Ruthenium-iridium mixed oxide catalysts for electrolysis of water

Abstract

The invention relates to a powdered catalyst material, which is particularly suitable for use in the oxygen evolution reaction in the electrolysis of water. The catalyst material comprises an unsupported ruthenium-iridium oxide, wherein the weight ratio of iridium (Ir) to ruthenium (Ru) is not greater than 4.5 relative to the total weight of the unsupported ruthenium-iridium oxide. The unsupported ruthenium-iridium oxide exhibits a powder conductivity of at least 30 S / cm. The invention also relates to a method for preparing such a powdered catalyst material, a composition, a catalyst layer, an electrode and an electrochemical device containing the powdered catalyst material, and a method for producing hydrogen using the powdered catalyst material.

Description

[0001] This invention relates to a powdered catalyst material, which is particularly suitable for the oxygen evolution reaction in the electrolysis of water. The invention also relates to a method for preparing such a powdered catalyst material, a composition containing the powdered catalyst material, a catalyst layer, electrodes and an electrochemical device, and a method for producing hydrogen using the powdered catalyst material.

[0002] Hydrogen is seen as the energy carrier of the future because it allows for sustainable energy storage, long-term availability, and can also be produced using renewable energy technologies.

[0003] Currently, steam reforming is the most common method for producing hydrogen. In steam reforming, methane and steam are converted into hydrogen and CO. Water electrolysis is another variation of hydrogen production. High-purity hydrogen can be obtained through water electrolysis.

[0004] Various technologies exist in the field of water electrolysis, particularly alkaline water electrolysis (AEL), acidic water electrolysis using polymer electrolyte membranes (PEM), and high-temperature solid oxide electrolysis.

[0005] A water electrolysis cell consists of a half-cell with an electrode where the oxygen evolution reaction (OER) occurs, and another half-cell with an electrode where the hydrogen evolution reaction (HER) occurs. The two half-cells are separated from each other by a separator, an ion-conducting membrane, or a ceramic element. The electrode where the oxygen evolution reaction occurs is called the anode.

[0006] A review of water electrolysis technology, particularly PEM water electrolysis, can be found in, for example, M. Carmo et al., International Journal of Hydrogen Energy, 38, 2013, pp. 4,901-4,934; and A. Buttler, H. Spliethoff, Ren. Sus. Energy Rev., 82, 2018, pp. 2,440-2,454.

[0007] In PEM water electrolysis cells, the polymer membrane serves as a proton transport medium and electrically insulates the electrodes from each other. For example, catalyst compositions for the oxygen evolution reaction and hydrogen evolution reaction are applied as anodes and cathodes to the front and back of the membrane (catalyst-coated membrane CCM), thereby obtaining a membrane-electrode assembly (MEA).

[0008] The oxygen evolution reaction that occurs at the anode of a PEM water electrolysis cell can be represented by the following reaction equation:

[0009] 2 H2O 4 H + + O2 + 4 e -

[0010] Due to its complex reaction mechanism, the oxygen evolution reaction (OER) using mature materials exhibits slow reaction kinetics, which is why a significant overpotential must be overcome at the anode to achieve a sufficiently high conversion rate. Furthermore, the OER through the membrane used occurs under strongly acidic (i.e., low pH) and strongly oxidizing conditions.

[0011] Effective operation of water electrolysis cells requires the presence of a catalyst. Due to the highly corrosive conditions at the anode (low pH, significant overvoltage), suitable catalyst materials particularly include noble metals such as ruthenium and iridium, as well as their oxides.

[0012] Pure ruthenium oxide exhibits high intrinsic activity for the oxygen evolution reaction (OER), but it is corroded in acidic media during O2 formation and rapidly loses its activity. Besides ruthenium oxide, iridium oxide (IrO) is another suitable alternative. x IrO2 is also an excellent electrocatalyst for OER. Crystalline IrO2 is one of the most resistant materials to O2 formation conditions in strongly acidic environments, but it exhibits lower activity than RuO2. Furthermore, the noble metals present in this material are expensive, and their availability is limited. In the publications “Analysis of Voltage Losses in PEM Water Electrolyzers with LowPlatinum Group Metal Loadings,” J. Electrochem. Soc. 165, 2018, F305-F314, and “Current Challenges in Catalyst Development for PEM Water Electrolyzers,” Chem. Ing. Tech., 2020, 92, pp. 1-2, 31-39, it is mentioned that the typical current iridium loading level on the anode side of catalyst-coated membranes is approximately 2 mg iridium / cm³. 2 The coating surface is coated, but the load level must still be significantly reduced to allow for large-scale use of PEM electrolysis based on the availability of iridium.

[0013] For OER in acidic electrolytes, mixed oxides such as Ir x Ru 1-x O2 appears to offer a good trade-off in terms of activity and stability. Attempts to form stable and efficient catalysts by combining materials are known, but have not yet been fully successful, because the amount of iridium or noble metals in the electrode has not been sufficiently reduced due to the material properties (high density and morphology).

[0014] The prior art primarily assumes that the corresponding unsupported catalyst materials cannot meet the requirements, as described in EP1701790 A1. To increase the conductivity of the catalyst materials and conserve precious metals, they are typically applied to suitable support materials. However, CN 116479466 A describes a method that proposes an unsupported ruthenium-iridium mixed oxide. However, known catalyst materials have not yet exhibited entirely suitable properties, particularly when used in electrodes, especially regarding the increased layer resistance observed in catalyst layers employing such materials.

[0015] The Adams method is commonly used to prepare pure iridium oxide and ruthenium-iridium oxides. In the method, described in detail by Adams and Shriner in 1923, one or more metal chloride precursors react with NaNO3 and then melt in air at elevated temperatures. The properties of the prepared metal oxides depend on the reaction parameters, particularly the temperature and duration of the heat treatment, and the precursor compounds used.

[0016] The object of this invention is to overcome at least one drawback of the prior art. One object of this invention is to provide a catalyst material for the oxygen evolution reaction in acidic water electrolysis (PEM water electrolysis) that exhibits both improved activity and long-term stability. Furthermore, the proportion of iridium in the catalyst material should be as low as possible, which should also allow for a cost-effective catalyst material.

[0017] Another objective is to ensure that the catalyst layer can be prepared from the catalyst material to be supplied, particularly the anode in the membrane electrode assembly, which has the lowest possible iridium loading per unit area (i.e., per cm²). 2 The membrane has the lowest possible iridium content and remains highly active in relation to the oxygen evolution reaction. Another objective is to ensure that the corresponding electrode has low sheet resistance.

[0018] According to the invention, at least one of these objectives is achieved by a powdered catalyst material comprising unsupported ruthenium-iridium oxide, wherein the weight ratio of iridium (Ir) to ruthenium (Ru) is not greater than 4.5 relative to the total weight of the ruthenium-iridium oxide, characterized in that the unsupported ruthenium-iridium oxide has a powder conductivity of at least 30 S / cm.

[0019] The catalyst material according to the present invention exhibits high catalytic activity for the oxygen evolution reaction and is stable under the specified conditions. The reaction is carried out under highly corrosive conditions, typically at pH below 3 and a potential exceeding 1.5V. 电池 The following steps were performed. Because the total iridium content remained low, a cost-effective catalyst material was obtained. This catalyst material allowed the iridium loading in the electrode to be reduced to below 0.3 mg (Ir) / cm³. 2 The range.

[0020] In the context of this invention, it has been surprisingly found that a trade-off can be achieved between the lowest possible iridium content and high activity for the oxygen evolution reaction if the weight ratio of iridium is adjusted to minimize powder conductivity, thereby satisfying the conditions described above. Furthermore, such catalyst materials have proven particularly suitable for preparing electrode layers with advantageously low layer resistance.

[0021] The catalyst material according to the invention is particularly suitable as a catalyst for the oxygen evolution reaction in water electrolysis. It also exhibits activity in CO2 electrolysis, electrochemical peroxide preparation, and as an additive in the anode of fuel cells.

[0022] Typically, such catalyst materials are applied to support materials primarily to improve the distribution of nanoparticles, and secondarily to increase conductivity to a practical level. However, conductive supports, especially those used in electrochemical applications, often undergo corrosion under oxidizing conditions, thus losing at least some of their conductivity and / or degrading. Surprisingly, it has been found that catalyst materials with a minimum powder conductivity of 30 S / cm and low iridium content can also be used unloaded.

[0023] This invention relates to a catalyst material. A "catalyst" is a catalytically active material used in a specific application.

[0024] The powdered catalyst material comprises ruthenium-iridium oxide; preferably, apart from unavoidable impurities, the powdered catalyst material consists of ruthenium-iridium oxide. In the context of this application, such oxides are understood to be materials composed of ruthenium, iridium, and oxygen. It is a homogeneous mixed oxide (solid solution); in other words, it is not a multi-component system or composite material. The presence of the mixed oxide can be detected, for example, by X-ray diffraction experiments. In particular, no signal from the individual oxides (ruthenium oxide and iridium oxide) appears in the XRD pattern. Only signals from the mixed oxide are received, which are not only visible in the signal pattern but also reflected in the diffraction angles, which differ from those of the pure oxides.

[0025] Preferably, the composition of the ruthenium-iridium oxide corresponds to formula Ir x Ru 1-x O y Where x is less than 1 and greater than 0, and y is in the range of 1.5 to 2. Perhaps more preferably, y is less than 2. In such cases, oxygen can be present in substoichiometric amounts; in particular, ruthenium-iridium oxides have proven advantageous in terms of both their activity and stability.

[0026] The catalyst material may optionally contain metals other than iridium and ruthenium, for example, the amount of these other metals relative to the total weight of the catalyst material is at most and includes 5% by weight, advantageously at most and includes 1% by weight. In other words, apart from unavoidable impurities, the metals in the catalyst material are preferably composed of iridium and ruthenium. The weight ratio of iridium, ruthenium, and oxygen is preferably 100% by weight; in other words, apart from unavoidable impurities, the catalyst material is preferably composed of iridium, ruthenium, and oxygen.

[0027] Preferably, the proportion of iridium in the ruthenium-iridium oxide does not exceed 70% by weight, particularly not more than 65% by weight, and especially preferably not more than 55% by weight, relative to the total weight of the ruthenium-iridium oxide. For example, the ruthenium-iridium oxide contains 10% to 70% by weight, more preferably 15% to 65% by weight of iridium.

[0028] Preferably, the proportion of ruthenium in the ruthenium-iridium oxide is more than 15% by weight, particularly more than 25% by weight, and especially preferably more than 35% by weight, relative to the total weight of the ruthenium-iridium oxide. For example, the ruthenium-iridium oxide contains 15% to 70% by weight, more preferably 25% to 65% by weight of ruthenium.

[0029] The weight ratio of iridium (Ir) to ruthenium (Ru) relative to the total weight of the ruthenium-iridium oxide is no greater than 4.5. Catalyst materials with this composition have been found to exhibit improved activity. The weight ratio of Ir to Ru can be determined by inductively coupled plasma optical emission spectrometry (ICP-OES) as described herein. Preferably, the weight ratio of Ir to Ru relative to the total weight of the ruthenium-iridium oxide is no greater than 4.0, specifically no greater than 3.5.

[0030] The catalyst material according to the invention is in powder form; in other words, the catalyst material comprises particles, and more particularly, the material is composed of particles. As is known to those skilled in the art, powdered material is understood to be a material composed of particles that are not connected to each other. However, the particles can be in the form of loose or solid aggregates. In other words, it is not a monolithic material or a layer of material, but an aggregate of individual particles. These individual particles can also optionally consist of multiple particles—for example, sintered nanoparticles.

[0031] Powdered catalyst materials can have a variety of particle shapes. For example, the particles can be irregularly shaped, or they can have defined shapes; for example, they can be spherical, elliptical, plate-like, or rod-like. The particles can be porous and / or have cavities, or neither porous nor have cavities. They can have smooth or rough or structured outer surfaces. The particles can also be in aggregate form.

[0032] The average particle size d of the catalyst material50 Preferably less than 8 μm, particularly less than 6 μm, and especially preferably less than 5 μm. The particle size distribution can be determined by laser diffraction according to ISO standard 13320:2020. 50 and d 90 The value of can be calculated from the volume distribution curve. Here, for example, "d" 50 This means that 50% by volume of the particles have a diameter lower than this value. Preferably, the average particle size d of the catalyst material is... 50 The range is from 0.5µm to 8µm, preferably from 0.8µm to 6µm, and particularly preferably from 1.0µm to 5µm.

[0033] d of catalyst materials 90 The value is preferably less than 10 μm, particularly less than 8 μm, and particularly preferably less than 6 μm. Here, "d" 90 This means that 90% by volume of the particles have a diameter lower than this value. Preferably, the catalyst material has a diameter of d. 90 The value is in the range of 1.0µm to 10.0µm, preferably in the range of 1.5µm to 8.0µm, and particularly preferably in the range of 2.0µm to 6.0µm.

[0034] Particularly suitable are powdered catalyst materials, which contain d 90 With d 50 The ratio of particles is less than 2.5, particularly less than 2.0, and especially preferably less than 1.5.

[0035] Ruthenium-iridium oxide is unsupported. In other words, ruthenium-iridium oxide is not present on and / or attached to the support material. "Unsupported" material should be specifically understood as the opposite of "supported" material; "supported" catalyst material should be understood by those skilled in the art as a material in which the catalytically active substance is present, attached to, or located on the corresponding support material and is bonded or immobilized to the support material by physical or chemical bonds. The catalytically active substance may be bonded or immobilized to the support material, for example, by ionic or covalent bonds or by non-specific interactions such as van der Waals forces.

[0036] Surprisingly, it has been found that catalyst materials with the properties protected by the claims are also suitable for applications with low iridium content in electrodes used for oxygen evolution reactions, even without a support material. Using the catalyst material according to the invention, it is possible to achieve an iridium content of less than 60% by weight in the electrode relative to the total weight of the catalyst material and ionomer used in the corresponding electrode layer.

[0037] Commonly used support materials increase the electrical conductivity of the catalyst material and allow for the use of reduced amounts of iridium in electrode applications, particularly for pure iridium oxide. Surprisingly, in the context of this invention, it has been found that the iridium loading on the electrode can also be reduced using the catalyst material according to the invention, without requiring a support material.

[0038] Unsupported ruthenium-iridium oxide exhibits a powder conductivity of at least 30 S / cm. The powder conductivity of the catalyst material can be determined according to the powder conductivity measurement method described herein.

[0039] It has been found that minimum powder conductivity within this range ensures particularly high catalytic activity in catalyst materials. Catalyst materials with low powder conductivity result in high resistance in the catalyst layer of the electrode during water electrolysis, thus significantly reducing the efficiency of PEM electrolysis. In the anode of a water electrolysis cell, the catalyst-containing coating present on the membrane can, for example, be adjacent to a porous transport layer (PTL). The porous transport layer is made of titanium, for example, in which a thin oxide layer can be formed on the metal. If the catalyst material or catalyst layer has low conductivity (the conductivity of the catalyst layer is determined by the layer resistance), this can lead to an undesirable increase in contact resistance at the interface between the catalyst-containing coating and the porous transport layer, thus adversely affecting the efficiency of the water electrolysis cell.

[0040] Preferably, the unloaded ruthenium-iridium oxide has a powder conductivity of at least 40 S / cm, particularly at least 50 S / cm. Suitable ranges for powder conductivity are, for example, 30 S / cm to 190 S / cm, particularly 40 S / cm to 120 S / cm, and particularly preferably 50 S / cm to 110 S / cm.

[0041] Preferably, the unsupported ruthenium-iridium oxide exhibits at least one maximum value in the XRD spectrum (Cu Kα) in the range of 66° to 67° (2θ). The XRD spectrum can be obtained according to the method described below. Particularly preferred are catalyst materials that do not exhibit any signals originating from the metallic Ir phase (reference: 00-046-1044), pure IrO2 phase (reference: 00-043-1027), metallic Ru phase (reference: 00-006-0663), or pure RuO2 phase (reference: 00-043-1019) in the XRD spectrum. Phase identification is performed by comparing the X-ray diffraction pattern with a corresponding reference in the ICCD (International Data Center for Diffraction) database. Particularly preferred are the unsupported ruthenium-iridium oxides having a rutile structure.

[0042] Preferably, the unloaded ruthenium-iridium oxide has grains in the range of 1 nm to 10 nm, particularly in the range of 2 nm to 7 nm, and particularly preferably in the range of 2.5 nm to 5.1 nm, as determined by XRD reflection at 28° (2Θ) as described below.

[0043] Advantageously, the electrochemical activity of the powdered catalyst material, as described below, determined by the current density (in A / g(Ir)) relative to the RHE (reversible hydrogen electrode) at 1.5V, is in the range of 200 A / g(Ir) to 5,000 A / g(Ir), preferably in the range of 250 A / g(Ir) to 3,500 A / g(Ir).

[0044] Preferably, the unloaded ruthenium-iridium oxide has a molecular weight of at least 80 μm. 2 / g, especially at least 100m 2 / g, particularly preferably at least 120m 2 / g BET surface area. A large BET surface area means that more active sites of the catalyst material can be reached, thus increasing the activity, especially the mass activity.

[0045] In a preferred embodiment, the BET surface area is 80m². 2 / g to 350m 2 Within the range of / g, especially in the range of 100m 2 / g to 300m 2 Within the range of / g, particularly preferably within 120m 2 / g to 250m 2 Within the range of / g.

[0046] Template methods can be used to increase the BET surface area of ​​catalyst materials. Alternatively, pore-forming agents are used as additives in the synthesis, as described, for example, in CN 114164458 A. However, such additives must be removed again in additional process steps after synthesis. In the context of this invention, it is recognized that suitable unloaded ruthenium-iridium oxides can preferably be prepared without the use of such pore-forming agents. Examples of pore-forming additives are known to those skilled in the art; these examples include amino acids, carbonates, and carboxylates.

[0047] The preparation of powdered catalyst materials can be carried out, for example, by modifying the "Adams melting process," a method known to those skilled in the art. In the Adams melting process, aqueous metal precursor compounds are typically reacted with alkali metal nitrates to form metal-containing nitrate intermediates. These intermediates are then calcined to obtain the corresponding metal oxides.

[0048] The preparation of powdered catalyst materials can be carried out, for example, by a method comprising the following sequential steps:

[0049] (i) Provides a composition containing a solvent, an iridium precursor component, and a ruthenium precursor component.

[0050] (ii) Contact the composition with a salt containing an oxygen donor.

[0051] (iii) Heat treatment under oxidizing conditions.

[0052] The present invention also relates to a corresponding method for preparing powdered catalyst materials as described herein.

[0053] In this type of preparation method, the prepared ruthenium-iridium oxide contains only oxidized iridium and ruthenium; in other words, the prepared powdered catalyst material does not contain any metallic iridium and / or ruthenium. Such materials are resistant to dissolution in the surrounding electrolyte under the highly corrosive conditions of OER.

[0054] Steps (i) through (iii) are consecutive steps; these steps can be direct consecutive steps without intermediate steps, but the method may also include additional intermediate steps.

[0055] Preferably, during the preparation of the catalyst material, no conditions are applied that could reduce the iridium precursor component and / or ruthenium precursor component to metallic iridium or ruthenium.

[0056] The composition provided in step (i) contains a solvent. In this context, "solvent" means that the solvent contains at least one liquid substance in which the iridium precursor component and the ruthenium precursor component are soluble. Those skilled in the art will therefore recognize that the composition provided in step (i) contains the iridium precursor component and the ruthenium precursor component in dissolved form, and is therefore not a dispersion system. In other words, the composition typically does not contain any undissolved substances, i.e., it does not contain precipitates or deposits. At least one solvent may contain multiple chemical substances; that is, the solvent may also be a mixture of solvents.

[0057] The solvent may be selected from the group consisting of free water and organic solvents. The organic solvent may be selected from a variety of common organic solvents. Advantageously, the organic solvent is substantially volatile under the processing conditions of the composition. The organic solvent may be, for example, an alcohol, such as methanol or ethanol. Preferably, the solvent consists of at least 80% by volume, more preferably at least 90% by volume, and particularly at least 95% by volume of water. It may be advantageous for the solvent to consist entirely of water.

[0058] Advantageously, the composition comprises at least 30% by weight, particularly preferably at least 40% by weight, and very particularly preferably at least 50% by weight of solvent, in each case relative to the total weight of the solvent, the iridium precursor component, and the ruthenium precursor component. In a preferred embodiment, the composition comprises from 20% by weight to 99.5% by weight, preferably from 30% by weight to 95% by weight of solvent.

[0059] The composition also contains an iridium precursor component and a ruthenium precursor component. The iridium and ruthenium precursor components are one or more iridium compounds and one or more ruthenium compounds. Suitable precursor components are, for example, salts and acids of iridium and ruthenium. Typically, the oxidation states of iridium and / or ruthenium in the noble metal-containing precursor compounds are +III or +IV. Suitable iridium or ruthenium salts are the corresponding halide salts, chloride complexes, nitrates, or acetates.

[0060] Suitable iridium(III) or iridium(IV) compounds are known to those skilled in the art. For example, iridium(III) or iridium(IV) compounds are salts (e.g., iridium halides, such as IrCl3 or IrCl4; whose anion is a chloride complex IrCl6). 2- The composition contains iridium(IV) halides, particularly iridium(IV) chloride. (The salts may contain iridium nitrate or iridium acetate) or iridium-containing acids, such as H₂IrCl₆. In a preferred embodiment, the composition contains iridium(IV) halides, particularly iridium(IV) chloride.

[0061] The amount of iridium in the composition can vary widely and is determined by the intended composition of the catalyst material. "Amount of iridium" refers to the proportion of iridium in the composition; in other words, it does not refer to the total amount of the iridium precursor component. Particularly good results are obtained when the composition contains at least 0.5% by weight, particularly at least 1% by weight, preferably at least 5% by weight, and preferably at least 10% by weight of iridium. Preferably, the composition contains 0.5% to 60% by weight of iridium relative to the total weight of the composition comprising the solvent, the iridium precursor component, and the ruthenium precursor component. In one embodiment, the composition contains 1% to 50% by weight, preferably 5% to 40% by weight of iridium.

[0062] Suitable ruthenium(III) or ruthenium(IV) compounds are also known to those skilled in the art. For example, ruthenium(III) or ruthenium(IV) compounds are salts (e.g., ruthenium halides, such as RuCl3 or RuCl4; whose anion is a chloride complex RuCl6). 2- The composition contains ruthenium (ruthenium nitrate, ruthenium nitrite nitrate, or ruthenium acetate) or ruthenium-containing acids such as H₂RuCl₆. In a preferred embodiment, the composition contains ruthenium (IV) halide, particularly Ru(IV) chloride.

[0063] The amount of ruthenium in the composition can vary widely and is determined by the intended composition of the catalyst material. "Amount of ruthenium" refers to the proportion of ruthenium in the composition; in other words, it does not refer to the total amount of the ruthenium precursor component. Particularly good results are obtained when the composition contains at least 0.5% by weight, particularly at least 1% by weight, preferably at least 5% by weight, and preferably at least 10% by weight of ruthenium. Preferably, the composition contains 0.5% to 60% by weight of ruthenium relative to the total weight of the composition comprising the solvent, the iridium precursor component, and the ruthenium precursor component. In one embodiment, the composition contains 1% to 50% by weight, preferably 5% to 40% by weight of ruthenium.

[0064] The proportion of iridium and ruthenium in the composition is, for example, in the range of 1 wt% to 85 wt%, particularly in the range of 5 wt% to 75 wt%.

[0065] Preferably, the composition has a pH of ≤ 7, more preferably ≤ 5. For example, the composition has a pH of 1-7, more preferably 2-6 or 3-5.

[0066] Preferably, based on the ratio of iridium and ruthenium in the respective precursor components, the iridium precursor components and the ruthenium precursor components are present in a molar ratio of 2:1 to 1:10, particularly in a molar ratio of 1:1 to 1:9.

[0067] In step (i), a composition containing an iridium precursor component and a ruthenium precursor component is provided. The precursor components may be provided in one step, i.e., simultaneously dissolved in a solvent, but they may also be provided in successive steps. A composition may also be provided such that one of the precursor components is present in solution, and at least one additional precursor component is added in solution or undissolved form. When the precursor components are provided as separate compositions, these compositions may contain the same or different solvents or mixtures of solvents.

[0068] Advantageously, the composition is mixed during delivery, for example, by stirring.

[0069] Preferably, the composition does not contain any pore-forming additives. Examples of pore-forming components are known to those skilled in the art; in particular, polymeric components such as surfactants or polyols, as well as carbonates, should be mentioned. Advantageously, the entire process is carried out without the use of pore-forming additives.

[0070] In step (ii), the composition is contacted with a salt containing an oxygen donor. A salt containing an oxygen donor is understood to mean a salt capable of releasing oxygen in a chemical reaction. Such a salt can act as a source of reactive oxygen species, which act as oxidants.

[0071] The salt containing oxygen donors is preferably a salt containing nitrates or peroxides.

[0072] In the context of this application, nitrate is understood to be a salt of nitrate, i.e., a salt containing a nitrate anion (NO3). - These nitrates can be, for example, alkali metal nitrates, alkaline earth metal nitrates, nonmetal nitrates, or mixtures thereof; alkali metal nitrates are preferred. Suitable examples of nitrates are potassium nitrate, sodium nitrate, lithium nitrate, rubidium nitrate, cesium nitrate, barium nitrate, calcium nitrate, or ammonium nitrate.

[0073] In the context of this application, a peroxide-containing salt is understood to have a peroxide anion (O2). 2- Salts containing peroxides. These peroxide-containing salts can be, for example, alkali metal peroxides, alkaline earth metal peroxides, or mixtures thereof; alkali metal peroxides are preferred. Examples of suitable peroxide-containing salts are potassium peroxide, sodium peroxide, rubidium peroxide, cesium peroxide, barium peroxide, or calcium peroxide.

[0074] The oxygen donor salt is preferably added in a molar excess relative to the added molar fractions of the iridium and ruthenium precursor components, for example, in a ratio of at least 2:1, particularly at least 3:1, and particularly preferably at least 5:1. The excess may be between 2 molar equivalents and 100 molar equivalents, more preferably between 3 molar equivalents and 70 molar equivalents, and particularly preferably between 5 molar equivalents and 50 molar equivalents.

[0075] When the composition is contacted with a salt containing an oxygen donor, the salt can be in dissolved or solid form. When the salt containing the oxygen donor is used in dissolved form, the solvent used can be the same as the solvent used in the composition from step (i), but other solvents or solvent combinations may also be used. Preferably, the salt containing the oxygen donor is added in solid form.

[0076] A salt containing an oxygen donor can be added to the composition, or conversely, the composition can be added to a salt containing an oxygen donor.

[0077] Advantageously, the composition and the oxygen donor salt are mixed during contact, for example by stirring. It is advantageous to allow a sufficiently long time for mixing of the composition and the oxygen donor salt.

[0078] If the contact is carried out at elevated temperatures—for example, in the range of 20°C to 80°C—it may be advantageous.

[0079] Optionally, but preferably, a drying step may be performed after step (ii) and before step (iii), in which the solvent of the composition is completely or partially removed.

[0080] Drying can be carried out in the sense of almost completely removing the solvent, or in the sense of removing the solvent until the desired residual content is reached. If necessary, drying can be assisted by reduced pressure, and drying can be carried out, for example, at temperatures ranging from 20°C to 150°C.

[0081] The composition obtained after step (ii), or optionally the composition subjected to additional steps, is heat-treated under oxidizing conditions in step (iii). In this case, the precursor compound decomposes to form a mixed oxide according to the invention.

[0082] Preferably, the heat treatment is carried out in a closed process chamber—for example, in a furnace—where continuous atmosphere exchange occurs.

[0083] The heat treatment is preferably carried out in the presence of oxygen.

[0084] In a preferred embodiment, an oxygen-containing gas is supplied to the process chamber during heat treatment. The oxygen content in the gas is preferably at least 5% by volume, more preferably at least 10% by volume, and even more preferably at least 15% by volume. The gas may also contain other components—such as nitrogen, argon, carbon dioxide, or water. The gas may, for example, be air.

[0085] The air exchange rate during heat treatment is preferably at least 15 hours. -1 More preferably at least 30 hours -1 Specifically for at least 65 hours -1 Air exchange rate describes the ratio of the supply air volume flow rate to the volume of the process chamber, and is a measure of the rate at which the gas volume in the process chamber is exchanged.

[0086] The heat treatment is preferably carried out for a period of 0.5 h to 24 h, particularly for a period of 2 h to 18 h.

[0087] Heat treatment can be performed at temperatures below 1,000°C, below 800°C, below 600°C, below 400°C, or below 300°C. Heat treatment is preferably performed in the range of 250°C to 600°C, and particularly in the range of 350°C to 500°C. The above temperatures or temperature ranges should be understood as target temperatures achieved after the heating phase.

[0088] Therefore, at the start of heat treatment, the optionally dried composition from step (ii) is heated, typically from room temperature to a predefined target temperature. It has proven advantageous that heating during heat treatment is carried out at a heating rate of 1°C / min to 10°C / min, particularly 3°C / min to 5°C / min.

[0089] If a drying step is not performed before heat treatment, the solvent in the composition is removed first during the heating stage.

[0090] The target temperature is maintained, for example, for at least 1 hour, more preferably for at least 3 hours, during the heat treatment.

[0091] The method may also include additional steps, such as additional washing steps, additional filtration steps, and / or additional steps to reduce the size of the main obtained particles, such as grinding or crushing.

[0092] The present invention also relates to a catalyst composition containing

[0093] -The above-mentioned powdered catalyst material, and

[0094] - Ionomers, especially ionomers containing sulfonic acid groups (e.g., fluorinated ionomers containing sulfonic acid groups).

[0095] Suitable ionomers are known to those skilled in the art. For example, fluorinated ionomers containing sulfonic acid groups are copolymers comprising vinyl fluoride (e.g., tetrafluoroethylene) and fluorovinyl ethers containing sulfonic acid groups (e.g., perfluorovinyl ethers containing sulfonic acid groups) as monomers. An overview of these ionomers can be found, for example, in the following publication: A. Kusoglu and AZ Weber in Chem. Rev., 2017, 117, pp. 987-1, 104.

[0096] The composition is, for example, an ink containing a liquid medium in addition to a powdered catalyst material and an ionomer. The liquid medium contains, for example, one or more short-chain alcohols (e.g., methanol, ethanol, or n-propanol, or a mixture of at least two of these alcohols). The powdered catalyst material is present in the ink at a concentration of, for example, 5%-60% by weight, more preferably 10%-50% by weight, or 20%-40% by weight. The ionomer is present in the ink at a concentration of, for example, 5%-50% by weight, more preferably 10%-30% by weight.

[0097] Depending on the intended application of the composition, the composition may also contain other components, such as hydrophilic or hydrophobic additives.

[0098] To prepare catalyst layers, such as those for electrodes or catalyst-coated films, such catalyst inks can be applied to gas diffusion layers (GDLs), current collectors, films, transfer layers, or separators using commonly known deposition methods. These deposition methods include printing methods such as screen printing or inkjet printing, spraying methods, or gap coating techniques.

[0099] The composition can also be in solid form. For example, the anode of a water electrolysis battery can contain such a composition as a catalyst layer.

[0100] The present invention further relates to catalyst layers comprising the powdered catalyst material or the composition described herein—for example, as a catalyst layer in an electrode, particularly in an anode for water electrolysis.

[0101] The characteristics of the catalyst layer, such as thickness, catalyst loading, porosity, pore size distribution, average pore size and hydrophobicity, depend on whether it is applied to the anode or the cathode, and are known to those skilled in the art.

[0102] The oxygen evolution reaction (OER) occurs at the anode of the electrolyzer. Preferably, the water electrolysis is PEM (proton exchange membrane) water electrolysis, meaning the OER preferably occurs under acidic conditions. When used as an electrocatalyst for the OER, the catalyst material according to the invention allows for a low iridium loading while still ensuring a low overpotential and very good long-term stability in the electrolyzer. As used herein, the terms "iridium loading" or "catalyst loading" refer to the mass of iridium or catalyst material per unit area of ​​electrode layer.

[0103] The loading of the catalyst material, particularly the anode catalyst layer, i.e., the catalytically active oxygen evolution component, is preferably 1.5 mg / cm² per unit area of ​​the electrode. 2 Or even lower, for example, 1.25 mg / cm³ 2 Or smaller, 1.0 mg / cm³ 2 or smaller, 0.75 mg / cm³ 2 or smaller, 0.5 mg / cm 2 Or smaller, or 0.25 mg / cm³ 2 Or even less. A preferred loading rate can be 0.02 mg / cm³. 2 Up to 1.0 mg / cm 2 Within the range, particularly preferably within 0.05 mg / cm³. 2 Up to 0.5 mg / cm 2 Within the range. If the loading is less than 0.02 mg / cm³. 2 If the loading exceeds 1.0 mg / cm³, the durability may be insufficient, and if the loading exceeds 1.0 mg / cm³, the durability may be insufficient. 2 This amount may increase the cost of the catalyst material relative to or relative to its performance.

[0104] In a preferred embodiment, the catalyst layer has a sheet resistance of less than 15 kΩ / sq, particularly less than 12 kΩ / sq, and especially preferably less than 10 kΩ / sq. The sheet resistance of the catalyst layer can be determined according to the following method.

[0105] The catalyst layer thickness is advantageously at least 1 μm, typically at least 5 μm. The catalyst layer thickness can be up to 15 μm, typically up to 10 μm.

[0106] The present invention also relates to an electrochemical device comprising the aforementioned powdered catalyst material, the aforementioned catalyst composition, the aforementioned catalyst layer, or the aforementioned electrode. The present invention further relates to the use of the aforementioned powdered catalyst material, the aforementioned catalyst composition, or the aforementioned catalyst layer in an electrochemical device.

[0107] The electrochemical device can be an electrolyzer, particularly a water electrolyzer such as a PEM water electrolyzer, or a fuel cell such as a PEM fuel cell. As in any water electrolyzer, the PEM water electrolyzer of the present invention also comprises at least one half-cell containing an anode and at least one half-cell containing a cathode, in which the oxygen evolution reaction occurs and in which the hydrogen evolution reaction occurs. Preferably, the catalyst material is located in the half-cell in which the oxygen evolution occurs (i.e., on the anode side of the electrolyzer). When the catalyst material is present together with the catalyst on the carbon support in the PEM fuel cell, it can improve the corrosion stability of the carbon support. The PEM fuel cell can also be a regenerated PEM fuel cell.

[0108] The present invention further relates to the use of the above-mentioned powdered catalyst material as a catalyst for the oxygen evolution reaction in water electrolysis, and the use of the above-mentioned catalyst composition or the above-mentioned catalyst layer for the reaction.

[0109] In another aspect, the present invention relates to a method for preparing hydrogen by electrolysis using the above-described powdered catalyst material, the above-described catalyst composition, or the above-described catalyst layer.

[0110] The measurement methods used in this invention are specified below. If no test method is specified, appropriate ISO methods valid as of the filing date of this application are used to determine the parameters in question. If specific measurement conditions are not specified, measurements are performed at room temperature (298.15 K) and standard pressure (100 kPa).

[0111] Measurement methods

[0112] Powder conductivity

[0113] Conductivity was measured by four-point resistance measurements at room temperature. Powder conductivity measurements were performed using a device based on those described by Marinho et al. (Powder Technology 221 (2012) 351-358). This device consisted of a conductive fixed mold to which an insulating ceramic sleeve with an inner diameter of 1.2 cm was vertically mounted. The fixed mold sealed the bottom of the ceramic sleeve. After filling with 15 mL of sample material, a force of 2 kN was applied to the powder sample through a conductive movable mold using a hydraulic press; this force corresponded to a contact pressure of 17.7 MPa. The distance d between the fixed mold and the movable mold, corresponding to the height of the compressed powder bed, was determined using a digital dial indicator over the travel distance. To measure conductivity, an impedance spectroscopy method was used, with a 10 mV AC voltage applied using a voltage regulator (Gamry Reference 3000) in the frequency range of 100 Hz to 20,000 Hz. The conductivity of the powder was calculated from the resistance R (in ohms) measured at 1,000 Hz as follows:

[0114] Electrical conductivity = d / (R*A)

[0115] d: Distance between the two molds

[0116] R: Measured resistance

[0117] A: Electrode area

[0118] The resistance of the device itself (the fixed and movable molds in contact with each other without powder, and the cable contacts) is less than 10. -6 Ω·m, which does not affect powder measurement.

[0119] BET surface area

[0120] According to the BET theory (multi-point method, ISO 9277:2010), the BET surface area was determined using nitrogen as the adsorbate at 77 K. Measurements were performed using a NOVA 3000 (Quantachrome) operating according to the SMART method (adaptive feed rate adsorption method). Alumina (SARM catalog number 2001, 13.92m) from Quantachrome was used. 2 / g and SARM directory number 2004, 214.15m 2 / g) was used as a reference material. Initially, the sample was dried under vacuum in the measuring cell of the apparatus at 200°C for 10 hours. After cooling, the weight of the sample was determined. To degas the sample, the measuring cell was evacuated to a final pressure of 10 mbar. Data analysis was performed using NovaWin 11.04 software. Multipoint analysis was performed at 15 measurement points, and the resulting specific total surface area (BET) was... 总) with m 2 / g represents the value. The measuring cell was cooled to 77 K in a liquid nitrogen bath. For adsorption, a molecular cross-sectional area of ​​0.162 nm at 77 K was used. 2 The calculation is performed using N2 4.0.

[0121] precious metal content of catalyst materials

[0122] The contents of iridium and ruthenium were determined by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0123] Powder X-ray diffraction (P-XRD)

[0124] Powder X-ray diffraction (P-XRD) data were collected using a Bruker AXS D8 diffractometer: using a reflection geometry mode and Cu K0... α Radiation was measured in steps of 0.04° within the range of 10° < 20 < 130°. Peak phase refinement was modeled using reference data from the NIST660 LaB6 database. The reflection of the rutile phase was corrected using a series of reflections with independent sample broadening to obtain the grain size along the crystallographic plane. For the material of this invention, reflections at 28° (2θ), corresponding to the (110) lattice plane, were used.

[0125] Particle size distribution (d 50 , d 90 ) by laser diffraction

[0126] To determine the particle size distribution, laser diffraction was performed according to ISO standard 13320:2020. Measurements were conducted using a Partica LA-950V2 (HORIBA) laser granulator equipped with two laser diodes at wavelengths of 650 nm (5 mW) and 405 nm (3 mW) and a wet dispersion unit (Aqua Flow). Measurements were performed at an ambient temperature of 23°C. A mixture of isopropanol and deionized water (1:1) was used as the measurement medium. The mixture was degassed in the dispersion unit using the built-in stirrer at 3,500 rpm and ultrasonically treated with maximum power for 10 seconds. The sample was pre-dispersed using an ultrasonic probe for 30 seconds. The sample was added dropwise to the dispersion unit until the transmittance of the laser beam used decreased by 3%–7%. Volume-based values ​​(d) were determined using LA-950 software. 50 d 90 Fraunhofer's theory is used for particles larger than 10 μm, while Mie's theory is used for particles smaller than 10 μm.

[0127] Layer resistance

[0128] The sheet resistance R□ was determined at room temperature using a 4-point resistance meter (SD-810, Nagy Messsysteme GmbH). The sheet to be measured (10cm × 30cm) was placed on a non-conductive substrate. Measurement was performed by bringing the sheet into contact with a probe (SQKR-25, Nagy Messsysteme GmbH) with four conductive measuring tips (rhodium-plated and spring-loaded support contacts) spaced 2.5mm apart.

[0129] Electrochemical measurements using a rotating disk electrode (RDE)

[0130] The oxygen reduction activity of the catalyst material was determined using measurements with a rotating disk electrode (RDE). For this purpose, the onset potential of oxygen evolution (expressed in V) and the current density (expressed in mA / cm²) at 1.5 V relative to the RHE (reversible hydrogen electrode) were measured. 2 (Represented). The catalyst sample was dispersed in Nafion aqueous solution (1 wt% of 5 wt% alcohol solution (Aldrich)) and immobilized on a glassy carbon electrode. Cyclic voltammetry was recorded at 60 °C in sulfuric acid (0.5 mol / L). The counter electrode was Pt, the reference electrode was a calomel electrode (SI-Analytics), and the sampling rate was 10 mV / s. The fifth scan of the voltammetry curve running between 1.0 V and 1.8 V was used to generate quasi-steady-state conditions.

[0131] Electrochemical Measurements in CCM

[0132] To determine the electrochemical activity of the catalyst material in the coated membrane (catalyst-coated membrane, CCM), measurements were taken at a depth of 5 cm. 2 Efficiency of a single cell with active area. The cell consists of carbon plates with parallel straight-channel flow fields on the anode and cathode sides. A 1 mm thick platinum-coated titanium sintered material is used as a porous transport layer on the anode side. Carbon paper (Toray TGP-H-120) is used as a gas diffusion layer on the cathode side. Deionized water with a conductivity of less than 1 μS / cm is circulated on the anode side.

[0133] In the first series of experiments, by using 0.2 A / cm in each case... 2 and 1A / cm 2 Conditioning was performed by maintaining the current density for 30 minutes and the voltage at 1.65V for 2.5 hours.

[0134] Then, at 60℃ and 80℃, the current density was increased from a small value to a large value (A / cm). 2 To plot the current-voltage characteristic curve (polarization curve), in each case at 2.0 A / cm 2The holding time at different current points was 5 minutes.

[0135] The measurement curve was obtained using resistance calibration at 1.45V. 无iR The current density was measured at the voltage point. The current density was normalized to the Ir loading [mg / cm³]. 2 Then, the mass activity is calculated.

[0136] Degradation was determined using accelerated testing methods.

[0137] To determine the stability of the catalyst material, accelerated degradation tests were performed using a setup for measuring electrochemical activity. For this purpose, the active area was reduced to 1 cm². 2 To simulate accelerated aging, the following procedure is used:

[0138] Conditioning was performed as described for determining electrochemical activity. Then, as described above, polarization curves were plotted at 80°C, up to a maximum of 6 A / cm. 2 The current density point was determined. This curve defines the initial state (early lifetime, BOL). Subsequently, a potential window from 1.4V to 1.9V was scanned at 500mV / s using a sawtooth pattern for 10,000 cycles. The polarization curve was then recorded again at 80°C, up to a maximum of 6A / cm. 2 The current density point is determined. This procedure is repeated twice more to obtain a total of 30,000 stress cycles, plus additional polarization curves after 20,000 and 30,000 cycles. The polarization curve after 30,000 cycles will be labeled EOL (End of Life).

[0139] The invention will be explained in more detail with reference to the following embodiments.

[0140] IE1

[0141] To prepare 50 g of the mixed oxide, 64.59 g of Ir chloride (IrCl4*H2O - 52.89% Ir; 178 mmol) was dissolved in 50 mL of water (mineralized). Then, 32.64 g of Ru chloride solution (RuCl3 solution 23.6% Ru; 76 mmol) was added, and the solution was stirred at room temperature. Subsequently, 20 molar equivalents of sodium nitrate in solid form (432.2 g) were added, and the mixture was stirred at an elevated temperature until completely dissolved. The mixture was dried in a porcelain bowl, and then transferred to a furnace.

[0142] The furnace was heated from room temperature to the target temperature of 370°C at a heating rate of 5°C / min. The temperature was then maintained for 6 hours with an air flow rate of 400 L / min.

[0143] After cooling to room temperature, the black solid was washed with 50L of demineralized water through a filter funnel, and finally dried overnight at 120°C in a vacuum drying oven.

[0144] IE2

[0145] To prepare 50 g of the mixed oxide, 57.99 g of Ir chloride (IrCl4*H2O - 52.9% Ir; 160 mmol) was dissolved in 80 mL of demineralized water. Then, 45.64 g of Ru chloride solution (RuCl3 solution 23.6% Ru; 107 mmol) was added, and the solution was stirred at room temperature. Subsequently, 20 molar equivalents of sodium nitrate in solid form (452 ​​g) were added, and the mixture was stirred at an elevated temperature until completely dissolved. The remaining preparation process was similar to IE1.

[0146] IE3

[0147] To prepare 50 g of the mixed oxide, 50.82 g of Ir chloride (IrCl4*H2O - 52.9% Ir; 140 mmol) was dissolved in 50 mL of demineralized water. Then, 59.91 g of Ru chloride solution (RuCl3 solution 23.6% Ru; 140 mmol) was added, and the solution was stirred at room temperature. Subsequently, 20 molar equivalents of sodium nitrate in solid form (476 g) were added, and the mixture was stirred at an elevated temperature until completely dissolved. The remaining preparation process was similar to that of IE1.

[0148] IE4

[0149] To prepare 50 g of the mixed oxide, 42.84 g of Ir chloride (IrCl4*H2O - 52.9% Ir; 118 mmol) was dissolved in 60 mL of demineralized water. Then, 75.78 g of Ru chloride solution (RuCl3 solution 23.6% Ru; 177 mmol) was added, and the solution was stirred at room temperature. Subsequently, 20 molar equivalents of sodium nitrate in solid form (502 g) were added, and the mixture was stirred at an elevated temperature until completely dissolved. The remaining preparation process was similar to IE1.

[0150] IE5

[0151] To prepare 50 g of the mixed oxide, 33.96 g of Ir chloride (IrCl4*H2O - 52.9% Ir; 94 mmol) was dissolved in 50 mL of demineralized water. Then, 93.39 g of Ru chloride solution (RuCl3 solution 23.6% Ru; 218 mmol) was added, and the solution was stirred at room temperature. Subsequently, 20 molar equivalents of sodium nitrate in solid form (530 g) were added, and the mixture was stirred at an elevated temperature until completely dissolved. The remaining preparation process was similar to IE1.

[0152] CE1

[0153] To prepare 50 g of the mixed oxide, 70.52 g of Ir chloride (IrCl4*H2O - 52.9% Ir; 194 mmol) was dissolved in 60 mL of demineralized water. Then, 20.79 g of Ru chloride solution (RuCl3 solution 23.6% Ru; 49 mmol) was added, and the solution was stirred at room temperature. Subsequently, 20 molar equivalents of sodium nitrate in solid form (413 g) were added, and the mixture was stirred at an elevated temperature until completely dissolved. The remaining preparation process was similar to IE1.

[0154] CE2

[0155] To prepare 50 g of iridium oxide, 79.84 g of Ir chloride (IrCl4*H2O - 52.9% Ir; 224 mmol) was dissolved in 60 mL of demineralized water. Then, 20 molar equivalents of sodium nitrate in solid form (380 g) were added, and the mixture was stirred at an elevated temperature until completely dissolved. The remaining preparation process was similar to that of IE1.

[0156] Preparation of coated membranes (CCM)

[0157] To prepare the coated membrane (catalyst-coated membrane, CCM), the catalyst material was dispersed in an ink with water (ultrapure), a solvent (a mixture of 1-propanol and ethanol, 70-30% by weight), and an ionomer solution (Nafion D2020, Chemours), and applied to a membrane containing a fluorinated polymer with sulfonic acid groups to form the anode. The coating was applied using a decal transfer method, transferring a PTFE transfer membrane to a polymer membrane (Nafion 212, 50µm, Chemours). The catalyst material discussed was used on the anode side; the carbon-supported Pt catalyst and the fluorinated ionomer were used on the cathode side.

[0158] The PTFE membrane was coated using a Mayer rod coater. A 5cm section was punched out from the dried layer. 2The sized decals were pressed onto the polymer membrane under pressure (2.5 MPa) and temperature (155 °C). The loading was determined by weighing the PTFE before and after the transfer process.

[0159] Table 1 summarizes the characterization results of the catalyst materials in terms of their composition, powder conductivity, particle size, BET surface area, and RDE measured activity. All catalysts according to the present invention have shown high activity in half-cell measurements.

[0160] Table 1: Characterization of catalyst materials

[0161]

[0162] Table 2 summarizes the characterization results of the coated films in terms of composition, layer resistance, and electrochemical activity. In each case, the catalyst material loading was 1 mg / cm³. 2 .

[0163] Table 2: Characterization of the coated film

[0164]

[0165] Figure 1 Measurement curves for determining the activity of the catalyst material are shown (cell voltage as a function of current density). In parallel, the high-frequency resistance is determined by electrochemical impedance spectroscopy measurements at the aforementioned current points, allowing for correction of the cell resistance (without iR, dashed line).

[0166] In both the measurement curve (solid line) and the resistance correction curve (dashed line), all materials according to the present invention exhibit increased activity compared to the comparative example (identifiable by a downward shift in the polarization curve). Furthermore, data show that the reduction in iridium content in the electrode results in a lower polarization rate below 0.1 A / cm². 2 Improved activity is visible within the current density range. In particular, comparison with CE1 shows that high powder conductivity is insufficient to produce CCM with high activity.

[0167] Figure 2 The polarization curves of different catalyst materials as the number of cycles increases are shown. The figure compares the results for IE1, IE3, and IE5 with those for CE2. The catalyst material according to the invention exhibits the same stability as the highly stable but significantly less active material from CE2. This can be seen from the almost constant curve profiles after 10,000, 20,000, and 30,000 (=EOL) cycles compared to the corresponding initial curve (BOL).

[0168] The results shown indicate that the catalyst material according to the invention can be used to manufacture an anode that exhibits very high electrochemical activity and high corrosion stability despite a low iridium loading per unit area.

Claims

1. A powdered catalyst material, said powdered catalyst material comprising unsupported ruthenium-iridium oxide, The weight ratio of iridium (Ir) to ruthenium (Ru) relative to the total weight of the ruthenium-iridium oxide is no greater than 4.

5. Its features The unloaded ruthenium-iridium oxide exhibits a powder conductivity of at least 30 S / cm.

2. The powdered catalyst material according to claim 1, wherein the proportion of iridium relative to the total weight of the ruthenium-iridium oxide is less than 70% by weight.

3. The powdered catalyst material according to claim 1 or 2, wherein the average particle size d 50 Less than 8μm.

4. The powdered catalyst material according to any one of the preceding claims, wherein the particles of the catalyst material have a d 90 With d 50 The particle size ratio is less than 2.

5.

5. The powdered catalyst material according to any one of the preceding claims, wherein the unloaded ruthenium-iridium oxide has at least one maximum value in the XRD spectrum (Cu Kα) in the range of 66° to 67° (2Θ).

6. The powdered catalyst material according to any one of the preceding claims, wherein the unloaded ruthenium-iridium oxide has grain size in the range of 1 nm to 10 nm as determined by XRD reflection at 28° (2Θ).

7. The powdered catalyst material according to any one of the preceding claims, wherein the unsupported ruthenium-iridium oxide has a molecular weight of at least 80 μm. 2 / g BET surface area.

8. The powdered catalyst material according to any one of the preceding claims, wherein the electrochemical activity, determined as a current density in A / g(Ir) relative to RHE at 1.5V, is in the range of 200 A / g(Ir) to 5,000 A / g(Ir).

9. A method for preparing a powdered catalyst material according to any one of claims 1 to 8, the method comprising the following sequential steps: (i) Provides a composition containing a solvent, an iridium precursor component, and a ruthenium precursor component. (ii) Contact the composition with a salt containing an oxygen donor. (iii) Heat treatment under oxidizing conditions.

10. The method of claim 9, wherein the composition does not contain any pore-forming additives.

11. A composition comprising: - Powdered catalyst material according to any one of claims 1 to 8, - Ionic polymers, especially those containing sulfonic acid groups.

12. A catalyst layer comprising a powdered catalyst material according to any one of claims 1 to 8.

13. The catalyst layer according to claim 12, wherein the catalyst layer exhibits a sheet resistance of less than 15 kΩ / sq.

14. An electrochemical device comprising a powdered catalyst material according to any one of claims 1 to 8.

15. A method for producing hydrogen by electrolysis of a powdered catalyst material according to any one of claims 1 to 8.

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