Ni (CN) 2 / NiS2 heterostructure self-supporting electrode and preparation method and application thereof

Abstract

The invention relates to the technical field of electro-catalysis, in particular to a Ni (CN) 2 / NiS2 heterostructure self-supporting electrode and a preparation method and application thereof, and the Ni (CN) 2 / NiS2 heterostructure self-supporting electrode comprises a three-dimensional conductive carrier and a Ni (CN) 2 / NiS2 heterostructure nanosheet loaded on the conductive carrier. The preparation method comprises the following steps: firstly, synthesizing a Ni-HCP precursor on a three-dimensional conductive carrier by adopting a hydrothermal method, and carrying out dehydration and low-temperature partial vulcanization to obtain a Ni (CN) 2 / NiS2 composite nano heterostructure self-supporting electrode; according to the Ni (CN) 2 / NiS2 heterostructure self-supporting electrode prepared by the method, the characteristics of high specific surface area and rapid electron transmission channel of the precursor are reserved, the formed Ni (CN) 2 / NiS2 heterostructure interface further optimizes the electronic structure of the material surface, and the Ni (CN) 2 / NiS2 heterostructure self-supporting electrode has relatively high electro-catalytic urea oxidation performance while meeting low-cost synthesis.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalysis, and in particular to a Ni(CN)2 / NiS2 heterostructure self-supporting electrode, a preparation method thereof and an application thereof. Background Art

[0002] Hydrogen (H2) is expected to be a substitute for traditional fossil fuels due to its zero emissions and high-quality energy density. Compared with the industrial production of hydrogen using natural gas or water gas, hydrogen production by water electrolysis is a clean and promising technology, but this technology still faces the problem of high energy consumption, which is mainly due to the slow oxygen evolution reaction (OER) process on the anode. Replacing the high-potential oxygen evolution reaction (OER) with the urea oxidation reaction (UOR) with a lower theoretical potential can not only achieve efficient hydrogen production, but also degrade urea wastewater. However, in actual electrolysis operations, an efficient electrocatalyst is still required to accelerate the urea oxidation reaction on the anode. At present, noble metal-based catalysts (such as Pt, Pd, IrO2) have shown good electrocatalytic activity for UOR. However, the high cost and scarcity of resources limit their wide application in the above systems. Therefore, it is crucial to develop cost-effective non-noble metal-based catalysts for UOR electrocatalysis.

[0003] Among many non-noble metal-based catalysts, nickel-based catalysts have received extensive attention due to the abundant reserves, low price, and easy extraction of nickel. Research shows that nickel-based catalysts have obvious UOR performance, which is closely related to the high-valent Ni species formed in-situ during the electrocatalytic UOR reaction. Nickel can form compounds or alloys with various non-metals and metals, thereby optimizing the electronic structure of nickel and significantly improving the UOR performance of nickel-based catalysts. However, some reported nickel-based catalysts still have problems such as poor conductivity or insufficient exposure of active sites, resulting in low catalytic activity. Transition metal sulfides have diverse electronic structures due to their unique d electron orbits and electrical properties, and have excellent redox and catalytic activities. Constructing a heterostructure can synergistically integrate the characteristics and advantages of the two components at the interface, further improving the catalytic performance of the material by adjusting the surface electronic structure of the material and optimizing the active sites. Summary of the Invention

[0004] In view of this, the present invention proposes a Ni(CN)2 / NiS2 heterostructure self-supporting electrode, a preparation method thereof and an application thereof, to solve the problems of poor conductivity, low activity and insufficient stability of the current single nickel-based powder catalyst.

[0005] The technical solution of the present invention is realized as follows: The present invention provides a Ni(CN)2 / NiS2 heterostructure self-supporting electrode, including a three-dimensional conductive carrier and Ni(CN)2 / NiS2 heterostructure nanosheets loaded on the conductive carrier.

[0006] Among them, the present invention utilizes the excellent electrical conductivity and unique three-dimensional three-dimensional network structure of the conductive carrier, and uses it as a substrate to in-situ load Ni(CN)2 nanosheets to increase the number of active sites of the material and improve the utilization rate of active substances. In addition, the inherent processing performance of the conductive carrier is used to reduce the use of additives such as adhesives to avoid their influence on the catalytic activity of the material.

[0007] Ni(CN)2 nanosheets grow tightly on the surface of the three-dimensional conductive carrier. After low-temperature partial sulfidation, NiS2 nanoparticles are uniformly attached to the surface of Ni(CN)2 nanosheets, forming a Ni(CN)2 / NiS2 heterostructure. The formation of the Ni(CN)2 / NiS2 heterostructure enhances the electrical conductivity of Ni(CN)2, adjusts the electronic structure of the catalyst surface, and significantly improves the catalytic activity of the electrode.

[0008] The present invention also provides a preparation method of a Ni(CN)2 / NiS2 heterostructure self-supporting electrode, comprising the following steps:

[0009] S1. Mix nickel salt, trisodium citrate and surfactant and dissolve them in water to obtain a first mixed solution, then add a K2[Ni(CN)4] solution for mixing to obtain a second mixed solution, and perform a hydrothermal reaction on the three-dimensional conductive carrier and the second mixed solution to obtain a Ni-HCP nanosheet array supported by the three-dimensional conductive carrier;

[0010] S2. Dehydrate the Ni-HCP nanosheet array supported by the three-dimensional conductive carrier to obtain a Ni(CN)2 nanosheet array supported by the three-dimensional conductive carrier;

[0011] S3. Place the sulfur source and Ni(CN)2 supported by the three-dimensional conductive carrier at the upper and lower ends of the porcelain boat respectively, and perform low-temperature sulfidation treatment to obtain a Ni(CN)2 / NiS2 heterostructure self-supporting electrode.

[0012] The preparation method of the Ni(CN)2 / NiS2 heterostructure self-supporting electrode provided by the present invention realizes the controllable synthesis of high-performance electrocatalytic materials through a simple hydrothermal method combined with dehydration and low-temperature sulfidation treatment. Its remarkable technical effects are manifested in that: this method uses a three-dimensional conductive carrier (such as nickel foam) as a substrate, and in-situ grows a nickel-nickel Hofmann-type coordination polymer (Ni-HCP) nanosheet array by hydrothermal reaction. After precisely controlled dehydration and partial sulfidation treatment, a unique Ni(CN)2 / NiS2 heterointerfacial structure is formed, which not only retains the characteristics of the precursor's high specific surface area and fast electron transport channels, but also optimizes the surface electronic structure of the material through the heterointerfacial interface.

[0013] Further, before the hydrothermal reaction between the three-dimensional conductive carrier and the second mixed solution, pretreatment of the three-dimensional conductive carrier is also included. The pretreatment includes sequentially pickling, alcohol washing, and water washing the three-dimensional conductive carrier. More preferably, the pickling solution is hydrochloric acid, and the alcohol washing solution is ethanol. The oxides existing on the surface of the three-dimensional conductive carrier can be removed by pickling, and the oil stains on the surface of the three-dimensional conductive carrier can be removed by alcohol washing.

[0014] On the basis of the above technical solution, preferably, in step S1, in the first mixed solution, the concentration of nickel ions is 0.025 - 0.075 mmol / mL, the concentration of trisodium citrate is 0.03 - 0.06 mmol / mL, the concentration of the surfactant is 2.5 - 20.0 mg / mL, the concentration of the K2[Ni(CN)4] solution is 0.025 - 0.075 mmol / mL, and the volume ratio of the K2[Ni(CN)4] solution to the first mixed solution is 1:1.

[0015] On the basis of the above technical solution, preferably, in step S1, the three-dimensional conductive carrier is any one of nickel foam, stainless steel, titanium mesh, and carbon fiber.

[0016] On the basis of the above technical solution, preferably, in step S1, the surfactant is one or more of polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, and cetyltrimethylammonium chloride.

[0017] On the basis of the above technical solution, preferably, in step S1, the temperature of the hydrothermal reaction is 80 - 150 °C, and the time of the hydrothermal reaction is 4 - 16 h.

[0018] On the basis of the above technical solution, preferably, in step S2, the temperature of the dehydration treatment is 200 - 280 °C, the heating rate of the dehydration treatment is 5 °C / min, the time of the dehydration treatment is 0.5 - 2 h, and the atmosphere of the dehydration treatment is an inert atmosphere.

[0019] On the basis of the above technical solution, preferably, in step S3, the temperature of the low-temperature vulcanization treatment is 250 - 350 °C, the heating rate during the vulcanization process is 2 - 10 °C / min, the time of the low-temperature vulcanization treatment is 0.5 - 1 h, and the atmosphere of the low-temperature vulcanization treatment is an inert atmosphere.

[0020] On the basis of the above technical solution, preferably, in step S3, the sulfur source is one or more of thiourea, sulfur powder, and thioacetamide; more preferably, the sulfur source is thiourea, and its addition amount is 10 - 40 mg.

[0021] The present invention also provides an application of the Ni(CN)2 / NiS2 heterostructure self-supporting electrode in the electrocatalytic urea oxidation reaction.

[0022] The Ni(CN)2 / NiS2 heterostructure self-supporting electrode of the present invention, its preparation method and application have the following beneficial effects compared with the prior art:

[0023] (1) In the present invention, a simple hydrothermal method is used to in-situ grow two-dimensional nickel-nickel Hofmann-type coordination polymer (Ni-HCP) nanosheets on the surface of a three-dimensional conductive carrier. Without a binder, the three-dimensional open structure of the conductive carrier can effectively increase the specific surface area and conductivity of the material, increasing the number of catalytic active sites and the utilization rate of active substances.

[0024] (2) In the present invention, Ni-HCP supported on a three-dimensional conductive carrier is used as a precursor. This material itself has a high specific surface area and a fast electron transport channel. After dehydration and low-temperature partial sulfidation, the obtained Ni(CN)2 / NiS2 heterostructure self-supporting electrode not only retains the nanosheet array structure of the precursor but also further enriches the active sites, accelerating the rates of ion diffusion and electron conduction, thereby promoting the reaction kinetics of electrocatalytic UOR.

[0025] (3) The preparation method disclosed in the present invention is simple, has a low production cost, involves green and environmentally friendly raw materials, is easy to operate and control in the preparation process, has good electrocatalytic UOR performance and stability, and is easy to realize industrial production. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 Scanning electron microscope images of the Ni(CN)2 / NiS2 electrodes prepared in Example 1, Example 2, Example 3, and Example 4 of the present invention;

[0028] Figure 2 Scanning electron microscope image of the Ni(CN)2 / NiS2 electrode prepared in Example 1 of the present invention;

[0029] Figure 3 Scanning electron microscope image of the Ni(CN)2 / NF electrode prepared in Comparative Example 1 of the present invention;

[0030] Figure 4 Scanning electron microscope image of the NiS2 / NF electrode prepared in Comparative Example 2 of the present invention;

[0031] Figure 5Scanning electron microscopy image of the Ni(CN)2 / NiS2 / NF-70 electrode prepared as Comparative Example 3 of the present invention

[0032] Figure 6 X-ray diffraction patterns of the materials obtained in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention;

[0033] Figure 7 High-resolution Ni 2p spectra of the materials obtained in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention;

[0034] Figure 8 High-resolution transmission electron microscopy image of the material obtained in Example 1 of the present invention;

[0035] Figure 9 Electrocatalytic UOR polarization curves of the materials obtained in Example 1, Example 2, Example 3 and Example 4 of the present invention;

[0036] Figure 10 Electrocatalytic UOR polarization curves of the materials obtained in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention;

[0037] Figure 11 Electrocatalytic UOR stability test results of the Ni(CN)2 / NiS2 / NF-20 electrode prepared in Example 1 of the present invention. Detailed implementation manners

[0038] Next, in combination with the implementation manners of the present invention, the technical solutions in the implementation manners of the present invention will be clearly and completely described. Obviously, the described implementation manners are only a part of the implementation manners of the present invention, rather than all of the implementation manners. Based on the implementation manners in the present invention, all other implementation manners obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0039] Example 1

[0040] This example provides a Ni(CN)2 / NiS2 heterostructure self-supporting electrode and a preparation method thereof, including the following steps:

[0041] (1) Preparation of the precursor: Dissolve 1.5 mmol of nickel acetate, 1.4 mmol of trisodium citrate, and 0.075 g of PVP (molecular weight 44000) in 30 mL of H2O and form a first mixed solution by magnetic stirring; dissolve 1.5 mmol of K2Ni(CN)4 in 30 mL of H2O to form a K2Ni(CN)4 solution. Then, slowly pour the K2Ni(CN)4 solution into the first mixed solution, continuously stir for 30 s to obtain a second mixed solution, place the second mixed solution in a 100 mL inner reactor, and obliquely place a clean nickel foam (0.5×4.0 cm 2 ). Then, place the reactor in an oven at 120 °C for hydrothermal reaction for 12 h. After the reaction is completed, take out the nickel foam, wash it 3 times with deionized water, and dry it in a vacuum oven at 60 °C for 12 h to obtain the Ni-HCP / NF nanosheet array.

[0042] (2) Preparation of the Ni(CN)2 nanosheet array: Place the cut Ni-HCP / NF (0.5×2.0 cm 2 ) in a temperature-programmed tube furnace, heat it to 260 °C at a rate of 5 °C / min under an inert atmosphere protection and hold for 1 h to dehydrate to obtain the Ni(CN)2 nanosheet array supported by nickel foam (Ni(CN)2 / NF).

[0043] (3) Preparation of the Ni(CN)2 / NiS2 heterostructure self-supporting electrode: Place 20 mg of thiourea and the Ni(CN)2 / NF material at the upper and lower ends of the same porcelain boat respectively, heat it to 300 °C at a rate of 5 °C / min under an inert atmosphere protection for sulfidation for 0.5 h to obtain the Ni(CN)2 / NiS2 / NF-20 electrode.

[0044] Example 2

[0045] This example provides a Ni(CN)2 / NiS2 heterostructure self-supporting electrode and its preparation method. The preparation method is the same as that of Example 1, only changing the amount of thiourea used in step (3) to 10 mg, and finally obtaining the Ni(CN)2 / NiS2 / NF-10 electrode.

[0046] Example 3

[0047] This example provides a Ni(CN)2 / NiS2 heterostructure self-supporting electrode and its preparation method. The preparation method is the same as that of Example 1, only changing the amount of thiourea used in step (3) to 30 mg, and finally obtaining the Ni(CN)2 / NiS2 / NF-30 electrode.

[0048] Example 4

[0049] This example provides a self-supporting Ni(CN)2 / NiS2 heterostructure electrode and its preparation method. The preparation method is the same as that in Example 1, except that the amount of thiourea used in step (3) is changed to 40 mg, and finally the Ni(CN)2 / NiS2 / NF-40 electrode is prepared.

[0050] Example 5

[0051] This example provides a self-supporting Ni(CN)2 / NiS2 heterostructure electrode and its preparation method, including the following steps:

[0052] (1) Preparation of the precursor: Dissolve 0.75 mmol of nickel acetate, 0.9 mmol of trisodium citrate, and 0.3 g of PVP (molecular weight 44000) in 30 mL of H2O and form a first mixed solution by magnetic stirring; dissolve 0.75 mmol of K2Ni(CN)4 in 30 mL of H2O to form a K2Ni(CN)4 solution. Then, slowly pour the K2Ni(CN)4 solution into the first mixed solution, continuously stir for 30 s to obtain a second mixed solution, place the second mixed solution in the inner liner of a 100 mL reaction kettle, and obliquely place a clean nickel foam (0.5×4.0 cm 2 ), and then place the reaction kettle in an oven at 80 °C for hydrothermal reaction for 16 h. After the reaction is completed, take out the nickel foam, wash it 3 times with deionized water, and dry it in a vacuum oven at 60 °C for 12 h to obtain the Ni-HCP / NF nanosheet array.

[0053] (2) Preparation of the Ni(CN)2 nanosheet array: Place the cut Ni-HCP / NF (0.5×2.0 cm 2 ) in a programmed temperature tube furnace, heat it to 200 °C at a rate of 5 °C / min under an inert atmosphere protection and keep it for 2 h to dehydrate to obtain the Ni(CN)2 nanosheet array supported by nickel foam (Ni(CN)2 / NF).

[0054] (3) Preparation of the Ni(CN)2 / NiS2 heterostructure self-supporting electrode: Place 20 mg of thiourea and the Ni(CN)2 / NF material at the upper and lower ends of the same porcelain boat respectively, heat it to 350 °C at a rate of 2 °C / min under an inert atmosphere protection and sulfide for 0.8 h to obtain the Ni(CN)2 / NiS2 / NF-50 electrode.

[0055] Example 6

[0056] This example provides a self-supporting Ni(CN)2 / NiS2 heterostructure electrode and its preparation method, including the following steps:

[0057] (1) Preparation of precursor: Dissolve 2.25 mmol of nickel acetate, 1.8 mmol of trisodium citrate, and 0.6 g of PVP (molecular weight 44000) in 30 mL of H2O and form a first mixed solution by magnetic stirring; dissolve 2.25 mmol of K2Ni(CN)4 in 30 mL of H2O to form a K2Ni(CN)4 solution. Then, slowly pour the K2Ni(CN)4 solution into the first mixed solution, and after continuously stirring for 30 s, a second mixed solution is obtained. Place the second mixed solution in the inner liner of a 100 mL autoclave, and obliquely place a clean nickel foam (0.5×4.0 cm 2 ). Then, place the autoclave in an oven at 150 °C for hydrothermal reaction for 4 h. After the reaction is completed, take out the nickel foam, wash it 3 times with deionized water, and dry it in a vacuum oven at 60 °C for 12 h to obtain the Ni-HCP / NF nanosheet array.

[0058] (2) Preparation of Ni(CN)2 nanosheet array: Place the cut Ni-HCP / NF (0.5×2.0 cm 2 ) in a programmed temperature tube furnace, heat it to 280 °C at a rate of 5 °C / min under the protection of an inert atmosphere and keep it at this temperature for 0.5 h to dehydrate and obtain the Ni(CN)2 nanosheet array supported by nickel foam (Ni(CN)2 / NF).

[0059] (3) Preparation of Ni(CN)2 / NiS2 heterostructure self-supporting electrode: Place 20 mg of sulfur powder and the Ni(CN)2 / NF material at the upper and lower ends of the same porcelain boat respectively, heat it to 350 °C at a rate of 10 °C / min under the protection of an inert atmosphere for sulfidation for 0.5 h to obtain the Ni(CN)2 / NiS2 / NF-60 electrode.

[0060] Comparative Example 1

[0061] This comparative example provides a nickel foam-supported nickel cyanide (Ni(CN)2 / NF) nanosheet array and its preparation method. The preparation method is the same as that in Example 1, only the low-temperature part of the sulfidation process in step (3) is omitted, and the Ni(CN)2 / NF electrode is directly obtained after dehydration.

[0062] Comparative Example 2

[0063] This comparative example provides a nickel foam-supported nickel sulfide (NiS2 / NF) nanosheet array and its preparation method. The preparation method is the same as that in Example 1, only the amount of thiourea used in step (3) is changed to 500 mg, and the Ni-HCP / NF is completely sulfided to obtain the NiS2 / NF electrode.

[0064] Comparative Example 3

[0065] This comparative example provides a nickel foam-supported Ni(CN)2 / NiS2 heterostructure self-supporting electrode and its preparation method. The preparation method is the same as that of Example 1, except that the surfactant PVP is not added in step (1), and finally the Ni(CN)2 / NiS2 / NF-70 electrode is obtained.

[0066] Application Example

[0067] Using the self-supporting electrodes obtained in the above examples and comparative examples as the working electrodes, a carbon rod as the counter electrode, and a Hg / HgO electrode as the reference electrode, linear cyclic voltammetry scanning and current-time response tests were carried out under a three-electrode system to evaluate their UOR electrocatalytic activity and stability. The test electrolyte was a mixed solution of 0.5 M urea + 1.0 M potassium hydroxide.

[0068] The commercial RuO2 (99.95 wt.%) catalyst was loaded on the surface of nickel foam at the same loading amount for comparison. The preparation method was as follows: The calculated commercial RuO2 (99.95 wt.%) catalyst was dispersed in an absolute ethanol solution, and then drop-coated on a clean nickel foam to prepare a RuO2 / nickel foam (RuO2 / NF) electrode. The UOR activity test was carried out in the same manner as above. The test results are shown in Table 1.

[0069] Table 1 Comparison of UOR performance tests of each catalyst sample

[0070]

[0071]

[0072] As can be seen from Table 1, under the same electrochemical test conditions, the Ni(CN)2 / NiS2 / NF-20 electrode obtained in Example 1 of the present invention has the lowest potential required to reach the same current density compared to the electrodes prepared in Comparative Example 2, Example 3, Example 4, Comparative Example 1, Comparative Example 2, and the commercial noble metal-based catalyst (RuO2 / NF), indicating its excellent UOR electrocatalytic performance.

[0073] Figure 1 The scanning electron microscope images of the electrodes prepared in Examples 1-4 are shown, where Figure 1 a and Figure 2 The scanning electron microscope image of the Ni(CN)2 / NiS2 / NF-20 electrode prepared in Example 1 is shown. It can be seen from the figure that the Ni(CN)2 / NiS2 heterostructure grows uniformly on the surface of the nickel foam substrate in the form of nanosheets. A small amount of NiS2 particles can be observed anchored on the surface of Ni(CN)2, and there are slight cracks on the surface of the Ni(CN)2 nano main body. Figure 1b shows the scanning electron microscopy image of the Ni(CN)2 / NiS2 / NF-10 electrode prepared in Example 2. It can be seen from the figure that a small amount of NiS2 particles are anchored on the surface of the Ni(CN)2 nano matrix. Figure 1 c shows the scanning electron microscopy image of the Ni(CN)2 / NiS2 / NF-30 electrode prepared in Example 3. It can be seen from the figure that a large number of NiS2 particles are anchored on the surface of the Ni(CN)2 nano matrix. Figure 1 d shows the scanning electron microscopy image of the Ni(CN)2 / NiS2 / NF-40 electrode prepared in Example 4. It can be seen from the figure that the surface of the Ni(CN)2 nanosheets is completely wrapped by NiS2 particles. By comparing the SEM images of the materials obtained in Example 1, Example 2, Example 3 and Example 4, it is found that with the increase of the thiourea dosage, the more NiS2 particles on the surface.

[0074] Figure 3 The scanning electron microscopy image of the Ni(CN)2 / NF electrode prepared in Comparative Example 1 is shown. It can be seen from the figure that the smooth-surfaced Ni(CN)2 grows uniformly on the nickel foam substrate in the form of nanosheets.

[0075] Figure 4 The scanning electron microscopy image of the NiS2 / NF electrode prepared in Comparative Example 2 is shown. It can be seen from the figure that the rough-surfaced NiS2 grows uniformly on the nickel foam substrate in the form of nanosheets, and the nanosheets are composed of NiS2 nanoparticles.

[0076] Figure 5 The scanning electron microscopy image of the Ni(CN)2 / NiS2 / NF-70 electrode prepared in Comparative Example 3 is shown. It can be seen from the figure that compared with the materials obtained in Example 1, Example 2, Example 3 and Example 4, the lateral size of the Ni(CN)2 nanosheets obtained without adding surfactant is only about 500 nm.

[0077] Figure 6The X-ray diffraction patterns of the materials obtained in Example 1, Comparative Example 1, and Comparative Example 2 are shown. The four peaks located at the crystal planes of 31.5°, 35.3°, 38.8°, and 53.6° respectively belong to the (200), (210), (211), and (311) crystal planes of NiS2 (PDF#11-0099); the peaks located at the crystal planes of 18.3°, 27.8°, 29.2°, 37.1°, 41.8°, 47.2°, 53.5°, 57.1°, 62.0°, 77.5°, and 70.1° respectively belong to the (110), (001), (210), (220), (310), (221), (400), (330), (401), and (510) crystal planes of Ni(CN)2 (PDF#27-0864). By comparison, obvious diffraction peaks of Ni(CN)2 and NiS2 are present on the XRD of the material prepared in Example 1, and the characteristics corresponding to the (001) plane of Ni(CN)2 and the (200) plane of NiS2 are relatively strong, indicating that the material is composed of the composite of Ni(CN)2 and NiS2. Compared with the main peak of NiS2, the intensity of the characteristic peak of the (200) plane of the material prepared in Example 1 is significantly weakened, indicating that the main body of the material is Ni(CN)2, and a part of NiS2 is stacked on the outer layer.

[0078] Figure 7 The high-resolution Ni 2p spectra of the materials obtained in Example 1, Comparative Example 1, and Comparative Example 2 are shown. Figure 8 The high-resolution transmission electron microscopy image of the electrode prepared in Example 1 is shown. It can be seen from the figure that the lattice fringe with a distance of 0.215 nm is attributed to the (310) lattice plane of Ni(CN)2, and the lattice distance of 0.232 nm belongs to the (211) lattice plane of NiS2. In addition, the heterointerfaces between Ni(CN)2 and NiS2 are also observed at other positions, further verifying the successful formation of the Ni(CN)2 / NiS2 heterostructure.

[0079] Figure 9 The UOR current-time response curves of the electrodes prepared in Examples 1-4 are shown; Figure 10 The electrocatalytic UOR polarization curves of the materials obtained in Example 1, Comparative Example 1, and Comparative Example 2 are shown. It can be seen from the figure that in the electrocatalytic urea oxidation reaction, the Ni(CN)2 / NiS2 / NF-20 electrode prepared in Example 1 of the present invention only requires a potential of 1.42 V (vs. RHE) to output a high current density of 100 mA cm -2 which is significantly better than the electrodes prepared in Example 2, Example 3, Example 4, Comparative Example 1, Comparative Example 2, and the commercial noble metal-based catalyst (RuO2 / NF); Figure 11Shows the electrocatalytic UOR stability test results of the material obtained in Example 1. It can be seen from the figure that after continuous catalysis for 25 h at a high current density of 100 mA cm -2 , the retention rate of the UOR current density of this catalyst reaches more than 85%, showing good stability. The main reason for the decrease in the current density is the decrease in the electrolyte concentration.

[0080] The above performance tests show that the Ni(CN)2 / NiS2 / NF composite nano-heterostructure self-supporting electrode material obtained by dehydrating and partially sulfiding the Ni-HCP / NF precursor can effectively improve the catalytic activity of electrocatalytic urea oxidation. This is closely related to the excellent conductivity and space utilization rate given by the three-dimensional nickel foam substrate to the material, as well as the large specific surface area of the Ni(CN)2 / NiS2 composite nano-heterostructure material itself, the rich catalytic active sites at the heterointerface, and the fast electron conduction speed.

[0081] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A Ni(CN)2 / NiS2 heterostructure self-supporting electrode, characterized in that, It includes a three-dimensional conductive carrier and Ni(CN)₂ / NiS₂ heterostructure nanosheets supported on the conductive carrier.

2. The preparation method of a Ni(CN)2 / NiS2 heterostructure self-supporting electrode according to claim 1, characterized in that: It includes the following steps: S1. Mix nickel salt, trisodium citrate, and a surfactant and dissolve them in water to obtain a first mixed solution. Then add a K₂[Ni(CN)₄] solution for mixing to obtain a second mixed solution. Perform a hydrothermal reaction on the three-dimensional conductive carrier and the second mixed solution to obtain a Ni-HCP nanosheet array supported by the three-dimensional conductive carrier; S2. Dehydrate the Ni-HCP nanosheet array supported by the three-dimensional conductive carrier to obtain a Ni(CN)₂ nanosheet array supported by the three-dimensional conductive carrier; S3. Place the sulfur source and the Ni(CN)₂ supported by the three-dimensional conductive carrier at the upper and lower ends of a porcelain boat respectively, and perform low-temperature sulfidation treatment to obtain a Ni(CN)₂ / NiS₂ heterostructure self-supporting electrode.

3. The preparation method of a Ni(CN)2 / NiS2 heterostructure self-supporting electrode according to claim 2, wherein: In step S1, in the first mixed solution, the concentration of nickel ions is 0.025 - 0.075 mmol / mL, the concentration of trisodium citrate is 0.03 - 0.06 mmol / mL, the concentration of the surfactant is 2.5 - 20.0 mg / mL, the concentration of the K₂[Ni(CN)₄] solution is 0.025 - 0.075 mmol / mL, and the volume ratio of the K₂[Ni(CN)₄] solution to the first mixed solution is 1:

1.

4. The preparation method of a Ni(CN)2 / NiS2 heterostructure self-supporting electrode according to claim 2, characterized in that: In step S1, the three-dimensional conductive carrier is any one of nickel foam, stainless steel, titanium mesh, and carbon fiber.

5. The preparation method of a Ni(CN)2 / NiS2 heterostructure self-supporting electrode according to claim 2, characterized in that: In step S1, the surfactant is one or more of polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, and cetyltrimethylammonium chloride.

6. The preparation method of a Ni(CN)2 / NiS2 heterostructure self-supporting electrode according to claim 2, characterized in that: In step S1, the temperature of the hydrothermal reaction is 80 - 150 °C, and the time of the hydrothermal reaction is 4 - 16 h.

7. The preparation method of a Ni(CN)2 / NiS2 heterostructure self-supporting electrode according to claim 2, characterized in that: In step S2, the temperature of the dehydration treatment is 200 - 280 °C, the time of the dehydration treatment is 0.5 - 2 h, and the atmosphere of the dehydration treatment is an inert atmosphere.

8. The preparation method of a Ni(CN)2 / NiS2 heterostructure self-supporting electrode according to claim 2, characterized in that: In step S3, the temperature of the low-temperature sulfidation treatment is 250 - 350 °C, the time of the low-temperature sulfidation treatment is 0.5 - 1 h, and the atmosphere of the low-temperature sulfidation treatment is an inert atmosphere.

9. The preparation method of a Ni(CN)2 / NiS2 heterostructure self-supporting electrode according to claim 2, wherein: In step S3, the sulfur source is one or more of thiourea, sulfur powder, and thioacetamide, and the addition amount of the sulfur source is 10 - 40 mg.

10. Application of a Ni(CN)₂ / NiS₂ heterostructure self-supporting electrode as described in claim 1 in an electrocatalytic urea oxidation reaction.

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