Production of catalytically coated anion exchange membranes

Abstract

The invention relates to catalytically coated anion exchange membranes and their production. Catalytically active coated anion exchange membranes are used in electrochemical cells, in particular for water electrolysis. It is an object of the invention to provide a method for the production of electrocatalytically active coated anion exchange membranes, the coating of which is porous and thus the electrocatalytically active sites present in the coating have good accessibility to the reactants. The basic idea of the method according to the invention is to add a particulate inorganic material as a spacer into the catalyst coating to consolidate the coating and then to leach the inorganic material out of the coating. The leaching converts the inorganic material into a water-soluble product which can be easily washed out of the coating. The particulate inorganic material leaves cavities (pores) at the locations where it previously existed within the coating. Thus, the inorganic material functions as a structure-defining agent within the coating composition, which function disappears during the catalytically active coating process.

Description

[0001] This invention relates to catalytically coated anion exchange membranes and their production. Catalytically coated anion exchange membranes are used in electrochemical cells, particularly for water electrolysis.

[0002] Anion exchange membranes (AEMs) are installed in electrochemical cells. They are typically used to prevent the mixing of substances produced in the cell (such as hydrogen and oxygen) while allowing ionic charge transport. As a result, electrochemical reactions carried out in the cell become more efficient and significantly safer.

[0003] One example of an electrochemical process utilizing anion exchange membranes is the production of hydrogen and oxygen through alkaline water splitting. This is achieved by using an anion exchange membrane as a separator between the battery electrodes. For this reason, the process is also known as AEM water electrolysis (AEMWE). Because the reaction occurs in an alkaline medium, AEM water electrolysis is often also referred to as alkaline membrane water electrolysis.

[0004] In AEM water electrolysis, the electrochemical cell is filled with water or an alkaline aqueous electrolyte, and a voltage is applied between the anode and the cathode. At the cathode, water (H₂O) decomposes into hydrogen gas (H₂) and hydroxide ions (OH⁻). - (Formula K). The anion exchange membrane transports hydroxide ions to the anode side, where they are oxidized to oxygen (O2) (Formula A). This results in oxygen being released on the anode side, while hydrogen is released on the cathode side. Therefore, the anode side is also called the oxygen side, and the cathode side is also called the hydrogen side.

[0005] 2H2O+2e - →H2+2OH - (K) Reduction / Cathode Reaction 2OH - →1 / 2O2 + H2O + 2e - (A) Oxidation / anodic reaction To achieve the aforementioned effects, the anion exchange membrane must conduct hydroxide ions between the anode and cathode. Simultaneously, it must be electrically insulating to prevent short circuits between the anode and cathode. Finally, if possible, the anion exchange membrane must be gas-tight to prevent backmixing of the formed gases. Furthermore, the anion exchange membrane must withstand the alkaline conditions present in AEM water electrolysis. These properties are satisfied by specific anion-conducting polymers (also known as anion-conducting ionomers).

[0006] To accelerate the reaction, catalytically active or activatable materials (also known as electrocatalysts) are introduced on both the cathode and anode sides. This is achieved by introducing a catalytically active or activatable layer into the battery or by applying a catalytically active or activatable coating to the battery components. These can be present on a substrate material specifically introduced into the battery for this purpose or on a porous transport layer (catalyst-coated substrate, CCS), or the membrane can be directly coated with a catalytically active material (catalyst-coated membrane, CCM).

[0007] An excellent overview of the construction and materials of the electrochemical cells currently used in AEM water electrolysis is given by Miller, Hamish Andrew et al.: Green hydrogen from anion exchange membrane water electrolysis: a review of recent developments in critical materials and operating conditions. Sustainable Energy Fuels, 2020, 4, 2114 DOI: 10.1039 / c9se01240k.

[0008] Now that the fundamental issues regarding the selection of materials and operating conditions have been resolved, the question that arises in developing systems for operating electrochemical processes is how to manufacture the individual components of an electrochemical cell on an industrial scale.

[0009] Therefore, for energy efficiency, the internal resistance of the electrochemical cell should be kept as low as possible. This can be achieved by placing the electrodes very close to the separator and the electrocatalyst as close as possible to the corresponding electrodes, using a compact structure.

[0010] One way to achieve this compact structure is the previously mentioned CCM design, in which the anion exchange membrane is coated with a catalytically active material. The anion exchange membrane thus prepared carries the catalyst during battery assembly. In this way, catalyst handling is eliminated during battery assembly, and a compact battery structure is achieved, which promises low internal resistance.

[0011] When coating anion exchange membranes with electrocatalysts, it is important to note that the substrate (membrane) and the coating material (catalyst) are very different: the membrane is typically composed of a special ion-conducting polymer (ionomer) in membrane form, while the electrocatalyst used is usually a particulate metal, metal oxide, or organometallic complex. To immobilize the catalytically active particles on the membrane, a polymer binder is used, which adheres the particles to the membrane. The binder can also be an ionomer made from a material similar to that used in anion exchange membranes. Due to the heterogeneity of the materials involved, the production of CCMs is not straightforward.

[0012] When immobilizing the electrocatalyst on the AEM, it is crucial to ensure that the catalyst particles are not completely surrounded by polymer binders. This is because it prevents reaction participants from contacting the catalytically active sites. In extreme cases, this could mean that the electrochemical reaction simply does not occur as expected. However, even if only some catalytically active sites are blocked by the polymer, this can lead to reduced efficiency because the amount of introduced catalyst is not fully utilized. Especially when using expensive noble metal catalysts such as iridium (Ir), ruthenium (Ru), platinum (Pt), gold (Au), silver (Ag), palladium (Pd), rhenium (Re), or rhodium (Rh), for the economic viability of the entire method, as much of the noble metal as possible present in the CCM as possible should be catalytically usable and not unnecessarily coated by the polymer. Furthermore, many electrochemical processes generate gases, such as molecular oxygen (O2) and hydrogen (H2), in AEM-based water electrolysis according to reactions (A) and (K). These gases form particularly at the interface between the membrane and the electrocatalyst, where they must be absorbed by the electrolyte. If the electrocatalytic active particles are too tightly encapsulated by polymer binders, these gases cannot escape from the CCM unimpeded, which in turn negatively impacts process efficiency. On the other hand, insufficient adhesion of the catalyst particles to the membrane has the effect that formed bubbles cause the particles to detach from the membrane, and the electrolyte washes the particles away. As a result, the catalytic activity of the CCM decreases over time.

[0013] Therefore, the goal is to securely anchor the electrocatalytically active particles to the AEM (Alternating Electrocatalytic Membrane) while simultaneously allowing good accessibility of reactants to the catalytically active sites. One approach to achieving this is to make the catalytically active coating of the CCM (Chemical Molecular Medium) porous.

[0014] For example, EP 4183900 A1 proposes using polymers with inherent microporous properties (PIM) as adhesion promoters between the catalyst and the substrate. Embedding the catalyst in the PIM matrix makes the catalytically active coating on the substrate generally porous. However, the polymers with inherent microporous properties described therein are not ionicly conductive themselves. For example, in the case of AEMWE, this means that hydroxide ions (OH-) are not ionicly conductive. -After passing through the membrane, the ions flow to the catalytic active sites only via the aqueous electrolyte. Therefore, hydroxide ions do not reach the catalyst directly, but rather via an indirect route. This reduces the current density in the cell, and thus the method appears to be less energy efficient compared to a CCM in which the catalyst particles are immobilized on a substrate using an ion-conductive binder (ionomer).

[0015] In the field of fuel cells employing proton-conducting polymer membranes (proton exchange membranes - PEMs), it is known that PEMs can be fitted with a catalyst coating filled with porous silica (WO 2023096229 A1, WO 2023096230 A1, CN114164438 B, JP 2023134869 A). This porous silica-filled layer allows for better permeability of the membrane to hydrogen and oxygen. However, because the membrane material used only conducts protons (H... + Therefore, it cannot be used for alkaline water electrolysis because, as mentioned above, the presence of hydroxide ions (OH-) is required here. - ) conductivity.

[0016] Min-Ha Kim's research group took another approach to make the catalyst layer of CCS slightly more porous: Kim et al.: Fe-doped Co3O4 nanostructures prepared via hard-templatemethod and used for the oxygen evolution reaction in alkaline media. Journal of Industrial and Engineering Chemistry, Volume 123, 2023, Pages 436-446, https: / / doi.org / 10.1016 / j.jiec.2023.03.062.

[0017] Kim et al. coated silica beads with iron-doped cobalt oxide and contacted the resulting material with a potassium hydroxide solution (KOH). The mixture was then washed with water and ethanol and heat-treated. In this way, Kim et al. leach the silica beads, leaving the remaining electrocatalyst with a porous structure. The porous, now silica-free electrocatalyst was processed into an ink and applied to a graphite electrode. The catalytically active graphite electrode (CCS) was assembled with an AEM and another electrode to obtain a membrane electrode assembly (MEA), which was then used for alkaline water electrolysis. The extent to which this procedure is suitable for applying electrocatalytically active porous materials to anion-conducting membranes has not been reported.

[0018] To address this prior art, the present invention aims to provide a method for producing an anion exchange membrane with an electrocatalytically coated coating. The coating is porous, thus ensuring good accessibility of the electrocatalytically active sites within the coating to the reactants. This good accessibility guarantees high reaction efficiency. Furthermore, the coating exhibits good permeability, while the membrane as airtight as possible overall. Additionally, the electrocatalysts present in the coating have good adhesion to the anion exchange membrane, preventing them from being washed out by the electrolyte. The catalytically coated anion exchange membrane also possesses good hydroxide ion conductivity and is stable in alkaline media, enabling its use in alkaline water electrolysis.

[0019] This objective is achieved by preparing a catalytically coated anion exchange membrane as follows: a) Provide a substrate containing or composed of anion-conducting membrane material; b) Provide a composition comprising at least one solvent, at least one polymer dissolved in the solvent, at least one particulate electrocatalyst, and particulate inorganic material other than the electrocatalyst; c) Applying the composition to the substrate such that the substrate acquires an applied coating containing the composition; d) Remove the solvent from the applied coating, such that the substrate obtains a layer in which the particulate electrocatalyst and different particulate inorganic materials are enriched and the particulate electrocatalyst and different particulate inorganic materials are fixed on the substrate by the polymer; e) Provide an alkaline aqueous solution containing at least one alkali metal selected from sodium, potassium and lithium; f) Contact the layer with the alkaline aqueous solution; g) React at least a portion of the particulate inorganic material within the layer with the alkaline solution to obtain at least one product; h) Wash at least a portion of the product out of the layer.

[0020] In this way, a catalytically coated anion exchange membrane is obtained, comprising a substrate and a layer applied thereon, wherein the layer now has openings.

[0021] Therefore, the present invention first provides a corresponding method for producing catalytically coated anion exchange membranes.

[0022] The basic idea of ​​the method according to the invention is to add particulate inorganic material as a spacer to the catalyst coating to solidify the coating, and then leach the inorganic material from the coating. Leaching converts the inorganic material into a water-soluble product that can be easily washed out of the coating. Cavities (pores) are left at the locations where the particulate inorganic material was previously present within the coating. Therefore, the particulate inorganic material functions as a structure definer within the coating composition, a function that disappears during the catalytically active coating process.

[0023] Therefore, the production process can be roughly divided into two parts.

[0024] In the first part, a coating composition containing inorganic materials is applied to and solidified onto a substrate. Thus, particulate electrocatalysts and various inorganic materials are fixed together on the substrate by means of a polymer. The polymer acts as a bonding promoter between the substrate and the particles (inorganic materials and electrocatalyst) applied thereon. Adhesion is achieved by dissolving the polymer in a solvent and applying it to the substrate together with the electrocatalyst and inorganic materials. The applied coating is solidified by removing the solvent from the applied coating again (e.g., by drying). During this process, the polymer precipitates from the solution and binds the particles to the substrate. In this way, a precursor for the subsequent catalytic coating of the anion exchange membrane is formed. The coating of the precursor is not yet porous and still contains particulate inorganic materials.

[0025] In the second part of the method, the precursor is then contacted with an alkali metal hydroxide (leaching). This converts the inorganic particulate material within the coating into a washable product. The type of washable product formed during leaching depends on the choice of inorganic material and alkali.

[0026] Suitable particulate inorganic materials, especially silicon dioxide (silicon dioxide-SiO2) and alumina (alumina-Al2O3) and their mixtures (silicon dioxide / alumina).

[0027] When the particulate inorganic material used is silicon dioxide and the alkali used is potassium hydroxide (KO), the particulate silicon dioxide (SiO2) present in the precursor coating is converted into the products potassium silicate (K2SiO3) and water (H2O): SiO2 + 2KOH → K2SiO3 + H2O (1) The potassium silicate product is water-soluble and has good washability from the layer. The same is true for the product water.

[0028] If a different alkali metal (e.g., lithium or sodium) is used instead of potassium for leaching, lithium silicate or sodium silicate is formed similarly to formula (1).

[0029] If the particulate inorganic material used is alumina (Al2O3), it will form a water-soluble aluminate with the alkali. For example, if the alkali used is sodium hydroxide (NaOH), then according to formula (2), the product formed is sodium aluminate (NaAl(OH)4): Al2O3+2 NaOH+3H2O→2NaAl(OH)4 (2) Sodium aluminate is water-soluble and can be easily washed out.

[0030] It is also possible to use granular silica and granular alumina, or a mixture of both, simultaneously. In this case, the above reactions proceed in parallel during leaching, and correspondingly, multiple products are obtained in parallel.

[0031] The silicates and / or aluminates present in the leaching coating can then be washed out of the coating with an aqueous solution, thereby giving the coating porosity. The polymer and particulate electrocatalyst are unaffected by leaching and washing, and ultimately form the catalytically active coating of the finished anion exchange membrane.

[0032] This invention also provides a final product, namely an anion exchange membrane with a porous catalytically active coating. This also applies to anion exchange membranes obtainable by the methods described herein.

[0033] Another aspect of the subject of this invention is a precursor for a catalytically coated anion exchange membrane, wherein the precursor still contains particulate inorganic material in its coating and still does not have any significant pores.

[0034] This is because the method according to the invention has the particular advantage that its two parts can be carried out in two different locations. For example, it is conceivable to produce the precursor (first part) in a CCM device and then install the precursor into an electrochemical cell. The second part of the method, namely, shaping the precursor into a final anion exchange membrane with a porous coating by leaching and washing, is carried out only while it is inside the electrochemical cell, i.e., at the location where the CCM is subsequently used. This is because treatment with alkali and subsequent coating washing can generally be carried out without difficulty in the cell, since the cell is alkali-resistant and has devices for contacting the coating with alkali or washing liquid. These devices are the same as those required for pumping electrolyte through the cell during the electrolytic operation of the cell. Since alkali is used as the electrolyte in alkaline water electrolysis in any case, leaching and washing can be performed using the subsequent electrolyte in the simplest case. In the extreme case, the formation of the CCM is completed only during the electrolytic operation. In this way, the production of the CCM is simplified because no additional preparation of alkali metal hydroxide is required. The electrolyte required in any case is only used for the shaping process.

[0035] Because of this preferred mode of production at two different locations, the present invention further provides precursors for catalytically coated anion exchange membranes that need to be transported between these locations.

[0036] As already mentioned, silica, alumina, or mixtures thereof can be specifically used as particulate inorganic materials in the method of the present invention. This is because these substances form water-soluble products with alkali metals present in the alkali. Inorganic substances can also be used if they are in solid particulate form under processing conditions and can react with the alkali to obtain washable and, under optimal conditions, water-soluble products.

[0037] To impart extremely fine porosity to this layer, the inorganic material used should be in the form of a very fine powder. Pyrolytic alumina and / or silica produced by flame pyrolysis are preferred. These materials are exceptionally fine and pure.

[0038] The production of alumina and / or silica via flame pyrolysis has been implemented on an industrial scale, and is described in particular by C. Schulze Isfort, M. Rochnia: Production and physico-chemical characterisation of nanoparticles, Toxicology Letters, Volume 186, Issue 3, 2009, Pages 148-151, ISSN 0378-4274, DOI 10.1016 / j.toxlet.2008.11.021 and by Bogdan, Anatoli and M. Kulmala: "Pyrogenic Silica and Alumina", in Encyclopedia of Surface and Colloid Science, Third Edition. (2015) DOI 10.1081 / E-ESCS3-120000089.

[0039] The primary characteristic of inorganic materials obtained through flame pyrolysis is their high specific surface area. Under optimal conditions, the specific surface area of ​​particulate inorganic materials, as determined by the BET method, is over 50 m². 2 / g to 450m 2 Between / g. For example, the Aerosil® 300 mentioned above has approximately 300m³. 2 / g of BET surface area. BET surface area is typically measured by nitrogen adsorption via Brunauer, Emmett, Teller: Brunauer, S., Emmett, PH, Teller, E.: Adsorption of Gases inMultimolecular Layers. Journal of the American Chemical Society. Vol. 60,Issue 2, 1938, Pages 309–319, Determined by known methods according to DOI: 10.1021 / ja01269a023.

[0040] BET surface area can be measured automatically using commercially available instruments, such as the Micromeritics 5 TriStar II 3020 V1.03.

[0041] Particulate inorganic materials suitable for the intended purpose are available from Evonik under the brand names AEROSIL® (pyrolytic silica) and AEROXID® (pyrolytic alumina). These specifically include, but are not limited to, the following products: AEROSIL® OX 50, AEROSIL® 90, AEROSIL® 200, AEROSIL® 300, AEROSIL® 380, or AEROXID® 130. These materials have a 10m... 2 / g to 1000m 2 / g, preferably 50m 2 / g to 400m 2 Specific surface area (BET) per g. Additionally, pyrolytic metal oxides and silica already dispersed in water or solvents can be used. Such materials are available from Evonik, for example, under the brand names AERODISP® or VP Disp®. These specifically include, but are not limited to, the following products: AERODISP® W1226, AERODISP® W 7225, AERODISP® W 7512 S, AERODISP® W7520, AERODISP® W7622, ​​VP Disp® W 7610 S, or AERODISP® W 925.

[0042] One characteristic of pyrolytic silica is that its primary particles combine to form branched aggregates (secondary particles), thereby creating a particularly advantageous porous structure within the layer. The primary particles have a particle size of up to 20 nm, while the aggregates have a particle size of approximately 100 nm.

[0043] As an alternative to pyrolytic silica, precipitated silica can also be used as a particulate inorganic material. By properly grinding precipitated silica, it can be obtained at a particle size of 50 μm.2 / g to 400m 2 Specific surface area (BET) within a preferred range of / g. Precipitated silica can be, for example, branded under the name SIPERNAT® derived from Evonik.

[0044] The solvent used in the composition is used to dissolve the polymer that is also present in the composition. Particularly suitable solvents for this purpose have been found to be dimethyl sulfoxide (DMSO), ethanol (EtOH), and acetonitrile (ACN). These solvents can be used alone or in mixtures with each other.

[0045] Desirablely, in addition to the solvent, different liquid dispersion media are added to the composition. Dispersion media are particularly needed when the solid content of the composition formed from electrocatalysts and inorganic materials is so high compared to the solvent that the composition cannot be reasonably processed. Adding a dispersion media reduces the overall solid content of the composition, resulting in lower viscosity and better processability. The composition is then diluted with a dispersion media.

[0046] Regardless of the established viscosity and formulation, the composition will always form a dispersion, i.e., a liquid phase having a polymer dissolved in a solvent and any liquid dispersion medium, and a second solid phase having an electrocatalyst and an inorganic material. Depending on the established viscosity and solid content, the composition can be considered a slurry or paste.

[0047] Suitable dispersion media for diluting the composition include water (H2O), N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAC), acetone (ACT), and 2-propanol (IPA). These dispersion media can be used alone or in mixtures with each other.

[0048] If desired, the composition may also contain additional auxiliaries or additives, such as, in particular, dispersants, rheology modifiers, or surfactants. It is preferable not to add such auxiliaries or additives so that the subsequent catalyst layer does not contain any destructive, electrocatalytically inert foreign matter. However, in many cases, the presence of conductive additives is necessary to increase or even establish the conductivity of the subsequent layer. This is because many ionomers are only ionicly conductive but have almost no conductivity to electrons. Typical conductive additives are carbon black, especially specialty carbon blacks such as Ketjenblack® from Nouryon or Vulcan® XC72 from Cabot Corporation.

[0049] The main components of the catalyst layer to be produced are particulate electrocatalyst, a polymer immobilizing the particulate electrocatalyst on the membrane, and pores. The pores in this layer are empty, but when the anion exchange membrane is used as intended, these pores are filled with liquid electrolyte.

[0050] An electrocatalyst is a substance that exhibits catalytic activity in an electrochemical reaction, or is activated to perform catalytic activity. Based on current research, the following elements can be used in this method in pure form, as oxides, as hydroxides, or as oxide hydroxides: iridium (Ir), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), ruthenium (Ru), copper (Cu), molybdenum (Mo), zinc (Zn), lead (Pb), manganese (Mn), tungsten (W), platinum (Pt), sulfur (S), tin (Sn), gold (Au), silver (Ag), palladium (Pd), rhenium (Re), and rhodium (Rh). These elements can be used as electrocatalysts in pure form, as oxides, as hydroxides, or as oxides, either alone or in combination in each case.

[0051] Very particularly preferred is the processing of platinum or platinum alloy (Pt / C) or nickel-iron (oxide) hydroxyl oxide (NiFe) supported on carbon as an electrocatalyst. a O b H c The composition is as follows. Subscripts a, b, and c are real numbers in the range from 0 to 8. Subscripts a, b, and c may be the same or different. Ideally, the nickel-iron ratio in nickel-iron (oxide) hydroxyoxides should be in the range of 2:1 to 10:1.

[0052] As previously mentioned, the polymer at least functions as a binder to immobilize the electrocatalyst on the membrane. Since hydroxide ions transported by the anion exchange membrane must contact the catalytically active sites of the electrocatalyst, an ionicly conductive connection between the electrocatalyst and the membrane is required. In its simplest case, this is achieved by an electrolyte introduced into the pores of the layer during use. Alternatively, an ionicly conductive material can be added to the composition, which is embedded in the polymer and imparts a certain degree of ionic conductivity. However, it is preferable to use a polymer with inherent conductivity to hydroxide ions as a binder. Such anion-conducting polymers are also called ionomers and are preferably used as binders here. This is because the use of ionomers opens up additional ionicly conductive connections from the membrane to the catalytically active sites through the ionomer. This allows for improved electrolysis efficiency. In a particularly preferred embodiment of the invention, the composition therefore contains an anion-conducting polymer.

[0053] In the simplest case, commercially available anionic conductive polymers are used. These are typically polymers with cationic groups. These groups are either grafted onto the main chain or are part of the main chain. The cationic groups are typically quaternary trialkylammonium salts. The main chain is typically polystyrene, polysulfone, polyethersulfone, polyarylether, polybenzimidazole, or polyphenylene ether, usually in a fluorinated form.

[0054] The drawback of these ionomers is that they typically contain fluorine, thus facing increasing reservations. Therefore, it is better to use fluorine-free anionic conductive polymers.

[0055] These are known. It is preferred to use those fluorine-free ionomers having one of the following three structures (I), (II), or (III): (I) In (I), X is a structural unit containing a positively charged nitrogen atom, which is related to C. 1 and C 2 Bonded, and bonded by two bonds to one or two hydrocarbon groups containing 1 to 12, preferably 1 to 6, more preferably 1 or 5 carbon atoms. Furthermore, in (I), Z contains a relation to C. 3 and C 4 The structural unit comprises a bonded carbon atom and at least one aromatic six-membered ring directly bonded to one of the oxygen atoms, wherein the aromatic six-membered ring may be substituted by one or more halogen groups and / or one or more C1 to C4 alkyl groups; (II) In (II), X is a structural unit containing a positively charged nitrogen atom, which is related to C. 1 and C 2 Bonded, and bonded by two bonds to one or two hydrocarbon groups containing 1 to 12, preferably 1 to 6, more preferably 1 or 5 carbon atoms. Furthermore, in (II), Z contains a relation to C. 3 and C 4 The structural unit comprises a bonded carbon atom and an aromatic six-membered ring directly bonded to one of the oxygen atoms, wherein the aromatic six-membered ring may be substituted at the 3 and 5 positions with the same or different C1 to C4 alkyl groups, particularly with methyl, isopropyl or tert-butyl, preferably with methyl. (III) In (III), X is a ketone group or a sulfone group; In (III), Z is a structural unit containing at least one tertiary carbon atom and at least one aromatic six-membered ring, wherein the aromatic six-membered ring is directly bonded to one of the two oxygen atoms; Furthermore, in (III), Y is a structural unit containing at least one nitrogen atom with a positive charge, wherein the nitrogen atom is bonded to structural unit Z.

[0056] Fluorine-free ionomers having structures (I), (II), and (III) are suitable for use in anion exchange membranes and for immobilizing catalysts on membranes. Furthermore, these ionomers exhibit excellent processability in the method according to the invention, particularly at low temperatures below 70°C. These polymers having structures (I), (II), and (III) should be present at least in the composition. These ionomers are known from patent applications EP3770201A1, EP4032934A1, and EP4059988A1.

[0057] The substrate to which the catalyst layer is applied must consist of or contain at least an anion-conducting membrane material so that OH ions can be exchanged via a subsequent anion exchange membrane. If the membrane material is an organic polymer, it should be considered an ionomer. The ionomer used as the membrane material is preferably the same as the ionomer used as the binder. This allows for particularly good bonding between the electrocatalyst and the substrate, and enables good ion conduction. It is also advantageous to use one ionomer each as a binder and as a membrane material, these ionomers having the same repeating units but differing in chain length. In this case, the membrane material and the polymer are not identical, but are chemically very similar. This results in, for example, greater stability of the substrate. Therefore, in a preferred embodiment of the invention, the membrane material and the polymer have the same repeating units.

[0058] Ionomers used as membrane materials and / or as (adhesive) polymers should have a hydroxide ion specific conductivity S, preferably between 50 mS / cm and 150 mS / cm. The aforementioned fluorine-free ionomers achieve a specific conductivity of approximately 100 mS / cm. Currently, the specific conductivity of ionomers is typically between 5 mS / cm and 300 mS / cm. These conductivity values ​​are based on hydroxide ion (OH-) concentrations. - Specific conductivity is also often used in relation to chloride ions (Cl). - The value of chloride ions is approximately one-fifth of that of hydroxide ions.

[0059] The specific conductivity S of the ionomer to hydroxide ions was measured as follows: The ionomer solution was uniformly coated onto a glass plate using a doctor blade. After drying at 80°C for 3 hours, the thickness of the dried layer was determined. This thickness should be in the range of 60-120 μm and should be substantially constant throughout the entire area. The ionomer film was then separated from the glass plate by placing it in a 1M KOH solution. This yielded the ionomer film.

[0060] This is followed by an ion exchange operation, ideally carried out under CO2-free conditions using a glove box and / or a tightly sealable container. CO2 removal aims to prevent CO2 formation by OH groups in the potassium hydroxide solution or ionomer layer. -Ions form carbonates. A 1M potassium hydroxide solution (from Carl Roth's standard solution; K017.1) is used for ion exchange. The contact between the ionomer membrane required for ion exchange and the potassium hydroxide solution is carried out in a tightly sealable container.

[0061] The tightly sealable box is first washed once with potassium hydroxide solution in a glove box, then injected with the solution to ensure good coverage of the ionomer membrane. The box is then tightly sealed. Afterward, the sealed box is placed in a water-filled agitated bath at 60°C for 1 hour. This is done outside the glove box. This is repeated three times, each time using fresh potassium hydroxide solution.

[0062] After undergoing three ion-exchange cycles at 60°C for 1 hour each, the ionomer membrane was again contacted with fresh potassium hydroxide solution and agitated in a 60°C water bath for 2 days. Ultrapure water was then used to wash the ionomer membrane. All washing operations in this step were also performed in a glove box. At the beginning of this step, the potassium hydroxide solution present in the container was removed, and for this purpose, the container was rinsed twice with ultrapure water. The container was then filled with fresh ultrapure water and washed in a 60°C water bath for 20 minutes. Thus, the ionomer membrane was converted to hydroxide ions and washed away.

[0063] For conductivity measurements, a punch is used to punch out rectangular sheets of 25 mm × 15 mm size from the washed ionomer membrane (in hydroxyl form), and these are referred to below as "test ionomer membranes".

[0064] A test ionomer membrane is installed in each conductivity measurement cell, which can be used to measure the ionic conductivity in the membrane plane. This is done while rinsing the membrane with deionized water. The inherent conductivity of the membrane can be calculated from the measurement geometry (electrode spacing or area, membrane thickness, and membrane width), and this is equal to the conductivity of the ionomer.

[0065] The measurement cell and measurement process (in this case, the Nafion® 117 membrane) are described in section “2.6 Conductivity determination” of the preprint by María Jesús González-Pabón et al., High-performance biodegradable membrane for point of need paper-based micro-scale microbial fuel cell analytical devices. bioRxiv 351890;doi: https: / / doi.org / 10.1101 / 351890.

[0066] This also includes methods for calculating the conductivity of a membrane based on its measured geometry.

[0067] The substrate used is typically a flat membrane, plate, or preform composed of or containing at least anion-conducting membrane material. The substrate should not be porous but rather dense so that gas exchange through the membrane is impossible. Only the layers should be porous. The thickness of the substrate should be approximately 15 μm to 110 μm. The length and width of the substrate are determined by the area of ​​the cell. Typically, continuous ionomer membranes in strip form are used as the substrate and coated in segments or continuously. If coating is done in strip form (as a roll-to-roll process), the finished anion exchange membrane or its precursor is cut from the roll.

[0068] As already mentioned, the production of the catalytically coated anion exchange membrane of the present invention can be broadly divided into two parts: the first part is used to produce the precursor, and the second part is used to shape the precursor, thereby providing a catalytically coated anion exchange membrane in an operable form.

[0069] The following steps relate to the second part of the method, namely the molding of the precursor. f) Contact the layer with an alkaline aqueous solution; g) Reacting at least a portion of the inorganic material with an alkali metal to obtain a product within the layer; h) Wash at least a portion of the product out of the layer; i) Obtain a catalytically coated anion exchange membrane comprising the substrate and a layer applied thereon, wherein the layer now has openings.

[0070] In a preferred variation of the method, this part of the process is carried out within the electrochemical cell. This means that the precursor is installed into the electrochemical cell and molding is performed in situ (i.e., at the final intended location of the catalytically coated anion exchange membrane, i.e., within the cell). In-situ molding is particularly feasible when the electrochemical cell is intended to operate in an alkaline medium under any circumstances, such as for alkaline membrane water electrolysis. In this case, the cell components are stable to the alkaline medium, so leaching of the layers does not damage the cell. In the simplest case, the alkaline aqueous solution used is the alkaline electrolyte required for operation of the electrochemical cell under any circumstances. Due to the degradation and contamination of the electrolyte caused by the reaction of organic materials and the elution of the resulting products, the electrolyte usually needs to be replaced at the end of molding.

[0071] Especially when the catalytically coated anion exchange membrane is not intended for use in an alkaline medium, leaching should not be performed within the cell to avoid damaging it. Therefore, in the second method variant, the following steps are performed outside the electrochemical cell (non-in-situ): f) Contact the layer with the alkaline aqueous solution; g) Reacting at least a portion of the inorganic material with the alkali metal to obtain a product within the layer; h) Wash at least a portion of the product out of the layer; i) Obtain an anion exchange membrane comprising the substrate and the layer applied thereon, wherein the layer now has openings.

[0072] Then, after the precursor preparation, the membrane is directly formed, preferably in an integrated roll-to-roll process, so that the catalytically coated anion exchange membrane is wound into a roll in its final porous form. In battery manufacturing, which is separate from membrane production, the formed membrane is rewound, completed, and assembled.

[0073] In addition to the two molding variants described here, hybrid forms are of course conceivable, in which molding begins in a non-in-situ manner and is completed in situ. Thus, some of steps f) through i) are performed in one or the other location, or these steps are not fully performed in one location but end only in another.

[0074] In both in situ and exositu variants, the following steps can be performed at least partially simultaneously, for example, in a flow process: f) Contact the layer with the alkaline aqueous solution; g) Reacting at least a portion of the inorganic material with the alkali metal to obtain a product within the layer; h) At least a portion of the product is eluted from the layer. Thus, elution begins even while the reaction is still in progress. This can increase the reaction rate because the reaction product is removed from the reaction. Preferably, all three steps are performed simultaneously.

[0075] In a particularly preferred variant of the method, not only the layer but also the substrate is in contact with an alkaline aqueous solution, especially simultaneously.

[0076] The idea behind this measure is to subject the anion-conducting membrane material present in the substrate to ion exchange in order to impart high ionic conductivity. Ion exchange converts the ionomer into its hydroxide form. In this way, the substrate can be used particularly efficiently as an anion-conducting membrane. Ion exchange and leaching of the inorganic material can preferably be carried out in one step, i.e., simultaneously, so that the process is not unnecessarily prolonged. No additional production aids are required, as both leaching and ion exchange can be carried out using potassium hydroxide or sodium hydroxide solutions. When ion exchange and leaching occur simultaneously, this can be in-situ or ex-situ.

[0077] Preferably, the substrate is contacted with an alkaline aqueous solution at a temperature between 20°C and 75°C for a period of 1 hour to 24 hours. Ion exchange should be as complete as possible. Ideally, complete ion exchange cannot be achieved with acceptable cost and inconvenience. Based on the amount of ions originally present in the anion-conducting membrane material, the actual ion exchange level is 75% to 99%.

[0078] Ion exchange primarily involves membrane materials. If the layer containing the electrocatalyst also includes ionomers, it will also undergo ion exchange.

[0079] It is recommended to replace the alkaline aqueous solution during ion exchange, as the exchanged ions become concentrated in the alkaline solution. Replacement allows for more complete ion exchange. Replacing the alkaline aqueous solution during ion exchange is preferable, especially when ion exchange is performed in situ within an electrochemical cell, as the cell is thus less likely to be significantly contaminated by the exchanged ions.

[0080] The present invention also provides a catalytically coated anion exchange membrane that can be prepared by this method. It comprises a substrate containing or composed of anion-conducting membrane material and a layer at least applied to the substrate, wherein a particulate electrocatalyst is enriched in the layer, wherein the electrocatalyst is fixed to the substrate by a polymer, and wherein the layer has openings. The thickness of the layer is preferably from about 3 μm to 15 μm. The total thickness of the anion exchange membrane is preferably between 15 μm and 120 μm.

[0081] The present invention further provides a precursor for a catalytically coated anion exchange membrane. The precursor further comprises a substrate and at least a layer applied to the substrate, the substrate containing or being composed of anion-conducting membrane material, wherein particulate electrocatalysts and various particulate inorganic materials are enriched in the layer, and wherein the electrocatalysts and inorganic materials are immobilized on the substrate by a polymer.

[0082] The difference between the precursor and the final catalytically coated anion exchange membrane lies primarily in the fact that it is essentially non-porous.

[0083] Furthermore, the difference between the precursor and the formed CCM lies in the physical composition of the layers. The precursor contains a higher degree of particulate inorganic material, while the formed CCM contains at most unconverted residues and any residues of products that were converted into inorganic materials during the leaching process but were not washed out.

[0084] If the particulate inorganic material is silicon dioxide and / or aluminum oxide and the base is potassium hydroxide or sodium hydroxide, the preferred content or expected residual content of these substances or their reaction products is listed in Table 1: Table 1: Preferred contents of silica, alumina, silicates and aluminates

[0085] All values ​​given in Table 1 should be considered as weight percentages relative to the total mass of the layer. These values ​​relate to the sum of the individual weight percentages of each substance given in that row. If a substance is not present in the layer, the sum corresponds to the weight percentage of the substance that is present.

[0086] The reason for the high silicate content (up to 6%) before leaching is that some ionomers have reactive OH groups, which begin to convert silica into silicates even before contact with the alkaline solution. The same applies to the conversion of alumina to aluminate, as this conversion occurs in the presence of water, which is present in the membrane as a production residue or comes from air moisture.

[0087] Example The invention will now be described in detail with reference to embodiments. In this regard, the accompanying drawings illustrate: Figure 1 Apply the composition to the substrate; Figure 2 : A substrate with an applied coating; Figure 3 : Remove solvent from the applied coating; Figure 4 Precursor; Figure 5 : To bring the layer into contact with an alkaline aqueous solution; Figure 6 At least a portion of the alkali metal silicate is washed out from the layer; Figure 7 Anion exchange membrane with a porous coating; Figure 8 EDX spectrum of CCM precursor produced from silica before leaching; Figure 9 EDX spectrum of CCM produced from silica after leaching; Figure 10 Electrolysis measurement comparison between the CCM (circular symbol, solid line) produced according to the present invention and the conventional CCM (square symbol, dashed line).

[0088] A method for producing a catalyst-coated anion exchange membrane is schematically shown in Figures 1 to 7 middle.

[0089] First, a substrate 1 is provided. Substrate 1 contains a membrane material with specific conductivity to anions. Available membrane materials are, in particular, anion-conducting polymers, called ionomers. Substrate 1 is typically a flat anion exchange membrane (AEM) in the form of a membrane composed of the membrane material. Alternatively, a composite material can be used as substrate 1, which, in addition to the membrane material, also contains reinforcing materials. Typically, substrate 1 itself does not possess inherent catalytic activity. However, substrate 1 can be provided with a coating that performs functions other than catalysis, such as protecting the membrane material. Such an optional coating is not shown in the accompanying drawings.

[0090] Additionally, composition 2 is provided, which substantially comprises the following components: a solid particulate electrocatalyst 3, a solid particulate silica 4, and a liquid solution 5, wherein the liquid solution 5 contains a solvent and a polymer dissolved in the solvent (solution 5 in...). Figure 1 and 2 (Represented as a clear liquid). Composition 2 may optionally contain other components, such as a dispersion medium or dispersion aid. Due to its solid and dissolved components, composition 2 is in the form of a suspension. Depending on the formulation and processing temperature, composition 2 can have a relatively low or relatively high viscosity. In addition to the presence of silica 4, composition 2 corresponds to a conventional catalyst slurry or catalyst paste for catalytically active coating of membranes (CCMs) or electrodes (CCS).

[0091] Composition 2 is applied to substrate 1. This is done in a conventional manner by direct coating (using a coating stick or a slit die, by spraying, by screen printing) or indirectly via a transfer medium (called decal). Since this application corresponds to the prior art, therefore... Figure 1 The operation is shown in a very simplified form.

[0092] Composition 2 is applied to substrate 1 to obtain coating 6 applied to substrate 1 in the form of a layer. Figure 2 The thickness of the applied coating 2 and the substrate 1 is... Figure 2 Not shown to scale. In industrial applications, the thickness of substrate 1 is approximately 50 μm to 70 μm, while the applied coating 6 is very thin, approximately 10 μm to 20 μm. The transparent solution 5 is still present in the applied coating 6.

[0093] In the next step, the solvent 7 present in solution 5 is removed from the applied coating 6. In the simplest case, this is accomplished by drying. Figure 3 A schematic diagram illustrates how solvent 7 evaporates from the applied coating 6. Due to the extraction of solvent 7, polymer 8, previously dissolved in the solution, precipitates and forms a solid matrix surrounding the particulate materials 3 and 4. The surface of the matrix is ​​not actually like... Figures 3 to 7The middle part is clearly defined as shown in a simplified form. Instead, polymer 8 is deposited on and around the individual particles 3 and 4, bridging the voids and thus forming an irregular, non-planar surface.

[0094] When the drying process is complete, the matrix of polymer 8 extends through the entire thickness of the applied coating 6 up to the substrate 1. Figure 4 Thus, substrate 1 obtains a solid layer 9 formed of polymer 8, electrocatalyst 3, and silica 4. Since polymer 8 also adheres to substrate 1, electrocatalyst 3 and silica 4 are fixed to the substrate by polymer 8. At this stage of the process, precursor 10 is obtained, which is substrate 1 firmly coated with layer 9 containing polymer 8, electrocatalyst 3, and silica 4. Precursor 10 can certainly be used as a catalytically active coated anion exchange membrane (CCM), but it is less effective compared to the subsequent final product because layer 9 is non-porous and also contains electrochemically inert silica 4.

[0095] Precursor 10 is converted into the final product in the second part of the method (molding).

[0096] Therefore, layer 9 of precursor 10 is first contacted with an alkaline aqueous solution, such as potassium hydroxide (solution) (KOH). Figure 5 The contact shown only schematically can be achieved in the simplest case by applying potassium hydroxide solution to layer 9 with a brush or by immersing it in a potassium hydroxide solution (KOH) bath.

[0097] The hydroxide present in the alkaline solution reacts with the particulate silica 4 present in layer 9 to yield the corresponding alkali metal silicate. When potassium hydroxide solution (KOH) is used here, potassium silicate 11 and liquid water (H₂O) are formed according to equation (1).

[0098] Since potassium silicate 11 is water-soluble, it can be washed out of layer 9 using water (H2O) or an aqueous washing solution; see also Figure 6 Pores 12 are left in the matrix of polymer 8 where silica or potassium silicate particles were previously present. This makes layer 9 porous.

[0099] The production process is completed through the molding process that has already begun. Figure 7 A schematic diagram of the resulting final product 13, an anion exchange membrane, is shown. This anion exchange membrane comprises a substrate 1 and a layer 9 applied thereon, which contains a particulate electrocatalyst 3 and a polymer matrix 8 now comprising pores 12. Furthermore, layer 9 of the final product 13 also contains isolated unconverted silica 4 and unwashed potassium silicate 11, because neither the reaction nor the washing process was completely completed to 100%, particularly in the interface region 14 between layer 9 and substrate 1.

[0100] In practice, the interface region 14 is not a clear boundary between layer 9 and substrate 1. Instead, it is a transition zone where the concentrations of electrocatalyst 3 and pores 12 decrease in the direction toward substrate 1, while the concentration of membrane material increases in that direction. This is especially true when polymer 8 and membrane material are the same anion-conducting material (ionomer) or when both materials have at least the same repeating units. This is because, in this case, the solvent present in composition 2 also partially dissolves the membrane material, causing the catalyst particles 3 present at the bottom of the applied coating 6 to partially penetrate into the partially dissolved substrate 1. Simultaneously, this creates a good ion-conducting contact between the matrix and substrate 1, allowing hydroxide ions to be directly guided from substrate 1 via polymer 8 to the catalytically active sites of electrocatalyst 3. The gas formed there can escape from layer 9 through pores 12. It should be noted that, in this context, substrate 1 is not completely dissolved, as otherwise it would become porous and thus lose its integrity. Substrate 1 should always be airtight so that gas exchange via the membrane is impossible.

[0101] Figure 7 The final product 13 shown has only one catalytically active layer 9 on one side of the substrate 1. In practice, it is meaningful to coat both sides of the substrate 1, i.e., coating the first side with a first electrocatalyst for catalytic anodic reaction and the opposite second side of the substrate 1 with a second electrocatalyst for catalytic cathodic reaction. This is in Figure 7 Not shown in the image.

[0102] Experimental data The following example of a platinum / carbon-based catalyst layer is used to describe a method for preparing porous catalyst layers for AEM applications. Therefore, the effectiveness of this invention is verified experimentally.

[0103] 1. Production of ionomers (not part of this invention) Anion-conducting cationic polymers were synthesized according to Example 3 of EP3770201A1.

[0104] 2. Preparation of anion exchange membranes (not part of this invention) The cationic polymer synthesized in step 1 was then used to prepare anionic conductive membranes, as described in Example 4 of EP3770201A1.

[0105] 3. Provide silica-free compositions (refer to experiments, not part of this invention). A screw-topped wide-mouth flask was filled to one-third full using yttrium-stabilized zirconia grinding balls (5 mm in diameter). Then, two parts by weight of catalyst powder (carbon-supported platinum, 50% platinum loading) were introduced into the flask. Next, 19 parts by weight of water were added, the flask was capped, and the flask was vibrated for 1 minute using a "lab dancer" vortex mixer (IKA). The flask was reopened, 19 parts by weight of ethanol was added, the flask was sealed again, and the flask was vibrated for another 1 minute. The flask was then alternately placed on a tilt-and-roll mixer at 60 rpm for at least 5 hours, and then in an ultrasonic bath (180 W) for 5 minutes. This was repeated twice. In each case, 76 parts by weight of water and 76 parts by weight of ethanol were added, and the mixture was vibrated for 1 minute using a vortex mixer. Finally, add the ionomer solution (5% ionomer in DMSO; as produced in 1.) until the ionomer solids content is 14% of the total solids content, seal the container, and roll the solution on a tilting roller mixer for 1 hour, and finally place it in an ultrasonic bath at 180 W for 5 minutes.

[0106] 4. A composition comprising silica (part of this invention) is provided. The preparation using silica is largely similar to the preparation of the reference composition described in section 3 above, except that silica is added separately when water and ethanol are added at the end: A screw-topped wide-mouth flask was filled to one-third full with yttrium-stabilized zirconia grinding balls (5 mm in diameter). Then, two parts by weight of catalyst powder (carbon-supported platinum, 50% platinum loading) were introduced into the flask. Next, 19 parts by weight of water were added, the flask was capped, and the flask was vibrated for 1 minute using a "lab dancer" vortex mixer (IKA). The flask was reopened, 19 parts by weight of ethanol was added, the flask was sealed again, and the flask was vibrated for another 1 minute. The flask was then alternately placed on a tilting roller mixer at 60 rpm for at least 5 hours, and in an ultrasonic bath (180 W) for 5 minutes. This was repeated twice. In each case, 0.6 parts by weight of silica, 76 parts by weight of water, and 76 parts by weight of ethanol were added, and the mixture was vibrated for 1 minute using a vortex mixer. The silica was then sized to have a BET surface area of ​​300 m². 2 A 10% (g) aqueous dispersion of silica (AEROSIL® 300) is added. The amount of water in the dispersion is included in the total amount of water added.

[0107] Finally, add the ionomer solution (5% ionomer prepared according to 1, dissolved in DMSO) until the solid content of the ionomer accounts for 14% of the total solid content, seal the container, and roll the solution on a tilting roller mixer for 1 hour, and finally place it in an ultrasonic bath at 180W for 5 minutes.

[0108] 5. Coating a substrate with a silica-free composition (not an invention) For the reference experiment (without silica), the composition provided in 3. was applied to a substrate using a spray gun. The substrate was the anion-conducting membrane provided in 2. During coating, the membrane was fixed to a heated (60°C) surface.

[0109] Adjust coating parameters to achieve approximately 90 layers, 0.45 mg Pt / cm 2 Achieve a uniform platinum area loading. Ensure each individual layer is substantially dry before applying the corresponding next layer. Finally, allow the coated film to dry completely on a heated surface for 30 minutes.

[0110] In this way, CCM is obtained. It can be used in alkaline water electrolysis just like conventional CCM without silica.

[0111] 6. Coating a substrate with a composition containing silica (part of this invention) For the experiments of this invention using silica, the composition provided in section 4 was applied to a substrate using a sprayer. The substrate was the anion-conducting membrane provided in section 2. During coating, the membrane was fixed to a surface heated to 60°C.

[0112] Adjust coating parameters to achieve approximately 90 layers, 0.45 mg Pt / cm 2 Achieve a uniform platinum area loading. Ensure each individual layer is substantially dry before applying the corresponding next layer. Finally, allow the coated film to dry completely on a heated surface for 30 minutes.

[0113] In this way, CCM is obtained. CCM is a precursor for the final catalytically coated anion exchange membrane. However, even in this state, it can be used as CCM in alkaline water electrolysis.

[0114] 7. Molding / Leaching Process To convert the CCMs obtained in 5. and 6. to their hydroxide form, both samples were placed in 1 MkOH at room temperature for 3 hours. Simultaneously with ion exchange within the membrane, most of the silica present in the coating (in the case of the precursor in 6.) was converted to water-soluble potassium silicate and partially leached out. In this way, catalytically coated anion exchange membranes (CCMs) were obtained in each case.

[0115] 8. Energy-dispersive X-ray analysis of coated films To understand the leaching process, the CCM produced from silica in step 6 was examined before and after leaching in step 7 by energy-dispersive X-ray analysis (EDX). Figure 8 The spectrum before leaching is shown; Figure 9 The spectrum after leaching is shown. Comparing the two spectra, it is clear that the peak size at approximately 1.7 keV decreases significantly, while the changes in other peaks are relatively small. As shown in the figure, the mentioned peak belongs to silicon dioxide (Si-Kα). The reduction in the peak size indicates that the amount of silicon dioxide in the CCM is significantly reduced after leaching.

[0116] 9. Test the catalyst-coated membrane in an electrolysis test cell. The coated and leached membrane (active Pt / C catalyst coating area is 16 cm²) 2 The tests were conducted in an electrolysis test cell (BalticFuelCells GmbH, Germany). A catalyst layer was used as the cathode catalyst. On the anode side, a dimensionally stable porous stainless steel electrode was used. During the electrolysis experiments, the measuring cell was heated to 60°C and rinsed with 1M KOH solution on both the anode and cathode sides. Current-voltage characteristic curves were recorded. Figure 10 Center (circular symbol, solid line).

[0117] The conventionally manufactured CCM was also tested under the same conditions as described in section 5. The corresponding current-voltage characteristic curves are also plotted using square symbols and dashed lines. Figure 10 middle.

[0118] The graph plots the required voltage relative to an externally applied current per unit area. This is achieved with a constant current per unit area (e.g., 1500 mA / cm²). 2 At this voltage level, lower voltage is preferred because the electrical energy required to produce the same amount of hydrogen at the same production rate decreases, thus increasing efficiency. Of particular relevance to industrial applications is voltage exceeding 500 mA / cm². 2 The current intensity per unit area. It can be seen that, in the case of the CCM produced according to the present invention, the current-voltage characteristic curve at higher current densities is lower than that of the (non-invented) CCM produced for reference. The lower current density results in lower energy consumption at the same voltage, therefore the CCM produced according to the present invention has a lower specific energy requirement.

[0119] 10. Conclusion from Figure 10 A comparison of the current-voltage characteristic curves shows that, according to the present invention, CCM produced by using silica and subsequent leaching achieves higher efficiency in alkaline water splitting than conventionally produced CCM. The higher efficiency is due to the porosity imparted to the layer by leaching, which in turn improves the accessibility of the catalytically active sites.

[0120] List of reference numerals 1. Base 2. Composition 3. Electrocatalysts 4. Silicon dioxide 5 solutions 6. Applied coating 7 Solvents 8 Polymers 9th floor 10 precursors 11 Potassium silicate 12 pores 13 Final Products 14 Interface Area KOH (potassium hydroxide solution) H2O water

Claims

1. A method for preparing a catalytically coated anion exchange membrane, comprising the following steps: a) Provide a substrate containing or composed of anion-conducting membrane material; b) Provide a composition comprising at least one solvent, at least one polymer dissolved in the solvent, at least one particulate electrocatalyst, and particulate inorganic material other than the electrocatalyst; c) Applying the composition to the substrate such that the substrate acquires an applied coating containing the composition; d) Remove the solvent from the applied coating, such that the substrate obtains a layer in which the particulate electrocatalyst and different particulate inorganic materials are enriched and the particulate electrocatalyst and different particulate inorganic materials are fixed on the substrate by the polymer; e) Provide an alkaline aqueous solution containing at least one alkali metal selected from sodium, potassium and lithium; f) Contact the layer with the alkaline aqueous solution; g) React at least a portion of the particulate inorganic material with the alkaline solution to obtain at least one product within the layer; h) Wash at least a portion of the product out of the layer; i) Obtaining a catalytically coated anion exchange membrane, the catalytically coated anion exchange membrane comprising the substrate and the layer applied to the substrate, wherein the layer now has openings.

2. The method according to claim 1, characterized in that, The particulate inorganic material contains silicon dioxide and / or aluminum oxide.

3. The method according to claim 1 or 2, characterized in that, The particulate inorganic material satisfies at least one of the following conditions: α) The BET surface area value of the granular inorganic material is 50m². 2 / g and 450m 2 The BET surface area is between / g, wherein the surface area is determined by nitrogen adsorption using the method of Brunauer, Emmett, Teller, DOI 10.1021 / ja01269a023; β) The particulate inorganic material includes aggregates of primary particles; γ) The particulate inorganic material is obtained by flame pyrolysis.

4. The method according to claim 1, 2 or 3, characterized in that, The solvent is selected from the following solvents: dimethyl sulfoxide (DMSO), ethanol (EtOH), and acetonitrile (ACN).

5. The method according to any one of claims 1 to 4, characterized in that, The composition also contains a dispersion medium other than the solvent.

6. The method according to claim 5, characterized in that, The dispersion medium is selected from the following dispersion media: water (H2O), N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAC), acetone (ACT), and 2-propanol (IPA).

7. The method according to any one of claims 1 to 6, characterized in that... At least some of the following steps are carried out within an electrochemical cell: f) Contact the layer with the alkaline aqueous solution; g) Reacting at least a portion of the inorganic material with the alkali metal to obtain a product within the layer; h) Wash at least a portion of the product out of the layer; i) Obtain a catalytically coated anion exchange membrane comprising the substrate and the layer applied to the substrate, wherein the layer now has openings.

8. The method according to any one of claims 1 to 6, characterized in that... At least some of the following steps are performed outside the electrochemical cell: f) Contact the layer with the alkaline aqueous solution; g) Reacting at least a portion of the inorganic material with an alkali metal to obtain a product within the layer; h) Wash at least a portion of the product out of the layer; i) Obtain a catalytically coated anion exchange membrane comprising the substrate and the layer applied to the substrate, wherein the layer now has openings.

9. The method according to any one of claims 1 to 8, characterized in that... The following steps are performed at least partially simultaneously: f) Contact the layer with the alkaline aqueous solution; g) Reacting at least a portion of the inorganic material with the alkali metal to obtain a product within the layer; h) Wash at least a portion of the product out of the layer.

10. The method according to any one of claims 1 to 9, characterized in that, The substrate is also in contact with the alkaline aqueous solution, so that the membrane material undergoes at least partial ion exchange.

11. The method according to claim 10, characterized in that, Both the layer and the substrate are in contact with the alkaline aqueous solution.

12. The method according to claim 10 or 11, characterized in that, Replace the alkaline aqueous solution.

13. A catalytically coated anion exchange membrane obtainable by the method according to any one of claims 1 to 12.

14. A catalytically coated anion exchange membrane, comprising a substrate containing or composed of anion-conducting membrane material and at least one layer applied to the substrate, wherein the layer is enriched with particulate electrocatalyst, and wherein the electrocatalyst is immobilized on the substrate by a polymer, characterized in that... The layer has openings.

15. The catalytically coated anion exchange membrane according to claim 13 or 14, characterized in that, The layer contains silicon dioxide and / or aluminum oxide, wherein the total content of silicon dioxide and aluminum oxide is between 0.2% by weight and 25% by weight, based on the total mass of the layer.

16. A precursor for a catalytically coated anion exchange membrane, comprising a substrate containing or composed of anion-conducting membrane material and at least one layer applied to the substrate, wherein particulate electrocatalyst and various particulate inorganic materials are enriched in the layer, and wherein the electrocatalyst and inorganic materials are fixed to the substrate by a polymer.

17. The precursor according to claim 16, characterized in that, The layer contains silicon dioxide and / or aluminum oxide, wherein the total content of silicon dioxide and aluminum oxide is between 10% by weight and 60% by weight, based on the total mass of the layer.

18. The article of manufacture according to any one of claims 1 to 17, characterized in that, The polymer is anionic.

19. The article of claim 18, characterized in that, The membrane material and the polymer have the same repeating units.

20. The article of manufacture according to any one of claims 1 to 19, characterized in that, The polymer and / or the membrane material have a high hydroxyl ion (OH) ion content. - It has a specific conductivity S, which is measured by hydroxide ion exchange, where S is between 5 mS / cm and 300 mS / cm or between 50 mS / cm and 150 mS / cm.

21. The article of manufacture according to any one of the preceding claims, characterized in that, The membrane material and / or the polymer are fluorine-free.

22. The article of manufacture according to any one of the preceding claims, characterized in that, The substrate is dense.

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