Electrocatalyst, method for preparing the same, and use thereof

Abstract

The application discloses an electrocatalyst and a preparation method and application thereof, and belongs to the field of electrocatalysts. The electrocatalyst is composed of a conductive substrate and an active component; the active component is in-situ grown on the surface of the conductive substrate; the structural formula of the active component is CoFe-(74+88); CoFe-(74+88) is a cobalt-iron bimetal-organic framework containing CoFe-MOF-74 and CoFe-MIL-88; and the CoFe-(74+88) is in-situ grown on the surface of the conductive substrate in the form of two-dimensional nanosheets. The electrocatalyst prepared by the application has high active site exposure and excellent oxygen evolution catalytic activity, the catalytic effect in an alkaline electrolyte system is continuous and stable, and the electrocatalyst has great practical application value.

Description

Technical Field

[0001] This application relates to an electrocatalyst, its preparation method, and its application, and belongs to the field of electrocatalysis. Background Technology

[0002] With the continuous development of society, the demand for energy has increased dramatically. The consumption of large quantities of fossil fuels has led to serious energy crises and environmental pollution. Therefore, the development and utilization of clean and sustainable new energy sources have attracted increasing attention. Hydrogen energy, as a green energy source, is considered an ideal alternative to fossil fuels due to its high energy density, high conversion efficiency, abundant sources, and clean and pollution-free characteristics. Electrocatalytic water splitting for hydrogen production is a promising method, as the process is clean and pollution-free and can achieve large-scale hydrogen production. The electrocatalytic water splitting process mainly consists of the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Compared to the HER, the OER involves a four-electron transfer process, making the reaction complex and exhibiting kinetic lag. Therefore, the OER primarily determines the efficiency of the entire electrocatalytic water splitting process.

[0003] Currently, noble metal (Ir and Ru)-based catalysts exhibit good catalytic activity and stability in the oxygen evolution reaction (OER). However, due to the scarcity and high cost of noble metals on Earth, large-scale production and application are difficult. Therefore, developing low-cost, high-performance non-noble metal-based, especially transition metal-based (such as Co, Fe, Ni, and Mn) OER electrocatalysts is of great significance.

[0004] Metal-organic frameworks (MOFs) are organic-inorganic hybrid materials formed by the self-assembly of metal ions or ion clusters and organic ligands through coordination bonds. Compared with traditional inorganic materials, MOFs possess advantages such as high specific surface area, large pore size, designable and tunable pore structure, and functionalizability, exhibiting excellent performance in various fields including catalysis, adsorption, gas storage, and drug delivery. In recent years, their application in electrochemistry has also been increasingly reported. Typically, MOFs are used as sacrificial templates, and MOF-derived materials are obtained through calcination. While materials obtained using this method exhibit good electrocatalytic performance, the inherent structure of MOFs collapses during calcination, their pores become blocked or destroyed, metals aggregate, and active sites are lost, failing to fully utilize the advantages of the MOF's inherent structure.

[0005] Existing research indicates that unsaturated coordination metal sites in metal-organic frameworks (MOFs) are beneficial for promoting catalytic reactions. Through rational design, MOFs can be made to exhibit a two-dimensional nanosheet structure, thereby exposing more unsaturated coordination metal sites and effectively reducing electron transport resistance, thus improving the catalytic performance of the material. However, most MOFs have a single component structure, and electrocatalysts containing bimetallic MOFs are rarely reported; breakthroughs in this area are urgently needed. Summary of the Invention

[0006] In view of this, the present invention provides an electrocatalyst, its preparation method and application, the main purpose of which is to synthesize an electrocatalyst with a bimetallic-organic framework in one step to improve its activity and stability in water electrolysis.

[0007] According to one aspect of this application, an electrocatalyst is provided, the electrocatalyst comprising a conductive substrate and an active component grown in situ on the surface of the conductive substrate;

[0008] The active ingredient has the structural formula CoFe-(74+88), which is a cobalt-iron bimetallic-organic framework containing CoFe-MOF-74 and CoFe-MIL-88.

[0009] The conductive substrate is selected from nickel substrate, nickel-iron substrate, iron substrate or copper substrate.

[0010] According to another aspect of this application, a method for preparing the above-mentioned electrocatalyst is provided, comprising the following steps:

[0011] In a sealed container, a cobalt source, an iron source, an organic ligand, a solvent, and a conductive substrate are mixed, heat-treated, and dried (vacuum dried) to obtain the electrocatalyst.

[0012] The conductive substrate is cleaned;

[0013] The cleaning process includes ultrasonic treatment of the conductive substrate in a hydrochloric acid solution, followed by cleaning with ethanol and water and vacuum drying to obtain a clean conductive substrate.

[0014] The concentration of the hydrochloric acid solution is 1–3 mol / L;

[0015] The ultrasound session lasted 15–20 minutes.

[0016] The vacuum drying temperature is 60–80°C;

[0017] The vacuum drying time is 6 to 10 hours.

[0018] The cobalt source is selected from at least one of cobalt nitrate, cobalt acetate, or cobalt chloride;

[0019] The iron source is selected from at least one of ferrous acetate, ferrous chloride, ferrous sulfate, ferric chloride, ferric nitrate, and ferric sulfate.

[0020] The organic ligand is selected from 2,5-dihydroxyterephthalic acid and / or 2-aminoterephthalic acid;

[0021] The solvent is selected from at least one of N,N-dimethylformamide, ethanol, and water.

[0022] The molar ratio of the cobalt source, iron source, and organic ligand is 0.1–0.3:0:05–0.15:0.1–0.3.

[0023] The heat treatment temperature is 100–120°C;

[0024] The heat treatment time is 12 to 30 hours.

[0025] The drying temperature is 60–100°C;

[0026] The drying time is 6 to 12 hours.

[0027] According to another aspect of this application, an electrode material is provided, the electrode material comprising the electrocatalyst described above.

[0028] According to another aspect of this application, the above-described electrocatalyst is provided for use in alkaline electrocatalytic oxygen evolution.

[0029] A standard three-electrode system is adopted, with the working electrode being the electrocatalyst CoFe-(74+88), the reference electrode being a mercury / mercury oxide electrode, and the counter electrode being a platinum sheet or a graphite electrode.

[0030] This invention provides a specific method for preparing a two-dimensional nanosheet structured electrocatalyst for alkaline electrocatalytic oxygen evolution, comprising the following steps:

[0031] (1) Weigh out cobalt nitrate hexahydrate, ferric chloride hexahydrate, ferrous chloride tetrahydrate, 2,5-dihydroxyterephthalic acid and 2-aminoterephthalic acid and add them to a mixed solution of N,N-dimethylformamide, ethanol and deionized water. After thorough sonication and complete dissolution, a precursor solution is obtained.

[0032] (2) Place the nickel foam in the solution prepared in step (1) and sonicate thoroughly;

[0033] (3) Transfer the solution and nickel foam obtained in step (2) into a reaction vessel, seal it, and react at 100-120℃ for 12-30h. After the reaction is completed, cool it naturally to room temperature, wash it with N,N-dimethylformamide and methanol, and dry it under vacuum to obtain a cobalt-iron bimetallic-organic framework (CoFe-(74+88)) two-dimensional nanosheet electrocatalyst grown on nickel foam.

[0034] The two-dimensional nanosheet structured electrocatalyst for alkaline electrocatalytic oxygen evolution provided by this invention is a cobalt-iron bimetallic-organic framework two-dimensional nanosheet synthesized by solvothermal method with cobalt and iron as metal centers and 2,5-dihydroxyterephthalic acid and 2-aminoterephthalic acid as organic ligands, based on nickel foam as the substrate material.

[0035] The beneficial effects that this application can produce include:

[0036] (1) This invention provides a two-dimensional electrocatalyst (CoFe-(74+88)) grown in situ on the surface of nickel foam for alkaline electrocatalytic oxygen evolution and its preparation method.

[0037] (2) The nickel foam provided by the present invention has a three-dimensional porous structure and excellent conductivity. As a conductive substrate, it can be used directly as a working electrode to prepare electrocatalysts, effectively improving the catalytic activity and stability of the material.

[0038] (3) The CoFe-(74+88) provided by the present invention introduces two metal-organic framework materials, CoFe-MOF-74 and CoFe-MIL-88, through a one-step solvothermal method. The two-dimensional nanosheet structure presents is conducive to fully exposing unsaturated coordination metal sites, increasing contact with electrolyte, reducing transport resistance, shortening mass transfer path, and enhancing electrocatalytic oxygen evolution performance.

[0039] (4) The preparation method of the nano-electrocatalyst CoFe-(74+88) with bimetallic organic framework material provided by the present invention is simple, easy to implement, low in cost, and highly controllable. It can be directly used as a working electrode, which is conducive to large-scale production and has broad application prospects. Attached Figure Description

[0040] Figure 1 The flowchart shows the preparation process of CoFe-(74+88) prepared in Example 1 of this invention.

[0041] Figure 2 This is a transmission electron microscope image of CoFe-(74+88) prepared in Example 1 of the present invention;

[0042] Figure 3 The linear sweep voltammetry curve of the electrocatalytic oxygen evolution of CoFe-(74+88) prepared in Example 1 of this invention is shown. The electrolyte is a 1.0 mol / L KOH aqueous solution.

[0043] Figure 4 The Tafel slope curve of CoFe-(74+88) prepared in Example 1 of this invention is shown.

[0044] Figure 5The stability test result of CoFe-(74+88) prepared in Example 1 of this invention at a current density of 10 mA cm-2 is shown. Detailed Implementation

[0045] The present application is further illustrated below with reference to specific embodiments. The following descriptions are merely a few embodiments of the present application and are not intended to limit the present application in any way. Although the present application discloses preferred embodiments as follows, they are not intended to limit the present application. Any modifications or variations made by those skilled in the art without departing from the scope of the technical solution of the present application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

[0046] Unless otherwise specified, the raw materials used in the embodiments of this application are all purchased commercially and used directly without any special treatment.

[0047] Unless otherwise specified, the analytical methods in the embodiments all adopt conventional instrument or equipment settings and conventional analytical methods.

[0048] The analysis method in the embodiments of the present invention is as follows:

[0049] The transmission electron microscopy (TEM) method was as follows: the sample was tested using a transmission electron microscope (model FEI Tecnai G2 F30S-TWIN).

[0050] The test method for electrocatalytic oxygen evolution is as follows: sample testing is performed using an electrochemical workstation (model: CHI760E).

[0051] Example 1

[0052] The present invention is in accordance with the following Figure 1 The method shown is used to prepare a two-dimensional nanosheet structured electrocatalyst (CoFe-(74+88)), and the steps are as follows:

[0053] (1) Cut the nickel foam into 3cm×1cm×2mm pieces, place them in 1mol / L hydrochloric acid solution and sonicate for 15min, then sonicate in anhydrous ethanol for 15min, rinse repeatedly with anhydrous ethanol, and finally place them in a vacuum drying oven and dry at 60℃ for 2h, and store for later use.

[0054] (2) Weigh 0.108 mmol of cobalt nitrate hexahydrate, 0.075 mmol of ferrous chloride tetrahydrate, 0.017 mmol of ferric chloride hexahydrate, 0.050 mmol of 2,5-dihydroxyterephthalic acid and 0.050 mmol of 2-aminoterephthalic acid and add them to a mixed solution of 10 mL of N,N-dimethylformamide, 0.6 mL of anhydrous ethanol and 0.6 mL of deionized water. Sonicate thoroughly for 30 min. Then transfer to a 20 mL polytetrafluoroethylene reactor and add the treated nickel foam. Solvothermal reaction at 120 °C for 24 h.

[0055] (3) After the reactor was naturally cooled to room temperature, it was washed with N,N-dimethylformamide and methanol, and then dried under vacuum to obtain a cobalt-iron bimetallic-organic framework two-dimensional nanosheet electrocatalyst (CoFe-(74+88)).

[0056] Depend on Figure 2 It can be seen that CoFe-(74+88) exhibits a two-dimensional nanosheet structure, confirming the successful formation of the two-dimensional nanosheet structure.

[0057] The electrocatalytic oxygen evolution performance of the two-dimensional nanosheet structure electrocatalyst CoFe-(74+88) prepared in Example 1 of this invention was tested using a 1 mol / L KOH solution. The test procedure is as follows:

[0058] Using a Shanghai Chenhua CHI760E workstation and a standard three-electrode system, with CoFe-(74+88) as the working electrode, a mercury / mercuric oxide electrode as the reference electrode, and a graphite electrode as the counter electrode, the linear sweep voltammetry curves of the electrocatalyst were tested within a potential range of 0.2–0.7 V at a scan rate of 5 mV s⁻¹. The corresponding Tafel slope curves were obtained from the linear sweep voltammetry curves. In addition, the current density of CoFe-(74+88) was set to a constant 10 mA cm⁻², and the potential change during catalytic oxygen evolution was recorded to determine the stability of CoFe-(74+88) in the electrocatalytic oxygen evolution process.

[0059] Test results are as follows Figure 3 , 4 As shown in Figure 5; Figure 3 The figure shown is a linear sweep voltammetric curve of CoFe-(74+88) in alkaline solution. CoFe-(74+88) has an overpotential as low as 185mV at a current density of 10mA cm-2.

[0060] Figure 4 The graph shown is the Tafel slope curve for CoFe-(74+88), with a value of 43.6 mV dec⁻¹, indicating that it has good reaction kinetics.

[0061] Figure 5 This indicates that CoFe-(74+88) exhibits excellent long-term stability under 30h working conditions.

[0062] Example 2

[0063] This embodiment follows the following... Figure 1 The method shown is used to prepare a two-dimensional nanosheet structured electrocatalyst (CoFe-(74+88)), and the steps are as follows:

[0064] (1) Cut the nickel foam into 3cm×1cm×2mm pieces, place them in 1mol / L hydrochloric acid solution and sonicate for 15min, then sonicate in anhydrous ethanol for 15min, rinse repeatedly with anhydrous ethanol, and finally place them in a vacuum drying oven and dry at 60℃ for 2h, and store for later use.

[0065] (2) Weigh 0.129 mmol of cobalt nitrate hexahydrate, 0.113 mmol of ferrous chloride tetrahydrate, 0.080 mmol of ferric chloride hexahydrate, 0.075 mmol of 2,5-dihydroxyterephthalic acid and 0.025 mmol of 2-aminoterephthalic acid and add them to a mixed solution of 10 mL of N,N-dimethylformamide, 0.6 mL of anhydrous ethanol and 0.6 mL of deionized water. Sonicate thoroughly for 30 min. Then transfer to a 20 mL polytetrafluoroethylene reactor and add the treated nickel foam. Solvothermal reaction at 120 °C for 24 h.

[0066] (3) After the reactor was naturally cooled to room temperature, it was washed with N,N-dimethylformamide and methanol, and then dried under vacuum to obtain a cobalt-iron bimetallic-organic framework two-dimensional nanosheet electrocatalyst (CoFe-(74+88)).

[0067] The test method for the electrocatalytic oxygen evolution performance is the same as in Example 1.

[0068] Example 3

[0069] This embodiment follows the following... Figure 1 The method shown is used to prepare a two-dimensional nanosheet structured electrocatalyst (CoFe-(74+88)), and the steps are as follows:

[0070] (1) Cut the nickel foam into 3cm×1cm×2mm pieces, place them in 1mol / L hydrochloric acid solution and sonicate for 15min, then sonicate in anhydrous ethanol for 15min, rinse repeatedly with anhydrous ethanol, and finally place them in a vacuum drying oven and dry at 60℃ for 2h, and store for later use.

[0071] (2) Weigh 0.123 mmol of cobalt nitrate hexahydrate, 0.101 mmol of ferrous chloride tetrahydrate, 0.011 mmol of ferric chloride hexahydrate, 0.067 mmol of 2,5-dihydroxyterephthalic acid and 0.033 mmol and add them to a mixed solution of 10 mL of N,N-dimethylformamide, 0.6 mL of anhydrous ethanol and 0.6 mL of deionized water, and sonicate thoroughly for 30 min; then transfer to a 20 mL polytetrafluoroethylene reactor and add the treated nickel foam, and solvothermal react at 120 °C for 20 h;

[0072] (3) After the reactor was naturally cooled to room temperature, it was washed with N,N-dimethylformamide and methanol, and then dried under vacuum to obtain a cobalt-iron bimetallic-organic framework two-dimensional nanosheet electrocatalyst (CoFe-(74+88)).

[0073] The test method for the electrocatalytic oxygen evolution performance is the same as in Example 1.

[0074] Example 4

[0075] This embodiment follows the following... Figure 1 The method shown is used to prepare a two-dimensional nanosheet structured electrocatalyst (CoFe-(74+88)), and the steps are as follows:

[0076] (1) Cut the nickel foam into 3cm×1cm×2mm pieces, place them in 1mol / L hydrochloric acid solution and sonicate for 15min, then sonicate in anhydrous ethanol for 15min, rinse repeatedly with anhydrous ethanol, and finally place them in a vacuum drying oven and dry at 60℃ for 2h, and store for later use.

[0077] (2) Weigh 0.094 mmol of cobalt nitrate hexahydrate, 0.05 mmol of ferrous chloride tetrahydrate, 0.022 mmol of ferric chloride hexahydrate, 0.033 mmol of 2,5-dihydroxyterephthalic acid and 0.067 mmol and add them to a mixed solution of 10 mL of N,N-dimethylformamide, 0.6 mL of anhydrous ethanol and 0.6 mL of deionized water, and sonicate thoroughly for 30 min; then transfer to a 20 mL polytetrafluoroethylene reactor and add the treated nickel foam, and solvothermal react at 120 °C for 15 h;

[0078] (3) After the reactor was naturally cooled to room temperature, it was washed with N,N-dimethylformamide and methanol, and then dried under vacuum to obtain a cobalt-iron bimetallic-organic framework two-dimensional nanosheet electrocatalyst (CoFe-(74+88)).

[0079] The test method for the electrocatalytic oxygen evolution performance is the same as in Example 1.

[0080] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. An electrocatalyst, characterized in that, The electrocatalyst consists of a conductive substrate and active components grown in situ on the surface of the conductive substrate; The active ingredient has the structural formula CoFe-(74+88), which is a cobalt-iron bimetallic-organic framework containing CoFe-MOF-74 and CoFe-MIL-88. The conductive substrate is selected from nickel substrate, nickel-iron substrate, iron substrate or copper substrate.

2. A method for preparing the electrocatalyst according to claim 1, characterized in that, Includes the following steps: In a sealed container, a cobalt source, an iron source, an organic ligand, a solvent, and a conductive substrate are mixed, heat-treated, and dried to obtain the electrocatalyst.

3. The preparation method according to claim 2, characterized in that, The conductive substrate is cleaned; The cleaning process includes ultrasonic treatment of the conductive substrate in a hydrochloric acid solution, followed by cleaning with ethanol and water and vacuum drying to obtain a clean conductive substrate. The concentration of the hydrochloric acid solution is 1–3 mol / L; The ultrasound session lasted 15–20 minutes. The vacuum drying temperature is 60–80°C; The vacuum drying time is 6 to 10 hours.

4. The preparation method according to claim 2, characterized in that, The cobalt source is selected from at least one of cobalt nitrate, cobalt acetate, or cobalt chloride; The iron source is selected from at least one of ferrous acetate, ferrous chloride, ferrous sulfate, ferric chloride, ferric nitrate, and ferric sulfate. The organic ligand is selected from 2,5-dihydroxyterephthalic acid and / or 2-aminoterephthalic acid; The solvent is selected from at least one of N,N-dimethylformamide, ethanol, and water.

5. The preparation method according to claim 2, characterized in that, The molar ratio of the cobalt source, iron source, and organic ligand is 0.1–0.3:0:05–0.15:0.1–0.

3.

6. The preparation method according to claim 2, characterized in that, The heat treatment temperature is 100–120°C; The heat treatment time is 12 to 30 hours.

7. The preparation method according to claim 2, characterized in that, The drying temperature is 60–100°C; The drying time is 6 to 12 hours.

8. An electrode material, characterized in that, The electrode material includes the electrocatalyst as described in claim 1.

9. The application of the electrocatalyst according to claim 1 in alkaline electrocatalytic oxygen evolution.

10. The application according to claim 9, characterized in that, A standard three-electrode system is adopted, with the working electrode being the electrocatalyst CoFe-(74+88), the reference electrode being a mercury / mercury oxide electrode, and the counter electrode being a platinum sheet or a graphite electrode.

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