A bimetallic metal-organic framework catalyst, a preparation method thereof and application thereof in active oxygen assisted membrane-free electrolytic ammonia oxidation for preparing nitrite

Abstract

The application belongs to the technical field of electrocatalysis, and discloses a bimetallic fluorinated metal organic framework catalyst, a preparation method thereof and application of the catalyst in active oxygen assisted membrane-free electrolytic ammonia oxidation for preparing nitrite, wherein the catalyst is prepared by self-assembly of Cu 2+ , Ni 2+ and a tetrakisfluorophthalic acid ligand through a solvothermal method, and there is a directional electron transfer effect between Cu and Ni. The application utilizes the Cu / Ni bimetallic electron synergistic effect to precisely regulate the d-band center of the catalyst, and a membrane-free electrolysis device is matched to save an expensive proton exchange membrane. The application provides a new efficient and feasible path for green, economical and scaled electrocatalytic synthesis of nitrite.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, specifically to a bimetallic fluorinated metal-organic framework catalyst, its preparation method, and its application in reactive oxygen species-assisted membrane-free electrolytic oxidation of ammonia to nitrite. Background Technology

[0002] Nitrites are a crucial class of inorganic chemical raw materials with wide applications in food processing, dye preparation, metallurgy, and pharmaceutical synthesis. Currently, large-scale industrial production of nitrites mainly relies on the traditional thermocatalytic ammonia oxidation process. This method typically requires a high-temperature environment above 800°C, where noble metal catalysts such as platinum-rhodium alloys are used to catalytically oxidize ammonia with air to produce nitrogen oxides, which are then absorbed and converted by alkaline solution to obtain nitrites.

[0003] Although the process is relatively mature, it still has significant drawbacks: high energy consumption, stringent reaction conditions, reliance on scarce precious metal catalysts, and the generation of environmental pollutants such as nitrogen oxides during the reaction. Furthermore, the complex process route and high equipment investment further restrict its sustainable development. With the advancement of green chemistry concepts and electrosynthesis technologies, electrocatalytic ammonia oxidation has opened up a new, mild, and clean pathway for the synthesis of nitrite. This technology can directly convert ammonia into high-value-added nitrite under ambient temperature and pressure conditions using electrical energy, theoretically possessing outstanding advantages such as high efficiency, strong controllability, and environmental friendliness. In recent years, researchers have conducted extensive research on the development of highly efficient AOR electrocatalysts (such as metal oxides and hydroxyl oxides) and their applications in electrolytic cells.

[0004] Current electrocatalytic ammonia oxidation technology faces numerous bottlenecks: high overpotential leading to high energy consumption, poor selectivity for target products, insufficient long-term catalyst stability, strong dependence on expensive and easily degradable proton exchange membranes, and a lack of efficient reactive oxygen species utilization mechanisms. These problems directly result in insufficient economic viability and feasibility of the nitrite electrocatalytic synthesis route, making it difficult to compete with existing thermocatalytic processes. Currently, no effective solutions have been proposed to address these technical issues. Summary of the Invention

[0005] The purpose of this invention is to provide a bimetallic fluorinated metal-organic framework catalyst, its preparation method, and its application in active oxygen-assisted membrane-free electrolytic ammonia oxidation to nitrite, so as to solve the problems of high energy consumption, poor selectivity, insufficient stability, dependence on expensive proton exchange membranes, and low active oxygen utilization efficiency of existing ammonia oxidation to nitrite technologies mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A bimetallic fluorinated metal-organic framework catalyst, characterized in that its general chemical formula is Cu x Ni-F-MOF, where x = 1, 2 or 3; The catalyst is made of Cu 2+ Ni 2+ It is formed by solvothermal self-assembly with tetrafluoroterephthalic acid ligand, exhibiting a nanosheet or nanoparticle morphology, with its d-band center located at -3.19 to -3.25 eV, and an electron transfer from Ni to Cu exists between Cu and Ni.

[0007] Furthermore, x=2, i.e., Cu2Ni-F-MOF.

[0008] A method for preparing a bimetallic fluorinated metal-organic framework catalyst specifically includes the following steps: S1, First, Cu(NO3)2·3 O (x mmol) and Ni(NO3)2·6 O (1 mmol) was dissolved in 10 mL of DMF; S2. Next, dissolve tetrafluoroterephthalic acid (87.5 mg) and hexamethylenetetramine (125 mg) in 10 mL of DMF; S3. Then mix the solutions obtained in step S1 and step S2 and stir for 30 min. S4. Transfer the mixture to a hydrothermal reactor and keep it at 120℃ for 48 hours. S5. Finally, centrifuge to collect the precipitate, wash alternately with DMF and deionized water, and dry at 60℃ for 12 h to obtain Cu. x Ni-F-MOF.

[0009] A method for the electrocatalytic oxidation of ammonia to nitrite based on a bimetallic fluorinated metal-organic framework catalyst, wherein the catalyst serves as the working electrode, and a constant potential of 1.5–1.8 V vs RHE is applied in an alkaline electrolyte containing 0.5 mol L⁻¹ –1 KOH, 50 mmol / L –1 N OH and 10 mmol L –1 Furthermore, the constant potential is 1.6 V vs RHE.

[0010] Furthermore, the reaction is carried out at room temperature for 1–24 hours, with an ammonia conversion rate ≥95% and a nitrite Faraday selectivity ≥90%.

[0011] Furthermore, the aforementioned ·OH radicals are generated at the Ni sites of the catalyst upon activation. These ·OH radicals react with *NH4+ adsorbed on the catalyst surface. x Species directly couple, achieving the formation of low-barrier nitrogen-oxygen bonds.

[0012] A membrane-free electrolysis device includes an anode chamber, a cathode chamber, and an electrode assembly disposed between them. The anode and cathode chambers are not separated by a proton exchange membrane or ion exchange membrane, and the distance between the anode and cathode is 1–3 cm. Furthermore, the working electrode is a composite electrode formed by coating a catalyst onto a conductive substrate, wherein the conductive substrate is selected from carbon paper, nickel foam, or titanium mesh.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The reactive oxygen species-assisted mechanism provided by the present invention reduces the onset potential of AOR from approximately 1.48 V in the traditional alkaline system. RHE Reduced to approximately 1.30 V RHE The overpotential decreased by 180 mV. This is because H₂O₂, under the action of a catalyst, can be activated at a low potential to generate highly reactive ·OH radicals. These radicals directly participate in the breaking of the NH bond and the nitrogen-oxygen coupling process, bypassing the high energy barrier of generating reactive oxygen species at a high potential in the traditional pathway. This allows the ammonia oxidation reaction to be started and carried out efficiently at a milder potential, directly reducing energy consumption.

[0014] At a constant potential of 1.6 V for 10 hours RHE In the test, the ammonia conversion rate reached 98.8%, and the residual ammonia in the electrolyte after the reaction was less than 0.5 mmol / L. –1 The extremely high ammonia conversion rate indicates that the method of this invention can almost completely convert the raw ammonia into the product, greatly improving atom economy and raw material utilization, and reducing the burden of subsequent separation and purification and waste treatment costs. Ni-F-MOF catalysts exhibited superior performance compared to contrasting catalysts (Cu-F-MOF, The AOR activity of Ni-F-MOF and CuNi-F-MOF was measured, with an electrochemical active area (ECSA) value of 6.39 mF cm⁻¹. –2 The efficiency is higher than other catalysts. The electronic synergistic effect between Cu and Ni optimizes the d-band center and enhances the adsorption capacity for reaction intermediates. At the same time, the in-situ reconstruction of the catalyst during the reaction forms a stable high-valence Ni active phase, thus ensuring that it maintains high activity and structural stability during long-term reactions. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is an embodiment of the present invention, showing the preparation method of a bimetallic fluorinated metal-organic framework catalyst, and SEM images of (a)-(b) Cu-F-MOF, (c)-(d) Cu3Ni-F-MOF, (e)-(f) Cu2Ni-F-MOF and (g)-(h) CuNi-F-MOF in active oxygen-assisted membrane-free electrolytic ammonia oxidation to nitrite. Figure 2 This invention relates to a bimetallic fluorinated metal-organic framework catalyst, its preparation method, and its application in the active oxygen-assisted membrane-free electrolytic oxidation of ammonia to nitrite: (a) high-resolution XPS spectra of Cu 2p and (b) Ni 2p; (c) XPS valence band spectrum of the catalyst. Figure 3 This invention relates to a bimetallic fluorinated metal-organic framework catalyst, its preparation method, and its application in the reactive oxygen species-assisted membrane-free electrolytic oxidation of ammonia to nitrite: (a) nitrite yield and selectivity of Cu2Ni-F-MOF at different voltages; (b) ammonia concentration and ammonia conversion rate; (c) UV-Vis spectra of the Cu2Ni-F-MOF electrolyte nitrate system at different voltages; (d) nitrate yield and selectivity of Cu2Ni-F-MOF at different voltages; and (e) 1.6 V. RHE Graphs showing nitrite yield, selectivity, and (f) ammonia concentration and ammonia conversion for the catalyst; Figure 4 This invention relates to a bimetallic fluorinated metal-organic framework catalyst, its preparation method, and its application in the active oxygen-assisted membrane-free electrolytic oxidation of ammonia to nitrite: (a) ammonia concentration and conversion rate within 0-10 h; (b) yield and selectivity of AOR to nitrite within 0-10 h; (c) CV curves of Cu-F-MOF, (d) Cu3Ni-F-MOF, (e) Cu2Ni-F-MOF, and (f) CuNi-F-MOF; and (g) scan rate and corresponding Cdl value plots of the catalyst. Figure 5 This is a CV curve of Cu2Ni-F-MOF in different electrolytes, based on a bimetallic fluorinated metal-organic framework catalyst according to an embodiment of the present invention, its preparation method, and its application in active oxygen-assisted membrane-free electrolytic ammonia oxidation to nitrite. Figure 6 The images show in-situ Raman spectra of a Cu2Ni-F-MOF electrode in electrolytes containing H2O2 and (b) without H2O2, according to an embodiment of the present invention, a bimetallic fluorinated metal-organic framework catalyst, its preparation method, and its application in active oxygen-assisted membrane-free electrolytic oxidation of ammonia to nitrite. Figure 7 This is an in-situ EPR spectrum of a Cu2Ni-F-MOF electrode at different potentials in (a) a system without H2O2 and (b) a system with H2O2, according to an embodiment of the present invention, a bimetallic fluorinated metal-organic framework catalyst, its preparation method and its application in active oxygen-assisted membrane-free electrolytic ammonia oxidation to nitrite. Detailed Implementation

[0017] The invention will now be further described with reference to the accompanying drawings and specific embodiments: Example 1 Please see Figures 1-7 As shown: A catalyst based on a bimetallic fluorinated metal-organic framework, characterized in that its general chemical formula is: Ni-F-MOF, where x = 1, 2 or 3; The catalyst is made of Cu 2+ Ni 2+ It is formed by solvothermal self-assembly with tetrafluoroterephthalic acid ligand, exhibiting a nanosheet or nanoparticle morphology, with its d-band center located at -3.19 to -3.25 eV, and an electron transfer from Ni to Cu exists between Cu and Ni.

[0018] Preparation of Ni-F-MOF (x = 1, 2, 3) catalysts: Cu(NO3)2·3H2O (x mmol) and Ni(NO3)2·6H2O (1 mmol) were dissolved in 10 mL of DMF. Similarly, tetrafluoroterephthalic acid (87.5 mg) and C6H2O were dissolved in 1 mL of DMF. 12 N4 (125 mg) was dissolved in 10 mL of DMF. The two solutions were then mixed and stirred for 30 min. Next, the mixture was sealed in a hydrothermal reactor and heated to 120 °C for 48 h. A brown precipitate was collected by centrifugation, washed repeatedly with alternating amounts of DMF and H2O, and dried at 60 °C for 12 h to obtain the CuNi-F-MOF catalyst.

[0019] Preparation of Cu-F-MOF catalyst: Cu(NO3)2·3H2O (4 mmol) was dissolved in 10 mL of DMF. Similarly, tetrafluoroterephthalic acid (87.5 mg) and C6H12N4 (125 mg) were dissolved in 10 mL of DMF. The two solutions were then mixed and stirred for 30 min. Next, the mixture was sealed in a hydrothermal reactor and heated to 130 °C for 48 h. The resulting brown precipitate was collected by centrifugation, washed repeatedly with DMF and H2O alternately, and dried at 60 °C for 12 h to obtain the Cu-F-MOF catalyst.

[0020] Example 2 Based on Example 1, a method for preparing a bimetallic fluorinated metal-organic framework catalyst specifically includes the following steps: S1, First, Cu(NO3)2·3 O (x mmol) and Ni(NO3)2·6 O (1 mmol) was dissolved in 10 mL of DMF; S2. Next, dissolve tetrafluoroterephthalic acid (87.5 mg) and hexamethylenetetramine (125 mg) in 10 mL of DMF; S3. Then mix the solutions obtained in step S1 and step S2 and stir for 30 min. S4. Transfer the mixture to a hydrothermal reactor and keep it at 120℃ for 48 hours. S5. Finally, centrifuge to collect the precipitate, wash alternately with DMF and deionized water, and dry at 60℃ for 12 h to obtain Cu. x Ni-F-MOF.

[0021] Example 3 A method for the electrocatalytic oxidation of ammonia to nitrite based on a bimetallic fluorinated metal-organic framework catalyst is disclosed. First, the catalyst is used as the working electrode, and a constant potential of 1.5–1.8 V vs RHE is applied in an alkaline electrolyte containing 0.5 mol L⁻¹ –1 KOH, 50 mmol / L –1 NH4OH and 10 mmol L –1 H2O2, with a constant potential of 1.6 V vs RHE; The reaction was then carried out at room temperature for 1–24 hours, with an ammonia conversion rate ≥95% and a nitrite Faraday selectivity ≥90%. ·OH radicals are generated at the Ni sites of the catalyst upon activation. These ·OH radicals react with *N adsorbed on the catalyst surface. Species directly couple, achieving the formation of low-barrier nitrogen-oxygen bonds.

[0022] A membrane-free electrolysis device includes an anode chamber, a cathode chamber, and an electrode assembly placed between the two. There is no proton exchange membrane or ion exchange membrane separating the anode chamber and the cathode chamber. The distance between the anode and cathode is 1–3 cm. The working electrode is a composite electrode formed by coating a catalyst onto a conductive substrate. The conductive substrate is selected from carbon paper, nickel foam, or titanium mesh.

[0023] Example 4 Based on Example 3, the prepared catalyst has a well-defined crystal structure and nano-morphology (such as nanosheets or nanoparticles). Its core feature lies in the electronic interaction between Cu and Ni, which modulates the d-band center of the catalyst (e.g., the d-band center of Cu2Ni-F-MOF is -3.19 eV), placing it in an optimal position for the intermediate of ammonia oxidation reaction (e.g., *NH4+). x The position of the adsorption strength of *OOH is determined. This regulation of electronic structure is fundamental to achieving efficient catalysis. Characterization results show that the catalyst contains uniformly distributed C, O, Cu, Ni, N, and F elements, and there is electron transfer between Cu and Ni (from Ni to Cu), forming an electronic environment conducive to catalysis.

[0024] Reaction system construction (hydrogen peroxide as oxidation mediator): The key to this invention lies in the introduction of a reactive oxygen species-assisted mechanism, wherein the ammonia oxidation reaction is carried out in an alkaline electrolyte, preferably 0.5 mol / L. –1 A KOH solution is used, and an ammonia source is added to the electrolyte, preferably at a concentration of 50 mmol / L. –1 NH4OH. A certain concentration of H2O2 (e.g., 10 mmol L) is added to the above electrolyte. –1 H₂O₂ acts as an oxidation mediator. Under the action of a catalyst (especially at Ni sites), H₂O₂ can be activated at a lower potential to generate highly active ·OH radicals (hydroxyl radicals).

[0025] Innovative reaction mechanism (direct coupling mechanism between ·OH and *NHx): Active oxygen generates H2O2, which activates the catalyst surface: H2O2 + Ni(II) → Ni(III) + •OH + OH − .

[0026] In-situ reconstruction: Under the combined action of an electric field and H2O2, the catalyst precursor undergoes in-situ reconstruction to form a Cu-NiOOH active phase containing high-valence Ni(III).

[0027] The ammonia oxidation pathway: The generated ·OH radicals act as a reactive oxygen source, directly coupling with NHx* species adsorbed on the catalyst surface. This significantly lowers the energy barrier for ammonia dehydrogenation and nitrogen-oxygen coupling steps, avoiding the high-potential dependence of the traditional pathway. This mechanism was confirmed by in-situ spectroscopic methods.

[0028] Reaction conditions: Thanks to the reactive oxygen species-assisted mechanism, the reaction initiation potential is reduced from approximately 1.48 V. RHE Reduced to approximately 1.30V RHE The preferred applied potential range is 1.5 V. RHE Up to 1.8 V RHE At 1.6 V RHE Under these conditions, the selectivity for nitrite can reach 93.4%, with a yield of 11.56 mmol / L. –1 h –1 cm –2 The reaction takes place at room temperature. It can operate stably for extended periods; for example, a 10-hour constant potential test showed that the ammonia conversion rate could reach 98.8%.

[0029] Through the above-described solution of the present invention, the present invention... (1) Significantly reduces reaction overpotential, resulting in outstanding energy-saving effect. The reactive oxygen species-assisted mechanism provided by this invention lowers the onset potential of AOR from approximately 1.48V in the traditional alkaline system. RHE Reduced to approximately 1.30 V RHE The overpotential decreased by 180 mV. This is because H₂O₂, under the action of a catalyst, can be activated at a low potential to generate highly reactive ·OH radicals. These radicals directly participate in the breaking of the NH bond and the nitrogen-oxygen coupling process, bypassing the high energy barrier of generating reactive oxygen species at a high potential in the traditional pathway. This allows the ammonia oxidation reaction to be started and carried out efficiently at a milder potential, directly reducing energy consumption.

[0030] (2) Significantly increases reaction rate and current density In the three-electrode system, at 2.0 V RHE Under these conditions, the current density of AOR decreases from 140.3 mA cm⁻¹ in the alkaline system. –2 Increased to 201.5 mA cm –2 The current density increased by 43.0%. This significant increase in current density directly reflects the accelerated reaction rate. This is attributed to the optimized electronic structure of the Cu2Ni-F-MOF catalyst, which provides more active sites, and the reactive oxygen species-assisted mechanism, which greatly accelerates the reaction kinetics.

[0031] (3) Achieve highly selective nitrite synthesis and effectively suppress side reactions. At 1.6 V RHEAt the optimized potential, the selectivity for nitrite reached 93.4%. Simultaneously, the yield of ammonia to nitrite conversion reached 11.56 mmol L⁻¹. –1 h –1 cm –2 The high selectivity indicates that the present invention successfully guides the reaction pathway toward the target product. This is because the reactive oxygen species-assisted pathway dominates at a lower potential, effectively suppressing the oxygen evolution reaction (OER) and the side reaction pathway of excessive oxidation to nitrate that are prone to occur at higher potentials. This is confirmed by the low nitrate yield in the product analysis.

[0032] (4) Achieve near-complete ammonia conversion and high raw material utilization rate. At a constant potential of 1.6 V for 10 hours RHE In the test, the ammonia conversion rate reached 98.8%, and the residual ammonia in the electrolyte after the reaction was less than 0.5 mmol / L. –1 The extremely high ammonia conversion rate indicates that the method of the present invention can almost completely convert the raw material ammonia into the product, which greatly improves the atom economy and raw material utilization rate, and reduces the burden of subsequent separation and purification and waste treatment costs.

[0033] (5) The catalyst exhibits excellent catalytic activity and stability. The Cu2Ni-F-MOF catalyst exhibited superior AOR activity compared to comparative catalysts (Cu-F-MOF, Cu3Ni-F-MOF, CuNi-F-MOF), with an electrochemical active area (ECSA) value of 6.39 mF cm⁻¹. –2 The efficiency is higher than that of other catalysts. The electronic synergistic effect between Cu and Ni optimizes the d-band center and enhances the adsorption capacity for reaction intermediates. At the same time, the in-situ reconstruction of the catalyst during the reaction forms a stable high-valence Ni active phase, thus ensuring that it maintains high activity and structural stability during long-term reactions.

[0034] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "screw connection," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0035] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0037] 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 catalyst based on a bimetallic fluorinated metal-organic framework, characterized in that, Its general chemical formula is Ni-F-MOF, where x = 1, 2 or 3; The catalyst is made of Cu 2+ N 2+ It is formed by solvothermal self-assembly with tetrafluoroterephthalic acid ligand, exhibiting a nanosheet or nanoparticle morphology, with its d-band center located at -3.19 to -3.25 eV, and an electron transfer from Ni to Cu exists between Cu and Ni.

2. The catalyst based on a bimetallic fluorinated metal-organic framework according to claim 1, characterized in that, The x=2 refers to Cu2Ni-F-MOF.

3. A method for preparing a bimetallic fluorinated metal-organic framework catalyst as described in claim 1, characterized in that, Specifically, the following steps are included: S1. First, dissolve Cu(NO3)2·3H2O (x mmol) and Ni(NO3)2·6H2O (1 mmol) in 10 mL of DMF; S2. Next, dissolve tetrafluoroterephthalic acid (87.5 mg) and hexamethylenetetramine (125 mg) in 10 mL of DMF; S3. Then mix the solutions obtained in step S1 and step S2 and stir for 30 min. S4. Transfer the mixture to a hydrothermal reactor and keep it at 120℃ for 48 hours. S5. Finally, centrifuge to collect the precipitate, wash alternately with DMF and deionized water, and dry at 60℃ for 12 h to obtain... Ni-F-MOF.

4. A method for electrocatalytic ammonia oxidation to nitrite based on a bimetallic fluorinated metal-organic framework catalyst as described in claim 1, characterized in that, The catalyst serves as the working electrode, and an voltage of 1.5–1.8 V is applied in the alkaline electrolyte. RHE The electrolyte contains 0.5 mol L⁻¹ and is at a constant potential. –1 KOH, 50 mmol / L –1 NH4OH and 10 mmol L –1 .

5. The method for electrocatalytic ammonia oxidation to nitrite based on a bimetallic fluorinated metal-organic framework catalyst according to claim 4, characterized in that, The constant potential is 1.6 V. RHE .

6. The method for electrocatalytic ammonia oxidation to nitrite based on a bimetallic fluorinated metal-organic framework catalyst according to claim 4, characterized in that, The reaction is carried out at room temperature for 1–24 hours, with an ammonia conversion rate of ≥95% and a nitrite Faraday selectivity of ≥90%.

7. The method for electrocatalytic ammonia oxidation to nitrite based on a bimetallic fluorinated metal-organic framework catalyst according to claim 4, characterized in that, The ·OH radicals are generated at the Ni sites of the catalyst upon activation. These ·OH radicals react with *N adsorbed on the catalyst surface. Species directly couple, achieving the formation of low-barrier nitrogen-oxygen bonds.

8. A membrane-free electrolysis apparatus, comprising the method for electrocatalytic ammonia oxidation to nitrite based on a bimetallic fluorinated metal-organic framework catalyst as described in any one of claims 4-7, characterized in that, The device includes an anode chamber, a cathode chamber, and an electrode assembly placed between them. There is no proton exchange membrane or ion exchange membrane separating the anode chamber and the cathode chamber, and the distance between the anode and cathode is 1–3 cm.

9. The membrane-free electrolysis device according to claim 8, characterized in that, The working electrode is a composite electrode formed by coating a catalyst onto a conductive substrate, wherein the conductive substrate is selected from carbon paper, nickel foam, or titanium mesh.

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