Electrochemically mediated gas capture, including from low-concentration streams

Abstract

Methods, devices, and systems are provided for the electrochemical separation of a target gas from a gas mixture. In some cases, a target gas, such as carbon dioxide, is captured using an electrochemical cell (e.g., by binding to an electroactive species in a reduced state) and released as needed. Some embodiments are particularly useful for selectively capturing the target gas with little or no reaction with oxygen gas that may be present in the gas mixture. Some such embodiments can be useful in applications involving separation from gas mixtures with relatively low concentrations of the target gas, such as direct air capture and ventilated air processing.

Description

[Technical Field]

[0001] Related Applications This application is a continuation-in-part of U.S. patent application Ser. No. 16 / 659,398, filed October 21, 2019, entitled "Electrochemically Mediated Gas Capture, Including from Low Concentration Streams," and a continuation-in-part of International Patent Application No. PCT / US2019 / 057224, filed October 21, 2019, entitled "Electrochemically Mediated Gas Capture, Including from Low Concentration Streams," each of which claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 62 / 892,962, filed August 28, 2019, entitled "Electrochemically Mediated Carbon Capture from Low Concentration Streams," the entire contents of which are incorporated herein by reference for all purposes.

[0002] Technical Field SUMMARY OF THE INVENTION Methods, devices, and systems for the electrochemical separation of a target gas from a gas mixture are generally described. [Background technology]

[0003] background Efforts have been made to remove target species from gas mixtures. For example, over the last two decades, efforts have been made to mitigate global warming by curbing anthropogenic carbon dioxide (CO2) emissions. Several approaches, such as traditional thermal methods, have been pursued to address carbon dioxide capture at various stages of its production: either after combustion capture at power plants or after its concentration from the atmosphere, where it is then pressurized and stored in geological formations or converted to commercially useful compounds. Other potential applications of target gas removal include removing target gas directly from air or from ventilated air. Improved devices, methods, and / or systems are desirable. Summary of the Invention [Means for solving the problem]

[0004] overview Methods, devices, and systems are provided for the electrochemical separation of a target gas from a gas mixture. In some cases, a target gas, such as carbon dioxide, is captured using an electrochemical cell and optionally released (e.g., by binding to an electroactive species in a reduced state). Some embodiments are particularly useful for selectively capturing a target gas with little to no reaction with oxygen gas that may be present in the gas mixture. Some such embodiments may be useful in applications involving separation from gas mixtures having relatively low concentrations of the target gas, such as direct air capture and ventilation processes. The subject matter of the present invention includes, in some cases, interrelated products, alternative solutions to a particular problem, and / or multiple different uses of one or more systems and / or articles.

[0005] In one aspect, an electrochemical cell is described. In some embodiments, the electrochemical cell includes a negative electrode containing a first electroactive species; a positive electrode; and a separator between the negative and positive electrodes, which may contain a conductive liquid. The first electroactive species has an oxidized state and at least one reduced state, where the species can combine with a target gas but reaction with oxygen (O) is thermodynamically unfavorable at at least one temperature. In some embodiments, the first electroactive species has at least one reduced state where the species can combine with a target gas but reaction with oxygen (O) is thermodynamically unfavorable at at least one temperature greater than or equal to 223 K and less than or equal to 573 K. In some embodiments, the first electroactive species has at least one reduced state where the species can combine with a target gas but reaction with oxygen (O) is thermodynamically unfavorable at at least one temperature greater than or equal to 223 K and less than or equal to 373 K.

[0006] In some embodiments, the electrochemical cell includes a negative electrode including a first electroactive species immobilized thereon; and a positive electrode; the first electroactive species has an oxidized state and at least one reduced state, where the species is capable of combining with a target gas but reaction with oxygen (O) is thermodynamically unfavorable at at least one temperature. In some embodiments, the first electroactive species has at least one reduced state, where the species is capable of combining with a target gas but reaction with oxygen (O) is thermodynamically unfavorable at at least one temperature greater than or equal to 223 K and less than or equal to 573 K. In some embodiments, the first electroactive species has at least one reduced state, where the species is capable of combining with a target gas but reaction with oxygen (O) is thermodynamically unfavorable at at least one temperature greater than or equal to 223 K and less than or equal to 373 K.

[0007] In another aspect, a gas separation system is described. In some embodiments, the gas separation system includes a plurality of electrochemical cells in fluid communication with a gas inlet and a gas outlet, and the gas separation system is configured to separate 0.003 kg of gas at a gas flow rate greater than or equal to 0.001 L / sec and less than or equal to 500 L / sec. 標的ガス / (kg 床tb ) wherein kg 床 is the floor weight, and t b is the breakthrough time for the gas separation system.

[0008] In another aspect, a method for at least partial gas separation is described. In some embodiments, the method includes: applying a potential difference across an electrochemical cell; exposing a gas mixture containing a target gas to the electrochemical cell; and during and / or after applying a first potential difference, removing a quantity of the target gas from the gas mixture, wherein any oxygen gas (O) present in the gas mixture by volume percent less than or equal to 0.1% is removed from the gas mixture.

[0009] In some embodiments, the method includes applying a first potential difference across the electrochemical cell; exposing a first amount of an input gas mixture including a target gas to the electrochemical cell; combining at least a portion of the target gas with electroactive species in the electrochemical cell during and / or after applying the first potential difference to produce a first treated gas mixture having a lower amount of 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 bound to the electroactive species to produce a second treated gas mixture, wherein during and / or after releasing, the method further includes 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 applying a vacuum to the electrochemical cell to remove at least some or all of the released target gas from the electrochemical cell.

[0010] Other advantages and novel features of the present invention will become apparent from the following detailed description of various non-limiting embodiments of the invention when considered in conjunction with the accompanying figures. In cases where the present specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification will control.

[0011] Non-limiting embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, which are schematic and not intended to be drawn to scale. Each identical or nearly identical component shown in the drawings is typically represented by a single numeral. For clarity, not every component is labeled in every drawing, nor is every component in every embodiment of the present invention shown, unless illustration is necessary for those skilled in the art to understand the invention. [Brief explanation of the drawings]

[0012] [Figure 1A] 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. [Figure 1B] 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. [Figure 2] FIG. 2 shows a schematic exploded view of an exemplary electrochemical cell according to one or more embodiments. [Figure 3A] FIG. 3A shows an exploded schematic of an electrochemical cell operating in a charging mode according to one or more embodiments. [Figure 3B] FIG. 3B shows an exploded schematic view of an exemplary electrochemical cell operating in a discharge mode according to one or more embodiments. [Figure 4] FIG. 4 shows a schematic diagram of an exemplary gas separation system according to one or more embodiments. [Figure 5A] FIG. 5A shows a schematic diagram of an exemplary system for conducting a gas separation process according to one or more embodiments. [Figure 5B] FIG. 5B shows a schematic diagram of an exemplary system including a flow field for performing a gas separation process, according to one or more embodiments. [Figure 5C] 5C-5E show side schematic views of exemplary flow field channel patterns according to one or more embodiments. [Figure 5D] 5C-5E show side schematic views of exemplary flow field channel patterns according to one or more embodiments. [Figure 5E] 5C-5E show side schematic views of exemplary flow field channel patterns according to one or more embodiments. [Figure 6] FIG. 6 shows a schematic diagram of an exemplary gas separation system according to one or more embodiments. [Figure 7A] FIG. 7A shows a schematic diagram of an exemplary system for performing a gas separation process, according to one or more embodiments. [Figure 7B] FIG. 7B shows a schematic diagram of an exemplary system for performing a gas separation process according to one or more embodiments. [Figure 8A] 8A-8B show schematic diagrams of methods for flowing gas through a bed of an electrochemical device according to one or more embodiments. [Figure 8B] 8A-8B show schematic diagrams of methods for flowing gas through a bed of an electrochemical device according to one or more embodiments. [Figure 9] FIG. 9 shows tabulated electrochemical data for various quinones and oxygen gas according to one or more embodiments. [Figure 10A] FIG. 10A shows a schematic diagram of an exemplary system including multiple electrochemical cells for performing a gas separation process, according to one or more embodiments. [Figure 10B] FIG. 10B shows a schematic diagram of an exemplary system including multiple electrochemical cells electrically connected in parallel to perform a gas separation process, according to one or more embodiments. [Figure 10C] FIG. 10C shows a schematic diagram of an exemplary system including multiple electrochemical cells electrically connected in series to perform a gas separation process, according to one or more embodiments. [Figure 11] FIG. 11 shows a schematic diagram of an exemplary system including multiple electrochemical cells electrically connected in series to perform a gas separation process, and one or more electrically conductive materials between the electrochemical cells, according to one or more embodiments. [Figure 12] Figures 12A-12D show the cyclic voltammetry of 2-chloro-9,10-anthraquinone (AQ-Cl) (Figure 12A), the ester derivative of 9,10-anthraquinone (AQ-COO-C3H7) (Figure 12B), 9,10-anthraquinone (AQ) (Figure 12C), and the ether derivative of 9,10-anthraquinone (AQ-O-C3H7) (Figure 12D) in a solution of 0.1 M [n-Bu4N]PF6 in DMF saturated with either N2 (left) or CO2 (right). [Figure 13] Figures 13A-13B show the cyclic voltammetry of p-benzoquinone (BQ) (Figure 13A) and p-naphthoquinone (p-NQ) (Figure 13B) added to a solution of 0.1 M [n-BuN]PF in DMF saturated with either N or CO. [Figure 14] FIG. 14 shows the cyclic voltammetry of p-naphthoquinone (p-NQ) added to a solution of 0.1 M [n-BuN]PF in DMF saturated with increasing concentrations of CO gas (with balance N). [Figure 15] Figure 15 shows the cyclic voltammetry of 5 mM p-naphthoquinone (p-NQ) added to a solution of 0.1 M [n-BuN]PF in DMF saturated with 20% CO (with balance N) at various scan rates. [Figure 16]Figures 16A-16B show the cyclic voltammetry of 9,10-phenanthrenequinone (PQ) (Figure 16A) and o-naphthoquinone (o-NQ) (Figure 16B) added to a solution of 0.1 M [n-BuN]PF in DMF saturated with either N or CO. DETAILED DESCRIPTION OF THE INVENTION

[0013] Detailed Description Methods, devices, and systems are provided for the electrochemical separation of a target gas from a gas mixture. In some cases, a target gas such as carbon dioxide is captured and optionally released using an electrochemical cell (e.g., by binding to an electroactive species in a reduced state). Some embodiments may be particularly useful for selectively capturing a target gas with little or no reaction with oxygen that may be present in the gas mixture. Some such embodiments may be useful in applications involving separation from gas mixtures with relatively low concentrations of the target gas, such as direct air capture and ventilation processes. Certain such embodiments are less energy intensive and less expensive than certain existing technologies, such as thermal or pressure swing target gas separation.

[0014] In some embodiments, methods for at least partially separating gas mixtures, as well as electrochemical cells and gas separation systems that can be useful for such applications, are generally described. Certain embodiments relate to applying a potential difference across an electrochemical cell and exposing a gas mixture (e.g., a low-concentration mixture such as ambient air or ventilated air) containing a target gas (e.g., CO) to the electrochemical cell. The electrochemical cell may include electrodes containing certain electroactive species (e.g., certain optionally substituted quinones or polymeric derivatives thereof) that can access states generated by the electrochemical potential that can react with the target gas but cannot react with potentially interfering species such as oxygen gas. Reaction between the electroactive species and oxygen gas may be reduced or avoided by careful selection of the electroactive species (e.g., selecting an electroactive species that has a reduced state that can combine with the target gas but in which reaction with oxygen is thermodynamically unfavorable). Certain other chemical species relate to methods of gas flow during the capture and release process, as well as gas separation systems that can capture target gases with high productivity, even from low-concentration gas mixtures.

[0015] The capture of target gases, including from low-concentration target gas streams, can be valuable, but is difficult to do inexpensively and without using energy-intensive methods. Existing conventional methods and systems have many drawbacks, including high energy requirements and waste. Furthermore, conventional thermal methods of capturing target gases (e.g., carbon dioxide) often fail to meet the very stringent efficiency and capacity standards set by regulatory agencies.

[0016] As a specific example of carbon dioxide gas removal, while most such applications target high CO2 concentration (3%-15%) streams from industrial power generation and other such point sources, it may be desirable to extract CO2 from enclosed spaces for ventilation purposes in buildings and vehicles or for the indoor environmental control systems of spacecraft and submarines, where the maximum allowable CO2 concentration in the occupied space is 5,000 ppm (or 0.5%). However, the low concentrations of CO2 in such applications pose challenges, likely due to low propulsion forces and the large amounts of other chemical species present in the air besides CO2. Such concerns are also prevalent with direct air capture of CO2 from the atmosphere at concentrations of approximately 400 ppm, which may merit consideration as a long-term mitigation strategy.

[0017] With particular reference to electrochemical CO capture (although related to other target gases), the electrochemistry of O can play an important role in the electrochemically mediated separation of target CO, particularly in gas mixtures with relatively high oxygen concentrations and / or relatively low CO concentrations (e.g., ventilation applications, direct air capture applications, etc.). Certain electroactive species that may be suitable for reacting with CO in their reduced states may also be capable of reacting with O. As a non-limiting example, quinones typically undergo two successive one-electron reductions in aprotic electrolyte solutions (e.g., conductive liquids), and the two reduced states have been observed to effectively complex with CO. In the context of the present disclosure, the standard reduction potential for activating quinones has been found to be an important parameter in identifying redox-active molecules suitable for electrochemical CO separation. In aprotic electrolyte solutions, one-electron reduction of dissolved O gas generates stable superoxide ions (O), which can be effective nucleophiles. - ) The superoxide ion undergoes the addition of nucleophiles to the carbonyl atom, which then bind to electron-withdrawing leaving groups such as acid anhydrides and esters. Previous studies have shown that the superoxide ion reacts with CO2 in aprotic electrolyte solutions to form an anion radical intermediate, CO4 -and then peroxodicarbonate, C2O6 2- Furthermore, in the context of this disclosure, it has been observed that the use of common alkyl carbonate electrolytes, such as propylene carbonate and ethylene carbonate, is not recommended if superoxide ions are generated in any electrochemical process. Therefore, the standard reduction potential for the one-electron reduction of O is an important parameter that helps identify suitable redox-active molecules for electrochemical CO separation. Furthermore, chemical oxidation of an electrochemically reduced (activated) electrode by molecular oxygen can generate a charge imbalance in the electrochemical cell. In some cases, this charge imbalance can render the target gas capture electrode inactive toward the target gas.

[0018] Certain methods and electrochemical cells that exploit these insights have been developed and are generally described herein. In some cases, the methods and electrochemical cells and systems relate to electroswing adsorption (ESA) processes that remove a target gas from a gas mixture, potentially with little to no removal of any oxygen gas present.

[0019] In one embodiment, an electrochemical cell is described. FIG. 1A shows a schematic diagram of an exemplary electrochemical cell 100, including an anode 110 and a cathode 120. In certain cases, the electrochemical cell is suitable for reacting with a target gas from a gas mixture in any of a variety of applications, including at least partially separating the target gas mixture having a relatively low concentration of the target gas (e.g., ambient air, ventilated air, etc.). As used herein, the term "electrochemical cell" refers to a device in which redox half-reactions occur at the anode and cathode. The term "electrochemical cell" is intended to include devices that meet these criteria, even if the cell's behavior can arguably be characterized as more pseudocapacitive than faradaic, and thus might otherwise be referred to as a type of capacitor.

[0020] As mentioned 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 internal electrons are injected during the charging process. For example, with reference to FIG. 1A , when electrochemical cell 100 is charged (e.g., via application of an electric potential by an external power source), electrons pass through an external circuit (not shown) and enter negative electrode 110. Thus, in some cases, chemical species associated with the negative electrode can be reduced to a reduced state (a state having an increased number of electrons) during the charging process of the electrochemical cell.

[0021] An electrochemical cell may include a positive electrode. As used herein, the positive electrode of an electrochemical cell refers to the electrode from which electrons are removed during a charging process. For example, referring again to FIG. 1A, when electrochemical cell 100 is charged (e.g., via application of an electric potential by an external power source), electrons enter an external circuit (not shown) from positive electrode 120. Thus, in some cases, chemical species associated with the positive electrode can be oxidized to an oxidized state (a state having a reduced number of electrons) during the charging process of the electrochemical cell.

[0022] In some embodiments, the negative electrode includes a first electroactive species. As used herein, electroactive species generally refers to an agent (e.g., a chemical entity) that undergoes oxidation or reduction upon exposure to an electric potential in an electrochemical cell. It should be understood that when an electrode includes an electroactive species, the electroactive species may be located on the surface of the electrode, at least partially within the electrode (e.g., within the pores of the electrode), or both. For example, in some embodiments, the negative electrode 110 in FIG. 1 includes a first electroactive species. The first electroactive species may be on or near the surface of the negative electrode 110, the first electroactive species may be within at least a portion of the negative electrode 110, or a combination of both.

[0023] In some embodiments, the first electroactive species is immobilized on the negative electrode. Such embodiments may be distinguished from other systems in which the electroactive species is freely transported from one electrode to another, for example, via advection. As is generally understood, a chemical species immobilized on an electrode (e.g., a negative electrode) cannot freely diffuse out of the electrode or dissociate under a given set of conditions. The electroactive species can be immobilized on the electrode in various ways. For example, in some cases, the electroactive species can be immobilized on the electrode by binding (e.g., covalent bonding, ionic bonding, and / or intramolecular interactions, such as electrostatic forces, van der Waals forces, hydrogen bonding, etc.) to the surface of the electrode or to a chemical species or material attached to the electrode. In some embodiments, the electroactive species can be immobilized on the electrode by adsorption onto the electrode. In some cases, the electroactive species can be immobilized on the electrode by polymerization on the electrode. In certain cases, the electroactive species can be immobilized on the electrode by inclusion in a composition that is attached or deposited on the electrode (e.g., a coating, a composite layer, etc.). In certain cases, the electroactive species (e.g., polymeric or molecular electroactive material) infiltrates the microfiber or nanofiber or carbon nanotube mat, thus immobilizing the electroactive material to the mat. The mat may provide enhanced surface area for contact with electrolyte and gas, as well as an extended network for electrical 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 infiltrates the pores of the electrode, or as a composition that at least partially encapsulates components of the electrode, such as the fibers or nanotubes of the electrode).Such gels (e.g., hydrogels, ionogels, organogels, etc.) containing electroactive species may be prepared prior to association with the electrode (e.g., applied as a coating forming a layer), or the gel may be prepared in the presence of the electrode by contacting the electrode with a gel precursor (e.g., a prepolymer solution containing the electroactive species) (e.g., via coating or immersion), and then gel formation may be initiated (e.g., via crosslinking via introduction of a crosslinking agent, a radical initiator, heating, and / or exposure to electromagnetic radiation (e.g., ultraviolet radiation)).

[0024] In some embodiments, described in more detail below, the negative electrode includes an electroactive composite layer that includes an immobilized polymer composite of an electroactive and another material (e.g., a carbonaceous material). For example, in some embodiments, the electroactive composite layer includes a composite of a polymer that includes a first electroactive species (e.g., a redox-active polymer having a reduction potential in the range described below) and carbon nanotubes (CNTs).

[0025] 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, neutral benzoquinone can be considered an oxidized state, semiquinone (the product of adding one electron to neutral benzoquinone) can be considered one reduced state, and benzoquinone dianion (the product of adding one electron to neutral benzoquinone) can be considered another reduced state.

[0026] In some embodiments, the first electroactive species has at least one reduced state in which the species is capable of combining with a target gas (e.g., CO). A species capable of combining with a target gas generally refers to the ability of the species to undergo a combining reaction with the target gas to a degree and at a rate sufficiently sufficient to produce a useful gas separation process. For example, a species capable of combining with a target gas has a reduced state in which the species is capable of combining with the target gas at a rate sufficient to produce a useful gas separation process.1 M -1 Greater than or equal to 10 2 M -1 Greater than or equal to and / or up to 10 3 M -1 The chemical species may have a binding constant up to or above room temperature (23°C). The chemical species capable of binding with the target gas may be capable of binding with the target gas on a time scale on the order of minutes, seconds, milliseconds, or even just microseconds or shorter. The chemical species may be capable of binding with the target gas at at least one temperature (e.g., at least one temperature greater than or equal to 223K and less than or equal to 573K, e.g., 298K). In some embodiments, the chemical species may be capable of binding with the target gas at a first temperature, but binding with the target gas at a second temperature is thermodynamically and / or kinetically unfavorable. Such temperature dependence may be based on the temperature dependence of the change in Gibbs free energy between the chemical species (e.g., a reduced quinone) and the target gas (e.g., carbon dioxide). With the insights and guidance of the present disclosure, one skilled in the art will be able to select an appropriate temperature to promote binding between the chemical species in its at least one reduced state and the target gas.

[0027] In some embodiments, the first electroactive species has an oxidized state capable of releasing a 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 the particular intended application. For example, in some embodiments, when CO2 is the target gas, the selected first electroactive species has a 10 1 From 10 3 M -1 In some embodiments, the selected electroactive species may have a binding constant for carbon dioxide of 10 1 From 10 3 M -1The quinones may have binding constants for different target gases of 1000 kJ / s. It has been observed that some quinones can be used as suitable electroactive species. In some embodiments, in the presence of CO, an optionally substituted quinone may be reduced (e.g., in a single step or multiple steps) to its semiquinone or dianion, which then binds to CO to form a complex. Other electroactive species that can form a covalent bond with CO after reduction to form a carboxylate moiety may also be used.

[0028] In some embodiments, the first electroactive species has at least one reduced state where the species can combine with the target gas, but there is at least one temperature (e.g., 298 K) where it is thermodynamically unfavorable for the species to react with oxygen (O). In certain cases, the first electroactive species has at least one reduced state where the species can combine with the target gas, but there is at least one temperature (e.g., 298 K) where it is kinetically unfavorable for the species to react with oxygen (O) because the rate constant for the reaction is too low to cause the reaction to occur on time scales commensurate with gas capture, such as microseconds, milliseconds, seconds, or minutes. As discussed above, the ability of the electroactive species to react with the target gas but not with oxygen (at least in a thermodynamically and / or kinetically favorable manner) can be useful in certain applications where there is a relatively high amount of oxygen in the gas mixture to be separated, or when the target gas is present in relatively low amounts (whereby, if oxygen is present, it must compete with oxygen gas to react with the at least one reduced state). In some embodiments, the first electroactive species has at least one reduced state in which the species can combine with the target gas but it is thermodynamically unfavorable for the species to react with oxygen (O) at temperatures greater than or equal to 223 K, greater than or equal to 248 K, greater than or equal to 273 K, greater than or equal to 298 K, and / or at least one temperature in the range of up to 323 K, up to 348 K, up to 373 K, up to 398 K, up to 423 K, up to 448 K, up to 473 K, up to 498 K, up to 523 K, up to 548 K, up to 573 K, or higher. In some embodiments, the first electroactive species has at least one reduced state in which the species can combine with the target gas but it is thermodynamically unfavorable for the species to react with oxygen (O) at a temperature of 298 K. As used herein, a reaction that is thermodynamically unfavorable at a given temperature has a positive change in Gibbs free energy (ΔG rxnFor example, a reaction between at least one reduced species and oxygen gas may have a Gibbs free energy change (ΔG) greater than 0 kcal / mol, greater than or equal to +0.1 kcal / mol, greater than or equal to +0.5 kcal / mol, greater than or equal to +1 kcal / mol, greater than or equal to +2 kcal / mol, greater than or equal to +3 kcal / mol, greater than or equal to +5 kcal / mol, and / or at most +8 kcal / mol, at most +10 kcal / mol, at most +20 kcal / mol, or greater. rxn ) at at least one temperature in the range of 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 at least one reduced species and oxygen gas has a Gibbs free energy change (ΔG) of greater than 0 kcal / mol, greater than or equal to +0.1 kcal / mol, greater than or equal to +0.5 kcal / mol, greater than or equal to +1 kcal / mol, greater than or equal to +2 kcal / mol, greater than or equal to +3 kcal / mol, greater than or equal to +5 kcal / mol, and / or up to +8 kcal / mol, up to +10 kcal / mol, up to +20 kcal / mol, or more. rxn ) at a temperature of 298K.

[0029] Nevertheless, in the context of the present disclosure, it has been discovered that some electroactive species capable of binding with a target gas may be reactive with oxygen or its reduction products (e.g., superoxide ions, peroxide dianions, 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 with which the target gas is captured, or superoxide ions or peroxide ions may have deleterious reactivity with components of the electrochemical cell (e.g., the electroactive species, the target gas, the separator, the conductive liquid, if present, etc.). However, in the context of the present disclosure, it has been discovered that some specific electroactive species may have at least one reduced state that is capable of binding to the target gas but whose reaction with oxygen (O) is thermodynamically and / or kinetically unfavorable. Examples and selection criteria for some such electroactive species are described in more detail below.

[0030] In some embodiments, the standard reduction potential for generating at least one reduced state of the first electroactive species in the conductive liquid is a ratio of oxygen gas (O) and superoxide ions (O - ) than the standard reduction potential for the interconversion between O2 and O2. Such a standard reduction potential may contribute to at least one reduced species that is capable of binding to the target gas while being thermodynamically unfavorable for reacting with oxygen gas. For example, in a conductive liquid of 0.1 M n-tetrabutylammonium hexafluorophosphate in dimethylformamide (DMF) at room temperature, the (O2 / O2 - ) redox couple may have a standard reduction potential of -1.35 V relative to a given reference. Thus, any suitable electroactive species having a standard reduction potential more positive than -1.35 V relative to the given reference in the conductive liquid at room temperature may be oxygen gas (O) and superoxide ion (O -) in the conductive liquid. In some embodiments, the standard reduction potential for interconversion between the oxidized state and the at least one reduced state of the first electroactive species in the conductive liquid is greater than the standard reduction potential for interconversion between the oxidized state and the at least one reduced state of superoxide (O - ) and peroxide (O2 2- ) is more positive than the standard reduction potential for interconversion with

[0031] Those skilled in the art, with the benefit of this disclosure, will be able to determine the standard reduction potential for an electroactive species in a given conductive liquid. For example, cyclic voltammetry, linear sweep voltammetry, or any other suitable electrochemical technique for measuring the standard reduction potential can be used. In some cases, for example, where the cyclic voltammetry wave is irreversible for the electroactive species, the standard reduction potential can be approximated using any suitable technique known to those skilled in the art, such as peak potential. The standard reduction potential may depend on the temperature at which it is measured. In some embodiments, the standard reduction potential is measured at one of the temperatures mentioned above, such as 298 K.

[0032] In some embodiments, the standard reduction potential for generation of at least one reduced state of the first electroactive species in the conductive liquid is at least 5 mV, at least 10 mV, at least 20 mV, at least 50 mV, at least 100 mV, at least 200 mV, at least 400 mV, or more than the standard reduction potential for generation of at least one reduced state of the first electroactive species in the conductive liquid. - ) is more positive than the standard reduction potential for the interconversion between oxygen gas (O) and superoxide ion (O). As an example, if the interconversion between oxygen gas and superoxide ion in a conductive liquid is −1.35 V relative to a given reference and an electroactive species has a standard reduction potential of −1.00 V relative to that given reference for the generation of the reduced state of the species, then the electroactive species has a standard reduction potential of −1.00 V relative to that given reference for the generation of the reduced state of the species. -In some embodiments, the standard reduction potential for generation of a reduced state of at least one of the first electroactive species in the conductive liquid is 350 mV more positive than the standard reduction potential for the interconversion between oxygen gas (O) and superoxide ions (O) by a value less than or equal to 1 V, less than or equal to 900 mV, less than or equal to 800 mV, less than or equal to 600 mV, or less than or equal to 500 mV. - ) is more positive than the standard reduction potential for the interconversion between

[0033] In some embodiments, the standard reduction potential for generation of the reduced state of at least one of the first electroactive species in the conductive liquid is at least 5 mV, at least 10 mV, at least 20 mV, at least 50 mV, at least 100 mV, at least 200 mV, at least 400 mV, or more than the standard reduction potential for generation of the reduced state of the first electroactive species in the conductive liquid. - ) and peroxide dianion (O2 2- In some embodiments, the standard reduction potential for the generation of a reduced state of at least one of the first electroactive species in the conductive liquid is less than or equal to 1 V, less than or equal to 900 mV, less than or equal to 800 mV, less than or equal to 600 mV, or less than or equal to 500 mV, relative to the standard reduction potential for the interconversion between superoxide ion (O2) and the first electroactive species (O2). - ) and peroxide dianion (O2 2- ) is more positive than the standard reduction potential for the interconversion between

[0034] The first electroactive species may be of any suitable form, provided that it satisfies at least one of the criteria required herein. In some embodiments, the first electroactive species is or includes a molecular species. For example, the first electroactive species may be or include an organic molecule. The first electroactive species may include one or more functional groups capable of binding to 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 a portion of a polymer, such as a redox-active polymer. The first electroactive species may be a portion 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 polymer material immobilized on the negative electrode 110 of the electrochemical cell 100.

[0035] In some embodiments, the first electroactive species is or includes an optionally substituted quinone (i.e., the quinone may include functional groups and / or other moieties or linkages attached to the quinone's main structure). In certain cases, the first electroactive species is or includes a redox-active polymer that includes an optionally substituted quinone. The selection of a substituent (e.g., a 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. Those skilled in the art, with the benefit of this disclosure, will understand how to determine which substituent or combination of substituents on the optionally substituted quinone is suitable for the first electroactive species based, for example, on synthetic feasibility and resulting standard reduction potential. Exemplary functional groups with which the optionally substituted quinones may be functionalized include, but are not limited to, halo (e.g., chloro, bromo, iodo), 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-C18 alkyl), heteroalkyl, alkoxy, glycoxy, polyalkylene glycoxy (e.g., polyethylene glycoxy), imino, polyimino, branched or unbranched alkenyl, branched or unbranched alkynyl, aryl, heteroaryl, heterocyclyl, nitro, nitrile, thiyl, and / or carbonyl groups, any of which are optionally substituted. The first electroactive species optionally substituted quinone has the formula (IA) and (IB): [ka] and may comprise one or more structures selected from: In the formula, R 1 , R2 , R 3 , and R 4 may be the same or different and are hydrogen, halo (e.g., chloro, bromo, iodo), 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-C18 alkyl), heteroalkyl, alkoxy, glycooxy, polyalkylene glycooxy (e.g., polyethylene glycooxy), imino, polyimino, branched or unbranched alkenyl, branched or unbranched alkynyl, aryl, heteroaryl, heterocyclyl, nitro, nitrile, thiyl, and / or carbonyl groups, any of which may be optionally substituted; and / or R 1 ~R 4 Any two adjacent groups in the may be joined to form an optionally substituted ring.

[0036] In some embodiments, the optionally substituted quinone is or includes an optionally substituted naphthoquinone. In certain cases, the optionally substituted quinone is or includes an optionally substituted anthraquinone. In some embodiments, the optionally substituted quinone is or includes an optionally substituted phenanthrenequinone (also referred to as an optionally substituted phenanthrenedione). The substituents (e.g., functional groups) may be any of those listed above.

[0037] In some embodiments, the electroactive species is or includes one or more of the following: phenanthrenequinone esters (PQ-esters), iodo-phenanthrenequinones (PQ-I), di-iodo-phenanthrenequinones (PQ-I), phenanthrenequinones (PQ), ortho-naphthoquinones (o-NQ), dimethyl-para-naphthoquinones (p-NQ-Me), para-naphthoquinones (p-NQ), di-tert-butyl-benzoquinones (TBQ), and benzoquinones (BQ), the structures of which are shown below: [ka] In the formula, R 5 is an optionally substituted branched or unbranched C1 to C18 alkyl (eg, methyl, ethyl, propyl, butyl, etc.).

[0038] In some cases, other positional isomers of the above non-limiting examples of electroactive species are suitable as well (eg, with substituents at various positions on the quinone).

[0039] 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 may 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 optionally substituted quinones covalently bonded to the backbone. The backbone generally refers to the longest series of covalently bonded atoms that together create a continuous chain of polymer molecules. In certain other cases, the optionally substituted quinones described herein may be part of the backbone of the redox-active polymer.

[0040] The electroactive species (e.g., the first electroactive species) may comprise a crosslinked polymeric material. For example, in some embodiments, the electroactive species comprises or is incorporated into a hydrogel, an ionogel, an organogel, or a combination thereof. Such crosslinked polymeric materials are generally known in the art and, in some cases, may comprise the electroactive species described herein as part of their three-dimensional structure (e.g., via covalent bonding). However, in some embodiments, the electroactive species is incorporated into the crosslinked polymeric material via adsorption (e.g., physisorption and / or chemisorption). In some embodiments, the electroactive species comprises an extended network structure. 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 may comprise functionalized graphene, functionalized carbon nanotubes, functionalized carbon nanoribbons, edge-functionalized graphite, or a combination thereof.

[0041] In some embodiments, a separator is located between the negative electrode and the positive electrode. For example, referring to FIG. 1B, separator 130 is located between negative electrode 110 and positive electrode 120. The separator can serve as a protective layer that can prevent the respective electrochemical reactions at each electrode from interfering with each other. The separator may help electronically isolate the negative electrode and positive electrode from each other and / or from other components in the electrochemical cell to prevent short circuits. Those skilled in the art, with the benefit of this disclosure, will be able to select an appropriate separator. The separator may include a porous structure. In some cases, the separator is or includes a porous solid material. In some embodiments, the separator is or includes a membrane. The separator membrane may be made of a suitable material. For example, the separator membrane may be or include a plastic film. Non-limiting examples of included plastic films include polyamide, polyolefin resin, polyester resin, polyurethane resin, or acrylic resin, containing lithium carbonate, potassium hydroxide, or sodium-potassium peroxide dispersed therein. Materials for the separator may include cellulose membranes, polymeric materials, or polymer-ceramic composites. Other examples of separators include polyvinylidene difluoride (PVDF) separators, PVDF-alumina separators, or Celgard.

[0042] In some embodiments, an electrochemical cell includes one or more separators that contain or are capable of containing a conductive liquid (e.g., an ionic liquid). For example, referring to FIG. 1B , separator 130 of electrochemical cell 100 may contain or be capable of containing a conductive liquid. A conductive liquid generally refers to a liquid that has a relatively high conductivity at room temperature (23° C.). A conductive liquid may have a conductivity high enough to facilitate electrochemical reactions in an electrochemical circuit including a negative electrode and a positive electrode. A conductive liquid is generally ionically conductive in that it can facilitate the transport of ions. However, a conductive liquid generally has a relatively low electronic conductivity (e.g., conductivity due to the movement of electronic charges, such as via electrons or holes) to prevent short-circuiting of the electrochemical cell.

[0043] In some cases, a separator containing a conductive liquid is at least partially (or completely) impregnated with the conductive liquid. For example, the separator may absorb a certain amount of conductive liquid after immersion, coating, soaking, or other techniques involving the conductive liquid. In some such cases where the separator is porous, some or all of the separator's pores (inside the separator and / or near the surface) may become at least partially filled with the conductive liquid. In some embodiments, the separator is saturated with the conductive liquid. A separator saturated with the conductive liquid generally refers to a separator containing the maximum amount of conductive liquid that can be contained within the volume of the separator at room temperature (23°C) and ambient pressure. In some embodiments, the electrochemical cell may be provided without the presence of a conductive liquid in the separator, but the separator may contain a conductive liquid when put into operation to perform a gas separation process. One way in which the separator may be able to contain a conductive liquid is by having a relatively high porosity and / or by containing a material capable of absorbing and / or wetting the conductive liquid.

[0044] In some embodiments, the conductive liquid comprises an ionic liquid, such as a room temperature ionic liquid ("RTIL"). RTIL electrolytes have low volatility (i.e., a room temperature vapor pressure of 10 -5 Pa, e.g., 10 -10 From 10 -5 Pa), which may reduce the risk of drying out of the electrode and allow gas to flow through the electrode without significant loss of evaporation or entrainment. In some embodiments, the ionic liquid comprises substantially all (e.g., at least 80% by volume, at least 90% by volume, at least 95% by volume, at least 98% by volume, at least 99% by volume, at least 99.9% by volume) of the conductive liquid.

[0045] Ionic liquids can include an anion component and a cation component. Anions of ionic liquids include, but are not limited to, halides, sulfates, sulfonates, carbonates, bicarbonates, phosphates, nitrates, acetates, PF6 - , BF4 -, triflate, nonaflate, bis(triflyl)amide, trifluoroacetate, heptafluorobutanoate, haloaluminate, triazolidine, and amino acid derivatives (e.g., proline with the nitrogen proton removed). Cations of the ionic liquids may include, but are not limited to: imidazolium, pyridinium, pyrrolidinium, phosphonium, ammonium, sulfonium, thiazolium, pyrazolium, piperidinium, triazolium, pyrazolium, oxazolium, guanadinium, and dialkylmorpholinium. In some embodiments, room temperature ionic liquids include imidazolium as the cationic component. As an example, in some embodiments, room temperature ionic liquids include 1-butyl-3-methylimidazolium (“Bmim”) as the cationic component. In some embodiments, room temperature ionic liquids include bis(trifluoromethylsulfonyl)imide (“TFN”) as the anionic component. In some embodiments, the room temperature ionic liquid has the following formula (IIA): [ka] The compound includes 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][TFN]) represented by the formula:

[0046] In some embodiments, the room temperature ionic liquid has the following formula (IIB): [ka] and 1-butyl-3-methylimidazolium tetrafluoroborate (BF4) ([Bmin][BF4]), represented by

[0047] In some embodiments, the conductive liquid comprises a low-volatility electrolyte solution. For example, the conductive liquid may comprise 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 comprise N,N-dimethylformamide (DMF) or the like.

[0048] With respect to the positive electrode, in some embodiments, the positive electrode includes a second electroactive species. The second electroactive species may be of 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 the second electroactive species. The complementary electroactive layer may be in the form of a composite and thus may be a complementary electroactive composite layer. In operation, this second electroactive species may serve as an electron source for the reduction of the first electroactive species present in the negative electrode. Similarly, the second electroactive species may serve as a sink for electrons during the oxidation of the first electroactive species. In this manner, the electroactive layer of the positive electrode may 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 includes a polymer that includes ferrocene (e.g., as a moiety attached to the polymer backbone). In some embodiments, the second electroactive species includes a metallocene (e.g., ferrocene). In some such cases, the second electroactive species includes a redox-active polymer that includes a metallocene. As a non-limiting embodiment, the redox-active polymer includes polyvinylferrocene. As another example, the second electroactive species can include a polymer that includes a thiophene. In some such cases, the second electroactive species includes poly(3-(4-fluorophenyl)thiophene). In some embodiments, the second electroactive species includes phenothiazine. As another example, in some embodiments, the second electroactive species includes (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (referred to as "TEMPO"), or a derivative thereof (e.g., including optional substituents). In certain cases, the second electroactive species comprises a faradaic redox species having a standard reduction potential at least 0.5 volts (V), at least 0.6 V, at least 0.8 V, and / or up to 1.0 V, up to 1.5 V, or more positive than the primary reduction potential of the first electroactive species.

[0049] 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). Examples of carbonaceous materials include carbon nanotubes (e.g., single-walled carbon nanotubes, multi-walled carbon nanotubes), carbon black, Ketjen Black, carbon black Super P, or graphene. Other materials are possible. In certain cases, the second electroactive species can be immobilized on the positive electrode by being included in a composition (e.g., a coating, composite layer, etc.) applied or deposited on the positive electrode. In certain cases, the second electroactive species (e.g., a polymer or molecular electroactive material) infiltrates a microfiber, nanofiber, or carbon nanotube mat associated with the positive electrode, such that the second electroactive species is immobilized relative to the mat in the positive electrode. The second electroactive species can also be part of a gel associated with the positive electrode in the same or similar manner as described above for the first electroactive species.

[0050] According to one or more embodiments, the electroactive composite layer of the positive electrode can have a specific weight ratio of electroactive material to carbonaceous material. The weight ratio can be selected to facilitate a high 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 can be between 1:2 and 2:1. In some embodiments, the ratio can be 1:1. Other ratios are possible.

[0051] 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 , the negative electrode 110 includes a composite electroactive composite layer 114 facing the positive electrode 120, according to certain embodiments. In certain 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 may also be referred to as a complementary electroactive composite layer, since the electroactive species therein serve as an electron acceptor or electron source for the electroactive material of the negative electrode. In some cases, the electroactive composite layer of an electrode (e.g., negative electrode, positive electrode) spans the entire thickness dimension of the electrode. For example, the electroactive composite layer may intercalate throughout the 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 intercalates through a portion of the electrode's thickness, but not the entire thickness. In certain 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.).

[0052] In some embodiments, the electroactive species of the electrodes (e.g., a first electroactive species of the negative electrode, a second electroactive species of the positive electrode) are part of an electroactive composite layer. For example, in FIG. 1B , electroactive composite layer 114 includes a first electroactive species described herein, according to some embodiments. Similarly, in some embodiments, electroactive composite layer 124 includes a second electroactive species (e.g., polyvinylferrocene).

[0053] The negative electrode electroactive composite layer can also include a carbonaceous material in addition to the electroactive species. 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 include immobilizing and / or coating electroactive species (e.g., in polymeric, molecular, or other form) in / on microfibers, nanofibers, or carbon nanotube mats by intercalation, grafting, chemical vapor deposition (CVD), or otherwise.

[0054] According to one or more embodiments, the electroactive composite layer of the negative electrode can have a specific weight ratio of electroactive species to carbonaceous material. The weight ratio can be selected to facilitate a high current per mass of electroactive material. In some embodiments, the weight ratio of the mass of electroactive material to the mass of carbonaceous material can be between 1:1 and 1:10. In some embodiments, the ratio can be 1:3. Other ratios are possible.

[0055] The negative electrode may further include a gas permeation layer. The gas permeation layer (which may also be referred to as a substrate layer) may be adjacent to the electroactive composite layer and face outward from the electrochemical cell. In some embodiments, the gas permeation layer is in contact with the first electroactive species. In some such cases, the gas permeation layer is in direct contact with the first electroactive species, and in other such cases, the gas permeation layer is in indirect contact with the first electroactive species. When a portion (e.g., a layer) is referred to as "on" or "in contact with" another portion, it should be understood that the portion can be directly on the other portion, or that an intervening portion (e.g., layer) may be present (in which case the portion is understood as "indirectly on" or "in indirect contact with" the other portion). A portion "directly on" or "in direct contact with" another portion means that no intervening portion is present. Also, when a portion is referred to as "on" or "in contact with" another portion, it should be understood that the portion can cover all or part of the other portion. In some embodiments, the gas permeable layer is in contact (eg, in direct contact or indirect contact) with the electroactive composite layer of the negative electrode.

[0056] The gas stream can diffuse through the gas permeable layer and contact the electroactive composite layer. The gas permeable layer can include an electrically conductive solid material and act as a current collector in the cell.

[0057] The gas permeable layer may comprise a porous material. In some embodiments, the gas permeable layer has a porosity of, for example, 60% or more, 70% or more, 75% or more, 80% or more, or more. In some embodiments, the gas permeable layer has a porosity of 85% or less, 90% or less, or more. Combinations of these ranges are possible. For example, in some embodiments, the gas permeable layer of the negative electrode has a porosity of 60% or more and 90% or less. Other porosities are also possible. 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 nonwoven carbon mats. Other materials may also be used.

[0058] In some embodiments, the electrochemical cell includes a single negative electrode, while 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 includes a second negative electrode. A positive electrode can be present between the first negative electrode and the second negative electrode. The second negative electrode can also include a first electroactive species. The second negative electrode can be identical in construction and composition to the first negative electrode. In some embodiments, the electrochemical cell includes one or more negative electrodes, two or more negative electrodes, three or more negative electrodes, five or more negative electrodes, ten or more negative electrodes, and / or up to 15 negative electrodes, up to 20 negative electrodes, up to 50 negative electrodes, or more.

[0059] In some embodiments, the electrochemical cell includes a single separator (e.g., between the negative electrode and the positive electrode), while 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 includes a second separator. In some embodiments in which a second negative electrode is present, the second separator can be present between the positive electrode and the second negative electrode. The second separator may be identical in construction and composition to the first separator. In certain cases, the second separator can include a conductive liquid (e.g., be saturated with a conductive liquid). In some embodiments, the electrochemical cell includes one or more separators, two or more separators, three or more separators, five or more separators, ten or more separators, and / or up to 15 separators, up to 20 separators, up to 50 separators, or more. In some cases, each of the separators is present between the respective negative and positive electrodes.

[0060] In some embodiments of electrochemical cells in which a positive electrode has negative electrodes on either side (e.g., a first negative electrode and a second negative electrode), the positive electrode includes a second electroactive species facing each of the negative electrodes. In some such embodiments, the positive electrode includes two complementary electroactive composite layers, each facing one of the negative electrodes.

[0061] The positive electrode may further include a substrate layer disposed adjacent to or between one or more electroactive composite layers. The substrate layer may be in direct or indirect contact with one or more electroactive composite layers. The substrate layer of the positive electrode may comprise the same or a different material as the substrate layer of the negative electrode (if present). For example, the substrate layer may comprise a material such as carbon paper (treated, TEFLON®-treated, or untreated), carbon cloth, or a nonwoven carbon mat. In some embodiments, the substrate may comprise, for example, a mat including carbon nanotubes, microfibers, nanofibers, or a combination thereof. Other materials are also possible. The substrate layer of the positive electrode may comprise a conductive material and act as a current collector in the cell. In some embodiments, the substrate comprises a metal and / or a metal alloy. For example, the substrate may include a metal and / or metal alloy foil (e.g., having a relatively small thickness of 200 microns or less, 100 microns or less, 10 microns or less, and / or only 1 micron or less). Examples of suitable foils may include, but are not limited to, aluminum foil and titanium foil. As a specific example, in some embodiments, a positive electrode includes a substrate between a first complementary electroactive composite layer facing a first negative electrode and a second complementary electroactive composite layer facing a second negative electrode. In this situation, the electroactive composite layer of a positive electrode can face a particular electrode (e.g., a negative electrode) if a line extending from a majority of the electroactive composite layer can intersect that electrode without passing through the substrate. An object (e.g., an electroactive composite layer) can face another object if it contacts the other object or if one or more intermediate materials are disposed between the surface and the other object. For example, two objects facing each other can be in contact or can include one or more intermediate materials (eg, separators) between them.

[0062] FIG. 2 illustrates an example of an electrochemical cell having one or more of the aforementioned components according to some, but not necessarily all, embodiments. The electrochemical cell 100 includes a positive electrode 120 between two negative electrodes 110. A separator 130 separates the positive and negative electrodes 120. Each of the negative electrodes 110 includes an optional gas permeable layer 112 located 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 substrate layer 122 and two complementary electroactive composite layers 124 thereon. The various components of the electrochemical cell 100, including the aforementioned electrode materials (e.g., electroactive species), can have certain characteristics described throughout this disclosure. For example, the configuration of two outward-facing negative electrodes 110 shown in FIG. 2 may, in some cases, offer the advantage of doubling the gas adsorption area exposed to gas compared to an electrochemical cell including a single negative electrode and a single positive electrode. The electrochemical device can be provided in any of a variety of forms, depending on the desired application and / or properties of the fluid mixture. The electrochemical device can be configured to electrochemically capture and / or separate Lewis acid gases from a gas mixture. In some such cases, the electrochemical device includes a chamber having a gas or vacuum headspace that can be at least partially filled with the gas fluid mixture. In some such embodiments, the fluid inlet of the chamber is fluidly connected to a source of the gas mixture and one or more components for transporting the gas mixture, such as a pump or vacuum valve and associated valves.

[0063] According to one or more embodiments, the target gas includes 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 includes a gas that can complex with the electroactive species of the negative electrode when the electroactive species is in its reduced state (e.g., by binding to the species in its reduced state). According to one or more embodiments, the target gas includes carbon dioxide (CO2). According to one or more embodiments, the target gas includes sulfur dioxide (SO2). According to one or more embodiments, the target gas includes borane (BR3), where 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 includes one chemical species (one type of molecule). In some embodiments, the target gas includes more than one chemical 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 concentration and stripping of the target gas may be controlled by applying an appropriate potential difference applied across the electrochemical cell.

[0064] 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 outside air). Ambient air generally refers to air found in an unenclosed location, such as outdoors. In some such cases, the electrochemical cell is used for direct air capture. The systems and methods described herein can be useful techniques for extracting target gases, such as carbon dioxide, directly from ambient air (e.g., for reducing greenhouse gas levels) without the need to pre-concentrate the target gas. Certain aspects of the present disclosure make the systems and methods described herein particularly useful for direct air capture (e.g., being able to bind to target gases while being thermodynamically unfavorable for reacting with major components of ambient air, such as oxygen).

[0065] 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 before exposure to the electrochemical cell is less than or equal to 500 ppm, less than or equal to 450 ppm, less than or equal to 400 ppm, less than or equal to 350 ppm, less than or equal to 300 ppm, less than or equal to 200 ppm, or even lower. In some embodiments, the concentration of the target gas in the gas mixture is as low as 100 ppm, as low as 50 ppm, as low as 10 ppm, or even lower. 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 500 ppm, or as low as 10 ppm. In some embodiments where the target gas is carbon dioxide, the concentration of carbon dioxide in the gas mixture before exposure to the electrochemical cell is less than or equal to 500 ppm, less than or equal to 450 ppm, less than or equal to 350 ppm, or lower. In some embodiments, the concentration of carbon dioxide in the gas mixture before exposure to the electrochemical cell is greater than or equal to 300 ppm, greater than or equal to 350 ppm, or higher. Combinations of these ranges are possible. For example, in some embodiments, the concentration of carbon dioxide in the gas mixture before exposure to the electrochemical cell is greater than or equal to 300 ppm and less than or equal to 400 ppm, or greater than or equal to 300 ppm and less than or equal to 500 ppm.

[0066] 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 ventilated air. The ventilated air may be air from an enclosed or at least partially enclosed space (e.g., air is circulated within the enclosed space). Examples of spaces within which the gas mixture (e.g., ventilated air) may be located include, but are not limited to, enclosed buildings, partially ventilated spaces, vehicle cabins, occupied submersibles, aircraft, and the like.

[0067] The concentration of the target gas in the ventilated air may be higher than that in ambient air, but lower than that typical for industrial processes. In some embodiments, the concentration of the target gas in the gas mixture before exposure to the electrochemical cell is less than or equal to 5,000 ppm, less than or equal to 4,000 ppm, less than or equal to 2,000 ppm, less than or equal to 1,000 ppm, or lower. In some embodiments, the concentration of the target gas in the gas mixture (e.g., in the case of ventilated air / enclosed space air) is as low as 1,000 ppm, as low as 800 ppm, as low as 500 ppm, as low as 200 ppm, as low as 100 ppm, as low as 10 ppm, or lower. 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 5,000 ppm, or as low as 500 ppm. In some embodiments where the target gas is carbon dioxide, the concentration of carbon dioxide in the gas mixture prior to exposure to the electrochemical cell is less than or equal to 5,000 ppm, less than or equal to 4,000 ppm, less than or equal to 2,000 ppm, less than or equal to 1,000 ppm, less than or equal to 500 ppm, or lower. 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 10 ppm, greater than or equal to 100 ppm, greater than or equal to 300 ppm, greater than or equal to 500 ppm, greater than or equal to 1,000 ppm, greater than or equal to 2,000 ppm, 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 500 ppm and less than or equal to 5,000 ppm, or greater than or equal to 10 ppm and less than or equal to 5,000 ppm.

[0068] In some embodiments, the gas mixture includes oxygen gas (O). Some such embodiments include cases where the gas mixture includes ambient air or ventilated air, or even higher purity oxygen gas mixtures. In some, but not necessarily all, embodiments, the gas mixture has a relatively high concentration of oxygen gas (e.g., before exposure to the electrochemical cell). Certain aspects of the systems and methods described herein (e.g., selection of specific electroactive species, methods of handling gases in the system, etc.) may contribute to the ability to capture target gases in gas mixtures where oxygen gas is present without harmful interference. In some embodiments, oxygen gas is present in the gas mixture (e.g., prior to exposure to an electrochemical cell) at a concentration greater than or equal to 0% by volume, greater than or equal to 0.1% by volume, greater than or equal to 1% by volume, greater than or equal to 2% by volume, greater than or equal to 5% by volume, greater than or equal to 10% by volume, greater than or equal to 20% by volume, greater than or equal to 50% by volume, greater than or equal to 75% by volume, greater than or equal to 90% by volume, greater than or equal to 95% by volume, greater than or equal to 99% by volume, greater than or equal to 99.9% by volume, greater than or equal to 99.99% by volume, or greater than or equal to. In some embodiments, oxygen gas is present in the gas mixture at a concentration of substantially less than or equal to 100% by volume, less than or equal to 99.9999% by volume, less than or equal to 99.999% by volume, less than or equal to 99.99% by volume, less than or equal to 99.9% by volume, less than or equal to 99.9% by volume, less than or equal to 99.9% by volume, less than or equal to 99% by volume, less than or equal to 95% by volume, less than or equal to 90% by volume, less than or equal to 75% by volume, less than or equal to 50% by volume, less than or equal to 25% by volume, less than or equal to 21% by volume, less than or equal to 10% by volume, less than or equal to 5% by volume, less than or equal to 2% by volume, or less. Combinations of these ranges are possible.For example, in some embodiments, oxygen gas is present in the gas mixture at concentrations greater than or equal to 0% by volume and substantially less than or equal to 100% by volume (e.g., for specialized high O combustion processes), greater than or equal to 0% by volume and less than or equal to 50% by volume, greater than or equal to 0% by volume and less than or equal to 21% by volume (e.g., in incomplete combustion processes), and greater than or equal to 10% by volume and less than or equal to 25% by volume (e.g., for ventilated air or direct air capture processes).

[0069] In some embodiments, the gas mixture undergoing at least partial gas separation contains water vapor. The gas mixture may be or include ambient air or ventilated air, and thus may include water vapor, for example. 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 greater than 10% at at least one temperature in the range between -50°C and 100°C. 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 lower at at least one temperature in the range between -50°C and 100°C.

[0070] The gas mixture (e.g., input gas mixture) that undergoes at least partial separation by exposure to the electrochemical cell may have any of a variety of pressures when exposed to the electrochemical cell. For example, the gas mixture may have a 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 more. The gas mixture may have any of these pressure values ​​while containing the target gas and oxygen in any of the concentration ranges described above.

[0071] According to one or more embodiments, the electrochemical cells generally described herein can 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, while in certain cases, the air is ambient air (e.g., in direct air capture embodiments). However, the gas mixture is not limited to such embodiments. For example, in some embodiments, the gas mixture is gas from an industrial process (e.g., flue gas). In some embodiments, the electrochemical cell can be operated to perform a gas separation process involving a gas mixture. For example, the electrochemical cell can be operated to remove a portion of a target gas from the gas mixture. In some such cases, operating the electrochemical cell includes exposing the gas mixture to the electrochemical cell. The gas mixture can be exposed to the electrochemical cell such that the target gas binds to the first electroactive species to produce a treated gas mixture having a lower amount of target gas than the gas mixture initially exposed to the electrochemical cell (sometimes referred to as the "input gas mixture").

[0072] The process of at least partially separating the target gas from the gas mixture may include applying a potential difference across an electrochemical cell. Those skilled in the art will understand, with the benefit of this disclosure, how to apply a potential across an electrochemical cell. One way to apply the potential is by connecting the negative and positive electrodes to a suitable power source capable of polarizing the negative and positive electrodes. In some embodiments, the power supply to the system is a DC voltage. Non-limiting examples include batteries, power grids, renewable power suppliers (e.g., wind turbines, photovoltaic cells, tidal energy generators), generators, and the like. The power source may include one or more such power suppliers (e.g., batteries and photovoltaic cells).

[0073] In some embodiments, the process further includes exposing the electrochemical cell to the gas mixture. The potential difference may be applied during at least a portion of the time the gas mixture is exposed to the electrochemical cell. However, some embodiments include applying the potential difference before exposing the gas mixture to the electrochemical cell. In other words, in some embodiments, exposing the gas pressure to the electrochemical cell occurs during and / or after applying the potential difference across the electrochemical cell. In some embodiments, exposing the gas mixture to the electrochemical cell includes introducing a gas stream containing a target gas (e.g., CO) into the electrochemical cell to combine the target gas with a first electroactive species to produce a treated gas mixture (e.g., a treated gas stream).

[0074] According to some embodiments, application of a positive voltage to an electrochemical cell during a charging mode causes a redox half-reaction at the negative electrode, resulting in the reduction of an electroactive species. As discussed herein, the electroactive species of the negative electrode are selected for their higher affinity for a target gas (e.g., CO) when in a reduced state relative to when in an oxidized state. By reducing the electroactive species and passing a gas mixture (e.g., ventilated air, ambient air, industrial gas stream) across the surface of the negative electrode, the target gas (e.g., CO) can bind to the electroactive species. In this manner, the target gas can be removed from the gas mixture to provide a treated gas mixture (e.g., containing a lower amount of target gas than the gas mixture).

[0075] As a non-limiting example, in some embodiments where the electroactive species at the negative electrode is an optionally substituted quinone, the electroactive species can be reacted with an optionally substituted quinone by the following reaction (1): [ka] to at least one of its reduced states by

[0076] Again by way of non-limiting example, in some embodiments where the electroactive species is reduced in the presence of a target gas comprising carbon dioxide, reaction (2) below can be performed: [ka] occurs.

[0077] In some embodiments, a first electroactive species (e.g., an optionally substituted quinone) is reduced at the negative electrode, while a 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 a source of electrons to drive the reduction of the first electroactive species.

[0078] Again by way of non-limiting example, in some embodiments in which the electroactive species of the positive electrode comprises polyvinylferrocene, this second electroactive species can be reacted with polyvinylferrocene by the following reaction (3): [ka] It may be oxidized by

[0079] Each of reactions (1)-(3) is shown to occur in one direction, but some reversibility may be exhibited. As will be appreciated by those skilled in the art, similar reactions may occur using different chemical species.

[0080] In some embodiments, the second electroactive species comprises an intercalation compound. For example, the second electroactive species may comprise a metal ion intercalation compound. One exemplary class of intercalation compounds comprises metal oxides. The intercalation compound may comprise an alkali metal ion intercalation compound, such as lithium ion and / or sodium ion. In some embodiments, the intercalation compound comprises an alkali metal ion transition metal oxide (e.g., lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and / or lithium oxide containing cobalt, manganese, and / or nickel). In some embodiments, the intercalation compound comprises an alkali metal transition metal polyoxyanion, such as a lithium transition metal phosphate. One example of a lithium transition metal phosphate suitable for the positive electrode is lithium iron phosphate (LiFePO4). In some embodiments, during a charge mode, oxidation of a second electroactive species in the form of an alkali metal ion intercalation compound (e.g., LiFePO) provides a source of electrons to drive the reduction of the first electroactive species, while simultaneously releasing alkali metal ions (e.g., lithium ions) that can shuttle through the electrolyte (e.g., on or in the separator, if present) to the negative electrode to maintain charge balance and complete the electrochemical circuit. Conversely, during a discharge mode, reduction of the second electroactive species in the form of an alkali metal ion intercalation compound provides an acceptor for electrons from the oxidation of the first electroactive species, while alkali metal ions (e.g., lithium ions) can shuttle from a region near the negative electrode through the electrolyte (e.g., on or in the separator, if present) toward the positive electrode, where they can intercalate into the intercalation compound and maintain charge balance.

[0081] According to one or more embodiments, after charging the electrochemical cell by applying a potential difference across the positive and negative electrodes, electrons flow from the moiety of the second electroactive species (e.g., ferrocene (Fc) units in the pVFc-CNT composite) on the positive electrode, thus oxidizing the second electroactive species (e.g., converting ferrocene to ferrocenium (Fc + ) (as shown by reaction (3)), which flows through an external circuit to the anode. At the anode, the first electroactive species (e.g., the optionally substituted quinone unit in the CNT composite) is reduced (e.g., to the semiquinone or dianion form of the optionally substituted quinone) in the presence of the target gas (e.g., CO), which then diffuses into the anode. In its reduced state, the electroactive species (e.g., the optionally substituted quinone dianion) readily binds to CO via a covalent bond to form a complex, as shown in equation (2).

[0082] The potential difference applied across the electrochemical cell may have a specific voltage during the charging mode. The potential difference applied across the electrochemical cell may depend, for example, on the standard reduction potential for generation of at least one reduced state of the first electroactive species and, if present, the standard reduction potential for interconversion between the reduced and oxidized states of the second electroactive species. In some embodiments, the potential difference is at least 0 V, at least 0.1 V, at least 0.2 V, at least 0.5 V, at least 0.8 V, at least 1.0 V, at least 1.5 V, or higher. In some embodiments, the potential difference is less than or equal to 2.0 V, less than or equal to 1.5 V, less than or equal to 1.0 V, less than or equal to 0.5 V, or less. Combinations of these voltages are also possible. For example, in some embodiments, the potential difference applied across the electrochemical cell is at least 0.5 V and less than or equal to 2.0 V. Other values ​​are also possible.

[0083] FIG. 3A shows an exploded view of an exemplary electrochemical cell 100a operating in a charging mode, according to one or more embodiments. Components of the electrochemical cell 100a may be as described with respect to the electrochemical cell 100 described herein with respect to FIG. 2. As shown in FIG. 3A, a power source 140a and wiring 150a are used to apply a potential difference across the electrochemical cell, according to certain embodiments. This, according to certain embodiments, induces electron flow 160a in the external circuit 150a, directing the electrons to each primary electroactive composite layer 114a of the negative electrode 110a. In some embodiments, a redox half-cell reaction occurs in the electroactive composite layer 114a to reduce a first electroactive species immobilized within layer 114a. In its reduced state, the electroactive species, according to certain embodiments, exhibits an increased affinity for a target gas in a gas mixture (not shown). The target gas in the gas stream can permeate through the gas permeable layer 112a of the anode and bind to the reduced material in the composite layer 114a.

[0084] In some embodiments, a relatively large amount of target gas is removed from the gas mixture during the processes described herein. Removal of a relatively large amount of target gas can be beneficial in any of a variety of applications, such as, in some cases, capturing gases that may be harmful if released into the atmosphere for environmental reasons. As an example, in some embodiments, the target gas comprises carbon dioxide, and removing a relatively high amount of carbon dioxide from the gas mixture can also be beneficial for limiting greenhouse gas emissions of a process (e.g., an industrial or transportation process) or reducing the amount of carbon dioxide in a space or atmosphere (for thermodynamic reasons related to heating and air conditioning processes or for environmental reasons).

[0085] In some embodiments, the amount of target gas in the treated gas mixture (e.g., a gas mixture from which a quantity of target gas is removed after exposure to an 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 than the amount (in volume percent) of target gas in the original gas mixture before treatment (e.g., the amount of target gas in the gas mixture before exposure to an 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 or equal to 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 than the amount of target gas (by volume percent) in the original gas mixture before treatment.

[0086] In some embodiments, the amount of target gas in the treated gas mixture (e.g., a gas mixture from which a quantity of target gas is removed after exposure to an 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 than the amount (in mole percent) of target gas in the original gas mixture before separation (e.g., the amount of target in the gas mixture before exposure to an electrochemical cell). In some embodiments, the amount of target gas and treated gas mixture is greater than or equal to 0.001%, greater than or equal to 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 of target gas (in mole percent) in the original gas mixture before treatment.

[0087] In some embodiments, the methods described herein can be used to remove a quantity of target gas from a gas mixture (e.g., during and / or after applying a potential across the electrochemical cell), while also removing a relatively low amount of any oxygen gas (O) that may be present in the gas mixture. In some such cases, this is beneficial because reactivity with oxygen gas can be detrimental to the performance of the described systems and methods (e.g., reduced capture efficiency, damage to electrochemical cell components, etc.). Any of several features described herein, alone or in combination, can contribute to the ability to remove a quantity of target gas from a gas mixture, while also removing a relatively low amount of any oxygen that may be present in the gas mixture. For example, the use of a first electroactive species at the negative electrode having a reduced state in which the species can combine with the target gas but in which reactivity with oxygen is thermodynamically unfavorable, can enable removal of a relatively high amount of target gas due to little to no oxygen gas transfer.

[0088] One non-limiting way in which a target gas can be removed from a gas mixture with little to no oxygen gas being removed is by applying a particular potential across the electrochemical cell during at least a portion of operation. For example, in the context of the present disclosure, it has been discovered that a potential (e.g., a first potential) can be applied across the electrochemical cell that is sufficient to reduce a first electroactive species to at least one reduced state capable of reacting with the target gas, but is insufficient for the active species (or the electrode itself) to reach a state capable of reacting with oxygen (e.g., to form superoxide ions or peroxide dianions). Judicious selection of the first electroactive species can make it possible to apply such a potential, whereas certain conventional electroactive species cannot. The potential applied across the electrochemical cell is such that the electrode potential of the negative electrode is positive (e.g., by being greater than or equal to 10 mV, greater than or equal to 50 mV, greater than or equal to 100 mV, greater than or equal to 200 mV, greater than or equal to 5 mV, and / or up to or greater than 1 V) relative to the standard reduction potential for the interconversion of oxygen gas and superoxide ions or superoxide ions and peroxide ions.

[0089] In some embodiments, a quantity of target gas (e.g., CO) is removed from the gas mixture during and / or after 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 even lower, of any oxygen gas (volume %) present in the gas mixture is removed from the gas mixture. In some embodiments, a quantity of target gas is removed from the gas mixture during and / or after application of the potential difference, and no oxygen gas is removed from the gas mixture (e.g., during removal of the target gas). These ranges for removing oxygen from the gas mixture may be achievable even when oxygen gas is present in the gas mixture in relatively high amounts (e.g., greater than or equal to 0% by volume, greater than or equal to 1% by volume, greater than or equal to 5% by volume, greater than or equal to 10% by volume, greater than or equal to 21% by volume, greater than or equal to 50% by volume, and / or up to 75% by volume, up to 90% by volume, up to 99% by volume, substantially 100% by volume, or more).

[0090] In some, but not necessarily all, cases where oxygen is present in the gas mixture, an amount of oxygen gas is removed from the gas mixture during at least a portion of the time that an amount of target gas is removed from the gas mixture (e.g., during and / or after application of the electrochemical potential). In some such embodiments, the ratio of the amount of target gas removed to the amount of oxygen gas removed is greater than or equal to a relatively high value. The ratio may be relatively high, in the case where the reaction between at least one electroactive species in a reduced state formed during and / or after application of the potential across the electrodes and the target gas (e.g., CO) is thermodynamically more favorable than the active species with oxygen gas. In some embodiments, the ratio of the amount of target gas removed to the amount of oxygen gas 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.

[0091] In some embodiments, a positive electrode (e.g., positive electrode 120a in FIG. 3A) serves as a source of electrons during operation in a charging mode. In FIG. 3A, according to certain embodiments, a corresponding redox half-cell reaction occurs in the complementary electroactive composite layer 124a of the positive electrode 120a, oxidizing the electroactive species. The oxidation reaction can release electrons from the complementary electroactive species (e.g., polyvinylferrocene). These electronic reaction products may then travel within the substrate layer 122a and / or external wiring 150a to complete the circuit, according to certain embodiments. A separator 130a separates the positive and negative electrodes 120a and 110a, according to certain embodiments.

[0092] According to one or more embodiments, operating the electrochemical cell further includes applying a second potential across the electrochemical cell to release the target gas bound to the first electroactive species. In some embodiments, releasing the target gas produces a product or treated gas mixture having a higher concentration of the target gas than the initial gas mixture exposed to the electrochemical cell (e.g., a target gas-rich gas mixture, such as a target gas-rich gas stream). According to some embodiments, after the electrochemical cell has operated in a charge mode for a period of time during which the target gas is bound to the first electroactive species at the negative electrode, operation may be switched to a discharge mode. During operation in the discharge mode, the applied voltage is switched to provide electron flow in the opposite direction from that during the charge mode. While operating in the discharge mode, a negative voltage may be applied across the electrochemical cell. During the discharge mode, a redox half-reaction occurs at the negative electrode, oxidizing the first electroactive species at the negative electrode. During operation in the discharge mode, the target gas may be released from the electroactive species bound thereto at the negative electrode.

[0093] According to some embodiments, where the electroactive species of the negative electrode is an optionally substituted quinone, the electroactive species is reacted with the quinone via the following reaction (4): [ka] is oxidized during the discharge mode according to

[0094] According to some embodiments, the electroactive species is oxidized after binding to a target gas comprising carbon dioxide, as shown in reaction (5): [ka] may occur.

[0095] According to some embodiments, a first electroactive species (e.g., including an optionally substituted quinone) is oxidized at the negative electrode while a second electroactive species (e.g., polyvinylferrocene) is reduced at the positive electrode. During the discharge mode, the reduced second electroactive species serves as an electron acceptor.

[0096] According to some embodiments, where the electroactive species of the positive electrode comprises polyvinylferrocene, this second electroactive species is reacted with the positive electrode via the following reaction (6): [ka] will be reduced according to the

[0097] Each of reactions (4)-(6) is shown to occur in one direction, but some reversibility may be demonstrated. Similar reactions may occur using different chemical species, as will be understood by those of skill in the art with the benefit of this disclosure.

[0098] According to some such embodiments, the electroactive species at the negative electrode are oxidized by discharging the electrochemical cell when the polarization of the external circuit changes, allowing electrons to flow in the reverse direction compared to the charging process. The covalent bond formed between the optionally substituted quinone and the CO molecule is broken (as shown in reaction (5)), releasing CO gas that diffuses out of the negative electrode, and the electrons flow to the positive electrode, resulting in Fc + The unit is reduced to Fc (according to certain embodiments, as shown in reaction (6)). According to some such embodiments, polyvinylferrocene may serve as an electron source for the reduction of an optionally substituted quinone or as an electron acceptor for the oxidation of a carbon dioxide adduct of an optionally substituted quinone.

[0099] The potential difference across the electrochemical cell may have a particular voltage during the discharge mode. For example, in some embodiments, the potential difference may be less than 0 V, less than or equal to −0.5 V, less than or equal to −1.0 V, or less than or equal to −1.5 V. In some embodiments, the potential difference may be at least −2.0 V, at least −1.5 V, at least −1.0 V, or at least −0.5 V. Combinations of these voltages are also possible, such as at least −2.0 V and less than or equal to −0.5 V. Other values ​​are also possible.

[0100] FIG. 3B shows an exploded view of an exemplary electrochemical cell 100b operating in a discharge mode according to one or more embodiments. The components of the electrochemical cell 100b are the same as those of the cell 100a of FIG. 3A, according to certain embodiments. However, according to certain embodiments, the voltage applied by the power supply 140b is changed to create a potential difference through external wiring 150b that reverses the direction of the electron flow 160b relative to the direction of the electron flow 160a of FIG. 3A. In the discharge mode, according to some embodiments, a redox half-cell reaction occurs in the electroactive composite layer 114b of the anode 110b, oxidizing the first electroactive species immobilized in layer 114b. In some embodiments, in its oxidized state, the first electroactive species exhibits a reduced affinity for the target gas, causing the target gas to be released from the electroactive material. The released target gas may exit through the gas permeable layer 112b and be directed toward further processing, sequestration, or other desired destination. Meanwhile, in some embodiments, the positive electrode 120b acts as an electron acceptor during operation in a discharge mode. A half-cell reaction occurs in the complementary electroactive composite layer 124b of the positive electrode 120b, according to some embodiments, to reduce a second electroactive species. In some embodiments, during the reduction reaction, electrons traveling through the wiring 150b and substrate layer 122b combine with the complementary electroactive species, enabling a complete circuit. A separator 130b separates the positive and negative electrodes 120b and 110b, according to some, but not necessarily all, embodiments.

[0101] According to one or more embodiments, one or more electrochemical cells described herein may be incorporated into a gas separation system. The gas separation system may include a plurality of electrochemical cells in fluid communication with a gas inlet and a gas outlet according to any of the embodiments described herein.

[0102] The gas separation system may include an external circuit connecting the negative electrode (or first and second negative electrodes, if both are present) and positive electrode of each electrochemical cell to a power source configured to apply a potential difference across the negative electrode(s) and positive electrode of each electrochemical cell.

[0103] FIG. 4 shows a schematic diagram of an exemplary gas separation system 400 according to one or more embodiments. The system 400 includes a housing 460 having an inlet 470 and an outlet 480, according to certain embodiments. An electrochemical cell 405 is positioned within the housing. While only one cell 405 is shown in FIG. 4 for simplicity, it will be readily understood that multiple cells 405 can be positioned within the housing 460. A power source 440, which may be positioned inside or outside the housing 460, is connected to the cell 405, according to certain embodiments. According to certain embodiments, the negative electrode(s) 410 are connected to the power source 440 through wire 450a, while the positive electrode is connected via wire 450b. As described elsewhere herein, a voltage is applied to operate the cell(s) in a charging mode, while a gas mixture to be at least partially separated (e.g., a gas stream such as ventilated air or ambient air) is delivered via the inlet 470. In some embodiments, the gas mixture includes a target gas designed to be at least partially removed by system 400. The gas mixture then passes near cell 405, particularly near anode(s) 410. In some embodiments, a first electroactive species in at least one of its reduced states in anode 410 binds to the target gas and removes at least a portion of it from the gas mixture. An optional second anode 410, second separator 420, and corresponding wiring 450a are shown in dashed lines, according to certain embodiments. While the embodiment shown in FIG. 4 and other figures optionally includes a housing, it should be understood that the electrochemical cell can be positioned in a variety of environments, for example, in-line in a conduit or in other manners without a housing.

[0104] FIG. 5A shows a schematic diagram of an exemplary system for performing a gas separation process in a charging mode, according to one or more embodiments. In FIG. 5A, a potential difference is applied across each of the electrochemical cells, so that each operates in a charging mode, according to certain embodiments. In the charging mode, according to certain embodiments, a redox reaction (e.g., reduction) of a first electroactive species at the anode 510 increases the affinity between the electroactive species and a target gas 590. A gas mixture 575 including the target gas 590 is introduced into the system and passes near the anode 510. The increased affinity, according to certain embodiments, causes the target gas (e.g., CO) to bind to the electroactive material. In this manner, at least a portion of the target gas is separated from the gas mixture 575 to produce a treated gas mixture 585.

[0105] In some embodiments, a gas separation system includes a plurality of electrochemical cells, and a flow field exists between at least a portion (e.g., some or all) of the plurality of electrochemical cells. By way of example, FIG. 5B shows a schematic diagram of an exemplary system including a flow field 511 separating electrochemical cells 500 that performs a gas separation process during a charging mode, according to one or more embodiments. It should be understood that when a first object exists between a second object and a third object, it can be between the entire first object and the entire second object, or between a portion of 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 of the adjacent electrochemical cells, such that there are no intervening structures / layers between the flow field and the electrochemical cells. However, in some embodiments, the flow field between two adjacent electrochemical cells is indirectly adjacent to one or two cells, such that there are one or more intervening structures / layers, such as conductive solids.

[0106] A flow field generally refers to a solid structure configured to define a path through which a fluid can flow. In some cases, a flow field includes a solid article that defines pores or channels for fluid flow while allowing the fluid to be exposed to adjacent structures. Suitable materials for the solid article in a flow field include, but are not limited to, polymeric materials (e.g., plastics), metals / metal alloys, graphite, and composite materials (e.g., graphite-polymer composites). In some embodiments, a flow field includes a solid article that includes one or more surfaces with patterned channels. The channel pattern can be selected to effectively distribute the 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. 5C, 5D, and 5E show schematic side views of a flow field with a serpentine pattern 511a, a flow field with a parallel pattern 511b, and a flow field with an interdigitated pattern 511c, each with fluid flow directions shown as arrows according to certain embodiments. The flow field channel patterns can be formed by, for example, etching, cutting, stamping, molding, milling, or additive manufacturing. In some embodiments, the flow field comprises a porous solid. For example, the flow field can comprise carbon fiber paper, felt or cloth, or metal foam.

[0107] In FIG. 5B , gas 590 from fluid mixture 575 is distributed along the facial area of ​​electrode 510 via flow field 511 (e.g., via channels not shown). In the context of the present disclosure, it has been found that flow fields can help distribute the gas mixture relatively uniformly across the electrode and can help regulate the duration of gas exposure to the electrode (e.g., to promote efficient capture of the target gas). A relatively uniform gas distribution can increase efficiency by utilizing a greater percentage of the electrode area (e.g., containing at least one reduced-state electroactive species) for binding the target gas. In some embodiments, during at least a portion of the charging process, the flux of the gas mixture across at least 25%, at least 50%, at least 75%, at least 90%, at least 95%, or more of the facial area of ​​the negative electrode of the system is within 50%, 25%, 15%, 10%, 5%, 2%, 1%, or less of the average flux across the entire facial area of ​​the negative electrode during the charging process.

[0108] According to certain embodiments, the system 400 shown in FIG. 4 may also be operated in a discharge mode by changing the applied voltage from the power supply 440 to cause electron flow to reverse the direction of flow in the charge mode. This change causes different redox reactions at the negative electrode 410, one of which, for example, oxidizes a first electroactive species at the negative electrode. Such a change in the electroactive oxidation state may cause the target gas to be released from the electroactive species, producing a treated gas mixture having a higher amount of target gas than the original gas mixture (e.g., input gas mixture). The treated gas mixture may exit through outlet 480 or an alternative outlet (not shown).

[0109] In some, but not necessarily all, embodiments, it would be counterproductive to simultaneously introduce a gas stream undergoing at least partial gas separation through inlet 470 because operation in discharge mode would cause the target gas material to be released. Therefore, during operation in discharge mode, inlet 470 is closed or a different stream (e.g., a waste stream) is redirected to the inlet. However, in certain embodiments, a second portion of the gas mixture that will undergo at least partial gas separation is introduced through inlet 470 while operation in discharge mode occurs.

[0110] According to some, but not necessarily all, embodiments, a gas separation system includes a first set of electrochemical cells and a second set of electrochemical cells. Each of the first and second sets may include one or more electrochemical cells described throughout this disclosure. The first and second sets may be configured to alternately run in parallel, such that one set of cells operates in a charge mode and captures a target gas (e.g., CO) from a gas mixture, while another set of cells operates in a discharge mode and releases the target gas (e.g., CO). The system may include separate housings for each set of electrochemical cells. The system may further include conduits and valves configured to direct flow in a desired manner. The gas separation system may allow for continuous or semi-continuous separation of a gas mixture (e.g., a gas stream) that is directed at a given moment to a set of cells operating in a charge / capture mode, while a treated mixture enriched in a particular target gas is produced by another set of cells operating in a discharge / release mode. Furthermore, additional sets of electrochemical cells may be added in parallel or in series as needed for the application.

[0111] 6 shows an example embodiment of such a gas separation system. In gas separation system 600, a first set of electrochemical cells 605a is positioned in a first housing 660a, and a second set of electrochemical cells 605b is positioned in a second housing 660b. A conduit connects gas inlet 670 to housing inlets 672a and 672b. Valve 684 may be configured to direct flow to either set 605a or 605b depending on which is currently operating in charging mode.

[0112] During operation, a gas stream containing a target gas (e.g., CO) may be introduced into gas separation system 600 via inlet 670. According to certain embodiments, when first set of cells 605a operates in a charge / capture mode, valve 684 may be configured to direct the flow into the vicinity of first set of cells 605a, where the target gas may combine with electroactive species in cells 605a to produce a treated gas mixture (with a reduced concentration of target gas) that may then exit housing 660a via outlet 673a. An additional valve 686a downstream of housing outlet 673a may be configured to direct the treated gas stream through treated gas outlet 680.

[0113] A first set of cells 605a may operate in a charge mode, while a second set of cells 605b may operate in a discharge mode, in which case previously stored target gas is released from the electroactive material of the second set of cells 605b. In the illustrated embodiment, valve 684 is configured to isolate the gas mixture from the set of cells 605b operating in a discharge mode. Release of the target gas from the set of cells 605b produces a target gas-enriched gas mixture, which then exits housing 660b via outlet 673b. Alternatively, valve 686b may be configured to isolate the target gas-enriched gas mixture from treated outlet 680b and direct the target gas-enriched stream to waste outlet 682b, where the target gas-enriched stream may undergo further processing, storage, etc.

[0114] After operating in the above manner for a period of time, the modes of cells 605a and 605b may be reversed. The first set of cells 605b is then operated in discharge mode to release accumulated target gas from their electrodes. During this period, valve 684 is reconfigured to isolate the process stream from the first set of cells 605a. During this period, valve 686a is reconfigured to direct the target-rich stream toward waste outlet 682a.

[0115] Meanwhile, the operation of the second set of cells 605b is reversed, as they operate in a charging mode to capture the target gas and produce a treated stream. The inlet valve 684 is configured to direct the treated gas mixture from the system inlet 670 through a conduit to the second set of cells 605b via the second housing inlet 672b. The outlet valve 686b is again configured to direct the treated gas mixture to the outlet 680.

[0116] In such an approach, according to certain embodiments, various sets of cells 605a and 605b may cycle through modes that together may provide continuous or semi-continuous separation of the gas stream, including the target gas. While the particular embodiment shown in Figure 6 illustrates one particular arrangement of system components (e.g., valves, conduits, inlets, and outlets), it will be understood that various configurations can be provided to still achieve the goal of providing continuous operation with isolated treated and target gas-rich streams.

[0117] 7A shows a schematic diagram of an exemplary system similar to that of FIG. 6 for performing a gas separation process, where, according to one or more embodiments, a first set of cells 705a operates in a charge mode, while a second set of cells 705b operates in a discharge mode. In the charge mode, an applied voltage induces a redox reaction (e.g., reduction) of the electroactive species at the negative electrode 710a, increasing the affinity between the first electroactive species and the target gas 790. A gas stream 575 containing the target gas 590 is introduced into the set of cells 705a and passes near the negative electrode 510a. The increased affinity causes the target gas (e.g., CO) 790 to bind 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.

[0118] In this discharge mode, according to certain embodiments, a second applied voltage that causes electron flow in the opposite direction to that during the charge mode induces a second redox reaction (e.g., oxidation) of the first electroactive species at 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.

[0119] Figure 7B shows a schematic diagram of an exemplary system similar to that of Figure 6 for performing a gas separation process, but with the mode of operation shown and described in Figure 7A reversed. In Figure 7B, according to one particular embodiment, the voltage applied across a first set of cells 705a is varied, causing cells 705a to operate in a discharge mode, releasing stored target gas 790 from anode 710a to produce a target gas-rich gas mixture. Meanwhile, the voltage applied across a second set of cells 705b is also varied, causing them to operate in a charge mode. Target gas 790 of process stream 775 couples to anode 710b to produce treated stream 785.

[0120] As described above, a gas separation system can include multiple electrochemical cells electrically connected in parallel or in series. Those skilled in the art with the benefit of this disclosure will generally understand how to electrically connect electrochemical cells to form a circuit. Such connection can be achieved by establishing a conductive path for electron flow between the electrodes of the electrochemical cells (i.e., establishing electrical coupling between the electrodes). In some cases, the conductive path can 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 path can be established by wiring the electrodes of the electrochemical cells. The electrochemical cells can have any of the configurations described above. For example, in some embodiments, some or all of the electrochemical cells of the system have a single negative electrode (e.g., containing a first electroactive species), a single positive electrode (e.g., containing a second electroactive species), and, optionally, a separator between the first and second positive electrodes. 10A shows a schematic diagram of an arrangement of electrochemical cells 1100 in one such system 1000, where each electrochemical cell 1100, in turn, includes an anode 1010, an optional separator 1020, and a cathode 1030, according to one particular embodiment. A gas mixture 1075 including a target gas can be introduced into the system such that the gas mixture 1075 passes adjacent to the anode 1010 of a first electrochemical cell 110 and the cathode 1030 of an adjacent second electrochemical cell 1100. While FIG. 10A shows three electrochemical cells 1100, it should be understood that any of a variety of suitable numbers of electrochemical cells can be used in a gas separation system (e.g., electrically connected in parallel or series) as needed depending on the requirements of a particular application.

[0121] In other embodiments, some or all of the electrochemical cells of the gas separation system include a positive electrode (e.g., including a second electroactive species), a first negative electrode (e.g., including a first electroactive species), a second negative electrode (e.g., including 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 Figures 1B and 2.

[0122] 10B shows a schematic diagram of a configuration in which multiple electrochemical cells 1100 of system 1000 are electrically connected in parallel, according to certain embodiments. In the 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 a power source). For example, in FIG. 10B, each negative electrode 1010 is electrically coupled to a first terminal of the power source via wire 115, and each positive electrode 1030 is electrically coupled to a second terminal of the power source via wire 116, according to certain embodiments.

[0123] 10C shows a schematic diagram of a configuration in which multiple electrochemical cells 11000 of system 1000 are electrically connected in series, according to certain embodiments. In the series configuration, the positive electrode of a first electrochemical cell is electrically connected to the negative electrode of a second electrochemical cell in the system. For example, in FIG. 10B, according to certain embodiments, the negative electrode 1010 of a first electrochemical cell 1100a is electrically connected to the positive electrode 1030 of a second electrochemical cell 1100b via wire 1017, and the negative electrode 1010 of the second electrochemical cell 1100b is electrically connected to the positive electrode 1030 of a third electrochemical cell 1100c via wire 1018. Furthermore, according to certain embodiments, the positive electrode 1030 of the first electrochemical cell 1100a is electrically coupled to a first terminal of the power source via wire 114, and the negative electrode 1030 of the third electrochemical cell 1100a is electrically coupled to a second terminal of the power source via wire 119.

[0124] In the context of the present disclosure, it has been determined that certain configurations of a gas separation system including multiple electrochemical cells electrically connected in series can promote relatively efficient charge transport and / or gas transport. For example, in some embodiments, conductive materials between the electrochemical cells can establish a conductive path other than using external wiring. For example, a gas separation system can include a first electrochemical cell and a second electrochemical cell electrically connected in series, where an electrical connection is established through one or more conductive materials between the first and second electrochemical cells. For example, any of a variety of suitable conductive materials can be disposed between the electrochemical cells to establish an electrical connection between the negative electrode of the first electrochemical cell and the positive electrode of the second electrochemical cell. For example, the conductive material can be a conductive solid. The conductive solid can 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 mat (e.g., carbon nanotube mat), Ketjen Black, carbon black Super P, graphene, etc. In some embodiments, the carbonaceous material is a porous carbonaceous material described elsewhere herein. In some embodiments, the conductive solid comprises a composite of a conductive solid and a binder resin. In some embodiments, the conductive solid between the electrochemical cells comprises a conductive polymer material.

[0125] In some, but not necessarily all, embodiments, the conductive material between the electrochemical cells comprises a bipolar plate. It should be understood that, in the context of the present disclosure, the plate need not necessarily be flat. Bipolar plates are known to those skilled in the art and are typically used in fields other than gas separation, such as in fuel cells. The bipolar plate may be configured to separate a fluid (e.g., gas) in contact with the positive electrode from a fluid in contact with the negative electrode. The bipolar plate may comprise a conductive solid, such as steel, titanium, or graphite.

[0126] In some embodiments, at least a portion of the multiple electrochemical cells (e.g., connected in series) are separated by a flow field. As previously discussed, locating a flow field between adjacent electrochemical cells can promote beneficial gas distribution and relatively efficient interaction (e.g., for bonding) between the gas and the electrodes. In some embodiments, the bipolar plates described above include flow fields (e.g., by etching fluid pathways on one or both sides of the plate), while in other embodiments, different flow fields are used instead of or in addition to the bipolar plates containing flow fields.

[0127] FIG. 11 shows a schematic diagram of an exemplary gas separation system 1000 including electrochemical cells 1100 electrically connected in series via one or more conductive materials between the cells, according to certain embodiments. In FIG. 11, the system 1000 includes conductive solid material in the form of bipolar plates 1012 and ribs 1014. The ribs of the gas separation system may be made from any of the conductive solid materials described above. In the embodiment shown in FIG. 11, a first electrochemical cell 1100a is separated from a second electrochemical cell 1100b via the bipolar plates 1012 and ribs 1014. The bipolar plates 1012 and 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 conductive path for the series connection. Other electrochemical cells in the system may be electrically connected in a similar manner. While FIG. 11 illustrates bipolar plates and ribs, such illustration is non-limiting and other configurations are possible (e.g., no bipolar plates, no ribs, etc.). FIG. 11 also illustrates flow fields 1011, as needed, to separate electrochemical cells 1100, according to certain embodiments. In some embodiments, one or more components (e.g., conductive solids, e.g., ribs) can establish channels between the negative and positive electrodes of adjacent electrochemical cells. For example, ribs 1014 in FIG. 11 can have dimensions such that channels 1013 establish a path for gas (e.g., a gas mixture) to flow between electrochemical cells 1011 and interact with the electrodes. For example, gas mixture 1075 can pass between first electrochemical cell 1100a and second electrochemical cell 1100b via channels 1013 and flow fields 1011, according to certain embodiments.

[0128] The flow of current in certain of the aforementioned embodiments encounters less electrical resistance than in other configurations. For example, in some embodiments where electrochemical cells are connected in series through conductive material between at least a portion of a stack of electrochemical cells, current can flow in a direction perpendicular to the stack. FIG. 11 illustrates such an example, where current can flow in a direction x perpendicular to the electrochemical cells 1100, while the gas mixture 1075 can flow in a direction parallel to the electrochemical cells 1100. In FIG. 11 , the path along which the current travels is relatively short and determined by the thickness of the bipolar plates 1012 and ribs 1014. In some embodiments, the thickness of one or more conductive solids between the electrochemical cells is 10 mm or less, 5 mm or less, 2 mm or less, 1 mm or less, and / or no more than 0.5 mm, no more than 0.2 mm, no more than 0.1 mm, or even less. In contrast, in embodiments in which electrochemical cells are electrically connected in parallel or electrically connected in series via external wiring, current must flow up to the entire height and / or length of the electrodes (e.g., the electrode current collectors) and through the electrode tabs to reach the external wiring. Such height and / or length may be, for example, at least 1 cm, at least 2 cm, at least 5 cm, at least 10 cm, and / or up to 20 cm, up to 50 cm, up to 100 cm, or more. In such embodiments, the greater the distance that current must travel, generally the greater the overall resistance of the cell, which may reduce the charge transport and / or energy efficiency of the methods for separating at least some gases described herein.

[0129] The electrochemical cells, systems, and methods described herein may be implemented in a variety of applications. Some electrochemical cells or cell sets may be scaled as needed to meet the requirements of a particular application. In some embodiments, the systems and methods described herein may be used to extract CO2 from ambient air and from enclosed spaces, such as airtight buildings, vehicle cabins—reducing heating costs by introducing air for ventilation—and submarines and space capsules, where increased CO2 levels could be catastrophic. In embodiments directed to the power industry, they may be used to capture various concentrations of post-combustion carbon dioxide. In some embodiments, the systems and methods are suitable for separating target gases from industrial flue gases. They may also be used to capture sulfur dioxide and other gases from flue gases. In embodiments directed to the oil and gas industry, the disclosed systems and methods may be used to capture carbon dioxide and other gases from various processes and divert them for downstream compression and / or processing. The disclosed systems and methods may be applied to capture carbon dioxide from combusted natural gas used to heat greenhouses in warm and cold climates, and then direct the captured dioxide into the greenhouse for use by plants to photosynthesize, i.e., to provide nutrition to the plants.

[0130] In some embodiments, the gas separation systems described herein are capable of capturing a target gas at a relatively high productivity. At a given gas flow rate through the gas separation system, the productivity at which the gas separation system captures the target gas from a gas mixture is generally measured in terms of the mass of target gas (measured herein in kg) captured during the gas capture process. 標的ガス ) is calculated by dividing the mass of the bed of the gas separation system (herein referred to as kg 床 The ratio is divided by the breakthrough time (t bThe term "bed" generally refers to the absorbent material of a gas separation system, such as the layer of electroactive species (e.g., the primary electroactive composite layer) of an electrochemical cell described herein. Those skilled in the art will appreciate that the breakthrough time of a gas separation system generally refers to the time required to reach electrode saturation or the time at which the outlet target gas concentration begins to increase as the gas mixture flows through the system during the capture process. Relatively high productivity may be desirable in some cases, in which case the gas separation system may be used when the gas separation system is relatively small (e.g., a total volume of 1,000 ft ). 3 Less than or equal to 500ft 3 Less than or equal to 200ft 3 Less than or equal to 100ft 3 Less than or equal to 50ft 3 Less than or equal to 25ft 3 Less than or equal to 10ft 3 Less than or equal to, and / or 5ft 3 About 2ft 3 About 1 ft 3 As low as 0.1ft 3 It is desirable to operate at high efficiency even at low or even low capacities (e.g., as low as 1000 kJ / cm2 or less). Some such small gas separation systems are believed to be particularly useful in ventilation systems or systems for direct air capture. One or more of the features described herein may contribute to a gas separation system having relatively high productivity, such as the use of specific electroactive species, the use of porous electrodes, and the use of an electrochemical cell having a first anode, a second anode, and a cathode located between the first and second anodes.

[0131] In some embodiments, the gas separation system has a gas flow rate of greater than or equal to 0.001 L / sec and less than or equal to 500 L / sec, and a gas flow rate of greater than or equal to 0.003, greater than or equal to 0.005, greater than or equal to 0.01, greater than or equal to 0.02, greater than or equal to 0.03 kg 標的ガス / (kg 床t b In some embodiments, the gas separation system is configured to have a productivity for capture of a target gas (e.g., CO) greater than or equal to, or greater than 0.05, less than or equal to, 0.04, less than or equal to, 0.03, less than or equal to, 0.02, 0.015 kg / s at a gas stream flow rate of greater than or equal to, 0.001 L / s and less than or equal to, 500 L / s. 標的ガス / (kg 床 t b ) or less. In some embodiments, the gas separation system allows these ranges of productivity even for gas mixtures containing the target gas at relatively low concentrations and / or for gas mixtures containing potentially interfering gases, such as oxygen gas, due to the involvement of certain features described herein. While the gas separation system may be configured to achieve the above-described productivity when operated within the described flow rate ranges, it should be understood that the gas separation system may, in some cases, be operated at flow rates outside the range of indicated flow rates, provided that the indicated productivity is achieved under such same configuration (e.g., electrochemical cell type, dimensions, and configuration). In some embodiments, the flow rates described herein refer to the flow rate of gas flow per 100 cm of anode surface area. For example, in some embodiments, the flow rates described herein refer to the flow rate of gas flow per 100 cm of anode surface area. 2 In this context, the negative electrode surface area can be the sum of the surface areas across multiple negative electrodes in an electrochemical cell, across multiple stacks of electrochemical cells in a system. In some embodiments, the flow rates described herein refer to the gas flow rate per stack of electrochemical cells in a system. For example, in some embodiments, the flow rates described herein refer to the gas flow rate per 10 electrochemical cells in a system.

[0132] According to one or more embodiments, a gas mixture (e.g., a gas stream such as an input gas stream) is introduced into a gas separation system at a particular flow rate. In some embodiments, the flow rate is greater than or equal to 0.001 L / sec, greater than or equal to 0.005 L / sec, greater than or equal to 0.01, greater than or equal to 0.05 L / sec, greater than or equal to 0.1 L / sec, greater than or equal to 0.5 L / sec, greater than or equal to 1 L / sec, greater than or equal to 5 L / sec, greater than or equal to 10 L / sec, greater than or equal to 50 L / sec, greater than or equal to 100 L / sec, or higher. In some embodiments, the flow rate of the gas mixture (e.g., a gas stream, such as an input gas stream) is less than or equal to 500 L / sec, less than or equal to 400 L / sec, less than or equal to 300 L / sec, less than or equal to 200 L / sec, less than or equal to 100 L / sec, less than or equal to 50 L / sec, less than or equal to 10 L / sec, less than or equal to 1 L / sec, less than or equal to 0.5 L / sec, less than or equal to 0.1 L / sec, or lower. Combinations of these ranges are possible. For example, in some embodiments, the flow rate is greater than or equal to 0.001 L / sec and less than or equal to 500 L / sec. As noted above, in some embodiments, these flow rates are greater than or equal to 100 cm 2 In some embodiments, these flow rates are per 10 electrochemical cells in the system.

[0133] Certain aspects described herein relate to methods for 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 amount of an input gas mixture containing the target gas to the electrochemical cell. The first amount of input gas mixture may be exposed by flowing it as a gas stream into the electrochemical cell (or a gas separation system including multiple electrochemical cells), as shown in FIGS. 5-7B. In some embodiments, during and / or after applying the first potential difference, a portion of the target gas combines with electroactive species in the electrochemical cell to produce a first treated gas mixture. For example, the target gas (e.g., carbon dioxide) may combine with a first electroactive species at the negative electrode of the electrochemical cell when the first electroactive species is in at least one of its reduced states generated by application of a potential across the electrochemical cell. Combination of the target gas with the electroactive species can result in a treated gas mixture having a lower amount of target gas than the first gas mixture (as described above with respect to the ranges for the amount of target gas removed). Figures 8A-8B and Example 2 below describe exemplary methods of flowing the input gas mixture and the 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 gases may be flowed through the electrochemical system before and / or after the second gas is flowed.

[0134] In some cases, a second potential difference is applied across the electrochemical cell after at least a portion of the target gas is bound to the electroactive species. The second potential difference may be different from the first potential difference. In some embodiments, applying the second potential difference results in releasing some or all of the target gas bound to the electroactive species to produce a second treated gas mixture. The second treated gas mixture may have a higher amount of target gas than the input gas mixture. For example, the target gas may be present in the second treated gas mixture in an amount that is 10%, 20%, 50%, 100%, 200%, 1000%, and / or up to 2,000%, 5,000%, 10,000%, or more by volume than the first amount in the gas mixture.

[0135] In some embodiments, during and / or after releasing the target gas from the electroactive species, the method further includes flowing a second gas through the electrochemical cell to remove at least some 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%, greater than 99.99%, greater than or equal to 99.999%, greater than or equal to 99.9999%). For example, the second gas may be substantially pure CO2. As another example, the second gas may include water vapor.

[0136] One exemplary situation in which it may be useful to pass a second gas through the electrochemical cell to remove at least some or all of the released target gas from the electrochemical cell is when the amount of captured target gas is greater than the bed volume of the electrochemical cell. In some such cases, more than one bed volume of the target gas binds to the first electroactive species. For example, in some cases, the volume of the target gas captured by the electrochemical cell is 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 than the bed volume of the electrochemical cell. In some such cases where the volume of the captured target gas is greater than the bed volume of the electrochemical cell, more than one bed volume of the target gas is released from the first electroactive species. In these cases, the release of the captured target gas may cause the electrochemical cell to have a gas pressure greater than the ambient gas pressure. In some such cases, the released target gas will then flow out of the electrochemical cell due to the pressure differential created by the ambient atmosphere until about one bed volume of target gas remains. To remove the remaining released target gas, a second gas may be flowed into the electrochemical cell. In some cases, a substantially pure target gas (e.g., CO) flows through the interior to remove the remaining target gas. In other cases, an inert gas (e.g., nitrogen gas, N) flows through the electrochemical cell to remove the remaining released target gas.

[0137] Another situation in which it may be beneficial to flow a second gas through the electrochemical cell to remove at least some or all of the released target gas from the electrochemical cell is when the amount of captured target gas is less than or equal to the volume of the electrochemical cell bed. For example, in some cases, the volume of the 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 as low as 0.2 times, as low as 0.1 times, as low as 0.01 times, or even lower than the volume of the electrochemical cell bed. In some such cases, the pressure within the electrochemical cell bed is 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 capable of transporting the target gas without reacting with the target gas or components of the electrochemical cell. The carrier gas may be easily separable from the target gas via any of a variety of inexpensive or energy-intensive techniques as an initial separation of the target gas from the gas mixture. For example, the target gas and carrier gas may be separable via 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 substantially pure target gas (e.g., substantially pure CO2). In some cases, the carrier gas includes water vapor. In some embodiments, the second gas (e.g., carrier gas) is a second portion of the input gas mixture. For example, in ventilation applications, a quantity of target gas may be removed from the ventilated air during application of a first potential across the electrochemical cell, then during and / or after release of the target gas, and the ventilated air flows through the electrochemical cell to remove the released target gas.

[0138] In some embodiments, during and / or after the step of releasing the target gas, the method further includes applying a vacuum to the electrochemical cell to remove at least some or all of the released target gas from the electrochemical cell. Those skilled in the art, given the benefit of this disclosure, will understand suitable techniques and equipment for applying a vacuum to the electrochemical cell. For example, a vacuum pump may be fluidly connected to the gas outlet of the electrochemical cell. The vacuum pump may operate to create a negative pressure differential between the floor of the electrochemical cell and a downstream location. This vacuum may provide sufficient force to force the target gas released during the above-mentioned releasing step out of the electrochemical cell. A vacuum may be applied such that the pressure within 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 lower. A vacuum may be applied such that the pressure within the electrochemical cell during and / or after the 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 terrestrial ambient conditions at sea level, such that a vacuum condition establishes a pressure within the electrochemical cell during and / or after release of the target gas of less than or equal to 760 torr, less than or equal to 100 torr, less than or equal to 10 torr, etc. However, the environment surrounding the gas separation system may be pressurized, such as when the gas separation system is within a pressurized structure such as a spacecraft (which may be pressurized to 1.2 times atmospheric pressure at the interface level).In some such pressurized environments, a vacuum establishes a pressure within the electrochemical cell during and / or after release of the target gas, eg, 2000 torr, less than 1000 torr, etc.

[0139] In some embodiments in which a target gas (e.g., CO) is released from an electrochemical cell, the released target gas may be handled in any of a variety of ways. For example, the released target gas may be exhausted from the electrochemical cell (and gas separation system) at the same partial pressure established after the initial release. The released target gas may then be discharged into the ambient environment as exhaust or directed (e.g., via stream) to further downstream processing. In some embodiments, the released target gas may be incorporated into a fluid mixture (e.g., a gas mixture) having a relatively high partial pressure of the target gas (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 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, or higher). In some embodiments, the partial pressure of the resulting fluid mixture is greater than supercritical (e.g., greater than 130 bar for carbon dioxide). Incorporation into a fluid mixture may, in some cases, be achieved by combining the released target gas with a 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. Those skilled 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 cell, for example, using standard compressor equipment and techniques.

[0140] In some embodiments, the negative electrode or a portion thereof (e.g., the electroactive composite layer of the negative electrode, if present) has a specific capacity to absorb a target gas (e.g., CO). For example, in some embodiments, the negative electrode or a portion thereof (e.g., the electroactive composite layer of the negative electrode, if present) has a specific capacity to absorb a target gas (e.g., CO). 2 At least 0.01 mol per m 2 At least 0.02 mol per m 2 In some embodiments, the negative electrode or a portion thereof (e.g., the electroactive composite layer of the negative electrode, if present) has an absorption capacity of at least 0.05 mol / m or greater. 2 Less than or equal to 0.1 mol per m 2 Less than or equal to 0.08 mol per m 2 Less than or equal to 0.5 mol per m 2 Combinations of these ranges are possible. For example, in some embodiments, the negative electrode or a portion thereof (e.g., the electroactive composite layer of the negative electrode, if present) has an absorption capacity of less than, equal to, or less than 0.03 mol per m 2 At least 0.01 mol per m 2 Less than or equal to 0.1 mol per m 2 At least 0.01 mol per m 2 has an absorption capacity of less than or equal to 0.03 mol per 1000 mg of water.

[0141] In some embodiments, the negative electrode or a portion thereof (e.g., the electroactive composite layer of the negative electrode, if present) can absorb a target gas (e.g., CO) at a particular rate. For example, in some embodiments, the negative electrode or a portion thereof (e.g., the electroactive composite layer of the negative electrode, if present) can absorb a target gas (e.g., CO) at a particular rate. 2 At least 0.0001 mol per second, 1 m 2 At least 0.0002 mol per second, 1 m 2In some embodiments, the negative electrode or a portion thereof (e.g., the electroactive composite layer of the negative electrode, if present) has an absorption capacity rate of at least 0.0005 mol per second, or greater. 2 0.001 mol or less per second, 1 m 2 0.0008 mol or less per second, 1 m per second 2 In some embodiments, the electroactive composite layer has an absorption capacity rate of 1 m per second or less. 2 At least 0.0001 per second and 1 m per second 2 The absorbency rate is 0.0005 mol / L or less. Other absorbency rates are possible.

[0142] In some embodiments, the electroactive composite layer of the negative electrode is, for example, 5 cm 2 Greater than or equal to 8cm 2 Greater than or equal to 10cm 2 Greater than or equal to and / or 10cm 2 Up to 20cm 2 Up to 50cm 2 Up to 1m 2 The surface area exposed to the gas mixture may be up to or greater than 1000 nm. Other values ​​are possible.

[0143] In some embodiments, at least some or all of the electrodes (e.g., negative electrodes, positive electrodes) described herein comprise a porous material. The porous electrodes may be made from any suitable material and / or may be configured in any suitable shape or size. In a non-limiting embodiment, the electrodes comprise a porous carbonaceous material. The term carbonaceous material has its ordinary meaning in the art and refers to a material comprising carbon or graphite that is electrically conductive. 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 partially from a carbonaceous material, or the carbonaceous material may be deposited over an underlying material. The underlying material generally 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 electrically conductive materials are described herein.

[0144] In some embodiments, the electrodes (e.g., negative electrode, positive electrode) are porous. The porosity of an electrode can be measured as the percentage or fraction of void space in the electrode. The percent porosity of an electrode can be measured using techniques known to those skilled in the art, such as the volume / density method, the water saturation method, the water evaporation method, mercury intrusion porosimetry, and nitrogen gas adsorption. 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 up to 90% porous, up to 85% porous, up to 80% porous, up to 70% porous, up to 50% porous, up to 30% porous, up to 20% porous, up to 10% porous, or less. Combinations of these ranges are possible. For example, the electrode can be at least 10% porous and up to 90% porous. The pores may be open pores (e.g., with at least some of the open pores and / or other pores at the outer surface of the electrode). 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 and the inner core of the electrode is substantially non-porous (e.g., 20% or less porous, 10% or less porous, 5% or less porous, 1% or less, or less). In certain embodiments, the entire electrode is substantially porous.

[0145] In some embodiments, the electrochemical cell has a specific cycle time. The cycle time of an electrochemical cell generally refers to the time it takes to perform one charge mode and one discharge mode. 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 3600 seconds or less, 2400 seconds or less, 1800 seconds or less, or less. Combinations of these ranges are possible. For example, in some embodiments, the cycle time is at least 60 seconds and 3600 seconds or less, or at least 300 seconds and 1800 seconds or less.

[0146] According to some embodiments, the electrochemical cell and its components have a particular thickness depending on the desired application (e.g., ventilation system air gas separation, 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 750 μm or less, 600 μm or less, 500 μm or less, 300 μm or less, 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 750 μm or less. In some embodiments, the electrochemical cell has a thickness of at least 10 μm and 750 μm or less.

[0147] In some embodiments, the negative electrode 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 electrode or positive electrode has a thickness of 200 μm or less, 150 μm or less, 100 μm or less, or less. Combinations of these ranges are possible. For example, in some embodiments, the negative electrode or positive electrode has a thickness of at least 50 μm and 200 μm or less. In some embodiments, the negative electrode or positive electrode has a thickness of at least 0.5 μm and 200 μm or less.

[0148] In some embodiments, the negative or positive electrode electroactive composite layer has a thickness of at least 10 nm, at least 20 nm, at least 40 nm, 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 negative or positive electrode electroactive composite layer has a thickness of 200 μm or less, 150 μm or less, 100 μm or less, 50 μm or less, 20 μm or less, 10 μm or less, 5 μm or less, 2 μm or less, 1 μm or less, 0.5 μm or less, 0.2 μm or less, 0.1 μm or less, or less. Combinations of these ranges are possible. For example, in some embodiments, the negative or positive electrode electroactive composite layer has a thickness of 10 μm or more and 200 μm or less, hi some embodiments, the negative or positive electrode electroactive composite layer has a thickness of 10 nm or more and 100 nm or less, or 50 nm or more and 500 nm or less.

[0149] The various components of the systems, such as electrodes (e.g., negative electrodes, positive electrodes), power sources, electrolytes, separators, containers, electrical circuits, insulating materials, etc., can be fabricated by one skilled in the art from any of a variety of components. The components can be molded, machined, extruded, pressed, isopressed, infiltrated, coated, or formed by any other suitable technique in the green or fired state. One skilled in the art can readily identify techniques for forming the components of the systems herein.

[0150] The electrodes (e.g., negative electrodes, positive electrodes) described herein can be of any suitable size or shape. Non-limiting examples of shapes include sheets, cubes, cylinders, hollow tubes, spheres, etc. The electrodes can be of any suitable size depending on the application for which they are used (e.g., gas separation from ventilated air, direct air capture, etc.). In addition, the electrodes can include means for connecting the electrode to another electrode, a power source, and / or another electrical device.

[0151] Various electrical components of the system can be in electrical communication with at least one other electrical component by a means for connection. The means for connection can be any material that allows electrical flow to occur between a first component and a second component. A non-limiting example of a means for connecting two electrical components is wiring comprising a conductive material (e.g., copper, silver, etc.). In some cases, the system can also include electrical connectors between two or more components (e.g., wiring and electrodes). In some cases, the wiring, electrical connectors, or other means for connection can be selected to have a low material resistance. In some cases, the resistance can be substantially lower than the resistance of the electrodes, electrolyte, and / or other components of the system.

[0152] U.S. Provisional Application No. 62 / 892,962, filed August 28, 2019, and entitled "Electrochemically Mediated Carbon Capture from Low Concentration Streams," U.S. Patent Application No. 15 / 335,258, filed October 26, 2016, and entitled "Electrochemical Process for Gas Separation," U.S. Patent Application No. 16 / 659,398, filed October 21, 2019, and entitled "Electrochemically Mediated Gas Capture, Including from Low Concentration Streams," and International Patent Application No. PCT / US2019 / 057224, filed October 21, 2019, and entitled "Electrochemically Mediated Gas Capture, Including from Low Concentration Streams," are each incorporated herein by reference in their entirety for all purposes.

[0153] The following examples are intended to illustrate certain embodiments of the present invention, but do not exemplify the full scope of the invention. [Example]

[0154] Example 1 This example describes experiments, embodiments, and non-limiting theory regarding the influence of oxygen electrochemistry and reactivity 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 provided by way of example only.

[0155] In electrochemical processes, superoxide ions can be generated via heterogeneous one-electron reduction at the electrode surface or via a homogeneous one-electron transfer reaction between redox-active molecules and dissolved O2. In DMF electrolyte solution, O2 has been reported to exhibit quasi-reversible electron transfer, such that superoxide ions are formed at a half-wave potential of -1.35 V (0.87 V vs. standard calomel electrode (SCE) reference electrode). In order to limit or prevent the generation of superoxide via heterogeneous reduction at the electrode surface, in the context of the present disclosure, it has been discovered that the half-wave reduction potential for activating quinones should, in some cases, be more positive than the half-wave potential for the formation of superoxide ions. Furthermore, reduced quinones can undergo a homogeneous one-electron transfer reaction with O2 when the half-wave reduction potential of the quinone is more negative than that of O2. The formation of superoxide ions is

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[0156] Based on the reaction constants, weakly associated quinones are not suitable for electrochemical CO separation in the presence of O under the conditions measured because electron transfer from the dianionic quinone to O is favored and can generate superoxide ions in the system. Several strongly associated quinones were determined to be suitable for electrochemical CO separation in the presence of O:PQ-ester (phenanthrenequinone ethyl ester), PQ-I, PQ-I2, PQ, o-NQ, p-NQ-Me2, p-NQ, TBQ, and BQ. The peak potentials of the reduction wave under N2 and CO2 for the various quinone structures measured in this example are summarized in Figure 9. Figure 9 shows tabulated cyclic voltammetry results for 20 mM solutions of the various quinones shown in Scheme 1 in dry 0.1 M n-tetrabutylammonium hexafluorophosphate ([n-BuN]PF) dimethylformamide (DMF) electrolyte saturated with either N (top circular symbols, connected by a line for each quinone) or CO (bottom circular symbols for each quinone) at a scan rate of 100 mV / s. The filled circular symbols represent the half-wave potentials for the first electron transfer from the quinone to the semiquinone (right-hand symbol) and the second electron transfer from the semiquinone, which occurs at a more negative electrode potential (left-hand symbol). The half-wave potentials can be used to approximate the standard reduction potentials of the conversions. Scheme 1. Structures and names of the quinone molecules measured in this example. [ka]

[0157] The two reduction waves and larger negative electrode potentials required for the carboxylation of weakly complexed quinones preclude their use as complexing agents in CO separation in certain cases. This is not the case for some strongly complexing quinones that have shown suitable redox properties for the effective separation of CO from gas mixtures, particularly those containing O. During the complexation step, these compounds can be electrochemically activated to form semiquinones, whose electrode potentials range from -0.87 V to -1.07 V, more positive than the -1.35 V at which unwanted superoxide anions are formed on the electrode, as desired in this case.

[0158] These experimental results demonstrate that it is possible to determine suitable electroactive species that have at least one reduced state that can bind with an exemplary target gas (CO) while being unable to react with oxygen gas. This example also demonstrates one exemplary approach to making such a determination for a given candidate electroactive species.

[0159] Example 2 This example describes embodiments and non-limiting theory regarding exemplary target gas (e.g., CO) capture and release methods and methods described herein, including for ventilation and direct air capture applications. The materials and parameter values ​​described in this example are non-limiting and exemplary only.

[0160] The device of this example can be used in several carbon capture applications with low concentration or CO2-rich streams and compositions at a variety of potential scales. These applications can be categorized into those where the goal is CO2 extraction and those where the goal is CO2 upgrading for downstream sequestration or processing.

[0161] When CO2 capture isn't important In these applications, the released CO2 is typically discarded due to its small volume compared to the total gas volume being processed outside of direct air capture (DAC). Therefore, this mode of operation is primarily of interest for applications where the feed concentration is <1% CO2 (10,000 ppm), favoring ventilation applications. Here, CO2 is removed from the input gas mixture (the "feed stream") to saturate the electrochemical cell bed. Pure CO2 is then released into the same inlet stream, which is used to purge the bed during the release that regenerates the bed. The energy cost of capture may not be significant in this mode, since the bed must be regenerated much less frequently than in other modes, approximately 10–50 times per day. Also, the energy cost of advection of inlet air through a fan is comparable to the capture energy. Therefore, full-bed activation and full-bed regeneration can be performed prior to adsorption. This increases the capture energy to approximately 120 kJ / mol. FIG. 8A shows a schematic diagram of a non-limiting example of how to flow the input gas mixture and other gases (eg, second gas) under these conditions.

[0162] Ventilation (supply concentration: 1,000 to 5,000 ppm CO2) The removal of metabolic CO2 from buildings and other structures has recently gained momentum to improve the efficiency of HVAC (heating, ventilation, and air conditioning) systems through reduced heating requirements for incoming air. Indoor CO2 concentrations in occupied areas are maintained below 5,000 ppm by constantly replacing indoor air with fresh outdoor air up to 10 times per day. The moderate temperatures required for air replacement, whether for cooling or heating, often result in prohibitive energy consumption typical of residential and commercial buildings. However, it is understood that indoor air can be recirculated for longer periods of time with intermittent replacement at smaller volumes if CO2 is removed from the air.

[0163] CO can be captured directly from recirculated air by the electrochemical cell and gas separation system described herein, while removing volatile organic compounds (VOCs) and other indoor air contaminants, which occur at concentrations <100 ppm, through physical filtration and occasional dehumidification. The feed air, depleted of CO after capture, is used to purge the bed after release, where the bed outlet stream is diverted outdoors. Constant-current release at high currents can be achieved with high bed regeneration rates, but not complete generation.

[0164] The required bed volume per person can be calculated by scaling the fabricated device to approximately 22 mol / day. A CO2 generation rate per person and a bed saturation period of approximately 0.5 hours, i.e., a regeneration frequency of approximately 50 s / day, 0.8–1 × 10 -2 m 3 (8-10 L) of electrochemical cell bed is required per person. This can be easily integrated into existing HVAC systems and provides 7.5 L / sec. 1 Given standard ventilation requirements of 200 kJ / mol and a 25°C temperature difference between indoors and outdoors, energy consumption reductions of up to 60% can be expected. Heating or cooling at this ventilation rate would require >150 W, while at an anthropogenic rate of 250 μmol / sec at 120 kJ / mol, the electrochemical method described herein would require approximately 30 W. By reducing the total air displacement requirement to 20% of the mandated value, total energy consumption should not exceed 60 W.

[0165] The electrochemical cell and gas separation systems and methods described herein can also be used for vehicle cabin ventilation, with an operating mode very similar to that for indoor ventilation, potentially with smaller beds and more frequent regeneration. Additionally, electrochemical ventilation units can be installed on spacecraft and space stations where CO2 removal is the only possible ventilation mechanism. Current NASA requirements for the International Space Station (ISS) call for the removal of approximately 4 kg / day of CO2. Current pressure swing adsorption (PSA) or temperature swing adsorption (TSA) systems operate at 300 W. Bed regeneration in this case can be achieved by releasing pure CO2 into the vacuum of space by opening and closing an inlet valve. However, more recently, NASA's "zero waste" policy has focused on the efficient utilization of captured CO2 to other useful compounds and oxygen. In this case, the electrochemical system described herein must operate in CO2 capture mode.

[0166] The importance of CO2 capture One potential use of CO2 capture in this mode of operation is upgrading the CO2 concentration from low inlet concentrations to nearly pure CO2 for downstream sequestration or utilization. CO2 capture by the electrochemical methods described herein in this mode proceeds in a similar manner as before. When high feed concentrations and capture energy are important, adsorption can be achieved by half-bed activation followed by potentiostatic capture. Full-bed activation is also possible when the inlet concentration is very low, but disconnecting the power supply is desirable.

[0167] However, pure CO2 release is achieved by rinsing the bed with a stream of pure CO2 just before breakthrough to remove the CO2-lean gas column, followed by sealing the inlet. This is followed by a final column of CO2 removal by rinsing with pure N2, as shown in Figure 6. The flow rates of pure CO2 and N2 during the rinse step are very high, before and after release, respectively, achieving Re>2000 and ensuring a steep plug flow front. This minimizes mixing at the gas column interfaces and allows for a sharp transition from one gas to another at the outlet. Figure 8B shows a schematic diagram of a non-limiting example of how the inlet gas mixture and other gases (e.g., second gas) can be flowed under these conditions.

[0168] The water content in exhaust air—and in indoor air—can have adverse effects on electrochemical cells, including dissociation of the electrolyte ionic liquid (IL) and reducing electrode capacity by competing with CO2 to react with the reduced quinone. This can be avoided in some cases by using a hydrophobic IL that repels water from the wet electrode. Hydrophobic ILs are typically bis[(trifluoromethyl)sulfonyl]imide [TfN - ], further improving the solubility of CO2 in the IL and potentially enhancing its transport through the electrode.

[0169] Direct Air Capture (DAC) (e.g., supply concentration: 300-400 ppm CO2) DAC has gained attention due to the growing interest in carbon-negative technologies as a means of offsetting carbon footprints. However, most existing sorbent materials considered or developed for DAC require the generation of heat; a process associated with energy loss to the sorbent and other matrix materials used.

[0170] The thermodynamic minimum work for 100% recovery of CO2 at 100% purity from a binary gas mixture is:

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[0171] The capture process can proceed through either half-bed or full-bed activation. However, due to the energy economy of DAC technology, it is sometimes recommended to activate a half-bed followed by constant potential capture. The release process may follow the scheme described in Figure 8B to enable pure CO2 capture. The bed regeneration frequency in DAC is very small, even for small beds at reasonable inlet flow rates, and capture periods can be on the order of days.

[0172] The electrochemical systems and methods described herein have been determined to enable DAC at approximately 45 kJ / mol, lower than many thermally regenerated systems (55-130 kJ / mol), although additional dissipation can occur when operating a fan to force air advection through the electrochemical cell. The electrochemical devices described herein have been fabricated and found to have a pressure drop of 100 Pa or less at flow rates of 1-2 L / min. However, larger pressure differentials may be required in some cases to allow for physical filtration of dust and other air contaminants.

[0173] Example 3 This example describes experiments, embodiments, and non-limiting theory regarding the electrochemically mediated reactivity of certain electroactive species with target gases. The materials and parameter values ​​described in this example are non-limiting and exemplary only.

[0174] To demonstrate the non-limiting reactivity of electroactive species with carbon dioxide, cyclic voltammetry experiments were performed on the optionally substituted quinones described above in the presence of carbon dioxide and in an inert nitrogen atmosphere. Cyclic voltammetry of weakly complexing quinones was also performed.

[0175] Cyclic voltammetry measurements were performed in a standard three-electrode cell using a Parstat 3000-A potentiostat equipped with VersaStudio™ software from Princeton Applied Research. Electrochemical measurements were performed in a glass cell, and the solution temperature was maintained at a defined temperature. A platinum working electrode was purchased from BASi. A platinum wire served as the counter electrode, and a leakless Ag / AgCl reference electrode was used. Ferrocene was used as the internal standard. An electrolyte of 0.1 M [n-BUN]PF in DMF was used. The solution was carefully purged with nitrogen with gentle stirring for 30 minutes, and a nitrogen atmosphere was maintained throughout the electrochemical experiments.

[0176] Weakly complexing quinones The five weakly complexing quinones described in Example 1 were classified based on their reactivity with carbon dioxide after electrochemical reduction. The weakly complexing quinones were tetrachloro-p-benzoquinone (BQ-Cl), 2,7-dichlorobenzoquinone (BQ-Cl), 2-3-dichloro-p-naphthoquinone (p-NQ-Cl), 2-chloro-9,10-anthraquinone (AQ-Cl), 9,10-anthraquinone 2-propanoic acid ester (AQ-COO-C3H7), and 9,10-anthraquinone butyramide derivative (AQ-CONH-C4H9) based on the effect of their interaction with CO2 on their redox properties. Figure 12a shows the cyclic voltammograms of AQ-Cl under N2 (left) and CO2 (right) atmospheres at a scan rate of 100 mV / s. The results for AQ-Cl are representative of the four other indicated weakly complexing quinones. When the electrolyte solution was saturated with CO2, no change was observed in either the cathodic or anodic waves of the first electron transfer (more positive potential), but the cathodic wave of the second electron transfer shifted positive, and the oxidation wave showed characteristics indicative of irreversibility at the scan rate used. In Figure 12A, AQ-Cl under N2 atmosphere reacted with ferrocenium / ferrocene (Fc + The results showed two reversible single-electron transfer processes, with the first half-wave potential at -1.26 V and the second at -2.00 V vs. HCl / Fc. When CO2 was introduced into the solution, no change was observed in the cathodic peak current and position relative to the first electron transfer, but a positive shift in the second cathodic wave indicated the occurrence of reductive addition of CO2 to the AQ-Cl dianion. This chemical reaction between the dianion and CO2 is thought to occur via a nucleophilic addition reaction between the oxyanion and the electropositive carbon atom of the CO2 molecule.

[0177] The value of the binding constant for the complexation of CO2 with the dianion of a weakly complexing quinone is given by the equation

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[0178] The variation in the CO2 binding constants for BQ-Cl2, BQ-Cl4, and p-NQ-Cl2 is attributed to the resonance and inductive stabilization effects of the oxyanion due to electron-withdrawing substituents on the quinoid ring structure. Greater stabilization of the oxyanion reduces its nucleophilic reactivity toward CO2 addition, decreasing the CO2 binding constant. The decrease in the CO2 binding constant for p-NQ-Cl2 over, for example, the BQ-Cl2 dianion, was attributed primarily to resonance stabilization via electron delocalization within the aromatic phenyl group fused to the quinone ring structure, consistent with the effect of resonance stabilization on the basicity of aromatic oxide anions observed in phenol and 1-naphthol molecules. In dilute aqueous solution, the pK of phenol (phenoxide) b =3.11) is 1-naphthol (naphthoxide pK b = 3.66). In organic solvents, the strength of an oxyanion as a Lewis base is reflected in its hydrogen-bonding power. The lower CO2 binding constant measured for BQ-Cl4 compared to BQ-Cl2 can be attributed primarily to the electron-withdrawing properties of the chlorine side groups; the replacement of two hydrogen atoms of BQ-Cl2 by two chlorine atoms allowed for greater stabilization of the dianion BQ-Cl4 and a decrease in the nucleophilicity of this anion toward CO2.

[0179] Condensation of an aromatic benzene group with a quinone ring has been shown to have less of an effect on the resonance stabilization of oxyanions than attachment of an electron-withdrawing group to the quinone ring structure. Thus, replacement of an electron-withdrawing group with a fused aromatic phenyl group increased the CO2 binding constant, as demonstrated for the anthraquinone derivatives AQ-Cl, AQ-CONH-C4H9, and AQ-COO-C3H7, classified as weakly complexing quinones, because the addition of CO2 did not affect the reduction and oxidation waves of the first electron transfer, whereas the half-wave electron transfer shifted positively.

[0180] Electrochemistry of strongly complexing quinones in the presence of CO2 Addition of CO2 to quinones that interact strongly with CO2 resulted in cyclic voltammetric waves that were significantly different from those discussed for the weakly complexing quinones. The 11 quinones referenced in Example 1 were classified as strongly complexing quinones: BQ, p-NQ, AQ, AQ-O-C3H7, o-NQ, PQ, DBQ, TBQ, p-NQ-Me2, PQ-I, and PQ-I2. The following discussion of the first six compounds as these quinones presented unique cyclic voltammograms across the full interaction range.

[0181] The anthraquinone derivative, AQ-COO-C3H7, exhibited the strongest CO2 binding constant among a group of weakly complexing quinones. The electron-withdrawing nature of the carbonyl group (C=O) of the ester substituent reduces the Lewis basicity of the oxyanion, which is thought to limit its CO2 binding constant. Replacement of the ester group with any electron-donating substituent is thought to result in an increase in the CO2 binding constant. The electrochemical behavior of two anthraquinone derivatives, AQ-COO-C3H7 and AQ-O-C3H7, with opposite inductive effects was compared with that of the unsubstituted anthraquinone molecule, AQ, but the inductive effects of the hydrogen substituents were between those of the ester and ether groups.

[0182] Figures 12B–12D show cyclic voltammetry data at a scan rate of 100 mV / s for AQ-COO-C3H7, AQ, and AQ-O-C3H7 in DMF electrolyte saturated with N2 (left) and in CO2 atmosphere (right), respectively. The cyclic voltammograms of AQ-COO-C3H7, AQ, and AQ-O-C3H7 showed two single-electron transfer waves in N2 separated by approximately 0.7 V. As with other weakly complexing quinones, the peak current and position of the first reduction wave for AQ-COO-C3H7 remained unchanged when the electrolyte solution was saturated with CO2, but the second reduction wave shifted positively (Figure 12B). With both hydrogen and ether substituents, the CO binding constant is expected to be stronger than that of the ester group, and therefore a larger positive shift of the second reduction wave was observed for AQ and AQ-O-C3H7 (Figures 12C and 12D, respectively). The positive shift of the second (more negative) reduction wave was accompanied by an increase in the first cathodic current. The second reduction wave showed only a shoulder in the case of AQ (Figure 12C), and none was observed in the case of AQ-O-C3H7 (Figure 12D). The first cathodic peak current for AQ increased from 56 μA to 70 μA, while the cathodic peak current for AQ-O-C3H7 increased from 56 μA to 83 μA. Only one oxidation wave was observed in the voltammograms of AQ and AQ-O-C3H7, and the current of that oxidation wave was higher under CO2 than under N2. The increase in current during the first oxidation wave is believed to correspond to the oxidation of the quinone-CO monoadducts to release CO and regenerate semiquinones, which were immediately oxidized to the native quinone species. The electrode potential for oxidizing the monoadducts is sufficiently energetic to further oxidize the semiquinones thus generated, resulting in a simultaneous two-oxidation process.

[0183] Quinones with electron-donating substituents were predicted to have stronger CO2 binding constants. Based on their molecular structures, the oxyanions of BQ and p-NQ should have higher CO2 binding constants than both AQ and AQ-O-C3H7. According to the concept of resonance stabilization and its effect on the basicity of aromatic oxyanions described earlier, the basicity of the p-NQ oxyanion was predicted to be between that of BQ and AQ. Without the fused aromatic phenyl ring, the BQ oxyanion is the strongest Lewis base of these three quinones.

[0184] Figures 13A-13B show cyclic voltammetry of p-benzoquinone (BQ) (Figure 13A) and p-naphthoquinone (p-NQ) (Figure 13B) solutions in 0.1 M [n-BuN]PF in DMF saturated with either N or CO at a scan rate of 100 mV / s using quinone concentrations of 4 mM (left) and 20 mM (right). Two well-separated electrochemical waves were observed for BQ and p-NQ solutions under nitrogen. In the presence of CO, these quinones showed a significant increase in the first electron transfer peak current, attributed to two successive electron transfers at this reduction potential, and a disappearance of the second electron transfer reduction wave, which can be attributed to the rapid disproportionation of the semiquinone to give a single adduct dianion and a neutral quinone.

[0185] At a BQ concentration of 4 mM, the presence of CO2 increased the peak current of the first electron transfer from 24.5 μA to 36.0 μA, or about 47%. At 20 mM BQ, the current increase reached 54%. Similarly, at 4 mM p-NQ, the peak current increased from 22.6 μA to 30.3 μA, or about 34%; whereas at 20 mM p-NQ, the peak current increased from 77.6 μA to 135.5 μA, or about 75%. This indicated that the formation of single adduct dianions of BQ and p-NQ depends on the concentration of their semiquinones in the boundary layer at the electrode surface.

[0186] Figures 13A-13B show that the voltammograms for BQ and p-NQ revealed two oxidation waves at two oxidation potentials, due to electron abstraction from the interacting dianion quinone and CO2 products, corresponding to two different oxidation mechanisms. These are indicated by downward arrows in Figures 13A-13B. The first oxidation wave was attributed to the CO2 mono-adduct, and the second, which occurred at a less negative potential, was attributed to the di-adduct oxidation process. For BQ, the anodic peak current for the mono-adduct was observed at -0.83 V, while the anodic peak current for the di-adduct was observed at -0.32 V. For p-NQ, the anodic peak current for the mono-adduct oxidation process was observed at -1.01 V, while the anodic peak current for the di-adduct was observed at -0.50 V.

[0187] Mechanistic analysis of the electrochemistry of p-naphthoquinone and subsequent addition of CO2 A deeper mechanistic analysis was performed on p-NQ to more fully understand the mechanism of electrochemically induced reductive CO addition. This was done by studying the CV of p-NQ under increasing concentrations of CO and remaining N. Figure 14 shows the cyclic voltammetry of a 5 mM p-naphthoquinone (p-NQ) solution in 0.1 M [n-BuN]PF in DMF saturated with increasing concentrations of CO gas (remaining N) at a scan rate of 500 mV / s using a glassy carbon working electrode. The CV in Figure 14 shows a clear trend of the appearance of new peaks and the decline of others at very low concentrations of CO. The discussion that follows will constantly refer to Figure 14 and will explain the main features observed through thermodynamic and kinetic phenomena.

[0188] The first major observation from the CV in Figure 14 is the presence of two reduced species, semiquinone NQ ·- and quinol dianion NQ 2- The behavior of NQ is significantly different in the presence of CO2. ·- The cathodic peak of the first reduction, where CO2 occurs, had a very slightly decreasing intensity with increasing concentration of CO2, indicating a relatively weak equilibrium with CO2.

[0189] The semiquinone monoadduct resulting from this equilibrium possesses an electron density acquired in the first reduction wave shift from the conjugation of the naphthoquinone aromatic ring to that of the newly added carboxylate moiety, which is isolated from the rest of the molecule via the newly formed σ bond. This causes relative neutralization of the aromatic ring, allowing a second electron to be acquired at more positive potentials, i.e., at or a few tens of mV below the first reduction potential as seen in Figure 13B and at 100% CO CV in Figure 14. This is thought to be primarily because the reduction of the quinone at the electrode interface occurs via electron transfer from the electrode to the aromatic conjugated system.

[0190] At low concentrations of CO2, such as 0.5 and 1.0% CO2 CV in Figure 14, the forward reaction rate for the semiquinone monoadduct formation reaction was relatively slow, and the cathodic peak between the first and second reduction waves appeared near the second reduction wave. As the CO2 concentration increased, at 20 and 100% CO2 CV, this peak shifted in a more positive direction, and in the case of 100% CO2, it merged with the cathodic peak of the first reduction wave, causing a shift in peak position due to a convolution effect. This peak is thought to be essentially caused by kinetic effects: NQ ·- is formed in the first reduction wave near the electrode, it reacts with CO2 in the electrode's diffusion layer to form a semiquinone diadduct, which can then accept a second electron at a more positive reduction potential. However, during the negative (cathodic) sweep of the CV, the glassy carbon electrode experiences an increasingly negative potential and thus an increasingly large overpotential, η (η = E 印加 -E 平衡 and E 平衡 is obtained from the Nernst equation). This is the Butler-Volmer equation

number

[0191] The position of the peak between the two reduction peaks in Figure 14 is the rate of chemical formation of semiquinones, which depends on the concentration of CO2 dissolved in the electrolyte - the bimolecular reaction rate r = k[NQ ·- The rate of reaction is thought to be strictly determined by competition between the rate of ][CO2] and the rate of electrochemical reduction of the semiquinone monoadduct to the dianion monoadduct. The rate constant for the bimolecular reaction is k ca. 25 M -1 seconds -1 This is estimated to be the rate of formation of the semiquinone monoadduct, approximately 5 × 10 under CV and 20% CO2 conditions. -3 M seconds -1 The dependence of this peak position on scan rate can be seen in Figure 15, which shows cyclic voltammetry of a 5 mM p-naphthoquinone (p-NQ) solution in 0.1 M [n-Bu4N]PF6 in DMF saturated with 20% CO2 (rest N2) at various scan rates using a glassy carbon working electrode. In Figure 15, at low scan rates of 50–100 mV / s, the peak merges with the cathodic peak of the first reduction wave, while at higher scan rates, which are believed to be greater than the time constant of the chemical reaction, a second peak appears and shifts more negatively from the first peak. The intensity of this peak also increases relative to the first reduction wave because the electrochemical reaction occurring later in the chemical reaction occurs at a larger overpotential. The voltage distance between the two cathodic peaks corresponds to the time required for the chemical reaction to proceed.

[0192] The second chemical reaction of the dianion diadduct proceeds as expected and does not contribute significantly to the electrochemical behavior beyond thermodynamic stabilization of the dianion diadduct.

[0193] Steric effects of para versus ortho-quinones Quinones exist in two isomeric forms, 1,4-cyclohexadienedione (para-quinone) and 1,2-cyclohexadienedione (ortho-quinone). The above discussion focused on the association of CO2 with the dianion of para-quinone. The association of CO2 with the isomeric forms of two ortho-quinones, PQ and AQ, and o-NQ and p-NQ, is evaluated. In dilute aqueous solution, deprotonated hydrobenzoquinone (pK b =3.65) is the deprotonated catechol (pK b = 4.15); therefore, the dianion of ortho-quinone was considered to be less basic than that of para-quinone. Figures 16A-16B show the cyclic voltammetry of 9,10-phenanthrenequinone (PQ) (Figure 16A) and o-naphthoquinone (o-NQ) (Figure 16B) in a solution of 0.1 M [n-BuN]PF in DMF saturated with either N or CO, using a platinum electrode at a scan rate of 100 mV / s and quinone concentrations of 4 mM (left) and 20 mM (right). As shown in Figures 16A-16B, in nitrogen-saturated DMF electrolyte solution, PQ exhibited two typical electrochemical waves corresponding to the formation of a semiquinone and a dianionic quinone, respectively. The half-wave potential for the first electron transfer with PQ occurred at −1.09 V and the second at −1.96 V, a separation of approximately 0.87 V. This value was larger than the half-wave potential separation observed for AQ, which was approximately 0.75 V. Similarly, the potential separation for o-NQ, approximately 0.89 V, was slightly wider than the 0.87 V for p-NQ. The larger potential separation for ortho-quinone is likely due to the closer proximity of the two oxyanions at positions C1 and C2, which experience greater electrostatic repulsion.

[0194] The addition of CO2 to a DMF solution containing PQ resulted in a significant increase in the peak current of the first electron transfer and the disappearance of the second electron transfer reduction wave (Figure 16A). This was significantly different from the trend observed in the cyclic voltammogram for AQ (Figure 12C), which still showed a shoulder in the reduction wave due to the second electron transfer under a CO2 atmosphere. These results suggest that PQ has a stronger coupling with CO2 than AQ. The increase in the PQ peak current of the first electron transfer was due to two consecutive electron transfers in the first reduction wave. The addition of CO2 to a DMF solution containing o-NQ also resulted in a significant increase in the peak current of the first electron transfer, and no separate reduction wave of the second electron transfer was observed (Figure 16B). At a PQ concentration of 4 mM (Figure 16), the addition of CO2 increased the peak current of the first electron transfer from 22 μA to 39 μA, i.e., an increase of approximately 77%. At a PQ concentration of 20 mM (Figure 16B), the percentage increase in current dropped to 71%. An even more significant drop in the percentage increase in current with increasing quinone concentration was observed for o-NQ. At a 4 mM concentration (Figure 16B), the percentage increase in peak current was approximately 93%, whereas at a 20 mM concentration, the percentage increase in peak current was only approximately 84%. The trend in the increase in peak current with increasing quinone concentration and the difference from the results obtained for para-quinone suggested a different mechanism of CO2 binding. In the case of ortho-quinone, the linear dependence of the peak current increase on the relative concentration of CO2 to quinone suggested a mechanism of electron transfer, followed by a chemical step, followed by electron transfer (ECE). A carbonate complex is formed by an initial one-electron reduction of the neutral quinone to form a semiquinone, which then complexes with CO2. This intermediate complex is thought to immediately undergo a second, one-electron reduction in proximity to the electrode surface to form the mono(carbonate) of the dianionic quinone. Complexation of the semiquinone with CO2 was confirmed by a small positive shift in the first electron transfer when the electrolyte was saturated with CO2. The positive shift for o-NQ was approximately 38 mV, and for PQ it was approximately 14 mV.

[0195] As observed and discussed above, the voltammograms of PQ and o-NQ in CO2-saturated DMF electrolyte showed two oxidation waves (Figures 16A-16B), corresponding to the oxidation of the CO2 monoadduct and diadduct, respectively. The relative peak currents of these oxidation waves suggested that a portion of the dianion quinone-CO2 complexes within the diffusion layer on the electrode surface, which undergoes each oxidation process. The concentration of dissolved CO2 in the DMF electrolyte at 1 bar CO2 pressure was approximately 0.175 M, or 44 times higher than the quinone concentration at 4 mM. At the same CO2 concentration and 20 mM quinone loading, the relative concentration of dissolved CO2 to quinone was 8.75. As the relative CO2 concentration increased, the equilibrium position shifted to avoid dissociation of the CO2-dianion quinone diadduct; therefore, the relative peak currents of the two oxidations were lower at 4 mM than at 20 mM quinone solution, as shown in Figure 16.

[0196] The experiments described in this example demonstrate reactivity between certain electroactive species (e.g., certain semiquinones) and carbon dioxide at relatively positive potentials. As noted above, incorporation of certain of the described electroactive species (e.g., strongly complexing, optionally substituted quinones) into an electrochemical cell, with the insights and guidance of the present disclosure, can facilitate the electrochemically mediated capture of carbon dioxide under conditions where relatively little (or no) electrochemically mediated reactivity occurs with other species, such as O.

[0197] While several embodiments of the present invention have been described and illustrated herein, those skilled in the art will readily envision various other means and / or structures for performing the functions and / or obtaining one or more of the results and / or advantages described herein, and each such variation and / or modification 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 vary depending on the specific application or applications for which the teachings of the present invention 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. Accordingly, it should be understood that the foregoing embodiments are presented by way of example only, and that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described and claimed. The present invention 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 is within the scope of the present invention, provided that such features, systems, articles, materials, and / or methods are not mutually inconsistent.

[0198] As used herein and in the claims, the phrase "at least a portion" means some or all. "At least a portion" may mean, according to certain embodiments, at least 1%, at least 2%, at least 5%, at least 10%, at least 25%, at least 50%, at least 75%, at least 90%, at least 95%, or at least 99% by weight, and / or in certain embodiments, up to 100% by weight. "At least a portion" may, according to certain embodiments, mean at least 1%, at least 2%, at least 5%, at least 10%, at least 25%, at least 50%, at least 75%, at least 90%, at least 95%, or at least 99% by volume, and / or in certain embodiments, up to 100% by volume. "At least a portion" may mean, according to certain embodiments, 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%.

[0199] The indefinite articles "a" and "an," as used herein in the specification and claims, unless clearly indicated to the contrary, should be understood to mean "at least one."

[0200] The phrase "and / or," as used herein in the specification and claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are present conjunctively in some cases and disjunctively in other cases. Unless clearly indicated to the contrary, other elements may optionally be present other than the elements specifically identified by the "and / or" clause, whether associated with specifically identified elements or not. Thus, as a non-limiting example, a reference to "A and / or B," when used in conjunction with open-ended language such as "comprising," can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); and so forth.

[0201] As used herein and in the claims, "or" should be understood to have the same meaning as "and / or" as defined above. For example, when separating items in a list, "or" or "and / or" should be interpreted as being inclusive, i.e., including at least one of a number or list of elements, but also including more than one, and optionally including additional unlisted items. Terms clearly indicating the contrary, such as "only one of" or "exactly one of," or, when used in the claims, "consisting of," only refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or," as used herein, should be interpreted to indicate exclusive alternatives (i.e., "one or the other, but not both") only when preceded by exclusive terms such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of," when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0202] As used in this specification and claims, the phrase "at least one," 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 in the list of elements, and not excluding any combination of elements in the list of elements. This definition also allows for elements, if desired, to be present other than those specifically identified in the list of elements to which the phrase "at least one" refers, whether related to the specifically identified elements or not. 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 to, in one embodiment, at least one A, optionally including more than one, with no B present (optionally including elements other than B); in another embodiment, at least one B, optionally including more than one, with no A present (optionally including elements other than A); in yet another embodiment, at least one A, optionally including more than one, and at least one B, optionally including other elements; etc.

[0203] In the claims and the foregoing specification, 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. Only the transitional phrases "consisting of" and "consisting essentially of" shall be closed or semi-closed transitional phrases, respectively, as set forth in the U.S. Patent and Trademark Office Manual of Examining Procedures, Section 2111.03. The present invention provides, for example, the following items. (Item 1) a negative electrode containing a first electroactive species; A positive electrode and a separator between the negative electrode and the positive electrode, which may contain a conductive liquid; wherein the first electroactive species comprises: In the oxidized state, The activated species can combine with the target gas, but oxygen (O 2 ) is thermodynamically unfavorable at at least one temperature, and having Electrochemical cell. (Item 2) a negative electrode including a first electroactive species immobilized thereon; Positive electrode and wherein the first electroactive species comprises: In the oxidized state, The activated species can combine with the target gas, but oxygen (O 2 ) is thermodynamically unfavorable at at least one temperature, and having Electrochemical cell. (Item 3) a plurality of electrochemical cells in fluid communication with the gas inlet and the gas outlet; 1. A gas separation system comprising: 0.003 kg at a gas flow rate greater than or equal to 0.001 L / s and less than or equal to 500 L / s 標的ガス / (kg 床 t b )(in the formula, kg 床 is the floor weight, and t b is the breakthrough time for said gas separation system. (Item 4) 4. The electrochemical cell of any one of items 1 to 3, wherein the electrochemical cell comprises a negative electrode comprising a first electroactive species. (Item 5) The first electroactive species is in an oxidized state and the active species is capable of combining with a target gas, but oxygen (O 2 5. The electrochemical cell of any one of items 1 to 4, having at least one reduced state in which reaction with . (Item 6) The first electroactive species is in an oxidized state and the active species is capable of combining with a target gas, but oxygen (O 2 6. The electrochemical cell of any one of items 1 to 5, wherein the reaction with ZnO is thermodynamically unfavorable at at least one temperature greater than or equal to 223 K and less than or equal to 573 K. (Item 7) The first electroactive species is in an oxidized state and the active species is capable of combining with a target gas, but oxygen (O 2 7. The electrochemical cell of any one of items 1 to 6, wherein the reaction with ZnO is thermodynamically unfavorable at at least one temperature greater than or equal to 223 K and less than or equal to 373 K. (Item 8) The first electroactive species is capable of combining with a target gas, but oxygen (O 2 8. The electrochemical cell of any one of items 1 to 7, having at least one reduced state in which reaction with . (Item 9) 9. The electrochemical cell according to any one of items 1, 3 to 8, wherein the first electroactive species is immobilized on the negative electrode. (Item 10) 10. The electrochemical cell of any one of items 1-2, 4-9, wherein the negative electrode comprises a primary electroactive composite layer comprising the first electroactive species. (Item 11) The first electroactive species is in an oxidized state and the active species is capable of combining with a target gas, but oxygen (O 2 11. The electrochemical cell of any one of items 1 to 2 and 4 to 10, wherein the electrochemical cell has at least one reduced state in which a reaction with (Item 12) The standard reduction potential for generation of the reduced state of at least one of the first electroactive species in the conductive liquid is oxygen gas (O 2 ) and superoxide (O 2 - 12. The electrochemical cell according to any one of items 1 to 2 and 4 to 11, wherein the potential is more positive than the standard reduction potential for the interconversion between HCl and HCl. (Item 13) The standard reduction potential for generation of the reduced state of at least one of the first electroactive species in the conductive liquid is greater than or equal to superoxide (O 2 - ) and peroxide (O 2 2- 13. The electrochemical cell according to any one of items 1 to 2 and 4 to 12, wherein the potential is more positive than the standard reduction potential for the interconversion of HCl with HCl. (Item 14) 14. The electrochemical cell of any one of items 1 to 2, 4 to 13, wherein the first electroactive species is part of a polymeric material immobilized on the negative electrode. (Item 15) 15. The electrochemical cell of any one of items 1-2, 4-14, wherein the first electroactive species comprises an optionally substituted quinone. (Item 16) The first electroactive species has the formula (IA) and (IB):

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Claims

1. An electrochemical cell for separating carbon dioxide from a gas mixture, said 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, which may contain a conductive liquid, the conductive liquid having a conductivity that facilitates electrochemical reactions in an electrochemical circuit including the negative electrode and the positive electrode; wherein the first electroactive species comprises: In the oxidized state, The active species can combine with carbon dioxide but not with oxygen (O ２ ) is thermodynamically unfavorable at at least one temperature, and having Electrochemical cell.

2. The standard reduction potential for generation of the reduced state of at least one of the first electroactive species in the conductive liquid is greater than or equal to the standard reduction potential of oxygen gas (O ２ ) and superoxide (O ２ － 10. The electrochemical cell of claim 1, wherein the potential is more positive than the standard reduction potential for the interconversion between HCl and HCl.

3. The standard reduction potential for generation of the reduced state of at least one of the first electroactive species in the conductive liquid is greater than or equal to superoxide (O ２ － ) and peroxide (O ２ ２－ 3. The electrochemical cell of claim 1, wherein the potential is more positive than the standard reduction potential for the interconversion of HCl with HCl.

4. An electrochemical cell for separating carbon dioxide from a gas mixture, said electrochemical cell comprising: a negative electrode comprising a first electroactive species immobilized thereon; Positive electrode and wherein the first electroactive species comprises: In the oxidized state, The active species can combine with carbon dioxide but not with oxygen (O ２ ) is thermodynamically unfavorable at at least one temperature, and having Electrochemical cell.

5. The first electroactive species is in an oxidized state and the active species is capable of combining with carbon dioxide but oxygen (O ２ 5. The electrochemical cell of claim 1, wherein the electrochemical cell has at least one reduced state in which reaction with ZnO is thermodynamically unfavorable at at least one temperature greater than or equal to 223 K.

6. The first electroactive species is in an oxidized state and the active species is capable of combining with carbon dioxide but oxygen (O ２ and at least one reduced state in which reaction with HCl is thermodynamically unfavorable at at least one temperature greater than or equal to 223 K and less than or equal to 573 K.

7. The first electroactive species is in an oxidized state and the active species is capable of combining with carbon dioxide but oxygen (O ２ 7. The electrochemical cell of claim 1, wherein the electrochemical cell has at least one reduced state in which reaction with ZnO is thermodynamically unfavorable at at least one temperature greater than or equal to 223 K and less than or equal to 373 K.

8. The first electroactive species is capable of combining with carbon dioxide but not with oxygen (O ２ 8. The electrochemical cell of claim 1, having at least one reduced state in which reaction with .alpha.-hydroxybenzoate is thermodynamically unfavorable at 298K.

9. 9. The electrochemical cell of any one of claims 1 to 3 and 5 to 8, wherein the first electroactive species is immobilized on the negative electrode.

10. 10. The electrochemical cell of claim 1, wherein the negative electrode comprises an electroactive composite layer comprising the first electroactive species.

11. The electrochemical cell of claim 10 , wherein the electroactive composite layer comprises a carbonaceous material.

12. The first electroactive species is in an oxidized state, and the active species can combine with carbon dioxide but not oxygen (O ２ 12. The electrochemical cell of claim 1, wherein the reaction of HCl with HCl has a change in Gibbs free energy greater than or equal to 0 kcal / mol at at least one temperature in the range greater than or equal to 223 K and less than or equal to 573 K.

13. 13. The electrochemical cell of any one of claims 1 to 12, wherein the first electroactive species is part of a polymeric material immobilized on the negative electrode.

14. 14. The electrochemical cell of any one of claims 1 to 13, wherein the first electroactive species comprises a substituted or unsubstituted quinone.

15. The first electroactive species has formula (IA) and (IB): 【Chemistry 12】 and In the formula, R １ , R ２ , R ３ , and R ４ may be the same or different and can be hydrogen, halo, hydroxyl, carboxylate / carboxylic acid, sulfonate / sulfonic acid, alkylsulfonate / alkylsulfonic acid, phosphonate / phosphonic acid, alkylphosphonate / alkylphosphonic acid, acyl, amino, amido, quaternary ammonium, branched or unbranched alkyl, heteroalkyl, alkoxy, glycoxy, polyalkyleneglycoxy, imino, polyimino, branched or unbranched alkenyl, branched or unbranched alkynyl, aryl, heteroaryl, heterocyclyl, nitro, nitrile, thiyl, and / or carbonyl groups, any of which may be substituted or unsubstituted, and / or R １ ~R ４ 15. The electrochemical cell of any one of claims 1 to 14, wherein any two adjacent groups of can join to form a substituted or unsubstituted ring.

16. The first electroactive species is selected from the group consisting of phenanthrenequinone esters (PQ-esters), iodo-phenanthrenequinones (PQ-I), di-iodo-phenanthrenequinones (PQ-I), and the like. ２ ), phenanthrenequinone (PQ), ortho-naphthoquinone (o-NQ), dimethyl-para-naphthoquinone (p-NQ-Me ２ ), para-naphthoquinone (p-NQ), di-tert-butyl-benzoquinone (TBQ), and benzoquinone (BQ), the structures of which are as follows: 【Chemistry 13】 wherein R ５ 16. The electrochemical cell of any one of claims 1 to 15, wherein is a substituted or unsubstituted branched or unbranched C1 to C18 alkyl.

17. 17. The electrochemical cell of claim 1, wherein the negative electrode comprises a gas permeable layer.

18. 18. The electrochemical cell of claim 1, wherein the negative electrode is porous.

19. 19. The electrochemical cell of any one of claims 3 to 18, wherein the electrochemical cell comprises a separator between the negative electrode and the positive electrode, which can contain a conductive liquid.

20. 20. The electrochemical cell of any one of claims 1 to 3 and 19, wherein the separator contains a conductive liquid.

21. 21. The electrochemical cell of any one of claims 1 to 3 and 19 to 20, wherein the separator is saturated with the conductive liquid.

22. 22. The electrochemical cell of claim 20, wherein the conductive liquid comprises a non-volatile electrolyte.

23. 23. The electrochemical cell of any one of claims 20 to 22, wherein the conductive liquid comprises an ionic liquid at room temperature.

24. 24. The electrochemical cell of claim 23, wherein the room temperature ionic liquid comprises 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (Bmim) as a cationic constituent.

25. The room temperature ionic liquid contains bis(trifluoromethylsulfonyl)imide (TF) as an anion component. ２ 25. The electrochemical cell of any one of claims 23 to 24, comprising:

26. 26. The electrochemical cell of any one of claims 1 to 25, wherein the positive electrode comprises a second electroactive species.

27. 27. The electrochemical cell of claim 26, wherein the positive electrode comprises a gas permeable layer and a complementary electroactive composite layer comprising the second electroactive species.

28. 28. The electrochemical cell of any one of claims 26-27, wherein the second electroactive species comprises a redox active polymer.

29. 30. The electrochemical cell of claim 28, wherein the redox active polymer comprises polyvinylferrocene.

30. 30. The electrochemical cell of any one of claims 26 to 29, wherein the second electroactive species comprises an intercalation compound.

31. The intercalation compound is lithium iron phosphate (LiFePO ４ 31. The electrochemical cell of claim 30 comprising:

32. the negative electrode is a first negative electrode, and the electrochemical cell further comprises: a second negative electrode containing a first electroactive species; a second separator between the positive electrode and the second negative electrode, the second separator being capable of being saturated with a conductive liquid; 32. The electrochemical cell of any one of claims 1 to 31, comprising:

33. 33. The electrochemical cell of claim 32, 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.

34. A gas separation system comprising a plurality of electrochemical cells according to any one of claims 1 to 33 in fluid communication with a gas inlet and a gas outlet.

35. 0.003 kg at a gas flow rate of greater than or equal to 0.001 L / s and less than or equal to 500 L / s 標的ガス / (kg 床 t ｂ kg), wherein kg 床 is the floor weight, and t ｂ 35. The gas separation system of claim 34, wherein: is the breakthrough time for the gas separation system.

36. 0.05 kg at a gas flow rate of greater than or equal to 0.001 L / s and less than or equal to 500 L / s 標的ガス / (kg 床 t ｂ 36. The gas separation system of any one of claims 34 to 35, configured to have a productivity for capturing carbon dioxide less than or equal to 1000 kJ / L.

37. The flow rate of the gas stream is 100 cm of negative electrode area in the system. ２ The gas separation system according to any one of claims 35 to 36,

38. 38. The gas separation system of any one of claims 35 to 37, wherein the flow rate of the gas stream is per 10 electrochemical cells of the plurality of electrochemical cells in the system.

39. 39. The gas separation system of any one of claims 34 to 38, wherein the plurality of electrochemical cells are electrically connected in parallel.

40. 40. The gas separation system of any one of claims 34 to 39, wherein the plurality of electrochemical cells are electrically connected in series.

41. 41. The gas separation system of any one of claims 34 to 40, wherein there is a flow field between at least some of the plurality of electrochemical cells.

42. 42. The gas separation system of any one of claims 40-41, 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.

43. 43. The gas separation system of claim 42, wherein the one or more electrically conductive materials comprise bipolar plates.

44. Applying a potential difference across the electrochemical cell of any one of claims 1 to 33; exposing the gas mixture comprising carbon dioxide to the electrochemical cell; and combining at least a portion of the carbon dioxide with the first electroactive species to produce a treated gas mixture having a lower amount of the carbon dioxide than the gas mixture; 1. A method for at least partial gas separation comprising:

45. applying a potential difference across one or more than one electrochemical cell of the plurality of electrochemical cells in the gas separation system of any one of claims 34 to 43; exposing the gas mixture including carbon dioxide to the one or more electrochemical cells; and combining at least a portion of the carbon dioxide with the first electroactive species to produce a treated gas mixture having a lower amount of the carbon dioxide than the gas mixture; 1. A method for at least partial gas separation comprising:

46. Applying a potential difference across the electrochemical cell of any one of claims 1 to 33; exposing a gas mixture comprising carbon dioxide to the electrochemical cell; and removing an amount of said carbon dioxide from said gas mixture during and / or after application of said first potential difference. and, in volume percent, any oxygen gas (O ２ ) less than or equal to 0.1% of the total carbon dioxide is removed from the gas mixture; A method for at least partial gas separation.

47. applying a first potential difference across the electrochemical cell of any one of claims 1 to 33; exposing a first amount of an input gas mixture comprising carbon dioxide to the electrochemical cell; combining at least a portion of the carbon dioxide with electroactive species in the electrochemical cell during and / or after application of the first potential difference to produce a first treated gas mixture having a lower amount of carbon dioxide than the input gas mixture; applying a second potential difference to the electrochemical cell; and Releasing some or all of the carbon dioxide bound to the electroactive species to produce a second treated gas mixture. and during and / or after said release, (a) flowing a second gas through the electrochemical cell to remove at least some or all of the released carbon dioxide from the electrochemical cell; and / or (b) applying a vacuum to the electrochemical cell to remove at least some or all of the released carbon dioxide from the electrochemical cell; The method further comprises:

48. 48. The method of claim 47, wherein the concentration of carbon dioxide is less than or equal to 5,000 ppm.

49. 49. The method of any one of claims 47 to 48, wherein the concentration of carbon dioxide is less than or equal to 500 ppm.

50. The gas mixture is oxygen gas (O ２ 50. The method of any one of claims 47 to 49, comprising:

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