Membrane-electrode assembly, water electrolysis cell, method for producing a platinum-containing component, and catalytic composition

Abstract

The invention relates to a membrane-electrode assembly (1) which comprises a cathode (2), an anode (3), and a proton-conductive membrane (4) arranged between the cathode (2) and the anode (3), wherein the anode (3) comprises a catalytic composition (5), wherein the catalytic composition (5) comprises an oxygen evolution catalyst (6) and a platinum-containing component (7), and wherein the platinum-containing component (7) comprises a ceramic material (8) having a platinum coating (9).

Description

[0001] HOEFER & PARTNER

[0002] GNT260304PCT 03 / 25 / 2026 Applicant:

[0003] Greenerity GmbH

[0004] Industrial Area South E11

[0005] 63755 Alzenau

[0006] Membrane electrode arrangement, water electrolysis cell, method for producing a platinum-containing component and a catalytic composition

[0007] Description

[0008] The invention relates to a highly efficient membrane electrode arrangement with very good long-term stability and to a water electrolysis cell which, due to the use of the membrane electrode arrangement, is also characterized by very good performance combined with high long-term stability. Furthermore, the present invention also relates to a method for producing a platinum-containing component and a method for producing a catalytic composition.

[0009] To improve the efficiency of membrane electrode assemblies (MEAs), there is a general tendency to reduce the catalyst content in the electrodes. However, very low catalyst concentrations, for example in the anode of an MEA, result in a reduced anode layer thickness due to the low catalyst loading. This, in turn, negatively impacts the efficiency of the MEA, as the reactants flowing through the anode in the layer thickness direction have fewer opportunities for catalytic reaction, and the transverse electrical conductivity in the layer suffers. The reduced layer thickness also negatively affects the long-term stability of the electrodes.

[0010] CN 2023 10668243 A aims to provide an anode catalyst layer that forms a uniform film and delivers high performance even with low iridium loading. To achieve this, the anode catalyst layer incorporates an iridium-based catalyst and conductive particles containing, for example, iridium black, silver, gold, or nickel. A disadvantage of this prior art is that the performance of the MEA is still too low for standard applications.

[0011] EP 3748039 A1 also addresses the provision of a polymer membrane-based electrolysis cell that exhibits high performance despite a lower catalyst loading and is further characterized by high stability and low manufacturing costs. EP 3748039 A1 solves this problem through a specific layer arrangement, in which, in addition to an anode and a cathode, transport layers near the anode and near the cathode are provided, and an intermediate layer comprising electrically conductive nanofibers is provided between a transport layer and the anode or the cathode. Furthermore, at least one of the catalytically active layers comprises a mixture of catalytically active nanoparticles and electrically conductive nanofibers. Alternatively, one of the transport layers can also comprise electrically conductive nanofibers.A disadvantage of this state of the art is that a multilayer structure must be produced, which entails additional production effort, also in terms of cost. If only the performance of a single catalytically active layer with catalytically active nanoparticles and electrically conductive nanofibers is achieved, the layer thickness is too thin and does not achieve sufficient long-term stability, while performance is rather mediocre.

[0012] Based on this prior art, the object of the present invention is to provide a MEA that, at low catalyst loading, is characterized by very good performance, i.e., low cell voltage, and also by very good long-term stability. Furthermore, it is an object of the present invention to provide a water electrolysis cell that, due to the use of the MEA according to the invention, also exhibits very good performance and high long-term stability. Finally, it is an object of the present invention to provide a method for producing a platinum-containing component that serves as a catalyst and is characterized by high long-term stability.Another object of the present invention is to provide a method for producing a catalytic composition which is also characterized by very good long-term stability, low loading with catalytically active substances and very good distribution of the catalytically active substances.

[0013] These problems are solved by the features of the independent claims. The dependent claims contain advantageous further developments and embodiments of the invention.

[0014] Accordingly, the problem is solved by a MEA comprising a cathode, an anode, and a proton-conducting membrane situated between these electrodes, the anode being specifically designed as detailed below. The MEA is not limited in its specific design but is particularly suitable for water electrolysis and is preferably used for this purpose.

[0015] The anode comprises a catalytic composition which, when the MEA is used in an electrolysis cell, catalyzes the reaction of water to oxygen and protons. According to the present invention, this catalytic composition comprises an oxygen evolution catalyst (hereinafter referred to as OER). OERs are known in the art and typically comprise at least one noble metal. The catalytic activity of the MEA is controlled by the OER. Since the cost of an OER is relatively high, it is preferred that the OER content in the anode be as low as possible.

[0016] In addition, the anode contains an electrically conductive platinum-containing component. This electrically conductive platinum-containing component is characterized by the fact that it comprises a ceramic material as a substrate, and platinum, in the form of a platinum coating, coats the ceramic material.

[0017] The ceramic material is essentially unrestricted in shape and composition. However, the ceramic material is not present as a continuous layer, but rather as particles and aggregates of these particles. The shape of the particles is also unrestricted, and in addition to round shapes, branched and fibrous shapes are possible. It has been found that adding the ceramic material increases the anode layer thickness without compromising performance. Furthermore, adding the ceramic material does not increase the cell voltage during operation of the MEA according to the invention, thus maintaining particularly high catalytic activity. It is especially advantageous for increasing the layer thickness that the ceramic material is present in the anode in particulate form and not as a layer.Due to the poorly oriented arrangement of the ceramic particles, which often differ in shape and aggregation, the layer thickness of the anode can be significantly increased with a smaller amount of ceramic material, resulting in particularly good long-term stability.

[0018] The ceramic material therefore offers significant advantages in terms of the long-term stability of the anode, and consequently also of the MEA and the resulting water electrolysis cell. Naturally, two or more ceramic materials can also be used in combination.

[0019] Where quantities of ceramic material are specified below, these apply to the total quantity of all ceramic materials used in the anode when two or more ceramic materials are used. A platinum content in the catalytic composition is essential to generate sufficient electrical conductivity in the anode so that the catalytic reactions can proceed unimpeded, which is beneficial to the efficiency of the MEA. Instead of simply adding the platinum to the catalytic composition as an admixture, according to the invention, the platinum is present in the form of a platinum coating that coats the ceramic material. The ceramic material and the platinum coating together constitute the platinum-containing component. This has the advantage that the platinum is locally fixed, so that it is not carried out of the anode and therefore no longer available for catalysis.This improves electrical conductivity and, secondly, has the advantage of allowing better control of the platinum distribution in the anode. The costs for the MEA according to the invention can also be reduced as a result.

[0020] In the platinum-containing component, the platinum coating can consist of a single platinum component or two or more platinum components can be used in combination. Any quantities specified below relating to the platinum-containing component or the platinum component apply to the total quantity of all platinum components used in the anode when two or more platinum components are used. The platinum coating of the platinum-containing component is preferably pure metallic platinum and / or platinum oxide, particularly in a hydrated form. Furthermore, alloys of platinum with at least one alloying element selected from Au, Ir, Co, Ni, and Ru can also be used. However, the total content of the alloying elements must not exceed 30% by mass, based on the total mass of the alloy.

[0021] The form and structure of the catalytic composition are not limited in detail, except that the ceramic material has a platinum coating. Different ceramic materials with different platinum coatings can also be combined. The OER can be present as a mixture with the platinum-containing component, but is preferably deposited on the platinum-containing component.

[0022] Preferably, the catalytic composition is present as a coating on the membrane of the MEA and / or may be combined with a binder (a proton-conducting binder; an ionomer). If a binder is used, the binder and the catalytic composition, comprising the platinum-containing component and an OER catalyst, are homogeneously mixed and form a thin electrode. The binder ensures good electrode cohesion and sufficiently high proton conductivity. The volume fraction of the ionomer, in other words, the binder, in the total volume of all solid components is preferably 25 to 45% by volume. More preferably, the anode comprises only an anode layer in which the catalytic composition is present.By using the specifically designed catalytic composition, an MEA can be provided that is characterized by high efficiency and very good long-term stability.

[0023] According to a further advantageous development, the ceramic material has a reduced surface area. Since ceramic materials are formed from metal oxides, reduced-surface ceramic materials are characterized by a surface in which the metal oxides have been reduced to the corresponding suboxides. Thus, the surface of the ceramic material contains not only the corresponding metal oxides but also their associated suboxides. Suboxides are oxides in which the oxygen content is substoichiometric to that of the oxide with the highest oxidation state of the oxide-forming metal. The proportion of each oxide can be measured using XPS. The reduced-surface ceramic material is produced by a corresponding reaction during the manufacture of the platinum-containing component, as will be explained in detail below.The advantage of using a surface-reduced ceramic material is that, because the ceramic material is more conductive, the platinum is deposited more effectively and uniformly. This, in turn, increases the overall electrical conductivity of the platinum-containing component.

[0024] Due to its excellent stability and inertness towards the reactions occurring in the anode, the ceramic material is preferably selected from Ti2, Sn2, fluoride-doped Sn2, Zr2, Si2, Nb2Os, Ta2Os, WO3, as well as alloys and mixtures thereof, and is further preferably selected from fluoride-doped Sn2, Zr2, Nb2Os, and Ta2Os. As already stated, the structure of the ceramic material is not further restricted and can be in particulate, i.e., particularly round, form, but can also exhibit branched or fibrous structures. Aggregates of these structures are also possible.

[0025] According to a further advantageous development, the BET specific surface area of ​​the ceramic material (8) is 1 to 100 m² 2 / g and especially 4 to 30 m 2 / g. As can be seen from the values, the BET specific surface area of ​​the ceramic material is relatively low. This has proven advantageous with regard to platinum coating, since the platinum coating is thus located almost exclusively on the surface of the ceramic material, and consequently the required electrical conductivity can be achieved in the desired range even with low platinum concentrations. If the specific surface area were above 30 m², 2 / g and especially above 100 m 2 If the ceramic material were located at / g, it would be very porous, meaning it would have cavities that could absorb the platinum, thus shielding it and preventing it from contributing to the electrical conductivity of the anode, or only contributing to a limited extent.

[0026] The OER can be present in the catalytic composition as a mixture with the platinum-containing component. However, it is preferred that the OER is supported on the platinum-containing component. This means that the OER can be present either directly on the ceramic material or on the platinum coating. This has the advantage that the OER can be selectively distributed within the catalytic composition, so that the reaction to be catalyzed can be carried out uniformly across the anode, thereby also promoting the longevity of the MEA.

[0027] To improve electrical conductivity, the degree of platinum coating of the ceramic material, measured by transmission electron spectroscopy (TEM), is in the range of 40 to 100%, and particularly in the range of 70 to 100%. According to the present invention, the degree of coating is understood to be the percentage of the surface of the ceramic material that is covered with platinum.

[0028] Also preferred, in view of improving the electrical conductivity of the anode, the volume fraction of the platinum coating, based on the total volume of the platinum-containing component, is 8 to 33%. For a given BET surface area of ​​the ceramic material, a higher volume fraction means that both the thickness of the platinum coating is greater and that the degree of coating increases with the volume fraction of the platinum coating.

[0029] For reasons of high efficiency and performance, the OER comprises at least one precious metal, advantageously selected from iridium (Ir) and / or ruthenium (Ru). This means that the OER can include both metallic iridium and / or metallic ruthenium, as well as compounds thereof, particularly their oxides.

[0030] Furthermore, the efficiency of the OER, and thus also of the MEA, can be advantageously increased by ensuring that the crystallite size of the OER, as measured by X-ray diffraction (XRD), is between 2 and 30 nm, and particularly between 5 and 12 nm. The crystallite size is especially relevant in the embodiment where the OER is deposited on the platinum-containing component. For a given amount of OER, the smaller the crystallite size, the more efficient the anode reaction, simply due to the limited number of surface reaction sites available on the OER.

[0031] Due to the specific composition of the catalytic composition in the MEA according to the invention, the volume fraction of OER can be relatively small. With a view to good efficiency of the reaction to be catalyzed by the OER in the anode, the volume fraction of the OER, based on the total volume of the catalytic composition, is preferably in the range of 5 to 30% and particularly in the range of 10 to 21%. This corresponds, assuming that iridium oxide is used as the OER, to a density of 10 g / cm³. 3 , and Nb20s as a ceramic material with a density of 4.6 g / cm³ 3 , in approximately a weight fraction of 10 to 30 wt%, based on the total mass of the catalytic composition. In contrast, Ta20s has a density of 8.2 g / cm³. 3When used as a ceramic material, a weight fraction of iridium oxide of 8 to 22 wt% in the catalytic composition is sufficient to achieve the preferred volume fraction of iridium oxide.

[0032] Also in the interest of further increasing the efficiency of the MEA, it is preferred if the areal weight of the OER in the anode, based on the precious metal of the OER, is 0.02 mg / cm². 2 up to 0.30 mg / cm² 2 , in particular 0.10 mg / cm² 2 up to 0.28 mg / cm² 2 and in particular 0.15 mg / cm² 2 up to 0.25 mg / cm² 2 This means that if, for example, a precious metal compound, such as an oxide of a precious metal, is used as the OER, the amount of OER refers to the amount of precious metal contained in the oxide. A conversion can be easily performed using the amount of substance and the molar weight of the OER. The areal weight here refers to the active geometric area of ​​the anode and is given in mg / cm². 2The OER, as already explained in the English description, serves to generate oxygen from water. As can be seen from the information on the basis weight, the precious metal content in the anode is preferably extremely low, so that high efficiency of the MEA can be achieved from an economic point of view. It goes without saying that two or more OERs can also be used in combination. However, if two or more OERs are used in combination according to the invention, the basis weight refers to the total amount of all OERs in the anode.

[0033] For reasons of stability and also for good processability, the layer thickness of the anode is 2 to 6 pm.

[0034] Furthermore, a water electrolysis cell comprising the MEA according to the invention is also described according to the invention. Due to the use of the MEA according to the invention in the water electrolysis cell according to the invention, the latter is also characterized by very good performance combined with high long-term stability.

[0035] Furthermore, a method for producing a platinum-containing component is also disclosed according to the invention. As already explained in detail above for the MEA according to the invention, a platinum-containing component is understood to be a component comprising a ceramic material having a platinum coating. According to the method according to the invention, in one step a) a ceramic material and a platinum precursor compound are provided. The ceramic material is present in its unreduced form, i.e., as it is commonly available on the market. The specific platinum precursor compound is not limited. It is therefore a commercially available platinum precursor compound that can be converted to platinum by reduction.

[0036] Then, in step b), the ceramic material and the platinum precursor compound are reduced, resulting in a surface-reduced ceramic material and a platinum coating. The platinum coating coats the surface of the ceramic material.

[0037] The reduction of the ceramic material and the platinum precursor compound can be performed either consecutively or simultaneously. While the platinum precursor compound is converted to platinum during the reduction process, the ceramic material is only reduced on its surface. This can be detected using XPS.

[0038] It has proven particularly preferred that a reducing agent used in step b) is a glycol, specifically selected from butane-1,2-diol, butane-1,3-diol, butane-1,4-diol, butane-2,3-diol, propane-1,2-diol, propane-1,3-diol, and ethylene glycol. Propane-1,2-diol, propane-1,3-diol, butane-1,4-diol, and ethylene glycol are preferred. The use of a glycol is advantageous over other reducing agents because the reduction is carried out in such a way that the surface of the ceramic material is also reduced. Other commercially available reducing agents react more selectively with the platinum precursor compound.

[0039] Furthermore, it is advantageous if a surface-directing agent, such as iodine, an iodide, bromine, a bromide, a nitrite, nitrous oxide, carbon monoxide, or a cyanide, is present during step b). Mixtures of these surface-directing agents can also be used. The surface-directing agent prevents platinum from depositing on platinum. Thus, the platinum must deposit on free surface sites of the ceramic material, which increases the coverage. Due to its good adsorption properties on ceramic materials and its good reduction properties, the platinum precursor compound is preferably selected from H₂PtCl₆, H₂Pt(OH)₆, Pt(NH₃)₄Cl₂, Pt(NH₃)₄(NO₃)₂, Pt(NH₃)₄CO₃, Na₂PtCl₆, Na₂Pt(OH)₆, and PtCl₄.

[0040] To increase electrical conductivity, the platinum-containing component contains 29 to 81% by mass of the ceramic material and 19 to 71% by mass of the platinum from the platinum precursor compound, both based on the total mass of the platinum-containing component. The mass fraction of the ceramic component and the platinum depends on the density of the ceramic material. Ultimately, the decisive factor is the volume fraction of the ceramic component and the platinum, resulting from their masses and densities. For example, when using Nb₂O₃ as the ceramic component with a density of 4.6 g / cm³, the volume fraction is... 3 A preferred mass fraction of ceramic material is 29 to 70%. When using Ta₂O₃ with a density of 8.2 g / cm³ 3 , a preferred mass fraction of ceramic material is 44 to 81%.

[0041] For complete deposition of platinum on the ceramic material, it has proven advantageous to maintain a temperature between 140 and 230 °C, preferably 140 and 180 °C, during step b). Temperatures, particularly below 140 °C, lead to incomplete reduction of the platinum precursor compound and thus, in some ceramic materials, to insufficient coating. The upper temperature limit is not particularly restrictive and depends on the reducing agent and / or the solvent. When using propylene glycol or ethylene glycol, an upper temperature of 180 °C is preferred, taking into account the boiling point at 1013 hPa and thermal stability. Higher temperatures may be possible when using reducing agents with a higher boiling point, such as...1,4-Butanediol can be used, or if the reduction is carried out in an autoclave, so that the reaction takes place at increased pressure, leading to an increase in the boiling point. For reasons of stability and from an economic point of view, a reaction temperature of less than 230 °C is preferred.

[0042] The platinum-containing component produced in the manner described above can be particularly preferably used in the MEA according to the invention.

[0043] Furthermore, the invention also describes a method for producing a catalytic composition that can also be used in the MEA according to the invention. The catalytic composition comprises the platinum-containing component described above, which is produced according to the method also described above, and additionally an OER.

[0044] Thus, the process according to step b) of the process for producing a platinum-containing component comprises a step c) of depositing an OER onto the platinum-containing component, thereby obtaining the catalytic composition. The OER can be deposited onto the ceramic material or, preferably, onto the platinum coating, or onto both. The efficiency of the OER deposition can be improved by carrying out the deposition of the OER in step c) according to one of the following methods:

[0045] OERs can be deposited either by alkaline hydrolysis of an OER precursor compound, such as IrCh, or by precipitation from a colloidal OER dispersion. The latter process differs technically from simply mixing and co-dispersing an OER and the platinum-containing component. The difference lies in the fact that a colloidal dispersion is stable; that is, the OER particles do not tend to aggregate or sediment over short periods. For them to precipitate, an active step must be taken to destabilize the dispersion (for example, a change in pH, a change in ion strength, high shear, or similar). Therefore, mixtures are not stable in themselves.

[0046] According to another alternative method, the OER can be deposited by thin-film deposition, selected from chemical or physical vapor deposition (CVD, PVD) or atomic layer deposition (ALD), which yields very thin layers of OER, which is preferred in terms of having the lowest possible content of OER in the catalytic composition.

[0047] Preferably, the process is carried out with the provision that the OER is deposited by precipitation from a colloidal OER dispersion, wherein the pH value during acidification lies between the isoelectric point of the OER and the isoelectric point of the platinum-containing component. This results in particularly efficient OER deposition.

[0048] Advantageously, the mass fraction of the ceramic material in the catalytic composition is 23 to 73%, the mass fraction of the platinum from the platinum precursor compound is 15 to 64%, and the mass fraction of the OER is 8 to 32%, each based on the total mass of the catalytic composition. Particularly preferably, the mass fraction of the ceramic material is 39 to 49%, the mass fraction of the platinum from the platinum precursor compound is 35 to 45%, and the mass fraction of the OER is 11 to 21%, each based on the total mass of the catalytic composition.

[0049] EXAMPLES

[0050] Synthesis of a platinum shell on niobium oxide

[0051] Example 1

[0052] 1.0 g of a commercial niobium oxide ceramic powder (Ceramic grade, Taniobis GmbH, Germany) with a BET specific surface area of ​​6.5 m² 2 / g (Determination of the specific surface area of ​​solids by gas adsorption - BET method according to (ISO 9277:2022)) was dispersed in ethylene glycol. The pH was adjusted to 10 to 11 and the dispersion was heated to 180°C. After one hour, the dispersion was cooled back to 150°C and 3.58 g of a commercial platinum salt (tetraamineplatinum dichloride, Umicore, Germany) were added. After one hour, the powdered product was centrifuged, washed four times with ultrapure water, and dried overnight at 80°C.

[0053] Example 2

[0054] 2.4 g of a commercial niobium oxide ceramic powder (Ceramic grade, Taniobis GmbH, Germany) with a BET specific surface area of ​​6.5 m² 2The product was dispersed in ethylene glycol. The pH was adjusted to 10–11, and the dispersion was heated to 180°C. After one hour, the dispersion was cooled to 150°C, and 2.87 g of a commercial platinum salt (tetraamine platinum dichloride, Umicore, Germany) were added. After one hour, the powdered product was centrifuged, washed four times with ultrapure water, and dried overnight at 80°C.

[0055] Example 3

[0056] 1.0 g of a commercial niobium oxide ceramic powder (Ceramic grade, Taniobis GmbH, Germany) with a BET specific surface area of ​​6.5 m² 2The product was dispersed in ethylene glycol. The pH was adjusted to 10–11, and the dispersion was heated to 180°C. After one hour, 1.79 g of a commercial platinum salt (tetraamineplatinum dichloride, Umicore, Germany) was added. After another hour, the powdered product was centrifuged, washed four times with ultrapure water, and dried overnight at 80°C.

[0057] Example 4

[0058] 0.67 g of a commercial niobium oxide ceramic powder (Ceramic grade, Taniobis GmbH, Germany) with a BET specific surface area of ​​6.5 m² 2 1 g and 2.39 g of a commercial platinum salt (tetraamineplatinum dichloride, Umicore, Germany) were dispersed in ethylene glycol. The pH was adjusted to 10–11 and the dispersion was heated to 150°C. After one hour, the powdered product was centrifuged, washed four times with ultrapure water, and dried overnight at 80°C.

[0059] Example 5

[0060] 1.0 g of a commercial niobium oxide ceramic powder (Ceramic grade, Taniobis GmbH, Germany) with a BET specific surface area of ​​6.5 m² 2 1.79 g of a commercial platinum salt (tetraamineplatinum dichloride, Umicore, Germany) were dispersed in ethylene glycol. The pH was adjusted to 10–11 and the dispersion was heated to 180°C. After one hour, the powdered product was centrifuged, washed four times with ultrapure water, and dried overnight at 80°C.

[0061] Example 6

[0062] 3.0 g of a commercial niobium oxide ceramic powder (Ceramic grade, Taniobis GmbH, Germany) with a BET specific surface area of ​​6.5 m² 2The product was dispersed in ethylene glycol. The pH was adjusted to 10–11, and the dispersion was heated to 180°C. After one hour, the dispersion was cooled to 150°C, and 5.36 g of a commercial platinum salt (tetraamineplatinum dichloride, Umicore, Germany) were added. After one hour, the powdered product was centrifuged, washed four times with ultrapure water, and dried overnight at 80°C.

[0063] Example 7

[0064] 0.8 g of a commercial silica powder (Nanopowder 12 nm, Sigma Aldrich, USA) and 5.73 g of a commercial platinum salt (tetraamine platinum dichloride, Umicore, Germany) were dispersed in ethylene glycol. The pH was adjusted to 10–11 and the dispersion was heated to 130°C. After one hour, the powdered product was centrifuged, washed four times with ultrapure water, and dried overnight at 80°C.

[0065] Example 8

[0066] 1.33 g of a commercial niobium oxide ceramic powder (Ceramic grade, Taniobis GmbH, Germany) with a BET specific surface area of ​​6.5 m² 2 1 g and 4.78 g of a commercial platinum salt (tetraamineplatinum dichloride, Umicore, Germany) were dispersed in ethylene glycol. The pH was adjusted to 10–11 and the dispersion was heated to 130°C. After one hour, the powdered product was centrifuged, washed four times with ultrapure water, and dried overnight at 80°C.

[0067] Example 9

[0068] 2.4 g of a commercial niobium oxide ceramic powder (Ceramic grade, Taniobis GmbH, Germany) with a BET specific surface area of ​​6.5 m² 2The product was dispersed in ethylene glycol. The pH was adjusted to 10–11, and the dispersion was heated to 180°C. After one hour, the dispersion was cooled to 130°C, and 2.87 g of a commercial platinum salt (tetraamine platinum dichloride, Umicore, Germany) were added. After one hour, the powdered product was centrifuged, washed four times with ultrapure water, and dried overnight at 80°C.Real Real Real Real Platinum Theoretical Platinum Ceramic Platinum Ceramic Crystallite Determination Platinum mass mass mass volume volume Platinum Yield size yield yield / nm degree Example 1 67% 60% 40% 24% 76% 90% + 8 78% + Example 2 40% 39% 61% 12% 88% 98% + 7 62% + Example 3 50% 60% 40% 24% 76% 120% + 9 58% + Example 4 67% 52% 48% 19% 81% 78% + 7 75% + Example 5 50% 46% 54% 15% 85% 92% + 9 64% + Example 6 50% 42% 58% 13% 87% 84% + 6 / / Example 7 80% 24% 76% 6% 94% 30% - 5 17% - Example 8 67% 12% 88% 3% 97% 18% - 5 / / .

[0069]

[0070] Example 9 40% 22% 78% 6% 94% 55% 0 7 57% +Deposition of IrOx on Pt / NbzOs

[0071] 0.8 g of iridium chloride (CIA hydrate, Umicore, Germany) were dissolved in 100 mL of ultrapure water. The pH was adjusted to 10. The solution was held at room temperature for one hour and maintained at pH 10. The solution was then slowly heated to 70°C and maintained at pH 10. After two hours, 2 g of the platinum-containing component from Example 6 were added and dispersed. The pH was adjusted to 7.5 and the solution was cooled to room temperature. The product was centrifuged and washed three times with ultrapure water. It was then dried overnight at 80°C. The composition of the final catalyst, in other words the catalytic composition, was determined by ICP analysis and is shown in the following table:

[0072] Pt- Ceramic- OER- Pt- Ceramic- OER- Mass- Mass- Mass- Volume- Volume- content content content content content content content

[0073]

[0074] 34% 46% 20% 11% 74% 15%

[0075] Elemental composition via ICP

[0076] To determine the elemental composition, the sample was digested in an alkaline melt, dissolved in aqua regia, and measured on an Agilent ICP-OES 5800 (Agilent, Australia / USA). The signal was referenced against a platinum NIST standard.

[0077] Phase analysis using XRD

[0078] Phase analysis was performed using X-ray diffraction on an Aeris instrument (Malvern Panalytical, The Netherlands). Platinum crystallite size was determined by Rietveld refinement.

[0079] Coverage analysis

[0080] The coverage was determined by TEM analysis. Imaging was performed on a JEM-2100 (Jeol, Japan). The images were subsequently analyzed using imageJ software by calculating the ratio of platinum-covered area to the total particle area.

[0081] Example of ink production for anode

[0082] 2.2 g of the catalytic composition (IrOx on Pt / NbzOs from Example 6) were mixed with 2.56 g of ionomer dispersion Nation® D2020 (Chemours, USA) with an ionomer content of 21.3 wt%. Subsequently, 2.2 g of water and 13.1 g of 1-propanol were added. The mixture was dispersed for 60 min using a bead mill with spherical zirconia beads with a diameter of 1 mm. The quality of the dispersion was visually verified by checking for the absence of catalyst aggregates. The dispersion quality was further confirmed by good coating quality, i.e., no visible aggregates or streaks in either the wet or dry film.

[0083] Manufacturing anodes on a decal

[0084] The anode ink was applied to a glass fiber reinforced PTFE substrate, in other words a decal, using a wire bar applicator. The wet film thickness was adjusted by selecting a wire bar applicator with a suitable diameter to achieve an iridium metal loading (based on the basis weight of the OER) of 0.15 mg / cm². 2 To obtain the desired result, after coating, the wet layer was dried in an oven at 110 °C for 5 minutes. The actual iridium metal loading was determined gravimetrically by measuring the exact decal weight before and after lamination of the catalyst-coated membrane (prepared as described below).

[0085] Production of catalyst-coated membranes (MEA / CCMs)

[0086] CCMs were manufactured using a Nation® N115 membrane (Chemours) in a press using a decal process. For this purpose, the membranes were positioned between anode and cathode decals (7.1 cm x 7.1 cm) and pressed at a temperature of 180 °C and a pressure of 1.5 MPa for 1 minute, so that the electrode layers were transferred from the decal substrate to the membranes.

[0087] The cathode was identical for all CCMs and consisted of a catalyst in which platinum was supported on carbon, and a Nation® ionomer binder. The catalyst-to-ionomer weight ratio in the cathode was 3:1, and the platinum loading was 0.3 mg / cm². 2 The cathode was also applied to glass fiber reinforced PTFE.

[0088] Determination of platinum yield

[0089] The platinum yield was determined from the ratio of platinum deposited on the ceramic to the platinum used in the platinum precursor compound. Further details, advantages, and features of the present invention will become apparent from the following description of exemplary embodiments with reference to the drawing. Fig. 1 shows a cross-sectional view of a MEA according to a first embodiment.

[0090] Fig. 2 shows a catalytic composition according to a second embodiment in section and

[0091] Fig. 3 shows a catalytic composition according to a third embodiment in section.

[0092] The figures show only the essential elements and components of the present invention. All other elements and components have been omitted for clarity. Furthermore, identical reference numerals denote identical elements / components.

[0093] Figure 1 shows in detail an MEA 1 according to an advantageous embodiment. In this embodiment, a membrane 4 is surrounded on one side by a cathode 2 and on the opposite side by an anode 3. The membrane 4 is thus located between the cathode 2 and the anode 3. The anode 3 is a single layer. The MEA 1 can be used, in particular, in a water electrolysis cell and is therefore designed as a water electrolysis MEA. The MEA 1 is designed as a catalyst-coated membrane (CCM), in which the electrodes 2 and 3 are directly coated onto the membrane 4, for example, by means of a decal process.

[0094] The anode 3 contains a catalytic composition 5. This comprises an OER 6 and a platinum-containing component 7. The platinum-containing component 7 in turn comprises a ceramic material 8 coated with a platinum coating 9.

[0095] The ceramic material is preferably selected from TiÜ2, SNIÜ2, fluoride-doped SNIÜ2, ZrÜ2, SiÜ2, Nb20s, Ta2Os, WO3 as well as alloys thereof and mixtures thereof and advantageously has a BET specific surface area of ​​1 to 100 m² 2 / g. Preferably, the ceramic material is selected from fluoride-doped SnO₂, ZrO₂, Nb₂O₃, and Ta₂O₃. The platinum coating 9 coats the ceramic material 8, wherein the ceramic material 8 can be in the form of particles, i.e., round but also branched or fibrous particles and their aggregates.

[0096] The platinum coating 9 comprises platinum as the main component and preferably consists of platinum and / or platinum compounds. The catalytic composition 5 also comprises at least one OER 6. This preferably comprises iridium and / or ruthenium. The OER 6 is preferably supported on the platinum-containing component 7, as will be explained in more detail with reference to Figures 2 and 3. The basis weight of the OER 6 in the anode 3, based on the precious metal of the OER 6, is particularly 0.02 mg / cm². 2 up to 0.30 mg / cm² 2 , in particular 0.10 mg / cm² 2 up to 0.28 mg / cm² 2 and in particular 0.15 mg / cm² 2 up to 0.25 mg / cm² 2 , and is therefore very small. This would normally lead to a very small layer thickness S of the anode 3, which would be unfavorable in terms of the effectiveness of the MEA 1, but even more so would lead to low stability, especially over the lifetime of the MEA 1.

[0097] The layer thickness S of the anode 3 is, as shown here, 2 to 6 pm. This is possible because the anode 3 comprises the catalytic composition 5, which, in addition to the OER 6, includes a platinum-containing component 7 containing a high proportion of ceramic material 8. The fact that the ceramic material 8 is coated with a platinum coating 9 also improves the electrical conductivity and the transverse conductivity in the anode 3, which further enhances the effectiveness of the MEA 1. The platinum coating 9 is also characterized by good stability, so that the electrical conductivity can be maintained at a consistently high level. The catalytic composition 5 is dispersed in an ionomer binder and applied to the membrane 4. The volume fraction of the ionomer 10 in relation to the total volume of all solid components is preferably 25 to 45% by volume.The volume fraction of the catalytic composition in relation to the total volume of all solid components is preferably 55 to 75% by volume. To achieve a continuous electron transport path, and thus good layer conductivity, the particles of the catalytic composition 5 must be in direct contact with each other. The representation in Fig. 1 is therefore to be understood as schematic and does not mean that the particles are isolated from each other in the anode 3.

[0098] Fig. 2 shows a catalytic composition 5 according to a second embodiment in section.

[0099] A platinum coating 9 is applied to a ceramic material 8. The degree of coverage of the ceramic material 8 by the platinum coating 9 is 40 to 100%. The ceramic material 8 and the platinum coating 9 together form a platinum-containing component 7. The volume fraction of the platinum coating 9, relative to the total volume of the platinum-containing component 7, is in the range of 8 to 33%. This volume fraction is sufficiently high to ensure good electrical conductivity within an anode 3. While the proportion of platinum coating 9 can be higher, this generally only increases the cost of the catalytic composition 5, since the platinum is sufficiently dispersed by the coating of the ceramic material 8 to maintain a very high transverse conductivity.

[0100] The platinum-containing component 7 can be produced by providing the ceramic material 8 and a platinum precursor compound, and then reducing them to obtain a reduced ceramic material 8 and the platinum coating 9. The reduction can be carried out consecutively or simultaneously, and preferably at a temperature in the range of 140°C to 230°C, and preferably from 140°C to 180°C. A glycol is particularly suitable as the reducing agent, since this gently reduces the surface of the ceramic material 8, which has a positive effect on the adhesion of the platinum coating 9 and also on the electrical conductivity of the catalytic composition 5.

[0101] An OER 6 is deposited on the platinum coating 9. The following deposition methods are used: alkaline hydrolysis of an oxygen evolution catalyst precursor compound (e.g., IrCl), precipitation from a colloidal oxygen evolution catalyst dispersion, or thin-film deposition, selected from chemical or physical vapor deposition (CVD, PVD) or atomic layer deposition (ALD).

[0102] In the resulting catalytic composition 5, the mass fraction of the ceramic material 8 is 23 to 73%, the mass fraction of the platinum 9 from the platinum precursor compound is 15 to 64%, and the mass fraction of the OER 8 is 32%, each based on the total mass of the catalytic composition 5. Particularly preferably, the mass fraction of the ceramic material is 39 to 49%, the mass fraction of the platinum from the platinum precursor compound is 35 to 45%, and the mass fraction of the OER is 11 to 21%, each based on the total mass of the catalytic composition.

[0103] Fig. 3 shows a cross-sectional view of a catalytic composition 5 according to a third embodiment. The difference from the catalytic composition 5 in Fig. 2 is that the OER is deposited on the surface of the ceramic material 8. Furthermore, the ceramic material 8 consists of an aggregate of particles of the ceramic material 8.

[0104] For the effectiveness of the catalytic composition 5, it is essentially irrelevant whether the OER 6 is deposited on the ceramic material 8 or on the platinum coating 9; however, it has proven advantageous for the production process that the OER 6 is deposited on the platinum coating 9, as shown in Fig. 2. In addition to the foregoing written description of the invention, explicit reference is hereby made to the graphical representation of the invention in the figures for its supplementary disclosure. List of reference numerals

[0105] 1 MEA

[0106] 2 Cathode

[0107] 3 Anode

[0108] 4 proton-conducting membrane 5 catalytic composition 6 OER

[0109] 7 platinum-containing components

[0110] 8 ceramic material

[0111] 9 Platinum coating

[0112] 10 Ionomer

Claims

Claims 1. Membrane electrode arrangement (1) comprising a cathode (2), an anode (3) and a proton-conducting membrane (4) arranged between the cathode (2) and the anode (3), wherein the anode (3) comprises a catalytic composition (5), wherein the catalytic composition (5) comprises an oxygen evolution catalyst (6) and a platinum-containing component (7), wherein the platinum-containing component (7) comprises a ceramic material (8) having a platinum coating (9).

2. Membrane electrode arrangement (1) according to claim 1, wherein the ceramic material (8) has a reduced surface area.

3. Membrane electrode arrangement (1) according to one of the preceding claims, wherein the ceramic material (8) is selected from TiCh, SnC>2, fluoride-doped SnC>2, ZrC>2, SiC>2, Nb2C>5, Ta2Os, WO3 and alloys thereof and mixtures thereof, preferably selected from fluoride-doped SnC>2, ZrC>2, Nb2Os, and Ta2Os alloys thereof and mixtures thereof.

4. Membrane electrode arrangement (1) according to one of the preceding claims, wherein a BET specific surface area of ​​the ceramic material (8) is 1 to 100 m² 2 / g, especially 4 to 30 m 2 / g.

5. Membrane electrode arrangement (1) according to one of the preceding claims, wherein the oxygen evolution catalyst (6) is supported on the platinum-containing component (7).

6. Membrane electrode arrangement (1) according to one of the preceding claims, wherein the degree of coating of the ceramic material (8) by the platinum coating (9) is 40 to 100%, in particular 70 to 100%.

7. Membrane electrode arrangement (1) according to one of the preceding claims, wherein a volume fraction of the platinum coating (9), based on the total volume of the platinum-containing component (7), is 8 to 33%.

8. Membrane electrode arrangement (1) according to any one of the preceding claims, wherein the oxygen evolution catalyst (6) comprises iridium and / or ruthenium.

9. Membrane electrode arrangement (1) according to any one of the preceding claims, wherein the crystallite size of the oxygen evolution catalyst (6) is 2 to 30 nm, in particular 5 to 12 nm.

10. Membrane electrode arrangement (1) according to one of the preceding claims, wherein a volume fraction of the oxygen evolution catalyst (6), based on the total volume of the catalytic composition (5), is 5 to 30% and in particular 10 to 21%.

11. Membrane electrode arrangement (1) according to one of the preceding claims, wherein an areal weight of the oxygen evolution catalyst (6) in the anode, based on the noble metal of the oxygen evolution catalyst (6), is 0.02 mg / cm². 2 up to 0.30 mg / cm² 2 , in particular 0.10 mg / cm² 2 up to 0.28 mg / cm² 2 and in particular 0.15 mg / cm² 2 up to 0.25 mg / cm² 2 amounts.

12. Membrane electrode arrangement (1) according to one of the preceding claims (1), wherein the layer thickness (S) of the anode is 2 to 6 pm.

13. Water electrolysis cell comprising a membrane electrode arrangement (1) according to one of the preceding claims.

14. Method for producing a platinum-containing component (7), wherein the platinum-containing component (7) comprises a ceramic material (8) having a platinum coating (9), the method comprising the following steps: a) Providing a ceramic material (8) and a platinum precursor compound and b) Reducing the ceramic material (8) and the platinum precursor compound to obtain a reduced ceramic material and a platinum coating (9), where the reduction of the ceramic material and the platinum precursor compound is carried out consecutively or simultaneously.

15. The method of claim 14, wherein a reducing agent used in step b) is a glycol, in particular selected from butane-1,2-diol, butane-1,3-diol, butane-1,4-diol, butane-2,3-diol, propane-1,2-diol, propane-1,3-diol, and ethylene glycol.

16. A method according to claim 14 or 15, wherein a surface-directing agent is present during step b).

17. A method according to any one of claims 14 to 16, wherein the platinum precursor compound is selected from H2PtCI6, H2Pt(OH)6, Pt(NH3)4CI2, Pt(NH3)4(NO3)2, Pt(NH3)4CO3, Na2PtCI6, Na2Pt(OH)6, and PtCI4.

18. Method according to any one of claims 14 to 17, wherein in the platinum-containing component (7) a mass fraction of the ceramic material (8) is 29 to 81% and a mass fraction of the platinum (9) from the platinum precursor compound is 19 to 71%, based on the total mass of the platinum-containing component (7).

19. Method according to any one of claims 14 to 18, wherein the temperature during step b) is in a range of 140 to 230°C, preferably in a range of 140 to 180°C.

20. A method for producing a catalytic composition (5) comprising the production of a platinum-containing component (7) according to any one of claims 14 to 19, wherein the method according to step b) comprises a step c) of depositing an oxygen evolution catalyst (6) on the platinum-containing component (7) to obtain the catalytic composition (5).

21. The method of claim 20, wherein in step c) the deposition of the oxygen evolution catalyst (6) is carried out by: - alkaline hydrolysis of an oxygen evolution catalyst precursor compound or - precipitation from a colloidal oxygen evolution catalyst dispersion or - Thin-film deposition, selected from chemical or physical vapor deposition or atomic layer deposition.

22. Method according to claim 20 or 21, wherein the deposition of the oxygen evolution catalyst (6) is carried out by precipitation from a colloidal oxygen evolution catalyst dispersion, wherein during this precipitation the pH value during acidification is between the isoelectric point of the oxygen evolution catalyst (6) and the isoelectric point of the platinum-containing component (7).

23. Method according to any one of claims 20 to 22, wherein in the catalytic composition (5) a mass fraction of the ceramic material (8) is 23 to 73%, a mass fraction of the platinum from the platinum precursor compound is 15 to 64%, and a mass fraction of the oxygen evolution catalyst (6) is 8 to 32%, based on the total mass of the catalytic composition (5).

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