A preparation method of an iridium oxide catalyst

Abstract

A preparation method of an iridium oxide catalyst belongs to the field of hydrogen production by water electrolysis. The preparation method includes: a first reaction solution in which an initial catalyst is dispersed, the initial catalyst containing iridium dioxide; a second reaction solution in which a reducing agent is dissolved; injecting the first reaction solution and the second reaction solution into a microchannel continuous flow reactor for continuous reduction reaction so that part of the iridium dioxide is reduced to iridium sesquioxide. The iridium oxide catalyst prepared by this preparation method has both better activity and better stability.

Description

Technical Field

[0001] This application relates to the field of hydrogen production by water electrolysis, and more particularly, to a method for preparing an iridium oxide catalyst. Background Art

[0002] The application of hydrogen energy can reduce carbon emissions and has a revolutionary impact on achieving carbon neutrality and carbon peak. Currently, the most recognized green and sustainable method for producing hydrogen internationally is electrochemical water splitting, and the electrochemical cracking of water is an efficient and green technology for generating highly purified gaseous hydrogen. Among various water electrolysis technologies, proton exchange membrane water electrolysis (PEMWE) is attractive due to its ideal gas separation, high hydrogen purity, high current density, and rapid response. However, compared with the hydrogen evolution reaction (HER) at the cathode, the oxygen evolution reaction (OER) at the anode operates slowly, severely limiting the overall efficiency. Iridium-based catalysts are oxygen evolution catalysts, but their insufficient intrinsic activity in acidic conditions also limits the further application of PEMWE.

[0003] The rutile-phase iridium oxide obtained by high-temperature oxidation has a phenomenon of insufficient intrinsic activity. Usually, the intrinsic activity of rutile-phase iridium oxide is improved by doping heteroelements or creating defects, specifically including: doping heteroelements, reducing the oxidation temperature, or reducing the oxidation time. However, after doping heteroelements, the stability of the iridium oxide catalyst decreases, unable to meet the lifetime requirements of the water electrolysis catalyst. If the oxidation temperature is reduced or the oxidation time is reduced, the obtained catalyst may be in an amorphous state. The catalyst in this state has sufficient intrinsic activity but its catalyst stability is not good enough to meet the lifetime requirements of the water electrolysis catalyst. Summary of the Invention

[0004] This application provides a method for preparing an iridium oxide catalyst, which can alleviate the problems of poor activity and poor stability of existing iridium oxide catalysts.

[0005] The embodiments of this application are implemented as follows:

[0006] In a first aspect, an embodiment of this application provides a method for preparing an iridium oxide catalyst, which includes: a first reaction solution in which an initial catalyst is dispersed, the initial catalyst containing iridium dioxide; a second reaction solution in which a reducing agent is dissolved; injecting the first reaction solution and the second reaction solution into a microchannel continuous flow reactor for continuous reduction reaction to reduce part of the iridium dioxide to iridium sesquioxide.

[0007] In the preparation method of the iridium oxide catalyst provided by the embodiments of the present application, since trivalent iridium ions are in a highly active valence state relative to tetravalent iridium ions, part of the iridium dioxide is reduced to iridium sesquioxide, so that both iridium dioxide and iridium sesquioxide exist in the final iridium oxide catalyst. By using iridium in different valence states to cooperate with each other, the activity and stability of the iridium oxide catalyst are effectively enhanced. Further, by introducing a microchannel continuous flow reactor, a liquid-liquid phase continuous reduction reaction can be carried out in the microchannel continuous flow reactor, which not only realizes the continuous preparation of the iridium oxide catalyst with a composite valence state, but also is conducive to making the prepared iridium oxide catalyst with a composite valence state have better activity and stability.

[0008] In some possible embodiments, the above reducing agent includes at least one of sodium borohydride and potassium borohydride.

[0009] In some possible embodiments, the temperature of the above reduction reaction is 30-100°C.

[0010] In some possible embodiments, the mass ratio of the above iridium dioxide to the reducing agent is 3:1-10:1.

[0011] In some possible embodiments, the flow rates of the above first reaction solution and the second reaction solution are 5-20 ml / min respectively.

[0012] In some possible embodiments, the flow rates of the above first reaction solution and the second reaction solution are the same.

[0013] In some possible embodiments, the solvents of the above first reaction solution and the second reaction solution are polyols respectively.

[0014] In some possible embodiments, the solvents of the above first reaction solution and the second reaction solution are the same.

[0015] In some possible embodiments, the residence time of the above first reaction solution and the second reaction solution in the microchannel continuous flow reactor is 2-8 min.

[0016] In some possible embodiments, the particle size of the above initial catalyst is: 0.1 μm ≤ D50 ≤ 1 μm, and 1 μm ≤ D90 ≤ 5 μm. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, so they should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0018] Figure 1 XRD patterns of the iridium oxide catalysts prepared in Example 1 and Comparative Example 1;

[0019] Figure 2 LSV performance comparison diagrams of the iridium oxide catalysts prepared in Example 1 and Comparative Example 1 before and after 3000 cycles of CV accelerated cycling tests. Detailed implementation manners

[0020] The implementation schemes of the present application will be described in detail below in conjunction with examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specified in the examples, the operations are carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained by purchasing in the market.

[0021] The following specifically describes the preparation method of the iridium oxide catalyst according to the examples of the present application:

[0022] The preparation method of the iridium oxide catalyst provided by the present application includes: a first reaction solution in which an initial catalyst is dispersed, the initial catalyst containing iridium dioxide; a second reaction solution in which a reducing agent is dissolved; injecting the first reaction solution and the second reaction solution into a microchannel continuous flow reactor for continuous reduction reaction, so that part of the iridium dioxide is reduced to iridium sesquioxide.

[0023] The continuous reduction reaction means that the first reaction solution and the second reaction solution are continuously input and mixed into the microchannel continuous flow reactor, the mixed material input into the microchannel is output along the microchannel towards the outlet, and a reduction reaction continuously occurs during the transportation process, so as to output a composite-valence iridium oxide catalyst at the outlet of the microchannel, realizing the continuous preparation of the composite-valence iridium oxide catalyst.

[0024] In the above preparation method of the iridium oxide catalyst, on the one hand, based on the fact that the trivalent iridium ion is a highly active valence state relative to the tetravalent iridium ion, part of the iridium dioxide is reduced to iridium sesquioxide, so that both iridium dioxide and iridium sesquioxide exist in the final iridium oxide catalyst, and the iridium with different valence states cooperate with each other to effectively enhance the activity and stability of the iridium oxide catalyst; on the other hand, by introducing the microchannel continuous flow reactor, a liquid-liquid phase continuous reduction reaction can be carried out in the microchannel continuous flow reactor, which can not only realize large-scale production, but also is beneficial to further improving the activity and stability of the composite-valence iridium oxide catalyst.

[0025] It is understandable that the initial catalyst can be entirely composed of active components with catalytic performance, or can be composed of a carrier and active components supported on the carrier. Among them, the active component is iridium dioxide, or the active component is a mixture of iridium dioxide and other catalytically active materials. The carrier includes but is not limited to carbon carriers (carbon carriers such as, but not limited to, one or more of carbon black, carbon nanotubes, carbon fibers, graphene), and can also be any one of γ-Al2O3, SiO2, ZrO2, TiO2, molecular sieves, etc.

[0026] Optionally, the initial catalyst is iridium dioxide, which can be purchased on the market or prepared by oneself. The self-preparation method includes: mixing and dissolving an iridium precursor, sodium nitrate and water, stirring and evaporating the obtained solution at 95 - 100 °C, annealing and oxidizing the evaporated powder at 500 °C for 30 min, and then dissolving in water and filtering under positive pressure to obtain rutile-phase iridium oxide powder.

[0027] In some possible embodiments, the above-mentioned reducing agent includes at least one of sodium borohydride and potassium borohydride.

[0028] The above-mentioned reducing agent has a good reduction effect and can reduce iridium dioxide to iridium sesquioxide at a lower temperature.

[0029] In some possible embodiments, the temperature of the above-mentioned reduction reaction is 30 - 100 °C.

[0030] At the above temperature, iridium dioxide can be reduced to iridium sesquioxide by sodium borohydride and / or potassium borohydride at a lower temperature.

[0031] Exemplarily, the temperature of the above-mentioned reduction reaction is any value among 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C or between any two values.

[0032] Optionally, the temperature of the reduction reaction is 40 - 100 °C. Within the above temperature range, the finally obtained iridium oxide catalyst not only has good activity but also has good stability.

[0033] Optionally, the temperature of the reduction reaction is 70 - 100 °C. Within the above temperature range, the iridium oxide catalyst not only has excellent activity but also has good stability.

[0034] In some possible embodiments, the mass ratio of iridium dioxide to the reducing agent is 3:1 - 10:1.

[0035] By controlling the mass ratio of iridium dioxide to the reducing agent within a reasonable range, part of the iridium dioxide is reduced to iridium sesquioxide, and the finally obtained iridium oxide catalyst has good activity and good stability.

[0036] Exemplarily, the mass ratio of iridium dioxide to the reducing agent is any value among 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 or between any two of these values.

[0037] In some possible embodiments, the flow rates of the above-mentioned first reaction solution and second reaction solution are respectively 5 - 20 ml / min.

[0038] By controlling their flow rates, a part of the iridium dioxide is reduced to iridium sesquioxide, and the resulting iridium oxide catalyst has good activity and good stability.

[0039] Exemplarily, the flow rates of the first reaction solution and the second reaction solution are respectively any value among 5 ml / min, 7 ml / min, 10 ml / min, 13 ml / min, 15 ml / min, 20 ml / min or between any two of these values.

[0040] In some possible embodiments, the flow rates of the above-mentioned first reaction solution and second reaction solution are the same.

[0041] By controlling the flow rates of the first reaction solution and the second reaction solution to be the same, it is convenient to accurately control the reaction efficiency and results.

[0042] It can be understood that the first reaction solution and the second reaction solution are simultaneously delivered into the channels of the microchannel continuous flow reactor, so as to accurately control the reaction efficiency and results.

[0043] In some possible embodiments, the solvents of the above-mentioned first reaction solution and second reaction solution are respectively polyols.

[0044] The polyol is used as a solvent to dissolve the reducing agent and disperse the initial catalyst. Since the polyol has a certain viscosity, it can slow down the flow rates of the first reaction solution and the second reaction solution in the microchannel continuous flow reactor, enabling the iridium dioxide and the reducing agent to fully contact and causing a part of the iridium dioxide to be reduced to iridium sesquioxide.

[0045] The polyol includes at least one of ethylene glycol, propylene glycol, glycerol, butanediol, isopentanediol. For example, the polyol is a single ethylene glycol, propylene glycol, glycerol or isopentanediol, or it can be a mixed alcohol of ethylene glycol and propylene glycol, or a mixed alcohol of glycerol, butanediol, isopentanediol.

[0046] Exemplarily, the polyol is ethylene glycol.

[0047] In some possible embodiments, the solvents of the above-mentioned first reaction solution and second reaction solution are the same.

[0048] In some possible embodiments, the residence time of the above-mentioned first reaction solution and second reaction solution in the microchannel continuous flow reactor is 2 - 8 min.

[0049] The residence time here actually refers to the total contact time of the first reaction solution and the second reaction solution in the microchannel continuous flow reactor. The residence time can be controlled by controlling the channel length of the continuous flow reactor, so that the final iridium oxide catalyst can be directly output from the channel outlet after the reaction in the microchannel continuous flow reactor. It should be noted that according to the residence time of the first reaction solution and the second reaction solution in the microchannel continuous flow reactor, since the residence time is short, it can be further explained that the role of the polyol is not a reduction role.

[0050] Optionally, the channel diameter size is 0.5 - 3.5 mm, and those skilled in the art can also adjust it according to actual needs.

[0051] Optionally, the particle size of the above-mentioned initial catalyst is: 0.1 μm ≤ D50 ≤ 1 μm, and 1 μm ≤ D90 ≤ 5 μm. Further optionally, the particle size of the above-mentioned initial catalyst is: 0.3 μm ≤ D50 ≤ 0.7 μm, 2 μm ≤ D90 ≤ 3 μm.

[0052] Based on the small diameter of the microchannels of the microchannel continuous flow reactor, when the particle size of the initial catalyst dispersed in the first reaction solution is within the above range, it is beneficial to avoid blockage and enable the reduction reaction to proceed smoothly.

[0053] Optionally, the preparation method of the iridium oxide catalyst further includes: after the continuous reduction reaction is completed, filtering the obtained product, washing the filter residue after filtration, and when the conductivity of the filtrate is less than 10 us / cm, it indicates that the impurity removal is completed, and the filter residue can be dried to obtain the iridium oxide catalyst. Among them, positive pressure filtration can be used for filtration.

[0054] The following further describes in detail the preparation method of the iridium oxide catalyst of the present application in combination with examples.

[0055] Example 1

[0056] A preparation method of an iridium oxide catalyst, which includes:

[0057] S1. Weigh 5.878 g of chloroiridic acid solution (mass fraction: 37%) and add it to 100 ml of water to disperse evenly, then add 18.2 g of sodium nitrate to it and dissolve it completely. Finally, place the above solution in an oil bath at 100 °C and stir to evaporate to dryness. Load the evaporated powder into a porcelain boat and put it into a muffle furnace at 500 °C for annealing oxidation for 30 min, then add water to dissolve and perform positive pressure filtration to obtain rutile phase iridium oxide powder.

[0058] S2. Disperse 3 g of the rutile-phase iridium oxide powder in 100 ml of ethylene glycol by ultrasonic treatment to obtain a first reaction solution. The particle size of the rutile-phase iridium oxide powder dispersed in the first reaction solution is as follows: D50 is 0.4 μm, and D90 is 3 μm.

[0059] Disperse and dissolve 1 g of sodium borohydride in 100 ml of ethylene glycol by ultrasonic treatment to obtain a second reaction solution.

[0060] Transfer the first reaction solution and the second reaction solution to syringes respectively, and inject them into a microchannel continuous flow reactor at a rate of 10 ml / min respectively for continuous reduction reaction. The residence time in the microchannel continuous flow reactor is 2 min, and the microchannel continuous flow reactor is heated by circulating water to keep the reduction reaction temperature at 70 °C.

[0061] Place the solution after the reaction in a positive pressure filtration tank for cleaning. The criterion for the end of cleaning is that the conductivity of the filtrate is less than 10 us / cm. Dry the filter residue to obtain the iridium oxide catalyst.

[0062] Example 2

[0063] The difference from Example 1 is only that: the microchannel continuous flow reactor is heated by circulating water to keep the reduction reaction temperature at 30 °C.

[0064] Example 3

[0065] The difference from Example 1 is only that: the microchannel continuous flow reactor is heated by circulating water to keep the reduction reaction temperature at 40 °C.

[0066] Example 4

[0067] The difference from Example 1 is only that: the microchannel continuous flow reactor is heated by circulating water to keep the reduction reaction temperature at 100 °C.

[0068] Example 5 The difference from Example 1 is only that: the mass ratio of iridium dioxide to the reducing agent is 4:1.

[0069] Example 6

[0070] The difference from Example 1 is only that: the mass ratio of iridium dioxide to the reducing agent is 5:1.

[0071] Example 7

[0072] The difference from Example 1 is only that: the mass ratio of iridium dioxide to the reducing agent is 10:1.

[0073] Example 8

[0074] The difference from Example 1 is only that: the flow rates of the first reaction solution and the first reaction solution are both 5 ml / min.

[0075] Example 9

[0076] The difference from Example 1 is only that the flow rates of the first reaction solution and the first reaction solution are both 15 ml / min.

[0077] Example 10

[0078] The difference from Example 1 is only that the flow rates of the first reaction solution and the first reaction solution are both 20 ml / min.

[0079] Example 11

[0080] The difference from Example 1 is only that the residence time of the first reaction solution and the second reaction solution in the microchannel continuous flow reactor is 8 min.

[0081] Comparative Example 1

[0082] It directly uses the rutile-phase iridium oxide powder obtained in step S1 of Example 1 as the iridium oxide catalyst.

[0083] Figure 1 XRD patterns of the iridium oxide catalysts prepared in Example 1 and Comparative Example 1 are shown. According to Figure 1 It can be seen that Comparative Example 1 is of rutile phase. Although a small part of Example 1 is reduced, its crystal form is still of rutile phase and still has good stability.

[0084] Comparative Example 2

[0085] The difference from Example 1 is only that without using the microchannel continuous flow reactor, sodium borohydride and iridium oxide are directly mixed and reacted in an oil bath at 70 °C for 2 min, and the iridium oxide catalyst is obtained by positive pressure filtration.

[0086] Comparative Example 3

[0087] The difference from Example 1 is only that without using the microchannel continuous flow reactor, sodium borohydride and iridium oxide are directly mixed and reacted in an oil bath at 70 °C for 120 min, and the iridium oxide catalyst is obtained by positive pressure filtration.

[0088] Comparative Example 4

[0089] The difference from Example 1 is only that sodium borohydride and iridium oxide are reacted in the microchannel continuous flow reactor at 150 °C, and the catalyst is obtained by positive pressure filtration.

[0090] Comparative Example 5

[0091] The difference from Example 1 is only that the microchannel continuous flow reactor uses circulating water heating to keep the reduction reaction temperature at 130 °C.

[0092] Comparative Example 6

[0093] The difference from Example 1 is only that: the mass ratio of iridium dioxide to the reducing agent is 1:1.

[0094] Comparative Example 7

[0095] The difference from Example 1 is only that: the mass ratio of iridium dioxide to the reducing agent is 1:2.

[0096] Comparative Example 8

[0097] Iridium dioxide and iridium sesquioxide with a mass ratio of 1:1 were stirred and mixed for dispersion for 60 min at 600 rmp to obtain an iridium oxide catalyst.

[0098] Test Example 1

[0099] The oxygen evolution activity and durability of the catalysts provided in the above Examples 1-11 and Comparative Examples 1-8 were studied by electrochemical tests.

[0100] Among them, the electrochemical tests were carried out on a CHI660E electrochemical workstation and a rotating disk electrode device of Shanghai Chenhua. The main electrochemical performance tests on the catalysts were cyclic voltammetry (CV) tests and linear sweep voltammetry (LSV) tests. All electrode potentials in the experiments were normalized using a reversible hydrogen electrode (RHE).

[0101] (1) Preparation of the working electrode

[0102] Weigh 8 mg of each of the above catalysts and add them to a test tube. Pipette 2 ml of the prepared dispersion (obtained by mixing 300 ml of isopropanol, 100 ml of water, and 0.31 g of 5 wt% Nafion solution) into it. Ultrasonically disperse the resulting mixed solution for 20 min to obtain a uniform catalyst ink. Then pipette 10 μL of the catalyst ink and evenly drop it on a pre-polished and cleaned gold electrode (with an area of 0.196 cm 2 ) to wait for it to air dry naturally to form a catalytic layer, and the working electrodes corresponding to each example and comparative example can be obtained.

[0103] An Ag / AgCl electrode was used as the reference electrode, and a platinum electrode was used as the auxiliary electrode.

[0104] 2) Electrochemical performance test

[0105] The potential range of the cyclic voltammetry test (Cyclic voltammogram, CV) was 1.2 - 1.6 vs RHE (0.544 - 0.944 vs Hg2SO4). Before each test, saturated N2 needed to be introduced (in an anaerobic environment), and scanned at a scan rate of 100 mV s -1 until the CV curve was stable to fully activate the catalyst.

[0106] Linear sweep voltammetry: To evaluate the OER electrocatalytic performance of the catalyst materials and their performance during this reaction, anodic polarization measurements were carried out, and LSV curves were obtained from the results of linear sweep voltammetry (LSV), where the LSV scan rate was 50 mV·s -1 , the scanning range was 1.2 - 1.6 vs RHE, and the scanning speed was 50 mV·s -1 , and the rotation speed of the rotating disk electrode was 1600 rpm.

[0107] In the LSV curve, the overpotential magnitude corresponding to 10 mA cm -2 was used to judge the quality of the OER performance. The overpotential refers to the difference between the actual potential and the equilibrium potential when the current density reaches a specified level, and it directly reflects the catalytic activity of the electrocatalytic or photoelectrocatalytic reaction. The closer the overpotential is to 0 V, the better the performance of the catalyst, the lower the actual voltage required to reach the relative current density, the relatively smaller the energy consumption, the higher the catalytic activity, and the better the OER performance.

[0108] 3) Accelerated durability test

[0109] To study the stability of the prepared catalysts in an acidic electrochemical environment, each catalyst was subjected to an accelerated durability test (ADT), and scanned 3000 cycles at a scanning rate of 100 mV s -1 between 1.2 - 1.6 vs RHE (0.544 - 0.944 vs Hg2SO4). Before and after the cycle, CV and LSV data were collected according to the above method, and the electrochemical stability of the catalyst was evaluated by comparing the overpotential loss amount (decay rate %) of the catalyst at different numbers of cycles.

[0110] The results are shown in Table 1 and Figure 2 as follows.

[0111] Table 1 Test results

[0112]

[0113] According to the comparison between Examples 1 - 11 and Comparative Example 1, it can be seen that the preparation method adopted in this application can improve the activity of the catalyst while having better durability.

[0114] Figure 2 It is a comparison chart of the LSV performance of the iridium oxide catalysts prepared in Example 1 and Comparative Example 1 before and after 3000 cycles of CV accelerated cycling test.

[0115] According to Table 1, Figure 1 andFigure 2 It can be seen that Comparative Example 1 is in the rutile phase. Therefore, the LSV curves before and after 3000 cycles of CV accelerated cycle tests coincide. After 3000 cycles of CV accelerated durability tests, the decay rate of the catalyst is 0, showing excellent durability. Although part of the rutile phase in the iridium oxide catalyst prepared in Example 1 of the present application is reduced, the LSV curves before and after 3000 cycles of CV accelerated cycle tests basically coincide, and the decay rate is only 0.39%. Moreover, the activity has been significantly improved. That is to say, compared with Comparative Example 1, the iridium oxide catalyst prepared in Example 1 has excellent durability while significantly improving the activity.

[0116] According to Example 1 and Comparative Examples 1-2, it can be seen that if the microchannel continuous flow reactor is not used and the heating reaction is directly carried out, the reaction efficiency is extremely low at 2 min, and the activity has basically not been improved compared with Comparative Example 1.

[0117] According to Example 1 and Comparative Example 3, in Comparative Example 3, the microchannel continuous flow reactor is not used, but the reaction is directly carried out in an oil bath at 70 °C for a long time. Although the activity of the catalyst can be significantly improved, the stability of the prepared catalyst is poor. After 3000 cycles of CV accelerated durability tests, the decay rate of the catalyst is as high as 8.8%, which cannot meet the life requirements of the electrolytic water catalyst.

[0118] According to Examples 1-4 and Comparative Examples 4-5, it can be seen that reducing iridium dioxide at a reduction temperature of 30-150 °C can reduce iridium dioxide and improve the activity of the catalyst. However, if the temperature is too high, although the activity can be further improved, its stability is significantly deteriorated. Therefore, when the reduction reaction temperature is 30 °C - 100 °C, preferably 40-100 °C, better stability and activity can be achieved.

[0119] According to Example 1, 5-7 and Comparative Examples 6-7, when the mass ratio of iridium dioxide to the reducing agent is between 3:1 and 10:1, preferably between 3:1 and 5:1, the prepared catalyst has better stability and activity.

[0120] According to Comparative Example 8, although the iridium oxide catalyst can be prepared by directly mixing and dispersing iridium dioxide and iridium sesquioxide for a long time, and the activity is improved by the complexation of different valence states, the stability of the iridium oxide catalyst is poor and the preparation time is long.

[0121] The above are only specific embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A preparation method of an iridium oxide catalyst, characterized in that, Comprising: A first reaction solution in which an initial catalyst is dispersed, the initial catalyst containing iridium dioxide; A second reaction solution in which a reducing agent is dissolved; Injecting the first reaction solution and the second reaction solution into a microchannel continuous flow reactor for continuous reduction reaction so that part of the iridium dioxide is reduced to iridium sesquioxide; The reducing agent includes at least one of sodium borohydride and potassium borohydride, the temperature of the reduction reaction is 30-100 °C, and the residence time of the first reaction solution and the second reaction solution in the microchannel continuous flow reactor is 2-8 min.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the iridium dioxide to the reducing agent is 3:1-10:

1.

3. The preparation method according to any one of claims 1-2, characterized in that, The flow rates of the first reaction solution and the second reaction solution are 5-20 ml / min respectively.

4. The preparation method according to any one of claims 1-2, characterized in that, The flow rates of the first reaction solution and the second reaction solution are the same.

5. The preparation method according to any one of claims 1-2, characterized in that, The solvents of the first reaction solution and the second reaction solution are polyols respectively.

6. The preparation method according to any one of claims 1-2, characterized in that, The solvents of the first reaction solution and the second reaction solution are the same.

7. The preparation method according to any one of claims 1-2, characterized in that, The particle size of the initial catalyst is: 0.1 μm ≤ D50 ≤ 1 μm, and 1 μm ≤ D90 ≤ 5 μm.

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