Preparation method of Fe3O4 / Fe / C catalyst and positive electrode for neutral zinc-air battery

Abstract

The invention belongs to the field of electro-catalysis, and particularly relates to a preparation method of a Fe3O4 / Fe / C catalyst and a positive electrode for a neutral zinc-air battery. According to the method, a high-energy ball mill is utilized, iron balls are used for ball milling of carbon powder, impact among the iron balls produces abrasion to enable iron atoms to be attached to a carbon substrate, then the carbon powder subjected to ball milling is placed in a tubular furnace with mixed gas, part of iron elementary substances are oxidized into ferroferric oxide, and the needed catalyst is obtained. Compared with the prior art, a mechanical ball milling method is used, the preparation method is simple and convenient, the cost is low, ORR and OER reaction kinetics can be accelerated, and when the material is applied to the neutral zinc-air battery, voltage polarization can be reduced, the energy efficiency of the battery can be improved, and the cycle life of the battery can be prolonged.

Description

Technical Field

[0001] The invention belongs to the field of electrocatalysis, and in particular relates to a Fe3O4 / Fe / C catalyst for a neutral zinc-air battery and a preparation method thereof. Background Art

[0002] Zinc-air batteries have the advantages of high theoretical energy density (1086Wh / Kg), good safety, abundant raw material sources, low cost and environmental friendliness, and are a strong candidate for the next generation of energy storage batteries. At present, zinc-air batteries are mainly used as primary batteries, the most common of which are hearing aid button batteries, and people try to use them in buses, but these are non-rechargeable batteries and can only be discarded when the power is exhausted, or replace the zinc plate to replenish the negative electrode active material for continued use. This method causes a lot of waste on the zinc plate, so it cannot be applied on a large scale. At present, most of the research on rechargeable zinc-air batteries uses strong alkaline electrolytes, such as high concentrations of potassium hydroxide, but many side reactions will occur under alkaline electrolytes, including self-corrosion of the zinc negative electrode, hydrogen evolution, passivation, electrolyte carbonation and positive electrode degradation. These problems lead to poor cycle reversibility of alkaline zinc-air batteries and cannot be commercially applied.

[0003] According to reports, researchers have developed a near-neutral zinc acetate electrolyte, which shows good deposition and stripping effects in zinc-zinc batteries, and the cycle stability is much higher than that of zinc-zinc batteries using alkaline electrolytes. The reason is that the mild zinc acetate electrolyte does not produce zinc dendrites and corrosion and other side reactions, which improves the reversibility of the zinc negative electrode. At the same time, the zinc-air battery using zinc acetate electrolyte shows good cycle stability. However, the lack of corresponding ORR / OER bifunctional catalytic materials in this electrolyte system leads to large voltage polarization of the battery and low energy efficiency. Therefore, it is necessary to develop an efficient bifunctional catalyst for use in a neutral zinc acetate system to reduce the voltage polarization of the battery and improve energy efficiency. Summary of the invention

[0004] In view of the problems of large battery polarization and low energy efficiency in the above-mentioned neutral zinc-air battery, the present invention provides a Fe3O4 / Fe / C catalyst, which can accelerate the ORR / OER reaction kinetics, improve energy efficiency, reduce voltage polarization, and improve cycle stability. The method has the advantages of simple preparation process, no use of any chemical solvents, high material input-output ratio, environmental friendliness, etc., and has the potential for large-scale production.

[0005] In order to achieve the above object, the present invention adopts the following scheme:

[0006] A Fe3O4 / Fe / C catalyst for a neutral zinc-air battery, characterized in that the catalyst comprises ferrosoferric oxide, iron and a carbon substrate, and the total content of ferrosoferric oxide and iron does not exceed 5% of the total mass.

[0007] Furthermore, the mass ratio of ferroferric oxide: iron: carbon substrate is 2:1:97.

[0008] A method for preparing a Fe3O4 / Fe / C catalyst for a neutral zinc-air battery comprises the following steps:

[0009] Step 1: Add pure iron balls and carbon powder into the ball mill, fill with protective inert gas and seal the mouth of the mill;

[0010] Step 2: After setting the speed and ball milling time, start the ball mill;

[0011] Step 3: After the ball milling process is stopped, the obtained catalyst precursor, i.e., carbon powder containing a small amount of nano-iron element, is completely cooled and taken out, and transferred to a tube furnace under inert gas protection, and subjected to high-temperature heat treatment under mixed gas;

[0012] The mixed gas is a mixture of O2 with an oxygen content of 1 to 3% and Ar or a mixture of O2 and N2.

[0013] Furthermore, in step 1, the carbon powder is one or more of carbon black, graphite, carbon nanotubes, graphene, Ketjen black, and acetylene black.

[0014] Furthermore, in step 1, the diameter of the iron ball is 3 to 8 mm, two or more sizes of the spheres are selected, and the total input amount is just enough to cover the bottom of the ball mill. At the same time, the carbon powder input amount does not exceed one half of the total volume of the ball mill.

[0015] Furthermore, in step 2, the rotation speed is set to 400-900 RPM, and the total ball milling time is 2-20 hours, wherein the mill is stopped for 10 minutes after running for 30 minutes.

[0016] Furthermore, in step 3, the heat treatment procedure is to raise the temperature to 800°C under a nitrogen or argon atmosphere at a heating rate of 4 to 8°C / min, then introduce a mixed gas at 800°C with a gas flow rate of 40 to 100 sccm, and keep warm for 15 to 40 minutes, then introduce nitrogen or argon again and keep warm for 80 to 105 minutes. After completely cooling down, take out the sample to obtain the desired catalyst.

[0017] A method for preparing a positive electrode of a neutral zinc-air battery using a Fe3O4 / Fe / C catalyst, the method comprising:

[0018] The catalyst, binder and solvent are stirred and mixed to form a slurry, the slurry is evenly coated on the current collector, and after standing and drying, a positive electrode sheet is obtained.

[0019] Furthermore, the mass ratio of the catalyst, the binder and the solvent is one of 8:2:10 or 9:1:10, the current collector is one of carbon paper, carbon cloth, nickel mesh or titanium mesh, the binder is one of polyvinylidene fluoride or polytetrafluoroethylene, and the solvent is one of isopropanol or ethanol.

[0020] Compared with other existing technologies, the beneficial effects of the present invention are as follows:

[0021] The Fe3O4 / Fe / C catalyst and preparation method thereof provided by the present invention are as follows: iron balls and carbon powders of a certain mass ratio are loaded into a ball milling jar, and under the vibration of a high-energy ball mill, the surface of the iron balls is worn, and iron atoms are driven into the surface of the carbon substrate, so that the carbon after ball milling contains elemental iron, which is heated in a mixed gas, and part of Fe is oxidized to Fe3O4, thereby obtaining a Fe3O4 / Fe / C catalyst with high catalytic activity. The present invention uses a mechanical ball milling method to prepare an iron-containing catalyst, and the preparation method is simpler than the previous method, does not require the use of chemical solvents, uses very few chemicals, has the characteristics of green environmental protection and low cost, and at the same time, the method has a high material input-output ratio and has the potential for large-scale production and preparation. The catalyst is used as a positive electrode catalyst layer material for a neutral zinc-air battery, which improves the ORR and OER reaction kinetics, improves the discharge potential, and reduces the charging potential, thereby having higher energy efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the XRD curve diagram of Example 1.

[0023] Figure 2 This is the XRD curve diagram of Example 2.

[0024] Figure 3 The charge and discharge cycle curves of Example 1 and Comparative Example 1 are shown in FIG.

[0025] Figure 4 The charge and discharge cycle curves of Example 2 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0026] Example 1

[0027] A Fe3O4 / Fe / C catalyst for a neutral zinc-air battery and a preparation method thereof, the specific implementation methods are as follows:

[0028] 40g of solid pure iron balls with a diameter of 6mm and 1g of commercial carbon black Vulcan XC-72R were added to the ball mill, and the mouth of the mill was sealed; the speed was set to 800RPM, and the ball milling time was 5 hours, with 30min of operation and 10min of shutdown. After the ball milling was completed, the product was taken out after cooling for 6 hours, and the product was placed in a tubular furnace, heated to 800℃ under argon atmosphere, with a heating rate of 5℃ / min, and then an O2 / Ar mixed gas with an oxygen content of 2% was introduced at 800℃, and kept warm for 30min, and then argon was introduced and kept warm for 90min. After the temperature was completely cooled, the sample was taken out to obtain the desired catalyst.

[0029] The prepared catalyst was tested by XRD. Figure 1 It can be seen that in addition to the diffraction peak of the carbon (002) crystal plane at about 26°, diffraction peaks of Fe3O4 and Fe appeared, which means that the Fe3O4 / Fe / C catalyst was successfully prepared by ball milling and heat treatment.

[0030] The catalyst, polytetrafluoroethylene and isopropanol were mixed in a mass ratio of 9:1:10, stirred evenly to obtain a slurry, and the slurry was evenly coated on the hydrophobic carbon paper. After standing and drying, the positive electrode sheet was obtained. The positive electrode sheet was used as the positive electrode of the zinc-air battery, the zinc sheet was used as the negative electrode, the diaphragm was GF / A, the electrolyte was 1 mol / L Zn(OAC)2 solution, and the battery mold was a Swagelok type. The assembled battery was cycle tested, and the test results are as follows: Figure 3 shown.

[0031] Example 2

[0032] A Fe3O4 / Fe / C catalyst for a neutral zinc-air battery and a preparation method thereof, the specific implementation methods are as follows:

[0033] 40g of solid pure iron balls with a diameter of 6mm and 1g of commercial carbon black Vulcan XC-72R were added to the ball mill, and the mouth of the mill was sealed; the speed was set to 800RPM and the total milling time was 10 hours, with 30min of operation and 10min of shutdown. After the ball milling was completed, the product was taken out after cooling for 6 hours, and the product was placed in a tubular furnace, heated to 800℃ under argon atmosphere, with a heating rate of 5℃ / min, and then an O2 / Ar mixed gas with an oxygen content of 2% was introduced at 800℃, and kept warm for 30min, and then argon was introduced and kept warm for 90min. After the temperature was completely cooled, the sample was taken out to obtain the desired catalyst.

[0034] The prepared catalyst was tested by XRD. Figure 2It can be seen that in addition to the diffraction peak of the carbon (002) crystal plane at about 26°, diffraction peaks of Fe3O4 and Fe appeared, which means that the Fe3O4 / Fe / C catalyst was successfully prepared by ball milling and heat treatment.

[0035] The catalyst, polytetrafluoroethylene and isopropanol were mixed in a mass ratio of 9:1:10, stirred evenly to obtain a slurry, and the slurry was evenly coated on the hydrophobic carbon paper. After standing and drying, the positive electrode sheet was obtained. The positive electrode sheet was used as the positive electrode of the zinc-air battery, the zinc sheet was used as the negative electrode, the diaphragm was GF / A, the electrolyte was 1 mol / L Zn(OAC)2 solution, and the battery mold was a Swagelok type. The assembled battery was cycle tested, and the test results are as follows: Figure 4 shown.

[0036] Comparative Example 1

[0037] Commercial carbon black Vulcan XC-72R was used as the positive electrode catalyst material. The catalyst, polytetrafluoroethylene and isopropanol were mixed in a mass ratio of 9:1:10, stirred evenly to obtain a slurry, and the slurry was evenly coated on the hydrophobic carbon paper. After standing and drying, the positive electrode sheet was obtained. The positive electrode sheet was used as the positive electrode of the zinc-air battery, the zinc sheet was used as the negative electrode, the diaphragm was GF / A, the electrolyte was 1 mol / L Zn(OAC)2 solution, and the battery mold was a Swagelok type. The assembled battery was cycle tested, and the test results are as follows: Figure 3 and Figure 4 shown.

[0038] according to Figure 3 and Figure 4 The test results show that at 0.1 mA cm -2 During the current density cycle test, both Example 1 and Example 2 have higher discharge potential and lower charge potential than Comparative Example 1, that is, smaller voltage polarization and higher energy efficiency, indicating that the improved catalyst of the present invention can accelerate the ORR and OER reaction kinetics in a neutral zinc-air battery.

[0039] In summary, the Fe3O4 / Fe / C catalyst material has many advantages: simple preparation method, green and environmentally friendly, low preparation cost, high input-output ratio, and is expected to be prepared on a large scale. At the same time, when the catalyst is applied to the positive electrode catalyst layer of a neutral zinc-air battery, it can effectively reduce the overpotential of the battery, improve energy efficiency, and enhance the cycle performance of the battery.

Claims

1. A Fe3O4 / Fe / C catalyst for a neutral zinc-air battery, characterized in that: The catalyst comprises ferroferric oxide, iron and a carbon substrate, and the total content of ferroferric oxide and iron does not exceed 5% of the total mass.

2. The Fe3O4 / Fe / C catalyst for a neutral zinc-air battery according to claim 1, characterized in that: The mass ratio of ferroferric oxide: iron: carbon substrate is 2:1:

97.

3. A method for preparing a Fe3O4 / Fe / C catalyst for a neutral zinc-air battery, comprising the following steps: Step 1: Add pure iron balls and carbon powder into the ball mill, fill with protective inert gas and seal the mouth of the mill; Step 2: After setting the speed and ball milling time, start the ball mill; Step 3: After the ball milling process is stopped, the obtained catalyst precursor, i.e., carbon powder containing a small amount of nano-iron element, is completely cooled and taken out, and transferred to a tube furnace under inert gas protection, and subjected to high-temperature heat treatment under mixed gas; The mixed gas is a mixture of O2 with an oxygen content of 1 to 3% and Ar or a mixture of O2 and N2.

4. A method for preparing a Fe3O4 / Fe / C catalyst for a neutral zinc-air battery as claimed in claim 3, characterized in that: In step 1, the carbon powder is one or more of carbon black, graphite, carbon nanotubes, graphene, Ketjen black, and acetylene black.

5. The method for preparing a Fe3O4 / Fe / C catalyst for a neutral zinc-air battery according to claim 3, characterized in that: In step 1, the diameter of the iron ball is 3 to 8 mm, and two or more sizes of balls are selected. The total input amount is just enough to cover the bottom of the ball mill, and the carbon powder input amount does not exceed half of the total volume of the ball mill.

6. A method for preparing a Fe3O4 / Fe / C catalyst for a neutral zinc-air battery as claimed in claim 3, characterized in that: In step 2, the rotation speed is set to 400-900 RPM, and the total ball milling time is 2-20 hours, wherein the mill is stopped for 10 minutes after running for 30 minutes.

7. A method for preparing a Fe3O4 / Fe / C catalyst for a neutral zinc-air battery as claimed in claim 3, characterized in that: In step 3, the heat treatment procedure is to raise the temperature to 800°C under a nitrogen or argon atmosphere at a heating rate of 4 to 8°C / min, then introduce a mixed gas at 800°C with a gas flow rate of 40 to 100 sccm, and keep warm for 15 to 40 minutes, then introduce nitrogen or argon again and keep warm for 80 to 105 minutes. After completely cooling, take out the sample to obtain the desired catalyst.

8. A method for preparing a positive electrode of a neutral zinc-air battery using a Fe3O4 / Fe / C catalyst as claimed in claim 3, the method comprising: The catalyst, binder and solvent are stirred and mixed to form a slurry, the slurry is evenly coated on the current collector, and after standing and drying, a positive electrode sheet is obtained.

9. A method for preparing a positive electrode of a neutral zinc-air battery using a Fe3O4 / Fe / C catalyst as claimed in claim 8, characterized in that: The mass ratio of the catalyst, the binder and the solvent is one of 8:2:10 or 9:1:10, the current collector is one of carbon paper, carbon cloth, nickel mesh or titanium mesh, the binder is one of polyvinylidene fluoride or polytetrafluoroethylene, and the solvent is one of isopropanol or ethanol.

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