A simple MOF-derived Fe single-site oxygen reduction electrocatalyst and its preparation method and application

Abstract

The present invention discloses a simple MOF-derived Fe single-site oxygen reduction electrocatalyst and its preparation method and application. The method includes: dissolving a nitrogen-containing organic ligand and a metal salt in a nitrobenzene / methanol mixed solution to synthesize MOF, and obtaining the MOF-derived Fe single-site oxygen reduction electrocatalyst after filtration, drying, grinding and calcination. The present invention uses a novel MOF as a precursor to construct a well-defined electrocatalyst by partially replacing Zn with Fe, where Fe exists in the form of Fe-N single sites. The prepared material exhibits excellent electrocatalytic activity and stability in the oxygen reduction reaction, and shows good discharge performance when assembled as a positive electrode material in a zinc-air battery. This type of material is of great significance in the preparation methodology of oxygen electrocatalysts and the application of zinc-air batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and mainly relates to a simple MOF-derived Fe single-site oxygen reduction electrocatalyst, a preparation method thereof, and an application thereof in a zinc-air battery. Background Art

[0002] The consumption of fossil energy and the resulting environmental pollution problems are becoming increasingly prominent. The clean and efficient utilization of renewable energy and the development of low-carbon technologies are of great significance to the sustainable development of the national economy. Zinc-air batteries have become a research hotspot in the current energy field due to their advantages such as low cost, environmental friendliness, high safety, and high specific energy density. However, due to the bottleneck of the slow oxygen reduction reaction kinetics during the discharge process, it is still necessary to use precious metal platinum as a catalyst to improve the electrode reaction kinetics. However, the high cost and resource scarcity of precious metal platinum limit its commercial application. Therefore, the design and development of non-precious metal oxygen reduction catalysts are particularly important.

[0003] So far, Fe-containing nitrogen-doped carbon materials have played an important role in the field of zinc-air batteries due to their excellent oxygen reduction reaction catalytic activity. Methodologically, Fe ions can partially replace Zn ions [Electrochimica Acta, 2021, 137408] to coordinate with ligands. In the prepared material, N atoms coordinate with Fe to form Fe-N bonds, and further improve the oxygen reduction electrocatalytic activity through electronic structure regulation (Junxing Han, Hongliang Bao, Jian-Qiang Wang, Lirong Zheng, Shaorui Sun, Zhong Lin Wang, Chunwen Sun, 3D N-doped ordered mesoporous carbon supported single-atom Fe-N-C catalysts with superior performance for oxygen reduction reaction and zinc-air battery, Applied Catalysis B: Environmental, Volume 280, 2021, 119411, ISSN 0926-3373.). Although the catalytic activity of the materials prepared at present can reach the level of precious metal platinum, acid washing and other operations are required during the material preparation process, and the process is cumbersome. Therefore, the development of a simple oxygen reduction electrocatalyst is of great significance for promoting the industrial application of fuel cells. Summary of the Invention

[0004] To overcome the deficiencies of the above-mentioned existing preparation processes, the primary objective of the present invention is to provide a simple method for preparing a MOF-derived Fe single-site oxygen reduction electrocatalyst.

[0005] Another objective of the present invention is to provide a MOF-derived Fe single-site oxygen reduction electrocatalyst prepared by the above method.

[0006] A further objective of the present invention is to provide the application of the above MOF-derived Fe single-site oxygen reduction electrocatalyst in a zinc-air battery.

[0007] The objectives of the present invention are achieved through the following solutions:

[0008] A simple method for preparing a MOF-derived Fe single-site oxygen reduction electrocatalyst, comprising the following steps:

[0009] (1) Dissolve a nitrogen-containing organic ligand in a nitrobenzene / methanol mixed solution, add a metal salt, and stir vigorously until the solution becomes light yellow and turbid to obtain a light yellow solid precipitate;

[0010] (2) Filter, wash, and vacuum dry the precipitate obtained in step (1) to obtain MOF (metal-organic framework material);

[0011] (3) Mix the MOF obtained in step (2) with a small amount of nitrogen source and grind thoroughly, then perform argon calcination treatment and ammonia calcination treatment to obtain a MOF-derived Fe single-site oxygen reduction electrocatalyst.

[0012] Further, the nitrogen-containing organic ligand in step (1) is 2,4,6-tris(4-pyridyl)-1,3,5-triazine (tpt), and the structural formula is as follows:

[0013]

[0014] Further, the molar volume ratio of the nitrogen-containing organic ligand to nitrobenzene in step (1) is 1:196 - 1:204 mmol / mL, and the volume ratio of nitrobenzene to methanol in step (1) is 5:1 - 8:1.

[0015] Further, the metal salt in step (1) includes a divalent zinc salt and a divalent iron salt. The divalent zinc salt is zinc bromide, and the divalent iron salt is one or more of ferrous chloride, ferrous acetate, and ferrous bromide; the molar ratio of the divalent zinc salt to the divalent iron salt is 16:9 - 16:3.

[0016] Further, the temperature of the vacuum drying in step (2) is 60 - 80 °C, and the time of the vacuum drying is 6 - 12 h.

[0017] Further, the nitrogen source in step (3) is melamine.

[0018] Furthermore, in terms of parts by mass (mg), the proportions of the above raw materials are as follows:

[0019]

[0020] Furthermore, for the argon calcination treatment described in step (3), the steps include: heating the ground powder at a rate of 5 - 10 °C / min to 150 - 280 °C and holding for 20 - 30 minutes, then heating at a rate of 10 - 20 °C / min to 900 - 1000 °C, holding for 1 - 1.5 hours, and then naturally cooling. For the ammonia calcination treatment described in step (3), the steps include: placing the sample after argon treatment in a porcelain boat, first passing argon for 30 minutes to remove air, then heating at a rate of 10 - 20 °C / min to 250 - 300 °C and holding for 20 - 30 minutes, and finally heating at a rate of 20 - 30 °C / min to 900 - 1100 °C, replacing argon with ammonia and treating for 2 - 10 minutes and then naturally cooling.

[0021] The present invention provides a MOF-derived Fe single-site oxygen reduction electrocatalyst prepared by the above preparation method. Using a novel MOF as a precursor, a well-defined electrocatalyst is constructed by partially replacing Zn with Fe, where Fe exists in the form of Fe-N single sites.

[0022] The present invention provides an application of a MOF-derived Fe single-site oxygen reduction electrocatalyst in the preparation of a zinc-air battery. Using 2,4,6-tris(4-pyridyl)-1,3,5-triazine (tpt) to synthesize a MOF precursor, which has a large specific surface area. The coordination of Fe and N regulates the electronic structure, and the obtained material can be used as the cathode material of a high-performance zinc-air battery.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] (1) The preparation method of a MOF-derived Fe single-site oxygen reduction electrocatalyst provided by the present invention uses a novel nitrogen-containing organic ligand as the organic ligand, which has a high nitrogen content. After Fe ions replace Zn ions, they coordinate with N to form Fe-N;

[0025] (2) The preparation method of a MOF-derived Fe single-site oxygen reduction electrocatalyst provided by the present invention uses Zn as a medium, which can better disperse Fe and prevent agglomeration;

[0026] (3) The MOF-derived Fe single-site oxygen reduction electrocatalyst provided by the present invention has a large specific surface area, which is beneficial to the mass transfer during the oxygen reduction reaction process;

[0027] (4) The MOF-derived Fe single-site oxygen reduction electrocatalyst prepared by the present invention has excellent electrocatalytic activity and stability towards the oxygen reduction reaction, and also has good battery performance in a zinc-air battery;

[0028] (5) The MOF precursor prepared by the present invention can be synthesized rapidly and in large quantities, and the catalyst material can be obtained after subsequent calcination treatment without any post-treatment. The process is simple and easy to scale up. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Transmission electron microscopy image of the catalyst Fe 10 -N-C-NH3 prepared in Example 1;

[0030] Figure 2 X-ray diffraction patterns of Fe 10 -N-C, Fe 10 -N-C-NH3 and N-C prepared in Comparative Example 1;

[0031] Figure 3 N2 adsorption-desorption isotherms of Fe 10 -N-C, Fe 10 -N-C-NH3 and N-C prepared in Comparative Example 1 and platinum-carbon catalyst in 0.1 M KOH solution;

[0032] Figure 4 Linear sweep voltammograms of Fe 10 -N-C, Fe 10 -N-C-NH3 and N-C prepared in Comparative Example 1 and platinum-carbon catalyst in 0.1 M KOH solution;

[0033] Figure 5 Discharge polarization curve of the catalyst Fe 10 -N-C-NH3 prepared in Example 1 in a zinc-air battery. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The present invention will be further described in detail below with reference to the accompanying drawings, but the implementation and protection of the present invention are not limited thereto. It should be noted that for the processes not specifically described in detail below, those skilled in the art can implement or understand them with reference to the prior art. The reagents or instruments used without indicating the manufacturer are regarded as conventional products that can be obtained through commercial purchase.

[0035] Example 1

[0036] Fe 10 -N-C-NH3 was prepared by the following steps:

[0037] (1) ZnFe 10Preparation of -MOF: Add 320mL of nitrobenzene and 40mL of methanol to a 500mL three-necked flask, mix well, add 500mg of 2,4,6-tris(4-pyridine)-1,3,5-triazine (tpt), and heat to completely dissolve it (clear solution). Dissolve 540mg of ZnBr2 and 114mg of FeCl2 in 80mL of methanol solution, and add dropwise to the nitrobenzene / methanol mixed solution containing 2,4,6-tris(4-pyridine)-1,3,5-triazine (tpt) under stirring until the solution becomes light yellow and turbid. Filter the light yellow solid precipitate under reduced pressure and vacuum dry it at 60°C for 8h. The obtained material is named ZnFe 10 -MOF;

[0038] (2)Fe 10 Preparation of -NC: Weigh 500 mg of ZnFe 10 -MOF, 40 mg of melamine was added as a nitrogen source, and both were ground thoroughly and placed in a porcelain boat for argon calcination. The tubular furnace was set to heat up to 150°C at 10°C / min and keep warm for 25 minutes, then to 900°C at 20°C / min, kept warm for 1 hour, and finally cooled naturally. The obtained material was named Fe 10 -NC;

[0039] (3)Fe 10 Preparation of -NC-NH3: The sample Fe 10 -NC was placed in a porcelain boat, and argon was introduced into the quartz tube for 30 minutes. First, the temperature was raised from 25°C to 300°C at 20°C / min. The porcelain boat was pushed to the heating center and kept for 20 minutes to remove the moisture of the material. Then the porcelain boat was pulled out of the high temperature zone. After the tube furnace was raised to 1000°C at 30°C / min, the argon was replaced with ammonia (80mL / min). The porcelain boat was pushed to the heating center again, and after 5 minutes of timing, the porcelain boat was pulled out, the ammonia was converted to argon, and the temperature was naturally lowered to obtain the catalyst Fe 10 -NC-NH3.

[0040] Figure 1 The catalyst Fe prepared in Example 1 10 -Transmission electron microscopy (TEM) image of NC-NH3. From the TEM image, it can be seen that there are no obvious iron particles on the carbon substrate.

[0041] Example 2

[0042] The preparation of Fe5-NC-NH3 includes the following steps:

[0043] (1) Preparation of ZnFe5-MOF: Add 320 mL of nitrobenzene and 40 mL of methanol to a 500 mL three-necked flask, mix well, add 500 mg of 2,4,6-tris(4-pyridine)-1,3,5-triazine (tpt), and heat to completely dissolve (clear solution). Dissolve 540 mg of ZnBr2 and 57 mg of FeCl2 in 80 mL of methanol solution, and add dropwise to the nitrobenzene / methanol mixed solution containing 2,4,6-tris(4-pyridine)-1,3,5-triazine (tpt) while stirring until the solution becomes light yellow and turbid. Filter the obtained light yellow solid precipitate under reduced pressure and vacuum dry at 60 °C for 8 h. The obtained material is named ZnFe5-MOF;

[0044] (2) Preparation of Fe5-NC: Weigh 500 mg of ZnFe5-MOF, add 40 mg of melamine as a nitrogen source, grind both thoroughly and place in a porcelain boat for argon calcination. Set the tubular furnace to heat up to 150°C at 10°C / min and keep it for 25 min, then heat up to 900°C at 20°C / min, keep it for 1 h, and finally cool naturally. The resulting material is named Fe5-NC;

[0045] (3) Preparation of Fe5-NC-NH3: The argon-treated sample Fe5-NC was placed in a porcelain boat, and argon was introduced into a quartz tube for 30 minutes. The temperature was first increased from 25°C to 300°C at 20°C / min. The porcelain boat was pushed to the heating center and kept for 20 minutes to remove moisture from the material. The porcelain boat was then pulled out of the high-temperature zone. After the tube furnace was raised to 1000°C at 30°C / min, the argon was replaced with ammonia (80 mL / min). The porcelain boat was pushed to the heating center again. After 5 minutes of timing, the porcelain boat was pulled out, the ammonia was converted to argon, and the temperature was naturally lowered to obtain the catalyst Fe5-NC-NH3.

[0046] Comparative Example 1

[0047] The preparation of NC includes the following steps:

[0048] (1) Preparation of Zn-MOF: Add 320 mL of nitrobenzene and 40 mL of methanol to a 500 mL three-necked flask, mix well, add 500 mg of 2,4,6-tris(4-pyridine)-1,3,5-triazine (tpt), and heat to completely dissolve it (clear solution). Dissolve 540 mg of ZnBr2 in 80 mL of methanol solution, and add it dropwise to the nitrobenzene / methanol mixed solution containing 2,4,6-tris(4-pyridine)-1,3,5-triazine (tpt) while stirring until the solution becomes white and turbid, filter under reduced pressure, and vacuum dry at 60 °C for 8 h. The resulting material is named Zn-MOF;

[0049] (2) Preparation of NC: Weigh 500 mg of Zn-MOF, add 40 mg of melamine as a nitrogen source, grind both thoroughly, and place them in a porcelain boat for argon calcination. Set the program of the tubular furnace to increase the temperature to 150°C at 10°C / min and keep it at this temperature for 25 min, then increase the temperature to 900°C at 20°C / min, keep it at this temperature for 1 h, and finally cool it down naturally to obtain NC material.

[0050] Figure 2 Fe prepared in Example 1 10 -NC、Fe 10 -NC-NH3 and the X-ray diffraction patterns of NC prepared in Comparative Example 1, by Figure 2 It can be seen that Fe 10 -NC-NH3、Fe 10 Both -NC and NC contain only graphitized carbon, no iron particles, and no obvious metal agglomeration.

[0051] Figure 3 Fe prepared in Example 1 10 -NC、Fe 10 -NC-NH3 and N2 adsorption-desorption isotherms of NC prepared in Comparative Example 1. The specific surface area of NC is 796.5 m 2 / g,Fe 10 -NC has a specific surface area of 1046.2 m 2 / g,Fe 10 -The specific surface area of NC-NH3 is 1526.9m 2 / g. The results show that Fe 10 The specific surface area of -NC-NH3 is much higher than that of the previous two, indicating that the introduction of Fe unit sites and ammonia calcination treatment can effectively increase the specific surface area of the material. A larger specific surface area is beneficial to material transport during the oxygen reduction reaction.

[0052] Example 3

[0053] Example 1 Preparation of Fe 10 -NC、Fe 10 -NC-NH3 and NC prepared in Comparative Example 1 are used as oxygen reduction electrocatalysts in zinc-air batteries. The steps of electrode preparation and battery performance testing are as follows:

[0054] (1) Accurately weigh 10 mg of catalyst Fe 10 -NC was placed in a 2.0 mL glass vial, and 1.0 mL of ethanol solution containing 0.84 wt.% Nafion was injected, and ultrasonic treatment was performed for 1 h to obtain a uniformly dispersed slurry. Then 10.0 μL of the slurry was dropped onto the surface of a φ5 mm glassy carbon electrode and allowed to dry naturally to obtain a modified electrode. 10-N-C-NH3 and N-C were used to prepare the modified electrode in the same way as Fe10-N-C.

[0055] (2) The modified electrode was tested for the oxygen reduction reaction under alkaline conditions on a CHI 730 electrochemical workstation. The counter electrode was a Pt electrode, the reference electrode was a saturated calomel electrode, and the electrolyte was 0.1 M KOH solution. The tests were carried out under N2 saturation and O2 saturation respectively. First, cyclic voltammetry (CV) was performed in the N2-saturated electrolytic cell to activate the modified electrode. The test parameters of CV were: the test potential window was 0 - 1.23 V (vs. RHE), and the scan rate was 20 mV·s -1 , and 20 cycles were carried out. Then, linear sweep voltammetry (LSV) was performed in the O2-saturated electrolytic cell to obtain the oxygen reduction polarization curve. The test parameters were: the test potential window was 0 - 1.23 V (vs. RHE), the scan rate was 5 mV·s -1 , and the rotation speed of the rotating disk was 1600 rpm.

[0056] (3) The zinc-air battery test was carried out on a CHI 730 electrochemical workstation and a NEWARE battery test system. A two-electrode system was used, in which the zinc sheet was used as the counter electrode, the carbon paper loaded with the catalyst was used as the working electrode, and the electrolyte was 6 M KOH and 0.2 M Zn(OAc)2 solution. The preparation method of the carbon paper loaded with the catalyst was: the catalyst loading was 1 mg·cm -2 , the mass ratio of the Nafion solution to the catalyst was 1:9, the volume ratio of the added ethanol to water was 1:1, and after ultrasonic treatment for 30 min, it was coated on the diffusion layer carbon paper that had been treated for hydrophobicity.

[0057] Figure 4 For the Fe prepared in Example 1 10 -N-C, Fe 10 -N-C-NH3, the N-C prepared in Comparative Example 1, and the platinum-carbon catalyst, the linear sweep voltammetry curves in 0.1 M KOH solution are shown by Figure 4 It can be seen that the oxygen reduction onset potentials of the platinum-carbon catalyst Pt / C, the N-C prepared in Comparative Example 1, the Fe 10 -N-C prepared in Example 1, and Fe 10 -N-C-NH3 are 0.93 V, 0.94 V, 0.96 V, and 0.99 V respectively; the half-wave potentials are 0.84 V, 0.81 V, 0.88 V, and 0.92 V respectively. The oxygen reduction onset potential and half-wave potential of Fe 10 -N-C-NH3 are both better than those of the platinum-carbon catalyst Pt / C, Fe 10 -N-C, and N-C. It can be seen that Fe 10-N-C-NH3 has significantly better oxygen reduction catalytic ability than several other catalysts, indicating that this material has excellent electrocatalytic activity for the oxygen reduction reaction; judging from the current density trend, the current decay of Fe 10 -N-C-NH3 is not obvious, reflecting good stability.

[0058] Figure 5 For the Fe 10 -N-C-NH3 catalyst prepared in Example 1, the discharge polarization curve in the zinc-air battery is as follows. From Figure 5 it can be seen that for Fe 10 -N-C-NH3, the voltage values at 10 mA / cm 2 , 50 mA / cm 2 and 100 mA / cm 2 are 1.29 V, 1.18 V, and 1.07 V respectively, and the power density is 203.79 mW / cm 2 , indicating that the Fe 10 -N-C-NH3 catalyst, as the positive electrode material of the zinc-air battery, has good battery performance in the zinc-air battery.

[0059] The above embodiments are only the preferred embodiments of the present invention, which are only used to explain the present invention, rather than limiting the present invention. Any changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit and essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A preparation method of a simple MOF-derived Fe single-site oxygen reduction electrocatalyst, characterized in that, The steps include: (1) dissolving a nitrogen-containing organic ligand in a nitrobenzene / methanol mixed solution, adding a metal salt, and stirring to obtain a light yellow solid precipitate; (2) filtering, washing, and vacuum drying the precipitate in step (1) to obtain MOF; (3) mixing the MOF described in step (2) with a nitrogen source and grinding the mixture sufficiently, and then subjecting the mixture to argon calcination and ammonia calcination to obtain a MOF-derived Fe single-site oxygen reduction electrocatalyst; The nitrogen-containing organic ligand in step (1) is 2,4,6-tris(4-pyridine)-1,3,5-triazine, and has the following structural formula: The molar volume ratio of the nitrogen-containing organic ligand to nitrobenzene in step (1) is 1:196 to 1:204 mmol / mL, and the volume ratio of nitrobenzene to methanol in step (1) is 5:1 to 8:1; Calculated by weight, the proportions of each raw material are as follows: The argon calcination treatment in step (3) comprises: heating the ground powder to 150-280°C at a rate of 5-10°C / min and keeping the temperature for 20-30 minutes, then heating the powder to 900-1000°C at a rate of 10-20°C / min, keeping the temperature for 1-1.5 hours, and then cooling naturally; the ammonia calcination treatment in step (3) comprises: placing the argon-treated sample in a porcelain boat, first passing argon for 30 minutes to exclude air, then heating the powder to 250-300°C at a rate of 10-20°C / min and keeping the temperature for 20-30 minutes, and finally heating the powder to 900-1100°C at a rate of 20-30°C / min, replacing the argon with ammonia for 2-10 minutes, and then cooling naturally.

2. The preparation method of the MOF-derived Fe single-site oxygen reduction electrocatalyst according to claim 1, wherein, The metal salt in step (1) comprises a divalent zinc salt and a divalent iron salt, wherein the divalent zinc salt is zinc bromide, and the divalent iron salt is one or more of ferrous chloride, ferrous acetate, and ferrous bromide; and the molar ratio of the divalent zinc salt to the divalent iron salt is 16:9 to 16:

3.

3. The preparation method of the MOF-derived Fe single-site oxygen reduction electrocatalyst according to claim 1, characterized in that, The vacuum drying temperature in step (2) is 60 to 80° C., and the vacuum drying time is 6 to 12 hours.

4. The preparation method of the MOF-derived Fe single-site oxygen reduction electrocatalyst according to claim 1, wherein The nitrogen source in step (3) is melamine.

5. A MOF-derived Fe single-site oxygen reduction electrocatalyst prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the MOF-derived Fe single-site oxygen reduction electrocatalyst according to claim 5 in the preparation of zinc-air batteries.

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