Carbon nanocage-supported iron-based metal para-site catalyst and its preparation method and application

Abstract

The present invention belongs to the field of catalyst technology, in particular to a carbon nano cage loaded iron metal para-site catalyst and its preparation method and application. Its preparation method is based on uniformly dispersed Zn-Co (or Zn-Ni) based metal organic framework nanocubes as raw materials, while wrapping Zn-ZIF-8 outside and performing S doping, then reintroducing Zn-ZIF-8 shells and Fe or Ni ions by epitaxial growth; finally, after high-temperature carbonization, two different metal nanoparticles (Co-Fe, Ni-Fe and Co-Ni) are achieved. They are respectively embedded in N / S co-doped carbon skeletons. The hollow structure of the catalyst can increase the active area and improve the reaction rate. The N / S co-doped carbon skeleton can further increase the conductivity of the catalyst and enhance its long-term stability. The present invention belongs to a bifunctional catalyst, which can drive oxygen reduction and oxygen evolution reactions simultaneously to meet the needs of rechargeable zinc-air batteries. Therefore, this work provides a reasonable and effective method for developing bifunctional electrocatalysts.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, in particular to a carbon nanocage-supported iron-based metal para-site catalyst and a preparation method and application thereof. Background Art

[0002] Zinc-air batteries (ZABs) are considered to be important devices for achieving sustainable conversion of electrical and chemical energy due to their high energy density, safety, reliability, low cost, and environmental friendliness. ZABs primarily rely on oxygen catalytic reactions at the air cathode, namely the oxygen reduction reaction (ORR) during discharge and the oxygen evolution reaction (OER) during charge. Because ORR and OER typically follow multi-electron transfer processes, the sluggish kinetics and resulting high overpotentials require advanced catalysts to accelerate these reactions. Although noble metal-based catalysts such as Pt / C and IrO2 / RuO2 can accelerate the reaction kinetics of ORR and OER, their high cost, lack of bifunctional catalytic activity, and poor durability have limited the further development of ZABs. Therefore, the design of efficient, stable, economical, and environmentally friendly bifunctional electrocatalysts is crucial for the large-scale commercial application of ZABs.

[0003] Although there are many reports on non-precious metal-based bifunctional catalysts, the active sites are often buried in the bulk of the catalyst, making it impossible to fully expose the active sites, which is obviously not conducive to efficient catalytic reactions. On the other hand, in the catalyst design process, in addition to considering the exposure of the active sites, the modulation of the local structure of the catalyst active sites should also be considered. Specifically, how to utilize the interactions between the various active sites in the catalyst to achieve charge redistribution, and then optimize the adsorption / desorption energy barrier of the modulation reaction intermediates to accelerate the electrocatalytic reaction process is still a major technical challenge. Summary of the Invention

[0004] One of the purposes of the present invention is to provide a method for preparing a carbon nanocage-supported iron-based metal para-site catalyst. The catalyst prepared by this method has a typical hollow nanobox structure. This structure has a higher specific surface area and can therefore accommodate more active sites, and has good conductivity and electrocatalytic performance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a carbon nanocage-supported iron-based metal para-site catalyst, comprising the following steps:

[0006] S1. Preparation of Zn-A-ZIF nanocubes

[0007] Dissolve 2-methylimidazole in deionized water at a concentration of 0.00649-0.0649 g / mL and stir to form solution 1;

[0008] Dissolve nitric acid hexahydrate A, zinc nitrate hexahydrate, and cetyltrimethylammonium bromide (CTAB) in deionized water and stir to form solution 2, wherein the concentration of nitric acid hexahydrate A is 0.000291-0.00291 g / mL, the concentration of zinc nitrate hexahydrate is 0.003273-0.03273 g / mL, and the concentration of CTAB is 0.00005-0.0005 g / mL;

[0009] Solution 1 and solution 2 were mixed in a volume ratio of 7:1 under stirring, and the mixture was allowed to stand in a water bath at 30-60°C. The precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, and then dried to obtain Zn-A-ZIF nanocubes.

[0010] S2. Preparation of sulfur-doped Zn-A-ZIF@Zn-ZIF-8 nanocubes

[0011] Dispersing Zn-A-ZIF nanocubes, polyvinylpyrrolidone (PVP), and 2-methylimidazole in methanol to obtain solution 3, wherein the concentration of Zn-A-ZIF nanocubes is 0.0001-0.001 g / mL, the concentration of polyvinylpyrrolidone (PVP) is 0.0003-0.003 g / mL, and the concentration of 2-methylimidazole is 0.005-0.05 g / mL;

[0012] Dissolve zinc nitrate hexahydrate in methanol at a concentration of 0.0039-0.039 g / mL to obtain solution 4;

[0013] Solution 3 and solution 4 were mixed at a volume ratio of 10:1 and allowed to stand. The resulting precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, and dried. The resulting Zn-A-ZIF@Zn-ZIF-8 nanocubes were dispersed in methanol at a dispersion concentration of 0.00033-0.0033 g / mL to obtain solution 5.

[0014] Sodium sulfide nonahydrate was dissolved in deionized water at a concentration of 0.0015-0.015 g / mL to obtain solution 6. Solution 5 and solution 6 were mixed in a volume ratio of 3:2 and allowed to stand. The resulting precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, and dried to obtain sulfur-doped Zn-A-ZIF@Zn-ZIF-8 nanocubes.

[0015] S3. Preparation of sulfur-doped Zn-A-ZIF@Zn-ZIF-8@Zn-B-ZIF-8 nanocubes

[0016] Sulfur-doped Zn-A-ZIF@Zn-ZIF-8 nanocubes and 2-methylimidazole were dispersed in methanol to obtain solution 7, wherein the concentration of sulfur-doped Zn-A-ZIF@Zn-ZIF-8 nanocubes was 0.00027-0.0027 g / mL and the concentration of 2-methylimidazole was 0.000943-0.00943 g / mL; zinc nitrate hexahydrate was dissolved in methanol at a concentration of 0.0014-0.014 g / mL to obtain solution 8;

[0017] Solution 7 and solution 8 were mixed in a volume ratio of 3:4 and allowed to stand. The resulting precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, dried, and then dispersed in methanol at a dispersion concentration of 0.0005-0.005 g / mL to obtain solution 9.

[0018] Dissolve acetic acid B in deionized water at a concentration of 0.0005-0.005 g / mL to obtain solution 10;

[0019] Solution 9 and solution 10 were mixed in a volume ratio of 3:1 and allowed to stand. The resulting precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, and then dried to obtain sulfur-doped Zn-A-ZIF@Zn-ZIF-8@Zn-B-ZIF-8 nanocubes.

[0020] S4. Preparation of carbon nanocage-supported iron-based metal para-site catalysts

[0021] The sulfur-doped Zn-A-ZIF@Zn-ZIF-8@Zn-B-ZIF-8 nanocubes were loaded into a porcelain boat and then placed in a tube furnace. The mixture was calcined at 500-700°C for 1-2 hours at a heating rate of 1-10°C / min under a nitrogen atmosphere, then heated to 920-1000°C for 1-5 hours, and then cooled to room temperature under a nitrogen flow to obtain a carbon nanocage-supported iron-based metal para-site catalyst.

[0022] The elements A and B are different and are both one of Fe, Co and Ni.

[0023] Further improvement of the preparation method of carbon nanocage-supported iron-based metal para-site catalysts:

[0024] Preferably, when solution 1 and solution 2 are mixed in a volume ratio of 7:1 in step S1, the mass ratio of 2-methylimidazole in solution 1 to nitric acid hexahydrate A, zinc nitrate hexahydrate, and CTAB in solution 2 is 9.08:0.0582:0.6545:0.01.

[0025] Preferably, when solution 3 and solution 4 are mixed in a volume ratio of 10:1 in step S2, the mass ratio of Zn-A-ZIF nanocubes, polyvinylpyrrolidone (PVP), 2-methylimidazole in solution 3 to zinc nitrate hexahydrate in solution 4 is 0.1:0.3:5:0.39.

[0026] Preferably, when solution 5 and solution 6 are mixed in a volume ratio of 3:2 in step S2, the mass ratio of Zn-A-ZIF@Zn-ZIF-8 nanocubes in solution 5 to sodium sulfide nonahydrate in solution 6 is 1:3.

[0027] Preferably, when solution 7 and solution 8 are mixed in a volume ratio of 3:4 in step S3, the mass ratio of sulfur-doped Zn-A-ZIF@Zn-ZIF-8 nanocubes and 2-methylimidazole in solution 7 to zinc nitrate hexahydrate in solution 8 is 0.081:0.2829:0.56.

[0028] Preferably, when solution 9 and solution 10 are mixed in a volume ratio of 3:1 in step S3, the mass ratio of the product in solution 9 to the acetic acid B in solution 10 is 3:1.

[0029] The second object of the present invention is to provide a carbon nanocage-supported iron-based metal para-site catalyst prepared by any of the above preparation methods.

[0030] The third object of the present invention is to provide an application of the above-mentioned carbon nanocage-supported iron-based metal para-site catalyst in zinc-air batteries.

[0031] The beneficial effects of the present invention compared to the prior art are:

[0032] 1) The present invention provides a method for preparing carbon nanocage-supported iron-based metal para-site catalysts. First, a chemical reaction is used to form a highly ordered crystalline structure, namely, nanocubes, with highly controllable pore structure and surface properties. S doping and Fe or Ni adsorption are achieved through coprecipitation and encapsulation with two layers of ZIF-8, respectively. Finally, pyrolysis is performed under a nitrogen atmosphere to form a Co-Fe (Ni-Fe or Co-Ni) para-site electrocatalyst. At high temperature, the two metal ions are reduced to their elemental form by the adjacent ligands. Simultaneously, the two metal ions are embedded in the nitrogen-sulfur co-doped carbon nanocages carbonized with S-doped 2-methylimidazole ligands. Separated by the ZIF-8 coating, the two metals do not form an alloy, preventing spontaneous metal aggregation, but instead form a para-site structure. After rigorous high-temperature treatment, the morphology undergoes little noticeable change, and the cubic shape is well maintained, but the surface becomes slightly roughened. This evolved morphology is desirable because it provides more active sites for catalytic reactions, thereby promoting the adsorption of various species. Therefore, nanocages embedded with Co-Fe (Ni-Fe or Co-Ni) pairs of sites were prepared. Since the reaction is carried out at 920-1000°C, which is higher than the boiling point of zinc, the zinc component in the precursor will evaporate and escape. Sulfur doping in this catalyst can promote the catalytic activity and stability of the carbon matrix in electrocatalysis and improve its electrochemical performance. Specifically, sulfur doping can introduce some impurity energy levels, improve the conductivity of the carbon matrix, and make it easier to accept electrons, thereby promoting the reaction. In addition, sulfur doping can also change the surface chemical properties of the carbon matrix, increase its interaction with the catalyst and reactants, and further improve the activity of the reaction. Therefore, sulfur doping is an important means to improve the catalytic performance of carbon matrices in electrocatalysis; finally, since Zn-Co-ZIF has the same structure as ZIF-8, a layer of ZIF-8 can be grown on the outer layer through seed epitaxy to better load the Fe source. Due to the isolation effect of the first layer of ZIF-8, Co and Fe do not form an alloy structure during carbonization, but form a para-site structure; the catalyst prepared by this method has a typical hollow nanobox structure, which has a higher specific surface area and can accommodate more active sites, has good conductivity and electrocatalytic performance, and has broad application prospects in electrocatalysis.

[0033] 2) The present invention has low energy consumption and simple synthesis steps, requiring only stirring and heating. The resulting electrocatalyst has a yield of up to 90%, high purity, good crystallinity, and exhibits superior electrocatalytic activity compared to commercial catalysts. The zinc-air battery catalyst is very environmentally friendly, without the use of toxic or hazardous raw materials. The catalyst is low-cost and uses non-precious metals instead of precious metal catalysts. When used in zinc-air batteries, it can achieve a long cycle life, making it a stable and long-lasting electrocatalyst.

[0034] 3) From the perspective of the catalyst structure, the catalyst of the present invention has a typical hollow nanobox structure, which has a higher specific surface area and can therefore accommodate more active sites. The thin shell also accelerates the mass transfer process during the electrocatalytic process. The main skeleton of the catalyst is nitrogen-sulfur co-doped carbon, which has good conductivity and can therefore enhance the mass transfer and charge transfer process of the electrocatalytic reaction.

[0035] From the perspective of catalyst composition, the Co-Fe (Ni-Fe or Co-Ni) in the catalyst of the present invention is embedded in the nitrogen-sulfur co-doped carbon matrix to form a para-site structure, forming a para-site catalyst; due to the synergistic effect between the multiple components, the charge transfer at the interface is promoted, the adsorption / desorption energy barrier of the reaction intermediates is optimized, and the reaction kinetics are accelerated, thus exhibiting excellent electrocatalytic performance.

[0036] From the perspective of catalytic function, unlike commercial Pt / C catalysts that are only suitable for non-rechargeable zinc-air batteries (because the discharge process requires good oxygen evolution performance), the catalyst of the present invention is a bifunctional catalyst that can both catalyze the oxygen reduction reaction and drive the oxygen evolution reaction, meeting the needs of rechargeable zinc-air batteries; and the performance of the catalyst is better than that of commercial oxygen reduction catalysts (Pt / C) and oxygen evolution catalysts (RuO2), showing potential application prospects to replace commercial precious metal catalysts.

[0037] The Co-Fe para-site electrocatalyst of the present invention has an ORR half-wave potential of 0.903 V (the higher the voltage, the better the performance) and a limiting current of 5.89 mA / cm 2 On the oxygen evolution curve, the catalyst of the present invention reaches a current density of 10 mA / cm 2 The required voltage is 1.526 V (the lower the voltage, the better the performance), and the corresponding overpotential is as low as 296 mV; the performance of both OER and ORR is excellent.

[0038] The Ni-Fe para-site electrocatalyst of the present invention drives the oxygen reduction reaction at a current density of 10 mA / cm 2 The overpotential of the oxygen evolution reaction is 315mV, showing excellent electrocatalytic oxygen evolution activity. For the oxygen reduction reaction, the half-wave potential is 0.892V and the limiting current is 5.65mA / cm 2 The performance of both OER and ORR is excellent.

[0039] The Co-Ni para-site electrocatalyst of the present invention drives the oxygen reduction reaction at a current density of 10 mA / cm 2The overpotential of the oxygen evolution reaction is 306mV, showing excellent electrocatalytic oxygen evolution activity. For the oxygen reduction reaction, the half-wave potential is 0.886V and the limiting current is 5.52mA / cm 2 The performance of both OER and ORR is excellent.

[0040] 4) The para-site structure of the catalyst obtained by the present invention is different from the conventional alloy structure in the past. Instead, it adopts the para-site structure to enhance the synergistic effect, which provides a new approach to the construction of efficient bifunctional electrocatalysts. Due to the presence of ZIF-8, the Co in the core and the Fe in the shell are prevented from forming an alloy, and a para-site structure is formed. This excellent structure gives extremely high catalytic efficiency. The electronic synergistic effect of the para-site structure can regulate the local charge distribution of adjacent electrons and increase the catalytic activity of ORR and OER. The hollow structure of the catalyst can increase the active area, provide more active sites, and increase the reaction rate. The structure in which N and S are co-doped into the carbon skeleton further increases the conductivity of the device, while providing protection for the Fe and Co metal sites, enhancing the stability of the device in long-term operation, and providing more possibilities for practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Flow chart for the preparation of nitrogen-sulfur co-doped carbon-based nanocages supported on Co-Fe para-site electrocatalysts;

[0042] Figure 2 The X-ray powder diffraction pattern of nitrogen-sulfur co-doped carbon-based nanocages supported on Co-Fe para-site electrocatalysts and the X-ray powder diffraction standard cards of Fe and Co;

[0043] Figure 3 for Figure 2 A partial magnified image of the X-ray powder diffraction standard card;

[0044] Figure 4 It is the Fe signal in the X-ray photoelectron spectrum of the Co-Fe para-site electrocatalyst supported by nitrogen-sulfur co-doped carbon-based nanocages;

[0045] Figure 5 is the Co signal in the X-ray photoelectron spectrum of the Co-Fe para-site electrocatalyst supported by nitrogen-sulfur co-doped carbon-based nanocages;

[0046] Figure 6 is the C signal in the X-ray photoelectron spectrum of the Co-Fe para-site electrocatalyst supported by nitrogen-sulfur co-doped carbon-based nanocages;

[0047] Figure 7 is the N signal in the X-ray photoelectron spectrum of nitrogen-sulfur co-doped carbon-based nanocages supported on Co-Fe para-site electrocatalysts;

[0048] Figure 8 is the S signal in the X-ray photoelectron spectrum of the Co-Fe para-site electrocatalyst supported by nitrogen-sulfur co-doped carbon-based nanocages;

[0049] Figure 9 Transmission electron microscopy image of nitrogen-sulfur co-doped carbon-based nanocages loaded with Co-Fe para-site electrocatalysts;

[0050] Figure 10 High-resolution transmission electron microscopy image of nitrogen-sulfur co-doped carbon-based nanocages loaded with Co-Fe para-site electrocatalysts;

[0051] Figure 11 Raman spectra of nitrogen-sulfur co-doped carbon-based nanocages loaded with Co-Fe para-site electrocatalysts;

[0052] Figure 12 The oxygen evolution reaction curves of nitrogen-sulfur co-doped carbon-based nanocages supported on Co-Fe para-site electrocatalysts and noble metal RuO2;

[0053] Figure 13 The oxygen reduction reaction curves of nitrogen-sulfur co-doped carbon-based nanocages supported on Co-Fe para-site electrocatalysts and noble metal Pt / C are shown;

[0054] Figure 14 The charge-discharge polarization curves of the Co-Fe para-site electrocatalyst supported on nitrogen-sulfur co-doped carbon-based nanocages and the charge-discharge polarization curves of the Pt / C and RuO2 mixed catalysts;

[0055] Figure 15 These are the charge-discharge curves of nitrogen-sulfur co-doped carbon-based nanocages loaded with Co-Fe para-site electrocatalysts, as well as the charge-discharge curves of Pt / C and RuO2 mixed catalysts. DETAILED DESCRIPTION

[0056] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0057] Example 1

[0058] This embodiment provides a method for preparing a nitrogen-sulfur co-doped carbon-based nanocage-supported Co-Fe para-site electrocatalyst, which specifically includes the following steps:

[0059] S1. Preparation of Zn-Co-ZIF nanocubes

[0060] 2-Methylimidazole was dissolved in deionized water at a concentration of 0.0908 g / mL and stirred to form solution 1; cobalt nitrate hexahydrate, zinc nitrate hexahydrate, and cetyltrimethylammonium bromide (CTAB) were dissolved in deionized water and stirred to form solution 2, wherein the concentration of cobalt nitrate hexahydrate in solution 2 was 0.003173 g / mL, the concentration of zinc nitrate hexahydrate was 0.03245 g / mL, and the concentration of CTAB was 0.0005 g / mL;

[0061] Solution 1 and solution 2 were mixed in a volume ratio of 7:1 under stirring. After continuing stirring for a period of time, the solution was allowed to stand in a water bath at 40°C. The resulting precipitate was collected by centrifuge, washed with deionized water and anhydrous ethanol, and then dried to obtain Zn-Co-ZIF nanocubes.

[0062] S2. Preparation of sulfur-doped Zn-Co-ZIF@Zn-ZIF-8 nanocubes

[0063] Zn-Co-ZIF nanocubes, polyvinylpyrrolidone (PVP), and 2-methylimidazole were dispersed in methanol to obtain solution 3, wherein the concentration of Zn-Co-ZIF nanocubes was 0.001 g / mL, the concentration of polyvinylpyrrolidone (PVP) was 0.003 g / mL, and the concentration of 2-methylimidazole was 0.05 g / mL;

[0064] Zinc nitrate hexahydrate was dissolved in methanol at a concentration of 0.039 g / mL to obtain solution 4;

[0065] Solutions 3 and 4 were fully mixed in a volume ratio of 10:1 and allowed to stand. The resulting precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, and dried to obtain Zn-Co-ZIF@Zn-ZIF-8 nanocubes. The resulting product was dispersed in methanol at a concentration of 0.002 g / mL to obtain solution 5. Sodium sulfide nonahydrate was dissolved in deionized water at a concentration of 0.015 g / mL to obtain solution 6. Solutions 5 and 6 were fully mixed in a volume ratio of 3:2 and allowed to stand. The resulting precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, and dried to obtain sulfur-doped Zn-Co-ZIF@Zn-ZIF-8 nanocubes.

[0066] S3. Preparation of sulfur-doped Zn-Co-ZIF@Zn-ZIF-8@Zn-Fe-ZIF-8 nanocubes

[0067] Sulfur-doped Zn-Co-ZIF@Zn-ZIF-8 nanocubes and 2-methylimidazole were dispersed in methanol to obtain solution 7, wherein the concentration of sulfur-doped Zn-Co-ZIF@Zn-ZIF-8 nanocubes was 0.0027 g / mL and the concentration of 2-methylimidazole was 0.00943 g / mL; zinc nitrate hexahydrate was dissolved in methanol at a concentration of 0.014 g / mL to obtain solution 8; solutions 7 and 8 were fully mixed in a volume ratio of 3:4 and allowed to stand, and the resulting precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, and dried. Sulfur-doped Zn-Co-ZIF@Zn-ZIF-8@Zn-ZIF-8 nanocubes were prepared; the resulting product was dispersed in methanol at a concentration of 0.005 g / mL to obtain solution 9; ferric acetate was dissolved in deionized water at a concentration of 0.006 g / mL to obtain solution 10; solutions 9 and 10 were thoroughly mixed in a volume ratio of 3:1 and allowed to stand, the resulting precipitate was collected by centrifugation, then washed with deionized water and anhydrous ethanol and dried to obtain sulfur-doped Zn-Co-ZIF@Zn-ZIF-8@Zn-Fe-ZIF-8 nanocubes;

[0068] S4. Preparation of Nitrogen-Sulfur Co-doped Carbon-Based Nanocages Supported with Co-Fe Para-Site Electrocatalysts

[0069] The sulfur-doped Zn-Co-ZIF@Zn-ZIF-8@Zn-Fe-ZIF-8 was loaded into a porcelain boat and then placed in a tube furnace. The boat was calcined at 600°C for 1 hour at a heating rate of 3°C / min under a nitrogen atmosphere, then heated to 920°C for 2 hours. The boat was then cooled to ambient temperature under a nitrogen flow to prepare the nitrogen-sulfur co-doped carbon-based nanocage-supported Co-Fe para-site electrocatalyst.

[0070] The process of synthesizing the nitrogen-sulfur co-doped carbon-based nanocages loaded with Co-Fe para-site electrocatalysts is as follows: Figure 1 shown.

[0071] Figure 2 and Figure 3 ( Figure 2 (Local magnification) is the X-ray diffraction pattern of the nitrogen-sulfur co-doped carbon-based nanocage-supported Co-Fe para-site electrocatalyst and the corresponding XRD standard cards Co (ICDD 00-015-0806) and Fe (ICDD01-087-0722). Through XRD testing, it can be found that graphitic carbon has a broad diffraction peak at 25°, confirming the presence of the carbon matrix in the catalyst. It is worth noting that there are three characteristic peaks at 44.3°, 51.4° and 75.6°, corresponding to the (111), (200) and (220) crystal planes of metal Co (ICDD: 00-015-0806), and a peak at 44.8° corresponding to the Fe (110) crystal plane.

[0072] Figure 4 It is the Fe signal in the X-ray photoelectron spectrum of the Co-Fe para-site electrocatalyst supported by nitrogen-sulfur co-doped carbon-based nanocages; the signals at 706.9 eV and 720.0 eV correspond to metallic Fe, 709.6 eV and 723.4 eV correspond to Fe-N bonds, 711.5 eV and 724.7 eV correspond to divalent Fe, and 714.5 eV and 728.4 eV correspond to trivalent Fe, proving the presence of Fe components in the catalyst.

[0073] Figure 5 It is the Co signal in the X-ray photoelectron spectrum of the Co-Fe para-site electrocatalyst supported by nitrogen-sulfur co-doped carbon-based nanocages; the peaks at 778.4eV and 793.6eV correspond to metallic Co, 780.4eV and 796.6eV correspond to Co-N bonds, 782.3eV and 798.4eV correspond to Co-O bonds, and 784.9eV and 802.9eV correspond to satellite peaks, proving the presence of Co components in the catalyst.

[0074] Figure 6 It is the C signal in the X-ray photoelectron spectrum of the Co-Fe para-site electrocatalyst supported by nitrogen-sulfur co-doped carbon-based nanocages; the four peaks located at 283.6, 284.3, 284.9 and 286.1 eV correspond to CS, CC, C=C and CN components, respectively, proving the presence of C component in the catalyst and the successful doping of N and S.

[0075] Figure 7 It is the N signal in the X-ray photoelectron spectrum of the Co-Fe para-site electrocatalyst supported by nitrogen-sulfur co-doped carbon-based nanocages; the signal at 398.4 eV is pyridine-N, 399.4 eV is MN structure, 400.8 eV is pyrrole-N, and 403.4 eV is graphite-N, proving the presence of N components in the catalyst.

[0076] Figure 8 It is the S signal in the X-ray photoelectron spectrum of the Co-Fe para-site electrocatalyst supported by nitrogen-sulfur co-doped carbon-based nanocages; the four peaks located at 161.5, 163.2, 164.8 and 168.0 eV correspond to the configurations of MS, CS, C=S and S-Ox, respectively, proving the presence of S components in the catalyst.

[0077] Figure 9 This is a transmission electron micrograph of a nitrogen-sulfur co-doped carbon-based nanocage loaded with Co-Fe para-site electrocatalyst. Figure 9Not only can the expected hollow structure be seen, but also a large number of nanoparticles inside the cavity are revealed. This hollow structure combined with the nanoparticles can increase the contact between the active center and the electrolyte during the catalytic reaction, accelerate the inflow and outflow of gases, and thus improve the catalytic efficiency of the product.

[0078] Figure 10 This is a high-resolution transmission electron microscopy image of nitrogen-sulfur co-doped carbon-based nanocages loaded with Co-Fe para-site electrocatalysts. Figure 10 The lattice spacing of Co and Fe at 0.204 nm and 0.202 nm is shown, corresponding to the (111) crystal plane of the Co component and the (110) crystal plane of the Fe component, respectively, indicating that Co and Fe form para sites. In the same HRTEM image, the Co and Fe components are also found to be embedded in the N and S co-doped carbon skeleton (depicted as C). It can be inferred that the outer carbon skeleton not only protects the active sites from electrolyte corrosion but also increases conductivity.

[0079] Figure 11 This is the Raman spectrum of nitrogen-sulfur co-doped carbon-based nanocages loaded with Co-Fe para-site electrocatalysts. Figure 11 It can be clearly seen that at 1340cm -1 and 1595cm -1 There are two obvious peaks. Generally, the relative intensity ratio of peak D and peak G (I D / I G ) to determine the degree of graphitization of the carbon material. According to calculations, the I D / I G It is about 0.88, indicating that it has a high degree of graphitization, which can reduce the oxidation degree of carbon in the sample at high oxidation potential.

[0080] Figure 12 The oxygen evolution reaction curve of nitrogen-sulfur co-doped carbon-based nanocage supported Co-Fe para-site electrocatalyst and the oxygen evolution reaction curve of commercial noble metal RuO2 are shown in Figure 2. The catalyst has a current density of 10 mA / cm 2 The corresponding overpotential is 296 mV, which is superior to the 302 mV of noble metals, demonstrating a certain degree of superiority. This indicates that the para-site structure can regulate the electronic structure of the catalyst, promote charge transfer, optimize the adsorption and desorption energy barriers of reaction intermediates, and ultimately enhance the electrocatalytic activity.

[0081] Figure 13 is the oxygen reduction reaction curve of nitrogen-sulfur co-doped carbon-based nanocage supported Co-Fe para-site electrocatalyst and precious metal Pt / C, Figure 9 It can be seen that the half-wave potential of the obtained electrocatalyst is 0.903V and the limiting current is 5.89mA / cm 2The half-wave potential of commercial precious metal Pt / C is 0.835V and the limiting current is 5.31mA / cm 2 Therefore, the performance of the Co-Fe para-site electrocatalyst is better than that of the precious metal Pt / C. This shows that the para-site structure can regulate the electronic structure of the catalyst, promote charge transfer, optimize the adsorption and desorption energy barriers of reaction intermediates, and ultimately improve the electrocatalytic activity.

[0082] Figure 14 The charge-discharge polarization diagram of nitrogen-sulfur co-doped carbon-based nanocages loaded with Co-Fe para-site electrocatalysts in reversible zinc-air batteries. 2 When the ΔE of the electrocatalyst is 0.80V, while that of the precious metal Pt / C+RuO2 is 1.23V, the performance of our electrocatalyst is better than that of the precious metal Pt / C+RuO2.

[0083] Figure 15 The charge-discharge curves of a nitrogen-sulfur co-doped carbon nanocage-supported Co-Fe para-site electrocatalyst in a reversible zinc-air battery show that the battery can last up to 120 hours, with ΔE = 0.179V at 2 hours and ΔE = 0.320V at 79 hours, both exceeding those of the precious metal Pt / C + RuO2.

[0084] Example 2

[0085] This embodiment provides a method for preparing a nitrogen-sulfur co-doped carbon-based nanocage-supported Ni-Fe para-site electrocatalyst, which specifically includes the following steps:

[0086] S1. Preparation of Zn-Ni-ZIF nanocubes

[0087] 2-Methylimidazole was dissolved in deionized water at a concentration of 0.0908 g / mL and stirred to form solution 1; nickel nitrate hexahydrate, zinc nitrate hexahydrate, and cetyltrimethylammonium bromide (CTAB) were dissolved in deionized water and stirred to form solution 2, wherein the concentration of nickel nitrate hexahydrate in solution 2 was 0.003173 g / mL, the concentration of zinc nitrate hexahydrate was 0.03245 g / mL, and the concentration of CTAB was 0.0005 g / mL;

[0088] Solution 1 and solution 2 were mixed in a volume ratio of 7:1 under stirring. After continuing stirring for a period of time, the solution was allowed to stand in a water bath at 40°C. The resulting precipitate was collected by centrifuge, washed with deionized water and anhydrous ethanol, and then dried to obtain Zn-Ni-ZIF nanocubes.

[0089] S2. Preparation of sulfur-doped Zn-Ni-ZIF@Zn-ZIF-8 nanocubes

[0090] Zn-Ni-ZIF nanocubes, polyvinylpyrrolidone (PVP) and 2-methylimidazole were dispersed in methanol to obtain solution 3, wherein the concentration of Zn-Ni-ZIF nanocubes was 0.001 g / mL, the concentration of polyvinylpyrrolidone (PVP) was 0.003 g / mL, and the concentration of 2-methylimidazole was 0.05 g / mL; zinc nitrate hexahydrate was dissolved in methanol at a concentration of 0.039 g / mL to obtain solution 4; solutions 3 and 4 were fully mixed at a volume ratio of 10:1 and allowed to stand, and the resulting precipitate was collected by centrifugation, and then The resulting solution was then washed with deionized water and anhydrous ethanol and dried to obtain Zn-Ni-ZIF@Zn-ZIF-8 nanocubes. The resulting product was dispersed in methanol at a concentration of 0.002 g / mL to obtain solution 5. Sodium sulfide nonahydrate was dissolved in deionized water at a concentration of 0.015 g / mL to obtain solution 6. Solutions 5 and 6 were fully mixed in a volume ratio of 3:2 and allowed to stand. The resulting precipitate was collected by centrifugation and then washed with deionized water and anhydrous ethanol and dried to obtain sulfur-doped Zn-Ni-ZIF@Zn-ZIF-8 nanocubes.

[0091] S3. Preparation of sulfur-doped Zn-Ni-ZIF@Zn-ZIF-8@Zn-Fe-ZIF-8 nanocubes

[0092] Sulfur-doped Zn-Ni-ZIF@Zn-ZIF-8 nanocubes and 2-methylimidazole were dispersed in methanol to obtain solution 7, wherein the concentration of sulfur-doped Zn-Ni-ZIF@Zn-ZIF-8 nanocubes was 0.0027 g / mL and the concentration of 2-methylimidazole was 0.00943 g / mL; zinc nitrate hexahydrate was dissolved in methanol at a concentration of 0.014 g / mL to obtain solution 8; solutions 7 and 8 were fully mixed in a volume ratio of 3:4 and allowed to stand, and the resulting precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, and dried. Sulfur-doped Zn-Ni-ZIF@Zn-ZIF-8@Zn-ZIF-8 nanocubes were prepared; the resulting product was dispersed in methanol at a concentration of 0.005 g / mL to obtain solution 9; ferric acetate was dissolved in deionized water at a concentration of 0.006 g / mL to obtain solution 10; solutions 9 and 10 were thoroughly mixed in a volume ratio of 3:1 and allowed to stand, the resulting precipitate was collected by centrifugation, then washed with deionized water and anhydrous ethanol and dried to obtain sulfur-doped Zn-Ni-ZIF@Zn-ZIF-8@Zn-Fe-ZIF-8 nanocubes;

[0093] S4. Preparation of Nitrogen-Sulfur Co-doped Carbon-Based Nanocages Supported with Ni-Fe Para-Site Electrocatalysts

[0094] The sulfur-doped Zn-Ni-ZIF@Zn-ZIF-8@Zn-Fe-ZIF- was loaded into a porcelain boat and then placed in a tube furnace. The boat was calcined at 600°C for 1 hour at a heating rate of 3°C / min under a nitrogen atmosphere, then heated to 920°C for 2 hours. The boat was then cooled to ambient temperature under a nitrogen flow to prepare the nitrogen-sulfur co-doped carbon-based nanocage-supported Ni-Fe para-site electrocatalyst.

[0095] The results show that the Ni-Fe para-site electrocatalyst prepared in this embodiment can be loaded with nitrogen-sulfur co-doped carbon-based nanocages at a current density of 10 mA / cm 2 The overpotential of oxygen evolution reaction is 310mV, showing excellent electrocatalytic oxygen evolution activity. For oxygen reduction reaction, the half-wave potential is 0.892V and the limiting current is 5.65mA / cm 2 When the catalyst is used as the air electrode, the assembled rechargeable zinc-air battery is 2 The △E is 0.86V at 2h and the charge and discharge time of the battery can reach 110 hours. The △E is 0.266V at 2h and 0.382V at 79h, which are both better than the precious metal Pt / C+RuO2.

[0096] Example 3

[0097] This embodiment provides a method for preparing a nitrogen-sulfur co-doped carbon-based nanocage-supported Co-Ni para-site electrocatalyst, which specifically includes the following steps:

[0098] S1. Preparation of Zn-Co-ZIF nanocubes

[0099] 2-Methylimidazole was dissolved in deionized water at a concentration of 0.0908 g / mL and stirred to form solution 1; cobalt nitrate hexahydrate, zinc nitrate hexahydrate, and cetyltrimethylammonium bromide (CTAB) were dissolved in deionized water and stirred to form solution 2, wherein the concentration of cobalt nitrate hexahydrate in solution 2 was 0.003173 g / mL, the concentration of zinc nitrate hexahydrate was 0.03245 g / mL, and the concentration of CTAB was 0.0005 g / mL;

[0100] Solution 1 and solution 2 were mixed in a volume ratio of 7:1 under stirring. After continuing stirring for a period of time, the solution was allowed to stand in a water bath at 40°C. The resulting precipitate was collected by centrifuge, washed with deionized water and anhydrous ethanol, and then dried to obtain Zn-Co-ZIF nanocubes.

[0101] S2. Preparation of sulfur-doped Zn-Co-ZIF@Zn-ZIF-8 nanocubes

[0102] Zn-Co-ZIF nanocubes, polyvinylpyrrolidone (PVP) and 2-methylimidazole were dispersed in methanol to obtain solution 3, wherein the concentration of Zn-Co-ZIF nanocubes was 0.001 g / mL, the concentration of polyvinylpyrrolidone (PVP) was 0.003 g / mL, and the concentration of 2-methylimidazole was 0.05 g / mL; zinc nitrate hexahydrate was dissolved in methanol at a concentration of 0.039 g / mL to obtain solution 4; solutions 3 and 4 were fully mixed at a volume ratio of 10:1 and allowed to stand, and the resulting precipitate was collected by centrifugation. The nanocubes were then washed with deionized water and anhydrous ethanol and dried to obtain Zn-Co-ZIF@Zn-ZIF-8. The resulting product was dispersed in methanol at a concentration of 0.002 g / mL to obtain solution 5. Sodium sulfide nonahydrate was dissolved in deionized water at a concentration of 0.015 g / mL to obtain solution 6. Solutions 5 and 6 were thoroughly mixed in a volume ratio of 3:2 and allowed to stand. The resulting precipitate was collected by centrifugation and then washed with deionized water and anhydrous ethanol and dried to obtain sulfur-doped Zn-Co-ZIF@Zn-ZIF-8 nanocubes.

[0103] S3. Preparation of sulfur-doped Zn-Co-ZIF@Zn-ZIF-8@Zn-Ni-ZIF-8 nanocubes

[0104] Sulfur-doped Zn-Co-ZIF@Zn-ZIF-8 nanocubes and 2-methylimidazole were dispersed in methanol to obtain solution 7, wherein the concentration of sulfur-doped Zn-Co-ZIF@Zn-ZIF-8 nanocubes was 0.0027 g / mL and the concentration of 2-methylimidazole was 0.00943 g / mL; zinc nitrate hexahydrate was dissolved in methanol at a concentration of 0.014 g / mL to obtain solution 8; solutions 7 and 8 were fully mixed in a volume ratio of 3:4 and allowed to stand, and the resulting precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, and dried. Sulfur-doped Zn-Co-ZIF@Zn-ZIF-8@Zn-ZIF-8 nanocubes were prepared; the resulting product was dispersed in methanol at a concentration of 0.005 g / mL to obtain solution 9; nickel acetate was dissolved in deionized water at a concentration of 0.006 g / mL to obtain solution 10; solutions 9 and 10 were thoroughly mixed in a volume ratio of 3:1 and allowed to stand, the resulting precipitate was collected by centrifugation, then washed with deionized water and anhydrous ethanol and dried to obtain sulfur-doped Zn-Co-ZIF@Zn-ZIF-8@Zn-Ni-ZIF-8 nanocubes;

[0105] S4. Preparation of Nitrogen-Sulfur Co-doped Carbon-Based Nanocages Supported Co-Ni Para-Site Electrocatalysts

[0106] The sulfur-doped Zn-Co-ZIF@Zn-ZIF-8@Zn-Ni-ZIF-8 was loaded into a porcelain boat and then placed in a tube furnace. The boat was calcined at 600°C for 1 hour at a heating rate of 3°C / min under a nitrogen atmosphere, then heated to 920°C for 2 hours. The boat was then cooled to ambient temperature under a nitrogen flow to prepare the nitrogen-sulfur co-doped carbon-based nanocage-supported Co-Ni para-site electrocatalyst.

[0107] The results show that the nitrogen-sulfur co-doped carbon-based nanocage loaded Co-Ni para-site electrocatalyst prepared in this embodiment has a current density of 10 mA / cm 2 The overpotential of the oxygen evolution reaction is 306mV, showing excellent electrocatalytic oxygen evolution activity. For the oxygen reduction reaction, the half-wave potential is 0.886V and the limiting current is 5.52mA / cm 2 When the catalyst is used as the air electrode, the assembled rechargeable zinc-air battery is 2 The △E is 0.92V at 2h and the charge and discharge time of the battery can reach 100 hours. The △E is 0.358V at 2h and 0.552V at 79h, which are both better than the precious metal Pt / C+RuO2.

[0108] Those skilled in the art will appreciate that the foregoing descriptions are merely specific embodiments of the present invention, and not exhaustive. It should be noted that numerous variations and modifications are possible for those skilled in the art, and all such variations and modifications that do not exceed the scope of the claims should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon nanocage-supported iron-based metal para-site catalyst, comprising the following steps: S1. Preparation of Zn-A-ZIF nanocubes Dissolve 2-methylimidazole in deionized water at a concentration of 0.00649-0.0649 g / mL and stir to form solution 1; Dissolve nitric acid hexahydrate A, zinc nitrate hexahydrate, and cetyltrimethylammonium bromide (CTAB) in deionized water and stir to form solution 2, wherein the concentration of nitric acid hexahydrate A is 0.000291-0.00291 g / mL, the concentration of zinc nitrate hexahydrate is 0.003273-0.03273 g / mL, and the concentration of CTAB is 0.00005-0.0005 g / mL; Solution 1 and solution 2 were mixed in a volume ratio of 7:1 under stirring, and the mixture was allowed to stand in a water bath at 30-60°C. The precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, and then dried to obtain Zn-A-ZIF nanocubes. S2. Preparation of sulfur-doped Zn-A-ZIF@Zn-ZIF-8 nanocubes Dispersing Zn-A-ZIF nanocubes, polyvinylpyrrolidone (PVP), and 2-methylimidazole in methanol to obtain solution 3, wherein the concentration of Zn-A-ZIF nanocubes is 0.0001-0.001 g / mL, the concentration of polyvinylpyrrolidone (PVP) is 0.0003-0.003 g / mL, and the concentration of 2-methylimidazole is 0.005-0.05 g / mL; Dissolve zinc nitrate hexahydrate in methanol at a concentration of 0.0039-0.039 g / mL to obtain solution 4; Solution 3 and solution 4 were mixed at a volume ratio of 10:1 and allowed to stand. The resulting precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, and dried. The resulting Zn-A-ZIF@Zn-ZIF-8 nanocubes were dispersed in methanol at a dispersion concentration of 0.00033-0.0033 g / mL to obtain solution 5. Sodium sulfide nonahydrate was dissolved in deionized water at a concentration of 0.0015-0.015 g / mL to obtain solution 6. Solution 5 and solution 6 were mixed in a volume ratio of 3:2 and allowed to stand. The resulting precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, and dried to obtain sulfur-doped Zn-A-ZIF@Zn-ZIF-8 nanocubes. S3. Preparation of sulfur-doped Zn-A-ZIF@Zn-ZIF-8@Zn-B-ZIF-8 nanocubes Sulfur-doped Zn-A-ZIF@Zn-ZIF-8 nanocubes and 2-methylimidazole were dispersed in methanol to obtain solution 7, wherein the concentration of sulfur-doped Zn-A-ZIF@Zn-ZIF-8 nanocubes was 0.00027-0.0027 g / mL and the concentration of 2-methylimidazole was 0.000943-0.00943 g / mL; zinc nitrate hexahydrate was dissolved in methanol at a concentration of 0.0014-0.014 g / mL to obtain solution 8; Solution 7 and solution 8 were mixed in a volume ratio of 3:4 and allowed to stand. The resulting precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, dried, and then dispersed in methanol at a dispersion concentration of 0.0005-0.005 g / mL to obtain solution 9. Dissolve acetic acid B in deionized water at a concentration of 0.0005-0.005 g / mL to obtain solution 10; Solution 9 and solution 10 were mixed in a volume ratio of 3:1 and allowed to stand. The resulting precipitate was collected by centrifugation, washed with deionized water and anhydrous ethanol, and then dried to obtain sulfur-doped Zn-A-ZIF@Zn-ZIF-8@Zn-B-ZIF-8 nanocubes. S4. Preparation of carbon nanocage-supported iron-based metal para-site catalysts The sulfur-doped Zn-A-ZIF@Zn-ZIF-8@Zn-B-ZIF-8 nanocubes were loaded into a porcelain boat and then placed in a tube furnace. The mixture was calcined at 500-700°C for 1-2 hours at a heating rate of 1-10°C / min under a nitrogen atmosphere, then heated to 920-1000°C for 1-5 hours, and then cooled to room temperature under a nitrogen flow to obtain a carbon nanocage-supported iron-based metal para-site catalyst. in, The elements A and B are different and are both one of Fe, Co and Ni.

2. The method for preparing the carbon nanocage-supported iron-based metal para-site catalyst according to claim 1, characterized in that: When solution 1 and solution 2 are mixed in a volume ratio of 7:1 in step S1, the mass ratio of 2-methylimidazole in solution 1 to nitric acid hexahydrate A, zinc nitrate hexahydrate, and CTAB in solution 2 is 9.086:0.0582:0.6545:0.

01.

3. The method for preparing the carbon nanocage-supported iron-based metal para-site catalyst according to claim 1, characterized in that: When solution 3 and solution 4 are mixed in a volume ratio of 10:1 in step S2, the mass ratio of Zn-A-ZIF nanocubes, polyvinylpyrrolidone PVP, and 2-methylimidazole in solution 3 to zinc nitrate hexahydrate in solution 4 is 0.1:0.3:5:0.

39.

4. The method for preparing the carbon nanocage-supported iron-based metal para-site catalyst according to claim 1, characterized in that: When solution 5 and solution 6 are mixed in a volume ratio of 3:2 in step S2, the mass ratio of Zn-A-ZIF@Zn-ZIF-8 nanocubes in solution 5 to sodium sulfide nonahydrate in solution 6 is 1:

3.

5. The method for preparing the carbon nanocage-supported iron-based metal para-site catalyst according to claim 1, characterized in that: When solution 7 and solution 8 are mixed in a volume ratio of 3:4 in step S3, the mass ratio of sulfur-doped Zn-A-ZIF@Zn-ZIF-8 nanocubes and 2-methylimidazole in solution 7 to zinc nitrate hexahydrate in solution 8 is 0.081:0.2829:0.

56.

6. The method for preparing the carbon nanocage-supported iron-based metal para-site catalyst according to claim 1, characterized in that: When solution 9 and solution 10 are mixed in a volume ratio of 3:1 in step S3, the mass ratio of the product in solution 9 to the acetic acid B in solution 10 is 3:

1.

7. A carbon nanocage-supported iron-based metal para-site catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the carbon nanocage-supported iron-based metal para-site catalyst according to claim 7 in zinc-air batteries.

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