ZIF-8 derived Pt / Fe-N-C bimetallic monatomic catalyst and preparation method thereof

Abstract

The invention belongs to the technical field of electrochemical catalysis, and particularly relates to a ZIF-8 derived Pt / Fe-N-C bimetallic monatomic catalyst and a preparation method thereof. Comprising the following steps: S1, preparing an NC material; s2, dipping an iron salt solution onto the NC material obtained in the step S1, drying, and then carrying out carbon thermal shock (CTS) treatment to obtain an Fe-N-C monatomic material; s3, platinum salt and a nitrogen source are coordinated and then added into the Fe-N-C monatomic material obtained in the step S2, CTS is carried out after drying, and the Pt / Fe-N-C bimetallic monatomic catalyst is obtained. The stability of the Fe-N-C catalyst is improved by increasing Pt atoms, the Fe-N-C catalyst shows efficient alkaline oxygen reduction catalytic activity when being used for an oxygen reduction reaction, meanwhile, compared with a commercial Pt / C catalyst, the mass activity is improved by more than 20 times, the energy efficiency is improved, and the use of precious metal is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical catalysis, and specifically relates to a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst and a preparation method thereof. Background Art

[0002] In recent years, car battery explosions have been common. Lithium-ion batteries are prone to lithium dendrites, which can cause battery short circuits and explosions. In addition, lithium-ion batteries have a low specific energy density (200Wh / kg), so a battery with strong safety and high specific energy density is needed to replace them. Aqueous zinc-air batteries are a new type of environmentally friendly and pollution-free energy because their positive electrode reactant is oxygen in the air.

[0003] At present, zinc-air batteries are widely used in hearing aids, and the cathode catalyst of commercial zinc-air batteries is 20% Pt / C, which has problems such as high production cost and insufficient durability. Non-precious metal catalysts have always attracted widespread attention due to their low cost and high durability. However, current non-precious metal catalysts have problems such as unstable adsorption with oxygen intermediates and high impedance, which leads to slow kinetics of oxygen reduction reaction. The preparation of simple and efficient low-Pt cathode catalysts has always been the focus and challenge of research.

[0004] Patent CN202311749080.6 discloses a preparation method and application of Fe and Pt diatomic catalysts. First, the Fe salt and nitrogen source added to carbon black are pyrolyzed by high temperature treatment to obtain Fe single-atom catalysts, and then H2PtCl6·6H2O is loaded by impregnation method. After co-annealing, the Fe and Pt diatomic catalysts are cooled, washed, centrifuged, dried, and ground. However, the preparation process of this method is relatively long and the yield is not high.

[0005] Patent CN202111541453.1 discloses a nanocarbon-supported platinum-iron bimetallic catalyst, its preparation method, and its application in the selective oxidation reaction of CO in a hydrogen-rich atmosphere. The catalyst uses nanocarbon as a carrier, firstly loads platinum and iron on a nanocarbon carrier material by a coprecipitation method, obtains a nanocarbon-supported platinum-iron catalyst precursor, and then places the precursor in a mixed atmosphere of hydrogen and helium for reduction treatment to obtain a nanocarbon-supported platinum-iron bimetallic catalyst. However, in this technical solution, Pt does not exist in a single atom form, and the utilization rate of Pt is low.

[0006] Therefore, how to adopt a simple and rapid method to prepare Pt / Fe bimetallic single atom catalysts to improve the utilization rate of Pt is an urgent problem that needs to be solved. Summary of the invention

[0007] In view of this, the present invention proposes a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst and a preparation method thereof to solve the problems of long preparation process and low utilization rate of precious metals in the prior art bimetallic catalysts.

[0008] The technical solution of the present invention is achieved in this way:

[0009] In a first aspect, the present invention provides a method for preparing a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst, comprising the following steps:

[0010] S1. Preparation of NC materials;

[0011] S2, impregnating the iron salt solution onto the NC material obtained in step S1, and performing CTS after drying to obtain Fe-NC single atom material;

[0012] S3, after coordinating the platinum salt with the nitrogen source, adding it to the Fe-NC single atom material obtained in step S2, drying it, and performing CTS to obtain a Pt / Fe-NC bimetallic single atom catalyst.

[0013] In the present invention, a carbon thermal shock treatment (CTS) strategy is adopted to limit the particle growth. By performing time-precise CTS pyrolysis on spatially confined precursors (such as multi-metal organic frameworks MOFs), the growth of metal particles is effectively inhibited and the formation of bimetallic single atom catalysts is promoted. This CTS method has the following advantages: (1) The rapid heating and cooling process effectively limits the migration and aggregation of metal atoms, significantly increasing the probability of single atom formation. (2) The precisely controlled pyrolysis time ensures that the metal atoms can be evenly dispersed on the carbon support without forming large-sized particles. (3) During the CTS process, the rapid decomposition and reconstruction of the MOF precursor helps to form a stable metal-nitrogen-carbon (MNC) structure, further fixing the single atoms. (4) This method can also retain the porous structural characteristics of MOF to a certain extent, forming a carbon support with a layered structure, which is conducive to exposing more active sites and promoting the penetration of electrolytes. Through this unique CTS method, we can efficiently prepare uniformly distributed Pt / Fe bimetallic single atom catalysts and significantly improve their catalytic activity and stability. This method is not only applicable to the Pt / Fe system, but can also be extended to the preparation of other multi-metal single-atom catalysts, providing a new approach for the development of high-performance electrocatalytic materials.

[0014] In addition, in the present invention, a two-step method is used to synthesize the Pt / Fe-NC bimetallic single-atom catalyst in steps. From the perspective of metal dispersion control, the two-step method can ensure the formation of FeN4 sites and then accurately control the introduction of Pt. In the one-step method, PtFe exists at the same time and competes with each other for N coordination sites, resulting in uneven distribution. From a structural perspective, the two-step method forms a stable FeN4 structure, which is conducive to the subsequent anchoring of Pt single atoms. The one-step method leads to disordered metal-nitrogen coordination, making it difficult to form a PtFe bimetallic single-atom structure.

[0015] On the basis of the above technical solution, preferably, step S1 specifically comprises: mixing a zinc salt solution with an organic ligand solution, preparing ZIF-8 by magnetic stirring, using ZIF-8 as a template, and obtaining a NC material having a MOF morphology after pyrolysis.

[0016] On the basis of the above technical scheme, preferably, the zinc salt is any one of zinc nitrate, zinc chloride, zinc acetate, and zinc acetylacetonate, the organic ligand is an imidazole compound, the concentration of the zinc salt solution is 0.1-0.4 mol / L, the concentration of the organic ligand solution is 0.4-1.6 mol / L, and the magnetic stirring reaction time is 6-48h.

[0017] Furthermore, the zinc salt solution is an alcohol solution of zinc salt, and the organic ligand solution is an alcohol solution of organic ligand; the magnetic stirring speed is 800-1500rpm; after the magnetic stirring reaction is completed, the mixed solution is centrifuged, washed, and dried to obtain ZIF-8, wherein the detergent is at least one of methanol, ethanol, isopropanol and N,N-dimethylformamide, and the role of the detergent is to wash away impurities such as the coordinated ligand; the centrifugal speed is 5000-10000rpm, and the centrifugal time is 1-5min.

[0018] Based on the above technical solution, preferably, the pyrolysis reaction specifically includes: heating ZIF-8 to 900-1100°C at a rate of 5-10°C / min, and keeping the temperature for 30-60min. The atmosphere of the pyrolysis reaction can be any one of vacuum, air, argon, nitrogen, ammonia and argon-hydrogen mixed gas.

[0019] Based on the above technical solution, preferably, in step S2, the concentration of iron in the iron salt solution is 0.1-0.3 mol / L, and the impregnation load is 0.01-5 wt.%. The iron salt can be any one of chloride, nitrate, acetate and acetylacetonate, and the solvent of the iron salt solution can be any one of water, ethanol, DMF and petroleum ether.

[0020] On the basis of the above technical solution, preferably, in step S2, the heating power supply of CTS is a pulse power supply, the pulse current waveform is a square wave, the current is 10-60A, the voltage is 20-60V, the pulse frequency is 0.1-1Hz, the heating temperature is 1300-1800℃, and the heating time is 100-300ms.

[0021] Specifically, the square wave pulse current provides stable energy transmission, so that the heating process can be precisely controlled to avoid overheating or uneven heating, thereby improving the consistency and repeatability of material processing. CTS is performed at 1300-1800℃ and 80-120ms. The transient high temperature helps the uniform dispersion and stable existence of metal atoms on the carbon carrier, preventing the metal atoms from aggregating to form clusters or nanoparticles. At the same time, the transient high temperature treatment can promote the reorganization of the internal structure of the carbon carrier to form a more stable metal-nitrogen-carbon (MNC) coordination environment; through high temperature treatment in an extremely short time, a strong thermal shock is generated. This rapid temperature change helps to limit the migration and aggregation of metal atoms and promote the formation of single-atom catalysts. The short high temperature treatment reduces the diffusion time of metal atoms, thereby effectively inhibiting the growth of metal particles and ensuring that the metal atoms are evenly dispersed on the carbon carrier in the form of single atoms.

[0022] On the basis of the above technical scheme, preferably, the platinum salt is any one of chloroplatinic acid, platinum nitrate, and platinum acetate, the nitrogen source is at least one of dimethylimidazole, o-phenanthroline, pyridine and 2,2'-bipyridine, the molar ratio of the platinum salt to the nitrogen source is 0.02-1:0.02-10, more preferably, the molar ratio of the platinum salt to the nitrogen source is 0.5:10, and the mass proportion of Pt in the Pt / Fe-NC precursor is 0.1-5wt%.

[0023] On the basis of the above technical solution, preferably, in step S3, the heating power supply of CTS is a pulse power supply, the pulse current waveform is a square wave, the current is 10-60A, the voltage is 20-60V, the pulse frequency is 0.1-1Hz, the heating temperature is 1000-1500℃, and the heating time is 100-200ms.

[0024] Specifically, the heating temperature in step S3 is relatively low in order to avoid destroying the Fe-NC structure that has been formed and to prevent Fe atoms from migrating or agglomerating at excessively high temperatures; and platinum has a relatively low melting point and a relatively high atomic mobility, and a relatively low temperature is conducive to the formation and fixation of Pt single atoms.

[0025] In a second aspect, the present invention provides a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst prepared by the preparation method described above.

[0026] In a third aspect, the present invention provides an application of a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst in a non-precious metal catalyst.

[0027] The ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst and the preparation method thereof of the present invention have the following beneficial effects compared with the prior art:

[0028] (1) The present invention uses rapid pyrolysis of CTS to perform time-accurate CTS pyrolysis on spatially confined precursors (such as multi-metal organic frameworks MOFs), effectively inhibiting the growth of metal particles and promoting the formation of bimetallic single-atom catalysts. The precisely controlled pyrolysis time ensures that the metal atoms can be evenly dispersed on the carbon carrier without forming large-sized particles.

[0029] (2) The present invention increases the stability of the Fe-NC catalyst by adding Pt atoms. After the introduction of Pt, Fe-NC forms a double coordination bond of Pt-Fe and Pt-N, which greatly improves the stability of the catalyst. Pt atoms can also reduce the generation of the intermediate product hydrogen peroxide, further improving the stability of Fe-NC;

[0030] (3) The Pt / Fe-NC bimetallic single-atom catalyst prepared by the present invention exhibits efficient alkaline oxygen reduction catalytic activity for oxygen reduction reaction. At the same time, compared with the commercial Pt / C catalyst, the mass activity is increased by 20 times, which improves energy efficiency and reduces the use of precious metals. The characteristics of the present invention are that the synthetic catalyst is prepared quickly, and the existence of Pt in the form of a single atom greatly improves the utilization rate of precious metals. The open circuit voltage of the catalyst used in rechargeable zinc-air batteries is as high as 1.51V, and it also exhibits excellent energy conversion efficiency and cycle stability. It is expected to become a catalyst material for large-scale application of rechargeable zinc-air batteries, thereby replacing precious metal-based catalysts and reducing production and use costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 Surface morphology of ZIF-8 and NC materials of the present invention;

[0033] Figure 2 X-ray diffraction patterns of Pt / Fe-NC catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention;

[0034] Figure 3 This is a surface morphology of the Pt / Fe-NC bimetallic single atom catalyst prepared in Example 1 of the present invention;

[0035] Figure 4 This is a spherical aberration corrected scanning transmission electron micrograph of the Pt / Fe-NC bimetallic single atom catalyst prepared in Example 1 of the present invention;

[0036] Figure 5 1 is an LSV curve diagram of the Pt / Fe-NC bimetallic single atom catalyst prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention.

[0037] Figure 6 This is a graph showing the cyclic charge and discharge stability of the zinc-air battery of Example 1 of the present invention and commercial Pt / C. DETAILED DESCRIPTION

[0038] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Example 1

[0040] This embodiment provides a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst and a preparation method thereof, comprising the following steps:

[0041] S1. Dissolve 6.78g Zn(NO3)·6H2O in 200ml methanol solution and 7.88g dimethylimidazole in 200ml methanol solution. Ultrasonicate them in an ultrasonic machine for 15min respectively until they are completely dissolved in the methanol solution. Pour the dimethylimidazole methanol solution into the zinc nitrate methanol solution and continue ultrasonicating for 15min. Place the mixed solution on a magnetic stirrer and stir at 1200rpm for 12h to produce a milky white suspension. Centrifuge and wash the suspension 3 times, with a centrifugal speed of 8000rpm, a centrifugal time of 3min, and a detergent of methanol. Dry it in a vacuum dryer at 60°C for 360min to obtain ZIF-8.

[0042] 300 mg of ZIF-8 was placed in a magnetic boat and heated to 1000°C at a rate of 8°C. After annealing at 1000°C in an argon atmosphere for 30 min, the NC material with MOF morphology was obtained.

[0043] S2, 267μl of 0.2mol / L FeCl3·6H2O ethanol solution was impregnated and loaded onto 100mg NC material, and manually ground in a mortar until the ethanol was completely evaporated, and collected as Fe-NC precursor. The Fe-NC precursor was placed on a 1.5cm*4cm carbon cloth, and the carbon cloth was clamped at both ends of a pulse power supply for CTS in an argon atmosphere, wherein the pulse current waveform was set to a square wave, the current was 35A, the voltage was 40V, the pulse frequency was 0.5Hz, and the Fe-NC single atom catalyst was obtained by CTS at 1800℃ for 100ms;

[0044] S3, 25μl 0.2mol / L chloroplatinic acid and 25μl 0.2mol / L o-phenanthroline were coordinated for 5min, the suspension was impregnated and loaded on 100mg Fe-NC, and manually ground in a mortar until the ethanol was completely evaporated, and collected as a Pt / Fe-NC precursor. The Pt / Fe-NC precursor was prepared by CTS, in which the pulse current waveform was set to a square wave, the current was 35A, the voltage was 40V, the pulse frequency was 0.5Hz, and CTS was performed at 1000℃ for 100ms to obtain a Pt / Fe-NC bimetallic single atom catalyst.

[0045] Example 2

[0046] This embodiment provides a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst and a preparation method thereof, comprising the following steps:

[0047] S1 is the same as in Example 1;

[0048] S2, 267μl of 0.2mol / L FeCl3·6H2O ethanol solution was impregnated and loaded onto 100mg NC material, and manually ground in a mortar until the ethanol was completely evaporated, and collected as Fe-NC precursor. The Fe-NC precursor was placed on a 1.5cm*4cm carbon cloth, and the carbon cloth was clamped at both ends of a pulse power supply for CTS in an argon atmosphere, wherein the pulse current waveform was set to a square wave, the current was 35A, the voltage was 40V, the pulse frequency was 0.5Hz, and the Fe-NC single atom catalyst was obtained at 1300℃CTS300ms;

[0049] S3, 25μl 0.2mol / L chloroplatinic acid and 25μl 0.2mol / L o-phenanthroline were coordinated for 5min, the suspension was impregnated and loaded on 100mg Fe-NC, and manually ground in a mortar until the ethanol evaporated completely, and collected as a Pt / Fe-NC precursor. The Pt / Fe-NC precursor was subjected to CTS, in which the pulse current waveform was set to a square wave, the current was 35A, the voltage was 40V, the pulse frequency was 0.5Hz, and CTS was performed at 1300℃ for 200ms to obtain a Pt / Fe-NC bimetallic single atom catalyst.

[0050] Example 3

[0051] This embodiment provides a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst and a preparation method thereof, comprising the following steps:

[0052] S1. Dissolve 8.92g Zn(NO3)·6H2O in 300mL methanol solution and 11.54g dimethylimidazole in 300mL methanol solution, and ultrasonicate them in an ultrasonic machine for 15min respectively until they are completely dissolved in the methanol solution. Then pour the dimethylimidazole methanol solution into the zinc nitrate methanol solution and continue ultrasonicating for 15min. Place the mixed solution on a magnetic stirrer and stir at 800rpm for 48h to produce a milky white suspension. Centrifuge and wash the suspension 3 times, with a centrifugal speed of 5000rpm, a centrifugal time of 5min, and a detergent of methanol. Dry it in a vacuum dryer at 60℃ for 360min to obtain ZIF-8.

[0053] 300 mg of ZIF-8 was placed in a magnetic boat and heated to 900°C at a rate of 5°C. After annealing at 900°C in an argon atmosphere for 60 min, the NC material with MOF morphology was obtained.

[0054] S2, 1.79 μL of 0.1 mol / L FeCl3·6H2O ethanol solution was impregnated and loaded onto 100 mg of NC material, and the material was manually ground in a mortar until the ethanol was completely evaporated, and then collected as Fe-NC precursor. The Fe-NC precursor was placed on a 1.5 cm*4 cm carbon cloth, and the carbon cloth was clamped at both ends of a pulse power supply for CTS in an argon atmosphere, wherein the pulse current waveform was set to a square wave, the current was 10 A, the voltage was 20 V, and the pulse frequency was 0.1 Hz. Fe-NC single atom catalyst was obtained at 1600 ° C CTS for 200 ms;

[0055] S3, 2.56μL 0.2mol / L H2PtCl6·6H2O ethanol solution was mixed with 1281.5μL 0.2mol / L o-phenanthroline ethanol solution, the coordination reaction was carried out for 4min, the suspension was impregnated and loaded on 100mg Fe-NC, and manually ground in a mortar until the ethanol was completely evaporated, and collected as Pt / Fe-NC precursor. The Pt / Fe-NC precursor was subjected to CTS, in which the pulse current waveform was set to square wave, the current was 10A, the voltage was 20V, the pulse frequency was 0.1Hz, and the CTS was 220ms at 1000℃ to obtain the Pt / Fe-NC bimetallic single atom catalyst.

[0056] Example 4

[0057] This embodiment provides a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst and a preparation method thereof, comprising the following steps:

[0058] S1. Dissolve 35.70g Zn(NO3)·6H2O in 300mL methanol solution and 46.14g dimethylimidazole in 300mL methanol solution. Ultrasonicate them in an ultrasonic machine for 15min respectively until they are completely dissolved in the methanol solution. Pour the dimethylimidazole methanol solution into the zinc nitrate methanol solution and continue ultrasonicating for 15min. Place the mixed solution on a magnetic stirrer and stir at 1500rpm for 6h to produce a milky white suspension. Centrifuge and wash the suspension 3 times, with a centrifugal speed of 10000rpm, a centrifugal time of 1min, and a detergent of methanol. Dry it in a vacuum dryer at 60°C for 360min to obtain ZIF-8.

[0059] 300 mg of ZIF-8 was placed in a magnetic boat, heated to 1100°C at a rate of 10°C, annealed at 1100°C in an argon atmosphere for 30 min, and then naturally cooled to room temperature to obtain NC materials with MOF morphology;

[0060] S2, 298μL of 0.3mol / L FeCl3·6H2O ethanol solution was impregnated and loaded onto 100mg NC material, and manually ground in a mortar until the ethanol was completely evaporated, and collected as Fe-NC precursor. The Fe-NC precursor was placed on a 1.5cm*4cm carbon cloth, and the carbon cloth was clamped at both ends of a pulse power supply for CTS in an argon atmosphere, wherein the pulse current waveform was set to a square wave, the current was 60A, the voltage was 60V, the pulse frequency was 1Hz, and the Fe-NC single atom catalyst was obtained at 1800℃CTS100ms;

[0061] S3, 128.15μL 0.2mol / L H2PtCl6·6H2O ethanol solution was mixed with 2.56μL 0.2mol / L o-phenanthroline ethanol solution, the coordination reaction was carried out for 6min, the suspension was impregnated and loaded on 100mg Fe-NC, and manually ground in a mortar until the ethanol was completely evaporated, and collected as a Pt / Fe-NC precursor. The Pt / Fe-NC precursor was subjected to CTS, in which the pulse current waveform was set to a square wave, the current was 60A, the voltage was 60V, the pulse frequency was 1Hz, and the CTS was 1500℃ for 180ms to obtain a Pt / Fe-NC bimetallic single atom catalyst.

[0062] Comparative Example 1

[0063] This comparative example provides a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst and a preparation method thereof, comprising the following steps:

[0064] S1. Dissolve 6.78g Zn(NO3)·6H2O in 300ml methanol solution and 7.88g dimethylimidazole in 300ml methanol solution, and ultrasonicate them in an ultrasonic machine for 15min respectively until they are completely dissolved in the methanol solution. Then pour the dimethylimidazole methanol solution into the zinc nitrate methanol solution and continue ultrasonicating for 15min. Place the mixed solution on a magnetic stirrer and stir at 1200rpm for 12h to produce a milky white suspension. Centrifuge and wash the suspension 3 times, with the centrifugal speed at 8000rpm, the centrifugal time for 3min, and the detergent being methanol. Dry it at 60℃ in a vacuum dryer for 360min to obtain ZIF-8.

[0065] 300 mg of ZIF-8 was placed in a magnetic boat and heated to 1000°C at a rate of 8°C. After annealing at 1000°C in an argon atmosphere for 30 min, the NC material with MOF morphology was obtained.

[0066] S2, 267μl of 0.2mol / L FeCl3·6H2O ethanol solution was impregnated and loaded onto 100mg NC material, and manually ground in a mortar until the ethanol was completely evaporated, and collected as Fe-NC precursor. The Fe-NC precursor was placed on a 1.5cm*4cm carbon cloth, and the carbon cloth was clamped at both ends of a pulse power supply for CTS in an argon atmosphere, wherein the pulse current waveform was set to a square wave, the current was 35A, the voltage was 40V, the pulse frequency was 0.5Hz, and the Fe-NC single atom catalyst was obtained at 1800℃CTS100ms;

[0067] S3, 25μl 0.2mol / L chloroplatinic acid was impregnated and loaded on 100mg Fe-NC, and manually ground in a mortar until the ethanol was completely evaporated, and collected as a Pt / Fe-NC precursor. The Pt / Fe-NC precursor was subjected to CTS, in which the pulse current waveform was set to a square wave, the current was 35A, the voltage was 40V, the pulse frequency was 0.5Hz, and the CTS was performed at 1800℃ for 100ms to obtain a Pt / Fe-NC bimetallic single atom catalyst.

[0068] Comparative Example 2

[0069] This comparative example provides a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst and a preparation method thereof, comprising the following steps:

[0070] S1. Dissolve 6.78g Zn(NO3)·6H2O in 300ml methanol solution and 7.88g dimethylimidazole in 300ml methanol solution, and ultrasonicate them in an ultrasonic machine for 15min respectively until they are completely dissolved in the methanol solution. Then pour the dimethylimidazole methanol solution into the zinc nitrate methanol solution and continue ultrasonicating for 15min. Place the mixed solution on a magnetic stirrer and stir at 1200rpm for 12h to produce a milky white suspension. Centrifuge and wash the suspension 3 times, with the centrifugal speed at 8000rpm, the centrifugal time for 3min, and the detergent being methanol. Dry it at 60℃ in a vacuum dryer for 360min to obtain ZIF-8.

[0071] 300 mg of ZIF-8 was placed in a magnetic boat and heated to 1000°C at a rate of 8°C. After annealing at 1000°C in an argon atmosphere for 30 min, the NC material with MOF morphology was obtained.

[0072] S2, impregnate 267μl of 0.2mol / L FeCl3·6H2O ethanol solution onto 100mg NC material, place in a mortar and grind manually until ethanol evaporates completely, collect as Fe-NC precursor. Place the Fe-NC precursor in a magnetic boat, anneal in a tube furnace at 1300℃ and argon atmosphere for 60min, and then cool naturally to room temperature to obtain Fe-NC single atom catalyst;

[0073] S3, 25μl 0.2mol / L chloroplatinic acid and 25μl 0.2mol / L o-phenanthroline were coordinated for 5min, the suspension was impregnated and loaded on 100mg Fe-NC, and manually ground in a mortar until the ethanol evaporated completely, and collected as Pt / Fe-NC precursor. Pt / Fe-NC was placed in a magnetic boat, annealed in a tube furnace at 1300℃ and argon atmosphere for 60min, and then naturally cooled to room temperature to obtain a Pt / Fe-NC bimetallic single atom catalyst.

[0074] Comparative Example 3

[0075] This comparative example provides a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst and a preparation method thereof, comprising the following steps:

[0076] S1. Dissolve 6.78g Zn(NO3)·6H2O in 300ml methanol solution and 7.88g dimethylimidazole in 300ml methanol solution, and ultrasonicate them in an ultrasonic machine for 15min respectively until they are completely dissolved in the methanol solution. Then pour the dimethylimidazole methanol solution into the zinc nitrate methanol solution and continue ultrasonicating for 15min. Place the mixed solution on a magnetic stirrer and stir at 1200rpm for 12h to produce a milky white suspension. Centrifuge and wash the suspension 3 times, with the centrifugal speed at 8000rpm, the centrifugal time for 3min, and the detergent being methanol. Dry it at 60℃ in a vacuum dryer for 360min to obtain ZIF-8.

[0077] 300 mg of ZIF-8 was placed in a magnetic boat and heated to 1000°C at a rate of 8°C. After annealing at 1000°C in an argon atmosphere for 30 min, the NC material with MOF morphology was obtained.

[0078] S2, 267μl of 0.2mol / L FeCl3·6H2O ethanol solution, 25μl of 0.2mol / L chloroplatinic acid and 25μl of 0.2mol / L dimethylimidazole were coordinated for 10min, the suspension was impregnated and loaded on 100mg NC material, placed in a mortar and manually ground until the ethanol evaporated completely, and collected as Pt / Fe-NC precursor. The Pt / Fe-NC precursor was placed on a 1.5cm*4cm carbon cloth, and the carbon cloth was clamped at both ends of a pulse power supply for CTS in an argon atmosphere, wherein the pulse current waveform was set to a square wave, the current was 35A, the voltage was 40V, the pulse frequency was 0.5Hz, and the CTS was performed at 1500℃ for 200ms to obtain a Pt / Fe-NC bimetallic single atom catalyst.

[0079] Performance Testing

[0080] The electrocatalytic performance of the Pt / Fe-NC bimetallic single atom catalysts prepared in the examples and comparative examples was tested, and the specific test steps are as follows:

[0081] 5 mg of the catalysts of Examples 1, 2, 3, 4 and Comparative Examples 1 and 2 were mixed with 500 ul isopropanol, 500 μL deionized water, and 20 μL Nafion, and then ultrasonicated for 20 min until the catalyst was evenly dispersed into Ink. 10 μL Ink was evenly dropped on the surface of the clean disk electrode head. After drying, it was placed on a rotating disk electrode device as a working electrode, Hg / HgO as a reference electrode, a Pt sheet as a counter electrode, and 0.1 M KOH as an electrolyte for electrochemical testing to evaluate the catalytic performance. Before the test, high-purity O2 was continuously introduced into the electrolyte for 30 min, and CV (cyclic voltammetry) activation was performed, and the scanning speed was controlled at 100 Mv s -1After CV activation, LSV (linear cyclic voltammetry) was performed, and the scanning speed was controlled at 5 Mv s -1 The scanning was performed with IR compensation of 90% and the rotation speed of the disk electrode of 1600 rpm. The test results are shown in Table 1.

[0082] Table 1 ORR activity of catalysts

[0083]

[0084] Figure 1 Figure 2 shows the surface morphology of ZIF-8 and NC materials obtained after pyrolysis. It can be seen from the figure that nitrogen-doped carbon retains its original morphology, which is attributed to the relatively mild pyrolysis conditions in the tube furnace.

[0085] Figure 2 X-ray diffraction patterns (XRD) of Pt / Fe-NC catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2 show that no crystalline phase of metal / metal oxide / alloy is formed in Example 1, while crystalline phase of metal / metal oxide / alloy appears in both Comparative Example 1 and Comparative Example 2, indicating that the Pt and Fe loaded in Example 1 exist in the form of single atoms on the carbon substrate.

[0086] Figure 3 This is the surface morphology of the Pt / Fe-NC bimetallic single atom catalyst synthesized in Example 1. The catalyst retains the structure of MOF, which is attributed to the preparation by rapid heating and cooling at the millisecond level; at the same time, the carbon support is partially graphitized, so CTS not only retains a high specific surface area, but also increases conductivity.

[0087] Figure 4 The spherical aberration corrected scanning transmission electron microscopy (ac-STEM-HAADF) image of the Pt / Fe-NC bimetallic single atom catalyst synthesized in Example 1 shows uniformly dispersed atomic-level bright spots, supporting the conclusion that Fe and Pt exist in single atomic form.

[0088] Figure 5 The scanning rate of Example 1, Comparative Example 1 and Comparative Example 2 in an O2-saturated 0.1 M KOH solution was 5 Mv s -1 and the LSV curve of the disk electrode rotation speed of 1600rpm under the conditions of 90% IR compensation. It can be seen from the figure that compared with comparative examples 1-2, the Pt / Fe-NC bimetallic single atom catalyst prepared in Example 1 has the best ORR activity, and the half-wave potential is 0.936 vs. RHE.

[0089] Figure 6 The cyclic charge-discharge stability diagram of the zinc-air battery of Example 1 and commercial Pt / C. -2Under the load of 5mA / cm -2 The long-term charge and discharge performance of ZAB of Example 1 and commercial Pt / C was evaluated at a current density of 30 minutes per cycle (discharge for 15 minutes and charge for 15 minutes). As can be seen from the figure, Example 1 can stably operate for 1120 cycles within 560 hours; however, the commercial Pt / C completely failed after 75 hours of operation.

[0090] It can be seen from Table 1 that the Pt / Fe-NC bimetallic single atom catalyst prepared in the present invention has good ORR activity.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst, characterized in that: The following steps are involved: S1. Preparation of NC materials; S2, impregnating the iron salt solution onto the NC material obtained in step S1, and performing CTS after drying to obtain Fe-NC single atom material; S3, after coordinating the platinum salt with the nitrogen source, adding it to the Fe-NC single atom material obtained in step S2, drying it, and performing CTS to obtain a Pt / Fe-NC bimetallic single atom catalyst.

2. The method for preparing a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst according to claim 1, characterized in that: Step S1 specifically includes: mixing a zinc salt solution with an organic ligand solution, preparing ZIF-8 by magnetic stirring, using ZIF-8 as a template, and obtaining a NC material with a MOF morphology after thermal decomposition.

3. The method for preparing a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst as claimed in claim 2, characterized in that: The zinc salt is any one of zinc nitrate, zinc chloride, zinc acetate, and zinc acetylacetonate, the organic ligand is an imidazole compound, the concentration of the zinc salt solution is 0.1-0.4 mol / L, the concentration of the organic ligand solution is 0.4-1.6 mol / L, the molar ratio of the zinc salt to the organic ligand is 1:3-5, and the magnetic stirring reaction time is 6-48h.

4. The method for preparing a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst as claimed in claim 2, characterized in that: The pyrolysis reaction specifically includes: heating the ZIF-8 to 900-1100° C. at a rate of 5-10° C. / min, and keeping the temperature for 30-60 minutes.

5. The method for preparing a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst as claimed in claim 1, characterized in that: In step S2, the concentration of iron in the iron salt solution is 0.1-0.3 mol / L, and the impregnation loading is 0.01-5 wt.%.

6. The method for preparing a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst according to claim 1, characterized in that: In step S2, the heating power supply of CTS is a pulse power supply, the current is 10-60A, the voltage is 20-60V, the pulse frequency is 0.1-1Hz, the heating temperature is 1300-1800°C, and the heating time is 100-300ms.

7. The method for preparing a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst according to claim 1, characterized in that: The platinum salt is any one of chloroplatinic acid, platinum nitrate, and platinum acetate, the nitrogen source is at least one of dimethylimidazole, o-phenanthroline, pyridine, and 2,2'-bipyridine, the molar ratio of the platinum salt to the nitrogen source is 0.02-1:0.02-10, and the mass proportion of Pt in the Pt / Fe-NC precursor is 0.1-5wt%.

8. The method for preparing a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst according to claim 1, characterized in that: In step S3, the heating power supply of CTS is a pulse power supply, the current is 10-60A, the voltage is 20-60V, the pulse frequency is 0.1-1Hz, the heating temperature is 1000-1500°C, and the heating time is 100-200ms.

9. A ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. Use of a ZIF-8 derived Pt / Fe-NC bimetallic single atom catalyst as claimed in claim 9 in an oxygen reduction catalyst.

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