Method for the preparation of a catalyst coated membrane (CCM)

Abstract

5 The present invention relates to a method for the preparation of a catalyst coated membrane (CCM), wherein the method comprises the steps a) to d). In addition, the present invention relates to a catalyst coated membrane (CCM) obtained by the inventive process and to its use in fuel cells and electrolyzers.

Description

[0001] BASF SE 240322W001

[0002] Method for the preparation of a catalyst coated membrane (COM)

[0003] Description

[0004] The present invention relates to a method for the preparation of a catalyst coated membrane (COM), wherein the method comprises the steps a) to d). In addition, the present invention relates to a catalyst coated membrane (COM) obtained by the inventive process and to its use in fuel cells and electrolyzers.

[0005] Hydrogen has the potential to play a key role in achieving the European Union's climate and energy objectives, such as reducing greenhouse gas emissions, increasing energy efficiency, and promoting renewable energy sources. Hydrogen can be produced from a variety of sources, including renewable energy sources such as wind and solar power coupled with PEM (proton exchange membrane) electrolyzers. When produced from renewable sources, hydrogen can be a clean and sustainable energy carrier that can be used in various sectors, such as transport, industry, and heating. In the transport sector, hydrogen can be used in PEM fuel cell vehicles, providing a zero-emission alternative to traditional fossil fuel-powered vehicles. In the industrial sector, hydrogen can be used as a feedstock or fuel for various processes, such as refining, chemical production, and steelmaking. Hydrogen can also be used in the heating sector, providing a low-carbon alternative to natural gas. For example, hydrogen can be blended with natural gas in the existing natural gas network or used in dedicated hydrogen networks.

[0006] The proton exchange membrane (PEM) plays a crucial role in fuel cells and electrolyzers. It is responsible for the conduction of protons (H+) across the cell, separation of product gases and electrical insulation of the electrodes. The most commonly materials used to produce PEMs are based on perfluorinated sulfonic acid (PFSA). This group of materials is known for their high proton conductivity, chemical stability, and mechanical durability. Besides their advantageous properties PFSA materials have also disadvantages including among others high cost and environmental aspects.

[0007] There are several techniques to coat proton exchange membranes (PEMs) with catalyst layers (CL). Besides spraying the so-called decal transfer method is used to prepare catalyst coated membranes (CCMs). The decal transfer method is a technique used to transfer a catalyst layer (CL) onto a proton exchange membrane (PEM). The process typically involves the following steps:

[0008] 1. In a first step, the catalyst layer (CL) is prepared, wherein the catalyst layer (CL) is typically prepared separately on a temporary substrate or carrier material (CM). This involves depositing a catalyst ink onto the carrier material (CM) using techniques such as spray coating, screen printing, inkjet printing or slot die coating. The catalyst ink may comprise catalyst nanoparticles supported on a

[0009] EB24-0322PC October 1 , 2025 BASF SE 240322W001

[0010] 2 conductive material, along with solvents, binders, and ionomers to enhance adhesion and stability.

[0011] 2. In a second step, the catalyst layer (CL) is dried on the carrier material (CM) to remove solvents and ensure proper adhesion. Curing may also be performed to enhance the stability and durability of the catalyst layer (CL).

[0012] 3. In a third step, the dried and cured catalyst layer (CL) on the carrier material (CM) is transferred onto a proton exchange membrane (PEM). This is typically done by pressing the carrier material (CM) with the catalyst layer (CL) onto the PEM using heat and pressure, wherein the catalyst layer (CL) adheres to the PEM, and the carrier material (CM) is peeled away, leaving the catalyst layer (CL) on the proton exchange membrane.

[0013] 4. In a fourth step, the obtained catalyst coated membrane (CCM) undergoes posttreatment and conditioning steps as required. This may include ion exchange or surface modification to optimize the properties of the catalyst coated membrane (CCM).

[0014] The decal transfer method offers advantages such as precise control over catalyst loading and distribution, as well as the ability to transfer catalyst layers (CL) onto various proton exchange membranes (PEMs). It can be a useful technique for producing catalyst coated membranes (CCMs) with high performance and uniformity.

[0015] However, an important issue during the decal transfer of catalyst layers (CL) onto proton exchange membranes (PEMs) is the thermal stability of typical catalysts based on Pt / C materials and other components in the catalyst layer (CL). It is well known that thermal decomposition of carbon catalyst support and binder in catalyst layer (CL) occurs when the temperature increases above 150 °C (O.A. Baturina, S.R. Aubuchon, Thermal Stability in Air of Pt / C Catalysts and PEM Fuel Cell Catalyst Layers, Chem. Mater. 2006, 18, 1498-1504). Therefore, it’s crucial to keep the temperature during decal transfer below 150 °C and, as a result, it is impossible to carry out a decal transfer of catalyst layers (CL) onto proton exchange membranes (PEMs) having high glass transition temperatures above 150 °C, for example, onto PEMs comprising a sulfonated poly(phenylene oxide) polymer, a sulfonated polyetheretherketone polymer or a sulfonated polyarylene ether sulfone polymer.

[0016] The object of the present invention therefore was to provide an improved catalyst coated membrane (CCM) which can be used in fuel cells and electrolyzers. The catalyst coated membrane (CCM) should be chemically and mechanically stable and easy to produce at relatively low costs.

[0017] EB24-0322PC BASF SE 240322W001

[0018] 3

[0019] This object is achieved by a method for the preparation of a catalyst coated membrane (CCM), wherein the method comprises the steps a) providing a membrane (M), wherein the membrane (M) comprises a polymer (P), wherein the polymer (P) has a glass transition temperature TG(P)> 150 °C, b) providing a carrier material (CM), wherein the carrier material (CM) comprises a catalyst layer (CL), c) pressing the carrier material (CM) comprising the catalyst layer (CL) onto the membrane (M) at a temperature Tc)< 150 °C, wherein the catalyst layer (CL) is transferred from the carrier material (CM) onto the membrane (M) and the catalyst coated membrane (CCM) is obtained, and d) separating the carrier material (CM) from the catalyst coated membrane (CCM), wherein the membrane (M) provided in step a) i) comprises from 5 to 20% by weight, based on the total weight of the membrane (M), of at least one aprotic polar solvent (APS), or ii) is treated with at least one aprotic polar solvent (APS) before step c).

[0020] It has surprisingly been found that, by using a membrane (M) provided according to i) or ii), wherein the membrane (M) comprises a polymer (P), wherein the polymer (P) has a glass transition temperature TG(P)> 150 °C, it is possible to carry out a decal transfer of catalyst layers (CL) onto this membrane (M). The catalyst coated membrane (CCM) obtained by the inventive process can successfully be used in fuel cells and electrolyzers.

[0021] Furthermore, the inventive catalyst coated membranes (CCMs) show better mechanical properties, for example, an improved elongation at break, compared to the mechanical properties of CCMs of the prior art.

[0022] A further advantage of the catalyst coated membranes (CCMs) are their much lower production costs compared to the production costs of, for example, CCMs comprising Nation®.

[0023] In addition, in case i), expensive extraction processes to remove the at least one aprotic polar solvent (APS) from the membrane (M) can be avoided because, the at least one aprotic polar solvent (APS) can easily be removed after the preparation of the catalyst coated membrane (CCM).

[0024] EB24-0322PC BASF SE 240322W001

[0025] 4

[0026] The present invention will be described in more detail hereinafter.

[0027] Method for the preparation of a catalyst coated membrane (CCM)

[0028] The method for the preparation of a catalyst coated membrane (CCM) comprises the steps a) to d), wherein step a) can be carried out before step b), after step b) or simultaneously with step b).

[0029] Preferably, step c) is carried out after steps a) and b), and step d) is preferably carried out after step c).

[0030] Step a)

[0031] In step a), a membrane (M) is provided, wherein the membrane (M) comprises a polymer (P), wherein the polymer (P) has a glass transition temperature TG(P)> 150 °C.

[0032] The measurement of the glass transition temperature TG(P)is carried out in a differential scanning calorimeter DSC 2000 (TA Instruments) at a heating rate of 20 K / min. For the measurement, approximately 5 mg of the substance are sealed in an aluminum crucible. In the first heating run, the samples are heated to 280°C, then rapidly cooled to -100°C and then, in the second heating run, heated to 280°C at 20 K / min. The respective TG(P)value is determined from the second heating run. Preferably, the polymer (P) has a glass transition temperature TG(P)> 175 °C, more preferably a glass transition temperature TG(P)> 200 °C.

[0033] Therefore, another object of the present invention is a method, wherein the polymer (P) has a glass transition temperature TG(P)> 175 °C, preferably a glass transition temperature TG(P)> 200 °C.

[0034] Examples of polymers (P) having a glass transition temperature TG(P)> 150 °C are polymers selected from the group consisting of sulfonated poly(phenylene oxide) polymers, sulfonated polyetheretherketone polymers and sulfonated polyarylene ether sulfone polymers.

[0035] Therefore, another object of the present invention is a method, wherein the polymer (P) is selected from the group consisting of sulfonated poly(phenylene oxide) polymers, sulfonated polyetheretherketone polymers and sulfonated polyarylene ether sulfone polymers.

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[0037] 5

[0038] In a preferred embodiment, the polymer (P) is a sulfonated polyarylene ether sulfone polymer. In an especially preferred embodiment, the polymer (P) is a sulfonated polyphenylenesulfone (sPPSU).

[0039] Preparation of a sulfonated polyarylene ether sulfone polymer

[0040] In case the polymer (P) is a sulfonated polyarylene ether sulfone polymer, the sulfonated polyarylene ether sulfone polymer is preferably prepared by a process comprising step I) converting a reaction mixture (RG) comprising the components (A1), (A2), (B), (C) and (D) described below.

[0041] Therefore, another object of the present invention is a method, wherein the polymer (P) is a sulfonated polyarylene ether sulfone polymer, wherein the sulfonated polyarylene ether sulfone polymer (sP) is prepared by a process comprising the step

[0042] I) converting a reaction mixture (RG) comprising as components

[0043] (A1) at least one non-sulfonated aromatic dihalogen sulfone, (A2) at least one sulfonated aromatic dihalogen sulfone,

[0044] (B) at least one aromatic dihydroxy component,

[0045] (C) at least one carbonate component, and

[0046] (D) at least one aprotic polar solvent.

[0047] In this case, the components (A1), (A2) and (B) enter a polycondensation reaction. Component (D) acts as a solvent and component (C) acts as a base to deprotonate component (B) during the condensation reaction.

[0048] The reaction mixture (RG) is understood to mean the mixture that is used according to the present invention for preparing the sulfonated polyarylene ether sulfone polymer. In the present case all details given with respect to the reaction mixture (RG) thus, relate to the mixture that is present prior to the polycondensation. The polycondensation takes place during the process in which the reaction mixture (RG) reacts by polycondensation of components (A1), (A2) and (B) to give the target product, the sulfonated polyarylene ether sulfone polymer. The mixture obtained after the polycondensation which comprises the sulfonated polyarylene ether sulfone polymer target product is also referred to as product mixture (PG). The product mixture (PG) usually furthermore comprises the at least one aprotic polar solvent (component (D)) and a halide compound. The halide compound is formed during the conversion of the reaction mixture (RG). During the conversion first, component (C) reacts with component (B) to deprotonate component (B). Deprotonated component (B) then reacts with components (A1) and / or (A2) wherein the halide compound is formed. This process is known to the person skilled in the art.

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[0051] The components of the reaction mixture (RG) are generally reacted concurrently. The individual components may be mixed in an upstream step and subsequently be reacted. It is also possible to feed the individual components into a reactor in which these are mixed and then reacted.

[0052] In the process, the individual components of the reaction mixture (RG) are generally reacted concurrently in step I). This reaction is preferably conducted in one stage. This means, that the deprotonation of component (B) and also the condensation reaction between components (A1), (A2) and (B) take place in a single reaction stage without isolation of the intermediate products, for example, the deprotonated species of component (B).

[0053] The process according to step I) is carried out according to the so called “carbonate method”. The process is not carried out according to the so called “hydroxide method”. This means, that the process is not carried out in two stages with isolation of phenolate anions. Therefore, in a preferred embodiment, the reaction mixture (RG) is essentially free from sodium hydroxide and potassium hydroxide. More preferably, the reaction mixture (RG) is essentially free from alkali metal hydroxides and alkali earth metal hydroxides.

[0054] The term “essentially free” in the present case is understood to mean that the reaction mixture (RG) comprises less than 100 ppm, preferably less than 50 ppm of sodium hydroxide and potassium hydroxide, preferably of alkali metal hydroxides and alkali earth metal hydroxides, based on the total weight of the reaction mixture (RG).

[0055] It is furthermore preferred that the reaction mixture (RG) does not comprise toluene. It is particularly preferred that the reaction mixture (RG) does not comprise any substance which forms an azeotrope with water.

[0056] The ratio of component (A1), component (A2) and component (B) derives in principle from the stoichiometry of the polycondensation reaction which proceeds with theoretical elimination of hydrogen chloride and is established by the person skilled in the art in a known manner.

[0057] Preferably, the ratio of halogen end groups derived from components (A1) and (A2) to phenolic end groups derived from component (B) is adjusted by controlled establishment of an excess of components (A1) and (A2) in relation to component (B) as starting compound.

[0058] More preferably, the molar ratio of components (A1) and (A2) to component (B) is from 1 to 1.08, especially from 1 to 1.06, most preferably from 1 to 1.05.

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[0061] Preferably, the conversion in the polycondensation reaction is at least 0.9.

[0062] Process step I) for the preparation of the sulfonated polyarylene ether sulfone polymer is typically carried out under conditions of the so called “carbonate method”. This means that the reaction mixture (RG) is reacted under the conditions of the so called “carbonate method”. The reaction (polycondensation reaction) is generally conducted at temperatures in the range from 80 to 250 °C, preferably in the range from 100 to 220 °C. The upper limit of the temperature is determined by the boiling point of the at least one aprotic polar solvent (component (D)) at standard pressure (1013.25 mbar). The reaction is generally carried out at standard pressure. The reaction is preferably carried out over a time interval of 2 to 12 h.

[0063] The isolation of the sulfonated polyarylene ether sulfone polymer obtained in the process in the product mixture (PG) may be carried out for example by precipitation of the product mixture (PG) in water, in an alcohol or mixtures of water with an alcohol. Preferably, the isolation of the obtained sulfonated polyarylene ether sulfone polymer is carried out by precipitation of the product mixture (PG) in isopropanol. The precipitated sulfonated polyarylene ether sulfone polymer can subsequently be extracted with water and then be dried. In one embodiment of the invention, the precipitate can also be taken up in an acidic medium. Suitable acids are for example organic or inorganic acids for example carboxylic acid such as acetic acid, propionic acid, succinic acid or citric acid and mineral acids such as hydrochloric acid, sulfuric acid or phosphoric acid.

[0064] It is possible to filter the product mixture (PG) after step I). The halide compound can thereby be removed.

[0065] The present invention therefore also provides a process wherein the process furthermore comprises step

[0066] II) filtration of the product mixture (PG) obtained in step I).

[0067] Component (A 1)

[0068] The reaction mixture (RG) comprises at least one non-sulfonated aromatic dihalogen sulfone as component (A1). Preferably, the reaction mixture (RG) comprises from 40 to 70 mol-% and most preferably from 45 to 65 mol-% of at least one non-sulfonated aromatic dihalogen sulfone as component (A1), based on the sum of the mol-% of components (A1) and (A2).

[0069] The term “at least one non-sulfonated aromatic dihalogen sulfone” in the present case, is understood to mean exactly one non-sulfonated aromatic dihalogen sulfone and also mixtures of two or more non-sulfonated aromatic dihalogen sulfones.

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[0072] The at least one non-sulfonated aromatic dihalogen sulfone (component (A1)) is preferably at least one non-sulfonated aromatic dihalodiphenyl sulfone.

[0073] “Non-sulfonated” within the context of the present invention means that the aromatic dihalogen sulfone does not comprise groups resulting from the sulfonation of the aromatic dihalogen sulfone. Processes for the sulfonation are known to the skilled person. In particular, “non-sulfonated” within the context of the present invention means that the aromatic dihalogen sulfone does not comprise any -SO2X group wherein X is selected from the group consisting of OH, O and one cation equivalent and a halogen such as Cl, Br or I.

[0074] “One cation equivalent” within the context of the present invention means one cation of a single positive charge or one charge equivalent of a cation with two or more positive charges, for example Li+, Na+, K+, Mg2+, Ca2+or NH4+.

[0075] Component (A1) is preferably used as a monomer. This means that the reaction mixture (RG) comprises component (A1) preferably as a monomer and not as a prepolymer.

[0076] Preferred non-sulfonated aromatic dihalogen sulfones are non-sulfonated 4,4‘-dihalodiphenyl sulfones. Particular preference is given to 4,4‘-dichlorodiphenyl sulfone, 4,4‘-difluorodiphenyl sulfone and / or 4,4‘-dibromodiphenyl sulfone. 4,4‘-dichlorodiphenyl sulfone and 4,4‘-difluorodiphenyl sulfone are particularly preferred, while 4,4‘-dichlorodiphenyl sulfone is most preferred.

[0077] Another object of the present invention is therefore also a method wherein component (A1) is selected from the group consisting of 4,4’-dichlorodiphenyl sulfone and 4,4’-difluorodiphenyl sulfone.

[0078] The present invention therefore also relates to a use wherein component (A1) comprises at least 40 % by weight of at least one non-sulfonated aromatic dihalogen sulfone selected from the group consisting of 4,4‘-dichlorodiphenyl sulfone and 4,4‘-difluorodiphenyl sulfone, based on the total weight of component (A1) in the reaction mixture (RG).

[0079] In a particularly preferred embodiment, component (A1) comprises at least 80 % by weight, preferably at least 90 % by weight, more preferably at least 98 % by weight, of at least one non-sulfonated aromatic dihalogen sulfone selected from the group consisting of 4,4‘-dichlorodiphenyl sulfone and 4,4‘-difluorodiphenyl sulfone, based on the total weight of component (A1) in the reaction mixture (RG).

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[0082] In a further particularly preferred embodiment, component (A1) consists essentially of at least one non-sulfonated aromatic dihalogen sulfone selected from the group consisting of 4,4‘-dichlorodiphenyl sulfone and 4,4‘-difluorodiphenyl sulfone.

[0083] “Consisting essentially of”, in the present case is understood to mean that component (A1) comprises more than 99 % by weight, preferably more than 99.5 % by weight, particularly preferably more than 99.9 % by weight of at least one non-sulfonated aromatic dihalogen sulfone compound selected from the group consisting of 4,4‘-dichlorodiphenyl sulfone and 4,4‘-difluorodiphenyl sulfone, based in each case on the total weight of component (A1) in the reaction mixture (RG). In these embodiments, 4,4‘-dichlorodiphenyl sulfone is particularly preferred as component (A1).

[0084] In a further preferred embodiment, component (A1) consists of 4,4‘-dichlorodiphenyl sulfone.

[0085] Component (A2)

[0086] The reaction mixture (RG) comprises at least one sulfonated aromatic dihalogen sulfone as component (A2).

[0087] The term “at least one sulfonated aromatic dihalogen sulfone” in the present case, is understood to mean exactly one sulfonated aromatic dihalogen sulfone and also mixtures of two or more sulfonated aromatic dihalogen sulfones.

[0088] “Sulfonated” within the context of the present invention means that the aromatic dihalogen sulfone comprises at least one group resulting from the sulfonation of the aromatic dihalogen sulfone. The sulfonation of aromatic dihalogen sulfones is known to the skilled person. In particular, “sulfonated” means that the aromatic dihalogen sulfone comprises at least one -SO3Y group wherein Y is hydrogen or a cation equivalent.

[0089] “Cation equivalent” within the context of the present invention means a cation of a single positive charge or one charge equivalent of a cation with two or more positive charges, for example Li+, Na+, K+, Mg2+, Ca2+, NH4+, preferably Na+, K+.

[0090] “At least one -SO3Y group” within the context of the present invention means precisely one -SO3Y group and also two or more -SO3Y groups. Preferred are precisely two -SO3Y groups. This means that the at least one sulfonated aromatic dihalogen sulfone is preferably at least one disulfonated aromatic halogen sulfone.

[0091] Another object of the present invention is therefore also a method wherein component (A2) is at least one disulfonated aromatic dihalogen sulfone.

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[0093] 10

[0094] The reaction mixture (RG) comprises preferably from 30 to 60 mol-% and more preferably from 35 to 55 mol-% of at least one sulfonated aromatic dihalogen sulfone as component (A2), based on the sum of the mol-% of components (A1) and (A2).

[0095] The sum of the mol-% of components (A1) and (A2) usually is 100 mol-%.

[0096] In a preferred embodiment, the reaction mixture (RG) comprises component (A1) in an amount of from 40 to 70 mol-% and component (A2) in an amount of from 30 to 60 mol- %, based on the sum of the mol-% of components (A1) and (A2).

[0097] Therefore, another object of the present invention is also a method wherein the reaction mixture (RG) comprises component (A1) in an amount of from 40 to 70 mol-% and component (A2) in an amount of from 30 to 60 mol-%, based on the sum of the mol-% of components (A1) and (A2).

[0098] Component (A2) is preferably selected from the group consisting of 4,4‘-dichlorodiphenyl sulfone-3,3’-disulfonic acid, 4,4‘-difluorodiphenylsulfone-3,3’-disulfonic acid, 4,4'- dichloro-diphenylsulfone-3,3'-disulfonic acid disodium salt, 4,4'-dichlorodiphenylsulfone- 3,3'-disulfonic acid dipotassium salt, 4,4'-difluorodiphenylsulfone-3,3'-disulfonic acid disodium salt and 4,4'-difluorodiphenylsulfone-3,3'-disulfonic acid dipotassium salt.

[0099] It is furthermore preferred that component (A2) comprises at least 50 % by weight of at least one sulfonated aromatic dihalogen sulfone selected from the group consisting of 4,4‘-dichlorodiphenyl sulfone-3,3’-disulfonic acid, 4,4‘-difluorodiphenylsulfone-3,3’-di- sulfonic acid, 4,4'-dichlorodiphenylsulfone-3,3'-disulfonic acid disodium salt, 4,4'- dichlorodiphenylsulfone-3,3'-disulfonic acid dipotassium salt, 4,4'-difluoro- diphenylsulfone-3,3'-disulfonic acid disodium salt and 4,4'-difluorodiphenylsulfone-3,3'- disulfonic acid dipotassium salt, based on the total weight of component (A2).

[0100] The present invention therefore also relates to a use wherein component (A2) comprises at least 50 % by weight of at least one sulfonated aromatic dihalogen sulfone selected from the group consisting of 4,4‘-dichlorodiphenyl sulfone-3,3’-disulfonic acid, 4,4‘- difluorodiphenylsulfone-3,3’-disulfonic acid, 4,4'-dichlorodiphenylsulfone-3,3'-disulfonic acid disodium salt, 4,4'-dichlorodiphenylsulfone-3,3'-disulfonic acid dipotassium salt, 4,4'-difluorodiphenylsulfone-3,3'-disulfonic acid disodium salt and 4,4'-difluorodiphenyl- sulfone-3,3'-disulfonic acid dipotassium salt, based on the total weight of component (A2) in the reaction mixture (RG).

[0101] In a particularly preferred embodiment component (A2) comprises at least 80 % by weight, preferably at least 90 % by weight, more preferably at least 98 % by weight of at least one sulfonated aromatic dihalogen sulfone selected from the group consisting of 4,4‘-dichlorodiphenyl sulfone-3,3’-disulfonic acid, 4,4‘-

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[0103] 11 difluorodiphenylsulfone-3,3’-disulfonic acid, 4,4'-dichlorodiphenylsulfone-3,3'-disulfonic acid disodium salt, 4,4'-dichlorodiphenylsulfone-3,3'-disulfonic acid dipotassium salt, 4,4'-difluorodiphenylsulfone-3,3'-disulfonic acid disodium salt and 4,4'- difluorodiphenylsulfone-3,3'-disulfonic acid dipotassium salt, based on the total weight of component (A2) in the reaction mixture (RG).

[0104] The terms “sulfonic acid” and “-SO3Y group” in the context of component (A2) are used synonymously and have the same meaning. The term “sulfonic acid” in the 4,4’-dichlorodiphenyl sulfone-3,3’-disulfonic acid and 4,4‘-difluorodiphenyl sulfone-3,3’-disulfonic acid therefore means “-SO3Y group” wherein Y is hydrogen or a cation equivalent.

[0105] In a further particularly preferred embodiment component (A2) consists essentially of at least one sulfonated aromatic dihalogen sulfone selected from the group consisting of 4,4‘-dichlorodiphenyl sulfone-3,3’-disulfonic acid, 4,4‘-difluorodiphenyl sulfone-3,3’-di- sulfonic acid, 4,4'-dichlorodiphenylsulfone-3,3'-disulfonic acid disodium salt, 4,4'- dichlorodiphenylsulfone-3,3'-disulfonic acid dipotassium salt, 4,4'-difluorodiphenyl- sulfone-3,3'-disulfonic acid disodium salt and 4,4'-difluorodiphenylsulfone-3,3'-disulfonic acid dipotassium salt.

[0106] “Consisting essentially of” in the present case is understood to mean that component (A2) comprises more than 95 % by weight, preferably more than 97 % by weight, particularly preferably more than 99 % by weight of at least one sulfonated aromatic dihalogen sulfone selected from the group consisting of 4,4‘-dichlorodiphenyl sulfone-3,3’-disulfonic acid, 4,4‘-difluorodiphenyl sulfone-3,3’-disulfonic acid, 4,4'- dichlorodiphenylsulfone-3,3'-disulfonic acid disodium salt, 4,4'-dichlorodiphenylsulfone- 3,3'-disulfonic acid dipotassium salt, 4,4'-difluorodiphenylsulfone-3,3'-disulfonic acid disodium salt and 4,4'-difluorodiphenylsulfone-3,3'-disulfonic acid dipotassium salt, based on the total weight of component (A2) in the reaction mixture (RG).

[0107] 4,4'-dichlorodiphenylsulfone-3,3'-disulfonic acid dipotassium salt and 4,4'-dichloro- diphenylsulfone-3,3'-disulfonic acid disodium salt are particularly preferred as component (A2).

[0108] In a further particularly preferred embodiment, component (A2) consists of 4,4'- dichlorodiphenylsulfone-3,3'-disulfonic acid dipotassium salt or 4,4'-dichloro- diphenylsulfone-3,3'-disulfonic acid disodium salt.

[0109] Component (B)

[0110] The reaction mixture (RG) comprises at least one aromatic dihydroxy component (B). The term “at least one aromatic dihydroxy component”, in the present case, is understood to

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[0112] 12 mean exactly one aromatic dihydroxy component and also mixtures of two or more aromatic dihydroxy components. Preferably, component (B) is precisely one aromatic dihydroxy component or a mixture of precisely two aromatic dihydroxy components. Most preferred component (B) is precisely one aromatic dihydroxy component.

[0113] The aromatic dihydroxy components used are typically components having two phenolic hydroxyl groups. Since the reaction mixture (RG) comprises at least one carbonate component, the hydroxyl groups of component (B) in the reaction mixture (RG) may be present partially in deprotonated form.

[0114] Component (B) is preferably used as a monomer. This means that the reaction mixture (RG) comprises component (B) preferably as monomer and not as prepolymer.

[0115] Preferably, component (B) is selected from the group consisting of 4,4’- dihydroxybiphenyl, 4,4'-dihydroxydiphenylsulfone, bisphenol A (2,2-bis(4- hydroxyphenyl)propane), 4,4'-dihydroxybenzophenone and hydroquinone. From among the aforementioned aromatic dihydroxy components, 4,4’-dihydroxybiphenyl, 4,4'- dihydroxydiphenyl sulfone and bisphenol A are preferable, while 4,4’-dihydroxybiphenyl is particularly preferable.

[0116] The present invention accordingly also provides a method wherein component (B) is selected from the group consisting of 4,4‘-dihydroxybiphenyl, 4,4'-dihydroxydiphenyl sulfone, bisphenol A, 4,4'-dihydroxybenzophenone and hydroquinone.

[0117] Said 4,4’-dihydroxybiphenyl, said 4,4'-dihydroxydiphenyl sulfone, said bisphenol A (2,2- bis(4-hydroxyphenyl)propane), said 4,4'-dihydroxybenzophenone and said hydroquinone may here be used in pure form or as a technical-grade product, which may comprise up to 2 wt%, preferably up to 1 wt% and more preferably up to 0.5 wt% of impurities, all based on the overall weight of the 4,4’-dihydroxybiphenyl, 4,4'- dihydroxydiphenyl sulfone used, the bisphenol A (2,2-bis(4-hydroxyphenyl)propane) used, the 4'4-dihydroxybenzophenone used and the hydroquinone used. Any impurities present are included in the wt% percentages relating to component (B).

[0118] Preferably, component (B) comprises not less than 80 wt%, preferably not less than 90 wt% and more preferably not less than 98 wt% of 4,4'-dihydroxybiphenyl, based on the overall weight of component (B) in reaction mixture (RG).

[0119] The weight percentages here in relation to component (B) further relate to the sum total of the 4,4’-dihydroxybiphenyl, 4,4'-dihydroxydiphenyl sulfone, bisphenol A (2,2-bis-(4- hydroxyphenyl)propane), 4,4'-dihydroxybenzophenone and hydroquinone used.

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[0121] 13

[0122] In a further particularly preferred embodiment, component (B) consists essentially of at least one aromatic dihydroxy component selected from the group consisting of 4,4’- dihydroxybiphenyl, 4,4'-dihydroxydiphenyl sulfone, bisphenol A (2,2-bis(4-hydroxy- phenyl)propane), 4,4’-dihydroxybenzophenone and hydroquinone. What is meant herein by "consisting essentially of" is that component (B) comprises more than 99 wt%, preferably more than 99.5 wt% and more preferably more than 99.9 wt% of at least one aromatic dihydroxy component selected from the group consisting of 4,4’- dihydroxybiphenyl, 4,4'-dihydroxydiphenyl sulfone, bisphenol A (2,2-bis(4- hydroxyphenyl)propane), 4,4'-dihydroxybenzophenone and hydroquinone, all based on the overall weight of component (B) in reaction mixture (RG). In these embodiments, 4,4’- dihydroxybiphenyl, bisphenol A and 4,4'-dihydroxydiphenyl sulfone are particularly preferable for use as component (B), while 4,4'-dihydroxybiphenyl is most preferable.

[0123] It is preferable that the sulfonated polyarylene ether sulfone polymers have halogen groups, in particular terminal chlorine groups.

[0124] Component (C)

[0125] The reaction mixture (RG) comprises at least one carbonate component as component (C). The term “at least one carbonate component” in the present case, is understood to mean exactly one carbonate component and also mixtures of two or more carbonate components. The at least one carbonate component is preferably at least one metal carbonate. The metal carbonate is preferably anhydrous.

[0126] Preference is given to alkali metal carbonates and / or alkaline earth metal carbonates as metal carbonates. At least one metal carbonate selected from the group consisting of sodium carbonate, potassium carbonate and calcium carbonate is particularly preferred as metal carbonate. Potassium carbonate is most preferred.

[0127] For example, component (C) comprises at least 50 % by weight, more preferred at least 70 % by weight and most preferred at least 90 % by weight of potassium carbonate based on the total weight of the at least one carbonate component in the reaction mixture (RG).

[0128] Another object of the present invention is therefore also a method wherein component (C) comprises at least 50 % by weight of potassium carbonate, based on the total weight of component (C).

[0129] In a preferred embodiment component (C) consists essentially of potassium carbonate.

[0130] “Consisting essentially of” in the present case is understood to mean that component (C) comprises more than 99 % by weight, preferably more than 99.5 % by weight, particular

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[0132] 14 preferably more than 99.9 % by weight of potassium carbonate based in each case on the total weight of component (C) in the reaction mixture (RG).

[0133] In a particularly preferred embodiment component (C) consists of potassium carbonate.

[0134] Potassium carbonate having a volume weighted average particle size of less than 200 pm, preferably of less than 100 pm, more preferably of less than 50 pm, is particularly preferred as potassium carbonate. The volume weighted average particle size of the potassium carbonate is determined in a suspension of potassium carbonate in N-methylpyrrolidone using a particle size analyser.

[0135] In a preferred embodiment, the reaction mixture (RG) does not comprise any alkali metal hydroxides or alkaline earth metal hydroxides.

[0136] Component (D)

[0137] The reaction mixture (RG) comprises at least one aprotic polar solvent as component (D). “At least one aprotic polar solvent”, according to the invention, is understood to mean exactly one aprotic polar solvent and also mixtures of two or more aprotic polar solvents.

[0138] Suitable aprotic polar solvents are, for example, selected from the group consisting of anisole, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, N-ethylpyrrolidone, sulfolane and N-dimethylacetamide.

[0139] Preferably, component (D) is selected from the group consisting of N-methylpyrrolidone, N-dimethylacetamide, dimethyl sulfoxide, sulfolane and dimethylformamide. N-methylpyrrolidone is particularly preferred as component (D).

[0140] Another object of the present invention is therefore also a method wherein component (D) is selected from the group consisting of N-methylpyrrolidone, N-dimethylacetamide, dimethyl sulfoxide, sulfolane and dimethylformamide.

[0141] It is preferred that component (D) comprises at least 50 % by weight of at least one solvent selected from the group consisting of N-methylpyrrolidone, N- dimethylacetamide, dimethyl sulfoxide, sulfolane and dimethylformamide, based on the total weight of component (D) in the reaction mixture (RG). N-methylpyrrolidone is particularly preferred as component (D).

[0142] In a further preferred embodiment, component (D) consists essentially of N-methylpyrrolidone.

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[0145] “Consist essentially of’, in the present case, is understood to mean that component (D) comprises more than 98 % by weight, particularly preferably more than 99 % by weight, more preferably more than 99.5 % by weight, of at least one aprotic polar solvent selected from the group consisting of N-methylpyrrolidone, N-dimethylacetamide, dimethylsulfoxide, sulfolane and dimethylformamide with preference given to N- methylpyrrolidone.

[0146] In a preferred embodiment, component (D) consists of N-methylpyrrolidone. N-methylpyrrolidone is also referred to as NMP or N-methyl-2-pyrrolidone.

[0147] Sulfonated polyarylether sulfone polymer

[0148] The sulfonated polyarylene ether sulfone polymer obtained by the above-described process comprises units that are derived from component (A1) and from component (B), as well as units that are derived from component (A2) and from component (B). In a preferred embodiment, the sulfonated polyarylene ether sulfone polymer consists of units that are derived from component (A1) and from component (B), as well as units that are derived from component (A2) and from component (B).

[0149] Preferred sulfonated polyarylene ether sulfone polymers comprise repeating units of the general formula I: where t and q : are each independently 0, 1 , 2 or 3,

[0150] Q, T and Y: are each independently a chemical bond or selected from -O-,

[0151] -S-, -SO2-, -S(=O)-, -C(=O)-, -N=N-, and -CRaRb-, wherein Raand Rbare each independently a hydrogen atom or a C C12-alkyl, C C^-alkoxy or C6-C18-aryl group, and wherein at least one of Q, T and Y is -SO2-,

[0152] Ar and Ar1: are each independently C6-C18aryl, wherein said C6-C18aryl is unsubstituted or substituted with at least one substituent selected from CTC12alkyl, CTC12alkoxy, C6-C18aryl, halogen and -SO3X,

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[0154] 16 p, m, n, and k: are each independently 0, 1 , 2, 3 or 4, with the proviso that the sum total of p, m, n and k is not less than 1 , and

[0155] X: is hydrogen or one cation equivalent.

[0156] If Q, T, or Y, with the abovementioned preconditions, is a chemical bond, this means that the adjacent group on the left-hand side and the adjacent group on the right-hand side have direct linkage to one another by way of a chemical bond.

[0157] Raand Rbare preferably each independently hydrogen or C C12alkyl.

[0158] Preferred C C12alkyl groups include linear and branched, saturated alkyl groups of 1 to 12 carbon atoms. The following moieties are suitable in particular: C C6alkyl, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, 2- or 3-methylpentyl or comparatively long-chain moieties such as unbranched heptyl, octyl, nonyl, decyl, undecyl, lauryl, and the branched analogs thereof.

[0159] Alkyl moieties in the CrC12alkoxy groups used include the above-defined alkyl groups of 1 to 12 carbon atoms. Preferably used cycloalkyl moieties include in particular C3-C12cycloalkyl moieties, e.g., cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclopropylmethyl, cyclopropylethyl, cyclopropylpropyl, cyclobutylmethyl, cyclobutylethyl, cyclopentylethyl, -propyl, -butyl, -pentyl, -hexyl, -cyclohexylmethyl, -dimethyl, -trimethyl.

[0160] Ar and Ar1are each independently C6-C18aryl. Proceeding from the starting materials hereinbelow, Ar preferably derives from an electron-rich aromatic substance very susceptible to electrophilic attack, preferably selected from the group consisting of sulfonated or unsulfonated hydroquinone, resorcinol, dihydroxynaphthalene, in particular 2,7-dihydroxynaphthalene and 4,4'-bisphenol. Ar1is preferably an unsubstituted C6or C12arylene group.

[0161] Ar and Ar1in the preferred embodiment of formula (I) are each preferably selected independently from sulfonated or unsulfonated 1 ,4-phenylene, 1 ,3-phenylene, naphthylene, in particular 2,7-dihydroxynaphthalene and 4,4'-bisphenylene.

[0162] The membrane (M) of the present invention preferably comprises at least one sulfonated polyarylene ether sulfone polymer having the following structural units (la) to (II):

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[0165] I, k, m, n, o, p are each independently 0, 1 , 2, 3 or 4 subject to the proviso that the sum total of I, k, m, n, o and p is >1 , and

[0166] X is hydrogen or one cation equivalent.

[0167] By "one cation equivalent" in the context of the present invention is meant one cation of a single positive charge or one charge equivalent of a cation with two or more positive charges, for example Li, Na, K, Mg, Ca, NH4, preferably Na, K.

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[0169] 19

[0170] In addition to the preferred building blocks (la) to (II), preference is also given to those structural units in which one or more unsulfonated 1 ,4-dihydroxyphenyl units are replaced by resorcinol or dihydroxynaphthalene.

[0171] Copolymers constructed of the various structural units in combination or of sulfonated and non-sulfonated structural units are also usable.

[0172] Structural units (la), (lb), (If) and (Ij) or copolymers thereof are used with particular preference as repeat unit of general formula (I).

[0173] In one particularly preferred embodiment, Ar is 1 ,4-phenylene, t is 1 , T is a chemical bond, Y is -SO2-, q is 0, p is 0, m is 0, n is 1 and k is 1. Sulfonated polyarylene ether sulfone polymers constructed of this recited structural repeat unit are denoted sulfonated polyphenylenesulfone (sPPSU).

[0174] In another particularly preferred embodiment, Ar is 1 ,4-phenylene, t is 0, Y is -SO2-, q is 0, n is 1 and k is 1. Sulfonated polyarylene ether sulfone polymers constructed of this recited structural repeat unit are denoted sulfonated polyether ether sulfones (sPEES).

[0175] In an especially particularly preferred embodiment, the sulfonated polyarylene ether sulfone polymer is a sulfonated polyphenylenesulfone (sPPSU).

[0176] The sulfonated polyarylene ether sulfone polymers preferably used in the method according to the present invention preferably have a viscosity number of 20 ml / g to 150 ml / g, preferably of 20 ml / g to 120 ml / g. This viscosity number is quantified according to DIN EN ISO 1628-1 in a 1 % solution of N-methylpyrrolidone (NMP) at 25°C.

[0177] The weight average molecular weight (Mw) of the sulfonated polyarylene ether sulfone polymer preferably used in the method of the present invention is generally in the range from 10 000 to 250 000 g / mol, preferably in the range from 15 000 to 200 000 g / mol and more preferably in the range from 18 000 to 180 000 g / mol. The weight average molecular weights (Mw) are measured using gel permeation chromatography (GPC). Dimethylacetamide (DMAc) was used as solvent and narrowly distributed polymethyl methacrylate was used as standard in the measurement.

[0178] Preferably, the sulfonation degree of the sulfonated polyarylene ether sulfone polymer is at least 30 mol-%, more preferably at least 35 mol-%. The sulfonation degree of the sulfonated polyarylene ether sulfone polymer is determined by1H-NMR-spectroscopy.

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[0180] 20

[0181] Sulfonated polyetheretherketone polymer

[0182] As sulfonated polymers furthermore sulfonated polyetheretherketones (sPEEK) can be used. Such polymers can be prepared by sulfonation of polyetheretherketone. The sPEEK is also soluble in dipolar aprotic solvents. Details about this class of polymers are given in the literature (S. Rowshanzamur et.al., Int. J. Hydrogen Energy 35 (2010) 9349).

[0183] Sulfonated poly(phenylene oxide) polymer

[0184] Sulfonated poly(phenylene oxide) polymers are also suitable for this application, particularly sulfonated 2,6-diphenyl polyphenylene oxide can be used. The synthesis of 2,6-diphenyl polyphenylene oxide is known from the patent literature (US 3,432,466, 11.03.1969).

[0185] Membrane (M)

[0186] The membrane (M) provided in step a) i) comprises from 5 to 20% by weight, based on the total weight of the membrane (M), of at least one aprotic polar solvent (APS), or ii) is treated with at least one aprotic polar solvent (APS) before step c).

[0187] Alternative i)

[0188] In case the membrane (M) provided in step a) comprises from 5 to 20% by weight, based on the total weight of the membrane (M), of at least one aprotic polar solvent (APS), the membrane (M) is preferably obtained by a solution casting process in which a solvent (the at least one aprotic polar solvent (APS)) comprised in the casted solution is evaporated. Usually the solution (S) is casted on a support, which might be another polymer like cellulose acetate or polyethylene terephthalate.

[0189] The membrane (M) is in this case preferably a dense membrane. If the membrane (M) is a dense membrane, then the membrane (M) typically comprises virtually no pores.

[0190] The membrane might also be reinforced by a non-woven, the non-woven preferably has a thickness of 15 to 70 pm and preferably consists of polyphenylensulfide fibers, polyetheretherketone fibers, LC polyester fibers or polyester fibers.

[0191] The membrane (M) can have any thickness. For example, the thickness of the membrane (M) is in the range from 2 to 1000 pm, preferably in the range from 3 to 600 pm and most preferably in the range from 5 to 450 pm.

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[0194] Preferably, the membrane (M) is prepared by a method comprising the steps

[0195] 1) providing a solution (S) which comprises the polymer (P) and the at least one aprotic polar solvent (APS),

[0196] 2) casting the solution (S) provided in step 1) to obtain a film of the solution (S), and

[0197] 3) evaporating the at least one aprotic polar solvent (APS) from the film of the solution (S) obtained in step 2) to obtain the membrane (M) which is in the form of a film.

[0198] Therefore, another object of the present invention is also a method wherein, in case i), the membrane (M) is prepared by a method comprising the steps

[0199] 1) providing a solution (S) which comprises the polymer (P) and the at least one aprotic polar solvent (APS),

[0200] 2) casting the solution (S) provided in step 1) to obtain a film of the solution (S), and

[0201] 3) evaporating the at least one aprotic polar solvent (APS) from the film of the solution (S) obtained in step 2) to obtain the membrane (M) which is in the form of a film.

[0202] Step 1)

[0203] In step 1) a solution (S) is provided which comprises the polymer (P) and the at least one aprotic polar solvent (APS).

[0204] “At least one aprotic polar solvent” within the context of the present invention means precisely one aprotic polar solvent and also a mixture of two or more aprotic polar solvents.

[0205] The solution (S) can be provided in step 1) by any method known to the skilled person. For example, the solution (S) can be provided in step 1) in customary vessels which may comprise a stirring device and preferably a temperature control device. Preferably, the solution (S) is provided by dissolving the polymer (P) in the at least one aprotic polar solvent (APS).

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[0208] The dissolution of the polymer (P) in the at least one aprotic polar solvent (APS) to provide the solution (S) is preferably carried out under agitation.

[0209] Step 1) is preferably carried out at elevated temperatures, especially in the range from 20 to 120 °C, more preferably in the range from 40 to 100 °C. A person skilled in the art will choose the temperature in accordance with the at least one aprotic polar solvent (APS).

[0210] The solution (S) preferably comprises the polymer (P) completely dissolved in the at least one aprotic polar solvent (APS). This means that the solution (S) preferably comprises no solid particles of the polymer (P). Therefore, the polymer (P) preferably cannot be separated from the at least one aprotic polar solvent (APS) by filtration.

[0211] The solution (S) preferably comprises from 0.001 to 50 % by weight of the polymer (P) based on the total weight of the solution (S). More preferably, the solution (S) in step 1) comprises from 0.1 to 30 % by weight of the polymer (P) and most preferably the solution (S) comprises from 0.5 to 25 % by weight of the polymer (P) based on the total weight of the solution (S).

[0212] As the at least one aprotic polar solvent (APS), any solvent known to the skilled person for the polymer (P) is suitable. Preferably, the at least one aprotic polar solvent (APS) is soluble in water. Therefore, the at least one aprotic polar solvent (APS) is preferably selected from the group consisting of anisole, dimethylformamide, dimethylsulfoxide, sulfolane, N-methylpyrrolidone, N-ethylpyrrolidone, N-dimethylacetamide, y- butyrolactone, dimethyl sulfone, N-Formylmorpholine, tetraethylene glycol dimethyl ether, tetramethyl urea and 1 ,3-Dimethyl-2-imidazolidinone. N-methylpyrrolidone and dimethyllactamide are particularly preferred.

[0213] Another object of the present invention is therefore also a method wherein the at least one aprotic polar solvent (APS) is selected from the group consisting of anisole, dimethylformamide, dimethylsulfoxide, sulfolane, N-methylpyrrolidone, N-ethylpyrrolidone, N-dimethylacetamide, y-butyrolactone, dimethyl sulfone, N- Formylmorpholine, tetraethylene glycol dimethyl ether, tetramethylurea and 1 ,3- Dimethyl-2-imidazolidinone.

[0214] The solution (S) preferably comprises in the range from 50 to 99.999 % by weight of the at least one aprotic polar solvent (APS), more preferably in the range from 70 to 99.9 % by weight and most preferably in the range from 75 to 99.5 % by weight of the at least one aprotic polar solvent (APS) based on the total weight of the solution (S).

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[0216] 23

[0217] To the person skilled in the art, it is clear that the percentages by weight of the polymer (P) and the at least one aprotic polar solvent (APS) comprised in the solution (S) typically add up to 100 % by weight.

[0218] The duration of step 1) may vary between wide limits. The duration of step 1) is preferably in the range from 10 min to 48 h (hours), especially in the range from 10 min to 24 h and more preferably in the range from 15 min to 12 h. A person skilled in the art will choose the duration of step 1) so as to obtain a homogeneous solution of the polymer (P) in the at least one aprotic polar solvent (APS).

[0219] For the polymer (P) comprised in the solution (S) the embodiments and preferences given for the polymer (P) obtained in the process described above hold true.

[0220] It is possible to filter the solution (S) provided in step 1) before the at least one aprotic polar solvent (APS) is separated from the solution (S) in steps 2) and 3) to obtain a filtered solution (fS). The following embodiments and preferences for separating the at least one aprotic polar solvent (APS) from the solution (S) apply equally for separating the at least one aprotic polar solvent (APS) from the filtered solution (fS) which is preferably used in this embodiment of the invention.

[0221] Step 2)

[0222] In step 2), the solution (S) provided in step 1) is casted to obtain a film of the solution (S).

[0223] The solution (S) can be casted by any method known to the skilled person. Usually, the solution (S) is cast with a casting knife that is heated to a temperature in the range from 20 to 150 °C, preferably in the range from 40 to 100°C.

[0224] The solution (S) is usually casted on a substrate that does not react with the polymer (P) or the at least one aprotic polar solvent (APS) comprised in the solution (S).

[0225] Suitable substrates are known to the skilled person and are, for example, selected from other polymers like cellulose acetate, polyolefins, polyacrylonitrile, and polyesters like polyethylene terephthalate.

[0226] Step 3)

[0227] In step 3), the at least one aprotic polar solvent (APS) is evaporated from the film of the solution (S) obtained in step 2) to obtain the membrane (M) which is in the form of a film. The membrane (M) then still comprises from 5 to 20% by weight, preferably from 5.5 to 19% by weight, more preferably from 6 to 18% by weight, based on the total weight of the membrane (M), of the at least one aprotic polar solvent (APS).

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[0230] This means that the membrane (M) is formed by evaporating the at least one aprotic polar solvent (APS) from a film of the solution (S).

[0231] The membrane (M) comprises preferably at least 80 % by weight of the polymer (P), more preferably at least 81 % by weight and most preferably at least 82 % by weight of the polymer (P), based on the total weight of the membrane (M).

[0232] During the formation of the membrane (M) the polymer (P) is separated from the at least one aprotic polar solvent (APS). Therefore, the obtained membrane (M) is essentially free from the at least one aprotic polar solvent (APS).

[0233] “Essentially free” within the context of the present invention means that the membrane (M) comprises at most 20 % by weight, preferably at most 19 % by weight and particularly preferably at most 18 % by weight of the at least one aprotic polar solvent (APS), based on the total weight of the membrane (M). The membrane (M) comprises at least 5 % by weight, preferably at least 5.5 % by weight and particularly preferably at least 6 % by weight of the at least one aprotic polar solvent (APS), based on the total weight of the membrane (M).

[0234] Alternative ii)

[0235] In case the membrane (M) provided in step a) is treated with at least one aprotic polar solvent (APS) before step c), the membrane (M) is preferably not obtained by a solution casting process. In this case the membrane (M) comprises preferably < 5 % by weight, based on the total weight of the membrane (M), of at least one aprotic polar solvent (APS).

[0236] Therefore, in case ii), the membrane (M) provided in step a) is treated with at least one aprotic polar solvent (APS) before step c). The treatment is carried out either by the membrane (M) being coated with the at least one aprotic polar solvent (APS) or by the membrane (M) being immersed in the at least one aprotic polar solvent (APS).

[0237] Therefore, another object of the present invention is a method wherein, in case ii), the membrane (M) is coated with the at least one aprotic polar solvent (APS) or the membrane (M) is immersed in the at least one aprotic polar solvent (APS).

[0238] It should be mentioned that also an alternative iii) could be possible, namely, to treat the carrier material (CM) provided in step b) with at least one aprotic polar solvent (APS) before step c). This treatment could also be carried out either by the carrier material (CM) being coated with the at least one aprotic polar solvent (APS) or by the carrier material (CM) being immersed in the at least one aprotic polar solvent (APS).

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[0241] Step b)

[0242] In step b), a carrier material (CM) is provided, wherein the carrier material (CM) comprises a catalyst layer (CL).

[0243] The carrier material (CM) can be provided in any way known to a skilled person. In a preferred embodiment, the carrier material (CM) provided in step b) is obtained by depositing a catalyst ink onto the carrier material (CM), wherein the catalyst ink comprises catalytic nanoparticles supported on a conductive material, binders and ionomers.

[0244] Therefore, another object of the present invention is also a method wherein the carrier material (CM) provided in step b) is obtained by depositing a catalyst ink onto the carrier material (CM), wherein the catalyst ink comprises catalytic nanoparticles supported on a conductive material, binders and ionomers.

[0245] The deposition can also be carried out by any method known to a skilled person. In a preferred embodiment, the deposition is carried out by spray coating, screen printing, inkjet printing or slot die coating.

[0246] Another object of the present invention is therefore also a method wherein the deposition is carried out by spray coating, screen printing, inkjet printing or slot die coating.

[0247] It should be mentioned that, depending on the application, also two carrier materials (CM) can be provided, for example, one carrier material (CM) comprising the catalyst layer (CL) for the anode and one carrier material (CM) comprising the catalyst layer (CL) for the cathode. The above-mentioned embodiments and preferences for the provision of one carrier material (CM) apply equally for the provision of two carrier materials (CM).

[0248] Step c)

[0249] In step c), the carrier material (CM) comprising the catalyst layer (CL) is pressed onto the membrane (M) at a temperature Tc)< 150 °C, wherein the catalyst layer (CL) is transferred from the carrier material (CM) onto the membrane (M) and the catalyst coated membrane (CCM) is obtained.

[0250] In a preferred embodiment, the temperature Tc)is in the range from 100 to 145 °C, preferably in the range from 110 to 140 °C.

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[0252] 26

[0253] The pressing is preferably conducted at a pressure in the range from 20 to 40 bars, preferably for a period in the range from 1 to 20 minutes, more preferably for a period in the range from 5 to 15 minutes.

[0254] In case two carrier materials (CM) are provided in step b), the carrier materials (CM) are, preferably simultaneously, pressed onto the membrane (M) so that, for example, one side of the membrane (M) is coated with the catalyst layer (CL) for the anode and the opposite is coated with the catalyst layer (CL) for the cathode.

[0255] Step d)

[0256] In step d), the carrier material (CM) is separated from the catalyst coated membrane (CCM).

[0257] The separation is preferably carried out by peeling away the carrier material (CM), leaving the catalyst layer (CL) on the membrane (M).

[0258] In case two carrier materials (CM) are pressed onto the membrane (M) in step c), these two carrier materials (CM) are separated from the catalyst coated membrane (CCM) in step d), leaving the catalyst layer (CL) for the anode and the catalyst layer (CL) for the cathode on the membrane (M).

[0259] Step e)

[0260] After step d) a step e) may be carried out, in which the at least one aprotic polar solvent (APS) is extracted from the catalyst coated membrane (CCM). In one embodiment, the extraction is carried out in water at a temperature in the range from 20 to 90 °C, preferably for 0.25 to 3 hours. However, it is also possible that the extraction is carried out in aqueous acidic solution.

[0261] Another object of the present invention is also the catalyst coated membrane (CCM) obtained by the inventive method.

[0262] The catalyst coated membrane (CCM) can be either a membrane (M) coated with a catalyst layer (CL) for the anode or the cathode on one side, or a membrane (M) coated with two catalyst layers (CL), wherein one side of the membrane (M) is coated with the catalyst layer (CL) for the anode and the opposite is coated with the catalyst layer (CL) for the cathode.

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[0265] The catalyst coated membrane (CCM) obtained by the inventive method can be used in fuel cells and electrolyzers.

[0266] Another object of the present invention is therefore also the use of an inventive catalyst coated membrane (CCM) in fuel cells and electrolyzers.

[0267] The present invention is further elucidated by the following examples without limiting it thereto.

[0268] Components used

[0269] Component (A1): DCDPS: 4,4'-dichlorodiphenyl sulfone

[0270] Component (A2): sDCDPS: 3,3’-Disodiumdisulfone-4,4’-dichlorodiphenyl sulfone

[0271] Component (B): 4,4'-dihydroxybiphenyl

[0272] Component (C): Potassium carbonate: K2CO3; anhydrous; volume-average particle size of 32.6 pm

[0273] Component (D): NMP: N-methylpyrrolidone, anhydrous

[0274] General procedures

[0275] The viscosity number VN of the sulfonated polyarylene ether sulfone polymer is measured according to DIN ISO 1628-1 in a 0.5% by weight NMP solution.

[0276] The incorporation ratio (the incorporation rate) of the sDCDPS (Component (A2)) is determined by1H-NMR in CDCI3.

[0277] The isolation of the sulfonated polyarylene ether sulfone polymer is carried out by dripping an NMP solution of the sulfonated polyarylene ether sulfone polymer into isopropanole at room temperature. The drop height is 0.5 m. The throughput is about 2.5 I per hour. The obtained precipitate is then extracted with water (water throughput 160 l / h) at 85 °C for twenty hours. The material is then dried at a temperature below the glass transition temperature TG(p) to a residual moisture content of less than 2% by weight.

[0278] The filtration of the mixture after reaction is done in a heated metal pressure filter using a filter with a 5 pm pore size and 3 bar N2-pressure. The filter is heated to 60 °C to reduce the viscosity of the mixture.

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[0281] Synthesis of the sulfonated polyarylene ether sulfone polymer

[0282] Example Ex. 1

[0283] In a 4-liter glass reactor fitted with a thermometer, a gas inlet tube and a Dean-Stark- trap, 384.794 g (1.34 mol) of DCDPS, 343.875 g (0.7 mol) of sDCDPS, 372.42 g (2.00 mol) 4,4'-dihydroxybiphenyl and 400.809 g (2.90 mol) of potassium carbonate were suspended in 1250 ml NMP in a nitrogen atmosphere.

[0284] The mixture was heated to 190°C within one hour. In the following, the reaction time shall be understood to be the time during which the reaction mixture was maintained at 190 °C. The water that was formed in the reaction was continuously removed by distillation.

[0285] After a reaction time of 8.5 hours, the reaction was stopped by the addition of 1750 ml NMP and cooling down to room temperature (within one hour). The potassium chloride formed in the reaction was removed by filtration. The obtained polymer solution was then precipitated in isopropanol, the resulting polymer precipitate was separated and then extracted with hot water (85°C) for 20 h. Then the material was dried at 120°C for 24 h at reduced pressure (< 100 mbar). The properties of the obtained sulfonated polyphenylenesulfone sPPSU 1 are summarized in table 1.

[0286] Table 1

[0287] As can be seen from table 1 , the sPPSU product has a high viscosity number and a high degree of sulfonated units.

[0288] EB24-0322PC BASF SE 240322W001

[0289] 29

[0290] Preparation of inventive catalyst coated membranes (CCMs) (Inventive examples 11 and 121

[0291] Membrane preparation

[0292] The respective polymer sPPSU 1 was dissolved in NMP at a concentration of 20 wt.%, wherein a solution (S) was obtained. The obtained solution (S) was then filtered. Then, the solution (S) was doctor bladed onto a substrate foil employing an Erichsen Coatmaster 510 at 60°C with a speed of 5 mm / s to obtain a film of the solution (S). The thickness of the wet film was 400 pm. The film was pre-dried at 60°C on a hot plate and then at 100°C in the vacuum for 1 day to obtain the membrane (M).

[0293] Preparation of catalyst layers (CLs)

[0294] Catalyst layers (CLs) for anode (Ir-black, I rO2) and cathode (Pt-black, Pt / C) were coated onto a substrate foil (Daicel Corporation) (carrier material (CM)) using doctor blade coating method and / or bar coaters to obtain a loading of 0.25 mgPt / cm2to 1.0 mgPt / cm2on the cathode side and 0.35 mgir / cm2to 2.0 mgir / cm2on the anode side. The catalyst ink for coating was prepared via dispersing the catalyst into a mixture of water and isopropanol. Nation in the ratio of 1 :2 Nafion:Catalyst was added to the suspension. The ink was then ultrasonicated for 9 min.

[0295] Preparation of the catalyst coated membranes (CCMs) (Decal transfer method) (Inventive Examples 11 and 12)

[0296] The catalyst layers (CLs) were transferred to the membrane (M) by hot-pressing for 10 min at 30 bars and a temperature of 135 or 120 °C.

[0297] Post treatment of the catalyst coated membrane (CCMs)

[0298] The obtained CCMs were activated in 1.0 M H2SO4at 80 °C for 2h and washed in DI water at 80 °C for 2h. The activated CCMs were then stored in DI water until use.

[0299] Preparation of comparative catalyst coated membrane (CCM) at a temperature T > 150 °C (Comparative example C3)

[0300] Membrane preparation

[0301] The preparation of the membrane (M) is carried out analogous to inventive examples 11 and I2.

[0302] EB24-0322PC BASF SE 240322W001

[0303] 30

[0304] Preparation of catalyst layers (CLs)

[0305] The preparation of the catalyst layers (CLs) is also carried out analogous to inventive examples 11 and I2.

[0306] Preparation of the catalyst coated membrane (CCM)

[0307] The catalyst layers were transferred to the membrane (M) by hot-pressing for 10 min at 30 bars and a temperature of 180 °C.

[0308] Post treatment of the catalyst coated membrane (CCM)

[0309] The obtained CCM was activated in 1.0 M H2SO4at 80 °C for 2h and washed in DI water at 80 °C for 2h. The activated CCM was then stored in DI water until use. t coated membranes (CCMs) via coating

[0310] For the spray coating an activated membrane (M) was used. The membrane (M) was obtained in the Na+ / K+salt form. To be able to coat the catalyst onto the membrane (M) via spray coating, a dry membrane (M) in H+form was necessary. This was obtained by first activating the membrane (M) in 0.5 M H2SO4at 80 °C for 2h and then in DI water at 80 °C for 2h. The activated membrane (M) was then stored in DI water until use.

[0311] The wet membrane (M) was placed between two porous PE sheets (Bel-Art Fritware® #H 13638-0518 - medium porosity) which were clamped with retaining clips. This ensured that the membrane (M) could dry without wrinkling. The clamped sheets were placed into the fume hood for drying at room temperature overnight.

[0312] The dried membrane (M) was placed onto a heated vacuum table which was maintained at 60 °C and a stainless-steel screen with a square cutout of 25 cm2was placed onto the membrane (M). The catalyst layer, Pt black (BASF Rome 3491) on the cathode and Ir black (Premetec) on the anode, was spray coated onto the membrane (M) with an air brush to obtain a loading of 1 mgPtcm-2and 2 mg,rcm-2on cathode and anode side, respectively. The ink for coating was prepared via dispersing the catalyst into a mixture of water and EFKA solution (EFKA 4585, IPA, MiliQ Water). Nation in the ratio of 1 :2 Nafion:Catalyst was added to the suspension. The ink was then stirred overnight and then ultrasonicated for 3 min with a sonication horn. After depositing the anode and cathode catalyst layer the catalyst coated membrane was fed through a calender which was maintained at 130 °C.

[0313] EB24-0322PC BASF SE 240322W001

[0314] The membrane (M) of C5 has a higher NMP content as the membrane (M) of C4. A Nation® 117 membrane treated was also coated for comparison with the same catalyst layers (Comparative example C6).

[0315] Characterization of the catalyst coated membranes (CCMs)

[0316] The mechanical properties of the CCMs were tested in a tensile test. The CCMs were activated with 0.5 M H2SO4and then stored in VE-water until the measurements were done. The tensile specimen (length 50 mm, width 8 mm) are then punched out of the wet CCMs and immediately fixed in the tensile testing machine, the testing speed was 1 mm / min to determine the E-Modulus and then 50 mm / min until the break of the sample. For each film, 5 samples were tested.

[0317] The catalyst coated membranes (CCMs) were tested in a 3.98 cm2test hardware manufactured by Fraunhofer. The electrolysis cell was maintained at 80 °C and fed with DI water both on anode and cathode at 100 mL min’1. Bekaert porous transport layers (BEKIPOR ® 2GDL40-1.0) were used on both sides. The current density was 2 A / cm2.

[0318] The results of the testing are summarized in table 2.

[0319] Table 2

[0320] From table 2, it can be seen that the inventive catalyst coated membranes (CCMs) have surprisingly superior mechanical properties (Elongation at break) and perform for much higher run times in a cell test.

[0321] EB24-0322PC

Claims

BASF SE 240322W00132Claims1. Method for the preparation of a catalyst coated membrane (CCM), wherein the method comprises the steps a) providing a membrane (M), wherein the membrane (M) comprises a polymer (P), wherein the polymer (P) has a glass transition temperature TG(P) ** 150 °C, b) providing a carrier material (CM), wherein the carrier material (CM) comprises a catalyst layer (CL), c) pressing the carrier material (CM) comprising the catalyst layer (CL) onto the membrane (M) at a temperature Tc)< 150 °C, wherein the catalyst layer (CL) is transferred from the carrier material (CM) onto the membrane (M) and the catalyst coated membrane (CCM) is obtained, and d) separating the carrier material (CM) from the catalyst coated membrane (CCM), wherein the membrane (M) provided in step a) i) comprises from 5 to 20% by weight, based on the total weight of the membrane (M), of at least one aprotic polar solvent (APS), or ii) is treated with at least one aprotic polar solvent (APS) before step c).

2. Method according to claim 1 , wherein the at least one aprotic polar solvent (APS) is selected from the group consisting of anisole, dimethylformamide, dimethylsulfoxide, sulfolane, N-methylpyrrolidone, N-ethylpyrrolidone, N- dimethylacetamide, ybutyrolactone, dimethyl sulfone, N-Formylmorpholine, tetraethylene glycol dimethyl ether, tetramethylurea and 1,3-Dimethyl-2- imidazolidinone.EB24-0322PCBASF SE 240322W001333. Method according to claim 1 or 2, wherein the polymer (P) i) has a glass transition temperature TG(P)> 175 °C, preferably a glass transition temperature TG(P)> 200 °C, and / or ii) is selected from the group consisting of sulfonated poly(phenylene oxide) polymers, sulfonated polyetheretherketone polymers and sulfonated polyarylene ether sulfone polymers.

4. Method according to claim 3, wherein the polymer (P) is a sulfonated polyarylene ether sulfone polymer, wherein the sulfonated polyarylene ether sulfone polymer is prepared by a process comprising the stepI) converting a reaction mixture (RG) comprising as components(A1) at least one non-sulfonated aromatic dihalogen sulfone,(A2) at least one sulfonated aromatic dihalogen sulfone,(B) at least one aromatic dihydroxy component,(C) at least one carbonate component, and(D) at least one aprotic polar solvent.

5. Method according to claim 4, wherein component (A1) is selected from the group consisting of 4,4’-dichlorodiphenyl sulfone and 4,4’-difluorodiphenyl sulfone.

6. Method according to claim 4 or 5, wherein component (A2) is at least one disulfonated aromatic dihalogen sulfone.

7. Method according to any one of claims 4 to 6, wherein component (B) is selected from the group consisting of 4,4‘-dihydroxybiphenyl, 4,4'-dihydroxy- diphenyl sulfone, bisphenol A, 4,4'-dihydroxybenzophenone and hydroquinone.

8. Method according to any one of claims 4 to 7, wherein component (C) comprises at least 50 wt.-% of potassium carbonate, based on the total weight of component (C).

9. Method according to any one of claims 4 to 8, wherein component (D) is selected from the group consisting of N-methylpyrrolidone, N-dimethyl- acetamide, dimethyl sulfoxide, sulfolane and dimethylformamide.EB24-0322PCBASF SE 240322W0013410. Method according to any one of claims 4 to 9, wherein the reaction mixture (RG) comprises component (A1) in an amount of from 40 to 70 mol-% and component (A2) in an amount of from 30 to 60 mol-%, based on the sum of the mol-% of components (A1) and (A2).

11. Method according to any one of claims 1 to 10, wherein the carrier material (CM) provided in step b) is obtained by depositing a catalyst ink onto the carrier material (CM), wherein the catalyst ink comprises catalytic nanoparticles supported on a conductive material, binders and ionomers.

12. Method according to claim 11, wherein the deposition is carried out by spray coating, screen printing, inkjet printing or slot die coating.

13. Method according to any one of claims 1 to 12, wherein, in case i), the membrane (M) is prepared by a method comprising the steps1) providing a solution (S) which comprises the polymer (P) and the at least one aprotic polar solvent (APS),2) casting the solution (S) provided in step 1) to obtain a film of the solution (S), and3) evaporating the at least one aprotic polar solvent (APS) from the film of the solution (S) obtained in step 2) to obtain the membrane (M) which is in the form of a film.

14. Method according to any one of claims 1 to 12, wherein, in case ii), the membrane (M) is coated with the at least one aprotic polar solvent (APS) or the membrane (M) is immersed in the at least one aprotic polar solvent (APS).

15. Catalyst coated membrane (CCM) obtained by a method according to any one of claims 1 to 14.

16. Use of a catalyst coated membrane (CCM) according to claim 15 in fuel cells and electrolyzers.EB24-0322PC

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