Preparation method and application of a hollow nanobox-like iron-nitrogen-carbon oxygen reduction catalyst

Abstract

The application discloses a preparation method of a hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst and application thereof. The method uses silicalite as a three-dimensional structure sacrifice template, block copolymer as a modifier, and nitrogen-containing polymer monomer as a reaction precursor to prepare polymer directional coating silicalite based on a region-selective induced deposition strategy. Then, a nitrogen-containing iron source is added and fully mixed, and the catalyst is obtained by carbonization and etching agent removal of the silicalite template, and finally, the iron-nitrogen-carbon oxygen reduction catalyst with a hollow nanobox-shaped structure is obtained. The method is simple and reliable, raw materials are easy to obtain, and the prepared catalyst material has a unique hollow nanobox-shaped structure. The micro / intermediate pore reaction channel effectively enhances the exposure probability of active sites, shortens the diffusion path of reactants, significantly reduces the kinetic barrier in the mass transfer process, and the hollow nanobox-shaped structure promotes the 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 application relates to the technical field of non-noble metal oxygen reduction catalysts, in particular to a preparation method of a hollow nanobox-like iron-nitrogen-carbon oxygen reduction catalyst and application thereof in zinc-air battery devices. BACKGROUND

[0002] Oxygen reduction reaction (ORR) is the core electrochemical process of 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. The four-electron transfer reaction has a significant kinetic lag phenomenon, and requires a high-efficiency catalyst to reduce the activation overpotential to meet the industrial application requirements. At present, platinum-based catalysts are still the preferred material for ORR catalysts due to their excellent intrinsic activity, but are limited by the scarcity of noble metal reserves and high cost, which restricts their large-scale commercial application. Under this background, developing non-noble metal catalysts with high catalytic activity, excellent stability and cost advantage has become a key technical path to break through the bottleneck of ZABs industrialization.

[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. This kind of catalyst is considered to be the most promising non-noble metal catalyst system due to its excellent oxygen reduction catalytic performance and cost advantage. Studies have shown that the activity source of Fe-N-C catalyst lies in its nanometer Fe clusters and atomic-level dispersed Fe-N xThe coordination structure synergistically enhances the intrinsic activity by designing the size of Fe cluster and regulating the coordination configuration. Although the existing technology has further improved the activity of Fe-N-C catalysts by strategies such as nitrogen-doped gradient design, Fe cluster nanocrystallization and d-band center regulation, there is still a certain gap compared with platinum-based catalysts. This activity difference directly causes the surge in the loading amount of Fe-N-C catalysts in the cathode of ZABs, resulting in the thickness of the catalytic layer reaching 5-10 times that of the platinum-based system, thereby causing multiple mass transfer limitations: (1) the over-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, and the accessibility and utilization rate of active sites decrease; (3) the penetration of liquid electrolyte is blocked, leading to the deterioration of electrochemical wettability and the loss of effective electrochemical active area. These multi-scale mass transfer bottlenecks are coupled with each other, which ultimately restricts 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 micro-nano directional mass transfer channels and high-density active sites, and realize the synergistic optimization of oxygen diffusion path, three-phase reaction interface and electrolyte wettability, has become a core technical problem that needs to be solved to break through the performance bottleneck of ZABs. SUMMARY

[0004] The purpose of the present application is to solve the problems of non-noble metal catalytic layer in zinc-air battery, and provide a kind of hollow nanometer box-like iron-nitrogen-carbon oxygen reduction catalyst. The unique microstructure of the catalyst can significantly reduce the oxygen mass transfer resistance in the catalytic layer, effectively improve the energy density and power density of zinc-air battery.

[0005] The present application provides a preparation method, which can obtain an oxygen reduction catalyst with hollow box structure, high utilization rate of non-noble metal active sites, good electrolyte permeability and high electrochemical wettability, and low mass transfer kinetic resistance, suitable for application in zinc-air battery.

[0006] The purpose of the present application is realized by the following technical solutions:

[0007] The present application provides a preparation method of hollow nanometer box-like iron-nitrogen-carbon oxygen reduction catalyst, comprising the following steps:

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

[0009] Silicalite, block copolymer and nitrogen-containing precursor were dissolved in a mixture of deionized water and anhydrous ethanol, and ultrasonic treatment was carried out under continuous stirring until the mixture was homogeneous, to obtain a milky white solution; the milky white solution was added to a Tris buffer solution with a pH of about 10, and the pH of the solution was adjusted to 8.5 using an acidic solution, and after reaction under certain conditions, the polymer directional coated silicalite was obtained after washing, centrifugation, filtration and drying.

[0010] (2) Preparation of hollow nanobox-like iron-nitrogen-carbon oxygen reduction catalyst

[0011] In step (1), the polymer is used to coat the silicalite, a nitrogen-containing iron source and deionized water are added, and ultrasonic mixing is performed until uniform. After reaction under certain conditions, the product is washed, centrifuged, filtered, dried, and then carbonized by heating in a tube furnace under argon atmosphere and cooled. The template is removed by etching agent, and then filtered and dried to obtain the hollow nanobox-like 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 deionized water to anhydrous ethanol in step (1) is 1:(0.3-0.4).

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

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

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

[0018] Preferably, the mass ratio of the polymer used to coat 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 a ferrous phthalocyanine salt.

[0020] Preferably, the certain conditions in step (2) are continuous stirring for 2 h, stirring speed of 500 rpm, and reaction temperature of 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 etching agent in step (2) is hydrofluoric acid with a concentration of 20-40wt%, and the etching time is 4 h.

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

[0024] The hollow nanobox-like iron-nitrogen-carbon as an application in the aspect of oxygen reduction catalysts, preferably zinc-air batteries.

[0025] Preferably, the hollow nanobox-like 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, saturated Ag / AgCl is used as the reference electrode, and 250 mL of saturated oxygen 0.1M potassium hydroxide solution is used as the electrolyte in the electrochemical workstation with a three-electrode system to test the electrocatalytic performance at a rotating speed of 1600 rpm.

[0026] Preferably, a zinc plate is used as the anode, the self-prepared hollow nanobox-like iron-nitrogen-carbon catalyst is used as the cathode catalytic layer, and a carbon paper gas diffusion layer is combined to form a cathode air electrode, and 6M potassium hydroxide solution is used as the electrolyte. The zinc-air battery is prepared by assembling the above components, wherein the cathode is directly exposed to air without additional oxygen supply. The constant current discharge test is performed on the assembled zinc-air battery by using a battery test system, 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, the polarization curve and power density curve tests are performed to analyze the output performance and power characteristics of the battery.

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

[0028] (1) The present application prepares the hollow nanobox-like iron-nitrogen-carbon catalyst by a simple area-selective deposition method. The catalyst has fully exposed inner / outer surfaces and permeable micro / intermediate pore structures, which effectively enhances the exposure probability of active sites, significantly improves the ion transmission efficiency and electrolyte wettability, helps to form a rich electrode / electrolyte interface, and synergistically improves the utilization rate of active sites.

[0029] (2) The clear hollow box-like structure provided by the present application shortens the diffusion path of oxygen in the catalytic layer, thereby significantly reducing the kinetic resistance in the reactant transmission process.

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

[0031] (4) The hollow nanobox-like iron-nitrogen-carbon catalyst is used as the catalytic layer of the zinc-air battery, and the power density of the zinc-air battery reaches 162mW cm -2 The catalyst of the present application provides key material support for the development of high-power density ZABs. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1Scanning electron microscope image of Fe-N-HOCNs-900 prepared for Example 1.

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

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

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

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

[0037] Figure 6 Digital photograph of Fe-N-HOCNs-900 catalyst prepared for Example 1 applied as catalytic layer in zinc-air battery.

[0038] Figure 7 Power density curves of Fe-N-HOCNs-900 prepared for Example 1, Fe-N-HOCNs-1000 prepared for Example 2 and Fe-N-C-900 prepared for Comparative Example 1, Comparative Example 2 commercial 20% Pt / C catalyst applied as catalytic layer in zinc-air battery. DETAILED DESCRIPTION

[0039] The above summary of the application will be further explained in the following examples, which should not be construed as limiting the scope of the above subject matter of the application to the examples only, but rather the technical solutions based on the above summary of the application are within the scope of the application.

[0040] Example 1

[0041] (1) Preparation of polymer directed coated siliceous zeolite

[0042] 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 ionized water and 8 g of anhydrous ethanol, and ultrasonically mixed at room temperature until a milky white solution was formed; the milky white solution was added to 50 mL of a 0.1M Tris buffer solution with a pH of about 10.1, and the pH of the solution was adjusted to 8.5 using a certain amount of 0.1M hydrochloric acid solution, and then continuously stirred for 6 h at a stirring speed of 500 rpm and a reaction temperature of 30°C; the polymer directionally coated silicalite was obtained by centrifugal washing three times with deionized water, filtration, and drying at 80°C under vacuum for 12 h, and was recorded as Si-1@HO-mPDA.

[0043] (2) Preparation of hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst

[0044] 5.0 g of Si-1@HO-mPDA in step (1) was added with 100 mg of phthalocyanine ferrous salt and 50 g of anhydrous ethanol, and ultrasonically mixed until uniform, continuously stirred for 2 h at a stirring speed of 500 rpm and a reaction temperature of 25°C, centrifugal washed three times with deionized water, filtered, dried at 80°C under vacuum for 12 h, then carbonized in a tube furnace under an argon atmosphere at a carbonization temperature of 900°C and a carbonization time of 2 h, and etched with 30 wt% hydrofluoric acid for 4 h. After filtration, vacuum drying was performed at 80°C for 12 h to obtain the hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst, which was recorded as Fe-N-HOCNs-900.

[0045] Example 2

[0046] (1) Preparation of polymer directionally coated silicalite

[0047] 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 ionized water and 8 g of anhydrous ethanol, and ultrasonically mixed at room temperature until a milky white solution was formed; the milky white solution was added to 50 mL of a 0.1M Tris buffer solution with a pH of about 10.2, and the pH of the solution was adjusted to 8.5 using a certain amount of 0.1M hydrochloric acid solution, and then continuously stirred for 4 h at a stirring speed of 500 rpm and a reaction temperature of 30°C; the polymer directionally coated silicalite was obtained by centrifugal washing three times with deionized water, filtration, and drying at 80°C under vacuum for 12 h, and was recorded as Si-1@HO-mPDA.

[0048] (2) Preparation of hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst

[0049] Take 5.0 g of Si-1@HO-mPDA in step (1), add 100 mg of phthalocyanine ferrous salt and 50 g of anhydrous ethanol, and ultrasonic mix uniformly, continuously stirring for 2 h, stirring speed 500 rpm, reaction temperature 25℃, centrifugal washing with deionized water for 3 times, filtration, drying at 80℃ under vacuum condition for 12 h, then carbonization in a tube furnace under argon atmosphere, heating rate 5℃ / min, carbonization temperature 1000℃, carbonization time 2 h, then etching with 30wt% hydrofluoric acid, etching time 4 h. After filtration, vacuum drying at 80℃ for 12 h, hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst is obtained, recorded as Fe-N-HOCNs-1000.

[0050] Example 3

[0051] (1) Preparation of polymer oriented coated siliceous zeolite

[0052] Dissolve 1.8 g of siliceous zeolite, 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 anhydrous ethanol, ultrasonic mix uniformly at room temperature to form a milky white solution; add the milky white solution to 50 mL of 0.1M Tris buffer solution with pH about 10.4, adjust the pH of the solution to 8.5 with a certain amount of 0.1M hydrochloric acid solution, then continuously stirring for 4 h, stirring speed 500 rpm, reaction temperature 30℃, centrifugal washing with deionized water for 3 times, filtration, drying at 80℃ under vacuum condition for 12 h to obtain polymer oriented coated siliceous zeolite, recorded as Si-1@HO-mPAN.

[0053] (2) Preparation of hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst

[0054] Take 5.0 g of Si-1@HO-mPAN in step (1), add 100 mg of phthalocyanine ferrous salt and 30 g of anhydrous ethanol, and ultrasonic mix uniformly, continuously stirring for 2 h, stirring speed 500 rpm, reaction temperature 25℃, centrifugal washing with deionized water for 3 times, filtration, drying at 80℃ under vacuum condition for 12 h, then carbonization in a tube furnace under argon atmosphere, heating rate 5℃ / min, carbonization temperature 700℃, carbonization time 2 h, then etching with 30wt% hydrofluoric acid, etching time 4 h. After filtration, vacuum drying at 80℃ for 12 h, hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst is obtained, recorded as Fe-N-HOCNs-700.

[0055] Example 4

[0056] (1) Preparation of polymer oriented coated siliceous zeolite

[0057] 1.8 g of silicalite, 7.0 g of P105 and 6.0 g of pyrrole were dissolved together in a mixed solution of 30 g of ionized water and 15 g of anhydrous ethanol. After being mixed uniformly at room temperature for 5 min, the mixture was stirred for 30 min until a milky white solution appeared. The milky white solution was added to 50 mL of 0.1M 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 0.1M hydrochloric acid solution. The solution was continuously stirred for 6 h at a stirring speed of 500 rpm, and the reaction temperature was 80℃. The polymer directionally coated silicalite was obtained by centrifugal washing with deionized water for 3 times, filtration, and drying at 80℃ under vacuum for 12 h, and was recorded as Si-1@HO-mPPy.

[0058] (2) Preparation of hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst

[0059] 5.0 g of Si-1@HO-mPPy in step (1) was added with 100 mg of phthalocyanine ferrous salt and 50 g of anhydrous ethanol, and was ultrasonically mixed uniformly. The mixture was continuously stirred for 2 h at a stirring speed of 500 rpm and a reaction temperature of 25℃. The hollow nanobox-shaped iron-nitrogen-carbon oxygen reduction catalyst was obtained by centrifugal washing with deionized water for 3 times, filtration, drying at 80℃ under vacuum for 12 h, carbonization in a tube furnace under an argon atmosphere at a carbonization temperature of 800℃ and a carbonization time of 2 h, and etching with 30 wt% hydrofluoric acid for 4 h. After filtration, the catalyst was dried at 80℃ under vacuum for 12 h, and was recorded as Fe-N-HOCNs-800.

[0060] Example 5

[0061] With reference 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 by 6.0 g of P108 and 6.0 g of o-phenylenediamine, and the carbonization condition in Example 1(2) is adjusted to 600℃, and other conditions remain unchanged, to obtain the Fe-N-HOCNs-600 catalyst.

[0062] Example 6

[0063] With reference 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 by 7.0 g of P105 and 6.0 g of pyrrole, and the carbonization condition in Example 1(2) is adjusted to a temperature rising rate of 7℃ / min and a carbonization temperature of 850℃, and other conditions remain unchanged, to obtain the Fe-N-HOCNs-850 catalyst.

[0064] Example 7

[0065] With reference to Example 1, the difference is that 0.3 g P123, 5.7 g F127, and 9.0 g dopamine in Example 1(1) are replaced by 5.4 g P127 and 5.6 g aniline, and the carbonization conditions in Example 1(2) are adjusted to a temperature- increasing rate of 8 ℃ / min and a carbonization temperature of 950 ℃, and other conditions remain unchanged, to obtain a Fe-N-HOCNs-950 catalyst.

[0066] Example 8

[0067] With reference to Example 1, the difference is that 0.3 g P123, 5.7 g F127, and 9.0 g dopamine in Example 1(1) are replaced by 6.5 g P123 and 7.0 g pyrrole, and the carbonization conditions in Example 1(2) are adjusted to 1100 ℃, and other conditions remain unchanged, to obtain a Fe-N-HOCNs-1100 catalyst.

[0068] Comparative Example 1

[0069] This comparative example takes commercial 20wt% Pt / C as a control.

[0070] Comparative Example 2

[0071] With reference to Example 1, the difference is that no block polymer is added in Example 1(1), and other conditions remain unchanged, to obtain a Fe-N-C-900 catalyst.

[0072] Comparative Example 3

[0073] Comparative Example 3 differs from Example 1 only in that the silicon zeolite template in Example 1(1) is replaced by silicon nanospheres, and other conditions remain unchanged, and the final product is recorded as Fe-N-HONPs-900.

[0074] Comparative Example 4

[0075] Comparative Example 4 differs from Example 1 only in that the silicon zeolite template added in Example 1(1) is removed, and other conditions remain unchanged, and the final product is recorded as Fe-N-NPs-900.

[0076] Comparative Example 5

[0077] Comparative Example 5 differs from Example 1 only in that the etchant used in Example 1(2) is replaced by 10wt% hydrochloric acid, and other conditions remain unchanged, and the final product is recorded as Fe-N-SiCNs-900.

[0078] Comparative Example 6

[0079] Comparative Example 6 differs from Example 1 only in that the nitrogen-containing iron source used in Example 1(2) is replaced by iron nitrate, and other conditions remain unchanged, and the final product is recorded as Fe-HOCNs-900.

[0080] Comparative Example 7

[0081] The only difference between Comparative Example 7 and Example 1 is the removal of the nitrogen-containing iron source added in Example 1 (2), while other conditions remain unchanged. The final product is HOCNs-900.

[0082] Comparative Example 8

[0083] The only difference between Comparative Example 8 and Example 1 is that the carbonization conditions in Example 1(2) were adjusted to a heating rate of 15°C / min, while other conditions remained unchanged. The final product was denoted as Fe-N-CNs-900. Fast .

[0084] Comparative Example 9

[0085] The only difference between Comparative Example 9 and Example 1 is that the carbonization conditions in Example 1 (2) were adjusted to use a 5% hydrogen-argon mixture, while other conditions remained unchanged. The final product was denoted as Fe-HOCNs-900.

[0086] Comparative Example 10

[0087] The only difference between Comparative Example 10 and Example 1 is the removal of the nitrogen-containing polymer monomer added in Example 1 (1), while other conditions remain unchanged. The final product is denoted as Fe-N-900.

[0088] Comparative Example 11

[0089] The only difference between Comparative Example 11 and Example 1 is that the nitrogen-containing polymer added in Example 1 (1) is replaced with urea, while other conditions remain unchanged. The final product is denoted as Fe-N-CNs-900.

[0090] Comparative Example 12

[0091] The only difference between Comparative Example 12 and Example 1 is that the ferrous phthalocyanine salt added in Example 1 (2) is replaced with cobalt phthalocyanine, while other conditions remain unchanged. The final product is denoted as Co-N-HOCNs-900.

[0092] Comparative Example 13

[0093] The only difference between Comparative Example 13 and Example 1 is that the ferrous phthalocyanine salt added in Example 1 (2) is replaced with nickel phthalocyanine salt, while other conditions remain unchanged. The final product is denoted as Ni-N-HOCNs-900.

[0094] Comparative Example 14

[0095] The only difference between Comparative Example 14 and Example 1 is that the 100 mg ferrous phthalocyanine salt added in Example 1 (2) was replaced with 300 mg ferrous phthalocyanine salt, while other conditions remained unchanged. The final product was denoted as Fe. 300-N-HOCNs-900.

[0096] Comparative Example 15

[0097] The only difference between Comparative Example 15 and Example 1 is that the 100 mg ferrous phthalocyanine salt added in Example 1 (2) was replaced with 10 mg ferrous phthalocyanine salt, while other conditions remained unchanged. The final product was denoted as Fe. 10 -N-HOCNs-900.

[0098] Performance testing

[0099] 1. Microstructure

[0100] Figures 1-2 SEM images of the Si-1@HO-mPDA and Fe-N-HOCNs-900 catalysts prepared in Example 1 are shown below. Figure 1 It can be seen that after block polymer modification and dopamine coating treatment, the framework polydopamine in the obtained Si-1@OP-mPDA is concentrated only on specific crystal planes and crystal plane-to-crystal plane junctions of the silica zeolite template. Figure 2 It can be seen that the Fe-N-HOCNs-900 catalyst prepared after carbonization and etching template treatment exhibits a hollow nanobox structure with a strong rigidity of the framework, ensuring the stability of the box structure. In addition, the presence of mesoporous structures can be clearly observed in its framework.

[0101] Figure 3 The image shows a scanning electron microscope (SEM) image of Fe-NC-900 prepared in Comparative Example 1. Compared to Example 1, Comparative Example 1 did not include a block polymer during preparation, resulting in non-selective, fully coated deposition of dopamine on the silica zeolite surface. After carbonization and etching to remove the template, a hollow nanobox structure could not be formed.

[0102] 2. Component analysis

[0103] Figure 4 The wide-angle X-ray diffraction pattern of the Fe-N-HOCNs-900 catalyst prepared in Example 1 is shown below, where: the horizontal axis 2-Theta represents the diffraction angle 2θ, and the vertical axis Intensity represents the intensity of the diffraction peak. Figure 2 It can be seen that Fe-N-HOCNs-900 exhibits carbon (002) diffraction peaks near 26.0°, indicating that mPDA can be transformed into a graphitic carbon structure after heat treatment. Furthermore, FeN was observed near 43.5°, 50.7°, and 74.6°. 0.0324peaks of (111), (200) and (220) of Fe2O3. The diffraction peaks of (110), (200) and (211) of Fe were observed near 44.6°, 65.0° and 82.3°, indicating that Fe nanoclusters and Fe-N x site structure.

[0104] 3. Catalytic activity

[0105] 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 dispersed with anhydrous ethanol, a proton conductor binder (5% Nafion solution) was added and ultrasonic dispersion was performed for 30 min to prepare catalyst ink (20 μL of the proton conductor binder was contained in 1 mL of the catalyst ink). The prepared catalyst ink was dropped onto the surface of a glassy carbon electrode, and the catalyst film was naturally dried to form a catalyst film, which was used as a working electrode for subsequent tests. In the test, a platinum wire was used as a counter electrode, and silver chloride was used as a reference electrode, and the electrode potential was converted to a 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 scanning voltammogram (LSV) of the oxygen reduction catalyst prepared in Examples 1-4 and Comparative Examples 1-2 is shown in FIG. 1 (in the figure, the horizontal axis Potential is voltage, and the vertical axis Current density is current density). The oxygen reduction half-wave potential of each catalyst is shown in Table 1. Figure 5

[0106] Table 1

[0107]

[0108]

[0109] As can be seen from Table 1, the oxygen reduction half-wave potential of the oxygen reduction catalyst prepared in Example 1 in the alkaline electrolyte (saturated oxygen 0.1 M potassium hydroxide) is 0.83 V, and the oxygen reduction catalyst has excellent oxygen reduction catalytic performance.

[0110] Examples 2-7 relative to Example 1, due to the different carbonization conditions and nitrogen-containing precursor types, the specific surface area of the active site carbon matrix is reduced and the micro / mesoporous structure is collapsed, and the types and distribution of the nitrogen-containing functional groups are affected, thereby causing the exposure probability and types of part of the catalytically active sites in the catalyst to change. However, due to the fact that the oxygen reduction catalysts prepared in Examples 2-7 still have Fe-N x active sites and a three-dimensional nanoscale hollow box structure, the oxygen reduction half-wave potential of the oxygen reduction catalysts in the alkaline electrolyte (0.1 M potassium hydroxide) can still reach 0.78-0.82 V, and the oxygen reduction catalysts exhibit good oxygen reduction catalytic performance.​

[0111] Comparative Example 1 The oxygen reduction half-wave potential of commercial 20wt% Pt / C is only 0.81 V, which 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 20wt% Pt / C catalyst

[0112] Comparative Examples 2-5 Although the same carbonization temperature is used, the types of block polymers and silicalite precursors are adjusted during the preparation process, which results in the inability of the material to form a hollow nanobox structure. The lack of hollow structure increases the mass transfer resistance of the catalyst, and the exposure rate of active sites decreases. The oxygen reduction half-wave potential is only 0.72-0.77 V, and the oxygen reduction catalytic performance is lower than that of Example 1.

[0113] Comparative Examples 6-7 Although the same carbonization temperature is used, the nitrogen-containing iron source is changed or removed during the preparation process, which makes it impossible for the material to form high-activity Fe-N x active sites, and the catalyst activity decreases significantly. The oxygen reduction half-wave potential is only 0.65-0.78 V, and the oxygen reduction catalytic performance is much lower than that of Example 1.

[0114] Comparative Examples 8-9 Although the same carbonization temperature is used, the heating rate is increased or the carbonization atmosphere composition is changed, which induces thermal gradient effect in the graphitization process of the carbon matrix or induces structure transformation of the active sites. Too fast heating rate causes uneven heating of the carbon skeleton, which induces local structure collapse and lattice distortion, resulting in deterioration of the overall structure stability of the material. In addition, the intervention of reducing atmosphere promotes irreversible phase transition of Fe-N x active sites to Fe elemental phase, causing irreversible loss of active sites. The oxygen reduction half-wave potential is only 0.71-0.74 V, and the oxygen reduction catalytic performance is still lower than that of Example 1.

[0115] Comparative Examples 10-11 Although the same carbonization temperature is used, the polymer monomer is removed or changed during the preparation process, which results in the inability to provide sufficient carbon source, making it impossible to stably construct the hollow nanobox structure. This causes an increase in mass transfer resistance of the catalyst and a lack of active sites. The oxygen reduction half-wave potential is only 0.72-0.75 V, and the oxygen reduction catalytic performance is lower than that of Example 1.

[0116] Comparative Examples 12-13 Although the same carbonization temperature is used, other phthalocyanine metal salts are used during the preparation process, although the hollow nanobox structure of the material can be maintained at high temperature, and Co-N x , Ni-N x active sites are generated, but the intrinsic activity is lower than that of Fe-N xThe oxygen reduction half-wave potential is only 0.69-0.72 V, and the oxygen reduction catalytic performance is lower than that of Example 1.

[0117] Comparative Examples 14-15, although using the same carbonization temperature, the use amount of phthalocyanine ferrous salt is adjusted in the preparation process, and the too low use amount leads to the loss of active sites of Fe-N x active sites, and too much use amount leads to the agglomeration of active sites of Fe-N x active sites and the transformation to Fe element, and the catalytic activity is reduced, and the oxygen reduction half-wave potential is only 0.78-0.79 V, and the oxygen reduction catalytic performance is significantly lower than that of Example 1.

[0118] 4. Zinc-air battery performance test

[0119] The oxygen reduction catalyst ink prepared in Examples 1-2 and Comparative Examples 1-2 is respectively drop-coated on the surface of carbon paper as an air cathode. Zinc foil is used as anode, and a mixture of 6.0 M potassium hydroxide solution and 0.2 M zinc acetate solution is used as electrolyte to assemble a zinc-air battery.

[0120] Figure 6 The Fe-N-HOCNs-900 catalyst prepared in Example 1 is used as a catalytic layer to successfully light up the LED lamp in the zinc-air battery.

[0121] Figure 7 The discharge power density test of the catalysts of Examples 1-2 and Comparative Examples 1-2 as the cathode catalytic layer of the zinc-air battery, and the power density of the zinc-air battery assembled by the Fe-N-HOCNs-900 catalyst prepared in Example 1 can reach 162 mWcm -2 , which is significantly higher than that of 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, and the performance advantage is derived from the unique hollow box structure: the structure significantly shortens the diffusion path of oxygen molecules in the catalytic layer by constructing a hierarchical pore network (mesopore / micropore cooperative system), and reduces the gas-liquid interface mass transfer resistance; at the same time, the synergistic effect of three-dimensional through-pore and high-density Fe-N x active sites effectively promotes the oxygen diffusion kinetics process at the three-phase interface, and provides a key material solution for the performance optimization of the zinc-air battery.

[0122] For those skilled in the art of the present application, without departing from the concept of the present application, can make several simple deductions or substitutions, without having to go through the creative labor. Therefore, the simple improvements made by the person skilled in the art according to the disclosure of the present application, should be within the scope of protection of the present application. The above examples are the preferred embodiments of the present application, any similar process and equivalent changes made, should belong to the protection scope of the present application.

Claims

1. A method for preparing a hollowed nanobox-like iron-nitrogen-carbon oxygen reduction catalyst, characterized in that, Comprising the following steps: (1) mixing and dispersing a silicon zeolite sacrificial template, a block copolymer and a nitrogen-containing polymer monomer in a solution, further adding the mixed solution to a Tris buffer solution with a pH of 10, adjusting the pH of the solution to 8.5 using an acidic solution, and performing a polymerization reaction under certain conditions, followed by centrifugal filtration and vacuum drying to obtain a polymer directionally coated silicon zeolite; (2) mixing and stirring the polymer directionally coated silicon zeolite with a nitrogen-containing iron source, and after reaction under certain conditions, removing the template by carbonization treatment and etchant to finally obtain an iron-nitrogen-carbon oxygen reduction catalyst with a hollow nanobox structure; The block copolymer of step (1) comprises one or more of F127, F108, P123 and P105 in the Pluronic series; The nitrogen-containing polymer monomer of step (1) comprises one or more of dopamine, aniline, o-phenylenediamine, p-phenylenediamine and pyrrole; The nitrogen-containing iron source of step (2) comprises one or more of phthalocyanine ferrous salt, tetraphenylporphyrin iron and hemin chloride; The carbonization treatment of step (2) comprises an inert gas atmosphere of argon, a heating rate of 3-10 ℃ / min, a carbonization temperature of 800-1100 ℃, and a carbonization time of 2-4 h; The etchant for removing the template of step (2) comprises 20-40 wt% hydrofluoric acid as the etchant.

2. The preparation method of the hollow nanobox-like Fe-N-C oxygen reduction catalyst according to claim 1, characterized in that, The mass ratio of the silicon zeolite sacrificial template, the block copolymer and the nitrogen-containing polymer monomer of step (1) is 1:(2-4):(5-10).

3. The preparation method of the hollow nanobox-like Fe-N-C oxygen reduction catalyst according to claim 1, characterized in that, The mixed solution of step (1) is a mixed solution of water and anhydrous ethanol with a mass ratio of 1:(0.1-1.0).

4. The preparation method of the hollow nanobox-like Fe-N-C oxygen reduction catalyst according to claim 1, characterized in that, The certain conditions of step (1) are: continuous stirring of the solution for 6-9 h, stirring speed of 400-600 rpm, and reaction temperature of 10-40 ℃.

5. The method for preparing the hollow nanobox-like Fe-N-C oxygen reduction reaction catalyst according to claim 1, characterized in that, The mass ratio of the polymer directionally coated silicon zeolite and the nitrogen-containing iron source of step (2) is 1:(0.01-0.10).

6. The use of the hollowed nanobox-like Fe-N-C oxygen reduction catalyst according to claim 1, characterized in that, Applied to zinc-air batteries.

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