Oxygen evolution reaction catalyst and method for preparing the same

Abstract

This specification describes a process for preparing an oxygen evolution reaction catalyst, the process comprising: (i) mixing iridium powder and a peroxide salt to produce a powder mixture; (ii) heat-treating the powder mixture; (iii) dissolving the product from (ii) in water to produce a solution; (iv) lowering the pH of the solution from (iii) to affect precipitation and form a solid and a supernatant; (v) separating the solid from the supernatant; and (vi) drying the solid. The oxygen evolution catalyst that can be obtained by this process is also described.

Description

[Technical Field]

[0001] The present invention relates to an iridium-containing oxygen evolution reaction (OER) catalyst and a method for preparing the same. [Background technology]

[0002] Oxygen evolution (OER) catalysts are essential components of fuel cells and water electrolyzers. The OER reaction under acidic conditions is approximated by the following equation: 2H₂O → O₂ + 4H + +4e -

[0003] Iridium oxide catalysts are widely used in this reaction. Despite being broadly called "iridium oxide," most "iridium oxide" catalysts are likely mixtures of iridium oxide species such as IrO2, Ir2O3, and / or IrO(OH)2. Therefore, "iridium oxide" is often referred to as IrOx.

[0004] Ideally, OER catalysts used in fuel cells or water electrolyzers should have good activity per gram of iridium and high stability under the operating conditions of the fuel cell or water electrolyzer. IrOx catalysts can be prepared in various degrees of crystallinity, ranging from essentially amorphous to highly crystalline.

[0005] The paper "Synthesis and Optimisation of IrO2 Electrocatalyst by Adams Fusion Method for Solid Polymer Electrolyte Electrophices" (Micro and Nanosystems 2012, 4, 186-191) describes the preparation of iridium dioxide using the Adams fusion method. The Adams fusion method involves fusing a metal chloride precursor with sodium nitrate in high-temperature air and has been used to prepare various noble metal oxides. In this paper, H2IrCl6 and NaNO3 were mixed in isopropanol, the isopropanol was removed by heating in an oven, and the resulting catalyst precursor / salt mixture was then reacted in a preheated furnace. The resulting metal oxide was cooled, washed with ultrapure water to remove excess NaNO3, and then dried in an oven at 100°C. In all cases, amorphous iridium oxide was obtained. In all samples, a peak assigned to the (10¹) reflection of IrO2 was observed at 2θ ~ 34 ~ 35°.

[0006] The paper "Iridium Oxide for the Oxygen Evolution Reaction: Correlation between Particle Size, Morphology, and the Surface Hydroxo Layer from Operdo XAS" (Chem. Mater. 2016, 28, 6591-6604) describes the preparation of iridium oxide by the Adams fusion method. This method avoids chloride contamination of the product by using Ir(acac)3 as a starting material and employing a chloride-free synthesis.

[0007] The paper "Assessing the Potential of Co-Pt Bronze for Electrocatalysis in Acidic Media" (Catalysis 2018, 8, 258) describes comparative tests of Co-Pt bronze against relatively crystalline iridium oxide and relatively amorphous iridium oxide, the latter of which is sold by Alfa Aesar under the brand name Premion® with product number 43396.

[0008] International publication no. 2017 / 149130(A1) is 50m 2 S above / g BET This document describes catalytic materials for the electrochemical oxidation of water, comprising amorphous Ir-oxohydroxyl. A method for producing the material is also described, comprising a step of microwave-assisted heat treatment of a basic solution of an Ir(III) complex or Ir(IV) complex, wherein the basic solution contains hydroxide ions in a ratio satisfying 50:1 > hydroxide:Ir (moles / mol) ≥ 1:100.

[0009] International Publication No. 2018 / 224771(A1) describes a material comprising iridium and / or iridium oxide (IrO2), which is microporous and in the form of micron or submicron spheres. The material is preferably amorphous. A method for producing the material is also described, which comprises (i) preparing an aqueous solution or suspension comprising at least one iridium precursor and at least one pologen or pore-forming agent selected from one of organic polymers and copolymers and mixtures thereof; (ii) spraying the aqueous solution or suspension from step (i) to form solid composite beads; and (iii) firing the solid composite beads.

[0010] International Publication No. 2022 / 102580(A1) describes iridium oxide materials having a peak intensity ratio of (110) peak to (101) peak of 0.65 or less. The (110) peak is located at 2θ = 28° ± 1°, and the (101) peak is located at 2θ = 35° ± 1°. Methods for preparing the materials are also described, which include preparing a suspension of iridium nanoparticles or a solution of an iridium compound, and treating the resulting suspension or solution with high-temperature, high-pressure water.

[0011] International Publication No. 2022 / 138309(A1) has a total pore volume of 0.20 cm³. 3 The document describes iridium-containing oxides having a concentration of 1 / g or more (calculated by the BJH method from nitrogen adsorption / desorption isotherm measurements) and an average pore size of 7.0 nm or more in the pore distribution. It also describes a method for producing the material, which includes mixing a dispersion of iridium nanoparticles or iridium hydroxide particles with water at a temperature of 100°C or higher and a pressure of 0.1 MPa or higher.

[0012] International Publication No. 2023 / 095858(A1) contains yttrium and iridium and has a BET specific surface area of ​​50 m². 2 An oxygen evolution reaction catalyst with a concentration of 1 / g or more is described. A method for producing the material is also described, which includes mixing a dispersion of yttrium nanoparticles and iridium nanoparticles, or a solution of a yttrium compound and an iridium compound, with water at a temperature of 100°C or higher and a pressure of 0.1 MPa or higher.

[0013] International Publication No. 2023 / 047103(A1) contains a mixture of IrO2 and Li3IrO4 phases, and in its XRD pattern, Li3IrO4 has reflections at 2θ=18° and 43°, and IrO2 has reflections at 2θ=28° and 54°, with an N2-BET surface area of ​​50 m². 2 This document describes OER catalysts with a concentration of 1 / g or higher. It also describes a method for producing catalysts, including a precipitation reaction from a solution containing iridium salt and lithium salt.

[0014] Chinese Patent No. 114369845(A) describes an IrOx nanocluster composite material having a hollow nanotube structure. The manufacturing method of the material is also described, including subjecting iridium chloride acid and barium chloride to a hydrothermal reaction, performing ultrasonic treatment to obtain a powder, treating the powder with dilute nitric acid, washing to obtain IrOx@BaCO3, and then further treating to obtain the IrOx nanocluster composite material.

[0015] Chinese Patent No. 116005185(A) describes a composite catalyst of iridium and iridium oxide. The XRD spectrogram of the catalyst shows characteristic peaks of elemental iridium but does not show characteristic peaks of iridium dioxide. The manufacturing method of the material is also described, which includes (i) mixing an iridium source and a complexing agent that is a polybasic acid or its soluble salt in water to prepare a solution, (ii) adjusting the pH value of the solution to 7 - 10, (iii) removing water to obtain a catalyst precursor, and (iv) firing the catalyst precursor in an oxygen-containing atmosphere.

[0016] Japanese Unexamined Patent Application Publication No. 2020132465(A) describes iridium oxide with a specific surface area of 150 m 2 / g or more. The manufacturing method of the material is also described, which includes hydrolyzing iridium chloride acid or its salt with aqueous ammonia and heating and drying in the presence of nitrate.

[0017] Korean Patent Publication No. 20220076414(A) describes an iridium oxide-based catalyst including rod-shaped crystalline iridium oxide and particulate amorphous iridium oxide formed on at least a part of the rod-shaped crystalline iridium oxide. The manufacturing method of the material is also described, which includes reacting an iridium precursor compound, a salt of an alkali or alkaline earth metal, and a compound of formula (I) (defined in the reference), firing the mixture to obtain rod-shaped crystalline iridium oxide, and mixing the rod-shaped crystalline iridium oxide with an iridium precursor compound and a polyhydric alcohol.

[0018] Amorphous or poorly crystalline iridium oxide materials are typically observed to be more active than crystalline iridium oxide, but this higher activity is obtained at the expense of operational stability. For operational stability, it is preferred that the iridium dissolution rate during operation is low. There is a need for alternative OER catalysts that have a good balance between catalytic activity and operational stability and can be produced by an expandable route. This route should ideally also avoid the use of expensive iridium salts used in many known syntheses of iridium OER catalysts. SUMMARY OF THE INVENTION

[0019] In a first aspect, the present invention provides a process for preparing an oxygen evolution reaction catalyst, the process comprising: (i) mixing iridium powder and a peroxide salt to produce a powder mixture; (ii) subjecting the powder mixture to a heat treatment; (iii) dissolving the product from (ii) in water to produce a solution; (iv) lowering the pH of the solution from (iii) to affect precipitation, forming a solid and a supernatant; (v) separating the solid from the supernatant; (vi) drying the solid.

[0020] An advantage of this process is that iridium powder is used as a raw material instead of the iridium salts used in many of the前述 syntheses of OER catalysts. Iridium powder is generally less expensive than iridium salts. Avoiding iridium salts, especially chloride salts, means that a product containing very low levels of chloride impurities can be produced. Chloride contamination in the product can affect the catalytic properties and performance because it can generate HCl and / or Cl2 during operation, which can damage the equipment.

[0021] A further advantage of this process is that it is possible to produce a product that does not contain iridium metal by controlling the fusion step (ii) and / or by performing filtration between steps (iii) and (iv). Iridium metal is thought to be less active or inert during OER, and thus the materials made by this process may be able to achieve equivalent OER activity using lower total iridium loading. Iridium may also dissolve under typical conditions of CCM operation, which is undesirable. Some sources of iridium metal have shapes that can cause damage to the membrane, which is a further reason why complete conversion of iridium metal is desirable.

[0022] A further advantage of this process is that by appropriately selecting the materials used to contain the powder mixture during step (ii), the resulting product can be made of transition metals containing very low amounts of contaminants. Some transition metals, particularly copper, chromium and cobalt, are known to catalyze the formation of oxidizing species that can damage the membrane of CCM (see the paper "A comparative study of several transition metals in Fenton-like reaction systems at circum-neutral pH" Acta Chim. Slov. 2003, 50, 619-632), and it is particularly advantageous to avoid these metals.

[0023] This process produces an OER catalyst with a good balance between activity and operational stability. The catalyst produced after the drying step (vi) typically has a BET surface area of 10 - 50 m 2 / g and is pseudo-amorphous. As used herein, the term "pseudo-amorphous" means that the material shows a single maximum in the region of 2θ = 25 - 38° in its XRD spectrum. Despite being pseudo-amorphous, this material has excellent operational stability, showing only low levels of iridium dissolution. If a more crystalline catalyst is desired, the process may include a further step of calcining the material from step (vi).

[0024] This process may include a subsequent step of incorporating the catalyst into a catalyst coating film. This process may also include a subsequent step of incorporating the catalyst coating film into a fuel cell or water electrolytic cell.

[0025] In a second aspect, the present invention provides an iridium-based oxygen evolution catalyst that can be obtained or obtained by a process according to the first aspect of the present invention.

[0026] In a third aspect, the present invention provides an iridium-based oxygen evolution reaction catalyst, The catalyst exhibits a single maximum value in its XRD spectrum in the region 2θ = 25~38°. The catalyst is 10-50m 2 Having a BET surface area of ​​ / g, The content of any individual transition metal other than iridium, when measured by inductively coupled plasma mass spectrometry (ICP-MS), is between 0 and 600 ppm.

[0027] The OER catalysts according to the second and third aspects of the present invention are particularly useful in water electrolysis and fuel cell applications, for example, as part of a catalyst coating film for a fuel cell or water electrolysis cell.

[0028] A fourth aspect of the present invention provides a catalyst coating film containing an OER catalyst according to the second aspect.

[0029] A fifth aspect of the present invention provides a fuel cell or water electrolytic cell comprising a catalyst coating film according to the third aspect. [Brief explanation of the drawing]

[0030] [Figure 1] The X-ray diffraction (XRD) spectra of the materials from Example 1, compared with database values ​​for iridium and iridium dioxide, are shown. [Modes for carrying out the invention]

[0031] Any subtitles are for convenience only and are not intended to limit the present invention.

[0032] Raw materials and mixing process (i) The term "powder" as used in relation to iridium powder is intended to encompass both spherical powder and irregularly shaped powder such as iridium sponge. Iridium powder preferably has a total impurity content of up to 1% (i.e., 99+% iridium), preferably up to 0.5% (i.e., 99.5+% iridium), and more preferably up to 0.1% (i.e., 99.9+% iridium), in each case minimizing the impurity content in the iridium oxide catalyst. For demanding applications requiring particularly low impurity levels, iridium powder preferably has a total impurity content of up to 0.05% (i.e., 99.95+% iridium).

[0033] The role of the peroxide salt is to oxidize the iridium powder. In preferred embodiments, the peroxide salt is a Group I or Group II peroxide salt, preferably a Group I peroxide salt. Preferred salts are sodium peroxide and barium peroxide, which are commercially available. Sodium peroxide is particularly preferred. The peroxide salt may be in the form of beads or powder.

[0034] The molar ratio of Ir to peroxide should preferably be 1:≥3. Conversion was insufficient at molar ratios of 1:<3. While there is no specific upper limit on the amount of peroxide equivalent, excessive amounts should be avoided for process safety, cost reasons, and to prevent contamination of the product by metal ions from the peroxide. The molar ratio of Ir to peroxide is preferably 1:3 to 1:10, more preferably 1:4 to 1:10, and more preferably 1:6 to 1:9.

[0035] In step (i), it is preferable not to add any components other than iridium powder and peroxide salt.

[0036] Fusion process (ii) In step (ii), a mixture of iridium and a peroxide salt (hereinafter referred to as the "powder mixture") is subjected to heat treatment. This is referred to herein as the fusion step. The product of this step is iridium dioxide and a metal iridite (M2IrO3(M + ) and MIrO3(M 2+ It is thought to be a mixture of oxide species including )).

[0037] The fusion of iridium powder and sodium peroxide is publicly known and is described in the paper "Chemical Dissolution of Iridium Powder Using Alkali Fusion Followed by High-Temperature Leaching" Materials Transactions Vol. 52, No. 11 (2011) pp. 2067-2070. In this reference, iridium powder and sodium peroxide are mixed using a planetary ball mill with zirconia balls in an Ir:Na2O2 molar ratio ranging from 1:0.8 to 1:2.0. The ground material is transferred to a nickel crucible and heated in an electric furnace in air at either 500°C or 600°C for either 4 hours or 24 hours. This reference describes the fusion of iridium powder and sodium peroxide, and the leaching of iridium from the resulting fusion product, but does not describe the isolation of the OER catalyst.

[0038] Various different heating techniques can be used in the fusion process.

[0039] In one method, the fusion process is carried out in a stationary oven or furnace. In this technique, the powder mixture is held in a container (e.g., a tray) inside the oven or furnace.

[0040] In an alternative method, the fusion process is carried out using a belt oven or belt furnace. In this technique, the powder mixture is held in a container (e.g., a tray) and passed through the oven or furnace by a belt. The oven or furnace can be designed for single-zone or multi-zone operation. Such ovens and furnaces are commercially available.

[0041] Static ovens and belt ovens typically generate heat that is transferred to powder mixtures. Static ovens and belt ovens typically include fans to help ensure uniform heat distribution throughout the oven.

[0042] Static furnaces and belt furnaces can be heated by any suitable means known to those skilled in the part. Preferred heating methods include combustion heating, electric heating, electric arc heating, induction heating, microwave heating, or infrared heating.

[0043] In alternative methods, the fusion process is carried out using a rotary or calcining furnace. A rotary or calcining furnace typically comprises a rotating drum that is externally heated. The use of rotary calcination is preferred over the use of a stationary oven, stationary furnace, belt oven, or belt furnace because rotary calcination helps to mix the powders, and the mixing of the powders helps to ensure a uniform distribution of heat, which is considered beneficial in achieving high iridium conversion and more consistent product quality. If the process is operated continuously, the drum may be tilted to control the residence time of the powders in the drum. The use of rotary calcination also offers health and safety benefits because the operator is more fully protected from the reaction mixture than with other techniques. Rotary or calcining furnaces are commercially available.

[0044] In alternative methods, the fusion process is carried out in a fluidized bed or furnace. In a fluidized bed or furnace, a gas passes through the powder mixture so that the powder mixture exhibits fluid properties.

[0045] In an alternative method, the fusion process is carried out using a hot plate, with the powder mixture held in a suitable container on the hot plate.

[0046] In the alternative method, the fusion process is carried out using a combustion flame (e.g., a Bunsen burner) on a powder mixture held in a suitable container.

[0047] The applicant has found that under the oxidation conditions of process (ii), metals on the surfaces of equipment used to contain the powder mixture can contaminate the product. The presence of certain transition metals in the OER catalyst can catalyze the formation of OH and O2H radicals, which can cause defects in the CCM and shorten the CCM's lifespan, and should therefore be avoided in principle. Product contamination can be avoided by appropriately selecting the materials used to contain the powder mixture. "Used to contain the powder mixture" means the surface of any equipment that comes into contact with the powder mixture during the fusion process. For example, in the case of a stationary oven, stationary furnace, or belt furnace, product contamination can be avoided by using a tray in which at least the surface of the tray that comes into contact with the powder mixture is made of appropriately selected material. In the case of a rotary or calcining furnace, the inner surface of the drum is made of appropriately selected material.

[0048] In one preferred embodiment, the material used to contain the powder mixture is a metal oxide. A preferred material is aluminum oxide.

[0049] In a preferred embodiment, the material used to contain the powder mixture is stainless steel. The preferred stainless steel is chromium-nickel-molybdenum austenitic stainless steel. Particularly preferred stainless steel contains 16.0–18.0 wt% Cr, 10.0–14.0 wt% Ni, 2.00–3.00 wt% Mo, 0.08 wt% C, 2.00 wt% Mn, 0.045 wt% P, 0.03 wt% S, 0.75 wt% Si, 0.1 wt% N, and the remainder Fe, and this steel is often called Type 316.

[0050] The powder mixture is heated to a temperature and duration suitable for achieving the desired conversion of iridium metal to an oxide species. It will be understood that the temperature and duration may vary depending on the choice of equipment and scale used. Those skilled in the art can determine the conditions suitable for a given equipment and scale.

[0051] Dissolution step (iii) The mixture from step (ii) is typically cooled to room temperature and then dissolved or dispersed in water, preferably deionized water (DI). The solution immediately turns deep blue. The mixture is preferably stirred to ensure that the soluble iridium species are completely dissolved. Stirring for 30 minutes is usually sufficient. Dissolution is typically carried out at room temperature. The total iridium concentration before the start of step (iv) is 10-100 g. Ir / L, preferably 10-80g Ir / L, for example, 10-60g Ir / L, 10-30g Ir / L, or 15-25g Ir It is preferable that the iridium concentration is / L. The iridium concentration is considered important for controlling the properties of the material formed in step (iv). To avoid doubt, if 100g of iridium powder is used in step (ii) and 5L of DI is used in step (iii), the iridium concentration is 20g Ir It is / L.

[0052] In any step between steps (iii) and (iv), the solution can be filtered to remove unreacted iridium particles.

[0053] Acidification step (iv) The solution from step (iii) is acidified, during which a precipitate is formed. Although the chemical properties of this precipitate are not yet fully understood, pH control during the acidification step is considered important for preparing a catalyst with the correct properties. It is preferable to gradually decrease the pH within the range of pH 3.0 to 3.5. Precipitation can still be achieved at pH levels above 3.5, and even at alkaline pH levels, but the resulting product is more difficult to wash, and therefore impurities may remain in the final product. To avoid chloride contamination in the product, it is preferable to adjust the pH using an acid other than HCl. Nitric acid is a preferred acid for pH adjustment. The precipitate produces a solid and a supernatant.

[0054] After the pH has decreased, the mixture may be optionally diluted by adding water, preferably DI water. The mixture is preferably diluted to achieve an iridium concentration of 40-60% of the original concentration. For example, if the iridium concentration before step (iv) is 20 g Ir If the value is / L, the mixture will be 8-12g Ir It is diluted to achieve an iridium concentration of / L.

[0055] Filtration step (v) After acidification and any dilution, the solid and supernatant are separated, preferably by filtration. The solid is washed with water, preferably DI, to remove soluble impurities.

[0056] Drying process (vi) Next, the filtered solid is dried. If a hydrate is desired, the solid should be dried at a temperature of approximately 55°C. To obtain a dehydrated product, a higher temperature, preferably around 150°C, should be used, such as 120-180°C, or 130-170°C. The drying time depends on the equipment and scale used, but those skilled in the art can determine appropriate conditions.

[0057] The material formed after step (vi) may be described as amorphous or having low crystallinity. If a more crystallinity material is desired, the process may include an optional step of calcining the material from step (vi) to increase its degree of crystallinity.

[0058] Crushing In any process, the dry material, which may be optionally first calcined, is ground to an appropriate particle size. Any suitable grinding method can be used. The ground material is then sieved to obtain the desired particle size fraction. The ground material is generally filtered using a series of sieves, the final of which is a US mesh 200 (retaining a size greater than 75 μm). Powder exceeding this size is returned to the grinding process.

[0059] Incorporation into catalyst coating film This process may include a subsequent step of incorporating the catalyst into a catalyst coating film. The catalyst coating film generally includes a film having an anode catalyst layer on its first surface and a cathode catalyst layer on its second surface.

[0060] This process may also include a subsequent step of incorporating the catalyst coating film into a fuel cell or water electrolyzer.

[0061] catalyst The catalyst produced by this process has a higher oxygen content than expected from pure IrO2. The catalyst is thought to contain at least some IrO(OH)2 in addition to IrO2 and / or Ir2O3.

[0062] The catalyst, when measured according to the method described in the experimental section, was 10-50 m 2 / g of S BET It has a surface area. The catalyst is 10-40 m 2 / g, preferably 10-35mg 2 / g, preferably 10-30mg 2 / g, preferably 15-30mg 2 / g, 15-25m 2 / g, or 18-24m 2 / g of S BETIt is preferable to have a large surface area.

[0063] In some embodiments, iridium metal may also be present, and its presence can be identified by sharp peaks at 2θ = 41°, 47°, and 83° in the XRD spectrum. Alternatively, iridium metal may be absent from the catalyst, and its absence can be identified by the absence of sharp peaks at 2θ = 41°, 47°, and 83°. As described above, the presence of iridium metal can be avoided by filtering the solution between steps (iii) and (iv) to remove unreacted iridium particles, and / or by controlling the oxidation conditions in step (ii) to oxidize all of the iridium powder.

[0064] The catalyst, as measured by inductively coupled plasma mass spectrometry (ICP-MS), typically contains at least 70% by weight of iridium, preferably at least 75% by weight of iridium, preferably 75-85% by weight of iridium, and more preferably 78-82% by weight of iridium.

[0065] By using iridium powder with appropriately low impurity content in step (i) and incorporating the mixture used in step (ii) using appropriate materials, it is possible to produce an amorphous, low-surface-area OER catalyst with particularly low transition metal impurity content. The catalyst according to a third aspect of the present invention has a content of any individual transition metal other than iridium, which, as measured by inductively coupled plasma mass spectrometry (ICP-MS) analysis, is 0 to 600 ppm, preferably 0 to 500 ppm, for example, 0 to 400 ppm, 0 to 300 ppm, or 0 to 200 ppm. For demanding applications and especially when a long lifetime is required, it is preferable that the content of any individual transition metal other than iridium be 0 to 100 ppm.

[0066] In preferred embodiments, the catalyst has a content of any individual transition metal other than iridium of 0 to 500 ppm, preferably 0 to 250 ppm. To avoid doubt, the total amount of non-iridium transition metals may exceed 500 ppm. For demanding applications, and especially when a long lifespan is required, the catalyst preferably has a content of any individual transition metal other than iridium of 0 to 100 ppm.

[0067] The catalyst preferably has a maximum particle size of 75 μm or less. This corresponds to a catalyst that can pass through US Mesh 200. This particle size is typically suitable for incorporation into layers of fuel cells or water electrolyzers. [Examples]

[0068] BET surface area The sample was placed in a small valve tube with a diameter of 3 / 8 inch. The amount of sample was selected to fill at least 1 / 3 of the valve. To obtain the surface area, the sample was degassed at room temperature for 10 minutes, followed by treatment at 300°C for 1 hour under a flow of N2, and then gradually cooled to room temperature under a flow of N2. The N2BET surface area was measured using a Micromeritics® TriStar II Plus instrument. The surface area value calculated from this technique is m² per gram of catalyst. 2 That is the case.

[0069] XRD XRD analysis was performed using a Bruker D8 Advance Davinci diffractometer equipped with a Lynxeye-XE PSD detector with a 0.0125° Ni filter. This analysis was performed at ambient temperature using Cu Kα (λ=1.5406+1.54439 Å) radiation. Phase identification was performed using Bruker AXS Diffrac EVA V5 (2010-2018) software and the PDF-4+ database (2020 release).

[0070] Impurity content The impurity content was measured by inductively coupled plasma mass spectrometry (ICP-MS) using an Agilent 725 ICP-OES instrument.

[0071] Example 1 Iridium powder (300 g, 400 mesh (corresponding to a particle size of less than 23 μm)) was combined with 900 g of sodium peroxide, and the mixture was coarsely ground until well mixed. The mixture was transferred to a nickel crucible and heated with a natural gas flame (temperature approximately 500°C) while stirring with a nickel rod to avoid agglomeration. After the mixture showed signs of visible red heat, heating was stopped, and the mixture was allowed to cool for 60-90 minutes. After cooling, the mixture was dissolved in 14 L of DI water and stirred for 30 minutes to ensure complete dissolution. Reagent-grade nitric acid was added until the pH dropped to approximately 3.25. After reaching the target pH, the mixture was diluted with 14 L of DI water, stirred, and then allowed to settle for 1 hour. The solid was collected via a Buchner funnel equipped with a vacuum pump and washed with 150 L of DI water at 75°C. The solid was collected and dried in a tray in an oven at 150°C for 10 hours. The solid was crushed and sieved using a series of sieves, with the final sieve being US mesh 200 (retaining a size greater than 75 μm).

[0072] The XRD spectrum of the catalyst is shown in Figure 1. Peaks at 2θ = 40, 44, and 59 indicate the presence of unreacted iridium metal. A broad peak around 2θ = 33° indicates the presence of amorphous IrO2.

[0073] The catalyst is 22m 2 / g of S BET It contained [the characteristic]. The residual iridium content was approximately 8%.

[0074] The Ni content of the catalyst was 654 ppm.

[0075] Iridium dissolution rate (%) of the catalyst in Example 1 and two commercially available iridium oxide materials: 1.47 V / A / g Ir The current density (measure of activity) and surface area values ​​are reported in Table 1. The catalysts were tested under identical conditions.

[0076] [Table 1]

[0077] Despite the relatively low surface area of ​​Example 1, this catalyst exhibited activity comparable to commercially available materials with much higher surface areas. Furthermore, this material had a lower iridium dissolution rate than commercially available materials.

[0078] Example 2 Iridium powder (300 g) and sodium peroxide (900 g) were mixed in a mortar and pestle until the mixture was visually homogeneous. The mixture was then fed in small batches into a continuous rotating furnace or cauldron set to 450°C. The inner surface of the rotating furnace or cauldron was stainless steel. The rotation speed and incline were selected to achieve approximately 60% iridium metal conversion. The solid was cooled, then dissolved, acidified, and precipitated according to the conditions used in Example 1.

[0079] The product is 15.7m 2 / g of S BET It contained [the characteristic]. The residual iridium content was approximately 40%.

[0080] The highest levels of transition metal impurities were Rh 87 ppm, Cr 86 ppm, and Fe 61 ppm.

[0081] Example 2 demonstrates that by appropriately selecting the materials used to incorporate the powder mixture in step (ii), it is possible to produce a product containing very low levels of transition metal contaminants.

Claims

1. A process for preparing an iridium-based oxygen evolution reaction catalyst, (i) A step of mixing iridium powder and peroxide salt to produce a powder mixture, (ii) A step of heat treatment of the powder mixture, (iii) A step of dissolving the product from (iii) in water to produce a solution, The steps include lowering the pH of the solution from (iv)(iii) to affect precipitation and form a solid and a supernatant, (v) A step of separating the solid from the supernatant, (vi) A process comprising the step of drying the solid.

2. The process according to claim 1, wherein the peroxide salt is sodium peroxide.

3. The process according to claim 1 or 2, wherein the iridium powder and the peroxide salt are mixed in a molar ratio of 1:4 to 1:

10.

4. The process according to any one of claims 1 to 3, wherein the surface of any equipment that comes into contact with the powder mixture in step (ii) is a metal oxide or stainless steel.

5. The process according to claim 4, wherein the surface of any equipment that comes into contact with the powder mixture in step (ii) is made of chromium-nickel-molybdenum austenitic stainless steel.

6. Step (ii) is the process according to any one of claims 1 to 5, which is carried out in a stationary oven, stationary furnace, belt furnace, or rotary or baking furnace.

7. The process according to any one of claims 1 to 5, wherein step (ii) is performed in a belt oven.

8. The process according to any one of claims 1 to 5, wherein step (ii) is carried out in a fluidized bed or a furnace.

9. The process according to any one of claims 1 to 5, wherein step (ii) is carried out using a hot plate, with the powder mixture held in a suitable container on the hot plate.

10. The process according to any one of claims 1 to 5, wherein step (ii) is carried out using a combustion flame in the powder mixture held in a suitable container.

11. The total iridium content in the solution formed in step (iv) is 10 to 30 g. Ｉｒ The process according to any one of claims 1 to 10, wherein the process is / L.

12. The process according to any one of claims 1 to 11, wherein in step (iv), an acid other than HCl is used to lower the pH.

13. The process according to any one of claims 1 to 11, wherein in step (iv), the pH is reduced using nitric acid.

14. The process according to any one of claims 1 to 13, further comprising a step of firing the material from step (vi).

15. The process according to any one of claims 1 to 14, further comprising a subsequent step of incorporating the catalyst into a catalyst coating film.

16. The process according to claim 14, further comprising a subsequent step of incorporating the catalyst coating film into a fuel cell or a water electrolytic cell.

17. An iridium-based oxygen evolution catalyst obtained or obtainable by the process described in any one of claims 1 to 14.

18. iridium-based oxygen evolution reaction catalyst, The catalyst exhibits a single maximum value in its XRD spectrum in the region 2θ = 25 to 38°. The catalyst is 10 to 50 m ２ Having a BET surface area of ​​ / g, An iridium-based oxygen evolution catalyst in which the content of any individual transition metal other than iridium is 0 to 600 ppm, as measured by inductively coupled plasma mass spectrometry (ICP-MS).

19. The catalyst is 10 to 40 m ２ The catalyst according to claim 18, having a BET surface area of ​​1 / g.

20. The catalyst according to claim 18 or claim 19, wherein the catalyst does not contain iridium metal.

21. The catalyst according to any one of claims 18 to 20, wherein the catalyst has a maximum particle size of 75 μm or less.

22. A catalyst coating film comprising the oxygen evolution reaction catalyst according to any one of claims 17 to 21.

23. A fuel cell or water electrolytic cell comprising the catalyst coating film described in claim 22.

Images