A preparation method and application of a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material

Abstract

The application relates to a preparation method of a catalyst for alkaline water electrolysis hydrogen production, and relates to a preparation method of a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material. The application aims to solve the problems of high cost and low catalytic activity of the existing catalyst for alkaline water electrolysis hydrogen production. The application utilizes the hydrogen bond and electrostatic interaction between the nickel hydroxide nanosheet and the polyacid, and obtains a polyacid-nickel hydroxide nanosheet composite based on the molecular assembly principle. After nitrogenization treatment, the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material is prepared, which has the advantages of close combination between components, uniform distribution, easy regulation of components, stable structure, rich active sites and the like. When the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material is applied as a catalyst for electrocatalytic hydrogen evolution reaction, the current density is 10 mAcm ‑2 Under alkaline conditions, the required overpotential is only 34 mV, which lays a foundation for the design and preparation of electrochemical hydrogen evolution catalysts used under alkaline conditions in the future.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a catalyst for hydrogen production by alkaline electrolysis of water. BACKGROUND

[0002] Hydrogen energy, as a secondary energy source with high energy density and environmental protection, is expected to replace traditional fossil energy. However, at present, hydrogen is mainly obtained by natural gas pyrolysis and coal gasification, accompanied by the release of carbon dioxide by-products, so it is urgent to develop more environmentally friendly and efficient hydrogen production technologies. Alkaline electrolysis of water for hydrogen production has become the most promising green hydrogen production approach. At present, noble metal Pt is the best HER catalyst in performance, but its reserves are scarce and the price is high, which cannot realize large-scale hydrogen production application, so it is necessary to develop abundant, low-cost and efficient non-noble metal catalysts to replace Pt group catalysts, increase the number of active sites and increase the intrinsic activity, promote mass transfer and charge transfer to improve the alkaline hydrogen evolution activity. Metal nitride, especially molybdenum (nickel) nitride, has the characteristics of Pt-like electronic structure, low cost, good electrical conductivity, high catalytic activity and high stability, and has been considered as a very promising hydrogen evolution electrocatalyst, but the catalytic activity is still far from that of the commercial Pt / C catalyst. SUMMARY

[0003] The purpose of the present application is to solve the problems of high cost and low catalytic activity of the existing catalyst for hydrogen production by alkaline electrolysis of water, and to provide a preparation method and application of a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material.

[0004] The present application constructs a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction nanomaterial with close contact, creates more active sites by regulating the interface charge distribution, especially by introducing vanadium with rich valence into the molybdenum nitride lattice to regulate its electronic structure and optimize the adsorption energy of the reaction intermediates, which is expected to obtain an alkaline efficient hydrogen evolution catalyst material; at the same time, the construction of an ultrathin nanosheet with a large specific surface area and structural stability is beneficial to provide more exposed active sites and help mass transfer and charge transfer, and is concerned. The present application proposes to construct an ultrathin sheet layer nanomaterial with close contact of vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction particle assembly, which increases the number of active sites while improving the intrinsic activity, thereby reducing the overpotential and increasing the unit mass electrocatalytic hydrogen production efficiency, which has practical application significance.

[0005] A preparation method of a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material, specifically completed by the following steps:

[0006] I. Dissolve nickel nitrate and urea in a mixed solution of deionized water and ethylene glycol to obtain solution I;

[0007] II. Solution I is transferred to a hydrothermal reactor for hydrothermal reaction, and the suspension obtained after the hydrothermal reaction is centrifuged, washed and dried to obtain nickel hydroxide nanosheets;

[0008] III. The polyacid is dissolved in anhydrous ethanol to obtain solution II;

[0009] IV. The nickel hydroxide nanosheets are dispersed in anhydrous ethanol, and solution II is added under stirring, and the suspension is obtained after stirring for a period of time; the obtained suspension is centrifuged, washed and dried to obtain a polyacid-nickel hydroxide nanosheet composite;

[0010] V. The polyacid-nickel hydroxide nanosheet composite is placed in a tube furnace, and ammonia gas is introduced into the tube furnace for nitriding treatment under an ammonia atmosphere to obtain a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material.

[0011] The vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material is used as a catalyst for alkaline electrolytic water hydrogen production.

[0012] The present application utilizes the hydrogen bond and electrostatic interaction between nickel hydroxide nanosheets and polyacid, and obtains a polyacid-nickel hydroxide nanosheet composite based on the principle of molecular assembly. After nitriding treatment, a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material is prepared. The obtained vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material has the advantages of tight combination between components, uniform distribution, easy control of components, stable structure, and rich active sites. When used as a catalyst for electrocatalytic hydrogen evolution reaction, the current density is 10 mAcm -2 -34 mV under alkaline conditions, which lays a foundation for the design and preparation of electrochemical hydrogen evolution catalysts used under alkaline conditions in the future.

[0013] In summary, the present application also has the following beneficial effects:

[0014] I. The present application can realize controllable synthesis of the composite material by adjusting the material feeding ratio, stirring speed, heat treatment temperature and time, etc.

[0015] II. The present application synthesizes a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material with a two-dimensional nanosheet assembly structure through simple electrostatic adsorption and other intermolecular forces. Compared with traditional preparation methods, this method can controllably obtain vanadium doping in one step, and helps to maintain the integrity of the sheet structure, prevent agglomeration during the formation of nitrides at high temperatures, and has the characteristics of relative simplicity and good repeatability. This method can be applied to large-scale synthesis of the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material.

[0016] Third, the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material prepared by the present application can effectively replace the expensive noble metal Pt catalyst, and has important guiding significance for the design and actual commercial application of the electrocatalytic alkaline water decomposition to produce hydrogen in the future. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is the X-ray powder diffraction pattern of the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material prepared in Example One;

[0018] Figure 2 is the scanning electron microscope image of the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material prepared in Example One;

[0019] Figure 3 is the transmission electron microscope image of the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material prepared in Example One;

[0020] Figure 4 is the linear sweep voltammetry curve of the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material prepared in Example One, the molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material prepared in Example Two, and the Pt / C catalyst. DETAILED DESCRIPTION

[0021] Detailed implementation one: a preparation method of a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material, which is completed according to the following steps:

[0022] I. Dissolve nickel nitrate and urea in a mixed solution of deionized water and ethylene glycol to obtain solution I;

[0023] II. Transfer solution I into a hydrothermal reaction kettle for hydrothermal reaction, and centrifuge, wash and dry the suspension obtained after the hydrothermal reaction to obtain nickel hydroxide nanosheets;

[0024] III. Dissolve the polyacid in anhydrous ethanol to obtain solution II;

[0025] IV. Disperse the nickel hydroxide nanosheets in anhydrous ethanol, and then add solution II under stirring, and stir for a period of time to obtain a suspension; centrifuge, wash and dry the obtained suspension to obtain a polyacid-nickel hydroxide nanosheet composite;

[0026] V. Put the polyacid-nickel hydroxide nanosheet composite into a tube furnace, introduce ammonia gas into the tube furnace, and perform nitriding treatment under the ammonia gas atmosphere to obtain a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material.

[0027] Specific embodiment two: the difference between this embodiment and specific embodiment one is that the mass ratio of urea to nickel nitrate in step one is 1:(1-3); the volume ratio of deionized water to ethylene glycol in the mixed solution of deionized water and ethylene glycol in step one is 1:(0.5-1.5); the mass ratio of nickel nitrate to the mixed solution of deionized water and ethylene glycol in step one is (0.22-0.66 g):(20-60 mL). The other steps are the same as specific embodiment one.

[0028] Specific embodiment three: the difference between this embodiment and one of specific embodiments one or two is that the temperature of the hydrothermal reaction in step two is 140-180℃, and the time of the hydrothermal reaction is 2-8 h. The other steps are the same as specific embodiments one or two.

[0029] Specific embodiment four: the difference between this embodiment and one of specific embodiments one to three is that the polyacid in step three is phosphomolybdovanadic acid, phosphomolybdic acid, ammonium molybdate or silicomolybdic acid. The other steps are the same as specific embodiments one to three.

[0030] Specific embodiment five: the difference between this embodiment and one of specific embodiments one to four is that the mass ratio of the polyacid to anhydrous ethanol in step three is 1:(200-600). The other steps are the same as specific embodiments one to four.

[0031] Specific embodiment six: the difference between this embodiment and one of specific embodiments one to five is that the speed of stirring in step four is 300-600 rpm, and the time of stirring is 6-24 h. The other steps are the same as specific embodiments one to five.

[0032] Specific embodiment seven: the difference between this embodiment and one of specific embodiments one to six is that the mass ratio of the nickel hydroxide nanosheet to anhydrous ethanol in step four is 1:(400-500); the mass ratio of the nickel hydroxide nanosheet to the polyacid in solution II in step four is 5:(1-4). The other steps are the same as specific embodiments one to six.

[0033] Specific embodiment eight: the difference between this embodiment and one of specific embodiments one to seven is that the process of the nitriding treatment in step five is to increase the temperature from room temperature to 400-500℃ at a temperature increasing rate of 1-5℃ / min, and to nitride at 400-500℃ for 2-4 h. The other steps are the same as specific embodiments one to seven.

[0034] Specific embodiment nine: the difference between this embodiment and one of specific embodiments one to eight is that the flow rate of ammonia gas in step five is 10-30 mL / min. The other steps are the same as specific embodiments one to eight.

[0035] Specific implementation ten: the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material is used as a catalyst for alkaline electrolytic water hydrogen production.

[0036] The beneficial effects of the present application are verified by the following examples:

[0037] Example 1: A preparation method of a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material (V-MoN / Ni3N), specifically completed by the following steps:

[0038] I. 0.52 g of nickel nitrate and 0.22 g of urea were dissolved in a mixed solution of 16 mL of deionized water and 24 mL of ethylene glycol to obtain solution I;

[0039] II. Solution I was transferred to a hydrothermal reaction kettle for hydrothermal reaction, and the obtained suspension after hydrothermal reaction was centrifuged, washed with deionized water, and dried to obtain nickel hydroxide nanosheets;

[0040] The temperature of the hydrothermal reaction in step two is 140°C, and the hydrothermal reaction time is 4h;

[0041] III. 0.05 g of polyacid was dissolved in 20 mL of anhydrous ethanol to obtain solution II;

[0042] The polyacid in step three is phosphomolybdovanadic heteropoly acid;

[0043] IV. 0.1 g of nickel hydroxide nanosheets was dispersed in 40 mL of anhydrous ethanol, and then solution II was added under stirring conditions. The stirring speed was 500 rpm, and the stirring time was 12 h. The obtained suspension was obtained by electrostatic adsorption. The obtained suspension was centrifuged, washed with deionized water, and dried to obtain a polyacid-nickel hydroxide nanosheet composite;

[0044] V. The polyacid-nickel hydroxide nanosheet composite was placed in a tube furnace, and ammonia gas was introduced into the tube furnace. Nitriding treatment was carried out under ammonia gas atmosphere to obtain a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material (V-MoN / Ni3N);

[0045] The nitriding treatment process in step V is as follows: the temperature is raised from room temperature to 450°C at a rate of 2°C / min, and the nitriding is carried out at 450°C for 3h;

[0046] The flow rate of ammonia gas in step V is 20 mL / min.

[0047] The preparation method of the phosphomolybdovanadic heteropoly acid in step III of Example 1 is as follows:

[0048] ①, 12.2 g sodium metavanadate is dissolved in 50 mL hot water with temperature of 80 ℃ to obtain sodium metavanadate aqueous solution;

[0049] ②, 3.55 g disodium hydrogen phosphate is dissolved in 50 mL water to obtain disodium hydrogen phosphate aqueous solution;

[0050] ③, the disodium hydrogen phosphate aqueous solution is added to the sodium metavanadate aqueous solution, cooled to room temperature, and then 2.5 mL of 98% concentrated sulfuric acid is added to obtain an orange-red solution;

[0051] ④, 60.5 g sodium molybdate is dissolved in 100 mL water to obtain a sodium molybdate solution; the sodium molybdate solution is added dropwise to the orange-red solution, and then 42.5 mL of 98% concentrated sulfuric acid is added, cooled to room temperature, and then an appropriate amount of diethyl ether is added for extraction, the middle layer is reserved, and finally the fume hood is passed until the diethyl ether is completely volatilized to obtain an orange sample, which is phosphomolybdovanadic heteropoly acid (H5PV2Mo 10 O 40 ).

[0052] Figure 1 is the X-ray powder diffraction pattern of the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material prepared in Example 1;

[0053] As can be seen from Figure 1 , at 36.21°, 49.01°, respectively, belong to the (200), (202) crystal faces of MoN; at 42.11°, belong to the (002) crystal face of Ni3N; at 44.51°, 51.85°, 76.37°, respectively, belong to the (111), (200), (220) crystal faces of Ni.

[0054] Figure 2 is the scanning electron microscope image of the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material prepared in Example 1;

[0055] As can be seen from Figure 2 , the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material is a two-dimensional sheet structure composed of nanosheets with a particle diameter of about 30 nm, and has a porous structure.

[0056] Figure 3 is the transmission electron microscope image of the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material prepared in Example 1;

[0057] As can be seen from Figure 3It can be seen that: the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material is assembled by small particles, and the thin sheet exhibits a rich porous structure. The high-resolution transmission electron microscopy image shows that the crystal face spacing of 0.222 nm is the (200) crystal face of molybdenum nitride, the crystal face spacing of 0.213 nm belongs to the (002) crystal face of nickel nitride, and the crystal face spacing of 0.204 nm belongs to the (111) crystal face of nickel, which proves the successful construction of the multi-phase heterojunction.

[0058] Example two: a preparation method of a molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material (MoN / Ni3N), specifically completed by the following steps:

[0059] I. 0.52g of nickel nitrate and 0.22g of urea were dissolved in a mixed solution of 16mL of deionized water and 24mL of ethylene glycol to obtain solution I;

[0060] II. Solution I was transferred to a hydrothermal reaction kettle for hydrothermal reaction, and the suspension obtained after the hydrothermal reaction was centrifuged, washed with deionized water, and dried to obtain nickel hydroxide nanosheets;

[0061] The temperature of the hydrothermal reaction in step two is 140°C, and the hydrothermal reaction time is 4h;

[0062] III. 0.05g of polyacid was dissolved in 20mL of anhydrous ethanol to obtain solution II;

[0063] The polyacid in step three is phosphomolybdic acid;

[0064] IV. 0.1g of nickel hydroxide nanosheets was dispersed in 40mL of anhydrous ethanol, and then solution II was added under stirring conditions. The stirring speed was 500rpm, and the stirring time was 12h. The suspension was obtained by electrostatic adsorption. The obtained suspension was centrifuged, washed with deionized water, and dried to obtain a polyacid-nickel hydroxide nanosheet composite;

[0065] V. The polyacid-nickel hydroxide nanosheet composite was placed in a tube furnace, and ammonia gas was introduced into the tube furnace to perform nitriding treatment under an ammonia atmosphere to obtain a molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material (MoN / Ni3N);

[0066] The nitriding treatment process in step V is: heating from room temperature to 450°C at a heating rate of 2°C / min, and nitriding at 450°C for 3h;

[0067] The flow rate of ammonia gas in step V is 20mL / min.

[0068] Figure 4The linear sweep voltammetry curves of the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material prepared in Example 1, the molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material prepared in Example 2, and the Pt / C catalyst are shown in FIG. 2. The test process is as follows: 2.5 mg of the catalyst sample to be tested is weighed and dispersed in 0.5 mL of a mixed solution (including 25 μL of a 5% Nafion solution and a water / ethanol volume ratio of 1:1), and ultrasonically dispersed for 1 hour to form a concentration of 5 mg mL -1 A uniform dispersion of the catalyst was evenly dropped onto the nickel foam. After drying, the electrochemical test could be performed. In the electrocatalytic hydrogen evolution test, the carbon rod was used as the counter electrode, the Hg / HgO electrode was used as the reference electrode, the nickel foam coated with the catalyst to be tested was used as the working electrode, and the electrolyte was 1M KOH. The linear cyclic voltammetry scan rate was 5mV s -1 , scanning range -1 V to 0 V. All potentials were calibrated using a reversible hydrogen electrode (RHE).

[0069] from Figure 4 It can be seen that the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material prepared in Example 1 as a catalyst for alkaline electrocatalytic hydrogen evolution has a current density of 10 mA cm -2 The required overpotential is only 34 mV, which is very close to the 29 mV@10 mA cm of commercial Pt / C. -2 The molybdenum nitride-nickel nitride-nickel three-phase heterojunction prepared in Example 2 was -2 The overpotential is 54 mV. The above results show that vanadium doping can effectively improve the catalytic activity of the material. Especially when the current density is greater than 30 mA cm -2 When the catalyst is prepared, the catalytic activity of the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material is significantly better than that of the commercial 20% Pt / C catalyst, indicating that the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material with large specific surface area and stable structure plays an important role in improving the catalytic activity.

Claims

1. A method for preparing a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material, characterized in that The preparation method is specifically completed according to the following steps: I. Dissolving nickel nitrate and urea in a mixed solution of deionized water and ethylene glycol to obtain solution I; II. Transferring solution I into a hydrothermal reaction kettle to perform hydrothermal reaction, and performing centrifugation, washing and drying on the suspension obtained after the hydrothermal reaction to obtain nickel hydroxide nanosheets; III. Dissolving a polyacid in anhydrous ethanol to obtain solution II; The polyacid in step III is phosphomolybdovanadic acid; IV. Dispersing the nickel hydroxide nanosheets in anhydrous ethanol, and then adding solution II under stirring, stirring for a period of time to obtain a suspension; performing centrifugation, washing and drying on the obtained suspension to obtain a polyacid-nickel hydroxide nanosheet composite; V. Placing the polyacid-nickel hydroxide nanosheet composite into a tube furnace, introducing ammonia gas into the tube furnace, and performing nitriding treatment under the ammonia gas atmosphere to obtain a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material.

2. The preparation method of the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material according to claim 1, characterized in that The mass ratio of urea to nickel nitrate in step I is 1:(1-3); the volume ratio of deionized water to ethylene glycol in the mixed solution of deionized water and ethylene glycol in step I is 1:(0.5-1.5); and the mass ratio of nickel nitrate to the mixed solution of deionized water and ethylene glycol in step I is (0.22g-0.66g):(20mL-60mL).

3. The preparation method of the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material according to claim 1, characterized in that The temperature of the hydrothermal reaction in step II is 140-180℃, and the time of the hydrothermal reaction is 2-8h.

4. The preparation method of the vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material according to claim 1, characterized in that The mass ratio of the polyacid to anhydrous ethanol in step III is 1:(200-600).

5. The method for preparing a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material according to claim 1, characterized in that The stirring speed in step IV is 300-600rpm, and the stirring time is 6-24h.

6. The method for preparing a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material according to claim 1, characterized in that The mass ratio of the nickel hydroxide nanosheets to anhydrous ethanol in step IV is 1:(400-500); and the mass ratio of the nickel hydroxide nanosheets to the polyacid in solution II in step IV is 5:(1-4).

7. The method for preparing a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material according to claim 1, characterized in that The nitriding treatment process in step V is: heating from room temperature to 400-500℃ at a heating rate of 1-5℃ / min, and nitriding at 400-500℃ for 2-4h.

8. The method for preparing a vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material according to claim 1, characterized in that The flow rate of the ammonia gas in step V is 10-30mL / min.

9. The vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material prepared by the preparation method according to claim 1, characterized in that The vanadium-doped molybdenum nitride-nickel nitride-nickel three-phase heterojunction composite material is used as a catalyst for alkaline electrolytic water hydrogen production.

Images