Diatomic catalyst as well as preparation method and application thereof

Abstract

The invention provides a diatomic catalyst as well as a preparation method and application thereof, and belongs to the technical field of electrochemical catalysis. The preparation method of the diatomic catalyst comprises the following steps: adding a nitrogen-containing carbon material into a transition metal-containing solution, and carrying out primary impregnation reaction to obtain primary impregnated powder; under the protective gas atmosphere, the powder obtained after first-time dipping is subjected to first-time roasting at the temperature of 900 DEG C-1100 DEG C, and mixture powder is obtained; adding the mixture powder into a ferricyanide solution, and carrying out second-time impregnation reaction to obtain second-time impregnated powder; and performing secondary roasting on the powder subjected to secondary impregnation at 900-1100 DEG C in a protective gas atmosphere to obtain the diatomic catalyst. In the preparation process, high-temperature roasting etching operation and metal dipping operation are adopted at the same time, and the bifunctional catalyst with diatomic-scale bimetal or diatomic-scale monometal catalytic sites is effectively synthesized.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic chemistry, and more particularly to a dual-atom catalyst and its preparation method and application. Background Art

[0002] Single-atom catalysts have a very low metal loading rate, which can greatly save costs. At the same time, they have the advantages of high intrinsic activity, selectivity, and high atomic utilization rate. The basic structure of a single-atom catalyst is that on a support with coordinating atoms, the coordinating atoms are connected to metal atoms to form catalytic active sites. The catalytic activity and selectivity depend on the metal atoms and their surrounding ligand environment, as well as the support structure. Therefore, inexpensive metal atoms with oxygen reduction reaction (ORR) activity can be searched for, and the support and its coordination environment can be optimized to develop non-precious metal single-atom catalysts.

[0003] In the past few decades, due to the limited use of noble metal catalysts, the development of platinum-free catalyst materials is gradually replacing platinum-based metal catalysts in the market. Among many such materials, M-N-C type catalysts formed by N coordinated to C in an atomically dispersed form have been proven to have excellent ORR performance under alkaline electrolyte conditions due to their large specific surface area and numerous electrochemically active sites, and have become one of the most promising cathode bifunctional catalysts.

[0004] Currently, the oxygen reduction performance of the most promising single-atom catalysts such as iron, cobalt, and manganese in relevant research is close to or even exceeds that of platinum-carbon, providing new ideas for the preparation of ORR catalysts. Transition metal-based carbon nitride materials are the most promising next-generation platinum catalyst replacement materials due to their good ORR intrinsic activity and cost advantages. The general synthesis strategy of existing dual-atom catalysts is to mechanically mix different metal ions with catalyst precursor materials and then calcine them. Due to the free movement of molecules, the active sites of the dual-atom catalysts formed freely without regulation are very likely to be mainly single-atom sites and coexist with dual-atom sites. The synergistic cooperation of dual-atom sites cannot be fully demonstrated in the catalyst material, and the problems of insufficient intrinsic activity and unreasonable active site design have hindered the application of non-precious metal catalysts in zinc-air batteries. Summary of the Invention

[0005] In view of the above problems, the present invention provides a dual-atom catalyst, a preparation method thereof, and an application thereof. In the preparation process of the present invention, high-temperature calcination etching operation and metal impregnation operation are simultaneously adopted, effectively synthesizing a bifunctional catalyst with dual-atom-level dual-metal or dual-atom-level single-metal catalytic sites. A non-precious metal catalyst that can prepare a half-wave potential level exceeding that of commercial Pt / C catalysts and has oxygen evolution efficiency can be applied to zinc-air batteries. The operation of the present invention is simple, environmentally friendly, and low-cost, suitable for large-scale preparation. The dual-atom bifunctional catalyst can greatly improve the reaction efficiency of the oxygen reduction and oxygen evolution processes of the air electrode in zinc-air batteries, realizing the efficient reaction of zinc-air batteries.

[0006] The first object of the present invention is to provide a preparation method of a dual-atom catalyst, comprising the following steps: Add carbon materials to the transition metal solution and perform the first impregnation reaction at room temperature to obtain the powder after the first impregnation.

[0007] Under the atmosphere of a protective gas, calcine the powder after the first impregnation at 900 °C to 1100 °C to obtain a mixture powder.

[0008] Add the mixture powder to the ferrocyanide solution and perform the second impregnation reaction at room temperature to obtain the powder after the second impregnation.

[0009] Under the atmosphere of a protective gas, calcine the powder after the second impregnation at 900 °C to 1100 °C to obtain the dual-atom catalyst.

[0010] In the present invention, metal ions are adsorbed on the surface of carbon materials through electrostatic interaction or van der Waals force. The porous structure and high specific surface area of carbon materials help to enhance this adsorption. At the same time, the solution penetrates through capillary action in the pores of carbon materials, and metal ions enter the interior of the pores accordingly and remain in the pores after drying. Then, the calcination process further converts metal ions into metal oxides or elemental substances, enhancing the loading effect.

[0011] In a preferred embodiment of the present invention, the ratio of carbon materials to the transition metal solution is 5 mg: 3 ml.

[0012] The concentration of the transition metal solution is 0.1 mmol / L to 0.3 mmol / L.

[0013] In a preferred embodiment of the present invention, the time of the first calcination is 1 h to 2 h.

[0014] In a preferred embodiment of the present invention, the ratio of the mixture powder to the ferrocyanide solution is 5 mg: 3 ml.

[0015] The concentration of the ferrocyanide solution is 0.1 mmol / L to 0.3 mmol / L.

[0016] In a preferred embodiment of the present invention, the time of the second calcination is 1 h to 2 h.

[0017] In a preferred embodiment of the present invention, the time of the first impregnation reaction is 12 h to 14 h.

[0018] In a preferred embodiment of the present invention, the time of the second impregnation reaction is 12 h to 14 h.

[0019] In a preferred embodiment of the present invention, the transition metal is one or two of iron, cobalt and nickel. When selecting, the required transition metal can be selected according to the needs, so that the finally prepared catalyst is a dual-atom catalyst. Taking the transition metal as iron as an example, the transition metal solution includes iron nitrate solution, iron chloride solution or iron phthalocyanine solution.

[0020] The ferrocyanide solution is potassium ferrocyanide solution.

[0021] The second object of the present invention is to provide a dual-atom catalyst prepared by the above preparation method.

[0022] The third object of the present invention is the application of the above dual-atom catalyst in an alkaline zinc-air battery.

[0023] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention discloses a preparation method of a dual-atom catalyst based on the impregnation method. The catalyst material is an Fe-M-N-C catalyst system. The transition metal is physically adsorbed on the surface of the nitrogen-containing carbon material during the first impregnation process to form single-atom-level catalytic active sites. Then, during the first calcination process, the transition metal ions (M) form M-N-C chemical bonds with the nitrogen-containing carbon carrier to form stable catalytic active single-atom sites. During the second impregnation process, the transition metal ions coordinate with [Fe(CN)6]³⁻ to form a dual-metal atom coordination structure. During the second calcination process, M-Fe and N-M-Fe-N chemical bonds are formed, thereby forming catalytic active sites with dual-metal synergistic cooperation effects. The prepared catalyst material can effectively improve the intrinsic activity of the catalytic active sites, and at the same time can reasonably regulate and construct dual-atom sites, thereby improving the microscopic catalytic efficiency during the catalytic process and realizing the high catalytic activity of the catalyst. Through the application of the present invention, the oxygen reduction (ORR) and oxygen evolution (OER) efficiencies of non-precious metal bifunctional catalysts are effectively improved.

[0024] 2. When the present invention prepares the dual-atom catalyst, it is prepared by the methods of impregnation adsorption and calcination, which has simple operation, is green and environmentally friendly, and is suitable for large-scale preparation. Description of the Drawings

[0025] Figure 1ORR reaction curves for different embodiments.

[0026] Figure 2 OER reaction curves for different embodiments.

[0027] Figure 3 Schematic diagram of aberration-corrected electron microscopy of dual atoms in Example 1. Detailed implementation manners

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] The ferrocyanide ion [Fe(CN)6]³⁻ is a six-coordinate complex. The central iron ion (Fe³⁺) coordinates with six cyanide ions (CN⁻), and transition metal ions have strong coordination ability. When ferrocyanide meets transition metal ions in solution, a ligand exchange reaction may occur: the transition metal ions can exchange with the CN⁻ ligands in [Fe(CN)6]³⁻ to form a new complex. Starting from this, in the present invention, through the first impregnation reaction, using a relatively low metal ion concentration, with a polar homogeneous solution as the solvent in the transition metal solution, the transition metal is in full contact with the carbon material matrix, and thus is physically adsorbed on the surface of the carbon material matrix. Since the transition metal concentration is low, metal cluster sites are avoided from forming, but single-atom-level catalytic active sites are formed. Then, the first calcination is carried out under an inert gas. During the high-temperature carbonization process, the physically adsorbed transition metal ions (M) form M-N-C chemical bonds with the surrounding nitrogen-containing carbon carriers, thereby generating stable catalytic active single-atom sites. Then, the second impregnation is carried out again. Due to the strong coordination ability of [Fe(CN)6]³⁻, compared with the carbon matrix, it is more likely to combine with transition metal ions with strong electron-donating ability. The transition metal ions and [Fe(CN)6]³⁻ are successfully coordinated to form a dual-metal atom coordination structure. After forming M-Fe bonds and M-N chemical bonds during the calcination process, catalytic active sites with dual-metal synergistic cooperation effects are further formed.

[0030] When preparing the present invention, the carbon material should have a certain nitrogen content. The higher the nitrogen content, the easier it is to form stable coordinated chemical bonds with metals. For example, pyrrole itself contains nitrogen elements and can be directly used to prepare nitrogen-containing carbon materials. For carbon materials without nitrogen elements, such as glucose, substances containing nitrogen elements, such as melamine, need to be additionally configured and added.

[0031] In the following examples, conventional instruments and equipment in the art are used. For the experimental methods without specific conditions noted in the following examples, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. In the following examples, various raw materials are used. Unless otherwise specified, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0032] Example 1 Step 1: Take 0.96 g of NaOH and add it to 7 ml of deionized water, and add 1.78 g of l-glutamic acid and 6 ml of acetone thereto; then slowly add 3 g of stearoyl chloride and 5 ml of 2 M NaOH solution to the solution at room temperature while maintaining pH = 12, and continuously react for 1.5 h; add 1 M HCl solution to the obtained solution until pH = 1; wash the obtained solid by centrifugation with distilled water until pH = 7, and then wash it with petroleum ether 6 times; vacuum dry the obtained solid at 60 °C for 24 h to obtain the template material n-stearoyl-l-glutamic acid.

[0033] Step 2: Dissolve 0.06 mmol of n-stearoyl-l-glutamic acid in 13 ml of methanol, add 160 μl of pyrrole and 60 ml of deionized water thereto, and stir for 20 min; then dropwise add 1.5 ml of 2.4 M ammonium persulfate solution, and stir and react at a rotation speed of 300 r / min under an ice-water bath condition for 10 min; filter the obtained solution, and wash it three times with deionized water and alcohol; finally, freeze-dry the obtained solid to obtain the chiral polypyrrole precursor.

[0034] Step 3: Take the chiral polypyrrole precursor powder and an equal mass of KOH, heat it to 700 °C at a rate of 5 °C / min under a nitrogen atmosphere, keep it warm for two hours, and then cool it with the furnace; after filtration, washing and drying, obtain the metal-free catalyst powder.

[0035] Step 4: Prepare an iron 3+ nitrate solution with a molar concentration of 0.3 mmol / L. Take 50 mg of the metal-free catalyst powder obtained in Step 3 and add it to 30 ml of the iron nitrate solution, and stir at room temperature for 12 h; filter the obtained solution, and wash it three times with deionized water and alcohol; freeze-dry the obtained solid to obtain a powder; heat the dried powder to 900 °C at a rate of 5 °C / min under a nitrogen atmosphere, keep it warm for two hours, and then cool it with the furnace to obtain a mixture powder.

[0036] Step 5: Prepare [Fe(CN)6] 3-50 mg of the mixture powder obtained in step 4 was added to 30 ml of K3[Fe(CN)6] solution with a molar concentration of 0.3 mmol / L, and stirred for 12 hours at room temperature; the obtained solution was filtered and washed three times with deionized water and alcohol; the obtained solid was freeze-dried; the dried powder was heated to 900°C at a rate of 5°C / min under a nitrogen atmosphere, kept warm for two hours, and cooled with the furnace. The Fe-Fe-NC catalyst with precisely constructed diatomic structures was obtained.

[0037] Example 2 Step 1, take 0.96g NaOH and add it to 7ml deionized water, and add 1.78g l-glutamic acid and 6ml acetone thereto; then slowly add 3g stearoyl chloride and 5ml 2M NaOH solution to the solution at room temperature and keep pH=12, and continue the reaction for 1.5h; add 1M HCl solution to the obtained solution until pH=1; centrifuge and wash the obtained solid with distilled water to pH=7, and then wash it with petroleum ether 6 times; vacuum dry the obtained solid at 60°C for 24h to obtain the template material n-stearoyl-l-glutamic acid.

[0038] Step 2: Take 0.06 mmol n-stearoyl-l-glutamic acid and dissolve it in 13 ml methanol, add 160 μl pyrrole and 60 ml deionized water, and stir for 20 minutes; then add 1.5 ml 2.4M ammonium persulfate solution dropwise, and stir at 300 r / min in an ice water bath for 10 minutes; filter the obtained solution, and wash it three times with deionized water and alcohol; finally, freeze-dry the obtained solid to obtain a chiral polypyrrole precursor.

[0039] Step 3: Take the chiral polypyrrole precursor powder and an equal mass of KOH, heat it to 700°C at a rate of 5°C / min under a nitrogen atmosphere, keep it warm for two hours, and cool it with the furnace; after filtration, washing and drying, obtain a catalyst powder without metal loading.

[0040] Step 4: Configure Co 2+ Cobalt nitrate, Fe with a molar concentration of 0.3mmol / L 3+ 50 mg of the catalyst powder without metal loading obtained in step 3 was added to 30 ml of a mixed solution of ferric nitrate with a molar concentration of 0.3 mmol / L, and the mixture was stirred for 12 h at room temperature; the obtained solution was filtered, and washed three times with deionized water and alcohol; the obtained solid was freeze-dried; the dried powder was heated to 900 ° C at a rate of 5 ° C / min under a nitrogen atmosphere, kept warm for two hours, and cooled with the furnace to obtain a mixture powder.

[0041] Step 5: Configure [Fe(CN)6]3- A K3[Fe(CN)6] solution with a molar concentration of 0.3 mmol / L. Take 50 mg of the mixture powder obtained in step 4 and add it to 30 ml of the K3[Fe(CN)6] solution, and stir for 12 h at room temperature; filter the obtained solution by suction, and wash it three times with deionized water and alcohol; freeze-dry the obtained solid; heat the dried powder to 900 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for two hours, and cool with the furnace. A Fe-Co-N-C catalyst with precisely constructed dual atoms is prepared.

[0042] Example 3 Step 1: First, under heating conditions of 60 °C, add 16 g of sodium chloride, 40 mg of ferric chloride hexahydrate, 2 g of glucose, and 2 g of dicyandiamide to 44 mL of deionized water and dissolve completely. After stirring evenly, a homogeneous light orange solution is formed; for the convenience of subsequent freeze-drying, divide the light orange solution into multiple portions and transfer them to multiple plastic containers, then pour liquid nitrogen into them in a multiple-sufficient manner for sufficient freezing; then place the frozen product together with the container in a freeze-dryer that has been pre-started and cooled, and perform freeze-drying for 24 h to obtain solid powder.

[0043] Step 2: Put the obtained solid powder into a tube furnace for heating and carbonization. The specific heating program uses a heating rate of 5 °C·min -1 The heating rate is used to heat up to 550 °C and hold for 1 hour, then rise to 900 °C at the same heating rate, hold for 2 hours, and then cool naturally with the furnace; after pickling and suction filtration, a three-dimensional honeycomb porous carbon material is obtained.

[0044] Step 3: Take 150 ml of methanol and add 2 g of P123 and 3.4 g of 2-methylimidazole to it. Take another 150 ml of methanol and add 2.97 g of zinc nitrate, 120 mg of cobalt nitrate, and 60 mg of three-dimensional honeycomb porous carbon. Mix the two and react under the condition of 60 °C. Finally, wash and dry the reaction product to obtain a three-dimensional ZIF porous carbon catalyst precursor material.

[0045] Step 4: Take the three-dimensional ZIF porous carbon catalyst precursor material and heat it to 900 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for two hours, and cool with the furnace; after suction filtration, washing, and drying, a mixture powder is obtained.

[0046] Step 5: Prepare [Fe(CN)6] 3-A K3[Fe(CN)6] solution with a molar concentration of 0.3 mmol / L. Take 50 mg of the mixture powder and add it to 30 ml of this solution. Stir at room temperature for 12 h; filter the resulting solution by suction and wash it three times with deionized water and alcohol; freeze-dry the obtained solid; heat the dried powder to 900 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for two hours, and cool it with the furnace. A Fe-Co-N-C catalyst with precisely constructed dual atoms is prepared.

[0047] Example 4 Step 1: Take 0.96 g of NaOH and add it to 7 ml of deionized water, and add 1.78 g of l-glutamic acid and 6 ml of acetone thereto; then slowly add 3 g of stearoyl chloride and 5 ml of 2 M NaOH solution to the solution at the same time at room temperature and maintain pH = 12, and continue the reaction for 1.5 h; add 1 M HCl solution to the obtained solution until pH = 1; wash the obtained solid by centrifugation with distilled water until pH = 7, and then wash it 6 times with petroleum ether; vacuum-dry the obtained solid at 60 °C for 24 h to obtain the template material n-stearoyl-l-glutamic acid.

[0048] Step 2: Dissolve 0.06 mmol of n-stearoyl-l-glutamic acid in 13 ml of methanol, add 160 μl of pyrrole and 60 ml of deionized water thereto, and stir for 20 min; then dropwise add 1.5 ml of 2.4 M ammonium persulfate solution, and stir and react at a rotation speed of 300 r / min under an ice-water bath condition for 10 min; filter the resulting solution by suction and wash it three times with deionized water and alcohol; finally, freeze-dry the obtained solid to obtain the chiral polypyrrole precursor.

[0049] Step 3: Take the chiral polypyrrole precursor powder and an equal mass of KOH and heat it to 700 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for two hours, and cool it with the furnace; after suction filtration, washing, and drying, obtain the metal-free catalyst powder.

[0050] Step 4: Prepare 3+ A ferric nitrate solution with a molar concentration of 0.1 mmol / L. Take 50 mg of the metal-free catalyst powder obtained in Step 3 and add it to 30 ml of the ferric nitrate solution. Stir at room temperature for 14 h; filter the resulting solution by suction and wash it three times with deionized water and alcohol; freeze-dry the obtained solid to obtain a powder; heat the dried powder to 1000 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for 1.5 hours, and cool it with the furnace to obtain the mixture powder.

[0051] Step 5: Prepare [Fe(CN)6] 3-A K3[Fe(CN)6] solution with a molar concentration of 0.1 mmol / L. Take 50 mg of the mixture powder obtained in step 4 and add it to 30 ml of the K3[Fe(CN)6] solution. Stir at room temperature for 13 h. Filter the resulting solution by suction and wash it three times with deionized water and alcohol. Freeze-dry the obtained solid. Heat the dried powder to 1000 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for 1.5 hours, and cool it with the furnace. A Fe-Fe-N-C catalyst with precisely constructed dual atoms is prepared.

[0052] Example 5 Step 1: Take 0.96 g of NaOH and add it to 7 ml of deionized water. Then add 1.78 g of l-glutamic acid and 6 ml of acetone to it. Subsequently, slowly add 3 g of stearoyl chloride and 5 ml of 2 M NaOH solution to the solution at the same time while maintaining the pH = 12, and continue the reaction for 1.5 h. Add 1 M HCl solution to the obtained solution until the pH = 1. Centrifuge and wash the obtained solid with distilled water until the pH = 7, and then wash it 6 times with petroleum ether. Vacuum-dry the obtained solid at 60 °C for 24 h to obtain the template material n-stearoyl-l-glutamic acid.

[0053] Step 2: Dissolve 0.06 mmol of n-stearoyl-l-glutamic acid in 13 ml of methanol. Add 160 μl of pyrrole and 60 ml of deionized water to it, and stir for 20 min. Then gradually add 1.5 ml of 2.4 M ammonium persulfate solution, and stir and react at a rotation speed of 300 r / min under an ice-water bath condition for 10 min. Filter the resulting solution by suction and wash it three times with deionized water and alcohol. Finally, freeze-dry the obtained solid to obtain the chiral polypyrrole precursor.

[0054] Step 3: Take the chiral polypyrrole precursor powder and an equal mass of KOH, heat it to 700 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for two hours, and cool it with the furnace. After suction filtration, washing, and drying, obtain the metal-free catalyst powder.

[0055] Step 4: Prepare a 2+ mixed solution of cobalt nitrate with a molar concentration of 0.2 mmol / L and 3+ iron nitrate with a molar concentration of 0.3 mmol / L. Take 50 mg of the metal-free catalyst powder obtained in step 3 and add it to 30 ml of this solution. Stir at room temperature for 13 h. Filter the resulting solution by suction and wash it three times with deionized water and alcohol. Freeze-dry the obtained solid. Heat the dried powder to 1100 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for 1 hour, and cool it with the furnace to obtain the mixture powder.

[0056] Step 5: Prepare [Fe(CN)6]3- A K3[Fe(CN)6] solution with a molar concentration of 0.2 mmol / L. Take 50 mg of the mixture powder obtained in step 4 and add it to 30 ml of the K3[Fe(CN)6] solution. Stir at room temperature for 14 h; filter the resulting solution by suction, and wash it three times with deionized water and alcohol; freeze-dry the resulting solid; heat the dried powder to 1100 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for 1 hour, and cool with the furnace. A Fe-Co-N-C catalyst with precisely constructed dual atoms is prepared.

[0057] Comparative Example 1 Step 1: Take 0.96 g of NaOH and add it to 7 ml of deionized water, and add 1.78 g of l-glutamic acid and 6 ml of acetone thereto; then slowly add 3 g of stearoyl chloride and 5 ml of 2 M NaOH solution to the solution at the same time at room temperature and maintain pH = 12, and continue the reaction for 1.5 h; add 1 M HCl solution to the resulting solution until pH = 1; centrifuge and wash the resulting solid with distilled water until pH = 7, and then wash it 6 times with petroleum ether; vacuum-dry the resulting solid at 60 °C for 24 h to obtain the template material n-stearoyl-l-glutamic acid.

[0058] Step 2: Dissolve 0.06 mmol of n-stearoyl-l-glutamic acid in 13 ml of methanol, add 160 μl of pyrrole and 60 ml of deionized water thereto, and stir for 20 min; then dropwise add 1.5 ml of 2.4 M ammonium persulfate solution, and stir and react at a rotation speed of 300 r / min under an ice-water bath condition for 10 min; filter the resulting solution by suction, and wash it three times with deionized water and alcohol; finally, freeze-dry the resulting solid to obtain a chiral polypyrrole precursor.

[0059] Step 3: Take the chiral polypyrrole precursor powder and an equal mass of KOH, heat it to 700 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for two hours, and cool with the furnace; filter by suction, wash, and dry to obtain a metal-free catalyst powder.

[0060] Step 4: Prepare 3+ A ferric nitrate solution with a molar concentration of 0.3 mmol / L. Take 50 mg of the metal-free catalyst powder obtained in step 3 and add it to 30 ml of the ferric nitrate solution. Stir at room temperature for 12 h; filter the resulting solution by suction, and wash it three times with deionized water and alcohol; freeze-dry the resulting solid to obtain a powder; heat the dried powder to 900 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for two hours, and cool with the furnace to obtain a mixture powder.

[0061] Step 5: Prepare Fe 3+A ferric nitrate solution with a molar concentration of 0.3 mmol / L. Take 50 mg of the mixture powder obtained in step 4 and add it to 30 ml of the ferric nitrate solution. Stir at room temperature for 12 h; filter the resulting solution by suction and wash it three times with deionized water and alcohol; freeze-dry the obtained solid; heat the dried powder to 900 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for two hours, and cool with the furnace. A Fe-Fe-N-C catalyst with theoretical diatoms is prepared.

[0062] Comparative Example 2 Step 1: Take 0.96 g of NaOH and add it to 7 ml of deionized water, and add 1.78 g of l-glutamic acid and 6 ml of acetone thereto; then slowly add 3 g of stearoyl chloride and 5 ml of 2 M NaOH solution to the solution at the same time at room temperature and maintain pH = 12, and continue the reaction for 1.5 h; add 1 M HCl solution to the obtained solution until pH = 1; centrifuge and wash the obtained solid with distilled water until pH = 7, and then wash it 6 times with petroleum ether; vacuum-dry the obtained solid at 60 °C for 24 h to obtain the template material n-stearoyl-l-glutamic acid.

[0063] Step 2: Dissolve 0.06 mmol of n-stearoyl-l-glutamic acid in 13 ml of methanol, add 160 μl of pyrrole and 60 ml of deionized water thereto, and stir for 20 min; then dropwise add 1.5 ml of 2.4 M ammonium persulfate solution and stir and react at a rotation speed of 300 r / min under an ice-water bath condition for 10 min; filter the resulting solution by suction and wash it three times with deionized water and alcohol; finally, freeze-dry the obtained solid to obtain a chiral polypyrrole precursor.

[0064] Step 3: Take the chiral polypyrrole precursor powder and an equal mass of KOH and heat it to 700 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for two hours, and cool with the furnace; filter by suction, wash, and dry to obtain a metal-free catalyst powder.

[0065] Step 4: Prepare Fe 3+ A ferric nitrate solution with a molar concentration of 0.6 mmol / L, prepare [Fe(CN)6] 3- A K3[Fe(CN)6] solution with a molar concentration of 0.6 mmol / L. Take 50 mg of the metal-free catalyst powder obtained in step 3 and add it to 15 ml of the ferric nitrate solution and 15 ml of the K3[Fe(CN)6] solution. Stir at room temperature for 12 h; filter the resulting solution by suction and wash it three times with deionized water and alcohol; freeze-dry the obtained solid to obtain a powder; heat the dried powder to 900 °C at a rate of 5 °C / min under a nitrogen atmosphere, hold for two hours, and cool with the furnace to prepare a Fe-Fe-N-C catalyst with theoretical diatoms.

[0066] The prepared M-N-C catalyst with a helical morphology was used for performance testing in a three-electrode system. The establishment of this test system included the following steps: Step 1: Take 3 mg of the catalyst material, add 600 μL of an ethanol solution containing 2% nafion by volume fraction, and ultrasonically disperse it in ice water for 2 h to prepare a catalyst slurry.

[0067] Step 2: Prepare 250 ml of a KOH solution with a molar concentration of 0.1 mol / L or 1 mol / L.

[0068] Step 3: Coat 40 μL of the catalyst slurry on a glassy carbon electrode with an electrode area of 0.196 cm 2 ².

[0069] Step 4: Take a platinum wire, fix one end of the platinum wire to the outlet of the hydrogen generator so that stable and continuous hydrogen bubbles cover the platinum wire, and connect the other end to the three-electrode test system. Connect the Ag / AgCl reference electrode to the three-electrode test system at the same time, and measure the potential difference between the Ag / AgCl reference electrode and the standard hydrogen electrode.

[0070] Step 5: Use the glassy carbon electrode as the working electrode, Ag / AgCl as the reference electrode, and a graphite rod as the counter electrode. Test the ORR performance in a 0.1 mol / L KOH solution and the OER performance in a 1 mol / L KOH solution.

[0071] Figure 1 In [context not clear], the half-wave potential of Example 1 has exceeded that of the commercial Pt / C catalyst, and the half-wave potentials of Example 2 and Example 3 have also approached the level of the commercial Pt / C. Moreover, the half-wave potentials of Example 1 and Example 3 are higher than those of Comparative Example 1 and Comparative Example 2. When preparing Comparative Example 1, in Step 5, a ferric nitrate solution was directly added for preparation. Since ferric nitrate and the iron single atoms in the catalyst material both have an electron-losing effect and cannot attract each other to form precise double-atom sites but are randomly distributed single-atom / double-atom sites, the configuration of the intermediate in the oxygen reduction reaction changes, thus affecting the adsorption and desorption process of the intermediate in the oxygen reduction catalytic reaction and degrading the reaction rate. When preparing Comparative Example 2, it was prepared by a one-step method. However, due to the large contact area between the polar metal-containing ions and the porous catalyst material in the polar solution, the adsorption process is still random, resulting in a change in the configuration of the intermediate in the oxygen reduction reaction, thus affecting the adsorption and desorption process of the intermediate in the oxygen reduction catalytic reaction and degrading the reaction rate. This proves that the method of the present invention for precisely constructing double atoms is effective. The half-wave potentials of the three examples are all higher than that of Comparative Example 1, proving that the K3[Fe(CN)6] solution plays a decisive role in precisely constructing double atoms.

[0072] Figure 2 Among them, the potentials of Examples 1, 2, and 3 at a current density of 10 mA / cm -2 are all at 1.6 V or less than 1.6 V, approaching that of commercial RuO2 catalysts, demonstrating their certain OER performance.

[0073] Figure 3 The TEM image of Example 1 was taken under the high-angle annular dark field of a double aberration-corrected electron microscope. The bright spots marked by the circles in the figure are the intuitive display of the dual-atom active sites composed of metals, indicating that the metals in the catalyst prepared by the present invention are in atomic form.

[0074] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concepts. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications that fall within the scope of the present invention.

[0075] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A preparation method of a dual-atom catalyst, characterized in that, It includes the following steps: Add the nitrogen-containing carbon material into the solution containing transition metal, and carry out the first impregnation reaction to adsorb the transition metal onto the surface of the nitrogen-containing carbon material to obtain the powder after the first impregnation; Under the atmosphere of protective gas, calcine the powder after the first impregnation at 900 °C to 1100 °C for the first time. During the calcination process, chemical bonds are formed between the transition metal and the C-N bond of the nitrogen-containing carbon material to obtain the mixture powder; Add the mixture powder into the ferrocyanide solution, and carry out the second impregnation reaction to coordinate the transition metal with ferrocyanide to obtain the powder after the second impregnation; Under the atmosphere of protective gas, calcine the powder after the second impregnation at 900 °C to 1100 °C for the second time. During the calcination process, chemical bonds are formed among the transition metal, ferrocyanide radical and the C-N bond of the nitrogen-containing carbon material to obtain the dual-atom catalyst.

2. The preparation method of a dual-atom catalyst according to claim 1, characterized in that, The ratio of the carbon material to the solution containing transition metal is 5 mg: 3 mL; The concentration of the transition metal solution is 0.1 mmol / L to 0.6 mmol / L.

3. The preparation method of a dual-atom catalyst according to claim 1, characterized in that, The time for the first calcination is 1 h to 2 h.

4. The preparation method of a dual-atom catalyst according to claim 1, characterized in that, The ratio of the mixture powder to the ferrocyanide solution is 5 mg: 3 mL; The concentration of the ferrocyanide solution is 0.1 mmol / L to 0.3 mmol / L.

5. The preparation method of a dual-atom catalyst according to claim 1, wherein, The time for the second calcination is 1 h to 2 h.

6. The preparation method of a dual-atom catalyst according to claim 1, wherein, The time for the second impregnation reaction is 12 h to 14 h.

7. The preparation method of a dual-atom catalyst according to claim 1, characterized in that, The transition metal is one or two of iron, cobalt and nickel.

8. The preparation method of a dual-atom catalyst according to claim 1, characterized in that, The ferrocyanide solution is potassium ferrocyanide solution.

9. A dual-atom catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. An application of the dual-atom catalyst according to claim 9 in an alkaline zinc-air battery.

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