Transition metal electrocatalysts enriched with twin structures, methods of making and using the same

Abstract

The application belongs to the technical field of electrocatalysts, and discloses a preparation method of a transition group metal electrocatalyst rich in twin crystal structures, which comprises the following steps: dissolving a water-soluble transition group metal salt, a certain amount of sodium citrate and polyvinylpyrrolidone in water in a certain component ratio to form a solution A; dissolving a Prussian blue analogue in water to form a solution B; under stirring, the solution B is added to the solution A, and stirring is continued for a certain time to perform reaction; the obtained precipitate is washed and dried, and then carbonization treatment is performed under the protection of an inert atmosphere; after the carbonized sample is pickled by an acidic solution, centrifugal separation, washing and drying are performed to obtain the transition group metal electrocatalyst rich in twin crystal structures. The electrocatalyst synthesized by the preparation method has a metal and carbon material composite composition, has excellent catalytic performance on different reactions such as OER, ORR and HER in an alkaline environment, and has good stability.

Description

Technical Field

[0001] This invention relates to the field of electrocatalyst technology, specifically to a transition metal electrocatalyst rich in twinned structures, its preparation method, and its application. Background Technology

[0002] Because fossil fuels cause numerous environmental problems (e.g., the greenhouse effect), technologies related to the acquisition and utilization of clean energy have received widespread attention and research worldwide. Typical examples include metal-air batteries, hydrogen-oxygen fuel cells, and water electrolysis for hydrogen production. These technologies essentially utilize redox reactions involving multiple electron transfers to convert electrical energy into chemical energy. For instance, the charging and discharging reactions of metal-air batteries, which can store energy on a large scale, are oxygen evolution (OER) and oxygen reduction (ORR), respectively; the fuel cell reaction essentially utilizes the oxidation of hydrogen (HOR) and reduction of oxygen (ORR) to generate electrical energy; and in water electrolysis for hydrogen production as a green high-energy fuel, oxygen evolution (OER) and hydrogen evolution (HER) reactions occur at the positive and negative electrodes under an applied voltage. Therefore, the use of electrocatalysts plays a crucial role in promoting these redox reactions involving multiple electron transfers, effectively reducing overvoltage and improving the energy conversion efficiency of corresponding clean energy devices.

[0003] However, a common problem faced by the clean energy technologies listed above is the lack of inexpensive, efficient, and stable electrocatalysts. For example, the most efficient electrocatalyst for the hydrogen evolution reaction in water electrolysis is expensive platinum, which is costly and easily poisoned by methanol and CO; the most effective electrocatalysts for the OER and ORR reactions are expensive precious metals such as Ir / Ru and Pt.

[0004] Transition metal-based electrocatalysts, due to their tunable 3d orbitals, exhibit catalytic performance comparable to that of noble metals while possessing good stability, thus becoming an important direction in electrocatalyst development. In particular, multifunctional transition metal-based electrocatalysts can demonstrate high electrocatalytic activity for a variety of redox reactions, such as OER / ORR / HER. Therefore, this could further reduce catalyst costs, facilitating the popularization and promotion of the aforementioned clean energy technologies. However, a low-cost method for preparing multifunctional transition metal-based electrocatalysts is still lacking. Furthermore, the performance of currently prepared multifunctional electrocatalysts still falls far short of that of their corresponding noble metal-based electrocatalysts.

[0005] For example, patent CN113388847B discloses a metal sulfide / nitrogen-doped carbon electrocatalyst, which essentially involves carbonizing a Prussian blue homologue followed by ammonia etching and atmospheric sulfidation to form a heterostructure. While the product exhibits stable activity, its preparation process is complex and prone to wastewater and gas pollution. Furthermore, the product only demonstrates good catalytic activity for HER and OER in alkaline media. The electrocatalyst synthesized by the method described in this application is a metal / nitrogen-doped carbon electrocatalyst composite containing abundant nanotwinned structures. The preparation process is simple and easy, with almost no emissions. It exhibits excellent catalytic performance for various reactions such as OER, ORR, and HER in alkaline environments, and demonstrates good stability.

[0006] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of this application and facilitating understanding by those skilled in the art. It should not be assumed that these technical solutions are known to those skilled in the art simply because they have been described in the background section of this application. Summary of the Invention

[0007] In view of the above-mentioned shortcomings, this invention provides a transition metal electrocatalyst rich in twinned structures, its preparation method, and its applications. This invention provides a transition metal-based composite electrocatalyst that simultaneously introduces dispersed single / dual-atom structures, alloy particles, and, most importantly, twinned structures through controlled carbonization and in-situ crystal transformation. The electrocatalyst synthesized by the method of this application is a metal-carbon composite material, exhibiting excellent catalytic performance for various reactions such as OER, ORR, and HER in an alkaline environment, and demonstrating good stability.

[0008] To achieve the above objectives, the present invention provides a method for preparing a transition metal electrocatalyst rich in twinned structures, comprising the following steps:

[0009] Step 1: Dissolve a water-soluble transition metal salt with a certain ratio, as well as a certain amount of sodium citrate and polyvinylpyrrolidone in water to form solution A; dissolve a Prussian blue analogue in water to form solution B;

[0010] Step 2: Under stirring conditions, add solution B to solution A and continue stirring for a certain period of time to carry out the reaction. After washing and drying the precipitate obtained from the reaction, perform carbonization treatment under an inert atmosphere.

[0011] Step 3: After the carbonized sample is acid-washed with an acidic solution, it is then centrifuged, washed, and dried to obtain a transition metal electrocatalyst rich in twinned structures.

[0012] According to one aspect of the present invention, in step 1, the transition metal includes two or more metals selected from Fe, Co, and Ni, and the water-soluble transition metal salt includes any one or more of the sulfate, acetate, chloride, and nitrate salts corresponding to the transition metal.

[0013] According to one aspect of the invention, the water-soluble transition metal salt comprises a cobalt salt and a nickel salt, wherein the water-soluble transition metal salt and the Prussian blue analogue are integrally present, and the molar ratio of cobalt to nickel is 7:2.

[0014] According to one aspect of the present invention, the molar ratio of sodium citrate to the total metal ions in the water-soluble transition metal salt is 0.1-1:1-5; the mass ratio of polyvinylpyrrolidone to the total metal ions in the water-soluble transition metal salt is 0.1-1:1-5 (g / mmol).

[0015] According to one aspect of the invention, in step 1, the Prussian blue analogue includes one or more of K3Co(CN)6, Na3Co(CN)6, K3Fe(CN)6, and Na3Fe(CN)6.

[0016] According to one aspect of the present invention, in step 2, the reaction time for continuing stirring for a certain period of time is 1 to 12 hours; the inert atmosphere is Ar or N2; the carbonization treatment specifically involves heating to 500 to 900°C at a rate of 1 to 10°C / min and holding at that temperature for 0.5 to 5 hours.

[0017] According to one aspect of the invention, in step 3, H in the acidic solution + The concentration of ions is 0.1–7 mol / L.

[0018] According to one aspect of the present invention, in step 3, the pickling temperature is room temperature to 100°C, and the pickling time is 0.5 to 72 hours.

[0019] Based on the same inventive concept, the present invention also provides a transition metal electrocatalyst rich in twin structures prepared by any of the above preparation methods. The electrocatalyst utilizes the fact that when alloy particles of different components of transition metals are carbonized at a certain temperature, carbon coating and in-situ phase structure transformation occur simultaneously, inducing the generation of a large number of intracrystalline twin structures. Combined with nitrogen-doped carbon, metal atom-doped carbon, and alloy particles, a multi-level multi-site catalytic system is formed.

[0020] Based on the same inventive concept, this invention also discloses an application of the above-mentioned transition metal electrocatalyst rich in twinned structure or the transition metal electrocatalyst rich in twinned structure prepared by any of the above preparation methods. The specific application of the electrocatalyst is to accelerate the evolution of oxygen, the reduction of oxygen and the evolution of hydrogen in an alkaline environment.

[0021] Mechanism of this invention: This invention uses Prussian blue analogues of transition metals as templates to prepare transition metal-carbon composites via a one-step carbonization method. Due to the porous metal-organic framework structure of Prussian blue analogues, controlled carbonization results in the formation of a porous carbon matrix containing a metal-NC structure. Through compositional design, transition metals can also polymerize into metal or alloy nanoparticles. Moreover, under appropriate composition and conditions, the metal / alloy nanoparticles undergo a phase transition from a high-temperature phase to a low-temperature phase after carbonization, which easily induces intracrystalline twinning, further modulating catalytic performance. Acid washing removes the exposed metal / alloy particles, leaving behind carbon-coated metal / alloy nanoparticle structures. The resulting composite electrocatalyst rich in twinned structures exhibits good conductivity and multifunctional catalytic activity, effectively reducing the overpotentials of OER, ORR, and HER under alkaline conditions, and demonstrating excellent long-term stability. This method has significant theoretical and practical implications for the development of non-noble metal-based multifunctional electrocatalysts and energy conversion and storage devices.

[0022] The beneficial effects of this invention are:

[0023] The structural morphology of this invention is a composite structure of carbon@alloy particles doped with Co / Ni / N. This invention utilizes the simultaneous carbon coating and in-situ phase transformation (e.g., the fcc-hcp phase transformation of Co7Ni2 alloy nanoparticles during carbonization and cooling at a certain temperature) of alloy particles with different transition metal compositions. This induces a large number of intracrystalline twin structures, which, combined with nitrogen-doped carbon, metal atom-doped carbon, and alloy particles, form a unique multi-level, multi-site catalytic system. Ultimately, this multi-level composite structure endows it with high catalytic activity for various reactions (such as OER, ORR, HER, etc.) in alkaline environments, while also possessing good stability. Attached Figure Description

[0024] Figure 1 (a) is a morphology image of the electrocatalyst of Example 1 of the present invention under low magnification transmission, which includes nanoparticles and hollow carbon spheres. Figure 1 (b) is Figure 1 (a) Morphology of hollow carbon spheres under high magnification transmission; Figure 1 (c) is Figure 1 (a) Morphology of hollow carbon spheres under high magnification dark field transmission, with bright spots representing metal atoms doped into the carbon matrix; Figure 1 (d) is Figure 1 (a) Morphology of Co7Ni2 nanoparticles under high magnification transmission; Figure 1 (e) is Figure 1 (d) An IFFT image of the boxed area, which clearly shows the twin structure;

[0025] Figure 2 (a) is a morphology image of the electrocatalyst of Comparative Example 1 of the present invention under low magnification transmission, which includes nanoparticles and hollow carbon spheres. Figure 2 (b) is Figure 2 (a) shows the morphology of the electrocatalyst under high magnification transmission, where hollow carbon structure and nanoparticles coexist. Figure 2 (c) is Figure 2 (a) Morphology of hollow carbon spheres under high magnification dark field transmission, with bright spots representing metal atoms doped into the carbon matrix; Figure 2 (d) is Figure 2 (a) Morphology of Co5Ni4 nanoparticles under high magnification transmission. Their structure is uniform, consisting of a pure fcc phase, without lattice distortion or other abnormalities. Figure 1 (d) Similar twinning structures;

[0026] Figure 3 (a) is a high-magnification dark-field transmission morphology image of the hollow carbon structure of the electrocatalyst of Comparative Example 2 of the present invention, wherein bright spots represent metal atoms doped into the carbon matrix. Figure 3 (b) is Figure 3 (a) Morphology of Co6Ni3 nanoparticles under high-resolution transmission imaging. Their structure is uniform, consisting of a pure fcc phase, without lattice distortion or other abnormalities. Figure 1 (d) Similar twinning structures; Figure 3 (c) is a high-magnification dark-field transmission morphology image of the hollow carbon structure of the electrocatalyst of Comparative Example 3 of the present invention, where the bright spots represent metal atoms doped into the carbon matrix. Figure 3 (d) is Figure 3 (c) shows the morphology of the Co-Co nanoparticles under high-resolution transmission. Their structure is uniform, consisting of a pure hcp phase, without lattice distortion or other abnormalities. Figure 1 (d) Similar twinning structures; Figure 3 (e) is a high-magnification dark-field transmission morphology image of the hollow carbon structure of the electrocatalyst of Comparative Example 4 of the present invention, where the bright spots represent metal atoms doped into the carbon matrix. Figure 3 (f) is Figure 3 (e) shows the morphology of the Co3Ni6 nanoparticles under high-resolution transmission. Their structure is uniform, consisting of a pure fcc phase, without lattice distortion or other abnormalities. Figure 1 (d) Similar twinning structures;

[0027] Figure 4(a) LSV curves of the OER reaction of the electrocatalysts of Example 1 and Comparative Examples 1-4 in 1 M KOH solution at a rotating disk speed of 1600 rpm. Figure 4 (b) LSV curves of the HER reaction of the electrocatalysts of Example 1 and Comparative Examples 1-4 in 1M KOH solution at a rotating disk speed of 1600 rpm. Figure 4 (c) LSV curves of the ORR reaction of the electrocatalysts of Example 1 and Comparative Examples 1-4 in 0.1M KOH solution at a rotating disk speed of 1600 rpm;

[0028] Figure 5 (a) is a physical image of the zinc-air battery device for preparing and testing the electrocatalyst according to Example 1 of the present invention; Figure 5 (b) is the discharge voltage-discharge current density and battery output power density curve of the electrocatalyst described in Example 1 of the present invention; Figure 5 (c) is the battery cycle curve of the electrocatalyst described in Example 1 of the present invention. The blue arrows in the figure represent the addition of electrolyte.

[0029] Figure 6 The electrocatalyst described in Example 1 of this invention is used as the positive and negative electrode electrocatalyst for water electrolysis and cracking stability test curves. The inset images are photos of the corresponding devices.

[0030] Figure 7 (a) Stability test of the electrocatalyst described in Example 1 of the present invention at different voltages; Figure 7 (b) is a high-resolution transmission image of the electrocatalyst described in Example 1 of the present invention after OER stabilization test. The white arrows indicate the twin structure that still exists. Figure 7 (c) is a high-resolution transmission image of the electrocatalyst described in Example 1 of the present invention after HER stabilization test. The white arrows indicate the twin structure that still exists. Figure 7 (d) is a high-resolution transmission image of the electrocatalyst described in Example 1 of the present invention after ORR stability test. The white arrows indicate the twin structure that still exists. Detailed Implementation

[0031] To make the present invention easier to understand, specific embodiments are described below to further illustrate the invention. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical terms used below have the same meaning as understood by those skilled in the art; unless otherwise specified, the raw materials and reagents involved herein can be purchased commercially or obtained by known methods.

[0032] Currently, a common problem facing clean energy technologies is the lack of inexpensive, efficient, and stable electrocatalysts.

[0033] To address the above problems, this invention provides a method for preparing a transition metal electrocatalyst rich in twinned structures, comprising the following steps:

[0034] Step 1: Dissolve a water-soluble transition metal salt with a certain ratio, as well as a certain amount of sodium citrate and polyvinylpyrrolidone in water to form solution A; dissolve a Prussian blue analogue in water to form solution B;

[0035] Preferably, in step 1, the transition metal includes two or more metals selected from Fe, Co, and Ni, and the water-soluble transition metal salt includes any one or more of the sulfate, acetate, chloride, and nitrate salts corresponding to the transition metal. Preferably, the water-soluble transition metal salt includes cobalt salt and nickel salt, and the water-soluble transition metal salt and Prussian blue analogue are used as a whole, wherein the molar ratio of cobalt to nickel is 7:2. Preferably, the molar ratio of sodium citrate to the total metal ions in the water-soluble transition metal salt is 0.1–1:1–5; more preferably, the molar ratio of sodium citrate to the total metal ions in the water-soluble transition metal salt is 1:1; the mass ratio of polyvinylpyrrolidone to the total metal ions in the water-soluble transition metal salt is 0.1–1:1–5 (g / mmol); more preferably, the mass ratio of polyvinylpyrrolidone to the total metal ions in the water-soluble transition metal salt is 1:6 (g / mmol). Preferably, in step 1, the Prussian blue analogue includes one or more of K3Co(CN)6, Na3Co(CN)6, K3Fe(CN)6, and Na3Fe(CN)6.

[0036] Step 2: Under stirring conditions, add solution B to solution A and continue stirring for a certain period of time to carry out the reaction. After washing and drying the precipitate obtained from the reaction, perform carbonization treatment under an inert atmosphere.

[0037] Preferably, in step 2, the reaction time for continued stirring is 1–12 hours; the inert atmosphere is Ar or N2; the carbonization treatment specifically involves heating to 500–900°C at a rate of 1–10°C / min and holding at that temperature for 0.5–5 hours; more preferably, the reaction time for continued stirring is 12 hours; the inert atmosphere is N2; the carbonization treatment specifically involves heating to 600°C at a rate of 5°C / min and holding at that temperature for 1 hour. Preferably, the carbonization treatment is specifically carried out in a tube furnace.

[0038] Step 3: After the carbonized sample is acid-washed with an acidic solution, it is then centrifuged, washed, and dried to obtain a transition metal electrocatalyst rich in twinned structures.

[0039] Preferably, in step 3, the H in the acidic solution + The concentration of ions is 0.1–7 mol / L; more preferably, the acidic solution contains H+. + The concentration of ions is 0.5–4 mol / L. Preferably, in step 3, the acid washing temperature is room temperature to 100°C, the acid washing time is 0.5–72 hours, and the acidic solution is preferably hydrochloric acid; more preferably, the acid washing temperature is room temperature to 80°C, and the acid washing time is 24 hours.

[0040] The following detailed explanation is further illustrated with specific examples.

[0041] Example 1

[0042] A method for preparing a transition metal electrocatalyst rich in twinned structures:

[0043] 4 mmol CoSO4·7H2O, 2 mmol Ni(CH3COO)2·4H2O, 1 g polyvinylpyrrolidone (PVP), and 6 mmol sodium citrate dihydrate (Na3C6H5O7·2H2O) were dissolved in 40 ml of deionized water to form solution A; 3 mmol K3Co(CN)6 was also dissolved in 40 ml of deionized water to form solution B. Solution B was slowly added to solution A with stirring at room temperature and stirring was continued for 12 hours. The resulting precipitate was washed and dried, and then heated to 600 °C at a rate of 5 °C / min and held for 1 hour under a N2 atmosphere. Finally, the carbonized sample was stirred in 4 M HCl solution at 80 °C for 24 hours. Finally, it was washed and dried to obtain the final product. The total content ratio of Co to Ni was 7 (4 mmol CoSO4 + 3 mmol K3Co(CN)6):2. Its morphology and structure are as follows. Figure 1 As shown.

[0044] Comparative Example 1

[0045] Based on Example 1, CoSO4·7H2O and Ni(CH3COO)2·4H2O were changed to 2 mmol and 4 mmol, respectively, while the other preparation methods remained exactly the same as in Example 1, resulting in Comparative Example 1. The total content ratio of Co to Ni was 5 (2 mmol CoSO4 + 3 mmol K3Co(CN)6):4. Its morphology and structure are as follows... Figure 2 As shown.

[0046] Comparative Example 2

[0047] Based on Example 1, CoSO4·7H2O and Ni(CH3COO)2·4H2O were changed to 3 mmol and 3 mmol respectively, while the other preparation methods were exactly the same as in Example 1, resulting in Comparative Example 2. The total content ratio of Co to Ni was 6 (3 mmol CoSO4 + 3 mmol K3Co(CN)6):3. Its morphology and structure are as follows... Figure 3 As shown in (ab).

[0048] Comparative Example 3

[0049] Based on Example 1, CoSO4·7H2O and Ni(CH3COO)2·4H2O were changed to 6 mmol and 0 mmol, respectively, while the other preparation methods remained exactly the same as in Example 1, resulting in Comparative Example 3. The total content ratio of Co to Ni was 9 (6 mmol CoSO4 + 3 mmol K3Co(CN)6):0. Its morphology and structure are as follows: Figure 3 (cd) shown.

[0050] Comparative Example 4

[0051] Based on Example 1, CoSO4·7H2O and Ni(CH3COO)2·4H2O were changed to 0 mmol and 6 mmol, respectively, while the other preparation methods remained exactly the same as in Example 1, resulting in Comparative Example 4. The total content ratio of Co to Ni was 3 (0 mmol CoSO4 + 3 mmol K3Co(CN)6):6. Its morphology and structure are as follows: Figure 3 As shown in (ef).

[0052] Performance testing and results analysis:

[0053] The final products obtained in Examples 1 and 1-4 were ultrasonically mixed with propanol / ethanol / water and Nafion solution, and then drop-coated onto a glassy carbon electrode. Linear sweep voltammetry was performed in a 0.1–1.0 M KOH electrolyte to obtain the following results: Figure 4 The LSV curves shown in Figure 1 and the electrocatalytic performance shown in Table 1 are on the right. Figure 1As can be seen from Table 1, Example 1 significantly reduced the overpotentials for oxygen evolution, hydrogen evolution, and oxygen reduction, demonstrating optimal multifunctional catalytic characteristics.

[0054] Table 1:

[0055]

[0056] It should be noted that in Table 1:

[0057] a. This refers to a current density of 10 mA / cm² during the OER reaction. -2 The smaller the overvoltage, the better the OER performance.

[0058] b. This refers to an electrode current density reaching 10 mA / cm² during the HER reaction. -2 The smaller the overvoltage, the better the HER performance.

[0059] cE 1 / 2 It refers to the voltage at which the ORR reaches half of the saturation current; the higher the value, the smaller the ORR overpotential.

[0060] Depend on Figure 1 , Figure 2 and Figure 3 It is evident that the electrocatalyst structure of this invention simultaneously contains a diatomic structure, alloy particles, and, most importantly, a twinned structure. From Figure 4 It is known that the electrocatalyst of the present invention exhibits high catalytic activity for oxygen evolution (OER), 4-electron oxygen reduction (ORR), and hydrogen evolution reaction (HER) under alkaline conditions due to the combined action of three possible active sites. Figure 5-7 It can be seen that the electrocatalyst of Example 1, as the only catalyst in the actual electrochemical device, has high catalytic performance and good stability, thus improving the energy efficiency of the device.

[0061] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a transition metal electrocatalyst rich in twinned structures, characterized in that, Includes the following steps: Step 1: Dissolve a water-soluble transition metal salt in a certain proportion, along with a certain amount of sodium citrate and polyvinylpyrrolidone, in water to form solution A; dissolve a Prussian blue analog in water to form solution B; wherein the water-soluble transition metal salt is a cobalt salt and a nickel salt, and the water-soluble transition metal salt and the Prussian blue analog are used as a whole, wherein the molar ratio of cobalt to nickel is 7:2; the Prussian blue analog is one or more of K3Co(CN)6 and Na3Co(CN)6; Step 2: Under stirring conditions, add solution B to solution A and continue stirring for a certain period of time to allow the reaction to proceed. After washing and drying the precipitate obtained from the reaction, perform carbonization treatment under an inert atmosphere. The reaction time is 1-12 hours. The inert atmosphere is Ar or N2. The carbonization treatment specifically involves heating to 600°C at a rate of 1-10°C / min and holding at that temperature for 0.5-5 hours. Step 3: After the carbonized sample is acid-washed with an acidic solution, it is then centrifuged, washed, and dried to obtain a transition metal electrocatalyst rich in twinned structures.

2. The method for preparing a transition metal electrocatalyst rich in twinned structures according to claim 1, characterized in that, In step 1, the water-soluble transition metal salt includes any one or more of the sulfates, acetates, chlorides, and nitrates corresponding to the transition metals.

3. The method for preparing a transition metal electrocatalyst rich in twinned structures according to claim 1, characterized in that, The molar ratio of sodium citrate to the total metal ions in the water-soluble transition metal salt is 0.1~1:1~5; the molar ratio of the mass of polyvinylpyrrolidone to the total metal ions in the water-soluble transition metal salt is 0.1~1:1~5, where mass is measured in g and molar amount is measured in mmol.

4. The method for preparing a transition metal electrocatalyst rich in twinned structures according to claim 1, characterized in that, In step 3, the H in the acidic solution + The concentration of ions is 0.1~7 mol / L.

5. The method for preparing a transition metal electrocatalyst rich in twinned structures according to claim 1, characterized in that, In step 3, the pickling temperature is room temperature to 100°C, and the pickling time is 0.5 to 72 hours.

6. A transition metal electrocatalyst rich in twinned structures prepared by any one of the preparation methods described in claims 1-5, characterized in that, The electrocatalyst utilizes the carbonization of alloy particles of different transition metals at a certain temperature, which simultaneously undergoes carbon coating and in-situ phase structure transformation, inducing the generation of a large number of intracrystalline twin structures. Combined with nitrogen-doped carbon, metal atom-doped carbon, and alloy particles, a multi-level, multi-site catalytic system is formed.

7. The application of a transition metal electrocatalyst rich in twinned structure prepared by any one of the preparation methods of claims 1-5 or the transition metal electrocatalyst rich in twinned structure according to claim 6, characterized in that, The specific application of the electrocatalyst is to accelerate the evolution of oxygen, the reduction of oxygen, and the evolution of hydrogen in an alkaline environment.

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