Ultra-stable difunctional monatomic electrocatalyst and preparation method thereof

Abstract

The invention discloses a preparation method of an ultra-stable difunctional monatomic electrocatalyst, which comprises the following steps: dissolving 2-methylimidazole in an organic solvent, simultaneously dissolving Co (NO3) 2.6 H2O, CoSO4. 7H2O and Zn (NO3) 2.6 H2O in the same volume of solvent, mixing and stirring the two solutions, centrifugally recovering the synthesized purple precipitate, drying and grinding into powder; the powder is subjected to heat preservation in a tubular furnace in an inert atmosphere at 900-1100 DEG C for 1-3 h to obtain black powder, a certain amount of iron metal salt is added into the black powder, then grinding is carried out for 0.5-1 h, sieving is carried out, heat preservation is carried out in the inert atmosphere at 100-300 DEG C for 2-4 h, heat preservation is carried out at 800-1000 DEG C for 2-4 h, and cooling is carried out to obtain the catalyst. By integrating the advantages of directly modified ligands (single atoms) and indirectly modified ligands (small nano-particles), the electronic state and the substrate structure of SACs are synergistically adjusted, so that the yield of a byproduct H2O2 is remarkably reduced, the graphitization degree of a carbon substrate is enhanced, and meanwhile, the ORR and OER bifunctional activity and the cycling stability of the catalyst are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic materials, and specifically relates to an ultra-stable bifunctional single-atom electrocatalyst. The present invention also relates to a method for preparing the electrocatalyst. Background Art

[0002] Currently, noble metal catalysts (such as Pt / C or RuO2) show excellent activity in catalyzing ORR or OER, but their limited availability and high cost still hinder their widespread application. In recent years, single-atom catalysts (SACs) have attracted attention due to their unique electronic structure and maximum atomic utilization, especially MNC catalysts formed by transition metals (Fe, Co, Mn, Cu, etc.) coordinated with nitrogen in carbon matrix, which are considered to be the most promising non-noble metal alternatives to noble metal catalysts. However, despite the extensive exploration of the structure-activity relationship of SACs, the corresponding structure-stability relationship is still lacking in-depth understanding, and the lack of activity and durability will limit the practical application of catalysts. The kinetic loss of SACs is mainly attributed to the dissolution (demetallization) of active metal sites and the corrosion of carbon phase, which are caused by the oxidative attack of byproducts H2O2 and hydroxyl radicals (·OH) during the working process of the catalyst. Therefore, reducing the H2O2 production and improving the antioxidant capacity of the carbon substrate are two feasible strategies to enhance the stability.

[0003] Academician Sun Shigang's research group proposed in [Energy&Environmental Science, 14 (2021) 5958-5967] to use the gas phase thermal diffusion method to sublimate cobalt acetylacetonate onto Co-NC to obtain a catalyst with composite active sites containing Co nanoclusters and CoN4 single atom sites, which can effectively promote the dissociative adsorption of O2, enhance the adsorption of oxygen free radicals, inhibit the formation of H2O2, and improve the durability of the catalyst. Fan Hongjin et al. from Nanyang Technological University proposed in [ACS nano, 17 (2023)8622-8633] to synthesize a bimetallic single atom catalyst with Fe4 / Ni4 nanoclusters. There is a strong interaction between the in-situ generated Fe (Ni) atomic clusters and the carbon support, inducing a high graphitization level of the carbon support, which is conducive to electron transfer and enhanced corrosion resistance. The aqueous zinc-air batteries (ZABs) prepared with it have a high charge / discharge rate of 40 mA cm -2The long-term cycling stability of more than 110 h at a high current density of 1.5 Å is shown in Figure 2. In recent years, although many works have been devoted to improving the performance of MNC catalysts, few works have taken into account both activity and durability. For example, improving the high graphitization degree of SACs improves the antioxidant capacity of the carbon substrate, but it may also lead to defects and lack of nitrogen doping sites, thereby reducing some active sites and causing its ORR or OER activity to decrease. Therefore, it is very difficult to obtain a dual-improvement strategy for SACs. Summary of the invention

[0004] The purpose of the present invention is to provide an ultra-stable bifunctional single-atom electrocatalyst, which integrates the advantages of short-range (direct ligand single atom) and long-range (metal alloy nanoparticles) to synergistically regulate the electronic state and substrate structure of SACs, provide an overall defect-rich, locally highly graphitized carbon substrate, and solve the problem of easily damaging the activity when increasing the high graphitization degree of the SACs carbon substrate.

[0005] Another object of the present invention is to provide a method for preparing the electrocatalyst and to provide a design of an efficient and stable bifunctional catalyst.

[0006] The technical solution adopted by the present invention is: an ultra-stable bifunctional single-atom electrocatalyst, the chemical formula of the ultra-stable bifunctional single-atom electrocatalyst is FeCo / Co-NC, the structure of the FeCo alloy in the catalyst is 10-50 nanometer nanoparticles coated with a 2-5 nm thick carbon layer, in addition, Fe single atoms and Co single atoms are uniformly distributed on the carbon substrate, the mass fraction of Fe in FeCo / Co-NC is 0.5%-2%, and the mass fraction of Co is 2%-5%.

[0007] Another technical solution adopted by the present invention is: a method for preparing an ultra-stable bifunctional single-atom electrocatalyst, which is specifically carried out according to the following steps: Step 1, dissolving 2-methylimidazole in an organic solvent, and dissolving a certain proportion of Co(NO3)2·6H2O, CoSO4·7H2O and Zn(NO3)2·6H2O in the same volume of organic solvent, combining the above two solutions and stirring for 8 h to 16 h, centrifuging at 10000 r / min to 12000 r / min for 5 min to 8 min, repeating the centrifugation process 3 to 5 times, removing the supernatant, recovering the purple precipitate, then drying, taking out and grinding into powder; Step 2: Place the powder obtained in step 1 on a magnetic boat and put it into a tube furnace, fill the tube furnace with an inert atmosphere, raise the temperature of the tube furnace to 900°C to 1100°C, keep it warm for 1h to 3h, and then cool it to room temperature to obtain a powder to be treated, named Co-NC; Step 3: Add iron metal salt to the Co-NC obtained in step 2, grind for 0.5-1 h, and then sieve to obtain a solid powder. Place the solid powder on a magnetic boat and put it into a tubular furnace. Fill the tubular furnace with an inert atmosphere and keep it at 100-300 ° C for 2-4 h. Then heat the tubular furnace to 800-1000 ° C and keep it for 2-4 h. After the insulation is completed, cool it to room temperature to finally obtain FeCo / Co-NC.

[0008] Another technical solution adopted by the present invention is characterized in that: In step 1, the organic solvent is any one of ethanol, methanol, anhydrous ethanol or anhydrous methanol.

[0009] Co in Co(NO3)2·6H2O and CoSO4·7H2O in step 1 2+ Total amount and Zn(NO3)2·6H2O 2+ The molar ratio of the total amount is 1:4.

[0010] In step 1, the ratio of Co(NO3)2·6H2O to CoSO4·7H2O is any one of 2:1, 1:1, 1:2, 1:3 or 1:4.

[0011] In step 2 and step 3, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0012] The iron metal salt in step 3 is FeCl3, Fe2(NO3)3, Fe(SCN)3, FeCl2, C 15 H 21 FeO6 or C 10 H 10 Any one of Fe.

[0013] In step 3, the mass ratio of Co-NC to the iron metal salt is any one of 5:1, 10:1, 20:1, 30:1, or 40:1.

[0014] Beneficial effects of the present invention: Compared with the existing single-atom MNC electrocatalyst, the present invention has the following advantages: (1) FeCo alloy nanoparticles coated with nanocarbon layers induce a high degree of graphitization in the local SACs. This local high degree of graphitization significantly improves the resistance to oxidative attack by H2O2 and ·OH, thereby reducing the corrosion of the carbon substrate. The H2O2 corrosion test verified that the catalyst's ability to resist oxidative attack by H2O2 was significantly improved. More importantly, the construction of multiple sites reduced the catalyst's H2O2 yield from nearly 40% to less than 10%, which greatly reduced the metal active sites and carbon substrate from being attacked by highly reactive oxygen species (ROS) from the intermediate H2O2, further improving the catalytic stability.

[0015] (2) The FeCo alloy nanoparticles coated with nanocarbon layers synergistically regulate the electronic structure of the active sites, promote efficient electron transfer, enhance catalytic activity, and achieve a dual improvement in catalyst activity and stability. j=10 −E 1 / 2 ) is crucial for evaluating the bifunctional electrocatalytic activity. The ΔE value of the present invention is only 0.627 V, which is lower than that of the commercial 20% Pt / C+RuO2 catalyst (0.774 V), indicating that the FeCo / Co-NC catalyst has excellent bifunctional catalytic performance, even surpassing most of the reported bifunctional catalysts.

[0016] (3) The present invention demonstrates optimal ion adsorption and complete desorption in the electrolyte of zinc-air batteries (ZABs) through dissipative quartz crystal microbalance (QCM) testing. Therefore, the present invention exhibits excellent cycling stability in assembled liquid ZABs and flexible ZABs, showing its great potential in energy devices.

[0017] (4) The preparation process of the present invention is simple and easy to operate, and the proportions of various drugs can be expanded simultaneously, so that large-scale production is possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is an X-ray diffraction (XRD) pattern of the ultrastable bifunctional single-atom electrocatalyst of Example 5 of the present invention; Figure 2 This is a high-resolution transmission image of Example 5 of the ultrastable bifunctional single-atom electrocatalyst of the present invention; Figure 3 This is a high-angle annular dark field image-scanning transmission electron microscopy (HAADFSTEM) image of Example 5 of the ultrastable bifunctional single-atom electrocatalyst of the present invention; Figure 4 is a bifunctional catalytic performance diagram of Example 5 of the ultrastable bifunctional single-atom electrocatalyst of the present invention; Figure 5 is a graph of the H2O2 generation rate of Example 5 of the ultrastable bifunctional single-atom electrocatalyst of the present invention; Figure 6 This is a comparison diagram of the electrocatalytic activity of Example 5 of the ultrastable bifunctional single-atom electrocatalyst of the present invention; Figure 7 This is a liquid ZABs cycle performance diagram of Example 5 of the ultra-stable bifunctional single-atom electrocatalyst of the present invention. DETAILED DESCRIPTION

[0019] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] Ultra-stable bifunctional single-atom electrocatalysts, the chemical formula of the ultra-stable bifunctional single-atom electrocatalyst is FeCo / Co-NC. The structure of FeCo / Co-NC is 10 nm~50 nm FeCo alloy nanoparticles coated by a 2~5 nm thick carbon layer. The Fe single atoms and Co single atoms in FeCo / Co-NC are evenly distributed on the carbon substrate. The mass fraction of Fe in FeCo / Co-NC is 0.5%~2%, and the mass fraction of Co is 2%~5%. The ultra-stable bifunctional single-atom electrocatalyst is synthesized by step-by-step pyrolysis to synthesize diatomic and metal alloy nanoparticles rooted in the MNC matrix. The introduction of diatomic changes the electronic structure of active sites and introduces more defective active sites on the carbon substrate. At the same time, the metal alloy nanoparticles are used to catalyze the carbon layer surrounding the particles during the high-temperature synthesis process to induce a high degree of graphitization of the SACs locally, improve the resistance to H2O2 and ·OH oxidation attacks, and thus reduce the corrosion of the carbon substrate. Ultimately, the activity and stability are improved.

[0021] The preparation method of the ultra-stable bifunctional single-atom electrocatalyst is specifically carried out according to the following steps: Step 1, dissolving 2-methylimidazole in 50-200 ml of an organic solvent, and dissolving Co(NO3)2·6H2O, CoSO4·7H2O and Zn(NO3)2·6H2O in the same volume of an organic solvent, mixing the two solutions for 8 h to 16 h, centrifuging at 10000 r / min to 12000 r / min for 5 min to 8 min, repeating the centrifugation step 3 to 5 times to obtain a mixed solution, removing the supernatant at the top of the mixed solution, recovering the purple precipitate at the bottom of the mixed solution, washing the purple precipitate with anhydrous ethanol four times, and then drying the purple precipitate and grinding it into powder; Step 2: Place the powder on a magnetic boat and put it into a tube furnace, fill the tube furnace with an inert atmosphere, raise the temperature of the tube furnace to 900°C to 1100°C, keep it warm for 1h to 3h, and then cool it to room temperature to obtain a treated powder, named Co-NC; Step 3: Add iron metal salt to the Co-NC obtained in step 2, grind for 0.5h~1h and then sieve to obtain solid powder, place the solid powder on a magnetic boat and put it into a tubular furnace, fill the tubular furnace with an inert atmosphere, keep it at 100℃~300℃ for 2h~4h, then heat the tubular furnace to 800℃~1000℃, keep it at this temperature for 2h~4h, wait for the insulation to end, cool to room temperature, and finally obtain FeCo / Co-NC.

[0022] Example 1 The method for preparing an ultra-stable bifunctional single-atom electrocatalyst is specifically carried out in the following steps: Dissolve 2.23 g of 2-methylimidazole in 50 ml of anhydrous methanol, and dissolve 82.3 mg of Co(NO3)2·6H2O, 78.7 mg of CoSO4·7H2O, and 1.67 g of Zn(NO3)2·6H2O in 50 ml of anhydrous methanol. The two solutions were quickly combined and stirred at room temperature for 12 h. The synthesized purple precipitate was recovered by centrifugation, washed with anhydrous methanol four times, and then vacuum dried at 70 °C for 12 h. After the obtained powder was fully ground, it was precipitated at 5 °C min in an Ar atmosphere. -1 The temperature was raised to 1000℃ at a heating rate of 200℃ and kept at this temperature for 2 hours to obtain a treated powder named Co-NC. 10 mg of iron acetylacetonate was added to 0.1 g of Co-NC, and then ground for 1 hour and sieved. The obtained solid powder was heated at 2℃ min under argon atmosphere. −1 The heating rate was kept at 180 °C for 3 h and then increased at 5 °C min -1 The temperature was raised to a target temperature of 950°C at a heating rate and kept at that temperature for 3 h. The FeCo / Co-NC obtained after cooling was the catalyst of the present invention.

[0023] Example 2 The method for preparing an ultra-stable bifunctional single-atom electrocatalyst is specifically carried out in the following steps: 4.46 g of 2-methylimidazole was dissolved in 100 ml of anhydrous methanol, and 81.4 mg of Co(NO3)2·6H2O, 236.1 mg of CoSO4·7H2O, and 3.34 g of Zn(NO3)2·6H2O were dissolved in 100 ml of anhydrous methanol. The two solutions were quickly combined and stirred at room temperature for 15 h. The synthesized purple precipitate was recovered by centrifugation, washed with anhydrous methanol four times, and then vacuum dried at 80 °C for 12 h. The obtained powder was fully ground and then precipitated at 5 °C min in an Ar atmosphere. -1 The temperature was raised to 950℃ at a heating rate of 200℃ and kept at this temperature for 2 h to obtain a treated powder named Co-NC. 10 mg of iron acetylacetonate was added to 0.1 g of Co-NC, and then ground for 1 h and sieved. The obtained solid powder was heated at 2℃ min under argon atmosphere. -1 The heating rate was kept at 200 °C for 3 h and then increased at 5 °C min -1 The temperature was raised to a target temperature of 950°C at a heating rate and kept at that temperature for 3 h. The FeCo / Co-NC obtained after cooling was the catalyst of the present invention.

[0024] Example 3 The method for preparing an ultra-stable bifunctional single-atom electrocatalyst is specifically carried out in the following steps: 8.92 g of 2-methylimidazole was dissolved in 200 ml of anhydrous ethanol, and 162.8 mg of Co(NO3)2·6H2O, 472.2 mg of CoSO4·7H2O, and 6.68 g of Zn(NO3)2·6H2O were dissolved in 200 ml of anhydrous ethanol. The two solutions were quickly combined and stirred at room temperature for 16 h. The synthesized purple precipitate was recovered by centrifugation, washed with anhydrous ethanol four times, and then vacuum dried at 80 °C for 12 h. The obtained powder was fully ground and then precipitated at 5 °C min in a nitrogen atmosphere. -1 The temperature was raised to 1000 °C at a heating rate of 1.50 °C and kept at this temperature for 2 h to obtain a powder to be treated, named Co-NC. 10 mg of iron acetylacetonate was added to 0.2 g of Co-NC, and then ground for 1 h and sieved. The obtained solid powder was heated at 2 °C min under Ar atmosphere. -1 The heating rate was kept at 200 °C for 3 h and then increased at 5 °C min -1 The temperature was raised to a target temperature of 900°C at a heating rate and kept at that temperature for 3 h. The FeCo / Co-NC obtained after cooling was the catalyst of this example.

[0025] Example 4 The method for preparing an ultra-stable bifunctional single-atom electrocatalyst is specifically carried out in the following steps: 8.92 g of 2-methylimidazole was dissolved in 200 ml of anhydrous ethanol, and 329.2 mg of Co(NO3)2·6H2O, 314.8 mg of CoSO4·7H2O, and 6.68 g of Zn(NO3)2·6H2O were dissolved in 200 ml of anhydrous ethanol. The two solutions were quickly combined and stirred at room temperature for 16 h. The synthesized purple precipitate was recovered by centrifugation, washed with anhydrous ethanol four times, and then vacuum dried at 70 °C for 12 h. The obtained powder was fully ground and then precipitated at 5 °C min in a nitrogen atmosphere. -1 The temperature was raised to 1000℃ at a heating rate of 200℃ and kept at this temperature for 2 h to obtain a treated powder named Co-NC. 10 mg of FeCl2 was added to 0.3 g of Co-NC, and then ground for 1 h and sieved. The obtained solid powder was heated at 2℃ min-1 under a nitrogen atmosphere. -1 The heating rate was 180 °C for 3 h and then 5 °C min -1 The temperature was raised to a target temperature of 950° C. at a heating rate and kept at that temperature for 3 h. The FeCo / Co-NC obtained after cooling was the catalyst of this example.

[0026] Example 5 The method for preparing an ultra-stable bifunctional single-atom electrocatalyst is specifically carried out in the following steps: 4.46 g of 2-methylimidazole was dissolved in 100 ml of anhydrous ethanol, and 219.6 mg of Co(NO3)2·6H2O, 104.9 mg of CoSO4·7H2O, and 3.34 g of Zn(NO3)2·6H2O were dissolved in 100 ml of anhydrous ethanol. The two solutions were quickly combined and stirred at room temperature for 16 h. The synthesized purple precipitate was recovered by centrifugation, washed with anhydrous ethanol five times, and then vacuum dried at 80 °C for 12 h. The obtained powder was fully ground and then precipitated at 5 °C min in a nitrogen atmosphere. -1 The temperature was raised to 950℃ at a heating rate of 1.50℃ and kept at this temperature for 3 h to obtain a powder to be treated, named Co-NC. 40 mg of Fe2(NO3)3 was added to 0.2 g of Co-NC, and then ground for 0.5 h and sieved. The obtained solid powder was heated at 2℃ min-1 in a nitrogen atmosphere. -1 The heating rate was kept at 200 °C for 3 h and then increased at 5 °C min -1 The temperature was raised to a target temperature of 900°C at a heating rate and kept at that temperature for 3 h. The FeCo / Co-NC obtained after cooling was the catalyst of this example.

[0027] The catalysts of the present invention were all tested by linear sweep voltammetry (LSV) on a rotating disk electrode (RDE) to evaluate their electrocatalytic activity for ORR. Based on the excellent ORR / OER bifunctional performance in the half-cell, liquid ZABs were assembled using the catalysts of the present invention as air cathodes. Among them, zinc plates were used as anodes and electrolytes of 6 M KOH electrolytes containing 0.2 M Zn(OAc)2 were used to test the cyclic stability of the catalysts of the present invention in liquid ZABs.

[0028] like Figure 1 As shown, it is the XRD pattern of the single-atom catalyst FeCo / Co-NC prepared in this example. Figure 1 It can be seen that there is an obvious diffraction peak at about 44.8°, which corresponds to the (110) plane of the FeCo alloy (JCPDS 44-1433), proving that there are iron-cobalt nanoparticles in this example.

[0029] like Figure 2 As shown, it is a high-resolution transmission image of the single-atom catalyst FeCo / Co-NC prepared in this example. It is found that metal nanoparticles with a diameter of about 10~50 nm appear on the carbon substrate, and the FeCo alloy nanoparticles are encapsulated by a carbon shell with a thickness of about 1nm~5nm.

[0030] like Figure 3As shown, this is a high-angle annular dark field image-scanning transmission electron microscopy (HAADFSTEM) image of the single-atom catalyst FeCo / Co-NC prepared in this example, in which single-atom particles with a particle radius of 1Å~2Å can be clearly seen.

[0031] like Figure 4 , which is a bifunctional catalytic performance diagram of the ultrastable bifunctional single-atom electrocatalyst prepared in this embodiment. The ΔE value of this embodiment is only 0.627 V, which has excellent bifunctional catalytic performance.

[0032] like Figure 5 As shown, the ultra-stable bifunctional single-atom electrocatalyst prepared in this example was measured by a rotating ring disk electrode (RRDE) at a speed of 1600 rpm to test the H2O2 generation rate diagram (H2O2%) during the ORR process. The corresponding H2O2 yield in this example dropped from nearly 40% to less than 10%. This greatly reduces the metal active sites and carbon substrates from being attacked by highly reactive oxygen species (ROS) from the intermediate H2O2, thereby improving the catalytic stability.

[0033] like Figure 6 As shown in FIG. 1 , the electrocatalytic activity comparison diagram of the ultrastable bifunctional single-atom electrocatalyst prepared in this embodiment before and after H2O2 etching at 900 rpm is measured. 1 / 2 It only decreased by 35 mV, which means that the carbon substrate of this example was not damaged by H2O2 etching, revealing the significant improvement of the catalyst stability due to the unique structure with multiple sites.

[0034] like Figure 7 The figure shows the cycle performance of liquid ZABs assembled with the ultrastable bifunctional single-atom electrocatalyst prepared in this example as an air cathode (compared with Pt / C+IrO2). -2 The results show that the long-term stability of the ZABs is more than 1100 h, which is much longer than that of the commercially available Pt / C+IrO2. This embodiment shows excellent cycling stability in the assembled liquid ZABs, demonstrating its great potential in energy devices.

[0035] The present invention simultaneously improves the activity and stability by constructing multi-site SACs with Fe / Co single atoms and FeCo alloy nanoparticles. This unique multi-site FeCo / Co-NC catalyst can adjust the electronic structure of Fe and Co sites to regulate the ORR path, thereby significantly reducing the byproduct H2O2 rate and significantly improving the activity. In addition, it also shows good OER activity, thus having excellent bifunctional performance with a ΔE value of 0.627 V. More importantly, the small FeCo alloy nanoparticles induce localized high graphitization, which enhances the antioxidant capacity of the carbon substrate. As expected, the FeCo / Co-NC-based liquid ZABs exhibited a high oxidation resistance at 10 mA cm -2 The results show that the catalysts exhibit remarkable stability for 1100 h under low temperature. This work provides insights into the development of durable, highly active non-precious metal catalysts in the field of ZABs, and the method is simple and can be mass-produced, making it more suitable for commercial applications.

[0036] Example 6 The ultra-stable bifunctional single-atom electrocatalyst of this embodiment has a chemical formula of FeCo / Co-NC. The structure of FeCo / Co-NC is a 10 nm FeCo alloy nanoparticle coated with a 2 nm thick carbon layer. The Fe single atom and the Co single atom in FeCo / Co-NC are evenly distributed on the carbon substrate. The mass fraction of Fe in FeCo / Co-NC is 0.5%, and the mass fraction of Co is 2%. The ultra-stable bifunctional single-atom electrocatalyst is synthesized by step-by-step pyrolysis to synthesize diatomic and metal alloy nanoparticles rooted in the MNC matrix. The introduction of diatomic changes the electronic structure of the active site and introduces more defective active sites on the carbon substrate. At the same time, the metal alloy nanoparticles are used to catalyze the carbon layer surrounding the particles during the high-temperature synthesis process to induce a high degree of graphitization of the SACs locally, thereby improving the resistance to oxidation attacks by H2O2 and OH, thereby reducing the corrosion of the carbon substrate. Finally, the dual improvement of activity and stability is achieved.

[0037] Example 7 The ultra-stable bifunctional single-atom electrocatalyst of this embodiment has a chemical formula of FeCo / Co-NC. The structure of FeCo / Co-NC is a 50 nm FeCo alloy nanoparticle coated with a 5 nm thick carbon layer. The Fe single atom and the Co single atom in FeCo / Co-NC are evenly distributed on the carbon substrate. The mass fraction of Fe in FeCo / Co-NC is 2%, and the mass fraction of Co is 5%. The ultra-stable bifunctional single-atom electrocatalyst is synthesized by step-by-step pyrolysis to synthesize diatomic and metal alloy nanoparticles rooted in the MNC matrix. The introduction of diatomic changes the electronic structure of the active site and introduces more defective active sites on the carbon substrate. At the same time, the metal alloy nanoparticles are used to catalyze the carbon layer surrounding the particles during the high-temperature synthesis process to induce a high degree of graphitization of the SACs locally, thereby improving the resistance to oxidation attacks by H2O2 and ·OH, thereby reducing the corrosion of the carbon substrate. Finally, the dual improvement of activity and stability is achieved.

[0038] Example 8 The ultra-stable bifunctional single-atom electrocatalyst of this embodiment has a chemical formula of FeCo / Co-NC. The structure of FeCo / Co-NC is a 30 nm FeCo alloy nanoparticle coated by a 4 nm thick carbon layer. The Fe single atom and the Co single atom in FeCo / Co-NC are evenly distributed on the carbon substrate. The mass fraction of Fe in FeCo / Co-NC is 1.2%, and the mass fraction of Co is 3%. The ultra-stable bifunctional single-atom electrocatalyst is synthesized by step-by-step pyrolysis to synthesize diatomic and metal alloy nanoparticles rooted in the MNC matrix. The introduction of diatomic changes the electronic structure of the active site and introduces more defective active sites on the carbon substrate. At the same time, the metal alloy nanoparticles are used to catalyze the carbon layer surrounding the particles during the high-temperature synthesis process to induce a high degree of graphitization of the SACs locally, thereby improving the resistance to oxidation attacks by H2O2 and ·OH, thereby reducing the corrosion of the carbon substrate. Finally, the dual improvement of activity and stability is achieved.

Claims

1. Ultrastable bifunctional single-atom electrocatalyst, characterized in that: The chemical formula of the ultra-stable bifunctional single-atom electrocatalyst is FeCo / Co-NC. The structure of the FeCo alloy in the catalyst is 10-50 nanometer nanoparticles coated with a 2-5 nm thick carbon layer. In addition, Fe single atoms and Co single atoms are uniformly distributed on the carbon substrate. The mass fraction of Fe in the FeCo / Co-NC is 0.5%-2%, and the mass fraction of Co is 2%-5%.

2. A method for preparing an ultrastable bifunctional single-atom electrocatalyst, characterized in that: Follow these steps: Step 1, dissolving 2-methylimidazole in 50-200 ml of an organic solvent, and dissolving Co(NO3)2·6H2O, CoSO4·7H2O and Zn(NO3)2·6H2O in the same volume of an organic solvent, mixing the two solutions for 8 h to 16 h, centrifuging at 10000 r / min to 12000 r / min for 5 min to 8 min, repeating the centrifugation step 3 to 5 times to obtain a mixed solution, removing the supernatant at the top of the mixed solution, recovering the purple precipitate at the bottom of the mixed solution, vacuum drying the purple precipitate, and grinding it into powder; Step 2: Place the powder in a magnetic boat and put it into a tube furnace, fill the tube furnace with an inert atmosphere, raise the temperature of the tube furnace to 900° C. to 1100° C., keep it warm for 1 h to 3 h, and then cool it to room temperature to obtain a powder to be treated, named Co-NC; Step 3: Add iron metal salt to the Co-NC obtained in step 2, grind for 0.5 to 1 h, and then sieve to obtain a solid powder. Place the solid powder in a magnetic boat and put it into a tubular furnace. Fill the tubular furnace with an inert atmosphere and keep it at 100° C. to 300° C. for 2 h to 4 h. Then, heat the tubular furnace to 800° C. to 1000° C. and keep it for 2 h to 4 h. After the insulation is completed, cool it to room temperature to finally obtain FeCo / Co-NC.

3. The method for preparing the ultrastable bifunctional single-atom electrocatalyst according to claim 2, characterized in that: The organic solvent in step 1 is any one of ethanol, methanol, anhydrous ethanol or anhydrous methanol.

4. The method for preparing the ultrastable bifunctional single-atom electrocatalyst according to claim 2, characterized in that: Co(NO3)2·6H2O, CoSO4·7H2O in step 1 2+ Total amount and Zn(NO3)2·6H2O 2+ The molar ratio of the total amount is 1:

4.

5. The method for preparing the ultrastable bifunctional single-atom electrocatalyst according to claim 2, characterized in that: The ratio of Co(NO3)2·6H2O and CoSO4·7H2O in step 1 is any one of 2:1, 1:1, 1:2, 1:3 or 1:

4.

6. The method for preparing the ultrastable bifunctional single-atom electrocatalyst according to claim 2, characterized in that: The inert atmosphere in step 2 and step 3 is a nitrogen atmosphere or an argon atmosphere.

7. The method for preparing the ultrastable bifunctional single-atom electrocatalyst according to claim 2, characterized in that: The iron metal salt in step 3 is FeCl3, Fe2(NO3)3, Fe(SCN)3, FeCl2, C 15 H 21 FeO6 or C 10 H 10 Any one of Fe.

8. The method for preparing the ultrastable bifunctional single-atom electrocatalyst according to claim 2, characterized in that: In the step 3, the mass ratio of Co-NC to the iron metal salt is any one of 5:1, 10:1, 20:1, 30:1, or 40:1.

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