Catalyst inks with high solids ratio that can be used with doctor blades

Abstract

The invention relates to a catalyst ink, a method for coating a substrate with said ink, a coated substrate obtained using said method and the use thereof. The technical problem addressed by the invention is to provide a catalyst ink having a high solids content and at the same time still being readily applicable using a doctor blade. The catalyst ink should contain as little as possible any solvent known to have carcinogenic, mutagenic or reproductive toxicity. The coated substrate produced using the catalyst ink should be particularly useful in alkaline membrane water electrolysis as a catalytically active or activatable anion exchange membrane. The technical problem is solved by a solvent mixture containing an alkanol and acetonitrile. The improvement is that both the weight proportion of acetonitrile and the weight proportion of alkanol are greater than the weight proportion of binder contained in the catalyst ink.

Description

[0001] This invention relates to catalyst inks, methods for coating substrates with the inks, coated substrates obtained by the methods, and their uses.

[0002] "Catalyst ink" is a term from the field of electrochemical battery assembly manufacturing. An electrochemical battery is a device used to carry out electrochemical reactions. In an electrochemical reaction, substances are converted in the presence of electrical energy, either absorbing or releasing it. To carry out these reactions particularly efficiently, in many cases, the reaction is appropriately conducted in the presence of a so-called electrocatalyst. An electrocatalyst is a substance capable of accelerating a desired electrochemical reaction, or even enabling the reaction to occur, without being consumed in large quantities during the process. Electrocatalysts are often particulate inorganic materials, typically metals or metal oxides.

[0003] In order for electrochemical reactions to occur in the presence of an electrocatalyst, the electrocatalyst must be incorporated into the electrochemical cell. In the industrial design of electrochemical cells, this is typically achieved by providing the components of the electrochemical cell with an electrocatalytically active or activatable coating containing the electrocatalyst.

[0004] Suitable components to be coated include, in particular, membranes or electrodes, or fluid technology devices such as gas distributors. When a membrane has been provided with a catalytically active or activatable coating, this is referred to in the field as a catalyst-coated membrane (CCM). When the electrodes or other components of a battery have been coated with an electrocatalyst, this is referred to as a catalyst-coated substrate (CCS).

[0005] In this context, the term "substrate" is generally used for the object to be coated. This can typically be a component of an electrochemical cell, such as a membrane or electrode; however, the term also includes auxiliary elements not incorporated into the cell, such as transfer substrates used for indirectly coating electrodes or membranes.

[0006] The catalyst ink is a mixture of at least one particulate electrocatalyst and at least one binder in a liquid solution in a solvent. The catalyst ink is intended to be applied to a substrate to be coated. After application, the catalyst ink is dried, causing the solvent to evaporate and the binder to precipitate from the solution. The electrocatalyst and binder remain and together form a catalytically active or activatable coating on the substrate. The electrocatalyst imparts its catalytic activity to the coating, while the binder immobilizes the electrocatalyst on the substrate. The binder precipitated from the solution forms a solid matrix bonded to the substrate, within which the particulate electrocatalyst is dispersed.

[0007] The adhesive is typically a polymer. Polymers with a certain degree of ionic conductivity, known as ionomers, are widely used as adhesives. Ionomers that exhibit conductivity to anions are known, as are those that exhibit conductivity to cations.

[0008] Since ionomers do not exhibit significant electron conductivity, some catalyst inks also contain conductive additives such as carbon black.

[0009] In addition, catalyst inks may also contain processing aids such as surfactants or rheology modifiers.

[0010] Finally, the catalyst ink may also contain a liquid dispersion medium, which reduces the viscosity of the ink. The catalyst ink is diluted with the dispersion medium. Volatile substances such as water or ethanol are widely used as dispersion media, evaporating along with the solvent during the drying process.

[0011] Therefore, catalyst inks can be regarded as precursors for the catalytic activity of the substrate to be prepared or for coatings that can be activated.

[0012] The selection of electrocatalysts, binders, and any conductive additives is guided by the intended use of the coated component, more specifically by the electrochemical reaction to be performed and the location where the component is used, such as on the anode or cathode side of an electrochemical cell.

[0013] In contrast, the selection of solvents and optionally present processing aids or dispersion media is guided by the specifications of the desired coating technology: both solvents and dispersion media are removed during the drying process and therefore do not constitute part of the subsequent catalytically active or activatable coating. Thus, the selection of solvents and dispersion media gives the ink the desired processability. If this cannot be achieved solely through skillful selection of solvents and dispersion media, processing aids are required. However, since these processing aids can remain in the coating under uncertain conditions and negatively impact the efficiency of the electrochemical reaction, a good catalytic ink should ideally work without such processing aids.

[0014] This invention specifically relates to the optimal selection of solvents and optionally present dispersion media. Its primary objective is to achieve a high solids content in catalyst inks so that as much layering material as possible can be applied to the substrate per unit time during coating. Solids content describes the sum of all ink components remaining as solids on the substrate after drying, i.e., the non-volatile components of the ink. These are primarily precipitated binders and electrocatalysts. Solvents and any dispersion media are not included in the solids content because they are removed during drying. Instead, to achieve a high solids content, the proportion of volatile components such as solvents and any dispersion media must be reduced.

[0015] Another objective of this invention is to adjust the dynamic viscosity of the catalyst ink so that it can be processed quickly and with high quality. In particular, the catalyst ink should be able to be applied to the substrate by a bar coater, as bar coating is an efficient coating method that provides high coating quality and is easy to control. Unfortunately, there is a trade-off between high solids content and good bar coatability, because excessively high solids content will increase the viscosity of the catalyst ink so much that bar coating is no longer possible.

[0016] Based on these general technical specifications, the technical objectives are reinforced by combining the following existing technologies: A specific form of electrochemical reaction is alkaline membrane electrolysis (AEMWE). It uses electrical energy to produce hydrogen (H2) and oxygen (O2) from water (H2O). AEMWE is considered a technology for the sustainable production of "green" hydrogen, provided that the required electricity comes from renewable energy sources.

[0017] A review of the structure and materials of the electrochemical cells currently used in AEMWE is provided by the following literature: Miller, Hamish Andrew et al.: Green hydrogen from anion exchangemembrane water electrolysis: a review of recent developments in critical materials and operating conditions. Sustainable Energy Fuels, 2020, 4, 2114DOI: 10.1039 / c9se01240k Especially for the membranes used in the production of AEMWE, it is necessary to target anions, more precisely, hydroxide ions (OH-). - Polymers that exhibit conductivity.

[0018] Polymers exhibiting anion conductivity are known from patent applications EP3770201A1, EP4032934A1, and EP4059988A1. They are suitable for producing anion exchange membranes (AEMs). These can then be used in alkaline water electrolysis. None of the AEMs disclosed in the aforementioned documents possess catalytic activity.

[0019] In the production of AEM, the ionomers disclosed in EP3770201A1 and EP4032934A1 are dissolved in N,N-dimethylacetamide (DMAC) and / or N,N-dimethylformamide (DMF). Because DMAC and DMF are known to be carcinogenic, mutagenic, or reproductively toxic (CMR), they are classified as CMR substances under REACH regulations, requiring costly safety measures in industrial processing.

[0020] In the synthesis of the ionomer precursor described in EP4059988A1, dimethyl sulfoxide (DMSO) and acetonitrile (ACN) were used. Neither of these solvents is classified as a CMR substance. However, EP4059988A1 did not take advantage of this because DMAC was still used as a solvent in the casting process: therefore, the production of anion exchange membranes still requires handling CMR substances, which increases production costs.

[0021] The catalyst ink prepared from the ionomers disclosed in the aforementioned cited literature is also disclosed in WO2023088714A1. This catalyst ink contains DMSO as a solvent and an additional ethanol / water mixture as a dispersion medium. This ink is used to produce CCM or CCS suitable for use in AEMWE. Although the description in WO2023088714A1 indicates that the ink can be bar coated, the experimental section used an ultrasonic sprayer to apply the catalyst ink to various substrates. In fact, the experiments presented herein demonstrate that the catalyst ink disclosed in WO2023088714A1 cannot be bar coated. Furthermore, the catalyst content of this ink is calculated to be approximately 11 mg / ml, which is good for a spray-coated ink but still quite low for a bar-coated ink.

[0022] European patent application 24152389.3 by the same applicant (not yet published at the time of filing) describes a catalyst ink whose binder is prepared according to EP3770201A1. The catalyst ink also contains silica, DMSO, ethanol, and water. The specification also mentions that DMSO, ethanol, and acetonitrile can be used as solvents, i.e., used alone or mixed with each other. No mixing ratio is specified. Furthermore, experiments presented herein show that neither ethanol alone nor acetonitrile alone can dissolve the polymer disclosed in EP3770201A1.

[0023] Koch et al. developed an alternative rod-coated catalyst ink for coating anion exchange membranes: Koch, S., Metzler, L., Kilian, SK, Heizmann, PA, Lombeck, F., Breitwieser, M., Vierrath, S., Toward Scalable Production: Catalyst-CoatedMembranes (CCMs) for Anion-Exchange Membrane water Electrolysis via DirectBar Coating. Adv. Sustainable Syst. 2023, 7, 2200332. DOI: 10.1002 / adsu.202200332 Unfortunately, this ink also contains a CMR substance as a solvent, namely methanol. Industrial production in regions where REACH regulations are in effect also comes with high costs in this regard.

[0024] In this context, the technical objective is to specify a catalyst ink that has a high solids content while still being satisfactorily suitable for bar coating. The catalyst ink should, as far as possible, be free of any solvents known to be carcinogenic, mutagenic, or reproductively toxic. The coated substrate produced using the catalyst ink is particularly intended for use as a catalytically active or activatable anion exchange membrane in alkaline membrane water electrolysis.

[0025] This objective is achieved by the catalyst ink according to claim 1.

[0026] Therefore, the present invention provides a catalyst ink having the following characteristics: a) The catalyst ink comprises a solid electrocatalyst in particulate form; b) The catalyst ink comprises a liquid solvent mixture containing at least acetonitrile and at least one alkanol; c) The catalyst ink comprises a binder dissolved in the solvent mixture, the binder being an anion-conducting polymer containing at least one structure corresponding to one of the following formulas (I), (II), and (III): (I) In (I), X is a structural element containing a positively charged nitrogen atom bonded to C1 and C2, and bonded to one or two hydrocarbon groups via two bonds, the hydrocarbon groups comprising 1 to 12, preferably 1 to 6, particularly preferably 1 or 5 carbon atoms. Furthermore, in (I), Z is a structural unit containing carbon atoms bonded to C3 and C4, and containing 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 bonded to C1 and C2, and bonded to one or two hydrocarbon groups via two bonds, the hydrocarbon groups comprising 1 to 12, preferably 1 to 6, particularly preferably 1 or 5 carbon atoms. Furthermore, in (II), Z is a structural unit containing carbon atoms bonded to C3 and C4, and containing at least one 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 substituted with methyl, isopropyl or tert-butyl, preferably substituted with methyl. (III) In (III), X is a ketone or sulfone group; in (III), Z is a structural unit comprising at least one tertiary carbon atom and at least one aromatic six-membered ring, wherein the aromatic six-membered ring is directly connected to one of two oxygen atoms; and in (III), Y is a structural unit comprising at least one positively charged nitrogen atom connected to the structural unit Z. The improvement in the catalyst ink is that the weight proportions of acetonitrile and alkanol are both greater than the weight proportion of the binder. These weight proportions are based on the total weight of the catalyst ink in each case.

[0027] This invention is based on the surprising discovery that the binders of formula (I), (II), or (III) of interest can be dissolved in a combination of alkanol (ROH) and acetonitrile (ACN). This discovery is therefore surprising because, until now, CMR substances such as DMAC or DMF have been described as suitable solvents for these ionomers. Furthermore, these ionomers are not soluble in pure ethanol or pure acetonitrile: only mixtures of acetonitrile and alkanol can dissolve the relevant binders. To obtain an ink that is easy to process, the ratio of alkanol to acetonitrile must each be greater than the ratio of the binder. This also refers to the weight ratio based on the total weight of the ink.

[0028] Another unexpected effect is that using a solvent mixture of ACN and ROH can significantly increase the solids content of the ink.

[0029] Fortunately, all of this involves using potentially CMR-free solvent cocktails, which have lower safety requirements for production than, for example, processing DMAC-based inks.

[0030] In this context, "potentially CMR-free" means that inks according to the invention can be formulated without solvents known to be carcinogenic, mutagenic, or reproductively toxic. However, alkanols that are subject to corresponding suspicion, such as methanol, may still be used in the formulation. In some cases, it may be advantageous for the processability of the ink to use CMR-related alkanols as solvents, thereby allowing for higher safety precautions during coating. If this is not desired, the formulations of the present invention also permit the use of alkanols that are not classified as CMR substances, such as 2-propanol.

[0031] In solvent mixtures, ACN and ROH can exist in different proportions. It is important that both substances are present, and that their respective weight proportions are greater than the weight proportion of the binder. For example, the weight ratio of acetonitrile to alkanol can range from 1:10 to 17:1.

[0032] By adding dimethyl sulfoxide (DMSO) as a solvent to the ink, it is possible to formulate inks with exceptionally good stick coating properties and exceptionally high solids content. DMSO is not related to CMR.

[0033] If the viscosity of the catalyst ink is too high, it can be diluted with a dispersion medium. Unlike solvent mixtures, dispersion media do not dissolve binders. However, particulate electrocatalysts can be dispersed in a dispersion medium. The simplest method is to use water as the dispersion medium because it is volatile and inexpensive. Furthermore, it is not a CMR substance. Therefore, in a particular embodiment of the invention, the catalyst ink additionally contains water. The weight proportion of water can be greater than any other weight proportion of the other components of the catalyst ink. Nevertheless, the catalyst ink should not contain significantly more water than other components.

[0034] A specific recommended formulation of an advantageous catalyst ink with high solids content is listed in Table 1.

[0035] Table 1: Advantageous formulations of catalyst inks according to the present invention

[0036] It goes without saying that the total weight percentage of all components listed in Table 1 does not exceed 100% by weight. However, the total may not reach 100% by weight, i.e., when the catalyst ink contains other components not listed in Table 1. Advantageously, the catalyst ink consists only of the components listed in Table 1. In this case, the total weight percentage of all components listed in Table 1 is exactly 100% by weight.

[0037] As an alkanol ROH, in principle any alkanol can be used. Examples include: methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, and 2-propanol. Secondary or tertiary alkanols, such as propane-1,2-diol, can also be used. Alkanols derived from cycloalkanes, such as cyclohexanol, can also be used. Ethanol (EtOH) is preferred as an alkanol because it is not classified as a CMR substance. 1-Propanol or 2-propanol can also be used, as they are not CMR-related. This also applies to propane-1,2-diol. Of course, mixtures of these alkanols can also be used. When using a mixture of two or more alkanols, the minimum and maximum proportions refer to the weight percentages of the mixture, i.e., the sum of the weight percentages of all alkanols.

[0038] Preferably, the catalyst ink is formulated such that the binder is completely dissolved in the solvent mixture. This is because if the binder partially precipitates from the solvent mixture, the ink will clump and become unprocessable. Preferably, the ink contains no other binder besides the necessary binder containing the structure of formula (I), (II), or (III).

[0039] To avoid introducing any interfering substances into the catalyst layer that could impair electrolysis, the catalyst ink should, as far as possible, consist only of the components explicitly mentioned above. However, in some cases, it may still be necessary to add other components to the catalyst ink besides those listed above. These can be organic or inorganic additives, such as dispersants, rheology modifiers, surfactants, or conductive additives. Specific examples of other components are silica or carbon black. Carbon black is a conductive additive, while silica is suitable as a rheology modifier.

[0040] The characteristic value of the dynamic viscosity η of the catalyst ink should be within 10. 1 mPas and 10 4 The dynamic viscosity η was measured at 25°C using a rotational rheometer with a plate-plate geometry. The plate diameter was 40 mm, and the gap between the plates was 1 mm. The dynamic viscosity was measured at 0.1 s⁻¹. -1 up to 1000s -1 Measurements were taken at increasing shear rates, using 1 s. -1The dynamic viscosity is used as an characteristic value. Suitable rotational rheometers with plate-plate geometry are available, for example, from Malvern Kinexus.

[0041] The catalyst ink according to the present invention has been developed for producing substrates for catalyst coating. A corresponding coating method using the ink according to the present invention includes at least the following steps: i) Provide substrate; ii) Provide a catalyst ink according to the invention; iii) Apply the catalyst ink to the substrate; iv) Dry the catalyst ink applied to the substrate.

[0042] Therefore, the present invention also provides a production method.

[0043] A notable characteristic of the ink is its excellent bar coating properties. Therefore, it is preferable to apply the catalyst ink to the substrate by bar coating.

[0044] Anion-conducting membranes are preferably used as the substrate. Catalytically active or activatable AEMs are produced by coating with catalyst ink.

[0045] Particularly preferably, the substrate used is an AEM containing at least one structure according to formula (I), (II), or (III). This means that the membrane and the adhesive are essentially composed of the same ionomer. This results in particularly good adhesion between the catalyst layer and the membrane.

[0046] The advantages of the catalyst ink according to the invention not only affect production costs but also result in better products: experiments show that the ink according to the invention leads to better efficiency in substrates coated with it, which is likely attributable to better coating quality. Therefore, the invention also provides a catalyst-coated substrate, which can be obtained using the ink according to the invention via the coating method according to the invention.

[0047] Since the advantages of the substrate according to the invention are particularly evident in AEMWE, namely the increased efficiency, the invention also provides the use of the catalyst-coated substrate according to the invention in alkaline water electrolysis. This use is achieved by performing alkaline water electrolysis in the presence of the catalyst-coated substrate. The electrocatalyst present in the catalyst layer catalyzes the electrochemical reaction. The catalyst layer can also serve as an electrode. If AEM is used as the substrate, it acts as a membrane for AEMWE and absorbs hydroxide ions (OH-). - It is transported from the cathode chamber to the anode chamber of the electrochemical cell.

[0048] Based on the current state of research, the following elements can be used in the catalyst ink according to the present invention, either in pure form or as oxides, hydroxides, hydroxyoxides, or phosphides: 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), rhodium (Rh), and cerium (Ce). Therefore, these elements, individually or in combination, can be used as electrocatalysts in pure form or as oxides, hydroxides, or hydroxyoxides. The electrocatalyst is incorporated into the ink in particulate form, i.e., as powder or granules.

[0049] Very particularly preferred is the formulation of a catalyst ink containing platinum or platinum alloy (Pt / C) or nickel-iron (oxide) hydroxide (NiFe) supported on carbon as an electrocatalyst. a O b H c ) or nickel-iron phosphate (NiFe a P b The subscripts a, b, and c are real numbers in the range 0 to 8. The subscripts a, b, and c can be the same or different. The nickel-iron ratio in nickel-iron (oxide) hydroxides is ideally in the range of 2:1 to 10:1.

[0050] Example The following section first examines the dissolution behavior of the ionomer of interest. Then, nine different catalyst inks are prepared from this ionomer, differing in the solvents used. These nine inks are then used to prepare catalyst layers on anion exchange membranes. Finally, the performance of the catalyst-coated AEMs in water electrolysis is compared. This experimentally supports the effects achieved by the present invention.

[0051] 1. Preparation of ionomers (not part of this invention) An anion-conducting cationic polymer was synthesized according to Example 3 of EP3770201A1. The polymer was initially provided as a solution and processed into a powder by drying. Subsequently, to minimize residual solvent content, the dried polymer was further dried in a vacuum drying oven at 80°C for 48 hours.

[0052] 2. Experiments on the solubility of the ionomer in ethanol, 1-propanol, and 2-propanol Three containers were prepared for this purpose: the first contained 27g of ethanol, the second contained 27g of 1-propanol, and the third contained 27g of 2-propanol. 3g of the cationic polymer synthesized in Example 1 was added to each of these containers, and the containers were sealed and shaken at 60°C for 4 hours. The result in each case was a slightly swollen, softened polymer mass at the bottom of the container, which did not dissolve significantly.

[0053] 2 之二 Regarding the solubility of the ionomer in propane-1,2-diol, 1-butanol, cyclohexanol, 1-heptanol, and 1-octanol. experiment Five containers were prepared for this purpose: the first contained 9g of propane-1,2-diol, the second contained 9g of 1-butanol, the third contained 9g of cyclohexanol, the fourth contained 9g of 1-heptanol, and the fifth contained 9g of 1-octanol. 1g of the cationic polymer synthesized in Example 1 was added to each of these containers, and the containers were sealed and shaken at 60°C for 4 hours. The result was that in each case, there were some slightly swollen polymer clumps at the bottom of the container, which did not dissolve significantly.

[0054] 3. Experiment on the solubility of ionomers in acetonitrile Therefore, 3g of the cationic polymer synthesized in Example 1 was added to a container containing 27g of acetonitrile and shaken at 60°C for 4 hours. No significant polymer dissolution was observed in this case.

[0055] 4. Experiments on the solubility of ionomers in mixtures of ethanol, 1-propanol, or 2-propanol with acetonitrile. Three containers were prepared for this purpose: the first contained 13.5 g of ethanol and 13.5 g of acetonitrile; the second contained 13.5 g of 1-propanol and 13.5 g of acetonitrile; and the third contained 13.5 g of 2-propanol and 13.5 g of acetonitrile. 3 g of the cationic polymer synthesized in Example 1 was added to each of these containers, and the mixture was shaken at 60°C for 4 hours. The result was an almost transparent solution. The polymer had dissolved in all three containers.

[0056] 4 之二 Regarding the grouping of ionomers in propane-1,2-diol, 1-butanol, cyclohexanol, 1-heptanol, and 1-octanol with acetonitrile. Experiment on solubility in a mixture Five containers were prepared for this purpose: the first contained 4.5 g of propane-1,2-diol, the second 4.5 g of 1-butanol, the third 4.5 g of cyclohexanol, the fourth 4.5 g of 1-heptanol, and the fifth 4.5 g of 1-octanol. 4.5 g of acetonitrile and 1 g of the cationic polymer synthesized in Example 1 were added to each of these containers, and the containers were sealed and shaken at 60°C for 4 hours. The result was an almost transparent solution with a pale yellow tint. The polymer dissolved in all three containers.

[0057] 5. Interim findings The ionomers studied are soluble in solvent mixtures of ethanol and acetonitrile, but not in ethanol or acetonitrile alone. This also applies to mixtures of 1-propanol and acetonitrile, as well as mixtures of 2-propanol and acetonitrile. This also applies similarly to all other combinations of alkanols and acetonitrile tested here.

[0058] 6. Preparation of anion exchange membranes (not part of this invention) Anion-conducting membranes were prepared using the cationic polymer synthesized in Example 1, as described in Example 4 of EP3770201A1. For this purpose, a polymer solution before drying was used.

[0059] 7. Preparation of conventional catalyst inks (not part of this invention) Catalyst-containing dispersions were prepared using the cationic polymer synthesized in Example 1, as described in Example 12 of WO2023088714A1.

[0060] The ionomer was first dissolved in dimethyl sulfoxide for 16 hours under stirring and heating (60°C). Subsequently, the carbon-supported platinum (Pt / C, ~50 wt%) catalyst was dispersed in a dispersion medium consisting of equal volumes of water and ethanol, and sonicated in an ice bath at 30 W (BRANSONIC™ B-1200 E2, from Branson Ultrasonics Corporation, Brookfield, CT, US) for 30 minutes. After adding the ionomer solution (50 mg / ml in DMSO), it was further dispersed in an ice bath at 30 W for 1 minute, followed by dispersion at 2500 rpm for 10 seconds using an oscillator (MS1 Minishaker, from IKA, Staufen, DE). The proportions were selected according to Table 1, Example 12 of WO2023088714A1. Therefore, the catalyst content was set at 11 mg / ml, with three parts by mass of Pt / C catalyst particles and one part by mass of ionomer solids. This produced a low-viscosity catalyst ink.

[0061] 8. Preparation of catalyst ink with increased solids content (not part of this invention) Since the catalyst ink prepared in Example 7 has a relatively low catalyst content of only 11 mg / ml, and its viscosity does not appear to be optimal for bar coating, the goal is to maximize the solids content while maintaining the solvent ratio and the ionomer to catalyst ratio. If the intention is to keep the mass ratio of ethanol:water:DMSO = 0.405:0.512:0.083 and the catalyst:ionomer ratio = 3:1 constant, the ionomer solution is a limiting factor, as a 20% by weight ionomer content in DMSO can no longer be easily dispersed. Therefore, an ink with a catalyst solids content of 5.73% by weight was prepared according to the same procedure as described in Example 7. The carbon-supported platinum (Pt / C, ~50% by weight) catalyst was dispersed in a dispersion medium consisting of equal volumes of water and ethanol and ultrasonicated in an ice bath at 30 W (BRANSONIC™ B-1200 E2, from BransonUltrasonics Corporation, Brookfield, CT, US) for 30 minutes. After adding the ionomer solution (20 wt% in DMSO), the mixture was further dispersed for 1 minute in an ice bath using ultrasound at 30 W, followed by dispersion for 10 seconds at 2500 rpm using a shaker (MS1 Minishaker, from IKA, Staufen, DE). This produced a catalyst ink with increased viscosity compared to the catalyst ink prepared in Example 7.

[0062] 8 之二 Provision of catalyst ink according to the present invention based on EtOH-ACN As a composition of the present invention, 13.85 g of catalyst-containing ink was prepared. For this purpose, under oxygen-free conditions, 3 g of Pt / C (Pt ~ 50 wt%) was first weighed into a shatterproof container (100 ml volume), followed by the addition of 8.5 g of acetonitrile and shaking. 2.35 g of an ionomer solution, consisting of 15 wt% ionomer solids from Example 1, 42.5 wt% ethanol, and 42.5 wt% acetonitrile, was added to the catalyst-containing composition. The mixture was dispersed in a stirred mixer (Lau, Germany) using grinding balls (total 30 g, 3 mm diameter) for 2 hours, followed by 120 minutes. The solids content of the catalyst ink was correspondingly 24.2 wt%.

[0063] 8 之三 Provision of catalyst ink based on EtOH-ACN-H2O according to the present invention As another composition of the present invention, 14.32 g of catalyst-containing ink was prepared. For this purpose, under oxygen-free conditions, 3 g of Pt / C (Pt ~ 50 wt%) and 6 g of ultrapure water were first weighed into a shatterproof container (100 ml volume), followed by the addition of 0.5 g of acetonitrile and 0.5 g of ethanol and shaking. 4.32 g of an ionomer solution, consisting of 10 wt% ionomer solids from Example 1, 45 wt% ethanol, and 45 wt% acetonitrile, was added to the catalyst-containing composition. The mixture was dispersed in a stirred mixer (Lau, Germany) for 120 minutes using grinding balls (total 30 g, 3 mm diameter). The solids content of the catalyst ink was correspondingly 24.0 wt%.

[0064] 9. Provision of catalyst ink according to the present invention based on H2O-DMSO-EtOH-ACN As another composition of the present invention, 14.6 g of catalyst-containing ink was prepared. For this purpose, under oxygen-free conditions, 3 g of Pt / C (Pt ~ 50 wt%) was first weighed into a shatterproof container (100 ml volume), followed by the addition of 6 g of ultrapure water and 2 g of DMSO and shaking. 3.6 g of an ionomer solution, consisting of 12 wt% ionomer solids from Example 1, 20 wt% ethanol, 20 wt% acetonitrile, and 48 wt% DMSO, was added to the catalyst-containing composition. The mixture was dispersed in a stirred mixer (Lau, Germany) for 120 minutes using grinding balls (total 30 g, 3 mm diameter). The solids content of the catalyst ink was correspondingly 23.5 wt%.

[0065] 9 之二 Provision of catalyst ink according to the present invention based on EtOH-ACN-H2O-C As another composition of the present invention, 15.1 g of catalyst-containing ink was prepared. For this purpose, under oxygen-free conditions, 3 g of Pt / C (Pt ~ 50 wt%) and 0.1 g of carbon black (Ketjenblack® 600JD) were first weighed into a shatterproof container (100 ml volume), followed by the addition of 6.4 g of ultrapure water and 2 g of DMSO and shaking. 3.6 g of an ionomer solution, consisting of 12 wt% ionomer solids from Example 1, 20 wt% ethanol, 20 wt% acetonitrile, and 48 wt% DMSO, was added to the catalyst-containing composition. The mixture was dispersed in a stirred mixer (Lau, Germany) for 120 minutes using grinding balls (total 30 g, 3 mm diameter). The solids content of the catalyst ink (ionomer dry weight, electrocatalyst + carbon black) was correspondingly 23.4 wt%.

[0066] 9 之三 Provision of catalyst ink according to the present invention based on EtOH-ACN-H2O-SiO2 As another composition of the present invention, 15.1 g of catalyst-containing ink was prepared. For this purpose, under oxygen-free conditions, 3 g of Pt / C (Pt ~ 50 wt%) was first weighed into a shatterproof container (100 ml volume), followed by the addition of 6 g of silica dispersion (5% in H₂O), 0.5 g of water, and 2 g of DMSO, and the mixture was shaken. 3.6 g of an ionomer solution, consisting of 12 wt% ionomer solids from Example 1, 20 wt% ethanol, 20 wt% acetonitrile, and 48 wt% DMSO, was added to the catalyst-containing composition. The mixture was dispersed in a stirred mixer (Lau, Germany) for 120 minutes using grinding balls (total 30 g, 3 mm diameter). The solid content of the catalyst ink (ionomer dry mass, electrocatalyst + silica) was correspondingly 24.7 wt%.

[0067] 9 之四 Provision of catalyst ink according to the present invention based on H2O-DMSO-EtOH-ACN As another example of the composition of the present invention, 10.2 g of catalyst-containing ink was prepared. For this purpose, under oxygen-free conditions, 1 g of Pt / C (Pt ~ 50 wt%) was first weighed into a shatterproof container (100 ml volume), followed by the addition of 6 g of ultrapure water and 2 g of DMSO and shaking. 1.2 g of an ionomer solution, consisting of 12 wt% ionomer solids from Example 1, 20 wt% ethanol, 20 wt% acetonitrile, and 48 wt% DMSO, was added to the catalyst-containing composition. The mixture was dispersed in a stirred mixer (Lau, Germany) for 120 minutes using grinding balls (total 30 g, 3 mm diameter). The solids content of the catalyst ink was correspondingly 11.2 wt%.

[0068] 9 之五 Provision of catalyst ink based on 2-propanol-ACN according to the present invention As a composition of the present invention, 14.85 g of catalyst-containing ink was prepared. For this purpose, under oxygen-free conditions, 3 g of Pt / C (Pt ~ 50 wt%) was first weighed into a shatterproof container (100 ml volume), followed by the addition of 1.0 g of acetonitrile and 8.5 g of 2-propanol and shaken. 2.35 g of an ionomer solution, consisting of 10 wt% ionomer solids from Example 1, 45 wt% 2-propanol, and 45 wt% acetonitrile, was added to the catalyst-containing composition. The mixture was dispersed in a stirred mixer (Lau, Germany) using grinding balls (total 30 g, 3 mm diameter) for 2 hours, followed by 120 minutes. The solids content of the catalyst ink was correspondingly 21.78 wt%.

[0069] 10. Apply conventional ink to the film using a bar coater (not part of this invention). For a comparative experiment using the formulation WO2023088714 (Example 12), the catalyst ink provided in Example 7 was applied to the anion-conducting membrane prepared in Example 6 using an automated bar coater (Elcometer 4340, feed rate 5 mm / s, spiral coating bar, 60 µm). The coated AEM was then dried in a laboratory oven at 80 °C for 10 minutes. The result, referred to as membrane A, is visible in... Figure 1 .

[0070] Figure 1 Photograph of film A coated with conventional ink. like Figure 1 As can be seen, the membrane underwent intense curling during the coating process. This resulted in uneven coating. However, the catalyst-coated AEM obtained in this manner is, in principle, suitable for water electrolysis.

[0071] 11. Apply an ink with increased solids content (not according to the invention) to the film using a bar coater. (Part of the invention) For the second comparative experiment, the composition provided in Example 8 was applied to the membrane prepared in Example 6 using an automated bar coater (Elcometer 4340, feed rate 5 mm / s, spiral coating bar, 60 µm). The coated membrane was then dried in a laboratory oven at 80 °C for 10 minutes. The result, referred to as membrane B, is visible in... Figure 2 .

[0072] Figure 2 Photograph of film B coated with ink not according to the present invention. like Figure 2 It is evident that the film underwent slight curling during the coating process. The coating exhibits many locations with relatively thin layers, which... Figure 2 White spots are visible in the image. In principle, the obtained coating is suitable as an electrode for water electrolysis, but it is not optimal.

[0073] 12. Coating a film with the catalyst ink according to the invention (part of the invention) For the coatings of the present invention using the formulation containing ACN / ROH, Example 8 was applied using an automated bar coater (Elcometer 4340, feed rate 5 mm / s, spiral coating bar, 60 µm). 之二 Up to 9 之五 The inks provided were each applied to the film prepared according to Example 6. The coated films were then dried in a laboratory oven at 80°C for 10 minutes. For use with Example 8... 之二 The formulation was coated with a film, and a second bar coating was performed at the same location using the same parameters. The results are referred to as films C to I, and can be observed in... Figures 3 to 8 .

[0074] Figure 3 In Example 8之二 Photograph of the coated film C Figure 4 In Example 8 之三 Photograph of the coated film D Figure 5 Photograph of film E coated in Example 9 Figure 6 In Example 9 之二 Photograph of the coated film F Figure 7 In Example 9 之三 Photograph of the coated film G Figure 8 In Example 9 之四 Photograph of the coated film H Figure 9 Example 9 之五 Photograph of the coated film I In the coating, the membrane is only slightly bent, resulting in a relatively uniform coating that is suitable as an electrode for water electrolysis.

[0075] 13. Test the catalyst-coated membrane in an electrolysis test cell. The performance of catalyst-coated membranes in alkaline water electrolysis (AEMWE) was compared.

[0076] The films coated with the catalysts from Examples 10, 11, and 12 had an active area of ​​25 cm². 2 The tests were conducted in an electrolytic cell. A catalyst layer was used as the cathode catalyst. Dimensionally stable porous stainless steel electrodes were used on each anode side. 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. Characteristic current-voltage characteristic curves are shown below. Figure 10 Table 2 shows the legend.

[0077] Figure 10 The current-voltage characteristic curve of the tested CCM Table 2: Figure 10 Legend

[0078] The graph plots the required voltage against an externally applied current density. At a constant current density (e.g., 1000 mA / cm²),... 2 At this voltage level, lower voltage is preferred because, at the same production rate, less electrical energy is required to produce the same amount of hydrogen, thus increasing efficiency. For industrial applications, voltages exceeding 500 mA / cm² are particularly relevant. 2The current density is [not specified]. It can be seen that, in the case of the CCM prepared using the catalyst ink of the present invention, the current-voltage characteristic curve at a higher current density is lower than that of the CCM prepared for comparison. The lower current density results in lower power consumption at the same voltage, and therefore the CCM prepared using the ink according to the present invention has a lower specific energy requirement.

[0079] 14. Conclusion from Figure 10 A comparison of the current-voltage characteristic curves shows that the CCM prepared with the catalyst ink according to the present invention achieves higher efficiency in alkaline water splitting than the two CCMs based on different solvent mixtures. This higher efficiency can be explained by the fact that the coating is more uniform and a slightly thicker catalyst layer can be applied due to the increased viscosity.

[0080] It has thus been demonstrated that, thanks to the solvent mixture selected according to the invention, better results can be obtained than might be achieved simply by increasing the solids content of conventional catalyst inks.

Claims

1. Catalyst ink, which contains the following components: a) Solid electrocatalysts in particulate form; b) A liquid solvent mixture containing at least acetonitrile and at least one alkanol; c) An adhesive dissolved in the solvent mixture, the adhesive being an anionic polymer containing at least one structure corresponding to one of the following formulas (I), (II), and (III): (I) in, In (I), X is a structural unit containing a positively charged nitrogen atom, which is related to C. 1 and C 2 The hydrocarbon group is bonded to one or two hydrocarbon groups by two bonds, the hydrocarbon groups comprising 1 to 12, preferably 1 to 6, particularly preferably 1 or 5 carbon atoms. Furthermore, in (I), Z is a structural unit that contains elements related to C. 3 and C 4 The bonded carbon atom, and comprising 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 The hydrocarbon group is bonded to one or two hydrocarbon groups by two bonds, the hydrocarbon groups comprising 1 to 12, preferably 1 to 6, particularly preferably 1 or 5 carbon atoms. Furthermore, in (II), Z is a structural unit that contains elements related to C. 3 and C 4 The carbon atoms are bonded together, and the aromatic six-membered ring is included in the form of at least one 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 or sulfone group; in (III), Z is a structural unit comprising at least one tertiary carbon atom and at least one aromatic six-membered ring, wherein the aromatic six-membered ring is directly connected to one of two oxygen atoms; and in (III), Y is a structural unit comprising at least one positively charged nitrogen atom connected to the structural unit Z. Its features are, The acetonitrile has a greater weight proportion than the adhesive. Furthermore, the weight proportion of the alkanol is greater than the weight proportion of the adhesive. The weight ratios mentioned therein are based on the total weight of the catalyst ink in each case.

2. The catalyst ink according to claim 1, wherein the weight ratio of acetonitrile to alkanol is between 1:10 and 17:

1.

3. The catalyst ink according to claim 1 or 2, characterized in that, The catalyst ink also contains water.

4. The catalyst ink according to claim 1, 2, or 3, characterized in that, The catalyst ink also contains dimethyl sulfoxide.

5. The catalyst ink according to any one of claims 1 to 4, characterized in that, In each case, based on the total weight of the catalyst ink, the weight percentage of the components is within the following range, provided that the sum of the weight percentages of all components listed herein does not exceed 100% by weight:

6. The catalyst ink according to any one of claims 1 to 5, characterized in that, The alkanol is ethanol, 2-propanol, 1-propanol, or a mixture thereof.

7. The catalyst ink according to any one of claims 1 to 5, characterized in that, The alkanol is propane-1,2-diol or 1-butanol or cyclohexanol or 1-heptanol or 1-octanol or a mixture thereof.

8. The catalyst ink according to any one of claims 1 to 7, characterized in that, The adhesive is completely dissolved in the solvent mixture.

9. The catalyst ink according to any one of claims 1 to 8, further comprising at least one other component different from the aforementioned components.

10. The catalyst ink according to claim 9, characterized in that, The other components are dispersants, rheology modifiers, surfactants, or conductive additives.

11. The catalyst ink according to any one of claims 1 to 10, having a dynamic viscosity η, the characteristic value of which is determined according to the method defined in the specification, characterized in that, The characteristic value of the dynamic viscosity η is between 10 mPas and 10 4 Between mPas.

12. The catalyst ink according to any one of claims 1 to 11, characterized in that, The electrocatalyst contains at least one element selected from the group consisting of 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), rhodium (Rh), and cerium (Ce), wherein the element exists in its pure form or as an oxide, as a hydroxide, as a hydroxyoxide, or as a phosphide.

13. A method for producing a catalyst-coated substrate, comprising at least the following steps: i) Provide substrate; ii) Provide a catalyst ink according to any one of claims 1 to 12; iii) Apply the catalyst ink to the substrate; iv) Dry the catalyst ink applied to the substrate.

14. The method according to claim 13, characterized in that, The catalyst ink is applied to the substrate by bar coating.

15. The method according to claim 13 or 14, characterized in that, The substrate is an anion-conducting membrane.

16. The method according to claim 15, characterized in that, The anion-conducting membrane contains at least one structure corresponding to one of formulas (I), (II), and (III) as defined in claim 1.

17. A catalyst-coated substrate, which can be obtained by the method according to any one of claims 13 to 16.

18. Use of the catalyst-coated substrate according to claim 17 in electrochemical water splitting in an alkaline medium.

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