Proton exchange membrane

Abstract

The present invention provides a proton exchange membrane comprising a blend of a first ionomer comprising a first backbone covalently bonded to a first side chain and a second ionomer comprising a second backbone covalently bonded to a second side chain; wherein each of the first side chain and the second side chain comprises a sulfonic acid end group; wherein the relaxation modulus of the membrane formed from the first ionomer is at most 1 / 10, preferably at most 1 / 100, of the relaxation modulus of the membrane formed from the second ionomer; and wherein the relaxation modulus of the membrane formed from the second ionomer is greater than 10000 MPa.

Description

Technical Field

[0001] This invention relates to a proton exchange membrane (PEM) and a method for manufacturing the same. In particular, this invention relates to a PEM comprising a blend of a first ionomer and a second ionomer. PEMs are particularly suitable for use in electrochemical devices such as fuel cells and / or water electrolyzers. Background Technology

[0002] A fuel cell is an electrochemical cell comprising two electrodes separated by an electrolyte. Fuel (e.g., hydrogen, alcohol (such as methanol or ethanol), or formic acid) is supplied to the anode, and an oxidant (e.g., oxygen or air) is supplied to the cathode. Electrochemical reactions occur at the electrodes, and the chemical energy of the fuel and oxidant is converted into electrical energy and heat. Electrocatalysts are used to facilitate 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 properties of the electrolyte used. The electrolyte is usually a solid polymer membrane, which is electrically insulating but ionicly conductive. In a proton exchange membrane fuel cell (PEMFC), the membrane is proton-conductive, and protons generated at the anode are transported across the membrane to the cathode, where they mix with oxygen to form water.

[0004] An electrolyzer is an electrochemical device used to electrolyze water to produce high-purity hydrogen and oxygen. Electrolyzers can operate in both alkaline and acidic systems. Those electrolyzers employing PEM (proton exchange membrane) are called proton exchange membrane water electrolyzers (PEMWE).

[0005] Conventional proton-conducting membranes used in PEMFCs or PEMWEs are typically formed from sulfonated perfluorinated polymer materials (generally referred to as perfluorinated sulfonic acid (PFSA) ionomers). As an alternative to PFSA-type ionomers, proton-conducting membranes based on partially fluorinated or non-fluorinated hydrocarbon polymers can be used.

[0006] Depend on The article titled "Perfluorosulfonic Acid Membranes for Fuel Cell and Electrolyser Applications" published on its website (available at https: / / www.sigmaaldrich.com / GB / en / technical-documents / technical-article / materials-science-and-engineering / batteries-supercapacitors-and-fuel-cells / perfluorosulfonic-acid-membranes) provides an overview of PFSA ionomer types, their composition, structure, and synthetic routes, as well as membrane properties and durability.

[0007] Examples of such ionomers include those sold under the following trade names: (EIDuPontde Nemours and Co.), (Asahi Kasei), (Asahi Glass Company) (Solvay Specialty Polymers) and (3M Corporation).

[0008] The Chemical Engineering Journal Advances, 2022, 12, 100372, titled "Advances in perfluorosulfonic acid-based proton exchange membranes for fuel cell applications: A review," provides a review of perfluorosulfonic acid-based membranes for fuel cell applications, and particularly the development of polymer composite membranes incorporating a variety of multifunctional organic, inorganic, and hybrid fillers.

[0009] The journal *Chemical Engineering Science*, 2023, 280, 119051, published a paper titled "Manufacturing defects in slot die coated polymer electrolyte membrane for fuel cell application," which identifies PEM degradation as one of the major obstacles to the commercialization of PEM fuel cells. The paper determines that manufacturing defects can significantly contribute to membrane degradation in the fuel cell environment, serving as an initial source of degradation during use. The membrane discussed is a Nafion membrane manufactured using a roll-to-roll process. ® D-2021 is cast onto polyethylene terephthalate (PET) film, wherein the quality of the cast film is disclosed to be affected by coating thickness, solution flow rate, slit die width, and substrate speed.

[0010] Despite these developments, there remains a need in the art for higher quality proton exchange membranes with fewer manufacturing defects that do not compromise proton exchange properties, in order to subsequently improve the effectiveness and durability / lifespan of electrolysis devices incorporated into such PEMs.

[0011] Therefore, the object of the present invention is to provide a proton exchange membrane suitable for electrochemical devices such as PEMWE and PEMFC, and a method for manufacturing the same, or at least to provide a commercially viable alternative thereof, which has improved robustness and stability compared to known membranes. Detailed Implementation

[0012] Therefore, a first aspect of the present invention provides a proton exchange membrane comprising a blend of a first ionomer and a second ionomer, the first ionomer comprising a first main chain covalently bonded to a first side chain, and the second ionomer comprising a second main chain covalently bonded to a second side chain.

[0013] Each of the first and second side chains contains a sulfonic acid end group;

[0014] The relaxation modulus of the film formed by the first ionomer is at most 1 / 10, preferably at most 1 / 100, of the relaxation modulus of the film formed by the second ionomer; and

[0015] The relaxation modulus of the film formed by the second ionomer is greater than 10,000 MPa.

[0016] This disclosure will now be described further. In the following paragraphs, different aspects / implementations of this disclosure are defined in more detail. Unless expressly stated to the contrary, each aspect / implementation so defined may be combined with any other aspect / implementation or multiple aspects / implementations. In particular, any feature indicated as preferred or advantageous may be combined with one or more other features indicated as preferred or advantageous.

[0017] This invention relates to a proton exchange membrane comprising a blend of a first ionomer and a second ionomer. Ionomers are well known in the art, particularly for manufacturing proton exchange membranes for devices such as fuel cells. An ionomer is a polymer containing electrically neutral repeating units forming a main chain (i.e., a polymer backbone), wherein ionizable / ionizable units are covalently bonded as side-chain portions (i.e., side chains) randomly or periodically along the main chain to a portion of the repeating units of the main chain. Typically, the polymer backbone is ethylene-based (i.e., C2 repeating units, for example based on C2H4 or preferably C2F4). Thus, in the proton exchange membrane of this invention, the first ionomer comprises a first main chain covalently bonded to a first side chain, and the second ionomer comprises a second main chain covalently bonded to a second side chain. One end of each chain is covalently bonded to a carbon atom of the main chain (i.e., instead of, for example, a hydrogen or fluorine atom). Each of the first and second side chains comprises a sulfonic acid end group. That is, the first and second ionomers are sulfonic acid ionomers, wherein the side chains are capped by sulfonic acid moieties (i.e., -SO3H or -S(=O)2-OH) that provide ionizable groups.

[0018] As noted in the IUPAC definition of ionomers, ionic groups are typically present in sufficient quantities to cause microphase separation between the ionic domains and the continuous polymer phase. The ionic domains act as physical crosslinks.

[0019] The first and second ionomers exist as a blend. That is, the proton exchange membrane contains a mixture of the first and second ionomers, preferably a substantially homogeneous blend.

[0020] The inventors have discovered that films formed from preferred ionomers result in significant manufacturing defects, particularly breakage. Specifically, preferred ionomers are those that exhibit advantageous proton exchange properties, such as ion exchange capacity, proton conductivity, and / or water absorption. For example, Aquivion... ® The membranes exhibit high thermal stability (due to increased Tg) and higher proton conductivity (achieved through the use of ionomers with lower EW) even at low relative humidity, making them attractive for high-temperature, higher-performance PEMFCs and PEMWEs. These properties are generally achieved by using "short side chains," and such ionomers can be referred to as SSC ionomers. On the other hand, Nafion... ®Ionomers are examples of “long side-chain” or LSC ionomers. The inventors have found that fracture is a particular problem for ionomers with high equivalence weights and have found that the relaxation modulus of films formed from such ionomers is used to characterize those ionomers that exhibit an increased tendency to fracture during manufacturing.

[0021] Therefore, according to the first aspect, the relaxation modulus of the film formed solely from one of the ionomers of the blend (i.e., the second ionomer) is greater than 10,000 MPa. While there is no specific upper limit, the relaxation modulus of the film formed from the second ionomer can be at most 100,000 MPa, or at most 50,000 MPa, and in some embodiments at most 20,000 MPa. In some preferred embodiments, the relaxation modulus of the film formed from the second ionomer is at least 11,000 MPa, preferably at least 12,000 MPa.

[0022] The inventors have surprisingly discovered that, through blending with another ionomer (i.e., the first ionomer), the proton exchange membrane formed from this blend exhibits a lower relaxation modulus than expected. The relaxation modulus of the membrane formed from the first ionomer is at most 1 / 10, preferably at most 1 / 100, of the relaxation modulus of the membrane formed from the second ionomer. Preferably, the first ionomer is therefore an LSC ionomer.

[0023] As used herein, the relaxation modulus is a value measured over 10 minutes at 80°C and 0% relative humidity (RH) with a strain of 2.5%. When preparing films by casting, 10 minutes is a typical duration for the solvent evaporation step. Therefore, this represents the relevant time period during which film rupture may occur. The relaxation modulus can also be referred to as the stress relaxation modulus and provides a value of stress normalized to the applied strain. Such measurement techniques are well-known, using dynamic mechanical analyzers, so as to be part of common knowledge for those skilled in the art. For example, such measurements can be performed on 20 μm thick films with widths of 6 mm to 8 mm and gauge lengths of 5.5 mm to 6.5 mm.

[0024] Although the properties of the first ionomer (or the expected properties of the membrane formed from the first ionomer) are not as favorable as those of the second ionomer, its effect on the relaxation modulus of the blend membrane is far greater than expected, and this effect has been found to reduce the likelihood of breakage during manufacturing (particularly through the preferred casting method described further in detail herein). This allows the proton exchange membrane to be formed from a relatively small amount of the first ionomer (and thus retains a larger amount of the preferred second ionomer), thereby mitigating any adverse effects on the final membrane properties (such as proton exchange capacity) while significantly reducing manufacturing defects. By using such blends, the inventors have been able to manufacture membranes with minimal breakage, and in some preferred embodiments, to manufacture breakage-free membranes.

[0025] Although composite membranes are disclosed in some embodiments of the prior art, these composites are designed to reinforce the membrane to improve its elasticity after expected degradation during use. The prior art does not consider the technical features necessary to improve the quality of membranes thus manufactured. Therefore, the proton exchange membrane thus manufactured according to the present invention is less prone to degradation and can provide an electrolysis device with greater durability, thus increasing lifespan without the need for composite materials. However, proton exchange membranes may also contain such composite materials known in the art, but in some preferred embodiments, the proton exchange membrane consists of a blend of ionomers.

[0026] Preferably, the relaxation modulus of the membrane comprising the ionomer blend is less than 10,000 MPa, more preferably less than 7,500 MPa. While there is no particular lower limit, the relaxation modulus of the membrane can be greater than 1,000 MPa, and can be at least 2,000 MPa, and in some embodiments at least 3,000 MPa, when a larger amount of the preferred first ionomer is included to convey the preferred membrane properties. More preferably, the relaxation modulus of the membrane is less than 6,000 MPa, as this has been found to provide a substantially fracture-free membrane.

[0027] In view of the above, it is preferable that, alternatively or additionally, the relaxation modulus of the film formed from the first ionomer is less than 1000 MPa, preferably less than 100 MPa. Although there is no specific lower limit, the relaxation modulus of the film formed from the first ionomer can be at least 10 MPa.

[0028] The first and / or second ionomers present in the blend may be partially fluorinated, but are preferably fully fluorinated (i.e., perfluorinated) because such ionomers typically provide greater proton conductivity, etc. Therefore, it is preferred that both the first and second ionomers are fully fluorinated. As those skilled in the art will understand, partial fluorination means that a portion of the present CH bonds is formally replaced by CF bonds. In some embodiments, one of the main chain or side chain may be fully fluorinated while the other is non-fluorinated to provide a partially fluorinated ionomer.

[0029] As described herein, the blend may contain a relatively small amount of the first ionomer, and can achieve a significant reduction in membrane breakage during manufacturing. Preferably, the membrane contains at least 5% by weight, more preferably at least 10% by weight, of the first ionomer based on the weight of the blend. A particular advantage of the membrane of the present invention is that the benefits can be achieved with a much lower amount of the first ionomer than intended. To maintain the preferred properties resulting from the presence of the second ionomer, it is preferred that the membrane contains at most 40% by weight of the first ionomer, preferably at most 25% by weight, more preferably at most 20% by weight, and even more preferably at most 15% by weight. Preferably, the membrane contains at least 60% by weight of the second ionomer, preferably at least 75% by weight, more preferably at least 80% by weight, and even more preferably at least 85% by weight; and / or at most 95% by weight of the second ionomer, preferably at most 90% by weight. In some preferred embodiments, the blend consists of both the first and second ionomers.

[0030] Typically, each ionomer has an equivalent weight (EW) of up to 1100 and / or at least 450. Preferably, the second ionomer has a relatively high equivalent weight, such as at least 850 or at least 900. Generally, it is preferred that the first ionomer has a lower equivalent weight than the second ionomer. The difference in EW can be, for example, at least 50 or at least 100. In some preferred embodiments, the first ionomer has an equivalent weight of 600 to 850, and the second ionomer has an equivalent weight of 850 to 1100. The equivalent weight can be readily measured using acid titration after hydroxide exchange. For example, a membrane sample can be vacuum dried at about 110°C for up to 16 hours to obtain about 2 g of dry membrane. The membrane can then be immersed in about 30 mL of 0.1 M NaOH solution to replace the protons in the membrane with sodium ions. Titration is then performed by neutralization, for example using 0.1 M hydrochloric acid, to determine the number of exchangeable protons, and thus the EW can be calculated.

[0031] Therefore, a preferred embodiment of the proton exchange membrane is a membrane comprising a blend of a first ionomer and a second ionomer, the first ionomer comprising a first main chain covalently bonded to a first side chain, and the second ionomer comprising a second main chain covalently bonded to a second side chain;

[0032] Each of the first and second side chains contains a sulfonic acid end group;

[0033] The relaxation modulus of the film formed by the second ionomer is greater than 10,000 MPa, and the relaxation modulus of the film formed by the first ionomer is less than 1,000 MPa.

[0034] The blend contains 10% to 40% by weight of the first ionomer; and

[0035] Each ionomer has an equivalent weight of 450 to 1100.

[0036] The thickness of the proton exchange membrane will depend on its intended use. For example, a proton exchange membrane used in a water electrolyzer will typically be thicker than one used in a fuel cell, but this may not always be the case. Typically, at 0% relative humidity, the thickness of the proton exchange membrane is at least about 5 micrometers. Preferably, the thickness of the proton-conducting membrane is at least about 6 micrometers, at least about 7 micrometers, at least about 8 micrometers, at least about 9 micrometers, or at least about 10 micrometers. Typically, at 0% relative humidity, the thickness of the proton-conducting membrane is less than or equal to about 200 micrometers, such as less than or equal to about 150 micrometers, less than or equal to about 100 micrometers, less than or equal to about 50 micrometers, less than or equal to about 30 micrometers, less than or equal to about 25 micrometers, or less than or equal to about 20 micrometers. The membrane thickness can be determined by analyzing scanning electron microscopy (SEM) images of the membrane's cross-section. Preferably, at 0% relative humidity, the thickness of the proton-conducting film is in the range of about 5 micrometers to about 200 micrometers, about 6 micrometers to about 100 micrometers, about 6 micrometers to about 50 micrometers, about 7 micrometers to about 30 micrometers, or about 8 micrometers to about 20 micrometers and includes the end values.

[0037] In some embodiments, the first ionomer and / or the second ionomer may be characterized independently or together with the relaxation modulus of the film formed from such ionomers relative to the length of the side chains. Preferably, the chain length of the first side chain between the first main chain and the end group is greater than the chain length of the second side chain between the second main chain and the end group. Chain length refers to the minimum number of atoms between the end group (sulfur atom in the case of an ionizable end group being sulfonic acid) and the carbon atom of the repeating unit of the main chain to which the side chain is covalently bonded.

[0038] Preferably, the first ionomer is an LSC ionomer, and the second ionomer is an SSC ionomer. Therefore, it is preferred that the second side chain has a chain length of at most 5 atoms, more preferably at most 4 atoms. Preferably, the second side chain has a chain length of at least 2 atoms and / or at most 4 atoms, and more preferably a chain length of 3 atoms. Preferably, the first side chain has a chain length of at least 4 atoms, more preferably at least 5 atoms, more preferably at least 6 atoms and / or at most 10 atoms, more preferably at least 5 atoms, more preferably at least 6 atoms and / or at most 8 atoms, and preferably a chain length of 5 or 6 atoms, more preferably 6 atoms.

[0039] Typically, the side chains of the first and second ionomers are each independently linear or branched alkyl groups (and, as described herein, preferably fully fluorinated). Additionally, one or more non-adjacent, non-terminal carbon atoms of the alkyl group may be substituted with oxygen atoms. Preferably, the side chain is covalently bonded to the main chain via oxygen atoms (oxygen substitution, if present, is understood to provide an ether, and for example, a ketone or ester group may be absent). In a preferred embodiment, the first side chain is branched.

[0040] In some implementations, the first sidechain is represented by the following formula:

[0041]

[0042] Wherein a is 2 or greater (preferably up to 6, preferably 2, 3 or 4), and each R is independently selected from H, F, Cl, alkyl, perfluoroalkyl, perchloroalkyl and perfluorochloroalkyl (wherein the alkyl, perfluoroalkyl, perchloroalkyl and perfluorochloroalkyl may have 1 to 10, such as 1 to 3, carbon atoms, and in some embodiments may be 1), preferably selected from H, F and perfluoroalkyl, for example:

[0043]

[0044] Where X is F or Cl, and b and c are each greater than 1 (where b + c = a).

[0045] In some implementations, the second sidechain is represented by the following formula:

[0046]

[0047] Where d is 1 to 4, preferably 1 to 3, and most preferably 2. Preferably, R' is as described above for R, or is selected from H or F.

[0048] Therefore, in a preferred embodiment, the first side chain is -O-CR2-CR(CR3)-O-(CR2)2-SO3H, and the second side chain is -O-(CR'2)2-SO3H, wherein each R and R' is independently selected from H and F, preferably wherein R=R'=F.

[0049] Proton exchange membranes comprising blends of ionomers as described herein can be further characterized with respect to the molar ratio and / or weight ratio of the side chains and main chain provided by each ionomer.

[0050] In some embodiments, the molar ratio of the first side chain to the second side chain is at least 0.07:1, such as at least 0.15:1, such as at least 0.2:1. In some embodiments, the molar ratio of the first side chain to the second side chain is at most 1:1, such as at most 0.5:1.

[0051] In some embodiments, the ionomer blend comprises 5% to 60% by weight of a first side chain, such as 10% to 50% by weight, or 20% to 40% by weight, based on the weight of the side chain. In some embodiments, the ionomer blend comprises 1% to 20% by weight of a first side chain, such as 2% to 15% by weight, based on the weight of the blend. In some embodiments, the ionomer blend comprises 95% to 40% by weight of a second side chain, such as 90% to 50% by weight, or 80% to 60% by weight, based on the weight of the side chain. In some embodiments, the ionomer blend comprises 10% to 20% by weight of a second side chain, preferably 15% to 18% by weight, based on the weight of the ionomer blend. In some embodiments, the ionomer blend comprises 60% to 89% by weight of a first main chain and a second main chain, preferably 67% to 83% by weight, based on the weight of the ionomer blend. When the ionomer blend consists of a first ionomer and a second ionomer, the sum of the first side chain and the second side chain, as well as the first main chain and the second main chain, is equal to 100 by weight.

[0052] On the other hand, the present invention provides a proton exchange membrane comprising a blend of a first ionomer and a second ionomer, the first ionomer comprising a first main chain covalently bonded to a first side chain, and the second ionomer comprising a second main chain covalently bonded to a second side chain;

[0053] Each of the first and second side chains contains a sulfonic acid end group; and

[0054] The chain length of the first side chain between the first main chain and the end group is greater than the chain length of the second side chain between the second main chain and the end group, wherein the chain length of the second side chain is at most 5 atoms.

[0055] A catalyst-coated membrane is also provided, comprising a proton exchange membrane as described herein, 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.

[0056] The catalyst layer comprises one or more electrocatalysts. These electrocatalysts may independently be finely ground, unsupported metal powders or supported catalysts consisting of small nanoparticles dispersed on a conductive particulate carbon support. The electrocatalyst metal is suitably selected from...

[0057] (i) One or more platinum group metals (platinum, palladium, rhodium, ruthenium, iridium and osmium);

[0058] (ii) Gold or silver;

[0059] (iii) Base metals;

[0060] Or an alloy or mixture containing one or more of these metals or their oxides.

[0061] The preferred electrocatalyst metal is platinum, which can form alloys 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. 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 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 resulting electrocatalyst. The exact electrocatalyst used will depend on the reaction it is intended to catalyze, and its selection is within the capabilities of a person skilled in the art.

[0062] 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 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 will be known to those skilled in the art.

[0063] A membrane electrode assembly is also provided, comprising a proton exchange membrane as described herein and a gas diffusion electrode and / or a porous transport layer on a first and / or second surface of the proton exchange membrane. A membrane electrode assembly is also provided, comprising a catalyst-coated proton-conducting membrane and a gas diffusion layer or porous transport layer present on at least one catalyst layer. The anode and cathode gas diffusion layers are suitably based on conventional gas diffusion substrates. Typical substrates include nonwoven paper or mesh comprising a carbon fiber web and a thermosetting resin binder (e.g., TGP-H series carbon fiber paper from Toray Industries Inc., Japan; H2315 series from Freudenberg FCCT KG, Germany; or SGL Technologies GmbH, Germany). Series, or from Ballard Power Systems Inc. (Series), or woven carbon cloth. Before being incorporated into the MEA, carbon paper, fiber mesh, or cloth may undergo 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 dopant material (such as amorphous carbon black) from a liquid suspension, or more hydrophobic by impregnating the porous structure of the substrate with a colloidal suspension of a polymer (such as PTFE or FEP), followed by drying and heating above the melting point of the polymer. For applications such as PEMFCs, a microporous layer can also be applied to the gas diffusion substrate on the surface that will contact the catalyst layer. The microporous layer typically comprises a mixture of carbon black and a polymer (such as polytetrafluoroethylene (PTFE)). Porous transport layers are suitably based on conventional porous transport substrates, such as titanium mesh.

[0064] In another aspect, the present invention provides an electrochemical device comprising a proton exchange membrane, a catalyst-coated membrane, or a membrane electrode assembly as described herein. The electrochemical device may be a fuel cell, such as a proton exchange membrane fuel cell. The electrochemical device may also be an electrolyzer, such as a water electrolyzer.

[0065] In another aspect, the present invention provides a method for forming a proton exchange membrane as described herein, the method comprising:

[0066] (i) Dispersing the first ionomer and the second ionomer in a solvent to form a dispersion;

[0067] (ii) Coat the surface of the substrate with the dispersion to a wet thickness of 50 μm to 1 mm;

[0068] (iii) Evaporating the solvent and annealing the coated substrate to form a film; and

[0069] (iv) Remove the membrane from the substrate.

[0070] The inventors have discovered that fracture is a particular problem when forming proton exchange membranes using solution casting methods, especially when using high EW ionomers and, more significantly, relatively polar solvents. Such manufacturing problems can be mitigated by modifying various parameters, such as solvent evaporation (drying) and annealing temperature profiles, solvent selection based on volatility, and coating thickness. For continuous roll-to-roll casting methods, modifications can also be made, for example, to the solution flow rate and substrate velocity.

[0071] However, the inventors surprisingly discovered that this problem can be solved simply by forming a film using an ionomer blend, specifically a blend comprising ionomers that individually form films with different relaxation moduli. Therefore, the films described herein can be readily available or obtained by the method described herein.

[0072] The method involves dispersing each of a first ionomer and a second ionomer in a solvent to form a dispersion. The ionomer may be dissolved, or the ionomer dispersion may be a fine suspension comprising ionomer particles, and is preferably a homogeneous dispersion. Dispersions of PFSA ionomers are conventional in the art. Many different ionomers suitable for the present invention are commercially available and can be provided as dry solids or as dispersions (typically in water or alcohol-water mixtures). In some embodiments, the method may therefore include drying the aqueous dispersion to increase the ionomer concentration, or completely drying the ionomer. Alternatively, suitable ionomers can be manufactured using conventional synthetic organic chemistry techniques. Those skilled in the art can readily and definitively verify the relaxation modulus value, as described herein, of the film formed from any ionomer.

[0073] Preferred solvents are polar protic solvents, typically water and / or alcohol solvents. Preferably, the solvent consists of an alcohol and optionally water. Preferably, the solvent comprises an alcohol having 1 to 5 carbon atoms. Ethanol (i.e., having 2 carbon atoms) is particularly suitable. Preferably, the solvent contains 50% to 95% by weight of alcohol, more preferably 60% to 80% by weight.

[0074] In some preferred embodiments, the dispersion comprises a first ionomer and a second ionomer in total amounts of 10% to 40% by weight, preferably 20% to 30% by weight, based on the weight of the dispersion. Preferably, the dispersion comprises 1% to 6% by weight of the first ionomer and / or 9% to 34% by weight of the second ionomer based on the weight of the dispersion.

[0075] The method further includes coating the surface of the substrate with a dispersion to a wet thickness of 50 μm to 1 mm. Preferably, the dispersion is coated onto the substrate by gap coating or roll-to-roll (R2R) coating. Gap coating techniques may include using a coating blade or scraper of a film coater, thereby applying the coating to the substrate and then through a gap between the blade and a support roller. R2R coating techniques may include slit die coating, in which the coating is extruded onto the substrate by gravity or under pressure via a slit, or, for example, concave coating.

[0076] In some preferred embodiments, the surface of the substrate is formed of fluorinated ethylene propylene (FEP) or poly(4,4'-oxydiphenylene-pyromellitictetramethylimide). Such surfaces have low adhesion and facilitate subsequent film removal. The substrate may include a polyester backing with an FEP coating, such as those available from... Those obtained. Poly(4,4'-oxydiphenylene-pyromellitictetracarboximide) substrates can be obtained from Obtain, and can be called The surface thickness can range from 10 μm to 200 μm.

[0077] The method further includes evaporating the solvent and annealing the coated substrate to form a film, and removing the film from the substrate (e.g., by peeling the film off the substrate).

[0078] The evaporation and annealing of the solvent may include sequential heating steps. Evaporation may include evaporating the solvent under ambient conditions (i.e., without heating and / or under a gas stream such as air or nitrogen). Evaporation may also include heating the substrate to temperatures up to 120°C, for example up to 100°C, to substantially dry the coated dispersion. Preferably, annealing includes heating the coated substrate to temperatures between 120°C and 240°C, such as 140°C to 200°C. The coated substrate may be annealed at such temperatures for 1 minute to 20 minutes. Attached Figure Description

[0079] The invention will now be further described with reference to the following non-limiting drawings, in which:

[0080] Figure 1 Fluorinated ionomers suitable for use in the membranes of the present invention are shown.

[0081] Figure 2 An exemplary perfluorinated ionomer suitable for use as a first ionomer in the membrane of the present invention is shown.

[0082] Figure 3 An exemplary perfluorinated ionomer suitable for use as a second ionomer in the membrane of the present invention is shown.

[0083] Figure 4 This is a scatter plot of the relaxation modulus of the membrane manufactured according to the embodiment, measured at 10 minutes.

[0084] Figure 1 The chemical structure of ionomer 100 is shown. Ionomer 100 comprises a main-chain polymer backbone based on repeating units of tetrafluoroethylene (i.e., C2F4), wherein a portion of the repeating units are replaced by side chains 105. Figure 1 (Shown as "SC"). The degree of substitution is determined by the number of unsubstituted repeating units, as shown by "m"—the value of m determines the equivalent weight. An ionomer is a polymer containing a large number of repeating units—tetrafluoroethylene and side-chain substituted tetrafluoroethylene units, as shown by "n" in the case of ionomer 100.

[0085] Figure 2 An exemplary perfluorinated ionomer 200 suitable for use as a first ionomer in the membrane of the present invention is shown. Ionomer 200 comprises a main-chain polymer backbone 205 ( Figure 2 The diagram, denoted as "MC", illustrates the structure of the "long side chains" 210 of the main polymer backbone (e.g., as shown in the image). Figure 1The side chain 105 shown here (in this case, ionomer 100 / 200 illustrates the AGC PFSA ionomer used in the examples below) has a long side chain 210 covalently bonded to the main chain 205, specifically via an oxygen atom, wherein another atom within chain 210 is an oxygen atom providing the ether. Side chain 210 is branched and contains a -CF3 moiety. Long side chain 210 contains a sulfonic acid end group 215. Chain length 220 is 6 atoms, as determined by the minimum number of atoms in the (fluoro)alkyl chain between the sulfur atom of end group 215 and the main chain 205.

[0086] Figure 3 An exemplary perfluorinated ionomer 300 suitable for use as a second ionomer in the membranes of the present invention is shown. Ionomer 300 comprises a main-chain polymer backbone 305 ( Figure 3 The diagram, denoted as "MC", illustrates the structure of the "short side chain" 210 of the main polymer backbone (e.g., as shown in the image). Figure 1 The side chain 105 shown here (in this case, ionomer 100 / 300 shows the Solvay PFSA ionomer used in the following examples) has a short side chain 310 covalently bonded to the main chain 305, specifically via an oxygen atom. The short side chain 310 contains a sulfonic acid end group 315. The chain length 320 is 3 atoms.

[0087] Figure 4 It is a scatter plot of the relaxation modulus of the membrane manufactured according to the embodiment, measured at 10 minutes, wherein the concentration of the first ionomer varies in weight % relative to the total weight of the first and second ionomers.

[0088] Example

[0089] Membrane preparation

[0090] The perfluorosulfonic acid ionomer (PFSA) dispersion was obtained from Solvay and AGC. The PFSA ionomer from AGC was based on... Figure 2 The LSC ionomer has an equivalent weight of approximately 720. The PFSA ionomer from Solvay is based on... Figure 3The SSC ionomers, having an equivalent weight of approximately 980, were used. Each PFSA dispersion was poured into a shallow dish lined with Teflon and placed under a weak airflow to allow the solvent to evaporate at room temperature over approximately three days. The remaining solid PFSA blocks after solvent evaporation were placed overnight in a 30°C oven under vacuum to remove any residual moisture. PFSA dispersions for membrane casting were prepared by mixing varying amounts of AGC solid PFSA with the balance of Solvay solid PFSA as described in Table 1 below. Solid PFSA was mixed with 70% by weight of ethanol solvent (the balance being water) to achieve a total PFSA content of 25% by weight. Glass vials containing Solvay and AGC PSA solids and solvent were placed on a roller conveyor at 60 rpm for one day to ensure complete dispersion of the PFSA. The blended PFSA dispersions were used within one week of preparation.

[0091] Approximately 1.5 mL of the blended PFSA dispersion was coated onto a 75 μm thick Diacel FEP-coated polyester backing film using an Elcometer 4340 electric membrane coater and a steel coating blade. Prior to coating, the Diacel backing film was thoroughly cleaned with 35% 2-propanol (balance: water) and a lint-free wiping agent. The stretching speed was 10 mm / s, the coating blade gap was 300 μm, and the coating temperature was 20 °C. After coating, the solvent was allowed to evaporate at room temperature for 10 minutes, and then the PFSA-coated Diacel backing film was placed in a Binder oven at 100 °C for 10 minutes to further evaporate the solvent. The PFSA-coated Diacel backing film was then annealed in another oven at 160 °C for 12 minutes. The blended PFSA film was obtained by peeling the PFSA coating off the Diacel backing film. The final PFSA film thickness, measured using a Fischer magnetic induction thickness gauge at ambient temperature and relative humidity, was 20 ± 2 μm. The relaxation modulus of each membrane is measured according to the method described in this paper.

[0092] Stress relaxation measurement

[0093] Instantaneous tensile stress relaxation measurements were performed using a TA Instruments Discovery DMA 850 Dynamic Mechanical Analyzer equipped with a membrane tension clamp and a relative humidity (RH) unit. Strips of the membrane were longitudinally cut using a die, with typical strip widths between 6 mm and 8 mm. The membrane thickness was measured at at least 20 ± 2 μm at at least five locations using a Fischer MMS Inspection DFT magnetic induction thickness gauge. The membrane strips were clamped in the DMA 850 membrane tension clamp with a torque of 3 in-pounds and a gauge length between 5.6 mm and 6 mm. Each sample was equilibrated for 45 minutes at 80°C and 0% RH under a preload of 50 mN. Tensile stress relaxation measurements were then performed by applying a 2.5% step strain to the sample for 60 minutes, while simultaneously measuring the force required to hold the sample at 2.5% strain as a function of time t. The stress relaxation modulus E(t) is obtained by normalizing the measured force F(t) with the sample cross-sectional area A and the applied strain ε0: E(t) = F(t) / Aε0.

[0094] Table 1 :

[0095]

[0096] These results are plotted on Figure 4 These examples demonstrate a surprising effect: advantageously, only a small amount of the first ionomer is needed to provide a greater reduction in the relaxation modulus of the blended film than expected, compared to the relaxation modulus of films formed individually by each ionomer. This is beneficial because it allows the blend to maintain a higher proportion of the more desirable SSC ionomer in order to preserve the useful proton exchange properties of the film. Thus, as little as 5% by weight of the first ionomer is sufficient to cause a significant reduction in the relaxation modulus of the blend, which in turn reduces the degree of breakage in the final film. Furthermore, the inventors have found that breakage can be completely avoided with as little as 15% by weight of the first ionomer.

[0097] As used herein, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the / described” include plural references. The term “comprising” is intended to be interpreted as including such features but not excluding others, and also as including feature options that must be limited to those features described. In other words, the term also includes the limitations “consistently made of” (intended to indicate that certain additional components may be present, provided they do not substantially affect the essential characteristics of the described feature) and “consisting of” (intended to indicate that other features may be excluded such that, if these components were expressed as percentages of their proportions, they would total 100%, taking into account any unavoidable impurities), unless the context clearly indicates otherwise.

[0098] The lower and upper limits of the values ​​of the features described herein can preferably be combined to provide a closed range.

[0099] It should be understood that although the terms “first,” “second,” etc., may be used herein to describe various characteristics (e.g., ionomers), these characteristics should not be limited by these terms. These terms are only used to distinguish one characteristic from another or additional characteristics. In cases where the membrane contains more than two ionomers, it should be understood that a third or additional ionomer will individually satisfy the requirements described herein with respect to the first or second ionomer. In other words, the first ionomer may, for example, comprise a blend of the first ionomer, wherein the blend is present in the amounts described herein, and each ionomer of the blend individually satisfies the parameters described for the first ionomer (e.g., relaxation modulus).

[0100] The detailed description above has been provided by way of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments shown herein will be apparent to those skilled in the art and remain within the scope of the appended claims and their equivalents.

[0101] To avoid any doubt, the full text of all recognized references is incorporated herein by reference.

[0102] Some embodiments of the present invention are set forth in the following numbered clauses:

[0103] 1. A proton exchange membrane comprising a blend of a first ionomer and a second ionomer, the first ionomer comprising a first main chain covalently bonded to a first side chain, and the second ionomer comprising a second main chain covalently bonded to a second side chain;

[0104] Each of the first and second side chains contains a sulfonic acid end group;

[0105] The relaxation modulus of the film formed by the first ionomer is at most 1 / 10, preferably at most 1 / 100, of the relaxation modulus of the film formed by the second ionomer; and

[0106] The relaxation modulus of the membrane formed from the second ionomer is greater than 10,000 MPa.

[0107] 2. The proton exchange membrane according to any of the preceding clauses, wherein the relaxation modulus of the membrane is less than 10,000 MPa, preferably less than 7,500 MPa.

[0108] 3. The proton exchange membrane according to any of the preceding clauses, wherein the relaxation modulus of the membrane formed from the first ionomer is less than 1000 MPa, preferably less than 100 MPa.

[0109] 4. The proton exchange membrane according to any of the preceding clauses, wherein the thickness of the membrane is less than 200 μm.

[0110] 5. The proton exchange membrane according to any of the preceding clauses, wherein the membrane comprises:

[0111] At least 5% by weight of the first ionomer, preferably at least 10% by weight; and / or

[0112] Up to 40% by weight of the first ionomer, preferably up to 25% by weight.

[0113] 6. The proton exchange membrane according to any of the preceding clauses, wherein the membrane comprises:

[0114] At least 60% by weight of the second ionomer, preferably at least 75% by weight; and / or

[0115] Up to 95% by weight of the second ionomer, preferably up to 90% by weight.

[0116] 7. The proton exchange membrane according to any of the preceding clauses, wherein the first ionomer and / or the second ionomer is partially fluorinated, preferably fully fluorinated.

[0117] 8. The proton exchange membrane according to any of the preceding clauses, wherein the first ionomer has an equivalent weight of 600 to 850, and wherein the second ionomer has an equivalent weight of 850 to 1100.

[0118] 9. A proton exchange membrane according to any of the preceding clauses, wherein the first ionomer has a lower equivalent weight than the second ionomer, preferably wherein the difference in equivalent weight between the first ionomer and the second ionomer is at least 50.

[0119] 10. An electrochemical device comprising a proton exchange membrane according to any of the preceding clauses, preferably a water electrolyzer or a fuel cell.

[0120] 11. A method for forming a proton exchange membrane according to any one of clauses 1 to 9, the method comprising:

[0121] (i) Dispersing the first ionomer and the second ionomer in a solvent to form a dispersion;

[0122] (ii) Coat the surface of the substrate with the dispersion to a wet thickness of 50 μm to 1 mm;

[0123] (iii) Evaporating the solvent and annealing the coated substrate to form a film; and

[0124] (iv) Remove the membrane from the substrate.

[0125] 12. The method according to Clause 11, wherein the dispersion comprises a total amount of the first ionomer and the second ionomer in an amount of 10% to 40% by weight, preferably 20% to 30% by weight, based on the weight of the dispersion.

[0126] 13. The method according to Clause 11 or Clause 12, wherein the dispersion comprises 1% to 6% by weight of the first ionomer and / or 9% to 34% by weight of the second ionomer based on the weight of the dispersion.

[0127] 14. The method according to any one of clauses 11 to 13, wherein the solvent consists of an alcohol and optionally water, preferably wherein the alcohol has 1 to 5 carbon atoms.

[0128] 15. The method according to Clause 14, wherein the solvent comprises 50% to 95% by weight of an alcohol, preferably 60% to 80% by weight, based on the weight of the solvent.

[0129] 16. The method according to any one of clauses 11 to 15, wherein the surface of the substrate is formed of fluorinated ethylene propylene (FEP) or poly(4,4'-oxodiphenylene-pyromellitictetracarboximide), preferably having a thickness of 10 μm to 200 μm.

[0130] 17. The method according to any one of clauses 11 to 16, wherein the dispersion is coated onto the substrate by gap coating or roll-to-roll coating.

[0131] 18. The method according to any one of clauses 11 to 17, wherein annealing comprises heating the coated substrate to a temperature of 120°C to 240°C, preferably for 1 minute to 20 minutes.

Claims

1. A proton exchange membrane comprising a blend of a first ionomer and a second ionomer, the first ionomer comprising a first main chain covalently bonded to a first side chain, and the second ionomer comprising a second main chain covalently bonded to a second side chain; Each of the first side chain and the second side chain contains a sulfonic acid end group; The relaxation modulus of the film formed by the first ionomer is at most 1 / 10, preferably at most 1 / 100, of the relaxation modulus of the film formed by the second ionomer; and The relaxation modulus of the membrane formed from the second ionomer is greater than 10,000 MPa.

2. The proton exchange membrane according to any of the preceding claims, wherein the relaxation modulus of the membrane is less than 10000 MPa, preferably less than 7500 MPa.

3. The proton exchange membrane according to any of the preceding claims, wherein the relaxation modulus of the membrane formed from the first ionomer is less than 1000 MPa, preferably less than 100 MPa.

4. The proton exchange membrane according to any of the preceding claims, wherein the thickness of the membrane is less than 200 μm.

5. The proton exchange membrane according to any preceding claim, wherein the membrane comprises: At least 5% by weight of the first ionomer, preferably at least 10% by weight; and / or Up to 40% by weight of the first ionomer, preferably up to 25% by weight.

6. The proton exchange membrane according to any preceding claim, wherein the membrane comprises: At least 5% by weight of the first ionomer.

7. The proton exchange membrane according to any preceding claim, wherein the membrane comprises: Up to 15% by weight of the first ionomer.

8. The proton exchange membrane according to any preceding claim, wherein the membrane comprises: At least 60% by weight of the second ionomer, preferably at least 75% by weight; and / or Up to 95% by weight of the second ionomer, preferably up to 90% by weight.

9. The proton exchange membrane according to any preceding claim, wherein the membrane comprises: At least 85% by weight of the second ionomer.

10. The proton exchange membrane according to any preceding claim, wherein the membrane comprises: Up to 95% by weight of the second ionomer.

11. The proton exchange membrane according to any of the preceding claims, wherein the first ionomer and / or the second ionomer is partially fluorinated, preferably fully fluorinated.

12. The proton exchange membrane according to any of the preceding claims, wherein the first ionomer has an equivalent weight of 600 to 850, and wherein the second ionomer has an equivalent weight of 850 to 1100.

13. The proton exchange membrane according to any of the preceding claims, wherein the first ionomer has a lower equivalent weight than the second ionomer, preferably wherein the difference in equivalent weight between the first ionomer and the second ionomer is at least 50%.

14. The proton exchange membrane according to any of the preceding claims, wherein the first ionomer is a long-side-chain ionomer, and the length of the first side chain is at least 6 atoms.

15. The proton exchange membrane according to any of the preceding claims, wherein the second ionomer is a short-side-chain ionomer, and the length of the second side chain is at most 4 atoms.

16. An electrochemical device comprising a proton exchange membrane according to any of the preceding claims, preferably a water electrolyzer or a fuel cell.

17. A method for forming a proton exchange membrane according to any one of claims 1 to 15, the method comprising: (i) Dispersing the first ionomer and the second ionomer in a solvent to form a dispersion; (ii) Coat the surface of the substrate with the dispersion to a wet thickness of 50 μm to 1 mm; (iii) Evaporating the solvent and annealing the coated substrate to form a film; and (iv) Remove the membrane from the substrate.

18. The method of claim 17, wherein the dispersion comprises a total amount of the first ionomer and the second ionomer in an amount of 10% to 40% by weight, preferably 20% to 30% by weight, based on the weight of the dispersion.

19. The method of claim 17 or claim 18, wherein the dispersion comprises 1% to 6% by weight of the first ionomer and / or 9% to 34% by weight of the second ionomer based on the weight of the dispersion.

20. The method according to any one of claims 17 to 19, wherein the solvent consists of an alcohol and optionally water, preferably wherein the alcohol has 1 to 5 carbon atoms.

21. The method of claim 20, wherein the solvent comprises 50% to 95% by weight of an alcohol, preferably 60% to 80% by weight, based on the weight of the solvent.

22. The method according to any one of claims 17 to 21, wherein the surface of the substrate is formed of fluorinated ethylene propylene (FEP) or poly(4,4'-oxodiphenylene-pyromellitic tetroxide), preferably having a thickness of 10 μm to 200 μm.

23. The method according to any one of claims 17 to 22, wherein the dispersion is coated onto the substrate by gap coating or roll-to-roll coating.

24. The method according to any one of claims 17 to 23, wherein annealing comprises heating the coated substrate to a temperature of 120°C to 240°C, preferably for 1 minute to 20 minutes.

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