Preparation method and application of amorphous iron-doped ruthenium oxide nanosheet catalyst

Abstract

The invention discloses a preparation method and application of an amorphous iron-doped ruthenium oxide nanosheet catalyst, and the preparation method comprises the following steps: weighing ruthenium acetylacetonate, ferrous acetylacetonate and potassium bromide, adding deionized water and absolute ethyl alcohol, and stirring until the solution is clear and transparent dark red; immersing the pretreated carbon paper into the mixed solution, and drying in a drying oven; and placing the dried carbon paper in a tubular furnace, maintaining the temperature at 260 DEG C for 0.5 h, washing with deionized water and ethanol, and drying at room temperature to obtain the amorphous iron-doped ruthenium oxide nanosheet catalyst. The amorphous iron-doped ruthenium oxide nanosheet grows on a carbon paper substrate by adopting a solid phase-molten salt method. The electronic structure of ruthenium is regulated and controlled through iron doping, adsorption of nitric oxide gas is enhanced, meanwhile, the catalyst has more catalytic active sites due to the amorphous structure, and efficient and high-selectivity synthesis of ammonia can be achieved when the catalyst is applied to an electrochemical NO reduction reaction due to the comprehensive influence of the factors.

Description

Technical Field

[0001] The invention relates to the technical field of nanomaterials, and in particular to a preparation method and application of an amorphous iron-doped ruthenium oxide nanosheet catalyst. Background Art

[0002] Nitric oxide (NO) is one of the main air pollutants. Its elevated concentration can cause serious environmental problems such as acid rain, photochemical smog and ozone layer depletion, and endanger human health. Selective catalytic reduction (SCR) is currently the most common method for NO removal, but due to high operating costs and potential secondary pollution, this method has low sustainability. The electrocatalytic NO reduction reaction (NORR) uses renewable electricity to convert NO into high-value-added NH3, which not only meets the need for NO emission reduction, but also provides a green and sustainable solution for replacing the energy-intensive Haber-Bosch process for ammonia synthesis.

[0003] Selecting a suitable cathode material is the key and difficulty of the electrocatalytic NO reduction reaction. The electronic structure and active sites on the surface of the electrocatalyst are important factors that determine its catalytic activity. Compared with highly crystalline materials, amorphous materials have more unsaturated atoms that can serve as catalytic active sites, which enhances their catalytic activity. In addition, by doping with heterogeneous metal elements, the electronic structure of the reaction active sites can be effectively regulated, thereby optimizing the interaction strength between the reaction intermediates and the catalyst and reducing the reaction energy barrier of the key step. Therefore, designing and synthesizing efficient amorphous electrocatalysts to achieve highly selective synthesis of ammonia remains a huge challenge. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a preparation method and application of an amorphous iron-doped ruthenium oxide nanosheet catalyst, which adopts a solid phase-molten salt method to grow amorphous iron-doped ruthenium oxide nanosheets on a carbon paper substrate and is used for efficient and selective electrochemical NO reduction to synthesize ammonia.

[0005] The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0006] A method for preparing an amorphous iron-doped ruthenium oxide nanosheet catalyst comprises the following steps:

[0007] (1) Weighing ruthenium acetylacetonate, ferrous acetylacetonate and potassium bromide, adding deionized water and anhydrous ethanol, and stirring continuously at room temperature until the solution presents a clear and transparent dark red color; immersing the pretreated carbon paper in the above mixed solution, and drying in an oven at 20 to 50° C. until the liquid is completely evaporated;

[0008] (2) The carbon paper with dark red precipitate on the surface obtained in step 1 is placed in the center of a tube furnace. In an air atmosphere, the temperature is increased to 260° C. at a rate of 3 to 5° C. / min and maintained for 0.5 h. The obtained sample is rinsed with deionized water and ethanol and dried at room temperature to obtain an amorphous iron-doped ruthenium oxide nanosheet catalyst.

[0009] Preferably, in the above technical solution, in step (1), the mass ratio of the ruthenium acetylacetonate, the ferrous acetylacetonate and the potassium bromide is (6-8):(1-2):(12-18).

[0010] Preferably, in the above technical solution, in step (1), the volume ratio of the anhydrous ethanol to the deionized water is 6:1; the mass volume ratio of the ruthenium acetylacetonate to the anhydrous ethanol is (6-8):(5-8).

[0011] Preferably, in the above technical solution, in step (1), the size of the carbon paper is 1×3 cm 2 The carbon paper pretreatment is to boil the carbon paper at 60° C. for 24 hours with a mixed solution of water, concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:1:1 before use.

[0012] Preferably, in the above technical solution, in step (1), the oven temperature is 20 to 30° C., and the drying time is 12 to 14 hours.

[0013] An amorphous iron-doped ruthenium oxide nanosheet catalyst.

[0014] Application of an amorphous iron-doped ruthenium oxide nanosheet catalyst in electrochemical NO reduction to ammonia synthesis.

[0015] Preferably, in the above technical scheme, in the electrochemical NO reduction synthesis of ammonia, the electrolyte is 0.5M Na2SO4 solution, the prepared amorphous iron-doped ruthenium oxide nanosheets are used as working electrodes, Ag / AgCl electrodes are used as reference electrodes, carbon rods are used as counter electrodes, and when NO is used as the reaction gas, at low overpotential, the Faraday efficiency of synthesizing ammonia can reach 98%.

[0016] A device for synthesizing ammonia by electrochemical NO reduction, wherein the device uses an amorphous iron-doped ruthenium oxide nanosheet catalyst as a working electrode.

[0017] A method for improving the efficiency of ammonia synthesis, wherein an amorphous iron-doped ruthenium oxide nanosheet catalyst is used to electrochemically reduce NO to synthesize ammonia.

[0018] The above technical solution of the present invention has the following beneficial effects:

[0019] The present invention adopts a solid phase-molten salt method to grow amorphous iron-doped ruthenium oxide nanosheets on a carbon paper substrate. Ruthenium-based catalysts have excellent catalytic activity in other nitrogen cycle reactions such as nitrate electroreduction to synthesize ammonia. Iron-based catalysts are the main catalysts used in industrial ammonia synthesis. They are widely used in nitrogen cycle research due to their excellent performance and low price.

[0020] The present invention regulates the electronic structure of ruthenium and enhances the adsorption of nitric oxide gas by iron doping, and at the same time the amorphous structure enables the catalyst to have more catalytic active sites. The combined influence of the above factors enables the catalyst to be used in the electrochemical NO reduction reaction to achieve efficient and highly selective synthesis of ammonia. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0022] Figure 1 This is the morphology and element distribution diagram of amorphous iron-doped ruthenium oxide nanosheet catalyst.

[0023] Figure 2 This is the XRD comparison diagram of amorphous iron-doped ruthenium oxide and undoped iron ruthenium oxide material.

[0024] Figure 3 Linear sweep voltammetry curves of amorphous iron-doped ruthenium oxide and undoped iron ruthenium oxide during electrocatalytic NO reduction.

[0025] Figure 4 Faradaic efficiency of electrocatalytic NO reduction to ammonia over amorphous Fe-doped ruthenium oxide. DETAILED DESCRIPTION

[0026] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

[0027] The chemical reagents used in the present invention are analytically pure ruthenium acetylacetonate, ferrous acetylacetonate, potassium bromide and anhydrous ethanol.

[0028] Cut the carbon paper into 1×3cm 2 , boil the mixed solution of water, concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:1:1 at 60℃ for 24h. Rinse with water several times, then rinse with ethanol, and it can be used after rinsing clean.

[0029] Example 1

[0030] Step 1: Weigh 80 mg of ruthenium acetylacetonate, 14 mg of ferrous acetylacetonate and 150 mg of potassium bromide, add 60 mL of anhydrous ethanol and 10 mL of deionized water, and continue stirring at room temperature until the solution becomes a clear, transparent dark red color. Immerse the treated carbon paper in the above mixed solution and dry it in an oven at 25°C until the liquid is completely evaporated.

[0031] Step 2: Place the carbon paper with dark red precipitate on the surface obtained in step 1 in the center of a tube furnace, and heat it to 260°C at a rate of 5°C / min in an air atmosphere and keep it for 30 minutes. After cooling naturally to room temperature, take out the sample, rinse it with deionized water and ethanol, and dry it at room temperature to obtain iron-doped ruthenium oxide nanosheets.

[0032] Example 2

[0033] Step 1: Weigh 96 mg of ruthenium acetylacetonate, 17 mg of ferrous acetylacetonate and 180 mg of potassium bromide, add 72 mL of anhydrous ethanol and 12 mL of deionized water, and continue stirring at room temperature until the solution becomes a clear, transparent dark red color. Immerse the treated carbon paper in the above mixed solution and dry it in an oven at 25°C until the liquid is completely evaporated.

[0034] Step 2: Place the carbon paper with dark red precipitate on the surface obtained in step 1 in the center of a tube furnace, and heat it to 260°C at a rate of 5°C / min in an air atmosphere and keep it for 30 minutes. After cooling naturally to room temperature, take out the sample, rinse it with deionized water and ethanol, and dry it at room temperature to obtain iron-doped ruthenium oxide nanosheets.

[0035] Example 3

[0036] Step 1: Weigh 67 mg of ruthenium acetylacetonate, 12 mg of ferrous acetylacetonate and 125 mg of potassium bromide, add 54 mL of anhydrous ethanol and 9 mL of deionized water, and continue stirring at room temperature until the solution becomes a clear, transparent dark red color. Immerse the treated carbon paper in the above mixed solution and dry it in an oven at 25°C until the liquid is completely evaporated.

[0037] Step 2: Place the carbon paper with dark red precipitate on the surface obtained in step 1 in the center of a tube furnace, and heat it to 260°C at a rate of 5°C / min in an air atmosphere and keep it for 30 minutes. After cooling naturally to room temperature, take out the sample, rinse it with deionized water and ethanol, and dry it at room temperature to obtain iron-doped ruthenium oxide nanosheets.

[0038] Application Example 1

[0039] The specific steps of conducting an electrochemical NO reduction test using the amorphous iron-doped ruthenium oxide nanosheets prepared by the present invention are as follows:

[0040] (1) A standard three-electrode system was used to test in an H-type electrolytic cell with two chambers separated by a Nafion membrane. The electrolyte was a 0.5 M Na2SO4 solution. The amorphous iron-doped ruthenium oxide nanosheets obtained in Example 1 were used as the working electrode, the Ag / AgCl electrode was used as the reference electrode, and the carbon rod was used as the counter electrode. The electrochemical workstation was connected.

[0041] (2) Before the electrochemical test, argon (Ar) was passed through the cathode electrolyte for 20 minutes, and then nitric oxide (NO) gas was passed through for 20 minutes until the solution was saturated. The electrocatalytic activity of amorphous iron-doped ruthenium oxide nanosheets in saturated electrolytes of Ar and NO was tested by linear sweep voltammetry (LSV). The linear sweep voltammetry (LSV) curve was repeatedly scanned, and constant potential electrolysis (it) was performed after reaching a steady state. The results show that the Faraday efficiency of ammonia can reach ~98%.

[0042] like Figure 1 As shown in FIG. 1 , the synthesized material is in the form of nanosheets supported on carbon fibers, and the Ru, O, and Fe elements are evenly distributed on the nanosheets. Figure 2 As shown in the figure, the XRD peaks are all diffraction peaks of the carbon paper substrate, and no other peaks are observed, indicating that the material has an amorphous structure. Figure 3 As shown in the figure, the current density of electrocatalytic NO reduction is significantly greater than that in the blank Ar atmosphere, indicating that the material has electrocatalytic NO reduction activity, and the amorphous iron-doped ruthenium oxide has a larger current than the undoped iron ruthenium oxide catalyst during the electrocatalytic NO reduction process, indicating that its electrocatalytic activity is higher. Figure 4 As shown, the Faraday efficiency of electrocatalytic NO reduction to produce ammonia at different potentials presents a volcano-like state, and the highest Faraday efficiency of synthetic ammonia can reach ~98%, showing excellent synthetic ammonia performance.

[0043] According to the present invention, the process parameters are adjusted to achieve the preparation of amorphous iron-doped ruthenium oxide nanosheets, which have the same performance as the present invention and can be used to synthesize ammonia by electrochemical NO reduction.

[0044] Although the present invention has been disclosed as above by the embodiments, it is not intended to limit the present invention. Any person skilled in the art may make various choices and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention is limited by the claims and their equivalents.

Claims

1. A method for preparing an amorphous iron-doped ruthenium oxide nanosheet catalyst, characterized in that: The following steps are involved: (1) Weighing ruthenium acetylacetonate, ferrous acetylacetonate and potassium bromide, adding deionized water and anhydrous ethanol, and stirring continuously at room temperature until the solution presents a clear and transparent dark red color; immersing the pretreated carbon paper in the above mixed solution, and drying in an oven at 20 to 50° C. until the liquid is completely evaporated; (2) The carbon paper with dark red precipitate on the surface obtained in step 1 is placed in the center of a tube furnace. In an air atmosphere, the temperature is increased to 260° C. at a rate of 3 to 5° C. / min and maintained for 0.5 h. The obtained sample is rinsed with deionized water and ethanol and dried at room temperature to obtain an amorphous iron-doped ruthenium oxide nanosheet catalyst.

2. The method for preparing the amorphous iron-doped ruthenium oxide nanosheet catalyst according to claim 1, characterized in that: In step (1), the mass ratio of the ruthenium acetylacetonate, the ferrous acetylacetonate and the potassium bromide is (6-8):(1-2):(12-18).

3. The method for preparing the amorphous iron-doped ruthenium oxide nanosheet catalyst according to claim 2, characterized in that: In step (1), the volume ratio of the anhydrous ethanol to the deionized water is 6:1; the mass volume ratio of the ruthenium acetylacetonate to the anhydrous ethanol is (6-8):(5-8).

4. The method for preparing the amorphous iron-doped ruthenium oxide nanosheet catalyst according to claim 1, characterized in that: In step (1), the size of the carbon paper is 1×3 cm 2 The carbon paper pretreatment is to boil the carbon paper at 60° C. for 24 hours with a mixed solution of water, concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:1:1 before use.

5. The method for preparing the amorphous iron-doped ruthenium oxide nanosheet catalyst according to claim 1, characterized in that: In step (1), the oven temperature is 20 to 30° C. and the drying time is 12 to 14 hours.

6. An amorphous iron-doped ruthenium oxide nanosheet catalyst prepared according to any one of the preparation methods of claims 1-5.

7. Use of an amorphous iron-doped ruthenium oxide nanosheet catalyst prepared by any one of claims 1 to 5 in electrochemical NO reduction to synthesize ammonia.

8. The use according to claim 7, characterized in that: In the electrochemical NO reduction ammonia synthesis, the electrolyte is a 0.5M Na2SO4 solution, the prepared amorphous iron-doped ruthenium oxide nanosheet is used as a working electrode, the Ag / AgCl electrode is used as a reference electrode, the carbon rod is used as a counter electrode, and when NO is used as a reaction gas, at a low overpotential, the Faraday efficiency of the ammonia synthesis can reach 98%.

9. A device for electrochemical NO reduction to synthesize ammonia, characterized in that: The device uses the amorphous iron-doped ruthenium oxide nanosheet catalyst prepared by any preparation method described in claims 1-5 as a working electrode.

10. A method for improving the efficiency of synthetic ammonia, characterized in that: In the method, the amorphous iron-doped ruthenium oxide nanosheet catalyst prepared by any one of the preparation methods described in claims 1-5 is used to electrochemically reduce NO to synthesize ammonia.

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