Composite material for electro-catalytic nitrate reduction and preparation method and application thereof

Abstract

The invention discloses a composite material for electrocatalytic nitrate reduction and a preparation method and application thereof, and belongs to the technical field of electrocatalyst.The preparation method of the composite material comprises the following steps that a first cobalt source, an iron source, a fluorine source, urea and a first solvent are mixed, a conductive substrate is added, a first solvothermal reaction is carried out, and a second solvothermal reaction is carried out; a Fe-Co (OH) F precursor loaded on the conductive substrate is obtained; and mixing the conductive substrate loaded with the Fe-Co (OH) F precursor, a second cobalt source, an organic ligand and a second solvent, and carrying out a second solvothermal reaction to obtain the Fe-Co (OH) F / Co-TEPB composite material. The prepared composite material for electro-catalysis nitrate radical reduction has high specific surface area and excellent conductivity, shows excellent NO3RR performance through the synergistic effect of interface double active sites in combination with an enhanced electron transfer mechanism, has extremely high ammonia yield and Faraday efficiency, is excellent in stability, and can be applied to the field of electrochemical catalysis. The method has a wide application prospect in the fields of nitrate wastewater treatment and ammonia synthesis.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, specifically to a composite material for the electrocatalytic reduction of nitrate, its preparation method, and its application. Background Technology

[0002] With the rapid development of industry and agriculture, the amount of nitrates (NO3) in water bodies has increased. - Pollution is becoming increasingly serious, posing a threat to the ecological environment and human health. Meanwhile, ammonia (NH3), as an important chemical raw material and a potential clean energy carrier, has attracted much attention for its synthesis. The electrocatalytic nitrate reduction reaction (NO3RR) is a process that converts harmful NO3 into nitrogenous compounds. - The green technology for converting NH3 into high-value-added NH3 has attracted much attention due to its advantages such as mild reaction conditions and ease of control.

[0003] Developing efficient, stable, and low-cost electrocatalysts is crucial for the large-scale application of NO3RR technology. Current research focuses on catalysts primarily consisting of noble metal and non-noble metal materials. While noble metal catalysts (such as Pt and Ru) exhibit high activity, their high cost and scarcity limit their application. Therefore, developing high-performance non-noble metal catalysts has become a research hotspot.

[0004] Transition metal hydroxides and metal-organic frameworks (MOFs) have shown great potential in catalysis due to their unique structures and tunable electronic properties. However, single-component materials often have limitations in conductivity, number of active sites, or adsorption capacity for reaction intermediates, restricting their catalytic performance. Therefore, the core challenge in improving the catalytic performance of NO3RR lies in how to combine materials with different functions through rational structural design to construct heterostructures with synergistic effects. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a composite material for electrocatalytic nitrate reduction, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, embodiments of the present invention provide the following technical solution: a method for preparing a composite material for electrocatalytic nitrate reduction, comprising the following steps:

[0007] A first cobalt source, an iron source, a fluorine source, urea, and a first solvent are mixed, added to a conductive substrate, and subjected to a first solvothermal reaction to obtain a Fe-Co(OH)F precursor loaded on a conductive substrate.

[0008] A conductive substrate loaded with Fe-Co(OH)F precursor, a second cobalt source, an organic ligand, and a second solvent are mixed and subjected to a second solvothermal reaction to obtain the Fe-Co(OH)F / Co-TEPB composite material; the organic ligand is 1,2,4,5-tetra-(pyridin-4-yl)benzene.

[0009] Preferably, the molar ratio of the first cobalt source, iron source, fluorine source and urea is (30-50):(0.5-1.5):(80-120):200.

[0010] Preferably, the mass ratio of the second cobalt source, the organic ligand, and urea is (1-3):(1-3):60.

[0011] Preferably, the first cobalt source and the second cobalt source are both divalent cobalt salts; the iron source is a trivalent iron salt; the fluorine source is ammonium fluoride; and the first solvent and the second solvent are independently deionized water or methanol.

[0012] Preferably, the first solvent is deionized water, the first cobalt source is cobalt nitrate hexahydrate, and the iron source is ferric nitrate nonahydrate.

[0013] Preferably, the temperature of the first solvothermal reaction is 120-140°C.

[0014] Preferably, the second solvent is methanol, and the second cobalt source is anhydrous cobalt nitrate.

[0015] Preferably, the temperature of the second solvothermal reaction is 80-90°C.

[0016] Another objective of this invention is to provide a composite material for electrocatalytic nitrate reduction prepared by the above-described preparation method, wherein the composite material is a heterostructure in which Co-TEPB nanosheets are grown on the surface of Fe-Co(OH)F nanowires.

[0017] Another object of the present invention is to provide an application of the above-mentioned composite material in electrocatalytic nitrate reduction.

[0018] The composite material for electrocatalytic nitrate reduction provided by this invention has a high specific surface area and excellent conductivity. Through the synergistic effect of two active sites at the interface (Fe sites for adsorption activation and Co sites for hydrogenation) and combined with an enhanced electron transfer mechanism, it exhibits excellent NO3RR performance, extremely high ammonia yield and Faraday efficiency, and excellent stability. It has broad application prospects in the fields of nitrate wastewater treatment and ammonia synthesis. Attached Figure Description

[0019] Figure 1The images show SEM images of Fe-Co(OH)F / Co-TEPB obtained in Example 1; in the images, a is a SEM image with a scale bar of 2 μm; b is a SEM image with a scale bar of 200 nm.

[0020] Figure 2 The images show TEM images of Fe-Co(OH)F / Co-TEPB obtained in Example 1. In the images, a is the overall TEM image; b is a magnified view of Region 1; c is a magnified view of Region 2; d is an intensity analysis diagram of the lattice fringes in c; and e shows the fine arrangement at the atomic level.

[0021] Figure 3 The image shows the XRD pattern of Fe-Co(OH)F / Co-TEPB obtained in Example 1.

[0022] Figure 4 The images show SEM images of Fe-Co(OH)F obtained in Example 1; in the images, a is an SEM image with a scale bar of 2 μm; b is an SEM image with a scale bar of 200 nm.

[0023] Figure 5 The image shows the XRD pattern of Fe-Co(OH)F obtained in Example 1.

[0024] Figure 6 The image shows a SEM image of Co(OH)F obtained in Comparative Example 1; in the image, a is a SEM image with a scale bar of 2 μm; b is a SEM image with a scale bar of 200 nm.

[0025] Figure 7 The XRD pattern of Co(OH)F obtained in Comparative Example 1;

[0026] Figure 8 The image shows the SEM images of Co-TEPB obtained in Comparative Example 2; in the image, a is the SEM image with a scale bar of 2 μm; b is the SEM image with a scale bar of 200 nm.

[0027] Figure 9 The images show the FT-IR spectra of the materials obtained in Example 1 and Comparative Example 2.

[0028] Figure 10 The LSV curves are for nitrate reduction in electrolyte of the materials obtained in Examples 1-3 and Comparative Example 1.

[0029] Figure 11 The ammonia faradaic efficiency of nitrate reduction in electrolyte for Fe-Co(OH)F / Co-TEPB obtained in Example 1.

[0030] Figure 12The ammonia Faraday efficiency of nitrate reduction in electrolyte for Fe-Co(OH)F obtained in Example 1.

[0031] Figure 13 The ammonia faradaic efficiency of nitrate reduction in electrolyte for Co(OH)F obtained in Comparative Example 1.

[0032] Figure 14 The amount of ammonia produced by nitrate reduction in the electrolyte of Fe-Co(OH)F / Co-TEPB obtained in Example 1.

[0033] Figure 15 The amount of ammonia produced by the reduction of nitrate ions in the electrolyte of Fe-Co(OH)F obtained in Example 1 is shown.

[0034] Figure 16 The amount of ammonia produced by the reduction of nitrate ions in the electrolyte of Co(OH)F obtained in Comparative Example 1 is shown.

[0035] Figure 17 Cyclic stability test of Fe-Co(OH)F / Co-TEPB obtained in Example 1 in electrolyte. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] In one embodiment of the present invention, a composite material for electrocatalytic nitrate reduction is provided, which is a heterostructure in which Co-TEPB nanosheets are grown on the surface of Fe-Co(OH)F nanowires; wherein Fe-Co(OH)F serves as a precursor and active site support, and Co-TEPB serves as a conductive layer and catalytic active layer. The heterostructure interface formed by the two can regulate the electronic structure of the dual active sites, wherein the Fe sites promote the adsorption and activation of nitrate, and the Co sites dominate the hydrogenation reaction, thereby synergistically improving the catalytic performance.

[0038] In another embodiment of the present invention, a method for preparing a composite material for electrocatalytic nitrate reduction is also provided. This method is simple to operate, and by constructing a MOF-on-Hydroxide heterostructure, the resulting composite material exhibits extremely high activity, selectivity, and stability in NO3RR. Specifically, the method for preparing the composite material includes the following steps:

[0039] S1. Synthesis of iron-doped cobalt fluoride Fe-Co(OH)F precursor nanoarray on conductive substrate by hydrothermal method: Mix the first cobalt source, iron source, fluorine source, urea and the first solvent, add to the conductive substrate, and carry out the first solvothermal reaction to obtain the Fe-Co(OH)F precursor loaded on the conductive substrate.

[0040] S2. A conductive substrate loaded with Fe-Co(OH)F precursor, a second cobalt source, an organic ligand, and a second solvent are mixed and subjected to a second solvothermal reaction to grow Co-TEPB nanosheets, forming a Fe-Co(OH)F / Co-TEPB MOF-on-Hydroxide heterostructure, thus obtaining the Fe-Co(OH)F / Co-TEPB composite material.

[0041] The organic ligand is 1,2,4,5-tetra-(pyridin-4-yl)benzene (TEPB); the molar ratio of the first cobalt source, iron source, fluorine source and urea is (30-50):(0.5-1.5):(80-120):200; the mass ratio of the second cobalt source, organic ligand and urea is (1-3):(1-3):60; the electronic structure of the composite material can be optimized by adjusting the amount of iron doping in this embodiment of the invention.

[0042] In practical applications, the conductive substrate can be carbon cloth, but is not limited to it; the first cobalt source and the second cobalt source are both divalent cobalt salts, such as cobalt nitrate, cobalt chloride or cobalt acetate; the iron source is a trivalent iron salt, such as ferric nitrate, ferric chloride or ferric sulfate; the fluorine source is ammonium fluoride; the first solvent and the second solvent are independently deionized water or methanol.

[0043] In a preferred embodiment of the present invention, the first solvent is deionized water, the first cobalt source is cobalt nitrate hexahydrate, and the iron source is ferric nitrate nonahydrate; the temperature of the first solvothermal reaction is 120-140°C, preferably 120°C, and the reaction time is 4-12 hours, preferably 6 hours.

[0044] In a preferred embodiment of the present invention, the second solvent is methanol, and the second cobalt source is anhydrous cobalt nitrate; the temperature of the second solvothermal reaction is 80-90°C, preferably 85°C, and the reaction time is 24-48 hours, preferably 48 hours. Through this step, a conductive metal-organic framework (MOF) material Co-TEPB can be grown in situ on the Fe-Co(OH)F precursor.

[0045] In the embodiments of the present invention, the Fe-Co(OH)F / Co-TEPB composite material prepared by the above preparation method has high specific surface area and conductivity, as well as high activity and good catalytic stability.

[0046] In another embodiment of the present invention, the application of the above-mentioned Fe-Co(OH)F / Co-TEPB composite material in electrocatalytic nitrate reduction is also provided, specifically for the treatment of ammonia synthesis or nitrate wastewater. When the Fe-Co(OH)F / Co-TEPB composite material is used as a catalyst for nitrate reduction, it exhibits good catalytic activity and stability in an electrolyte containing 1M KOH and 0.1M KNO3.

[0047] In practical applications, the Fe-Co(OH)F / Co-TEPB composite material can be directly used as the working electrode, with a test electrode area of ​​0.5*0.5cm². 2 In this embodiment of the invention, there are no specific requirements for the area of ​​the test electrode.

[0048] In this embodiment of the invention, the Fe-Co(OH)F / Co-TEPB composite material can be directly used as a nitrate reduction catalyst; as a nitrate reduction catalyst, the Fe-Co(OH)F / Co-TEPB composite material can increase the rate of ammonia production from nitrate reduction, thereby improving the performance of nitrate reduction.

[0049] The following embodiments are some specific implementation examples of the present invention in practical applications, but are not limited thereto.

[0050] Example 1: This example provides a method for preparing a composite material for electrocatalytic nitrate reduction, specifically including the following steps:

[0051] S1. Dissolve 0.582 g of cobalt nitrate hexahydrate (2 mmol), 0.02 g of ferric nitrate nonahydrate (0.05 mmol), 0.1852 g of ammonium fluoride (5 mmol), and 0.6 g of urea (10 mmol) in deionized water to form a homogeneous solution. Immerse a clean piece of carbon cloth (CC) in the above solution, transfer it to a reaction vessel, and carry out a hydrothermal reaction at 120 °C for 6 h. After the reaction is completed, allow it to cool naturally to room temperature, remove the product, wash it several times with deionized water and ethanol, and dry it to obtain the Fe-Co(OH)F nanoarray loaded on the carbon cloth.

[0052] S2. The carbon cloth loaded with Fe-Co(OH)F, 0.02 g of anhydrous cobalt nitrate and 0.02 g of organic ligand TEPB were dispersed together in 10 mL of methanol solvent; then the mixture was transferred to a reaction vessel and subjected to a solvothermal reaction at 85 °C for 48 h; after the reaction was completed, the mixture was allowed to cool naturally, the product was taken out, washed three times with methanol, and dried to obtain the Fe-Co(OH)F / Co-TEPB composite material grown on the carbon cloth.

[0053] Example 2: This example provides a method for preparing a composite material for electrocatalytic nitrate reduction, specifically including the following steps:

[0054] S1. Dissolve 0.582 g of cobalt nitrate hexahydrate (2 mmol), 0.02 g of ferric nitrate nonahydrate (0.05 mmol), 0.1852 g of ammonium fluoride (5 mmol), and 0.6 g of urea (10 mmol) in deionized water to form a homogeneous solution. Immerse a clean piece of carbon cloth (CC) in the above solution, transfer it to a reaction vessel, and carry out a hydrothermal reaction at 120 °C for 6 h. After the reaction is completed, allow it to cool naturally to room temperature, remove the product, wash it several times with deionized water and ethanol, and dry it to obtain the Fe-Co(OH)F nanoarray loaded on the carbon cloth.

[0055] S2. The carbon cloth loaded with Fe-Co(OH)F, 0.01g of anhydrous cobalt nitrate and 0.01g of organic ligand TEPB were dispersed together in 10mL of methanol solvent; then the mixture was transferred to a reaction vessel and subjected to a solvothermal reaction at 85℃ for 48h; after the reaction was completed, the mixture was naturally cooled, the product was taken out, washed with methanol 3 times, and dried to obtain the Fe-Co(OH)F / Co-TEPB-1 composite material grown on the carbon cloth.

[0056] Example 3: This example provides a method for preparing a composite material for electrocatalytic nitrate reduction, specifically including the following steps:

[0057] S1. Dissolve 0.582 g of cobalt nitrate hexahydrate (2 mmol), 0.02 g of ferric nitrate nonahydrate (0.05 mmol), 0.1852 g of ammonium fluoride (5 mmol), and 0.6 g of urea (10 mmol) in deionized water to form a homogeneous solution. Immerse a clean piece of carbon cloth (CC) in the above solution, transfer it to a reaction vessel, and carry out a hydrothermal reaction at 120 °C for 6 h. After the reaction is completed, allow it to cool naturally to room temperature, remove the product, wash it several times with deionized water and ethanol, and dry it to obtain the Fe-Co(OH)F nanoarray loaded on the carbon cloth.

[0058] S2. The carbon cloth loaded with Fe-Co(OH)F, 0.03g of anhydrous cobalt nitrate and 0.03g of organic ligand TEPB were dispersed together in 10mL of methanol solvent; then the mixture was transferred to a reaction vessel and subjected to a solvothermal reaction at 85℃ for 48h; after the reaction was completed, the mixture was naturally cooled, the product was taken out, washed with methanol 3 times, and dried to obtain the Fe-Co(OH)F / Co-TEPB-2 composite material grown on the carbon cloth.

[0059] Comparative Example 1: This comparative example provides a Co(OH)F material, the preparation method of which includes the following steps:

[0060] 0.582 g of cobalt nitrate hexahydrate (2 mmol), 0.1852 g of ammonium fluoride (5 mmol), and 0.6 g of urea (10 mmol) were dissolved in deionized water to form a homogeneous solution. A clean piece of carbon cloth (CC) was immersed in the above solution and transferred to a reaction vessel. The reaction was carried out at 120 °C for 6 h using hydrothermal methods. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The product was then removed, washed several times with deionized water and ethanol, and dried to obtain the Co(OH)F material loaded on the carbon cloth.

[0061] Comparative Example 2: This comparative example provides a Co-TEPB material, the preparation method of which includes the following steps:

[0062] 0.02 g of anhydrous cobalt nitrate and 0.02 g of organic ligand TEPB were dispersed together in 10 mL of methanol solvent; the mixture was transferred to a reaction vessel and subjected to a solvothermal reaction at 85 °C for 48 h; after the reaction was completed, the mixture was allowed to cool naturally, the product was removed, washed three times with methanol, and dried to obtain Co-TEPB material.

[0063] Structural Characterization and Performance Testing: I. The Fe-Co(OH)F / Co-TEPB composite material prepared in Example 1 was characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). The results are as follows: Figures 1-3 As shown.

[0064] in, Figure 1 These are SEM images of the Fe-Co(OH)F / Co-TEPB composite material. The SEM images show that Fe-Co(OH)F / Co-TEPB grows vertically in a nanoarray on carbon cloth. In Fe-Co(OH)F / Co-TEPB, nanosheet structures are clearly visible on the nanowire surface, exhibiting a multi-level morphological structure composed of numerous interwoven nanosheets and nanorods / sheets. Furthermore, the SEM images indicate that the Fe-Co(OH)F / Co-TEPB composite material possesses the potential for a high specific surface area, which may provide more active sites for catalytic reactions.

[0065] Figure 2 This is a high-resolution transmission electron microscope image of the Fe-Co(OH)F / Co-TEPB composite material, revealing the heterogeneous interface of the material, in which the crystalline Fe-Co(OH)F and the amorphous Co-TEPB are clearly visible. Figure 2 d is a Figure 2 Intensity analysis of the lattice fringes in c reveals a highly regular periodic structure. Figure 2The images show a finely arranged structure at the atomic level. These images confirm that the Fe-Co(OH)F / Co-TEPB composite material successfully forms a crystalline / amorphous heterostructure. This interfacial structure can typically promote charge transfer and produce a synergistic effect, thereby enhancing catalytic activity. Figure 2 This further confirms that the crystal structure of Fe-Co(OH)F (the lattice spacing of 0.252 nm corresponds to its (111) crystal plane) and the surrounding amorphous Co-TEPB layer form a clear heterogeneous interface.

[0066] Figure 3 The XRD pattern of the Fe-Co(OH)F / Co-TEPB composite material is shown. Figure 3 The XRD patterns show that the diffraction peaks of Fe-Co(OH)F / Co-TEPB are consistent with the Co(OH)F structure (PDF#00-050-0827), and there are no diffraction peaks of Fe-related species, indicating that Fe exists in a doped form. No obvious Co-TEPB characteristic peaks were observed in the Fe-Co(OH)F / Co-TEPB composite material, which may be attributed to the formation of amorphous MOFs.

[0067] II. The Fe-Co(OH)F material prepared in step S1 of Example 1, the Co(OH)F material prepared in Comparative Example 1, and the Co-TEPB material prepared in Comparative Example 2 were characterized by SEM and XRD, respectively. The results are as follows: Figures 4-8 As shown.

[0068] in, Figure 4 This is a SEM image of the Fe-Co(OH)F material. The SEM image shows that the Fe-Co(OH)F material is composed of a large number of thin nanowires or nanoneedles, which grow vertically on carbon cloth in a needle-like nanoarray.

[0069] Figure 5 This is the XRD pattern of Fe-Co(OH)F material; from Figure 5 The XRD pattern shows that the Fe-Co(OH)F diffraction peaks are consistent with the Co(OH)F structure (PDF#00-050-0827), and there are no diffraction peaks of Fe-related species, indicating that Fe exists in the form of doping.

[0070] Figure 6 This is a SEM image of pure Co(OH)F material. Figure 6 The material exhibits a three-dimensional microsphere structure resembling a sea urchin, composed of numerous nanoneedles, which grow vertically on the carbon cloth in a needle-like nanoarray.

[0071] Figure 7 This is the XRD pattern of Co(OH)F material; from Figure 7The XRD pattern shows that the diffraction peaks of Co(OH)F are consistent with the structure of Co(OH)F (PDF#00-050-0827), confirming that the synthesized material is Co(OH)F crystal.

[0072] Figure 8 These are SEM images of Co-TEPB material; by Figure 8 It can be seen that Co-TEPB is a stacked layered nanosheet structure.

[0073] III. The Fe-Co(OH)F and Fe-Co(OH)F / Co-TEPB composite materials prepared in Example 1, as well as the Co-TEPB material prepared in Comparative Example 2, were characterized by Fourier transform infrared spectroscopy (FT-IR). The results are as follows: Figure 9 As shown. Figure 9 These are the FT-IR spectra of three materials: Fe-Co(OH)F / Co-TEPB, Fe-Co(OH)F, and Co-TEPB. By comparison, Fe-Co(OH)F / Co-TEPB simultaneously contains the vibrational peaks of v(OH) and v(Co / Fe-O) in Fe-Co(OH)F, as well as the characteristic peaks of v(C=C) and v(CN) in Co-TEPB. This confirms from the perspective of chemical bonding that the composite material is successfully composed of two components. Figure 9 The FT-IR spectra showed C=C and CN vibrational peaks of the Co-TEPB ligand. Meanwhile, Fe-Co(OH)F / Co-TEPB exhibited additional C=C and CN vibrational peaks of the TEPB ligand compared to Fe-Co(OH)F, confirming the presence of the MOF in Example 1.

[0074] IV. The Fe-Co(OH)F and Fe-Co(OH)F / Co-TEPB composite materials obtained in Example 1, the Fe-Co(OH)F / Co-TEPB-1 composite material obtained in Example 2, the Fe-Co(OH)F / Co-TEPB-2 composite material obtained in Example 3, and the Co(OH)F material obtained in Comparative Example 1 were directly used as working electrodes, with a Pt sheet as the counter electrode and an Hg / HgO electrode as the reference electrode. NO3RR tests were performed in a 1M KOH electrolyte containing 0.1M KNO3. During the test, argon gas was continuously introduced into the electrolyte to maintain argon saturation. The test results are as follows: Figures 10-17 As shown.

[0075] in, Figure 10These are linear sweep voltammetry (LSV) curves of different materials in an electrolyte containing nitrate. The curves compare the catalytic activity of Co(OH)F, Fe-Co(OH)F, and two different ratios of Fe-Co(OH)F / Co-TEPB composites. At the same potential, the Fe-Co(OH)F / Co-TEPB prepared in Example 1 exhibits the highest reduction current density and the lowest overpotential, indicating that it has the best catalytic activity for the nitrate reduction reaction.

[0076] Figure 11 , Figure 12 and Figure 13 These three graphs show the Faradaic efficiency (FE) of Fe-Co(OH)F / Co-TEPB, Fe-Co(OH)F, and Co(OH)F at different potentials for the catalytic reduction of nitrate to ammonia. Comparing the three graphs reveals that Fe-Co(OH)F / Co-TEPB maintains an extremely high Faradaic efficiency close to 100% over a wide potential range (-0.2V to -0.5V). At -0.4V, its Faradaic efficiency reaches as high as 99.63% (close to 100%), significantly better than Fe-Co(OH)F (approximately 90%) and Co(OH)F (approximately 66%), indicating its extremely high selectivity and excellent Faradaic efficiency.

[0077] Figure 14 , Figure 15 and Figure 16 These three graphs show the ammonia production of Fe-Co(OH)F / Co-TEPB, Fe-Co(OH)F, and Co(OH)F, respectively. Figure 14 and Figure 15 The comparison showed that the ammonia production rate of Fe-Co(OH)F / Co-TEPB was significantly higher than that of Fe-Co(OH)F and Co(OH)F at all test potentials. For example, at -0.4V, the ammonia production of Fe-Co(OH)F / Co-TEPB exceeded 22.45 mg·h⁻¹. -1 ·cm -2 The composite material prepared in this embodiment of the invention exhibits excellent ammonia production, which further proves that the composite material has superior catalytic activity.

[0078] Figure 17 The stability of the Fe-Co(OH)F / Co-TEPB composite material was demonstrated during 24-cycle testing. Throughout the 24 cycles, the ammonia production and Faradaic efficiency showed almost no decline, remaining at consistently high levels, exhibiting excellent catalytic stability. This indicates that the Fe-Co(OH)F / Co-TEPB composite material prepared in the embodiments of this invention possesses excellent long-term operational stability.

[0079] In summary, the preparation method provided by the embodiments of the present invention is simple, and the obtained Fe-Co(OH)F / Co-TEPB composite material effectively utilizes the synergistic effect of dual active sites by constructing a unique MOF-on-Hydroxide heterostructure, significantly improving the performance of electrocatalytic reduction of nitrate to ammonia, exhibiting excellent catalytic activity, selectivity and stability, and has broad application prospects in the fields of nitrate wastewater treatment and ammonia synthesis.

[0080] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification.

Claims

1. A method for preparing a composite material for electrocatalytic nitrate reduction, characterized in that, Includes the following steps: A first cobalt source, an iron source, a fluorine source, urea, and a first solvent are mixed, added to a conductive substrate, and subjected to a first solvothermal reaction to obtain a Fe-Co(OH)F precursor loaded on a conductive substrate. A conductive substrate loaded with Fe-Co(OH)F precursor, a second cobalt source, an organic ligand, and a second solvent are mixed and subjected to a second solvothermal reaction to obtain the Fe-Co(OH)F / Co-TEPB composite material; the organic ligand is 1,2,4,5-tetra-(pyridin-4-yl)benzene.

2. The method for preparing the composite material for electrocatalytic nitrate reduction according to claim 1, characterized in that, The molar ratio of the first cobalt source, iron source, fluorine source and urea is (30-50):(0.5-1.5):(80-120):

200.

3. The method for preparing the composite material for electrocatalytic nitrate reduction according to claim 2, characterized in that, The mass ratio of the second cobalt source, organic ligand and urea is (1-3):(1-3):

60.

4. The method for preparing the composite material for electrocatalytic nitrate reduction according to any one of claims 1-3, characterized in that, The first cobalt source and the second cobalt source are both divalent cobalt salts; the iron source is a trivalent iron salt; the fluorine source is ammonium fluoride; and the first solvent and the second solvent are independently deionized water or methanol.

5. The method for preparing the composite material for electrocatalytic nitrate reduction according to claim 4, characterized in that, The first solvent is deionized water, the first cobalt source is cobalt nitrate hexahydrate, and the iron source is ferric nitrate nonahydrate.

6. The method for preparing the composite material for electrocatalytic nitrate reduction according to claim 5, characterized in that, The temperature of the first solvothermal reaction is 120-140℃.

7. The method for preparing the composite material for electrocatalytic nitrate reduction according to claim 4, characterized in that, The second solvent is methanol, and the second cobalt source is anhydrous cobalt nitrate.

8. The method for preparing the composite material for electrocatalytic nitrate reduction according to claim 7, characterized in that, The temperature of the second solvothermal reaction is 80-90℃.

9. A composite material for electrocatalytic nitrate reduction prepared by the method according to any one of claims 1-8, characterized in that, The composite material is a heterostructure in which Co-TEPB nanosheets are grown on the surface of Fe-Co(OH)F nanowires.

10. The application of the composite material as described in claim 9 in the electrocatalytic nitrate reduction reaction.

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