Monolayer iridium oxide nanosheet, preparation method and application thereof in electrocatalytic oxygen evolution reaction

Abstract

The application relates to a single-atomic-layer iridium oxide nanosheet, a preparation method thereof and application of the single-atomic-layer iridium oxide nanosheet in an electrocatalytic oxygen evolution reaction, and belongs to the technical field of inorganic nanometer functional materials. Through a whole-process technology of "precursor synthesis of accurate occupation of honeycomb center sites - gradient step-by-step proton exchange topological locking - directional shearing ball milling limit peeling", a single-atomic-layer iridium oxide nanosheet with an IrO6 octahedral co-edge connection and a graphite-like honeycomb topological structure is prepared, and the product has a thickness of 0.4-0.5 nm. The application solves the problems that existing honeycomb layered iridium-based oxides are difficult to be peeled into a single atomic layer, an acid treatment is easy to damage the skeleton, and peeling is easy to introduce defects. The obtained nanosheet has an oxygen evolution overpotential of about 250 mV at a current density of 10 mA / cm 2 2 in a 0.1M HClO4 electrolyte, and has excellent catalytic activity and structural stability, and has a wide application prospect in the field of proton exchange membrane water electrolysis.

Description

Technical Field

[0001] This invention belongs to the field of inorganic nanomaterials technology, specifically relating to a single-atom-layer iridium oxide nanosheet, its preparation method, and its application in the electrocatalytic oxygen evolution reaction. Background Technology

[0002] Under the "dual carbon" strategic goal, green hydrogen has become a core carrier for building a new energy system and achieving deep decarbonization. Proton exchange membrane electrolysis (PEMWE) technology, with its fast response speed, wide operating current density, high hydrogen purity, and perfect compatibility with the intermittent power generation characteristics of renewable energy sources such as wind and solar power, has become one of the core mainstream technologies for large-scale green hydrogen production. The oxygen evolution reaction (OER) at the anodic apex of PEMWE is a four-electron transfer process with high reaction kinetic barriers, representing the energy efficiency bottleneck of the entire electrolysis system. More importantly, this reaction must be carried out under extremely harsh conditions of strong acid media and high oxidation potential, requiring the catalyst to simultaneously meet three core indicators: first, high intrinsic catalytic activity to drive the rapid reaction at low overpotentials; second, full exposure and accessibility of active sites to maximize the utilization of precious metal atoms; and third, extremely strong structural stability to inhibit the dissolution of active components and structural collapse under strong acid and high potentials, meeting the requirements of long-term industrial operation.

[0003] In acidic OER systems, iridium-based oxides are currently the only catalytic system that combines catalytic activity with long-term operational potential. However, the scarcity of iridium in the Earth's crust and its high market price severely limit the large-scale application of PEMWE technology. Currently commercially available rutile iridium dioxide (IrO2) catalysts can only expose a limited number of active sites on the particle surface; bulk iridium atoms cannot participate in the catalytic reaction, resulting in extremely low utilization of the precious metal atoms. Furthermore, their intrinsic catalytic activity is limited by the rigid crystal coordination environment, reaching only 10 mA / cm². 2 The industrial standard current density typically requires an overpotential of over 300 mV, resulting in high energy consumption and costs. To improve the performance of iridium-based catalysts, researchers both domestically and internationally have conducted extensive studies on iridium-containing multi-metal oxides. Iridium-based catalysts with structures such as perovskite and pyrochlore have been reported. These materials can significantly enhance intrinsic catalytic activity by optimizing the electronic structure of Ir sites through lattice modulation. However, these materials generally suffer from a core defect of insufficient structural stability: in acidic OER processes, alkali metal and alkaline earth metal cations in their lattice readily dissolve rapidly in strong acids, causing the collapse of the three-dimensional crystal framework. Simultaneously, irreversible reconstruction occurs on the material surface, generating amorphous IrO. x H yAlthough the reconstructed phase possesses certain catalytic activity, it will continuously dissolve and be lost under high oxidation potential, resulting in a rapid decline in catalytic performance within tens of hours, which cannot meet the industrial requirements for long-term stable operation of PEMWE electrolyzers.

[0004] Honeycomb layered iridium oxides are a special type of structural material with a natural two-dimensional layered framework. Their core structural unit is a rigid honeycomb-shaped two-dimensional layer formed by IrO6 octahedra connected by shared edges. Compared to three-dimensional perovskite structures, the two-dimensional layer is more conducive to the exposure of active sites, and the covalently bonded rigid framework has stronger resistance to reconstruction and dissolution, exhibiting potential for both high activity and high stability in acidic OERs. However, in current technologies, the pure-phase synthesis of this type of material relies on high-temperature solid-phase reactions, resulting in products that are mostly micron-sized bulk materials. There are extremely strong electrostatic interactions between the metal cations in the interlayer and honeycomb centers and the layers. Conventional liquid-phase ultrasonic exfoliation and small-molecule intercalation exfoliation techniques can only achieve a few-layer thinning of the material, failing to break through the single-atom-layer limit. This results in most of the active sites within the layers being buried, unable to fully contact the electrolyte, and the catalytic potential of the material cannot be fully released. Currently reported single-atom-layer iridium-based materials mostly rely on ultra-demanding preparation processes such as chemical vapor deposition (CVD) and molecular beam epitaxy (MBE), which involve large equipment investments, high preparation costs, and extremely low product yields, limiting their application to basic laboratory research and failing to meet the demands of large-scale preparation and industrial applications. Meanwhile, single-atom-layer iridium-based materials prepared by liquid-phase methods generally suffer from severe lattice disruption and numerous structural defects, making it difficult to balance high activity and long-term stability in the harsh environment of acidic OERs. Therefore, developing a simple, highly controllable, and scalable preparation method to construct iridium oxide nanosheets possessing a complete honeycomb topological framework, extreme single-atom-layer thickness, high intrinsic activity, and strong acid stability is crucial to overcoming the performance bottlenecks of existing iridium-based catalysts and promoting the large-scale application of PEMWE technology. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a single-atom-layer iridium oxide nanosheet, its preparation method, and its application in the electrocatalytic oxygen evolution reaction. This invention pioneers a complete process of "precursor synthesis with precise occupancy of the honeycomb central site—gradient stepwise proton exchange topological locking—directional shear ball milling ultimate exfoliation," achieving for the first time the large-scale controllable preparation of single-atom-layer iridium oxide nanosheets with a complete graphene-like honeycomb topology. The resulting product exhibits both high activity and long-term stability in the acidic oxygen evolution reaction, and the preparation process is simple, controllable, and easily scalable.

[0006] The method for preparing a single-atom-layer iridium oxide nanosheet according to the present invention comprises the following steps:

[0007] (1) Two-step gradient solid-state synthesis of A 0.5 (B 0.33Ir 0.67 O2 precursor: Weigh the Ir source, B element source, and A element compound according to the stoichiometric ratio, add 1-3 wt% anhydrous ethanol to the above raw materials, and wet grind for 2-4 hours until uniformly mixed. Pre-sinter the resulting mixed powder at a heating rate of 2-5 °C / min to 400-600 °C for 2-6 hours, and then naturally cool to 20-30 °C to obtain the pre-sintered material. Grind the pre-sintered material again, then add 1-3 wt% of the homologous metal chloride confining agent. First, heat to 700-900 °C at a rate of 1-3 °C / min and hold for 4-8 hours to complete crystallization. Then, heat to 950-1100 °C at a rate of 0.5-2 °C / min and hold for 12-24 hours. Finally, naturally cool to 20-30 °C to obtain pure-phase layered iridium A. 0.5 (B 0.33 Ir 0.67 O2 precursors enable precise placement of element B in the center of the IrO6 honeycomb skeleton;

[0008] (2) Gradient stepwise proton exchange: The A obtained in step (1) 0.5 (B 0.33 Ir 0.67 O2 precursor is added to a low-concentration acid solution of 0.05~0.2 mol / L, A 0.5 (B 0.33 Ir 0.67 The ratio of O2 precursor mass to low-concentration acid solution volume is 1g: 50-100mL. The mixture is stirred and soaked at 60-100 rpm for 12-24 hours to selectively exchange A-site cations in the interlayer and widen the interlayer spacing. Then, it is washed 2-4 times by centrifugation with deionized water. The precipitate is added to a mixture of a weak ligand at 0.005-0.02 mol / L and an inorganic acid at 0.5-1 mol / L, and stirred and soaked for 24-72 hours to completely dissolve the B-site cations in the honeycomb center. Simultaneously, the weak ligand locks the IrO6 framework structure. The mixture is then washed multiple times with deionized water until neutral. The precipitate is dried at 50-70℃ for 10-15 hours to obtain protonated layered iridium oxide H. 0.83 Ir 0.67 O2;

[0009] (3) Directional shear ball milling peeling: The H obtained in step (2) 0.83 Ir 0.67 O2, intercalation dispersant, mixed-size ZrO2 microspheres, and mixed alcohol solvent are mixed at a mass ratio of 10:1~2:40~60:180~220 and ball milled at a speed gradient to achieve non-destructive ultimate exfoliation. The ball milling product is filtered to remove the ZrO2 microspheres, and the resulting suspension is purified by two-step centrifugation and fractionation. The resulting precipitate is redispersed in deionized water and then freeze-dried under vacuum to obtain the single-atom-layer iridium oxide nanosheets of the present invention.

[0010] In the above operation method, the Ir source includes, but is not limited to, one or a mixture of several of iridium oxide, iridium chloride, iridium hydroxyoxide, iridium acetate, iridium acetylacetone, chloroiridium acid, potassium hexachloroiridium, and sodium hexachloroiridium.

[0011] In the above operation method, the source of element B includes, but is not limited to, one or a mixture of several of the oxides, chlorides, hydroxides, carbonates, acetates, and acetylacetone salts of elements such as Li, Na, Mn, Co, Ni, Zn, and Ru whose radii are close to the pore size of the IrO6 honeycomb skeleton.

[0012] In the above operation method, the A element compound includes, but is not limited to, one or a mixture of several of the corresponding carbonates, phosphates, hydroxides, chlorides, and nitrates of alkali metals and alkaline earth metals such as K, Mg, Ca, Sr, and Ba.

[0013] In the above operation method, the homologous metal chloride confinement agent includes, but is not limited to, one or a mixture of several chlorides homologous to the A-site element, such as potassium chloride, magnesium chloride, strontium chloride, calcium chloride, and barium chloride.

[0014] In the above operation method, the low-concentration acid solution includes, but is not limited to, one or a mixture of several of the following: acetic acid solution, citric acid solution, hydrochloric acid solution, sulfuric acid solution, and perchloric acid solution.

[0015] In the above operation method, the weak ligand includes, but is not limited to, one or a mixture of several of ammonium fluoride, ammonium fluoroborate, and potassium fluoride, and the inorganic acid is one or a mixture of several of hydrochloric acid, sulfuric acid, and perchloric acid.

[0016] In the above operation method, the intercalation dispersant includes, but is not limited to, a composite system composed of two or more of the following: alkyltrimethylammonium chloride with a carbon chain length of 12-18, alkyltrimethylammonium bromide with a carbon chain length of 12-18, sodium alkylbenzene sulfonate with a carbon chain length of 12-18, polyvinylpyrrolidone, and polyethylene glycol monomethyl ether.

[0017] In the above operation method, ZrO2 microspheres with a mixed particle size of 0.1~0.5mm are used as the grinding medium and are mixed and used in different particle size ratios.

[0018] In the above operation method, the mixed alcohol includes, but is not limited to, a mixture of two or more of anhydrous ethanol, isopropanol, ethylene glycol, propylene glycol, and glycerol.

[0019] In the above operation method, the ratio of the total moles of Ir and B elements to the moles of A element is 2:1; layered iridium salt A 0.5 (B 0.33 Ir 0.67The number of moles n of the O2 precursor, and the H in the low-concentration acid solution and inorganic acid mixture used for proton exchange. + The molar ratio of the number of moles m is 1:1~20.

[0020] The ball milling process involves milling at a speed gradient of 150-250 r / min for 0.5-3 hours, then at 300-400 r / min for 12-24 hours, and finally at 450-550 r / min for 0.5-3 hours. The temperature is controlled at ≤30℃ throughout the process, with a 10-20 minute pause for heat dissipation every 30 minutes of milling.

[0021] The two-step centrifugal fractionation purification involves centrifuging the suspension at 2000-4000 rpm for 15-30 min, collecting the supernatant, and then centrifuging the supernatant at 10000-15000 rpm for 20-40 min to collect the precipitate.

[0022] In step (3), the temperature for vacuum freeze drying is -10℃ to -50℃, and the time is 24 to 48 hours.

[0023] The single-atom-layer iridium oxide nanosheets of this invention are prepared by the above method. The thickness of the single-atom-layer iridium oxide nanosheets is 0.4~0.5 nm, and the framework is formed by IrO6 octahedra connected by a common edge to form a graphene-like honeycomb topology. There are no obvious lattice defects, and the framework can remain stable in acidic electrolytes. The dissolution of iridium is negligible.

[0024] Another object of the present invention is to provide the application of the above-described single-atom-layer iridium oxide nanosheets in the electrocatalytic acidic oxygen evolution reaction.

[0025] Beneficial effects

[0026] 1. This invention achieves a single-atom-layer iridium oxide with a complete honeycomb topology for the first time by precisely occupying precursor sites, thus achieving 100% utilization of precious metal atoms. At the same time, the rigid covalent framework endows the material with strong resistance to strong acid dissolution and reconstruction, solving the pain point of existing catalysts that "high activity and high stability cannot be obtained at the same time".

[0027] 2. This invention pioneers three core processes: gradient solid-state sintering, stepwise proton exchange, and shear ball milling. These processes solve the problems of existing technologies, such as the inability to precisely control the occupancy of metal sites, the easy destruction of the framework by acid treatment, and the easy introduction of defects by peeling. The preparation process is simple and controllable, requires no expensive equipment, and is easy to scale up.

[0028] 3. The atomic-layer iridium oxide nanosheets obtained in this invention achieve a current-to-weight ratio of 10 mA / cm² in a 0.1 M HClO₄ electrolyte. 2The overpotential at current density is only 250mV, which is far superior to commercial IrO2 catalysts. At the same time, the amount of iridium dissolved is negligible in long-cycle electrolysis, which has broad application prospects in the field of proton exchange membrane water electrolysis. Attached Figure Description

[0029] Figure 1 Layered iridium K prepared in Example 1 0.5 (Na 0.33 Ir 0.67 X-ray diffraction (XRD) pattern (a), scanning electron microscope (SEM) image (b), and schematic diagram of crystal structure (c) of O2;

[0030] Figure 2 Atomic force microscopy (AFM) image and thickness curve (a) and transmission electron microscopy (TEM) image (b) of the monolayer iridium oxide nanosheets prepared in Example 1;

[0031] Figure 3 Linear sweep voltammetry (LSV) curves of the oxygen evolution reaction between the single-atom-layer iridium oxide nanosheets prepared in Example 1 and commercial IrO2 in 0.1M HClO4;

[0032] Figure 4 : 10 mA / cm² of the monolayer iridium oxide nanosheet in Example 1 2 The constant potential stability curve (a) and iridium extraction curve (b) under current density. Detailed Implementation

[0033] The present invention will be further described in detail below through specific embodiments. These embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention. Conventional adjustments to process parameters made by those skilled in the art without departing from the core spirit of the present invention are all within the scope of protection of the present invention.

[0034] Example 1

[0035] The specific steps for preparing single-atom-layer iridium oxide nanosheets in this embodiment are as follows:

[0036] (1) Two-step gradient solid-state synthesis of A 0.5 (B 0.33 Ir 0.67O2 precursor: Weigh 0.2 mmol Na2CO3, 0.8 mmol Ir elemental, and 0.3 mmol K2CO3, add them to an agate mortar, add 1 wt% anhydrous ethanol to the above raw materials, and wet grind for 3 h until uniformly mixed. The resulting mixed powder is heated to 550 °C at a rate of 3 °C / min for pre-sintering for 4 h, and then naturally cooled to 25 °C to obtain the pre-sintered material. The pre-sintered material is ground again for 1 h, and then 2 wt% KCl confinement agent is added to the pre-sintered material. The temperature is increased to 850 °C at a rate of 2 °C / min and held for 6 h to complete crystallization. Then the temperature is slowly increased to 1050 °C at a rate of 1 °C / min and held for 24 h. Finally, it is naturally cooled to 25 °C to obtain 220 mg of pure phase layered iridium salt precursor. Figure 1 XRD results of a confirm that the precursor has a chemical composition of K. 0.5 (Na 0.33 Ir 0.67 )O2.

[0037] (2) Gradient stepwise proton exchange: Take 1g of K 0.5 (Na 0.33 Ir 0.67 O2 was added to 100 mL of 0.1 mol / L acetic acid solution (pH=3.5), and the mixture was stirred at 80 rpm for 24 h. Then, it was washed twice with deionized water by centrifugation. The precipitate was added to 100 mL of HClO4 solution containing ammonium fluoride (0.01 mol / L) and HClO4 (0.5 mol / L). The mixture was stirred at 150 rpm for 48 h. Then, it was washed three times with deionized water until neutral, and the precipitate was dried at 60 °C for 12 h. Through gradient stepwise proton exchange, the precursor K... 0.5 (Na 0.33 Ir 0.67 All K and Na in O2 were replaced with H, yielding 0.8 g of protonated layered iridium oxide H. 0.83 Ir 0.67 O2.

[0038] Stripping: Take 1g of protonated layered iridium oxide H 0.83 Ir 0.67O2 was mixed with 0.1 g of cetyltrimethylammonium chloride-polyethylene glycol composite dispersant, 5 g of mixed-size ZrO2 microspheres (0.1 mm: 0.3 mm = 1:2), and 20 g of ethanol-isopropanol mixed solvent (volume ratio 3:1). The mixture was placed in a ball mill and milled at 200 r / min for 1 h, 350 r / min for 18 h, and 480 r / min for 1 h, with the temperature controlled at ≤30℃ throughout the process, and a 15 min pause for heat dissipation every 30 min. After ball milling, the ZrO2 microspheres were removed by filtration. The suspension was centrifuged at 3000 rpm for 20 min to collect the supernatant, and then centrifuged at 12000 rpm for 30 min to collect the precipitate. The precipitate was redispersed in deionized water and then freeze-dried at -40℃ for 24 h to obtain 0.43 g of single-atom-layer iridium oxide nanosheets with a thickness of 0.46 nm.

[0039] Performance testing: A three-electrode system was used, with 0.1M HClO4 as the electrolyte, a saturated calomel electrode as the reference electrode, and a platinum wire as the counter electrode. The single-atom-layer iridium oxide nanosheets prepared in this embodiment were coated onto a glassy carbon electrode (3 mm in diameter, with a loading of 0.28 mg). Ir / cm 2 The catalyst was used as the working electrode. Catalyst activity was evaluated by linear sweep voltammetry (scan rate 1 mV / s), with a current density of 10 mA / cm². 2 Stability is assessed using the constant potential-time curve.

[0040] The structure and properties of the nanosheets obtained in Example 1 were studied. Figure 1 a is a layered iridium salt K 0.5 (Na 0.33 Ir 0.67 The XRD pattern of the O2 precursor indicates that a pure phase sample was obtained. Figure 1 b is K 0.5 (Na 0.33 Ir 0.67 The SEM image of O2 shows that the synthesized sample has obvious layered characteristics, and the size is mainly distributed between 200 and 300 nm. Figure 1 c is K 0.5 (Na 0.33 Ir 0.67 The schematic diagram of the crystal structure of O2 clearly shows the layered characteristics and the graphene-like topology composed of IrO6 octahedra within the layers.

[0041] Figure 2 a shows the AFM image and thickness curve of a single-atom-layer iridium oxide nanosheet. It can be seen that the thickness of the nanosheet is about 0.5 nanometers, which is a single-atom-layer structure. Figure 2 b is a TEM image of the nanosheet, showing a distinct sheet-like morphology.

[0042] Figure 3 The LSV curves for monolayer iridium oxide nanosheets and commercial IrO2 reflect the potential of the catalyst at different current densities (relative to the reversible hydrogen electrode). At 10 mA / cm²... 2 At the given current density, the overpotential of the nanosheet catalyst is approximately 250 mV, which is 60 mV lower than that of a commercial IrO2 catalyst with the same loading. A low overpotential indicates good catalyst performance and lower energy consumption required to produce the same amount of hydrogen.

[0043] Figure 4 a represents the 10 mA / cm² value of the nanosheet catalyst. 2 The constant potential stability curve under current density shows that it can operate stably for nearly 1700 hours without significant degradation. Figure 4 b is the iridium extraction curve of the nanosheet catalyst during the oxygen evolution process. The iridium extraction amount is only 0.028%, which shows that the material has excellent catalytic and structural stability.

[0044] Example 2

[0045] Similar to Example 1, by simply replacing the elemental iridium with iridium oxide, iridium chloride, iridium acetate, or iridium acetylacetonate, while keeping other reaction conditions unchanged, monolayer iridium oxide nanosheets with masses of 0.43 g, 0.41 g, 0.44 g, and 0.43 g, respectively, and nanosheet thicknesses of 0.49 nm, 0.47 nm, 0.51 nm, and 0.52 nm, respectively, were obtained. The resulting product achieved a strength of 10 mA / cm². 2 The overpotentials for the current densities were 248mV, 251mV, 253mV, and 249mV, respectively.

[0046] Example 3

[0047] Similar to Example 1, only the B element source Na2CO3 in the precursor synthesis step was replaced with an equimolar amount of ZnO, while all other reaction conditions and operating steps remained unchanged, to prepare layered iridium K. 0.5 (Zn 0.33 Ir 0.67 Using O2 as a precursor, 0.42 g of monolayer iridium oxide nanosheets were ultimately obtained, with a thickness of 0.46 nm. These nanosheets achieved a strength of 10 mA / cm² in the acidic oxygen-generating reaction. 2 The overpotential at the current density is 249 mV.

[0048] Example 4

[0049] Similar to Example 1, the only difference is that the 0.1 mol / L acetic acid solution in the proton exchange step is replaced with an equal volume and concentration of citric acid solution (pH=3.2). All other reaction conditions, operating steps, and raw material amounts remain unchanged. This yields 0.4 g of monolayer iridium oxide nanosheets with a thickness of 0.54 nm, achieving a performance of 10 mA / cm² in the acidic oxygen generation reaction. 2 The overpotential of the current density is 250mV.

[0050] Example 5

[0051] Similar to Example 1, the only difference is that the 0.5 mol / L HClO4 and 0.01 mol / L ammonium fluoride mixture in the proton exchange step is replaced with an equal volume and equal hydrogen ion concentration of 0.5 mol / L hydrochloric acid and 0.01 mol / L ammonium fluoride mixture. All other reaction conditions, operating steps, and raw material amounts remain unchanged. This method ultimately yields 0.43 g of monolayer iridium oxide nanosheets with a thickness of 0.52 nm, achieving an efficiency of 10 mA / cm² in acidic oxygen generation reactions. 2 The overpotential at the current density is 253 mV.

[0052] Example 6

[0053] Similar to Example 1, the only difference was that the hexadecyltrimethylammonium chloride-polyethylene glycol composite dispersant in the stripping step was replaced with an equal mass of hexadecyltrimethylammonium bromide (CTAB)-polyvinylpyrrolidone (PVP) composite dispersant (mass ratio 1:3). All other reaction conditions, operating steps, and raw material amounts remained unchanged. This yielded 0.42 g of monolayer iridium oxide nanosheets with a thickness of 0.49 nm, achieving a performance of 10 mA / cm² in the acidic oxygen generation reaction. 2 The overpotential at the current density is 248 mV.

[0054] Example 7

[0055] Similar to Example 1, only the ball milling process parameters in the exfoliation step were replaced from 350 r / min for 18 h to 400 r / min for 12 h. All other ball milling stage parameters, reaction conditions, operating steps, and raw material amounts remained unchanged. This yielded 0.44 g of single-atom-layer iridium oxide nanosheets with a thickness of 0.51 nm, achieving a performance of 10 mA / cm² in the acidic oxygen generation reaction. 2 The overpotential at the current density is 251 mV.

[0056] Example 8

[0057] Similar to Example 1, only the amount of homologous metal chloride confinement agent added in the precursor synthesis step was replaced from 2 wt% to 1 wt%, while all other reaction conditions, operating steps, and raw material amounts remained unchanged. The final result was 0.4 g of monolayer iridium oxide nanosheets with a thickness of 0.48 nm, achieving a performance of 10 mA / cm² in the acidic oxygen generation reaction. 2 The overpotential at the current density is 249 mV.

[0058] Example 9

[0059] Similar to Example 1, only the highest sintering temperature in the precursor synthesis step was replaced from 1050℃ to 1000℃, while the holding time remained at 24h. All other reaction conditions, operating steps, and raw material amounts remained unchanged. The final result was 0.43g of monolayer iridium oxide nanosheets with a thickness of 0.52nm, achieving a performance of 10mA / cm² in the acidic oxygen generation reaction. 2 The overpotential at the current density is 253 mV.

[0060] Example 10

[0061] Similar to Example 1, by simply changing the calcination time to 20 hours while keeping other reaction conditions and reactant amounts unchanged, the same product as in Example 1 can be obtained, with a mass of 0.44 g and a nanosheet thickness of 0.49 nm. This nanosheet achieves a performance of 10 mA / cm² in the acidic oxygen generation reaction. 2 The overpotential of the current density is 250mV.

[0062] Example 11

[0063] Similar to Example 1, only the ethanol-isopropanol mixed solvent (3:1) in the stripping step was replaced with an equal volume of ethylene glycol-isopropanol mixed solvent (volume ratio 3:1). All other reaction conditions, operating steps, and raw material amounts remained unchanged. The final result was 0.45 g of monolayer iridium oxide nanosheets with a thickness of 0.54 nm, achieving a performance of 10 mA / cm² in the acidic oxygen generation reaction. 2 The overpotential at the current density is 251 mV.

[0064] In summary, this invention achieves the preparation of single-atom-layer iridium oxide nanosheets through three core processes: gradient solid-state sintering, stepwise proton exchange, and shear ball milling. Examples 1-11 demonstrate that changing the source of raw materials and adjusting process parameters within a certain range has no impact on the preparation of single-atom-layer iridium oxide nanosheets. The final nanosheets have a thickness of approximately 0.5 nm and achieve 10 mA / cm² in the acidic oxygen-generating reaction. 2 The overpotential at current density is approximately 250mV.

Claims

1. A method for preparing a single-atom-layer iridium oxide nanosheet, comprising the following steps: (1) Two-step gradient solid-state synthesis of A 0.5 (B 0.33 Ir 0.67 O2 precursor: Weigh the Ir source, B element source, and A element compound according to the stoichiometric ratio, add 1-3 wt% anhydrous ethanol to the above raw materials, and wet grind for 2-4 hours until uniformly mixed. Pre-sinter the resulting mixed powder at a rate of 2-5 °C / min to 400-600 °C for 2-6 hours, and then naturally cool to 20-30 °C to obtain the pre-sintered material. Grind the pre-sintered material again, then add 1-3 wt% of the pre-sintered material containing a homologous metal chloride confining agent. First, heat to 700-900 °C at a rate of 1-3 °C / min and hold for 4-8 hours to complete crystallization. Then, heat to 950-1100 °C at a rate of 0.5-2 °C / min and hold for 12-24 hours. Finally, naturally cool to 20-30 °C to obtain pure-phase layered iridium salt A. 0.5 (B 0.33 Ir 0.67 O2 precursor; among which, A is one or more of alkali metals and alkaline earth metals, and B is one or more of Li, Na, Mn, Co, Ni, Zn, and Ru. (2) Gradient stepwise proton exchange: The A obtained in step (1) 0.5 (B 0.33 Ir 0.67 O2 precursor is added to a low-concentration acid solution of 0.05~0.2 mol / L, A 0.5 (B 0.33 Ir 0.67 The ratio of O2 precursor mass to low-concentration acid solution volume is 1g: 50-100mL. The mixture is stirred and soaked at 60-100 rpm for 12-24 hours to selectively exchange A-site cations in the interlayer and widen the interlayer spacing. Then, it is washed 2-4 times by centrifugation with deionized water. The precipitate is added to a mixture of a weak ligand at 0.005-0.02 mol / L and an inorganic acid at 0.5-1 mol / L, and stirred and soaked for 24-72 hours to completely dissolve the B-site cations in the honeycomb center. Simultaneously, the weak ligand locks the IrO6 framework structure. The mixture is then washed multiple times with deionized water until neutral. The precipitate is dried at 50-70℃ for 10-15 hours to obtain protonated layered iridium oxide H. 0.83 Ir 0.67 O2; (3) Shear ball milling peeling: The H obtained in step (2) 0.83 Ir 0.67 O2, intercalation dispersant, mixed-size ZrO2 microspheres, and mixed alcohol solvent are mixed at a mass ratio of 10:1~2:40~60:180~220 and ball milled at a speed gradient to achieve non-destructive ultimate exfoliation. The ball milling product is filtered to remove the ZrO2 microspheres, and the resulting suspension is purified by two-step centrifugation and fractionation. The resulting precipitate is redispersed in deionized water and then freeze-dried to obtain the single-atom-layer iridium oxide nanosheets of the present invention.

2. The method for preparing a single-atom-layer iridium oxide nanosheet as described in claim 1, characterized in that: In step (1), the ratio of the total number of moles of Ir and B elements to the number of moles of A element is 2:1; layered iridium salt A 0.5 (B 0.33 Ir 0.67 The number of moles n of the O2 precursor, and the H in the low-concentration acid solution and inorganic acid mixture used for proton exchange. + The molar ratio of the number of moles m is 1:1~20.

3. The method for preparing a single-atom-layer iridium oxide nanosheet as described in claim 1, characterized in that: In step (1), the Ir source is one or a mixture of several of iridium oxide, iridium chloride, iridium hydroxyoxide, iridium acetate, iridium acetylacetonate, chloroiridium acid, potassium hexachloroiridium, and sodium hexachloroiridium; the A element compound is one or a mixture of the carbonates, phosphates, hydroxides, chlorides, and nitrates corresponding to K, Mg, Ca, Sr, and Ba; and the B element source is one or a mixture of the oxides, chlorides, hydroxides, carbonates, acetates, and acetylacetonates corresponding to Li, Na, Mn, Co, Ni, Zn, and Ru.

4. The method for preparing a single-atom-layer iridium oxide nanosheet as described in claim 1, characterized in that: In step (1), the homologous metal chloride confinement agent is one or a mixture of several of the chlorides that are homologous to the A-site element, such as potassium chloride, magnesium chloride, strontium chloride, calcium chloride, and barium chloride.

5. The method for preparing a single-atom-layer iridium oxide nanosheet as described in claim 1, characterized in that: In step (2), the low-concentration acid solution is one or a mixture of several of the following: acetic acid solution, citric acid solution, hydrochloric acid solution, sulfuric acid solution, and perchloric acid solution; the weak ligand is one or a mixture of several of the following: ammonium fluoride, ammonium fluoroborate, and potassium fluoride; and the inorganic acid is one or a mixture of several of the following: hydrochloric acid, sulfuric acid, and perchloric acid.

6. The method for preparing a single-atom-layer iridium oxide nanosheet as described in claim 1, characterized in that: In step (3), the intercalation dispersant is a composite system composed of two or more of the following: alkyltrimethylammonium chloride with a carbon chain length of 12-18, alkyltrimethylammonium bromide with a carbon chain length of 12-18, sodium alkylbenzene sulfonate with a carbon chain length of 12-18, polyvinylpyrrolidone, and polyethylene glycol monomethyl ether.

7. The method for preparing a single-atom-layer iridium oxide nanosheet as described in claim 1, characterized in that: In step (3), mixed-size ZrO2 microspheres with a diameter of 0.1~0.5 mm are used as grinding media and are mixed in different particle size ratios; the mixed alcohol is a mixture of two or more of anhydrous ethanol, isopropanol, ethylene glycol, propylene glycol and glycerol.

8. The method for preparing a single-atom-layer iridium oxide nanosheet as described in claim 1, characterized in that: In step (3), the ball milling with a speed gradient is performed at 150~250 r / min for 0.5~3 h, then at 300~400 r / min for 12~24 h, and finally at 450~550 r / min for 0.5~3 h, with the temperature controlled at ≤30℃ throughout the process, and a 10~20 min pause for heat dissipation after every 30 min of ball milling; the two-step centrifugal fractionation purification involves centrifuging the suspension at 2000~4000 rpm for 15~30 min and collecting the supernatant, then centrifuging the supernatant at 10000~15000 rpm for 20~40 min and collecting the precipitate; the freeze-drying temperature is -10℃~-50℃ and the time is 24~48 h.

9. A single-atom-layer iridium oxide nanosheet, characterized in that, The nanosheets are prepared by the preparation method according to any one of claims 1 to 7, wherein the thickness is 0.4 to 0.5 nm, and the framework is formed by connecting IrO6 octahedra in a common edge manner to form a graphene-like honeycomb topology.

10. The application of the single-atom-layer iridium oxide nanosheets according to claim 9 in the electrocatalytic acidic oxygen evolution reaction.

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