Self-supporting Ni-Co-S compound nanosheet growing on foamed nickel as well as preparation method and application of self-supporting Ni-Co-S compound nanosheet

Abstract

The invention provides a self-supporting Ni-Co-S compound nanosheet growing on foamed nickel and a preparation method and application thereof.The preparation method comprises the steps that firstly, an aqueous solution of 2-methylimidazole and an aqueous solution of cobalt nitrate hexahydrate are mixed and stirred to be uniform, the treated foamed nickel is put into the mixture, a reaction is conducted for a period of time at the room temperature, and the self-supporting Ni-Co-S compound nanosheet growing on the foamed nickel is obtained; and cleaning and drying for later use. And then, putting the dried foamed nickel into an ethanol solution of nickel nitrate hexahydrate, reacting at room temperature, cleaning and drying for later use. And finally, putting the foamed nickel into an ethanol solution containing thioacetamide, carrying out hydrothermal reaction to obtain the catalyst, and washing and drying the catalyst for later use. The obtained self-supporting Ni-Co-S compound nanosheet catalyst growing on the foamed nickel has excellent electro-catalysis urea oxidation performance and rapid charge transfer and dynamics, and the current density of 200 mA cm <-2 > can be achieved only by 1.35 V (vs.RHE).

Description

Technical Field

[0001] The invention belongs to the technical field of electrocatalysis, and in particular relates to a self-supporting Ni-Co-S composite nanosheet grown on nickel foam, and a preparation method and application thereof. Background Art

[0002] At present, with the proposal of my country's carbon peak and carbon neutrality goals, the demand for clean energy is increasing. Compared with a series of clean energy such as solar energy, wind energy, and hydropower, hydrogen energy has become an ideal candidate for the new generation of clean energy due to its high energy density, cleanliness, high combustion calorific value, and sustainability. Among the many hydrogen production technologies, water electrolysis technology is relatively mature and flexible in production, but its slow OER process kinetics have limited the development of water electrolysis hydrogen production. The use of electrocatalytic UOR to replace the anode OER of traditional electrocatalytic water splitting has two main advantages: one is that it can be coupled to the cathode HER for hydrogen production; the other is that since urea in the environment containing industrial and agricultural wastewater and domestic wastewater is harmful to the environment, electrocatalytic UOR also has the advantage of treating urea-containing wastewater.

[0003] Researchers have found that transition metal Ni has high efficiency in catalyzing urea decomposition and is economical and applicable. In addition, Ni-based catalysts not only have adjustable structures, but also can improve electrocatalytic performance by adjusting electron transfer and mass transfer. However, most pure Ni-based catalysts cannot achieve high current density at low overpotentials and have poor stability. Transition metal sulfides are conducive to further research on urea catalytic oxidation performance due to their high utilization rate and excellent catalytic activity and stability. In other works, materials prepared by high-temperature calcination and other methods are required to be calcined at high temperature under an inert atmosphere during the preparation process. This step not only increases cost and energy consumption, but also may cause the material structure to be partially destroyed due to high temperature, affecting the uniform distribution of active sites. In addition, the MOF skeleton after calcination is sulfurized to form a heterojunction structure, which may weaken the binding force between the nickel foam substrate and the catalyst due to high temperature, resulting in insufficient long-term stability. Based on the above research background, we prepared self-supporting Ni-Co-S composite nanosheet arrays (Ni-Co-S NSAs / NF) grown on nickel foam to improve catalytic activity and urea decomposition rate. Summary of the invention

[0004] In view of the problems existing in the current transition metal Ni-based catalysts, the present invention provides a self-supporting Ni-Co-S composite nanosheet grown on nickel foam and a preparation method and application thereof. The method provides a larger specific surface area and more active sites. The introduction of S enhances the conductivity of the catalyst, promotes the formation of NiOOH intermediates, and improves its intrinsic activity. The method mainly solves the problems of insufficient catalyst activity and poor stability.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for preparing a self-supporting Ni-Co-S composite nanosheet catalyst grown on nickel foam comprises the following steps: (1) treating the nickel foam by first cleaning it with acetone to remove surface impurities, then treating it with hydrochloric acid to increase its hydrophilicity, then cleaning it with water and anhydrous ethanol, and storing it in anhydrous ethanol to obtain a treated nickel foam; (2) dissolving 2-methylimidazole in deionized water and stirring with a magnetic device to form a solution A; dissolving cobalt nitrate hexahydrate in deionized water and stirring with a magnetic device to form a solution B; pouring solution A into solution B and stirring with a magnetic device to obtain a mixed liquid; (3) placing the nickel foam obtained in step (1) in the mixed liquid obtained in step (2) to react at room temperature, then taking out and washing with ultrapure water, drying and setting aside; (4) placing the nickel foam obtained in step (3) in an ethanol solution of nickel nitrate hexahydrate, reacting at room temperature, then taking out and washing it with ethanol, drying it for later use; (5) placing the nickel foam obtained in step (4) in an ethanol solution of thioacetamide, subjecting it to hydrothermal reaction for a period of time, cooling it to room temperature, washing it with ethanol, drying it and storing it for later use, thereby obtaining a self-supporting Ni-Co-S composite nanosheet catalyst grown on the nickel foam.

[0006] Furthermore, in step (1), the concentration of hydrochloric acid is 0.2-2.0 M, in step (2), the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:5-1:10, in step (4), the molar amount of nickel nitrate hexahydrate is 0-0.001 mol, and in step (5), the molar amount of thioacetamide is 0-0.01 mol.

[0007] Furthermore, the reaction time at room temperature in step (3) and step (4) is 1 to 6 hours, the hydrothermal reaction temperature in step (5) is 80 to 200° C., and the reaction time is the same as that in steps (3) and (4). After the reaction, a nickel foam loaded with a catalyst is obtained.

[0008] Furthermore, deionized water is used for washing and separation in step (3), and ethanol is used for washing and separation in step (4).

[0009] In steps (3), (4) and (5), the vacuum drying temperature is 40 to 200 °C and the drying time is 8 to 24 hours.

[0010] The invention also provides a self-supporting Ni-Co-S composite nanosheet catalyst grown on foamed nickel prepared according to the method, which maintains the morphology of the nanosheet.

[0011] The present invention also provides an application of the self-supporting Ni-Co-S composite nanosheet catalyst grown on nickel foam in catalyzing urea oxidation, comprising the following steps: S1: washing and drying the self-supporting Ni-Co-S composite nanosheet catalyst grown on nickel foam and setting it aside as a working electrode, a platinum sheet electrode as a counter electrode, and an Ag / AgCl electrode as a reference electrode; S2: Using alkaline aqueous solution containing urea as electrolyte in H-type electrolytic cell to study the urea catalytic oxidation performance, the electrolyte used in each single cell is 30-100 ml; S3: The electrolyte used in the test is a potassium hydroxide solution containing urea, where the urea concentration is 0~0.5 M and the KOH concentration is 0~1.5 M; S4: The pH range of the electrolyte used in the test is 10~14; The beneficial effects of the present invention are as follows: in the process of preparing a self-supporting Ni-Co-S composite nanosheet catalyst grown on nickel foam, 2-methylimidazole and cobalt nitrate hexahydrate produce coordination to form nanosheet structure crystals (ZIF-67), which are loaded on the treated nickel foam and have the characteristics of large specific surface area and high porosity. After using ZIF-67 as a template, cation replacement is performed and etching is performed with nickel nitrate hexahydrate to obtain NiCo LDH after cation replacement. Then, the just prepared precursor is subjected to sulfurization treatment, and a bimetallic Ni-Co-S composite nanosheet catalyst is obtained by a hydrothermal method. The catalyst has a large specific surface area and a controllable and adjustable structure of two-dimensional nanosheets, which provide more active sites for the reaction. Compared with the three-dimensional cross-shaped nanosheet structure formed by the heterojunction structure, the density of the active sites is higher. In addition, the introduction of S enhances the conductivity of the catalyst, promotes the generation of NiOOH intermediates, and improves its intrinsic activity. The synergistic effect between the bimetallic sulfides in the catalyst not only promotes charge transfer, but also accelerates the decomposition of urea, ensuring the continuous urea oxidation reaction. In terms of the process, the preparation method uses room temperature reaction and hydrothermal method throughout the process, without the need for high-temperature calcination, low energy consumption and simple process, suitable for large-scale production, avoiding the shortcomings of high-temperature calcination that may be caused by equipment limitations in industrial applications. In addition, the material obtained by this method has good electrocatalytic urea oxidation performance. Compared with the same type of catalyst prepared by calcination, the material prepared by the present invention reaches 200 mA cm -2 The current density required is only 1.35 V (vs. RHE) and the Tafel slope is 21.3 mV dec -1The Ni-Co-S composite nanosheet catalyst grown on nickel foam prepared by the present invention provides a new strategy for designing efficient and low-cost urea point oxidation catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0013] Figure 1 X-ray diffraction patterns of ZIF-67 NSAs and NiCo LDH NSAs prepared in comparative example; Figure 2 is the X-ray diffraction pattern of Ni-Co-S NSAs / NF prepared in Example 1; Figure 3 Scanning electron microscope images of Ni-Co-S NSAs / NF prepared in Example 1 and ZIF-67 NSAs / NF and NiCoLDH NSAs / NF prepared in the comparative example (a. ZIF-67 NSAs / NF, b. NiCo LDH NSAs / NF, c. Ni-Co-SNSAs / NF); Figure 4 LSV curves of Ni-Co-S NSAs / NF prepared in Example 1 and ZIF-67 NSAs / NF, NiCoLDH NSAs / NF, and ZIF-67-S NSAs / NF prepared in comparative example in 1M KOH solution containing 0.33M urea; Figure 5 The Ni-Co-S NSAs / NF prepared in Example 1 and the ZIF-67 NSAs / NF, NiCoLDH NSAs / NF, and ZIF-67-S NSAs / NF prepared in the comparative example were -2 and 200 mA cm -2 Comparison of electrode potentials for urea oxidation reaction below; Figure 6 The Tafel slopes of the Ni-Co-S NSAs / NF prepared in Example 1 and the ZIF-67 NSAs / NF, NiCoLDH NSAs / NF, and ZIF-67-S NSAs / NF prepared in the comparative example; Figure 7LSV curves of NiCo LDH NSAs / NF prepared in Comparative Example 5 at different reaction times in a 1 M KOH solution containing 0.33 M urea. DETAILED DESCRIPTION

[0014] The present invention will be further described below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention, and those skilled in the art in this field can make some non-essential improvements and adjustments based on the content of the above invention.

[0015] Example 1 The preparation method of the Ni-Co-S composite nanosheet catalyst (Ni-Co-S NSAs / NF) grown on nickel foam in this embodiment comprises the following steps: (1) First, the nickel foam is treated by washing it with acetone to remove organic impurities on the surface, then treating it with 1.0M hydrochloric acid to remove inorganic impurities on the surface and increase its hydrophilicity, then washing it with water, then washing it with anhydrous ethanol, and sealing it in anhydrous ethanol; (2) Dissolve 1.31 g of 2-methylimidazole in 40 ml of ultrapure water and stir magnetically to form solution A; dissolve 0.58 g of cobalt nitrate hexahydrate (M=291.035 g / mol) in 40 ml of ultrapure water and stir magnetically to form solution B; quickly pour solution A into solution B, mix well, place nickel foam NF in it, and react at room temperature for 4 h; (3) The NF obtained in step (2) is taken out, cleaned with ultrapure water, and dried at 60° C. for later use, thereby obtaining ZIF-67 self-supportingly grown on NF (ZIF-67 NSAs-NF); (4) Dissolve 0.13 g nickel nitrate hexahydrate (M = 290.735 g / mol) in 30 ml ethanol solution, add the precursor ZIF-67 NSAs-NF obtained in step (3) and react at room temperature for 3 h; (5) The NF obtained in step (4) was taken out and washed with ultrapure water, dried at 60 ° C for use, and Ni, Co double metal hydroxide was obtained, referred to as NiCo LDH NSAs / NF; (6) 80 mg of thioacetamide (M = 75.133 g / mol) was dissolved in 40 ml of ethanol, and the NiCoLDH NSAs / NF obtained in step (5) was placed in the above solution, and then placed in a 100 ml reactor, reacted at 120 ° C for 4 h, cooled to room temperature, taken out, washed with anhydrous ethanol, and dried at 60 ° C for use, to obtain Ni, Co bimetallic sulfide (Ni-Co-S NSAs / NF); Example 2 The preparation method of the Ni-Co-S composite nanosheet catalyst (Ni-Co-S NSAs / NF-1) grown on nickel foam in this embodiment comprises the following steps: (1) First, the nickel foam is treated by washing it with acetone to remove organic impurities on the surface, then treating it with 1.0M hydrochloric acid to remove inorganic impurities on the surface and increase its hydrophilicity, then washing it with water, then washing it with anhydrous ethanol, and sealing it in anhydrous ethanol; (2) Dissolve 1.31 g of 2-methylimidazole in 40 ml of ultrapure water and stir magnetically to form solution A; dissolve 0.58 g of cobalt nitrate hexahydrate (M=291.035 g / mol) in 40 ml of ultrapure water and stir magnetically to form solution B; quickly pour solution A into solution B, mix well, place nickel foam NF in it, and react at room temperature for 4 h; (3) The NF obtained in step (2) is taken out, cleaned with ultrapure water, and dried at 60° C. for later use, thereby obtaining ZIF-67 self-supportingly grown on NF (ZIF-67 NSAs-NF); (4) Dissolve 0.13 g nickel nitrate hexahydrate (M = 290.735 g / mol) in 30 ml ethanol solution, add the precursor ZIF-67 NSAs-NF obtained in step (3) and react at room temperature for 2 h; (5) The NF obtained in step (4) was taken out and cleaned with ultrapure water, and dried at 60° C. for later use to obtain Ni, Co double metal hydroxide, which was recorded as NiCo LDH NSAs / NF; (6) 80 mg of thioacetamide (M = 75.133 g / mol) was dissolved in 40 ml of ethanol. The NiCoLDH NSAs / NF obtained in step (5) was placed in the above solution and then placed in a 100 ml reactor. The reaction was carried out at 120 °C for 4 h. After cooling to room temperature, the catalyst was taken out, washed with anhydrous ethanol, and dried at 60 °C for later use. Thus, a Ni-Co-S composite nanosheet catalyst grown on nickel foam (Ni-Co-SNSAs / NF-1) was obtained.

[0016] Example 3 The preparation method of the Ni-Co-S composite nanosheet catalyst (Ni-Co-S NSAs / NF-2) grown on nickel foam in this embodiment comprises the following steps: (1) First, the nickel foam is treated by washing it with acetone to remove organic impurities on the surface, then treating it with 1.0M hydrochloric acid to remove inorganic impurities on the surface and increase its hydrophilicity, then washing it with water, then washing it with anhydrous ethanol, and sealing it in anhydrous ethanol; (2) Dissolve 1.31 g of 2-methylimidazole in 40 ml of ultrapure water and stir magnetically to form solution A; dissolve 0.58 g of cobalt nitrate hexahydrate (M=291.035 g / mol) in 40 ml of ultrapure water and stir magnetically to form solution B; quickly pour solution A into solution B, mix well, place nickel foam NF in it, and react at room temperature for 4 h; (3) The NF obtained in step (2) is taken out, cleaned with ultrapure water, and dried at 60° C. for later use, thereby obtaining ZIF-67 self-supportingly grown on NF (ZIF-67 NSAs-NF); (4) Dissolve 0.13 g nickel nitrate hexahydrate (M = 290.735 g / mol) in 30 ml ethanol solution, place the precursor ZIF-67 NSAs-NF obtained in step (3) in it, and react at room temperature for 4 h; (5) The NF obtained in step (4) was taken out and cleaned with ultrapure water, and dried at 60° C. for later use to obtain Ni, Co double metal hydroxide, which was recorded as NiCo LDH NSAs / NF; (6) 80 mg of thioacetamide (M = 75.133 g / mol) was dissolved in 40 ml of ethanol. The NiCoLDH NSAs / NF obtained in step (5) was placed in the above solution and then placed in a 100 ml reactor. The reaction was carried out at 120 °C for 4 h. After cooling to room temperature, the reaction mixture was taken out, washed with anhydrous ethanol, and dried at 60 °C for later use. Thus, a Ni-Co-S composite nanosheet catalyst grown on nickel foam (Ni-Co-SNSAs / NF-2) was obtained.

[0017] Comparative Example 1 The preparation of ZIF-67 NSAs was carried out without adding nickel foam, and only the processes (2) and (3) of Example 1 were performed.

[0018] Comparative Example 2 The preparation of NiCo LDH NSAs was carried out without adding nickel foam, and only the processes (2) to (5) of Example 1 were performed.

[0019] Comparative Example 3 The preparation of ZIF-67 NSAs-NF only involved processes (1) to (3) of Example 1.

[0020] Comparative Example 4 The preparation of ZIF-67-S NSAs-NF only involved processes (1) to (3) and (6) of Example 1.

[0021] Comparative Example 5 The preparation of NiCo LDH NSAs / NF was performed by only performing the process steps (1) to (5) of Example 1 as follows: (1) First, the nickel foam is treated by washing it with acetone to remove organic impurities on the surface, then treating it with 1.0M hydrochloric acid to remove inorganic impurities on the surface and increase its hydrophilicity, then washing it with water, then washing it with anhydrous ethanol, and sealing it in anhydrous ethanol; (2) Dissolve 1.31 g of 2-methylimidazole in 40 ml of ultrapure water and stir magnetically to form solution A; dissolve 0.58 g of cobalt nitrate hexahydrate in 40 ml of ultrapure water and stir magnetically to form solution B; quickly pour solution A into solution B, mix well, place nickel foam NF therein, and react at room temperature for 4 h; (3) The NF obtained in step (2) is taken out, cleaned with ultrapure water, and dried at 60° C. for later use, thereby obtaining ZIF-67 self-supportingly grown on NF (ZIF-67 NSAs-NF); (4) Dissolve 0.13 g nickel nitrate hexahydrate in 30 ml ethanol solution, place the precursor ZIF-67 NSAs-NF obtained in step (3) in it, and react at room temperature for 3 h; (5) The NF obtained in step (4) was taken out, cleaned with ultrapure water, and dried at 60° C. to obtain Ni, Co double hydroxide, which was recorded as NiCo LDH NSAs / NF.

[0022] The Ni,Co double hydroxides corresponding to the replacement time in step (4) were adjusted to 1 h, 2 h, 3 h and 4 h, respectively, and were denoted as NiCo-LDH NSAs / NF-1, NiCo-LDH NSAs / NF-2, NiCo-LDH NSAs / NF-3 and NiCo-LDHNSAs / NF-4.

[0023] The X-ray diffraction patterns of ZIF-67 NSAs prepared in Comparative Example 1 and NiCo LDH NSAs prepared in Comparative Example 2 are shown in FIG. Figure 1 As shown, the results indicate that the ZIF-67 template was successfully prepared without the addition of nickel foam. After Ni salt replacement, the characteristic peaks of ZIF-67NSAs disappeared, and the characteristic peaks of NiCo LDH NSAs appeared, indicating that the cation exchange was successfully achieved.

[0024] The X-ray diffraction pattern of Ni-Co-S NSAs / NF prepared in Example 1 is as follows: Figure 2 As shown in the results, in addition to NF (PDF#04-0850), three characteristic peaks appeared, which were attributed to NiS (PDF#12-0041), Ni 3 S 2 (PDF#44-1418),Co 3 S 4(PDF#42-1448), indicating that Ni-Co-S composite nanosheet catalysts grown on nickel foam (Ni-Co-S NSAs / NF) were successfully prepared.

[0025] The scanning electron micrographs of the Ni-Co-S NSAs / NF prepared in Example 1 and the ZIF-67 NSAs / NF and NiCo LDH NSAs / NF prepared in the comparative example (a. ZIF-67 NSAs / NF, b. NiCo LDH NSAs / NF, c. Ni-Co-S NSAs / NF) are shown in FIG. Figure 3 As shown in Figure 1, Figure a shows that the ZIF-67 template has a nanosheet structure, which is evenly arranged vertically on the nickel foam substrate. Compared with the ZIF-67 NSAs / NF, the nanosheets of the NiCo LDH NSAs / NF in Figure b are thinner and have a porous structure. After hydrothermal sulfurization, as shown in Figure c, the Ni-Co-S NSAs / NF maintains the morphology of the nanosheets, but the surface becomes rougher.

[0026] The LSV curves of the Ni-Co-S NSAs / NF prepared in Example 1 and the ZIF-67 NSAs / NF, NiCo LDHNSAs / NF, and ZIF-67-S NSAs / NF prepared in the comparative example in 1M KOH solution containing 0.33M urea are shown in FIG. Figure 4 As shown, the results show that the Ni-Co-S NSAs / NF catalyst of the embodiment exhibits better UOR activity than other comparative examples ZIF-67-S NSAs / NF, NiCo LDH NSAs / NF and ZIF-67 NSAs / NF.

[0027] The Ni-Co-S NSAs / NF prepared in Example 1 and the ZIF-67 NSAs / NF, NiCo LDHNSAs / NF, and ZIF-67-S NSAs / NF prepared in the comparative example were -2 and 200 mA cm -2 The electrode potential comparison of urea oxidation reaction under Figure 5 As shown in the figure, it was found that Ni-Co-S NSAs / NF had the smallest overpotential and the best performance.

[0028] The Tafel slopes of the Ni-Co-S NSAs / NF prepared in Example 1 and the ZIF-67 NSAs / NF, NiCo LDHNSAs / NF, and ZIF-67-S NSAs / NF prepared in the comparative example are as follows: Figure 6As shown in the figure, the Tafel slopes obtained from their UOR polarization curves are used to explore the reaction kinetics of these catalysts. The lower the catalytic slope, the faster the transfer kinetics of the catalyst and the better the catalytic performance. As shown in the figure, the slope of the Ni-Co-S NSAs-NF electrode is 21.3 mV dec-1, which is smaller than that of NiCo-LDH NSAs / NF (71.2 mV dec-1), ZIF-67 NSAs-NF (36.7 mV dec-1) and ZIF-67-SNSAs / NF (41.8 mV dec-1), indicating that its kinetic rate is faster and the UOR catalytic kinetics are superior.

[0029] The LSV curves of NiCo LDH NSAs / NF prepared in Comparative Example 5 with different reaction times in 1M KOH solution containing 0.33M urea are shown in Figure 7 As shown in the figure, NiCo-LDH NSAs / NF-1, NiCo-LDH NSAs / NF-2, NiCo-LDHNSAs / NF-3 and NiCo-LDH NSAs / NF-4 represent replacement times of 1 h, 2 h, 3 h and 4 h, respectively. The electrochemical test results show that when the Ni salt replacement time is 3 h, the overpotential of NiCo-LDH NSAs / NF-3 is the smallest, indicating that its urea oxidation performance is optimal. A short replacement time will result in too little Ni ion content in the catalyst and low catalytic activity. Too long a replacement time will result in too little Co content and an increase in the initial oxidation potential, which will affect the UOR activity of the catalyst.

[0030] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing a self-supporting Ni-Co-S composite nanosheet grown on nickel foam, characterized in that The steps include: (1) treating the nickel foam by first cleaning it with acetone to remove surface impurities, then treating it with hydrochloric acid to increase its hydrophilicity, then cleaning it with water and anhydrous ethanol, and storing it in anhydrous ethanol to obtain a treated nickel foam; (2) dissolving 2-methylimidazole in deionized water and stirring with a magnetic stirrer to form a solution A; Dissolve cobalt nitrate hexahydrate in deionized water and stir magnetically to form solution B; pour solution A into solution B and stir magnetically to obtain a mixed liquid; (3) placing the nickel foam treated in step (1) into the mixed liquid obtained in step (2), reacting at room temperature, then taking out, washing with ultrapure water, and drying for later use; (4) placing the nickel foam obtained in step (3) in an ethanol solution of nickel nitrate hexahydrate, reacting at room temperature, then taking out and washing it with ethanol, drying it for later use; (5) placing the nickel foam obtained in step (4) in an ethanol solution of thioacetamide, subjecting it to hydrothermal reaction for a period of time, cooling it to room temperature, washing it with ethanol, drying it and storing it for later use, thereby obtaining a self-supporting Ni-Co-S composite nanosheet grown on the nickel foam.

2. The method for preparing the self-supporting Ni-Co-S composite nanosheets grown on nickel foam according to claim 1, characterized in that: In step (1), the concentration of hydrochloric acid is 0.2~2.0 M.

3. The method for preparing the self-supporting Ni-Co-S composite nanosheets grown on nickel foam according to claim 1, characterized in that: In step (2), the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:5 to 1:

10.

4. The method for preparing the self-supporting Ni-Co-S composite nanosheets grown on nickel foam according to claim 1, characterized in that: The concentration of nickel nitrate hexahydrate in step (4) is 0.01-0.03 M, and the reaction time at room temperature in steps (3) and (4) is 1-6 hours.

5. The method for preparing the self-supporting Ni-Co-S composite nanosheets grown on nickel foam according to claim 1, characterized in that: The amount of thioacetamide in step (5) is 0.01-0.04 M, the hydrothermal reaction temperature in step (5) is 80-200° C., and the hydrothermal reaction time is 1-6 hours.

6. The method for preparing the self-supporting Ni-Co-S composite nanosheets grown on nickel foam according to claim 1, characterized in that: The drying in steps (3), (4) and (5) is performed by vacuum drying, the vacuum drying temperature is 40-200°C, and the drying time is 8-24 hours.

7. The self-supporting Ni-Co-S composite nanosheet grown on nickel foam obtained by the preparation method according to any one of claims 1 to 6, characterized in that: The nanosheet-like morphology ensures a large specific surface area, provides abundant active sites, and facilitates the electron transfer and mass transfer processes.

8. The use of the self-supporting Ni-Co-S composite nanosheets grown on nickel foam as a catalyst in catalyzing urea oxidation reaction as claimed in claim 7, characterized in that The following steps are involved: S1: washing and drying the self-supporting Ni-Co-S composite nanosheet catalyst grown on nickel foam and setting it aside as a working electrode, a platinum sheet electrode as a counter electrode, and an Ag / AgCl electrode as a reference electrode; S2: The test was carried out in an H-type electrolytic cell using an alkaline aqueous solution containing urea as the electrolyte.

9. The use according to claim 8, characterized in that: The electrolyte used in the test is a potassium hydroxide solution containing urea, in which the urea concentration is 0~0.5 M and the KOH concentration is 0~1.5 M; the pH range of the electrolyte used in the test is 10~14, and each single tank uses 30-100 ml of electrolyte.

10. The use according to claim 8, characterized in that: The self-supported Ni-Co-S composite nanosheet catalyst grown on nickel foam can achieve 200 mA cm at a voltage of only 1.35 V vs. RHE. -2 The current density is 21.3 mV dec. -1 , the catalytic activity was greatly improved.

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