Nano iridium oxide catalyst as well as preparation method and application thereof

Abstract

The invention discloses a nano iridium oxide catalyst as well as a preparation method and application thereof, and relates to the field of catalytic material preparation. The preparation method of the nano iridium oxide catalyst comprises the steps of ultrasonic reaction of a mixed solution, drying and calcining, acid treatment and the like. The preparation method of the iridium oxide catalyst provided by the invention can realize uniform oxidation in a low-temperature environment with a small amount of oxidation auxiliary agent, and solves the problem that a large amount of nitrate and peroxide are adopted in the traditional synthesis process; the iridium oxide synthesized by the method has the advantages of adjustable crystallization degree in the range of 20-100%, small and uniform particle size, large specific surface area and certain growth orientation, thereby enhancing the activity of the catalyst and solving the problem that the growth of the catalyst is difficult to control in the actual production process.

Description

Technical Field

[0001] The invention relates to the technical field of catalytic material preparation, and in particular to a nano iridium oxide catalyst, a preparation method and application thereof. Background Art

[0002] As my country's hydrogen energy industry has gradually been elevated to the level of a national energy strategy, hydrogen production technology has received more and more attention. As the only hydrogen production technology that can be coupled with renewable energy power generation, proton exchange membrane (PEM) water electrolysis hydrogen production technology has irreplaceable advantages in many aspects such as hydrogen production purity, device compactness, response speed to input power supply, and safety. At present, the main factor that constrains the energy conversion efficiency of PEM water electrolysis hydrogen production technology is the oxygen evolution reaction at the anode end. Due to the slow kinetics of this half-reaction, it largely determines the energy consumption, power and life of the electrolyzer (Chem. Rev., 2010, 110, 6474-6502). Therefore, improving the catalytic activity of the anode catalyst and reducing the overpotential of the oxygen evolution reaction in PEM water electrolysis technology are one of the important ways to improve the performance of this technology. In terms of the selection of anode catalysts, currently only iridium-based oxides can maintain catalytic activity for a long time under these conditions (strong acid, strong oxidizing properties), and iridium dioxide (IrO 2 ) is a commercial catalyst for PEM water electrolysis technology. Its catalytic activity still needs to be further improved. The most significant way to improve the activity of iridium oxide is to regulate its crystal orientation and degree of crystallization. However, the current technology for preparing catalysts has poor uniformity and has high requirements for synthesis equipment. In addition, a large amount of nitrates and peroxides are used in the synthesis process, the reaction conditions are high, and the content of harmful substances in the product is high.

[0003] The preparation methods of iridium oxide are mainly Adams method and sol-gel method. The Adams method usually requires a large amount of nitrate (the molar ratio of precious metal to nitrate is close to 1:10-20) to embed iridium salt, while the sol-gel method requires precious metal salt, nitrate, polyol, polyacid to undergo condensation reaction to generate metal coordination complex colloid to achieve uniform oxidation, and the by-products are not only large in number, but also polluting.

[0004] For example, Chinese patent application CN104209121A discloses a method for electrolyzing IrO 2 The preparation method of the catalyst comprises: dissolving sodium hydroxide in deionized water, then adding chloroiridic acid to obtain a first solution; reacting the first solution in an oil bath, stirring and cooling to room temperature after the reaction to obtain a second solution; adding acid to the second solution, adjusting pH, centrifuging, and drying to obtain iridium hydroxide; burning the iridium hydroxide in an air atmosphere to obtain IrO for water electrolysis. 2Catalyst. Chinese Patent Application CN114072939A discloses a method for preparing a catalyst composition, including: depositing an iridium-containing solid on a support material in an aqueous medium containing an iridium compound under the condition of pH ≥ 9; separating and drying the support material carrying the iridium-containing solid from the aqueous medium, wherein the support material carrying the iridium-containing solid does not undergo heat treatment at a temperature exceeding 250 °C for a duration exceeding 1 hour.

[0005] From the perspective of the prior art, the method of mixing a soluble iridium-based precursor with water and carrying out a hydrolysis reaction under alkaline conditions to obtain iridium hydroxide, and then heating and decomposing the iridium hydroxide to produce a nano iridium oxide catalyst is relatively conventional. However, the processes of heating and decomposing the iridium hydroxide in the second step and subsequent treatment steps are different. The degree of crystallization can affect the catalytic activity of the catalyst (Gao H, Xiao Z, Du S, et al. Reducing the Ir-O Coordination Number in Anodic Catalysts based on IrO x Nanoparticles towards Enhanced Proton-exchange-membrane Water Electrolysis. Angewandte Chemie International Edition, 2023, 62(49): e202313954.). Generally, the lower the degree of crystallization, the higher the catalytic activity. However, with a lower degree of crystallization, the catalytic stability of the material often decreases (Geiger S, Kasian O, Ledendecker M, et al. The stability number as a metric for electrocatalyst stability benchmarking. Nature Catalysis, 2018, 1(7): 508-515.). Therefore, it is crucial to adjust the influence of the degree of crystallization of the catalyst on the performance according to the application environment of the material. In addition, different growth and exposure surfaces of the material can affect the catalytic activity, so it is also crucial to be able to adjust the orientation of the catalyst (Nga Ngo T H, Love J, O'Mullane A P. Investigating the Influence of Amorphous / Crystalline Interfaces on the Stability of IrO 2for the Oxygen Evolution Reaction in Acidic Electrolyte.ChemElectroChem,2023,10(24):e202300438.). There is no prior art reporting the control of the crystallization degree and the generation of a nano iridium oxide catalyst with a growth orientation. Summary of the Invention

[0006] In view of this, the main object of the present invention is to provide a nano iridium oxide catalyst, its preparation method and application, in order to at least partially solve the above technical problems.

[0007] To achieve the above object, in the first aspect of the present invention, a nano iridium oxide catalyst is provided, and the crystallization degree of the nano iridium oxide catalyst can be adjusted within the range of 20%-100%, for example, it can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100% or all values within the range. Due to space limitations, they will not be elaborated here;

[0008] Preferably, the nano iridium oxide catalyst has a growth orientation.

[0009] Preferably, the noble metal dissolution rate of the nano iridium oxide catalyst is 0.01%-1.3%, for example, it can be 0.02%, 0.025%, 0.35%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3% or all values within the range. Due to space limitations, they will not be elaborated here; and / or

[0010] The electrochemically active area of the nano iridium oxide catalyst is 17.72 - 32.44 C / cm 2 , for example, it can be 17.72 C / cm 2 , 18 C / cm 2 , 19 C / cm 2 , 20 C / cm 2 , 21 C / cm 2 , 22 C / cm 2 , 23 C / cm 2 , 24 C / cm 2 , 25 C / cm 2 , 26 C / cm 2 , 27 C / cm 2 , 28 C / cm 2 , 29 C / cm 2 , 30 C / cm2 , 31 C / cm 2 , 32 C / cm 2 Or all values within the said range, which will not be elaborated due to space limitations.

[0011] Preferably, when the nano iridium oxide catalyst works within the overpotential range of 230 - 304 mV (such as 230 mV, 240 mV, 250 mV, 260 mV, 270 mV, 272 mV, 275 mV, 278 mV, 280 mV, 283 mV, 285 mV, 287 mV, 290 mV, 292 mV, 295 mV, 297 mV, 300 mV, 304 mV or all values within the said range, which will not be elaborated due to space limitations), a current density of 10 mA / cm 2 can be generated; and / or

[0012] when the nano iridium oxide catalyst works within the overpotential range of 390 - 480 mV (such as 390 mV, 395 mV, 400 mV, 405 mV, 410 mV, 415 mV, 420 mV, 425 mV, 430 mV, 435 mV, 440 mV, 445 mV, 450 mV, 455 mV, 460 mV, 465 mV, 470 mV, 475 mV, 480 mV or all values within the said range, which will not be elaborated due to space limitations), a current density of 100 mA / cm 2 is generated.

[0013] Second, the present invention provides a preparation method of the nano iridium oxide catalyst as described in the first aspect, and the method includes the following steps:

[0014] 1) Dissolve n mol of iridium source, x mol of alkali salt and y mol of nitrate in water to obtain a mixed solution and heat it (corresponding to reaction equations ① and ②);

[0015] 2) Dry the mixed solution obtained in step 1), heat the dried solid sample (when the calcination temperature exceeds the nitrate decomposition temperature, corresponding to reaction equation ③), and cool it to room temperature to obtain a powder (the black powder is the prepared IrO x material);

[0016] 3) Protonate the powder obtained in step 2) to obtain the nano iridium oxide catalyst (mainly for purification).

[0017] Principle of the present invention: By controlling the iridium source and alkali salt to form iridium hydroxide colloid, and then promoting the decomposition and uniform oxidation of iridium hydroxide with the help of the ionic assistant of nitrate.

[0018] ① Adding a weakly basic salt to promote the reaction / adding a strong base to directly form iridium hydroxide:

[0019] Ir +3 / +4 +H 2 O→Ir(OH) 3 / 4 +H + or Ir +3 / +4 +3 / 4OH - →Ir(OH) 3 / 4

[0020] ② Heating:

[0021] ③ When the temperature reaches the decomposition temperature of the nitrate, decompose the nitrate to generate a nano iridium oxide catalyst:

[0022] IrO x +NO 3 - →IrO 2 +NO 2 ↑+O 2 ↑

[0023] The purpose of heating in step 1) is to achieve the weak oxidation of iridium, so as to achieve the uniform preparation of crystalline metal oxides; at the same time, this temperature does not reach the thermal decomposition temperature of the nitrate, and the nitrate can promote the oxidation of metals in the solution (for reference, see the literature "Ultrafast Formation of Amorphous Bimetallic Hydroxide Films on 3D Conductive Sulfide Nanoarrays for Large-Current-Density Oxygen Evolution Electrocatalysis", which realizes the rapid oxidation of nickel foam in an aqueous solution of sodium nitrate), making it play a role in promoting decomposition (catalyst). In addition, in a liquid-phase homogeneous reaction environment, compared with the solid-phase environment of the Adams method, the nitrate is more uniformly dispersed and more fully combined with the noble metal, so that the more uniform oxidation of the noble metal can be achieved, and the amount of nitrate used can be reduced by using this method, realizing the reduction of the emission of polluting by-products. In addition, by using liquid-phase in-situ nitrate oxidation, the oriented growth of iridium oxide can be promoted, and the active crystal plane component can be improved.

[0024] Preferably, in step 1), x:n≥1, that is, the molar number of hydroxide ions or bicarbonate ions or carbonate ions is greater than or equal to the molar number of the noble metal; y:n≥1, that is, the molar number of nitrate ions is greater than or equal to the molar number of the noble metal; as shown in reaction equation ①, after the Ir ions are hydrolyzed to iridium hydroxide, H + is generated, and the solution is weakly acidic. When a weak base or basic substance is added, H +, according to the principle of chemical equilibrium shift, the equilibrium will shift towards the direction of generating iridium hydroxide, that is, it will promote the hydrolysis of iridium. Therefore, as long as a weak base or basic substance can react with H + it can play a role. When using a strong base represented by sodium hydroxide, hydroxide ions and Ir ions can directly form iridium hydroxide (as shown in the direct reaction with OH - in reaction equation ①). Among them, strong and weak bases are distinguished according to the degree of ionization: strong bases refer to those that are almost completely ionized in aqueous solution, producing a large number of hydroxide ions (OH-), including but not limited to sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2), etc. Weak bases refer to those that are only partially ionized in aqueous solution, producing fewer hydroxide ions, including but not limited to ammonia water (NH3·H2O), magnesium hydroxide (Mg(OH)2), aluminum hydroxide (Al(OH)3), sodium carbonate, etc. It can also be distinguished according to the pH of the solution: when the pH value of the solution is close to or equal to 14, it indicates that the solution is very alkaline. When the pH value of the solution is usually less than 14 and greater than 7, it indicates that the solution has a weak alkalinity. And / or

[0025] The iridium source in step 1) is any one or a mixture of at least two of iridium salts; and / or

[0026] The iridium salts include but are not limited to potassium hexachloroiridate(IV), sodium hexachloroiridate(IV), potassium hexachloroiridate(III), sodium hexachloroiridate(III), iridium chloride, or chloroiridic acid; and / or

[0027] The base salt in step 1) is any one or a mixture of at least two of the base salts of lithium, sodium, potassium, rubidium, magnesium, calcium, or strontium metals; and / or

[0028] The base salt can be any one or a mixture of at least two of the salts of hydroxides, carbonates, or bicarbonates; and / or

[0029] The nitrate in step 1) is any one or a mixture of at least two of ammonium nitrate, potassium nitrate, sodium nitrate, lithium nitrate, rubidium nitrate, strontium nitrate, calcium nitrate, or barium nitrate; and / or

[0030] The heating in step 1) can be any one of ultrasonic, microwave, or heating plate heating; and / or

[0031] The heating time is at least 30 min, for example, it can be 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, or all values within the range. Due to space limitations, they are not listed here.

[0032] Preferably, the drying in step 2) is as follows: drying in an environment of 120 - 200 °C (for example, it can be 125 °C, 130 °C, 135 °C, 140 °C, 145 °C, 150 °C, 155 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C or all values within the range, which are not listed here due to space limitations) for 2 - 10 h (for example, it can be 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h or all values within the range, which are not listed here due to space limitations); and / or

[0033] The heating rate of the heating-up in step 2) is 0.5 - 10 °C / min. For example, it can be 1 °C / min, 1.5 °C / min, 2 °C / min, 2.5 °C / min, 3 °C / min, 3.5 °C / min, 4 °C / min, 4.5 °C / min, 5 °C / min, 5.5 °C / min, 6 °C / min, 6.5 °C / min, 7 °C / min, 7.5 °C / min, 8 °C / min, 8.5 °C / min, 9 °C / min, 9.5 °C / min or all values within the range, which are not listed here due to space limitations; and / or

[0034] The heating-up in step 2) is to heat to 100 - 400 °C or above 400 °C; the heating temperature varies according to the degree of crystallization. Weakly crystalline iridium oxide can be synthesized within 100 - 400 °C; strongly crystalline iridium oxide needs to be heated above 400 °C for ≥1 h; the decomposition temperature of nitrate is around 400 °C. Therefore, under the condition of 100 - 400 °C, nitrate is not decomposed or not completely decomposed, and it plays a role in promoting decomposition (catalyst), and can generate weakly crystalline iridium oxide. In addition, nitrate can also achieve uniform oxidation of precious metals and reduce the emission of polluting by-products. Moreover, by using in-situ nitrate oxidation in the liquid phase, it can promote the oriented growth of iridium oxide and increase the content of active crystal planes. Under the condition of above 400 °C, nitrate is completely decomposed, generating strong oxidizing properties, so strongly crystalline iridium oxide can be generated. Therefore, the present invention mainly realizes the control of the crystallization degree of iridium oxide by controlling the temperature and time of this step. Among them, by comparing the integrated intensity (I) of the (101) diffraction peak of iridium oxide with the standard integrated intensity (I 0 ) of the same diffraction peak of the completely crystalline phase, the percentage of crystallinity can be obtained. The formula can be: crystallinity (%) = (I / I 0 ) × 100%. and / or

[0035] The heating time in step 2) is 1 - 3 h, for example, it can be 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h, 2 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or all values within the range. Due to space limitations, they are not listed one by one.

[0036] Preferably, in step 3), the protonation is to soak the black powder in a strong acid solution; and / or

[0037] The strong acid solution is any one or a combination of at least two of hydrochloric acid, glacial acetic acid, perchloric acid or nitric acid; and / or

[0038] The concentration of the strong acid is 0.5 - 6 mol / L, for example, it can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L or all values within the range. Due to space limitations, they are not listed one by one; and / or

[0039] The soaking time is 0.5 - 10 h, for example, it can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h or all values within the range. Due to space limitations, they are not listed one by one;

[0040] Preferably, the preparation method includes the following steps:

[0041] 1) Preparation of the mixed solution: Dissolve n mol of iridium source, x mol of alkali salt and y mol of nitrate in water to obtain a mixed solution and heat it;

[0042] Wherein, x:n≥1, y:n≥1; the iridium source is any one or a mixture of at least two of potassium hexachloroiridate(IV), sodium hexachloroiridate(IV), potassium hexachloroiridate(III), sodium hexachloroiridate(III), iridium chloride or chloroiridic acid; the alkali salt is any one or a mixture of at least two of alkali salts of lithium, sodium, potassium, rubidium, magnesium, calcium or strontium metals; the alkali salt can be any one or a mixture of at least two of salts of hydroxides, carbonates or bicarbonates; the nitrate is any one or a mixture of at least two of ammonium nitrate, potassium nitrate, sodium nitrate, lithium nitrate, rubidium nitrate, strontium nitrate, calcium nitrate or barium nitrate; the heating can be any one of ultrasonic, microwave or heating plate heating; the heating time is at least 30 min;

[0043] 2) Drying and calcination: The mixed solution obtained in step 1) is dried at a temperature of 120 - 200 °C for 2 - 10 h. The dried solid sample is heated at a rate of 0.5 - 10 °C / min to 100 - 400 °C or above 400 °C for 1 - 3 h, and then cooled to room temperature to obtain a black powder;

[0044] 3) Acid treatment: The black powder obtained in step 2) is soaked in a strong acid solution for 0.5 - 10 h, then washed with ethanol 3 - 5 times, centrifuged and the sample is collected. After drying, a nano iridium oxide catalyst is obtained; The strong acid solution is any one or a combination of at least two of hydrochloric acid, glacial acetic acid, perchloric acid or nitric acid; The concentration of the strong acid is 0.5 - 6 mol / L.

[0045] In a third aspect, the present invention provides the use of the nano iridium oxide catalyst described in the first aspect as an anode catalyst in the proton exchange membrane electrolytic water hydrogen production reaction.

[0046] Based on the above technical solutions, the nano iridium oxide catalyst, its preparation method and application provided by the present invention, compared with the prior art, at least have one of the following beneficial effects:

[0047] The oriented growth iridium oxide catalyst and its preparation method of the present invention can be used as an anode catalyst in PEM electrolytic water technology. This preparation method can achieve uniform oxidation in a small amount of oxidation aids and low-temperature environment, and solves the problem of using a large amount of nitrates and peroxides in the traditional synthesis process;

[0048] The crystallinity of the iridium oxide synthesized by the method of the present invention can be adjusted, the particle size is small and uniform, it has a large specific surface area, and has a certain growth orientation, thereby improving the catalyst activity, and the reaction process is simple and easy to scale up, solving the problem that it is difficult to control the growth of the catalyst in the actual production process. Description of the drawings

[0049] Figure 1 is the XRD data diagram of the iridium oxide prepared in Example 1 and Example 8;

[0050] Figure 2 is the transmission electron microscope image of the iridium oxide; Among them,

[0051] Figure 2 a is the transmission electron microscope image of the iridium oxide in Example 1 (unit length 2 nm);

[0052] Figure 2 b is the transmission electron microscope image of the iridium oxide in Example 1 (unit length 5 nm);

[0053] Figure 2 c is the transmission electron microscope image of the iridium oxide in Comparative Example 1 (unit length 10 nm);Figure 2 d is the transmission electron microscope image of the iridium oxide of Comparative Example 1 (unit length 5 nm);

[0054] Figure 3 is the polarization curve graph of the iridium oxide prepared in Example 1 and the commercially available iridium oxide catalyst;

[0055] Figure 4 is the current test curve graph of the iridium oxide prepared in Example 1 and the commercially available iridium oxide catalyst; Figure 5 is the time-current cycling test curve graph of Example 1, Example 8 and the commercially available iridium oxide catalyst. Detailed implementation manners

[0056] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further elaborates on the present invention in detail with reference to specific embodiments and the accompanying drawings.

[0057] The products prepared by the preparation methods of iridium oxide catalysts in the prior art have poor homogeneity and high requirements for synthesis devices; in addition, a large amount of nitrates and peroxides are used in the synthesis process, the reaction conditions are relatively high and the content of harmful substances in the products is relatively high. Through painstaking research, the inventors of the present invention have optimized and improved the above steps, so that uniform oxidation of precious metals can be achieved at a lower temperature and with less nitrates, reducing the emission of polluting by-products; it can also promote the oriented growth of iridium oxide and increase the active crystal plane components.

[0058] Specifically, in the first aspect of the present invention, a nano iridium oxide catalyst is disclosed, and the crystallization degree of the nano iridium oxide catalyst is adjustable within the range of 20%-100%.

[0059] In a preferred embodiment, the nano iridium oxide catalyst has a growth orientation.

[0060] In a preferred embodiment, the precious metal dissolution rate of the nano iridium oxide catalyst is 0.01%-1.3%; and / or

[0061] the electrochemically active area of the nano iridium oxide catalyst is 17.72 - 32.44 C / cm 2 .

[0062] In a preferred embodiment, when the nano iridium oxide catalyst works in the overpotential range of 230 - 304 mV, it can generate a current density of 10 mA / cm 2 ; and / or

[0063] when the nano iridium oxide catalyst works in the overpotential range of 390 - 480 mV, it generates a current density of 100 mA / cm 2 .

[0064] In a second aspect, the present invention provides a method for preparing a nano iridium oxide catalyst, the method comprising the following steps:

[0065] 1) Preparation of a mixed solution: Dissolve n mol of an iridium source, x mol of an alkali salt, and y mol of a nitrate in water to obtain a mixed solution and heat it;

[0066] Wherein, the alkali salt is not the so-called industrial alkali salt. The main components of the industrial alkali salt are Ca(OH) 2 , activated clay, which is a kind of salt of table salt and can be applied to the building materials field, metallurgical industry, etc. The alkali salt mentioned here refers to the salts of alkali metals and alkaline earth metals.

[0067] 2) Drying and calcination: Dry the mixed solution obtained in step 1), heat the dried solid sample, and cool it to room temperature to obtain a black powder;

[0068] 3) Acid treatment: Protonate the black powder obtained in step 2) to obtain a nano iridium oxide catalyst. During the process, for example, the product can also be purified by washing with ethanol, centrifuging and collecting the sample, and drying, etc.

[0069] In a preferred embodiment, in step 1), x:n≥1, that is, the number of moles of hydroxide or bicarbonate or carbonate is greater than or equal to the number of moles of the noble metal; y:n≥1, that is, the number of moles of nitrate is greater than or equal to the number of moles of the noble metal; and / or

[0070] The iridium source in step 1) is any one or a mixture of at least two of iridium salts; and / or

[0071] The iridium salts include but are not limited to potassium hexachloroiridate(IV), sodium hexachloroiridate(IV), potassium hexachloroiridate(III), sodium hexachloroiridate(III), iridium chloride, chloroiridic acid, or iridium acetate; and / or

[0072] The alkali salt in step 1) is any one or a mixture of at least two of the alkali salts of lithium, sodium, potassium, rubidium, magnesium, calcium, or strontium metals; and / or

[0073] The alkali salt can be any one or a mixture of at least two of the salts of hydroxides, carbonates, or bicarbonates; and / or

[0074] The nitrate in step 1) is any one or a mixture of at least two of ammonium nitrate, potassium nitrate, sodium nitrate, lithium nitrate, rubidium nitrate, strontium nitrate, calcium nitrate, or barium nitrate; and / or

[0075] The heating in step 1) can be any one of ultrasonic, microwave, or heating table heating; and / or

[0076] The heating time is at least 30 min, for example, it can be 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, or all values within the range. Due to space limitations, they are not listed one by one;

[0077] In a preferred embodiment, the drying in step 2) is as follows: drying in an environment of 120 - 200 °C (for example, it can be 125 °C, 130 °C, 135 °C, 140 °C, 145 °C, 150 °C, 155 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C, or all values within the range. Due to space limitations, they are not listed one by one) for 2 - 10 h (for example, it can be 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h, or all values within the range. Due to space limitations, they are not listed one by one); and / or

[0078] The heating rate of the heating-up in step 2) is 0.5 - 10 °C / min. For example, it can be 1 °C / min, 1.5 °C / min, 2 °C / min, 2.5 °C / min, 3 °C / min, 3.5 °C / min, 4 °C / min, 4.5 °C / min, 5 °C / min, 5.5 °C / min, 6 °C / min, 6.5 °C / min, 7 °C / min, 7.5 °C / min, 8 °C / min, 8.5 °C / min, 9 °C / min, 9.5 °C / min, or all values within the range. Due to space limitations, they are not listed one by one; and / or

[0079] The heating-up in step 2) is to heat to 100 - 400 °C or above 400 °C; the heating temperature varies according to the degree of crystallization. Weakly crystalline iridium oxide can be synthesized within 100 - 400 °C; strongly crystalline iridium oxide needs to be heated at ≥400 °C for ≥1 h; and / or

[0080] The heating time of the heating-up in step 2) is 1 - 3 h. For example, it can be 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h, 2 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h, or all values within the range. Due to space limitations, they are not listed one by one;

[0081] In a preferred embodiment, the protonation in step 3) is to soak the powder in a strong acid solution; and / or

[0082] The strong acid solution is any one or a combination of at least two of hydrochloric acid, glacial acetic acid, perchloric acid or nitric acid; and / or

[0083] The concentration of the strong acid is 0.5 - 6 mol / L. For example, it can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L or all values within the range. Due to space limitations, they are not listed here; and / or

[0084] The soaking time is 0.5 - 10 h. For example, it can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h or all values within the range. Due to space limitations, they are not listed here;

[0085] In a preferred embodiment, the preparation method comprises the following steps:

[0086] 1) Preparation of the mixed solution: Dissolve n mol of iridium source, x mol of alkali salt and y mol of nitrate in water to obtain a mixed solution and heat it;

[0087] Among them, x:n≥1, y:n≥1; the iridium source is any one or a mixture of at least two of potassium hexachloroiridate(IV), sodium hexachloroiridate(IV), potassium hexachloroiridate(III), sodium hexachloroiridate(III), iridium chloride or chloroiridic acid; the alkali salt is any one or a mixture of at least two of alkali salts of lithium, sodium, potassium, rubidium, magnesium, calcium or strontium metals; the alkali salt can be any one or a mixture of at least two of salts of hydroxides, carbonates or bicarbonates; the nitrate is any one or a mixture of at least two of ammonium nitrate, potassium nitrate, sodium nitrate, lithium nitrate, rubidium nitrate, strontium nitrate, calcium nitrate or barium nitrate; the heating can be any one of ultrasonic, microwave or heating on a heating table; the heating time is at least 30 min;

[0088] 2) Drying and calcination: Dry the mixed solution obtained in step 1) at a temperature of 120 - 200 °C for 2 - 10 h, heat the dried solid sample at a rate of 0.5 - 10 °C / min to 100 - 400 °C or above 400 °C for 1 - 3 h, and cool to room temperature to obtain a black powder;

[0089] 3) Acid treatment: Immerse the black powder obtained in step 2) in a strong acid solution for 0.5 - 10 h, then wash it with ethanol 3 - 5 times, centrifuge and collect the sample, and obtain the nano iridium oxide catalyst after drying; the strong acid solution is any one or a combination of at least two of hydrochloric acid, glacial acetic acid, perchloric acid or nitric acid; the concentration of the strong acid is 0.5 - 6 mol / L.

[0090] In the third aspect, the present invention provides the application of the nano iridium oxide catalyst described in the first aspect as an anode catalyst in the proton exchange membrane electrolytic water hydrogen production reaction.

[0091] The present invention will be further described and illustrated below through specific examples. It should be noted that the following examples are only illustrative and not used to limit the present invention.

[0092] Example 1

[0093] (1) Preparation of the mixed solution: Weigh 0.0067 mol of iridium chloride, 0.0134 mol of sodium hydroxide, and 0.02 mol of sodium nitrate and dissolve them in a mixed solvent of 200 mL of water, and perform ultrasonic reaction for about 30 min; place the above mixed solution on a heating table and react for 40 min;

[0094] (2) Dry the mixed solution obtained in step (1) at a temperature of 120 - 200 °C for 5 h, place the dried solid sample in a muffle furnace and heat it at a heating rate of 10 °C / min, then heat it at 300 °C for 1.5 h, and naturally cool it to room temperature to obtain a black powder;

[0095] (3) Acid treatment: Immerse the black powder obtained in step (2) in 1 mol / L hydrochloric acid for 10 h, after sufficient protonation, then wash it with ethanol 3 - 5 times, centrifuge and collect the sample, and obtain IrO x material.

[0096] Example 2 (changing the type of iridium salt)

[0097] (1) Preparation of the mixed solution: Weigh 0.0067 mol of iridium chlorate, 0.0134 mol of sodium hydroxide, and 0.02 mol of sodium nitrate and dissolve them in a mixed solvent of 200 mL of water, and perform ultrasonic reaction for about 30 min; place the above mixed solution on a heating table and react for 40 min;

[0098] (2) Dry the mixed solution obtained in step (1) at a temperature of 120 - 200 °C for 10 h, place the dried solid sample in a muffle furnace and heat it at a heating rate of 5 °C / min, then heat it at 300 °C for 1.5 h, and naturally cool it to room temperature to obtain a black powder;

[0099] (3) Acid treatment: The black powder obtained in step (2) is soaked in 1 mol / L hydrochloric acid for 10 h. After sufficient protonation, it is washed with ethanol 3 - 5 times, centrifuged, and the sample is collected. After drying, IrO x material is obtained.

[0100] Example 3 (changing the type of alkali salt)

[0101] (1) Preparation of the mixed solution: Weigh 0.0067 mol of iridium chloride, 0.0134 mol of sodium bicarbonate, and 0.03 mol of sodium nitrate and dissolve them in a mixed solvent of 200 mL of water. React under ultrasonic for about 30 min; Place the above mixed solution on a heating platform and react for 40 min;

[0102] (2) The mixed solution obtained in step (1) is dried at a temperature of 120 - 200 °C for 2 h. The dried solid sample is placed in a muffle furnace and heated at a heating rate of 0.6 °C / min, then heated at 100 °C for 1.5 h, and naturally cooled to room temperature to obtain a black powder;

[0103] (3) Acid treatment: The black powder obtained in step (2) is soaked in 1 mol / L hydrochloric acid for 10 h. After sufficient protonation, it is washed with ethanol 3 - 5 times, centrifuged, and the sample is collected. After drying, IrO x material is obtained.

[0104] Example 4 (changing the amount of alkali salt)

[0105] (1) Preparation of the mixed solution: Weigh 0.0067 mol of iridium chloride, 0.0201 mol of sodium hydroxide, and 0.02 mol of sodium nitrate and dissolve them in a mixed solvent of 200 mL of water. React under ultrasonic for about 30 min; Place the above mixed solution on a heating platform and react for 60 min;

[0106] (2) The mixed solution obtained in step (1) is dried at a temperature of 120 - 200 °C for 6 h. The dried solid sample is placed in a muffle furnace and heated at a heating rate of 8 °C / min, then heated at 380 °C for 1.5 h, and naturally cooled to room temperature to obtain a black powder;

[0107] (3) Acid treatment: The black powder obtained in step (2) is soaked in 2.5 mol / L perchloric acid for 5 h. After sufficient protonation, it is washed with ethanol 3 - 5 times, centrifuged, and the sample is collected. After drying, IrO x material is obtained.

[0108] Example 5 (changing the amount of alkali salt)

[0109] (2) Preparation of the mixed solution: Weigh 0.0067 mol of iridium chloride, 0.0067 mol of sodium hydroxide, and 0.02 mol of sodium nitrate and dissolve them in a mixed solvent of 200 mL of water, and perform ultrasonic reaction for about 30 min; place the above mixed solution on a heating table and react for 50 min;

[0110] (2) Dry the mixed solution obtained in step (1) at a temperature of 120 - 200 °C for 4 h. Place the dried solid sample in a muffle furnace and heat it at a heating rate of 7 °C / min, then heat it at 300 °C for 1.5 h, and naturally cool it to room temperature to obtain a black powder;

[0111] (3) Acid treatment: Immerse the black powder obtained in step (2) in 6 mol / L hydrochloric acid for 0.6 h. After sufficient protonation, wash it with ethanol 3 - 5 times, centrifuge and collect the sample, and dry it to obtain IrO x material.

[0112] Example 6 (changing the type of nitrate)

[0113] (1) Preparation of the mixed solution: Weigh 0.0067 mol of iridium chloride, 0.0134 mol of sodium bicarbonate, and 0.02 mol of zinc nitrate and dissolve them in a mixed solvent of 200 mL of water, and perform ultrasonic reaction for about 30 min; place the above mixed solution on a heating table and react for 35 min;

[0114] (2) Dry the mixed solution obtained in step (1) at a temperature of 120 - 200 °C for 8 h. Place the dried solid sample in a muffle furnace and heat it at a heating rate of 5 °C / min, then heat it at 400 °C for 3 h, and naturally cool it to room temperature to obtain a black powder;

[0115] (3) Acid treatment: Immerse the black powder obtained in step (2) in 0.5 mol / L nitric acid for 10 h. After sufficient protonation, wash it with ethanol 3 - 5 times, centrifuge and collect the sample, and dry it to obtain IrO x material.

[0116] Example 7 (changing the amount of nitrate)

[0117] (1) Preparation of the mixed solution: Weigh 0.0067 mol of iridium chloride, 0.0134 mol of sodium bicarbonate, and 0.0335 mol of sodium nitrate and dissolve them in a mixed solvent of 200 mL of water, and perform ultrasonic reaction for about 30 min; place the above mixed solution on a heating table and react for 40 min;

[0118] (2) The mixed solution obtained in step (1) is dried at a temperature of 120 - 200 °C for 5 h. The dried solid sample is placed in a muffle furnace and heated at a heating rate of 0.5 °C / min, and then heated at 400 °C for 1.5 h, and naturally cooled to room temperature to obtain a black powder;

[0119] (3) Acid treatment: The black powder obtained in step (2) is soaked in 1 mol / L glacial acetic acid for 10 h. After sufficient protonation, it is washed with ethanol 3 - 5 times, centrifuged and the sample is collected, and after drying, IrO x material is obtained.

[0120] Example 8 (changing the calcination temperature)

[0121] (1) Preparation of the mixed solution: Weigh 0.0067 mol of iridium chloride, 0.0134 mol of sodium hydroxide, and 0.02 mol of sodium nitrate and dissolve them in a mixed solvent of 200 mL of water, and ultrasonically react for about 30 min; The above mixed solution is placed on a heating table and reacted for 30 min;

[0122] (2) The mixed solution obtained in step (1) is dried at a temperature of 120 - 200 °C for 5 h. The dried solid sample is placed in a muffle furnace and heated at a heating rate of 10 °C / min, and then heated at 500 °C for 1 h, and naturally cooled to room temperature to obtain a black powder;

[0123] (3) Acid treatment: The black powder obtained in step (2) is soaked in 6 mol / L hydrochloric acid for 0.5 h. After sufficient protonation, it is washed with ethanol 3 - 5 times, centrifuged and the sample is collected, and after drying, IrO 2 material is obtained.

[0124] Example 9 (changing the calcination time)

[0125] (1) Preparation of the mixed solution: Weigh 0.0067 mol of iridium chloride, 0.0134 mol of sodium hydroxide, and 0.02 mol of sodium nitrate and dissolve them in a mixed solvent of 200 mL of water, and ultrasonically react for about 30 min; The above mixed solution is placed on a heating table and reacted for 30 min;

[0126] (2) The mixed solution obtained in step (1) is dried at a temperature of 120 - 200 °C for 5 h. The dried solid sample is placed in a muffle furnace and heated at a heating rate of 10 °C / min, and then heated at 400 °C for 3 h, and naturally cooled to room temperature to obtain a black powder;

[0127] (3) Acid treatment: The black powder obtained in step (2) is soaked in 6 mol / L hydrochloric acid for 0.5 h. After sufficient protonation, it is washed with ethanol 3 - 5 times, centrifuged and the sample is collected, and after drying, IrO xMaterial

[0128] Comparative Example 1

[0129] Comparative Example 1 is a commercially available iridium oxide catalyst, and the key product information is as follows:

[0130] Manufacturer: Alfa Aesar, Alfa Aesar (China) Chemical Co., Ltd.

[0131] Chinese Name: Iridium(IV) oxide powder, 99%

[0132] English Name: Iridium(IV)oxide powder, 99%

[0133] CAS: 12030-49-8

[0134] Packaging Information: 1g

[0135] Remarks: A17849

[0136] Three-electrode test

[0137] The IrO prepared in Examples 1-8 x materials and commercially available iridium oxide catalysts were placed at different overpotentials to achieve a current density of 10 mA / cm 2 , and the test results are shown in Table 1. It can be seen that the iridium oxide catalysts prepared in Examples 1-8 are all lower than Comparative Example 1, indicating that the catalytic activities of the iridium oxide catalysts in Examples 1-8 are generally higher than that of Comparative Example 1; among them, the crystallinities of Examples 1-7 are lower, with more catalytic active sites, so the catalytic activities are higher and the overpotentials are much higher than that of Comparative Example 1; although the crystallinity of Example 8 is higher, its catalytic activity is also higher than that of Comparative Example 1. The test results of achieving a current density of 10 mA / cm 2 are similar to those of achieving a current density of 10 mA / cm 2 , and it can also show that the catalyst activities of Examples 1-8 are higher than that of Comparative Example 1.

[0138] Catalyst electrochemically active surface area test

[0139] By testing the cyclic voltammetry in the non-Faradaic current range (in this patent, it is 0.4 - 1.4 V vs. RHE, and a wider range can be extended, such as 0 - 1.4 V vs. RHE), the capacitive charge Q can be obtained by integrating the current in the test voltage window range. Since Q includes the positive and negative scan ranges, it needs to be divided by 2 and then normalized with the working electrode area S to obtain the electrochemically active surface area:

[0140] The formula is: Electrochemically active surface area = Q / 2S

[0141] The test results are shown in Table 1. It can be seen that the electrochemically active surface area of the nano-IrO₂ catalysts in Examples 1-9 of the present invention ranges from 17.72 to 32.44 C / cm 2 , which is much higher than that of the commercially available nano-IrO₂ catalyst in Comparative Example 1. The electrochemically active surface area is the part of the catalyst that actually plays a catalytic role. The higher the surface area, the more active sites the catalyst can provide under the same mass. These active sites are the places where the catalytic reaction occurs. Therefore, the increase in the number of active sites directly enhances the catalytic activity of the catalyst. In addition, due to the increase in the number of active sites, the contact opportunity between the reactant molecules and the catalyst surface increases, thus accelerating the adsorption, conversion, and desorption processes of the reactant molecules on the catalyst surface, and further increasing the rate of the catalytic reaction. Therefore, it shows that the nano-IrO₂ catalyst prepared by the method of the present invention has more catalytic sites and higher catalytic efficiency.

[0142] Table 1 Three-electrode test results

[0143]

[0144]

[0145] Crystallinity test

[0146] Integral intensity ratio (I / I 0 ): By comparing the integral intensity (I) of the (101) diffraction peak of IrO₂ with the standard integral intensity (I 0 ) of the same diffraction peak of the fully crystalline phase, the percentage of the crystallization degree can be obtained.

[0147] The formula is: Crystallization degree (%) = (I / I 0 ) × 100%

[0148] The IrO x materials prepared in the examples were tested for the crystallization degree, and the following results were obtained:

[0149] The crystallization degree of the IrO x material in Example 1: 20%;

[0150] The crystallization degree of the IrO x material in Example 2: 27%;

[0151] The crystallization degree of the IrO x material in Example 3: 23%;

[0152] The crystallization degree of the IrO x material in Example 4: 35%;

[0153] The crystallization degree of the IrO x material in Example 5: 24%;

[0154] IrO of Example 6 x Degree of crystallization of the material: 46%;

[0155] IrO of Example 7 x Degree of crystallization of the material: 60%;

[0156] IrO of Example 8 x Degree of crystallization of the material: 100%;

[0157] IrO of Example 9 x Degree of crystallization of the material: 70%.

[0158] It shows that the degree of crystallization of the nano iridium oxide catalyst provided by the present invention can be adjusted within the range of 20-100%.

[0159] Catalyst material stability test

[0160] By testing the concentration of precious metals in the electrolyte after testing the catalytic stability (the current density is 10 mA / cm 2 , and in the 10-hour catalytic stability test), the mass a of the precious metals dissolved by the catalyst during the catalytic process can be obtained, and then divided by the total amount b of the catalyst used in the catalytic test, the catalyst material stability can be obtained. The smaller the dissolution ratio, the higher the material stability:

[0161] The formula is: Metal dissolution ratio (%) = a / b

[0162] The results are shown in Table 2. It can be seen that the precious metal dissolution ratios of Examples 1-9 are generally lower than that of Comparative Example 1, indicating that there is an inverse relationship between the degree of crystallization and the material stability of the nano iridium oxide catalyst in the present invention. The precious metal dissolution range of the present invention is 0.01%-1.3%, and the material stability is higher than that of the commercially available nano iridium oxide catalyst.

[0163] Table 2 Material stability test

[0164] Test object Noble metal dissolution ratio (%) Example 1 1.3 Example 2 1.1 Example 3 1.2 Example 4 0.5 Example 5 0.8 Example 6 1.0 Example 7 0.2 Example 8 0.01 Example 9 0.046 Comparative example 1 2.9％

[0165] Figure 1 It is the X-ray diffraction test data (XRD) diagram of Example 1 and Example 8. The gray line corresponds to the IrO in Example 1 x material, belonging to a weaker crystallinity (the calcination temperature is lower than 400°C; the peaks in the XRD diagram are relatively wide); the black corresponds to the IrO of Example 8 2The material belongs to a relatively high crystallinity (calcination temperature higher than 400 °C; the peaks in the XRD pattern are relatively sharp). It shows that the crystallinity (intensity, a.u.) of the iridium oxide product can be regulated by the method of the present invention, and the material crystallization has an obvious growth orientation, with the orientation peak at 35 degrees, corresponding to the (101) crystal plane. According to the literature report, the catalytic activity of this crystal plane is higher than that of the (110) crystal plane (Stoerzinger K A, Qiao L, Biegalski M D, et al. Orientation-dependent oxygen evolution activities of rutile IrO 2 and RuO 2 . The journal of physical chemistry letters, 2014, 5(10):1636 - 1641.).

[0166] Figure 2 are the transmission electron microscope images of the iridium oxide catalyst prepared in Example 1 and the iridium oxide catalyst in Comparative Example 1, which prove that the sample size is small; it can be seen that the particle size of the IrO x material prepared in Example 1 is 1 - 2 nm, and the particle size uniformity is good ( Figure 2 a and Figure 2 b); while the iridium oxide catalyst in Comparative Example 1 is generally about 15 - 20 nm, and the uniformity is not as good as that in Example 1 ( Figure 2 c and Figure 2 d).

[0167] Figure 3 are the polarization curve graphs of the iridium oxide prepared in Example 1 and the commercially available iridium oxide catalyst. The abscissa is the potential and the ordinate is the current density. From the Figure 3 test results, it can be seen that at the same potential, the current density generated by the iridium oxide catalyst prepared in Example 1 is higher than that of the iridium oxide catalyst in Comparative Example 1.

[0168] Figure 4 is the time - current test curve graph. When the IrO x material prepared in Example 1 is placed at an over - potential of 270 mV, a current density of 10 mA / cm 2 can be achieved, and when operating at this current density for 10 h, the decay rate is only 0.15 mV / h. While the iridium oxide catalyst in Comparative Example 1 requires an over - potential of 316 mV to reach a current density of 10 mA / cm 2 , and after 10 h of catalytic stability test, the over - potential has increased by 23 mV. It shows that at the same time and the same current density operation, the potential of the catalyst prepared in Example 1 is more stable; it shows that the IrO xThe catalyst can be used as an excellent anode water oxidation catalyst material for PEM electrolyzed water. The excellent catalytic performance may be due to the relatively low crystallinity of the IrOx catalyst, which has more catalytic active sites, so the activity of the catalyst is higher.

[0169] Figure 5 It is the time-current cycling test curve graph of Example 1, Example 8 and commercially available iridium oxide catalyst. From Figure 5 the current density range, it can be seen that by comparing the examples and the comparative examples, the integral area of current and voltage is larger, which can also illustrate that the electrochemically active surface area of the examples of the present invention is larger and the catalytic activity is greater.

[0170] In summary, the oriented growth iridium oxide catalyst and its preparation method provided by the present invention can be used as an anode catalyst in PEM electrolyzed water technology. This preparation method can achieve uniform oxidation in a small amount of oxidation aids and at a low temperature environment, solving the problem of using a large amount of nitrates and peroxides in the traditional synthesis process; the crystallinity of the iridium oxide synthesized by this method can be adjusted within the range of 20-100%, the particle size is small and uniform, it has a large specific surface area and a certain growth orientation, thus improving the catalyst activity, and the reaction process is simple and easy to scale up, solving the problem that it is difficult to control the growth of the catalyst in the actual production process.

[0171] The specific embodiments described above further elaborate on the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A nano iridium oxide catalyst, characterized in that: The crystallization degree of the nano-iridium oxide catalyst can be adjusted within the range of 20%-100%.

2. The nano iridium oxide catalyst according to claim 1, characterized in that The nano iridium oxide catalyst has a growth orientation.

3. The nano iridium oxide catalyst according to claim 1, characterized in that The noble metal dissolution rate of the nano-iridium oxide catalyst is 0.01%-1.3%; and / or The electrochemical active area of ​​the nano-iridium oxide catalyst is 17.72-32.44 C / cm 2 .

4. The nano iridium oxide catalyst according to claim 1, characterized in that The nano-iridium oxide catalyst can generate 10 mA / cm when operating in the overpotential range of 230-304 mV. 2 current density; and / or The nano-iridium oxide catalyst generates 100 mA / cm when operating in the overpotential range of 390-480 mV. 2 of current density.

5. A method for preparing a nano-iridium oxide catalyst according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) dissolving n mol of an iridium source, x mol of an alkali salt and y mol of a nitrate in water to obtain a mixed solution and heating the solution; (2) drying the mixed solution obtained in step (1), heating the dried solid sample, and cooling it to room temperature to obtain a powder; (3) Protonating the powder obtained in step (2) to obtain a nano-iridium oxide catalyst.

6. The preparation method according to claim 5, characterized in that: In step (1), x:n≥1, i.e., the number of moles of hydroxide or bicarbonate or carbonate is greater than or equal to the number of moles of the noble metal; y:n≥1, i.e., the number of moles of nitrate is greater than or equal to the number of moles of the noble metal; and / or The iridium source in step (1) is any one or a mixture of at least two iridium salts; The iridium salt includes, but is not limited to, potassium hexachloroiridate (IV), sodium hexachloroiridate (IV), potassium hexachloroiridate (III), sodium hexachloroiridate (III), iridium chloride, chloroiridic acid or iridium acetate; and / or The alkali salt in step (1) is any one or a mixture of at least two of the alkali salts of lithium, sodium, potassium, rubidium, magnesium, calcium or strontium metals; and / or The alkali salt may be any one of a hydroxide salt, a carbonate salt or a bicarbonate salt, or a mixture of at least two of them; and / or The nitrate in step (1) is any one of ammonium nitrate, potassium nitrate, sodium nitrate, lithium nitrate, rubidium nitrate, strontium nitrate, calcium nitrate or barium nitrate, or a mixture of at least two thereof; and / or The heating treatment in step (1) is any one of ultrasonic, microwave or heating on a heating table; and / or The heating time is at least 30 minutes.

7. The preparation method according to claim 5, characterized in that: The drying treatment in step (2) is: drying in an environment of 120-200° C. for 2-10 hours; and / or The heating rate of the heating in step (2) is 0.5-10°C / min; and / or The heating in step (2) is heating to 100-400° C. or above 400° C.; and / or The heating time in step (2) is 1-3 hours.

8. The preparation method according to claim 5, characterized in that: The protonation treatment in step (3) is to immerse the powder in a strong acid solution; and / or The strong acid solution is any one of hydrochloric acid, glacial acetic acid, perchloric acid or nitric acid, or a combination of at least two thereof; and / or The concentration of the strong acid solution is 0.5-6 mol / L; and / or The soaking time is 0.5-10h.

9. The preparation method according to claim 5, characterized in that: The preparation method comprises the following steps: (1) dissolving n mol of an iridium source, x mol of an alkali salt and y mol of a nitrate in water to obtain a mixed solution and heating the solution; wherein x:n≥1, y:n≥1; the iridium source is any one of potassium hexachloroiridate (IV), sodium hexachloroiridate (IV), potassium hexachloroiridate (III), sodium hexachloroiridate (III), iridium chloride or chloroiridic acid, or a mixture of at least two of them; the alkali salt is any one of alkali salts of lithium, sodium, potassium, rubidium, magnesium, calcium or strontium metal, or a mixture of at least two of them; the alkali salt is any one of a hydroxide salt, a carbonate or a bicarbonate, or a mixture of at least two of them; the nitrate is any one of ammonium nitrate, potassium nitrate, sodium nitrate, lithium nitrate, rubidium nitrate, strontium nitrate, calcium nitrate or barium nitrate, or a mixture of at least two of them; the heating treatment is any one of ultrasonic, microwave or heating on a heating table; the heating time is at least 30 minutes; (2) drying the mixed solution obtained in step (1) at a temperature of 120-200° C. for 2-10 h, heating the dried solid sample to 100-400° C. or above 400° C. at a rate of 0.5-10° C. / min for 1-3 h, and cooling to room temperature to obtain a black powder; (3) Soaking the black powder obtained in step (2) in a strong acid solution for 0.5-10 hours, washing with ethanol for 3-5 times, centrifuging and collecting the sample, and drying to obtain a nano-iridium oxide catalyst; the strong acid solution is any one of hydrochloric acid, glacial acetic acid, perchloric acid or nitric acid, or a combination of at least two of them; the concentration of the strong acid is 0.5-6 mol / L.

10. Use of the nano-iridium oxide catalyst according to any one of claims 1 to 4 as an anode catalyst in a proton exchange membrane water electrolysis hydrogen production reaction.

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