A method for preparing high-purity manganese dioxide as an oxygen electrode catalyst for zinc-air batteries

Abstract

This invention discloses a method for preparing high-purity manganese dioxide, an oxygen electrode catalyst for zinc-air batteries. Addressing the environmental problems associated with using concentrated sulfuric acid or nitric acid as catalysts in the preparation of manganese dioxide for oxygen reduction batteries, as well as the corrosion of production equipment and safety hazards to operators during the production process, this invention proposes a method using a solid acid catalyst, acidic cation exchange resin, to replace concentrated sulfuric acid or nitric acid as the acid catalyst for preparing manganese dioxide for oxygen reduction batteries. Acidic cation exchange resins, especially strongly acidic cation exchange resins, contain sulfonic acid groups, which can completely ionize to release hydrogen ions, thus replacing sulfuric acid or nitric acid as the acid catalyst for preparing manganese dioxide. Furthermore, strongly acidic cation exchange resins can be regenerated and recycled.

Description

Technical Field

[0001] This invention relates to the field of chemical materials technology, specifically to a method for preparing high-purity manganese dioxide as an oxygen electrode catalyst for zinc-air batteries. Background Technology

[0002] Zinc-air batteries are favored for their high energy density, low cost, and stable performance, but air batteries also suffer from a low oxygen reduction rate. Many studies have shown that noble metals perform better in catalyzing oxygen reduction, but their high price hinders large-scale commercial application.

[0003] Due to its unique polycrystalline structure, outstanding physicochemical properties (superior oxygen reduction catalytic performance), environmental friendliness, and low price, manganese dioxide has not only become a research hotspot in the industry but has also been widely used as a catalytic material for the oxygen reduction electrode in zinc-air batteries.

[0004] However, the current commercial production process for manganese dioxide, a catalyst for oxygen reduction electrodes, generally uses concentrated sulfuric acid or nitric acid as a catalyst. Both concentrated sulfuric acid and nitric acid not only easily corrode equipment but also pose potential safety hazards to production operators. In particular, they generate large amounts of acidic waste liquid that require treatment, significantly increasing production costs. Furthermore, even after treatment, they still place a tremendous burden on the environment.

[0005] Therefore, under the current trend of increasingly pursuing green production, there is an urgent need to provide an environmentally friendly preparation method to solve the environmental problems caused by using concentrated sulfuric acid or nitric acid as catalysts. Summary of the Invention

[0006] In view of this, to solve the aforementioned technical problems, the purpose of this invention is to propose a method for preparing high-purity manganese dioxide, an oxygen electrode catalyst for zinc-air batteries. Addressing the environmental problems associated with using concentrated sulfuric acid or nitric acid as catalysts, as well as the corrosion of production equipment and safety hazards to operators during the production process, this invention uses an acidic cation exchange resin instead of concentrated sulfuric acid as the acid catalyst to prepare the oxygen reduction catalyst manganese dioxide. This not only allows for regeneration and recycling, reducing production costs, but also significantly reduces the generation of waste acid. Furthermore, in actual production, it eliminates the safety hazards posed by concentrated sulfuric acid to production equipment and operators.

[0007] The technical solution adopted is as follows:

[0008] A method for preparing high-purity manganese dioxide as an oxygen electrode catalyst for zinc-air batteries includes the following steps:

[0009] S1. Take acidic cation exchange resin and add water to soak the acidic cation exchange resin. Stir until it is smooth. While stirring, cool down to a low temperature. Then add high-purity graphite and stir for 20 minutes to make the graphite evenly dispersed in the system.

[0010] S2. Continue to add KMnO4 under stirring conditions, stir for 20 min until homogeneous, and react for 24 h under low temperature conditions;

[0011] S3. After the reaction is complete, add 3 times the volume of clear saturated saline solution, stir for 10 minutes, let stand, and allow the acidic cation exchange resin to float. Then, use a filter bag to remove the floating acidic cation exchange resin.

[0012] S4. Use PP filter cloth to filter out the solid precipitate, and then wash it repeatedly with deionized water until the pH of the washing solution is 7.

[0013] S5. Filter the solid product and place it in an 80°C forced-air drying oven to dry for 24 hours. After drying, manganese dioxide product is obtained.

[0014] S6. Prepare a working electrode using the obtained manganese dioxide material and characterize its electrochemical performance.

[0015] Furthermore, in S1, the acidic cation exchange resin is a strong acidic cation exchange resin or a weak acidic cation exchange resin.

[0016] Furthermore, in S1, the acidic cation exchange resin is a strongly acidic cation exchange resin, which is a macroporous or gel-type strongly acidic cation exchange resin.

[0017] Furthermore, in S1 and S2, the molar ratio of KMnO4 to graphite is greater than 4:3.

[0018] Further, in S2, the low temperature condition is -10 to 10°C. Preferably, it is -5 to 5°C, and more preferably, it is 0°C.

[0019] Furthermore, in S2, the low-temperature condition is -5 to 5°C.

[0020] Furthermore, in S2, the low-temperature condition is 0°C.

[0021] The beneficial effects of this invention are as follows:

[0022] This invention addresses the environmental problems associated with using concentrated sulfuric acid or nitric acid as catalysts in the preparation of manganese dioxide, a catalyst material for oxygen reduction batteries, as well as the corrosion of production equipment and safety hazards to operators during the production process. It proposes a method for preparing manganese dioxide as an oxygen reduction catalyst using a solid acid catalyst, acidic cation exchange resin, instead of concentrated sulfuric acid or nitric acid. Acidic cation exchange resins, especially strongly acidic cation exchange resins, contain sulfonic acid groups, which can completely ionize to release hydrogen ions, thus replacing sulfuric acid or nitric acid as an acid catalyst in the preparation of manganese dioxide. Furthermore, strongly acidic cation exchange resins can be regenerated and recycled. Attached Figure Description

[0023] Figure 1 The graph shows the electrochemical performance characterization results of the working electrode prepared in Example 1.

[0024] Figure 2 The graph shows the electrochemical performance characterization results of the working electrode prepared in Example 2.

[0025] Figure 3 The graph shows the electrochemical performance characterization results of the working electrode prepared in Example 3.

[0026] Figure 4 The graph shows a comparison of the electrochemical performance characterization results of the working electrodes prepared in Examples 1-3 and Comparative Example 1.

[0027] Figure 5 The image shows the XRD pattern of the sample. Detailed Implementation

[0028] The present invention will be described in detail below through specific embodiments. However, the uses and purposes of these exemplary embodiments are only for illustrating the present invention and do not constitute any limitation on the actual protection scope of the present invention, nor are they intended to limit the protection scope of the present invention to these embodiments.

[0029] Example 1

[0030] The preparation method of high-purity manganese dioxide catalyst for the oxygen electrode of zinc-air battery in this embodiment includes the following steps:

[0031] I. Preparation of Manganese Dioxide

[0032] S1. Take 20 mL of strong acid cation exchange resin (model: 001×7), add 100 mL of deionized water, stir for 5 min, then add 1.2 g of high-purity graphite, stir for 20 min, so that the graphite and strong acid cation exchange resin are evenly mixed.

[0033] S2. Cool down to 0℃, add 25g KMnO4 (purity >99.5%) under stirring, stir for 20min until uniform, and then let the reaction stand at 0℃ for 24h.

[0034] S3. Filter the mixture of manganese dioxide solid and strong acid cation exchange resin into 100 ml of clear saturated saline solution. The strong acid cation exchange resin will float to the top, while the manganese dioxide solid will sink. Scoop out the floating strong acid cation exchange resin, then filter to obtain the manganese dioxide solid precipitate.

[0035] S4. Wash the manganese dioxide solid precipitate with deionized water until the pH of the washing solution is neutral. Place the washed manganese dioxide solid in an 80℃ drying oven for 24 hours to obtain 11.02g of high-purity manganese dioxide solid (purity ≈99.50%), with a yield of about 95.0%.

[0036] II. Electrode Preparation

[0037] S6. The gas diffusion electrode is mainly composed of three layers: activated carbon on the side in contact with the electrolyte, a waterproof diffusion layer on the side facing the air, and a nickel mesh current collector in the middle. The active layer is composed of the prepared manganese dioxide catalyst (80% by mass), conductive agent Vulcan XC-72 (10wt%) and PTFE (10%).

[0038] S7. Add anhydrous ethanol to form a slurry. Then, use two pieces of nickel foam in a sandwich-like structure and press for 3 minutes under a pressure of 5×103 kg·cm-2 and a temperature of 120℃ to obtain the working electrode. The catalyst loading is 5 mg·cm-2.

[0039] The air diffusion electrode prepared in this embodiment underwent linear scanning in 6 mol / L KOH solution at a scan rate of 1 mV / s. The electrochemical performance characterization results of the working electrode are as follows: Figure 1 As shown.

[0040] Example 2

[0041] In this embodiment, the preparation method of high-purity manganese dioxide as the oxygen electrode catalyst for a zinc-air battery involves immersing the strongly acidic cation exchange resin used in Example 1 in 5% hydrochloric acid for 2 hours. Then, it is washed with deionized water until the pH of the washing solution reaches 6-7. The hydrogen ion concentration of the used hydrochloric acid is measured; if necessary, an appropriate amount of hydrochloric acid can be added to achieve a hydrogen ion concentration of 1.40 M for regeneration.

[0042] Following the process described in Example 1, manganese dioxide was prepared by catalysis using regenerated resin. 10.98 g of high-purity manganese dioxide solid was obtained, with a purity of approximately 99.45% and a yield of approximately 94.69%, showing no significant difference from Example 1.

[0043] Electrode preparation and electrochemical performance testing were performed according to the method in Example 1, and the results are as follows: Figure 2 As shown, there is no difference from Example 1, which demonstrates that the regenerated exchange resin is feasible.

[0044] Example 3

[0045] In this embodiment, the preparation method of high-purity manganese dioxide as the oxygen electrode catalyst for a zinc-air battery involves immersing the strongly acidic cation exchange resin used in Example 2 in 5% hydrochloric acid for 2 hours. Then, it is washed with deionized water until the pH of the washing solution reaches 6-7. The hydrogen ion concentration of the used hydrochloric acid is measured; if necessary, an appropriate amount of hydrochloric acid can be added to achieve a hydrogen ion concentration of 1.40 M for regeneration.

[0046] Following the process described in Example 1, manganese dioxide was prepared by catalysis using regenerated resin. 10.88 g of high-purity manganese dioxide solid was obtained, with a purity of approximately 99.15% and a yield of approximately 93.79%, showing no significant difference from Example 1.

[0047] Electrode preparation and electrochemical performance testing were performed according to the method in Example 1, and the results are as follows: Figure 3 As shown, there is no difference from Example 1, which demonstrates that the regenerated exchange resin is feasible.

[0048] Comparative Example 1

[0049] The preparation method of high-purity manganese dioxide catalyst for the oxygen electrode of the zinc-air battery in this comparative example includes the following steps:

[0050] I. Preparation of Manganese Dioxide

[0051] S1. Take 50 mL of 18.4 M sulfuric acid (analytical grade) and store it at -5 °C for 0.5 h. Then, add 1.2 g of high-purity graphite and stir for 20 min to make the graphite uniformly dispersed in the sulfuric acid solution.

[0052] S2. Add 25g KMnO4 (purity >99.5%, analytical grade), stir well, and place the reaction solution at -5℃ for 24h. The product is washed repeatedly with distilled water until the pH of the washing solution is 7. After filtration, the product is dried in an 80℃ forced-air drying oven for 24h to obtain 9.64g of manganese dioxide solid (purity ≈99.05%), with a yield of 83.14%.

[0053] Electrode preparation and electrochemical performance testing were performed according to the method in Example 1. The results compared with the previous three examples are as follows: Figure 4 As shown, the results indicate that the linear scan of catalytic oxygen reduction is basically consistent between the preparation of manganese dioxide using strong acid cation exchange resin and the direct use of strong acid. This suggests that renewable strong acid cation exchange resin can be used for preparation, achieving "zero" acid emissions.

[0054] The samples prepared in this embodiment are all α-type manganese dioxide, and the XRD patterns are shown below. Figure 5 As shown. Under the condition of adjusting the acid concentration, it is possible to prepare manganese dioxide with different morphologies or different crystal forms in this embodiment, all of which are within the scope of this patent. The morphology of the product can be granular, linear, or flower-like.

[0055] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing high purity zinc-air battery oxygen electrode catalyst manganese dioxide, characterized in that, The method comprises the following steps: S1. Take an acidic cation exchange resin, add water, soak the acidic cation exchange resin, just stir smoothly, and then add high-purity graphite under the condition of low temperature while stirring, stir for 20 min, and then make the graphite uniformly dispersed in the system; S2. Continue to add KMnO4 under stirring, stir for 20 min to be uniform, and then react for 24 h under the condition of low temperature; S3. After the reaction is completed, add 3 times the volume of clear saturated brine, stir for 10 min, stand still, make the acidic cation exchange resin float, and then use a filter bag to fish out the floating acidic cation exchange resin; S4. Use a PP filter cloth to filter out the solid precipitate, and then use deionized water to wash multiple times until the PH of the washing liquid is 7; S5. Filter the solid product, and then place it in a blast drying oven at 80℃ to dry for 24 h, and then the manganese dioxide product is obtained after drying; S6. Use the obtained manganese dioxide material to prepare a working electrode, and then characterize the electrochemical performance.

2. The method of claim 1, wherein the method is characterized by: In S1, the acidic cation exchange resin is a strong acidic cation exchange resin or a weak acidic cation exchange resin.

3. The method for preparing high-purity manganese dioxide as the oxygen electrode catalyst for zinc-air batteries according to claim 2, characterized in that, In S1, the acidic cation exchange resin is a macroporous strong acidic cation exchange resin or a gel type strong acidic cation exchange resin.

4. The method of claim 1, wherein the method is characterized by: In S1 and S2, the molar ratio of KMnO4 to the graphite is greater than 4:

3.

5. The method of claim 1, wherein the method is characterized by: In S2, the low temperature condition is -10~10℃.

6. The method of claim 5, wherein the manganese dioxide is prepared by the steps of: a) mixing manganese carbonate with a reducing agent; b) heating the mixture to a temperature of 300-400°C; c) cooling the mixture to room temperature; d) mixing the cooled mixture with a solvent; and e) filtering the mixture to obtain the manganese dioxide. In S2, the low temperature condition is -5~5℃.

7. The method of claim 6, wherein the manganese dioxide is prepared by the steps of: a) mixing manganese carbonate with a reducing agent; b) heating the mixture to a temperature of 300-400°C; c) cooling the mixture to room temperature; d) mixing the cooled mixture with a solvent; and e) filtering the mixture to obtain the manganese dioxide. In S2, the low temperature condition is 0℃.

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