In-situ spontaneous surface restructuring CuFe-G nitrate reduction ammonia catalyst and preparation method and application thereof

Abstract

The application discloses an in-situ self-surface reconstruction CuFe-G nitrate reduction ammonia catalyst and a preparation method and application thereof, and relates to the technical field of catalysts.The method comprises the following steps: stirring and dissolving a copper source and citrate in deionized water, adding potassium ferrocyanide, uniformly mixing, standing for 12-36 hours, collecting the precipitate after standing, and washing and vacuum drying the precipitate to prepare a Cu2[Fe(CN)6] precursor; and calcining the Cu2[Fe(CN)6] precursor under a mixed atmosphere of hydrogen and inert gas at 700-900 DEG C for 1-4 hours to obtain the CuFe-G nitrate reduction ammonia catalyst.The CuFe-G catalyst prepared by the application benefits from the band modulation of alloying, initiates the spontaneous conversion from NO3 ‑ to NO2 ‑ , and simultaneously forms a stable CuFeO x ultra-thin layer through surface reconstruction without dynamic evolution.The stable CuFeO x ultra-thin layer can optimize the adsorption of key intermediate products, catalyze the reduction of NO3 ‑ and NO2 ‑ in series, further broaden the nitrate reduction potential range, and improve the Faraday efficiency of the nitrate reduction ammonia method.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a CuFe-G nitrate reduction ammonia catalyst with in-situ spontaneous surface reconstruction and a preparation method and application thereof. BACKGROUND

[0002] The production of ammonia using the traditional Haber-Bosch route results in huge energy consumption and environmental crisis. The electrochemical conversion of NO3 - to NH3 is considered as a promising alternative to the Haber-Bosch route. Transition metal Cu has good adsorption capacity for intermediate species such as NO3 - , NO2 - , NO, etc., and thus has great potential in the catalytic conversion of NO3 - to NH3. However, when the Cu-based electrocatalytic system is powered by intermittent renewable energy sources (such as solar energy, wind energy, etc.), the fluctuation of the electric potential will cause changes in the reaction conditions on the surface of the catalyst, which may interfere with the active sites of the catalyst, making the originally efficient electrocatalytic reaction unstable, thereby leading to a decrease in the Faraday efficiency. The decrease in the Faraday efficiency means that more electric energy is consumed by non-target reactions, reducing the catalytic efficiency and selectivity of the catalyst, and ultimately affecting the overall performance of the electrocatalytic process. Therefore, how to alleviate the impact of electric potential fluctuation on the performance of the catalyst through reasonable material design is the key and main challenge to improve the nitrate reduction ammonia production of Cu-based materials. SUMMARY

[0003] In view of the deficiencies in the above background art, the present application mainly solves the problem of reduction in the Faraday efficiency of nitrate reduction ammonia production caused by intermittent renewable energy fluctuations in the existing Cu-based catalysts. The present application provides a CuFe-G nitrate reduction ammonia catalyst with in-situ spontaneous surface reconstruction and a preparation method and application thereof. The CuFe-G catalyst is successfully constructed through reasonable material design, which benefits from the band modulation of alloying, and initiates the spontaneous conversion of NO3 - to NO2 - , accompanied by the formation of a stable CuFeO x ultrathin layer without dynamic evolution. The stable CuFeO x ultrathin layer can optimize the adsorption of key intermediate products, catalyze the reduction of NO3 - and NO2 - in series, thereby widening the potential range of nitrate reduction and improving the Faraday efficiency of nitrate reduction ammonia production. The prepared catalyst can perform electrocatalytic nitrate reduction ammonia production in a wide potential range, and the catalyst prepared by the method has the characteristics of low loading, high activity and strong durability.

[0004] The first objective of this invention is to provide a method for preparing an in-situ spontaneously reconstructed surface CuFe-G nitrate reduction catalyst for ammonia production, comprising the following steps:

[0005] The copper source and citrate were dissolved in deionized water by stirring, and then potassium ferrocyanide was added. After mixing evenly, the mixture was allowed to stand for 12-36 hours. The precipitate was then collected, washed, and vacuum dried to obtain the Cu2[Fe(CN)6] precursor.

[0006] The Cu2[Fe(CN)6] precursor was calcined at 700-900℃ for 1-4 hours in a mixed atmosphere of hydrogen and inert gas to obtain the CuFe-G nitrate reduction catalyst for ammonia production.

[0007] Preferably, the heating rate during calcination is 2~10 °C / min. -1 .

[0008] Preferably, the molar ratio of the copper source to the citrate is 1:1 to 3.

[0009] Preferably, the copper source is one or more of copper nitrate, copper chloride, and copper sulfate.

[0010] Preferably, the citrate is one or more of sodium citrate and potassium citrate.

[0011] Preferably, the molar ratio of the copper source to potassium ferrocyanide is 1:1 to 3.

[0012] Preferably, in the mixed atmosphere of hydrogen and inert gas, the hydrogen accounts for 5% of the volume ratio; the gas velocity of the mixed atmosphere is 10~100 sccm.

[0013] Preferably, the vacuum drying temperature is 40~80 ℃ and the drying time is 4~12 h.

[0014] The second objective of this invention is to provide an in-situ spontaneous surface reconstruction CuFe-G nitrate reduction catalyst for ammonia production.

[0015] The third objective of this invention is to provide an application of an in-situ spontaneously reconstructed surface CuFe-G nitrate reduction ammonia catalyst in electrocatalytic nitrate reduction ammonia production.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] This invention provides an in-situ spontaneous surface reconstruction CuFe-G nitrate reduction ammonia catalyst, its preparation method, and its application. This invention utilizes an impregnation method to remove K+ from potassium ferrocyanide. + Replace and substitute with Cu 2+The Cu2[Fe(CN)6] precursor was successfully prepared, and the crystal structure of the catalyst was subsequently optimized through heat treatment.

[0018] Surface active sites were identified, resulting in a CuFe bimetallic catalyst supported on graphene Garphene.

[0019] The advantages of the catalyst provided by this invention are reflected in the following aspects.

[0020] (1) High catalytic activity sites: Thanks to the band modulation of alloying, CuFe-G initiates the catalytic activity from NO3- - To NO2 - The spontaneous transformation, accompanied by surface reconstruction, forms a stable CuFeO. x Ultrathin layers, without dynamic evolution. Stable CuFeO x Ultrathin layers can optimize the adsorption of key intermediates and catalyze NO3 in series. - and NO2 - Reduction. Furthermore, the graphene-Garphene support can promote electron transfer during the reduction of nitrate to ammonia, accelerating reaction kinetics.

[0021] (2) Widened potential range: Thanks to the band modulation of alloying, CuFe-G initiates the potential range from NO3. - To NO2 - The spontaneous transformation, accompanied by surface reconstruction, forms a stable CuFeO. x Ultrathin layers, without dynamic evolution. Stable CuFeO x The ultrathin layer can maintain the reaction conditions on the catalyst surface, ensuring that the active sites of the catalyst participate in the nitrate reduction to ammonia production throughout the process, thereby achieving efficient ammonia production over a wide potential range.

[0022] (3) Excellent stability: The CuFe-G nitrate reduction ammonia catalyst exhibits excellent cycle stability under neutral nitrate reduction ammonia production conditions, ensuring its reliability for long-term use.

[0023] (4) Low cost and easy preparation: Cu-based catalysts are inexpensive and CuFe-G nitrate reduction catalysts are relatively simple to prepare and have good industrial application prospects.

[0024] Furthermore, the in-situ spontaneously reconstructed surface CuFe-G nitrate reduction ammonia production catalyst of the present invention exhibits efficient and stable ammonia production over a wide potential range in neutral electrolytes. It demonstrates a Faradaic efficiency exceeding 95% for electrocatalytic nitrate reduction to ammonia production over a wide potential range of -0.7 V to -1.0 V vs. RHE, achieving 8.03 mgh at -1.0 V vs. RHE. -1 mg cat-1 The method for preparing the in-situ spontaneous surface reconstruction CuFe-G nitrate reduction ammonia catalyst of the present invention is simple, low-cost, requires little equipment investment, is highly controllable, has mild reaction conditions, occupies little space, and is environmentally friendly, and can be used in the field of nitrate reduction ammonia production. Attached Figure Description

[0025] Figure 1 X-ray diffraction pattern of the Cu2[Fe(CN)6] precursor prepared in Example 1;

[0026] Figure 2 Scanning electron microscope image of the Cu2[Fe(CN)6] precursor prepared in Example 1;

[0027] Figure 3 X-ray diffraction pattern of the CuFe-G nitrate reduction catalyst for ammonia production prepared in Example 1;

[0028] Figure 4 Transmission electron microscopy image of the CuFe-G nitrate reduction catalyst for ammonia production prepared in Example 1;

[0029] Figure 5 Here is a high-resolution transmission electron microscope image of the CuFe-G nitrate reduction catalyst for ammonia production prepared in Example 1;

[0030] Figure 6 Linear sweep voltammogram of the CuFe-G nitrate reduction catalyst prepared in Example 1;

[0031] Figure 7 The diagram shows the Faradaic efficiency of the CuFe-G nitrate reduction catalyst for ammonia production prepared in Example 1.

[0032] Figure 8 The graph shows the ammonia yield of the CuFe-G nitrate reduction catalyst prepared in Example 1.

[0033] Figure 9 The cyclic stability diagram is shown for the CuFe-G nitrate reduction catalyst prepared in Example 1.

[0034] Figure 10 This is a transmission electron microscope image of the CuFe-G nitrate reduction catalyst for ammonia production prepared in Example 1 after in-situ spontaneous surface reconstruction.

[0035] Figure 11 The graph shows the ammonia yield of the CuFe-G-1 nitrate reduction catalyst prepared in Example 2.

[0036] Figure 12 The graph shows the ammonia yield of the CuFe-G-2 nitrate reduction catalyst prepared in Example 3.

[0037] Figure 13 The graph shows the ammonia yield of the CuFe-G-3 nitrate reduction catalyst prepared in Example 4. Detailed Implementation

[0038] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0039] The purpose of this invention is to provide an in-situ spontaneous surface reconstruction CuFe-G nitrate reduction ammonia catalyst, its preparation method, and its application, in order to solve the problem of reduced Faraday efficiency of existing Cu-based catalysts due to intermittent renewable energy fluctuations. This is mainly achieved by mitigating the impact of potential fluctuations on catalyst performance through reasonable material design, thereby realizing efficient ammonia production over a wide potential range.

[0040] To achieve the above objectives, the first aspect of the present invention provides a method for preparing an in-situ spontaneously reconstructed surface CuFe-G nitrate reduction catalyst for ammonia production, comprising the following steps:

[0041] The copper source and citrate were dissolved in deionized water by stirring, and then potassium ferrocyanide was added. After mixing evenly, the mixture was allowed to stand for 12-36 hours. The precipitate was then collected, washed, and vacuum dried to obtain the Cu2[Fe(CN)6] precursor.

[0042] The Cu2[Fe(CN)6] precursor was calcined at 700-900℃ for 1-4 hours in a mixed atmosphere of hydrogen and inert gas to obtain the CuFe-G nitrate reduction catalyst for ammonia production.

[0043] The heating rate during calcination is 2~10 ℃ min. -1 .

[0044] The molar ratio of the copper source to the citrate is 1:1 to 3.

[0045] The copper source is one or more of copper nitrate, copper chloride, and copper sulfate.

[0046] The citrate is one or more of sodium citrate and potassium citrate.

[0047] The molar ratio of the copper source to potassium ferrocyanide is 1:1 to 3.

[0048] In a mixed atmosphere of hydrogen and an inert gas, the hydrogen accounts for 5% of the volume; the gas velocity of the mixed atmosphere is 10~100 sccm.

[0049] The vacuum drying temperature is 40~80 ℃, and the drying time is 4~12 h.

[0050] An exemplary method for preparing an in-situ spontaneously reconstructed surface CuFe-G nitrate reduction catalyst for ammonia production includes:

[0051] Step 1: Preparation of Cu2[Fe(CN)6] precursor: First, copper source and citrate were dissolved in deionized water by stirring. Then, potassium ferrocyanide was added to the mixed solution and dissolved completely. The solution was then allowed to stand for 12-36 hours to promote the reaction. Subsequently, the supernatant was removed by decantation, and the lower precipitate was collected, washed with deionized water, and vacuum dried to successfully obtain the Cu2[Fe(CN)6] precursor.

[0052] Step 2: In a 5% H2 / Ar atmosphere, the Cu2[Fe(CN)6] precursor is heated at 2~10 °C for min. -1 The heating rate was adjusted, and the catalyst was calcined at different temperatures for 1-4 hours, then naturally cooled to room temperature to obtain CuFe-G nitrate reduction catalyst for ammonia production.

[0053] The copper source mentioned in step one is one or more of copper nitrate, copper chloride, and copper sulfate.

[0054] The citrate mentioned in step one is one or more of sodium citrate and potassium citrate.

[0055] The molar ratio of the copper source and citrate in step one is 1:1 to 3.

[0056] The stirring described in step one is performed at a speed of 60-600 rpm for 5-60 minutes.

[0057] In the mixed solution described in step one, the concentration of the copper source is 0.005~0.5 mol L. -1 The citrate concentration is 0.005~1.5 mol L. -1 .

[0058] The molar ratio of copper source to potassium ferrocyanide mentioned in step one is 1:1~3.

[0059] The number of times the deionized water is washed in step one is 2 to 5.

[0060] The vacuum drying temperature in step one is 40~80 ℃, and the drying time is 4~12 h.

[0061] The H2 / Ar gas introduction rate in step two is 10~100 sccm.

[0062] The different temperatures mentioned in step two are 750, 800, 850, and 900 ℃.

[0063] A second aspect of this invention provides an in-situ spontaneous surface reconstruction CuFe-G nitrate reduction catalyst for ammonia production. This catalyst uses graphene as a support, with CuFe bimetallic alloy clusters loaded onto graphene (G).

[0064] The third aspect of this invention provides the application of an in-situ spontaneously reconstructed surface CuFe-G nitrate reduction ammonia catalyst in electrocatalytic nitrate reduction ammonia production.

[0065] It should be noted that, unless otherwise specified, the experimental methods used in this invention are all conventional methods; and the reagents and materials used, unless otherwise specified, are all commercially available.

[0066] Example 1

[0067] A method for preparing an in-situ spontaneously reconstructed surface CuFe-G nitrate reduction catalyst for ammonia production comprises the following steps:

[0068] Step 1: Preparation of Cu2[Fe(CN)6] precursor: First, 4 mmol of copper nitrate trihydrate (II) (Cu(NO3)2·3H2O) and 9 mmol of sodium citrate were dissolved in 50 ml of deionized water. Then, 6 mmol of potassium ferrocyanide (K3[Fe(CN)6]) was added to the mixed solution and dissolved completely. The solution was then allowed to stand for 24 hours to promote the reaction. Subsequently, the supernatant was removed by decantation, and the lower precipitate was collected, washed three times with deionized water, and dried under vacuum at 60 °C for 6 h to successfully obtain the Cu2[Fe(CN)6] precursor.

[0069] Step 2: The Cu2[Fe(CN)6] precursor was subjected to a 5% H2 / Ar atmosphere with a purge rate of 30 sccm and a temperature of 5 °C / min. -1 The heating rate was adjusted, and the catalyst was calcined at 850 °C for 2 h, then naturally cooled to room temperature to obtain the CuFe-G nitrate reduction catalyst for ammonia production.

[0070] Figure 1 The image shows the X-ray diffraction pattern of the Cu2[Fe(CN)6] precursor prepared in step one of this embodiment. The successful synthesis of the Cu2[Fe(CN)6] precursor is confirmed by combining the XRDPDF standard card.

[0071] Figure 2 The image shows a scanning electron microscope (SEM) image of the Cu2[Fe(CN)6] precursor prepared in step one of this embodiment 1. The synthesized precursor Cu2[Fe(CN)6] exhibits a cubic morphology.

[0072] Figure 3The image shows the X-ray diffraction pattern of the CuFe-G nitrate reduction ammonia catalyst prepared in step two of Example 1. The CuFe-G nitrate reduction ammonia catalyst is composed of nanoparticles of Cu and nanoparticles of Fe.

[0073] Figure 4 This is a transmission electron microscope image of the CuFe-G nitrate reduction ammonia catalyst prepared in step two of Example 1. The synthesized CuFe-G has a nanosphere morphology with an average diameter of about 150 nm and a shell thickness of 25 nm.

[0074] Figure 5 This is a high-resolution transmission electron microscope image of the CuFe-G nitrate reduction ammonia catalyst prepared in step two of Example 1. The lattice spacings of 0.34 nm and 0.204 nm correspond to the (002) crystal plane of Graphene and the (110) crystal plane of CuFe alloy, respectively.

[0075] Figure 6 This is a linear sweep voltammogram (LSV) of the CuFe-G nitrate reduction ammonia catalyst prepared in Example 1. Electrocatalyst ink was prepared using the CuFe-G nitrate reduction ammonia catalyst prepared in Example 1. 5 mg of the electrocatalyst was dispersed in a mixed solution of 500 μL deionized water, 450 μL ethanol, and 50 μL 5 wt.% Nafion solution. 25 μL of the electrocatalyst ink was coated onto carbon paper (0.5 cm * 0.5 cm). The carbon paper coated with the electrocatalyst ink, a Pt sheet, and Ag / AgCl (0.5 M K₂SO₄ + 0.1 M KNO₃) were used as the working electrode, counter electrode, and reference electrode, respectively, and connected to a Chenhua 760e electrochemical workstation. The LSV curve was recorded within a potential window of 0.2 V to -0.4 V, with a scan rate of 5 mV s relative to the reversible hydrogen electrode (RHE). -1 It also features iR compensation. CuFe-G achieves 35.16 mA cm⁻¹ at a potential of -0.3 V vs. RHE. -2 The current density.

[0076] Figure 7 This is a Faraday efficiency plot for the CuFe-G nitrate reduction ammonia catalyst prepared in Example 1. In the potential range of -0.7 V to -1.0 V vs. RHE, the Faraday efficiencies of CuFe-G are recorded as 99.78 ± 4.73%, 98.66 ± 4.17%, 97.91 ± 3.51%, and 99.63 ± 2.94%. These consistently high efficiencies exceeding 95% highlight the excellent performance of the electrocatalytic reduction of nitrate to ammonia production over a wide potential window.

[0077] Figure 8This is a graph showing the ammonia yield of the CuFe-G nitrate reduction catalyst prepared in Example 1. In the potential range of -0.7 V to -1.0 V vs. RHE, the corresponding NH3 yield of CuFe-G is 4.50 ± 0.69 mg h⁻¹. -1 mg cat -1 5.25±0.91 mg h -1 mg cat -1 6.04±0.65 mg h -1 mg cat -1 8.03±0.67 mg h -1 mg cat -1 .

[0078] Figure 9 This is a cyclic stability graph of the CuFe-G nitrate reduction catalyst for ammonia production prepared in Example 1. Even after seven cycles and a cumulative 70 h, its Faradaic efficiency remains above 95%, highlighting the excellent catalytic stability of CuFe-G.

[0079] Figure 10 This is a transmission electron microscope (TEM) image of the CuFe-G nitrate reduction catalyst for ammonia production prepared in Example 1 after in-situ spontaneous surface reconstruction. (The image shows the catalyst in NO3.) - To NO2 - During the spontaneous transformation process, a stable CuFeO is formed along with surface reconstruction. x Ultra-thin layer.

[0080] Example 2

[0081] A method for preparing a CuFe-G-1 nitrate reduction catalyst for ammonia production comprises the following steps:

[0082] Step 1: The preparation process of Cu2[Fe(CN)6] precursor is the same as in Example 1.

[0083] Step 2: The Cu2[Fe(CN)6] precursor was subjected to a 5% H2 / Ar atmosphere with a purge rate of 30 sccm and a temperature of 5 °C / min. -1 The heating rate was adjusted, and the catalyst was calcined at 700 °C for 2 h, then naturally cooled to room temperature to obtain CuFe-G-1 nitrate reduction catalyst for ammonia production.

[0084] Figure 11 This is a graph showing the ammonia yield of the CuFe-G-1 nitrate reduction catalyst prepared in Example 2. At a potential of -1.0 V vs. RHE, the NH3 yield is 5.09 mg h⁻¹. -1 mgcat -1 .

[0085] Example 3

[0086] A method for preparing a CuFe-G-2 nitrate reduction catalyst for ammonia production comprises the following steps:

[0087] Step 1: The preparation process of Cu2[Fe(CN)6] precursor is the same as in Example 1.

[0088] Step 2: The Cu2[Fe(CN)6] precursor was subjected to a 5% H2 / Ar atmosphere with a purge rate of 30 sccm and a temperature of 5 °C / min. -1 The heating rate was adjusted, and the catalyst was calcined at 800 °C for 2 h, then naturally cooled to room temperature to obtain CuFe-G-2 nitrate reduction catalyst for ammonia production.

[0089] Figure 12 This is a graph showing the ammonia yield of the CuFe-G-2 nitrate reduction catalyst prepared in Example 3. At a potential of -1.0 V vs. RHE, the NH3 yield is 7.42 mg h⁻¹. -1 mg cat -1 .

[0090] Example 4

[0091] A method for preparing a CuFe-G-3 nitrate reduction catalyst for ammonia production comprises the following steps:

[0092] Step 1: The preparation process of Cu2[Fe(CN)6] precursor is the same as in Example 1.

[0093] Step 2: The Cu2[Fe(CN)6] precursor was subjected to a 5% H2 / Ar atmosphere with a purge rate of 30 sccm and a temperature of 5 °C / min. -1 The heating rate was adjusted, and the catalyst was calcined at 900 °C for 2 h, then naturally cooled to room temperature to obtain CuFe-G-3 nitrate reduction catalyst for ammonia production.

[0094] Figure 13 This is a graph showing the ammonia yield of the CuFe-G-3 nitrate reduction catalyst prepared in Example 4. At a potential of -1.0 V vs. RHE, the NH3 yield is 6.18 mg h⁻¹. -1 mg cat -1 .

[0095] In summary, this invention provides a method for preparing and applying an in-situ spontaneously reconstructed surface CuFe-G nitrate reduction ammonia catalyst. It primarily addresses the problem of reduced Faradaic efficiency in existing Cu-based catalysts due to intermittent renewable energy fluctuations. First, a Cu2[Fe(CN)6] precursor was synthesized via impregnation. Then, the Cu2[Fe(CN)6] precursor was heat-treated to obtain the CuFe-G nitrate reduction ammonia catalyst. The prepared CuFe-G catalyst benefits from band modulation through alloying, initiating the reduction of nitrogen from NO3-. - To NO2 - The spontaneous transformation, accompanied by surface reconstruction, forms a stable CuFeO. x Ultrathin layers, without dynamic evolution. Stable CuFeO x Ultrathin layers can optimize the adsorption of key intermediates and catalyze NO3 in series. - and NO2 - The reduction process broadens the potential range of nitrate reduction and simultaneously improves the Faraday efficiency of nitrate reduction for ammonia production.

[0096] This invention describes preferred embodiments and their effects. However, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to include both the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0097] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for the preparation of a CuFe-G nitrate-reducing ammonia synthesis catalyst which is self-surface-reconstructing in situ, characterized in that The method comprises the following steps: The copper source and citrate are stirred and dissolved in deionized water, and then potassium ferrocyanide is added. After uniform mixing, the mixture is allowed to stand for 12-36 hours, and then the precipitate after standing is collected. The precipitate is washed and vacuum dried to obtain a Cu2[Fe(CN)6] precursor; The Cu2[Fe(CN)6] precursor is calcined at 700-900°C for 1-4 hours in a mixed gas atmosphere of hydrogen and inert gas to obtain a CuFe-G nitrate reduction ammonia catalyst.

2. The process for the preparation of in-situ self-generated surface reconstructed CuFe-G nitrate-reducing ammonia catalyst according to claim 1, characterized by, The temperature increase rate at the time of calcination is 2 to 10°C / min -1 .

3. The method for in-situ self-surface restructuring CuFe-G nitrate reduction to ammonia catalyst preparation according to claim 1, characterized in that, The mass ratio of the copper source to the citrate is 1:1-3.

4. The method for in-situ self-surface restructuring CuFe-G nitrate reduction to ammonia catalyst preparation according to claim 1, characterized in that, The copper source is one or more of copper nitrate, copper chloride, and copper sulfate.

5. The method for in-situ spontaneous surface restructuring CuFe-G nitrate reduction to ammonia catalyst preparation according to claim 1, characterized in that, The citrate is one or more of sodium citrate and potassium citrate.

6. The method for in-situ spontaneous surface restructuring CuFe-G nitrate reduction to ammonia catalyst preparation according to claim 1, characterized in that, The mass ratio of the copper source to the potassium ferrocyanide is 1:1-3.

7. The method for in-situ spontaneous surface restructuring CuFe-G nitrate reduction to ammonia catalyst preparation according to claim 1, characterized in that, In the mixed gas atmosphere of hydrogen and inert gas, the volume ratio of hydrogen is 5%; and the gas rate of the mixed gas atmosphere is 10-100 sccm.

8. The method for in-situ spontaneous surface restructuring CuFe-G nitrate reduction to ammonia catalyst preparation according to claim 1, characterized in that, The temperature of the vacuum drying is 40-80°C, and the drying time is 4-12 hours.

9. An in-situ self-surface reconstructed CuFe-G nitrate reduction ammonia catalyst prepared by the method of any one of claims 1-8.

10. Use of the in-situ self-surface reconstructed CuFe-G nitrate reduction ammonia catalyst of claim 9 in electrocatalytic reduction of nitrate to produce ammonia.

Images