A ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material and its preparation method and application

Abstract

The present invention belongs to the technical field of electrode catalysts for batteries and water electrolysis, and discloses a ZnS / Co heterojunction composite nitrogen-sulfur-doped carbon material, its preparation method, and application. ZnS nanospheres and ZIF-67 are uniformly mixed in a mass ratio of 1:1 to 1:30 and calcined at 600 to 1000°C to obtain the composite material. The composite material is composed of a zinc sulfide / cobalt nanoparticle heterostructure uniformly dispersed in a nitrogen-sulfur-doped carbon matrix, wherein small zinc sulfide nanoparticles are coated on the surface of large cobalt nanoparticles to form a core-shell heterostructure. The zinc sulfide nanoparticles have a diameter of 2 to 5 nm, and the cobalt nanoparticles have two sizes: a large size of 20 to 100 nm and a small size of 2 to 10 nm. The nitrogen-sulfur-doped carbon has a dodecahedral structure with a diameter of 200 to 500 nm. When this composite material is used as a positive electrode catalyst for liquid rechargeable zinc-air batteries, the charge and discharge performance has obvious advantages; when used as an anode catalyst for AEM water electrolysis, its performance is better than commercial platinum carbon and ruthenium dioxide, and it can operate stably for more than 600 hours.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery and water electrolysis electrode catalysts, and specifically relates to a ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material and a preparation method and application thereof. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] With high theoretical energy density (1086 Wh kg -1 ) and low-cost zinc-air batteries (ZABs)—rechargeable energy storage devices—hold broad application prospects. However, the slow oxygen reduction and evolution reactions (ORR and OER) at the air cathode are key challenges hindering the development of Zn-air batteries. While some precious metal catalysts, such as Pt / C and RuO2, exhibit high activity for ORR / OER, their scarce resources and high cost severely hinder their large-scale application. Furthermore, in alkaline anion exchange membrane (AEM) water electrolysis, the anodic OER, involving a four-electron transfer process, represents a key bottleneck limiting overall energy efficiency. While the AEM system offers the advantages of acid-free and low-cost catalysts, its operating environment (pH 10–14) places stringent demands on the catalyst: it must withstand long-term corrosion from strongly alkaline media while also exhibiting high OER catalytic activity and long-term stability. Currently, commercially available IrO2 and RuO2 catalysts are expensive and prone to lattice oxygen dissolution at high potentials, severely hindering the large-scale application of AEM water electrolysis. Therefore, the research and development of inexpensive, efficient and stable non-precious metal oxygen electrocatalysts is of great significance to the development of metal-air batteries and AEM water electrolysis.

[0004] Cobalt nanoparticle / carbon composites derived from ZIF-67, which is rich in cobalt, nitrogen, and carbon, have great application potential as cathode catalyst materials. However, conventional pyrolysis processes often lead to the agglomeration of single non-metallic dopant atoms and larger metal nanoparticles. Moreover, during the catalytic process, metal particles are easily detached from the carbon matrix or reagglomerated, which are factors that limit the activity and stability of the material. Therefore, how to obtain multi-element non-metallic heteroatom doping through simple operations while firmly anchoring, uniformly dispersing, and refining the size of cobalt nanoparticles, creating abundant active sites while improving stability, is the key and difficulty in the research of cobalt nanoparticles and nitrogen-doped carbon composites as electrocatalysts. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention aims to provide a ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material and its preparation method and application.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a ZnS / Co heterojunction composite nitrogen- and sulfur-doped carbon material, comprising the following steps:

[0008] The cobalt source and 2-methylimidazole were mixed in a methanol solvent according to a certain proportion, ultrasonically dispersed for 10-60 minutes, and stirred at 20-35°C for 1-10 hours. After the reaction was completed, the solid-liquid separation was performed and the purple ZIF-67 powder was obtained after drying.

[0009] The ZnS nanospheres and ZIF-67 are mixed uniformly at a mass ratio of 1:1 to 30, and calcined at 600-1000°C for 1 to 5 hours to obtain the product.

[0010] In some embodiments, the ZnS nanospheres are prepared by dissolving a zinc source in ethylene glycol, adding thiourea and polyvinyl pyrrolidone, mixing, and performing a hydrothermal reaction. After the reaction is completed, the ZnS nanospheres are washed and dried to obtain the ZnS nanospheres.

[0011] Among them, ethylene glycol, as the reaction solvent, can dissolve other reactants and provide a uniformly dispersed and rapid liquid-phase reaction environment; thiourea is the sulfur source for the formation of ZnS nanospheres. It decomposes at high temperature, releasing sulfur and then combining with zinc to form fine ZnS; and polyvinyl pyrrolidone molecules act as a surfactant, adsorbing on the surface of the ZnS nanospheres, reducing the surface energy of the nanoparticles and preventing the ZnS nanoparticles from agglomerating, resulting in nanospheres with uniform particle size and good dispersion.

[0012] Preferably, the zinc source is zinc nitrate, zinc acetate, zinc sulfate or zinc chloride.

[0013] Preferably, the mass ratio of zinc source, thiourea, polyvinyl pyrrolidone and ethylene glycol is 2:0.6:0.4 to 0.8:70.

[0014] Preferably, the temperature of the hydrothermal reaction is 100-150°C, and the reaction time is 10-30h; more preferably, the temperature of the hydrothermal reaction is 120-150°C, and the reaction time is 20-30h; further preferably, the temperature of the hydrothermal reaction is 135-145°C, and the reaction time is 20-25h.

[0015] Preferably, the mass ratio of ZnS nanospheres to ZIF-67 is 1:1 to 30; more preferably, the mass ratio of ZnS nanospheres to ZIF-67 is 1:5 to 20; and even more preferably, the mass ratio of ZnS nanospheres to ZIF-67 is 1:8 to 12.

[0016] Preferably, acetone, deionized water and ethanol are used to clean the ZnS nanospheres in sequence.

[0017] Among them, acetone is miscible with solvents such as ethylene glycol, reducing the solubility of ZnS in the solution and promoting the precipitation of ZnS nanospheres. In addition, acetone, deionized water, and ethanol all have the function of dissolving and removing residual impurities. Through repeated ultrasonic cleaning, deionized water can fully contact the surface of the nanospheres, flushing away impurities and further improving the purity of the product. For example, deionized water can remove residual water-soluble impurities such as unreacted salts and solvents. Ethanol has strong solubility and volatility, and can remove residual acetone, water, and some other organic impurities. It is miscible with acetone and water, displacing them from the surface of the nanospheres, and then taking away the impurities as the ethanol evaporates, thereby achieving the dual effects of cleaning and drying.

[0018] Preferably, the drying temperature is 50-80°C, more preferably 60-70°C.

[0019] In some embodiments, the cobalt source is cobalt nitrate, cobalt acetate, cobalt sulfate, or cobalt chloride.

[0020] Preferably, the molar ratio of the cobalt source to 2-methylimidazole is 1:2 to 6, more preferably 1:3 to 5, and even more preferably 1:4.

[0021] In some embodiments, the calcination temperature is 750-850° C., and the calcination time is 2-4 hours.

[0022] Preferably, the calcination temperature is 800° C. and the calcination time is 3 h.

[0023] In a second aspect, the present invention provides a ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material prepared by the preparation method;

[0024] The ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material is composed of a zinc sulfide / cobalt nanoparticle heterostructure uniformly dispersed in a nitrogen-sulfur doped carbon matrix, wherein small zinc sulfide nanoparticles are coated on the surface of large cobalt nanoparticles to form a core-shell heterostructure.

[0025] The diameter of the zinc sulfide nanoparticles is 2 to 5 nm, and the cobalt nanoparticles have two sizes, a large size of 20 to 100 nm and a small size of 2 to 10 nm;

[0026] Nitrogen and sulfur doped carbon has a dodecahedral structure with a diameter of 200 ~ 500 nm.

[0027] In a third aspect, the present invention provides the use of the ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material as a cathode catalyst for batteries and / or water electrolysis.

[0028] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0029] The present invention utilizes the decomposition and reconstruction of zinc sulfide to refine some ZIF-67-derived cobalt nanoparticles to smaller sizes, forming ultrafine zinc sulfide nanoparticles coated on the surface of larger cobalt nanoparticles. The composite material consists of a heterostructure of zinc sulfide / cobalt nanoparticles uniformly dispersed in a nitrogen-sulfur-doped carbon matrix, with the fine zinc sulfide nanoparticles coating the surface of larger cobalt nanoparticles. The ultrafine zinc sulfide nanoparticles have a diameter of 2 to 5 nm and are derived by decomposing and reconstructing zinc sulfide nanospheres with a diameter of 150 to 200 nm. The graded cobalt nanoparticles come in two sizes: a large one of 20 to 100 nm and a small one of 2 to 10 nm. The nitrogen-sulfur-doped carbon, with a dodecahedral-like structure and a diameter of 200 to 500 nm, is derived from the carbonization of ZIF-67.

[0030] The cobalt nanoparticle / carbon composites directly derived from ZIF-67 reported so far struggle to simultaneously produce cobalt nanoparticles in two distinct size ranges (small size: 2 to 10 nm, large size: 20 to 50 nm). Furthermore, the pyrolysis of zinc sulfide nanospheres reported so far is mostly used as a self-sacrificial template to create micro-nanopores, and there have been no reports of using it to refine cobalt nanoparticles and form heterogeneous structures.

[0031] When the ZnS / Co heterojunction composite nitrogen-sulfur-doped carbon material prepared by the present invention is used as a positive electrode catalyst for liquid rechargeable zinc-air batteries, the charge-discharge potential difference and cycle life both exceed those of commercial platinum carbon and ruthenium dioxide; when used as an anode catalyst for AEM water electrolysis, the performance is better than that of commercial platinum carbon and ruthenium dioxide, and stable operation exceeds 600 hours.

[0032] The preparation method of the present invention can obtain the ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material only through simple physical mixing and high-temperature calcination. The preparation method is simple and convenient for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0034] Figure 1are SEM images of ZnS nanospheres in the examples, wherein the scale bar in (a) is 1 μm, the scale bar in (b) is 500 nm, and the scale bar in (c) is 200 nm;

[0035] Figure 2 are SEM images of CoNCs in the examples, where the scale bar in (a) is 1 μm, the scale bar in (b) is 200 nm, and the scale bar in (c) is 100 nm;

[0036] Figure 3 are SEM images of the ZnS / Co / NSC materials in the examples, where the scale bar in (a) is 1 μm, the scale bar in (b) is 200 nm, and the scale bar in (c) is 100 nm;

[0037] Figure 4 (a-b) TEM images and (c-d) high-magnification TEM images of ZnS / Co / NSC in the examples, where the scale bar in (a) is 100 nm, the scale bar in (b) is 50 nm, the scale bar in (c) is 5 nm, and the scale bar in (d) is 5 nm;

[0038] Figure 5 is the XRD pattern of CoNC and ZnS / Co / NSC in the embodiment;

[0039] Figure 6 is the Raman image of CoNC and ZnS / Co / NSC in the embodiment;

[0040] Figure 7 In the figure, (a) shows the ORR of CoNC, ZnS / Co / NSC and commercial Pt / C; (b) shows the OER polarization curves of CoNC, ZnS / Co / NSC and RuO2;

[0041] Figure 8 The ORR cycle stability characterization diagrams of ZnS / Co / NSC and commercial Pt / C in the embodiment are shown in Figure 1, where (a) is the voltage range of 0.2~1.0 and (b) is the voltage range of 0.75~0.90.

[0042] Figure 9 The OER cycle stability characterization diagram of ZnS / Co / NSC and commercial Pt / C in the embodiment;

[0043] Figure 10 (a) Open circuit voltage curve of liquid rechargeable zinc-air battery catalyzed by ZnS / Co / NSC, Pt / C, and RuO2 in the embodiment, (b) 10 mA cm -2 (c) discharge curve and battery capacity under different current densities, (d) comparison of long-term cycle charge and discharge curves;

[0044] Figure 11 In the figure, (a) is a comparison of the initial activation voltage of AEM water electrolysis with ZnS / Co / NSC or RuO2 as the anode and Pt / C as the cathode, and (b) is a long-term stability test diagram of ZnS / Co / NSC as the anode;

[0045] Figure 12 1 is a comparison chart of the ORR / OER performance of Examples 1 to 4 at different calcination temperatures, wherein (a) is a comparison chart of the ORR performance of the four electrode materials; (b) is a comparison chart of the OER performance of the four electrode materials;

[0046] Figure 13 1 is a comparison chart of the ORR / OER performance of electrode materials with different mass ratios in Example 1, Example 5 and Example 6, wherein (a) is a comparison chart of the ORR of the three electrode materials; (b) is a comparison chart of the OER performance of the three electrode materials. DETAILED DESCRIPTION

[0047] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0048] The present invention will be further described below with reference to the embodiments.

[0049] Example 1

[0050] First, ZnS nanospheres were synthesized via a hydrothermal method: 2 g of zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) was dissolved in 70 mL of ethylene glycol, followed by the addition of 0.6 g of thiourea (CH₄N₂S) and 0.8 g of polyvinylpyrrolidone (PVP, K30). After stirring for 30 minutes, the mixture was hydrothermally heated at 140°C for 24 hours. After cooling to room temperature, the sample was removed and the white precipitate was repeatedly ultrasonically cleaned with acetone, deionized water, and ethanol. Finally, the ZnS nanospheres were obtained by drying at 70°C.

[0051] Secondly, ZIF-67 was synthesized by dissolving 1 mmol of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 4 mmol of 2-methylimidazole in 20 mL of methanol solution, ultrasonically dispersing them for 15 minutes, and then mixing them. The mixed solution was stirred at room temperature for 6 hours, centrifuged, washed, and dried. The purple powder obtained was the ZIF-67 material.

[0052] Finally, the synthesized ZnS and ZIF-67 were evenly mixed in a mass ratio of 1:10 and calcined in a tube furnace at 800 °C for 3 h to obtain the ZnS / Co / NSC sample (ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material).

[0053] If ZIF-67 is directly calcined at 800 °C in a tube furnace and kept warm for 3 h, the obtained sample is CoNC (comparison sample).

[0054] Figure 1 The SEM images of the prepared ZnS nanospheres and ZnS / Co / NSC are shown in Figure 2. Figure 1 As can be seen in (a), (b) and (c), the prepared ZnS particles are spherical with uniform size and a diameter of about 150 ~ 200 nm.

[0055] Figure 2 The SEM image of the prepared CoNC shows that the prepared CoNC particles are uniform in size and dodecahedral structure, with a size of about 200 ~ 500 nm. Figure 2 As described in (a) above. And through the magnified image, we can see the obvious metal agglomeration phenomenon. The dodecahedron is composed of dense large metal particles, and the size of the large metal particles is about 20 ~ 100nm, as shown in the figure. Figure 2 As shown in (b) and (c).

[0056] Figure 3 The SEM image of the prepared ZnS / Co / NSC material shows that the material still retains a good dodecahedral structure with a size of about 200 ~ 500 nm. Figure 3 As shown in (a), the stability of its structure is further confirmed. After calcination with zinc sulfide, its dodecahedral structure is not destroyed. However, compared with CoNC, the large metal particles in the ZnS / Co / NSC material are significantly reduced (20 ~ 100 nm), and a large number of small metal particles (2 ~ 10 nm) appear, as shown in Figure 2. Figure 3 As shown in (b) and (c), two sizes of metal particles are clearly embedded in the polyhedral carbon matrix.

[0057] Figure 4 TEM and HRTEM images of the prepared materials. Figure 4In (a), larger metal nanoparticles with diameters ranging from 20 to 100 nm are clearly visible. The enlarged image (b) clearly shows that in addition to the larger metal nanoparticles, the synthesized ZnS / Co / NSC composite also contains uniformly dispersed smaller metal nanoparticles with diameters ranging from 2 to 10 nm. The presence of two distinct types of metal nanoparticles with distinct size boundaries is evident.

[0058] Through high magnification TEM images, Figure 4 In (c) and (d), the lattice stripes of large and small metal nanoparticles correspond to the metal Co (111) crystal plane, and the surface of large cobalt particles is also dispersed and covered with many small metal particles. The lattice spacing corresponds to different crystal planes of ZnS, and the size of ZnS particles is 2 ~ 5 nm.

[0059] The above analysis confirms the successful synthesis of ZnS / Co heterojunction composite nitrogen-sulfur doped carbon materials, and provides strong evidence for the refinement and coating of ZnS on some cobalt nanoparticles to form ZnS / Co heterostructures.

[0060] Figure 5 The XRD patterns of the prepared CoNC and ZnS / Co / NSC are shown below. The XRD pattern of CoNC shows two carbon peaks centered at 24° and 44°, as well as several sharp peaks, which correspond to the standard card of metallic Co and prove the presence of metallic Co in the material. However, for the ZnS / Co / NSC material, in addition to the carbon peaks and the metallic cobalt peaks, there are also several sharp peaks, which can be well corresponding to ZnS, further proving the co-existence of ZnS and elemental Co in the material, corresponding to the TEM image above.

[0061] It can be seen by Raman light ( Figure 6 ), after the introduction of ZnS, the D band and G band intensities of ZnS / Co / NSC did not change significantly compared with CoNC materials. D / I G The value is also a key parameter to measure the disorder of the material. D / I G The value is not much different from that of CoNC material, which shows that the introduction of ZnS has no significant effect on the graphitization degree of the catalyst material.

[0062] like Figure 7As shown in (a), the ORR performance of ZnS / Co / NSC, CoNC and commercial Pt / C (20 wt%, Aladdin reagent) catalysts were compared. The limiting current density of ZnS / Co / NSC (7.13 mA cm -2 ) is much higher than that of CoNC (5.39 mA cm -2 ) and commercial Pt / C (5.24 mA cm -2 The half-wave potential of the ZnS / Co / NSC is around 0.822 V, while that of the commercial Pt / C electrode is around 0.856 V, a difference of only 34 mV. This difference significantly exceeds that of the CoNC, further demonstrating the excellent ORR catalytic performance of the ZnS / Co / NSC catalyst material.

[0063] Its OER performance is as follows Figure 7 As shown in (b), at 10 mA cm -2 The potential at 1.62 V is only 40 mV higher than commercial RuO2 and significantly lower than the comparative CoNC (1.82 V). The excellent ORR / OER performance of the ZnS / Co / NSC material is attributed to the fact that the decomposition and reconstruction of ZnS refines some ZIF-67-derived cobalt nanoparticles to smaller sizes and modifies the remaining large cobalt nanoparticles. Furthermore, the addition of N / S to the carbon matrix changes the electron distribution on the catalyst, accelerating reaction kinetics and improving mass transfer efficiency, contributing to the catalyst's high ORR / OER activity.

[0064] like Figure 8 As shown in (a) and (b), after 10,000 continuous cycles, the half-wave potential of the ZnS / Co / NSC material decayed by only 13 mV, while the commercial Pt / C material decayed by 16 mV under the same voltage conditions, demonstrating the superior ORR stability of the ZnS / Co / NSC material. This advantage is attributed to the firm anchoring of the cobalt nanoparticles, which allows for uniform dispersion and refinement of their size, creating abundant active sites and promoting the ORR reaction. This enables the ZnS / Co / NSC catalyst to maintain efficient catalytic performance over long periods of operation, demonstrating excellent electrochemical stability.

[0065] like Figure 9 As shown in Figure 2, after 3000 cycles, the ZnS / Co / NSC showed a high -2 The overpotential of ZnS / Co / NSC material decays by only 33 mV, while that of commercial RuO2 material decays by 103 mV, indicating that ZnS / Co / NSC material also has the same advantage in OER stability.

[0066] Figure 10 For the performance test of ZnS / Co / NSC, Pt / C, RuO2 in liquid rechargeable zinc-air batteries, Figure 10 As can be seen in (a), ZnS / Co / NSC as the positive electrode electrocatalyst of liquid rechargeable zinc-air battery has an open circuit potential of 1.506 V, which is higher than that of Pt / C catalyzed liquid zinc-air battery (1.467 V). At the same time, the liquid rechargeable zinc-air battery catalyzed by ZnS / Co / NSC has a higher open circuit potential at 10 mA cm -2 The discharge capacity was 796 mAh g -1 Zn The battery capacity is also higher than that of Pt / C catalyzed liquid zinc-air battery (684 mAh g -1 Zn ), with a larger battery capacity ( Figure 10 (b)).

[0067] At different current densities (5, 10, 20, 30, 40, 50 mA cm -2 ) is close to that of Pt / C catalyzed liquid zinc-air batteries, which has good rate performance and can adapt to discharge at different current densities, such as Figure 10 As shown in (c).

[0068] The ZnS / Co / NSC-catalyzed liquid rechargeable zinc-air battery exhibits excellent charge-discharge performance during long-term cycling. Figure 10 As shown in (d), both the cycle life and charge-discharge potential difference are superior to those of the Pt / C-catalyzed liquid zinc-air battery. The ZnS / Co / NSC-catalyzed liquid rechargeable zinc-air battery can stably cycle for over 400 cycles. Compared to the charge-discharge potential difference of 0.866 V in the first cycle, the charge-discharge potential difference after 400 cycles only increased by 0.03 V, demonstrating excellent performance and lifespan for the liquid rechargeable zinc-air battery.

[0069] Figure 11 The performance of ZnS / Co / NSC as anode catalyst in AEM water electrolysis was tested (the cathode was Pt / C catalyst). Figure 11 As can be seen in (a), ZnS / Co / NSC as the anode catalyst of AEM water electrolysis has a voltage of 1.654V after 1800 min of activation, which is lower than Pt / C+RuO2 (1.683V); Next, in the long-term stability test of 600 h, Pt / C+ZnS / Co / NSC showed high stability without attenuation, as shown in Figure 2. Figure 11As shown in (b), the above demonstrates that ZnS / Co / NSC has high activity and long-term stability in AEM water electrolysis.

[0070] Example 2

[0071] The difference between Example 2 and Example 1 is that the final calcination temperature is 700° C., and the obtained sample is ZnS / Co / NSC-700.

[0072] Example 3

[0073] The difference between Example 3 and Example 1 is that the final calcination temperature is 900° C., and the obtained sample is ZnS / Co / NSC-900.

[0074] Example 4

[0075] The difference between Example 4 and Example 1 is that the final calcination temperature is 1000° C., and the obtained sample is ZnS / Co / NSC-1000.

[0076] Figure 12 The ORR / OER performance of Examples 1 to 4 with different calcination temperatures is compared. Figure 12 As can be seen in (a), the half-wave potential of ZnS / Co / NSC-800 is much better than that of ZnS / Co / NSC-700 (0.783 V), ZnS / Co / NSC-900 (0.785 V) and ZnS / Co / NSC-1000 (0.789 V). This is attributed to the lower degree of graphitization of the carbon substrate caused by the lower temperature. If the carbonization temperature is too high, the original framework structure will be destroyed, resulting in a decrease in catalytic performance. Similarly, the ZnS / Co / NSC sample at 800 ° C also shows the best OER performance (1.62 V) (as shown in Figure 2). Figure 12 (b)). This demonstrates that appropriate carbonization temperature is of great significance to the improvement of catalyst performance.

[0077] Example 5

[0078] The difference between Example 5 and Example 1 is that the synthesized ZnS and ZIF-67 are finally mixed uniformly at a mass ratio of 1:5 to obtain a ZnS / Co / NSC-1:5 sample.

[0079] Example 6

[0080] The difference between Example 6 and Example 1 is that the synthesized ZnS and ZIF-67 are finally mixed uniformly at a mass ratio of 1:20 to obtain a ZnS / Co / NSC-1:20 sample.

[0081] Figure 13The ORR / OER performance of Example 1, Example 5, and Example 6 with different mass ratios is compared. As shown in (a), when the mass ratio is 1:10, the sample exhibits the highest half-wave potential, which is better than the ORR performance exhibited when the mass ratio is 1:5 and 1:20 (the half-wave potential of ZnS / Co / NSC-1:5 is 0.799 V, and the half-wave potential of ZnS / Co / NSC-1:20 is 0.801 V). As shown in (b), for OER performance, at 10 mA cm -2 When the ZnS / Co / NSC-1:5 ratio was 1.65 V, and the ZnS / Co / NSC-1:20 ratio was 1.66 V, both higher than the ZnS / Co / NSC-1:10 ratio (1.62 V). This is because a small amount of ZnS cannot sufficiently refine and modify the cobalt nanoparticles, while an excessive amount of ZnS will affect the exposure of active sites, thereby affecting the catalytic performance of the samples.

[0082] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material, characterized by: The steps include: The cobalt source and 2-methylimidazole were mixed in a proportion and dissolved in an alcohol solvent, ultrasonically dispersed, and stirred at 20-35°C for 1-10 hours. After the reaction was completed, the solid-liquid separation was performed and ZIF-67 was obtained after drying. The ZnS nanospheres and ZIF-67 were mixed uniformly at a mass ratio of 1:5-20 and calcined at 750-850℃ for 2-4h to obtain the product. The ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material is composed of a zinc sulfide / cobalt nanoparticle heterostructure uniformly dispersed in a nitrogen-sulfur doped carbon matrix, wherein the ZnS nanoparticles obtained by decomposing and reconstructing the ZnS nanospheres are coated on the surface of the cobalt nanoparticles to form a core-shell heterostructure; The preparation method of the ZnS nanospheres comprises the following steps: dissolving a zinc source in ethylene glycol, adding thiourea and polyvinyl pyrrolidone, mixing, and then performing a hydrothermal reaction. After the reaction is completed, the ZnS nanospheres are washed and dried to obtain the ZnS nanospheres.

2. The method for preparing the ZnS / Co heterojunction composite nitrogen-sulfur-doped carbon material according to claim 1, characterized in that: The zinc source is zinc nitrate, zinc acetate, zinc sulfate or zinc chloride.

3. The method for preparing the ZnS / Co heterojunction composite nitrogen- and sulfur-doped carbon material according to claim 1, characterized in that: The mass ratio of zinc source, thiourea, polyvinyl pyrrolidone and ethylene glycol is 2:0.6:0.4~0.8:

70.

4. The method for preparing the ZnS / Co heterojunction composite nitrogen- and sulfur-doped carbon material according to claim 1, characterized in that: The ZnS nanospheres were cleaned with acetone, deionized water and ethanol in sequence.

5. The method for preparing the ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material according to claim 1, characterized in that: The cobalt source is cobalt nitrate, cobalt acetate, cobalt sulfate or cobalt chloride.

6. The method for preparing the ZnS / Co heterojunction composite nitrogen- and sulfur-doped carbon material according to claim 1, characterized in that: The molar ratio of the cobalt source to 2-methylimidazole is 1:2-6.

7. A ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material, characterized by: Prepared by the preparation method according to any one of claims 1 to 6; The ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material is composed of a zinc sulfide / cobalt nanoparticle heterostructure uniformly dispersed in a nitrogen-sulfur doped carbon matrix, wherein small zinc sulfide nanoparticles are coated on the surface of large cobalt nanoparticles to form a core-shell heterostructure; The diameter of the zinc sulfide nanoparticles is 2-5 nm, and the cobalt nanoparticles have two sizes, a large size of 20-100 nm and a small size of 2-10 nm; Nitrogen and sulfur doped carbon has a dodecahedral structure with a diameter of 200~500nm.

8. Use of the ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material according to claim 7 as a cathode catalyst for batteries or water electrolysis.

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