Interfaces for carbon oxide electrolyzer bipolar membranes.

Abstract

Presented herein are membrane electrode assemblies (MEAs) for reducing carbon oxides. According to various embodiments, the MEAs are configured to reduce CO 2 , including by mitigating the deleterious effects of current fluctuations on the MEA. X A bipolar membrane MEA with an interface made of nanoparticles is described, which is designed to address the unique challenges of

Description

[Technical Field]

[0001] Incorporation by Reference The PCT Request Form is filed contemporaneously with this application as part of the present application. Each application to which this application claims benefit or priority identified in the contemporaneously filed PCT Request Form is incorporated herein by reference in its entirety for all purposes. [Background technology]

[0002] Anthropogenic carbon dioxide emissions are linked to climate change, and growing concerns about global greenhouse gas emissions have led to increased interest in technologies that can recycle CO2 into high-value products.

[0003] CO X The electrochemical reduction of CO (e.g., CO, CO, or a combination thereof) only combines three inputs: CO X、 These inputs are a source of protons, and electricity. These inputs are converted into fuels, chemicals, and other products such as methanol, ethanol, carbon monoxide, and acetic acid. However, achieving industrial-scale electrochemical reactions has been difficult, in part due to a lack of suitable reactors. One issue that must be addressed is the potentially variable or unreliable power supply. Interruptions due to power outages and planned shutdowns for maintenance and recovery processes can lead to degradation of electrochemical reactor components. Therefore, a robust electrochemical reactor that can withstand electrical fluctuations can be advantageous.

[0004] The discussion of the background art provided herein is intended to generally present the context for the present disclosure. The work of the presently named inventors, to the extent that it is described in this background art section, and work in the described aspects that may not have qualified as art at the time of filing this application, are not admitted expressly or implicitly as prior art to the present disclosure. Summary of the Invention

[0005] Presented herein are membrane electrode assemblies (MEAs) for reducing carbon oxides. According to various embodiments, the MEAs are configured to reduce CO 2 , including by mitigating the deleterious effects of current fluctuations on the MEA. X A bipolar membrane MEA with an interface area that mitigates or prevents these effects is described.

[0006] Thus, in a first aspect, the present disclosure encompasses a membrane electrode assembly. In some embodiments, the membrane electrode assembly comprises a cathode catalyst layer, an anode catalyst layer, and a bipolar membrane disposed between the cathode catalyst layer and the anode catalyst layer, the bipolar membrane comprising an anion-conducting polymer layer, a cation-conducting polymer layer, and an interfacial region between the anion-conducting polymer layer and the cation-conducting polymer layer, the interfacial region comprising nanoparticles.

[0007] In some embodiments, the interface region is about 1 to 10 micrometers thick.

[0008] In some embodiments, the interface region is about 1 to 5 micrometers thick.

[0009] In some embodiments, the ratio of the thickness of the anion-conducting polymer layer to the thickness of the interfacial region is at least 10:1.

[0010] In some embodiments, the nanoparticles are carbon nanoparticles or magnesium oxide nanoparticles.

[0011] In some embodiments, the interfacial region also includes an ion-conducting polymer.

[0012] In some embodiments, the nanoparticles are iridium, platinum, titanium, or gold.

[0013] In some embodiments, the cation-conducting polymer layer is disposed between the anode catalyst layer and the anion-conducting polymer layer.

[0014] In some embodiments, the cathode catalyst layer comprises a reduction catalyst and an anion-conducting polymer.

[0015] In some embodiments, the anode catalyst layer comprises an oxidation catalyst and a cation-conducting polymer.

[0016] In a second aspect, the present disclosure provides a CO X In some embodiments, the membrane electrode assembly includes a CO reduction reactor. X an anode catalyst layer having a catalyst configured to reduce CI, an anion-conducting polymer layer, a cation-conducting polymer layer, and an interfacial region between the anion-conducting polymer layer and the cation-conducting polymer layer, the interfacial region comprising nanoparticles.

[0017] In some embodiments, the interface region is about 1 to 10 micrometers thick.

[0018] In some embodiments, the interface region is about 1 to 5 micrometers thick.

[0019] In some embodiments, the ratio of the thickness of the anion-conducting polymer layer to the thickness of the interfacial region is at least 10:1.

[0020] In some embodiments, the nanoparticles are carbon nanoparticles or magnesium oxide nanoparticles.

[0021] In some embodiments, the interfacial region also includes an ion-conducting polymer.

[0022] In some embodiments, the nanoparticles comprise iridium, platinum, titanium, or gold.

[0023] In some embodiments, the cation-conducting polymer layer is disposed between the anode catalyst layer and the anion-conducting polymer layer.

[0024] In some embodiments, the cathode catalyst layer also includes an anion-conducting polymer.

[0025] In some embodiments, the anode catalyst layer comprises an oxidation catalyst and a cation-conducting polymer.

[0026] In some embodiments, CO X The reduction reactor is a carbon dioxide reduction reactor.

[0027] In a third aspect, the present disclosure provides a CO X In some embodiments, the method includes electrochemically reducing carbon oxides to CO X providing a CO reduction reactor; X and electrochemically reducing carbon oxides at the cathode of the electrolyzer to produce carbon-containing products, X The reduction reactor comprises a membrane electrode assembly having a cathode catalyst layer, an anode catalyst layer, and a bipolar membrane disposed between the cathode catalyst layer and the anode catalyst layer, the bipolar membrane comprising an anion-conducting polymer layer, a cation-conducting polymer layer, and an interfacial region between the anion-conducting polymer layer and the cation-conducting polymer layer, the interfacial region comprising nanoparticles.

[0028] In some embodiments, CO X The reduction reactor is subjected to fluctuations in electrical current.

[0029] In some embodiments, the current fluctuations are caused by a recovery process, a power interruption, a current reversal, or a power outage.

[0030] In some embodiments, the carbon oxide is carbon dioxide.

[0031] In some embodiments, the carbon-containing product is carbon monoxide, a hydrocarbon, formic acid, an alcohol, or a combination thereof.

[0032] In some embodiments, the interface region is about 1 to 10 micrometers thick.

[0033] In some embodiments, the interface region is about 1 to 5 micrometers thick.

[0034] In some embodiments, the ratio of the thickness of the anion-conducting polymer layer to the thickness of the interfacial region is at least 10:1.

[0035] In some embodiments, the nanoparticles are carbon nanoparticles or magnesium oxide nanoparticles.

[0036] In some embodiments, the interfacial region also includes an ion-conducting polymer.

[0037] In some embodiments, the nanoparticles comprise iridium, platinum, titanium, or gold.

[0038] In some embodiments, the cation-conducting polymer layer is disposed between the anode catalyst layer and the anion-conducting polymer layer.

[0039] In some embodiments, the anion-conducting polymer layer is disposed between the cathode catalyst layer and the cation-conducting polymer layer.

[0040] In some embodiments, the cathode catalyst layer comprises a reduction catalyst and an anion-conducting polymer.

[0041] In some embodiments, the anode catalyst layer comprises an oxidation catalyst and a cation-conducting polymer.

[0042] In a fourth aspect, the present disclosure encompasses a membrane electrode assembly. In some embodiments, the membrane electrode assembly comprises a cathode catalyst layer, an anode catalyst layer, and a bipolar membrane disposed between the cathode catalyst layer and the anode catalyst layer, the bipolar membrane comprising an anion-conducting polymer layer, a cation-conducting polymer layer, and an interfacial region between the anion-conducting polymer layer and the cation-conducting polymer layer, the interfacial region including the ion-conducting polymer layer and nanoparticles dispersed therein.

[0043] In some embodiments, the ion-conducting polymer layer comprises a sulfonated fluoropolymer.

[0044] In some embodiments, the sulfonated fluoropolymer is a sulfonated tetrafluoroethylene-based fluoropolymer copolymer.

[0045] In some embodiments, the nanoparticles are carbon nanoparticles.

[0046] In some embodiments, the interface region is about 1 to 10 micrometers thick.

[0047] In some embodiments, the interface region is about 1 to 5 micrometers thick.

[0048] In some embodiments, the ratio of ion-conducting polymer to carbon nanoparticles in the ion-conducting polymer layer is from about 2:1 weight percent to about 1:0.1 weight percent.

[0049] In some embodiments, the ratio of ion-conducting polymer to carbon nanoparticles in the ion-conducting polymer layer is about 1:1 weight percent.

[0050] In some embodiments, the ratio of the thickness of the anion-conducting polymer layer to the thickness of the interfacial region is at least 10:1.

[0051] In some embodiments, the cation-conducting polymer layer is disposed between the anode catalyst layer and the anion-conducting polymer layer.

[0052] In some embodiments, the anion-conducting polymer layer is disposed between the cathode catalyst layer and the cation-conducting polymer layer.

[0053] In some embodiments, the cathode catalyst layer comprises a reduction catalyst and an anion-conducting polymer.

[0054] In some embodiments, the ion-conducting polymer in the interfacial region is the same polymer as the cation-conducting polymer in the cation-conducting polymer layer.

[0055] In some embodiments, the ion-conducting polymer in the interfacial region is the same polymer as the anion-conducting polymer in the anion-conducting polymer layer.

[0056] In some embodiments, the interfacial region comprises an anion-conducting polymer and a cation-conducting polymer.

[0057] In some embodiments, the ion-conducting polymer in the interfacial region is a different cation-conducting polymer than the cation-conducting polymer in the cation-conducting polymer layer.

[0058] In some embodiments, the ion-conducting polymer in the interfacial region is a different anion-conducting polymer than the anion-conducting polymer in the anion-conducting polymer layer. These and other aspects of the disclosure are further described below with reference to the drawings. [Brief explanation of the drawings]

[0059] [Figure 1]FIG. 1 is a schematic diagram of a carbon dioxide (CO) electrolysis device configured to receive water and CO (e.g., humidified or dry gaseous CO) as reactants at a cathode and output carbon monoxide (CO) as a product, according to certain disclosed embodiments. [Figure 2] FIG. 1 is a schematic diagram of a bipolar interface of an MEA according to certain disclosed embodiments. [Figures 3A-3D] FIG. 1 is a schematic diagram of a bipolar interface of an MEA configured to resist delamination in accordance with certain disclosed embodiments. [Figure 4] FIG. 1 is a schematic diagram of layers of an MEA including an anion-conducting polymer layer (AEM) and a polymer electrolyte membrane (PEM), according to certain disclosed embodiments. [Figure 5] FIG. 1 is a block diagram that schematically illustrates an exemplary electrolysis device for reducing carbon oxides, which may include cells including MEAs (membrane electrode assemblies), according to certain disclosed embodiments. [Figure 6] 1 is a graph of a study comparing a membrane electrode assembly without carbon nanoparticles (control) with a membrane electrode assembly having an interface between carbon nanoparticles and an ion-conducting polymer (CNI) in the presence of an electric current over time, according to certain embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0060] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the presented embodiments. The disclosed embodiments may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail in order to avoid unnecessarily obscuring the disclosed embodiments. While the disclosed embodiments will be described in connection with specific embodiments, it will be understood that they are not intended to limit the disclosed embodiments.

[0061] definition As used herein, the term "about" is understood to contemplate slight increases and / or decreases beyond the stated value, where the changes do not materially affect the desired function of the parameter beyond the stated value(s). In some cases, "about" includes ±10% of the stated value. As used herein, the term modifies any stated value, range of values, or one or more end points of a range.

[0062] As used herein, the terms "top," "bottom," "upper," "above," "below," "over," "above," and "below" are used to indicate relative relationships between structures. The use of these terms does not indicate or require that a particular structure must be located in a particular location within the device.

[0063] "Electrochemical cell" includes electrolysis devices such as CO2 electrolyzers and water electrolyzers. It also includes some forms of CO2 purification devices that utilize faradaic reactions, particularly at the anode and / or cathode.

[0064] "Carbon oxides" (CO X ) include carbon dioxide (CO2), carbon monoxide (CO), carbonate ions (CO3 2- ), bicarbonate ion (HCO3 - ), and any combination thereof.

[0065] A "mixture" contains two or more components and may contain components other than those identified unless otherwise specified.

[0066] A "porosity enhancer" is a substance that increases the void space within a layer or network. A porosity enhancer can increase the void space within a polymer membrane layer.

[0067] A "voltage attenuator" is an agent that reduces the voltage rise that occurs after current reduction and / or shutoff of a carbon dioxide reduction reactor.

[0068] "Ion-conducting polymer" is used herein to describe a polymer electrolyte having a specific conductivity for anions and / or cations greater than about 1 mS / cm.

[0069] The terms "micrometer" and "micron," and the abbreviations "μm" and "um," are used interchangeably to refer to microns. Unless otherwise specified, ranges described herein (e.g., 10 micrometers to 20 micrometers, 0.25 to 127, 1 to 90%, etc.) include the endpoints of those ranges.

[0070] Introduction and Background The membrane electrode assembly (MEA) is as described herein. X CO can be used in the reduction reactor. X are carbon dioxide (CO2), carbon monoxide (CO), and CO3 2- (carbonate ion), HCO3 - (bicarbonate ions), or a combination thereof. The MEA includes an anode layer, a cathode layer, an electrolyte, and optionally one or more other layers. The layers can be solid and / or flexible materials. The layers can include polymers, such as ion-conducting polymers.

[0071] In use, the cathode of the MEA generates CO by combining three inputs: X Promotes the electrochemical reduction of CO X , ions (e.g., protons), and electrons that chemically react. Reduction reactions can produce CO, hydrocarbons, and / or organic compounds containing oxygen and hydrogen, such as methanol, ethanol, and acetic acid. In use, the anode of the MEA promotes electrochemical oxidation reactions, such as the electrolysis of water, to produce elemental oxygen and protons. The cathode and anode may contain catalysts to promote the respective reactions.

[0072] The configuration and arrangement of the layers in the MEA allows for XHigh yields of reduction products may be promoted. To this end, the MEA may promote any one or more of the following conditions: (a) minimal parasitic reduction reactions (non-CO) at the cathode; X (b) CO reduction reaction at the anode or elsewhere in the MEA X (c) maintains the physical integrity of the MEA during the reaction (e.g., prevents delamination of the MEA layers); and (d) CO X (e) preventing crossover of reduction products; (f) maintaining a favorable cathode / anode environment for oxidation / reduction; (g) providing a pathway for desired ions to travel between the cathode and anode while blocking undesired ions; and (h) minimizing voltage losses.

[0073] CO X Specific issues regarding the reduction of Polymer-based membrane assemblies such as MEAs have been used in various electrolysis systems, such as water electrolyzers, and in various galvanic systems, such as fuel cells. X The reduction of ions causes problems that do not occur, or occur to a lesser extent, in water electrolysis devices and fuel cells.

[0074] For example, in many applications, CO X The reduction MEAs must have a lifetime of at least about 50,000 hours (about 5 years of continuous operation), which is significantly longer than the expected lifetime of fuel cells for automotive applications (about 5,000 hours). X The reduction MEA is required to have a lifespan of more than 50,000 hours (approximately 5 years of continuous operation), which is significantly longer than the expected lifespan of a fuel cell for automotive applications (approximately 5,000 hours). X For reduction MEAs, at least about 500 cm 2 An electrode having a geometric surface area (without considering pores and other non-planar features) of 0.1 mm can be used.

[0075] CO XReduction reactions can be carried out in an operating environment that facilitates mass transport of specific reactant and product species and suppresses parasitic reactions. Fuel cell and water electrolysis MEAs often cannot create such an operating environment. For example, such MEAs may promote undesirable parasitic reactions, such as gaseous hydrogen generation at the cathode and / or gaseous CO production at the anode.

[0076] In some systems, CO X The rate of reduction is determined by the amount of gaseous CO at the cathode. X Limited by the availability of reactants. In contrast, the rate of water electrolysis is not significantly limited by the availability of reactants. Liquid water tends to be readily accessible to the cathode and anode, allowing the electrolyzer to operate at close to the maximum possible current density.

[0077] MEA Configuration General layout of the MEA In certain embodiments, the MEA has a cathode layer, an anode layer, and a polymer electrolyte membrane (PEM) between the anode and cathode layers. The polymer electrolyte membrane provides ionic communication between the anode and cathode layers while preventing electronic communication that could result in a short circuit. The cathode layer includes a reduction catalyst and a first ion-conducting polymer. The cathode layer may also include an ionic and / or electronic conductor. The anode layer includes an oxidation catalyst and a second ion-conducting polymer. The anode layer may also include an ionic and / or electronic conductor. The PEM includes a third ion-conducting polymer.

[0078] In some embodiments, the MEA includes a cathode buffer layer between the cathode layer and the polymer electrolyte membrane, the cathode buffer including a fourth ion-conducting polymer.

[0079] In some embodiments, the MEA includes an anode buffer layer between the anode layer and the polymer electrolyte membrane, the anode buffer comprising a fifth ion-conducting polymer.

[0080] Three classes of ion-conducting polymers are available for specific MEA designs: anion conductors, cation conductors, and mixed cation and anion conductors. In some embodiments, at least two of the first, second, third, fourth, and fifth ion-conducting polymers are from different classes of ion-conducting polymers.

[0081] Conductivity and selectivity in ion-conducting polymer MEA layers The term "ion-conducting polymer" is used herein to describe a polymer electrolyte having a specific conductivity for anions and / or cations greater than about 1 mS / cm. The term "anion conductor" refers to an ion-conducting polymer that conducts primarily anions (although there may still be a small amount of cation conduction) and has an anion mobility number greater than about 0.85 at a thickness of about 100 microns. The terms "cation conductor" and / or "cation-conducting polymer" refer to an ion-conducting polymer that conducts primarily cations (e.g., there may still be an incidental amount of anion conduction) and has a cation mobility number greater than about 0.85 at a thickness of about 100 microns. For ion-conducting polymers described as conducting both anions and cations ("cation and anion conductors"), neither the anions nor the cations have a mobility number greater than about 0.85 or less than about 0.15 at a thickness of about 100 microns. To say that a material conducts ions (anions and / or cations) is to say that the material is an ion-conducting material or ionomer. Examples of each class of ion-conducting polymer are given in the table below. [Table 1]

[0082] Some Class A ion-conducting polymers are known by trademarks such as 2259-60 (Pall RAI), AHA (Tokuyama Co.), fumasep® FAA- (fumatech GmbH), Sustanion®, Morgane ADP (Solvay), or Tosoh anion exchange membrane material Tosflex® SF-17. Further Class A ion-conducting polymers include HNN5 / HNN8 (Ionomr), FumaSep (Fumatech), TM1 (Orion), and PAP-TP (W7energy). Some Class C ion-conducting polymers are known by various formulations, such as the trade names Nafion® (DuPont™), GORE-SELECT® (Gore), fumapem® (fumatech GmbH), and Aquivion® PFSA (Solvay).

[0083] Polymer Structure Examples of polymer structures that can include ionizable or ionic moieties and can be used as ion-conducting polymers in the MEAs described herein are provided below. Ion-conducting polymers can be suitably used in any of the MEA layers that include ion-conducting polymers. Charge conduction through the material can be controlled by the type and amount of charge provided by the ionizable / ionic moieties (e.g., anionic and / or cationic charges on the first structure). Furthermore, the composition can include polymers, homopolymers, copolymers, block copolymers, polymer blends, other polymer-based forms, or other useful combinations of repeating monomer units. As described below, the ion-conducting polymer layer can 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., two or more ion-conducting polymer layers of an MEA) can be crosslinked.

[0084] Non-limiting monomer units include one or more of the following: [ka] wherein Ar is an optionally substituted arylene or aromatic; Ak is an optionally substituted alkylene group, haloalkylene group, aliphatic group, heteroalkylene group, or heteroaliphatic group; and L is a linking moiety (e.g., any described herein) or —C(R 7 )(R 8 ). Still other non-limiting monomer units can include arylene, aryleneoxy, alkylene, or combinations thereof, such as optionally substituted (aryl)(alkyl)ene (e.g., -Ak-Ar- or -Ak-Ar-Ak- or -Ar-Ak-, where Ar is an optionally substituted arylene and Ak is an optionally substituted alkylene). One or more of the monomer units can be optionally substituted with one or more ionizable or ionic moieties (e.g., as described herein).

[0085] One or more monomer units can be combined to form a polymer unit. Non-limiting polymer units include any of the following:

[0086] [ka] where Ar, Ak, L, n, and m can be any of those described herein. In some embodiments, each m is independently an integer of 0 or greater than 1. In other embodiments, Ar can include two or more arylene or aromatic groups.

[0087] 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 of the blocks or regions described herein.

[0088] Examples of polymer structures include those set forth in any one of formulas (I) to (V) and (X) to (XXXIV), or salts thereof. In some embodiments, the polymer structure is a copolymer and includes a first polymer structure selected from any one of formulas (I) to (V), or a salt thereof, and a second polymer structure including an optionally substituted aromatic, an optionally substituted arylene, a structure selected from any one of formulas (I) to (V), and (X) to (XXXIV), or a salt thereof.

[0089] In one embodiment, the ion-conducting polymer has a weight average molecular weight (Mw) of at least 10,000 g / mol, or from about 5,000 to 2,500,000 g / mol, and in another embodiment, a number average molecular weight (Mn) of at least 20,000 g / mol, or from about 2,000 to 2,500,000 g / mol.

[0090] In any embodiment described 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 1 to 1,000,000, e.g., 10 to 1,000,000, 100 to 1,000,000, 200 to 1,000,000, 500 to 1,000,000, or 1,000 to 1,000,000.

[0091] Non-limiting polymer structures include: [ka] or a salt thereof, wherein: R 7 , R 8 , R 9 , and R 10 are each independently an electron-withdrawing moiety, H, an optionally substituted aliphatic, alkyl, heteroaliphatic, heteroalkylene, aromatic, aryl, or arylalkylene, where R 7 or R 8 At least one of R may contain an electron-withdrawing moiety, or R 7and R 8 or R 9 and R 10 can be combined to form an optionally substituted cyclic group. Ar includes or is an optionally substituted aromatic or arylene (e.g., any of those described herein); each n is independently an integer greater than or equal to 1; Each of rings a-c is optionally substituted; Each of rings a to c can be optionally substituted; rings a to c, R 7 , R 8 , R 9 , and R 10 optionally includes an ionizable or ionic moiety. Further non-limiting polymer structures can include one or more of the following: [ka] or a salt thereof, wherein R 7 can be any of those described herein (e.g., formulas (I)-(V)); n is 1 or greater; Each L8A, LB', and LB ’’ is independently a connected part: each X 8A , X 8A’ , X 8A’’ , XB', and X B’’ is independently an ionizable or ionic moiety. Still other polymer structures include: [ka] TIFF2025535276000008.tif211159TIFF2025535276000009.tif102159 or salts thereof, During the ceremony, R 1 , R2 , R 3 , R 7 , R 8 , R 9 , and R 10 are each independently an electron-withdrawing moiety, H, an optionally substituted aliphatic, alkyl, heteroaliphatic, heteroalkylene, aromatic, aryl, or arylalkylene, where R 7 or R 8 At least one of R may contain an electron-withdrawing moiety, or R 7 and R 8 or R 9 and R 10 can be combined to form an optionally substituted cyclic group. each Ak is or includes an optionally substituted aliphatic, alkylene, haloalkylene, heteroaliphatic, or heteroalkylene; each Ar is or includes an optionally substituted arylene or aromatic; L, L 1 , L 2 , L 3 , and L 4 each is independently a linking moiety; each of n, n1, n2, n3, n4, m, m1, m2, and m3 is independently an integer of 1 or greater; q is 0, 1, 2, or more; Each of rings a-i is optionally substituted; Each ring a~i, R 7 , R 8 , R 9 , and R 10 optionally includes an ionizable or ionic moiety.

[0092] In certain embodiments (e.g., Formula (XIV) or (XV)), each of the nitrogen atoms on ring a and / or ring b is substituted with an optionally substituted aliphatic, alkyl, aromatic, aryl, ionizable, or 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 or ionic moiety (e.g., any of those described herein). In other embodiments, oxygen atoms present in the polymer structure (e.g., Formula XXVIII) can be substituted with an alkali dopant (e.g., K + ) can be associated with

[0093] In particular examples, Ar, one or more of rings a-i (e.g., rings a, b, f, g, h, or i), L, L 1 , L 2 , L 3 , L 4 , Ak, R 7 , R 8 , R 9 , and / or R 10 can be optionally substituted with one or more ionizable or ionic moieties and / or one or more electron-withdrawing groups. Ar, rings (e.g., rings a-i), L, Ak, R 7 , R 8 , R 9 , and R 10 Further non-limiting substituents include one or more of those 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.

[0094] In some embodiments, R 1 , R 2 , and R 3 Each of R is independently H, optionally substituted aromatic, aryl, aryloxy, or arylalkylene. In other embodiments (e.g., of Formulas (I)-(V) or (XII)), R 7In yet another embodiment, R 8 , R 9 , and / or R 10 includes an ionizable or ionic moiety.

[0095] As an example, a polymer subunit may lack an ionic moiety. Alternatively, the polymer subunit may include an ionic moiety on the Ar group, the L group, both the Ar group and the L group, or may be incorporated as part of the L group. Non-limiting examples of ionizable and ionic moieties include cationic groups, anionic groups, and multi-ionic groups described herein.

[0096] In any of the embodiments described herein, the electron withdrawing moiety may 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 ), sulfuric acid (e.g., -OS(=O)2(OR S1 )), sulfonate (—SO3H), sulfonyl (e.g., —SO2—CF3), difluoroboranyl (—BF2), borono (B(OH)2), thiocyanato (—SCN), or piperidinium.

[0097] Still other non-limiting phosphate groups can include derivatives of phosphoric acid, such as orthophosphate, pyrophosphate, tripolyphosphate, tetrapolyphosphate, trimetaphosphate, and / or phosphoric anhydride, or combinations thereof.

[0098] Further polymer units include poly(benzimidazole) (PBI), polyphenylene (PP), polyimide (PI), poly(ethyleneimine) (PEI), sulfonated polyimide (SPI), polysulfone (PSF), sulfonated polysulfone (SPSF), poly(ether ether ketone) (PEEK), PEEK containing cardo groups (PEEK-WC), polyethersulfone (PES), sulfonated polyethersulfone (SPES), sulfonated poly(ether ether ketone) (SPEEK), SPEEK with cardo groups (SPEEK-WC), poly(p-phenylene oxide) (PPO), sulfonated polyphenylene oxide (SPPO), ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), and polytetrafluoroethylene (PTFE). tetrafluoroethylene (PTFE), poly(epichlorohydrin) (PECH), poly(styrene) (PS), sulfonated poly(styrene) (SPS), hydrogenated poly(butadiene-styrene) (HPBS), styrene divinylbenzene copolymer (SDVB), styrene-ethylene-butylene-styrene (SEBS), sulfonated bisphenol-A-polysulfone (SPSU), poly(4-phenoxybenzoyl-1,4-phenylene) (PPBP), sulfonated poly(4-phenoxybenzoyl-1,4-phenylene) (SPPBP), poly(vinyl alcohol) (PVA), poly(phosphazenes), poly(aryloxyphosphazenes), polyetherimides, and combinations thereof.

[0099] Crosslinking In some embodiments, crosslinking exists within and / or between ion-conducting polymer layers. Crosslinking within the material is facilitated by the use of a crosslinking reagent. For example, the composition can include polymer units, and a crosslinking reagent can be used to provide crosslinks between the polymer units. For example, if the polymer units (P1 and P2) include leaving groups, a diamine crosslinking reagent (e.g., H2N-Ak-NH2) can be used to react with the polymer units by displacing the leaving groups and forming an amino-containing crosslinker within the composition (e.g., to form P1-NH-Ak-NH-P2). The crosslinker can be introduced by forming a polymer composition and then exposing the composition to a crosslinking reagent to form the crosslinker.

[0100] Depending on the functional groups present in the material, cross-linking reagents can include nucleophilic groups (e.g., amine or hydroxyl) or electrophilic groups (e.g., carbonyl). Thus, non-limiting cross-linking reagents can include amine-containing reagents, hydroxyl-containing reagents, carboxylic acid-containing reagents, acyl halide-containing reagents, and the like. Additional cross-linking reagents include: [ka] and the like: Ak is an optionally substituted aliphatic or alkylene; Ar is an optionally substituted aromatic or arylene; L is a linking moiety (e.g., a covalent bond, optionally substituted alkylene, aliphatic, etc., any of those described herein); L3 is an integer of 2 or greater (e.g., 2, 3, 4, 5, 6, or more); X is halo, hydroxyl, optionally substituted amino (e.g., NR N1 R N2 , where R N1 and R N2are independently H or optionally substituted alkyl), hydroxyl, carboxyl, acyl halide (e.g., —C(O)—R, where R is halo), carboxaldehyde (e.g., —C(O)H), or optionally substituted alkyl. Non-limiting cross-linking reagents can include terephthalaldehyde, glutaraldehyde, ortho-xylene, para-xylene, meta-xylene, or polyamines such as diamines, triamines, tetraamines, pentaamines, 1,6-diaminohexane (hexanediamine), 1,4-diaminobutane, 1,8-diaminooctane, propane-1,2,3-triamine, [1,1′:3′,1″-terphenyl]-4,4″,5′-triamine, and the like.

[0101] After reaction with the cross-linking reagent, the composition can contain one or more cross-linking agents within the composition. If the cross-linking reagent is divalent, the cross-linking agent can be present between any two of the polymer structures, polymer units, and ionizable / ionic moieties (e.g., between two polymer units, between two ionizable / ionic moieties, etc.). If the cross-linking reagent is trivalent or greater, the cross-linking agent can be present between any n polymer units, linking moieties, ionizable moieties, and / or ionic moieties. Non-limiting cross-linking agents present in the composition include those formed after reaction with the cross-linking reagent. Thus, examples of cross-linking agents include: [ka] wherein Ak is an optionally substituted aliphatic or optionally substituted alkylene, Ar is an optionally substituted aromatic or optionally substituted arylene, L is a linking moiety (e.g., a covalent bond, optionally substituted alkylene, optionally substituted aliphatic, etc., as described herein), L3 is an integer of 2 or greater (e.g., 2, 3, 4, 5, 6, or more), and X' is a reacted form of X. In some embodiments, X' is absent, -O-, -NR N1 -, -C(O)-, or -Ak-; RN1 is H or optionally substituted alkyl, and Ak is optionally substituted alkylene, optionally substituted heteroalkylene, optionally substituted aliphatic, or optionally substituted heteroaliphatic.

[0102] Ionizable and Ionizable Moieties The polymers described herein include one or more ionizable or ionic moieties. Such moieties may include anionic or cationic charges, such as in ionic moieties. Alternatively, the ionizable moieties include functional groups that can be readily converted to ionic moieties, such as carboxyl (-COH) ionizable moieties, which can be readily deprotonated to form carboxylate anions (-CO). As used herein, the terms "ionizable" and "ionic" are used interchangeably.

[0103] Moieties can be characterized as acidic moieties (e.g., moieties that can be deprotonated or that can carry a negative charge) or basic moieties (e.g., moieties that can be protonated or that can carry a positive charge). In certain embodiments, moieties can be multi-ionic moieties, which can include multiple acidic moieties, multiple basic moieties, or combinations thereof (e.g., zwitterionic moieties, etc.). Further moieties can include zwitterionic moieties, such as those that include an anionic moiety (e.g., hydroxyl or deprotonated hydroxyl) and a cationic moiety (e.g., ammonium).

[0104] The ionic moieties herein can be connected to the parent structure via one or more linking moieties. Furthermore, a single ionic moiety can extend from a single linking moiety, or multiple ionic moieties can have one or more linking moieties therebetween. For example, an ionic moiety can have any of the following structures: -L A -X A or -L A -(L A’ -X A )L2 or -L A -(X A -L A’ -X A’ ) L2 or -L A -X A -L A’ -X A’ -L A" -X A” , where each L A , L A’ , and L.A. ’’ is a linking moiety (e.g., any of those described herein); each X A , X A’ , and X A’’ L independently comprises an acidic moiety, a basic moiety, a polyionic moiety, a cationic moiety, or an anionic moiety; and L is an integer of 1, 2, 3, or more (e.g., 1 to 20). A and L A1’ is -(CH2) L1 -, -O(CH2) L1 -, -(CF2) L1 -, -O(CF2) L1 - or -S(CF2) L1 -, L1 is an integer from 1 to 3; X A is any ionizable or ionic moiety described herein.

[0105] Non-limiting ionizable or ionic moieties include carboxy (-COH), carboxylate anion (-COH), - ), guanidinium cation, sulfo (-SO2OH), sulfonate anion (-SO2O - ), sulfonium cation, sulfate, sulfate ion, phosphono (e.g., -P(=O)(OH)2), phosphonate anion, phosphate, phosphate anion, phosphonium cation, phosphazenium cation, amino (e.g., -NR N1 R N2), ammonium cations (e.g., aliphatic or aromatic ammonium), heterocyclic cations (e.g., piperidinium, pyrrolidinium, pyridinium, pyrazolium, imidazolium, quinolinium, isoquinolinium, acridinium, quinolinium, isoquinolinium, acridinium, pyridazinium, pyrimidinium, pyrazinium, phenazinium, 1,4-diazabicyclo[2.2.2]octane (DABCO) cation, 4-methyl-1,4-diazoniabicyclo[2.2.2]octan-1-yl (MAABCO), 1-benzyl-1,4-diazoniabicyclo[2.2.2]octane (BABCO) cation), or salt forms thereof. Such moieties can be associated with one or more counterions. For example, a cationic moiety can be associated with one or more anionic counterions, and an anionic moiety can be associated with one or more cationic counterions.

[0106] Arylene group Certain moieties herein (e.g., polymer units, linking moieties, and the like) may contain optionally substituted arylene. Such arylene groups include any polyvalent (e.g., divalent, trivalent, tetravalent, etc.) group having one or more aromatic groups, which may include heteroaromatic groups. Non-limiting aromatic groups (e.g., Ar) may include any of the following: [ka] wherein each of rings a-i is optionally substituted (e.g., with any of the optional substituents described herein for alkyl or aryl, or any of the optional ionizable moieties described herein); L' is a linking moiety (e.g., any of those described herein), and R' and R" are each independently H, optionally substituted alkyl, optionally substituted aryl, or an ionizable moiety described herein. Non-limiting substituents for rings a-i include one or more of those described herein for aryl, such as alkyl, alkoxy, alkoxyalkyl, amino, aminoalkyl, aryl, arylalkylene, aryloyl, aryloxy, arylalkoxy, cyano, hydroxy, hydroxyalkyl, nitro, halo, and haloalkyl. In some embodiments, L' is a covalent bond, -O-, -NR N1 -, -C(O)-, optionally substituted alkylene, heteroalkylene, or arylene.

[0107] Further non-limiting examples of arylene include phenylene (e.g., 1,4-phenylene, 1,3-phenylene, etc.), biphenylene (e.g., 4,4'-biphenylene, 3,3'-biphenylene, 3,4'-biphenylene, etc.), terphenylene (e.g., 4,4'-terphenylene), diphenyl ether, anthracene (e.g., 9,10-anthracene), naphthalene (e.g., 1,5-naphthalene, 1,4-naphthalene, 2,6-naphthalene, 2,7-naphthalene, etc.), tetrafluorophenylene (e.g., 1,4-tetrafluorophenylene, 1,3-tetrafluorophenylene), and the like.

[0108] Non-limiting examples of linking moieties for arylene include any of those described herein. In some embodiments, L' is one or more ionizable or ionic moieties described herein that are substituted. In certain embodiments, L' is an optionally substituted alkylene. Non-limiting substituents for L' include -L A -X A In the formula, LA is a linking moiety (e.g., any of those described herein, such as -Ak-, -O-Ak-, -Ak-O-, -Ar-, -O-Ar-, or -Ar-O-, where Ak is an optionally substituted alkylene and Ar is an optionally substituted arylene), X A is an acidic moiety, a basic moiety, or multiple ionic moieties.

[0109] connecting part Certain chemical functionalities herein may include a linking moiety between a parent structure and another moiety (e.g., an ionic moiety), or between two (or more) other moieties. 1 , L 2 , L 3 , L 4 , L A , L A’ , L A’’ , L B’ , L B’’ , L 8A etc.) can be any useful polyvalent group, such as optionally substituted aliphatic, heteroaliphatic, aromatic, or heteroaromatic polyvalent forms.

[0110] In any embodiment herein, a linking moiety (e.g., L, L 1 , L 2 , L 3 , or L 4 ) represents a covalent bond, a spirocyclic bond, -O-, -NR N1 -, -C(O)-, -C(O)O-, -OC(O)-, -SO2-, optionally substituted aliphatic, alkylene (e.g., -CH2-, -C(CH3)2-, or -CR2-, where R is H, alkyl, or haloalkyl), alkyleneoxy, haloalkylene (e.g., -CF2- or -C(CF3)2-hydroxyalkylene, heteroaliphatic, heteroalkylene, aromatic, arylene, aryleneoxy, heterocyclic, heterocyclyldiyl, -SO2-NR N1 -Ak-, -(O-Ak) L1 -SO2-NR N1 -Ak-, -Ak-, -Ak-(O-Ak)L1 -, -(O-Ak) L1 -, -(Ak-O) L1 -, -C(O)O-Ak-, -Ar-, or -Ar-O-, and combinations thereof. In certain embodiments, Ak is an optionally substituted aliphatic, alkylene, or haloalkylene; R N1 is H, optionally substituted alkyl, or aryl; Ar is optionally substituted aromatic or arylene; and L1 is an integer from 1 to 3.

[0111] In other embodiments, L is optionally substituted C 1-6 aliphatic, C 1-6 Alkylene, or C 1-6 The use of short linkers may provide more extensive polymer networks because they minimize self-cyclization reactions.

[0112] In some embodiments, the linking moiety is -(CH) L1 -, -O(CH2) L1 -, -(CF2) L1 -, -O(CF2) L1 - or -S(CF2) L1 -, where L1 is an integer from 1 to 3. In other embodiments, the linking moiety is -Ak-O-Ar-Ak-O-Ak- or -Ak-O-Ar-, where Ak is an optionally substituted alkylene or haloalkylene, and Ar is an optionally substituted arylene. Non-limiting examples of substitutions on Ar include -SO2-Ph, where Ph can be unsubstituted or substituted with one or more halo.

[0113] The polymers described with reference to the above table and formulas (I)-(V) and (X)-(XXXIV), including homopolymers and copolymers thereof, which may optionally be crosslinked and may contain any of the linking moieties, arylene groups, and ionic moieties described above, may be used in one or more layers of an MEA, such as the cathode catalyst layer, anode catalyst layer, polymer electrolyte membrane (PEM) layer, cathode buffer layer, and / or anode buffer layer, as appropriate.

[0114] CO X Bipolar MEA for reduction In certain embodiments, the MEA includes a bipolar interface having an anion-conducting polymer on the cathode side of the MEA and an interface-forming cation-conducting polymer on the anode side of the MEA. In some implementations, the cathode includes a first catalyst and an anion-conducting polymer. In certain embodiments, the anode includes a second catalyst and a cation-conducting polymer. In some implementations, a cathode buffer layer located between the cathode and the PEM includes an anion-conducting polymer. In some embodiments, an anode buffer layer located between the anode and the PEM includes a cation-conducting polymer.

[0115] In operation, an MEA with a bipolar interface transfers ions through the polymer electrolyte, electrons through the metal and / or carbon in the cathode and anode layers, and liquids and gases through pores within the layers.

[0116] In embodiments employing an anion-conducting polymer in the cathode and / or cathode buffer layer, the MEA can reduce or block undesired reactions that produce undesired products and reduce the overall efficiency of the cell. In embodiments employing a cation-conducting polymer in the anode and / or anode buffer layer, the MEA can reduce or block undesired reactions that reduce the production of desired products and reduce the overall efficiency of the cell.

[0117] For example, at potential levels used for cathodic reduction of CO2, hydrogen ions can be reduced to hydrogen gas. This is a parasitic reaction; the current that could be used to reduce CO2 is instead used to reduce the hydrogen ions. Hydrogen ions can be produced by various oxidation reactions occurring at the anode of the CO2 reduction reactor, migrate through the MEA, and reach the cathode, where they are reduced to produce hydrogen gas. The extent to which this parasitic reaction can proceed corresponds to the concentration of hydrogen ions present at the cathode. Therefore, the MEA may use anion-conducting materials in the cathode layer and / or cathode buffer layer. The anion-conducting materials at least partially block hydrogen ions from reaching the catalytic sites at the cathode. As a result, the parasitic production of hydrogen gas is reduced, improving the production rate of CO2 or other products and the overall efficiency of the process.

[0118] Another process that can be avoided is the transport of carbonate or bicarbonate ions to the anode to effectively remove CO from the cathode. At the cathode, aqueous carbonate or bicarbonate ions can be produced from CO. If such ions reach the anode, they can decompose and release gaseous CO. As a result, CO is net transported from the cathode to the anode, where it is not reduced and is lost along with oxidation products. To prevent carbonate and bicarbonate ions produced at the cathode from reaching the anode, the polymer electrolyte membrane and / or anode buffer layer may contain a cation-conducting polymer that, at least in part, blocks the transport of anions, such as bicarbonate or carbonate ions, to the anode.

[0119] Thus, in some designs, a bipolar membrane structure increases the pH at the cathode to facilitate CO2 reduction, while a cation-conducting polymer (e.g., a proton exchange layer) prevents CO2, anions (e.g., bicarbonate, carbonate), hydrogen, and CO2 reduction products (e.g., CO, methane, ethylene, alcohols) from passing to the anode side of the cell.

[0120] An exemplary MEA for reducing carbon oxides has a cathode layer and an anode layer separated by an ion-conducting polymer layer that provides a pathway for ion migration between the cathode and anode layers. In certain embodiments, the cathode layer comprises an anion-conducting polymer and / or the anode layer comprises a cation-conducting polymer. In certain embodiments, the cathode and / or anode layers of the MEA are porous. The pores can facilitate gas and / or fluid transport and can increase the amount of catalyst surface area available for reaction.

[0121] The ion-conducting layer may include two or three sublayers: a polymer electrolyte membrane (PEM), an optional cathode buffer layer, and / or an optional anode buffer layer. One or more layers within the ion-conducting layer may be porous. In certain embodiments, at least one layer is non-porous, so that reactants and products from the cathode cannot pass to the anode via gas and / or liquid transport, and vice versa. In certain embodiments, the PEM layer is non-porous. Exemplary properties of the anode and cathode buffer layers are described elsewhere herein.

[0122] 1 shows a CO electrolyzer 103 configured to receive water (HO) and CO (e.g., humidified or dry gaseous CO) as reactants at the cathode 105 and output CO as a product. The electrolyzer 103 is also configured to receive water as a reactant at the anode 107 and output gaseous oxygen. The electrolyzer 103 includes a bipolar layer having an anion-conducting polymer 109 adjacent to the cathode 105 and a cation-conducting polymer 111 (shown as a proton exchange membrane) adjacent to the anode 107.

[0123] As shown in the close-up inset of the bipolar interface 113 of the electrolyzer 103, the cathode 105 includes an anion exchange polymer (in this example, the same anion conducting polymer 109 as in the bipolar layer), electronically conducting carbon support particles 117, and metal nanoparticles 119 supported on the support particles. CO and water are transported through pores (such as pore 121) to reach the metal nanoparticles 119, where they are converted into hydroxides (OH - ) ions to produce bicarbonate ions and reduction reaction products (not shown). CO may also reach the metal nanoparticles 119 by transport within the anion exchange polymer 109.

[0124] Hydrogen ions are transported from the anode 107 and through the cation-conducting polymer 111 until they reach the bipolar interface 113, where they are prevented from further transport to the cathode by the anion-exchange polymer 109. At the interface 113, the hydrogen ions may react with bicarbonate or carbonate ions to produce carbonic acid (HCO), which may decompose to produce CO and water. As described herein, the resulting CO may be carried in the gas phase and returned to the cathode 105 via a pathway within the MEA, where it may be reduced. The cation-conducting polymer 111 prevents the transport of anions, such as bicarbonate ions, to the anode. At the anode 207, the anions may react with protons to release CO, but this CO is no longer available to participate in reduction reactions at the cathode.

[0125] As shown, a cathode buffer layer with an anion-conducting polymer can work in concert with the cathode and its anion-conducting polymer to block the transport of protons to the cathode, whereas an anode buffer layer, if present, with an MEA employing the appropriate type of conductive ion-conducting polymer in the cathode, anode, and cathode buffer layer, can prevent the transport of cations to the cathode and anions to the anode, which again can come into contact within interior regions of the MEA, such as the membrane layer.

[0126] As illustrated in Figure 1, bicarbonate and / or carbonate ions can combine with hydrogen ions between the cathode and anode layers to form carbonic acid, which can decompose to form gaseous CO. Delamination of the MEA can be observed, which is believed to be due to the evolution of gaseous CO, as it has no easy route to escape.

[0127] The delamination problem can be solved by using a cathode buffer layer with pores. One possible explanation for its effectiveness is that the pores provide a pathway through which gaseous carbon dioxide can escape and return to the cathode for reduction. In some embodiments, the cathode buffer layer is porous, but at least one layer between the cathode and anode layers is non-porous. This prevents the passage of gas and / or bulk liquid between the cathode and anode layers, while also preventing delamination. For example, a non-porous layer can prevent the passage of water directly from the anode to the cathode. The porosity of various layers within the MEA is further discussed elsewhere in this document.

[0128] Example of a bipolar MEA As an example, the MEA includes a cathode layer including a reduction catalyst and a first anion-conducting polymer (e.g., Sustainion, FumaSepFAA-3, Tokuyama anion exchange polymer); an anode layer including an oxidation catalyst and a first cation-conducting polymer (e.g., PFSA polymer); a membrane layer including a second cation-conducting polymer and disposed between the cathode layer and the anode layer to conductively connect the cathode layer and the anode layer; and a cathode buffer layer including a second anion-conducting polymer (e.g., Sustainion, FumaSepFAA-3, Tokuyama anion exchange polymer) and disposed between the cathode layer and the membrane layer to conductively connect the cathode layer and the membrane layer. In this example, the cathode buffer layer can have a porosity of about 1 to 90 volume percent, but can additionally or alternatively have any suitable porosity (e.g., no porosity). In other examples, the cathode buffer layer can have any suitable porosity (eg, 0.01 to 95%, 0.1 to 95%, 0.01 to 75%, 1 to 95%, 1 to 90%, etc.).

[0129] If the porosity is too high, the ionic conductivity of the buffer layer may decrease. In some embodiments, the porosity is 20% or less, and in particular embodiments, it is 0.1-20%, 1-10%, or 5-10%. Porosity within these ranges may be sufficient to allow the movement of water and / or CO2 without loss of ionic conductivity. Porosity may be measured as described below.

[0130] In a related example, the membrane electrode assembly can include an anode buffer layer containing a third cation-conducting polymer, disposed between the membrane layer and the anode layer and conductively connecting them. The anode buffer layer preferably has a porosity of about 1 to 90 volume percent, but can additionally or alternatively have any suitable porosity (e.g., including no porosity). However, in other configurations and examples, the anode buffer layer can have any suitable porosity (e.g., 0.01 to 95%, 0.1 to 95%, 0.01 to 75%, 1 to 95%, 1 to 90%). As with the cathode buffer layer, in some embodiments, the porosity is 20% or less, e.g., 0.1 to 20%, 1 to 10%, or 5 to 10%.

[0131] In one example, the anode buffer layer can be used in an MEA having a cathode catalyst layer containing an anion exchange polymer, a cathode buffer layer containing an anion exchange polymer, a membrane containing a cation exchange polymer, and an anode buffer layer containing an anion exchange polymer. In such a structure, the anode buffer layer can be porous, which facilitates the transport of water to the membrane / anode buffer layer interface. At this interface, the water splits, producing protons that migrate through the membrane and hydroxides that migrate to the anode catalyst layer. One advantage of this structure is that it can be used with low-cost hydroxide oxidation catalysts (e.g., NiFeO) that are stable only under basic conditions. X ) may be possible.

[0132] In another specific example, the membrane electrode assembly includes a cathode layer including a reduction catalyst and a first anion-conducting polymer (e.g., Sustainion, FumaSepFAA-3, Tokuyama anion exchange polymer), an anode layer including an oxidation catalyst and a first cation-conducting polymer, a membrane layer including a second anion-conducting polymer (e.g., Sustainion, FumaSepFAA-3, Tokuyama anion exchange polymer) disposed between the cathode layer and the anode layer and conductively connecting the cathode layer and the anode layer, and an anode buffer layer including the second cation-conducting polymer disposed between the anode layer and the membrane layer and conductively connecting the anode layer and the membrane layer.

[0133] An MEA comprising an anion exchange polymer membrane and an anode buffer layer containing a cation exchange polymer can be used for the reduction of CO. In this case, water forms at the membrane / anode buffer layer interface. Pores in the anode buffer layer can facilitate water removal. One advantage of this structure is its acid stability (e.g., IrO X ) hydroxylation catalyst.

[0134] In a related example, the membrane electrode assembly can include a cathode buffer layer comprising a third anion-conducting polymer and disposed between the cathode layer and the membrane layer, thereby conductively connecting the cathode layer and the membrane layer. The third anion-conducting polymer can be the same as or different from the first and / or second anion-conducting polymer. The cathode buffer layer preferably has a porosity of about 1 to 90 volume percent, but can additionally or alternatively have any suitable porosity (e.g., including no porosity). However, in other configurations and examples, the cathode buffer layer can have any suitable porosity (e.g., 0.01 to 95%, 0.1 to 95%, 0.01 to 75%, 1 to 95%, 1 to 90%). In some embodiments, the porosity is 20% or less, and in particular embodiments, it is 0.1 to 20%, 1 to 10%, or 5 to 10%.

[0135] In one example, a cathode catalyst layer consisting of 4 nm diameter Au nanoparticles was supported on Vulcan XC72R carbon and mixed with TM1 (mTPN-1) anion-exchange polymer electrolyte (manufactured by Orion). The layer thickness was approximately 15 μm, Au / (Au+C) = 20 wt%, the TM1 to catalyst mass ratio was 0.32, and the mass loading was 1.4–1.6 mg / cm. 2 The anion exchange polymer layer, consisting of TM1 and PTFE particles, is approximately 200 nanometers in diameter. The molecular weight of TM1 is 30kJ to 45kJ. The layer thickness is approximately 15 μm. The PTFE may introduce approximately 8% porosity. The proton exchange membrane layer is composed of a perfluorosulfonic acid polymer (e.g., Nafion 117). The thickness is approximately 183 μm. The membrane may form a continuous layer that prevents significant gas (CO2, CO, H2) transport through the layer. The anode catalyst layer is composed of 10 μm-thick Ir or IrO nanoparticles (aggregates of 100 to 200 nm).

[0136] Various features and embodiments of MEAs are described in U.S. Patent Application Publication No. 2017 / 0321334 [OPUSP001B], published November 9, 2017, and U.S. Patent Application Publication No. 20190226103 [OPUSP005], published July 25, 2019, which are incorporated by reference in their entireties. All publications referenced herein are incorporated by reference as if fully set forth herein in their entirety.

[0137] Each layer of the MEA Cathode catalyst layer - general structure As mentioned above, the cathode of the MEA (also called the cathode layer or cathode catalyst layer) X This facilitates the conversion of CO X It is a porous layer containing a catalyst for the reduction reaction.

[0138] In some embodiments, the cathode catalyst layer comprises a blend of reduced catalyst particles, electronically conductive support particles supporting the reduced catalyst particles, and a cathode ion-conducting polymer. In some embodiments, the reduced catalyst particles are blended with the cathode ion-conducting polymer without a support.

[0139] Examples of materials that can be used for the reduction catalyst particles include, but are not limited to, transition metals such as V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Au, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, and Hg, and combinations thereof, and / or any other suitable materials. Other catalyst materials can include alkali metals, alkaline earth metals, lanthanides, actinides, and post-transition metals, such as Sn, Si, Ga, Pb, Al, Tl, Sb, Te, Bi, Sm, Tb, Ce, Nd, and In, or combinations thereof, and / or any other suitable catalyst materials. The choice of catalyst depends on the specific reaction taking place at the cathode of the CRR.

[0140] The catalyst may be in the form of nanoparticles ranging in size from about 1 to 100 nm, or particles ranging in size from about 0.2 to 10 nm, or particles ranging in size from about 1 to 1000 nm, or any other suitable range. In addition to nanoparticles and larger particles, films and nanostructured surfaces can also be used.

[0141] If used, the electronically conductive support particles in the cathode can be carbon particles of various forms. Other possible conductive support particles include boron-doped diamond or fluorine-doped tin oxide. In one arrangement, the conductive support particles are vulcanized carbon. The conductive support particles can be nanoparticles. The size range of the conductive support particles is about 20 nm to 1000 nm or any other suitable range. Conductive support particles are particularly useful if they are compatible with the chemistry present in the cathode when the CRR is operating, are reductively stable, have a high hydrogen evolution overpotential, and do not participate in any electrochemical reactions.

[0142] For example, the size of metal nanoparticles may be in the range of about 1 to 100 nm, e.g., 2 to 20 nm, for composite catalysts such as Au / C, and about 20 to 200 nm for carbon support materials. For pure metal catalysts such as Ag or Cu, the particles have a wide range of crystal grain size, from 2 to 500 nm. Agglomerations can be even larger, reaching the micrometer range.

[0143] Typically, such conductive support particles are larger than the reduced catalyst particles, and each conductive support particle can support many reduced catalyst particles. In some embodiments, there can be two different types of catalysts supported on catalyst support particles, such as carbon particles. A first type of catalyst particle and a second type of catalyst particle are attached to the catalyst support particles. In various configurations, there can be only one type of catalyst particle attached to the catalyst support particle, or there can be two or more types of catalyst particles.

[0144] The use of two catalysts can be useful in certain embodiments. For example, one catalyst can be good at one reaction (e.g., CO -> CO) and a second catalyst can be good at another reaction (e.g., CO -> CH). Overall, the catalyst layer converts CO to CH, but different steps in the reaction are carried out over different catalysts.

[0145] The electronically conductive support may be in forms other than particles, such as tubes (e.g., carbon nanotubes) and sheets (e.g., graphene). Structures with a large surface area relative to their volume are useful for providing sites for attachment of catalyst particles.

[0146] In addition to the reduction catalyst particles and the electronically conductive support particles, the cathode catalyst layer may include an ionically conductive polymer. There is a tradeoff in selecting the amount of cathode ionically conductive polymer in the cathode. It can be important to include enough cathode ionically conductive polymer to provide sufficient ionic conductivity. However, it is also important for the cathode to be porous to allow easy transport of reactants and products and to maximize the amount of catalytic surface area available for reaction. In various configurations, the cathode ionically conductive polymer may comprise 30-70 wt%, 20-80 wt%, or 10-90 wt%, or any other suitable range, of the material in the cathode layer. The amount (by weight) of ionically conductive polymer in the cathode depends on the CO X The porosity and ionic conductivity of the cathode layer are selected to provide the maximum current density for reducing . In some embodiments, it may be 20 to 60 wt % or 20 to 50 wt %. Exemplary thicknesses of the cathode catalyst layer range from about 80 nm to 300 μm.

[0147] In addition to the reduced catalyst particles, the cathode ionically conductive polymer, and, if present, the electronically conductive support, the cathode catalyst layer may also contain other additives such as PTFE.

[0148] In addition to the polymer to catalyst mass ratio, the catalyst layer also has a mass loading (mg / cm 2 Porosity can be characterized by its density and porosity. Porosity can be determined by a variety of methods. One method involves multiplying the loading of each component (e.g., catalyst, support, and polymer) by its density. These are summed to determine the thickness of the material that the components occupy. Dividing this by the known total thickness gives the fraction of the layer that is filled with material. Subtracting 1 from this fraction gives the fraction of the layer assumed to be void (e.g., the fraction of the layer assumed to be filled with air or other gas or vacuum) (porosity). Methods such as mercury porosimetry or image processing of TEM images can also be used.

[0149] Catalyst layers can also be characterized by their roughness. The surface features of a catalyst layer can affect the resistance in a membrane electrode assembly. An overly rough catalyst layer can result in interfacial gaps between the catalyst and the microporous layer. These gaps prevent the continuous transfer path of electrons from the current collector to the catalyst area, thereby increasing the contact resistance. Interfacial gaps can also be a site for water accumulation, which adversely affects the mass transport of reactants and products. On the other hand, an extremely smooth surface can result in poor adhesion between layers. The roughness of a catalyst layer can affect the electrical contact resistance and concentration polarization losses. Surface roughness can be measured using various techniques (e.g., mechanical stylus method, optical profilometry, atomic force microscopy) and is defined as the high-frequency and short-wave components of the actual surface. The arithmetic mean height S a is a commonly used parameter to evaluate surface roughness. Numerically, it is calculated by integrating the absolute heights of the valleys and peaks on the surface relative to the mean plane over the entire geometric area of ​​the sample. In some embodiments, the S of the catalyst layer a Values ​​in the range of 0.50 to 1.10 μm or 0.70 to 0.90 μm can be used.

[0150] Examples of cathode catalyst layers for CO, methane, and ethylene / ethanol production are shown below. CO production: 4 nm diameter nanoparticles were supported on Vulcan XC72R carbon and mixed with TM1 anion-exchange polymer electrolyte (Orion). The layer was approximately 15 μm thick, with a Au / (Au+C) ratio of 30%, a TM1 to catalyst mass ratio of 0.32, a mass loading of 1.4–1.6 mg / cm², and an estimated porosity of 0.47. Methane production: Cu nanoparticles of 20–30 nm size were supported on Vulcan XC72R carbon and mixed with FAA-3 anion-exchange solid polymer electrolyte (Fumatech). The mass ratio of FAA-3 to catalyst was 0.18. The estimated Cu nanoparticle loading was approximately 7.1 μg / cm. 2 and 1 to 100 μg / cm 2 It is a wide range. Ethylene / ethanol production: Cu nanoparticles of 25–80 nm size were mixed with FAA-3 anion-exchange solid polymer electrolyte (Fumatech). The mass ratio of FAA-3 to catalyst was 0.10. Pure AEM was deposited either on a Sigracet 39BC GDE or on a polymer electrolyte membrane. The estimated Cu nanoparticle loading was 270 μg / cm. 2 is. Bipolar MEA for methane production: The catalyst ink consists of 20 nm Cu nanoparticles (Premetek 40% Cu / Vulcan XC-72) supported on Vulcan carbon and mixed with FAA-3 anion-exchange solid polymer electrolyte (Fumatech). The mass ratio of FAA-3 to catalyst is 0.18. The cathode is formed by ultrasonic spray deposition of the catalyst ink onto a bipolar membrane consisting of FAA-3 anion-exchange solid polymer electrolyte spray-coated onto a Nafion (PFSA) 212 (e.g., fuel cell) membrane. The anode consists of IrRuOx, which is 3 mg / cm. 2 The MEA is constructed by sandwiching a porous carbon gas diffusion layer (Sigracet 39BB) between the Cu catalyst-coated bipolar membranes. Bipolar MEAs for ethylene production: The catalyst ink consists of pure 80 nm Cu nanoparticles (Sigma-Aldrich) mixed with FAA-3 anion-exchange solid polymer electrolyte (Fumatech), with a mass ratio of FAA-3 to catalyst of 0.09. The cathode is formed by ultrasonic spray deposition of the catalyst ink onto a bipolar membrane consisting of FAA-3 anion-exchange solid polymer electrolyte spray-coated onto a Nafion (PFSA) 115 (e.g., fuel cell) membrane. The anode consists of IrRuOx, which is 3 mg / cm. 2 The MEA is constructed by sandwiching a porous carbon gas diffusion layer (Sigracet 39BB) between the Cu catalyst-coated bipolar membranes. CO production: 4 nm diameter nanoparticles were supported on Vulcan XC72R carbon and mixed with TM1 anion exchange polymer electrolyte (Orion). The layer was approximately 14 microns thick with Au / (Au+C) = 20%. The TM1 to catalyst mass ratio was 0.32, resulting in a mass loading of 1.4-1.6 mg / cm. 2 and the estimated porosity of the catalyst layer is 0.54. CO production: 45 nm diameter nanoparticles were supported on Vulcan XC72R carbon and mixed with TM1 anion exchange polymer electrolyte (Orion). The layer was approximately 11 microns thick with Au / (Au+C) = 60%. The TM1 to catalyst mass ratio was 0.16, resulting in a mass loading of 1.1-1.5 mg / cm. 2 and the estimated porosity of the catalyst layer is 0.41. CO production: 4 nm diameter nanoparticles were supported on Vulcan XC72R carbon and mixed with TM1 anion exchange polymer electrolyte (Orion). The layer was approximately 25 microns thick with Au / (Au+C) = 20%. The TM1 to catalyst mass ratio was 0.32, resulting in a mass loading of 1.4-1.6 mg / cm. 2 and the estimated porosity of the catalyst layer is 0.54.

[0151] The function, materials, and structure of the components of the cathode catalyst layer are further described below.

[0152] Cathode catalyst layer - Function The main function of the cathode catalyst layer is to X The objective of the present invention is to provide a catalyst for the reduction of HCl. An exemplary reaction is: CO2+2H + +2e-->CO+H2O.

[0153] The cathode catalyst layer X It also has multiple functions that facilitate conversion: these include water management, gas transport, reactant delivery to the metal catalyst, product removal, stabilization of the metal catalyst particle structure, electron and ion conduction to the metal catalyst, and mechanical stability within the MEA.

[0154] Certain features and challenges are unique to CRRs and are not found in MEA assemblies for other applications, such as fuel cells or water electrolyzers. These challenges include the cathode catalyst layer of the MEA allowing gas (e.g., CO2 or CO) migration and gas (e.g., ethylene, methane, CO) or liquid (e.g., ethanol) transport. The cathode catalyst layer also prevents water accumulation that can block gas transport. Additionally, CO X Catalysts for reduction are less developed than catalysts such as platinum that can be used in hydrogen fuel cells. As a result, CO reduction catalysts generally have poor stability. These features, their specific challenges, and ways to address them are discussed below.

[0155] Water management (cathode catalyst layer) The cathode catalyst layer facilitates water movement and prevents water from being trapped in the cathode catalyst layer. Trapped water can be used to remove CO X may prevent the catalyst from accessing the cathode catalyst layer and / or prevent reaction products from migrating out of the cathode catalyst layer.

[0156] Water management challenges are unique to CRRs in many ways. For example, compared to the oxygen electrode of a PEM fuel cell, a CRR uses a much lower gas flow rate. A CRR uses a much lower CO XTo achieve higher utilization, lower flow rates may be used. Because vapor-phase water removal is determined by the volumetric gas flow rate, much less vapor-phase water removal occurs in a CRR. CRRs can operate at higher pressures (e.g., 100 si to 450 psi) than fuel cells; at higher pressures, the volumetric flow rate decreases for the same molar flow rate, and vapor-phase water removal also decreases. As a result, liquid water is present in the MEA of a CRR and can be removed. In some MEAs, the ability to remove vapor-phase water is further limited by temperature limitations not present in fuel cells. For example, the reduction of CO2 to CO2 can occur at approximately 50°C, while the production of ethylene and methane may occur at 20°C to 25°C. This compares to the typical operating temperatures of 80°C to 120°C for fuel cells. As a result, there is more liquid-phase water to remove.

[0157] Properties that affect the ability of a cathode catalyst layer to remove water include porosity; pore size; pore size distribution; hydrophobicity; the relative amounts of ion-conducting polymer, metal catalyst particles, and electronically conductive support; layer thickness; and the distribution of catalyst throughout the layer and the ion-conducting polymer distributed throughout the layer and around the catalyst.

[0158] The porous layer provides a pathway for water to escape. In some embodiments, the cathode catalyst layer has a pore size distribution that includes pores between 1 nm and 100 nm in size and pores at least 1 micron in size. This size distribution can aid in water removal. The porous structure can be formed by one or more of the following: pores within the carbon support material; stacked pores between stacked spherical carbon nanoparticles; secondary stacked pores (micrometer scale) between agglomerated carbon spheres; or an inert filler material (e.g., PTFE) with an interface between the carbon and the porous inert filler material; the interface creating irregular pores ranging from several hundred nanometers to micrometers.

[0159] The cathode catalyst layer may have a thickness that contributes to water management. A thicker layer allows the catalyst, and therefore the reaction, to be distributed over a larger area, which spreads out the water distribution and thus makes it easier to manage.

[0160] Ion-conducting polymers with non-polar, hydrophobic backbones can be used in the cathode catalyst layer. In some embodiments, the cathode catalyst layer may include a hydrophobic polymer, such as PTFE, in addition to the ion-conducting polymer. In some embodiments, the ion-conducting polymer may be a component of a copolymer that also includes a hydrophobic polymer. In some embodiments, the ion-conducting polymer has hydrophobic and hydrophilic regions. The hydrophilic regions may support water transport, and the hydrophobic regions may support gas transport.

[0161] Gas transport (cathode catalyst layer) The cathode catalyst layer is structured for the transport of gases, specifically CO X is transported to the catalyst, and gas-phase reaction products (e.g., CO, ethylene, methane, etc.) are transported from the catalyst bed.

[0162] Certain challenges related to gas transport are unique to CRR. Gases must be transported both in and out of the cathode catalyst layer, resulting in CO X In PEM fuel cells, gas (O2 or H2) is transported and either none or product water is exhausted. In PEM water electrolyzers, water is a reactant with the O2 and H2 gas products.

[0163] Operating conditions such as pressure, temperature, and flow rate through the reactor affect gas transport. Cathode catalyst layer properties that affect gas transport include porosity, pore size and distribution, layer thickness, and ion exchange resin distribution.

[0164] In some embodiments, the ionomer has minimal contact with the catalyst. For example, in embodiments using a carbon support, the ionomer may minimize contact with the catalyst and form a continuous network along the surface of the carbon. The ionomer, support, and catalyst may be designed so that the ionomer has a higher affinity for the support surface than for the catalyst surface. This may facilitate gas transport to and from the catalyst without being blocked by the ionomer, allowing the ionomer to conduct ions to and from the catalyst.

[0165] Ionomer (cathode catalyst layer) The ionomer may have several functions, such as holding the particles of the catalyst layer together and allowing the movement of ions through the cathode catalyst layer. In some cases, the interaction of the ionomer with the catalyst surface may result in the formation of CO X This creates an environment favorable for the reduction of CO, which may increase selectivity to the desired product and / or reduce the voltage required for the reaction. Importantly, ionomers are ion-conducting polymers, allowing the movement of ions through the cathode catalyst layer. For example, hydroxide, bicarbonate, and carbonate ions are transported through the cathode catalyst layer to CO. X It is removed from the surface of the catalyst where reduction occurs. In the following description, the ionomer in the cathode catalyst layer may be referred to as the first ion-conducting polymer.

[0166] The first ion-conducting polymer may comprise at least one ion-conducting polymer that is an anion conductor, which may be advantageous as it may increase the pH compared to proton conductors.

[0167] In some embodiments, the first ion-conducting polymer may include one or more covalently bonded positively charged functional groups configured to transport mobile negatively charged ions. The first ion-conducting polymer may be selected from the group consisting of aminated tetramethylpolyphenylene; poly(ethylene-co-tetrafluoroethylene)-based quaternary ammonium polymers, quaternized polysulfones, blends thereof, and / or other suitable ion-conducting polymers. The first ion-conducting polymer may be configured to dissolve bicarbonate or hydroxide salts.

[0168] In some embodiments, the first ion-conducting polymer can include at least one ion-conducting polymer that is a cation and anion conductor. The first ion-conducting polymer can be selected from the group consisting of polyethers capable of transporting cations and anions and polyesters capable of transporting cations and anions. The first ion-conducting polymer can be selected from the group consisting of polyethylene oxide, polyethylene glycol, polyvinylidene fluoride, and polyurethane.

[0169] Cation and anion conductors increase the pH (compared to pure cation conductors). Furthermore, in some embodiments, it may be advantageous to use cation and anion conductors rather than the 2D interface of anion- and cation-conducting polymers to promote acid-base recombination in a larger volume. This can disperse water and CO2 formation, heat production, and potentially lower membrane resistance by reducing the barrier to acid-base reactions. All of this can be advantageous in avoiding product and heat buildup and reducing resistive losses in the MEA, leading to lower cell voltage.

[0170] Typical anion-conducting polymers have a polymer backbone with covalently attached positively charged functional groups. In some embodiments, this may include positively charged nitrogen groups. In some embodiments, the polymer backbone is non-polar, as described above. The polymer may be of any suitable molecular weight, for example, from 25,000 g / mol to 150,000 g / mol, although it will be understood that polymers outside this range may also be used.

[0171] A particular challenge with ion-conducting polymers in CRRs is that CO2 can dissolve or solubilize in the polymer electrolyte, making it less mechanically stable and prone to swelling, allowing the polymer to move more freely. This reduces the mechanical stability of the overall catalyst layer and polymer electrolyte membrane. In some embodiments, polymers that are less susceptible to CO2 plasticization are used. Also, unlike water electrolyzers and fuel cells, conducting carbonate and bicarbonate ions is a key parameter for CO2 reduction.

[0172] The introduction of polar functional groups, such as hydroxyl and carboxyl groups, which can form hydrogen bonds, leads to the formation of a pseudo-crosslinked network. The addition of crosslinking agents, such as ethylene glycol and aluminum acetylacetonate, can strengthen the anion-exchange polymer layer and reduce CO2 plasticization of the polymer. Additives, such as polydimethylsiloxane copolymers, can also be useful in reducing CO2 plasticization.

[0173] According to various embodiments, the ion-conducting polymer may have a bicarbonate ion conductivity of at least 6 mS / cm, and in some embodiments, at least 12 mS / cm, is chemically and mechanically stable at temperatures up to 80° C., and is soluble in organic solvents used during fabrication, such as methanol, ethanol, and isopropanol. XThey are stable (chemically stable and have stable solubility) in the presence of reduction products. Ion-conducting polymers can also be characterized by their ion-exchange capacity, i.e., the total number of active sites or functional groups responsible for ion exchange, which in some embodiments can range from 2.1 mmol / g to 2.6 mmol / g. In some embodiments, ion-conducting polymers with low IEC, e.g., 1 mmol / g or 1.5 mmol / g, can be used.

[0174] The examples of anion-conducting polymers shown in the table above are designated as Class A ion-conducting polymers. A specific example of an anion-conducting polymer is Orion mTPN1 (also referred to herein as Orion TM1), which has a m-triphenylfluoroalkyl backbone and trimethylammonium (TMA+) as the cationic group. The chemical structure is shown below. [ka]

[0175] Additional examples include anion exchange membranes produced by Fumatech and Ionomr. Fumatech FumaSep FAA-3 ionomer is in the Br-form. Polybenzimidazole-based anion exchange polymer / membrane produced by Ionomr is in the I-form, AF-1-HNN8-50-X.

[0176] The as-received polymer can be prepared by exchanging anions (eg, I − , Br − , etc.) with bicarbonate ions.

[0177] Also, as noted above, in certain embodiments, the ionomer can be a cation-conducting and anion-conducting polymer. Exemplary Class B ion-conducting polymers are shown in the table above.

[0178] Metal catalyst (cathode catalyst layer) Metal catalysts areX The metal catalyst catalyzes the reduction reaction(s). The metal catalyst is typically a nanoparticle, although in some embodiments, larger particles, thin films, and nanostructured surfaces may also be used. The specific morphology of the nanoparticle may expose and stabilize active sites with higher activity.

[0179] Metal catalysts are often composed of pure metals (e.g., Cu, Au, Ag), although certain alloys or other bimetallic systems have high activity and may be used for specific reactions. The choice of catalyst can be guided by the desired reaction. For example, Au may be used to produce CO; Cu may be used to produce methane and ethylene. Other metals, alloys, and bimetallic systems, such as silver, may also be used. CO reduction has a high overpotential over known catalysts compared to other well-known electrochemical reactions, such as the hydrogen evolution reaction and the oxygen evolution reaction. Even small amounts of contaminants can poison catalysts for CO conversion. Also, as mentioned above, metal catalysts such as Cu, Au, and Ag are less developed than catalysts such as platinum, which are used in hydrogen fuel cells.

[0180] Different metal catalyst materials can be selected, at least in part, based on the desired product and MEA operation. For example, nanowires have high selectivity for ethylene production, and triangular Cu nanoplates have high selectivity for methane. Nanocubes have shown good selectivity for ethylene in AEM MEAs. Gold nanoparticles with a narrow size distribution (e.g., 2-6 nm) and uniform distribution on the carbon surface have resulted in higher current efficiency and durability.

[0181] Metal catalyst properties that affect the performance of the cathode catalyst layer include size, size distribution, uniformity of coverage on the support particles, shape, quantity (characterized as weight of metal / weight of metal + weight of carbon, or mass of particles per geometric area of ​​catalyst layer), surface area (actual metal catalyst surface area per volume of catalyst layer), purity, and the presence of synthetically poisoned surface ligands.

[0182] Nanoparticles can be synthesized by any suitable method, for example, Phan et al., "Role of Capping Agent in Wet Synthesis of Nanoparticles," J. Phys. Chem. A 2018, 121, 17, 3213-3219; Bakshi, "How Surfactants Control Crystal Growth of Nanomaterials," Cryst. Growth Des. 2016, 16, 2, 1104-1133; and Morsy, "Role of Surfactants in Nanotechnology and Their Applications," Int. J. Curr. Microbiol. App. Sci. 2014, 3, 5, 237-260, which are incorporated herein by reference.

[0183] In some embodiments, metal nanoparticles are provided free of toxic surface ligands. This can be achieved by using an ionomer as a ligand to guide the synthesis of the nanocrystalline catalyst. The surface of the metal nanocatalyst is directly connected to the ion-conducting ionomer. This eliminates the need to treat the catalyst surface to allow contact between the ionomer and the metal, improving contact.

[0184] In some embodiments, the metal catalyst may be disposed on a carbon support. For CO production, examples include Premetek 20 wt% Au (Au particle size 4-6 nm) supported on Vulcan XC-72R carbon and 30% Au / C (Au particle size 5-7 nm) supported on Vulcan XC-72R. For methane production, examples include Premetek 20 wt% Cu (Cu particle size 20-30 nm) supported on Vulcan XC-72R carbon. In some embodiments, the metal catalyst may be unsupported. For ethylene production, examples of unsupported metal catalysts include Sigma-Aldrich unsupported Cu particle size 80 nm and thin Cu layers (10-100 nm) deposited by e-beam or sputtering.

[0185] Support (cathode catalyst layer) The support for the cathode catalyst layer serves several functions: it stabilizes the metal nanoparticles to prevent agglomeration, disperses catalytic sites throughout the catalyst layer, and diffuses reactant loss and product formation. It also provides electrical conduction paths to the metal nanoparticles. For example, carbon particles clump together, so that contacting carbon particles provide electrical conduction paths. The voids between the particles form a porous network through which gases and liquids can travel.

[0186] In some embodiments, carbon supports developed for fuel cells can be used. Many different types have been developed; they are typically 50 nm to 500 nm in size and are available in a variety of shapes (spheres, nanotubes, sheets (e.g., graphene)), porosity, surface area per volume, electrical conductivity, and functional groups (N-doped, O-doped, etc.).

[0187] The support may be hydrophobic and may have an affinity for the metal nanoparticles.

[0188] Examples of carbon blacks that can be used are: ·Vulcan XC-72R-Density, 256mg / cm2, 30~50nm ·Ketjen Black-Hollow structure, density 100~120mg / cm2,30~50nm Printex Carbon, 20~30nm

[0189] Anode catalyst layer The anode of the MEA, also called the anode layer or anode catalyst layer, facilitates the oxidation reaction. It is a porous layer that contains a catalyst for the oxidation reaction. Examples of reactions include: 2H2O->4H + +4e - +O2 (in the acidic environment of proton-exchange polymer electrolytes - bipolar membranes); or 4OH->4e -+O2 + 2H2O (in the basic environment of anion-exchange polymer electrolyte)

[0190] Oxidation of other materials can be performed, such as hydrocarbons to CO2, or chloride ions to chlorine gas, or hydrogen gas to hydrogen ions.

[0191] In some embodiments, the anode comprises a blend of an oxidation catalyst and an anode ion-conducting polymer. Depending on the reactants and anode catalyst(s) provided to the anode, various oxidation reactions can occur at the anode. In one configuration, the oxidation catalyst is selected from the group consisting of metals and oxides, Ir, Pt, Ni, Ru, Pd, Au, and alloys thereof, IrRu, PtIr, Ni, NiFe, stainless steel, and combinations thereof. The oxidation catalyst can further comprise conductive support particles selected from the group consisting of carbon, boron-doped diamond, and titanium.

[0192] The oxidation catalyst can be in the form of a structured mesh or in the form of particles. When 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. It is particularly useful if the conductive support particles are compatible with the chemistry present in the anode and oxidatively stable so as not to participate in any electrochemical reactions when the CRR operates. This is particularly useful when the conductive support particles are selected based on the voltage and reactants at the anode. In some configurations, the conductive support particles are titanium, which is suitable for high voltages. In other configurations, the conductive support particles are carbon, which may be most useful at low voltages. Generally, such conductive support particles are larger than the oxidation catalyst particles, and each conductive support particle can support many oxidation catalyst particles. An example of such an arrangement is shown in Figure 1 and discussed above with respect to the cathode catalyst layer. 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 may be in the form of an oxide, particularly under reaction conditions.

[0193] In some embodiments, the MEA has an anode layer including an oxidation catalyst and a second ion-conducting polymer. The second ion-conducting polymer can include one or more polymers containing covalently attached negatively charged functional groups configured to transport positively charged mobile ions. The second ion-conducting polymer can be selected from the group consisting of 2-[1-[difluoro-[(trifluoroethynyl)oxy)methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2-tetrafluoro-, including ethanesulfonyl fluoride tetrafluoroethylene, tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octene sulfate copolymer, other perfluorosulfonic acid polymers, and blends thereof. Examples of cation-conducting polymers include, for example, Nafion 115, Nafion 117, and / or Nafion 211.

[0194] There are tradeoffs in selecting the amount of ion-conducting polymer in the anode. It is important to include enough anode ion-conducting polymer to provide sufficient ionic conductivity. However, it is also important for the anode to be porous to allow easy transport of reactants and products and to maximize the amount of catalytic surface area available for reaction. In various configurations, the ion-conducting polymer in the anode comprises about 50% by weight of the layer, or about 5-20%, 10-90%, 20-80%, 25-70%, or any suitable range. This is particularly useful when the anode can withstand high voltages, e.g., greater than about 1.2 V vs. the reversible hydrogen electrode. It is particularly useful for the anode 240 to be porous in order to maximize the catalytic surface area available for reaction and to facilitate gas and liquid transport.

[0195] As an example of a metal catalyst, Ir particles or IrOx particles (100-200 nm) and Nafion ionomer form a porous layer of about 10 μm. The amount of metal catalyst is about 0.5-3 g / cm. 2 is.

[0196] In some embodiments, NiFeOx or NiOx is used for basic reactions.

[0197] PEM (MEA layer description) The MEA includes a polymer electrolyte membrane (PEM) disposed between and conductively connected to the anode and cathode catalyst layers. The PEM has high ionic conductivity (greater than about 1 mS / cm) and is mechanically stable. Mechanical stability can be demonstrated in various ways, such as high tensile strength, modulus, elongation at break, and tear resistance. Many commercially available PEMs can be used. Examples include, but are not limited to, various Nafion® formulations, GORE-SELECT, FumaPEM® (PFSA) (FuMA-Tech GmbH), and Aquivion® (PFSA) (Solvay).

[0198] In one arrangement, the PEM includes at least one ion-conducting polymer that is a cation conductor. The third ion-conducting polymer can include covalently attached negatively charged functional groups configured to transport positively charged mobile ions. The third ion-conducting polymer can be selected from the group consisting of 2-[1-[difluoro-[(trifluoroethynyl)oxy)methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2-tetrafluoro-, including ethanesulfonyl fluoride tetrafluoroethylene, tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octene sulfate copolymer, other perfluorosulfonic acid polymers, and blends thereof. Cathode buffer layer (MEA layer description)

[0199] It is important to note that if the polymer electrolyte membrane is a cation conductor and conducts protons, it will contain a high concentration of protons during CRR operation, while the cathode operates optimally when protons are present at a low concentration. It can be useful to include a cathode buffer layer between the polymer electrolyte membrane and the cathode to provide a transition region from a high concentration of protons to a low concentration of protons. In one configuration, the cathode buffer layer is an ion-conducting polymer with many of the same properties as the ion-conducting polymer in the cathode. The cathode buffer layer creates a transition region of proton concentration from the polymer electrolyte membrane, which has a high proton concentration, to the cathode, which has a low proton concentration. Within the cathode buffer layer, protons from the polymer electrolyte membrane encounter anions from the cathode, which neutralize each other. The cathode buffer layer can help ensure that a significant number of protons do not reach the cathode from the polymer electrolyte membrane and increase the proton concentration. If the proton concentration in the cathode is too high, CO X A high concentration of protons is considered to be in the range of approximately 10 to 0.1 molar, and a low concentration is considered to be less than approximately 0.01 molar.

[0200] The cathode buffer layer can contain a single polymer or multiple polymers. When the cathode buffer layer contains multiple polymers, the multiple polymers can be mixed together or arranged in separate adjacent layers. Examples of materials that can be used for the cathode buffer layer include, but are not limited to, FumaSep FAA-3, Tokuyama anion exchange membrane materials, and polyether-based polymers (e.g., polyethylene oxide (PEO)) and blends thereof. Further examples are provided in the cathode catalyst layer section above.

[0201] The thickness of the cathode buffer layer is determined by the low proton concentration. X The thickness is selected to be sufficient to provide high reduction activity. This sufficiency may vary for different cathode buffer layer materials. In some embodiments, the thickness of the cathode buffer layer is approximately 200 nm to 100 μm, or 300 nm to 75 μm, or 500 nm to 50 μm, or any suitable range.

[0202] In some embodiments, the cathode buffer layer is less than 50 μm, e.g., 1-25 μm, or 1-5 μm, 5-15 μm, or 10-25 μm. Using a cathode buffer layer in this range of thickness can reduce the proton concentration in the cathode while maintaining overall cell conductivity. In some embodiments, ultrathin layers (100 nm-1 μm, and in some embodiments, submicron) can be used. As noted above, in some embodiments, the MEA does not have a cathode buffer layer. In some such embodiments, the anion-conducting polymer in the cathode catalyst layer is sufficient. The cathode buffer layer thickness can be characterized relative to the PEM.

[0203] Water and CO2 formed at the interface between the cathode buffer layer and the PEM can delaminate the MEA to which the polymer layer is attached. The delamination problem can be solved by employing a cathode buffer layer with inert filler particles and associated pores. One possible explanation for this effectiveness is that the pores provide a pathway through which gaseous carbon dioxide can escape and return to the cathode where it can be reduced.

[0204] Suitable materials for the inert filler particles include, but are not limited to, TiO2, silica, PTFE, zirconia, and alumina. In various configurations, the size of the inert filler particles ranges from 5 nm to 500 μm, or from 10 nm to 100 μm, or any suitable size range. These particles are generally spherical.

[0205] If the volume of PTFE (or other filler) is too high, the polymer electrolyte is diluted to the point that ionic conductivity is low. If the volume of polymer electrolyte is too high, the PTFE is diluted to the point that porosity is no longer useful. In many embodiments, the mass ratio of polymer electrolyte / PTFE is 0.25 to 2, more particularly 0.5 to 1. The volume ratio of polymer electrolyte / PTFE (or, more generally, polymer electrolyte / inert filler) is 0.25 to 3, 0.5 to 2, 0.75 to 1.5, or 1.0 to 1.5.

[0206] In other arrangements, porosity is achieved by using specific processing methods when the layer is formed. One example of such a processing method is laser ablation, which creates nano- to micro-sized channels in the layer. Another example is mechanically drilling the layer to create channels therethrough. Another example is appropriately adjusting conditions during ultrasonic spray deposition of the layer to make it porous.

[0207] In one arrangement, the cathode buffer layer has a porosity of 0.01% to 95% (e.g., within a range generally defined by weight, volume, mass, etc.). However, in other arrangements, the cathode buffer layer can have any suitable porosity (e.g., 0.01 to 95%, 0.1 to 95%, 0.01 to 75%, 1 to 95%, 1 to 90%). In some embodiments, the porosity is 50% or less, e.g., 0.1 to 50%, 5 to 50%, 20 to 50%, 5 to 40%, 10 to 40%, 20 to 40%, or 25% to 40%. In some embodiments, the porosity is 20% or less, e.g., 0.1 to 20%, 1 to 10%, or 5 to 10%.

[0208] The porosity of the cathode buffer layer or any layer of the MEA may be measured as described above for the catalyst layer by methods such as mercury porosimetry, x-ray diffraction (SAXS or WAXS), using the mass and thickness of the components, and image processing of TEM images to calculate filled and empty space. Porosity is measured when the MEA is completely dry, as materials expand to varying degrees when exposed to water during operation. As described further below, porosity may be determined using the measured mass and thickness of the layer and the known density of the layer's material(s).

[0209] The porosity of the layers of the MEA (such as the cathode buffer layer) is discussed in more detail below.

[0210] Anode buffer layer (MEA layer description) In some CRR reactions, bicarbonate is produced at the cathode. The presence of a polymer that blocks bicarbonate transport between the cathode and anode can be useful in preventing bicarbonate migration from the cathode. As bicarbonate migrates, it may carry some CO2 with it, potentially reducing the amount of CO2 available for reaction at the cathode. In some configurations, the polymer electrolyte membrane contains a polymer that blocks bicarbonate ion transport. Examples of such polymers include, but are not limited to, Nafion® formulations, GORE-SELECT, FumaPEM® (PFSA) (FuMA-Tech GmbH), and Aquivion® (PFSA) (Solvay). In other configurations, an anode buffer layer is present between the polymer electrolyte membrane and the anode, which blocks bicarbonate transport. If the polymer electrolyte membrane is an anion conductor or does not block bicarbonate transport, an additional anode buffer layer to prevent bicarbonate transport can be useful. Materials that can be used to block bicarbonate transport include, but are not limited to, Nafion® formulations, GORE-SELECT, FumaPEM® (PFSA) (FuMA-Tech GmbH), and Aquivion® (PFSA) (Solvay). Of course, if no bicarbonate is present in the CRR, it is not particularly desirable to include bicarbonate-blocking functionality in the ion exchange layer.

[0211] In another embodiment of the present invention, the anode buffer layer provides a region of proton concentration transition between the polymer electrolyte membrane and the anode. The proton concentration in the polymer electrolyte membrane depends on both its composition and the ions conducting it. For example, a Nafion polymer electrolyte membrane has a high proton concentration. A hydroxide-conducting FumaSep FAA-3 polymer electrolyte membrane has a low proton concentration. For example, if the desired proton concentration at the anode differs from that of the polymer electrolyte membrane by more than three orders of magnitude, the anode buffer layer can be useful for facilitating the transition from the proton concentration of the polymer electrolyte membrane to the desired proton concentration at the anode. The anode buffer layer can include a single polymer or multiple polymers. When the anode buffer layer includes multiple polymers, the multiple polymers can be mixed together or arranged in separate adjacent layers. Materials that may be useful for providing regions for pH change include, but are not limited to, Nafion, FumaSep FAA-3, Sustainion®, Tokuyama anion exchange polymers, and polyether-based polymers such as polyethylene oxide (PEO), blends thereof, and / or any other suitable materials. A high concentration of protons is considered to be in the range of approximately 10 to 0.1 molar, and a low concentration is considered to be less than approximately 0.01 molar. Ion-conducting polymers can be classified into different classes based on the type(s) of ion they conduct. This is discussed in more detail above. There are three classes of ion-conducting polymers listed in the table above. In one embodiment of the present invention, at least one of the ion-conducting polymers in the cathode, anode, polymer electrolyte membrane, cathode buffer layer, and anode buffer layer is of a different class than at least one of the others.

[0212] Layer porosity In some embodiments, one or more of the layers of the MEA contain pores that allow gas and liquid transport. These pores are distinct from the ion-conducting channels that allow ion conduction. In many polymer electrolytes (e.g., PFSA), ion conduction occurs through pores that carry a stationary charge. Mobile cations hop between oppositely charged stationary groups along the ion-conducting channel. Such channels can have variable widths; for PFSA materials, the diameter of the ion-conducting channel ranges from a narrow region of about 10 A to a wide region of about 40 A. In anion-conducting polymer materials, the channel diameter can be as large as about 60 A, with a minimum width of the narrow region of the channel.

[0213] For efficient ion conduction, polymer electrolytes are hydrated, and therefore, the ion-conducting channels also contain water. It is common for some water molecules to move along with the mobile ions in a process called electroosmotic drag. Typically, one to five water molecules are moved by electroosmotic drag per mobile ion. The structure of the ion-conducting channels and the degree of electroosmotic drag may vary for different polymer electrolytes or ion-conducting materials. These ion-conducting channels allow ions to move along with some water molecules, but uncharged molecules cannot move efficiently through them. Also, large amounts of water that are not associated with ions cannot pass through these channels. The solid (i.e., nonporous) membrane of the polymer electrolyte blocks most of the CO2 and products of CO2 electrolysis from passing through these channels. The typical permeability of CO2, water, and H2 through a wet Nafion 117PFSA membrane at 30°C is approximately 8.70 x 106 mol cm. -1 s -1 Pa -1 , 4.2 (mol / cm-s-bar) x 10 9 , and 3.6 (mol / cm-s-bar) x 10 11The permeability depends on the temperature, hydration, and nature of the polymer electrolyte material. In ion-conducting channels with variable diameters, bulk movement of uncharged molecules and liquids / gases may be blocked, at least in the narrow part of the channel.

[0214] Pores with diameters larger than the ion-conducting channels described above allow the passage of not only ions but also bulk liquids and gases. The polymer electrolyte membrane layer of an MEA typically does not contain pores of this type because the membrane is required to separate the reactants and products at the cathode from those at the anode. However, other layers of the MEA may have pores of this type. For example, the cathode catalyst layer may be porous, allowing the CO reactant to pass through. X can reach the catalyst, and CO X The products of reduction are allowed to migrate out of the catalyst layer, thereby exiting the gas distribution layer and into the electrolyzer flow paths. As used herein, the term "pore" refers to pores other than the ion-conducting channels in the ionomer. In some embodiments, the pores in the anion-conducting polymer layers in the MEA have a minimum cross-sectional dimension of at least 60 Å. In some embodiments, the pores in the cation-conducting polymer layers in the MEA have a minimum cross-sectional dimension of at least 20 Å. This is to distinguish the pores that allow gas / liquid transport from the ion-conducting channels described above.

[0215] It may be useful if some or all of the following layers are porous: the cathode, cathode buffer layer, anode, and anode buffer layer. In some configurations, porosity is achieved in these layers by combining inert filler particles with a polymer. Suitable materials for the inert filler particles include, but are not limited to, TiO2, silica, PTFE, zirconia, and alumina. In various configurations, the size of the inert filler particles ranges from 5 nm to 500 microns, or from 10 nm to 100 microns, or any suitable size range. In other configurations, porosity is achieved by using specific processing methods when the layer is formed. One example of such a processing method is laser ablation, which creates nano- to micro-sized channels in the layer. Laser ablation can additionally or alternatively create porosity in the layer through subsurface ablation. Subsurface ablation can create cavities in the layer when a beam is focused at a point within the layer, vaporizing the material of the layer near that point. This process can be repeated to form voids throughout the layer, resulting in porosity within the layer. Layer-by-layer MEA layer formation methods, such as ultrasonic spray deposition, can be used to form MEA layers with controlled porosity. A dry deposition can result in faster drying of the layer and a more porous final deposit. A higher substrate temperature, slower deposition rate, a higher nozzle height above the substrate, or higher volatility of the deposition ink can be used to make the layer more porous. A wet deposition can result in slower drying of the layer and a denser, more compacted final deposit of multiple layers. A lower substrate temperature, faster deposition rate, a lower spray nozzle height above the substrate, and lower volatility of the deposition ink can be used to reduce the porosity of the layer. For example, room temperature ultrasonic spray deposition can result in a denser layer, while ultrasonic spray deposition at 50°C can result in a more porous layer.

[0216] In some embodiments, the following conditions may be used to form a layer having a porosity of at least 1%, e.g., 1-90%, 1-50%, or 1-30% porosity: substrate temperature, at least 40°C; deposition rate, at most 0.8 mL / min, e.g., 0.2-0.8 mL / min; nozzle height, at least 50 mm, e.g., 50-75 mm; solvent, having a volatility of at least 90-100% (e.g., ethanol).

[0217] In some embodiments, the following conditions may be used to form a non-porous layer or a layer with less than 1% porosity: substrate temperature, less than 40°C; deposition rate, greater than 0.8 mL / min and up to 10 mL / min; nozzle height, less than 50 mm; solvent, with low volatility of at least 90-100% (e.g., 50-90% volatile solvent content such as ethanol, or 50-100% medium volatility solvent such as glycol ether).

[0218] The cavity volume may be measured by laser power (e.g., higher laser power corresponds to larger cavity volume), but may additionally or alternatively be measured by beam focal spot size or any other suitable laser parameter. In another example, a layer is mechanically perforated to form channels through the layer. The porosity can have any suitable distribution within the layer (e.g., uniform, increasing porosity gradient through the layer, random porosity gradient, decreasing porosity gradient).

[0219] The porosity of the above and other examples and variations thereof (e.g., the porosity of the cathode buffer layer, the porosity of the anode buffer layer, the porosity of the membrane layer, the porosity of the cathode layer, the porosity of the anode layer, the porosity of other suitable layers, etc.) preferably has a uniform distribution, but can additionally or alternatively have any suitable distribution (e.g., a random distribution, a gradient of increasing pore size through or within the layer, a gradient of decreasing pore size through or within the layer, etc.). The porosity can be formed by any suitable mechanism, such as inert filler particles (e.g., diamond particles, boron-doped diamond particles, polyvinylidene fluoride / PVDF particles, polytetrafluoroethylene / PTFE particles, etc.), and any other suitable mechanism for forming substantially non-reactive regions within the polymer layer. The inert filler particles can have any suitable size, from a minimum of about 10 nanometers to a maximum of about 200 nanometers, and / or any other suitable dimension or distribution of dimensions.

[0220] As described above, the cathode buffer layer preferably has a porosity of about 1 to 90 volume percent, but can additionally or alternatively have any suitable porosity (e.g., including no porosity). However, in other arrangements and examples, the cathode buffer layer can have any suitable porosity (e.g., 0.01 to 95%, 0.1 to 95%, 0.01 to 75%, 1 to 95%, 1 to 90%, etc.). In some embodiments, the porosity is 20% or less, e.g., 0.1 to 20%, 1 to 10%, or 5 to 10%.

[0221] In some embodiments, the cathode buffer layer is porous, but at least one layer between the cathode and anode layers is non-porous. This prevents the passage of gas and / or bulk liquid between the cathode and anode layers, while also preventing delamination. For example, a non-porous layer can prevent the direct passage of water from the anode to the cathode.

[0222] The porosity of the cathode buffer layer or any layer of the MEA can be measured as described above for the catalyst layer by methods such as mercury porosimetry, x-ray diffraction (SAXS or WAXS), using the mass and thickness of the components, and image processing of TEM images to calculate filled and empty space. Porosity is measured when the MEA is completely dry, as materials expand to varying degrees when exposed to water during operation. Porosity can be determined using the known density of the material, the actual weight of the layer per specific area, and the estimated volume of the layer based on area and thickness. The formula is:

[0223]

number

[0224] As noted above, the density of the material is known and the layer loading and thickness are measured. For example, the measured amount is 1.69 mg / cm 2 The polymer electrolyte layer is composed of: 42 wt. % anion exchange polymer electrolyte (density, 1196 mg / cm 3 ), 58wt% PTFE (density 2200mg / cm 3 ) and a total layer thickness of 11.44 microns, porosity:

[0225]

number

[0226] As noted above, the polymer electrolyte layer may have ion-conducting channels that do not readily allow gas / liquid transport. In the above calculations, these ion-conducting channels are considered non-porous; that is, the density of the non-porous material (42 wt. % anion-exchange polymer electrolyte) includes the ion-conducting channels, and is defined as non-porous by the calculations.

[0227] In another example, the ion-conducting layer without filler is porous. Porosity may be introduced, for example, by appropriate deposition conditions. The measured mass of the porous polymer electrolyte layer is 2.1 g / cm. 2 and has a thickness of 19 micrometers. The known density of a polymer electrolyte with ion-conducting channels but no pores is 1196 g / cm 3 The porosity is calculated as follows:

[0228]

number

[0229] Fabrication of MEAs CO X MEAs for reducing CO₂ can be fabricated using a variety of techniques. In various embodiments, fabrication of the MEAs involves multiple steps. Small variations in the fabrication process parameters can have a large impact on performance.

[0230] In certain embodiments, fabrication of the MEA involves using a polymer electrolyte membrane (e.g., Nafion PEM) layer and depositing or otherwise forming an anion exchange polymer electrolyte layer and a cathode catalyst layer on the cathode side of the membrane, and depositing or otherwise forming an anode catalyst layer on the anode side of the membrane. An alternative route is to fabricate the catalyst layer on a porous gas diffusion layer (e.g., carbon for the cathode or titanium for the anode) and sandwich the membrane (which may also include an anion exchange layer) between the porous layers containing the catalyst. In certain embodiments, the catalyst layer is fabricated by creating an ink in which solid catalyst and support particles and polymer electrolyte are dispersed in a solvent. The ink may be applied to the polymer electrolyte membrane or GDL by various methods. The solvent is then evaporated, leaving a porous, solid catalyst layer.

[0231] Imaging methods may be used to characterize thickness, uniformity, and surface roughness: thickness should be consistent and controllable, and uniformity should be smooth and as defect-free as possible.

[0232] Various techniques may be used to form each layer of the MEA. Generally, these techniques form a layer on a substrate, such as a PEM layer or GDL, as described herein. Examples of such techniques include ultrasonic spray deposition, doctor blade coating, gravure, screen printing, slot die coating, and decal transfer.

[0233] Catalyst inks using anion exchange polymers have not been well studied (especially for certain polymers) and do not have the same solution structure as typical Nafion-based inks used in fuel cells and electrolyzers. The formulations and steps required to form well-dispersed, stable catalyst inks were not known. Nafion is believed to form micelle-like structures that can be suspended relatively easily in aqueous media. Other ion-conducting polymers, particularly some anion-conducting polymers, do not form such structures and are therefore more difficult to provide as suspensions.

[0234] In certain embodiments, the catalyst layer ink is prepared by mixing a metal or a metal supported on a carbon catalyst with an ion-conducting polymer (e.g., an anion-conducting polymer) and dispersing it in a solvent (such as alcohol) by sonication.

[0235] As indicated, specific fabrication techniques utilize doctor blade application, screen printing, decal transfer, electrospinning, etc. Roll-to-roll techniques such as gravure or microgravure, slot die coating, etc. may be used for high throughput processing.

[0236] In some embodiments, the cathode side of the MEA is fabricated by first depositing an anion exchange polymer electrolyte layer on top of a cation exchange polymer electrolyte membrane. A second layer of cathode catalyst is then applied onto the anion exchange layer. This process produces a catalyst-coated membrane. A gas diffusion electrode can be prepared by depositing a catalyst onto the gas diffusion layer. An anion exchange layer can be deposited onto the catalyst layer or membrane. The layers can be pressed together inside the electrolysis cell to create a functioning device. Many methods can be used to fabricate the anion exchange polymer layer and the cathode catalyst layer, such as doctor blade, gravure or microgravure, slot die, decal transfer, screen printing, ultrasonic spray deposition, etc. A more detailed description of MEA cathode fabrication using ultrasonic spray deposition is provided below:

[0237] The cathode side of the MEA is fabricated by first forming a solution of the polymer electrolyte (approximately 1-25 wt%) in a suitable solvent (ethanol, n-propanol, isopropanol, or a solvent with high volatility and / or low boiling point that will evaporate in a reasonable timescale during fabrication. Mixtures of solvents containing one or more high-boiling components can be used. The polymer electrolyte solution is extruded at a desired flow rate through an ultrasonic spray deposition nozzle. The ultrasonic spray deposition nozzle is held at a desired frequency to disperse the polymer electrolyte solution into fine droplets, which are then forced by an air stream onto the polymer electrolyte membrane substrate. The polymer electrolyte membrane may be treated with heat, solvent, or other methods prior to deposition. Small droplets of polymer electrolyte solution land on a polymer electrolyte membrane substrate, where the solvent evaporates, leaving behind an encapsulated polymer electrolyte. An ultrasonic spray deposition nozzle passes back and forth over the substrate multiple times in a desired pattern and at a desired speed, building up a polymer electrolyte layer on top of the membrane substrate until the desired thickness is reached. This process is repeated with solutions of catalyst particles, anion-exchange polymer electrolyte and / or other additives, and an appropriate solvent or mixture of solvents. This solution is referred to as the catalyst ink. The catalyst ink is deposited by ultrasonic spray deposition using the same or different fabrication parameters to form a cathode catalyst layer on top of the anion-exchange polymer layer on the cathode side of the MEA.

[0238] MEA Expansion As indicated, certain applications of MEAs for reducing COx may require relatively large formats. For example, some MEAs have a size of at least about 500 cm. 2 In some other embodiments, the MEA has a larger active surface area (excluding pores), for example, at least about 650 cm 2 or 1500cm 2 is.

[0239] To create MEAs with such large effective surface areas, it is necessary to select an appropriate manufacturing process, one that can support both a large amount of catalyst ink and a large surface area to which the catalyst ink is applied. Scaling up the catalyst ink requires a specific method for dispersing the catalyst particles to ensure good dispersion in a large volume. The ink can be tailored to a desired degree of dispersion and characterized using dynamic light scattering (DLS). The ink must be stable within the time range of the layer deposition.

[0240] Additionally, humidity and temperature must be tightly controlled: since the evaporation rate and process affect the resulting deposition, it is useful to control these within a 1-2 degree temperature window and roughly a 5% RH range.

[0241] For ultrasonic spray deposition, a thin line of catalyst ink is laid down by a moving ultrasonic nozzle. For larger MEA areas, it may be necessary to increase the nozzle movement speed and ink flow rate. The flow rate and movement speed are controlled at 25 cm. 2 From 650cm 2 This increases by at least two times when moving to MEAs on the scale of 650 cm. The water in the solvent is important, and adding more water to the ink helps the droplets stack more smoothly. For example, 2 For an MEA of about 20% water, a formulation containing about 20% water may be used.

[0242] Because catalyst inks generally have relatively low stability, certain embodiments are designed to allow for relatively short fabrication times for MEAs, even for large active areas. For example, 650 cm 2 For spraying, deposition times of about 2 hours for the ionomer layer and 1 hour for the catalyst layer may be used, which is relatively fast for such large areas and can be achieved using high flow rates and transport speeds.

[0243] MEA expansion example Below is an example of scale-up of MEA fabrication: 25cm 2 From 650cm2 Here is an example of scaling up to

[0244] Adjusting the solvent mixture (ratio of water to alcohol): Depending on the size of the spray scale, adjusting the solvent to 10% to 20% water can significantly help the surface uniformity of the surface.

[0245] Deposition parameters: For the ionomer layer: the flow rate is increased from 0.4 mL / min to 0.8 mL / min and the migration speed is changed from 50 mm / sec to 100 mm / sec. For the catalyst layer: the flow rate is increased from 0.25 mL / min to 0.5 mL / min, and the transport speed is changed from 80 mm / sec to 160 mm / sec.

[0246] Morphology and thickness: Thickness can be determined by looking at the fabricated layer thickness in SEM images. Characterization data can be adjusted to match the thickness. Morphology is controlled by parameters such as moisture content and fabrication.

[0247] For example, 1500cm 2 When the flow rate and the movement speed are further increased, for example, in the range of 0.25 to 2 mL / min and 30 to 200 mm / sec.

[0248] The deposition rate can be further increased, for example, to 5-8 mL / min or 5-15 mL / min, by increasing the weight of solids in the solution. In some embodiments, the solution may be greater than 5 wt. %, greater than 10 wt. %, greater than 20 wt. %, or greater than 30 wt. %.

[0249] MEA post-processing After fabrication of the MEA, additional processing can be used to improve performance. Examples of types of performance improvements include lifespan and voltage. These improvements can be significant in MEAs that have structural modifications resulting from processing, including improved adhesion between layers.

[0250] Examples of MEA post-processing Hot pressing: Heating the MEA under pressure to bond the layers. Hot pressing is a process sometimes used in the fabrication of MEAs, such as the membrane and catalyst layers, and sometimes the GDL, are pressed together at a desired temperature for a period of time. Hot pressing can be used to reduce interfacial resistance, increase adhesion between layers, and "melt" the layers together to help prevent delamination. Exemplary times, temperatures, and pressures are shown below: Duration: Approximately 2 to 10 minutes (MEA only); 1.5 to 2 minutes (MEA + gas distribution layer (GDL)); the "MEA + GDL" may be pressed at least twice to form a stable assembly. ·Temperature: Approx. 100℃~195℃; Pressure: 28 psi to 2900 psi. In one example, about 300 psi to 600 psi can be used for a 3x3 inch 1 / 2 MEA, but the MEA can withstand about 2500 psi without a GDL.

[0251] The hot-pressing temperature is typically selected to be above the glass transition temperature of the polymer electrolyte, but below the temperature at which any material in the MEA is structurally or chemically damaged. The glass transition temperature is the temperature above which the polymer electrolyte softens, which may allow the polymer electrolyte at the layer interface to deform, forming sufficient contact with reduced ion transport resistance and improving adhesion.

[0252] Hydration: Prior to cell assembly, the MEA is immersed in water or an aqueous solution to wet the polymer electrolyte.

[0253] Nafion or other polymer electrolyte MEAs are boiled, which permanently changes the polymer electrolyte macrostructure and increases the amount of water in the polymer matrix, improving ionic conductivity but also increasing the water transport number.

[0254] Heating and drying can permanently reduce the moisture content and reduce the amount of water transported through the polymer electrolyte during operation. Exemplary times and temperatures for heating various MEAs are as follows: [Table 2]

[0255] Stabilized interfaces between MEA layers Water and CO2 formed at the interface between an anion-conducting layer (e.g., cathode buffer layer) and a cation-conducting membrane (e.g., PEM) where the polymer layers connect can separate or delaminate the two layers. The reactions at the bipolar interface are shown in Figures 1 and 2.

[0256] Furthermore, instead of losing CO to the anode, it is desirable to return CO to the cathode of the cell where it can be reduced. This allows pathways (e.g., pores) in the anion exchange layer (e.g., cathode buffer layer and / or cathode layer) to both remove water and CO from the interface and return CO to the cathode where it can react, preventing delamination.

[0257] Figure 2 is similar to Figure 1 but includes additional information regarding mass transport at the bipolar interface and the production of CO2 and water. For example, it shows that on the cathode side, hydroxide and CO2 react to produce bicarbonate ions, which migrate toward the bipolar interface 213. On the anode side, hydrogen ions produced by the oxidation of water migrate toward the bipolar interface 213, where they react with bicarbonate ions to produce water and CO2, both of which must be allowed to escape without damaging the bipolar layer.

[0258] 2 shows the water transport pathways, including (a) electroosmotic drag by anions from the cathode to the interface 213, (b) electroosmotic drag by cations from the anode to the interface 213, and (c) diffusion. Water evaporates at the anode and cathode.

[0259] Various MEA designs include features that resist delamination, and in some cases provide a path for reaction products to leave the interface region. In some embodiments, the bipolar interface is flat. However, in some designs, the interface is provided with a gradient and / or interlocking structure. These are described in more detail below with reference to Figures 3A, 3B, 3C, and 3D, which show bipolar interfaces of MEA designs configured to resist delamination.

[0260] Interfacial engineering can be used to reduce leakage of unwanted co-ions through the anion exchange membrane (AEM) and cation exchange membrane (CEM) and improve the mechanical stability of the bipolar membrane with better adhesion. Chemical and physical modifications to the interface can be used to achieve these two goals. As described in more detail below, the AEM and CEM layers can be chemically bonded through multiple crosslinking pathways (side chain, main chain, main chain to side chain, and triple crosslinks). In some embodiments, the AEM and CEM layers are interpenetrating. This can include one or more of a gradient of anion exchange polymer and a cation exchange polymer, a mixture of anion exchange polymer and a cation exchange polymer, and / or a protrusion where at least one polymer extends into the other.

[0261] There are also different methods for physically modifying the interface. Hot pressing the AEM and CEM at temperatures close to their respective glass transition temperatures can enhance adhesion between the AEM and CEM. In some embodiments, adhesion is improved by increasing the interfacial surface area by electrospinning the anion-exchange and cation-exchange layers. In such embodiments, the anion-cation-exchange ionomer and cation-exchange ionomer have similar swelling properties to avoid delamination. Adding a small concentration of a third polymer (e.g., PTFE) to the entangled ionomer may also facilitate water removal from the interface. Both the surfaces of the CEM and AEM can be intentionally roughened by plasma surface treatment, etching, or hot pressing with a woven or patterned fabric. One or more of these techniques may be used to increase contact between the AEM and CEM.

[0262] In some embodiments, the interface includes a gradient. For example, a gradient may be formed by using two nozzles during spray deposition and adding anion exchange polymer with varying relative amounts of polymer during deposition of the cation exchange layer. Similarly, cation exchange polymer may be added during deposition of the anion exchange layer. For example, with reference to FIG. 2 , the gradient may extend across substantially all or a portion of the anion exchange region and the cation exchange region, such that the anion exchange region has primarily anion exchange polymer adjacent to the cathode, with an increasing relative amount of cation exchange polymer migrating from the cathode toward the interface 213. Similarly, the cathode exchange region has primarily cation exchange polymer adjacent to the anode, with an increasing relative amount of anion exchange polymer migrating from the anode toward the interface 213. In some embodiments, there are pure anion exchange regions and pure cation exchange regions, with a gradient between the two.

[0263] In some embodiments, the layers of the bipolar membrane are fused together. This can be achieved by choosing an appropriate solvent. For example, Nafion is at least slightly soluble in a water / ethanol mixture. Using that mixture (or another solvent in which the cation-conducting polymer dissolves) as the solvent for the anion-conducting polymer can result in Nafion or other cation-conducting polymer being at least slightly soluble and fused to the interface. In some embodiments, this results in a thin gradient, for example, extending 0.5-10% of the thickness of the anion-conducting polymer layer.

[0264] In some embodiments, the interface comprises a mixture of polymers. Figure 3A shows a bipolar interface 313 in which a cation-conducting polymer 321 and an anion-conducting polymer 319 are mixed. The example in Figure 3A shows a portion of an anion-conducting polymer layer 309 and a portion of a cation-conducting polymer layer 311. Anion-conducting polymer layer 309 is a pure anion-conducting polymer, and cation-conducting polymer layer 311 is a pure cation-exchange polymer. Cation-conducting polymer 321 can be the same as or different from the cation-conducting polymer in cation-conducting polymer layer 311. Anion-conducting polymer 319 can be the same as or different from the anion-conducting polymer in anion-conducting polymer layer 309.

[0265] In some embodiments, the interface includes a third material that physically reinforces the interface. For example, FIG. 3B shows an example of material 330 spanning interface 313. That is, material 330 resides partially within anion-conducting polymer layer 309 and cation-conducting polymer layer 311. Thus, material 330 can bond the two layers in a manner that resists delamination. In one example, material 330 is an inert material, such as PTFE, polyvinylidene difluoride (PVDF), or charged colloidal spheres, e.g., surface-modified metal hydroxide spheres, e.g., Al(OH)3 with trimethylaluminum (TMA). The inert material may be in the form of a web or mesh with gaps that can be filled with an ionomer. Such an interface can be fabricated, for example, by casting or otherwise applying a cation-conducting polymer and an anion-conducting polymer to opposite sides of a PTFE mesh or similar structure, followed by hot-press bonding.

[0266] FIG. 3C shows a bipolar interface 313 having cation-conducting polymer protrusions 340 extending from the cation-conducting polymer layer 311 toward the anion-conducting polymer layer 309. These protrusions may mechanically strengthen the interface 313, preventing delamination when CO2 and water are produced at the interface. In some embodiments, the protrusions extend from the anion-conducting polymer layer 309 to the cation-conducting polymer layer 311. In certain embodiments, the protrusions extend in both directions. Exemplary dimensions are in-plane dimensions of 10 μm to 1 mm, although smaller dimensions (e.g., 500 nm to 1 μm) are also possible. The out-of-plane dimensions may be, for example, 10 to 75% or 10 to 50% of the total thickness of the anion-exchange layer. The protrusions may be fabricated by suitable techniques, such as lithography techniques, or by spraying a polymer onto a patterned mesh and then removing it. Surface roughness techniques may also be used to create the protrusions. In some embodiments, the protrusions may be formed from different materials, such as, for example, non-ionically conductive polymers, ceramics, or metals, which are useful for securing the polymer layers together and mechanically strengthening the interface.

[0267] 3D shows a bipolar interface 313 having an interfacial region 350 disposed between the cation-conducting polymer layer 311 and the anion-conducting polymer layer 309. The interfacial region 350 is or includes a third material. In some embodiments, the third material is mixed with one or both of the polymers. In some embodiments, the third material separates the polymers and is not mixed with them.

[0268] The third material is generally confined to the interfacial region 350. It may be mixed with one or both of the cationically and anionically conductive polymers and does not extend beyond region 350.

[0269] In some embodiments, the third material may be in particulate form. The particles may be mixed with other components, such as ion-conducting polymers and additives. The particles may be of any suitable shape, such as spherical, fibrous, or tubular. In some embodiments, the particles are nanoparticles. They may or may not be in the form of aggregates. Aggregates include spherical aggregates, ellipsoidal aggregates, linear aggregates, branched aggregates, and combinations thereof.

[0270] In some embodiments, the particles are or comprise carbon, including single-walled or multi-walled carbon nanotubes, fullerenes, spherical carbon particles, carbon powder, and the like.

[0271] In some embodiments, the particles are ceramic nanoparticles, including inorganic solids composed of oxides, carbides, carbonates, and phosphates. In a particular example, the nanoparticles may be magnesium oxide. In some embodiments, the particles are metal nanoparticles, such as iridium, gold, platinum, or titanium. In some embodiments, the particles are polymer- or lipid-based nanoparticles.

[0272] In some embodiments, the nanoparticles may be about 1 nanometer to about 250 nanometers in size, or about 10 nanometers to about 100 nanometers. In some embodiments, the nanoparticles are about 50 nanometers. Size refers to the average diameter. Particle aggregates may have larger diameters, for example, on the 250 micrometer scale.

[0273] Carbon nanoparticles have a large specific surface area and high electrical conductivity due to their sp2 hybridized carbon atom structure. In some embodiments, they may be functionalized covalently or non-covalently. Covalent functionalization can be direct or indirect. For example, aromatic molecules such as 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) may be used to improve the electrical properties of carbon nanotubes by linking π electrons between the aromatic molecule and the nanotube.

[0274] In some embodiments, the third material is or includes one or more porosity enhancers. Any particulate third material can be a porosity enhancer, with the aggregate particles packing to introduce porosity. Porosity enhancers are further described above with respect to porosity in the various layers of the MEA. Porosity can also be introduced in the interface region by any suitable method, such as by a suitable spray deposition technique, the use of a pore-forming agent, etc. The porosity enhancer in the interface region can be different from that in the cathode buffer layer.

[0275] In some embodiments, the third material is or includes a voltage attenuating agent. The porosity enhancers described above can act as voltage attenuating agents.

[0276] The large surface area of ​​nanoparticles gives them the ability to absorb discharge currents, such as those that occur during power interruptions, recovery processes, unplanned power outages, or equipment shutdowns. Because the AEM / PEM interface is a low surface area interface, introducing granular material at the interface beneficially increases the surface area for absorbing discharge currents. If the discharge current is absorbed, any hypothesized voltage rise due to a power interruption can be reduced.

[0277] During operation of the carbon oxide reduction reactor, a recovery process may be periodically performed, as described in more detail below. During the recovery process, cell selectivity may be increased; however, the desired selectivity improvement may be accompanied by an undesirable, irreversible voltage increase. The irreversible voltage increase may cause harmful membrane degradation. The use of a voltage attenuator material, such as carbon nanoparticles, at the interface of the AEM and PEM facilitates the recovery process and reduces or prevents voltage-induced degradation. Thus, a more aggressive recovery process may be performed.

[0278] In some embodiments, the third material is or includes a water splitting catalyst. When the electrochemical cell is turned off, an energy-intensive water splitting process can occur at the interface between the anion exchange membrane and the proton exchange membrane, resulting in membrane degradation. This is a reverse reaction, and during normal operation, water and carbon dioxide build up at the interface. Water is consumed during the reverse reaction. This leads to higher resistance and increased heat generation, which can cause membrane degradation. When particulate materials such as carbon nanoparticles are used at the interface, they can act as catalysts, facilitating the water splitting process and reducing membrane degradation. Similarly, other catalytic materials can perform the same function. Suitable catalysts may include iridium, gold, platinum, or titanium.

[0279] In some embodiments, the third material is a mixture composed of particles dispersed within a polymer. The polymer and nanoparticle mixture may be made by dissolving the polymer in a solvent. The dissolved polymer is then combined with the nanoparticles and vigorously mixed or sonicated to create a stable, well-dispersed mixture that is spray-deposited onto the film. In some embodiments, the film surface may be roughened prior to spray-deposition of the polymer / nanoparticle interfacial mixture.

[0280] In some embodiments, the polymer is an ion-conducting polymer. Useful ion-conducting polymers include those listed in the polymer structure section above. In some embodiments, the polymer has a molecular weight of 100 g / mol or greater. In some embodiments, the ion-conducting polymer is an anion-conducting polymer, a cation-conducting polymer, or an anion- and cation-conducting polymer listed in the ion-conducting polymers table above. In some embodiments, the polymer is a cation-conducting polymer, such as a sulfonated tetrafluoroethylene-based fluoropolymer copolymer. Examples include Nafion 115, Nafion 117, Nafion 211, Nafion 324, Nafion 350, Nafion 417, Nafion 424, Nafion 438, Nafion 450, Nafion 521, or Nafion 551. The polymer may be dissolved in a suitable solvent for spray application. In certain embodiments, the solvent includes ethanol, 1-propanol, 2-propanol, water, or a mixture thereof. The concentration of the polymer in the solvent may range from about 1 weight percent to about 20 weight percent.

[0281] For example, the third material can be a mixture of a cationically conductive sulfonated tetrafluoroethylene-based fluoropolymer copolymer and carbon nanoparticles. The ratio of polymer to nanoparticles can be from about 10:1 to about 1:0.01, or from about 5:1 to about 2:1, by weight percent. In some embodiments, the ratio is about 1:1, by weight percent.

[0282] According to various embodiments, the ion-conducting polymer in the interfacial region may be the same as that in the cation-conducting polymer layer or the anion-conducting polymer layer. In some embodiments, the ion-conducting polymer in the interfacial region is different from that in the cation-conducting polymer layer and the anion-conducting polymer layer. In some embodiments, the interfacial region may include a third material (e.g., carbon nanoparticles) embedded in both the anion-conducting polymer layer and the cation-conducting polymer layer.

[0283] In some embodiments, the interfacial region 350 may be about 0.1 to about 20 micrometers thick, or about 1 to about 10 micrometers thick, or about 1 to about 5 micrometers thick. In some embodiments, the interfacial region is 3 micrometers thick. The ratio of the thickness of the anion-conducting polymer layer to the interfacial region is about 20:1, 10:1, or 2:1.

[0284] The present disclosure also includes methods for mitigating the effects of current fluctuations. In some embodiments, a method for mitigating the effects of current fluctuations in a bipolar membrane electrochemical cell includes providing an electrochemical cell having a bipolar membrane, the bipolar membrane comprising an anion-conducting polymer layer, a cation-conducting polymer layer, and an interfacial layer between the anion-conducting polymer layer and the cation-conducting polymer layer of the bipolar membrane, the interfacial layer comprising nanoparticles, such as carbon nanoparticles; and applying a current fluctuation to the electrochemical cell, thereby inhibiting degradation of at least one of the anion-conducting polymer layer or the cation-conducting polymer layer caused by the electrical current fluctuations.

[0285] In some embodiments, the electrical current fluctuations are due to turning the cell on and off. In some embodiments, the current fluctuations are caused by power interruptions, current reversals, or power outages. In some embodiments, degradation of the anion-conducting polymer layer and the cation-conducting polymer layer caused by current fluctuations is reduced. In some embodiments, the lifespan of the bipolar membrane electrochemical cell is extended.

[0286] Referring again to FIG. 3D, in some embodiments, for example, the third material can be additive, as described in more detail below. In some embodiments, the third material can be a blend of an anion-conducting ionomer and a cation-conducting ionomer at the interface. For example, it can be a mixture of 5 wt. % Nafion ionomer and 2 wt. % Orion mTPN1. In some embodiments, the third material can include an ion acceptor and donor, which can be mixed or provided as separate layers.

[0287] In some embodiments, the interfacial region contains additives to facilitate acid-base reactions and prevent delamination. In some embodiments, the additives may facilitate diffusion of acid-base recombination over a larger volume rather than just at the two-dimensional interface between the anion-conducting polymer and the cation-conducting polymer. This can lower the membrane resistance by dispersing water and CO2 formation, heat generation, and reducing the barrier to acid-base reactions. This can be advantageous in avoiding product heat buildup and reducing resistive losses in the MEA, leading to reduced cell voltage. Additionally, the additives help prevent material degradation at the interface due to heat and gas generation.

[0288] Examples of additives that facilitate acid-base reactions include molecules with both proton and anion acceptors, such as ionic liquids containing 1-butyl-3-methylimidazolium hydroxide. Other ionic liquids, such as those with any of the following ionic groups, can also be used: N,N,N,N-tetraalkylammonium (e.g., N,N,N,N-tetramethylammonium, N,N-dimethyl-N,N-dipropylammonium, or N-methyl-N,N,N-tri-C 1-12 alkylammonium), N,N,N-trialkylammonium-1-yl (e.g., N,N,N-trimethylammonium-1-yl, N-methyl-N,N-dipropylammonium-1-yl, or N,N,N-tri-C 1-12 alkylammonium-1-yl), N,N,N-trialkyl-N-alkoxyalkylammonium (e.g., N,N,N-trimethyl-N-alkoxyalkylammonium, N-methyl-N,N-diethyl-N-methoxyethylammonium, or N,N,N-tri-C 1-12 Alkyl-NC 1-6 Alkoxy-C 1-6 alkylammonium), N,N-dialkyl-N-alkoxyalkylammonium-1-yl (e.g., N,N-dimethyl-N-alkoxyalkylammonium-1-yl or N,N-di-C 1-12 Alkyl-NC 1-6 Alkoxy-C 1-6 alkylammonium-1-yl), N,N-dialkylpyrrolidinium (e.g., N,N-dimethylpyrrolidinium, N-methyl-N-ethylpyrrolidinium, or N-methyl-NC 1-12 alkylpyrrolidinium), N-alkylpiperidinium-1-yl (e.g., N-methylpiperidinium-1-yl or NC 1-12 alkylpiperidinium-1-yl), N,N-dialkylpiperidinium (e.g., N,N-dimethylpiperidinium, N-methyl-N-ethylpiperidinium, or N-methyl-NC 1-12alkylpiperidinium), N-alkylpiperidinium-1-yl (e.g., N-methylpiperidinium-1-yl or NC 1-12 alkylpiperidinium-1-yl), N,N,4-trialkylpiperidinium (e.g., N,N,4-trimethylpiperidinium, N,4-dimethyl-N-ethylpiperidinium, or N-methyl-N,4-di-C 1-12 alkylpiperidinium), N,4-dialkylpiperidinium-1-yl (e.g., N,4-dimethylpiperidinium-1-yl or N,4-di-C 1-12 alkylpiperidinium-1-yl), N,N,3,5-tetraalkylpiperidinium (e.g., N,N,3,5-tetramethylpiperidinium, N,3,5-trimethyl-N-ethylpiperidinium, or N-methyl-N,3,5-tri-C 1-12 alkylpiperidinium), N,3,5-trialkylpiperidinium-1-yl (e.g., N,3,5-trimethylpiperidinium-1-yl or N,3,5-tri-C 1-12 alkylpiperidinium-1-yl), N,N,2,6-tetraalkylpiperidinium (e.g., N,N,2,6-tetramethylpiperidinium, N,2,6-trimethyl-N-ethylpiperidinium, or N-methyl-N,2,6-tri-C 1-12 alkylpiperidinium), N,2,6-trialkylpiperidinium-1-yl (e.g., N,2,6-trimethylpiperidinium-1-yl or N,2,6-tri-C 1-12 alkylpiperidinium-1-yl), N,N-dialkylazepanium (e.g., N,N-dimethylazepanium, N-methyl-N-ethylazepanium, or N-methyl-NC 1-12 alkylazepanium), N-alkylazepanium-1-yl (e.g., N-methylazepanium-1-yl or NC 1-12 alkylazepanium-1-yl), N,N-dialkylmorpholinium (e.g., N,N-dimethylmorpholinium, N-methyl-N-ethylmorpholinium, or N-methyl-NC 1-12alkylmorpholinium), N-alkylmorpholinium-4-yl (e.g., N-methylmorpholinium-4-yl, or NC 1-12 alkylmorpholinium-4-yl), N1,N3-dialkylimidazolium (e.g., N1,N3-dimethylimidazolium, N1-ethyl-N3-methylimidazolium, or N1-C 1-12 alkyl-N3-methyl-imidazolium), N3-alkylimidazolium-1-yl (e.g., N3-methylpiperidinium-1-yl or N3-C 1-12 alkylpiperidinium-1-yl), 1-alkyl-1-azabicyclo[2.2.2]octane (e.g., 1-methyl-1-azabicyclo[2.2.2]octane or 1-C 1-12 alkyl-1-azabicyclo[2.2.2]octane) or 1-azoniabicyclo[2.2.2]octan-1-yl, each of which can be optionally substituted (e.g., substituted on the ring by one or more alkyl and / or substituted on the alkyl by one or more heteroatoms).

[0289] In some embodiments, a different ionomer may be used than that of the anion-conducting polymer layer and the cation-conducting polymer layer. For example, a relatively highly conductive anion exchange material, such as Sustanion, may be used. Such anion exchange materials may not be selective enough for use as a cathode buffer layer, but may be used at the interface.

[0290] In certain examples, an ionomer may be used at the interface that has a higher ion exchange capacity than at least one of the ionomers of the bipolar membrane. Such ionomers may not be suitable for the layers of the bipolar membrane, for example, due to their tendency to swell or lack of stability, but can be added to the interface. In certain examples, ionomers with improved adhesion and physical contact may be used. Interfacial polymers that penetrate both layers may be used to improve adhesion. The ionomer at the interface may itself have multiple sublayers. In one example, a third ionomer may have a central region with more voids disposed between denser regions.

[0291] In some embodiments, the ionomer used at the interface is a different anion-exchange ionomer from the anion-conducting polymer of the anion-conducting polymer layer and may be referred to as an interfacial AEM to distinguish it from the bulk AEM of the anion-conducting polymer layer. In some such embodiments, the interfacial AEM has a lower water uptake than the anion-conducting polymer layer to match that of the PFSA or other cation-conducting polymer. This may help prevent delamination at the interface while maintaining a higher ion exchange capacity (IEC). Both the high IEC and low water uptake of the interfacial ionomer may help minimize cation crossover from the anode side. The lower water uptake may be due to the interfacial ionomer having smaller ion-conducting channels than the anion-conducting polymer of the bipolar membrane. The higher IEC may be due to a higher concentration of cationic functional groups on the interfacial ionomer. One or both of these features may be present in the interfacial ionomer, limiting cations from the cathode.

[0292] In certain embodiments, applying a forward bias to the bipolar membrane causes ion recombination at the interface, resulting in the formation of products such as water. The interfacial layer should be mechanically robust during ion recombination (i.e., indicating sufficient adhesion between the AEM and CEM of the bipolar membrane) while minimizing leakage of unwanted co-ions through the AEM and CEM. In some embodiments, the AEM interface has a thickness of 0.1% to 10% of the thickness of the bulk AEM, with example thicknesses of bulk AEM ranging from 5 to 80 μm. The volume percent of the interfacial AEM 1 and 90 can be kept relatively low to avoid additional ohmic resistance across the bipolar membrane. The water absorption rate of the interfacial AEM may range from 0% to 25% to avoid membrane delamination due to mismatched expansion characteristics between the adjacent AEM and CEM. At some interfaces, the AEM may have an ion exchange capacity (IEC) of 2.5 to 3.0 mmol / g. In some such embodiments, the IEC of the bulk AEM may be lower than the IEC of the interfacial AEM, ranging from 1.5 to 2.5 mmol / g. The high density of positively charged functional groups at the interface (i.e., high IEC) serves to electrostatically repel undesired co-ions (e.g., H+ or K+) from transporting into the bulk AEM via the Donnan exclusion effect.

[0293] Examples of additional materials that may be present at the interface include block copolymers with differently charged groups (e.g., cationic and anionic static charge groups), cation-conducting polymer and anion-conducting polymer resin materials, ion donors, e.g., oxides such as graphene oxide, catalysts for acid / base recombination, catalysts that react with H2 and O2 diffusing from the anode and cathode, water splitting catalysts, CO2 absorbing materials, and H2 absorbing materials.

[0294] In some embodiments, the anion-conducting polymer and the cation-conducting polymer of the bipolar membrane have the same backbone but different fixed charge groups. As an example, Orion ionomers may be used with different fixed charge groups. The ionomers are more compatible and less prone to peeling.

[0295] In the above example, interface 313 may be a three-dimensional volume having a thickness of 1% to 90% of the total thickness of the bipolar membrane, or 5% to 90%, 10% to 80%, 20% to 70%, 30% to 60% of the total thickness of the bipolar membrane. In some embodiments, this is less than half of the total thickness, e.g., 0.1% to 30%, 5% to 25%, 5% to 20%, 5% to 15%, or 0.5% to 5%.

[0296] Any of the above bipolar interfaces may be hot-pressed, particularly between the anion-exchange membrane layer and the cation-exchange membrane layer, to soften the polymer electrolyte and thereby allow it to fuse.

[0297] In some embodiments, the bipolar AEM / PEM interface comprises a relatively smooth PEM layer in contact with a rough AEM layer. For example, in such embodiments, the arithmetic mean height (S a ) can be in the range of approximately 0-0.2 μm. The AEM layer in contact with the PEM layer can have a higher roughness, in some embodiments having a Sa in the range of 0.2-0.5 μm, 0.4-1.5 μm, or 0.6-1 μm. The roughness of the AEM creates a discontinuous interface with the PEM. The Sa of the AEM layer in contact with the PEM a can be reduced to approximately 0-0.2 μm or 0-1 μm by modifying the fabrication parameters, for example, by partially dissolving the polymer electrolyte with a solvent followed by evaporation to leave a smoother surface, or by hot pressing. The AEM layer can be substantially continuously non-porous or can contain pores that allow gas and / or water transport, with typical porosity ranges of 0.1%-90%, 1%-20%, and 5%-15%.

[0298] In another embodiment, the surface of the PEM membrane is a The roughness of the AEM layer in contact with the PEM membrane may be 5-10 μm, 1-5 μm, 0.2-1 μm, or 0.4-0.6 μm. In some such embodiments, the AEM layer in contact with the PEM membrane has an S of approximately 0-1 μm, or approximately 0-0.2 μm.a or S in the range of 2 to 5 μm, 0.4 to 1.5 μm, or 0.6 to 1.0 μm. a The AEM may be substantially continuous and non-porous or may contain pores that allow gas and / or water transport, with typical porosity ranges of 0.1% to 90%, 1% to 20%, and 5% to 15%.

[0299] In some embodiments, a crosslinking agent may be added to covalently crosslink one polymer of the bipolar membrane. The crosslinking agent may be used at the interface of the ion-conducting polymer layer. Each layer may contain one or more polymers, each characterized by an attached backbone and side chains. The crosslinking reaction may occur not only at the interface, but also between the crosslinker and (i) two or more side chains, (ii) two or more main chains, or (iii) a combination of two or more side chains and backbone(s).

[0300] The crosslinking agent can be divalent, trivalent, tetravalent, or other higher valent. In this manner, the crosslinking agent can react with any number of reactive groups present in the cation-conducting, anion-conducting, or mixed interface of the cation-conducting and anion-conducting polymer layers. In some embodiments, the crosslinking agent: [ka] are listed, wherein Ak is an optionally substituted aliphatic, alkylene, cycloaliphatic, or cycloalkylene; Ar is an optionally substituted aromatic, arylene, heteroaromatic, or heteroarylene; L is a linking moiety (e.g., any of those described herein); L3 is an integer of 2 or greater; and X is halo, hydroxyl, optionally substituted amino (e.g., NR N1 R N2 , where R N1 and R N2are independently H or optionally substituted alkyl), carboxyl, acyl halide (e.g., —C(O)—R, where R is halo), carboxaldehyde (e.g., —C(O)H), or optionally substituted alkyl.

[0301] Non-limiting examples of crosslinking agents include terephthalaldehyde, glutaraldehyde, orthoxylene, para-xylene, meta-xylene, or polyamines, diamines, triamines, tetraamines, pentaamines, etc., such as 1,6-diaminohexane (hexanediamine, DHA), N,N'-dimethyl-1,6-hexanediamine, N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA), 1,3-diaminopropane, N,N'-dimethyl-1,3-propanediamine, N,N,N',N'-tetramethyl-1,3 -propanediamine, 1,4-diaminobutane, N,N'-dimethyl-1,4-butanediamine, N,N,N',N'-tetramethyl-1,4-butanediamine, 1,8-diaminooctane, N,N'-dimethyl-1,8-octanediamine, N,N,N',N'-tetramethyl-1,8-octanediamine, propane-1,2,3-triamine, [1,1':3',1''-terphenyl]-4,4''-5'-triamine, 1,3,5-triazine-2,4,6-triamine (melamine), and the like can be mentioned.

[0302] In some embodiments, a crosslinking agent is used to crosslink between side groups of the first and second polymer layers. The side groups can include reactive groups that are present within the material or attached in any useful manner. [ka]

[0303] For example, if the polymer layer contains an ionic or ionizable side group (e.g., —SO2OH, —CO2H, etc.), this group can be converted to provide a reactive group (e.g., a halo group or a leaving group).

[0304] In one non-limiting embodiment, as seen in step (i) of Scheme I above, the first polymer (1) contains an ionic side group (—SO OH), which is converted to a reactive group (—SO Cl in (2)) using thionyl chloride. Meanwhile, the second polymer may contain reactive side group(s) (e.g., halides such as bromides, haloalkyls, or other leaving groups) as shown in (4). Crosslinks are formed between the reactive groups using a crosslinking agent. As shown in step (ii) of Scheme I above, the reactive groups in the first polymer (2) and the second polymer (4) react with the crosslinking agent, which is a polyamine (3). In this way, crosslinks (5) are formed at the interface and between the side groups. As an example, polymer layers can be crosslinked based on the formation of two or more covalent bonds (e.g., N-S covalent bonds, N-C covalent bonds, or C-C covalent bonds).

[0305] In other embodiments, the crosslinking agent forms crosslinks between the backbones of the first polymer layer and the second polymer layer. [ka]

[0306] In one non-limiting embodiment, as shown in Scheme II above, the first polymer (6) and the second polymer (8) contain an aryl backbone. A crosslinking agent is then used to react with the backbone groups. When the crosslinking agent is a polyhydroxyalkyl, such as (7), the two polymer layers can be crosslinked by acid catalysis in the presence of a proton source, such as an organic acid (e.g., trifluoromethanesulfonic acid, sulfuric acid, methanesulfonic acid, trifluoroacetic acid, p-toluenesulfonic acid, etc.). As an example, the hydroxyalkyl crosslinking agent can be a tertiary alcohol that is protonated by a Brønsted acid, losing water as a by-product and forming a tertiary carbocation intermediate. This intermediate can easily react with the π electrons of the aromatic backbone through electrophilic substitution. In this manner, the aromatic backbone of the polymer layer can be grafted with the crosslinking agent to form a dense polymer matrix.

[0307] In yet other embodiments, a crosslinking agent is used to bridge the linkages between the side group(s) of the first polymer layer and the backbone(s) of the second polymer layer, e.g., the side groups can be converted to nucleophiles and the backbone can contain electrophiles. [ka]

[0308] In one non-limiting embodiment, as shown in Scheme III above, the first polymer (1) contains an ionic side group (—SOOH), which is converted to a reactive group (—SOCl in (2)) using thionyl chloride, and then aminated to form a reactive nucleophilic group (e.g., —SONR in (10)). N1 R N2 The second polymer (8) can contain an aryl backbone capable of reacting with a polyvalent crosslinker. For example, the crosslinker (11) can be a hydroxyhaloalkyl, which can be reacted via an acid-catalyzed Friedel-Crafts alkylation reaction to yield an alkylated polymer (12). Finally, the first polymer (10) bearing nucleophilic groups can be reacted with the second polymer (12) bearing electrophilic groups to yield a crosslinked polymer (13). Alternative chemicals, reactive groups, electrophiles, and nucleophiles, can be used to provide reactive pairs within the first and second polymers that can react at the interface.

[0309] MEA layer thickness In certain embodiments, the polymer electrolyte membrane and adjacent cathode buffer layer or other anion-conducting polymer layer may have relative thicknesses that facilitate fabrication of the MEA and / or improve operational performance.

[0310] The MEA sublayers may include an anion-conducting polymer layer (AEM), which may be a cathode buffer layer, a polymer electrolyte membrane (PEM), which may be a cation-conducting polymer layer (e.g., a proton exchange polymer layer), or an anion-conducting polymer layer. In some embodiments, the PEM is relatively thicker than the anion-conducting polymer layer. For example, the PEM is about 120 micrometers thick, and the AEM is about 10-30 or 10-20 micrometers thick. The PEM may provide mechanical stability to the AEM.

[0311] In some cases, anion-conducting polymers are significantly less conductive than cation-conducting polymers. Therefore, a relatively thin cathode buffer is used to provide the benefits of a cathode buffer layer (e.g., an anion-conducting polymer layer) without significantly increasing the overall resistance of the MEA. However, if the cathode buffer layer is too thin, it becomes difficult to handle during MEA fabrication and other situations. Therefore, in certain embodiments, a thin cathode buffer layer is fabricated on top of a relatively thick PEM layer, such as a cation-conducting polymer layer. The anion-conducting polymer layer may be fabricated on the PEM layer, for example, using any of the fabrication techniques described elsewhere herein.

[0312] In various embodiments, the polymer electrolyte membrane layer is about 20 microns to 200 microns thick. In some embodiments, the polymer electrolyte membrane layer is about 60 microns to 120 microns thick. In some embodiments, a thin polymer electrolyte membrane layer, about 20 microns to 60 microns thick, is used. In some embodiments, a relatively thick polymer electrolyte layer (about 120-200 microns thick) is used.

[0313] In some embodiments, a thinner cathode buffer layer is used in combination with a thin polymer electrolyte membrane. This may facilitate returning CO formed at the interface to the cathode rather than the anode. In some embodiments, a thicker cathode buffer layer is used in combination with a thick polymer electrolyte membrane. In some embodiments, this may result in a lower cell voltage.

[0314] Factors that can affect the thickness of the cathode buffer layer include the ion selectivity of the anion-conducting polymer, the porosity of the anion-conducting polymer, and the compatibility of the anion-conducting polymer with the polymer electrolyte membrane.

[0315] Many anion-conducting polymers have selectivity in the 95% range for anions, with approximately 5% of the current being for cations. By using highly selective anion-conducting polymers with selectivity greater than 99% for anions, it is possible to achieve a significant reduction in thickness while still providing sufficient buffering.

[0316] The mechanical strength of the anion-conducting layer can also affect its thickness, with a mechanically stable layer allowing for thinner layers. The thickness of the anion-conducting layer may be reduced by reducing the porosity of the anion-conducting polymer.

[0317] In some implementations, the cathode buffer layer or other anion-conducting polymer layer abutting the polymer electrolyte membrane is about 5-50 micrometers, 5-40 micrometers, 5-30 micrometers, 10-25 micrometers, or 10-20 micrometers thick. In some embodiments, the use of a more than 99% selective polymer allows the cathode buffer layer to be reduced to 2-10 microns.

[0318] In some cases, the thickness ratio of the polymer electrolyte membrane to the adjacent anion-conducting polymer layer is about 3:1 to 90:1, with higher ratios being used for highly selective anion-conducting polymer layers. In some embodiments, the ratio is 2:1 to 13:1, 3:1 to 13.1, or 7:1 to 13.1.

[0319] In certain embodiments, a relatively thin PEM improves several aspects of MEA performance. Referring to FIG. 4 , for example, the polymer electrolyte membrane 405 may have a thickness of approximately 50 micrometers, and the anion-conducting layer 403 may have a thickness of approximately 10-20 micrometers. A thin PEM favors the migration of water generated at the AEM / PEM interface to the anode. The gas pressure at the cathode side of the cell is 80-450 psi, which causes water present at the interface to migrate to the anode. However, in some cases, a thick PEM can cause a large portion of the water to migrate through the AEM to the cathode, causing flooding. Using a thin PEM can avoid flooding.

[0320] In some embodiments, the thin PEM can have a thickness of 10 micrometers to 50 micrometers, 30 micrometers to 50 micrometers, or 25 micrometers to 35 micrometers. In some such embodiments, the AEM can have a similar thickness to the PEM, such as 5 micrometers to 50 micrometers, 5 micrometers to 30 micrometers, or 10 micrometers to 20 micrometers. The PEM:AEM thickness ratio can be 1:2 to 1:1 when using a PEM with a thickness of 10 to 30 micrometers, 1:2 to 2:1 when the PEM thickness is 30-50 micrometers, and 1:1 to 3:1 when the PEM thickness is 20 to 35 microns. As described in more detail below, AEMs in these thickness ranges can be useful for water management.

[0321] Commercially available anion and cation exchange membranes typically have known thicknesses. For example, Nafion® membranes have the following dry thicknesses: [Table 3]

[0322] Using that known thickness, the thickness ratio can be determined. For example, as described above in the cathode buffer layer section, if the AEM has a thickness of about 200 nm to 100 μm, 300 nm to 75 μm, or 500 nm to 50 μm, the PEM:AEM thickness ratio can be determined as follows: [Table 4]

[0323] The AEM may have a thickness that aids in water management, as discussed further below.

[0324] Water Management CO X One of the major challenges in electrolyzers is water management on the cathode side, which can lead to hydration of the polymer electrolyte and / or CO X While water must be present to participate in the reduction reaction, if there is an excess of water, CO X This is to block the transport of cations to the cathode catalyst. Water can be transported in polymer electrolyte systems by two main methods: electroosmotic drag and diffusion. Through diffusion, water moves from regions of high concentration to regions of low concentration, and the rate of water transport depends on the diffusion coefficient, which is an intrinsic property of the polymer electrolyte material. Electroosmotic drag is the movement of water molecules along with ions through the polymer electrolyte. In cation exchange membrane systems, water is transported from the anode to the cathode along with the migration of cations. In anion exchange membrane systems, water moves in the opposite direction to the anions.

[0325] In bipolar membranes (such as cation-exchange and anion-exchange membranes), the net transport of water from the anode to the cathode can be controlled by varying the thickness and / or material properties of the anion-exchange and cation-exchange polymer electrolyte layers.

[0326] In some embodiments, the AEM may have a thickness of 5 to 80 microns, 5 to 50 microns, 5 to 40 microns, or 5 to 30 microns. As described below, a relatively thick AEM may aid in water management and preventing spalling, thereby extending life. However, this thickness also contributes to high voltage and low efficiency. Thus, in some embodiments, the AEM may be no more than 50 microns thick.

[0327] The table below shows the net water transport per ionic charge through the polymer electrolyte from the anode to the cathode of a COx electrolyzer when the thickness of the anion-exchange polymer electrolyte layer and the thickness of the cation-exchange membrane are varied. Increasing the thickness of the anion-exchange polymer electrolyte layer reduces the net water transport from the anode to the cathode. Increasing the molecular weight of the anion-exchange polymer reduces the diffusion coefficient of water through the anion-exchange layer. This has the same effect of reducing the net water transport per ionic charge from the anode to the cathode of the device.

[0328] Nafion 115 (PFSA cation exchange membrane, 127 microns thick) [Table 5]

[0329] [Table 6]

[0330] Thus, in some embodiments, the ratio of the thickness of the cation exchange membrane to the thickness of the anion exchange membrane (i.e., the PEM:AEM ratio) in a bipolar MEA does not exceed 7:1, is 5:1, 3:1, 2:1, 1.5:1, 1:1, or 1:1.5.

[0331] [Table 7]

[0332] Thus, in some embodiments, the molecular weight of the anion exchange polymer electrolyte can be at least 50 kg / mol, at least 60 kg / mol, at least 70 kg / mol, at least 80 kg / mol, or at least 90 kg / mol.

[0333] In some embodiments, the AEM polymer may be crosslinked to reduce water migration from the anode to the cathode.

[0334] CO2 electrolyzer 5 illustrates an exemplary system 500 of a carbon oxide reduction reactor 503 (often referred to herein as an electrolyzer), which may include cells including membrane electrode assemblies (MEAs). The reactor may include multiple stacked cells or MEAs. System 500 includes an anode subsystem 501 associated with the anode of reduction reactor 503 and a cathode subsystem 502 associated with the cathode of reduction reactor 503. System 500 is an example of a system that may be used to use or implement any of the methods or operating conditions described above.

[0335] As shown, the cathode subsystem includes a carbon oxide source 509 configured to provide a feed stream of carbon oxides to the cathode of the reduction reactor 503, which, during operation, may produce an output stream at the cathode that includes the product(s) of the reduction reaction. The product stream may include unreacted carbon oxides and / or hydrogen. See 508.

[0336] The carbon oxide source 509 is coupled to a carbon oxide flow controller 513 configured to control the volumetric or mass flow rate of the carbon oxide to the reduction reactor 503. One or more other components may be disposed on the flow path from the carbon oxide source 509 to the cathode of the reduction reactor 503. For example, an optional humidifier 504 may be installed on the path and configured to humidify the carbon oxide feed stream. The humidified carbon oxide can wet one or more polymer layers of the MEA, thereby preventing these layers from drying out. Another component that may be disposed on the flow path is a purge gas inlet coupled to a purge gas source 517. In certain embodiments, the purge gas source 517 is configured to supply purge gas during periods when the current to the cell(s) of the reduction reactor 503 is paused. In some implementations, flowing the purge gas over the 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 thereof.

[0337] In various embodiments, a CO2 purification device described herein (not shown in FIG. 5) is located upstream of source 509. The CO2 purification device may be considered part of the cathode subsystem.

[0338] During operation, the output stream from the cathode flows through conduit 507, which is connected to a backpressure controller 515 configured to maintain the pressure on the cathode side of the cell within a certain range (e.g., about 50-800 psig, depending on system configuration). The output stream may provide reduction product 508 to one or more components (not shown) for separation and / or concentration.

[0339] In certain embodiments, the cathode subsystem is configured to controllably recycle unreacted carbon oxides from the exhaust stream back to the cathode of the reduction reactor 503. In some implementations, the output stream is stripped of the reduction product(s) and / or hydrogen before recycling the carbon oxides. Depending on the configuration and operating parameters of the MEA, 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 combination thereof. In certain embodiments, one or more components (not shown) for removing water from the product stream are disposed downstream from 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 dry gas, such as for downstream processes, as needed. In some implementations, the recycled carbon oxides may be combined with fresh carbon oxides from a source 509 upstream of the cathode. Although not shown in FIG. 5, there are one or more optional separation components that may be positioned in the path of the cathode exhaust stream and configured to concentrate, separate, and / or store the reduction products from the reduction product stream.

[0340] As shown in FIG. 5 , the anode subsystem is configured to provide an anode feed stream to the anode side of the carbon oxide reduction reactor 503. In certain embodiments, the anode subsystem includes an anode water source (not shown) configured to supply fresh anode water to a recirculation loop that includes an anode water reservoir 519 and an anode water flow controller 511. The anode water flow controller 511 is configured to control the flow rate of anode water to and from the anode of the reduction reactor 503. In the illustrated embodiment, the anode water recirculation loop is coupled to components for adjusting the composition of the anode water. These may include a water reservoir 521 and / or an anode water additive source 523. The water reservoir 521 is configured to provide water (the water circulating in the anode water recirculation loop) having a different composition than the anode water tank 519. In one example, the water in the water reservoir 521 is pure water that can dilute solutes or other components in the circulating anode water. The pure water may be conventional deionized water or may be ultrapure water, for example, having a resistivity of at least about 15 MOhm-cm or greater than 18.0 MOhm-cm. The anode water additive source 523 is configured to supply salts and / or other component solutes to the circulating anode water.

[0341] During operation, the anode subsystem may provide water or other reactants to the anode of reactor 503, where they at least partially react to produce oxidation products, such as oxygen. The products, along with unreacted anode feed material, are provided to the reduction reactor outlet stream. Although not shown in FIG. 5, there are one or more optional separation components that may be positioned in the path of the anode exhaust stream and configured to concentrate, separate, and / or store the oxidation products from the anode product stream.

[0342] System 500 may include other control functions. For example, a temperature controller may be configured to heat and / or cool carbon oxide reduction reactor 503 at appropriate times during operation. In the illustrated embodiment, temperature controller 505 is configured to heat and / or cool the anode water supplied to the anode water recirculation loop. For example, temperature controller 505 may include or be coupled to heaters and / or coolers that can heat or cool the water in anode water reservoir 519 and / or the water in water reservoir 521. In some embodiments, system 500 includes temperature controllers configured to directly heat and / or cool components other than the anode water components. Examples of other components in the cell or stack and carbon oxide flow to the cathode:

[0343] In certain embodiments, system 500 is configured to regulate the flow rate of carbon oxide to the cathode and / or the flow rate of anode feed material to the anode in reactor 503. Components that may be controlled for this purpose may include a carbon oxide flow controller 513 and an anode water controller 511.

[0344] Certain components of system 500 may operate to control the composition of the carbon oxide feed stream and / or the anode feed stream. For example, water reservoir 521 and / or anode water additive source 523 may be controlled to adjust the composition of the anode feed stream. In some cases, additive source 523 may be configured to adjust the concentration of one or more solutes, such as one or more salts, in the aqueous anode feed stream.

[0345] In some cases, such a controller, temperature controller 505, is configured to adjust the temperature of one or more components of system 500 based on the phase of operation. For example, the temperature of cell 503 may increase or decrease during break-in, during current interruptions during normal operation, and / or during storage.

[0346] In some embodiments, the carbon oxide electrolytic reduction system is configured to allow for easy removal of the reduction cell from other system components. This can be useful when the cell needs to be removed for storage, maintenance, refurbishment, etc. In the illustrated embodiment, isolation valves 525a and 525b are configured to block fluid communication from cell 503 to the carbon oxide source, cathode source, and backpressure controller 515, respectively. Additionally, isolation valves 525c and 525d are configured to block fluid communication between cell 503 and the anode water inlet and outlet, respectively.

[0347] The carbon oxide reduction reactor 503 may be operated under the control of one or more electrical power sources and associated controllers. See block 533. The electrical power sources and controllers 533 may be programmed or otherwise configured to control the current supplied to the electrodes of the reduction reactor 503 and / or to control the voltage applied to the electrodes. Any of the current profiles described herein may be programmed into the power sources and controllers 533.

[0348] In certain embodiments, the electrical power source and controller 533 performs some, but not all, of the operations necessary to implement the control profile of the carbon oxide reduction reactor 503. A system operator or other responsible party, in conjunction with the electrical power source and controller 533, can completely define the schedule and / or profile of the electrical current applied to the reduction reactor 503. In certain embodiments, the electrical power source and controller 533 controls the operation of a carbon oxide purifier disposed upstream of the carbon oxide source 509.

[0349] In certain embodiments, the electrical power source and controller operates in conjunction with one or more other controllers or control mechanisms associated with other components of system 500. For example, electrical power source and controller 533 may act in conjunction with a controller to control the purification of carbon oxides, the delivery of carbon oxides to the cathode, the supply of anode water to the anode, the addition of pure water or additives to the anode water, and any combination of these functions. In some implementations, one or more controllers are configured to control or operate in cooperation to control any combination of the following functions: applying current and / or voltage to the reduction cell 503, controlling backpressure (e.g., via backpressure controller 515), supplying purge gas (e.g., using purge gas component 517), delivering carbon oxide (e.g., via carbon oxide flow controller 513), humidifying carbon oxide in the cathode feed stream (e.g., via humidifier 504), anode water flow to and / or from the anode (e.g., via anode water flow controller 511), and anode water composition (e.g., via anode water source 505, pure water reservoir 521, and / or anode water additive component 523).

[0350] In the illustrated embodiment, the voltage monitoring system 534 is used to determine the voltage between the anode and cathode of an MEA cell or the voltage between any two electrodes of a cell stack (e.g., to determine the voltage between all cells in a multi-cell stack). In certain embodiments, the voltage monitoring system 534 is configured to work in conjunction with the power supply 533 to maintain the reduction cell 503 within a specified voltage range. For example, if the cell voltage falls outside a defined range (as determined by the voltage monitoring system 534), the power supply can be configured to provide a current or voltage to the electrodes to maintain the cell voltage within the specified range.

[0351] 5 may employ a control system including 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 measurement instruments, chromatography systems, optical sensors such as absorbance measurement tools, and the like. Such sensors may be coupled to the inlets and / or outlets of the MEA cells (e.g., in the flow field), reservoirs for holding anode water, pure water, salt solutions, and the like, and / or other components of the carbon oxide electroreduction system.

[0352] Various functions that may be controlled by one or more controllers include applying current and / or voltage to carbon oxide reduction cells, controlling the backpressure at the outlet from the cathode of such cells, supplying purge gas to the cathode inlet, delivering carbon oxide to the cathode inlet, humidifying the carbon oxide in the cathode feed stream, flowing anode water to and / or from the anode, and controlling the anode feed composition. Any one or more of these functions may have a dedicated controller for controlling only that function. Any two or more of these functions may share a controller. In some embodiments, a hierarchical structure of controllers is employed, with at least one master controller providing direction to two or more component controllers. For example, a system may include a master controller configured to provide high-level control commands to (i) the power supplies to the carbon oxide reduction cells, (ii) the cathode feed stream flow controllers, and (iii) the anode feed stream flow controllers. For example, a programmable logic controller (PLC) may be used to control the individual components of the system.

[0353] The controller may be integrated with electronics for controlling the operation of the electrolytic cell before, during, and after the reduction of carbon oxides. The controller may control various components or subparts of one or more electrolytic carbon oxide reduction systems. Depending on the process requirements and / or system type, the controller may be programmed to control any of the processes disclosed herein, such as gas delivery, temperature settings (e.g., heating and / or cooling), pressure settings, power settings (e.g., voltage and / or current delivered to the electrodes of the MEA cell), liquid flow rate settings, fluid delivery settings, and dosing of purified water and / or salt solutions. These controlled processes may be connected to or interfaced with one or more systems working in conjunction with the electrolytic carbon oxide reduction system.

[0354] The controller may include any number of processors and / or memory devices. The controller may include control logic, such as software or firmware, or may execute instructions provided by other sources. In various embodiments, the controller is an electronic device having various integrated circuits, logic, memory, and / or software that receive instructions, issue instructions, and control operations described herein. The integrated circuits may include chips in firmware format 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). The program instructions may be instructions communicated to the controller in the form of various individual settings (or program files) that define operating parameters for executing processes on one or more components of the carbon oxide electroreduction system. The operating parameters, in some embodiments, may be part of a recipe defined by a process engineer to execute one or more processing steps during the production of specific reduction products, such as carbon monoxide, hydrocarbons, and / or other organic compounds.

[0355] In some implementations, the controller may be part of or coupled to a computer that is integrated into the system, coupled to the system, networked to the system, or a combination thereof. For example, the controller may utilize and / or execute instructions stored remotely (e.g., in the "cloud"). The computer allows remote access to the system, which may enable monitoring the current progress of the electrolysis operation, examining the history of past electrolysis operations, examining trends or performance metrics from multiple electrolysis operations, modifying parameters of a current process, setting process steps after a current process, or initiating a new process. In some examples, a remote computer (e.g., a server) may provide process recipes to the system over a network, which may include a local network or the Internet. The remote computer may include a user interface that allows input or programming of parameters and / or settings, which are communicated from the remote computer to the system. In some examples, the controller receives instructions in the form of data specifying parameters for each of the process steps to be performed during one or more operations.

[0356] The controller may be distributed, such as including one or more individual controllers networked together to operate toward a common purpose, such as directing current to the MEA cells or other process control described herein. An example of a distributed control system for such a purpose includes one or more processors on the system for electrolytic reduction of carbon oxides and one or more processors located remotely (e.g., at the platform level or as part of a remote computer) and combined to control the process.

[0357] Controllers and any of various associated computational elements, such as processors, memories, instructions, routines, models, or other components, may be described or claimed as being "configured" to perform a task(s). In this context, the phrase "configured" is used to denote structure by indicating that a component has structure (e.g., stored instructions, circuitry, etc.) that, when operating, performs a task(s). Thus, a controller and / or associated components may be said to be configured to perform a task even if the specified components are not necessarily currently operating (e.g., not turned on).

[0358] Controllers and other components "configured" to perform operations may be implemented as hardware, e.g., circuits, memory storing executable program instructions to perform the operations, etc. Furthermore, controllers and other components "configured" to perform operations may be implemented as hardware that is operated by software and / or firmware (e.g., an FPGA or a general-purpose processor running software) to operate in a manner that can perform the described task(s). Furthermore, "configured" can also refer to one or more memories or memory elements that store computer-executable instructions for performing the described task(s). Such memory elements may include memory on a computer chip with processing logic.

[0359] Non-computational elements such as reactors, electrolyzers, membrane assemblies, layers, and catalyst particles may also be "configured" to perform a particular function. In this context, the phrase "configured" indicates that the referenced structure has one or more characteristics that enable it to perform the function. Examples of such characteristics include physical and / or chemical properties such as dimensions, composition, porosity, etc.

[0360] Collection process As noted above, in some embodiments, a bipolar interface including a region having one or more of a particulate third material, a porosity enhancer, a voltage attenuator, and / or a catalyst may be particularly advantageous in the context of a recovery process.

[0361] In certain embodiments, the sequence of operations involves temporarily deviating from normal operating conditions and flowing water or other liquid to the cathode, or flowing gas to the cathode under non-standard conditions. It has been found that flowing water to the cathode and / or flowing gas (e.g., gas other than the normal carbon oxide reactant) to the cathode can facilitate recovery of carbon oxide electrolyzer performance. This alternative sequence of operations is sometimes referred to as a "recovery process" or "recovery sequence."

[0362] After the carbon oxide electrolyzer has operated under normal conditions for a period of time, such as several thousand hours, a recovery process may be performed. After the recovery process is completed, the electrolyzer may return to normal operation. The recovery process may be performed repeatedly over the useful life of the electrolyzer or over the life of one or more of its associated components, such as the MEAs(s), gas diffusion layer (GDL)(s), and flow path(s). For example, the recovery process may be performed every 1000 to 10,000 hours of the useful life.

[0363] While many embodiments disclosed herein are presented as procedures for restoring lost performance of a carbon oxide electrolyzer, some embodiments relate to protecting a carbon oxide electrolyzer from the harmful effects of some unexpected events, such as loss of power to the electrolyzer. The carbon oxide electrolyzer may be placed into a protection mode if it is determined that an unexpected event is occurring or may soon occur. If not mitigated, such an unexpected event could cause damage to the electrolyzer or the infrastructure supporting the electrolyzer.

[0364] In some implementations, any of the operations for performing recovery described herein, or any combination of such operations, may be used to protect a carbon oxide electrolyzer.

[0365] In some embodiments, the electrolyzer and / or associated control system executes a protective mode by: (a) determining that an unexpected, potentially harmful event is occurring or is likely to occur in the future, and that such unexpected event, if not mitigated, could result in damage or degradation to the carbon oxide electrolyzer; and (b) taking one or more protective actions to reduce the likelihood of damage or degradation to the carbon oxide electrolyzer if the unexpected event continues to occur or actually occurs in the future.

[0366] Examples of unexpected events that may trigger protective operation include a sudden reduction or loss of input material such as anolyte or carbon oxides (e.g., CO), a reduction or loss of heating or cooling gas, or loss of power to the electrolyzer. If the input material is significantly reduced or lost, it may be necessary to adjust the power to the electrolyzer to create an open circuit voltage or no current. Loss of power to the electrolyzer may cause the electrolyzer to suddenly or gradually discharge from its operating voltage to an uncontrolled voltage, such as the open circuit voltage or zero voltage.

[0367] Examples of protective actions to mitigate the effects of an unexpected event include applying a relatively low current density to the electrolyzer, transitioning the voltage of the electrolyzer to an open circuit voltage, reducing or tapering off the current applied to the electrolyzer, etc. Any of these protective actions may be applied for a limited time, such as only while the unexpected event continues to occur or until the likelihood of such an event occurring has significantly decreased.

[0368] In some embodiments, protective operation results in the current density of the electrolyzer being a relatively small forward current density (compared to normal operation), i.e., about 1-50 mA / cm 2or approximately 5 to 25 mA / cm 2 (For example, about 10 mA / cm 2 ) or to about 0.3% to 20% of the current density under normal operating conditions.

[0369] In some embodiments, protective operation involves reducing the current to the electrolyzer. The ramp may have any shape or slope. In some cases, the average ramp rate from full current (normal operation) to final current is about 0.1-1 mA / cm. 2 / min, or approximately 1 to 10mA / cm 2 / min. In some cases, the ramp control is stepwise. The number of steps, the time length of the steps, and the magnitude of the change in current density of the steps may vary. By way of example, the ramp may have about 2 to 50 steps, or about 5 to 30 steps. By way of further example, the duration of a step may be about 1 second to 100 seconds, or about 5 seconds to 50 seconds. By way of further example, the magnitude of the current of the step may be about 0.1 to 10 mA / cm. 2 or approximately 0.5 to 5 mA / cm 2 may be.

[0370] In one example, a step profile may include a series of steps, each with much smaller values ​​(e.g., approximately 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 mA / cm 2 ), each for a fixed time (e.g., about 30 seconds each), the current density of the electrolyzer is adjusted to a normal operating value (e.g., about 300 mA / cm 2 ~2A / cm 2 ) and then set the final current output to maintain the electrolyzer at open circuit for approximately 5-10 minutes.

[0371] In some embodiments, the electrolyzer returns from recovery or protection modes to normal operating conditions via a current ramp control. Such a return ramp control may have any of the characteristics specified for reducing the current, but in the opposite direction, i.e., from low to high current density.

[0372] Exemplary Collection Process In one example, the recovery process involves pausing the current to the electrolyzer, then flowing water to the cathode, and then resuming current flow to the electrolyzer. In another example, the recovery process involves pausing the current to the electrolyzer, then flowing gas to the cathode, then flowing water to the cathode, then flowing gas again to the cathode, and finally resuming normal operation by flowing current through the cell. Below are some further example recovery sequences:

[0373] In some examples, the recovery operation involves contacting the cathode with water while no current is flowing through the cathode. In some implementations, a relatively small amount of current flows while water is present at the cathode. In some cases, this current flows in the reverse direction (anode to cathode for carbon oxide reduction). As an example, in the reverse direction while water is present, the current may be approximately 1 mA / cm 2 A current not exceeding 1000 kJ / cm flows through the cathode. In some examples, for part of the recovery process, water flows over the cathode rather than statically contacting the cathode. Examples of recovery operations involving flowing or contacting water include Examples 1, 2, 3, and 4.

[0374] Exemplary Recovery Sequence 1 Normal operation (possibly including pulsed current or voltage). Turn off or greatly reduce the current. Water is introduced to the cathode by flowing or otherwise contacting the cathode. Current is turned on or increased to normal operating levels to re-establish normal operation (eg, flowing reactant gases at normal operating pressures and flow rates). In some embodiments, the recovery operation includes turning off the current, flowing water through the cathode, and then drying the cathode. The drying operation is optionally performed using a different gas, such as a reactant gas, a reforming reactant gas, or an inert gas.

[0375] Example Recovery Sequence 2 Normal operation (possibly including pulsed current or voltage). Turn off or greatly reduce the current. Water is introduced to the cathode by flowing or otherwise contacting the cathode. The cathode is dried (for example, by passing a gas through the cathode). Current is turned on or increased to normal operating levels to re-establish normal operation (eg, flowing reactant gases at normal operating pressures and flow rates). In some embodiments, the recovery operation involves flowing water to the cathode without flowing gas (reactant or other gas) to the cathode.

[0376] Exemplary Recovery Sequence 3 Normal operation (possibly including pulsed current or voltage). Turn off or greatly reduce the current. The back pressure is released and the flow of reactant gases to the cathode is stopped. Water is introduced to the cathode. The cathode is dried (for example, by passing a gas through the cathode). The current is turned on or increased to normal operating levels to re-establish normal operation (eg, reactant gases flowing at normal operating pressures and flow rates).

[0377] Note that the steps of stopping the gas flow and releasing or reducing the back pressure can be performed in either order: if the process uses gases different from the reactants, it may be necessary to release the gas pressure first and then stop the flow.

[0378] Exemplary Recovery Sequence 4 Normal operation (possibly including pulsed current or voltage). Turn off or significantly reduce the cell current. The back pressure is released and the flow of reactant gases to the cathode is stopped. Under alternative conditions, gas is flowed to the cathode. Stop the gas flow. Water is introduced to the cathode by flowing or otherwise contacting the cathode. Contact of the water with the cathode is stopped. Dry gas is flowed to the cathode. A reactive gas is flowed to the cathode. The current is turned on or increased to normal operating levels and normal operation is re-established.

[0379] In some embodiments, the recovery process involves stopping the flow of current and then flowing a gas, which may be a reactive gas or a non-reactive gas. If the gas is not a reactive gas, the gas flows for a period of time, after which the flow of the reactive gas resumes and the current is turned back on. In some embodiments, the non-reactive gas is air, an oxidizing gas, an inert gas, a combination thereof, or a modified composition of the reactive gas. In some such embodiments, water does not flow to the cathode for at least a portion of the time while the gas is flowing. Examples of recovery operations involving a gas flow in which the gas flow does not contact water for at least a portion of the time include Examples 5, 6, and 7.

[0380] Exemplary Recovery Sequence 5 Normal operation (possibly including pulsed current or voltage). Turn off or greatly reduce the current. The reactant gas back pressure is released and the reactant gas to the cathode is turned off. A gas other than the reactive gas is passed through the cathode for a certain period of time. The reactant gases are reintroduced at normal operating pressures and flow rates. The current is turned on or increased to re-establish normal operation.

[0381] In some embodiments, the recovery process involves stopping the flow of electrical current, then flowing the reactant gases at low pressure and / or flow rate for a period of time, then increasing the reactant gas pressure and / or flow rate to normal operating pressure, and finally returning the electrical current to normal levels. In some such embodiments, water does not flow to the cathode.

[0382] Example Recovery Sequence 6 Normal operation (possibly including pulsed current or voltage). Turn off or greatly reduce the current. Gases (and optionally reactant gases) are flowed to the cathode under alternative conditions, such as at reduced flow rates. The current is turned on or increased to re-establish normal operation.

[0383] Exemplary Recovery Sequence 7 Normal operation (possibly including pulsed current or voltage). Turn off or greatly reduce the current. The pressure of the reactant gas to the cathode is reduced for a period of time. The reactant gas pressure is increased to normal operating pressure. The current is turned on or increased to re-establish normal operation.

[0384] Exemplary Recovery Sequence 8 Normal operation (possibly including pulsed current or voltage). The current to the electrolyzer is reduced by ramp control, and in some cases a small reverse current is applied. Gas (optionally a reactant gas) is passed through the cathode (applied with a low current (which may be a low reverse current)) under alternative conditions, such as reduced flow rate and / or pressure. The positive current is increased by ramp control. Full normal operating conditions are re-established, including full positive current and full flow of reactant gas.

[0385] Exemplary Recovery Sequence 9 Normal operation (possibly including pulsed current or voltage). Apply a low reverse current (either ramp controlled or direct transition). Gas (optionally a reactant gas) is passed through the cathode (applied with a low current (which may be a low reverse current)) under alternative conditions, such as reduced flow rate and / or pressure. The positive current is increased by ramp control. Full normal operating conditions are re-established, including full positive current and full flow of reactant gas.

[0386] Exemplary Recovery Sequence 10 Normal operation (possibly including pulsed current or voltage). The power supply or associated circuitry is adjusted to short circuit the electrolytic device or to reach a potential below the open circuit voltage. Gas (and optionally reactant gas) is passed to the cathode under alternative conditions, such as reduced flow rate and / or pressure (the electrolyzer is held at open circuit voltage or short circuit). Full normal operating conditions are re-established, including normal electrolyzer operating potentials and full flow of reactant gases.

[0387] Exemplary Protection Procedure 11 Normal operation (possibly including pulsed current or voltage). Determine the likelihood of unexpected adverse events occurring. The electrolyzer is put into a protection mode (examples of protection mode operating conditions include applying a relatively low current density to the electrolyzer, bringing the electrolyzer voltage to the open circuit voltage, reducing or ramping down the current applied to the electrolyzer). The adverse event is determined to no longer be a threat. Restore full normal operating conditions.

[0388] Exemplary Collection Sequence 12 Normal operation (possibly including pulsed current or voltage). The power supply or associated circuitry is adjusted to reach and maintain the open circuit voltage. Gas (and optionally reactant gas) is passed to the cathode under alternative conditions, such as reduced flow rate and / or pressure (the electrolyzer is held at open circuit voltage or short circuit). Full normal operating conditions are re-established, including normal electrolyzer operating potentials and full flow of reactant gases.

[0389] Process parameters related to the recovery process The following describes in turn the various operations involved in the collection process.

[0390] Normal operation As previously mentioned, the carbon oxide electrolyzer may operate normally for a period of time before a recovery procedure is performed. Normal operation may include a set of normal operating conditions, as described elsewhere herein. These conditions may include (a) normal reactant gas flow (which may be characterized by normal levels of reactant gas pressure and flow rate or velocity at the cathode), (b) reactant gas composition, (c) set temperature or temperature profile, (d) current or voltage magnitude (possibly having a non-constant waveform), or (e) a combination thereof. In some embodiments, during normal operation, the current or voltage has a pulsed or paused profile in which the magnitude of the current in the electrolyzer is temporarily and periodically decreased or increased.

[0391] Normal operation may involve converting carbon oxides in the reactant gas to carbon-containing products. In some embodiments, the carbon oxides are CO and / or CO, and the carbon-containing reduction products include CO, hydrocarbons, and / or organic oxygen-containing compounds. Typically, during normal operation, liquid (e.g., water) is not introduced to the cathode via the carbon oxide inlet or other source external to the MEA. However, during normal operation, liquid in the form of a mist or droplets may contact the cathode along with the inlet gas.

[0392] In various embodiments, the electrolytic device operates normally for a period of time before the recovery procedure. For example, the electrolytic device may operate under normal conditions for at least about 100 hours before performing the recovery procedure. In some cases, the normal operation period lasts for at least about 1000 hours, or at least about 2000 hours, or at least about 5000 hours, or at least about 10,000 hours before performing the recovery procedure. After the recovery procedure, the electrolytic device may return to normal operation for an extended period of time, such as at least about 100 hours. Subsequent normal operation periods may continue uninterrupted by another recovery process or termination of the electrolytic device. In some implementations, recovery processes are performed periodically during the life of the electrolytic device, but each instance of a recovery process is separated by a minimum normal operation period, such as at least about 100 hours, or at least about 500 hours, or at least about 1000 hours.

[0393] Reduction or cessation of current In certain embodiments, the recovery procedure involves stopping the flow of current to the electrolyzer, reducing the magnitude of the current density, or reversing the direction of the current at the cathode. While the reduction in current can be significant, it is meant not to have a deleterious effect on the electrolyzer or any of its components (such as the cathode catalyst layer). For example, the current should not corrode or degrade catalytic components such as metals, carbon support materials, or polymers. As an example, the current is reduced by at least about 50%. In some examples, the reduced current density at the cathode is at most about 100 mA / cm of the planar surface area of ​​the cathode. 2 This current density may be applied when gas and / or water is supplied to the cathode from outside the MEA.

[0394] In some cases, the recovery procedure involves, at least temporarily, applying a current in the reverse direction (i.e., an anodic current through the cathode side of the cell). A small anodic current (cathode side) can help recover performance at the electrolyzer cathode during subsequent normal operation. This can refresh the catalyst surface.

[0395] In some embodiments, a current or voltage ramp control is applied to the carbon oxide electrolyzer for either recovery or protection. As noted above in connection with the description of the protection mode, the ramp control can have any shape or slope. In some cases, the average ramp rate from full current (normal operation) to final current is about 20 mA / cm. 2 / min or less, or approximately 1 to 10mA / cm 2 / min, or approximately 0.5 to 1 mA / cm 2 / min. In some cases, the ramp control is stepwise. The number of steps, the time length of the steps, and the magnitude of the change in current density of the steps may vary. By way of example, the ramp may have about 2 to 50 steps, or about 5 to 30 steps. By way of further example, the duration of a step may be about 1 second to 100 seconds, or about 5 seconds to 50 seconds. By way of further example, the magnitude of the current of the step may be about 0.1 to 10 mA / cm. 2 or approximately 0.5 to 5 mA / cm 2 may be.

[0396] Current stop period In certain embodiments, the duration of current cessation in the recovery procedure is from about 5 minutes to several days (e.g., 10 days), hi certain embodiments, the duration of current cessation is from about 10 minutes to about 300 minutes, or from about 15 minutes to 60 minutes.

[0397] When changing the current from normal operation at the start of the recovery process, the current may be reduced by an abrupt stop (single step change), a ramped down, and / or multiple steps.

[0398] In certain embodiments in which a reverse current is applied, the duration of the reverse current applied to the cathode is from about 5 seconds to 60 minutes, or from about 5 minutes to 60 minutes.

[0399] Short circuit In some embodiments, the electrolyzer of the power supply supplying power to the carbon oxide electrolyzer is short-circuited while in recovery mode or protection mode. A short circuit can occur when the electronic resistance in the circuit is not large enough to prevent current flow between the anode and cathode. In such a case, the potential(s) of the anode and cathode are equal; that is, the cell voltage is 0 volts. In the event of a short circuit, the electrolyzer discharges from its normal operating state or open circuit voltage. During a short circuit in the electrolyzer, the cell voltage shifts to a level lower than the open circuit voltage.

[0400] During recovery or protection mode, the short circuit condition may be maintained for a specified period of time. In some embodiments, the short circuit mode is maintained for about 30 minutes or less, or about 10 minutes or less, or about 5 minutes or less, or about 1-5 minutes. Upon exiting the short circuit condition, the electrolyzer may return to normal operating voltage and, in some cases, return completely to normal operation.

[0401] A short circuit and associated discharge process, in which current flows in the reverse direction, may provide oxidizing conditions to the catalyst (e.g., a gold catalyst), which enhances catalytic efficiency, for example, by creating additional active surface area and / or removing potential impurities or intermediates. + , H + , COOH - , HCO3 - , CO3( 2- ), OH - , or any combination of positive and / or negative ions, may also be depleted. A short circuit can cause water electrolysis at the MEA interface (e.g., between the PEM and AEM in a bipolar MEA) and / or at the cathode, which can provide drier conditions and lead to better carbon oxide (e.g., CO2) mass transport. A short circuit can temporarily change the local environment, such as pH or ion concentration at the cathode, which can improve the selectivity of CO2 reduction. A change from low to high pH or from low to high potassium concentration can improve the selectivity of certain reactions, such as the CO2 production reaction.

[0402] In certain embodiments, the system applies a short circuit when the selectivity of CO2 to CO reduction falls below a certain target value and / or when it is desirable to extend the life of the electrolyzer, e.g., several hundred hours. In certain embodiments, the system applies a short circuit to periodically (e.g., repeatedly) regain reaction selectivity to reach a certain decay rate target within a certain time range. For example, the system may perform a recovery operation whenever the selectivity drops to a certain value (e.g., about 90% or less). In another approach, a recovery operation is performed every time the electrolyzer operates normally for a specified period of time (e.g., about 200-500 hours). In another approach, a recovery operation is performed every time the electrolyzer selectivity exhibits a threshold drop (e.g., about 10% or more).

[0403] Open circuit voltage In some embodiments, the carbon oxide electrolyzer reaches or is maintained at an open-circuit voltage during recovery or protection. Open-circuit voltage refers to the voltage difference between the anode and cathode when no net electrochemical reaction is occurring at the anode or cathode. This can occur when no current is flowing between the anode and cathode. An open-circuit potential can be achieved by opening a switch in the circuit comprising the electrolyzer and power source, breaking the conductive path between the anode and / or cathode. An open-circuit potential can also be achieved by employing a very high impedance element in the circuit comprising the power source and electrolyzer. Such a resistor has the effect of completely blocking or nearly blocking all current flow between the anode and cathode of the electrolyzer.

[0404] In some cases, placing the electrolyzer in or reaching the OCV while maintaining a similar CO gas flow rate at the cathode may provide relatively dry conditions, which may improve CO mass transport. Placing the electrolyzer in or reaching the OCV may flush out potential intermediates or impurities on the surface of the catalyst even when no electrochemical reaction is occurring. In some cases, placing the electrolyzer in or reaching the OCV temporarily changes the local environment at the cathode, such as pH or ion concentration, which may improve, for example, the selectivity of CO reduction over CO production.

[0405] Various situations and applications may benefit from setting the electrolyzer to or having access to the OCV. In some cases, the OCV is used when a moderate recovery of selectivity is desired and / or when the electrolyzer voltage needs to be maintained at a relatively high level compared to short circuit conditions.

[0406] reverse current As shown, in some embodiments, a reverse current is applied to the carbon oxide electrolyzer during recovery or protection. Forward current is the current applied to the carbon oxide electrolyzer during normal operation. Electrons can be supplied from the power source to the cathode, causing reduction, and electrons can be withdrawn from the anode, causing oxidation. During reverse current, the flow of electrons is reversed, such that an electrode that functions as a cathode during normal operation functions as an anode during reverse current application, and an electrode that functions as an anode during normal operation functions as a cathode during reverse current application.

[0407] Typically, the reverse current is maintained below a level at which carbon and / or other materials in the cathode catalyst oxidize or corrode. In some embodiments, the reverse current is maintained at a level below which the magnitude of the reverse current is about -100 mA / cm. 2 or less, or approximately -5 to -100mA / cm 2In some embodiments, the reverse current is applied for about 100 minutes or less, or about 50 minutes or less, or about 30 seconds to 20 minutes. As a further example, the reverse current is applied for about 1 mA / cm of the surface area of ​​the cathode. 2 or less, or about 0.5mA / cm 2 In some cases, the reverse current flow is maintained at or below a level that causes the cell voltage to not exceed about 1.25 V (for reactant gas) and 2.5 V (for oxidizing gas such as air), or not exceed about 0.5 V (for reactant gas) and 2 V (for oxidizing gas such as air). In certain embodiments employing reverse current, such current is maintained at or below about 0.6 coulombs / cm of cathode surface area. 2 It is limited to the following:

[0408] Once application of the reverse current is complete, the electrolyzer returns to normal operating current, and may even return to normal operation entirely. In certain embodiments, the final value of the reverse current is achieved by ramping to the final value. The ramp rates and / or step ramp procedures described herein can be used for protection modes or to achieve reduced current values.

[0409] Among the potential benefits of exposing a carbon oxide electrolyzer to reverse current are the benefits described herein in short circuit applications. Similarly, exposing a carbon oxide electrolyzer to reverse current may find similar applications as in short circuit applications.

[0410] The type of gas that entered the cathode (before contact with water) In some implementations of the capture process, gas flows to the cathode for a period of time after the current is stopped or reduced. This gas is sometimes referred to herein as the "recovery gas." In some cases, the recovery gas has the same composition as the carbon oxide reactants flowing during normal operation, and sometimes flows at a different pressure and / or flow rate than those used in normal operation. For example, the gases flowing during normal operation and during the capture process contain defined concentrations of carbon dioxide or carbon monoxide. In some cases, during the capture process, the recovery gas flowing to the cathode has a different composition than the reactant gas. In some cases, the recovery process gas has a lower concentration of carbon oxide reactants compared to the reactant gas. In some cases, the recovery process gas includes an inert gas that is not present (or present at a different concentration) in the normal process gas. Examples of inert gases include noble gases (e.g., Ar, He, or Kr) or nitrogen. In some cases, the capture process gas is or includes air. In some cases, the capture gas includes an oxidizing gas, such as oxygen. In some cases, the oxidizing gas is simply air, which may contain approximately 21% oxygen. In other cases, the oxidizing gas is oxygen or another oxidizing agent supplied separately from air. For example, oxygen produced at the electrolyzer anode during normal operation can be used as the oxidizing recovery gas. In some implementations, the recovery gas is humidified. In some embodiments, the component gas includes carbon dioxide, air, water, an inert gas, or a combination thereof.

[0411] In some examples, the recovery gas is 100% or pure reactive gas. In some examples, the recovery gas is 100% or pure inert gas. In some examples, the recovery gas includes a reactive gas and an inert gas in any ratio. In some examples, the recovery gas includes an oxidizing gas and an inert gas in any ratio. In some examples, the recovery gas is a humidified gas having water vapor present at a concentration of about 0-2% by volume. In some cases, the humidified gas includes a reactive gas, an inert gas, an oxidizing gas, or any combination thereof.

[0412] Cathode gas pressure (before contact with water) In some embodiments, after the current is terminated or reduced, the pressure of the recovery gas flowing to the cathode may be at the normal operating pressure of the electrolyzer cell. In some embodiments, after the current is terminated or reduced, the cathode gas backpressure is reduced, for example, to 0 psig. The cathode gas backpressure may be controlled by a pressure regulator located downstream of the cathode in the gas flow path. After the cathode gas backpressure is reduced, recovery gas may be present, and may optionally flow under a pressure of about 0 to 600 psig, or about 0 to 400 psig, or about 0 to 50 psig.

[0413] Gas flow rate through the cathode (before contact with water) In certain embodiments where a collection gas is flowed after the current is reduced or stopped, the gas is supplied at a rate of about 0-50 sccm / cm of the planar surface area of ​​the cathode. 2 , or about 10-30 sccm / cm of the planar surface area of ​​the cathode 2 The flow rates presented here are per surface area of ​​the cathode (e.g., 1 cm of the planar surface of the cathode). 2 Please note that the dimensions are provided per 25cm. 2 For an electrolysis device with a cathode having a surface area of ​​1000 nm, the gas flow rate may be approximately 500 sccm. The gas flow rate may vary linearly or nonlinearly with the surface area of ​​the cathode. The flow rate values ​​presented here may be instantaneous or average flow rates.

[0414] Gas flow period at the cathode (before contact with water) In embodiments where a recovery gas flows to the cathode, the recovery procedure may continue for a period of time after the current is stopped or reduced. In certain embodiments, the period of gas flow or residence at the cathode is about 30 minutes to 10 days, or about 1 hour to 2 days. The duration of gas flow in a recovery procedure may depend at least in part on the gas flow rate (e.g., the average flow rate, if the flow rate varies). For example, a low or zero flow rate for several days may have the same effect as a high flow rate for several minutes or hours. As yet another example, the range of gas flow rate and / or exposure time may be from 30 minutes to several days. However, a flow rate of 50 sccm / cm 2 In this case, the maximum contact / flow time may be about 5 hours.

[0415] In some embodiments, the stripping gas is flowed to the cathode before contacting the water or other liquid at the cathode. The flow of the stripping gas may be stopped before contacting the liquid.

[0416] Composition of water in contact with the cathode As shown, various recovery processes involve contacting the cathode with a liquid, such as water. When referring to water herein, it should be understood that a wide range of purity levels can be used in the recovery process. In some embodiments, the water is deionized water, such as deionized water having a resistivity of at least about 1 megaohm, or at least about 10 megaohms, or at least about 18 megaohms. In some embodiments, the water includes one or more dissolved solutes or suspended components. Examples of dissolved solutes include bicarbonate, carbonate, sulfate, hydrogensulfate, formate, acetate, and halides. By way of example, the solute can be a metal (e.g., sodium, potassium, or cesium) or an ammonium salt of these anions. In certain embodiments, the recovered process water includes bicarbonate at a concentration of up to about 10 mM bicarbonate ion, or up to about 5 mM bicarbonate ion, or up to about 2 mM bicarbonate ion. In some embodiments, the recovered process water has a composition that matches or is similar to the composition of the anode water used during normal operation. Examples of anode water compositions are described in U.S. Patent Application Publication No. 2019 / 063471, filed November 26, 2019, which is incorporated herein by reference in its entirety.

[0417] Water flow rate at the cathode The water optionally flows while in contact with the cathode. In some embodiments, the water flow rate to the cathode is 1 cm / cm of planar surface area of ​​the cathode. 2 As an example, the water flow rate is approximately 20 ml / min per 1 cm of cathode planar surface area. 2 The flow rate is approximately 2-10 ml / min per MEA. In some embodiments, the flow rate is limited based on the pump and associated hardware. Note that the water supplied to the cathode as part of the recovery process is typically supplied from outside the MEA, e.g., from the carbon oxide inlet to the cathode, rather than through the MEA and from the anode.

[0418] Time for water to flow from the cathode In certain embodiments, the time for which water flows to the cathode is about 1 to 100 minutes, or about 2 to 50 minutes, or about 5 to 15 minutes.

[0419] Drying process after water flow (gas flow) If water does not contact the cathode, a drying operation may be performed, which can occur after contact with water, before resuming normal operation, or possibly during the initial resumption of operation.

[0420] Drying may be performed using any gas composition that removes moisture from the cathode. Such gases may be referred to herein as "drying gases." Examples of gases that may be present in the drying gas include air, reactive gases, and inert gases. Examples of inert gases include noble gases (e.g., He, Ar, Kr) and nitrogen. When reactive gases are used, they may be used at concentrations different from those used in normal operation. For example, carbon dioxide may be present at 50% (molar) in the reactants and 20% (molar) in the drying gas.

[0421] The physical mechanism by which the dry gas removes water from the cathode may include pushing or forcing the water away from the cathode by contacting the cathode with the gas at a pressure and / or velocity sufficient to remove the liquid water.

[0422] The water may be removed, or alternatively, by evaporation to a dry gas. To this end, the relative humidity of the dry gas entering the cathode may be controlled to facilitate evaporation. In some embodiments, the dry gas may have a very low relative humidity (e.g., about 0-100%), while in other embodiments it may have a higher value, which may be desirable to ensure that the MEA does not dry out and lose water to the point where its performance is compromised.

[0423] Drying time In certain embodiments, the drying time for the cathode is about 0 to 500 minutes, or about 2 to 100 minutes, or about 5 to 30 minutes.

[0424] In some embodiments, the drying operation continues until there is no liquid water (e.g., water droplets or mist) downstream of the cathode. In some embodiments, the drying operation continues until the humidity of the drying gas entering the cathode is approximately the same as the humidity of the drying gas exiting the cathode.

[0425] Restarting the flow or reactant gas If drying by a reactant gas is not performed, the recovery process transitions from a dry gas flow to a reactant gas flow. This may involve re-establishing normal operating gas pressure at the cathode, for example, by adjusting the setting of a pressure regulator downstream of the cathode. If a dry gas is the reactant gas, the transition from a dry gas flow to a reactant gas flow need not occur, or in some cases, the transition occurs but represents only a change in gas flow rate, pressure, composition, or a combination thereof.

[0426] Post-withdrawal current ramp rate In some embodiments, at the end of the recovery operation, the current is restarted either directly to the original value or in a stepped increase with some ramp control.

[0427] Optional voltage scan In some embodiments, the recovery process is performed by a voltage or current scan. The voltage or current scan may be performed repeatedly in alternating directions between two endpoints. The voltage scan may be performed by cyclic voltammetry. In some cases, the voltage or current scan is performed during the recovery process while the current is otherwise stopped. In some cases, the voltage or current scan is performed while gas is flowing to the cathode, but water is not contacting the cathode. For example, in any of the recovery procedure examples 2-4 above, the voltage or current scan may be performed during the gas drying operation. In some examples, the voltage or current scan is performed during the gas contacting operation that occurs before contact with water. See recovery procedure examples 3 and 4 above. In some examples, the voltage or current scan is performed during a gas contacting operation that is not related to the water contacting operation. See recovery procedure examples 5-7 above.

[0428] A voltage or current scan can have various effects on the electrolyzer cell or its cathode.

[0429] Working Example: -The charging overpotential of the carbon material in the electrode, which occurs due to strong polarization, is alleviated by stopping the current for different lengths of time. -Cleaning of the electrode surface (removal of impurities / unwanted intermediates) by changing the adsorption / desorption environment at zero or slight anodic voltage or under air exposure. -CO X The cathode catalytic sites are repositioned in a more favorable direction for the reduction of . -Maintains moisture in the MEA.

[0430] The voltage scan can be characterized by an initial cathode voltage E0 (V), an upper cathode voltage limit V1 (V), a lower cathode voltage limit V2 (V), and a scan rate S (mV / s). In some embodiments, E0 ranges from about -1 V to 1.2 V relative to the RHE. In some embodiments, E1 ranges from about -1 V to 1.2 V. In some embodiments, E2 ranges from about -1 V to 1.2 V. In some embodiments, S ranges from about -10,000 to -0.1 mV / s, or about 0.1 to 10,000 mV / s. The scan direction can be positive or negative, with positive meaning that the first sweep is in the positive direction and negative meaning that the first sweep is in the negative direction. The scan rates in the positive and negative directions can be the same or different. The number of scans (n) can be in the range of about 1 to 1,000.

[0431] Temperature change during recovery operation In certain embodiments, the temperature of the electrolyzer cell remains unchanged during the recovery operation. In certain embodiments, the temperature of the electrolyzer cell changes during the recovery operation. The temperature change may be driven by a temperature controller, water flowing to the cathode, gas flowing to the cathode, or any combination thereof. In some embodiments, the temperature of the electrolyzer cell increases during the recovery operation. In some embodiments, the temperature of the electrolyzer cell decreases, for example, by about 5-25°C during the recovery operation.

[0432] experiment The ability of the interface components to mitigate the effects of electrical interruptions, in accordance with certain embodiments of the present invention, is illustrated in Figure 6. Each data point represents power to the cell being turned on and off (mimicking a power interruption). The data is for a 300 mA / cm 2 20 min at 0 mA / cm 2 Measurements were taken under current oscillation conditions for 10 minutes, with a maximum reverse bias of 30 seconds (reverse current of up to 50 mA / cm). 2 ) may be included.

[0433] The top plot shows CO selectivity, the middle plot shows voltage, and the bottom plot shows resistance. Electrochemical cells without at least one porosity enhancer interface (control) show a gradual increase in resistance over time. However, when an interface composed of a carbon and Nafion blend (CNI) is tested under the same conditions, no resistance is built up. A mitigated voltage drop is evident.

[0434] In Figure 6, the top graph is NFY_CO or CO selectivity, where NFY is the normalized faradaic yield. This is a measure of how much of the applied current converts CO2 to CO, with 98% of the current converting CO2 to CO. As expected, the data is similar for the CNI and control. The middle graph shows voltage (a measure of energy efficiency). The bottom graph shows resistance. Figure 6 shows a clear trend where the porous interface completely prevents any increase in voltage with discharge.

[0435] The interface configuration was a 1:1 weight ratio of carbon to Nafion nanoparticles applied to a thickness of 3 microns. The Nafion component was a 5 wt% polymer solution. While not being bound to a specific mechanism, the increased resistance exhibited by the interface-free cell may be due to the decomposition of the AEM and PEM materials. Notably, selectivity remained high throughout the process.

[0436] Other Embodiments and Conclusions Although omitted for purposes of brevity, system and / or method embodiments may include any combination and permutation of the various system components and various method processes, where one or more instances of the methods and / or processes described herein may be performed asynchronously (e.g., sequentially), simultaneously (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.

[0437] Although the foregoing embodiments have been described in some detail for clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the processes, systems, and apparatus of the embodiments of the present invention. Accordingly, the embodiments of the present invention should be considered as illustrative rather than restrictive, and the embodiments are not limited to the details provided herein.

Claims

1. a cathode catalyst layer; an anode catalyst layer; a bipolar membrane disposed between the cathode catalyst layer and the anode catalyst layer; A membrane electrode assembly comprising: the bipolar membrane comprises an anion-conducting polymer layer, a cation-conducting polymer layer, and an interfacial region between the anion-conducting polymer layer and the cation-conducting polymer layer; The membrane electrode assembly, wherein the interfacial region comprises nanoparticles.

2. 10. The membrane electrode assembly of claim 1, wherein the interface region is about 1 to 10 micrometers thick.

3. 10. The membrane electrode assembly of claim 1, wherein the interface region is about 1 to about 5 micrometers thick.

4. 10. The membrane electrode assembly of claim 1, wherein the ratio of the thickness of the anion-conducting polymer layer to the thickness of the interfacial region is at least 10:

1.

5. The membrane electrode assembly of claim 1 , wherein the nanoparticles comprise carbon nanoparticles or magnesium oxide nanoparticles.

6. The membrane electrode assembly of claim 1 , wherein the interfacial region further comprises an ion-conducting polymer.

7. The membrane electrode assembly of claim 1 , wherein the nanoparticles comprise iridium, platinum, titanium, or gold.

8. 2. The membrane electrode assembly according to claim 1, wherein the cation-conducting polymer layer is disposed between the anode catalyst layer and the anion-conducting polymer layer.

9. 10. The membrane electrode assembly of claim 1, wherein the cathode catalyst layer comprises a reduction catalyst and an anion-conducting polymer.

10. 10. The membrane electrode assembly of claim 1, wherein the anode catalyst layer comprises an oxidation catalyst and a cation-conducting polymer.

11. CO2 containing a membrane electrode assembly Ｘ A reduction reactor comprising: The membrane electrode assembly CO Ｘ a cathode catalyst layer including a catalyst configured to reduce an anode catalyst layer; a bipolar membrane disposed between the cathode catalyst layer and the anode catalyst layer, the bipolar membrane comprises an anion-conducting polymer layer, a cation-conducting polymer layer, and an interfacial region between the anion-conducting polymer layer and the cation-conducting polymer layer; The membrane electrode assembly, wherein the interfacial region comprises nanoparticles.

12. 12. The CO2 of claim 11, wherein the interface region is about 1 to 10 micrometers thick. Ｘ Reduction reactor.

13. 12. The CO2 of claim 11, wherein the interface region is about 1 to about 5 micrometers thick. Ｘ Reduction reactor.

14. 12. The CO2 of claim 11, wherein the ratio of the thickness of the anion-conducting polymer layer to the thickness of the interfacial region is at least 10:

1. Ｘ Reduction reactor.

15. 12. The CO of claim 11, wherein the nanoparticles comprise carbon nanoparticles or magnesium oxide nanoparticles. Ｘ Reduction reactor.

16. 12. The CO2 of claim 11, wherein the interfacial region further comprises an ion-conducting polymer. Ｘ Reduction reactor.

17. 12. The CO of claim 11, wherein the nanoparticles comprise iridium, platinum, titanium, or gold. Ｘ Reduction reactor.

18. 12. The CO2 electrode of claim 11, wherein the cation-conducting polymer layer is disposed between the anode catalyst layer and the anion-conducting polymer layer. Ｘ Reduction reactor.

19. 12. The CO2 fuel cell of claim 11, wherein the cathode catalyst layer further comprises an anion-conducting polymer. Ｘ Reduction reactor.

20. 12. The CO2 of claim 11, wherein the anode catalyst layer comprises an oxidation catalyst and a cation-conducting polymer. Ｘ Reduction reactor.

21. 12. The CO2 reduction reactor of claim 11 . Ｘ Reduction reactor.

22. CO Ｘ 1. A method for electrochemically reducing (a) CO Ｘ providing carbon oxides to a reduction reactor; (b) CO Ｘ electrochemically reducing the carbon oxides at the cathode of an electrolyzer to produce carbon-containing products; The CO Ｘ The reduction reactor is a cathode catalyst layer; an anode catalyst layer; a bipolar membrane disposed between the cathode catalyst layer and the anode catalyst layer; the bipolar membrane comprises an anion-conducting polymer layer, a cation-conducting polymer layer, and an interfacial region between the anion-conducting polymer layer and the cation-conducting polymer layer; the interfacial region comprising nanoparticles, Ｘ A method for electrochemically reducing

23. The CO Ｘ 23. The method of claim 22, wherein the reduction reactor is subjected to a fluctuation in current.

24. 24. The method of claim 23, wherein the current fluctuations are caused by a recovery process, a power interruption, a current reversal, or a power outage.

25. 23. The method of claim 22, wherein the carbon oxide is carbon dioxide.

26. 23. The method of claim 22, wherein the carbon-containing products comprise carbon monoxide, hydrocarbons, formic acid, alcohols, or combinations thereof.

27. 23. The method of claim 22, wherein the interface region is about 1 to 10 micrometers thick.

28. The method of claim 22, wherein the interface region is about 1 to about 5 micrometers thick.

29. 25. The method of claim 24, wherein the ratio of the thickness of the anion-conducting polymer layer to the thickness of the interfacial region is at least 10:

1.

30. 23. The method of claim 22, wherein the nanoparticles comprise carbon nanoparticles or magnesium oxide nanoparticles.

31. 23. The method of claim 22, wherein the interfacial region further comprises an ion-conducting polymer.

32. 23. The method of claim 22, wherein the nanoparticles comprise iridium, platinum, titanium, or gold.

33. 23. The method of claim 22, wherein the cation-conducting polymer layer is disposed between the anode catalyst layer and the anion-conducting polymer layer.

34. 23. The method of claim 22, wherein the anion-conducting polymer layer is disposed between the cathode catalyst layer and the cation-conducting polymer layer.

35. 23. The method of claim 22, wherein the cathode catalyst layer comprises a reduction catalyst and an anion-conducting polymer.

36. 23. The method of claim 22, wherein the anode catalyst layer comprises an oxidation catalyst and a cation-conducting polymer.

37. a cathode catalyst layer; an anode catalyst layer; a bipolar membrane disposed between the cathode catalyst layer and the anode catalyst layer; A membrane electrode assembly comprising: a membrane electrode assembly, wherein the bipolar membrane has an anion-conducting polymer layer, a cation-conducting polymer layer, and an interfacial region between the anion-conducting polymer layer and the cation-conducting polymer layer, the interfacial region comprising an ion-conducting polymer layer and nanoparticles dispersed in the ion-conducting polymer layer.

38. 38. The membrane electrode assembly of claim 37, wherein the ion-conducting polymer layer comprises a sulfonated fluoropolymer.

39. 39. The membrane electrode assembly of claim 38, wherein the sulfonated fluoropolymer is a sulfonated tetrafluoroethylene-based fluoropolymer copolymer.

40. 38. The membrane electrode assembly of claim 37, wherein the nanoparticles comprise carbon nanoparticles.

41. 38. The membrane electrode assembly of claim 37, wherein the interface region is about 1 to 10 micrometers thick.

42. 38. The membrane electrode assembly of claim 37, wherein the interface region is about 1 to about 5 micrometers thick.

43. 41. The membrane electrode assembly of claim 40, wherein the ratio of ion-conducting polymer to carbon nanoparticles in the ion-conducting polymer layer is from about 2:1 weight percent to about 1:0.1 weight percent.

44. 41. The membrane electrode assembly of claim 40, wherein the ratio of ion-conducting polymer to carbon nanoparticles in the ion-conducting polymer layer is about 1:1 weight percent.

45. 38. The membrane electrode assembly of claim 37, wherein the ratio of the thickness of the anion-conducting polymer layer to the thickness of the interfacial region is at least 10:

1.

46. 38. The membrane electrode assembly of claim 37, wherein the cation-conducting polymer layer is disposed between the anode catalyst layer and the anion-conducting polymer layer.

47. 38. The membrane electrode assembly of claim 37, wherein the anion-conducting polymer layer is disposed between the cathode catalyst layer and the cation-conducting polymer layer.

48. 38. The membrane electrode assembly of claim 37, wherein the cathode catalyst layer comprises a reduction catalyst and an anion conducting polymer.

49. 38. The membrane electrode assembly of claim 37, wherein the anode catalyst layer comprises an oxidation catalyst and a cation-conducting polymer.

50. 38. The membrane electrode assembly of claim 37, wherein the ion-conducting polymer in the interfacial region is the same polymer as the cation-conducting polymer in the cation-conducting polymer layer.

51. 38. The membrane electrode assembly of claim 37, wherein the ion-conducting polymer in the interfacial region is the same polymer as the anion-conducting polymer in the anion-conducting polymer layer.

52. 38. The membrane electrode assembly of claim 37, wherein the interfacial region comprises an anion conducting polymer and a cation conducting polymer.

53. 38. The membrane electrode assembly of claim 37, wherein the ion-conducting polymer in the interfacial region is a different cation-conducting polymer than the cation-conducting polymer in the cation-conducting polymer layer.

54. 38. The membrane electrode assembly of claim 37, wherein the ion-conducting polymer in the interfacial region is a different anion-conducting polymer than the anion-conducting polymer in the anion-conducting polymer layer.

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