Carbon-nitrogen coated AB2 type hydrogen storage alloy and preparation method thereof

Abstract

The invention relates to the technical field of hydrogen storage, and discloses a carbon and nitrogen coated AB2 type hydrogen storage alloy and a preparation method thereof.The preparation method comprises the following steps that methane, ammonia gas and hydrogen are used for conducting chemical vapor deposition on the AB2 type hydrogen storage alloy, and the carbon and nitrogen coated AB2 type hydrogen storage alloy is obtained; the flow ratio of the methane to the ammonia gas to the hydrogen is 1: (1-3): (10-20). According to the method, a carbon-nitrogen coating layer is formed on the surface of the AB2 type hydrogen storage alloy by controlling the flow ratio of methane to ammonia gas to hydrogen, so that the generation of oxides on the surface of the AB2 type hydrogen storage alloy is effectively avoided, active sites originally existing on the surface of the AB2 type hydrogen storage alloy cannot be blocked, and the activation time of the AB2 type hydrogen storage alloy is shortened.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrogen storage, and more particularly to a carbon-nitrogen-coated AB2-type hydrogen storage alloy and a preparation method thereof. BACKGROUND

[0002] AB2-type hydrogen storage alloy is a hydrogen storage material composed of two main metal elements, A site usually contains Ti, Zr and other metals, and B site contains Cr, Mn, Fe, Ni and other transition metals. AB2-type hydrogen storage alloy usually has C14 Laves phase crystal structure, so it has good stability and reversibility in the process of hydrogen absorption and hydrogen release. In addition, the hydrogen storage capacity of AB2-type hydrogen storage alloy can be as high as 2.0wt%, and it also has fast hydrogen absorption and release rate and strong cycle stability. Therefore, AB2-type hydrogen storage alloy is widely used in hydrogen fuel cell, vehicle-mounted hydrogen storage material and other fields.

[0003] Because the activity of AB2-type hydrogen storage alloy is strong, it is easy to be oxidized in air, which leads to a significant decrease in hydrogen storage capacity and cycle life, especially leading to a too long activation time of AB2-type hydrogen storage alloy.

[0004] Therefore, it is of great significance to develop a preparation method of carbon-nitrogen-coated AB2-type hydrogen storage alloy to shorten the activation time of AB2-type hydrogen storage alloy. SUMMARY

[0005] The present application aims to solve the problem of too long activation time of AB2-type hydrogen storage alloy in the prior art, and provides a carbon-nitrogen-coated AB2-type hydrogen storage alloy and a preparation method thereof.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] In a first aspect, the present application provides a preparation method of a carbon-nitrogen-coated AB2-type hydrogen storage alloy, comprising the following steps:

[0008] Chemical vapor deposition (CVD) of AB2-type hydrogen storage alloy is carried out by using methane, ammonia and hydrogen, to obtain a carbon-nitrogen-coated AB2-type hydrogen storage alloy;

[0009] The flow ratio of the methane, ammonia and hydrogen is 1:(1-3):(10-20).

[0010] The application forms a carbon-nitrogen coating layer on the surface of the AB2 type hydrogen storage alloy by controlling the flow ratio of methane, ammonia and hydrogen, which can effectively prevent the oxidation reaction of the AB2 type hydrogen storage alloy surface with oxygen, thereby effectively avoiding the formation of oxides on the surface of the AB2 type hydrogen storage alloy, and is beneficial to shorten the activation time of the AB2 type hydrogen storage alloy; at the same time, the specific flow ratio of methane, ammonia and hydrogen forms a carbon-nitrogen coating layer with porosity and / or sp 2 -sp 3 The hybrid mixed structure allows hydrogen atoms to diffuse through the interstitial space of the lattice during the hydrogen absorption and desorption process, does not affect the adsorption / dissociation of hydrogen, and does not block the active sites originally present on the surface of the AB2 type hydrogen storage alloy, thereby facilitating the shortening of the activation time of the AB2 type hydrogen storage alloy.

[0011] Preferably, the flow ratio of methane, ammonia and hydrogen is one of 1:1:10, 1:1:11, 1:1:12, 1:1:13, 1:1:14, 1:1:15, 1:1:16, 1:1:17, 1:1:18, 1:1:19, 1:1:20, 1:2:11, 1:2:12, 1:2:13, 1:2:14, 1:2:15, 1:2:16, 1:2:17, 1:2:18, 1:2:19, 1:2:20, 1:3:11, 1:3:12, 1:3:13, 1:3:14, 1:3:15, 1:3:16, 1:3:17, 1:3:18, 1:3:19, 1:3:20 or a range value between any two thereof.

[0012] More preferably, the flow ratio of methane, ammonia and hydrogen is 1:(2-3):(10-15).

[0013] Preferably, the flow of methane is one of 5sccm, 6sccm, 7sccm, 8sccm, 9sccm, 10sccm, 11sccm, 12sccm, 13sccm, 14sccm, 15sccm or a range value between any two thereof.

[0014] More preferably, the flow of methane is 5-15sccm.

[0015] Preferably, the temperature of the chemical vapor deposition is one of 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃ or a range value between any two thereof.

[0016] Preferably, the temperature of the chemical vapor deposition is 450-850℃.

[0017] More preferably, the temperature of the chemical vapor deposition is 600-800℃.

[0018] The present application can further optimize the structure of the carbon-nitrogen coating layer formed on the surface of the AB2-type hydrogen storage alloy by further controlling the temperature of the chemical vapor deposition, thereby further shortening the activation time of the AB2-type hydrogen storage alloy.

[0019] Preferably, the time of the chemical vapor deposition is 1-3h, and specifically 1-2h.

[0020] Preferably, the carrier gas of the chemical vapor deposition is argon.

[0021] Preferably, the main phase of the AB2-type hydrogen storage alloy is C14 Laves phase.

[0022] Preferably, the chemical formula of the AB2-type hydrogen storage alloy is AB2, wherein A is at least one of Ti and Zr, and B is at least one of Cr, Mn, Fe and Ni.

[0023] More preferably, the AB2-type hydrogen storage alloy is at least one of TiCrMn, TiZrCrMn, TiMn, TiCrNi and TiFeNi.

[0024] Preferably, the AB2-type hydrogen storage alloy needs to be subjected to at least one of pickling and ball milling before the chemical vapor deposition (CVD).

[0025] In the present application, the purpose of pickling and / or ball milling of the AB2-type hydrogen storage alloy before the chemical vapor deposition (CVD) is to remove the oxides on the surface of the AB2-type hydrogen storage alloy.

[0026] More preferably, the acid used in the pickling is at least one of sulfuric acid, hydrochloric acid and nitric acid.

[0027] More preferably, the concentration of the acid used in the pickling is 1-2mol / L.

[0028] More preferably, the pickling is performed by ultrasonic cleaning.

[0029] More preferably, the time of the pickling is 3-15min, and preferably 5-15min.

[0030] More preferably, the rotation speed of the ball milling is 250-350rpm.

[0031] More preferably, the time of the ball milling is 0.5-3h, and specifically 1.5-3h.

[0032] Preferably, the preparation method of the AB2-type hydrogen storage alloy is as follows:

[0033] Mixing metals according to the element proportion of the AB2 type hydrogen storage alloy chemical general formula, vacuum arc melting is carried out.

[0034] More preferably, the current of the vacuum arc melting is 90-110 A.

[0035] More preferably, the number of times of the vacuum arc melting is 1-5 times, and the time of each vacuum arc melting is 40-60 s.

[0036] More preferably, the number of times of the vacuum arc melting is one of 1 time, 2 times, 3 times, 4 times, 5 times or a range value between any two.

[0037] More preferably, the vacuum degree of the vacuum arc melting is 1x10 -3 Pa-2x10 -3 Pa.

[0038] More preferably, the vacuum arc melting is carried out under a protective atmosphere.

[0039] More preferably, the protective atmosphere is at least one of argon, nitrogen and helium.

[0040] In the second aspect, the application provides a carbon-nitrogen coated AB2 type hydrogen storage alloy prepared by the preparation method in the first aspect.

[0041] Compared with the prior art, the application has the following beneficial effects:

[0042] The application forms a carbon-nitrogen coating layer on the surface of the AB2 type hydrogen storage alloy by controlling the flow ratio of methane, ammonia and hydrogen, which can effectively prevent the oxidation reaction of the AB2 type hydrogen storage alloy surface with oxygen, thereby effectively avoiding the generation of oxides on the surface of the AB2 type hydrogen storage alloy, and being conducive to shortening the activation time of the AB2 type hydrogen storage alloy; at the same time, the porosity and / or sp 2 -sp 3 Hybrid mixed structure allows hydrogen atoms to diffuse through the interstitial space of the lattice during hydrogen absorption and desorption, does not affect the adsorption / dissociation of hydrogen, and does not block the active sites originally existing on the surface of the AB2 type hydrogen storage alloy, thereby being conducive to shortening the activation time of the AB2 type hydrogen storage alloy. DETAILED DESCRIPTION

[0043] In order to better illustrate the purpose, technical scheme and advantages of the application, the application will be further described below in combination with specific embodiments.

[0044] The experimental methods in the following examples not otherwise specified are generally in accordance with conventional conditions in the art or in accordance with the conditions recommended by the manufacturer; the raw materials, reagents, etc. used, if not otherwise specified, are all commercially available raw materials and reagents.

[0045] Example 1

[0046] The present embodiment provides a carbon-nitrogen-coated AB2-type hydrogen storage alloy, and a preparation method thereof, which comprises the following steps:

[0047] S1. The metals Ti, Cr and Mn are mixed according to the element ratio of the general chemical formula of the AB2-type hydrogen storage alloy Ti1Cr1Mn1, and vacuum arc melting is continuously carried out for 4 times under the conditions of a protective atmosphere of argon and a vacuum degree of 2x10 -3 Pa, including: first vacuum arc melting at a current of 90 A for 60 s, second vacuum arc melting at a current of 90 A for 60 s, third vacuum arc melting at a current of 100 A for 60 s, and fourth vacuum arc melting at a current of 110 A for 60 s; after the 4 times of vacuum arc melting, a block-shaped AB2-type hydrogen storage alloy (TiCrMn) is obtained;

[0048] S2. The block-shaped AB2-type hydrogen storage alloy prepared in step S1 is placed in a 1 mol / L aqueous hydrochloric acid solution for ultrasonic cleaning for 5 min to complete pickling; then, the block-shaped AB2-type hydrogen storage alloy is first washed with deionized water until the washing agent after washing is neutral (detected by PH paper), then washed with anhydrous ethanol for 3 times, and vacuum dried at 60℃ for 2h in a vacuum box; the dried block-shaped AB2-type hydrogen storage alloy is placed in a ball milling tank with grinding balls at a mass ratio of 1:20, and ball milling is carried out at a speed of 300 rpm for 2h;

[0049] S3. The AB2-type hydrogen storage alloy treated in step S2 is placed in a CVD reaction furnace, and a gas flow control system is started; argon gas (100 sccm) is used as a carrier gas, 12 sccm of methane (CH4), 24 sccm of ammonia (NH3) and 180 sccm of hydrogen (H2) are introduced, and chemical vapor deposition is carried out at 600℃ for 2h to obtain a carbon-nitrogen-coated AB2-type hydrogen storage alloy;

[0050] In step S3, the flow ratio of the methane, ammonia and hydrogen is 1:2:15.

[0051] The main phase of the AB2-type hydrogen storage alloy (TiCrMn) is C14 Laves phase.

[0052] Examples 2-5 and Comparative Examples 1-5

[0053] Examples 2-5 and Comparative Examples 1-5 provide different carbon-nitrogen coated AB2-type hydrogen storage alloys, which are different from Example 1 in that the flow ratio of methane, ammonia and hydrogen is different, and the rest are consistent with Example 1, as shown in the following table:

[0054] Table 1 Flow ratio of methane, ammonia and hydrogen in Examples 1-5 and Comparative Examples 1-5

[0055]

[0056] Examples 6-8

[0057] Examples 6-8 provide different carbon-nitrogen coated AB2-type hydrogen storage alloys, which are different from Example 1 in that the temperature of chemical vapor deposition in step S3 is different, and the rest are consistent with Example 1, as shown in the following table:

[0058] Table 2 Temperature of chemical vapor deposition in Examples 1, 6-8

[0059] Temperature for chemical vapor deposition / °C Example 1 600 Example 6 800 Example 7 450 Example 8 850

[0060] Example 9

[0061] This example provides a carbon-nitrogen coated AB2-type hydrogen storage alloy, which is different from Example 1 in that only 1 vacuum arc melting is performed, and the rest are consistent with Example 1, as follows:

[0062] The method for preparing a carbon-nitrogen coated AB2-type hydrogen storage alloy comprises the following steps:

[0063] S1. According to the element ratio of the chemical formula of the AB2-type hydrogen storage alloy Ti1Cr1Mn1, the metals Ti, Cr and Mn are mixed, and the vacuum arc melting is performed under the conditions of a protective atmosphere of argon, a vacuum degree of 2×10 -3 Pa, a current of 100 A, and a time of 240 s; after 1 vacuum arc melting is completed, a block-shaped AB2-type hydrogen storage alloy is obtained;

[0064] S2. Consistent with Example 1;

[0065] S3. Consistent with Example 1;

[0066] In step S3, the flow ratio of methane, ammonia and hydrogen is 1:2:15;

[0067] The main phase of the AB2-type hydrogen storage alloy (TiCrMn) is C14 Laves phase.

[0068] Example 10

[0069] The embodiment provides a carbon-nitrogen-coated AB2 type hydrogen storage alloy, which is different from that in Embodiment 1 in that the AB2 type hydrogen storage alloy is TiCrNi, and the rest is consistent with Embodiment 1, and the specific implementation is as follows.

[0070] The preparation method of the carbon-nitrogen-coated AB2 type hydrogen storage alloy comprises the following steps:

[0071] S1. The metals Ti, Cr and Ni are mixed according to the element ratio of the chemical general formula Ti1Cr1Ni1 of the AB2 type hydrogen storage alloy, and under the conditions of a protective atmosphere of argon and a vacuum degree of 2*10 -3 Pa, four vacuum arc melting operations are continuously performed, including: the first vacuum arc melting operation is performed under a current of 90 A for 60 s, the second vacuum arc melting operation is performed under a current of 90 A for 60 s, the third vacuum arc melting operation is performed under a current of 100 A for 60 s, and the fourth vacuum arc melting operation is performed under a current of 110 A for 60 s; after the four vacuum arc melting operations are completed, the AB2 type hydrogen storage alloy (TiCrNi) in a block shape is obtained.

[0072] S2. The step is consistent with Embodiment 1.

[0073] S3. The step is consistent with Embodiment 1.

[0074] In step S3, the flow rate ratio of the methane, the ammonia and the hydrogen is 1:2:15.

[0075] The main phase of the AB2 type hydrogen storage alloy (TiCrNi) is a C14 Laves phase.

[0076] Embodiment 11

[0077] The embodiment provides a carbon-nitrogen-coated AB2 type hydrogen storage alloy, which is different from that in Embodiment 1 in that the AB2 type hydrogen storage alloy is TiFeNi, and the rest is consistent with Embodiment 1, and the specific implementation is as follows.

[0078] The preparation method of the carbon-nitrogen-coated AB2 type hydrogen storage alloy comprises the following steps:

[0079] S1. The metals Ti, Fe and Ni are mixed according to the element ratio of the chemical general formula Ti1Fe1Ni1 of the AB2 type hydrogen storage alloy, and under the conditions of a protective atmosphere of argon and a vacuum degree of 2*10 -3 Pa, four vacuum arc melting operations are continuously performed, including: the first vacuum arc melting operation is performed under a current of 90 A for 60 s, the second vacuum arc melting operation is performed under a current of 90 A for 60 s, the third vacuum arc melting operation is performed under a current of 100 A for 60 s, and the fourth vacuum arc melting operation is performed under a current of 110 A for 60 s; after the four vacuum arc melting operations are completed, the AB2 type hydrogen storage alloy (TiFeNi) in a block shape is obtained.

[0080] S2. The same as example 1;

[0081] S3. The same as example 1;

[0082] In step S3, the flow ratio of the methane, ammonia and hydrogen is 1:2:15;

[0083] The main phase of the AB2-type hydrogen storage alloy (TiFeNi) is C14 Laves phase.

[0084] Comparative example 6

[0085] This comparative example provides a carbon-nitrogen coated AB2-type hydrogen storage alloy, which is different from example 1 in that acetylene is used instead of methane, and the rest is the same as example 1.

[0086] Comparative example 7

[0087] This comparative example provides a carbon-nitrogen coated AB2-type hydrogen storage alloy, which is different from example 1 in that nitrogen is used instead of ammonia, and the rest is the same as example 1.

[0088] Comparative example 8

[0089] This comparative example provides a carbon-nitrogen coated AB2-type hydrogen storage alloy, which is different from example 1 in that carbon monoxide is used instead of hydrogen, and the rest is the same as example 1.

[0090] Comparative example 9

[0091] This comparative example provides a carbon-nitrogen coated AB-type hydrogen storage alloy, which is different from example 1 in that AB-type hydrogen storage alloy (TiNi) is used instead of AB2-type hydrogen storage alloy (TiCrMn), and the rest is the same as example 1, as follows:

[0092] The method for preparing the carbon-nitrogen coated AB-type hydrogen storage alloy comprises the following steps:

[0093] S1. According to the element ratio of the general formula of AB-type hydrogen storage alloy Ti1Ni1, the metals Ti and Ni are mixed, and under the condition of protective atmosphere argon and vacuum degree 2×10 -3 Pa, continuous vacuum arc melting is carried out 4 times, including: first vacuum arc melting at 90A current for 60s, second vacuum arc melting at 90A current for 60s, third vacuum arc melting at 100A current for 60s, and fourth vacuum arc melting at 110A current for 60s; After the 4 times of vacuum arc melting, the AB-type hydrogen storage alloy in block shape is obtained;

[0094] S2. The block-shaped AB-type hydrogen storage alloy prepared in step S1 is put into a 1 mol / L dilute hydrochloric acid aqueous solution for ultrasonic cleaning for 5 min to complete pickling; then, the block-shaped AB-type hydrogen storage alloy is first washed with a detergent deionized water until the detergent after washing is neutral (determined by PH paper), then washed with anhydrous ethanol for 3 times, and vacuum dried at 60°C in a vacuum box for 2 h; the dried block-shaped AB-type hydrogen storage alloy and the grinding balls are put into a ball milling tank at a mass ratio of 1:20, and ball milling is carried out at a speed of 300 rpm for 2 h;

[0095] S3. The AB-type hydrogen storage alloy treated in step S2 is put into a CVD reaction furnace, a gas flow control system is started, argon gas (100 sccm) is used as a carrier gas, 12 sccm of methane (CH4), 24 sccm of ammonia (NH3) and 180 sccm of hydrogen (H2) are introduced at 600°C, and chemical vapor deposition is carried out for 2 h to obtain a carbon-nitrogen coated AB-type hydrogen storage alloy;

[0096] In step S3, the flow ratio of the methane, ammonia and hydrogen is 1:2:15.

[0097] Comparative Example 10

[0098] This comparative example provides an AB2-type hydrogen storage alloy, which is an AB2-type hydrogen storage alloy (TiCrMn) treated in step S2 of Example 1.

[0099] Comparative Example 11

[0100] This comparative example provides an AB2-type hydrogen storage alloy, which is a block-shaped AB2-type hydrogen storage alloy (TiCrMn) prepared in step S1 of Example 1.

[0101] Comparative Example 12

[0102] This comparative example provides a carbon nanotube coated AB2-type hydrogen storage alloy, and the preparation method comprises the following steps:

[0103] The AB2-type hydrogen storage alloy (TiCrMn) treated in step S2 of Example 1 is put into a 1 mol / L Co(NO3)2 solution (solvent is water) for 0.5 h of immersion, the AB2-type hydrogen storage alloy is taken out by centrifugation, and then a 0.4 mol / L glucose solution (solvent is water) is added, and transferred to a high-temperature furnace for calcination at 600°C for 3 h under the protection of inert argon gas; during calcination, the glucose undergoes carbonization reaction under the action of the catalyst Co(NO3)2, and the carbon atoms are decomposed and carbon nanotubes are grown on the surface of the AB2-type hydrogen storage alloy, thereby obtaining a carbon nanotube coated AB2-type hydrogen storage alloy;

[0104] The ratio of the mass of the AB2-type hydrogen storage alloy to the volume of the Co(NO3)2solution is 1 g:25 mL, and the ratio of the mass of the AB2-type hydrogen storage alloy to the volume of the glucose solution is 1 g:20 mL.

[0105] Comparative Example 13

[0106] This comparative example provides a TiO2-coated AB2-type hydrogen storage alloy, and a preparation method thereof includes the following steps:

[0107] The AB2-type hydrogen storage alloy (TiCrMn) treated by step S2 of Example 1 is added into a 1 mol / L tetrabutyl titanate ethanol solution, and stirred and dispersed, and then deionized water is added to initiate a hydrolysis reaction to form a TiO2sol, and the sol is centrifuged to separate out a gel, which is dried in an oven at 60°C for 6 h, and then transferred into a tube furnace, and calcined at 500°C for 2 h under the protection of argon to obtain a TiO2-coated AB2-type hydrogen storage alloy.

[0108] The ratio of the mass of the AB2-type hydrogen storage alloy to the volume of the tetrabutyl titanate ethanol solution is 1 g:15 mL, and the ratio of the mass of the AB2-type hydrogen storage alloy to the volume of the deionized water is 1 g:15 mL.

[0109] Performance test

[0110] The hydrogen storage alloys of the examples and comparative examples are subjected to the following performance tests:

[0111] (1) Measurement of activation time:

[0112] 1 g of the hydrogen storage alloy is vacuumized at 1×10 -4 MPa pressure and 473 K temperature, and then heated to 423 K, and then activated at 3 MPa hydrogen pressure and the timing is started, and the pressure data recorded by the automatic PCT test device is observed, and when the pressure no longer changes, the value of the time is recorded, which is the activation time of the hydrogen storage alloy.

[0113] (2) Measurement of cycle capacity retention rate:

[0114] The palladium-plated AB2-type hydrogen storage alloy (about 1.5 g in mass) of each example or comparative example is placed in an automatic PCT test device, and high-purity hydrogen containing 100 ppm of oxygen (volume fraction 99.99% H2+volume fraction 0.01% O2) is used as a gas source, and the hydrogen absorption temperature is 25°C, the hydrogen absorption pressure is 6.0 MPa, the hydrogen desorption temperature is 200°C, the hydrogen absorption time is 15 min, the hydrogen desorption time is 25 min for one hydrogen absorption and desorption cycle, and multiple hydrogen absorption and desorption cycles are repeatedly performed, and the cycle capacity retention rate (%) is calculated according to the following formula:

[0115] Cycle capacity retention rate (%)=(Q100 / Q1)×100%.

[0116] Q100 is the maximum hydrogen absorption amount of the 100th hydrogen absorption and desorption cycle; Q1 is the maximum hydrogen absorption amount of the first hydrogen absorption and desorption cycle.

[0117] (3) -40℃ activation test:

[0118] The palladium-plated AB2-type hydrogen storage alloy of each example or comparative example was crushed and sieved to obtain a test sample with a particle size of 100 mesh. The test sample was vacuumed for 10 min and then placed in an environment at -40℃. The hydrogen absorption kinetics test was directly performed under a high-purity hydrogen atmosphere at 3 MPa, and the hydrogen absorption kinetics curve was recorded. It was observed whether the activated hydrogen absorption amount could reach more than 80% of the theoretical hydrogen absorption amount. If yes, it indicated that the palladium-plated AB2-type hydrogen storage alloy could be directly activated at -40℃.

[0119] The experimental results are shown in the following table:

[0120] Table 3: Performance test results of each example and comparative example

[0121]

[0122]

[0123] As can be seen from Table 3, the carbon-nitrogen-coated AB2-type hydrogen storage alloy prepared by controlling the flow ratio of methane, ammonia and hydrogen has a shorter activation time and a higher cycle capacity retention rate.

[0124] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A method for preparing a carbon-nitrogen coated AB2-type hydrogen storage alloy, characterized in that, Includes the following steps: AB2 hydrogen storage alloy was obtained by chemical vapor deposition of methane, ammonia and hydrogen. The flow rate ratio of methane, ammonia and hydrogen is 1:(1-3):(10-20).

2. The method for preparing the carbon-nitrogen-coated AB2-type hydrogen storage alloy as described in claim 1, characterized in that, The flow rate ratio of methane, ammonia and hydrogen is 1:(2-3):(10-15).

3. The method for preparing the carbon-nitrogen-coated AB2-type hydrogen storage alloy as described in claim 1, characterized in that, The temperature for chemical vapor deposition is 450-850℃.

4. The method for preparing the carbon-nitrogen-coated AB2-type hydrogen storage alloy as described in claim 1, characterized in that, The temperature for chemical vapor deposition is 600-800℃.

5. The method for preparing the carbon-nitrogen-coated AB2-type hydrogen storage alloy as described in claim 1, characterized in that, Includes at least one of the following (1)-(2): (1) The flow rate of the methane is 5-15 sccm; (2) The chemical formula of the AB2 type hydrogen storage alloy is AB2, wherein A is at least one of Ti and Zr, and B is at least one of Cr, Mn, Fe and Ni.

6. The method for preparing the carbon-nitrogen-coated AB2-type hydrogen storage alloy as described in claim 1, characterized in that, Before chemical vapor deposition, the AB2 type hydrogen storage alloy needs to undergo at least one of the following processes: pickling and ball milling.

7. The method for preparing the carbon-nitrogen-coated AB2-type hydrogen storage alloy as described in claim 6, characterized in that, Includes at least one of the following (1)-(4): (1) The acid used for pickling is at least one of sulfuric acid, hydrochloric acid, and nitric acid; (2) The concentration of the acid used in the pickling is 1-2 mol / L; (3) The rotational speed of the ball mill is 250-350 rpm; (4) The ball milling time is 0.5-3h.

8. The method for preparing the carbon-nitrogen-coated AB2-type hydrogen storage alloy as described in claim 1, characterized in that, The preparation method of the AB2 type hydrogen storage alloy is as follows: Metals were mixed according to the elemental ratios of the general chemical formula for AB2 type hydrogen storage alloys and then subjected to vacuum arc melting.

9. The method for preparing the carbon-nitrogen-coated AB2-type hydrogen storage alloy as described in claim 8, characterized in that, Includes at least one of the following (1)-(3): (1) The current of the vacuum arc melting is 90-110A; (2) The number of vacuum arc meltings is 1-5 times, and the time of each vacuum arc melting is 40-60s; (3) The vacuum degree of the vacuum arc melting is 1×10⁻⁶. -3 Pa-2×10 -3 Pa.

10. A carbon-nitrogen coated AB2-type hydrogen storage alloy, characterized in that, It is prepared by any one of the preparation methods described in claims 1-9.

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