression. According to the Butler-Volmer expression

(where i is electrochemically opposite to Faraday)Should the current flow be correlated), the overpotential η drives the kinetics of the second reduction of the semiquinone monoadduct (i.e., the reduction of the semiquinone monoadduct), which increases exponentially until it is counteracted by the transport resistance, i.e., the depletion of the reactant in the electrode diffusion layer. This is believed to result in a kinetic cathodic peak occurring between two thermodynamic cathodic peaks (which correspond to the two reduction waves of p-NQ).

The position of the peak between the two reduction peaks in fig. 14 is believed to be strictly governed by the chemical formation rate of the semiquinone (which depends on the CO dissolved in the electrolyte)₂Concentration) -bimolecular reaction rate r ═ k [ NQ ]^·-][CO₂]Competition between the rate of electrochemical reduction of semiquinone monoadduct to dianion monoadduct. The rate constant for bimolecular reactions was estimated to be k at about 25M^-1Second of^-1This is at CV and 20% CO₂Under conditions to give about 5X 10^-3M seconds^-1Rate of semiquinone monoadduct formation. The position dependence of this peak on scan rate can be seen in fig. 15, which shows the use of a glassy carbon working electrode at different scan rates at 20% CO₂Saturation (with N)₂Equilibrium) of 0.1M [ n-Bu ] in DMF₄N]PF₆Cyclic voltammetry of a solution of 5mM to naphthoquinone (p-NQ). In fig. 15, at low scan rates of 50 mV/sec to 100 mV/sec, this peak merges with the cathodic peak of the first reduction wave, while at higher scan rates (believed to be greater than the time constant of the chemical reaction), the second peak appears and moves negatively away from the first peak. The intensity of this peak is also increased relative to the first reduction wave, since the electrochemical reaction, which only takes place after the chemical reaction has taken place, takes place at a greater overpotential. The voltage difference between the two cathodic peaks corresponds to the time required to carry out the chemical reaction.

The second chemical reaction of the dianion bis-adduct proceeds as expected and does not contribute much to the electrochemical behaviour beyond the thermodynamic stabilisation of the dianion bis-adduct.

Steric effect of para-quinone and ortho-quinone

Quinones exist in two isomeric forms: 1, 4-cyclohexadienedione (p-quinone) and 1, 2-Cyclohexadienedione (o-quinone). The above discussion has focused on the dianion of p-quinone with CO₂To (3) is performed. To CO₂The association with two ortho-quinones, PQ (an isomeric form of AQ) and o-NQ (an isomeric form of p-NQ), was evaluated. In dilute aqueous solution, deprotonated hydrobenzoquinone (pK)_b3.65) ratio of deprotonated catechol (pk)_b4.15) greater alkalinity; therefore, it is considered that the basicity of the divalent anion of o-quinone is smaller than that of-quinone. FIGS. 16A-16B show quinone concentrations at 4mM (left) and 20mM (right) using platinum electrodes at a scan rate of 100 mV/sec over N₂Or CO₂0.1M [ n-Bu ] in saturated DMF₄N]PF₆Cyclic voltammetry of 9, 10-Phenanthrenequinone (PQ) (fig. 16A) and o-naphthoquinone (o-NQ) (fig. 16B) in solution. As shown in fig. 16A to 16B, PQ shows two typical electrochemical waves in DMF electrolyte solution saturated with nitrogen, corresponding to the formation of semiquinone and dianion quinone, respectively. In the case of PQ, the half-wave potential for the first electron transfer occurs at-1.09V and the half-wave potential for the second electron transfer occurs at-1.96V, with a spacing of about 0.87V. This value is greater than the half-wave potential separation of about 0.75V observed for AQ. Similarly, the potential interval of o-NQ is about 0.89V, slightly wider than the 0.87V potential interval of p-NQ. It is believed that the larger potential separation of the o-quinone is due to the presence of a metal at C₁And C₂The two oxygen anions in the position in close proximity (which experience greater electrostatic repulsion).

Addition of CO to a DMF solution containing PQ₂The peak current leading to the first electron transfer increased substantially and the reduction wave of the second electron transfer disappeared (fig. 16A), significantly different from the trend observed in the cyclic voltammogram of AQ due to CO (fig. 12C)₂The second electron transfer under the atmosphere still shows a shoulder shape in the reduction wave. These results indicate that PQ and CO₂Is stronger than AQ and CO₂The association of (2). The increase in PQ peak current for the first electron transfer is due to two consecutive electron transfers at the first reduction wave. Introducing CO₂Addition to the DMF solution containing o-NQ also resulted in a significant increase in peak current for the first electron transfer, and no observation was madeA separate reduction wave to second electron transfer (fig. 16B). CO at a PQ concentration of 4mM (FIG. 16)₂The addition of (c) increases the peak current of the first electron transfer from 22 μ a to 39 μ a, i.e. about 77%. At a PQ concentration of 20mM (FIG. 16B), the percentage of current increase decreased to 71%. In the case of o-NQ, a more significant decrease in the percentage of current increase was observed with increasing quinone concentration. At the 4mM concentration (fig. 16B), the percent increase in peak current was about 93%, while at the 20mM concentration, the percent increase in peak current was only about 84%. The difference in the trend of increasing peak current with increasing quinone concentration indicates that CO is present according to the results obtained for p-quinone₂Different mechanisms of binding. For ortho-quinone, peak current follows CO₂The linear dependence on the increase in the relative concentration ratio of quinone indicates the following mechanism: electron transfer, followed by a chemical step, followed by electron transfer (ECE). The carbonate complex is formed by the initial one-electron reduction of a neutral quinone to form a semiquinone, which is then reacted with CO₂And (4) compounding. This intermediate complex is believed to undergo a second one-electron reduction immediately below the surface of the electrode in close proximity to form the mono (carbonate) of the dianionic quinone. When the electrolyte passes through CO₂When saturated, semiquinone with CO₂The recombination of (a) is evidenced by a small positive shift in the first electron transfer. The positive shift of o-NQ is about 38mV and the positive shift of PQ is about 14 mV.

As observed and discussed above, PQ and o-NQ are being CO-passed₂Voltammograms in saturated DMF electrolytes show two oxidation waves (FIGS. 16A to 16B), corresponding to CO respectively₂Oxidation of mono-and bis-adducts. The relative peak currents of these oxidation waves give the dianion quinone-CO that undergoes each oxidation process in the diffusion layer on the electrode surface₂Indication of the fraction of complex. CO dissolved in DMF electrolyte solution₂Concentration of 1 bar CO₂About 0.175M under pressure, or about 44 times the 4mM quinone concentration. In the same CO₂Dissolved CO at a concentration of 20mM quinone loading₂The relative concentration to quinone was 8.75. With respect to CO₂The increase in concentration and shift of equilibrium position are detrimental to CO₂Divalent anionDissociation of the daughter quinone double adduct, the relative peak current of the two oxidation reactions in the case of the 4mM quinone solution was lower than the relative peak current of the two oxidation reactions in the case of the 20mM quinone solution, as shown in fig. 16.

The experiments described in this example demonstrate the reactivity between certain electroactive species (e.g., certain semiquinones) and carbon dioxide at relatively positive potentials. As described above, with the knowledge and guidance of the present disclosure, incorporation of certain electroactive species (e.g., strongly complexing optionally substituted quinones) as described into electrochemical cells can facilitate electrochemically-mediated carbon dioxide capture under the following conditions: under the conditions described, with other substances, e.g. O₂Relatively little (or no) electrochemically mediated reactivity.

While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present disclosure is directed to each individual feature, system, article, material, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, and/or methods, if such features, systems, articles, materials, and/or methods are not mutually inconsistent, is included within the scope of the present invention.

As used herein in the specification and claims, the phrase "at least a portion of" means some or all. According to certain embodiments, "at least a portion" may mean at least 1 weight%, at least 2 weight%, at least 5 weight%, at least 10 weight%, at least 25 weight%, at least 50 weight%, at least 75 weight%, at least 90 weight%, at least 95 weight%, or at least 99 weight%, and/or in certain embodiments, up to 100 weight%. According to certain embodiments, "at least a portion" may mean at least 1 volume%, at least 2 volume%, at least 5 volume%, at least 10 volume%, at least 25 volume%, at least 50 volume%, at least 75 volume%, at least 90 volume%, at least 95 volume%, or at least 99 volume%, and/or in certain embodiments, up to 100 volume%. According to certain embodiments, "at least a portion" may mean at least 1 mol%, at least 2 mol%, at least 5 mol%, at least 10 mol%, at least 25 mol%, at least 50 mol%, at least 75 mol%, at least 90 mol%, at least 95 mol%, or at least 99 mol%, and/or in certain embodiments, up to 100 mol%.

Unless explicitly indicated to the contrary, as used herein in the specification and in the claims, the term "without a quantitative modification" is to be understood to mean "at least one".

The phrase "and/or" as used herein in the specification and in the claims should be understood to mean "either or both" of the elements so combined, i.e., the elements are present together in some cases and separately in other cases. Unless explicitly stated to the contrary, other elements may optionally be present in addition to the elements specifically indicated by the "and/or" clause, whether related or unrelated to those elements specifically indicated. Thus, as a non-limiting example, when used in conjunction with an open-ended language such as "comprising" reference to "a and/or B" may mean a, in one embodiment, without B (optionally including elements other than B); in another embodiment, B may be referred to without a (optionally including elements other than a); in yet another embodiment, may refer to both a and B (optionally including other elements); and so on.

As used herein in the specification and in the claims, "or/and" should be understood to have the same meaning as "and/or" as defined above. For example, when items in a list are separated, "or/or" and/or "should be interpreted as being inclusive, i.e., including at least one of a plurality of elements or a list of elements, but also including more than one, and optionally additional unlisted items. To the contrary, terms such as "only one of" or "exactly one of," or "consisting of," when used in the claims, are intended to mean that there is exactly one element in a plurality or list of elements. In general, the term "or/and" when preceded by an exclusive term (e.g., "any," "one," "only one," or "exactly one") as used herein should only be construed to indicate an exclusive alternative (i.e., "one or the other but not both"). To "consisting essentially of" when used in the claims shall have its ordinary meaning as used in the patent law field.

As used herein in the specification and in the claims, the phrase "at least one," when referring to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements, and not excluding any combinations of elements in the list of elements. The definition also allows that elements other than those specifically identified in the list of elements referred to by the phrase "at least one" may optionally be present, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, "at least one of a and B" (or, equivalently, "at least one of a or B," or, equivalently, "at least one of a and/or B") can refer, in one embodiment, to at least one a, optionally including more than one a, with no B present (and optionally including elements other than B); in another embodiment, it may refer to at least one B, optionally including more than one B, with no a present (and optionally including elements other than a); in yet another embodiment, it may refer to at least one a, optionally including more than one a, and at least one B, optionally including more than one B (and optionally including other elements); and so on.

In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. As described in the united states patent office patent inspection program manual, section 2111.03, the transitional phrases "consisting of and" consisting essentially of shall be closed or semi-closed transitional phrases, respectively.

Claims

1. An electrochemical cell, comprising:

a negative electrode comprising a first electroactive species;

a positive electrode; and

a separator between the negative electrode and the positive electrode, the separator capable of containing an electrically conductive liquid;

wherein the first electroactive species has:

an oxidation state; and

at least one reduced state in which the substance is capable of bonding with a target gas, but for which oxygen (O) is present at least one temperature₂) The reaction of (a) is thermodynamically unfavorable.

2. An electrochemical cell, comprising:

a negative electrode comprising a first electroactive species immobilized on the negative electrode; and

a positive electrode;

wherein the first electroactive species has:

an oxidation state; and

at least one reduced state in which the species is capable of bonding with a target gas, but at least one temperature for the at least one reduced stateOxygen (O) at a lower temperature₂) The reaction of (a) is thermodynamically unfavorable.

3. A gas separation system, comprising:

a plurality of electrochemical cells in fluid communication with the gas inlet and the gas outlet, wherein:

the gas separation system is configured to have a gas flow rate of 0.003kg or greater at or equal to 0.001L/sec and 500L/sec or less_{Target gas}/(kg_Bedt_b) In kg, wherein_BedIs the bed weight and t_bIs the breakthrough time of the gas separation system.

4. The electrochemical cell of any one of claims 1 to 3, wherein the electrochemical cell comprises a negative electrode comprising a first electroactive species.

5. The electrochemical cell of any one of claims 1 to 4, wherein the first electroactive species has an oxidized state, and at least one reduced state in which the species is capable of bonding with a target gas, but for which oxygen (O) is reacted at least one temperature greater than or equal to 223K₂) The reaction of (a) is thermodynamically unfavorable.

6. The electrochemical cell of any one of claims 1 to 5, wherein the first electroactive species has an oxidized state, and at least one reduced state in which the species is capable of bonding with a target gas, but for which oxygen (O) is reacted at least one temperature greater than or equal to 223K and less than or equal to 573K₂) The reaction of (a) is thermodynamically unfavorable.

7. An electrochemical cell according to any one of claims 1 to 6, wherein the first electroactive species has an oxidised state, and at least one reduced state, in which it is in the oxidised stateThe substance is capable of bonding with a target gas in at least one reduced state, but is capable of bonding with oxygen (O) at least one temperature greater than or equal to 223K and less than or equal to 373K for the at least one reduced state₂) The reaction of (2) is thermodynamically unfavorable.

8. The electrochemical cell of any one of claims 1 to 7, wherein the first electroactive species has at least one reduced state in which the species is capable of bonding with a target gas, but for which oxygen (O) is present at 298K₂) The reaction of (a) is thermodynamically unfavorable.

9. The electrochemical cell of any one of claims 1, 3 to 8, wherein the first electroactive species is immobilized on the negative electrode.

10. The electrochemical cell of any one of claims 1-2, 4-9, wherein the negative electrode comprises a primary electroactive composite layer comprising the first electroactive species.

11. The electrochemical cell of any one of claims 1 to 2, 4 to 10, wherein the first electroactive species has an oxidized state, and at least one reduced state in which the species is capable of bonding with a target gas, but for which oxygen (O) is present at 298K₂) The reaction of (a) is thermodynamically unfavorable.

12. The electrochemical cell of any one of claims 1 to 2, 4 to 11, wherein a standard reduction potential ratio for generating the at least one reduced state of the first electroactive species in the conductive liquid is for oxygen (O)₂) And superoxide (O)₂ ^-) The standard reduction potential correction of interconversion between.

13. According to claims 1 to 2, 4 to 12The electrochemical cell of any one of, wherein the standard reduction potential ratio for producing the at least one reduced state of the first electroactive species in the conductive liquid is for superoxide (O)₂ ^-) With peroxides (O)₂ ^2-) The standard reduction potential correction of interconversion.

14. The electrochemical cell of any one of claims 1-2, 4-13, wherein the first electroactive species is a portion of a polymeric material immobilized on the negative electrode.

15. The electrochemical cell of any one of claims 1-2, 4-14, wherein the first electroactive species comprises an optionally substituted quinone.

16. The electrochemical cell of any one of claims 1 to 2, 4 to 15, wherein the first electroactive species comprises one or more of the structures selected from formulas (IA) and (IB):

wherein R is¹、R²、R³And R⁴May be the same or different, and may be hydrogen, halogen, hydroxyl, carboxylate/carboxylic acid, sulfonate/sulfonic acid, alkyl sulfonate/alkyl sulfonic acid, phosphonate/phosphonic acid, alkyl phosphonate/alkyl phosphonic acid, acyl, amino, amido, quaternary ammonium, branched or unbranched alkyl, heteroalkyl, alkoxy, dialkoxy, polyalkylene dialkoxy, imino, polyimino, branched or unbranched alkenyl, branched or unbranched alkynyl, aryl, heteroaryl, heterocyclyl, nitro, nitrile, thio, and/or carbonyl, any of which is optionally substituted, and/or R¹To R⁴Any two adjacent groups of (a) may be linked together to form an optionally substituted ring.

17. Root of herbaceous plantThe electrochemical cell of any one of claims 1-2, 4-16, wherein the first electroactive species comprises one or more of: phenanthrenequinone ester (PQ-ester), iodophenanthrenequinone (PQ-I), diiodophenanthrenequinone (PQ-I)₂) Phenanthrenequinone (PQ), o-naphthoquinone (o-NQ), and dimethyl-p-naphthoquinone (p-NQ-Me)₂) P-naphthoquinone (p-NQ), di-tert-butyl benzoquinone (TBQ), and Benzoquinone (BQ) having the following structures:

wherein R is⁵Is an optionally substituted branched or unbranched C1 to C18 alkyl group.

18. The electrochemical cell of any one of claims 1-2, 4-17, wherein the negative electrode comprises a gas permeable layer.

19. The electrochemical cell of any one of claims 1-2, 4-18, wherein the negative electrode is porous.

20. The electrochemical cell of any one of claims 1 to 2, 4 to 19, wherein the electrochemical cell comprises a separator between the negative electrode and the positive electrode, the separator capable of containing an electrically conductive liquid.

21. The electrochemical cell of claim 20, wherein the separator comprises the electrically conductive liquid.

22. The electrochemical cell of any one of claims 20 to 21, wherein the separator is saturated with the electrically conductive liquid.

23. The electrochemical cell of any one of claims 20 to 22, wherein the electrically conductive liquid comprises a non-volatile electrolyte.

24. The electrochemical cell of any one of claims 20 to 23, wherein the electrically conductive liquid comprises a room temperature ionic liquid.

25. The electrochemical cell of claim 24, wherein the room temperature ionic liquid comprises 1-butyl-3-methylimidazole

Bis (trifluoromethylsulfonyl) imide (Bmim) as a cationic component.

26. The electrochemical cell of any one of claims 24 to 25, wherein the room temperature ionic liquid comprises bis (trifluoromethylsulfonyl) imide (TF)₂N) as an anionic component.

27. The electrochemical cell of any one of claims 1-2, 4-26, wherein the positive electrode comprises a second electroactive species.

28. The electrochemical cell of claim 27, wherein the positive electrode comprises a gas permeable layer and a complementary electroactive composite layer comprising the second electroactive species.

29. The electrochemical cell of any one of claims 1-2, 4-28, wherein the negative electrode is a first negative electrode, and the electrochemical cell further comprises:

a second negative electrode comprising the first electroactive species; and

a second separator between the positive electrode and the second negative electrode that is saturable with a conductive liquid.

30. The electrochemical cell of any one of claims 1 to 2, 4 to 29, wherein the positive electrode comprises a substrate between a first complementary electroactive composite layer facing the first negative electrode and a second complementary electroactive composite layer facing the second negative electrode.

31. The electrochemical cell of any one of claims 27 to 30, wherein the second electroactive species comprises a redox-active polymer.

32. The electrochemical cell of any one of claims 31, wherein the redox-active polymer comprises polyvinylferrocene.

33. The electrochemical cell of any one of claims 27 to 32, wherein the second electroactive species comprises an intercalation compound.

34. The electrochemical cell of claim 33, wherein the intercalation compound comprises lithium iron phosphate (LiFePO)₄)。

35. The electrochemical cell of any one of claims 10 to 34, wherein the primary electroactive composite layer comprises a carbonaceous material.

36. The electrochemical cell of any one of claims 1 to 35, wherein the target gas comprises carbon dioxide.

37. A gas separation system comprising a plurality of electrochemical cells of claims 1-2, 4-36 in fluid communication with a gas inlet and a gas outlet.

38. The gas separation system of claim 37, configured to have greater than or equal to 0.003kg at a gas flow rate greater than or equal to 0.001L/sec and less than or equal to 500L/sec_{Target gas-}(kg_Bedt_b) In kg, wherein_BedIs the bed weight and t_bIs the breakthrough time of the gas separation system.

39. According to claim 3 and37-38 configured to have a gas flow rate of less than or equal to 0.05kg at a gas flow rate of greater than or equal to 0.001L/sec and less than or equal to 500L/sec_{Target gas}/(kg_Bedt_b) For capturing the productivity of the target gas.

40. The gas separation system of any one of claims 3, 37-39, wherein the gas flow rate is per 100cm in the system²Airflow rate of the negative electrode area.

41. The gas separation system of any one of claims 3, 37-40, wherein the gas flow rate is the gas flow rate of every 10 electrochemical cells in the plurality of electrochemical cells in the system.

42. The gas separation system of any one of claims 3 and 37-41, wherein the plurality of electrochemical cells are electrically connected in parallel.

43. The gas separation system of any one of claims 3 and 37-41, wherein the plurality of electrochemical cells are electrically connected in series.

44. The gas separation system of any one of claims 3 and 37-43, wherein a flow field exists between at least some of the plurality of electrochemical cells.

45. The gas separation system of any one of claims 43-44, wherein a first electrochemical cell and a second electrochemical cell of the plurality of electrochemical cells electrically connected in series are electrically connected via one or more electrically conductive materials between the first electrochemical cell and the second electrochemical cell.

46. The gas separation system of claim 45, wherein the one or more electrically conductive materials comprise a bipolar plate.

47. A method of at least partial gas separation, the method comprising:

applying a potential difference across the electrochemical cell of any one of claims 1 to 36;

exposing a gas mixture to the electrochemical cell; and

bonding at least a portion of a target gas with a first electroactive species to produce a treated gas mixture having a lower amount of the target gas than the gas mixture.

48. A method of at least partial gas separation, the method comprising:

in the gas separation system of any one of claims 3 and 37-46, applying a potential difference across one or more of the plurality of electrochemical cells;

exposing the gas mixture to the one or more electrochemical cells; and

49. A method of at least partial gas separation, the method comprising:

applying a potential difference across the electrochemical cell;

exposing a gas mixture comprising a target gas to an electrochemical cell; and

removing an amount of the target gas from the gas mixture during and/or after the application of the first potential difference,

wherein any oxygen (O) present in the gas mixture₂) Less than or equal to 0.1% by volume is removed from the gas mixture.

50. A method, comprising:

applying a first potential difference across the electrochemical cell;

exposing a first amount of an input gas mixture comprising a target gas to the electrochemical cell;

bonding at least a portion of the target gas with an electroactive species of the electrochemical cell during and/or after applying the first potential difference to produce a first treated gas mixture having a lower amount of the target gas than the first gas mixture;

applying a second potential difference across the electrochemical cell; and

releasing some or all of the target gas bonded to the electroactive species to produce a second treated gas mixture;

wherein during and/or after the releasing, the method further comprises:

(a) flowing a second gas through the electrochemical cell to remove at least some or all of the released target gas from the electrochemical cell, and/or

(b) Applying vacuum conditions to the electrochemical cell to remove at least some or all of the released target gas from the electrochemical cell.

51. The method of any one of claims 49-50, wherein the target gas comprises carbon dioxide.

52. The method of any one of claims 49-51, wherein the concentration of the target gas is less than or equal to 5,000 ppm.

53. The method of any one of claims 49-52, wherein the concentration of the target gas is less than or equal to 500 ppm.

54. The method of any one of claims 49-53, wherein the gas mixture comprises oxygen (O)₂)。

55. The method of any one of claims 49-54, wherein the oxygen (O)₂) To be greater thanOr equal to 0% by volume or greater than or equal to 10% by volume.

56. The method of any one of claims 49-55, wherein the oxygen (O)₂) Is present in the gas mixture at a concentration of less than or equal to substantially 100 volume percent, less than or equal to 50 volume percent, less than or equal to 25 volume percent, or less than or equal to 21 volume percent.

57. The method of any one of claims 49-56, wherein there is no O₂Gas is removed from the gas mixture.

58. The method of any one of claims 49 to 57, wherein an amount of oxygen is removed from the gas mixture, wherein the ratio of the amount of target gas removed to the amount of oxygen removed is greater than or equal to 10: 1.

59. The method of any one of claims 49-58, wherein the gas mixture has a relative humidity of 0% to 100%.

60. The method of any one of claims 49-59, wherein the gas mixture is one of: ambient air, air in an enclosed space, air in a partially ventilated space.

61. The method of any one of claims 49-60, wherein the gas mixture is air in one of a cabin, a manned submersible, or an airplane.

62. The method of any one of claims 49 to 61, wherein during and/or after said releasing, a second gas is flowed through said electrochemical cell to remove at least some or all of the released target gas from the electrochemical cell.

63. The method of any one of claims 50 to 62, wherein the second gas is an inert gas.

64. The method of any one of claims 50-63, wherein the second gas is a carrier gas.

65. The method of any one of claims 50-62, 64, wherein the second gas is substantially pure CO₂。

66. The method of any one of claims 50-64, wherein the second gas comprises steam.

67. The method of any one of claims 50 to 66, wherein the second gas is a second portion of the gas mixture.

68. The method of any one of claims 49 to 67, wherein the electrochemical cell comprises a first electroactive species, and more than one bed volume of the target gas is bound to the first electroactive species.

69. The method of claim 68, wherein more than one bed volume of the target gas is released from the first electroactive species.

70. The method of any one of claims 50 to 69, wherein vacuum conditions are applied to the electrochemical cell during and/or after the releasing to remove at least some or all of the released target gas from the electrochemical cell.

71. The method of any one of claims 49 to 70, wherein the electrochemical cell comprises a negative electrode comprising a first electroactive species.

72. According to claim 71The method of (a), wherein the first electroactive species has at least one reduced state in which the species is capable of bonding with a target gas but for which oxygen (O) is present at 298K₂) The reaction of (a) is thermodynamically unfavorable.

73. The method of any one of claims 71 to 72, wherein the first electroactive species is immobilized on the negative electrode.

74. The method of any one of claims 71-73, wherein the negative electrode comprises a primary electroactive composite layer comprising the first electroactive species.

75. The method of any one of claims 71 to 74, wherein the first electroactive species has an oxidised state, and at least one reduced state in which the species is capable of bonding with a target gas but for which oxygen (O) is associated at least one temperature₂) The reaction of (a) is thermodynamically unfavorable.

76. The method of any one of claims 71 to 75, wherein the first electroactive species has an oxidised state, and at least one reduced state in which the species is capable of bonding with a target gas, but for which oxygen (O) is reacted at least one temperature greater than or equal to 223K and less than or equal to 573K₂) The reaction of (a) is thermodynamically unfavorable.

77. The method of any one of claims 71 to 76, wherein the first electroactive species has an oxidised state, and at least one reduced state in which the species is capable of bonding with a target gas, but for which oxygen (O) is reacted at least one temperature greater than or equal to 223K and less than or equal to 373K₂) Is thermodynamically inIs disadvantageous.

78. The method of any one of claims 71 to 77, wherein the first electroactive species has an oxidised state, and at least one reduced state in which the species is capable of bonding with a target gas, but for which oxygen (O) is present at 298K₂) The reaction of (a) is thermodynamically unfavorable.

79. The method of any one of claims 71 to 78, wherein the standard reduction potential ratio for producing the at least one reduced state of the first electroactive species in the electrically conductive liquid is for oxygen (O)₂) And superoxide (O)₂ ^-) The standard reduction potential correction of interconversion between.

80. The method according to any one of claims 71 to 79, wherein the standard reduction potential ratio for producing the at least one reduced state of the first electroactive species in the conductive liquid is for superoxide (O)₂ ^-) With peroxides (O)₂ ^2-) The standard reduction potential correction of interconversion.

81. The method of any one of claims 71 to 80, wherein the first electroactive species is part of a polymeric material immobilized on the negative electrode.

82. The method of any one of claims 71-81, wherein the first electroactive species comprises an optionally substituted quinone.

83. The method of any one of claims 71 to 82, wherein the first electroactive species comprises one or more of the structures selected from formulae (IA) and (IB):

84. The method of any one of claims 71 to 83, wherein the first electroactive species comprises one or more of: phenanthrenequinone ester (PQ-ester), iodophenanthrenequinone (PQ-I), diiodophenanthrenequinone (PQ-I)₂) Phenanthrenequinone (PQ), o-naphthoquinone (o-NQ), and dimethyl-p-naphthoquinone (p-NQ-Me)₂) P-naphthoquinone (p-NQ), di-t-butyl benzoquinone (TBQ), and Benzoquinone (BQ):

85. The method according to any one of claims 71 to 84, wherein the negative electrode comprises a gas permeable layer.

86. The method of any one of claims 71 to 85, wherein the negative electrode is porous.

87. The method of any one of claims 71-86, wherein the electrochemical cell comprises a separator between the negative electrode and positive electrode, the separator capable of containing an electrically conductive liquid.

88. The method of claim 87, wherein the separator comprises the electrically conductive liquid.

89. The method of any one of claims 87 to 88, wherein the spacer is saturated with the electrically conductive liquid.

90. The method of any one of claims 87 to 89 wherein the electrically conductive liquid comprises a non-volatile electrolyte.

91. The method of any one of claims 87 to 90 wherein the electrically conductive liquid comprises a room temperature ionic liquid.

92. The method of claim 91, wherein the room temperature ionic liquid comprises 1-butyl-3-methylimidazole

Bis (trifluoromethylsulfonyl) imide (Bmim) as a cationic component.

93. The method of any one of claims 91 to 92, wherein the room temperature ionic liquid comprises bis (trifluoromethylsulfonyl) imide (TF)₂N) as an anionic component.

94. The method of any one of claims 49-93, wherein the electrochemical cell comprises a positive electrode comprising a second electroactive species.

95. The method of any one of claims 49-94, wherein the positive electrode comprises a gas permeable layer and a complementary electroactive composite layer comprising a second electroactive species.

96. The method of any one of claims 71-95, wherein the negative electrode is a first negative electrode, and the electrochemical cell further comprises:

a second negative electrode comprising the first electroactive species; and

a second separator between the positive electrode and the second negative electrode, the second separator being capable of being saturated with a conductive liquid.

97. The method according to any one of claims 94 to 96, wherein the positive electrode comprises a substrate between a first complementary electroactive composite layer facing the first negative electrode and a second complementary electroactive composite layer facing the second negative electrode.

98. The method of any one of claims 94-97, wherein the second electroactive species comprises a redox-active polymer.

99. The method of claim 98, wherein the redox-active polymer comprises polyvinylferrocene.

100. The electrochemical cell of any one of claims 94 to 99, wherein the second electroactive species comprises an intercalation compound.

101. The electrochemical cell of claim 100, wherein the intercalation compound comprises lithium iron phosphate (LiFePO)₄)。

102. The method of any one of claims 74-101, wherein the primary electroactive composite layer comprises a carbonaceous material.