ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electrode catalysts of batteries and electrolyzed water, and discloses a ZnS / Co heterojunction composite nitrogen-sulfur-doped carbon material and a preparation method and application thereof.The ZnS / Co heterojunction composite nitrogen-sulfur-doped carbon material is obtained by evenly mixing ZnS nanospheres and ZIF-67 according to the mass ratio of 1: 1-1: 30 and conducting calcination at the temperature of 600-1000 DEG C. The prepared composite material is composed of zinc sulfide / cobalt nanoparticle heterostructures uniformly dispersed in a nitrogen-sulfur-doped carbon matrix, and fine zinc sulfide nanoparticles coat the surfaces of large-size cobalt nanoparticles to form a core-shell heterostructure; the diameter of the zinc sulfide nanoparticles is 2-5 nm, the cobalt nanoparticles have two sizes, the large size is 20-100 nm, and the small size is 2-10 nm; the nitrogen and sulfur doped carbon is of a dodecahedron-like structure, and the diameter of the nitrogen and sulfur doped carbon is 200-500 nm. When the composite material is used as a positive electrode catalyst of a liquid rechargeable zinc-air battery, the charging and discharging performance has obvious advantages; when used as an AEM electrolyzed water anode catalyst, the platinum-carbon-ruthenium oxide catalyst has better performance than commercial platinum-carbon and ruthenium dioxide, and can stably operate for more than 600 hours.

Description

Technical Field

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

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

[0003] A rechargeable energy storage device, a zinc-air battery (ZAB) with a high theoretical energy density (1086 Wh kg -1 ) and low cost has broad application prospects. However, the slow oxygen reduction and evolution reactions (ORR and OER) in the air cathode are the key problems affecting the development of zinc-air batteries. Although some noble metal catalysts, such as Pt / C, RuO 2 etc. have high activity for ORR / OER, rare resources and high costs seriously hinder their large-scale application. In addition, in the technology of alkaline anion exchange membrane (AEM) electrolyzed water, the anodic OER involves a four-electron transfer process and becomes the core bottleneck restricting the overall energy efficiency. Although the AEM system has the advantages of no acid corrosion and low-cost catalysts, its working environment (pH 10 - 14) poses strict requirements on the catalyst: it must withstand the long-term erosion of a strong alkaline medium and also have high catalytic activity and long-term stability for OER. Currently, commercial IrO 2 , RuO 2 catalysts are expensive and prone to lattice oxygen dissolution at high potentials, seriously hindering the large-scale application of AEM electrolyzed water. Therefore, the development of inexpensive, efficient, and stable non-noble metal oxygen electrocatalysts is of great significance for the development of metal-air batteries and AEM electrolyzed water.

[0004] Using ZIF-67-derived cobalt nanoparticles / carbon composite materials rich in cobalt, nitrogen, and carbon elements as the positive electrode catalyst material has great application potential. However, conventional pyrolysis processes often result in single non-metal doped atoms and large metal nanoparticle agglomeration, and during the catalytic process, metal particles are also easily detached from the carbon matrix or re-agglomerated, which are all factors limiting the activity and stability of the material. Therefore, how to obtain multi-element non-metal heteroatom doping through simple operations, while firmly anchoring, uniformly dispersing, and refining the size of cobalt nanoparticles, creating rich active sites while improving stability, is the research focus and difficulty of cobalt nanoparticles and nitrogen-doped carbon composite materials as electrocatalysts. Summary of the Invention

[0005] Aiming at the deficiencies existing in the prior art, the purpose of the present invention is to provide a ZnS / Co heterojunction composite nitrogen and sulfur doped carbon material, a preparation method thereof, and an application thereof.

[0006] To achieve the above object, the present invention is realized by the following technical solutions: 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: Mix a cobalt source and 2-methylimidazole in proportion and dissolve them in a methanol solvent, ultrasonically disperse for 10 - 60 min, and stir and react at 20 - 35 °C for 1 - 10 h. After the reaction is completed, perform solid-liquid separation, and after drying, obtain purple ZIF-67 powder; Mix ZnS nanospheres and ZIF-67 evenly at a mass ratio of 1:1 - 30, and calcine at 600 - 1000 °C for 1 - 5 h to obtain the product.

[0007] In some embodiments, the method for preparing the ZnS nanospheres is as follows: dissolve a zinc source in ethylene glycol, add thiourea and polyvinylpyrrolidone, mix well, and then perform a hydrothermal reaction. After the reaction is completed, wash and dry to obtain ZnS nanospheres.

[0008] Among them, ethylene glycol as the reaction solvent can dissolve other reactants, providing a uniform dispersion and rapid liquid-phase reaction environment; thiourea is the sulfur source for generating ZnS nanospheres, which decomposes at high temperature, releases sulfur and combines with zinc to form fine ZnS; while the polyvinylpyrrolidone molecules act as surfactants, adsorbing on the surface of the ZnS nanospheres, reducing the surface energy on the surface of the nanoparticles, preventing the aggregation of ZnS nanoparticles, and obtaining nanospheres with uniform particle size and good dispersibility.

[0009] Preferably, the zinc source is zinc nitrate, zinc acetate, zinc sulfate or zinc chloride.

[0010] Preferably, the mass ratio of the zinc source, thiourea, polyvinylpyrrolidone and ethylene glycol is 2:0.6:0.4 - 0.8:70.

[0011] Preferably, the temperature of the hydrothermal reaction is 100 - 150 °C, and the reaction time is 10 - 30 h; more preferably, the temperature of the hydrothermal reaction is 120 - 150 °C, and the reaction time is 20 - 30 h; even more preferably, the temperature of the hydrothermal reaction is 135 - 145 °C, and the reaction time is 20 - 25 h.

[0012] Preferably, the mass ratio of ZnS nanospheres to ZIF-67 is 1:1 - 30; more preferably, the mass ratio of ZnS nanospheres to ZIF-67 is 1:5 - 20; even more preferably, the mass ratio of ZnS nanospheres to ZIF-67 is 1:8 - 12.

[0013] Preferably, acetone, deionized water, and ethanol are used in sequence to clean the ZnS nanospheres.

[0014] 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 and wash away the impurities, 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 can be miscible with acetone and water, displace them from the surface of the nanospheres, and then carry away the impurities with the volatilization of ethanol, thus achieving the dual effects of cleaning and drying.

[0015] Preferably, the drying temperature is 50 - 80 °C, and more preferably 60 - 70 °C.

[0016] In some embodiments, the cobalt source is cobalt nitrate, cobalt acetate, cobalt sulfate, or cobalt chloride.

[0017] Preferably, the molar ratio of the cobalt source to 2-methylimidazole is 1:2 - 6, more preferably 1:3 - 5, and even more preferably 1:4.

[0018] In some embodiments, the calcination temperature is 750 - 850 °C, and the calcination time is 2 - 4 h.

[0019] Preferably, the calcination temperature is 800 °C, and the calcination time is 3 h.

[0020] In a second aspect, the present invention provides a ZnS / Co heterojunction composite nitrogen and sulfur-doped carbon material prepared by the preparation method; The ZnS / Co heterojunction composite nitrogen and sulfur-doped carbon material is composed of zinc sulfide / cobalt nanoparticle heterostructures uniformly dispersed in a nitrogen and sulfur-doped carbon matrix. Among them, fine zinc sulfide nanoparticles are coated on the surface of large-sized cobalt nanoparticles, forming a core-shell heterostructure; The diameter of the zinc sulfide nanoparticles is 2 - 5 nm, and the cobalt nanoparticles have two sizes, the large size is 20 - 100 nm, and the small size is 2 - 10 nm; The nitrogen and sulfur-doped carbon is in a dodecahedron-like structure, and its diameter is 200 - 500 nm.

[0021] In a third aspect, the present invention provides the application of the ZnS / Co heterojunction composite nitrogen and sulfur-doped carbon material as a positive electrode catalyst for batteries and / or electrolytic water.

[0022] The beneficial effects obtained by one or more of the above embodiments of the present invention are as follows: By utilizing the decomposition and reconstruction of zinc sulfide, the present invention refines some ZIF-67-derived cobalt nanoparticles to obtain smaller sizes and forms ultrafine zinc sulfide nanoparticles coated on the surface of large-sized cobalt nanoparticles. The composite material consists of a zinc sulfide / cobalt nanoparticle heterostructure uniformly dispersed in a nitrogen and sulfur-doped carbon matrix, wherein the fine zinc sulfide nanoparticles are coated on the surface of the large-sized cobalt nanoparticles. The diameter of the ultrafine zinc sulfide nanoparticles is 2 - 5 nm and they are obtained by the decomposition and reconstruction of zinc sulfide nanospheres with a diameter of 150 - 200 nm; the hierarchical cobalt nanoparticles have two sizes, the large size is 20 - 100 nm and the small size is 2 - 10 nm; the nitrogen and sulfur-doped carbon is in a dodecahedron-like structure with a diameter of 200 - 500 nm and is obtained by the carbonization of ZIF-67.

[0023] It is difficult for the cobalt nanoparticle / carbon composite materials directly derived from ZIF-67 reported currently to simultaneously achieve cobalt nanoparticles in two obvious size ranges (the small size is 2 - 10 nm and the large size is 20 - 50 nm); in addition, the pyrolysis effect of the zinc sulfide nanospheres reported currently is mostly used as a self-sacrificial template to create micro-nano pores, and there is no report on using it to refine cobalt nanoparticles and form a heterostructure.

[0024] When the ZnS / Co heterojunction composite nitrogen and sulfur-doped carbon material prepared by the present invention is used as the positive electrode catalyst of a liquid rechargeable zinc-air battery, both the charge-discharge potential difference and the cycle life exceed those of commercial platinum-carbon and ruthenium dioxide; when used as the anode catalyst for AEM electrolyzed water, the performance is better than that of commercial platinum-carbon and ruthenium dioxide, and it can operate stably for more than 600 hours.

[0025] The preparation method of the present invention can obtain the ZnS / Co heterojunction composite nitrogen and sulfur-doped carbon material only through simple physical mixing and high-temperature calcination. The preparation method is simple and convenient for industrial production. Description of the Drawings

[0026] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0027] Figure 1 It is the SEM image of the ZnS nanospheres in the embodiment, 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; Figure 2It is the SEM image of CoNC in the example. Among them, 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; Figure 3 It is the SEM image of the ZnS / Co / NSC material in the example. Among them, 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; Figure 4 It is the (a - b) TEM image and (c - d) high - magnification TEM image of ZnS / Co / NSC in the example. Among them, 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; Figure 5 It is the XRD pattern of CoNC and ZnS / Co / NSC in the example; Figure 6 It is the Raman pattern of CoNC and ZnS / Co / NSC in the example; Figure 7 Among them, (a) is the ORR of CoNC, ZnS / Co / NSC and commercial Pt / C; (b) is the OER polarization curve of CoNC, ZnS / Co / NSC and RuO 2 ; Figure 8 It is the ORR cycle stability characterization diagram of ZnS / Co / NSC and commercial Pt / C in the example. Among them, (a) is the voltage range of 0.2 - 1.0, and (b) is the voltage range of 0.75 - 0.90; Figure 9 It is the OER cycle stability characterization diagram of ZnS / Co / NSC and commercial Pt / C in the example; Figure 10 It is the ZnS / Co / NSC, Pt / C, RuO 2 -catalyzed liquid rechargeable zinc - air battery (a) open - circuit voltage curve, (b) discharge curve and battery capacity at 10 mA cm -2 -2, and (c) rate performance at different current densities, (d) comparison diagram of long - time cyclic charge - discharge curves; Figure 11 Among them, (a) is the comparison diagram of the initial activation voltage of AEM electrolyzed water with ZnS / Co / NSC or RuO 2 used as the anode and Pt / C used as the cathode, and (b) is the long - time stability test diagram with ZnS / Co / NSC used as the anode; Figure 12Figure for comparing the ORR / OER performance of Examples 1 to 4 at different calcination temperatures. Among them, (a) is the ORR comparison diagram of four electrode materials; (b) is the OER performance comparison diagram of four electrode materials. Figure 13 Figure for comparing the ORR / OER performance of electrode materials with different mass ratios in Examples 1, 5, and 6. Among them, (a) is the ORR comparison diagram of three electrode materials; (b) is the OER performance comparison diagram of three electrode materials. Detailed implementation mode

[0028] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further explanations 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 of ordinary skill in the technical field to which the present invention belongs.

[0029] The present invention will be further described below in conjunction with examples.

[0030] Example 1 First, ZnS nanospheres were synthesized by a hydrothermal method: 2 g of zinc nitrate hexahydrate (Zn(NO 3 ) 2 ·6H 2 O) was dissolved in 70 mL of ethylene glycol, and then 0.6 g of thiourea (CH 4 N 2 S) and 0.8 g of polyvinylpyrrolidone (PVP, K30) were added. After stirring for 30 min, hydrothermal treatment was carried out and maintained at 140 °C for 24 h. After cooling to room temperature, the sample was taken out, and the white precipitate was ultrasonically cleaned repeatedly with acetone, deionized water, and ethanol, and finally dried at 70 °C to obtain ZnS nanospheres.

[0031] Secondly, ZIF-67 was synthesized: 1 mmol of cobalt nitrate hexahydrate (Co(NO 3 ) 2 ·6H 2 O) and 4 mmol of 2-methylimidazole were dissolved in 20 mL of methanol solution and ultrasonically dispersed for 15 min and then mixed. The mixed solution was stirred at room temperature for 6 h and then centrifuged, washed, and dried to obtain the purple powder, which is the ZIF-67 material.

[0032] Finally, the above-synthesized ZnS and ZIF-67 were mixed evenly at a mass ratio of 1:10 and calcined in a tube furnace at a calcination temperature of 800 °C for 3 h to obtain a ZnS / Co / NSC sample (ZnS / Co heterojunction composite nitrogen and sulfur-doped carbon material).

[0033] If ZIF-67 is directly calcined in a tube furnace at 800 °C for 3 h, the obtained sample is CoNC (control sample).

[0034] Figure 1 SEM images of the prepared ZnS nanospheres and ZnS / Co / NSC are shown. From Figure 1 panels (a), (b), and (c), it can be seen that the prepared ZnS particles are spherical with uniform size, and the diameter is about 150 - 200 nm.

[0035] Figure 2 SEM image of the prepared CoNC is shown. It can be seen from the figure that the prepared CoNC particles are in the form of uniform dodecahedra with a size of about 200 - 500 nm, as Figure 2 described in panel (a). And through the enlarged image, obvious metal agglomeration can be seen. The dodecahedron is composed of dense large metal particles with a size of about 20 - 100 nm, as Figure 2 shown in panels (b) and (c).

[0036] Figure 3 SEM image of the prepared ZnS / Co / NSC material is shown. It can be seen that the material still retains a good dodecahedral structure with a size of about 200 - 500 nm, as Figure 3 described in panel (a), further confirming the stability of its structure. 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 Figure 3 shown in panels (b) and (c), clearly showing two sizes of metal particles embedded in the polyhedral carbon matrix.

[0037] Figure 4 TEM and HRTEM images of the prepared materials are shown. From Figure 4 panel (a), larger-sized metal nanoparticles with a diameter of 20 - 100 nm can be clearly seen. Through the enlarged panel (b), it can be clearly seen that in the synthesized ZnS / Co / NSC composite material, in addition to the larger-sized metal nanoparticles, there are also small-sized metal nanoparticles uniformly dispersed, with a diameter of 2 - 10 nm. There are obviously two metal nanoparticles with distinct size boundaries.

[0038] Through the high-magnification TEM image, Figure 4In (c) and (d), the lattice fringes of both large-sized and small-sized metal nanoparticles correspond to the (111) crystal plane of metallic Co, and many fine metal particles are also dispersedly coated on the surface of the large-sized cobalt particles. The lattice spacing corresponds to different crystal planes of ZnS, and the size of the ZnS particles is 2 - 5 nm.

[0039] The above analysis confirms the successful synthesis of the ZnS / Co heterojunction composite nitrogen and sulfur-doped carbon material, and provides strong evidence that ZnS is refined and partially coated with cobalt nanoparticles to form a ZnS / Co heterostructure.

[0040] Figure 5 XRD patterns of the prepared CoNC and ZnS / Co / NSC are shown. The XRD pattern of CoNC shows two carbon peaks centered at 24° and 44°, and there are several sharp peaks, which correspond to the standard card of metallic Co, proving the existence of metallic Co in the material. However, for the ZnS / Co / NSC material, in addition to the carbon peaks and metallic cobalt peaks, there are also several sharp peaks, and these peaks can well correspond to ZnS, further proving the coexistence of ZnS and elemental Co in the material, corresponding to the above TEM images.

[0041] It can be seen from the Raman spectrum ( Figure 6 ), after the introduction of ZnS, the intensities of the D band and G band of ZnS / Co / NSC do not change significantly compared with the CoNC material. In addition, the I D / I G value is also a key parameter for measuring the degree of disorder of the material. The I D / I G value of the ZnS / Co / NSC material is not much different from that of the CoNC material, which all indicates that the introduction of ZnS has little effect on the graphitization degree of the catalyst material.

[0042] As shown in (a) of Figure 7 , the ORR performance of ZnS / Co / NSC, CoNC and commercial Pt / C (20 wt%, Aladdin reagent) catalysts was 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 ZnS / Co / NSC is around 0.822 V, and that of the commercial Pt / C electrode is around 0.856 V. The difference between them is only 34 mV, which significantly exceeds that of CoNC. This further demonstrates the excellent ORR catalytic performance of the ZnS / Co / NSC catalyst material.

[0043] Its OER performance is as Figure 7 shown in (b) below. The potential at 10 mA cm -2 is 1.62 V, only 40 mV higher than that of commercial RuO 2 and much lower than that of the comparative sample CoNC (1.82 V). The excellent ORR / OER performance of the ZnS / Co / NSC material is due to the fact that after the decomposition and reconstruction of ZnS, some of the cobalt nanoparticles derived from ZIF-67 are refined to smaller sizes, and the remaining large-sized cobalt nanoparticles are modified. In addition, the addition of N / S in the carbon matrix causes changes in the electron distribution on the catalyst, accelerating the reaction kinetics and improving the mass transfer efficiency, which contributes to the high ORR / OER activity of the catalyst material.

[0044] As Figure 8 shown in (a) and (b) below, after 10,000 continuous cycles, the half-wave potential of ZnS / Co / NSC only decays by 13 mV, while the commercial Pt / C material decays by 16 mV under the same voltage conditions, demonstrating the advantage of the ZnS / Co / NSC material in terms of ORR stability. This advantage is attributed to the fact that the cobalt nanoparticles are firmly anchored, refined in size while being uniformly dispersed, creating abundant active sites and promoting the ORR reaction. This enables the ZnS / Co / NSC catalyst to maintain high catalytic performance during long-term operation and exhibit excellent electrochemical stability.

[0045] As Figure 9 shown below, after 3,000 continuous cycles, the overpotential of ZnS / Co / NSC at 10 mA cm -2 only decays by 33 mV, while the commercial RuO 2 material decays by 103 mV, indicating that the ZnS / Co / NSC material also has the same advantage in terms of OER stability.

[0046] Figure 10 Performance tests of ZnS / Co / NSC, Pt / C, and RuO 2 in a liquid rechargeable zinc-air battery are shown below. Figure 10As can be seen from Fig. (a), as the positive electrode electrocatalyst of a liquid rechargeable zinc-air battery, ZnS / Co / NSC obtains an open-circuit potential of 1.506 V, which is higher than that of the liquid zinc-air battery catalyzed by Pt / C (1.467 V). At the same time, the liquid rechargeable zinc-air battery catalyzed by ZnS / Co / NSC discharges at 10 mA cm -2 to obtain a battery capacity of 796 mAh g -1 Zn , which is also higher than that of the liquid zinc-air battery catalyzed by Pt / C (684 mAh g -1 Zn ), showing a relatively large battery capacity ( Figure 10 Fig. (b)).

[0047] The rate performance at different current densities (5, 10, 20, 30, 40, 50 mA cm -2 ) is close to that of the liquid zinc-air battery catalyzed by Pt / C, showing good rate performance and being able to adapt to discharge at different current densities, as shown in Figure 10 Fig. (c).

[0048] As shown in Fig. (d), during the long-term cyclic charge and discharge process of the liquid rechargeable zinc-air battery catalyzed by ZnS / Co / NSC, both the cycle life and the charge-discharge potential difference are better than those of the liquid zinc-air battery catalyzed by Pt / C. The liquid rechargeable zinc-air battery catalyzed by ZnS / Co / NSC can stably cycle more than 400 times. Compared with the charge-discharge potential difference in the first cycle (0.866 V), the charge-discharge potential difference after 400 cycles only increases by 0.03 V, showing good performance and life of the liquid rechargeable zinc-air battery. Figure 10

[0049] Figure 11 Figure 11 Fig. (a) shows the performance test of ZnS / Co / NSC as the anode catalyst in AEM electrolyzed water (the cathode is the Pt / C catalyst). As can be seen from Fig. (a), as the anode catalyst of AEM electrolyzed water, ZnS / Co / NSC has a voltage of 1.654 V after 1800 min of activation, which is lower than that of Pt / C+RuO Figure 11 (1.683 V); Next, in the long-term stability test of 600 h, Pt / C+ZnS / Co / NSC shows high stability without attenuation, as shown in 2 Fig. (b). The above proves that ZnS / Co / NSC has high activity and long-term stability in AEM electrolyzed water. Figure 11

[0050] Example 2 Example 2 is different from Example 1 in that the final calcination temperature is 700 °C, and the obtained sample is ZnS / Co / NSC-700.

[0051] Example 3 Example 3 is different from Example 1 in that the final calcination temperature is 900 °C, and the obtained sample is ZnS / Co / NSC-900.

[0052] Example 4 Example 4 is different from Example 1 in that the final calcination temperature is 1000 °C, and the obtained sample is ZnS / Co / NSC-1000.

[0053] Figure 12 For the comparison of the ORR / OER performance of Examples 1 to 4 at different calcination temperatures. As can be seen from Figure 12 Figure (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 fact that a lower temperature results in a lower degree of graphitization of the carbon substrate, while too high a carbonization temperature will damage the original framework structure, leading to a decline 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 12 Figure (b)). It is proved that an appropriate carbonization temperature is of great significance for improving the performance of the catalyst.

[0054] Example 5 Example 5 is different from Example 1 in that the finally synthesized ZnS and ZIF-67 are uniformly mixed at a mass ratio of 1:5 to obtain the ZnS / Co / NSC-1:5 sample.

[0055] Example 6 Example 6 is different from Example 1 in that the finally synthesized ZnS and ZIF-67 are uniformly mixed at a mass ratio of 1:20 to obtain the ZnS / Co / NSC-1:20 sample.

[0056] Figure 13ORR / OER performance comparison of Examples 1, 5 and 6 with different mass ratios. As shown in (a), when the mass ratio is 1:10, the sample exhibits the highest half-wave potential, which is superior to the ORR performance when the mass ratios are 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 the OER performance, at 10 mA cm -2 −2, the potential of ZnS / Co / NSC-1:5 is 1.65 V, and the potential of ZnS / Co / NSC-1:20 is 1.66 V, both higher than the potential of ZnS / Co / NSC-1:10 (1.62 V). This is because the addition of a small amount of ZnS cannot provide sufficient effect of refining and modifying cobalt nanoparticles, while the introduction of excessive ZnS will affect the exposure of active sites, thereby affecting the catalytic performance of the sample.

[0057] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, 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 method for preparing a ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material, characterized in that: The steps include: The cobalt source and 2-methylimidazole were mixed in proportion and dissolved in an alcohol solvent, ultrasonically dispersed, and stirred at 20 to 35°C for 1 to 10 hours. After the reaction was completed, the solid and liquid were separated and dried to obtain ZIF-67. The ZnS nanospheres and ZIF-67 are uniformly mixed in a mass ratio of 1:1 to 30, and calcined at 600 to 1000 °C for 1 to 5 hours to obtain the product.

2. The method for preparing the ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material according to claim 1, characterized in that: The preparation method of the ZnS nanospheres is as follows: dissolving a zinc source in ethylene glycol, adding thiourea and polyvinyl pyrrolidone, mixing well, and then performing a hydrothermal reaction. After the reaction is completed, washing and drying are performed to obtain ZnS nanospheres.

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

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

70.

5. The method for preparing the ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material according to claim 2, characterized in that: The ZnS nanospheres were cleaned with acetone, deionized water and ethanol in turn.

6. 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.

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

8. The method for preparing the ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material according to claim 1, characterized in that: The calcination temperature is 750-850°C, and the calcination time is 2-4 hours.

9. A ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8; 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 fine zinc sulfide nanoparticles are coated on the surface of large-sized cobalt nanoparticles to form a core-shell heterostructure; 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; Nitrogen and sulfur doped carbon has a dodecahedral structure with a diameter of 200 ~ 500 nm.

10. Use of the ZnS / Co heterojunction composite nitrogen-sulfur doped carbon material according to claim 9 as a positive electrode catalyst for batteries and / or water electrolysis.

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