HYBRID CO2 CAPTURE and ELECTROLYSIS

Abstract

A system contains a CO2 purifier and a CO2 electrolyzer. In operation, the CO2 purifier selectively captures CO2 from a gas stream and then releases purified CO2 as an output. The purified CO2 is then provided as an input to the cathode of the CO2 electrolyzer. The CO2 electrolyzer can electrochemically reduce the CO2 to a carbon-containing product (CCP) that may be stored, consumed, used to synthesize a valuable product, etc. The purifier may be an electrochemical cell that allows at least some non-CO2 inlet components to pass without being absorbed. Depending on the composition of the inlet stream, examples of non-absorbed components include water, nitrogen, carbon monoxide, oxygen, and sulfur-containing compounds.

Description

INCORPORATION BY REFERENCE

An Application Data Sheet is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or priority to as identified in the concurrently filed Application Data Sheet is incorporated by reference herein in their entireties and for all purposes.

FIELD

The present disclosure relates to electrochemical cells for carbon dioxide enrichment and the integration of such cells with carbon dioxide electrolyzers.

BACKGROUND

Greenhouse gas emissions such as carbon dioxide (CO₂) can have a potential impact on the climatic environment if left uncontrolled. The conversion of fossil fuels such as coal or natural gas into energy is a major source of greenhouse gas emissions. There is an urgent need for a system for more effective management of these CO₂ emissions. Improvements in carbon capture technology whereby a stream of low-quality and/or low-concentration gas is converted to a stream of higher quality and/or higher concentration of gas are of great interest to manufacturing and energy industries where the gases are generated.

Temperature swing processes have been explored for CO₂ capture utilizing aqueous amine absorbents. However, the methods employed are energy-intensive; so there is a continuing need for better solutions to the ongoing issues with CO₂ emissions.

Electrochemical separation methods such as electro-swing adsorption are a possible approach to management of gases such as CO₂. Yet there remains a continuing need to refine the electrochemical systems utilized for CO₂ enrichment.

SUMMARY

The present disclosure relates to electrochemical cells for CO₂ enrichment and the integration of such cells with CO₂ electrolyzers.

Aspects of this disclosure pertain to systems that may be characterized by the following features: (I) a source of hydrogen; (II) a CO₂ purifier comprising: (a) an inlet for receiving impure CO₂, (b) a cathode coupled to the inlet for receiving impure CO₂, (c) an inlet for receiving hydrogen from the source of hydrogen; (d) an anode coupled to the inlet for receiving hydrogen; and (e) an outlet for providing purified CO₂ and coupled to the anode; and (III) a CO₂ electrolyzer configured to receive the purified CO₂ from the CO₂ purifier. The CO₂ electrolyzer includes a cathode configured to electrochemically reduce CO₂ to produce a carbon containing product.

In certain embodiments, the CO₂ purifier additionally includes a membrane between the anode and the cathode, wherein the membrane is conductive to electrons and ions. The membrane may be conductive to anions. In certain embodiments, the CO₂ purifier additionally includes a membrane between the anode and the cathode, wherein the membrane comprises a filler. As examples, the filler may include a fluorocarbon polymer, a fullerene, a metal, a reduced graphene oxide, or any combination thereof.

In some implementations, the CO₂ purifier does not include wires to an external circuit. In some implementations, the anode and cathode of the CO₂ purifier are not connected to electrical wires.

In certain embodiments, the system is configured to transport O₂ produced by the CO₂ electrolyzer to the cathode of the CO₂ purifier. In certain embodiments, the system is configured to transport O₂ produced by the water electrolyzer to the cathode of the CO₂ purifier. In certain embodiments, the source of hydrogen is a water electrolyzer configured to electrolyze water and produce the hydrogen. In some implementations, the CO₂ electrolyzer is directly coupled to the CO₂ purifier and is configured to directly receive the purified CO₂ from the CO₂ purifier.

In certain embodiments, the carbon containing product contains CO, a hydrocarbon, formic acid, an alcohol, or any combination thereof. In certain embodiments, the carbon containing product is carbon monoxide, and the system is configured to combine the carbon monoxide with a portion of the hydrogen produced by the water electrolyzer.

In some embodiments, the system additionally includes a controller configured to cause electrical energy to be applied to the CO₂ electrolyzer to cause the cathode to electrochemically reduce the CO₂ to produce the carbon containing product. Such controller may be further configured to cause electrical energy to be applied to the water electrolyzer to cause the water electrolyzer to produce the hydrogen.

Some aspects of this disclosure pertain to methods that may be characterized by the following operations:

• • (a) purifying CO₂ from an impure CO₂ stream by
    • (i) contacting the impure CO₂ stream with a cathode of a CO₂ purifier,
    • (ii) contacting hydrogen with an anode of the CO₂ purifier, and
    • (iii) recovering purified CO₂ from an outlet of the CO₂ purifier, which outlet is coupled to the anode of the CO₂ purifier; and
  • (b) electrochemically reducing the purified CO₂ by an electrolysis process including:
    • (i) providing the purified CO₂ to a CO₂ electrolyzer, and
    • (ii) electrochemically reducing the purified CO₂ electrolyzer at a cathode of the CO₂ electrolyzer to produce a carbon containing product.

In certain embodiments, the methods additionally include electrolyzing water to produce the hydrogen. In some embodiments, the methods apply electrical energy to the CO₂ electrolyzer to cause the cathode to electrochemically reduce the CO₂ to produce the carbon containing product and applying electrical energy to a water electrolyzer to cause the water electrolyzer to produce the hydrogen.

In certain embodiments, the CO₂ purifier additionally includes a membrane between the anode and the cathode, wherein the membrane is conductive to electrons and ions. In some cases, the membrane is conductive to anions. In certain embodiments, the CO₂ purifier additionally includes a membrane between the anode and the cathode, wherein the membrane comprises a filler. As examples, the filler may include a fluorocarbon polymer, a fullerene, a metal, a reduced graphene oxide, or any combination thereof.

In some implementations, the operation of purifying CO₂ from the impure CO₂ stream is performed without the CO₂ purifier receiving electrical energy from an external circuit.

In certain embodiments, the methods additionally include contacting oxygen, along with the impure CO₂ stream, with the cathode of the CO₂ purifier. Such embodiments may include transporting O₂ produced by the CO₂ electrolyzer to the cathode of the CO₂ purifier.

In certain embodiments, the carbon containing product comprises CO, a hydrocarbon, formic acid, an alcohol, or any combination thereof. In certain embodiments, the carbon containing product is carbon monoxide. In such embodiments, the methods may additionally include combining the carbon monoxide with hydrogen to produce syngas.

In certain embodiments, the methods additionally include directly transporting the purified CO₂ from the CO₂ purifier to an inlet of the CO₂ electrolyzer.

In the above-described aspects of the disclosure, any combination of the one or more dependent features may be implemented together with, or apart from, one another when used with the primary aspect. Additional aspects and features of the disclosure will be presented below, sometimes with reference to associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram schematically illustrating components and electrochemical reactions of an electrochemical CO₂ purifier.

FIG. 1B is a block diagram schematically illustrating a system integrating an electrochemical CO₂ purifier and a CO₂ electrolyzer. The CO₂ purifier receives hydrogen from a water electrolyzer and O₂ and CO₂ from an impure CO₂ stream. The system produces syngas.

FIG. 2 is a block diagram schematically illustrating a system integrating an electrochemical CO₂ purifier and a CO₂ electrolyzer. The CO₂ purifier receives hydrogen from a water electrolyzer and O₂ and CO₂ from air. The CO₂ electrolyzer and the water electrolyzer are controlled by a common controller.

FIG. 3 is a block diagram schematically illustrating a system integrating an electrochemical CO₂ purifier and a CO₂ electrolyzer. The CO₂ purifier receives hydrogen from a water electrolyzer, CO₂ from an impure CO₂ stream, and O₂ from the CO₂ electrolzyer. The system produces syngas.

FIG. 4 depicts an example system for a carbon oxide reduction reactor that may include a cell comprising an MEA (membrane electrode assembly).

FIG. 5 depicts an example MEA for use in CO_x reduction. The MEA has a cathode layer and an anode layer separated by an ion-conducting polymer layer.

DETAILED DESCRIPTION

Terminology

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terms presented immediately below may be more fully understood by reference to the remainder of the specification. The following descriptions are presented to provide context and an introduction to the complex concepts described herein. These descriptions are not intended to limit the full scope of the disclosure.

An “electrochemical cell” includes electrolyzers such as CO₂ electrolyzers and water electrolyzers. It also includes some forms of CO₂ purifiers, particularly those that employ faradaic reactions at an anode and/or a cathode.

A “carbon oxide” includes carbon dioxide (CO₂), carbon monoxide (CO), carbonate ions (CO₃²⁻), bicarbonate ions (HCO₃⁻), and any combinations thereof.

A “mixture” contains two or more components and unless otherwise stated may contain components other than the identified components.

A “CO₂ purifier” is a device configured to purify CO₂ from an impure CO₂ source or feed stream. There are various types of CO₂ purifier that employ various operating principles. Some purifiers rely on a CO₂ sorbent that selectively binds to CO₂ under a first condition and releases purified CO₂ under second condition. Because these purifiers operate in different phases between which process conditions “swing,” such purifiers are sometimes referred to as “swing” devices. Examples include temperature swing devices, pressure swing devices, and electro-swing devices. Some purifiers do not employ swing conditions. Some examples of such purifiers employ electrochemical cells such as electrodialysis cells. Because of its function, a CO₂ purifier is sometimes referred to as a CO₂ separator or as a CO₂ scrubber.

As used herein, the term “about” is understood to account for minor increases and/or decreases beyond a recited value, which changes do not significantly impact the desired function the parameter beyond the recited value(s). In some cases, “about” encompasses +/−10% of any recited value. As used herein, this term modifies any recited value, range of values, or endpoints of one or more ranges.

As used herein, the terms “top,” “bottom,” “upper,” “lower,” “above,” and “below” are used to provide a relative relationship between structures. The use of these terms does not indicate or require that a particular structure must be located at a particular location in the apparatus.

By “aliphatic” is meant a hydrocarbon group having at least one carbon atom to 50 carbon atoms (C_1-50), such as one to 25 carbon atoms (C_1-25), or one to ten carbon atoms (C_1-10), and which includes alkanes (or alkyl), alkenes (or alkenyl), alkynes (or alkynyl), including cyclic versions thereof, and further including straight- and branched-chain arrangements, and all stereo and position isomers as well. Such an aliphatic can be unsubstituted or substituted with one or more groups, such as groups described herein for an alkyl group.

The term “acyl,” or “alkanoyl,” as used interchangeably herein, represents an alkyl group, as defined herein, or hydrogen attached to the parent molecular group through a carbonyl group, as defined herein. This group is exemplified by formyl, acetyl, propionyl, butanoyl, and the like. The alkanoyl group can be substituted or unsubstituted. For example, the alkanoyl group can be substituted with one or more substitution groups, as described herein for alkyl. In some embodiments, the unsubstituted acyl group is a C_2-7 acyl or alkanoyl group. In particular embodiments, the alkanoyl group is —C(O)-Ak, in which Ak is an alkyl group, as defined herein.

By “alkoxy” is meant —OR, where R is an optionally substituted alkyl group, as described herein. Exemplary alkoxy groups include methoxy, ethoxy, butoxy, trihaloalkoxy, such as trifluoromethoxy, etc. The alkoxy group can be substituted or unsubstituted. For example, the alkoxy group can be substituted with one or more substitution groups, as described herein for alkyl. Exemplary unsubstituted alkoxy groups include C_1-3, C_1-6, C_1-12, C_1-16, C_1-18, C_1-20, or C_1-24 alkoxy groups.

By “alkoxyalkyl” is meant an alkyl group, as defined herein, which is substituted with an alkoxy group, as defined herein. Exemplary unsubstituted alkoxyalkyl groups include between 2 to 12 carbons (C_2-12 alkoxyalkyl), as well as those having an alkyl group with 1 to 6 carbons and an alkoxy group with 1 to 6 carbons (i.e., C_1-6 alkoxy-C_1-6 alkyl).

By “alkyl” and the prefix “alk” is meant a branched or unbranched saturated hydrocarbon group of 1 to 24 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, n-pentyl, isopentyl, s-pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, eicosyl, tetracosyl, and the like. The alkyl group can be cyclic (e.g., C_3-24 cycloalkyl) or acyclic. The alkyl group can be branched or unbranched. The alkyl group can also be substituted or unsubstituted. For example, the alkyl group can be substituted with one, two, three or, in the case of alkyl groups of two carbons or more, four substituents independently selected from the group consisting of: (1) C_1-6 alkoxy (e.g., —O-Ak, wherein Ak is optionally substituted C_1-6 alkyl); (2) C_1-6 alkylsulfinyl (e.g., —S(O)-Ak, wherein Ak is optionally substituted C_1-6 alkyl); (3) C_1-6 alkylsulfonyl (e.g., —SO₂-Ak, wherein Ak is optionally substituted C_1-6 alkyl); (4) amino (e.g., —NR^N1R^N2, where each of R^N1 and R^N2 is, independently, H or optionally substituted alkyl, or R^N1 and R^N2, taken together with the nitrogen atom to which each are attached, form a heterocyclyl group); (5) aryl; (6) arylalkoxy (e.g., —O-L-Ar, wherein L is a bivalent form of optionally substituted alkyl and Ar is optionally substituted aryl); (7) aryloyl (e.g., —C(O)—Ar, wherein Ar is optionally substituted aryl); (8) azido (e.g., —N₃); (9) cyano (e.g., —CN); (10) carboxyaldehyde (e.g., —C(O)H); (11) C_3-8 cycloalkyl (e.g., a monovalent saturated or unsaturated non-aromatic cyclic C_3-8 hydrocarbon group); (12) halo (e.g., F, Cl, Br, or I); (13) heterocyclyl (e.g., a 5-, 6- or 7-membered ring, unless otherwise specified, containing one, two, three, or four non-carbon heteroatoms, such as nitrogen, oxygen, phosphorous, sulfur, or halo); (14) heterocyclyloxy (e.g., —O-Het, wherein Het is heterocyclyl, as described herein); (15) heterocyclyloyl (e.g., —C(O)-Het, wherein Het is heterocyclyl, as described herein); (16) hydroxyl (e.g., —H); (17) N-protected amino; (18) nitro (e.g., —NO₂); (19) oxo (e.g., ═O) or hydroxyimino (e.g., ═N—OH); (20) C_3-8 spirocyclyl (e.g., an alkylene or heteroalkylene diradical, both ends of which are bonded to the same carbon atom of the parent group); (21) C_1-6 thioalkoxy (e.g., —S-Ak, wherein Ak is optionally substituted C_1-6 alkyl); (22) thiol (e.g., —SH); (23) —CO₂R^A, where R^A is selected from the group consisting of (a) hydrogen, (b) C_1-6 alkyl, (c) C_4-18 aryl, and (d) (C_4-18 aryl) C_1-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl group and Ar is optionally substituted aryl); (24) —C(O)NR^BR^C, where each of R^B and R^C is, independently, selected from the group consisting of (a) hydrogen, (b) C_1-6 alkyl, (c) C_4-18 aryl, and (d) (C_4-18 aryl) C_1-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl group and Ar is optionally substituted aryl); (25) —SO₂R^D, where le is selected from the group consisting of (a) C_1-6 alkyl, (b) C_4-18 aryl, and (c) (C_4-18 aryl) C_1-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl group and Ar is optionally substituted aryl); (26) —SO₂NR^ER^F, where each of R^E and R^F is, independently, selected from the group consisting of (a) hydrogen, (b) C_1-6 alkyl, (c) C_4-18 aryl, and (d) (C_4-18 aryl) C_1-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl group and Ar is optionally substituted aryl); and (27) —NR^GR^H, where each of R^G and R^H is, independently, selected from the group consisting of (a) hydrogen, (b) an N-protecting group, (c) C_1-6 alkyl, (d) C_2-6 alkenyl (e.g., optionally substituted alkyl having one or more double bonds), (e) C_2-6 alkynyl (e.g., optionally substituted alkyl having one or more triple bonds), (f) C_4-18 aryl, (g) (C_4-18 aryl) C_1-6 alkyl (e.g., L-Ar, wherein L is a bivalent form of optionally substituted alkyl group and Ar is optionally substituted aryl), (h) C_3-8 cycloalkyl, and (i) (C_3-8 cycloalkyl) C_1-6 alkyl (e.g., -L-Cy, wherein L is a bivalent form of optionally substituted alkyl group and Cy is optionally substituted cycloalkyl, as described herein), wherein in one embodiment no two groups are bound to the nitrogen atom through a carbonyl group or a sulfonyl group. The alkyl group can be a primary, secondary, or tertiary alkyl group substituted with one or more substituents (e.g., one or more halo or alkoxy). In some embodiments, the unsubstituted alkyl group is a C_1-3, C_1-6, C_1-12, C_1-16, C_1-18, C_1-20, or C_1-24 alkyl group.

By “alkylene” is meant a multivalent (e.g., bivalent, trivalent, tetravalent, etc.) form of an alkyl group, as described herein. Exemplary alkylene groups include methylene, ethylene, propylene, butylene, etc. In some embodiments, the alkylene group is a C_1-3, C_1-6, C_1-12, C_1-16, C_1-18, C_1-20, C_1-24, C_2-3, C_2-6, C_2-12, C_2-16, C_2-18, C_2-20, or C_2-24 alkylene group. The alkylene group can be branched or unbranched. The alkylene group can be saturated or unsaturated (e.g., having one or more double bonds or triple bonds). The alkylene group can also be substituted or unsubstituted. For example, the alkylene group can be substituted with one or more substitution groups, as described herein for alkyl. In one instance, a substituted alkylene group can include an optionally substituted haloalkylene (e.g., an optionally substituted alkylene substituted with one or more hydroxyl groups, as defined herein), an optionally substituted haloalkylene (e.g., an optionally substituted alkylene substituted with one or more halo groups, as defined herein), and the like.

By “alkyleneoxy” is meant an alkylene group, as defined herein, attached to the parent molecular group through an oxygen atom.

By “amino” is meant —NR^N1R^N2, where each of R^N1 and R^N2 is, independently, H, optionally substituted alkyl, optionally substituted cycloalkyl, or optionally substituted aryl; or R^N1 and R^N2, taken together with the nitrogen atom to which each are attached, form an optionally substituted heterocyclyl group or heterocycle, as defined herein; or R^N1 and R^N2, taken together, form an optionally substituted alkylene or heteroalkylene (e.g., as described herein).

By “aminoalkyl” is meant an alkyl group, as defined herein, substituted by an amino group, as defined herein. Non-limiting aminoalkyl groups include -L-—NR^N1R^N2, where L is a multivalent alkyl group, as defined herein; each of R^N1 and R^N2 is, independently, H, optionally substituted alkyl, or optionally substituted aryl; or R^N1 and R^N2, taken together with the nitrogen atom to which each are attached, form a heterocyclyl group, as defined herein.

By “ammonium” is meant a group including a protonated nitrogen atom N⁺. Exemplary ammonium groups include —N⁺R^N1R^N2R^N3 where each of R^N1, R^N2, and R^N3 is, independently, H, optionally substituted alkyl, optionally substituted cycloalkyl, or optionally substituted aryl; or R^N1 and R^N2, taken together with the nitrogen atom to which each are attached, form an optionally substituted heterocyclyl group or heterocycle; or R^N1 and R^N2, taken together, form an optionally substituted alkylene or heteroalkylene (e.g., as described herein); or R^N1 and R^N2 and R^N3, taken together with the nitrogen atom to which each are attached, form an optionally substituted heterocyclyl group or heterocycle, such as a heterocyclic cation.

By “aromatic” is meant a cyclic, conjugated group or moiety of, unless specified otherwise, from 5 to 15 ring atoms having a single ring (e.g., phenyl) or multiple condensed rings in which at least one ring is aromatic (e.g., naphthyl, indolyl, or pyrazolopyridinyl); that is, at least one ring, and optionally multiple condensed rings, have a continuous, delocalized π-electron system. Typically, the number of out of plane π-electrons corresponds to the Huckel rule (4n+2). The point of attachment to the parent structure typically is through an aromatic portion of the condensed ring system. Such an aromatic can be unsubstituted or substituted with one or more groups, such as groups described herein for an alkyl or aryl group. Yet other substitution groups can include aliphatic, haloaliphatic, halo, nitrate, cyano, sulfonate, sulfonyl, or others.

By “aryl” is meant a group that contains any carbon-based aromatic group including, but not limited to, phenyl, benzyl, anthracenyl, anthryl, benzocyclobutenyl, benzocyclooctenyl, biphenylyl, chrysenyl, dihydroindenyl, fluoranthenyl, indacenyl, indenyl, naphthyl, phenanthryl, phenoxybenzyl, picenyl, pyrenyl, terphenyl, and the like, including fused benzo-C_4-8 cycloalkyl radicals (e.g., as defined herein) such as, for instance, indanyl, tetrahydronaphthyl, fluorenyl, and the like. The term aryl also includes “heteroaryl,” which is defined as a group that contains an aromatic group that has at least one heteroatom incorporated within the ring of the aromatic group. Examples of heteroatoms include, but are not limited to, nitrogen, oxygen, sulfur, and phosphorus. Likewise, the term non-heteroaryl, which is also included in the term aryl, defines a group that contains an aromatic group that does not contain a heteroatom. The aryl group can be substituted or unsubstituted. The aryl group can be substituted with one, two, three, four, or five substituents independently selected from the group consisting of: (1) C_1-6 alkanoyl (e.g., —C(O)-Ak, wherein Ak is optionally substituted C_1-6 alkyl); (2) C_1-6 alkyl; (3) C_1-6 alkoxy (e.g., —O-Ak, wherein Ak is optionally substituted C_1-6 alkyl); (4) C_1-6 alkoxy-C_1-6 alkyl (e.g., -L-O-Ak, wherein L is a bivalent form of optionally substituted alkyl group and Ak is optionally substituted C_1-6 alkyl); (5) C_1-6 alkylsulfinyl (e.g., —S(O)-Ak, wherein Ak is optionally substituted C_1-6 alkyl); (6) C_1-6 alkylsulfinyl-C_1-6 alkyl (e.g., -L-S(O)-Ak, wherein L is a bivalent form of optionally substituted alkyl group and Ak is optionally substituted C_1-6 alkyl); (7) C_1-6 alkylsulfonyl (e.g., —SO₂-Ak, wherein Ak is optionally substituted C_1-6 alkyl); (8) C_1-6 alkylsulfonyl-C_1-6 alkyl (e.g., -L-SO₂-Ak, wherein L is a bivalent form of optionally substituted alkyl group and Ak is optionally substituted C_1-6 alkyl); (9) aryl; (10) amino (e.g., —NR^N1R^N2, where each of R^N1 and R^N2 is, independently, H or optionally substituted alkyl, or R^N1 and R^N2, taken together with the nitrogen atom to which each are attached, form a heterocyclyl group); (11) C_1-6 aminoalkyl (e.g., an alkyl group, as defined herein, substituted by one or more —NR^N1R^N2 groups, as described herein); (12) heteroaryl (e.g., a subset of heterocyclyl groups (e.g., a 5-, 6- or 7-membered ring, unless otherwise specified, containing one, two, three, or four non-carbon heteroatoms), which are aromatic); (13) (C_4-18 aryl) C_1-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl and Ar is optionally substituted aryl); (14) aryloyl (e.g., —C(O)-Ar, wherein Ar is optionally substituted aryl); (15) azido (e.g., —N₃); (16) cyano (e.g., —CN); (17) C_1-6 azidoalkyl (e.g., an alkyl group, as defined herein, substituted by one or more azido groups, as described herein); (18) carboxyaldehyde (e.g., —C(O)H); (19) carboxyaldehyde-C_1-6 alkyl (e.g., an alkyl group, as defined herein, substituted by one or more carboxyaldehyde groups, as described herein); (20) C_3-8 cycloalkyl (e.g., a monovalent saturated or unsaturated non-aromatic cyclic C_3-8 hydrocarbon group); (21) (C_3-8 cycloalkyl) C_1-6 alkyl (e.g., an alkyl group, as defined herein, substituted by one or more cycloalkyl groups, as described herein); (22) halo (e.g., F, Cl, Br, or I); (23) C_1-6 haloalkyl (e.g., an alkyl group, as defined herein, substituted by one or more halo groups, as described herein); (24) heterocyclyl (e.g., a 5-, 6- or 7-membered ring, unless otherwise specified, containing one, two, three, or four non-carbon heteroatoms, such as nitrogen, oxygen, phosphorous, sulfur, or halo); (25) heterocyclyloxy (e.g., —O-Het, wherein Het is heterocyclyl, as described herein); (26) heterocyclyloyl (e.g., —C(O)-Het, wherein Het is heterocyclyl, as described herein); (27) hydroxyl (e.g., —OH); (28) C_1-6 hydroxyalkyl (e.g., an alkyl group, as defined herein, substituted by one or more hydroxyl, as described herein); (29) nitro (e.g., —NO₂); (30) C_1-6 nitroalkyl (e.g., an alkyl group, as defined herein, substituted by one or more nitro, as described herein); (31) N-protected amino; (32) N-protected amino-C_1-6 alkyl (e.g., an alkyl group, as defined herein, substituted by one or more N-protected amino groups); (33) oxo (e.g., ═O) or hydroxyimino (e.g., ═N—OH); (34) C_1-6 thioalkoxy (e.g., —S-Ak, wherein Ak is optionally substituted C_1-6 alkyl); (35) thio-C_1-6 alkoxy-C_1-6 alkyl (e.g., -L-S-Ak, wherein L is a bivalent form of optionally substituted alkyl and Ak is optionally substituted C_1-6 alkyl); (36) —(CH₂)_rCO₂R^A, where r is an integer of from zero to four, and R^A is selected from the group consisting of (a) hydrogen, (b) C_1-6 alkyl, (c) C_4-18 aryl, and (d) (C_4-18 aryl) C_1-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl and Ar is optionally substituted aryl); (37) —(CH₂)_rCONR^BR^C, where r is an integer of from zero to four and where each R^B and R^C is independently selected from the group consisting of (a) hydrogen, (b) C_1-6 alkyl, (c) C_4-18 aryl, and (d) (C_4-18 aryl) C_1-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl and Ar is optionally substituted aryl); (38) —(CH₂)_rSO₂R^D, where r is an integer of from zero to four and where R^D is selected from the group consisting of (a) C_1-6 alkyl, (b) C_4-18 aryl, and (c) (C_4-18 aryl) C_1-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl and Ar is optionally substituted aryl); (39) —(CH₂)_rSO₂NR^ER^F, where r is an integer of from zero to four and where each of R^E and R^F is, independently, selected from the group consisting of (a) hydrogen, (b) C_1-6 alkyl, (c) C_4-18 aryl, and (d) (C_4-18 aryl) C_1-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl and Ar is optionally substituted aryl); (40) —(CH₂)_rNR^GR^H, where r is an integer of from zero to four and where each of R^G and R^H is, independently, selected from the group consisting of (a) hydrogen, (b) an N-protecting group, (c) C_1-6 alkyl, (d) C_2-6 alkenyl (e.g., optionally substituted alkyl having one or more double bonds), (e) C_2-6 alkynyl (e.g., optionally substituted alkyl having one or more triple bonds), (f) C_4-18 aryl, (g) (C_4-18 aryl) C_1-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl and Ar is optionally substituted aryl), (h) C_3-8 cycloalkyl, and (i) (C_3-8 cycloalkyl) C_1-6 alkyl (e.g., -L-Cy, wherein L is a bivalent form of optionally substituted alkyl and Cy is optionally substituted cycloalkyl, as described herein), wherein in one embodiment no two groups are bound to the nitrogen atom through a carbonyl group or a sulfonyl group; (41) thiol (e.g., —SH); (42) perfluoroalkyl (e.g., an alkyl group having each hydrogen atom substituted with a fluorine atom); (43) perfluoroalkoxy (e.g., —OR^f, where R^f is an alkyl group having each hydrogen atom substituted with a fluorine atom); (44) aryloxy (e.g., —OAr, where Ar is optionally substituted aryl); (45) cycloalkoxy (e.g., —O-Cy, wherein Cy is optionally substituted cycloalkyl, as described herein); (46) cycloalkylalkoxy (e.g., —O-L-Cy, wherein L is a bivalent form of optionally substituted alkyl and Cy is optionally substituted cycloalkyl, as described herein); and (47) arylalkoxy (e.g., —O-L-Ar, wherein L is a bivalent form of optionally substituted alkyl and Ar is optionally substituted aryl). In particular embodiments, an unsubstituted aryl group is a C_4-18, C_4-14, C_4-12, C_4-10, C_6-18, C_6-14, C_6-12, or C_6-10 aryl group.

By “arylalkoxy” is meant an arylalkylene group, as defined herein, attached to the parent molecular group through an oxygen atom. In some embodiments, the arylalkoxy group is —O-Ak-Ar, in which Ak is an optionally substituted alkylene, as defined herein, and Ar is an optionally substituted aryl, as defined herein.

By “(aryl)(alkyl)ene” is meant a bivalent form including an arylene group, as described herein, attached to an alkylene or a heteroalkylene group, as described herein. In some embodiments, the (aryl)(alkyl)ene group is -L-Ar- or -L-Ar-L- or -Ar-L-, in which Ar is an arylene group and each L is, independently, an optionally substituted alkylene group or an optionally substituted heteroalkylene group.

By “arylalkylene” is meant an aryl group, as defined herein, attached to the parent molecular group through an alkylene group, as defined herein. In some embodiments, the arylalkylene group is -Ak-Ar, in which Ak is an optionally substituted alkylene, as defined herein, and Ar is an optionally substituted aryl, as defined herein. The arylalkylene group can be substituted or unsubstituted. For example, the arylalkylene group can be substituted with one or more substitution groups, as described herein for aryl and/or alkyl. Exemplary unsubstituted arylalkylene groups are of from 7 to 16 carbons (C_7-16 arylalkylene), as well as those having an aryl group with 4 to 18 carbons and an alkylene group with 1 to 6 carbons (i.e., (C_4-18 aryl)C_1-6 alkylene).

By “arylene” is meant a multivalent (e.g., bivalent, trivalent, tetravalent, etc.) form of an aryl group, as described herein. Exemplary arylene groups include phenylene, naphthylene, biphenylene, triphenylene, diphenyl ether, acenaphthenylene, anthrylene, or phenanthrylene. In some embodiments, the arylene group is a C_4-18, C_4-14, C_4-12, C_4-10, C_6-18, C_6-14, C_6-12, or C_6-10 arylene group. The arylene group can be branched or unbranched. The arylene group can also be substituted or unsubstituted. For example, the arylene group can be substituted with one or more substitution groups, as described herein for aryl.

By “aryleneoxy” is meant an arylene group, as defined herein, attached to the parent molecular group through an oxygen atom.

By “aryloxy” is meant —OR, where R is an optionally substituted aryl group, as described herein. In some embodiments, an unsubstituted aryloxy group is a C_4-18 or C_6-18 aryloxy group.

By “aryloyl” is meant an aryl group that is attached to the parent molecular group through a carbonyl group. In some embodiments, an unsubstituted aryloyl group is a C_7-11 aryloyl or C_5-19 aryloyl group. In particular embodiments, the aryloyl group is —C(O)—Ar, in which Ar is an aryl group, as defined herein.

By “boranyl” is meant a —BR₂ group, in which each R, independently, can be H, halo, or optionally substituted alkyl.

By “borono” is meant a —BOH₂ group.

By “carboxyl” is meant a —CO₂H group.

By “carboxylate anion” is meant a —CO₂⁻ group.

By “covalent bond” is meant a covalent bonding interaction between two components. Non-limiting covalent bonds include a single bond, a double bond, a triple bond, or a spirocyclic bond, in which at least two molecular groups are bonded to the same carbon atom.

By “cyano” is meant a —CN group.

By “cyclic group” is used herein to refer to either aryl groups, non-aryl groups (e.g., cycloalkyl or heterocycloalkyl groups), or both. Cyclic groups have one or more ring systems that can be substituted or unsubstituted. A cyclic group can contain one or more aryl groups, one or more non-aryl groups, or one or more aryl groups and one or more non-aryl groups.

By “cycloalkyl” is meant a monovalent saturated or unsaturated non-aromatic cyclic hydrocarbon group of from three to ten carbons (e.g., C_3-8 or C_3-10), unless otherwise specified, and is exemplified by cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, bicyclo[2.2.1.]heptyl, and the like. The term cycloalkyl also includes “cycloalkenyl,” which is defined as a non-aromatic carbon-based ring composed of three to ten carbon atoms and containing at least one double bound, i.e., C═C. Examples of cycloalkenyl groups include, but are not limited to, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclopentadienyl, cyclohexenyl, cyclohexadienyl, and the like. The cycloalkyl group can also be substituted or unsubstituted. For example, the cycloalkyl group can be substituted with one or more groups including those described herein for alkyl.

By “halo” is meant F, Cl, Br, or I.

By “haloalkyl” is meant an alkyl group, as defined herein, substituted with one or more halo.

By “haloalkylene” is meant an alkylene group, as defined herein, substituted with one or more halo.

By “heteroaliphatic” is meant an aliphatic group, as defined herein, including at least one heteroatom to 20 heteroatoms, such as one to 15 heteroatoms, or one to 5 heteroatoms, which can be selected from, but not limited to oxygen, nitrogen, sulfur, silicon, boron, selenium, phosphorous, and oxidized forms thereof within the group.

By “heteroalkyl” is meant an alkyl group, as defined herein, containing one, two, three, or four non-carbon heteroatoms (e.g., independently selected from the group consisting of nitrogen, oxygen, phosphorous, sulfur, selenium, or halo).

By “heteroalkylene” is meant an alkylene group, as defined herein, containing one, two, three, or four non-carbon heteroatoms (e.g., independently selected from the group consisting of nitrogen, oxygen, phosphorous, sulfur, selenium, or halo). The heteroalkylene group can be saturated or unsaturated (e.g., having one or more double bonds or triple bonds). The heteroalkylene group can be substituted or unsubstituted. For example, the heteroalkylene group can be substituted with one or more substitution groups, as described herein for alkyl.

By “heteroaryl” is meant a subset of heterocyclyl groups, as defined herein, which are aromatic, i.e., they contain 4n+2 pi electrons within the mono- or multicyclic ring system.

The term “heterocycloalkyl” is a type of cycloalkyl group as defined above where at least one of the carbon atoms and its attached hydrogen atoms, if any, are replaced by O, S, N, or NH. The heterocycloalkyl group and heterocycloalkenyl group can be substituted or unsubstituted. The cycloalkenyl group and heterocycloalkenyl group can be substituted with one or more groups including, but not limited to, alkyl, alkoxy, alkenyl, alkynyl, aryl, heteroaryl, aldehyde, amino, carboxylic acid, sulfonic acid, sulfinic acid, fluoroacid, phosphonic acid, ester, ether, halide, hydroxy, ketone, nitro, cyano, azido, silyl, sulfonyl, sulfinyl, or thiol, as described herein.

By “heterocycle” is meant a compound having one or more heterocyclyl moieties. Non-limiting heterocycles include optionally substituted imidazole, optionally substituted triazole, optionally substituted tetrazole, optionally substituted pyrazole, optionally substituted imidazoline, optionally substituted pyrazoline, optionally substituted imidazolidine, optionally substituted pyrazolidine, optionally substituted pyrrole, optionally substituted pyrroline, optionally substituted pyrrolidine, optionally substituted tetrahydrofuran, optionally substituted furan, optionally substituted thiophene, optionally substituted oxazole, optionally substituted isoxazole, optionally substituted isothiazole, optionally substituted thiazole, optionally substituted oxathiolane, optionally substituted oxadiazole, optionally substituted thiadiazole, optionally substituted sulfolane, optionally substituted succinimide, optionally substituted thiazolidinedione, optionally substituted oxazolidone, optionally substituted hydantoin, optionally substituted pyridine, optionally substituted piperidine, optionally substituted pyridazine, optionally substituted piperazine, optionally substituted pyrimidine, optionally substituted pyrazine, optionally substituted triazine, optionally substituted pyran, optionally substituted pyrylium, optionally substituted tetrahydropyran, optionally substituted dioxine, optionally substituted dioxane, optionally substituted dithiane, optionally substituted trithiane, optionally substituted thiopyran, optionally substituted thiane, optionally substituted oxazine, optionally substituted morpholine, optionally substituted thiazine, optionally substituted thiomorpholine, optionally substituted cytosine, optionally substituted thymine, optionally substituted uracil, optionally substituted thiomorpholine dioxide, optionally substituted indene, optionally substituted indoline, optionally substituted indole, optionally substituted isoindole, optionally substituted indolizine, optionally substituted indazole, optionally substituted benzimidazole, optionally substituted azaindole, optionally substituted azaindazole, optionally substituted pyrazolopyrimidine, optionally substituted purine, optionally substituted benzofuran, optionally substituted isobenzofuran, optionally substituted benzothiophene, optionally substituted benzisoxazole, optionally substituted anthranil, optionally substituted benzisothiazole, optionally substituted benzoxazole, optionally substituted benzthiazole, optionally substituted benzthiadiazole, optionally substituted adenine, optionally substituted guanine, optionally substituted tetrahydroquinoline, optionally substituted dihydroquinoline, optionally substituted dihydroisoquinoline, optionally substituted quinoline, optionally substituted isoquinoline, optionally substituted quinolizine, optionally substituted quinoxaline, optionally substituted phthalazine, optionally substituted quinazoline, optionally substituted cinnoline, optionally substituted naphthyridine, optionally substituted pyridopyrimidine, optionally substituted pyridopyrazine, optionally substituted pteridine, optionally substituted chromene, optionally substituted isochromene, optionally substituted chromenone, optionally substituted benzoxazine, optionally substituted quinolinone, optionally substituted isoquinolinone, optionally substituted carbazole, optionally substituted dibenzofuran, optionally substituted acridine, optionally substituted phenazine, optionally substituted phenoxazine, optionally substituted phenothiazine, optionally substituted phenoxathiine, optionally substituted quinuclidine, optionally substituted azaadamantane, optionally substituted dihydroazepine, optionally substituted azepine, optionally substituted diazepine, optionally substituted oxepane, optionally substituted thiepine, optionally substituted thiazepine, optionally substituted azocane, optionally substituted azocine, optionally substituted thiocane, optionally substituted azonane, optionally substituted azecine, etc. Optional substitutions include any described herein for aryl. Heterocycles can also include cations and/or salts of any of these (e.g., any described herein, such as optionally substituted piperidinium, optionally substituted pyrrolidinium, optionally substituted pyrazolium, optionally substituted imidazolium, optionally substituted pyridinium, optionally substituted quinolinium, optionally substituted isoquinolinium, optionally substituted acridinium, optionally substituted phenanthridinium, optionally substituted pyridazinium, optionally substituted pyrimidinium, optionally substituted pyrazinium, optionally substituted phenazinium, or optionally substituted morpholinium).

By “heterocyclyl” is meant a 3-, 4-, 5-, 6- or 7-membered ring (e.g., a 5-, 6- or 7-membered ring), unless otherwise specified, containing one, two, three, or four non-carbon heteroatoms (e.g., independently selected from the group consisting of nitrogen, oxygen, phosphorous, sulfur, selenium, or halo). The 3-membered ring has zero to one double bonds, the 4- and 5-membered ring has zero to two double bonds, and the 6- and 7-membered rings have zero to three double bonds. The term “heterocyclyl” also includes bicyclic, tricyclic and tetracyclic groups in which any of the above heterocyclic rings is fused to one, two, or three rings independently selected from the group consisting of an aryl ring, a cyclohexane ring, a cyclohexene ring, a cyclopentane ring, a cyclopentene ring, and another monocyclic heterocyclic ring, such as indolyl, quinolyl, isoquinolyl, tetrahydroquinolyl, benzofuryl, benzothienyl and the like. Heterocyclics include acridinyl, adenyl, alloxazinyl, azaadamantanyl, azabenzimidazolyl, azabicyclononyl, azacycloheptyl, azacyclooctyl, azacyclononyl, azahypoxanthinyl, azaindazolyl, azaindolyl, azecinyl, azepanyl, azepinyl, azetidinyl, azetyl, aziridinyl, azirinyl, azocanyl, azocinyl, azonanyl, benzimidazolyl, benzisothiazolyl, benzisoxazolyl, benzodiazepinyl, benzodiazocinyl, benzodihydrofuryl, benzodioxepinyl, benzodioxinyl, benzodioxanyl, benzodioxocinyl, benzodioxolyl, benzodithiepinyl, benzodithiinyl, benzodioxocinyl, benzofuranyl, benzophenazinyl, benzopyranonyl, benzopyranyl, benzopyrenyl, benzopyronyl, benzoquinolinyl, benzoquinolizinyl, benzothiadiazepinyl, benzothiadiazolyl, benzothiazepinyl, benzothiazocinyl, benzothiazolyl, benzothienyl, benzothiophenyl, benzothiazinonyl, benzothiazinyl, benzothiopyranyl, benzothiopyronyl, benzotriazepinyl, benzotriazinonyl, benzotriazinyl, benzotriazolyl, benzoxathiinyl, benzotrioxepinyl, benzoxadiazepinyl, benzoxathiazepinyl, benzoxathiepinyl, benzoxathiocinyl, benzoxazepinyl, benzoxazinyl, benzoxazocinyl, benzoxazolinonyl, benzoxazolinyl, benzoxazolyl, benzylsultamyl benzylsultimyl, bipyrazinyl, bipyridinyl, carbazolyl (e.g., 4H-carbazolyl), carbolinyl (e.g., β-carbolinyl), chromanonyl, chromanyl, chromenyl, cinnolinyl, coumarinyl, cytdinyl, cytosinyl, decahydroisoquinolinyl, decahydroquinolinyl, diazabicyclooctyl, diazetyl, diaziridinethionyl, diaziridinonyl, diaziridinyl, diazirinyl, dibenzisoquinolinyl, dibenzoacridinyl, dibenzocarbazolyl, dibenzofuranyl, dibenzophenazinyl, dibenzopyranonyl, dibenzopyronyl (xanthonyl), dibenzoquinoxalinyl, dibenzothiazepinyl, dibenzothiepinyl, dibenzothiophenyl, dibenzoxepinyl, dihydroazepinyl, dihydroazetyl, dihydrofuranyl, dihydrofuryl, dihydroisoquinolinyl, dihydropyranyl, dihydropyridinyl, dihydroypyridyl, dihydroquinolinyl, dihydrothienyl, dihydroindolyl, dioxanyl, dioxazinyl, dioxindolyl, dioxiranyl, dioxenyl, dioxinyl, dioxobenzofuranyl, dioxolyl, dioxotetrahydrofuranyl, dioxothiomorpholinyl, dithianyl, dithiazolyl, dithienyl, dithiinyl, furanyl, furazanyl, furoyl, furyl, guaninyl, homopiperazinyl, homopiperidinyl, hypoxanthinyl, hydantoinyl, imidazolidinyl, imidazolinyl, imidazolyl, indazolyl (e.g., 1H-indazolyl), indolenyl, indolinyl, indolizinyl, indolyl (e.g., 1H-indolyl or 3H-indolyl), isatinyl, isatyl, isobenzofuranyl, isochromanyl, isochromenyl, isoindazoyl, isoindolinyl, isoindolyl, isopyrazolonyl, isopyrazolyl, isoxazolidiniyl, isoxazolyl, isoquinolinyl, isoquinolinyl, isothiazolidinyl, isothiazolyl, morpholinyl, naphthindazolyl, naphthindolyl, naphthiridinyl, naphthopyranyl, naphthothiazolyl, naphthothioxolyl, naphthotriazolyl, naphthoxindolyl, naphthyridinyl, octahydroisoquinolinyl, oxabicycloheptyl, oxauracil, oxadiazolyl, oxazinyl, oxaziridinyl, oxazolidinyl, oxazolidonyl, oxazolinyl, oxazolonyl, oxazolyl, oxepanyl, oxetanonyl, oxetanyl, oxetyl, oxtenayl, oxindolyl, oxiranyl, oxobenzoisothiazolyl, oxochromenyl, oxoisoquinolinyl, oxoquinolinyl, oxothiolanyl, phenanthridinyl, phenanthrolinyl, phenazinyl, phenothiazinyl, phenothienyl (benzothiofuranyl), phenoxathiinyl, phenoxazinyl, phthalazinyl, phthalazonyl, phthalidyl, phthalimidinyl, piperazinyl, piperidinyl, piperidonyl (e.g., 4-piperidonyl), pteridinyl, purinyl, pyranyl, pyrazinyl, pyrazolidinyl, pyrazolinyl, pyrazolopyrimidinyl, pyrazolyl, pyridazinyl, pyridinyl, pyridopyrazinyl, pyridopyrimidinyl, pyridyl, pyrimidinyl, pyrimidyl, pyronyl, pyrrolidinyl, pyrrolidonyl (e.g., 2-pyrrolidonyl), pyrrolinyl, pyrrolizidinyl, pyrrolyl (e.g., 2H-pyrrolyl), pyrylium, quinazolinyl, quinolinyl, quinolizinyl (e.g., 4H-quinolizinyl), quinoxalinyl, quinuclidinyl, selenazinyl, selenazolyl, selenophenyl, succinimidyl, sulfolanyl, tetrahydrofuranyl, tetrahydrofuryl, tetrahydroisoquinolinyl, tetrahydroisoquinolyl, tetrahydropyridinyl, tetrahydropyridyl (piperidyl), tetrahydropyranyl, tetrahydropyronyl, tetrahydroquinolinyl, tetrahydroquinolyl, tetrahydrothienyl, tetrahydrothiophenyl, tetrazinyl, tetrazolyl, thiadiazinyl (e.g., 6H-1,2,5 -thiadiazinyl or 2H, 6H-1,5,2-dithiazinyl), thiadiazolyl, thianthrenyl, thianyl, thianaphthenyl, thiazepinyl, thiazinyl, thiazolidinedionyl, thiazolidinyl, thiazolyl, thienyl, thiepanyl, thiepinyl, thietanyl, thietyl, thiiranyl, thiocanyl, thiochromanonyl, thiochromanyl, thiochromenyl, thiodiazinyl, thiodiazolyl, thioindoxyl, thiomorpholinyl, thiophenyl, thiopyranyl, thiopyronyl, thiotriazolyl, thiourazolyl, thioxanyl, thioxolyl, thymidinyl, thyminyl, triazinyl, triazolyl, trithianyl, urazinyl, urazolyl, uretidinyl, uretinyl, uricyl, uridinyl, xanthenyl, xanthinyl, xanthionyl, and the like, as well as modified forms thereof (e.g., including one or more oxo and/or amino) and salts thereof. The heterocyclyl group can be substituted or unsubstituted. For example, the heterocyclyl group can be substituted with one or more substitution groups, as described herein for aryl.

By “heterocyclyldiyl” is meant a bivalent form of a heterocyclyl group, as described herein. In one instance, the heterocyclyldiyl is formed by removing a hydrogen from a heterocyclyl group. Exemplary heterocyclyldiyl groups include piperdylidene, quinolinediyl, etc. The heterocyclyldiyl group can also be substituted or unsubstituted. For example, the heterocyclyldiyl group can be substituted with one or more substitution groups, as described herein for heterocyclyl.

By “hydroxyl” is meant an —OH group.

By “hydroxyalkyl” is meant an alkyl group, as defined herein, substituted with one or more hydroxyl.

By “hydroxyalkylene” is meant an alkylene group, as defined herein, substituted with one or more hydroxy.

By “nitro” is meant an —NO₂ group.

By “phosphate” is meant a group derived from phosphoric acid. One example of phosphate includes a —O—P(═O)(OR^P1)(OR^P2) or —O—[P(═O)(OR^P1)—O]_P3—R^P2 group, where each of R^P1 and R^P2, is, independently, H, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aryl, or optionally substituted arylalkylene, and where P3 is an integer from 1 to 5. Yet other examples of phosphate include orthophosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, trimetaphosphoric acid, and/or phosphoric anhydride, or combinations thereof.

By “phosphono” or “phosphonic acid” is meant a —P(O)(OH)₂ group.

By “spirocyclyl” is meant an alkylene diradical, both ends of which are bonded to the same carbon atom of the parent group to form a spirocyclyl group and also a heteroalkylene diradical, both ends of which are bonded to the same atom. Non-limiting alkylene and heteroalkylene groups for use within a spirocyclyl group includes C_2-12, C_2-11, C_2-10, C_2-9, C_2-8, C_2-7, C_2-6, C_2-5, C_2-4, or C_2-3 alkylene groups, as well as C_1-12, C_1-11, C_1-10, C_1-9, C_1-8, C_1-7, C_1-6, C_1-5, C_1-4, C_1-3, or C_1-2 heteroalkylene groups having one or more heteroatoms.

By “sulfate” is meant a group derived from sulfuric acid. One example of sulfate includes a —O—S(═O)₂(OR^S1) group, where R^S1 is H, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aryl, or optionally substituted arylalkylene.

By “sulfo” or “sulfonic acid” is meant an —S(O)20H group.

By “sulfonyl” is meant an —S(O)₂— or —S(O)₂R group, in which R can be H, optionally substituted alkyl, or optionally substituted aryl. Non-limiting sulfonyl groups can include a trifluoromethylsulfonyl group (—SO₂—CF₃ or Tf).

By “thiocyanato” is meant an —SCN group.

By “salt” is meant an ionic form of a compound or structure (e.g., any formulas, compounds, or compositions described herein), which includes a cation or anion compound to form an electrically neutral compound or structure. Salts are well known in the art. For example, non-toxic salts are described in Berge S M et al., “Pharmaceutical salts,” J. Pharm. Sci. 1977 January; 66(1):1-19; and in “Handbook of Pharmaceutical Salts: Properties, Selection, and Use,” Wiley-VCH, April 2011 (2nd rev. ed., eds. P. H. Stahl and C. G. Wermuth. The salts can be prepared in situ during the final isolation and purification of the compounds of the invention or separately by reacting the free base group with a suitable organic acid (thereby producing an anionic salt) or by reacting the acid group with a suitable metal or organic salt (thereby producing a cationic salt). Representative anionic salts include acetate, adipate, alginate, ascorbate, aspartate, benzenesulfonate, benzoate, bicarbonate, bisulfate, bitartrate, borate, bromide, butyrate, camphorate, camphorsulfonate, chloride, citrate, cyclopentanepropionate, digluconate, dihydrochloride, diphosphate, dodecylsulfate, edetate, ethanesulfonate, fumarate, glucoheptonate, gluconate, glutamate, glycerophosphate, hemisulfate, heptonate, hexanoate, hydrobromide, hydrochloride, hydroiodide, hydroxy ethanesulfonate, hydroxynaphthoate, iodide, lactate, lactobionate, laurate, lauryl sulfate, malate, maleate, malonate, mandelate, mesylate, methanesulfonate, methylbromide, methylnitrate, methyl sulfate, mucate, 2-naphthalenesulfonate, nicotinate, nitrate, oleate, oxalate, palmitate, pamoate, pectinate, persulfate, 3-phenylpropionate, phosphate, picrate, pivalate, polygalacturonate, propionate, salicylate, stearate, subacetate, succinate, sulfate, tannate, tartrate, theophyllinate, thiocyanate, triethiodide, toluenesulfonate, undecanoate, valerate salts, and the like. Representative cationic salts include metal salts, such as alkali or alkaline earth salts, e.g., barium, calcium (e.g., calcium edetate), lithium, magnesium, potassium, sodium, and the like; other metal salts, such as aluminum, bismuth, iron, and zinc; as well as nontoxic ammonium, quaternary ammonium, and amine cations, including, but not limited to ammonium, tetramethylammonium, tetraethylammonium, methylamine, dimethylamine, trimethylamine, triethylamine, ethylamine, pyridinium, and the like. Other cationic salts include organic salts, such as chloroprocaine, choline, dibenzylethylenediamine, diethanolamine, ethylenediamine, methylglucamine, and procaine. Yet other salts include ammonium, sulfonium, sulfoxonium, phosphonium, iminium, imidazolium, benzimidazolium, amidinium, guanidinium, phosphazinium, phosphazenium, pyridinium, etc., as well as other cationic groups described herein (e.g., optionally substituted i soxazolium, optionally substituted oxazolium, optionally substituted thiazolium, optionally substituted pyrrolium, optionally substituted furanium, optionally substituted thiophenium, optionally substituted imidazolium, optionally substituted pyrazolium, optionally substituted isothiazolium, optionally substituted triazolium, optionally substituted tetrazolium, optionally substituted furazanium, optionally substituted pyridinium, optionally substituted pyrimidinium, optionally substituted pyrazinium, optionally substituted triazinium, optionally substituted tetrazinium, optionally substituted pyridazinium, optionally substituted oxazinium, optionally substituted pyrrolidinium, optionally substituted pyrazolidinium, optionally substituted imidazolinium, optionally substituted isoxazolidinium, optionally substituted oxazolidinium, optionally substituted piperazinium, optionally substituted piperidinium, optionally substituted morpholinium, optionally substituted azepanium, optionally substituted azepinium, optionally substituted indolium, optionally substituted isoindolium, optionally substituted indolizinium, optionally substituted indazolium, optionally substituted benzimidazolium, optionally substituted isoquinolinum, optionally substituted quinolizinium, optionally substituted dehydroquinolizinium, optionally substituted quinolinium, optionally substituted isoindolinium, optionally substituted benzimidazolinium, and optionally substituted purinium). Yet other salts can include an anion, such as a halide (e.g., F⁻, Cl⁻, Br⁻, or I⁻), a hydroxide (e.g., OH⁻), a borate (e.g., tetrafluoroborate (BF₄⁻), a carbonate (e.g., CO₃²⁻or HCO₃⁻), or a sulfate (e.g., SO₄²⁻).

By “leaving group” is meant an atom (or a group of atoms) with electron withdrawing ability that can be displaced as a stable species, taking with it the bonding electrons, or an atom (or a group of atoms) that can be replaced by a substitution reaction. Examples of suitable leaving groups include H, halides, and sulfonates including, but not limited to, triflate (-OTf), mesylate (-OMs), tosylate (-OTs), brosylate (-OBs), acetate, Cl, Br, and I.

By “attaching,” “attachment,” or related word forms is meant any covalent or non-covalent bonding interaction between two components. Non-covalent bonding interactions include, without limitation, hydrogen bonding, ionic interactions, halogen bonding, electrostatic interactions, π bond interactions, hydrophobic interactions, inclusion complexes, clathration, van der Waals interactions, and combinations thereof.

Context

Aspects of this disclosure relate to integration of a CO₂ purifier with a CO₂ electrolyzer. In operation, the CO₂ purifier selectively captures CO₂ from a gas stream and then releases purified CO₂ as an output. The purified CO₂ is then provided as an input to the cathode of the CO₂ electrolyzer. The CO₂ electrolyzer can electrochemically reduce the CO₂ to a carbon-containing product (CCP) that may be stored, consumed, used to synthesize a valuable product, etc.

Various types of CO₂ purifier may be employed. In some embodiments, the purifier comprises an electrochemical cell having an anode and a cathode. The electrochemical cell may employ a polymer or other material that selectively absorbs CO₂ and subsequently releases the CO₂ . The purifier allows at least some non-CO₂ inlet components to pass without being absorbed. Depending on the composition of the inlet stream, examples of non-absorbed components include water, nitrogen, carbon monoxide, oxygen, sulfur-containing compounds, and the like.

CO₂ Purifiers

In certain embodiments, a CO₂ purifier removes CO₂ from an air or other source stream and provides two outlet streams: a purified CO₂ stream and a CO₂-depleted stream. The CO₂ purifier may operate in a continuous mode: i.e., it may provide a continuous stream of purified CO₂.

In some embodiments, a CO₂ purifier is electrochemically driven. In such embodiments, the purifier may include an anode, a cathode, and a membrane separator, which may comprise an ionically conductive solid or gel. It may be immobilized or otherwise held stationary in the purifier.

In some embodiments, the CO₂ purifier is powered by a chemical source such as molecular hydrogen and molecular oxygen, optionally from air.

As an example, the cathode reduces O₂ to hydroxide ions (OH⁻). The hydroxide ions, in turn, react with CO₂ in an impure CO₂ inlet stream to produce carbonate ions and/or bicarbonate ions. In some embodiments, the O₂ and CO₂ reactants are present in air flowed to the cathode. In some cases, O₂ is provided from a separate source such as an electrolyzer anode output.

In the membrane, the carbonate and/or bicarbonate ions move from the cathode toward the anode. In some implementations, the purifier employs a species that electrochemically interacts with carbonate and/or bicarbonate at an anode to facilitate generation of carbon dioxide. An example of such species is a hydrogen ion, which may be produced from molecular hydrogen at the anode. Thus, in some embodiments, as the carbonate/bicarbonate ions moves across the membrane, they experience a pH gradient and become increasingly acidic. When encountering hydrogen ions, the carbonate converts to bicarbonate, and the bicarbonate converts to CO₂, which may be released as purified CO₂. At the anode, hydrogen from an input stream is oxidized to hydrogen ions, which maintain the acidic environment and consequently the pH gradient across the membrane.

The membrane permits transport of anions, notably carbonate and/or bicarbonate ions. In some embodiments, the membrane is electronically and ionically conductive. For example, the membrane may conduct both electrons and anions. The membrane may transport electrons and anions simultaneously. In some cases, electrons generated from molecular hydrogen oxidation at the anode move across the membrane to the cathode where they participate in the electrochemical reduction of molecular oxygen.

In some implementations, molecular hydrogen flows into an inlet at the anode side of the CO₂ purifier and purified CO₂ flow out an outlet at the anode. The purified CO₂ may contain some unreacted hydrogen. In some implementations, air or another CO₂ source flows into an inlet to the cathode side of the CO₂ purifier, and CO₂-depleted gas flows out an outlet at the cathode. If the source of CO₂ does not contain molecular oxygen—as may be the case when the inlet is not air—some oxygen can be added to the cathode inlet. In some embodiments, that oxygen may be generated by a CO₂ electrolyzer and/or by a water electrolyzer.

In many implementations, the cathode does not facilitate reduction of nitrogen, water, and/or certain other components of an impure CO₂-containing input stream, which components could, in theory, produce species that would transport to the anode and be converted back to the original component.

FIG. 1A illustrates an electrochemical CO₂ purification cell 101 configured to produce purified CO₂ 105 from an impure source 103. As shown, electrochemical cell 101 includes a cathode 107 where CO₂ is selectively removed from source 103 and an anode 109 where purified CO₂ 105 is released. At cathode 107, oxygen such as molecular oxygen is reduced in the presence of water to produce hydroxide ions, which react with CO₂ from the impure source 103 to produce carbonate ions. Cathode 107 may include a catalyst such as platinum to facilitate the reduction of oxygen.

Electrochemical CO₂ purification cell 101 also includes an anion conducting membrane 111 between cathode 107 and anode 109. Carbonate ions produced at cathode 107 transport across membrane 111, where they encounter a pH gradient as they move toward anode 109. The gradient transitions from more basic to more acidic from the cathode to the anode. Over the course, the transport, carbonate ions become protonated to produce bicarbonate ions.

At or near cathode 107, arriving bicarbonate and/or carbonate ions react with hydrogen ions to produce water and CO₂. The CO₂ released at cathode 107 is purified vis-à-vis the CO₂ in source 103 because other components of source 103 do not enter cell 101. In essence, cell 101 acts as a filter that selectively passes CO₂ from cathode 107 to anode 109.

In some embodiments, the electrons that reduce oxygen at the cathode and that are donated by oxidation of hydrogen at the anode flow through an external circuit. In some embodiments, the electrons move through membrane 111 without the intervention of an external circuit. In such embodiments, membrane 111 is conductive to not only carbonate and/or bicarbonate anions but to electrons as well.

In embodiments employing a membrane that conducts both anions and electrons, the electron flow shorts the device. This allows a compact design because electrons need not travel to an external circuit. In fact, in some designs, the CO₂ purifier does not require electrical wires or current collectors.

In some cases, the anode/membrane/cathode stack is spirally wound into a compact cylindrical structure. An example of such CO₂ purifier structure is provided in L. Shi et al., “A shorted membrane electrochemical cell powered by hydrogen to remove CO₂ from the air feed of hydroxide exchange membrane fuel cells” nature energy, which is incorporated herein by reference in its entirety.

In embodiments in which the membrane is not electronically conductive, the CO₂ purifier may be coupled to an external circuit that is optionally configured to control and/or monitor the electrical driving force for O₂ reduction at the cathode and for hydrogen oxidation at the anode.

The anode and cathode of an electrochemical CO₂ purification cell may have many different forms and compositions. Depending on the overall design of the purifier cell, they may be electronically conductive, and they may be solid structures that are resistant to the physical and chemical environments to which they are exposed. Either or both of them may take the form of sheets, meshes, foams, screens, and the like.

In embodiments where the membrane is electronically conductive and no external circuit is used, the anode and cathode do not require electronically conductive current collectors. In both types of purifier designs, the cathode side of the cell may include an element that facilitates delivery of an input gas stream containing impure CO₂ gas to active sites on the cathode. Examples of such elements include meshes and gas diffusion layers. Similarly, the anode side of the cell may include an element that facilitates removal of product gas (typically primarily purified CO₂) from the anode.

The cathode may include a cathode catalyst material that facilitates reduction of oxygen and/or associated conversion of carbon dioxide to carbonate and/or bicarbonate ion. Examples of such cathode catalyst material include noble metals such as platinum, platinum alloys, platinum supported on carbon, platinum alloys supported on carbon, materials comprising one or more transition metals along with nitrogen and/or carbon, and the like.

The anode may include an anode catalyst material that facilitates oxidation of hydrogen and/or an associated conversion of carbonate and/or bicarbonate ions to carbon dioxide. Examples of such anode catalyst materials include platinum, platinum alloys, platinum supported on carbon, palladium alloys supported on carbon, materials comprising one or more transition metals together with nitrogen and/or carbon, and the like.

In embodiments in which an external circuit is employed and the membrane does not conduct electrons, the anode and cathode may contain electronically conductive current collectors. Examples of electronically conductive materials that may be employed as current collectors include carbon, steel, aluminum, copper, nickel, noble metals, and alloys containing any of these.

A membrane in an electrochemical CO₂ purifier typically includes at least an ionically conductive component. In some embodiments, it also includes an electronically conductive component. In some examples, the membrane comprises an anion-exchange membrane (AEM) containing a conductive additive such as carbon particles.

The ion conducting component of a membrane may be an AEM that conducts carbonate and bicarbonate ions. In certain embodiments, the ion conducting component is a solid that retains shape during the conditions to which the purifier is exposed during operation. Generally, the ion conducting component is chemically stable in that it withstands the harsh electrochemical conditions encountered during operation.

As indicated, in some embodiments, the membrane includes a component that conducts electrons. In some embodiments, the electronically conductive component is provided as a filler material. In some embodiment, the electronically conductive component of the membrane comprises carbon in some form. As examples, the conductive additive may comprise graphite, carbon black, a fullerene (e.g., carbon nanotubes), and the like. Other examples include metals and reduced graphene oxides. In various embodiments, the electronically conductive component is supported within a matrix or support structure comprising primarily the ion conducting component.

The AEM component of the membrane can be made of any of many different chemical compositions. The AEM polymer will include one or more types of fixed, positively charged moieties. Examples of such moieties include quaternary ammonium groups, cyclic amines, imines, sulfur-contain groups, and the like. Examples include pyridinium, guanidinium, imidazolium, sulfonium, and the like.

In certain embodiments, the AEM polymer includes a polyarylene backbone with piperidinium cation pendant groups. Examples of such structures include

• • each of R⁹ and R¹⁰ is, independently, H, optionally substituted aliphatic, optionally substituted alkyl, optionally substituted heteroaliphatic, optionally substituted heteroalkyl, optionally substituted aromatic, optionally substituted aryl, or optionally substituted arylalkylene, or wherein R⁹ and R¹⁰ can be taken together to form an optionally substituted cyclic group (e.g., which can optionally be substituted with an ionizable moiety or an ionic moiety);
  • n is an integer of 1 or more;
  • q is 0, 1, 2, or more;
  • each of ring a, ring b, and/or ring c can, independently, be optionally substituted; and
  • wherein one or more of ring a, ring b, ring c, R⁹, and R¹⁰ can optionally include an ionizable moiety or an ionic moiety.

In any embodiment herein, the optionally substituted arylene or optionally substituted rings a-c is substituted with one or more substituents, and wherein the substituent is selected from the group consisting of alkyl, alkoxy, alkoxyalkyl, amino, aminoalkyl, aryl, arylalkylene, aryloyl, aryloxy, arylalkoxy, cyano, hydroxy, hydroxyalkyl, nitro, halo, and haloalkyl.

In any embodiment herein, at least one of rings a-c includes an ionizable moiety or an ionic moiety.

In any embodiment herein, R⁹ and R¹⁰ can be taken together to form an optionally substituted cyclic group. In particular embodiments, the optionally substituted cyclic group can optionally be substituted with an ionizable moiety or an ionic moiety.

In any embodiment herein, the composition includes a polymer or a copolymer.

In any embodiment herein, the composition includes a film, a membrane, or a cross-linked polymeric matrix. In some embodiments, a membrane contains a polymer or copolymer together with one or more filler particles. Examples of the filler particles include, optionally, fluorocarbon polymers (e.g., PTFE), fullerenes (e.g., carbon nanotubes), reduced graphene oxide, metals, and the like.

In some embodiments, an AEM polymer is synthesized by a method including:

• • providing one or more polymeric units in the presence of an interpenetrating agent and a Friedel-Crafts alkylation agent, wherein the interpenetrating agent includes a core moiety Z and the Friedel-Crafts alkylation agent includes a haloalkyl group and a reactive group, thereby forming an initial polymer having a reactive group; and
  • substituting the reactive group with an ionic moiety, thereby providing an ionic polymer.

Additional compounds and synthetic routes are schematically depicted here:

As examples, n+m can be from about 10 to 500. In certain embodiments, n is about 1-99% of the total of n+m. In certain embodiments, m is about 1-99% of the total of n+m.

CO₂ Sources for the CO₂ Purifier

A carbon dioxide purifier such as one integrated with a carbon dioxide electrolyzer, as described herein, may receive impure CO₂ that originates from any of various sources. Examples include air or other ambient gas, combustion output gases, and factory output such as output from a cement plant or a steelmaking plant. Combustion gases may be produced by, for example, a turbine, an engine, or other device that may be provided in stationary structure (e.g., a powerplant) or in a mobile structure (e.g., a transportation vehicle). In certain embodiments, impure CO₂ is from tailpipe exhaust. Typically, though not necessarily, the CO₂ provided to purifier is in gaseous form.

An integrated CO₂ purifier and CO₂ electrolyzer system may include a connection between a CO₂ containing output of a device such as an energy conversion device (e.g., a combustion turbine or fuel cell) and an input of the CO₂ purifier. The CO₂ containing output of such device may be connected to a gas compression system and/or other system, which then connects to an input of a CO₂ purifier of the disclosure. Multiple CO₂ generating devices and/or gas compression systems may be connected to a CO₂ purifier. The carbon dioxide containing output may be stored in a storage vessel.

A source of CO₂ may be connected directly to an input of a CO₂ purifier. In some embodiments, the carbon dioxide serves as the input to the cathode of an electrochemical CO₂ purifier via, e.g., a cathode flow field and/or a gas diffusion layer, etc. In some embodiments, the CO₂ is provided to a purifier after being compressed by, e.g., a gas compression system. In some embodiments, CO₂ provided to a CO₂ purifier may be recycled from a chemical reaction of a carbon-containing product of the CO₂ electrolyzer.

Impure CO₂ provided as input to a carbon dioxide purifier may have a range of concentrations. In certain embodiments, impure carbon dioxide provided to a carbon dioxide purifier has a concentration of about 20% or less, or about 0.01% to about 70% by volume or molar. In certain embodiments, carbon dioxide provided to a carbon dioxide purifier has a concentration of about 0.04% to about 70% by volume or molar. The CO₂ provided as input to a CO₂ purifier integrated with a CO₂ electrolyzer may be or may comprise air.

H₂ Sources for the CO₂ Purifier

As indicated, some electrochemical CO₂ purification cells employ hydrogen as an input gas. The hydrogen is oxidized at the electrochemical cell's anode to produce hydrogen ions that react with carbonate and/or bicarbonate ions to produce CO₂. The hydrogen may come from any of many different types of hydrogen sources. In some embodiments, the hydrogen is provided from a storage tank, which may be filled on site or obtained from any commercial source.

In some embodiments, the hydrogen is obtained from a water electrolyzer. A water electrolyzer reduces water at a cathode to produce molecular hydrogen and oxides water at an anode to produce molecular oxygen. In certain embodiments, a water electrolyzer comprises an MEA between (or including) the anode and cathode. In some embodiments, the MEA comprises a polymer electrolyte such as a proton exchange membrane. Examples of such proton exchange membranes include fluorocarbon polymers with pendant anions such as sulfonate groups (e.g., Nafions™) and hydrocarbon variants. In some embodiments, the MEA has one or more attributes of a CO₂ electrolyzer's MEA such as conductivity, transference number, chemical composition, thickness, and the like. Examples of attributes of CO₂ electrolyzers are described below.

In some implementations, the water electrolyzer shares infrastructure with a CO₂ electrolyzer that utilizes purified CO₂ from a purifier as described herein.

Output of CO₂ Purifier

In certain embodiments, purified carbon dioxide output from a purifier and provided to a carbon dioxide electrolyzer has a concentration of at least about 20% by volume or mole, or at least about 40% by volume or mole, or at least about 75% by volume or mole, or at least about 90% by volume or mole. In certain embodiments, carbon dioxide provided to a carbon dioxide reduction reactor has a concentration of about 40 to 60% by volume or mole.

Example Integrated CO₂ Purification and Electrolysis Systems

Some systems employ one or more CO₂ purifiers integrated with one or more CO₂ electrolyzers. As indicated, a CO₂ purifier may employ a cathode that captures CO₂ and an anode that releases CO₂.

FIGS. 1B, 2, and 3 depict embodiments of an integrated system comprising a CO₂ purifier and a CO₂ electrolyzer. The electrolyzer produces one or more CO₂ reduction products that may be used as an input to one or more downstream unit operations such as syngas formation. As explained, a system comprising an electrochemical CO₂ purifier integrated with a CO₂ electrolzyer receives impure CO₂ as an input and produces high-quality CO or other carbon-contain reduction product as an output.

As depicted in FIG. 1B, an example integrated system 131 includes a CO₂ purifier 133 and a CO₂ electrolyzer 135. When carbon dioxide from an impure CO₂ stream 137 is introduced to purifier 133, the carbon dioxide in the stream selectively reacts at a cathode and an anode produces CO₂ that is removed as a CO₂ stream 141. In the depicted embodiment, the impure CO₂ stream 137 includes some O₂ that is available to electrochemically react at the cathode of CO₂ purifier 133.

The mixture of CO₂ and O₂ 137 is directed to electrochemical CO₂ purifier 133, where the O₂ is reduced produce hydroxide ion and the CO₂ reacts with the hydroxide ion to produce carbonate ion. These reactions take place on the cathode of purifier 133. After contacting the cathode, gas stream 137 flow out of purifier 133, but it is depleted of some CO₂ and O₂ . The output stream is illustrated by reference numeral 139.

On the anode side of purifier 133, carbonate and or bicarbonate ions are protonated to produce CO₂. Because the non-CO₂ components in input stream 137 are not substantially consumed at cathode of purifier 133, the CO₂ 141 produced on the anode side is purified with respect to the impure CO₂ in inlet stream 137.

In system 131, the purified CO₂ stream 141 is directed to the cathode side of CO₂ electrolyzer 135, where the CO₂ is reduced to produce CO. The CO exits the cathode side of CO₂ electrolyzer 135 in a CO stream 143. Concurrent with the reduction of CO₂ to CO, the electrolyzer 135 oxidizes water from an input stream 145 to its anode where the water is oxidized to produce O₂ in an outlet stream 147.

Electrochemical CO₂ purifier 133 oxidizes molecular hydrogen to produce protons at its anode. As explained, molecular hydrogen may be oxidized to produce protons while releasing electrons, which may flow either to an external circuit or through a membrane in the purifier to the cathode side of the purifier. The protons produced by hydrogen at the anode of purifier 133 produce a pH gradient between the anode and cathode of the purifier. The locally low pH at the cathode allows carbonate or bicarbonate to react and release the purified CO₂ in stream 141. In system 131, a hydrogen stream 149 is produced from an input water stream 151 by a water electrolyzer 153. At the anode of water electrolyzer 153, an input stream of water 155 is oxidized produce an output gaseous stream of oxygen 157.

In system 131, some of the hydrogen produced by water electrolyzer 153 is diverted to mix with carbon monoxide in electrolyzer output stream 143 to produce syngas 159, which may be used directly or stored for later use.

A carbon dioxide electrolyzer requires electrical energy to reduce purified CO₂ to CO or other carbon-containing product. Similarly, a water electrolyzer, if used in the system, requires a source of electrical energy to electrolyze water to hydrogen and oxygen. And, in certain embodiments, electrochemical carbon dioxide purifier also employs an externally generated electrical potential to facilitate the reactions that produce purified CO₂. Any two or three of these electrochemical units may share infrastructure such as electrical controller, a power supply, power conducting transmission lines, and the like in an integrated system.

Turning now to FIG. 2, a system 201 includes a water electrolyzer 203, and electrochemical CO₂ purifier 205, and a CO₂ electrolyzer 207. In the depicted embodiment, system 201 also includes a controller 209 that controls delivery of electrical power to water electrolyzer 203 and to CO₂ electrolyzer 207. Note that CO₂ purifier 205 is not electrically connected to controller 209. In some embodiments, CO₂ purifier 205 has an electronically conductive membrane that allows electrons to move between the cathode where oxygen is reduced and the anode where hydrogen is oxidized, without the need for electrical circuit. The oxidation reaction of molecular hydrogen and the reduction reaction of molecular oxygen provides driving force for the electrochemical reactions occurring in CO₂ purifier 205.

In operation, a stream of water 211 is provided to water electrolyzer 203, which generates a gaseous hydrogen stream 213, which is, in turn, directed to CO₂ purifier 205. System 201 is configured direct an airstream 215 to CO₂ purifier 205. The airstream includes a relatively low concentration of CO₂ (e.g., about 0.04% by volume) as well as O₂. The O₂ and CO₂ react at the cathode of CO₂ purifier 205 to produce carbonate and or bicarbonate ions. Hydrogen from stream 213 reacts at the anode of CO₂ purifier 205 to produce hydrogen ions which react with bicarbonate ions to produce purified CO₂ which exits CO₂ purifier 205 via a purified CO₂ stream 217. The carbon dioxide in stream 217 is reduced at a cathode in CO₂ electrolyzer 207. The reduction product is provided in a stream 219.

It should be understood that while the system in FIG. 2 is illustrated as employing an airstream 215 as a source of CO₂ and O₂ to CO₂ purifier 205, other sources of O₂ and CO₂ may be used in lieu of or to supplement airstream 215. In practice, the CO₂ to the purifier can come from a variety of sources, not necessarily air. Examples of other sources include flue gas, combustion gas, etc. Further, O₂ can come from any of a variety of sources. One such example is illustrated in FIG. 3.

As illustrated in FIG. 3, a system 301 includes an electrochemical CO₂ purifier 305 that receives an O₂ stream 325 generated by a CO₂ electrolyzer 307. Together with O₂ from stream 325, purification unit 305 receives CO₂ from an impure CO₂ stream 315. The O₂ and CO₂ react at the purifier's cathode to produce carbonate and or bicarbonate ions. Carbon dioxide, purification cell 305 receives hydrogen via a stream 313 generated by a water electrolyzer 303. Water electrolyzer 303 receives, as an input, water from a stream 311. Acting upon the CO₂, O₂, and hydrogen input to its electrodes, CO₂ purifier 305 generates purified CO₂, which is exits the purifier via a stream 317. The purified CO₂ is provided to the cathode of CO₂ electrolyzer 307, where it is reduced to produce CO that exits electrolyzer via a stream 321. Carbon dioxide electrolyzer 307 also receives water via a water stream 319 as an input to its anode and produces the O₂ for stream 325 as an output from its anode.

The CO in stream 321 may be mixed with hydrogen in a stream 323 obtained from water electrolyzer 303. The stream 323 is separated from or diverted from hydrogen stream 313 which is provided as an input to CO₂ purifier 305. Together, the hydrogen from stream 323 and the CO from stream 321 is combined to form syngas 309, which may be stored or utilized directly.

Note that while FIG. 3 depicts CO as the cathode output of CO₂ electrolyzer 307, in related embodiments, other carbon-containing reduction products may be used or provided in lieu of or in conjunction with CO. Further, CO or any other carbon-containing reduction product produced by CO₂ electrolyzer 307 may, in alternative embodiments, be used for other applications in lieu of or together with syngas 309.

In addition to the CO₂ purifier and electrolyzer, an integrated system may include components for capturing, conveying, and/or storing impure CO₂ that is to be provided to the purifier. Similarly, any such components may be provided for purified CO₂ produced by the CO₂ purifier. Alternatively, or in addition, an integrated system may include components for capturing, conveying, and/or storing one or more outputs of a CO₂ electrolyzer.

In some embodiments, purified CO₂ produced by a CO₂ purifier is provided directly from an output of the purifier to an input of a CO₂ electrolyzer. In some embodiments, purified CO₂ produced by a CO₂ purifier is first provided to pressure adjusting component, a temperature adjusting component, and/or or a humidifier before it is provided as an input of a CO₂ electrolyzer. In some embodiments, purified CO₂ produced by a CO₂ purifier is first provided to storage vessel before it is provided as an input of a CO₂ electrolyzer. A “storage device” is a container or containment region that can hold a material such as purified CO₂, or mixture containing purified CO₂ and one or more other components. In some embodiments, a storage device is a vessel configured to hold a gas or liquid at a pressure higher than ambient or local pressure. A storage device may contain a metal or ceramic wall or chamber. In some embodiments, a storage device includes a natural or geological structure such as a salt dome or a depleted oil or gas field.

In some embodiments, an integrated system includes one or more components for using or converting CO₂ reduction products from the CO₂ electrolyzer. Such components may be employed downstream of the electrolyzer. As illustrated in FIGS. 1B and 3, CO produced by a CO₂ electrolyzer may be combined with H₂ to produce a syngas. The syngas may be used directly or stored for later use. There are many other uses for CO or other carbon containing product produced by the CO2 electrolyzer. Examples are presented in PCT Application No. PCT/US2021/044378, filed Aug. 3, 2021, which is incorporated herein by reference in its entirety.

CO₂ Electrolyzer Outputs

An integrated CO₂ purifier and CO₂ electrolyzer system may output one or more chemically reduced CO₂ products from the electrolyzer's cathode. Such outputs may include one or more carbon-containing products such as carbon monoxide, one or more hydrocarbons (e.g., methane, ethene, and/or ethane), one or more alcohols (e.g., methanol, ethanol, n-propanol, and/or ethylene glycol), one or more aldehydes (e.g., glycolaldehyde, acetaldehyde, glyoxal, and/or propionaldehyde), one or more ketones (e.g., acetone and/or hydroxyacetone), one or more carboxylic acids (e.g., formic acid and/or acetic acid), and any combination thereof. The electrolyzer's cathode may also produce H₂. A CO₂ purifier and electrolyzer integrated system may output one or more chemically oxidized H₂O products such as oxygen. Additional outputs of an electrolyzer may include unreacted CO₂ and/or unreacted H₂O.

A CO₂ electrolyzer of the disclosure may be directly connected (e.g., via the cathode flow field and/or gas diffusion layer) to a downstream system. In some embodiments, the downstream system is or comprises a purification system; a gas compression system; or both a purification system and a gas compression system, in either order; which then optionally connect to an input of a downstream reactor and/or to one or more storage devices. Multiple purification systems and/or gas compression systems may be employed. In various embodiments, a carbon-containing product, hydrogen, and/or oxygen produced by a carbon oxide electrolyzer is provided to a storage vessel for the carbon-containing product and/or a storage vessel for the oxygen.

An integrated CO₂ electrolyzer and CO₂ purifier a described herein may be configured, designed, and/or controlled in a manner that allows the electrolyzer to produce one or more CO₂ electrolysis products in a quantity, concentration, and/or ratio suitable for any of various downstream processes such as producing valuable carbon-containing products such as plastics and/or producing fuels such as syngas or naphtha. In certain embodiments, a CO₂ electrolyzer is configured to produce a hydrocarbon such as methane or ethene which may be combusted and/or utilized by fuel-cell to generate electrical energy.

Different CO₂ electrolyzers (e.g., including different layer stacks, catalysts and/or catalyst layers, PEMs, flow fields, gas diffusion layers, cell compression configurations, and/or any other suitable aspects, etc.) can be used to produce different reduction products; however, different reduction products can additionally or alternatively be produced by adjusting the operation parameters, and/or be otherwise achieved.

CO₂ Electrolyzer

Carbon Oxide Electrolyzer Design and Operating Conditions

A carbon oxide electrolyzer's design and operating conditions can be tuned for particular applications. Often this involves designing or operating the electrolyzer in a manner that produces a cathode output having specified compositions. In some implementations, one or more general principles may be applied to operate an electrolyzer in a way that produces a required output stream composition.

High CO₂ Reduction Product (Particularly CO) to CO₂ Ratio Operating Parameter Regime

In certain embodiments, an electrolyzer is configured to produce, and when operating actually produce, an output stream having a CO:CO₂ molar ratio of at least about 1:1 or at least about 1:2 or at least about 1:3. A high CO output stream may alternatively be characterized as having a CO concentration of at least about 25 mole %, or at least about 33 mole %, or at least about 50 mole %.

In certain embodiments, this high carbon monoxide output concentration is obtained by operating a carbon dioxide electrolyzer in a manner that produces any one of or any combination of the following operating conditions:

• • a current density of at least about 300 mA/cm², at the cathode,
  • a CO₂ stoichiometric flow rate (as described elsewhere herein) of at most about 4, or at most about 2.5, or at most about 1.5,
  • a temperature of at most about 80° C. or at most about 65° C.,
  • a pressure range of about 75 to 400 psig,
  • an anode water composition of about 0.1 to 50 mM bicarbonate salt, and
  • an anode water pH of at least about 1.

In certain embodiments, the electrolyzer may be built to favor high CO:CO₂ molar ratios or concentrations, as defined here, by using a carbon dioxide electrolyzer having any one of or any combination of the following properties:

• • relatively small nanoparticle cathode catalysts (e.g., having largest dimensions of, on average, about 0.1-15 nm),
  • gold as the cathode catalyst material,
  • a cathode catalyst layer thickness of about 5-20 um,
  • a cathode gas diffusion layer (GDL) with a microporous layer (MPL),
  • a cathode GDL with PTFE present at about 1-20 wt %, or about 1-10 wt %, or about 1-5 wt %,
  • a GDL that has a thickness of at least about 200 um,
  • a bipolar MEA having an anion-exchange cathode buffer layer having a thickness of at least about 5 um, and
  • a cathode flow field having parallel and/or serpentine flow paths.

High Reduction Product to Hydrogen Product Stream Operating Parameter Regime

In certain embodiments, a carbon dioxide electrolyzer is configured to produce, and when operating actually produces, an output stream having CO:H₂ in a molar ratio of at least about 2:1.

In certain embodiments, such product rich output concentration is obtained by operating a carbon dioxide electrolyzer in a manner that produces any one of or any combination of the following operating conditions:

• • a current density at the cathode of at least about 300 mA/cm²,
  • a CO₂ mass transfer stoichiometric flow rate to the cathode of at least about 1.5, or at least about 2.5, or at least about 4,
  • a temperature of at most about 80° C.,
  • a pressure in the range of about 75 to 400 psig,
  • an anode water composition of about 0.1 mM to 50 mM bicarbonate salt, and
  • an anode water pH of greater than about 1.

In certain embodiments, the electrolyzer may be built to favor product-rich molar ratios or concentrations, as defined here, by using a carbon dioxide electrolyzer having any one of or any combination of the following properties:

• • relatively small nanoparticle catalysts (e.g., having largest dimensions of, on average, about 0.1-15 nm),
  • gold as the cathode catalyst material,
  • a cathode catalyst layer thickness of about 5-20 um,
  • a cathode gas diffusion layer with a microporous layer (MPL),
  • a cathode GDL with PTFE present at about 1-20 wt %, or about 1-10 wt %, or about 1-5 wt %,
  • a cathode GDL that has a thickness of at least about 200 um, and
  • a bipolar MEA having an anion-exchange layer with a thickness of at least about 5 um.

Hydrocarbon Reduction Product

In energy conversion processes that require methane and/or ethene inputs, a carbon oxide electrolyzer may be designed to favor production of these hydrocarbons. In some embodiments, the electrolyzer cathode employs a transition metal such as copper as a reduction catalyst. See for example PCT Patent Application Publication No. 2020/146402, published Jul. 16, 2020, and titled “SYSTEM AND METHOD FOR METHANE PRODUCTION,” which is incorporated herein by reference in its entirety. Electrolysis systems for producing ethene may be configured to recycle some hydrocarbon product of a carbon oxide electrolyzer back to the cathode and/or provide two more electrolyzers operating in series, with the cathode output of a first electrolyzer feeding the input to a cathode of a second electrolyzer. See for example PCT Patent Application No. PCT/US2021/036475, filed Jun. 8, 2021, and titled “SYSTEM AND METHOD FOR HIGH CONCENTRATION OF MULTIELECTRON PRODUCTS OR CO IN ELECTROLYZER OUTPUT,” which is incorporated herein by reference in its entirety.

Carbon Oxide Electrolyzer Embodiments

FIG. 4 depicts an example system 401 for a carbon oxide reduction reactor or electrolyzer 403 that may include a cell comprising a MEA (membrane electrode assembly). The reactor may contain multiple cells or MEAs arranged in a stack. System 401 includes an anode subsystem that interfaces with an anode of electrolyzer 403 and a cathode subsystem that interfaces with a cathode of electrolyzer 403. System 401 is an example of a system that may be used with or to implement any of the methods or operating conditions described above.

As depicted, the cathode subsystem includes a carbon oxide source 409 configured to provide a feed stream of carbon oxide to the cathode of electrolyzer 403, which, during operation, may generate an output stream 408 that includes product(s) of a reduction reaction at the cathode. The product stream 408 may also include unreacted carbon oxide and/or hydrogen.

The carbon oxide source 409 is coupled to a carbon oxide flow controller 413 configured to control the volumetric or mass flow rate of carbon oxide to electrolyzer 403. One or more other components may be disposed on a flow path from flow carbon oxide source 409 to the cathode of electrolyzer 403. For example, an optional humidifier 404 may be provided on the path and configured to humidify the carbon oxide feed stream. Humidified carbon oxide may moisten one or more polymer layers of an MEA and thereby avoid drying such layers. Another component that may be disposed on the flow path is a purge gas inlet coupled to a purge gas source 417. In certain embodiments, purge gas source 417 is configured to provide purge gas during periods when current is paused to the cell(s) of electrolyzer 403. In some implementations, flowing a purge gas over an MEA cathode facilitates recovery of catalyst activity and/or selectivity. Examples of purge gases include carbon dioxide, carbon monoxide, hydrogen, nitrogen, argon, helium, oxygen, and mixtures of any two or more of these. Further details of MEA cathode purge processes and systems are described in US Patent Application Publication No. 20220267916, published Aug. 25, 2022, which is incorporated herein by reference in its entirety.

During operation, the output stream from the cathode flows via a conduit 407 that connects to a backpressure controller 415 configured to maintain pressure at the cathode side of the cell within a defined range (e.g., about 50 to 800 psig, depending on the system configuration). The output stream may provide the reaction products 408 to one or more components (not shown) for separation and/or concentration.

In certain embodiments, the cathode subsystem is configured to controllably recycle unreacted carbon oxide from the outlet stream back to the cathode of electrolyzer 403. In some implementations, the output stream is processed to remove reduction product(s) and/or hydrogen before recycling the carbon oxide. Depending upon the MEA configuration and operating parameters, the reduction product(s) may be carbon monoxide, hydrogen, hydrocarbons such as methane and/or ethylene, oxygen-containing organic compounds such as formic acid, acetic acid, and any combinations thereof. In certain embodiments, one or more components, not shown, for removing water from the product stream are disposed downstream form the cathode outlet. Examples of such components include a phase separator configured to remove liquid water from the product gas stream and/or a condenser configured to cool the product stream gas and thereby provide a dry gas to, e.g., a downstream process when needed. In some implementations, recycled carbon oxide may mix with fresh carbon oxide from source 409 upstream of the cathode.

As depicted in FIG. 4, an anode subsystem is configured to provide an anode feed stream to an anode side of the carbon oxide electrolyzer 403. In certain embodiments, the anode subsystem includes an anode water source, not shown, configured to provide fresh anode water to a recirculation loop that includes an anode water reservoir 419 and an anode water flow controller 411. The anode water flow controller 411 is configured to control the flow rate of anode water to or from the anode of electrolyzer 403. In the depicted embodiment, the anode water recirculation loop is coupled to components for adjusting the composition of the anode water. These may include a water reservoir 421 and/or an anode water additives source 423. Water reservoir 421 is configured to supply water having a composition that is different from that in anode water reservoir 419 (and circulating in the anode water recirculation loop). In one example, the water in water reservoir 421 is pure water that can dilute solutes or other components in the circulating anode water. Pure water may be conventional deionized water even ultrapure water having a resistivity of, e.g., at least about 15 MOhm-cm or over 18.0 MOhm-cm. Anode water additives source 423 is configured to supply solutes such as salts and/or other components to the circulating anode water. Examples of anode water salts for various carbon oxide electrolyzer configurations are presented in US Patent Application Publication No. 20200240023, published Jul. 30, 2020, which is incorporated herein by reference in its entirety.

During operation, the anode subsystem may provide water or other reactant to the anode of electrolyzer 403, where it at least partially reacts to produce an oxidation product such as oxygen. The product along with unreacted anode feed material is provided in a reduction reactor outlet stream. Not shown in FIG. 4 is an optional separation component that may be provided on the path of the anode outlet stream and configured to concentrate or separate the oxidation product from the anode product stream.

Other control features may be included in system 401. For example, a temperature controller may be configured to heat and/or cool the carbon oxide electrolyzer 403 at appropriate points during its operation. In the depicted embodiment, a temperature controller 405 is configured to heat and/or cool anode water provided to the anode water recirculation loop. For example, the temperature controller 405 may include or be coupled to a heater and/or cooler that may heat or cool water in anode water reservoir 419 and/or water in reservoir 421. In some embodiments, system 401 includes a temperature controller configured to directly heat and/or cool a component other than an anode water component. Examples of such other components in the cell or stack and the carbon oxide flowing to the cathode.

Depending upon the phase of the electrochemical operation, including whether current is paused to carbon oxide reduction electrolyzer 403, certain components of system 401 may operate to control non-electrical operations. For example, system 401 may be configured to adjust the flow rate of carbon oxide to the cathode and/or the flow rate of anode feed material to the anode of electrolyzer 403. Components that may be controlled for this purpose may include carbon oxide flow controller 413 and anode water controller 411.

In addition, depending upon the phase of the electrochemical operation including whether current is paused, certain components of system 401 may operate to control the composition of the carbon oxide feed stream and/or the anode feed stream. For example, water reservoir 421 and/or anode water additives source 423 may be controlled to adjust the composition of the anode feed stream. In some cases, additives source 423 may be configured to adjust the concentration of one or more solutes such as one or more salts in an aqueous anode feed stream.

In some cases, a temperature controller such controller 405 is configured to adjust the temperature of one or more components of system 401 based on a phase of operation. For example, the temperature of cell 403 may be increased or decreased during break-in, a current pause in normal operation, and/or storage.

In some embodiments, a carbon oxide electrolytic reduction system is configured to facilitate removal of a reduction cell from other system components. This may be useful with the cell needs to be removed for storage, maintenance, refurbishment, etc. In the depicted embodiments, isolation valves 425a and 425b are configured to block fluidic communication of cell 403 to a source of carbon oxide to the cathode and backpressure controller 415, respectively. Additionally, isolation valves 425c and 425d are configured to block fluidic communication of cell 403 to anode water inlet and outlet, respectively.

The carbon oxide reduction electrolyzer 403 may also operate under the control of one or more electrical power sources and associated controllers. See, block 433. Electrical power source and controller 433 may be programmed or otherwise configured to control current supplied to and/or to control voltage applied to the electrodes in reduction electrolyzer 403. The current and/or voltage may be controlled to execute the current schedules and/or current profiles described elsewhere herein. For example, electrical power source and controller 433 may be configured to periodically pause current applied to the anode and/or cathode of reduction electrolyzer 403. Any of the current profiles described herein may be programmed into power source and controller 433.

In certain embodiments, electric power source and controller 433 performs some but not all the operations necessary to implement desired current schedules and/or profiles in the carbon oxide reduction electrolyzer 403. A system operator or other responsible individual may act in conjunction with electrical power source and controller 433 to fully define the schedules and/or profiles of current applied to reduction electrolyzer 403. For example, an operator may institute one or more current pauses outside the set of current pauses programmed into power source and controller 433.

In certain embodiments, the electrical power source and an optional, associated electrical power controller acts in concert with one or more other controllers or control mechanisms associated with other components of system 401. For example, electrical power source and controller 433 may act in concert with controllers for controlling the delivery of carbon oxide to the cathode, the delivery of anode water to the anode, the addition of pure water or additives to the anode water, and any combination of these features. In some implementations, one or more controllers are configured to control or operate in concert to control any combination of the following functions: applying current and/or voltage to reduction cell 403, controlling backpressure (e.g., via backpressure controller 415), supplying purge gas (e.g., using purge gas component 417), delivering carbon oxide (e.g., via carbon oxide flow controller 413), humidifying carbon oxide in a cathode feed stream (e.g., via humidifier 404), flow of anode water to and/or from the anode (e.g., via anode water flow controller 411), and anode water composition (e.g., via anode water source 405, pure water reservoir 421, and/or anode water additives component 423).

In the depicted embodiment, a voltage monitoring system 434 is employed to determine the voltage across an anode and cathode of an MEA cell or across any two electrodes of a cell stack, e.g., determining the voltage across all cells in a multi-cell stack. The voltage determined in this way can be used to control the cell voltage during a current pause, inform the duration of a pause, etc. In certain embodiments, voltage monitoring system 434 is configured to work in concert with power supply 433 to cause reduction cell 403 to remain within a specified voltage range. For example, power supply 433 may be configured to apply current and/or voltage to the electrodes of reduction cell 403 in a way that maintains the cell voltage within a specified range during a current pause. If, for example during a current pause, the cell's open circuit voltage deviates from a defined range (as determined by voltage monitoring system 434), power supply may be configured to apply current or voltage to the electrodes to maintain the cell voltage within the specified range.

An electrolytic carbon oxide reduction system such as that depicted in FIG. 4 may employ control elements or a control system that includes one or more controllers and one or more controllable components such as pumps, sensors, dispensers, valves, and power supplies. Examples of sensors include pressure sensors, temperature sensors, flow sensors, conductivity sensors, voltmeters, ammeters, electrolyte composition sensors including electrochemical instrumentation, chromatography systems, optical sensors such as absorbance measuring tools, and the like. Such sensors may be coupled to inlets and/or outlets of an MEA cell (e.g., in a flow field), in a reservoir for holding anode water, pure water, salt solution, etc., and/or other components of an electrolytic carbon oxide reduction system.

Among the various functions that may be controlled by one or more controllers are: applying current and/or voltage to a carbon oxide reduction cell, controlling backpressure on an outlet from a cathode on such cell, supplying purge gas to a cathode inlet, delivering carbon oxide to the cathode inlet, humidifying carbon oxide in a cathode feed stream, flowing anode water to and/or from the anode, and controller anode feed composition. Any one or more of these functions may have a dedicated controller for controlling its function alone. Any two or more of these functions may share a controller. In some embodiments, a hierarchy of controllers is employed, with at least one master controller providing instructions to two or more component controllers. For example, a system may comprise a master controller configured to provide high level control instructions to (i) a power supply to a carbon oxide reduction cell, (ii) a cathode feed stream flow controller, and (iii) an anode feed stream flow controller. For example, a programmable logic controller (PLC) may be used to control individual components of the system.

In certain embodiments, a control system is configured to control the flow rate of one or more feed streams (e.g., a cathode feed stream such as a carbon oxide flow and an anode feed stream) in concert with a current schedule. For example, the flow of carbon oxide or a purge gas may be turned on, turned off, or otherwise adjusted when current applied to an MEA cell is reduced, increased, or paused.

A controller may include any number of processors and/or memory devices. The controller may contain control logic such software or firmware and/or may execute instructions provided from another source. A controller may be integrated with electronics for controlling operation the electrolytic cell before, during, and after reducing a carbon oxide. The controller may control various components or subparts of one or multiple electrolytic carbon oxide reduction systems. The controller, depending on the processing requirements and/or the type of system, may be programmed to control any of the processes disclosed herein, such as delivery of gases, temperature settings (e.g., heating and/or cooling), pressure settings, power settings (e.g., electrical voltage and/or current delivered to electrodes of an MEA cell), liquid flow rate settings, fluid delivery settings, and dosing of purified water and/or salt solution. These controlled processes may be connected to or interfaced with one or more systems that work in concert with the electrolytic carbon oxide reduction system.

In various embodiments, a controller comprises electronics having various integrated circuits, logic, memory, and/or software that receive instructions, issue instructions, control operations described herein. The integrated circuits may include chips in the form of firmware that store program instructions, digital signal processors (DSPs), chips defined as application specific integrated circuits (ASICs), and/or one or more microprocessors, or microcontrollers that execute program instructions (e.g., software). Program instructions may be instructions communicated to the controller in the form of various individual settings (or program files), defining operational parameters for carrying out a process on one or more components of an electrolytic carbon oxide reduction system. The operational parameters may, in some embodiments, be part of a recipe defined by process engineers to accomplish one or more processing steps during generation of a particular reduction product such as carbon monoxide, hydrocarbons, and/or other organic compounds.

The controller, in some implementations, may be a part of or coupled to a computer that is integrated with, coupled to the system, otherwise networked to the system, or a combination thereof. For example, the controller may utilize instructions stored remotely (e.g., in the “cloud”) and/or execute remotely. The computer may enable remote access to the system to monitor current progress of electrolysis operations, examine a history of past electrolysis operations, examine trends or performance metrics from a plurality of electrolysis operations, to change parameters of current processing, to set processing steps to follow a current processing, or to start a new process. In some examples, a remote computer (e.g., a server) can provide process recipes to a system over a network, which may include a local network or the internet. The remote computer may include a user interface that enables entry or programming of parameters and/or settings, which are then communicated to the system from the remote computer. In some examples, the controller receives instructions in the form of data, which specify parameters for each of the processing steps to be performed during one or more operations.

The controller may be distributed, such as by comprising one or more discrete controllers that are networked together and working towards a common purpose, such as applying current to an MEA cell and other process controls described herein. An example of a distributed control system for such purposes includes one or more processors on a system for electrolytically reducing a carbon oxide and one or more processors located remotely (such as at the platform level or as part of a remote computer) that combine to control a process.

Controllers and any of various associated computational elements including processors, memory, instructions, routines, models, or other components are sometimes described or claimed as “configured to” perform a task or tasks. In such contexts, the phrase “configured to” is used to denote structure by indicating that the component includes structure (e.g., stored instructions, circuitry, etc.) that performs a task or tasks during operation. As such, a controller and/or associated component can be said to be configured to perform the task even when the specified component is not necessarily currently operational (e.g., is not on).

Controllers and other components that are “configured to” perform an operation may be implemented as hardware—for example, circuits, memory storing program instructions executable to implement the operation, etc. Additionally, controllers and other components “configured to” perform an operation may be implemented as hardware that is manipulated by software and/or firmware (e.g., an FPGA or a general-purpose processor executing software) to operate in manner that is capable of performing the recited task(s). Additionally, “configured to” can refer to one or more memories or memory elements storing computer executable instructions for performing the recited task(s). Such memory elements may include memory on a computer chip having processing logic.

Non-computation elements such as reactors such electrolyzers, membrane assemblies, layers, and catalyst particles may also be “configured” to perform certain functions. In such contexts, the phrase “configured to” indicate that the referenced structure has one or more features that allow the function to be performed. Examples of such features include physical and/or chemical properties such as dimensions, composition, porosity, etc.

MEA Embodiments

MEA Overview

In various embodiments, an MEA contains an anode layer, a cathode layer, electrolyte, and optionally one or more other layers. The layers may be solids and/or gels. The layers may include polymers such as ion-conducting polymers.

When in use, the cathode of an MEA promotes electrochemical reduction of CO_x by combining three inputs: CO_x, ions (e.g., hydrogen ions, bicarbonate ions, or hydroxide ions) that chemically react with CO_x, and electrons. The reduction reaction may produce CO, hydrocarbons, and/or hydrogen and oxygen-containing organic compounds such as methanol, ethanol, and acetic acid. When in use, the anode of an MEA promotes an electrochemical oxidation reaction such as electrolysis of water to produce elemental oxygen and protons. The cathode and anode may each contain catalysts to facilitate their respective reactions.

During operation of an MEA, ions move through a polymer-electrolyte, while electrons flow from an anode, through an external circuit, and to a cathode. In some embodiments, liquids and/or gas move through or permeates the MEA layers. This process may be facilitated by pores in the MEA.

The compositions and arrangements of layers in the MEA may promote high yield of a CO_x reduction products. To this end, the MEA may facilitate any one or more of the following conditions: (a) minimal parasitic reduction reactions (non-CO_x reduction reactions) at the cathode; (b) low loss of CO_x reactants to the anode or elsewhere in the MEA; (c) physical integrity of the MEA during the reaction (e.g., the MEA layers remain affixed to one another); (d) prevent CO_x reduction product cross-over; (e) prevent oxidation product (e.g., O₂ ) cross-over; (f) a suitable environment at the cathode for the reduction reaction; (g) a pathway for desired ions to travel between cathode and anode while blocking undesired ions; and (h) low voltage operation.

CO_x Reduction Considerations

For many applications, an MEA for CO, reduction requires a lifetime on the order of about 50,000 hours or longer (approximately five years of continuous operation), which is significantly longer than the expected lifespan of a fuel cell for automotive applications; e.g., on the order of 5,000 hours. And for various applications, an MEA for CO_x reduction employs electrodes having a relatively large surface area by comparison to MEAs used for fuel cells in automotive applications. For example, MEAs for CO_x reduction may employ electrodes having surface areas (without considering pores and other nonplanar features) of at least about 500 cm².

CO_x reduction reactions may be implemented in operating environments that facilitate mass transport of particular reactant and product species, as well as to suppress parasitic reactions. Fuel cell and water electrolyzer MEAs often cannot produce such operating environments. For example, such MEAs may promote undesirable parasitic reactions such as gaseous hydrogen evolution at the cathode and/or gaseous CO₂ production at the anode.

In some systems, the rate of a CO_x reduction reaction is limited by the availability of gaseous CO_x reactant at the cathode. By contrast, the rate of water electrolysis is not significantly limited by the availability of reactant: liquid water tends to be easily accessible to the cathode and anode, and electrolyzers can operate close to the highest current density possible.

MEA Configurations

In certain embodiments, an MEA has a cathode layer, an anode layer, and a polymer electrolyte membrane (PEM) between the anode layer and the cathode layer. The polymer electrolyte membrane provides ionic communication between the anode layer and the cathode layer, while preventing electronic communication that would produce a short circuit. The cathode layer includes a reduction catalyst and, optionally, an ion-conducting polymer (sometimes called an ionomer). The cathode layer may also include an electron conductor and/or an additional ion conductor. The anode layer includes an oxidation catalyst and, optionally, an ion-conducting polymer. The anode layer may also include an electron conductor and/or an additional ion conductor. The PEM comprises an ion-conducting polymer. In certain embodiments, the MEA has a cathode buffer layer between the cathode layer and the polymer electrolyte membrane. The cathode buffer comprises an ion-conducting polymer.

The ion-conducting polymers in the PEM, the cathode, the anode, and the cathode buffer layer, if present, may each be different from one another in composition, conductivity, molecular weight, or other property. In some cases, two or more of these polymers are identical or substantially identical. For example, the ion-conducting polymer in the cathode and cathode buffer layer may be identical.

In certain embodiments, the MEA has an anode buffer layer between the anode layer and the polymer electrolyte membrane. The anode buffer layer also comprises an ion-conducting polymer, which may have the same properties as any of the other ion-conducting polymers (e.g., the ion-conducting polymer in the anode). Or the ion-conducting layer of the anode buffer layer may be different from every other ion-conducting layer in the MEA.

In connection with certain MEA designs, there may be three available classes of ion-conducting polymers: anion-conductors, cation-conductors, and mixed cation-and-anion-conductors. In certain embodiments, at least two of the first, second, third, fourth, and fifth ion-conducting polymers are from different classes of ion-conducting polymers.

In certain embodiments, an MEA has a bipolar interface, which means that it has one layer of anion-conducting polymer in contact with a layer of cation-conducting polymer. One example of an MEA with a bipolar interface is an anion-conducting cathode buffer layer adjacent to (and in contact with) a cation-conducting PEM. In certain embodiments, an MEA contains only anion-conducting polymer between the anode and the cathode. Such MEAs are sometimes referred to as “AEM only” MEAs. Such MEAs may contain one or more layers of anion-conducing polymer between the anode and the cathode.

Ion-Conducting Polymers for MEA Layers

The term “ion-conducting polymer” or “ionomer” is used herein to describe a polymer that conducts ions (anions and/or cations) is to say that the material is an ion-conducting material or ionomer. In certain embodiments, an MEA contains one or more ion-conducting polymers having a specific conductivity of about 1 mS/cm or greater for anions and/or cations. The term “anion-conductor” describes an ion-conducting polymer that conducts anions primarily (although there will still be some small amount of cation conduction) and has a transference number for anions of about 0.85 or greater at around 100 micrometers thickness. The terms “cation-conductor” and/or “cation-conducting polymer” describe an ion-conducting polymer that conducts cations primarily (e.g., there can still be an incidental amount of anion conduction) and has a transference number for cations of about 0.85 or greater at about 100 micrometers thickness. For an ion-conducting polymer that is described as conducting both anions and cations (a “cation-and-anion-conductor”), neither the anions nor the cations have a transference number greater than about 0.85 or less than about 0.15 at about 100 micrometers thickness. Examples of ion-conducting polymers of each class are provided in the below Table 1.

Ion-Conducting Polymers
Class	Description	Common Features	Examples
A. Anionconducting	Greater than	Positively charged	Quaternary ammonium
	approximately 1	functional groups	or cyclic amine
	mS/cm specific	are covalently	moieties on
	conductivity for	bound to the	polyphenylene
	anions, which	polymer backbone	backbone; aminated
	have a		tetramethyl
	transference		polyphenylene;
	number greater		poly(ethylene-co-
	than		tetrafluoroethylene)-
	approximately		based quaternary
	0.85 at about 100		ammonium polymer;
	micron thickness		quaternized polysulfone
B.	Greater than	Salt is soluble in	polyethylene oxide;
Conducts both anions and	approximately 1	the polymer and	polyethylene glycol;
cations	mS/cm conductivity	the salt ions can	poly(vinylidene
	for ions (including	move through the	fluoride); polyurethane
	both cations and	polymer material
	anions), which have a
	transference number
	between
	approximately
	0.15 and 0.85 at
	around 100 micron
	thickness
C.	Greater than	Negatively	perfluorosulfonic acid
Cationconducting	approximately 1	charged functional	polytetrafluoroethylene
	mS/cm specific	groups are	co-polymer;
	conductivity for	covalently bound	sulfonated poly(ether
	cations, which have a	to the polymer	ketone);
	transference number	backbone	poly(styrene sulfonic
	greater than		acid- co-maleic acid)
	approximately 0.85 at
	around 100
	micron thickness

Polymeric Structures

Examples of polymeric structures that can include an ionizable moiety or an ionic moiety and be used as ion-conducting polymers (ionomers) in the MEAs described here are provided below. The ion-conducting polymers may be used as appropriate in any of the MEA layers that include an ion-conducting polymer. Charge conduction through the material can be controlled by the type and amount of charge (e.g., anionic and/or cationic charge on the polymeric structure) provided by the ionizable/ionic moieties. In addition, the composition can include a polymer, a homopolymer, a copolymer, a block copolymer, a polymeric blend, other polymer-based forms, or other useful combinations of repeating monomeric units. As described below, an ion conducting polymer layer may include one or more of crosslinks, linking moieties, and arylene groups according to various embodiments. In some embodiments, two or more ion conducting polymers (e.g., in two or more ion conducting polymer layers of the MEA) may be crosslinked.

Non-limiting monomeric units can include one or more of the following:

in which Ar is an optionally substituted arylene or aromatic; Ak is an optionally substituted alkylene, haloalkylene, aliphatic, heteroalkylene, or heteroaliphatic; and L is a linking moiety (e.g., any described herein) or can be —C(R⁷)(R⁸)—. Yet other non-limiting monomeric units can include optionally substituted arylene, aryleneoxy, alkylene, or combinations thereof, such as optionally substituted (aryl)(alkyl)ene (e.g., -Ak-Ar- or -Ak-Ar-Ak- or -Ar-Ak-, in which Ar is an optionally substituted arylene and Ak is an optionally substituted alkylene). One or more monomeric units can be optionally substituted with one or more ionizable or ionic moieties (e.g., as described herein).

One or more monomeric units can be combined to form a polymeric unit. Non-limiting polymeric units include any of the following:

in which Ar, Ak, L, n, and m can be any described herein. In some embodiments, each m is independently 0 or an integer of 1 or more. In other embodiments, Ar can include two or more arylene or aromatic groups.

Other alternative configurations are also encompassed by the compositions herein, such as branched configurations, diblock copolymers, triblock copolymers, random or statistical copolymers, stereoblock copolymers, gradient copolymers, graft copolymers, and combinations of any blocks or regions described herein.

Examples of polymeric structures include those according to any one of formulas (I)-(V) and (X)-(XXXIV), or a salt thereof. In some embodiments, the polymeric structures are copolymers and include a first polymeric structure selected from any one of formulas (I)-(V) or a salt thereof; and a second polymeric structure including an optionally substituted aromatic, an optionally substituted arylene, a structure selected from any one of formulas (I)-(V) and (X)-(XXXIV), or a salt thereof.

In one embodiment, the MW of the ion-conducting polymer is a weight-average molecular weight (Mw) of at least 10,000 g/mol; or from about 5,000 to 2,500,000 g/mol. In another embodiment, the MW is a number average molecular weight (Mn) of at least 20,000 g/mol; or from about 2,000 to 2,500,000 g/mol.

In any embodiment herein, each of n, n1, n2, n3, n4, m, m1, m2, or m3 is, independently, 1 or more, 20 or more, 50 or more, 100 or more; as well as from 1 to 1,000,000, such as from 10 to 1,000,000, from 100 to 1,000,000, from 200 to 1,000,000, from 500 to 1,000,000, or from 1,000 to 1,000,000.

Non-limiting polymeric structures can include the following:

or a salt thereof, wherein: each of R⁷, R⁸, R⁹, and R¹⁰ is, independently, an electron-withdrawing moiety, H, optionally substituted aliphatic, alkyl, heteroaliphatic, heteroalkylene, aromatic, aryl, or arylalkylene, wherein at least one of R⁷ or R⁸ can include the electron-withdrawing moiety or wherein a combination of R⁷ and R⁸ or R⁹ and R¹⁰ can be taken together to form an optionally substituted cyclic group;

• • Ar comprises or is an optionally substituted aromatic or arylene (e.g., any described herein);
  • each of n is, independently, an integer of 1 or more;
  • each of rings a-c can be optionally substituted; and
  • rings a-c, R⁷, R⁸, R⁹, and R¹⁰ can optionally comprise an ionizable or ionic moiety.

Further non-limiting polymeric structures can include one or more of the following:

or a salt thereof, wherein:

• • R⁷ can be any described herein (e.g., for formulas (I)-(V));
  • n is from 1 or more;
  • each L^8A, L^8B′, and L^B″ is, independently, a linking moiety; and
  • each X^8A, X^8A′, X^8A″, X^B′, and X^B″ is, independently, an ionizable or ionic moiety.

Yet other polymeric structures include the following:

or a salt thereof, wherein:

• • each of R¹, R², R³, R⁷, R⁸, R⁹, and R¹⁰ is, independently, an electron-withdrawing moiety, H, optionally substituted aliphatic, alkyl, heteroaliphatic, heteroalkylene, aromatic, aryl, or arylalkylene, wherein at least one of R⁷ or R⁸ can include the electron-withdrawing moiety or wherein a combination of R⁷ and R⁸ or R⁹ and R¹⁰ can be taken together to form an optionally substituted cyclic group;
  • each Ak is or comprises an optionally substituted aliphatic, alkylene, haloalkylene, heteroaliphatic, or heteroalkylene;
  • each Ar is or comprises an optionally substituted arylene or aromatic;
  • each of L, L¹, L², L³, and L⁴ is, independently, a linking moiety;
  • each of n, ¹, n², n³, n⁴, m, m¹, m², and m³ is, independently, an integer of 1 or more;
  • q is 0, 1, 2, or more;
  • each of rings a-i can be optionally substituted; and
  • rings a-i, R⁷, R⁸, R⁹, and R¹⁰ can optionally include an ionizable or ionic moiety.

In particular embodiments (e.g., of formula (XIV) or (XV)), each of the nitrogen atoms on rings a and/or b are substituted with optionally substituted aliphatic, alkyl, aromatic, aryl, an ionizable moiety, or an ionic moiety. In some embodiments, one or more hydrogen or fluorine atoms (e.g., in formula (XIX) or (XX)) can be substituted to include an ionizable moiety or an ionic moiety (e.g., any described herein). In other embodiments, the oxygen atoms present in the polymeric structure (e.g., in formula XXVIII) can be associated with an alkali dopant (e.g., K⁺).

In particular examples, Ar, one or more of rings a-i (e.g., rings a, b, f, g, h, or i), L, L¹, L², L³, L⁴, Ak, R⁷, R⁸, R⁹, and/or R¹⁰ can be optionally substituted with one or more ionizable or ionic moieties and/or one or more electron-withdrawing groups. Yet other non-limiting substituents for Ar, rings (e.g., rings a-i), L, Ak, R⁷, R⁸, R⁹, and R¹⁰ include one or more described herein, such as cyano, hydroxy, nitro, and halo, as well as optionally substituted aliphatic, alkyl, alkoxy, alkoxyalkyl, amino, aminoalkyl, aryl, arylalkylene, aryloyl, aryloxy, arylalkoxy, hydroxyalkyl, and haloalkyl.

In some embodiments, each of R¹, R², and R³ is, independently, H, optionally substituted aromatic, aryl, aryloxy, or arylalkylene. In other embodiments (e.g., of formulas (I)-(V) or (XII)), R⁷ includes the electron-withdrawing moiety. In yet other embodiments, R⁸, R⁹, and/or R¹⁰ includes an ionizable or ionic moiety.

In one instance, a polymeric subunit can lack ionic moieties. Alternatively, the polymeric subunit can include an ionic moiety on the Ar group, the L group, both the Ar and L groups, or be integrated as part of the L group. Non-limiting examples of ionizable and ionic moieties include cationic, anionic, and multi-ionic group, as described herein.

In any embodiment herein, the electron-withdrawing moiety can include or be an optionally substituted haloalkyl, cyano (CN), phosphate (e.g., —O(P═O)(OR^P1)(OR^P2) or —O—[P(═O)(OR^P1)—O]_P3—R^P2), sulfate (e.g., —O—S(═O)₂(OR^S1)), sulfonic acid (—SO₃H), sulfonyl (e.g., —SO₂—CF₃), difluoroboranyl (—BF₂), borono (B(OH)₂), thiocyanato (—SCN), or piperidinium. Yet other non-limiting phosphate groups can include derivatives of phosphoric acid, such as orthophosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, trimetaphosphoric acid, and/or phosphoric anhydride, or combinations thereof.

Yet other polymeric units can include poly(benzimidazole) (PBI), polyphenylene (PP), polyimide (PI), poly(ethyleneimine) (PEI), sulfonated polyimide (SPI), polysulfone (PSF), sulfonated polysulfone (SPSF), poly(ether ketone) (PEEK), PEEK with cardo groups (PEEK-WC), polyethersulfone (PES), sulfonated polyethersulfone (SPES), sulfonated poly(ether ketone) (SPEEK), SPEEK with cardo groups (SPEEK-WC), poly(p-phenylene oxide) (PPO), sulfonated polyphenylene oxide (SPPO), ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), poly(epichlorohydrin) (PECH), poly(styrene) (PS), sulfonated poly(styrene) (SPS), hydrogenated poly(butadiene-styrene) (HPBS), styrene divinyl benzene copolymer (SDVB), styrene-ethylene-butylene-styrene (SEBS), sulfonated bisphenol-A-polysulfone (SPSU), poly(4-phenoxy benzoyl-1,4-phenylene) (PPBP), sulfonated poly(4-phenoxy benzoyl-1,4-phenylene) (SPPBP), poly(vinyl alcohol) (PVA), poly(phosphazene), poly(aryloxyphosphazene), polyetherimide, as well as combinations thereof.

In some embodiments, any one or more of these polymers described in this section may be used in a membrane of a CO2 purifier (such a membrane 111) as described herein.

Bipolar MEA for CO_x Reduction

In certain embodiments, the MEA includes a bipolar interface having an anion-conducting polymer on the cathode side of the MEA and an interfacing cation-conducting polymer on the anode side of the MEA. In some implementations, the cathode contains a first catalyst and an anion-conducting polymer. In certain embodiments, the anode contains a second catalyst and a cation-conducting polymer. In some implementations, a cathode buffer layer, located between the cathode and PEM, contains an anion-conducting polymer. In some embodiments, an anode buffer layer, located between the anode and PEM, contains a cation-conducting polymer.

In embodiments employing an anion-conducting polymer in the cathode and/or in a cathode buffer layer, the MEA can decrease or block unwanted reactions that produce undesired products and decrease the overall efficiency of the cell. In embodiments employing a cation-conducting polymer in the anode and/or in an anode buffer layer can decrease or block unwanted reactions that reduce desired product production and reduce the overall efficiency of the cell.

For example, at levels of electrical potential used for cathodic reduction of CO₂, hydrogen ions may be reduced to hydrogen gas. This is a parasitic reaction; current that could be used to reduce CO₂ is used instead to reduce hydrogen ions. Hydrogen ions may be produced by various oxidation reactions performed at the anode in a CO₂ reduction reactor and may move across the MEA and reach the cathode where they can be reduced to produce hydrogen gas. The extent to which this parasitic reaction can proceed is a function of the concentration of hydrogen ions present at the cathode. Therefore, an MEA may employ an anion-conducting material in the cathode layer and/or in a cathode buffer layer. The anion-conducting material at least partially blocks hydrogen ions from reaching catalytic sites on the cathode. As a result, parasitic production of hydrogen gas decreases and the rate of production of CO or other carbon-containing product increases.

Another reaction that may be avoided is reaction of carbonate or bicarbonate ions at the anode to produce CO₂. Aqueous carbonate or bicarbonate ions may be produced from CO₂ at the cathode. If such ions reach the anode, they may react with hydrogen ions to produce and release gaseous CO₂. The result is net movement of CO₂ from the cathode to the anode, where it does not get reduced and is lost with oxidation products. To prevent the carbonate and bicarbonate ion produced at the cathode from reaching the anode, the anode and/or an anode buffer layer may include a cation-conducting polymer, which at least partially blocks the transport of negative ions such as bicarbonate ions to the anode.

Thus, in some designs, a bipolar membrane structure raises the pH at the cathode to facilitate CO₂ reduction while a cation-conducting polymer such as a proton-exchange layer prevents the passage of significant amounts of CO₂ and CO₂ reduction products (e.g., bicarbonate) to the anode side of the cell.

An example MEA 500 for use in CO_x reduction is shown in FIG. 5. The MEA 500 has a cathode layer 520 and an anode layer 540 separated by an ion-conducting polymer layer 560 that provides a path for ions to travel between the cathode layer 520 and the anode layer 540. In certain embodiments, the cathode layer 520 includes an anion-conducting polymer and/or the anode layer 540 includes a cation-conducting polymer. In certain embodiments, the cathode layer and/or the anode layer of the MEA are porous. The pores may facilitate gas and/or fluid transport and may increase the amount of catalyst surface area that is available for reaction.

The ion-conducting layer 560 may include two or three sublayers: a polymer electrolyte membrane (PEM) 565, an optional cathode buffer layer 525, and/or an optional anode buffer layer 545. One or more layers in the ion-conducting layer may be porous. In certain embodiments, at least one layer is nonporous so that reactants and products of the cathode cannot pass via gas and/or liquid transport to the anode and vice versa. In certain embodiments, the PEM layer 565 is nonporous. Example characteristics of anode buffer layers and cathode buffer layers are provided elsewhere herein. In certain embodiments, the ion-conducting layer includes only a single layer or two sublayers.

In some embodiments, a carbon oxide electrolyzer anode contains a blend of oxidation catalyst and an ion-conducting polymer. There are a variety of oxidation reactions that can occur at the anode depending on the reactant that is fed to the anode and the anode catalyst(s). In one arrangement, the oxidation catalyst is selected from the group consisting of metals and oxides of Ir, Pt, Ni, Ru, Pd, Au, and alloys thereof, IrRu, PtIr, Ni, NiFe, stainless steel, and combinations thereof. The oxidation catalyst can further contain conductive support particles such as carbon, boron-doped diamond, titanium, and any combination thereof.

As examples, the oxidation catalyst can be in the form of a structured mesh or can be in the form of particles. If the oxidation catalyst is in the form of particles, the particles can be supported by electronically conductive support particles. The conductive support particles can be nanoparticles. The conductive support particles may be compatible with the chemicals that are present in an electrolyzer anode when the electrolyzer is operating and are oxidatively stable so that they do not participate in any electrochemical reactions. It is especially useful if the conductive support particles are chosen with the voltage and the reactants at the anode in mind. In some arrangements, the conductive support particles are titanium, which is well-suited for high voltages. In other arrangements, the conductive support particles are carbon, which can be most useful at low voltages. In some embodiments, such conductive support particles are larger than the oxidation catalyst particles, and each conductive support particle can support one or more oxidation catalyst particles. In one arrangement, the oxidation catalyst is iridium ruthenium oxide. Examples of other materials that can be used for the oxidation catalyst include, but are not limited to, those listed above. It should be understood that many of these metal catalysts can be in the form of oxides, especially under reaction conditions.

As mentioned, in some embodiments, an anode layer of an MEA includes an ion-conducting polymer. In some cases, this polymer contains one or more covalently bound, negatively charged functional groups configured to transport mobile positively charged ions. Examples of the second ion-conducting polymer include ethanesulfonyl fluoride, 2-[1-[difluoro-[(trifluoroethenyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoro-, with tetrafluoroethylene, tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acid copolymer, other perfluorosulfonic acid polymers and blends thereof. Commercially available examples of cation-conducting polymers include e.g., Nafion 115, Nafion 117, and/or Nafion 211. Other examples of cationic conductive ionomers described above are suitable for use in anode layers.

There may be tradeoffs in choosing the amount of ion-conducting polymer in the anode. For example, an anode may include enough anode ion-conducting polymer to provide sufficient ionic conductivity, while being porous so that reactants and products can move through it easily. An anode may also be fabricated to maximize the amount of catalyst surface area that is available for reaction. In various arrangements, the ion-conducting polymer in the anode makes up about 10 and 90 wt %, or about 20 and 80 wt %, or about 25 and 70 wt % of the total anode mass. As an example, the ion-conducting polymer may make up about 5 and 20 wt % of the anode. In certain embodiments, the anode may be configured to tolerate relatively high voltages, such as voltages above about 1.2 V vs. a reversible hydrogen electrode. In some embodiments, an anode is porous in order to maximize the amount of catalyst surface area available for reaction and to facilitate gas and liquid transport.

In one example of a metal catalyst, Ir or IrOx particles (100-200 nm) and Nafion ionomer form a porous layer approximately 10 μm thick. Metal catalyst loading is approximately 0.5-3 g/cm². In some embodiments, NiFeOx is used for basic reactions.

In some embodiments, the MEA and/or the associated cathode layer is designed or configured to accommodate gas generated in situ. Such gas may be generated via various mechanisms. For example, carbon dioxide may be generated when carbonate or bicarbonate ions moving from the cathode toward the anode encounter hydrogen ions moving from the anode toward the cathode. This encounter may occur, for example, at the interface of anionic and cationic conductive ionomers in a bipolar MEA. Alternatively, or in addition, such contact may occur at the interface of a cathode layer and a polymer electrolyte membrane. For example, the polymer electrolyte membrane may contain a cationic conductive ionomer that allows transport of protons generated at the anode. The cathode layer may include an anion conductive ionomer.

Left unchecked, the generation of carbon dioxide or other gas may cause the MEA to delaminate or otherwise be damaged. It may also prevent a fraction of the reactant gas from being reduced at the anode.

The location within or adjacent to an MEA where a gas such as carbon dioxide is generated in situ may contain one or more structures designed to accommodate such gas and, optionally, prevent the gas from reaching the anode, where it would be otherwise unavailable to react.

In certain embodiments, pockets or voids are provided at a location where the gas is generated. These pockets or voids may have associated pathways that allow the generated gas to exit from the MEA, optionally to the cathode where, for example, carbon dioxide can be electrochemically reduced. In certain embodiments, an MEA includes discontinuities at an interface of anionic and cationic conductive ionomer layers such as at such interface in a bipolar MEA. In some embodiments, a cathode structure is constructed in a way that includes pores or voids that allow carbon dioxide generated at or proximate to the cathode to evacuate into the cathode.

In some embodiments, such discontinuities or void regions are prepared by fabricating in MEA in a way that separately fabricates anode and cathode structures, and then sandwiches to the two separately fabricated structures together in a way that produces the discontinuities or voids.

In some embodiments, and MEA structure is fabricated by depositing copper or other catalytic material onto a porous or fibrous matrix such as a fluorocarbon polymer and then coating the resulting structure with an anionic conductive ionomer. In some embodiments, the coated structure is then attached to the remaining MEA structure, which may include an anode and a polymer electrolyte membrane such as a cationic conductive membrane.

In some embodiments, a cathode has a porous structure and the/or an associated cathode buffer layer that has a porous structure. The pores may be present in an open cell format that allows generated carbon dioxide or other gas to find its way to the cathode.

In some MEAs, an interface between an anion conducting layer and a cation conducting layer (e.g., the interface of a cathode buffer layer and a PEM) includes a feature that resists delamination caused by carbon dioxide, water, or other material that may form at the interface. In some embodiments, the feature provides void space for the generated material to occupy until as it escapes from an MEA. In some examples, natural porosity of a layer such as an anion conducting layer provides the necessary void space. An interconnected network of pores may provide an escape route for carbon dioxide or other gas generated at the interface. In some embodiments, an MEA contains interlocking structures (physical or chemical) at the interface. In some embodiments, an MEA contains discontinuities at the interface. In some embodiments, an MEA contains of a fibrous structure in one layer adjacent the interface. A further discussion of interfacial structures between anion and cation conducting layers of MEAs is contained in Published PCT Application No. 2021/108446, published Jun. 3, 2021, and titled “MEMBRANE ELECTRODE ASSEMBLY FOR CO_x REDUCTION,” which is incorporated herein by reference in its entirety.

Other Embodiments and Conclusion

Although omitted for conciseness, embodiments of the system and/or method can include every combination and permutation of the various system components and the various method processes, wherein one or more instances of the method and/or processes described herein can be performed asynchronously (e.g., sequentially), concurrently (e.g., in parallel), or in any other suitable order by and/or using one or more instances of the systems, elements, and/or entities described herein.

As a person skilled in the art will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims.

Claims

1. A system comprising: a source of hydrogen;a CO2 purifier comprising: (a) an inlet for receiving impure CO2, (b) a cathode coupled to the inlet for receiving impure CO2, (c) an inlet for receiving hydrogen from the source of hydrogen; (d) an anode coupled to the inlet for receiving hydrogen; and (e) an outlet for providing purified CO2 and coupled to the anode; anda CO2 electrolyzer configured to receive the purified CO2 from the CO2 purifier, the CO2 electrolyzer comprising a cathode configured to electrochemically reduce CO2 to produce a carbon containing product.

2. The system of claim 1, wherein the CO2 purifier further comprises a membrane between the anode and the cathode, wherein the membrane is conductive to electrons and ions.

3. The system of claim 2, wherein the membrane is conductive to anions.

4. The system of claim 1, wherein the CO2 purifier further comprises a membrane between the anode and the cathode, wherein the membrane comprises a filler.

5. The system of claim 4, wherein the filler comprises a fluorocarbon polymer, a fullerene, a metal, a reduced graphene oxide, or any combination thereof.

6. The system of claim 1, wherein the CO2 purifier does not include wires to an external circuit.

7. The system of claim 1, wherein the anode and the cathode of the CO2 purifier are not connected to electrical wires.

8. The system of claim 1, wherein the system is configured to transport O2 produced by the CO2 electrolyzer to the cathode of the CO2 purifier.

9. The system of claim 1, wherein the system is configured to transport O2 produced by the water electrolyzer to the cathode of the CO2 purifier.

10. The system of claim 1, wherein the carbon containing product is carbon monoxide.

11. The system of claim 10, wherein the system is configured to combine the carbon monoxide with a portion of the hydrogen produced by the water electrolyzer.

12. The system of claim 1, wherein the CO2 electrolyzer is directly coupled to the CO2 purifier and is configured to directly receive the purified CO2 from the CO2 purifier.

13. The system of claim 1, further comprising a controller configured to cause electrical energy to be applied to the CO2 electrolyzer to cause the cathode to electrochemically reduce the CO2 to produce the carbon containing product.

14. The system of claim 13, wherein the controller is further configured to cause electrical energy to be applied to the water electrolyzer to cause the water electrolyzer to produce the hydrogen.

15. The system of claim 1, wherein the carbon containing product comprises CO, a hydrocarbon, formic acid, an alcohol, or any combination thereof.

16. The system of claim 1, wherein the source of hydrogen is a water electrolyzer configured to electrolyze water and produce the hydrogen.

17. A method comprising: (a) purifying CO2 from an impure CO2 stream by (i) contacting the impure CO2 stream with a cathode of a CO2 purifier,(ii) contacting hydrogen with an anode of the CO2 purifier, and(iii) recovering purified CO2 from an outlet of the CO2 purifier, which outlet is coupled to the anode of the CO2 purifier; and(b) electrochemically reducing the purified CO2 by an electrolysis process comprising: (i) providing the purified CO2 to a CO2 electrolyzer, and(ii) electrochemically reducing the purified CO2 electrolyzer at a cathode of the CO2 electrolyzer to produce a carbon containing product.

18. The method of claim 17, further comprising electrolyzing water to produce the hydrogen.

19. The method of claim 17, wherein the CO2 purifier further comprises a membrane between the anode and the cathode, wherein the membrane is conductive to electrons and ions.

20. The method of claim 19, wherein the membrane is conductive to anions.

21. The method of claim 17, wherein the CO2 purifier further comprises a membrane between the anode and the cathode, wherein the membrane comprises a filler.

22. The method of claim 21, wherein the filler comprises a fluorocarbon polymer, a fullerene, a metal, a reduced graphene oxide, or any combination thereof.

23. The method of claim 17, wherein purifying CO2 from the impure CO2 stream is performed without the CO2 purifier receiving electrical energy from an external circuit.

24. The method of claim 17, further comprising contacting oxygen, along with the impure CO2 stream, with the cathode of the CO2 purifier.

25. The method of claim 24, further comprising transporting O2 produced by the CO2 electrolyzer to the cathode of the CO2 purifier.

26. The method of claim 17, wherein the carbon containing product is carbon monoxide.

27. The method of claim 26, further comprising combining the carbon monoxide with hydrogen to produce syngas.

28. The method of claim 17, further comprising directly transporting the purified CO2 from the CO2 purifier to an inlet of the CO2 electrolyzer.

29. The method of claim 17, further comprising applying electrical energy to the CO2 electrolyzer to cause the cathode to electrochemically reduce the CO2 to produce the carbon containing product, and applying electrical energy to a water electrolyzer to cause the water electrolyzer to produce the hydrogen.

30. The method of claim 17, wherein the carbon containing product comprises CO, a hydrocarbon, formic acid, an alcohol, or any combination thereof.