Enhanced ion conducting membranes

Abstract

According to the present invention there is provided an enhanced ion conducting membrane, the enhanced ion conducting membrane comprising: an ion conducting polymer; and a porous mat of nanofibers. The porous mat of nanofibers is impregnated with an ionically conductive polymer. The nanofibers comprise a cross-linked polymer, wherein the cross-linked polymer is ionically non-conductive. The cross-linked polymer comprises a heterocycle-based polymer backbone comprising a basic functional group, and a linking chain linking at least two heterocycle-based polymer backbones via a linking group. The porous mat of nanofibers has a tear index of at least 15 mN m2 / g.

Description

Technical Field

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

[0002] A fuel cell is an electrochemical cell comprising 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. An electrochemical reaction occurs at the electrodes, and the chemical energy of the fuel and oxidant is converted into electrical energy and heat. An electrocatalyst is 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 generally classified according to the nature of the electrolyte used. The electrolyte is usually a solid polymer membrane, where the membrane is electrically insulating but ionically conductive. In a proton exchange membrane fuel cell (PEMFC), the membrane is proton conductive and the protons generated at the anode are transported across the membrane to the cathode where they combine with oxygen to form water.

[0004] Electrolyzer is an electrochemical device for electrolyzing water to produce high purity hydrogen and oxygen. Electrolyzer can be operated in alkaline and acidic systems. Those electrolyzers using solid proton conductive polymer electrolyte membrane or proton exchange membrane (PEM) are called proton exchange membrane water electrolyzer (PEMWE). Those electrolyzers using solid anion conductive polymer electrolyte membrane or anion exchange membrane (AEM) are called anion exchange membrane water electrolyzer (AEMWE).

[0005] The main component of a fuel cell or water electrolyzer is a membrane electrode assembly (MEA). An MEA is typically composed of five layers. The middle layer is a polymer ion-conducting membrane. On either side of the ion-conducting membrane there is an electrocatalyst layer, which contains an electrocatalyst designed for a specific electrolysis reaction. Finally, adjacent to each electrocatalyst layer is a gas diffusion layer and / or a porous transport layer, which is porous and conductive and allows reactants to reach the electrocatalyst layer and conduct the current generated by the electrochemical reaction.

[0006] Conventional ion-conducting membranes used in PEMFC or PEMWE are usually formed of sulfonated perfluorinated polymer materials, generally 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. Due to the advantages obtained (improved ionic conductivity, improved water transport, etc.), the latest developments in fuel cells and electrolyzers require thinner membranes, and therefore, in order to provide the mechanical properties required to increase resistance to premature failure, reinforcements (usually expanded polytetrafluoroethylene (ePTFE)) are embedded in the membrane.

[0007] Although such reinforced membranes generally have lower proton conductivity when compared to unreinforced membranes of the same thickness, the improvement in mechanical properties enables the use of thinner films with lower electrical resistance.

[0008] Other types of reinforcements have also been proposed, for example as disclosed in WO2011 / 149732 and WO2016 / 020668.

[0009] Li and Liu; J Mater. Chem. A., 2013, 1, 1171 discloses a polyelectrolyte composite membrane of polybenzimidazole and cross-linked polybenzimidazole-polybenzoxazine electrospun nanofibers for proton exchange membrane fuel cells. The membrane is doped with 85% phosphoric acid, which makes the polymer of the composite membrane proton conductive (including the polymer of the nanofibers). It is desirable to develop an enhanced ion conductive membrane with improved mechanical properties. Summary of the invention

[0010] Although enhanced membranes (such as those described above) have allowed the use of thinner membranes while maintaining mechanical strength, drawbacks remain. In particular, limitations are seen in actual operations, where humidity conditions can change very dramatically from relatively high levels (such as when starting from cold conditions) to very dry levels (operating at maximum rated power density) in a short period of time, where the membrane can degrade to levels higher than acceptable. In accelerated stress tests designed to simulate and accelerate this operation, wet / dry cycle accelerated stress tests cause swelling / de-swelling of the membrane so that these membrane degradation effects can be observed more quickly.

[0011] It is an object of the present invention to provide an improved enhanced ion conducting membrane suitable for use in electrochemical devices such as fuel cells and electrolysers and in particular having improved properties for large scale manufacture.

[0012] Therefore, in a first aspect of the present invention, there is provided an enhanced ion conducting membrane, the enhanced ion conducting membrane comprising:

[0013] Ion-conducting polymers; and

[0014] a porous mat of nanofibers impregnated with an ionically conductive polymer;

[0015] wherein the nanofibers comprise a cross-linked polymer, wherein the cross-linked polymer is ionically non-conductive and comprises:

[0016] a heterocyclic-based polymer backbone comprising basic functional groups, and

[0017] a linking chain connecting at least two heterocycle-based polymer backbones via a linking group,

[0018] The porous mat of nanofibers has a strength of at least 15 mN m 2 / g tear index.

[0019] The porous mat of nanofibers (sometimes also referred to as a "nanofiber mat") provides mechanical reinforcement to the ion-conducting membrane. The porous mat of nanofibers may be in the form of a non-woven fabric material.

[0020] The term tear index (mN m 2 / g) refers to the maximum tear strength (mN) divided by the basis weight (g / m 2 ). The tear strength can be measured according to ASTM D1938.

[0021] In a second aspect, there is provided an enhanced ion conducting membrane comprising:

[0022] Ion-conducting polymers; and

[0023] a porous mat of nanofibers impregnated with an ionically conductive polymer;

[0024] wherein the nanofibers comprise a cross-linked polymer, wherein the cross-linked polymer is ionically non-conductive and comprises:

[0025] a heterocyclic-based polymer backbone comprising basic functional groups, and

[0026] A linking chain connecting at least two heterocycle-based polymer backbones via a linking group, wherein each linking group (A) is independently selected from the group comprising:

[0027]

[0028] Among them C 1 Chemically bonded to the heterocycle based polymer backbone.

[0029] In another aspect, there is provided an enhanced ion conducting membrane comprising:

[0030] Ion-conducting polymers; and

[0031] a porous mat of nanofibers impregnated with an ionically conductive polymer;

[0032] wherein the nanofibers comprise a cross-linked polymer, wherein the cross-linked polymer is ionically non-conductive and comprises:

[0033] a heterocyclic-based polymer backbone comprising basic functional groups, and

[0034] a linking chain connecting at least two heterocycle-based polymer backbones via a linking group;

[0035] wherein the porous pad has an average thickness of 10 μm or less, and the enhanced ion-conductive membrane has a secant elastic modulus of at least 30 MPa at 8% strain when measured in the machine direction at a temperature of 80°C and 90% relative humidity (RH), and the enhanced ion-conductive membrane has a secant elastic modulus of at least 30 MPa at 8% strain when measured in the transverse direction at a temperature of 80°C and 90% RH, wherein the machine direction and the transverse direction are perpendicular.

[0036] In a third aspect, there is provided a method of producing an enhanced ion conducting membrane, the method comprising the steps of:

[0037] providing a substrate;

[0038] A formulation for electrospinning is provided, the formulation comprising a solvent, a cross-linking agent and a heterocyclic-based polymer comprising a basic functional group,

[0039] electrospinning the formulation onto a substrate to form a porous mat of nanofibers;

[0040] treating the porous pad to react the heterocyclic-based polymer and the cross-linking agent to form a cross-linked polymer comprising a heterocyclic-based polymer backbone chain containing a basic functional group and a linking chain connecting at least two heterocyclic-based polymer backbone chains via a linking group; and

[0041] The porous mat is impregnated with an ion-conducting polymer.

[0042] In a fourth aspect, the present invention provides a method for producing an enhanced ion conducting membrane, the method comprising the steps of:

[0043] providing a substrate;

[0044] providing a first formulation for electrospinning, the first formulation comprising a solvent and a heterocyclic-based polymer comprising a basic functional group,

[0045] electrospinning the first formulation onto a substrate to form a porous mat of nanofibers;

[0046] providing a second formulation comprising a cross-linking agent;

[0047] impregnating the porous pad with a second formulation, and then treating the porous pad to react the heterocyclic-based polymer and the cross-linking agent to form a cross-linked polymer comprising a heterocyclic-based polymer backbone chain containing a basic functional group and a linking chain connecting at least two heterocyclic-based polymer backbone chains via a linking group; and

[0048] The porous mat is impregnated with an ion-conducting polymer.

[0049] In a fifth aspect, there is provided a cross-linkable porous mat of nanofibers, the nanofibers comprising:

[0050] a heterocyclic-based polymer comprising a basic functional group, wherein the heterocyclic-based polymer is ionically non-conductive; and

[0051] Crosslinking agents comprising at least two terminal epoxy groups are preferred.

[0052] In a sixth aspect, there is provided a reinforcing component for reinforcing an ion-conducting membrane, the reinforcing component comprising:

[0053] A porous mat of nanofibers comprising a cross-linked polymer, wherein the cross-linked polymer is ionically non-conductive and comprising:

[0054] a heterocyclic-based polymer backbone comprising basic functional groups, and

[0055] A connecting chain connecting at least two heterocyclic-based polymer backbones via a connecting group, wherein the porous mat of nanofibers has a molecular weight of at least 15 mN m 2 / g tear index. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 is a schematic diagram of an ion conductive membrane of the present invention;

[0057] Figure 2 is a schematic diagram of an exemplary method of the present invention;

[0058] Figure 3 is a schematic diagram of an exemplary method of the present invention;

[0059] Figure 4 is a SEM image of a porous mat of nanofibers according to an embodiment of the present invention;

[0060] Figures 5 to 8 is a graph of force (N) as a function of extension (mm);

[0061] Fig. 9 is a diagram of an exemplary reaction between PBI and a cross-linking agent;

[0062] Fig.10is a graph of stress versus strain of the enhanced ion conducting membrane measured in the machine direction (MD) and transverse direction (TD) at 80°C and 90% RH; and

[0063] Fig.11 is a graph of the OCV response to the removal of the pressure differential as a function of the number of stress cycles. DETAILED DESCRIPTION

[0064] The preferred and / or optional features of the present invention will now be described. Unless the context otherwise requires, any aspect of the present invention may be combined with any other aspect of the present invention. Unless the context otherwise requires, any of the preferred or optional features of any aspect may be combined with any aspect of the present invention individually or in combination.

[0065] The present invention provides an enhanced ion conducting membrane, such as an electrolyte membrane, comprising a porous mat of nanofibres impregnated with an ion conducting polymer. Preferably, the porous mat is substantially completely impregnated with the ion conducting polymer. Figure 1 A schematic diagram of an ion conducting membrane of the present invention is shown. Preferably, the enhanced ion conducting membrane is an enhanced proton conducting membrane.

[0066] The porous mat provides mechanical reinforcement for the ion-conducting membrane. The porous mat is suitably formed of entangled nanofibers. The nanofibers are ion-non-conductive. For example, the nanofibers are suitably free of sulfonic acid groups and / or phosphate groups. The ion-conducting membrane is suitably free of phosphoric acid. The nanofibers include cross-linked polymers, which are ion-non-conductive. The nanofibers include entangled discrete nanofibers. For example, the nanofibers may cross each other or be twisted together with other nanofibers or themselves. The porous mat of nanofibers may be in the form of a nonwoven fabric material. Suitably, the nanofibers have a substantially random orientation in the plane (i.e., the xy plane) of the enhanced ion-conducting membrane.

[0067] The porous pad may have a strength of 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 45mN m 2 / g tear index. The tear index is the ratio of the maximum tear strength (mN) to the basis weight (g / m 2 )’s business.

[0068] The nanofibres suitably have a diameter of 50nm-700nm, suitably 200nm-600nm, and preferably 250nm-550nm.

[0069] The length of the nanofibers is not critical to the present invention, but each nanofiber should be long enough (eg, several millimeters or centimeters) to entangle with one or more other nanofibers or with itself.

[0070] The nanofibres are suitably spun nanofibres, ie the nanofibres are formed using a spinning technique. Examples of suitable spinning techniques include, but are not limited to, electrospinning and dynamo spinning.

[0071] The cross-linked polymer comprises a polymer backbone based on a heterocycle and a connecting chain. The connecting chain connects at least two polymer backbones based on a heterocycle via a connecting group. Suitably, the cross-linked polymer is essentially composed of a polymer backbone based on a heterocycle, a connecting chain and an optional second polymer (or is composed of it), wherein the second polymer is ion non-conductive.

[0072] The polymer backbone based on heterocycles includes basic functional groups, such as nitrogen-containing basic functional groups. The nitrogen-containing basic functional groups can be nitrogen with lone pairs of electrons. The polymer backbone based on heterocycles also includes a connection site that is chemically bonded (e.g., covalently bonded) to a linking group. The connection site can be a heteroatom, such as N. The heteroatom can be a part of a heterocycle.

[0073] Suitably, each linking group (A) is independently selected from the group comprising:

[0074] as well as Among them C 1 Chemically bonded to the heterocyclic-based polymer backbone. For example, C 1 It can be chemically bonded to a heteroatom (such as N) on the heterocycle-based polymer backbone. Preferably, the linking group (A) is -[C 1 H2CH(OH)]-. The linking group A may be derived from a cross-linking agent comprising a terminal epoxy functional group, such as a terminal glycidyl ether group.

[0075] Suitably, the cross-linked polymer is insoluble in organic solvents, and in particular the cross-linked polymer is insoluble in N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc) or dimethyl sulfoxide (DMSO), suitably insoluble in DMAc or DMSO, and preferably insoluble in DMAc.

[0076] The polymer backbone based on heterocycles can be derived from basic heterocycle-based polymers, including polybenzimidazoles, polypyridines, polypyrimidines, polybenzothiazoles, polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, polytriazoles, polyoxazoles, polybenzoxazoles, polythiazoles, polypyrazoles and derivatives thereof. Suitably, the polymer backbone based on heterocycles is derived from functionalized polyazoles or zwitterionic polyazoles, such as polybenzimidazoles, polytriazoles, polythiazoles and polyoxadiazoles and derivatives thereof; most suitably, polybenzimidazoles.

[0077] The cross-linked polymer may comprise the same or different types of heterocyclic-based polymer backbones. For example, the cross-linked polymer may comprise a first type of heterocyclic-based polymer backbone and a second type of heterocyclic-based polymer backbone, wherein the first type and the second type of heterocyclic-based polymer backbones are different in the sense that they have different chemical structures / compositions. The connecting chain may connect the same or different types of heterocyclic-based polymer backbones, for example, the connecting chain may connect the first type of heterocyclic-based polymer backbone with the second type of heterocyclic-based polymer backbone.

[0078] The cross-linked polymer is cross-linked by a linking chain. Each linking chain connects at least two heterocyclic-based polymer backbones via at least two linking groups. That is, a heterocyclic-based polymer backbone is bonded to another heterocyclic-based polymer backbone via at least two linking groups and a linking chain. Cross-linking improves the mechanical and tensile properties of the porous mat of nanofibers, and thereby improves the mechanical and tensile properties of the enhanced ion-conducting membrane.

[0079] The linking group suitably comprises a carbon C 1 , which is chemically bonded (e.g., covalently bonded) to the heterocycle-based polymer backbone, such as at an attachment site on the heterocycle-based polymer backbone. The attachment chain has a different chemical structure from the heterocycle-based polymer backbone.

[0080] The connecting chain can be non-polymeric or polymeric, preferably non-polymeric. The connecting chain can be aliphatic, aromatic or a combination of aliphatic and aromatic parts. Preferably, the connecting chain is aliphatic. Most preferably, the connecting chain is non-polymeric and aliphatic. For example, the connecting chain can be a straight or branched aliphatic chain. Preferably, the connecting chain includes an alkyl chain and / or an alkoxy chain, such as a glycol chain. "Alkyl" refers to a straight or branched hydrocarbon group, optionally substituted by 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.

[0081] The connecting chain may be free of cyclic groups, such as cyclic aromatic groups and cycloalkyl groups. Preferably, the connecting chain is free of fused rings, including carbocyclic fused rings and heterocyclic fused rings, such as benzoxazine.

[0082] The linking chain may have a chemical formula selected from the group consisting of:

[0083]

[0084] in:

[0085] A is a linking group, and each linking group A is independently selected from the group comprising:

[0086]

[0087] R 1 Selected from the group consisting of: aliphatic C 1-15 Alkyl chain, preferably C 1-10 alkyl chain, and more preferably C 1-6 Alkyl chain; alkoxy chain, for example a glycol chain, such as [CH2CH2O] m 、[CH2CH(CH3)O] m , [CH2CH2CH2O] m ; Aryloxy chain, or a combination thereof;

[0088] X and Y are each independently selected from the group consisting of: O, [N(R 7 )], [OCH2CH2] n 、[OCH2CH(CH3)] n 、[O(CH2)3] n and no atoms;

[0089] R 2 and R 7 Each independently selected from the group consisting of: H, C 1-5 Alkyl chain and [(CH2) p A],

[0090] m and n are each independently in the range of 1 to 225 and inclusive,

[0091] R 3 and R 4 Each independently selected from aliphatic C 1-5 Alkyl chain; alkoxy chain, such as a glycol chain; or no atom;

[0092] R a , R b , R c , R d , R 5 and R 6 are each independently selected from H, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl; and

[0093] p is an integer ranging from 1 to 5, inclusive.

[0094] Preferably, X and Y are each independently selected from: O and [N(R 7 )]. In some embodiments, X and Y are the same, for example, both X and Y can be O. In other embodiments, both X and Y can be [N(R 7 )].

[0095] Preferably, R 2 is H or [(CH2) p A], and more preferably [(CH2) p A].

[0096] Preferably, R 3 and R 4 Each independently is an aliphatic C 1-3 Alkyl chain or no atom.

[0097] Preferably, R 5 and R 6 Each is independently selected from H or methyl. 5 and R 6 In other embodiments, R 5 and R 6 All are H.

[0098] Preferably, R 7 is H or [(CH2) p A], and more preferably [(CH2) p A].

[0099] Preferably, R a , R b , R c , R d Each is independently H or methyl, and most preferably H. For example, R a , R b , R c , R d Each may be hydrogen.

[0100] Preferably, m and n are each independently in the range of 1 to 150 and including 1 to 150, more preferably in the range of 1 to 130 and including 1 to 130, more preferably in the range of 1 to 100 and including 1 to 100, and even more preferably in the range of 1 to 50 and including 1 to 50.

[0101] Preferably, p is an integer in the range of 1 to 3, preferably 1 or 2, and most preferably 1.

[0102] Preferably, the linking chain is selected from the group consisting of:

[0103]

[0104]

[0105] wherein q is in the range of 1 to 225 and inclusive, preferably about 130, and r is in the range of 1 to 225 and inclusive.

[0106] Preferably, p ranges from 1 to 3 and includes 1 to 3. Preferably, q is from 1 to about 130. Preferably, r ranges from 1 to 100 and includes 1 to 100.

[0107] Nanofibers may include a cross-linked polymer and a second polymer, such as a blend or mixture. The second polymer is ion non-conductive. The second polymer is different from (i.e., in the sense that it has different chemical compositions) a heterocyclic polymer derived from a heterocyclic polymer backbone. The second polymer may be a partially fluorinated or perfluorinated polymer or a hydrocarbon polymer. Preferably, the second polymer is a partially fluorinated or perfluorinated polymer. For example, the second polymer may be selected from the group comprising: poly (vinylidene fluoride) (PVDF), polytetrafluoroethylene (PTFE), poly (vinylidene fluoride-to-hexafluoropropylene) (PVDF-HFP), polyimide (PI), polyetherimide (PEI), polyaryletherketone (PAEK), polyarylethersulfone, polyphenylene sulfide (PPS), polyvinylpyrrolidone (PVP). Preferably, the second polymer is PVDF.

[0108] Providing a porous mat comprising a cross-linked polymer and a second polymer can further improve the mechanical and tensile properties of the porous mat, and thus the enhanced ion conducting membrane.

[0109] 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. The tear strength may be measured according to ASTM D1938.

[0110] The porous mat of nanofibers may have an ultimate tensile strength of at least 25 MPa, preferably at least 30 MPa, when measured in the machine direction. The porous mat of nanofibers may have an ultimate tensile strength of at least 25 MPa, preferably at least 30 MPa, when measured in the cross direction. Most preferably, the porous mat of nanofibers may have an ultimate tensile strength of at least 25 MPa, preferably at least 30 MPa, when measured in the machine direction; and the porous mat of nanofibers may have an ultimate tensile strength of at least 25 MPa, preferably at least 30 MPa, when measured in the cross direction. The machine direction and the cross direction are perpendicular. 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 may be in the range of 0.5 to 2, preferably 0.6 to 1.5. The porous mat of nanofibers may 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 porous mat of nanofibers may 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 porous mat of nanofibers 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 has a strain at break of 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 may be determined by performing a stress-strain test on the porous mat. For example, a sample (80 mm x 10 mm) of a nanofiber porous mat can be prepared with the longer dimension parallel to the machine direction or transverse direction when measuring the stress-strain relationship in the machine direction or transverse direction, respectively. At room temperature (20°C ± 3°C) and 30%-50% relative humidity (RH), the sample can be clamped between the tensile test fixtures of a universal mechanical tester and pulled at a tensile rate of 20 mm / min until the sample breaks. A stress-strain graph is plotted from which the ultimate tensile strength and fracture strain can be derived. The thickness of the porous mat required for stress-strain testing can be measured by cross-sectional imaging using a scanning electron microscope (SEM) (e.g., a JEOL JSM-IT300LV SEM) after resin embedding and measuring the edge-to-edge thickness of the mat using a SEM integrated ruler.

[0111] For example, when measured at 80° C., 90% RH and a stress gradient of 0.2 MPa / min, the reinforced ion-conducting membrane may have a secant modulus of elasticity (also referred to herein as “secant modulus”) measured in the machine 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. For example, when measured at 80° C., 90% RH and a stress gradient of 0.2 MPa / min, the reinforced ion-conducting membrane may 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. The ratio of the secant modulus of elasticity (at 8% strain) measured in the machine direction of the enhanced ion-conducting membrane to the secant modulus of elasticity (at 8% strain) measured in the transverse direction can be in the range of 0.75 to 1.4, preferably in the range of 0.80 to 1.3, and more preferably in the range of 0.90 to 1.2, and most preferably about 1.0. This ratio close to 1.0 indicates an isotropic enhanced ion-conducting membrane. When the secant modulus is measured in the machine direction or the transverse direction, respectively, the secant modulus of elasticity can be measured by sampling a rectangular strip of the enhanced ion-conducting membrane having a size of 60 mm×6 mm, wherein the longer dimension is parallel to the machine direction or the transverse direction of the enhanced ion-conducting membrane. The thickness of the sample is measured using a low-force, high-precision measuring instrument (e.g., a Mitutoyo VL-50-B micrometer), wherein a motorized mandrel is used to obtain a measurement reading with a measuring force of 0.01 N and a temperature of 20°C±3°C and a relative humidity (RH) of 30%-50%. The sample is mounted in a dynamic force mechanical analyzer (DMA) (e.g., Q800 available from TA Instruments) equipped with a relative humidity control chamber and a tensile (thin film) fixture that can be set to a spacing of approximately 16 mm and tightened with a torque of 3 in lbs (~0.34 N·m). Using automation of the DMA, the sample length can be determined, and an experiment including the following parameters / steps can be performed: pre-force 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. Where "measure length" sets the length of the sample to 0% strain. Since the peak gradient of the stress / strain relationship does not occur at 0% strain under these conditions, the secant modulus is used. The stress at 8% strain is divided by 0.08 to obtain the secant modulus value. The value of 8% strain is selected because this is generally the upper limit of the in-plane swelling of the reinforced membrane in fuel cell or electrolyzer operation.

[0112] The porous pad suitably has an open structure and a porosity in the range of 70%-98%, suitably 80%-95%, suitably 85%-95% and preferably 90%-95%. The porosity is determined by the ratio of the bulk mass of the porous pad (determined by its geometric dimensions and its mass) to the known density of the polymer.

[0113] The porous pad suitably has a 2 Up to 7g / m 2 range, preferably 1.5 g / m 2 Up to 4g / m 2 The average basis weight in the range.

[0114] The porous pad in the electrolyte membrane suitably has a maximum thickness of 50 μm, 30 μm, suitably 25 μm and preferably 20 μm. The porous pad in the electrolyte membrane suitably has a minimum thickness of about 2 μm, preferably 3 μm, and suitably 5 μm. The porous pad in the electrolyte membrane may have a thickness within a range including any combination of the above upper and lower limits. Preferably, the porous pad 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 suitably 5 μm or less. Preferably, the porous pad 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 pad in the electrolyte membrane may be a range including any combination of the above upper and lower limits. The thickness of the porous pad is measured by cross-sectional imaging using a scanning electron microscope (SEM) (e.g., JEOL JSM-IT300LV SEM) after resin embedding and measuring the edge-to-edge thickness of the pad using a SEM integrated ruler.

[0115] In some preferred embodiments suitable for fuel cells or electrolyzers, and particularly suitable for fuel cells, the enhanced ion-conducting membrane may have an average thickness of less than 20 μm, preferably ≤16 μm, more preferably ≤15 μm, and most preferably ≤12 μm or less. In other preferred embodiments particularly suitable for electrolyzers, the ion-conducting membrane may have an average thickness in the range of 40 μm to 150 μm, preferably 50 μm to 100 μm, and more preferably 50 μm to 80 μm. The thickness of the enhanced ion-conducting membrane can be measured using a low-force, high-precision measuring instrument (e.g., VL-50BLitematicTM available from Mitutoyo (UK) Ltd.), which can give a direct reading of the membrane thickness. Use a motorized mandrel to obtain a measurement reading with a measurement force of 0.01 N. At least three readings are obtained from different positions 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%.

[0116] To form a porous mat, the nanofibers are suitably formed on a suitable substrate or surface by a spinning technique. For example, the nanofibers may be formed using electrospinning.

[0117] In such Figure 2 In the first embodiment of the method shown, the electrospinning preparation comprises at least one heterocyclic-based polymer, a cross-linking agent and an optional second polymer together in a suitable solvent (such as an organic solvent) or a suitable solvent mixture. The solvent may comprise at least one (or consist of) of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc) and / or dimethyl sulfoxide (DMSO), suitably DMAc and / or DMSO, and preferably DMAc. A suitable solvent mixture may be a uniform mixture of two or more solvents. The electrospinning preparation may be a solution or a dispersion. A syringe pump is used to push the electrospinning preparation through a needle, wherein the needle maintains a potential difference relative to the substrate / surface. The electrospun nanofibers are collected on a substrate (such as a drum collector) that moves in translation and rotation, and the substrate is disposed at a distance from the needle, such as about 10cm-15cm from the needle. The fiber morphology is obtained by controlling the preparation parameters (such as concentration), and the mat thickness and uniformity are controlled by the deposition time and the collector rotation / translation speed. The porous pad is treated to react the heterocyclic-based polymer and the crosslinking agent. The reactive groups on the heterocyclic-based polymer react with the reactive groups on the crosslinking agent. The reaction forms a crosslinked polymer comprising a heterocyclic-based backbone and connecting chains as described above. When a second polymer is present, the second polymer is suitably non-reactive to the crosslinking agent during the crosslinking treatment.

[0118] The cross-linking treatment may be a heat treatment or a light treatment. The heat treatment may include heating the porous mat to a temperature of at least 80°C, preferably at least 85°C. The light treatment may include irradiating the porous mat with UV light to initiate the cross-linking reaction. In this case, the electrospinning formulation may further include at least one photoinitiator.

[0119] There is no need for any further processing of the porous mat, for example any densification process such as calendaring or welding.

[0120] The crosslinking agent may be a liquid. The liquid crosslinking agent is preferably miscible with the solvent. Alternatively, the crosslinking agent may be a solid. Preferably, the solid crosslinking agent is soluble in the solvent.

[0121] The electrospinning formulation may also include a second polymer. In such an embodiment, the porous mat of nanofibers may include a crosslinked polymer and a second polymer. Preferably, the second polymer is non-reactive to the crosslinking agent. That is, during the step of treating the porous mat, the second polymer does not chemically react with the crosslinking agent.

[0122] In some embodiments, the method includes providing another preparation for electrospinning, wherein the other preparation comprises a second polymer. The second polymer is ionically non-conductive. Preferably, the second polymer is non-reactive to the cross-linking agent. The method may include electrospinning the preparation and the other preparation onto a substrate simultaneously.

[0123] The amount of crosslinker present in the electrospinning formulation may be in the range of 1 wt.% to 20 wt.%, preferably in the range of 3 wt.% to 15 wt.%. The amount of crosslinker may be in the range defined by any combination of the above upper and lower limits.

[0124] The formulation may include a heterocyclic-based polymer and a cross-linking agent in amounts such that the molar ratio of reactive groups on the heterocyclic-based polymer to reactive groups on the cross-linking agent is in the range of and including 25:1 to 1:2, preferably in the range of and including 20:1 to 1:1, and more preferably in the range of and including 10:1 to 1.5:1. The molar ratio of reactive groups on the heterocyclic-based polymer to reactive groups on the cross-linking agent may be within a range defined by any combination of the above limitations.

[0125] exist Figure 3 In the second embodiment of the method shown, the first electrospinning formulation is included in at least one heterocyclic-based polymer in a suitable solvent (such as an organic solvent) or a suitable solvent mixture. The solvent may include at least one (or consist of) of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc) and / or dimethyl sulfoxide (DMSO), suitably DMAc and / or DMSO, and preferably DMAc. The first electrospinning formulation may be a solution or a dispersion. A syringe pump is used and a high voltage is applied to the needle to push the first electrospinning formulation through the needle. The electrospun nanofiber mat is collected on a substrate (such as a drum collector) that moves in translation and rotation, and the substrate is disposed at a distance from the needle, such as about 10cm-15cm from the needle. The fiber morphology is obtained by controlling formulation parameters (such as concentration), and the mat thickness and uniformity are controlled by the deposition time and the collector rotation / translation speed.

[0126] The second formulation comprises a cross-linking agent and an optional solvent (or consists of it). For example, the second formulation can be a liquid cross-linking agent optionally in a suitable solvent. Alternatively, the second formulation can be a solid cross-linking agent dissolved in a suitable solvent. The solvent can be an organic solvent, such as dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), methyl isobutyl ketone (MIBK), acetone, benzene, butanol, ethylene glycol, ethanol, methanol, propanol, toluene, water, 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-based polymer and the cross-linking agent as described in the first embodiment of the method. The heterocyclic-based polymer and the cross-linking agent may be present in amounts such that the molar ratio of reactive groups on the heterocyclic-based polymer to reactive groups on the cross-linking agent is in the range of and including 25:1 to 1:2, preferably in the range of and including 20:1 to 1:1, and more preferably in the range of and including 10:1 to 1.5:1. The molar ratio of reactive groups on the heterocyclic-based polymer to reactive groups on the cross-linking agent may be within the range defined by any combination of the above limitations.

[0127] There is no need for any further processing of the porous mat, for example any densification process such as calendaring or welding.

[0128] The first formulation may further comprise a second polymer. The second formulation may further comprise a second polymer. In such an embodiment, the porous mat of nanofibers may be a mixture of a crosslinked polymer and a second polymer. Preferably, the second polymer is non-reactive to the crosslinking agent. That is, during the step of treating the porous mat, the second polymer does not chemically react with the crosslinking agent.

[0129] The step of impregnating the porous pad with the second formulation may include spraying, electrospraying, screen printing, rotary screen printing, inkjet printing, brushing, painting, immersion or dip coating, rod coating, pad coating, gravure printing; gap coating techniques such as knife or doctor blade on a roller (whereby the coating is applied to the substrate and then passes through the gap between the knife and the support roller); slot die (slot, extrusion) coating (whereby the coating is extruded through a slot onto the substrate by gravity or under pressure); metered rod application, such as coating with a Meyer rod and gravure printing.

[0130] The cross-linked polymer is suitably formed by cross-linking at least one heterocyclic polymer containing a basic functional group with a suitable cross-linking agent. The heterocyclic polymer contains at least one reactive group for reacting with the cross-linking agent to form a cross-linked polymer. For example, the reactive group can be a nucleophile, such as an amine (e.g., a primary amine or a secondary amine) or an imine. The reactive group can be a part of a heterocycle.

[0131] Suitable heterocyclic polymers, preferably basic heterocyclic polymers, include polybenzimidazoles, polypyridines, polypyrimidines, polybenzothiazoles, polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, polytriazoles, polybenzoxazoles, polyoxazoles, polythiazoles, polypyrazoles and derivatives thereof. Preferably, the heterocyclic polymer is selected from polybenzimidazoles, polypyridines, polypyrimidines, polybenzothiazoles, polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, polytriazoles, polyoxazoles, polythiazoles, polypyrazoles and derivatives thereof. Suitably, the polymer is a functionalized polyazole or a zwitterionic polyazole, such as polybenzimidazoles, polytriazoles, polythiazoles and polyoxadiazoles and derivatives thereof; most preferably, polybenzimidazoles.

[0132] The cross-linking agent suitably comprises at least two terminal epoxy groups, preferably at least two terminal glycidyl ether groups.

[0133] The cross-linking agent may have a chemical formula selected from the group consisting of:

[0134]

[0135] in:

[0136] R 1 Selected from the group consisting of: aliphatic C 1-15 Alkyl chain, preferably C 1-10 alkyl chain, and more preferably C 1-6 Alkyl chain; alkoxy chain, for example a glycol chain, such as [CH2CH2O] m 、[CH2CH(CH3)O] m , [CH2CH2CH2O] m ; Aryloxy chain, or a combination thereof;

[0137] X and Y are each independently selected from the group consisting of: O, [N(R 7 )], [OCH2CH2] n 、[OCH2CH(CH3)] n 、[O(CH2)3] n and no atoms;

[0138] R 2 and R 7 Each independently selected from the group consisting of: H, C 1-5 Alkyl chain and C 1-5 Combination of alkyl chains with terminal epoxy groups;

[0139] m and n are each independently in the range of 1 to 225 and inclusive,

[0140] R 3 and R4 Each independently selected from aliphatic C 1-5 an alkyl chain; an alkoxy chain, such as a glycol chain; or no atom; and

[0141] R a , R b , R c , R d , R 5 and R 6 Each is independently selected from H, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl.

[0142] Preferably, X and Y are each independently selected from: O and [N(R 7 )]. In some embodiments, X and Y are the same, for example, both X and Y can be O. In other embodiments, both X and Y can be [N(R 7 )].

[0143] Preferably, R 2 is H or C combined with a terminal epoxy group 1-3 Alkyl chains, and more preferably CH2 combined with a terminal epoxy group, ie [CH2CHOCH2].

[0144] Preferably, R 3 and R 4 Each independently is an aliphatic C 1-3 Alkyl chain or no atom.

[0145] Preferably, R 5 and R 6 Each is independently selected from H or methyl. 5 and R 6 In other embodiments, R 5 and R 6 All are H.

[0146] Preferably, R 7 is H or C in combination with a terminal epoxy group 1-3 Alkyl chains, and more preferably CH2 combined with a terminal epoxy group, ie [CH2CHOCH2].

[0147] Preferably, R a , R b , R c , R d Each is independently H or methyl, and most preferably H.

[0148] Preferably, m and n are each independently in the range of 1 to 150 and including 1 to 150, more preferably in the range of 1 to 130 and including 1 to 130, more preferably in the range of 1 to 100 and including 1 to 150, and even more preferably in the range of 1 to 50 and including 1 to 50.

[0149] Preferably, the crosslinking agent can be selected from 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, polyethylene glycol diglycidyl ether, bisphenol A diglycidyl ether, bis[4-(glycidyloxy)phenyl]methane, bisphenol A propoxylated diglycidyl ether, N,N-diglycidyl-4-glycidyloxyaniline, tris(2,3-epoxypropyl)isocyanurate, 1,3-butanediol diglycidyl ether.

[0150] Fig. 9 An exemplary cross-linking reaction is shown in which a heterocyclic-based polymer 900 reacts with a cross-linking agent 910 to form a cross-linked polymer 920. Reactive groups 905 on the heterocyclic-based polymer 900 react with reactive groups 915 on the cross-linking agent 910. In this example, the heterocyclic-based polymer 900 is polybenzimidazole, the cross-linking agent 910 is 1,4-butanediol diglycidyl ether (BDDGE), and the reactive groups on the cross-linking agent are terminal epoxy groups. The cross-linked polymer 920 includes a heterocyclic-based polymer backbone 930 and a connecting chain 940 that connects two heterocyclic-based polymer backbones 930 via a connecting group 950.

[0151] The porous mat of nanofibers comprising the crosslinked polymer is then impregnated with an ion-conducting polymer to form an enhanced ion-conducting membrane, such as an enhanced electrolyte membrane. As part of a roll-to-roll process, the porous mat of nanofibers can be impregnated with an ion-conducting polymer. Such enhanced ion-conducting membranes are used as membrane layers in electrochemical devices such as fuel cells and water electrolyzers.

[0152] The ion conducting polymer may be a proton conducting polymer or an anion conducting polymer, such as a hydroxy anion conducting polymer. Preferably, the ion conducting polymer is a proton conducting polymer. Typically, the ion conducting polymer comprises a sulfonic acid group. Suitably, the ion conducting polymer is a perfluorinated sulfonic acid ionomer, or a partially fluorinated or non-fluorinated hydrocarbon sulfonic acid or phosphoric acid ionomer. Examples of suitable proton conducting polymers include partially fluorinated or perfluorinated sulfonic acid polymers, such as perfluorosulfonic acid ionomers (e.g. (EIDuPont de Nemours and Co.), (Asahi Kasei), Aquivion TM (Solvay Specialty Polymers), (Asahi Glass Co.); or ionomers based on sulfonated hydrocarbons, such as those available from FuMA-Tech GmbH (as P, E or K series products), those obtained by JSR Corporation, Toyobo Corporation, etc. Examples of suitable anionic conductive polymers include A901 manufactured by Tokuyama Corporation and Fumasep FAA from FuMA Technology Co., Ltd. Typically, ion conductive polymers have an equivalent weight of about 1100 or less, typically about 900 or less, and suitably about 850 or less. Typically, ion conductive polymers have an equivalent weight of at least about 450. The equivalent weight of ion conductive polymers can be easily measured using acid titration after hydroxide exchange. For example, a membrane sample can be vacuum dried at about 110° C. for 16 hours to obtain a dry membrane of about 2 g. The film can then be immersed in about 30 mL of a 0.1 N NaOH solution to replace the protons in the membrane with sodium ions. Titration is then performed by neutralization, for example using 0.1 N hydrochloric acid, to determine the number of exchangeable protons, and thus the EW can be calculated.

[0153] The porous mat is substantially completely impregnated with the ion-conducting polymer to form an ion-conducting (electrolyte) membrane. "Substantially completely impregnated" means that at least 80%, suitably at least 90%, suitably at least 95% and ideally 100% of the pores of the porous mat are filled with the ion-conducting polymer.

[0154] Suitably, an excess of ion-conducting polymer is present on both surfaces of the ion-conducting (electrolyte) membrane to aid adhesion to the catalyst layer.

[0155] The porous mat can be impregnated with the ion-conducting polymer by the following method. An ion-conducting polymer layer (in solution / dispersion) is cast onto a support material. While the ion-conducting polymer layer is still wet, the porous nanofiber mat is placed into the wet layer and the ion-conducting polymer is impregnated into one face of the porous mat. Another ion-conducting polymer layer is applied to the second face of the porous mat and impregnated into the porous mat from the second face. The impregnated porous mat is dried and suitably annealed to form an ion-conducting (electrolyte) membrane.

[0156] The solution / dispersion of the ion-conducting polymer may comprise additional components, such as short nanofibers, for example 1 μm to 50 μm.

[0157] In the final electrolyte membrane of the invention, the weight ratio of ion conducting polymer to nanofibres is suitably greater than 70:30, and preferably greater than 90:10. Suitably, the ratio of ion conducting polymer to nanofibres is less than 98:2. In this context, nanofibres refer to nanofibres in a porous mat.

[0158] The thickness of the porous mat in the electrolyte membrane is suitably distributed over at least 50%, suitably 60%, more suitably 70%, more suitably 80%, more suitably at least 85%, and most suitably at least 90% of the thickness of the final electrolyte membrane. The porous mat extends over the thickness of the membrane so that the thickness of the electrolyte membrane and the thickness of the porous mat are substantially equal; however, in practice, the thickness of the electrolyte membrane may be slightly thicker than the thickness of the porous mat, so that the thickness of the porous mat is at most 99%, such as 95%, of the thickness of the electrolyte membrane.

[0159] Having the porous mat distributed over at least 80% of the electrolyte membrane thickness enhances the stability (mechanical and chemical) of the final electrolyte membrane.

[0160] The electrolyte membrane of the invention may comprise more than one porous mat, for example two porous mats distributed over at least 50%, and suitably at least 80%, of the thickness of the electrolyte membrane.

[0161] The present invention also provides a catalytic electrolyte membrane comprising a catalyst layer and the electrolyte membrane of the present invention.

[0162] The catalyst layer comprises one of a plurality of electrocatalysts. The one or more electrocatalysts are independently finely divided unsupported metal powders, or supported catalysts in which small nanoparticles are dispersed on a conductive granular carbon support. The electrocatalyst metal is suitably selected from

[0163] (i) platinum group metals (platinum, palladium, rhodium, ruthenium, iridium and osmium),

[0164] (ii) gold or silver,

[0165] (iii) base metals,

[0166] Or an alloy or mixture comprising one or more of these metals or their oxides. The preferred electrocatalyst metal is platinum, which may be alloyed with other noble metals or alkali metals. The base metal is tin or a transition metal that is not a noble metal. The noble metal is a platinum group metal (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. If the electrocatalyst is a supported catalyst, the loading of the metal particles on the carbon support material is appropriately in the range of 10wt%-90wt%, preferably 15wt%-75wt% of the weight of the resulting electrocatalyst.

[0167] The exact electrocatalyst used will depend on the reaction it is intended to catalyze, and its selection is within the capabilities of the skilled artisan.

[0168] The catalyst layer is suitably applied to the first and / or second side of the electrolyte membrane in the form of an organic or aqueous ink. The ink may suitably contain other components, such as an ion-conducting polymer as described in EP0731520, which is included to improve the ionic conductivity within the layer. Alternatively, the catalyst layer may be applied by decal transfer of a previously prepared catalyst layer.

[0169] The catalyst layer may also contain additional components. Such additional components include, but are not limited to, catalysts that promote oxygen evolution 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 will be known to those skilled in the art.

[0170] The present invention also provides a membrane electrode assembly, which comprises the electrolyte membrane of the present invention and a gas diffusion electrode on a first surface and / or a second surface of the electrolyte membrane.

[0171] The present invention also provides a membrane electrode assembly, which comprises the catalytic electrolyte membrane of the present invention and a gas diffusion layer or a porous transport layer present on at least one catalyst layer.

[0172] The membrane electrode assembly can be made in a variety of ways, including but not limited to:

[0173] (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 (an anode and a cathode);

[0174] (ii) the catalytic ion conducting (electrolyte) membrane of the present invention having a catalyst layer on one side may be sandwiched between a gas diffusion layer or a porous transport layer and a gas diffusion electrode or a catalyst-coated porous transport layer, the gas diffusion layer or the porous transport layer contacting the side of the catalytic ion conducting (electrolyte) membrane having the catalyst component, or;

[0175] (iii) The catalytic ion-conducting (electrolyte) membrane of the present invention having catalyst components 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, such as one gas diffusion layer and one porous transport layer.

[0176] The anode and cathode gas diffusion layers are suitably based on conventional gas diffusion substrates. Typical substrates include nonwoven papers or webs comprising a carbon fiber mesh and a thermosetting resin binder (e.g., TGP-H series carbon fiber papers available from Toray Industries Inc., Japan, or H2315 series available from Freudenberg FCCT KG, Germany, or TEFLON® available from SGL Technologies GmbH, Germany). series, or from Ballard Power Systems Inc. Series), or woven carbon cloth. Before being incorporated into the MEA, the carbon paper, fiber mesh or cloth may have a further treatment to make it more wettable (hydrophilic) or more waterproof (hydrophobic). The nature of any treatment will depend on the type of fuel cell and the operating conditions to be used. The substrate can be made more wettable by impregnating the material (such as amorphous carbon black) from a liquid suspension, or the substrate can be made more hydrophobic by impregnating the pore structure of the substrate with a colloidal suspension of a polymer (such as PTFE or polyfluoroethylene propylene (FEP)), then drying and heating to above the melting point of the polymer. For applications such as PEMFC, a microporous layer can also be applied to the gas diffusion substrate on the face that will contact the electrocatalyst layer. The microporous layer typically comprises a mixture of carbon black and a polymer (such as polytetrafluoroethylene (PTFE)).

[0177] The porous transport layer is suitably based on a conventional porous transport substrate, such as a titanium mesh.

[0178] The present invention also provides an electrochemical device comprising an enhanced ion conductive membrane (e.g., an electrolyte membrane), a catalytic enhanced ion conductive membrane, or a membrane electrode assembly as described above. The electrochemical device may be a fuel cell, such as a proton exchange membrane fuel cell. The electrochemical device may be an electrolyzer, such as a water electrolyzer.

[0179] The present invention will now be further described with reference to the following examples, which are intended to be illustrative rather than limiting of the present invention.

[0180] Example

[0181] As detailed in Table 1, formulations suitable for electrospinning were prepared in dimethylacetamide (DMAc) 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 fluoride) (PVDF).

[0182] Table 1

[0183] PBI / weight% Crosslinker type Crosslinking agent / weight% PVDF / weight% Preparation 1 18 BDDGE 5.5 Preparation 2 18 BDDGE 6.7 Preparation 3 18 BDDGE 7.7 Preparation 4 13 BDDGE 3.6 6.5 Preparation 5 19 Preparation 6 13 6.8 Preparation 7 16 BADGE 8.6

[0184] The formulation was electrospun onto the substrate using the following parameters: 15 kV applied voltage, 0.15 mL / hr flow rate; 22 gauge needle size; 10 cm needle collector distance; 800 rpm drum collector rotation speed; and 10 mm / s translation speed. The electrospun mat was removed from the substrate.

[0185] For cross-linking, the porous mat is heat treated by maintaining at a temperature ranging from 85° C. to 120° C. for 1 to 24 hours until the cross-linking reaction is complete.

[0186] Table 2 shows some properties of the porous mats prepared using the formulation. The cross-linked porous mats of all Examples and the porous mats of Comparative Examples are ionically non-conductive.

[0187] Table 2

[0188]

[0189] The term "tear index" as used herein refers to the maximum tear strength (mN) divided by the average basis weight (g / m 2 ).

[0190] Figure 4 A scanning electron microscope (SEM) image of the electrospun mat of Example 2 is shown. The nanofibers are crossed and entangled with each other. The nanofibers are randomly oriented in the xy plane (i.e., in the planar direction). The cross-linked electrospun mat contains nanofibers with fiber diameters ranging from ˜200 nm to 700 nm.

[0191] Figures 5 to 7 A graph of force (in N) as a function of elongation (in mm) before and after crosslinking treatment is shown. In each case, the porous pad has a significantly higher maximum tear strength after crosslinking treatment. The tear strength can be determined by performing a trouser tear test according to ASTM D1938. In these examples, the test specimens were prepared by cutting a 70 mm x 30 mm cut from the porous pad. In addition, a 25 mm slit was cut from the midpoint of the shorter edge along the central axis to form two tongues. The two tongues were clamped in the fixture of a universal mechanical tester with a 5 kN load cell attached and pulled at a crosshead speed of 50 mm / min. The results are recorded as a graph of force (N) versus elongation (mm). The maximum tear strength is recorded at an elongation of up to 30 mm.

[0192] Figure 8 A graph of force (N) as a function of elongation (mm) is shown for Example 2, Example 5, and Example 6 and Comparative Example 4 and Comparative Example 5. Forming a porous mat of nanofibers comprising a crosslinked polymer provides a significant improvement in tear strength compared to Comparative Example 4 (i.e., a non-crosslinked PBI mat) and Comparative Example 5 (i.e., a mixture of non-crosslinked PBI and PVDF). The combination of a crosslinked polymer with a second polymer (e.g., PVDF) provides an unexpectedly significant improvement in maximum tear strength at comparable basis weights.

[0193] After heat treatment, the cross-linked porous mat is insoluble in organic solvents such as dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), and dimethylsulfoxide (DMSO).

[0194] In addition, after the crosslinking treatment, the water contact angle on the surface of the crosslinked porous mat of Examples 1 to 5 is low. For example, the water contact angles measured for Comparative Example 4 and Example 2 are 113° and 99°, respectively. The crosslinked porous mat has a beneficial property that facilitates impregnation with an ion-conducting polymer such as a partially fluorinated or perfluorinated sulfonic acid ion-conducting polymer. Using the The contact angle was measured using a drop shape analyzer DSA30 from Krüss GmbH and Krüss DSA4 software. A 6 μL drop of deionized water was dispensed onto the surface of the nanofiber mat at room temperature (20°C-25°C) and 30 images were taken at a frequency of one image per second. Krüss DSA4 software was used to determine the drop shape and contact angle.

[0195] The porous pad of Example 1 has 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 >45 MPa when measured in the transverse direction. The porous pad of Example 3 has an ultimate tensile strength of about 54 MPa and a strain at break of 56% when measured in the machine direction. The porous pad of Example 3 has an ultimate tensile strength of about 44 MPa and a strain at break of 14% when measured in the transverse direction. In contrast, Comparative Example 4 has an ultimate tensile strength of 4 MPa and a strain at break of 65% to 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 transverse direction. Compared to the porous pad of Comparative Example 4, the mechanical properties of the porous pads of Examples 1 and 3 are more conducive to use as a reinforcing component in a roll-to-roll manufacturing process.

[0196] Impregnation with ion-conducting polymer

[0197] The porous pad can be used as an enhanced component as part of a roll-to-roll process for manufacturing an enhanced ion-conducting membrane, wherein the ion-conducting polymer is impregnated with the porous pad. A typical method includes forming an enhanced ion-conducting membrane by a series of coating processes, wherein a dispersion of an ion-conducting polymer (e.g., a PFSA ion-conducting polymer) is deposited and then dried before a subsequent coating process. For example, three coatings can be used. The porous pad can be introduced into the ion-conducting membrane as part of a second coating process so that the dispersion of the ion-conducting polymer impregnates the pores of the porous pad. In some embodiments, the method may include more or less coating processes, such as two coating processes, to obtain an enhanced ion-conducting membrane with the same or similar structure.

[0198] The porous mat of the present invention has favorable properties for industrial scale processing, such as roll-to-roll processing. The resulting enhanced ion-conducting membrane comprises a reinforced membrane layer (i.e., comprising a porous mat) sandwiched between two unreinforced membrane layers. Such an enhanced ion-conducting membrane can be used as a catalytically enhanced ion-conducting membrane, a membrane electrode assembly, or an electrolyte membrane layer in an electrochemical device such as a fuel cell and a water electrolyzer.

[0199] The porous mat of Example 2 was used as a reinforcing component in a roll-to-roll process to manufacture a membrane electrode assembly (MEA1). A dispersion of an ion-conducting polymer (3M, EW800) was impregnated into the porous mat and dried to form an enhanced ion-conducting membrane (Mem 1). The thickness of the reinforcing component in the membrane was about 5 μm. The total membrane thickness was about 15 μm. The enhanced ion-conducting membrane (Mem 1) had a secant modulus of 52.2 MPa in the machine direction (MD) (at 8% strain) and a secant modulus of 52.9 MPa in the transverse direction (TD) (at 8% strain) (as shown in Figure 1). Fig.10 The reinforced ion conductive membrane of Example 2 (Mem 1) exhibited similar elastic moduli in both the machine direction and the transverse direction, 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. In comparison, a 15 μm thick membrane reinforced with the nanofiber mat of Comparative Example 5 (Mem 2) exhibited a ratio of the secant modulus in the machine direction (at 8% strain) to the secant modulus in the transverse direction (at 8% strain) of 0.78 (as shown). Fig.10 As a further comparison, a known expanded polytetrafluoroethylene (ePTFE) reinforcement component (basis weight 4.7 g / m 2 The ratio of the secant modulus in the machine direction (at 8% strain) to the secant modulus in the transverse direction (at 8% strain) of the 15 μm thick contrast enhanced ion conducting membrane (Mem 3) is 1.5, indicating a higher degree of anisotropy compared to Mem 1 and Mem 2 (e.g. Fig.10 As shown). In addition, the secant modulus (at 8% strain) of Mem 1 in the transverse direction is 1.85 times higher than the secant modulus (at 8% strain) of the comparative ePTFE reinforced membrane (Mem3) in the machine direction. Therefore, the present invention enables the use of thinner reinforcing components (and therefore 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, it is expected that thinner ion-conducting membranes will lead to improved transmembrane ionic conductivity and improved battery performance. The secant modulus (at 8% strain) was measured using the method described above.

[0200] Mem 1 and Mem 3 were used to manufacture membrane electrode assemblies MEA1 and MEA2, respectively. The cathode catalyst layer (0.4 mgp t / cm 2 50 wt. % Pt / C) and anode catalyst layer (0.08 mg Pt / C) t / cm 2 The catalyst-coated ion-conducting membrane (active area of ​​50 cm) was prepared by transferring 60 wt.% Pt / C and tantalum iridium oxide oxygen evolution reaction (OER) catalyst to either side of the ion-conducting membrane (thickness of 15 μm). 2 ).

[0201] A gas diffusion layer (Sigracet 22BB, available from SGL Carbon) was applied to each face of each catalyst coated ion conducting membrane to form a membrane electrode assembly (MEA). The gas diffusion layer used was a carbon fiber paper having a hydrophobic microporous layer comprising carbon and PTFE applied to the face in contact with the catalyst coated ion conducting membrane.

[0202] MEA durability test

[0203] Durability testing was performed on a test bench obtained from Greenlight Innovation at 50 cm 2 Combined open circuit voltage-RH cycle (COCV-RH) accelerated stress test:

[0204] The COCV-RH test was performed in three phases: conditioning, diagnostic, and stress conditions. The test was performed by drawing 500 mA / cm at 80°C, 100 kPag on the anode and cathode, and 100% RH inlet on the anode and cathode. 2 The cells were conditioned at a current density of 1000 rpm for 10 h. After conditioning, diagnostic and stress conditioning phases were alternated until sample failure.

[0205] The diagnosis was carried out at 80°C and mainly included voltage diagnosis, which was completed under OCV, 100% RH on anode and cathode, and three pressure conditions of 50kPag / 50kPag (point 1), 50kPag / ambient (point 2) and ambient / ambient (point 3) (anode / cathode).

[0206] The stress conditions were at OCV, 90°C, ambient pressure on the anode and cathode, cycling between 0% relative humidity (RH) and 100% RH conditions (1500 wet / dry cycles per stage) before returning to the diagnostic stage.

[0207] The open circuit voltage measured at point 2 minus the open circuit voltage measured at point 3 (in the diagnostic phase) is a parameter that can be used as a proxy for gas crossover. Fig.11 The OCV response to the removal differential pressure (V) is shown as a function of completed wet / dry cycles for MEA 1 and a comparative ePTFE reinforced membrane electrode assembly (MEA2). When the OCV response curve to the removal differential pressure as a function of completed wet / dry cycles shows an abrupt change in gradient, the part is considered to have failed. MEA1 exhibited significantly improved durability performance during MEA durability testing compared to the conventional ePTFE reinforced membrane (MEA2).

[0208] Without wishing to be bound by theory, the inventors believe that this may be due to the phase separation and continuity of the electrospun mat and the ionic crosslinking (acid-base interactions or hydrogen bonding) between the ion-conductive 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 this direction, but restricts swelling in the in-plane direction because the fibers are inelastic.

[0209] In addition, the heterocyclic-based polymers used to form the electrospun mats have antioxidant properties and can contribute to the stability of the electrolyte membrane by scavenging destructive species such as peroxyl radicals. Due to these antioxidant properties, it may no longer be necessary to incorporate antioxidants or hydrogen peroxide decomposition catalysts (such as ceria) into the membrane.

Claims

1. An enhanced ion conductive membrane, comprising: Ion-conducting polymers; and a porous mat of nanofibers, said porous mat of nanofibers impregnated with said ion-conducting polymer; wherein the nanofibers comprise a cross-linked polymer, wherein the cross-linked polymer is ionically non-conductive and comprises: a heterocyclic-based polymer backbone comprising basic functional groups, and a linking chain connecting at least two of the heterocycle-based polymer backbones via a linking group; wherein the porous mat of nanofibers has a strength of at least 15 mN m 2 / g tear index.

2. The enhanced ion conducting membrane according to claim 1, wherein each linking group (A) is independently selected from the group consisting of: as well as Among them C 1 Chemically bonded to the heterocycle based polymer backbone.

3. The enhanced ion conducting membrane according to claim 1 or 2, wherein the connecting chain has a chemical formula selected from the group consisting of: as well as in: A is the linking group, and each linking group A is independently selected from the group comprising: as well as R 1 Selected from the group consisting of: aliphatic C 1-15 Alkyl chain, preferably C 1-10 alkyl chain, and more preferably C 1-6 Alkyl chain; alkoxy chain, for example a glycol chain, such as [CH2CH2O] m 、[CH2CH(CH3)O] m , [CH2CH2CH2O] m ; Aryloxy chain, or a combination thereof; X and Y are each independently selected from the group consisting of: O, [N(R 7 )], [OCH2CH2] n 、[OCH2CH(CH3)] n 、[O(CH2)3] n and no atoms; R 2 and R 7 Each independently selected from the group consisting of: H, C 1-5 Alkyl chain and (CH2) p A; m and n are each independently in the range of 1 to 225 and inclusive, R 3 and R 4 Each independently selected from aliphatic C 1-5 Alkyl chain; alkoxy chain, such as 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, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl; and p is an integer ranging from 1 to 5, inclusive.

4. The enhanced ion conducting membrane of claim 2, wherein the connecting chain is selected from the group consisting of: wherein q is in the range of 1 to 225 and includes 1 to 225, and r is in the range of 1 to 225 and includes 1 to 225.

5. An enhanced ion conducting membrane according to any preceding claim, wherein the connecting chains are aliphatic.

6. The enhanced ion conducting membrane according to claim 5, wherein the connecting chain is a linear or branched aliphatic chain.

7. An enhanced ion conducting membrane according to any preceding claim, wherein C 1 The heteroatom is chemically bonded to the heterocycle-based polymer backbone.

8. An enhanced ion conducting membrane according to any preceding claim, wherein the cross-linked polymer is insoluble in organic solvents such as dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethylacetamide (DMAc) and dimethyl sulfoxide (DMSO).

9. An enhanced ion conducting membrane according to any preceding claim, wherein the basic functional groups comprise nitrogen-containing basic functional groups.

10. An enhanced ion conducting membrane according to any preceding claim, wherein the heterocyclic based polymer backbone is selected from the group consisting of polybenzimidazole, polypyridine, polypyrimidine, polybenzothiazole, polyoxadiazole, polyquinoline, polyquinoxaline, polythiadiazole, polytriazole, polyoxazole, polybenzoxazole, polythiazole, polypyrazole and derivatives thereof.

11. The enhanced ion conducting membrane of claim 10, wherein the heterocyclic based polymer backbone is selected from the group consisting of polybenzimidazole, polytriazole, polythiazole, polyoxadiazole and derivatives thereof.

12. An enhanced ion conducting membrane according to any preceding claim, wherein the nanofibres are spun nanofibres.

13. An enhanced ion conducting membrane according to any preceding claim, wherein the nanofibers further comprise a second polymer, wherein the second polymer is ionically non-conductive.

14. The enhanced 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), polyaryletherketone (PAEK), polyarylethersulfone, polyphenylene sulfide (PPS), polyvinylpyrrolidone (PVP).

15. An enhanced ion conducting membrane according to any preceding claim, 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, wherein the machine direction and the cross direction are perpendicular.

16. An enhanced ion-conducting membrane according to any preceding claim, 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, wherein the machine direction and the cross direction are perpendicular.

17. An enhanced ion-conducting membrane according to any preceding claim, wherein the porous mat of nanofibers has a strain at break of at least 5% when measured in the machine direction and / or transverse direction at a temperature of 20°C ± 3°C, a relative humidity of 30%-50% and a tensile rate of 20 mm / min, wherein the machine direction and the transverse direction are perpendicular.

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

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

20. An enhanced ion conducting membrane according to any one of claims 18 to 20 having an average thickness of less than 16 μm.

21. An electrochemical device, such as a fuel cell or an electrolyser, comprising an enhanced ion conducting membrane according to any preceding claim.

22. A method of producing an enhanced ion conducting membrane, the method comprising the steps of: providing a substrate; A formulation for electrospinning is provided, the formulation comprising a solvent, a cross-linking agent and a heterocyclic-based polymer comprising a basic functional group, electrospinning the formulation onto the substrate to form a porous mat of nanofibers; treating the porous pad to react the heterocyclic-based polymer and the cross-linking agent to form a cross-linked polymer comprising a heterocyclic-based polymer backbone chain containing a basic functional group and a linking chain connecting at least two of the heterocyclic-based polymer backbone chains via a linking group; and The porous mat is impregnated with an ionically conductive polymer.

23. The method of claim 22, wherein the cross-linking agent is a liquid and is miscible with the solvent.

24. The method of claim 22, wherein the cross-linking agent is solid and soluble in the solvent.

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

26. The method according to any one of claims 22 to 24, wherein the method further comprises the following steps: providing another formulation for electrospinning, the other formulation comprising a second polymer, wherein the second polymer is ionically non-conductive; as well as The formulation and the further formulation are simultaneously electrospun onto the substrate.

27. A method according to claim 25 or 26, wherein during the step of treating the porous pad, the second polymer is non-reactive towards the cross-linking agent.

28. The method of any one of claims 22 to 27, wherein the formulation comprises the heterocyclic-based polymer and the cross-linking agent in amounts such that the molar ratio of reactive groups on the heterocyclic-based polymer to reactive groups on the cross-linking agent is in the range of and including 25:1 to 1:

2.

29. A method of producing an enhanced ion conducting membrane, the method comprising the steps of: providing a substrate; providing a first formulation for electrospinning, the first formulation comprising a solvent and a heterocyclic-based 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 pad with the second formulation, and then treating the porous pad to react the heterocyclic-based polymer and the cross-linking agent to form a cross-linked polymer comprising a heterocyclic-based polymer backbone chain containing a basic functional group and a linking chain connecting at least two of the heterocyclic-based polymer backbone chains via a linking group; and The porous mat is impregnated with an ionically conductive polymer.

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 ionically non-conductive.

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 crosslinking agent comprises at least two terminal epoxy groups.

33. The method according to any one of claims 22 to 32, wherein the cross-linking agent has a chemical formula selected from the group consisting of: as well as in: R 1 Selected from the group consisting of: aliphatic C 1-15 Alkyl chain, preferably C 1-10 alkyl chain, and more preferably C 1-6 Alkyl chain; alkoxy chain, for example a glycol chain, such as [CH2CH2O] m 、[CH2CH(CH3)O] m , [CH2CH2CH2O] m ; Aryloxy chain, or a combination thereof; X and Y are each independently selected from the group consisting of: O, [N(R 7 )], [OCH2CH2] n 、[OCH2CH(CH3)] n 、[O(CH2)3] n and no atoms; R 2 and R 7 Each independently selected from the group consisting of: H, C 1-5 Alkyl chain and C with terminal epoxy group 1-5 Alkyl chain; m and n are each independently in the range of 1 to 225 and inclusive, R 3 and R 4 Each independently selected from aliphatic C 1-5 an alkyl chain; an alkoxy chain, such as a glycol chain; or no atom; and R 5 and R 6 Each is independently selected from H, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl.

34. The method according to any one of claims 22 to 33, wherein the crosslinking agent is selected from: 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, polyethylene glycol diglycidyl ether, bisphenol A diglycidyl ether, bis[4-(glycidyloxy)phenyl]methane, bisphenol A propoxylated diglycidyl ether, N,N-diglycidyl-4-glycidyloxyaniline, tris(2,3-epoxypropyl)isocyanurate, 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 cross-linking agent is a heat treatment.

36. An enhanced ion conducting membrane obtainable by a method according to any one of claims 22 to 35.

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