reinforced ion-conductive membrane

Abstract

According to the present invention, there is provided a reinforced ion-conducting membrane comprising an ion-conducting polymer and a porous mat of nanofibers. The nanofiber porous mat is impregnated with the ion-conducting polymer. The nanofibers comprise a crosslinked polymer, which is non-ion-conductive. The crosslinked polymer comprises a heterocyclic polymer backbone containing a basic functional group and a linking chain connecting at least two heterocyclic polymer backbones via a linking group. The nanofiber porous mat has a resistance to at least 15 mN m 2 / g tear index.

Description

[Technical Field]

[0001] The present invention relates to reinforced ion-conducting membranes, such as reinforced electrolyte membranes. Specifically, the present invention relates to reinforced proton exchange membranes and methods for making the same. The reinforced ion-conducting membranes may be suitable for use in electrochemical devices, such as fuel cells and / or electrolyzers. [Background technology]

[0002] A fuel cell is an electrochemical cell containing two electrodes separated by an electrolyte. A fuel, e.g., hydrogen, an alcohol such as methanol or ethanol, or formic acid, is supplied to the anode, and an oxidant, e.g., oxygen or air, is supplied to the cathode. Electrochemical reactions occur at the electrodes, converting the chemical energy of the fuel and oxidant into electrical energy and heat. Electrocatalysts are used to promote the electrochemical oxidation of the fuel at the anode and the electrochemical reduction of oxygen at the cathode.

[0003] Fuel cells are usually classified according to the nature of the electrolyte used. In most cases, the electrolyte is a solid polymer membrane, which is electronically insulating but ionically conductive. In proton exchange membrane fuel cells (PEMFCs), the membrane conducts protons, and protons generated at the anode are transported through the membrane to the cathode, where they combine with oxygen to form water.

[0004] Electrolyzers are electrochemical devices for electrolyzing water to produce high-purity hydrogen and oxygen. Electrolyzers can operate in both alkaline and acidic systems. Those electrolyzers that use a solid proton-conducting polymer electrolyte membrane or proton exchange membrane (PEM) are known as proton exchange membrane water electrolyzers (PEMWE). Those electrolyzers that utilize a solid anion-conducting polymer electrolyte membrane or anion exchange membrane (AEM) are known as anion exchange membrane water electrolyzers (AEMWE).

[0005] The main component of a fuel cell or water electrolysis device is the membrane electrode assembly (MEA). The MEA typically consists of five layers. The central layer is a polymeric ion-conducting membrane. On either side of the ion-conducting membrane are electrocatalyst layers containing electrocatalysts designed for specific electrolysis reactions. Finally, adjacent to each electrocatalyst layer are gas diffusion layers and / or porous transport layers that are porous and electrically conductive, allowing reactants to reach the electrocatalyst layer and conduct the electrical current generated by the electrochemical reaction.

[0006] Conventional ion-conducting membranes used in PEMFCs or PEMWEs are generally formed from sulfonated, fully fluorinated polymer materials (often commonly referred to as perfluorinated sulfonic acid (PFSA) ionomers). As an alternative to PFSA-type ionomers, ion-conducting membranes based on partially fluorinated or non-fluorinated hydrocarbon sulfonated or phosphonated polymers can be used. Recent developments in fuel cells and electrolyzers require thinner membranes for the benefits they offer (improved ionic conductivity, improved water transport, etc.), and therefore reinforcing materials, typically expanded polytetrafluoroethylene (ePTFE), are embedded within the membrane to provide the mechanical properties needed to increase resistance to premature failure.

[0007] Such reinforced membranes often have lower proton conductivity when compared to unreinforced membranes of the same thickness, but the improved mechanical properties allow for the use of thinner membranes with lower electrical resistance.

[0008] Other types of reinforcements have also been proposed, as disclosed, for example, in WO 2011 / 149732 and WO 2016 / 020668.

[0009] Li and Liu, J. Mater. Chem. A., 2013, 1, 1171, disclose a polymer electrolyte composite membrane of polybenzimidazole and crosslinked polybenzimidazole-polybenzoxazine electrospun nanofibers for proton exchange membrane fuel cells. The membrane was doped with 85% phosphoric acid to make the polymer of the composite membrane (including the polymer of the nanofiber) proton conductive. It is desirable to develop a reinforced ion-conducting membrane with improved mechanical properties. Summary of the Invention

[0010] While the reinforced membranes described above have allowed for the use of thinner membranes while maintaining mechanical strength, drawbacks remain. Specifically, limitations are seen in real-world operation, where humidity conditions can fluctuate significantly over short periods of time, from relatively high levels (such as during start-up from cold conditions) to very dry levels (such as during operation at maximum rated power density), where membrane degradation can occur to levels higher than acceptable. In accelerated stress tests designed to mimic and accelerate this operation, wet / dry cycling accelerated stress tests induce membrane swelling / de-swelling so that these membrane degradation effects can be observed more quickly.

[0011] It is an object of the present invention to provide improved reinforced ionically conductive membranes suitable for use in electrochemical devices such as fuel cells and electrolyzers, and in particular having improved properties for large-scale manufacturing.

[0012] Thus, in a first aspect of the present invention there is provided a reinforced ion-conducting membrane comprising: an ion-conducting polymer; a porous mat of nanofibers impregnated with an ion-conducting polymer; the nanofibers comprise a crosslinked polymer, the crosslinked polymer being ionically non-conductive; a heterocyclic polymer backbone containing a basic functional group; a linking chain connecting at least two of the heterocyclic polymer backbones via a linking group; The porous nanofiber mat has a resistance of at least 15 mN m 2 A reinforced ion-conducting membrane having a tear index of 1 / g is provided.

[0013] The porous mat of nanofibers (sometimes referred to as a "nanofiber mat") provides mechanical reinforcement for the ion-conducting membrane. The porous mat of nanofibers may be in the form of a nonwoven material.

[0014] As used herein, "tear index" (mN m 2 The term grammage (g / m 2) The tear strength can be measured according to ASTM D1938.

[0015] In a second aspect, there is provided a reinforced ion-conducting membrane comprising: an ion-conducting polymer; a porous mat of nanofibers impregnated with an ion-conducting polymer; the nanofibers comprise a crosslinked polymer, the crosslinked polymer being ionically non-conductive; a heterocyclic polymer backbone containing a basic functional group; a linking chain connecting at least two of the heterocyclic polymer backbones via linking groups, each linking group (A) independently being:

[0016] [ka] is selected from the group consisting of In the formula, C 1 is chemically bonded to the heterocyclic-based polymer backbone; and a linking group.

[0017] In a further aspect, there is provided a reinforced ion-conducting membrane comprising: an ion-conducting polymer; a porous mat of nanofibers impregnated with an ion-conducting polymer; the nanofibers comprise a crosslinked polymer, the crosslinked polymer being ionically non-conductive; a heterocyclic polymer backbone containing a basic functional group; a linking chain connecting at least two of the heterocyclic polymer backbones via a linking group; A reinforced ion-conductive membrane is provided, wherein the porous mat has an average thickness of 10 μm or less, and the reinforced ion-conductive membrane has a secant modulus at 8% strain of at least 30 MPa when measured in the machine direction at a temperature of 80° C. and a relative humidity (RH) of 90%, and a secant modulus at 8% strain of at least 30 MPa when measured in the cross direction at a temperature of 80° C. and a RH of 90%, and the machine and cross directions are perpendicular.

[0018] In a third aspect, there is provided a method for producing a reinforced ion-conducting membrane, the method comprising: providing a substrate; Providing a formulation for electrospinning, the formulation comprising a solvent, a crosslinker, and a heterocyclic polymer comprising a basic functional group; electrospinning the formulation onto a substrate to form a porous mat of nanofibers; treating the porous mat to react the heterocyclic polymers with a crosslinking agent, thereby forming a crosslinked polymer comprising heterocyclic polymer backbones containing basic functional groups and linking chains connecting at least two of the heterocyclic polymer backbones via linking groups; impregnating the porous mat with an ion-conducting polymer.

[0019] In a fourth aspect, there is provided a method for producing a reinforced ion-conducting membrane, the method comprising: providing a substrate; Providing a first formulation for electrospinning, the first formulation comprising a solvent and a heterocyclic polymer comprising a basic functional group; electrospinning the first formulation onto a substrate to form a porous mat of nanofibers; providing a second formulation comprising a cross-linking agent; impregnating the porous mat with a second formulation and then treating the porous mat to react the heterocyclic polymers with the crosslinking agent, thereby forming a crosslinked polymer comprising heterocyclic polymer backbones containing basic functional groups and linking chains connecting at least two of the heterocyclic polymer backbones via linking groups; impregnating the porous mat with an ion-conducting polymer.

[0020] In a fifth embodiment, there is provided a crosslinkable porous mat of nanofibers, the nanofibers comprising: a heterocyclic polymer containing a basic functional group, wherein the heterocyclic polymer is non-ionically conductive; and a crosslinking agent, preferably comprising at least two terminal epoxide groups. A crosslinkable porous mat of nanofibers is provided.

[0021] In a sixth aspect, there is provided a reinforcement component for strengthening an ion-conducting membrane, the reinforcement component comprising: a porous mat of nanofibers, the nanofibers comprising a cross-linked polymer, the cross-linked polymer being ionically non-conductive; a heterocyclic polymer backbone containing a basic functional group; a linking chain connecting at least two of the heterocyclic polymer backbones via a linking group, wherein the porous mat of nanofibers has a tensile strength of at least 15 mN m 2 A reinforcing component is provided that includes a porous mat of nanofibers having a tear index of 1 / g. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram of an ion-conducting membrane of the present invention. [Figure 2] 1 is a schematic diagram of an exemplary process of the present invention. [Figure 3] 1 is a schematic diagram of an exemplary process of the present invention. [Figure 4] 1 is an SEM image of a porous mat of nanofibers according to one embodiment of the present invention. [Figure 5] 1 is a plot of force (N) as a function of extension (mm). [Figure 6] 1 is a plot of force (N) as a function of extension (mm). [Figure 7] 1 is a plot of force (N) as a function of extension (mm). [Figure 8] 1 is a plot of force (N) as a function of extension (mm). [Figure 9] 1 is a scheme of an exemplary reaction between PBI and a crosslinker. [Figure 10] 1 is a plot of stress versus strain for a reinforced ion-conducting membrane measured in the machine direction (MD) and transverse direction (TD) at 80° C. and 90% RH. [Figure 11] 1 is a plot of the OCV response to removal of differential pressure as a function of the number of stress cycles. DETAILED DESCRIPTION OF THE INVENTION

[0023] Preferred and / or optional features of the invention will now be described. Any aspect of the invention may be combined with any other aspect of the invention unless the context requires otherwise. Any preferred or optional feature of any aspect may be combined with any aspect of the invention, singly or in any combination, unless the context requires otherwise.

[0024] The present invention provides a reinforced ion-conducting membrane, such as an electrolyte membrane, comprising a porous mat of nanofibers, the porous mat being impregnated with an ion-conducting polymer. Preferably, the porous mat is essentially completely impregnated with the ion-conducting polymer. Figure 1 shows a schematic diagram of an ion-conducting membrane of the present invention. Preferably, the reinforced ion-conducting membrane is a reinforced proton-conducting membrane.

[0025] The porous mat provides mechanical reinforcement for the ion-conducting membrane. The porous mat is preferably formed from entangled nanofibers. The nanofibers are ion-nonconductive. For example, the nanofibers preferably lack sulfonic acid and / or phosphate groups. The ion-conducting membrane is preferably lacking phosphate. The nanofibers comprise a cross-linked polymer that is ion-nonconductive. The nanofibers comprise entangled individual nanofibers. For example, the nanofibers may cross each other or be interwoven with other nanofibers or with themselves. The porous mat of nanofibers may be in the form of a nonwoven material. Preferably, the nanofibers have a substantially random orientation in the plane of the reinforced ion-conducting membrane (i.e., the xy plane).

[0026] The porous mat must be at least 15 mN m 2 / g, preferably at least 20 mN m 2 / g, preferably at least 25 mN m 2 / g, preferably at least 30 mN m 2 / g, preferably at least 35 mN m 2 / g, preferably at least 40 mN m 2 / g, preferably at least 45 mN m 2 / g. The tear index is a function of the maximum tear strength (mN) and the basis weight (g / m 2 ) is the quotient of

[0027] The nanofibers suitably have a diameter of 50 to 700 nm, suitably 200 to 600 nm, and preferably 250 to 550 nm.

[0028] The length of the nanofibers is not critical to the invention, but each nanofiber should be long enough (e.g., several millimeters or centimeters) to become entangled with either one or more other nanofibers or with itself.

[0029] The nanofibers are preferably spun nanofibers, i.e., the nanofibers are formed using a spinning technique. Examples of suitable spinning techniques include, but are not limited to, electrospinning and force spinning.

[0030] The crosslinked polymer comprises a heterocyclic polymer backbone and a linking chain. The linking chain connects at least two of the heterocyclic polymer backbones via a linking group. Preferably, the crosslinked polymer consists essentially of (or consists of) the heterocyclic polymer backbone, the linking chain, and optionally a second polymer, wherein the second polymer is non-ionically conductive.

[0031] The heterocyclic polymer backbone comprises a basic functional group, such as a nitrogen-containing basic functional group. The nitrogen-containing basic functional group can be a nitrogen having a lone pair of electrons. The heterocyclic polymer backbone further comprises a linking moiety that is chemically bonded (e.g., covalently bonded) to a linking group. The linking moiety can be a heteroatom, such as N. The heteroatom can be part of a heterocycle.

[0032] Preferably, each linking group (A) is independently:

[0033] [ka] is selected from the group consisting of In the formula, C 1 is chemically bonded to the heterocyclic polymer backbone. For example, C 1 can be chemically bonded to a heteroatom such as N on the heterocyclic polymer backbone. Preferably, the linking group (A) is -[C 1 HCH(OH)]—. Linking group A can be derived from a crosslinker that contains a terminal epoxide functionality, such as a terminal glycidyl ether group.

[0034] Preferably, the crosslinked polymer is insoluble in organic solvents, in particular, the crosslinked polymer is insoluble in N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc) or dimethylsulphoxide (DMSO), preferably in DMAc or DMSO, and preferably in DMAc.

[0035] The heterocyclic polymer backbone can be derived from a basic heterocyclic polymer, including polybenzimidazole, poly(pyridine), poly(pyrimidine), polybenzothiazole, polyoxadiazole, polyquinoline, polyquinoxaline, polythiadiazole, polytriazole, polyoxazole, polybenzoxazole, polythiazole, polypyrazole, and derivatives thereof. Preferably, the heterocyclic polymer backbone is derived from a functionalized or zwitterionic polyazole, such as polybenzimidazole, polytriazole, polythiazole, and polydithiazole, and derivatives thereof, most preferably polybenzimidazole.

[0036] The crosslinked polymer can comprise the same or different types of heterocyclic polymer backbones. For example, the crosslinked polymer can comprise a first type of heterocyclic polymer backbone and a second type of heterocyclic polymer backbone, where the first type and the second type of heterocyclic polymer backbone are different in the sense that they have different chemical structures / compositions. The linking chain can connect the same or different types of heterocyclic polymer backbones, for example, the linking chain can connect the first type of heterocyclic polymer backbone to the second type of heterocyclic polymer backbone.

[0037] The crosslinked polymers are crosslinked by linking chains. Each linking chain connects at least two of the heterocyclic polymer backbones via at least two linking groups. That is, one heterocyclic polymer backbone is attached to another heterocyclic polymer backbone via at least two linking groups and a linking chain. The crosslinking improves the mechanical and tensile properties of the porous mat of nanofibers, thereby improving the mechanical and tensile properties of the reinforced ion-conducting membrane.

[0038] The linking group is preferably a carbon C 1 which is chemically attached (e.g., covalently attached) to the heterocyclic polymer backbone, e.g., at a linking site on the heterocyclic polymer backbone. The linking chain has a different chemical structure than the heterocyclic polymer backbone.

[0039] The linking chain can be non-polymeric or polymeric, preferably non-polymeric. The linking chain can be aliphatic, aromatic, or a combination of aliphatic and aromatic moieties. Preferably, the linking chain is aliphatic. Most preferably, the linking chain is non-polymeric and aliphatic. For example, the linking chain can be a linear or branched aliphatic chain. Preferably, the linking chain comprises an alkoxy chain, such as an alkyl chain and / or a glycol chain. "Alkyl" refers to a linear or branched hydrocarbon group optionally substituted with a heteroatom such as O, N, or S. The term "glycol chain" includes chains comprising ethylene glycol, poly(ethylene glycol), propylene glycol, and / or poly(propylene glycol) groups.

[0040] The linking chain may be devoid of cyclic groups, such as cyclic aromatic groups and cycloalkyl groups. Preferably, the linking chain is devoid of fused rings, including fused carbocyclic and fused heterocyclic rings, such as benzoxazines.

[0041] The linking chain is

[0042] [ka] and may have a chemical formula selected from the group consisting of: During the ceremony, A is a linking group, and each linking group A is independently

[0043] [ka] is selected from the group consisting of R 1 is an aliphatic C 1~15 Alkyl chain, preferably C 1~10 Alkyl chains, and more preferably C 1~6 Alkyl chains; alkoxy chains, e.g., [CH2CH2O] m , [CH2CH(CH3)O] m , [CH2CH2CH2O] m Glycol chains such as; aryloxy chains,

[0044] [ka] or a combination thereof; X and Y each independently represent O, [N(R 7 )], [OCH2CH2] n , [OCH2CH(CH3)] n , [O(CH2)3] n and no atom; R 2 and R 7 are each independently H, C 1~5 Alkyl chains, and [(CH2) p A], m and n each independently range from 1 to 225, inclusive; R 3 and R 4 are each independently an aliphatic C 1~5 an alkyl chain; an alkoxy chain, e.g., a glycol chain; or no atom; R a , R b , R c , R d , R 5 , and R6 are each independently selected from H, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, or tert-butyl; p is an integer ranging from 1 to 5, inclusive.

[0045] Preferably, X and Y are each independently O and [N(R 7 In some embodiments, X and Y are the same, e.g., X and Y can both be O. In other embodiments, X and Y are both selected from the group of [N(R 7 ] can be.

[0046] Preferably, R 2 is H or [(CH2) p A], more preferably [(CH2) p A].

[0047] Preferably, R 3 and R 4 are each independently an aliphatic C 1~3 It is an alkyl chain or has no atoms.

[0048] Preferably, R 5 and R 6 are each independently selected from H or methyl. In some embodiments, R 5 and R 6 and R are both methyl. 5 and R 6 are both H.

[0049] Preferably, R 7 is H or [(CH2) p A], more preferably [(CH2) p A].

[0050] Preferably, R a , R b , R c , R dare each independently H or methyl, most preferably H. For example, R a , R b , R c , R d may each be hydrogen.

[0051] Preferably, m and n each independently range from 1 to 150, more preferably from 1 to 130, more preferably from 1 to 100, and even more preferably from 1 to 50, inclusive.

[0052] Preferably, p is an integer in the range of 1 to 3, preferably 1 or 2, and most preferably 1.

[0053] Preferably, the linking chain is

[0054] [ka] wherein q ranges from 1 to 225, inclusive, preferably about 130; and r ranges from 1 to 225, inclusive.

[0055] Preferably, p ranges from 1 to 3, inclusive. Preferably, q ranges from 1 to about 130. Preferably, r ranges from 1 to 100, inclusive.

[0056] The nanofibers can include a crosslinked polymer and a second polymer, for example, as a blend or mixture. The second polymer is ionically non-conductive. The second polymer is different (i.e., has a different chemical composition) from the heterocyclic polymer from which the heterocyclic polymer backbone is derived. The second polymer can be a partially or fully fluorinated polymer or a hydrocarbon polymer. Preferably, the second polymer is a partially or fully fluorinated polymer. For example, the second polymer can be selected from the group consisting of poly(vinylidene difluoride) (PVDF), polytetrafluoroethylene (PTFE), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyimide (PI), polyetherimide (PEI), poly(aryl ether ketone) (PAEK), poly(aryl ether sulfone), poly(phenylene sulfide) (PPS), and polyvinylpyrrolidone (PVP). Preferably, the second polymer is PVDF.

[0057] By providing a porous mat comprising a crosslinked polymer and a second polymer, the mechanical and tensile properties of the porous mat, and thus the reinforced ion-conducting membrane, can be further improved.

[0058] The porous mat of the present invention may have a maximum tear strength of at least 38 mN, preferably at least 40 mN, preferably at least 50 mN, more preferably at least 60 mN, more preferably at least 70 mN, more preferably at least 80 mN, more preferably at least 90 mN, and more preferably at least 100 mN. Tear strength may be measured according to ASTM D1938.

[0059] The nanofiber porous mat can have an ultimate tensile strength of at least 25 MPa, preferably at least 30 MPa, when measured in the machine direction. The nanofiber porous mat can have an ultimate tensile strength of at least 25 MPa, preferably at least 30 MPa, when measured in the cross direction. Most preferably, the nanofiber porous mat can have an ultimate tensile strength of at least 25 MPa, preferably at least 30 MPa, when measured in the machine direction, and the nanofiber porous mat can have an ultimate tensile strength of at least 25 MPa, preferably at least 30 MPa, when measured in the cross direction. The machine and cross directions are perpendicular. The ratio of the ultimate tensile strength of the nanofiber porous mat measured in the machine direction to the ultimate tensile strength of the nanofiber porous mat measured in the cross direction can be in the range of 0.5 to 2, preferably 0.6 to 1.5. The nanofiber porous mat can have a strain at break of at least 5%, preferably at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, and preferably at least 50% when measured in the machine direction. The nanofiber porous mat can have a strain at break of at least 5%, preferably at least 10%, and more preferably at least 15% when measured in the cross direction. Preferably, the nanofiber porous mat has a strain at break of at least 5%, preferably at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, and preferably at least 50% when measured in the machine direction, and at least 5%, preferably at least 10%, and more preferably at least 15% when measured in the cross direction. The ultimate tensile strength and strain at break can be determined by performing stress-strain tests on the porous mat.For example, when measuring the stress-strain relationship in the longitudinal or transverse direction, a nanofiber porous mat sample (80 mm x 10 mm) can be prepared with the longer dimension parallel to the longitudinal or transverse direction, respectively. The sample can be clamped between the tensile test fixtures of a universal mechanical testing machine and pulled at an extension rate of 20 mm / min at room temperature (20°C ± 3°C) and 30-50% relative humidity (RH) until the sample breaks. A stress-strain graph can be plotted, from which the ultimate tensile strength and strain at break can be derived. The thickness of the porous mat required for stress-strain testing can be measured by cross-sectional imaging after resin embedding using a scanning electron microscope (SEM) (e.g., a JEOL JSM-IT300LV SEM) and measuring the thickness from edge to edge of the mat using an integrated ruler.

[0060] The reinforced ion-conducting membrane may, for example, have a secant modulus (also referred to herein as "secant modulus") measured in the longitudinal direction (at 8% strain) of at least 30 MPa, and preferably at least 35 MPa, more preferably at least 40 MPa, more preferably at least 45 MPa, and most preferably at least 50 MPa, when measured at 80°C, 90% RH, and a stress gradient of 0.2 MPa / min. The reinforced ion-conducting membrane may, for example, have a secant modulus (at 8% strain) measured in the transverse direction of at least 30 MPa, preferably at least 35 MPa, more preferably at least 40 MPa, more preferably at least 45 MPa, and most preferably at least 50 MPa, when measured at 80°C, 90% RH, and a stress gradient of 0.2 MPa / min. The reinforced ion-conductive membrane may have a ratio of the secant modulus (at 8% strain) measured in the longitudinal direction to the secant modulus (at 8% strain) measured in the transverse direction in the range of 0.75 to 1.4, preferably in the range of 0.80 to 1.3, more preferably in the range of 0.90 to 1.2, and most preferably about 1.0. A ratio value close to 1.0 indicates an isotropic reinforced ion-conductive membrane. The secant modulus can be measured by sampling a rectangular strip of the reinforced ion-conductive membrane with dimensions of 60 mm x 6 mm, with the longer dimension parallel to either the longitudinal or transverse direction of the reinforced ion-conductive membrane, when measuring the secant modulus in the longitudinal or transverse direction, respectively. The thickness of the sample was measured using a low-force, high-precision gauge instrument (e.g., a Mitutoyo VL-50-B micrometer). This instrument uses a motorized spindle to take readings at a measuring force of 0.01 N, a temperature of 20°C ± 3°C, and a relative humidity (RH) of 30 to 50%. The sample was placed in a dynamic mechanical analyzer (DMA) (e.g., Q800 available from TA Instruments) equipped with a relative humidity control chamber and tensile (film) clamps, which were set approximately 16 mm apart and could be tightened to a torque of 3 in lbs (approximately 0.34 N m).DMA automation can be used to determine the length of the sample, and an experiment can be run that includes the following parameters / steps: preforce 0.001 N; measure length; set relative humidity to 90% and temperature to 80°C; hold for 120 minutes; measure length; ramp stress at 0.2 MPa / min. Here, "measure length" sets the length of the sample to 0% strain. The secant modulus is used because the peak slope of the stress / strain relationship does not occur at 0% strain under these conditions. The stress at 8% strain is divided by 0.08 to obtain the secant modulus value. The 8% strain value is chosen because this is typically the upper limit for in-plane swelling of reinforced membranes in fuel cell or electrolyzer operation.

[0061] The porous mat preferably has an open structure and a porosity in the range of 70-98%, preferably 80-95%, preferably 85-95%, and preferably 90-95%, where the porosity is determined from the ratio of the volumetric mass of the porous mat, determined from its geometric dimensions and its mass, to the known density of the polymer.

[0062] The porous mat preferably has a density of 1 g / m 2 ~7g / m 2 in the range of 1.5 g / m 2 ~4g / m 2 The average basis weight ranges from 1.0 to 1.0.

[0063] The porous mat in the electrolyte membrane preferably has a maximum thickness of 50 μm, 30 μm, preferably 25 μm, and preferably 20 μm. The porous mat in the electrolyte membrane preferably has a minimum thickness of about 2 μm, preferably 3 μm, and preferably 5 μm. The porous mat in the electrolyte membrane can have a thickness in a range including any combination of the aforementioned upper and lower limits. Preferably, the porous mat in the electrolyte membrane has an average thickness of 10 μm or less, more preferably 8.0 μm or less, and even more preferably 7.0 μm or less, or preferably 5 μm or less. Preferably, the porous mat in the electrolyte membrane has an average thickness of at least 2 μm, preferably at least 3 μm, and more preferably at least 5 μm. The average thickness of the porous mat in the electrolyte membrane can be in a range including any combination of the aforementioned upper and lower limits. The thickness of the porous mats was measured by cross-sectional imaging using a scanning electron microscope (SEM) (e.g., JEOL JSM-IT300LV SEM) after resin embedding, using an SEM integrated ruler to measure the edge-to-edge thickness of the mat.

[0064] In some preferred embodiments suitable for use in fuel cells or electrolyzers, particularly those suitable for use in fuel cells, the reinforced ion-conducting membrane can have an average thickness of less than 20 μm, preferably 16 μm or less, more preferably 15 μm or less, and most preferably 12 μm or less. In other preferred embodiments particularly suitable for use in electrolyzers, the ion-conducting membrane can have an average thickness ranging from 40 μm to 150 μm, preferably 50 μm to 100 μm, and more preferably 50 μm to 80 μm. The thickness of the reinforced ion-conducting membrane can be measured using a low-force, high-precision gauge instrument (e.g., the VL-50B Litematic™ available from Mitutoyo (UK) Ltd.), which provides a direct reading of the membrane thickness. Measurement readings are taken using a motorized spindle with a measuring force of 0.01 N. At least three readings are taken from different locations on the ion-conducting membrane layer (before the catalyst layer is added) at a temperature of 20°C ± 3°C and a relative humidity (RH) of 30-50%.

[0065] To form the porous mat, the nanofibers are formed onto a suitable substrate or surface, preferably by a spinning technique. For example, the nanofibers can be formed using electrospinning.

[0066] In a first embodiment of the process shown in Figure 2, the electrospinning formulation comprises at least one heterocyclic polymer, a crosslinker, and optionally a second polymer in a suitable solvent, such as an organic solvent or a suitable solvent mix. The solvent can comprise (or consist of) at least one of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), and / or dimethyl sulfoxide (DMSO), preferably DMAc and / or DMSO, and preferably DMAc. A suitable solvent mix can be a homogenous mixture of two or more solvents. The electrospinning formulation can be a solution or dispersion. The electrospinning formulation is extruded through a needle using a syringe pump, and the needle is maintained at a potential difference relative to the substrate / surface. The electrospun nanofibers are collected on a translationally and rotationally moving substrate (e.g., a rotating drum collector) set at a distance from the needle, for example, about 10-15 cm from the needle. The fiber morphology is achieved by controlling formulation parameters such as concentration, while the thickness and uniformity of the mat are controlled by deposition time and collector rotation / translation speed. The porous mat is treated to react the heterocyclic polymer with the crosslinking agent. The reactive groups on the heterocyclic polymer react with the reactive groups on the crosslinking agent. This reaction forms a crosslinked polymer comprising the heterocyclic backbone and linking chains described above. If a second polymer is present, the second polymer is preferably unreactive with the crosslinking agent during the crosslinking process.

[0067] The crosslinking treatment can be a heat treatment or a light treatment. Heat treatment can include heating the porous mat to a temperature of at least 80°C, preferably at least 85°C. Light treatment can include irradiating the porous mat with UV light to initiate the crosslinking reaction. In such cases, the electrospinning formulation can also include at least one photoinitiator.

[0068] The porous mat does not need to be subjected to any further processing, for example any densification process such as calendering or welding.

[0069] The crosslinker may be a liquid. A liquid crosslinker is preferably miscible with the solvent. Alternatively, the crosslinker may be a solid. Preferably, a solid crosslinker is soluble in the solvent.

[0070] The electrospinning formulation can further include a second polymer. In such embodiments, the porous mat of nanofibers can include a crosslinked polymer and a second polymer. Preferably, the second polymer is non-reactive with the crosslinking agent. That is, the second polymer does not chemically react with the crosslinking agent during the process of treating the porous mat.

[0071] In some embodiments, the method includes providing a further formulation for electrospinning, the further formulation including a second polymer. The second polymer is non-ionically conductive. Preferably, the second polymer is non-reactive with crosslinkers. The method can include simultaneously electrospinning the formulation and the further formulation onto a substrate.

[0072] The crosslinker may be present in the electrospinning formulation in an amount ranging from and including 1% to 20% by weight, preferably 3% to 15% by weight. The amount of crosslinker may be within a range defined by any combination of the upper and lower limits set forth above.

[0073] The formulation can include a heterocyclic polymer and a crosslinker in an amount such that the molar ratio of reactive groups on the heterocyclic polymer to reactive groups on the crosslinker ranges from and includes 25:1 to 1:2, preferably 20:1 to 1:1, and more preferably 10:1 to 1.5:1. The molar ratio of reactive groups on the heterocyclic polymer to reactive groups on the crosslinker can be within a range defined by any combination of the foregoing limits.

[0074] In a second embodiment of the process shown in Figure 3, the first electrospinning formulation comprises at least one heterocyclic polymer in a suitable solvent, such as an organic solvent or a suitable solvent mix. The solvent can comprise (or consist of) at least one of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), and / or dimethyl sulfoxide (DMSO), preferably DMAc and / or DMSO, and preferably DMAc. The first electrospinning formulation can be a solution or dispersion. The first electrospinning formulation is extruded through a needle using a syringe pump and applying high voltage to the needle. The electrospun nanofiber mat is collected on a translationally and rotationally moving substrate (e.g., a rotating drum collector) set at a distance from the needle, e.g., about 10-15 cm from the needle. Fiber morphology is obtained by controlling formulation parameters such as concentration, while mat thickness and uniformity are controlled by deposition time and collector rotation / translation speed.

[0075] The second formulation comprises (or consists of) a crosslinker and, optionally, a solvent. For example, the second formulation can be a liquid crosslinker, optionally in a suitable solvent. Alternatively, the second formulation can be a solid crosslinker dissolved in a suitable solvent. The solvent can be an organic solvent such as dimethylformamide (DMF), dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), methylisobutylketone (MIBK), acetone, benzene, butanol, ethylene glycol, ethanol, methanol, propanol, toluene, water, or xylene. Preferably, the second formulation is a solution. The second formulation is impregnated into the electrospun nanofiber mat. After impregnation, the porous mat is treated to react the heterocyclic polymer with the crosslinker, as described in connection with the first embodiment of the process. The heterocyclic polymer and crosslinker can be present in amounts such that the molar ratio of reactive groups on the heterocyclic polymer to reactive groups on the crosslinker ranges from, and includes, 25:1 to 1:2, preferably 20:1 to 1:1, and more preferably 10:1 to 1.5:1. The molar ratio of reactive groups on the heterocyclic polymer to reactive groups on the crosslinker can be within the range defined by any combination of the foregoing limits.

[0076] The porous mat does not need to be subjected to any further processing, for example any densification process such as calendering or welding.

[0077] The first formulation can further include a second polymer. The second formulation can further include a second polymer. In such embodiments, the nanofiber porous mat can be a mixture of the crosslinked polymer and the second polymer. Preferably, the second polymer is non-reactive with the crosslinking agent. That is, the second polymer does not chemically react with the crosslinking agent during the process of treating the porous mat.

[0078] The process of impregnating the porous mat with the second formulation can include spraying, electrospraying, screen printing, rotary screen printing, inkjet printing, brush coating, painting, dipping or dipping, bar coating, pad coating, gravure; gap coating techniques such as knife or doctor blade over roll (whereby the coating is applied to the substrate and then passes through a gap between a knife and a support roller); slot die (slot, extrusion) coating (whereby the coating is squeezed onto the substrate through a slot by gravity or under pressure); metering rod application such as Meyer bar and gravure coating.

[0079] The crosslinked polymer is preferably formed by crosslinking at least one heterocyclic polymer containing a basic functional group with a suitable crosslinking agent. The heterocyclic polymer contains at least one reactive group for reacting with the crosslinking agent to form the crosslinked polymer. For example, the reactive group can be a nucleophile such as an amine (e.g., a primary or secondary amine) or an imine. The reactive group can be part of a heterocycle.

[0080] Suitable heterocyclic polymers, preferably basic heterocyclic polymers, include polybenzimidazoles, poly(pyridines), poly(pyrimidines), polybenzothiazoles, polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, polytriazoles, polybenzoxazoles, polyoxazoles, polythiazoles, polypyrazoles, and derivatives thereof. Preferably, the heterocyclic polymer is selected from polybenzimidazoles, poly(pyridines), poly(pyrimidines), polybenzothiazoles, polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, polytriazoles, polyoxazoles, polythiazoles, polypyrazoles, and derivatives thereof. Preferably, the polymer is a functionalized polyazole or zwitterionic polyazole, such as polybenzimidazoles, polytriazoles, polythiazoles, and polydithiazoles, and derivatives thereof, most preferably polybenzimidazoles.

[0081] The crosslinker suitably contains at least two terminal epoxide groups, preferably at least two terminal glycidyl ether groups.

[0082] The crosslinking agent is

[0083] [ka] and may have a chemical formula selected from the group consisting of: During the ceremony, R 1 is an aliphatic C 1~15 Alkyl chain, preferably C 1~10 Alkyl chains, and more preferably C 1~6 Alkyl chains; alkoxy chains, e.g., [CH2CH2O] m , [CH2CH(CH3)O] m , [CH2CH2CH2O] m Glycol chains such as; aryloxy chains,

[0084] [ka] or a combination thereof; X and Y each independently represent O, [N(R 7 )], [OCH2CH2] n , [OCH2CH(CH3)] n , [O(CH2)3] n and no atom; R 2 and R 7 each independently represents an H, C in combination with a terminal epoxide group 1~5 Alkyl chain, and C 1~5 alkyl chains, m and n each independently range from 1 to 225, inclusive; R 3 and R 4 are each independently an aliphatic C 1~5 an alkyl chain; an alkoxy chain, e.g., a glycol chain; or no atom; R a , R b , R c , R d , R 5 , and R 6 are each independently selected from H, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, or tert-butyl.

[0085] Preferably, X and Y are each independently O and [N(R 7 In some embodiments, X and Y are the same, e.g., X and Y can both be O. In other embodiments, X and Y are both selected from the group of [N(R 7 ] can be.

[0086] Preferably, R 2 is H or C in combination with a terminal epoxide group 1~3 It is an alkyl chain, more preferably a CH2 in combination with a terminal epoxide group, ie, [CH2CHOCH2].

[0087] Preferably, R 3 and R 4 are each independently an aliphatic C 1~3 It is an alkyl chain or has no atoms.

[0088] Preferably, R 5 and R 6 are each independently selected from H or methyl. In some embodiments, R 5 and R 6 and R are both methyl. 5 and R 6 are both H.

[0089] Preferably, R 7 is H or C in combination with a terminal epoxide group 1~3 It is an alkyl chain, more preferably a CH2 in combination with a terminal epoxide group, ie, [CH2CHOCH2].

[0090] Preferably, R a , R b , R c , R d are each independently H or methyl, most preferably H.

[0091] Preferably, m and n each independently range from 1 to 150, more preferably from 1 to 130, more preferably from 1 to 100, and even more preferably from 1 to 50, inclusive.

[0092] Preferably, the crosslinking agent may be selected from the group consisting of 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, poly(ethylene glycol) diglycidyl ether, bisphenol A diglycidyl ether, bis[4-(glycidyloxy))phenyl]methane, bisphenol A propoxylate diglycidyl ether, N,N-diglycidyl-4-glycidyloxy)aniline, tris(2,3-epoxypropyl)isocyanurate, 1,3-butanediol diglycidyl ether.

[0093] 9 shows an exemplary cross-linking reaction in which a heterocyclic polymer 900 reacts with a cross-linker 910 to form a cross-linked polymer 920. Reactive groups 905 on the heterocyclic polymer 900 react with reactive groups 915 on the cross-linker 910. In this example, the heterocyclic polymer 900 is polybenzimidazole, the cross-linker 910 is 1,4-butanediol diglycidyl ether (BDDGE), and the reactive groups on the cross-linker are terminal epoxide groups. The cross-linked polymer 920 includes heterocyclic polymer backbones 930 and linking chains 940 that connect two heterocyclic polymer backbones 930 via linking groups 950.

[0094] The porous mat of nanofibers containing the crosslinked polymer is then impregnated with an ion-conducting polymer to form a reinforced ion-conducting membrane, such as a reinforced electrolyte membrane. The porous mat of nanofibers can be impregnated with the ion-conducting polymer as part of a roll-to-roll process. Such reinforced ion-conducting membranes have applications as membrane layers in electrochemical devices such as fuel cells and water electrolyzers.

[0095] The ion-conducting polymer may be a proton-conducting polymer or an anion-conducting polymer, such as a hydroxyl anion-conducting polymer. Preferably, the ion-conducting polymer is a proton-conducting polymer. Typically, the ion-conducting polymer contains sulfonic acid groups. Suitably, the ion-conducting polymer is a perfluorinated sulfonic acid ionomer, or a partially fluorinated or non-fluorinated hydrocarbon sulfonic acid or phosphate ionomer. Examples of suitable proton-conducting polymers include partially or fully fluorinated sulfonic acid polymers, such as perfluorosulfonic acid ionomers (e.g., Nafion® (EI DuPont de Nemours and Co.), Aciplex® (Asahi Kasei), Aquivion™ (Solvay Specialty Polymers), Flemion® (Asahi Glass Co.); or ionomers based on sulfonated hydrocarbons, such as those available as fumapem® P, E, or K series products from FuMA-Tech GmbH, JSR Corporation, Toyobo Corporation, and other companies. Examples of suitable anion-conducting polymers include A901 from Tokuyama Corporation and Fumasep® from FuMA-Tech GmbH. Examples of suitable ion-conducting polymers include FAA. Typically, ion-conducting polymers have an equivalent weight of about 1100 or less, typically about 900 or less, and preferably about 850 or less. Typically, ion-conducting polymers have an equivalent weight of at least about 450. The equivalent weight of an ion-conducting polymer can be easily determined using acid titration after hydroxide exchange. For example, a membrane sample can be vacuum-dried at about 110°C for 16 hours to obtain about 2 g of dried film. The film can then be immersed in about 30 mL of 0.1 N NaOH solution to replace the protons in the membrane with sodium ions. Neutralization titration can then be performed, for example, using 0.1 N hydrochloric acid, to determine the number of exchangeable protons, and thus the EW can be calculated.

[0096] The porous mat is essentially completely impregnated with the ion-conducting polymer to form the ion-conducting (electrolyte) membrane. By "essentially completely impregnated" is meant that at least 80%, preferably at least 90%, preferably at least 95%, and ideally 100% of the pores of the porous mat are filled with the ion-conducting polymer.

[0097] Preferably, there is excess ion-conducting polymer on both sides of the ion-conducting (electrolyte) membrane to aid adhesion to the catalyst layer.

[0098] A porous mat can be impregnated with an ion-conducting polymer by the following process: A layer of ion-conducting polymer (in solution / dispersion) is cast onto a support material. While the layer of ion-conducting polymer is still wet, a porous nanofiber mat is placed on the wet layer and the ion-conducting polymer is impregnated into one side of the porous mat. A further layer of ion-conducting polymer is applied to the second side of the porous mat and impregnated into the porous mat from the second side. The impregnated porous mat is dried and preferably annealed to form an ion-conducting (electrolyte) membrane.

[0099] The ion-conducting polymer solution / dispersion may contain additional components, such as short nanofibers, eg, 1-50 μm.

[0100] In the final electrolyte membrane of the present invention, the weight ratio of ion-conducting polymer to nanofibers is suitably greater than 70:30, and preferably greater than 90:10. Suitably, the ratio of ion-conducting polymer to nanofibers is less than 98:2. In this context, nanofibers refers to the nanofibers in the porous mat.

[0101] The thickness of the porous mat in the electrolyte membrane preferably spans at least 50%, preferably 60%, more preferably 70%, more preferably 80%, more preferably at least 85%, and most preferably at least 90% of the thickness of the final electrolyte membrane. The porous mat extends across the thickness of the membrane so that the thicknesses of the electrolyte membrane and the porous mat are essentially equal, although in practice the thickness of the electrolyte membrane may be slightly greater than the thickness of the porous mat such that the thickness of the porous mat is up to 99%, e.g., 95%, of the thickness of the electrolyte membrane.

[0102] Distributing the porous mat over at least 80% of the thickness of the electrolyte membrane improves the stabilization (mechanical and chemical) of the final electrolyte membrane.

[0103] The electrolyte membrane of the present invention may comprise two or more porous mats, for example two porous mats, distributed over at least 50% and preferably at least 80% of the thickness of the electrolyte membrane.

[0104] The present invention also provides a catalyzed electrolyte membrane comprising a catalyst layer and an electrolyte membrane of the present invention.

[0105] The catalyst layer comprises one or more electrocatalysts, which may independently be finely divided unsupported metal powders or supported catalysts, where small nanoparticles are dispersed on a conductive particulate carbon support. The electrocatalyst metals are preferably: (i) platinum group metals (platinum, palladium, rhodium, ruthenium, iridium, and osmium); (ii) gold or silver; (iii) base metals; or alloys or mixtures containing one or more of these metals or their oxides. A preferred electrocatalyst metal is platinum, which may be alloyed with other noble or base metals. Base metals are non-noble tin or transition metals. Noble metals are platinum group metals (platinum, palladium, rhodium, ruthenium, iridium, or osmium), gold, or silver. Suitable base metals include copper, cobalt, nickel, zinc, iron, titanium, molybdenum, vanadium, manganese, niobium, tantalum, chromium, and tin. Preferred base metals are nickel, copper, cobalt, and chromium. More preferred base metals are nickel, cobalt, and copper. When the electrocatalyst is a supported catalyst, the loading of metal particles on the carbon support material is suitably in the range of 10 to 90 wt. %, preferably 15 to 75 wt. %, of the weight of the resulting electrocatalyst.

[0106] The exact electrocatalyst used will depend on the reaction it is intended to catalyze, and its selection is within the ability of one skilled in the art.

[0107] The catalyst layer is preferably applied to the first and / or second side of the electrolyte membrane as an organic or aqueous ink. The ink may preferably contain other components, such as an ion-conducting polymer as described in EP 0 731 520, which are included to improve ionic conductivity within the layer. Alternatively, the catalyst layer may be applied by decal transfer of a pre-prepared catalyst layer.

[0108] The catalyst layer may further comprise additional components, including, but not limited to, catalysts that facilitate oxygen generation and are therefore beneficial in cell reversal situations and high potential excursions, or hydrogen peroxide decomposition catalysts. Examples of such catalysts and any other additives suitable for inclusion in the catalyst layer are known to those skilled in the art.

[0109] The present invention further provides a membrane electrode assembly comprising an electrolyte membrane of the present invention and a gas diffusion electrode on the first side and / or the second side of the electrolyte membrane.

[0110] The present invention further provides a membrane electrode assembly comprising a catalyzed electrolyte membrane of the present invention and a gas diffusion layer or porous transport layer overlying at least one catalyst layer.

[0111] The membrane electrode assembly may be fabricated in a number of ways, including but not limited to the following. (i) The ion-conducting (electrolyte) membrane of the present invention may be sandwiched between a first gas diffusion electrode or porous transport layer and a second gas diffusion electrode or porous transport layer (one anode and one cathode); (ii) A catalyzed ion-conducting (electrolyte) membrane of the present invention having a catalyst layer on one side thereof may be sandwiched between a gas diffusion layer or porous transport layer and a gas diffusion electrode or catalyst-coated porous transport layer, with the gas diffusion layer or porous transport layer contacting the side of the catalyzed ion-conducting (electrolyte) membrane having the catalyst component; or (iii) A catalyzed ion-conducting (electrolyte) membrane of the present invention having a catalyst component on both sides may be sandwiched between a first gas diffusion layer or porous transport layer and a second gas diffusion layer or porous transport layer, for example, between one gas diffusion layer and one porous transport layer.

[0112] The anode and cathode gas diffusion layers are preferably based on conventional gas diffusion substrates. Typical substrates include nonwoven papers or webs comprising a carbon fiber network and a thermosetting resin binder (e.g., the TGP-H series of carbon fiber papers available from Toray Industries Inc., Japan, or the H2315 series available from Freudenberg FCCT KG, Germany, or the Sigracet® series available from SGL Technologies GmbH, Germany, or Ballard Power Systems Examples of suitable carbon substrates include the AvCarb® series from Carbon Fiber Materials, Inc., or carbon fiber cloth. Carbon paper, web, or cloth can be further treated before being incorporated into an MEA to enhance either wettability (hydrophilicity) or moisture resistance (hydrophobicity). The nature of any optional treatment depends on the type of fuel cell and the operating conditions used. The substrate can be made more wettable by incorporating materials such as amorphous carbon black by impregnation from a liquid suspension, or made more hydrophobic by impregnating the substrate's pore structure with a colloidal suspension of a polymer such as PTFE or polyfluoroethylenepropylene (FEP), followed by drying and heating above the polymer's melting point. For applications such as PEMFCs, a microporous layer may be applied to the gas diffusion substrate on the side that will contact the electrode catalyst layer. The microporous layer typically comprises a mixture of carbon black and a polymer such as polytetrafluoroethylene (PTFE).

[0113] The porous transport layer is preferably based on a conventional porous transport substrate such as titanium mesh.

[0114] The present invention further provides an electrochemical device comprising an enhanced ion-conducting membrane (e.g., an electrolyte membrane), a catalyzed enhanced ion-conducting membrane, or a membrane electrode assembly as described above. The electrochemical device can be a fuel cell, such as a proton exchange membrane fuel cell. The electrochemical device can be an electrolysis device, such as a water electrolysis device.

[0115] The present invention will now be further described with reference to the following examples, which are intended to be illustrative and not limiting. [Example]

[0116] Formulations suitable for electrospinning containing poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole] (PBI), a crosslinker (e.g., 1,4-butanediol diglycidyl ether (BDDGE) or bisphenol A diglycidyl ether (BADGE)), and / or poly(vinylidene difluoride) (PVDF) were prepared in dimethylacetamide (DMAc) as detailed in Table 1.

[0117] [Table 1]

[0118] The formulations were electrospun onto the substrate using the following parameters: applied voltage 15 kV, flow rate 0.15 mL / hr, needle size 22 gauge, needle-collector distance 10 cm, drum collector rotation speed 800 rpm, and translation speed 10 mm / sec. The electrospun mat was removed from the substrate.

[0119] For cross-linking, the porous mat was heat treated by holding it at a temperature ranging from 85°C to 120°C for 1 to 24 hours until the cross-linking reaction was complete.

[0120] Table 2 shows some properties of the porous mats made using the formulations. All of the crosslinked porous mats of the Examples and Comparative Examples were non-ionically conductive.

[0121] [Table 2]

[0122] The term "tear index" as used herein refers to the average basis weight (g / m 2 It is used to refer to the maximum tear strength (mN) divided by the tensile strength (mN).

[0123] Figure 4 shows a scanning electron microscope (SEM) image of the electrospun mat of Example 2. The nanofibers cross and intertwine with each other. The nanofibers are randomly oriented in the xy plane (i.e., in planar directions). The crosslinked electrospun mat contains nanofibers with fiber diameters ranging from approximately 200 to 700 nm.

[0124] Figures 5-7 show plots of force (N) as a function of elongation (mm) before and after crosslinking. In both cases, the porous mats had significantly higher maximum tear strength after crosslinking. Tear strength can be determined by performing a trouser tear test according to ASTM D1938. In these examples, test specimens were prepared by cutting 70 x 30 mm specimens from the porous mat. A 25 mm slit was then cut from the midpoint of the short edge along the central axis to form two tongues. The two tongues were clamped in the grips of a universal mechanical testing machine equipped with a 5 kN load cell and pulled at a crosshead speed of 50 mm / min. Results were recorded as graphs of force (N) versus elongation (mm). The maximum tear strength was recorded at an elongation of up to 30 mm.

[0125] 8 shows plots of force (N) as a function of elongation (mm) for Examples 2, 5, and 6 and Comparative Examples 4 and 5. Forming a porous mat containing nanofibers of crosslinked polymer provided significant improvements in tear strength compared to Comparative Example 4 (i.e., a non-crosslinked PBI mat) and Comparative Example 5 (i.e., a blend of non-crosslinked PBI and PVDF). Combinations including a crosslinked polymer with a second polymer (e.g., PVDF) unexpectedly provided significant improvements in maximum tear strength at the same basis weight.

[0126] After heat treatment, the crosslinked porous mat was insoluble in organic solvents such as dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO).

[0127] Additionally, the water contact angles on the surface of the crosslinked porous mats of Examples 1 to 5 were lower after the crosslinking treatment. For example, the water contact angles measured for Comparative Example 4 and Example 2 were 113° and 99°, respectively. The crosslinked porous mats possessed beneficial properties for facilitating impregnation with ion-conducting polymers, such as partially or fully fluorinated sulfonic acid ion-conducting polymers. Contact angles were measured using a Drop Shape Analyzer, DSA30, from KRUSS GmbH, and Kruss DSA4 software. A 6 μL droplet of deionized water was dispensed onto the surface of the nanofiber mat at room temperature (20–25°C), and 30 images were taken at a frequency of 1 image per second. The drop shape and contact angle were determined using Kruss DSA4 software.

[0128] The porous mat of Example 1 had an ultimate tensile strength of 37 MPa and a strain at break of 49% when measured in the machine direction, and an ultimate tensile strength of over 45 MPa when measured in the cross direction. The porous mat of Example 3 had an ultimate tensile strength of about 54 MPa and a strain at break of 56% when measured in the machine direction. The porous mat of Example 3 had an ultimate tensile strength of about 44 MPa and a strain at break of 14% when measured in the cross direction. In contrast, the porous mat of Comparative Example 4 had an ultimate tensile strength of 4 MPa and a strain at break of 65-75% when measured in the machine direction, and an ultimate tensile strength of 15 MPa and a strain at break of 13% when measured in the cross direction. The mechanical properties of the porous mats of Examples 1 and 3 were more advantageous for use as reinforcing components in roll-to-roll manufacturing processes than the porous mat of Comparative Example 4.

[0129] Impregnation with ion-conducting polymers The porous mat can be used as a reinforcing component as part of a roll-to-roll process for producing a reinforced ion-conducting membrane in which an ion-conducting polymer is impregnated into the porous mat. A typical process involves forming the reinforced ion-conducting membrane through a series of coating passes in which a dispersion of an ion-conducting polymer (e.g., a PFSA ion-conducting polymer) is deposited and then dried before a subsequent coating pass. For example, three coating passes can be used. The porous mat can be introduced to the ion-conducting membrane as part of the second coating pass so that the dispersion of the ion-conducting polymer impregnates the pores of the porous mat. In some embodiments, the process can include more or fewer coating passes, for example, two coating passes, to achieve a reinforced ion-conducting membrane with the same or similar structure.

[0130] The porous mat of the present invention has advantageous properties for industrial-scale processing, such as roll-to-roll processing. The resulting reinforced ion-conducting membrane comprises a reinforced membrane layer (i.e., comprising a porous mat) sandwiched between two unreinforced membrane layers. Such reinforced ion-conducting membranes can have applications as catalyzed reinforced ion-conducting membranes, membrane electrode assemblies, or electrolyte membrane layers in electrochemical devices such as fuel cells and water electrolyzers.

[0131] The porous mat of Example 2 was used as a reinforcing component in a roll-to-roll process to fabricate a membrane electrode assembly (MEA1). A dispersion of an ion-conducting polymer (3M, EW800) was impregnated into the porous mat and dried to form a reinforced ion-conducting membrane (Mem1). The thickness of the reinforcing component in the membrane was approximately 5 μm. The total membrane thickness was approximately 15 μm. The reinforced ion-conducting membrane (Mem1) had a secant modulus in the machine direction (MD) of 52.2 MPa (at 8% strain) and a secant modulus in the transverse direction (TD) of 52.9 MPa (at 8% strain) (shown in FIG. 10). The reinforced ion-conducting membrane (Mem1) of Example 2 exhibited similar elastic moduli in both the machine and transverse directions, indicating a substantially isotropic membrane. For example, the ratio of the secant modulus in the machine direction (at 8% strain) to the secant modulus in the transverse direction (at 8% strain) was 0.99. By comparison, a 15 μm thick membrane reinforced using the nanofiber mat of Comparative Example 5 (Mem2) exhibited a ratio of longitudinal secant modulus (at 8% strain) to transverse secant modulus (at 8% strain) of 0.78 (shown in FIG. 10). As a further comparison, a known expanded polytetrafluoroethylene (ePTFE) reinforcing element (basis weight 4.7 g / m) 2 The ratio of the longitudinal secant modulus (at 8% strain) to the transverse secant modulus (at 8% strain) of a comparative 15 μm-thick reinforced ion-conducting membrane (Mem3) using ePTFE (Mem1) was 1.5, indicating a higher degree of anisotropy compared to Mem1 and Mem2 (shown in FIG. 10 ). Furthermore, the transverse secant modulus (at 8% strain) of Mem1 was 1.85 times higher than the longitudinal secant modulus (at 8% strain) of the comparative ePTFE-reinforced membrane (Mem3). Thus, the present invention allows for the use of thinner reinforcement components (and thus thinner ion-conducting membranes) while still maintaining acceptable mechanical properties, such as tear strength and tensile strength, required for industrial processing (e.g., roll-to-roll manufacturing). In turn, thinner ion-conducting membranes are expected to result in improved ionic conductivity across the membrane and improved battery performance. The secant modulus (at 8% strain) was measured using the method described above.

[0132] Mem1 and Mem3 were used to fabricate membrane electrode assemblies MEA1 and MEA2, respectively. The cathode catalyst layer (0.4 mg Pt / cm 2 % Pt / C with a loading of 0.08 mg Pt / cm 2 Catalyst-coated ion-conducting membranes (50 cm) were prepared by transferring 60 wt. % Pt / C and iridium tantalum oxide oxygen evolution reaction (OER) catalysts with a loading of 1000 μm onto both sides of the ion-conducting membrane (15 μm thick) using a decal transfer process. 2 (having an active area of ​​1000 nm) was prepared.

[0133] A gas diffusion layer (Sigracet 22 BB, commercially available from SGL Carbon) was applied to each side of each catalyst-coated ion-conducting membrane to form a membrane electrode assembly (MEA). The gas diffusion layers used were carbon fiber paper with a carbon-containing hydrophobic microporous layer and PTFE applied to the side in contact with the catalyst-coated ion-conducting membrane.

[0134] MEA durability test Durability testing was performed on a test stand available from Greenlight Innovations at a 50cm 2 Combined Open Circuit Voltage-RH Cycling (COCV-RH) Accelerated Stress Test: The COCV-RH test was performed using three general stages: conditioning, diagnostic, and stress conditions: 80°C, 100 kPa on the anode and cathode, 100% RH inlet on the anode and cathode for 10 hours, 500 mA / cm 2 The cell was conditioned by drawing a current density of 1000 kJ / s. After adjusting the diagnostic and stress conditions, the steps were alternated until the sample failed.

[0135] Diagnostics were performed at 80°C and completed primarily at 100% RH on the OCV, anode, and cathode, and three pressure conditions: 50 kPag / 50 kPag (point 1), 50 kPag / ambient (point 2), and ambient / ambient (point 3) (anode / cathode).

[0136] The stress conditions were OCV, 90°C, ambient pressure on the anode and cathode, cycling between 0% relative humidity (RH) and 100% RH conditions (1,500 wet / dry cycles per stage), followed by a return to the diagnostic stage.

[0137] The open-circuit voltage measured at point 2 subtracted from the open-circuit voltage measured at point 3 (during the diagnostic phase) is a parameter that can be used as a proxy for gas crossover. FIG. 11 shows this OCV response to removal of differential pressure (V) as a function of completed wet / dry cycles for MEA1 and a comparative ePTFE-reinforced membrane electrode assembly (MEA2). A part was considered to have failed when the plot of the OCV response to removal of differential pressure as a function of completed wet / dry cycles exhibited a sudden change in slope. MEA1 exhibited significantly improved durability performance during MEA durability testing compared to the conventional ePTFE-reinforced membrane (MEA2).

[0138] Without wishing to be bound by theory, the inventors believe this may be due to the phase separation and continuity of the electrospun mat, as well as ionic crosslinking (acid-base interactions, or hydrogen bonding) between the ion-conducting polymer and the surface of the nanofibers in the electrospun web. In addition, the electrospun mat allows for greater swelling in the thickness direction because the fibers can move relative to each other in the thickness direction, but swelling in the in-plane direction is limited because the fibers are not elastic.

[0139] Furthermore, the heterocyclic polymers used to form the electrospun mats have antioxidant properties and can contribute to the stability of the electrolyte membrane by scavenging damaging species such as peroxy free radicals. Due to these antioxidant properties, it may no longer be necessary to incorporate antioxidants or hydrogen peroxide decomposition catalysts (e.g., ceria) into the membrane.

Claims

1. 1. A reinforced ion-conducting membrane comprising: an ion-conducting polymer; a porous mat of nanofibers impregnated with said ion-conducting polymer; the nanofibers comprise a crosslinked polymer, the crosslinked polymer being ionically non-conductive; a heterocyclic polymer backbone containing a basic functional group; and a linking chain connecting at least two of the heterocyclic polymer backbones via a linking group; The porous mat of nanofibers has a viscosity of at least 15 mN m ２ A reinforced ion-conducting membrane having a tear index of 1 / g.

2. Each linking group (A) is independently 【Chemistry 1】 is selected from the group consisting of In the formula, C １ 10. The reinforced ion-conducting membrane of claim 1, wherein is chemically bonded to the heterocyclic polymer backbone.

3. The linking chain is 【Chemistry 2】 having a chemical formula selected from the group consisting of: wherein A is the linking group, and each linking group A is independently: 【Transformation 3】 is selected from the group consisting of R １ But aliphatic C １～１５ Alkyl chain, preferably C １～１０ Alkyl chains, and more preferably C １～６ Alkyl chains; alkoxy chains, for example, [CH ２ CH ２ O] ｍ , [CH ２ CH (CH ３ ) O] ｍ , [CH ２ CH ２ CH ２ O] ｍ glycol chains such as; aryloxy chains, 【Chemistry 4】 or a combination thereof; X and Y are each independently O, [N(R ７ ) ], [OCH ２ CH ２ ] ｎ , [OCH ２ CH (CH ３ )] ｎ , [O(CH ２ ) ３ ] ｎ and no atom; R ２ and R ７ are each independently H, C １～５ Alkyl chains, and (CH ２ ) ｐ A is selected from the group consisting of m and n each independently range from 1 to 225, inclusive; R ３ and R ４ each independently represents an aliphatic C １～５ an alkyl chain; an alkoxy chain, e.g., a glycol chain; or no atom; R ａ , R ｂ , R ｃ , R ｄ , R ５ , and R ６ are each independently selected from H, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, or tert-butyl; 3. The reinforced ion-conducting membrane of claim 1 or 2, wherein p is an integer ranging from 1 to 5, inclusive.

4. The linking chain is 【Transformation 5】 wherein q is in the range of 1 to 225, inclusive, and r is in the range of 1 to 225, inclusive.

5. The reinforced ion-conducting membrane of any one of claims 1 to 4, wherein the linking chains are aliphatic.

6. 6. The reinforced ion-conducting membrane of claim 5, wherein the connecting chain is a linear or branched aliphatic chain.

7. C １ The reinforced ion-conducting membrane of any one of claims 1 to 6, wherein is chemically bonded to a heteroatom of the heterocyclic polymer backbone.

8. 8. The reinforced ion-conducting membrane of any one of claims 1 to 7, wherein the crosslinked polymer is insoluble in organic solvents such as dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), and dimethylsulfoxide (DMSO).

9. The reinforced ion-conducting membrane of any one of claims 1 to 8, wherein the basic functional groups comprise nitrogen-containing basic functional groups.

10. 10. The reinforced ion-conducting membrane of any one of claims 1 to 9, wherein the heterocyclic polymer backbone is selected from the group consisting of polybenzimidazoles, poly(pyridines), poly(pyrimidines), polybenzothiazoles, polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, polytriazoles, polyoxazoles, polybenzoxazoles, polythiazoles, polypyrazoles, and derivatives thereof.

11. 11. The reinforced ion-conducting membrane of claim 10, wherein the heterocyclic polymer backbone is selected from the group consisting of polybenzimidazoles, polytriazoles, polythiazoles, polydithiazoles, and derivatives thereof.

12. The reinforced ion-conducting membrane of any one of claims 1 to 11, wherein the nanofibers are spun nanofibers.

13. 13. The reinforced ion-conducting membrane of any one of claims 1 to 12, wherein the nanofibers further comprise a second polymer, the second polymer being non-ion-conductive.

14. 14. The reinforced ion-conducting membrane of claim 13, wherein the second polymer is selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyimide (PI), polyetherimide (PEI), poly(aryl ether ketone) (PAEK), poly(aryl ether sulfone), poly(phenylene sulfide) (PPS), polyvinylpyrrolidone (PVP).

15. 15. The reinforced ion-conducting membrane of any one of claims 1 to 14, wherein the porous mat of nanofibers has an ultimate tensile strength of at least 25 MPa when measured in the machine direction and / or the cross direction, the machine direction and the cross direction being perpendicular.

16. 16. The reinforced ion-conducting membrane of any one of claims 1 to 15, wherein the ratio of the ultimate tensile strength of the porous mat of nanofibers measured in the machine direction to the ultimate tensile strength of the porous mat of nanofibers measured in the cross direction is in the range of 0.5 to 2, and the machine direction and the cross direction are perpendicular.

17. 17. The reinforced ion-conducting membrane of any one of claims 1 to 16, wherein the porous mat of nanofibers has a strain at break of at least 5% when measured in the machine direction and / or the cross direction at a temperature of 20°C ± 3°C, a relative humidity of 30 to 50%, and an extension rate of 20 mm / min, wherein the machine direction and the cross direction are perpendicular.

18. 1. A reinforced ion-conducting membrane comprising: an ion-conducting polymer; a porous mat of nanofibers impregnated with said ion-conducting polymer; the nanofibers comprise a crosslinked polymer, the crosslinked polymer being ionically non-conductive; a heterocyclic polymer backbone containing a basic functional group; and a linking chain connecting at least two of the heterocyclic polymer backbones via a linking group; 1. A reinforced ion-conducting membrane, wherein the porous mat has an average thickness of 10 μm or less, and the reinforced ion-conducting membrane has a secant modulus at 8% strain of at least 30 MPa when measured in the machine direction at 80° C. and 90% RH, and a secant modulus at 8% strain of at least 30 MPa when measured in the cross direction at 80° C. and 90% RH, and the machine direction and the cross direction are perpendicular.

19. 20. The reinforced ion-conducting membrane of claim 18, wherein the porous mat has an average thickness of 7 μm or less.

20. The reinforced ion-conducting membrane of any one of claims 18 to 20, having an average thickness of less than 16 μm.

21. 21. An electrochemical device, such as a fuel cell or electrolyzer, comprising the reinforced ion-conducting membrane of any one of claims 1 to 20.

22. 1. A method for producing a reinforced ion-conducting membrane, said method comprising: providing a substrate; Providing a formulation for electrospinning, the formulation comprising a solvent, a crosslinker, and a heterocyclic polymer comprising a basic functional group; electrospinning the formulation onto the substrate to form a porous mat of nanofibers; treating the porous mat to react the heterocyclic polymers with the crosslinking agent, thereby forming a crosslinked polymer comprising heterocyclic polymer backbones containing basic functional groups and linking chains connecting at least two of the heterocyclic polymer backbones via linking groups; impregnating said porous mat with an ion-conducting polymer.

23. 23. The method of claim 22, wherein the crosslinker is a liquid and miscible with the solvent.

24. 23. The method of claim 22, wherein the crosslinker is a solid and soluble in the solvent.

25. 25. The method of any one of claims 22 to 24, wherein the formulation further comprises a second polymer, the second polymer being non-ionically conductive.

26. The method comprises: providing a further formulation for electrospinning, said further formulation comprising a second polymer, said second polymer being ionically non-conductive; The method of any one of claims 22 to 24, further comprising the step of co-electrospinning the formulation and the further formulation onto the substrate.

27. 27. The method of claim 25 or 26, wherein the second polymer is non-reactive with the cross-linking agent during the step of treating the porous mat.

28. 28. The method of any one of claims 22 to 27, wherein the formulation comprises the heterocyclic polymer and the crosslinker in amounts such that the molar ratio of reactive groups on the heterocyclic polymer to reactive groups on the crosslinker ranges from, and includes, 25:1 to 1:

2.

29. 1. A method for producing a reinforced ion-conducting membrane, said method comprising: providing a substrate; Providing a first formulation for electrospinning, the first formulation comprising a solvent and a heterocyclic polymer comprising a basic functional group; electrospinning the first formulation onto the substrate to form a porous mat of nanofibers; providing a second formulation comprising a cross-linking agent; impregnating the porous mat with the second formulation and then treating the porous mat to react the heterocyclic polymers with the crosslinking agent, thereby forming a crosslinked polymer comprising heterocyclic polymer backbones containing basic functional groups and linking chains connecting at least two of the heterocyclic polymer backbones via linking groups; impregnating said porous mat with an ion-conducting polymer.

30. 30. The method of claim 29, wherein the first formulation further comprises a second polymer and / or the second formulation further comprises a second polymer, wherein the second polymer is non-ionically conductive.

31. 31. The method of claim 29 or 30, wherein the step of impregnating the porous mat with the second formulation comprises electrospraying.

32. The method of any one of claims 22 to 31, wherein the crosslinker comprises at least two terminal epoxide groups.

33. The crosslinking agent is 【Transformation 6】 having a chemical formula selected from the group consisting of: During the ceremony, R １ But aliphatic C １～１５ Alkyl chain, preferably C １～１０ Alkyl chains, and more preferably C １～６ Alkyl chains; alkoxy chains, for example, [CH ２ CH ２ O] ｍ , [CH ２ CH (CH ３ ) O] ｍ , [CH ２ CH ２ CH ２ O] ｍ glycol chains such as; aryloxy chains, 【Transformation 7】 or a combination thereof; X and Y are each independently O, [N(R ７ ) ], [OCH ２ CH ２ ] ｎ , [OCH ２ CH (CH ３ )] ｎ , [O(CH ２ ) ３ ] ｎ and no atom; R ２ and R ７ each independently containing H, C together with a terminal epoxide group １～５ Alkyl chain, and C １～５ alkyl chains, m and n each independently range from 1 to 225, inclusive; R ３ and R ４ each independently represents an aliphatic C １～５ an alkyl chain; an alkoxy chain, e.g., a glycol chain; or no atom; R ５ and R ６ is each independently selected from H, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, or tert-butyl.

34. 34. The method of any one of claims 22 to 33, wherein the crosslinking agent is selected from the group consisting of 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, poly(ethylene glycol) diglycidyl ether, bisphenol A diglycidyl ether, bis[4-(glycidyloxy)phenyl]methane, bisphenol A propoxylate diglycidyl ether, N,N-diglycidyl-4-glycidyloxy)aniline, tris(2,3-epoxypropyl)isocyanurate, and 1,3-butanediol diglycidyl ether.

35. The method of any one of claims 22 to 34, wherein the step of treating the porous mat to react the heterocyclic-based polymer and the crosslinking agent is a heat treatment.

36. A reinforced ion-conducting membrane obtainable by the method according to any one of claims 22 to 35.

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