Iridium-based catalyst, preparation method thereof and application of iridium-based catalyst in proton exchange membrane water electrolysis hydrogen production

Abstract

The invention relates to an iridium-based catalyst, a preparation method thereof and application of the iridium-based catalyst in proton exchange membrane water electrolysis hydrogen production, the iridium-based catalyst is a material with a three-dimensional porous structure, and the iridium-based catalyst contains more than 80% by mass of iridium element; a characteristic peak of elemental iridium exists in an XRD spectrogram of the iridium-based catalyst. Compared with an existing iridium black catalyst, when the iridium-based catalyst disclosed by the invention is used for producing hydrogen by electrolyzing water, the usage amount of the catalyst can be reduced, and meanwhile, the iridium-based 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-based catalyst, and in particular, to an iridium-based catalyst and a preparation method thereof, as well as use thereof in hydrogen production by proton exchange membrane water electrolysis. Background Art

[0002] Hydrogen is an ideal candidate for future fossil fuel replacements. It boasts high energy efficiency, produces zero-carbon water, and is produced from abundant raw materials. To better develop and utilize these new energy sources, it's necessary to develop matching electrochemical energy storage and conversion devices.

[0003] Hydrogen production from water electrolysis is favored by the industry due to its distinct advantages, including abundant raw materials, mild conditions, and high product purity. Among these, proton exchange membrane water electrolysis (PEMWE) is currently a highly regarded advanced water electrolysis hydrogen production technology, offering advantages such as faster response, high ionic conductivity, a wide operating temperature and pressure range, high current density, and high hydrogen purity.

[0004] It is worth noting that anode catalyst is a key research direction in PEMWE hydrogen production technology. The oxidation reaction of water occurs at the anode to generate oxygen. Since it is an upward 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 medium at the anode lead to the need for further improvement in the stability of the catalyst.

[0005] The anode catalysts of commercial proton exchange membrane water electrolysis are iridium black and iridium oxide. Iridium black has relatively higher activity and better conductivity, while iridium oxide has better stability. The current amount of iridium in membrane electrodes is generally higher than 2mg / cm 2 However, it is very expensive. Therefore, in order to reduce the cost of iridium-based 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-based catalysts, especially the electrochemical performance for high currents.

[0006] Commercial anode catalysts for proton exchange membrane water electrolysis (PEM) are bulk catalysts composed of iridium and its oxides. Reducing the iridium loading through supported catalyst strategies requires developing new supports with excellent conductivity, strong corrosion resistance, easy catalyst anchoring, and high dispersion. Carbon supports struggle to meet these requirements.

[0007] Furthermore, the current synthesis of metal / alloy-based and oxide-based catalysts with novel micromorphologies typically requires the use of surfactants, reducing agents, nitrates, templates, and organic solvents, leading to 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

[0008] In response to the shortcomings of existing commercial iridium black catalysts, the purpose of the present disclosure is to provide an iridium-based catalyst, a preparation method thereof, and its use in proton exchange membrane water electrolysis to produce hydrogen. When used for water electrolysis to produce hydrogen, the iridium-based catalyst has excellent mass transfer effect and conductivity, maintains high catalytic activity while having excellent stability, and can also reduce the iridium loading and reduce the cost of using the iridium-based catalyst.

[0009] In order to achieve the above-mentioned objectives, the first aspect of the present disclosure provides an iridium-based catalyst, which is a material with a three-dimensional porous structure, and the iridium-based catalyst contains an iridium element with a mass fraction of more than 80%; the XRD spectrum of the iridium-based catalyst contains a characteristic peak of elemental iridium.

[0010] Optionally, the iridium-based catalyst contains iridium element in an amount of 80 to 95% by mass.

[0011] Optionally, the iridium-based catalyst contains 2 to 16% by mass of oxygen.

[0012] Optionally, the iridium-based catalyst satisfies at least one of the following conditions: the three-dimensional porous structure comprises mesopores and macropores; and / or the porosity of the iridium-based catalyst is greater than 40%, preferably 70-90%; and / or the specific surface area of ​​the iridium-based catalyst is greater than 65 m 2 / g, preferably 70 to 95m 2 / g.

[0013] Optionally, the total pore volume of the catalyst is 0.08 to 0.18 cm 3 / g, preferably 0.1 to 0.16 cm 3 / g.

[0014] Optionally, the apparent mass volume ratio of the iridium-based catalyst is not higher than 0.55 g / cm 3 , preferably 0.15 to 0.35 g / cm 3 , more preferably 0.20 to 0.30 g / cm 3 .

[0015] Optionally, the three-dimensional porous structure of the iridium-based catalyst is formed by connecting nanosheets; the average thickness of the nanosheets is 2 to 8 nm, preferably 3.5 to 6.5 nm.

[0016] Optionally, in the XRD spectrum of the iridium-based catalyst, the half-maximum width of the (111) crystal plane diffraction peak of elemental iridium is 0.8 to 1.0°, preferably 0.85 to 1.0°, and there is no diffraction peak of crystalline iridium oxide in the XRD spectrum of the iridium-based catalyst.

[0017] Optionally, the XRD spectrum of the iridium-based catalyst further comprises characteristic peaks of amorphous iridium oxide.

[0018] Optionally, the XPS spectrum of the iridium-based catalyst contains a characteristic peak of elemental Ir and an optional characteristic peak of Ir-O, wherein the Ir of elemental iridium is 0 4f 7 / 2 The binding energy of the peak is 61.0~61.4eV.

[0019] A second aspect of the present disclosure provides a method for preparing an iridium-based catalyst, the method comprising:

[0020] (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;

[0021] (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;

[0022] (3) calcining the aerogel, and subjecting the obtained calcined product to a post-treatment process or not, to obtain the iridium-based catalyst; the calcination temperature is above 320° C.;

[0023] Wherein, the complexing agent in step (1) is a polycarboxylate having a hydroxyl group, and the polysaccharide is selected from one or more of the alkali metal salts of alginic acid, the alkali metal salts of carboxymethyl cellulose and the alkali metal salts of hyaluronic acid.

[0024] 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 (0.25-20):1, preferably (0.5-10):1.

[0025] 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.

[0026] Optionally, in step (3), the calcination conditions include: calcination temperature of 320-550°C, preferably 325-420°C; time of 0.5-6h, preferably 2-3h; heating rate of 1-10°C / min, preferably 2-8°C / min.

[0027] Optionally, in step (3), the post-treatment process 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.

[0028] The third aspect of the present disclosure provides an iridium-based catalyst prepared by the preparation method described in the second aspect of the present disclosure.

[0029] A fourth aspect of the present disclosure provides a use of the iridium-based catalyst described in the first aspect and / or the third aspect of the present disclosure in hydrogen production by proton exchange membrane water electrolysis.

[0030] A fifth aspect of the present disclosure provides a membrane electrode, which includes a proton exchange membrane and an anode catalyst layer coated on the proton exchange membrane, wherein the anode catalyst layer includes the iridium-based catalyst described in the first aspect and / or the third aspect of the present disclosure.

[0031] A sixth aspect of the present disclosure provides a water electrolyzer, which includes the membrane electrode described in the fifth aspect of the present disclosure.

[0032] Through the above technical solution, the present disclosure provides an iridium-based catalyst and its preparation method and its use in proton exchange membrane water electrolysis for hydrogen production, wherein the iridium-based catalyst is basically composed of elemental iridium and has a stable and loose three-dimensional porous structure, so that the catalyst has a large specific surface area and high porosity, and therefore has better mass transfer performance and apparent catalytic activity. Furthermore, the catalyst can be a three-dimensional porous structure containing continuous mesopores and macropores connected by nanosheets of very small thickness, which has both the high activity of nanomaterials and can avoid the deactivation of catalyst nanoparticles due to aggregation, so that the catalyst maintains a high catalytic activity while having excellent stability. Furthermore, the three-dimensional porous structure of the catalyst is conducive to fully exposing the active sites inside the material, improving the utilization rate of the iridium element, thereby reducing the iridium load and reducing the cost of the iridium-based catalyst. When the iridium-based catalyst of the present disclosure is applied to water electrolysis for hydrogen production, it has excellent oxygen evolution activity, a small initial overpotential, a lower Tafel slope than commercial iridium black catalysts, and a smaller increase in the final overpotential after stability testing compared to the initial overpotential, and has good industrial application prospects. In addition, the preparation method provided by the present disclosure is simple, convenient and highly economical.

[0033] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] 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:

[0035] Figure 1 is a SEM image of catalyst C1 prepared in Example 1 of the present disclosure;

[0036] Figure 2 is the XRD pattern of catalyst C1 prepared in Example 1 of the present disclosure;

[0037] Figure 3 is a TEM image of catalyst C1 prepared in Example 1 of the present disclosure;

[0038] Figure 4 is a BET diagram of catalyst C1 prepared in Example 1 of the present disclosure;

[0039] Figure 5 is the XPS spectrum of Ir 4f of catalyst C1 prepared in Example 1 of the present disclosure;

[0040] Figure 6 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;

[0041] Figure 7is the XRD pattern of catalyst C2 prepared in Example 2 of the present disclosure;

[0042] Figure 8 is a cyclic voltammogram of catalyst C2 prepared in Example 2 of the present disclosure;

[0043] Figure 9 is the XRD pattern of catalyst C3 prepared in Example 3 of the present disclosure;

[0044] Figure 10 This is a diagram of bubble discharge when commercial iridium black is coated on carbon paper to prepare an electrode for water electrolysis reaction. DETAILED DESCRIPTION

[0045] 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.

[0046] Terminology Notes:

[0047] 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.

[0048] In a first aspect, the present disclosure provides an iridium-based catalyst, which is a material having a three-dimensional porous structure and contains iridium elements with a mass fraction of more than 80%. The XRD spectrum of the iridium-based catalyst contains characteristic peaks of elemental iridium.

[0049] The term "three-dimensional porous structure material" 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 is 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. 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.

[0050] 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.

[0051] In the present disclosure, the term "amorphous" refers to a state other than a crystalline state, including an amorphous state and a pseudo-crystalline state. In the present disclosure, amorphous iridium oxide exists in an amorphous state and / or a pseudo-crystalline state.

[0052] In the present disclosure, the contents of iridium and oxygen are obtained by XRF testing.

[0053] The iridium-based 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.

[0054] The iridium-based catalyst provided by the present disclosure is basically composed of elemental iridium and has a stable and loose three-dimensional porous microstructure, so that the catalyst has a large specific surface area and porosity, which is conducive to promoting the mass transfer process and improving the apparent catalytic activity; and the catalyst is a three-dimensional porous material formed by connecting nanosheets, which not only has the high activity of nanomaterials, but also can avoid catalyst agglomeration and deactivation, and to a large extent solves the activity and stability problems of nanomaterials, so that the catalyst has excellent acidic electrochemical activity and stability. At the same time, the three-dimensional 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, thereby reducing the use cost of the iridium-based catalyst.

[0055] In one embodiment of the present disclosure, the mass fraction of the iridium element in the iridium-based catalyst can be 80%, 82%, 84%, 86%, 88%, 91%, 94% or 97%, or the mass fraction of the iridium element is within the numerical range between any two of them. Preferably, the iridium-based catalyst contains an iridium element with a mass fraction of 80 to 95%. In the above embodiment, by selecting the preferred content of iridium element, it is beneficial to further improve the conductivity of the catalyst and thus improve its electrocatalytic activity. The content of iridium element in the iridium-based catalyst disclosed herein is obtained by XRF testing.

[0056] The iridium-based catalysts disclosed herein may contain a certain amount of oxygen. This oxygen may be introduced as impurities during catalyst preparation, oxidized during iridium calcination, or absorbed by the catalyst itself. The oxygen content of the catalyst surface can be determined through XPS analysis, such as by detecting Ir-O bonds or by direct oxygen detection.

[0057] In one embodiment of the present disclosure, the iridium-based catalyst contains oxygen in an amount of 2%, 3%, 5%, 7%, 9%, 12%, 14% or 16% by mass, or the mass fraction of the oxygen element is within a numerical range between any two of them; preferably, it contains oxygen in an amount of 2 to 16% by mass, and further preferably, it contains oxygen in an amount of 3 to 14% by mass.

[0058] The iridium-based catalyst disclosed herein is a three-dimensional porous material, and the three-dimensional porous structure mainly comprises mesopores and macropores, and has a high porosity. In one embodiment, the porosity of the iridium-based catalyst is greater than 40%, preferably 70-90%, 70-80%, or 75-80%. In the above embodiment, the iridium-based catalyst has a large porosity, which is conducive to promoting mass transfer.

[0059] In one embodiment of the present disclosure, the specific surface area of ​​the iridium-based catalyst is greater than 65 m 2 / g, preferably 70 to 95m 2 / g, 70~90m 2 / g or 70~80m 2 In the above embodiment, the iridium-based catalyst has a large specific surface area, which is beneficial to improving the mass specific activity.

[0060] In one embodiment, the apparent mass volume ratio of the iridium-based 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-based catalyst is 0.15 to 0.35 g / cm 3 , preferably 0.20 to 0.30 g / cm 3 In one embodiment, the total pore volume of the iridium-based catalyst is 0.08 to 0.18 cm 3 / g, preferably 0.1 to 0.16 cm 3 / g.

[0061] In the above embodiment, the iridium-based catalyst has a loose three-dimensional porous structure with a high degree of bulkiness, which not only helps improve the mass transfer effect of the catalyst and thus the electrocatalytic activity of the catalyst, but also significantly improves the dispersion of the catalyst slurry during the manufacture of the membrane electrode, thereby reducing the catalyst loading. 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 pore volume measured in this manner is the pore volume of pores with relatively small pore sizes (2 to 200 nm) in the catalyst.

[0062] In one embodiment, the three-dimensional porous structure of the iridium-based catalyst disclosed herein comprises continuously distributed mesopores and macropores, which constitute a continuous mesopore-macroporous multi-level pore structure as a whole, thereby further facilitating the mass transfer process. For example, the three-dimensional porous structure comprises 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 may 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, thereby constituting a multi-level pore structure, and "multi-level pores with continuously distributed mesopores-macroporous with a pore size" refers to a multi-level pore structure composed of continuous macropores (pore size 50 to 200 nm) and 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 are present in the range of 2 nm to 200 nm. 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.

[0063] In further embodiments, the three-dimensional porous structure of the iridium-based 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-based 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%.

[0064] Iridium is one of the densest elements in existence. The density of metallic iridium is as high as 22.65g / cm 3 The iridium-based 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-based catalyst includes mesopores and macropores. Therefore, the apparent mass volume ratio of the iridium-based catalyst is much lower than the density of the above-mentioned metallic iridium, and the iridium-based catalyst has the above-mentioned higher surface area. These physical properties further indicate that the iridium-based catalyst disclosed in the present disclosure has a loose and porous structure.

[0065] In one embodiment of the present disclosure, the iridium-based catalyst has a microstructure formed by connecting nanosheets, specifically a three-dimensional porous structure formed by connecting nanosheets in three-dimensional space; in a preferred embodiment, the entity part of the three-dimensional porous microstructure of the iridium-based catalyst of the present disclosure is formed by interconnecting a plurality of sheet-like nanosheets, the sheet-like nanosheets extending to form the pore walls ("walls") of a plurality of holes, and the nanosheets also covering the holes to form the "surfaces" of the holes, the nanosheets serving as the "surfaces" and "walls" are connected or overlapped with each other, and the holes between the nanosheets are staggered and connected, thereby forming a three-dimensional porous microstructure, such as Figure 1 shown.

[0066] The iridium-based catalyst disclosed herein has a three-dimensional porous structure formed by continuous nanosheets. The nanosheets are relatively small, resulting in a porous material with high porosity and bulkiness. The nanosheets are, for example, less than 500 nm in size. In a preferred embodiment, the microstructure contains substantially no portions thicker than 20 nm. That is, the nanosheets forming the pore walls of the three-dimensional porous material are substantially no thicker than 20 nm. Preferably, the nanosheets have a thickness of 2 to 8 nm, and more preferably, 3.5 to 6.5 nm. Because the nanosheets are so thin, they can be referred to as two-dimensional nanosheets. Thus, the iridium-based catalyst disclosed herein has the high catalytic activity of nanomaterials. At the same time, because it is a three-dimensional structure formed by continuous extension of nanosheets and interconnected in three-dimensional space, the catalyst has a large porosity and fluffiness. The three-dimensional structure of the catalyst has continuously distributed mesopores and macropores, especially a certain number of macropores larger than 200nm, making the catalyst as a whole more loose and porous, which is conducive to improving mass transfer efficiency and apparent activity, and avoiding the aggregation and deactivation of nanocatalyst materials, improving the dispersion performance of the catalyst in the slurry, largely solving the activity and stability problems of nanomaterials, and reducing the use of iridium-based catalysts. The average thickness of the nanosheets was measured using SEM and statistically analyzed using Nano Measurer 1.2 software.

[0067] In one embodiment of the present disclosure, the iridium-based catalyst mainly contains elemental iridium, and the continuous nanosheets in the iridium-based catalyst are formed by closely arranging and interconnecting a plurality of elemental iridium nanocrystals. The average particle size of the elemental iridium nanocrystals can be 1 to 8 nm, preferably 2 to 5 nm. In the above embodiment, the grain size of the elemental iridium nanocrystals is relatively small, and the thickness of the formed nanosheets is also relatively thin, for example, the thickness is only 2 to 8 nm, which makes the internal structure of the iridium-based catalyst of the three-dimensional porous material composed of nanosheets more loose. In a preferred embodiment, the nanosheets formed by small-sized nanocrystals have a wrinkled graphene-like shape, which is beneficial to further improve the apparent activity of the catalyst. In the present disclosure, the size of the nanoparticles can be obtained by TEM testing.

[0068] In one embodiment of the present disclosure, the iridium-based catalyst mainly contains elemental iridium. In this case, the XRD spectrum of the iridium-based catalyst basically only has the characteristic diffraction peak of elemental iridium, and there is no diffraction peak of crystalline iridium oxide, for example, there is no diffraction peak of rutile iridium dioxide. In this case, the iridium-based catalyst of the present disclosure is an iridium metal catalyst. Specifically, the XRD spectrum of the iridium-based catalyst shows an obvious main diffraction peak of elemental iridium near 2θ=40.7°. The main diffraction peak is the (111) crystal plane diffraction peak of elemental iridium. The (111) crystal plane diffraction peak has a large intensity and a sharp peak shape. Furthermore, the half-peak width of the (111) crystal plane diffraction peak is 0.8~1.0°, preferably 0.85~1.0°. In the above embodiment, the crystallinity of the elemental iridium contained in the catalyst is good, and the presence of elemental iridium is conducive to enhancing the conductivity of the iridium-based catalyst and improving the OER performance.

[0069] In another embodiment, the iridium-based catalyst further comprises iridium oxide, such as amorphous iridium oxide, on the basis of metallic iridium. At this point, the iridium-based catalyst forms a composite catalyst of metallic iridium and iridium oxide. In the XRD spectrum of the iridium-based catalyst (i.e., the composite catalyst of iridium and iridium oxide), in addition to the characteristic peak of elemental iridium, it also comprises a characteristic peak attributable to amorphous iridium oxide. Specifically, the XRD spectrum of the composite catalyst of elemental iridium and amorphous iridium oxide shows a characteristic peak of amorphous iridium oxide with obvious peak broadening near 2θ=33.6°, and the half-peak width of the characteristic peak is 5-6°, preferably 5.2-5.6°; the characteristic peak of elemental iridium appears near 2θ=40.8°, and the half-peak width of the preferred elemental iridium characteristic peak is 0.6-2.0°, preferably 0.8-1.2°.

[0070] In one embodiment, the high-resolution transmission electron microscopy image of the iridium-based catalyst shows that the interior of the catalyst also has a continuous mesoporous-macroporous three-dimensional structure, and the pore walls are composed of small-sized nanocrystals, which is beneficial to increase the electrochemical active area and promote mass transfer effects, thereby improving catalytic activity.

[0071] In one embodiment of the present disclosure, the XPS spectrum of the iridium-based catalyst contains characteristic peaks of elemental iridium, wherein the Ir 0 4f 7 / 2 The binding energy of the peak is 61.0 to 61.4 eV. 0 4f 7 / 2The peak has shifted toward the high electron binding energy direction relative to the standard position (60.9 eV), for example, by 0.1 to 0.5 eV, indicating that the surface elemental iridium disclosed herein is in a relatively electron-deficient state, which is conducive to binding and adsorbing oxygen intermediates. Optionally, there is also an Ir-O peak in the XPS spectrum of the iridium-based catalyst, indicating that there is also an iridium oxide, such as an iridium oxide layer, on the surface of the catalyst. The "surface layer" refers to an area with a detection depth of less than 10 nm from the outer surface of the catalyst, specifically, the detection depth of XPS shall prevail.

[0072] In another embodiment of the present disclosure, the iridium-based catalyst is a composite catalyst of iridium and amorphous iridium oxide, wherein the amorphous iridium oxide catalyst is rich in highly active Ir 4+ and Ir 3+ , which is beneficial to improve the intrinsic OER activity of the catalyst. In the above embodiment, the XPS Ir 4f spectrum of the iridium-based catalyst, Ir 4+ 4f 7 / 2 The binding energy of the peak is 61-62 eV; Ir 3+ 4f 7 / 2 The binding energy of the peak is 62-63 eV. In a preferred embodiment, the Ir 4f spectrum obtained by fitting the XPS Ir 4f spectrum of the amorphous iridium oxide catalyst is 3+ The molar percentage of Ir is 20 to 50%, preferably 25 to 40%. 3+ The ratio of the molar number of the iridium oxide to the total molar number of the Ir species is 20 to 50%, preferably 25 to 40%. This shows that the surface layer of the amorphous iridium oxide catalyst disclosed in the present invention is rich in highly active Ir 3+ , which is beneficial to improving the intrinsic OER activity of the catalyst. The "surface layer" in this disclosure 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.

[0073] A second aspect of the present disclosure provides a method for preparing an iridium-based catalyst, the method comprising:

[0074] (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;

[0075] (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;

[0076] (3) calcining the aerogel, and subjecting the obtained calcined product to a post-treatment process or not, to obtain the iridium-based catalyst; the calcination temperature is above 320° C.;

[0077] Wherein, the complexing agent in step (1) is a polycarboxylate having a hydroxyl group, and the polysaccharide is selected from one or more of the alkali metal salts of alginic acid, the alkali metal salts of carboxymethyl cellulose and the alkali metal salts of hyaluronic acid.

[0078] The disclosed method uses specific polysaccharides and complexing agents to form a hydrosol containing an iridium source. This hydrosol is then dried to produce a three-dimensional, sheet-like aerogel precursor. This aerogel is then calcined at a specific temperature to produce a three-dimensional, porous iridium-based catalyst primarily composed of elemental iridium. This aerogel preparation method differs from existing aerogel preparation methods in that the aerogel is formed directly from a flowable hydrosol by drying, without forming a hydrogel prior to aerogel production.

[0079] The preparation method provided by the present disclosure is simple and convenient, the synthetic route is green and economical, and the obtained iridium-based catalyst has a novel three-dimensional porous loose structure. The microstructure shows that the structure is composed of very thin nanosheets connected together, with a large specific surface area. Therefore, it can have both high catalytic activity and high stability, and has excellent electrochemical catalytic performance, and can be used in the electrolysis of water to produce hydrogen.

[0080] The term "sol" in the present disclosure is defined as a dispersion system having fluidity and a viscosity greater than that of water.

[0081] 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 or 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; when the polysaccharide is selected from an alkali metal salt of hyaluronic acid, it can be sodium hyaluronate or potassium hyaluronate.

[0082] In one embodiment of the present disclosure, the iridium source precursor can use various iridium source precursors known to those skilled in the art. Preferably, 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, wherein the alkali metal salts of chloroiridic acid include sodium chloroiridate and potassium chloroiridate.

[0083] In the present disclosure, the polycarboxylic acid having a hydroxyl group may be a carboxylic acid having 1 to 4 hydroxyl groups, 2 to 4 carboxyl groups, and a total carbon number of 3 to 10.

[0084] In one embodiment, the polycarboxylic acid having a hydroxyl group has 1 to 2 hydroxyl groups. In one embodiment of the present disclosure, the polycarboxylic acid having a hydroxyl group has 2 to 3 carboxyl groups. In one embodiment of the present disclosure, the polycarboxylic acid having a hydroxyl group has a total carbon number of 4 to 8.

[0085] In one embodiment of the present disclosure, the polycarboxylic acid having a hydroxyl group is at least one selected from malic acid, citric acid, isocitric acid, hydroxymalonic acid, tartaric acid, 3-hydroxy-3-methylglutaric acid, and mevalonic acid. In one embodiment of the present disclosure, the salt of the polycarboxylic acid having a hydroxyl group may each independently be an alkali metal salt or an alkaline earth metal salt. More preferably, the salt of the polycarboxylic acid having a hydroxyl group may each independently be an alkali metal salt.

[0086] In one embodiment of the present disclosure, the salts of the polycarboxylic acid having a hydroxyl group may each independently be a sodium salt, a potassium salt, a calcium salt, or an ammonium salt.

[0087] 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.

[0088] In one embodiment of the present disclosure, the molar ratio of the iridium source precursor to the complexing agent is (0.25-20):1, preferably (0.5-10):1.

[0089] In the above embodiment, the selection of preferred components and contents is conducive to the synthesis of a more loose and porous iridium-based catalyst, and further improves the specific surface area and stability of the catalyst.

[0090] 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.

[0091] 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.

[0092] In one embodiment of the present disclosure, 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 the formation of a suitable three-dimensional aerogel intermediate and more accurately controlling the pyrolysis process; selecting a preferred freeze drying can obtain an aerogel with a more favorable porous structure. In one embodiment of the present disclosure, after freeze drying, the temperature is further raised to 10 to 40°C for drying.

[0093] 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.

[0094] In one embodiment of the present disclosure, in step (3), the calcination conditions include: the calcination temperature is above 320°C and does not destroy the three-dimensional porous structure, preferably 320-550°C, more preferably 320-450°C, and further preferably 325-420°C; the calcination time is 0.5-6h, preferably 1-4h, more preferably 2-3h; the heating rate is 1-10°C / min, preferably 2-8°C / min. In the above embodiment, by selecting the preferred calcination conditions, it is beneficial to convert the porous aerogel into an iridium-based catalyst with a three-dimensional porous structure. Under the aforementioned calcination conditions, the obtained iridium-based catalyst is basically composed of iridium element. In the present disclosure, the calcined product is not subjected to annealing treatment.

[0095] In one embodiment of the present disclosure, the calcination is performed in an air atmosphere.

[0096] 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 process includes washing and / or a second drying of the calcined product.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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, the preferred washing and second drying are more conducive to removing impurities such as inorganic salts, carbon, and metal elements remaining on the catalyst surface.

[0101] The third aspect of the present disclosure provides an iridium-based catalyst prepared by the method described in the second aspect of the present disclosure.

[0102] A fourth aspect of the present disclosure provides a use of the iridium-based catalyst described in the first aspect and / or the third aspect of the present disclosure in hydrogen production by proton exchange membrane water electrolysis.

[0103] Compared with commercial iridium black catalysts, the iridium-based catalyst provided by the present invention can reduce the amount of catalyst used when used for PEM water electrolysis to produce hydrogen, and at the same time has excellent electrochemical catalytic performance, a small initial overpotential, a low Tafel slope, and a small increase in the final overpotential after stability testing compared to the initial overpotential, and has good industrial application prospects.

[0104] A fifth aspect of the present disclosure provides a membrane electrode, which includes a proton exchange membrane and an anode catalyst layer coated on the proton exchange membrane, wherein the anode catalyst layer includes the iridium-based catalyst described in the first aspect and / or the third aspect of the present disclosure.

[0105] In a specific embodiment of the present disclosure, the iridium-based catalyst is used as an oxygen evolution catalyst for a membrane electrode, which can achieve higher catalytic activity and stability while reducing the amount of iridium used.

[0106] A sixth aspect of the present disclosure provides a water electrolyzer, which includes the membrane electrode described in the fifth aspect of the present disclosure.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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 the measured pore volume is the pore volume of all pores with a pore size between 2 and 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 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 between 2 and 200 nm. The calculated porosity is also the minimum porosity of the catalyst.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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).

[0116] The crystal structure and nanoparticle size of the catalyst were analyzed using TEM. The following instruments, methods, and conditions were used: a JEM-2100 high-resolution transmission electron microscope (HRTEM) (JEOL Ltd.) at an accelerating voltage of 200 kV; and a JEOL ARM 200F spherical aberration-corrected scanning transmission electron microscope (CS-STEM) at an accelerating voltage of 200 kV, equipped with energy-dispersive X-ray spectroscopy (EDS). Analyses were performed using the accompanying DigitalMicrograph 3.9.1 software.

[0117] 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.

[0118] Example 1

[0119] (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;

[0120] (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;

[0121] (3) The aerogel was placed in a muffle furnace in an air atmosphere with a certain flow rate, and calcined at 330°C for 2.5 hours with a heating rate of 8°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 alcohol-water mixed solutions until the pH of the supernatant was 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. Catalyst 1 was collected and labeled as C1. Its composition is shown in Table 1.

[0122] The total pore volume of catalyst C1 prepared in this example is 0.117 cm 3 / g, with a specific surface area of ​​72.7m 2 / g, and the apparent mass volume ratio is 0.26g / cm 3 The specific surface area of ​​the micropores accounts for 15.2% of the specific surface area of ​​the entire catalyst.

[0123] The SEM image of catalyst C1 prepared in this example is shown in Figure 1 , XRD spectrum see Figure 2 , TEM image see Figure 3 , BET chart Figure 4 , the XPS spectrum of Ir 4f is shown in Figure 5 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 6 .

[0124] According to Table 1 and Figure 1It can be seen that catalyst C1 has a three-dimensional porous microstructure composed of continuous nanosheets, which is rich in mesopores and macropores and has a relatively low micropore content. The "surface" of the translucent thin layer covering the pores and the pore walls of the internal pores are both formed by interconnected nanosheets of multiple sheet-like entities, that is, nanosheets are interconnected in three-dimensional space, and the nanosheets are composed of multiple interconnected nanocrystals of elemental iridium. The average grain size of the elemental iridium nanocrystals is 3.5 nm, and the average thickness of the nanosheets is only 4 nm, indicating that catalyst C1 has a loose three-dimensional porous microstructure and a large porosity and specific surface area, which is beneficial to improving the mass transfer effect and apparent electrochemical activity of the catalyst, while reducing the amount of catalyst used.

[0125] Figure 2 The XRD spectrum of catalyst C1 shows that there is an obvious characteristic diffraction peak of elemental iridium at 2θ=40.7°, but no characteristic diffraction peak of crystalline iridium oxide. The half-peak width of the main diffraction peak of elemental iridium is 0.979°, indicating that the grain size of elemental iridium is small, which is beneficial to enhancing the conductivity of the catalyst and improving the OER performance.

[0126] Figure 3 This is the transmission electron microscope image of the iridium-based catalyst C1. It can be clearly seen that the interior of the catalyst also has a continuous mesoporous-macroporous three-dimensional structure. At the same time, the nanosheets that constitute the pore walls are composed of small-sized elemental iridium nanocrystals connected to each other, which corresponds well to the SEM image. It is beneficial to increase the electrochemical active area and promote the mass transfer effect, thereby improving the catalytic activity.

[0127] Figure 4 It shows that the three-dimensional porous structure of catalyst C1 is rich in macropores and mesopores, and the pore size distribution is uniform and continuous, and the pore size distribution curve has no obvious peak.

[0128] Figure 5 The high-resolution XPS spectrum of catalyst C1 shows that the Ir 4f characteristic peaks of elemental iridium and the Ir-O peaks of slight surface oxidation appear. The Ir 4f characteristic peaks of elemental iridium at the binding energy of 61.2 eV are 0 4f 7 / 2 Peak, the Ir 0 4f 7 / 2 The peak shifted by 0.3 eV relative to the standard position (60.9 eV) toward higher electron binding energies, indicating that the surface iridium of catalyst C1 is relatively electron-deficient, which is beneficial for promoting oxygen evolution in acidic water electrolysis. The "surface" refers to the region less than 10 nm deep from the catalyst's outer surface, specifically based on the XPS detection depth.

[0129] Figure 6It 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.

[0130] Example 2

[0131] The same as Example 1, except that: in step (3), the aerogel was placed in a muffle furnace and calcined at 400°C for 2.5h with a heating rate of 4°C / min, and finally the catalyst 2 was collected and marked as C2. Its composition is shown in Table 1.

[0132] The XRD pattern of catalyst C2 prepared in this example is shown in FIG. Figure 7 , cyclic voltammogram is shown in Figure 8 .

[0133] Figure 7 The XRD spectrum of catalyst C2 shows that there is an obvious characteristic diffraction peak of elemental iridium at 2θ=40.7°, and a slight characteristic diffraction peak of amorphous iridium oxide at 2θ=33.8°. The half-peak width of the main diffraction peak of elemental iridium is 1.013°.

[0134] Figure 8 The cyclic voltammetry curve shows that the catalyst C2 has a redox peak in the potential range of 0.4V to 0.6V vs. RHE (Ir 0 / Ir 3+ ), a clear redox peak appears 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 area is larger, indicating that catalyst C2 has more active sites, which is beneficial to improving its electrochemical activity.

[0135] Example 3

[0136] (1) Weighing 0.8 g of sodium alginate 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 8:1, and then adjusting the pH of the mixture to 6.5 to obtain an iridium source solution;

[0137] (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;

[0138] (3) The aerogel was placed in a muffle furnace in an air atmosphere with a certain flow rate and calcined at 370°C for 2 hours at a heating rate of 8°C / min to obtain a calcined product. The calcined product was naturally cooled to room temperature and 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. Catalyst 3 was collected and labeled as C3. Its composition is shown in Table 1.

[0139] The XRD pattern of catalyst C3 prepared in this example is shown in FIG. Figure 9 .

[0140] Figure 9 The XRD spectrum of catalyst C3 shows that there is an obvious characteristic diffraction peak of elemental iridium at 2θ=40.7°, and an obvious characteristic diffraction peak of amorphous iridium oxide at 2θ=33.8°. The half-peak width of the main diffraction peak of elemental iridium is 1.939°, indicating that the size of the nanoparticles is smaller.

[0141] Comparative Example 1

[0142] The same as Example 1, except that: the first sol was not used, and the IrCl3 complex solution prepared in step (1) was directly oven-dried. The prepared iridium precursor powder was then placed in a muffle furnace in an air atmosphere with a certain flow rate and calcined at 330°C for 2.5 hours at a heating rate of 5°C / min. Finally, comparative catalyst 1 was collected and labeled as D1. Its composition is shown in Table 1. SEM test results show that D1 does not have a three-dimensional porous structure.

[0143] Comparative Example 2

[0144] Commercial iridium black was used as comparative catalyst 2, marked as D2, and was purchased from Alfa Company with product number 010746.

[0145] Table 1 Structural characteristics of catalysts prepared in different embodiments and comparative examples

[0146]

[0147] As can be seen from the data in Table 1 above, compared with the prior art, the iridium-based catalysts prepared in Examples 1 to 3 have a three-dimensional porous structure and contain an iridium element with a mass fraction of more than 80%, a porosity greater than 75%, and a significantly smaller apparent mass-to-volume ratio, a very high fluffiness, and a large specific surface area. This iridium-based catalyst has a high mass transfer effect and conductivity, maintains high catalytic activity while also having excellent stability. When used for hydrogen production by electrolysis of water, the amount of catalyst used can be reduced. 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 amount of catalyst is required to achieve similar catalytic performance.

[0148] Test cases 1 to 4

[0149] The iridium-based catalysts prepared in Examples 1 to 3 of the present disclosure and the comparative catalyst prepared in Comparative Example 1 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 0.5MH2SO4 solution or a 0.1M HClO4 solution. The catalyst to be tested was ultrasonically uniformly dispersed in a mixed solution of isopropanol, water and Nafion, dropped onto the surface of the glassy carbon electrode, and naturally dried to obtain a working electrode. The catalyst loading was 0.38mg / cm 2 The test temperature was 20-25°C. Oxygen was introduced for at least 30 minutes before the test to saturate the solution with oxygen. The rotation speed was 2500 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.

[0150] Table 2 Electrochemical catalytic properties of catalysts prepared in different examples and comparative examples

[0151]

[0152] From the data in Table 2 above, it can be seen that compared with the comparative catalyst D1, when 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 embodiments of the present disclosure exhibited superior acidic electrochemical oxygen evolution activity and higher stability, with a smaller initial overpotential and lower Tafel slope. Furthermore, the catalysts disclosed herein possess a three-dimensional porous structure composed of interconnected nanosheets and exhibit a high degree of bulkiness, which prevents catalyst aggregation and deactivation. This allows for significantly reduced catalyst usage while achieving higher catalytic activity, enabling high-performance, low-iridium-loading applications.

[0153] Test Example 5

[0154] The catalytic performance of the commercial iridium black of D2 was tested under the same conditions as in Test Examples 1 to 4. The results showed that the catalysts C1 to C3 prepared in the embodiments of the present disclosure had lower overpotentials and lower Tafel slopes than D2 overall. The stability test results showed that the overpotential of the commercial iridium black increased by more than 70 mV compared with that before the test, and its stability was far inferior to that of the catalysts C1 to C3 prepared in the embodiments of the present disclosure. This indicates that the catalyst prepared in the embodiments of the present disclosure has a three-dimensional porous structure formed by connected nanosheets, which significantly improves the stability of the catalyst while improving the catalytic activity.

[0155] Figure 10 This is a diagram of bubble discharge during the electrolysis of water using commercial iridium black, tested under the same conditions as in Example 1. The diagram shows that bubbles on the electrode surface of commercial iridium black are significantly larger during the reaction, and bubbles do not readily desorb from the electrode surface, indicating that D2 has poor mass transfer performance, making it unsuitable for maintaining high oxygen evolution performance at high current densities.

[0156] 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.

[0157] 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.

[0158] 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-based catalyst, characterized in that The iridium-based catalyst is a material with a three-dimensional porous structure, and the iridium-based catalyst contains iridium elements with a mass fraction of more than 80%. The XRD spectrum of the iridium-based catalyst has a characteristic peak of elemental iridium.

2. The iridium-based catalyst according to claim 1, characterized in that The iridium-based catalyst contains iridium element in an amount of 80 to 95% by mass.

3. The iridium-based catalyst according to claim 1 or 2, characterized in that The iridium-based catalyst contains oxygen element with a mass fraction of 2 to 16%.

4. The iridium-based catalyst according to claim 1, characterized in that The iridium-based catalyst satisfies at least one of the following conditions: The three-dimensional porous structure comprises mesoporous and macroporous structures; and / or, The porosity of the iridium-based catalyst is greater than 40%, preferably 70 to 90%; and / or, The specific surface area of ​​the iridium-based catalyst is greater than 65m 2 / g, preferably 70 to 95m 2 / g.

5. The iridium-based catalyst according to claim 1, characterized in that The total pore volume of the catalyst is 0.08 to 0.18 cm 3 / g, preferably 0.1 to 0.16 cm 3 / g.

6. The iridium-based catalyst according to claim 1, characterized in that The apparent mass volume ratio of the iridium-based catalyst is not higher than 0.55 g / cm 3 , preferably 0.15 to 0.35 g / cm 3 , more preferably 0.20 to 0.30 g / cm 3 .

7. The iridium-based catalyst according to claim 1, characterized in that The three-dimensional porous structure of the iridium-based catalyst is formed by connecting nanosheets; the average thickness of the nanosheets is 2 to 8 nm, preferably 3.5 to 6.5 nm.

8. The iridium-based catalyst according to claim 1, characterized in that In the XRD spectrum of the iridium-based catalyst, the half-maximum width of the (111) crystal plane diffraction peak of elemental iridium is 0.8 to 1.0°, preferably 0.85 to 1.0°, and there is no diffraction peak of crystalline iridium oxide in the XRD spectrum of the iridium-based catalyst.

9. The iridium-based catalyst according to claim 1, characterized in that The XRD spectrum of the iridium-based catalyst also contains characteristic peaks of amorphous iridium oxide.

10. The iridium-based catalyst according to claim 1, characterized in that The XPS spectrum of the iridium-based catalyst contains characteristic peaks of elemental Ir and optional characteristic peaks of Ir-O. 0 4f 7 / 2 The binding energy of the peak is 61.0~61.4eV.

11. A method for preparing an iridium-based 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, and subjecting the obtained calcined product to a post-treatment process or not, to obtain the iridium-based catalyst; the calcination temperature is above 320° C.; Wherein, the complexing agent in step (1) is a polycarboxylate having a hydroxyl group, and the polysaccharide is selected from one or more of the alkali metal salts of alginic acid, the alkali metal salts of carboxymethyl cellulose and the alkali metal salts of hyaluronic acid.

12. The preparation method according to claim 11, 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 (0.25-20):1, preferably (0.5-10):

1.

13. The preparation method according to claim 11, 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.

14. The preparation method according to claim 11, characterized in that In step (3), the calcination conditions include: calcination temperature of 320-550°C, preferably 325-420°C; time of 0.5-6h, preferably 2-3h; heating rate of 1-10°C / min, preferably 2-8°C / min.

15. The preparation method according to claim 11, characterized in that In step (3), the post-treatment process 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.

16. An iridium-based catalyst prepared by the preparation method according to any one of claims 11 to 15.

17. Use of the iridium-based catalyst according to any one of claims 1 to 10 and 16 in hydrogen production by proton exchange membrane water electrolysis.

18. A membrane electrode, characterized in that The membrane electrode comprises a proton exchange membrane and an anode catalyst layer coated on the proton exchange membrane, wherein the anode catalyst layer comprises the iridium-based catalyst according to any one of claims 1 to 10 and 16.

19. A water electrolyzer, characterized in that: The water electrolyzer comprises the membrane electrode according to claim 18.

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