Copper-nickel heterojunction catalyst and preparation method and application thereof

Abstract

The invention discloses a copper-nickel heterojunction catalyst as well as a preparation method and application thereof, and belongs to the field of transition metal catalysts. According to the copper-nickel heterojunction catalyst, a copper source and foamed nickel with a three-dimensional porous structure serve as raw materials, copper coexists in three valence states of Cu0, Cu1 + and Cu2 + in the catalyst, the leading valence state of nickel is Ni < 2 + >, and the catalyst contains oxygen vacancy defects and lattice dislocations. According to the catalyst, porous foamed nickel serves as a substrate, a copper-nickel oxide precursor is formed through an electro-deposition method and wet chemical oxidation, then heat treatment is conducted on the copper-nickel oxide precursor, and a heterogeneous interface rich in high-density lattice defects is constructed. The heterojunction catalyst shows remarkable catalytic activity in the application of producing ammonia by electrochemical reduction of nitrate. The copper-nickel heterojunction catalyst provided by the invention can achieve the effects of rich lattice defects and excellent electro-catalytic performance.

Description

Technical Field

[0001] The present invention relates to a transition metal catalyst, in particular to a copper-nickel heterojunction catalyst and a preparation method and application thereof. Background Art

[0002] Ammonia (NH3) is an important basic chemical raw material and clean energy carrier in modern industry. It plays an important role in agricultural fertilization, chemical synthesis and energy storage and transportation. Although the traditional Haber-Bosch process is mature, it relies on high temperature and high pressure conditions, resulting in huge energy consumption and serious carbon emissions, which limits the green and sustainable development of the ammonia industry. At the same time, the large amount of nitrate (NO3 - The problem of water pollution caused by nitrate electrochemical reduction of ammonia (NO3RR) has become increasingly prominent, prompting nitrate electrochemical reduction of ammonia (NO3RR) to become a key research direction for achieving green ammonia synthesis and environmental governance.

[0003] Catalysts have a significant impact on product formation and energy efficiency during electrochemical nitrate reduction (ENR). Heterojunction materials, due to their unique interfacial electronic structure and synergistic catalytic effects, are being used to enhance NO₃RR performance. High-performance heterojunctions can modulate active site electron density and accelerate intermediate conversion, thereby increasing ammonia yield and selectivity.

[0004] The preparation methods of heterojunction materials mainly include traditional wet chemical methods and mechanical mixing. This method is prone to interface fracture due to phase interface stress concentration, which in turn reduces the mechanical strength and cyclic stability of the material, limits the synergistic improvement of catalytic activity and long-term durability, and affects its practical application effect and promotion. In addition, it is difficult for a single heterojunction material to take into account and optimize the energy barriers at different stages of the electrochemical reaction, which restricts the further improvement of the overall catalytic performance. Copper-nickel heterojunction is considered to be a highly promising NO3RR catalytic system due to the excellent catalytic ammonia synthesis ability of copper and the good electronic regulation function of nickel. However, its preparation process still lacks efficient interface construction methods, making it difficult to achieve stable and efficient synergistic catalysis. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a copper-nickel heterojunction catalyst rich in lattice defects and excellent electrocatalytic performance.

[0006] Another object of the present invention is to provide a method for preparing a copper-nickel heterojunction catalyst with high preparation efficiency and improved catalytic performance of the material.

[0007] Another object of the present invention is to provide a copper-nickel heterojunction catalyst with high ammonia production efficiency and high Faraday efficiency for use in nitrate ammonia production.

[0008] Technical solution: The copper-nickel heterojunction catalyst of the present invention uses a copper source and a nickel foam with a three-dimensional porous structure as raw materials. The copper in the catalyst is Cu 0 、Cu 1+ 、Cu 2+ Three valence states coexist, and the dominant valence state of nickel is Ni 2+ , the catalyst contains oxygen vacancy defects and lattice dislocations.

[0009] The method for preparing the copper-nickel heterojunction catalyst of the present invention comprises the following steps:

[0010] (1) pre-treating nickel foam;

[0011] (2) using the pretreated nickel foam as a substrate material, and uniformly growing copper on the surface of the nickel foam by an electrodeposition method;

[0012] (3) performing oxidation treatment on the electrodeposited material;

[0013] (4) heat-treating the oxide obtained in step (3) to prepare a copper-nickel heterojunction catalyst rich in lattice defects. Through the heat treatment, deep control of the material microstructure and synergistic optimization of the interface properties are achieved, significantly enhancing the intrinsic performance of the material.

[0014] Preferably, in step (2), the source of copper is a sodium sulfate electrolysis system containing copper ions, and the electrolyte is a composite electrolyte composed of sodium sulfate and copper sulfate.

[0015] Preferably, in the step (2), the electrodeposition time is 800-1000s, more preferably 1000s.

[0016] Preferably, in step (3), the solution used for oxidation treatment is a strong oxidizing solution composed of sodium hydroxide and persulfate.

[0017] Preferably, in step (3), the oxidation treatment time is 15-20 min, more preferably 20 min.

[0018] Preferably, in the step (4), the heat treatment temperature is 550-600° C. and the time is 2 hours.

[0019] Preferably, in the step (4), the heat treatment is carried out in a nitrogen atmosphere with a nitrogen flow rate of 50-200 mL / min.

[0020] The application of the heterojunction catalyst in the production of ammonia from nitrates of the present invention comprises the following steps: an electrochemical test system adopts a standard three-electrode configuration, with the heterojunction catalyst as the working electrode, and the cathode chamber and the anode chamber are respectively containing and not containing NO3 - of KOH solution.

[0021] Principle of invention: Copper (Cu)-based catalysts are regarded as one of the core materials for NO3RR research due to their excellent nitrate adsorption capacity and unique electronic structure. However, the adsorption capacity of copper-based catalysts for active hydrogen (H*) is relatively weak, which seriously restricts the intermediate hydrogenation process, resulting in a significant decrease in the conversion efficiency of nitrate reduction to ammonia. Transition metal nickel (Ni) has excellent water-splitting ability and can efficiently promote the dissociation of water molecules to generate a large amount of active hydrogen (H*). These active hydrogens serve as key active substances for hydrogenation intermediates (such as *NO, *NH2) in the nitrate reduction process, and can significantly accelerate the conversion of nitrate to ammonia.

[0022] The present invention makes full use of the unique three-dimensional porous structure (porosity 85% to 95%) of the nickel foam substrate to achieve a significant improvement in the mass transfer efficiency of reactants on a microscopic scale. The porous structure not only increases the exposed area of the catalytic active sites, but also provides an ideal microscopic mass transfer channel for the electrocatalytic reaction. The electron redistribution effect at the heterojunction interface further optimizes the adsorption capacity of nitrates, effectively accelerates the breaking of the NO bond, and promotes the efficient generation of ammonia. In this solution, the nickel foam not only serves as a physical support, but the nickel substrate can also form a heterojunction interface with the electrodeposited copper species, enhancing the catalytic activity through lattice defects and electron transfer.

[0023] The heterojunction catalyst prepared by this method enables copper and nickel to exert a synergistic catalytic effect in the heterojunction material. The material is prepared through a collaborative process of electrodeposition, redox oxidation, and program-controlled calcination, achieving nanoscale structural regulation at the material interface and significantly optimizing the microscopic interface structure of the copper-nickel heterojunction. Specifically, an electrochemical in-situ deposition method is used to ensure the high uniformity and structural stability of the copper-nickel heterojunction material at the microscale, laying the foundation for improving the activity of the catalyst; a wet chemical oxidation method is used to change the valence state of the substrate material; and the calcination process effectively induces lattice distortion and defect formation at the interface by regulating temperature conditions. High-resolution transmission electron microscopy (HRTEM) shows the presence of a large number of interface defects and lattice dislocations in the material. These defect structures provide abundant active sites for catalytic reactions. At the same time, X-ray photoelectron spectroscopy (XPS) further reveals the regulation of the electronic state of the copper-nickel interface, which helps to optimize the electronic structure of the catalytic active sites and promote charge separation and transport during the catalytic process. Electrochemical testing results show that compared to the uncalcined sample (NiCu-P), the calcined catalyst (NiCu / HIC) exhibits a significantly increased electrochemically active surface area (ECSA) and lower charge transfer impedance, further confirming a significant increase in the number of active sites. Consequently, the enriched lattice defects and optimized electronic structure provide an efficient catalytic pathway for the nitrate reduction reaction, achieving a synergistic improvement in catalytic activity and Faradaic efficiency.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) This method utilizes the different electronic structures and chemical properties of copper and nickel to enable the two to play a synergistic catalytic role in the heterojunction material, thereby significantly improving its catalytic performance; (2) By regulating the calcination temperature, the diffusion of copper-nickel interface atoms and the generation of directional defects are driven, so that the material is rich in lattice defects, thereby providing abundant active sites, providing an efficient catalytic pathway for the nitrate reduction to ammonia production reaction; (3) During the calcination process, a single-step heat treatment is innovatively adopted to replace the traditional multi-stage alloying process. Compared with the traditional high-temperature metallurgical method, this process achieves the simultaneous optimization of lattice defect density and catalytic activity under mild conditions, significantly simplifies the process complexity, and provides a cost-effective solution for large-scale production; (4) The heterojunction catalyst prepared by this method exhibits excellent ammonia yield (up to 23.1 mg cm) under alkaline conditions. -2 h -1 ) and Faraday efficiency (up to 98.5%). The high Faraday efficiency indirectly proves that the NO3RR reaction has good selectivity; at the same time, it has good long-term cycle stability and maintains stable and efficient catalytic activity after 20 consecutive cycles, which fully verifies its great potential in practical industrial applications; (5) The present invention provides a breakthrough system solution with high efficiency, low energy consumption and low carbon emissions for green ammonia synthesis and nitrate pollution control, reflecting the great value of scientific and technological innovation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a high-resolution transmission electron micrograph of the NiCu / HIC prepared in Example 1;

[0026] Figure 2 X-ray photoelectron spectra of NiCu / HIC prepared in Example 1 and NiCu-P prepared in Comparative Example 4;

[0027] Figure 3 The Raman spectrum and X-ray diffraction pattern of the material NiCu / HIC prepared in Example 1, wherein 3a is the Raman spectrum and 3b is the X-ray diffraction pattern;

[0028] Figure 4 The three materials (3D-HPNF, NiCu-P, NiCu / HIC) prepared in Example 1 and Comparative Examples 3-4 were tested with and without NO3 - Comparison of LSV curves in KOH ( Figure 4 a) Double layer capacitance comparison chart ( Figure 4 b) Tafel comparison chart ( Figure 4 c) and AC impedance comparison chart ( Figure 4 d);

[0029] Figure 5 This is a comparison chart of the ammonia production performance of the materials (3D-HPNF, NiCu-P, NiCu / HIC) prepared in Example 1 and Comparative Examples 3-4;

[0030] Figure 6 This is a stability test diagram of NiCu / HIC prepared in Example 1;

[0031] Figure 7 This is a comparison chart of the ammonia production performance of the materials obtained in Examples 1-3 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be further described below in conjunction with embodiments.

[0033] Example 1

[0034] The method for preparing the copper-nickel heterojunction catalyst of the present invention comprises the following steps:

[0035] (1) Pretreatment of nickel foam

[0036] ① Substrate pretreatment is a key prerequisite for material preparation. The nickel foam substrate is cut into standardized small pieces of 1.0 cm × 2.0 cm to provide standardized geometric dimensions for subsequent processing.

[0037] ② Using a gradient cleaning strategy, 1M hydrochloric acid solution is preferred for deep surface treatment of the nickel foam substrate; with the assistance of ultrasound, the stubborn oxide layer and microscopic impurities on the substrate surface are effectively removed, significantly improving the activity and cleanliness of the substrate surface; after treatment, deionized water is used for repeated rinsing to ensure that the substrate surface reaches an ideal state of high cleanliness, and then it is fully dried in a constant temperature drying oven at 60°C.

[0038] ③ Using high-purity anhydrous ethanol as the cleaning medium, ultrasonic surface cleaning is performed again. This step further removes any surface grease, organic impurities, and microscopic contaminants, providing an extremely clean substrate surface for electrocatalytic material preparation. After cleaning, the substrate is rinsed with deionized water to remove any residual ethanol and microscopic impurities, and then thoroughly dried in a constant temperature drying oven at 60°C.

[0039] (2) Preparation of nickel foam with surface-loaded nano-copper

[0040] ① The electrode system adopts a standard three-electrode configuration, with the nickel foam pretreated in step (1) as the working electrode, a high-purity platinum sheet electrode to provide stable and uniform current transmission, and a saturated calomel electrode to ensure the accuracy of potential measurement.

[0041] ② The electrolyte selected 12.5 mL of 0.50 M anhydrous sodium sulfate as the base solution, and introduced 12.5 mL of 70 mM copper sulfate as the active ion source.

[0042] ③ In-situ electrochemical deposition was employed, with chronoamperometry controlling the growth of copper nanoparticles. Key electrolysis parameters were set as follows: a constant potential of -0.8V vs. RHE to effectively control the electrochemical reduction process; a rotor stirring speed of 700 rpm to promote uniform electrolyte diffusion and suppress local concentration gradients; and an electrolysis time of 1000 seconds to ensure controlled growth and uniform distribution of copper nanoparticles. After deposition, the material was thoroughly dried at 60°C to obtain the electrodeposited material.

[0043] (3) Oxidation treatment of the electrodeposited material

[0044] ① Immerse the electrodeposited material in an alkaline oxidizing solution prepared from 2.5M sodium hydroxide and 0.125M persulfate, and regulate the surface morphology and chemical composition of the material through chemical surface modification strategies.

[0045] ② In a room temperature environment, a wet chemical oxidation reaction is performed with a reaction time controlled at 20 minutes to achieve in-situ chemical modification and precise functionalization of the material surface.

[0046] ③ After the reaction is completed, rinse repeatedly with high-purity deionized water to remove the active chemical species remaining on the surface, and then place the sample in a constant temperature drying oven at 60℃ to fully dry.

[0047] (4) Preparation of a copper-nickel heterojunction catalyst rich in lattice defects, the resulting material is named NiCu / HIC

[0048] The material obtained in step (3) was transferred to a tubular high-temperature reactor. In a flowing nitrogen atmosphere, the reaction system was heated to 550°C at a heating rate of 5°C / min and maintained at 550°C for 2 hours. The resulting material was named NiCu / HIC.

[0049] The application of the copper-nickel heterojunction catalyst of the present invention in producing ammonia from nitrate comprises the following steps:

[0050] The test platform uses a CHI 760E electrochemical workstation equipped with an H-type electrolytic cell isolated by Nafion 115 membrane to ensure the standardization and repeatability of experimental conditions. The electrochemical test system adopts a standard three-electrode configuration, with a platinum electrode and a saturated calomel electrode as the counter electrode and reference electrode respectively, and the copper-nickel heterojunction material (NiCu / HIC) prepared by the present invention as the working electrode. The reaction area is 1cm 2, providing a microscopic interface for evaluating electrocatalytic performance. 60 mL of a 1 M KOH solution containing 100 mM KNO₃ was added to the cathode chamber, while 60 mL of a 1 M KOH solution without KNO₃ was added to the anode chamber to create an electrochemical reaction environment simulating nitrate reduction in water.

[0051] Example 2

[0052] The similarities between this embodiment and embodiment 1 are not repeated here, and the differences are as follows:

[0053] The maximum temperature in step (4) is 600°C.

[0054] Example 3

[0055] The similarities between this embodiment and embodiment 1 are not repeated here, and the differences are as follows:

[0056] The maximum temperature in step (4) is 570°C.

[0057] Example 4

[0058] The similarities between this embodiment and embodiment 1 are not repeated here, and the differences are as follows:

[0059] The electrolysis time of the electrodeposition in step (2) is 800s.

[0060] Example 5

[0061] The similarities between this embodiment and embodiment 1 are not repeated here, and the differences are as follows:

[0062] The electrolysis time of the electrodeposition in step (2) is 900s.

[0063] Example 6

[0064] The similarities between this embodiment and embodiment 1 are not repeated here, and the differences are as follows:

[0065] The oxidation time in step (3) is 15 min.

[0066] Comparative Example 1

[0067] The similarities between this comparative example and Example 1 are not repeated here, except that:

[0068] The maximum temperature in step (4) is 500°C.

[0069] Comparative Example 2

[0070] The similarities between this comparative example and Example 1 are not repeated here, except that:

[0071] The maximum temperature in step (4) is 650°C.

[0072] Comparative Example 3

[0073] Only pretreatment was performed on the nickel foam without the electrodeposition, oxidation, and heat treatment of steps (2) to (4). The resulting material was named 3D-HPNE.

[0074] Comparative Example 4

[0075] The similarities between this comparative example and Example 1 are not repeated here, except that:

[0076] Only the pretreatment and electrodeposition treatment of steps (1)-(2) are performed on the nickel foam, and the oxidation and heat treatment of steps (3)-(4) are not performed. The obtained material is named NiCu-P.

[0077] To evaluate the electrocatalytic performance of the material, linear sweep voltammetry (LSV), double layer capacitance, Tafel slope and electrochemical impedance spectroscopy (EIS) were used for comprehensive testing. Figure 4 Subsequently, an electrolysis test was conducted at a potential range of -0.7 V vs. RHE for 1 hour under uniform stirring conditions at 700 rpm to simulate the actual nitrate reduction process in water.

[0078] In order to quantitatively evaluate the ammonia production performance of the catalyst material, UV-visible spectrophotometry (Shimadzu UV-2600i) was used to detect NH4 + The results are as follows Figure 5-7 shown.

[0079] Figure 1 (a) High-resolution transmission electron microscopy (HRTEM) image of NiCu / HIC, showing three lattice fringes, belonging to the NiO (220) crystal plane, the Cu2O (111) crystal plane, and the CuO (002) crystal plane, confirming the presence of a heterogeneous structure. Furthermore, local lattice distortion and dislocations are visible in the HRTEM image, indicating the presence of significant lattice dislocations in the material, enabling nanoscale structural control at the material interface. Figure 1 b is the selected area electron diffraction (SAED) image of NiCu / HIC, showing a series of diffraction rings corresponding to the main crystal planes of the Cu2O and NiO phases, revealing a polycrystalline structure and consistent with the HRTEM results.

[0080] The valence state of the elements in the heterostructure can be confirmed by X-ray photoelectron spectroscopy (XPS). Figure 2 The XPS full spectrum analysis of the NiCu / HIC material in a confirms the presence of Cu, Ni and O elements. Figure 2Figure b shows the O1s spectra of NiCu-P and NiCu / HIC. The results show that the peaks of NiCu / HIC shift toward higher binding energies compared to NiCu-P, indicating that oxygen may combine with the metal to form an oxide. This also shows that the two substances are not only physically bound but also tightly combined into a heterojunction structure. More importantly, the shape and peak position structure of the O1s peak in NiCu / HIC reveal the presence of oxygen vacancy defects, which affect the electron density distribution by changing the chemical environment of oxygen. Figure 2 The Cu 2p spectrum of c shows Cu 2+ 、Cu 1+ and Cu 0 species signal, showing Cu 0 / Cu 1+ The dominant valence state of NiCu is also shown in the spectrum of NiCu / HIC. 2+ The species signal shows the diversity of Cu valence states in the material. δ+ The species has a lower reaction energy barrier in the NO3RR process, which is beneficial to the adsorption, activation and desorption processes of the intermediates. Therefore, the diversity of Cu valence states is conducive to improving the catalytic performance of the material. Figure 2 d shows the high-resolution Ni2p spectrum of NiCu / HIC, showing that Ni 2p 3 / 2 and Ni 2p 1 / 2 The typical peaks and related satellite peaks reveal that the dominant valence state of Ni in NiCu / HIC is Ni 2+ .

[0081] Figure 3 The Raman spectrum and X-ray diffraction (XRD) pattern of NiCu / HIC are shown below. These patterns clearly show the valence composition and different crystal planes of the target NiCu / HIC after undergoing electrochemical deposition, chemical oxidation, and thermal reduction. This further confirms that NiCu / HIC is a heterojunction formed by high-temperature thermal decomposition of Cu and Ni. The formation of this structure creates a potential difference, accelerating the charge transfer rate, and thus speeding up the reaction kinetics and improving reaction efficiency.

[0082] Figure 4 a is a comparison of the linear sweep voltammetry (LSV) curves of 3D-HPNF, NiCu-P and NiCu / HIC. The analysis results show that 3D-HPNF and NiCu-P exhibit low activity in the tested potential range, while in NO3 - In the presence of , the current density of NiCu / HIC increased significantly, indicating that NiCu / HIC has unique activity for nitrate reduction reaction. Figure 4b is a comparison of the double-layer capacitance of 3D-HPNF, NiCu-P, and NiCu / HIC materials, among which NiCu / HIC shows the best double-layer capacitance, indicating that it has superior electron transport properties and catalytic activity. These results further confirm that NiCu / HIC has excellent electrochemical properties. Figure 4 The Tafel curve comparison shown in c confirms that NiCu / HIC has a higher electrochemical reaction rate. In addition, Figure 4 The electrochemical impedance spectroscopy comparison shown in Figure d also confirms the excellent electrocatalytic performance of NiCu / HIC. Its smaller radius indicates that NiCu / HIC has lower charge transfer resistance, which means a higher electron transfer rate. In summary, by regulating the calcination process conditions, the migration and reconstruction of interfacial atoms are promoted, effectively introducing a high density of lattice defects and forming a heterojunction interface, which in turn enables the resulting material to possess excellent performance in electrocatalytic nitrate reduction.

[0083] Figure 5 Electrolysis of 3D-HPNF, NiCu-P and NiCu / HIC for 1 hour at -0.7V vs. RHE potential to remove 0.1M NO3 - The performance comparison chart can be used to evaluate the ammonia production rate and Faradaic efficiency of the material's electrocatalytic reduction of nitrate. The ammonia production rate and Faradaic efficiency were measured using the indigo blue colorimetric method. Through comparison, it can be found that the ammonia production and Faradaic efficiency of NiCu / HIC have been greatly improved, with Faradaic efficiency reaching over 90% and ammonia production rate reaching 19 mg cm -2 h -1 , indicating that the heterojunction rich in lattice defects has excellent performance in electrocatalytic nitrate reduction.

[0084] The stability of materials is a key indicator for evaluating material performance. Figure 6 The stability test diagram of the NiCu / HIC heterojunction catalyst obtained in Example 1 after 20 cycles of use is shown in FIG. Figure 6 It can be seen that the catalytic activity of NiCu / HIC does not show a significant attenuation trend even after being recycled 20 times in alkaline electrolyte, indicating that the material has good stability.

[0085] like Figure 7 As shown, the ammonia production performance of the materials obtained in Examples 1-3 (heat treatment temperature of 550°C-600°C) and Comparative Examples 1-2 (heat treatment temperature of 500°C and 650°C, respectively) was characterized. Figure 7 Electrolysis of five materials for NO3 removal at -0.7 V vs. RHE for 1 hour -Experimental data shows that the defect-rich heterojunction material formed after heat treatment at 550°C-600°C exhibits excellent ammonia production performance and high Faradaic efficiency, with similar efficiencies. In contrast, the heterojunction catalysts obtained after heat treatment at 500°C and 650°C exhibit significantly lower ammonia production performance and Faradaic efficiency.

Claims

1. A copper-nickel heterojunction catalyst, characterized in that: The copper source and the nickel foam with three-dimensional porous structure are used as raw materials. The copper in the catalyst is Cu 0 、Cu 1+ 、Cu 2+ Three valence states coexist, and the dominant valence state of nickel is Ni 2+ , the catalyst contains oxygen vacancy defects and lattice dislocations.

2. A method for preparing the copper-nickel heterojunction catalyst according to claim 1, characterized in that: The following steps are involved: (1) pre-treating nickel foam; (2) using the pretreated nickel foam as a substrate material, and uniformly growing copper on the surface of the nickel foam by an electrodeposition method; (3) performing oxidation treatment on the electrodeposited material; (4) heat-treating the oxide obtained in step (3) to prepare a copper-nickel heterojunction catalyst rich in lattice defects.

3. The preparation method according to claim 2, characterized in that In the step (2), the source of copper is a sodium sulfate electrolysis system containing copper ions, and the electrolyte is a composite electrolyte composed of sodium sulfate and copper sulfate.

4. The preparation method according to claim 2, characterized in that In the step (2), the electrodeposition time is 800-1000s.

5. The preparation method according to claim 2, characterized in that In the step (3), the solution used for the oxidation treatment is a strong oxidizing solution composed of sodium hydroxide and persulfate.

6. The preparation method according to claim 2, characterized in that In the step (3), the oxidation treatment time is 15-20 minutes.

7. The preparation method according to claim 2, characterized in that In the step (4), the heat treatment temperature is 550-600°C and the time is 2 hours.

8. The preparation method according to claim 2, characterized in that In the step (4), the heat treatment process is carried out in a nitrogen atmosphere with a nitrogen flow rate of 50-200 mL / min.

9. Use of the heterojunction catalyst according to claim 1 in producing ammonia from nitrate.

10. The use according to claim 9, characterized in that The electrochemical test system adopts a standard three-electrode configuration, with the heterojunction catalyst as the working electrode, and the cathode chamber and the anode chamber containing and not containing NO3 respectively. - of KOH solution.

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