Membrane Electrode Assembly for COx Reduction

Abstract

This disclosure provides a membrane electrode assembly (MEA) for CO x reduction. According to various embodiments, the MEA is configured to address the challenges x specific to CO, including managing water in the MEA. Bipolar and anion exchange membrane (AEM)-only MEAs, their compositions, and related manufacturing methods are described.

Description

[0001] Incorporation by reference

[0002] A PCT request form is filed concurrently with this specification as part of this application. Each application for which the benefit or priority is claimed in the concurrently filed PCT application form is incorporated herein by reference in its entirety and for all purposes.

[0003] Statement of government support

[0004] This invention was made with government support under grants NNX17CJ02C awarded by the National Aeronautics and Space Administration, 1738554 awarded by the National Science Foundation, and DE-FE0031712 awarded by the Department of Energy. The government has certain rights in this invention.

[0005] Under a user agreement No. FP00003032 between Opus 12, Inc. and the Regents of the University of California for the management and operation of Ernest Orlando Lawrence Berkeley National Laboratory for the United States Department of Energy, the government has certain rights in this invention. Summary of the invention

[0006] Provided herein are membrane electrode assemblies (MEAs) for CO x reduction. According to various embodiments, the MEA is configured to address the CO x specific challenges, including managing water in the MEA. Bipolar and anion exchange membrane (AEM)-only MEAs are described.

[0007] One aspect of the present disclosure relates to a membrane electrode assembly comprising a cathode catalyst layer; an anode catalyst layer; and a bipolar membrane disposed between the cathode catalyst layer and the anode catalyst layer, wherein the bipolar membrane comprises an anion-conducting polymer layer, a cation-conducting polymer layer, and a bipolar interface between the anion-conducting polymer layer and the cation-conducting polymer layer, wherein the cation-conducting polymer layer is disposed between the anode catalyst layer and the anion-conducting polymer layer, and the bipolar interface is characterized by or comprises one or more of the following:

[0008] Covalent crosslinking of the cation-conducting polymer layer and the anion-conducting polymer layer;

[0009] Interpenetration of the anion-conducting polymer layer and the cation-conducting polymer layer; and

[0010] A layer of a second anion-conducting polymer, wherein the ion-exchange capacity of the second anion-conducting polymer is higher than the ion-exchange capacity of the anion-conducting polymer of the anion-conducting polymer layer.

[0011] In some embodiments, the bipolar interface is characterized by the interpenetration of an anion-conducting polymer layer and a cation-conducting polymer layer, and the interpenetrated region is between 10% and 75% of the total thickness of the anion-conducting layer including the interpenetrated region. In some embodiments, the bipolar interface includes protrusions, and the size of the protrusions in a plane parallel to the plane of the anion-conducting polymer layer (in-plane size) is 10 μm - 1 mm. In some embodiments, the bipolar interface is characterized by the interpenetration of an anion-conducting polymer layer and a cation-conducting polymer layer, and the bipolar interface includes protrusions, and the thickness of each protrusion is between 10% and 75% of the total thickness of the anion-conducting polymer layer. In some embodiments, the bipolar interface is characterized by the interpenetration of an anion-conducting polymer layer and a cation-conducting polymer layer, and the bipolar interface includes a gradient of the anion-conducting polymer and / or the cation-conducting polymer. In some embodiments, the bipolar interface is characterized by the interpenetration of an anion-conducting polymer layer and a cation-conducting polymer layer, and the bipolar interface includes a mixture of the anion-conducting polymer and / or the cation-conducting polymer.

[0012] In some embodiments, the bipolar interface includes a layer of a second anion-conducting polymer, and further, wherein the thickness of the layer of the second anion-conducting polymer is between 0.1% and 10% of the thickness of the anion-conducting polymer layer. In some embodiments, the bipolar interface includes a layer of a second anion-conducting polymer, and further, wherein the ion exchange capacity (IEC) of the second anion-conducting polymer is between 2.5 and 3.0 mmol / g. For the ISSE, the IEC of the anion-conducting polymer is between 1.5 and 2.5 mmol / g. In some embodiments, the bipolar interface includes a layer of a second anion-conducting polymer, wherein the second anion-conducting polymer has a lower water absorption rate than the anion-conducting polymer of the anion-conducting polymer layer.

[0013] In some embodiments, the bipolar interface includes a covalent crosslinking between the cation-conducting polymer layer and the anion-conducting polymer layer, and the covalent crosslinking includes a material having a structure of one of the following formulas (I)-(V), (X)-(XXXIV) described further below or a salt thereof.

[0014] In some embodiments, the bipolar interface includes a covalent crosslinking between the cation-conducting polymer layer and the anion-conducting polymer layer, and wherein the covalent crosslinking includes a material having a structure of one of the following formulas (I)-(V):

[0015] or a salt thereof,

[0016] wherein:

[0017] R 7 、R8 , R 9 and R 10 each independently is an electron-withdrawing structural moiety, H, optionally substituted aliphatic, alkyl, heteroaliphatic, heteroalkylene, aromatic, aryl, or arylalkylene, wherein at least one of R 7 or R 8 may contain an electron-withdrawing structural moiety, or R 7 and R 8 or R 9 and R 10 in combination may together form an optionally substituted cyclic group;

[0018] Ar comprises or is an optionally substituted aromatic or arylene;

[0019] each n is independently an integer of 1 or greater;

[0020] each of rings a-c may be optionally substituted; and

[0021] rings a-c, R 7 , R 8 , R 9 and R 10 may optionally contain an ionizable or ionic structural moiety.

[0022] ISSE, R 7 or R 8 contains an electron-withdrawing structural moiety selected from: optionally substituted haloalkyl, cyano, phosphate / ester, sulfate / ester, sulfonic acid, sulfonyl, difluoroboranyl, dihydroxyboron, cyanothio, and piperidine.

[0023] In some embodiments, the bipolar interface comprises a covalent crosslink between a cation-conducting polymer layer and an anion-conducting polymer layer, and wherein the covalent crosslink comprises a material having a structure of one of the following formulas:

[0024] or a salt thereof, wherein:

[0025] Ar is or comprises an optionally substituted arylene or aromatic;

[0026] Ak is or comprises an optionally substituted alkylene, haloalkylene, aliphatic, heteroalkylene, or heteroaliphatic; and

[0027] L is a linking structural moiety, and

[0028] wherein one of Ar, Ak, and / or L is optionally substituted by one or more ionizable or ionic structural moieties.

[0029] In some embodiments, the bipolar interface comprises a covalent crosslinking of a cation-conducting polymer layer and an anion-conducting polymer layer, and wherein the covalent crosslinking comprises a crosslinking agent having a structure of one of the following formulas:

[0030] Wherein:

[0031] Ak is an optionally substituted aliphatic or optionally substituted alkylene;

[0032] Ar is an optionally substituted aromatic or optionally substituted arylene;

[0033] L is a linking structural moiety;

[0034] L3 is an integer of 2 or greater; and

[0035] X’ is absent, -O-, -NR N1 -, -C(O)- or -Ak-, wherein R N1 is hydrogen or an optionally substituted alkyl, and Ak is an optionally substituted alkylene, optionally substituted heteroalkylene, optionally substituted aliphatic or optionally substituted heteroaliphatic.

[0036] In some embodiments, the covalent crosslinking comprises a material having one or more ionizable or ionic structural moieties selected from: -L A -X A , -L A -(L A’ -X A ) L2 , -L A -(X A -L A’ -X A’ ) L2 and -L A -X A -L A’ -X A’ -L A” -X A” ; wherein:

[0037] Each L A , L A’ and L A” is independently a linking structural moiety;

[0038] Each X A , X A’ and X A” is independently comprises an acidic structural moiety, a basic structural moiety, a polyionic structural moiety, a cationic structural moiety or an anionic structural moiety; and

[0039] L2 is an integer of 1 or greater.

[0040] In some such embodiments, each X A , X A’ and X A” independently comprises a carboxyl group, a carboxylate anion, a guanidinium cation, a sulfo group, a sulfonate anion, a sulfonium cation, a sulfate / ester, a sulfate anion, a phosphonyl group, a phosphonate anion, a phosphate / ester, a phosphate anion, a cation, a phosphazene cation, an amino group, an ammonium cation, a heterocyclic cation, or a salt form thereof.

[0041] In some embodiments, the linking structural moiety comprises a covalent bond, a spiro bond, -O-, -NR N1 -, -C(O)-, -C(O)O-, -OC(O)-, -SO2-, an optionally substituted aliphatic, alkylene, alkoxy, haloalkylene, hydroxyalkylene, heteroaliphatic, heteroalkylene, aromatic, arylene, aryloxy, heteroaromatic, heterocyclic or heterocyclyldiyl.

[0042] Another aspect of the present disclosure relates to a membrane electrode assembly (MEA) comprising: a cathode layer; an anode layer; and a bipolar membrane disposed between the cathode layer and the anode layer, wherein the bipolar membrane comprises a cation-conducting polymer layer and an anion-conducting polymer layer, wherein the cation-conducting polymer layer is disposed between the anode layer and the anion-conducting polymer layer, and wherein the thickness of the anion-conducting polymer layer is between 5 and 80 microns.

[0043] In some embodiments, the thickness of the anion-conducting polymer layer is between 5 and 50 microns. In some embodiments, the thickness of the anion-conducting polymer layer is between 5 and 40 microns. In some embodiments, the thickness of the anion-conducting polymer layer is between 5 and 30 microns.

[0044] In some embodiments, the molecular weight of the anion-conducting polymer is at least 30 kg / mol, at least 45 kg / mol or at least 60 kg / mol.

[0045] In some embodiments, the ratio of the thickness of the cation-conducting polymer layer to the thickness of the anion-conducting polymer layer is at least 3:1. In some embodiments, the ratio of the thickness of the cation-conducting polymer layer to the thickness of the anion-conducting polymer layer is at least 7:1. In some embodiments, the ratio of the thickness of the cation-conducting polymer layer to the thickness of the anion-conducting polymer layer is at least 13:1.

[0046] In some embodiments, the ratio of the thickness of the cation-conducting polymer layer to the thickness of the anion-conducting polymer layer is not greater than 3:1. In some embodiments, the ratio of the thickness of the cation-conducting polymer layer to the thickness of the anion-conducting polymer layer is not greater than 2:1. In some embodiments, the ratio of the thickness of the cation-conducting polymer layer to the thickness of the anion-conducting polymer layer is not greater than 1:1.

[0047] Another aspect of the present disclosure relates to a membrane electrode assembly, comprising a cathode catalyst layer; an anode catalyst layer; and a bipolar membrane disposed between the cathode catalyst layer and the anode catalyst layer, wherein the bipolar membrane comprises an anion-conducting polymer layer, a cation-conducting polymer layer, and a bipolar interface between the anion-conducting polymer layer and the cation-conducting polymer layer, wherein the cation-conducting polymer layer is disposed between the anode catalyst layer and the anion-conducting polymer layer, and the bipolar interface is characterized by or comprises one or more of the following:

[0048] · Materials selected from the following: ionic liquids, non-ionic conducting polymers; metals, oxide ion donors, catalysts; CO2 absorption materials, and H2 absorption materials; and

[0049] · Materials that extend across and mechanically strengthen the interface.

[0050] Another aspect of the present disclosure relates to a membrane electrode assembly (MEA), comprising: a cathode layer; an anode layer; and a bipolar membrane disposed between the cathode layer and the anode layer, wherein the bipolar membrane comprises a cation-conducting polymer layer and an anion-conducting polymer layer, wherein the cation-conducting polymer layer is disposed between the anode layer and the anion-conducting polymer layer, and the molecular weight of the anion-conducting polymer is at least 30 kg / mol. In some embodiments, it is at least 45 kg / mol or at least 60 kg / mol.

[0051] Methods for manufacturing an MEA and an MEA with only an anion exchange membrane (AEM) are also provided. These and other aspects of the present disclosure are further discussed below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Shows a membrane electrode assembly used in a water electrolysis reactor for producing hydrogen and oxygen.

[0053] Figure 2 Is a schematic diagram of a membrane electrode assembly (MEA) for use in a CO x reduction reactor (CRR) according to various embodiments.

[0054] Figure 3It is a schematic diagram of a carbon dioxide (CO2) electrolyzer configured to receive water and CO2 (e.g., moist or dry gaseous CO2) as reactants at the cathode and discharge carbon monoxide (CO) as a product.

[0055] Figure 4 Shows an example configuration of a CO x reduction MEA with a cathode catalyst layer, an anode catalyst layer, and an anion-conducting polymer electrolyte membrane (PEM).

[0056] Figure 5 Shows an example configuration of a CO reduction MEA5 with a cathode catalyst layer, an anode catalyst layer, and an anion-conducting PEM.

[0057] Figure 6 Is a schematic diagram showing possible morphologies of two different types of catalysts loaded on catalyst support particles.

[0058] Figure 7 Shows examples of the shape and size of metal catalyst particles.

[0059] Figure 8 Shows an example of a method according to some embodiments, where an ionomer is used as a ligand to direct the synthesis of a nanocrystal catalyst.

[0060] Figure 9 Is a schematic diagram of the bipolar interface of the MEA.

[0061] Figure 10A –10D is a schematic diagram of the bipolar interface of an MEA configured to resist delamination.

[0062] Figure 11 Is a schematic diagram of the layers of the MEA, the layers of the MEA comprising an anion-conducting polymer layer (AEM) and a polymer electrolyte membrane (PEM).

[0063] Figure 12 Shows the CO x Faraday efficiency of an electrolyzer.

[0064] Figure 13 Shows the CO x cell voltage of an electrolyzer with an AEM of different thicknesses. DETAILED DESCRIPTION OF THE INVENTION

[0066] Introduction and Purpose of the MEA

[0067] Here, a membrane electrode assembly (MEA) is described. It can be used in a CO x reduction reactor. CO xMay be carbon dioxide (CO2), carbon monoxide (CO), CO3 2- (carbonate ion), HCO3 - (bicarbonate ion) or combinations thereof. The MEA contains an anode layer, a cathode layer, an electrolyte, and optionally one or more other layers. The layers can be solid and / or soft materials. The layers can contain polymers such as ion-conducting polymers.

[0068] When in use, the cathode of the MEA promotes the electrochemical reduction of CO x by combining the following three inputs: CO x , ions (such as protons) that chemically react with CO x , and electrons. The reduction reaction can produce CO, hydrocarbons, and / or oxygen- and hydrogen-containing organic compounds such as methanol, ethanol, and acetic acid. When in use, the anode of the MEA promotes an electrochemical oxidation reaction, such as electrolyzing water to produce elemental oxygen and protons. Both the cathode and the anode can contain catalysts to promote their respective reactions.

[0069] The composition and configuration of the layers in the MEA can promote a high yield of CO x reduction products. To this end, the MEA can promote any one or more of the following: (a) minimal parasitic reduction reactions (non-CO x reduction reactions) at the cathode; (b) low loss of CO x reactants at the anode or elsewhere in the MEA; (c) maintaining the physical integrity of the MEA during the reaction (e.g., preventing delamination of the MEA layers); (d) preventing the passage of CO x reduction products; (e) preventing the passage of oxidation products (such as O2); (f) maintaining a suitable environment at the cathode / anode for proper oxidation / reduction; (g) providing a path for the desired ions to move between the cathode and the anode while blocking the undesired ions; and (h) minimizing voltage losses.

[0070] CO x reduction specific problems

[0071] Polymeric membrane assemblies such as MEAs have been used in various electrolysis systems such as water electrolysis devices and various current systems such as fuel cells. However, CO x reduction presents problems not encountered or less encountered in water electrolysis devices and fuel cells.

[0072] For example, for many applications, the MEA for CO x reduction requires a lifespan on the order of about 50,000 hours or longer (continuous operation for about five years), which is significantly longer than the expected lifespan of fuel cells for automotive applications; for example, on the order of 5,000 hours. And, for various applications, compared to the MEA of fuel cells used in automotive applications, the MEA for CO xThe reduced MEA employs an electrode having a relatively large geometric surface area. For example, for CO x The reduced MEA can employ an electrode having a geometric surface area (excluding pores and other non-planar features) of at least about 500 cm 2 .

[0073] CO x The reduction reaction can be carried out in an operating environment that promotes the mass transfer of specific reactant and product species and inhibits parasitic reactions. Fuel cell and water electrolysis device MEAs typically cannot create such an operating environment. For example, such MEAs can promote undesired parasitic reactions, such as gaseous hydrogen evolution at the cathode and / or gaseous CO2 production at the anode.

[0074] In some systems, the rate of the CO x reduction reaction is limited by the availability of the gaseous CO x reactant at the cathode. In contrast, the rate of water electrolysis is not significantly limited by reactant availability: liquid water tends to easily enter the cathode and anode, and the electrolysis device can operate at near the highest possible current density.

[0075] MEA Structure

[0076] General Configuration of MEA

[0077] In some embodiments, the MEA has a cathode layer, an anode layer, and a polymer electrolyte membrane (PEM) between the anode layer and the cathode layer. The polymer electrolyte membrane provides ionic connectivity between the anode layer and the cathode layer while preventing electronic connectivity that would cause a short circuit. The cathode layer contains a reduction catalyst and a first ion-conducting polymer. The cathode layer may also contain an ion conductor and / or an electron conductor. The anode layer contains an oxidation catalyst and a second ion-conducting polymer. The anode layer may also include an ion conductor and / or an electron conductor. The PEM contains a third ion-conducting polymer.

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

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

[0080] For some MEA designs, there are three classes of available ion-conducting polymers: 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] As background, as Figure 1As shown, a membrane electrode assembly (MEA) 100 for water electrolysis has a cathode 120 and an anode 140 separated by an ion-conducting polymer 160, which provides a path for ions to travel between the cathode 120 and the anode 140. Both the cathode 120 and the anode 140 contain an ion-conducting polymer and catalyst particles. One or both may also include an electronically-conducting catalyst support. The ion-conducting polymers in the cathode 120, anode 140, and ion-conducting polymer layer 160 are all cation conductors or all anion conductors.

[0082] MEA 100 is not suitable for use in a carbon dioxide reduction reactor (CRR). When all of the ion-conducting polymers are cation conductors, the environment favors H2 generation at the cathode layer (an unwanted side reaction). The production of hydrogen reduces the rate of CO x product production and reduces the overall efficiency of the process.

[0083] When all of the ion-conducting polymers are anion conductors, CO2 reacts with hydroxide ions in the ion-conducting polymer at the cathode to form bicarbonate anions. The electric field in the reactor causes the bicarbonate anions to move from the cathode side of the cell to the anode side of the cell. At the anode, the bicarbonate anions can decompose back to CO2 and hydroxide. This results in a net movement of CO2 from the cathode to the anode of the cell, where it does not react and is diluted by the anode reactants and products. This loss of CO2 on the anode side of the cell reduces the efficiency of the process.

[0084] Conductivity and selectivity of ion-conducting polymers for MEA layers

[0085] The term "ion-conducting polymer" is used herein to describe a polymeric electrolyte having a specific conductivity greater than about 1 mS / cm for anions and / or cations. The term "anion conductor" describes an ion-conducting polymer that predominantly conducts anions (although there will still be a small amount of cation conduction) and has an anion transference number greater than about 0.85 at a thickness of about 100 microns. The term "cation conductor" and / or "cation-conducting polymer" describes an ion-conducting polymer that predominantly conducts cations (e.g., there may still be an incidental amount of anion conduction) and has a cation transference number greater than about 0.85 at a thickness of about 100 microns. For an ion-conducting polymer described as conducting both anions and cations ("cation-and-anion conductor"), neither the anion nor the cation transference number is 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 an ionomer. Examples of each class of ion-conducting polymer are provided in the table below.

[0086]

[0087] Some Class A ion-conducting polymers are known under the following trade names, for example: 2259-60 (Pall RAI), AHA from Tokuyama Co, FAA- (fumatech GbbH), Morgane ADP from Solvay or the SF-17 of the anion exchange membrane material of Tosoh. Other Class A ion-conducting polymers include HNN5 / HNN8 from Ionomr, FumaSep from Fumatech, TM1 from Orion, and PAP-TP from W7energy. Some Class C ion-conducting polymers are known under the following trade names, for example: (DuPont (DuPont TM )、 (Gore)、 (fumatech GmbH) and various formulations of PFSA (Solvay).

[0088] Polymer Structures

[0089] Examples of polymer structures that may include ionizable structural moieties or ionic structural moieties and are used as ion-conducting polymers in the MEAs described herein are provided below. The ion-conducting polymers can be suitably used in any MEA layer containing the ion-conducting polymers. Charge conduction through the material can be controlled by the type and amount of charge (e.g., anionic and / or cationic charges in the polymer structure) provided by the ionizable / ionic structural moieties. Additionally, the composition can include polymers, homopolymers, copolymers, block copolymers, polymer blends, other forms of polymer classes, or other useful combinations of repeating monomer units. As described below, according to various embodiments, the ion-conducting polymer layer can include one or more of crosslinks, linking structural moieties, and arylene groups. In some embodiments, two or more ion-conducting polymers can be crosslinked (e.g., in two or more ion-conducting polymer layers of the MEA).

[0090] Non-limiting monomer units can include one or more of the following:

[0091] wherein, Ar is an optionally substituted arylene or aromatic; Ak is an optionally substituted alkylene, haloalkylene, aliphatic, heteroalkylene, or heteroaliphatic; and L is a linking structural moiety (e.g., any linking structural moiety described herein) or can be -C(R 7 )(R 8)-. Some other non-limiting monomer units may include optionally substituted arylene, aryloxy, alkylene, or combinations thereof, such as optionally substituted (aryl)sub(alkyl) (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 monomer units may optionally be substituted with one or more ionizable or ionic moieties (e.g., as described herein).

[0092] One or more monomer units can be combined to form a polymer unit. Non-limiting polymer units include any of the following:

[0093] wherein, Ar, Ak, L, n, and m can be any of those described herein. In some embodiments, each m is independently 0 or 1 or an integer greater than 1. In other embodiments, Ar can include two or more arylene or aromatic groups.

[0094] Other alternative configurations are also included in the compositions herein, such as branched configurations, diblock copolymers, triblock copolymers, random or statistical copolymers, stereoblock copolymers, gradient copolymers, graft copolymers, and combinations of any blocks or regions described herein.

[0095] Examples of polymer structures include those polymer structures according to any one of formulas (I)-(V) and (X)-(XXXIV) or their salts. In some embodiments, the polymer structure is a copolymer and includes a first polymer structure selected from any one of formulas (I)-(V) or their salts; and a second polymer structure, the second polymer structure including an optionally substituted aromatic, an optionally substituted arylene, a structure selected from any one of formulas (I)-(V) and (X)-(XXXIV) or their salts.

[0096] In one embodiment, the MW of the ion-conducting polymer is a weight-average molecular weight (Mw) of at least 10000 g / mol, or about 5000 - 2500000 g / mol. In another embodiment, the MW is a number-average molecular weight (Mn) of at least 20000 g / mol, or about 2000 - 2500000 g / mol.

[0097] In any of the embodiments herein, each of n, n1, n2, n3, n4, m, m1, m2, or m3 is independently 1 or greater, 20 or greater, 50 or greater, 100 or greater, and 1 to 1000000, such as 10 to 1000000, 100 to 1000000, 200 to 1000000, 500 to 1000000, or 1000 to 1000000.

[0098] The non-limiting polymer structure may comprise the following:

[0099] or a salt thereof, wherein:

[0100] R 7 、R 8 、R 9 and R 10 each independently is an electron-withdrawing structural moiety, H, optionally substituted aliphatic, alkyl, heteroaliphatic, heteroalkylene, aromatic, aryl, or arylalkylene, wherein at least one of R 7 or R 8 may comprise an electron-withdrawing structural moiety, or a combination of R 7 and R 8 or R 9 and R 10 may together form an optionally substituted cyclic group;

[0101] Ar comprises or is an optionally substituted aromatic or arylene (e.g., any of those described herein);

[0102] Each n is independently an integer of 1 or greater;

[0103] Each of rings a-c may be optionally substituted; and

[0104] Rings a-c, R 7 、R 8 、R 9 and R 10 may optionally comprise ionizable or ionic structural moieties.

[0105] Additionally, the non-limiting polymer structure may comprise one or more of the following:

[0106]

[0107] or a salt thereof, wherein:

[0108] R 7 may be any of those described herein (e.g., chemical formulas (I)-(V));

[0109] n is 1 or greater;

[0110] Each L 8A 、L B’ and L B” is independently a linking structural moiety; and

[0111] Each X 8A 、X 8A’ 、X 8A” 、X B’ and X B”Independently an ionizable or ionic structural moiety.

[0112] Some other polymer structures comprise the following:

[0113]

[0114] or a salt thereof, wherein:

[0115] R 1 、R 2 、R 3 、R 7 、R 8 、R 9 and R 10 each independently is an electron-withdrawing structural moiety, H, optionally substituted aliphatic, alkyl, heteroaliphatic, heteroalkylene, aromatic, aryl, or arylalkylene, wherein at least one of R 7 or R 8 may comprise an electron-withdrawing structural moiety, or a combination of R 7 and R 8 or R 9 and R 10 may together form an optionally substituted cyclic group;

[0116] Each Ak is or comprises optionally substituted aliphatic, alkylene, haloalkylene, heteroaliphatic or heteroalkylene;

[0117] Each Ar is or comprises optionally substituted arylene or aromatic;

[0118] L, L 1 、L 2 、L 3 and L 4 each independently is a linking structural moiety;

[0119] Each of n, n1, n2, n3, n4, m, m1, m2 and m3 independently is an integer of 1 or greater;

[0120] q is 0, 1, 2 or greater;

[0121] Each of rings a-i may optionally be substituted; and

[0122] Rings a-i, R 7 、R 8 、R 9 and R 10 may optionally comprise an ionizable or ionic structural moiety.

[0123] In certain embodiments (e.g., having the chemical formula (XIV) or (XV)), each nitrogen atom on ring a and / or b is substituted with an optionally substituted aliphatic, alkyl, aromatic, aryl, ionizable moiety, or ionic moiety. In some embodiments, one or more hydrogen or fluorine atoms may be substituted (e.g., in formula (XIX) or (XX)) to incorporate an ionizable moiety or ionic moiety (e.g., any of those described herein). In other embodiments, an oxygen atom present in the polymer structure (e.g., in formula XXVIII) may associate with a base dopant (e.g., K + )

[0124] In a particular example, Ar, one or more of rings a-i (e.g., ring 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 may optionally be substituted with one or more ionizable or ionic moieties and / or one or more electron-withdrawing groups. Other non-limiting substituents of Ar, the rings (e.g., rings a-i), L, Ak, R 7 , R 8 , R 9 and R 10 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, aroyl, aryloxy, arylalkoxy, hydroxyalkyl, and haloalkyl.

[0125] In some embodiments, each of R 1 , R 2 and R 3 is independently H, an optionally substituted aromatic, aryl, aryloxy, or arylalkylene. In other embodiments (e.g., having the formula (I)-(V) or (XII)), R 7 includes an electron-withdrawing moiety. In yet other embodiments, R 8 , R 9 and / or R 10 include an ionizable or ionic moiety.

[0126] In one example, the 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 and L groups, or incorporated as part of the L group. Non-limiting examples of ionizable and ionic moieties include cationic, anionic, and polyionic groups, as described herein.

[0127] In any embodiment of the present disclosure, the electron-withdrawing structural moiety may comprise or be an optionally substituted haloalkyl, cyano (CN), phosphate / ester (e.g., -O(P═O)(OR P1 )(OR P2 ) or -O-[P(═O)(OR P1 )-O] P3 -R P2 ), sulfate / ester (e.g., -O-S(═O)2(OR S1 )), sulfonic acid (-SO3H), sulfonyl (e.g., -SO2-CF3), difluoroboryl (-BF2), dihydroxyboryl (B(OH)2), thiocyanato (-SCN) or piperidine. Some other non-limiting phosphate groups may comprise derivatives of phosphoric acid, such as orthophosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, metaphosphoric acid and / or phosphoric anhydride or combinations thereof.

[0128] Some other polymer units may comprise poly(benzimidazole) (PBI), polyphenylene (PP), polyimide (PI), poly(ethyleneimine) (PEI), sulfonated polyimide (SPI), polysulfone (PSF), sulfonated polysulfone (SPSF), poly(ether ether ketone) (PEEK), phenolphthalein-based PEEK (PEEK-WC), polyethersulfone (PES), sulfonated polyethersulfone (SPES), sulfonated poly(ether ether ketone) (SPEEK), phenolphthalein-based SPEEK (SPEEK-WC), poly(phenylene oxide) (PPO), sulfonated polyphenylene oxide (SPPO), ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), poly(epichlorohydrin) (PECH), poly(styrene) (PS), sulfonated poly(styrene) (SPS), hydrogenated poly(butadiene-styrene) (HPBS), styrene divinylbenzene copolymer (SDVB), styrene-ethylene-butene-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(phosphazene), poly(aryloxyphosphazene), polyetherimide and combinations thereof.

[0129] Crosslinking

[0130] In some embodiments, crosslinking is present within and / or between the ion-conducting polymer layers. Crosslinking within the material can be facilitated by using a crosslinking reagent. For example, the composition can comprise polymer units and the crosslinking reagent can be used to provide crosslinking between the polymer units. For example, if the polymer units (P1 and P2) contain leaving groups, a diamine crosslinking reagent (e.g., H2N-Ak-NH2) can be used to react with the polymer units by replacing the leaving groups and forming an amino-containing crosslinker within the composition (e.g., thereby forming P1-NH-Ak-NH-P2). Crosslinking can be introduced by forming a polymer composition and then exposing the composition to the crosslinking reagent to form the crosslinker.

[0131] Depending on the functional groups present in the material, the crosslinking reagent can comprise a nucleophilic group (e.g., amine or hydroxyl) or an electrophilic group (e.g., carbonyl). Thus, non-limiting crosslinking reagents can include amine-containing reagents, hydroxyl-containing reagents, carboxylic acid-containing reagents, acyl halide-containing reagents, etc. Additionally, the crosslinking reagent can comprise:

[0132] wherein Ak is an optionally substituted aliphatic or alkylene group; Ar is an optionally substituted aromatic or arylene group; L is a linking moiety (e.g., any of those herein, e.g., a covalent bond, an optionally substituted alkylene group, aliphatic, etc.); L3 is an integer of 2 or greater (e.g., 2, 3, 4, 5, 6 or greater); and X is a halogen, a hydroxyl group, an optionally substituted amino group (e.g., NR N1 R N2 wherein R N1 and R N2 each independently is H or an optionally substituted alkyl group), a hydroxyl group, a carboxyl group, an acyl halide (e.g., -C(O)-R where R is a halogen), a carboxyaldehyde (e.g., -C(O)H) or an optionally substituted alkyl group. Non-limiting crosslinking reagents can include terephthalaldehyde, glutaraldehyde, o-xylene, p-xylene, m-xylene, or polyvalent amines such as diamines, triamines, tetraamines, pentamines, etc., including 1,6-diaminohexane (hexamethylenediamine), 1,4-diaminobutane, 1,8-diaminooctane, propane-1,2,3-triamine, [1,1':3',1″-terphenyl]-4,4″,5'-triamine, etc.

[0133] After reacting the crosslinking reagent, the composition may contain one or more crosslinking agents within the composition. If the crosslinking reagent is divalent, the crosslinking agent may be present between any combination of polymer structures, polymer monomers, and ionizable / ionic moieties (e.g., between two polymer units, between two ionizable / ionic moieties, etc.). If the crosslinking reagent is trivalent or has a higher n valence state, the crosslinking agent may be present between any n of polymer units, linking moieties, ionizable moieties, and / or ionic moieties. Non-limiting crosslinking agents present in the composition include those formed after reacting the crosslinking reagent. Thus, examples of crosslinking agents may include:

[0134] 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., any of those herein, e.g., a covalent bond, optionally substituted alkylene, optionally substituted aliphatic, etc.), L3 is an integer of 2 or greater (e.g., 2, 3, 4, 5, 6 or greater), and X’ is the form of X after reaction. In some embodiments, X’ is absent, -O-, -NR N1 -, -C(O)- or -Ak-, wherein R N1 is hydrogen or an optionally substituted alkyl, and Ak is an optionally substituted alkylene, optionally substituted heteroalkylene, optionally substituted aliphatic or optionally substituted heteroaliphatic.

[0135] Ionizable and ionic moieties

[0136] The polymers described herein contain one or more ionizable or ionic moieties. For example, in the ionic moiety, such a moiety may contain an anion or cationic charge. Alternatively, an ionizable moiety contains a functional group that can be readily converted into an ionic moiety, e.g., an ionizable moiety of a carboxyl group (-CO2H) that can be readily deprotonated to form a carboxylate anion (-CO2 - ). As used herein, the terms “ionizable” and “ionic” may be used interchangeably.

[0137] The structural moiety can be characterized as an acidic structural moiety (e.g., a structural moiety that can be deprotonated or carry a negative charge) or a basic structural moiety (e.g., a structural moiety that can be protonated or carry a positive charge). In certain embodiments, the structural moiety can be a multi-ionic structural moiety, which can include multiple acidic structural moieties, multiple basic structural moieties, or a combination thereof (e.g., in zwitterionic structural moieties). Additionally, the structural moiety can include zwitterionic structural moieties such as those that include anionic structural moieties (e.g., hydroxyl or deprotonated hydroxyl) and cationic structural moieties (e.g., ammonium).

[0138] Via one or more linking structural moieties, the ionic structural moieties herein can be linked to a parent structure. Moreover, a single ionic structural moiety can extend from a single linking structural moiety, or multiple ionic structural moieties can have one or more linking structural moieties therebetween. For example, the ionic structural 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 structural moiety (e.g., any of those described herein); each X A , X A’ and X A” independently includes an acidic structural moiety, a basic structural moiety, a multi-ionic structural moiety, a cationic structural moiety, or an anionic structural moiety; and L2 is an integer of 1, 2, 3, or greater (e.g., 1 to 20). Non-limiting L A and L A1’ can be -(CH2) L1 -, -O(CH2) L1 -, -(CF2) L1 -, -O(CF2) L1 -, or -S(CF2) L1 -, where L1 is an integer of 1 to 3; and X A is an ionizable or ionic structural moiety as described herein.

[0139] Non-limiting ionizable or ionic structural moieties include carboxyl (-CO2H), carboxylate anion (-CO2 - ), guanidinium cation, sulfo (-SO2OH), sulfonate anion (-SO2O - ), sulfonium cation, sulfate / ester, sulfate anion, phosphonyl (e.g., -P(=O)(OH)2), phosphonate anion, phosphate / ester, phosphate anion, cation, phosphazene cation, amino (e.g., -NR N1 R N2 ), ammonium cation (e.g., aliphatic or aromatic ammonium), heterocyclic cation (e.g., including piperidine pyrrolidine pyridine pyrazole imidazole quinoline isoquinoline acridine quinoline isoquinoline acridine pyridazine pyrimidine pyrazine phenazine 1,4-diazabicyclo[2.2.2]octane (DABCO) cation, 4-methyl-1,4-diazabicyclo[2.2.2]oct-1-yl (MAABCO) cation, and 1-benzyl-1,4-diazabicyclo[2.2.2]octane (BABCO) anion), or their salt forms. Such structural moieties can associate with one or more counterions. For example, a cationic structural moiety can associate with one or more anionic counterions, and an anionic structural moiety can associate with one or more cationic counterions.

[0140] Arylene group

[0141] Certain structural moieties herein (e.g., polymer units, linking structural moieties, etc.) can include optionally substituted arylene. Such arylene groups include any polyvalent (e.g., divalent, trivalent, tetravalent, etc.) group having one or more aromatic groups, and the aromatic groups can include heteroaromatic groups. Non-limiting aromatic groups (e.g., for Ar) can include any of the following: Each of rings a-i may optionally be substituted with, for example, any of the optional substituents described herein for alkyl or aryl; or any of the ionic moieties described herein; L’ is a linking moiety (e.g., any linking moiety described herein); and each of R’ and R” is independently H, optionally substituted alkyl, optionally substituted aryl, or an ionic moiety, as described herein. Non-limiting substituents for rings a-i include one or more of the substituents described herein for aryl, such as alkyl, alkoxy, alkoxyalkyl, amino, aminoalkyl, aryl, arylalkylene, aroyl, aryloxy, arylalkoxy, cyano, hydroxy, hydroxyalkyl, nitro, halogen, and haloalkyl. In some embodiments, L’ is a covalent bond, -O-, -NR N1 -, -C(O)-, optionally substituted alkylene, heteroalkylene, or arylene.

[0142] Other non-limiting arylenes may 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), etc.

[0143] Non-limiting examples of the linking moiety of arylene include any of the linking moieties herein. In some embodiments, L’ is substituted with one or more ionizable or ionic moieties described herein. In certain embodiments, L’ is optionally substituted alkylene. Non-limiting substituents of L’ may include -L A -X A , where L A is a linking moiety (e.g., any linking moiety described herein, such as -Ak-, -O-Ak-, -Ak-O-, -Ar-, -O-Ar-, or -Ar-O-, where Ak is optionally substituted alkylene and Ar is optionally substituted arylene), and X A is an acidic moiety, a basic moiety, or a polyionic moiety.

[0144] Linking moiety

[0145] Certain chemical functional groups herein may include a linking moiety between the parent structure and another moiety (e.g., an ionic moiety) or between two (or more) other moieties. Linking moieties (e.g., L, L 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 in polyvalent form.

[0146] In any embodiment herein, the linking structural moiety (e.g., L, L 1 , L 2 , L 3 or L 4 ) comprises a covalent bond, a spiro 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), alkoxy, haloalkylene (e.g., -CF2- or -C(CF3)2-), hydroxyalkylene, heteroaliphatic, heteroalkylene, aromatic, arylene, aryloxy, heterocycle, heterocyclodiyl, -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 a particular embodiment, Ak is optionally substituted aromatic, 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.

[0147] In other embodiments, L is optionally substituted C 1-6 aliphatic, C 1-6 alkylene or C 1-6 heteroalkylene. The use of short linking groups can provide a denser polymer network, as shorter linking groups can minimize cyclization reactions.

[0148] In some embodiments, the linking structural moiety is -(CH2) L1 (-), -O(CH2) L1 (-), -(CF2) L1 (-), -O(CF2) L1 (-), or -S(CF2) L1-, wherein L1 is an integer from 1 to 3. In other embodiments, the linking structure moiety is -Ak-O-Ar-Ak-O-Ak- or -Ak-O-Ar-, wherein Ak is an optionally substituted alkylene or haloalkylene, and Ar is an optionally substituted arylene. Non-limiting substituents of Ar include -SO2-Ph, wherein Ph may be unsubstituted or substituted with one or more halogens.

[0149] Referring to the tables and chemical formulas (I)-(V) and (X)-(XXXIV), the polymers described above include their homopolymers and copolymers, and they may be optionally crosslinked and may include any of the linking structure moieties. The arylene groups and ionic structure moieties as described above may be appropriately used in one or more layers of an MEA including a cathode catalyst layer, an anode catalyst layer, a polymer electrolyte membrane (PEM) layer, a cathode buffer layer, and / or an anode buffer layer.

[0150] For CO x Reductive bipolar MEA

[0151] In some embodiments, the MEA includes a bipolar interface, having an anion-conducting polymer on the cathode side of the MEA and an interfacial cation-conducting polymer on the anode side of the MEA. In some embodiments, the cathode contains a first catalyst and an anion-conducting polymer. In some embodiments, the anode contains a second catalyst and a cation-conducting polymer. In some embodiments, the cathode buffer layer located between the cathode and the PEM contains an anion-conducting polymer. In some embodiments, the anode buffer layer located between the anode and the PEM contains a cation-conducting polymer.

[0152] During operation, the MEA with a bipolar interface allows ions to move through the polymer electrolyte, allows electrons to move through the metal and / or carbon in the cathode layer and the anode layer, and allows liquids and gases to move through the pores in the layers.

[0153] In embodiments where an anion-conducting polymer is used in the cathode and / or the cathode buffer layer, the MEA can reduce or prevent undesirable reactions that produce unwanted products and reduce the overall efficiency of the cell. In embodiments where a cation-conducting polymer is used in the anode and / or the anode buffer layer, undesirable reactions that reduce the production of desired products and reduce the overall efficiency of the cell can be reduced or prevented.

[0154] For example, at the potential levels used for CO2 cathodic reduction, 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 hydrogen ions. Hydrogen ions can be generated by various oxidation reactions occurring at the anode of the CO2 reduction reactor and can migrate across the MEA and reach the cathode where they can be reduced to produce hydrogen gas. The extent to which this parasitic reaction can occur is a function of the concentration of hydrogen ions present at the cathode. Accordingly, the MEA can use an anion-conducting material in the cathode layer and / or the cathode buffer layer. The anion-conducting material at least partially prevents hydrogen ions from reaching the catalytic sites on the cathode. As a result, the parasitic production of hydrogen gas is reduced and the production rate of CO or other products and the overall efficiency of the process are increased.

[0155] Another process that can be avoided is the transport of carbonate or bicarbonate ions to the anode, thereby effectively removing CO2 from the cathode. Aqueous carbonate or bicarbonate ions can be produced from CO2 at the cathode. If these ions reach the anode, they can decompose and release gaseous CO2. The result is a net movement of CO2 from the cathode to the anode where the CO2 is not reduced and is lost along with the oxidation products. To prevent the carbonate and bicarbonate ions produced at the cathode from reaching the anode, the polymer electrolyte membrane and / or the anode buffer layer can include a cation-conducting polymer that at least partially prevents the transport of negative ions such as bicarbonate or carbonate ions to the anode.

[0156] Accordingly, in some designs, the bipolar membrane structure raises the pH at the cathode to facilitate CO2 reduction, while a cation-conducting polymer such as a proton exchange layer prevents a significant amount of CO2, negative ions (such as bicarbonate, carbonate), hydrogen, and CO2 reduction products (such as CO, methane, ethylene, alcohols) from entering the anode side of the cell.

[0157] Figure 2 An example MEA 200 for use in CO x reduction is shown. The MEA 200 has a cathode layer 220 and an anode layer 240 separated by an ion-conducting polymer layer 260 that provides a path for ions to travel between the cathode layer 220 and the anode layer 240. In some embodiments, the cathode layer 220 includes an anion-conducting polymer and / or the anode layer 240 includes a cation-conducting polymer. In some embodiments, the cathode layer and / or the anode layer of the MEA is porous. The pores can facilitate gas and / or fluid transport and can increase the amount of catalyst surface area available for reaction.

[0158] The ion conduction layer 260 may include two or three sublayers: a polymer electrolyte membrane (PEM) 265, an optional cathode buffer layer 225, and / or an optional anode buffer layer 245. One or more of the layers in the ion conduction layer may be porous. In some embodiments, at least one layer is non-porous such that reactants and products of the cathode cannot reach the anode by gas and / or liquid transport and vice versa. In some embodiments, the PEM layer 265 is non-porous. Example properties of the anode buffer layer and the cathode buffer layer are provided elsewhere herein.

[0159] Figure 3 Shown is a CO2 electrolysis device 303 configured to receive water and CO2 (e.g., moist or dry gaseous CO2) as reactants at a cathode 305 and discharge CO as a product. The electrolysis device 303 is further configured to receive water as a reactant at an anode 307 and discharge gaseous oxygen. The electrolysis device 303 includes a bipolar layer having an anion-conducting polymer 309 adjacent to the cathode 305 and a cation-conducting polymer 311 (illustrated as a proton exchange membrane) adjacent to the anode 307.

[0160] As shown in the enlarged inset of the bipolar interface 313 in the electrolysis device 303, the cathode 305 includes an anion-exchange polymer (which in this example is the same anion-conducting polymer 309 in the bipolar layer), conductive carbon carrier particles 317, and metal nanoparticles 319 supported on the carrier particles. CO2 and water are transported through pores such as pore 321 and reach the metal nanoparticles 319 where they react, in this case with hydroxide ions, to produce bicarbonate ions and reduction reaction products (not shown). CO2 may also reach the metal nanoparticles 319 by transport within the anion-exchange polymer 315.

[0161] Hydrogen ions are transported from the anode 307 and pass through the cation-conducting polymer 311 until they reach the bipolar interface 313 where the anion-exchange polymer 309 blocks their further transport towards the cathode. At the interface 313, the hydrogen ions may react with bicarbonate or carbonate ions to produce carbonic acid (H2CO3) which may decompose to produce CO2 and water. As explained herein, the CO2 produced may be provided in the gas phase and a path should be provided in the MEA to return it to the cathode 305 where it may be reduced. The cation-conducting polymer 311 blocks the transport of anions such as bicarbonate ions towards the anode where they may react with protons and release CO2 which would not be able to participate in the reduction reaction at the cathode.

[0162] As shown, a cathode buffer layer having an anion-conducting polymer can work in concert with the cathode and its anion-conducting polymer to block proton transport to the cathode. Although a MEA employing ion-conducting polymers of the appropriate electronic conduction type in the cathode, anode, cathode buffer layer, and anode buffer layer (if present) can prevent cation transport to the cathode and anion transport to the anode, cations and anions can still contact in the internal regions of the MEA, such as in the membrane layer.

[0163] As Figure 3 shown, bicarbonate and / or carbonate ions combine with hydrogen ions between the cathode layer and the anode layer to form carbonic acid, which can decompose to form gaseous CO2. It has been observed that the MEA sometimes delaminates, which may be due to the production of this gaseous CO2 and the lack of an easy escape path for the CO2.

[0164] The delamination problem can be addressed by employing a cathode buffer layer having pores. One possible explanation for its effectiveness is that the pores provide a path for the gaseous carbon dioxide to escape back to the cathode, where it can be reduced. In some embodiments, the cathode buffer layer is porous, but at least one layer between the cathode layer and the anode layer is non-porous. This can prevent gases and / or large masses of liquid from passing between the cathode layer and the anode layer while still preventing delamination. For example, the non-porous layer can prevent water from passing directly from the anode to the cathode. The porosity of the layers in the MEA is further described elsewhere in this document.

[0165] Example of a bipolar MEA

[0166] As an example, the MEA includes a cathode layer, an anode layer, a membrane layer, and a cathode buffer layer. The cathode layer includes a reduction catalyst and a first anion-conducting polymer (such as Sustainion, FumaSep FAA-3, Tokuyama anion exchange polymer). The anode layer includes an oxidation catalyst and a first cation-conducting polymer (such as a PFSA polymer). The membrane layer includes a second cation-conducting polymer and is disposed between the cathode layer and the anode layer to conductively connect the cathode layer and the anode layer. The cathode buffer layer includes a second anion-conducting polymer (such as Sustainion, FumaSep FAA-3, Tokuyama anion exchange polymer) and is 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 between about 1 and 90 volume percent, but as a supplement or as an alternative, can have any suitable porosity (including, for example, no porosity). In other examples, the cathode buffer layer can have any suitable porosity (e.g., 0.01 - 95%, 0.1 - 95%, 0.01 - 75%, 1 - 95%, 1 - 90%, etc.).

[0167] Excessive porosity can reduce the ionic conductivity of the buffer layer. In some embodiments, the porosity is 20% or less, and in certain embodiments, it is 0.1 - 20%, 1 - 10%, or 5 - 10%. The porosity within these ranges may be sufficient to allow the movement of water and / or CO2 without loss of ionic conductivity. The porosity can be measured as further described below.

[0168] In a related example, the membrane electrode assembly may include an anode buffer layer that includes a third cation-conducting polymer and is disposed between the membrane layer and the anode layer to conductively connect the membrane layer and the anode layer. The anode buffer layer preferably has a porosity between about 1 and 90 volume percent, but as a supplement or alternative, it may have any suitable porosity (including, for example, no porosity). However, in other settings and examples, the anode buffer layer may have any suitable porosity (e.g., between 0.01 - 95%, 0.1 - 95%, 0.01 - 75%, 1 - 95%, 1 - 90%). Similar to the cathode buffer layer, in some embodiments, the porosity is 20% or less, such as 0.1 - 20%, 1 - 10%, or 5 - 10%.

[0169] In one example, the anode buffer layer can be used in a MEA that has: a cathode catalyst layer with an anion-exchange polymer, a cathode buffer layer with an anion-exchange polymer, a membrane with a cation-exchange polymer, and an anode buffer layer with an anion-exchange polymer. In this structure, the anode buffer layer can be porous to facilitate the transport of water to the membrane / anode buffer layer interface. Water will decompose at this interface, generating protons that travel through the membrane and hydroxide ions that travel towards the anode catalyst layer. One advantage of this structure is the possible use of low-cost water oxidation catalysts (such as NiFeO x ) that are stable only under alkaline conditions.

[0170] In another specific example, the membrane electrode assembly includes a cathode layer, an anode layer, a membrane layer, and an anode buffer layer. The cathode layer includes a reduction catalyst and a first anion-conducting polymer (such as Sustainion, FumaSep FAA-3, Tokuyama anion-exchange polymer). The anode layer includes an oxidation catalyst and a first cation-conducting polymer. The membrane layer includes a second cation-conducting polymer (such as Sustainion, FumaSep FAA-3, Tokuyama anion-exchange polymer) and is disposed between the cathode layer and the anode layer to conductively connect the cathode layer and the anode layer. The anode buffer layer includes a second cation-conducting polymer and is disposed between the anode layer and the membrane layer to conductively connect the anode layer and the membrane layer.

[0171] An MEA containing an anion exchange polymer membrane and an anode buffer layer containing a cation exchange polymer can be used for CO reduction. In this case, water will form at the membrane / anode buffer layer interface. The pores in the anode buffer layer can facilitate water removal. One advantage of this structure would be the use of an acid-stable (e.g., IrO x ) water oxidation catalyst.

[0172] In related examples, the membrane electrode assembly can include a cathode buffer layer that includes a third anion-conducting polymer and is disposed between the cathode layer and the membrane layer to conductively connect 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 polymers. The cathode buffer layer preferably has a porosity between about 1 and 90 volume percent, but as a supplement or alternative, can have any suitable porosity (including, for example, no porosity). However, in other settings and examples, the cathode buffer layer can have any suitable porosity (e.g., between 0.01-95%, 0.1-95%, 0.01-75%, 1-95%, 1-90%). In some embodiments, the porosity is 20% or less, and in certain embodiments, is 0.1-20%, 1-10%, or 5-10%.

[0173] In one example, the cathode catalyst layer contains Au nanoparticles with a diameter of 4 nm, which are loaded on Vulcan XC72R carbon and mixed with a TM1 (mTPN-1) anion exchange polymer electrolyte (from Orion). The layer thickness is ~15 μm, Au / (Au + C) = 20 wt%, the mass ratio of TM1 to the catalyst is 0.32, and the mass loading is 1.4-1.6 mg / cm 2 (total Au + C), and the estimated porosity is 0.56. The anion exchange polymer layer contains TM1 and PTFE particles. The diameter of the PTFE is about 200 nm. The molecular weight of TM1 is 30k - 45k. The thickness of the layer is ~15 um. The PTFE can introduce a porosity of about 8%. The proton exchange membrane layer contains a perfluorosulfonic acid polymer (e.g., Nafion 117). The thickness is about 183 um. The membrane forms a continuous layer that prevents significant movement of gases (CO2, CO, H2) through the layer. The anode catalyst layer contains 10 um thick Ir or IrO x nanoparticles (100-200 nm aggregates).

[0174] For CO x reduction, an MEA with only an anion exchange membrane

[0175] In some embodiments, the MEA does not contain a cation-conducting polymer layer. In such embodiments, the electrolyte is not a cation-conducting polymer and the anode (if it contains an ion-conducting polymer) does not contain a cation-conducting polymer. Examples are provided herein.

[0176] A membrane electrode assembly (MEA) with only an anion exchange membrane (AEM) (only AEM) allows for anion conduction across the MEA. In embodiments where none of the MEA layers are significantly conductive to cations, hydrogen ions have limited mobility in the MEA. In some embodiments, a membrane with only AEM provides a high pH environment (e.g., at least about pH 7), and can promote CO2 and / or CO reduction by suppressing the parasitic hydrogen evolution reaction at the cathode. Like other MEA designs, an MEA with only AEM allows ions (especially anions such as hydroxide ions) to move through the polymer electrolyte. In some embodiments, the pH can be lower; a pH of 4 or higher may be high enough to suppress hydrogen evolution. An MEA with only AEM also allows electrons to move to and through the metal and carbon in the catalyst layer. In embodiments where there are pores in the anode layer and / or the cathode layer, an MEA with only AEM allows liquids and gases to move through the pores.

[0177] In some embodiments, an MEA with only AEM comprises an anion exchange polymer electrolyte membrane with an electrocatalyst layer on either side (cathode and anode). In some embodiments, one or both electrocatalyst layers also contain an anion exchange polymer electrolyte.

[0178] In some embodiments, an MEA with only AEM is formed by depositing a cathode electrocatalyst layer and an anode electrocatalyst layer onto a porous conductive support such as a gas diffusion layer to form a gas diffusion electrode (GDE), and sandwiching the anion exchange membrane between the gas diffusion electrodes.

[0179] In some embodiments, an MEA with only AEM is used for CO2 reduction. Using an anion exchange polymer electrolyte avoids the low pH environment that is detrimental to CO2 reduction. Additionally, when using an AEM, water is transported away from the cathode catalyst layer, thus preventing water accumulation (flooding), which can block the transport of reactant gases to the cathode of the cell.

[0180] Water transport in the MEA occurs through multiple mechanisms, including diffusion and electroosmotic drag. In some embodiments, at the current density of the CO2 electrolysis device described herein, electroosmotic drag is the dominant mechanism. When ions move through the polymer electrolyte, water is dragged along with the ions. For cation exchange membranes, such as Nafion membranes, the amount of water transport is well characterized and is understood to depend on the pretreatment / hydration of the membrane. Protons move from the positive potential to the negative potential (anode to cathode), each carrying 2 - 4 water molecules, depending on the pretreatment. In anion exchange polymers, the same type of effect occurs. Hydroxide, bicarbonate, or carbonate ions "drag" water molecules with them as they move through the polymer electrolyte. In an anion exchange MEA, the ions move from the negative voltage to the positive voltage, thus from the cathode to the anode, and the ions carry water molecules with them, moving water from the cathode to the anode in the process.

[0181] In some embodiments, only the EMA of the AEM is used for the CO reduction reaction. Different from the CO2 reduction reaction, CO reduction does not produce carbonate or bicarbonate anions that can be transported to the anode and release valuable reactants.

[0182] Figure 4 An example configuration of a CO x reduction MEA 401 is shown with a cathode catalyst layer 403, an anode catalyst layer 405, and an anion - conducting PEM 407. In some embodiments, the cathode catalyst layer 403 comprises metal catalyst particles (e.g., nanoparticles) that are unloaded or loaded on a conductive substrate such as carbon particles. In some embodiments, the cathode catalyst layer 403 further comprises an anion - conducting polymer. The metal catalyst particles can catalyze CO xReduction, particularly at a pH greater than a threshold pH, e.g., which can be pH 4 - 7, depending on the catalyst. In some embodiments, the anode catalyst layer 405 comprises metal oxide catalyst particles (e.g., nanoparticles) that are unloaded or loaded on a conductive substrate such as carbon particles. In some embodiments, the anode catalyst layer 403 further comprises an anion-conducting polymer. Examples of metal oxide catalyst particles for the anode catalyst layer 405 include iridium oxide, nickel oxide, nickel iron oxide, iridium ruthenium oxide, platinum oxide, etc. The anion-conducting PEM 407 can comprise any of a variety of anion-conducting polymers, such as HNN5 / HNN8 from Ionomr, FumaSep from Fumatech, TM1 from Orion, PAP-TP from W7energy, Sustainion from Dioxide Materials, etc. These and other anion-conducting polymers can be used, having an ion exchange capacity (IEC) in the range of 1.1 to 2.6 mmol / g, a working pH range of 0 - 14, acceptable solubility in some organic solvents, reasonable thermal and mechanical stability, good ionic conductivity / ASR, and an acceptable water uptake / swelling ratio. The polymer can be chemically exchanged into some anions to replace halogen anions before use. In some embodiments, the IEC of the anion-conducting polymer can be 1 to 3.5 mmol / g.

[0183] As Figure 4 shown, CO can be provided to the cathode catalyst layer 403 x e.g., CO2 gas. In some embodiments, CO2 can be provided through a gas diffusion electrode. In the cathode catalyst layer 403, CO2 reacts to produce a reduction product, typically denoted as C x O y H z . Anions generated at the cathode catalyst layer 403 can include hydroxide, carbonate, and / or bicarbonate. These anions can diffuse, migrate, or otherwise move to the anode catalyst layer 405. At the anode catalyst layer 405, an oxidation reaction such as the oxidation of water can occur to produce dioxygen and hydrogen ions. In some applications, the hydrogen ions can react with hydroxide, carbonate, and / or bicarbonate to produce water, carbonic acid, and / or CO2. Fewer interfaces result in lower resistance. In some embodiments, a highly basic environment is maintained to achieve C2 and C3 hydrocarbon synthesis.

[0184] Figure 5 Shows an example configuration of a CO reduction MEA 501 having a cathode catalyst layer 503, an anode catalyst layer 505, and an anion-conducting PEM 507. Generally, the configuration of the MEA501 can be similar to Figure 4The structure of MEA 401 in []. However, the cathode catalyst can be selected to promote the CO reduction reaction, which means that different reduction catalysts will be used in the CO and CO2 reduction embodiments.

[0185] In some embodiments, only the MEA of AEM can be beneficial for CO reduction. The water uptake of the AEM material can be selected to help regulate the moisture at the catalyst interface, thereby improving the CO availability of the catalyst. For this reason, only the AEM membrane can be beneficial for CO reduction. Since the bipolar membrane has better resistance to CO2 dissolution and crossover in the alkaline anode electrolyte medium, it can be more beneficial for CO2 reduction.

[0186] In various embodiments, the cathode catalyst layer 503 comprises metal catalyst particles (e.g., nanoparticles) that are unloaded or loaded on a conductive substrate such as carbon particles. In some embodiments, the cathode catalyst layer 503 further comprises an anion-conducting polymer. In some embodiments, the anode catalyst layer 505 comprises metal oxide catalyst particles (e.g., nanoparticles) that are unloaded or loaded on a conductive substrate such as carbon particles. In some embodiments, the anode catalyst layer 503 further comprises an anion-conducting polymer. Examples of the metal oxide catalyst particles for the anode catalyst layer 505 can include those determined for Figure 4 the anode catalyst layer 405 of []. The anion-conducting PEM 507 can comprise any of a variety of anion-conducting polymers, such as those determined for Figure 4 the PEM 407 of [].

[0187] As Figure 5 shown, CO gas can be provided to the cathode catalyst layer 503. In some embodiments, CO can be provided through a gas diffusion electrode. At the cathode catalyst layer 503, CO reacts to produce reduction products, generally denoted as C x O y H z .

[0188] The anions generated at the cathode catalyst layer 503 can include hydroxide ions. These anions can diffuse, migrate, or otherwise move to the anode catalyst layer 505. At the anode catalyst layer 505, oxidation reactions such as the oxidation of water can occur to produce dioxygen and hydrogen ions. In some applications, the hydrogen ions can react with the hydroxide ions to form water.

[0189] Although the general structure of MEA 501 is similar to that of MEA 401, there are some differences in the MEA. First, for CO reduction, the MEA may be wetter, which helps to keep the polymer electrolyte hydrated. In addition, for CO2 reduction, a large amount of CO2 can be transferred to the anode of the MEA with only AEM, such as Figure 4As shown. For CO reduction, significant CO gas crossover is unlikely. In this case, the reaction environment can be very alkaline. MEA materials (including catalysts) can be selected to have good stability in a high pH environment. In some embodiments, a thinner membrane can be used for CO reduction instead of CO2 reduction.

[0190] Example of MEA with only AEM

[0191] 1. Deposit copper metal (USRN 40 nm thick Cu, ~0.05 mg / cm 2 ) onto a porous carbon sheet (Sigracet 39BC gas diffusion layer) by electron beam deposition. Deposit Ir metal nanoparticles at a loading of 3 mg / cm 2 onto a porous titanium sheet by drop casting. Sandwich an anion exchange membrane (25 - 50 μm, 80 mS / cm 2 OH− conductivity, 2 - 3 mS / cm 2 HCO3 - conductivity, 33 - 37% water uptake) obtained from Ionomr between the porous carbon sheet with the electrocatalyst layer and the porous titanium sheet, where the electrocatalyst layer faces the membrane.

[0192] 2. Sigma Aldrich 80 nm spherical Cu nanoparticles are mixed with the FumaSep FAA - 3 anion exchange solid polymer electrolyte obtained from Fumatech, with a FumaSep FAA - 3 to catalyst mass ratio of 0.10, set as described above.

[0193] 3. The catalyst ink is made of pure 80 nm Cu nanoparticles (Sigma Aldrich) mixed with the FumaSep FAA - 3 anion exchange solid polymer electrolyte (Fumatech), with a FumaSep FAA - 3 to catalyst mass ratio of 0.09. The cathode is formed by ultrasonic spray deposition of the catalyst ink onto a porous carbon gas diffusion layer (Sigracet 39BB). The anode contains IrO x metal nanoparticles sprayed onto a porous titanium sheet. Sandwich the anion exchange membrane (Ionomr Innovations, Aemion 25 - 50 μm thickness, 80 mS / cm 2 OH− conductivity, 2 - 3 mS / cm 2 HCO3− conductivity, 33 - 37% water uptake) between the Cu catalyst - coated carbon gas diffusion layer cathode and the IrO x coated porous titanium anode, with the Cu catalyst - coated side facing the membrane, thus forming the MEA.

[0194] U.S. Patent Application Publication No. 2017 / 0321334 [OPUSP001B], published on November 9, 2017, and U.S. Patent Application Publication No. 2019 / 0226103 [OPUSP005], published on July 25, 2019, describe various features and examples of MEA, which are incorporated herein by reference in their entirety. All publications mentioned herein are incorporated by reference in their entirety as if fully set forth herein.

[0195] Layers of MEA

[0196] Cathode Catalyst Layer - General Structure

[0197] As described above, the cathode of the MEA, also known as the cathode layer or cathode catalyst layer, facilitates CO x conversion. It is a porous layer containing a catalyst for the CO x reduction reaction.

[0198] In some embodiments, the cathode catalyst layer contains a blend of reduction catalyst particles, electronically conductive support particles that provide a support for the reduction catalyst particles, and a cathode ion-conducting polymer. In some embodiments, the reduction catalyst particles are blended with the cathode ion-conducting polymer without a support.

[0199] 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 occurring at the cathode of the CRR.

[0200] The catalyst can be in the form of nanoparticles having a size range of from about 1 to 100 nm, or particles having a size range of from about 0.2 to 10 nm, or particles having a size range of from about 1 to 1000 nm or any other suitable range. In addition to nanoparticles and larger particles, membranes and nanostructured surfaces can also be used.

[0201] If used, the electron-conducting carrier particles in the cathode can be various forms of carbon particles. Other possible conducting carrier particles include boron-doped diamond or fluorine-doped tin oxide. In one setting, the conducting carrier particles are Vulcan carbon. The conducting carrier particles can be nanoparticles. The size range of the conducting carrier particles is between about 20 nm and 1000 nm or any other suitable range. They are particularly useful if the conducting carrier particles are compatible with the chemicals present in the cathode during CRR operation, are reduction-stable, and have a high hydrogen evolution overpotential such that they do not participate in any electrochemical reactions.

[0202] For composite catalysts such as Au / C, the example metal nanoparticle size can be in the range of about 1 - 100 nm (e.g., 2 nm - 20 nm), and the carbon as the support material can be about 20 - 200 nm in size. For pure metal catalysts such as Ag or Cu, the particles have a wide range of grain sizes from 2 nm to 500 nm. Agglomeration can even be up to the micron range.

[0203] Generally, such conducting carrier particles are larger than the reduction catalyst particles, and each conducting carrier particle can carry a number of reduction catalyst particles. Figure 6 is a schematic diagram showing a possible morphology of two different types of catalysts loaded on a catalyst support particle 610, such as a carbon particle. A first type of catalyst particle 630 and a second type of second catalyst particle 650 are attached to the catalyst support particle 610. In various settings, only one type of catalyst particle or more than two types of catalyst particles are attached to the catalyst support particle 610.

[0204] Using two types of catalysts can be useful in some embodiments. For example, one catalyst can be good at one reaction (e.g., CO2 → CO), while the second catalyst is good at another reaction (e.g., CO → CH4). Overall, the catalyst layer will perform the conversion of CO2 to CH4, but different steps in the reaction will be carried out with different catalysts.

[0205] The electron-conducting carrier can also be in forms other than particles, including tubes (e.g., carbon nanotubes) and sheets (e.g., graphene). Structures with a high surface area to volume ratio can be used to provide attachment sites for the catalyst particles.

[0206] In addition to the reduction catalyst particles and the electron conducting support particles, the cathode catalyst layer can include an ion conducting polymer. There is a trade-off in selecting the amount of the cathode ion conducting polymer in the cathode. It is important to include sufficient cathode ion conducting polymer to provide sufficient ionic conductivity. But it is also important that the cathode is porous so that reactants and products can move through the cathode easily and to maximize the amount of catalyst surface area available for the reaction. In various settings, the cathode ion conducting polymer is between 30 and 70 wt%, between 20 and 80 wt%, or between 10 and 90 wt% or any other suitable range of the materials in the cathode layer. The wt% of the ion conducting polymer in the cathode is selected to obtain the cathode layer porosity and ionic conductivity so as to provide the highest current density for CO x reduction. In some embodiments, it can be between 20 and 60 wt% or between 20 and 50 wt%. An example thickness range of the cathode catalyst layer is from about 80 nm to 300 μm.

[0207] In addition to the reduction catalyst particles, the cathode ion conducting polymer, and (when present) the electron conducting support, the cathode catalyst layer can include other additives such as PTFE.

[0208] In addition to the polymer:catalyst mass ratio, the catalyst layer can be characterized by the mass loading (mg / cm 2 ) and the porosity. The porosity can be determined in various ways. In one method, the loading of each component (e.g., catalyst, support, and polymer) is multiplied by its respective density. These are added up to determine the thickness occupied by the components in the material. Then it is divided by the known total thickness to obtain the percentage of the layer filled by the material. Then the resulting percentage is subtracted from 1 to obtain the percentage of the layer that is considered void space (e.g., filled with air or other gas or vacuum), i.e., the porosity. Methods such as mercury intrusion porosimetry or image processing of TEM images can also be used.

[0209] The catalyst layer can also be characterized by its roughness. The surface properties of the catalyst layer can affect the resistance across the membrane electrode assembly. An overly rough catalyst layer may lead to interfacial gaps between the catalyst and the microporous layer. These gaps impede the continuous path of electrons from the current collector to the catalytic region, thus increasing the contact resistance. The interfacial gaps can also serve as locations for water accumulation, which is harmful to the mass transport of reactants and products. On the other hand, an extremely smooth surface may suffer from poor interlayer adhesion. The catalyst layer roughness can affect the electrical contact resistance and the concentration polarization loss. The surface roughness can be measured using different techniques (such as mechanical stylus method, optical profilometry, or atomic force microscopy) and is defined as the high-frequency short-wavelength component of the real surface. The arithmetic mean height S ais a parameter commonly used to evaluate surface roughness. Numerically, it is calculated by integrating the absolute heights of valleys and peaks on the surface relative to the mean plane over the entire geometric area of the sample. In some embodiments, a catalyst layer S between 0.50 - 1.10 μm or 0.70 - 0.90 μm can be used a value.

[0210] Examples of cathode catalyst layers for CO, methane, and ethylene / ethanol production are given below.

[0211] · CO production: Au nanoparticles with a diameter of 4 nm are loaded on Vulcan XC72R carbon and mixed with the TM1 anion exchange polymer electrolyte obtained from Orion. The layer thickness is about 15 μm, Au / (Au + C) = 30%, the mass ratio of TM1 to the catalyst is 0.32, and the mass loading is 1.4 - 1.6 mg / cm 2 , and the estimated porosity is 0.47

[0212] · Methane production: Cu nanoparticles with a size of 20 - 30 nm are loaded on Vulcan XC72R carbon and mixed with the FAA-3 anion exchange solid polymer electrolyte obtained from Fumatech. The mass ratio of FAA-3 to the catalyst is 0.18. The estimated Cu nanoparticle loading is ~7.1 μg / cm 2 , in a relatively wide range of 1 - 100 μg / cm 2

[0213] · Ethylene / ethanol production: Cu nanoparticles with a size of 25 - 80 nm are mixed with the FAA-3 anion exchange solid polymer electrolyte obtained from Fumatech. The mass ratio of FAA-3 to the catalyst is 0.10. Deposited on Sigracet39BC GDE for pure AEM or on the polymer electrolyte membrane. The estimated Cu nanoparticle loading is 270 μg / cm 2 .

[0214] · Bipolar MEA for methane production: The catalyst ink is made of 20 nm Cu nanoparticles (Premetek 40% Cu / Vulcan XC-72) loaded on Vulcan carbon and mixed with the FAA-3 anion exchange solid polymer electrolyte (Fumatech), and the mass ratio of FAA-3 to the catalyst is 0.18. The cathode is formed by ultrasonic spraying deposition of the catalyst ink onto a bipolar membrane, which contains the FAA-3 anion exchange solid polymer electrolyte sprayed on a Nafion (PFSA) 212 (Fuel Cell Etc) membrane. The anode contains IrRuO x , which is at 3 mg / cm 2 ​The loading amount was sprayed onto the opposite side of the bipolar membrane. The porous carbon gas diffusion layer (Sigracet 39BB) was sandwiched between the Cu catalyst-coated bipolar membranes to form the MEA.

[0215] · Bipolar MEA for ethylene production: The catalyst ink was made from pure 80 nm Cu nanoparticles (Sigma Aldrich) mixed with FAA-3 anion exchange solid polymer electrolyte (Fumatech), and the mass ratio of FAA-3 to the catalyst was 0.09. The cathode was formed by ultrasonic spraying and depositing the catalyst ink onto the bipolar membrane, which consisted of FAA-3 anion exchange solid polymer electrolyte sprayed on a Nafion (PFSA) 115 (Fuel Cell Etc) membrane. The anode contained IrRuO x which was sprayed onto the opposite side of the bipolar membrane at a loading of 3 mg / cm 2 The porous carbon gas diffusion layer (Sigracet 39BB) was sandwiched between the Cu catalyst-coated bipolar membranes to form the MEA.

[0216] · CO production: Au nanoparticles with a diameter of 4 nm were loaded on Vulcan XC72R carbon and mixed with TM1 anion exchange polymer electrolyte obtained from Orion. The layer thickness was approximately 14 μm, and Au / (Au + C) = 20%. The mass ratio of TM1 to the catalyst was 0.32, and the mass loading was 1.4 - 1.6 mg / cm 2 The estimated porosity in the catalyst layer was 0.54.

[0217] · CO production: Au nanoparticles with a diameter of 45 nm were loaded on Vulcan XC72R carbon and mixed with TM1 anion exchange polymer electrolyte obtained from Orion. The layer thickness was approximately 11 μm, and Au / (Au + C) = 60%. The mass ratio of TM1 to the catalyst was 0.16, and the mass loading was 1.1 - 1.5 mg / cm 2 The estimated porosity in the catalyst layer was 0.41.

[0218] · CO production: Au nanoparticles with a diameter of 4 nm were loaded on Vulcan XC72R carbon and mixed with TM1 anion exchange polymer electrolyte obtained from Orion. The layer thickness was approximately 25 μm, and Au / (Au + C) = 20%. The mass ratio of TM1 to the catalyst was 0.32, and the mass loading was 1.4 - 1.6 mg / cm 2 The estimated porosity in the catalyst layer was 0.54.

[0219] The functions, materials, and structures of the cathode catalyst layer components are further described below.

[0220] Cathode catalyst layer - Function

[0221] The main function of the cathode catalyst layer is to provide a catalyst for CO x reduction. An example reaction is:

[0222] CO2 + 2H + + 2e - → CO + H2O.

[0223] The cathode catalyst layer also has many other functions that facilitate the conversion of CO x These functions include water management, gas transport, reactant delivery to the metal catalyst, product removal, stabilizing the particulate structure of the metal catalyst, electron and ion conduction to the metal catalyst, and mechanical stability within the MEA.

[0224] Some functions and challenges are specific to CRR and are not found in MEA components used for other applications such as fuel cells or water electrolysis devices. These challenges include the cathode catalyst layer of the MEA taking in gases (e.g., CO2 or CO) and outputting gases (e.g., ethylene, methane, CO) or liquids (e.g., ethanol). The cathode catalyst layer also prevents the accumulation of water that can impede gas transport. In addition, the development of catalysts for CO x reduction is not as advanced as catalysts such as platinum that are available for hydrogen fuel cells. As a result, COx reduction catalysts are generally less stable. These functions, their specific challenges, and how they can be addressed are described below.

[0225] Water Management (Cathode Catalyst Layer)

[0226] The cathode catalyst layer promotes the movement of water to prevent it from being trapped in the cathode catalyst layer. Trapped water can impede the entry of CO x into the catalyst and / or impede the removal of reaction products from the cathode catalyst layer.

[0227] Water management challenges are specific to CRR in many ways. For example, compared to the oxygen electrode of a PEM fuel cell, the gas flow rates used in CRR are much lower. CRR can also use lower flow rates to achieve the input of CO xHigh utilization. The removal of gaseous water is determined by the gas volumetric flow rate, so much less gaseous water removal occurs in the CRR. The CRR can also operate at higher pressures (e.g., 100 psi - 450 psi) than fuel cells; at higher pressures, the same molar flow rate results in a lower volumetric flow rate and less gaseous water removal. Thus, the liquid water in the MEA of the CRR will be removed. For some MEAs, the ability to remove gaseous water is further limited by temperature limitations not present in fuel cells. For example, the reduction of CO2 to CO can occur at about 50 °C, while ethylene and methane production can occur at 20 °C - 25 °C. This is compared to the typical operating temperature of fuel cells of 80 °C to 120 °C. Thus, there is more liquid water to remove.

[0228] Properties that affect the water removal ability of the cathode catalyst layer include porosity; pore size; pore size distribution; hydrophobicity; the relative amounts of ion-conducting polymer, metal catalyst particles, and electron-conducting carriers; the thickness of the layer; the distribution of the catalyst throughout the layer; and the distribution of the ion-conducting polymer through the layer and around the catalyst.

[0229] The porous layer allows a path for water escape. In some embodiments, the pore size distribution of the cathode catalyst layer includes pores with sizes from 1 nm to 100 nm and pores with sizes of at least 1 micron. This size distribution can contribute to water removal. The porous structure can be formed by one or more of the following: pores within a carbon support material; stacked pores between stacked spherical carbon nanoparticles; secondary stacked pores (micrometer scale) between agglomerated carbon spheres; or porosity introduced by an inert filler (e.g., PTFE), where the interface between PTFE and carbon also creates irregular pores ranging from a few hundred nanometers to microns.

[0230] The cathode catalyst layer can have a thickness that aids in water management. Using a thicker layer allows the catalyst to be distributed over a larger volume, thus spreading the reaction over a larger volume. This disperses the water distribution and makes it easier to manage.

[0231] An ion-conducting polymer having a non-polar hydrophobic backbone can be used in the cathode catalyst layer. In some embodiments, in addition to the ion-conducting polymer, the cathode catalyst layer can also contain a hydrophobic polymer such as PTFE. In some embodiments, the ion-conducting polymer can be a component of a copolymer that also contains a hydrophobic polymer. In some embodiments, the ion-conducting polymer has hydrophobic regions and hydrophilic regions. The hydrophilic regions can support water movement and the hydrophobic regions can support gas movement.

[0232] Gas transport (cathode catalyst layer)

[0233] The cathode catalyst layer can be configured for gas transport. Specifically, CO xTransferred to the catalyst, and the gaseous reaction products (such as CO, ethylene, methane, etc.) are output from the catalyst layer.

[0234] Some of the challenges related to gas transport are specific to the CRR. Gas transport into and out of the cathode catalyst layer - CO x Input and products such as CO, ethylene, and methane are output. In a PEM fuel cell, the input gases (O2 or H2) are present, but no water substance or product is output. In a PEM water electrolysis device, water is the reactant and O2 and H2 are the gas products.

[0235] Operating conditions affect gas transport, and these operating conditions include pressure, temperature, and the flow rate through the reactor. The properties of the cathode catalyst layer that affect gas transport include: porosity; pore size and distribution; layer thickness; and ionomer distribution.

[0236] In some embodiments, the ionomer-catalyst contact is minimized. For example, in embodiments using a carbon support, the ionomer can form a continuous network along the carbon surface with minimal contact with the catalyst. The ionomer, support, and catalyst can be designed such that the affinity of the ionomer for the support surface is higher than that for the catalyst surface. This helps gas transport to and from the catalyst without being blocked by the ionomer, while allowing the ionomer to conduct ions to and from the catalyst.

[0237] Ionomer (cathode catalyst layer)

[0238] The ionomer can have several functions, including holding the particles of the catalyst layer together and allowing ions to move through the cathode catalyst layer. In some cases, the interaction between the ionomer and the catalyst surface can create an environment favorable for CO x reduction, thereby increasing the selectivity for the desired product and / or reducing the voltage required for the reaction. Importantly, the ionomer is an ion-conducting polymer, thus allowing ions to move through the cathode catalyst layer. For example, hydroxide, bicarbonate, and carbonate ions are removed from the catalyst surface where CO x reduction occurs. In the following description, the ionomer in the cathode catalyst layer may be referred to as the first ion-conducting polymer.

[0239] The first ion-conducting polymer can comprise at least one ion-conducting polymer that is an anion conductor. This can be advantageous because it increases the pH compared to a proton conductor.

[0240] In some embodiments, the first ion-conducting polymer may comprise one or more covalently-bonded positively charged functional groups that are configured to transport mobile negatively charged ions. The first ion-conducting polymer may be selected from aminated tetramethylpolyphenylene; poly(ethylene-co-tetrafluoroethylene)-based quaternary ammonium polymers; quaternized polysulfone), blends thereof, and / or any other suitable ion-conducting polymer. The first ion-conducting polymer may be configured to dissolve salts of bicarbonate or hydroxide.

[0241] In some embodiments, the first ion-conducting polymer may comprise at least one ion-conducting polymer that is a cation and anion conductor. The first ion-conducting polymer may be selected from polyethers capable of transporting cations and anions and polyesters capable of transporting cations and anions. The first ion-conducting polymer may be selected from polyethylene oxide, polyethylene glycol, polyvinylidene fluoride, and polyurethane.

[0242] Cation and anion conductors will increase the pH (compared to pure cation conductors). Additionally, in some embodiments, it may be advantageous to use cation and anion conductors to facilitate acid-base recombination in a larger volume rather than at the 2D interface of an anion-conducting polymer and a cation-conducting polymer. This can disperse water and CO2 formation, heat generation, and potentially reduce the membrane resistance by decreasing the activation energy of the acid-base reaction. All of these can be beneficial in helping to avoid the accumulation of products, heat, and reduce resistive losses in the MEA, resulting in a lower cell voltage.

[0243] Typical anion-conducting polymers have a polymer backbone to which covalently-bonded positively charged functional groups are attached. In some embodiments, these may comprise 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, such as 25,000 g / mol - 150,000 g / mol, but it should be understood that polymers outside of this range may be used.

[0244] Special challenges for ion-conducting polymers in CRR include: CO2 can dissolve or solubilize the polymer electrolyte, making them mechanically less stable, prone to swelling, and allowing the polymer to move more freely. This makes the entire catalyst layer and polymer electrolyte membrane mechanically less stable. In some embodiments, polymers that are not prone to CO2 plasticization are used. Additionally, unlike water electrolysis devices and fuel cells, conducting carbonate and bicarbonate ions are key parameters for CO2 reduction.

[0245] Introducing polar functional groups, such as hydroxyl and carboxyl groups that can form hydrogen bonds, results in the formation of a pseudo-crosslinked network. Crosslinking agents such as ethylene glycol and aluminum acetylacetonate can be added to strengthen the anion exchange polymer layer and inhibit polymer CO2 plasticization. Additives such as polydimethylsiloxane copolymers can also help alleviate CO2 plasticization.

[0246] According to various embodiments, the ion-conducting polymer may have a bicarbonate ion conductivity of at least 6 mS / cm, or in some embodiments at least 12 mS / cm, which is chemically and mechanically stable at temperatures of 80 °C and lower and is soluble in organic solvents used during manufacturing, such as methanol, ethanol, and isopropyl alcohol. In the presence of the CO x reduction product, the ion-conducting polymer is stable (chemically stable and has a stable solubility). The ion-conducting polymer may also be characterized by its ion exchange capacity (the total number of active sites or functional groups responsible for ion exchange), which, in some embodiments, may range from 2.1 mmol / g to 2.6 mmol / g. In some embodiments, an ion-conducting polymer with a lower IEC, such as greater than 1 or 1.5 mmol / g, may be used.

[0247] Examples of anion-conducting polymers are given in the table above 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 meta-terphenyl fluoroalkylene as the main chain and trimethylammonium (TMA+) as the cationic group. The chemical structure is shown below.

[0248]

[0249] Additional examples include anion exchange membranes produced by Fumatech and Ionomr. The Fumatech FAA-3 ionomer exists in the Br- form. The polybenzimidazole-based anion exchange polymer / membrane produced by Ionomr exists in the I- form, such as AF-1-HNN8-50-X.

[0250] The polymer in the received state can be prepared by exchanging the anion (such as I - 、Br - etc.) with bicarbonate.

[0251] In addition, as described above, in some embodiments, the ionomer may be a cationic and cation-conducting polymer. Examples are given in the table above as Class B ion-conducting polymers.

[0252] Metal catalyst (cathode catalyst layer)

[0253] The metal catalyst catalyzes the CO x reduction reaction(s). The metal catalyst is typically nanoparticles, but in some embodiments, larger particles, membranes, and nanostructured surfaces may be used. The specific morphology of the nanoparticles can expose and stabilize active sites with greater activity.

[0254] Metal catalysts typically include pure metals (e.g., Cu, Au, Ag), but specific alloys or other bimetallic systems can be highly active and used in some reactions. The choice of catalyst can be guided by the desired reaction. For example, for CO production, Au can be used; for methane and ethylene production, Cu can be used. Other metals can be used, including Ag, alloys, and bimetallic systems. CO2 reduction has a high overpotential compared to other well-known electrochemical reactions such as hydrogen evolution and oxygen evolution on known catalysts. Small amounts of contaminants can poison the catalysts used for CO2 conversion. And as mentioned above, metal catalysts such as Cu, Au, and Ag are not as well-developed as catalysts used in hydrogen fuel cells such as platinum.

[0255] Different metal catalyst materials can be selected at least in part based on the desired product and MEA operation. For example, 1D nanowires (the rightmost image) have a higher selectivity for ethylene production, while triangular Cu nanosheets (the second from the left) show a higher selectivity for methane. Nanotubes (the leftmost) show good selectivity for ethylene in an AEM MEA. Gold nanoparticles with a narrow size distribution (e.g., 2 - 6 nm) and uniformly distributed on the carbon surface result in higher current efficiency and durability.

[0256] Metal catalyst properties that affect the performance of the cathode catalyst layer include size, size distribution, uniformity of coverage on the support particles, shape, loading (characterized as metal weight / metal weight + carbon weight or characterized as the particle mass per unit geometric area of the catalyst layer), surface area (actual metal catalyst surface area / volume of the catalyst layer), purity, and the presence of toxic surface ligands from synthesis.

[0257] Nanoparticles can be synthesized by any suitable method, such as those described below: 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. Appl. Sci. 2014, 3, 5, 237 - 260, which are incorporated herein by reference.

[0258] In some embodiments, metal nanoparticles are provided without a toxic surface ligand. This can be achieved by using an ionomer as a ligand to direct the synthesis of the nanocrystal catalyst, as Figure 8 shown. The surface of the metal nanocatalyst is directly connected to the ion-conducting ionomer. This avoids having to treat the catalyst surface to allow the ionomer to contact the metal and improve the contact.

[0259] In some embodiments, the metal catalyst can be disposed on a carbon support. For CO production, examples include Premetek 20 wt% Au supported on Vulcan XC-72R carbon, where the Au particle size is 4 - 6 nm, and 30% Au / C supported on Vulcan XC-72R, where the Au particle size is 5 - 7 nm. For methane, examples include Premetek 20 wt% Cu supported on Vulcan XC-72R carbon, where the Cu particle size is 20 - 30 nm. In some embodiments, the metal catalyst can be unsupported. For ethylene production, examples of unsupported metal catalysts include Sigma Aldrich unsupported Cu 80 nm particle size and electron beam or sputter deposited 10 nm to 100 nm thin Cu layers.

[0260] Support (cathode catalyst layer)

[0261] The support of the cathode catalyst layer has several functions. It stabilizes the metal nanoparticles to prevent them from agglomerating and distributes the catalytic sites throughout the catalyst layer volume to disperse the loss of reactants and the formation of products. It also forms an electron conduction path to the metal nanoparticles. For example, carbon particles are stacked together such that the contacting carbon particles provide an electron conduction path. The void spaces between the particles form a porous network through which gases and liquids can travel.

[0262] In some embodiments, carbon supports developed for fuel cells can be used. Many different types have been developed; they are typically sized 50 nm - 500 nm and can be obtained in different shapes (spheres, nanotubes, sheets (e.g., graphene)), porosities, surface area / volume, conductivities, functional groups (N-doped, O-doped, etc.).

[0263] The support can be hydrophobic and have an affinity for metal nanoparticles.

[0264] Examples of carbon blacks that can be used include:

[0265] ·Vulcan XC-72R - density is 256 mg / cm 2 , 30 - 50 nm

[0266] ·Ketjen Black - Hollow structure, density 100 - 120 mg / cm 2 , 30 - 50 nm

[0267] ·Printex Carbon, 20 - 30 nm

[0268] Anode catalyst layer

[0269] The anode of the MEA, also known as the anode layer or anode catalyst layer, facilitates the oxidation reaction. It is a porous layer containing a catalyst for the oxidation reaction. Examples of the reaction are:

[0270] 2H2O → 4H + + 4e - + O2 (in the acidic environment of the proton exchange polymer electrolyte - bipolar membrane); or

[0271] 4OH - → 4e - + O2 + 2H2O (in the alkaline environment of the anion exchange polymer electrolyte)

[0272] Oxidation of other materials can also occur, such as oxidation of hydrocarbons to produce CO2 or oxidation of chloride ions to produce chlorine gas, or oxidation of hydrogen to produce hydrogen ions.

[0273] In some embodiments, referring to Figure 2 , the anode 240 contains a blend of an oxidation catalyst and an anode ion - conducting polymer. Multiple oxidation reactions can occur at the anode, depending on the reactants supplied to the anode and the one (or more) anode catalysts. In one setup, the oxidation catalyst is selected from the following metals and oxides: Ir, Pt, Ni, Ru, Pd, Au, and their alloys, IrRu, PtIr, Ni, NiFe, stainless steel, and combinations thereof. The oxidation catalyst can also include conductive support particles selected from carbon, boron - doped diamond, and titanium.

[0274] The oxidation catalyst can be in the form of a structured grid or in the form of particles. If the oxidation catalyst is in particle form, 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 chemicals present in the anode 240 during CRR operation and are oxidation - stable so that they do not participate in any electrochemical reactions. It is particularly useful if the conductive support particles are selected considering the voltage and reactants at the anode. In some setups, the conductive support particle is titanium, which is very suitable for high voltages. In other setups, the conductive support particle is carbon, which can 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 this setup isFigure 3 As shown and discussed above with respect to the cathode catalyst layer. In one setting, the oxidation catalyst is iridium ruthenium oxide. Examples of other materials that can be used for the oxidation catalyst include, but are not limited to, those listed above. It should be understood that many of these metal catalysts can be in the form of oxides, especially under the reaction conditions.

[0275] In some embodiments, the MEA has an anode layer that includes an oxidation catalyst and a second ion-conducting polymer. The second ion-conducting polymer can include one or more polymers that contain covalently bonded negatively charged functional groups that are configured to transport mobile positively charged ions. The second ion-conducting polymer can be selected from: ethylsulfonyl fluoride, 2-[1-[difluoro-[(trifluorovinyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoro-, copolymer with tetrafluoroethylene, tetrafluoroethylene-perfluoro-3,6-dioxo-4-methyl-7-octene sulfonic acid copolymer, other perfluorosulfonic acid polymers, and blends thereof. Examples of cation-conducting polymers include, for example, Nafion 115, Nafion 117, and / or Nafion 211.

[0276] There is a trade-off 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. But it is also important that the anode is porous so that reactants and products can move easily through the anode and to maximize the amount of surface area of the catalyst available for the reaction. In various settings, the ion-conducting polymer in the anode accounts for about 50 wt% of the layer, or between about 5 - 20 wt%, 10 to 90 wt%, 20 - 80 wt%, 25 - 70 wt%, or any suitable range. It is particularly useful if the anode 240 can withstand a high voltage, such as a voltage of about 1.2 V higher than the reversible hydrogen electrode. It is particularly useful if the anode 240 is porous in order to maximize the amount of catalyst surface area available for the reaction and to facilitate gas and liquid transport.

[0277] In one example of a metal catalyst, Ir or IrOx particles (100 - 200 nm) and Nafion ionomer form a porous layer about 10 μm thick. The metal catalyst loading is about 0.5 - 3 g / cm 2 。

[0278] In some embodiments, NiFeOx or NiO x is used for alkaline reactions.

[0279] PEM (MEA layer description)

[0280] The MEA includes a polymer electrolyte membrane (PEM) disposed between and conductively coupled to the anode catalyst layer and the cathode catalyst layer. Refer toFigure 2 , the polymer electrolyte membrane 265 has a high ionic conductivity (greater than about 1 mS / cm) and is mechanically stable. Mechanical stability can be demonstrated in a variety of ways, such as by high tensile strength, modulus of elasticity, elongation at break, and tear resistance. Many commercially available membranes can be used for the polymer electrolyte membrane 265. Examples include but are not limited to various formulations, GORE-SELECT, (PFSA) (FuMA-Tech GmbH) and (PFSA) (Solvay).

[0281] In one setting, the PEM comprises at least one ion-conducting polymer, which is a cation conductor. The third ion-conducting polymer may comprise one or more covalently bound negatively charged functional groups that are configured to transport mobile positively charged ions. The third ion-conducting polymer is selected from: ethylsulfonyl fluoride, 2-[1-[difluoro-[(trifluorovinyl)oxy]methyl]1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoro-, copolymers with tetrafluoroethylene, tetrafluoroethylene-perfluoro-3,6-dioxo-4-methyl-7-octene sulfonic acid, other perfluorosulfonic acid polymers, and blends thereof.

[0282] Cathode buffer layer (MEA layer description)

[0283] Reference Figure 2 , it is important to note that when the polymer electrolyte membrane 265 is a cation conductor and conducts protons, it contains a high concentration of protons during CRR operation, while the cathode 220 operates optimally in the presence of low proton concentrations. A cathode buffer layer 225 included between the polymer electrolyte membrane 265 and the cathode 220 to provide a transition region from high proton concentration to low proton concentration can be useful. In one setting, the cathode buffer layer 225 is an ion-conducting polymer having many of the same properties as the ion-conducting polymer in the cathode 220. The cathode buffer layer 225 provides a region for the transition of proton concentration from the polymer electrolyte membrane 265 having a high proton concentration to the cathode 220 having a low proton concentration. Within the cathode buffer layer 225, protons from the polymer electrolyte membrane 265 encounter anions from the cathode 220, and they neutralize each other. The cathode buffer layer 225 helps ensure that a harmful amount of protons from the polymer electrolyte membrane 265 do not reach the cathode 220 and increase the proton concentration. If the proton concentration of the cathode 220 is too high, CO x reduction does not occur. A high proton concentration is considered to be in the range of about 10 to 0.1 moles, while a low concentration is considered to be less than about 0.01 moles.

[0284] The cathode buffer layer 225 may comprise a single polymer or multiple polymers. If the cathode buffer layer 225 comprises multiple polymers, the multiple polymers may be mixed together or may be disposed in separate adjacent layers. Examples of materials that may be used for the cathode buffer layer 225 include, but are not limited to, FumaSep FAA-3, Tokuyama anion exchange membrane materials, and polyether polymers such as polyethylene oxide (PEO) and blends thereof. Further examples were given in the discussion of the cathode catalyst layer above.

[0285] Due to the low proton concentration, a sufficient cathode buffer layer thickness is selected to make the CO x reduction activity high. This sufficiency may vary for different cathode buffer layer materials. In some embodiments, the thickness of the cathode buffer layer is between about 200 nm and 100 μm, between 300 nm and 75 μm, between 500 nm and 50 μm, or any suitable range.

[0286] In some embodiments, the cathode buffer layer is less than 50 μm, such as 1-25 μm, such as 1-5 μm, 5-15 μm, or 10-25 μm. By using a cathode buffer layer within this thickness range, the proton concentration in the cathode can be reduced while maintaining the overall conductivity of the cell. In some embodiments, an ultra-thin layer (100 nm - 1 μm, sub-micron in some embodiments) may be used. Also, as discussed 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 thickness of the cathode buffer layer may be characterized relative to the thickness of the PEM.

[0287] Water and CO2 formed at the interface of the cathode buffer layer and the PEM may delaminate the MEA with polymer layers connected. The delamination problem can be solved by using a cathode buffer layer with inert filler particles and associated pores. One possible explanation for its effectiveness is that the pores create a path for gaseous carbon dioxide to escape back to the cathode, where it can be reduced.

[0288] Materials suitable as inert filler particles include, but are not limited to: TiO2, silica, PTFE, zirconia, and alumina. In various settings, the size of the inert filler particles is between 5 nm and 500 μm, between 10 nm and 100 μm, or any suitable size range. The particles may generally be spherical.

[0289] If the volume of PTFE (or other filler) is too large, it will dilute the polymer electrolyte to a degree where the ionic conductivity is low. An excessive volume of polymer electrolyte will dilute the PTFE to a degree where it is not helpful for porosity. In many embodiments, the mass ratio of polymer electrolyte / PTFE is from 0.25 to 2, and more particularly from 0.5 to 1. The volume ratio of polymer electrolyte / PTFE (or more generally, polymer electrolyte / inert filler) can be from 0.25 to 3, 0.5 to 2, 0.75 to 1.5, or 1.0 to 1.5.

[0290] In other settings, when forming the layer, porosity is achieved by using specific processing methods. An example of such a processing method is laser ablation, where nano- to micro-sized channels are formed in the layer. Another example is mechanically piercing the layer to form channels through the layer. Another example is appropriately adjusting the conditions during ultrasonic spray deposition of the layer so that it is porous.

[0291] In one setting, the cathode buffer layer has a porosity between 0.01% and 95% (e.g., approximately therebetween, by weight, by volume, by mass, etc.). However, in other settings, the cathode buffer layer can have any suitable porosity (e.g., 0.01 - 95%, 0.1 - 95%, 0.01 - 75%, 1 - 95%, 1 - 90%). In some embodiments, the porosity is 50% or less, such as 0.1 - 50%, 5 - 50%, 20 - 50%, 5 - 40%, 10 - 40%, 20 - 40%, or 25% - 40%. In some embodiments, the porosity is 20% or lower, such as 0.1 - 20%, 1 - 10%, or 5 - 10%.

[0292] The porosity of the cathode buffer layer or any layer in the MEA can be measured as described above for the catalyst layer, including using the mass loading and thickness of the components, by methods such as: mercury intrusion porosimetry, X-ray diffraction (SAXS or WAXS), and image processing of TEM images to calculate the filled space relative to the void space. The porosity is measured when the MEA is completely dry because the material swells to different degrees when exposed to water during operation. As further described below, the porosity can be determined using the measured loading and thickness of the layer and the known density of one or more materials of the layer.

[0293] The porosity in each layer of the MEA (including the cathode buffer layer) is further described below.

[0294] Anode buffer layer (MEA layer description)

[0295] In some CRR reactions, bicarbonate is produced at the cathode 220. It may be useful if there is a polymer that blocks the transport of bicarbonate at some point between the cathode 220 and the anode 240, thereby preventing the migration of bicarbonate away from the cathode. It is possible that some CO2 is carried away when bicarbonate migrates, which reduces the amount of CO2 available for the reaction at the cathode. In one setup, the polymer electrolyte membrane 265 includes a polymer that blocks the transport of bicarbonate. Examples of such polymers include, but are not limited to Formulations, GORE-SELECT, (PFSA) (FuMA-Tech GmbH) and (PFSA) (Solvay). In another setup, there is an anode buffer layer 245 between the polymer electrolyte membrane 265 and the anode 240 that blocks the transport of bicarbonate. If the polymer electrolyte membrane is an anion conductor or does not block the transport of bicarbonate, then an additional anode buffer layer to prevent the transport of bicarbonate may be useful. Materials that can be used to block the transport of bicarbonate include, but are not limited to Formulations, GORE-SELECT, (PFSA) (FuMA-Tech GmbH) and (PFSA) (Solvay). Of course, if there is no bicarbonate in the CRR, it is not particularly desirable to include a bicarbonate-blocking feature in the ion exchange layer 260.

[0296] In another embodiment of the present invention, the anode buffer layer 245 provides a region where the proton concentration transitions between the polymer electrolyte membrane 265 and the anode 240. The proton concentration in the polymer electrolyte membrane 265 depends on both its composition and the ions it conducts. For example, the Nafion polymer electrolyte membrane 265 that conducts protons has a high proton concentration. The FumaSep FAA-3 polymer electrolyte membrane 265 that conducts hydroxide has a low proton concentration. For example, if the desired proton concentration at the anode 240 differs from the polymer electrolyte membrane 265 by more than three orders of magnitude, then the anode buffer layer 245 can be used to achieve the transition from the proton concentration of the polymer electrolyte membrane 265 to the desired proton concentration at the anode. The anode buffer layer 245 can include a single polymer or multiple polymers. If the anode buffer layer 245 includes multiple polymers, the multiple polymers can be mixed together or can be arranged in separate adjacent layers. Materials that can be used to provide a pH transition region include, but are not limited to: Nafion, FumaSep FAA-3, Tokuyama anion exchange polymers and polyether polymers such as polyethylene oxide (PEO), blends thereof, and / or any other suitable materials. High proton concentrations are considered to be in the range of about 10 to 0.1 moles, while low concentrations are considered to be less than about 0.01 moles. Ion-conducting polymers can be classified into different categories based on the type(s) of ions they conduct. This has been discussed in more detail above. There are three categories of ion-conducting polymers described in Table 4 above. In one embodiment of the present invention, at least one of the ion-conducting polymers in the cathode 220, anode 240, polymer electrolyte membrane 265, cathode buffer layer 225, and anode buffer layer 245 is from a different category than at least one other.

[0297] Layer porosity

[0298] In some embodiments, one or more of the layers of the MEA contain pores that permit the transport of gases and liquids. These pores are different from the ion-conducting channels that permit ion conduction. In many polymer electrolytes (e.g., PFSA), ion conduction occurs through pores lined with fixed charges. Mobile cations hop between oppositely charged fixed groups that line the ion-conducting channels. Such channels can have variable widths; for PFSA materials, the ion-conducting channel diameters range from a narrow region of about to a wider region of about . In anion-conducting polymer materials, the channel diameters can be larger, reaching a minimum width of about in the narrow region of the channel.

[0299] For efficient ion conduction, the polymer electrolyte is hydrated, so the ion-conducting channels also contain water. In a process called electroosmotic drag, some water molecules typically move with the mobile ions; by electroosmotic drag, each mobile ion typically moves 1 - 5 water molecules. The ion-conducting channel structure and the extent of electroosmotic drag can vary with different polymer electrolytes or ion-conducting materials. Although these ion-conducting channels allow ions to move with some water molecules, they do not allow uncharged molecules to move effectively through them. They also do not allow bulk water that is not associated with ions to move through them. The solid (i.e., non-porous) membrane of the polymer electrolyte blocks most of the CO2 and CO2 electrolysis products from passing through. The typical permeabilities of CO2, water, and H2 through a wet Nafion 117 PFSA membrane at 30 °C are about 8.70×10 6 mol cm cm-2s-1·Pa-1, 4.2 (mol / cm-s-bar)×10 9 and 3.6 (mol / cm-s-bar)×10 11Permeability depends on temperature, hydration, and the properties of the polymer electrolyte material. In ion-conducting channels with variable diameters, the bulk movement of uncharged molecules and liquids / gases can be blocked at least in the narrow portions of the channels.

[0300] The larger-diameter pores of the ion-conducting channels allow large clusters of liquids and gases to pass through, not just ions. The polymer electrolyte membrane layer of the MEA typically does not contain this type of pore because the membrane needs to separate the reactants and products at the cathode from those at the anode. However, other layers of the MEA can have this type of pore. For example, the cathode catalyst layer can be porous to allow the reactant CO x to reach the catalyst and allow the product of CO x reduction to pass through the gas diffusion layer and out of the catalyst layer, and out of the flow field of the electrolysis device. As used herein, the term pore refers to pores in the ionomer other than the ion-conducting channels. In some embodiments, the pores of the anion-conducting polymer layer in the MEA have a minimum cross-sectional size of at least In some embodiments, the pores of the cation-conducting polymer layer in the MEA have a minimum cross-sectional size of at least This is to distinguish the pores that allow gas / liquid transport from the ion-conducting channels described above.

[0301] It may be useful if some or all of the following layers are porous: cathode 220, cathode buffer layer 225, anode 240, and anode buffer layer 245. In some settings, porosity is achieved by combining inert filler particles with a polymer in these layers. Materials suitable as inert filler particles include, but are not limited to: TiO2, silica, PTFE, zirconia, and alumina. In various settings, the size of the inert filler particles is between 5 nm and 500 μm, between 10 nm and 100 μm, or any suitable size range. In other settings, when forming the layer, porosity is achieved by using specific processing methods. An example of such a processing method is laser ablation, in which nano- to micro-sized channels are formed in the layer. As a supplement or as an alternative, laser ablation can achieve porosity in the layer through subsurface ablation. Subsurface ablation can form voids within the layer. When the beam is focused at a point within the layer, the layer material near that point is vaporized. This process can be repeated to form voids throughout the layer, thereby achieving porosity in the layer. A sub-layer-by-sub-layer method of forming the MEA layer, such as ultrasonic spray deposition, can be used to form an MEA layer with controlled porosity. Dry deposition can result in faster drying of the layer and a more porous final deposition. One or more of a high substrate temperature, a slow deposition rate, a high height of the nozzle from the substrate, and a high volatility of the deposited ink can be used to make the layer more porous. Wet deposition can result in slower drying of the layer and densification and compaction of several of the ultimately deposited layers. One or more of a low substrate temperature, a fast deposition rate, a low height of the nozzle from the substrate, and a low volatility of the deposited ink can be used to make the layer less porous. For example, room temperature ultrasonic spray deposition can result in a relatively dense layer and 50 °C ultrasonic spray deposition can result in a relatively porous layer.

[0302] In some embodiments, a layer having a porosity of at least 1%, such as a porosity of 1 - 90%, 1 - 50%, or 1 - 30%, can be formed using the following conditions: a substrate temperature of at least 40 °C; a deposition rate of no greater than 0.8 mL / min, such as 0.2 - 0.8 mL / min; a height of the nozzle of at least 50 mm, such as 50 - 75 mm; and a solvent volatility of at least 90 - 100% (such as ethanol).

[0303] In some embodiments, a layer having a non-porous layer or a layer with a porosity of less than 1% can be formed using the following conditions: a substrate temperature less than 40 °C; a deposition rate greater than 0.8 mL / mi and up to 10 mL / min; a height of the nozzle less than 50 mm; and a solvent volatility of less than at least 90 - 100% (such as a 50 - 90% volatile solvent content such as ethanol or a 50 - 100% medium volatility solvent such as ethylene glycol ether).

[0304] The volume of the voids can be determined by the laser power (e.g., a higher laser power corresponds to a larger void volume), but as a supplement or as an alternative, it can be determined by the focus size of the light beam or any other suitable laser parameter. Another example is mechanically piercing a layer to form a channel through the layer. The porosity can have any suitable distribution in the layer (e.g., uniform, an increasing porosity gradient across the layer, a random porosity gradient, a decreasing porosity gradient across the layer, a periodic porosity, etc.).

[0305] The porosity of the above examples and other examples and variations (e.g., the porosity of the cathode buffer layer, the anode buffer layer, the membrane layer, the cathode layer, the anode layer, other suitable layers, etc.) preferably has a uniform distribution, but as a supplement or as an alternative, it can have any suitable distribution (e.g., a randomized distribution, an increasing pore size gradient through or across the layer, a decreasing pore size gradient through or across 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, such as a minimum of about 10 nanometers and a maximum of about 200 nanometers, and / or any other suitable size or size distribution.

[0306] As discussed above, the cathode buffer layer preferably has a porosity of about 1 to 90 volume percent, but as a supplement or as an alternative, it can have any suitable porosity (including, for example, no porosity). However, in other settings and examples, the cathode buffer layer can have any suitable porosity (e.g., 0.01 - 95%, 0.1 - 95%, 0.01 - 75%, 1 - 95%, 1 - 90%, etc.). In some embodiments, the porosity is 20% or less, such as 0.1 - 20%, 1 - 10%, or 5 - 10%.

[0307] In some embodiments, the cathode buffer layer is porous, but at least one layer between the cathode layer and the anode layer is non-porous. This can prevent gases and / or large masses of liquid from passing between the cathode layer and the anode layer while still preventing delamination. For example, the non-porous layer can prevent water from directly reaching the cathode from the anode.

[0308] The porosity of the cathode buffer layer or any layer in the MEA can be measured as described above for the catalyst layer, including using the mass loading and thickness of the components, by methods such as: mercury intrusion porosimetry, X-ray diffraction (SAXS or WAXS), and image processing of TEM images to calculate the filled space relative to the void space. The porosity is measured when the MEA is completely dry because the material swells to different degrees when exposed to water during operation. The porosity can be determined using the known density of the material, the actual weight of the layer per given area, and the estimated volume of the layer based on that area and thickness. The equation is as follows:

[0309]

[0310] As described above, the density of the material is known, and the layer loading and thickness are measured. For example, in a polymer electrolyte layer with a measured loading of 1.69 mg / cm 2 the polymer electrolyte layer consists of 42 wt% of an anion exchange polymer electrolyte with a density of 1196 mg / cm 3 and 58 wt% of PTFE with a density of 2200 mg / cm 3 and its total layer thickness is 11.44 microns, and its porosity is:

[0311]

[0312] As described above, the polymer electrolyte layer can have ion conduction channels that do not easily permit gas / liquid transport. In the above calculations, these ion conduction channels are considered non-porous; that is, the density of the above non-porous material (42 wt% anion exchange polymer electrolyte) includes the ion conduction channels and is defined as non-porous by calculation.

[0313] In another example, the ion conduction layer without fillers is porous. For example, porosity can be introduced through appropriate deposition conditions. The measured loading of the porous polymer electrolyte layer is 2.1 g / cm 2 and the thickness is 19 microns. The known density of the polymer electrolyte with ion conduction channels but no pores is 1196 g / cm 3 . Then, its porosity is calculated as:

[0314]

[0315] MEA Fabrication

[0316] The MEA for CO x reduction can be fabricated using various techniques. In various embodiments, the fabrication of the MEA employs multiple steps. Small differences in the parameters of the fabrication process can result in large differences in performance.

[0317] In some embodiments, MEA fabrication employs a polymer electrolyte membrane (e.g., Nafion PEM) layer, and an anion exchange polymer electrolyte layer and a cathode catalyst layer are deposited or otherwise formed on the cathode side of the membrane, and an anode catalyst layer is deposited or otherwise formed on the anode side of the membrane. An alternative approach is to fabricate the catalyst layers on a porous gas diffusion layer (e.g., carbon for the cathode or titanium for the anode) and sandwich the membrane (which may contain an anion exchange layer) between the catalyst-containing porous layers. In some embodiments, the catalyst layers are fabricated by making an ink of solid catalyst and carrier particles and a polymer electrolyte dispersed in a solvent. The ink can be applied to the polymer electrolyte membrane or GDL by a variety of methods. The solvent is then evaporated, leaving a porous solid catalyst layer.

[0318] Imaging methods can be used to characterize thickness, uniformity, and surface roughness. The thickness should be consistent and controllable, and the uniformity should be smooth and as defect-free as possible.

[0319] A variety of techniques can be employed to form the various layers of the MEA. Generally, these techniques form layers on a substrate such as the PEM layer or GDL mentioned herein. Examples of such techniques include ultrasonic spray deposition, knife coating, gravure printing, screen printing, slot die coating, and decal transfer.

[0320] Catalyst inks using anion exchange polymers have not been well studied (especially for some polymers) and do not have the same solution structure as typical Nafion-like inks used in fuel cells and electrolysis devices. The formulations and procedures required to form a well-dispersed and stable catalyst ink are not well understood. It is believed that Nafion forms a micelle-like structure that allows for relatively easy suspension in an aqueous medium. Other ion-conducting polymers, especially some anion-conducting polymers, do not form such a structure and are thus more difficult to provide as a suspension.

[0321] In some 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 ethanol) by sonication.

[0322] As previously mentioned, some fabrication techniques utilize knife coating, screen printing, decal transfer, electrospinning, etc. Roll-to-roll techniques such as gravure or microgravure or slot die coating can be used for high-throughput processing.

[0323] In some embodiments, the cathode side of the MEA is fabricated by first depositing a layer of an anion exchange polymer electrolyte over a cation exchange polymer electrolyte membrane. Then, a second cathode catalyst layer is applied over the anion exchange layer. This process results in a catalyst-coated membrane. The gas diffusion electrode can be prepared by depositing a catalyst onto a gas diffusion layer. The anion exchange layer can be deposited onto the catalyst layer or the membrane. Then, the layers can be pressed together inside an electrolyzer to prepare a functional device. Many methods can be used, including knife coating, gravure or microgravure, slot die coating, decal transfer, screen printing, ultrasonic spray deposition, etc. to fabricate the anion exchange polymer layer and the cathode catalyst layer. A more detailed description of fabricating the MEA cathode using ultrasonic spray deposition is as follows:

[0324] The cathode side of the MEA is fabricated by first forming a solution of a polymer electrolyte (about 1 - 25 wt%) in a suitable solvent such as ethanol, n-propanol, isopropanol, or other solvents with high vapor pressure and / or low boiling point that will evaporate within a reasonable time period during fabrication. A mixture of the solvent with one or more higher boiling point components can be used. The polymer electrolyte solution is pushed through an ultrasonic spray deposition nozzle at a desired flow rate. The ultrasonic spray deposition nozzle is held at a desired frequency to disperse the polymer electrolyte solution into small droplets, which are then pushed onto the polymer electrolyte membrane substrate by an air stream. The polymer electrolyte membrane can be treated with heat, solvent, or other means prior to deposition. The small droplets of the polymer electrolyte solution land on the polymer electrolyte membrane substrate, the solvent evaporates, and the entrained polymer electrolyte is left behind. The ultrasonic spray deposition nozzle is moved back and forth across the substrate multiple times at a desired speed in a desired pattern to accumulate a layer of polymer electrolyte over the membrane substrate until a desired thickness is reached. Then, the process is repeated using a solution of catalyst particles, anion exchange polymer electrolyte, and / or other additives, and a suitable solvent or mixture of solvents; this solution is called the catalyst ink. The catalyst ink is deposited using ultrasonic spray deposition with the same or different fabrication parameters to form a cathode catalyst layer over the anion exchange polymer layer on the cathode side of the MEA.

[0325] MEA Scale-up

[0326] As previously mentioned, some applications of the CO x reduction using MEA may require relatively large sizes. For example, some MEAs have an active surface area (excluding pores) of at least about 500 cm 2 . And, in some other embodiments, the MEA has an even larger active surface area (excluding pores), or for example, at least about 650 cm 2 or 1500 cm 2 .

[0327] To enable the MEA to have such a large active surface area, an appropriate manufacturing process must be selected, i.e., a process that can support a large volume of catalyst ink and a large surface area for applying the catalyst ink. 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 set to a target dispersion, which can be characterized using dynamic light scattering (DLS). The ink should be stable within the time range of layer deposition.

[0328] In addition, humidity and temperature should be strictly controlled. The evaporation rate and process affect the final deposition, so controlling these within a 1 - 2 degree temperature window and a range of approximately 5% RH is useful.

[0329] For ultrasonic spray deposition, thin lines of catalyst ink are laid by moving an ultrasonic nozzle. For larger area MEAs, it may be necessary to increase the nozzle movement speed and the ink flow rate. From 25 cm 2 scaled up to 650 cm 2 MEA, the flow rate and movement speed are at least doubled. Water in the solvent is important and adding more water to the ink helps the droplets stack more smoothly. For example, about 20% water in the formulation can be used for a 650 cm 2 MEA.

[0330] Catalyst inks are generally relatively unstable, so in some embodiments, the MEA manufacturing time is designed to be relatively short, even with a large active area. As an example, for a 650 cm 2 spray, the deposition time of the ionomer layer can be about 2 hours and the deposition time of the catalyst layer can be about 1 hour. This is relatively fast for such a large area and can be achieved using fast flow rates and movement speeds.

[0331] MEA Scaling - up Example

[0332] The following are examples of scaling up MEA manufacturing. Examples are provided for scaling up from 25 cm 2 to 650 cm 2 .

[0333] Solvent mixture adjustment (water - to - alcohol ratio): Depending on the spray scale, adjusting the solvent from 10% water to 20% water significantly contributes to surface uniformity

[0334] Deposition parameters:

[0335] · For the ionomer layer: The flow rate is increased from 0.4 mL / min to 0.8 mL / min and the movement speed is changed from 50 mm / s to 100 mm / s

[0336] ·For the catalyst layer: The flow rate is increased from 0.25 mL / min to 0.5 mL / min and the moving speed is changed from 80 mm / s to 160 mm / s

[0337] Morphology and thickness: The thickness can match that viewed in the SEM image of the fabricated layer. The characteristic data can be adjusted to match the thickness. The morphology is controlled by parameters such as water content and fabrication.

[0338] For further scale-up, e.g., to 1500 cm 2 , the flow rate and moving speed can be further increased, e.g., in the range of 0.25 - 2 mL / min and 30 - 200 mm / s.

[0339] The deposition rate can be further increased by increasing the weight of the solid in the solution, e.g., to 5 - 8 mL / min or 5 - 15 mL / min. In some embodiments, the solution can be greater than 5 wt%, greater than 10 wt%, greater than 20 wt%, or greater than 30 wt%.

[0340] MEA post-treatment

[0341] After fabricating the MEA, additional treatments can be used to improve performance. For example, the types of performance improvements include lifetime and voltage. These improvements can manifest in the MEA with structural changes caused by the treatment, including better interlayer adhesion.

[0342] MEA post-treatment examples

[0343] Hot pressing: Heating the MEA under pressure to bond the layers together. Hot pressing is a step sometimes used in MEA fabrication, where the MEA containing the membrane and catalyst layer and sometimes the GDL are compressed together at a desired temperature for a period of time. Hot pressing is used to reduce the interfacial resistance and improve the interlayer adhesion and can help to "melt" the layers together to prevent delamination. The following gives examples of time, temperature, and pressure:

[0344] · Time: about 2 min to 10 min (MEA only); 1.5 min to 2 min (MEA + gas diffusion layer (GDL)); "MEA + GDL" can be pressed at least twice to form a stable component

[0345] · Temperature: about 100 °C to 195 °C;

[0346] · Pressure: 28 psi to 2900 psi. In one example, for a 3×3 inch 1 / 2 MEA it can be about 300 psi to 600 psi, but in the absence of the GDL, the MEA can withstand about 2500 psi;

[0347] Typically, the temperature of the hot pressing is selected such that it is greater than the glass transition temperature of the polymer electrolyte but less than the temperature at which any material structure damage or chemical damage to the MEA occurs. The glass transition temperature is greater than the temperature at which the polymer electrolyte softens, which allows the polymer electrolyte at the layer interface to deform and form better contact with lower ionic transport resistance and better adhesion.

[0348] Hydration: Before the electrolyzer assembly, the MEA is soaked in water or an aqueous solution to wet the polymer electrolyte

[0349] Boil the Nafion or other polymer electrolyte MEA. This permanently changes the macroscopic structure of the polymer electrolyte and increases the water content in the polymer matrix. This improves the ionic conductivity and also increases the water transport rate.

[0350] Heating and drying. This permanently reduces the water content and can reduce the amount of water transported through the polymer electrolyte during operation. The following are example times and temperatures for heating various MEAs.

[0351] MEA Time (hours) Temperature (°C) <![CDATA[Nafion 115 25cm 2 1 / 2 MEA]]> 24 10-30 <![CDATA[Nafion 115 100cm 2 1 / 2 MEA]]> 48 10-30 <![CDATA[Nafion 117 25, 100cm 2 1 / 2 MEA]]> 24 10-30 <![CDATA[Nafion 212 1 / 2 MEA]]> 24 10-30 <![CDATA[Nafion 211 1 / 2 MEA]]> 24 10-30

[0352] 1 / 2 MEA refers to a polymer electrolyte membrane coated with an anode catalyst layer on one side.

[0353] A stable interface between MEA layers

[0354] Water and CO2 formed at the interface between the anion-conducting layer (e.g., cathode buffer layer) and the cation-conducting membrane (e.g., PEM) can cause these two layers to separate or delaminate at the polymer layer junction. Reactions at the bipolar interface are as Figure 3 and 9 shown.

[0355] In addition, it is desirable for CO2 to return to the cathode of the electrolyzer, where it can be reduced rather than lost to the anode. Therefore, the paths (e.g., pores) in the anion exchange layer (e.g., cathode buffer layer and / or cathode layer) provide a way to remove water and CO2 from the interface to prevent delamination and return CO2 to the cathode, where CO2 can react.

[0356] Figure 9 Similar to Figure 3 but Figure 9 includes additional information related to the mass transport and generation of CO2 and water at the bipolar interface. For example, it shows that hydroxide and CO2 react on the cathode side to form bicarbonate ions, and the bicarbonate ions move towards the bipolar interface 913. On the anode side, the hydrogen ions generated by water oxidation move towards the bipolar interface 913, and at the bipolar interface, the hydrogen ions react with the bicarbonate ions to produce water and CO2, and both water and CO2 should be allowed to escape without damaging the bipolar layer.

[0357] Figure 9 The water transport paths are also depicted, including (a) electroosmotic drag of anions from the cathode to the interface 9, (b) electroosmotic drag of cations from the anode to the interface 913, and (c) diffusion. Water evaporates at the anode and cathode.

[0358] Various MEA designs contain features that resist delamination and optionally provide a path for reaction products to leave the interfacial region. In some embodiments, the bipolar interface is flat. However, in some designs, the interface has a compositional gradient and / or an interlocking structure. Further description of these is provided below with reference to Figure 10A 、 10B 、10C, and 10D, which illustrate bipolar interfaces of MEA designs configured to resist delamination.

[0359] The designed interface can be used to reduce unwanted co-ion leakage through the anion exchange membrane (AEM) and the cation exchange membrane (CEM) and improve the mechanical stability of the bipolar membrane with better adhesion. Chemical and physical modifications of the interface can be used to achieve these two goals. As further described below, the AEM and CEM layers can be chemically bonded through various crosslinking paths: side chain, main chain, main chain to side chain, and triple crosslinking. In some embodiments, the AEM layer and the CEM layer interpenetrate. This can include one or more of the following: gradients of anion exchange polymers and cation exchange polymers, mixtures of anion exchange polymers and cation exchange polymers, and / or protrusions of at least one polymer extending into the other.

[0360] There are also different ways to physically modify the interface. Thermally pressing them near the glass transition temperatures of the AEM and CEM respectively can improve the adhesion between the AEM and CEM. In some embodiments, the adhesion is improved by electrospinning the anion exchange layer and the cation exchange layer to increase the interfacial surface area. In such embodiments, the anion exchange ionomer and the cation exchange ionomer have similar swelling properties to avoid delamination. Adding a low concentration of a third polymer (such as PTFE) to the entangled ionomers can also facilitate the removal of water from the interface. The surfaces of both the CEM and the AEM can be deliberately roughened by plasma surface treatment, etching, or thermally pressing with woven or patterned fabrics. One or more of these techniques can be used to improve the contact between the AEM and CEM.

[0361] In some embodiments, the interface contains a gradient. For example, a gradient can be formed by using two nozzles during spray deposition and adding an anion exchange polymer, where the relative amount of the polymer varies during the deposition of the cation exchange layer. Similarly, a cation exchange polymer can be added during the deposition of the anion exchange layer. For example, with reference to Figure 9, the gradient can extend through substantially all or part of the anion exchange region and the cation exchange region such that the anion exchange region mainly has an anion exchange polymer adjacent to the cathode, where the relative amount of the cation exchange polymer increases when moving from the cathode towards the interface 913. Similarly, the cathode exchange region mainly has a cation exchange polymer adjacent to the anode cathode, where the relative amount of the anion exchange polymer increases when moving from the anode towards the interface 913. In some embodiments, there are pure anion exchange regions and pure cation exchange regions with a gradient therebetween.

[0362] In some embodiments, the layers of the bipolar membrane are fused together. This can be achieved by selecting a suitable solvent. For example, Nafion is at least slightly soluble in a water / ethanol mixture. By using this mixture (or another solvent that can dissolve the cation-conducting polymer) as the solvent for the anion-conducting polymer, it can cause Nafion or other cation-conducting polymers to at least slightly dissolve and fuse into the interface. In some embodiments, this results in a thin gradient, e.g., a gradient extending 0.5 - 10% into the thickness of the anion-conducting polymer layer.

[0363] In some embodiments, the interface comprises a mixture of polymers. Figure 10A The bipolar interface 1013 is shown, where the cation-conducting polymer 1021 and the anion-conducting polymer 1019 are mixed. In Figure 10A the example, a part of the anion-conducting polymer layer 1009 and a part of the cation-conducting polymer layer 1011 are shown. The anion-conducting polymer layer 1009 can be a pure anion-conducting polymer, while the cation-conducting polymer layer 1011 can be a pure cation exchange polymer. The cation-conducting polymer 1021 can be the same or different cation-conducting polymer as in the cation-conducting polymer layer 1011. The anion-conducting polymer 1019 can be the same or different anion-conducting polymer as in the anion-conducting polymer layer 1009.

[0364] In some embodiments, the interface comprises a third material that physically enhances the interface. For example, Figure 10BAn example of material 1030 across interface 1013 is shown. That is, material 1030 is partially located in the anion-conducting polymer layer 1009 and the cation-conducting polymer layer 1011. Thus, material 1030 can bond these two layers in a way that resists delamination. In one example, material 1030 is an inert material such as PTFE, polyvinylidene fluoride (PVDF), charged colloidal spheres such as surface-modified metal hydroxide spheres such as Al(OH)3 with trimethylaluminum (TMA). The inert material can be in the form of a network or grid with gaps that can be filled with ionomers. This interface can be fabricated, for example, by casting or otherwise applying the cation-conducting polymer and the anion-conducting polymer on opposite sides of a PTFE grid structure or a similar structure, and then thermally pressing.

[0365] Figure 10C The bipolar interface 1013 is shown, which has protrusions 1040 of cation-conducting polymer extending from the cation-conducting polymer layer 1011 into the anion-conducting polymer layer 1009. These protrusions can mechanically strengthen the interface 1013 such that there is no delamination when CO2 and water are generated at the interface. In some embodiments, the protrusions extend from the anion-conducting polymer layer 1009 into the cation-conducting polymer layer 1011. In some embodiments, the protrusions extend in both directions. Example dimensions are in-plane dimensions of 10 μm - 1 mm, but smaller dimensions (e.g., 500 nm - 1 μm) are also possible. The out-of-plane dimension can be, for example, 10 - 75% or 10 - 50% of the total thickness of the anion-exchange layer. For example, the protrusions can be fabricated by any suitable technique such as photolithography or by spraying a polymer into a patterned grid and then removing the grid. Surface roughening techniques can also be used to generate the protrusions. In some embodiments, the protrusions can be formed of different materials such as non-ion-conducting polymers, ceramics, or metals to help interlock the polymer layers and mechanically strengthen the interface.

[0366] Figure 10D The bipolar interface 1013 with a third material 1050 is shown, which is disposed between one or more of the cation-conducting polymer layer 1011 and the anion-conducting polymer layer 1009 or blended from one or more of the cation-conducting polymer layer 1011 into the anion-conducting polymer layer 1009. For example, in some embodiments, the third material 1050 can be an additive, as further discussed below. In some embodiments, the third material 1050 can be a blend of anion-conducting ionomer and cation-conducting ionomer at the interface. For example, it can be a mixture of Nafion 5 wt% ionomer and Orion 2 wt% mTPN1. In some embodiments, the third material can include ion acceptors and donors mixed together or provided as separate layers.

[0367] In some embodiments, the interface includes additives that facilitate acid-base reactions and prevent delamination. In some embodiments, the additives can promote acid-base recombination to a larger volume rather than only at the 2D interface of the anion-conducting polymer and the cation-conducting polymer. This disperses water and CO2 formation, heat generation, and can reduce the membrane resistance by lowering the activation energy of the acid-base reaction. These effects can help avoid the accumulation of products and heat, as well as reduce the resistance losses in the MEA, resulting in a lower cell voltage. Additionally, it helps avoid degradation of the materials at the interface due to heat and gas generation.

[0368] Examples of additives that facilitate acid-base reactions include molecules that are both proton acceptors and anion acceptors, such as hydroxide-containing ionic liquids, where 1-butyl-3-methylimidazolium hydroxide is a specific example. Other ionic liquids can also be used, including those having one of the following ionic groups: 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-N-C 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-N-C 1-6 alkoxy-C 1-6 alkylammonium-1-yl), N,N-dialkylpyrrolidine (e.g., N,N-dimethylpyrrolidine N-methyl-N-ethylpyrrolidine or N-methyl-N-C 1-12 alkylpyrrolidine ), N-alkylpyrrolidine -1-yl (e.g., N-methylpyrrolidine -1-yl, or N-C 1-12 alkylpyrrolidine -1-yl), N,N-dialkylpiperidine (e.g., N,N-dimethylpiperidine N-methyl-N-ethylpiperidine or N-methyl-N-C 1-12 alkylpiperidine ), N-alkylpiperidine -1-yl (e.g., N-methylpiperidine -1-yl or N-C 1-12 alkylpiperidine -1-yl), N,N,4-trialkylpiperidine (e.g., N,N,4-trimethylpiperidine N,4-dimethyl-N-ethylpiperidine or N-methyl-N,4-di-C 1-12 alkylpiperidine ), N,4-dialkylpiperidine -1-yl (e.g., N,4-dimethylpiperidine -1-yl or N,4-di-C 1-12 alkylpiperidine -1-yl), N,N,3,5-tetraalkylpiperidine (e.g., N,N,3,5-tetramethylpiperidine N,3,5-trimethyl-N-ethylpiperidine or N-methyl-N,3,5-tri-C 1-12 alkylpiperidine ), N,3,5-trialkylpiperidine -1-yl (e.g., N,3,5-trimethylpiperidine -1-yl or N,3,5-tri-C 1-12 alkylpiperidine -1-yl), N,N,2,6-tetraalkylpiperidine (e.g., N,N,2,6-tetramethylpiperidine N,2,6-trimethyl-N-ethylpiperidine or N-methyl-N,2,6-tri-C 1-12 alkylpiperidine ), N,2,6-trialkylpiperidine -1-yl (e.g., N,2,6-trimethylpiperidine -1-yl or N,2,6-tri-C 1-12 alkylpiperidine -1-yl), N,N-dialkylazepanium (azepanium) (e.g., N,N-dimethylazepanium N-methyl-N-ethylazepanium or N-methyl-N-C 1-12 alkylazepanium ), N-alkylazepanium -1-yl (e.g., N-methylazepanium -1-yl or N-C 1-12 alkyl azide (-1-yl), N,N-dialkylmorpholine (e.g., N,N-dimethylmorpholine N-methyl-N-ethylmorpholine or N-methyl-N-C 1-12 alkylmorpholine ), N-alkylmorpholine -4-yl (e.g., N-methylmorpholine -4-yl or N-C 1-12 alkylmorpholine -4-yl), N1,N3-dialkylimidazole (e.g., N1,N3-dimethylimidazole N1-ethyl-N3-methylimidazole or N1-C 1-12 alkyl-N3-methyl-imidazole ), N3-alkylimidazole -1-yl (e.g., N3-methylpiperidine -1-yl or N3-C 1-12 alkylpiperidine -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]oct-1-yl, wherein each of these may be optionally substituted (e.g., substituted on the ring by one or more alkyl groups and / or on the alkyl group by one or more heteroatoms).

[0369] In some embodiments, an ionomer different from the ionomers of the anion-conducting polymer layer and the cation-conducting polymer layer may be used. For example, an anion exchange material with a relatively high conductivity, such as Sustainion, may be used. The selectivity of such an anion exchange material may not be sufficient to be used as a cathode buffer layer, but it can be used at the interface.

[0370] In a specific example, an ionomer may be used at the interface, which has a higher ion exchange capacity than at least one of the ionomers in the bipolar membrane. Such an ionomer may not be suitable for the layers of the bipolar membrane, for example due to a swelling tendency or lack of stability, but it can be added at the interface. In a specific example, an ionomer that improves adhesion and physical contact may be used. The polymer at the interface of the two layers can be used to improve adhesion. The ionomer at the interface may itself have multiple sublayers. In one example, the third ionomer may have a central region with a higher void space disposed between denser regions.

[0371] In some embodiments, the ionomer used at the interface is an anion exchange ionomer that is different from the anion-conducting polymer layer's anion-conducting polymer and can 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 the water uptake of PFSA or other cation-conducting polymers. This can help prevent delamination at the interface while maintaining a high ion exchange capacity (IEC). Both the higher IEC and lower water uptake of the interfacial ionomer can help minimize the crossing of cations from the anode side. Since the ion conduction channels in the interfacial ionomer are smaller than those in the anion-conducting polymer of the bipolar membrane, a lower water uptake can result. The higher IEC can be obtained due to the higher concentration of cationic functional groups on the interfacial ionomer. One or both of these characteristics can be present in the interfacial ionomer and can limit cations from the cathode.

[0372] In certain embodiments, when a positive bias is applied across the bipolar membrane, ion recombination occurs at the interface to form products such as water. The interfacial layer should be mechanically robust during ion recombination (e.g., exhibit good adhesion between the AEM and CEM of the bipolar membrane), while minimizing the leakage of unwanted co-ions through the AEM and CEM. In some embodiments, the thickness of the interfacial AEM is 0.1%-10% of the bulk AEM thickness, where examples of the bulk AEM thickness are 5-80 μm. The interfacial AEM can be 1 to 90 volume percent to remain relatively low to avoid additional ohmic resistance across the bipolar membrane. The water uptake of the interfacial AEM can be 0%-25% to avoid membrane delamination due to the mismatch in swelling properties between the adjacent AEM and CEM. In some, the interfacial AEM can have an ion exchange capacity (IEC) in the range of 2.5-3.0 mmol / g. In some such embodiments, the IEC of the bulk AEM is lower than that of the interfacial AEM and can be 1.5-2.5 mmol / g. The high density of positively charged functional groups (i.e., high IEC) at the interface serves to electrostatically repel unwanted co-ions (e.g., H+ or K+) from being transported into the bulk AEM via the Donnan exclusion effect.

[0373] Additional examples of materials that can be present at the interface include: block copolymers with different charged groups (e.g., cationic and anionic fixed charge groups), cationic and anionic conducting polymers, resin materials, ion donors such as oxides including graphene oxide, catalysts for acid / base recombination, catalysts that react H2 and O2 diffusing from the anode and cathode, water splitting catalysts, CO2 absorbing materials, and H2 absorbing materials.

[0374] In some embodiments, the anion-conducting polymer and the cation-conducting polymer of the bipolar membrane have the same main chain, which has different fixed charge groups. As an example, Orion ionomers can be used with different fixed charge groups. The ionomers are more compatible and less prone to delamination.

[0375] In the above example, the thickness of the interface 1013 can be a three-dimensional volume between 1% and 90% of the total thickness of the bipolar membrane, or between 5% and 90% of the total thickness of the bipolar membrane, or between 10% and 80%, or between 20% and 70%, or between 30% and 60%. In some embodiments, it is less than half of the total thickness, including between 1% and 45%, between 5% and 45%, between 5% and 40%, or between 5% and 30%.

[0376] Any of the above bipolar interfaces may not be thermocompressed. In particular, between the anion exchange and cation exchange membrane layers, thermocompression can soften the polymer electrolyte and allow them to melt together.

[0377] In some embodiments, the bipolar AEM / PEM interface comprises a relatively smooth PEM layer in contact with a rougher AEM layer. For example, in such an embodiment the PEM arithmetic mean height (S a ) can range from close to 0 to 0.2 μm. The AEM layer in contact with the PEM layer can have a higher roughness, and in some embodiments, its S a is in the range of 0.2 to 0.5 μm, in the range of 0.4 to 1.5 μm or in the range of 0.6 to 1 μm. The roughness of the AEM and PEM can create a discontinuous interface. The S a of the AEM layer in contact with the PEM can be reduced to close to 0 to 0.2 μm or close to 0 to 1 μm by changing the manufacturing parameters, for example by treating with a solvent that partially dissolves the polymer electrolyte before evaporation to leave a smoother surface or by thermocompression. The AEM layer can be substantially continuous and pore-free, or it can contain pores with a typical porosity range that can be 0.1 to 90%, 1 - 20% and 5 - 15% to allow gas and / or water movement.

[0378] In another embodiment, the surface of the PEM membrane can be roughened to an S a of 5 to 10 μm, 1 to 5 μm, 0.2 to 1 μm or 0.4 to 0.6 μm. In some such embodiments, the AEM layer in contact with the PEM membrane can have an S a of close to 0 to 1 μm or close to 0 to 0.2 μm, or it can be rougher, with an S aIn the range of 2 to 5 μm, in the range of 0.4 to 1.5 μm, or in the range of 0.6 to 1.0 μm. The AEM can be substantially continuous and pore-free, or it can contain pores with a typical porosity range of 0.1 to 90%, 1 - 20%, and 5 - 15% to allow the movement of gas and / or water.

[0379] In some embodiments, a crosslinking agent can be added to covalently crosslink the two polymers of the bipolar membrane. The crosslinking agent can be used at the interface between the ion-conducting polymer layers. Each layer can contain one or more polymers, where each polymer can be characterized by a main chain and side chains attached to the main chain. The crosslinking reaction can occur at the interface and between the crosslinking agent and (i) two or more side chains, (ii) two or more main chains, or (iii) a combination of two or more side chains and main chains.

[0380] The crosslinking agent can be divalent, trivalent, tetravalent, or other higher valences. In this way, the crosslinking agent can react with any number of reactive groups present at the interfaces within the cation-conducting polymer layer, anion-conducting polymer layer, or mixed cation- and anion-conducting polymer layer. In some embodiments, the crosslinking agent comprises:

[0381]

[0382] where 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 (such as any linking moiety herein); L3 is an integer of 2 or greater; and X is a halogen, hydroxyl, optionally substituted amino (such as NR N1 R N2 wherein R N1 and R N2 each independently is H or an optionally substituted alkyl), carboxyl, acyl halide (such as -C(O)-R where R is a halogen), carboxyl aldehyde (such as -C(O)H), or an optionally substituted alkyl.

[0383] Non-limiting crosslinking agents can include terephthalaldehyde, glutaraldehyde, o-xylene, p-xylene, m-xylene, or polyvalent amines such as diamines, triamines, tetraamines, pentamines, etc., including 1,6-diaminohexane (hexamethylenediamine, 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), etc.

[0384] In some embodiments, the crosslinking agent is used to crosslink between the side chain groups of the first polymer layer and the second polymer layer. The side chain groups can include reactive groups present within the material or implanted in any useful manner.

[0385]

[0386] For example, if the polymer layer contains ionic or ionizable side chain groups (such as -SO2OH, -CO2H, etc.), then such groups can be converted to provide reactive groups (such as halogens or leaving groups). In one non-limiting embodiment, as can be seen in step (i) of Scheme I above, the first polymer (1) contains an ionic side chain group (-SO2OH), which is converted to a reactive group (-SO2Cl in (2)) by using thionyl chloride. Subsequently, as in (4), the second polymer can also contain reactive side chain group(s) (e.g., a halogen group such as -Br, a haloalkyl group, or another leaving group). By using a crosslinking agent, a crosslink is formed between the reactive groups. As can be seen 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 polyvalent amine (3). In this way, a crosslink (5) is formed at the interface and between the side chain groups. In one example, the polymer layer can be crosslinked based on the formation of two or more covalent bonds (such as N-S covalent bonds, N-C covalent bonds, or C-C covalent bonds).

[0387] In other embodiments, the crosslinking agent forms a crosslink between the main chains of the first polymer layer and the second polymer layer.

[0388]

[0389] In a non-limiting embodiment, as seen in Scheme II above, the first polymer (6) and the second polymer (8) comprise an aryl backbone. A crosslinking agent is then used to react with backbone groups. If the crosslinking agent is a polyvalent hydroxyalkyl such as (7), the two polymer layers can be crosslinked in an acid-catalyzed manner 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.). In one example, the hydroxyalkyl crosslinking agent can be a tertiary alcohol, which is protonated by a Bronsted acid, loses water as a byproduct, and forms a tertiary carbocation intermediate. Subsequently, this intermediate can readily react with the π electrons of the aromatic backbone based on electrophilic substitution. In this method, the aromatic backbones from the polymer layers can be grafted with the crosslinking agent to form a high-density polymer matrix.

[0390] In other embodiments, the crosslinking agent is used for crosslinking between the side chain group(s) of the first polymer layer and the backbone(s) of the second polymer layer. For example, the side chain group can be converted into a nucleophile, and the backbone can contain an electrophile.

[0391]

[0392] In a non-limiting embodiment, as seen in Scheme III above, the first polymer (1) comprises an ionic side chain group (-SO2OH), which is converted into a reactive group (-SO2Cl in (2)) by using thionyl chloride and then aminated to provide a reactive nucleophilic group (e.g., sulfonamide such as -SO2NR N1 R N2 ). The second polymer (8) can comprise an aryl backbone, which can react with a polyvalent crosslinking agent. For example, the crosslinking agent (11) can be a hydroxyhaloalkyl, which can react by way of an acid-catalyzed Friedel-Crafts alkylation reaction to provide an alkylated polymer (12). Finally, the first polymer (10) having a nucleophilic group can react with the second polymer (12) having an electrophilic group to provide a crosslinked polymer (13). Alternative chemical reagents, reactive groups, electrophiles, and nucleophiles can be used to provide reactive pairs in the first and second polymers that can react at the interface.

[0393] Layer thickness of MEA

[0394] In some embodiments, the polymer electrolyte membrane and an adjacent cathode buffer layer or other anion-conducting polymer layer can have relative thicknesses that facilitate the fabrication and / or operating performance of the MEA.

[0395] Figure 11Depicts an example of a partial layer of the MEA, which partial layer includes: an anion-conducting polymer layer (AEM) 1103, which may be a cathode buffer layer; and a polymer electrolyte membrane (PEM) 1105, which may be a cation-conducting polymer layer (e.g., a proton exchange polymer layer) or an anion-conducting polymer layer. In this example, the PEM 1105 is relatively thick compared to the anion-conducting polymer layer 1103. For example, compared to the thickness of the AEM 1103 being about 10 - 30 or 10 - 20 microns, the PEM 1105 may be 120 microns. The PEM 1105 may provide mechanical stability to the AEM 1103.

[0396] In some cases, the conductivity of an anion-conducting polymer such as those used in the anion-conducting polymer layer 1103 is significantly less than that of a cation-conducting polymer such as those used in the PEM 1105. Thus, to provide the benefits of a cathode buffer layer (e.g., the anion-conducting polymer layer 1103) without significantly increasing the total resistance of the MEA, a relatively thin cathode buffer layer is used. However, when the cathode buffer layer becomes too thin, it becomes difficult to manipulate during the manufacture of the MEA and in other situations. Thus, in some 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 using any fabrication technique described elsewhere herein, for example.

[0397] In various embodiments, the thickness of the polymer electrolyte membrane layer is between about 20 microns and 200 microns. In some embodiments, the thickness of the polymer electrolyte membrane layer is between about 60 microns and 120 microns. In some embodiments, a thin polymer electrolyte membrane layer is used, which has a thickness between about 20 microns and 60 microns. In some embodiments, a relatively thick polymer electrolyte layer is used, which has a thickness between about 120 microns and 200 microns.

[0398] In some embodiments, a thinner cathode buffer layer is used with a thinner polymer electrolyte membrane. This may facilitate the movement of CO2 formed at the interface back to the cathode rather than to the anode. In some embodiments, a thicker cathode buffer layer is used with a thicker polymer electrolyte membrane. In some embodiments, this may cause a reduction in the cell voltage.

[0399] 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 conformability of the anion-conducting polymer coated on the polymer electrolyte membrane.

[0400] Many anion-conducting polymers have an anion selectivity in the range of 95%, with about 5% of the current being cations. Anion-conducting polymers with higher selectivity (anion selectivity greater than 99%) allow for a significant reduction in thickness while providing adequate buffering.

[0401] The mechanical strength of the anion-conducting layer can also affect its thickness, and a mechanically stable layer can achieve a thinner layer. Reducing the porosity of the anion-conducting polymer can reduce the thickness of the anion-conducting layer.

[0402] In some embodiments, the thickness of the cathode buffer layer or other anion-conducting polymer layer adjacent to the polymer electrolyte membrane is between about 5 and 50 microns, 5 to 40 microns, 5 to 30 microns, 10 to 25 microns, or 10 to 20 microns. In some embodiments, using a polymer with >99% selectivity can allow the cathode buffer layer to be reduced to between 2 and 10 microns.

[0403] In some cases, the ratio of the thickness of the polymer electrolyte membrane to the adjacent anion-conducting polymer layer is about 3:1 - 90:1, and the higher-end ratio is used with a highly selective anion-conducting polymer layer. In some embodiments, the ratio is about 2:1 - 13:1, about 3:1 - 13.1, or about 7:1 - 13.1.

[0404] In some embodiments, a relatively thin PEM improves some aspects of MEA performance. Refer to Figure 11 , for example, the thickness of the polymer electrolyte membrane 1105 can be about 50 microns, while the thickness of the anion-conducting layer can be between about 10 and 20 microns. A thin PEM is beneficial for the water generated at the AEM / PEM interface to move towards the anode. The gas pressure on the cathode side of the cell can be 80 - 450 psi, which causes the water at the interface to move towards the anode. However, in some cases, a thick PEM can cause most of the water to move through the AEM to the cathode, resulting in overflow. By using a thin PEM, overflow can be avoided.

[0405] In some embodiments, the thickness of the thin PEM can be 10 microns to 50 microns, 30 microns to 50 microns, or 25 microns to 35 microns. In some such embodiments, the AEM can have a thickness similar to that of the PEM, such as 5 microns to 50 microns, 5 microns to 30 microns, or 10 microns to 20 microns. When using a PEM with a thickness of 10 - 30 microns, the PEM:AEM thickness ratio can be 1:2 to 1:1; when using a PEM with a thickness of 30 - 50 microns, it can be 1:2 to 2:1; or when the PEM thickness is 20 - 35 microns, it can be 1:1 to 3:1. As further described below, AEMs within these thickness ranges can be used for water management.

[0406] Commercially available anion exchange membranes and cation exchange membranes typically have a known thickness. For example, the membrane has a dry thickness as follows:

[0407] Membrane type Thickness (μm) Nafion 117 183 Nafion 115 127 Nafion 211 25.4

[0408] Such known thicknesses can be used to determine thickness ratios. For example, if the thickness of the AEM is between about 200 nm and 100 μm, between 300 nm and 75 μm, between 500 nm and 50 μm, as discussed above for the cathode buffer layer, the PEM:AEM thickness ratio can be determined as follows:

[0409] PEM membrane type Example range of PEM:AEM N117 1.83-915；2.44-610；3.66-366 N115 1.27-635；1.69-423；2.54-254 N211 0.25-127；0.34-84.7；0.51-50.8

[0410] The AEM can have a thickness that aids in water management, as discussed further below.

[0411] Water management

[0412] As described above, CO x One of the key challenges in an electrolysis device is managing the water in the cathode, since water is needed for the polymer electrolyte to be hydrated and / or to participate in the CO x reduction reaction, but not so much that it impedes the transport of CO x to the cathode catalyst. In a polymer electrolyte system, water can be transported mainly by two methods: by electroosmotic drag and by diffusion. By diffusion, water will move from a high concentration region to a low concentration region, and the rate of water transport depends on the diffusion coefficient, which is an inherent property of the polymer electrolyte material. Electroosmotic drag is the movement of water molecules with ions as they cross the polymer electrolyte. In a cation exchange membrane system, water will be transported as cations move from the anode to the cathode, while in an anion exchange membrane system water moves with anions in the opposite direction.

[0413] For bipolar membranes (including cation exchange membranes and anion exchange membranes), the net movement of water from the anode to the cathode can be managed by varying the thickness and / or the material properties of the anion exchange polymer electrolyte layer and the cation exchange polymer electrolyte layer.

[0414] In some embodiments, the thickness of the AEM can be between 5 and 80 microns, 5 to 50 microns, 5 to 40 microns, or 5 to 30 microns. As described below, a relatively thick AEM can aid in water management and prevent delamination, extending the lifespan. However, the thickness also results in a higher voltage and lower efficiency. Thus, in some embodiments, the AEM can be no more than 50 microns thick.

[0415] The following table shows the amount of CO per ionic charge moving through the polymer electrolyte when the thickness of the anion exchange polymer electrolyte layer and the cation exchange membrane thickness are varied xNet water transport from the anode to the cathode in the electrolysis device. When the thickness of the anion exchange polymer electrolyte layer increases, the net movement of water from the anode to the cathode decreases. Increasing the molecular weight of the anion exchange polymer, which reduces the diffusion coefficient of water through the anion exchange layer, has a similar effect of reducing the net movement of water per ionic charge from the anode to the cathode of the device.

[0416] Nafion 115 (PFSA cation exchange membrane thickness 127 microns)

[0417]

[0418] Nafion 212 (PFSA cation exchange membrane thickness 50.8 microns)

[0419]

[0420]

[0421] Thus, in some embodiments, the ratio of the thickness of the cation exchange membrane to the thickness of the anion exchange membrane in the bipolar MEA (i.e., the PEM:AEM ratio) is not greater than 7:1, 5:1, 3:1, 2:1, 1.5:1, 1:1, or 1:1.5.

[0422] Nafion 115 (PFSA cation exchange membrane thickness 127 microns) with anion exchange polymer electrolyte layers of different molecular weights

[0423]

[0424] 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.

[0425] In some embodiments, the AEM polymer can be crosslinked to reduce water movement from the anode to the cathode.

[0426] Figure 12 Shows the CO of a bipolar MEA with AEMs of different thicknesses x Faradaic efficiency of the electrolysis device. Nafion115 (127 microns) is used for the PEM. Results for the MEA without an AEM are also shown. Figure 13 Shows the cell voltage.

[0427] The electrolysis device is gradually increased to High current density. The Faraday efficiency is the efficiency of transferring charge in a system that facilitates an electrochemical reaction. Notably, 0 micrometers (no AEM) has a Faraday efficiency close to 0, while the MEA with 3.5 micrometers AEM has a Faraday efficiency below 80%. This indicates that there is a minimum thickness of AEM for good performance in a bipolar MEA, which in some embodiments can be 5 micrometers or 7 micrometers. Similar results are expected for other operating conditions and bipolar MEAs.

[0428] The MEA with an AEM between 7.5 and 25 micrometers has a Faraday efficiency close to 100% during operation. The MEA with 30 micrometers AEM operates at a Faraday efficiency close to 100% at the start, and the performance degrades after about 6 hours. This indicates that delamination may occur. For MEAs with up to 50 micrometers AEM, manufacturing and / or operating conditions can be modified to reduce delamination and achieve performance comparable to that of MEAs with 7.5, 15, and 25 micrometers AEM.

[0429] In the above description, the terms "micrometer" and "micron" and the abbreviations "μm" and "um" are used interchangeably to denote a micrometer. Unless otherwise specified, ranges in this document (e.g., 10 micrometers to 20 micrometers, 0.25 - 127, between 1 and 90%, etc.) include the endpoints of these ranges.

Claims

1. A membrane electrode assembly comprising: A cathode catalyst layer; An anode catalyst layer; and A bipolar membrane disposed between the cathode catalyst layer and the anode catalyst layer, wherein, The bipolar membrane comprises an anion-conducting polymer layer, a cation-conducting polymer layer, and a bipolar interface between the anion-conducting polymer layer and the cation-conducting polymer layer, wherein the cation-conducting polymer layer is disposed between the anode catalyst layer and the anion-conducting polymer layer, and the bipolar interface is characterized by or comprises one or more of the following: Covalent crosslinking of the cation-conducting polymer layer and the anion-conducting polymer layer; Interpenetration of the anion-conducting polymer layer and the cation-conducting polymer layer; and A layer of a second anion-conducting polymer, wherein the ion exchange capacity of the second anion-conducting polymer is higher than the ion exchange capacity of the anion-conducting polymer in the anion-conducting polymer layer.

2. The membrane electrode assembly according to claim 1, wherein, The bipolar interface is characterized by the interpenetration of the anion-conducting polymer layer and the cation-conducting polymer layer, and the bipolar interface comprises protrusions, and the in-plane dimension of the protrusions in the plane parallel to the anion-conducting polymer layer is 10 μm - 1 mm.

3. The membrane electrode assembly according to claim 1, wherein, The bipolar interface is characterized by the interpenetration of the anion-conducting polymer layer and the cation-conducting polymer layer; and the bipolar interface comprises protrusions, and the thickness of each protrusion is between 10% and 75% of the total thickness of the anion-conducting polymer layer.

4. The membrane electrode assembly according to claim 1, wherein, The bipolar interface is characterized by the interpenetration of the anion-conducting polymer layer and the cation-conducting polymer layer, and the bipolar interface comprises a gradient of the anion-conducting polymer and / or the cation-conducting polymer.

5. The membrane electrode assembly according to claim 1, wherein, The bipolar interface is characterized by the interpenetration of the anion-conducting polymer layer and the cation-conducting polymer layer, and the bipolar interface comprises a mixture of the anion-conducting polymer and / or the cation-conducting polymer.

6. The membrane electrode assembly according to claim 1, wherein, The bipolar interface comprises a layer of a second anion-conducting polymer, and further, the thickness of the layer of the second anion-conducting polymer is between 0.1% and 10% of the thickness of the anion-conducting polymer layer.

7. The membrane electrode assembly according to claim 1, wherein The bipolar interface comprises a layer of a second anion-conducting polymer, and further, the ion exchange capacity IEC of the second anion-conducting polymer is between 2.5 and 3.0 mmol / g.

8. The membrane electrode assembly according to claim 7, wherein, The ion exchange capacity IEC of the anion-conducting polymer is between 1.5 and 2.5 mmol / g.

9. The membrane electrode assembly according to claim 1, wherein, The bipolar interface comprises a layer of a second anion-conducting polymer, and the second anion-conducting polymer has a lower water absorption rate than the anion-conducting polymer in the anion-conducting polymer layer.

10. The membrane electrode assembly according to claim 1, wherein, The bipolar interface comprises covalent crosslinking of the cation-conducting polymer layer and the anion-conducting polymer layer, and the covalent crosslinking comprises a material comprising a structure of one of formulas (I)-(V): (I), (II), (III), (IV), (V), or a salt thereof, wherein: R 7 、R 8 、R 9 and R 10 each independently is H, optionally substituted alkyl, heteroalkylene, aryl, or arylalkylene, wherein the combination of R 7 and R 8 or R 9 and R 10 may together form an optionally substituted cyclic group; Ar comprises or is an optionally substituted arylene; Each n is independently an integer of 1 or greater; Each of rings a - c may be optionally substituted; and Rings a-c, R 7 , R 8 , R 9 and R 10 optionally may contain ionizable or ionic structural moieties.

11. The membrane electrode assembly according to claim 1, wherein, The bipolar interface comprises a covalent crosslink of the cation-conducting polymer layer and the anion-conducting polymer layer, and the covalent crosslink comprises a material that comprises a structure of one of formulas (I)-(V): (I), (II), (III), (IV), (V), or a salt thereof, wherein: R 7 、R 8 、R 9 and R 10 each independently is an electron-withdrawing structural moiety or H, wherein R 7 or R 8 at least one of them may contain an electron-withdrawing structural moiety, or R 7 and R 8 or R 9 and R 10 in combination may together form an optionally substituted cyclic group; Ar comprises or is an optionally substituted arylene; Each n is independently an integer of 1 or greater; Each of rings a-c is optionally substituted; and Rings a-c, R 7 , R 8 , R 9 and R 10 optionally may contain ionizable or ionic structural moieties.

12. The membrane electrode assembly according to claim 11, wherein, R 7 or R 8 comprises an electron-withdrawing structural moiety selected from the group consisting of: optionally substituted haloalkyl, cyano, phosphate ester, sulfate ester, sulfonic acid group, sulfonyl group, difluoroboryl group, dihydroxyboryl group, cyanothio group, and piperidine .

13. The membrane electrode assembly according to claim 1, wherein, The bipolar interface comprises a covalent crosslink of the cation-conducting polymer layer and the anion-conducting polymer layer, and the covalent crosslink comprises a material that comprises a structure of one of the following formulas: , , , , or a salt thereof, wherein: Ar is or comprises an optionally substituted arylene; Ak is or comprises an optionally substituted alkylene, haloalkylene, or heteroalkylene; and L is a linking structural moiety, and wherein one of Ar, Ak, and / or L is optionally substituted by one or more ionizable or ionic structural moieties.

14. The membrane electrode assembly according to claim 1, wherein, The bipolar interface comprises a covalent crosslink of the cation-conducting polymer layer and the anion-conducting polymer layer, and the covalent crosslink comprises a crosslinking agent that comprises a structure of one of the following formulas: , or , wherein: Ar is an optionally substituted arylene; L is a linking structural moiety; L3 is an integer of 2 or greater; and X’ is absent, -O-, -NR N1 -, -C(O)- or -Ak-, where R N1 is hydrogen or optionally substituted alkyl, and Ak is an optionally substituted alkylene or an optionally substituted heteroalkylene.

15. The membrane electrode assembly according to any one of claims 10-14, wherein, The covalent cross-linking comprises a material that includes one or more ionizable or ionic moieties selected from the following: -L A -X A , -L A -(L A’ -X A ) L2 , -L A -(X A -L A’ -X A’ ) L2 and -L A -X A -L A’ -X A’ -L A” -X A” ; wherein: Each L A , L A’ and L A” is independently a connecting structure part; Each X A , X A’ and X A” independently comprises an acidic structural moiety, a basic structural moiety, a multi-ionic structural moiety, a cationic structural moiety or an anionic structural moiety; and L2 is an integer of 1 or greater.

16. The membrane electrode assembly according to claim 15, wherein, Each X A , X A’ and X A” independently contains a carboxyl group, a carboxylate anion, a guanidinium cation, a sulfo group, a sulfonate anion, a sulfonium cation, a sulfate ester, a sulfate anion, a phosphoryl group, a phosphonate anion, a phosphate ester, a phosphate anion, a cation, a phosphazene a cation, an amino group, an ammonium cation, or a heterocyclic cation.

17. The membrane electrode assembly according to any one of claims 13-14, wherein, The connecting structure part includes a covalent bond, a spiro ring bond, -O-, -NR N1 -, -C(O)-, -C(O)O-, -OC(O)-, -SO2-, an alkylene group, an alkoxy group, a haloalkylene group, a hydroxyalkylene group, a heteroalkylene group, an arylene group, an aryloxy group, or a heterocyclic diyl group.

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