Ammonia decomposition catalyst based on lithium intercalation MXene material and preparation method and application thereof

Abstract

The invention discloses an ammonia decomposition catalyst based on a lithium intercalation MXene material as well as a preparation method and application of the ammonia decomposition catalyst, and belongs to the technical field of catalyst materials. The ammonia decomposition catalyst provided by the invention comprises MXene and lithium metal loaded in a layered structure of the MXene, wherein the content of the lithium metal in the ammonia decomposition catalyst is 0.5-2.5 wt%. The prepared ammonia decomposition catalyst is a lithium intercalation MXene material, the surface electron state density of MXene is regulated and controlled through lithium intercalation, the ammonia decomposition reaction energy barrier can be reduced, the exposure degree of active sites is improved, and high catalytic activity and stability are shown at the temperature of 200-550 DEG C. Experiments show that the ammonia conversion rate at 550 DEG C is close to 100%, and the performance is kept stable in continuous reaction for 30 hours. In conclusion, the invention provides a novel catalyst solution for efficient and controllable ammonia decomposition hydrogen production.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst materials, and specifically relates to an ammonia decomposition catalyst based on lithium intercalation MXene material, and a preparation method and application thereof. Background Art

[0002] As an important chemical raw material and energy carrier, ammonia's efficient decomposition to produce hydrogen is crucial for realizing a hydrogen economy. To achieve this, highly active ammonia decomposition catalysts with high stability at relatively low temperatures are required.

[0003] MXene, a novel two-dimensional material, exhibits great potential in catalysis due to its excellent electrical conductivity, rich surface chemical properties, and tunable interlayer structure. However, pure MXene materials have limited catalytic active sites, making them difficult to meet the requirements for efficient ammonia decomposition. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide an ammonia decomposition catalyst based on lithium intercalated MXene material, and its preparation method and application. The catalyst has the advantages of high activity and good stability, and can be used to efficiently catalyze the decomposition of ammonia to produce hydrogen.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] An ammonia decomposition catalyst based on a lithium intercalated MXene material, the ammonia decomposition catalyst comprising MXene and lithium metal supported in the MXene layered structure, wherein the content of lithium metal in the ammonia decomposition catalyst is 0.5-2.5 wt%; the chemical formula of the ammonia decomposition catalyst is Li / M n+1 X n , wherein: M is a transition metal element; X is a carbon element or a nitrogen element; n is 1, 2 or 3; there are some surface termination groups such as -OH, -F, and -O on the surface of the ammonia decomposition catalyst.

[0007] As a further preferred embodiment of the above solution of the present invention, the transition metal element is Ti, V, Cr, Nb or Mo; and X is carbon.

[0008] The present invention also provides a method for preparing the above-mentioned ammonia decomposition catalyst, comprising the following steps:

[0009] S1. The transition metal powder, aluminum powder, and carbon powder were mixed in proportion and subjected to high-energy ball milling using a carbide ball mill and grinding balls. The milled powder was then annealed in a muffle furnace to obtain a MAX phase powder.

[0010] S2. Slowly add the MAX phase powder to the HF solution and place it in an oil bath electromagnetic stirring reactor. The reaction is allowed to react in the oil bath to complete the etching process. The reaction solution is then placed in a centrifuge tube, added with an appropriate amount of deionized water, and centrifuged. Repeat the centrifugation and washing with deionized water five or six times until the supernatant is nearly neutral. The precipitate is then freeze-dried to obtain MXene.

[0011] S3. Li ions are inserted using an electrochemical method; the prepared MXene powder, conductive agent (conductive carbon black) and binder (polyvinylidene fluoride) are mixed and placed in an NMP (N-methylpyrrolidone) solution for mixing and stirring. After stirring evenly, the mixed slurry is coated on a titanium foil, and then the prepared electrode is dried in a vacuum oven to obtain a titanium foil coated with MXene.

[0012] S4. Electrochemical Li intercalation is performed using a three-electrode system, with MXene-coated titanium foil as the working electrode, standard Hg / Hg2Cl2 as the reference electrode (RE), and titanium foil as the counter electrode; LiOH is used as the ion source, and cyclic voltammetry is used for multiple cycles to insert Li, and finally the conductive agent and binder in the working electrode are removed to obtain the target product. The present invention uses cyclic voltammetry to complete the intercalation of metallic lithium into MXene, which has the advantage of being able to monitor the intercalation process in situ and in real time, and select the optimal intercalation conditions through the potential change in the dynamic range. For the insertion process of Li ions, cyclic voltammetry can monitor the information of the insertion amount changing with the potential. In addition, since cyclic voltammetry is performed at a lower current density, the risk of crystallization or destruction of the electrode structure can be avoided, so that the product has good structural stability and performance.

[0013] As a further preferred embodiment of the above-mentioned solution of the present invention, in step S1, the ball-to-material ratio of the ball milling process is 10:1-20:1; the rotation speed is 300-600 rpm, and the duration is 10-50 hours.

[0014] and / or, in step S1, the annealing temperature is 600-1000° C.;

[0015] As a further preferred embodiment of the above solution of the present invention, in step S2, the concentration of the HF solution is 30-50%;

[0016] and / or, in step S2, the temperature of the oil bath is 10-30° C., and the time is 8-24 hours;

[0017] And / or, in step S2, the centrifugal speed is 3000-5000 r / min, and the duration is 5-10 min;

[0018] and / or, in step S3, the molar ratio of MXene:conductive carbon black:polyvinylidene fluoride (PVDF) in the mixed slurry is 3-7:1-3:1-3;

[0019] And / or, in step S3, the area of ​​the titanium foil is 1-3 cm 2 , the mass density of each electrode is 1-2 mg / cm 2 ;

[0020] And / or, in step S3, the temperature of the vacuum oven is 60-80°C and the time is 8-12 hours;

[0021] and / or, in step S4, the concentration of the LiOH solution is 0.2-0.4 M;

[0022] And / or, in step S4, the scan rate of the cyclic voltammetry is 1-10 mV s -1 ; The number of scans is 1-10 times.

[0023] The present invention also provides a method for producing hydrogen by decomposing ammonia, which comprises the following steps: loading the ammonia decomposition catalyst as described above or the ammonia decomposition catalyst prepared by the preparation method as described above into a quartz tube of an ammonia decomposition hydrogen production reaction device, and performing an ammonia decomposition reaction in a pure ammonia atmosphere to obtain hydrogen and nitrogen.

[0024] As a further preferred embodiment of the above embodiment of the present invention, the ammonia decomposition catalyst is in powder or granular form;

[0025] And / or, the temperature of the ammonia decomposition reaction is 200-550°C, the space velocity is 6000-36000h -1 .

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The ammonia decomposition catalyst prepared by the present invention is a lithium intercalated MXene material. By regulating the surface electronic state density of MXene through lithium intercalation, the energy barrier of the ammonia decomposition reaction (such as NH bond rupture and N≡N activation) can be reduced, and the reaction kinetics can be promoted; at the same time, the layered structure of MXene is further peeled off after lithium intercalation, exposing abundant edge active sites, effectively improving the NH3 adsorption and decomposition efficiency. The present invention uses metallic lithium to intercalate MXene because lithium has a smaller ionic radius and higher activity. Its special chemical properties make the intercalated MXene have unique advantages in regulating the electronic state density and interlayer structure, thereby significantly reducing the energy barrier of the ammonia decomposition reaction. And Na + , K +Other cations, such as MXene, cannot achieve similar structural optimization effects due to their larger ionic radius and lower reactivity. By adjusting the lithium intercalation amount or the elemental composition of the MXene, the requirements of different industrial scenarios can be precisely adapted. In particular, the lithium intercalation amount in the present invention is controlled to be 0.5-2.5wt% of the catalyst mass. If the lithium intercalation amount is too low, the modification effect will be insignificant. If the lithium intercalation amount is too high, it will destroy the interlayer structure of the MXene, causing the layers to pile up and cover the active sites, thereby reducing the catalytic reaction activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 XRD patterns of multilayer Ti3C2 prepared in Example 2 of the present invention before and after Li intercalation;

[0029] Figure 2 This is a scanning electron microscope photograph of the multilayer Ti3C2 prepared in Example 2 of the present invention;

[0030] Figure 3 This is a transmission electron microscope photograph of the multilayer Ti3C2 prepared in Example 2 of the present invention;

[0031] Figure 4 Activity diagrams of the ammonia decomposition hydrogen production catalysts prepared in Examples 1-2 and Comparative Examples 1-5 under different temperatures for thermal catalytic ammonia decomposition;

[0032] Figure 5 This is a graph showing the long-term stability test of the ammonia decomposition hydrogen production catalyst prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0033] To facilitate understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The reagents used in the present invention are all commercially available products and are commercially available. The Li content in the products prepared in the following examples and comparative examples was measured using ICP characterization technology.

[0035] Example 1

[0036] This embodiment provides a Li / Ti3C2 ammonia decomposition catalyst prepared by an electrochemical Li intercalation method. The preparation method of the ammonia decomposition hydrogen production catalyst of this embodiment includes the following steps:

[0037] S1. Ti powder, Al powder, and carbon powder were mixed in a molar ratio of 3:1:2. The mixture was subjected to high-energy ball milling using a cemented carbide ball mill with grinding balls at a ball-to-material ratio of 20:1 and a rotation speed of 400 rpm for 24 hours. The milled powder was then annealed at 800°C in a muffle furnace to obtain Ti3AlC2.

[0038] S2. Disperse the Ti3AlC2 obtained in step S1 in a 30% HF solution and place in an oil bath electromagnetic stirring reactor. React at 30°C for 16 hours. Then, place the reaction solution in a centrifuge tube, add an appropriate amount of deionized water, and centrifuge at 4500 rpm for 10 minutes. Repeat the centrifugation and washing with deionized water five or six times until the supernatant is nearly neutral. The precipitate is freeze-dried to obtain multilayer Ti3C2.

[0039] S3. Disperse Ti3C2, conductive carbon black, and PVDF in NMP at a molar ratio of 3:2:2. Stir thoroughly and apply the slurry evenly on a 1*2cm titanium foil. The mass density is 1mg / cm 2 ; Place the coated titanium foil in a vacuum oven and dry it at 70°C for 12 hours to obtain a titanium foil coated with Ti3C2.

[0040] S4. Electrochemical Li intercalation was performed using a three-electrode system with Ti3C2-coated titanium foil as the working electrode, standard Hg / Hg2Cl2 as the reference electrode (RE), and titanium foil as the counter electrode. 0.2 M LiOH was used as the ion source, and the scan rate was set to 10 s. -1 Cyclic voltammetry was performed for 8 cycles to insert 0.57 wt% Li. The intercalated catalyst was calcined at 450 °C for 2 h, then washed with deionized water to neutrality and dried to remove PVDF and conductive carbon black to obtain a 0.57 wt% Li / Ti3C2 ammonia decomposition catalyst.

[0041] Example 2

[0042] This embodiment provides a Li / Ti3C2 ammonia decomposition catalyst prepared by an electrochemical Li intercalation method. The preparation method of the ammonia decomposition hydrogen production catalyst of this embodiment includes the following steps:

[0043] S1. Ti powder, Al powder, and carbon powder were mixed in a molar ratio of 3:1:2. The mixture was subjected to high-energy ball milling using a cemented carbide ball mill with grinding balls at a ball-to-material ratio of 10:1 and a rotation speed of 500 rpm for 48 hours. The milled powder was then annealed at 800°C in a muffle furnace to obtain Ti3AlC2.

[0044] S2. Disperse the Ti3AlC2 obtained in step S1 in a 40% HF solution and place in an oil bath electromagnetic stirring reactor. React at 25°C for 24 hours. Then, place the reaction solution in a centrifuge tube, add an appropriate amount of deionized water, and centrifuge at 5000 rpm for 8 minutes. Repeat the centrifugation and washing with deionized water five or six times until the supernatant is nearly neutral. The precipitate is freeze-dried to obtain multilayer Ti3C2.

[0045] S3. Disperse Ti3C2, conductive carbon black, and PVDF in NMP at a molar ratio of 3:1:2. Stir thoroughly and apply the slurry evenly on a 1*2cm titanium foil. The mass density of the electrode is 2mg / cm 2 ; The coated titanium foil was placed in a vacuum oven and dried at 70°C for 16 hours to obtain a titanium foil coated with Ti3C2.

[0046] S4. Electrochemical Li intercalation was performed using a three-electrode system with Ti3C2-coated titanium foil as the working electrode, standard Hg / Hg2Cl2 as the reference electrode (RE), and titanium foil as the counter electrode. 0.4 M LiOH was used as the ion source, and the scan rate was set to 1 s. -1 Cyclic voltammetry was performed for 5 cycles to insert 1.9 wt% Li. The intercalated catalyst was calcined at 450 °C for 2 h and then washed with deionized water to neutrality to remove PVDF and conductive carbon black. Finally, a 1.9 wt% Li / Ti3C2 ammonia decomposition catalyst was obtained after drying.

[0047] Figure 1 The MXene support Ti3C2 prepared in this example and the ammonia decomposition hydrogen production catalyst 0.57wt% Li / Ti3C2 were characterized by XRD (XRD, Cu-Kα, ) showed a distinct TiC phase, corresponding to the standard card (PDF#32-1383). However, due to the low amount of Li ion insertion, the corresponding Li peak did not appear in the spectrum.

[0048] Figure 2 This is a scanning electron microscope photograph of the Ti3C2 support prepared in Example 2, obtained by scanning electron microscope characterization. Figure 3 This is a transmission electron microscope photograph of the multilayer Ti3C2 prepared in Example 2 of the present invention. It can be observed from the figure that Ti3C2 has a classic accordion structure, and the distance between layers provides sufficient space for the insertion of Li ions.

[0049] Comparative Example 1

[0050] This embodiment provides a Li / Nb2C ammonia decomposition catalyst prepared by an electrochemical Li intercalation method. The preparation method of the ammonia decomposition hydrogen production catalyst of this embodiment includes the following steps:

[0051] S1. Nb powder, Al powder, and carbon powder were mixed in a molar ratio of 2:1:1. The mixture was subjected to high-energy ball milling using a cemented carbide ball mill with grinding balls at a ball-to-material ratio of 20:1 and a rotation speed of 400 rpm for 24 hours. The milled powder was then annealed at 800°C in a muffle furnace to obtain Nb2AlC.

[0052] S2. Disperse the Nb2AlC obtained in step S1 in a 30% HF solution and place in an oil bath electromagnetic stirring reactor. React at 30°C for 16 hours. Then, place the reaction solution in a centrifuge tube, add an appropriate amount of deionized water, and centrifuge at 4500 rpm for 10 minutes. Repeat the centrifugation and washing with deionized water five or six times until the supernatant is nearly neutral. The precipitate is freeze-dried to obtain multilayer Nb2C.

[0053] S3. Disperse Nb2C, conductive carbon black, and PVDF in a molar ratio of 3:2:2 in NMP. Stir thoroughly and evenly coat the slurry on a 1*2 cm titanium foil. The mass density of the electrode is 1 mg / cm 2 ; The coated titanium foil was placed in a vacuum oven and dried at 70°C for 12 hours to obtain a titanium foil coated with Nb2C.

[0054] S4. Electrochemical Li intercalation was performed using a three-electrode system with Nb2C-coated titanium foil as the working electrode, standard Hg / Hg2Cl2 as the reference electrode (RE), and titanium foil as the counter electrode. 0.2 M LiOH was used as the ion source, and the scan rate was set to 10 s. -1 Cyclic voltammetry was performed for 8 cycles to insert 0.42 wt% Li. The intercalated catalyst was calcined at 450 °C for 2 h, washed with deionized water until neutral, and then dried to remove PVDF and conductive carbon black to obtain a 0.42 wt% Li / Nb2C ammonia decomposition catalyst.

[0055] Comparative Example 2

[0056] This embodiment provides a Li / Nb2C ammonia decomposition catalyst prepared by an electrochemical Li intercalation method. The preparation method of the ammonia decomposition hydrogen production catalyst of this embodiment includes the following steps:

[0057] S1. Nb powder, Al powder, and carbon powder were mixed in a molar ratio of 2:1:1. The mixture was subjected to high-energy ball milling using a cemented carbide ball mill with grinding balls at a ball-to-material ratio of 10:1 and a rotation speed of 500 rpm for 48 hours. The milled powder was then annealed at 800°C in a muffle furnace to obtain Nb2AlC.

[0058] S2. Disperse the Nb2AlC obtained in step S1 in a 40% HF solution and place in an oil bath electromagnetic stirring reactor. React at 25°C for 24 hours. Then, place the reaction solution in a centrifuge tube, add an appropriate amount of deionized water, and centrifuge at 5000 rpm for 8 minutes. Repeat the centrifugation and washing with deionized water five or six times until the supernatant is nearly neutral. The precipitate is freeze-dried to obtain multilayer Nb2C.

[0059] S3. Disperse Nb2C, conductive carbon black, and PVDF in a molar ratio of 3:1:1 in NMP. Stir thoroughly and evenly coat the slurry on a 1*2cm titanium foil. The mass density of the electrode is 2mg / cm 2 ; The coated titanium foil was placed in a vacuum oven and dried at 70°C for 16 hours to obtain a titanium foil coated with Nb2C.

[0060] S4. Electrochemical Li intercalation was performed using a three-electrode system with Nb2C-coated titanium foil as the working electrode, standard Hg / Hg2Cl2 as the reference electrode (RE), and titanium foil as the counter electrode. 0.4 M LiOH was used as the ion source, and the scan rate was set to 1 s. -1 Cyclic voltammetry was performed for five cycles to insert 1.6 wt% Li. The intercalated catalyst was calcined at 450 °C for 2 h, washed with deionized water until neutral, and then dried to remove PVDF and conductive carbon black to obtain a 1.6 wt% Li / Nb2C ammonia decomposition catalyst.

[0061] Comparative Example 3

[0062] Compared with Example 2, steps S1 to S3 in this comparative example are the same as those in Example 2, and the only difference is step S4. The process of S4 in this comparative example is as follows:

[0063] S4. Electrochemical Li intercalation was performed using a three-electrode system with Ti3C2-coated titanium foil as the working electrode, standard Hg / Hg2Cl2 as the reference electrode (RE), and titanium foil as the counter electrode. 0.2 M LiOH was used as the ion source, and the scan rate was set to 10 s. -1 Cyclic voltammetry was performed for 5 cycles to insert 0.17 wt% Li. The intercalated catalyst was calcined at 450 °C for 2 h, then washed with deionized water to neutrality and dried to remove PVDF and conductive carbon black to obtain a 0.17 wt% Li / Ti3C2 ammonia decomposition catalyst.

[0064] Comparative Example 4

[0065] Compared with Example 2, steps S1 to S3 in this comparative example are the same as those in Example 2, and the only difference is step S4. The process of S4 in this comparative example is as follows:

[0066] S4. Electrochemical Li intercalation was performed using a three-electrode system with Ti3C2-coated titanium foil as the working electrode, standard Hg / Hg2Cl2 as the reference electrode (RE), and titanium foil as the counter electrode. 0.5 M LiOH was used as the ion source, and the scan rate was set to 1 s. -1 Cyclic voltammetry was performed for 7 cycles to insert 3.4 wt% Li. The intercalated catalyst was calcined at 450 °C for 2 h, then washed with deionized water to neutrality and dried to remove PVDF and conductive carbon black to obtain a 3.4 wt% Li / Ti3C2 ammonia decomposition catalyst.

[0067] Test Example 1

[0068] The catalytic activity of the products prepared in the above embodiments and comparative examples for catalytic ammonia decomposition to produce hydrogen was tested, wherein the method for producing hydrogen by ammonia decomposition is as follows: 500 mg of ammonia decomposition hydrogen production catalyst was loaded into a quartz reaction tube of an ammonia decomposition fixed bed reactor, the ammonia flow rate was set to 10 mL / min, and the ammonia decomposition reaction was carried out at 300°C, 350°C, 400°C, 450°C, 500°C, and 550°C, respectively. The tail gas was detected and analyzed by a gas chromatograph GC-9790Plus, and the catalytic activity was determined by the conversion rate of ammonia decomposition. The test results are as follows: Figure 4 shown.

[0069] from Figure 4 It can be seen that the activity of the prepared catalyst increases significantly with increasing temperature, and Li intercalation can effectively enhance the ammonia decomposition activity of the MXene material. Specifically, at 550°C, the ammonia decomposition conversion rate of 1.9 wt% Li / Ti3C2 reaches nearly 100%. However, when the Li content in the catalyst is further increased, when the lithium content reaches 3.4 wt% as in Comparative Example 4, the catalytic performance of the resulting catalyst decreases.

[0070] Test Example 2

[0071] The stability of the catalytic activity of the catalyst prepared in Example 2 for hydrogen production by ammonia decomposition was tested by loading 500 mg of the ammonia decomposition catalyst into a quartz reaction tube of an ammonia decomposition fixed-bed reactor, setting the ammonia flow rate to 10 mL / min, and conducting an ammonia decomposition reaction at 500°C for 30 hours. The tail gas was detected and analyzed by a gas chromatograph GC-9790 Plus, and the catalytic activity was determined by the conversion rate of ammonia decomposition. The test results of the ammonia decomposition conversion rate at different times are shown in FIG. Figure 5 shown.

[0072] from Figure 5It can be seen that the ammonia decomposition catalyst prepared in Example 2 maintained almost the same ammonia conversion rate during the long-term ammonia decomposition reaction of 30 hours, indicating that the ammonia decomposition hydrogen production catalyst prepared in this application has good stability.

[0073] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0074] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. An ammonia decomposition catalyst based on lithium intercalated MXene material, characterized by: The ammonia decomposition catalyst comprises MXene and lithium metal supported in the MXene layered structure, wherein the content of lithium metal in the ammonia decomposition catalyst is 0.5-2.5 wt %. The chemical formula of the ammonia decomposition catalyst is Li / M n+1 X n , wherein: M is a transition metal element; X is a carbon element or a nitrogen element; and n is 1, 2 or 3.

2. The ammonia decomposition catalyst according to claim 1, characterized in that: The transition metal element is Ti, V, Cr, Nb or Mo; and X is carbon.

3. A method for preparing the ammonia decomposition catalyst according to claim 1 or 2, characterized in that: The following steps are involved: Preparation of MXene; MXene, a conductive agent, and a binder are added to a solvent and mixed uniformly to obtain a mixed slurry, the mixed slurry is coated on a surface of a titanium foil, and the titanium foil coated with MXene is obtained after drying; Using titanium foil coated with MXene as the working electrode, standard Hg / Hg2Cl2 as the reference electrode, titanium foil as the counter electrode, and LiOH solution as the ion source, cyclic voltammetry was performed for multiple cycles to insert Li into MXene. Finally, the conductive agent and binder in the working electrode were removed to obtain the target product.

4. The method for preparing an ammonia decomposition catalyst according to claim 3, wherein: The method for preparing MXene is as follows: transition metal powder, aluminum powder and carbon powder are mixed in proportion and then ball-milled. The ball-milled material is annealed to obtain MAX phase powder; The MAX phase powder is added to an HF solution for etching, and MXene is obtained through separation, washing, and freeze-drying.

5. The method for preparing an ammonia decomposition catalyst according to claim 4, wherein: The transition metal powder is one of Ti, V, Cr, Nb, and Mo; And / or, the ball-to-material ratio in the ball milling process is 10:1-20:1; the rotation speed is 300-600 rpm, and the duration is 10-50 hours; And / or, the annealing treatment temperature is 600-1000°C.

6. The method for preparing an ammonia decomposition catalyst according to claim 4, wherein: The concentration of the HF solution is 30-50%.

7. The method for preparing an ammonia decomposition catalyst according to claim 3, wherein: The molar ratio of the MXene, the conductive agent, and the binder is (3-7): (1-3): (1-3).

8. The method for preparing an ammonia decomposition catalyst according to claim 3, wherein: The conductive agent is conductive carbon black; And / or, the binder is polyvinylidene fluoride; and / or, the concentration of the LiOH solution is 0.2-0.4 M; And / or, the scan rate of the cyclic voltammetry is 1-10 mV s -1 ; The number of scans is 1-10 times.

9. A method for producing hydrogen by decomposing ammonia, characterized in that: The ammonia decomposition catalyst as claimed in claim 1 or 2 is loaded into an ammonia decomposition hydrogen production reaction device, and an ammonia decomposition reaction is carried out in a pure ammonia atmosphere to obtain hydrogen and nitrogen.

10. The method for producing hydrogen by decomposing ammonia according to claim 9, characterized in that: The temperature of the ammonia decomposition reaction is 200-550°C.

Images