A two-phase coexisting manganese oxide and a preparation method and application thereof

Abstract

The application discloses a two-phase coexisting manganese oxide, which is a MnO2 / Mn3O4 mixed-phase manganese oxide grown on a substrate, and the MnO2 / Mn3O4 mixed-phase manganese oxide has a cluster-like morphology formed by accumulation of nanoparticles; and a preparation method thereof comprises the following steps: adding a bromide salt and water into a reaction container, stirring under air, then adding a manganese salt and uniformly mixing; and then dropping the obtained mixed solution on the substrate in a quantitative manner, and performing a one-step heating reaction in air to obtain the MnO2 / Mn3O4 mixed-phase manganese oxide. 2 / The two-phase coexisting manganese oxide can be used as a water oxidation electrode and can exhibit excellent catalytic activity and stability in a full pH range; and the preparation method is simple, convenient to operate and suitable for popularization and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of water oxidation catalysts, and particularly relates to a manganese oxide suitable for two-phase coexistence in a full pH range, and a preparation method and application thereof. Background Art

[0002] As a secondary energy source, hydrogen has the advantages of diverse sources, cleanliness, high efficiency, sustainable utilization, and wide range of uses. It is of great significance to ensuring energy security and responding to climate change. It is an ideal carrier for promoting the large-scale utilization of renewable energy and an important boost to achieving green and low-carbon energy transformation. Among them, hydrogen production by electrolysis of water is the main way to prepare "green hydrogen" in the future. In order to be suitable for various application scenarios, electrocatalysts must be able to perform well in a wide pH range to adapt to different proton concentrations in the electrocatalytic process. Many transition metal-based electrocatalysts perform well in concentrated alkaline electrolytes (pH greater than 13), but are prone to corrosive decomposition under low pH working conditions.

[0003] RuO2 and IrO2 are well-known high-performance OER electrocatalysts at low pH, although these catalysts have a low -2 While these materials exhibit low overpotentials at low current densities, they face challenges such as insufficient exposure of active sites and slow mass and charge transfer, making it difficult to achieve high current densities. Furthermore, the release of O2 bubbles, oxidation and corrosion at high potentials, and stripping can lead to long-term operational stability of the catalytic electrode. Furthermore, RuO2 and IrO2 are both scarce precious metal materials, making large-scale commercial applications difficult.

[0004] Among the transition metal-based non-noble metal oxides, manganese oxide (MnO x ) has a rich valence state and crystal structure, and exhibits excellent performance in various electrochemical reactions. Manganese oxides can act as efficient bifunctional electrocatalysts for ORR and OER under alkaline conditions; some manganese-based oxides can be used as OER catalysts in acidic media, but most of the reported catalytic activities are very limited, at 10 mA cm -2 The overpotential under low pH is usually greater than 500 mV, which makes it difficult to apply commercially. It is necessary to further improve the OER activity of this type of manganese-based materials in low pH environment. Summary of the Invention

[0005] The main purpose of the present invention is to address the problems and shortcomings of the existing technology and provide a manganese oxide with coexistence of MnO2 and Mn3O4 (referred to as two-phase manganese oxide), and to simultaneously introduce high water oxidation activity Mn into the catalyst. 3+The nanoparticle structure constructed at the same time can achieve a large specific surface area, so that it can be used as a water oxidation electrode in the entire pH range, showing excellent catalytic activity and stability; and the preparation method involved is relatively simple and easy to operate, which is suitable for promotion and application.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A two-phase coexisting manganese oxide is a MnO2 / Mn3O4 mixed-phase manganese oxide grown on a substrate, wherein the atomic percentage of Mn is 25.09-52.05% and the atomic percentage of O is 47.95-74.91%.

[0008] Furthermore, the MnO2 / Mn3O4 mixed-phase manganese oxide has a clustered morphology formed by accumulation of nanoparticles, and the size of the nanoparticles is 20 to 80 nm.

[0009] Furthermore, the substrate is a conductive substrate.

[0010] The above-mentioned method for preparing a two-phase coexisting manganese oxide comprises the following steps: adding bromine salt and water into a reaction vessel, stirring them in air, then adding manganese salt and mixing them evenly; then dropping the obtained mixture onto a substrate in a quantitative manner, and performing a one-step heating reaction in air to obtain MnO 2 / Manganese oxide in which two phases of Mn3O4 coexist.

[0011] In the above scheme, the stirring treatment time is 3 to 6 hours.

[0012] In the above solution, the substrate is preferably a conductive substrate, specifically including any one of carbon cloth, carbon paper, graphite felt, carbon fiber, bio-carbon material, etc.

[0013] Furthermore, the biocarbon material can be a carbon material obtained by calcining fruit shells or mollusk shells.

[0014] In the above scheme, the manganese salt includes one or more of Mn(NO3)2, MnSO4, MnCl2, etc.

[0015] In the above scheme, the bromide salt includes one or more of NH4Br, NaBr, and KBr.

[0016] In the above scheme, in the mixed solution, the mass concentration of manganese salt is 20-60%, and the concentration of bromide salt is 0.1-2.0 mol / L.

[0017] In the above scheme, the heating reaction temperature in air is 150-400° C. and the time is 2-12 hours.

[0018] Furthermore, the heating reaction adopts a heating rate of 5-25°C / min.

[0019] The present invention also provides an application of the two-phase coexisting manganese oxide in water oxidation reaction in a full pH range.

[0020] Furthermore, the full pH range is pH values ​​0 to 14.

[0021] Furthermore, the specific application method includes: using the two-phase coexisting manganese oxide as an oxygen evolution electrode for oxidation reactions of acidic water, neutral water, and alkaline water.

[0022] The two-phase coexistence of manganese oxide of the present invention is used to generate a -2 At current densities of 10 mA cm-1, the OER overpotentials required in acidic, neutral, and alkaline media are as low as 255, 267, and 175 mV, respectively, much lower than those of pure MnO2 samples. -2 It can operate stably for more than 500 hours in acidic, neutral and alkaline solutions at a constant current density, and its water oxidation performance has no obvious attenuation.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention first stirs a bromine salt solution, then mixes it with a manganese salt and heats it in one step, and prepares the two-phase coexisting manganese oxide on a substrate, preferably a conductive substrate such as a conductive carbon material; wherein, in the stirring step, the bromine salt is first oxidized in air to Br - and liquid bromine coexistence system, and then under air and heating conditions, Mn 2+ Direct oxidation to form Mn-containing 3+ The obtained two-phase manganese oxide has a clustered morphology formed by the accumulation of nanoparticles, which can fully expose the active sites. At the same time, the formation of Mn3O4 increases the Mn with high OER activity. 3+ The species content and the combined effect of multiple means can effectively improve the catalytic activity and stability of the obtained manganese oxide and effectively broaden its pH value application range;

[0025] 2. The two-phase manganese oxide provided by the present invention is used as an OER electrode, which can show excellent catalytic activity and stability in the entire pH range (pH 0-14), providing a new idea for the preparation of high-performance water oxidation catalysts;

[0026] 3. The preparation method of the present invention is simple, easy to operate, and suitable for popularization and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1XRD spectra of two-phase MnO2 / Mn3O4 and pure MnO2 prepared in Example 1 and Comparative Example 1.

[0028] Figure 2 Scanning electron microscope (SEM) images of two-phase MnO2 / Mn3O4 and pure MnO2 prepared in Example 1 and Comparative Example 1 at different magnifications.

[0029] Figure 3 The OER performance comparison diagram of the MnO2 / Mn3O4 two-phase manganese oxide obtained in Example 1 in an acidic electrolyte (0.5M H2SO4) with the noble metal IrO2 sample and the products obtained in Comparative Examples 1 to 3, including: (a) linear sweep voltammetry (LSV) curve comparison diagram of the products obtained in Example and Comparative Example 1 and the noble metal IrO2 sample; (b) electrochemical impedance spectroscopy (EIS); (c) Faraday efficiency test; (d) linear sweep voltammetry curve comparison diagram of Example 1 and Comparative Examples 1 to 3; (e) the product obtained in Example 1 at 10mAcm -2 Stability test curves under current density and acidic conditions.

[0030] Figure 4 Comparison of the OER performance of the MnO2 / Mn3O4 two-phase manganese oxide obtained in Example 1 in a neutral electrolyte (PBS solution) and the precious metal IrO2 sample: (a) linear sweep voltammetry (LSV) curve; (b) electrochemical impedance spectroscopy (EIS); (c) Faraday efficiency test; (d) at 10 mA cm -2 Stability test curve under current density.

[0031] Figure 5 Comparison of the OER performance of the MnO2 / Mn3O4 two-phase manganese oxide obtained in Example 1 in alkaline electrolyte (1M KOH) and the commercial precious metal IrO2 sample: (a) linear sweep voltammetry (LSV) curve; (b) electrochemical impedance spectroscopy (EIS); (c) Faraday efficiency test; (d) at 10 mA cm -2 Performance curve of stable test under current density. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0033] Example 1

[0034] A manganese oxide with coexisting MnO2 / Mn3O phases, grown on a carbon cloth substrate, exhibiting a clustered morphology formed by accumulation of nanoparticles; the specific preparation steps are as follows:

[0035] Prepare a 1.6 mol / L NH4Br uniform solution, stir it in air for 5 h, then add Mn(NO3)2 (the concentration of manganese nitrate in the solution is 40 wt%) to the obtained bromine-based solution; -2 A drop amount of the coating was dropped onto the clean carbon cloth, and the mixture was heated to 250°C on a hot plate at a heating rate of 10°C / min, and kept warm for 5.5 hours. After the reaction was completed, it was cooled to room temperature to obtain two-phase manganese oxide MnO2 / Mn3O4.

[0036] The product obtained in this example was tested by inductively coupled plasma resonance spectroscopy (ICP-OES), and the atomic percentage of Mn was found to be 47.57%, and the atomic percentage of O was found to be 52.43%.

[0037] Example 2

[0038] A manganese oxide with coexisting MnO2 / Mn3O phases, grown on a carbon paper substrate, exhibits a clustered morphology formed by accumulation of nanoparticles. The specific preparation steps are as follows:

[0039] Prepare a 1.0 mol / L NaBr solution, stir it in air for 4 h, and then add MnSO4 (the concentration of manganese sulfate in the solution is 50 wt%) to the obtained bromine solution; -2 The solution was dropped onto the clean carbon paper and heated to 300°C on a hot plate at a heating rate of 10°C / min. The mixture was kept warm for 9 hours. After the reaction was completed, the mixture was cooled to room temperature to obtain a two-phase manganese oxide MnO2 / Mn3O4.

[0040] The product obtained in this example was subjected to ICP-OES analysis, which showed that the atomic percentage of Mn was 39.46%, and the atomic percentage of O was 60.54%.

[0041] Example 3

[0042] A manganese oxide with coexisting MnO2 / Mn3O phases, grown on a carbon fiber substrate, exhibits a clustered morphology formed by accumulation of nanoparticles. The specific preparation steps are as follows:

[0043] Prepare a 2.0 mol / L NH4Br solution, stir it in air for 6 h, and then add MnCl2 (the concentration of manganese chloride in the solution is 60 wt%) to the obtained bromine solution; -2A drop amount of the coating was dropped onto the cleaned carbon fiber, heated to 400°C on a hot plate at a heating rate of 10°C / min, and kept warm for 12 hours. After the reaction was completed and cooled to room temperature, a two-phase manganese oxide MnO2 / Mn3O4 was obtained.

[0044] The product obtained in this example was subjected to ICP-OES analysis, which showed that the atomic percentage of Mn was 52.05%, and the atomic percentage of O was 47.95%.

[0045] Example 4

[0046] A manganese oxide with coexisting MnO2 / Mn3O phases, grown on a carbon cloth substrate, exhibiting a clustered morphology formed by accumulation of nanoparticles; the specific preparation steps are as follows:

[0047] Prepare a 0.1 mol / L KBr uniform solution, stir it in air for 3 h, then add MnSO4 (the concentration of manganese sulfate in the solution is 20 wt%) to the obtained bromine-based solution; -2 A drop amount of the coating was dropped onto the clean carbon cloth, and the mixture was heated to 150°C at a heating rate of 10°C / min on a hot plate. The reaction was allowed to proceed for 2 hours. After the reaction was completed and cooled to room temperature, a two-phase manganese oxide MnO2 / Mn3O4 was obtained.

[0048] The product obtained in this example was subjected to ICP-OES analysis, which showed that the atomic percentage of Mn was 25.09%, and the atomic percentage of O was 74.91%.

[0049] Example 5

[0050] A manganese oxide with coexisting MnO2 / Mn3O phases, grown on a graphite felt substrate, exhibiting a clustered morphology formed by accumulation of nanoparticles; the specific preparation steps are as follows:

[0051] Prepare a 0.5 mol / L KBr uniform solution, stir it in air for 5 h, then add Mn(MO3)2 (the concentration of manganese nitrate in the solution is 30 wt%) to the obtained bromine-based solution; -2 A drop amount of the coating was dropped onto the cleaned graphite felt, and the mixture was heated to 200°C on a hot plate at a heating rate of 10°C / min. The mixture was kept warm for 4 hours. After the reaction was completed, the mixture was cooled to room temperature to obtain two-phase manganese oxide MnO2 / Mn3O4.

[0052] The product obtained in this example was subjected to ICP-OES analysis, which showed that the atomic percentage of Mn was 31.98%, and the atomic percentage of O was 68.02%.

[0053] Comparative Example 1

[0054] A pure phase MnO2 electrocatalyst, the preparation method of which comprises the following steps:

[0055] The carbon cloth was soaked in concentrated nitric acid, ultrasonically cleaned three times with deionized water, and then ultrasonically cleaned three times with anhydrous ethanol; a 40% manganese nitrate solution was added at 150 μL cm -2 A drop amount of the solution was dropped onto a clean carbon cloth, and the solution was heated to 250°C on a hot plate at a heating rate of 10°C / min and reacted for 5.5 hours. After the reaction was completed, the solution was cooled to room temperature to obtain pure phase manganese oxide MnO2.

[0056] Comparative Example 2

[0057] A method for preparing manganese oxide induced by chloride salt comprises the following steps:

[0058] Prepare a 1.6 mol / L NH4Cl uniform solution, stir it in air for 5 h, then add Mn(NO3)2 (the concentration of manganese nitrate in the solution is 40 wt%) to the obtained bromine-based solution; -2 A drop amount of the solution was dropped onto a clean carbon cloth, and the solution was heated to 250°C on a hot plate at a heating rate of 10°C / min, and kept warm for 5.5 hours. After the reaction was completed, the solution was cooled to room temperature to obtain manganese oxide induced by chloride salt.

[0059] Comparative Example 3

[0060] A manganese oxide directly induced by a bromine salt, the preparation method of which comprises the following steps:

[0061] Prepare a 1.6 mol / L NH4Br uniform solution, add Mn(NO3)2 to the solution (the concentration of manganese nitrate in the solution is 40 wt%); -2 A drop amount of the solution was dropped onto a clean carbon cloth, and the solution was heated to 250°C at a heating rate of 10°C / min on a hot plate. The solution was kept warm for 5.5 hours and cooled to room temperature to obtain manganese oxide directly induced by bromine salt.

[0062] The pure phase MnO2 and two-phase MnO2 / Mn3O4 prepared in Comparative Example 1 and Example 1 were characterized by XRD. Specifically, the prepared catalyst was subjected to X'pert PROMPD X-ray diffractometer (XRD) to determine the crystal structure of the sample. The conditions were Cu Kα monochromatic radiation and a scanning range of 20° to 80°. The obtained XRD spectra were shown in FIG. Figure 1The results showed that the characteristic peaks in the XRD pattern of pure MnO2 matched those of MnO2 (PDF#30-0820), indicating that manganese dioxide was successfully synthesized. After the addition of bromine-containing reagents during the preparation process, some new peaks appeared in the obtained MnO2-based products, which matched those of Mn3O4 (PDF#24-0734), indicating that the introduction of bromine can effectively promote the formation of MnO2 and Mn3O4 complexes.

[0063] The pure phase MnO2 and two-phase MnO2 / Mn3O4 prepared in Comparative Example 1 and Example 1 were characterized by SEM. The specific steps were as follows: the surface morphology of the prepared catalyst was measured on a JOELSEM-6700E scanning electron microscope (SEM); the results are shown in FIG. Figure 2 It can be seen that the pure MnO2 obtained in Comparative Example 1 exhibits a bulk structure; the product obtained after the introduction of Br in the preparation method described in Example 1 is a clustered structure formed by the accumulation of nanoparticles ( Figure 2 c), can fully expose the active sites.

[0064] The products obtained in Example 1 and Comparative Examples 1 to 3, as well as the precious metal IrO2 sample, were subjected to electrocatalytic oxygen evolution reaction performance tests. The specific steps were as follows: using a three-electrode system of a CHI660E electrochemical workstation, Ag / AgCl electrode, Hg / HgO electrode, and calomel electrode as reference electrodes under acidic, neutral, and alkaline conditions, respectively, the prepared sample as the working electrode, the graphite electrode as the counter electrode, and the electrolytes were 0.5 mol / L H2SO4 solution (pH 0), PBS solution, and 1 mol / L KOH solution (pH 14), respectively, at room temperature of 25°C. Before the test, cyclic voltammetry scanning was performed on the samples to activate and stabilize the samples. The linear sweep voltammetry (LSV) curve with 90% IR compensation was used to evaluate the activity of the electrode, and the scan rate was 2 mV s -1 The measurement range of the electrochemical impedance spectroscopy (EIS) of the electrode is 1000kHz~0.1Hz. -1The stability of the electrode was tested at a constant current density of . The Faraday efficiency test was conducted in a gas chromatograph. The specific steps are: clean the H-type reactor with deionized water, pour the electrolyte into the cathode chamber and the anode chamber respectively, so that the liquid levels are at the same level, and leave a certain volume of cavity above the anode chamber to collect oxygen products. High-purity carbon dioxide (99.99%) gas was introduced into the cathode chamber and the anode chamber for 30 minutes respectively to make the electrolyte reach a CO2 saturated state. The sample was then activated, and the CHI660E electrochemical workstation it mode was selected. Each time the charge reached a constant value of 15C, the potential was stopped. Then a 500μL gas sample was taken from the top space of the anode chamber with a sampling needle (Hamilton) and injected into the gas chromatograph. The GC-2014 gas chromatograph was used to test the O2 content. The results are shown in Figure 3 ,in, Figure 3 (a) shows the linear sweep voltammetry (LSV) curves of MnO2 / Mn3O4 two-phase manganese oxide and commercial IrO2 samples in 0.5 mol / L H2SO4 solution (pH 0). Compared with other samples, MnO2 / Mn3O4 sample has significantly improved OER performance, with the LSV curves at 10 mA cm -2 At a current density of 1.5 Å, the required OER overpotential is only as low as 255 mV, which is better than the commercial IrO2 sample (317 mV). At the same time, the formation of two-phase oxides is also conducive to improving conductivity, thereby promoting rapid electron transfer on the catalyst, as shown in Figure 3 (b) The electrochemical impedance spectroscopy diagram shows that the MnO2 / Mn3O4 two-phase manganese oxide has the smallest charge transfer resistance. Figure 3 (c) The Faradaic efficiency of the MnO2 / Mn3O4 sample obtained in Example 1 is 98%, demonstrating its good OER selectivity. Figure 3 (d) shows the linear sweep voltammetry (LSV) curves of the samples of Example 1 and Comparative Examples 1-3 in 0.5 mol / L H2SO4 solution. The results show that the products obtained in Comparative Examples 1-3 cannot achieve effective catalytic effect under acidic conditions. In addition, Figure 3 (e) The stability test shows that the MnO2 / Mn3O4 sample obtained in Example 1 has a high stability at 10 mA cm -2 The oxidation performance of the device did not show any significant attenuation after running in an acidic solution for 500 hours at a constant current density of 1.5 GHz.

[0065] Figure 4(a) shows the linear sweep voltammetry (LSV) curves of MnO2 obtained in Comparative Example 1, MnO2 / Mn3O4 two-phase manganese oxide obtained in Example 1, and commercial IrO2 samples in PBS solution (pH 7). Compared with other samples, the MnO2 / Mn3O4 sample obtained in the present invention has significantly improved OER performance, with a maximum OER of 10 mA cm -2 At a current density of 1.5 Å, the required OER overpotential is only as low as 267 mV, which is better than the commercial IrO2 sample (432 mV). At the same time, the formation of two-phase oxides is also conducive to improving conductivity, thereby promoting rapid electron transfer on the catalyst, as shown in Figure 4 (b) The electrochemical impedance spectroscopy diagram shows that the MnO2 / Mn3O4 two-phase manganese oxide has the smallest charge transfer resistance. Figure 4 (c) It can be seen that the Faradaic efficiency of MnO2 / Mn3O4 obtained by the present invention is 96.1%, which proves its good OER selectivity. In addition, Figure 4 (c) The stability test results show that the MnO2 / Mn3O4 sample obtained in the present invention has a stability of 10mAcm -2 The oxidation performance of the device did not show any significant attenuation after running at a constant current density of 1.5 GHz in a neutral solution for 700 hours.

[0066] Figure 5 (a) shows the linear sweep voltammetry (LSV) curves of MnO2 obtained in Comparative Example 1, MnO2 / Mn3O4 two-phase manganese oxide obtained in Example 1, and commercial IrO2 samples in 1 mol / L KOH solution (pH 14). Compared with other samples, the MnO2 / Mn3O4 sample has significantly improved OER performance, with a maximum OER of 10 mA cm -2 At a current density of 1.5 Å, the required OER overpotential is only as low as 175 mV, which is better than the commercial IrO2 sample (258 mV). At the same time, the formation of two-phase oxides is also conducive to improving conductivity, thereby promoting rapid electron transfer on the catalyst, as shown in Figure 5 (b) The electrochemical impedance spectroscopy diagram shows that MnO2 / Mn3O4 has the smallest charge transfer resistance. Figure 5 (c) It can be seen that the Faradaic efficiency of the present invention is 93.1%, which proves its good OER principle. Figure 5 (d) shows the stability test results of MO2 / Mn3O4 sample at 10mAcm -2 The oxidation performance of the device did not show any significant attenuation after running in alkaline solution for 500 hours at a constant current density of 1.5 GHz.

[0067] The MnO2 / Mn3O4 two-phase coexisting manganese oxides obtained in Examples 1 to 5 were used to prepare oxygen evolution electrodes. The specific steps were as follows: using a three-electrode system of a CHI660E electrochemical workstation, an Ag / AgCl electrode as a reference electrode, the prepared sample as a working electrode, a graphite electrode as a counter electrode, and a 0.5 mol / L H2SO4 solution as the electrolyte. The conditions were room temperature (25°C). Different samples were tested at 10 mA cm -2 The overpotentials of acidic water oxidation at current densities of are shown in Table 1.

[0068] Table 1 Summary of the acidic water oxidation performance of MnO2 / Mn3O4 samples prepared in different embodiments

[0069]

[0070] The above embodiments are merely examples for illustrative purposes only and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications may be made based on the above descriptions. It is not necessary and impossible to enumerate all implementation methods here. Therefore, any obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for preparing a two-phase coexisting manganese oxide, characterized in that: The method comprises the following steps: adding bromine salt and water into a reaction vessel, stirring the mixture in air, and then adding manganese salt and mixing the mixture uniformly; then dropping the mixture onto a substrate in a quantitative manner, and performing a one-step heating reaction in air to prepare manganese oxide in which MnO2 / Mn3O4 two phases coexist; The two-phase coexisting manganese oxide is a MnO2 / Mn3O4 mixed-phase manganese oxide grown on a substrate, wherein the atomic percentage of Mn is 25.09-52.05%, and the atomic percentage of O is 47.95-74.91%.

2. The preparation method according to claim 1, characterized in that The MnO2 / Mn3O4 mixed-phase manganese oxide has a cluster morphology formed by accumulation of nanoparticles, and the size of the nanoparticles is 20-80 nm.

3. The preparation method according to claim 1, characterized in that The stirring treatment time is 3 to 6 hours.

4. The preparation method according to claim 1, characterized in that The substrate includes any one of carbon cloth, carbon paper, graphite felt, carbon fiber, and biocarbon material.

5. The preparation method according to claim 1, characterized in that The manganese salt includes one or more of Mn(NO3)2, MnSO4, and MnCl2; the bromine salt includes one or more of NH4Br, NaBr, and KBr.

6. The preparation method according to claim 1, characterized in that In the obtained mixed solution, the mass concentration of manganese salt is 20-60%, and the concentration of bromide salt is 0.1-2.0 mol / L.

7. The preparation method according to claim 1, characterized in that The heating reaction temperature in air is 150~400℃ and the time is 2~12h.

8. Use of the two-phase coexisting manganese oxide prepared by the preparation method according to any one of claims 1 to 7 in a water oxidation reaction, characterized in that: The pH value in the water oxidation reaction is 0-14.

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