A method for preparing a coconut shell carbon transition metal bifunctional catalyst and its application.

Abstract

This invention provides a method for preparing a coconut shell carbon transition metal bifunctional catalyst, comprising the following steps: S1, carbonizing and grapheneizing coconut shell to obtain grapheneized coconut shell carbon; S2, doping the grapheneized coconut shell carbon with nitrogen and sulfur to obtain nitrogen and sulfur-doped grapheneized coconut shell carbon; S3, preparing a nickel-cobalt-iron LDH catalyst via a hydrothermal method; S4, combining the nitrogen and sulfur-doped grapheneized coconut shell carbon with the nickel-cobalt-iron LDH catalyst via an aqueous phase ultrasonic method to obtain a NiCoFe / NSC bifunctional catalyst. The coconut shell carbon transition metal bifunctional catalyst, when used as a cathode electrocatalyst material in zinc-air batteries, exhibits excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of fuel cell cathode electrocatalyst preparation technology, and particularly to a method for preparing a coconut shell carbon transition metal bifunctional catalyst and its application. Background Technology

[0002] Traditional fossil fuels face challenges such as insufficient natural reserves, low conversion efficiency, and toxic byproduct pollution. Therefore, seeking new energy sources with ample reserves, high conversion efficiency, and environmental friendliness has become a mainstream research direction. Zinc-air batteries have attracted widespread attention from researchers due to their advantages such as high theoretical energy density, inexpensive and abundant raw materials, and safety and stability. However, the efficiency and cycle life of zinc-air batteries are limited by the electrocatalyst. Traditional anodic oxidation-reduction reactions (ORR) and cathodic oxidation reactions (OER) require two different catalysts for promotion, resulting in low energy conversion efficiency. Therefore, researching an electrocatalyst with both ORR and OER functions is of great significance for improving the efficiency of zinc-air batteries.

[0003] Currently, widely used Pt / C catalysts have become a serious obstacle to the commercialization of fuel cells due to their scarcity, high cost, poor stability, and susceptibility to poisoning. Therefore, in recent years, seeking and preparing high-performance, low-cost, stable, and poison-resistant non-precious metal catalysts has become one of the popular research topics for researchers. At present, non-precious metal catalysts are mainly divided into two categories: one is transition metal-nitrogen-carbon catalysts, and the other is non-metallic heteroatom-doped carbon catalysts. Transition metal-nitrogen-carbon materials face huge challenges in preparation: (1) transition metals will condense into particles under high temperature conditions, which will reduce the intrinsic activity and number density of active sites; (2) the collapse of carbon material structure and the presence of a large amount of amorphous carbon will reduce the specific surface area and cause insufficient conductivity. At present, the key indicator for evaluating powdered bifunctional catalysts is the oxygen evolution reaction at a current density of 10 mA / cm². 2 The difference between the potential at time ΔE and the half-wave potential of oxygen reduction is of great significance for developing bifunctional electrocatalysts for oxygen evolution and oxygen reduction reactions of non-noble metals.

[0004] Therefore, it is of great significance to develop a low-cost, high-performance, stable, and toxic non-precious metal catalyst to replace Pt / C catalysts in zinc-air batteries by selecting materials and optimizing preparation methods. Summary of the Invention

[0005] To address at least one deficiency or improvement need in the existing technology, this invention proposes a method for preparing a coconut shell carbon transition metal bifunctional catalyst and its application. The aim is to construct a high-performance and stable transition metal-based catalyst to further improve the electrochemical performance of zinc-air battery cathode materials.

[0006] The technical solution of this invention is implemented as follows:

[0007] A method for preparing a coconut shell carbon transition metal bifunctional catalyst includes the following steps:

[0008] S1. Preparation of graphene-modified coconut shell carbon

[0009] Coconut shells are carbonized, mixed with concentrated sulfuric acid in an ice-water bath, and potassium permanganate is added until the solution turns brown. The reaction is carried out in a water bath at 30-40°C, and hydrogen peroxide is added until the solution turns pale golden yellow. The mixture is allowed to stand, the supernatant is removed, hydrochloric acid solution is added and mixed, centrifuged, the supernatant is removed, washed, and freeze-dried to obtain graphene-modified coconut shell carbon.

[0010] S2, graphene-modified coconut shell carbon doped with nitrogen and sulfur

[0011] Graphene-modified coconut shell carbon was dispersed in a solvent, silica was added, and the mixture was sonicated. After removing the solvent, a solid was obtained, which was then mixed and ground with nitrogen-containing and sulfur-containing compounds. After calcination in an inert gas atmosphere, the solid was soaked in a strong acid, centrifuged, washed, and dried to obtain nitrogen- and sulfur-doped graphene-modified coconut shell carbon.

[0012] S3, hydrothermal method for producing nickel-cobalt-iron LDH catalyst

[0013] Nickel chloride, cobalt chloride, ferric chloride and water are mixed to obtain metal solution A; sodium carbonate and water are mixed to obtain alkaline solution B; A and B are mixed and reacted at 100-150℃ for 15-20 hours, cooled, centrifuged and washed, and dried to obtain nickel-cobalt-iron LDH catalyst.

[0014] Preparation of S4, NiCoFe / NSC bifunctional catalysts

[0015] The nitrogen-sulfur-doped grapheneized coconut shell carbon in S2 and the nickel-cobalt-iron LDH catalyst in S3 were mixed in water, ultrasonicated, centrifuged and washed, and dried to obtain a coconut shell carbon transition metal bifunctional catalyst, denoted as NiCoFe / NSC.

[0016] Preferably, the molar ratio of nickel chloride, cobalt chloride, and ferric chloride in S3 is 1:4~8:1~5; and the molar percentage of Fe in the total molar percentage of Ni, Co, and Fe is less than 50%.

[0017] Preferably, in step S1, the coconut shell carbonization specifically involves drying the coconut shell, crushing it, and placing it in a tube furnace for carbonization under an argon atmosphere at 600°C; the concentration of the hydrochloric acid solution is 5 wt%; the freeze-drying specifically involves first freezing at -5 to -20°C for 5-8 hours, and then freeze-drying at -60 to -45°C for 36-42 hours.

[0018] Preferably, the solvent in S2 is 98-99.8 vol% ethanol, and the silica is hydrophilic nano-silica; the mass ratio of the graphene-modified coconut shell carbon to the hydrophilic nano-silica is 1:5; the solvent removal method is secondary rotary evaporation under normal and low pressure conditions, wherein the normal pressure rotary evaporation temperature is 70-80℃, the low pressure is 0.09 MPa, and the low pressure rotary evaporation temperature is 55-60℃; the strong acid is hydrofluoric acid.

[0019] Preferably, the inert gas in S2 is nitrogen, the nitrogen-containing compound is melamine, and the sulfur-containing compound is dibenzyl disulfide; the molar ratio of the solid, melamine, and dibenzyl disulfide is 6:5:5; the tubular furnace is heated to 300°C, maintained for 10 min, then heated to 900°C, and heated at 900°C for 1 h, with a heating rate of 5°C / min.

[0020] Preferably, the centrifugal cleaning involves first washing with deionized water 2-4 times, then washing with anhydrous ethanol 2-4 times, with a centrifugal cleaning speed of 3000-4000 rad / min.

[0021] Preferably, the mass ratio of nitrogen-sulfur-doped grapheneized coconut shell carbon to nickel-cobalt-iron LDH catalyst in S4 is 1:1.

[0022] The present invention also provides a coconut shell carbon transition metal bifunctional catalyst prepared by the above preparation method.

[0023] This invention also provides the application of the coconut shell carbon transition metal bifunctional catalyst prepared by the above preparation method in zinc-air batteries.

[0024] The present invention also provides a zinc-air battery, wherein the anode is a zinc sheet and the cathode is an air electrode, the air electrode comprising nickel foam, carbon paper coated with a coconut shell carbon transition metal bifunctional catalyst prepared by the above preparation method, and an air diffusion layer.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] This invention obtains nitrogen-sulfur-doped graphene-coated coconut shell carbon by doping it with nitrogen and sulfur. The nitrogen-sulfur-doped graphene-coated coconut shell carbon is then combined with a nickel-cobalt-iron (LCH) catalyst prepared by a hydrothermal method using an aqueous ultrasonic method to obtain a nitrogen-sulfur-doped graphene-coated coconut shell carbon-supported nickel-cobalt-iron LDH bifunctional catalyst, namely the NiCoFe / NSC bifunctional catalyst. This catalyst achieves OER / ORR bifunctionality and exhibits superior electrochemical performance. The coconut shell carbon transition metal bifunctional catalyst (nitrogen-sulfur-doped graphene-coated coconut shell carbon-supported nickel-cobalt-iron LDH bifunctional catalyst) obtained by this invention, when assembled into a zinc-air battery, exhibits excellent charge-discharge cycle stability. Attached Figure Description

[0027] Figure 1 The OER polarization curves are for the coconut shell carbon transition metal bifunctional catalysts prepared in Examples 1-3 of this invention.

[0028] Figure 2 The ORR polarization curves are for the coconut shell carbon transition metal bifunctional catalysts prepared in Examples 1-3 and Comparative Example 1 of this invention.

[0029] Figure 3 The coconut shell carbon transition metal bifunctional catalyst prepared in Example 1 of this invention was used in a zinc-air battery at 10 mAcm⁻¹ -2 The stability of charge-discharge cycles. Detailed Implementation

[0030] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0031] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0032] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0033] Example 1

[0034] A method for preparing a coconut shell carbon transition metal bifunctional catalyst includes the following steps:

[0035] S1. Preparation of graphene-modified coconut shell carbon

[0036] S1.1 Collect enough coconut shells, remove the coconut meat, break the coconut shells into fragments, dry them at 80℃ for 24 hours, crush the dried coconut shells, sieve them, and obtain particles through a 100-mesh sieve.

[0037] S1.2. The particles from S1.1 are placed in a tube furnace and carbonized at 600℃ under an argon atmosphere for 2.5 hours to obtain a preliminary coconut shell carbon sample.

[0038] S1.3 Take 5g of coconut shell carbon and 115ml of concentrated sulfuric acid and stir them in an ice-water bath. Then add potassium permanganate until the solution turns brown. Remove the ice-water bath and react in a water bath at 35±5℃ for 8 hours.

[0039] S1.4. Add 750ml of deionized water intermittently and stir for 10 minutes, then add 25ml of hydrogen peroxide and stir until the solution turns pale golden yellow.

[0040] S1.5. Let the solution in S1.4 stand for 10 hours, remove the supernatant, add 200 ml of 5 wt% hydrochloric acid solution, mix well and centrifuge. After centrifugation, remove the supernatant and add an appropriate amount of deionized water to wash. Repeat this process several times, then pour the remaining solution into a petri dish and freeze at -10℃ for 5 hours. Transfer it to a freeze dryer and freeze dry at -50℃ for 36 hours to obtain the graphene-modified coconut shell carbon sample.

[0041] S2, graphene-modified coconut shell carbon doped with nitrogen and sulfur

[0042] S2.1. 0.1 g of graphene-modified coconut shell carbon was ultrasonically dispersed in 500 ml of 98 vol% ethanol, and 0.5 g of hydrophilic nano-SiO2 (15 nm) was added. After ultrasonication, the ethanol was removed by rotary evaporation at 80 °C and 0.09 MPa at 55 °C to obtain a sheet-like solid, which was then dried in an oven at 80 °C.

[0043] S2.2 Take 0.6 g of the flake solid obtained in S2.1 and mix and grind it with 0.5 g of melamine and 0.5 g of dibenzyl disulfide. Place the mixture in a tube furnace and heat it to 300 °C under a nitrogen atmosphere for 10 min. Then heat it to 900 °C and heat it at 900 °C for 1 h at a heating rate of 5 °C / min.

[0044] S2.3 The product obtained after heating in S2.2 is soaked in 50 mL of hydrofluoric acid for 24 h to remove silicon dioxide. Then, it is centrifuged to remove residual hydrofluoric acid. The centrifugation is performed by first washing with deionized water 3 times and then washing with anhydrous ethanol 3 times. The centrifugation speed is 3000 rad / min. The obtained product is placed in a vacuum drying oven and dried at 80 ℃ for 8 h to obtain nitrogen and sulfur doped grapheneized coconut shell carbon.

[0045] S3, hydrothermal method for producing nickel-cobalt-iron LDH catalyst

[0046] S3.1 Mix 8 mmol of nickel chloride, cobalt chloride, and ferric chloride in a molar ratio of 1:6:3 in a 50 ml beaker, add 20 ml of ultrapure water to dissolve, and prepare a 0.4 mol / L mixed metal solution A.

[0047] S3.2 Weigh 5.299g Na2CO3 (500 mmol) using weighing paper and place it in a 50 ml beaker. Dissolve it in a small amount of water and then transfer it to a 50 ml volumetric flask and make up to volume to prepare a 1 mol / L solution B.

[0048] S3.3. Pipette 20 ml of solution A and 16 ml of solution B into a 100 ml beaker and stir vigorously for 0.5 hours. Transfer the stirred liquid to a 50 ml reactor liner and react at 100 °C for 20 hours. When cooled to room temperature, centrifuge to clean the product. The centrifugation cleaning is performed by first washing with deionized water 3 times and then washing with anhydrous ethanol 3 times. The centrifugation speed is 4000 rad / min. Then dry at 80 °C to obtain powdered nickel cobalt iron LDH (layered double hydroxide) catalyst.

[0049] Preparation of S4, NiCoFe / NSC bifunctional catalysts

[0050] S4.1 Take 0.5g of nitrogen-sulfur-doped graphene-modified coconut shell carbon from S2.3 and 0.5g of nickel-cobalt-iron LDH catalyst from S3.2, mix them in ultrapure water at a 1:1 ratio, and sonicate at room temperature for 2h at an ultrasonic power of 230W. Centrifuge to clean the product. The cleaning process involves washing three times with deionized water and then three times with anhydrous ethanol at a centrifugation speed of 4000 rad / min. Subsequently, dry at 80℃ to obtain the coconut shell carbon transition metal bifunctional catalyst (nitrogen-sulfur-doped graphene-modified coconut shell carbon supported nickel-cobalt-iron LDH bifunctional catalyst, denoted as Ni). 0.1 Co 0.6 Fe 0.3 / NSC bifunctional catalyst).

[0051] Example 2

[0052] A method for preparing a coconut shell carbon transition metal bifunctional catalyst includes the following steps:

[0053] S1. Preparation of graphene-modified coconut shell carbon

[0054] S1.1 Collect enough coconut shells, remove the coconut meat, break the coconut shells into fragments, dry them at 80℃ for 24 hours, crush the dried coconut shells, sieve them, and obtain particles through a 100-mesh sieve.

[0055] S1.2. The particles from S1.1 are placed in a tube furnace and carbonized at 600℃ under an argon atmosphere for 2.5 hours to obtain a preliminary coconut shell carbon sample.

[0056] S1.3 Take 5g of coconut shell carbon and 115ml of concentrated sulfuric acid and stir them in an ice-water bath. Then add potassium permanganate until the solution turns brown. Remove the ice-water bath and react in a water bath at 35±5℃ for 8 hours.

[0057] S1.4. Add 750ml of deionized water intermittently and stir for 10 minutes, then add 25ml of hydrogen peroxide and stir until the solution turns pale golden yellow.

[0058] S1.5. Let the solution in S1.4 stand for 10 hours, remove the supernatant, add 200 ml of 5 wt% hydrochloric acid solution, mix well and centrifuge. After centrifugation, remove the supernatant and add an appropriate amount of deionized water to wash. Repeat this process several times, then pour the remaining solution into a petri dish and freeze at -5℃ for 8 hours. Transfer it to a freeze dryer and freeze dry at -60℃ for 36 hours to obtain the graphene-modified coconut shell carbon sample.

[0059] S2, graphene-modified coconut shell carbon doped with nitrogen and sulfur

[0060] S2.1. 0.1 g of graphene-modified coconut shell carbon was ultrasonically dispersed in 500 ml of 98 vol% ethanol. 0.5 g of hydrophilic nano-SiO2 (15 nm) was added and ultrasonicated thoroughly. The ethanol was then removed by rotary evaporation at 80 °C and 0.09 MPa at 55 °C to obtain a sheet-like solid, which was then dried in an oven at 80 °C.

[0061] S2.2 Take 0.6 g of the flake solid obtained in S2.1 and mix and grind it with 0.5 g of melamine and 0.5 g of dibenzyl disulfide. Place the mixture in a tube furnace and heat it to 300 °C under a nitrogen atmosphere. Maintain the temperature for 10 min, then heat it to 900 °C and heat it at 900 °C for 1 h at a heating rate of 5 °C / min.

[0062] S2.3 The product obtained after heating in S2.2 is soaked in 50 mL of hydrofluoric acid for 24 h to remove silicon dioxide. Then, it is centrifuged to remove residual hydrofluoric acid. The centrifugation is performed by first washing with deionized water 3 times and then washing with anhydrous ethanol 3 times. The centrifugation speed is 3000 rad / min. The obtained product is placed in a vacuum drying oven and dried at 80 ℃ for 12 h to obtain nitrogen and sulfur doped grapheneized coconut shell carbon.

[0063] S3, hydrothermal method for producing nickel-cobalt-iron LDH catalyst

[0064] S3.1 Mix 8 mmol of nickel chloride, cobalt chloride, and ferric chloride in a molar ratio of 1:4:5 in a 50 ml beaker, add 20 ml of ultrapure water to dissolve, and prepare a 0.4 mol / L mixed metal solution A.

[0065] S3.2 Weigh 5.299g Na2CO3 (500 mmol) using weighing paper and place it in a 50 ml beaker. Dissolve it in a small amount of water and then transfer it to a 50 ml volumetric flask and make up to volume to prepare a 1 mol / L solution B.

[0066] S3.3. Pipette 20 ml of solution A and 16 ml of solution B into a 100 ml beaker and stir vigorously for 0.5 hours. Transfer the stirred liquid to a 50 ml reactor liner and react at 150 °C for 15 hours. When cooled to room temperature, centrifuge to clean the product. The centrifugation cleaning is performed by first washing with deionized water 3 times and then washing with anhydrous ethanol 3 times. The centrifugation speed is 4000 rad / min. Then dry at 80 °C to obtain powdered nickel-cobalt-iron LDH catalyst.

[0067] Preparation of S4, NiCoFe / NSC bifunctional catalysts

[0068] S4.1 Take 0.5g of nitrogen-sulfur-doped graphene-supported coconut shell carbon from S2.3 and 0.5g of nickel-cobalt-iron LDH catalyst from S3.2, mix them in ultrapure water at a 1:1 ratio, sonicate at room temperature for 2h at an ultrasonic power of 230W, centrifuge and wash by first washing with deionized water 3 times and then with anhydrous ethanol 3 times, centrifuge at a speed of 4000 rad / min, and then dry at 80℃ to obtain the coconut shell carbon transition metal bifunctional catalyst (nitrogen-sulfur-doped graphene-supported coconut shell carbon nickel-cobalt-iron LDH bifunctional catalyst, denoted as Ni). 0.1 Co 0.4 Fe 0.5 / NSC bifunctional catalyst).

[0069] Example 3

[0070] A method for preparing a coconut shell carbon transition metal bifunctional catalyst includes the following steps:

[0071] S1. Preparation of graphene-modified coconut shell carbon

[0072] S1.1 Collect enough coconut shells, remove the coconut meat, break the coconut shells into fragments, dry them at 80℃ for 24 hours, crush the dried coconut shells, sieve them, and obtain particles through a 100-mesh sieve.

[0073] S1.2. The particles from S1.1 are placed in a tube furnace and carbonized at 600℃ under an argon atmosphere for 2.5 hours to obtain a preliminary coconut shell carbon sample.

[0074] S1.3 Take 5g of coconut shell carbon and 115ml of concentrated sulfuric acid and stir them in an ice-water bath. Then add potassium permanganate until the solution turns brown. Remove the ice-water bath and react in a water bath at 35±5℃ for 8 hours.

[0075] S1.4. Add 750ml of deionized water intermittently and stir for 10 minutes, then add 25ml of hydrogen peroxide and stir until the solution turns pale golden yellow.

[0076] S1.5. Let the solution in S1.4 stand for 10 hours, remove the supernatant, add 200 ml of 5 wt% hydrochloric acid solution, mix well and centrifuge. After centrifugation, remove the supernatant and add an appropriate amount of deionized water to wash. Repeat this process several times, then pour the remaining solution into a petri dish and freeze at -20℃ for 5 hours. Transfer it to a freeze dryer and freeze dry at -45℃ for 42 hours to obtain the graphene-modified coconut shell carbon sample.

[0077] S2, graphene-modified coconut shell carbon doped with nitrogen and sulfur

[0078] S2.1. 0.1 g of graphene-modified coconut shell carbon was ultrasonically dispersed in 500 ml of 98 vol% ethanol. 0.5 g of hydrophilic nano-SiO2 (15 nm) was added and ultrasonicated thoroughly. The ethanol was then removed by rotary evaporation at 80 °C and 0.09 MPa at 55 °C to obtain a sheet-like solid, which was then dried in an oven at 80 °C.

[0079] S2.2 Take 0.6 g of the flake solid obtained in S2.1 and mix and grind it with 0.5 g of melamine and 0.5 g of dibenzyl disulfide. Place the mixture in a tube furnace and heat it to 300 °C under a nitrogen atmosphere. Maintain the temperature for 10 min, then heat it to 900 °C and heat it at 900 °C for 1 h at a heating rate of 5 °C / min.

[0080] S2.3 The product obtained after heating in S2.2 is soaked in 50 mL of hydrofluoric acid for 36 h to remove silicon dioxide. Then, it is centrifuged to remove residual hydrofluoric acid. The centrifugation is performed by first washing with deionized water 3 times and then washing with anhydrous ethanol 3 times. The centrifugation speed is 3000 rad / min. The obtained product is placed in a vacuum drying oven and dried at 80 ℃ for 12 h to obtain nitrogen and sulfur doped grapheneized coconut shell carbon.

[0081] S3, hydrothermal method for producing nickel-cobalt-iron LDH catalyst

[0082] S3.1 Mix 8 mmol of nickel chloride, cobalt chloride, and ferric chloride in a molar ratio of 1:8:1 in a 50 ml beaker, add 20 ml of ultrapure water to dissolve, and prepare a 0.4 mol / L mixed metal solution A.

[0083] S3.2 Weigh 5.299g Na2CO3 (500 mmol) using weighing paper and place it in a 50 ml beaker. Dissolve it in a small amount of water and then transfer it to a 50 ml volumetric flask and make up to volume to prepare a 1 mol / L solution B.

[0084] S3.3. Pipette 20 ml of solution A and 16 ml of solution B into a 100 ml beaker and stir vigorously for 0.5 hours. Transfer the stirred liquid to a 50 ml reactor liner and react at 100 °C for 20 hours. When cooled to room temperature, centrifuge to clean the product. The centrifugation cleaning is performed by first washing with deionized water 3 times and then washing with anhydrous ethanol 3 times. The centrifugation speed is 4000 rad / min. Then dry at 80 °C to obtain powdered nickel-cobalt-iron LDH catalyst.

[0085] Preparation of S4, NiCoFe / NSC bifunctional catalysts

[0086] S4.1 Take 0.5g of nitrogen-sulfur-doped graphene-supported coconut shell carbon from S2.3 and 0.5g of nickel-cobalt-iron LDH catalyst from S3.2, mix them in ultrapure water at a 1:1 ratio, sonicate at room temperature for 2h at an ultrasonic power of 230W, centrifuge and wash by first washing with deionized water 3 times and then with anhydrous ethanol 3 times, centrifuge at a speed of 4000 rad / min, and then dry at 80℃ to obtain the coconut shell carbon transition metal bifunctional catalyst (nitrogen-sulfur-doped graphene-supported coconut shell carbon nickel-cobalt-iron LDH bifunctional catalyst, denoted as Ni). 0.1 Co 0.8 Fe 0.1 / NSC bifunctional catalyst).

[0087] Comparative Example 1

[0088] The difference between this comparative example and Example 1 is that the coconut shell carbon is not doped with nitrogen and sulfur, and step S2, which involves graphene-modified coconut shell carbon doped with nitrogen and sulfur, is omitted. All other steps are the same as in Example 1, and the resulting target product is Ni. 0.1 Co 0.6 Fe 0.3 / C.

[0089] Comparative Example 2

[0090] The difference between this comparative example and Example 1 is that the molar ratio of nickel chloride, cobalt chloride, and ferric chloride in step S3.1 is 1:3:6. The other steps are the same as in Example 1, and the resulting target product is Ni. 0.1 Co 0.3 Fe 0.6 / NSC.

[0091] Experimental Example 1: OER electrochemical testing of materials using a three-electrode system

[0092] Examples 1-3 show the preparation of coconut shell carbon transition metal bifunctional catalysts (nitrogen-sulfur-doped graphene-coated coconut shell carbon supported nickel-cobalt-iron LDH bifunctional catalysts Ni). 0.1 Co 0.6 Fe 0.3 / NSC, Ni 0.1 Co 0.4 Fe 0.5 / NSC, Ni 0.1 Co 0.8 Fe 0.1 Ni prepared by / NSC) and Comparative Examples 1 and 2 0.1 Co 0.6 Fe 0.3 / C、Ni 0.1 Co 0.3 Fe 0.6 The / NSC catalyst was tested using a CHI760E electrochemical workstation at 25°C. A homogeneous mixture was prepared by sonicating 5 mg of catalyst, 1425 μL of anhydrous ethanol, and 75 μL of Nafion solution (5 wt%) for at least 30 min. 20 μL of this mixture was then dropped onto an L-shaped glassy carbon electrode for testing. A three-electrode system was formed, using the L-shaped glassy carbon electrode as the working electrode, a platinum wire electrode as the counter electrode, and a mercury / mercury oxide electrode (Hg / HgO) as the reference electrode. The tests were conducted in 1 M KOH electrolyte. The results are shown in Table 1.

[0093] Table 1 Electrochemical test results

[0094]

[0095] Table 1 shows that the coconut shell carbon transition metal bifunctional catalysts (nitrogen-sulfur-doped graphene-coated coconut shell carbon supported nickel-cobalt-iron LDH bifunctional catalysts) prepared in Examples 1-3 of this invention have good OER activity, and their OER polarization curves are shown in the figure. Figure 1 As shown. The OER activity of the catalyst prepared in Comparative Example 2 was lower than that in Example 1. This is because when the Fe content exceeds 50%, scanning electron microscopy shows that an LDH (layered double hydroxide) structure cannot be formed. The interlayer anions of the LDH structure are beneficial to the OER reaction and thus to the improvement of activity.

[0096] Experimental Example 2: ORR electrochemical testing of materials using a three-electrode system

[0097] Examples 1-3 show the preparation of coconut shell carbon transition metal bifunctional catalysts (nitrogen-sulfur-doped graphene-coated coconut shell carbon supported nickel-cobalt-iron LDH bifunctional catalysts Ni). 0.1 Co 0.6 Fe 0.3 / NSC, Ni 0.1 Co 0.4 Fe 0.5 / NSC, Ni 0.1 Co 0.8 Fe 0.1 Ni prepared by / NSC) and Comparative Examples 1 and 2 0.1 Co0.6 Fe 0.3 / C、Ni 0.1 Co 0.3 Fe 0.6 The / NSC catalyst was tested using a CHI760E electrochemical workstation at 25°C. A homogeneous mixture was prepared by mixing 5 mg of catalyst, 1425 μL of anhydrous ethanol, and 75 μL of Nafion solution (5 wt%), and ultrasonicating for at least 30 min. 20 μL of this mixture was then dropped onto a disc electrode for testing. A three-electrode system was formed, using the disc electrode as the working electrode, a platinum wire electrode as the counter electrode, and a mercury / mercury oxide electrode (Hg / HgO) as the reference electrode. The tests were conducted in 0.1 M KOH electrolyte, and the results are shown in Table 2.

[0098] Table 2 Electrochemical test results

[0099]

[0100] As shown in Table 2, the coconut shell carbon transition metal bifunctional catalysts (nitrogen-sulfur-doped graphene-coated coconut shell carbon supported nickel-cobalt-iron LDH bifunctional catalysts) prepared in Examples 1-3 of this invention exhibit good ORR activity. The ORR polarization curves of the bifunctional catalysts prepared in Examples 1-3 and Comparative Example 1 are shown below. Figure 2 As shown, the ORR activity of the catalyst prepared in Example 1 is significantly improved compared with that of Comparative Example 1 (coconut shell carbon without nitrogen and sulfur modification). This is because the highly electronegative N atoms can induce electron transfer of C atoms, thereby improving the adsorption capacity and conductivity of grapheneized coconut shell carbon. S doping can generate an uneven spin density distribution to regulate the electronic structure. Under the combined effect of N and S, the ORR catalytic activity of coconut shell carbon is improved.

[0101] Experimental Example 3: Performance Testing of Catalyst-Induced Zinc-Air Batteries

[0102] The coconut shell carbon transition metal bifunctional catalyst (nitrogen-sulfur-doped graphene-coated coconut shell carbon-supported nickel-cobalt-iron LDH bifunctional catalyst Ni) prepared in Example 1 was used. 0.1 Co 0.6 Fe 0.3 The / NSC) was used in practical application tests in zinc-air batteries (ZABs), with zinc sheet as the anode, and air electrode (foamed nickel, carbon paper coated with catalyst and air diffusion layer) as the cathode. The electrolyte was a mixed aqueous solution of 6M KOH + 0.2M Zn(OAc)2.

[0103] The results are as follows Figure 3 As shown, the coconut shell carbon transition metal bifunctional catalyst (nitrogen-sulfur-doped graphene-coated coconut shell carbon supported nickel-cobalt-iron LDH bifunctional catalyst Ni) prepared in Example 1 was used. 0.1 Co 0.6Fe 0.3 / NSC) assembled into a zinc-air battery, at 10mAcm -2 At current densities of [specific values], zinc-air batteries exhibit excellent charge-discharge cycle stability.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a coconut shell carbon transition metal bifunctional catalyst, characterized in that, Includes the following steps: S1. Preparation of graphene-modified coconut shell carbon Coconut shells are carbonized, mixed with concentrated sulfuric acid in an ice-water bath, and potassium permanganate is added until the solution turns brown. The reaction is carried out in a water bath at 30-40°C, and hydrogen peroxide is added until the solution turns pale golden yellow. The mixture is allowed to stand, the supernatant is removed, hydrochloric acid solution is added and mixed, centrifuged, the supernatant is removed, washed, and freeze-dried to obtain graphene-modified coconut shell carbon. S2, graphene-modified coconut shell carbon doped with nitrogen and sulfur Graphene-modified coconut shell carbon was dispersed in a solvent, silica was added, and the mixture was sonicated. After removing the solvent, a solid was obtained, which was then mixed and ground with nitrogen-containing and sulfur-containing compounds. After calcination in an inert gas atmosphere, the solid was soaked in a strong acid, centrifuged, washed, and dried to obtain nitrogen- and sulfur-doped graphene-modified coconut shell carbon. S3, hydrothermal method for producing nickel-cobalt-iron LDH catalyst Nickel chloride, cobalt chloride, ferric chloride and water are mixed to obtain metal solution A; sodium carbonate and water are mixed to obtain alkaline solution B; A and B are mixed and reacted at 100-150℃ for 15-20 hours, cooled, centrifuged and washed, and dried to obtain nickel-cobalt-iron LDH catalyst. Preparation of S4, NiCoFe / NSC bifunctional catalysts The nitrogen-sulfur-doped grapheneized coconut shell carbon in S2 and the nickel-cobalt-iron LDH catalyst in S3 were mixed in water, ultrasonicated, centrifuged and washed, and dried to obtain a coconut shell carbon transition metal bifunctional catalyst, denoted as NiCoFe / NSC.

2. The method for preparing a coconut shell carbon transition metal bifunctional catalyst according to claim 1, characterized in that, The molar ratio of nickel chloride, cobalt chloride, and ferric chloride in S3 is 1:4~8:1~5; the molar percentage of Fe in the total molar percentage of Ni, Co, and Fe is less than 50%.

3. The method for preparing a coconut shell carbon transition metal bifunctional catalyst according to claim 1, characterized in that, The coconut shell carbonization in S1 specifically involves drying the coconut shell, crushing it, and placing it in a tube furnace for carbonization under an argon atmosphere at 600°C; the concentration of the hydrochloric acid solution is 5 wt%; the freeze-drying specifically involves first freezing at -5 to -20°C for 5-8 hours, and then freeze-drying at -60 to -45°C for 36-42 hours.

4. The method for preparing a coconut shell carbon transition metal bifunctional catalyst according to claim 1, characterized in that, The solvent in S2 is 98-99.8 vol% ethanol, and the silica is hydrophilic nano-silica; the mass ratio of graphene-modified coconut shell carbon to hydrophilic nano-silica is 1:5; the solvent removal method is to perform secondary rotary evaporation under normal pressure and low pressure conditions, wherein the normal pressure rotary evaporation temperature is 70-80℃, the low pressure is 0.09 MPa, and the low pressure rotary evaporation temperature is 55-60℃; the strong acid is hydrofluoric acid.

5. The method for preparing a coconut shell carbon transition metal bifunctional catalyst according to claim 1, characterized in that, The inert gas in S2 is nitrogen, the nitrogen-containing compound is melamine, and the sulfur-containing compound is dibenzyl disulfide; the molar ratio of the solid, melamine, and dibenzyl disulfide is 6:5:5; the calcination procedure is as follows: heat to 300 °C, maintain for 10 min, then heat to 900 °C, and heat at 900 °C for 1 h, with a heating rate of 5 °C / min.

6. The method for preparing a coconut shell carbon transition metal bifunctional catalyst according to claim 1, characterized in that, The centrifugal cleaning process involves first washing with deionized water 2-4 times, then washing with anhydrous ethanol 2-4 times, with a centrifugal speed of 3000-4000 rad / min.

7. The method for preparing a coconut shell carbon transition metal bifunctional catalyst according to claim 1, characterized in that, The mass ratio of nitrogen-sulfur-doped graphene-modified coconut shell carbon to nickel-cobalt-iron LDH catalyst in S4 is 1:

1.

8. A coconut shell carbon transition metal bifunctional catalyst, characterized in that, The catalyst is prepared by the preparation method according to any one of claims 1-7.

9. The application of the coconut shell carbon transition metal bifunctional catalyst prepared by any one of claims 1-7 in zinc-air batteries.

10. A zinc-air battery, characterized in that, The anode is a zinc sheet, and the cathode is an air electrode. The air electrode includes nickel foam, carbon paper coated with the coconut shell carbon transition metal bifunctional catalyst prepared by any one of claims 1-7, and an air diffusion layer.

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