Reinforced ion-conducting membrane

Abstract

The present invention provides a reinforced ion-conductive membrane comprising (a) a reinforced layer containing a porous polymer structure and (b) a polymer ion-conductive membrane material impregnated within the porous polymer structure. The porous polymer structure contains a polymer backbone based on nitrogen-containing heterocycles, and the polymer ion-conductive membrane material has a transition temperature Tα in the range of 60°C to 80°C.

Description

Technical Field

[0001] The present invention relates to a reinforced ion conductive membrane. Specifically, the present invention relates to a reinforced proton exchange membrane and a method for manufacturing the same. The reinforced ion conductive membrane may be suitable for use in electrochemical devices such as fuel cells and / or electrolyzers.

Background Art

[0002] A fuel cell is an electrochemical cell that includes two electrodes separated by an electrolyte. A fuel, such as hydrogen, an alcohol such as methanol or ethanol, or formic acid, is supplied to the anode, and an oxidant, such as oxygen or air, is supplied to the cathode. An electrochemical reaction occurs at the electrodes, and the chemical energy of the fuel and the oxidant is converted into electrical energy and heat. An electrode catalyst 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 typically classified according to the nature of the electrolyte used. In many cases, the electrolyte is a solid polymer membrane that is electronically insulating but ionically conductive. In a proton exchange membrane fuel cell (PEMFC), the membrane is proton conductive, 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 used to produce high-purity hydrogen and oxygen by electrolyzing water. Electrolyzers can operate in both alkaline and acidic systems. Those using solid proton-conducting polymer electrolyte membranes or proton exchange membranes (PEMs) are known as proton exchange membrane water electrolyzers (PEMWEs). Those utilizing solid anion-conducting polymer electrolyte membranes or anion exchange membranes (AEMs) are known as anion exchange membrane water electrolyzers (AEMWEs).

[0005] Conventional ion-conducting membranes used in PEMFC or PEMWE 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.

[0006] Recent developments in fuel cells and electrolytic devices necessitate thinner membranes to achieve the benefits (such as improved ion conductivity and water transport). However, it is also essential that the membranes possess high durability under the often harsh operating conditions of fuel cells or electrolytic devices, and that such components do not lead to premature system failure.

[0007] To provide the mechanical properties necessary to increase resistance to premature failure, reinforcing materials, typically stretched polytetrafluoroethylene (ePTFE), are embedded within the membrane. Other types of reinforcing materials have also been proposed. For example, International Publication No. 2016020668(A1) discloses that heterocyclic polymers can be used as reinforcing components.

[0008] Under the operating conditions of fuel cells and electrolytic devices, there is a need to develop improved ion-conducting membranes with enhanced durability. [Overview of the Initiative]

[0009] The object of the present invention is to provide an improved reinforced ion-conducting film that is suitable for use in electrochemical devices such as fuel cells and electrolytic devices, and in particular has improved durability.

[0010] Therefore, in a first aspect of the present invention, the reinforced ion conductive film is, (a) A reinforced layer comprising a porous polymer structure, and (b) A polymer ion-conducting film material impregnated within a porous polymer structure, A reinforced ion-conducting film is provided, wherein the porous polymer structure includes a polymer backbone based on nitrogen-containing heterocycles, and the polymer ion-conducting film material has a transition temperature Tα in the range of 60 to 80°C.

[0011] Surprisingly, the combination of a reinforced layer containing a nitrogen-containing heterocyclic polymer and an ion-conductive film material having a selected transition temperature Tα was found to result in film components for electrochemical devices with extremely good durability, as shown in the examples.

[0012] The reinforced ion-conducting membrane of the first embodiment is particularly suitable for use as an electrolyte membrane in fuel cells and electrolytic devices.

[0013] The reinforced ion-conducting film of the first embodiment can be advantageously used to produce a catalyst coating film having high durability. Accordingly, a second embodiment of the present invention provides a catalyst coating film for a fuel cell or water electrolyzer, comprising a reinforced ion-conducting film according to the first embodiment, wherein a cathode catalyst layer is applied to a first surface of the film and / or an anode catalyst layer is applied to a second surface of the film. [Brief explanation of the drawing]

[0014] [Figure 1] The results of the periodic open-circuit voltage-relative humidity (COCV-RH) accelerated stress tests for Example 1 and Comparative Examples 1 and 2 are shown. [Figure 2] The results of the periodic open-circuit voltage-relative humidity (COCV-RH) accelerated stress tests for Example 2 and Comparative Example 3 are shown. [Modes for carrying out the invention]

[0015] The following describes preferred and / or optional features of the present invention. Any aspect of the present invention can be combined with any other aspect of the present invention unless otherwise required by context. Any preferred or optional feature of any aspect can be combined with any aspect of the present invention, individually or in combination, unless otherwise required by context.

[0016] The present invention provides a reinforced ion-conducting membrane, such as a polymer electrolyte membrane, comprising a reinforced layer and a polymer membrane ion-conducting polymer. The inventors have confirmed that the use of a polymer membrane ion-conducting polymer having a transition temperature Tα in the range of 60 to 80°C is particularly advantageous when combined with a reinforced porous polymer structure containing a nitrogen-containing heterocyclic skeleton such as polybenzimidazole.

[0017] Typically, porous nitrogen-containing heterocyclic polymer structures exhibit higher rigidity compared to other reinforcing materials, such as those based on aliphatic skeletons. To maintain high membrane conductivity, it is necessary to impregnate the polymer ion-conducting membrane material within the porous polymer structure. While not theoretically bound, the use of polymer ion-conducting membrane materials with transition temperatures Tα in the range of 60–80°C is considered advantageous in combination with such reinforcing materials because the impregnated membrane material has a greater ability to absorb and diffuse stress resulting from strains generated during operation under fluctuating relative humidity compared to ion-conducting membrane materials with higher Tα transition temperatures. This results in a reduction of defect and crack formation in the membrane material, which can lead to membrane rupture during use (typically involving changes in membrane water content that cause swelling or shrinkage of the impregnated ion-conducting membrane material). Furthermore, nitrogen-containing heterocyclic polymer structures have been found to offer additional durability advantages related to the capture of radical species formed during membrane operation.

[0018] The reinforced ion-conducting film includes a reinforcement layer comprising a porous polymer structure that provides mechanical reinforcement to the ion-conducting film, and includes a polymer backbone based on a nitrogen-containing heterocycle. The nitrogen-containing heterocycle may include a basic functional group. The nitrogen-containing basic functional group may be nitrogen having a lone pair of electrons. Preferably, the polymer backbone can be selected from polybenzimidazole, poly(pyridine), poly(pyrimidine), polybenzothiazole, polyoxadiazole, polyquinoline, polyquinoxaline, polythiadiazole, polytriazole, polyoxazole, polybenzoxazole, polythiazole, polypyrazole, and their derivatives. Preferably, the polymer backbone is derived from functionalized polyazoles or zwitterionic polyazoles, such as polybenzimidazole, polytriazole, polythiazole, and polydithiazole, and their derivatives, most preferably polybenzimidazole. Those skilled in the art will understand that the polymer skeleton may contain more than one type of nitrogen-containing heterocycle, or a mixture of nitrogen-containing heterocycles and other aliphatic or aromatic groups.

[0019] Preferably, the porous polymer structure includes a porous mat of nanofibers. The porous mat is preferably formed from entangled nanofibers. Typically, the nanofibers are ionically nonconductive. For example, the nanofibers preferably lack sulfonic acid groups and / or phosphate groups. The nanofibers may consist of entangled individual nanofibers. For example, the nanofibers may intersect with each other or be woven with other nanofibers or with themselves. The porous mat of nanofibers may also be in the form of a nonwoven material. Preferably, the nanofibers have a substantially random orientation in the plane (i.e., the xy plane) of the reinforced ion-conductive film. The nanofibers preferably have a diameter of 50 to 700 nm, preferably 200 to 600 nm, and more preferably 250 to 550 nm. The length of the nanofibers is not important to the present invention, but each nanofiber should be long enough (e.g., several millimeters or several centimeters) to entangle with one or more other nanofibers or with itself. Preferably, the nanofibers are spun nanofibers, that is, nanofibers are formed using spinning techniques. Examples of suitable spinning techniques include, but are not limited to, electrospinning and force spinning.

[0020] The porous polymer structure may include a second polymer, which is typically ionically nonconductive. The second polymer is different from the heterocyclic polymer from which the heterocyclic polymer backbone is derived (i.e., it has a different chemical composition). The second polymer may 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), polyethersulfone (PES), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyimide (PI), polyetherimide (PEI), poly(aryl ether ketone) (PAEK), poly(aryl ethersulfone), poly(phenylene sulfide) (PPS), and polyvinylpyrrolidone (PVP). Preferably, the second polymer is PVDF. By providing a porous polymer structure, such as a porous mat of nanofibers, that includes a polymer containing a polymer backbone based on nitrogen-containing heterocyclic rings and a second polymer, the mechanical and tensile properties of the porous polymer structure, and therefore the reinforced ion-conducting film, can be further improved.

[0021] The porous polymer structure may preferably not contain a second polymer. The porous polymer structure may preferably not contain PTFE. The porous polymer structure may preferably consist essentially of a polymer having a nitrogen-containing heterocyclic-based backbone. The porous polymer structure may preferably be formed from a polymer having a nitrogen-containing heterocyclic-based backbone of at least 95% by weight, such as at least 98% by weight, based on the total weight of the porous polymer structure.

[0022] The porous polymer structure preferably has an average basis weight in the range of 2 ~7 g / m 2 Preferably in the range of 1.5 g / m 2 ~4 g / m 2 Or preferably in the range of 1.5 g / m 2 ~3 g / m 2 Or 1.5 g / m 2 ~3 g / m 2 The average basis weight is determined from the porous polymer structure in the absence of the enhanced ion conductive membrane, i.e., before incorporation into the membrane. It will be understood that when the porous polymer structure has more than one reinforcing layer, the average basis weight refers to the average basis weight of the individual porous polymer structures incorporated into the enhanced ion conductive membrane.

[0023] Preferably, the porous polymer structure in the enhanced ion conductive membrane has a maximum thickness of 100% of the thickness of the enhanced ion conductive membrane, such as 90%, 80%, 70%, 60%, or 50% of the thickness of the enhanced ion conductive membrane. The porous polymer structure in the enhanced ion conductive membrane preferably has a minimum thickness of 5% of the thickness of the enhanced ion conductive membrane, such as 10%, 15%, 20%, 25%, or 30% of the thickness of the enhanced ion conductive membrane. The porous polymer structure of the enhanced ion conductive membrane may preferably have a thickness in the range of 5 to 95% of the thickness of the enhanced ion conductive membrane, such as in the range of 10 to 90% or 20 to 80% of the thickness of the enhanced ion conductive membrane. When the enhanced ion conductive membrane has more than one enhanced layer, it will be understood that the maximum and / or minimum thickness is the sum of the thicknesses of each porous polymer structure. The thickness of that or each porous polymer structure as part of the enhanced ion conductive membrane can be determined, for example, from a scanning electron microscope (SEM) image of the cross-section of the enhanced ion conductive membrane.

[0024] The polymer ion conductive membrane material has a transition temperature Tα in the range of 60 to 80°C. The ion conductive membrane material exhibits a thermal transition between a state where clusters of ionic groups are closely associated and a state where the interaction between these clusters is weakened, thus enabling long-range molecular motion. This transition is described as an alpha transition, and the transition temperature is Tα or T alpha. The transition temperature Tα of the ion conductive membrane material is measured by subjecting a sample of the membrane to dynamic mechanical analysis at a relative humidity of 0%, a vibration frequency of 1 Hz, and a temperature sweep rate of 1°C / min. The transition temperature Tα is preferably derived from a plot of tan delta against temperature and is the temperature at which the tan delta value is at its maximum.

[0025] The polymer ion conductive membrane material may preferably have a transition temperature Tα in the range of 62 to 78°C, such as 63 to 77°C, 64 to 76°C, or 65 to 75°C.

[0026] The polymer ion-conducting membrane material is impregnated into a porous polymer structure. Preferably, the porous polymer structure is essentially completely impregnated with the polymer ion-conducting membrane material.

[0027] An ion-conductive (electrolyte) membrane is formed by essentially completely impregnating a porous polymer structure with an ion-conductive membrane material. "Essentially completely impregnated" means that at least 80%, preferably at least 90%, preferably at least 95%, and ideally 100% of the pores of the porous polymer structure are filled with the ion-conductive polymer.

[0028] Preferably, an excess of conductive film material is present on both sides of the ion-conducting (electrolyte) film to aid in adhesion to the catalyst layer.

[0029] Preferably, the ion-conducting membrane material is formed from a proton-conducting polymer. Preferably, the ion-conducting membrane material contains a sulfonic acid group. Preferably, the ion-conducting membrane material contains a perfluorinated sulfonic acid (PFSA) ionomer, a partially fluorinated sulfonic acid ionomer, a non-fluorinated hydrocarbon sulfonic acid ionomer, or a mixture thereof. It may be even more preferable that the ion-conducting membrane material contains a perfluorinated sulfonic acid ionomer or a partially fluorinated sulfonic acid ionomer. It may be particularly preferable that the ion-conducting membrane material contains a perfluorinated sulfonic acid ionomer. The ion-conducting membrane material may also contain a blend of proton-conducting polymers, for example, a blend of perfluorinated sulfonic acid ionomers. The Tα of the proton-conducting polymer can be changed, for example, by incorporating a modified monomer. For example, U.S. Patent No. 11,492,431B2 (incorporated herein by reference) discloses that Tα can be varied by incorporating perfluoroalkyl vinyl ether and / or perfluoroalkoxyalkyl allyl ether monomers. Ion-conductive membrane materials may preferably contain perfluorinated sulfonic acid ionomers incorporating perfluoroalkyl vinyl ether and / or perfluoroalkoxyalkyl allyl ether monomers. The Tα of the membrane material can be readily determined by those skilled in the art as described herein. Suitable ion-conductive polymers useful for forming ion-conductive membrane materials having a desired range of Tα are known to those skilled in the art and include PFSA ionomer IQ171 (AGCInc).

[0030] Preferably, the reinforced ion-conducting film has a thickness of at least about 5 μm at 0% relative humidity. It may be preferable that the reinforced ion-conducting film has a thickness of at least about 6 μm, 7 μm, 8 μm, 9 μm, or at least about 10 μm. Typically, the thickness of the reinforced ion-conducting film at 0% relative humidity may be preferably about 200 μm, for example, 150 μm or less, 100 μm or less, 50 μm or less, 30 μm or less, 25 μm or less, or 20 μm or less. The film thickness can be determined by analysis of scanning electron microscope (SEM) images of the film's cross-section. The film may have thicknesses ranging from 5 μm to 200 μm, 6 to 100 μm, 6 to 50 μm, 7 to 30 μm, or 8 to 20 μm at 0% relative humidity.

[0031] A reinforced ion-conducting film can appropriately contain one reinforcement layer. Preferably, the reinforced ion-conducting film has one reinforcement layer and a thickness in the range of 8 μm to 30 μm at 0% relative humidity. Such film materials have an excellent combination of durability and conductivity. In some applications, a thicker film is preferred, for example, to reduce hydrogen crossover in electrolytic equipment applications. It may be preferable that the reinforced ion-conducting film has one reinforcement layer and a thickness in the range of 30 μm to 70 μm at 0% relative humidity.

[0032] A reinforced ion-conducting membrane may appropriately contain two or more reinforcement layers. Preferably, the reinforced ion-conducting membrane has two reinforcement layers and a thickness in the range of 60 μm to 90 μm at 0% relative humidity. Such a membrane provides an excellent combination of durability and strength while maintaining high ion conductivity. Such a membrane may be particularly useful when there is a large difference in gas pressure on both sides of the membrane during operation.

[0033] The advantages of using polymer ion-conducting membrane materials having a transition temperature Tα in the range of 60-80°C are particularly observable when the relative proportion of the reinforcing material is relatively high, which provides additional constraints on the expansion of the ion-conducting material. Preferably, the porous polymer structure is present in a total content of at least about 10 volume% based on the total volume of the reinforcing ion-conducting membrane. The volume% of the porous polymer structure refers to the space occupied by the porous polymer structure without the ion-conducting membrane material (i.e., before it is incorporated into the membrane), and is calculated as a percentage of the total volume of the reinforcing ion-conducting membrane (the volumes of the porous polymer structure and membrane are measured at 0% relative humidity). The porous polymer structure may be present in a total content of at least about 12 volume%, at least 15 volume%, or at least 18 volume%. The porous polymer structure may be present in a total content in the range of 10-30 volume%. In the case of a reinforcing ion-conducting membrane having two or more reinforcing layers, it will be understood by those skilled in the art that the total content of the porous polymer structure is calculated as the sum of the volumes of each porous polymer structure incorporated into the membrane.

[0034] The use of polymer ion-conducting film materials with a transition temperature Tα in the range of 60-80°C is also considered particularly useful when the reinforced ion-conducting film has high resistance to elongation under tension at high temperatures and high humidity. Such resistance to elongation at high temperatures and high humidity is beneficial in avoiding durability problems that may arise, for example, from cracking of the applied catalyst layer or changes in the expansion coefficient of the MEA components.

[0035] Therefore, preferably, the reinforced ion-conducting film has a longitudinal (MD) stress of at least 3.0 MPa at 8% strain at 80°C and 90% relative humidity. Preferably, the reinforced ion-conducting film has a longitudinal (MD) stress of at least 3.5, at least 4.0, at least 4.5, at least 5.0, at least 5.5, at least 6.0, at least 6.5, or at least 7.0 MPa at 8% strain at 80°C and 90% relative humidity. The maximum longitudinal (MD) stress is not particularly limited in the present invention, but is typically less than 10 MPa, for example, in the range of 3.0 to 10 MPa.

[0036] Preferably, the reinforced ion-conducting film has a transverse (TD) stress of at least 2.5 MPa at 8% strain at 80°C and 90% relative humidity. The reinforced ion-conducting film may preferably have a transverse (MD) stress of at least 3.0, at least 3.5, at least 4.0, at least 4.5, at least 5.0, at least 5.5, or at least 6.0 at 8% strain at 80°C and 90% relative humidity. The maximum longitudinal (MD) stress is not particularly limited in this invention, but is typically less than 8 MPa, for example, in the range of 2.5 to 8 MPa.

[0037] The stress (transverse and longitudinal) at 8% strain at 80°C and 90% relative humidity can be measured by subjecting a film sample to dynamic mechanical analysis at a stress gradient rate of 0.2 MPa / min at a relative humidity of 80°C and 90% relative humidity.

[0038] Polymer ion-conducting membrane materials typically have an equivalent weight (EW) in the range of 450–1000, for example, 450–900, 450–850, or 450–800. The copolymer equivalent is the weight of copolymer required to provide 1 mole of exchangeable protons. The copolymer equivalent 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 about 2 g of dry 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. Then, a titration by neutralization can be performed using, for example, 0.1 N hydrochloric acid to determine the number of exchangeable protons, and thus the EW can be calculated.

[0039] The reinforced ion-conducting membrane may further contain additives such as supported or unsupported recombining catalyst particles, for example, platinum catalyst particles (optionally on a carbon or metal oxide support), and radical scavengers (for example, cerium-containing compounds or manganese-containing compounds, for example, cerium oxide, metallic cerium oxide, manganese oxide, or cerium salts or manganese salts). The reinforced ion-conducting membrane may preferably contain cerium oxide, for example, nanoparticle-sized cerium oxide. The inventors have found that porous polymer structures containing a polymer backbone based on nitrogen-containing heterocycles such as polybenzimidazole have the ability to remove radical species. Therefore, the reinforced ion-conducting membrane may preferably not contain cerium-containing compounds or manganese-containing compounds (for example, cerium-containing compounds or manganese-containing compounds, for example, cerium oxide, metallic cerium oxide, manganese oxide, or cerium salts or manganese salts). In this specification, "free from cerium-containing compounds or manganese-containing compounds" means that the reinforced ion-conducting film is completely free of intentionally added cerium-containing compounds or manganese-containing compounds; however, this does not exclude the presence of impurity levels of cerium-containing compounds or manganese-containing compounds.

[0040] Reinforced ion-conducting films can be manufactured using methods known to those skilled in the art. Porous polymer structures may be appropriately formed on a suitable substrate or surface by spinning techniques; for example, porous polymer structures may be formed using electrospinning.

[0041] In one example of a suitable process, an electrospinning formulation is provided comprising at least one nitrogen-containing heterocyclic polymer and optionally a second polymer in a suitable solvent or a suitable solvent mixture, such as an organic solvent. The solvent may appropriately contain (or consist of) at least one of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), and / or dimethyl sulfoxide (DMSO), preferably DMAc and / or DMSO. The electrospinning formulation may be a solution or a dispersion. The electrospinning formulation is extruded through a needle using a syringe pump, and the needle is maintained at a potential difference with respect to the substrate / surface. The electrospinned nanofibers are collected on a translating and rotationally moving substrate (e.g., a rotating drum collector) set at a distance from the needle, e.g., about 10-15 cm away from the needle. The fiber morphology is obtained by controlling formulation parameters such as concentration, while the thickness and uniformity of the mat are controlled by the deposition time and the collector rotation / translational speed.

[0042] A porous polymer structure is impregnated with an ion-conducting polymer to form a reinforced ion-conducting film. The porous polymer structure can be impregnated with the ion-conducting polymer as part of a roll-to-roll process.

[0043] A porous polymer structure 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 carrier material. While the layer of ion-conducting polymer is still wet, the porous polymer structure is placed on the wet layer, allowing the ion-conducting polymer to impregnate one side of the porous polymer structure. A further layer of ion-conducting polymer is applied to a second side of the porous polymer structure, allowing it to impregnate the porous polymer structure from the second side. The impregnated porous polymer structure is dried, and preferably annealed, to form an ion-conducting (electrolyte) film.

[0044] The present invention also provides a catalyst coating film including the above-described reinforced ion-conducting film, having a cathode catalyst layer applied to a first surface of the film and / or an anode catalyst layer applied to a second surface of the film.

[0045] The catalyst layer comprises one or more electrode catalysts. Each of the one or more electrode catalysts is independently a finely pulverized unsupported metal powder or a supported catalyst, and the small nanoparticles are dispersed on a conductive fine-particle carbon support. The electrode catalyst metal is preferably, (i) Platinum group metals (platinum, palladium, rhodium, ruthenium, iridium, and osmium), (ii) Gold or silver, (iii) base metals; Alternatively, an alloy or mixture containing one or more of these metals or their oxides may be selected. A preferred electrode catalyst metal is platinum, which can be alloyed with other noble or base metals. Base metals are tin or transition metals that are not noble metals. Noble metals are platinum group metals (platinum, palladium, rhodium, ruthenium, iridium, or osmium), gold, or silver. Preferred 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 electrode catalyst is a supported catalyst, the amount of metal particles packed on the carbon support material is preferably in the range of 10 to 90% by weight, more preferably 15 to 75% by weight, of the weight of the resulting electrode catalyst.

[0046] The exact electrode catalyst used will depend on the reaction intended to be catalyzed, and its selection is within the capabilities of those skilled in the art.

[0047] The catalyst layer is preferably applied as an organic or aqueous ink to the first and / or second surface of the electrolyte membrane. The ink may preferably contain other components to improve ionic conductivity within the layer. Alternatively, the catalyst layer can be applied by decal transfer of a pre-prepared catalyst layer.

[0048] The catalyst layer may further contain additional components. Such additional components include, but are not limited to, catalysts that facilitate oxygen evolution and are therefore beneficial in cell inversion conditions and high potential shifts, 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.

[0049] The present invention further provides a membrane electrode assembly comprising the reinforced ion-conducting membrane of the present invention and a gas diffusion electrode and / or porous transport layer on the first and / or second surface of the ion-conducting membrane.

[0050] The present invention further provides a membrane electrode assembly comprising a catalyst-coated ion-conducting membrane and a gas diffusion layer or porous transport layer present on at least one catalyst layer.

[0051] The membrane electrode assembly may be fabricated in a number of ways, including but not limited to the following: (i) The ion-conductive (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) The catalytic ion conductive (electrolyte) membrane of the present invention having a catalyst layer on one side may be sandwiched between a gas diffusion layer or porous transport layer and a gas diffusion electrode or catalyst-coated porous transport layer, and the gas diffusion layer or porous transport layer is in contact with the side of the catalytic ion conductive (electrolyte) membrane having the catalyst component, or (iii) The catalytic ion conductive (electrolyte) membrane of the present invention having catalytic 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, for example, between one gas diffusion layer and one porous transport layer.

[0052] The anode and cathode gas diffusion layers are preferably based on conventional gas diffusion substrates. Typical substrates include nonwoven paper or webs containing a network of carbon fibers and a thermosetting resin binder (e.g., TGP-H series carbon fiber paper available from Toray Industries Inc., Japan, or H2315 series available from Freudenberg FCCT KG, Germany, or Sigracet® series available from SGL Technologies GmbH, Germany, or Ballard Power Systems). Examples include the AvCarb® series from Inc., or carbon fiber cloth. Carbon paper, web, or cloth can be further processed and incorporated into the MEA to enhance either wettability (hydrophilicity) or moisture resistance (hydrophobicity). The properties of any treatment depend on the type of fuel cell and the operating conditions under which it is used. The substrate can be made more wettable by incorporating materials such as amorphous carbon black through impregnation from a liquid suspension, or its hydrophobicity can be enhanced by impregnating the pore structure of the substrate with a colloidal suspension of a polymer such as PTFE or polyfluoroethylene propylene (FEP), followed by drying and heating above the melting point of the polymer. In applications such as PEMFCs, a microporous layer may be applied to the gas diffusion substrate on the surface that will come into contact with the electrode catalyst layer. The microporous layer typically contains a mixture of carbon black and a polymer such as polytetrafluoroethylene (PTFE).

[0053] The porous transport layer is preferably based on a conventional porous transport substrate such as titanium mesh.

[0054] The present invention further provides an electrochemical device comprising a reinforced ion-conducting membrane (e.g., an electrolyte membrane), a catalytically reinforced ion-conducting 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 electrolytic device, such as a water electrolytic device.

[0055] The present invention will be further described with reference to the following examples, which are illustrative and not intended to limit the present invention. [Examples]

[0056] Measurement of Tα Tα was measured using a TA instruments Q800 DMA equipped with a film tension clamp. Relative humidity was set to 0% by using a dry gas and in-line moisture trap. A 6 mm wide film sample was placed vertically between two clamps, separated by 16 mm. The instrument was set to the following settings: Oscillation frequency: 1Hz Mode: "Multi-frequency distortion" Amplitude: 10μm Static F:0.001N Force Track: 125% Minimum OscF:0.0001N Stabilization cycle: 4 Average cycle: 3

[0057] The sample was equilibrated at 30°C for one hour. Then, the temperature was gradient at a rate of 1.00°C / min to at least 120°C.

[0058] The data was analyzed by plotting Tan(δ) versus T using either TA Instruments' "Universal Analysis" or "Trios" software. The plot was then smoothed using a "region width" of 0.5°C, and Tα was defined as the temperature at which the smoothed Tan(δ) was at its maximum value.

[0059] Tensile strength measurement A rectangular film sample with a width of 6 mm is cut, and its thickness is then measured using a Mitutoyo VL-50 micrometer with a force of 0.01 N. The sample is then mounted on a TA Instruments Q800 Dynamic Mechanical Analyser (torque settings available upon request), with the clamps set approximately 16 mm apart. The length of the sample is precisely measured by the Q800 instrument using a force of 0.001 N. The temperature is increased to 80°C and the humidity to 90% RH while maintaining an initial force of 0.001 N and recording points every 2 seconds. The stress is then sloped at a rate of 0.2 MPa / min until the movable clamp reaches the end of its range of motion. The stress (MPa) at 8% strain can be determined from the stress-against-strain plot.

[0060] Formation of polybenzimidazole-reinforced materials Porous mats of polybenzimidazole nanofibers were prepared using poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole] by electrospinning using a method similar to that described in International Publication No. 2016 / 020668.

[0061] General method - Formation of ion-conducting films Ion-conductive films with a target thickness of 10 to 15 μm and containing polymer reinforcement were fabricated using a roll-to-roll process involving three coating passes performed with a dispersion of ion-conductive polymer in propanol-water containing a cerium radical scavenging additive. The first pass deposited an ion-conductive polymer layer on a PET backing sheet. After drying this layer, a second layer impregnated with polymer reinforcement was deposited. The second layer was then dried before the deposition (and subsequent drying) of a third layer containing the ion-conductive polymer. The formed films were annealed at a temperature higher than the glass transition temperature of the ion-conductive polymer. After annealing, the films were tested to determine the T-alpha of the ion-conductive film material.

[0062] The membrane was manufactured using the following combination:

[0063] [Table 1]

[0064] COCV-RH cycle accelerated stress test The membrane electrode assembly (MEA) was formed from a membrane manufactured using a hot-press method. A platinum-carbon catalyst layer was applied to each side of the membrane to form a concentrated chemical chamber (CCM), a hot-press seal was applied around the edges of the CCM to leave a defined active region, and then a gas diffusion layer was added to each side to form the MEA.

[0065] Each MEA was subjected to a periodic open-circuit voltage-relative humidity (COCV-RH) cycling test at 90°C, and the differential pressure across the membrane was detected every 1000 cycles. Membrane failure was detected as a sharp increase in the pressure difference from its nominal baseline. The results are shown in Figure 4. As can be seen from this figure, the MEA formed from the membranes fabricated in Example 1 showed a significant improvement in MEA durability compared to either (i) the combination of high-T alpha ionomer and PBI reinforcement, or (ii) the combination of ePTFE reinforcement and low-T alpha ionomer.

[0066] Additional examples Further films were fabricated using a different PFSA ionomer.

[0067] [Table 2]

[0068] Figure 5 shows the combined results of OSV and RH cycle accelerated stress tests on MEAs incorporating the films formed in Example 2 and Comparative Example 3. The results indicate that the combination of PBI reinforcement and a film material with a Tα of approximately 75°C provides extremely high durability, greater than that achieved with films formed from the same PFSA ionomer but with ePTFE reinforcement.

Claims

1. A reinforced ion-conducting film, (a) A reinforced layer containing a porous polymer structure, and (b) comprising a polymer ion conductive film material impregnated within the porous polymer structure, The porous polymer structure comprises a polymer backbone based on a nitrogen-containing heterocycle, and the polymer ion-conducting film material has a transition temperature Tα in the range of 60°C to 80°C, thereby providing a reinforced ion-conducting film.

2. The reinforced ion-conducting film according to claim 1, wherein the polymer ion-conducting film material has a transition temperature Tα in the range of 65 to 75°C.

3. The reinforced ion-conducting film according to claim 1 or claim 2, wherein the film has a thickness of at least about 8 μm, for example, in the range of 10 to 100 μm, at a relative humidity of 0%.

4. The reinforced ion-conducting film according to any one of claims 1 to 3, wherein the porous polymer structure includes a porous mat of nanofibers.

5. The reinforced ion-conducting film according to any one of claims 1 to 4, wherein the nanofiber is a spun nanofiber.

6. The reinforced ion-conducting membrane according to any one of claims 1 to 5, wherein the porous polymer structure is present in a total content of at least about 10 volume percent based on the total volume of the reinforced ion-conducting membrane.

7. The reinforced ion-conducting film according to any one of claims 1 to 6, wherein the film has a longitudinal (MD) stress of at least 3.0 MPa at 80°C and 90% relative humidity and 8% strain.

8. The reinforced ion-conducting film according to any one of claims 1 to 7, wherein the film has a transverse (TD) stress of at least 2.5 MPa at 8% strain at 80°C and 90% relative humidity.

9. The reinforced ion-conducting film according to any one of claims 1 to 8, wherein the polymer ion-conducting film material is a proton-conducting polymer.

10. The reinforced ion-conducting film according to any one of claims 1 to 9, wherein the ion-conducting film material contains a sulfonic acid group.

11. The reinforced ion-conducting film according to any one of claims 1 to 10, wherein the ion-conducting film material is a perfluorinated sulfonic acid ionomer, or a partially fluorinated or non-fluorinated hydrocarbon sulfonic acid ionomer.

12. The reinforced ion-conducting film according to any one of claims 1 to 11, wherein the porous polymer structure further comprises a second polymer, and the second polymer is ion-nonconductive.

13. The reinforced ion-conducting film according to claim 12, wherein the second polymer is selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethersulfone (PES), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyimide (PI), polyetherimide (PEI), poly(aryletherketone) (PAEK), poly(arylethersulfone), poly(phenylene sulfide) (PPS), and polyvinylpyrrolidone (PVP).

14. The reinforced ion-conducting film according to any one of claims 1 to 13, wherein the polymer skeleton based on a nitrogen-containing heterocycle is selected from the group consisting of polybenzimidazole, poly(pyridine), poly(pyrimidine), polybenzothiazole, polyoxadiazole, polyquinoline, polyquinoxaline, polythiadiazole, polytriazole, polyoxazole, polybenzoxazole, polythiazole, polypyrazole, and derivatives thereof.

15. The reinforced ion-conducting film according to any one of claims 1 to 14, wherein the polymer skeleton based on the nitrogen-containing heterocycle is polybenzimidazole or a derivative thereof.

16. A reinforced ion-conductive film according to any one of claims 1 to 15, comprising two or more reinforcing layers.

17. The reinforced ion-conducting film according to claim 15, wherein the thickness at 0% relative humidity is in the range of 60 to 100 μm.

18. A reinforced ion-conducting film according to any one of claims 1 to 17, comprising a recombination catalyst.

19. A reinforced ion-conducting film according to any one of claims 1 to 18, which does not contain a cerium-containing compound or a manganese-containing compound.

20. The reinforced ion-conductive film according to any one of claims 1 to 19, wherein the polymer ion-conductive film material has an equivalent amount in the range of 450 to 1000, for example, 450 to 850.

21. A catalyst coating film for a fuel cell or water electrolysis device, comprising a reinforced ion-conducting film according to any one of claims 1 to 20, wherein a cathode catalyst layer is applied to a first surface of the film and / or an anode catalyst layer is applied to a second surface of the film.

22. (i) a reinforced ion-conducting membrane according to any one of claims 1 to 20, (ii) a catalyst coating membrane according to claim 21, and at least one gas diffusion layer or porous transport layer, a membrane electrode assembly for a fuel cell or water electrolysis device.

23. A water electrolysis device or fuel cell comprising the catalyst coating film according to claim 21 or the membrane electrode assembly according to claim 22.

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