Catalyst for lithium-mediated ammonia synthesis, preparation method, working electrode and electrolysis device

Abstract

The invention provides a catalyst for lithium-mediated ammonia synthesis, a preparation method of the catalyst, a working electrode and an electrolysis device, and belongs to the technical field of solid-electrolyte membranes. The catalyst comprises a matrix layer and a coating layer coating the surface of the matrix layer, wherein the matrix layer is made of ferromanganese oxide; the coating layer is a carbon fluoride layer; the surface of the catalyst has a highly polarized interface. According to the catalyst, the surface of a ferromanganese oxide is coated with a carbon fluoride layer through a direct packaging method, and when the catalyst is used as a working electrode, a semi-ionic C-F bond is generated, the higher polarization degree is shown, the electrochemical activity is good, and formation of lithium fluoride is greatly enhanced, so that components of a solid-electrolyte interface are accurately regulated and controlled, and the electrochemical performance of the catalyst is improved. The method can be used for promoting the transmission of lithium ions in the electrolyte, accurately regulating and controlling the components of lithium fluoride on a solid-electrolyte interface, promoting the lithium-mediated ammonia synthesis performance, effectively improving the ammonia production rate and Faraday efficiency, and realizing efficient ammonia synthesis in an organic system.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of solid - electrolyte membranes, and particularly relates to a catalyst for lithium - mediated ammonia synthesis, a preparation method thereof, a working electrode, and an electrolysis device. Background Art

[0002] Ammonia, as a high - value - added chemical, has a wide range of applications in the industrial field. Its high volumetric energy density makes it an ideal hydrogen storage carrier, thus attracting much attention. Currently, industrial ammonia synthesis mainly relies on the Haber - Bosch process, but this process has significant drawbacks. It not only requires harsh conditions of high temperature (400 - 500 °C) and high pressure (up to 200 bar), and its energy consumption accounts for 1 - 2% of the global total energy consumption; moreover, a large amount of CO2 emissions will be generated during the steam reforming process for hydrogen production. Therefore, developing green and efficient ammonia synthesis methods has become an important research direction at present.

[0003] Electrochemical ammonia synthesis methods have received extensive attention because they can be carried out at room temperature and atmospheric pressure. Among them, Li - NRR is currently the only technical route proven to have industrial potential. This process mainly includes three key steps: lithium deposition, reaction of lithium with nitrogen, and protonation of lithium nitride. The kinetic processes of these reactions are mainly controlled by the mass transfer efficiency of Li + , N2 and H + . And in the electrolyte, the lithium salt will preferentially undergo a co - reduction reaction with the solvent to form a SEI film. The physical and chemical properties of the SEI film not only determine the diffusion rate of reactants, but also directly affect the uniformity of Li + deposition and the selectivity of ammonia. Therefore, the composition and structure of the SEI film are key and important issues for lithium - mediated ammonia synthesis.

[0004] Currently, significant progress has been made in controlling the SEI film by adjusting the electrolyte composition. However, the co - reduction of lithium salts, proton donors, and organic solvents on the electrode surface will still form uneven and high - impedance lithium dendrites, which in turn form dead lithium, resulting in low Faraday efficiency and ammonia yield for electrochemical lithium - mediated ammonia synthesis. Summary of the Invention

[0005] The present disclosure aims to solve at least one of the technical problems existing in the prior art, and provides a catalyst for lithium - mediated ammonia synthesis, a preparation method thereof, a working electrode, and an electrolysis device.

[0006] In one aspect of the present disclosure, a catalyst for lithium - mediated ammonia synthesis is provided. The catalyst includes a matrix layer and a coating layer wrapped on the surface of the matrix layer; wherein,

[0007] the matrix layer is manganese - iron oxide;

[0008] the coating layer is a carbon fluoride layer;

[0009] The surface of the catalyst has a highly polarized interface.

[0010] On the other hand, the present disclosure provides a method for preparing the catalyst as described above, the method comprising:

[0011] Adding polyvinylidene fluoride to a solvent and performing ultrasonic treatment to form a fluorine source solution;

[0012] Adding Mn3O4 / γ-Fe2O3 to the fluorine source solution and stirring at room temperature to form a suspension;

[0013] Performing oil bath heat treatment, cooling treatment, and tube furnace calcination treatment on the suspension in sequence to induce the formation of C-F bonds and generate a highly polarized interface, thereby obtaining the Mn3O4 / γ-Fe2O3–FC catalyst.

[0014] Optionally, the mass ratio of polyvinylidene fluoride to Mn3O4 / γ-Fe2O3 is 1:(8 - 11).

[0015] Optionally, the stirring time at room temperature is 5 - 7 hours.

[0016] Optionally, the temperature of the oil bath heat treatment is 130 - 150 °C and the time is 10 - 15 hours.

[0017] Optionally, the temperature of the tube furnace calcination treatment is 450 - 550 °C and the time is 0.5 - 1.5 hours.

[0018] On the other hand, the present disclosure provides a working electrode for lithium-mediated ammonia synthesis, the working electrode comprising a substrate material and a catalyst coated on the surface of the substrate material, and the catalyst is the catalyst as described above.

[0019] On the other hand, the present disclosure provides an electrolysis device for lithium-mediated ammonia synthesis, the electrolysis device comprising a working electrode, a counter electrode, a reference electrode, and an electrolyte; wherein,

[0020] The working electrode is the working electrode as described above.

[0021] Optionally, the electrolyte comprises an organic solvent, a lithium salt, and a proton source.

[0022] Optionally, the organic solvent comprises any one of tetrahydrofuran, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and dioxolane; and / or,

[0023] The lithium salt comprises at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium hexafluoroarsenate; and / or,

[0024] The proton source includes at least one of methanol, ethanol, propanol, and butanol.

[0025] The present disclosure provides a catalyst for lithium-mediated ammonia synthesis, a preparation method thereof, a working electrode, and an electrolysis device. The catalyst includes a substrate layer and a coating layer wrapped on the surface of the substrate layer; wherein, the substrate layer is a manganese-iron oxide; the coating layer is a carbon fluoride layer; and the surface of the catalyst has a highly polarized interface. This catalyst coats a carbon fluoride layer on the surface of manganese-iron oxide through a direct encapsulation method. When used as a working electrode, it generates a semi-ionic C-F bond, exhibits a higher degree of polarization, has good electrochemical activity, greatly enhances the formation of lithium fluoride, thereby precisely regulating the composition of the solid-electrolyte interface, promoting the transport of lithium ions in the electrolyte, being able to precisely regulate the composition of lithium fluoride at the solid-electrolyte interface, promoting the performance of lithium-mediated ammonia synthesis, effectively improving the ammonia production rate and Faraday efficiency, and achieving efficient ammonia synthesis in an organic system. Description of the Drawings

[0026] Figure 1 It is a flowchart of the preparation method of the catalyst for lithium-mediated ammonia synthesis according to the specific embodiment of the present disclosure;

[0027] Figure 2 It is the LSV curves of the manganese-iron oxide coated with a highly polarized interface as the working electrode in Example 1 and Comparative Example 1 of the present disclosure when introducing N2 and Ar respectively.

[0028] Figure 3 It is the ammonia production Faraday efficiency and yield of the manganese-iron oxide coated with a highly polarized interface at different potentials in Example 1 of the present disclosure.

[0029] Figure 4 It is the different ammonia production Faraday efficiencies and yields when different catalysts in Example 1 and Comparative Examples 1-4 of the present disclosure are used as working electrodes. Specific Embodiments

[0030] To enable those skilled in the art to better understand the technical solutions of the present disclosure, the present disclosure will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present disclosure, which are a part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present disclosure.

[0031] In some descriptions of the present disclosure, terms such as "including" or "comprising" neither limit the mentioned shapes, numbers, steps, actions, operations, components, elements and / or their groups, nor exclude the appearance or addition of one or more other different shapes, numbers, steps, actions, operations, components, elements and / or their groups.

[0032] In one aspect of the present disclosure, a catalyst for lithium-mediated ammonia synthesis is proposed. The catalyst includes a matrix layer and a coating layer wrapped on the surface of the matrix layer; wherein, the matrix layer is manganese iron oxide; the coating layer is a carbon fluoride layer; and the surface of the catalyst has a highly polarized interface.

[0033] In this embodiment, manganese iron oxide is used as the matrix layer, and a carbon fluoride layer is coated on its surface to generate an extremely high polarized interface on its surface. When used as a working electrode for lithium-mediated ammonia synthesis, it can generate semi-ionic C-F bonds, showing a higher degree of polarization, so that there is an abundant lithium fluoride component in the solid-electrolyte interface, improving the transmission rate of lithium ions in the electrolyte, quickly and efficiently realizing the performance of lithium-mediated ammonia synthesis, and further improving the Faraday efficiency and ammonia yield of electrochemical lithium-mediated ammonia synthesis.

[0034] It should be noted that the catalyst of this embodiment is obtained by a direct encapsulation method, that is, using Mn3O4 / γ-Fe2O3 as a substrate, polyvinylidene fluoride providing a fluorine source, and dimethylformamide as a solvent. After stirring, oil bath heat treatment, and tube furnace calcination, C-F bond formation is induced to generate a highly polarized interface. For the specific process, please refer to the following description.

[0035] As Figure 1 shown, in another aspect of the present disclosure, a preparation method S100 of a catalyst for lithium-mediated ammonia synthesis is provided, which specifically includes the following steps S110 to S130:

[0036] S110. Add polyvinylidene fluoride to a solvent and perform ultrasonic treatment to form a fluorine source solution.

[0037] Specifically, add 0.01 - 0.03 parts by mass of polyvinylidene fluoride to 20 - 40 parts by volume of the solvent and perform ultrasonic treatment for 0.5 - 1.5 hours to uniformly disperse it to form a fluorine source solution, that is, polyvinylidene fluoride is used to provide a fluorine source.

[0038] In some preferred embodiments, the solvent can preferably be a dimethylformamide solution.

[0039] S120. Add Mn3O4 / γ-Fe2O3 to the fluorine source solution and stir at room temperature to form a suspension.

[0040] Specifically, 0.1-0.3 parts by mass of the Mn3O4 / γ-Fe2O3 sample is added to the uniformly dispersed fluorine source solution, and stirred at room temperature for 5-7 hours to form a stable suspension.

[0041] It should be noted that the mass ratio of polyvinylidene fluoride to Mn3O4 / γ-Fe2O3 is 1:(8-11). For example, 1:8, 1:9, 1:10, 1:11, etc. can be preferably selected.

[0042] It should be understood that the above parts by mass can be in grams or in parts by mass of other units. For example, polyvinylidene fluoride is 0.01-0.03 g, and the Mn3O4 / γ-Fe2O3 sample is 0.1-0.3 g. Correspondingly, the unit of the volume fraction of the solvent added is mL, that is, the solvent is 20-40 mL.

[0043] S130. The suspension is successively subjected to oil bath heat treatment, cooling treatment, and tube furnace calcination treatment to induce the formation of C-F bonds and generate a highly polarized interface, obtaining the Mn3O4 / γ-Fe2O3–FC sample.

[0044] Specifically, the suspension is placed in an environment of 130-150 °C for heat treatment for 10-15 hours. After treatment, the sample is cooled to room temperature, and the obtained powder is transferred to a tube furnace. Under an Ar atmosphere, it is heated from room temperature to 450-550 °C at a heating rate of 5 °C / min and held for 0.5-1.5 hours to complete the carbonization process. Finally, the carbonized product is centrifuged and repeatedly washed with ethanol until the washing liquid is colorless. The washed sample is placed in a vacuum dryer at 60 °C to finally obtain the Mn3O4 / γ-Fe2O3–FC sample.

[0045] In some preferred embodiments, the temperature of the oil bath heat treatment can be preferably 140 °C, and the time of the heat treatment can be preferably 12 hours.

[0046] In some other preferred embodiments, the calcination temperature can be preferably 500 °C, and the time can be preferably 1 hour.

[0047] The carbon fluoride layer-coated manganese iron oxide of this embodiment is obtained by the direct encapsulation method of Mn3O4 / γ-Fe2O3.

[0048] On the other hand, the present disclosure proposes a working electrode for lithium-mediated ammonia synthesis. The working electrode includes a substrate material and a catalyst coated on the surface of the substrate material. That is to say, the working electrode includes a substrate material and a carbon fluoride layer-coated manganese iron oxide coated on the surface of the substrate material.

[0049] In some preferred embodiments, the substrate material of the working electrode can be carbon paper, carbon cloth, nickel foam, etc.

[0050] On the other hand, the present disclosure provides an electrolysis device for lithium-mediated ammonia synthesis, which includes a three-electrode system composed of a working electrode, a counter electrode, and a reference electrode, as well as an electrolyte solution.

[0051] In some preferred embodiments, the working electrode is manganese iron oxide coated with a carbon fluoride layer, the counter electrode is a graphite rod, a platinum sheet, a platinum mesh, a platinum wire, etc., and the reference electrode is a platinum wire, forming a three-electrode system. By precisely regulating the composition of lithium fluoride at the solid-electrolyte interface, the performance of lithium-mediated ammonia synthesis is promoted. Experimental results show that this system can achieve a high ammonia production rate and Faraday efficiency, realizing efficient ammonia synthesis in an organic system.

[0052] In some other preferred embodiments, the electrolyte solution includes an organic solvent, a lithium salt, and a proton source.

[0053] As a further preferred option, the organic solvent includes any one of tetrahydrofuran, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and dioxolane.

[0054] As a further preferred option, the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium hexafluoroarsenate. In addition, the concentration of the lithium salt is 0.1 - 1 M; preferably, the concentration is 0.2 - 0.5 M.

[0055] As a further preferred option, the proton source includes at least one of methanol, ethanol, propanol, and butanol. In addition, the concentration of the proton source is 1 - 2%; preferably, the concentration is 2%.

[0056] In some other preferred embodiments, during the electrocatalytic process, nitrogen can be introduced, and the flow rate of the introduced nitrogen reaction stream is 30 - 100 sccm.

[0057] The present disclosure provides a catalyst for lithium-mediated ammonia synthesis, its preparation method, a working electrode, and an electrolysis device. Compared with the prior art, the present disclosure has the following beneficial effects:

[0058] (1) Regulating the composition of the SEI film: In the lithium-mediated ammonia synthesis method of the present disclosure, manganese iron oxide coated with a carbon fluoride layer can form semi-ionic C-F bonds, showing a higher degree of polarization. This process can regulate the composition of lithium fluoride in the SEI film, making it richer in lithium fluoride;

[0059] (2) Increasing the mobility of lithium ions: In the lithium-mediated ammonia synthesis method of the present disclosure, the SEI film can be made to contain abundant lithium fluoride, thereby increasing the vertical mobility of lithium ions on the SEI film;

[0060] (3) Improve the Faradaic efficiency and production rate of ammonia: By reasonably regulating parameters such as the catalyst and electrolyte, the present disclosure optimizes the composition and structure of the SEI film, effectively improving the Faradaic efficiency and ammonia production rate. The Faradaic efficiency of ammonia can almost reach 50%, and the ammonia production rate can reach 3 nmol s -1 cm -2 .

[0061] The preparation method and specific application of the catalyst for lithium-mediated ammonia synthesis will be further described below with specific examples:

[0062] Example 1

[0063] This example presents a method for lithium-mediated ammonia synthesis using a catalyst with a highly polarized interface coating, and the specific operations are as follows:

[0064] S1. Weigh 0.02 g of polyvinylidene fluoride and add it to 30 mL of dimethylformamide solution, then sonicate for 1 hour to form a uniformly dispersed fluorine source solution. Add 0.2 g of Mn3O4 / γ-Fe2O3 NCs sample to the uniformly dispersed fluorine source solution and stir at room temperature for 6 hours to form a stable suspension. Subsequently, place the suspension in an environment of 140 °C for heat treatment overnight. After treatment, cool the sample to room temperature, transfer the obtained powder to a tubular furnace, and under an Ar atmosphere, heat from room temperature to 500 °C at a heating rate of 5 °C / min and hold for 1 h to complete the carbonization process. Finally, centrifuge the carbonized product and wash it repeatedly with ethanol until the washing liquid is colorless. Place the washed sample in a vacuum dryer at 60 °C to finally obtain the Mn3O4 / γ-Fe2O3–FC (labeled as MF-FC) sample.

[0065] S2. In a glove box filled with argon, add a certain amount of lithium tetrafluoroborate to tetrahydrofuran to obtain a solution with a lithium tetrafluoroborate concentration of 0.2 M. Then, add a 2% ethanol solution to the above solution and stir magnetically to obtain a uniformly dispersed electrolyte containing lithium salt and proton source.

[0066] S3. Spray or drop the manganese-iron oxide catalyst with a highly polarized interface coating obtained in step S1 on a hydrophilic carbon paper with an area of 1x1 cm 2 as a working electrode for standby.

[0067] [[ID=2】7]S4. Use the manganese-iron oxide catalyst with a highly polarized interface coating loaded on the carbon paper as the working electrode, a platinum sheet as the counter electrode, and a platinum wire as the reference electrode to construct a three-electrode system; the volume of the electrolyte is 50 mL.

[0068] S5. Control the flow rate of the reaction gas at 50 sccm with a glass rotor flowmeter, and the gas raw material composition used is: high-purity nitrogen.

[0069] S6. Collect its linear voltammetry curve with an electrochemical workstation, observe the current density and lithium deposition potential, characterize the catalytic activity of the manganese-iron oxide catalyst with a highly polarized interface coated by dipole-ordered arrangement using the constant current method, determine the ammonia content in the liquid phase with a UV-visible spectrophotometer, and calculate the Faraday efficiency and ammonia production rate.

[0070] Constant voltage electrolysis performance under normal temperature and pressure: Pour the prepared non-aqueous electrolyte into a well-dried electrolytic cell. Use the manganese-iron oxide with a highly polarized interface as the working electrode, a platinum sheet as the counter electrode, and a platinum wire as the reference electrode to construct a three-electrode system for electrochemical performance testing. The specific testing process is as follows: At normal temperature (25 °C), the above electrolytic cell is subjected to constant potential electrolysis for 7200 s at different potentials. The electrolysis and assembly processes ensure strict airtight conditions, and there is always no water and oxygen in the electrolyte. The mechanism steps of this process are as follows: First, on the surface of the working electrode, lithium ions and the solvent in the electrolyte interact, and an SEI film is preferentially formed on the electrode surface. Inside the SEI film, the electrochemically reduced active metallic lithium spontaneously reacts with the saturated nitrogen in the electrolyte to form lithium nitride. Subsequently, lithium nitride undergoes a protonation reaction with the proton source in the solution to produce ammonia. After electrolysis, the electrolyte is mixed evenly and sampled, and the UV-visible spectrophotometer is used to measure the ammonia content in the electrolyte. [[ID=..]]

[0071] The Faraday efficiency of the electrolytic cell is calculated by the following formula:

[0072] The electric charge actually consumed to produce the product ammonia / the total electric charge flowing through the external circuit × 100%

[0073] The ammonia production rate of the electrolytic cell is obtained by the following formula:

[0074] The amount of ammonia produced (ug) / (electrolysis duration h * electrode surface area cm 2 )

[0075] As Figure 2 shown, through LSV testing, the results show that when electrolysis is carried out in an N2-saturated electrolyte, MF-FC exhibits a higher current density than in an Ar-saturated electrolyte, indicating that MF-FC as the working electrode is beneficial for the progress of nitrogen reduction.

[0076] As Figure 3 and Figure 4 shown, according to the above formula calculation, the electrolytic cell of Example 1 has a Faraday efficiency of 49.23% and an ammonia production rate of 3.01 nmol s -1 cm -2 (-3.5 V vs. platinum wire); in addition, compared with the catalysts and electrolysis conditions described in Comparative Examples 1-4 below, MF-FC exhibits the best lithium-mediated ammonia synthesis performance.

[0077] Comparative Example 1

[0078] S1. Weigh 0.02 g of polyvinylidene fluoride, add it to 30 mL of dimethylformamide solution, and ultrasonically treat it for 1 hour to form a uniformly dispersed solution. Add 0.2 g of Mn3O4 / γ-Fe2O3 NCs sample to the uniformly dispersed solution and stir at room temperature for 6 hours to form a stable suspension. Subsequently, place the suspension in an environment of 140 °C and perform heat treatment overnight. After treatment, cool the sample to room temperature, transfer the obtained powder to a tubular furnace, and under an Ar atmosphere, heat it from room temperature to 500 °C at a heating rate of 5 °C / min and hold for 1 h to complete the carbonization process. Finally, centrifuge the carbonized product and wash it repeatedly with ethanol until the washing liquid is colorless. Place the washed sample in a vacuum dryer at 60 °C to finally obtain the Mn3O4 / γ-Fe2O3–FC (labeled as MF-FC) sample.

[0079] S2. In a glove box filled with argon, add a certain amount of lithium tetrafluoroborate to tetrahydrofuran to obtain a solution with a lithium tetrafluoroborate concentration of 0.2 M. Then, add a 2% ethanol solution to the above solution and obtain a uniformly dispersed electrolyte containing lithium salt and proton source after magnetic stirring.

[0080] S3. Spray or drop the manganese-iron oxide catalyst coated with a highly polarized interface on a hydrophilic carbon paper with an area of 1x1 cm 2 as a working electrode for standby.

[0081] S4. Use the manganese-iron oxide catalyst coated with a highly polarized interface loaded on the carbon paper as the working electrode, a platinum sheet as the counter electrode, and a platinum wire as the reference electrode to construct a three-electrode system; the volume of the electrolyte is 50 mL.

[0082] S5. Control the flow rate of the reaction gas to be 50 sccm with a glass rotameter. The gas raw material composition used in the experiment is: high-purity argon.

[0083] S6. Use an electrochemical workstation to collect its linear voltammogram, observe the current density and lithium deposition potential, use the constant current method to characterize the catalytic activity of the manganese-iron oxide catalyst with a highly polarized interface and dipole ordered arrangement, use an ultraviolet-visible spectrophotometer to determine the ammonia content in the liquid phase, and calculate the Faraday efficiency and ammonia production rate.

[0084] Furthermore, under the same test conditions as in Example 1, as Figure 4 shown, the Faraday efficiency of the electrolytic cell in this Example 2 is 1.48%, and the ammonia production rate is 0.14 nmol s -1 cm -2 (-3.5 V vs. platinum wire).

[0085] Comparative Example 2

[0086] S1. Dissolve 0.17 g of manganese acetate, 827 μL of oleylamine, and 157 μL of oleic acid in 15 mL of xylene, and stir well until a homogeneous solution is formed. While stirring, slowly heat the solution to 90 °C. Subsequently, quickly inject 1 mL of deionized water and maintain at 90 °C for 1.5 hours. After the reaction is completed, separate the product by centrifugation and wash it with ethanol multiple times until the washing solution is completely colorless. Finally, dry the sample under vacuum at 60 °C to obtain the Mn3O4 NCs (labeled as M) sample.

[0087] S2. In a glove box filled with argon, add a certain amount of lithium tetrafluoroborate to tetrahydrofuran to obtain a solution with a lithium tetrafluoroborate concentration of 0.2 M. Then, add a 2% ethanol solution to the above solution, and after magnetic stirring, obtain an electrolyte containing lithium salt and proton source with uniform dispersion.

[0088] S3. Spray or drop the coated Mn3O4 NCs catalyst on a hydrophilic carbon paper with an area of 1 x 1 cm 2 as the working electrode for standby.

[0089] S4. Use the coated Mn3O4 NCs catalyst loaded on the carbon paper as the working electrode, a platinum sheet as the counter electrode, and a platinum wire as the reference electrode to construct a three-electrode system; the volume of the electrolyte is 50 mL.

[0090] S5. Control the flow rate of the reaction gas at 50 sccm with a glass rotor flowmeter. The gas raw material composition used in the experiment is: high-purity nitrogen.

[0091] S6. Use an electrochemical workstation to collect its linear voltammogram, observe the current density and lithium deposition potential, characterize the catalytic activity by the constant current method, use an ultraviolet-visible spectrophotometer to determine the ammonia content in the liquid phase, and calculate the Faraday efficiency and ammonia production rate.

[0092] Furthermore, under the same test conditions as in Example 1, as Figure 4 shown, the Faraday efficiency of the electrolytic cell in this Comparative Example 1 is 4.64%, and the ammonia production rate is 0.39 nmol s -1 cm -2 (-3.5 V vs. platinum wire).

[0093] Comparative Example 3

[0094] S1. Weigh 0.25 g of the sample synthesized in Comparative Example 1 and add it to 15 mL of xylene solution. Stir at room temperature for 30 minutes until evenly dispersed. Slowly add 3.34 mL of water-soluble iron(II) perchlorate (1.5 M) to the above solution, heat it to 90 °C under stirring, and maintain this temperature for 1.5 hours to ensure sufficient reaction. After the reaction is completed, centrifuge the resulting product and wash it with ethanol multiple times until the washing liquid is colorless. Place the washed sample in a vacuum dryer at 60 °C to obtain the Mn3O4 / γ-Fe2O3 NCs (labeled as MF) sample.

[0095] S2. In a glove box filled with argon, add a certain amount of lithium tetrafluoroborate to tetrahydrofuran to obtain a solution with a lithium tetrafluoroborate concentration of 0.2 M. Then, add a 2% ethanol solution to the above solution, and after magnetic stirring, obtain an electrolyte containing lithium salt and proton source that is evenly dispersed.

[0096] S3. Spray or drop-coat the coated Mn3O4 / γ-Fe2O3 NCs catalyst on a hydrophilic carbon paper with an area of 1 x 1 cm 2 for use as a working electrode.

[0097] S4. Use the coated Mn3O4 / γ-Fe2O3 NCs catalyst loaded on the carbon paper as the working electrode, a platinum sheet as the counter electrode, and a platinum wire as the reference electrode to construct a three-electrode system; the volume of the electrolyte is 50 mL.

[0098] S5. Use a glass rotameter to control the flow rate of the reaction gas to 50 sccm, and the gas raw material composition used in the experiment is: high-purity nitrogen.

[0099] S6. Use an electrochemical workstation to collect its linear voltammogram, observe the current density and lithium deposition potential, characterize the catalytic activity by the constant current method, use an ultraviolet-visible spectrophotometer to determine the ammonia content in the liquid phase, and calculate the Faraday efficiency and ammonia production rate.

[0100] Further, under the same test conditions as in Example 1, as Figure 4 shown, the Faraday efficiency of the electrolytic cell in this Comparative Example 2 is 20.97%, and the ammonia production rate is 1.61 nmol s -1 cm -2 (-3.5 V vs. platinum wire).

[0101] Comparative Example 4

[0102] S1. Weigh 0.2 g of the sample synthesized in Comparative Example 2 (Mn3O4 NCs sample), add it to 30 mL of dimethylformamide solution, and stir at room temperature for 6 hours to form a stable suspension. Place the suspension under the reaction conditions of 140 °C and perform heat treatment overnight to promote the full conversion of reactants. After the heat treatment is completed, cool the sample to room temperature, transfer the obtained powder to a tubular furnace, and under an Ar atmosphere, heat from room temperature to 500 °C at a heating rate of 5 °C / min and hold for 1 h for carbonization treatment. After carbonization, centrifuge the product and wash it with ethanol multiple times until the washing liquid is colorless. Finally, place the washed sample in a vacuum dryer at 60 °C to obtain the Mn3O4 / γ-Fe2O3-C (labeled as MF-C) sample.

[0103] S2. In a glove box filled with argon, add a certain amount of lithium tetrafluoroborate to tetrahydrofuran to obtain a solution with a lithium tetrafluoroborate concentration of 0.2 M. Then, add a 2% ethanol solution to the above solution and obtain a uniformly dispersed electrolyte containing lithium salt and proton source after magnetic stirring.

[0104] S3. Spray or drop-coat the Mn3O4 / γ-Fe2O3-C catalyst coating on a hydrophilic carbon paper with an area of 1 x 1 cm 2 as a working electrode for standby.

[0105] S4. Use the Mn3O4 / γ-Fe2O3-C catalyst coating loaded on the carbon paper as the working electrode, a platinum sheet as the counter electrode, and a platinum wire as the reference electrode to construct a three-electrode system; the volume of the electrolyte is 50 mL L.

[0106] S5. Use a glass rotameter to control the flow rate of the reaction gas to 50 sccm, and the gas raw material composition used in the experiment is: high-purity nitrogen.

[0107] S6. Use an electrochemical workstation to collect its linear voltammetry curve, observe the current density and lithium deposition potential, characterize the catalytic activity by the constant current method, use an ultraviolet-visible spectrophotometer to determine the ammonia content in the liquid phase, and calculate the Faraday efficiency and ammonia production rate.

[0108] Furthermore, under the same test conditions as in Example 1, as Figure 4 shown, the Faraday efficiency of the electrolytic cell in this Comparative Example 3 is 12.41%, and the ammonia production rate is 0.85 nmol s -1 cm -2 (-3.5 V vs. platinum wire).

[0109] It is understandable that the above embodiments are merely exemplary embodiments adopted to illustrate the principles of the present disclosure. However, the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present disclosure, and these modifications and improvements are also regarded as the protection scope of the present disclosure.

Claims

1. A catalyst for lithium-mediated ammonia synthesis, characterized in that, The catalyst includes a matrix layer and a coating layer wrapped on the surface of the matrix layer; wherein, the matrix layer is manganese iron oxide; the coating layer is a carbon fluoride layer; the surface of the catalyst has a highly polarized interface.

2. A method for preparing the catalyst as described in claim 1, characterized in that, The method includes: Adding polyvinylidene fluoride into a solvent and performing ultrasonic treatment to form a fluorine source solution; Adding Mn3O4 / γ-Fe2O3 into the fluorine source solution and stirring at room temperature to form a suspension; Performing oil bath heat treatment, cooling treatment, and tube furnace calcination treatment on the suspension in sequence to induce the formation of C-F bonds, generate a highly polarized interface, and obtain the Mn3O4 / γ-Fe2O3–FC catalyst.

3. The method according to claim 2, wherein The mass ratio of the polyvinylidene fluoride to Mn3O4 / γ-Fe2O3 is 1:(8 - 11).

4. The method according to claim 2, wherein The stirring time at room temperature is 5 - 7 hours.

5. The method according to claim 2, wherein The temperature of the oil bath heat treatment is 130 - 150 °C, and the time is 10 - 15 hours.

6. The method according to claim 2, wherein The temperature of the tube furnace calcination treatment is 450 - 550 °C, and the time is 0.5 - 1.5 hours.

7. A working electrode for lithium-mediated ammonia synthesis, characterized in that, The working electrode includes a substrate material and a catalyst wrapped on the surface of the substrate material, and the catalyst is the catalyst described in Claim 1.

8. An electrolysis device for lithium-mediated ammonia synthesis, characterized in that, The electrolysis device includes a working electrode, a counter electrode, a reference electrode, and an electrolyte; wherein, the working electrode is the working electrode described in Claim 7.

9. The electrolysis device according to claim 8, characterized in that, The electrolyte includes an organic solvent, a lithium salt, and a proton source.

10. The electrolysis device according to claim 9, characterized in that, The organic solvent includes any one of tetrahydrofuran, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane; and / or, The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroarsenate; and / or, The proton source includes at least one of methanol, ethanol, propanol, butanol.

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