A method for electrocatalytic synthesis of ammonia and nitrate from N2 using an oxygen-mediated strategy.

Abstract

The application discloses a method for realizing electrocatalytic N2 synthesis of ammonia and nitrate by an oxygen-mediated strategy, and belongs to the field of nanomaterials, energy environment science and engineering. The method uses a conductive substrate coated with Fe3O4@C superlattice array nanomaterial as a working electrode; the Fe3O4@C superlattice array nanomaterial is a superlattice structure with Fe3O4 coated by carbon in an ordered array, the Fe3O4@C is in a two-dimensional sheet structure in an array form, and the C is filled between Fe3O4 nanoparticles and has a connecting effect while coating the Fe3O4 nanoparticles. The method for realizing electrocatalytic N2 synthesis of ammonia and nitrate by the oxygen-mediated strategy uses an electrocatalytic N2 activation system, which moderately adsorbs oxygen species as an electronic medium, injects oxygen lone pair electrons into a N2 antibonding pi orbital, simultaneously, a positive center attracts N2 lone pair electrons, double polarization weakens N≡N bond, and an O-N2 key intermediate is formed.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials and energy and environmental science and engineering, and particularly relates to a method for electrocatalytic synthesis of ammonia and nitrate from N2 using an oxygen-mediated strategy. Background Technology

[0002] Electrocatalytic N2 activation technology is considered an ideal alternative to traditional thermocatalytic processes because it can operate in aqueous systems at room temperature and pressure and can be directly coupled with wind and solar power systems. However, after more than a decade of development, this technology still faces many challenges, the most direct being the extremely high N≡N bond energy of N2 (941 kJ / mol). -1 The N2 activation reaction is characterized by extremely low solubility (0.6 mM in water at 25 °C) and intense competing reactions. For example, the hydrogen evolution reaction (HER) in the electrocatalytic N2 reduction reaction and the oxygen evolution reaction (OER) in the electrocatalytic N2 oxidation reaction are two highly competitive reactions. These two reactions result in low Faradaic efficiency (FE) for the N2 activation reaction, and the electrocatalytic N2 activation reaction remains far from practical application. It is worth noting that almost all existing research on electrocatalytic N2 activation employs a "high-purity N2" feed strategy to avoid potential oxygen reduction (ORR) competing reactions, significantly increasing costs. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for electrocatalytic synthesis of ammonia and nitrate from N2 using an oxygen-mediated strategy.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for electrocatalytic synthesis of ammonia and nitrate from N2 using an oxygen-mediated strategy employs a conductive substrate coated with Fe3O4@C superlattice array nanomaterials as the working electrode. The Fe3O4@C superlattice array nanomaterials are a superlattice structure in which carbon-coated Fe3O4 forms an ordered array. Fe3O4@C forms a two-dimensional sheet-like structure in an array, with C filling the spaces between the Fe3O4 nanoparticles. C not only coats the Fe3O4 nanoparticles but also acts as a connector.

[0006] In the oxygen-mediated strategy for electrocatalytic N2 synthesis of ammonia, high-purity air is used as the reaction gas, and the electrolyte is a solution of 0.01~0.2 M HCl, H2SO4, etc.

[0007] In the oxygen-mediated strategy for electrocatalytic synthesis of nitrate from N2, N2 is used as the reaction gas, and the electrolyte is a 0.0~0.5 M K2SO4 or Na2SO4 solution.

[0008] The oxygen-mediated strategy for electrocatalytic N2 synthesis of ammonia and nitrate is carried out in an H-type reaction cell with a three-electrode system.

[0009] Among them, the loading amount of Fe3O4@C superlattice array nanomaterials on the conductive substrate is 0.5 mg cm⁻¹. -2 .

[0010] Specifically, the conductive substrate coated with Fe3O4@C superlattice array nanomaterials is formed by dispersing Fe3O4@C superlattice array nanomaterials and binders in a solvent to form catalyst ink, and then coating the catalyst ink onto the conductive substrate and drying it to serve as the working electrode for the electrocatalytic reaction.

[0011] The binder is Nafion D520 perfluorosulfonic acid resin solution, and the solvent is isopropanol solution.

[0012] The amounts of Fe3O4@C superlattice array nanomaterials, solvent, and binder were 5 mg, 950 μL, and 50 μL, respectively.

[0013] The conductive substrate can be one or more of carbon paper, carbon cloth, and glassy carbon electrodes.

[0014] The preparation method of Fe3O4@C superlattice array nanomaterials includes the following steps:

[0015] S1: The ferric oleate precursor and the template agent are thoroughly mixed at a mass ratio of 1:10 to 1:20, and then annealed in an inert atmosphere containing hydrogen at a temperature of 400℃ to 500℃ for 1 to 3 hours.

[0016] S2: The annealed product is washed and then freeze-dried to obtain Fe3O4@C superlattice array nanomaterials. The freeze-drying time is 10-20 h. The freeze-drying is carried out in a commonly used laboratory freeze dryer at a temperature of -50℃ to -80℃ and a vacuum degree usually below 10 Pa.

[0017] The volume fraction of hydrogen in the inert atmosphere containing hydrogen is 5-10%.

[0018] The template agent is one or more of sodium chloride, potassium chloride, and potassium sulfate.

[0019] The ferric oleate precursor is prepared by the following steps: adding a metal salt and a long-chain fatty acid alkali metal salt to a mixed solution containing an extractant at a molar ratio of 1:3 to 1:5, dissolving them and reacting them fully at 60 to 70°C for 5 to 10 hours, collecting the upper layer solution of dispersed ferric oleate, and allowing it to stand to obtain the ferric oleate precursor.

[0020] The metal salt is one or more of ferric chloride, ferric sulfate, and ferric nitrate;

[0021] The long-chain fatty acid alkali metal salts are one or more of sodium oleate, potassium oleate, sodium stearate, potassium stearate, sodium palmitate, and sodium laurate;

[0022] The mixed solution containing the extractant is a mixture of water, alcohol and extractant, wherein the alcohol is a volatile alcohol (methanol, ethanol, isopropanol, etc.), and the extractant is one or more of cyclohexane, n-hexane, heptane, toluene and petroleum ether, wherein the volume ratio of water to alcohol is 1:0.5 to 1:1.5, and the volume ratio of water to extractant is 1:1 to 1:2.

[0023] The beneficial effects of this invention are as follows:

[0024] (1) The oxygen-mediated strategy of the present invention for the electrocatalytic synthesis of ammonia and nitrate from N2 employs an electrocatalytic N2 activation system. Appropriately adsorbed oxygen species act as electron mediators—oxygen lone pairs of electrons are injected into the antibonded π orbitals of N2. Simultaneously, positively charged centers attract N2 lone pairs of electrons, resulting in dual polarization that weakens the N≡N bond and forms the key O–N2 intermediate. This mechanism breaks through the traditional approach of "strict oxygen removal to prevent competition," cleverly utilizing intrinsic or introduced oxygen in the reaction system to balance N2 adsorption activation with the suppression of excessive oxygen / hydrogen evolution competition.

[0025] (2) The present invention constructs a superlattice structure of carbon-coated Fe3O4 in an ordered array by combining water-soluble salt template agents such as NaCl with confined pyrolysis. It has both a two-dimensional sheet-like morphology and a carbon connection layer between particles, which not only improves conductivity, but also stabilizes the electronic state of Fe3O4 surface through confinement effect.

[0026] (3) The preparation route of the Fe3O4@C superlattice array nanomaterial of the present invention is simple, the composition is controllable, and it is easy to scale up. It avoids complex crystal plane regulation or the introduction of noble metals, and is suitable for large-scale preparation of nanocatalytic materials.

[0027] (4) The Fe3O4@C superlattice array nanomaterial of the present invention can be bidirectionally controlled in different gas phases and electrolytes: it can efficiently reduce ammonia production when air is used as the gas source (FE up to 33.12%), and oxidize nitrate to nitrate in a neutral sulfate medium when pure N2 is used as the gas source (FE up to 16.84%). This "one material, two uses" characteristic simplifies the design of catalyst systems for green nitrogen cycle technology.

[0028] (5) The synthesis of Fe3O4@C superlattice array nanomaterials of the present invention does not require precision equipment, the annealing temperature is moderate (400℃~500℃), and the template is easy to remove; the electrocatalysis is carried out in an aqueous phase system at room temperature and pressure, which can be directly coupled with renewable energy power, avoiding the high temperature and high pressure, precious metal dependence and long process problems of the Haber-Bosch and Ostwald methods, and has the potential to transition to the production of low-energy-consumption, low-carbon-emission nitrogen-containing chemicals. Attached Figure Description

[0029] Figure 1 Transmission electron microscopy image of the Fe3O4@C superlattice array nanomaterial prepared in Example 1 of the present invention.

[0030] Figure 2 EDS linear scan image of the superlattices between Fe3O4@C superlattice array nanomaterials prepared in Example 1 of the present invention.

[0031] Figure 3 The image shows the XRD pattern of the Fe3O4@C superlattice array nanomaterial prepared in Example 1 of this invention.

[0032] Figure 4 The image shows the Raman spectrum of the Fe3O4@C superlattice array nanomaterial prepared in Example 1 of this invention.

[0033] Figure 5 The figure shows the Faraday efficiency test results of the oxygen-mediated strategy for electrocatalytic N2 synthesis of ammonia in Example 1 of the present invention.

[0034] Figure 6 The LSV (linear sweep voltammetry) curves for the electrocatalytic synthesis of nitrate from N2 using the oxygen-mediated strategy in Example 1 of this invention are shown.

[0035] Figure 7 The graph shows the Faraday efficiency test results of the oxygen-mediated strategy for electrocatalytic N2 synthesis of nitrate in Example 1 of the present invention.

[0036] Figure 8 This is a DEMS spectrum of the electrocatalytic N2 synthesis of ammonia achieved by the oxygen-mediated strategy in Example 1 of the present invention.

[0037] Figure 9 This is a DEMS spectrum of the electrocatalytic synthesis of nitrate from N2 using the oxygen-mediated strategy in Example 1 of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0039] Example 1:

[0040] Part 1: Preparation of Fe3O4@C superlattice array nanomaterials.

[0041] Specifically, the steps include the following:

[0042] S0: Preparation of ferric oleate precursor: Add 10 mmol of ferric chloride and 30 mmol of sodium oleate to a mixed solution of 60 mL of water, 60 mL of ethanol and 120 mL of n-hexane. After reacting fully at 60~70℃ for 5 hours, collect the upper n-hexane organic solution of dispersed ferric oleate, let it stand for a period of time, and obtain the ferric oleate precursor after the n-hexane evaporates.

[0043] S1: Mix 1.2 g of ferric oleate precursor and 12 g of NaCl thoroughly, and then anneal at 400 °C for 2 h in an Ar atmosphere containing 10 vol% H2 (i.e., the volume fraction of H2 is 10%).

[0044] S2: The annealed product is thoroughly washed with deionized water to remove NaCl, and then freeze-dried (in a -55℃ cold trap under a vacuum of <10 Pa for 12 h) to obtain Fe3O4@C superlattice array nanomaterials.

[0045] Figure 1 Transmission electron micrograph of the Fe3O4@C superlattice array nanomaterial prepared in Example 1 of this invention. Figure 1 It can be seen that the nanoparticles form a two-dimensional sheet-like structure in an array.

[0046] Figure 2 EDS linear scan images of the superlattices between the superlattices of the Fe3O4@C superlattice array nanomaterial prepared in Example 1 of this invention. From... Figure 2 The EDS linear scan image between the two particles shows an enhancement of the carbon signal between the iron oxide (Fe3O4) particles, indicating that carbon fills the spaces between the iron oxide particles.

[0047] Figure 3 The image shows the XRD pattern of the Fe3O4@C superlattice array nanomaterial prepared in Example 1 of this invention. Figure 3 The XRD pattern matches the standard card PDF#75-0033 Fe3O4, indicating that Fe3O4 was synthesized.

[0048] Figure 4 The image shows the Raman spectrum of the Fe3O4@C superlattice array nanomaterial prepared in Example 1 of this invention. A distinct D / G peak characteristic signal, belonging to carbon, can be observed. Based on the above test results, the synthesized material is a carbon-coated Fe3O4 superlattice array nanomaterial.

[0049] Part 2: Oxygen-mediated strategy for electrocatalytic N2 activation to synthesize ammonia.

[0050] (1) Accurately weigh 5 mg of Fe3O4@C superlattice array nanomaterials and disperse them in 950 μL isopropanol + 50 μL Nafion (perfluorosulfonic acid resin) binder, and sonicate for 30 min to form a uniform catalyst ink. Then add 100 μL of catalyst ink to 1 It was placed on a 1 cm layer of hydrophobically treated carbon paper and dried to serve as the working electrode for the electrocatalytic reaction.

[0051] (2) The electrocatalytic N2 activation for ammonia synthesis was tested in an H-type reaction cell with a three-electrode system. The H-type reaction cell was separated by a cleaned Nafion 117 proton exchange membrane (DuPont, reinforced perfluorosulfonic acid membrane). The carbon paper with Fe3O4@C superlattice array nanomaterials prepared above was used as the working electrode, the Pt sheet electrode was used as the counter electrode, and Ag / AgCl filled with saturated KCl was used as the reference electrode. 0.1 M HCl was used as the electrolyte, and electrolysis was carried out for a certain period of time at different potentials. High-purity air was continuously bubbled in as the reaction gas during the reaction.

[0052] Figure 5 This is a graph showing the Faraday efficiency test results for the electrocatalytic N2 synthesis of ammonia using the oxygen-mediated strategy in Example 1 of the present invention. From... Figure 5 As can be seen, the maximum ammonia synthesis efficiency of this embodiment can reach 33.12%.

[0053] Both the reduction and oxidation of N2 require oxygen to combine with N2 molecules to form... The intermediates were further investigated using electrochemical in-situ mass spectrometry (DEMS) to detect small molecule intermediates in the electrocatalytic synthesis of ammonia and nitrate, thereby verifying the oxygen-mediated reaction mechanism of ammonia and nitrate synthesis. Figure 8 This is a DEMS spectrum of the electrocatalytic N2 synthesis of ammonia using the oxygen-mediated strategy in Example 1 of this invention. Figure 8 As can be seen from the data, during the reduction process, as LSV proceeds, the O2 signal weakens while the signals of intermediates such as N2O and NH3 and products strengthen. This indicates that in the process of direct electrocatalytic air synthesis of ammonia, oxygen mediates the linkage of N2, which is then gradually reduced by hydrogenation to synthesize ammonia.

[0054] The principle of oxygen-mediated strategy for electrocatalytic N2 activation to synthesize ammonia is as follows:

[0055] (1) ( (representing the active site), oxygen participates in the reaction first and is adsorbed at the active site;

[0056] (2) The adsorbed oxygen dissociates with hydrogen, producing ;

[0057] (3) , Hydrogenation dissociates to produce Used for N2 adsorption;

[0058] (4) N2 molecules adsorb onto oxygen atoms;

[0059] (5) oxygen-mediated adsorption , hydrogenation activation;

[0060] (6) , Hydrogenation ;

[0061] (7) , Hydrogenation, the first Shedding;

[0062] (8) , Hydrogenation ;

[0063] (9) , Hydrogenation ;

[0064] (10) , Hydrogenation, synthesis .

[0065] Steps (1) to (3) involve the adsorption and activation of oxygen during the catalytic reaction. Steps (4) to (10) involve the adsorption of nitrogen and the sequential hydrogenation of the two adsorbed nitrogen atoms to synthesize ammonia.

[0066] Part 3: Oxygen-mediated strategy for electrocatalytic N2 oxidation to nitrate synthesis.

[0067] The electrocatalytic N2 activation synthesis of nitrate was also performed in an H-type reaction cell with a three-electrode system. The rest was the same as in Part II, except that 0.1 M K2SO4 was used as the electrolyte, different potentials were selected for electrolysis for a certain time, and high-purity N2 was continuously bubbled in as the reaction gas.

[0068] Figure 6 The LSV curve for the electrocatalytic synthesis of nitrate from N2 using the oxygen-mediated strategy in Example 1 of this invention is shown. Figure 6 As can be seen, the current density is greater under N2 saturation than under Ar saturation, indicating that N2 participates in the catalytic reaction.

[0069] Figure 7The graph shows the Faraday efficiency test results of the oxygen-mediated strategy for electrocatalytic N2 synthesis of nitrate in Example 1 of the present invention. Figure 7 The results show that the Fe3O4@C superlattice array nanomaterial can achieve a maximum nitrate synthesis Faraday efficiency of 16.84%.

[0070] Figure 9 This is a DEMS spectrum of the electrocatalytic synthesis of nitrate from N2 using the oxygen-mediated strategy in Example 1 of this invention. With the appearance of the LSV signal, the signals of intermediates such as O2, N2O, NO, and NO2 gradually increase, indicating that oxygen-mediated synthesis of nitrate from N2 can be achieved during the eNOR process.

[0071] The principle of the oxygen-mediated strategy for electrocatalytic N2 activation to synthesize nitrate is as follows:

[0072] (1) ( (Representing the active site), hydrolysis, producing Intermediate;

[0073] (2) , Dissociation ;

[0074] (3) , Participate in the reaction, adsorbed on superior;

[0075] (4) The OH groups generated by water dissociation are adsorbed on N2;

[0076] (5) The OH groups generated by water dissociation are adsorbed in ;

[0077] (6) , Dissociate H + ;

[0078] (7) The OH groups generated by water dissociation are adsorbed in ;

[0079] (8) The first Dissociation;

[0080] (9) The OH groups generated by water dissociation are adsorbed in ;

[0081] (10) ; Dissociate H + ;

[0082] (11) The OH groups generated by water dissociation are adsorbed in ;

[0083] (12) Ultimately produced .

[0084] In this invention, on the surface of Fe3O4@C superlattice array nanomaterials, moderately adsorbed oxygen species may act as "electron mediators" to regulate the adsorption of N2, and the lone pair electrons of oxygen can be injected into the antibonding of N2. The Fe3O4@C superlattice array nanomaterials of this invention can attract lone pairs of electrons from N2, polarizing the N2 molecule through a dual action, inducing a configurational change in N2 adsorption, and thus improving N2 activation efficiency. To achieve this, a suitable amount of oxygen can be introduced during the electrocatalytic N2 reduction process, utilizing appropriate adsorbed oxygen species as N2 adsorption sites. Conversely, during the electrocatalytic N2 oxidation process, spontaneously generated oxygen species during the OER (oxygen evolution reaction) can be used as N2 adsorption sites. The Fe3O4@C superlattice array nanomaterials of this invention can hinder the excessive reaction of adsorbed oxygen species, maintaining their synthesized electronic state structure to participate in the N2 activation reaction. This "oxygen-mediated N2 activation" mechanism overcomes the efficiency bottleneck of existing eNRR (electrochemical nitrogen reduction reaction) and eNOR (electrochemical nitrogen oxidation reaction).

[0085] Example 2:

[0086] Part 1: Preparation of Fe3O4@C superlattice array nanomaterials. This includes the following steps:

[0087] S0: Add 5 mmol of ferric sulfate and 25 mmol of sodium stearate to a mixed solution of 60 mL of water, 30 mL of ethanol and 60 mL of cyclohexane. After reacting at 60-70°C for 5 hours, collect the upper cyclohexane organic solution of the dispersed ferric oleate, let it stand for a period of time, and obtain the ferric oleate precursor after the cyclohexane evaporates.

[0088] S1: Mix 1.2 g of ferric oleate precursor and 24 g of KCl thoroughly, and then anneal at 500 °C for 1 h in an Ar atmosphere containing 5 vol% H2.

[0089] S2: The annealed product is thoroughly washed with deionized water to remove KCl, and then freeze-dried (in a -60℃ cold trap under a vacuum of <10 Pa for 20 h) to obtain Fe3O4@C superlattice array nanomaterials.

[0090] Part 2: Oxygen-mediated strategy for electrocatalytic N2 activation to synthesize ammonia.

[0091] (1) Accurately weigh 5 mg of the Fe3O4@C superlattice array nanomaterial prepared in Part 1 and disperse it in 950 μL isopropanol + 50 μL Nafion (perfluorosulfonic acid resin) binder, and sonicate for 30 min to form a uniform catalyst ink. Then add 100 μL of catalyst ink to 1 It was placed on a 1 cm layer of hydrophobically treated carbon paper and dried to serve as the working electrode for the electrocatalytic reaction.

[0092] (2) The electrocatalytic N2 activation synthesis of ammonia was tested in an H-type reaction cell with a three-electrode system. The H-type reaction cell was separated by a cleaned Nafion 117 proton exchange membrane (DuPont, reinforced perfluorosulfonic acid membrane). The carbon paper with Fe3O4@C superlattice array nanomaterials prepared above was used as the working electrode, the Pt sheet electrode was used as the counter electrode, and Ag / AgCl filled with saturated KCl was used as the reference electrode. Electrolysis was carried out using 0.05 M H2SO4 as the electrolyte, and high-purity air was continuously bubbled in as the reaction gas during the reaction.

[0093] Tests have shown that this embodiment can achieve a maximum ammonia synthesis Faraday efficiency of 28.64%.

[0094] Example 3:

[0095] Part 1: Preparation of Fe3O4@C superlattice array nanomaterials.

[0096] Specifically, the steps include the following:

[0097] S0: Add 5 mmol of ferric chloride and 20 mmol of sodium oleate to a mixed solution of 60 mL of water, 90 mL of methanol, and 100 mL of toluene. After reacting at 60-70°C for 10 hours, collect the upper layer of toluene organic solution that disperses ferric oleate. Let it stand for a period of time until the toluene evaporates to obtain the ferric oleate precursor.

[0098] S1: Mix 2 g of ferric oleate and 30 g of NaCl thoroughly, and then anneal at 400 °C for 3 h in an atmosphere of 8 vol% H2 / Ar.

[0099] S2: Finally, wash thoroughly with deionized water to remove NaCl, and freeze-dry (freeze-dry for 10 h in a -70℃ cold trap under vacuum <10Pa) to obtain Fe3O4@C superlattice array nanomaterials.

[0100] Part 2: Oxygen-mediated strategy for electrocatalytic N2 oxidation to nitrate synthesis.

[0101] (1) Accurately weigh 5 mg of the Fe3O4@C superlattice array nanomaterials prepared in Part 1 and disperse them in 950 μL isopropanol + 50 μL Nafion (perfluorosulfonic acid resin) binder, and sonicate for 30 min to form a uniform catalyst ink. Then add 100 μL of catalyst ink to 1 It was placed on a 1 cm layer of hydrophobically treated carbon paper and dried to serve as the working electrode for the electrocatalytic reaction.

[0102] (2) The electrocatalytic N2 oxidation to nitrate synthesis test was carried out in an H-type reaction cell with a three-electrode system. The H-type reaction cell was separated by a cleaned Nafion 117 proton exchange membrane (DuPont, reinforced perfluorosulfonic acid membrane). The carbon paper with Fe3O4@C superlattice array nanomaterials prepared above was used as the working electrode, the Pt sheet electrode was used as the counter electrode, and Ag / AgCl filled with saturated KCl was used as the reference electrode. Electrolysis was carried out with 0.01 M Na2SO4 solution as the electrolyte, and N2 was continuously bubbled in as the reaction gas during the reaction.

[0103] Tests showed that this embodiment can achieve a maximum nitrate synthesis Faraday efficiency of 15.2%.

[0104] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention. The above embodiments are provided only for the purpose of describing the present invention and are not intended to limit the present invention. Parts not described in detail in this specification are well-known in the art and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. All equivalent substitutions and modifications made without departing from the spirit and principle of the present invention should be covered within the scope of the present invention.

Claims

1. A method for electrocatalytic synthesis of ammonia and nitrate from N2 using an oxygen-mediated strategy, characterized in that, A conductive substrate coated with Fe3O4@C superlattice array nanomaterial is used as the working electrode; wherein, the Fe3O4@C superlattice array nanomaterial is a superlattice structure in which carbon-coated Fe3O4 forms an ordered array, and Fe3O4@C forms a two-dimensional sheet structure in an array form, with C filling between Fe3O4 nanoparticles, and C also having a connecting function while coating Fe3O4 nanoparticles; In the method of achieving electrocatalytic N2 synthesis of ammonia using an oxygen-mediated strategy, high-purity air is used as the reaction gas, and the electrolyte is 0.01~0.2 M HCl or H2SO4 solution; In the method for electrocatalytic synthesis of nitrate from N2 using an oxygen-mediated strategy, N2 is used as the reactant gas, and the electrolyte is a 0.0~0.5 M K2SO4 or Na2SO4 solution.

2. The method for electrocatalytic synthesis of ammonia and nitrate from N2 using the oxygen-mediated strategy according to claim 1, characterized in that, The oxygen-mediated strategy for electrocatalytic N2 synthesis of ammonia and nitrate is carried out in an H-type reaction cell with a three-electrode system.

3. The method for electrocatalytic synthesis of ammonia and nitrate from N2 using the oxygen-mediated strategy according to claim 1, characterized in that, The loading of Fe3O4@C superlattice array nanomaterials on a conductive substrate was 0.5 mg cm⁻¹. -2 .

4. The method for electrocatalytic synthesis of ammonia and nitrate from N2 using the oxygen-mediated strategy according to claim 1, characterized in that, The conductive substrate coated with Fe3O4@C superlattice array nanomaterials is specifically formed by dispersing Fe3O4@C superlattice array nanomaterials and binders in a solvent to form catalyst ink, and then coating the catalyst ink onto the conductive substrate. After drying, it serves as the working electrode for electrocatalytic reactions. The binder is Nafion D520 perfluorosulfonic acid resin solution, and the solvent is isopropanol solution.

5. The method for electrocatalytic synthesis of ammonia and nitrate from N2 using an oxygen-mediated strategy according to any one of claims 1 to 4, characterized in that, The preparation method of Fe3O4@C superlattice array nanomaterials includes the following steps: S1: The ferric oleate precursor and the template agent are thoroughly mixed at a mass ratio of 1:10 to 1:20, and then annealed in an inert atmosphere containing hydrogen at a temperature of 400℃ to 500℃ for 1 to 3 hours. S2: The annealed product is washed and then freeze-dried to obtain Fe3O4@C superlattice array nanomaterials. The freeze-drying time is 10-20 h.

6. The method for electrocatalytic N2 synthesis of ammonia and nitrate using the oxygen-mediated strategy according to claim 5, characterized in that, The volume fraction of hydrogen in the inert atmosphere containing hydrogen is 5-10%.

7. The method for electrocatalytic N2 synthesis of ammonia and nitrate using the oxygen-mediated strategy according to claim 5, characterized in that, The template agent is one or more of sodium chloride, potassium chloride, and potassium sulfate.

8. The method for electrocatalytic N2 synthesis of ammonia and nitrate using the oxygen-mediated strategy according to claim 5, characterized in that, The ferric oleate precursor is prepared by the following steps: adding a metal salt and a long-chain fatty acid alkali metal salt to a mixed solution containing an extractant at a molar ratio of 1:3 to 1:5, dissolving them and reacting them fully at 60 to 70°C for 5 to 10 hours, collecting the upper layer solution of dispersed ferric oleate, and allowing it to stand to obtain the ferric oleate precursor. The metal salt is one or more of ferric chloride, ferric sulfate, and ferric nitrate; The long-chain fatty acid alkali metal salts are one or more of sodium oleate, potassium oleate, sodium stearate, potassium stearate, sodium palmitate, and sodium laurate; The mixed solution containing the extractant is a mixture of water, alcohol and extractant, wherein the alcohol is a volatile alcohol, and the extractant is one or more of cyclohexane, n-hexane, heptane, toluene and petroleum ether, wherein the volume ratio of water to alcohol is 1:0.5 to 1:1.5, and the volume ratio of water to extractant is 1:1 to 1:2.

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