ZIF-Derived CoZnS Electrode Material and Its Preparation Method and Application

Abstract

The present invention belongs to the technical field of electrode materials, specifically a ZIF-derived CoZnS electrode material and its preparation method and application. In the present invention, soluble cobalt salt and soluble zinc salt are used as raw materials, NH4F is used as a buffer and structure-directing agent, urea is used to provide a weak alkaline environment, and a nickel foam-CoZn precursor is prepared by a solvothermal reaction. Then, through the coordination of 2-methylimidazole with the nickel foam-CoZn precursor, it is coordinated and converted into ZIF, and then the ZIF-67 structure is introduced to obtain a ZIF-derived precursor. By controlling the sulfidation conditions of the ZIF-derived precursor, a ZIF-derived CoZnS electrode material is prepared. The ZIF-derived CoZnS electrode material has a uniform MOF structure and a three-dimensional array, providing sufficient active sites and a stable physical structure for subsequent electrocatalytic hydrogen evolution reaction, overcoming the technical defect of low catalytic site density in the prior art.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode materials, and particularly relates to a ZIF-derived CoZnS electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] As a highly potential sustainable clean energy, hydrogen energy has become one of the ideal alternatives to fossil fuels due to its zero-emission and high energy density characteristics. However, traditional hydrogen production methods often have high energy consumption, high costs, and some processes rely on fossil fuels, which limit the large-scale commercial application of hydrogen energy. Therefore, exploring efficient and environmentally friendly hydrogen production technologies, especially catalytic hydrogen evolution reactions driven by renewable energy, has become a current research hotspot.

[0003] Currently, the production routes of hydrogen include different methods such as fossil fuel reforming and electrolysis of water. Among these methods, water electrolysis is considered a promising hydrogen production method because it is environmentally friendly and the reactant water is abundant and renewable. Therefore, increasing attention has been paid to the research of electrode materials for water splitting. To achieve efficient and economical hydrogen production by electrolyzing water, the key lies in developing electrocatalysts with high catalytic performance, high stability, and low cost. Currently, the catalysts used in electrochemical water splitting technology mainly include several categories based on noble metals, transition metals, and metal-organic framework compounds. The challenge is that metal catalysts have poor stability in acidic environments, while noble metal-based catalysts have disadvantages such as high cost and scarce sources. Moreover, noble metal-based catalysts require a relatively high overpotential for hydrogen evolution reactions in alkaline media and are not suitable for large-scale industrial applications.

[0004] Currently, two-dimensional transition metal sulfide materials have attracted extensive attention in the catalytic field due to their unique atomic configuration and electronic structure. Research shows that the catalytic active sites of two-dimensional transition metal sulfide materials are generally coordinatively unsaturated atoms at the edges, while a large number of atoms on their basal planes do not actually participate in the catalytic process, thus unable to exhibit the advantages of the high specific surface area of two-dimensional materials. Then, when preparing two-dimensional transition metal sulfide materials, more active edges need to be constructed on their two-dimensional layered structure. Currently, most sulfide preparations still use the liquid-phase coprecipitation method to expand their specific surface area, but this method has limited effect on increasing the edge position of two-dimensional transition metal sulfide materials and cannot break away from the two-dimensional layered structure. Therefore, the electrocatalytic hydrogen evolution performance of two-dimensional transition metal sulfide materials is still not ideal. Summary of the Invention

[0005] Aiming at the deficiencies of the above-mentioned existing technologies, the present invention provides a ZIF-derived CoZnS electrode material, its preparation method and application. The present invention uses soluble cobalt salts and soluble zinc salts as raw materials, NH4F as a buffer and structure-directing agent, and urea to provide a weak alkaline environment. A nickel foam-CoZn precursor is prepared by a solvothermal reaction. Then, through the coordination of 2-methylimidazole, it coordinates with the nickel foam-CoZn precursor. Moreover, since the nickel foam-CoZn precursor has a small crystal form, it will continuously convert towards ZIF, promoting the coordination reaction process. Subsequently, a ZIF-67 structure is introduced to obtain a ZIF-derived precursor. Then, by controlling the sulfidation conditions of the ZIF-derived precursor, a ZIF-derived CoZnS electrode material with a stable three-dimensional structure is prepared. The ZIF-derived CoZnS electrode material prepared by the method of the present invention has a large and uniform MOF structure and a three-dimensional array, which provides sufficient active sites and a stable physical structure for the subsequent electrocatalytic hydrogen evolution reaction. Moreover, the CoZnS electrode material has more active edges, so it exhibits more catalytic sites, overcoming the technical defect of the low catalytic site density of two-dimensional transition metal sulfide materials in the prior art.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A preparation method of a ZIF-derived CoZnS electrode material, characterized by comprising the following steps:

[0008] Using soluble Zn salts and soluble Co salts as raw materials, NH4F as a buffer and structure-directing agent, the buffer can maintain the pH of the mixed solution, and the structure-directing agent can guide the growth of zinc cobalt hydroxide. Urea is used to provide a weak alkaline environment. The soluble Zn salt, soluble Co salt, NH4F and urea are mixed in water to obtain a mixed solution. After immersing nickel foam into the mixed solution, a solvothermal reaction is carried out, and zinc cobalt hydroxide with a lamellar array structure grows in-situ on the three-dimensional nickel foam substrate to obtain a nickel foam-CoZn precursor.

[0009] Dissolve 2-methylimidazole in water to obtain a 2-methylimidazole solution.

[0010] Immerse the nickel foam-CoZn precursor into the 2-methylimidazole solution and let it stand. During the standing process, 2-methylimidazole coordinates with zinc ions and cobalt ions on the nickel foam-CoZn precursor to form large coordination groups. Moreover, since the nickel foam-CoZn precursor has a small crystal form, it will continuously convert towards ZIF, promoting the coordination reaction process. Subsequently, ZIF-67 is introduced onto the nickel foam-CoZn precursor to obtain a ZIF-derived precursor.

[0011] Mix the ZIF-derived precursor with Na2S in water and carry out a hydrothermal reaction. During the hydrothermal process, S 2-An anion exchange reaction is carried out with the organic coordination groups on ZIF-67 to obtain a porous structure, and the zinc ions and cobalt ions of the ZIF-derived precursor are sulfided to obtain a ZIF-derived CoZnS electrode material.

[0012] Preferably, the molar ratio of Zn of the soluble Zn salt 2+ to Co of the soluble Co salt 2+ is 1:1-3, the molar ratio of Zn 2+ to Co 2+ can be regulated, and the amount of Co 2+ can be slightly higher than the amount of Zn 2+ .

[0013] Preferably, in the mixed solution, the concentration of NH4F is 0.1-0.4 mol / L, and the concentration of urea is 0.2-0.4 mol / L, so that the pH of the mixed solution is greater than 7 and less than 9.

[0014] Preferably, the conditions of the solvothermal reaction are: heating at 110-140 °C for 5-10 h.

[0015] Preferably, the mass ratio of 2-methylimidazole to the CoZn precursor on the nickel foam-CoZn precursor is 50-70:1.

[0016] Preferably, the standing time ≥ 2 h.

[0017] Preferably, the mass ratio of the ZIF-derived precursor minus the nickel foam to the mass of Na2S is 1:1-4, and the mass ratio of the two is obtained through experimental screening.

[0018] Preferably, the conditions of the hydrothermal reaction are: hydrothermal reaction at 80-100 °C for 6-10 h. If the hydrothermal time is too short, the sulfidation reaction is insufficient, the sulfide is not completely formed, and the porous structure is limited; if the hydrothermal time is too long, over-sulfidation will occur, and the sulfide will agglomerate during this process, resulting in a decrease in the specific surface area. If the temperature is too low, the reaction rate is too low, and if the temperature is too high, the reaction is too violent, destroying the overall structure of the ZIF-derived CoZnS electrode material.

[0019] The present invention also protects the ZIF-derived CoZnS electrode material prepared by the above preparation method.

[0020] The present invention also protects the application of the ZIF-derived CoZnS electrode material in the preparation of an electrocatalytic hydrogen evolution cathode material.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. The present invention uses soluble Zn salt, soluble Co salt, NH4F, urea and nickel foam as raw materials. First, a nickel foam-CoZn precursor is prepared through a solvothermal reaction. Among them, NH4F serves as a buffer and a structure-directing agent, and urea provides a weak alkaline environment. In the obtained nickel foam-CoZn precursor, zinc cobalt hydroxide with a lamellar array structure is prepared on the three-dimensional nickel foam substrate. The lamellae interpenetrate with each other, so it has a large specific surface area, which provides a large-area template for the synthesis of the subsequent ZIF-derived CoZnS electrode material. Then, the nickel foam-CoZn precursor is immersed in 2-methylimidazole. 2-methylimidazole coordinates with zinc ions and cobalt ions. Moreover, the crystal form of the nickel foam-CoZn precursor is small, so it will continuously transform into ZIF, promoting the coordination reaction process. Subsequently, ZIF-67 is in-situ introduced onto the nickel foam-CoZn precursor, that is, ZIF-67 directly transforms and grows on the lamellae of the nickel foam-CoZn precursor. Therefore, it inherits the large specific surface area of the nickel foam-CoZn precursor. At the same time, in the present invention, a metal precursor and an organic ligand are combined to form a metal-organic ligand to obtain a ZIF-derived precursor. Then, the ZIF-derived precursor is sulfided using sodium sulfide. During the sulfidation process, S 2- undergoes an anion exchange reaction with the organic coordination groups on ZIF-67. The organic coordination groups with a larger radius come out of ZIF-67, and the S 2- with a smaller radius enters into ZIF-67, further creating pores and further expanding the specific surface area. The increased specific surface area has more active edges, increasing the catalytic site density, and obtaining a ZIF-derived CoZnS electrode material.

[0023] 2. The ZIF-derived CoZnS electrode material prepared by the method of the present invention has a large specific surface area and sufficient catalytic sites, which benefits from the array framework and MOF three-dimensional structure of the ZIF-derived CoZnS electrode material. The array framework comes from: preparing a CoZn precursor array framework by the solvothermal method, then realizing the in-situ introduction of ZIF on the array framework, and finally using S 2- to undergo an anion exchange reaction with the organic coordination groups in ZIF, further creating pores while maintaining the array framework. The obtained ZIF-derived CoZnS electrode material has the advantages of a large specific surface area, controllable structure and adjustable porosity, overcoming the technical defect that the effect of increasing the edge position of the existing two-dimensional transition metal sulfide material is limited, resulting in a low catalytic site density.

[0024] 3. The present invention uses nickel foam as the substrate, on which zinc cobalt hydroxide is loaded to obtain a nickel foam-CoZn precursor. Then, a ZIF structure is in-situ introduced on this basis, and finally, it is sulfided to obtain a ZIF-derived CoZnS electrode material. Among them, nickel foam provides a stable growth framework for ZIF, and its excellent conductivity accelerates the electron transfer rate of the CoZnS electrode material; the sacrificial template zinc cobalt hydroxide is used to achieve the ordered arrangement of MOF and construct a three-dimensional ZIF-derived CoZnS electrode material. At this time, ZIF provides more active edges for the CoZnS electrode material, showing more catalytic sites; the CoZnS electrode material has a binary metal center, and the synergistic catalysis between CoS and ZnS promotes the adsorption and desorption reaction steps of active hydrogen atoms in the hydrogen evolution reaction, improving the hydrogen production efficiency.

[0025] 4. Through the analysis of the prepared ZIF-derived CoZnS electrode material, the results show that the ZIF-derived CoZnS electrode material has excellent catalytic activity. The ZIF-derived CoZnS electrode material has a stable structure and presents nanosheets and nanowires, which means that the ZIF-derived CoZnS electrode material has a large specific surface area, can provide more active sites, and has a small impedance radius. The reaction of the ZIF-derived CoZnS electrode material is easier to proceed, and the electron transfer is more rapid.

[0026] 5. The present invention provides a method for using the sacrificial template zinc cobalt hydroxide to achieve the ordered arrangement of MOF and constructs a three-dimensional catalyst. The method of the present invention has good feasibility and provides a demonstration for the construction of subsequent three-dimensional catalytic materials. Description of the Drawings

[0027] Figure 1 SEM images of the CoZnS-0.2 electrode of Example 2 at different magnification ratios, where (a) is the low magnification image and (b) is the high magnification image.

[0028] Figure 2 Among them, (a) is the XRD pattern of the NF-CoZn precursor of Example 1, (b) is the XRD pattern of the ZIF of Example 1, and (c) is the XRD pattern of the CoZnS of Example 2.

[0029] Figure 3Among them, (a) is the LSV diagram of the CoZnS-0.1 electrode of Example 1, the CoZnS-0.2 electrode of Example 2, the CoZnS-0.3 electrode of Example 3, and the CoZnS-0.4 electrode of Example 4, and (b) is the EIS diagram of the CoZnS-0.1 electrode of Example 1, the CoZnS-0.2 electrode of Example 2, the CoZnS-0.3 electrode of Example 3, and the CoZnS-0.4 electrode of Example 4.

[0030] Figure 4 Among them, (a) is the LSV diagram of the NF-Zn precursor of Comparative Example 1, the NF-Co precursor of Comparative Example 2, and the NF-CoZn precursor of Example 1, and (b) is the EIS diagram of the NF-Zn precursor of Comparative Example 1, the NF-Co precursor of Comparative Example 2, and the NF-CoZn precursor of Example 1. Detailed implementation manners

[0031] The following is a detailed description of the specific implementation manners of the present invention, but it should be understood that the protection scope of the present invention is not limited by the specific implementation manners. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0032] Under standard conditions, the free energy change of the water splitting reaction is 237.2 kJ mol -1 , and according to the Nernst equation, the theoretical decomposition voltage of water is 1.23 V. In fact, in the electrochemical process, electrochemical polarization, concentration polarization, and solution resistance factors are usually encountered. The combined action of these factors causes the electrode potential to not be maintained at the theoretically balanced state, resulting in an additional overpotential. To address this challenge and improve the system efficiency, the use of highly efficient electrocatalysts is crucial. The ZIF-derived CoZnS electrode material provided by the present invention can effectively reduce the additional energy required in the water splitting process, that is, the overpotential, thereby enhancing the energy conversion efficiency.

[0033] The following uses examples and comparative examples to study the technical solutions of the present invention. The specific research methods and results are as follows:

[0034] Example 1

[0035] The preparation method of the ZIF-derived CoZnS electrode material includes the following steps:

[0036] S1. Clean the nickel foam. The cleaning method is: alternately ultrasonically clean the nickel foam with deionized water and ethanol for 10 s each time to obtain clean nickel foam.

[0037] S2. Weigh 0.22 g of Zn(NO3)2, 0.44 g of Co(NO3)2, 0.22 g of NH4F and 0.9 g of urea, and then dissolve them together in 60 mL of deionized water. At this time, the molar ratio of Zn 2+ to Co 2+ is 1:2, the concentration of NH4F is 0.2 mol / L, and the concentration of urea is 0.25 mol / L. After continuously stirring at room temperature for 10 min, transfer it to a 100 mL reaction kettle. Put the clean nickel foam from step S1 into the reaction kettle, and then place it in a forced-air drying oven. After reacting at 120 °C for 6 h, collect the product, wash it successively, and vacuum-dry it at 60 °C to obtain a nickel foam-CoZn precursor, denoted as NF-CoZn precursor.

[0038] S3. Dissolve 1.25 g of dimethylimidazole in 20 mL of deionized water, stir evenly to obtain a dimethylimidazole solution. Place the NF-CoZn precursor from step S2 in the dimethylimidazole solution and let it stand for 3 h. At this time, the mass ratio of dimethylimidazole to the CoZn precursor on the nickel foam-CoZn precursor is 50:1. Then wash and dry it for 6 h to obtain a ZIF-derived precursor.

[0039] S4. Dissolve 0.1 g of Na2S in 60 mL of deionized water to obtain a Na2S solution. Place the ZIF-derived precursor in the Na2S solution. At this time, the mass ratio of the ZIF-derived precursor minus the nickel foam to the mass of Na2S is 1:1. Hydrothermally react at 90 °C in a reaction kettle for 8 h, and then vacuum-dry it at 60 °C to constant weight to obtain a CoZnS-0.1 electrode.

[0040] Example 2

[0041] The preparation method of the ZIF-derived CoZnS electrode material is the same as the preparation steps in Example 1, except that the mass of Na2S is replaced from 0.1 g to 0.2 g, and it includes the following steps:

[0042] S1. Wash the nickel foam to obtain clean nickel foam.

[0043] S2. Weigh 0.22 g of Zn(NO3)2, 0.44 g of Co(NO3)2, 0.22 g of NH4F and 0.9 g of urea, and then dissolve them together in 60 mL of deionized water. After continuously stirring at room temperature for 10 min, transfer it to a 100 mL reaction kettle. Put the clean nickel foam from step S1 into the reaction kettle, and then place it in a forced-air drying oven. After reacting at 120 °C for 6 h, collect the product, wash it successively, and vacuum-dry it at 60 °C to obtain a nickel foam-CoZn precursor, denoted as NF-CoZn precursor.

[0044] S3. Dissolve 1.25 g of dimethylimidazole in 20 mL of deionized water, stir evenly to obtain a dimethylimidazole solution. Place the NF-CoZn precursor in step S2 into the dimethylimidazole solution and let it stand for 3 h, then wash and dry for 6 h to obtain a ZIF-derived precursor.

[0045] S4. Dissolve 0.2 g of Na2S in 60 mL of deionized water to obtain a Na2S solution. Place the ZIF-derived precursor in the Na2S solution. At this time, the mass ratio of the ZIF-derived precursor minus nickel foam to the mass of Na2S is 1:2. Hydrothermally react in a reaction kettle at 90 °C for 8 h, and then vacuum dry at 60 °C to constant weight to obtain a CoZnS-0.2 electrode.

[0046] Example 3

[0047] The preparation method of the ZIF-derived CoZnS electrode material is the same as the preparation steps in Example 1, except that the mass of Na2S is replaced from 0.1 g to 0.3 g, and it includes the following steps:

[0048] S1. Wash the nickel foam to obtain clean nickel foam.

[0049] S2. Weigh 0.22 g of Zn(NO3)2, 0.44 g of Co(NO3)2, 0.22 g of NH4F and 0.9 g of urea, then dissolve them together in 60 mL of deionized water. After continuously stirring at room temperature for 10 min, transfer them into a 100 mL reaction kettle. Put the clean nickel foam in step S1 into the reaction kettle, and then place it in a forced air drying oven. React at 120 °C for 6 h, collect the product, wash it successively, and vacuum dry at 60 °C to obtain a nickel foam-CoZn precursor, denoted as NF-CoZn precursor.

[0050] S3. Dissolve 1.25 g of dimethylimidazole in 20 mL of deionized water, stir evenly to obtain a dimethylimidazole solution. Place the NF-CoZn precursor in step S2 into the dimethylimidazole solution and let it stand for 3 h, then wash and dry for 6 h to obtain a ZIF-derived precursor.

[0051] S4. Dissolve 0.3 g of Na2S in 60 mL of deionized water to obtain a Na2S solution. Place the ZIF-derived precursor in the Na2S solution. At this time, the mass ratio of the ZIF-derived precursor minus nickel foam to the mass of Na2S is 1:3. Hydrothermally react in a reaction kettle at 90 °C for 8 h, and then vacuum dry at 60 °C to constant weight to obtain a CoZnS-0.3 electrode.

[0052] Example 4

[0053] The preparation method of the ZIF-derived CoZnS electrode material is the same as the preparation steps of Example 1, except that the mass of Na2S is replaced from 0.1 g to 0.4 g, and it includes the following steps:

[0054] S1. Clean the nickel foam to obtain clean nickel foam.

[0055] S2. Weigh 0.22 g of Zn(NO3)2, 0.44 g of Co(NO3)2, 0.22 g of NH4F and 0.9 g of urea, then dissolve them together in 60 mL of deionized water. After continuously stirring at room temperature for 10 min, transfer the solution into a 100 mL reaction kettle. Put the clean nickel foam obtained in step S1 into the reaction kettle, and then place it in a forced-air drying oven. React at 120 °C for 6 h, collect the product, wash it successively, and vacuum dry it at 60 °C to obtain a nickel foam-CoZn precursor, denoted as NF-CoZn precursor.

[0056] S3. Dissolve 1.25 g of dimethylimidazole in 20 mL of deionized water, stir evenly to obtain a dimethylimidazole solution. Place the NF-CoZn precursor obtained in step S2 in the dimethylimidazole solution and let it stand for 3 h, then wash and dry it for 6 h to obtain a ZIF-derived precursor.

[0057] S4. Dissolve 0.4 g of Na2S in 60 mL of deionized water to obtain a Na2S solution. Place the ZIF-derived precursor in the Na2S solution. At this time, the mass ratio of the ZIF-derived precursor minus the nickel foam to the mass of Na2S is 1:4. Hydrothermally react in a reaction kettle at 90 °C for 8 h, and then vacuum dry it at 60 °C to constant weight to obtain a CoZnS-0.4 electrode.

[0058] Example 5

[0059] The preparation method of the ZIF-derived CoZnS electrode material includes the following steps:

[0060] S1. Clean the nickel foam. The cleaning method is: alternately ultrasonically clean the nickel foam with deionized water and ethanol for 10 s each time to obtain clean nickel foam.

[0061] S2. Weigh 0.22 g of Zn(NO3)2, 0.22 g of Co(NO3)2, 0.11 g of NH4F and 1.44 g of urea, then dissolve them together in 60 mL of deionized water. At this time, Zn 2+ and Co 2+The molar ratio is 1:1, the concentration of NH4F is 0.1 mol / L, the concentration of urea is 0.4 mol / L. After continuously stirring at room temperature for 10 min, it is transferred into a 100 mL reaction kettle. The cleaned nickel foam from step S1 is put into the reaction kettle, and then placed in a forced-air drying oven. After reacting at 140 °C for 5 h, the product is collected, and successively washed and vacuum dried at 60 °C to obtain a nickel foam-CoZn precursor, denoted as NF-CoZn precursor.

[0062] S3. Dissolve dimethylimidazole in 20 mL of deionized water, stir evenly to obtain a dimethylimidazole solution. Place the NF-CoZn precursor from step S2 in the dimethylimidazole solution and let it stand for 3 h. At this time, the mass ratio of dimethylimidazole to the CoZn precursor on the nickel foam-CoZn precursor is 60:1. Then wash and dry for 6 h to obtain a ZIF-derived precursor.

[0063] S4. Take 0.2 g of Na2S and dissolve it in 60 mL of deionized water to obtain a Na2S solution. Place the ZIF-derived precursor in the Na2S solution, carry out hydrothermal reaction at 80 °C in a reaction kettle for 10 h, and then vacuum dry at 60 °C to constant weight to obtain a ZIF-derived CoZnS electrode material.

[0064] Example 6

[0065] A preparation method of a ZIF-derived CoZnS electrode material, comprising the following steps:

[0066] S1. Clean the nickel foam. The cleaning method is: alternately ultrasonically clean the nickel foam with deionized water and ethanol for 10 s each time to obtain cleaned nickel foam.

[0067] S2. Weigh 0.22 g of Zn(NO3)2, 0.66 g of Co(NO3)2, 0.44 g of NH4F and 0.72 g of urea, and then dissolve them together in 60 mL of deionized water. At this time, the molar ratio of Zn 2+ and Co 2+ is 1:3, the concentration of NH4F is 0.4 mol / L, the concentration of urea is 0.2 mol / L. After continuously stirring at room temperature for 10 min, it is transferred into a 100 mL reaction kettle. The cleaned nickel foam from step S1 is put into the reaction kettle, and then placed in a forced-air drying oven. After reacting at 110 °C for 10 h, the product is collected, and successively washed and vacuum dried at 60 °C to obtain a nickel foam-CoZn precursor, denoted as NF-CoZn precursor.

[0068] S3. Dissolve dimethylimidazole in 20 mL of deionized water and stir evenly to obtain a dimethylimidazole solution. Place the NF-CoZn precursor in step S2 into the dimethylimidazole solution and let it stand for 3 h. At this time, the mass ratio of dimethylimidazole to the CoZn precursor on the nickel foam-CoZn precursor is 70:1. Then wash and dry for 6 h to obtain a ZIF-derived precursor.

[0069] S4. Dissolve 0.3 g of Na2S in 60 mL of deionized water to obtain a Na2S solution. Place the ZIF-derived precursor in the Na2S solution and carry out a hydrothermal reaction at 100 °C in a reaction kettle for 6 h, and then vacuum dry at 60 °C to constant weight to obtain a ZIF-derived CoZnS electrode material.

[0070] Comparative Example 1

[0071] The preparation method of the NF-Zn precursor is the same as that of Example 1, except that the reactants do not contain Co(NO3)2, and it includes the following steps:

[0072] Dissolve 0.22 g of Zn(NO3)2, 0.22 g of NH4F, and 0.9 g of urea in 60 mL of deionized water. Continuously stir at room temperature for 10 min and then transfer it to a 100 mL reaction kettle. Place the washed nickel foam into the reaction kettle, put it into a forced-air drying oven, react at 120 °C for 6 h, collect the product and wash it, and then vacuum dry at 60 °C to obtain the NF-Zn precursor.

[0073] Comparative Example 2

[0074] The preparation method of the NF-Co precursor is the same as that of Example 1, except that the reactants do not contain Zn(NO3)2, and it includes the following steps:

[0075] Dissolve 0.44 g of Co(NO3)2, 0.22 g of NH4F, and 0.9 g of urea in 60 mL of deionized water. Continuously stir at room temperature for 10 min and then transfer it to a 100 mL reaction kettle. Place the washed nickel foam into the reaction kettle, put it into a forced-air drying oven, react at 120 °C for 6 h, collect the product and wash it, and then vacuum dry at 60 °C to obtain the NF-Co precursor.

[0076] In Examples 1-6 of the present invention, ZIF-derived CoZnS electrode materials with excellent electrocatalytic hydrogen evolution performance, capable of achieving a large hydrogen evolution reaction current under lower overpotential conditions, that is, higher hydrogen evolution efficiency, are prepared. Taking the ZIF-derived CoZnS electrode materials of Examples 1-4 as examples for research, and comparing them with the NF-Zn precursor of Comparative Example 1 and the NF-Co precursor of Comparative Example 2, the specific research methods and results are as follows:

[0077] Figure 1 (a) is the SEM image of the CoZnS-0.2 electrode of Example 2 at low magnification. It can be seen from the figure that the surface of the prepared CoZnS-0.2 electrode is evenly distributed and has a stable structure, which enables the CoZnS-0.2 electrode to maintain a high activity even after multiple uses, extending the service life of the ZIF-derived CoZnS electrode material. Figure 1 (b) is the SEM image of the CoZnS-0.2 electrode at high magnification. It can be seen from the figure that the prepared CoZnS-0.2 electrode presents uniform, thin nanosheets and nanowires. The thickness of the nanosheets is about 100 μm. Both nanowire and nanosheet structures are shown in the scanning electron micrograph. The nanowire structure provides a high specific surface area and excellent electron transport path, which is beneficial to rapid charge transfer and high reaction activity. The nanosheet structure usually has a relatively large planar size and a relatively small thickness. Such a structure can further increase the specific surface area of the CoZnS electrode, especially in the direction perpendicular to the plane of the ZIF-derived CoZnS electrode material, which is beneficial to the rapid diffusion and adsorption or desorption process of electrolyte ions, and is very favorable for improving the electrochemical energy storage and conversion efficiency.

[0078] Figure 2 (a) is the XRD pattern of the NF-CoZn precursor. By comparing several peaks at diffraction angles of 18°, 32°, and 58°, which correspond to the (001), (101), and (110) crystal planes of the cobalt hydroxide PDF standard card, this indicates that the NF-CoZn precursor exists in the form of cobalt hydroxide. There are some peak shifts in the image, which are caused by the doping of zinc element in the NF-CoZn precursor. Figure 2 (b) is the XRD pattern of ZIF. By comparing with the standard card, it is concluded that the prepared sample is ZIF-67. Figure 2 (c) is the XRD pattern of the CoZnS-0.2 electrode of Example 2. The peaks at diffraction angles of 31°, 38°, and 55° correspond to the (311), (400), and (440) crystal planes of the cobalt sulfide PDF standard card (PDF#42-1448), indicating that sulfur element is indeed incorporated into the final sample. Through XRD image analysis, the present invention successfully prepares the NF-CoZn precursor, the ZIF-derived precursor, and the ZIF-derived CoZnS electrode material.

[0079] In order to further explore the electrocatalytic activity of the prepared ZIF-derived CoZnS electrode material, LSV and EIS tests were carried out on the electrode material. The catalytic hydrogen evolution activity of the prepared ZIF-derived CoZnS electrode material was tested in 1 mol / L NaOH solution using a typical three-electrode system.

[0080] Construction of a three - electrode system: The ZIF - derived CoZnS electrode materials of Examples 1 - 4 were used as the working electrodes respectively, the Hg / HgO electrode was used as the reference electrode, and the platinum sheet electrode was used as the counter electrode. One end of the working electrode, reference electrode, and counter electrode was jointly placed into a 1 mol / L NaOH solution, and the other end was jointly electrically connected to an electrochemical workstation.

[0081] Figure 3 (a) shows the LSV diagrams of CoZnS - 0.1 electrode, CoZnS - 0.2 electrode, CoZnS - 0.3 electrode, and CoZnS - 0.4 electrode. At the same current density (100 mA cm -2 ), the CoZnS - 0.2 electrode has a smaller over - potential, which is 350 mV. The over - potentials of CoZnS - 0.1, CoZnS - 0.3, and CoZnS - 0.4 electrodes are 400 mV, 450 mV, and 460 mV respectively. The CoZnS - 0.2 electrode has a smaller over - potential, so it is judged that the CoZnS - 0.2 electrode has the best hydrogen evolution performance.

[0082] Figure 3 (b) shows the EIS diagrams of CoZnS - 0.1 electrode, CoZnS - 0.2 electrode, CoZnS - 0.3 electrode, and CoZnS - 0.4 electrode. It can be seen from the figure that the CoZnS - 0.2 electrode has a smaller impedance radius, and the impedance is 20 Ω. The impedance radii of CoZnS - 0.1 electrode, CoZnS - 0.3 electrode, and CoZnS - 0.4 electrode increase in turn, and the impedances are 30 Ω, 33 Ω, and 43 Ω respectively. The CoZnS - 0.2 electrode has the smallest impedance radius, indicating a lower electron transfer resistance, which means that the reaction of the CoZnS - 0.2 electrode is easier to proceed and the electron transfer is faster. It means high catalytic activity. A smaller impedance represents a smaller resistance of the catalytic layer to the reaction, thus making the reaction rate faster and reducing the possibility of electron recombination. This can also correspond to the above SEM diagrams. The ZIF - derived CoZnS electrode material obtained after sulfidation has a larger specific surface area and better catalytic performance.

[0083] As a comparative experiment, the amounts of Co and Zn were changed, and NF - Co precursor and NF - Zn precursor were prepared respectively. Figure 4 (a) shows the LSV diagrams of the NF - Co precursor of Comparative Example 2, the NF - Zn precursor of Comparative Example 1, and the NF - CoZn precursor of Example 1. It can be seen from the figure that at the same current density (100 mA cm -2)Under the following conditions, the overpotential of the NF-CoZn precursor is the lowest, with a magnitude of 320 mV. The overpotentials of the NF-Zn precursor and the NF-Co precursor are 350 mV and 380 mV respectively. From this, it is judged that the catalytic performance of the NF-CoZn precursor is better. At the same time, through calculation, it is known that the Tafel slope of the NF-CoZn precursor is smaller, which means that in the electrochemical reaction, as the current density increases, the required overpotential increases relatively slowly. The reaction kinetics is more favorable, and the electron transfer on the surface of the ZIF-derived CoZnS electrode material is relatively rapid, enabling a higher reaction rate to be achieved at a lower overpotential.

[0084] Figure 4 (b) is the EIS diagram of the NF-Co precursor of Comparative Example 2, the NF-Zn precursor of Comparative Example 1, and the NF-CoZn precursor of Example 1. It can be seen from the figure that the impedance radius of the NF-CoZn precursor is smaller, with a magnitude of 40 Ω. The impedance radii of the NF-Zn precursor and the NF-Co precursor increase in sequence, and the impedances are 70 Ω and 130 Ω respectively. The NF-CoZn precursor has the smallest impedance radius, the best catalytic performance, and a faster electron transfer speed. When compared with the NF-Zn precursor and the NF-Co precursor, it is judged that the NF-CoZn precursor has a larger specific surface area and more active sites, which can fully contact the reactants, thereby accelerating the progress of the chemical reaction, further increasing the reaction rate, and improving the catalytic efficiency.

[0085] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications. The above-described embodiments are only preferred embodiments given to fully illustrate the present invention, and the scope of protection is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is subject to the claims.

Claims

1. A method for preparing a ZIF-derived CoZnS electrode material, characterized in that: The steps include: Using soluble Zn salt and soluble Co salt as raw materials, NH4F as a buffer and structure directing agent, and urea to provide a weak alkaline environment, the soluble Zn salt, the soluble Co salt, NH4F and urea are mixed in water to obtain a mixed solution, and nickel foam is immersed in the mixed solution, and a solvothermal reaction is performed to in-situ grow zinc cobalt hydroxide on the nickel foam to obtain a nickel foam-CoZn precursor; Dissolving dimethylimidazole in water to obtain a dimethylimidazole solution; The nickel foam-CoZn precursor is immersed in a dimethylimidazole solution and allowed to stand. During the standing process, the dimethylimidazole coordinates with the zinc ions and cobalt ions on the nickel foam-CoZn precursor to obtain a ZIF-derived precursor; The ZIF-derived precursor and Na2S were mixed in water and subjected to a hydrothermal reaction. During the hydrothermal process, S 2- An anion exchange reaction is carried out with the organic coordination groups on ZIF-67 to obtain a porous structure, and the zinc ions and cobalt ions of the ZIF-derived precursor are sulfided to obtain the ZIF-derived CoZnS electrode material.

2. The method for preparing the ZIF-derived CoZnS electrode material according to claim 1, characterized in that: Zn in soluble Zn salts 2+ Co with soluble Co salts 2+ The molar ratio is 1:1-3.

3. The method for preparing the ZIF-derived CoZnS electrode material according to claim 1, characterized in that: In the mixed solution, the concentration of NH4F is 0.1-0.4 mol / L, and the concentration of urea is 0.2-0.4 mol / L.

4. The method for preparing the ZIF-derived CoZnS electrode material according to claim 1, characterized in that: The conditions of the solvothermal reaction are: heating at 110-140°C for 5-10h.

5. The method for preparing the ZIF-derived CoZnS electrode material according to claim 1, characterized in that: The mass ratio of dimethylimidazole to the CoZn precursor on the nickel foam-CoZn precursor is 50-70:

1.

6. The method for preparing the ZIF-derived CoZnS electrode material according to claim 1, characterized in that: Standing time ≥ 2h.

7. The method for preparing the ZIF-derived CoZnS electrode material according to claim 1, characterized in that: The mass ratio of the ZIF-derived precursor minus the nickel foam to Na2S is 1:1-4.

8. The method for preparing the ZIF-derived CoZnS electrode material according to claim 1, characterized in that: The conditions of the hydrothermal reaction are: hydrothermal reaction at 80-100°C for 6-10h.

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