Preparation method of bimetallic single atom catalyst based on electrochemical dynamic regulation

Abstract

The present invention discloses a method for preparing a bimetallic single-atom catalyst based on electrochemical dynamic regulation. A conductive MOF centered on zinc and a second 3d transition metal and a binder are uniformly mixed and coated on the surface of a glassy carbon electrode to prepare a working electrode. A high-purity iron sheet is used as a counter electrode, and a silver-silver chloride electrode is used as a reference electrode. A three-electrode system is formed in a neutral buffer solution. The in-situ, precise synthesis and embedding of the bimetallic single-atom catalytic center and the recycling and reuse of metallic zinc are achieved through constant potential electrochemical dynamic regulation technology. The present invention successfully optimizes the electron transfer path of the metal site in the catalyst through an electrochemical regulation strategy, making the transfer of electrons in the catalytic reaction more efficient and orderly, thereby improving the catalytic efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cell catalysts, and in particular relates to a method for preparing a bimetallic single-atom catalyst based on electrochemical dynamic regulation. Background Art

[0002] As a key device for converting hydrogen energy into electric energy, fuel cells have broad application prospects in transportation, energy storage, etc. due to their advantages such as zero pollution, rapid response, and energy conversion not limited by the Carnot cycle. One of the pain points in the commercial application of fuel cells is the high cost due to the use of precious metal catalysts such as Pt. Another prerequisite for commercialization is that the catalyst needs to have sufficient stability to maintain the service life of the fuel cell. Therefore, the development of non-precious metal-based catalysts with high durability is of great significance to the development of fuel cells.

[0003] Bimetallic single-atom catalysts have the advantages of atomically dispersed active sites and synergistic catalysis, and have received a lot of attention in catalytic reactions. Currently reported bimetallic single-atom catalysts are mainly prepared by high-temperature pyrolysis strategies. Although the catalysts synthesized by this strategy have excellent catalytic activity, the high-temperature pyrolysis process easily leads to the agglomeration of metal atoms, which has the characteristics of complexity, uncertainty and uncontrollable distribution of active sites, which poses a challenge to the controllable synthesis of active sites. Therefore, achieving controllable synthesis of bimetallic single-atom catalysts with clear active sites is of great significance to reducing the cost and large-scale application of fuel cells. Summary of the invention

[0004] The technical problem solved by the present invention is to provide a method for preparing a bimetallic single-atom catalyst based on electrochemical dynamic regulation, which is used for catalyzing ORR at the cathode of a fuel cell and can significantly improve the energy conversion efficiency and durability of the fuel cell. The electrochemical regulation strategy successfully optimizes the electron transfer path of the metal site in the catalyst, making the transfer of electrons in the catalytic reaction more efficient and orderly, thereby improving the catalytic efficiency. The synthesis conditions of the catalyst are mild, environmentally friendly, and can achieve the recycling of metallic zinc, showing efficient application potential in the field of fuel cells.

[0005] In order to solve the above technical problems, the present invention adopts the following technical scheme: a preparation method of a bimetallic single-atom catalyst based on electrochemical dynamic regulation, and its specific preparation process is: a conductive MOF centered on zinc and a second 3d transition metal and a binder are evenly mixed and coated on the surface of a glassy carbon electrode to prepare a working electrode, a high-purity iron sheet is used as a counter electrode, and a silver-silver chloride electrode is used as a reference electrode to form a three-electrode system in a neutral buffer solution. The in-situ, precise synthetic embedding of the bimetallic single-atom catalytic center and the recovery and recycling of metallic zinc are realized through constant potential electrochemical dynamic regulation technology. During the constant potential electrochemical regulation process, the deposition potential is -0.2~0.8V, and the deposition time is 100~800s.

[0006] The preparation method of the bimetallic single-atom catalyst based on electrochemical dynamic regulation, the specific preparation steps are:

[0007] Step S1: Disperse zinc nitrate, a second 3d transition metal nitrate and a conductive ligand in a mixed solution of dimethylformamide and water, stir and mix them evenly, and then transfer them to a polytetrafluoroethylene reactor, react at 200-260° C. for 6-12 hours, cool to room temperature, pour out the supernatant, wash the precipitate at the bottom with dimethylformamide, and then vacuum dry to obtain a conductive ZnM-MOF precursor;

[0008] Step S2: weighing raw materials according to the mass ratio of ZnM-MOF precursor: binder: isopropanol: water of 1:3:3:3, uniformly dispersing the raw materials by ultrasonication to obtain a suspension containing ZnM-MOF, and then drop-coating the suspension on the surface of a glassy carbon electrode to prepare a working electrode, using a high-purity iron sheet as a counter electrode, a silver-silver chloride electrode as a reference electrode, and a neutral buffer solution as an electrolyte to form a three-electrode system for constant potential electrochemical regulation, wherein the deposition potential is -0.2~0.8V, and the deposition time is 100~800s;

[0009] Step S3: During the constant potential electrochemical regulation process, the electrochemical impedance of the working electrode is monitored in situ, with a starting voltage of -0.2~0.8V, a high frequency of 100Hz, and a low frequency of 0.01Hz. The electrochemical impedance of the working electrode shows a trend of first increasing and then decreasing during the constant potential electrochemical regulation process. When the impedance stabilizes to below 10W, it indicates that the surface composition of the working electrode is stable, that is, a bimetallic single-atom catalyst with a clear structure is obtained, and ultimately the in-situ, precise synthetic embedding of the bimetallic single-atom catalytic center and the recovery and recycling of metallic zinc are realized.

[0010] It is further defined that in step S1, the second 3d transition metal nitrate is one or more of chromium nitrate, cobalt nitrate, nickel nitrate and copper nitrate.

[0011] It is further defined that the conductive ligand in step S1 is one or more of 2,3,6,7,10,11-hexa(alkylthio)triphenyl, hexaaminotriphenylene, hexahydroxytriphenylene and hexamercaptotriphenylene.

[0012] It is further defined that the molar ratio of the zinc nitrate, the second 3d transition metal nitrate and the conductive ligand in step S1 is 1:1:1-2.

[0013] It is further defined that the binder in step S2 is a 5 wt % perfluorosulfonic acid (Nafion) solution or polyvinyl alcohol (PVA).

[0014] It is further defined that the neutral buffer solution in step S3 is 1.0 M neutral phosphate buffer or 0.5 M neutral acetate buffer.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0016] 1. The present invention uses conductive MOF as a precursor, and realizes the in-situ, precisely controllable synthesis and embedding of bimetallic single-atom catalytic centers with clear active site structures through electrochemical regulation and replacement, so that catalytic active sites with clearer structures can be obtained in-situ without high-temperature calcination. The selection of conductive MOF not only avoids the high energy input required for high-temperature pyrolysis and the environmental problems caused, but also solves the problems of agglomeration and active site ambiguity caused by the pyrolysis process, ensures the clear structure of the active sites in the catalyst and gives excellent electron conduction ability, optimizes the electron transmission path of the active center during the reaction, and effectively improves the catalytic activity and durability in the fuel cell.

[0017] 2. The three-dimensional conductive MOF in the present invention not only has a clear bimetallic single atom center, but also retains the three-dimensional porous structure and high specific surface area of ​​MOF, which not only helps to fully expose the active sites, but also solves the problem of insufficient mass transfer during the operation of the fuel cell, especially under high current, thereby improving the catalytic efficiency.

[0018] 3. The present invention uses an electrochemical regulation replacement method to obtain a bimetallic single-atom catalyst, which can more effectively regulate the electronic coupling interaction between metals and thus improve the catalytic activity. This electronic coupling interaction can effectively enhance the synergistic effect between the two metals, improve the catalytic activity, enhance the binding ability between the metal and the ligand, and alleviate the problem of insufficient stability caused by demetallization during long-term operation of the metal.

[0019] 4. The synthesis conditions of the present invention are mild. The electrochemically regulated replacement method not only obtains a bimetallic single-atom catalyst with a controllable structure, but also realizes the recycling and reuse of zinc. The preparation of traditional single-atom catalysts often requires metallic zinc as a sacrificial agent. Although a monodispersed catalyst is finally obtained by this method, it is accompanied by the consumption of zinc resources. After the electrochemically regulated replacement in the present invention, the zinc ions in the precursor enter the electrolyte, and then can be redeposited by dynamically adjusting the electrode potential to achieve the purpose of recycling and reuse. For example, in the subsequent preparation process, by adjusting the electrode potential to -1.5V~-1.0V, the zinc ions dissolved in the electrolyte are redeposited on the surface of the working electrode, thereby completing the recycling and reuse of zinc.

[0020] 5. In the traditional preparation method, zinc is usually used as a sacrificial agent in the preparation of catalysts, especially in the synthesis of single-atom catalysts, where the role of zinc is to provide support sites or form templates. However, in this way, the removal of zinc is usually achieved by high-temperature pyrolysis or chemical treatment, which directly leads to the consumption of zinc. During the high-temperature pyrolysis process, the zinc element will volatilize or be discharged in the form of waste residue, resulting in a waste of zinc resources and producing by-products such as zinc vapor or waste residue. If these by-products are directly discharged without treatment, they may cause pollution to the soil and water bodies, endangering the ecological environment and human health. In contrast, the electrochemical regulation method proposed in the present invention realizes the recycling of zinc through potential control, which not only reduces the consumption of zinc, but also avoids the pollution problem in high-temperature treatment, and is therefore more environmentally friendly.

[0021] In summary, the present invention not only utilizes the excellent conductivity of conductive MOF, but also realizes the precise embedding of bimetallic single atoms through electrochemical dynamic control technology, creating efficient and stable catalytic active centers. At the same time, the catalyst synthesis conditions are mild, the recovery rate of zinc is significantly improved, and it has significant environmental friendliness. This innovative technology can develop a new, high-performance catalytic material, which shows high-efficiency application potential in the field of fuel cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the XRD pattern of the bimetallic single atom catalyst prepared in Example 1;

[0023] Figure 2 The different catalysts prepared in Example 1 and Comparative Examples 1 to 3 are 2 Saturated 0.1M HClO 4 ORR polarization curve in solution at a rotation speed of 1600 rpm and a scan rate of 5 mV s -1 ;

[0024] Figure 3 The different catalysts prepared in Example 1 and Comparative Examples 1 to 3 are 2Saturated 0.1M HClO 4 Stability curve in solution. DETAILED DESCRIPTION

[0025] In order to better illustrate the above technical solution, the above technical solution will be described in detail below in conjunction with specific embodiments. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies based on the above content of the present invention belong to the scope of the present invention.

[0026] The electrochemical test was carried out in a standard three-electrode system, and the glassy carbon electrode was polished before use. A glassy carbon electrode coated with conductive ZnM-MOF was used as a working electrode, wherein the catalyst was prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3, a high-purity iron sheet was used as a counter electrode, a silver-silver chloride electrode was used as a reference electrode, and a 1M neutral phosphate buffer was used as an electrolyte. Example 1

[0027] Step S1: 0.5 mol zinc nitrate, 0.5 mol chromium nitrate and 1 mol conductive ligand hexaaminotriphenylene are dispersed in a mixed solution of 60 mL dimethylformamide and water, stirred and mixed evenly, and then transferred to a polytetrafluoroethylene reactor, reacted at 240° C. for 12 h, cooled to room temperature, washed three times with dimethylformamide and vacuum dried to obtain a conductive ZnCr-MOF precursor.

[0028] Step S2: Take 10 mg of the conductive ZnCr-MOF precursor obtained in step S1, and weigh the raw materials according to the mass ratio of conductive ZnCr-MOF precursor: binder Nafion solution: isopropanol: water of 1:3:3:3, disperse the above raw materials in a mixed solution of isopropanol and water to obtain a suspension containing ZnCr-MOF, and then drop the suspension on the surface of a glassy carbon electrode to obtain a uniformly dispersed ZnCr-MOF working electrode, use a high-purity iron sheet as a counter electrode, a silver-silver chloride electrode as a reference electrode, and a 1M neutral phosphate buffer as an electrolyte to form a three-electrode system for constant potential electrochemical regulation, wherein the deposition potential is 0.08V, and the deposition time is 300s. At the beginning of electrodeposition, the zinc ions replaced in the solution form a new phase on the electrode surface, that is, the zinc element begins to nucleate and grow, and then the crystal nuclei gradually grow to form a continuous zinc metal layer. After the reaction is completed, the obtained metal layer is taken out to realize the recovery of metallic zinc.

[0029] Step S3: During the above-mentioned constant potential electrochemical regulation process, the electrochemical impedance of the working electrode is monitored in situ, with a starting voltage of 0.1V, a high frequency of 100Hz, and a low frequency of 0.01Hz. The electrochemical impedance shows a trend of first increasing and then decreasing during the constant potential electrochemical regulation process. When the impedance stabilizes to below 10W, it indicates that the surface composition of the working electrode is stable, that is, a bimetallic single atom catalyst is obtained, and ultimately the precise synthesis and embedding of the bimetallic single atom catalytic center and the recovery and recycling of metallic zinc are achieved.

[0030] Comparative Example 1 (Ordinary three-dimensional MOF instead of conductive MOF)

[0031] Step S1: 0.5 mol zinc nitrate, 0.5 mol chromium nitrate and 1 mol triphenyl terephthalate ligand are dispersed in a mixed solution of 60 mL dimethylformamide and water, stirred and mixed evenly, and then transferred to a polytetrafluoroethylene reactor, reacted at 240° C. for 12 h, cooled to room temperature, washed three times with dimethylformamide and vacuum dried to obtain a ZnCr-MOF precursor.

[0032] Step S2: Take 10 mg of the ZnCr-MOF precursor obtained in step S1 and weigh the raw materials respectively according to the mass ratio of ZnCr-MOF precursor: binder Nafion solution: isopropanol: water of 1:3:3:3, disperse the above raw materials in a mixed solution of isopropanol and water to obtain a suspension containing ZnCr-MOF, and then drop the suspension on the surface of the glassy carbon electrode to obtain a working electrode with ZnCr-MOF uniformly dispersed, use a high-purity iron sheet as a counter electrode, a silver-silver chloride electrode as a reference electrode, and 1M neutral phosphate buffer as an electrolyte to form a three-electrode system for constant potential electrochemical regulation, wherein the deposition potential is 0.08 V and the deposition time is 300 s.

[0033] Step S3: During the above-mentioned constant potential electrochemical regulation process, the electrochemical impedance of the working electrode is monitored in situ, with an initial voltage of 0.1V, a high frequency of 100Hz, and a low frequency of 0.01Hz. The electrochemical impedance shows a trend of gradually decreasing during the constant potential electrochemical regulation process. When the impedance stabilizes to below 10W, it indicates that the electrode surface composition is stable, and the catalyst is obtained.

[0034] Comparative Example 2 (Single Metal Site Replacing Bimetallic Single Atom Site)

[0035] Step S1: 0.5 mol zinc nitrate and 0.5 mol conductive ligand hexaaminotriphenylene are dispersed in 60 mL of a mixed solution of dimethylformamide and water, stirred and mixed evenly, and then transferred to a polytetrafluoroethylene reactor, reacted at 240° C. for 12 h, cooled to room temperature, washed three times with dimethylformamide, and then vacuum dried to obtain a conductive Zn-MOF precursor.

[0036] Step S2: Take 10 mg of the conductive Zn-MOF precursor obtained in step S1, and weigh the raw materials separately according to the mass ratio of conductive Zn-MOF precursor: binder Nafion solution: isopropanol: water of 1:3:3:3, disperse the above raw materials in a mixed solution of isopropanol and water to obtain a suspension containing Zn-MOF, and then drop the suspension on the surface of the glassy carbon electrode to obtain a working electrode with Zn-MOF uniformly dispersed, use a high-purity iron sheet as the counter electrode, a silver-silver chloride electrode as the reference electrode, and 1M neutral phosphate buffer as the electrolyte to form a three-electrode system for constant potential electrochemical regulation, wherein the deposition potential is 0.08 V and the deposition time is 300 s.

[0037] Step S3: During the above-mentioned constant potential electrochemical regulation process, the electrochemical impedance of the working electrode is monitored in situ, with an initial voltage of 0.1V, a high frequency of 100Hz, and a low frequency of 0.01Hz. The electrochemical impedance shows a trend of first increasing and then decreasing during the constant potential electrochemical regulation process. When the impedance stabilizes to below 10W, it indicates that the electrode surface composition is stable, and the catalyst is obtained.

[0038] Comparative Example 3 (Conventional pyrolysis method replaces electrochemical regulation method)

[0039] Step S1: 0.5 mol zinc nitrate, 0.5 mol iron nitrate, 0.5 mol chromium nitrate and 1 mol conductive ligand hexaaminotriphenylene are dispersed in a mixed solution of 60 mL dimethylformamide and water, stirred and mixed evenly, and then transferred to a polytetrafluoroethylene reactor, reacted at 240 ° C for 12 h, cooled to room temperature, washed three times with dimethylformamide and vacuum dried to obtain a conductive ZnFeCr-MOF precursor.

[0040] Step S2: 500 mg of the conductive ZnFeCr-MOF precursor obtained in step S1 was ground evenly with 5 g of melamine and heated at 5 °C min under an argon atmosphere. -1 The temperature was raised to 950°C at a heating rate to remove metal Zn by thermal decomposition, and finally cooled to room temperature to obtain the catalyst.

[0041] The conductive MOF framework-embedded bimetallic single-atom catalytic center prepared by the present invention has excellent ORR activity and stability in fuel cells. It can be seen from Example 1 and Comparative Examples 1 to 3 that the conductive MOF framework-embedded bimetallic single-atom catalyst prepared in Example 1 has a large half-wave potential and stability. By analyzing Example 1 and Comparative Examples 1 to 3, it can be found that key factors such as the selection of suitable conductive ligands and electrochemical constant potential deposition regulation are very important for the precise synthesis of bimetallic single-atom catalysts, and the electronic regulation between sites can be fully utilized to achieve synergistic effects. The present invention not only realizes the in-situ precise embedding and controllable synthesis of bimetallic single atoms, but also optimizes the electron transfer path in the catalytic material, making the transfer of electrons in the catalytic reaction more efficient and orderly, thereby improving the catalytic activity. In addition, the catalyst synthesis conditions are mild, the recovery rate of zinc is significantly improved, and the waste of zinc and environmental pollution are reduced.

[0042] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a bimetallic single-atom catalyst based on electrochemical dynamic regulation, characterized in that The specific preparation process is as follows: a conductive MOF centered on zinc and a second 3d transition metal and a binder are evenly mixed and coated on the surface of a glassy carbon electrode to prepare a working electrode, a high-purity iron sheet is used as a counter electrode, and a silver-silver chloride electrode is used as a reference electrode to form a three-electrode system in a neutral buffer solution. The in-situ, precise synthesis and embedding of the bimetallic single-atom catalytic center and the recycling of metallic zinc are achieved through constant potential electrochemical dynamic control technology. During the constant potential electrochemical control process, the deposition potential is -0.2~0.8V, and the deposition time is 100~800s. The specific preparation steps of the bimetallic single atom catalyst are: Step S1: Dispersing zinc nitrate, a second 3d transition metal nitrate and a conductive ligand in a mixed solution of dimethylformamide and water, stirring and mixing them evenly, and then transferring them to a polytetrafluoroethylene reactor, reacting at 200-260° C. for 6-12 hours, cooling to room temperature, pouring off the supernatant, washing the precipitate at the bottom with dimethylformamide, and then vacuum drying to obtain a conductive ZnM-MOF precursor, wherein the second 3d transition metal nitrate is one or more of chromium nitrate, cobalt nitrate, nickel nitrate and copper nitrate, and the conductive ligand is one or more of 2,3,6,7,10,11-hexa(alkylthio)triphenyl, hexaaminotriphenylene, hexahydroxytriphenylene and hexamercaptotriphenylene; Step S2: weighing raw materials according to the mass ratio of ZnM-MOF precursor: binder: isopropanol: water of 1:3:3:3, uniformly dispersing the raw materials by ultrasonication to obtain a suspension containing ZnM-MOF, and then drop-coating the suspension on the surface of a glassy carbon electrode to prepare a working electrode, using a high-purity iron sheet as a counter electrode, a silver-silver chloride electrode as a reference electrode, and a neutral buffer solution as an electrolyte to form a three-electrode system for constant potential electrochemical regulation, wherein the deposition potential is -0.2~0.8V, and the deposition time is 100~800s; Step S3: During the constant potential electrochemical regulation process, the electrochemical impedance of the working electrode is monitored in situ, with a starting voltage of -0.2~0.8V, a high frequency of 100Hz, and a low frequency of 0.01Hz. The electrochemical impedance of the working electrode shows a trend of first increasing and then decreasing during the constant potential electrochemical regulation process. When the impedance stabilizes to below 10W, it indicates that the surface composition of the working electrode is stable, that is, a bimetallic single-atom catalyst with a clear structure is obtained, and ultimately the in-situ, precise synthetic embedding of the bimetallic single-atom catalytic center and the recovery and recycling of metallic zinc are realized.

2. The method for preparing a bimetallic single-atom catalyst based on electrochemical dynamic regulation according to claim 1, characterized in that: In step S1, the molar ratio of zinc nitrate, the second 3d transition metal nitrate and the conductive ligand is 1:1:1-2.

3. The method for preparing a bimetallic single-atom catalyst based on electrochemical dynamic regulation according to claim 1, characterized in that: The binder in step S2 is a 5 wt % perfluorosulfonic acid solution or polyvinyl alcohol (PVA).

4. The method for preparing a bimetallic single-atom catalyst based on electrochemical dynamic regulation according to claim 1, characterized in that: The neutral buffer solution in step S3 is 1.0 M neutral phosphate buffer or 0.5 M neutral acetate buffer.

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