Oxygen evolution reaction catalyst and preparation method thereof

Abstract

The present specification describes a process for preparing an oxygen evolution reaction catalyst, the process comprising the steps of: (i) mixing an 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) reducing the pH of the solution from (iii) to affect precipitation and form solids and a supernatant; (v) separating the solid from the supernatant; and (vi) drying the solid. An oxygen evolution catalyst obtainable by the process is also described.

Description

Technical Field

[0001] This invention relates to iridium-containing oxygen evolution reaction (OER) catalysts and their preparation methods. Background Technology

[0002] Oxygen evolution reaction (OER) catalysts are important components in fuel cells and water electrolyzers. The OER reaction under acidic conditions is approximated by the following equation:

[0003] 2H₂O→O₂+4H + +4e -

[0004] Iridium oxide catalysts are widely used in this reaction. Although widely referred to as "iridium oxide," most "iridium oxide" catalysts are more likely mixtures of iridium oxides, such as IrO2, Ir2O3, and / or IrO(OH)2. Therefore, "iridium oxide" is often referred to as IrOx.

[0005] Ideally, OER catalysts used in fuel cells or water electrolyzers should exhibit good iridium activity per gram and high stability under the operating conditions of the fuel cell or water electrolyzer. IrOx catalysts can be prepared with a variety of crystallinities, ranging from substantially amorphous to highly crystalline.

[0006] The article “Synthesis and Optimization of IrO2 Electrocatalysts by Adams Fusion Method for Solid Polymer Electrolyte Electrolysers” (Microsystems and Nanosystems, 2012, 4, 186-191) describes the preparation of iridium dioxide using the Adams Fusion Method. The Adams Fusion Method involves melting a metal chloride precursor with sodium nitrate in air at high temperatures and has been used to prepare various noble metal oxides. In this paper, H2IrCl6 and NaNO3 were mixed in isopropanol, which 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 then cooled, washed with ultrapure water to remove excess NaNO3, and then dried in an oven at 100 °C. Amorphous iridium oxide was obtained in all cases. A (101) reflectance peak assigned to IrO2 at 2θ–34–35° was observed in all samples.

[0007] The article "Iridium Oxide for the Oxygen Evolution Reaction: Correlation between Particle Size, Morphology, and the Surface Hydroxo Layer from OperandoXAS" (Materials Chemistry, 2016, 28, 6591-6604) describes the preparation of iridium oxide via the Adams melt method. This method uses Ir(acac)3 as a raw material and avoids chloride contamination of the product by using a chloride-free synthesis.

[0008] The article “Assessing the Potential of Co-Pt Bronze for Electrocatalysis in Acidic Media” (Catalysis 2018, 8, 258) describes a comparative test of Co-Pt bronze relative to relatively crystalline iridium oxide and relatively amorphous iridium oxide, the latter using Alfa Aesar's Premion. ® The brand is sold as product number 43396.

[0009] WO2017 / 149130A1 describes a catalytically active material for the electrochemical oxidation of water, which contains S BET ≥50m 2 / g of amorphous oxo-iridium hydroxide. A method for producing this material is also described, comprising the step of microwave-assisted heat treatment of an alkaline solution of an Ir(III) or Ir(IV) complex, wherein the alkaline solution contains hydroxide ions in a ratio satisfying 50:1 > hydroxide:iridium (mol / mol) ≥ 1:100.

[0010] WO2018 / 224771A1 describes a material containing iridium and / or iridium oxide (IrO2), which is microporous and in the form of micron or submicron spheres. Preferably, the material is amorphous. A method for producing the material is also described, comprising the steps of: (i) preparing an aqueous solution or suspension containing at least one iridium precursor and at least one pore-forming agent or pore-forming agent selected from organic polymers and copolymers and mixtures thereof; (ii) atomizing the aqueous solution or suspension from step (i) to form solid composite beads; and (iii) calcining the solid composite beads.

[0011] WO2022 / 102580A1 describes an iridium oxide material in which the peak intensity ratio of the (110) peak to the (101) peak is 0.65 or less. The (110) peak is at 2θ = 28° ± 1°, and the (101) peak is at 2θ = 35° ± 1°. A method for preparing this material is also described, comprising 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.

[0012] WO2022 / 138309A1 describes an iridium-containing oxide with a 0.20 cm⁻¹ content. 3 The total pore volume is / g or greater (calculated by nitrogen adsorption / desorption isotherm measurements using the BJH method), and the pore distribution has an average pore size of 7.0 nm or greater. A method for manufacturing this material is also described, comprising 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.

[0013] WO2023 / 095858A1 describes an oxygen evolution reaction catalyst containing oxides comprising yttrium and iridium and having a 50m 2 / g or greater BET specific surface area. A method for manufacturing the material is also described, which includes mixing a dispersion of yttrium nanoparticles and iridium nanoparticles, or a solution of yttrium compounds and iridium compounds with water at a temperature of 100°C or higher and a pressure of 0.1 MPa or higher.

[0014] WO2023 / 047103A1 describes an OER catalyst comprising a mixture of IrO2 and Li3IrO4 phases, which exhibits reflectance at 2θ = 18° and 43° for Li3IrO4 and at 2θ = 28° and 54° for IrO2 in its XRD pattern, and has a ≥50 nm flux density. 2 / g N2-BET surface area. A method for manufacturing the catalyst is also described, which involves a precipitation reaction from a solution containing iridium and lithium salts.

[0015] CN114369845A describes an IrOx nanocluster composite material with a hollow nanotube structure. A method for manufacturing this material is also described, comprising hydrothermally reacting chloroiridic acid with barium chloride and then sonicating to obtain a powder, treating the powder with dilute nitric acid and washing it to obtain IrOx@BaCO3, and then further processing it to obtain the IrOx nanocluster composite material.

[0016] CN116005185A describes a composite catalyst of iridium and iridium oxide, wherein the XRD pattern of the catalyst shows characteristic peaks of elemental iridium but not characteristic peaks of iridium dioxide. A method for manufacturing this material is also described, comprising: (i) mixing an iridium source and a complexing agent in water to form a solution, the complexing agent being a polybasic acid or a soluble salt thereof; (ii) adjusting the pH of the solution to 7-10; (iii) removing water to obtain a catalyst precursor; and (iv) calcining the catalyst precursor in an oxygen-containing atmosphere.

[0017] JP2020132465A describes a specific surface area of ​​150 m². 2 / g or greater of iridium oxide. A method for manufacturing this material is also described, comprising: hydrolyzing chloroiridium acid or a salt thereof with ammonia and heating and drying in the presence of nitrate.

[0018] KR20220076414A describes an iridium oxide-based catalyst comprising rod-shaped crystalline iridium oxide and particulate amorphous iridium oxide formed on at least a portion of the rod-shaped crystalline iridium oxide. A method for producing this material is also described, comprising: reacting an iridium precursor compound, a salt of an alkali metal or alkaline earth metal, and a compound of formula (I) (as defined in the references); calcining the mixture to obtain rod-shaped crystalline iridium oxide; and mixing the rod-shaped crystalline iridium oxide with an iridium precursor compound and a polyol.

[0019] It is generally observed that amorphous or poorly crystallized iridium oxide materials are more active than crystalline iridium oxide, but this higher activity comes at the cost of operational stability. For operational stability reasons, low iridium solubility during operation is preferred. Alternative OER catalysts that achieve a good balance between catalytic activity and operational stability are needed, which can be manufactured via scalable routes. Ideally, this route should also avoid the use of expensive iridium salts employed in the synthesis of many known iridium OER catalysts. Summary of the Invention

[0020] In a first aspect, the present invention provides a method for preparing an oxygen evolution reaction catalyst, the method comprising the following steps:

[0021] (i) Mixing iridium powder and peroxide salt to produce a powder mixture;

[0022] (ii) Heat-treat the powder mixture;

[0023] (iii) Dissolve the product from (ii) in water to produce a solution;

[0024] (iv) Lower the pH of the solution from (iii) to affect precipitation and form a solid and a supernatant;

[0025] (v) Separate the solid from the supernatant; and

[0026] (vi) Dry the solid.

[0027] The advantage of this method is that it uses iridium powder as a raw material, rather than iridium salts used in the synthesis of many previously described OER catalysts. Iridium powder is generally less expensive than iridium salts. Avoiding the use of iridium salts, especially chloride salts, means that products with very low chloride impurity content can be produced. Chloride contamination in the product can affect catalytic properties and performance because HCl and / or Cl2 may be generated during operation, potentially damaging the equipment.

[0028] Another beneficial effect of this method is that, by controlling the fusion step (ii) and / or by filtering between steps (iii) and (iv), products free of iridium can be produced. Iridium is considered to be of low or no activity in OER, therefore materials prepared by this method may be able to achieve comparable OER activity with a lower total iridium loading. Iridium may also dissolve under typical CCM operating conditions, which is undesirable. Some iridium sources have geometries that can damage the film, which is another reason why complete iridium conversion is necessary.

[0029] Another beneficial effect of this method is that, by appropriately selecting the material used to contain the powder mixture during step (ii), a product with extremely low levels of transition metal contaminants can be produced. It is known that some transition metals, particularly copper, chromium, and cobalt, can catalyze the formation of oxidants that can damage the CCM membrane (see the article "A comparative study of several transition metals in Fenton-like reaction systems at circum-neutral pH" Acta Chim. Slov. 2003, 50, 619-632), and avoiding the use of these metals is particularly advantageous.

[0030] The OER catalyst produced by this method exhibits a good balance between activity and operational stability. The catalyst produced after the drying step (vi) typically has a 10m... 2 / g to 50m 2 The material has a BET surface area of ​​ / g and is pseudo-amorphous. As used herein, the term "pseudo-amorphous" refers to a material exhibiting a single maximum value in its XRD spectrum in the region of 2θ = 25–38°. Despite being pseudo-amorphous, the material exhibits excellent operational stability, showing only low iridium solubility. If a catalyst with higher crystallinity is required, the method may include an additional step of calcining the material from step (vi).

[0031] The method may include subsequent steps of incorporating a catalyst into a catalyst-coated membrane. The method may also include subsequent steps of incorporating the catalyst-coated membrane into a fuel cell or a water electrolyzer.

[0032] In a second aspect, the present invention provides an iridium-based oxygen evolution reaction catalyst that can be obtained or obtained by the method described in the first aspect of the present invention.

[0033] In a third aspect, the present invention provides an iridium-based oxygen evolution reaction catalyst, wherein:

[0034] The catalyst exhibits a single maximum value in its XRD spectrum in the region of 2θ = 25-38°.

[0035] The catalyst has 10m 2 / g to 50m 2 / g of BET surface area;

[0036] When measured by inductively coupled plasma mass spectrometry (ICP-MS), the content of any single transition metal other than iridium ranges from 0 ppm to 600 ppm.

[0037] The OER catalysts according to the second and third aspects of the invention are particularly useful in water electrolysis and fuel cell applications, for example as part of a catalyst coating membrane for fuel cells or water electrolyzers.

[0038] In a fourth aspect of the invention, a catalyst-coated film is provided, comprising the OER catalyst according to the second aspect.

[0039] In a fifth aspect of the invention, a fuel cell or water electrolyzer is provided, comprising a catalyst-coated membrane according to the third aspect. Attached Figure Description

[0040] Figure 1 The X-ray diffraction (XRD) spectra of the material from Example 1 are shown compared with database values ​​of iridium and iridium dioxide. Detailed Implementation

[0041] Any subheadings are for convenience only and are not intended to limit the invention.

[0042] Raw materials and mixing - Step (i)

[0043] The term "powder" used in conjunction with iridium powder is intended to encompass both spherical powders and irregular powders, such as iridium sponges. Preferably, the iridium powder has a total impurity content of up to 1% (i.e., 99+% iridium), more preferably up to 0.5% (i.e., 99.5+% iridium), and more preferably up to 0.1% (i.e., 99.9+% iridium), minimizing the impurity content in the iridium oxide catalyst in each case. For demanding applications requiring particularly low impurity levels, preferably, the iridium powder has a total impurity content of up to 0.05% (i.e., 99.95+% iridium).

[0044] The peroxide salt serves as iridium oxide powder. In a preferred embodiment, 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, as they are commercially available. Sodium peroxide is particularly preferred. The peroxide salt can be in the form of beads or powder.

[0045] Preferably, the molar ratio of iridium to peroxide salt should be 1:≥3. When the molar ratio is 1:<3, the conversion rate is insufficient. Although there is no particular upper limit to the equivalent amount of peroxide salt, for process safety and cost considerations, and to avoid product contamination by metal ions in the peroxide salt, an excess of peroxide salt should be avoided. Preferably, the molar ratio of iridium to peroxide salt is 1:3 to 1:10, more preferably 1:4 to 1:10, and more preferably 1:6 to 1:9.

[0046] Preferably, in step (i), no other components are added except for iridium powder and peroxide salt.

[0047] Fusion - Step (ii)

[0048] In step (ii), the mixture of iridium and peroxide salt (hereinafter referred to as the "powder mixture") is heat-treated; this is referred to herein as the fusion step. The product of this step is considered to be a mixture of oxidizing substances, including iridium dioxide and metal iridium salts (M₂IrO₃ (M + ) and MirO3 (M 2+ )).

[0049] The fusion of iridium powder and sodium peroxide is known and described in the article "Chemical Dissolution of Iridium Powder Using Alkali Fusion Followed by High-Temperature Leaching" (Materials Review, Vol. 52, No. 11 (2011), pp. 2067-2070). In that reference, iridium powder and sodium peroxide were mixed using a planetary ball mill with zirconia balls at an Ir:Na₂O₂ molar ratio ranging from 1:0.8 to 1:2.0. The milled material was transferred to a nickel crucible and heated in an electric furnace at 500°C or 600°C in air for 4 hours or 24 hours. Although the reference describes the fusion of iridium powder and sodium peroxide, and the leaching of iridium from the resulting fusion product, it does not describe the separation of the OER catalyst.

[0050] A variety of different heating techniques can be used in the fusion process.

[0051] In one method, the fusion step is carried out in a static oven or static furnace. In this technique, the powder mixture is held in a container (e.g., a tray) within the oven or furnace.

[0052] In alternative methods, a belt oven or belt furnace is used for the fusion step. In this technique, the powder mixture is held in a container (e.g., a tray) and passed through the oven or furnace via a belt. The oven or furnace can be designed for single-zone or multi-zone operation. Such ovens and furnaces are commercially available.

[0053] Static ovens and belt ovens typically generate heat that is transferred to the powder mixture. Static ovens and belt ovens usually include fans to help distribute heat evenly throughout the oven.

[0054] Static furnaces and belt furnaces can achieve heating by any suitable means known to those skilled in the art. Preferred heating methods include: combustion heating, electric heating, electric arc heating, induction heating, microwave heating, or infrared heating.

[0055] In alternative methods, a rotary calcining furnace is used for the fusion step. Rotary calcining furnaces typically consist of an externally heated rotating drum. Using rotary calcination is superior to using static ovens, static furnaces, belt ovens, or belt furnaces because rotary calcination mixes the powders, thus helping to ensure a uniform distribution of heat, which is considered beneficial for achieving high iridium conversion rates and more consistent product quality. If the method is operated continuously, the drum can be tilted to control the residence time of the powder within the drum. Using rotary calcination also offers health and safety benefits, as the operator is more thoroughly isolated from the reactant mixture compared to other techniques. Rotary calcining furnaces are commercially available.

[0056] In an alternative method, the fusion step is carried out in a fluidized bed calciner. In the fluidized bed calciner, gas is passed through the powder mixture, causing the powder mixture to exhibit fluid-like properties.

[0057] In an alternative method, a hot plate is used for the melting step, wherein the powder mixture is held in a suitable container on the hot plate.

[0058] In an alternative method, a combustion flame (e.g., a Bunsen burner) is used for the fusion step, wherein the powder mixture is held in a suitable container.

[0059] The applicant has discovered that, under the oxidizing conditions of step (ii), metals on the surfaces of the equipment used to contain the powder mixture may contaminate the product. Ideally, the presence of certain transition metals in the OER catalyst should be avoided, as they can catalyze the formation of OH and O2H radicals, which can lead to defects in the CCM and shorten its lifespan. Contamination of the product can be avoided by appropriately selecting the material used to contain the powder mixture. “Used to contain the powder mixture” refers to the surface of any equipment that comes into contact with the powder mixture during the fusion step. For example, in the case of a static oven, static furnace, or belt furnace, contamination of the product can be avoided by using a tray, wherein at least the tray surface in contact with the powder mixture is made of an appropriately selected material. In the case of a rotary kiln, the inner surface of the drum is made of an appropriately selected material.

[0060] In a preferred embodiment, the material used to contain the powder mixture is a metal oxide. Alumina is a preferred material.

[0061] In a preferred embodiment, the material used to contain the powder mixture is stainless steel. Preferred stainless steel is chromium-nickel-molybdenum austenitic stainless steel. Particularly preferred stainless steel contains 16.0 wt% to 18.0 wt% Cr, 10.0 wt% to 14.0 wt% Ni, 2.00 wt% to 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, with the balance being Fe; this steel is commonly referred to as type 316.

[0062] The powder mixture is heated at a temperature and duration suitable for achieving the desired conversion of iridium metal to its oxide form. It should be understood that the temperature and duration can vary depending on the choice and scale of the equipment used. A skilled technician will be able to determine the appropriate conditions for a given piece of equipment and scale.

[0063] Dissolving - Step (iii)

[0064] 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. Preferably, the mixture is stirred to ensure complete dissolution of the soluble iridium; stirring for 30 minutes is usually sufficient. Dissolution is typically carried out at room temperature. Preferably, the total iridium concentration before the start of step (iv) is 10 g. Ir / L to 100g Ir / L, preferably 10g Ir / L to 80g Ir / L, for example, 10g Ir / L to 60g Ir / L, 10g Ir / L to 30g Ir / L or 15g Ir / L to 25g Ir / L. The concentration of iridium is considered important in controlling the properties of the material formed in step (iv). To avoid ambiguity, 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 / L.

[0065] In an optional step between steps (iii) and (iv), the solution may be filtered to remove unreacted iridium particles.

[0066] Acidification - Step (iv)

[0067] The solution from step (iii) is acidified, during which a precipitate forms. Although the chemical composition is not fully understood, pH control during the acidification step is considered important in preparing a catalyst with the correct properties. Preferably, the pH is gradually decreased to a range of 3.0 to 3.5. Precipitation can still be achieved at pH values ​​above 3.5, even at alkaline pH levels, but the resulting product is more difficult to wash, and impurities may remain in the final product. To avoid chloride contamination in the product, a non-HCl acid is preferred for pH adjustment. Nitric acid is the preferred acid for pH adjustment. Precipitation produces a solid and a supernatant.

[0068] Once the pH value decreases, the mixture can optionally be diluted by adding water (preferably DI water). Preferably, the mixture is diluted to achieve an iridium concentration of 40% to 60% of the original concentration. For example, if the iridium concentration before step (iv) was 20g... Ir / L, then dilute the mixture to reach 8g. Ir / L to 12g Ir / L iridium concentration.

[0069] Filtering - Step (v)

[0070] After acidification and optional dilution, the solids and supernatant are preferably separated by filtration. The solids are washed with water (preferably DI) to remove soluble impurities.

[0071] Drying - Step (vi)

[0072] The filtered solid is then dried. If hydrates are required, the solid should be dried at a temperature of about 55°C. To obtain a dehydrated product, a higher temperature should be used, preferably about 150°C, for example 120°C to 180°C, such as 130°C to 170°C. The duration of the drying step will depend on the equipment and scale used, but a skilled technician will be able to determine the appropriate conditions.

[0073] The material formed after step (vi) can be described as amorphous or poorly crystallized. If a material with higher crystallinity is required, the method may include an optional step of calcining the material from step (vi) to increase its crystallinity.

[0074] Grinding

[0075] In an optional step, the dried material, optionally calcined first, is ground to a suitable particle size. Any suitable grinding method can be used. The ground material is then sieved to the desired particle size fraction. Typically, a series of sieves is used to filter the ground material, with the final sieve being a US Mesh 200 (retaining sizes greater than 75 μm). Any excessively large powder is returned to the grinding step.

[0076] Incorporated into the catalyst coating film

[0077] This method may include subsequent steps of incorporating a catalyst into a catalyst-coated membrane. The catalyst-coated membrane typically comprises a membrane having an anodic catalyst layer on a first side and a cathode catalyst layer on a second side.

[0078] The method may also include subsequent steps of incorporating a catalyst-coated membrane into a fuel cell or a water electrolyzer.

[0079] catalyst

[0080] The catalyst produced by this method has a higher oxygen content than expected from pure IrO2. It is believed that, in addition to IrO2 and / or Ir2O3, the catalyst may also contain at least some IrO(OH)2.

[0081] When measured according to the method described in the experimental section, the S of the catalyst BET Surface area is 10m² 2 / g to 50m 2 / g. Preferably, the catalyst's S BET Surface area is 10m² 2 / g to 40m 2 / g, preferably 10m 2 / g to 35m 2 / g, preferably 10m 2 / g to 30m 2 / g, preferably 15m 2 / g to 30m 2 / g, 15m 2 / g to 25m 2 / g or 18m 2 / g to 24m 2 / g.

[0082] In some embodiments, iridium metal may also be present, which can be identified by the sharp peaks at 2θ = 41°, 47°, and 83° in the XRD spectrum. Alternatively, the catalyst may be iridium metal-free, which can be identified by the absence of sharp peaks at 2θ = 41°, 47°, and 83°. As mentioned 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 iridium powder.

[0083] When measured by inductively coupled plasma mass spectrometry (ICP-MS), the catalyst typically contains at least 70% by weight of iridium, preferably at least 75% by weight of iridium, more preferably 75% to 85% by weight of iridium, and more preferably 78% to 82% by weight of iridium.

[0084] If iridium powder with a suitable low impurity content is used in step (i), and suitable materials are used to contain the mixture used in step (ii), an amorphous, low-surface-area OER catalyst with particularly low transition metal impurity content can be produced. The catalyst according to the third aspect of the invention has a content of any single transition metal other than iridium, which, when measured by inductively coupled plasma mass spectrometry (ICP-MS), is from 0 ppm to 600 ppm, preferably from 0 ppm to 500 ppm, such as from 0 ppm to 400 ppm, 0 ppm to 300 ppm, or 0 ppm to 200 ppm. For demanding applications and those requiring particularly long lifetimes, a content of any single transition metal other than iridium of 0 ppm to 100 ppm is preferred.

[0085] In a preferred embodiment, the catalyst contains any single transition metal other than iridium in an amount ranging from 0 ppm to 500 ppm, preferably from 0 ppm to 250 ppm. For the avoidance of doubt, the total amount of transition metals other than iridium may exceed 500 ppm. For demanding applications and those requiring particularly long lifespans, the catalyst preferably contains any single transition metal other than iridium in an amount ranging from 0 ppm to 100 ppm.

[0086] Preferably, the catalyst has a maximum particle size of ≤75µm. This corresponds to a catalyst passing through US Mesh 200. This particle size is generally suitable for incorporation into layers in fuel cells or water electrolyzers.

[0087] Example

[0088] BET surface area

[0089] Place the sample in a small 3 / 8" diameter spherical tube. Select a sample volume to fill at least 1 / 3 of the spherical tube. Provide surface area and degas at room temperature for 10 minutes, then treat at 300°C for 1 hour under a flow of N2, followed by gradual cooling to room temperature under a flow of N2. Use Micromeritics. ™ The TriStar II Plus instrument is used to measure the surface area of ​​N2BET. The surface area value calculated using this technique is m. 2 per gram of catalyst.

[0090] XRD

[0091] XRD analysis was performed using a Bruker D8 AdvanceDavinci diffractometer with a Lynxeye-XE PSD detector and a 0.0125°Ni filter. Analysis was conducted using Cu Kα (λ = 1.5406 + 1.54439 Å) radiation at ambient temperature. Phase identification was performed using Bruker AXS Diffrac Eva V5 (2010–2018) software and the PDF-4+ database (2020 version).

[0092] impurity content

[0093] The impurity content was measured using an Agilent 725 ICP-OES instrument via inductively coupled plasma mass spectrometry (ICP-MS).

[0094] Example 1

[0095] 300 g of iridium powder (400 mesh, corresponding to a particle size below 23 μm) was mixed with 900 g of sodium peroxide, and the mixture was coarsely ground until thoroughly mixed. The mixture was transferred to a nickel crucible and heated by a natural gas flame (temperature approximately 500 °C) while stirring with a nickel rod to prevent clumping. Once the mixture showed obvious signs of red-hot discoloration, heating was stopped, and the mixture was allowed to cool for 60 to 90 minutes. Once cooled, 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 decreased to approximately 3.25. Once the target pH was reached, the mixture was diluted with 14 L of DI water, stirred, and then allowed to settle for 1 hour. The solid was collected through 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 an oven at 150 °C on a tray for 10 hours. The solid was ground and sieved through a series of sieves, with the final sieve being US Mesh 200 (retaining sizes greater than 75 μm).

[0096] The XRD spectrum of the catalyst is in Figure 1 As shown in the figure, the peaks at 2θ = 40, 44, and 59 indicate the presence of unreacted iridium metal. The broad peak near 2θ = 33° indicates the presence of amorphous IrO2.

[0097] S of catalyst BET 22m 2 / g. The residual iridium content is approximately 8%.

[0098] The catalyst has a Ni content of 654 ppm.

[0099] Table 1 records the iridium solubility percentage (1.47 V / A / g) of the catalyst and two commercially available iridium oxide materials in Example 1. Ir The values ​​of current density (a measure of activity) and surface area were measured. The catalyst was tested under the same conditions.

[0100]

[0101] Table 1.

[0102] Although the surface area of ​​Example 1 is relatively low, the catalyst exhibits activity comparable to commercially available materials with much higher surface areas. Furthermore, this material shows lower iridium dissolution than commercially available materials.

[0103] Example 2

[0104] Iridium powder (300 g) and sodium peroxide (900 g) were mixed in a pestle and mortar until the mixture was visually homogeneous. It was then gradually fed into a continuous rotary calcining furnace set at 450°C. The inner surface of the rotary calcining furnace was stainless steel. The rotation speed and inclination were selected to achieve approximately 60% conversion of iridium metal. The solid was allowed to cool, and then dissolved, acidified, and precipitated under the conditions used in Example 1.

[0105] S of the product BET It is 15.7m 2 / g. The residual iridium content is approximately 40%.

[0106] The highest contents of transition metal impurities are: Rh 87ppm; Cr 86ppm; Fe 61ppm.

[0107] Example 2 shows that by appropriately selecting the material used to contain the powder mixture in step (ii), a product with extremely low levels of transition metal contaminants can be produced.

Claims

1. A method for preparing an iridium-based oxygen evolution reaction catalyst, the method comprising the following steps: (i) Mixing iridium powder and peroxide salt to produce a powder mixture; (ii) subjecting the powder mixture to heat treatment; (iii) Dissolve the product from (ii) in water to produce a solution; (iv) Lower 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) Dry the solid.

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

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

10.

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

5. The method of claim 4, wherein the surfaces of any equipment in contact with the powder mixture in step (ii) are made of chromium-nickel-molybdenum austenitic stainless steel.

6. The method according to any one of claims 1 to 5, wherein step (ii) is carried out in a static oven, a static furnace, a belt furnace or a rotary kiln.

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

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

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

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

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

12. The method according to any one of claims 1 to 11, wherein in step (iv), a non-HCl acid is used to lower the pH.

13. The method according to any one of claims 1 to 11, wherein in step (iv), nitric acid is used to lower the pH.

14. The method according to any one of claims 1 to 13, the method comprising another step of calcining the material from step (vi).

15. The method according to any one of claims 1 to 14, the method comprising the subsequent step of incorporating the catalyst into a catalyst-coated film.

16. The method of claim 14, the method comprising the subsequent step of incorporating the catalyst coating into a fuel cell or a water electrolyzer.

17. An iridium-based oxygen evolution reaction catalyst that is obtained or obtainable by the method according to any one of claims 1 to 14.

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

19. The catalyst according to claim 18, wherein the catalyst has a concentration of 10m 2 / g to 40m 2 / g of BET surface area.

20. The catalyst according to claim 18 or claim 19, wherein the catalyst is free of 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.

22. A catalyst-coated membrane comprising an oxygen evolution reaction catalyst according to any one of claims 17 to 21.

23. A fuel cell or water electrolyzer comprising a catalyst-coated membrane according to claim 22.

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