Enhanced ion conducting membranes

Abstract

The present invention provides a reinforced ion conducting membrane comprising: (a) a reinforcement layer comprising a porous polymer structure; and (b) a polymer ion conducting membrane material impregnated within the porous polymer structure; wherein the porous polymer structure comprises a polymer backbone based on a nitrogen-containing heterocyclic ring, and the polymer ion-conducting membrane material has a transition temperature T [alpha] in the range of from 60 DEG C to 80 DEG C and including end values.

Description

Technical Field

[0001] The present invention relates to enhanced ion-conducting membranes. In particular, the present invention relates to enhanced proton exchange membranes and methods for making the same. The enhanced ion-conducting membranes are suitable for use in electrochemical devices such as fuel cells and / 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 that is electrically insulating but ionically conductive. In a proton exchange membrane fuel cell (PEMFC), the membrane is proton-conducting and transports protons generated at the anode 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 operate in alkaline and acidic systems. Those electrolyzers adopting solid proton-conducting polymer electrolyte membrane or proton exchange membrane (PEM) are called proton exchange membrane water electrolyzer (PEMWE). Those electrolyzers utilizing solid anion-conducting polymer electrolyte membrane or anion exchange membrane (AEM) are called anion exchange membrane water electrolyzer (AEMWE).

[0005] Conventional ion-conducting membranes used in PEMFCs or PEMWEs are typically formed from sulfonated perfluorinated polymer materials, often collectively 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 electrolyzers require thinner membranes because of the advantages this offers (improved ionic conductivity, improved water transport, etc.). However, it is also important that the membranes have high durability under the typically harsh operating conditions of a fuel cell or electrolyzer so that such components do not cause premature failure of the system.

[0007] To provide the desired mechanical properties and enhance resistance to premature failure, reinforcements, typically expanded polytetrafluoroethylene (ePTFE), can be embedded within the membrane. Other types of reinforcements have also been proposed. For example, WO2016020668A1 discloses the use of heterocyclic polymers as reinforcing components.

[0008] There remains a need to develop improved ion-conducting membranes having enhanced durability under fuel cell and electrolyzer operating conditions. Summary of the Invention

[0009] 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 durability.

[0010] Therefore, in a first aspect of the present invention, there is provided an enhanced ion-conducting membrane comprising:

[0011] (a) a reinforcement layer comprising a porous polymer structure; and

[0012] (b) a polymer ion-conducting membrane material impregnated in a porous polymer structure;

[0013] The porous polymer structure comprises a nitrogen-containing heterocycle-based polymer backbone, and the polymer ion-conducting membrane material has a transition temperature Ta in the range of 60°C to 80°C, inclusive.

[0014] Surprisingly, it was found that using a combination of a reinforcement layer comprising a nitrogen-containing heterocycle-based polymer and an ion-conducting membrane material having a selected transition temperature Ta can result in membrane components with excellent durability for electrochemical devices, as shown in the Examples.

[0015] The enhanced ion-conducting membrane of the first aspect is particularly suitable for use as an electrolyte membrane in fuel cells and electrolysers.

[0016] The enhanced ion-conducting membrane of the first aspect can be advantageously used to produce a catalyst-coated membrane having high durability. Therefore, in a second aspect of the present invention, there is provided a catalyst-coated membrane for a fuel cell or a water electrolyzer, the catalyst-coated membrane comprising the enhanced ion-conducting membrane according to the first aspect, wherein a cathode catalyst layer is applied to a first side of the membrane and / or an anode catalyst layer is applied to a second side of the membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Results of cyclic open circuit voltage-relative humidity (COCV-RH) accelerated stress tests of Example 1 and Comparative Examples 1 and 2 are shown.

[0018] Figure 2 The results of cyclic open circuit voltage-relative humidity (COCV-RH) accelerated stress tests of Example 2 and Comparative Example 3 are shown. DETAILED DESCRIPTION

[0019] 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, either individually or in combination.

[0020] The present invention provides a reinforced ion-conducting membrane, such as a polymer electrolyte membrane, comprising a reinforcement layer and a polymer membrane ion-conducting polymer. The present inventors have determined that the use of a polymer membrane ion-conducting polymer having a transition temperature, Tα, in the range of 60° C. to 80° C., inclusive, is particularly advantageous when combined with a reinforced porous polymer structure comprising a backbone having a nitrogen-containing heterocycle, such as polybenzimidazole.

[0021] Generally, compared with other reinforcing materials (such as those based on aliphatic main chains), porous nitrogen-containing heterocyclic polymer structure has increased rigidity. In order to maintain high membrane conductivity, it is necessary to impregnate polymer ion conductive membrane material in porous polymer structure. Without being bound by theory, it is believed that it is advantageous to use in combination with such reinforcing materials the polymer ion conductive membrane material with a transition temperature Tα in the range of 60 ℃ to 80 ℃ and including end values, because compared with the ion conductive membrane material with a higher Tα transition temperature, the impregnated membrane material can better absorb and diffuse the stress caused by the strain occurring during operation under the relative humidity of fluctuations. This results in a reduction in the formation of defects and cracks in the membrane material, which may cause the membrane to rupture during use (this is generally related to the change of membrane water content, causing the ion conductive membrane material of the impregnation to swell or shrink). In addition, it has been found that nitrogen-containing heterocyclic polymer structure can provide additional durability benefits, which are associated with removing free radical species formed during membrane operation.

[0022] The enhanced ion-conducting membrane comprises a reinforcing layer comprising a porous polymer structure that provides mechanical reinforcement for the ion-conducting membrane and comprises a polymer backbone based on a nitrogen-containing heterocycle. The nitrogen-containing heterocycle may comprise a basic functional group. The nitrogen-containing basic functional group may be nitrogen with a lone pair of electrons. The polymer backbone may be suitably derived from polybenzimidazole, polypyridine, polypyrimidine, polybenzothiazole, polyoxadiazole, polyquinoline, polyquinoxaline, polythiadiazole, polytriazole, polyoxazole, polybenzoxazole, polythiazole, polypyrazole and their derivatives. Suitably, the polymer backbone is derived from a functionalized polyazole or a zwitterionic polyazole, such as polybenzimidazole, polytriazole, polythiazole and polyoxadiazole and their derivatives; the most suitable is polybenzimidazole. It will be understood by those skilled in the art that the polymer backbone may comprise more than one type of nitrogen-containing heterocycle, or a mixture of nitrogen-containing heterocycles with other aliphatic or aromatic groups.

[0023] Suitably, the porous polymer structure comprises a porous mat of nanofibers. The porous mat is suitably formed by entangled nanofibers. Generally, the nanofibers are ion-nonconductive. For example, the nanofibers suitably do not contain sulfonic acid groups and / or phosphoric acid groups. The nanofibers may comprise discrete nanofibers that are entangled. 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 non-woven fabric material. Suitably, the nanofibers have a substantially random orientation in the plane (i.e., xy plane) of the enhanced ion-conducting membrane. The nanofibers suitably have a diameter of 50nm to 700nm, suitably 200nm to 600nm and preferably 250nm to 550nm. The length of the nanofibers is not important for the present invention, but each nanofiber should be long enough (e.g., several millimeters or centimeters) to entangle with one or more other nanofibers or with itself. The nanofibers are suitably spun nanofibers, i.e., the nanofibers are formed using spinning technology. Examples of suitable spinning technologies include, but are not limited to, electrospinning and power spinning.

[0024] The porous polymer structure may include a second polymer that is generally ion-nonconductive. The second polymer is different from (that is, in the sense that it has different chemical compositions) a polymer based on a heterocycle derived from a polymer backbone based on a heterocycle. 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 consisting of poly (vinylidene fluoride) (PVDF), polytetrafluoroethylene (PTFE), polyethersulfone (PES), 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. Providing a porous polymer structure (such as a porous mat of nanofibers) can further improve the mechanical and tensile properties of the porous polymer structure, and therefore improve the enhanced ion-conducting membrane, the porous polymer structure including a polymer and a second polymer containing a polymer backbone based on a nitrogen-containing heterocycle.

[0025] Preferably, the porous polymer structure does not comprise a second polymer. Preferably, the porous polymer structure does not comprise PTFE. Preferably, the porous polymer structure consists essentially of a polymer having a backbone based on a nitrogen-containing heterocycle. Preferably, the porous polymer structure is formed from at least 95 wt%, such as at least 98 wt%, of a polymer having a backbone based on a nitrogen-containing heterocycle, based on the total weight of the porous polymer structure.

[0026] The porous polymer structure suitably has a 2 Up to 7g / m 2range, preferably 1.5g / m 2 Up to 4g / m 2 In the range of, or preferably in the range of 1.5g / m 2 Up to 3g / m 2 or 1.5g / m 2 Up to 3g / m 2 The average basis weight is determined for the porous polymer structure in the absence of a reinforced ion-conducting membrane, i.e., prior to incorporation into the membrane. It should be understood that where the porous polymer structure has more than one reinforcement layer, the average basis weight refers to the average basis weight of each individual porous polymer structure incorporated into the reinforced ion-conducting membrane.

[0027] Suitably, the maximum thickness of the porous polymer structure in the enhanced ion-conducting membrane is 100% of the thickness of the enhanced ion-conducting membrane, such as a maximum thickness of 90%, 80%, 70%, 60% or 50% of the thickness of the enhanced ion-conducting membrane. Suitably, the minimum thickness of the porous polymer structure in the enhanced ion-conducting membrane is 5% of the thickness of the enhanced ion-conducting membrane, such as a minimum thickness of 10%, 15%, 20%, 25% or 30% of the thickness of the enhanced ion-conducting membrane. Preferably, the thickness of the porous polymer structure in the enhanced ion-conducting membrane may be in the range of 5% to 95% of the thickness of the enhanced ion-conducting membrane and inclusive, such as a thickness in the range of 10% to 90% or 20% to 80% of the thickness of the enhanced ion-conducting membrane and inclusive. It will be understood that where the enhanced ion-conducting membrane has more than one reinforcement layer, the maximum and / or minimum thickness is the sum of the thicknesses of each porous polymer structure. The thickness of the or each porous polymer structure as a proportion of the enhanced ion conducting membrane may be determined, for example, from a scanning electron microscope (SEM) image of a cross-section of the enhanced ion conducting membrane.

[0028] The polymeric ion-conducting membrane material has a transition temperature, Tα, in the range of 60°C to 80°C, inclusive. The ion-conducting membrane material exhibits a thermal transition between a state in which clusters of ionic groups are tightly associated and a state in which the interactions between those clusters are weakened, thereby allowing long-range molecular motion. This transition is described as an alpha transition, and the transition temperature is Tα or Tα. The transition temperature, Tα, of the ion-conducting membrane material is measured by dynamic mechanical analysis of a membrane sample at 0% relative humidity, an oscillation frequency of 1 Hz, and a temperature scan rate of 1°C / min. The transition temperature, Tα, is suitably derived from a graph of Tanδ versus temperature and is the temperature at which the Tanδ value is a maximum.

[0029] It may be preferred that the polymeric ion conducting membrane material has a transition temperature Ta in the range of 62 to 78°C inclusive, such as 63 to 77°C, 64 to 76°C or 65 to 75°C.

[0030] The polymeric ion conducting membrane material is impregnated within the porous polymer structure. Preferably, the porous polymer structure is substantially completely impregnated with the polymeric ion conducting membrane material.

[0031] The porous polymer structure is substantially completely impregnated with the ion-conducting membrane material 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 polymer structure are filled with the ion-conducting polymer.

[0032] Suitably, excess membrane material is present on both surfaces of the ion-conducting (electrolyte) membrane to aid adhesion to the catalyst layer.

[0033] Suitably, the ion-conducting membrane material is formed by a proton-conducting polymer. Preferably, the ion-conducting membrane material comprises a sulfonic acid group. The ion-conducting membrane material preferably comprises 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 further preferred that the ion-conducting membrane material comprises a perfluorinated sulfonic acid ionomer or a partially fluorinated sulfonic acid ionomer. It may be particularly preferred that the ion-conducting membrane material comprises a perfluorinated sulfonic acid ionomer. The ion-conducting membrane material may comprise a blend of proton-conducting polymers, such as a blend of perfluorinated sulfonic acid ionomers. The Tα of the proton-conducting polymer may be changed, for example, by incorporating a modified monomer. For example, US 11,492,431 B2 discloses that incorporating a perfluoroalkyl vinyl ether and / or a perfluoroalkoxyalkyl allyl ether monomer can be used to change Tα, and the patent is incorporated herein by reference. Preferably, the ion-conducting membrane material comprises a perfluorinated sulfonic acid ionomer doped with perfluoroalkyl vinyl ether and / or perfluoroalkoxyalkyl allyl ether monomers. As described herein, one skilled in the art can readily determine the Tα of the membrane material. Suitable ion-conducting polymers for forming ion-conducting membrane materials having a Tα within the desired range are known to those skilled in the art and include PFSA ionomer IQ171 (AGC Inc).

[0034] Suitably, the enhanced ion-conducting membrane has a thickness of at least about 5 μm at 0% relative humidity. Preferably, the enhanced ion-conducting membrane has a thickness of at least about 6 μm, 7 mm, 8 mm, 9 μm or at least about 10 μm. Typically, the thickness of the enhanced ion-conducting membrane at 0% relative humidity is less than or equal to about 200 μm, such as less than or equal to 150 μm, less than or equal to 100 μm, less than or equal to 50 μm, less than or equal to 30 μm, less than or equal to 25 μm, or less than or equal to 20 μm. The thickness of the membrane can be determined by analyzing a scanning electron microscope (SEM) image of a cross-section of the membrane. Preferably, the membrane has a thickness in the range of 5 μm to 200 μm, 6 μm to 100 μm, 6 μm to 50 μm, 7 μm to 30 mm or 8 μm to 20 mm at 0% relative humidity and including end values.

[0035] The enhanced ion-conducting membrane may suitably include a reinforcement layer. Suitably, the enhanced ion-conducting membrane has a reinforcement layer and has a thickness in the range of 8 μm to 30 μm, inclusive, at 0% relative humidity. Such membrane materials have an excellent combination of durability and conductivity. For some applications, thicker membranes are preferred, for example, to reduce hydrogen permeation in electrolyzer applications. Preferably, the enhanced ion-conducting membrane has a reinforcement layer and has a thickness in the range of 30 μm to 70 μm, inclusive, at 0% relative humidity.

[0036] The reinforced ion-conducting membrane may suitably include two or more reinforcement layers. Suitably, the reinforced ion-conducting membrane has two reinforcement layers and has a thickness in the range of 60 μm to 90 μm, inclusive, at 0% relative humidity. Such membranes offer an excellent combination of durability and strength while maintaining high ionic conductivity. Such membranes may be particularly useful when there is a large gas pressure differential on opposite sides of the membrane during operation.

[0037] It is believed that when the relative proportion of reinforcing material is relatively high, the benefits of using polymer ion conductive membrane materials with a transition temperature Tα in the range of 60°C to 80°C and including end values can be particularly observed, which provides additional constraints on the expansion of the ion conductive material. Suitably, based on the total volume of the enhanced ion conductive membrane, the porous polymer structure is present in a total content of at least about 10% by volume. The volume % of the porous polymer structure refers to the space occupied by the porous polymer structure without ion conductive membrane material (i.e., before being incorporated into the membrane), and is calculated as the volume ratio of the total volume of the enhanced ion conductive membrane (wherein the volume of the porous polymer structure and the membrane is measured at 0% relative humidity). The porous polymer structure can be present in a total content of at least about 12% by volume, at least 15% by volume, or at least 18% by volume. The porous polymer structure can be present in a total content in the range of 10% to 30% by volume and including end values. Those skilled in the art will understand that in the case where the enhanced ion conductive membrane has two or more reinforcing layers, 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.

[0038] The use of polymeric ion-conducting membrane materials having a transition temperature, Tα, in the range of 60° C. to 80° C., inclusive, is also believed to be particularly useful when the enhanced ion-conducting membrane has a high resistance to stretching under tension at elevated temperatures and humidity. Such resistance to stretching at elevated temperatures and humidity is beneficial in avoiding durability issues that may arise, for example, from cracking of applied catalyst layers or varying expansion rates of MEA components.

[0039] Thus, suitably, the reinforced ion-conducting membrane 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 membrane has a longitudinal (MD) stress of at least 3.5 MPa, at least 4.0 MPa, at least 4.5 MPa, at least 5.0 MPa, at least 5.5 MPa, at least 6.0 MPa, at least 6.5 MPa, 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, within the range of 3.0 MPa to 10 MPa and including the end values.

[0040] Suitably, the reinforced ion-conducting membrane has a transverse direction (TD) stress of at least 2.5 MPa at 8% strain at 80°C and 90% relative humidity. Preferably, the reinforced ion-conducting membrane has a transverse direction (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 direction (MD) stress is not particularly limited in the present invention, but is typically less than 8 MPa, for example, in the range of 2.5 MPa to 8 MPa, inclusive.

[0041] The stress (in both the transverse and longitudinal directions) at 8% strain at 80°C and 90% relative humidity can be measured by dynamic mechanical analysis of film samples at 80°C and 90% relative humidity with a stress ramp rate of 0.2 MPa / min.

[0042] Polymer ion conducting membrane materials typically have an equivalent weight (EW) in the range of 450 to 1000 and including end values, such as 450 to 900, 450 to 850 or 450 to 800. The equivalent weight of a copolymer is the weight of the copolymer required to provide 1 mole of exchangeable protons. The equivalent weight of a copolymer can be easily measured using acid titration after hydroxide exchange. For example, a membrane sample can be vacuum dried at 110° C. for 16 hours to obtain a dry membrane of about 2 g. The membrane 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 therefore EW can be calculated.

[0043] The enhanced ion-conducting membrane may also include additives such as supported or unsupported composite catalyst particles, for example platinum catalyst particles (optionally on carbon or metal oxide supports), and free radical scavengers (such as cerium-containing or manganese-containing compounds, for example cerium oxide, cerium metal oxide, manganese oxide or cerium salts or manganese salts). Preferably, the enhanced ion-conducting membrane includes cerium oxide, for example nanoparticle cerium oxide. The inventors have found that porous polymer structures (such as polybenzimidazole) comprising polymer backbones based on nitrogen-containing heterocycles have the ability to remove free radical species. Therefore, preferably, the enhanced ion-conducting membrane does not include cerium-containing compounds or manganese-containing compounds (such as cerium-containing or manganese-containing compounds, for example cerium oxide, cerium metal oxide, manganese oxide or cerium salts or manganese salts). Not including cerium-containing compounds or manganese-containing compounds refers to in this article that the enhanced ion-conducting membrane does not have any intentionally added cerium-containing or manganese-containing compounds, but this does not exclude the presence of impurity levels of cerium-containing or manganese-containing compounds.

[0044] The enhanced ion conducting membrane may be manufactured using methods known to those skilled in the art.The porous polymer structure may suitably be formed onto a suitable substrate or surface by spinning techniques, for example the porous polymer structure may be formed using electrospinning.

[0045] In an example of a suitable method, an electrospinning formulation is provided, which is included in at least one nitrogen-containing heterocyclic polymer and an optional second polymer in a suitable solvent (such as an organic solvent or a suitable solvent mixture). The solvent may suitably include at least one of (or be composed of): N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc) and / or dimethyl sulfoxide (DMSO), suitably DMAc and / or DMSO. The electrospinning formulation may be a solution or a dispersion. A syringe pump is used to push the electrospinning formulation 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 10 cm to 15 cm from the needle. The fiber morphology is obtained by controlling formulation parameters (such as concentration), while mat thickness and uniformity are controlled by deposition time and collector rotation / translation speed.

[0046] The porous polymer structure is impregnated with an ion-conducting polymer to form an enhanced ion-conducting membrane.As part of a roll-to-roll process, the porous polymer structure can be impregnated with an ion-conducting polymer.

[0047] The porous polymer structure can be impregnated with an ion-conducting polymer by the following method. An ion-conducting polymer layer (in solution / dispersion) is cast onto a support material. When the ion-conducting polymer layer is still wet, the porous polymer structure is placed into the wet layer and the ion-conducting polymer is impregnated into one face of the porous polymer structure. Another ion-conducting polymer layer is applied to the second face of the porous polymer structure and impregnated into the porous polymer structure from the second face. The impregnated porous polymer structure is dried and suitably annealed to form an ion-conducting (electrolyte) membrane.

[0048] The present invention also provides a catalytically coated membrane comprising an enhanced ion conducting membrane as described above, wherein a cathode catalyst layer is applied to a first side of the membrane and / or an anode catalyst layer is applied to a second side of the membrane.

[0049] 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

[0050] (i) platinum group metals (platinum, palladium, rhodium, ruthenium, iridium and osmium),

[0051] (ii) gold or silver,

[0052] (iii) base metals,

[0053] Or an alloy or mixture comprising one or more of these metals or their oxides. The preferred electrocatalyst metal is platinum, which can form an alloy 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 suitably in the range of 10% to 90% by weight, preferably 15% to 75% by weight, of the weight of the resulting electrocatalyst.

[0054] 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.

[0055] 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 to improve ionic conductivity within the layer. Alternatively, the catalyst layer may be applied by decal transfer of a previously prepared catalyst layer.

[0056] The catalyst layer may also contain additional components. Such additional components include, but are not limited to, catalysts that promote oxygen evolution and thus are beneficial in cell reversal conditions 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.

[0057] The present invention also provides a membrane electrode assembly comprising the enhanced ion conductive membrane of the present invention and a gas diffusion electrode and / or a porous transport layer on the first side and / or the second side of the ion conductive membrane.

[0058] The present invention also provides a membrane electrode assembly comprising a catalyst-coated ion-conducting membrane and a gas diffusion layer or a porous transport layer present on at least one catalyst layer.

[0059] Membrane electrode assemblies can be made in a variety of ways, including but not limited to:

[0060] (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);

[0061] (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;

[0062] (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, for example one gas diffusion layer and one porous transport layer.

[0063] 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 GL 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)), followed by 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 side that will contact the electrocatalyst layer. The microporous layer typically comprises a mixture of carbon black and a polymer (such as polytetrafluoroethylene (PTFE)).

[0064] The porous transport layer is suitably based on a conventional porous transport substrate, such as titanium mesh.

[0065] The present invention also provides an electrochemical device comprising an enhanced ion-conducting membrane (e.g., an electrolyte membrane), a catalytic enhanced 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 electrolyzer, such as a water electrolyzer.

[0066] The present invention will now be further described with reference to the following examples, which are intended to illustrate but not to limit the present invention.

[0067] Example

[0068] Measurement of Tα

[0069] Tα was measured using a TA Instruments Q800 DMA equipped with a film tension clamp. Relative humidity was set to 0% using dry gas and an inline moisture trap. A 6 mm wide film sample was mounted vertically between two clamps approximately 16 mm apart. The instrument was set to the following settings:

[0070]

[0071] The sample was equilibrated at 30°C for 1 hour. The temperature was then increased to at least 120°C at a rate of 1.00°C / min.

[0072] The data were analyzed using TA Instruments' "Universal Analysis" or "Trios" software by plotting Tan(δ) versus T. The curve was then smoothed using a "band width" of 0.5°C, and Tα was taken as the temperature at which the smoothed Tan(δ) was at its maximum.

[0073] Tensile strength measurement

[0074] Cut 6mm wide rectangular film samples and measure their thickness using a VL-50 micrometer from Mitutoyo, which uses a force of 0.01N. The samples are then mounted in a Q800 dynamic mechanical analyzer from TA Instruments (torque settings are available upon request), with the fixtures set to be approximately 16mm apart. The sample length is accurately measured using a force of 0.001N using the Q800 instrument. Maintaining an initial force of 0.001N and recording a point every 2 seconds, the temperature is raised to 80°C and the humidity is raised to 90%RH. The stress is then gradually increased at a rate of 0.2MPa / min until the movable fixture reaches the end of its range of motion. The stress (MPa) at 8% strain can be determined from a stress versus strain graph.

[0075] Formation of polybenzimidazole reinforcement

[0076] Porous mats of polybenzimidazole nanofibers were prepared by electrospinning using poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] using a method similar to that described in WO 2016 / 020668.

[0077] General Methods - Formation of Ion-Conducting Membranes

[0078] The ion-conducting membranes with a target thickness of 10 μm to 15 μm and containing polymer reinforcements were manufactured using a roll-to-roll process that included three coating passes using a dispersion of an ion-conducting polymer in propanol-water containing a cerium radical scavenging additive. The first pass deposited a layer of the ion-conducting polymer onto a PET backing sheet. This layer was then dried, followed by the deposition of a second layer into which the polymer reinforcement was impregnated. The second layer was then dried, followed by the deposition (and subsequent drying) of a third layer containing the ion-conducting polymer. The resulting membrane was annealed at a temperature above the glass transition temperature of the ion-conducting polymer. After annealing, the membrane was tested to determine the Tα of the ion-conducting membrane material.

[0079] Prepare membranes with the following combination:

[0080]

[0081] COCV-RH Cyclic Accelerated Stress Test

[0082] The membrane electrode assembly (MEA) is formed from a membrane that is prepared using the following method: a carbon-supported platinum catalyst layer is applied on each side of the membrane using a hot press method to form a CCM, hot press sealing is performed around the edges of the CCM to leave a defined active area, and then a gas diffusion layer is added on each side to form the MEA.

[0083] Each MEA was subjected to cyclic open circuit voltage-relative humidity (COCV-RH) cycling testing at 90°C, where the pressure differential across the membrane was measured every 1,000 cycles. Membrane failure was detected as a sharp increase in the pressure differential from its nominal baseline. The results are shown in Figure 4. As can be seen from this figure, MEAs formed from the membrane prepared in Example 1 produced a significant improvement in MEA durability compared to the following combinations: (i) a combination of a high Tα ionomer and PBI reinforcement; or (ii) a combination of ePTFE reinforcement and a low Tα ionomer.

[0084] Additional Examples

[0085] Additional membranes were prepared using alternative PFSA ionomers:

[0086] Example reinforcers Ion-conducting polymers Film thickness (μm) Membrane Tα Example 2 <![CDATA[PBI(2.4g / m 2 )]]> PFSA Ionomer C 10 74℃ Comparative Example 3 <![CDATA[ePTFE(4.7g / m 2 )]]> PFSA Ionomer C 15 85℃

[0087] The results of OSV and RH cycle accelerated stress testing of a combination of MEAs incorporating membranes formed in Example 2 and Comparative Example 3 are shown in Figure 5. The results show that the combination of PBI reinforcement and a membrane material having a Ta of approximately 75°C provides extremely high durability, which is greater than the durability achieved by a membrane formed from the same PFSA ionomer but with ePTFE reinforcement.

Claims

1. An enhanced ion-conducting membrane, comprising: (a) a reinforcement layer comprising a porous polymer structure; as well as (b) a polymer ion-conducting membrane material impregnated within the porous polymer structure; wherein the porous polymer structure comprises a polymer backbone based on a nitrogen-containing heterocycle, and the polymer ion-conducting membrane material has a transition temperature Ta in the range of 60°C to 80°C, inclusive.

2. The enhanced ion conducting membrane of claim 1, wherein the polymeric ion conducting membrane material has a transition temperature Ta in the range of 65°C to 75°C, inclusive.

3. An enhanced ion conducting membrane according to claim 1 or claim 2, wherein the membrane has a thickness of at least about 8 μm, such as in the range of 10 μm to 100 μm, inclusive, at 0% relative humidity.

4. An enhanced ion conducting membrane according to any preceding claim, wherein the porous polymer structure comprises a porous mat of nanofibres.

5. The enhanced ion conducting membrane of claim 4, wherein the nanofibers are spun nanofibers.

6. The enhanced ion-conducting membrane of any preceding claim, wherein the porous polymer structure is present in a total amount of at least about 10% by volume, based on the total volume of the enhanced ion-conducting membrane.

7. An enhanced ion conducting membrane according to any one of the preceding claims, wherein the membrane has a machine direction (MD) stress of at least 3.0 MPa at 8% strain at 80°C and 90% relative humidity.

8. An enhanced ion conducting membrane according to any one of the preceding claims, wherein the membrane has a transverse direction (TD) stress of at least 2.5 MPa at 8% strain at 80°C and 90% relative humidity.

9. An enhanced ion conducting membrane according to any one of the preceding claims, wherein the polymeric ion conducting membrane material is a proton conducting polymer.

10. An enhanced ion conducting membrane according to any preceding claim, wherein the ion conducting membrane material comprises sulfonic acid groups.

11. An enhanced ion conducting membrane according to any one of the preceding claims, wherein the ion conducting membrane material is a perfluorinated sulfonic acid ionomer or a partially fluorinated or non-fluorinated hydrocarbon sulfonic acid ionomer.

12. The enhanced ion conducting membrane of any preceding claim, wherein the porous polymer structure comprises a second polymer, wherein the second polymer is ionically non-conductive.

13. The enhanced ion conducting membrane of 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), polyaryletherketone (PAEK), polyarylethersulfone, polyphenylene sulfide (PPS), polyvinylpyrrolidone (PVP).

14. An enhanced ion conducting membrane according to any one of the preceding claims, wherein the nitrogen-containing heterocycle-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.

15. An enhanced ion conducting membrane according to any one of the preceding claims, wherein the nitrogen-containing heterocycle based polymer backbone is polybenzimidazole or a derivative thereof.

16. An enhanced ion conducting membrane according to any preceding claim comprising two or more reinforcement layers.

17. The enhanced ion conducting membrane of claim 15, having a thickness in the range of 60 μm to 100 μm, inclusive, at 0% relative humidity.

18. An enhanced ion conducting membrane according to any preceding claim comprising a composite catalyst.

19. An enhanced ion conducting membrane according to any preceding claim which does not comprise a cerium-containing compound or a manganese-containing compound.

20. An enhanced ion conducting membrane according to any preceding claim, wherein the polymeric ion conducting membrane material has an equivalent weight in the range 450 to 1000 inclusive, such as 450 to 850.

21. A catalyst coated membrane for a fuel cell or water electrolyser, the catalyst coated membrane comprising the enhanced ion conducting membrane according to any one of claims 1 to 20, wherein a cathode catalyst layer is applied to a first side of the membrane and / or an anode catalyst layer is applied to a second side of the membrane.

22. A membrane-electrode assembly for a fuel cell or a water electrolyzer, the membrane-electrode assembly comprising (i) the enhanced ion-conducting membrane according to any one of claims 1 to 20; or (ii) The catalyst-coated membrane of claim 21; and at least one of a gas diffusion layer or a porous transport layer.

23. A water electrolyzer or a fuel cell comprising the catalyst-coated membrane according to claim 21 or the membrane-electrode assembly according to claim 22.

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