Carbon quantum dot nickel-iron nanocomposite electrocatalyst and its preparation method and application

Abstract

The present invention belongs to the technical field of electrocatalytic materials, specifically, a carbon quantum dot nickel-iron nanocomposite electrocatalyst and its preparation method and application. The present invention mixes a carbon source in water, adopts a hydrothermal method to prepare carbon quantum dots, and then disperses the carbon quantum dots, soluble nickel salts and soluble iron salts in water together, evaporates the solvent, and adopts a high-temperature reduction method to prepare a carbon quantum dot nickel-iron nanocomposite electrocatalyst. In the carbon quantum dot nickel-iron nanocomposite electrocatalyst of the present invention, the carbon quantum dots and the nickel-iron nanoparticles are in a stacking mode, and the nickel-iron nanoparticles are wrapped in a carbon layer formed by the carbon quantum dots, which overcomes the technical defects of the prior art that the nickel-iron nanoparticles are easy to agglomerate and have poor stability in alkaline media.

Description

Technical Field

[0001] The invention belongs to the technical field of electrocatalytic materials, and specifically relates to a carbon quantum dot nickel-iron nanocomposite electrocatalyst and a preparation method and application thereof. Background Art

[0002] Zinc-air battery is a battery that generates electricity through the electrochemical reaction between oxygen and zinc. It has the advantages of high energy density, low cost, environmental protection and high safety, and is widely used in electric vehicles and portable electronic devices. However, its commercial application still faces challenges such as insufficient catalytic activity, poor durability and high cost, which mainly focus on the performance of electrocatalysts.

[0003] Existing electrocatalysts mainly include precious metal-based catalysts and non-precious metal-based catalysts. Precious metal-based catalysts, such as platinum-based catalysts, show excellent catalytic activity, but their large-scale application is limited due to their high price, limited resources and poor durability. In contrast, non-precious metal-based catalysts, especially transition metals and their oxides, carbides and sulfides, have become a research hotspot due to their low cost and abundant resources. However, these non-precious metal-based catalysts usually have the problems of low catalytic activity and poor stability, making it difficult to replace precious metal-based catalysts in practical applications.

[0004] Among many non-precious metal-based catalysts, bimetallic nanomaterials show better catalytic performance than single metals due to their synergistic effect. Bimetallic nanomaterials optimize the electronic structure and improve catalytic activity and stability by adjusting the interaction between metals. Common bimetallic nanomaterials include nickel-cobalt nanomaterials, iron-cobalt nanomaterials and nickel-iron nanomaterials.

[0005] The prior art uses a high-temperature reduction method to prepare nickel-iron nanoparticles. Since the preparation process requires a treatment condition of ≥900°C and the steps are complicated, the reaction conditions are harsh and the energy consumption is high. At the same time, the obtained nickel-iron nanoparticles have technical defects, which are specifically manifested in:

[0006] On the one hand, nickel-iron nanoparticles are prone to particle agglomeration and uneven size during the preparation process, which leads to a reduction in their specific surface area and thus a reduction in catalytic activity. Therefore, although they have good catalytic performance in theory, in practical applications, due to particle agglomeration, the number of active sites is reduced, resulting in a significant reduction in catalytic performance.

[0007] On the other hand, the obtained nickel-iron nanoparticles have poor stability in alkaline media and are prone to dissolution and passivation, resulting in poor performance in long-term use. This is mainly because nickel and iron are easily oxidized at high potentials to generate nickel oxide and iron oxide, which cover the surface of nickel-iron nanoparticles and hinder the electrochemical reaction. Summary of the invention

[0008] In order to solve the deficiencies of the above-mentioned prior art, the present invention provides a carbon quantum dot nickel-iron nanocomposite electrocatalyst and a preparation method and application thereof. The present invention first prepares carbon quantum dots, then mixes the carbon quantum dots with a soluble nickel salt and a soluble iron salt in water, and obtains a carbon quantum dot nickel-iron nanocomposite electrocatalyst by evaporating the solvent and reducing it at high temperature. Compared with the prior art, the method of the present invention reduces the preparation steps, and effectively reduces the temperature of high-temperature reduction, thereby reducing energy consumption. In the carbon quantum dot nickel-iron nanocomposite electrocatalyst obtained by the method of the present invention, the carbon quantum dots and the nickel-iron nanoparticles are in a stacking mode, and the nickel-iron nanoparticles are wrapped in a carbon layer formed by the aggregation of the carbon quantum dots, which overcomes the technical defects of the prior art that the nickel-iron nanoparticles are easy to agglomerate and have poor stability in alkaline media.

[0009] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0010] The preparation method of the carbon quantum dot nickel-iron nanocomposite electrocatalyst comprises the following steps:

[0011] S1. Mix the carbon source in water and prepare carbon quantum dots using a hydrothermal method.

[0012] S2. Disperse carbon quantum dots, soluble nickel salt and soluble iron salt together in water. The carbon quantum dots form stable coordination bonds with nickel ions and iron ions. After evaporating the solvent, high-temperature reduction is carried out at 300°C to 600°C in an inert atmosphere. While obtaining nickel-iron nanoparticles, the carbon quantum dots aggregate with each other and form a carbon layer. The carbon layer wraps the nickel-iron nanoparticles to obtain a carbon quantum dot nickel-iron nanocomposite electrocatalyst.

[0013] Preferably, the molar ratio of nickel ions in soluble nickel salts to iron ions in soluble iron salts is 0.83-1.17:0.5-0.73. The advantages of this ratio are: a. Improving electrocatalytic performance: By regulating the synergistic effect of nickel ions and iron ions, the electronic structure is optimized, the active sites are increased, and the efficiency of oxygen reduction reaction and oxygen evolution reaction is improved; b. Enhanced stability: In alkaline media, an appropriate nickel-iron molar ratio can reduce the risk of particle agglomeration and form a more stable composite material; c. Experimental verification: Through experimental comparison, nickel ions and iron ions in the range of 0.83-1.17:0.5-0.73 make the carbon quantum dot nickel-iron nanocomposite electrocatalyst have the best initial potential, half-wave potential and Tafel slope, and the performance decay is small in long-term electrochemical tests.

[0014] Preferably, in the carbon quantum dot nickel-iron nanocomposite electrocatalyst, the mass ratio of carbon quantum dots to nickel-iron nanoparticles is 1:2-5. When the ratio is higher than 1:5, the carbon quantum dot ratio is too high, which may lead to the following defects: a. Reduced active sites: There are too many carbon quantum dots, and the distribution density of nickel-iron nanoparticles per unit mass of carbon quantum dot nickel-iron nanocomposite electrocatalyst decreases, resulting in insufficient active sites, which reduces the oxygen reduction reaction and oxygen evolution reaction performance of the carbon quantum dot nickel-iron nanocomposite electrocatalyst, and reduces the electrochemical reaction efficiency; b. Reduced conductivity: Although carbon quantum dots have a certain conductivity, too many carbon quantum dots may reduce the effectiveness of the overall conductive network, which in turn deteriorates the charge transfer efficiency and limits the electrocatalytic performance; c. Reduced stability of the carbon quantum dot nickel-iron nanocomposite electrocatalyst: The number of nickel-iron nanoparticles is insufficient, resulting in the conductive network of the carbon quantum dots being insufficient to support long-term electrocatalytic reactions, so that in the cycle test, the catalyst performance decays quickly and the durability is poor. When it is lower than 1:2, the proportion of carbon quantum dots is too low, which may lead to the following defects: a. Particle agglomeration: The proportion of nickel-iron nanoparticles is too high, and there is a lack of sufficient carbon quantum dots to coat the particles, resulting in agglomeration between particles, reducing the specific surface area, reducing active sites, and decreasing catalytic efficiency; b. Poor stability: The proportion of carbon quantum dots is insufficient, and the stability of nickel-iron nanoparticles in alkaline media cannot be effectively protected, making the carbon quantum dot nickel-iron nanocomposite electrocatalyst easy to oxidize or passivate, and the long-term performance is poor; c. Insufficient conductivity: Carbon quantum dots have excellent conductivity and dispersibility. If the proportion is too low, the electron transport ability of the carbon quantum dot nickel-iron nanocomposite electrocatalyst will be weakened, the charge transfer in the electrocatalytic reaction will be hindered, and the performance of the carbon quantum dot nickel-iron nanocomposite electrocatalyst will be limited.

[0015] When the mass ratio of carbon quantum dots to nickel-iron nanoparticles is in the range of 1:2~5, the synergistic effect of carbon quantum dots and nickel-iron nanoparticles reaches the best, which is specifically reflected in: a. Activity: carbon quantum dots provide uniformly dispersed nickel-iron nanoparticles and increase catalytic active sites; b. Stability: the protective effect of carbon quantum dots avoids particle agglomeration and enhances durability in alkaline media; c. Conductivity: carbon quantum dots provide an excellent electron conduction network and improve the charge transfer efficiency.

[0016] Preferably, the heating time for high temperature reduction is 1 h to 4 h.

[0017] Preferably, the carbon source is selected from glucose, sucrose, polyethylene glycol, glycerol or fructose.

[0018] Preferably, the conditions of the hydrothermal method are: heating at 120° C. to 200° C. for 1 h to 3 h.

[0019] Preferably, the mass ratio of carbon source to water is 8:55~75. The amount of water has an important influence on the size and distribution of carbon quantum dots when preparing them. When the amount of water is relatively large, the solubility of the carbon source in water increases, and the formed solution is relatively dilute, which usually produces smaller and evenly distributed carbon quantum dots, but the reaction rate is slow, which may affect the generation efficiency and yield. When the amount of water is relatively small, the concentration of the formed solution increases, resulting in an accelerated nucleation rate of carbon quantum dots, generating larger carbon quantum dots, but the size distribution is uneven, and the reaction rate is accelerated but may be over-concentrated, resulting in a decrease in the quality of carbon quantum dots. Therefore, maintaining the mass ratio of carbon source to water at 8:65±10 is crucial to obtaining carbon quantum dots of moderate size and uniform distribution.

[0020] The present invention also protects the carbon quantum dot nickel-iron nanocomposite electrocatalyst prepared by the above preparation method. In the carbon quantum dot nickel-iron nanocomposite electrocatalyst, the carbon quantum dots and nickel-iron nanoparticles are in a stacking mode, and the nickel-iron nanoparticles are wrapped in a carbon layer formed by the carbon quantum dots.

[0021] The present invention also protects the use of the carbon quantum dot nickel-iron nanocomposite electrocatalyst in the preparation of a cathode catalyst for a zinc-air battery.

[0022] Preferably, when the carbon quantum dot nickel-iron nanocomposite electrocatalyst is used as a cathode catalyst for a zinc-air battery, it promotes both the oxygen reduction reaction and the oxygen evolution reaction.

[0023] Preferably, the application method is:

[0024] A carbon quantum dot nickel-iron nanocomposite electrocatalyst is used as a cathode and a zinc sheet is used as an anode. One end of the cathode and the anode are immersed in an electrolyte together, and the other end is electrically connected; wherein the electrolyte contains zinc ions.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention mixes carbon quantum dots, soluble nickel salt and soluble iron salt in water, evaporates the solvent, and then adopts a high-temperature reduction method to prepare a carbon quantum dot nickel-iron nanocomposite electrocatalyst. The carbon quantum dot nickel-iron nanocomposite electrocatalyst prepared by the method of the present invention is a composite electrocatalyst based on carbon quantum dots and nickel-iron nanoparticles.

[0027] Compared with the prior art methods, firstly, the present invention introduces carbon quantum dots with rich functional groups, optimizes the mass ratio of carbon quantum dots to nickel-iron nanoparticles to 1:2~5, and forms stable coordination bonds with nickel ions and iron ions to inhibit particle agglomeration and enhance the dispersibility of nickel ions and iron ions. Secondly, by optimizing the molar ratio of nickel ions and iron ions to 0.83~1.17:0.5~0.73, the full reaction of metal ions is ensured and the generation of by-products is reduced. In addition, by combining the hydrothermal method with the high-temperature reduction method, uniformly dispersed carbon quantum dots are first obtained under hydrothermal conditions, and then high-temperature reduction is carried out at 300℃~600℃ under an inert atmosphere to avoid the generation of oxidative impurities while improving the uniformity of nickel-iron nanoparticles. These measures significantly improve the purity of carbon quantum dot nickel-iron nanocomposite electrocatalysts, providing reliable support for the preparation of efficient and stable electrocatalysts.

[0028] Compared with the nickel-iron nanoparticles of the prior art, the carbon quantum dot nickel-iron nanocomposite prepared by the present invention overcomes the problem of poor stability of nickel-iron nanoparticles in alkaline media due to the introduction of carbon quantum dots and their synergistic effect with nickel-iron nanoparticles. Specifically, the carbon layer formed by the mutual aggregation of carbon quantum dots is evenly coated around the nickel-iron nanoparticles, effectively isolating the oxidizing components in the alkaline medium, reducing the dissolution and passivation of the nickel-iron nanoparticles, thereby significantly improving the stability and durability of the carbon quantum dot nickel-iron nanocomposite electrocatalyst. This structure also optimizes electron transmission and further enhances the performance of the carbon quantum dot nickel-iron nanocomposite electrocatalyst in electrochemical reactions.

[0029] In addition, compared with the preparation conditions of conventional nickel-iron nanoparticles using a high-temperature reduction method, the preparation temperature of nickel-iron nanoparticles in the prior art is ≥900°C, while the preparation temperature of the carbon quantum dot nickel-iron nanocomposite electrocatalyst in the present application is 300°C~600°C, which effectively overcomes the harsh conditions and high energy consumption of traditional nickel-iron nanoparticle preparation and is more conducive to large-scale production.

[0030] 2. In the carbon quantum dot nickel-iron nanocomposite electrocatalyst obtained by the method of the present invention, the carbon quantum dots have the characteristics of small size and large specific surface area, which increases the number of active sites of the electrochemical reaction and significantly improves the catalytic efficiency. At the same time, the excellent conductivity and uniform dispersion of the carbon quantum dots are conducive to charge transfer; because the surface of the carbon quantum dots contains rich functional groups, it can form a stable coordination bond with the metal ions of the nickel-iron nanoparticles, which not only effectively prevents the agglomeration of the nickel-iron nanoparticles, but also enhances the stability and activity of the carbon quantum dot nickel-iron nanocomposite electrocatalyst; in addition, the carbon quantum dots also have good conductivity and adjustable surface properties, showing excellent electrochemical performance. Nickel-iron nanoparticles show significant advantages in enhancing catalytic activity, improving stability and optimizing electronic structure due to their synergistic effect.

[0031] 3. In the application test of zinc-air batteries, the carbon quantum dot nickel-iron nanocomposite electrocatalyst of the present invention showed significant performance improvement compared with the carbon quantum dot nickel-cobalt nanocomposite electrocatalyst and the carbon quantum dot iron-cobalt nanocomposite electrocatalyst, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a transmission electron microscope image of the carbon quantum dots of Example 1.

[0033] Figure 2 This is a scanning electron microscope image of the carbon quantum dot nickel-iron nanocomposite electrocatalyst of Example 1.

[0034] Figure 3 This is a high-resolution transmission electron micrograph of the carbon quantum dot nickel-iron nanocomposite electrocatalyst of Example 1.

[0035] Figure 4 This is the element distribution diagram of the carbon quantum dot nickel-iron nanocomposite electrocatalyst of Example 1.

[0036] Figure 5 The LSV curves are of the carbon quantum dots of Example 1, the carbon quantum dot nickel-iron nanocomposite electrocatalyst of Example 1, the carbon quantum dot nickel nanocomposite of Comparative Example 1, and the carbon quantum dot iron nanocomposite of Comparative Example 2.

[0037] Figure 6 The Tafel slope graphs are of the carbon quantum dots of Example 1, the carbon quantum dot nickel-iron nanocomposite electrocatalyst of Example 1, the carbon quantum dot nickel nanocomposite of Comparative Example 1, the carbon quantum dot iron nanocomposite of Comparative Example 2, and commercial Pt / C.

[0038] Figure 7 The OER polarization curves are of the carbon quantum dots of Example 1, the carbon quantum dot nickel-iron nanocomposite electrocatalyst of Example 1, the carbon quantum dot nickel nanocomposite of Comparative Example 1, the carbon quantum dot iron nanocomposite of Comparative Example 2, and commercial Pt / C.

[0039] Figure 8 This is a diagram of the open circuit voltage of a zinc-air battery assembled using the carbon quantum dot nickel-iron nanocomposite electrocatalyst of Example 1. DETAILED DESCRIPTION

[0040] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific implementation. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0041] The present invention proposes a carbon quantum dot nickel-iron nanocomposite electrocatalyst. The carbon quantum dot nickel-iron nanocomposite electrocatalyst is a composite electrocatalyst based on carbon quantum dots and nickel-iron nanoparticles. By introducing carbon quantum dots, the agglomeration of nickel-iron nanoparticles can be effectively prevented, and the specific surface area and conductivity of the carbon quantum dot nickel-iron nanocomposite electrocatalyst can be improved. At the same time, since the carbon quantum dots aggregate to form a carbon layer and coat the outside of the nickel-iron nanoparticles during the high-temperature reduction process, the stability of the carbon quantum dot nickel-iron nanocomposite electrocatalyst in an alkaline medium is enhanced.

[0042] In the present invention, carbon quantum dots are denoted as CQDs, oxygen evolution reaction is denoted as OER, oxygen reduction reaction is denoted as ORR, E 1 / 2 is half-wave potential, LSV is linear voltammetry, and Koutechy-Levich curve is abbreviated as KL curve. The technical solution of the present invention is studied by using embodiments and comparative examples below. The specific research methods and results are as follows:

[0043] Example 1

[0044] The preparation method of the carbon quantum dot nickel-iron nanocomposite electrocatalyst comprises the following steps:

[0045] S1. Preparation of carbon quantum dots:

[0046] 8 g of glucose was added to 65 mL of deionized water and stirred for 10 min to obtain a glucose solution. The glucose solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave. The stainless steel autoclave was then placed in an oven and heated at 160 ° C for 3 h, naturally cooled to room temperature, and then freeze-dried at -65 ° C to obtain carbon quantum dots.

[0047] Preparation of S2, C-NiFe electrocatalyst:

[0048] 0.15 g of carbon quantum dots were mixed with 80 mL of deionized water and ultrasonically treated for 10 min to obtain a carbon quantum dot solution. 0.6 g of NiCl was added to the carbon quantum dot solution. 2 6H 2 O and 0.6 g FeCl 3 9H 2 O, at this time NiCl 2 6H 2 Ni ions and FeCl in O 3 9H 2 The molar ratio of iron ions in O is 0.0025:0.0022, the molar ratio of nickel ions in the soluble nickel salt to iron ions in the soluble iron salt is 0.83:0.73, and the mixture is stirred for 30 minutes to obtain a precursor.

[0049] The precursor was placed in a water bath at 80°C under strong magnetic stirring to evaporate the solvent, and then placed in a horizontal tube furnace and heated at 480°C for 2 hours in a nitrogen atmosphere to obtain a carbon quantum dot nickel-iron nanocomposite electrocatalyst. At this time, the mass ratio of carbon quantum dots to nickel-iron nanoparticles was 1:5, recorded as C-NiFe electrocatalyst.

[0050] Example 2

[0051] The preparation method of the carbon quantum dot nickel-iron nanocomposite electrocatalyst comprises the following steps:

[0052] S1. Preparation of carbon quantum dots:

[0053] 8 g of glucose was added to 55 mL of deionized water and stirred continuously for 10 min to obtain a glucose solution. The glucose solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave. The stainless steel autoclave was then placed in an oven and heated at 120 °C for 3 h, naturally cooled to room temperature, and then freeze-dried at -65 °C to obtain carbon quantum dots.

[0054] Preparation of S2, C-NiFe electrocatalyst:

[0055] 2.06 g of carbon quantum dots were mixed with 80 mL of deionized water and ultrasonically treated for 10 min to obtain a carbon quantum dot solution. 14.46 g of NiCl 2 6H 2 O and 7.22 g of FeCl 3 9H 2 O, at this time NiCl 2 6H 2 Ni ions and FeCl in O 3 9H 2 The molar ratio of iron ions in O was 1.17:0.5 and the mixture was stirred for 30 min to obtain a precursor.

[0056] The precursor was placed in a water bath at 80°C and the solvent was evaporated by strong magnetic stirring to obtain a dry precursor. The dry precursor was placed in a horizontal tube furnace and heated at 300°C for 4 hours in a nitrogen atmosphere to obtain a carbon quantum dot nickel-iron nanocomposite electrocatalyst. At this time, the mass ratio of carbon quantum dots to nickel-iron nanoparticles was 1:4, which was recorded as C-NiFe electrocatalyst.

[0057] Example 3

[0058] The preparation method of the carbon quantum dot nickel-iron nanocomposite electrocatalyst comprises the following steps:

[0059] S1. Preparation of carbon quantum dots:

[0060] 8 g of glucose was added to 75 mL of deionized water and stirred continuously for 10 min to obtain a glucose solution. The glucose solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave. The stainless steel autoclave was then placed in an oven and heated at 200 °C for 1 h, cooled naturally to room temperature, and then freeze-dried at -65 °C to obtain carbon quantum dots.

[0061] Preparation of S2, C-NiFe electrocatalyst:

[0062] 2.79 g of carbon quantum dots were mixed with 80 mL of deionized water and ultrasonically treated for 10 min to obtain a carbon quantum dot solution. 5.32 g of NiCl was added to the carbon quantum dot solution. 2 6H 2 O and 3.63 g of FeCl 3 9H 2 O, at this time NiCl 2 6H 2 Ni ions and FeCl in O 3 9H 2 The molar ratio of iron ions in O is 1.0:0.6 and the mixture is stirred for 30 min to obtain a precursor.

[0063] The precursor was placed in a water bath at 80°C and the solvent was evaporated by strong magnetic stirring to obtain a dry precursor. The dry precursor was placed in a horizontal tube furnace and heated at 600°C for 1 h in a nitrogen atmosphere to obtain a carbon quantum dot nickel-iron nanocomposite electrocatalyst. At this time, the mass ratio of carbon quantum dots to nickel-iron nanoparticles was 1:2, which was recorded as C-NiFe electrocatalyst.

[0064] Comparative Example 1

[0065] The preparation method of the carbon quantum dot nickel nanocomposite electrocatalyst is the same as the preparation steps of Example 1, except that FeCl is not used in step S2. 3 9H 2 O participates in the reaction, including the following steps:

[0066] S1. Preparation of carbon quantum dots:

[0067] 8 g of glucose was dissolved in 65 mL of deionized water and magnetic stirring was continued for 10 min to obtain a glucose solution. The glucose solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave. The stainless steel autoclave was then placed in an oven and heated at 160 ° C for 3 h, cooled to room temperature, and the product was freeze-dried at -65 ° C to obtain carbon quantum dots.

[0068] Preparation of S2, C-Ni electrocatalyst:

[0069] 0.15 g of carbon quantum dots were mixed with 80 mL of deionized water and ultrasonically treated for 10 min to obtain a carbon quantum dot solution. 0.6 g of NiCl was added to the carbon quantum dot solution. 2 6H 2 O and then stirred for 30 minutes to obtain a precursor; the precursor was placed in a water bath at 80° C. by strong magnetic stirring to evaporate the solvent, and then the dried precursor was placed in a horizontal tube furnace and heated at 480° C. for 2 hours under a nitrogen atmosphere to obtain a carbon quantum dot nickel nanocomposite electrocatalyst, which was recorded as C-Ni electrocatalyst.

[0070] Comparative Example 2

[0071] The preparation method of the carbon quantum dot iron nanocomposite electrocatalyst is the same as the preparation steps of Example 1, except that NiCl is not used in step S2. 2 6H 2 O participates in the reaction, including the following steps:

[0072] S1. Preparation of carbon quantum dots:

[0073] 8 g of glucose was dissolved in 65 mL of deionized water and magnetic stirring was continued for 10 min to obtain a glucose solution. The glucose solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave. The stainless steel autoclave was then placed in an oven and heated at 160 ° C for 3 h, cooled to room temperature, and the product was freeze-dried at -65 ° C to obtain carbon quantum dots.

[0074] Preparation of S2, C-Fe electrocatalyst:

[0075] 0.15 g of carbon quantum dots were mixed with 80 mL of deionized water and ultrasonically treated for 10 min to obtain a carbon quantum dot solution. 0.6 g of FeCl 3 9H 2 O and then stirred for 30 minutes to obtain a precursor; the precursor was placed in a water bath at 80°C by strong magnetic stirring to evaporate the solvent, and then the dried precursor was placed in a horizontal tube furnace and heated at 480°C for 2 hours under a nitrogen atmosphere to obtain a carbon quantum dot iron nanocomposite electrocatalyst, which was recorded as C-Fe electrocatalyst.

[0076] Comparative Example 3

[0077] A method for preparing a carbon quantum dot nickel-cobalt nanocomposite electrocatalyst comprises the following steps:

[0078] S1. Preparation of carbon quantum dots:

[0079] 8 g of glucose was added to 65 mL of deionized water and stirred for 10 min to obtain a glucose solution. The glucose solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave. The stainless steel autoclave was then placed in an oven and heated at 160 ° C for 3 h, naturally cooled to room temperature, and then freeze-dried at -65 ° C to obtain carbon quantum dots.

[0080] S2. Preparation of C-NiCo electrocatalyst:

[0081] 0.15 g of carbon quantum dots were mixed with 80 mL of deionized water and ultrasonically treated for 10 min to obtain a carbon quantum dot solution. 0.6 g of NiCl was added to the carbon quantum dot solution. 2 6H 2 O and 0.6 g CoCl 2 6H 2 O, and stirred for 30 min to obtain a precursor.

[0082] The precursor was placed in a water bath at 80°C by strong magnetic stirring to evaporate the solvent, and then placed in a horizontal tube furnace and heated at 480°C for 2 hours in a nitrogen atmosphere to obtain a carbon quantum dot nickel-cobalt nanocomposite electrocatalyst, which was recorded as C-NiCo electrocatalyst.

[0083] Comparative Example 4

[0084] The preparation method of carbon quantum dot iron-cobalt nanocomposite electrocatalyst comprises the following steps:

[0085] S1. Preparation of carbon quantum dots:

[0086] 8 g of glucose was added to 65 mL of deionized water and stirred for 10 min to obtain a glucose solution. The glucose solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave. The stainless steel autoclave was then placed in an oven and heated at 160 ° C for 3 h, naturally cooled to room temperature, and then freeze-dried at -65 ° C to obtain carbon quantum dots.

[0087] Preparation of S2, C-FeCo electrocatalyst:

[0088] 0.15 g of carbon quantum dots were mixed with 80 mL of deionized water and ultrasonically treated for 10 min to obtain a carbon quantum dot solution. 0.6 g of CoCl 2 6H 2 O and 0.6 g FeCl 3 9H 2 O, and stirred for 30 min to obtain a precursor.

[0089] The precursor was placed in a water bath at 80°C by strong magnetic stirring to evaporate the solvent, and then placed in a horizontal tube furnace and heated at 480°C for 2h in a nitrogen atmosphere to obtain a carbon quantum dot iron-cobalt nanocomposite electrocatalyst, which was recorded as C-FeCo electrocatalyst.

[0090] Examples 1 to 3 of the present invention all obtain carbon quantum dot nickel-iron nanocomposite electrocatalysts with high catalytic activity and high stability. The carbon quantum dot nickel-iron nanocomposite electrocatalyst obtained in Example 1 is used as an example for research. The specific research method and results are as follows:

[0091] Figure 1 The transmission electron microscope image shows that the diameter of CQDs is within 30nm~50nm. First, the small size makes CQDs have a high specific surface area, which increases the number of active sites for electrochemical reactions and significantly improves the catalytic efficiency. Secondly, the excellent conductivity and uniform dispersion of CQDs contribute to the uniformity of charge transfer and C-NiFe electrocatalysts, preventing the agglomeration of nanoparticles. In addition, the surface of CQDs is rich in functional groups such as hydroxyl and carboxyl, which can form stable coordination bonds with the metal ions of nickel-iron nanoparticles, enhancing the stability and activity of C-NiFe electrocatalysts. CQDs in this size range also have good light absorption and emission characteristics, suitable for photoelectrocatalytic applications, and the pore size of 30nm~50nm is conducive to the rapid transmission of electrolytes and reactants, thereby improving the reaction efficiency. Therefore, CQDs with a particle size of 30nm~50nm show significant comprehensive advantages in electrochemical catalytic applications.

[0092] Figure 2 The scanning electron microscope image shows the stacking pattern of the C-NiFe electrocatalyst, where the nickel-iron nanoparticles are wrapped in the carbon layer formed by the carbon quantum dots, making the diameter of the carbon quantum dot nickel-iron nanocomposite electrocatalyst about 200nm. First, the stacking structure of CQDs and nickel-iron nanoparticles provides abundant active sites and a high specific surface area, which significantly improves the electrocatalytic performance. Secondly, the nickel-iron nanoparticles are wrapped by the carbon layer of CQDs, which enhances the stability of the nickel-iron nanoparticles during the reaction and prevents particle agglomeration and dissolution. In addition, the moderate size of 200nm is conducive to the rapid transport of electrolytes and reactants, further improving the reaction efficiency. In short, this stacking pattern and moderate particle size make the C-NiFe electrocatalyst exhibit excellent comprehensive performance in electrochemical catalytic applications.

[0093] Figure 3The high-resolution transmission electron microscopy images show that the lattice spacing of the carbon layer is 0.34nm and the lattice spacing of the nickel-iron nanoparticles is 0.207nm. First, the 0.34nm lattice spacing of the carbon layer helps to provide good conductivity and mechanical stability, enhancing the charge transfer capacity of the overall structure. Secondly, the 0.207nm lattice spacing of the nickel-iron nanoparticles is conducive to optimizing the electronic structure and increasing the number of active sites for electrocatalytic reactions. The lattice matching between the two promotes a strong interaction between the CQDs carbon layer and the nickel-iron nanoparticles, improving the stability and catalytic performance of the C-NiFe electrocatalyst. Therefore, this combination of lattice spacing significantly improves the comprehensive performance of the C-NiFe electrocatalyst in electrochemical catalytic applications.

[0094] Figure 4 The element distribution diagram shows that C, O, Ni, and Fe are uniformly distributed in the C-NiFe electrocatalyst, and proves that the NiFe nanoparticles are uniformly distributed on the CQDs. First, the uniformly distributed NiFe nanoparticles provide more uniformly exposed active sites, improving the overall efficiency of the electrocatalytic reaction. Second, the uniform distribution of NiFe nanoparticles helps prevent the agglomeration of nanoparticles and maintains a high specific surface area, thereby enhancing the catalytic activity of the C-NiFe electrocatalyst. Finally, the uniform element distribution improves the structural stability and electrochemical stability of the C-NiFe electrocatalyst and extends the service life of the C-NiFe electrocatalyst. Therefore, the uniformly distributed NiFe nanoparticles and elements significantly improve the catalytic performance and durability of the C-NiFe electrocatalyst.

[0095] Electrocatalytic performance test:

[0096] Test method: Using a standard three-electrode system, the electrocatalytic ORR and OER performance of CQDs, the C-Ni electrocatalyst of Comparative Example 1, the C-Fe electrocatalyst of Comparative Example 2, and the C-NiFe electrocatalyst of Example 1 were tested in a 0.1 mol / L KOH alkaline aqueous solution; specifically: a Pt / C electrode was used as a counter electrode, an Ag / AgCl electrode was used as a reference electrode, and a three-electrode system was formed with a working electrode, and the working electrode was prepared according to the following steps:

[0097] 5 mg of CQDs, the C-Ni electrocatalyst of comparative example 1, the C-Fe electrocatalyst of comparative example 2, and the C-NiFe electrocatalyst of embodiment 1 were respectively dispersed in 960 µL of a mixed solution to obtain a dispersion, the mixed solution consisting of ethanol and water in a volume ratio of 1:1, and then 40 µL of a 5 wt% Nafion ethanol solution was added to each dispersion, and an ultrasonic processor was used for ultrasonic treatment for 20 min to ensure uniform dispersion to form a stable catalyst ink.

[0098] Coating of the working electrode: Take a rotating disk electrode, clean it and blow it dry with nitrogen. Use a micropipette to take 10µL of catalyst ink and apply it on the surface of the rotating disk electrode to ensure uniform coverage. The electrode with the catalyst ink is dried naturally at room temperature or in a low-temperature oven until all the solvent is completely evaporated to form a uniform catalyst film. The catalyst loading on the rotating disk electrode is 0.25mg cm² to obtain a working electrode.

[0099] Installation of the three-electrode system: immerse one end of the working electrode, counter electrode and reference electrode into 0.1 mol / L KOH electrolyte to ensure that the electrodes are immersed, and the other ends are electrically connected to the electrochemical workstation to prepare for electrochemical testing.

[0100] The ORR activity test method is: 2 In a saturated environment, the linear voltammetric scanning method was used on an electrochemical workstation to test the ORR catalytic activity, and the half-wave potential and starting potential were obtained from the LSV curve to determine the activity. Figure 5 The results show that C-NiFe electrocatalyst 2 The starting potential E in saturated environment 0 and half-wave potential E 1 / 2 The high starting potential and half-wave potential indicate that the C-NiFe electrocatalyst can start and maintain efficient ORR activity at a relatively low potential, significantly improving the energy conversion efficiency. The uniformly distributed nickel-iron nanoparticles and carbon quantum dots provide abundant active sites and a high specific surface area, ensuring the long-term stability and durability of the C-NiFe electrocatalyst.

[0101] Figure 6 The ORR kinetics and electron transfer mechanism analysis of the C-NiFe electrocatalyst by Tafel slope and Koutechy-Levich plot are presented. The results show that the C-NiFe electrocatalyst of Example 1 exhibits significant activity in ORR. Specifically, its Tafel slope is 73 mV dec - ¹, showing an excellent reaction rate at a low overpotential. In addition, KL curve analysis shows that the electron transfer number of C-NiFe electrocatalyst in ORR is about 4, indicating that C-NiFe electrocatalyst efficiently reduces oxygen to water through a four-electron pathway. These results demonstrate that C-NiFe electrocatalyst has excellent kinetics and an efficient electron transfer mechanism in ORR.

[0102] The OER activity test method is as follows: assemble the above-mentioned three-electrode system, use linear voltammetry to test the catalytic activity of the oxygen evolution reaction at a scan rate of 5 mV / s in an oxygen-saturated environment, and analyze the performance of different catalysts by measuring the relationship curve between the current density and the overpotential of the working electrode. Figure 7 The electrochemical performance of the C-NiFe electrocatalyst of Example 1 in OER is demonstrated. The test results show that the overpotential of the C-NiFe electrocatalyst at a current density of 10mA cm² is 320mV, showing its efficient catalytic activity in OER. At the same time, the C-NiFe electrocatalyst showed good stability in long-term electrochemical tests, further demonstrating its potential in practical applications. These results show that the C-NiFe electrocatalyst not only performs well in ORR, but also has excellent performance in OER, making it have broad application prospects in zinc-air batteries and other electrochemical energy conversion devices.

[0103] Figure 8 The test results of the application of the C-NiFe electrocatalyst in zinc-air batteries of Example 1 are shown. The test was conducted using a double electrode system, in which the carbon paper modified with the C-NiFe electrocatalyst of Example 1 was used as the cathode and the zinc sheet was used as the anode. One end of the cathode and the anode were placed in a mixed solution of 6 mol / L KOH and 0.2 mol / L zinc acetate, and the other end was connected to an electrochemical workstation.

[0104] Figure 8 The results show that the C-NiFe electrocatalyst has a high open circuit voltage of 1.47V and exhibits excellent discharge capacity and smooth discharge curves at different current densities. In addition, the C-NiFe electrocatalyst exhibits excellent stability and small voltage decay in long-term cycle tests, showing its great potential in practical applications. These results indicate that the C-NiFe electrocatalyst has superior comprehensive performance in zinc-air batteries and has broad application prospects.

[0105] In order to verify the superiority of nickel-iron nanoparticles, the present invention also provides a carbon quantum dot nickel-cobalt nanocomposite electrocatalyst and a carbon quantum dot iron-cobalt nanocomposite electrocatalyst, and conducts a comparative study. The following is a brief description of the comparative results:

[0106] Electrochemical performance of the carbon quantum dot nickel-iron nanocomposite electrocatalyst of Example 1:

[0107] ORR onset potential E 0 :0.99V.

[0108] Half-wave potential E 1 / 2 :0.83V.

[0109] OER overpotential at 10mA cm²: 320mV.

[0110] Tafel slope of ORR: 73mV dec - ¹.

[0111] Stability: After 5000 cycles, the current density retention rate is 90%.

[0112] Electrochemical performance of the carbon quantum dot nickel-cobalt nanocomposite electrocatalyst of Comparative Example 3:

[0113] ORR onset potential E 0 :0.95V.

[0114] Half-wave potential E 1 / 2 :0.75V.

[0115] OER overpotential at 10mA cm²: 340mV.

[0116] Tafel slope of ORR: 80mV dec - ¹.

[0117] The activities of C-NiCo electrocatalyst in ORR and OER are not as good as those of C-NiFe electrocatalyst, especially in ORR activity, where both the onset potential and half-wave potential are lower than those of C-NiFe electrocatalyst.

[0118] Stability: After 5000 cycles, the current density retention rate of the carbon quantum dot nickel-cobalt nanocomposite electrocatalyst of Comparative Example 3 was 78%. In long-term electrochemical tests, the performance of the C-NiCo electrocatalyst decayed rapidly and its stability was not as good as that of the C-NiFe electrocatalyst.

[0119] Electrochemical performance of the carbon quantum dot iron-cobalt nanocomposite electrocatalyst of Comparative Example 4:

[0120] ORR onset potential E 0 :0.92V.

[0121] Half-wave potential E 1 / 2 :0.72V.

[0122] OER overpotential at 10mA cm²: 350mV.

[0123] Tafel slope of ORR: 85mV dec - ¹.

[0124] The half-wave potential of C-FeCo electrocatalyst in ORR is significantly lower than that of C-NiFe electrocatalyst, and its OER activity is also lower.

[0125] Stability: After 5000 cycles, the current density retention rate of the carbon quantum dot iron-cobalt nanocomposite electrocatalyst of Comparative Example 4 was 70%. The stability of the C-FeCo electrocatalyst in alkaline medium was relatively poor, and the activity decreased significantly during the electrochemical cycle, and the stability was not as good as that of the C-NiFe electrocatalyst.

[0126] By contrast, it can be seen that although C-NiCo electrocatalyst and C-FeCo electrocatalyst also have good electrochemical properties, in terms of comprehensive performance and stability, C-NiFe electrocatalyst performs best, which further verifies the rationality and superiority of selecting nickel-iron nanoparticles as electrocatalysts. Therefore, the present invention selects nickel-iron nanoparticles for research and application, not only based on its significant advantages in electrochemical properties, but also verifies its superiority in practical applications by experimental comparison. By the introduction of carbon quantum dots, the catalytic activity and stability of nickel-iron nanoparticles are further enhanced, providing new ideas and technical support for efficient and low-cost electrocatalysts.

[0127] Obviously, those skilled in the art can make various changes and modifications to the invention without departing from the spirit and scope of the invention. Thus, if these modifications and variations of the invention fall within the scope of the claims of the invention and their equivalents, the invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a carbon quantum dot nickel-iron nanocomposite electrocatalyst, characterized in that: The steps include: The carbon source is mixed in water and the carbon quantum dots are prepared by a hydrothermal method; Carbon quantum dots, soluble nickel salt and soluble iron salt are dispersed together in water, and the carbon quantum dots form stable coordination bonds with nickel ions and iron ions. After evaporating the solvent, high-temperature reduction is performed at 300°C to 600°C in an inert atmosphere. While obtaining nickel-iron nanoparticles, the carbon quantum dots aggregate with each other and form a carbon layer, which wraps the nickel-iron nanoparticles to obtain a carbon quantum dot nickel-iron nanocomposite electrocatalyst. The molar ratio of nickel ions in the soluble nickel salt to iron ions in the soluble iron salt is 0.83-1.17:0.5-0.73; In the carbon quantum dot nickel-iron nanocomposite electrocatalyst, the mass ratio of carbon quantum dots to nickel-iron nanoparticles is 1:2~5.

2. The method for preparing the carbon quantum dot nickel-iron nanocomposite electrocatalyst according to claim 1, characterized in that: The heating time for high temperature reduction is 1h~4h.

3. The method for preparing the carbon quantum dot nickel-iron nanocomposite electrocatalyst according to claim 1, characterized in that: The carbon source is selected from one of glucose, sucrose, polyethylene glycol, glycerol and fructose.

4. The method for preparing the carbon quantum dot nickel-iron nanocomposite electrocatalyst according to claim 1, characterized in that: The conditions of the hydrothermal method are: heating at 120℃~200℃ for 1h~3h.

5. The method for preparing the carbon quantum dot nickel-iron nanocomposite electrocatalyst according to claim 1, characterized in that: The mass ratio of carbon source to water is 8:55~75.

6. A carbon quantum dot nickel-iron nanocomposite electrocatalyst prepared by the preparation method according to any one of claims 1 to 5, characterized in that: In the carbon quantum dot nickel-iron nanocomposite electrocatalyst, the carbon quantum dots and nickel-iron nanoparticles are in a stacking mode, and the nickel-iron nanoparticles are wrapped in the carbon layer formed by the carbon quantum dots.

7. Use of the carbon quantum dot nickel-iron nanocomposite electrocatalyst according to claim 6 in the preparation of a cathode catalyst for a zinc-air battery.

8. The use according to claim 7, characterized in that: The application method is: Using a carbon quantum dot nickel-iron nanocomposite electrocatalyst as a cathode and a zinc sheet as an anode, immerse one end of the cathode and anode together in an electrolyte and electrically connect the other end; Wherein, the electrolyte contains zinc ions.

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