N-n type NiO / beta-Bi2O3 heterojunction catalyst as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of an n-n type NiO / beta-Bi2O3 heterojunction catalyst and application of the n-n type NiO / beta-Bi2O3 heterojunction catalyst in the process of electrocatalytic nitrogen reduction synthesis of ammonia (NRR), and belongs to the technical field of electrocatalytic materials. The n-n type NiO / beta-Bi2O3 heterojunction catalyst with excellent catalytic activity and stability is successfully prepared by mixing the prepared NiO rich in oxygen vacancies with a beta-Bi2O3 precursor solution and carrying out hydrothermal and programmed heating calcination. The synergistic effect of the two effectively improves the selectivity of nitrogen reduction and reduces the incidence rate of side reactions. By constructing an n-n type heterojunction structure and utilizing an electric field effect generated by a heterojunction interface, the adsorption capacity of nitrogen molecules on the surface of the catalyst is remarkably enhanced, so that the catalytic efficiency of a nitrogen reduction reaction is improved. Compared with a traditional single catalyst, the catalyst shows higher ammonia yield and better stability, and has a wide application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic materials, and specifically relates to a preparation method of an n-n type NiO / β-Bi2O3 heterojunction and its application in electrocatalytic ammonia synthesis. Background Art

[0002] Electrocatalytic nitrogen reduction to ammonia (NRR) is a green technology to replace the high-energy-consuming Haber-Bosch process. However, the existing catalytic systems are limited by bottlenecks such as high nitrogen adsorption energy barriers, sluggish reaction kinetics, and low efficiency. Although a variety of electrocatalytic materials have been used in the nitrogen reduction reaction at present, their catalytic performance still needs to be improved.

[0003] Although NiO and β-Bi2O3 have potential for synergistic catalysis, the traditional synthesis methods have significant heterojunction structure defects due to process limitations: the high-temperature solid-phase method is prone to induce excessive grain growth, while the hydrothermal method and the co-precipitation method face problems such as poor interfacial contact and uneven element distribution, resulting in particle agglomeration, insufficient specific surface area, and low carrier transport efficiency of the materials; at the same time, the existing heterojunction composite materials are prone to phase separation or component dissolution in the electrochemical environment due to weak interfacial bonding and poor structural stability, seriously restricting their catalytic activity and service life. In response to the above challenges, the present invention breaks through the limitations of traditional single synthesis paths, innovatively adopts a stepwise synthesis method of "pre-construction of oxygen vacancies - precise interfacial assembly", constructs a nanoscale n-n type NiO / β-Bi2O3 heterojunction through a molecular-level interfacial regulation strategy, greatly improves the integrity of heterojunction interface contact and optimizes the energy band gradient distribution, significantly enhances the interfacial electric field strength and the adsorption ability of reactants, and at the same time realizes the exposure of high-active sites and efficient charge transport through refined grain regulation, finally achieving breakthrough catalytic efficiency and stability at low overpotential. This technology not only provides an innovative solution for the nitrogen reduction system, but also its general interfacial engineering strategy can be extended to the field of clean energy conversion, showing broad application prospects. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a preparation method of an n-n type NiO / β-Bi2O3 heterojunction catalyst, which has excellent electrocatalytic nitrogen reduction to ammonia performance and can be applied to the process of nitrogen reduction to ammonia (NRR).

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A preparation method of an n-n type NiO / β-Bi2O3 heterojunction catalyst, comprising the following steps:

[0007] (1) Disperse NiO, Bi(NO3)3·5H2O, C6H5Na3O7 (trisodium citrate), CH4N2O (urea) and PVP (polyvinylpyrrolidone K30) in ultrapure water and stir strongly at room temperature for 1 h;

[0008] (2) Transfer the above mixed solution to a Teflon-lined autoclave. After hydrothermal reaction, cool to room temperature, collect and wash the precipitate;

[0009] (3) Vacuum dry the washed precipitate and calcine it at high temperature in an air atmosphere after drying.

[0010] Furthermore, the preparation of NiO in step (1) includes the following steps: Under the condition of constant temperature water bath, add NaOH dropwise to the aqueous solution of Ni(NO3)2 while stirring dropwise. After the reaction is completed, cool, filter and wash with water. Dry the washed Ni(OH)2 at a temperature below 80 °C; Put the dried Ni(OH)2 into a muffle furnace and heat and calcine it at 400 - 800 °C for 1 - 3 h to obtain NiO rich in oxygen vacancies. By calcining to pre-activate oxygen vacancies, NiO is transformed from a p-type semiconductor into an electron-rich n-type semiconductor for the formation of an n-n type NiO / β-Bi2O3 heterojunction.

[0011] Furthermore, the hydrothermal temperature in step (2) is 180 °C and the hydrothermal reaction time is 12 h.

[0012] Furthermore, the vacuum drying temperature in step (3) is 60 °C, the calcination heating rate is 10 °C / min, the calcination temperature is 350 °C, and the calcination time is 2 h.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] (1) Break through the randomness of the traditional mixed synthesis method and propose a step-by-step strategy of "pre-construction of oxygen vacancies - interfacial directed assembly". First, construct oxygen vacancy active sites in nickel oxide, and then precisely control the growth of the heterojunction interface by hydrothermal method. Compared with the traditional mixed synthesis method, this strategy effectively overcomes the two major problems of component segregation and structural disorder commonly existing in material synthesis and realizes the precise control of the heterojunction interface structure.

[0015] (2) NiO enriched with oxygen vacancies serves as an electron high-speed channel, forming a spatial coupling with the strong nitrogen adsorption sites of β-Bi2O3, significantly reducing the nitrogen activation energy barrier and accelerating the proton-electron co-transfer process, and significantly improving the catalytic efficiency and stability.

[0016] (3) By regulating the precursor ratio and reaction conditions, this method can be adapted to a multi-component oxide composite system. The obtained catalyst has both high nitrogen reduction activity and universality, and can be extended to clean energy fields such as carbon dioxide conversion and hydrogen evolution reaction. Description of the Drawings

[0017] Figure 1 SEM image (a) and HRTEM image (b) of the NiO / β-Bi2O3 catalyst in Example 1.

[0018] Figure 2 XRD patterns of the catalysts in Examples 1-5 and Comparative Examples 1-2.

[0019] Figure 3 UV / Vis DRS spectra (a), Kubelka-Munk spectra (b), Mott-Schottky spectra (c), and electronic band structure diagrams (d) of NiO and β-Bi2O3.

[0020] Figure 4 X-ray photoelectron spectroscopy (XPS): (a) full spectrum of NiO / β-Bi2O3 in Example 1, (b) Ni 2p spectra of NiO / β-Bi2O3 and NiO, (c) Bi 4f spectra of NiO / β-Bi2O3 and β-Bi2O3, (d) O 1s spectra of NiO / β-Bi2O3, NiO, and β-Bi2O3.

[0021] Figure 5 Electrocatalytic nitrogen reduction performance diagram of the NiO catalyst in Comparative Example 1.

[0022] Figure 6 Electrocatalytic nitrogen reduction performance diagram of the β-Bi2O3 catalyst in Comparative Example 2.

[0023] Figure 7 Electrocatalytic nitrogen reduction performance diagram of the NiO / β-Bi2O3 catalyst in Example 1.

[0024] Figure 8 Group diagram of the electrocatalytic nitrogen reduction performance of the catalysts in Examples 1-5 and Comparative Examples 1-3.

[0025] Figure 9 Cyclic voltammograms of NiO (a), β-Bi2O3 (b), and NiO / β-Bi2O3 in Example 1 (c), and comparison diagram of the electrochemical surface areas of the three (d). Detailed Embodiment

[0026] To make the content of the present invention more understandable, the present invention will be further described below through examples and drawings. Although the following description is elaborated through specific examples, this does not mean that the scope of the present invention is limited to these examples. Any equivalent changes and modifications that conform to the basic principles and technical solutions of the present invention should be regarded as part of the present invention.

[0027] Example 1

[0028] Dissolve 0.45 g of NiO, 0.96 g of Bi(NO3)3·5H2O, 1.76 g of C6H5Na3O7, 0.48 g of CH4N2O, and 1.0 g of PVP (K30) in 60 mL of ultrapure water, and then stir vigorously at room temperature for 1 h to ensure complete dissolution. At this time, the solution presents a relatively uniform mixing state to ensure that all components react fully. Subsequently, transfer the mixed solution to a 100 mL Teflon-lined autoclave and maintain the reaction time at 180 °C for 12 h to promote the chemical reaction between components and the formation of the material structure. After cooling to room temperature, collect the precipitate formed by the reaction and wash it multiple times with ethanol and ultrapure water to remove the solvent and unreacted impurities. Subsequently, place the product under vacuum drying conditions at 60 °C for drying. The dried powder is heated to 350 °C at a heating rate of 10 °C / min and heat-treated at this temperature for 2 h to finally obtain an n-n type NiO / β-Bi2O3 heterojunction catalyst. The molar ratio of Ni to Bi is 3:1.

[0029] Example 2

[0030] Change the amount of NiO to 0.15 g, and keep other preparation steps and reaction conditions the same as those in Example 1. The molar ratio of Ni to Bi is 1:1. The molar ratio of Ni / Bi in the NiO / β-Bi2O3 heterojunction catalyst will affect the properties of the final heterojunction interface and the electrocatalytic nitrogen synthesis ammonia performance by changing the interfacial charge distribution, adjusting the energy band structure, and affecting the crystal structure matching, etc.

[0031] Example 3

[0032] Change the amount of NiO to 0.30 g, and keep other preparation steps and reaction conditions the same as those in Example 1. The molar ratio of Ni to Bi is 2:1. The molar ratio of Ni / Bi in the NiO / β-Bi2O3 heterojunction catalyst will affect the properties of the final heterojunction interface and the electrocatalytic nitrogen synthesis ammonia performance by changing the interfacial charge distribution, adjusting the energy band structure, and affecting the crystal structure matching, etc.

[0033] Example 4

[0034] Change the amount of NiO to 0.60 g, and keep other preparation steps and reaction conditions the same as those in Example 1. The molar ratio of Ni to Bi is 4:1. The molar ratio of Ni / Bi in the NiO / β-Bi2O3 heterojunction catalyst will affect the properties of the final heterojunction interface and the electrocatalytic nitrogen synthesis performance by changing the interfacial charge distribution, regulating the energy band structure, and affecting the crystal structure matching, etc.

[0035] Example 5

[0036] Change the amount of NiO to 0.75 g, and keep other preparation steps and reaction conditions the same as those in Example 1. The molar ratio of Ni to Bi is 5:1. The molar ratio of Ni / Bi in the NiO / β-Bi2O3 heterojunction catalyst will affect the properties of the final heterojunction interface and the electrocatalytic nitrogen synthesis performance by changing the interfacial charge distribution, regulating the energy band structure, and affecting the crystal structure matching, etc.

[0037] Comparative Example 1

[0038] Add NaOH dropwise to the aqueous solution of Ni(NO3)2 under the condition of a 90 °C water bath and stir, stirring while adding. After the reaction is completed, cool, filter, wash with water, and dry at 80 °C to obtain Ni(OH)2, and then put it into a muffle furnace and heat it at 600 °C for 2 h to obtain NiO nanoparticles.

[0039] Comparative Example 2

[0040] Dissolve 0.96 g of Bi(NO3)3·5H2O, 1.76 g of C6H5Na3O7, 0.48 g of CH4N2O, and 1.0 g of PVP(K30) in 60 mL of ultrapure water, and then stir strongly at room temperature for 1 h. Secondly, transfer the mixed solution to a 100 mL Teflon-lined autoclave and react at 180 °C for 12 h. After the reaction is completed, cool to room temperature and collect the precipitate, and wash it with ethanol and water multiple times. The product is dried under vacuum at 60 °C, and the dried powder is heated to 350 °C at a heating rate of 10 °C / min and maintained at this temperature for 2 h to finally obtain orange-yellow β-Bi2O3.

[0041] Performance test of application examples

[0042] Comparative Example 3

[0043] Take 0.45 g of NiO in Comparative Example 1 and 0.466 g of β-Bi2O3 in Comparative Example 2, and obtain a physically mixed NiO / β-Bi2O3 composite with a molar ratio of Ni to Bi of 3:1 through simple physical mixing.

[0044] Figure 1SEM image (a) and HRTEM image (b) of the NiO / β-Bi2O3 catalyst of Example 1. The SEM image shows the microscopic morphology of the NiO / β-Bi2O3 composite material. The composite material exhibits a relatively uniform particle distribution. The high-resolution transmission electron microscope (HRTEM) image clearly shows the tight bonding between NiO and β-Bi2O3, forming a NiO / β-Bi2O3 heterojunction. Through the magnification analysis of the HRTEM image, the (220) crystal plane of NiO and the (400) crystal plane of β-Bi2O3 show clear lattice docking, and the lattice spacings are 0.15 nm and 0.193 nm respectively, further confirming the tight bonding of the two materials.

[0045] Figure 2 XRD patterns of the catalysts of Examples 1-5 and Comparative Examples 1-2. X-ray diffraction (XRD) analysis was carried out to study the material composition and crystal structure of the samples. By comparing the obtained diffraction curves with the standard PDF card of NiO [PDF#73-1523], the diffraction peaks at 37.2°, 43.2°, 62.8°, 75.3° and 79.3° correspond to the crystal planes (111), (200), (220), (311) and (222) respectively, while the diffraction peaks at 7.94°, 31.73°, 32.69°, 46.20°, 46.91°, 54.24° and 55.49° correspond to the (201), (002), (220), (222), (400), (203) and (421) crystal planes of β-Bi2O3 [PDF#78-1793]. It was observed that the diffraction peaks of NiO / β-Bi2O3 with different Ni / Bi molar ratios did not show obvious displacement, indicating that the crystal structure was not significantly affected by the formation of the heterostructure. There were not many impurity peaks. The strong and sharp diffraction peaks indicate that the samples have good crystallinity. At the same time, as the Ni / Bi molar ratio increased from 1:1 to 5:1, the intensity of the XRD characteristic peaks of NiO gradually increased, and the intensity of the XRD characteristic peaks of β-Bi2O3 gradually decreased, confirming that the synthesized NiO / β-Bi2O3 with different Ni / Bi molar ratios was in line with the experimental expected trend.

[0046] Figure 3(a) UV / Vis DRS diagrams, (b) Kubelka-Munk diagrams, (c) Mott-Schottky diagrams, and (d) electronic band structure diagrams of NiO and β-Bi2O3. Results of ultraviolet-visible diffuse reflectance spectroscopy (DRS) and Mott-Schottky curves. In this paper, through the study of DRS and Mott-Schottky curves, the band structures of NiO and β-Bi2O3 samples were systematically analyzed, and their application potential in electrocatalytic nitrogen reduction was deeply explored. First, through ultraviolet-visible diffuse reflectance spectroscopy (DRS) combined with Kubelka-Munk function conversion and Tauc plot analysis, see Figure 3 (a)(b). The band gaps (Eg) of NiO and β-Bi2O3 were determined to be 3.14 eV and 2.36 eV, respectively. Under a three-electrode system, Mott-Schottky tests were carried out at a frequency of 1 kHz and a scan rate of 10 mV / s to study the semiconductor type and flat-band potential characteristics of NiO and β-Bi2O3. The experimental results are as Figure 3 (c). Both of them showed a linear relationship with a positive slope in the Mott-Schottky diagram, conforming to the characteristics of a typical n-type semiconductor. Specifically, the flat-band potentials (E fb ) of NiO and β-Bi2O3 were -0.78 V and -0.68 V (vs. Ag / AgCl), respectively. According to the properties of n-type semiconductors, the conduction band (CB) potential is usually about 0.1 V lower than the flat-band potential. Therefore, the conduction band positions of NiO and β-Bi2O3 can be calculated to be -0.88 V and -0.78 V, respectively. Combining the conduction band position data, the valence band positions of NiO and β-Bi2O3 can be deduced to be +2.26 V and +1.58 V, respectively. This indicates that NiO and β-Bi2O3 form a typical type-II heterojunction band structure. The band structure is as Figure 3 (d) shown. Band alignment analysis shows that the built-in electric field (directed from β-Bi2O3 to NiO) formed at the heterojunction interface can effectively drive the photo-generated electrons to migrate from the conduction band of NiO to β-Bi2O3, while the holes are transferred in the opposite direction to the valence band of NiO. This spatial charge separation mechanism reduces the probability of interfacial carrier recombination and forms a local electron-rich region at the interface. This modulation of the electronic structure is of great significance for the catalytic performance. During the electrocatalytic nitrogen reduction reaction, the built-in electric field at the heterojunction interface can not only effectively enhance the electron transfer, promote the adsorption and activation of nitrogen molecules, but also improve the adsorption ability of the catalyst to intermediates, thus improving the efficiency of the catalytic reaction.

[0047] Figure 4X-ray photoelectron spectroscopy (XPS): (a) Survey spectrum of NiO / β-Bi2O3 in Example 1 (b) Ni 2p spectra of NiO / β-Bi2O3 and NiO in Example 1 (c) Bi 4f spectra of NiO / β-Bi2O3 and β-Bi2O3 in Example 1 (d) O 1s spectra of NiO / β-Bi2O3, NiO and β-Bi2O3 in Example 1. Through XPS measurement, the survey spectrum of NiO / β-Bi2O3 ( Figure 4 (a)) reveals the presence of Ni, Bi and O elements. Further tests were conducted on the detailed information about the chemical environment of these elements. And each spectrum was analyzed in detail. Figure 4 (b) shows the high-resolution Ni 2p spectra of NiO / β-Bi2O3 and NiO. The main peaks at binding energies of 853.88 eV and 871.27 eV correspond to the characteristic peaks of Ni 2 +, while the peaks at 856.17 eV and 873.05 eV are attributed to the satellite peaks of Ni 2+ . Meanwhile, satellite peaks of Ni 2p are observed at 861.12 eV and 879.57 eV. These characteristic peaks are common secondary peaks during the Ni 2p electron transition process. Compared with NiO that was also calcined at 350 °C again, the Ni 2p peaks of NiO / β-Bi2O3 show a shift of about 0.8 eV towards higher binding energy, indicating a decrease in the electron density on the Ni atoms. This change indicates that in the NiO / β-Bi2O3 composite material, the Ni 2+ state has undergone a change in electron density due to the interface effect, which may be related to the interaction with the electronic structure of β-Bi2O3. Figure 4 (c) shows the high-resolution Bi 4f spectra of NiO / β-Bi2O3 and β-Bi2O3. By fitting, the Bi 4f spectrum of NiO / β-Bi2O3 can be decomposed into two doublets. The peaks at 163.3 eV and 158 eV correspond to the binding energies of the Bi 4f 5 / 2 and 4f 7 / 2 orbits of β-Bi2O3. Compared with the corresponding peaks (163.8 eV and 158.5 eV) in β-Bi2O3, the Bi 4f peaks in NiO / β-Bi2O3 show a higher binding energy. This shift in binding energy indicates that the electron density of the β-Bi2O3 part in the NiO / β-Bi2O3 composite material has increased, while the electron density of the NiO part has decreased. This change in electron density further supports the phenomenon of directional electron transfer from NiO to β-Bi2O3 at the NiO / β-Bi2O3 heterojunction interface. Figure 4 (d) shows the high-resolution O 1s spectra of NiO, β-Bi2O3 and NiO / β-Bi2O3. Among them, there are lattice oxygen (OL ), oxygen vacancies (O V ), chemisorbed oxygen (O Chem ). It can be seen that NiO and NiO / β-Bi2O3 have abundant oxygen vacancies. Compared with the single component, the intensity of the oxygen vacancy peak in the composite material is enhanced by about 25% compared with NiO, and the O V / O L area ratio increases from 0.23 of pure β-Bi2O3 to 0.89, confirming a significant increase in the oxygen vacancy concentration at the heterojunction interface. The formation of this oxygen-deficient structure can be attributed to the lattice distortion caused by Ni-O-Bi bonding at the interface and the oxygen vacancy compensation effect generated to maintain charge balance during the electron transfer process. The increase in oxygen vacancies can not only act as active sites to promote the adsorption of reactants, but also improve the carrier migration efficiency by forming local intermediate energy levels, which is of great significance for enhancing the electrocatalytic performance. XPS system analysis shows that there is a significant electronic structure reconstruction effect at the NiO / β-Bi2O3 heterojunction interface. The positive shift (+0.8 eV) of the Ni 2p binding energy and the negative shift (-0.5 eV) of the Bi 4f binding energy form a mirror symmetry relationship. Combined with the significant increase in the oxygen vacancy concentration in the O1s spectrum, it is confirmed that there is a directional electron transfer from NiO to β-Bi2O3 at the interface. This charge redistribution phenomenon can be attributed to the interfacial electric field effect driven by the difference in Fermi levels between the two semiconductors, resulting in band bending and the formation of a type-II heterojunction structure. This interfacial electron transfer effect helps to improve the catalytic performance of the material, especially showing higher catalytic efficiency in applications such as the electrocatalytic nitrogen reduction reaction (ENRR).

[0048] Figure 5 is the electrocatalytic nitrogen reduction performance diagram of the NiO catalyst. The ammonia production rate is 16.05 μg h - 1 mg -1 cat at -0.4 V vs. RHE, and the Faraday efficiency is 18.77%.

[0049] Figure 6 is the electrocatalytic nitrogen reduction performance diagram of the β-Bi2O3 catalyst. The ammonia production rate is 12.02 μg h -1 mg -1 cat at -0.5 V vs. RHE, and the Faraday efficiency is 10.69%.

[0050] Figure 7 is the electrocatalytic nitrogen reduction performance diagram of the NiO / β-Bi2O3 catalyst of Example 1. The ammonia production rate is 26.29 μg h -1 mg -1 cat, the Faraday efficiency is 19.98%. Compared with the individual catalysts of NiO and β-Bi2O3, the ammonia production rate of this catalyst is significantly improved, showing good catalytic activity. The introduction of the heterojunction structure significantly improves the charge separation and transport efficiency of the catalyst, thus enhancing the reaction rate.

[0051] Figure 8 It is a group diagram of the electrocatalytic nitrogen reduction performance of the catalysts in Examples 1-5 and Comparative Examples 1-3. By synthesizing heterojunction NiO / β-Bi2O3 composites with different Ni and Bi molar ratios, the ammonia production rates of all of them are greater than those of NiO and β-Bi2O3. And the composite catalysts in Example 1 and Comparative Example 3 have the same Ni and Bi ratio, but the NiO / β-Bi2O3 composite with a heterojunction synthesized by the method in Example 1 shows a better effect. This illustrates the superiority of this method.

[0052] Figure 9 It is a comparison diagram of the cyclic voltammograms of NiO (a), β-Bi2O3 (b) and NiO / β-Bi2O3 (c) of Example 1 and the electrochemically active surface areas (d) of the three. To further compare the differences in the activities of NiO, β-Bi2O3 and NiO / β-Bi2O3, cyclic voltammetry tests were carried out in the non-Faraday region at different scan rates. As can be seen from the figure, the electrochemically active area of NiO / β-Bi2O3 is 1.26 times that of NiO and 4.94 times that of β-Bi2O3. With the increase in the active area, the number of active sites increases, so the production rate of ammonia generated by the adsorption and activation of nitrogen is higher.

[0053] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A preparation method of an n-n type NiO / β-Bi2O3 heterojunction catalyst, characterized in that: It includes the following steps: (1) Disperse NiO, Bi(NO3)3·5H2O, C6H5Na3O7, CH4N2O and PVP in ultrapure water and vigorously stir for 1 h at room temperature; (2) Carry out hydrothermal reaction on the mixed solution in step (1), then cool to room temperature, collect and wash the precipitate; (3) Vacuum dry the precipitate obtained in step (2) and then calcine it at high temperature in an air atmosphere to obtain the n-n type NiO / β-Bi2O3 heterojunction catalyst.

2. The preparation method of the n-n type NiO / β-Bi2O3 heterojunction catalyst according to claim 1, wherein: In step (2), the hydrothermal temperature is 180 °C and the time is 12 h.

3. The preparation method of the n-n type NiO / β-Bi2O3 heterojunction catalyst according to claim 1, characterized in that: In step (3), the vacuum drying temperature is 60 °C; the calcination heating rate is 10 °C / min, the calcination temperature is 350 °C, and the time is 2 h.

4. The preparation method of the n-n type NiO / β-Bi2O3 heterojunction catalyst according to claim 1, characterized in that: The preparation of NiO described in step (1) includes the following steps: Under the condition of constant temperature water bath, dropwise add NaOH into the Ni(NO3)2·6H2O solution while stirring. After the reaction is completed, cool, filter and wash with water to obtain Ni(OH)2. After drying at a temperature below 80 °C, heat and calcine it at 400 °C - 800 °C for 1 - 3 h to obtain NiO rich in oxygen vacancies.

5. An n-n type NiO / β-Bi2O3 heterojunction catalyst prepared by the method according to any one of claims 1-4, characterized in that: The molar ratio of Ni to Bi is 1 - 5:

1.

6. Application of the n-n type NiO / β-Bi2O3 heterojunction catalyst prepared by the method according to any one of claims 1 - 4 in the electrocatalytic nitrogen reduction reaction for ammonia synthesis.

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