Application of Molybdenum Disulfide and Lithium-Nitrogen Electrochemical Ammonia Synthesis Method and System

Abstract

The present invention provides an application of molybdenum disulfide and a method and system for electrochemically synthesizing ammonia from lithium-nitrogen. MoS2 is used as a catalyst in the electrochemical synthesis of ammonia from Li-N2. The Li-N2 electrochemical ammonia synthesis system includes a battery and an ammonia synthesis device, and the battery includes a positive electrode loaded with a MoS2 catalyst. The Li-N2 electrochemical ammonia synthesis method is carried out using the Li-N2 electrochemical ammonia synthesis system, and includes: during discharge, lithium and nitrogen react to generate Li3N; after the discharge is completed, humid argon is introduced, and the Li3N generated during the discharge reacts with water to generate LiOH and NH3, and the generated NH3 is discharged along with the introduced argon. The positive electrode loaded with the MoS2 catalyst has the characteristics of lower charging potential, higher N2 reduction potential, higher ammonia production and FE, etc., improving the performance of Li-N2 ammonia synthesis and providing new possibilities for the development of Li-N2 ammonia synthesis.

Description

Technical Field

[0001] The present invention belongs to the technical field of ammonia synthesis, and particularly relates to an application of MoS2 and a method and system for electrochemically synthesizing ammonia from Li-N2. Background Art

[0002] Ammonia, as an important raw material, has a wide range of applications in fields such as agriculture, industry, and military. The Haber-Bosch process for producing ammonia requires high temperature, high pressure, and expensive catalysts. In this process, nitrogen in the air is combined with pure H2 generated by endothermic steam-methane reforming, consuming a large amount of natural gas or other fossil resources (such as coal) and discharging a large amount of greenhouse gases into the atmosphere. On average, about 2.86 tons of carbon dioxide are released per ton of ammonia, and even in an energy-saving state, 1.6 tons of carbon dioxide are released per ton of ammonia, which poses a severe challenge to the environment. Based on this, those skilled in the art have started research on driving ammonia synthesis by renewable electric energy instead of heat energy. Electrochemically synthesizing ammonia from nitrogen under mild conditions using renewable electricity is an attractive alternative method that can replace the energy-consuming Haber-Bosch process, which dominates industrial ammonia production. However, the electrochemically synthesizing ammonia method faces considerable challenges. Due to the competitive relationship of the hydrogen evolution side reaction, the electrochemically synthesizing ammonia shows low selectivity and low conversion rate.

[0003] Based on this, how to improve the selectivity and conversion rate of electrochemically synthesizing ammonia is the problem that needs to be solved continuously in the current electrochemically synthesizing ammonia. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem of low selectivity and conversion rate of electrochemically synthesizing ammonia.

[0005] To solve the above problems, the present invention provides the following three aspects of technical solutions.

[0006] In the first aspect, the present invention provides an application of MoS2 as a catalyst in the electrochemically synthesizing ammonia from Li-N2.

[0007] During the process of electrochemically synthesizing ammonia from Li-N2, during the discharging process, lithium reacts with nitrogen to generate Li3N, and Li3N hydrolyzes into LiOH while releasing NH3.

[0008] According to the preferred embodiment of the first aspect, the MoS2 is one or a mixture of two or more of 1T-MoS2, 2H-MoS2, and MP-MoS2;

[0009] Furthermore, MoS2 can be prepared by the following method:

[0010] 1), Mixing a molybdenum source, a sulfur source, and a solvent to obtain a mixture; wherein, the solvent includes an organic solvent;

[0011] 2), Heat the mixture obtained in step 1) to carry out a solvothermal synthesis reaction;

[0012] 3), Centrifuge, wash, and dry the precipitate (black in color) obtained from the reaction in step 2) to obtain MP-MoS2 or 1T-MoS2;

[0013] Optionally, 4), Roast the MoS2 obtained in step 3) under an Ar atmosphere to obtain 2H-MoS2;

[0014] Furthermore, the solvent comprises an organic solvent and water; More specifically, the mass ratio of the organic solvent to water is 1:2;

[0015] More specifically, the organic solvent comprises N,N-dimethylformamide (DMF);

[0016] More specifically, in step 1), the mass ratio of the molybdenum source to the sulfur source is 0.54:1 - 0.8:1;

[0017] More specifically, the mass ratio of the sulfur source to the solvent volume is 0.025 g:1 mL - 0.033 g:1 mL;

[0018] More specifically, in step 2), the reaction temperature of the solvothermal synthesis is 180 °C - 200 °C;

[0019] More specifically, in step 2), the reaction time of the solvothermal synthesis is 24 h - 40 h;

[0020] More specifically, in step 3), vacuum drying is adopted for drying; Even more specifically, in step 3), the temperature of the vacuum drying is 60 °C - 90 °C; Even more specifically, in step 3), the time of the vacuum drying is 9 h - 12 h;

[0021] More specifically, in step 4), the roasting temperature is 350 °C - 450 °C;

[0022] More specifically, in step 4), the heating rate of the roasting is 2 °C / min - 5 °C / min;

[0023] In the above preparation method, in step 1), in the presence of an organic solvent as an inducer, sulfur vacancies are formed in-situ in molybdenum disulfide, which is the key to promoting the transformation from the 2H phase to the 1T phase; The organic solvent has a strong interaction with the surface of MoS2, reducing the total energy of MoS2 and enhancing the stability of the metallic (1T) phase; In step 3), the roasting treatment causes the metastable 1T (metallic phase) to transform into the more stable 2H (semiconductor phase).

[0024] Second aspect, the present invention provides a Li-N2 electrochemical ammonia synthesis system, wherein the Li-N2 electrochemical ammonia synthesis system includes a battery and an ammonia synthesis device; wherein, the battery includes a positive electrode loaded with a MoS2 catalyst.

[0025] According to a preferred embodiment of the second aspect, the MoS2 is one or a mixture of two or more of 1T-MoS2, 2H-MoS2, and MP-MoS2.

[0026] According to a preferred embodiment of the second aspect, the positive electrode loaded with the MoS2 catalyst is an air electrode loaded with the MoS2 catalyst;

[0027] Further, the positive electrode loaded with the MoS2 catalyst includes a foam iron electrode loaded with the MoS2 catalyst and / or a foam nickel electrode loaded with the MoS2 catalyst.

[0028] According to a preferred embodiment of the second aspect, the positive electrode loaded with the MoS2 catalyst can be prepared by the following method:

[0029] Mix MoS2, a conductive agent, a binder, and a solvent to obtain a mixed slurry;

[0030] Uniformly coat the mixed slurry on the electrode material, and after drying, obtain the positive electrode loaded with the MoS2 catalyst;

[0031] Further, mix MoS2, acetylene black (conductive agent), PVDF (binder), and NMP (solvent) to obtain a mixed slurry; furthermore, the mass ratio of MoS2: the mass of acetylene black: the sum of the mass of PVDF and NMP is 8-9:1:1; furthermore, the mass ratio of PVDF to NMP is 1:20;

[0032] Further, before coating, the electrode material is subjected to surface impurity removal treatment; furthermore, the electrode material is soaked in a mixed solution of acetone and absolute ethanol with a volume ratio of 1:1 and a 0.1M sulfuric acid solution respectively, and after soaking, ultrasonic treatment is carried out for 30 min to remove impurities on the surface of the electrode material, and then dried in a vacuum drying oven at 60 °C for 12 h to remove residual moisture and residual soaking solution.

[0033] According to a preferred embodiment of the second aspect, the MoS2 is one or a mixture of two or more of 1T-MoS2, 2H-MoS2, and MP-MoS2;

[0034] Further, MoS2 can be prepared by the following method:

[0035] 1), Mix a molybdenum source, a sulfur source, and a solvent to obtain a mixture; wherein, the solvent includes an organic solvent;

[0036] 2), Heat the mixture obtained in step 1) to carry out a solvothermal synthesis reaction;

[0037] 3), Centrifuge, wash, and dry the precipitate (black in color) obtained from the reaction in step 2) to obtain MP-MoS2 or 1T-MoS2;

[0038] Optionally, 4), Roast the MoS2 obtained in step 3) under an Ar atmosphere to obtain 2H-MoS2;

[0039] Furthermore, the solvent includes an organic solvent and water; Further still, the mass ratio of the organic solvent to water is 1:2;

[0040] Further still, the organic solvent includes N,N-dimethylformamide (DMF);

[0041] Further still, the mass ratio of the molybdenum source to the sulfur source in step 1) is 0.54:1 - 0.8:1;

[0042] Further still, the volume of the solvent is 20 ml - 35 ml;

[0043] Further still, in step 2), the reaction temperature of the solvothermal synthesis is 180 °C - 200 °C;

[0044] Further still, in step 2), the reaction time of the solvothermal synthesis is 24 h - 40 h;

[0045] Further still, in step 3), vacuum drying is adopted for drying; Still further, in step 3), the temperature of the vacuum drying is 60 °C - 90 °C; Still further, in step 3), the time of the vacuum drying is 9 h - 12 h;

[0046] Further still, in step 4), the roasting temperature is 350 °C - 450 °C;

[0047] Further still, in step 4), the heating rate of the roasting is 2 °C / min - 5 °C / min;

[0048] In the above preparation method, in step 1), in the presence of an organic solvent as an inducer, sulfur vacancies are in-situ formed in molybdenum disulfide, which is the key to promoting the transformation from the 2H phase to the 1T phase; The organic solvent has a strong interaction with the surface of MoS2, reducing the total energy of MoS2 and enhancing the stability of the metallic (1T) phase; In step 3), the roasting treatment causes the metastable 1T (metallic phase) to transform into the relatively stable 2H (semiconductor phase).

[0049] According to the preferred embodiment of the second aspect, the battery includes a Li negative electrode.

[0050] According to a preferred embodiment of the second aspect, the battery uses a solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in tetraethylene glycol dimethyl ether (TEGDME) as the electrolyte.

[0051] According to a preferred embodiment of the second aspect, the battery includes a glass fiber separator GF / D; further, the electrolyte of the battery is dropped onto the glass fiber separator GF / D.

[0052] According to a preferred embodiment of the second aspect, the battery includes a negative electrode case, a spring piece, a steel gasket, a negative electrode (such as a lithium sheet), a glass fiber separator GF / D impregnated with an electrolyte (such as LiTFSI / TEGDME electrolyte), a positive electrode loaded with a MoS2 catalyst (such as a positive electrode sheet loaded with a MoS2 catalyst), and a perforated positive electrode case arranged in sequence.

[0053] The ammonia synthesis device includes a device bottom plate, a battery fixing plate, and a device top plate that are detachably connected in sequence; wherein, a positive electrode flow channel plate is clamped between the device bottom plate and the battery fixing plate, and a negative electrode conductive plate is clamped between the battery fixing plate and the device top plate.

[0054] The battery fixing plate is provided with a battery placement through hole for placing the battery; the positive electrode flow channel plate is provided with a through hole corresponding to the position of the battery placement through hole of the battery fixing plate.

[0055] The device bottom plate is provided with an air inlet channel and an air outlet channel communicating with the outside. The device bottom plate is provided with a gas flow channel corresponding to the through hole of the positive electrode flow channel plate on the surface in contact with the positive electrode flow channel plate. The gas flow channel is communicated with the air inlet channel and the air outlet channel, and the gas in the gas flow channel can contact the positive electrode flow channel plate.

[0056] The battery placed in the battery placement through hole of the battery fixing plate can be connected to the negative electrode conductive plate and the positive electrode flow channel plate of the ammonia synthesis device through springs. Among them, the perforated positive electrode case of the battery is connected to the positive electrode flow channel plate of the ammonia synthesis device through a spring, and the negative electrode case of the battery is connected to the negative electrode conductive plate of the ammonia synthesis device through a spring.

[0057] When synthesizing ammonia using the ammonia synthesis system provided by the above preferred embodiment, nitrogen enters the ammonia synthesis device through the air inlet channel and the gas flow channel of the ammonia synthesis device, and enters the battery through the perforated positive electrode case of the battery. Then, a reaction occurs on the surface of the positive electrode of the battery loaded with a MoS2 catalyst to generate lithium nitride; stop introducing nitrogen, and introduce humid argon into the air inlet channel of the ammonia synthesis device. The humid argon enters the ammonia synthesis device through the air inlet channel and the gas flow channel of the ammonia synthesis device, and enters the battery through the perforated positive electrode case of the battery. The water in the humid argon reacts with lithium nitride to hydrolyze lithium nitride to generate lithium hydroxide and ammonia. The humid argon blows out the ammonia and flows through the air outlet channel of the ammonia synthesis device for collection, and lithium hydroxide adheres to the surface of the positive electrode of the battery.

[0058] In a third aspect, the present invention provides a method for electrochemically synthesizing ammonia from Li-N2, which is carried out using the above-mentioned Li-N2 electrochemical ammonia synthesis system. The method includes:

[0059] During discharge, nitrogen is introduced. Under the action of the active sites on the edges and basal planes of MoS2, nitrogen molecules are adsorbed on the surface of the positive electrode. Li at the negative electrode loses electrons to obtain Li + , Li + passes through the diaphragm from the negative electrode to the surface of the positive electrode and reacts with the nitrogen molecules adsorbed on the surface of the positive electrode to form lithium nitride; after the discharge is completed, moist argon is introduced, and the water in the moist argon causes the Li3N generated during the reaction in the discharge process to hydrolyze to generate LiOH and NH3, and the generated NH3 is discharged with the introduced argon.

[0060] During the above ammonia synthesis process, the active sites on the edges and basal planes of MoS2 contribute to the adsorption of nitrogen molecules on the positive electrode, thereby promoting the reduction of nitrogen during discharge.

[0061] The specific reactions during its discharge process are as follows:

[0062] Negative electrode reaction: Li - e - →Li +

[0063] Positive electrode reaction: 6Li + + N2 + 6e - →2Li3N

[0064] Total discharge reaction: 6Li + N2 → 2Li3N

[0065] After the discharge is completed, moist Ar is introduced into the device. The positive electrode reaction of the battery is:

[0066] Li3N + 3H2O → 3LiOH + NH3↑.

[0067] According to a preferred embodiment of the third aspect, the method for electrochemically synthesizing ammonia from Li-N2 further includes: collecting the NH3 discharged with the introduced argon using water.

[0068] According to a preferred embodiment of the third aspect, the method for electrochemically synthesizing ammonia from Li-N2 further includes: during charging, LiOH generated on the surface of the positive electrode loses electrons to generate Li + and O2, and Li + passes through the diaphragm from the positive electrode to the negative electrode interface to obtain electrons to generate Li, completing the recycling of lithium; during the process, the high intrinsic conductivity of MoS2 loaded on the positive electrode contributes to the faster transfer of Li + and electrons. The nanostructure and wide layer spacing of MoS2 provide a shorter diffusion path for Li+ Intercalation and deintercalation are easier;

[0069] Furthermore, during the charge and discharge process, the current density is 50 A·cm -2 ;

[0070] Furthermore, during one charge and discharge process, the charge and discharge capacity is 75 μAh - 150 μAh.

[0071] The specific reactions during the charging process are as follows:

[0072] Negative electrode reaction: Li + +e - →Li

[0073] Positive electrode reaction: 4LiOH → 4Li + +H2O + O2↑ + 4e -

[0074] According to the preferred embodiment of the third aspect, the purity of the introduced nitrogen is 99.99%.

[0075] According to the preferred embodiment of the third aspect, the purity of the introduced argon is 99.99%.

[0076] The positive electrode loaded with the MoS2 catalyst has the characteristics of a lower charging potential, a higher N2 reduction potential, a higher ammonia production, and a higher FE, etc., improving the performance of Li-N2 ammonia synthesis and providing new possibilities for the development of Li-N2 ammonia synthesis. Brief Description of the Drawings

[0077] Figure 1 It is a schematic diagram of the Li-N2 battery structure.

[0078] Figure 2 It is a schematic diagram of the ammonia synthesis device and its structure.

[0079] Figure 3 It is the XRD spectrum of the prepared 1T-MoS2, 2H-MoS2, and MP-MoS2.

[0080] Figure 4 It is the SEM image of the prepared 1T-MoS2.

[0081] Figure 5 It is the SEM image of the prepared 2H-MoS2.

[0082] Figure 6 It is the SEM image of the prepared MP-MoS2.

[0083] Figure 7 It is the Raman spectrum of the prepared 1T-MoS2, 2H-MoS2, and MP-MoS2.

[0084] Figure 8 XPS Mo 3d spectra of 1T-MoS2, 2H-MoS2, and MP-MoS2 prepared.

[0085] Figure 9 XPS S 2p spectra of 1T-MoS2, 2H-MoS2, and MP-MoS2 prepared.

[0086] Figure 10 CV curves of batteries with Fe / 1T-MoS2, Fe / 2H-MoS2, and Fe / MP-MoS2 as the positive electrode.

[0087] Figure 11 Discharge curves of batteries with Fe / 1T-MoS2, Fe / 2H-MoS2, and Fe / MP-MoS2 as the positive electrode.

[0088] Figure 12 Cycling curves of batteries with Fe / 1T-MoS2, Fe / 2H-MoS2, and Fe / MP-MoS2 as the positive electrode.

[0089] Figure 13 Absorbance test curves of Fe / 1T-MoS2, Fe / 2H-MoS2, and Fe / MP-MoS2 positive electrodes.

[0090] Figure 14 Comparison chart of ammonia production and FE of Li-N2 electrochemical synthesis of ammonia with Fe / 1T-MoS2, Fe / 2H-MoS2, and Fe / MP-MoS2 as the positive electrode. Detailed implementation mode

[0091] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solution of the present invention will be described in detail below, but it should not be construed as a limitation on the implementable scope of the present invention.

[0092] Example 1

[0093] This example provides 1T-MoS2 catalyst, 2H-MoS2 catalyst, and MP-MoS2 catalyst.

[0094] The 1T-MoS2 catalyst, 2H-MoS2 catalyst, and MP-MoS2 catalyst are prepared by the following method:

[0095] Dissolve 0.41 g of H 24 Mo7N6O 24·4H2O and 0.76 g of CH4N2S were added to a beaker containing 30 ml of a mixed solution (volume ratio of deionized water to N,N-dimethylformamide = 2:1). A magnetic stir bar was added to the beaker and stirred for 40 min using a magnetic stirrer to dissolve completely, obtaining a mixed solution;

[0096] The above mixed solution was poured into a reaction kettle with a Teflon liner of 100 ml volume and placed in a constant temperature oven. A solvothermal synthesis reaction was carried out at 200 °C for 24 h. After the reaction ended and cooled to room temperature, the cooled reaction product was poured into a 50 ml centrifuge tube, and then centrifuged at 9000 r / min for 8 min in a centrifuge to remove the supernatant. Then the precipitate (black) was centrifugally washed 3 - 4 times successively with deionized water and ethanol, and placed in a vacuum drying oven to dry at 60 °C for 12 h;

[0097] The dried product was ground into fine powder in a quartz mortar to obtain MP-MoS2.

[0098] 0.62 g of H 24 Mo7N6O 24 ·4H2O and 1.14 g of CH4N2S were added to a beaker containing 35 ml of N,N-dimethylformamide (DMF). A magnetic stir bar was added to the beaker and stirred for 40 min using a magnetic stirrer to dissolve completely, obtaining a mixed solution;

[0099] The above mixed solution was poured into a reaction kettle with a Teflon liner of 100 ml volume and placed in a constant temperature oven. A solvothermal synthesis reaction was carried out at 200 °C for 24 h. After the reaction ended and cooled to room temperature, the cooled reaction product was poured into a 50 ml centrifuge tube, and then centrifuged at 9000 r / min for 10 min in a centrifuge to remove the supernatant. Then the precipitate (black) was centrifugally washed 3 - 4 times successively with deionized water and ethanol, and placed in a vacuum drying oven to dry at 60 °C for 12 h;

[0100] The dried product was ground into fine powder in a quartz mortar to obtain 1T-MoS2.

[0101] 0.4 g of the prepared 1T-MoS2 was taken and placed in a ceramic crucible. The ceramic crucible was placed in a tubular furnace. Under an Ar gas environment, it was heated to 350 °C at a heating rate of 5 °C / min and calcined at 350 °C for 3 h. After calcination, it was cooled to room temperature and the ceramic crucible was taken out to obtain 2H-MoS2.

[0102] Figure 3XRD patterns of 1T-MoS2, 2H-MoS2, and MP-MoS2 prepared in this example. As can be seen from the figure, the distinct characteristic peaks of 2H-MoS2 at 14.0°, 33.2°, 39.7°, and 58.4° correspond to the (002), (100), (103), and (110) crystal planes of hexagonal prism MoS2 (PDF#731508), respectively. Four diffraction peaks of 1T-MoS2 appear at 8.7°, 17.4°, 32.6°, and 57.0°, corresponding to the (002), (004), (100), and (110) crystal planes of the 1T phase. Compared with the other two materials, the crystallinity of the prepared 1T-MoS2 is poor. MP-MoS2 has the same peaks at approximately 32.6° and 57.3°, which can be indexed to the (100) and (110) planes of the 1T phase. At the same time, the diffraction peak at approximately 14.4° corresponds to the (002) crystal plane of the 2H phase, and the diffraction peak at approximately 35.6° corresponds to the (102) crystal plane of MoS2, indicating that MP-MoS2 is a mixed crystal phase. The results of the XRD patterns show that 1T-MoS2, 2H-MoS2, and MP-MoS2 were successfully prepared by simple thermal reactions and calcination in different solvents.

[0103] Figure 4 SEM image of 1T-MoS2 prepared in this example. As can be seen from the figure, 1T-MoS2 as a whole presents nanosphere clusters aggregated by nanosheets. Figure 5 SEM image of 2H-MoS2 at a higher magnification. As can be seen from the figure, the morphology of 2H-MoS2 is nanosheet-like, and its nanosheet clusters are composed of multiple layers of nanosheets. Figure 6 SEM image of MP-MoS2 prepared in this example, showing a clearly layered nano-flower shape. This multi-layered nano-petal-like morphology structure has a large specific surface area, which is expected to increase the electrochemical active area of the electrode surface, improve the migration channels of lithium ions, and increase the NRR activity under the Li-N2 system.

[0104] Figure 7 Raman spectra of 1T-MoS2, 2H-MoS2, and MP-MoS2 prepared in this example. As can be seen, in the spectrum of 2H-MoS2, the two typical vibration peaks at 375.6 cm -1 and 403.4 cm -1 are generated by and A 1g of the 2H phase, respectively. On the contrary, in 1T-MoS2, three other peaks are observed at 145.7 cm -1 (J1), 280.1 cm -1 (E1g), and 334.5 cm -1 (J3), while the vibration peaks of the 2H phase and A1g It disappeared, which confirms that the organic solvent DMF as an inducing agent promotes the transformation of 2H to 1T phase. In addition, the vibration peaks of MP-MoS2 in the figure indicate all the characteristic peaks of 1T and 2H phases, including 145.7 cm -1 (J1), 280.1cm -1 (E1g), 334.4cm -1 (J3), 373.2cm -1 ( ) and 401.2cm -1 (A 1g ), indicating that MP-MoS2 is a mixed phase containing 2H and 1T.

[0105] like Figure 8 The XPS molybdenum spectra Mo3d of the prepared 1T-MoS2, 2H-MoS2 and MP-MoS2 show that 2H-MoS2 has obvious characteristic peaks at about 229.3eV and 232.5eV, which are consistent with the Mo in the 2H phase. 4+ 3D 5 / 2 and 3D 3 / 2 The binding energy of the orbitals is consistent, and Mo appears in the Mo3d spectrum of 2H-MoS2. 6+ peak, indicating that partial oxidation occurred during the calcination process. Due to the increase in electron density, the formation of 1T phase increased, and the Mo 4+ 3d 5 / 2 and Mo 4+ 3d 3 / 2 The orbital binding energies are 0.9 eV and 0.2 eV lower than those of 2H-MoS2, respectively. Figure 8 It is shown that the Mo3d peaks of 1T-MoS2 are located at about 229.3eV and 232.5eV, respectively, which are attributed to Mo 4+ 3D 5 / 2 and 3D 3 / 2 orbital, with a characteristic peak at about 226.6 eV belonging to the S 2s orbital, while the characteristic peak of 2H-MoS2 at 227.4 eV is consistent with the binding energy of the S 2s orbital. 4+ 3d 5 / 2 and Mo 4+ 3d 3 / 2 The binding energies of the orbitals are approximately 233.2 eV and 230.0 eV, respectively. The peak at approximately 227.2 eV can be attributed to the S2s orbital. The deconvoluted spectrum of Mo 3d of MP-MoS2 shows 1T phase and 2H phase, which is consistent with the Raman results.

[0106] Figure 9XPS Mo spectra S2p diagrams of the prepared 1T-MoS2, 2H-MoS2, and MP-MoS2. As can be seen from the figure, the characteristic peaks of 2H-MoS2 at approximately 163.3 eV and 162.1 eV are consistent with the binding energies of the 2p 1 / 2 and 2p 2 / 3 orbitals of the S element in the 2H phase. The characteristic peaks of 1T-MoS2 at 161.5 eV and 162.7 eV can be attributed to the S2p 2 / 3 orbital and the S2p 1 / 2 orbital respectively, which are about 0.6 eV lower than the corresponding values of the 2H phase. The S2p spectrum of MP-MoS2 shows that the two doublets with binding energies around 163.5 eV and 161.8 eV represent the 2H phase of MoS2, which is about 0.2 eV lower than the corresponding values of 2H-MoS2. In addition to the known doublets of the 2H phase, additional peaks are found at 161.5 eV and 162.8 eV, which are consistent with the binding energies of 1T-MoS2, further proving the formation of the metallic 1T phase in MP-MoS2. In summary, it is proved that different interactions between different solvents and MoS2 form different crystal phases.

[0107] Example 2

[0108] This example provides a positive electrode (Fe / 1T-MoS2) loaded with a 1T-MoS2 catalyst, a positive electrode (Fe / 2H-MoS2) loaded with a 2H-MoS2 catalyst, and a positive electrode (Fe / MP-MoS2) loaded with an MP-MoS2 catalyst.

[0109] Fe / 1T-MoS2, Fe / 2H-MoS2, and Fe / MP-MoS2 are prepared by the following method:

[0110] Use a punching machine to cut the iron foam into electrode sheets with a diameter of 14 mm. Immerse the electrode sheets in a mixed solution of acetone and absolute ethanol with a volume ratio of 1:1 and a 0.1 M sulfuric acid solution for 30 min. After immersion, perform ultrasonic treatment on the electrode sheets for 30 min to remove impurities on the surface of the electrode sheets. Finally, place the electrode sheets in a vacuum drying oven and dry them at 60 °C for 12 h to remove residual moisture and residual treatment solution for standby;

[0111] Mix the mixture of the 1T-MoS2 catalyst, acetylene black, PVDF, and NMP (mass ratio 1:20) prepared in the example according to a mass ratio of 8:1:1, and then mix the materials in a planetary mixer for 5 minutes to obtain a uniform slurry; coat the slurry evenly on the electrode sheets. After coating, place the electrode sheets in a vacuum drying oven and dry them at 60 °C for 12 h to obtain Fe / 1T-MoS2;

[0112] The mixture of the Fe / 2H-MoS2 catalyst prepared in the example, acetylene black, PVDF, and NMP (mass ratio 1:20) was mixed at a mass ratio of 8:1:1, and then mixed in a planetary and rotary mixer for 5 minutes to obtain a uniform slurry; the slurry was evenly coated on the electrode sheet, and after coating, the electrode sheet was placed in a vacuum drying oven and dried for 12 h at 60 °C to obtain Fe / Fe / 2H-MoS2;

[0113] The mixture of the MP-MoS2 catalyst prepared in the example, acetylene black, PVDF, and NMP (mass ratio 1:20) was mixed at a mass ratio of 8:1:1, and then mixed in a planetary and rotary mixer for 5 minutes to obtain a uniform slurry; the slurry was evenly coated on the electrode sheet, and after coating, the electrode sheet was placed in a vacuum drying oven and dried for 12 h at 60 °C to obtain Fe / MP-MoS2.

[0114] Example 3

[0115] In this example, three Li-N2 electrochemical ammonia synthesis systems were provided. These three Li-N2 electrochemical ammonia synthesis systems used batteries with Fe / 1T-MoS2 as the positive electrode, batteries with Fe / 2H-MoS2 as the positive electrode, and batteries with Fe / MP-MoS2 as the positive electrode, respectively.

[0116] The assembly of the battery was completed in an experimental glove box filled with argon (the water and oxygen content was less than 0.01 ppm); as Figure 1 shown, the battery was assembled in the order of negative electrode shell, spring sheet, steel gasket, lithium sheet, diaphragm impregnated with electrolyte, sheet-shaped positive electrode, and positive electrode shell with holes (19 holes) from bottom to top;

[0117] Among them, the positive electrodes were respectively the three positive electrodes provided in the above examples; the lithium sheet was the negative electrode, specifically a circular metal lithium sheet with a diameter of 16 mm; the diaphragm was a GF / D type glass fiber diaphragm, which was cut into a circular sheet with a diameter of 16 mm by a punching machine; the electrolyte was 1 M LiTFSI / TEGDME, and the amount of electrolyte dropped was 180 μL; the models of the negative electrode shell and the positive electrode shell were 2032 type button battery shells; the specification of the steel sheet was 16 mm (diameter) × 2.5 mm (thickness);

[0118] The assembled battery was installed in the ammonia synthesis device to obtain a Li-N2 electrochemical ammonia synthesis system. As Figure 2As shown in the figure, the ammonia synthesis device includes a device bottom plate 3, a battery fixing plate 6, and a device top plate 8 that are detachably connected in sequence. Among them, a positive electrode flow channel plate 5 is clamped between the device bottom plate 3 and the battery fixing plate 6, and a negative electrode conductive plate 7 is clamped between the battery fixing plate 6 and the device top plate 8. The battery fixing plate 6 is provided with a battery placement through hole for placing the battery. The positive electrode flow channel plate 5 is provided with a through hole corresponding to the position of the battery placement through hole of the battery fixing plate 6. The device bottom plate 3 is provided with an air inlet channel 1 and an air outlet channel 2 communicating with the outside. The device bottom plate 3 is provided with a gas flow channel 4 corresponding to the through hole of the positive electrode flow channel plate 5 on the surface in contact with the positive electrode flow channel plate 5. The gas flow channel 4 is communicated with the air inlet channel 1 and the air outlet channel 2, and the gas in the gas flow channel 4 can contact the positive electrode flow channel plate 5. The battery placed in the battery placement through hole of the battery fixing plate 6 can be connected to the negative electrode conductive plate 7 and the positive electrode flow channel plate 5 of the ammonia synthesis device through springs. Among them, the perforated positive electrode shell of the battery is connected to the positive electrode flow channel plate 5 of the ammonia synthesis device through a spring, and the negative electrode shell of the battery is connected to the negative electrode conductive plate 7 of the ammonia synthesis device through a spring.

[0119] Example 4

[0120] This embodiment provides a Li-N2 electrochemical ammonia synthesis method, which is carried out by using the three Li-N2 electrochemical ammonia synthesis systems provided in Example 3 respectively.

[0121] The steps are as follows:

[0122] During the discharging process, nitrogen gas (purity 99.99%) is introduced into the air inlet channel 1 of the ammonia synthesis device of the Li-N2 electrochemical ammonia synthesis system for 10 minutes. The nitrogen gas enters the ammonia synthesis device through the air inlet channel 1 and the gas flow channel 4 of the ammonia synthesis device, and enters the positive electrode part of the battery through the perforated positive electrode shell of the battery. Under the action of the active sites on the edge and basal plane of MoS2, nitrogen molecules are adsorbed on the positive electrode surface. The negative electrode Li loses electrons to obtain Li + Li + passes through the diaphragm from the negative electrode to the positive electrode surface and reacts with the nitrogen molecules adsorbed on the positive electrode surface to form lithium nitride; during the discharging process, a constant current and limited capacity discharging test is carried out by using a blue electric battery test device, and the test current density is 50 A·cm -2 and the limited capacity is 75 μAh;

[0123] After the discharging is completed, the nitrogen gas is stopped from being introduced, and humid argon gas is introduced into the air inlet channel 1 of the ammonia synthesis device of the Li-N2 electrochemical ammonia synthesis system for 10 minutes. The water in the humid argon gas causes the Li3N generated during the discharging process to hydrolyze to generate LiOH and NH3. The generated NH3 is discharged with the introduced argon gas, and the NH3 discharged with the introduced argon gas is collected by a centrifuge tube containing 10 ml of deionized water;

[0124] During charging, LiOH generated on the surface of the positive electrode loses electrons to form Li + and O2, and Li + travels from the positive electrode through the separator to the negative electrode interface, gains electrons to form Li, and completes the lithium recovery cycle; during this process, the high intrinsic conductivity of MoS2 loaded on the positive electrode helps the faster transfer of Li + and electrons. The nanostructure and wide layer spacing of MoS2 provide a shorter diffusion path, making the intercalation and deintercalation of Li + easier; during charging, the current density is 50 A·cm -2 .

[0125] A constant current and limited volume charging test was carried out on the Li-N2 electrochemical ammonia synthesis battery, and the program settings were the same as those of the discharge program.

[0126] In this example, the quantification of ammonia production used the indophenol blue method, and the production and Faraday efficiency were calculated using the standard curve and relevant calculation formulas.

[0127] Comparative Example 1

[0128] This comparative example provided a Li-N2 electrochemical ammonia synthesis method, which was carried out using the three Li-N2 electrochemical ammonia synthesis systems provided in Example 3 respectively.

[0129] The difference from Example 4 was only that, during discharge, instead of nitrogen, argon (purity 99.99%) was introduced into the ammonia synthesis device of the Li-N2 electrochemical ammonia synthesis system.

[0130] Comparative Example 2

[0131] This comparative example provided a Li-N2 electrochemical ammonia synthesis method.

[0132] The difference from Example 4 was only that a different Li-N2 electrochemical ammonia synthesis system was used. The positive electrode used in the battery of the Li-N2 electrochemical ammonia synthesis system in this comparative example was not the positive electrode prepared in Example 2 but a foam iron positive electrode (the foam iron was cut into electrode sheets with a diameter of 14 mm).

[0133] Figure 10 In it is the CV comparison diagram in the scanning voltage range of 0.5 - 3 V and the scanning rate of 0.2 mV / s. It can be seen from the figure that Fe / 1T-MoS2 has an obvious reduction peak (≈1.65 V vs Li / Li + ), which belongs to the reaction of N2 reduction to Li3N. Fe / MP-MoS2 has an obvious N2 reduction peak at about 1.85 V, and the reduction peak at about 1.0 V is the lithium intercalation potential of the material, while Fe / 2H-MoS2 shows a weak N2 reduction peak (≈1.5 V vs Li / Li +), which is attributed to the poor edge catalytic activity inherent in the semiconductor phase (2H) and the low NRR reaction activity. In addition, Fe / MP-MoS2 has a higher peak current and onset voltage than Fe / 1T-MoS2 and Fe / 2H-MoS2, and has a larger electrochemically active specific surface area, which helps to increase the contact area between the electrolyte and the electrode, shorten the path of lithium ion diffusion, and enhance the NRR activity of the Fe / MP-MoS2 positive electrode.

[0134] Figure 11 The discharge curves of Fe / 1T-MoS2, Fe / 2H-MoS2, and Fe / MP-MoS2 at 0.05 mA / cm 2 The current density is shown in the figure. It can be clearly seen from the figure that the discharge platforms of the three positive electrodes are all between 1.65 V and 1.70 V. The discharge platform of Fe / MP-MoS2 is slightly higher than that of Fe / 1T-MoS2 and Fe / 2H-MoS2, about 1.70 V, indicating that Fe / MP-MoS2 has higher NRR activity in the Li-N2 ammonia synthesis system.

[0135] At 0.05 mA / cm 2 The current density and a capacity of 0.075 mAh were used to perform charge-discharge tests on the three positive electrodes. From Figure 12 The charge-discharge curves can be seen that the batteries of the three positive electrodes of Fe / 1T-MoS2, Fe / 2H-MoS2, and Fe / MP-MoS2 can all achieve good cycling. In addition, the lowest discharge potential and the highest charge potential of the Fe / MP-MoS2 positive electrode are about 1.99 V and 2.61 V respectively, showing a smaller overpotential. In contrast, the batteries using the Fe / 1T-MoS2 positive electrode and the Fe / 2H-MoS2 positive electrode show a smaller discharge potential and a larger charge potential, 1.96 / 2.87 V and 1.86 / 2.94 V respectively, resulting in an increase in the battery overpotential and a lower charge-discharge energy efficiency. Therefore, the Fe / MP-MoS2 positive electrode material can provide a lower charge potential and is expected to achieve multiple cycles of ammonia production in the lithium-nitrogen system.

[0136] The indophenol blue method was used to perform a color reaction on the collected ammonia gas, and the absorbance of the color reagent was measured. Figure 13Absorbance curves of Fe / 1T-MoS2, Fe / 2H-MoS2, and Fe / MP-MoS2. It can be seen from the figure that the absorbance of the control group under Ar is extremely low, far lower than that under N2, indicating that the Li-N2 system can be active under N2 and the system is feasible. In addition, the absorbance of the Fe / MP-MoS2 cathode is higher than that of the Fe / 1T-MoS2 cathode and the Fe / 2H-MoS2 cathode, about 0.17, showing excellent Li-N2 ammonia synthesis performance. The absorbances of the Fe / 1T-MoS2 cathode and the Fe / 2H-MoS2 cathode are about 0.12 and 0.10 respectively, both higher than that of the unloaded iron foam cathode, showing certain Li-N2 ammonia synthesis performance.

[0137] Figure 14 Comparison chart of ammonia synthesis performance of iron foam cathodes loaded with 1T-MoS2, 2H-MoS2, and MP-MoS2. It can be clearly seen from the figure that the ammonia production in the control group under Ar is only trace (less than 0.05 μmol / cm 2 ), which may come from unavoidable trace contamination during the experiment. The ammonia production under N2 is significantly higher than that of the Ar control group, indicating that the ammonia in the Li-N2 system mainly comes from the introduced nitrogen. There are obvious differences in the ammonia production and Faraday efficiency (FE) of the batteries with different cathodes. The batteries with the Fe / 2H-MoS2 cathode have lower ammonia production and FE than those with the Fe / 1T-MoS2 cathode. The ammonia production and FE of the two are 0.11 μmol / cm 2 , 0.13 μmol / cm 2 and 12.2%, 14.4% respectively. This may be because the high intrinsic conductivity of 1T-MoS2 promotes the faster transfer of lithium ions and electrons, accelerating the formation of Li3N in the system. The batteries with the Fe / MP-MoS2 cathode have the highest ammonia production and FE, which are 0.17 μmol / cm 2 and 19.5% respectively. In summary, Fe / MP-MoS2 has the characteristics of lower charging potential, higher N2 reduction potential, higher ammonia production, and higher FE than Fe / 2H-MoS2 and Fe / 1T-MoS2, which is beneficial to the development of the catalyst in the Li-N2 ammonia synthesis system.

Claims

1. Application of MoS2 as a catalyst in ammonia synthesis of Li-N2 battery; Among them, The battery includes a positive electrode loaded with MoS2 catalyst, and the MoS2 is one or a mixture of two or more of 1T-MoS2, 2H-MoS2, and MP-MoS2; the MP-MoS2 is MoS2 containing a mixed phase of 2H and 1T.

2. The application according to claim 1, wherein MoS2 can be prepared by a preparation method including the following steps: 1), Mix a molybdenum source, a sulfur source, and a solvent to obtain a mixture; wherein, the solvent contains an organic solvent. 2), Heat the mixture obtained in step 1) to carry out a solvothermal synthesis reaction. 3), Centrifuge, wash, and dry the precipitate obtained in step 2) to obtain MP-MoS2 or 1T-MoS2.

3. The application according to claim 2, wherein The solvent contains an organic solvent and water.

4. The application according to claim 2, wherein The organic solvent contains N,N-dimethylformamide.

5. The application according to claim 2, wherein, In step 2), the reaction temperature of the solvothermal synthesis is 180°C - 200°C.

6. The application according to claim 2, wherein, The preparation method further includes: 4), Roast the MoS2 obtained in step 3) in an Ar environment to obtain 2H-MoS2.

7. The application according to claim 6, wherein, In step 4), the roasting temperature is 350°C - 450°C.

8. A Li-N2 battery ammonia synthesis system, wherein, The Li-N2 battery ammonia synthesis system includes a battery and an ammonia synthesis device; wherein, the battery includes a positive electrode loaded with MoS2 catalyst. Wherein, the MoS2 is one or a mixture of two or more of 1T-MoS2, 2H-MoS2, and MP-MoS2; the MP-MoS2 is MoS2 containing a mixed phase of 2H and 1T. Wherein, the ammonia synthesis device includes a device bottom plate, a battery fixing plate, and a device top plate which are detachably connected in sequence; between the device bottom plate and the battery fixing plate, a positive electrode flow channel plate is clamped, and between the battery fixing plate and the device top plate, a negative electrode conductive plate is clamped; the battery fixing plate is provided with a battery placement through hole for placing the battery; the positive electrode flow channel plate is provided with a through hole corresponding to the position of the battery placement through hole of the battery fixing plate; the device bottom plate is provided with an air inlet channel and an air outlet channel communicating with the outside, and on the surface of the device bottom plate in contact with the positive electrode flow channel plate, a gas flow channel is provided corresponding to the through hole of the positive electrode flow channel plate, and the gas flow channel communicates with the air inlet channel and the air outlet channel, and the gas in the gas flow channel can contact the positive electrode flow channel plate.

9. The system according to claim 8, wherein, MoS2 can be prepared by a preparation method including the following steps: 1), Mix a molybdenum source, a sulfur source, and a solvent to obtain a mixture; wherein, the solvent contains an organic solvent. 2), Heat the mixture obtained in step 1) to carry out a solvothermal synthesis reaction. 3), Centrifuge, wash, and dry the precipitate obtained in step 2) to obtain MP-MoS2 or 1T-MoS2.

10. The system according to claim 9, wherein, The solvent contains an organic solvent and water.

11. The system according to claim 9, wherein, The organic solvent contains N,N-dimethylformamide.

12. The system according to claim 9, wherein, In step 2), the reaction temperature of the solvothermal synthesis is 180°C - 200°C.

13. The system according to claim 9, wherein The preparation method further includes: 4), Roast the MoS2 obtained in step 3) in an Ar environment to obtain 2H-MoS2.

14. The system according to claim 13, wherein In step 4), the roasting temperature is 350°C - 450°C.

15. The system according to claim 8, wherein, The positive electrode loaded with the MoS2 catalyst is an air electrode loaded with the MoS2 catalyst.

16. The system according to claim 15, wherein, The positive electrode loaded with the MoS2 catalyst includes a foam iron electrode loaded with the MoS2 catalyst and / or a foam nickel electrode loaded with the MoS2 catalyst.

17. The system according to claim 8, wherein the battery includes a Li negative electrode; the battery uses a tetraethylene glycol dimethyl ether solution of lithium bis(trifluoromethanesulfonyl)imide as the electrolyte; the battery includes a glass fiber separator GF / D.

18. The system according to claim 8 or 17, wherein the battery includes a negative electrode case, a spring piece, a steel gasket, a negative electrode, a glass fiber separator GF / D infiltrated with the electrolyte, a positive electrode loaded with the MoS2 catalyst, and a perforated positive electrode case arranged in sequence; The battery placed in the battery placement through hole of the battery fixing plate can be connected to the negative electrode conductive plate and the positive electrode flow channel plate of the ammonia synthesis device through springs, wherein the perforated positive electrode case of the battery is connected to the positive electrode flow channel plate of the ammonia synthesis device through a spring, and the negative electrode case of the battery is connected to the negative electrode conductive plate of the ammonia synthesis device through a spring.

19. The system according to claim 18, wherein, The negative electrode is selected as a lithium sheet.

20. A method for synthesizing ammonia by a Li-N2 battery, which uses the Li-N2 battery ammonia synthesis system described in any one of claims 8-19, and the method includes: During the discharging process, nitrogen gas is introduced. Under the action of active sites on the edges and basal planes of MoS2, nitrogen molecules are adsorbed on the surface of the positive electrode. The negative electrode Li loses electrons to obtain Li + , Li + passes through the separator from the negative electrode to the surface of the positive electrode and reacts with the nitrogen molecules adsorbed on the surface of the positive electrode to form lithium nitride, so that lithium and nitrogen react to generate Li3N; after the discharging is completed, moist argon gas is introduced. The water in the moist argon gas hydrolyzes the Li3N generated during the discharging process to generate LiOH and NH3, and the generated NH3 is discharged with the introduced argon gas.

21. The method according to claim 20, wherein, The method for synthesizing ammonia by a Li-N2 battery further includes: collecting NH3 discharged with the introduced argon gas with water.

22. The method according to claim 20, wherein, The method for synthesizing ammonia in the Li-N2 battery further includes: during the charging process, LiOH generated on the surface of the positive electrode loses electrons to generate Li + and O2, and Li + reaches the negative electrode interface through the separator from the positive electrode to obtain electrons and generate Li, completing the recycling of lithium; during the process, the high intrinsic conductivity of MoS2 loaded on the positive electrode helps the faster transfer of Li + and electrons.

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