Iridium dioxide catalyst and preparation method and application thereof

Abstract

The invention relates to an iridium dioxide catalyst and a preparation method and application thereof, the iridium dioxide catalyst is a material with a three-dimensional porous structure, and the three-dimensional porous structure comprises mesopores and macropores; the characteristic peak of rutile type iridium dioxide exists in the XRD spectrogram of the iridium dioxide catalyst. When the catalyst disclosed by the invention is used as an anode catalyst in water electrolysis hydrogen production, the loading capacity of the catalyst can be effectively reduced, the dispersity is improved, and meanwhile, the catalyst has better mass transfer effect and conductivity, higher catalytic activity and excellent stability.

Description

Technical Field

[0001] The present disclosure relates to an iridium dioxide catalyst, and in particular, to an iridium dioxide catalyst and a preparation method and application thereof. Background Art

[0002] Proton exchange membrane water electrolysis hydrogen production technology (PEMWE) has the advantages of faster response speed, high ion conductivity, wide operating temperature and working pressure, high current density and hydrogen purity. It is an advanced water electrolysis hydrogen production technology that is currently highly praised by the industry.

[0003] Anode catalysts are a key research direction in PEMWE hydrogen production technology. Water oxidation occurs at the anode to generate oxygen. Since it is a rising reaction process of four-electron coupled protons, it exhibits a higher overpotential and slow oxygen evolution reaction kinetics. At the same time, the strong oxidizing conditions and strong acidic media at the anode lead to the need for further improvement in the stability of the catalyst. The existing commercial proton exchange membrane water electrolysis anode catalysts are iridium black and iridium oxide. Iridium black has relatively higher activity and better conductivity, while iridium oxide has better stability. At present, the amount of iridium used in membrane electrodes is generally higher than 2 mg / cm 2 However, it is very expensive. Therefore, in order to reduce the cost of iridium dioxide catalysts, on the one hand, it is necessary to reduce the amount of iridium in the membrane electrode while ensuring performance, and on the other hand, it is necessary to further improve the electrochemical activity and stability of iridium dioxide catalysts, especially the electrochemical performance for high currents.

[0004] The commercial anode catalyst for proton exchange membrane water electrolysis is a bulk catalyst composed of iridium and its oxide. If you want to use a supported strategy to reduce the amount of iridium metal, you need to develop a new carrier with good conductivity, strong corrosion resistance, easy catalyst anchoring and high dispersion. Carbon carriers are difficult to meet such requirements. Catalysts prepared by doping with other metal elements will face corrosion resistance problems after doping, which will affect stability. In addition, rutile iridium dioxide has higher stability than elemental iridium and amorphous iridium oxide, but its activity is relatively poor. How to develop an iridium dioxide catalyst with both high activity and stability still faces great challenges.

[0005] However, the current synthesis of oxide-based catalysts with novel micromorphologies typically requires the use of surfactants, reducing agents, nitrates, templates, and organic solvents, resulting in high production costs and the generation of large amounts of hazardous waste byproducts. Therefore, developing convenient, environmentally friendly, and cost-effective synthetic routes is crucial for industrial applications. Summary of the Invention

[0006] In response to the shortcomings of existing commercial iridium dioxide catalysts, the purpose of the present invention is to provide an iridium dioxide catalyst, a preparation method and application thereof. The iridium dioxide catalyst is basically composed of rutile iridium dioxide and has a rich pore structure and a large specific surface area. When used for electrolysis of water to produce hydrogen, it has excellent mass transfer effect and conductivity, maintains high catalytic activity while having excellent stability. The loose structure can also reduce the iridium loading of the catalyst and improve its dispersibility.

[0007] In order to achieve the above-mentioned objectives, the first aspect of the present disclosure provides an iridium dioxide catalyst, which is a material having a three-dimensional porous structure, and the three-dimensional porous structure comprises mesopores and macropores; the XRD spectrum of the iridium dioxide catalyst contains characteristic peaks of rutile iridium dioxide.

[0008] Optionally, the iridium dioxide catalyst contains iridium elements in an amount of 75% by mass or more, and preferably contains iridium elements in an amount of 76-84% by mass.

[0009] Optionally, the iridium dioxide catalyst contains 14-18% by mass of oxygen.

[0010] Optionally, the porosity of the iridium dioxide catalyst is greater than 50%, preferably 70-90%; and / or the specific surface area of ​​the iridium dioxide catalyst is 100-150m 2 / g, preferably 110 to 130 m 2 / g.

[0011] Optionally, the total pore volume of the iridium dioxide catalyst is 0.1 to 0.3 cm 3 / g, preferably 0.16 to 0.26 cm 3 / g.

[0012] Optionally, the apparent mass volume ratio of the iridium dioxide catalyst is not higher than 0.55 g / cm 3 , preferably 0.2 to 0.34 g / cm 3 , more preferably 0.22 to 0.3 g / cm 3 .

[0013] Optionally, the three-dimensional porous structure of the iridium dioxide catalyst is formed by connecting nanosheets; the average thickness of the nanosheets is 1.5 to 6.5 nm, preferably 2 to 4.5 nm.

[0014] Optionally, in the XRD spectrum of the iridium dioxide catalyst, the half-peak width of the main diffraction peak of rutile iridium dioxide is 1.5 to 3°, preferably 1.6 to 2.4°.

[0015] A second aspect of the present disclosure provides a method for preparing an iridium dioxide catalyst, the preparation method comprising:

[0016] (1) mixing a polysaccharide with water to form a first sol; mixing an iridium source precursor, a complexing agent, and water, and adjusting the pH of the resulting mixture to 5 to 10 to obtain an iridium source solution;

[0017] (2) mixing the first sol with the iridium source solution to form a second sol; and subjecting the second sol to a first drying to obtain an aerogel;

[0018] (3) calcining the aerogel at a temperature of 200° C. or higher without generating elemental iridium;

[0019] (4) subjecting the obtained calcined product to post-treatment or not, and then subjecting the obtained calcined product to annealing treatment, wherein the annealing treatment temperature is 330° C. or higher;

[0020] Wherein, the complexing agent is a polycarboxylate having a hydroxyl group, and the polysaccharide is one or more selected from the group consisting of an alkali metal salt of alginic acid, an alkali metal salt of carboxymethyl cellulose and an alkali metal salt of hyaluronic acid.

[0021] Optionally, in step (1), the iridium source precursor is selected from one or more of anhydrous iridium chloride, iridium chloride hydrate, chloroiridic acid, iridium acetylacetonate, iridium acetate and alkali metal salts of chloroiridic acid; and / or, the complexing agent is selected from one or more of alkali metal salts of citric acid, tartaric acid and malic acid; and / or, the molar ratio of the iridium source precursor to the complexing agent is (0.25-4):1, preferably (0.5-2):1.

[0022] Optionally, in step (2), the mass ratio of polysaccharide to iridium source precursor in the second sol is (0.1 to 20):1, preferably (0.2 to 10):1; and / or, the first drying includes supercritical drying and / or freeze drying, preferably freeze drying; the freeze drying conditions include: temperature of -30 to -20°C, preferably -25 to -20°C; time of 24 to 48 hours, preferably 36 to 48 hours.

[0023] Optionally, in step (3), the calcination conditions include: temperature of 220-300°C, preferably 250-280°C; time of 0.5-6h, preferably 2-3h; heating rate of 2-10°C / min, preferably 2-5°C / min.

[0024] Optionally, the post-treatment includes washing the calcined product and performing a second drying; the washing includes: sequentially performing acid washing, water washing and alcohol washing on the calcined product, the acid used for the acid washing is selected from one or more of dilute hydrochloric acid, sulfuric acid, nitric acid and acetic acid, and the alcohol used for the alcohol washing is selected from one or more of methanol, ethanol and isopropanol; and / or, the conditions for the second drying include: a temperature of 40 to 60°C, preferably 45 to 55°C; and a time of 2 to 24 hours, preferably 10 to 20 hours.

[0025] Optionally, in step (4), the annealing treatment conditions include: heating the calcined product in an air atmosphere to an annealing temperature; the annealing temperature is above 350°C, preferably 360-550°C, and the annealing holding time is 0.5-2h, preferably 1-2h.

[0026] The third aspect of the present disclosure provides an iridium dioxide catalyst prepared by the preparation method described in the second aspect of the present disclosure.

[0027] A fourth aspect of the present disclosure provides a use of the iridium dioxide catalyst described in the first aspect and / or the third aspect of the present disclosure in hydrogen production by PEM water electrolysis.

[0028] Optionally, the iridium dioxide catalyst is used as an oxygen evolution catalyst for PEM water electrolysis to produce hydrogen.

[0029] A fifth aspect of the present disclosure provides a membrane electrode, comprising a proton exchange membrane and an oxygen evolution catalyst layer coated on the proton exchange membrane, wherein the oxygen evolution catalyst layer comprises the iridium dioxide catalyst described in the first aspect and / or the third aspect.

[0030] A sixth aspect of the present disclosure provides a water electrolyzer, comprising an anode catalyst, wherein the anode catalyst is the iridium dioxide catalyst described in the first aspect and / or the third aspect of the present disclosure.

[0031] Through the above technical solution, the present disclosure provides an iridium dioxide catalyst and its preparation method and application, wherein the iridium dioxide catalyst is basically composed of rutile iridium dioxide, which is a stable and loose three-dimensional porous material with mesopores and macropores, so that the catalyst has a large specific surface area and high porosity, and therefore has better mass transfer performance and apparent catalytic activity. Further, the catalyst is a three-dimensional porous material formed by connecting nanosheets, which not only has the high catalytic activity of nanomaterials, but also can avoid the deactivation of catalyst aggregation, so that the catalyst maintains a high catalytic activity while having excellent stability, and solves the activity and stability problems of nanomaterials to a large extent. Furthermore, the catalyst has a micromorphology of a three-dimensional multi-level pore structure comprising continuously distributed mesopores and macropores, which can fully expose the active sites inside the material, improve the utilization rate of the iridium element, thereby reducing the iridium load, reducing the use cost of the iridium dioxide catalyst, and improving its dispersibility. The iridium dioxide catalyst provided by this disclosure improves the performance of existing iridium dioxide. When applied to water electrolysis for hydrogen production, it exhibits superior oxygen evolution activity, a low initial overpotential, a low Tafel slope, and a smaller increase in the final overpotential after stability testing compared to the initial overpotential, maintaining good stability and promising prospects for industrial application. Furthermore, the preparation method provided by this disclosure is simple, convenient, and highly economical.

[0032] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following detailed description, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0034] Figure 1 is a SEM image of catalyst C1 prepared in Example 1 of the present disclosure;

[0035] Figure 2 is the XRD pattern of catalyst C1 prepared in Example 1 of the present disclosure;

[0036] Figure 3 is the XPS spectrum of Ir 4f of catalyst C1 prepared in Example 1 of the present disclosure;

[0037] Figure 4 is a cyclic voltammogram of catalyst C1 prepared in Example 1 of the present disclosure;

[0038] Figure 5 This is a diagram of the bubble discharge when the catalyst C1 prepared in Example 1 of the present disclosure is coated on carbon paper to prepare an electrode for water electrolysis reaction;

[0039] Figure 6is a SEM image of commercial iridium dioxide D2 used in Comparative Example 2 of the present disclosure;

[0040] Figure 7 is a cyclic voltammogram of the commercial iridium dioxide D2 used in Comparative Example 2 of the present disclosure;

[0041] Figure 8 This is a diagram of bubble discharge when commercial iridium dioxide D2 used in Comparative Example 2 of the present disclosure is coated on carbon paper to prepare an electrode for water electrolysis reaction. DETAILED DESCRIPTION

[0042] The following describes the specific embodiments of the present disclosure in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0043] Terminology Notes:

[0044] The term "mesopore" is defined as pores with a pore diameter ranging from 2 nm to 50 nm, "macroporous" is defined as pores with a pore diameter greater than 50 nm; and "micropores" are defined as pores with a pore diameter less than 2 nm.

[0045] In a first aspect, the present disclosure provides an iridium dioxide catalyst, which is a material having a three-dimensional porous structure, wherein the three-dimensional porous structure comprises mesopores and macropores; and the XRD spectrum of the iridium dioxide catalyst contains characteristic peaks of rutile iridium dioxide.

[0046] The term "material with a three-dimensional porous structure" is defined as a material with a porosity greater than 15%, and the shape, existence form or distribution state of the pores in the material are not restricted. For example, it can be composed of mesopores with a pore diameter in the range of 2nm to 50nm and macropores with a pore diameter greater than 50nm, wherein the existence form of the pores may include cross-linked pores, through holes or blind holes, and the distribution state may include uniform or irregular distribution on the surface or inside of the material. In a preferred embodiment, the three-dimensional porous structure disclosed in the present invention includes continuously distributed mesopores and macropores, which constitute a continuous mesopore-macroporous multi-level pore structure as a whole.

[0047] In the XRD spectrum, the position of each peak is represented by 2θ. Due to instrument deviation, differences in measurement environment, etc., the results may vary. In the XRD spectrum, "near" each 2θ value means the range of ±0.2° of the 2θ value.

[0048] Iridium dioxide catalysts are generally more stable than iridium black catalysts and have better stability during long-term operation. The iridium dioxide catalyst provided by the present disclosure is basically composed of rutile-type iridium dioxide, and has a stable and loose mesoporous-macroporous three-dimensional porous structure, so that the catalyst not only has a large specific surface area and porosity, which is beneficial to promote the mass transfer process and improve the apparent catalytic activity, but also can avoid catalyst agglomeration and deactivation. Compared with existing commercial iridium dioxide catalysts, the iridium dioxide catalyst disclosed in the present disclosure has excellent acidic electrochemical activity and stability. At the same time, the loose porous structure of the catalyst can fully expose the active sites inside the material, improve the utilization rate of the iridium element, and help to reduce the iridium loading of the membrane electrode while maintaining or improving the catalytic activity, reduce the use cost of the iridium dioxide catalyst, and improve its dispersibility.

[0049] In the present disclosure, the iridium element in the iridium dioxide catalyst basically exists in the form of rutile iridium dioxide, and there is an obvious characteristic peak of rutile iridium dioxide in the XRD spectrum.

[0050] The iridium dioxide catalyst disclosed herein may contain a small amount or trace amount of other elements due to the presence of impurities in the synthetic raw materials, but these factors have no significant effect on the structural properties and catalytic performance of the final catalyst. The present disclosure does not need to limit the types and contents of these impurities.

[0051] In one embodiment of the present disclosure, the mass fraction of the iridium element in the iridium dioxide catalyst can be 74%, 76%, 78%, 80%, 81%, 84%, 86% or 88%, or the mass fraction of the iridium element is within the numerical range between any two of them. Preferably, the iridium dioxide catalyst contains an iridium element with a mass fraction of 76 to 84%. In the above embodiment, by selecting an iridium element with a preferred content, it is beneficial to further optimize the composition and structure of the catalyst, improve the conductivity of the catalyst, and then improve its electrocatalytic activity. The content of iridium in the iridium dioxide catalyst disclosed herein is obtained by XRF testing.

[0052] In one embodiment of the present disclosure, the iridium dioxide catalyst contains 15%, 17%, or 20% oxygen by mass, or an oxygen mass fraction within a range between any two of these, preferably 14% to 18% oxygen by mass. In the above embodiment, the oxygen in the iridium dioxide catalyst is primarily present in the form of an oxide.

[0053] In one embodiment of the present disclosure, the iridium dioxide catalyst has a relatively high porosity, for example, the porosity of the iridium dioxide catalyst is greater than 50%, preferably 65-90%, more preferably 70-90%, 70-85%, or 70-80%. In the above embodiment, the iridium dioxide catalyst has a relatively high porosity, which makes the catalyst more bulky, which is beneficial to promoting the mass transfer process.

[0054] In one embodiment, the specific surface area of ​​the iridium dioxide catalyst is 100 to 150 m 2 / g, preferably 110 to 130 m 2 In the above embodiment, the iridium dioxide catalyst has a large specific surface area, which is beneficial to improving the mass specific activity.

[0055] In one embodiment, the total pore volume of the iridium dioxide catalyst is 0.1 to 0.3 cm 3 / g, preferably 0.16 to 0.26 cm 3 / g.

[0056] In one embodiment, the apparent mass volume ratio of the iridium dioxide catalyst does not exceed 0.55 g / cm 3 , preferably not higher than 0.45g / cm 3 , further preferably not higher than 0.4g / cm 3 , further preferably not higher than 0.35g / cm 3 In a preferred embodiment, the apparent mass volume ratio of the iridium dioxide catalyst is 0.2 to 0.34 g / cm 3 , preferably 0.22 to 0.3 g / cm 3 .

[0057] In the above embodiment, the iridium dioxide catalyst has a loose, porous microstructure with a high degree of bulk, which is beneficial for improving the mass transfer efficiency of the catalyst, thereby increasing the electrocatalytic activity of the catalyst, while also reducing the iridium loading of the catalyst. The total pore volume is the volume of pores with a pore size range of 2 to 200 nm as measured by the BET test. It is understood that since the catalyst also contains macropores with a pore size greater than 200 nm, the measured pore volume is the pore volume of pores with relatively smaller pore sizes (2 to 200 nm) in the catalyst.

[0058] In one embodiment, the three-dimensional porous structure of the iridium dioxide catalyst disclosed herein comprises continuously distributed mesopores and macropores, which constitute a continuous mesopore-macroporous multi-level pore structure as a whole; for example, comprising continuously distributed mesopores and macropores with a pore size of 2 to 1000 nm, preferably 2 to 500 nm. Further, the three-dimensional pore structure of the catalyst can be a multi-level pore structure with continuously distributed mesopores and macropores, which can comprise continuously distributed mesopores-macroporous with a pore size of 2 to 200 nm and a certain number of macropores with a pore size > 200 nm. "Multi-level pores with continuously distributed mesopores-macroporous pores" refers to a multi-level pore structure composed of continuous macropores (pore size > 200 nm)-mesopores (pore size 2 to 50 nm) around macropores (pore size > 200 nm), wherein "continuous" refers to the presence of pores of various pore sizes, for example, pores of various pore sizes in the range of 2 nm to 200 nm exist. It is believed that mesopores provide a large specific surface area, expose more reaction sites, and participate in gas transport; while macropores, especially ultra-large pores with sizes of hundreds of nanometers, are very conducive to water transport and significantly reduce the apparent mass-to-volume ratio of the catalyst.

[0059] In a further embodiment, the three-dimensional porous structure of the iridium dioxide catalyst disclosed herein may further include micropores, wherein the micropores account for a relatively small proportion. In one specific embodiment, the specific surface area of ​​the micropores of the iridium dioxide catalyst relative to the specific surface area of ​​the catalyst as a whole is no greater than 35%, preferably no greater than 20%, more preferably no greater than 15%, and even more preferably no greater than 10%.

[0060] Iridium is one of the densest elements in existence. The density of metallic iridium is as high as 22.65g / cm 3 The iridium dioxide catalyst provided in the present disclosure has the above-mentioned loose and porous microstructure, especially the main part of the porous structure of the iridium dioxide catalyst includes mesopores and macropores. Therefore, the apparent mass volume ratio of the iridium dioxide catalyst is much lower than the density of the above-mentioned metallic iridium, and the iridium dioxide catalyst has the above-mentioned higher surface area. These physical properties further indicate that the iridium dioxide catalyst disclosed in the present disclosure has a loose and porous structure.

[0061] In one embodiment of the present disclosure, the three-dimensional porous structure of the iridium dioxide catalyst is formed by connecting very thin nanosheets, specifically, the three-dimensional porous structure formed by connecting nanosheets in three-dimensional space; in a preferred embodiment, the entity part of the microstructure of the iridium dioxide catalyst of the present disclosure is formed by connecting continuous sheet-like entities of nanosheets to each other, and the nanosheets extend to form the pore walls ("walls") of a plurality of holes, and the nanosheets also cover the holes to form the "surfaces" of the holes, and the nanosheets as the "surfaces" and "walls" are connected to each other or overlap each other, and the holes between the nanosheets are staggered and connected, thereby forming a three-dimensional porous microstructure, such as Figure 1 shown.

[0062] The iridium dioxide catalyst disclosed herein has a three-dimensional porous structure formed by continuous nanosheets. The nanosheets are small and very thin, resulting in a high porosity and bulkiness of the catalyst. The nanosheets have a size of, for example, less than 500 nm. In a preferred embodiment, the microstructure contains essentially no portions thicker than 10 nm, meaning that the thickness of the nanosheets forming the pore walls of the three-dimensional porous structure is substantially no greater than 10 nm. The nanosheets preferably have a thickness of 1.5 to 6.5 nm, and more preferably 2 to 4.5 nm. Because the nanosheets are so thin, they can be referred to as two-dimensional nanosheets. Thus, the iridium dioxide catalyst disclosed herein has the high catalytic activity of nanomaterials. At the same time, because it is a three-dimensional multi-level pore structure formed by continuous extension of nanosheets and interconnected in three-dimensional space, with continuously distributed mesopores and macropores, and particularly contains a certain number of macropores with a pore size of 200nm or more, the catalyst as a whole is more loose and porous, which is conducive to improving mass transfer efficiency and apparent activity, and avoids the deactivation of the iridium dioxide catalyst by aggregation, improves the dispersion performance of the catalyst in the slurry, and largely solves the activity and stability problems of the nanomaterials. It is also conducive to reducing the usage of the iridium dioxide catalyst. Among them, the average thickness of the nanosheets is measured by SEM and statistically analyzed using Nano Measurer 1.2 software.

[0063] In one embodiment of the present disclosure, the continuous nanosheets in the iridium dioxide catalyst are formed by closely arranging and interconnecting a plurality of small-sized nanocrystals of iridium dioxide, and the average particle size of the iridium dioxide nanocrystals is 2 to 6 nm, preferably 2 to 4 nm. In the above embodiment, the grain size of the iridium dioxide nanocrystals is relatively small, and the thickness of the formed nanosheets is also relatively thin, for example, the thickness is only 1.5 to 6.5 nm, so that the internal structure of the iridium dioxide catalyst composed of the nanosheets is looser, and the specific surface area and porosity are larger. In a preferred embodiment, the nanosheets formed by the small-sized nanocrystals have a wrinkled graphene-like shape, which is conducive to further improving the apparent activity of the catalyst. In the present disclosure, the size of the nanoparticles can be obtained by TEM testing.

[0064] In one embodiment of the present disclosure, the XRD spectrum of the iridium dioxide catalyst basically only has the characteristic diffraction peak of rutile iridium dioxide with a peak broadening, and the characteristic diffraction peak of elemental iridium does not appear. Specifically, the XRD spectrum of the rutile iridium dioxide catalyst shows an obvious main diffraction peak (101 crystal plane diffraction peak) of rutile iridium dioxide with a peak broadening near 2θ=34.8°, and the half-peak width of the main diffraction peak is 1.5~3°, preferably 1.6~2.4°. In the above embodiment, the relatively widened half-peak width indicates that the grain size of iridium dioxide is relatively small, which can bring more electrochemical active sites, which is beneficial to the improvement of OER performance.

[0065] In one embodiment of the present disclosure, the XPS Ir 4f spectrum of the iridium dioxide catalyst has characteristic peaks of Ir 4+ and a satellite peak, but does not have characteristic peaks of Ir 3+ , in particular, the binding energy of the Ir 4+ 4f 7 / 2 peak is between 61 and 62 eV. The surface layer of the iridium dioxide catalyst of the present disclosure is rich in high-valence Ir 4+ , which is beneficial to improve the stability of the catalyst. The "surface layer" refers to a region with a detection depth of less than 10 nm from the outer surface of the iridium dioxide catalyst, and in particular, the detection depth of XPS is used as a reference.

[0066] The second aspect of the present disclosure provides a preparation method of an iridium dioxide catalyst, which comprises:

[0067] (1) mixing polysaccharide with water to form a first sol; mixing iridium source precursor and complexing agent with water, adjusting the pH of the obtained mixed solution to 5-10 to obtain an iridium source solution;

[0068] (2) mixing the first sol with the iridium source solution to form a second sol; performing first drying on the second sol to obtain an aerogel;

[0069] (3) calcining the aerogel, the calcination temperature is above 200℃, and does not cause the generation of elemental iridium;

[0070] (4) performing or not performing post-treatment on the obtained calcined product, and then performing annealing treatment, the annealing temperature is above 330℃;

[0071] The complexing agent is a polycarboxylic acid salt with hydroxyl groups, and the polysaccharide is selected from one or more of alkali metal salts of alginic acid, alkali metal salts of carboxymethyl cellulose and alkali metal salts of hyaluronic acid.

[0072] The method of the present disclosure uses specific polysaccharides and complexing agents to form an iridium-containing hydrogel, and uses the three-dimensional sheet-shaped structure of the aerogel obtained by drying the hydrogel as a precursor, and performs calcination at a specific temperature to obtain a three-dimensional porous iridium dioxide catalyst mainly composed of iridium dioxide, and does not cause the generation of elemental iridium. The aerogel preparation method of the present disclosure is different from the existing aerogel preparation method. The aerogel of the present disclosure is directly formed by drying the flowable hydrogel, and does not form a hydrogel before the preparation of the aerogel.

[0073] The preparation method provided by the present disclosure is simple and convenient, the synthesis route is green and economical, the obtained iridium dioxide catalyst has a novel three-dimensional porous loose structure, the microstructure shows that the structure is connected by very thin nanosheets, has a large specific surface area, and thus can have high catalytic activity and high stability, and has excellent electrochemical catalytic performance, and can be used in water electrolysis to produce hydrogen.

[0074] The term "sol" in the present disclosure is defined as a dispersion system having fluidity and a viscosity greater than water.

[0075] In one embodiment of the present disclosure, in step (1), the polysaccharide is selected from one or more of an alkali metal salt of alginic acid, an alkali metal salt of carboxymethyl cellulose, and an alkali metal salt of hyaluronic acid. Preferably, in one embodiment, the alkali metal salt of each polysaccharide can be independently a sodium salt, a potassium salt. Specifically, when the polysaccharide is selected from an alkali metal salt of alginic acid, it can be sodium alginate or potassium alginate; when the polysaccharide is selected from an alkali metal salt of carboxymethyl cellulose, it can be sodium carboxymethyl cellulose or potassium carboxymethyl cellulose; and when the polysaccharide is selected from an alkali metal salt of hyaluronic acid, it can be sodium hyaluronate or potassium hyaluronate.

[0076] In one embodiment of the present disclosure, the iridium source precursor can use various types of iridium source precursors known to those skilled in the art, and preferably, the iridium source precursor is selected from one or more of anhydrous iridium chloride, iridium chloride hydrate, chloroiridic acid, acetylacetone iridium, iridium acetate, and an alkali metal salt of chloroiridic acid, wherein the alkali metal salt of chloroiridic acid includes sodium chloroiridate and potassium chloroiridate.

[0077] In the present disclosure, as the polybasic carboxylic acid having a hydroxyl group, it can be a carboxylic acid having 1 to 4 hydroxyl groups, 2 to 4 carboxyl groups, and a total carbon atom number of 3 to 10.

[0078] In one embodiment, the polybasic carboxylic acid having a hydroxyl group has 1 to 2 hydroxyl groups. In one embodiment of the present disclosure, the polybasic carboxylic acid having a hydroxyl group has 2 to 3 carboxyl groups. In one embodiment of the present disclosure, the polybasic carboxylic acid having a hydroxyl group has a total carbon atom number of 4 to 8.

[0079] In one embodiment of the present disclosure, the polybasic carboxylic acid having a hydroxyl group is at least one selected from malic acid, citric acid, isocitric acid, tartronic acid, tartaric acid, 3-hydroxy-3-methylglutaric acid, and mevalonic acid. In one embodiment of the present disclosure, the salt of the polybasic carboxylic acid having a hydroxyl group can be independently an alkali metal salt, an alkaline earth metal salt. More preferably, the salt of the polybasic carboxylic acid having a hydroxyl group can be independently an alkali metal salt.

[0080] In one embodiment of the present disclosure, the salt of the polybasic carboxylic acid having a hydroxyl group can be independently a sodium salt, a potassium salt, a calcium salt, and an ammonium salt.

[0081] In one embodiment of the present disclosure, the complexing agent is selected from one or more alkali metal salts of citric acid, tartaric acid and malic acid, and the alkali metal salt is preferably a sodium salt or a potassium salt; for example, the complexing agent can be sodium citrate, potassium citrate, sodium tartrate, potassium tartrate, sodium malate or potassium malate.

[0082] In one embodiment of the present disclosure, the molar ratio of the iridium source precursor to the complexing agent is (0.25-4):1, preferably (0.5-2):1. In the above embodiment, by selecting the preferred components and contents, it is beneficial to synthesize a more loose and porous iridium dioxide catalyst, further improving the specific surface area and stability of the catalyst.

[0083] In one embodiment, in step (1), the pH of the resulting mixed solution is adjusted to 5 to 10, preferably 6 to 10, which is conducive to forming a uniform and stable state of the iridium source solution. The pH can be adjusted using conventional methods and reagents in the art, such as ammonia water, alkali metal hydroxides or alkaline salts.

[0084] In one embodiment of the present disclosure, in step (2), the mass ratio of the polysaccharide to the iridium source precursor in the second sol is (0.1-20):1, preferably (0.2-10):1.

[0085] In one embodiment, the first drying includes supercritical drying and / or freeze drying. In a preferred embodiment, the drying is freeze drying, which is conducive to obtaining an aerogel with a porous structure, and the freeze drying conditions include: a temperature of -30 to -20°C, preferably -25 to -20°C; a time of 24 to 48 hours, preferably 36 to 48 hours. In the above embodiment, by selecting a preferred mass ratio, it is conducive to forming a more stable and porous three-dimensional aerogel intermediate and accurately controlling the pyrolysis process; by selecting the preferred freeze drying, an aerogel with a porous structure can be obtained. In one embodiment of the present disclosure, after freeze drying, the temperature is further raised to 10 to 40°C for drying.

[0086] In one embodiment of the present disclosure, in step (3), the aerogel is calcined to prepare a calcined product. In one embodiment of the present disclosure, the calcined product is the iridium-based catalyst of the present disclosure. In an embodiment in which the calcined product is further subjected to a post-treatment step, the product obtained by post-treatment after calcination is the iridium-based catalyst of the present disclosure.

[0087] In one embodiment of the present disclosure, in step (3), the calcination conditions include: a temperature of 220°C or more and does not result in the production of elemental iridium, preferably 250°C or more and does not result in the production of elemental iridium, further preferably 220-300°C, more preferably 250-280°C; a time of 0.5-6h, preferably 1-4h, more preferably 2-3h; a heating rate of 2-10°C / min, preferably 2-5°C / min. In the above embodiment, by selecting the preferred calcination conditions, it is beneficial to convert the porous aerogel into an iridium dioxide catalyst having a three-dimensional porous structure. Under the aforementioned calcination conditions, the obtained iridium dioxide catalyst is basically composed of rutile iridium dioxide.

[0088] In one embodiment of the present disclosure, the calcination is performed in an air atmosphere.

[0089] In one embodiment of the present disclosure, the calcined product in step (3) is optionally subjected to a post-treatment step, wherein the post-treatment comprises washing and / or a second drying of the calcined product.

[0090] In one embodiment, the washing in step (3) comprises: acid washing, water washing, and alcohol washing of the calcined product. In the washing, the order of acid washing, water washing, and alcohol washing is not particularly limited, and can be acid washing, water washing, and alcohol washing in sequence; or acid washing, alcohol washing, and water washing in sequence; or water washing, acid washing, and alcohol washing in sequence. In a preferred embodiment of the present disclosure, the washing in step (3) comprises: acid washing, water washing, and alcohol washing of the calcined product in sequence.

[0091] In one embodiment, in the washing of step (3), the acid used for the acid washing is selected from one or more of dilute hydrochloric acid, sulfuric acid, nitric acid and acetic acid, and the alcohol used for the alcohol washing is selected from one or more of methanol, ethanol and isopropanol, wherein the alcohol washing can use alcohol or a mixed solution of alcohol and water.

[0092] In one embodiment, the number of times of washing with each washing solution is not particularly limited, and those skilled in the art can appropriately select it according to needs, for example, 1 time, 2 times, 3 times, 4 times or 5 times.

[0093] In one embodiment, the second drying conditions include: a temperature of 40-60°C, preferably 45-55°C, and a time of 2-24 hours, preferably 10-20 hours. In the above embodiment, by selecting the preferred washing and second drying, impurities such as inorganic salts, carbon, and metal elements remaining on the catalyst surface can be further removed.

[0094] In one embodiment of the present disclosure, in step (4), the annealing treatment conditions include: heating the calcined product in an air atmosphere to an annealing temperature; the annealing temperature is 330°C or higher without destroying the three-dimensional porous structure, preferably 350°C or higher without destroying the three-dimensional porous structure, further preferably 360-550°C, and the annealing holding time is 0.5-2h, preferably 1-2h. In the above embodiment, by selecting the preferred annealing treatment, the elemental iridium on the catalyst surface can be controlled to be converted into rutile iridium dioxide, and the pore structure of the catalyst is substantially not affected.

[0095] The third aspect of the present disclosure provides an iridium dioxide catalyst prepared by the method described in the second aspect of the present disclosure.

[0096] A fourth aspect of the present disclosure provides a use of the iridium dioxide catalyst described in the first aspect and / or the third aspect of the present disclosure in hydrogen production by PEM water electrolysis.

[0097] In one embodiment of the present disclosure, the iridium dioxide catalyst is used as an oxygen evolution catalyst for PEM water electrolysis to produce hydrogen.

[0098] A fifth aspect of the present disclosure provides a membrane electrode, comprising a proton exchange membrane and an oxygen evolution catalyst layer coated on the proton exchange membrane, wherein the oxygen evolution catalyst layer comprises the iridium dioxide catalyst described in the first aspect and / or the third aspect.

[0099] A sixth aspect of the present disclosure provides a water electrolyzer, comprising an anode catalyst, wherein the anode catalyst is the iridium dioxide catalyst described in the first aspect and / or the third aspect of the present disclosure.

[0100] The iridium dioxide catalyst provided by the present disclosure can reduce the amount of catalyst used when used for hydrogen production by water electrolysis, while also exhibiting excellent electrochemical catalytic performance, a low initial overpotential, a low Tafel slope, and a small increase in the final overpotential after stability testing compared to the initial overpotential, showing promising prospects for industrial application. In specific embodiments of the present disclosure, the iridium dioxide catalyst is used as an oxygen evolution catalyst for hydrogen production by water electrolysis, which can reduce the amount of iridium used in the membrane electrode.

[0101] In this disclosure, the directly recorded contents shall prevail first, and any other matters or issues not mentioned shall be directly applicable to the existing knowledge in the art without any change.

[0102] The present disclosure is further illustrated by the following examples, but the present disclosure is not limited thereby. Unless otherwise specified, the raw materials used in the examples and comparative examples of the present disclosure were purchased from commercial sources and are pure reagents; the relevant reagents can be prepared into aqueous or alcohol solutions of a certain concentration for subsequent use.

[0103] Instrumental method for BET analysis: The model of the fully automatic BET specific surface area tester is JW-BK200C produced by Jingwei Gaobo. The test conditions include: the test principle is the static capacity method, the adsorption gas is N2, the adsorption temperature is 77K, the N2 adsorption and desorption curve of the catalyst is obtained by test, the multi-point BET specific surface area is obtained by analysis and calculation, the pore volume and pore size distribution are obtained by BJH method analysis, and the micropore analysis adopts the slit pore HK method.

[0104] Calculation of porosity: Porosity = 100% × pore volume / (pore volume + solid volume), where the pore volume is determined based on the BET test, with a pore size range of 2 to 200 nm. This means that the measured pore volume is the pore volume of all pores with a pore size range of 2 to 200 nm. The solid volume is calculated based on the mass and density of the catalyst. The solid volume of the catalyst is determined by dividing the iridium dioxide content by the density through XRF analysis. It is understood in the art that since the catalyst also contains macropores with a pore size greater than 200 nm, and the BET test pore size range is 2 to 200 nm, the pore volume measured in this manner is the pore volume of the relatively smaller pores of the catalyst with a pore size of 2 to 200 nm. Therefore, the calculated porosity is also the minimum porosity of the catalyst.

[0105] In the present disclosure, the apparent mass volume ratio is also called the apparent density, which refers to the ratio of the actual mass of the catalyst to the apparent volume. The apparent volume refers to the sum of the actual volume of the catalyst and the closed pore volume. The specific method for determining the apparent mass volume is as follows: the catalyst is sieved, and a catalyst with a particle size of 15 μm or less is selected as a sample. The sample is naturally placed in a precision graduated cylinder with a scale to 1-2 ml, and the volume value is read as the apparent volume. More specifically, the sample is poured freely into a precision graduated cylinder with a scale to 1-2 ml, the graduated cylinder is vertically tilted and slightly shaken so that its upper surface is parallel to the scale line, and the volume value is read as the apparent volume. For details, reference can be made to the determination method of loose bulk density in GB / T 13566.1-2008. Thus, the apparent mass volume ratio can be calculated, and the apparent mass volume ratio is measured three times and the average value is taken.

[0106] Instrumental method for mass transfer performance testing: A typical three-electrode system was used, and the constant current test was performed using a CHI760E electrochemical workstation. CV activation and stabilization were first performed, and non-wetted bubbles on the electrode surface were removed. Then, a constant current test was performed. A high-speed industrial camera was used to capture the bubbles generated on the electrode surface during the test.

[0107] Instrumental method for testing iridium content: An X-ray fluorescence spectrometer (XRF) was used, model Rigaku Priums IV, produced by Japan. The catalyst was pressed into pellets for full elemental analysis. Light elements such as C, H, and O were analyzed using more precise C, H, and O elemental analyzers. Prior to testing, the catalyst was not pre-treated with vacuum to remove water, oxygen, or other adsorption media.

[0108] X-ray diffraction (XRD) was used to analyze the phase and ratio of elemental iridium and iridium oxide in the catalyst bulk phase in the disclosed Examples and Comparative Examples. X-ray diffraction (XRD) analysis was performed using a Shimadzu XRD-6000 X-ray diffractometer. Test conditions included: tube voltage of 40 kV, tube current of 40 mA, Cu target Kα radiation, a 2θ scan range of 5°-80°, and a scan rate of 5° / min. The main peak was analyzed using the analyze half-width function in Jade 6.5 software.

[0109] SEM was used to analyze the morphological characteristics of the catalyst, the thickness of the nanosheets and the size of the nanoparticles, and NanoMeasurer 1.2 software was used for statistical analysis. The instrument, method and conditions for SEM analysis were as follows: the scanning electron microscope (SEM) model was a Hitachi S-4800 scanning electron microscope, the operating voltage was 5kV-20kV, and it was equipped with energy dispersive X-ray spectroscopy (EDS).

[0110] XPS was used to analyze the element types and contents of the catalyst surface layer. The instrument, method, and conditions for XPS analysis were as follows: an ESCALab220i-XL X-ray electron spectrometer equipped with Avantage V5.926 software produced by VG Scientific was used as the X-ray photoelectron spectrometer. The X-ray photoelectron spectrometer test conditions were as follows: the excitation source was monochromatic A1Kα X-ray with a power of 330 W, and the basic vacuum during the analysis was 3×10 -9 In addition, the electron binding energy was calibrated using the C1s peak of elemental carbon (284.8 eV) using CasaXPS 2.3.25PR 1.0.

[0111] Example 1

[0112] (1) Weighing 0.8 g of sodium alginate and dissolving it in ultrapure water to prepare a 0.8 wt% first sol; weighing appropriate amounts of IrCl3 and sodium citrate and dissolving them in ultrapure water to obtain a mixture having a molar ratio of IrCl3 to sodium citrate of 0.8:1, and then adjusting the pH of the mixture to 7.5 to obtain a uniform and stable iridium source solution;

[0113] (2) adding the iridium source solution to the first sol, stirring and dispersing the solution uniformly to obtain a second sol, wherein the mass ratio of the polysaccharide sodium alginate to the iridium source precursor IrCl3 in the second sol is 4:1; placing the second sol in a freeze drying oven for freeze drying at a temperature of -20°C for 40 hours until it becomes an aerogel with a porous structure;

[0114] (3) The aerogel is placed in a muffle furnace in an air atmosphere with a certain flow rate, and calcined at 280°C for 2.5 hours with a heating rate of 5°C / min to obtain a calcined product; the calcined product is naturally cooled to room temperature, and the cooled calcined product is centrifuged and washed several times in dilute acid, ultrapure water and alcohol-water mixed solutions until the pH of the supernatant is neutral, and then placed in a vacuum drying oven for a second drying at a temperature of 50°C and a time of 12 hours, and the second dried product is collected.

[0115] (4) The second dried product was placed in a muffle furnace and heated to an annealing temperature in an air atmosphere with a certain flow rate for annealing treatment. The annealing temperature was 360°C, the annealing holding time was 1.5 h, and the heating rate was 3°C / min. Catalyst 1 was collected and labeled as C1. Its composition is shown in Table 1.

[0116] The total pore volume of catalyst C1 prepared in this example is 0.212 cm 3 / g, and a specific surface area of ​​118.2m 2 / g, and the apparent mass volume ratio is 0.235g / cm 3 .

[0117] The SEM image of catalyst C1 prepared in this example is shown in Figure 1 , where the right picture is an enlarged picture of the white box area in the left picture; XRD spectrum is shown in Figure 2 , the XPS spectrum of Ir 4f is shown in Figure 3 , cyclic voltammetry spectrum see Figure 4 The bubble discharge diagram of the electrolytic water reaction when the catalyst C1 is coated on carbon paper to prepare an electrode is shown in FIG. Figure 5 .

[0118] According to Table 1 and Figure 1Catalyst C1 exhibits a three-dimensional porous structure composed of continuous, wrinkled graphene-like nanosheets. This structure is rich in a continuous, hierarchical meso-macroporous structure with minimal micropore content. Both the translucent "surface" covering the pores and the pore walls within them are formed by interconnected, multiple, sheet-like, wrinkled graphene-like nanosheets. Specifically, the nanosheets are interconnected in three dimensions. The nanosheets are composed of interconnected, small-sized iridium dioxide nanocrystals with an average grain size of 3.4 nm, resulting in a nanosheet thickness of only 3.8 nm. This indicates that Catalyst C1 possesses a loose, porous microstructure with a high porosity and specific surface area, which improves the catalyst's mass transfer efficiency and apparent electrochemical activity while also reducing catalyst dosage. Comparison with the SEM image of the unannealed material reveals that the pore structure characteristics of the unannealed material are retained after annealing.

[0119] Figure 2 The XRD spectrum of catalyst C1 shows that a broadened main diffraction peak of rutile iridium dioxide appears at 2θ=34.8°, and no characteristic diffraction peak of elemental iridium appears. The half-width of the main peak is 2.18°, which is relatively wide, indicating that the grain size is small, which can bring more electrochemical active sites and is beneficial to the improvement of OER performance.

[0120] Figure 3 The high-resolution XPS spectrum of Ir 4f showed that catalyst C1 had obvious Ir 4+ and satellite peaks, but no Ir 3+ The characteristic peaks of Ir 4+ 4f 7 / 2 The peak binding energy is at 61-62 eV, indicating that the surface of catalyst C1 is rich in high-valent Ir 4+ , which is beneficial to improving the stability of the catalyst. The "surface layer" refers to the area with a detection depth of less than 10nm from the outer surface of the catalyst. Specifically, it is based on the detection depth of XPS.

[0121] Figure 4 The cyclic voltammetry curve shows that the catalyst C1 has an obvious redox peak in the potential range of 0.8V~1.0V vs.RHE (Ir 3+ / Ir 4+ ), a clear redox peak appears in the potential range of 1.2V~1.4V vs.RHE (Ir 4+ / Ir 5+ ); At the same time, the peak current and area are larger, indicating that catalyst C1 has more active sites, which is beneficial to improving its electrochemical activity.

[0122] Figure 5It shows that the bubbles on the electrode surface of catalyst C1 during the reaction are very small and easily desorbed from the electrode surface, indicating that catalyst C1 has a good mass transfer effect and is conducive to maintaining a high oxygen evolution performance at a high current density.

[0123] Example 2

[0124] The same as Example 1, the only difference is that in step (4), the annealing temperature is 480°C, the holding time is 2h, and finally the catalyst 2 is collected and marked as C2. Its composition is shown in Table 1.

[0125] Example 3

[0126] (1) Weighing 0.8 g of sodium carboxymethyl cellulose and dissolving it in ultrapure water to prepare a 0.8 wt% first sol; taking an appropriate amount of chloroiridic acid solution and dispersing it in a solution containing sodium tartrate, wherein the molar ratio of chloroiridic acid to sodium tartrate in the obtained mixture is 1:1, and then adjusting the pH of the mixture to 6.5 to obtain an iridium source solution;

[0127] (2) adding the iridium source solution to the first sol, stirring and dispersing the solution uniformly to obtain a second sol, wherein the mass ratio of the polysaccharide to the iridium source precursor in the second sol is 0.5:1; placing the second sol in a freeze drying oven for freeze drying at a temperature of -25°C for 45 hours until the sol becomes an aerogel with a porous structure;

[0128] (3) The aerogel was placed in a muffle furnace in an air atmosphere with a certain flow rate, and calcined at 300°C for 2 hours with a heating rate of 3°C / min to obtain a calcined product. The calcined product was naturally cooled to room temperature, and the cooled calcined product was centrifuged and washed several times in dilute acid, ultrapure water, and an alcohol-water mixed solution until the pH of the supernatant was neutral. The product was then placed in a vacuum drying oven for a second drying at a temperature of 50°C for 14 hours, and the product after the second drying was collected.

[0129] (4) The second dried product was placed in a muffle furnace and heated to an annealing temperature in an air atmosphere with a certain flow rate for annealing treatment. The annealing temperature was 420°C, the holding time was 1 h, and the heating rate was 6°C / min. Catalyst 3 was collected and labeled as C3. Its composition is shown in Table 1.

[0130] Comparative Example 1

[0131] The same as Example 1, except that: the first sol is not used, and the IrCl3 complex solution prepared in step (1) is directly oven-dried; the prepared iridium precursor powder is then placed in a muffle furnace in an air atmosphere with a certain flow rate, calcined at 280°C for 2.5 hours, with a heating rate of 5°C / min, and subsequently washed and dried to obtain a second dried product; in step (4), the second dried product is annealed in an air atmosphere at 360°C for 1.5 hours, with a heating rate of 3°C / min, and collected to obtain comparative catalyst 1, labeled D1, whose composition is shown in Table 1. The SEM results of catalyst D1 show that it does not have a loose three-dimensional porous structure.

[0132] Comparative Example 2

[0133] Commercial rutile iridium dioxide (purchased from Alfa, product number A17849) was used as comparative catalyst 2, marked as D2, and its composition is shown in Table 1.

[0134] The SEM image of the comparative catalyst D2 is shown in Figure 6 , cyclic voltammogram is shown in Figure 7 , the bubble discharge diagram when the electrode is coated on carbon paper and electrolyzed water is shown in Figure 8 .

[0135] Figure 6 It shows that the commercial rutile iridium dioxide catalyst is a polyhedral block, the interior of the material is relatively compact, does not have a loose porous structure, and does not have a significant mesoporous-macroporous structure.

[0136] Figure 7 It shows that the peak current and peak area of ​​D2 within the same loading, scan rate and potential range are significantly smaller than those of C1 prepared in Example 1, indicating that D2 has fewer electrochemical active sites.

[0137] Figure 8 It shows that the bubbles on the electrode surface of D2 during the reaction are large and it is not easy to desorb from the electrode surface, indicating that D2 has poor mass transfer effect, which is not conducive to maintaining high oxygen evolution performance at high current density.

[0138] Table 1 Structural characteristics of catalysts prepared in different embodiments and comparative examples

[0139]

[0140] As can be seen from the data in Table 1 above, the iridium dioxide catalysts prepared in Examples 1 to 3 have a three-dimensional porous structure, and the three-dimensional porous structure contains mesopores and macropores, which gives the catalyst a large specific surface area and porosity while also having a small apparent mass-to-volume ratio and a very high fluffiness. When the iridium dioxide catalyst is used for electrolysis of water to produce hydrogen, it has a high mass transfer effect and conductivity, maintains high catalytic activity while also having excellent stability. At the same time, the porous structure can reduce the amount of catalyst used. The comparative catalysts provided in Comparative Examples 1 to 2 do not have a three-dimensional porous structure and high fluffiness, and a relatively large catalyst loading is required to achieve similar performance.

[0141] Test cases 1 to 5

[0142] The catalysts prepared in Examples 1 to 3 of the present disclosure and the comparative catalysts prepared in Comparative Examples 1 to 2 were used as oxygen evolution catalysts, and the electrochemical catalytic oxygen evolution performance was evaluated using the following test method. The electrochemical workstation model is PARSTAT3000A-DX, and the rotating disk electrode model is 636A. A three-electrode system was adopted, with a saturated calomel electrode (SCE) protected by a double salt bridge as the reference electrode, a high-purity graphite rod as the counter electrode, and a glassy carbon electrode as the working electrode. The electrolyte used under acidic conditions was a 0.5M H2SO4 solution. The catalyst to be tested was ultrasonically uniformly dispersed in a mixed solution of isopropanol, water, and Nafion, and dropped onto the surface of the glassy carbon electrode. After natural drying, the working electrode was obtained, and the catalyst loading was 0.38 mg / cm 2 The test temperature was 22-25°C. Oxygen was introduced for at least 30 minutes before the test to saturate the solution with oxygen. The rotation speed was 1600 rpm. The scan range of the cyclic voltammetry curve was 0 V to 1.20 V vs. SCE at a scan rate of 100 mV / s. The scan range of the linear polarization curve was 0.80 V to 1.4 V vs. SCE at a scan rate of 5 mV / s. The stability test scan range was 1.29 V to 1.54 V vs. RHE at a scan rate of 100 mV / s, and the number of scan cycles was 10,000. The test results are shown in Table 2.

[0143] Table 2 Electrochemical catalytic properties of catalysts prepared in different examples and comparative examples

[0144]

[0145] From the data in Table 2 above, it can be seen that compared with the comparative catalysts D1 to D2, when the catalysts C1 to C3 are used for electrolysis of water to produce hydrogen, the battery 2 and 50mA / cm 2The catalysts C1-C3 prepared in the present embodiment exhibited excellent acidic electrochemical oxygen evolution activity and high stability, with a lower initial overpotential and Tafel slope. The catalysts exhibited excellent acidic electrochemical oxygen evolution activity and high stability. Importantly, the catalysts exhibited high fluffiness, which prevented catalyst aggregation and deactivation. This significantly reduced catalyst usage while achieving higher catalytic activity, providing valuable insights for achieving high-performance low-iridium-loading applications.

[0146] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details of the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the scope of protection of the present disclosure.

[0147] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0148] In addition, the various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. An iridium dioxide catalyst, characterized in that The iridium dioxide catalyst is a material having a three-dimensional porous structure, wherein the three-dimensional porous structure comprises mesopores and macropores; and the XRD spectrum of the iridium dioxide catalyst contains characteristic peaks of rutile iridium dioxide.

2. The iridium dioxide catalyst according to claim 1, characterized in that The iridium dioxide catalyst contains iridium elements in an amount of 75% by mass or more, and preferably contains iridium elements in an amount of 76-84% by mass.

3. The iridium dioxide catalyst according to claim 1 or 2, characterized in that The iridium dioxide catalyst contains oxygen in a mass fraction of 14 to 18%.

4. The iridium dioxide catalyst according to claim 1, characterized in that The porosity of the iridium dioxide catalyst is greater than 50%, preferably 70 to 90%; and / or, The specific surface area of ​​the iridium dioxide catalyst is 100 to 150 m 2 / g, preferably 110 to 130 m 2 / g.

5. The iridium dioxide catalyst according to claim 1, characterized in that The total pore volume of the iridium dioxide catalyst is 0.1 to 0.3 cm 3 / g, preferably 0.16 to 0.26 cm 3 / g.

6. The iridium dioxide catalyst according to claim 1, characterized in that The apparent mass volume ratio of the iridium dioxide catalyst is not higher than 0.55 g / cm 3 , preferably 0.2 to 0.34 g / cm 3 , more preferably 0.22 to 0.3 g / cm 3 .

7. The iridium dioxide catalyst according to claim 1, characterized in that The three-dimensional porous structure of the iridium dioxide catalyst is formed by connecting nanosheets; the average thickness of the nanosheets is 1.5 to 6.5 nm, preferably 2 to 4.5 nm.

8. The iridium dioxide catalyst according to claim 1, characterized in that In the XRD spectrum of the iridium dioxide catalyst, the half-peak width of the main diffraction peak of rutile iridium dioxide is 1.5 to 3°, preferably 1.6 to 2.4°.

9. A method for preparing an iridium dioxide catalyst, characterized in that: The preparation method comprises: (1) mixing a polysaccharide with water to form a first sol; mixing an iridium source precursor, a complexing agent, and water, and adjusting the pH of the resulting mixture to 5 to 10 to obtain an iridium source solution; (2) mixing the first sol with the iridium source solution to form a second sol; and subjecting the second sol to a first drying to obtain an aerogel; (3) calcining the aerogel at a temperature of 200° C. or higher without generating elemental iridium; (4) subjecting the obtained calcined product to post-treatment or not, and then subjecting the obtained calcined product to annealing treatment, wherein the annealing treatment temperature is 330° C. or higher; Wherein, the complexing agent is a polycarboxylate having a hydroxyl group, and the polysaccharide is one or more selected from the group consisting of an alkali metal salt of alginic acid, an alkali metal salt of carboxymethyl cellulose and an alkali metal salt of hyaluronic acid.

10. The preparation method according to claim 9, characterized in that In step (1), the iridium source precursor is selected from one or more of anhydrous iridium chloride, iridium chloride hydrate, chloroiridic acid, iridium acetylacetonate, iridium acetate and alkali metal salts of chloroiridic acid; and / or, The complexing agent is selected from one or more alkali metal salts of citric acid, tartaric acid and malic acid; and / or, The molar ratio of the iridium source precursor to the complexing agent is (0.25-4):1, preferably (0.5-2):

1.

11. The preparation method according to claim 9, characterized in that In step (2), the mass ratio of polysaccharide to iridium source precursor in the second sol is (0.1-20):1, preferably (0.2-10):1; and / or, The first drying includes supercritical drying and / or freeze drying, preferably freeze drying; the freeze drying conditions include: temperature of -30 to -20°C, preferably -25 to -20°C; time of 24 to 48 hours, preferably 36 to 48 hours.

12. The preparation method according to claim 9, characterized in that In step (3), the calcination conditions include: temperature of 220-300°C, preferably 250-280°C; time of 0.5-6h, preferably 2-3h; heating rate of 2-10°C / min, preferably 2-5°C / min.

13. The preparation method according to claim 9, characterized in that The post-treatment includes washing and second drying the calcined product; The washing comprises: sequentially performing acid washing, water washing and alcohol washing on the calcined product, wherein the acid used in the acid washing is selected from one or more of dilute hydrochloric acid, sulfuric acid, nitric acid and acetic acid, and the alcohol used in the alcohol washing is selected from one or more of methanol, ethanol and isopropanol; and / or, The second drying conditions include: a temperature of 40 to 60° C., preferably 45 to 55° C.; and a time of 2 to 24 hours, preferably 10 to 20 hours.

14. The preparation method according to claim 9, characterized in that In step (4), the annealing treatment conditions include: heating the calcined product in an air atmosphere to an annealing temperature; the annealing temperature is above 350°C, preferably 360-550°C, and the annealing holding time is 0.5-2h, preferably 1-2h.

15. An iridium dioxide catalyst prepared by the preparation method according to any one of claims 9 to 14.

16. Use of the iridium dioxide catalyst according to any one of claims 1 to 8 and 15 in hydrogen production by PEM water electrolysis.

17. The use according to claim 16, characterized in that The iridium dioxide catalyst is used as an oxygen evolution catalyst for PEM water electrolysis to produce hydrogen.

18. A membrane electrode, characterized in that The membrane electrode comprises a proton exchange membrane and an oxygen evolution catalyst layer coated on the proton exchange membrane, wherein the oxygen evolution catalyst layer comprises the iridium dioxide catalyst according to any one of claims 1 to 8 and 15.

19. A water electrolyzer, characterized in that: The water electrolyzer comprises an anode catalyst, and the anode catalyst is the iridium dioxide catalyst according to any one of claims 1 to 8 and 15.

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