Preparation method and application of hollow nano box-shaped iron-nitrogen-carbon oxygen reduction catalyst

Abstract

The invention discloses a preparation method of a hollow nano box-shaped iron-nitrogen-carbon oxygen reduction catalyst and application of the hollow nano box-shaped iron-nitrogen-carbon oxygen reduction catalyst. According to the method, silica zeolite is used as a sacrificial template of a three-dimensional structure, a block copolymer is used as a modifier, a nitrogen-containing polymer monomer is used as a reaction precursor, and the polymer directionally-coated silica zeolite is prepared on the basis of a regioselective induced deposition strategy. And then adding a nitrogen-containing iron source and fully mixing, and removing the zeolite template through carbonization and an etching agent to finally obtain the iron-nitrogen-carbon oxygen reduction catalyst with a hollow nano box-shaped structure. The method is simple and reliable, the raw materials are easy to obtain, the prepared catalyst material has a unique hollow nano box-shaped structure, the active site exposure probability is effectively enhanced through a micro / mesoporous reaction channel, the diffusion path of reactants is shortened, the dynamic barrier in the mass transfer process is remarkably reduced, and the catalyst material has a good application prospect. The hollow nanometer box-shaped structure promotes rapid diffusion of oxygen in the catalyst layer. The catalyst shows excellent performance in a zinc-air battery device and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of non-precious metal oxygen reduction catalysts, and particularly relates to a preparation method of a hollow nano-box-shaped iron-nitrogen-carbon oxygen reduction catalyst and its application in a zinc-air battery device. Background Art

[0002] The oxygen reduction reaction (ORR) is the core electrochemical process for charge generation in green energy zinc-air batteries (ZABs), and its kinetic characteristics directly determine the energy conversion efficiency and cycle stability of the battery system. There is a significant kinetic retardation phenomenon in this four-electron transfer reaction, and it is necessary to rely on efficient catalysts to reduce the activation overpotential to meet the requirements of industrial applications. Currently, platinum-based catalysts are still the preferred materials for ORR catalysts due to their excellent intrinsic activity. However, limited by the scarcity of precious metal reserves and high costs, their large-scale commercial applications are restricted. Under this background, developing non-precious metal catalysts with high catalytic activity, excellent stability, and cost advantages has become the key technical path to break through the industrialization bottleneck of ZABs.

[0003] In recent years, transition metal-based materials represented by iron-nitrogen-carbon (Fe-N-C) catalysts have shown good application potential in the field of ZABs. Due to their excellent oxygen reduction catalytic performance and cost advantages, such catalysts are considered the most promising non-precious metal catalyst system for replacement. Research shows that the active origin of Fe-N-C catalysts lies in their nano Fe clusters and atomically dispersed Fe-N xThe synergistic effect of the coordination structure, and its intrinsic activity is enhanced through the design of Fe cluster size and the regulation of coordination configuration. Although the activity of Fe-N-C catalysts has been further improved by strategies such as nitrogen doping gradient design, Fe cluster nanosizing, and d-band center regulation in the existing technologies, there is still a certain gap compared with platinum-based catalysts. This activity difference directly leads to a sharp increase in the loading amount of Fe-N-C catalysts in the cathode of ZABs, resulting in the catalytic layer thickness reaching 5-10 times that of the platinum-based system, thus triggering multiple mass transfer limitations: (1) The overly thick catalytic layer prolongs the oxygen diffusion path, leading to a decrease in gas-phase transport efficiency; (2) The unreasonable distribution of the three-dimensional pore structure reduces the three-phase reaction interface, resulting in a decrease in the accessibility and utilization rate of active sites; (3) The hindered penetration of the liquid electrolyte leads to the deterioration of electrochemical wetting and the loss of effective electrochemical active area. These multi-scale mass transfer bottlenecks are coupled with each other, ultimately restricting the energy density and power output of ZABs. Therefore, how to break through the limitations of existing Fe-N-C catalysts, innovatively design a composite structure with both micro-nano directional mass transfer channels and high-density active sites, and achieve the synergistic optimization of oxygen diffusion path, three-phase reaction interface, and electrolyte wetting, has become the core technical problem that urgently needs to be solved to break through the performance bottleneck of ZABs. Summary of the Invention

[0004] The object of the present invention is to propose a hollow nano-box-shaped iron-nitrogen-carbon oxygen reduction catalyst for the problem existing in the non-precious metal catalytic layer of zinc-air batteries. The unique microstructure of this catalyst can significantly reduce the oxygen mass transfer resistance in the catalytic layer and effectively improve the energy density and power density of zinc-air batteries.

[0005] The present invention provides a preparation method that can obtain an oxygen reduction catalyst with a hollow box-shaped structure, high utilization rate of non-precious metal active sites, good electrolyte permeability, and high electrochemical wetting, and at the same time has low mass transfer kinetic resistance and is suitable for the application of zinc-air batteries.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] The present invention provides a preparation method for a hollow nano-box-shaped iron-nitrogen-carbon oxygen reduction catalyst, including the following steps:

[0008] (1) Preparation of polymer directionally coated silicalite

[0009] Dissolve silicalite, block copolymer, and nitrogen-containing precursor in a mixed solution of deionized water and absolute ethanol, ultrasonically stir continuously until evenly mixed to obtain a milky white solution; add the milky white solution to a Tris buffer solution with a pH of about 10, adjust the pH of the solution to 8.5 using an acidic solution, and after reacting under certain conditions, obtain polymer directionally coated silicalite through washing, centrifugation, filtration, and drying.

[0010] (2) Preparation of Hollow Nanobox-shaped Iron-Nitrogen-Carbon Oxygen Reduction Catalyst

[0011] Take the polymer in step (1) to directionally coat the silicalite, add a nitrogen-containing iron source and deionized water, and ultrasonically mix evenly. After reacting under certain conditions, wash, centrifuge, filter, and dry, then heat up for carbonization and cool in an argon atmosphere in a tubular furnace, and then remove the template with an etchant, filter, and dry to obtain a hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst.

[0012] Preferably, the block copolymer in step (1) is a mixture of F127 and P123 in the Pluronic series, and the mass ratio of P127 to F123 is 1:(10 - 20).

[0013] Preferably, the nitrogen-containing precursor in step (1) is dopamine.

[0014] Preferably, the mass ratio of the deionized water to absolute ethanol in step (1) is 1:(0.3 - 0.4).

[0015] Preferably, the reaction under certain conditions in step (1) is continuous stirring for 6 h, the stirring speed is 500 rpm, and the reaction temperature is 30 °C.

[0016] Preferably, the acidic solution in step (1) is 0.1 M hydrochloric acid.

[0017] Preferably, the washing solution in step (1) is deionized water, the number of centrifugation times is 4 times, and the vacuum drying temperature is 80 °C.

[0018] Preferably, the mass ratio of the polymer directionally coating the silicalite to the nitrogen-containing iron source in step (2) is 1:(0.01 - 0.10).

[0019] Preferably, the nitrogen-containing iron source in step (2) is ferrous phthalocyanine salt.

[0020] Preferably, the reaction under certain conditions in step (2) is continuous stirring for 2 h, the stirring speed is 500 rpm, and the reaction temperature is 25 °C.

[0021] Preferably, the carbonization heating rate in step (2) is 5 °C / min, the carbonization temperature is 900 °C, and the carbonization time is 2 h.

[0022] Preferably, the etchant in step (2) is hydrofluoric acid, the concentration is 20 - 40 wt%, and the etching time is 4 h.

[0023] Preferably, the drying temperature in step (2) is 80 °C and the time is 12 h.

[0024] In the technical solution of the present invention: the application of the hollow nano-box-shaped iron-nitrogen-carbon as an oxygen reduction catalyst is preferably a zinc-air battery.

[0025] Preferably, an electrochemical workstation with a three-electrode system is used. The hollow nano-box-shaped iron-nitrogen-carbon catalyst loaded on the rotating disk electrode is used as the working electrode, a platinum sheet is used as the counter electrode, and a saturated Ag / AgCl is used as the reference electrode. The electrolyte is 250 mL of 0.1 M potassium hydroxide solution saturated with oxygen. The electrocatalytic performance is tested at a rotation speed of 1600 rpm.

[0026] Preferably, a zinc plate is used as the anode, and the self-made hollow nano-box-shaped iron-nitrogen-carbon catalyst is used as the cathode catalytic layer. Combined with the carbon paper gas diffusion layer to form a cathode air electrode, and the electrolyte is 6 M potassium hydroxide solution. A zinc-air battery is prepared by assembling the above components, where the cathode is directly exposed to the air without additional oxygen supply. The assembled zinc-air battery is subjected to a constant current discharge test using a battery test system, and the discharge voltage and discharge time of the battery are recorded, and the specific capacity and energy density of the battery are calculated accordingly. At the same time, polarization curve and power density curve tests are carried out to analyze the output performance and power characteristics of the battery.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] (1) The present invention prepares a hollow nano-box-shaped iron-nitrogen-carbon catalyst by a simple regioselective deposition method. The catalyst has fully exposed inner / outer surfaces and a permeable micro / mesoporous structure, effectively enhancing the exposure probability of active sites, significantly improving the ion transport efficiency and electrolyte wettability, helping to form a rich electrode / electrolyte interface, and synergistically improving the utilization rate of active sites.

[0029] (2) The clear hollow box-shaped structure provided by the present invention shortens the diffusion path of oxygen in the catalytic layer, thus significantly reducing the kinetic resistance during the reactant transport process.

[0030] (3) The hollow nano-box-shaped iron-nitrogen-carbon catalyst prepared by the present invention exhibits excellent electrocatalytic activity in the oxygen reduction reaction. In a 0.1 M potassium hydroxide solution saturated with oxygen, its oxygen reduction half-wave potential reaches 0.83 V.

[0031] (4) The present invention uses the hollow nano-box-shaped iron-nitrogen-carbon catalyst as the catalytic layer of the zinc-air battery, enabling the power density of the zinc-air battery to reach 162 mW cm -2 , and the catalyst of the present invention provides key material support for the development of high-power density ZABs. Description of the Drawings

[0032] Figure 1Scanning electron microscope image of Si-1@HO-mPDA prepared in Example 1.

[0033] Figure 2 Scanning electron microscope image of Fe-N-HOCNs-900 prepared in Example 1.

[0034] Figure 3 Scanning electron microscope image of Fe-N-C-900 prepared in Comparative Example 1.

[0035] Figure 4 X-ray diffraction image of Fe-N-HOCNs-900 prepared in Example 1.

[0036] Figure 5 Linear sweep voltammograms of Fe-N-HOCNs-900 prepared in Example 1, Fe-N-HOCNs-1000 prepared in Example 2, Fe-N-HOCNs-700 prepared in Example 3, Fe-N-HOCNs-800 prepared in Example 4, Fe-N-C-900 prepared in Comparative Example 1, and commercial 20% Pt / C catalyst in saturated oxygen 0.1 M potassium hydroxide solution.

[0037] Figure 6 Digital photo of the application of the Fe-N-HOCNs-900 catalyst prepared in Example 1 as a catalytic layer in a zinc-air battery.

[0038] Figure 7 Power density curves of Fe-N-HOCNs-900 prepared in Example 1, Fe-N-HOCNs-1000 prepared in Example 2, Fe-N-C-900 prepared in Comparative Example 1, and commercial 20 wt% Pt / C catalyst as a catalytic layer in a zinc-air battery. Detailed Description of the Invention

[0039] The above content of the present invention will be further described in detail through examples below, but it should not be understood that the scope of the above subject matter of the present invention is limited to the following examples. All technologies implemented based on the above content of the present invention belong to the scope of the present invention. Example 1

[0040] (1) Preparation of polymer-oriented coated silicalite

[0041] 1.8 g of silicalite, 0.3 g of P123, 5.7 g of F127, and 9.0 g of dopamine were dissolved in a mixed solution of 20 g of deionized water and 8 g of absolute ethanol, and ultrasonically mixed evenly at room temperature until a milky white solution was formed; the milky white solution was added to 50 mL of 0.1 M Tris buffer solution with a pH of about 10.1, and the pH of the solution was adjusted to 8.5 with a certain amount of 0.1 M hydrochloric acid solution, and then continuously stirred for 6 h, the stirring speed was 500 rpm, the reaction temperature was 30 °C, and it was centrifugally washed 3 times with deionized water, filtered, and dried under vacuum at 80 °C for 12 h to obtain polymer directionally coated silicalite, denoted as Si-1@HO-mPDA.

[0042] (2) Preparation of hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst

[0043] Take 5.0 g of Si-1@HO-mPDA in step (1), add 100 mg of ferrous phthalocyanine salt and 50 g of absolute ethanol, and ultrasonically mix evenly, continuously stir for 2 h, the stirring speed is 500 rpm, the reaction temperature is 25 °C, centrifugally wash 3 times with deionized water, filter, and dry under vacuum at 80 °C for 12 h, then carbonize in a tubular furnace under an argon atmosphere at a heating rate of 5 °C / min, the carbonization temperature is 900 °C, the carbonization time is 2 h, and then etch with 30 wt% hydrofluoric acid for 4 h. After filtration, it was vacuum dried at 80 °C for 12 h to obtain a hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst, denoted as Fe-N-HOCNs-900. Example 2

[0044] (1) Preparation of polymer directionally coated silicalite

[0045] 1.8 g of silicalite, 6.0 g of F127 and 9.0 g of dopamine were dissolved in a mixed solution of 20 g of deionized water and 8 g of absolute ethanol, and ultrasonically mixed evenly at room temperature until a milky white solution was formed; the milky white solution was added to 50 mL of 0.1 M Tris buffer solution with a pH of about 10.2, and the pH of the solution was adjusted to 8.5 with a certain amount of 0.1 M hydrochloric acid solution, and then continuously stirred for 4 h, the stirring speed was 500 rpm, the reaction temperature was 30 °C, and it was centrifugally washed 3 times with deionized water, filtered, and dried under vacuum at 80 °C for 12 h to obtain polymer directionally coated silicalite, denoted as Si-1@HO-mPDA.

[0046] (2) Preparation of hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst

[0047] Take 5.0 g of Si-1@HO-mPDA from step (1), add 100 mg of ferrous phthalocyanine salt and 50 g of absolute ethanol, and ultrasonically mix them evenly. Stir continuously for 2 h at a stirring speed of 500 rpm and a reaction temperature of 25 °C. Centrifuge and wash with deionized water 3 times, filter, and dry under vacuum at 80 °C for 12 h. Then, carbonize in a tubular furnace under an argon atmosphere at a heating rate of 5 °C / min, a carbonization temperature of 1000 °C, and a carbonization time of 2 h. Then, etch with 30 wt% hydrofluoric acid for 4 h. Filter and dry under vacuum at 80 °C for 12 h to obtain a hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst, denoted as Fe-N-HOCNs-1000. Example 3

[0048] (1) Preparation of polymer-oriented coated silicalite

[0049] Dissolve 1.8 g of silicalite, 5.5 g of F108, and 5.0 g of aniline in a mixed solution of 30 g of deionized water and 10 g of absolute ethanol, and ultrasonically mix them evenly at room temperature until a milky white solution is formed. Add the milky white solution to 50 mL of 0.1 M Tris buffer solution with a pH of about 10.4, adjust the pH of the solution to 8.5 with a certain amount of 0.1 M hydrochloric acid solution, and then stir continuously for 4 h at a stirring speed of 500 rpm and a reaction temperature of 30 °C. Centrifuge and wash with deionized water 3 times, filter, and dry under vacuum at 80 °C for 12 h to obtain polymer-oriented coated silicalite, denoted as Si-1@HO-mPAN.

[0050] (2) Preparation of hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst

[0051] Take 5.0 g of Si-1@HO-mPAN from step (1), add 100 mg of ferrous phthalocyanine salt and 30 g of absolute ethanol, and ultrasonically mix them evenly. Stir continuously for 2 h at a stirring speed of 500 rpm and a reaction temperature of 25 °C. Centrifuge and wash with deionized water 3 times, filter, and dry under vacuum at 80 °C for 12 h. Then, carbonize in a tubular furnace under an argon atmosphere at a heating rate of 5 °C / min, a carbonization temperature of 700 °C, and a carbonization time of 2 h. Then, etch with 30 wt% hydrofluoric acid for 4 h. Filter and dry under vacuum at 80 °C for 12 h to obtain a hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst, denoted as Fe-N-HOCNs-700. Example 4

[0052] (1) Preparation of polymer-oriented coated silicalite

[0053] 1.8 g of silicalite, 7.0 g of P105 and 6.0 g of pyrrole were co-dissolved in a mixed solution of 30 g of deionized water and 15 g of absolute ethanol. After ultrasonic mixing for 5 min at room temperature, the mixture was continuously stirred for 30 min until a milky white solution appeared. The milky white solution was added to 50 mL of 0.1 M Tris buffer solution with a pH of about 9.9, and the pH of the solution was adjusted to 8.5 using a certain amount of 0.1 M hydrochloric acid solution. Then, the mixture was continuously stirred for 6 h at a stirring speed of 500 rpm and a reaction temperature of 80 °C. After centrifugal washing with deionized water three times, filtration, and drying under vacuum at 80 °C for 12 h, polymer-oriented coated silicalite was obtained, denoted as Si-1@HO-mPPy.

[0054] (2) Preparation of hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst

[0055] 5.0 g of Si-1@HO-mPPy from step (1) was taken, 100 mg of ferrous phthalocyanine salt and 50 g of absolute ethanol were added, and the mixture was ultrasonically mixed evenly and continuously stirred for 2 h at a stirring speed of 500 rpm and a reaction temperature of 25 °C. After centrifugal washing with deionized water three times, filtration, and drying under vacuum at 80 °C for 12 h, it was then carbonized in a tubular furnace under an argon atmosphere at a heating rate of 5 °C / min, a carbonization temperature of 800 °C, and a carbonization time of 2 h. Then, it was etched with 30 wt% hydrofluoric acid for 4 h. After filtration, it was dried under vacuum at 80 °C for 12 h to obtain a hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst, denoted as Fe-N-HOCNs-800. Example 5

[0056] Referring to Example 1, the difference is that 0.3 g of P123, 5.7 g of F127, and 9.0 g of dopamine in Example 1(1) were replaced with 6.0 g of P108 and 6.0 g of o-phenylenediamine, and at the same time, the carbonization conditions in Example 1(2) were adjusted to 600 °C, with other conditions remaining unchanged, to obtain the Fe-N-HOCNs-600 catalyst. Example 6

[0057] Referring to Example 1, the difference is that 0.3 g of P123, 5.7 g of F127, and 9.0 g of dopamine in Example 1(1) were replaced with 7.0 g of P105 and 6.0 g of pyrrole, and at the same time, the carbonization conditions in Example 1(2) were adjusted to a heating rate of 7 °C / min and a carbonization temperature of 850 °C, with other conditions remaining unchanged, to obtain the Fe-N-HOCNs-850 catalyst Example 7

[0058] Referring to Example 1, the difference is that 0.3 g of P123, 5.7 g of F127, and 9.0 g of dopamine in Example 1(1) are replaced with 5.4 g of P127 and 5.6 g of aniline. At the same time, the carbonization conditions in Example 1(2) are adjusted to a heating rate of 8 °C / min and a carbonization temperature of 950 °C, and other conditions remain unchanged, obtaining the Fe-N-HOCNs-950 catalyst. Example 8

[0059] Referring to Example 1, the difference is that 0.3 g of P123, 5.7 g of F127, and 9.0 g of dopamine in Example 1(1) are replaced with 6.5 g of P123 and 7.0 g of pyrrole. At the same time, the carbonization conditions in Example 1(2) are adjusted to 1100 °C, and other conditions remain unchanged, obtaining the Fe-N-HOCNs-1100 catalyst. Comparative Example 1

[0060] In this comparative example, commercial 20 wt% Pt / C is used as a control. Comparative Example 2

[0061] Referring to Example 1, the difference is that no block polymer is added in Example 1(1), and other conditions remain unchanged, obtaining the Fe-N-C-900 catalyst. Comparative Example 3

[0062] The difference between Comparative Example 3 and Example 1 is only that the zeolite template in Example 1(1) is replaced with silicon nanospheres, and other conditions remain unchanged. The final product is denoted as Fe-N-HONPs-900. Comparative Example 4

[0063] The difference between Comparative Example 4 and Example 1 is only that the zeolite template added in Example 1(1) is removed, and other conditions remain unchanged. The final product is denoted as Fe-N-NPs-900. Comparative Example 5

[0064] The difference between Comparative Example 5 and Example 1 is only that the etchant used in Example 1(2) is replaced with 10 wt% hydrochloric acid, and other conditions remain unchanged. The final product is denoted as Fe-N-SiCNs-900. Comparative Example 6

[0065] The difference between Comparative Example 6 and Example 1 is only that the nitrogen-containing iron source used in Example 1(2) is replaced with iron nitrate, and other conditions remain unchanged. The final product is denoted as Fe-HOCNs-900. Comparative Example 7

[0066] The difference between Comparative Example 7 and Example 1 is only that the nitrogen-containing iron source added in Example 1(2) is removed, and other conditions remain unchanged. The final product is denoted as HOCNs-900. Comparative Example 8

[0067] The difference between Comparative Example 8 and Example 1 is only that the carbonization conditions in Example 1(2) are adjusted to a heating rate of 15 °C / min, and other conditions remain unchanged. The final product is denoted as Fe-N-CNs-900 Fast 。 Comparative Example 9

[0068] The difference between Comparative Example 9 and Example 1 is only that the carbonization conditions in Example 1(2) are adjusted to use a 5% hydrogen-argon mixed gas, and other conditions remain unchanged. The final product is denoted as Fe-HOCNs-900. Comparative Example 10

[0069] The difference between Comparative Example 10 and Example 1 is only that the nitrogen-containing polymer monomer added in Example 1(1) is removed, and other conditions remain unchanged. The final product is denoted as Fe-N-900. Comparative Example 11

[0070] The difference between Comparative Example 11 and Example 1 is only that the nitrogen-containing polymer added in Example 1(1) is replaced by urea, and other conditions remain unchanged. The final product is denoted as Fe-N-CNs-900. Comparative Example 12

[0071] The difference between Comparative Example 12 and Example 1 is only that the ferrous phthalocyanine salt added in Example 1(2) is replaced by cobalt phthalocyanine, and other conditions remain unchanged. The final product is denoted as Co-N-HOCNs-900. Comparative Example 13

[0072] The difference between Comparative Example 13 and Example 1 is only that the ferrous phthalocyanine salt added in Example 1(2) is replaced by nickel phthalocyanine, and other conditions remain unchanged. The final product is denoted as Ni-N-HOCNs-900. Comparative Example 14

[0073] The difference between Comparative Example 14 and Example 1 is only that the 100 mg of ferrous phthalocyanine salt added in Example 1(2) is replaced by 300 mg of ferrous phthalocyanine salt, and other conditions remain unchanged. The final product is denoted as Fe 300 -N-HOCNs-900. Comparative Example 15

[0074] The difference between Comparative Example 15 and Example 1 is only that the 100 mg of ferrous phthalocyanine salt added in Example 1(2) is replaced by 10 mg of ferrous phthalocyanine salt, and other conditions remain unchanged. The final product is denoted as Fe 10 -N-HOCNs-900.

[0075] Performance Test

[0076] 1. Microstructure

[0077] Figures 1 - 2 These are the SEM images of the Si-1@HO-mPDA and Fe-N-HOCNs-900 catalysts prepared in Example 1 respectively. From Figure 1 it can be seen that after the treatment of block polymer modification and dopamine coating, the framework-like polydopamine in the obtained Si-1@OP-mPDA only grows concentratedly on the specific crystal planes and the crystal plane-crystal plane junctions of the silicalite template. Figure 2 It can be seen that the Fe-N-HOCNs-900 catalyst prepared after carbonization and template etching treatment presents a hollow nanobox-like structure, and the framework has strong rigidity, ensuring the stability of the box-like structure. In addition, the presence of mesoporous structure can be clearly observed in its framework.

[0078] Figure 3 This is the scanning electron microscope image of Fe-N-C-900 prepared in Comparative Example 1. Compared with Example 1, in Comparative Example 1, due to the absence of block polymer added during the preparation process, dopamine shows non-selective full-coverage deposition on the surface of silicalite. After carbonization and template removal by etching, a hollow nanobox-like structure fails to be formed.

[0079] 2. Composition Analysis

[0080] Figure 4 This is the wide-angle X-ray diffraction pattern of the Fe-N-HOCNs-900 catalyst prepared in Example 1, where: the abscissa 2-Theta represents the diffraction angle 2θ, and the ordinate Intensity represents the intensity of the diffraction peak. From Figure 2 it can be seen that Fe-N-HOCNs-900 shows a diffraction peak of carbon (002) near 26.0°, indicating that mPDA can be transformed into graphite carbon structure after heat treatment. In addition, diffraction peaks of FeN at (111), (200) and (220) are observed near 43.5°, 50.7° and 74.6°. Diffraction peaks of Fe at (110), (200) and (211) are observed near 44.6°, 65.0° and 82.3°, indicating that ferrous phthalocyanine salt forms Fe nanoclusters and Fe-N 0.0324 site structures under high-temperature carbonization. x

[0081] 3. Catalytic Activity

[0082] ​The oxygen reduction performance of the oxygen reduction catalysts prepared in Examples 1-8 and Comparative Examples 1-15 was tested using a three-electrode system. The specific steps are as follows: The oxygen reduction catalyst powders prepared in Examples 1-8 and Comparative Examples 1-15 were separately dispersed in absolute ethanol, and a proton conductor binder (5% Nafion solution) was added and ultrasonically dispersed for 30 min to prepare a catalyst ink (each 1 mL of the catalyst ink contains 20 μL of the proton conductor binder). The prepared catalyst ink was dropped onto the surface of a glassy carbon electrode and allowed to dry naturally to form a catalyst film, which was used as a working electrode for subsequent tests. During the test, a platinum wire was used as the counter electrode, silver chloride was used as the reference electrode, and the corresponding electrode potential was converted to the reversible hydrogen electrode (RHE) potential. Finally, the oxygen reduction catalytic performance of different samples in saturated oxygen 0.1 M potassium hydroxide was tested. The linear sweep voltammograms (LSV) of the oxygen reduction catalysts prepared in Examples 1-4 and Comparative Examples 1-2 are as Figure 5 shown (in the figure, the abscissa Potential is the voltage, and the ordinate Current density is the current density). The oxygen reduction half-wave potentials of each catalyst are shown in Table 1.

[0083] Table 1

[0084] As can be seen from Table 1, the oxygen reduction half-wave potential of the oxygen reduction catalyst prepared in Example 1 in an alkaline electrolyte (saturated oxygen 0.1 M potassium hydroxide) is 0.83 V, showing excellent oxygen reduction catalytic performance.

[0085] Compared with Example 1, in Examples 2-7, due to the different carbonization conditions and the types of nitrogen-containing precursors, the specific surface area of the active site carbon matrix decreased and the micro / mesoporous structure collapsed, which affected the types and distributions of nitrogen-containing functional groups, resulting in changes in the exposure probability and types of some catalytic active sites in the catalyst. However, since the oxygen reduction catalysts prepared in Examples 2-7 still have Fe-N x active sites and a three-dimensional nano-hollow box-like structure, their oxygen reduction half-wave potentials in an alkaline electrolyte (0.1 M potassium hydroxide) can still reach 0.78 - 0.82 V, showing good oxygen reduction catalytic performance.

[0086] Compared with Example 1, the oxygen reduction half-wave potential of commercial 20 wt% Pt / C in Comparative Example 1 is only 0.81 V, and its oxygen reduction catalytic performance is slightly lower than that of Example 1. This indicates that the catalyst prepared in Example 1 has better oxygen reduction catalytic performance than the commercial 20 wt% Pt / C catalyst

[0087] Comparative Examples 2-5 compared with Example 1, although the same carbonization temperature was used, but due to the adjustment of the types of block polymers and zeolite precursors during the preparation process, the material could not form a hollow nanobox structure. The lack of the hollow structure increased the mass transfer resistance of the catalyst, and at the same time, the exposure rate of active sites decreased. Its oxygen reduction half-wave potential was only 0.72-0.77 V, and the oxygen reduction catalytic performance was lower than that of Example 1.

[0088] Comparative Examples 6-7 compared with Example 1, although the same carbonization temperature was used, but due to the change or removal of the nitrogen-containing iron source during the preparation process, the material could not form highly active Fe-N x active sites, and the activity of the catalyst decreased significantly. Its oxygen reduction half-wave potential was only 0.65-0.78 V, and the oxygen reduction catalytic performance was far inferior to that of Example 1.

[0089] Comparative Examples 8-9 compared with Example 1, although the same carbonization temperature was used, but the heating rate was increased or the composition of the carbonization atmosphere was changed, which caused a thermal gradient effect during the graphitization of the carbon matrix, or induced a structural transformation of the active sites. The too fast heating rate led to uneven heating of the carbon skeleton, triggering local structure collapse and lattice distortion, resulting in deterioration of the overall structural stability of the material; in addition, the intervention of the reducing atmosphere promoted the irreversible phase change of the Fe-N x active sites, converting them into Fe elemental phase, causing irreversible loss of active sites. Its oxygen reduction half-wave potential was only 0.71-0.74 V, and the oxygen reduction catalytic performance was still lower than that of Example 1.

[0090] Comparative Examples 10-11 compared with Example 1, although the same carbonization temperature was used, but due to the removal or change of the polymer monomer during the preparation process, insufficient carbon source could not be provided, making it impossible to stably construct the hollow nanobox structure, resulting in an increase in the mass transfer resistance of the catalyst and the absence of active sites. Its oxygen reduction half-wave potential was only 0.72-0.75 V, and the oxygen reduction catalytic performance was lower than that of Example 1.

[0091] Comparative Examples 12-13 compared with Example 1, although the same carbonization temperature was used, but due to the use of other metal phthalocyanine salts during the preparation process, although the hollow nanobox structure of the material could be maintained at high temperature and Co-N x , Ni-N x active sites were generated, but the intrinsic activity was lower than that of Fe-N x , and its oxygen reduction half-wave potential was only 0.69-0.72 V, and the oxygen reduction catalytic performance was lower than that of Example 1.

[0092] Comparative Examples 14-15 compared with Example 1, although the same carbonization temperature was used, but due to the adjustment of the usage amount of ferrous phthalocyanine salt during the preparation process, too low usage amount led to the absence of Fe-N x active sites, and too much usage amount led to partial Fe-Nx Agglomeration occurs at the active sites and transformation into Fe elemental state leads to a decrease in catalytic activity. The oxygen reduction half-wave potential is only 0.78 - 0.79V, and the oxygen reduction catalytic performance is significantly lower than that of Example 1.

[0093] 4. Performance test of zinc-air battery

[0094] The oxygen reduction catalyst inks prepared in Examples 1 - 2 and Comparative Examples 1 - 2 were respectively drop-coated on the surface of carbon paper and used as the air cathode. Zinc foil was used as the anode, and a mixture of 6.0M potassium hydroxide solution and 0.2M zinc acetate solution was used as the electrolyte to assemble a zinc-air battery.

[0095] Figure 6 The Fe-N-HOCNS-900 catalyst prepared in Example 1 was used as the catalytic layer to successfully light up an LED lamp in the zinc-air battery.

[0096] Figure 7 For the discharge power density test of the catalysts in Examples 1 - 2 and Comparative Examples 1 - 2 as the cathode catalytic layer of the zinc-air battery, the power density of the zinc-air battery assembled with the Fe-N-HOCNs-900 catalyst prepared in Example 1 can reach 162mWcm -2 which is significantly higher than other catalysts. Experimental data show that the Fe-N-HOCNs-900 catalyst exhibits excellent catalytic activity and working condition adaptability in the zinc-air battery system. Its performance advantage stems from the unique hollow box-like structure: this structure constructs a hierarchical pore network (mesopore / micropore synergistic system), significantly shortening the diffusion path of oxygen molecules in the catalytic layer and reducing the mass transfer resistance at the gas-liquid interface; at the same time, the synergistic effect of three-dimensional through pores and high-density Fe-N x active sites effectively promotes the oxygen diffusion kinetic process at the three-phase interface, providing a key material solution for the performance optimization of zinc-air batteries.

[0097] For those of ordinary skill in the art to which the present invention pertains, several simple deductions or substitutions can be made without departing from the concept of the present invention, without the need for creative labor. Therefore, simple improvements made by those skilled in the art based on the disclosure of the present invention should fall within the protection scope of the present invention. The above embodiments are the preferred embodiments of the present invention, and all processes similar to the present invention and equivalent changes made shall fall within the protection scope of the present invention.

Claims

1. A preparation method and application of a hollow nano-box-shaped iron-nitrogen-carbon oxygen reduction catalyst, characterized in that, It includes the following steps: (1) Mix and disperse a zeolite - silicalite sacrificial template, a block copolymer, and a nitrogen - containing polymer monomer in a solution. Add the mixed solution to a Tris buffer solution with a pH of about 10, adjust the pH of the solution to 8.5 using an acidic solution, carry out a polymerization reaction under certain conditions, and then obtain polymer - directionally coated zeolite - silicalite through centrifugal filtration and vacuum drying; (2) Directionally coat the polymer - coated zeolite - silicalite and fully mix and stir it with a nitrogen - containing iron source. After reacting under certain conditions, remove the template through carbonization and an etching agent, and finally obtain an iron - nitrogen - carbon oxygen reduction catalyst with a hollow nanobox - like structure. The block copolymer described in step (1) includes one or more of F127, F108, P123, and P105 in the Pluronic series; The nitrogen - containing polymer monomer described in step (1) includes one or more of dopamine, aniline, o - phenylenediamine, p - phenylenediamine, and pyrrole; The nitrogen - containing iron source described in step (2) includes one or more of ferrous phthalocyanine salt, iron tetraphenylporphyrin, and hemin chloride; 2. The preparation method of a hollow nano-box-shaped iron-nitrogen-carbon oxygen reduction catalyst according to claim 1, characterized in that, The mass ratio of the zeolite - silicalite sacrificial template, the block copolymer, and the nitrogen - containing polymer monomer described in step (1) is 1:(2 - 4):(5 - 10).

3. The preparation method of a hollow nano-box-shaped iron-nitrogen-carbon oxygen reduction catalyst according to claim 1, characterized in that, The mixed solution described in step (1) is a mixed solution of water and absolute ethanol, and the mass ratio is 1:(0.1 - 1.0).

4. The preparation method of a hollow nano-box-shaped iron-nitrogen-carbon oxygen reduction catalyst according to claim 1, characterized in that, The certain conditions described in step (1) are: continuously stir the solution for 6 - 9 h, the stirring speed is 400 - 600 rpm, the reaction temperature is 10 - 40 °C, and wash and centrifuge 3 - 6 times.

5. The preparation method of a hollow nano-box-shaped iron-nitrogen-carbon oxygen reduction catalyst according to claim 1, characterized in that, The mass ratio of the polymer - directionally coated zeolite - silicalite to the nitrogen - containing iron source described in step (2) is 1:(0.01 - 0.10).

6. The preparation method of a hollow nano-box-shaped iron-nitrogen-carbon oxygen reduction catalyst according to claim 1, characterized in that, The carbonization heating rate described in step (2) is 3 - 10 °C / min, the carbonization temperature is 800 - 1100 °C, and the carbonization time is 2 - 4 h.

7. According to the application of a hollow nanobox - like iron - nitrogen - carbon oxygen reduction catalyst described in claim 1, the application is a zinc - air battery.

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