Nitrided coconut shell charcoal-vulcanized layered double hydroxide bifunctional catalyst as well as preparation method and application thereof

Abstract

The invention provides a nitrided coconut shell charcoal-vulcanized layered double hydroxide bifunctional catalyst as well as a preparation method and application thereof, and relates to the technical field of electrochemistry. The nitrided coconut shell charcoal-vulcanized layered double hydroxide bifunctional catalyst is prepared by the following steps: adding vulcanized layered double hydroxide and nitrided coconut shell charcoal in a mass ratio of (1-4): (1-4) into water, and carrying out ultrasonic treatment, centrifugation, washing and drying. The sulfurized layered double hydroxide in the bifunctional catalyst realizes excellent OER activity, pyridine N active sites are introduced into the nitrided coconut shell charcoal through KOH etching and melamine nitridation, meanwhile, the specific surface area and ORR activity of the coconut shell charcoal are improved, and the defect that a traditional carbon material is low in catalytic activity is overcome. The nitrided coconut shell charcoal and the sulfurized layered double hydroxide bifunctional catalyst take effect synergistically, and the problems that a traditional bifunctional catalyst is unbalanced in activity and short in cycle life are solved.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, and in particular to a bifunctional catalyst of nitrided coconut shell carbon-sulfurized layered double hydroxide, its preparation method, and its application. Background Technology

[0002] Zinc-air batteries are a type of energy storage device that uses oxygen (or pure oxygen) from the air as the positive electrode reactant, metallic zinc as the negative electrode, and an alkaline electrolyte as the electrolyte. This creates a redox environment within the battery, and the charging / discharging process is completed by the migration of OH- ions from the electrolyte between the electrodes to form a closed circuit. It is an extremely clean and novel energy storage device. Electrochemically rechargeable zinc-air batteries have attracted much attention due to their high energy density, high safety, environmental friendliness, and low cost.

[0003] In zinc-air battery systems, the catalyst is a key functional component of the air electrode. Its catalytic activity directly affects the kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), thus determining the battery's energy efficiency and cycle stability. Rechargeable zinc-air batteries have attracted widespread attention due to their advantages such as high theoretical energy density, good safety, environmental friendliness, and low cost.

[0004] The preparation techniques for bifunctional catalysts in existing technologies still face several challenges: 1. Most high-performance catalysts employ precious metal-based materials or involve complex multi-step synthesis processes, resulting in expensive raw materials, low yields, and significant waste, thus limiting their industrialization prospects. 2. Some composite catalysts suffer from problems such as weak interfacial bonding, insufficient electronic coupling, and limited interfacial charge transport, making it difficult to fully leverage the synergistic effect between different active components, leading to an activity mismatch between ORR / OER bifunctional catalysts. 3. At the high oxidation potential of OER, catalysts may undergo surface reconstruction, passivation, or loss of active components. Simultaneously, oxygen evolution bubble coverage increases interfacial mass transfer resistance, and structural instability ultimately leads to performance degradation.

[0005] Therefore, developing a catalyst that is simple to synthesize, low in cost, and possesses both high ORR / OER bifunctional activity and stable cycling is of great significance for the development of zinc-air batteries. Summary of the Invention

[0006] Therefore, this invention proposes a bifunctional catalyst of nitrided coconut shell carbon-sulfurized layered double hydroxide, its preparation method, and its application.

[0007] The technical solution of this invention is implemented as follows: A method for preparing a bifunctional catalyst of nitrided coconut shell carbon-sulfurized layered double hydroxide includes the following steps: adding sulfurized layered double hydroxide and nitrided coconut shell carbon in a mass ratio of 1-4:1-4 to water, ultrasonically treating, centrifuging, washing, and drying to obtain nitrided coconut shell carbon-sulfurized layered double hydroxide.

[0008] Furthermore, the total amount of the sulfurized layered double hydroxide and the nitrided coconut shell carbon has a solid-liquid ratio of 1:30-35 g / mL to water; the ultrasonic treatment is carried out at a temperature of 23-26℃ and a power of 200-230W for 2-3 hours.

[0009] Furthermore, the method for preparing the sulfide layered double hydroxide includes: (1) Add nickel salt, cobalt salt and iron salt to water to prepare metal salt solution, add Na2CO3 solution, stir, place in high pressure reactor for reaction, wash and dry to obtain layered double hydroxide; (2) Add the layered double hydroxide to Na2S solution, shake, let stand, wash and dry to obtain sulfide layered double hydroxide.

[0010] Further, in step (1), the mass ratio of the nickel salt, cobalt salt, and iron salt is 2.5-3.5:0.5-1.5:1; the concentration of the metal salt solution is 0.4-0.5 mol / L; the stirring is carried out at 400-500 rpm for 30-60 min; the volume ratio of the Na2CO3 solution to the metal salt solution is 0.8-1:1, and the concentration of the Na2CO3 solution is 1-1.2 mol / L; the reaction temperature in the high-pressure reactor is 100-120℃, and the reaction time is 18-20 h.

[0011] Furthermore, in step (2), the solid-liquid ratio of the layered double hydroxide to the Na2S solution is 1:20-30 g / mL; the concentration of the Na2S solution is 1-1.5 mol / L.

[0012] Furthermore, the preparation method of the nitrided coconut shell char includes: (1) Add coconut shell charcoal to a saturated KOH solution and stir, dry, calcine at high temperature under an inert atmosphere, cool with the furnace, add the product to an HCl solution and heat, filter and wash until neutral, centrifuge and dry to obtain activated coconut shell charcoal. (2) The activated coconut shell carbon and melamine were mixed and wet-milled, calcined at high temperature under an inert atmosphere, and cooled in the furnace to obtain nitrided coconut shell carbon.

[0013] In step (1), coconut shell carbon is etched in KOH to form a microporous-mesoporous multi-level structure, thereby increasing the specific surface area; in step (2), melamine decomposes into nitrogen free radicals, which react with carbon atoms on the surface of activated coconut shell carbon to form ORR active sites of pyridine N.

[0014] Furthermore, in step (1), the mass ratio of the coconut shell charcoal to the saturated KOH solution is 1:3-5; the high-temperature calcination under an inert atmosphere specifically involves heating to 750-800℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and maintaining it for 1-1.5h; the solid-liquid ratio of the product to the HCl solution is 1:10-20 g / mL; and the heating is performed at 85-95℃ for 30-60min.

[0015] Furthermore, in step (2), the mass ratio of the activated coconut shell charcoal to melamine is 1:2-5; the high-temperature calcination under an inert atmosphere is carried out under a nitrogen atmosphere, with the temperature increased to 900-950℃ at a rate of 5℃ / min and maintained for 2h.

[0016] A bifunctional catalyst of nitrided coconut shell carbon-sulfurized layered double hydroxide is prepared by any of the above preparation methods.

[0017] A bifunctional catalyst of nitrided coconut shell carbon-sulfurized layered double hydroxide, or a bifunctional catalyst of nitrided coconut shell carbon-sulfurized layered double hydroxide prepared by any of the above methods, is used in zinc-air batteries.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. The nitrided coconut shell carbon-sulfurized layered double hydroxide bifunctional catalyst prepared by this invention can achieve OER / ORR bifunctionality, has excellent electrochemical performance, stable structure, excellent cycle stability in zinc-air batteries, and low raw material cost. The preparation method is simple and easy to promote on a large scale.

[0019] 2. The sulfide-coated layered double hydroxide in the bifunctional catalyst of this invention achieves excellent OER activity. Nitrogenated coconut shell carbon, through KOH etching and melamine nitridation, introduces pyridine N active sites, simultaneously increasing the specific surface area and ORR activity of the coconut shell carbon, thus overcoming the low catalytic activity of traditional carbon materials. The synergistic effect of the nitrided coconut shell carbon-sulfide-coated layered double hydroxide bifunctional catalyst solves the problems of activity imbalance and short cycle life of traditional bifunctional catalysts. Attached Figure Description

[0020] Figure 1 The ORR performance diagram of the prepared catalyst is shown.

[0021] Figure 2 The diagram shows the OER performance of the prepared catalyst.

[0022] Figure 3 For 10 mA•cm 2 Graph of long-term battery cycle test at current density. Detailed Implementation

[0023] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0024] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0025] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0026] Preparation Example 1 Methods for preparing layered sulfur double hydroxides include: (1) NiCl2•6H2O, CoCl2•6H2O and FeCl3•6H2O in a mass ratio of 3:1:1 were added to water and mixed to prepare a 0.4 mol / L metal salt solution. A 1 mol / L Na2CO3 solution was added, with a volume ratio of Na2CO3 solution to metal salt solution of 0.8:1. The mixture was stirred at 500 rpm for 30 min, placed in a high-pressure reactor, and reacted at 100 °C for 20 h. After cooling to room temperature, the mixture was washed with deionized water and anhydrous ethanol, dried at 60 °C for 12 h, and ground to obtain a layered double hydroxide, denoted as LDH. (2) The layered double hydroxide was added to a 1 mol / L Na2S solution with a solid-liquid ratio of 1:30 g / mL, shaken, allowed to stand for 24 h, washed with deionized water, and dried under vacuum at 70 °C to obtain the sulfide layered double hydroxide, denoted as LDH-S.

[0027] Preparation Example 2 Methods for preparing nitrided coconut shell char include: (1) Add coconut shell charcoal with a mass ratio of 1:5 to a saturated KOH solution and stir and soak for 2 hours. Dry it and place it in a tube furnace. Under a nitrogen atmosphere, heat it to 800℃ at a heating rate of 5℃ / min and maintain it for 1 hour. Cool it with the furnace. Add the product to a 0.2mol / L HCl solution with a solid-liquid ratio of 1:10g / mL. Heat it at 90℃ for 30 minutes. Filter it, wash it until neutral, centrifuge and dry it to obtain activated coconut shell charcoal, which is denoted as CSC. (2) The activated coconut shell carbon and melamine were mixed at a mass ratio of 1:2, anhydrous ethanol was added and the mixture was ground until dry. The product was placed in a tube furnace and heated to 900°C at a heating rate of 5°C / min under a nitrogen atmosphere. The temperature was maintained for 2 hours and then cooled with the furnace to obtain nitrided coconut shell carbon, denoted as NCSC.

[0028] Example 1 A mixture of 0.015 g of sulfide layered double hydroxide and 0.015 g of nitrided coconut shell char (mass ratio 1:1) was added to 1 mL of water. The mixture was sonicated at 230 W for 2 h at 25 °C, centrifuged at 4000 rpm for 5 min, washed with anhydrous ethanol, and dried at 80 °C for 12 h to obtain nitrided coconut shell char-sulfide layered double hydroxide, denoted as NCSC. 0.5 / LDH-S 0.5 Bifunctional catalyst.

[0029] Example 2 A mixture of 0.024 g of sulfide layered double hydroxide and 0.006 g of nitrided coconut shell char (mass ratio 4:1) was added to 1 mL of water. The mixture was sonicated at 230 W for 2 h at 25 °C, centrifuged at 4000 rpm for 5 min, washed with anhydrous ethanol, and dried at 80 °C for 12 h to obtain nitrided coconut shell char-sulfide layered double hydroxide, denoted as NCSC. 0.2 / LDH-S 0.8 Bifunctional catalyst.

[0030] Example 3 A mixture of 0.006 g of sulfide layered double hydroxide and 0.024 g of nitrided coconut shell char (mass ratio 1:4) was added to 1 mL of water. The mixture was sonicated at 230 W for 2 h at 25 °C, centrifuged at 4000 rpm for 5 min, washed with anhydrous ethanol, and dried at 80 °C for 12 h to obtain nitrided coconut shell char-sulfide layered double hydroxide, denoted as NCSC. 0.8 / LDH-S 0.2 Bifunctional catalyst.

[0031] Comparative Example 1 The difference from Example 1 is that the sulfurized layered double hydroxide is replaced with a layered double hydroxide, i.e., NCSC is prepared. 0.5 / LDH 0.5 The bifunctional catalyst is otherwise consistent with Example 1.

[0032] Comparative Example 2 The difference from Example 1 is that nitrided coconut shell carbon is replaced with activated coconut shell carbon, i.e., CSC is prepared. 0.5 / LDH-S 0.5 The bifunctional catalyst is otherwise consistent with Example 1.

[0033] Comparative Example 3 The difference from Example 1 is that only coconut shell carbon nitride is used, i.e., an NCSC catalyst is prepared; otherwise, it is the same as Example 1.

[0034] Comparative Example 4 The difference from Example 1 is that only sulfide layered double hydroxides are prepared, i.e., LDH-S catalyst is prepared, while the rest is the same as Example 1.

[0035] Test Example 1 A slurry was prepared by mixing 5 mg of the catalysts prepared in Examples 1-3 and Comparative Examples 1-4, 2.5 mg of carbon black, and 1 mL of ethanol solution (ethanol:water volume ratio = 4:1). The slurry was ultrasonicated for 1.5 h, resulting in an ink-like consistency. A total of 20 μL of the slurry was measured and applied in two spin-coatings, 10 μL each time, with a loading area of ​​0.19625 cm². 2 .

[0036] 1. ORR Testing Method: Three-electrode system: a rotating disk is used as the working electrode, Hg / HgO as the reference electrode, and a platinum ring electrode as the counter electrode. The test is performed using a Chenhua workstation. A spin coater is used to coat the surface of the disk electrode with the catalyst, and after the catalyst is coated, the surface is wetted with deionized water.

[0037] Electrolyte: 0.1M KOH.

[0038] Oxygen activation CV: Before the test, oxygen was passed through for 30 minutes. Under the oxygen atmosphere, without rotation, the voltage was 0.2V → -0.8V for 10 cycles at 10mV / s. Nitrogen activation CV: Nitrogen gas was passed through for 20 minutes before the test. Under nitrogen atmosphere, without rotation, the voltage was 0.2V → -0.8V for 3 cycles at 10mV / s. LSV test: Under oxygen atmosphere, at 1600 rpm, within the range of 0.2→-0.8V (1.065-0.065V vs. RHE), 10mV / s.

[0039] The experimental results are shown in Table 1.

[0040] Table 1

[0041] As shown in Table 1, the catalyst prepared in Example 1 exhibits the best ORR performance. Data from Comparative Example 2 indicates that the ORR performance of the sample without nitridation of the coconut shell carbon decreases because the highly electronegative N atoms induce electron transfer from C atoms, enhancing the adsorption capacity and conductivity of the nitrided coconut shell carbon. (NCSC from Comparative Example 1...) 0.5 / LDH 0.5 Without vulcanization, the ORR performance of the samples did not change significantly.

[0042] 2. OER Testing Method: Three-electrode system: glassy carbon electrode as working electrode, Hg / HgO as reference electrode, and carbon rod electrode as counter electrode. Testing was performed using a Chenhua workstation. A spin coater was used to coat the catalyst onto the surface of the disc electrode. After catalyst coating, the surface was wetted with deionized water.

[0043] Nitrogen activation CV: Nitrogen gas was passed through for 30 minutes before the test. Under nitrogen atmosphere, the gas was circulated 20 times from 0.0V to 0.5V at 10mV / s. LSV test: Under nitrogen atmosphere, in the range of 0.2→0.8 V (1.124-1.724 V vs. RHE).

[0044] The experimental results are shown in Table 2.

[0045] Table 2

[0046] As shown in Table 2, the catalyst in Example 2 exhibits the best OER performance. Data from Comparative Example 1 indicates that the OER performance decreases when the layered double hydroxide is not sulfided. This is because sulfur doping can generate a non-uniform spin density distribution to modulate the electronic structure and enhance OER catalytic activity. (Comparative Example 2 CSC) 0.5 / LDH-S 0.5 Without nitriding, the OER performance decreases slightly.

[0047] 3. ΔE: Oxygen evolution reaction at a current density of 10 mA / cm² 2 The difference between the potential at time catalysis and the half-wave potential of oxygen reduction, ΔE, is used to measure a key indicator of a bifunctional catalyst. The smaller the ΔE, the better the bifunctional catalytic efficiency of the catalyst.

[0048] The results are shown in Table 3.

[0049] Table 3

[0050] As shown in Table 3, the catalyst prepared in Example 1 of this invention has the best bifunctional catalytic efficiency.

[0051] Test Example 2 The catalyst NCSC from Example 1 0.5 / LDH-S 0.5 The battery cycle test was conducted as follows: The assembly steps for zinc-air batteries (ZABs) include: during ZAB assembly, the anode and cathode are sequentially assembled into the battery template and then tightened and sealed with bolts. The battery structure from top to bottom is as follows: anode plate, Zn anode, anode separator, electrolyte flow channel plate, cathode separator, air cathode, and cathode plate. Finally, four long screws are used to evenly tighten the assembly to ensure consistency and good contact. The Zn anode uses a 2 mm thick zinc sheet, which is sanded before testing to remove the surface oxide layer and obtain a more uniform surface condition. The air cathode has a load of 1 mg / cm². 2 NCSC of Example 1 0.5 / LDH-S 0.5 The P2 substrate. After the battery is assembled, the battery is connected to the peristaltic pump line and run at a fixed speed for 5 minutes to allow the electrolyte (6 M KOH and 0.2 M (CH3COO)2Zn) to fully wet the electrodes and allow the system to reach a relatively stable working state. The peristaltic pump speed is set to n=20.0 rpm.

[0052] At 10 mA•cm 2 Long-term battery cycle testing was conducted at current density for 10 minutes per cycle (5 minutes each for charge and discharge). Results are shown in [link to relevant documentation]. Figure 3 ZABs achieved over 600 charge-discharge cycles, with a total runtime of up to 100 hours. This demonstrates exceptional longevity, thanks to NCSC... 0.5 / LDH-S 0.5 The electron redistribution of the composite structure endows the material with stable and efficient OER activity, reduces the oxidation potential during charging, and the porous carbon framework structure not only provides an ultra-high effective contact area, but its robust interfacial coupling also effectively prevents the physical shedding of active materials during long-term gas evolution, thereby ensuring the energy efficiency of the battery under high-current cycling. This invention's NCSC 0.5 / LDH-S 0.5 The catalyst exhibits excellent power output and ultra-long cycle life in actual ZABs, and has good practical application value.

[0053] 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 bifunctional catalyst of nitrided coconut shell carbon-sulfurized layered double hydroxide, characterized in that the steps include... include: A mixture of sulfide layered double hydroxide and nitrided coconut shell char in a mass ratio of 1-4:1-4 was added to water, ultrasonically treated, centrifuged, washed, and dried to obtain nitrided coconut shell char-sulfide layered double hydroxide.

2. The preparation method of the nitrided coconut shell carbon-sulfurized layered double hydroxide bifunctional catalyst as described in claim 1, characterized in that, The total amount of the sulfurized layered double hydroxide and the nitrided coconut shell carbon has a solid-liquid ratio of 1:30-35 g / mL to water; the ultrasonic treatment is carried out at a temperature of 23-26℃ and a power of 200-230W for 2-3 hours.

3. The preparation method of the nitrided coconut shell carbon-sulfurized layered double hydroxide bifunctional catalyst as described in claim 1, characterized in that, The method for preparing the sulfide layered double hydroxide includes: (1) Add nickel salt, cobalt salt and iron salt to water to prepare metal salt solution, add Na2CO3 solution, stir, place in high pressure reactor for reaction, wash and dry to obtain layered double hydroxide; (2) Add the layered double hydroxide to Na2S solution, shake, let stand, wash and dry to obtain sulfide layered double hydroxide.

4. The preparation method of the nitrided coconut shell carbon-sulfurized layered double hydroxide bifunctional catalyst as described in claim 3, characterized in that, In step (1), the mass ratio of the nickel salt, cobalt salt, and iron salt is 2.5-3.5:0.5-1.5:1; the concentration of the metal salt solution is 0.4-0.5 mol / L; the stirring is carried out at 400-500 rpm for 30-60 min; the volume ratio of the Na2CO3 solution to the metal salt solution is 0.8-1:1, and the concentration of the Na2CO3 solution is 1-1.2 mol / L; the reaction temperature in the high-pressure reactor is 100-120℃, and the reaction time is 18-20 h.

5. The preparation method of the nitrided coconut shell carbon-sulfurized layered double hydroxide bifunctional catalyst as described in claim 3, characterized in that, In step (2), the solid-liquid ratio of the layered double hydroxide to the Na2S solution is 1:20-30 g / mL; the concentration of the Na2S solution is 1-1.5 mol / L.

6. The preparation method of the nitrided coconut shell carbon-sulfurized layered double hydroxide bifunctional catalyst as described in claim 1, characterized in that, The method for preparing the nitrided coconut shell char includes: (1) Add coconut shell charcoal to a saturated KOH solution and stir, dry, calcine at high temperature under an inert atmosphere, cool with the furnace, add the product to an HCl solution and heat, filter and wash until neutral, centrifuge and dry to obtain activated coconut shell charcoal. (2) The activated coconut shell carbon and melamine were mixed and wet-milled, calcined at high temperature under an inert atmosphere, and cooled in the furnace to obtain nitrided coconut shell carbon.

7. The preparation method of the nitrided coconut shell carbon-sulfurized layered double hydroxide bifunctional catalyst as described in claim 6, characterized in that, In step (1), the mass ratio of the coconut shell charcoal to the saturated KOH solution is 1:3-5; the high-temperature calcination under an inert atmosphere specifically involves heating to 750-800℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and maintaining it for 1-1.5h; the solid-liquid ratio of the product to the HCl solution is 1:10-20g / mL; and the heating is performed at 85-95℃ for 30-60min.

8. The preparation method of the nitrided coconut shell carbon-sulfurized layered double hydroxide bifunctional catalyst as described in claim 6, characterized in that, In step (2), the mass ratio of activated coconut shell charcoal to melamine is 1:2-5; the high-temperature calcination under an inert atmosphere is carried out under a nitrogen atmosphere, with the temperature increased to 900-950℃ at a rate of 5℃ / min and maintained for 2h.

9. A bifunctional catalyst of nitrided coconut shell carbon and sulfide layered double hydroxide, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The nitrided coconut shell carbon-sulfurized layered double hydroxide bifunctional catalyst of claim 9 or the nitrided coconut shell carbon-sulfurized layered double hydroxide bifunctional catalyst prepared by any one of claims 1-8, is used in a zinc-air battery.

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