A high entropy oxide coating with a core-shell structure and its preparation method and application

Abstract

The present invention relates to a high entropy oxide coating with a core-shell structure, a preparation method and an application thereof, and belongs to the technical field of anode coatings. The preparation method of the present invention comprises the following steps: S1, placing a high entropy alloy powder into a powder feeder, and depositing the high entropy alloy powder on the surface of a substrate by atmospheric plasma spraying technology to obtain a high entropy oxide coating; the high entropy alloy powder is obtained by mixing at least five metal elements and drying; the molar ratio of each metal element in the high entropy alloy powder is equal; S2, closing the powder feeder, keeping other parameters unchanged, spraying and heating the high entropy oxide coating described in S1 to obtain a high entropy oxide coating with a core-shell structure. Due to the high entropy effect of the high entropy oxide and the use of the atmospheric plasma spraying process, the preparation method of the present invention does not require a binder, so that the coating morphology structure is controllable, the structure is more stable, and excellent OER performance is exhibited (overpotential is 316mV, Tafel slope is 46.8mV / dec).

Description

Technical Field

[0001] The present invention belongs to the technical field of anode coatings, and in particular relates to a high-entropy oxide coating with a core-shell structure, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the rapid development of the world economy, energy shortage and environmental pollution have become two major challenges facing mankind. Hydrogen energy has the characteristics of abundant resources, zero carbon emissions, high energy, easy storage and transportation, and is considered to be a new energy source that can replace traditional fossil fuels. Water electrolysis is an effective hydrogen production process. However, in the alkaline water electrolysis process, the anodic oxygen evolution reaction (OER, 4OH - The reaction (→2H2O + O2 + 4e) involves the migration of four electrons, requiring a high overpotential, limiting the overall efficiency of hydrogen production. To date, noble metal oxide catalysts such as RuO2 and IrO2 have been the most widely used in industrial production, but their high cost and scarcity have severely hindered large-scale industrial application. Therefore, the development of anode materials for water electrolysis that are abundant, inexpensive, simple to prepare, and possess excellent catalytic performance is crucial.

[0003] Transition metal-based catalysts exhibit excellent OER performance due to their advantages such as abundant sources, low cost, and adjustable electronic structure. Patent CN108311151 A discloses an oxygen evolution electrocatalyst based on a binary composite material of nickel-iron alloy / nickel-cobalt oxide and its preparation method. An oxygen evolution catalyst of a binary composite material of nickel-iron alloy / nickel-cobalt oxide is obtained by a template method, a heating reflux reaction, and a reduction roasting. Although this method has good oxygen evolution catalytic activity (at 10 mA cm -2 At a current density of , the overpotential is 286 mV), but the preparation method is complex and the conditions are harsh, making it difficult to achieve large-scale preparation.

[0004] High entropy oxides are a new type of oxide system that has just developed in recent years. They are defined as oxides with a single crystal structure obtained by solid-solution of five or more metal or non-metal oxides in equimolar or near-molar ratios. Due to the synergistic effect of various metal and non-metal elements, they usually exhibit application performance superior to traditional metal oxides, especially in energy production and storage and electrocatalytic materials. Patent CN113621988A discloses a high-efficiency oxygen evolution high-entropy amorphous oxide nanocatalyst and its preparation method and application. High-entropy amorphous oxide nanoparticles were prepared by low-temperature liquid-phase reduction and non-equilibrium synthesis strategies. However, the particles obtained by this method have a large particle size and use surfactants, which makes the exposed specific surface area of ​​the synthetic material small and has fewer active sites, which seriously affects its electrocatalytic performance in water splitting. Currently reported synthesis methods of high entropy oxides include spray pyrolysis, sol-gel combustion, solid-phase synthesis, wet chemical method, co-precipitation method, etc. However, the high-entropy oxides obtained by these methods, when used in water electrolysis anodes, usually need to be loaded on the surface of a conductive substrate (such as carbon materials, nickel, stainless steel, etc.). However, as the oxygen evolution reaction proceeds, interfacial debonding is likely to occur, seriously affecting the long-term stability of the electrode.

[0005] Therefore, in view of the problems of complex preparation methods, interface detachment, and poor stability of existing water electrolysis anode materials, it is necessary to use atmospheric plasma spraying technology to prepare a high-entropy oxide water electrolysis anode coating with a core-shell structure. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the problems of complex preparation method, interface shedding and poor stability of electrolytic water anode materials in the prior art.

[0007] To solve the above technical problems, the present invention provides a high entropy oxide coating with a core-shell structure, a preparation method and an application thereof.

[0008] The first object of the present invention is to provide a method for preparing a high entropy oxide coating having a core-shell structure, comprising the following steps:

[0009] S1. placing high entropy alloy powder into a powder feeder and depositing the high entropy alloy powder on the surface of a substrate by atmospheric plasma spraying technology to obtain a high entropy oxide coating; the high entropy alloy powder is obtained by mixing at least five metal elements and drying; the molar ratio of each metal element in the high entropy alloy powder is equal;

[0010] S2. Turn off the powder feeder, keep other parameters unchanged, and spray and heat the high entropy oxide coating described in S1 to obtain a high entropy oxide coating with a core-shell structure.

[0011] In one embodiment of the present invention, in S1, the high entropy alloy powder is selected from at least five of nickel, cobalt, copper, iron, manganese and chromium; and the particle size of the high entropy alloy powder is 15 μm-53 μm.

[0012] In one embodiment of the present invention, in S1, the drying temperature is 75°C-100°C, and the drying time is 10h-15h.

[0013] In one embodiment of the present invention, in S1, the conditions of the atmospheric plasma spraying technology are: spraying power of 30kW-40kW, current of 500A-650A, voltage of 50V-60V, argon flow rate of 40splm-50splm, hydrogen flow rate of 0splm-5splm, powder feeding amount of 15g / min-20g / min, spray gun moving speed of 400mm / s-600mm / s, spraying distance of 100mm-150mm, spraying cycle number of 4-8 times, and air is added during the spraying process. Generally, atmospheric plasma spraying technology uses an inert gas (such as hydrogen) as a working gas, which makes the sprayed material less likely to oxidize. Here, adding air during the spraying process can allow the high entropy alloy powder to contact with air under the action of plasma during spraying, making it easier to oxidize and more likely to obtain a high entropy oxide with a core-shell structure.

[0014] In one embodiment of the present invention, in S1, the material of the substrate is a nickel plate; and the surface of the substrate is sandblasted.

[0015] Furthermore, the sandblasting process uses 120# white corundum sand; the sandblasting pressure is 0.2MPa-0.4MPa, and the sandblasting time is 55s-65s.

[0016] Furthermore, after the sandblasting treatment, the substrate needs to be ultrasonically cleaned with kerosene, acetone or alcohol solution.

[0017] In one embodiment of the present invention, in S1, during the spray heating process, the center temperature of the flame flow is 10,000K-15,000K, and the number of cycles is 5-8. High-entropy alloy powders are relatively resistant to high temperatures and oxidation. Using atmospheric plasma spraying technology, which utilizes a plasma flame with an extremely high flame core temperature for spray heating, the surface high-entropy alloy can be easily oxidized into high-entropy oxides.

[0018] The second object of the present invention is to provide a high entropy oxide coating with a core-shell structure prepared by the method described above.

[0019] The third object of the present invention is to provide an anode, which is prepared from the high entropy oxide coating with a core-shell structure.

[0020] The fourth object of the present invention is to provide an application of the anode in water electrolysis.

[0021] The technical solution of the present invention has the following advantages over the prior art:

[0022] (1) The high-entropy oxide synthesized by the atmospheric plasma spraying method of the present invention has a core-shell structure, wherein the interior is a high-entropy alloy and the surface is a high-entropy oxide. This ensures, on the one hand, that the interior of the coating has excellent conductivity and that the substrate and the coating maintain good electron transport. On the other hand, the surface of the coating has excellent catalytic activity and can expose more catalytic active sites, thereby achieving more excellent electrocatalytic performance.

[0023] (2) The preparation method described in the present invention utilizes an atmospheric plasma spraying process to synthesize a high-entropy oxide coating with a core-shell structure, high mixing uniformity, and a loose and porous structure. This effectively increases the surface area, exposing more active sites. Furthermore, during the spraying process, the high-temperature treatment of the plasma spray gun can achieve a core-shell high-entropy oxide coating without any post-treatment, which is expected to be applied in industrial water electrolysis to produce hydrogen.

[0024] (3) The high entropy oxide in the high entropy oxide coating with a core-shell structure described in the present invention has four typical effects: thermodynamic high entropy effect, structural lattice distortion effect, slow diffusion effect, and cocktail effect. This makes the high entropy oxide have better performance than traditional metal oxides, such as forming a single solid solution phase, generating large lattice distortion, and rich oxygen vacancies, which effectively improves the electrocatalytic activity and stability. The high entropy oxide coating with a core-shell structure described in the present invention has excellent electrolytic water catalytic activity and stability. Oxygen defects are often used to adjust the electronic structure of materials, enrich the active sites of materials, and promote the charge transfer / separation of materials. Since atmospheric plasma spraying has extremely high temperatures, extremely cold and hot typical non-equilibrium processes, and the introduction of reducing gases, oxygen defects can be introduced synchronously during the deposition process. The surface of the high entropy oxide coating has a loose and porous surface structure and a large number of oxygen defects, which gives it more catalytic area and reaction active sites, shortens the mass and electron transmission path, and improves the electrolytic water catalytic activity.

[0025] (4) Due to the high entropy effect of high entropy oxide and the use of atmospheric plasma spraying process, the preparation method described in the present invention does not require a binder, making the coating morphology and structure controllable and more stable, and exhibiting excellent OER performance (overpotential of 316 mV and Tafel slope of 46.8 mV / dec). BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 This is an X-ray diffraction pattern of a high entropy oxide coating with a core-shell structure prepared in Example 3 of the present invention;

[0028] Figure 2 Microscopic morphology of a high-entropy oxide coating with a core-shell structure prepared in Example 3 of the present invention, wherein (a) is a 1000-fold magnified image of the surface, and (b) is a 10,000-fold magnified image of the surface;

[0029] Figure 3 The oxygen evolution linear scanning curve and 10 mA cm -2 Overpotential at current density of

[0030] Figure 4 Tafel slope plots of the coatings prepared in Examples 1-3 of the present invention and Comparative Examples 1-2;

[0031] Figure 5 Graphs showing the double layer capacitance and electrochemical active area of ​​the coatings prepared in Examples 1-3 of the present invention and Comparative Examples 1-2;

[0032] Figure 6 This is a stability test diagram of the high entropy oxide coating with a core-shell structure prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0034] In the present invention, unless otherwise specified, the substrate used in the embodiments of the present invention is a commercial perforated nickel plate with a diameter of 30 mm. The surface of the substrate is sandblasted with 120# white corundum sand. The sandblasting pressure is 0.3 MPa and the sandblasting time is 60 s. After sandblasting, the substrate is ultrasonically cleaned with an alcohol solution for 8 minutes.

[0035] Example 1

[0036] A high entropy oxide coating with a core-shell structure and a preparation method thereof, specifically comprising the following steps:

[0037] S1: Weigh 300 g of NiCoFeMnCr high entropy alloy powder as raw material in an equal molar ratio and place it in a drying oven for drying at 75°C for 12 h.

[0038] Among them, the particle size of NiCoFeMnCr high entropy alloy powder is 15μm-53μm.

[0039] S2: The substrate is clamped between two plates using a fixture, the dried NiCoFeMnCr high-entropy alloy powder is placed in a powder feeder, and a high-entropy oxide coating is deposited on the substrate by atmospheric plasma spraying;

[0040] Among them, the parameters of atmospheric plasma spraying are set as follows: spraying power of 30 kW, current of 520 A, voltage of 57 V, argon flow rate of 40 splm, hydrogen flow rate of 3 splm, powder feeding rate of 18.5 g / min, spray gun speed of 500 mm / s, spray distance of 110 mm, number of spraying times of 5 times, and air is added during the spraying process.

[0041] S3: After the spraying is completed, the powder feeder is turned off, other parameters remain unchanged, and spray heating is directly used to finally obtain a high entropy oxide coating with a core-shell structure;

[0042] The center temperature of the flame flow is about 10000K-15000K, and the number of spraying times is 5 times.

[0043] Example 2

[0044] A high entropy oxide coating with a core-shell structure and a preparation method thereof, specifically comprising the following steps:

[0045] S1: Weigh 300 g of NiCoFeMnCr high entropy alloy powder as raw material in an equal molar ratio and place it in a drying oven for drying at 75°C for 12 h.

[0046] Among them, the particle size of NiCoFeMnCr high entropy alloy powder is 15μm-53μm.

[0047] S2: The substrate is clamped between two plates using a fixture, the dried NiCoFeMnCr high-entropy alloy powder is placed in a powder feeder, and a high-entropy oxide coating is deposited on the substrate by atmospheric plasma spraying;

[0048] Among them, the parameters of atmospheric plasma spraying are set as follows: spraying power of 30 kW, current of 520 A, voltage of 57 V, argon flow rate of 40 splm, hydrogen flow rate of 3 splm, powder feeding rate of 18.5 g / min, spray gun speed of 500 mm / s, spray distance of 150 mm, number of spraying times of 5 times, and air is added during the spraying process.

[0049] S3: After the spraying is completed, the powder feeder is turned off, other parameters remain unchanged, and spray heating is directly used to finally obtain a high entropy oxide coating with a core-shell structure;

[0050] The center temperature of the flame flow is about 10000K-15000K, and the number of spraying times is 5 times.

[0051] Example 3

[0052] A high entropy oxide coating with a core-shell structure and a preparation method thereof, specifically comprising the following steps:

[0053] S1: Weigh 300 g of NiCoFeMnCr high entropy alloy powder as raw material in an equal molar ratio and place it in a drying oven for drying at 75°C for 12 h.

[0054] Among them, the particle size of NiCoFeMnCr high entropy alloy powder is 15μm-53μm.

[0055] S2: The substrate is clamped between two plates using a fixture, the dried NiCoFeMnCr high-entropy alloy powder is placed in a powder feeder, and a high-entropy oxide coating is deposited on the substrate by atmospheric plasma spraying;

[0056] Among them, the parameters of atmospheric plasma spraying are set as follows: spraying power of 30 kW, current of 520 A, voltage of 57 V, argon flow rate of 40 splm, hydrogen flow rate of 3 splm, powder feeding rate of 18.5 g / min, spray gun speed of 500 mm / s, spray distance of 150 mm, number of spraying times of 5 times, and air is added during the spraying process.

[0057] S3: After the spraying is completed, the powder feeder is turned off, other parameters remain unchanged, and spray heating is directly used to finally obtain a (NiCoFeMnCr)3O4 high entropy oxide coating with a core-shell structure;

[0058] The center temperature of the flame flow is about 10000K-15000K, and the number of spraying times is 8 times.

[0059] Comparative Example 1

[0060] The method is basically the same as Example 1, except that no air is added during the spraying process.

[0061] Comparative Example 2

[0062] The method is basically the same as Example 1, with the only difference being that after spraying is completed, the spray gun is no longer used for spray heating.

[0063] Test Example 1

[0064] The (NiCoFeMnCr)3O4 high entropy oxide coating prepared in Example 3 was subjected to X-ray diffraction (XRD) test, and the results were as follows: Figure 1 As shown. Figure 1 As can be seen in the figure, the diffraction peaks at 29.93°, 35.52°, 36.87°, 42.84°, 56.64°, 57.16°, 62.19°, and 66.43° closely match those of MnCr2O4 (PDF#75-1614). The diffraction peaks at 44.46° and 51.85° are attributed to the Ni matrix (PDF#87-0712). The diffraction peak at 74.60° represents the FCC phase (PDF#88-2323). This demonstrates the successful synthesis of a core-shell high-entropy oxide via atmospheric plasma spraying.

[0065] Test Example 2

[0066] The microstructure of the (NiCoFeMnCr)3O4 high entropy oxide coating prepared in Example 3 was characterized. Figure 2 As shown. Figure 2 It can be seen that the surface microstructure of the coating presents a large number of 10μm-30μm particle agglomeration structures, and obtains a loose and porous surface morphology. Such a surface morphology is conducive to increasing the reaction active area, which is conducive to full contact of the reaction medium during the electrocatalytic reaction, and effectively improving the subsequent electrolytic water catalytic activity.

[0067] Test Example 3

[0068] Electrochemical tests were performed using a typical three-electrode system, where the working electrode was a high-entropy oxide coating, the counter electrode was a graphite sheet, the reference electrode was a saturated Hg / HgO, and the test solution was a 1M KOH electrolyte. Linear sweep voltammetry tests were performed using an electrochemical workstation (Coster CS250H) (scan rate was 10 mV.s -1 ) and Tafel slope (Formula 1) and other electrochemical tests. dl The electrochemically active surface area of ​​the prepared samples was evaluated (Formula 2). The test conditions were: potential range 1.05-1.15V vs RHE, scan rates 10mV / s, 20mV / s, 40mV / s, 60mV / s, 80mV / s, 100mV / s. All potentials obtained in the experiment were IR-compensated. The results are shown in Figure 2. Figure 3-5 As shown:

[0069] η=a+b·log|j| Formula (1)

[0070]

[0071] Where a is a constant, b is the Tafel slope, i is the exchange current density, ECSA is the electrochemically active area, C dl is the double layer capacitance, Cs is the specific capacitance.

[0072] Depend on Figure 3 It can be seen that Examples 1-3 and Comparative Examples 1-2 have the same -2 The overpotentials at current densities of 361mV, 347mV, 316mV, 407mV, and 446mV respectively.

[0073] Depend on Figure 4 It can be seen that Examples 1-3 and Comparative Examples 1-2 are 61.4mV / dec, 57.1mV / dec, 46.8mV / dec, 253.2mV / dec, and 260.5mV / dec, respectively. From the test results, it can be seen that the present invention can prepare high-entropy oxide coatings that all show excellent OER performance, wherein Example 3 shows the lowest overpotential and Tafel slope, showing more superior electrochemical performance, indicating that with the increase of spraying distance, and high-temperature heating of the spray gun after spraying, the electrocatalytic performance of the high-entropy oxide coating can be increased. The overpotential and Tafel slope of Comparative Examples 1-2 are higher, indicating that without adding air or heating by the spray gun during the spraying process, the high-entropy oxide coating obtained will be difficult to form a core-shell structure, and less high-entropy oxide will be formed on the coating surface, which will have a certain impact on the subsequent electrocatalytic reaction activity and stability.

[0074] Depend on Figure 5 It can be seen that Example 3 has the largest C dl The value is 6.16mF cm -2 . However, the C of Example 1-2 and Comparative Example 1-2 dl The values ​​are 5.27mF cm -2 、4.84mF cm -2 、1.02mF cm -2 、0.79mF cm -2 , indicating that the core-shell structured high entropy oxide coating has a large specific surface area and electrochemically active specific surface area, thereby improving the OER electrocatalytic activity of the electrocatalyst.

[0075] Test Example 4

[0076] The stability of the core-shell high entropy oxide coating of Example 5 was tested for 10 h using an electrochemical workstation (Coster CS350H). The test parameters were: current density of 10 mA cm -2 The stability of the core-shell high entropy oxide coating was evaluated by the initial overpotential and the change in overpotential after 10 hours of cycling. Figure 6 As shown. Figure 6 It can be seen that at a current density of 10 mA cm -2When , the OER overpotential of Example 3 only increased by 43 mV, indicating that the prepared high entropy oxide water electrolysis anode coating has excellent stability.

[0077] Therefore, the atmospheric plasma spraying process provided by the present invention for preparing a high entropy oxide coating with a core-shell structure can greatly improve the electrochemical performance of the battery anode, and has significant economic benefits and application prospects.

[0078] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a high entropy oxide coating having a core-shell structure, characterized in that: The following steps are included: S1. Placing high entropy alloy powder into a powder feeder, and depositing the high entropy alloy powder on the surface of the substrate by atmospheric plasma spraying technology to obtain a high entropy oxide coating; the high entropy alloy powder is obtained by mixing at least five metal elements and drying; the molar ratio of each metal element in the high entropy alloy powder is equal; the high entropy alloy powder is selected from at least five of nickel, cobalt, copper, iron, manganese and chromium; the conditions of the atmospheric plasma spraying technology are: spraying power of 30 kW-40 kW, current of 500 A-650 A, voltage of 50 V-60 V, argon flow rate of 40 splm-50 splm, hydrogen flow rate of 0 splm-5 splm, powder feeding amount of 15 g / min-20 g / min, spray gun moving speed of 400 mm / s-600 mm / s, spraying distance of 100 mm-150 mm, number of spraying cycles of 4-8 times, and adding air during the spraying process; S2. Turn off the powder feeder, keep other parameters unchanged, and spray and heat the high entropy oxide coating described in S1 to obtain a high entropy oxide coating with a core-shell structure.

2. The method for preparing a high entropy oxide coating having a core-shell structure according to claim 1, wherein: In S1, the particle size of the high entropy alloy powder is 15 μm-53 μm.

3. The method for preparing a high entropy oxide coating having a core-shell structure according to claim 1, wherein: In S1, the drying temperature is 75°C-100°C, and the drying time is 10 h-15 h.

4. The method for preparing a high entropy oxide coating having a core-shell structure according to claim 1, wherein: In S1, the material of the substrate is a nickel plate; and the surface of the substrate is sandblasted.

5. The method for preparing a high entropy oxide coating having a core-shell structure according to claim 4, characterized in that: The sandblasting process uses 120# white corundum sand; the sandblasting pressure is 0.2 MPa-0.4 MPa, and the sandblasting time is 55s-65s.

6. The method for preparing a high entropy oxide coating having a core-shell structure according to claim 1, wherein: In S1, during the spray heating process, the center temperature of the flame flow is 10000 K-15000 K, and the number of cycles is 5-8 times.

7. A high entropy oxide coating with a core-shell structure prepared by the method according to any one of claims 1 to 6.

8. An anode, characterized in that The anode is prepared from the high entropy oxide coating with a core-shell structure as claimed in claim 7.

9. Use of the anode according to claim 8 in electrolysis of water.

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