High-entropy oxide stabilized noble metal monatomic catalyst, and preparation method and application thereof

Abstract

The present application relates to a kind of high-entropy oxide stable noble metal monatomic catalyst and its preparation method and application, utilize the defect structure and lattice distortion of high-entropy oxide (CePrYZrHf) Ox base, effectively enhance the stability of noble metal monatomic, to realize the higher noble metal monatomic load compared with low-entropy oxide CeO2.It is shown that noble metal monatomic exhibits excellent activity and long-term stability in electrocatalytic nitrate reduction reaction by using high-entropy oxide (CePrYZrHf) Ox carrier.Compared with prior art, the catalyst preparation method of the present application is simple, cost controllable, and has broad prospects in industrial application, especially suitable for efficient ammonia production and other environmentally friendly electrocatalytic reaction systems.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials and electrochemical technology, specifically relating to a high-entropy oxide-supported noble metal single-atom catalyst, its preparation method, and its application in electrocatalytic nitrate reduction. Background Technology

[0002] Ammonia (NH3) holds significant strategic importance in agriculture, industry, and defense, and is also a crucial carbon-free energy carrier. However, the traditional Haber-Bosch process for ammonia production is energy-intensive and requires high temperatures (400-500℃) and high pressures (20-30MPa), resulting in substantial greenhouse gas emissions. In recent years, nitrate (NO3) has become increasingly important. - Nitric acid, a common water pollutant, has become a potential nitrogen source to replace nitrogen (N2) in the electrochemical synthesis of ammonia. It mainly originates from livestock and poultry manure, industrial wastewater, fertilizers, and nuclear waste. Developing efficient electrocatalysts to convert nitric acid waste into value-added products such as ammonia not only provides a new pathway for waste treatment but also has significant economic and environmental benefits. In recent years, noble metal catalysts (such as Ru, Pd, and Pt) have demonstrated high efficiency and selectivity in electrocatalytic nitrate reduction to ammonia (NRA), but their high cost and scarcity limit large-scale application.

[0003] Patent application CN202211576434.7 discloses a catalyst for the electrocatalytic reduction of nitrate to ammonia, its preparation method, and its application. The catalyst comprises a conductive matrix and a metal component supported on the surface of the conductive matrix; the metal component includes Co and M elements; M element is selected from at least one of Cu, Ni, Fe, and Ag elements; the catalyst has a self-supporting plate-like structure within the conductive matrix; the prepared catalyst system has a self-supporting plate-like structure with a large specific surface area, uniform element dispersion, and high physical and structural stability, exhibiting a high Faradaic efficiency (96.3%) and ammonia production current density (453 mA / cm²) in the NRA reaction. -2 Although the scheme effectively reduces material costs, it still has the following shortcomings: (1) Catalytic activity depends on the alloy synergistic effect and lacks the ability to regulate the intermediate state of the reaction path; (2) Non-precious metals are prone to corrosion under reducing conditions, resulting in poor catalytic stability; (3) Its plate-like structure makes it difficult to accurately construct catalytic sites at the atomic scale, resulting in low atomic utilization and difficulty in further improving catalytic efficiency.

[0004] Therefore, developing highly active single-atom catalysts has become a promising solution to balance high efficiency, selectivity, and low cost. Because isolated metal atoms are uniformly dispersed on the substrate, these catalysts exhibit extremely high atom utilization, and their catalytic performance can be tunable through substrate engineering. However, single-atom catalysts still face challenges such as the tendency for metal atoms to aggregate and limited loading capacity, which severely affect their stability and catalytic efficiency in practical applications.

[0005] Metal oxides, with their unique surface acid-base and redox properties, have become ideal substrates for supporting noble metal single atoms. Their strong interactions with noble metals can not only effectively improve the stability of single-atom catalytic sites but also significantly enhance their catalytic activity. However, traditional low-entropy oxides have limited surface defect sites, making it difficult to support large numbers 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 raise the energy barriers 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 the high-entropy effect and its preparation method. The noble metal single-atom catalyst is a high-entropy hydroxy oxide catalyst supported on a noble metal single atom, and the molecular formula of the high-entropy hydroxy oxide is Zn. 3-x V2M x (OH)₂O₇·2H₂O (M is three or more of Ni, Co, Fe, Cu, Al, and Mn) is used to enhance the activity of the oxygen evolution reaction (OER) by loading noble metal atoms such as Au, Ru, In, and Pt onto it. Although this method improves 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 ability to regulate lattice distortion and defect structure is limited, and its electronic regulation effect on noble metal single atoms is weak.

[0007] In summary, no current technology can simultaneously achieve the high utilization rate, excellent stability, and high catalytic performance of noble metals in NRA reactions. Therefore, there is an urgent need to develop a novel high-entropy oxide substrate capable of stably anchoring single noble metal atoms at the atomic level and significantly enhancing their reactivity and selectivity in electrocatalytic nitrate reduction, thereby realizing an efficient, low-energy-consumption, and environmentally friendly ammonia synthesis pathway. Summary of the Invention

[0008] The purpose of this invention is to overcome the defects of the prior art by providing a high-entropy oxide-stabilized noble metal single-atom catalyst, its preparation method, and its application. This solves the problem of easy aggregation of noble metal single atoms during catalysis, significantly improves the atomic utilization and active surface area of ​​noble metals, and exhibits excellent catalytic activity and Faraday efficiency in the field of electrocatalytic reduction of nitrate to ammonia.

[0009] The objective of this invention can be achieved through the following technical solution: a method for preparing 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 of the above solution to 0.5-2, and then heat and stir it in an oil bath;

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

[0013] (4) After the turbid liquid has been left to stand and age for a period of time, it is transferred to a vacuum oven for drying.

[0014] (5) The dry gel obtained above is calcined 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 mentioned 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] Furthermore, 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. Preferably, the concentration of the hydroquinone aqueous solution is 1.14 mol / L. -1The molar ratio of hydroquinone to total metals is 66.1:1.

[0018] Further, 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 weight. Preferably, the amount of the noble metal chloride accounts for 3% of the total metal molar weight.

[0019] Furthermore, in step (2), a 30-40 wt% hydrochloric acid solution 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] Furthermore, in step (4), the settling temperature is 80-90℃ and the aging time is 2-5h; preferably, the settling temperature is 85℃ and the aging time is 3h.

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

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

[0024] The present invention also provides a method for preparing a high-entropy oxide-supported noble metal single-atom catalyst M-HEO.

[0025] This invention also provides an application of a high-entropy oxide-supported noble metal single-atom catalyst, which is used as a catalyst for the electrocatalytic reduction of nitrate. It exhibits excellent electrocatalytic nitrate reduction activity, with a maximum Faradaic efficiency of 91.3% and a corresponding ammonia yield of 5.79 mg / h. -1 mg cat. -1 .

[0026] In the high-entropy oxide-supported noble metal single-atom catalyst prepared in this invention, the noble metal single atoms are uniformly dispersed on the high-entropy oxide substrate, solving the problem of easy aggregation of noble metal single atoms during catalysis and significantly improving the atomic utilization and active surface area of ​​the noble metal. Furthermore, the defect structure and lattice distortion of the high-entropy oxide effectively enhance the stability of the noble metal single atoms, accelerating the kinetics of the electrochemical reaction. Therefore, this material exhibits excellent catalytic activity and Faradaic efficiency in the electrocatalytic reduction of nitrate to ammonia, and has broad application prospects.

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

[0028] 1) This 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, its defect structure and lattice distortion significantly enhance the anchoring ability and electronic structure regulation ability of noble metal single atoms. While ensuring high loading and dispersibility, it improves catalytic activity and cycle stability, making it particularly suitable for the efficient and stable synthesis of ammonia in electrocatalytic nitrate reduction reaction.

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

[0030] 3) The high-entropy oxide substrate in this invention can effectively suppress the aggregation of noble metal single atoms, enhance the stability of the catalyst, and reduce the activation energy in the electrochemical reaction, thereby accelerating the reaction kinetics.

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

[0032] 5) This invention demonstrates excellent catalytic activity and Faraday efficiency in the field of electrocatalytic nitrate reduction to ammonia production, and has good prospects for industrial application, promoting the development of sustainable ammonia production technology. Attached Figure Description

[0033] Figure 1 The images shown are (a) a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image and (b) a corresponding inverse fast Fourier transform (IFFT) image of (CePrYZrHf)Ox prepared in Example 2 of this invention.

[0034] Figure 2These are the electron paramagnetic resonance (EPR) spectra of (CePrYZrHf)Ox prepared in Example 2 of this invention and CeO2 prepared in Comparative Example 1.

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

[0036] Figure 4 The XRD diffraction patterns are those of high-entropy oxides (CePrYZrHf)Ox prepared in Examples 1-4, loaded with different contents of Ru species.

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

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

[0039] Figure 7 The Pd prepared in Examples 5-6 3％ -HEO and Pd 4％ XRD diffraction patterns of HEO material and Pd2%-CeO2 material prepared in Comparative Example 4.

[0040] Figure 8 The Pd obtained in Example 5 of this invention 3％ - HAADF-STEM image of HEO material and corresponding EDS elemental mapping.

[0041] Figure 9 The Pt prepared in Examples 7-8 3％ -HEO and Pt 4%-HEO material and Pt prepared in Comparative Example 5 2％ XRD diffraction pattern of CeO2 material.

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

[0043] Figure 11 It is Ru prepared in Example 1 3％ -HEO and Ru prepared in Example 4 4％ -Graph showing the Faradaic efficiency and ammonia yield of HEO material as an NRA electrocatalyst;

[0044] Figure 12The high-entropy oxides (CePrYZrHf)Ox prepared in Examples 1-4 are supported with different contents of Ru species, and Ru prepared in Comparative Example 2 is also present. 1％ - Comparison of Faraday efficiency and ammonia yield of CeO2 material at optimal potential;

[0045] Figure 13 It is Ru prepared in Example 1 3％ -HEO material as a NAR electrocatalyst cyclic test diagram at -0.5V vs. RHE.

[0046] Figure 14 It is Ru prepared in Example 1 3％ -Discharge curves and power density curves of zinc-nitrate batteries assembled using HEO materials. Detailed Implementation

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

[0048] Unless otherwise specified, all raw materials and equipment used in this invention are commercially available products. For example, the materials mentioned in the examples and comparative examples—hydroquinone, formaldehyde, RuCl3·3H2O, (NH4)2PdCl4, H2PtCl6, CeCl3·7H2O, PrCl3·7H2O, YCl3, ZrCl4, HfCl4, KNO3, K2SO4, Nafion (5 wt.%), and ethanol—were all purchased from Sigma Aldrich. Deionized water was used throughout the entire experiment.

[0049] Example 1

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

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

[0052] (2) Adjust the pH 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 while stirring moderately. Stop stirring when the solution becomes turbid.

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

[0055] (5) The dry gel obtained above was calcined in air at 950°C for 2 hours. The resulting high-entropy oxide-supported 3at%Ru single-atom material was named Ru. 3％ -HEO.

[0056] Example 2

[0057] Referring to Example 1, the only difference is that the mass of RuCl3·3H2O in Example 1 is changed to 0 mg, while everything else is the same as in Example 1. The high-entropy oxide material obtained is denoted as (CePrYZrHf)O. x .

[0058] Example 3

[0059] Referring to Example 1, the only difference is that the mass of RuCl3·3H2O in Example 1 was changed to 1.1 mg, while all other aspects were the same as in Example 1. The resulting high-entropy oxide loaded with 2 at.% Ru species was named Ru. 2％ -HEO.

[0060] Example 4

[0061] Referring to Example 1, the only difference is that the mass of RuCl3·3H2O in Example 1 was changed to 2.2 mg, while everything else remained the same as in Example 1. The resulting high-entropy oxide loaded with 4 at.% Ru species was named Ru. 4％ -HEO.

[0062] Example 5

[0063] Referring to Example 1, the only difference is that 1.6 mg RuCl3·3H2O in Example 1 was replaced with 2.2 mg (NH4)2PdCl6, while all other aspects remained the same as in Example 1. The resulting high-entropy oxide loaded with 3 at.% Pd species was named Pd. 3％ -HEO.

[0064] Example 6

[0065] Referring to Example 1, the only difference is that 1.6 mg RuCl3·3H2O in Example 1 was replaced with 2.9 mg (NH4)2PdCl6, while all other aspects remained the same as in Example 1. The resulting high-entropy oxide loaded with 4 at.% Pd species was named Pd. 4％ -HEO.

[0066] Example 7

[0067] Referring to Example 1, the only difference is that the 1.6 mg RuCl3·3H2O in Example 1 was replaced with 2.5 mg H2PtCl6, and everything else was the same as in Example 1. The resulting high-entropy oxide loaded with 3 at.% Pt species was named Pt. 3％ -HEO.

[0068] Example 8

[0069] Referring to Example 1, the only difference is that 1.6 mg RuCl3·3H2O in Example 1 was replaced with 3.4 mg H2PtCl6, and everything else was the same as in Example 1. The resulting high-entropy oxide loaded with 4 at.% Pt species was named Pt. 4％ -HEO.

[0070] Comparative Example 1

[0071] Referring to Example 1, the only difference is 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. All other aspects are the same as in Example 2. The resulting low-entropy oxide support cerium dioxide (CeO2) is named CeO2.

[0072] Comparative Example 2

[0073] Referring to Comparative Example 1, the only difference was that the mass of RuCl3·3H2O in Comparative Example 1 was changed to 0.5 mg, while all other aspects remained the same as in Comparative Example 1. The final CeO2-loaded 1 at.% Ru species was named Ru. 1％ -CeO2.

[0074] Comparative Example 3

[0075] Referring to Comparative Example 1, the only difference was that the mass of RuCl3·3H2O in Comparative Example 1 was changed to 1.1 mg, while all other aspects remained the same as in Comparative Example 1. The final CeO2-loaded 2 at.% Ru species was named Ru. 2％ -CeO2.

[0076] Comparative Example 4

[0077] Referring to Comparative Example 1, the only difference was that the mass of (NH4)2PdCl6 in Comparative Example 1 was changed to 1.5 mg, while all other aspects remained the same as in Comparative Example 1. The final CeO2-loaded 2 at.% Pd species was named Pd. 2％ -CeO2.

[0078] Comparative Example 5

[0079] Referring to Comparative Example 1, the only difference was that the mass of H2PtCl6 in Comparative Example 1 was changed to 1.7 mg, while all other aspects remained the same as in Comparative Example 1. The final CeO2-loaded 2 at.% Pt species was named Pt. 2％ -CeO2.

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

[0081] 1. 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 were characterized using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), electron paramagnetic resonance (EPR), X-ray diffraction (XRD), and an electrochemical workstation. The results are as follows:

[0082] turn out:

[0083] (1) The HAADF-STEM test results show that: Figure 1 As shown, the high-entropy oxide support (CePrYZrHf)O prepared in Example 2 x Atomic-resolution HAADF-STEM images ( Figure 1 a) and its inverse fast Fourier transform (IFFT) image ( Figure 1 b) Display (CePrYZrHf)O x The presence of lattice fringes in the crystal structure increases the diffusion and migration energy barrier for single atoms in noble metals.

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

[0085] (3) XRD test results show that: Figure 3 As shown, the XRD patterns of the low-entropy oxide CeO2 prepared in Comparative Examples 1-3 with different contents of Ru species 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) XRD test results show that: Figure 4 As shown, the XRD patterns of the high-entropy oxides prepared in Examples 1-4 with different contents of Ru species show that when the introduced Ru is less than 3 at%, (CePrYZrHf)O x The crystal phase remained intact, with no characteristic peaks from Ru species, indicating that Ru may exist in a single-atom form. However, when the Ru content increased to 4 at%, the characteristic diffraction peaks of RuO2 became clearly observable. Compared to CeO2 support, the high-entropy oxide (CePrYZrHf)O... x It can support a higher content of Ru single atoms.

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

[0088] (6) The test results of HAADF-STEM and the corresponding EDX element mapping show that: Figure 6 As shown, Ru was prepared in Example 1. 3％ -EDX element mapping of HEO material shows Ru 3％ The uniform distribution of Ce, Pr, Y, Zr, and Hf elements in HEO indicates the successful preparation of a single-phase solid solution high-entropy oxide. Furthermore, no Ru agglomeration was observed, suggesting that Ru single atoms are present in (CePrYZrHf)O. x Uniformly dispersed on nanoparticles.

[0089] (7) XRD test results show that: Figure 7 As shown, the Pd prepared in Examples 5-6 3％ -HEO and Pd 4％ -HEO material and Pd prepared in Comparative Example 4 2％ The XRD pattern of -CeO2 shows Pd 3％ - HEO lacks characteristic peaks for Pd species, while typical diffraction peaks of metallic Pd can be found in Pd. 4％ -HEO and Pd 2％ Observed in CeO2, indicating that compared to CeO2, the high-entropy oxide support (CePrYZrHf)O x It can support a higher content of Pd single atoms.

[0090] (8) The test results of HAADF-STEM and the corresponding EDX element mapping show that: Figure 8 As shown, Pd was prepared in Example 5. 3％ -HEO material EDX elemental mapping shows Pd 3％ The uniform distribution of Ce, Pr, Y, Zr, and Hf elements in HEO indicates the successful preparation of a single-phase solid solution high-entropy oxide. Furthermore, no Pd agglomeration was observed, suggesting that Pd single atoms are present in (CePrYZrHf)O. x Uniformly dispersed on nanoparticles.

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

[0092] (10) The test results of HAADF-STEM and the corresponding EDX element mapping show that: Figure 10 As shown, Pt was prepared in Example 7. 3％ -HEO material EDX elemental mapping shows Pt 3％ The uniform distribution of Ce, Pr, Y, Zr, and Hf elements in HEO indicates the successful preparation of a single-phase solid solution high-entropy oxide. Furthermore, no Pt agglomeration was observed, suggesting that Pt single atoms are present in (CePrYZrHf)O. x Uniformly dispersed on nanoparticles.

[0093] The catalysts obtained in each example and comparative example were used for electrocatalytic nitrate reduction. The specific process was as follows: Before electrochemical testing, the Nafion membrane was pretreated sequentially by boiling in 5% H₂O₂ aqueous solution for 1 h, boiling in deionized water for 1 h, boiling in 0.5M H₂SO₄ for 3 h, and finally boiling again in deionized water for 6 h to achieve complete protonation. Electrocatalytic performance testing was conducted on a CHI 660D electrochemical workstation using a three-electrode system, with the Ag / AgCl electrode as the reference electrode, a graphite rod as the counter electrode, and the catalyst supported on carbon paper (1×1 cm⁻¹). 2The working electrode is as follows: 5 mg of the prepared catalyst is weighed and added to 25 μL of 5 wt.% Nafion solution and 5 mL of anhydrous ethanol, and ultrasonically dispersed to form a uniform catalyst ink; then 0.5 mL of the ink is uniformly drop-coated onto a 1 cm² surface. 2 On carbon paper, after drying, it is used as the working electrode. All electrolytes used were 0.1M KOH solutions containing 10mM KNO3, and dissolved oxygen was removed by argon bubbling for 30 minutes before testing. Furthermore, to verify the practical application capability of the catalyst at the device level, a Ru-based... 3％ The zinc-nitrate battery of HEO was tested in an H-type electrolytic cell with a two-electrode system. (The measurement was performed using a 1×1 cm⁻¹ electrode.) 2 Ru 3％ -HEO-loaded carbon paper was used as the cathode, and placed in 0.5M NO3. - In 3M KOH electrolyte; at 1×1cm 2 Zinc foil was used as the anode and placed in a 0.2M Zn(Ac)2 / 3M KOH solution. The two electrodes were separated by a Nafion 117 membrane. Relevant battery test results were also recorded using a CHI 660D electrochemical workstation.

[0094] (11)Ru 3％ -HEO and Ru 4％ The NRA performance test results of HEO materials show that: Figure 11 As shown, Ru in Example 1 3％ The Faraday efficiency of -HEO exhibits a volcanic trend, peaking at 91.3% at -0.5V vs. RHE, corresponding to an ammonia yield of 5.79 mg h⁻¹. -1 mg cat. -1 far higher than Ru 4％ -HEO (75.6% and 2.61mg h) -1 mg cat. -1 This result indicates that Ru single atoms exhibit higher NRA catalytic activity compared to RuO2.

[0095] (12)(CePrYZrHf)O x Comparison of NRA performance at optimal potentials for high-entropy supports, Ru-HEO, and Ru-CeO2 materials, for example Figure 12 As shown: (CePrYZrHf)O of Example 2 x The high-entropy support exhibited very low Faradaic efficiency and ammonia yield, indicating its negligible NRA activity. The NRA performance of the Ru-HEO catalyst was significantly improved after the introduction of the Ru species, confirming the presence of (CePrYZrHf)O. xThe Ru species dispersed on the support are the main active sites for nitrate adsorption and activation. Furthermore, due to Ru... 3％ -HEO can achieve higher Ru single-atom loading, therefore its NRA performance is better than Ru 1％ -CeO2 is much better.

[0096] (13) In an H-type flow electrolytic cell, Ru is subjected to a potential of -0.5V. 3％ -HEO conducted long-term stability testing on NRA: such as Figure 13 As shown, nitrate reduction tests were conducted continuously for 150 hours at the optimal reduction potential of -0.5V vs. RHE. The current density and Faraday efficiency remained stable during the cyclic test, and the yield increased nearly linearly over time, indicating its excellent NRA stability.

[0097] (14) Based on Ru 3％ Performance tests of HEO's zinc-nitrate battery show that: Figure 14 As shown, based on Ru 3％ -HEO-assembled zinc-nitrate batteries achieve a current density as high as 10 mA / cm² at 0.52V. -2 At a voltage of 0.32V, the peak power density reaches 9.6mW / cm². -2 .

[0098] The performance results of each embodiment and comparative example are summarized below:

[0099]

[0100]

[0101] As shown in the table above, when noble metals are supported on the catalyst surface in single-atom form, they exhibit superior ammonia yield and Faradaic efficiency in the electrocatalytic nitrate reduction reaction. Furthermore, when high-entropy oxides are used as the catalyst substrate, their abundant defect structures and significant lattice distortion effects enable higher loading of noble metal single atoms and more uniform dispersion, resulting in significantly better overall NRA performance compared to the comparative catalysts using low-entropy oxides as supports.

[0102] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the invention patent should be included within the protection scope of the present invention patent.

Claims

1. A method for preparing a high-entropy oxide stabilized noble metal monatomic catalyst, characterized in that, The method comprises the following steps: (1) dissolving cerium salt, praseodymium salt, yttrium salt, zirconium salt and hafnium salt in an aqueous solution of hydroquinone, and dissolving noble metal chloride in the solution; (2) adjusting the pH value of the solution to 0.5-2, and then heating and stirring in an oil bath; (3) adding formaldehyde solution to the solution, and stopping stirring immediately when the solution becomes turbid; (4) placing the turbid solution to stand for a period of time, and then transferring the solution to a vacuum oven for drying treatment; (5) calcining the dry gel obtained in step (4) in air to obtain a high-entropy oxide supported noble metal monatomic catalyst.

2. The preparation method of the high-entropy oxide stabilized noble metal monatomic catalyst according to claim 1, 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.

3. The preparation method of the high-entropy oxide stabilized noble metal monatomic 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 metal is 80-20:

1.

4. The preparation method of the high-entropy oxide stabilized noble metal monatomic 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 noble metal chloride is 0-3.2% of the total metal molar amount.

5. The method of claim 1, wherein the high-entropy oxide stabilized noble metal monatomic catalyst is prepared by the steps of: preparing a solution of a noble metal salt and a high-entropy oxide salt; mixing the solution with a reducing agent; and heating the mixture to form the high-entropy oxide stabilized noble metal monatomic catalyst. In step (2), the pH value is adjusted by using a hydrochloric acid solution with a concentration of 30-40%, and the heating and stirring temperature is 80-90℃.

6. The method of claim 1, wherein the high-entropy oxide stabilized noble metal monatomic catalyst is prepared by the steps of: preparing a solution of a noble metal salt and a high-entropy oxide salt; mixing the solution with a reducing agent; and heating the mixture to form the high-entropy oxide stabilized noble metal monatomic catalyst. In step (3), the concentration of the formaldehyde solution is 30-40%, and the molar ratio of formaldehyde to hydroquinone is 1-2:

1.

7. The method for preparing a 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℃, and the aging time is 2-5 h; The vacuum drying temperature is 60-80℃, and the time is 18-36 h; In step (5), the calcination temperature is 900-1000℃, and the time is 2-5 h.

8. A high-entropy oxide supported noble metal monatomic catalyst prepared by the method of any one of claims 1-7.

9. Use of the high-entropy oxide supported noble metal single-atom catalyst according to claim 8, characterized in that, The catalyst was used as a catalyst for electrocatalytic reduction of nitrate, the highest Faraday efficiency was 91.3%, and the corresponding ammonia production rate was 5.79 mg h -1 mg cat. -1 .

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