Single-layer manganese dioxide nano material prepared by confinement dissolution method as well as preparation method and application thereof

Abstract

The invention provides a single-layer manganese dioxide nano material prepared by a confinement dissolution method as well as a preparation method and application thereof. The preparation method comprises the following steps: preparing manganese-based layered hydroxide; synthesizing a MnO2 nanosheet precursor; and carrying out confinement dissolution on the MnO2 nanosheet precursor, and carrying out confinement growth on the Mn-based oxide to obtain the single-layer manganese dioxide nano material. The obtained single-layer manganese dioxide nano material is uniform in transverse size, the single-layer rate is larger than or equal to 95%, the thickness is 0.4-0.8 nm, the specific surface area is large, rich defect sites are contained, and the single-layer manganese dioxide nano material can be stably dispersed in water under extremely high concentration, can be used as a good carrier for loading precious metal and shows excellent performance in the electrocatalytic hydrogen evolution process; meanwhile, great advantages are shown in the aspect of reducing the dosage of precious metal, so that the method has great application prospects in the field of electrocatalysis.

Description

Technical Field

[0001] The present invention belongs to the field of materials, and particularly relates to a confined dissolution method for monolayer manganese dioxide nanomaterials, a preparation method thereof, and an application thereof. Background Art

[0002] Manganese dioxide (MnO2), as a typical transition metal oxide, exhibits unique advantages in the fields of energy storage, catalytic conversion, and environmental remediation due to its rich crystal structures (such as α, β, δ, γ types, etc.) and adjustable nano-morphologies. The basic crystal unit of it is [MnO6] octahedron. Notably, when the dimension of MnO2 is reduced to the atomic monolayer thickness (<1.0 nm), its specific surface area can surge to the theoretical maximum value, exposing a high proportion of edge active sites. These characteristics endow it with excellent performance potential in the fields of electrocatalysis, supercapacitors, biomedicine, electrode materials, heavy metal adsorbents, and sensors.

[0003] Currently, the preparation of ultrathin MnO2 nanosheets mainly relies on two types of strategies: one is the redox reaction synthesis method based on precursors, and the other is the exfoliation method based on layered precursors. However, both of these methods have obvious limitations in the preparation of ultrathin MnO2 nanosheets. For the redox synthesis method, as shown in Chinese Patent CN106006746A, the MnO2 nanosheets prepared with potassium permanganate as the manganese source, ethylene glycol as the reducing agent, and sodium dodecyl sulfate as the surfactant have a thickness of 70 - 160 nm, which are actually stacked by hundreds of nanosheets, and the nanosheet thickness is relatively thick. For the exfoliation method, as shown in Chinese Patent CN108557893A, although ultrathin MnO2 nanosheets can be obtained by combining the layered MnO2 bulk nanomaterials with surfactant-assisted exfoliation, the monolayer rate of the exfoliated nanosheets is extremely low, and the exfoliation degree is uncontrollable, resulting in problems such as uneven thickness of the ultrathin nanosheets and wide lateral size distribution. Currently, there is a lack of a controllable preparation strategy to achieve the preparation of high-monolayer-rate MnO2 nanosheets. Therefore, developing a method for preparing monolayer MnO2 nanosheets with a high monolayer rate and scalable production is of great significance for promoting its applications in fields such as efficient catalysis and highly sensitive sensors. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the present invention provides a confined dissolution method for monolayer manganese dioxide nanomaterials, a preparation method thereof, and an application thereof. The monolayer MnO2 nanomaterials prepared by the present invention have a thickness of 0.4 - 0.8 nm, a monolayer rate ≥ 95%, uniform lateral dimensions, a very large specific surface area, and rich defect active sites on the surface. By anchoring a small amount of noble metals, the utilization efficiency of noble metals can be greatly improved, showing excellent electrocatalytic performance, greatly reducing the amount of noble metals used, and showing broad electrocatalytic application prospects.

[0005] The technical solution of the present invention is as follows: The present invention provides a confined dissolution method for monolayer manganese dioxide nanomaterials. The thickness of the manganese dioxide nanomaterials is 0.4 - 0.8 nm, belonging to single-molecule layer MnO2 nanosheets, with a monolayer rate ≥ 95%, a lateral size of 20 - 100 nm, and a specific surface area of 106 m 2 / g.

[0006] The present invention provides a preparation method for the above-mentioned confined dissolution method of monolayer manganese dioxide nanomaterials, including the steps: S1, preparation of manganese-based layered hydroxides; S2, synthesis of MnO2 nanosheet precursors; S3, confined dissolution of MnO2 nanosheet precursors and confined growth of Mn-based oxides to obtain monolayer manganese dioxide nanomaterials.

[0007] Preferably according to the present invention, in step S1, the manganese-based layered hydroxides are prepared by coprecipitation, hydrothermal method, mechanochemical method or reverse microemulsion method.

[0008] Preferably, the manganese-based layered hydroxides are prepared by coprecipitation or hydrothermal method: 1) Coprecipitation method: Dissolve manganese salts and metal salts in water to obtain solution A; simultaneously drip solution A and alkali solution into degassed water; then, after aging, filter, wash, and dry to obtain manganese-based layered hydroxides; 2) Hydrothermal method: Dissolve manganese salts, metal salts and urea in water, perform hydrothermal treatment, filter, wash, and dry to obtain manganese-based layered hydroxides.

[0009] Further preferably, in the preparation of manganese-based layered hydroxides by coprecipitation or hydrothermal method, the manganese salts are selected from one or a combination of two or more of Mn(NO3)2, MnSO4, MnCl2, Mn(CH3COO)2 or MnBr2; the metal salts are nitrates, hydrochlorides or sulfates of metals; the metal ions in the metal salts are selected from Mg 2+ , Cu 2+ , Zn 2+ , Ca 2+ , Co 2+ , Fe 2+ , Ni 2+ , Al 3+ or Fe 3+ in one or a combination of two or more of them.

[0010] Further preferably, in the preparation of manganese-based layered hydroxides by coprecipitation or hydrothermal method, the molar ratio of manganese salts to metal salts is (2 - 4):1.

[0011] Further preferably, in the preparation of manganese-based layered hydroxide by the coprecipitation method, the metal ion concentration of the metal salt in solution A is 0.01 - 2 mol / L.

[0012] Further preferably, in the preparation of manganese-based layered hydroxide by the coprecipitation method, the lye is an aqueous solution of potassium hydroxide, an aqueous solution of sodium hydroxide or ammonia water; the mass concentration of the lye is 5 - 25%.

[0013] Further preferably, in the preparation of manganese-based layered hydroxide by the coprecipitation method, the volume ratio of solution A to degassed water is (5 - 20):1.

[0014] Further preferably, in the preparation of manganese-based layered hydroxide by the coprecipitation method, the dropping is carried out under stirring and inert gas protection, and the pH of the reaction system is controlled to be 10 - 14.0 during the dropping process. The inert gas is nitrogen or argon.

[0015] Further preferably, in the preparation of manganese-based layered hydroxide by the coprecipitation method, the amount of the lye is used to adjust the pH of the final reaction system to 10 - 14.0.

[0016] Further preferably, in the preparation of manganese-based layered hydroxide by the coprecipitation method, the aging temperature is 20 - 100 °C, the aging time is 5 - 24 h, and the aging is carried out under stirring and inert gas protection. The inert gas is nitrogen or argon.

[0017] Further preferably, in the preparation of manganese-based layered hydroxide by the hydrothermal method, the molar ratio of manganese salt to urea is 1:(4 - 20).

[0018] Further preferably, in the preparation of manganese-based layered hydroxide by the hydrothermal method, the molar amount of the manganese salt and the volume ratio of water is 0.01 - 1 mol / L.

[0019] Further preferably, in the preparation of manganese-based layered hydroxide by the hydrothermal method, the hydrothermal treatment temperature is 120 - 180 °C, and the hydrothermal treatment time is 12 - 72 h.

[0020] According to the preference of the present invention, in step S2, the synthesis of the MnO2 nanosheet precursor is obtained by calcining the manganese-based layered hydroxide.

[0021] Preferably, the calcination temperature is 400 - 800 °C, and the calcination time is 1 - 5 h.

[0022] Preferably according to the present invention, in step S3, the synthesis method of the single-layer manganese dioxide nanomaterial is as follows: in an acidic environment, after the MnO2 nanosheet precursor is confined and dissolved, the Mn-based oxide is confined in the lamellar structure, and the single-layer manganese dioxide nanomaterial is obtained by confined growth along the lamellar structure. During the processes of confined dissolution and confined growth, metal elements other than Mn are etched and diffused into the solution, and the confined growth of the Mn-based oxide is restricted in the lamellar structure, and finally, MnO2 nanosheets with a single molecular layer thickness are formed.

[0023] Preferably according to the present invention, in step S3, the acidic environment is provided by an aqueous solution of an acid; the acid is selected from one or more mixed acids of inorganic acids or organic acids; the inorganic acid is selected from common inorganic acids such as hydrochloric acid, nitric acid or sulfuric acid, preferably sulfuric acid or nitric acid; the mass concentration of the aqueous solution of the acid is 3%-50%; the mass ratio of the MnO2 nanosheet precursor to the volume of the aqueous solution of the acid is 1: (30-100) g / mL.

[0024] Preferably according to the present invention, in step S3, the synthesis method of the single-layer manganese dioxide nanomaterial is as follows: disperse the MnO2 nanosheet precursor in an aqueous solution of an acid, and carry out confined dissolution and confined growth by ultrasonic stirring reaction at room temperature for 20-30 h, wash, and dry to obtain the single-layer manganese dioxide nanomaterial.

[0025] The present invention also provides the application of the above-mentioned single-layer manganese dioxide nanomaterial prepared by the confined dissolution method in electrocatalytic hydrogen evolution.

[0026] Preferably according to the present invention, the single-layer manganese dioxide nanomaterial is loaded with a noble metal for application in electrocatalytic hydrogen evolution. Preferably, the noble metal is Pt.

[0027] Preferably, the method for loading the noble metal on the single-layer manganese dioxide nanomaterial is as follows: Fully disperse the single-layer manganese dioxide nanomaterial in water, add a noble metal source, stir and react, filter, wash, dry, and then obtain the noble metal-MnO2 single-layer nanosheet catalyst through reduction.

[0028] Preferably, the mass ratio of the single-layer manganese dioxide nanomaterial to water is 1: (10-10000); the noble metal source is PtCl4; the mass ratio of the single-layer manganese dioxide nanomaterial to the noble metal source is (10-200):1; the stirring reaction temperature is room temperature, the stirring reaction time is 5-24 h; the reduction temperature is 300-650 °C, the reduction time is 0.5-3 h, the heating rate is 1-5 °C / min, and the reduction atmosphere is an Ar / H2 atmosphere.

[0029] The technical features and beneficial effects of the present invention are as follows: (1)The present invention utilizes a confinement dissolution and growth strategy to etch the remaining metal elements in the lamellar structure of the MnO2 nanosheet precursor. MnO2 is confined within the lamellae for confinement rearrangement growth, resulting in the preparation of single-layer MnO2 nanosheets with a thickness of 0.4 - 0.8 nm, a monolayer rate of ≥95%, uniform lateral dimensions of 20 - 100 nm, and a very large specific surface area.

[0030] (2)The surface of the single-layer MnO2 nanosheets synthesized by the confinement dissolution method contains a large number of defect sites, with a surface potential of 35 mV. They have excellent dispersion stability in water, with a maximum dispersion concentration of up to 5 g / L, which is of great significance in the fields of medicine, catalysis, and sensors.

[0031] (3)The surface of the single-layer MnO2 nanomaterial synthesized in the present invention has a large number of defect sites, which can anchor a small amount of noble metals. There is an excellent synergistic effect between the defects and the noble metals, which can greatly improve the utilization efficiency of the noble metals. In the fields of thermal catalysis, electrocatalysis, etc., it shows broad application prospects in high-stability, high-activity catalysts and reducing the use of extremely precious metals.

[0032] (4)The single-layer MnO2 nanomaterial synthesized in the present invention can exhibit excellent catalytic performance as a carrier for loading trace noble metals (such as Pt) during the electrocatalytic hydrogen evolution process. At a current density of 10 mA / cm -2 the overpotential is 29 mV, which is superior to that of commercial Pt / C catalysts (~40 mV); at an overpotential of 50 mV, the Pt mass activity is 76 times that of commercial Pt / C, greatly improving the utilization efficiency of the noble metals. At the same time, it has excellent stability and great application prospects in the field of catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Shows the XRD pattern of the single-layer MnO2 in Example 1 of the present invention.

[0034] Figure 2 Shows the TEM image of the single-layer MnO2 in Example 1 of the present invention.

[0035] Figure 3 Shows the HRTEM image of the single-layer MnO2 in Example 1 of the present invention.

[0036] Figure 4 Shows the AFM image of the single-layer MnO2 in Example 1 of the present invention.

[0037] Figure 5 Shows the nitrogen adsorption - desorption isotherm of the single-layer MnO2 in Example 1 of the present invention.

[0038] Figure 6 Shows the appearance photo of the single-layer MnO2 dispersion in Example 1 of the present invention.

[0039] Figure 7 shows the evaluation results of electrocatalytic hydrogen evolution performance, where Figure 7 a shows the linear sweep voltammetry curves of MnO2 in Example 1 of the present invention, Pt-MnO2 in the application example, and commercial Pt / C; Figure 7 b and Figure 7 c show the mass activities and the mass-specific activity diagrams at a 50 mV overpotential of Pt-MnO2 in the application example of the present invention and commercial Pt / C; Figure 7 d shows the stability test results of Pt-MnO2 in the application example of the present invention. Detailed implementation manners

[0040] The following further describes in detail the implementation manners of the present invention in conjunction with the drawings and examples. The following detailed description of the examples is used to exemplarily illustrate the present invention, but cannot be used to limit the scope of the present invention, that is, the present invention is not limited to the described examples.

[0041] Example 1 A preparation method of a single-layer manganese dioxide nanomaterial, comprising the steps of: (1) Dissolve 11.9 g (0.06 mol) of Mn(NO3)2·6H2O and 12.5 g (0.03 mol) of Al(NO3)3·9H2O in 200 mL of deionized water to obtain a mixed metal salt solution, and use ammonia water with a mass concentration of 5% as the alkali solution. Under nitrogen protection and magnetic stirring, simultaneously drop 200 mL of the mixed metal salt solution and the alkali solution into 20 mL of degassed water, control the relative dropping rate to maintain the pH value of the reaction system at 10.0, and the final pH of the system is 10.0 after dropping. Subsequently, stir at room temperature for 24 h under nitrogen protection, filter, wash, and dry to obtain Mn2Al LDHs.

[0042] (2) Calcinate the Mn2Al LDHs solid in a tube furnace at 500 °C for 1 hour to obtain a Mn2Al precursor, and the calcination atmosphere is nitrogen.

[0043] (3) Disperse 5 g of the Mn2Al precursor in 150 mL of a sulfuric acid aqueous solution with a mass concentration of 30%, ultrasonically stir for 24 h, filter, wash, and dry to obtain a single-layer manganese dioxide nanomaterial (single-layer MnO2 nanosheets).

[0044] Detect the single-layer manganese dioxide nanomaterial obtained in the above steps, Figure 1 shows the XRD (X-ray diffraction) pattern of the MnO2 material, which is consistent with the standard card JCPDS NO: 24-0735 (β-MnO2). Figure 2The TEM (transmission electron microscope) image of the MnO2 material of Example 1 is shown, showing the flaky morphology presented by the MnO2 nanosheets. Figure 3 The HRTEM (high-resolution transmission electron microscope) image of the MnO2 material is shown. The interplanar spacing of the MnO2 material is 0.24 nm, which is consistent with the (101) crystal plane of MnO2. Figure 4 The AFM (atomic force microscope) image of the MnO2 material is shown. The thickness of the synthesized MnO2 nanosheets is about 0.4 - 0.8 nm. Statistics show that the MnO2 monolayer rate ≥ 95%, and the lateral size of the nanosheets is uniform, with the lateral size of the nanosheets being 20 - 100 nm. Figure 5 It is the nitrogen adsorption - desorption isotherm of the MnO2 nanomaterial in Example 1. It is a type IV adsorption isotherm with an obvious H3 - type hysteresis loop, indicating the presence of a typical mesoporous structure. The specific surface area of the material reaches 106 m 2 / g. Figure 6 It is the appearance photo of the aqueous dispersion of the MnO2 nanomaterial in Example 1. The dispersion appears orange, and the color of the dispersion is dark brown at high concentrations. The MnO2 nanomaterial has extremely high dispersion stability, up to 5.0 g / L.

[0045] Example 2 A preparation method of a monolayer manganese dioxide nanomaterial is different from the preparation method of Example 1 only in that in step (1), 0.06 mol of MnCl2 and 0.03 mol of MgCl2 are respectively used to replace Mn(NO3)2·6H2O and Al(NO3)3·9H2O in Example 1, and the rest is the same as in Example 1, obtaining the monolayer MnO2 nanosheets of Example 2.

[0046] Example 3 A preparation method of a monolayer manganese dioxide nanomaterial is different from the preparation method of Example 1 only in that in step (1), an aqueous NaOH solution with a concentration of 1 mol / L is used to replace the ammonia water in Example 1, and the rest is the same as in Example 1, obtaining the monolayer MnO2 nanosheets of Example 3.

[0047] Example 4 A preparation method of a monolayer manganese dioxide nanomaterial is different from the preparation method of Example 1 only in that in step (1), the relative dropping rate is controlled to maintain the pH value of the reaction system at 13, and the final pH of the system after dropping is 13, and the rest is the same as in Example 1, obtaining the monolayer MnO2 nanosheets of Example 4.

[0048] Example 5 A preparation method of a single-layer manganese dioxide nanomaterial, which is different from the preparation method of Example 1 only in that in step (2), Mn2Al LDHs is calcined in a tube furnace at 400 °C for 1 hour to obtain a Mn2Al precursor, and the rest is the same as in Example 1, obtaining the single-layer MnO2 nanosheets of Example 5.

[0049] Example 6 A preparation method of a single-layer manganese dioxide nanomaterial, which is different from the preparation method of Example 1 only in that in step (2), the solid Mn2Al LDHs is calcined in a tube furnace at 800 °C for 1 hour to obtain a Mn2Al precursor, and the rest is the same as in Example 1, obtaining the single-layer MnO2 nanosheets of Example 6.

[0050] Example 7 A preparation method of a single-layer manganese dioxide nanomaterial, which is different from the preparation method of Example 1 only in that in step (3), the Mn2Al precursor is dispersed in an aqueous solution of H2SO4 with a mass concentration of 50%, and the rest is the same as in Example 1, obtaining the single-layer MnO2 nanosheets of Example 7.

[0051] Example 8 A preparation method of a single-layer manganese dioxide nanomaterial, which is different from the preparation method of Example 1 in that hydrothermal method is used to prepare Mn2Al LDHs, and the rest is the same as in Example 1, obtaining the single-layer MnO2 nanosheets of Example 8.

[0052] The specific operation of preparing Mn2Al LDHs by hydrothermal method is as follows: 0.014 mol of Mn(NO3)2 and 0.0067 mol of Al(NO3)2·9H2O are dissolved in 400 mL of deionized water, stirred for 20 min, then 14.00 g (0.23 mol) of urea is added, and then transferred to a polytetrafluoroethylene inner liner and aged at 120 °C for 48 h, filtered, washed, and dried to obtain Mn2Al LDHs.

[0053] Application Example 0.5 g of the single-layer MnO2 nanosheets obtained in Example 1 is fully dispersed in 100 mL of deionized water, 0.01 g of PtCl4 is added under stirring conditions, and stirring is continued for 12 h. After filtration, washing with water, and freeze-drying, the single-layer MnO2 nanosheets adsorbed with PtCl4 are obtained; the obtained nanosheets are placed in a tube furnace and calcined at 300 °C for 1 h in an Ar / H2 atmosphere (where the volume ratio of Ar to H2 is 19:1), with a heating rate of 2 °C / min, and after natural cooling, the Pt-loaded MnO2 single-layer nanosheet catalyst, i.e., Pt-MnO2, is obtained.

[0054] The electrocatalytic hydrogen evolution performance of the single-layer MnO2 nanosheets obtained in Example 1, Pt-MnO2 obtained in the application example, and commercial 20 wt% Pt / C was evaluated. The specific evaluation method is as follows: The above electrocatalytic samples were tested using a three-electrode system. The Ag / AgCl (saturated) electrode was used as the reference electrode, and a Pt sheet was used as the counter electrode. The test was carried out in a H2SO4 (0.5 M) electrolyte solution at a scan rate of 5 mV / s using a Shanghai Chenhua CHI660e electrochemical workstation. Method for fabricating the working electrode: Disperse 2 mg of the sample in 1 mL of a mixed solvent of water / ethanol (volume ratio 1:1), then add 50 µL of perfluorosulfonic acid membrane solution (Nafion) and 1.0 mg of carbon black as a conductive agent. Coat 6 µL of the catalyst dispersion on a glassy carbon electrode (with an area of 0.1256 cm 2 ), and the catalyst loading is approximately 0.095 mg / cm 2 . The polarization curve of the catalyst was tested using linear sweep voltammetry (LSV) at a scan rate of 5 mV / s, and the i-t curve was tested using chronoamperometry. The results were recorded in Figure 7 .

[0055] The LSV of the MnO2 in Example 1, Pt-MnO2 in the application example, and commercial Pt / C catalysts is shown in Fig. 7a. It can be seen that the MnO2 in Example 1 exhibits weak electrocatalytic activity; Pt-MnO2 exhibits excellent electrocatalytic HER activity, with an overpotential of 29 mV at a current density of 10 mA / cm -2 , which is superior to the commercial Pt / C catalyst (~40 mV), indicating a huge improvement in the electrocatalytic hydrogen evolution performance and demonstrating the synergistic effect between MnO2 and Pt. To more reasonably compare the catalytic performance, the electrocatalytic hydrogen evolution reaction activities of Pt-MnO2 in the application example and commercial Pt / C were both normalized to the mass activity, as shown in Figure 7 b. It can be seen that the mass activity of Pt-MnO2 is much higher than that of commercial Pt / C. At a 50 mV overpotential, the mass activity of Pt-MnO2 is 25.02 A / mg, which is 76 times that of commercial Pt / C (0.33 A / mg) ( Figure 7 c), greatly improving the utilization rate of precious metals. Moreover, this catalyst has good stability. When the stability was tested at an overpotential of 55 mV, the current density in its i-t curve remained basically constant for 10 h ( Figure 7 d). The single-layer MnO2 nanomaterial can serve as a good carrier for loading precious metals.

[0056] It should be noted that this application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments with the same composition and the same effect as the technical idea within the scope of the technical solution of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that those skilled in the art can think of to the embodiments, and other ways constructed by combining some of the constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A single-layer manganese dioxide nanomaterial prepared by a confinement dissolution method, characterized in that, The thickness of the manganese dioxide nanomaterial is 0.4 - 0.8 nm, belonging to single-molecule-layer MnO2 nanosheets, with a monolayer rate ≥ 95%, a lateral size of 20 - 100 nm, and a specific surface area of 106 m 2 / g.

2. The preparation method of the confined dissolution method single-layer manganese dioxide nanomaterial as described in claim 1 includes the steps: S1, preparation of manganese-based layered hydroxide; S2, synthesis of MnO2 nanosheet precursor; S3, confined dissolution of the MnO2 nanosheet precursor and confined growth of the Mn-based oxide to obtain the single-layer manganese dioxide nanomaterial.

3. The preparation method of the confined dissolution method single-layer manganese dioxide nanomaterial according to claim 2, characterized in that, In step S1, the manganese-based layered hydroxide is prepared by coprecipitation method, hydrothermal method, mechanochemical method or reverse microemulsion method.

4. The preparation method of the confined dissolution method single-layer manganese dioxide nanomaterial according to claim 3, characterized in that, The manganese-based layered hydroxide is prepared by coprecipitation method or hydrothermal method: 1) Coprecipitation method: Dissolve manganese salt and metal salt in water to obtain solution A; simultaneously drop solution A and alkali solution into degassed water; then carry out aging, filtration, washing and drying to obtain manganese-based layered hydroxide; 2) Hydrothermal method: Dissolve manganese salt, metal salt and urea in water, carry out hydrothermal treatment, filtration, washing and drying to obtain manganese-based layered hydroxide.

5. The preparation method of the confined dissolution method single-layer manganese dioxide nanomaterial according to claim 4, wherein, In the preparation of manganese-based layered hydroxide by coprecipitation method or hydrothermal method, one or more of the following conditions are included: i. The manganese salt is selected from one or a combination of two or more of Mn(NO3)2, MnSO4, MnCl2, Mn(CH3COO)2 or MnBr2; the metal salt is a nitrate, hydrochloride or sulfate of a metal; the metal ion in the metal salt is selected from Mg 2+ , Cu 2+ , Zn 2+ , Ca 2+ , Co 2 + , Fe 2+ , Ni 2+ , Al 3+ or Fe 3+ in one or a combination of two or more of them; ii. The molar ratio of manganese salt to metal salt is (2-4):

1.

6. The preparation method of the confined dissolution method single-layer manganese dioxide nanomaterial according to claim 4, characterized in that, One or more of the following conditions are included: i. In the preparation of manganese-based layered hydroxide by coprecipitation method, the metal ion concentration of the metal salt in solution A is 0.01-2 mol / L; ii. In the preparation of manganese-based layered hydroxide by coprecipitation method, the alkali solution is aqueous potassium hydroxide solution, aqueous sodium hydroxide solution or ammonia water; the mass concentration of the alkali solution is 5-25%; iii. In the preparation of manganese-based layered hydroxide by coprecipitation method, the volume ratio of solution A to degassed water is (5-20):1; iv. In the preparation of manganese-based layered hydroxide by coprecipitation method, the dropping is carried out under stirring and inert gas protection, and the pH of the reaction system is controlled to be 10.0-14.0 during the dropping process; the inert gas is nitrogen or argon; v. In the preparation of manganese-based layered hydroxide by coprecipitation method, the dosage of the alkali solution is to adjust the pH of the final reaction system to 10.0-14.0; vi. In the preparation of manganese-based layered hydroxide by coprecipitation method, the aging temperature is 20-100 °C and the aging time is 5-24 h; vii. In the preparation of manganese-based layered hydroxide by hydrothermal method, the molar ratio of manganese salt to urea is 1:(4-20); viii. In the preparation of manganese-based layered hydroxide by hydrothermal method, the molar amount of manganese salt and the volume ratio of water is 0.01-1 mol / L; ix. The hydrothermal treatment temperature is 120-180 °C and the hydrothermal treatment time is 12-72 h.

7. The preparation method of the confined dissolution method single-layer manganese dioxide nanomaterial according to claim 2, wherein, In step S2, the synthesis of the MnO2 nanosheet precursor is obtained by calcining the manganese-based layered hydroxide; preferably, the calcination temperature is 400-800 °C and the calcination time is 1-5 h.

8. The preparation method of the confined dissolution method single-layer manganese dioxide nanomaterial according to claim 2, wherein, In step S3, the synthesis method of the single-layer manganese dioxide nanomaterial is as follows: in an acidic environment, after the MnO2 nanosheet precursor is confined and dissolved, the Mn-based oxide is confined in the lamella, and the single-layer manganese dioxide nanomaterial is obtained by confined growth along the lamella; preferably, the acidic environment is provided by an aqueous solution of an acid; the acid is selected from one or more of inorganic acids or organic acids; the inorganic acid is selected from hydrochloric acid, nitric acid or sulfuric acid, preferably sulfuric acid or nitric acid; the mass concentration of the aqueous solution of the acid is 3%-50%; the mass ratio of the MnO2 nanosheet precursor to the volume of the aqueous solution of the acid is 1:(30-100) g / mL.

9. The preparation method of the confined dissolution method single-layer manganese dioxide nanomaterial according to claim 8, wherein, In step S3, the synthesis method of the single-layer manganese dioxide nanomaterial is as follows: disperse the MnO2 nanosheet precursor in an aqueous solution of an acid, and carry out confined dissolution and confined growth by ultrasonic stirring reaction at room temperature for 20-30 h, wash, and dry to obtain the single-layer manganese dioxide nanomaterial.

10. The application of the single-layer manganese dioxide nanomaterial prepared by the confined dissolution method as described in claim 1 in electrocatalytic hydrogen evolution; Preferably, the single-layer manganese dioxide nanomaterial is loaded with a noble metal for application in electrocatalytic hydrogen evolution; more preferably, the noble metal is Pt.

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