Iron and molybdenum co-modified nickel sulfide nanosheet array and preparation method and application thereof

Abstract

This invention discloses an iron and molybdenum co-modified nickel sulfide nanosheet array and its preparation method, relating to the field of seawater oxidation catalyst technology. The nickel sulfide nanosheet array is a rough nanosheet array assembled from 30-80 nm nanoparticles grown on a nickel foam substrate. The specific steps of the preparation method are: using a hydrothermal method to prepare a nickel hydroxide nanosheet array as a self-template, placing the nickel hydroxide nanosheet array in a substrate containing thiourea and Fe... 3+ and MoO4 2‑ A hydrothermal reaction was carried out in a solution to obtain an iron and molybdenum co-modified nickel sulfide nanosheet array. This invention develops a unique two-step hydrothermal method that uses nickel hydroxide nanosheets as a self-template to transform them into nickel sulfide while simultaneously introducing iron and molybdenum atoms, forming an iron and molybdenum co-modified nickel sulfide nanosheet array. The method is simple and efficient, and the iron and molybdenum co-modified nickel sulfide nanosheet array, as an oxidation electrode in alkaline water and seawater, exhibits excellent catalytic activity and stability.

Description

Technical Field

[0001] This invention relates to the field of seawater oxidation catalyst technology, specifically to an iron and molybdenum co-modified nickel sulfide nanosheet array, its preparation method, and its application. Background Technology

[0002] Electrolysis of water for hydrogen production not only produces high-purity hydrogen but also directly utilizes electricity generated from intermittent renewable energy sources such as wind or solar power, making it a promising and sustainable high-purity hydrogen production technology. In recent years, efforts have been focused on developing high-performance non-precious metal catalysts to improve the efficiency of electrolyzers, with some catalysts even achieving performance superior to precious metal catalysts. However, large-scale use of electrolyzers will exacerbate the pressure of freshwater scarcity. Considering the abundance of seawater resources on Earth, developing direct seawater electrolysis technology is not only convenient in terms of material sourcing but also allows for direct co-operation with coastal power generation facilities, making it a very promising technology. However, the realization of seawater electrolysis technology remains highly challenging, particularly regarding the anode reaction. Firstly, due to the large amount of chloride ions (~0.5 M) in seawater, the two-electron chloride evolution reaction is easily triggered at the anode, thus affecting the selectivity of the four-electron oxygen evolution reaction (OER). In alkaline media, Cl... - The ions will further react with OH- - The reaction forms hypochlorite (ClO) - The thermodynamic potential of this reaction is about 480 mV higher than that of OER, therefore a highly active OER catalyst needs to be developed to avoid ClO - The formation of [a substance] (ChemSusChem, 2016, 9, 962-972). Furthermore, during seawater electrolysis, the deposition of some insoluble precipitates and Cl [a substance] occur. - Ion corrosion can damage electrodes, affecting their activity and stability (Angew. Chem. Int. Ed., 2022, 61, e202210753).

[0003] Transition metal sulfides (TMS) possess excellent electronic structure and conductivity, making them widely used as OER catalysts. Recent studies have shown that TMS can generate a negatively charged sulfate passivation layer in situ during the OER process, thereby repelling Cl- from seawater. -The ions are located away from the catalyst interface, thus endowing the catalyst with excellent corrosion resistance, which is promising for use in the electrolysis of seawater to produce hydrogen at high current densities (Proc. Natl. Acad. Sci. USA, 116, 6624-6629). However, the OER activity of TMS currently does not meet the requirements for large-scale applications, especially at high current densities. Among many modification strategies, Fe metal atom modification has been shown to optimize the interaction strength between active sites and OER intermediates (ACS Catal., 2021, 11, 5601-5613), while Mo atom modification helps to construct multiple catalytic active sites (Nano Energy, 2021, 87, 106217). Although both metal atoms can improve OER activity, the effect of single metal atom modification is still limited. Therefore, if both heteroatoms are used to modify TMS (such as Ni3S2), not only can the effect of each metal being modified alone be achieved, but the synergistic effect between the heteroatoms will also lead to a "1 + 1 > 2" effect, thereby significantly improving the electrolytic activity of Ni3S2 in seawater and promoting the development of anode catalysts for seawater electrolysis. Summary of the Invention

[0004] The purpose of this invention is to provide a nickel sulfide nanosheet array, its preparation method, and its application, in order to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A nickel sulfide nanosheet array co-modified with iron and molybdenum is disclosed. The material is a nickel sulfide nanosheet array co-modified with iron and molybdenum grown on a nickel foam substrate, wherein the iron atom content is 2.45%~10.76% and the molybdenum atom content is 1.11%~8.99%.

[0007] Based on the above technical solutions, the present invention also provides the following optional technical solutions:

[0008] In one alternative: the nickel sulfide nanosheet array modified with iron and molybdenum is composed of stacked nanosheets with rough surfaces, and each nanosheet is assembled from nanoparticles of 30-80 nm in size.

[0009] A method for preparing a nickel sulfide nanosheet array co-modified with iron and molybdenum includes the following steps: Step S1: Prepare a nickel hydroxide nanosheet array as a self-template using a hydrothermal method; Step S2: Convert nickel hydroxide into nickel sulfide during the hydrothermal process, and simultaneously modify the nickel sulfide nanosheet array with iron and molybdenum atoms.

[0010] In one alternative, step S1 is as follows: the cleaned nickel foam is placed in 60 mL of a clear solution containing 0.05 mol / L Ni(NO3)2·6H2O, 0.167 mol / L urea and 0.067 mol / L ammonium fluoride, and reacted at 120 °C for 6 h using a hydrothermal method. After the reaction is complete and cooled to room temperature, the foam is rinsed clean and dried in an oven to obtain a nickel hydroxide nanosheet array grown on the nickel foam.

[0011] In one alternative embodiment, step S2 specifically involves placing a nickel hydroxide nanosheet array within a solution containing thiourea and Fe. 3+ and MoO4 2- A hydrothermal reaction was carried out in the solution to obtain an array of nickel sulfide nanosheets co-modified with iron and molybdenum.

[0012] In one alternative: the concentration of the thiourea is 0.01~0.10 mol / L, and the Fe... 3+ The solution is provided by Fe(NO3)3, Fe2(SO4)3, or FeCl3 at a concentration of 0.01~0.10 mol / L; the MoO4... 2- It is provided by Na2MoO4 or K2MoO4 at a concentration of 0.005~0.08 mol / L.

[0013] In one alternative: the hydrothermal reaction conditions in the hydrothermal method are 100~160℃, and the reaction time is 8~20 h.

[0014] Application of nickel sulfide nanosheet arrays modified with iron and molybdenum as described above in oxidation reactions in alkaline water or seawater.

[0015] In one alternative approach, the specific application method of the nickel sulfide nanosheet array co-modified by iron and molybdenum in the oxidation reaction of alkaline water or seawater is as follows: the nickel sulfide nanosheet array co-modified by iron and molybdenum is placed in an alkaline system as an oxygen evolution electrode for the oxidation reaction of alkaline water and seawater.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] 1. This invention innovatively develops a unique two-step hydrothermal method that utilizes nickel hydroxide nanosheets as a self-template to transform them into nickel sulfide while simultaneously introducing iron and molybdenum atoms, forming an iron and molybdenum co-modified nickel sulfide nanosheet array. The preparation method is simple and efficient. The sample is a rough nanosheet array composed of 30-80 nm nanoparticles grown on a nickel foam substrate, which can fully expose active sites. Simultaneously, the co-modification with iron and molybdenum enhances the conductivity of nickel sulfide and improves electron transfer ability, thereby promoting the reaction kinetics of the oxygen evolution reaction and ultimately significantly improving the seawater oxidation performance of the electrode.

[0018] 2. The nickel sulfide nanosheet array co-modified with iron and molybdenum provided in this invention exhibits excellent catalytic activity and stability as an oxidation electrode for alkaline water and seawater. At 10, 100, and 500 mA cm⁻¹, [the catalytic activity is achieved]. -2 At current densities of 100 mA cm⁻¹, the required overpotentials in alkaline aqueous solutions were as low as 194, 236, and 276 mV, and in alkaline seawater, they were 201, 251, and 308 mV, significantly lower than those required for iron-modified nickel sulfide and nickel sulfide samples alone. Simultaneously, the catalyst exhibited excellent performance at current densities of 100 mA cm⁻¹. -2 Operating at a constant current density for 1200 and 900 hours respectively, its seawater oxidation performance showed no significant decline. This performance is superior to most previously reported non-precious metal catalysts. Attached Figure Description

[0019] Figure 1 Images of nickel hydroxide (Ni(OH)2) nanosheet arrays grown on a nickel foam substrate after the first hydrothermal reaction, taken at different magnifications using scanning electron microscopy (SEM).

[0020] Figure 2 These are SEM images at different magnifications of an array of nickel sulfide nanosheets (denoted as FeMo-Ni3S2) modified with iron and molybdenum grown on a nickel foam substrate after the second hydrothermal reaction.

[0021] Figure 3 This is a distribution diagram of Ni, S, Fe, and Mo elements in FeMo-Ni3S2.

[0022] Figure 4 (a) is the XRD pattern of Ni(OH)2; (b)~(c) are the XRD comparison diagrams of FeMo-Ni3S2, Fe-Ni3S2 and Ni3S2; (d) is the Raman spectrum comparison diagram of FeMo-Ni3S2, Fe-Ni3S2 and Ni3S2.

[0023] Figure 5 Comparison of OER performance of FeMo-Ni3S2 with other samples in alkaline electrolyte (1 M KOH): (a) Linear sweep voltammetry (LSV) curve; (b) Comparison of overpotential at different current densities; (c) Tafel plot; (d) Electrochemical impedance spectroscopy (EIS).

[0024] Figure 6 Comparison of OER performance between FeMo-Ni3S2 alkaline seawater electrolyte (1 M KOH seawater) and other samples: (a) LSV curve; (b) Comparison of overpotential at different current densities; (c) Performance curves of stability test at different current densities. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The embodiments listed herein are merely illustrative and not intended to limit the scope of the invention. Any obvious modifications or alterations made to this invention do not depart from the spirit and scope of the invention.

[0026] Example 1

[0027] This invention discloses an iron and molybdenum co-modified nickel sulfide nanosheet array. The material is an iron and molybdenum co-modified nickel sulfide nanosheet array grown on a nickel foam substrate, wherein the iron atom content is 2.45%~10.76% and the molybdenum atom content is 1.11%~8.99%. The nickel sulfide nanosheet array is composed of stacked nanosheets with rough surfaces, and each nanosheet is assembled from nanoparticles of 30-80 nm.

[0028] This invention also discloses a method for preparing nickel sulfide nanosheet arrays co-modified with iron and molybdenum, the steps of which are as follows:

[0029] (1) The cleaned nickel foam was placed in 60 mL of a clear solution containing 0.05 mol / L Ni(NO3)2·6H2O, 0.167 mol / L urea and 0.067 mol / L ammonium fluoride, and reacted at 120 °C for 6 h using a hydrothermal method. After the reaction was completed and cooled to room temperature, it was rinsed clean and dried in an oven to obtain a nickel hydroxide (Ni(OH)2) nanosheet array grown on the nickel foam.

[0030] (2) Nickel hydroxide was converted to nickel sulfide using a second hydrothermal method, while Fe and Mo atoms were introduced. 0.033 mol / L thiourea, 0.05 mol / L Fe(NO3)2·9H2O and 0.013 mol / L Na2MoO4·2H2O were dissolved in 60 mL of deionized water and stirred for about 30 min. The nickel hydroxide nanosheet array was placed in this clear solution and reacted at 120 °C for 12 h using a hydrothermal method. After the reaction was completed and cooled to room temperature, the nanosheets were rinsed clean and dried in an oven to obtain a nickel sulfide nanosheet array (denoted as FeMo-Ni3S2) modified with iron and molybdenum grown on nickel foam.

[0031] (3) The prepared nickel sulfide nanosheet array modified with iron and molybdenum was used as the working electrode, the mercury oxide electrode as the reference electrode, and the graphite rod electrode as the counter electrode to form a three-electrode system, which was placed in an alkaline seawater solution to test its seawater oxidation performance.

[0032] Figure 1SEM images of Ni(OH)2 at different magnifications were shown, revealing a uniform and smooth array of nanosheets with a thickness of 10–30 nm grown on a nickel foam substrate.

[0033] Figure 2 The SEM images of FeMo-Ni3S2 at different magnifications show that the framework of the nanosheets is basically maintained, but the originally smooth nanosheets become very rough and are composed of very small nanoparticles (30~80 nm). This is because in the second hydrothermal process, hydroxyl groups are replaced by S atoms to form nickel sulfide, and Fe and Mo atoms are introduced at the same time, ultimately forming a rough array of Ni3S2 nanosheets co-modified by Fe and Mo.

[0034] Figure 3 The EDX test results of the TEM image show that Ni, Mo, Fe and S elements are uniformly distributed on the nanosheet, successfully proving the formation of nickel sulfide and that Fe and Mo are also incorporated into the nanosheet.

[0035] Figure 4 The characteristic peaks in the XRD pattern of (a) match those of Ni (PDF#4-850) and Ni(OH)2 (PDF#3-177), indicating the successful synthesis of nickel hydroxide. After the second hydrothermal reaction, Figure 4 (b) shows that the characteristic peaks of Ni(OH)2 have been completely transformed into Ni3S2 (PDF#44-1418), indicating the successful synthesis of nickel sulfide. The structure of Ni3S2 was not altered by Fe alone or by the combined modification of Fe and Mo. The peaks belonging to FeMoO4 observed on the FeMo-Ni3S2 sample are due to Fe during the second hydrothermal process. 3+ and MoO4 2- A small amount of precipitate formed during the reaction. Further observation is needed. Figure 4 (c) The XRD comparison image of the local magnification shows that the characteristic peak of Ni3S2 (110) after metal modification is significantly shifted compared to the pure Ni3S2 sample. This is due to the different atomic radii between Fe, Mo and Ni atoms, which also indicates that Fe and Mo are simultaneously incorporated into the Ni3S2 lattice. Figure 4 (d) shows a comparison of the Raman spectra of the three samples. It can be found that the characteristic peaks of Ni3S2 shifted after metal modification, and Mo-O bonds are present in the FeMo-Ni3S2 sample, consistent with the XRD results. In summary, the main components of the FeMo-Ni3S2 sample are a small amount of FeMoO4 and Ni3S2 co-doped with Fe and Mo.

[0036] Figure 5(a) and (b) show the linear sweep voltammetry (LSV) curves of FeMo-Ni3S2, Fe-Ni3S2, Ni3S2, and commercial IrO2 samples in 1 M KOH solution, along with detailed OER overpotential comparisons. Compared to other samples, the FeMo-Ni3S2 sample exhibits significantly improved OER performance at 10, 100, and 500 mA cm⁻¹. -2 At current densities, the required OER overpotential is only 194, 236, and 276 mV, far superior to commercially available IrO2 samples. Further calculations were performed on the Tafel slopes of these samples as follows: Figure 5 As shown in (c), the Tafel slope of FeMo-Ni3S2 is much smaller than that of other samples, at 38.3 mV dec. -1 This indicates that co-modification with Fe and Mo promotes faster OER reaction kinetics. Simultaneously, co-modification with Fe and Mo also improves the conductivity of Ni3S2, thereby promoting rapid electron transfer on the catalyst, as shown in... Figure 5 (d) shows the minimum charge transfer resistance of FeMo-Ni3S2 on the electrochemical impedance diagram.

[0037] Figure 6 The electrochemical performance test results of these samples in 1 M KOH seawater are presented. Figure 6 (a) and (b) show the LSV curves of FeMo-Ni3S2, Fe-Ni3S2, and Ni3S2 samples in 1 M KOH seawater solution, and the corresponding comparison of seawater oxidation overpotentials. Compared with other samples, the FeMo-Ni3S2 sample exhibits significantly improved seawater oxidation performance at 10, 100, and 500 mA cm⁻¹. -2 At current densities, the required OER overpotential is only as low as 201, 251, and 308 mV. Furthermore, as... Figure 6 (c) shows the stability test results, where the FeMo-Ni3S2 sample showed stability at 100 and 500 mA cm⁻¹. -2 Under constant current density, after 1200 and 900 hours of operation respectively, its seawater oxidation performance did not show significant degradation.

[0038] Example 2

[0039] This invention discloses an iron and molybdenum co-modified nickel sulfide nanosheet array. The material is an iron and molybdenum co-modified nickel sulfide nanosheet array grown on a nickel foam substrate, wherein the iron atom content is 2.45%~10.76% and the molybdenum atom content is 1.11~8.99%. The nickel sulfide nanosheet array is composed of stacked nanosheets with rough surfaces, and each nanosheet is assembled from nanoparticles of 30-80 nm.

[0040] This invention also discloses a method for preparing nickel sulfide nanosheet arrays co-modified with iron and molybdenum, the steps of which are as follows:

[0041] (1) The cleaned nickel foam was placed in 60 mL of a clear solution containing 0.05 mol / L Ni(NO3)2·6H2O, 0.167 mol / L urea and 0.067 mol / L ammonium fluoride, and reacted at 120 °C for 6 h using a hydrothermal method. After the reaction was completed and cooled to room temperature, the foam was rinsed clean and dried in an oven to obtain an array of nickel hydroxide nanosheets grown on the nickel foam.

[0042] (2) Nickel hydroxide was converted to nickel sulfide using a second hydrothermal method, while Fe and Mo atoms were introduced. 0.01 mol / L thiourea, 0.01 mol / L Fe(NO3)2·9H2O, and 0.005 mol / L Na2MoO4·2H2O were dissolved sequentially in 60 mL of deionized water, and the mixture was stirred for approximately 30 min. The nickel hydroxide nanosheet array was placed in this clear solution and reacted hydrothermally at 110 ℃ for 16 h. After the reaction was complete and cooled to room temperature, the nanosheets were rinsed clean and dried in an oven to obtain an iron and molybdenum co-modified nickel sulfide nanosheet array grown on nickel foam.

[0043] (3) The prepared nickel sulfide nanosheet array modified with iron and molybdenum was used as the working electrode, the mercury oxide electrode as the reference electrode, and the graphite rod electrode as the counter electrode to form a three-electrode system. The system was then placed in alkaline water and seawater solutions to test its seawater oxidation performance. The sample was tested at 10, 100, and 500 mA cm⁻¹. -2 The overpotential of seawater oxidation at the given current density is shown in Table 1.

[0044] Example 3

[0045] This invention discloses an iron and molybdenum co-modified nickel sulfide nanosheet array. The material is an iron and molybdenum co-modified nickel sulfide nanosheet array grown on a nickel foam substrate, wherein the iron atom content is 2.45%~10.76% and the molybdenum atom content is 1.11%~8.99%. The nickel sulfide nanosheet array is composed of stacked nanosheets with rough surfaces, and each nanosheet is assembled from nanoparticles of 30-80 nm.

[0046] This invention also discloses a method for preparing nickel sulfide nanosheet arrays co-modified with iron and molybdenum, the steps of which are as follows:

[0047] (1) The cleaned nickel foam was placed in 60 mL of a clear solution containing 0.05 mol / L Ni(NO3)2·6H2O, 0.167 mol / L urea and 0.067 mol / L ammonium fluoride, and reacted at 120 °C for 6 h using a hydrothermal method. After the reaction was completed and cooled to room temperature, the foam was rinsed clean and dried in an oven to obtain an array of nickel hydroxide nanosheets grown on the nickel foam.

[0048] (2) Nickel hydroxide was converted to nickel sulfide using a second hydrothermal method, while Fe and Mo atoms were introduced. 0.042 mol / L thiourea, 0.06 mol / L FeCl3·6H2O, and 0.025 mol / L Na2MoO4·2H2O were dissolved sequentially in 60 mL of deionized water, and the mixture was stirred for approximately 30 min. The nickel hydroxide nanosheet array was placed in this clear solution and reacted hydrothermally at 140 ℃ for 10 h. After the reaction was complete and cooled to room temperature, the nanosheets were rinsed clean and dried in an oven to obtain an iron and molybdenum co-modified nickel sulfide nanosheet array grown on nickel foam.

[0049] (3) The prepared nickel sulfide nanosheet array modified with iron and molybdenum was used as the working electrode, the mercury oxide electrode as the reference electrode, and the graphite rod electrode as the counter electrode to form a three-electrode system. The system was then placed in alkaline water and seawater solutions to test its seawater oxidation performance. The sample was tested at 10, 100, and 500 mA cm⁻¹. -2 The overpotential of seawater oxidation at the given current density is shown in Table 1.

[0050] Example 4

[0051] This invention discloses an iron and molybdenum co-modified nickel sulfide nanosheet array. The material is an iron and molybdenum co-modified nickel sulfide nanosheet array grown on a nickel foam substrate, wherein the iron atom content is 2.45%~10.76% and the molybdenum atom content is 1.11%~8.99%. The nickel sulfide nanosheet array is composed of stacked nanosheets with rough surfaces, and each nanosheet is assembled from nanoparticles of 30-80 nm.

[0052] This invention also discloses a method for preparing nickel sulfide nanosheet arrays co-modified with iron and molybdenum, the steps of which are as follows:

[0053] (1) The cleaned nickel foam was placed in 60 mL of a clear solution containing 0.05 mol / L Ni(NO3)2·6H2O, 0.167 mol / L urea and 0.067 mol / L ammonium fluoride, and reacted at 120 °C for 6 h using a hydrothermal method. After the reaction was completed and cooled to room temperature, the foam was rinsed clean and dried in an oven to obtain an array of nickel hydroxide nanosheets grown on the nickel foam.

[0054] (2) Nickel hydroxide was converted to nickel sulfide using a second hydrothermal method, while Fe and Mo atoms were introduced. 0.06 mol / L thiourea, 0.07 mol / L Fe2(SO4)3, and 0.03 mol / L K2MoO4 were dissolved sequentially in 60 mL of deionized water, and the mixture was stirred for approximately 30 min. The nickel hydroxide nanosheet array was placed in this clear solution and reacted hydrothermally at 120 ℃ for 14 h. After the reaction was complete and cooled to room temperature, the nanosheets were rinsed clean and dried in an oven to obtain an iron and molybdenum co-modified nickel sulfide nanosheet array grown on nickel foam.

[0055] (3) The prepared nickel sulfide nanosheet array modified with iron and molybdenum was used as the working electrode, the mercury oxide electrode as the reference electrode, and the graphite rod electrode as the counter electrode to form a three-electrode system. The system was then placed in alkaline water and seawater solutions to test its seawater oxidation performance. The sample was tested at 10, 100, and 500 mA cm⁻¹. -2 The overpotential of seawater oxidation at the given current density is shown in Table 1.

[0056] Example 5

[0057] This invention discloses an iron and molybdenum co-modified nickel sulfide nanosheet array. The material is an iron and molybdenum co-modified nickel sulfide nanosheet array grown on a nickel foam substrate, wherein the iron atom content is 2.45%~10.76% and the molybdenum atom content is 1.11%~8.99%. The nickel sulfide nanosheet array is composed of stacked nanosheets with rough surfaces, and each nanosheet is assembled from nanoparticles of 30-80 nm.

[0058] This invention also discloses a method for preparing nickel sulfide nanosheet arrays co-modified with iron and molybdenum, the steps of which are as follows:

[0059] (1) The cleaned nickel foam was placed in 60 mL of a clear solution containing 0.05 mol / L Ni(NO3)2·6H2O, 0.167 mol / L urea and 0.067 mol / L ammonium fluoride, and reacted at 120 °C for 6 h using a hydrothermal method. After the reaction was completed and cooled to room temperature, the foam was rinsed clean and dried in an oven to obtain an array of nickel hydroxide nanosheets grown on the nickel foam.

[0060] (2) Nickel hydroxide was converted to nickel sulfide using a second hydrothermal method, while Fe and Mo atoms were introduced. 0.042 mol / L thiourea, 0.042 mol / L Fe(NO3)2·9H2O, and 0.02 mol / L Na2MoO4·2H2O were dissolved sequentially in 60 mL of deionized water, and the mixture was stirred for approximately 30 min. The nickel hydroxide nanosheet array was placed in this clear solution and reacted hydrothermally at 100 ℃ for 20 h. After the reaction was complete and cooled to room temperature, the nanosheets were rinsed clean and dried in an oven to obtain an iron and molybdenum co-modified nickel sulfide nanosheet array grown on nickel foam.

[0061] (3) The prepared nickel sulfide nanosheet array modified with iron and molybdenum was used as the working electrode, the mercury oxide electrode as the reference electrode, and the graphite rod electrode as the counter electrode to form a three-electrode system. The system was then placed in alkaline water and seawater solutions to test its seawater oxidation performance. The sample was tested at 10, 100, and 500 mA cm⁻¹. -2 The overpotential of seawater oxidation at the given current density is shown in Table 1.

[0062] Example 6

[0063] This invention discloses an iron and molybdenum co-modified nickel sulfide nanosheet array. The material is an iron and molybdenum co-modified nickel sulfide nanosheet array grown on a nickel foam substrate, wherein the iron atom content is 2.45%~10.76% and the molybdenum atom content is 1.11%~8.99%. The nickel sulfide nanosheet array is composed of stacked nanosheets with rough surfaces, and each nanosheet is assembled from nanoparticles of 30-80 nm.

[0064] This invention also discloses a method for preparing nickel sulfide nanosheet arrays co-modified with iron and molybdenum, the steps of which are as follows:

[0065] (1) The cleaned nickel foam was placed in 60 mL of a clear solution containing 0.05 mol / L Ni(NO3)2·6H2O, 0.167 mol / L urea and 0.067 mol / L ammonium fluoride, and reacted at 120 °C for 6 h using a hydrothermal method. After the reaction was completed and cooled to room temperature, the foam was rinsed clean and dried in an oven to obtain an array of nickel hydroxide nanosheets grown on the nickel foam.

[0066] (2) Nickel hydroxide was converted to nickel sulfide using a second hydrothermal method, while Fe and Mo atoms were introduced. 0.1 mol / L thiourea, 0.1 mol / L Fe2(SO4)3, and 0.08 mol / L Na2MoO4·2H2O were dissolved in 60 mL of deionized water and stirred for about 30 min. The nickel hydroxide nanosheet array was placed in this clear solution and reacted hydrothermally at 100 °C for 20 h. After the reaction was complete and cooled to room temperature, the nanosheets were rinsed clean and dried in an oven to obtain an iron and molybdenum co-modified nickel sulfide nanosheet array grown on nickel foam.

[0067] (3) The prepared nickel sulfide nanosheet array modified with iron and molybdenum was used as the working electrode, the mercury oxide electrode as the reference electrode, and the graphite rod electrode as the counter electrode to form a three-electrode system. The system was then placed in alkaline water and seawater solutions to test its seawater oxidation performance. The sample was tested at 10, 100, and 500 mA cm⁻¹. -2 The overpotential of seawater oxidation at the given current density is shown in Table 1.

[0068] Table 1. Summary of seawater oxidation performance of FeMo-Ni3S2 samples prepared by different embodiments

[0069]

[0070] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. An array of nickel sulfide nanosheets co-modified with iron and molybdenum, characterized in that, The nickel sulfide nanosheet array is an iron and molybdenum co-modified nickel sulfide nanosheet array grown on a nickel foam substrate, wherein the iron atom content is 2.45%~10.76% and the molybdenum atom content is 1.11%~8.99%, and the nickel sulfide is nickel disulfide.

2. The nickel sulfide nanosheet array co-modified with iron and molybdenum according to claim 1, characterized in that, The nickel sulfide nanosheet array is composed of stacked nanosheets with rough surfaces, and each nanosheet is assembled from nanoparticles of 30-80 nm in size.

3. A method for preparing an array of nickel sulfide nanosheets co-modified with iron and molybdenum as described in claim 1 or 2, characterized in that, The process includes the following steps: Step S1: A nickel hydroxide nanosheet array is prepared using a hydrothermal method as a self-template; Step S2: Nickel hydroxide is converted into nickel sulfide again using the hydrothermal method, while iron and molybdenum atoms are jointly modified into the nickel sulfide nanosheet array.

4. The method for preparing the nickel sulfide nanosheet array co-modified with iron and molybdenum according to claim 3, characterized in that, The specific steps of step S1 are as follows: the cleaned nickel foam is placed in 60 mL of a clear solution containing 0.05 mol / L Ni(NO3)2·6H2O, 0.167 mol / L urea and 0.067 mol / L ammonium fluoride, and reacted at 120 °C for 6 h using a hydrothermal method. After the reaction is completed and cooled to room temperature, it is rinsed clean and dried in an oven to obtain a nickel hydroxide nanosheet array grown on the nickel foam.

5. The method for preparing the nickel sulfide nanosheet array co-modified with iron and molybdenum according to claim 3, characterized in that, The specific steps of step S2 are: placing the nickel hydroxide nanosheet array in a container containing thiourea and Fe... 3+ and MoO4 2- A hydrothermal reaction was carried out in the solution to obtain an array of nickel sulfide nanosheets co-modified with iron and molybdenum.

6. The method for preparing the nickel sulfide nanosheet array co-modified with iron and molybdenum according to claim 5, characterized in that, The concentration of the thiourea is 0.01~0.10 mol / L, and the Fe... 3+ The solution is provided by Fe(NO3)3, Fe2(SO4)3, or FeCl3 at a concentration of 0.01~0.10 mol / L; the MoO4 2- It is provided by Na2MoO4 or K2MoO4 at a concentration of 0.005~0.08 mol / L.

7. The method for preparing the nickel sulfide nanosheet array co-modified with iron and molybdenum according to claim 5, characterized in that, In step S2, the hydrothermal reaction conditions in the hydrothermal method are 100~160℃ and the reaction time is 8~20 h.

8. The application of the nickel sulfide nanosheet array modified with iron and molybdenum according to claim 1 or 2 in the oxidation reaction of alkaline water or seawater.

9. The application of the iron and molybdenum co-modified nickel sulfide nanosheet array according to claim 8 in the oxidation reaction of alkaline water or seawater, characterized in that, The specific application method is as follows: an array of nickel sulfide nanosheets modified with iron and molybdenum is placed in an alkaline system as an oxygen evolution electrode for the oxidation reaction of alkaline water and seawater.

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