PtCo alloy modified carbon nanosheet as well as preparation method and application thereof

Abstract

The invention discloses a PtCo alloy modified carbon nanosheet and a preparation method and application thereof.The method comprises the steps that a platinum source, a cobalt source, a nitrogen-containing organic matter, chitosan and molten salt are mixed and then subjected to ball milling treatment, and mixed powder is obtained; placing the mixed powder in a nitrogen atmosphere, and carrying out first carbonization treatment; then carrying out acid pickling treatment and drying to obtain an intermediate product; and placing the intermediate product in a mixed atmosphere of Ar and H2, and carrying out secondary carbonization treatment to prepare the PtCo alloy modified carbon nanosheet. According to the method, active sites are exposed through a porous structure, alloy inactivation is inhibited through carbon confinement, the stability of the material and the electrocatalytic activity are effectively improved, the method is reasonable in design and simple in preparation process, precious metal dependence is reduced, and the method has remarkable advantages in practical application in the fields of fuel cells, metal-air cells and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of electrocatalysis and energy storage materials, and relates to a PtCo alloy-modified carbon nanosheet and a preparation method and application thereof. Background Art

[0002] With the rapid advancement of industrial civilization, human demand for energy is expanding, which has prompted us to continuously explore and utilize new sustainable green energy. Advanced energy control devices such as fuel cells and metal-air batteries have emerged in this context. Among them, zinc-air batteries have become the focus of research in recent years due to their excellent high energy density and pollution-free characteristics. However, the practical application of zinc-air batteries is severely restricted by the slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). At present, although precious metal catalysts such as Pt, Ir, and Ru-based materials perform well in driving ORR and OER, their inherent limitations, such as limited reserves, high prices, insufficient stability, and easy poisoning, have greatly hindered the widespread application of zinc-air batteries. Therefore, in order to overcome these challenges, it has become a top priority to develop non-precious metal catalysts with low cost, high electrochemical activity, and stability.

[0003] Transition metals and their derivatives, such as Fe, Co, and Ni, have been confirmed to be active centers of OER, which provides new ideas for the research and development of non-precious metal catalysts. Based on this, many transition metal-based electrocatalysts, such as layered double hydroxides (LDHs), metal / graphene composites, bimetallic alloys, porous metal oxides, metal phosphides, and metal / porous carbons, have emerged and received widespread attention. These catalysts are not only expected to replace precious metal catalysts and reduce the cost of zinc-air batteries, but also to further improve the electrochemical activity and stability of zinc-air batteries by optimizing their structure and performance, thereby promoting the practical application of zinc-air battery technology.

[0004] In addition, in recent years, carbon-based functional materials derived from metal-organic frameworks have been used as ORR catalysts. These materials have different metal and N species, which are not only conducive to the construction of the structure but also can produce catalytic active centers. However, there is a common problem that the electrocatalytic activity and structural stability cannot be taken into account at the same time. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a PtCo alloy-modified carbon nanosheet and a preparation method and application thereof, thereby solving the technical problem that the carbon-based functional materials derived from metal organic frameworks in the prior art cannot take into account both electrocatalytic activity and structural stability.

[0006] The present invention is achieved through the following technical solutions: A preparation method of PtCo alloy-modified carbon nanosheets, comprising the following steps: S1: Mix a platinum source, a cobalt source, a nitrogen-containing organic compound, chitosan, and a molten salt, and then perform ball milling to obtain a mixed powder; S2: Place the mixed powder in a nitrogen atmosphere for the first carbonization treatment; then perform pickling treatment and drying to obtain an intermediate product; S3: Place the intermediate product in a mixed atmosphere of Ar and H 2 to perform secondary carbonization treatment to obtain the PtCo alloy-modified carbon nanosheets.

[0007] Preferably, the ratio of the platinum source, the cobalt source, the nitrogen-containing organic compound, chitosan, and the molten salt is (10~60) mg: (10~60) mg: (1~10) g: (1~10) g: (1~20) g.

[0008] Preferably, the ratio of the platinum source, the cobalt source, the nitrogen-containing organic compound, chitosan, and the molten salt is 30 mg: 30 mg: 4 g: 1 g: 10 g.

[0009] Preferably, the time of the ball milling treatment is 10~60 min.

[0010] Preferably, the temperature of the first carbonization treatment is 600~900 °C, and the time is 1~5 h.

[0011] Preferably, in the pickling treatment process, the acid used is hydrochloric acid, and the concentration is 1~5 mol / L.

[0012] Preferably, after the pickling treatment and drying, an intermediate product is obtained, wherein the drying temperature is 40~60 °C, and the time is 12~20 h.

[0013] Preferably, the temperature of the secondary carbonization treatment is 600~900 °C, and the time is 1~5 h.

[0014] A PtCo alloy-modified carbon nanosheet is prepared by the above method.

[0015] A zinc-air battery comprises the above-mentioned PtCo alloy-modified carbon nanosheet.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention discloses a preparation method of PtCo alloy-modified carbon nanosheets. In the first aspect, through simple ball milling treatment, the components are evenly mixed, and the molten salt is fully embedded in the mixture during the carbonization process. The molten salt is washed away during the pickling process, leaving a porous structure on the surface of the carbon material. That is, a "hard template" is formed by the molten salt during high-temperature carbonization, and a hierarchical porous structure (micropore-mesopore synergy) is formed after pickling, increasing the specific surface area and exposing more active sites. At the same time, the pore connectivity improves the mass transfer efficiency and reduces the mass transfer resistance, effectively promoting the diffusion of O 2 and H⁺ in the ORR reaction.

[0017] In the second aspect, during the first carbonization process, chitosan is converted into highly graphitized carbon at high temperature, providing mechanical strength support. The platinum source and cobalt source generate metal oxides, and at the same time, unstable oxides are removed by subsequent pickling, retaining highly active metal compounds. Then, secondary carbonization is carried out in a mixed atmosphere of Ar and H 2 . H 2 selectively etches the surface of the carbon layer at high temperature, forming edge defects and atomic-level vacancies, further increasing the density of active sites. The reducing atmosphere promotes the rearrangement of Pt and Co atoms to form a uniform PtCo alloy, avoiding phase separation and improving the stability of the material.

[0018] In the third aspect, the present invention reduces the d-band center of Pt by introducing Co, weakens the adsorption energy of oxygen intermediates (*O, *OH), and improves the ORR kinetics. Pyridine nitrogen / graphite nitrogen generated by the pyrolysis of nitrogen-containing organic compounds enhances the conductivity of the carbon skeleton and optimizes the catalytic activity of PtCo through electron transfer. PtCo nanoparticles are embedded in the nitrogen-doped carbon sheet layer, forming a strong metal-support interaction, inhibiting the migration and aggregation of alloy particles, and enabling the electron coupling of PtCo alloy and nitrogen-doped carbon, effectively improving the electrocatalytic performance of the material.

[0019] The present invention exposes active sites through a porous structure and inhibits alloy deactivation by carbon confinement, effectively improving the stability of the material and the activity of electrocatalysis. The method is reasonably designed, the preparation process is simple, the dependence on precious metals is reduced, and it has significant advantages in the practical applications of fuel cells, metal-air batteries and other fields.

[0020] Furthermore, one inventive aspect of the present invention lies in that the ratio of the platinum source, cobalt source, nitrogen-containing organic matter, chitosan, and molten salt is (10 - 60) mg : (10 - 60) mg : (1 - 10) g : (1 - 10) g : (1 - 20) g. First of all, within this ratio range, Pt and Co can be fully mixed and form a stable PtCo alloy during the carbonization process. This alloy structure helps to improve the electrocatalytic activity of the material because the synergistic effect of Pt and Co can optimize the adsorption and desorption ability of oxygen reduction reaction (ORR) intermediates. At the same time, an appropriate amount of Co can lower the d-band center of Pt, thereby weakening the adsorption energy of oxygen intermediates (such as O、 OH), and further enhancing the ORR kinetics. At the same time, this ratio ensures the uniform distribution of nitrogen atoms in the carbon nanosheets, enhances the electrical conductivity and catalytic activity, provides sufficient mechanical strength support, forms a hierarchical porous structure, increases the specific surface area and active site density, and improves the mass transfer efficiency.

[0021] Furthermore, one inventive aspect of the present invention lies in that the temperature of the secondary carbonization treatment is 600 - 900 °C and the time is 1 - 5 h. First of all, at a high temperature of 600 - 900 °C, Pt atoms and Co atoms can rearrange and alloy more fully to form a uniform PtCo alloy structure. This structure helps to improve the electrocatalytic activity of the material because the Pt and Co atoms in the alloy can act synergistically to optimize the adsorption and desorption ability of oxygen reduction reaction (ORR) intermediates. In addition, during the secondary carbonization treatment, the high temperature and long-time heating cause some carbon atoms on the surface of the carbon nanosheets to volatilize or rearrange, thereby forming more edge defects and atomic vacancies. These defects and vacancies help to increase the specific surface area of the material and expose more active sites. At the same time, by regulating the carbonization temperature and time, the size and distribution of the pore structure can be further regulated, thereby optimizing the catalytic performance of the material. At the same time, the high-temperature carbonization treatment also affects the electronic structure of nitrogen atoms in the carbon nanosheets, and then optimizes the catalytic activity of the PtCo alloy. The introduction of nitrogen atoms can change the electronic properties of the carbon skeleton and affect the catalytic performance of the PtCo alloy through the electron transfer effect. At an appropriate carbonization temperature and time, nitrogen atoms can be more uniformly distributed in the carbon nanosheets and form a strong interaction with the PtCo alloy, thereby enhancing the electrocatalytic activity of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 Scanning electron microscope images of the PtCo alloy modified carbon nanosheets prepared in Example 2 of the present invention at different magnifications; wherein the scale bar of (A) is 1.00 μm, the scale bar of (B) is 2.00 μm, and the scale bar of (C) is 3.00 μm; Figure 2 Polarization curve of the PtCo alloy modified carbon nanosheets prepared in Example 2 of the present invention and commercial Pt / C + RuO 2 ; Figure 3 Cyclic voltammetry characteristic curve of the PtCo alloy modified carbon nanosheets prepared in Example 2 of the present invention as an electrocatalyst and commercial Pt / C + RuO 2 ; Figure 4 Time-normalized current percentage relationship diagram of the PtCo alloy modified carbon nanosheets prepared in Example 2 of the present invention as an electrocatalyst and commercial Pt / C + RuO 2 ; Detailed implementation manners

[0024] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art regarding the present invention. In case of conflict, the definition in this specification shall prevail.

[0025] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0026] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0027] In this article, unless otherwise specified, terms such as "comprising", "including", "containing", "having", or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A only comprises a".

[0028] In this text, for the sake of concise description, not all possible combinations of all technical features in each implementation or embodiment are described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation or embodiment can be combined arbitrarily, and all possible combinations should be considered as the scope described in this specification.

[0029] The present invention provides a method for preparing PtCo alloy-modified carbon nanosheets, comprising the following steps: S1: Mix a platinum source, a cobalt source, a nitrogen-containing organic compound, chitosan, and a molten salt, and perform ball milling for 10 - 60 min to obtain a mixed powder; The platinum source is at least one of platinum acetylacetonate, platinum chloride, and platinum nitrate; preferably platinum acetylacetonate; The cobalt source is at least one of cobalt acetylacetonate, cobalt chloride, and cobalt nitrate; preferably cobalt acetylacetonate; The nitrogen-containing organic compound is at least one of urea, thiourea, and melamine; preferably urea; The molten salt is at least one of sodium chloride, potassium chloride, and zinc chloride; preferably sodium chloride.

[0030] Further, the ratio of the platinum source, the cobalt source, the nitrogen-containing organic compound, chitosan, and the molten salt is (10 - 60) mg : (10 - 60) mg : (1 - 10) g : (1 - 10) g : (1 - 20) g.

[0031] The ratio of the platinum source, the cobalt source, the nitrogen-containing organic compound, chitosan, and the molten salt is 30 mg : 30 mg : 4 g : 1 g : 10 g.

[0032] In the above process, the time of the ball milling treatment is 10 - 60 min. During the ball milling time of 10 - 60 min, components such as the platinum source, the cobalt source, the nitrogen-containing organic compound, chitosan, and the molten salt can be fully mixed under the action of the ball milling medium and the grinding balls. This mixing not only occurs on a macroscopic scale, but more importantly, realizes the uniform distribution of each component on a microscopic scale. The uniform mixing helps to form a uniform carbon nanosheet structure during the subsequent carbonization process, thereby ensuring that the PtCo alloy can be uniformly modified on the surface of the carbon nanosheets. In addition, the ball milling treatment can also refine the raw material particles, reducing their size to the nanometer level, which is crucial for forming small-sized PtCo alloy particles because small-sized alloy particles have a higher specific surface area and more active sites, thus being able to enhance the electrocatalytic activity of the material. An appropriate ball milling time can ensure that the raw materials receive sufficient energy input, thereby helping to form a stable carbon nanosheet structure during the carbonization process. Too short a ball milling time may lead to uneven mixing of the raw materials or insufficient particle refinement, while too long a ball milling time may introduce too many defects or cause structural damage.

[0033] S2: Place the mixed powder in a nitrogen atmosphere and perform the first carbonization treatment at 600 - 900 °C for 1 - 5 h; then perform pickling treatment with hydrochloric acid having a concentration of 1 - 5 mol / L, and dry at 40 - 60 °C for 12 - 20 h to obtain an intermediate product; In the above process, pickling with hydrochloric acid has good solubility for impurities such as metal oxides and carbonates. After the carbonization treatment, metal oxides and unstable compounds in the mixed powder can be effectively removed through the pickling action of hydrochloric acid, thereby ensuring the purity and quality of the final product. At the same time, the molten salt plays a role of "hard template" during the carbonization process, and the pickling treatment with hydrochloric acid can remove these molten salt templates, leaving a porous structure on the surface of the carbon material. This porous structure helps to increase the specific surface area of the material, expose more active sites, and improve the catalytic efficiency. In addition, the pickling treatment with hydrochloric acid can further optimize the structure of the PtCo alloy. By removing unstable compounds and impurities, it can promote the rearrangement and alloying of Pt and Co atoms on the surface of the carbon nanosheets, forming a more uniform and stable PtCo alloy structure, which helps to enhance the electrocatalytic activity and stability of the material.

[0034] S3: Place the intermediate product under a mixed atmosphere of Ar and H 2 and perform a second carbonization treatment at 600 - 900 °C for 1 - 5 h to obtain the carbon nanosheets modified with the PtCo alloy. In this step, the temperature of the second carbonization treatment is preferably 600 °C, and the time is preferably 2 h.

[0035] The present invention discloses a preparation method of carbon nanosheets modified with a PtCo alloy. After the reactants are mixed and ball-milled, the components are evenly mixed. The molten salt is fully embedded in the mixture during the carbonization process and is washed away during the pickling process, leaving a porous structure on the surface of the carbon material. The purpose of the first carbonization is to convert chitosan into a carbon material with performance, and convert metal oxides with poor catalytic performance into metal compounds during the pickling process under high temperature and pressure. The purpose of the second carbonization is to etch a porous structure on the material surface with the reducing gas hydrogen, which is more conducive to improving the catalytic activity. The present invention uses the molten salt method to introduce a rich pore structure on the biomass carbon substrate, increasing the electron transfer and the exposure of active sites. The unique structure of the carbon skeleton effectively inhibits the dissolution and aggregation of the PtCo alloy during the catalytic process, thereby significantly improving the overall catalytic performance and long-term operation stability. The present invention realizes the efficient preparation of the composite catalyst through simple ball-milling and heat treatment processes. At the same time, using chitosan as the carbon source reflects the efficient utilization of renewable resources and conforms to the concept of green chemistry.

[0036] In order to characterize the performance of the carbon nanosheets modified with the PtCo alloy prepared by the present invention during electrocatalysis, the following tests are carried out: (1) Prepare the working electrode: Uniformly coat the PtCo-CNS catalyst on a glassy carbon electrode or other suitable conductive substrate, ensuring that the catalyst layer is uniform and tightly attached.

[0037] Dry and fix the working electrode to ensure its stability during the test.

[0038] (2) Assemble the electrochemical cell: Use a standard three-electrode system, including a working electrode, a counter electrode (platinum wire electrode), and a reference electrode (reversible hydrogen electrode).

[0039] Inject an electrolyte solution (such as 0.1 M KOH solution) into the electrochemical cell, ensuring that all electrodes are immersed in the solution.

[0040] (3) Conduct a linear sweep voltammetry (LSV) test: Set the electrochemical workstation to run in linear sweep voltammetry mode.

[0041] Obtain the overpotential value from the LSV curve; (4) Conduct a cyclic voltammetry (CV) test: Set the electrochemical workstation to run in cyclic voltammetry mode.

[0042] Obtain the position of the oxygen reduction peak from the CV curve to determine the oxygen reduction potential.

[0043] It can be found through the test that the overpotential of the carbon nanosheets modified with PtCo alloy prepared in the present invention is 370 - 560 mV (vs. RHE), and the oxygen reduction potential in 0.1 M KOH solution is 0.7 - 0.9 V (vs. RHE).

[0044] Meanwhile, the stability of the carbon nanosheets modified with PtCo alloy prepared in the present invention as an electrocatalyst was tested by chronoamperometry. The test time was 10 hours. After 10 hours, the carbon nanosheets modified with PtCo alloy still maintained 85% - 91% of the initial current value as an electrocatalyst, indicating that the carbon nanosheets modified with PtCo alloy have good stability as an electrocatalyst.

[0045] The following further elaborates the present invention in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0046] In the following examples, conventional instruments and equipment in the art are used. For the experimental methods without specific conditions noted in the following examples, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. In the following examples, various raw materials are used. Unless otherwise specified, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0047] Example 1 A preparation method of PtCo alloy modified carbon nanosheets, comprising the following steps: S1: Weigh 40 mg of platinum acetylacetonate, 20 mg of cobalt acetylacetonate, 4 g of urea, 1 g of chitosan and 10 g of sodium chloride, mix them and carry out ball milling for 30 min to obtain a mixed powder; S2: Place the obtained mixed powder in a tube furnace, carbonize it at 900 °C for 2 h under a nitrogen atmosphere, treat the carbonized product with acid to remove excess inorganic salts and impurities, and then dry it.

[0048] S3: Place the dried precursor in a tube furnace, carbonize it at 600 °C for 2 h under an Ar / H 2 atmosphere to finally obtain PtCo modified carbon nanosheets. Example 2 S1: Weigh 30 mg of platinum acetylacetonate, 30 mg of cobalt acetylacetonate, 4 g of urea, 1 g of chitosan and 10 g of sodium chloride, mix them and carry out ball milling for 30 min to obtain a mixed powder; S2: Place the ball-milled mixed powder in a tube furnace, carbonize it at 900 °C for 2 h under a nitrogen atmosphere, treat the carbonized product with acid to remove excess inorganic salts and impurities, and then dry it.

[0049] S3: Place the dried precursor in a tube furnace, carbonize it at 600 °C for 2 h under an Ar / H 2 atmosphere to finally obtain PtCo modified carbon nanosheets (PtCo-CNS).

[0050] Example 3 S1: Weigh 20 mg of platinum acetylacetonate, 40 mg of cobalt acetylacetonate, 4 g of urea, 1 g of chitosan and 10 g of sodium chloride, mix them and carry out ball milling for 30 min to obtain a mixed powder; S2: Place the ball-milled mixed powder in a tube furnace, carbonize it at 900 °C for 2 h under a nitrogen atmosphere, treat the carbonized product with acid to remove excess inorganic salts and impurities, and then dry it.

[0051] S3: Place the dried precursor in a tube furnace and carbonize it at 600 °C for 2 h under an Ar / H 2 atmosphere, and finally obtain a PtCo-modified carbon nanosheet electrocatalyst. Example 4 S1: Weigh 60 mg of cobalt acetylacetonate, 4 g of urea, 1 g of chitosan, and 10 g of sodium chloride, mix them and carry out ball milling for 30 min to obtain a mixed powder; S2: Place the ball-milled mixed powder in a tube furnace and carbonize it at 900 °C for 2 h under a nitrogen atmosphere. Treat the carbonized product with an acid to remove excess inorganic salts and impurities, and then dry it.

[0052] S3: Place the dried precursor in a tube furnace and carbonize it at 600 °C for 2 h under an Ar / H 2 atmosphere, and finally obtain PtCo-modified carbon nanosheets. Example 5 S1: Weigh 60 mg of platinum acetylacetonate, 4 g of urea, 1 g of chitosan, and 10 g of sodium chloride, mix them and carry out ball milling for 30 min to obtain a mixed powder; S2: Place the ball-milled mixed powder in a tube furnace and carbonize it at 900 °C for 2 h under a nitrogen atmosphere. Treat the carbonized product with an acid to remove excess inorganic salts and impurities, and then dry it.

[0053] S3: Place the dried precursor in a tube furnace and carbonize it at 600 °C for 2 h under an Ar / H 2 atmosphere, and finally obtain PtCo-modified carbon nanosheets. Example 6 The present invention provides a method for preparing PtCo alloy-modified carbon nanosheets, comprising the following steps: S1: Mix 10 mg of platinum chloride, 10 mg of cobalt chloride, 1 g of urea, 2 g of chitosan, and 5 g of potassium chloride, and carry out ball milling for 10 min to obtain a mixed powder; S2: Place the mixed powder in a nitrogen atmosphere and carry out a first carbonization treatment at 600 °C for 5 h; then carry out pickling treatment with hydrochloric acid with a concentration of 1 mol / L and dry it at 40 °C for 20 h to obtain an intermediate product; S3: Place the intermediate product under a mixed atmosphere of Ar and H 2 and carry out a second carbonization treatment at 600 °C for 5 h to obtain the PtCo alloy-modified carbon nanosheets.

[0054] Example 7 The present invention provides a method for preparing PtCo alloy-modified carbon nanosheets, comprising the following steps: S1: Mix 30 mg of platinum nitrate, 40 mg of cobalt nitrate, 8 g of thiourea, 7 g of chitosan, and 15 g of sodium chloride, and then perform ball milling for 10 - 60 min to obtain a mixed powder; S2: Place the mixed powder in a nitrogen atmosphere and perform the first carbonization treatment at 800 °C for 3 h; then perform pickling treatment with hydrochloric acid with a concentration of 2 mol / L, and dry at 50 °C for 18 h to obtain an intermediate product; S3: Place the intermediate product in a mixed atmosphere of Ar and H 2 and perform the second carbonization treatment at 800 °C for 3 h to obtain the PtCo alloy - modified carbon nanosheets.

[0055] Example 8 The present invention provides a method for preparing PtCo alloy - modified carbon nanosheets, comprising the following steps: S1: Mix 60 mg of platinum acetylacetonate, 60 mg of cobalt chloride, 10 g of melamine, 9 g of chitosan, and 20 of zinc chloride, and then perform ball milling for 10 - 60 min to obtain a mixed powder; S2: Place the mixed powder in a nitrogen atmosphere and perform the first carbonization treatment at 900 °C for 1 h; then perform pickling treatment with hydrochloric acid with a concentration of 5 mol / L, and dry at 60 °C for 12 h to obtain an intermediate product; S3: Place the intermediate product in a mixed atmosphere of Ar and H 2 and perform the second carbonization treatment at 900 °C for 1 h to obtain the PtCo alloy - modified carbon nanosheets.

[0056] Figure 1 This is the scanning electron microscope image of the PtCo alloy - modified carbon nanosheets prepared in Example 2 of the present invention at different magnification factors; where the scale of (A) is 1.00 μm, the scale of (B) is 2.00 μm, and the scale of (C) is 3.00 μm. It can be seen from the figure that the PtCo alloy - modified carbon nanosheets are mainly composed of irregular carbon nanosheets with a thickness of about 100 nm, and there are abundant pore structures on the carbon nanosheets due to the salt template.

[0057] Figure 2 This is the polarization curve of the PtCo alloy - modified carbon nanosheets prepared in Example 2 of the present invention and commercial Pt / C + RuO 2 . It can be seen from the figure that the over - potential of PtCo - CNS is 390 mV, while that of commercial Pt / C + RuO 2The overpotential is 520 mV. The overpotential is the difference between the actual potential and the theoretical potential in an electrochemical reaction, which reflects the energy loss of the catalyst in promoting the reaction. The lower the overpotential, the smaller the energy loss of the catalyst in promoting the reaction, and the higher the catalytic efficiency. The overpotential of the carbon nanosheets modified with PtCo alloy prepared in Example 2 of the present invention is significantly lower than that of commercial Pt / C+RuO 2 , so the carbon nanosheets modified with PtCo alloy prepared in the present invention have good catalytic performance.

[0058] Figure 3 This is the cyclic voltammetry characteristic curve of the carbon nanosheets modified with PtCo alloy prepared in Example 2 of the present invention and commercial Pt / C+RuO 2 . It can be seen from the figure that the oxygen reduction potential of PtCo-CNS in 0.1 M KOH solution is 0.9 V, which is higher than that of commercial Pt / C+RuO 2 catalyst. The oxygen reduction potential is an important index for evaluating the catalytic activity of the catalyst for the oxygen reduction reaction. The higher the potential, the better the catalytic activity of the catalyst for the oxygen reduction reaction. Therefore, the advantage of PtCo-CNS in terms of oxygen reduction potential further proves its high catalytic activity.

[0059] Figure 4 This is the time-normalized current percentage relationship diagram of the carbon nanosheets modified with PtCo alloy prepared in Example 2 of the present invention as an electrocatalyst and commercial Pt / C+RuO 2 . It can be seen from the figure that after 10 hours of testing, the carbon nanosheets modified with PtCo alloy still maintain 91% of the initial current value when used as an electrocatalyst. Therefore, the PtCo-CNS catalyst has excellent long-term stability in the ORR and OER processes.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and do not limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a PtCo alloy-modified carbon nanosheet, characterized in that: The following steps are involved: S1: mixing a platinum source, a cobalt source, a nitrogen-containing organic matter, chitosan and a molten salt, and ball-milling the mixture to obtain a mixed powder; S2: placing the mixed powder in a nitrogen atmosphere for a first carbonization treatment; then performing an acid wash treatment and drying to obtain an intermediate product; S3: placing the intermediate product in a mixed atmosphere of Ar and H2 for secondary carbonization treatment to obtain the PtCo alloy-modified carbon nanosheets.

2. The method for preparing a PtCo alloy-modified carbon nanosheet according to claim 1, characterized in that: The ratio of the platinum source, the cobalt source, the nitrogen-containing organic matter, the chitosan and the molten salt is (10-60) mg: (10-60) mg: (1-10) g: (1-10) g: (1-20) g.

3. The method for preparing a PtCo alloy-modified carbon nanosheet according to claim 1, characterized in that: The ratio of the platinum source, the cobalt source, the nitrogen-containing organic matter, the chitosan and the molten salt is 30 mg: 30 mg: 4 g: 1 g: 10 g.

4. The method for preparing a PtCo alloy-modified carbon nanosheet according to claim 1, characterized in that: The ball milling treatment time is 10 to 60 minutes.

5. The method for preparing a PtCo alloy-modified carbon nanosheet according to claim 1, characterized in that: The temperature of the first carbonization treatment is 600-900° C. and the time is 1-5 hours.

6. The method for preparing a PtCo alloy-modified carbon nanosheet according to claim 1, characterized in that: During the pickling process, the acid used is hydrochloric acid with a concentration of 1-5 mol / L.

7. The method for preparing a PtCo alloy-modified carbon nanosheet according to claim 1, characterized in that: After the acid washing and drying, an intermediate product is obtained, wherein the drying temperature is 40-60° C. and the drying time is 12-20 hours.

8. The method for preparing a PtCo alloy-modified carbon nanosheet according to claim 1, characterized in that: The temperature of the secondary carbonization treatment is 600-900° C., and the time is 1-5 hours.

9. A PtCo alloy modified carbon nanosheet, characterized in that: Prepared by the method according to any one of claims 1 to 8.

10. A zinc-air battery, characterized in that: The invention comprises a PtCo alloy-modified carbon nanosheet as claimed in claim 9.

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