Preparation method and application of long-range ordered iridium-based monatomic catalyst

Abstract

The invention discloses a preparation method and application of a long-range ordered iridium-based monatomic catalyst. The preparation method comprises the following steps: grinding and mixing iridium salt, strontium salt and potassium hydroxide to obtain a mixed material; calcining the mixed material in an air atmosphere to obtain a primary product; washing the primary product for the first time, removing residual potassium ions through a cation exchange method, washing for the second time, and freezing through liquid nitrogen; and performing freeze drying on the primary product after liquid nitrogen freezing to obtain the long-range ordered iridium-based monatomic catalyst. According to the preparation method disclosed by the invention, the long-range ordered iridium-based monatomic catalyst is prepared, and iridium atoms have the characteristics of typical monatomic catalysts in the long-range ordered iridium-based monatomic catalyst and are regularly arranged in a long-range ordered manner; the catalyst has the advantages of high catalytic activity, excellent electro-catalytic stability, high monatomic loading capacity and the like; the synthesis method has the advantages of simplicity in operation, safety, high controllability and the like, is suitable for large-scale preparation of the OER electrocatalyst, and has a very wide application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of catalyst preparation, and in particular to a preparation method and application of a long-range ordered iridium-based single-atom catalyst. Background Art

[0002] With the development of society, energy crisis, environmental pollution and climate warming have become more serious. Developing sustainable clean energy is an effective way to solve this problem. Hydrogen is regarded as the best energy carrier to replace traditional fossil fuels because of its high energy density, pollution-free combustion products and multiple preparation methods. Among them, water electrolysis is one of the simplest methods. It uses electricity to electrolyze water into hydrogen and oxygen, which are precipitated at the cathode and anode respectively. It has the advantages of simple operation, high hydrogen evolution efficiency and high hydrogen preparation purity, and has received extensive attention and research.

[0003] Water electrolysis mainly includes two reactions, namely the cathode hydrogen evolution reaction (HER) and the anode oxygen evolution reaction (OER). The schematic diagram of water electrolysis is shown in Figure 1 As shown. Theoretically, the electromotive force of water electrolysis is 1.23V, but the existence of the (activation) energy barrier in the actual reaction process will cause the actual electromotive force to be much larger than this value, resulting in a huge waste of electrical energy. Compared with the hydrogen evolution process of two electrons transfer, the oxygen evolution process involving four electrons transfer and OH bond breakage is the main reason for the overpotential. Its reaction mechanism is more complicated, and the catalytic process also includes characteristics such as multi-proton coupling and multi-electron transfer, which makes its reaction kinetics slow. This has also become a key difficulty limiting its application in proton exchange membrane technology. According to the latest standards of the U.S. Department of Energy (DOE), only when the overpotential of OER is lower than 200mV can it be expected to meet the low energy efficiency of the system (44.7kWh kgH2 -1 ) goal. Proton exchange membrane technology is to isolate hydrogen and oxygen through proton exchange membrane to achieve the purpose of producing high-purity hydrogen. At present, compared with alkaline proton exchange membrane technology, acidic proton exchange membrane technology is more mature, which also makes water electrolysis under acidic conditions more meaningful. The working principle diagram of acidic proton exchange membrane is shown in the figure Figure 2 However, the lack of relevant efficient and stable acidic OER electrocatalysts remains the biggest challenge currently faced.

[0004] In order to solve this problem, the introduction of highly active electrocatalysts in the OER process can effectively accelerate the catalytic reaction rate and reduce the reaction energy barrier. Iridium-based materials are almost the only stable OER electrocatalysts under acidic conditions. Therefore, it is particularly important to develop iridium-based OER electrocatalysts with high activity and stability.

[0005] Since the concept of single-atom catalysts was proposed in 2011, they have received extensive attention and research in electrochemical energy storage and conversion, mainly due to their rich active sites, ultra-high atomic utilization, special geometric electronic structure and unique coordination environment. The active atoms of the single-atom catalysts reported so far show disordered arrangement characteristics, which usually results in low single-atom loading and unclear structure-activity relationship. The inventors can achieve long-range ordered arrangement of active atoms in metastable two-dimensional materials through the preparation of metastable two-dimensional materials. The preparation methods of metastable two-dimensional materials in the prior art each have their own advantages and disadvantages: the purity of metastable two-dimensional materials prepared by the chemical exfoliation method is very poor, and the reason for this phenomenon is the phase transition caused by incomplete exfoliation; the electron donor method is only applicable to phase control but not to morphology control. Therefore, in the process of synthesizing metastable two-dimensional electrocatalysts, additional driving force is often required to stabilize the two-dimensional morphology; the topological transformation method is suitable for the preparation of large-scale metastable two-dimensional materials, but this method generally requires a two-dimensional precursor as a template to maintain the two-dimensional morphology of the obtained material; the template growth method requires a good lattice match between the template and the material. The lack of a suitable template will make it impossible to control the selective growth of metastable two-dimensional materials.

[0006] Therefore, it has become a major challenge to prepare single-atom catalysts with long-range order by designing or improving synthetic strategies. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a preparation method and application of a long-range ordered iridium-based single-atom catalyst, to prepare an iridium-based single-atom catalyst, whose active atoms present a regular long-range ordered arrangement, and adjacent active atoms remain independent of each other, having the typical characteristics of a single-atom catalyst, and solving the problems of disordered arrangement of active atoms in existing single-atom catalysts, resulting in low single-atom loading, unclear structure-activity relationship, etc.; at the same time, the iridium-based single-atom catalyst has excellent oxygen evolution activity and stability in acidic media, and is expected to replace commercial iridium oxide and ruthenium oxide in industrial electrolyzed water.

[0008] In order to solve the above technical problems, the present invention provides a method for preparing a long-range ordered iridium-based single-atom catalyst, comprising the following steps:

[0009] S1, grinding and mixing iridium salt, strontium salt and potassium hydroxide to obtain a mixed material;

[0010] S2, heating the mixture to 800-850° C. and calcining in an air atmosphere to obtain a primary product;

[0011] S3, washing the primary product once with water, removing residual potassium ions by cation exchange, and freezing the primary product by liquid nitrogen after washing it twice;

[0012] S4. Freeze-drying the primary product after being frozen with liquid nitrogen to obtain an iridium-based single-atom catalyst with long-range order.

[0013] The synthesis method of the present invention is simple to operate, safe, and highly controllable, and can realize large-scale production; a long-range ordered iridium-based single-atom catalyst is prepared, and the product is a metastable two-dimensional metal oxide material, the main component of which is strontium iridate (Sr2IrO4), and its morphology presents the characteristics of a typical two-dimensional van der Waals material, wherein the iridium atoms therein have the characteristics of a typical single-atom catalyst and present a regular long-range ordered arrangement; the single-atom loading is high, and it has excellent oxygen evolution activity and stability in acidic media, and is expected to replace commercial iridium oxide and ruthenium oxide in industrial electrolyzed water, and has good application prospects.

[0014] Furthermore, the distance between adjacent iridium active atoms in the iridium-based single-atom catalyst is Each iridium active atom is isolated from each other and arranged in a long-range orderly manner.

[0015] Furthermore, in S1, the molar ratio of the iridium salt, the strontium salt and the potassium hydroxide is 1:2:(20-50).

[0016] Furthermore, in S1, the iridium salt is iridium trichloride (IrCl3) and / or iridium acetylacetonate (Ir(ac)3); the strontium salt is strontium chloride (SrCl2) and / or strontium nitrate Sr(NO3)2.

[0017] Furthermore, in S1, the grinding temperature is 20-25°C and the grinding time is 4-6h.

[0018] Further, in S2, the calcination is carried out in a tubular furnace with a heating rate of 5-10°C / min, a holding time of 2-4h, a cooling rate of 2-5°C / min, an air flow rate of 2-10L / min, and oxygen in the air plays a major role.

[0019] Furthermore, in S2, the mixed material is placed in a crucible with a corundum content of more than 95 wt%, and then the crucible is placed in a tubular furnace.

[0020] Furthermore, in S3, the first water wash and the second water wash both use deionized water and / or ultrapure water, wherein the first water wash is washed ≥ 5 times, and the second water wash is washed 3-10 times.

[0021] Furthermore, in S3, the cation exchange method is specifically: the primary product after one water washing is placed in an acid solution and soaked for 5-12 hours.

[0022] Furthermore, the acid solution is a hydrochloric acid solution or a potassium permanganate solution with a concentration of 0.01-0.1M.

[0023] Furthermore, in S3, the freeze drying temperature is -25°C to -80°C, the time is 24-72 hours, and the freeze drying utilizes the principle of sublimation to remove ultrapure water or deionized water.

[0024] The second aspect of the present invention provides the use of the long-range ordered iridium-based single-atom catalyst prepared by the preparation method of the first aspect in the electrolysis of water.

[0025] Beneficial effects of the present invention:

[0026] The preparation method of the present invention prepares a long-range ordered iridium-based single-atom catalyst, in which the iridium atoms have the characteristics of a typical single-atom catalyst and present a regular long-range ordered arrangement; the catalyst has the advantages of high catalytic activity, excellent electrocatalytic stability and high single-atom loading, and when the catalyst is applied to OER, the current density is 10 mA cm -2 The overpotential is only 190 mV, and its catalytic activity is much higher than that of commercial RuO2 and IrO2.

[0027] The synthesis method of the present invention has the advantages of simple operation, safety and strong controllability, and is suitable for the large-scale preparation of OER electrocatalysts in industry and has very broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the working principle of water electrolysis;

[0029] Figure 2 This is a schematic diagram of the working principle of the proton exchange membrane;

[0030] Figure 3 This is a schematic diagram of the synthesis process of Example 1 of the present invention;

[0031] Figure 4 is the XRD pattern of the catalyst prepared in Example 1 of the present invention;

[0032] Figure 5 is a SEM image of the catalyst prepared in Example 1 of the present invention;

[0033] Figure 6 is a TEM image of the catalyst prepared in Example 1 of the present invention;

[0034] Figure 7 is a spherical aberration electron microscope analysis image of the catalyst prepared in Example 1 of the present invention;

[0035] Figure 8 It is an electrochemical test diagram of the catalyst prepared in Example 1 of the present invention, rutile iridium oxide, iridium carbon and ruthenium oxide. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0037] Example 1

[0038] This embodiment relates to a method for preparing a long-range ordered iridium-based single-atom catalyst, comprising the following steps:

[0039] S1. Grind iridium trichloride, strontium chloride and potassium hydroxide in a molar ratio of 1:2:20 at room temperature for 5 hours and mix them evenly to obtain a mixed material;

[0040] S2, placing the mixed material in a crucible with a corundum content of more than 95wt%, and then placing it in a tubular furnace, introducing air at a rate of 5L / min for calcination, and the calcination parameters are: heating rate of 5°C / min, 800°C holding time of 3h, cooling rate of 3°C / min, cooling to room temperature, and obtaining a primary product;

[0041] S3, taking out the primary product, washing it with deionized water for 5 times, and then soaking it in 0.05M hydrochloric acid solution for 5 hours to remove residual potassium ions, washing it with deionized water for 3 times again, and then freezing it in liquid nitrogen;

[0042] S4. The primary product after being frozen by liquid nitrogen is freeze-dried at -30°C for 48 hours to obtain a long-range ordered iridium-based single-atom catalyst. The preparation method flow chart is as follows Figure 3 shown.

[0043] Test Case

[0044] The catalyst prepared in Example 1 was subjected to XRD analysis. Figure 4 As shown in Figure 2, the XRD pattern has obvious layered peaks of (0001), (0002), (0003), (0004) and (0005), which is consistent with the SEM ( Figure 5 ) and TEM( Figure 6 ), the catalyst material prepared in this example has a typical two-dimensional morphology and is a metastable two-dimensional metal oxide material, the main component of which is Sr2IrO4.

[0045] The catalyst prepared in Example 1 was analyzed by spherical aberration electron microscopy. Figure 7 a-7c, where the bright atoms are iridium and the dark atoms are strontium. From the spherical aberration electron microscope image, it is easy to measure the distance between adjacent iridium active atoms as high as It proves that each active iridium atom is isolated and has typical long-range ordered arrangement characteristics. Figure 7 d is the selected electron color of the catalyst, proving that it is consistent with the structure of the trigonal phase. Figure 7 e is the spherical aberration electron microscope image of the catalyst interface, showing that its interlayer spacing is This is also consistent with the d value corresponding to (0001) in XRD. It can be seen that the catalyst prepared in Example 1 has a trigonal phase structure with a unit cell parameter of and α=β=90°,γ=120°, and the space group was determined to be P-31m(162).

[0046] The catalyst prepared in Example 1 was subjected to electrochemical testing. The results showed that the metastable two-dimensional strontium iridate catalyst (M-Tri-Sr2IrO4) had excellent OER activity at 10 mA cm geo -2 The overpotential at the current density is only 190mV ( Figure 8 a), which is much lower than 300mV of rutile iridium oxide (Rutile-IrO2), 320mV of commercial iridium carbon (Ir / C) and 270mV of ruthenium oxide (RuO2). In addition, compared with rutile iridium oxide, commercial iridium carbon and ruthenium oxide, the catalyst has the lowest Tafel slope of 40.1mV dec -1 ( Figure 8 b), indicating that it has a faster kinetic rate. The electrochemical stability test shows that the metastable two-dimensional strontium iridate has a high current density of 10 mA cm geo -2 and 100mA cm geo -2 can run stably up to 407h and 112h respectively ( Figure 8 c), indicating its excellent OER stability.

[0047] In summary, the method of the present invention prepares a long-range ordered iridium-based single-atom catalyst, and the product is a metastable two-dimensional metal oxide material, the main component of which is strontium iridate (Sr2IrO4), and its morphology shows the characteristics of a typical two-dimensional van der Waals material. The iridium atoms have the characteristics of a typical single-atom catalyst and show a regular long-range ordered arrangement. In addition, the catalyst has the advantages of high catalytic activity, excellent electrocatalytic stability and high single-atom loading (44.5wt%), and can be applied to the field of water electrolysis. At the same time, the synthesis method of the present invention has the advantages of simple operation, safety and strong controllability, and is suitable for the large-scale preparation of OER electrocatalysts in industry, and has a very broad application prospect.

[0048] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A method for preparing a long-range ordered iridium-based single-atom catalyst, characterized in that: The steps include: S1, grinding and mixing iridium salt, strontium salt and potassium hydroxide to obtain a mixed material; S2, heating the mixture to 800-850° C. and calcining for 2-4 hours in an air atmosphere to obtain a primary product; S3, washing the primary product once with water, removing residual potassium ions by cation exchange, and freezing the primary product by liquid nitrogen after washing it twice; S4. Freeze-drying the primary product after being frozen with liquid nitrogen to obtain an iridium-based single-atom catalyst with long-range order.

2. The method for preparing a long-range ordered iridium-based single-atom catalyst according to claim 1, characterized in that: In S1, the molar ratio of the iridium salt, the strontium salt and potassium hydroxide is 1:2:(20-50).

3. The method for preparing a long-range ordered iridium-based single-atom catalyst according to claim 1, characterized in that: In S1, the iridium salt is iridium trichloride and / or iridium acetylacetonate; and the strontium salt is strontium chloride and / or strontium nitrate.

4. The method for preparing a long-range ordered iridium-based single-atom catalyst according to claim 1, characterized in that: In S1, the grinding temperature is 20-25°C and the grinding time is 4-6h.

5. The method for preparing a long-range ordered iridium-based single-atom catalyst according to claim 1, characterized in that: In S2, the calcination is carried out in a tubular furnace with a heating rate of 5-10°C / min, a cooling rate of 2-5°C / min, and an air flow rate of 2-10L / min.

6. The method for preparing a long-range ordered iridium-based single-atom catalyst according to claim 1, characterized in that: In S3, the first water washing and the second water washing are both carried out with deionized water and / or ultrapure water, wherein the number of washing times of the first water washing is ≥5 times, and the number of washing times of the second water washing is 3-10 times.

7. The method for preparing a long-range ordered iridium-based single-atom catalyst according to claim 1, characterized in that: In S3, the cation exchange method specifically comprises: soaking the primary product after one water washing in an acid solution for 5-12 hours.

8. The method for preparing a long-range ordered iridium-based single-atom catalyst according to claim 7, characterized in that: The acid solution is a hydrochloric acid solution or a potassium permanganate solution with a concentration of 0.01-0.1M.

9. The method for preparing a long-range ordered iridium-based single-atom catalyst according to claim 1, characterized in that: In S3, the freeze-drying temperature is -25°C to -80°C, and the time is 24-72 hours.

10. Use of an iridium-based single-atom catalyst with long-range order prepared by the preparation method according to any one of claims 1 to 9 in electrolysis of water.

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