A method for preparing a bifunctional electrocatalyst

Abstract

The application provides a preparation method of a bifunctional electrocatalyst. The bifunctional electrocatalyst is obtained by mixing FeCl3.9H2O, CoCl2.6H2O and NiCl2.6H2O with black polypyrrole powder, freeze-drying and annealing at 800 DEG C. The catalyst prepared by the method has excellent catalytic performance in OER / ORR reactions, and the preparation process is simple, the requirements for equipment and process conditions are low, and the catalyst is conducive to popularization and application. The application is applied to a zinc-air battery as an air positive electrode, and has excellent charge-discharge performance and cycle stability.

Description

TECHNICAL FIELD

[0001] The present application relates to a rechargeable zinc-air battery, which is applied to the technical field of electrochemical energy storage devices. BACKGROUND

[0002] In order to ensure the continuity and sustainability of energy use, energy storage technology has become increasingly important. At present, the commonly used batteries in the field of energy storage include lead-acid batteries, nickel-based batteries, lithium-based batteries, flow batteries, sodium-sulfur batteries, etc., among which lithium-ion batteries have the largest commercial scale. However, the lack of energy density (actual value is 150-250 Wh kg -1 ) and high cost limit the further development and application of lithium-ion batteries. Rechargeable metal-air batteries (MAB) have become a promising energy storage system with relatively high theoretical energy density (1350 Wh kg -1 ), excellent safety and environmental friendliness, and therefore have attracted extensive attention and are considered to be the ultimate solution for future electric vehicles and portable electronic devices. According to the classification of metal anodes, metal-air batteries can be divided into several different types. Among them, lithium-air batteries and zinc-air batteries are the most promising. On the one hand, high-activity metal lithium, high cost and flammable organic electrolyte all hinder the commercial application of lithium-air batteries. On the other hand, zinc has good stability in aqueous solution and is the metal with the highest specific capacity and the most active electrodeposition from aqueous electrolyte. Therefore, rechargeable zinc-air batteries are a promising energy storage and production technology. In addition, the key to its development is to develop ORR / OER bifunctional electrocatalysts with low cost, high activity, strong stability and simple preparation process. Unfortunately, the slow kinetics and excessively high reaction barrier of ORR and OER reactions lead to the decrease of electrochemical reaction rate and energy conversion efficiency, which seriously hinders the development of clean energy conversion technology. For this reason, researchers have carried out extensive research on noble metal-based catalysts (such as Pt, Ru and Ir) because they can greatly improve the reaction rate of ORR / OER. However, the high cost and single selectivity of these noble metal-based catalysts limit their application in electrocatalysis.

[0003] Compared to noble metals, transition metals are relatively inexpensive and abundant on Earth. In recent years, transition metal-based materials such as Mn, Co, Ni, and Fe have exhibited excellent catalytic activity, achieving significant progress in electrocatalysis efficiency (OER) and reactive oxygen species (ORR). Transition metal-based catalysts possess many different crystal structures and active defect sites, thanks to the variable valence states of transition metals. Furthermore, a large amount of work has focused on carbon materials, including various modification strategies such as heteroatom doping, transition metal doping, and defect introduction, which have proven to be effective methods for improving electrocatalytic efficiency. Studies have shown that nitrogen doping can improve the electrical conductivity and catalytic activity of materials. Doped carbon materials have the advantages of large specific surface area and numerous pores, which facilitates the exposure of more catalytic active sites and improves the ion and electron transfer efficiency of the material. Therefore, carbon-based transition metal composites show great potential in the field of electrocatalysis due to their advantages of low cost, high catalytic activity, and good stability. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a bifunctional electrocatalyst. This invention exhibits excellent catalytic performance in the OER / ORR reaction, and its preparation process is simple, with low requirements for equipment and process conditions, thus facilitating widespread application. When used as an air cathode in zinc-air batteries, this invention demonstrates excellent charge-discharge performance and cycle stability.

[0005] A method for preparing a bifunctional electrocatalyst, characterized by the following preparation steps:

[0006] (1) Dissolve methyl orange in ultrapure water to form a clear orange solution, then add FeCl3 to the solution and stir for 30 minutes to produce flocculation and precipitation. The mass ratio of FeCl3 to methyl orange is 1:4~1:5.

[0007] (2) Stir with a magnetic stirrer in a water bath at a constant temperature of 25 °C, then add pyrrole monomer and stir, and seal with sealing film. After 20-30 hours, separate the black product, filter with hot deionized water and ethanol alternately until the filtrate is colorless and clear, and finally dry in a vacuum drying oven at 60-100 °C for 8-12 hours and collect the black powder. The mass ratio of pyrrole monomer to FeCl3 is 1:1.8-2.2.

[0008] (3) Add FeCl3·9H2O, CoCl2·6H2O and NiCl2·6H2O to deionized water in a mass ratio of 4-6:1-2:2-3 and stir in a water bath for 0.5-2 hours until completely dissolved. Then add the black powder obtained in step (2) to the above solution and ultrasonically disperse for 30-60 minutes. The amount of black powder added is 1-1.5 times the mass of FeCl3·9H2O.

[0009] (4) The solution obtained in step (3) is placed in a refrigerator for pre-cooling, then placed in a freeze dryer. After 60-80 hours, the product is collected, and then heated to 800°C in a tube furnace and kept warm for 2-3 hours under N2 atmosphere.

[0010] (5) After naturally cooling to room temperature, wash and filter with 1M HCl and deionized water until the filtrate remains neutral, and finally dry in a vacuum drying oven.

[0011] Drying yields the bifunctional electrocatalyst.

[0012] The temperature of the water bath in step (3) is 40-60℃.

[0013] The heating rate in step (4) is 3-5 °C / min.

[0014] The drying temperature in step (5) is 70-80 °C and the drying time is 8-12 hours.

[0015] Beneficial effects:

[0016] This invention designs a bifunctional electrocatalyst based on a ternary alloy-doped nitrogen-carbon hollow nanotube structure (FeCoNi@hNCTs). First, PPy-NTs were prepared using a self-degradation template method. Due to their unique hollow structure and abundant nitrogen content, they are an ideal support for composite catalysts. During pyrolysis, the precursors obtained by freeze-drying iron, cobalt, nickel salts, and polypyrrole were annealed at 800°C, while the PPy-NTs substrate carbonized to form hollow nitrogen-doped carbon nanotubes. Due to the hollow tubular framework of PPy-NTs, the FeCoNi alloy is uniformly embedded within the carbon substrate after pyrolysis.

[0017] On the one hand, high-temperature annealing of the carbon matrix increases the degree of graphitization, reduces charge transfer resistance, and promotes electron transfer. On the other hand, the interconnected hollow tubular structure greatly improves the transport efficiency of ions and electrons and promotes oxygen diffusion; in addition, its unique tubular structure provides a large specific surface area, which is beneficial for exposing more active sites. Detailed Implementation

[0018] A method for preparing a bifunctional electrocatalyst, characterized by the following preparation steps:

[0019] (1) Dissolve methyl orange in ultrapure water to form a clear orange solution, then add FeCl3 to the solution and stir for 30 minutes to produce flocculation and precipitation. The mass ratio of FeCl3 to methyl orange is 1:4~1:5.

[0020] (2) Stir with a magnetic stirrer in a water bath at a constant temperature of 25 °C, then add pyrrole monomer and stir, and seal with sealing film. After 20-30 hours, separate the black product, filter with hot deionized water and ethanol alternately until the filtrate is colorless and clear, and finally dry in a vacuum drying oven at 60-100 °C for 8-12 hours and collect the black powder. The mass ratio of pyrrole monomer to FeCl3 is 1:1.8-2.2.

[0021] (3) Add FeCl3·9H2O, CoCl2·6H2O and NiCl2·6H2O to deionized water in a mass ratio of 4-6:1-2:2-3 and stir in a water bath for 0.5-2 hours until completely dissolved. Then add the black powder obtained in step (2) to the above solution and ultrasonically disperse for 30-60 minutes. The amount of black powder added is 1-1.5 times the mass of FeCl3·9H2O.

[0022] (4) The solution obtained in step (3) is placed in a refrigerator for pre-cooling, then placed in a freeze dryer. After 60-80 hours, the product is collected, and then heated to 800°C in a tube furnace and kept warm for 2-3 hours under N2 atmosphere.

[0023] (5) After naturally cooling to room temperature, wash and filter with 1M HCl and deionized water until the filtrate remains neutral, and finally dry in a vacuum drying oven.

[0024] Drying yields the bifunctional electrocatalyst.

[0025] The temperature of the water bath in step (3) is 40-60℃.

[0026] The heating rate in step (4) is 3-5 °C / min.

[0027] The drying temperature in step (5) is 70-80 °C and the drying time is 8-12 hours.

[0028] The catalyst prepared by this method was tested on the RRDE-3A device, and the overpotential of FeCoNi@hNCTs was found to be much smaller than that of commercial noble metal catalysts (RuO2), confirming its excellent OER performance. In addition, the test showed that the half-wave potential of the catalyst was close to that of commercial Pt / C, indicating that FeCoNi@hNCTs has ORR performance comparable to Pt / C.

[0029] Example

[0030] Example 1: 0.1964 g of methyl orange was dissolved in 120 mL of ultrapure water to form a clear orange solution. Then, 0.972 g of FeCl3 was added to the solution and stirred for 30 minutes, resulting in flocculation and precipitation. The color of the reaction system changed from clear orange to opaque dark red. The mixture was stirred with a magnetic stirrer in a water bath at a constant temperature of 25 °C. 420 μL of pyrrole monomer was then added and stirred, and the mixture was sealed with a sealing film. After 24 hours, the black product was separated and filtered alternately with hot deionized water and ethanol until the filtrate was colorless and clear. Finally, the filtrate was dried in a vacuum drying oven at 80 °C for 10 hours to obtain black polypyrrole powder. At room temperature, 173 mg of FeCl3·9H2O, 38 mg of CoCl2·6H2O, and 76 mg of NiCl2·6H2O were dissolved in 50 mL of deionized water and stirred at a constant temperature of 50 °C for 1 hour. Then, 200 mg of black polypyrrole powder was added to the above solution and sonicated for 30 minutes until the black powder was completely dispersed. The mixture was then pre-cooled in a refrigerator until frozen, and then placed in a freeze dryer at -50 °C for 72 hours to obtain a yellow flocculent substance. The mixture was then simply ground and kept at 800 °C for 2 hours under a nitrogen atmosphere. After naturally cooling to room temperature, it was washed with 1M HCl and repeatedly filtered with deionized water until the filtrate remained neutral. Finally, the product was dried in a vacuum drying oven at 80 °C for 10 hours and then collected.

[0031] ORR performance was tested on the RRDE-3A device, revealing an initial potential of 0.9 V and a half-wave potential of 0.82 V, close to the 0.84 V of commercial Pt / C catalysts. Chronoamperometry showed that the current remained above 90% after 10,000 s, demonstrating the catalyst's excellent stability. OER performance testing showed that the catalyst's overpotential was significantly lower than that of commercial noble metal catalysts (RuO2), and the smaller Tafel slope confirmed its high OER activity.

[0032] Example 2: 0.1964 g of methyl orange was dissolved in 120 mL of ultrapure water to form a clear orange solution. Then, 0.972 g of FeCl3 was added to the solution and stirred for 30 minutes, resulting in flocculation and precipitation. The color of the reaction system changed from clear orange to opaque dark red. The mixture was stirred with a magnetic stirrer in a water bath at a constant temperature of 25 °C. 420 μL of pyrrole monomer was then added and stirred, and the mixture was sealed with a sealing film. After 24 hours, the black product was separated and filtered alternately with hot deionized water and ethanol until the filtrate was colorless and clear. Finally, the filtrate was dried in a vacuum drying oven at 80 °C for 10 hours to obtain black polypyrrole powder. At room temperature, 140 mg of FeCl3·9H2O, 62 mg of CoCl2·6H2O, and 62 mg of NiCl2·6H2O were dissolved in 50 mL of deionized water and stirred at a constant temperature of 50 °C for 1 hour. Then, 200 mg of polypyrrole powder was added to the above solution and sonicated for 30 minutes until the black powder was completely dispersed. The mixture was then pre-cooled in a refrigerator until frozen, and then placed in a freeze dryer at -50 °C for 72 hours to obtain a yellow flocculent substance. The mixture was then simply ground and kept at 800 °C for 2 hours under a nitrogen atmosphere. After naturally cooling to room temperature, it was washed with 1M HCl and repeatedly filtered with deionized water until the filtrate remained neutral. Finally, the product was dried in a vacuum drying oven at 80 °C for 10 hours and then collected.

[0033] The catalyst activity was tested on the RRDE-3A device, and the overpotential was found to be 0.28 V, which is lower than that of commercial noble metal catalysts (RuO2), confirming its excellent OER performance. In addition, the test showed that the half-wave potential of the catalyst is close to that of commercial Pt / C, indicating that the catalyst has ORR performance comparable to Pt / C.

[0034] Comparative example: 200 mg CNT was dispersed in 200 mL of a mixed solution of HNO3 and H2O2 (V HNO3 V H2O2The mixture was stirred continuously at 60 °C for 5 h, washed with deionized water, filtered, and then vacuum dried to obtain surface-functionalized CNTs (F-CNTs). 100 mg of F-CNTs were then dispersed in 25 mL of dimethylformamide (DMF), followed by the addition of a FePc-CoPc / DMF solution (50 mg FePc and 50 mg CoPc dispersed in 50 mL DMF). After stirring for 6 hours, 3.0 g of melamine was added to the mixture. The mixture was then washed with DMF and vacuum dried to obtain FePc-CoPc and melamine-functionalized carbon nanotubes. Finally, the mixture was calcined at 420 °C for 2 h in a N2 atmosphere, then heated to 750 °C and held for 1 h. After cooling, impurities and residual FePc-CoPc and melamine were removed with 0.5 M H2SO4. The molar ratio of Fe-Co nanoparticles was approximately 1.2:1, denoted as Fe1.2Co@NC / NCNTs.

[0035] The ORR performance of the catalyst was tested on the RRDE-3A device, and the onset potential was found to be 0.84 V, with a half-wave potential of 0.81 V. The OER performance test showed that the overpotential of the catalyst was 0.35 V, which means that the bifunctional activity of the catalyst is obviously lower than that of FeCoNi@hNCTs.

Claims

1. A method for preparing a bifunctional electrocatalyst for zinc-air batteries, characterized in that... The preparation steps are as follows: (1) Dissolve methyl orange in ultrapure water to form a clear orange solution, then add FeCl3 to the solution and stir for 30 minutes to produce flocculation and precipitation. The mass ratio of FeCl3 to methyl orange is 1:4~1:

5. (2) Stir with a magnetic stirrer in a water bath at a constant temperature of 25 °C, then add pyrrole monomer and stir, and seal with sealing film. After 20-30 hours, separate the black product, filter with hot deionized water and ethanol alternately until the filtrate is colorless and clear, and finally dry in a vacuum drying oven at 60-100 °C for 8-12 hours and collect the black powder, wherein the mass ratio of pyrrole monomer to FeCl3 is 1:1.8-2.2; (3) Add FeCl3·9H2O, CoCl2·6H2O and NiCl2·6H2O to deionized water in a mass ratio of 4-6:1-2:2-3 and stir in a water bath for 0.5-2 hours until completely dissolved. Then add the black powder obtained in step (2) to the above solution and ultrasonically disperse for 30-60 minutes. The amount of black powder added is 1-1.5 times the mass of FeCl3·9H2O. (4) The solution obtained in step (3) is placed in a refrigerator for pre-cooling, then placed in a freeze dryer. After 60-80 hours, the product is collected, and then heated to 800°C in a tube furnace and kept warm for 2-3 hours under N2 atmosphere. (5) After naturally cooling to room temperature, wash and filter with 1M HCl and deionized water until the filtrate remains neutral, and finally dry in a vacuum drying oven. Drying yields the bifunctional electrocatalyst; In step (3), the water bath temperature is 40-60°C; in step (4), the heating rate is 3-5°C / min; and in step (5), the drying temperature is 70-80°C and the drying time is 8-12 hours.