Catalyst materials

Abstract

An oxygen-evolving catalyst material having a pyrochlore-type structure is provided, wherein (i) calcium and / or sodium are the A-site elements of the pyrochlore-type structure, (ii) iridium and / or ruthenium are the first B-site elements of the pyrochlore-type structure, (iii) niobium and / or tantalum are the second B-site elements of the pyrochlore-type structure, and (iv) the molar ratio of the A-site element to the first and second B-site elements is in the range of 0.8:1 to 1:1.

Description

[Technical Field] 【0001】 The present invention relates to a catalyst material suitable for use as a catalyst for oxygen evolution reaction (OER) in, for example, a water electrolyzer or fuel cell, and an improved process for producing the same. [Background technology] 【0002】 Electrolysis of water to produce high-purity hydrogen and oxygen can be performed in both alkaline and acidic systems. These electrolytic devices using solid proton-conducting polymer electrolyte membranes or proton exchange membranes (PEMs) are known as proton exchange membrane water electrolyzers (PEMWEs). These electrolytic devices utilizing solid anion-conducting polymer electrolyte membranes or anion exchange membranes (AEMs) are known as anion exchange membrane water electrolyzers (AEMWEs). 【0003】 Ion-conducting membranes such as PEMs and AEMs are also used in fuel cells. In a proton exchange membrane fuel cell (PEMFC), the membrane is proton-conducting, and protons generated at the anode are transported across the membrane to the cathode, where they combine with oxygen to form water. 【0004】 Catalyst-coated membranes (CCMs) can be used in electrochemical devices such as electrolytic devices and fuel cells. Such CCMs include ion-conducting membranes such as PEMs or AEMs, where an anode catalyst layer and / or a cathode catalyst layer are applied to one surface of the membrane, or where the anode and cathode catalyst layers are applied to both surfaces. 【0005】 In water electrolysis applications, hydrogen evolution reaction (HER) catalysts, such as platinum-containing HER catalysts like platinum on a carbon support, are used in the cathode catalyst layer. Oxygen evolution reaction (OER) catalysts are used in the anode catalyst layer of the electrolysis device. Catalysts containing iridium and / or ruthenium are well known for their excellent OER catalyst properties and are preferred materials for oxygen evolution reactions on the anode side of water electrolysis devices. 【0006】 In fuel cell applications, oxygen reduction reaction (ORR) catalysts are used in the cathode catalyst layer, and hydrogen oxidation reaction (HOR) catalysts are used in the anode catalyst layer. In PEMFC applications, suitable cathode and anode catalyst materials include platinum group metals (PGMs) or alloys of PGMs with one or more other metals, such as platinum, or alloys of platinum with one or more other metals. Iridium and / or ruthenium-containing OER catalysts may also be incorporated into the anode and / or cathode of fuel cells to improve the reversal resistance and stability of the battery during start / stop cycles. 【0007】 Materials with a pyrochlore-type structure are isomorphic to mineral pyrochlores and typically possess a cubic phase and space group Fd-3m. Such materials have A-site cations, B-site cations, and oxide anions. In some cases, hydroxyl anions and / or water molecules are known to occupy sites in the pyrochlore-type structure. Some of the A-sites may be empty. 【0008】 Iridium and / or ruthenium-containing materials with pyrochlore structures are promising candidates as OER catalysts for use in electrolytic devices and fuel cell applications. For example, Walton RI et al., Structural variety in iridate oxides and hydroxides from hydrothermal synthesis, Chem. Sci., 2011, 2, 1573, describes that iridium salts of the formula (Na,Ca)2Ir2O6·xH2O with pyrochlore structures can be formed via hydrothermal processes. 【0009】 While such pyrochlore materials offer high OER catalytic activity, they can suffer from problems such as the loss of iridium or ruthenium from their structure due to dissolution during electrochemical cycles, for example. 【0010】 The demand for hydrogen-based solutions is expected to increase dramatically in response to net-zero policies. This presents challenges to technologies utilizing iridium catalysts, given the relative scarcity of this element. Therefore, more effective catalysts that offer higher activity per unit mass of iridium are also needed. 【0011】 There is a need to develop iridium and ruthenium-based OER catalysts that have improved performance, for example, higher stability and / or increased catalytic activity with lower iridium metal loadings. [Overview of the Initiative] 【0012】 The inventors have surprisingly found that by incorporating selected elements into iridium and / or ruthenium pyrochlore materials, an oxygen evolution catalyst is provided that exhibits higher activity and improved stability than conventional iridium oxide electrode catalysts. 【0013】 Therefore, in a first aspect of the present invention, an oxygen evolution catalyst material having a pyrochlore-type structure, (i) Calcium and / or sodium as the A-site element of the pyrochlore-type structure, (ii) Iridium and / or ruthenium as the first B-site element of the pyrochlore-type structure, (iii) Having niobium and / or tantalum as the second B-site element of the pyrochlore-type structure, (iv) An oxygen generation catalyst material is provided, in which the molar ratio of the A-site element: the first and second B-site elements is within the range of 0.8:1 to 1:1. 【0014】 Preferably, such a material has a composition represented by the formula: (AA’) a (BB’)2O b X c (where A is Ca, A’ is Na, B is Ir and / or Ru, B’ is Nb and / or Ta, X is O, OH, H2O, or a combination thereof, 1.6 ≦ a ≦ 2.0, 5 ≦ b ≦ 7, and 0 ≦ c ≦ 2). 【0015】 In a second aspect of the present invention, a composition according to formula (1): (Ca 1-x Na x )2(Ir 1-y B’ y )2O 7-z .(H2O) n Formula (1) (where 0 ≦ x ≦ 0.5, 0 < y ≦ 0.6, 0 ≦ z ≦ 1, 0 ≦ n ≦ 2, and M is Nb, Ta, or a combination thereof) is provided with an oxygen generation catalyst material. 【0016】 The oxygen generation catalyst material can advantageously be blended with an ion-conductive polymer to form an ink. Therefore, in a third aspect of the present invention, an ink containing the oxygen generation catalyst material according to the first or second aspect and an ion-conductive polymer is provided. 【0017】 Such inks can be suitably applied to a substrate to produce a catalyst layer. Accordingly, a fourth aspect of the present invention provides a catalyst layer comprising an oxygen-evolving catalyst material according to the first or second aspect and an ion-conducting polymer. Preferably, the catalyst layer is an anode catalyst layer for a water electrolyzer. The oxygen-evolving catalyst material may be incorporated into a fuel cell catalyst layer, particularly a fuel cell anode catalyst layer, in combination with a hydrogen oxidation reaction (HOR) catalyst such as a platinum catalyst to improve battery reversal resistance. 【0018】 Such catalyst materials and catalyst layers can be used to form a catalyst coating film. Accordingly, a fifth aspect of the present invention provides a catalyst coating film comprising an oxygen-evolving catalyst material according to the first or second aspect, or a catalyst layer according to the fourth aspect. Preferably, the catalyst coating film constitutes a proton exchange membrane (PEM) or an anion exchange membrane (AEM). The oxygen-evolving catalyst material is preferably provided in an anode catalyst layer applied to the surface of the film. Such a CCM is suitable for use in water electrolyzers or fuel cells. 【0019】 The oxygen evolution catalyst material of the first or second embodiment can be advantageously produced by a hydrothermal process. Accordingly, a sixth embodiment of the present invention provides a method for producing the oxygen evolution catalyst material of the first or second embodiment, (i) A step of providing an aqueous mixture comprising at least one iridium and / or iridium source, at least one calcium and / or sodium source, at least one niobium and / or tantalum source, and a base, (ii) A step of treating an aqueous mixture under hydrothermal conditions, (iii) A step of isolating the oxygen evolution catalyst material, A method is provided that includes this. [Brief explanation of the drawing] 【0020】 [Figure 1]The results of electrochemical tests on the catalyst material and comparative material formed in Example 1 are shown. [Figure 2] The test results regarding iridium dissolution during electrochemical testing are shown. [Modes for carrying out the invention] 【0021】 The following describes preferred and / or optional features of the present invention. Any preferred and / or optional feature of any embodiment may be used individually or in combination with any other preferred and / or optional feature of any embodiment of the present invention, unless otherwise required by the context. 【0022】 The present invention provides an oxygen evolution reaction (OER) catalyst material having a pyrochlore-type structure, wherein (i) calcium and / or sodium as the A-site element of the pyrochlore-type structure, (ii) iridium and / or ruthenium as the first B-site element of the pyrochlore-type structure, and (iii) niobium and / or tantalum as the second B-site element of the pyrochlore-type structure, and the molar ratio of the A-site element to the first and second B-site elements is in the range of 0.8:1 to 1:1. Typically, the catalyst material has a crystalline structure having a space group Fd-3m. 【0023】 Preferably, such a material has the general formula: (AA') a (BB')2O b X c It can be represented by (wherein A is Ca, A' is Na, B is Ir and / or Ru, B' is Nb and / or Ta, X is O, OH, H2O, or a combination thereof, with 1.6 ≤ a ≤ 2.0, 5 ≤ b ≤ 7, and 0 ≤ c ≤ 2). In such materials, one or more A sites may remain empty, and the stoichiometric amount of the A site element in the crystal structure may decrease. Furthermore, in some examples, water molecules can occupy some empty sites, providing a hydrated or partially hydrated metal oxide material. 【0024】 The molar ratio of A:A' is preferably in the range of 2:0 to 1:1. The A-site cation is preferably Ca. It is preferably 1.7 ≤ a ≤ 2.0, 1.8 ≤ a ≤ 2.0, 1.9 ≤ a ≤ 2.0, or a is 2. 【0025】 The molar ratio of B:B' is preferably in the range of 0.95:0.05 to 0.40:0.60, for example, 0.9:0.1 to 0.5:0.5. B is preferably Ir, or a mixture of Ir and Ru. B' is preferably Nb, or a mixture of Nb and Ta. 【0026】 It may be preferable that 6 ≤ b ≤ 7. It may also be preferable that 0 ≤ c ≤ 1.8, 0 ≤ c ≤ 1.6, 0 ≤ c ≤ 1.4, 0 ≤ c ≤ 1.2, or 0 ≤ z ≤ 1.0. It may also be preferable that X is H2O. 【0027】 A person skilled in the art will understand that when calculating molar ratios involving more than one element, the ratio is between the totals of the elements involved. For example, a person skilled in the art will understand that the molar ratio of an A-site element to the first and second B-site elements is the ratio of (moles of Ca + moles of Na) : (moles of Ir + moles of Ru + moles of Nb + moles of Ta). 【0028】 The catalyst material may preferably have the composition shown in Formula 1. 【0029】 In equation 1, 0 ≤ × ≤ 0.5. It may be preferable that x = 0 ≤ x ≤ 0.45, 0 ≤ x ≤ 0.40, 0 ≤ x ≤ 0.35, 0 ≤ x ≤ 0.30, 0 ≤ x ≤ 0.25, 0 ≤ x ≤ 0.20, 0 ≤ x ≤ 0.15, 0 ≤ x ≤ 0.10, 0 ≤ x ≤ 0.05, or x = 0. 【0030】 In Formula 1, 0 < y ≤ 0.6. It may be preferable that 0 < y ≤ 0.5, 0 < y ≤ 0.4, 0 < y ≤ 0.3, 0 < y ≤ 0.2, 0 < y ≤ 0.1, or 0 < y ≤ 0.05. It may be preferable that 0.1 ≤ y ≤ 0.6, 0.1 ≤ y ≤ 0.5, 0.1 ≤ y ≤ 0.4, or 0.1 ≤ y ≤ 0.3. 【0031】 In Formula 1, 0 ≤ n ≤ 2. It may be preferable that 0 ≤ n ≤ 1.5, 0 ≤ n ≤ 1.0, 0 ≤ n ≤ 0.5, or n = 0. 【0032】 In Formula 1, B is Ir, Ru, or a combination thereof. It may be preferable that B is Ir or Ru. It may be preferable that B is a mixture of Ir and Ru. It may be preferable that B is Ir or a mixture of Ir and Ru. 【0033】 In Formula 1, B' is Nb, Ta, or a combination thereof. It may be preferable that B' is Nb or Ta. The oxygen generation catalyst material preferably has the general formula (Ca 1-x Na x )2(B 1-y1-y2 Nb y1 Ta y2 )2O 7-z .(H2O) z (where 0 < y1 + y2 ≤ 0.6). 【0034】 Preferably, the catalyst material is in particulate form. 【0035】 Preferably, the oxygen evolution catalyst material is in particulate form having an average particle size (Dv50) of less than 10 μm, preferably less than 5 μm, for example, in the range of 0.5 to 10 μm, or in the range of 1 to 5 μm. Unless otherwise specified herein, the term Dv50 as used herein refers to the median particle size in the volume-weighted distribution. Dv50 can be determined by laser diffraction. For example, Dv50 can be determined by suspending the particles in water and analyzing the particle size distribution by laser diffraction using, for example, a Malvern Mastersizer 3000. 【0036】 The inventors have found that catalyst materials can be prepared using a hydrothermal method. This method includes the step of providing an aqueous mixture comprising at least one iridium and / or ruthenium source, at least one calcium and / or sodium source, at least one niobium and / or tantalum source, and a base. 【0037】 Typically, at least one iridium and / or ruthenium source is a salt, such as an inorganic salt. Typically, at least one iridium and / or ruthenium source has iridium or ruthenium in a +3 oxidation state, such as iridium(III) salts and / or ruthenium(III) salts. At least one iridium and / or ruthenium source may be, for example, IrCl3, RuCl3, H2IrCl6, Ru(NO)(NO3)3, or a combination thereof. 【0038】 Typically, at least one calcium source is a salt, such as an inorganic calcium salt, or an oxide / peroxide, such as CaO2, Ca(NO3)2, or Ca(OH)2. Typically, at least one optional sodium source is a salt, such as an inorganic salt. At least one sodium source may be, for example, NaBrO3, NaOH, or Na2O2. 【0039】 Typically, at least one niobium and / or tantalum source is a salt, such as an inorganic salt, or an oxide / peroxide. Typically, at least one niobium and / or tantalum source has a metal in the +5 oxidation state. At least one M source may be, for example, Nb2O5, Ta2O5, NbCl5, and / or TaCl5. 【0040】 Those skilled in the art will understand that the elemental sources described herein may be in the form of hydrates. 【0041】 The aqueous mixture contains a metal hydroxide, such as a base like sodium hydroxide or potassium hydroxide. Potassium hydroxide is particularly preferred. The aqueous mixture may preferably have a pH of 12 or higher, 13 or higher, or 14 or higher. 【0042】 The aqueous mixture may contain an oxidizing agent. The oxidizing agent may be one of the elements necessary for the desired composition, such as iridium, ruthenium, calcium, sodium, niobium, or a tantalum source. For example, the oxidizing agent may be calcium peroxide, sodium peroxide, sodium bromate, or a combination thereof. Alternatively, the oxidizing agent may be a separate reactant, such as hydrogen peroxide. 【0043】 Aqueous mixtures are typically formed in a container suitable for hydrothermal treatment, such as an autoclave or other pressure vessel. 【0044】 Next, the aqueous mixture is treated under hydrothermal conditions. In the context of the present invention, treatment under hydrothermal conditions is understood as treatment of the aqueous mixture at high temperatures and a vapor pressure exceeding 1 bar. The aqueous mixture may preferably be treated under hydrothermal conditions at temperatures exceeding 200°C, for example in the range of 200 to 300°C, for example 225 to 275°C. The aqueous mixture may also preferably be treated under hydrothermal conditions for a period of at least 6 hours, or at least 12 hours, for example in the range of 12 to 48 hours. 【0045】 Furthermore, the hydrothermal treatment may preferably be carried out at a vapor pressure of 1 bar to 40 bar, particularly 1 bar to 10 bar. The aqueous mixture is typically reacted in a sealed or pressure vessel. The reaction is preferably carried out in an inert or protective gas atmosphere. Examples of suitable inert gases include nitrogen, argon, or mixtures thereof. 【0046】 After hydrothermal treatment, the oxygen-evolving catalyst material is isolated. Typically, the reaction mixture after hydrothermal treatment is filtered. Optionally, the formed catalyst material is washed. Preferably, the formed catalyst material is washed with water (such as deionized water). Then, typically, the catalyst material is dried by heating to a temperature in the range of 60-100°C. The product may be pulverized to remove large aggregates. For example, by using a mortar and pestle or by milling. 【0047】 The catalyst material can be used as an oxygen evolution reaction catalyst in the anode of water electrolysis devices, particularly PEMWEs. 【0048】 Catalyst materials can also be used in fuel cells such as PEMFCs, particularly in fuel cell anodes for the purpose of battery reversal resistance. 【0049】 Oxygen-evolving catalyst materials can typically be formulated as inks by dissolving or dispersing the catalyst material in a mixture of an ion-conducting polymer and water, or in a mixture of an ion-conducting polymer, water, and an organic solvent such as ethanol or propane-1-ol. Suitable ion-conducting polymers are known to those skilled in the art and include fluorinated ion-conducting polymers such as perfluorinated sulfonic acid (PFSA) ionomers, partially fluorinated sulfonated or phosphononated polymers, non-fluorinated hydrocarbon sulfonated or phosphononated polymers, or mixtures thereof. 【0050】 The ink may be used to form a catalyst layer. Such a layer preferably comprises a catalyst material and an ion-conducting polymer (a suitable ion-conducting polymer including those mentioned above with respect to the ink). The catalyst layer may also contain additional components such as additional catalysts and radical scavengers, as is known to those skilled in the art. 【0051】 The catalyst layer may form a component of a catalyst coating (CCM) that includes a film having a catalyst layer on its first surface and optionally a second catalyst layer on its second surface. Preferably, the film is a proton exchange film (PEM) or an anion exchange film (AEM). The film in the CCM may include additional components (e.g., recombinant catalysts, radical scavengers, reinforcing materials, multiple layers) as is known to those skilled in the art. 【0052】 Typically, CCMs are intended for use in water electrolysis devices such as PEM water electrolyzers. In such cases, a CCM typically comprises (i) an ion-conducting membrane having a first surface and a second surface; (ii) an anode layer on the first surface of the membrane, comprising the oxygen evolution catalyst material and ion-conducting polymer described herein; and (iii) a cathode catalyst layer on the first surface of the membrane, comprising a platinum-containing HER catalyst (e.g., a hydrogen evolution reaction (HER) catalyst such as platinum-supported carbon). 【0053】 CCM may also be suitable for use in fuel cells such as PEM fuel cells. In such cases, the CCM typically comprises (i) an ion-conducting film having a first surface and a second surface; (ii) an anode layer on the first surface of the film, comprising an oxygen evolution catalyst material described herein, a hydrogen oxidation reaction (HOR) catalyst, such as a platinum-containing hydrogen oxidation reaction (HOR) catalyst (e.g., platinum-supported carbon), and an ion-conducting polymer; and (iii) a cathode catalyst layer on the second surface of the film, comprising an oxygen reduction reaction (ORR) catalyst, such as a platinum-containing ORR catalyst (e.g., platinum-supported carbon). 【0054】 The present invention will now be described with reference to the following examples, which are provided to aid in understanding the invention and are not intended to limit its scope. [Examples] 【0055】 Example 1: (Ca)2(Ir 0.8 Nb 0.2 Synthesis of 2O6·H2O Iridium chloride (IrCl3·4H2O) (0.19 g), CaO2, and Nb2O5·H2O were added to 10M KOH (10 mL) in a molar ratio of 0.8(Ir):0.2(Nb):1:4, respectively. The mixture was stirred for 1 hour. The autoclave was then placed in an oven with a blower at 240°C for 4 days. The product was washed with deionized water and 3M nitric acid and dried overnight in air at 70°C. 【0056】 XRD analysis of the formed material revealed a pyrochlore-type structure. 【0057】 Preparation of a button electrode incorporating the material from Example 1 0.1g of catalyst, 0.1g of Nafion™ ionomer, and five yttrium-stabilized zirconia balls (5mm in diameter) were added to a 10mL mixing pot, and the contents were mixed three times using a FlackTek SpeedMixer (DAC 330-100 SE) (3000rpm for 3 minutes). Then, 2mL of deionized water, followed by 1.5mL of propane-1-ol, was added to the pot, and then mixed once using the SpeedMixer (3000rpm for 3 minutes). The ink was added to a Spray Gun (Bahco 1 / 4in Air Inlet (BSP), with a 1-2mm tip) and used to coat a square (9×9cm) Toray carbon paper (SUB0001 Batch SHF-2941C) with the catalyst. During spray coating, the carbon paper was placed on a 140°C hot plate (IKA C-MAG HS7) to evaporate. Circles (2 cm in diameter) were cut out from carbon paper, and each button was scanned 29 times using a Fischerscope XDV XRF device (30 seconds per scan) to determine the amount of Ir and Nb present. 【0058】 Electrochemical test Wet cell tests were performed in 0.1 M H2SO4 using a jacketed cell and a water bath to heat the water to 60°C. The experiment was performed using an Ag / AgCl (no leakage, approximately 3.5 M KCl, WPI) reference electrode. The button electrode was immersed in 35 mL of 0.1 M H2SO4 between PTFE mesh for 1 hour under vacuum to allow the solution to pass through the Toray paper and enter the pore structure. Five aliquots of approximately 2 mL each were taken throughout the test and analyzed by ICP-MS. The first aliquot (Assay 1) was taken from the solution used to immerse the button electrode, and a gold paper clip was attached to the button electrode to form the working electrode. The working electrode was then inserted into the cell along with a Pt counter electrode and 95 mL of 0.1 M H2SO4. After degassing the cell with nitrogen, electrochemical measurements were started. The initial redox behavior was characterized using cyclic voltammetry (CV). The cell was cycled at different scan speeds (100, 50, 10, and 5 mV s-1) between 0.0 and 1.35 V relative to RHE, and a second aliquot (Assay 2) was collected. An activity sweep was performed at 1 mV s-1 between 1.0 and 1.55 V relative to RHE at the beginning of life (BOL), and a third aliquot (Assay 3) was collected. Degradation was performed at 100 mV s-1 over 1000 cycles with a CV between 0.60 and 1.35 V relative to RHE, and a fourth aliquot was collected (Assay 4). The cell was cycled again at each of the scan speeds used to measure the initial redox behavior within the same potential range. An end of life (EOL) activity sweep was performed at 1 mV s-1 between 1.0 and 1.55 V relative to RHE, and a fifth aliquot was collected (Assay 5). 【0059】 Figure 1 shows the conventional technology of iridium pyrochlore (Ca) 2-xThe mass activity versus applied potential of the Nb-containing pyrochlore formed in Example 1 is shown in comparison to Ir2O6.xH2O and reference IrO2. This data indicates that high OER catalytic activity is maintained despite the substitution of niobium with iridium. 【0060】 Figure 2 shows the results of ICP-MS analysis of aliquots taken during electrochemical testing. This shows that the iridium leaching from the material of Example 1 is significantly less compared to the conventional pyrochlore material, which indicates higher catalyst stability under acidic conditions. 【0061】 Example 2: (Ca 1-x Na x )2(Nb 0.5 Ir 0.5 )2O 6.n Synthesis of H2O The materials were prepared by hydrothermal synthesis at 240°C. IrCl3 (1.5 mmol), NbCl5 (1.5 mmol), and Ca(NO3)2 (3 mmol) were stirred together in 12.5 mL of deionized (DI)H2O for 1 hour. The KOH required for the 2M final solution was dissolved in 10 mL of DI H2O and slowly added to the metal solution, stirring together, followed by the addition of 6 mmol of NaBrO3. The mixture was stirred for 1 hour, then transferred to a Teflon-lined autoclave, heated at 240°C for 24 hours, and cooled to room temperature. The black precipitate was collected by centrifugation, washed with DI H2O, and dried overnight at 100°C. 【0062】 XRD analysis of the formed material revealed a pyrochlore-type structure. 【0063】 Example 3: Ca 1-x Na x )2(Ta 0.5 Ir 0.5 )206. n Synthesis of H2O This example was prepared by the method of Example 2, except that TaCl5 (1.5 mmol) was used instead of NbCl5. 【0064】 XRD analysis of the formed material revealed a pyrochlore-type structure. 【0065】 Example 4 (Ca,Na)2(Ir 1-y B' y Synthesis of 2O6·H2O pyrochlore (y=0, 0.1, 0.2, 0.5, 0.8; B'=Nb,Ta) A series of pyrochlore materials, (Ca,Na)2(Ir 1-y B' y )2O6·H2O(y=0, 0.1, 0.2, 0.5, 0.8; B'=Nb, Ta) was prepared hydrothermally at 240°C. In a typical synthesis, a mixture of IrCl3 and NbCl5 / TaCl5 (total content of Ir and Nb / Ta: 3 mmol) was prepared in 10 mL of deionized water and added to the KOH solution. Then, 3 mmol of Ca(NO3)2 and 6 mmol of NaBrO3 were added, and the mixture was stirred for 1 hour. To ensure a 2 M KOH concentration in the final solution, the volume of the mixture was adjusted to 22.5 mL. The mixture was heated in a 45 mL Teflon-lined autoclave at 240°C for 24 hours and allowed to cool naturally to room temperature. The precipitate was collected by centrifugation, washed with deionized H2O, and dried overnight at 100°C. 【0066】 Example 5: (Ca,Na)2(Ru 0.5 Nb 0.5 )2O6 and (Ca,Na)2(Ru 0.5 Ta 0.5 ) Synthesis of 2O6 Mixed Nb / Ta ruthenium salts were prepared by hydrothermal synthesis at 240°C. A mixture of RuCl3 and NbCl5 / TaCl5 (total content of Ru and Nb / Ta: 3 mmol) was prepared in 10 mL of deionized water and added to a KOH solution. Then, 3 mmol of Ca(NO3)2 and 6 mmol of NaBrO3 were added, and the mixture was stirred for 1 hour. To ensure a 2 M KOH concentration in the final solution, the volume of the mixture was adjusted to 22.5 mL. The mixture was heated at 240°C for 24 hours in a 45 mL Teflon-lined autoclave and allowed to cool naturally to room temperature. The precipitate was collected by centrifugation, washed with DI H2O, and 100 o It was dried overnight in C. 【0067】 Electrode preparation After mixing the catalyst (100 mg) and deionized water (72 mg), Nafion ionomer dissolved in 1-propanol and water was added. The catalyst:Nafion ratio at the final electrode was 1:10. The contents were uniformly mixed using a FlackTek SpeedMixer (DAC 330-100 SE) in a 10 mL mixing pot containing five yttrium-stabilized zirconia balls (5 mm in diameter). The ink was prepared by mixing the contents at 3000 rpm for 15 minutes (5 minutes x 3). 【0068】 To coat the electrodes, add the ink to a spray gun (Bahco 1 / 4in Air Inlet (BSP), with a 1-2mm tip) and measure 7 x 7 cm. 2 The solution was sprayed onto a square sheet of Toray carbon paper (SUB0001 batch SHF-2941C). During spray coating, the carbon paper was placed on a 140°C hot plate (IKA C-MAG HS7) to evaporate the solvent. After drying the electrodes, circles (2 cm in diameter) were cut out from the carbon paper, and each button was scanned 29 times using a Fischerscope XDV XRF device (30 seconds per scan) to determine the amount of Ir and Nb / Ta loaded onto each circle. 【0069】 Table 1 shows the results of the OER catalytic activity test. This table shows that these materials exhibit promising catalytic activity despite the substitution of niobium or tantalum with iridium. 0.2 This sample exhibits lower activity than the other samples tested. 【0070】 [Table 1]

Claims

[Claim 1] An oxygen evolution catalyst material having a pyrochlore-type structure, (i) Calcium and / or sodium as the A-site element of the pyrochlore-type structure, (ii) Iridium and / or ruthenium as the first B-site element of the pyrochlore-type structure, (iii) Having niobium and / or tantalum as the second B-site element of the pyrochlore-type structure, (iv) A-site element: An oxygen-evolving catalyst material in which the molar ratio of the first and second B-site elements is in the range of 0.8:1 to 1:

1. [Claim 2] Composition (AA') ａ (BB') ２ O ｂ X ｃ (In the formula, A is Ca, A' is Na, B is Ir and / or Ru, B' is Nb and / or Ta, and X is O, OH, H) ２ The oxygen-evolving catalyst material according to claim 1, having O, or a combination thereof, wherein 1.6 ≤ a ≤ 2.0, 5 ≤ b ≤ 7, and 0 ≤ c ≤ 2. [Claim 3] An oxygen-evolving catalyst material according to claim 1 or 2, having a composition according to formula (1): (1 １－ｘ Na ｘ ) ２ (B １－ｙ B' ｙ ) ２ O ７－ｚ .(H ２ O) ｎ Formula (1) During the ceremony, 0 ≤ x ≤ 0.5, 0 < y ≤ 0.6, 0 ≤ z ≤ 1, 0 ≤ n ≤ 2, B is Ir, Ru, or a combination thereof. B' is Nb, Ta, or a combination thereof. [Claim 4] The oxygen-evolving catalyst material according to claim 2, wherein B' is Nb. [Claim 5] An oxygen-evolving catalyst material according to any one of claims 1 to 4, wherein 0 < y ≤ 0.

3. [Claim 6] The oxygen-evolving catalyst according to any one of claims 1 to 5, wherein B is Ir. [Claim 7] An oxygen evolution catalyst according to any one of claims 1 to 6, having a crystal structure with a space group Fd-3m. [Claim 8] A catalyst ink comprising an oxygen-evolving catalyst material according to any one of claims 1 to 7 and an ion-conducting polymer. [Claim 9] A catalyst layer comprising an oxygen-evolving catalyst material according to any one of claims 1 to 7 and an ion-conducting polymer. [Claim 10] A catalyst coating film comprising the oxygen-evolving catalyst material according to any one of claims 1 to 7 or the catalyst film according to claim 9. [Claim 11] A water electrolysis apparatus or fuel cell comprising the catalyst coating film described in claim 10. [Claim 12] A method for producing an oxygen-evolving catalyst material according to any one of claims 1 to 7, (i) A step of providing an aqueous mixture comprising at least one iridium and / or ruthenium source, at least one calcium and / or sodium source, at least one niobium and / or tantalum source, and a base, (ii) A step of treating the aqueous mixture under hydrothermal conditions, (iii) A method comprising the step of isolating the oxygen-evolving catalyst material.

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