CN114420959A

CN114420959A - FeNi prepared from biomass3Composite nitrogen-doped carbon nanotube bifunctional electrocatalyst

Info

Publication number: CN114420959A
Application number: CN202210239435.6A
Authority: CN
Inventors: 弓巧娟; 赵晓燕; 范嘉敏
Original assignee: Shanxi Jiashi New Energy Materials Co ltd; Yuncheng University
Current assignee: Shanxi Jiashi New Energy Materials Co ltd; Yuncheng University
Priority date: 2022-03-11
Filing date: 2022-03-11
Publication date: 2022-04-29

Abstract

The invention discloses FeNi prepared from biomass₃A composite nitrogen-doped carbon nanotube bifunctional electrocatalyst belongs to the technical field of zinc-air battery bifunctional electrocatalysts. The catalyst takes corncob activated carbon as an organic carbon source, melamine as a nitrogen source and FeCl₃•6H₂O and NiCl₂•6H₂O is a metal source and is obtained by a one-step pyrolysis method. The catalyst inherits the three-dimensional porous structure of the corncob and grows a large number of carbon nanotubes on the surface of the corncob, and FeNi alloy particles are wrapped in the carbon nanotubes. The catalyst shows good oxygen catalytic performance and stability in alkaline electrolyte, and the performance of Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) of the catalyst is superior to that of the current commercial noble metal catalyst, wherein the ORR performance is even superior to that of the current reported noble metal catalystLeading most FeNi alloy dual-function catalyst. The used raw materials are wide in source, renewable and simple in preparation process, and have great development potential in biomass recycling and application in the direction of zinc-air batteries.

Description

FeNi prepared from biomass3Composite nitrogen-doped carbon nano-particlesTube dual function electrocatalyst

Technical Field

The invention belongs to the technical field of zinc-air battery bifunctional electrocatalysts, and particularly relates to FeNi prepared from biomass₃A composite nitrogen-doped carbon nanotube bifunctional electrocatalyst, a preparation method and application thereof.

Background

Environmental problems associated with the large amount of biomass waste per year and the growing shortage of traditional energy sources are attracting increasing attention as renewable clean energy sources and storage and conversion devices therefor. The zinc-air battery has the advantages of high energy density, environmental protection, safe use and the like, and is considered to be an energy storage device with great development prospect. The key to restricting the application of zinc-air batteries is their slow ORR and OER kinetic reactions. Currently, platinum-based (Pt) catalysts and RuO₂/IrO₂Belongs to the most effective catalysts of ORR and OER, but the practical application of the zinc-air battery is greatly limited due to the defects that the high cost and the stability of noble metal are required to be improved, and the like. Therefore, designing and preparing the non-noble metal bifunctional catalyst with low cost and high efficiency is an effective way for developing the zinc-air battery.

The porous carbon nano material has a unique structure, good conductivity, large specific surface area and wide raw material sources, and is more and more concerned. Recent studies have shown that carbon materials doped with heteroatoms such as N, S, P exhibit higher ORR activity and stability in alkaline media, but research on their OER is still in the research stage. In order to obtain a catalyst having both ORR and OER catalytic activities, studies on the improvement of the performance of the bifunctional catalyst by compounding non-noble metals (Fe, Ni, Co, Mn, etc.) with carbon materials have been reported. Among them, the composite of transition metal and nitrogen-doped carbon material is considered as one of the most potential non-noble metal bifunctional catalysts.

The literature shows that the N-doped porous carbon composite FeNi alloy has excellent ORR and OER catalytic activity. Wang et al [ Energy Storage Mater, 2018(12):227]Peanut shells are used as a carbon source, and are activated by a solvothermal method and a pyrolysis method, and activated carbon and an iron source are mixedAnd calcining the mixture for 2 hours at 900 ℃ with a nickel source to obtain the FeNi doped porous carbon compound. It is superior to commercial noble metal catalysts (Pt/C and IrO) in alkaline solution₂ORR, OER catalytic activity and stability of/C). However, the preparation process is complicated, the pyrolysis temperature is high, and the preparation scheme needs to be further improved. Niu et al [ Jmater chem.A., 2020, 8(27): 13725]Wood chips are used as a carbon source, the N, Fe and Ni doped carbon nano tube is obtained by adopting a one-step pyrolysis method, the initial potential is 0.94V, and the half-wave potential is 0.82V. However, the ORR catalytic activity of the catalyst still has a large promotion space. Therefore, optimizing the preparation scheme and improving the catalytic activity of the ORR and OER of the catalyst are still key problems to be solved urgently.

Disclosure of Invention

The invention provides FeNi prepared from biomass, aiming at solving the problems that in the prior art, most biomass waste composite FeNi alloy is complex in preparation process, high in pyrolysis temperature, not beneficial to large-scale production, serious in metal particle agglomeration phenomenon, incapable of providing high catalytic performance and the like₃A composite nitrogen-doped carbon nanotube bifunctional electrocatalyst, a preparation method and application thereof.

Aiming at the problems, the invention selects biomass waste corncobs as a carbon source, melamine as a nitrogen source and FeCl₃•6H₂O and NiCl₂•6H₂O is an iron source and a nickel source, and the iron-nickel alloy @ N doped carbon nano tube (FeNi) is synthesized on a three-dimensional porous carbon substrate of the corncob by adopting a high-temperature pyrolysis method₃@ NCNT). The activated carbon generated by the corncobs is selected as the raw material, the original three-dimensional porous channel structure can be kept, a substrate is provided for the growth of the carbon nano tubes, the agglomeration of the carbon nano tubes caused by mass accumulation is avoided, and rich active sites are kept. The introduction of the iron source and the nickel source effectively solves the problem of single catalytic function of the catalyst, thereby improving the electrocatalytic performance of the catalyst.

The invention is realized by the following technical scheme: FeNi prepared from biomass₃The composite nitrogen-doped carbon nanotube bifunctional electrocatalyst is prepared by the following method: biomass waste corncob activated carbon is used as an organic carbon source,the catalyst is obtained by a one-step pyrolysis method and is marked as FeNi₃@ NCNT, FeNi is wrapped in the carbon nano tube, and the specific preparation method is as follows:

(1) preparing corncob activated carbon: weighing corncobs and KOH according to a certain mass ratio, soaking in ultrapure water for 10-12 h, and freeze-drying; calcining the dried sample at high temperature for 1.5-2.5 h under the protection of nitrogen; grinding and crushing the activated product, and putting the ground product into a container with 2-4 mol.L^-1Magnetically stirring the obtained solution for 2-6 hours, centrifuging, sequentially washing with water and alcohol until the solution is neutral, and carrying out vacuum drying on the sample at the temperature of 60-90 ℃ overnight to obtain the corncob activated carbon, wherein X corresponds to the calcination temperature of 700-900 ℃, and Y is the mass ratio of KOH to corncobs of 1: 2-1: 5.

(2)FeNi₃Preparation of @ NCNT catalyst: taking AC (nitrogen-doped corncob activated carbon) prepared in the step (1), melamine and FeCl with a certain mass concentration ratio₃•6H₂O and NiCl₂•6H₂Dissolving O in ultrapure water, performing ultrasonic treatment at normal temperature for 60-80 min, and freeze-drying; in N₂Calcining at 700-1000 ℃ for 1.5-2.5 h in the atmosphere to obtain the catalyst FeNi₃@ NCNT. The sample morphology is shown in fig. 1.

Preferably, in step (1), the corncobs used are sieved through a 100-mesh sieve.

Preferably, in the step (1), the mass ratio of the corncobs to the KOH is 1: 4.

Preferably, in the step (1), the immersion time is 10 hours.

Preferably, in step (1), the magnetic stirring time is 4 h.

Preferably, in the step (2), the calcination temperature is 800 ℃, and the pyrolysis temperature rise rate during high-temperature calcination is 5 ℃/min.

Preferably, in step (2), the mass ratio of AC to melamine is 1: 4.

Preferably, in step (2), FeCl₃•6H₂O and NiCl₂•6H₂The mass concentration ratio of O is 0:1, 1:0 or 1:3, FeCl₃•6H₂O concentration of 0-0.1 mmol/L, NiCl₂•6H₂The concentration of O is 0-0.3 mmol/L.

Compared with the prior art, the invention has the following beneficial effects: the invention provides FeNi prepared from biomass₃The composite nitrogen-doped carbon nanotube bifunctional electrocatalyst comprises the following components:

(1) the biomass waste corncob is selected as the carbon source, so that the source is wide, the cost is low, and the problems of waste of a large amount of waste biomass every year and environmental pollution caused by the waste can be solved. The corncob is used as a carbon source, an original three-dimensional porous channel structure can be reserved in the pyrolysis process, a substrate is provided for the growth of the carbon nano tube, the accumulation of the carbon nano tube is avoided, the transmission of electrolyte is facilitated, a large number of active sites are provided, and therefore the catalytic performance of the catalyst is improved.

(2) The preparation method adopted by the invention is a one-step pyrolysis method, is simple and is beneficial to large-scale production.

(3) FeNi prepared by the invention₃Compared with the related literature reports of most of the existing biomass-based composite FeNi alloy, the @ NCNT catalyst has better ORR performance, the initial potential can reach 1.01V, and the half-wave potential is 0.89V. The potential difference is only 0.75V, and the maximum power density can reach 142.9 mW.cm after the self-made zinc-air battery is assembled^-2。

(4) FeNi prepared by the invention₃@ NCNT catalyst 20% Pt/C and RuO compared to commercial catalyst₂The zinc-air battery has better ORR and OER performances and better stability, and has great development potential when applied to the direction of a zinc-air battery.

Drawings

FIG. 1(a) is a Scanning Electron Microscope (SEM) image of the corncob activated carbon obtained in example 1, and (b-c) are FeNi obtained in example 1₃Scanning Electron Microscope (SEM) images of @ NCNT at different magnifications, (d-e) are FeNi prepared in example 1₃Transmission Electron Microscopy (TEM) and High Resolution Transmission Electron Microscopy (HRTEM) images of @ NCNT.

FIG. 2 is an XRD spectrum of samples obtained in example 1, example 4 and example 5.

FIG. 3 shows the results of example 1, at 0.1 mol.L in the oxygen-saturated state^-1In KOH solution of (4), the sweeping speed is 100mVCV curve of s.

FIG. 4 shows the results of example 2, at 0.1 mol.L in the oxygen saturated state^-1In KOH solution (2), the rotation speed is 1600 rpm, and the sweep rate is 5 mV/s of the ORR polarization curve.

FIG. 5 shows the results of example 3, at 0.1 mol.L in the oxygen saturated state^-1In KOH solution (2), the rotation speed is 1600 rpm, and the sweep rate is 5 mV/s of the ORR polarization curve.

FIG. 6 shows the results of example 1, at 0.1 mol.L in the oxygen-saturated state^-1In KOH solution (2), the rotation speed is 1600 rpm, and the sweep rate is 5 mV/s of the ORR polarization curve.

FIG. 7 shows a sample obtained in example 1 at 0.1 mol.L^-1In KOH solution (b), the rotation speed was 1600 rpm, and the sweep rate was 5 mV/s.

FIG. 8 shows FeNi as a sample obtained in example 1₃@ NCNT, at 0.1 mol.L^-1After 5000 cycles of CV cycling, the ORR polarization curve of the KOH solution (2) was obtained.

FIG. 9 shows FeNi as a sample obtained in example 1₃@ NCNT, at 0.1 mol.L^-1After 5000 cycles of CV cycling, the OER polarization curve of the KOH solution (A) is obtained.

FIG. 10 shows FeNi as a sample obtained in example 1₃@ NCNT and 20% Pt/C + RuO₂And preparing a zinc-air battery, a discharge curve and a power density curve.

Detailed Description

The present invention is further illustrated by the following specific examples.

The corncobs used in the invention are all from the city of fortune, melamine and FeCl₃•6H₂O and NiCl₂•6H₂O was purchased from shanghai alading reagents ltd and had molecular weights of 126.15, 270.3, and 237.69, respectively.

The method used in all examples is a biomass-produced FeNi disclosed below₃The composite nitrogen-doped carbon nanotube bifunctional electrocatalyst is prepared by the following method: the biomass waste corncob activated carbon is used as an organic carbon source, a catalyst is obtained by adopting a one-step pyrolysis method and is marked as FeNi₃@NCNT，FeNiIs wrapped in the carbon nano tube, and the specific preparation method is as follows:

(2)FeNi₃Preparation of @ NCNT catalyst: taking AC prepared in the step (1), melamine and FeCl with a certain mass ratio and a certain concentration ratio of substances₃•6H₂O and NiCl₂•6H₂Dissolving O in ultrapure water, performing ultrasonic treatment at normal temperature for 60-80 min, and freeze-drying; in N₂Calcining at 700-1000 ℃ for 1.5-2.5 h in the atmosphere to obtain the catalyst FeNi₃@NCNT。

In the following examples: in the step (1), the adopted corncobs are sieved by a 100-mesh sieve, and the mass ratio of the adopted corncobs to KOH is selected from 1: 2-1: 5; in step (2), FeCl₃•6H₂O and NiCl₂•6H₂The mass concentration ratio of O is 0:1, 1:0 or 1:3, and the following examples are all selected within this range, FeCl₃•6H₂O concentration of 0-0.1 mmol/L, NiCl₂•6H₂The concentration of O is 0-0.3 mmol/L, and the pyrolysis temperature rise rate during high-temperature calcination is 5 ℃/min; the mass ratio of AC to melamine was 1: 4.

The corncobs used in the following examples are from the city of fortune, melamine, FeCl₃•6H₂O and NiCl₂•6H₂O was purchased from shanghai alading reagents ltd and had molecular weights of 126.15, 270.3, and 237.69, respectively.

Example 1:

FeNi₃The preparation method of the composite nitrogen-doped carbon nanotube bifunctional catalyst comprises the following steps:

(1) corn cobPreparing charcoal: weighing 100-mesh corncob and KOH at a mass ratio of 1:4, dissolving in 200mL of ultrapure water, soaking the mixture for 10h, freeze-drying the mixture, and collecting the product. In N₂Pyrolyzing at 800 deg.C for 2h in atmosphere, collecting product, grinding, pulverizing, and adding 3 mol.L^-1Magnetically stirring the solution for 4 hours, centrifuging, sequentially washing with water and alcohol to neutrality, and vacuum drying the washed sample at 80 ℃ overnight to obtain the corncob activated carbon AC-800-4.

(2)FeNi₃Preparation of @ NCNT catalyst: 0.2g of AC-800-4, 0.8 g of melamine and 0.00258 g of FeCl were taken₃•6H₂O and 0.00675 g NiCl₂•6H₂Dissolving O in 20 mL of ultrapure water, performing ultrasonic treatment at normal temperature for 60 min, and freeze-drying. In N₂Calcining at 800 ℃ for 2h under protection to obtain the catalyst FeNi₃@NCNT。

2 mg of FeNi are taken₃The @ NCNT catalyst is dispersed in 1 mL of ethanol and 8 mu L of 5% Nafion solution, and the solution is subjected to ultrasonic treatment for 60 min to obtain a uniformly dispersed suspension. Measuring and dropping the suspension on the surface of a glassy carbon electrode, wherein the loading capacity is 250 mu g/cm²And standing for 1h and then testing. Using an electrochemical workstation at 0.1 mol.L^-1In the KOH electrolyte solution, a three-electrode system is adopted to carry out cyclic voltammetry, linear sweep voltammetry and stability tests on the catalyst. The potentials of the electrochemical test are converted relative reversible hydrogen electrode potentials. The test results are shown in fig. 2 and 3.

Example 2

(1) Preparing corncob activated carbon: weighing 100-mesh corncob and KOH at a mass ratio of 1:3, dissolving in 200mL of ultrapure water, soaking the mixture for 11h, freeze-drying the mixture, and collecting the product. In N₂Pyrolyzing at 800 deg.C for 2h in atmosphere, collecting product, grinding, pulverizing, and adding 3 mol.L^-1Magnetically stirring for 5 h, centrifuging, washing with water and alcohol sequentially to neutrality, and vacuum drying the washed sample at 80 deg.C overnight to obtain corn cob activated carbon AC-800-X (X = 3).

Dispersing 2 mg of AC-800-X catalyst in 1 mL of ethanol and 8 mu L of 5% Nafion solution, and performing ultrasonic treatment for 60 min to obtain uniformly dispersed suspension. Measuring and dropping the suspension on the surface of a glassy carbon electrode, wherein the loading capacity is 250 mu g/cm²And standing for 1h and then testing. Using an electrochemical workstation at 0.1 mol.L^-1In the KOH electrolyte solution, a three-electrode system is adopted to carry out linear sweep voltammetry on the catalyst. The potentials of the electrochemical test are converted relative reversible hydrogen electrode potentials. The test results are shown in fig. 4.

Example 3

(1) Preparing corncob activated carbon: weighing 100-mesh corncob and KOH at a mass ratio of 1:4, dissolving in 200mL of ultrapure water, soaking the mixture for 12h, freeze-drying the mixture, and collecting the product. In N₂Pyrolyzing at 900 deg.C for 2 hr under atmosphere, collecting product, grinding, pulverizing, and adding 3 mol.L^-1Magnetically stirring for 6 h, centrifuging, washing with water and alcohol sequentially to neutrality, and vacuum drying the washed sample at 80 deg.C overnight to obtain corn cob activated carbon AC-Y-4(Y = 900).

2 mg of the AC-Y-4 catalyst is dispersed in 1 mL of ethanol and 8 mu L of 5% Nafion solution, and the mixture is subjected to ultrasonic treatment for 60 min to obtain a uniformly dispersed suspension. Dropping the suspension on the surface of a glassy carbon electrode with the loading of 250 mu g/cm²And standing for 1h and then testing. Using an electrochemical workstation at 0.1 mol.L^-1In the KOH electrolyte solution, a three-electrode system is adopted to carry out linear sweep voltammetry on the catalyst. The potentials of the electrochemical test are converted relative reversible hydrogen electrode potentials. The test results are shown in fig. 5.

Example 4

(1) Preparing corncob activated carbon: the preparation method is the same as the preparation method of the corncob activated carbon in the example 1.

(2) Preparation of Fe @ NCNT catalyst: 0.2g of AC-800-4, 0.8 g of melamine and 0.00258 g of FeCl were taken₃•6H₂Dissolving O in 20 mL of ultrapure water, performing ultrasonic treatment at normal temperature for 60 min, and freeze-drying. In N₂Calcining at 800 ℃ for 2h under protection to obtain the catalyst Fe @ NCNT.

2 mg of Fe @ NCNT catalyst is dispersed in 1 mL of ethanol and 8 mu L of 5% Nafion solution, and the solution is subjected to ultrasonic treatment for 60 min to obtain a uniformly dispersed suspension. Measuring and measuringThe suspension is dripped on the surface of a glassy carbon electrode, and the loading is 250 mu g/cm²And standing for 1h and then testing. Using an electrochemical workstation at 0.1 mol.L^-1In the KOH electrolyte solution, a three-electrode system is adopted to carry out linear sweep voltammetry on the catalyst. The potentials of the electrochemical test are converted relative reversible hydrogen electrode potentials. The test results are shown in fig. 2 and 3.

Example 5

(2) Preparation of Ni @ NCNT catalyst: 0.2g of AC-800-4, 0.8 g of melamine and 0.00675 g of NiCl were taken₂•6H₂Dissolving O in 20 mL of ultrapure water, performing ultrasonic treatment at normal temperature for 60 min, and freeze-drying. In N₂And calcining at 800 ℃ for 2h under protection to obtain the catalyst Ni @ NCNT.

2 mg of Ni @ NCNT catalyst is dispersed in 1 mL of ethanol and 8 mu L of 5% Nafion solution, and the solution is subjected to ultrasonic treatment for 60 min to obtain a uniformly dispersed suspension. Measuring and dropping the suspension on the surface of a glassy carbon electrode, wherein the loading capacity is 250 mu g/cm²And standing for 1h and then testing. Using an electrochemical workstation at 0.1 mol.L^-1In the KOH electrolyte solution, a three-electrode system is adopted to carry out linear sweep voltammetry on the catalyst. The potentials of the electrochemical test are converted relative reversible hydrogen electrode potentials. The test results are shown in fig. 2 and 3.

Example 6

Weighing 1 mg of 20% Pt/C and 1 mg of RuO₂Dispersing in 1 mL of ethanol and 8 mu L of 5% Nafion solution, and carrying out ultrasonic treatment for 60 min to obtain a uniformly dispersed suspension. The suspension is removed and dripped on the surface of a glassy carbon electrode, and the loading capacity is 250 mu g/cm²And standing for 1h and then testing. Using an electrochemical workstation at 0.1 mol.L^-1In the KOH electrolyte solution, a three-electrode system is adopted to carry out linear sweep voltammetry on the catalyst. The potentials of the electrochemical test are converted relative reversible hydrogen electrode potentials. The test results are shown in fig. 2 and 3.

FIG. 1(a) is an SEM of catalyst AC-800-4, and (b-d) is catalyst FeNi₃In SEM and TEM of @ NCNT, it can be seen that the porous structure of AC-800-4 is not destroyed after the metal precursor is added, and a large number of carbon nanotubes are grown on the surface thereof, and a large number of metal particles are wrapped in the carbon nanotubes. FIG. 1(e) shows FeNi₃HRTEM of @ NCNT, from which it can be seen that these nanoparticles have good lattice fringes with lattice spacings of 0.206 nm and 0.341 nm, assigned to the (002) plane of C and to FeNi, respectively₃The (111) plane of (1). Proves FeNi₃The presence of an alloy.

FIG. 2 shows AC-800-4, Fe @ NCNT, Ni @ NCNT and FeNi₃XRD spectrum of @ NCNT. As can be seen from the figure, all samples had a diffraction peak near 26.1 °, which was assigned to the (002) crystal plane of graphitic carbon. In addition, FeNi₃The @ NCNT shows diffraction peaks at 44.3 degrees, 51.5 degrees and 75.9 degrees, which are respectively attributed to FeNi₃The (111), (200) and (220) crystal planes of the alloy (PDF # 38-0419). Combining TEM analysis, further proving that Fe and Ni metals are doped into the carbon nano tube in the form of alloy, and successfully preparing FeNi₃The @ NTNC complex.

FIG. 3 shows AC-800-4, Fe @ NCNT, Ni @ NCNT, FeNi₃@ NCNT and 20% Pt/C + RuO₂CV curve of (2). The results show that all samples have distinct redox peaks, where FeNi is₃@ NCNT exhibits a more positive reduction potential (0.87V). Indicating FeNi₃@ NCNT has excellent ORR catalytic activity.

FIG. 4 is the ORR-LSV curves for AC-800-2, AC-800-3, AC-800-4 and AC-800-5. The result shows that the initial potential of AC-800-4 is more correct than that of other samples, and the limiting current density is higher and can reach 4.27 mA.cm^-2Much higher than AC-800-2 (3.78 mA.cm)^-2）、AC-800-3（3.78 mA•cm^-2) And AC-800-5 (3.91 mA.cm)^-2）。

FIG. 5 is the ORR-LSV curves for AC-700-4, AC-800-4, AC-900-4 and AC-1000-4. The results show that the half-wave potential of AC-800-4 is more positive than that of the other samples and the limiting current density is greater.

FIG. 6 shows AC-800-4, Fe @ NCNT, Ni @ NCNT, FeNi₃@ NCNT and 20% Pt/C + RuO₂ORR-LSV curve of (1). Results tableThe initial potential, half-wave potential and limiting current density of FeNi3@ NCNT are 1.01V, 0.89V and 5.46 mA.cm^-2Much higher than AC-800-4 (0.97V, 0.85V, 4.27 mA.cm)^-2）、Fe@NCNT（0.98V，0.87 V，4.63 mA•cm^-2) And Ni @ NCNT (0.98V, 0.88V, 4.51 mA.cm)^-2) Even better than commercial 20% Pt/C + RuO₂Initial potential (1.00V) and limiting current density (5.40 mA.cm)^-2）。

FIG. 7 shows Fe @ NCNT, Ni @ NCNT, FeNi₃@ NCNT and 20% Pt/C + RuO₂OER-LSV curve of (1). It can be seen from the figure that at 10 mA.cm^-2At current density of (2), FeNi in comparison with other catalysts₃@ NCNT exhibits the lowest overpotential (410 mV), even exceeding commercial 20% Pt/C + RuO₂(440 mV). The overpotentials for Fe @ NCNT, and Ni @ NCNT are 480 mV and 470 mV, respectively.

FIG. 8 shows FeNi₃ORR-LSV curves for the @ NCNT catalyst before and after 5000 CV cycles of testing. The results show that after 5000 CV cycles of test, the ORR curve has almost no change, which indicates that FeNi₃@ NCNT has good electrochemical stability.

FIG. 9 shows FeNi₃OER-LSV curves for the @ NCNT catalyst before and after 5000 CV cycles of testing. The results show that after 5000 CV cycles of test, the OER curve has almost no change, which indicates that FeNi₃@ NCNT has good electrochemical stability.

FIG. 10 shows FeNi₃@ NCNT and 20% Pt/C + RuO₂Respectively assembling a discharge curve and a power density curve after the self-made zinc-air battery is manufactured. FeNi₃@ NCNT at 0.57V, the current density reached 248.6 mA.cm^-2The highest power density reaches 142.9 mW.cm^-2Obviously higher than 20 percent of Pt/C + RuO of noble metal₂（132.5 mW•cm^-2). This indicates that FeNi₃@ NCNT has better discharge performance.

The scope of the invention is not limited to the above embodiments, and various modifications and changes may be made by those skilled in the art, and any modifications, improvements and equivalents within the spirit and principle of the invention should be included in the scope of the invention.

Claims

1. FeNi prepared from biomass₃The composite nitrogen-doped carbon nanotube bifunctional electrocatalyst is characterized in that: the preparation method comprises the following steps: the biomass waste corncob activated carbon is used as an organic carbon source, a catalyst is obtained by adopting a one-step pyrolysis method and is marked as FeNi₃@ NCNT, FeNi is wrapped in the carbon nano tube, and the specific preparation method is as follows:

(1) preparing corncob activated carbon: weighing corncobs and KOH according to a certain mass ratio, soaking in ultrapure water for 10-12 h, and freeze-drying; calcining the dried sample at high temperature for 1.5-2.5 h under the protection of nitrogen; grinding and crushing the activated product, and putting the ground product into a container with 2-4 mol.L^-1Magnetically stirring the obtained solution for 2-6 hours, centrifuging, sequentially washing with water and alcohol until the solution is neutral, and carrying out vacuum drying on the sample at the temperature of 60-90 ℃ overnight to obtain the corncob activated carbon, wherein X corresponds to the calcination temperature of 700-900 ℃, and Y is the mass ratio of KOH to corncobs of 1: 2-1: 5;

2. A biomass-produced FeNi according to claim 1₃The composite nitrogen-doped carbon nanotube bifunctional electrocatalyst is characterized in that: in the step (1), the adopted corncobs are sieved by a 100-mesh sieve.

3. A biomass-produced FeNi according to claim 1₃The composite nitrogen-doped carbon nanotube bifunctional electrocatalyst is characterized in that: in the step (1), the mass ratio of the adopted corncobs to the KOH is 1: 4.

4. A biomass-produced FeNi according to claim 1₃The composite nitrogen-doped carbon nanotube bifunctional electrocatalyst is characterized in that: in the step (1), the dipping time is 10 h.

5. A biomass-produced FeNi according to claim 1₃The composite nitrogen-doped carbon nanotube bifunctional electrocatalyst is characterized in that: in the step (1), the magnetic stirring time is 4 h.

6. A biomass-produced FeNi according to claim 1₃The composite nitrogen-doped carbon nanotube bifunctional electrocatalyst is characterized in that: in the step (2), the calcining temperature is 800 ℃, and the pyrolysis heating rate during high-temperature calcining is 5 ℃/min.

7. A biomass-produced FeNi according to claim 1₃The composite nitrogen-doped carbon nanotube bifunctional electrocatalyst is characterized in that: in the step (2), the mass ratio of the AC to the melamine is 1: 4.

8. A biomass-produced FeNi according to claim 1₃The composite nitrogen-doped carbon nanotube bifunctional electrocatalyst is characterized in that: in step (2), FeCl₃•6H₂O and NiCl₂•6H₂The mass concentration ratio of O is 0:1, 1:0 or 1: 3.

9. A biomass-produced FeNi of claim 1₃The application of the composite nitrogen-doped carbon nanotube bifunctional electrocatalyst is characterized in that: the FeNi₃The composite nitrogen-doped carbon nanotube is used as a zinc-air battery bifunctional catalyst.