Bimetallic phosphate / nitrogen-doped carbon hollow nanorods and their preparation method and use

Abstract

The present invention relates to the technical field of transition metal salt / carbon-based hollow nanorods, and in particular to a bimetallic phosphate / nitrogen-doped carbon hollow nanorod and its preparation method and use. In the present invention, a metal-organic framework material, namely MIL-88-Fe nanorods, is first prepared, and it is etched into a hollow structure by a phytic acid etching technique. Subsequently, a polydopamine shell is coated on its outer surface, and a ZIF-L-Co shell layer is introduced by epitaxial growth. After high-temperature pyrolysis, a bimetallic phosphate / nitrogen-doped carbon catalyst with a hollow nanorod structure is formed. The hollow structure of the catalyst increases the specific surface area and the electrochemically active area, and improves the rates of charge transfer and mass transfer. The present invention belongs to a bifunctional catalyst, which can drive the oxygen reduction reaction and the oxygen evolution reaction simultaneously, meeting the requirements of rechargeable zinc-air batteries. Therefore, this work provides a reasonable and effective method for the development of bifunctional electrocatalysts.

Description

Technical Field

[0001] The present invention relates to the technical field of bimetallic phosphate / nitrogen-doped carbon hollow nanorods, and particularly to a bimetallic phosphate / nitrogen-doped carbon hollow nanorod, a preparation method thereof, and uses thereof. Background Art

[0002] Due to the increasing environmental problems and the explosive growth of global energy demand, the development of sustainable energy materials and green nanotechnologies for constructing fuel cells, metal-air batteries, and water electrolysis systems has attracted extensive attention. Zinc-air batteries (ZABs) have the advantages of high energy density, safety and reliability, low cost, and environmental friendliness, and are considered important devices for realizing the sustainable conversion of electrical energy and chemical energy. During the charge and discharge processes of this battery, oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) occur on the electrodes respectively. Both of these processes involve four-electron transfer, and there is a problem of slow reaction kinetics, which limits the large-scale application of rechargeable zinc-air batteries.

[0003] Developing bifunctional catalysts to simultaneously improve the reaction rates of OER and ORR is the most effective way to solve the above problems. Generally, noble metal Pt is considered the best ORR catalyst, while Ru, Ir, and their corresponding oxides RuO2 and IrO2 are considered efficient OER catalysts. However, noble metals have low natural abundance, high price, poor durability, and the existing noble metals cannot simultaneously promote the OER and ORR reactions. Therefore, exploring catalysts with low cost and bifunctionality is crucial for promoting the development of reversible zinc-air batteries. Summary of the Invention

[0004] One of the purposes of the present invention is to provide a preparation method of a bimetallic phosphate / nitrogen-doped carbon hollow nanorod. The catalyst prepared by this method has a typical hollow nanorod structure, which makes the specific surface area higher, has more active sites, and can simultaneously improve the reaction rates of OER and ORR while being inexpensive.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: A preparation method of a bimetallic phosphate / nitrogen-doped carbon hollow nanorod, comprising the following steps:

[0006] S1. Dissolve fumaric acid in deionized water and stir well at 40 - 100 °C to form solution 1;

[0007] Dissolve a water-soluble iron salt in deionized water and stir evenly to form solution 2;

[0008] Mix solution 1 and solution 2 and stir. Transfer the mixture to a high-pressure reactor lined with polytetrafluoroethylene, keep it at 80 - 140 °C for 3 - 9 h, then centrifuge to collect the product, wash it with ethanol and dry it to obtain iron-based MIL-88-Fe solid nanorods;

[0009] S2. Disperse the iron-based MIL-88-Fe solid nanorods prepared in step S1 in deionized water, stir evenly to form solution 3, and prepare a phytic acid solution at the same time;

[0010] Mix solution 3 and the phytic acid solution, then place it in an oil bath at 60 - 120 °C for 2 - 5 h, centrifuge to collect the product, wash it with ethanol and dry it to obtain iron-based MIL-88-Fe hollow nanorods;

[0011] S3. Dissolve the iron-based MIL-88-Fe hollow nanorods prepared in step S2 in Tris buffer, and then add dopamine hydrochloride to form solution 4;

[0012] Stir solution 4 fully for reaction, then centrifuge to collect the product, wash it with ethanol and dry it to obtain iron-based hollow nanorods MIL-88-Fe wrapped with polydopamine PDA, denoted as MIL-88-Fe@PDA hollow nanorods;

[0013] S4. Disperse the MIL-88-Fe@PDA hollow nanorods and PVP prepared in step S3 in ethanol, stir fully to form solution 5;

[0014] Dissolve 2-methylimidazole in deionized water to form solution 6;

[0015] Dissolve cobalt nitrate hexahydrate in deionized water to form solution 7;

[0016] Then mix and stir solutions 5, 6, and 7 fully, then centrifuge to collect the precipitate, wash it with ethanol and dry it to obtain iron-based hollow nanorods wrapped with polydopamine and cobalt-based nanoparticles epitaxially grown on the surface of polydopamine, denoted as MIL-88-Fe@PDA@Co-ZIF-L hollow nanorods;

[0017] S5. Put the MIL-88-Fe@PDA@ZIF-L-Co hollow nanorods prepared in step S4 into a porcelain boat, and then place the porcelain boat in a tubular furnace. Under a nitrogen atmosphere, heat it to 200 - 400 °C and keep it for 0.5 - 2 h, then heat it to 600 - 800 °C and keep it for 1 - 6 h, and cool it to room temperature to obtain bimetallic phosphate / nitrogen-doped carbon hollow nanorods.

[0018] As a further improvement to the preparation method of bimetallic phosphate / nitrogen-doped carbon hollow nanorods:

[0019] Preferably, the water-soluble iron salt is one of iron(III) nitrate nonahydrate, iron(II) acetate tetrahydrate, and iron(III) chloride hexahydrate.

[0020] Preferably, the concentration of fumaric acid in Solution 1 is 0.603 - 6.03 mol / L, the concentration of the water-soluble iron salt in Solution 2 is 0.026 mol / L - 0.26 mol / L, the molar concentration ratio of fumaric acid in Solution 1 to the water-soluble iron salt in Solution 2 is 6.03:0.26, and Solutions 1 and 2 are mixed in a volume ratio of 4:1.

[0021] Preferably, in step S2, the concentrations of Solution 3 and the phytic acid solution are the same and are both 0.01 - 0.1 g / mL, and Solution 3 and the phytic acid solution are mixed in equal volumes.

[0022] Preferably, in Solution 4 of step S3, the concentration of the iron-based MIL-88-Fe hollow nanorods is 0.00125 - 0.0125 g / mL, and the concentration ratio of the iron-based MIL-88-Fe hollow nanorods to dopamine hydrochloride is 2:1.

[0023] Preferably, in Solution 5 of step S4, the dispersion concentrations of MIL-88-Fe@PDA and PVP are the same and are both 0.0008 - 0.008 g / mL; the concentration of 2-methylimidazole in Solution 6 is 0.00308 - 0.0328 g / mL; the concentration of cobalt(II) nitrate hexahydrate in Solution 7 is 0.00145 - 0.0145 g / mL.

[0024] Preferably, the concentration ratio of PVP in Solution 5, 2-methylimidazole in Solution 6, and cobalt(II) nitrate hexahydrate in Solution 7 is 8:30.8:14.5, and Solutions 5, 6, and 7 are mixed in a volume ratio of 8:8:5.

[0025] Preferably, in step S5, the heating rate of the tubular furnace is 1 - 10 °C / min.

[0026] The second object of the present invention is to provide a bimetallic phosphate / nitrogen-doped carbon hollow nanorod prepared by the preparation method of any one of the above.

[0027] The third object of the present invention is to provide an application of the above bimetallic phosphate / nitrogen-doped carbon hollow nanorod in a zinc-air battery.

[0028] The beneficial effects of the present invention compared with the prior art are as follows:

[0029] 1) The method for preparing the bimetallic phosphate / nitrogen-doped carbon hollow nanorods of the present invention is as follows: First, a solid core-shell structured MIL-88-Fe nanomaterial is prepared. Then, using the phytic acid etching technique, the solid MIL-88-Fe nanomaterial is etched into a hollow structure. Further, by utilizing the coating ability of polydopamine, a polydopamine shell is coated on the outer surface of the MIL-88-Fe hollow nanorods, thereby forming a MIL-88-Fe@PDA core-shell structure. Then, a layer of ZIF-L-Co is coated on its outer layer to form MIL-88-Fe@PDA@ZIF-L-Co. Finally, after high-temperature pyrolysis, its morphology does not change significantly, and the shape of the hollow carbon nanorods is well maintained.

[0030] 2) Hollow-structured materials have a high specific surface area, which can achieve rapid mass transfer and provide more active sites, thus accelerating surface / interface reactions. Their unique structure optimizes the effective specific surface area and charge and mass transfer during the electrocatalytic process, providing a highly promising platform for the preparation of novel electrocatalysts.

[0031] 3) Compared with the traditional solid rod-like structure, the bimetallic phosphate / nitrogen-doped carbon hollow nanorods prepared in the present invention have a higher specific surface area, so they can accommodate more active sites, and the thin shell layer will not hinder the mass transfer process during the electrocatalytic process; the main framework of the catalyst is nitrogen-doped carbon, which has good electrical conductivity, so it can accelerate the charge transfer process of the electrocatalytic reaction.

[0032] 4) Precious metals are expensive and have low natural reserves; in the bimetallic phosphate / nitrogen-doped carbon hollow nanorods prepared in the present invention, iron and cobalt are transition metals and are inexpensive; as a catalyst, the bimetallic phosphate / nitrogen-doped carbon hollow nanorods can not only catalyze the oxygen reduction reaction but also drive the oxygen evolution reaction, meeting the requirements of rechargeable zinc-air batteries.

[0033] 5) The bimetallic phosphate / nitrogen-doped carbon hollow nanorod catalyst prepared in the present invention has very good performance, better than that of the oxygen reduction catalyst (Pt / C) and the oxygen evolution catalyst (RuO2), showing potential application prospects to replace commercial precious metal catalysts, and the assembled zinc-air battery can be repeatedly charged and discharged for a long period. Description of the Drawings

[0034] Figure 1 is the flow chart for synthesizing the bimetallic phosphate / nitrogen-doped carbon hollow nanorod electrocatalyst of the present invention;

[0035] Figure 2 is the X-ray powder diffraction pattern of the bimetallic phosphate / nitrogen-doped carbon hollow nanorod electrocatalyst prepared in Example 1;

[0036] Figure 3Fe signal in the X-ray photoelectron spectrum of the bimetallic phosphate / nitrogen-doped carbon hollow nanorod electrocatalyst prepared in Example 1;

[0037] Figure 4 Co signal in the X-ray photoelectron spectrum of the bimetallic phosphate / nitrogen-doped carbon hollow nanorod electrocatalyst prepared in Example 1;

[0038] Figure 5 C signal in the X-ray photoelectron spectrum of the bimetallic phosphate / nitrogen-doped carbon hollow nanorod electrocatalyst prepared in Example 1;

[0039] Figure 6 N signal in the X-ray photoelectron spectrum of the bimetallic phosphate / nitrogen-doped carbon hollow nanorod electrocatalyst prepared in Example 1;

[0040] Figure 7 O signal in the X-ray photoelectron spectrum of the bimetallic phosphate / nitrogen-doped carbon hollow nanorod electrocatalyst prepared in Example 1;

[0041] Figure 8 P signal in the X-ray photoelectron spectrum of the bimetallic phosphate / nitrogen-doped carbon hollow nanorod electrocatalyst prepared in Example 1;

[0042] Figure 9 Raman spectrum of the bimetallic phosphate / nitrogen-doped carbon hollow nanorod electrocatalyst prepared in Example 1;

[0043] Figure 10 Transmission electron microscope image of the bimetallic phosphate / nitrogen-doped carbon hollow nanorod electrocatalyst prepared in Example 1;

[0044] Figure 11 High-resolution transmission electron microscope image of the bimetallic phosphate / nitrogen-doped carbon hollow nanorod electrocatalyst prepared in Example 1;

[0045] Figure 12 Oxygen evolution reaction curves of the bimetallic phosphate / nitrogen-doped carbon hollow nanorod electrocatalyst prepared in Example 1 and the noble metal RuO2; (Solid line - our synthesized catalyst; Dashed line - commercial RuO2 catalyst)

[0046] Figure 13 Oxygen reduction reaction curves of the bimetallic phosphate / nitrogen-doped carbon hollow nanorod electrocatalyst prepared in Example 1 and the noble metal Pt / C; (Solid line - our synthesized catalyst; Dashed line - commercial Pt / C catalyst)

[0047] Figure 14Charge-discharge polarization curves of the bimetallic phosphate / nitrogen-doped carbon hollow nanorods prepared in Example 1 as an electrocatalyst, and charge-discharge polarization curves of a RuO2 and Pt / C mixed catalyst; (solid line - the catalyst we synthesized; dashed line - the commercial RuO2 and Pt / C mixed catalyst).

[0048] Figure 15 Charge-discharge curves of the bimetallic phosphate / nitrogen-doped carbon hollow nanorods prepared in Example 1 as an electrocatalyst, and charge-discharge curves of a RuO2 and Pt / C mixed catalyst; (solid line - the catalyst we synthesized; dashed line - the commercial RuO2 and Pt / C mixed catalyst). Detailed implementation manners

[0049] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0050] Example 1

[0051] This example provides a preparation method for bimetallic phosphate / nitrogen-doped carbon hollow nanorods, including the following steps:

[0052] S1. Preparation of MIL-88-Fe solid nanorods

[0053] Dissolve fumaric acid in deionized water at a dissolution concentration of 6.03 mol / L, and stir in an oil bath at 70 °C for 10 min to form Solution 1;

[0054] Dissolve ferric nitrate nonahydrate in deionized water at a dissolution concentration of 0.26 mol / L, and stir evenly to form Solution 2;

[0055] Mix Solution 1 and Solution 2 according to a volume ratio of 4:1, stir for 10 min, then transfer to a high-pressure reaction kettle with a polytetrafluoroethylene liner, keep warm at 110 °C for 6 h, then centrifuge to collect the product, wash with ethanol and dry to obtain MIL-88-Fe solid nanorods;

[0056] S2. Preparation of MIL-88-Fe hollow nanorods

[0057] Disperse the MIL-88-Fe solid nanorods prepared in step S1 in deionized water at a dispersion concentration of 0.01 g / mL, stir evenly to form Solution 3; prepare a 0.1 mol / L phytic acid solution, mix it with Solution 3 according to a volume ratio of 1:1, then place it in an oil bath at 90 °C for 3 h, centrifuge to collect the product, wash with ethanol and dry to obtain MIL-88-Fe hollow nanorods;

[0058] S3. Synthesis of polydopamine-coated MIL-88-Fe hollow nanorods, MIL-88-Fe@PDA

[0059] The MIL-88-Fe hollow nanorods prepared in step S2 were dissolved in Tris buffer at a concentration of 0.00125 g / mL, and dopamine hydrochloride was added at a concentration of 0.000625 g / mL to form solution 4; solution 4 was stirred for 24 h, the product was collected by centrifugation, and the product was washed with ethanol and dried to obtain MIL-88-Fe@PDA hollow nanorods;

[0060] S4. Synthesis of MIL-88-Fe@PDA@ZIF-L-Co hollow nanorods

[0061] The MIL-88-Fe@PDA hollow nanorods and polyvinyl pyrrolidone (PVP) prepared in step S3 were dispersed in ethanol, wherein the dispersion concentration of MIL-88-Fe@PDA was 0.0008 g / mL, and the dispersion concentration of polyvinyl pyrrolidone (PVP) was 0.0008 g / mL, and stirred for 2 h to form solution 5;

[0062] Dissolve 2-methylimidazole in deionized water at a concentration of 0.00308 g / mL to form solution 6;

[0063] Dissolving cobalt nitrate hexahydrate in deionized water at a concentration of 0.00145 g / mL to form solution 7;

[0064] Then, solutions 5, 6, and 7 were fully mixed at a volume ratio of 8:8:5, stirred for 3 h, and then the precipitate was collected by centrifugation, washed with ethanol, and dried to obtain MIL-88-Fe@PDA@ZIF-L-Co hollow nanorods;

[0065] S5. Synthesis of bimetallic phosphate / nitrogen-doped carbon hollow nanorods

[0066] The MIL-88-Fe@PDA@ZIF-L-Co hollow nanorods prepared in step S4 were placed in a porcelain boat, and then the porcelain boat was placed in a tubular furnace. Under a nitrogen atmosphere, the temperature was increased to 300°C at a heating rate of 3°C / min and kept for 1 hour, then the temperature was increased to 700°C and kept for 2 hours, and then cooled to room temperature to obtain bimetallic phosphate / nitrogen-doped carbon hollow nanorods.

[0067] Figure 1The flow chart of the synthesized bimetallic phosphate / nitrogen-doped carbon hollow nanorods, and the preparation method includes the following processes: First, prepare MIL-88-Fe solid nanorods, then use phytic acid etching technology to etch the above solid nanorods into a hollow structure, and then coat a layer of polydopamine shell on the outer surface of the hollow structure to form a MIL-88-Fe@PDA core-shell structure. Then grow ZIF-L-Co on its surface, and then place it under high temperature for pyrolysis, and the morphology can be well maintained, that is, a catalyst with a hollow nanorod structure is formed; from the perspective of material evolution, fumaric acid and polydopamine in the MIL-88-Fe structure will be converted into a carbon matrix. Then we use phytic acid as the P source, and Fe in the MIL-88-Fe structure and Co in ZIF-L-Co will react with P to generate phosphates of Fe and Co, which are respectively located in the inner and outer layers of the hollow nanorods with polydopamine as the intermediate layer. Under the synergistic effect of the phosphates of Fe and Co, the mass transfer and charge transfer of the catalyst are accelerated, and its electrocatalytic performance is greatly enhanced.

[0068] Figure 2 The X-ray powder diffraction pattern of the synthesized bimetallic phosphate / nitrogen-doped carbon hollow nanorods and the corresponding standard cards. The standard card numbers are ICDD 00-034-1378 and ICDD 00-078-2285, which prove that the synthesized electrocatalyst contains phosphates of cobalt and iron.

[0069] Figure 3 The Fe signal in the X-ray photoelectron spectrum of the synthesized bimetallic phosphate / nitrogen-doped carbon hollow nanorods; located at 710.1 eV and 722.8 eV corresponding to Fe-N bonds, 711.6 eV and 724.7 eV corresponding to Fe-O bonds, 713.7 eV and 726.3 eV corresponding to trivalent Fe, and 716.8 eV and 729.6 eV corresponding to satellite peaks, which prove the presence of Fe components in the catalyst.

[0070] Figure 4 The Co signal in the X-ray photoelectron spectrum of the synthesized bimetallic phosphate / nitrogen-doped carbon hollow nanorods; located at 780.7 eV and 796.2 eV corresponding to Co-N bonds, 782.0 eV and 798.2 eV corresponding to divalent Co, and 785.6 eV and 802.7 eV corresponding to satellite peaks, which prove the presence of Co components in the catalyst.

[0071] Figure 5 The C signal in the X-ray photoelectron spectrum of the synthesized bimetallic phosphate / nitrogen-doped carbon hollow nanorods; the four peaks located at 284.3, 285.1, 285.8, and 288.8 eV correspond to C-C, C-P, C-N, and C=O components respectively, which prove the presence of C components in the catalyst.

[0072] Figure 6 The N signal in the X-ray photoelectron spectrum of the synthesized bimetallic phosphate / nitrogen-doped carbon hollow nanorods; the four peaks located at 398.1, 399.3, 400.4, and 401.2 eV correspond to pyridine-N, M-N structure, pyrrole-N, and graphitic-N respectively, demonstrating the presence of N component in the catalyst.

[0073] Figure 7 The O signal in the X-ray photoelectron spectrum of the synthesized bimetallic phosphate / nitrogen-doped carbon hollow nanorods; the O-P bond is located at 531.4 eV and the O-C bond is located at 533.1 eV, demonstrating the presence of O component in the catalyst.

[0074] Figure 8 The P signal in the X-ray photoelectron spectrum of the synthesized bimetallic phosphate / nitrogen-doped carbon hollow nanorods; the P-C bond is located at 133.8 eV and the P-O bond is located at 134.7 eV, demonstrating the presence of P component in the catalyst.

[0075] Figure 9 is the Raman spectrum of the bimetallic phosphate / nitrogen-doped carbon hollow nanorods; from Figure 9 it can be clearly seen that there are two obvious peaks at 1350 cm -1 and 1580 cm -1 respectively corresponding to the D band and G band of the carbon material. Among them, the ratio of the peak intensities of the D peak and G peak (I D / I G ) is an important parameter characterizing the graphitization degree of the carbon material, and the smaller the ratio, the higher the graphitization degree of the carbon material. According to the calculation, the I D / I G of the synthesized catalyst is about 0.95, which not only indicates that the catalyst contains carbon material but also has a high graphitization degree.

[0076] Figure 10 is the transmission electron microscope photograph of the bimetallic phosphate / nitrogen-doped carbon hollow nanorods. It can be seen from the figure that the morphology of the sample is a rod-like structure, and by careful observation, it can be found that the nanorods well maintain the hollow structure.

[0077] Figure 11 is the high-resolution transmission electron microscopy image of the bimetallic phosphate / nitrogen-doped carbon hollow nanorods. Figure 11 shows the lattice spacings of Co2P2O7 and Fe(PO3)2 at 0.351 nm and 0.186 nm respectively, corresponding to the (121) crystal plane of the Co2P2O7 component and the (133) crystal plane of the Fe(PO3)2 component.

[0078] Figure 12The oxygen evolution reaction curves of bimetallic phosphate / nitrogen-doped carbon hollow nanorods and the oxygen evolution reaction curves of noble metal RuO2. According to the calculation, it can be known that when using bimetallic phosphate / nitrogen-doped carbon hollow nanorods as the catalyst, the overpotential required when the current density reaches 10 mA / cm 2 is 291 mV, which is higher than the overpotential of 302 mV of noble metal RuO2, showing certain superiority. It indicates that the hollow structure increases the specific surface area, promotes charge transfer, optimizes the adsorption and desorption energy barriers of reaction intermediates, and ultimately improves the electrocatalytic activity.

[0079] Figure 13 The oxygen reduction reaction curves of bimetallic phosphate / nitrogen-doped carbon hollow nanorods and the oxygen reduction reaction curves of noble metal Pt / C. According to the calculation, it can be known that when using bimetallic phosphate / nitrogen-doped carbon hollow nanorods as the catalyst, the half-wave potential is 0.912 V and the limiting current is 6.32 mA / cm 2 ; it has better performance than noble metal Pt / C (0.835 V, 5.31 mA / cm 2 ).

[0080] Figure 14 The charge-discharge polarization curves of bimetallic phosphate / nitrogen-doped carbon hollow nanorods as an electrocatalyst. At a current density of 50 mA / cm 2 , the △E of bimetallic phosphate / nitrogen-doped carbon hollow nanorods is 1.0 V, and that of the RuO2 and Pt / C mixed catalyst is 1.360 V, showing certain superiority.

[0081] Figure 15 The charge-discharge curves of bimetallic phosphate / nitrogen-doped carbon hollow nanorods as an electrocatalyst. It can be seen from the figure that the charge-discharge duration of the battery exceeds 147 h, the △E is 0.14 V at 3 h; the △E is 0.35 V at 70 h; the △E is 0.64 V at 147 h, far superior to the RuO2 and Pt / C mixed catalyst.

[0082] Example 2

[0083] This example provides a preparation method of bimetallic phosphate / nitrogen-doped carbon hollow nanorods. The specific preparation steps refer to Example 1, and the only difference is that ferric acetate tetrahydrate is used in Solution 2 of Step S1, and finally bimetallic phosphate / nitrogen-doped carbon hollow nanorods are prepared.

[0084] Using the bimetallic phosphate / nitrogen-doped carbon hollow nanorods prepared in this example as the catalyst, it can be known through testing that the overpotential corresponding to the oxygen evolution reaction is 310 mV when the current density is 10 mA / cm 2 . For the oxygen reduction reaction, the half-wave potential is 0.893 V and the limiting current is 5.78 mA / cm2 When using this catalyst as the air electrode, the assembled rechargeable zinc-air battery has a ΔE of 0.85 V at a current density of 50 mA / cm 2 , and the charge-discharge duration of the battery can reach 135 hours. At 2 h, ΔE = 0.276 V, and at 79 h, ΔE = 0.353 V, both of which are superior to the noble metal Pt / C + RuO2.

[0085] Example 3

[0086] This example provides a method for preparing bimetallic phosphate / nitrogen-doped carbon hollow nanorods. The specific preparation steps refer to Example 1, except that ferric chloride hexahydrate is used in Solution 2 of Step S1, and bimetallic phosphate / nitrogen-doped carbon hollow nanorods are finally prepared.

[0087] Using the bimetallic phosphate / nitrogen-doped carbon hollow nanorods prepared in this example as the catalyst, it can be known through testing that the overpotential required when the current density reaches 10 mA / cm 2 is 312 mV; the half-wave potential is 0.889 V, and the limiting current is 5.64 mA / cm 2 ; the charge-discharge polarization curve of the bimetallic phosphate / nitrogen-doped carbon hollow nanorod catalyst as an electrocatalyst. At a current density of 50 mA / cm 2 , the ΔE of the bimetallic phosphate / nitrogen-doped carbon hollow nanorods is 1.34 V; the charge-discharge curve of the electrocatalyst. The charge-discharge duration of the battery exceeds 130 h. At 2 h, ΔE is 0.25 V; at 60 h, ΔE is 0.32 V; at 130 h, ΔE is 0.65 V.

[0088] Those skilled in the art should understand that the above are only several specific embodiments of the present invention, rather than all embodiments. It should be pointed out that many modifications and improvements can be made for those of ordinary skill in the art. All modifications or improvements that do not exceed the scope of the claims should be regarded as the protection scope of the present invention.

Claims

1. A preparation method of bimetallic phosphate / nitrogen-doped carbon hollow nanorods, characterized in that, It includes the following steps: S1. Dissolve fumaric acid in deionized water, and stir well at 40 - 100 °C to form Solution 1; Dissolve water-soluble iron salt in deionized water, and stir evenly to form Solution 2; Mix and stir Solution 1 and Solution 2, transfer them to a high-pressure reactor with a polytetrafluoroethylene liner, keep warm at 80 - 140 °C for 3 - 9 h, then centrifuge to collect the product, wash it with ethanol and dry it to obtain iron-based MIL-88-Fe solid nanorods; S2. Disperse the iron-based MIL-88-Fe solid nanorods prepared in Step S1 in deionized water, stir evenly to form Solution 3, and prepare phytic acid solution at the same time; Mix Solution 3 and phytic acid solution, then place them in an oil bath at 60 - 120 °C for 2 - 5 h, centrifuge to collect the product, wash it with ethanol and dry it to obtain iron-based MIL-88-Fe hollow nanorods; S3. Dissolve the iron-based MIL-88-Fe hollow nanorods prepared in Step S2 in Tris buffer solution, and then add dopamine hydrochloride to form Solution 4; Stir Solution 4 fully for reaction, then centrifuge to collect the product, wash it with ethanol and dry it to obtain iron-based hollow nanorods MIL-88-Fe wrapped with polydopamine PDA, denoted as MIL-88-Fe@PDA hollow nanorods; S4. Disperse the MIL-88-Fe@PDA hollow nanorods prepared in Step S3 and PVP in ethanol, and stir well to form Solution 5; Dissolve 2-methylimidazole in deionized water to form Solution 6; Dissolve cobalt nitrate hexahydrate in deionized water to form Solution 7; Then mix and stir Solution 5, Solution 6 and Solution 7 fully, then centrifuge to collect the precipitate, wash it with ethanol and dry it to obtain iron-based hollow nanorods wrapped with polydopamine and cobalt-based nanoparticles epitaxially grown on the surface of polydopamine, denoted as MIL-88-Fe@PDA@Co-ZIF-L hollow nanorods; S5. Put the MIL-88-Fe@PDA@ZIF-L-Co hollow nanorods prepared in Step S4 into a porcelain boat, then place the porcelain boat in a tube furnace, under a nitrogen atmosphere, heat up to 200 - 400 °C and keep warm for 0.5 - 2 h, then heat up to 600 - 800 °C and keep warm for 1 - 6 h, and cool to room temperature to obtain bimetallic phosphate / nitrogen-doped carbon hollow nanorods.

2. The preparation method of the bimetallic phosphate / nitrogen-doped carbon hollow nanorods according to claim 1, characterized in that, The water-soluble iron salt is one of iron nitrate nonahydrate, iron acetate tetrahydrate, and iron chloride hexahydrate.

3. The preparation method of the bimetallic phosphate / nitrogen-doped carbon hollow nanorods according to claim 1 or 2, characterized in that, The concentration of fumaric acid in Solution 1 is 0.603 - 6.03 mol / L, the concentration of water-soluble iron salt in Solution 2 is 0.026 mol / L - 0.26 mol / L, the molar concentration ratio of fumaric acid in Solution 1 to water-soluble iron salt in Solution 2 is 6.03:0.26, and Solution 1 and Solution 2 are mixed in a volume ratio of 4:

1.

4. The preparation method of the bimetallic phosphate / nitrogen-doped carbon hollow nanorods according to claim 1, wherein, In Step S2, the concentrations of Solution 3 and phytic acid solution are the same and are both 0.01 - 0.1 g / mL, and Solution 3 and phytic acid solution are mixed in equal volume.

5. The preparation method of the bimetallic phosphate / nitrogen-doped carbon hollow nanorods according to claim 1, wherein, In solution 4 in step S3, the concentration of iron-based MIL-88-Fe hollow nanorods is 0.00125 - 0.0125 g / mL, and the concentration ratio of iron-based MIL-88-Fe hollow nanorods to dopamine hydrochloride is 2:

1.

6. The preparation method of the bimetallic phosphate / nitrogen-doped carbon hollow nanorods according to claim 1, wherein, In solution 5 in step S4, the dispersion concentrations of MIL-88-Fe@PDA and PVP are the same and are both 0.0008 - 0.008 g / mL; the concentration of 2-methylimidazole in solution 6 is 0.00308 - 0.0328 g / mL; the concentration of cobalt nitrate hexahydrate in solution 7 is 0.00145 - 0.0145 g / mL.

7. The preparation method of the bimetallic phosphate / nitrogen-doped carbon hollow nanorods according to claim 6, wherein, The concentration ratio of PVP in solution 5, 2-methylimidazole in solution 6 to cobalt nitrate hexahydrate in solution 7 is 8:30.8:14.5, and solutions 5, 6, and 7 are mixed in a volume ratio of 8:8:

5.

8. The preparation method of the bimetallic phosphate / nitrogen-doped carbon hollow nanorods according to claim 1, wherein, In step S5, the heating rate of the tube furnace is 1 - 10 °C / min.

9. A bimetallic phosphate / nitrogen-doped carbon hollow nanorod prepared by the preparation method according to any one of claims 1 - 8.

10. Application of the bimetallic phosphate / nitrogen-doped carbon hollow nanorod electrocatalyst according to claim 9 in a zinc-air battery.

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