Preparation method of manganese dioxide supported monatomic silver catalyst and positive electrode film

Abstract

The application discloses a kind of manganese dioxide supported monatomic silver catalyst and preparation method of positive electrode film, comprising the following steps: S1.the potassium permanganate of a certain mass, manganese sulfate monohydrate and silver nitrate are mixed with deionized water respectively to prepare solution with different concentrations;S2.manganese sulfate monohydrate solution is added to potassium permanganate solution and is magnetically stirred, in the process of stirring, add conductive carbon black, after uniform mixing, obtain mixed solution A;S3.continuously keep the magnetic stirring speed of S2, and drop silver nitrate solution to mixed solution A to obtain mixed solution B;S4.mixed solution B is transferred to reaction kettle and is hydrothermally reacted, after reaction, the substance is centrifuged, and precipitate is obtained, after drying and grinding, catalyst MnO2 / C-Ag is obtained, i.e.manganese dioxide supported monatomic silver catalyst.The application can realize that silver monatomic atom is uniformly dispersed on the surface of manganese dioxide, silver monatomic atom and carrier interact strongly, and preparation process is simple, and cost is low.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and particularly relates to a method for preparing a manganese dioxide-supported single-atom silver catalyst and a positive electrode film. Background Technology

[0002] Alkaline aluminum-air batteries, as a novel green energy storage and conversion device, possess significant advantages such as abundant aluminum resources, low cost, high theoretical specific energy, environmental friendliness, and zero pollutant emissions. They have shown broad application prospects in portable electronic devices, new energy vehicles, and emergency power supplies, becoming one of the current research hotspots in the new energy field. The working principle of alkaline aluminum-air batteries mainly relies on the positive electrode oxygen reduction reaction (ORR) and the negative electrode aluminum oxidation reaction. The slow kinetics of the positive electrode oxygen reduction reaction is the core bottleneck restricting battery discharge performance, energy conversion efficiency, and cycle stability. Therefore, developing high-performance positive electrode oxygen reduction catalysts is crucial for promoting the industrial application of alkaline aluminum-air batteries.

[0003] Currently, cathode catalysts for alkaline aluminum-air batteries are mainly classified into noble metal catalysts, transition metal oxide catalysts, and carbon-based catalysts. Among them, platinum (Pt) noble metal catalysts have excellent oxygen reduction catalytic activity and stability, making them the best-performing cathode catalysts. However, their scarcity and high price significantly increase the production cost of batteries, hindering large-scale commercial application. Among non-noble metal catalysts, manganese dioxide (MnO2) has become one of the most promising cathode catalysts due to its good oxygen reduction catalytic activity in alkaline media. Its catalytic performance is closely related to its crystal structure, with α-MnO2 exhibiting superior catalytic activity compared to other crystal forms.

[0004] However, pure manganese dioxide catalysts suffer from poor conductivity, a limited number of catalytic active sites, and a tendency to agglomerate and collapse during cycling. These issues hinder their catalytic efficiency and stability, preventing them from meeting the practical application requirements of alkaline aluminum-air batteries and limiting their further promotion. To address these problems, researchers typically optimize manganese dioxide through modification methods such as metal doping, loading with noble metals, and composite carbon materials. Among these, silver (Ag) is a preferred noble metal component for modified manganese dioxide catalysts due to its excellent conductivity and oxygen reduction catalytic activity, as well as its lower cost compared to noble metals like platinum. However, existing preparation methods suffer from problems such as easy agglomeration of single-atom silver, complex processes, harsh reaction conditions, and weak interaction between silver and composite supports, limiting their practical application. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a manganese dioxide-supported single-atom silver catalyst and a positive electrode film, which can promote the oxygen reduction process of the positive electrode of an alkaline aluminum-air battery, accelerate the oxygen reduction reaction rate, and improve the overall performance of the aluminum-air battery.

[0006] To achieve the above objectives, the present invention provides a method for preparing a manganese dioxide-supported single-atom silver catalyst, comprising the following steps: S1. A certain mass of potassium permanganate, manganese sulfate monohydrate and silver nitrate are respectively mixed with deionized water to prepare solutions of different concentrations; S2. Add manganese sulfate monohydrate solution to potassium permanganate solution and stir magnetically. Add conductive carbon black during stirring and mix evenly to obtain mixed solution A. S3. Continue to maintain the magnetic stirring speed of S2, and add silver nitrate solution dropwise to mixed solution A to obtain mixed solution B; S4. Transfer the mixed solution B to the reactor for hydrothermal reaction. Centrifuge the reacted material to obtain the precipitate. After drying and grinding, obtain the catalyst MnO2 / C-Ag, which is a manganese dioxide supported single-atom silver catalyst.

[0007] The amount of silver nitrate used is 0.001~0.05g, and the mass ratio of potassium permanganate, manganese sulfate monohydrate and silver nitrate is 36.01~36.20:58.01~58.50:1.

[0008] The magnetic stirring speed in steps S2 and S3 is 300 rpm.

[0009] In step S4, the hydrothermal reaction temperature is 160 ℃, and the reaction time is 12 h. The centrifugation speed is 10000 rpm, the centrifugation time is 5 min, the drying temperature is 55 ℃, and the drying time is 12 h.

[0010] A method for preparing a positive electrode film includes the following steps: The manganese dioxide-supported single-atom silver catalyst, 60 wt.% PTFE emulsion, and ethanol were placed in a beaker and mixed. The beaker was heated in a water bath while being magnetically stirred. After the ethanol evaporated, a black dough-like substance was obtained. The black dough-like substance is rolled into a thin film. Then, it is repeatedly stacked in the order of waterproof and breathable membrane, nickel mesh, waterproof and breathable membrane, and catalyst film. After being rolled into a sheet, it is cut into appropriate sizes and aged to obtain the positive electrode film.

[0011] The mixing ratio of the manganese dioxide-supported single-atom silver catalyst, 60 wt.% PTFE emulsion, and ethanol is 1g:1.5g:50ml.

[0012] The water bath heating temperature is 80 ℃, and the magnetic stirring speed is 500 rpm.

[0013] The positive electrode film has a thickness of 0.15 mm, and the aging treatment conditions are: heating to 200 °C at a heating rate of 5 °C / min in an argon atmosphere in a tube furnace, and heating for 1 h.

[0014] An alkaline aluminum-air battery includes a full cell, an alkaline electrolyte, and a peristaltic pump. The full cell includes a battery clamp, which comprises a sealing rubber gasket, a reaction chamber, and a battery template. The reaction chamber consists of an inlet pipe and a reaction cavity (reaction area 1 cm²). 2 The aluminum sheet and the outlet pipe form a whole; the sealing rubber gasket is attached to both sides of the reaction chamber. By attaching the aluminum sheet and the positive electrode film to the sealing rubber gasket and closing the battery template, a full battery assembly is completed. The alkaline electrolyte is 4 mol / L. -1 KOH solution.

[0015] The alkaline electrolyte is stored in an electrolyte storage tank and connected to a peristaltic pump via a circulation pipe; The circulation pipe is connected to the inlet pipe and the outlet pipe; The positive electrode film is prepared using the aforementioned method.

[0016] Beneficial effects: (1) This invention strengthens the oxygen reduction active sites of manganese dioxide, greatly reduces the dependence of oxygen reduction catalyst on precious metals, reduces raw material costs, and is suitable for industrial production. (2) The catalyst synthesis method of the present invention is simple. The synthesized manganese dioxide is in the form of nanorods, which can provide adsorption sites for Ag single atoms, effectively promoting the oxygen reduction reaction process of the positive electrode of alkaline aluminum-air battery, and breaking through the performance bottleneck of traditional catalysts. (3) The catalyst synthesis and positive electrode film preparation process of the present invention are simple, do not require complex equipment or harsh conditions, are easy to scale up and have certain commercial prospects; (4) The prepared positive electrode film is used in aluminum-air batteries, which enable the batteries to have high energy density, stable discharge capability and long cycle life. Attached Figure Description

[0017] Figure 1 The catalyst MnO2 / C-Ag and the positive electrode film preparation process of Example 1 of this invention are shown below; Figure 2 This is a scanning electron microscope image of the catalyst MnO2 / C-Ag prepared in Example 1 of the present invention; Figure 3 This is a scanning electron microscope image of the catalyst film prepared in Example 1 of the present invention; Figure 4The image shows the XRD pattern of the catalyst MnO2 / C-Ag prepared in Example 1 of this invention. Figure 5 The ORR test curve of the catalyst MnO2 / C-Ag prepared in Example 2 of this invention; Figure 6 The graph shows the half-wave potential and limiting current of the catalyst MnO2 / C-Ag prepared in Example 2 of this invention. Figure 7 The power density and polarization curves of the alkaline aluminum-air battery prepared in Example 3 of this invention; Figure 8 The step discharge curve of the alkaline aluminum-air battery obtained in Example 3 of this invention; Figure 9 The capacity density curve of the alkaline aluminum-air battery prepared in Example 3 of the present invention after 1 h of constant current discharge. Figure 10 This is the cycle curve of the alkaline aluminum-air battery obtained in Example 3 of the present invention. Detailed Implementation

[0018] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the equipment used in the following embodiments is conventional equipment in the art; unless otherwise specified, the reagents used are commercially available products or prepared using conventional methods in the art. Specific details not described in the following embodiments can be achieved using conventional experimental methods in the art.

[0019] Example 1: A manganese dioxide-supported single-atom silver catalyst includes the following steps: Weigh 0.723 g of potassium permanganate, 1.166 g of manganese sulfate monohydrate, and 0.02 g of silver nitrate into different beakers. Add 30 ml of deionized water to the potassium permanganate beaker and the manganese sulfate monohydrate beaker to obtain a 0.1525 mol / L potassium permanganate solution and a 0.2300 mol / L manganese sulfate monohydrate solution, respectively. Add 20 ml of deionized water to the silver nitrate beaker to obtain a 0.0059 mol / L silver nitrate solution. Manganese sulfate monohydrate solution was added to potassium permanganate solution and magnetically stirred. During the stirring process, 0.2g of conductive carbon black was added. After uniform mixing, mixed solution A was obtained. The magnetic stirring speed was adjusted, and silver nitrate solution was added dropwise to mixed solution A to obtain mixed solution B. Mixed solution B was transferred to a polytetrafluoroethylene liner, which was then placed in a hydrothermal reactor. The reactor was then transferred to a box furnace for hydrothermal reaction at 160 °C for 12 h. After the reaction was complete, the solution was centrifuged at 10,000 rpm for 5 min. After drying at 55 °C for 12 h, the catalyst MnO2 / C-Ag was obtained, which is a manganese dioxide supported single-atom silver catalyst with a silver loading of 1 wt.%.

[0020] like Figure 2 As shown, scanning electron microscopy of the MnO2 / C-Ag catalyst clearly reveals that the catalyst obtained by this synthesis method has a nanorod structure, which can provide a large number of adsorption sites for single-atom Ag, thereby improving the oxygen reduction reaction at the positive electrode of the aluminum-air battery.

[0021] Example 2: Preparation of positive electrode film Weigh 1.0 g of the catalyst MnO2 / C-Ag prepared in Example 1, 1.5 g of 60 wt.% PTFE emulsion, and 50 mL of ethanol into a beaker and heat in a water bath while magnetically stirring. The water bath temperature is 80 ℃, and the magnetic stirring speed is 500 rpm. After the solution in the beaker has completely evaporated, a black dough-like mixture is obtained. Roll-press the mixture to obtain a catalyst film of 0.15 mm. Repeat the stacking process in the order of waterproof and breathable membrane, nickel mesh, waterproof and breathable membrane, and catalyst film, and roll-press it into a sheet again. After air-drying for 1 day, calcination aging treatment is performed by heating at 200 ℃ for 1 h in a tube furnace under an argon atmosphere to obtain the finished positive electrode film. Figure 3 As shown, scanning electron microscopy (SEM) of the positive electrode film clearly reveals a large number of uniformly dispersed nanorod-shaped catalyst MnO2 / C-Ag particles on the surface of the catalyst film. This indicates that the preparation method of the positive electrode film can ensure the uniform distribution of the catalyst on the catalyst film. Figure 4 The XRD characterization diagram shown also indicates that the catalyst has good crystallinity, and at the same time proves that the presence of carbon and silver does not interfere with the main phase structure, but is only supported on MnO2, which effectively shows that the catalyst is mainly MnO2.

[0022] Comparative Example 1 The difference from Example 1 is that in this comparative example: Step (1): Weigh 1.5 g of manganese acetate tetrahydrate into a beaker, add 100 mL of distilled water and stir for 30 minutes, then adjust the pH to 11 with sodium hydroxide. Step (2): Weigh 0.644 g of potassium permanganate, dissolve it in 50 mL of distilled water, and stir until well mixed; Step (3): Add the potassium permanganate solution prepared in step (2) dropwise to the solution prepared in step (1) and stir. Add 0.2 g of conductive carbon black during the stirring process. After the potassium permanganate solution is added, stir for 1 hour, filter, wash with distilled water, and then dry in an oven at 60 °C for 12 hours to obtain carbon supported on amorphous manganese dioxide catalyst.

[0023] Step (4): The material obtained in step (3) is treated with argon plasma for 8 hours to obtain manganese dioxide with oxygen vacancies.

[0024] Step (5): Prepare 25 mL of 0.02 M silver nitrate solution and disperse oxygen-rich manganese dioxide in it; Step (6) involves calcining manganese dioxide impregnated with silver nitrate at 750 °C with a heating rate of 5 °C / min to obtain the catalyst MnO2 / C-Ag with a silver loading of 13 wt.%.

[0025] Step (7) Weigh 1.0 g of the prepared catalyst MnO2 / C-Ag, 1.5 g of 60 wt.% PTFE emulsion, and 50 mL of ethanol into a beaker and heat in a water bath while stirring magnetically. The water bath heating temperature is 80 ℃ and the magnetic stirring speed is 500 rpm. After the solution in the beaker has completely evaporated, a black dough-like mixture is obtained. Roll it to obtain a catalyst film of 0.15 mm. Repeat the stacking of waterproof and breathable membrane, nickel mesh, waterproof and breathable membrane, and catalyst film in sequence, roll it into a sheet again, air dry it naturally for 1 day, and then perform calcination aging treatment. Heat it at a constant temperature of 200 ℃ for 1 h in a tube furnace under an argon atmosphere to obtain the finished positive electrode film.

[0026] Catalyst testing: ORR tests were performed on the catalysts (MnO2 / C-Ag) prepared in Example 1 (silver single atom loading 1 wt.%) and Comparative Example 1 (silver single atom loading 13 wt.%). Figure 5 , Figure 6 ). Figures 5-6 The electrochemical analysis was conducted using a rotating disk electrode apparatus in an environment with a 0.1 M KOH electrolyte and continuous oxygen flow. Figure 5 , Figure 6 The test needs to be conducted at 1600 rpm.

[0027] like Figure 5 , Figure 6 As shown, the catalyst ORR test range is 1.14 V (vs. RHE) - 0.44 V (vs. RHE), which is determined by reading... Figure 5The ORR curves at potentials of 1.05 V (vs. RHE) and 0.50 V (vs. RHE) allow for the calculation of the catalyst's half-wave potential, while the limiting current at 0.50 V (vs. RHE) indicates that the half-wave potential and limiting current of the catalyst (MnO2 / C-Ag) in Example 1 are 0.83 V and 6.15 mA cm⁻¹, respectively. -2 The half-wave potential and limiting current of Pt / C are 0.86 V and 4.72 mAcm, respectively. -2 The values ​​are close. The comparative catalyst has a half-wave potential and limiting current of 0.79 V and 3.97 mA cm⁻¹, respectively. -2 Half-wave potential is a key indicator of the intrinsic activity of a catalyst; the more positive the potential (the larger the value), the higher the catalyst activity. The half-wave potential of Example 1 is significantly higher than that of Comparative Example 1. This indicates that a small amount of silver (1 wt.%) can achieve an activation potential similar to that of a platinum catalyst, while increasing the silver loading (13 wt.%) in Comparative Example 1 actually reduced the intrinsic activity of the catalyst. Limiting current reflects the mass transfer capacity and the number of effective active sites of the catalyst during the reaction process; the higher the current density, the better the performance. The limiting current of Example 1 is not only much higher than that of Comparative Example 1, but also exceeds that of a commercial Pt / C catalyst. This indicates that the catalyst of Example 1 has better electron transport efficiency and more effective reactive sites, enabling it to support a higher reaction rate.

[0028] The manganese dioxide-supported single-atom silver catalyst prepared using the method of Example 1 exhibits highly dispersed silver atoms in a single-atom form, resulting in extremely high atom utilization. In contrast, the catalyst prepared using the method of Comparative Example 1 shows that silver atoms may have aggregated, forming nanoparticles. This reduces the number of active sites and may even cover the active sites on the support surface, thereby decreasing catalytic performance.

[0029] Battery test A full-cell test was conducted on the Shanghai Chenhua Electrochemical Workstation. The alkaline aluminum-air battery includes a full cell, an alkaline electrolyte, and a peristaltic pump. The full cell includes a battery clamp, which includes a sealing rubber gasket, a reaction chamber, and a battery template. The reaction chamber consists of an inlet pipe and a reaction cavity (reaction area 1 cm²). 2 The aluminum sheet and the outlet pipe form a whole; the sealing rubber gasket is attached to both sides of the reaction chamber. By attaching the aluminum sheet and the positive electrode film to the sealing rubber gasket and closing the battery template, a full battery assembly is completed. The alkaline electrolyte is 4 mol / L. -1 KOH solution.

[0030] The alkaline electrolyte is stored in an electrolyte storage tank and connected to a peristaltic pump via a circulation pipe; The circulation pipe is connected to the inlet pipe and the outlet pipe; The positive electrode membrane is composed of a waterproof and breathable membrane, a nickel mesh, a waterproof and breathable membrane and a catalyst film from bottom to top. The catalyst film is prepared by the preparation method described in Example 1, which is a catalyst MnO2 / C-Ag.

[0031] like Figure 7 As shown, the LSV test performed on the full cell has a test voltage range of 0 V (vs. SCE). -2 V(vs.SCE). This test reflects the power density and polarization curve of the full cell. The overall power density of the full cell is 60.80 mW / cm². -2 .

[0032] like Figure 8 A full-cell stepped discharge test was conducted, with the test performed sequentially at 1 mA cm⁻¹. -2 10 mA cm -2 20 mA cm -2 40 mA cm -2 60 mA cm -2 80 mA cm -2 100 mA cm -2 It then fell back to 80 mA cm -2 40 mA cm -2 20 mAcm -2 1 mA cm -2 The catalyst was subjected to discharge at various current densities for 600 s, and its performance was evaluated by the voltage response and stability at different current densities. The results show that the catalyst maintains stable output during high-current discharge; and after cycling under high-current conditions, its voltage response remains stable even at current densities up to 80 mA cm⁻¹. -2 40 mA cm -2 20 mA cm -2 1 mA cm -2 The voltage remains stable even at high current densities, with no significant voltage decay, demonstrating excellent stability and reversibility.

[0033] like Figure 9 As shown, at 20 mA cm -2 The cell was subjected to constant discharge at a current density for 1 h. The mass change of the aluminum electrode before and after discharge was measured, and the full cell capacity density was calculated. The results show that the full cell has a capacity density of 20 mA cm⁻¹. -2 Under certain conditions, the capacity density can reach 1250.30 mAh g. -1 .

[0034] like Figure 10 As shown, a full-cell cycle discharge performance test was conducted, with the battery at 20 mA cm⁻¹.-2 The catalyst was discharged at a constant current density for 60 min, followed by a 20 min resting period to measure the open-circuit potential, constituting one complete cycle. The cycle test results demonstrate that the catalyst system exhibits excellent stability during multiple battery start-ups and shutdowns, as well as prolonged discharges.

[0035] It should be understood that the above description of the preferred embodiments is quite detailed, but it should not be considered as a limitation on the scope of protection of this invention. Those skilled in the art, under the guidance of this invention, can make substitutions or modifications without departing from the scope of protection of the claims of this invention, and all such substitutions or modifications fall within the scope of protection of this invention. The scope of protection of this invention should be determined by the appended claims.

Claims

1. A method for preparing a manganese dioxide-supported single-atom silver catalyst, characterized in that, Includes the following steps: S1. A certain mass of potassium permanganate, manganese sulfate monohydrate and silver nitrate are respectively mixed with deionized water to prepare solutions of different concentrations; S2. Add manganese sulfate monohydrate solution to potassium permanganate solution and stir magnetically. Add conductive carbon black during stirring and mix evenly to obtain mixed solution A. S3. Continue to maintain the magnetic stirring speed of S2, and add silver nitrate solution dropwise to mixed solution A to obtain mixed solution B; S4. Transfer the mixed solution B to the reactor for hydrothermal reaction. Centrifuge the reacted material to obtain the precipitate. After drying and grinding, obtain the catalyst MnO2 / C-Ag, which is a manganese dioxide supported single-atom silver catalyst.

2. The method for preparing a manganese dioxide-supported single-atom silver catalyst according to claim 1, characterized in that, The amount of silver nitrate used is 0.001~0.05g, and the mass ratio of potassium permanganate, manganese sulfate monohydrate and silver nitrate is 36.01~36.20:58.01~58.50:

1.

3. The method for preparing a manganese dioxide-supported single-atom silver catalyst according to claim 1, characterized in that, The magnetic stirring speed in steps S2 and S3 is 300 rpm.

4. The method for preparing a manganese dioxide-supported single-atom silver catalyst according to claim 1, characterized in that, In step S4, the hydrothermal reaction temperature is 160 ℃, the reaction time is 12 h, the centrifugation speed is 10000 rpm, the centrifugation time is 5 min, the drying temperature is 55 ℃, and the drying time is 12 h.

5. A method for preparing a positive electrode film, characterized in that, Includes the following steps: The manganese dioxide-supported single-atom silver catalyst as described in any one of claims 1-4, 60 wt.% PTFE emulsion, and ethanol were placed in a beaker and mixed. The beaker was heated in a water bath while being magnetically stirred. After the ethanol evaporated, a black dough-like substance was obtained. The black dough-like substance is rolled into a thin film. Then, it is repeatedly stacked in the order of waterproof and breathable membrane, nickel mesh, waterproof and breathable membrane, and catalyst film. After being rolled into a sheet, it is cut into appropriate sizes and aged to obtain the positive electrode film.

6. The method for preparing a positive electrode film according to claim 5, characterized in that, The mixing ratio of the manganese dioxide-supported single-atom silver catalyst, 60 wt.% PTFE emulsion, and ethanol is 1g:1.5g:50ml.

7. The method for preparing a positive electrode film according to claim 5, characterized in that, The water bath heating temperature is 80 ℃, and the magnetic stirring speed is 500 rpm.

8. The method for preparing a positive electrode film according to claim 5, characterized in that, The positive electrode film has a thickness of 0.15 mm, and the aging treatment conditions are: heating to 200 °C at a heating rate of 5 °C / min in an argon atmosphere in a tube furnace, and heating for 1 h.

9. An alkaline aluminum-air battery, comprising a full battery, an alkaline electrolyte, and a peristaltic pump, characterized in that, The full battery includes a battery clamp, which comprises a sealing rubber gasket, a reaction chamber, and a battery template. The reaction chamber is composed of an inlet pipe, a reaction cavity, and an outlet pipe, forming a single unit. The reaction area of ​​the reaction cavity is 1 cm². 2 The sealing rubber gasket is attached to both sides of the reaction chamber. By attaching the aluminum sheet and the positive electrode film to the sealing rubber gasket and closing the battery template, a full battery assembly is completed. The alkaline electrolyte is 4 mol / L. -1 KOH solution. The alkaline electrolyte is stored in an electrolyte storage tank and connected to a peristaltic pump via a circulation pipe; The circulation pipe is connected to the inlet pipe and the outlet pipe; The positive electrode film is prepared by the preparation method described in claim 5.

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