Heteroatom-doped carbon nanohorn catalyst as well as preparation method and application thereof

Abstract

According to the heteroatom-doped carbon nanohorn catalyst and the preparation method and application thereof, doping elements are accurately introduced into a carbon nanohorn framework in the preparation process of the catalyst, a stable heterostructure is formed, two-dimensional adsorption and activation of O2 molecules on the surface of an electrode are effectively enhanced, a two-electron reduction path is remarkably promoted, and the heteroatom-doped carbon nanohorn catalyst is prepared. The four-electron reduction side reaction is inhibited, the H2O2 selectivity and the oxygen reduction reaction (ORR) activity are enhanced, and the H2O2 yield and the Faraday efficiency are remarkably improved. Meanwhile, the heteroatom-doped carbon nanohorn catalyst has high electrochemical stability in a chloride ion-containing system, shows excellent stability and corrosion resistance under a natural seawater condition, and is suitable for long-time continuous operation.

Description

Technical Field

[0001] The present invention relates to the field of electrocatalytic materials, and in particular to a heteroatom-doped carbon nanohorn catalyst for electrochemical synthesis of hydrogen peroxide from seawater, and a preparation method and application thereof. Background Art

[0002] Hydrogen peroxide (H2O2) is a green and efficient oxidant widely used in disinfection, environmental protection, chemical industry and other fields. The traditional industrial preparation method is mainly based on the anthraquinone method. Although this process has been commercialized, it has problems such as complex process, high energy consumption and organic solvent pollution, which makes it difficult to meet the needs of distributed and green production. In recent years, based on 2e - The electrochemical synthesis of H2O2 via the ORR pathway has attracted widespread attention due to its mild reaction conditions, pure products, and easy regulation.

[0003] However, in practical applications, especially in high-salinity seawater systems, electrocatalytic H2O2 synthesis still faces numerous challenges. First, the high concentration of chloride ions in seawater can easily corrode and poison the catalyst, reducing its activity and stability. Second, existing catalysts struggle to balance selectivity, current density, and Faradaic efficiency, making it difficult to maintain stable output at high current densities. Therefore, there is an urgent need to develop electrocatalytic materials that combine high activity, excellent selectivity, and resistance to chloride corrosion. Summary of the Invention

[0004] In light of the above, the present invention aims to address the problems of insufficient selectivity, poor chlorine corrosion resistance, and low stability associated with existing catalysts in the electrosynthesis of H2O2 from seawater. The invention provides a heteroatom-doped carbon nanohorn catalyst with high selectivity, high current adaptability, and excellent resistance to chlorine corrosion. This catalyst utilizes carbon nanohorns as its primary carbon-based framework. By doping with heteroatoms such as nitrogen (N), boron (B), phosphorus (P), and chlorine (Cl), the catalyst modulates its electronic structure, enhancing the activity and selectivity of the oxygen reduction reaction while also improving its electrochemical stability in chloride-containing systems.

[0005] To this end, in a first aspect, an embodiment of the present invention provides a heteroatom-doped carbon nanohorn catalyst, comprising a carbon-based framework with carbon nanohorns as the main body, and a heteroatom doping element distributed on the surface or in the pores of the carbon nanohorns, wherein the doping element is selected from one or more of nitrogen (N), boron (B), phosphorus (P), and chlorine (Cl). The heteroatom-doped carbon nanohorn catalyst is used for the electrochemical synthesis of H2O2.

[0006] Preferably, the doping element source is urea, ammonia, phosphorus trichloride, triphenylboron, boron trichloride, ammonium nitrate, phosphoric acid, sodium chloride, metal complexes containing organic ligands, and organic or inorganic compounds containing nitrogen (N), boron (B), phosphorus (P), and chlorine (Cl).

[0007] In a second aspect, an embodiment of the present invention provides a method for preparing the heteroatom-doped carbon nanohorn catalyst provided in the first aspect. The preparation method comprises: step S1: dispersing carbon nanohorns in an oxidant solution, ultrasonically treating the carbon nanohorns at room temperature, reflux stirring the carbon nanohorns in an oil bath for a certain period of time, washing the carbon nanohorns with deionized water until neutral, and drying the carbon nanohorns to obtain pretreated carbon nanohorns; step S2: uniformly mixing the pretreated carbon nanohorns with a selected doping element precursor in a certain proportion to form a precursor-loaded composite; step S3: placing the precursor-loaded composite in a tube furnace, heating and holding the composite under a protective atmosphere for a period of time to form a solid product having a stable heteroatom embedded structure; and step S4: removing the solid product, cleaning the solid product with an acidic solution by ultrasonic stirring, washing the solid product with deionized water until neutral, and drying the solid product to obtain the heteroatom-doped carbon nanohorn catalyst.

[0008] Preferably, in step S1, the oxidant is 65% concentrated nitric acid or 30% H2O2 aqueous solution; the ultrasonic treatment time is 30-60 minutes; the oil bath temperature is 60-80°C; the stirring time is 3-6 hours; the drying method is vacuum drying, the drying temperature is 60°C, and the drying time is 12-24 hours.

[0009] Preferably, in step S2, the doping element precursor is one or more combinations of urea, ammonia, phosphorus trichloride, triphenylboron, boron trichloride, ammonium nitrate, phosphoric acid, sodium chloride, metal complexes containing organic ligands, and organic or inorganic compounds containing nitrogen (N), boron (B), phosphorus (P), and chlorine (Cl).

[0010] Preferably, in step S2, the mass ratio of the carbon nanohorns to the doping element precursor is between 1:1 and 1:10; and the mixing method includes manual grinding, ball milling, and immersion.

[0011] Preferably, in step S3, the protective atmosphere is argon or nitrogen with a purity of ≥99.99%; the heating process is to heat the temperature to 600-900°C at a heating rate of 5-10°C / min, and the holding time is 1-4 hours.

[0012] Preferably, in step S4, the acidic solution is dilute hydrochloric acid with a concentration of 1 mol / L or sulfuric acid with a concentration of 0.5 mol / L; the drying method is vacuum drying, the drying temperature is 60° C., and the drying time is 12-24 hours.

[0013] In a third aspect, the embodiments of the present application provide a method for synthesizing H2O2 by seawater electrolysis, which comprises: coating the heteroatom-doped carbon nanohorn catalyst provided in the first aspect of the present application on the surface of carbon paper or carbon cloth as a cathode electrode, using a titanium mesh or iridium oxide coated electrode as an anode, and using natural seawater as an electrolyte to realize efficient synthesis of H2O2 at a constant potential of -0.6 V to -0.2 V vs. RHE.

[0014] In a fourth aspect, the embodiments of the present application provide a device for synthesizing H2O2 by seawater electrolysis, which applies the method for synthesizing H2O2 by seawater electrolysis provided in the third aspect of the present application, and the device comprises:

[0015] (1) Cathode: coating the heteroatom-doped carbon nanohorn catalyst as claimed in claim 1 or 2 on the surface of carbon paper or carbon cloth;

[0016] (2) Anode: titanium mesh or iridium oxide coated electrode;

[0017] (3) Electrolytic cell: made of corrosion-resistant polytetrafluoroethylene material, equipped with a temperature sensor, a pH probe and a constant potential power supply;

[0018] (4) Collection module: separate the cathode area by ion exchange membrane to realize continuous separation and collection of H2O2.

[0019] The heteroatom-doped carbon nanohorn catalyst provided in the embodiments of the present application precisely introduces the doping elements into the carbon nanohorn skeleton through heat treatment, molten salt method or gas phase doping, forms a stable heterostructure, effectively enhances the two-dimensional adsorption and activation of O2 molecules on the electrode surface, significantly promotes the two-electron reduction path, inhibits the four-electron reduction side reaction, significantly improves the yield and Faraday efficiency of H2O2, reduces the occurrence of side reactions, and reduces the cost of product separation and purification. At the same time, the introduction of heteroatoms enhances the corrosion resistance of the catalyst to chloride ions, improves the electrochemical stability of the catalyst in the chloride ion system, and enables it to operate stably for a long time in seawater with high salinity. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The preparation method flowchart of the heteroatom-doped carbon nanohorn catalyst provided in the embodiments of the present application;

[0021] Figure 2 The transmission electron microscope image of the heteroatom-doped carbon nanohorn catalyst prepared in the embodiment 1 of the present application;

[0022] Figure 3 The electrochemical performance curve (a) of the boron atom-doped carbon nanohorn catalyst prepared in the embodiment 1 of the present application in seawater and the H2O2 selectivity (b) at different potentials;

[0023] Figure 4 The H2O2 yield and Faraday efficiency versus time graph of the boron atom-doped carbon nanohorn catalyst prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0024] Embodiments of the present application are described in detail below with reference to several examples illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments described below are exemplary and intended to provide an explanation of the present application, and are not intended to restrict the present application.

[0025] The following disclosure provides many different embodiments, or examples, for implementing different structures of the present application. For purposes of explanation and non- limitation, specific details of certain examples are set forth. Of course, many modifications and variations will be apparent to those skilled in the art. It is intended that the present application encompass all such modifications and variations as fall within the scope of the present application. In addition, it is intended that the present application encompass all such modifications and variations as fall within the scope of the present application. It is intended that the present application encompass all such modifications and variations as fall within the scope of the present application. In addition, the present application is presented by way of example only and should not be taken as limiting. Furthermore, the various examples of the present application can be used together.

[0026] The present application aims to provide a heteroatom-doped carbon nanohorn (CNH) catalyst and a preparation method thereof. By using carbon nanohorns as a catalyst substrate, utilizing their natural tip aggregation and edge defect structure, and combining heteroatom doping regulation strategies (such as nitrogen, boron, phosphorus, chlorine, etc.), a carbon-based catalyst with regulated electronic structure and active site distribution is constructed. During the preparation process, the doping elements are precisely introduced into the carbon nanohorn skeleton through heat treatment, molten salt method, or gas phase doping, etc., forming a stable heterostructure, effectively enhancing the two-dimensional adsorption and activation of O2 molecules on the electrode surface, significantly promoting the two-electron reduction path, inhibiting the four-electron reduction side reaction, and at the same time, improving the electrochemical stability of the catalyst in the chlorine ion-containing system.

[0027] The first aspect embodiment of the present application provides a heteroatom-doped carbon nanotube catalyst, which comprises a carbon-based framework with carbon nanotubes as the main body, and a heteroatom-doped element distributed on the surface or channel of the carbon-based framework, wherein the doped element is selected from one or more of nitrogen (N), boron (B), phosphorus (P), and chlorine (Cl), and is used for electrochemical synthesis of H2O2. The source of the doped element can be urea, ammonia, phosphorus trichloride, triphenylboron, boron trichloride, ammonium nitrate, phosphoric acid, sodium chloride, or a metal complex containing an organic ligand, and an organic or inorganic compound containing nitrogen (N), boron (B), phosphorus (P), and chlorine (Cl) elements. The doped element improves the electronic structure regulation ability of the catalyst and the corrosion resistance to chlorine ions.

[0028] The heteroatom-doped carbon nanotube catalyst provided by the present embodiment optimizes the electronic structure by introducing heteroatoms into the carbon nanotube, enhances the H2O2 selectivity and oxygen reduction reaction (ORR) activity, and significantly improves the yield and faradic efficiency of H2O2. At the same time, the heteroatom-doped carbon nanotube catalyst has high electrochemical stability in a chlorine ion-containing system, and exhibits excellent stability and corrosion resistance under natural seawater conditions, and is suitable for long-term continuous operation.

[0029] The second aspect embodiment of the present application provides a preparation method of a heteroatom-doped carbon nanotube catalyst, as shown in Figure 1 The preparation method comprises the following steps:

[0030] Step S1: disperse the carbon nanotubes in an oxidizing agent solution, treat by ultrasonic at room temperature, then reflux and stir in an oil bath for a certain time, wash with deionized water until neutral, and dry to obtain pretreated carbon nanotubes;

[0031] The oxidizing agent can be 65% concentrated nitric acid or 30% concentration H2O2 aqueous solution; the ultrasonic treatment time can be 30-60 minutes; the oil bath temperature can be 60-80℃; the stirring time can be 3-6 hours; and the drying method can be vacuum drying, the drying temperature can be 60℃, and the drying time can be 12-24 hours.

[0032] The pretreated carbon nanotubes introduce oxygen-containing functional groups such as carboxyl and hydroxyl groups, and form defect sites on the surface of the carbon nanotubes, which provide active centers for the introduction of subsequent doped elements and enhance the binding ability of the subsequent carbon nanotubes and the doped elements.

[0033] Step S2: uniformly mix the pretreated carbon nanotubes and the selected doped element precursor in a certain proportion to form a precursor-loaded composite;

[0034] The doping element precursor can be one or more combinations of urea, ammonia, phosphorus trichloride, triphenylboron, boron trichloride, ammonium nitrate, phosphoric acid, sodium chloride, a metal complex containing an organic ligand, and an organic or inorganic compound containing nitrogen (N), boron (B), phosphorus (P), and chlorine (Cl) elements; the mass ratio of the carbon nanohorn to the doping element precursor is between 1:1 and 1:10; and the mixing mode can be manual grinding, ball milling, impregnation, or the like.

[0035] Step S3: The precursor-loaded mixture is placed in a tube furnace, heated and kept in a protective atmosphere for a period of time to form a solid product with a stable heteroatom-embedded structure.

[0036] The protective atmosphere can be argon or nitrogen with a purity of ≥99.99%; the heating process is to heat to 600-900℃ at a heating rate of 5-10℃ / min, and the holding time can be 1-4 hours. In this process, not only can the combination between the heteroatom and the carbon skeleton be promoted, but also a porous structure with rich active sites can be induced to form, thereby enhancing the electrocatalytic activity and the resistance to chlorine ion corrosion.

[0037] Step S4: The solid product is taken out, cleaned with an acid solution under ultrasonic stirring, washed with deionized water until neutral, and then dried to obtain a heteroatom-doped carbon nanohorn catalyst.

[0038] The acid solution can be dilute hydrochloric acid with a concentration of 1mol / L or sulfuric acid with a concentration of 0.5mol / L; and the drying mode can be vacuum drying, the drying temperature can be 60℃, and the drying time can be 12-24 hours.

[0039] The preparation method of the heteroatom-doped carbon nanohorn catalyst provided in the embodiments introduces the doping element into the carbon nanohorn skeleton precisely through heat treatment, molten salt method, or gas phase doping, forms a stable heterostructure, effectively enhances the two-dimensional adsorption and activation of O2 molecules on the electrode surface, significantly promotes the two-electron reduction path, suppresses the four-electron reduction side reaction, significantly improves the yield of H2O2 and the Faraday efficiency, reduces the occurrence of side reactions, and reduces the cost of product separation and purification. At the same time, the introduction of the heteroatom enhances the corrosion resistance of the catalyst to chlorine ions, improves the electrochemical stability of the catalyst in a chlorine ion-containing system, and enables the catalyst to operate stably for a long time in seawater with high salinity.

[0040] A third embodiment of the present invention provides a method for electrolyzing H2O2 by seawater. The method comprises: coating the heteroatom-doped carbon nanohorn catalyst provided in the first embodiment of the present invention on a carbon paper or carbon cloth surface as a cathode electrode, using a titanium mesh or iridium oxide-coated electrode as an anode, and using natural seawater as an electrolyte to achieve efficient H2O2 synthesis at a constant potential. The constant potential can range from -0.6V to 0.2V vs. RHE; the current density is controlled to be 10-50mA·cm -2 , control the electrolyte temperature to 20-40℃.

[0041] A fourth embodiment of the present invention provides a device for synthesizing H2O2 by electrolyzing seawater, the device comprising:

[0042] (1) Cathode: Coating the heteroatom-doped carbon nanohorn catalyst provided by the first embodiment of the present invention on the surface of carbon paper or carbon cloth;

[0043] (2) Anode: titanium mesh or iridium oxide coated electrode;

[0044] (3) Electrolytic cell: Made of corrosion-resistant polytetrafluoroethylene, equipped with a temperature sensor, pH probe and constant potential power supply;

[0045] (4) Collection module: The cathode area is separated by an ion exchange membrane to achieve continuous separation and collection of H2O2.

[0046] The specific process and effects of the preparation method of the heteroatom-doped carbon nanohorn catalyst of the present invention are further described in detail below with reference to some specific examples, but are not intended to limit the scope of protection of the present invention.

[0047] Example 1

[0048] This embodiment provides a method for preparing a heteroatom-doped carbon nanohorn catalyst, wherein the heteroatom is a boron atom. The preparation method comprises the following steps:

[0049] Step S1: Disperse 1 g of carbon nanohorns in concentrated nitric acid, sonicate at room temperature for 30 minutes, reflux in an 80°C oil bath with stirring for 6 hours, then repeatedly wash with deionized water until the washing liquid becomes neutral, and dry in a 60°C vacuum drying oven for 12 hours.

[0050] Step S2: Mix the pretreated carbon nanohorns with 5 g of triphenylboron and ball mill them for 3 hours to ensure uniform dispersion to form a precursor-loaded composite.

[0051] Step S3: placing the precursor-loaded mixture in a tube furnace and heat-treating it under argon protection at a heating rate of 5°C / min and a heat treatment temperature of 800°C for 4 hours to uniformly incorporate the boron element into the structure of the carbon nanohorns, thereby obtaining a solid product;

[0052] Step S4: The solid product is taken out, cleaned with an acidic solution by ultrasonic stirring, and then repeatedly washed with deionized water until the washing solution is neutral. The solid product is dried in a vacuum drying oven at 60° C. for 12 hours to obtain a boron atom-doped carbon nanohorn catalyst.

[0053] Figure 2 Shown is a transmission electron microscope image of the boron atom-doped carbon nanohorn catalyst prepared in this example.

[0054] Example 2

[0055] This embodiment provides a method for preparing a heteroatom-doped carbon nanohorn catalyst, wherein the heteroatom is a boron atom. In this embodiment, only the carbon nanohorns and triphenylboron are mixed in a mass ratio of 1:1, that is, 1g of carbon nanohorns is mixed with 1g of triphenylboron. The remaining steps are the same as in Example 1.

[0056] Example 3

[0057] This embodiment provides a method for preparing a heteroatom-doped carbon nanohorn catalyst, wherein the heteroatom is a boron atom. In this embodiment, only the carbon nanohorns and triphenylboron are mixed at a mass ratio of 1:10, that is, 1g of carbon nanohorns is mixed with 10g of triphenylboron. The remaining steps are the same as in Example 1.

[0058] Example 4

[0059] This embodiment provides a method for preparing a heteroatom-doped carbon nanohorn catalyst, wherein the heteroatom is a boron atom. In this embodiment, only the heat treatment temperature in step S3 is changed to 600° C., and the remaining steps are the same as in Example 1.

[0060] Example 5

[0061] This embodiment provides a method for preparing a heteroatom-doped carbon nanohorn catalyst, wherein the heteroatom is a boron atom. In this embodiment, only the heat treatment temperature in step S3 is changed to 900° C., and the remaining steps are the same as in Example 1.

[0062] To verify the quality of the finished heteroatom-doped carbon nanohorn catalysts prepared by the methods for preparing heteroatom-doped carbon nanohorn catalysts provided in the embodiments of the present invention, the boron-doped carbon nanohorn catalysts prepared in Examples 1-5 were coated onto a carbon paper electrode. Nafion solution was used as a binder, and an iridium oxide-coated titanium mesh was used as the anode. Natural seawater was filled in an electrolytic cell as the electrolyte, and a long-term electrolysis experiment was conducted at a potential of 0 V vs. RHE. The test results are shown in Table 1.

[0063] in, Figure 3 Shown are the electrochemical performance curves of the boron atom-doped carbon nanohorn catalyst prepared in Example 1 of the present invention in seawater and the H2O2 selectivity at different potentials.

[0064] Table 1. Test items and test results of Examples 1-5

[0065] Example No. <![CDATA[H2O2产率(mmol·L -1 ·h -1 )]]> Faraday efficiency Example 1 212.2 98％ Example 2 120.7 96％ Example 3 128.4 97％ Example 4 98.9 95％ Example 5 146.9 98％

[0066] The test results show that the heteroatom-doped carbon nanohorn catalyst prepared by the preparation method of the heteroatom-doped carbon nanohorn catalyst provided by the embodiment of the present invention can achieve a H2O2 yield of 80-220 mmol·L in the potential range of -0.6V to 0.2V vs. RHE. -1 ·h -1 , Faraday efficiency ≥95%.

[0067] In addition, to verify the long-term stability of the heteroatom-doped carbon nanohorn catalyst provided by the embodiment of the present invention in seawater electrolysis, the boron-doped carbon nanohorn catalyst prepared in Example 1 of the present invention was coated on a carbon paper electrode and subjected to a long-term electrolysis experiment in natural seawater. The constant potential was 0 V vs. RHE, the test time was 55 hours, and the H2O2 yield and Faradaic efficiency were measured every 10 hours. The test results are shown in Figure 2. Figure 4 shown.

[0068] from Figure 4 It can be seen that during the 55-hour electrolysis process, the H2O2 yield of the boron atom-doped carbon nanohorn catalyst remained stable, and the Faradaic efficiency exceeded 95%, with no obvious catalytic performance degradation, proving its long life and high efficiency in practical applications.

[0069] In summary, the heteroatom-doped carbon nanohorn catalyst prepared by the present method optimizes its electronic structure by introducing heteroatoms into the carbon nanohorns, enhancing its H2O2 selectivity and oxygen reduction reaction (ORR) activity, significantly improving H2O2 yield and Faradaic efficiency. Furthermore, the heteroatom-doped carbon nanohorn catalyst exhibits high electrochemical stability in chloride ion-containing systems. In natural seawater conditions, the catalyst exhibits excellent stability and corrosion resistance, making it suitable for long-term continuous operation.

[0070] Furthermore, the heteroatom-doped carbon nanohorn catalyst prepared by the preparation method of the present invention is not only suitable for the electrolysis of seawater to synthesize H2O2, but can also be used in a variety of fields such as seawater disinfection, marine anti-fouling, and degradation of marine pollutants. Specific application scenarios include:

[0071] (1) In-situ sterilization of seawater: H2O2 synthesized by seawater electrolysis is directly released into the seawater pipe network and aquaculture systems. Due to its strong oxidizing properties, H2O2 can destroy bacteria and algae cells, inhibit their reproduction, reduce the number of microorganisms in the water, create a healthy seawater aquaculture environment, reduce the risk of disease, and increase aquaculture returns.

[0072] (2) Marine pollution control: Synthesized H2O2 works synergistically with photocatalysis and Fenton systems. In the photocatalytic system, H2O2 acts as an electron acceptor, accelerating the separation of photogenerated electrons and holes, and enhancing the oxidative decomposition of organic pollutants in marine plastic microparticles. In the Fenton system, it reacts with ferrous ions to generate hydroxyl radicals, which efficiently degrade organic pollutants and heavy metal chelates, protecting the ecological balance of the ocean.

[0073] (3) Antifouling of hulls and marine equipment: Utilizing the slow-release properties of H2O2, it can be applied to the surface of equipment. The continuously released H2O2 can effectively inhibit the attachment of marine organisms such as algae and shellfish, reduce biofouling, lower equipment energy consumption and maintenance costs, extend equipment life, and ensure efficient and safe marine operations.

[0074] (4) Distributed green energy system: The heteroatom-doped carbon nanohorn catalyst prepared by the present invention is integrated into an offshore floating electrochemical system. With the help of solar or wind energy, H2O2 is synthesized from seawater as raw material to achieve chemical energy storage and on-site energy conversion.

[0075] (5) Polar and offshore emergency oxygen supply and water purification systems: Synthetic H2O2 can be used for emergency water disinfection, killing pathogens and providing safe drinking water. At the same time, the oxygen produced by the decomposition of H2O2 can meet emergency oxygen supply needs, providing strong support for deep-sea scientific research and island disaster prevention.

[0076] In the description of the specification, the description using the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the particular feature, structure, material or characteristic being described is included in at least one embodiment or example of the present application. The illustrative appearances of the above-mentioned terms in various places in the specification are not necessarily referred to the same embodiment or example. Moreover, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples. Furthermore, the description herein of certain examples does not necessarily exclude these examples from the scope of the application, and these examples can be combined with each other for the purpose of patentable inventions.

[0077] Although the embodiments of the present application have been shown and described, it would be appreciated by those skilled in the art that changes, modifications, alternatives and variations to these embodiments could be made without departing from the principles and spirit of the application, and the scope of the application is defined by the claims and their equivalents.

Claims

1. A heteroatom-doped carbon nanohorn catalyst, characterized in that: The heteroatom-doped carbon nanohorn catalyst includes a carbon-based framework with carbon nanohorns as the main body, and heteroatom doping elements distributed on the surface or in the pores of the carbon nanohorns. The doping elements are selected from one or more of nitrogen (N), boron (B), phosphorus (P), and chlorine (Cl). The heteroatom-doped carbon nanohorn catalyst is used for electrochemical synthesis of H2O2.

2. A heteroatom-doped carbon nanohorn catalyst according to claim 1, characterized in that: The doping element source is urea, ammonia, phosphorus trichloride, triphenylboron, boron trichloride, ammonium nitrate, phosphoric acid, sodium chloride or a metal complex containing an organic ligand and an organic or inorganic compound containing nitrogen (N), boron (B), phosphorus (P), and chlorine (Cl).

3. A method for preparing the heteroatom-doped carbon nanohorn catalyst according to claim 1, characterized in that: The preparation method comprises: Step S1: dispersing carbon nanohorns in an oxidant solution, subjecting the solution to ultrasonic treatment at room temperature, stirring under reflux in an oil bath for a certain period of time, washing the solution with deionized water until neutral, and drying the solution to obtain pretreated carbon nanohorns; Step S2: uniformly mixing the pretreated carbon nanohorns and the selected doping element precursor in a certain proportion to form a precursor-loaded composite; Step S3: placing the precursor-loaded mixture in a tube furnace, heating and keeping it warm for a period of time under a protective atmosphere to form a solid product with a stable heteroatom embedded structure; Step S4: taking out the solid product, washing it with an acidic solution under ultrasonic stirring, then washing it with deionized water until it is neutral, and then drying it to obtain a heteroatom-doped carbon nanohorn catalyst.

4. The method for preparing heteroatom-doped carbon nanohorn catalyst according to claim 3, wherein: In step S1, the oxidant is 65% concentrated nitric acid or a 30% H2O2 aqueous solution; the ultrasonic treatment time is 30-60 minutes; the oil bath temperature is 60-80°C; the stirring time is 3-6 hours; the drying method is vacuum drying, the drying temperature is 60°C, and the drying time is 12-24 hours.

5. The method for preparing heteroatom-doped carbon nanohorn catalyst according to claim 3, characterized in that: In step S2, the doping element precursor is one or more combinations of urea, ammonia, phosphorus trichloride, triphenylboron, boron trichloride, ammonium nitrate, phosphoric acid, sodium chloride, metal complexes containing organic ligands, and organic or inorganic compounds containing nitrogen (N), boron (B), phosphorus (P), and chlorine (Cl).

6. The method for preparing heteroatom-doped carbon nanohorn catalyst according to claim 3, characterized in that: In step S2, the mass ratio of the carbon nanohorns to the doping element precursor is between 1:1 and 1:10; and the mixing method includes manual grinding, ball milling, and immersion.

7. The method for preparing heteroatom-doped carbon nanohorn catalyst according to claim 3, characterized in that: In step S3, the protective atmosphere is argon or nitrogen with a purity of ≥99.99%; the heating process is to heat the temperature to 600-900°C at a heating rate of 5-10°C / min, and the holding time is 1-4 hours.

8. The method for preparing heteroatom-doped carbon nanohorn catalyst according to claim 3, characterized in that: In step S4, the acidic solution is dilute hydrochloric acid with a concentration of 1 mol / L or sulfuric acid with a concentration of 0.5 mol / L; the drying method is vacuum drying, the drying temperature is 60° C., and the drying time is 12-24 hours.

9. A method for synthesizing H2O2 by electrolysis of seawater, characterized in that: The method comprises: coating the heteroatom-doped carbon nanohorn catalyst according to claim 1 or 2 on the surface of carbon paper or carbon cloth as a cathode electrode, using a titanium mesh or an iridium oxide-coated electrode as an anode, using natural seawater as an electrolyte, and achieving efficient synthesis of H2O2 at a constant potential of -0.6V-0.2V vs. RHE.

10. A device for synthesizing H2O2 by electrolysis of seawater using the method for synthesizing H2O2 by electrolysis of seawater as claimed in claim 9, characterized in that: The device comprises: (1) Cathode: Coating the heteroatom-doped carbon nanohorn catalyst as described in claim 1 or 2 on the surface of carbon paper or carbon cloth; (2) Anode: titanium mesh or iridium oxide coated electrode; (3) Electrolytic cell: Made of corrosion-resistant polytetrafluoroethylene, equipped with a temperature sensor, pH probe and constant potential power supply; (4) Collection module: The cathode area is separated by an ion exchange membrane to achieve continuous separation and collection of H2O2.

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