Normal-temperature liquid-phase preparation method of MnO2 with crystalline / amorphous structure

Abstract

The invention belongs to the field of synthesis of inorganic nano materials, and particularly relates to a normal-temperature liquid-phase preparation method of MnO2 with a crystalline / amorphous structure. A normal-temperature liquid-phase preparation method of MnO2 with a crystalline / amorphous structure comprises the following steps: (1) dissolving a certain amount of manganese sulfate in deionized water, and then carrying out ultrasonic treatment, (2) adding a sodium hypochlorite aqueous solution into the manganese sulfate solution subjected to the ultrasonic treatment, and uniformly stirring and mixing at room temperature, thereby obtaining the MnO2 with the crystalline / amorphous structure. (3) carrying out sealed reaction on the suspension obtained in the step (2) at room temperature for several minutes; and (4) carrying out suction filtration on the product obtained after the reaction by using deionized water, washing and drying. The preparation method provided by the invention is simple and convenient to control, the reaction can be completed at room temperature, the method can be used for industrial large-scale production, and the prepared MnO2 with the crystalline / amorphous structure has good performance in electrochemical application.

Description

Technical Field

[0001] The present invention belongs to the field of inorganic nanomaterial synthesis, and particularly relates to a method for preparing MnO₂ with a crystalline / amorphous structure at room temperature in a liquid phase. Background Art

[0002] Manganese oxides and their derivatives have always been the focus in the field of electrochemistry. The variable valence state of Mn endows MnO₂ with good electrochemical properties. Its unique crystal structure and porous morphology provide a high specific surface area and good ion / electron transport channels, which contribute to improving the electrochemical properties of electrode materials. In addition, manganese oxide has high chemical stability and shows good durability under a wide potential range and different pH conditions, being suitable for long-term use. It exhibits excellent electrochemical activity in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and can significantly improve the charge-discharge efficiency and cycle stability of the battery. In addition, MnO₂ has a low cost, and can greatly reduce the battery manufacturing cost compared with noble metal catalysts (such as Pt, Ir). Its low cost, environmental friendliness and abundant natural resources also make it an ideal alternative material to traditional noble metal catalysts.

[0003] In recent years, amorphous metal oxides have received extensive attention due to their unique advantages, such as flexible structure, many defect structures and rich active centers. The oxides show remarkable activity in the oxygen evolution reaction. Although amorphous electrocatalysts have rich active centers, their poor stability hinders their large-scale application. Summary of the Invention

[0004] In order to overcome the disadvantages and deficiencies existing in the prior art, the primary object of the present invention is to provide a method for preparing MnO₂ with a crystalline / amorphous structure at room temperature in a liquid phase. The present invention prepares MnO₂ with a crystalline / amorphous structure by a simple chemical deposition method at room temperature.

[0005] The object of the present invention is achieved by the following technical solutions: A method for preparing MnO₂ with a crystalline / amorphous structure at room temperature in a liquid phase, comprising the following steps: (1) Dissolve a certain amount of manganese sulfate in deionized water, and then perform ultrasonic treatment; (2) Add an aqueous solution of sodium hypochlorite to the manganese sulfate solution after the ultrasonic treatment, and stir and mix evenly at room temperature; (3) Seal and react the suspension obtained in the above step at room temperature for several minutes; (4) After the reaction, filter, wash and dry the obtained product with deionized water.

[0006] The concentration of the manganese sulfate solution in the step (1) is 1-10 wt%.

[0007] The molar ratio of manganese sulfate to sodium hypochlorite in the step (1) is 1:(4-20).

[0008] The mass fraction of the sodium hypochlorite aqueous solution in step (2) is 7.5%.

[0009] The reaction time in step (3) is 15 minutes to 24 hours.

[0010] The present invention has the following advantages and effects compared with the prior art:

[0011] The preparation method provided by the present invention is simple and easy to control, the reaction can be completed at room temperature, it can be used for industrial scale-up production, and the prepared MnO2 with crystalline / amorphous structure has good performance in electrochemical applications. Description of the Drawings

[0012] Figure 1 It is the X-ray diffraction pattern of the catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention.

[0013] Figure 2 It is the scanning electron microscope image of the catalyst prepared in Example 1 of the present invention.

[0014] Figure 3 It is the transmission electron microscope image of the catalyst prepared in Example 1 of the present invention.

[0015] Figure 4 It is the transmission electron microscope image of the catalyst prepared in Comparative Example 1 of the present invention.

[0016] Figure 5 It is the scanning electron microscope image of the catalyst prepared in Comparative Example 2 of the present invention. Detailed Embodiments

[0017] The present invention will be further described below with reference to the embodiments. These embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following examples are usually carried out according to the conventional conditions in the art or according to the conditions recommended by the manufacturer; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention fall within the scope of protection required by the present invention.

[0018] Example 1

[0019] A method for preparing crystalline / amorphous MnO₂ at room temperature in liquid phase, comprising the following steps: Dissolve 5.9 mmol of MnSO₄ in 50 mL of deionized water, and then perform ultrasonic treatment for 2 minutes. Then add 40 ml of 7.5 wt% NaClO aqueous solution, stir and mix evenly at room temperature, and then seal and react for 15 minutes. After the reaction, a black precipitate is obtained. Filter the obtained product by suction, wash it with deionized water until the filtrate is transparent, and dry it at 60 °C to obtain crystalline / amorphous MnO₂. Subsequently, we tested and characterized the MnO₂ obtained above, and its XRD diffraction pattern is as Figure 1 shown. It can be seen from the figure that the prepared manganese oxide corresponds to MnO₂ indicated by the JCPDF standard card PDF#43-1456, and the weak and broad peaks shown in the XRD diffraction pattern correspond to the amorphous structure of the sample. From the scanning electron microscope image of the MnO₂ prepared in this example ( Figure 2 ), it can be seen that the MnO₂ is a nano-microsphere with wrinkles on the surface. From Figure 3 in the FETEM image, no long-range ordered lattice fringes are found, but there are quite a lot of short-range ordered lattice fringes in the nano-scale crystal regions, indicating that the crystalline / amorphous structure has been successfully constructed.

[0020] Comparative Example 1

[0021] A method for preparing MnO₂, comprising the following steps: Dissolve 5.9 mmol of MnSO₄ in 50 mL of deionized water, and then perform ultrasonic treatment for 2 minutes. Then add 1 g of 40 wt% NaMnO₄ aqueous solution, stir and mix evenly at room temperature, and then seal and react for 24 hours. After the reaction, a black precipitate is obtained. Filter the obtained product by suction, wash it with deionized water until the filtrate is transparent, and dry it at 60 °C to obtain amorphous MnO₂.

[0022] The XRD diffraction pattern of the product of this comparative example is as Figure 1 shown. It can be known that the prepared manganese oxide corresponds to MnO₂ indicated by the JCPDF standard card PDF#43-1456. Compared with the example, the diffraction peak near 12.2° disappears, indicating that the amorphization of the manganese oxide structure is enhanced. From Figure 4 in the FETEM image, no ordered lattice fringes are found, indicating that amorphous manganese oxide is constructed.

[0023] Comparative Example 2

[0024] A method for preparing γ-MnO₂, comprising the following steps: Dissolve 5.9 mmol of MnSO₄ in 50 mL of deionized water, and then perform ultrasonic treatment for 2 minutes. Then add 5 ml of 7.5 wt% NaClO aqueous solution, stir and mix evenly at room temperature, and then seal and react for 24 hours. After the reaction, a black precipitate is obtained. Filter the obtained product by suction, wash it with deionized water until the filtrate is transparent, and dry it at 60 °C to obtain γ-MnO₂.

[0025] The XRD diffraction pattern of the product of this comparative example is as Figure 1 shown. It can be seen that the prepared manganese oxide corresponds to γ-MnO2 indicated by the JCPDF standard card PDF#14-0644. It shows that crystalline / amorphous manganese oxide cannot be prepared when the amount of aqueous NaClO solution is small and the reaction time is long. From Figure 5 the scanning electron microscopy (SEM) image in

[0026] The above embodiments are preferred embodiments of the present invention. However, the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for preparing MnO₂ with a crystalline / amorphous structure at room temperature in a liquid phase, characterized in that, It includes the following steps: (1) Dissolve a certain amount of manganese sulfate in deionized water, and then perform ultrasonic treatment. (2) Add an aqueous solution of sodium hypochlorite to the manganese sulfate solution after the above ultrasonic treatment, and stir and mix evenly at room temperature. (3) Seal and react the suspension obtained in the above steps at room temperature for several minutes. (4) After the reaction, filter, wash, and dry the obtained product with deionized water.

2. The room-temperature liquid-phase preparation method of MnO₂ with a crystalline / amorphous structure according to claim 1, characterized in that, The concentration of the manganese sulfate solution in step (1) is 1-10 wt%.

3. The room-temperature liquid-phase preparation method of MnO₂ with a crystalline / amorphous structure according to claim 1, characterized in that, The molar ratio of manganese sulfate to sodium hypochlorite in step (2) is 1:(4-20).

4. The room-temperature liquid-phase preparation method of crystalline / amorphous MnO₂ according to claim 1, characterized in that, The mass fraction of the aqueous solution of sodium hypochlorite in step (2) is 7.5%.

5. The room-temperature liquid-phase preparation method of crystalline / amorphous-structured MnO₂ according to claim 1, characterized in that, The reaction time in step (3) is 15 minutes to 24 hours.

6. The room-temperature liquid-phase preparation method of crystalline / amorphous MnO2 according to claim 1, characterized in that, The manganese oxide obtained after the reaction in step (4) is MnO2 with a crystalline / amorphous structure.

Images