Two-dimensional ZIF-L skeleton, non-noble metal electrocatalyst and preparation method

Abstract

The invention relates to the technical field of redox catalysts, in particular to a two-dimensional ZIF-L skeleton, a non-noble metal electrocatalyst and a preparation method. The preparation method of the two-dimensional ZIF-L skeleton comprises the following steps: S1, preparing ZIF-L powder by using an imidazole compound aqueous solution and a soluble zinc salt aqueous solution as raw materials through a hydrothermal synthesis method; the concentration of the imidazole compound aqueous solution is 3-6 mol / L; and S2, carrying out wet ball milling on the ZIF-L powder and a solvent, and then drying to obtain the two-dimensional ZIF-L skeleton. By increasing the concentration of the raw material solution and cooperatively using wet ball milling, the size of the ZIF-L is reduced while the production efficiency is increased, and the catalyst prepared from the ZIF-L is excellent in half-wave potential and limiting current.

Description

Technical Field

[0001] The present invention relates to the technical field of redox catalysts, and particularly to a two-dimensional ZIF-L framework, a non-precious metal electrocatalyst and a preparation method thereof, and particularly to a two-dimensional ZIF-L framework, an Fe-N-C catalyst and a preparation method thereof. Background Art

[0002] Searching for environmentally friendly and efficient energy conversion and storage systems, such as proton exchange membrane fuel cells and metal-air batteries, is a current research hotspot. However, the low efficiency caused by the inherently slow kinetics of the oxygen reduction reaction (ORR) at the cathode is a huge obstacle to the commercialization of such devices. Although platinum-based metal catalysts are generally considered to be the most effective catalysts for accelerating reaction kinetics, their scarcity, high cost, etc. greatly limit the expansion of their application scale. Therefore, it is very necessary to design and explore efficient and low-cost non-precious metal electrocatalysts.

[0003] In recent years, carbon materials doped with transition metal atoms (Fe, Co, Ni, etc.) and heteroatoms (N, S, P, B, etc.), especially Fe-N-C materials, have been widely studied due to their excellent ORR performance comparable to that of benchmark catalysts (Pt / C). The substrates of such Fe-N-C catalysts are mostly obtained by pyrolyzing zeolitic imidazolate frameworks (ZIFs).

[0004] ZIFs are a subclass of metal-organic frameworks (MOFs) and have received extensive attention due to their low cost, rich pores, nitrogen self-doping, etc. The three-dimensional structure of ZIF-8 is one of the most commonly used ZIF types in the field of ORR, and its commonly used preparation method uses a large amount of methanol as a solvent. In contrast, the two-dimensional structure of ZIF-L uses water as a solvent, with lower preparation cost and more environmental friendliness. And in recent years, ZIF-L has been proven to have good application prospects in the preparation of oxygen reduction catalysts: for example, Wang et al. pyrolyzed bimetallic (Co / Zn) ZIF-L for the low-cost and simple preparation of Co nanoparticles encapsulated in nitrogen-doped carbon nanotubes (Co-N-CNTs), and the prepared Co-N-CNTs have excellent electrocatalytic activity and stability for ORR and OER. Zhou et al. prepared a novel 3D star-shaped hybrid MOF of ZIF-L and ZIF-8 as a precursor for constructing a single-atom catalyst (Co-N-C). Different from most reported Co single-atom catalysts derived from modified ZIF-8, the ligand ratio of ZIF-L in this hybrid MOF is relatively low, resulting in insufficient N coordination of Co, so it exhibits Co-N 3C unique coordination structure. And a preparation method of such a ZIF-L-derived multi-dimensional cross-linked structure Fe-N-C catalyst containing oxygen vacancies disclosed in the patent document with the publication number CN115440991A, which includes the following steps: Mix an aqueous solution of imidazole-based substances with a concentration of 0.8 - 1.2 mol / L and an aqueous solution of soluble zinc salt with a concentration of 0.1 - 1 mol / L and stir for 12 h - 24 h to synthesize two-dimensional ZIF-L leaf-like crystals; Mix the ZIF-L leaf-like crystals with an Fe-C mixture and stir for 24 - 85 h to obtain an Fe-N-C precursor mixture; Calcinate the Fe-N-C precursor mixture in a tube furnace to obtain the Fe-N-C catalyst.

[0005] Although ZIF-L has very considerable application potential in oxygen reduction, there is still a large gap from the standards of practical applications. This is mainly because the particle size of ZIF-L is relatively large, and the catalyst after pyrolysis is prone to agglomeration and caking, making it difficult to disperse evenly, thus affecting the activity and stability of the catalyst. Summary of the Invention

[0006] The present invention aims to solve the above problems and provides a two-dimensional ZIF-L framework, a non-precious metal electrocatalyst and a preparation method thereof, which can obtain a large number of ZIF-L framework carriers with small and uniform sizes. The catalyst prepared by pyrolyzing after absorbing non-precious metal salts with this framework is not easy to agglomerate and has excellent activity and stability.

[0007] The technical solution for the present invention to solve the problem is as follows: First, a preparation method of a two-dimensional ZIF-L framework is provided, including the following steps: S1. Using an aqueous solution of imidazole-based compound and an aqueous solution of soluble zinc salt as raw materials, ZIF-L powder is prepared by a hydrothermal synthesis method; the concentration of the aqueous solution of imidazole-based compound is 3 - 6 mol / L; S2. Wet ball-mill the ZIF-L powder together with a solvent, and then dry it to obtain a two-dimensional ZIF-L framework.

[0008] In this application, first, in order to control the size of the framework carrier, a wet ball milling technique was introduced. Then it was found that not any ZIF-L powder could obtain a framework carrier with small and uniform size under wet ball milling. Only when the raw material concentration in the process of preparing ZIF-L powder was controlled within a certain range could the technical effect of wet ball milling be significantly manifested. The inventor deduced that this might be related to the size and morphology of the ZIF-L powder. When the amount of raw material used was too small, there might be more bound water in the ZIF-L. The removal of water during the drying stage would cause capillary contraction, and the resulting capillary force would cause the particles to stick closely. The non-bridging hydrogen groups of adjacent particles would spontaneously transform into bridging hydroxyl groups, leading to the occurrence of hard agglomeration. Wet ball milling could not effectively control the size of hard agglomeration. When the amount of raw material used was too large, the crystal growth rate was too fast, and hard agglomeration problems would also occur. Only when the amount of raw material was within a certain range, the ZIF-L powder would only produce just the right amount of soft agglomeration. Coupled with the wet ball milling technique, a relatively large batch of two-dimensional ZIF-L framework carriers with small and uniform size could be obtained.

[0009] The concentration of the imidazole compound aqueous solution in the raw materials of this application should be controlled at 3 - 6 mol / L. For example, it can be 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L. Within the above concentration range, in combination with wet ball milling, sheet-like ZIF-L with small and uniform size can be obtained. At the same time, within this range, the higher the concentration of the imidazole compound aqueous solution, the better the performance in terms of both size and batch preparation. Therefore, the concentration is further preferably controlled at 5 - 6 mol / L.

[0010] The concentration of the soluble zinc salt aqueous solution depends on the concentration of the imidazole compound aqueous solution, as long as it can ensure that the ligand and metal ions can synthesize the two-dimensional ZIF-L framework. As a preference of the present invention, the molar ratio of the imidazole compound to the soluble zinc salt is controlled at (4 - 10):1. For example, it can be 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1. The molar ratio is further preferably controlled at (6 - 8):1.

[0011] Common imidazole compounds include 2-methylimidazole, 2,4-dimethylimidazole, etc. As a preference of the present invention, the imidazole compound is selected as 2-methylimidazole.

[0012] Common soluble zinc salts include zinc acetate, zinc nitrate, zinc chloride, zinc hydroxide, etc. As a preference of the present invention, the soluble zinc salt is selected as zinc nitrate hexahydrate.

[0013] In step S1, when performing hydrothermal synthesis, the synthesis conditions are generally not limited as long as the hydrothermal reaction can proceed smoothly. To further obtain ZIF-L that meets the requirements of wet ball milling in this application, as a preference of the present invention, under stirring conditions, the reaction is carried out at 20-70 °C for 0.5-24 h, and the ZIF-L powder is obtained after centrifugation and drying. The reaction temperature can be, for example, 20 °C, 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, and the reaction time can be, for example, 30 min, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h. Further preferably, under stirring conditions, the reaction is carried out at 40-60 °C for 0.5-2 h. It is most optimal to react at 40 °C for 30 min, and ZIF-L powder with the most suitable size and morphology for subsequent wet ball milling can be obtained in a relatively short time.

[0014] Among them, the stirring method is not limited, and can be, for example, one of mechanical stirring and magnetic stirring. The stirring speed is not limited and can be 100-500 rpm, such as 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm.

[0015] The conditions of centrifugation and drying should be restricted. As inferred above, excessive dehydration may lead to hard agglomeration. As a preference of the present invention, the number of centrifugation times is 2-5 times, the detergent used for centrifugation is deionized water, and the centrifugation speed is 8000-12000 rpm; the drying temperature is 50-80 °C, and the time is 6-18 h. The number of centrifugation times can be, for example, 2 times, 3 times, 4 times, 5 times, the centrifugation speed can be, for example, 8000 rpm, 9000 rpm, 10000 rpm, 11000 rpm, 12000 rpm, the drying temperature can be, for example, 50 °C, 60 °C, 70 °C, 80 °C, and the drying time can be, for example, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h. It is most optimal to centrifuge at 10000 rpm for 3 times and then dry at 60 °C for 12 h, and ZIF-L powder with the most suitable size and morphology for subsequent wet ball milling can be obtained.

[0016] In step S2, when performing wet ball milling, the selection of the solvent should be restricted to avoid the influence of the solvent on the ZIF-L powder. As a preference of the present invention, the boiling point of the solvent does not exceed 90 °C. It can be selected from at least one of methanol and ethanol, with ethanol being preferred.

[0017] The dosage ratio of ZIF-L powder to the solvent should be restricted. Excessive or insufficient solvent dosage will affect the final size and morphology of the ZIF-L powder, thereby affecting the performance of the catalyst obtained by pyrolyzing with ZIF-L as the carrier. As a preference of the present invention, the mass ratio of ZIF-L powder to the solvent is 1:(1 - 3), such as 1:1, 1:1.5, 1:2, 1:2.5, 1:3, and 1:2 is the best.

[0018] The ball milling conditions should be restricted. Too high a speed or too long a time may cause the collapse of micropores or mesopores in ZIF-L; too low a speed or too short a time may lead to incomplete size regulation of ZIF-L. As a preference of the present invention, the ball milling speed is 300 - 500 rpm, and the ball milling time is 0.5 - 4 h. The ball milling speed can be, for example, 300 rpm, 400 rpm, 500 rpm, and the ball milling time can be, for example, 30 min, 1 h, 2 h, 3 h, 4 h. Ball milling at 400 rpm for 2 h is the best, and the most suitable size can be obtained.

[0019] Secondly, another object of the present invention is to provide a two-dimensional ZIF-L framework prepared by the above method, which is small and uniform in size and can be used as an NC carrier.

[0020] Furthermore, another object of the present invention is to provide a preparation method of a non-noble metal catalyst, including the following steps: mixing a carrier with a salt solution of a non-noble metal and then pyrolyzing; the carrier is the two-dimensional ZIF-L framework prepared by the above method.

[0021] In this application, a catalyst is prepared by using a two-dimensional ZIF-L framework that is small and uniform in size as an NC carrier to absorb a salt solution of a non-noble metal and then pyrolyzing, so that the pyrolyzed catalyst is not easily agglomerated and has good dispersibility.

[0022] Among them, the selection of the non-noble metal should be restricted. When using the two-dimensional ZIF-L framework of this application as the NC carrier, Fe is the best non-noble metal. The selection of the iron salt is not restricted. As a preference of the present invention, the iron salt is selected from at least one of iron acetylacetonate, ferric chloride, and ferrous chloride. The dosage of the iron salt is not restricted. As a preference of the present invention, the addition amount of the Fe salt is calculated based on the Fe content in the final catalyst being 0.5 - 1.5 wt%, such as 0.5 wt%, 1 wt%, 1.5 wt%, and 1 wt% is the best.

[0023] The mixing method is not restricted. As a preference of the present invention, the carrier is mixed with the salt solution of the non-metal, and after stirring for 0.5 - 24 h with the solvent used in wet ball milling during the preparation process of the two-dimensional ZIF-L framework as the mixing solvent, rotary evaporation and drying are carried out to obtain a precursor; then the precursor is placed in N 2The catalyst is obtained by pyrolysis under an atmosphere. The stirring time can be, for example, 30 min, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, and 12 h is the best.

[0024] The pyrolysis conditions have an impact on the finally obtained catalyst, and the pyrolysis conditions should be restricted. As a preference of the present invention, the pyrolysis temperature is 900 - 1000 °C, and the time is 1 - 3 h. The pyrolysis temperature can be, for example, 900 °C, 950 °C, 1000 °C, and the time can be, for example, 1 h, 2 h, 3 h. Pyrolysis at 950 °C for 1 h is the best.

[0025] The rate of heating up to the pyrolysis temperature is not restricted. As a preference of the present invention, the heating rate is 2 - 5 °C / min, and can be, for example, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min.

[0026] Finally, another object of the present invention is to provide a non - noble metal catalyst prepared by the above method. This catalyst is used in redox reactions, has excellent catalytic performance, and has uniform particles.

[0027] Advantages of the present invention: 1. The present application provides a two - dimensional ZIF - L framework and its preparation method. By increasing the concentration of the raw material solution and using wet ball milling in combination, while increasing the production efficiency, the size of ZIF - L is also reduced, and a large number of two - dimensional ZIF - L frameworks with small and uniform sizes are obtained.

[0028] 2. The present application provides a non - noble metal catalyst, especially an Fe - N - C catalyst and its preparation method. Using the above - prepared two - dimensional ZIF - L framework with small and uniform sizes as the NC carrier to absorb Fe for pyrolysis, the obtained ORR catalyst has excellent catalytic performance. BET tests show that its specific surface area increases, enabling it to load more active sites, and electrochemical performance tests show that its half - wave potential and limiting current are both improved.

[0029] 3. The synthesis processes of the framework carrier and catalyst of this application are simple and very suitable for large-scale production. When preparing ZIF-L, by appropriately increasing the raw material mass and concentration, the preparation process does not become complex, and the performance of the obtained catalyst is greatly improved. Then, directly mix the ball-milled ZIF-L with iron salt, and perform one-step pyrolysis on the adsorbed ZIF-L to obtain the Fe-N-C catalyst without pickling. At the same time, the entire preparation process is green and environmentally friendly, the raw materials can be recycled, and the only solvents used throughout the process are two green solvents, ethanol and water. While collecting the ZIF-L solid by centrifugation, the remaining 2-methylimidazole in the liquid can be recycled and purified for reuse. And in the step of rotary evaporation and drying, the extracted ethanol can also be recycled. Description of the Drawings

[0030] Figure 1 is the scanning electron microscope image of ZIF-L obtained after wet ball milling in Example 1; Figure 2 is the N 2 adsorption-desorption isotherm curve of the Fe-N-C catalyst prepared in Example 1; Figure 3 is the pore size distribution diagram of the Fe-N-C catalyst prepared in Example 1; Figure 4 is the comparative diagram of linear sweep voltammetry curves of the Fe-N-C catalysts prepared in Example 1 and Comparative Example 1 in 0.1M KOH solution; Figure 5 is the comparative diagram of linear sweep voltammetry curves of the Fe-N-C catalysts prepared in Example 1 and Comparative Example 2 in 0.1M KOH solution; Figure 6 is the comparative diagram of linear sweep voltammetry curves of the Fe-N-C catalysts prepared in Examples 1-3 and Comparative Example 3 in 0.1M KOH solution; Figure 7 is the comparative diagram of linear sweep voltammetry curves of the Fe-N-C catalysts prepared in Example 1 and Example 4 in 0.1M KOH solution; Figure 8 is the comparative diagram of linear sweep voltammetry curves of the Fe-N-C catalysts prepared in Example 1 and Example 5 in 0.1M KOH solution; Figure 9 is the comparative diagram of linear sweep voltammetry curves of the Fe-N-C catalysts prepared in Example 1 and Example 6 in 0.1M KOH solution. Detailed Embodiments

[0031] The following are the detailed embodiments of the present invention. In combination with the drawings, the technical solutions of the present invention are further described, but the present invention is not limited to these embodiments.

[0032] Example 1 (1)A preparation method of a two-dimensional ZIF-L framework, comprising the following steps: S1. Using an aqueous solution of 2-methylimidazole and an aqueous solution of zinc nitrate hexahydrate as raw materials: Dissolve 189 g (about 2.305 mol) of 2-methylimidazole in 455 mL of water, and ultrasonically disperse it until completely dissolved to obtain an aqueous solution of 2-methylimidazole (concentration about 5.1 mol / L); Dissolve 112 g (about 0.376 mol) of zinc nitrate hexahydrate in 57 mL of water, and ultrasonically disperse it until completely dissolved to obtain an aqueous solution of zinc nitrate hexahydrate. The molar ratio of 2-methylimidazole to zinc nitrate hexahydrate is about 6.1:1.

[0033] Under mechanical stirring at a rotation speed of 300 rpm, mix the aqueous solution of 2-methylimidazole and the aqueous solution of zinc nitrate hexahydrate evenly at 40 °C, and react for 30 min to obtain a suspension. Centrifuge the suspension 3 times with deionized water, with a centrifuge speed of 10,000 rpm each time, and dry it at 60 °C for 12 h after centrifugation to obtain ZIF-L powder.

[0034] S2. Mix the above-mentioned ZIF-L powder and ethanol in a mass ratio of 1:2, place them in a ball milling jar for wet ball milling, with a ball milling speed of 400 rpm and a time of 2 h. Then take it out and dry it at 60 °C for 2 h to obtain a two-dimensional ZIF-L framework.

[0035] The scanning electron microscope image of the obtained two-dimensional ZIF-L framework is as Figure 1 shown, indicating that a flaky two-dimensional framework material is obtained.

[0036] (2)A non-noble metal catalyst, using the two-dimensional ZIF-L framework prepared above as a carrier, is prepared by the following steps: S3. Take 300 mg of the two-dimensional ZIF-L framework prepared above and mix it with 3.8 mg of iron acetylacetonate, then stir it with ethanol as a solvent for 12 h, and obtain a precursor powder after rotary evaporation and drying. Then heat the precursor powder in an N 2 atmosphere at a heating rate of 5 °C / min to 950 °C and pyrolyze it for 1 h to obtain an Fe-N-C catalyst.

[0037] The N 2 adsorption-desorption isotherm curve of the prepared Fe-N-C catalyst is as Figure 2 shown, and the pore size distribution diagram is as Figure 3 shown, indicating that a catalyst with a large specific surface area is obtained.

[0038] Example 2 (1)A method for preparing a two-dimensional ZIF-L framework is basically the same as that in Example 1, except that: in step S2, the ZIF-L powder and ethanol are mixed at a mass ratio of 1:1 and placed in a ball milling jar for wet ball milling.

[0039] (2)A non-noble metal catalyst, the preparation method of which is basically the same as that in Example 1, except that: the two-dimensional ZIF-L framework prepared in this example is used as the carrier.

[0040] Example 3 (1)A method for preparing a two-dimensional ZIF-L framework is basically the same as that in Example 1, except that: in step S2, the ZIF-L powder and ethanol are mixed at a mass ratio of 1:3 and placed in a ball milling jar for wet ball milling.

[0041] (2)A non-noble metal catalyst, the preparation method of which is basically the same as that in Example 1, except that: the two-dimensional ZIF-L framework prepared in this example is used as the carrier.

[0042] Example 4 (1)A method for preparing a two-dimensional ZIF-L framework is basically the same as that in Example 1, except that: In step S1, using an aqueous solution of 2-methylimidazole and an aqueous solution of zinc nitrate hexahydrate as raw materials: 126 g (about 1.536 mol) of 2-methylimidazole is dissolved in 455 mL of water and ultrasonically dispersed until completely dissolved to obtain an aqueous solution of 2-methylimidazole (concentration about 3.4 mol / L); 75 g (about 0.252 mol) of zinc nitrate hexahydrate is dissolved in 57 mL of water and ultrasonically dispersed until completely dissolved to obtain an aqueous solution of zinc nitrate hexahydrate. The molar ratio of 2-methylimidazole to zinc nitrate hexahydrate is about 6.1:1.

[0043] (2)A non-noble metal catalyst, the preparation method of which is basically the same as that in Example 1, except that: the two-dimensional ZIF-L framework prepared in this example is used as the carrier.

[0044] Example 5 (1)A method for preparing a two-dimensional ZIF-L framework is basically the same as that in Example 1, except that: In step S1, under mechanical stirring at a speed of 300 rpm, the aqueous solution of 2-methylimidazole and the aqueous solution of zinc nitrate hexahydrate are mixed evenly at 60 °C and reacted for 30 min to obtain a suspension. The suspension is centrifuged 3 times with deionized water, each time at a centrifugation speed of 10,000 rpm, and dried at 60 °C for 12 h after centrifugation to obtain ZIF-L powder.

[0045] (2) A non-noble metal catalyst, the preparation method of which is basically the same as that of Example 1, and the difference is only that: the two-dimensional ZIF-L framework prepared in this example is used as the carrier.

[0046] Example 6 (1) A preparation method of a two-dimensional ZIF-L framework is exactly the same as that of Example 1.

[0047] (2) A non-noble metal catalyst, the preparation method of which is basically the same as that of Example 1, and the difference is only that: In step S3, 300 mg of the two-dimensional ZIF-L framework prepared in Example 1 and 3.8 mg of iron acetylacetonate are mixed, and then stirred with ethanol as the solvent for 12 h. After rotary evaporation and drying, a precursor powder is obtained. Then the precursor powder is pyrolyzed at 1000 °C for 1 h under N 2 atmosphere at a heating rate of 5 °C / min to obtain an Fe-N-C catalyst.

[0048] Comparative Example 1 (1) A preparation method of a two-dimensional ZIF-L framework is basically the same as that of Example 1, and the difference is only that: In step S1, an aqueous solution of 2-methylimidazole and an aqueous solution of zinc nitrate hexahydrate are used as raw materials: 1.89 g (about 0.023 mol) of 2-methylimidazole is dissolved in 45.5 mL of water and ultrasonically dispersed until completely dissolved to obtain an aqueous solution of 2-methylimidazole (concentration about 0.51 mol / L); 1.12 g (about 0.00376 mol) of zinc nitrate hexahydrate is dissolved in 5.7 mL of water and ultrasonically dispersed until completely dissolved to obtain an aqueous solution of zinc nitrate hexahydrate. The molar ratio of 2-methylimidazole to zinc nitrate hexahydrate is about 6.1:1.

[0049] (2) A non-noble metal catalyst, the preparation method of which is basically the same as that of Example 1, and the difference is only that: the two-dimensional ZIF-L framework prepared in this comparative example is used as the carrier.

[0050] Comparative Example 2 (1) A preparation method of a two-dimensional ZIF-L framework is basically the same as that of Example 1, and the difference is only that: Ball milling is not carried out, and the ZIF-L powder prepared in step S1 of Example 1 is used as the two-dimensional ZIF-L framework.

[0051] (2) A non-noble metal catalyst, the preparation method of which is basically the same as that of Example 1, and the difference is only that: the two-dimensional ZIF-L framework prepared in this comparative example is used as the carrier.

[0052] Comparative Example 3 (1) A preparation method of a two-dimensional ZIF-L framework is basically the same as that of Example 1, and the difference is only that: In step S2, the ZIF-L powder is placed in a ball milling jar for dry ball milling at a ball milling speed of 400 rpm for 2 h. Then it is taken out and dried to obtain a two-dimensional ZIF-L framework.

[0053] (2) A non-noble metal catalyst has a preparation method basically the same as that of Example 1, except that: the two-dimensional ZIF-L framework prepared in this comparative example is used as the carrier.

[0054] Catalyst Performance Detection The comparative diagram of the linear sweep voltammetry curves of the Fe-N-C catalysts prepared in Examples 1 to 6 and Comparative Examples 1 to 3 in 0.1 M KOH solution is as Figures 4 - 9 shown.

[0055] As Figure 4 , for the comparison between Example 1 and Comparative Example 1, the difference between Example 1 and Comparative Example 1 is only that: in Example 1, about 5.1 moL / L of 2-methylimidazole is used as the raw material to prepare ZIF-L, and the limiting current density of the obtained catalyst is about 6.9 mA / cm 2 , and the half-wave potential is about 0.907 V. In Comparative Example 1, about 0.51 moL / L of 2-methylimidazole is used as the raw material to prepare ZIF-L, and the limiting current density of the obtained catalyst is about 5.3 mA / cm 2 , and the half-wave potential is about 0.874 V. It shows that in the case of using wet ball milling, the ZIF-L prepared from high-concentration raw materials has a smaller and more uniform size and morphology compared to that prepared from low-concentration raw materials. Therefore, the catalyst prepared with it as the carrier has a larger specific surface area and is not easy to agglomerate, and can obtain excellent electrochemical performance. Further, as Figure 7 , for the comparison between Example 1 and Example 4, the only difference between Example 1 and Example 4 is also the concentration of the raw materials. In Example 4, about 3.4 mol / L of 2-methylimidazole is used as the raw material to prepare ZIF-L, and the limiting current density of the obtained catalyst is about 5.5 mA / cm 2 , and the half-wave potential is about 0.902 V. Although the electrochemical performance of Example 4 is inferior to that of Example 1, the half-wave potential is also much better than that of Comparative Example 1. It shows that the catalysts with ZIF-L prepared under the conditions of using wet ball milling and the concentration of 2-methylimidazole raw materials in the range of 3 - 6 mol / L all have relatively excellent activities; at the same time, increasing the raw material concentration within this range can significantly increase the limiting current density of the catalyst and obtain a catalyst with more excellent electrochemical performance.

[0056] As Figure 5 , for the comparison between Example 1 and Comparative Example 2; as Figure 6, including the comparison between Example 1 and Comparative Example 3. The differences among Example 1, Comparative Example 2, and Comparative Example 3 are only as follows: wet ball milling with ethanol as the solvent was used in Example 1, no ball milling treatment was carried out in Comparative Example 2, and dry ball milling without adding any solvent was carried out in Comparative Example 3. Through Figure 5 and Figure 6 it can be seen that the limiting current densities of the catalysts obtained in Comparative Example 2 and Comparative Example 3 are significantly lower than those of the catalyst obtained in Example 1. It shows that when using high-concentration raw materials, the support obtained by wet ball milling treatment used in the catalyst can enable the catalyst to obtain more excellent electrochemical performance.

[0057] In summary, it can be known that the raw material concentration for preparing ZIF-L and whether the obtained ZIF-L is wet ball milled have significant effects on the electrochemical performance of the finally obtained catalyst. When the two characteristics are applied simultaneously, the limiting current density and half-wave potential of the catalyst can be significantly improved.

[0058] In addition, under the conditions of using high-concentration raw materials and wet ball milling, some other characteristics also have certain effects on the electrochemical performance of the finally obtained catalyst. Such as Figure 6 , Figure 6 also includes the comparison among Examples 1 to 3. The only difference among Examples 1 to 3 is the amount of ethanol solvent used in wet ball milling. Through Figure 6 it can be seen that compared with dry milling, wet milling can significantly improve the electrochemical performance of the obtained catalyst regardless of the amount of ethanol solvent used. Among them, the electrochemical performance of the catalyst finally obtained by wet ball milling with 2 times the mass of ethanol is the best.

[0059] Such as Figure 8 , for the comparison between Example 1 and Example 5. The differences between Example 1 and Example 5 are only as follows: ZIF-L was prepared at 40 °C in Example 1, and ZIF-L was prepared at 60 °C in Example 5. It can be seen that the temperature during the hydrothermal synthesis of ZIF-L has little effect on the electrochemical performance of the finally obtained catalyst, but preparing ZIF-L at 40 °C can relatively obtain a catalyst with slightly better half-wave potential.

[0060] Such as Figure 9 , for the comparison between Example 1 and Example 6. The differences between Example 1 and Example 6 are only as follows: pyrolysis was carried out at 950 °C in Example 1; pyrolysis was carried out at 1000 °C in Example 6. The limiting current density of the obtained catalyst is about 6.18 mA / cm 2, the half-wave potential is about 0.890 V. It can be seen that when using a ZIF-L framework support prepared with high-concentration raw materials and assisted by wet ball milling, regardless of the pyrolysis temperature, the limiting current density and half-wave potential of the catalyst are relatively large. However, a catalyst with more excellent electrochemical performance can be obtained by pyrolysis at 950 °C.

[0061] The specific embodiments described in this article are only examples to illustrate the spirit of the present invention. Those skilled in the art to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar methods for substitution, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A preparation method of a two-dimensional ZIF-L framework, characterized in that: It includes the following steps: S1. Using an aqueous solution of an imidazole compound and an aqueous solution of a soluble zinc salt as raw materials, ZIF-L powder is obtained by a hydrothermal synthesis method; the concentration of the aqueous solution of the imidazole compound is 3 - 6 mol / L; S2. Wet ball-mill the ZIF-L powder with a solvent, and then dry it to obtain a two-dimensional ZIF-L framework.

2. The preparation method of a two-dimensional ZIF-L framework according to claim 1, characterized in that: The concentration of the aqueous solution of the imidazole compound is 5 - 6 mol / L.

3. The preparation method of a two-dimensional ZIF-L framework according to claim 1, characterized in that: The mass ratio of the ZIF-L powder to the solvent is 1:(1 - 3).

4. The preparation method of a two-dimensional ZIF-L framework according to claim 3, characterized in that: The mass ratio of the ZIF-L powder to the solvent is 1:

2.

5. The preparation method of a two-dimensional ZIF-L framework according to claim 1, characterized in that: The hydrothermal synthesis method is: under stirring conditions, react at 20 - 70 °C for 0.5 - 24 h, and after centrifugation and drying, the ZIF-L powder is obtained.

6. The preparation method of a two-dimensional ZIF-L framework according to claim 1, characterized in that: The boiling point of the solvent does not exceed 90 °C.

7. A preparation method of a non-noble metal catalyst, characterized in that: It includes the following steps: Mix a carrier with a salt solution of a non-noble metal and then pyrolyze; the carrier is a two-dimensional ZIF-L framework prepared by the preparation method according to any one of claims 1 - 6.

8. The preparation method of a non-noble metal redox catalyst according to claim 7, characterized in that: The non-noble metal is Fe.

9. The preparation method of a non-noble metal redox catalyst according to claim 7, characterized in that: The pyrolysis temperature is 900 - 1000 °C, and the time is 1 - 3 h.

10. A non-noble metal catalyst prepared by the preparation method according to any one of claims 7 - 9.

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