Aldehyde group induced metal organic framework loaded silver nanoparticle composite nanosheet array electrode as well as preparation method and application of aldehyde group induced metal organic framework loaded silver nanoparticle composite nanosheet array electrode

Abstract

The invention provides a preparation method for in-situ introduction of silver nanoparticles at metal organic framework material coordination unsaturated metal active sites by taking aldehyde groups as built-in redox active sites. The method is used for solving the problem that a metal organic framework material with a single active metal site is difficult to be matched with multi-step electron transfer and intermediate conversion in a nitrate electroreduction ammonia preparation process at the same time, and the challenge that in the prior art, metal nanoparticles cannot be accurately introduced to the vicinity of a coordination unsaturated metal site of the metal organic framework material. According to the invention, the aldehyde group is implanted into the nickel-based metal organic framework material as a built-in redox active site, on one hand, the aldehyde group cannot be coordinated with a nickel metal site, so that a coordinated unsaturated nickel metal site is generated at the para-position of the aldehyde group; and on the other hand, the aldehyde group can induce in-situ loading of the silver nanoparticles at a coordinated unsaturated nickel metal site through a silver mirror reaction, so that the nickel metal organic framework and silver nanoparticle composite nanosheet array electrode with a serial catalytic action is formed.

Description

Technical Field

[0001] The invention belongs to the technical field of composite nanomaterials, and specifically relates to an aldehyde-induced metal organic framework loaded silver nanoparticle composite nanosheet array electrode and a preparation method and application thereof. Background Art

[0002] Ammonia (NH3) is an important chemical raw material and a potential zero-carbon energy source. However, due to the long-term use of ammonia, nitrogen oxides (NO3 - ,NO2 - ) accumulate excessively in the environment, endangering human health. Therefore, using electrochemical methods to reduce nitrides to ammonia can not only close the nitrogen cycle, but also help transform synthetic ammonia to renewable energy processes, which is in line with the country's requirements for developing new quality productivity. Given that transition metal elements (Mo, Fe, V, etc.) in natural biological enzymes have moderate adsorption energy for nitrogen oxides and their intermediates, developing transition metal-based electrocatalysts is a direct and effective method.

[0003] Metal-organic frameworks (MOFs) have a clear and adjustable spatial structure and metal sites, making them a potential class of enzyme-mimicking catalysts. The key is that the coordinated unsaturated metal sites of MOFs have catalytic properties similar to the uncoordinated active sites of biological enzymes. However, since the electroreduction of nitrate to ammonia involves the transformation of multiple reaction intermediates and electron transfer reactions, MOFs based on single metal sites currently face the problems of low selectivity and yield in the electroreduction of nitrate to ammonia. Based on this, the introduction of heterogeneous catalytic sites such as metal single atoms, metal nanoparticles, metal complexes, etc. into the MOFs structure can effectively form a tandem catalytic system with the coordinated unsaturated metal sites of MOFs, realizing proton-coupled electron transfer reactions at lower overpotentials and wider potential windows.

[0004] Taking metal nanoparticles as an example, the diversity of MOFs in composition and structure enables them to be used as carriers to modify metal nanoparticles. In this composite system, on the one hand, the spatial environment of MOFs can improve the dispersion and stability of metal nanoparticles. On the other hand, metal nanoparticles can coordinate with the unsaturated metal sites of MOFs to regulate multi-step electron and intermediate transfer reactions, thereby obtaining a tandem catalytic system with dual active sites. At present, researchers have developed a variety of methods to introduce metal nanoparticles into MOFs, such as solution impregnation, dual solvent method, chemical vapor deposition, solid grinding and thermal decomposition. However, these methods either involve complex reaction steps or are carried out under harsh conditions. In addition, the spatial distribution relationship between metal nanoparticles and the unsaturated metal sites of MOFs is unclear.

[0005] In response to the above problems, the present invention focuses on the cooperation of metal organic framework materials with metal nanoparticles, utilizes aldehyde-induced method, in situ reduction generates silver nanoparticles near the coordination unsaturated nickel sites of nickel metal organic framework materials, and explores a dual metal site series catalytic ammonia production electrode material. Summary of the invention

[0006] The purpose of the present invention is to solve the deficiency that the prior art cannot accurately realize the point-to-point generation of metal nanoparticles near the coordination unsaturated metal sites of metal organic framework materials, and provide an aldehyde-induced metal organic framework-loaded silver nanoparticle composite nanosheet array electrode and its preparation method and application. The nanosheet array can be directly used as a cathode electrode for the electroreduction of nitrate to produce ammonia.

[0007] The concept of the present invention:

[0008] In view of the difficulty of metal organic framework materials with a single active metal site to simultaneously match the multi-step electron transfer and intermediate conversion in the process of nitrate electroreduction to ammonia, and the problem that the existing technology cannot accurately introduce metal nanoparticles near the coordination unsaturated metal sites of metal organic framework materials, the research team of this application analyzed that the use of metal organic framework materials with redox activity can in situ induce the generation of metal nanoparticles at their coordination unsaturated metal sites. At the same time, through functional matching, the multi-step electron and intermediate transfer process in the process of nitrate to ammonia conversion can be satisfied; in addition, in order to overcome the problems of metal organic framework materials in terms of conductivity and stability, polyaniline is used to modify the surface of metal organic framework @ metal nanoparticles, which can not only improve its structural stability, but also serve as an electron transport layer to improve the kinetic activity of the overall electrode material. In view of this, the research team of the present invention intends to implant aldehyde groups as built-in redox active sites into nickel-based metal organic framework materials. On the one hand, the aldehyde groups cannot coordinate with the nickel metal sites to produce coordinatively unsaturated nickel metal sites at the para position of the aldehyde groups; on the other hand, the aldehyde groups can induce the in-situ loading of silver nanoparticles on the coordinatively unsaturated nickel metal sites through the silver mirror reaction, forming a nickel metal organic framework@silver nanoparticles@polyaniline composite nanosheet array electrode with tandem catalysis.

[0009] Based on the above invention concept, in order to achieve the above purpose, the technical solution provided by the present invention is:

[0010] An aldehyde-induced metal organic framework loaded silver nanoparticle composite nanosheet array electrode and its preparation method and application, which is special in that it includes a nickel foam substrate and a metal organic framework@silver nanoparticle@polyaniline nanosheet array grown on the nickel foam substrate as a whole;

[0011] Each composite nanosheet includes a two-dimensional nickel metal organic framework (Ni-MOFs) with a length of 2-4 microns, 5-6 nanometer silver nanoparticles anchored in the coordinatively unsaturated nickel metal sites, and a polyaniline shell with a thickness of 3-4 nanometers uniformly coated on the surface of the nickel metal organic framework@silver nanoparticles.

[0012] Furthermore, the nickel metal organic framework (Ni-MOFs) has an uncoordinated aldehyde functional group and a coordinated unsaturated Ni 2+ Active site;

[0013] Furthermore, there are mesopores of about 5 nanometers distributed in Ni-MOFs, which can simultaneously satisfy the diffusion and in-situ reduction of nitrate ions in Ni-MOFs;

[0014] Furthermore, the polyaniline nanoshell with a thickness of 3–4 nm can well preserve the structure of the Ni-MOFs@Ag composite nanosheet arrays and enhance their conductivity.

[0015] At the same time, the present invention also provides a method for preparing the above-mentioned aldehyde-induced metal organic framework-loaded silver nanoparticle composite nanosheet array electrode, which is special in that it includes the following steps:

[0016] 1) Preprocessing

[0017] Pre-treating the nickel foam substrate to remove organic impurities and oxides on the surface of the substrate, and drying the substrate for later use;

[0018] 2) Preparation of nickel metal organic framework nanosheet arrays containing coordinated unsaturated defect sites on the surface of nickel foam substrate

[0019] Immersing the nickel foam substrate pretreated in step 1) in a reaction vessel (e.g., a reaction kettle) containing a mixed solution of nickel chloride, 2,6-naphthalene dicarboxylic acid and p-chlorobenzoic acid, and reacting at 150° C. for 12 hours to obtain a metal organic framework nanoarray containing coordinated unsaturated defect sites on the surface of the nickel foam substrate, and then rinsing and drying;

[0020] 3) Preparation of Ni-MOF@Ag nanoparticle composite nanosheet arrays on the surface of nickel foam substrate

[0021] The Ni-MOFs nanosheet array containing coordinated unsaturated nickel defect sites obtained in step 2) is immersed in a mixed solution consisting of silver nitrate, ammonia water and water, and reacted at room temperature for 3 hours to obtain a nickel metal organic framework@silver nanoparticle composite nanosheet array on the surface of the nickel foam substrate, which is then rinsed and dried for later use;

[0022] 4) Preparation of Ni-MOF@Ag nanoparticles@Polyaniline composite nanosheet arrays on the surface of nickel foam substrate

[0023] The carbon foam nickel substrate with a nickel metal organic framework@silver nanoparticle composite nanosheet array grown on the surface obtained in step 3) is used as a working electrode, and a nickel metal organic framework@silver nanoparticle@polyaniline composite nanosheet array electrode is prepared by an electrodeposition method.

[0024] Furthermore, step 1) is specifically as follows: ultrasonically treating the nickel foam substrate with acetone and water in sequence to remove organic impurities adsorbed on the surface of the nickel foam substrate; then ultrasonically treating the nickel foam substrate with a hydrochloric acid solution to remove oxides on the surface of the nickel foam substrate, and then washing with water and drying.

[0025] Furthermore, in step 2), the molar ratio of nickel chloride: 2,6-naphthalene dicarboxylic acid: p-formylbenzoic acid is 30:30:1; the volume ratio of ethanol: water: N,N-dimethylformamide is 1:1:16; wherein the molar concentration of nickel chloride is 0.028 mol / L.

[0026] Furthermore, in step 3), the molar concentration of silver nitrate in the mixed solution is 0.105 mmol / L, and the pH of the mixed solution is adjusted to about 10 using ammonia water.

[0027] Further, in step 4), the platinum sheet is used as the counter electrode, the silver / silver chloride electrode with a built-in 3M potassium chloride aqueous solution is used as the reference electrode, and the mixed aqueous solution composed of sodium sulfate and aniline is used as the electrolyte. -2 Electrodeposition was performed for 900 s at a potential of 0.05 mol / L sodium sulfate and 0.01 mol / L aniline.

[0028] In addition, the present invention also provides the use of the aldehyde-induced metal organic framework-loaded silver nanoparticle composite nanosheet array electrode as a cathode electrode in electrocatalytic nitrate reduction to produce ammonia.

[0029] And the method of electrocatalytic reduction of nitrate to produce ammonia by using the above-mentioned aldehyde-induced metal organic framework-supported silver nanoparticle composite nanosheet array electrode is special in that:

[0030] In a three-electrode H-type electrolytic cell, the nickel metal organic framework@silver nanoparticles@polyaniline composite nanosheet array electrode was used as the working cathode, and an aqueous solution containing 0.1M potassium nitrate and 1M potassium hydroxide was used as the electrolyte. The electroreduction of nitrate to ammonia was carried out in the voltage range of -0.2 to -0.6V vsRHE. The test lasted for 1 hour.

[0031] Furthermore, the platinum sheet was used as the counter electrode, and the silver / silver chloride electrode containing a 3M potassium chloride aqueous solution was used as the reference electrode.

[0032] Mechanism of the present invention:

[0033] The present invention develops a method for inducing built-in aldehyde groups to accurately guide the in-situ generation of silver nanoparticles at the para-position of the coordination unsaturated metal site of the nickel metal organic framework material. In the synthesis process, a ligand containing an aldehyde group (such as p-aldehyde benzoic acid) is first introduced into the metal organic framework material matrix as a built-in redox active site. On the one hand, the aldehyde group cannot coordinate with the nickel metal site to generate a coordination unsaturated nickel metal site at the para-position of the aldehyde group; on the other hand, the aldehyde group can induce the in-situ loading of silver nanoparticles at the coordination unsaturated nickel metal site through the silver mirror reaction, forming a nickel metal organic framework@silver nanoparticles@polyaniline composite nanosheet array electrode with tandem catalysis.

[0034] The beneficial effects of the present invention are:

[0035] 1. The present invention uses aldehyde groups as built-in redox sites to in-situ anchor silver nanoparticles near the MOFs coordinated unsaturated metal sites to form a nickel metal organic framework@silver nanoparticle composite nanosheet array electrode with tandem catalysis. Aldehyde groups, as built-in redox active groups, play a crucial role in creating MOFs coordinated unsaturated metal sites and promoting in-situ nucleation of silver nanoparticles near the unsaturated metal sites of MOFs, solving the problem that the prior art is difficult to control the distribution of metal nanoparticles in the adjacent positions of the coordinated unsaturated metal sites.

[0036] 2. The present invention synthesized for the first time a nickel metal organic framework@silver nanoparticles@polyaniline composite nanosheet array electrode with a clear spatial distribution and used it for electrocatalytic nitrate reduction to produce ammonia. The optimal ammonia Faraday efficiency (86.2%) was achieved at a voltage of -0.2 V vs RHE, and the ammonia production rate was 0.163 mmolh -1 cm -2 .

[0037] 3. The present invention can prepare a series of M-MOFs@Ag@PANI (M=Fe, Co, No, Cu) composite nanoarray electrodes by regulating the types of MOFs metals.

[0038] 4. The silver nanoparticles of the present invention and the unsaturated coordinated nickel sites can form a tandem catalytic system to synergistically optimize the conversion process of nitrate to ammonia. On the one hand, the silver nanoparticles can convert nitrate into nitrite and diffuse to the coordinated unsaturated nickel sites to couple with adsorbed hydrogen to produce ammonia; on the other hand, the active hydrogen generated on the coordinated unsaturated nickel sites can overflow to the silver nanoparticles to participate in the conversion of nitrate to ammonia. Therefore, the combination of the nickel metal organic framework coordinated unsaturated metal sites and silver nanoparticles produces a mutually reinforcing tandem catalytic effect, enhances the catalytic efficiency of each other, and achieves a higher ammonia yield and Faraday efficiency at a lower overpotential and a wider potential window.

[0039] 5. The present invention reports a universal method for preparing a composite tandem catalyst based on MOFs and silver nanoparticles. This method uses aldehyde groups as built-in redox active sites to achieve precise in situ reduction of silver nanoparticles at the coordinated unsaturated metal sites of MOFs. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The scanning electron microscopy (SEM) photos of the nickel metal organic framework nanosheet array containing built-in aldehyde groups prepared by the present invention are as follows: a is a low-magnification SEM image, and b is a high-magnification SEM image;

[0041] Figure 2 The scanning electron microscope (SEM) photographs of the nickel metal organic framework@silver nanoparticle composite nanosheet array prepared by the present invention; a is a low-magnification SEM image, and b is a high-magnification SEM image;

[0042] Figure 3 The scanning electron microscope (SEM) photographs of the nickel metal organic framework@silver nanoparticles@polyaniline composite nanosheet array prepared by the present invention; a is a low-magnification SEM image, and b is a high-magnification SEM image;

[0043] Figure 4 is an X-ray diffraction (XRD) pattern of the nickel metal organic framework@silver nanoparticle composite nanosheet array prepared by the present invention;

[0044] Figure 5 A high resolution transmission electron microscopy (HRTEM) image of a nickel metal organic framework@silver nanoparticle composite nanosheet prepared by the present invention;

[0045] Figure 6 The graph is a graph of ammonia yield and Faraday efficiency obtained at different potentials for the nickel metal organic framework@silver nanoparticles@polyaniline composite nanosheet array prepared by the present invention. DETAILED DESCRIPTION

[0046] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0047] Example 1

[0048] Step 1: Take 2.4×3cm 2 The nickel foam was cleaned with acetone, hydrochloric acid, and water to remove organic impurities and oxides on its surface, and then dried for later use.

[0049] Step 2: Dissolve 1 mmol nickel chloride, 1 mmol 2,6-naphthalene dicarboxylic acid and 0.03 mmol p-formylbenzoic acid in a mixed solution consisting of 2 mL ethanol, 2 mL water and 32 mL N, N-dimethylformamide, pour the solution into a 50 mL hydrothermal kettle containing the nickel foam prepared in step 1), react at 150 ° C for 12 hours to prepare a nickel metal organic framework nanosheet array containing built-in aldehyde groups, then rinse with N, N-dimethylformamide, ultrapure water and ethanol and dry for use.

[0050] Step 3: Prepare 9.5 mL of 0.105 mmol L in a 10 mL beaker. -1 silver nitrate solution, and adjusting its pH to about 10 with ammonia water; fixing the nickel metal organic framework nanosheet array obtained in step 2) in a beaker, reacting at room temperature and 450 rpm for 3 hours, and washing with ultrapure water and ethanol to prepare a nickel metal organic framework@silver nanoparticle composite array sheet array.

[0051] Step 4: The nickel metal organic framework@silver nanoparticle composite nanosheet array obtained in step 3) was used as the working electrode, the Pt sheet was used as the counter electrode, the silver / silver chloride electrode with a built-in 3M KCl aqueous solution was used as the reference electrode, and the solution containing 50mM sodium sulfate and 0.01M aniline was used as the electrolyte. 1mA cm was applied to the working electrode at room temperature. -2 The nickel metal organic framework@silver nanoparticles@polyaniline composite nanosheet array electrode was obtained after 900s of electrodeposition.

[0052] Embodiment 2:

[0053] The method of Example 1 is adopted, except that 1 mmol of nickel chloride in step 2 is replaced by 1 mmol of cobalt chloride.

[0054] Embodiment 3:

[0055] The method of Example 1 is adopted, except that 1 mmol of nickel chloride in step 2 is replaced by 1 mmol of ferric chloride.

[0056] Embodiment 4:

[0057] The method of Example 1 is adopted, except that 1 mmol of nickel chloride in step 2 is replaced by 1 mmol of cupric chloride.

[0058] Results Analysis

[0059] like Figure 1 As shown, the structure of the nickel metal organic framework material with built-in aldehyde groups prepared in Example 1 was characterized by SEM. It was uniformly grown on the nickel foam substrate, and the overall length of the nanosheets was 3 microns.

[0060] like Figure 2 As shown, the structure of the prepared nickel metal organic framework@silver nanoparticle composite nanosheet array electrode was characterized by SEM, which maintained the morphological characteristics of the nickel metal organic framework nanosheet and was about 3 microns in length.

[0061] like Figure 3 As shown, XRD analysis demonstrated that after the in situ introduction of silver nanoparticles into the nickel-coordinated unsaturated metal sites, the nickel-metal organic framework@silver nanoparticle composite nanosheet arrays maintained the structure of the nickel-metal organic framework.

[0062] like Figure 4 As shown, through HRTEM characterization, in the nickel metal organic framework@silver nanoparticle composite nanosheet array prepared in this embodiment, silver exists in the form of nanoparticles, and the particle size is 5-6 nanometers, which is consistent with the pore size distribution of the prepared nickel metal organic framework material.

[0063] like Figure 5 As shown, the prepared nickel metal organic framework @ silver nanoparticles @ polyaniline composite nanosheet array electrode was structurally characterized by SEM, which maintained the morphological characteristics of the nickel metal organic framework nanosheets @ silver nanoparticles and had a length of about 3 microns.

[0064] In order to verify that the prepared nickel metal organic framework @ silver nanoparticles @ polyaniline composite nanosheet array electrode can be applied to the process of nitrate reduction to ammonia, the specific test steps of the nickel metal organic framework @ silver nanoparticles @ polyaniline composite nanosheet array electrode prepared by the present invention for nitrate electroreduction to ammonia are as follows: an H-type three-electrode electrolytic cell equipped with a proton exchange membrane (Nafion-117) is used, a 1M potassium hydroxide solution containing 0.1M potassium nitrate is used as an electrolyte, the nickel metal organic framework @ silver nanoparticles @ polyaniline composite nanosheet array prepared in the embodiment is used as a working electrode, a platinum sheet is used as a counter electrode, and a silver / silver chloride electrode with a built-in 3M KCl aqueous solution is used as a reference electrode, and a Swiss Metrohm electrochemical workstation (Autolab M204) is used for testing, as shown in FIG. Figure 6 As shown in Figure 2, the Ni-MOF@AgNP@PANI composite nanosheet array electrode has an ammonia yield ranging from 0.163 to 0.477 mmol h in a 1 M potassium hydroxide electrolyte containing 0.1 M potassium nitrate at a negative potential range of -0.2 to -0.6 V vs RHE. -1 cm -2 , especially at -0.2 V vs RHE, the best ammonia Faraday efficiency (86.3%) was achieved, and the ammonia production rate was 0.163 mmol h -1 cm -2 .

[0065] Therefore, the sample prepared by the method of the present invention has important development potential in the practical application of nitrate electroreduction to ammonia.

[0066] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should be included in the protection scope of the present invention.

Claims

1. An aldehyde-induced metal organic framework-loaded silver nanoparticle composite nanosheet array electrode, characterized in that: It includes a nickel foam substrate and a metal organic framework nanosheet array having unsaturated coordinated metal sites that is integrally grown on the nickel foam substrate; The composite nanosheets consist of 3-4 μm-long unsaturated Ni-rich 2+ The nickel metal organic framework has 3 sites, silver nanoparticles of about 5 nanometers anchored on the unsaturated nickel sites, and a polyaniline nanoshell uniformly coated on the surface of the nickel metal organic framework.

2. The aldehyde-induced metal organic framework-supported silver nanoparticle composite nanosheet array electrode according to claim 1, characterized in that: The nickel metal organic frame has mesopores of about 5 nanometers distributed inside; The nickel metal organic framework has unsaturated Ni 2+ metal sites; The substrate is nickel foam.

3. The aldehyde-induced metal organic framework-supported silver nanoparticle composite nanosheet array electrode according to any one of claims 1 or 2, characterized in that: The following steps are involved: 1) Preprocessing Pre-treating the nickel foam to remove organic impurities and oxides on the surface of the nickel foam and drying it for later use; 2) Preparation of nickel metal organic framework nanosheet arrays on nickel foam surface The nickel foam pretreated in step 1) is immersed in a reaction vessel containing a mixed solution of nickel chloride, 2,6-naphthalene dicarboxylic acid, p-formylbenzoic acid, ethanol, water and N,N-dimethylformamide, and subjected to a hydrothermal reaction at 150° C. for 10-15 hours to obtain a nickel metal organic framework nanosheet array on the surface of the nickel foam substrate, and then rinsed and dried; 3) Preparation of Ni-MOF@Ag nanoparticle composite nanosheet arrays on nickel foam surface The nickel foam substrate on which the nickel metal organic framework nanosheet array is grown prepared in step 2) is immersed in a mixed solution consisting of silver nitrate, ammonia water and water, and reacted at room temperature for 3 hours to obtain a nickel metal organic framework@silver nanoparticle composite nanosheet array on the surface of the nickel foam substrate; 4) Preparation of Ni-MOF@Ag nanoparticles@PANI composite nanosheet arrays on nickel foam surface The carbon foam nickel substrate with a nickel metal organic framework@silver nanoparticle composite nanosheet array grown on the surface obtained in step 3) is used as a working electrode, and a nickel metal organic framework@silver nanoparticle@polyaniline composite nanosheet array electrode is prepared by an electrodeposition method.

4. The method for preparing an aldehyde-induced metal organic framework-supported silver nanoparticle composite nanosheet array electrode according to claim 3, characterized in that: Step 1) is specifically as follows: The nickel foam substrate is ultrasonically treated with acetone and water in sequence to remove organic impurities adsorbed on the surface of the nickel foam substrate; then the nickel foam substrate is ultrasonically treated with a hydrochloric acid solution to remove oxides on the surface of the nickel foam substrate, and then washed with water and dried.

5. The method for preparing an aldehyde-induced metal organic framework-supported silver nanoparticle composite nanosheet array electrode according to claim 4, characterized in that: In step 2), the molar ratio of nickel chloride: 2,6-naphthalene dicarboxylic acid: p-formylbenzoic acid is 30:30:1; the volume ratio of ethanol: water: N,N-dimethylformamide is 1:1:16; wherein the molar concentration of nickel chloride is 0.028 mol / L.

6. The method for preparing an aldehyde-induced metal organic framework-supported silver nanoparticle composite nanosheet array electrode according to claim 5, characterized in that: In step 3), the molar concentration of silver nitrate in the mixed solution is 0.105 mmol / L, and the pH of the mixed solution is adjusted to about 10 using ammonia water.

7. The method for preparing an aldehyde-induced metal organic framework-supported silver nanoparticle composite nanosheet array electrode according to claim 6, characterized in that: In step 4), the platinum sheet is used as the counter electrode, the silver / silver chloride electrode with a built-in 3M potassium chloride aqueous solution is used as the reference electrode, and the mixed aqueous solution composed of sodium sulfate and aniline is used as the electrolyte. -2 Electrodeposition at potential for 900 s; Among them, the concentration of sodium sulfate is 0.05 mol / L, and the concentration of aniline is 0.01 mol / L.

8. Use of the aldehyde-induced metal organic framework-loaded silver nanoparticle composite nanosheet array electrode according to claim 1 or 2 as a cathode material in the electroreduction of nitrate to produce ammonia.

9. A method for producing ammonia by electroreducing nitrate using the aldehyde-induced metal organic framework-supported silver nanoparticle composite nanosheet array electrode of claim 1 or 2, characterized in that: In a three-electrode H-type electrolytic cell, the nickel metal organic framework@silver nanoparticles@polyaniline composite nanosheet array electrode was used as the working cathode, and an aqueous solution containing 0.1M potassium nitrate and 1M potassium hydroxide was used as the electrolyte. The electroreduction of nitrate to produce ammonia was carried out in the voltage range of -0.2 to -0.6V vs RHE. The test lasted for 1h.

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