Nanometer low-iridium high-entropy oxide, preparation method and application thereof

Abstract

This invention provides a nano-low-iridium high-entropy oxide, its preparation method, and its application, which have the following advantages: (1) Preparation method: A high diffusion reaction environment is constructed, and the formation of high-entropy metal oxides at low temperature is achieved through kinetic acceleration, avoiding high-temperature sintering and facilitating the generation of two-dimensional nanostructures; (2) Two-dimensional high-entropy structure: The two-dimensional nanostructure fully exposes the active sites, and the high configurational entropy improves the intrinsic activity and dispersion of iridium and ruthenium sites, reducing the amount of iridium used while maintaining high activity; the high-entropy effect and delayed diffusion effect inhibit element segregation and improve stability. (3) Catalytic application: The nano-low-iridium high-entropy oxide can achieve a dual improvement in activity and stability in processes such as oxygen evolution reaction, urea oxidation, and biomass oxidation.

Description

Technical Field

[0001] This invention relates to the field of high-entropy oxide technology, and in particular to a nano-low-iridium high-entropy oxide, its preparation method, and its application. Background Technology

[0002] Iridium-based nano-oxides, due to their unique electronic structure, high catalytic activity, and stability, have important applications in many cutting-edge technological fields, such as electrocatalysis and energy conversion, environmental catalysis, electronic devices and sensing, biomedicine, photoelectrochemistry and solar energy utilization, and high-temperature and extreme environment applications. However, despite their wide range of applications, the following factors severely limit their development and application: 1. The scarcity of iridium resources leads to high costs for iridium-based nano-oxides; 2. The complex preparation process of iridium-based nano-oxides results in high production costs and low production efficiency, failing to meet the requirements of technological development; 3. The poor catalytic activity and high-temperature stability of iridium-based nano-oxides make them prone to deactivation, limiting their lifespan. In recent years, high-entropy oxides have attracted widespread attention due to their unique "multi-principal synergistic effect" and "entropy-stabilized structure." High-entropy oxides consist of five or more metal elements in a near equimolar ratio forming a single solid solution phase. Their high configurational entropy can suppress elemental segregation and enhance structural stability; the electronic coupling between the multi-component components can optimize the electronic structure of active sites, while forming abundant defect sites through lattice distortion, further enhancing intrinsic catalytic activity. However, existing methods for synthesizing high-entropy oxides (such as the sol-gel method and high-temperature solid-state method) still face problems such as uneven element distribution and severe sintering at high temperatures, resulting in insufficient exposure of active sites. Therefore, how to improve the exposure of active sites and thus improve the performance of high-entropy oxides has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0003] The purpose of this invention is to provide a nano-low-iridium high-entropy oxide, its preparation method, and its application. The nano-low-iridium high-entropy oxide prepared by the method provided by this invention has a two-dimensional nanosheet morphology and exhibits excellent oxidation performance and good stability.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing nano-low iridium high-entropy oxides, comprising the following steps: (1) The metal salt precursor is mixed in a solvent and then dried to obtain a uniformly dispersed mixed powder; the metal salt precursor includes an iridium salt precursor, a ruthenium salt precursor and a mixed metal salt; the mixed metal salt is a mixture of iron salt, chromium salt, cobalt salt, sodium salt, nickel salt, copper salt and manganese salt, including at least iron salt, chromium salt and cobalt salt; the molar ratio of the iridium salt precursor, ruthenium salt precursor, iron salt, chromium salt and cobalt salt is (0.01~10):(0.01~10):(0.01~10):(0.01~10):(0.01~10); (2) The uniformly dispersed mixed powder from step (1) is mixed with molten salt and then calcined and cooled sequentially to obtain nano-low iridium high entropy oxide; The calcination temperature in step (2) is 300~1000℃, and the calcination time is 0.1~50h; The mass percentage of iridium in the nano-low iridium high entropy oxide is 1-99%.

[0005] Preferably, the iridium precursor in step (1) includes any one or more of iridium tetrachloride, iridium trichloride or its hydrate, iridium chloroacetate or its hydrate, ammonium iridium chloroacetate, potassium iridium chloroacetate, sodium iridium chloroacetate, potassium iridium bromoiritate, sodium iridium bromoiritate, iridium tricarbonyl chloride, tetrairidium dodecylcarbonyl and iridium iodide.

[0006] Preferably, the ruthenium precursor in step (1) includes any one or more of ruthenium trichloride or its hydrate, ammonium ruthenium chlororuthenate, potassium ruthenium chlororuthenate, sodium ruthenium chlororuthenate, ruthenium acetylacetone, ruthenium acetate, ruthenium bromide, ruthenium iodide, potassium perruthenium, ruthenium hexacarbonyl chloride, ruthenium dodecyltriruthenium, ruthenium red tetrahydrate, and ruthenium nitrosoacetate.

[0007] Preferably, in step (1), the sodium salt is sodium nitrate, sodium sulfate, or sodium chloride; the nickel salt is nickel nitrate hexahydrate, nickel chloride hexahydrate, or nickel sulfate hexahydrate; the copper salt is copper nitrate dihydrate, copper sulfate pentahydrate, or copper chloride dihydrate; the manganese salt is manganese nitrate hydrate, manganese sulfate hydrate, or manganese chloride tetrahydrate; the iron salt is any one of ferric nitrate nonahydrate, ferric sulfate, and ferric chloride; the chromium salt is chromium nitrate hexahydrate, chromium chloride hexahydrate, or chromium sulfate; and the cobalt salt is cobalt nitrate hexahydrate, cobalt chloride, or cobalt sulfate.

[0008] Preferably, the molten salt in step (2) includes any one or more of sodium chloride, sodium bromide, sodium nitrate, sodium carbonate, potassium chloride, potassium bromide, potassium nitrate, and potassium carbonate.

[0009] This invention provides nano-low iridium high entropy oxide prepared by the preparation method described in the above technical solution.

[0010] Preferably, the morphology of the nano-low iridium high entropy oxide is a two-dimensional nanosheet.

[0011] This invention provides the application of the nano-low iridium high entropy oxide described above in electrocatalysis and energy conversion, environmental catalysis, electronic devices and sensing, biomedicine and photoelectrochemistry and solar energy utilization.

[0012] Preferably, the electrocatalysis and energy conversion include water electrolysis for hydrogen production, fuel cells, and metal-air batteries; the environmental catalysis includes pollutant degradation and vehicle exhaust purification; the electronic devices and sensors are resistive random access memory; the biomedical aspect is biosensing; and the photoelectrochemistry and solar energy utilization are photoelectrochemical cells.

[0013] Preferably, the application method of the electrolysis of water to produce hydrogen is hydrogen production by oxygen evolution reaction or hydrogen production by total water electrolysis; The fuel cell is used in the cathode oxygen reduction reaction and / or to directly prepare a methanol fuel cell; The metal-air battery is used as an air electrode catalyst. The pollutant degradation is applied in the oxidation of organic matter or wastewater treatment. The application of the automotive exhaust purification method is for the preparation of a three-way catalytic converter; The resistive random access memory is used as an electrode material; The application of the biosensor is for the electrochemical detection of biomolecules; The photoelectrochemical cell is used as a co-catalyst for water oxidation.

[0014] This invention provides a method for preparing nano-low iridium high-entropy oxides, comprising the following steps: (1) mixing a metal salt precursor in a solvent and then drying it to obtain a uniformly dispersed mixed powder; the metal salt precursor includes an iridium salt precursor, a ruthenium salt precursor, and a mixed metal salt; the mixed metal salt is a mixture of iron salt, chromium salt, cobalt salt, sodium salt, nickel salt, copper salt, and manganese salt, including at least iron salt, chromium salt, and cobalt salt; the molar ratio of the iridium salt precursor, ruthenium salt precursor, iron salt, chromium salt, and cobalt salt is (0. .01~10): (0.01~10): (0.01~10): (0.01~10): (0.01~10); (2) The uniformly dispersed mixed powder in step (1) is mixed with molten salt and then calcined and cooled sequentially to obtain nano-low iridium high entropy oxide; the calcination temperature in step (2) is 300~1000℃ and the calcination time is 0.1~50h; the mass percentage content of iridium in the nano-low iridium high entropy oxide is 1~99%. The preparation method provided by this invention can provide a high diffusion rate reaction environment at relatively low temperatures, accelerating the kinetics of high-entropy metal oxide formation. This allows for the generation of high-entropy metal oxides at low temperatures (≤1000℃), effectively avoiding material sintering at high temperatures (≥1500℃), facilitating the formation of two-dimensional nanostructures, ensuring sufficient exposure of active sites, and simultaneously improving catalytic activity and stability. Iridium and ruthenium exhibit high activity in oxidation reactions. Constructing a high-entropy solid solution phase can increase the configurational entropy, resulting in highly dispersed IrRu sites and enhanced activity. The formation of two-dimensional nanostructures fully exposes active sites, reducing the amount of Ir required while achieving performance similar to pure Ir-based catalysts. Furthermore, the nano-low-iridium high-entropy oxides can suppress elemental segregation through high-entropy and delayed diffusion effects, effectively improving catalytic stability, ultimately achieving a dual improvement in activity and stability, exhibiting excellent performance in various oxidation processes. The results of the examples show that the preparation method provided by this invention yields nano-low-iridium high-entropy oxides with a mesoporous range of 2~50 nm, achieving 10 mA / cm² in OER reactions. 2 The overpotential of the current density is only 230 mV, indicating that it has excellent electrocatalytic OER performance; at the same time, after 5000 CV cycles, the current of the nano-low iridium high entropy oxide at a potential of 1.35V does not decay, indicating that the nano-low iridium high entropy oxide has good stability during application. Attached Figure Description

[0015] Figure 1 XRD pattern of the nano-low iridium high entropy oxide prepared in Example 1; Figure 2 TEM image of the nano-low iridium high entropy oxide prepared in Example 1; Figure 3 The image shows the elemental distribution of the nano-low iridium high-entropy oxide prepared in Example 1. Figure 4 LSV curve of the OER reaction of the nano-low iridium high entropy oxide prepared in Example 1; Figure 5 The CV cycle stability test curve of the nano-low iridium high entropy oxide prepared in Example 1 in the electrocatalytic OER reaction; Figure 6 The graph shows the conversion rate and yield of the nano-low iridium high entropy oxide prepared in Example 1 in the photocatalytic biomass oxidation reaction; Figure 7 The LSV curve of the nano-low iridium high entropy oxide prepared in Example 1 in the electrocatalytic urea oxidation reaction; Figure 8 LSV curve of the high-entropy oxide prepared in Comparative Example 1 in the electrocatalytic urea oxidation reaction; Figure 9 The CV cycle stability test curve of the high-entropy oxide prepared in Comparative Example 1 in the electrocatalytic OER reaction; Figure 10 LSV curves of the high-entropy oxide prepared in Comparative Example 2 in the electrocatalytic urea oxidation reaction; Figure 11 The CV cycle stability test curve of the high-entropy oxide prepared in Comparative Example 2 in the electrocatalytic OER reaction; Figure 12 LSV curve of the high-entropy oxide prepared in Comparative Example 3 in the electrocatalytic urea oxidation reaction; Figure 13 The CV cycle stability test curve of the high-entropy oxide prepared in Comparative Example 3 in the electrocatalytic OER reaction; Figure 14 LSV curves of the high-entropy oxide prepared in Comparative Example 4 in the electrocatalytic urea oxidation reaction; Figure 15 The CV cycle stability test curve of the high-entropy oxide prepared in Comparative Example 4 in the electrocatalytic OER reaction; Figure 16 LSV curves of the high-entropy oxide prepared in Comparative Example 5 in the electrocatalytic urea oxidation reaction; Figure 17 The CV cycle stability test curve of the high-entropy oxide prepared for Comparative Example 5 in the electrocatalytic OER reaction. Detailed Implementation

[0016] This invention provides a method for preparing nano-low iridium high-entropy oxides, comprising the following steps: (1) The metal salt precursor is mixed in a solvent and then dried to obtain a uniformly dispersed mixed powder; the metal salt precursor includes an iridium salt precursor, a ruthenium salt precursor and a mixed metal salt; the mixed metal salt is a mixture of iron salt, chromium salt, cobalt salt, sodium salt, nickel salt, copper salt and manganese salt, including at least iron salt, chromium salt and cobalt salt; the molar ratio of the iridium salt precursor, ruthenium salt precursor, iron salt, chromium salt and cobalt salt is (0.01~10):(0.01~10):(0.01~10):(0.01~10):(0.01~10); (2) The uniformly dispersed mixed powder from step (1) is mixed with molten salt and then calcined and cooled sequentially to obtain nano-low iridium high entropy oxide; The calcination temperature in step (2) is 300~1000℃, and the calcination time is 0.1~50h; The mass percentage of iridium in the nano-low iridium high entropy oxide is 1-99%.

[0017] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art or products prepared using preparation methods well known in the art.

[0018] In this invention, the metal salt precursor is mixed in a solvent and then dried to obtain a uniformly dispersed mixed powder.

[0019] In this invention, the metal salt precursor includes iridium salt precursor, ruthenium salt precursor and mixed metal salt.

[0020] In this invention, the iridium salt precursor preferably includes any one or more of iridium tetrachloride, iridium trichloride or its hydrate, iridium chloro-iridic acid or its hydrate, iridium acetate, ammonium iridium chloro-iridate, potassium iridium chloro-iridate, sodium iridium chloro-iridate, potassium iridium bromo-iridate, sodium iridium bromo-iridate, iridium tricarbonyl chloride, tetrairidium dodecylcarbonyl and iridium iodide, more preferably any one or more of iridium tetrachloride, iridium trichloride or its hydrate, iridium chloro-iridic acid, iridium acetate, ammonium iridium chloro-iridate, potassium iridium chloro-iridate and sodium iridium chloro-iridate.

[0021] In this invention, the ruthenium salt precursor preferably includes any one or more of ruthenium trichloride or its hydrate, ammonium ruthenium chlororuthenate, potassium ruthenium chlororuthenate, sodium ruthenium chlororuthenate, ruthenium acetylacetonate, ruthenium acetate, ruthenium bromide, ruthenium iodide, potassium perruthenium, ruthenium hexacarbonyl chloride, ruthenium dodecyltriruthenium, ruthenium red tetrahydrate, and ruthenium nitrosoacetate, more preferably any one or more of ruthenium trichloride or its hydrate, ammonium ruthenium chlororuthenate, potassium ruthenium chlororuthenate, sodium ruthenium chlororuthenate, and ruthenium acetylacetonate.

[0022] In this invention, the mixed metal salt is a mixture of iron, chromium, cobalt, sodium, nickel, copper, and manganese salts, including at least iron, chromium, and cobalt salts; the sodium salt is preferably sodium nitrate, sodium sulfate, or sodium chloride, more preferably sodium nitrate; the nickel salt is preferably nickel nitrate hexahydrate, nickel chloride hexahydrate, or nickel sulfate hexahydrate, more preferably nickel nitrate hexahydrate; the copper salt is preferably copper nitrate dihydrate, copper sulfate pentahydrate, or copper chloride dihydrate, more preferably copper nitrate dihydrate; the manganese salt is preferably manganese nitrate hydrate, manganese sulfate hydrate, or manganese chloride tetrahydrate, more preferably manganese nitrate hydrate; the iron salt is preferably any one of ferric nitrate nonhydrate, ferric sulfate, and ferric chloride, more preferably ferric nitrate nonhydrate; the chromium salt is preferably chromium nitrate hexahydrate, chromium chloride hexahydrate, or chromium sulfate, more preferably chromium nitrate hexahydrate; the cobalt salt is preferably cobalt nitrate hexahydrate, cobalt chloride, or cobalt sulfate, more preferably cobalt nitrate hexahydrate.

[0023] In this invention, the molar ratio of the iridium salt precursor, ruthenium salt precursor, iron salt, chromium salt and cobalt salt is (0.01~10):(0.01~10):(0.01~10):(0.01~10):(0.01~10), preferably (0.1~8):(0.1~8):(0.1~8):(0.1~8):(0.1~8), more preferably (1~5):(1~5):(1~5):(1~5):(1~5), and even more preferably (2~4):(2~4):(2~4):(2~4):(2~4):(2~4).

[0024] This invention uses the above-mentioned iridium and ruthenium precursors as raw materials, which have good solubility, which helps to mix them evenly and form a uniform high-entropy material in the subsequent calcination process; by screening specific transition metal combinations and introducing a lattice stress regulation mechanism, the dynamic optimization of active sites can be achieved.

[0025] In this invention, the solvent is preferably one or more of water, ethanol, methanol, and isopropanol, more preferably water. By employing the above-mentioned dissolution method, this invention can give the metal precursor good dissolving ability, while the solvent can evaporate quickly, facilitating subsequent drying.

[0026] In this invention, the preferred molar ratio of the iridium precursor to the solvent is (0.01~10) mmol:(10~30) mL, more preferably (0.1~8) mmol:(15~25) mL, and even more preferably (1~5) mmol:20 mL; the preferred molar ratio of the ruthenium precursor to the solvent is (0.01~10) mmol:(10~30) mL, more preferably (0.1~8) mmol:(15~25) mL, and even more preferably (1~5) mmol:20 mL. ol: 20 mL; the preferred ratio of the amount of iron salt to the volume of solvent is (0.01~10) mmol: (10~30) mL, more preferably (0.1~8) mmol: (15~25) mL, and even more preferably (1~5) mmol: 20 mL; the preferred ratio of the amount of chromium salt to the volume of solvent is (0.01~10) mmol: (10~30) mL, more preferably (0.1~8) mmol: (15~25) mL, and even more preferably (1~5) mmol: 20 mL; the preferred ratio of the amount of cobalt salt to the volume of solvent is (0.01~10) mmol:(10~30) mL, more preferably (0.1~8) mmol:(15~25) mL, and even more preferably (1~5) mmol:20 mL; the preferred ratio of the amount of nickel salt to the volume of solvent is (0.01~10) mmol:(10~30) mL, more preferably (0.1~8) mmol:(15~25) mL, and even more preferably (1~5) mmol:20 mL. mL; the preferred ratio of the amount of copper salt to the volume of solvent is (0.01~10) mmol:(10~30) mL, more preferably (0.1~8) mmol:(15~25) mL, and even more preferably (1~5) mmol:20 mL; the preferred ratio of the amount of manganese salt to the volume of solvent is (0.01~10) mmol:(10~30) mL, more preferably (0.1~8) mmol:(15~25) mL, and even more preferably (1~5) mmol:20 mL. This invention, by controlling the amount of mixed metal salts used, facilitates their dissolution in the solvent and the formation of a uniformly mixed solution.

[0027] This invention does not impose any particular limitation on the specific method of mixing, as long as the components are mixed evenly. In one embodiment, the mixing method can be stirring; the stirring time can be 10-60 minutes, for example, 20 minutes, 30 minutes, 40 minutes, or 50 minutes. This invention does not impose any particular limitation on the stirring rate; it can be determined based on the technical knowledge of those skilled in the art, as long as it avoids solution splashing.

[0028] In this invention, the drying method is preferably drying using a forced-air drying oven or rotary steaming. This invention does not have any particular limitation on the source of the equipment used for drying; commercially available forced-air drying ovens or rotary steaming equipment well-known to those skilled in the art can be used.

[0029] In this invention, the drying temperature is preferably 20-90°C. As one embodiment of this invention, the drying temperature can be 30°C, 40°C, 50°C, 60°C, 70°C, or 80°C. This invention does not have a specific limitation on the drying time, as long as constant weight is achieved. This invention removes solvents through drying.

[0030] After obtaining a uniformly dispersed mixed powder, the present invention mixes the uniformly dispersed mixed powder with molten salt and then calcines and cools it sequentially to obtain nano-low iridium high entropy oxide.

[0031] In this invention, the molten salt preferably includes any one or more of sodium chloride, sodium bromide, sodium nitrate, sodium carbonate, potassium chloride, potassium bromide, potassium nitrate, and potassium carbonate, more preferably sodium nitrate; the mass ratio of the iridium precursor to the molten salt is preferably (0.01~10) mmol:(1~5) g, more preferably (0.1~8) mmol:(2~4) g, and even more preferably (1~5) mmol:3 g. This invention does not have a specific limitation on the temperature of the molten salt, as long as it allows the metal salt to be in a molten state. This invention uses the aforementioned molten salt to accelerate the kinetics of high-entropy metal oxide formation, thereby generating high-entropy metal oxides at low temperatures (≤1000℃), effectively avoiding the performance degradation caused by catalyst sintering at high temperatures (≥1500℃), resulting in more stable nano-low-iridium high-entropy oxides with better catalytic performance.

[0032] In this invention, the calcination temperature is 300~1000℃; the calcination time is 0.1~50h; and the cooling method after calcination is preferably air cooling or wind cooling. As one embodiment of this invention, the calcination temperature can be 400℃, 500℃, 600℃, 700℃, 800℃, or 900℃; the calcination time can be 0.5h, 1h, 5h, 10h, 15h, 20h, 25h, 30h, 35h, 40h, or 45h; and the heating rate to the calcination temperature can be 1~100℃ / min, or even 5℃ / min, 10℃ / min, 20℃ / min, 30℃ / min, 40℃ / min, 50℃ / min, 60℃ / min, 70℃ / min, 80℃ / min, or 90℃ / min. By employing the above-mentioned process, this invention can obtain a highly crystalline mesoporous structure while reducing energy consumption, thereby significantly improving the unit mass activity and electrolysis tolerance.

[0033] In this invention, the cooling is preferably performed to cool to room temperature within 10 minutes. This invention does not impose any specific limitations on the cooling method, as long as the cooling rate requirement is met.

[0034] The present invention preferably further includes sequentially filtering and drying the cooled product. The present invention does not impose any particular limitations on the specific operations of the filtering and drying; any filtering and drying method well-known to those skilled in the art can be used to remove impurities.

[0035] In this invention, the weight percentage content of iridium in the nano-low-iridium high-entropy oxide is 1-99%. As one embodiment of this invention, the weight percentage content of iridium in the nano-low-iridium high-entropy oxide can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%. In this invention, iridium and ruthenium exhibit high activity for the OER reaction and are the main reactive sites. By constructing an IrRu high-entropy solid solution phase, IrRu sites can be highly dispersed, exposing a large number of active sites, reducing the amount of Ir used while achieving performance similar to pure Ir-based catalysts. Furthermore, the nano-low-iridium high-entropy oxide can effectively improve catalytic stability through the high-entropy effect and delayed diffusion effect, ultimately achieving a dual improvement in activity and stability.

[0036] The preparation method provided by this invention can provide a reaction environment with a high diffusion rate at a relatively low temperature, accelerating the kinetics of high-entropy metal oxide formation. This allows for the generation of high-entropy metal oxides at low temperatures (≤1000℃), effectively avoiding material sintering at high temperatures (≥1500℃). This facilitates the formation of two-dimensional nanostructures, ensuring full exposure of active sites and simultaneously improving catalytic activity and stability. Iridium and ruthenium have high activity in oxidation reactions. By constructing a high-entropy solid solution phase, the configurational entropy can be increased, resulting in highly dispersed IrRu sites and enhanced activity. The formation of two-dimensional nanostructures can fully expose active sites, reducing the amount of Ir required while achieving performance similar to pure Ir-based catalysts. Furthermore, the nano-low-iridium high-entropy oxides can also suppress elemental segregation through high-entropy and delayed diffusion effects, effectively improving catalytic stability. Ultimately, this achieves a dual improvement in activity and stability, exhibiting excellent performance in various oxidation processes.

[0037] The present invention also provides nano-low iridium high entropy oxide prepared by the preparation method described in the above technical solution.

[0038] In this invention, the morphology of the nano-low-iridium high-entropy oxide is preferably two-dimensional nanosheets. The nano-low-iridium high-entropy oxide provided by this invention has a relatively stable nanostructure and, when subsequently applied in the field of water electrolysis, possesses a large number of IrRu oxide catalytic active sites, which helps to promote the oxygen evolution reaction.

[0039] This invention also provides the application of the nano-low iridium high entropy oxide described above in electrocatalysis and energy conversion, environmental catalysis, electronic devices and sensing, biomedicine and photoelectrochemistry and solar energy utilization.

[0040] In this invention, the electrocatalysis and energy conversion preferably include water electrolysis for hydrogen production, fuel cells, and metal-air batteries; the application of water electrolysis for hydrogen production is preferably oxygen evolution reaction (OER) or overall water splitting for hydrogen production; the application of the fuel cell is preferably cathode oxygen reduction reaction (ORR) and / or direct methanol fuel cell (DMFC); the application of the metal-air battery is preferably as an air electrode catalyst.

[0041] In this invention, the environmental catalysis preferably includes pollutant degradation and vehicle exhaust purification; the pollutant degradation is preferably applied to organic matter oxidation or wastewater treatment; the organic matter preferably includes biomass or urea; and the vehicle exhaust purification is preferably applied to the preparation of a three-way catalytic converter.

[0042] In this invention, the electronic device and sensor are preferably resistive random access memory (RRAM); the resistive random access memory is preferably used as an electrode material.

[0043] In this invention, the biomedical aspect is preferably biosensing; and the application of the biosensing is preferably for the electrochemical detection of biomolecules.

[0044] In this invention, the photoelectrochemistry and solar energy utilization are preferably photoelectrochemical cells (PECs); the photoelectrochemical cells are preferably used as co-catalysts for water oxidation.

[0045] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0046] Example 1 A method for preparing a nano-low-iridium, high-entropy oxide comprises the following steps: (1) 0.1 mmol of chloroiridic acid, 0.1 mmol of ruthenium chloride, 0.1 mmol of ferric nitrate nonahydrate, 0.1 mmol of chromium nitrate hexahydrate and 0.1 mmol of cobalt nitrate hexahydrate were dissolved in 20 mL of water and stirred for 30 min. Then they were dried in an oven at 80 °C to obtain a uniformly dispersed mixed powder. (2) Add 3g of sodium nitrate to the crucible, and then heat it to 350°C in a muffle furnace until the sodium nitrate melts to obtain molten salt. Add the uniformly dispersed mixed powder obtained in step (1) to the molten salt and calcine it at 350°C for 2 hours. Then cool it to room temperature within 10 minutes. Finally, filter and dry it to obtain a two-dimensional nano-low iridium high entropy oxide.

[0047] Figure 1 The image shows the XRD pattern of the low-iridium, high-entropy oxide nanoparticles prepared in Example 1 of this invention. Figure 1 It can be seen that the nano-low iridium high-entropy oxide prepared by this invention is a single solid solution phase (PDF#24-0326), proving that it is a high-entropy phase.

[0048] Figure 2 and Figure 3 TEM images and corresponding elemental distributions of the nano-low-iridium high-entropy oxide prepared in Example 1 of this invention. Figure 2 It can be seen that the nano-low iridium high-entropy oxide prepared in this invention has a two-dimensional nanosheet structure. Figure 3 It can be seen that in the nano-low iridium high entropy oxide, Ir, Ru, Co, Fe, Cr and O elements are uniformly distributed without obvious segregation.

[0049] The low-iridium high-entropy oxide nanoparticles prepared in Example 1 were subjected to LSV (electrochemical testing method) testing for the OER reaction. The testing method was as follows: 1) The nano-low iridium high entropy oxide prepared in Example 1 was treated in 0.5 mol / L sulfuric acid at 80°C for 30 min, and then filtered, washed and dried sequentially. 2 mg of the treated nano-low iridium high entropy oxide was taken, and then 100 μL of deionized water, 100 μL of ethanol and 10 μL of 5% Nafion solution were added. The mixture was ultrasonically treated in an ultrasonic bath for 1 h to form a uniform catalyst dispersion. Subsequently, 3 μL of the catalyst dispersion was dropped onto a glassy carbon electrode with a diameter of 3 mm. After natural drying, it was used for LSV testing. 2) In the LSV test, 0.5 mol / L sulfuric acid was used as the electrolyte. A platinum sheet electrode was used as the counter electrode, and a Hg / Hg₂SO₄ electrode was used as the reference electrode. The scan range was 1.3~1.5 V vs RHE, and the scan rate was 5 mV / s. The LSV was cyclically scanned until the curves overlapped. The results obtained were as follows: Figure 4 As shown.

[0050] Figure 4 This is the LSV curve of the nano-low iridium high-entropy oxide prepared in Example 1 of the present invention. Figure 4 It can be seen that the nano-low iridium high-entropy oxide prepared by this invention has a performance of 10 mA / cm². 2 The overpotential is only 230 mV, indicating that it has excellent electrocatalytic OER performance.

[0051] The cyclic voltammetry (CV) test of the OER reaction was performed on the nano-low iridium high entropy oxide prepared in Example 1. The test method was as follows: 1) Take 5 mg of the nano-low iridium high-entropy oxide prepared in Example 1, then add 170 μL of deionized water, 300 μL of isopropanol and 30 μL of 5% Nafion solution, and sonicate in an ultrasonic bath for 0.5 h to form a uniform catalyst dispersion; then take 25 μL of the catalyst dispersion and dropwise add it to an active area of ​​0.5 × 0.5 cm. 2 The catalyst-loaded platinum-titanium felt was dried in an 80°C forced-air drying oven for 3 hours and then used for CV testing. 2) In the CV test, a 0.5 mol / L sulfuric acid solution was used as the electrolyte. A platinum sheet electrode was used as the counter electrode, and an Ag / AgCl electrode was used as the reference electrode. Before the CV test, an LSV test was performed on the electrode with a scan range of 0.55~1.35V and a scan rate of 5mV / s. The scan was repeated until the curves overlapped, and the curves were recorded. Then, a CV cycle test was performed on the electrode with the same scan range as the LSV test, a scan rate of 50mV / s, and 5000 scan cycles. After the CV cycle, the LSV test was performed again, and the current decay rate was obtained by comparing the curve with the LSV curve before the CV cycle. The results are as follows: Figure 5 As shown.

[0052] Figure 5 The image shows the CV cycle stability test curve of the nano-low iridium high-entropy oxide prepared in Example 1 of this invention. Figure 5 It can be seen that the nano-low iridium high entropy oxide prepared by this invention has no current decay at a potential of 1.35V after 5000 CV cycles, indicating that the nano-low iridium high entropy oxide has good stability in the application process.

[0053] The photocatalytic biomass oxidation of the nano-low iridium high-entropy oxide prepared in Example 1 was tested using the following method: 10 mg of the nano-low iridium high-entropy oxide prepared in Example 1 and 200 mg of xylose were dispersed in 20 mg of a 3 mol / L KOH solution. The resulting system was irradiated with a 10 W LED light source at 60 °C for 1 h. The conversion and yield obtained by high performance liquid chromatography after the reaction are shown in the figure below. Figure 6 As shown, by Figure 6It can be seen that the lactic acid yield is 86.3%, indicating that the nano-low iridium high entropy oxide prepared in this invention has good activity for photocatalytic biomass oxidation.

[0054] The nano-low iridium high-entropy oxide prepared in Example 1 was subjected to electrocatalytic urea oxidation testing. The testing method was as follows: 1) Take 5 mg of the nano-low iridium high-entropy oxide prepared in Example 1, then add 170 μL of deionized water, 300 μL of isopropanol and 30 μL of 5% Nafion solution, and sonicate in an ultrasonic bath for 0.5 h to form a uniform catalyst dispersion; then take 25 μL of the catalyst dispersion and dropwise add it to an active area of ​​0.5 × 0.5 cm. 2 The catalyst-loaded nickel foam was dried in a forced-air drying oven at 80°C for 3 hours and then used for CV testing. 2) In the LSV test, the electrolyte was a 1 mol / L KOH solution containing 0.33 mol / L urea. A graphite rod was used as the counter electrode, and an Ag / AgCl electrode was used as the reference electrode. Before the LSV test, CV activation was performed in a 1 mol / L KOH solution. The scan range was 0–1 V, the scan rate was 50 mV / s, and the number of scan cycles was 40. During the LSV test, the scan range was 0–1 V, and the scan rate was 5 mV / s. The results are as follows: Figure 7 As shown.

[0055] Depend on Figure 7 It can be seen that the overpotential of the nano-low iridium high entropy oxide prepared in Example 1 of the present invention is 1.02V in electrocatalytic urea oxidation, indicating that the prepared nano-low iridium high entropy oxide has good activity in electrocatalytic urea oxidation.

[0056] Comparative Example 1 A method for preparing a high-entropy oxide comprises the following steps: (1) 0.1 mmol of chloroiridic acid, 0.1 mmol of ferric nitrate nonahydrate, 0.1 mmol of chromium nitrate hexahydrate and 0.1 mmol of cobalt nitrate hexahydrate were dissolved in 20 mL of water and stirred for 30 min. Then they were dried in an oven at 80 °C to obtain a uniformly dispersed mixed powder. (2) Add 3g of sodium nitrate to the crucible, and then heat it to 350°C in a muffle furnace until the sodium nitrate melts to obtain molten salt. Add the uniformly dispersed mixed powder obtained in step (1) to the molten salt and calcine it at 350°C for 2 hours. Then cool it to room temperature within 10 minutes. Finally, filter and dry it to obtain high entropy oxide.

[0057] Figure 8 The LSV curve of the high-entropy oxide prepared in Comparative Example 1 in the electrocatalytic urea oxidation reaction. Figure 8It can be seen that its overpotential is 248mV, and its activity is lower than that of the nano-low iridium high entropy oxide prepared in Example 1.

[0058] Figure 9 The CV cycle stability test curves of the high-entropy oxide prepared in Comparative Example 1 in the electrocatalytic OER reaction are shown. Figure 9 It can be seen that the current decay rate is 3% after 5000 CV cycles, indicating that it has good stability.

[0059] Comparative Example 2 A method for preparing a high-entropy oxide comprises the following steps: (1) 0.1 mmol of ruthenium chloride, 0.1 mmol of ferric nitrate nonahydrate, 0.1 mmol of chromium nitrate hexahydrate and 0.1 mmol of cobalt nitrate hexahydrate were dissolved in 20 mL of water and stirred for 30 min. Then they were dried in an oven at 80 °C to obtain a uniformly dispersed mixed powder. (2) Add 3g of sodium nitrate to the crucible, and then heat it to 400℃ in a muffle furnace until the sodium nitrate melts to obtain molten salt. Add the uniformly dispersed mixed powder obtained in step (1) to the molten salt and calcine it at 400℃ for 2h. Then cool it to room temperature within 10min. Finally, filter and dry it to obtain high entropy oxide.

[0060] Figure 10 The LSV curve of the high-entropy oxide prepared in Comparative Example 2 in the electrocatalytic urea oxidation reaction. Figure 10 It can be seen that its overpotential is 233mV, and its activity is comparable to that of the nano-low iridium high entropy oxide prepared in Example 1.

[0061] Figure 11 The CV cycle stability test curves of the high-entropy oxide prepared in Comparative Example 2 in the electrocatalytic OER reaction are shown. Figure 11 It can be seen that the current decay rate after 5000 CV cycles is 42%, and its stability is lower than that of the nano-low iridium high entropy oxide prepared in Example 1.

[0062] Comparative Example 3 A method for preparing a high-entropy oxide comprises the following steps: (1) 0.2 mmol of chloroiridic acid, 0.2 mmol of ruthenium chloride, 0.2 mmol of ferric nitrate nonahydrate and 0.2 mmol of chromium nitrate hexahydrate were dissolved in 20 mL of water and stirred for 30 min. Then they were dried in an oven at 60 °C to obtain a uniformly dispersed mixed powder. (2) Add 3g of sodium nitrate to the crucible, and then heat it to 450°C in a muffle furnace until the sodium nitrate melts to obtain molten salt. Add the uniformly dispersed mixed powder obtained in step (1) to the molten salt and calcine it at 450°C for 1 hour. Then cool it to room temperature within 10 minutes. Finally, filter and dry it to obtain high entropy oxide.

[0063] Figure 12 The LSV curve of the high-entropy oxide prepared in Comparative Example 3 in the electrocatalytic urea oxidation reaction. Figure 12 It can be seen that its overpotential is 219mV, and its activity is higher than that of the nano-low iridium high entropy oxide prepared in Example 1. The reason may be that after removing a certain transition element, the proportion of highly active components such as Ir and Ru increases.

[0064] Figure 13 The CV cycle stability test curves of the high-entropy oxide prepared in Comparative Example 3 in the electrocatalytic OER reaction are shown. Figure 13 It can be seen that the current decay rate is 70% after 5000 CV cycles, and its stability is lower than that of the nano-low iridium high entropy oxide prepared in Example 1.

[0065] Comparative Example 4 A method for preparing a high-entropy oxide comprises the following steps: (1) 0.1 mmol of chloroiridic acid, 0.1 mmol of ruthenium chloride, 0.1 mmol of chromium nitrate hexahydrate and 0.1 mmol of cobalt nitrate hexahydrate were dissolved in 20 mL of water and stirred for 30 min. Then they were dried in an oven at 80 °C to obtain a uniformly dispersed mixed powder. (2) Add 3g of sodium nitrate to the crucible, and then heat it to 500℃ in a muffle furnace until the sodium nitrate melts to obtain molten salt. Add the uniformly dispersed mixed powder obtained in step (1) to the molten salt and calcine it at 500℃ for 0.5h. Then cool it to room temperature within 10min. Finally, filter and dry it to obtain high entropy oxide.

[0066] Figure 14 The LSV curves for the high-entropy oxide prepared in Comparative Example 4 during the electrocatalytic urea oxidation reaction are shown. Figure 14 It can be seen that its overpotential is 231mV, and its activity is comparable to that of the nano-low iridium high entropy oxide prepared in Example 1.

[0067] Figure 15 The CV cycle stability test curves for the high-entropy oxide prepared in Comparative Example 4 in the electrocatalytic OER reaction are shown. Figure 15 It can be seen that the current decay rate is 58% after 5000 CV cycles, and its stability is lower than that of the nano-low iridium high entropy oxide prepared in Example 1.

[0068] Comparative Example 5 A method for preparing a high-entropy oxide comprises the following steps: (1) 0.1 mmol of chloroiridic acid, 0.1 mmol of ruthenium chloride, 0.1 mmol of ferric nitrate nonahydrate and 0.1 mmol of cobalt nitrate hexahydrate were dissolved in 20 mL of water and stirred for 30 min. Then they were dried in an oven at 80 °C to obtain a uniformly dispersed mixed powder. (2) Add 3g of sodium nitrate to the crucible, and then heat it to 500℃ in a muffle furnace until the sodium nitrate melts to obtain molten salt. Add the uniformly dispersed mixed powder obtained in step (1) to the molten salt and calcine it at 500℃ for 0.5h. Then cool it to room temperature within 10min. Finally, filter and dry it to obtain high entropy oxide.

[0069] Figure 16 The LSV curve of the high-entropy oxide prepared in Comparative Example 5 in the electrocatalytic urea oxidation reaction. Figure 16 It can be seen that its overpotential is 238mV, and its activity is lower than that of the nano-low iridium high entropy oxide prepared in Example 1.

[0070] Figure 17 The CV cycle stability test curves of the high-entropy oxide prepared in Comparative Example 5 in the electrocatalytic OER reaction are shown. Figure 17 It can be seen that the current decay rate is 80% after 5000 CV cycles, and its stability is lower than that of the nano-low iridium high entropy oxide prepared in Example 1.

[0071] Based on the above analysis, and through the comparison of Example 1 and Comparative Examples 1-5, and... Figures 6-16The performance comparison shows that when the metal salt precursor is an iridium salt precursor, a ruthenium salt precursor, an iron salt, a chromium salt, or a cobalt salt, the prepared nano-low iridium high entropy oxide has high activity and low current decay rate after 5000 CV cycles, exhibiting good stability. However, in Comparative Examples 1 to 5, omitting any one of the iridium salt precursor, ruthenium salt precursor, iron salt, chromium salt, or cobalt salt affects both the activity and stability of the nano-low iridium high entropy oxide. For example, in Comparative Example 1, although the ruthenium salt precursor still exhibits good stability after omitting it, the current decay rate after 5000 CV cycles is still 3%, while in Example 1, there is no decay, and the activity is also reduced. In Comparative Example 2, omitting the iridium salt precursor did not significantly affect the activity, but the current decay rate after 5000 CV cycles was 42%, indicating a substantial decrease in stability. In Comparative Example 3, omitting the cobalt salt improved the activity of the high-entropy oxide, but the current decay rate after 5000 CV cycles reached 70%, resulting in a significant decrease in stability, failing to meet the technical requirements. In Comparative Examples 4 and 5, omitting the iron and chromium salts respectively resulted in a slight decrease in the activity of the high-entropy oxide, but the current decay rates after 5000 CV cycles were 58% and 80%, respectively, also showing a significant decrease in stability, failing to meet the technical requirements. Therefore, this invention, by using iridium salt precursors, ruthenium salt precursors, iron salts, chromium salts, and cobalt salts as raw materials to prepare nano-low-iridium high-entropy oxides, demonstrates that the synergistic effect of each metal element effectively improves the activity and stability of the nano-low-iridium high-entropy oxides. Omitting any component significantly impacts the performance of the nano-low-iridium high-entropy oxides.

[0072] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a nano-low-iridium high-entropy oxide, characterized in that, Includes the following steps: (1) The metal salt precursor is mixed in a solvent and then dried to obtain a uniformly dispersed mixed powder; the metal salt precursor includes an iridium salt precursor, a ruthenium salt precursor and a mixed metal salt; the mixed metal salt is a mixture of iron salt, chromium salt, cobalt salt, sodium salt, nickel salt, copper salt and manganese salt, including at least iron salt, chromium salt and cobalt salt; the molar ratio of the iridium salt precursor, ruthenium salt precursor, iron salt, chromium salt and cobalt salt is (0.01~10):(0.01~10):(0.01~10):(0.01~10):(0.01~10); (2) The uniformly dispersed mixed powder from step (1) is mixed with molten salt and then calcined and cooled sequentially to obtain nano-low iridium high entropy oxide; The calcination temperature in step (2) is 300~1000℃, and the calcination time is 0.1~50h; The mass percentage of iridium in the nano-low iridium high entropy oxide is 1-99%.

2. The preparation method according to claim 1, characterized in that, In step (1), the iridium precursor includes any one or more of iridium tetrachloride, iridium trichloride or its hydrate, iridium chloroacetate or its hydrate, iridium chloroiridate, ammonium iridium chloroiridate, potassium iridium chloroiridate, sodium iridium bromoiridate, iridium tricarbonyl chloride, tetrairidium dodecylcarbonyl and iridium iodide.

3. The preparation method according to claim 1, characterized in that, In step (1), the ruthenium precursor includes any one or more of ruthenium trichloride or its hydrate, ammonium ruthenium chlororuthenate, potassium ruthenium chlororuthenate, sodium ruthenium chlororuthenate, ruthenium acetylacetone, ruthenium acetate, ruthenium bromide, ruthenium iodide, potassium perruthenium, ruthenium hexacarbonyl chloride, ruthenium dodecyltriruthenium, ruthenium red tetrahydrate, and ruthenium nitrosoacetate.

4. The preparation method according to claim 1, characterized in that, In step (1), the sodium salt is sodium nitrate, sodium sulfate, or sodium chloride; the nickel salt is nickel nitrate hexahydrate, nickel chloride hexahydrate, or nickel sulfate hexahydrate; the copper salt is copper nitrate dihydrate, copper sulfate pentahydrate, or copper chloride dihydrate; the manganese salt is manganese nitrate hydrate, manganese sulfate hydrate, or manganese chloride tetrahydrate; the iron salt is any one of ferric nitrate nonahydrate, ferric sulfate, and ferric chloride; the chromium salt is chromium nitrate hexahydrate, chromium chloride hexahydrate, or chromium sulfate; and the cobalt salt is cobalt nitrate hexahydrate, cobalt chloride, or cobalt sulfate.

5. The preparation method according to claim 1, characterized in that, The molten salt in step (2) includes any one or more of sodium chloride, sodium bromide, sodium nitrate, sodium carbonate, potassium chloride, potassium bromide, potassium nitrate, and potassium carbonate.

6. The nano-low iridium high entropy oxide prepared by the preparation method according to any one of claims 1 to 5.

7. The nano-low-iridium high-entropy oxide according to claim 6, characterized in that, The morphology of the nano-low iridium high entropy oxide is a two-dimensional nanosheet.

8. The application of the nano-low iridium high entropy oxide described in claim 6 in electrocatalysis and energy conversion, environmental catalysis, electronic devices and sensing, biomedicine and photoelectrochemistry and solar energy utilization.

9. The application according to claim 8, characterized in that, The electrocatalysis and energy conversion include water electrolysis for hydrogen production, fuel cells, and metal-air batteries; the environmental catalysis includes pollutant degradation and vehicle exhaust purification; the electronic devices and sensors are resistive random access memory; the biomedicine is biosensing; and the photoelectrochemistry and solar energy utilization are photoelectrochemical cells.

10. The application according to claim 9, characterized in that, The application of hydrogen production through water electrolysis is either hydrogen production via oxygen evolution reaction or hydrogen production via total water electrolysis. The fuel cell is used in the cathode oxygen reduction reaction and / or to directly prepare a methanol fuel cell; The metal-air battery is used as an air electrode catalyst. The pollutant degradation is applied in the oxidation of organic matter or wastewater treatment. The application of the automotive exhaust purification method is for the preparation of a three-way catalytic converter; The resistive random access memory is used as an electrode material; The application of the biosensor is for the electrochemical detection of biomolecules; The photoelectrochemical cell is used as a co-catalyst for water oxidation.

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