Based on spinel Co x Mn 3-x A method for regulating the active sites on the surface of electrocatalysts by co-precipitation of O4

Abstract

The present invention relates to a spinel Co x Mn 3‑x The method for regulating the active sites on the surface of an electrocatalyst by a co-precipitation method of O4 comprises the following steps: dissolving a Co source and a Mn source in a solvent and mixing them uniformly to prepare a salt solution A containing Co and Mn; preparing a precipitant B of corresponding concentration, controlling the temperature of the precipitant B to be 1-100°C, and continuously stirring the precipitant B at a certain speed; dripping the salt solution A into the precipitant B at a uniform speed to obtain a suspension C, and stirring the suspension C uniformly; separating the suspension C into a solid and liquid, extracting a precipitate D, washing, drying, and grinding the precipitate D to obtain Co x Mn 3‑x An O4 precursor, where 0 < x < 3, is heat-treated to obtain the final product. Compared to existing technologies, the present invention can simultaneously control the physical and chemical characteristics of the material, such as the distribution of Co and Mn active sites on the surface and their occupancy ratio in the structure, during the synthesis process. This method offers the advantages of simplicity, energy conservation, economy, and suitability for large-scale production.

Description

Technical Field

[0001] The present invention relates to the field of electrocatalysts, and in particular to a spinel Co-based electrocatalyst. x Mn 3-x A new method and application for regulating the active sites on the surface of electrocatalysts of O4 (0<x<3). Background Art

[0002] To alleviate the energy crisis, sustainable clean energy technologies have become a key means, among which electrocatalysis is one of the important foundations. Electrocatalysis can achieve energy generation and efficient energy conversion, such as water electrolysis and the conversion between chemical energy and electrical energy in fuel cells. As the core component of the reaction electrode, the catalytic activity of the electrocatalyst determines the reaction rate of the electrode, which in turn affects the overall performance of the device. Currently, there are many factors that affect the performance of electrocatalysts, including composition, morphology, valence state, etc. However, the electrocatalytic reaction is a reaction that occurs on the catalyst surface. Therefore, regulating the electrocatalyst surface can achieve twice the result with half the effort in regulating the electrocatalytic performance of the material.

[0003] Composite materials of two or more metal elements can be prepared by coprecipitation, and have the advantages of uniform composition and fine particles. Some transition metal elements usually have multiple valence states and similar atomic properties, so they can be used as raw materials for synthesizing oxide catalysts by coprecipitation. In addition, spinel oxides containing transition metals, such as Co x Mn 3-x O₄ (0 < x < 3) is one of the most promising materials in the field of electrocatalysis. In addition to manipulating the bulk characteristics of these materials, the use of co-precipitation to fine-tune the proportion and occupancy of active sites on their surfaces, such as their physicochemical properties, can enhance their electrocatalytic performance, which is crucial for advancing clean energy technologies. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a spinel Co x Mn 3-x A method for regulating the active sites on the surface of electrocatalysts by co-precipitation of O4.

[0005] The purpose of the present invention can be achieved by the following technical solutions: a spinel Co x Mn 3-x The method for regulating the active sites on the surface of an electrocatalyst by co-precipitation of O4 comprises the following steps:

[0006] S01, dissolving a Co source and a Mn source in a molar ratio in accordance with a chemical formula in a solvent, and mixing them uniformly to prepare a salt solution A containing Co and Mn;

[0007] S02. Prepare a precipitant B of corresponding concentration, control the temperature of the precipitant B to be 1-100° C., and continuously stir the precipitant B at a constant speed using a mechanical stirring method;

[0008] S03, adding salt solution A to precipitant B at a uniform rate to obtain suspension C, and stirring evenly;

[0009] S04, separate the suspension C into solid and liquid, extract the precipitate D, wash, dry, grind, and obtain Co x Mn 3-x O4 precursor, where 0<x<3;

[0010] S05. Heat-treating the precursor to obtain a final product.

[0011] Furthermore, the Co x Mn 3-x The selection range of x in O4 is between 0.5 and 2.5.

[0012] Furthermore, in step S01, the Co source is a water-soluble cobalt salt, including but not limited to cobalt nitrate, cobalt sulfate, cobalt acetate, cobalt chloride, and water-soluble organic cobalt salts; the Mn source is a water-soluble manganese salt, including but not limited to manganese nitrate, manganese sulfate, manganese chloride, manganese acetate, and water-soluble organic manganese salts; and the solvent is deionized water or ultrapure water.

[0013] Furthermore, the pH value range of the precipitant B in step S02 should be selected to be pH ≥ 10, and the OH in the precipitant should be controlled. - The relationship between the molar concentration a of the ion and the molar concentrations b and c of Co and Mn cations in the salt solution A satisfies: a ≥ xb + yc, where x is the valence state of the Co ion and y is the valence state of the Mn ion.

[0014] Furthermore, the precipitant is prepared using at least one of NaOH, KOH, NH3·H2O, and NH4HCO3.

[0015] Furthermore, in step S02, the constant temperature of the precipitant B is selected to be between 60-80°C.

[0016] Furthermore, for each step involving stirring, the stirring rate is controlled between 300-800 rpm.

[0017] Furthermore, in step S03, the salt solution A is uniformly dripped into the precipitant B at a rate of 1 mL / min-3 mL / min; after the dropwise addition of solution A is completed, the suspension C is continuously stirred for 20 min-60 min.

[0018] Furthermore, in step S04, the solid-liquid separation of the suspension C is performed by centrifugation or static aging, and the precipitate is washed with deionized water or ultrapure water;

[0019] The precipitate D is dried in air or vacuum environment at a drying temperature between 40-80°C.

[0020] Furthermore, the heat treatment of the precursor in step S05 is performed under an atmosphere of air, hydrogen, nitrogen or oxygen;

[0021] The heat treatment temperature is between 400-800℃, the heating rate is 1℃ / min-10℃ / min, the holding time is 0.5h-6h, and the cooling rate is 1℃ / min-10℃ / min.

[0022] The catalyst prepared by the method of the present invention can be applied in the field of development of bifunctional electrocatalysts for oxygen electrodes and development of related devices.

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

[0024] This invention utilizes a coprecipitation method for the first time to regulate the active sites on the catalyst surface during precursor synthesis. This method exploits the different solubility products (Ksp) of Co and Mn metal cations in saturated alkaline solutions, resulting in different deposition rates. Furthermore, by controlling the Co / Mn ratio in the raw materials, the physicochemical properties of the catalyst, such as the ratio of Co and Mn active sites and the active element occupancy of Co and Mn, can be controlled during the nucleation process.

[0025] 2. The present invention can regulate the surface conditions of the material catalyst without other complicated surface post-treatments, thereby affecting the catalytic performance. The synthesis process is simple and easy to operate, and can be applied to low-cost, large-scale material production, promoting the development of clean energy technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The X-ray powder diffraction spectra of Example 1, Example 2, and Comparative Example 1 are shown;

[0027] Figure 2 The following are scanning electron microscope photos of Example 1, Example 2, and Comparative Example 1;

[0028] Figure 3 Energy distribution surface scanning analysis photos of Example 1, Example 2, and Comparative Example 1;

[0029] Figure 4 The crystal structure parameter refinement results of Example 1 and Comparative Example 1;

[0030] Figure 5 The voltage-current density (oxygen evolution reaction, oxygen reduction reaction) relationship curves obtained by testing Example 1, Example 2, and Comparative Example 1 on a rotating disk electrode are shown;

[0031] Figure 6 4 is a process flow chart of the method of the present invention. DETAILED DESCRIPTION

[0032] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0033] Example 1

[0034] A method for regulating the active sites on the surface of electrocatalysts based on the co-precipitation method of spinel Co2MnO4, such as Figure 6 As shown, the following steps are included:

[0035] 1) Dissolve the raw materials Co(NO3)2·6H2O and MnSO4·H2O in a molar ratio consistent with the chemical formula Co2MnO4 in 40 mL of deionized water to prepare a uniform Co and Mn mixed salt solution A.

[0036] 2) Preparation: 7.5 g of NaOH was dissolved in 100 mL of deionized water to obtain precipitant B. The precipitant B was heated to 75° C. and kept at a constant temperature.

[0037] 3) Using a mechanical stirring method, the precipitant B was stirred at a constant speed of 500 rpm.

[0038] 4) The prepared salt solution A containing Co and Mn was dripped into the precipitant B at a rate of 1 mL / min.

[0039] 5) After all the solution A is added dropwise to the precipitant, suspension C is obtained, which is stirred at a stirring speed of 500 rpm for 20 minutes.

[0040] 6) Use a centrifuge to separate the suspension C into solid and liquid, extract the precipitate D, and wash it three times with deionized water.

[0041] 7) Dry the precipitate D at a constant temperature of 50° C. in air, and grind it to obtain a Co 2 MnO 4 precursor.

[0042] 8) The precursor was heat treated in air at a heating rate of 1°C / min from room temperature to 600°C, kept at that temperature for 5 hours, and then cooled to room temperature at a cooling rate of 5°C / min to obtain Co2MnO4 with controlled surface active sites.

[0043] The Co2MnO4 prepared in Example 1 is a pure spinel phase, and the X-ray powder diffraction spectrum is as follows: Figure 1 The morphology of the sample is shown in Figure 2 As shown in a. Figure 3a The distribution of Co and Mn elements in the sample can be observed in the energy distribution surface scanning analysis photo. The material particles have a Mn-enriched surface, and the surface Co:Mn ratio is approximately equal to 1. Figure 4 The structural refinement results of a show that both sites 8a and 16d in the sample are occupied by a mixture of Co and Mn.

[0044] The material was installed in a rotating disk electrode test device and electrochemical performance tests were performed at room temperature. The oxygen evolution test was performed in oxygen-saturated 1M KOH, and the oxygen reduction test was performed in oxygen-saturated 0.1M KOH. The rotating disk speed was 1600 rpm. The results of the rotating disk electrode electrochemical performance test for catalytic oxygen evolution reaction are shown in Figure 2. Figure 5 As shown in a: When the potential reaches 1.64V, the measured current density reaches 100mA / cm 2 The results of catalytic oxygen reduction reaction are as follows. Figure 5 As shown in b: the half-wave potential is 0.83V, and the limiting current density can reach 5.8mA / cm 2 The results show that the surface-controlled Co2MnO4 electrocatalyst of the present invention has an excellent bifunctional electrocatalytic effect, and its effect is significantly improved compared with that of Comparative Example 1.

[0045] Example 2

[0046] A spinel Co 2.2 Mn 0.8 The method for regulating the active sites on the surface of an electrocatalyst by co-precipitation of O4 comprises the following steps:

[0047] 1) The chemical formula Co 2.2 Mn 0.8 The raw materials Co(NO3)2·6H2O and Mn(NO3)2·4H2O in a molar stoichiometric ratio of O4 were dissolved in 50 mL of ultrapure water to prepare a uniform Co and Mn salt solution A.

[0048] 2) Preparation: 8.5 g of NaOH was dissolved in 100 mL of deionized water to obtain precipitant B. The precipitant B was heated to 65° C. and kept at a constant temperature.

[0049] 3) Using a mechanical stirring method, the precipitant B was stirred at a constant speed of 800 rpm.

[0050] 4) The prepared salt solution A containing Co and Mn was dripped into the precipitant B at a rate of 2 mL / min.

[0051] 5) After all the precipitant is added to solution A, suspension C is obtained, which is stirred at 500 rpm for 40 minutes.

[0052] 6) After standing for 30 minutes, suspension C was immediately subjected to solid-liquid separation to extract precipitate D. Precipitate D was then washed three times with ultrapure water.

[0053] 7) Dry the precipitate D in a vacuum drying oven at 40°C and grind it to obtain Co 2.2 Mn 0.8 O4 precursor.

[0054] 8) The precursor was heat treated in nitrogen. The heat treatment process was as follows: heating from room temperature to 500°C at a heating rate of 1°C / min, keeping the temperature for 4 hours, and then cooling down to room temperature at a cooling rate of 5°C / min. 2.2 Mn 0.8 O4.

[0055] Co prepared in Example 2 2.2 Mn 0.8 O4 is a pure spinel phase, and the X-ray powder diffraction spectrum is as follows Figure 1 The SEM morphology of the sample is shown in Figure 2 As shown in b. Figure 3 b Energy distribution surface scanning analysis photo shows the distribution of Co and Mn elements in the sample. The material particles have a Mn-enriched surface, and the surface Co:Mn ratio is approximately equal to 1.2.

[0056] The material was installed in a rotating disk electrode test apparatus and electrochemical performance tests were performed at room temperature. The oxygen evolution reaction test was performed in oxygen-saturated 1M KOH, and the oxygen reduction reaction test was performed in oxygen-saturated 0.1M KOH. The rotating disk speed was 1600 rpm. The results of the rotating disk electrode electrochemical performance test for the catalytic oxygen evolution reaction are shown in FIG. Figure 5 As shown in a: When the potential reaches 1.62V, the measured current density reaches 100mA / cm 2 The results of catalytic oxygen reduction reaction are as follows. Figure 5 As shown in b: the half-wave potential is 0.827V, and the limiting current density can reach 5.6mA / cm 2 The results show that the surface-regulated Co 2.2 Mn 0.8 The O4 electrocatalyst has excellent bifunctional electrocatalytic effect. By adjusting the surface Co:Mn ratio, the OER performance is further improved.

[0057] Comparative Example 1

[0058] Co2MnO4 was synthesized using the conventional sol-gel method. The specific steps are as follows:

[0059] 1) Dissolve the raw materials Co(NO3)2·6H2O and Mn(NO4)2·4H2O in a molar ratio consistent with the chemical formula Co2MnO4 in 60 mL of deionized water to prepare a uniform Co and Mn salt solution A.

[0060] 2) Solution A was heated to 80° C. in a water bath and maintained at a constant temperature. 0.02 g of citric acid monohydrate and 100 μL of ethylene glycol were added and stirred continuously at 500 rpm. After 3 h, a gel-like precursor B was obtained.

[0061] 3) Dry the precursor B at a constant temperature of 50° C. in air and grind it into powder.

[0062] 4) The dried precursor B was heat treated in air by heating from room temperature to 400°C at a rate of 2°C / min, holding the temperature for 2 hours, then heating to 900°C at a rate of 5°C / min and holding the temperature for 3 hours, and then cooling to room temperature at a rate of 5°C / min. A comparative sample, Co2MnO4, was obtained.

[0063] The Co2MnO4 prepared in Comparative Example 1 is a pure spinel phase, and the X-ray powder diffraction spectrum is as follows: Figure 1 The SEM morphology of the sample is shown in Figure 2 As shown in c. Figure 3 c Energy distribution surface scanning analysis photo shows the distribution of Co and Mn elements in the sample, which are evenly distributed inside the particles without obvious other surface features. Figure 4 The structural refinement results of b show that the 8a and 16d sites in the sample are occupied by Mn and Co respectively, and there is no mixed occupancy.

[0064] The material was installed in a rotating disk electrode test apparatus and electrochemical performance tests were performed at room temperature. The oxygen evolution reaction test was performed in oxygen-saturated 1M KOH, and the oxygen reduction reaction test was performed in oxygen-saturated 0.1M KOH. The rotating disk speed was 1600 rpm. The results of the rotating disk electrode electrochemical performance test for the catalytic oxygen evolution reaction are shown in FIG. Figure 5 As shown in a: When the potential reaches 1.74V, the measured current density reaches 100mA / cm 2 The results of catalytic oxygen reduction reaction are as follows. Figure 5 As shown in b: the half-wave potential is 0.76V, and the limiting current density can reach 5.3mA / cm 2 Compared with Examples 1 and 2, the catalytic activity of the comparative example is significantly lower.

[0065] The above description of the examples is intended to facilitate understanding and application of the invention by persons of ordinary skill in the art. It should be understood that any technical solution that a person of ordinary skill in the art can arrive at based on the concepts of the present invention, through logical analysis, reasoning, or limited experimentation on the basis of existing technologies, without requiring creative effort, should fall within the scope of protection defined by the claims.

Claims

1. A spinel Co-based x Mn 3-x The method for regulating the active sites on the surface of an electrocatalyst by co-precipitation of O4 is characterized in that: The following steps are involved: S01, dissolving a Co source and a Mn source in a solvent and mixing them uniformly to prepare a salt solution A containing Co and Mn; S02, prepare the corresponding concentration of precipitant B, and control the temperature of precipitant B to be: 60-80℃, and stir precipitant B at a constant speed; the pH value range of precipitant B is selected to be pH ≥ 10, and control the OH in the precipitant - The relationship between the molar concentration a of the ion and the molar concentrations b and c of Co and Mn cations in the salt solution A satisfies: a ≥ xb + yc, where x is the valence of the Co ion and y is the valence of the Mn ion; S03. Add salt solution A to precipitant B at a uniform rate to obtain suspension C, and stir evenly; the rate of uniformly adding salt solution A to precipitant B is 1 mL / min-3 mL / min; after the addition of solution A is completed, the suspension C is stirred for 20 min-60 min; S04, separate the suspension C into solid and liquid, extract the precipitate D, wash, dry, grind, and obtain Co x Mn 3-x O4 precursor, where 0<x<3; S05. Heat-treating the precursor to obtain a final product.

2. The spinel Co-based x Mn 3-x The method for regulating the active sites on the surface of an electrocatalyst by co-precipitation of O4 is characterized in that: The Co x Mn 3-x The selection range of x in O4 is between 0.5 and 2.

5.

3. The spinel Co-based x Mn 3-x The method for regulating the active sites on the surface of an electrocatalyst by co-precipitation of O4 is characterized in that: In step S01, the Co source is a water-soluble cobalt salt, including cobalt nitrate, cobalt sulfate, cobalt chloride or a water-soluble organic cobalt salt; the Mn source is a water-soluble manganese salt, including manganese nitrate, manganese sulfate, manganese chloride or a water-soluble organic manganese salt; and the solvent is deionized water or ultrapure water.

4. The spinel Co-based x Mn 3-x The method for regulating the active sites on the surface of an electrocatalyst by co-precipitation of O4 is characterized in that: The precipitant is prepared using at least one of NaOH, KOH, NH3•H2O, and NH4HCO3.

5. The spinel Co-based x Mn 3-x The method for regulating the active sites on the surface of an electrocatalyst by co-precipitation of O4 is characterized in that: The stirring rate was between 300-800 rpm.

6. The spinel Co-based x Mn 3-x The method for regulating the active sites on the surface of an electrocatalyst by co-precipitation of O4 is characterized in that: In step S04, the solid-liquid separation of the suspension C is performed by centrifugation or static aging, and the precipitate is washed with deionized water or ultrapure water; The precipitate D is dried in air or vacuum environment at a drying temperature between 40-80°C.

7. The spinel Co-based quartz crystal according to claim 1 x Mn 3-x The method for regulating the active sites on the surface of an electrocatalyst by co-precipitation of O4 is characterized in that: The heat treatment of the precursor in step S05 is performed under air, nitrogen or oxygen atmosphere; The heat treatment temperature is between 400-800℃, the heating rate is 1℃ / min-10℃ / min, the holding time is 0.5h-6h, and the cooling rate is 1℃ / min-10℃ / min.

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