A transition metal-doped modified flaky iridium oxide catalyst, its preparation method and application

Abstract

The present invention belongs to the technical field of electrolyzed water catalysts, and particularly relates to a transition metal-doped modified flaky iridium oxide catalyst, a preparation method thereof, and an application thereof. The preparation method comprises the following steps: S1, mixing an iridium precursor, a transition metal precursor, sodium nitrate and a dispersant, and ball-milling to form a slurry, wherein the transition metal is one or more of Co, Ni and Mn, and the molar ratio of the iridium precursor to the transition metal precursor is 5:0.5-4; S2, drying the slurry; S3, calcining the slurry in an air atmosphere; S4, purifying the calcined product to obtain a transition metal-doped modified flaky iridium oxide. The method provided by the present invention can obtain a catalyst with a higher specific surface area and more active areas. It is active in the oxygen evolution reaction in an acidic environment, can well reduce the cell voltage of electrolyzed water for hydrogen production, can improve the electrocatalytic activity, stability and durability while reducing the content of the noble metal Ir, and significantly reduces the problem of the use cost of the catalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolyzed water catalysts, and particularly relates to a transition metal-doped modified flaky iridium oxide catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] With the gradual depletion of fossil fuel resources and the increasingly serious environmental pollution problems, hydrogen energy has received high attention due to its characteristics such as cleanness, high efficiency, stability, and renewability. Preparing hydrogen by electrolyzing water is one of the important development directions of renewable energy and is also the most common method for preparing hydrogen. In electrolyzed water, currently, the main electrolyzed water hydrogen production process devices are alkaline electrolyzers (AEM) and proton exchange membrane electrolyzers (PEM). Among them, PEM technology stores intermittent renewable energy by converting electrical energy into chemical energy. Moreover, different from AEM technology, PEM water electrolysis hydrogen production has many advantages such as fast reaction, high power density, flexible operation, high efficiency, and good matching with wind power and photovoltaic. Based on this, the PEM-based water electrolysis technology is considered the key technology for the effective utilization of hydrogen energy.

[0003] The electrolyzed water reaction includes the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode. From a kinetic perspective, the anode OER is a four-electron proton-coupled reaction, which requires a high overpotential, resulting in a low hydrogen evolution efficiency in the cathode half-reaction. This is the main part of the performance loss in the anode reaction of the proton exchange membrane water electrolyzer. Improving the OER catalytic performance of the catalyst is of great significance for electrocatalytic water decomposition.

[0004] Currently, among the electrolyzed water catalyst materials applied on the proton exchange membrane, only iridium oxide (IrO2) and ruthenium oxide show satisfactory activity and stability. The activity of iridium oxide is slightly worse than that of ruthenium oxide, but it shows good stability and can resist dissolution and leaching under highly acidic conditions at the anode. Therefore, iridium oxide is the main catalyst material. Traditional commercial iridium oxide presents small particles, has a small specific surface area, and is prone to agglomeration during the reaction. Flaky iridium oxide with a large specific surface area can be prepared by the Adams melting method, which is beneficial for increasing the reaction active area and the desorption of products. However, iridium (Ir) is a noble metal catalyst, with high cost, scarce resources, which limits its wide commercial application. By introducing non-noble metal doping, the cost can be reduced. However, the oxygen evolution activity and stability need to be improved, and it cannot meet the requirements of actual production.

[0005] Aiming at the deficiencies in the structure and preparation method of the current electrolyzed water anode iridium oxide catalyst, modifying the structure of iridium oxide to improve its catalytic activity and maintain stability is particularly important for the wide application of proton exchange membrane electrolyzers. Summary of the Invention

[0006] In view of the above problems in the prior art, the present invention provides a transition metal-doped modified flaky iridium oxide catalyst and a preparation method thereof, and provides the application of the transition metal-doped modified flaky iridium oxide catalyst in the field of water electrolysis to solve or at least alleviate some or all of the technical problems in the prior art.

[0007] To achieve the above object, the present invention is specifically realized through the following technical solutions:

[0008] The first aspect of the present invention provides a preparation method of a transition metal-doped modified flaky iridium oxide catalyst, comprising the following steps:

[0009] S1. Mix an iridium precursor, a transition metal precursor, sodium nitrate and a dispersant, and ball-mill to form a slurry, wherein the transition metal is one or more of Co, Ni and Mn, and the molar ratio of the iridium precursor to the transition metal precursor is 5:0.5-4;

[0010] S2. Dry the slurry;

[0011] S3. Calcinate the slurry in an air atmosphere;

[0012] S4. Purify the calcined product to obtain a transition metal-doped modified flaky iridium oxide.

[0013] Further, the molar ratio of the iridium precursor to the transition metal precursor is 5:0.5-2; more preferably, the molar ratio of the iridium precursor to the transition metal precursor is 5:1.

[0014] Further, the transition metal is Mn.

[0015] Further, in step S1, ball-milling to form a slurry includes the following steps: rotate counterclockwise for 30 min at a rotation speed of 180 rpm / min, then stay for 5 min, and then rotate clockwise for 30 min, and repeat 10 times to obtain a slurry with precursors fully mixed.

[0016] Further, in step S2, drying the slurry includes the following steps: heat the slurry from room temperature to 60-90 °C within 20 min, and keep it warm for 3-8 h to obtain a light brown powder.

[0017] Further, in step S3, calcining the slurry includes the following steps: heat it at a heating rate of 1-4 °C / min to 280-350 °C, keep it warm for 1-3 h, and then cool it down.

[0018] Further, in step S4, purifying the calcined product includes the following steps: soak the calcined product in deionized water for 0.5-4 h, then perform suction filtration, and dry the residue to obtain a transition metal-doped modified flaky iridium oxide.

[0019] The second aspect of the present invention provides a transition metal-doped and modified flaky iridium oxide catalyst prepared by the preparation method of the transition metal-doped and modified flaky iridium oxide catalyst as described above.

[0020] The third aspect of the present invention provides the application of the transition metal-doped and modified flaky iridium oxide catalyst as described above or the preparation method of the transition metal-doped and modified flaky iridium oxide catalyst as described above in water electrolysis.

[0021] The advantages and positive effects of the present invention are as follows:

[0022] 1. In the present invention, sodium nitrate is used as a template agent, an oxidizing agent and a pore-forming agent to promote the formation of a nano-scale and micro-scale flaky porous structure of iridium oxide. Through ball milling and high-temperature calcination, transition metals are doped into iridium oxide. The transition metals can effectively adjust the bond energy strength between iridium metal and oxygen in iridium oxide and adjust the outer electron structure of iridium. Therefore, an electrocatalyst with a higher specific surface area and more active areas is prepared. It is active in the oxygen evolution reaction in an acidic environment, can well reduce the cell voltage of hydrogen production by electrolyzing water in an acidic environment, and has excellent stability. In addition, the content of precious metals is significantly reduced compared with commercial iridium oxide. Compared with flaky pure iridium oxide and commercial bulk iridium oxide, while reducing the content of precious metal Ir, it can improve the electrocatalytic activity, stability and durability, and significantly reduce the problem of the use cost of the catalyst.

[0023] 2. The preparation method of the present invention has a simple preparation process, is environmentally friendly and energy-saving, and can be widely applied. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 It is the transition metal M doping model of the transition metal-doped and modified flaky iridium oxide catalyst in the embodiment of the present invention;

[0026] Figure 2 It is the X-ray diffraction patterns of the transition metal-doped and modified flaky iridium oxide catalysts Mn@IrO2, Co@IrO2 and Ni@IrO2, flaky IrO2 and commercial IrO2 catalysts prepared in Examples 1-3 of the present invention;

[0027] Figure 3X-ray photoelectron spectroscopy diagrams of the transition metal-doped modified flaky iridium oxide catalyst Mn@IrO2, flaky IrO2, and commercial IrO2 catalyst prepared in Example 1 of the present invention;

[0028] Figure 4 Scanning electron microscopy diagrams of the transition metal-doped modified flaky iridium oxide catalyst Mn@IrO2, flaky IrO2, and commercial IrO2 catalyst prepared in Example 1 of the present invention;

[0029] Figure 5 Transmission electron microscopy diagram of the transition metal-doped modified flaky iridium oxide catalyst Mn@IrO2 prepared in Example 1 of the present invention;

[0030] Figure 6 EDS mapping spectrum diagram of the transition metal-doped modified flaky iridium oxide catalyst Mn@IrO2 prepared in Example 1 of the present invention;

[0031] Figure 7 Oxygen evolution reaction curves of the transition metal-doped modified flaky iridium oxide catalysts Mn@IrO2, Co@IrO2, and Ni@IrO2, flaky IrO2, and commercial IrO2 catalyst prepared in Examples 1-3 of the present invention in acidic electrolyte;

[0032] Figure 8 Oxygen evolution reaction polarization curves of the transition metal-doped modified flaky iridium oxide catalyst Mn@IrO2 prepared in Example 1 of the present invention at different Mn feeding contents;

[0033] Figure 9 Polarization curve diagram of overall water electrolysis in an acidic environment of the transition metal-doped modified flaky iridium oxide catalyst Mn@IrO2 prepared in Example 1 of the present invention in a two-electrode system;

[0034] Figure 10 Curve of voltage change with time under the same current condition in an acidic environment of the transition metal-doped modified flaky iridium oxide catalyst Mn@IrO2 prepared in Example 1 of the present invention in a two-electrode system. Detailed implementation manners

[0035] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to examples. The examples described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] Based on the information contained in the present invention, various changes can be easily made to the precise description of the present invention by those skilled in the art without departing from the spirit and scope of the appended claims. It should be understood that the scope of the present invention is not limited to the defined processes, properties or components, as these embodiments and other descriptions are only for illustrative purposes of specific aspects of the present invention. In fact, all various changes that can be made by those skilled in the art in the relevant field to the embodiments of the present invention are covered within the scope of the appended claims.

[0037] For a better understanding of the present invention rather than limiting its scope, all numbers representing amounts, percentages and other numerical values used in the present invention should be understood to be modified by the word "about" in all cases. Therefore, unless otherwise specified, the numerical parameters listed in the specification and the appended claims are approximate values, which may be changed according to different desired properties. Each numerical parameter should at least be regarded as obtained according to the reported significant figures and by the conventional rounding method. In addition, the meanings of the similar words such as "comprising", "including", "containing", "having" are non-restrictive, that is, other steps and other components can be added without affecting the results.

[0038] To make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be described in detail below.

[0039] An embodiment of the present invention provides a preparation method of a transition metal-doped and modified flaky iridium oxide catalyst, comprising the following steps:

[0040] S1. Mix an iridium precursor, a transition metal precursor, sodium nitrate and a dispersant, and ball-mill to form a slurry, wherein the transition metal is one or more of Co, Ni and Mn, and the molar ratio of the iridium precursor to the transition metal precursor (calculated as iridium:transition metal) is 5:0.5 - 4;

[0041] S2. Dry the slurry;

[0042] S3. Calcinate the slurry in an air atmosphere;

[0043] S4. Purify the calcined product to obtain a transition metal-doped and modified flaky iridium oxide.

[0044] For the convenience of description, hereinafter, M is used to describe the transition metal, M = Co, Ni and / or Mn, and the transition metal-doped and modified flaky iridium oxide is named flaky M@IrO2.

[0045] In the present invention, sodium nitrate is used as a templating agent, an oxidizing agent, and a pore-forming agent. The excessive sodium nitrate serves as a template for the formation of flaky M@IrO2, promoting the formation of a flaky structure of iridium oxide (IrO2). Moreover, when sodium nitrate is calcined at high temperature, it decomposes to generate oxygen, which can supply the formation of oxides and produce sufficient pores in the flaky oxides, forming flaky porous iridium oxide at the nano-scale and micro-scale. This is beneficial to increasing its specific surface area. Furthermore, through ball milling and high-temperature calcination, the transition metal M is successfully doped into iridium oxide. Figure 1 The doping model of the transition metal M is shown. The doping of the M element is beneficial to changing the original microstructure of iridium oxide, effectively regulating the bond energy strength between iridium and oxygen in iridium oxide, adjusting the outer electron structure of iridium, and enhancing the catalytic activity of iridium oxide.

[0046] Compared with the commercially available iridium oxide catalyst in the market, doping the transition metal into the porous flaky iridium oxide to form an electrocatalyst with a high specific surface area has a higher specific surface area and more active areas to improve the catalytic activity and material utilization efficiency. Therefore, the transition metal-doped modified flaky iridium oxide catalyst prepared by the present invention is extremely active in the oxygen evolution reaction (OER) in an acidic environment, can well reduce the cell voltage for hydrogen production by electrolyzing water in an acidic environment, and has excellent stability. In addition, the content of precious metals is significantly reduced compared with commercial iridium oxide, significantly reducing the cost. Thus, the transition metal-doped modified flaky iridium oxide catalyst prepared by the above method of the present invention, in an acidic reaction environment, can improve the electrocatalytic activity, stability, and durability while reducing the content of the precious metal Ir compared with flaky pure iridium oxide and commercial bulk iridium oxide, effectively solving the high-cost problem of using precious metal catalysts in the industrial acidic electrolysis of water process. Moreover, the preparation method of the present invention has a simple preparation process, is environmentally friendly and energy-saving, and can be widely applied.

[0047] Adding a transition metal is beneficial to improving the iridium-oxygen bond in iridium oxide and optimizing the chemical state of iridium during the electrochemical reaction process, which is beneficial to enhancing the OER reaction activity during the anodic electrolysis process. However, when the content of the transition metal is too high, transition metal oxides will be formed during the preparation process and will undergo electrochemical dissolution at high potentials in an acidic environment. Therefore, an appropriate content of the transition metal is necessary for improving the catalytic performance. Preferably, the molar ratio of the iridium precursor to the transition metal precursor (calculated as iridium: transition metal) is 5:0.5 - 2, and more preferably 5:1.

[0048] Different transition metal dopings have different improvement efficiencies for the catalyst performance. Preferably, the transition metal is one or more of Co and Mn, and more preferably the transition metal is Mn. It has been confirmed by research that the doping of Mn is particularly obvious for improving the performance of the catalyst such as catalytic activity, stability, and durability.

[0049] Iridium precursors and transition metal precursors are used to provide an iridium source and a transition metal source. The present invention does not make special limitations on their types, as long as they can effectively form iridium ions and Co ions, Ni ions or Mn ions. In some embodiments, preferably, the iridium precursor is selected from one or more of iridium trichloride, iridium tetrachloride, chloroiridic acid, iridium acetate, ammonium chloroiridate and potassium hexachloroiridate; the transition metal precursor is selected from one or more of transition metal chlorides (MCl2), transition metal nitrates (M(NO3)2), and transition metal sulfates (MSO4).

[0050] The dispersant is a surfactant that can quickly wet the surface of solid particles and raise the energy barrier between solid particles to a sufficiently high level, facilitating the formation of a homogeneous slurry during the ball milling process of solid powder materials. The present invention does not make special limitations on the type of the dispersant. In some embodiments, the dispersant is selected from one or more of isopropanol and stearic acid.

[0051] Optionally, in step S1, ball milling to form a slurry includes the following steps: rotating counterclockwise for 30 min at a speed of 180 rpm / min, staying for 5 min, and then rotating clockwise for 30 min, repeating 10 times to obtain a slurry with well-mixed precursors.

[0052] Optionally, in step S2, drying the slurry includes the following steps: heating the slurry from room temperature to 60 - 90 °C within 20 min, and keeping warm for 3 - 8 h until isopropanol is completely removed to obtain a light brown powder. Preferably, the slurry is heated from room temperature to 75 °C and kept warm for 5 h.

[0053] Optionally, in step S3, calcining the slurry includes the following steps: heating at a heating rate of 1 - 4 °C / min to 280 - 350 °C, keeping warm for 1 - 3 h, and then cooling. Preferably, heating at a heating rate of 2 °C / min to 300 °C, keeping warm for 2 h, and then cooling.

[0054] Optionally, in step S4, purifying the calcined product includes the following steps: soaking the calcined product in deionized water for 0.5 - 4 h, then performing suction filtration, and drying the residue to obtain transition metal-doped and modified flaky iridium oxide. Specifically, the drying temperature is 40 - 80 °C, preferably 60 °C. There is a high content of template salt sodium nitrate in the calcined product. After washing away sodium nitrate with water, suction filtration and drying can obtain a pure flaky M@IrO2 catalyst.

[0055] Based on the same inventive concept, another embodiment of the present invention provides a transition metal-doped and modified flaky iridium oxide catalyst prepared by the preparation method of the transition metal-doped and modified flaky iridium oxide catalyst as described above.

[0056] The advantages of the transition metal-doped modified flaky iridium oxide catalyst and the preparation method of the transition metal-doped modified flaky iridium oxide catalyst as described above are the same as those over the prior art, and will not be elaborated herein.

[0057] Based on the same inventive concept, another embodiment of the present invention provides an application of the transition metal-doped modified flaky iridium oxide catalyst or the preparation method of the transition metal-doped modified flaky iridium oxide catalyst as described above in electrolyzing water, specifically as a catalyst for the oxygen evolution reaction in electrolyzing water.

[0058] The application advantages of the transition metal-doped modified flaky iridium oxide catalyst in electrolyzing water are the same as those of the transition metal-doped modified flaky iridium oxide catalyst over the prior art, and will not be elaborated herein.

[0059] The present invention will be further described below in conjunction with specific embodiments. For the experimental methods without specific conditions indicated in the following embodiments, they are generally carried out according to the conditions recommended by the manufacturer.

[0060] Example 1

[0061] A preparation method of a transition metal-doped flaky iridium oxide catalyst includes the following steps:

[0062] S1. Add 2 g of iridium chloride acid (5 mmol), 0.2 g of manganese chloride (1 mmol), 10 g of sodium nitrate, and 60 mL of isopropanol into a ball mill tank (mixed with clean zirconia particles for auxiliary grinding), maintain the rotation speed at 180 rpm / min, rotate counterclockwise for 30 min and then stay for 5 min, and then rotate clockwise for 30 min. Repeat this 10 times to fully rotate and grind the mixture to obtain a slurry with the precursor fully mixed.

[0063] S2. Transfer the obtained slurry to a 100 mL beaker, heat it from room temperature to 75 °C within 20 min, keep it warm for 5 h until the isopropanol is completely removed to obtain a light brown powder, transfer it to a mortar to remove the zirconia particles, and grind it into fine powder.

[0064] S3. Transfer the obtained fine powder to a muffle furnace, under air conditions, heat it at a heating rate of 2 °C / min to 300 °C, keep it warm for 2 h and then cool down.

[0065] S4. There is a high content of template salt sodium nitrate in the calcined product in the porcelain boat after cooling. Soak the calcined product in deionized water for 1 h and then filter it by suction. The residue is kept in an oven at 60 °C overnight to obtain flaky Mn@IrO2.

[0066] Example 2

[0067] A preparation method of a transition metal-doped flaky iridium oxide catalyst includes the following steps:

[0068] S1. Add 2 g of iridium chloride hydrate (5 mmol), 0.13 g of nickel chloride (1 mmol), 10 g of sodium nitrate, and 60 mL of isopropanol into a ball milling jar (assisted by mixing clean zirconia particles for grinding), maintain the rotation speed at 180 rpm / min, rotate counterclockwise for 30 min and then stop for 5 min, and then rotate clockwise for 30 min. Repeat this 10 times to fully rotate and grind the mixture, obtaining a slurry with the precursors fully mixed.

[0069] S2. Transfer the slurry obtained above to a 100 mL beaker, heat it from room temperature to 75 °C within 20 min, and keep it warm for 5 h until the isopropanol is completely removed, obtaining a light brown powder. Transfer it to a mortar to remove the zirconia particles and grind it into a fine powder.

[0070] S3. Transfer the fine powder obtained above to a muffle furnace, under air conditions, heat it to 300 °C at a heating rate of 2 °C / min, keep it warm for 2 h, and then cool it down.

[0071] S4. There is a high content of template salt sodium nitrate in the calcined product in the porcelain boat after cooling. Soak the calcined product in deionized water for 1 h and then filter it by suction. The residue can be kept in an oven at 60 °C overnight to obtain flaky Ni@IrO₂.

[0072] Example 3

[0073] A preparation method of a transition metal-doped flaky iridium oxide catalyst, comprising the following steps:

[0074] S1. Add 2 g of iridium chloride hydrate (5 mmol), 0.13 g of cobalt chloride (1 mmol), 10 g of sodium nitrate, and 60 mL of isopropanol into a ball milling jar (assisted by mixing clean zirconia particles for grinding), maintain the rotation speed at 180 rpm / min, rotate counterclockwise for 30 min and then stop for 5 min, and then rotate clockwise for 30 min. Repeat this 10 times to fully rotate and grind the mixture, obtaining a slurry with the precursors fully mixed.

[0075] S2. Transfer the slurry obtained above to a 100 mL beaker, heat it from room temperature to 75 °C within 20 min, and keep it warm for 5 h until the isopropanol is completely removed, obtaining a light brown powder. Transfer it to a mortar to remove the zirconia particles and grind it into a fine powder.

[0076] S3. Transfer the fine powder obtained above to a muffle furnace, under air conditions, heat it to 300 °C at a heating rate of 2 °C / min, keep it warm for 2 h, and then cool it down.

[0077] S4. After cooling, there is a high content of template salt sodium nitrate in the calcined product in the porcelain boat. The calcined product is soaked in deionized water for 1 h and then filtered by suction. The residue is kept in an oven at 60 °C overnight to obtain flaky Co@IrO2.

[0078] Example 4

[0079] This example aims to evaluate the performance of the catalysts prepared in Examples 1-3. The preparation method of flaky IrO2 for comparison is the same as that in Examples 1-3, except that the transition metal precursor is not added. The commercial IrO2 model is I102673, and the purity is >99.99%.

[0080] Figure 2 The X-ray diffraction (XRD) patterns of the transition metal-doped flaky iridium oxide catalysts prepared in Examples 1-3 of the present invention are shown. It can be seen from the figure that all the diffraction peaks of the samples can completely correspond to the iridium oxide standard card (15-0870). And with the doping of the transition metal, the main crystal plane (35 degrees) of iridium oxide shows a high-angle shift, indicating that the transition metal atoms have been successfully doped into the iridium oxide crystal lattice and changed its crystal structure.

[0081] Figure 3 The X-ray photoelectron spectroscopy (XPS) graphs of the transition metal-doped flaky iridium oxide catalyst Mn@IrO2, flaky IrO2, and commercial IrO2 prepared in Example 1 of the present invention are shown. Among them, the abscissa is the binding energy and the ordinate is the relative intensity. From Figure 3 it can be seen that the Mn element has been successfully doped into the flaky IrO2. And due to the addition of manganese (Mn), the binding energy of Ir has a relatively obvious increase compared with commercial iridium oxide, which means that its oxidation state has increased, which is beneficial to the improvement of the OER catalytic activity in an acidic environment.

[0082] Figure 4 The scanning electron microscopy (SEM) graphs of the transition metal-doped flaky iridium oxide catalyst Mn@IrO2, flaky IrO2, and commercial IrO2 prepared in Example 1 of the present invention are shown. The results are as Figure 4 shown. From Figure 4 it can be seen that the microscopic morphology of commercial IrO2 presents a blocky shape, while the flaky IrO2 prepared by the melting method and the Mn@IrO2 of the present invention present similar flaky shapes. The addition of Mn does not change the microscopic morphology of flaky iridium oxide.

[0083] Figure 5 The transmission electron microscopy graphs (TEM and HRTEM) of the transition metal-doped flaky iridium oxide catalyst Mn@IrO2, flaky IrO2, and commercial IrO2 prepared in Example 1 of the present invention are shown. From Figure 5It can be seen that Mn@IrO2 presents as flakes. Under high resolution, the obvious (101) plane stripes of iridium oxide and the corresponding crystal diffraction rings can be clearly seen, which is consistent with Figure 2 the XRD spectrum in , and its phase remains IrO2, and Mn only enters the IrO2 matrix as a dopant.

[0084] Figure 6 Figure shows the EDS mapping spectrum of the transition metal-doped flaky iridium oxide catalyst Mn@IrO2 prepared in Example 1 of the present invention. The elemental distribution (left figure) and its content (right figure) can be seen. From Figure 6 it can be seen that Mn, Ir, and O elements are uniformly distributed on the flaky iridium oxide, and the energy spectrum shows that the Mn content is not high, which is determined as a dopant element.

[0085] Oxygen evolution reaction curve test: The transition metal-doped flaky iridium oxide catalysts Mn@IrO2, Co@IrO2, Ni@IrO2 prepared in Examples 1-3, as well as flaky IrO2 and commercial IrO2 (model I102673, purity > 99.99%) were tested in an acidic electrolyte (0.5 M H2SO4) under a three-electrode system (the working electrode is a glassy carbon electrode; the counter electrode is a graphite rod; the reference electrode is a saturated calomel electrode), and the scanning rate is 5 mV s -1 . The oxygen evolution reaction curves at this time were measured. The catalysts to be tested were coated on the surface of the working electrode glassy carbon electrode. The results are as Figure 7 shown, where the abscissa is voltage and the ordinate is current density. From Figure 7 it can be seen that, compared with commercial IrO2 and flaky IrO2, in order to achieve the same current density (such as 10 mA cm -2 ), the voltages required for each catalyst are different, and the voltage required for flaky Mn@IrO2 is the lowest. This means that the doping of transition metals significantly improves the OER catalytic activity of iridium oxide, and the transition metal-doped flaky iridium oxide catalyst Mn@IrO2 prepared in Example 1 has better oxygen evolution activity, and the performance improvement is particularly obvious.

[0086] Figure 8 Figure shows the oxygen evolution reaction polarization curves measured under the above-mentioned three-electrode system and scanning rate of 5 mV s -1 when the Mn feeding content in the transition metal-doped flaky iridium oxide catalyst Mn@IrO2 prepared in Example 1 of the present invention is different. It can be seen from the figure that when the doping feeding amount is 1 mmol, that is, the molar ratio of Mn to Ir is 1:5, the performance of flaky Mn@IrO2 is the best.

[0087] Reaction curve test of overall electrolysis of water: Using the transition metal-doped flaky iridium oxide catalyst Mn@IrO2 prepared in Example 1 of the present invention and commercial IrO2 as the anodes respectively, and using a commercial Pt / C catalyst (model HPT020, 20% Pt / C) as the cathode, in an acidic electrolyte (0.5 M H2SO4), a two-electrode system was adopted to test the reaction curve of overall electrolysis of water at a scanning rate of 5 mV s -1 The results are as shown in Figure 9 . Among them, the abscissa is the voltage and the ordinate is the current density corresponding to the voltage. It can be seen from Figure 9 that for the two-electrode system with Mn@IrO2 as the anode, only 1.54 V is required to reach 10 mA·cm -2 (current density), while the commercial catalyst requires 1.6 V under the same conditions. This indicates that the transition metal-doped flaky iridium oxide catalyst Mn@IrO2 has better anodic water oxidation ability than commercial IrO2.

[0088] Stability test: Using the transition metal-doped flaky iridium oxide catalyst Mn@IrO2 prepared in Example 1 of the present invention as the anode and a commercial Pt / C catalyst (model HPT020, 20% Pt / C) as the cathode, in an acidic electrolyte (0.5 M H2SO4), a two-electrode system was adopted to measure the change curve of voltage with time under the same current condition. The results are as shown in Figure 10 . Among them, the abscissa is the time and the ordinate is the voltage. It can be seen from Figure 10 that the duration of the transition metal-doped flaky iridium oxide catalyst Mn@IrO2 prepared in Example 1 for stably decomposing water under different current densities remains at nearly 20 h, far exceeding commercial IrO2 and flaky IrO2, and has good stability and durability.

[0089] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a transition metal-doped and modified flaky iridium oxide catalyst, characterized in that, It includes the following steps: S1. Mix an iridium precursor, a transition metal precursor, sodium nitrate, and a dispersant, add them into a ball milling tank. Under the condition of a rotation speed of 180 rpm / min, rotate counterclockwise for 30 min, then stay for 5 min, and then rotate clockwise for 30 min. Repeat this 10 times to obtain a slurry with the precursors fully mixed. Herein, the transition metal is Mn, and the molar ratio of the iridium precursor to the transition metal precursor is 5:1; S2. Dry the slurry; S3. Under an air atmosphere, heat it at a heating rate of 1 - 4 °C / min to 280 - 350 °C, keep it warm for 1 - 3 h, and then cool it down to calcine the slurry; S4. Purify the calcined product to obtain a transition metal - doped and modified flaky iridium oxide.

2. The preparation method of the transition metal-doped and modified flaky iridium oxide catalyst according to claim 1, characterized in that, In step S2, drying the slurry includes the following steps: Heat the slurry from room temperature to 60 - 90 °C within 20 min, and keep it warm for 3 - 8 h to obtain a light brown powder.

3. The preparation method of the transition metal-doped and modified flaky iridium oxide catalyst according to claim 1, characterized in that, In step S4, purifying the calcined product includes the following steps: Soak the calcined product in deionized water for 0.5 - 4 h, then perform suction filtration, and dry the residue to obtain the transition metal - doped and modified flaky iridium oxide.

4. A transition metal-doped and modified flaky iridium oxide catalyst, characterized in that, It is prepared by the preparation method of the transition metal - doped and modified flaky iridium oxide catalyst according to any one of claims 1 - 3.

5. Application of the transition metal - doped and modified flaky iridium oxide catalyst according to claim 4 in electrolyzing water.

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