High-entropy oxide stable noble metal monatomic catalyst as well as preparation method and application thereof

Abstract

The invention relates to a high-entropy oxide stabilized noble metal monatomic catalyst as well as a preparation method and application thereof, the stability of noble metal monatomic is effectively enhanced by utilizing a defect structure and lattice distortion of a high-entropy oxide (CePrYZrHf) Ox substrate, so that the loading capacity of the noble metal monatomic is higher than that of a low-entropy oxide CeO2. By using a high-entropy oxide (CePrYZrHf) Ox carrier, precious metal single atoms show excellent activity and long-acting stability in an electro-catalysis nitrate radical reduction reaction. Compared with the prior art, the catalyst disclosed by the invention is simple and convenient in preparation method and controllable in cost, has a wide prospect in industrial application, and is particularly suitable for environment-friendly electro-catalytic reaction systems such as efficient ammonia production and the like.

Description

Technical Field

[0001] The present invention belongs to the technical fields of catalytic materials and electrochemistry, and particularly relates to a noble metal single atom catalyst stably supported by high-entropy oxides, a preparation method thereof, and an application thereof in electrocatalytic nitrate reduction. Background Art

[0002] Ammonia (NH3) is of great strategic significance in fields such as agriculture, industry, and national defense, and is also a key carbon-free energy carrier. However, the ammonia production process based on the traditional Haber-Bosch method has high energy consumption and needs to be carried out under high temperature (400 - 500 °C) and high pressure (20 - 30 MPa) conditions, accompanied by serious greenhouse gas emissions. In recent years, nitrate (NO3 - ) as a common water pollutant has become a potential nitrogen source for electrochemical ammonia synthesis instead of nitrogen (N2). It mainly comes from livestock manure, industrial wastewater, chemical fertilizers, and nuclear waste. Developing efficient electrocatalysts to convert nitrate waste into value-added products such as ammonia not only provides a new path for waste treatment but also has important economic and environmental benefits. In recent years, noble metal catalysts (such as Ru, Pd, Pt) have shown high efficiency and selectivity in electrocatalytic nitrate reduction to ammonia (NRA), but their high cost and scarcity limit large-scale applications.

[0003] Patent application CN202211576434.7 discloses a catalyst for electrocatalytic nitrate reduction to ammonia, a preparation method thereof, and an application thereof. The catalyst includes a conductive substrate and a metal component supported on the surface of the conductive substrate; the metal component includes Co element and M element; the M element is selected from at least one of Cu element, Ni element, Fe element, and Ag element; the catalyst has a self-supporting flaky structure of the conductive substrate; the prepared catalyst system is a self-supporting flaky structure, which has a large specific surface area, uniform element dispersion, high physical and structural stability, and shows a relatively high Faraday efficiency (96.3%) and ammonia production current density (453 mA cm -2 ). Although this solution effectively reduces the material cost, there are still the following deficiencies: (1) The catalytic activity depends on the alloy synergistic effect and lacks the ability to regulate the intermediate state of the reaction path; (2) Non-noble metals are prone to corrosion under reducing conditions, resulting in poor catalytic stability; (3) Its flaky structure is difficult to precisely construct catalytic sites at the atomic scale, with low atomic utilization rate and difficult to further improve the catalytic efficiency.

[0004] Therefore, in order to balance high efficiency, selectivity and low cost, the development of highly active single-atom catalysts has become a promising solution. Since isolated metal atoms are evenly dispersed on the substrate, this type of catalyst has extremely high atomic utilization, and its catalytic performance can be regulated through substrate engineering. However, single-atom catalysts still face challenges such as easy agglomeration of metal atoms and limited loading, which seriously affect their stability and catalytic efficiency in practical applications.

[0005] Metal oxides, with their unique surface acidity and alkalinity and redox properties, have become ideal substrates for loading noble metal single atoms. Their strong interaction with noble metals can not only effectively improve the stability of single-atom catalytic sites, but also is expected to significantly enhance their catalytic activity. However, traditional low-entropy oxides have limited surface defect sites, making it difficult to load a large number of noble metal single atoms. In contrast, the inherent defect structure and severe lattice distortion of high-entropy oxides not only provide more loading sites, but also increase the energy barrier for atomic diffusion and migration, thereby enhancing the dispersion of single atoms on the substrate and the stability of the catalyst. High-entropy oxides provide a new theoretical basis for the efficient stabilization of noble metal single-atom catalysts, and are expected to promote the widespread application of single-atom catalysts in energy conversion, environmental remediation, and chemical synthesis.

[0006] Patent application CN202211479510.2 discloses a noble metal single atom catalyst based on high entropy effect and a preparation method thereof. The noble metal single atom catalyst is a high entropy hydroxyl oxide catalyst supported by a noble metal single atom. The molecular formula of the high entropy hydroxyl oxide is Zn 3-x V2M x (OH)2O7·2H2O (M is three or more of Ni, Co, Fe, Cu, Al, and Mn), by loading precious metal atoms such as Au, Ru, In, and Pt on it to improve the oxygen evolution reaction (OER) activity. Although this scheme has improved the stability of single-atom loading, it still has the following problems: (1) Its research scope is limited to the oxygen evolution reaction and does not involve the electrocatalytic nitrate reduction reaction, lacking relevant application inspiration; (2) Its lattice distortion and defect structure control capabilities are limited, and its electronic regulation effect on precious metal single atoms is weak.

[0007] In summary, there is currently no technology that can take into account the high utilization rate, excellent stability and high catalytic performance of precious metals in NRA reactions. Therefore, it is urgent to develop a new type of high-entropy oxide substrate that can stably anchor precious metal single atoms at the atomic level and significantly improve their reactivity and selectivity in electrocatalytic nitrate reduction, so as to achieve an efficient, low-energy and environmentally friendly ammonia synthesis pathway. Summary of the invention

[0008] The object of the present invention is to overcome the defects of the above-mentioned existing technologies and provide a high-entropy oxide-stabilized noble metal single-atom catalyst, its preparation method and application, solve the problem that noble metal single atoms are prone to agglomeration during the catalytic process, significantly improve the atomic utilization rate and active surface area of noble metals, and exhibit excellent catalytic activity and Faraday efficiency in the field of electrocatalytic nitrate reduction to ammonia.

[0009] The object of the present invention can be achieved by the following technical solutions: A preparation method of a high-entropy oxide-stabilized noble metal single-atom catalyst, comprising the following steps:

[0010] (1) Dissolve rare earth and rare earth-like metal salts (such as cerium salts, praseodymium salts, yttrium salts, zirconium salts, hafnium salts, etc.) and noble metal chlorides in an aqueous solution of hydroquinone;

[0011] (2) Adjust the pH value of the above solution to 0.5 - 2, and then heat and stir in an oil bath;

[0012] (3) Add formaldehyde solution to the above solution, and immediately stop stirring when the solution becomes turbid;

[0013] (4) After standing and aging the turbid liquid for a period of time, transfer it to a vacuum oven for drying treatment;

[0014] (5) Calcinate the obtained xerogel in air to obtain a high-entropy oxide-supported noble metal single-atom catalyst (M-HEO).

[0015] Further, the rare earth and rare earth-like metal salts in step (1) include cerium salts, praseodymium salts, yttrium salts, zirconium salts and hafnium salts. Preferably, the cerium salt is cerium chloride heptahydrate (CeCl3·7H2O); the praseodymium salt is praseodymium chloride heptahydrate (PrCl3·7H2O), the yttrium salt is yttrium chloride (YCl3), the zirconium salt is zirconium tetrachloride (ZrCl4), and the hafnium salt is hafnium tetrachloride (HfCl4);

[0016] The molar ratio of cerium chloride heptahydrate (CeCl3·7H2O), praseodymium chloride heptahydrate (PrCl3·7H2O), yttrium chloride (YCl3), zirconium tetrachloride (ZrCl4), and hafnium tetrachloride (HfCl4) is 0.5 - 1:0.5 - 1:0.5 - 1:0.5 - 1:0.5 - 1. Preferably, the molar ratio of these five metal salts is 1:1:1:1:1.

[0017] Further, the concentration of hydroquinone in step (1) is 1 - 1.5 mol / L -1 , and the molar ratio of hydroquinone to the total metal is 80 - 20:1. Preferably, the concentration of the hydroquinone aqueous solution is 1.14 mol / L -1, the molar ratio of hydroquinone to total metal is 66.1:1.

[0018] Further, the noble metal chloride is one or more of ruthenium(III) chloride trihydrate (RuCl3·3H2O), ammonium hexachloropalladate((NH4)2PdCl6), or chloroplatinic acid (H2PtCl6), and the dosage of the noble metal chloride accounts for 0 - 3.2% of the total metal molar amount. Optionally, the dosage of the noble metal chloride accounts for 3% of the total metal molar amount.

[0019] Further, in step (2), a hydrochloric acid solution with a concentration of 30 - 40 wt% is used to adjust the pH value, and the heating and stirring temperature is 80 - 90 °C. The concentration of the hydrochloric acid solution is preferably 37 wt%, and the heating and stirring temperature is preferably 85 °C.

[0020] Further, in step (3), the concentration of the formaldehyde solution is 30 - 40 wt%, and the molar ratio of formaldehyde to hydroquinone is 1 - 2:1. Preferably, the concentration of the formaldehyde solution is 37 wt%, and the molar ratio of formaldehyde to hydroquinone is 1.97:1.

[0021] Further, in step (4), the standing temperature is 80 - 90 °C, and the aging time is 2 - 5 h; preferably, the standing temperature is 85 °C, and the aging time is 3 h.

[0022] The vacuum drying temperature is 60 - 80 °C, and the time is 18 - 36 h. Preferably, the vacuum drying temperature is 60 °C, and the time is 24 h.

[0023] Further, in step (5), the calcination temperature is 900 - 1000 °C, and the time is 2 - 5 h. Preferably, the calcination temperature is 950 °C, and the time is 2 h.

[0024] The present invention also provides a noble metal single-atom catalyst M-HEO supported on high-entropy oxide prepared by the above method.

[0025] The present invention also provides an application of the noble metal single-atom catalyst supported on high-entropy oxide. The catalyst is used as a catalyst for electrocatalytic nitrate reduction, and it exhibits excellent electrocatalytic nitrate reduction activity. The highest Faraday efficiency is 91.3%, and the corresponding ammonia production rate is 5.79 mg h -1 mg cat. -1 .

[0026] In the noble metal single-atom catalyst supported on high-entropy oxide prepared by the present invention, the noble metal single atoms are uniformly dispersed on the high-entropy oxide substrate, solving the problem of easy agglomeration of noble metal single atoms during the catalytic process, and significantly improving the atomic utilization rate and active surface area of noble metals. In addition, the defect structure and lattice distortion of the high-entropy oxide effectively enhance the stability of noble metal single atoms and accelerate the kinetics of electrochemical reactions. Therefore, this material exhibits excellent catalytic activity and Faraday efficiency in the field of electrocatalytic nitrate reduction to ammonia, and has broad application prospects.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) The present invention constructs a high-entropy oxide (CePrYZrHf)O composed of rare earth elements such as Ce, Pr, Y, Zr, and Hf x as a carrier. By using its defect structure and lattice distortion, the anchoring ability and electronic structure regulation ability of noble metal single atoms are significantly enhanced. While ensuring high loading and dispersion, the catalytic activity and cycle stability are improved, which is particularly suitable for the efficient and stable synthesis of ammonia in the electrocatalytic nitrate reduction reaction.

[0029] 2) The preparation method of the catalyst of the present invention is simple, green and environmentally friendly, and the cost is controllable, having broad prospects in industrial applications, especially suitable for environmentally friendly electrocatalytic reaction systems such as high-efficiency ammonia production.

[0030] 3) The high-entropy oxide substrate in the present invention can effectively inhibit the agglomeration problem of noble metal single atoms, enhance the stability of the catalyst, and at the same time reduce the activation energy in the electrochemical reaction, thereby accelerating the reaction kinetics.

[0031] 4) The high-entropy oxide substrate of the present invention has excellent corrosion resistance and oxidation resistance, providing a guarantee for the long-term stable operation of noble metal single atoms, and significantly improving the cycle stability of the electrocatalytic nitrate reduction reaction.

[0032] 5) The present invention demonstrates excellent catalytic activity and Faraday efficiency in the field of electrocatalytic nitrate reduction to ammonia, has good industrial application prospects, and promotes the development of sustainable ammonia production technology. Brief Description of the Drawings

[0033] Figure 1 are the (a) high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image and (b) corresponding inverse fast Fourier transform (IFFT) image of (CePrYZrHf)Ox prepared in Example 2 of the present invention;

[0034] Figure 2is the electron paramagnetic resonance (EPR) spectrogram of (CePrYZrHf)Ox prepared in Example 2 of the present invention and CeO2 prepared in Comparative Example 1;

[0035] Figure 3 are the X-ray diffraction (XRD) patterns of low-entropy oxide CeO2 loaded with different contents of Ru species prepared in Comparative Examples 1-3.

[0036] Figure 4 are the XRD patterns of high-entropy oxide (CePrYZrHf)Ox loaded with different contents of Ru species prepared in Examples 1-4.

[0037] Figure 5 is the HAADF-STEM image of the Ru 3％ -HEO material prepared in Example 1.

[0038] Figure 6 is the HAADF-STEM image of the Ru 3％ -HEO material prepared in Example 1 and the corresponding EDS elemental mapping images.

[0039] Figure 7 are the XRD patterns of the Pd 3％ -HEO and Pd 4％ -HEO materials and the Pd2%-CeO2 material prepared in Comparative Example 4.

[0040] Figure 8 is the HAADF-STEM image of the Pd 3％ -HEO material prepared in Example 5 of the present invention and the corresponding EDS elemental mapping images.

[0041] Figure 9 are the XRD patterns of the Pt 3％ -HEO and Pt4%-HEO materials and the Pt 2％ -CeO2 material prepared in Comparative Example 5.

[0042] Figure 10 is the HAADF-STEM image of the Pt 3％ -HEO material prepared in Example 7 and the corresponding EDS elemental mapping images.

[0043] Figure 11 is the Faraday efficiency and ammonia production rate diagram of the Ru 3％ -HEO prepared in Example 1 and the Ru 4％ -HEO material as an NRA electrocatalyst;

[0044] Figure 12The high-entropy oxide (CePrYZrHf)Ox prepared in Examples 1-4 is loaded with different contents of Ru species, and the Ru prepared in Comparative Example 2 1％ -Comparison chart of Faraday efficiency and ammonia production rate of CeO2 materials at the optimal potential;

[0045] Figure 13 The Ru prepared in Example 1 3％ -Cyclic test chart of Ru-HEO material as a NAR electrocatalyst at -0.5V vs. RHE.

[0046] Figure 14 The Ru prepared in Example 1 3％ -Discharge curve and power density curve of the zinc-nitrate battery assembled with Ru-HEO material. Detailed implementation manners

[0047] The embodiments of the present invention will be described in detail below. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0048] Unless otherwise specified, the raw materials and equipment used in the present invention are all commercially available products. For example, the material sources involved in the examples and comparative examples: hydroquinone, formaldehyde, RuCl3·3H2O, (NH4)2PdCl4, H2PtCl6, CeCl3·7H2O, PrCl3·7H2O, YCl3, ZrCl4, HfCl4, KNO3, K2SO4, Nafion (5wt.%), and ethanol are all purchased from Sigma Aldrich. Deionized water is used throughout the experimental process.

[0049] Example 1

[0050] As Figure 1 shown, this example provides a preparation method of a high-entropy oxide-stabilized noble metal single-atom material, including the following specific preparation steps:

[0051] (1) Dissolve 14.9 mg of CeCl3·7H2O, 14.9 mg of PrCl3·7H2O, 7.8 mg of YCl3, 9.3 mg of ZrCl4, 12.8 mg of HfCl4, and 1.6 mg of RuCl3·3H2O (Ru accounts for 3% of the total metal molar amount) in 12 mL of an aqueous solution containing 1.5 g of hydroquinone.

[0052] (2) Adjust the pH value of the above solution to 1 with 37% HCl solution, and then heat it in an oil bath at 85°C.

[0053] (3) Add 2 mL of 37 wt.% formaldehyde solution with moderate stirring and stop stirring when the solution becomes turbid.

[0054] (4) After aging the turbid solution at 85 °C for 3 hours, transfer it to an oven and dry it under vacuum at 60 °C for 24 h.

[0055] (5) Calcinate the obtained xerogel in air at 950 °C for 2 h. The finally obtained high-entropy oxide supported with 3 at% Ru single atoms is named Ru 3％ -HEO.

[0056] Example 2

[0057] Refer to Example 1, with the only difference being that the mass of RuCl3·3H2O in Example 1 is changed to 0 mg, and the rest are the same as in Example 1. The finally obtained high-entropy oxide material is denoted as (CePrYZrHf)O x .

[0058] Example 3

[0059] Refer to Example 1, with the only difference being that the mass of RuCl3·3H2O in Example 1 is changed to 1.1 mg, and the rest are the same as in Example 1. The finally obtained high-entropy oxide supported with 2 at.% Ru species is named Ru 2％ -HEO.

[0060] Example 4

[0061] Refer to Example 1, with the only difference being that the mass of RuCl3·3H2O in Example 1 is changed to 2.2 mg, and the rest are the same as in Example 1. The finally obtained high-entropy oxide supported with 4 at.% Ru species is named Ru 4％ -HEO.

[0062] Example 5

[0063] Refer to Example 1, with the only difference being that 1.6 mg of RuCl3·3H2O in Example 1 is changed to 2.2 mg of (NH4)2PdCl6, and the rest are the same as in Example 1. The finally obtained high-entropy oxide supported with 3 at.% Pd species is named Pd 3％ -HEO.

[0064] Example 6

[0065] Refer to Example 1, with the only difference being that 1.6 mg of RuCl3·3H2O in Example 1 is changed to 2.9 mg of (NH4)2PdCl6, and the rest are the same as in Example 1. The finally obtained high-entropy oxide supported with 4 at.% Pd species is named Pd 4％ -HEO.

[0066] Example 7

[0067] Referring to Example 1, the difference is only that 1.6 mg of RuCl3·3H2O in Example 1 is changed to 2.5 mg of H2PtCl6, and the rest are the same as in Example 1. The finally obtained high-entropy oxide supported 3 at.% Pt species is named Pt 3％ -HEO.

[0068] Example 8

[0069] Referring to Example 1, the difference is only that 1.6 mg of RuCl3·3H2O in Example 1 is changed to 3.4 mg of H2PtCl6, and the rest are the same as in Example 1. The finally obtained high-entropy oxide supported 4 at.% Pt species is named Pt 4％ -HEO.

[0070] Comparative Example 1

[0071] Referring to Example 1, the difference is only that the mass of CeCl3·7H2O in Example 2 is changed to 74.5 mg, and RuCl3·3H2O, PrCl3·7H2O, YCl3, ZrCl4 and HfCl4 are not added, and the rest are the same as in Example 2. The finally obtained low-entropy oxide support cerium dioxide (CeO2) is named CeO2.

[0072] Comparative Example 2

[0073] Referring to Comparative Example 1, the difference is only that the mass of RuCl3·3H2O in Comparative Example 1 is changed to 0.5 mg, and the rest are the same as in Comparative Example 1. The finally obtained CeO2 supported 1 at.% Ru species is named Ru 1％ -CeO2.

[0074] Comparative Example 3

[0075] Referring to Comparative Example 1, the difference is only that the mass of RuCl3·3H2O in Comparative Example 1 is changed to 1.1 mg, and the rest are the same as in Comparative Example 1. The finally obtained CeO2 supported 2 at.% Ru species is named Ru 2％ -CeO2.

[0076] Comparative Example 4

[0077] Referring to Comparative Example 1, the difference is only that the mass of (NH4)2PdCl6 in Comparative Example 1 is changed to 1.5 mg, and the rest are the same as in Comparative Example 1. The finally obtained CeO2 supported 2 at.% Pd species is named Pd 2％ -CeO2.

[0078] Comparative Example 5

[0079] Referring to Comparative Example 1, the difference is only that the mass of H2PtCl6 in Comparative Example 1 is changed to 1.7 mg, and the rest is the same as in Comparative Example 1. The finally obtained CeO2 supported with 2 at.% Pt species is named Pt 2％ -CeO2.

[0080] The performance of the catalysts obtained in each example and comparative example was tested as follows:

[0081] 1. Use high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), electron paramagnetic resonance (EPR), X-ray diffractometer (XRD) and electrochemical workstation to characterize the morphology, composition and electrochemical performance of the high-entropy oxide supported noble metal materials prepared in Examples 1-8 and the low-entropy oxide CeO2 supported noble metal materials prepared in Comparative Examples 1-5. The results are as follows:

[0082] It was found that:

[0083] (1) The HAADF-STEM test results show that: as Figure 1 shown, the atomic-resolution HAADF-STEM image of the high-entropy oxide support (CePrYZrHf)O x prepared in Example 2 ([[]] Figure 1 a) and its inverse fast Fourier transform (IFFT) image ([[]] Figure 1 b) show that there are lattice fringe distortions in (CePrYZrHf)O x , which is beneficial to increasing the diffusion and migration energy barriers of noble metal single atoms.

[0084] (2) The EPR test results show that: as Figure 2 shown, in the EPR spectra of the high-entropy oxide support (CePrYZrHf)O x prepared in Example 2 and the CeO2 support prepared in Comparative Example 1, it can be clearly observed that (CePrYZrHf)O x shows a stronger EPR signal at g = 2.003, indicating that (CePrYZrHf)O x has more abundant defects. This provides additional anchoring sites for the loading of noble metal single atoms.

[0085] (3) The XRD test results show that: as Figure 3 shown, the XRD patterns of the low-entropy oxide CeO2 supported with different contents of Ru species prepared in Comparative Examples 1-3 show that when the introduced Ru is less than 1 at%, the crystal phase of CeO2 remains intact and no characteristic peaks of Ru species appear, indicating that Ru may exist in the form of single atoms. However, when the Ru content increases to 2 at%, the characteristic diffraction peaks of RuO2 can be clearly observed.

[0086] (4) The XRD test results show that: as Figure 4 shown, the XRD patterns of the high-entropy oxides loaded with different contents of Ru species prepared in Examples 1-4 show that when the introduced Ru is less than 3 at%, the crystal phase of (CePrYZrHf)O x remains intact, and there are no characteristic peaks from the Ru species, indicating that Ru may exist in the form of single atoms. However, when the Ru content increases to 4 at%, the characteristic diffraction peaks of RuO2 can be clearly observed. Compared with the CeO2 support, the high-entropy oxide (CePrYZrHf)O x can load a higher content of Ru single atoms.

[0087] (5) The HAADF-STEM test results show that: as Figure 5 shown, the Ru 3％ -HEO prepared in Example 1 exhibits a three-dimensional network structure composed of numerous nanoparticles with a narrow size distribution and overlapping each other ( Figure 5 a). Measuring the lattice fringes of the nanoparticles in Ru 3％ -HEO gives 3.02 and ( Figure 5 b), corresponding to the (111) and (200) crystal planes of the cubic structure respectively.

[0088] (6) The HAADF-STEM and the corresponding EDX elemental mapping test results show that: as Figure 6 shown, the EDX elemental mapping of the Ru 3％ -HEO material prepared in Example 1 shows that the Ce, Pr, Y, Zr, and Hf elements in Ru 3％ -HEO are evenly distributed, indicating the successful preparation of the single-phase solid-solution high-entropy oxide. In addition, no agglomeration of the Ru element is observed, indicating that the Ru single atoms are evenly dispersed on the (CePrYZrHf)O x nanoparticles.

[0089] (7) The XRD test results show that: as Figure 7 shown, the XRD patterns of the Pd 3％ -HEO and Pd 4％ -HEO materials prepared in Examples 5-6 and the Pd 2％ -CeO2 prepared in Comparative Example 4 show that there are no characteristic peaks of the Pd species in Pd 3％ -HEO, while the typical diffraction peaks of metallic Pd can be observed in Pd 4％ -HEO and Pd 2％ -CeO2, indicating that compared with CeO2, the high-entropy oxide support (CePrYZrHf)O x can load a higher content of Pd single atoms.

[0090] (8) The HAADF-STEM and corresponding EDX elemental mapping test results show that: as Figure 8 shown, the EDX elemental mapping of the Pd 3％ -HEO material prepared in Example 5 shows that the Ce, Pr, Y, Zr, and Hf elements in Pd 3％ -HEO are evenly distributed, indicating the successful preparation of a single-phase solid solution high-entropy oxide. In addition, no agglomeration of Pd elements is observed, indicating that Pd single atoms are evenly dispersed on the (CePrYZrHf)O x nanoparticles.

[0091] (9) The XRD test results show that: as Figure 9 shown, the XRD patterns of the Pt 3％ -HEO and Pt 4％ -HEO materials prepared in Examples 7-8 and the Pt 2％ -CeO2 prepared in Comparative Example 5 show that the characteristic peaks of Pt species are missing in Pt 3％ -HEO, while the typical diffraction peaks of metallic Pt can be observed in Pt 4％ -HEO and Pt 2％ -CeO2, indicating that the high-entropy oxide support (CePrYZrHf)O x can support a higher content of Pt single atoms compared to CeO2.

[0092] (10) The HAADF-STEM and corresponding EDX elemental mapping test results show that: as Figure 10 shown, the EDX elemental mapping of the Pt 3％ -HEO material prepared in Example 7 shows that the Ce, Pr, Y, Zr, and Hf elements in Pt 3％ -HEO are evenly distributed, indicating the successful preparation of a single-phase solid solution high-entropy oxide. In addition, no agglomeration of Pt elements is observed, indicating that Pt single atoms are evenly dispersed on the (CePrYZrHf)O x nanoparticles.

[0093] The catalysts obtained in each example and comparative example were used for electrocatalytic nitrate reduction. The specific process was as follows: Before the electrochemical test, the Nafion membrane was pretreated: boiled in 5% H2O2 aqueous solution for 1 h, boiled in deionized water for 1 h, boiled in 0.5 M H2SO4 for 3 h, and finally boiled in deionized water again for 6 h to achieve complete protonation treatment. The electrocatalytic performance test was carried out on a CHI 660D electrochemical workstation using a three-electrode system, where the Ag / AgCl electrode was the reference electrode, the graphite rod was the counter electrode, and the catalyst-loaded carbon paper (1×1 cm 2) serves as the working electrode. The preparation method of the working electrode is as follows: Weigh 5 mg of the prepared catalyst, add it to 25 μL of 5 wt.% Nafion solution and 5 mL of absolute ethanol, and ultrasonically disperse to form a uniform catalyst ink; then take 0.5 mL of the ink and evenly drop-coat it on a 1 cm 2 carbon paper, and use it as the working electrode after drying. All electrolytes use a 0.1 M KOH solution containing 10 mM KNO3, and argon is bubbled through it for 30 minutes before testing to remove dissolved oxygen. In addition, to verify the actual application ability of the catalyst at the device level, a zinc-nitrate battery based on Ru 3％ -HEO was also constructed and tested in a two-electrode system H-type electrolytic cell. Using a 1×1 cm 2 Ru 3％ -HEO-loaded carbon paper as the cathode, placed in a 0.5 M NO3 - / 3 M KOH electrolyte; using a 1×1 cm 2 zinc foil as the anode, placed in a 0.2 M Zn(Ac)2 / 3 M KOH solution. The two electrodes are separated by a Nafion 117 membrane. The relevant battery test results were also recorded by a CHI 660D electrochemical workstation.

[0094] (11) The NRA performance test results of Ru 3％ -HEO and Ru 4％ -HEO materials show that: as Figure 11 shown, the Faraday efficiency of Ru 3％ -HEO in Example 1 shows a volcano-shaped trend, reaching a peak at -0.5 V vs. RHE, which is 91.3%, and the corresponding ammonia production rate is 5.79 mg h -1 mg cat. -1 , much higher than that of Ru 4％ -HEO (75.6% and 2.61 mg h -1 mg cat. -1 ). This result indicates that Ru single atoms have higher NRA catalytic activity than RuO2.

[0095] (12) The comparison of NRA performance at the optimal potential of (CePrYZrHf)O x high-entropy carrier, Ru-HEO and Ru-CeO2 materials is as Figure 12 shown: The (CePrYZrHf)O x high-entropy carrier in Example 2 shows very low Faraday efficiency and ammonia production rate, indicating its negligible NRA activity. After introducing Ru species, the NRA performance of the Ru-HEO catalyst has been significantly improved, confirming that (CePrYZrHf)O xThe Ru species dispersed on the support are the main active sites for nitrate adsorption and activation. In addition, since Ru 3％ -HEO can achieve a higher Ru single-atom loading, its NRA performance is much better than that of Ru 1％ -CeO2.

[0096] (13) In an H-type flow electrolytic cell, a long-term stability test of NRA was carried out on Ru 3％ -HEO at a potential of -0.5 V: As Figure 13 shown, the nitrate reduction test was continuously carried out for 150 h at the optimal reduction potential of -0.5 V vs. RHE. Both the current density and the Faraday efficiency remained stable during the cyclic test, and the production increased nearly linearly with time, indicating its excellent NRA stability.

[0097] (14) The performance test of the zinc-nitrate battery based on Ru 3％ -HEO shows that: As Figure 14 shown, the zinc-nitrate battery assembled based on Ru 3％ -HEO has a current density as high as 10 mA cm -2 at 0.52 V, and the peak power density reaches 9.6 mW cm -2 at 0.32 V.

[0098] The performance results of each example and comparative example are summarized as follows:

[0099]

[0100]

[0101] As can be seen from the above table, when the noble metal is loaded on the catalyst surface in the form of single atoms, it shows better ammonia production rate and Faraday efficiency in the electrocatalytic nitrate reduction reaction. When the high-entropy oxide is used as the catalyst support, due to its rich defect structure and significant lattice distortion effect, a higher noble metal single-atom loading and a more uniform dispersion effect can be achieved, so that the overall NRA performance is far better than that of the comparative catalyst using the low-entropy oxide as the support.

[0102] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the invention patent shall be included in the protection scope of the invention patent.

Claims

1. A method for preparing a high entropy oxide-stabilized noble metal single-atom catalyst, characterized in that: The following steps are involved: (1) dissolving rare earth and quasi-rare earth metal salts and noble metal chlorides in an aqueous solution of hydroquinone; (2) adjusting the pH value of the above solution to 0.5-2, and then heating and stirring in an oil bath; (3) Add formaldehyde solution to the above solution and stop stirring immediately when the solution becomes turbid; (4) After the turbid liquid is allowed to stand for a period of time and aged, it is transferred to a vacuum oven for drying; (5) The dry gel obtained above is calcined in air to obtain a high entropy oxide-supported noble metal single atom catalyst (M-HEO).

2. A high entropy oxide-stabilized noble metal single atom catalyst according to claim 1, characterized in that: The rare earth and quasi-rare earth metal salts described in step (1) include cerium salts, praseodymium salts, yttrium salts, zirconium salts and hafnium salts.

3. A high entropy oxide-stabilized noble metal single atom catalyst according to claim 2, characterized in that: The cerium salt is cerium chloride heptahydrate (CeCl3·7H2O); the praseodymium salt is praseodymium chloride heptahydrate (PrCl3·7H2O), the yttrium salt is yttrium chloride (YCl3), the zirconium salt is zirconium tetrachloride (ZrCl4), and the hafnium salt is hafnium tetrachloride (HfCl4); The molar ratio of cerium chloride heptahydrate (CeCl3·7H2O), praseodymium chloride heptahydrate (PrCl3·7H2O), yttrium chloride (YCl3), zirconium tetrachloride (ZrCl4), and hafnium tetrachloride (HfCl4) is 0.5-1:0.5-1:0.5-1:0.5-1:0.5-1.

4. A high entropy oxide-stabilized noble metal single atom catalyst according to claim 1, characterized in that: The concentration of hydroquinone in step (1) is 1-1.5 mol L -1 , the molar ratio of hydroquinone to total metals is 80-20:

1.

5. A high entropy oxide-stabilized noble metal single atom catalyst according to claim 1, characterized in that: The noble metal chloride is one or more of ruthenium chloride trihydrate (RuCl3·3H2O), ammonium hexachloropalladate ((NH4)2PdCl6), or hexachloroplatinic acid (H2PtCl6), and the amount of the noble metal chloride accounts for 0-3.2% of the total metal molar amount.

6. A high entropy oxide-stabilized noble metal single atom catalyst according to claim 1, characterized in that: In step (2), a hydrochloric acid solution with a concentration of 30-40% is used to adjust the pH value, and the heating and stirring temperature is 80-90°C.

7. A high entropy oxide-stabilized noble metal single atom catalyst according to claim 1, characterized in that: The concentration of the formaldehyde solution in step (3) is 30-40%, and the molar ratio of formaldehyde to hydroquinone is 1-2:

1.

8. The high entropy oxide-stabilized noble metal single atom catalyst according to claim 1, characterized in that: In step (4), the standing temperature is 80-90° C. and the aging time is 2-5 h; The vacuum drying temperature is 60-80°C and the time is 18-36h; In step (5), the calcination temperature is 900-1000° C. and the calcination time is 2-5 hours.

9. A high entropy oxide-supported noble metal single-atom catalyst M-HEO prepared by the method as claimed in any one of claims 1 to 8.

10. An application of the high entropy oxide supported noble metal single atom catalyst as claimed in claim 9, characterized in that: The catalyst was used as a catalyst for electrocatalytic nitrate reduction, and the highest Faradaic efficiency was 91.3%, corresponding to an ammonia yield of 5.79 mg h -1 mg cat. -1 .

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