A nickel-based catalyst electrode, its preparation method and application

Abstract

The application discloses a nickel-based catalyst electrode and a preparation method and application thereof, and relates to the technical field of catalyst electrode preparation. Alkaline salt obtained by grinding cationic hydroxide and a nickel source matrix are added into a crucible, and heating is performed until the alkaline salt is in a molten state; the nickel source matrix is subjected to immersion reaction in the alkaline molten salt to form nickel hydroxide containing corresponding cations on the surface of the nickel source matrix. The alkaline molten salt method is adopted to prepare the nickel-based catalyst doped with cations in one step, the nickel-based catalyst has an upright, ultrathin and non-agglomerated nanosheet structure, which is beneficial to increase exposure of active sites, promote effective discharge of bubbles in a large-current reaction process, meanwhile, the cations are inserted into the layered nickel hydroxide, the interlayer spacing is effectively adjusted, and the binding force of the catalyst to OH ‑ under alkaline conditions is optimized, the binding strength of nickel ions and ·OH can be effectively reduced, the performance of the catalyst in the oxygen evolution reaction is more excellent, and the oxygen evolution reaction activity of the catalyst is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalyst electrode preparation, in particular to a nickel-based catalyst electrode with an ultrathin non-aggregated nanosheet structure and a preparation method and application thereof. BACKGROUND

[0002] Layered double hydroxides (LDHs) are a kind of catalysts with highly adjustable catalytic performance, which are particularly suitable for oxygen evolution reaction (OER). Nickel hydroxide (Ni(OH)2) catalyst is an important layered double hydroxide catalyst, and is considered as a potential catalyst for oxygen evolution reaction due to its two-dimensional layered structure; the nickel hydroxide catalyst is also called nickel-based catalyst.

[0003] The oxygen evolution reaction mainly occurs in the near-surface region of the catalyst, however, the nickel-based catalyst is prone to accumulation when stored or loaded onto the electrode, which leads to difficulty in controlling the thickness and thus blocks the surface active sites required for the catalytic reaction.

[0004] At present, the hydrothermal method is a commonly used method for synthesizing nickel-based catalysts, but this method also easily causes the aggregation and restacking of the nickel-based catalyst sheet structure, thereby blocking the surface active sites required for the catalytic reaction; in addition, due to the strong ·OH free radical binding force of the Ni-based catalyst under alkaline conditions and the high energy barrier accompanied by the rate-determining step (RDS), the OER activity of the Ni-based catalyst is greatly limited. The above-mentioned deficiencies in preparation and processing methods limit the great application potential of the Ni-based LDH catalyst in low-cost and large-scale preparation. SUMMARY

[0005] Therefore, the present application provides a nickel-based catalyst electrode and a preparation method and application thereof, which at least partially solve the problems existing in the prior art.

[0006] One of the purposes of the present application is to provide a nickel-based catalyst electrode.

[0007] The second purpose of the present application is to provide a preparation method of the above-mentioned nickel-based catalyst electrode.

[0008] The third purpose of the present application is to provide an application of the above-mentioned nickel-based catalyst electrode in the oxygen evolution reaction.

[0009] In order to achieve the above-mentioned purposes of the present application, the following technical solutions are adopted:

[0010] In a first aspect, the present application provides a nickel-based catalyst electrode, which comprises a nickel source substrate and cation-doped nickel hydroxide nanosheets, the cation-doped nickel hydroxide nanosheets are vertically grown on the nickel source substrate and form a network-like nanosheet array.

[0011] The cation can be selected from K + , Na+ Cs + Li + Sr 2+ Ca 2+ and the like, and the hydroxides thereof can be molten at high temperatures, preferably K + K + The nickel hydroxide doped with K is named as K-Ni(OH)2.

[0012] The nickel source substrate can be a foamed nickel, and the pore size (the mesh size of the network structure) of the foamed nickel is 80-300 μm, preferably 100-250 μm.

[0013] Preferably, the average thickness of the cation-doped nickel hydroxide nanosheet is 0.04±0.018 μm.

[0014] Method for testing the average thickness of the nanosheet:

[0015] A photo of the nanosheet is taken by a scanning electron microscope, and the thickness of the nanosheet at different positions is extracted by software (such as image processing software like Image J), a frequency distribution histogram is drawn to count the thickness range distribution, and the average thickness is obtained.

[0016] In a second aspect, the present application provides a preparation method of the above-mentioned nickel-based catalyst electrode, comprising the following steps:

[0017] The alkaline salt obtained after grinding the cationic hydroxide and the nickel source substrate are added into a crucible, and heated to a molten state of the alkaline salt; the nickel source substrate is immersed in the molten alkaline salt for a soaking reaction to grow nickel hydroxide containing the corresponding cation on the surface of the nickel source substrate; the product obtained by the reaction is washed and dried to obtain the nickel-based catalyst electrode.

[0018] In some embodiments, the cationic hydroxide is one or more selected from KOH, NaOH, CsOH, LiOH, Sr(OH)2, Ca(OH)2, and preferably KOH.

[0019] In some embodiments, the grinding time is 0.5-8 h, preferably 2-4 h.

[0020] In some embodiments, the nickel source substrate is a foamed nickel, and the pore size of the foamed nickel is 80-300 μm, preferably 100-250 μm.

[0021] In some embodiments, the amount of the cationic hydroxide added is 4-10 g per 1×1 cm 2 of the nickel source substrate. The amount of the hydroxide can completely immerse the nickel source after the hydroxide is molten.

[0022] In some embodiments, the temperature for heating and melting is 200-600℃.

[0023] In some embodiments, the soaking reaction time is 0.5-10 h, preferably 4-8 h.

[0024] In some embodiments, the drying temperature is 45-100℃, and the drying time is 6-12 h.

[0025] The present application uses foamed nickel as a nickel source to grow nickel-based hydroxide in situ in an alkaline molten salt environment, the molten salt environment has high mass transfer rate, high concentration of OH - The nanosheet structure grown on the surface of foamed nickel is closely connected with the foamed nickel substrate, the nanosheet structure is in vertical orientation, the nanosheets form a nanosheet network array, there is no aggregation and stacking structure between the nanosheets, which is beneficial to increase the exposure of active sites, at the same time, the cations are inserted into the layered nickel hydroxide, which effectively adjusts the interlayer spacing and optimizes the binding force of the catalyst to ·OH in alkaline conditions, the inserted cations can competitively bind ·OH, which can effectively reduce the binding strength of nickel ions and ·OH, and then release nickel ions to participate in the oxygen evolution reaction, this mechanism helps to improve the electrocatalytic performance, so that the nickel-based catalyst performs more outstandingly in the oxygen evolution reaction, greatly improving its oxygen evolution reaction activity.

[0026] In a third aspect, the present application provides a use of the above-mentioned nickel-based catalyst electrode in the oxygen evolution reaction.

[0027] The present application has the following beneficial effects:

[0028] 1. The present application uses an alkaline molten salt method to prepare a nickel-based catalyst in one step, because the molten salt environment has excellent mass transfer rate, the synthesized nickel-based catalyst presents a vertical, ultra-thin and non-aggregated nanosheet structure; the vertical structure of the nickel-based catalyst is beneficial to increase the exposure of active sites and promote the effective discharge of gas bubbles in the large current reaction process, providing a new idea for the design of oxygen evolution catalysts in industrial environments;

[0029] 2. In addition, K + Cations such as K+ are inserted into the layered nickel hydroxide, which effectively adjusts the interlayer spacing of the layered nickel hydroxide and optimizes the binding force of the catalyst to ·OH in alkaline conditions, thereby improving its oxygen evolution activity and achieving the purpose of optimizing the electrocatalytic performance; because nickel ions have electrophilicity, the binding force between nickel ions and ·OH is strong, by introducing cations, the competitive binding can effectively reduce the binding strength of nickel ions and ·OH, and then release nickel ions to participate in the oxygen evolution reaction, this mechanism helps to improve the electrocatalytic performance, so that the nickel-based catalyst performs more outstandingly in the oxygen evolution reaction;

[0030] 3.Meanwhile, the preparation method of the present application expands the preparation route of the nickel-based catalyst, and has the characteristics of greenness, mildness and environmental protection. The nickel hydroxide catalyst synthesized by the method not only has high purity, but also has controllable structure, and can in-situ synthesize an ultra-thin and non-agglomerated nickel-based catalyst in a strong alkaline environment. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0032] Figure 1 The XRD pattern of the K-Ni(OH)2 catalyst prepared in Example 1 is shown;

[0033] Figure 2 The SEM pattern of the K-Ni(OH)2 catalyst prepared in Example 1 is shown;

[0034] Figure 3 The SEM-mapping pattern of the K-Ni(OH)2 catalyst prepared in Example 1 is shown;

[0035] Figure 4 The SEM pattern of the K-Ni(OH)2 catalyst prepared in Comparative Example 1 is shown;

[0036] Figure 5 The SEM pattern of the K-Ni(OH)2 catalyst prepared in Comparative Example 2 is shown;

[0037] Figure 6 The nanosheet thickness distribution pattern of the K-Ni(OH)2 catalyst prepared in Example 1 is shown. DETAILED DESCRIPTION

[0038] The embodiments of the present application will be described in detail below with reference to the drawings.

[0039] It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict; and all other embodiments obtained by those skilled in the art on the basis of the embodiments in the present disclosure without creative labor are within the scope of protection of the present disclosure.

[0040] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this disclosure, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0041] Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0042] raw material:

[0043] The nickel foam comes from Kunshan Lvchuang Electronic Technology Co., Ltd.

[0044] Example 1

[0045] The method for preparing the nickel-based catalyst electrode in this embodiment includes the following steps:

[0046] Grind 6 g of potassium hydroxide in a mortar for 3 hours; add the ground alkali salt to a crucible, along with a 1×1 cm piece of [unclear - possibly a type of mineral]. 2 The above mixture was heated to 400 °C to reach a molten state; it was then immersed in the reaction at 400 °C for 6 h. The product obtained from the reaction was washed with deionized water and dried to obtain potassium ion-doped nickel hydroxide.

[0047] The samples were characterized by XRD, such as Figure 1 As shown, characteristic diffraction peaks of Ni(OH)₂ appeared in the product. Characterization was performed using SEM, as shown... Figure 2 As shown, the surface of the nickel mesh is uniformly covered with upright nanosheet catalysts, and these upright nanosheet structures are free of agglomeration. Figure 3 The SEM-mapping results of K-Ni(OH)2 are shown, clearly demonstrating the uniform distribution of elements K, Ni and O, indicating that K was successfully doped into the Ni(OH)2 catalyst.

[0048] It should be noted that after potassium hydroxide is ground in a mortar for 3 hours, especially in a humid environment, potassium hydroxide will undergo a chemical reaction to produce other alkaline salts such as potassium carbonate. As a result, the final product after grinding is no longer pure potassium hydroxide, but exists in the form of alkaline salts.

[0049] Example 2

[0050] The method of preparing a nickel-based catalyst electrode of this example refers to Example 1, except that the molten salt environment is CsOH.

[0051] Example 3

[0052] The method of preparing a nickel-based catalyst electrode of this example refers to Example 1, except that the molten salt environment is NaOH.

[0053] Example 4

[0054] The method of preparing a nickel-based catalyst electrode of this example refers to Example 1, except that the molten salt environment is LiOH.

[0055] Example 5

[0056] The method of preparing a nickel-based catalyst electrode of this example refers to Example 1, except that the grinding time is 0.5 h.

[0057] Example 6

[0058] The method of preparing a nickel-based catalyst electrode of this example refers to Example 1, except that the grinding time is 8 h.

[0059] Example 7

[0060] The method of preparing a nickel-based catalyst electrode of this example refers to Example 1, except that the molten salt temperature is 200°C.

[0061] Example 8

[0062] The method of preparing a nickel-based catalyst electrode of this example refers to Example 1, except that the molten salt temperature is 600°C.

[0063] Example 9

[0064] The method of preparing a nickel-based catalyst electrode of this example refers to Example 1, except that the soaking time is 0.5 h.

[0065] Example 10

[0066] The method of preparing a nickel-based catalyst electrode of this example refers to Example 1, except that the soaking time is 10 h.

[0067] Example 11

[0068] The method of preparing a nickel-based catalyst electrode of this example refers to Example 1, except that the molten salt environment is Sr(OH)2.

[0069] Example 12

[0070] The method for preparing the nickel-based catalyst electrode in this example refers to Example 1, except that the molten salt environment is Ca(OH)2.

[0071] Performance test

[0072] The OER performance of the prepared catalyst samples was tested at room temperature in a 1.0 mol·L-1 KOH solution by using a three-electrode system. Among them, the Pt electrode was the counter electrode, the Hg / HgO electrode was the reference electrode, and the prepared nickel-based catalyst electrode was the working electrode. The linear sweep voltammetry (LSV) curve was obtained by scanning at a scan rate of 10 mV s-1. The results obtained at a current density of 100 mA cm-2 are shown in Table 1. -1 -1 -2

[0073] Table 1

[0074]

[0075] From the above Table 1, it can be seen that the performance of the oxygen evolution catalyst (K-Ni(OH)2) electrode sample prepared in Example 1 is the best, and the overpotential at a current density of 100 mA cm-2 is the smallest. -2

[0076] The present application prepares a cation-doped nanosheet-structured K-Ni(OH)2 oxygen evolution material in one step by an alkaline molten salt method. X-ray diffraction analysis confirms that the synthesized material is nickel hydroxide, and scanning electron microscopy characterizes the nanosheet morphology, and SEM mapping further verifies the uniform distribution of K, Ni and O elements.

[0077] Cation insertion induces the interlayer spacing of Ni(OH)2 to increase in the order of K + >Na + >Cs + >Li + >Sr 2+ >Ca 2+ , thereby enhancing its oxygen evolution activity. The preparation process is simple and efficient, realizing cation doping and morphology modification in one step, which provides a useful reference for the industrial design of nickel-based oxygen evolution catalysts. It also provides ideas for the development of renewable energy and related conversion and storage technologies.

[0078] Comparative Example 1

[0079] This comparative example uses a conventional hydrothermal method to prepare a Ni(OH)2 electrode, including the following steps:

[0080] ​​​​Dissolve 120 mg NiCl₂·6H₂O and 168 mg hexamethylenetetramine in a mixture of 27 mL water and 3 mL ethanol, stir vigorously for 20 min, and then transfer the solution to a 40 mL Teflon-coated stainless steel high-pressure reactor. Add a 1×1 cm [piece of material / material] to the mixed solution. 2 Nickel foam (pore size 230 μm) was heated at 120 °C for 12 h. After naturally cooling to room temperature, the reaction sample was removed, washed with deionized water, and dried.

[0081] Comparative Example 2

[0082] This comparative example uses an alkaline hydrothermal method to prepare a K-Ni(OH)2 electrode, which includes the following steps:

[0083] A 1×1 cm piece 2 Nickel foam (pore size 230 μm) was placed in 30 mL of KOH aqueous solution with pH=14. The solution and nickel foam were then transferred to a 40 mL Teflon stainless steel high-pressure reactor and heated at 120 °C for 12 h. After naturally cooling to room temperature, the reaction sample was removed, washed with deionized water, and dried.

[0084] Performance testing

[0085] The test conditions are the same as above, with a value of 10 mV s. -1 Linear scan voltammetry (LSV) curves were obtained by scanning at a specific scan rate. At 100 mA cm⁻¹ -2 The results obtained at the current density are shown in Table 2.

[0086] Table 2

[0087]

[0088] The experimental results show that the oxygen evolution catalyst (K-Ni(OH)2) sample obtained from alkaline molten salt exhibits the best performance at 100 mA cm⁻¹. -2 It exhibits the lowest overpotential at the specified current density. Compared to Ni(OH)2 synthesized by conventional external nickel source hydrothermal synthesis, it still demonstrates superior performance. Furthermore, the oxygen evolution catalyst (K-Ni(OH)2) synthesized by alkaline molten salt has better activity than K-Ni(OH)2 synthesized by alkaline aqueous solution.

[0089] Further, SEM images of Comparative Example 1 and Comparative Example 2 are provided, such as... Figure 4 and Figure 5 As shown, Comparative Example 1 (Ni(OH)2 synthesized hydrothermally with a conventional external nickel source) exhibits an aggregated nanoflower morphology, while Comparative Example 2 (K-Ni(OH)2 synthesized in an alkaline aqueous solution) exhibits wrinkled nanosheets. Both methods produce nanosheets with varying degrees of agglomeration, which hinders the removal of air bubbles.

[0090] The above merely provides the specific implementation of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A nickel-based catalyst electrode, characterized in that it comprises: A nickel source substrate and cation-doped nickel hydroxide nanosheets are grown vertically and intersectingly on the nickel source substrate to form a network of nanosheets. The cation is selected from K + Na + Cs + Li + 、Sr 2+ Ca 2+ One or more of them; The nickel source matrix is ​​nickel foam, and the pore size of the nickel foam is 80-300μm; The average thickness of the cation-doped nickel hydroxide nanosheets is 0.04 ± 0.018 μm.

2. The nickel-based catalyst electrode according to claim 1, characterized in that, The pore size of nickel foam is 100-250 μm.

3. A method for preparing a nickel-based catalyst electrode according to claim 1 or 2, characterized in that, Includes the following steps: The alkaline salt obtained by grinding the cationic hydroxide and the nickel source matrix are added to a crucible and heated until the alkaline salt is in a molten state. The nickel source matrix is ​​immersed in the molten alkaline salt to grow nickel hydroxide containing the corresponding cation on the surface of the nickel source matrix. The product obtained from the reaction is washed and dried to obtain a nickel-based catalyst electrode.

4. The preparation method according to claim 3, characterized in that, The grinding time is 0.5-8 h.

5. The preparation method according to claim 4, characterized in that, The grinding time is 2-4 hours.

6. The preparation method according to claim 3, characterized in that, Each piece is 1×1cm 2 The nickel source matrix has a cationic hydroxide content of 4-10 g.

7. The preparation method according to claim 3, characterized in that, The heating and melting temperature is 200-600℃.

8. The preparation method according to claim 3, characterized in that, The soaking reaction time is 0.5-10 h.

9. The preparation method according to claim 8, characterized in that, The soaking reaction time is 4-8 hours.

10. The preparation method according to claim 3, characterized in that, The drying temperature is 45-100℃, and the drying time is 6-12 h.

11. The application of a nickel-based catalyst electrode according to claim 1 or 2, or a nickel-based catalyst electrode prepared by any one of claims 3-10, in the oxygen evolution reaction.

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