Manganese nitride catalyst for oxygen evolution reaction and preparation method thereof

Abstract

This application discloses a manganese nitride catalyst for the oxygen evolution reaction and its preparation method, with the chemical formula MnN. 0.84 At 100mA / cm 2 The current density stabilizes for 300 hours; the current density is 10 mA / cm² at an overpotential of 475 mV. 2 The current density is 100 mA / cm² at an overpotential of 571 mV. 2 It exhibits excellent activity and stability. The raw materials are all inexpensive and readily available, and there is a variety of choices for metallic manganese, including pure manganese powder, manganese flakes, or electrodeposition growth on corrosion-resistant substrates such as Ti sheets, Ti meshes, and carbon cloth.

Description

TECHNICAL FIELD

[0001] The application relates to a manganese nitride catalyst for an oxygen evolution reaction and a preparation method thereof, and belongs to the field of catalyst preparation. BACKGROUND

[0002] Under the demand of low-carbon emission reduction in society, green hydrogen production technology has attracted widespread attention. Among various hydrogen production technologies, proton exchange membrane (PEM) electrolyzers have the advantages of fast response speed, large current density, high hydrogen production pressure, etc., and can adapt to the fluctuating characteristics of renewable energy power generation such as wind and solar energy, which is a suitable scheme for water electrolysis hydrogen production. In the water decomposition reaction, the oxygen evolution reaction (OER) is the rate-determining step, and the multi-electron-multiple-proton transfer in the process involves multiple reaction intermediates, which requires a high overpotential to overcome the slow kinetics, and an efficient and stable catalyst can greatly reduce the overpotential of the oxygen evolution reaction and improve the conversion efficiency of electrical energy to hydrogen energy.

[0003] Limited by the requirements of the acidic environment of the PEM electrolyzer, the high potential of the anode, and good electrical conductivity, the current OER catalysts for the PEM electrolyzer are mainly Ir, Ru, and other noble metal / oxide and binary and ternary alloy / mixed oxide. Non-noble metal-based catalysts will be severely corroded in this environment and may combine with sulfonic acid ions in the PEM, thereby reducing the proton transfer ability of the PEM. However, considering the scarcity and high price of noble metals, people still hope to continuously develop efficient and stable non-noble metal-based catalysts. Currently, non-noble metal catalysts capable of water oxidation in acidic media have been reported, such as Co3O4, Ag-Co3O4, gamma-MnO2, a-NiFeP, N-WC, etc. Among them, gamma-MnO2 reported by the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences can be stably operated for more than 8000 hours at a current density of 10 mA / cm 2 . This has achieved a breakthrough in the stability of non-noble metal OER catalysts in acidic media. However, the current reports still have the problems of high overpotential, low current density during stability testing, and poor stability, for example, gamma-MnO2 will have obvious catalyst dissolution problems at a large current density of 100 mA / cm 2 . The existence of these problems indicates that there is still a long way to go for non-noble metal OER catalysts in acidic media. SUMMARY

[0004] The technical problem to be solved by the present application is that when Mn or Co transition metal oxides are used to catalyze OER reaction in an acidic medium (0.5M or 1.0M sulfuric acid solution), the overpotential of the catalytic reaction is too high, or corrosion occurs, resulting in poor stability. Therefore, how to synthesize a non-noble metal catalyst with strong corrosion resistance becomes the key to solving the problem. Here, a specific structure of manganese nitride MnN0.84 is synthesized using manganese metal and ammonia gas as raw materials. The material can catalyze water oxidation reaction in an acidic medium (0.5M or 1.0M sulfuric acid solution), and has a low overpotential, and can be stable for more than 300 hours at a current density of 100mA / cm2.

[0005] According to one aspect of the present application, a manganese nitride catalyst for oxygen evolution reaction is provided, and the chemical formula of the manganese nitride catalyst is MnN 0.84 , and the pdf card is 04-024-8331.

[0006] The micro-morphology of the manganese nitride catalyst is a blocky particle with sharp corners; the particle size is 2-10μm.

[0007] The manganese nitride catalyst can be stably operated at a current density of 100mA / cm 2 for 300 hours.

[0008] The current density of the manganese nitride catalyst is 10mA / cm 2 when the overpotential is 475mV.

[0009] The current density of the manganese nitride catalyst is 100mA / cm 2 when the overpotential is 571mV.

[0010] According to another aspect of the present application, a preparation method of the above-mentioned manganese nitride catalyst for oxygen evolution reaction is provided, and at least the following steps are included:

[0011] The raw material containing elemental manganese is heated to a holding temperature under an NH3 gas atmosphere, and then naturally cooled to obtain the manganese nitride catalyst for oxygen evolution reaction.

[0012] The raw material containing elemental manganese is selected from elemental manganese powder, elemental manganese sheet or substrate coated with an elemental manganese film.

[0013] The particle size of the elemental manganese powder is less than 10μm; the mass percentage of manganese element is 99.6%.

[0014] The specific surface area to mass ratio of the elemental manganese sheet is 1.9-2.3cm 2 / g; the mass percentage of manganese element is 99.5%;

[0015] The elemental manganese sheet is pretreated.

[0016] The pretreatment process includes at least the following steps: immersing manganese flakes in a 0.1–1.0 M hydrochloric acid solution for 0.5–2 minutes; then polishing the surface after removal.

[0017] In the substrate coated with a thin film of manganese, the thickness of the thin film of manganese is 20-50 μm;

[0018] The substrate coated with the manganese film is obtained through the following steps:

[0019] The substrate with surface etching is electrodeposited in an electrolyte to obtain the substrate coated with a thin film of manganese.

[0020] The substrate is selected from carbon cloth, titanium sheet or titanium mesh;

[0021] The surface etching includes at least the following steps: immersing the substrate in a 5 wt% potassium hydroxide solution for 1 hour; then immersing the substrate in a 10 wt% oxalic acid solution for 2 hours; to obtain a surface-treated substrate;

[0022] The surface treatment temperature is 95°C.

[0023] The electrolyte contains a manganese source, tin dioxide, and a supporting electrolyte;

[0024] The manganese source is selected from at least one of manganese sulfate, manganese acetate, manganese chloride, or manganese acetylacetone;

[0025] The supporting electrolyte is selected from at least one of ammonium sulfate, ammonium acetate, or ammonium chloride;

[0026] The content of the manganese source is 50-250 g / L;

[0027] The content of the supporting electrolyte is 50-200 g / L;

[0028] The tin dioxide content is 0.01–0.1 g / L;

[0029] The electrodeposition process includes: using Ag / AgCl as a reference electrode; using a Mn sheet as a counter electrode; using a Ti sheet as a working electrode; and operating at -10 to -200 mA / cm². 2 Deposition was carried out under constant current for 0.5 to 4 hours.

[0030] When the raw material containing elemental manganese is a manganese sheet, the thickness of the manganese nitride catalyst used for the oxygen evolution reaction on the surface of the manganese sheet is 100-200 μm.

[0031] Preferably, when the raw material containing manganese is a substrate coated with a thin film of manganese, the thickness of the manganese nitride catalyst used for the oxygen evolution reaction on the surface of the substrate coated with the thin film of manganese is 20-50 μm.

[0032] The flow rate of the NH3 gas is 50–200 ml / min.

[0033] The heating rate is 5–10 °C / min;

[0034] The insulation temperature is 500–900℃;

[0035] The heat preservation time is 2 to 12 hours.

[0036] The beneficial effects that this application can produce include:

[0037] (1) A novel catalyst for the oxygen evolution reaction (OER) was proposed. MnN0.84 was applied to this reaction for the first time, demonstrating excellent activity and stability. The best activity was observed in a 1.0 M sulfuric acid solution at a current density of 10 mA / cm². 2 and 100mA / cm 2 Only overpotentials of 475mV and 571mV are required, especially at 100mA / cm. 2 The system remained stable after operating at the current density for 300 hours.

[0038] (2) The raw materials of the catalysts mentioned above in this application are all inexpensive and readily available, and there are various choices of metallic manganese. Pure manganese powder, manganese flakes, or electrodeposition growth on corrosion-resistant substrates, such as Ti flakes, Ti mesh, carbon cloth, etc. Attached Figure Description

[0039] Figure 1a The XRD pattern of manganese nitride obtained in Example 1 of this application; Figure 1b This is a SEM image of manganese nitride obtained in Example 1 of this application;

[0040] Figure 2a The XRD pattern of manganese nitride obtained in Example 2 of this application; Figure 2b This is a SEM image of manganese nitride obtained in Example 2 of this application;

[0041] Figure 3a The XRD pattern of manganese nitride obtained in Example 3 of this application; Figure 3b This is a SEM image of manganese nitride obtained in Example 3 of this application;

[0042] Figure 4 The LSV diagrams of the three working electrodes obtained in Test Example 2 of this application are shown below.

[0043] Figure 5The constant current test curves of the three working electrodes obtained in Test Example 2 of the present application. DETAILED DESCRIPTION

[0044] The present application is described in detail below with reference to examples, but the present application is not limited to these examples.

[0045] The raw materials in the examples of the present application are all purchased through commercial channels unless otherwise specified.

[0046] The analysis method in the examples of the present application is as follows:

[0047] The XRD instrument is an x-ray diffractometer of Japan Rigaku, the model is smartlab, the test range (2θ) is 10-90°, the scanning speed is 20° / min, and the test condition is atmospheric environment at room temperature.

[0048] The SEM instrument is a field emission scanning electron microscope of Japan Electronics, the model is JSM-7900F.

[0049] The linear scan curve (LSV) is tested by an electrochemical workstation of Shanghai Chenhua, the test system is a three-electrode system (the reference electrode is an Ag / AgCl electrode, the counter electrode is a platinum plate, and the working electrode is the working electrode I / II / III), and the sulfuric acid solution is 0.5M. The scanning voltage range (relative to the Ag / AgCl reference) is 1.0-1.6V, the scanning speed is 10mV / s, and the electrochemical data obtained by scanning is subjected to 90% IR compensation treatment.

[0050] The constant current test adopts the same electrochemical workstation and test condition, and the test current density is selected to be 100mA / cm 2 The voltage-time curve obtained by the test is subjected to 90% IR compensation treatment.

[0051] In order to further illustrate the present application, the following implementation examples are listed, but the present application is not limited thereto.

[0052] Example 1

[0053] 0.1g of manganese powder is spread on the bottom of a quartz boat to form a thin layer, which is placed in a quartz tube, air in the pipeline is replaced by Ar gas, 200ml / min of NH3 is introduced, the temperature is raised to 700℃ at a heating rate of 5℃ / min, the temperature is kept at this temperature for 12 hours, and then naturally cooled to room temperature. The obtained powder is ground to obtain the manganese nitride catalyst.

[0054] Figure 1a The XRD pattern of the manganese nitride catalyst obtained in Example 1 of the present application, from the figure, it can be seen that the obtained manganese nitride catalyst is mainly MnN 0.84 .

[0055] Figure 1b SEM of the manganese nitride catalyst obtained in Example 1 of the present application, it can be seen from the figure that the obtained manganese nitride catalyst is a large particle of 2-10 μm.

[0056] Example 2

[0057] The manganese sheet was first treated, the manganese sheet was soaked in 1.0 M hydrochloric acid solution for 1 minute, rinsed twice with water and then the surface was polished with 1000 mesh sandpaper, rinsed clean and dried after polishing. The polished manganese sheet was placed in a quartz tube, Ar gas was introduced to displace the air in the pipeline, 200 ml / min of NH3 was introduced, the temperature was increased to 700°C at a rate of 5°C / min, the temperature was kept at this temperature for 12 hours, and then naturally cooled to room temperature to obtain a manganese metal sheet containing the manganese nitride catalyst.

[0058] Figure 2a XRD of the manganese nitride catalyst obtained in Example 1 of the present application, it can be seen from the figure that the obtained manganese nitride catalyst is mainly MnN 0.84 .

[0059] Figure 2b SEM of the manganese nitride catalyst obtained in Example 1 of the present application, it can be seen from the figure that the obtained manganese nitride catalyst is a large particle of 2-10 μm, and it can be seen from the cross section that the layer of manganese nitride catalyst is about 150-200 μm thick.

[0060] Example 3

[0061] A titanium sheet was used as the substrate, a layer of manganese was first deposited on the surface, and then nitridation treatment was performed.

[0062] 1) The titanium sheet was treated, the Ti sheet was treated in 5 wt% KOH solution at 95°C for 1 hour, and then was placed in 10 wt% oxalic acid at 95°C for 2 hours to obtain a Ti sheet with etched surface. 2) The electrolyte was prepared, 200 g / L manganese sulfate, 150 g / L ammonium sulfate, and 0.02 g / L selenium dioxide. 3) Electrodeposition, Ar was introduced into the electrolytic cell to displace the air for 1 hour, Ag / AgCl was used as the reference electrode, Mn sheet was used as the counter electrode, and Ti sheet was used as the working electrode, Mn was deposited on the surface of the Ti sheet at a constant current of -40 mA / cm 2 2 hours to obtain a Ti sheet with Mn deposited on the surface. 3) Nitridation treatment, the Ti sheet was placed in a quartz tube, Ar gas was introduced to displace the air in the pipeline, 200 ml / min of NH3 was introduced, the temperature was increased to 700°C at a rate of 5°C / min, the temperature was kept at this temperature for 12 hours, and then naturally cooled to room temperature to obtain a Ti sheet containing the manganese nitride catalyst.

[0063] Figure 3aThe XRD pattern of the manganese nitride catalyst obtained in Example 1 of the present application is shown in Figure 1. It can be seen from the figure that the manganese nitride catalyst obtained is mainly MnN 0.84 .

[0064] Figure 3b The SEM pattern of the manganese nitride catalyst obtained in Example 1 of the present application is shown in Figure 2. It can be seen from the figure that the manganese nitride catalyst obtained is large particles of 2-10 um.

[0065] Test Example 1

[0066] Take 10 mg of the manganese nitride catalyst obtained in Example 1, add 800 ul of ethanol, 200 ul of water, and 400 ul of 5% nafion solution, and ultrasonicate for 1 hour. Then take 10 ul of the mixed solution and drop it on a glassy carbon electrode to obtain working electrode I.

[0067] The manganese metal sheet containing the manganese nitride catalyst obtained in Example 2 is used as working electrode II;

[0068] The Ti sheet containing the manganese nitride catalyst obtained in Example 3 is used as working electrode III.

[0069] Linear sweep (LSV) tests are carried out in a three-electrode system (the reference electrode is an Ag / AgCl electrode, the counter electrode is a platinum sheet, and the working electrode is working electrode I / II / III) and sulfuric acid solution (0.5 M). The electrochemical activity, including linear sweep (LSV) and constant current tests.

[0070] Figure 4 The LSV patterns of the three working electrodes obtained in Test Example 1 of the present application are shown in Figure 3. It can be seen from the figure that working electrodes I, II, and III require overpotentials of about 796 mV, 588 mV, and 644 mV, respectively, to achieve a current density of 100 mA / cm 2 . In comparison, the overpotential required by working electrode I is higher, which is mainly due to the fact that the manganese nitride of working electrode I is adhered to the base material by a binder, which can result in a lower catalyst density on the surface of the electrode and a higher internal resistance of the electrode, thus a higher overpotential. The catalysts of working electrodes II and III are tightly connected to the base, the internal resistance of the electrode is lower, the catalyst density is higher, and the overpotentials are close and lower.

[0071] Test Example 2

[0072] Constant current tests are carried out in a three-electrode system (the reference electrode is an Ag / AgCl electrode, the counter electrode is a platinum sheet, and the working electrode is working electrode I / II / III) and sulfuric acid solution (0.5 M).

[0073] Figure 5The constant current test figures of the three working electrodes obtained in Test Example 2 of the present application; it can be seen from the figures that when the constant current test is carried out at a current density of 100 mA / cm 2 2.12 V (vs RHE), the working electrode II is relatively stable at about 1.95 V (vs RHE) for more than 200 hours, and the working electrode III is relatively stable at about 1.89 V (vs RHE) for more than 300 hours. The reasons for the potential difference of the three working electrodes are consistent with those in the LSV test, and the working electrode II shows relatively better stability.

[0074] The above is only a few embodiments of the present application, and does not limit the present application in any form. Although the preferred embodiments are disclosed above, the present application is not limited thereto. Any skilled person in the art can make some changes or modifications to the above disclosed technical contents without departing from the scope of the technical solutions of the present application, and such changes or modifications are equivalent to equivalent embodiments, and all of them are within the scope of the technical solutions.

Claims

1. A manganese nitride catalyst for the oxygen evolution reaction, characterized in that, The chemical formula of the manganese nitride catalyst is MnN. 0.84 ; The particle size of the manganese nitride catalyst is 2~10 μm; The method for preparing the manganese nitride catalyst for the oxygen evolution reaction includes at least the following steps: The raw material containing elemental manganese is heated to the reaction temperature under an NH3 gas atmosphere, reacted at a constant temperature, and then cooled to obtain the manganese nitride catalyst used for the oxygen evolution reaction. The flow rate of the NH3 gas is 50~200 ml / min; The heating rate is 5~10℃ / min; The constant temperature is 500~900℃; The manganese nitride catalyst is at 100 mA / cm 2 The current density stabilizes for 300 hours. The manganese nitride catalyst exhibits a current density of 10 mA / cm² at an overpotential of 475 mV. 2 ; The manganese nitride catalyst exhibits a current density of 100 mA / cm² at an overpotential of 571 mV. 2 .

2. The catalyst according to claim 1, characterized in that, The raw material containing manganese is selected from manganese powder, manganese flakes, or a substrate coated with a thin film of manganese.

3. The catalyst according to claim 2, characterized in that, The manganese powder has particles with a diameter of less than 10 μm and a manganese content of 99.6% by mass.

4. The catalyst according to claim 2, characterized in that, The surface area to mass ratio of the manganese elemental sheet is 1.9~2.3 cm². 2 / g; the mass percentage of manganese is 99.5%.

5. The catalyst according to claim 2, characterized in that, In the substrate coated with a manganese elemental film, the thickness of the manganese elemental film is 20~50μm; The substrate coated with the manganese film is obtained through the following steps: The substrate with surface etching is electrodeposited in an electrolyte to obtain the substrate coated with a thin film of manganese. The substrate is selected from titanium sheet or titanium mesh; The surface etching includes at least the following steps: immersing the substrate in a 1-10 wt% potassium hydroxide solution for 0.5-2 hours; then immersing the substrate in a 5-10 wt% oxalic acid solution for 1-2 hours; to obtain a surface-treated substrate; The surface treatment temperature is 85~95℃.

6. The catalyst according to claim 5, characterized in that, The electrolyte contains a manganese source, tin dioxide, and a supporting electrolyte; The manganese source is selected from at least one of manganese sulfate, manganese acetate, manganese chloride, or manganese acetylacetone; The supporting electrolyte is selected from at least one of ammonium sulfate, ammonium acetate, or ammonium chloride; The content of the manganese source is 50~250g / L; The content of the supporting electrolyte is 50~200g / L; The content of tin dioxide is 0.01~0.1g / L.

7. The catalyst according to claim 1, characterized in that, When the raw material containing elemental manganese is a manganese sheet, the thickness of the manganese nitride catalyst used for the oxygen evolution reaction on the surface of the manganese sheet is 100~200μm.

8. The catalyst according to claim 1, characterized in that, When the raw material containing elemental manganese is a substrate coated with a thin film of elemental manganese, the thickness of the manganese nitride catalyst used for the oxygen evolution reaction on the surface of the substrate coated with the thin film of elemental manganese is 20~50μm.

9. The catalyst according to claim 1, characterized in that, The constant temperature period is 2 to 12 hours.

10. A method for producing hydrogen by water electrolysis, characterized in that, The manganese nitride catalyst for the oxygen evolution reaction as described in claims 1 to 9 is used.

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