Preparation method and application of phosphorus-doped iron-based double-monatomic catalyst

Abstract

The invention relates to a preparation method and application of a phosphorus-doped iron-based double-monatomic catalyst. According to the method, a novel three-dimensional star-shaped mixed MOF of ZIF-8 and ZIF-L is selected as a carbon substrate, the carbon substrate which has a good aperture structure, enhances mass transfer and can expose more active sites is obtained through structural complementation and synergistic effects of the ZIF-8 and the ZIF-L, and phytic acid is used as a phosphorus source to introduce phosphorus atom doping, so that the activity of the carbon substrate is improved. The adsorption capacity of iron-based double monatomic on an oxygen intermediate is adjusted, and a series of phosphorus-doped iron-based double monatomic catalysts loaded on a nitrogen-doped porous carbon substrate are prepared. The material obtained by the invention is applied to the field of electro-catalytic oxygen reduction as a catalytic main body, and high-efficiency and directional conversion of the zinc-air battery is realized.

Description

Technical Field

[0001] This invention relates to a method for preparing nitrogen-doped carbon-supported phosphorus-doped iron-based double single-atom catalysts and their application in electrocatalysis. Specifically, by utilizing metal-organic frameworks (MOFs) as a carbon substrate and doping with heteroatom phosphorus, the adsorption capacity of the oxygen reduction active center for reaction intermediates is rationally adjusted through phosphorus doping, resulting in the rational design and successful preparation of a highly efficient oxygen reduction catalyst. Background Art

[0002] The oxygen reduction reaction (ORR) is a key cathode reaction in clean energy conversion technologies such as fuel cells and metal-air batteries. Due to its slow kinetics, it must be promoted by catalysts. However, due to the high cost, limited resources, and poor stability of precious metals, people have begun to explore efficient electrocatalysts that do not contain precious metals. As a promising alternative, atomically dispersed single-atom catalysts (SACs) with excellent catalytic performance have great potential in the field of heterogeneous catalysis. As the distance between isolated metal atoms is shortened, diatomic catalysts (DACs) are formed, and the orbital overlap between metal sites will produce different electronic structures [ACS Catal. 2023, 13, 11127-11135]. Among them, iron-based double single-atom catalysts have attracted much attention in the oxygen reduction (ORR) reaction due to their high atomic utilization, tunable electronic structure, and dual-site synergistic effect. However, the weak oxygen adsorption capacity of iron-based double single atoms makes the oxygen reduction reaction difficult to proceed, slowing the ORR reaction rate and limiting the performance of iron-based double single atom catalysts [Energy Environ. Sci., 2024, 17, 4646-4657]. Therefore, it is necessary to find a way to adjust the appropriate adsorption capacity of iron-based double single atoms for oxygen intermediates to provide good ORR catalysis.

[0003] Furthermore, metal-organic frameworks (MOFs), a class of crystalline porous materials formed by the self-assembly of metal ions or clusters with organic ligands through coordination bonds, have garnered widespread attention in recent years due to their significant advantages. Their most prominent advantages are their extremely high surface area and porosity, with some MOFs boasting surface areas of thousands of square meters per gram. This provides a vast storage space and rich interaction interfaces for materials [Energy Environ. Sci., 2024, 17, 4010-4035]. Thanks to their highly designable structures, MOFs' pore size, shape, surface chemistry, and topology can be precisely tuned through careful selection of metal nodes and organic linkers, enabling "custom-tailored" materials. This easily functionalizable pore surface allows for the introduction of specific functional groups or active sites onto the frameworks, thereby endowing the materials with tailored properties, such as selective adsorption, efficient catalysis, or sensitive sensing. Furthermore, many MOFs can be synthesized under relatively mild conditions (e.g., solvothermal methods), facilitating material preparation and structural control. Combined with these advantages—ultra-high specific surface area and porosity, precisely controllable structural design, flexible surface functionalization capabilities, and relatively feasible synthetic routes—MOFs have become an extremely attractive multifunctional platform material, showing great application potential and broad development prospects in many cutting-edge fields such as gas storage (such as hydrogen and methane), carbon capture, efficient separation, heterogeneous catalysis, drug delivery, chemical sensing, and energy storage and conversion [ACS Nano 2025, 19, 13-20]. However, the single pore structure of a single MOF is single and cannot effectively carry out material transfer and expose more active sites [Angew. Chem. Int. Ed. 2020, 59, 1327-1333]. Therefore, it is necessary to find a suitable method to optimize the pore structure of MOF to provide a good reaction environment for the ORR reaction. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method and application of a phosphorus-doped iron-based double single-atom catalyst in response to the deficiencies in the current technology. The method uses a new three-dimensional star-shaped mixed MOF of ZIF-8 and ZIF-L as a carbon substrate. Through the structural complementarity and synergistic effect of ZIF-8 and ZIF-L, a carbon substrate with a good pore structure, enhanced mass transfer and the ability to expose more active sites is obtained. Phytic acid is used as a phosphorus source to introduce phosphorus atom doping, adjust the adsorption capacity of the iron-based double single atoms for oxygen intermediates, and prepare a series of phosphorus-doped iron-based double single-atom catalysts loaded on nitrogen-doped porous carbon substrates. The material obtained by the present invention is applied as a catalytic main body to the field of electrocatalytic oxygen reduction to achieve efficient and directional conversion of zinc-air batteries.

[0005] The technical solution of the present invention is:

[0006] A method for preparing a phosphorus-doped iron-based double single-atom catalyst, the method comprising the following steps:

[0007] (1) dissolving zinc nitrate hexahydrate, ferric nitrate nonahydrate, and cetyltrimethylammonium bromide in deionized water, and ultrasonically dispersing the mixture to obtain a first solution; dissolving dimethylimidazole in deionized water to obtain a second solution;

[0008] In the first solution, 500-700 mg of zinc nitrate hexahydrate, 30-70 mg of ferric nitrate nonahydrate, and 5-25 mg of hexadecyltrimethylammonium bromide are added per 5-30 mL of deionized water;

[0009] The mass ratio of ferric nitrate nine hydrate to zinc nitrate hexahydrate is 1:10-15;

[0010] In the second solution, add 4000-5500 mg of dimethylimidazole per 50-100 mL of deionized water;

[0011] (2) The second solution is quickly poured into the first solution, and then stirred for 2 to 5 hours. After centrifugation, the mixture is washed with deionized water and ethanol, and dried to obtain a metal skeleton primary product. The dried product is ground and carbonized at 900 to 1100° C. for 1 to 2 hours under the protection of argon to obtain an iron-based double single atom product.

[0012] Wherein, the volume ratio of the first solution to the second solution is 1:3 to 1:6;

[0013] (3) A phytic acid solution with a mass concentration of 40-80% is added to anhydrous methanol, and ultrasonicated for 0.2-0.5 h to uniformly disperse it. The product obtained in step (2) is then dissolved in the methanol-phytic acid mixture, ultrasonicated for 0.3-1 h, stirred at 20-50° C. for 3-12 h, washed and dried, ground, and carbonized at 800-900° C. under argon protection for 0.5-2 h; then added to a 1-2 M hydrochloric acid solution and stirred for 12-24 h. After washing and drying, a phosphorus-doped iron-based double single-atom catalyst is obtained.

[0014] The mass of phytic acid added to each 10-40 mL of methanol is 30-100 mg;

[0015] In step (1), the ultrasonic power is 100W to 500W;

[0016] In step (2), the stirring speed is 300-800 rpm; the centrifugal speed is 8000-1200 rpm;

[0017] In step (3), the ultrasonic power is 100W to 500W; the stirring speed is 300 to 800 rpm; and the centrifugal speed is 8000 to 1200 rpm.

[0018] The phosphorus-doped iron-based double single-atom catalyst prepared by the method is used as an oxygen reduction reaction catalyst and is applied to the catalytic layer material of the cathode material in a zinc-air battery.

[0019] In a zinc-air battery, the anode is a zinc plate, the cathode is the working electrode, a stainless steel mesh serves as the current collector, and a solution containing 3.0-10 M KOH and 0.1-0.5 M ZnCl2 serves as the electrolyte.

[0020] The working electrode of the zinc-air battery is prepared by adding a phosphorus-doped iron-based double single-atom catalyst and carbon black to a mixed solution, ultrasonically dispersing the mixture for 20-60 minutes to obtain a dispersion, dropping the dispersion onto a carbon cloth, and naturally drying the mixture at room temperature to obtain a working electrode.

[0021] Among them, every 50~90mm 2 Add 700-900 μL of dispersion onto the carbon cloth;

[0022] The mixed solution is composed of Nafion and anhydrous ethanol, and the volume ratio of Nafion to anhydrous ethanol solution is 1:9 to 1:20;

[0023] Add 3-6 mg of phosphorus-doped iron-based double single-atom catalyst and 1-4 mg of carbon black to every 1000-1200 μL of the mixed solution;

[0024] The essential features of the present invention are:

[0025] In current technologies, although iron-based single-atom catalysts exhibit good catalytic ability in the electrocatalytic oxygen reduction reaction, due to their simple structure, it is difficult to effectively balance the linear proportional relationship between oxygen adsorption and product desorption; iron-based double single-atom catalysts, as an extension of them, retain the special properties of each component, but the iron-based double single-atom catalysts have weak oxygen adsorption ability, resulting in difficulties in the oxygen adsorption stage during the catalytic process, which hinders subsequent reactions and slows down the oxygen reduction reaction; in both catalysts, the coordination environment of isolated metal atoms has a decisive influence on the catalytic performance.

[0026] The present invention introduces Fe atoms and hexadecyltrimethylammonium bromide before synthesizing MOF, controllably synthesizes ZIF-8 and ZIF-L three-dimensional star-shaped mixed MOFs, and loads iron-based double single-atom catalysts through in situ synthesis, and introduces phosphorus atoms by impregnation to obtain phosphorus-doped iron-based double single atoms. After phosphorus doping, the spin state of the iron active site is improved and the adsorption capacity for oxygen is enhanced. ZIF-8 and ZIF-L three-dimensional star-shaped mixed MOFs are used as carbon substrates. Their large specific surface area, good pore structure and interconnected three-dimensional network synergistically promote the efficient oxygen reduction electrocatalysis. The efficient oxygen reduction catalyst is rationally designed and prepared with the help of the synergistic effect of heteroatom phosphorus doping and iron-based double single atoms.

[0027] Beneficial effects of the present invention:

[0028] (1) The present invention provides a method for regulating the adsorption capacity of iron-based double single atoms for oxygen intermediates by phosphorus doping, and the dual MOF structure of ZIF-8 and ZIF-L provides a rich pore structure and more stable performance. The synergistic effect of the two provides good oxygen reduction performance and realizes efficient conversion of zinc-air batteries.

[0029] (2) The phosphorus-doped iron-based double single-atom catalyst obtained in the present invention exhibits excellent electrochemical performance under alkaline conditions for electrocatalytic oxygen reduction. The half-wave potential of the traditional iron-based single-atom catalyst under 0.1M potassium hydroxide is only 0.863V; the half-wave potential of the phosphorus-doped iron-based single-atom catalyst under 0.1M potassium hydroxide is 0.877V; the half-wave potential of the traditional iron-based double single-atom catalyst under 0.1M potassium hydroxide is 0.895V; and the synergistic effect of the phosphorus doping and iron-based double single atoms obtained in the present invention, as well as the large specific surface area, porous structure and interconnected three-dimensional network structure, greatly promote the activity of the catalyst, so that its half-wave potential can reach 0.914V, which is better than the 0.856V of the traditional platinum-carbon catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a scanning electron microscope image of FeP-NC obtained in Example 1 of the present invention.

[0031] Figure 2 The linear voltammetric scan curves (scan rate 10 mV / s, rotation speed 1600 rpm) of the FeP-NC and Pt / C catalysts obtained in Example 1 of the present invention in an oxygen-saturated 0.1 mol / L KOH solution.

[0032] Figure 3 This is a stability test of the FeP-NC and Pt / C catalysts obtained in Example 1 of the present invention.

[0033] Figure 4 This is a test of the methanol resistance of the FeP-NC and Pt / C catalysts obtained in Example 1 of the present invention.

[0034] Figure 5 This is the open circuit voltage test curve of the zinc-air battery with FeP-NC and Pt / C catalysts obtained in Example 1 of the present invention.

[0035] Figure 6 This is the zinc-air battery specific capacity test curve of the FeP-NC and Pt / C catalysts obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0037] Example 1

[0038] Weigh 594 mg of Zn(NO3)2·6H2O, 50 mg of Fe(NO3)3·9H2O and 10 mg of cetyltrimethylammonium bromide and dissolve them in 20 mL of deionized water. Ultrasonicate at an ultrasonic power of 400 W for 30 min, which is recorded as solution A.

[0039] 4500 mg of 2-methylimidazole was weighed and dissolved in 80 mL of deionized water, and ultrasonicated at an ultrasonic power of 400 W for 20 min. This solution was recorded as solution B.

[0040] Then, solution B was quickly poured into solution A under stirring, stirred at 500 rpm at 25°C for 3 h, centrifuged at 10,000 rpm, washed three times with deionized water and anhydrous ethanol, respectively, and then vacuum dried at 60°C to obtain a powdery substance.

[0041] The powder obtained above was ground for 0.3 h, and under argon conditions, the temperature was increased at a rate of 5°C / min and kept at 910°C for 2 h to obtain a Fe-NC double single-atom catalyst.

[0042] 40 mg of a 70% phytic acid solution (the same concentration of phytic acid is used in the following examples) was weighed and dissolved in 20 mL of anhydrous methanol. The solution was ultrasonically treated at an ultrasonic power of 400 W for 10 min to obtain a mixed solution. 100 mg of Fe-NC was then weighed and dissolved in the mixed solution. The solution was ultrasonically treated at an ultrasonic power of 400 W for 20 min. The solution was stirred at 500 rpm for 4 h at 25°C, centrifuged at 10,000 rpm, washed three times with methanol, and then dried in vacuo at 60°C.

[0043] The powder obtained above was ground for 0.2 h, and under argon conditions, the temperature was increased at a rate of 5°C / min and kept at 800°C for 0.5 h. The obtained powder was then added to a 1M hydrochloric acid solution and immersed in stirring for 12 h. After washing and drying, the FeP-NC catalyst was obtained.

[0044] 4 mg of FeP-NC and 2 mg of carbon black were weighed, and 950 μL of anhydrous ethanol and 50 μL of 0.5 wt.% Nafion solution were added, and ultrasonic dispersion was performed for 30 min to form a uniform dispersion.

[0045] 10 μL of the obtained evenly dispersed catalyst suspension was coated on the surface of a polished glassy carbon electrode with a diameter of 5 mm and dried naturally at room temperature.

[0046] All electrochemical tests in this invention were conducted using a CHI-760E electrochemical workstation and an RRDE rotating ring disk electrode apparatus to test the electrochemical performance. All electrochemical tests used a standard three-electrode system with a KOH solution (0.1 M) as the electrolyte. The working electrode was a disc glassy carbon electrode coated with catalyst ink, the reference electrode was a saturated calomel electrode (Hg / HgCl, SCE), and the counter electrode was a platinum wire (Pt). The electrode potential was converted to the standard hydrogen electrode (RHE) potential. At a test temperature of 20°C, the conversion formula is:

[0047] E(vs.RHE)=E(vs.SCE)+0.244+0.0592*PH

[0048] When tested in 0.1M KOH electrolyte:

[0049] E(vs.RHE)=E(vs.SCE)+1.01

[0050] The test process is to conduct electrochemical oxygen reduction test in 0.1M KOH electrolyte saturated with O2 at 0rpm with a voltage of 10mVs -1 The scan rate was set at 1600 rpm, from 1.21 V to 0.00 V, until the CV curve was stable. The catalyst was fully activated at a potential of 0.00-1.21 V, and the LSV test of the catalyst was performed at 1600 rpm. 1 / 2 ) can reach 0.914 V. The phosphorus-doped iron-based double single-atom catalyst prepared by the invention has high activity in electrochemical oxygen reduction.

[0051] In order to test the actual performance of the catalyst in ORR, it was integrated into a zinc-air battery device. First, 4.0 mg of ground catalyst and 2 mg of carbon black were added to a centrifuge tube, 50 μL of 5 wt.% Nafion solution and 950 μL of anhydrous ethanol were added, and a uniform catalyst ink was formed after ultrasound. Then 750 μL of catalyst ink was evenly added dropwise to a clean carbon cloth with a diameter of 1 cm (model HCP020) in 5 times. The anode and cathode of the battery were a polished zinc plate and a carbon cloth coated with the catalyst, respectively. A stainless steel mesh was used as a current collector, and a solution containing 6.0 M KOH and 0.2 M ZnCl2 was used as the battery electrolyte. The actual performance of the zinc-air battery was tested using the Shanghai Chenhua CHI-760E electrochemical workstation.

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing Example 1:

[0053] Figure 1This is a scanning electron micrograph of the FeP-NC obtained in Example 1. From the figure, one can see a three-dimensional star-shaped structure composed of spindle-shaped carbon nanorods about 300 nm long.

[0054] Figure 2 The test results of the FeP-NC and commercial platinum-carbon catalysts obtained in Example 1 are shown. The onset potential and half-wave potential are important indicators for evaluating the performance of oxygen reduction catalysts, while platinum-carbon catalysts are the standard for evaluating excellent catalysts. In the LSV curve, the platinum-carbon catalyst has an onset potential of 0.979V and a half-wave potential of 0.856V. The phosphorus-doped iron-based double single-atom catalyst prepared in this patent has an onset potential of 0.995V and a half-wave potential of 0.914V, which is better than the commercial platinum-carbon catalyst and has a much lower production cost than the commercial platinum-carbon catalyst.

[0055] Figure 3 This graph shows the stability of the FeP-NC catalyst obtained in Example 1 and a commercial platinum-carbon catalyst. After 25,000 seconds of stability testing, the FeP-NC catalyst still maintained 95% of the current density, surpassing the 85% achieved by the platinum-carbon catalyst. This demonstrates the excellent stability of the FeP-NC catalyst.

[0056] Figure 4 This graph shows the methanol poisoning resistance of the FeP-NC and commercial platinum-carbon catalysts obtained in Example 1. At 700 seconds, 3 mL of methanol was injected into an oxygen-saturated 0.1 mol / L KOH solution. The current of the platinum-carbon catalyst dropped to a very low level after the methanol injection, with a large fluctuation range. However, the phosphorus-doped iron-based double single-atom catalyst prepared in this patent maintained good performance after the slight fluctuation, demonstrating that the prepared catalyst has excellent oxygen reduction catalytic performance.

[0057] Figure 5 This graph shows the open-circuit voltage of a zinc-air battery using the FeP-NC catalyst obtained in Example 1 and a commercial platinum-carbon catalyst. The graph shows that the FeP-NC has an open-circuit voltage of 1.51 V, which is closer to the theoretical value of 1.65 V than the 1.46 V of the platinum-carbon catalyst. This demonstrates that the FeP-NC has good catalytic performance in zinc-air batteries.

[0058] Figure 6 This is a graph showing the specific capacity test of the zinc-air battery using FeP-NC and commercial platinum-carbon catalysts obtained in Example 1. The specific capacity of FeP-NC is 732 mAh g -1 , higher than the 689mAh g of platinum carbon -1 The theoretical maximum specific capacity of zinc-air batteries is about 820 mAh g -1The coulombic efficiency of FeP-NC can reach 89.27%, which is higher than the 84.02% of commercial platinum-carbon catalyst, indicating that FeP-NC has good catalytic performance in zinc-air batteries.

[0059] Example 2

[0060] Weigh 594 mg of Zn(NO3)2·6H2O, 50 mg of Fe(NO3)3·9H2O and 10 mg of cetyltrimethylammonium bromide and dissolve them in 20 mL of deionized water. Ultrasonicate at an ultrasonic power of 400 W for 30 min, which is recorded as solution A.

[0061] 4500 mg of 2-methylimidazole was weighed and dissolved in 80 mL of deionized water, and ultrasonicated at an ultrasonic power of 400 W for 20 min. This solution was recorded as solution B.

[0062] Then, solution B was quickly poured into solution A under stirring, stirred at 500 rpm at 25°C for 3 h, centrifuged at 10,000 rpm, washed three times with deionized water and anhydrous ethanol, respectively, and then dried in vacuum at 60°C.

[0063] The powder obtained above was ground and kept at 910°C for 2 hours at a heating rate of 5°C / min under argon. The powder was then added to a 1M hydrochloric acid solution and stirred for 12 hours. After washing and drying, the Fe-NC double single-atom catalyst was obtained.

[0064] The same electrochemical test method as in Example 1 was used.

[0065] The half-wave potential (E 1 / 2 ) is 0.895V.

[0066] Example 3

[0067] 594 mg of Zn(NO3)2·6H2O, 25 mg of Fe(NO3)3·9H2O and 10 mg of cetyltrimethylammonium bromide were weighed and dissolved in 20 mL of deionized water. The mixture was ultrasonicated at an ultrasonic power of 400 W for 30 min and recorded as solution A.

[0068] 4500 mg of 2-methylimidazole was weighed and dissolved in 80 mL of deionized water, and ultrasonicated at an ultrasonic power of 400 W for 20 min. This solution was recorded as solution B.

[0069] Then, solution B was quickly poured into solution A under stirring, stirred at 500 rpm at 25°C for 3 h, centrifuged at 10,000 rpm, washed three times with deionized water and anhydrous ethanol, respectively, and then dried in vacuum at 60°C.

[0070] The powder obtained above was ground and kept at 910°C for 2 h at a heating rate of 5°C / min under argon. The obtained powder was then added to a 1 M hydrochloric acid solution and stirred for 12 h. After washing and drying, Fe-NC SAC was obtained.

[0071] The same electrochemical test method as in Example 1 was used.

[0072] The half-wave potential (E 1 / 2 ) is 0.863V.

[0073] Example 4

[0074] 594 mg of Zn(NO3)2·6H2O, 25 mg of Fe(NO3)3·9H2O and 10 mg of cetyltrimethylammonium bromide were weighed and dissolved in 20 mL of deionized water. The mixture was ultrasonicated at an ultrasonic power of 400 W for 30 min and recorded as solution A.

[0075] 4500 mg of 2-methylimidazole was weighed and dissolved in 80 mL of deionized water, and ultrasonicated at an ultrasonic power of 400 W for 20 min. This solution was recorded as solution B.

[0076] Then, solution B was quickly poured into solution A under stirring, stirred at 500 rpm at 25°C for 3 h, centrifuged at 10,000 rpm, washed three times with deionized water and anhydrous ethanol, respectively, and then dried in vacuum at 60°C.

[0077] The powder obtained above was ground, and under argon conditions, the temperature was increased at a rate of 5°C / min and kept at 910°C for 2h to obtain a Fe-NC double single-atom catalyst.

[0078] 40 mg of phytic acid solution was dissolved in 20 mL of anhydrous methanol and ultrasonicated at an ultrasonic power of 400 W for 10 min. Then 100 mg of Fe-NC was dissolved in the mixed solution and ultrasonicated at an ultrasonic power of 400 W for 20 min. The mixture was stirred at 500 rpm for 4 h at 25 °C, centrifuged at 10,000 rpm, washed three times with methanol, and then dried in a vacuum at 60 °C.

[0079] The powder obtained above was ground and kept at 800°C for 0.5h under argon gas at a heating rate of 5°C / min. The powder was then added to a 1M hydrochloric acid solution and stirred for 12h. The FeP-NC SAC catalyst was obtained after washing and drying.

[0080] The same electrochemical test method as in Example 1 was used.

[0081] The half-wave potential (E 1 / 2) is 0.877V.

[0082] Example 5

[0083] Weigh 594 mg of Zn(NO3)2·6H2O, 50 mg of Fe(NO3)3·9H2O and 10 mg of cetyltrimethylammonium bromide and dissolve them in 20 mL of deionized water. Ultrasonicate at an ultrasonic power of 400 W for 30 min, which is recorded as solution A.

[0084] 4500 mg of 2-methylimidazole was weighed and dissolved in 80 mL of deionized water, and ultrasonicated at an ultrasonic power of 400 W for 20 min. This solution was recorded as solution B.

[0085] Then, solution B was quickly poured into solution A under stirring, stirred at 500 rpm at 25°C for 3 h, centrifuged at 10,000 rpm, washed three times with deionized water and anhydrous ethanol, respectively, and then dried in vacuum at 60°C.

[0086] The powder obtained above was ground, and under argon conditions, the temperature was increased at a rate of 5°C / min and kept at 910°C for 2h to obtain a Fe-NC double single-atom catalyst.

[0087] 80 mg of phytic acid solution was dissolved in 20 mL of anhydrous methanol and ultrasonicated at an ultrasonic power of 400 W for 10 min. Then 100 mg of Fe-NC was dissolved in the mixed solution and ultrasonicated at an ultrasonic power of 400 W for 20 min. The mixture was stirred at 500 rpm for 4 h at 25°C, centrifuged at 10,000 rpm, washed three times with methanol, and then dried in vacuo at 60°C.

[0088] The powder obtained above was ground and heated at a rate of 5°C / min under argon atmosphere at 800°C for 0.5h. The powder was then added to a 1M hydrochloric acid solution and stirred for 12h. After washing and drying, FeP 80 -NC catalyst.

[0089] The same electrochemical test method as in Example 1 was used.

[0090] FeP 80 -NC half-wave potential (E 1 / 2 ) is 0.887V.

[0091] Examples 2-5 are about changing the doping of single atoms, double single atoms and heteroatom phosphorus. The comparison results with Example 1 show that iron-based double single atoms have higher performance than iron-based single atoms; excessive phosphorus doping cannot improve the performance of the catalyst, but will also reduce the performance of the catalyst; appropriate phosphorus doping can change the spin state of the active site, appropriately adjust the adsorption capacity of oxygen intermediates, and further improve the performance of the catalyst.

[0092] From the above examples, it can be seen that the phosphorus-doped iron-based double single-atom catalyst FeP-NC prepared by the present invention uses a metal-organic framework as a precursor, inherits the morphology and porous structure of the metal-organic framework, is more conducive to the exposure of the catalyst active sites, electron transfer and material transport, and has a larger specific surface area, and prepares a uniformly distributed transition metal catalyst, which provides a valuable reference for the rational design and high-performance active center oxygen reduction electrocatalyst.

[0093] Matters not covered by the present invention are known technologies.

Claims

1. A method for preparing a phosphorus-doped iron-based double single-atom catalyst, characterized in that: The method comprises the following steps: (1) dissolving zinc nitrate hexahydrate, ferric nitrate nonahydrate, and cetyltrimethylammonium bromide in deionized water, and ultrasonically dispersing the mixture to obtain a first solution; dissolving dimethylimidazole in deionized water to obtain a second solution; In the first solution, 500-700 mg of zinc nitrate hexahydrate, 30-70 mg of ferric nitrate nonahydrate, and 5-25 mg of hexadecyltrimethylammonium bromide are added per 5-30 mL of deionized water; In the second solution, add 4000-5500 mg of dimethylimidazole per 50-100 mL of deionized water; (2) The second solution is quickly poured into the first solution, and then stirred for 2 to 5 hours. After centrifugation, the product is washed with deionized water and ethanol, and dried to obtain a metal skeleton primary product; the dried product is ground and carbonized at 900 to 1100°C for 1 to 2 hours under the protection of argon to obtain an iron-based double single atom product; Wherein, the volume ratio of the first solution to the second solution is 1:3 to 1:6; (3) adding the phytic acid solution to methanol, ultrasonicating for 0.2 to 0.5 hours to disperse it, then adding the iron-based double single atom product obtained in step (2), continuing ultrasonicating for 0.3 to 1 hour, stirring at 20-50°C for 3 to 12 hours, washing, drying, grinding, and then carbonizing at 800-900°C for 0.5 to 2 hours under the protection of argon; then adding to hydrochloric acid and stirring for 12 to 24 hours, washing and drying to obtain a phosphorus-doped iron-based double single atom catalyst; The mass of phytic acid added to every 10-40 mL of methanol is 30-80 mg and 80-150 mg of iron-based double single-atom product.

2. The method for preparing the phosphorus-doped iron-based double single-atom catalyst according to claim 1, wherein: The mass ratio of ferric nitrate nine hydrate to zinc nitrate hexahydrate is 1:10-15.

3. The method for preparing the phosphorus-doped iron-based double single-atom catalyst according to claim 1, wherein: In step (1), the ultrasonic power is 100W to 500W; In step (2), the stirring speed is 300-800 rpm; the centrifugal speed is 8000-1200 rpm; In step (3), the ultrasonic power is 100W to 500W; the stirring speed is 300 to 800 rpm; and the centrifugal speed is 8000 to 1200 rpm.

4. The method for preparing the phosphorus-doped iron-based double single-atom catalyst according to claim 1, wherein: In step (3), the mass concentration of phytic acid is 40-80%; the concentration of hydrochloric acid is 1-2M.

5. Use of the phosphorus-doped iron-based double single-atom catalyst prepared by the method according to claim 1, characterized in that: Catalytic layer material used as oxygen reduction reaction catalyst in cathode materials of zinc-air batteries.

6. The use according to claim 5, characterized in that In a zinc-air battery, the anode is a zinc plate, the cathode is the working electrode, a stainless steel mesh serves as the current collector, and a solution containing 3.0-10 M KOH and 0.1-0.5 M ZnCl2 serves as the electrolyte. The working electrode preparation method is as follows: adding phosphorus-doped iron-based double single-atom catalyst and carbon black to a mixed solution, ultrasonically dispersing for 20-60 minutes to obtain a dispersion, dropping the dispersion on a carbon cloth, and drying it naturally at room temperature to obtain a working electrode; wherein, every 50-90 mm 2 700-900 μL of dispersion was added to the carbon cloth; The mixed solution is composed of Nafion and anhydrous ethanol, and the volume ratio of Nafion to anhydrous ethanol solution is 1:9 to 1:20; 3 to 6 mg of phosphorus-doped iron-based double single-atom catalyst and 1 to 4 mg of carbon black are added to every 1000 to 1200 μL of the mixed solution.

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