Iron-molybdenum / nc catalyst, its preparation method and application

Abstract

This invention discloses an iron-molybdenum / NC catalyst, its preparation method, and its application, belonging to the field of electrocatalysts and their preparation technology. This invention solves the problems of low ORR activity and poor cycle stability in existing zinc-air battery cathode materials. Through a constant-temperature oil bath self-assembly strategy, this invention introduces sulfur and nitrogen sources and then uses a hydrogen / argon mixed calcination reduction method to generate a carbon nanotube-encapsulated dodecahedral substrate. A Fe3C and Mo2C heterojunction structure is formed on the dodecahedral substrate, resulting in a catalyst with excellent ORR activity and long-term stability. The ORR onset potential is 0.972V and the half-wave potential is 0.901V in 0.1M KOH medium. After 10,000 CV cycles, the potential decay is only 14mV. Furthermore, at 10mA cm⁻¹... ‑2 At a current density, it has a charge / discharge voltage gap of 0.90V and can continuously cycle charge / discharge for up to 380 hours.

Description

Technical Field

[0001] This invention relates to an iron-molybdenum / NC catalyst, its preparation method, and its application, belonging to the field of electrocatalysts and their preparation technology. Background Technology

[0002] Rechargeable liquid zinc-air batteries (ZABs) are among the most promising energy conversion devices, with high power density, environmental friendliness, high safety, and low cost, offering a broader commercial prospect.

[0003] However, the oxygen reduction reaction (ORR) in the ZAB discharge process, as the cathode reaction, plays a dominant role in the overall battery reaction due to its slow kinetics. Platinum (Pt)-based catalysts are widely used in ORR due to their high catalytic activity and selectivity, but their high cost and poor stability limit their commercial value. Therefore, based on the above issues, exploring non-precious metal catalysts with high ORR activity and stability is crucial for reducing costs and achieving industrial-scale production. Summary of the Invention

[0004] This invention addresses the aforementioned technical problems with existing cathode materials in zinc-air batteries by providing an iron-molybdenum / NC catalyst for improving the long-term charge-discharge cycle stability of zinc-air batteries and its preparation method.

[0005] The technical solution of the present invention:

[0006] One objective of this invention is to provide a method for preparing an iron-molybdenum / NC catalyst, which includes the following steps:

[0007] (1) Dissolve the metal salt, organic ligand and surfactant in DMF respectively, stir ultrasonically until completely dissolved, mix evenly, place in an oil bath and stir at a constant temperature to obtain a reaction solution;

[0008] (2) The reaction solution was refluxed and centrifuged after the reaction was completed. The solution was washed and dried under vacuum to obtain the precursor.

[0009] (3) After grinding and sieving the precursor, add nitrogen source, continue grinding until uniform, and then calcine in a reducing atmosphere.

[0010] (4) The calcined product was washed in deionized water, and then filtered, dried and ground to obtain the iron-molybdenum / NC catalyst.

[0011] Further specifying, the molar ratio of metal salt, organic ligand and surfactant in (1) is 1:(5-8):4.

[0012] To be further specified, metal salts include iron sources, molybdenum sources, and zinc sources.

[0013] Furthermore, the iron source is ferric chloride hexahydrate or / and ferric nitrate hexahydrate; the molybdenum source is ammonium molybdate or / and sodium molybdate dihydrate; and the zinc source is zinc chloride.

[0014] Furthermore, the molar ratio of the iron source to the molybdenum source is 1:1.

[0015] Further specifying, the surfactant is STAB.

[0016] Further specifying, the organic ligands include dimethylimidazole and 2-mercapto-1-methylimidazole.

[0017] Furthermore, the mass ratio of dimethylimidazole to 2-mercapto-1-methylimidazole is 9:1.

[0018] Further specified, (1) the oil bath temperature is 70℃ and the time is 6h.

[0019] Further specified, in (2) the centrifugation speed is 6050 r / min and the time is 3 min.

[0020] Further specify that (2) the solvent used in the washing process is ethanol or deionized water, and the number of washing times is 3 to 5.

[0021] Further specifying, in (3) the nitrogen source is melamine, and the mass ratio of the precursor to melamine is 50mg:10g.

[0022] Further specifying, the calcination process in (3) is as follows: the precursor and nitrogen source mixture is transferred to a tube furnace, nitrogen is introduced into the tube furnace for 30 minutes to remove air, then a hydrogen / argon mixture is continuously introduced, and the temperature is raised to 900°C at a rate of 10°C / min, held for 120 minutes, and then naturally cooled to room temperature.

[0023] The second objective of this invention is to provide an iron-molybdenum / NC catalyst prepared by the above method.

[0024] A third objective of this invention is to provide an application of the aforementioned iron-molybdenum / NC catalyst, specifically for the preparation of a cathode in a zinc-air battery.

[0025] Beneficial effects:

[0026] This invention utilizes a constant-temperature oil bath self-assembly strategy, introducing sulfur and nitrogen sources followed by a hydrogen / argon mixed calcination reduction method to generate a carbon nanotube-encapsulated dodecahedral substrate. A Fe3C and Mo2C heterojunction structure is then formed on this dodecahedral substrate. The synergistic effect between Fe3C and Mo2C gives the catalyst excellent ORR activity and long-term stability. In 0.1M KOH medium, the ORR onset potential reaches 0.972V, the half-wave potential is 0.901V, and after 10,000 CV cycles, the potential decay is only 14mV. Furthermore, at 10mAcm... -2 At a current density of [value missing], it exhibits a charge / discharge voltage gap of 0.90V and can withstand continuous charge / discharge cycles for up to 380 hours. Compared with existing technologies, it also has the following advantages:

[0027] (1) In this invention, 2-mercapto-1-methylimidazole and dimethylimidazole are combined as organic ligands, while a sulfur source is introduced to regulate the coordination structure and promote the ORR activity of the catalyst and the growth of carbon nanotubes on the dodecahedral substrate surface.

[0028] (2) This invention introduces a nitrogen source by adding melamine, which catalyzes the formation of carbon nanotube morphology on the surface of a dodecahedral substrate, thereby increasing the specific surface area and active sites and improving the catalyst activity. Attached Figure Description

[0029] Figure 1 Here is a scanning electron microscope image of the FeMo / NC catalyst prepared in Example 1;

[0030] Figure 2 In Figure 1, a is a transmission electron microscope image of the FeMo / NC catalyst prepared in Example 1, b is a magnified view of a, c is a lattice fringe spacing diagram, and d is an elemental analysis diagram.

[0031] Figure 3 The LSV comparison curves of the FeMo / NC catalyst prepared in Example 1 before and after 10,000 CV cycles are shown.

[0032] Figure 4 LSV comparison curves of commercial Pt / C catalysts before and after 10,000 CV cycles;

[0033] Figure 5 The following are the long-term operational stability curves of the FeMo / NC catalyst prepared in Example 1 and the commercial Pt / C catalyst under constant potential.

[0034] Figure 6 The FeMo / NC catalyst prepared in Example 1 and the commercial Pt / C catalyst were compared at 10 mA / cm². – 2 Charge-discharge stability curves at current density;

[0035] Figure 7 A scanning electron microscope image of the catalyst prepared in Comparative Example 1;

[0036] Figure 8 Scanning electron microscope (SEM) image of the catalyst prepared in Comparative Example 2;

[0037] Figure 9 The image shows a scanning electron microscope (SEM) image of the catalyst prepared in Comparative Example 3. Detailed Implementation

[0038] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0039] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0040] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0041] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, all materials, reagents, methods, and instruments used are conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art. Furthermore, all solid and liquid reagents used are of analytical grade.

[0042] Example 1

[0043] The preparation method of the FeMo / NC catalyst for long-term charge-discharge cycle stability of zinc-air batteries in this embodiment is as follows:

[0044] Step 1: Dissolve 15 mmol of zinc chloride, 0.25 mmol of ferric chloride hexahydrate, 0.25 mmol of ammonium molybdate, 81 mmol of dimethylimidazole, and 9 mmol of 2-mercapto-1-methylimidazole in 100 mL of DMF solution respectively. After sonicating and stirring for 30 min until completely dissolved, mix the solutions and stir evenly. Add 4 mmol of STAB and stir evenly. Transfer to an oil bath and heat and stir at 70 °C for 6 h until the solution turns orange-yellow to obtain the reaction solution.

[0045] Step 2: Place the reaction solution obtained in Step 1 in a constant temperature reaction environment of 70℃ to avoid the influence of temperature fluctuations on the synthesis. Before heating, ensure the oil bath level is 1 / 2 to 1 / 3 of the way up the reaction vessel. Then, first introduce cooling water from bottom to top, and then start heating. Heat to 70℃ for reflux reaction and react for 180 minutes. At the end of the reaction, remove the reaction flask from the oil bath and let it stand above the oil surface. After cooling, wipe the oil off the surface of the reaction flask with paper. Then, centrifuge at 6050 r / min for 3 minutes, wash three times with deionized water as solvent, and dry in a 70℃ vacuum oven for 10 hours to obtain the precursor.

[0046] Step 3: Grind 50mg of the precursor in a ball mill until uniform, then add 10mg of melamine and continue grinding until uniform to obtain a mixture. Transfer the mixture to a tube furnace, purge the air in the tube furnace with nitrogen for 30 minutes to prevent oxygen from oxidizing the catalyst, and then continuously purge with a hydrogen / argon mixture. Heat the mixture to 900℃ at a rate of 10℃ / min and calcine for 120 minutes. Allow it to cool naturally to room temperature to obtain the catalyst.

[0047] Step 4: Dissolve 50 mg of catalyst in 1000 mL of deionized water, stir for 8 h at 500 r / min, filter, and finally dry in a 60 °C vacuum oven for 8 h. After drying, grind evenly to obtain FeMo / NC catalyst.

[0048] The FeMo / NC catalyst obtained above was characterized, and the scanning electron microscope images are shown below. Figure 1 As shown. By Figure 1 It can be seen that the microstructure of the FeMo / NC catalyst is a dodecahedron encapsulated by carbon nanotubes, as shown in the transmission electron microscope. Figure 2 It can be seen that Fe3C and Mo2C heterostructures are loaded on the dodecahedron ( Figure 1 The presence of small black particles on the dodecahedron indicates a Fe3C and Mo2C heterostructure.

[0049] The ORR performance of the FeMo / NC catalyst obtained above was tested, and the specific operation procedure is as follows:

[0050] (1) Preparation of slurry: Weigh 5 mg of FeMo / NC catalyst and grind it thoroughly. Add 0.5 mL of binder 0.5% naphthol solution and 1.5 mL of dispersant ethanol and disperse it evenly by ultrasonication. Take 40 μL of sample with the injection needle and drop it onto the platinum carbon electrode located on the rotating disk. Dry it at room temperature to obtain the platinum carbon electrode coated with slurry.

[0051] (2) Setting up the test apparatus: A three-electrode system was formed with a platinum mesh as the counter electrode, a standard hydrogen electrode as the reference electrode, and a platinum carbon electrode coated with slurry as the working electrode. A 0.1M KOH electrolyte was prepared, and high-purity oxygen was continuously introduced into the electrolyte for 30 minutes until saturation. The ORR performance was tested. The voltage range was 0.2V to 1.2V. Activation was performed by cyclic voltammetry (CV), and the polarization curve was obtained by linear voltammetry (LSV). The scan rate during LSV testing was 0.01V / s, and the rotation speed was 1600rpm.

[0052] The obtained FeMo / NC catalyst ORR electrochemical performance was determined by Figure 3 As shown in Tables 1 and 2 below, by Figure 3 It can be seen that after 10,000 cycles of CV testing, the half-wave potential of the FeMo / NC catalyst only decreased by 14mV.

[0053] Table 1 Comparison of half-wave and onset potential of FeMo / NC catalyst after 10,000 CV cycles for durability.

[0054] Initial 10000th <![CDATA[E 1 / 2 (VvsRHE)]]> 0.901 0.887 <![CDATA[E onset (VvsRHE)]]> 0.972 0.962

[0055] Table 2 Comparison of charge / discharge voltage gaps for FeMo / NC catalysts at different current densities

[0056] <![CDATA[J(mA·cm -2 )]]> 10 ΔE(V) 0.9

[0057] The ORR electrochemical performance of the commercial Pt / C catalyst obtained by replacing the FeMo / NC catalyst in Example 1 with a commercial Pt / C catalyst is as follows: Figure 4 As shown in Tables 3 and 4 below, by Figure 4 It can be seen that the Pt / C catalyst decays by 36mV after 10,000 cycles, which is higher than that of the FeMo / NC catalyst.

[0058] Table 3 Comparison of half-wave and onset potentials of Pt / C catalyst before and after 10,000 CV cycles for durability.

[0059] Initial 10000th <![CDATA[E 1 / 2 (VvsRHE)]]> 0.885 0.864 <![CDATA[E onset (VvsRHE)]]> 1.000 0.925

[0060] Table 4. Pt / C catalyst at 10 mA / cm -2 Charge / discharge voltage gap under current density

[0061] <![CDATA[J(mA·cm -2 )]]> 10 ΔE(V) 1.2

[0062] As can be seen from Tables 1-4 above, the FeMo / NC catalyst prepared in Example 1 has a high half-wave potential and stability as an electrocatalyst for the ORR reaction, and also has great advantages compared with commercial catalysts.

[0063] Further characterization of the cycle stability yielded the following results: Figure 5 and Figure 6 As shown, by Figure 5 It can be seen that after 10,000 CV cycles, the potential decays by only 14 mV, while maintaining 93.3% of the limiting current density. From... Figure 6 It can be seen that the assembled liquid zinc-air battery operates at 10 mA cm⁻¹. -2 The voltage difference (ΔE) was 0.9V at the beginning, and after 350 hours of cycling stability testing, the voltage difference increased by only 0.02V, demonstrating excellent cycling stability.

[0064] Comparative Example 1:

[0065] The difference between this comparative example and Example 1 is that the amount of 2-mercapto-1-methylimidazole added in step 1 is 0, while the remaining process steps and parameter settings are the same as in Example 1.

[0066] The microstructure of the catalyst obtained in this comparative example was characterized, and the results are as follows: Figure 7 As shown, by Figure 7 It can be seen that without the addition of 2-mercapto-1-methylimidazole, the number of carbon nanotubes growing on the surface of the dodecahedron is small and their morphology and size are not uniform.

[0067] Comparative Example 2:

[0068] The difference between this comparative example and Example 1 is that the amount of melamine added in step 3 is 0, while the remaining process steps and parameter settings are the same as in Example 1.

[0069] The microstructure of the catalyst obtained in this comparative example was characterized, and the results are as follows: Figure 8 As shown, by Figure 8 It can be seen that without the addition of melamine, the surface of the dodecahedron shrinks, resulting in a smaller number of catalytic tubes.

[0070] Comparative Example 3:

[0071] The difference between this comparative example and Example 1 is that the centrifugal speed in step 2 is 5000 r / min, while the remaining process steps and parameter settings are the same as in Example 1.

[0072] The microstructure of the catalyst obtained in this comparative example was characterized, and the results are as follows: Figure 9 As shown, by Figure 9 It can be seen that the FeMo / NC catalyst synthesized after centrifugation at low speed is prone to aggregation, which is not conducive to the formation of uniformly sized dispersions after subsequent calcination.

[0073] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing an iron-molybdenum / NC catalyst, characterized in that, include: (1) Dissolve the metal salt, organic ligand, and surfactant separately in DMF, stir ultrasonically until completely dissolved, mix evenly, and place in an oil bath for constant temperature stirring to obtain a reaction solution; the organic ligands include dimethylimidazole and 2-mercapto-1-methylimidazole; (2) The reaction solution was refluxed and centrifuged after the reaction was completed. The solution was then washed and vacuum dried to obtain the precursor. The centrifugation speed was 6050 r / min. (3) After grinding and sieving the precursor, add nitrogen source, continue grinding until uniform, and then calcine under a reducing atmosphere; The nitrogen source is melamine; (4) The calcined product was washed in deionized water, and then filtered, dried and ground to obtain the iron-molybdenum / NC catalyst.

2. The preparation method according to claim 1, characterized in that, (1) The molar ratio of metal salt, organic ligand and surfactant is 1:(5~8):4; the metal salt includes iron source, molybdenum source and zinc source, and the surfactant is STAB.

3. The preparation method according to claim 2, characterized in that, The mass ratio of dimethylimidazole to 2-mercapto-1-methylimidazole is 9:

1.

4. The preparation method according to claim 2, characterized in that, The iron source is ferric chloride hexahydrate and / or ferric nitrate hexahydrate; the molybdenum source is ammonium molybdate and / or sodium molybdate dihydrate; the zinc source is zinc chloride; and the molar ratio of the iron source to the molybdenum source is 1:

1.

5. The preparation method according to claim 1, characterized in that, (1) The oil bath temperature is 70°C. o C, the time is 6 hours.

6. The preparation method according to claim 1, characterized in that, (2) The centrifugation time is 3 min.

7. The preparation method according to claim 1, characterized in that, (3) The mass ratio of the precursor to melamine is 50 mg: 10 g.

8. The preparation method according to claim 1, characterized in that, (3) The calcination process is as follows: the precursor and nitrogen source mixture is transferred to a tube furnace, nitrogen is introduced into the tube furnace for 30 minutes to purge the air, and then a hydrogen / argon mixture is continuously introduced at a rate of 10 o Heating rate increased to 900 °C / min o C, keep warm for 120 minutes, then let cool naturally to room temperature.

9. An iron-molybdenum / NC catalyst prepared by the method according to any one of claims 1 to 8.

10. An application of the iron-molybdenum / NC catalyst according to claim 9, characterized in that, Used to prepare the cathode for zinc-air batteries.

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