A carbon-based electrocatalytic material with a continuous network self-supporting structure and its preparation method

Abstract

This invention discloses a carbon-based electrocatalytic material with a continuous network self-supporting structure and its preparation method, belonging to the field of electrocatalytic material technology. It uses a carbon nanotube film with a continuous carbon nanotube network structure as a substrate, and uniformly coats a layer of polypyrrole electrocatalytic material with excellent hydrogen peroxide electrocatalytic performance onto the carbon nanotube network through in-situ polymerization. This preparation process and material structure utilize the carbon nanotube network in the carbon nanotube film to construct the continuous conductive network required for the catalytic electrode, efficiently supporting the large number of electrons required for the catalytic reaction at high-density active sites. This not only improves the bonding force between the electrocatalytic material and the carbon substrate but also eliminates the traditional process of coating the catalyst onto the supporting substrate material to prepare the catalytic electrode, simplifying the preparation process of the catalytic electrode. This invention directly uses polypyrrole as the electrocatalytic electrode (cathode) through in-situ coating, exhibiting excellent performance in the electrocatalytic preparation of hydrogen peroxide.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials technology, and particularly relates to a carbon-based electrocatalytic material with a continuous network self-supporting structure and its preparation method. Background Technology

[0002] Hydrogen peroxide (H2O2), also known as hydrogen peroxide solution, is a common oxidant. Its decomposition products are only water and oxygen, with no pollution, making it environmentally friendly. It is widely used in traditional chemical, fine chemical, paper and textile, wastewater treatment, environmental disinfection, and medical sterilization fields. The anthraquinone process is the most important method for producing hydrogen peroxide, accounting for over 95% of global hydrogen peroxide production. However, as a centralized, large-scale method for hydrogen peroxide production, the anthraquinone process has drawbacks such as high investment, high energy consumption, and heavy pollution, as well as safety hazards, requiring stringent requirements for the storage and transportation of hydrogen peroxide.

[0003] The electrocatalytic preparation of hydrogen peroxide via the two-electron oxygen reduction reaction is an ideal distributed method for hydrogen peroxide production because it does not require large-scale reaction equipment; the process conditions are mild, can be carried out at room temperature and pressure, and there is no coexistence of hydrogen and oxygen; the raw materials are simple, requiring only water and air; it can be used immediately after preparation, and the concentration is controllable; and it does not require storage or transportation.

[0004] The oxygen reduction reaction is complex, with numerous intermediate products and two competing reaction pathways: the two-electron reaction for hydrogen peroxide and the four-electron reaction for water. Therefore, the evaluation of a catalyst mainly considers its pathway selectivity, catalytic activity, and coulombic efficiency. Currently, common two-electron oxygen reduction catalysts mainly include noble metal-based and non-noble metal-based catalysts. Noble metal catalysts such as Pt and Au exhibit good catalytic performance, but their high cost limits their widespread application. Among non-noble metal-based catalysts, carbon-based catalysts, due to their low cost, good conductivity, and ease of modification, have become the most studied and commercially promising electrocatalyst matrix material for hydrogen peroxide production.

[0005] Carbon materials come in many forms, including graphite, carbon black, graphene, carbon nanotubes, porous carbon, carbon felt, and carbon cloth. These pure carbon materials are often insufficient to provide active sites for the two-electron oxygen reduction reaction, so oxidation and doping are commonly used to modify them and achieve highly efficient hydrogen peroxide electrocatalytic performance. Patent CN112225199A discloses an oxidative modification of carbon nanotubes using hydrochloric acid and hydrogen peroxide, resulting in a large number of carboxyl and hydroxyl groups on the surface of the carbon nanotubes, thereby enhancing their catalytic effect in the two-electron oxygen reduction to prepare hydrogen peroxide. Patent CN112442708A discloses a method for preparing nitrogen-doped carbon materials using glucose as a carbon source and dicyandiamine as a nitrogen source via pyrolysis, which can then be used as an electrocatalyst for the preparation of hydrogen peroxide. Patent CN114774971A discloses a nitrogen-doped carbon-based catalyst rich in oxygen functional groups prepared from chitosan, achieving a selectivity of 85-90% for hydrogen peroxide at 0-0.5V. CN114481200A discloses a carbon-based catalyst for the electrocatalytic preparation of hydrogen peroxide using nano-cobalt phosphide and nano-cobalt diphosphide as raw materials and co-doped with nitrogen and phosphorus. Patent CN117144395A discloses a method for preparing a boron-nitrogen co-doped carbon-based catalyst material, resulting in a catalyst with a Faraday efficiency of up to 98%.

[0006] The above patents illustrate that oxidation treatment, doping (single element doping or composite doping), and coating can all enable carbon-based materials to have good electrocatalytic performance in preparing hydrogen peroxide. However, the catalysts prepared by these methods are all dispersion systems and cannot be used directly as electrocatalytic electrodes. Usually, the catalyst is dispersed together with auxiliary materials such as binders (e.g., Nafion, PTFE, or PVDF) in a solvent to form a slurry, and then it is attached to an electrode substrate with a mechanical support structure (e.g., carbon paper, carbon felt, nickel foam, metal mesh, etc.) by coating, spraying, etc., in order to prepare an electrocatalytic electrode. Not only is the process complex and costly, but the degradation of the binder during the use of the catalytic electrode can lead to a decrease in the bonding force between the catalyst and the electrode substrate or even detachment, ultimately resulting in problems such as deterioration or even failure of the catalytic electrode performance.

[0007] Patent CN112191239A discloses a method that uses nickel foam as a supporting electrode and utilizes the incomplete combustion of ethanol on the surface of nickel foam to grow a nickel-oxygen co-doped carbon nanotube network in situ on the surface of nickel foam, exhibiting good electrocatalytic performance for the preparation of hydrogen peroxide. However, although this method does not require the use of a binder to connect the catalyst to the nickel foam substrate, the adhesion between the carbon nanotube catalyst and the metal substrate is relatively weak, and there is still a risk of detachment during use.

[0008] Patent CN117219797A discloses a self-supporting electrode for use in metal-air batteries. This involves first preparing a carbon fiber substrate via electrospinning, then loading metal-organic frameworks (MOFs) onto the carbon fiber using an in-situ growth method, followed by high-temperature calcination to obtain a MOF-derived carbon nanotube-coupled carbon fiber self-supporting electrode. Patent CN116426959A discloses a self-supporting electrode for electrocatalytic hydrogen evolution reaction, which involves depositing a nickel-based catalyst on the surface of carbon fiber paper via a hydrothermal reaction to obtain a nickel diselenide hierarchical nanoneedle array self-supporting catalytic electrode. Patent CN111769298A discloses a carbon nanotube-based self-supporting electrode supported on Fe-N single-atom clusters, which can be used as a cathode in zinc-ion batteries. Patent CN110067004A discloses a self-supporting electrode with a dual-carbon substrate (carbon paper and carbon nanotubes) supporting a Ni-WP catalyst and its preparation method; this material exhibits excellent electrocatalytic hydrogen production performance. Patent CN108380227A discloses a self-supporting electrocatalytic hydrogen production electrode using graphene or carbon nanotubes as a matrix and loading nickel phosphide via in-situ reaction. Patent CN116874040A discloses a self-supporting electrocatalytic electrode for electro-Fenton degradation and its preparation method, which involves uniformly dispersing iron salt and terephthalic acid in a solvent, and preparing carbon cloth loaded with iron phosphate through hydrothermal reaction and high-temperature calcination. In an electro-Fenton degradation test of methyl orange, this self-supporting electrolysis achieved a degradation rate of approximately 90% within 10 minutes.

[0009] Furthermore, patents CN116426960A, CN116429848A, CN116247228A, CN115911427A, CN115679684A, CN114632433A, CN115094432A, and CN114695904A all disclose inventions for preparing self-supporting electrocatalytic electrodes using carbon nanotubes, carbon paper, carbon cloth, carbon films, and other carbon fiber macrostructures as matrices, and supporting or synthesizing metal-based catalysts in situ. These self-supporting electrodes all use a carbon substrate with a network structure as the supporting framework, with the catalyst attached to the carbon substrate framework. This preparation process and material structure not only utilize the good conductivity of the carbon substrate to construct the conductive network of the electrode; it also improves the bonding force between the catalyst and the substrate, preventing the catalyst from detaching from the electrode substrate; and it is beneficial to increase the catalyst loading and improve the density of active sites.

[0010] Patent CN116815241A discloses a polypyrrole-coated carbon nanotube-based electrocatalytic material and its preparation method, exhibiting a two-electron electrocatalytic selectivity exceeding 90% and a Faradaic efficiency exceeding 90%. This material demonstrates excellent performance in the electrocatalytic production of hydrogen peroxide. More noteworthy is the material's unique structure, where the polymer completely encapsulates the carbon nanotubes, ensuring a strong bond between the polymer rich in active sites and the carbon nanotubes. However, because the prepared material is a dispersed system, two problems exist: first, a binder is still needed to attach the catalyst to the matrix, failing to address the issue of catalyst detachment during use; second, the dispersed catalyst system causes the carbon nanotubes to be separated by the coated polymer, preventing the formation of a continuous conductive network and hindering the full utilization of the excellent conductivity of the carbon nanotubes to efficiently support the large number of electrons required for the high-density active sites in the catalytic reaction. Summary of the Invention

[0011] To address the aforementioned technical problems, this invention proposes a carbon-based electrocatalytic material with a continuous network self-supporting structure and its preparation method. This invention uses carbon nanotube films, macroscopic carbon nanotubes with a continuous carbon nanotube network structure, as the substrate. After modification through coating, the films are directly used as electrocatalytic electrodes (cathodes), exhibiting excellent performance in the electrocatalytic preparation of hydrogen peroxide.

[0012] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing a carbon-based electrocatalytic material with a continuous network self-supporting structure, comprising the following steps: Step 1: Clean the carbon nanotube film. Activate the cleaned carbon nanotube film in a hydrogen peroxide aqueous solution. Disperse pyrrole evenly in water and add it to the hydrogen peroxide aqueous solution soaking the carbon nanotube film. Add ammonium persulfate and perform thorough ultrasonic dispersion. In this step, the order of adding each raw material must be strictly controlled (pyrrole and ammonium persulfate cannot coexist in the reaction system before adding hydrogen peroxide). Otherwise, the loading of polypyrrole on the carbon nanotube film will decrease, its coating uniformity will deteriorate, and more particulate polypyrrole that cannot be ultrasonically cleaned will form. This not only reduces the polymerization and deposition efficiency of the raw material pyrrole, but the adhesion of these residual particulate polypyrrole to the carbon nanotube film is also less than that of polypyrrole uniformly coated on the carbon nanotube network. In actual use, this will lead to accelerated catalyst deterioration. Step 2: The mixture system of carbon nanotube films obtained in Step 1 is refrigerated and allowed to stand, so that pyrrole can fully polymerize and adsorb onto the surface of the carbon nanotube films. Step 3: Place the mixture system of soaked carbon nanotube film obtained in step 2 in an oven to dry, and obtain carbon nanotube film material loaded with polypyrrole. Step 4: The carbon nanotube film material loaded with polypyrrole obtained in Step 3 is ultrasonically cleaned. Step 5: Anneal the material obtained in Step 4 to obtain the carbon-based electrocatalytic material with a continuous network self-supporting structure.

[0013] Furthermore, in step 1, the thickness of the carbon nanotube film is ≥1μm.

[0014] Furthermore, in step 1, the relationship between the mass of pyrrole added and the area of ​​the carbon nanotube film is 0~3 mg / cm². 2 And not zero. The loading of polypyrrole on carbon nanotube films increases with the ratio of the mass of added pyrrole to the area of ​​the carbon nanotube film, and when this ratio increases to 6 mg / cm², the loading increases further. 2 At this time, the pores of the carbon nanotube film are almost completely filled, which is detrimental to its catalytic performance. Therefore, this invention limits the relationship between the mass of pyrrole added and the area of ​​the carbon nanotube film to no more than 3 mg / cm². 2 .

[0015] Further, in step 1, the mass concentration of the hydrogen peroxide aqueous solution is ≥10%; Activation time ≥ 1 min. During the activation process, the device can be left to stand or combined with ultrasound. The mass ratio of pyrrole to ammonium persulfate is 1:(1~5). The mass ratio of hydrogen peroxide to ammonium persulfate in the hydrogen peroxide aqueous solution is greater than 3:1.

[0016] Furthermore, in step 2, the temperature of the refrigerated stand is higher than the freezing point of the system.

[0017] Furthermore, in step 4, the ultrasonic cleaning time is ≥2 min.

[0018] Furthermore, in step 5, the annealing process is carried out in an inert gas environment, the annealing temperature is 200~500℃, and the holding time is ≥0.5h.

[0019] The present invention also provides a carbon-based electrocatalytic material with a continuous network self-supporting structure prepared according to the above method.

[0020] The present invention also provides an application of the above-mentioned carbon-based electrocatalytic material with a continuous network self-supporting structure in the preparation of hydrogen peroxide, wherein the carbon-based electrocatalytic material with a continuous network self-supporting structure is directly used as the working electrode.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects: 1. The carbon-based electrocatalytic material of the present invention, with a continuous network self-supporting structure, is a self-supporting electrode based on polypyrrole-coated carbon nanotube substrate. It uses a carbon nanotube film with a continuous network structure as a supporting framework, and in-situ coats a polypyrrole catalyst onto the carbon nanotube framework. This preparation process and material structure not only utilize the excellent conductivity of carbon-based materials to construct a continuous conductive network for the electrode, efficiently supporting the large number of electrons required for catalytic reactions at high-density active sites, but also achieve self-support through the mechanical properties of the carbon nanotube film itself, eliminating the need for an additional supporting matrix material. 2. Compared with powdered electrocatalytic materials, the carbon-based electrocatalytic material of the present invention with a continuous network self-supporting structure is produced by in-situ polymerization of pyrrole on a network of carbon nanotubes, which uniformly and firmly coats the network of carbon nanotubes, improves the bonding force between the catalyst and the substrate, prevents the catalyst from falling off the electrode substrate, and improves the lifespan of the carbon-based electrocatalytic material with a continuous network self-supporting structure. 3. The carbon-based electrocatalytic material with a continuous network self-supporting structure prepared by this invention only requires activation, polymerization coating and annealing processes. The preparation method is simple, the material cost is low, and it can be industrialized for large-scale production. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The images are photographs and SEM images of carbon nanotube films taken with a camera, where a is the photograph and b is the SEM image. Figure 2 This is a SEM image of sample JP-1 prepared in Example 1; Figure 3 This is a SEM image of sample JP-2 prepared in Example 2; Figure 4 SEM image of sample TF-1 prepared in Comparative Example 1; Figure 5 SEM image of sample TF-2 prepared in Comparative Example 2; Figure 6 SEM image of sample TF-3 prepared in Comparative Example 3; Figure 7 The images are photographs and SEM images of the electrocatalyst P100 prepared in Comparative Example 4, where a is a photograph and b is an SEM image. Figure 8The graph shows the concentration and Faraday efficiency of hydrogen peroxide (H2O2) generated by electrolyzing samples JP-1 and JP-2 prepared in Examples 1 to 2 and samples TF-1, TF-2, TF-3, and TF4 prepared in Comparative Examples 1 to 4 in 0.1M KOH electrolyte for 0.5h. Figure 9 The Ampere curve and the cumulative concentration change of hydrogen peroxide (H2O2) generated are shown for sample JP-1 prepared in Example 1 as a catalytic electrode in 0.1M KOH electrolyte for 24 hours. Figure 10 The graph shows a comparison of the concentrations of hydrogen peroxide (H2O2) generated after ultrasonication in pure water for 30 minutes by sample JP-1 prepared in Example 1 and sample TF-4 prepared in Comparative Example 4, and then electrolyzing them in 0.1M KOH electrolyte for 0.5 h as catalytic electrodes. Detailed Implementation

[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0024] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0025] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0026] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0027] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0028] CN116815241A describes a three-tiered coating structure: polypyrrole-carbon nanotube-carbon fiber (carbon paper is composed of carbon fibers), in which polypyrrole is coated onto dispersed carbon nanotube powder particles, then made into a catalyst slurry containing a binder, and finally coated onto a conductive carbon substrate (such as carbon paper) by coating or spraying. This invention, however, involves in-situ coating of polypyrrole onto carbon nanotubes with a self-supporting network structure, representing a two-tiered polypyrrole-carbon nanotube coating structure. The advantage of this structure is that the catalyst polypyrrole is directly coated onto the main supporting structure, requiring no binder yet achieving a firm and uniform coating that will not detach during use.

[0029] Embodiments of the present invention provide a method for preparing a carbon-based electrocatalytic material with a continuous network self-supporting structure, comprising the following steps: Step 1: Clean the carbon nanotube film. Activate the cleaned carbon nanotube film in a hydrogen peroxide aqueous solution. Disperse pyrrole evenly in water and add it to the hydrogen peroxide aqueous solution soaking the carbon nanotube film. Add ammonium persulfate and perform thorough ultrasonic dispersion. In this step, it is necessary to strictly control the order of adding each raw material; otherwise, the loading of polypyrrole on the carbon nanotube film will decrease, its coating uniformity will deteriorate, and more particulate polypyrrole that cannot be ultrasonically cleaned will be formed. This not only reduces the polymerization and deposition efficiency of the raw material pyrrole, but the adhesion of these residual particulate polypyrrole to the carbon nanotube film is also less than that of polypyrrole uniformly coated on the carbon nanotube network. In actual use, this will lead to accelerated catalyst deterioration. Step 2: The mixture system of carbon nanotube films obtained in Step 1 is refrigerated and allowed to stand, so that pyrrole can fully polymerize and adsorb onto the surface of the carbon nanotube films. Step 3: Place the mixture system of soaked carbon nanotube film obtained in step 2 in an oven to dry, and obtain carbon nanotube film material loaded with polypyrrole. Step 4: The polypyrrole-loaded carbon nanotube film material obtained in Step 3 is ultrasonically cleaned. If ultrasonic cleaning is not performed, a large number of polypyrrole particles will accumulate on the surface of the carbon nanotube film, and the network of polypyrrole-loaded carbon nanotubes will not be exposed. Without the conductive support of the carbon nanotube network, the catalytic performance of these polypyrrole particles accumulated on the surface of the carbon nanotube film cannot be fully utilized. Step 5: Anneal the material obtained in Step 4 to obtain a carbon-based electrocatalytic material with a continuous network self-supporting structure.

[0030] In the following embodiments of the present invention, carbon nanotube films are prepared using a floating catalytic method, comprising the following steps: (1) Preparation: Heat the vertical tube furnace filled with hydrogen to 1150°C and keep it at a constant temperature; (2) Preparation of precursor solution: Prepare a mixed solution of ethanol, ferrocene and thiophene at a mass ratio of 800:15:8 and use it as the precursor solution; (3) High temperature synthesis: The precursor solution is placed in a microsyringe and hydrogen gas with a flow rate of 800 sccm is injected into the furnace from the top of the vertical tube furnace at a rate of 10 mL / h. (4) Collection of carbon nanotube film: 3 minutes after the start of injecting the precursor solution, a round semi-transparent film can be collected at the bottom of the vertical tube furnace. It is pulled onto an electric spindle with a collection roller with a diameter of 40 cm to obtain a carbon nanotube film with a continuous and uniform network structure. As the number of spindle rotations increases, the total thickness of the carbon nanotube film on the collection roller continues to increase. (5) Finished product: After continuously collecting carbon nanotube films on an electric spinning shaft for 5 hours, stop and spray ethanol onto the carbon nanotube film wrapped on a collecting roller with a diameter of 40 cm to shrink and densify it. Then remove the carbon nanotube film from the collecting roller to obtain a carbon nanotube film with a thickness of 20 μm.

[0031] In a preferred embodiment of the present invention, in step 1, the thickness of the carbon nanotube film is ≥1 μm, preferably 1~40 μm, and more preferably 20 μm.

[0032] In a preferred embodiment of the present invention, in step 1, the relationship between the mass of pyrrole added and the area of ​​the carbon nanotube film is ≥3 mg / cm². 2 The preferred relationship between the mass of pyrrole added and the area of ​​the carbon nanotube film is 1.5~3 mg / cm². 2 The loading of polypyrrole on carbon nanotube films increases with the ratio of the mass of added pyrrole to the area of ​​the carbon nanotube film. This ratio increases to 6 mg / cm². 2 At this time, the pores of the carbon nanotube film are almost completely filled, which is detrimental to its catalytic performance. Therefore, this invention limits the relationship between the mass of pyrrole added and the area of ​​the carbon nanotube film to ≥3 mg / cm². 2 .

[0033] In a preferred embodiment of the present invention, in step 1, the mass concentration of the hydrogen peroxide aqueous solution is ≥10%, preferably a hydrogen peroxide aqueous solution with a mass fraction of 10~30%; Activation time ≥ 1 min. During the activation process, the device can be left to stand or combined with ultrasound. The mass ratio of pyrrole to ammonium persulfate is 1:(1~5), preferably 3:10; The mass ratio of hydrogen peroxide to ammonium persulfate in the hydrogen peroxide aqueous solution is greater than 3:1, preferably (5~10):1, and more preferably 6:1.

[0034] In a preferred embodiment of the present invention, in step 2, the refrigerated standing temperature is preferably such that the system does not freeze (i.e., the refrigerated standing temperature is higher than the freezing point of the system), preferably 0~5°C, more preferably 4°C.

[0035] In a preferred embodiment of the present invention, in step 4, the ultrasonic cleaning time is ≥2 min, and preferably the ultrasonic cleaning time is 2~10 min.

[0036] In a preferred embodiment of the present invention, in step 5, the annealing treatment is carried out in an inert gas environment, the annealing temperature is 200~500℃, and the holding time is ≥0.5h; preferably, the annealing temperature is 300℃, the holding time is 2h, and the heating rate is 1℃ / min.

[0037] For example, the inert gas is argon.

[0038] Embodiments of the present invention also provide a carbon-based electrocatalytic material with a continuous network self-supporting structure prepared according to the above method.

[0039] The embodiments of the present invention also provide an application of the above-mentioned carbon-based electrocatalytic material with a continuous network self-supporting structure in the preparation of hydrogen peroxide, wherein the carbon-based electrocatalytic material with a continuous network self-supporting structure is directly used as the working electrode (cathode).

[0040] This invention utilizes carbon nanotube films, macroscopic carbon nanotubes with a continuous carbon nanotube network structure, as the substrate. A layer of polypyrrole electrocatalytic material with excellent hydrogen peroxide electrocatalytic performance is uniformly coated onto the carbon nanotube network through in-situ polymerization. This preparation process and material structure utilize the carbon nanotube network in the carbon nanotube film to construct the continuous conductive network required for the catalytic electrode, efficiently supporting the large number of electrons required for the catalytic reaction at high-density active sites. This not only significantly improves the bonding force between the polypyrrole electrocatalytic material and the carbon substrate, thus preventing catalyst detachment during use, but also achieves self-support through the mechanical properties of the carbon nanotube film itself, eliminating the need for an additional supporting substrate material. This simplifies the traditional process of coating the catalyst onto a supporting substrate to prepare the catalytic electrode. The modified polypyrrole obtained by in-situ coating is directly used as the electrocatalytic electrode (cathode), exhibiting excellent performance in the electrocatalytic preparation of hydrogen peroxide.

[0041] Unless otherwise specified, the room temperature in this invention is 25±2℃.

[0042] All raw materials used in the embodiments of the present invention were obtained through commercial purchase.

[0043] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0044] The technical solution of the present invention will be further illustrated by the following embodiments.

[0045] Example 1 A method for preparing a carbon-based electrocatalytic material with a continuous network self-supporting structure, comprising the following steps: Step 1: Place the carbon nanotube film with a cut surface size of 2×10cm and a thickness of 20μm into pure water and ultrasonically clean it for 5 minutes. Step 2: Remove the carbon nanotube film from the pure water, add it to 2g of 30% hydrogen peroxide, and sonicate for 5min. Step 3: Add 0.03g of pyrrole to 10g of purified water (i.e., the ratio of the mass of pyrrole added to the area of ​​the carbon nanotube film is 1.5mg / cm²). 2 The mixture was ultrasonically dispersed for 5 minutes to obtain a dispersion; then it was added to the system of step 2 and ultrasonicated for another 5 minutes. Step 4: Add 0.1g of ammonium persulfate to the mixture system obtained in Step 3 (i.e., the mass ratio of hydrogen peroxide to ammonium persulfate is 6:1, and the mass ratio of pyrrole to ammonium persulfate is 3:10), and continue sonication for 5 minutes to fully dissolve the ammonium persulfate. Step 5: Place the mixed liquid system of soaking carbon nanotube film obtained in step 4 into the refrigerator (4°C) and let it stand for 12 hours to obtain carbon nanotube film loaded with polypyrrole material (which is carbon nanotube film loaded with polypyrrole). Step 6: Place the material obtained in step 5 along with its container in an oven and bake at 60°C until it is dry and free of liquid phase. Step 7: Ultrasonic cleaning of the material obtained in Step 6: Place the material obtained in Step 6 in 50 mL of pure water and sonicate for 10 min. Step 8: Anneal the material obtained in Step 7. Annealing conditions: quartz tube furnace, argon atmosphere, exhaust gas from the tube for half an hour before heating, heat to 300℃ at 1℃ / min and hold for 2 hours, then cool naturally to obtain a carbon-based electrocatalytic material with a continuous network self-supporting structure, which is a self-supporting electrode material, denoted as JP-1.

[0046] Example 2 A method for preparing a carbon-based electrocatalytic material with a continuous network self-supporting structure is the same as in Example 1, except that the shearing plane size of the carbon nanotube film in step 1 is changed to 5×2cm, that is, the ratio of the mass of added pyrrole to the area of ​​the carbon nanotube film is 3mg / cm². 2 The resulting carbon-based electrocatalytic material with a continuous network self-supporting structure is designated as JP-2.

[0047] Comparative Example 1 A method for preparing a self-supporting electrode material is the same as in Example 1, except that the shearing surface size of the carbon nanotube film in step 1 is changed to 2.5 × 2 cm, that is, the ratio of the mass of added pyrrole to the area of ​​the carbon nanotube film is increased to 6 mg / cm². 2 The resulting self-supporting electrode material is denoted as TF-1.

[0048] Comparative Example 2 A method for preparing a self-supporting electrode material is the same as in Example 1, except that steps 2 and 4 are interchanged, and the resulting self-supporting electrode material is denoted as TF-2.

[0049] Comparative Example 3 A method for preparing a self-supporting electrode material is the same as in Example 1, except that step 7 is omitted. Instead, the carbon nanotube film loaded with polypyrrole obtained in step 6 is directly annealed (step 8) without ultrasonic cleaning to obtain the self-supporting electrode material, denoted as TF-3.

[0050] Comparative Example 4 This comparative sample was prepared according to Example 1 of patent CN 116815241 A: Step 1: Disperse 0.3g of multi-walled carbon nanotubes in 50mL of deionized water and stir continuously with magnetic force for 10 minutes to obtain a multi-walled carbon nanotube dispersion. Step 2: Slowly add 0.3g of pyrrole monomer to the multi-walled carbon nanotube dispersion prepared in Step 1, and continuously stir the dispersion magnetically for 10min. Step 3: Add 5.1g of hydrogen peroxide (mass fraction 30%) to the dispersion prepared in Step 2, and continuously stir magnetically during this process; Step 4: Dissolve 0.8g of ammonium persulfate in 10mL of deionized water, and add the ammonium persulfate solution to the dispersion prepared in Step 3. During this process, the mixture is continuously stirred magnetically. Step 5: The dispersion obtained in step 4 is magnetically stirred in an ice-water bath at 0°C for 6 hours. Step 6: Wash the dispersion obtained in step 5 by centrifugation with deionized water, methanol and acetone respectively. Step 7: The product obtained in step 6 is freeze-dried in a vacuum freeze dryer to finally obtain polypyrrole-coated multi-walled carbon nanotube catalyst powder, denoted as P100. Step 8: P100 powder is uniformly dispersed in a mixed solution of nafion, isopropanol and water with a volume ratio of 3:35:62 to obtain a slurry with a concentration of 1 mg / mL. This slurry is then drop-coated onto a commercial hydrophobic carbon paper electrode and dried at room temperature to obtain a hydrophobic carbon paper electrode loaded with carbon nanotube powder coated with polypyrrole, denoted as TF-4.

[0051] Performance tests and results: 1. Scanning electron microscopy test Scanning electron microscopy (SEM) was performed on the original carbon nanotube film and samples JP-1, JP-2, TF-1, TF-2, and TF-3 obtained from Examples 1, 2, 1, 2, and 3. The test results are as follows: Figures 1 to 6 As shown.

[0052] SEM images of samples JP-1 and JP-2 are as follows Figure 2 and Figure 3 As shown, under the process parameters of Examples 1 and 2, polypyrrole material can be uniformly coated on the network of carbon nanotubes in the carbon nanotube film, and there are fewer impurity particles on the material surface. Meanwhile, in comparison... Figure 2 and Figure 3 It can be seen that when the mass ratio of added pyrrole to the area of ​​the carbon nanotube film increases from 1.5 mg / cm², the effect is significant. 2 Increased to 3 mg / cm 2 At that time, the amount of polypyrrole loaded on the carbon nanotube film increases, and the porosity decreases.

[0053] SEM images of samples JP-1, JP-2 and TF-1 are shown below. Figure 2 , Figure 3 and Figure 4 As shown, the loading of polypyrrole on the carbon nanotube film increases with the ratio of the mass of added pyrrole to the area of ​​the carbon nanotube film. When this ratio increases to 6 mg / cm², the loading increases further. 2 At this time, the pores of the carbon nanotube film are almost completely filled, which will be detrimental to its catalytic performance.

[0054] SEM images of samples JP-1 and TF-2 are as follows Figure 2 and Figure 5As shown in the comparison, if steps 2 and 3 are swapped, the loading of polypyrrole on the carbon nanotube film decreases, its coating uniformity deteriorates, and more particulate polypyrrole that cannot be ultrasonically cleaned is formed. This not only reduces the polymerization and deposition efficiency of the raw material pyrrole, but also the adhesion between these residual particulate polypyrrole and the carbon nanotube film is not as good as that of polypyrrole uniformly coated on the carbon nanotube network. In actual use, this will lead to a faster rate of catalyst deterioration.

[0055] SEM images of samples JP-1 and TF-3 are as follows Figure 2 and Figure 6 As shown in the comparison, if step 6 is omitted, i.e. ultrasonic cleaning is not performed, a large number of polypyrrole particles will accumulate on the surface of the carbon nanotube film. The network of polypyrrole-loaded carbon nanotubes cannot be exposed. Without the conductive support of the carbon nanotube network, the catalytic performance of these polypyrrole particles accumulated on the surface of the carbon nanotube film cannot be fully utilized.

[0056] Macroscopic photograph of sample P100 as follows Figure 7 As shown in Figure a, the SEM image is as follows: Figure 7 As shown in b. From Figure 7 As can be seen from section a, P100 is macroscopically in powder form, so it needs to be prepared into a slurry containing a binder (such as Nafion) and coated onto a conductive substrate (such as commercial hydrophobic carbon paper) to form a catalytic electrode. As can be seen from section b, P100 is microscopically a carbon nanotube aggregate coated with polypyrrole. After these aggregates are coated and bonded to the carbon fiber conductive network of the carbon paper, electrons are transported through a three-level conductive chain of "carbon fiber with continuous conductive network in carbon paper - carbon nanotube - polypyrrole". This is more complex than the two-level conductive chain of "carbon nanotube with continuous conductive network - polypyrrole" in the self-supporting electrode JP-1.

[0057] 2. Electrocatalytic preparation of H2O2: Faraday efficiency and concentration of generated H2O2 were tested. Electrochemical experiments were conducted using the self-supporting electrodes JP-1 and JP-2 prepared in Examples 1 and 2, the self-supporting electrodes TF-1, TF-2, and TF-3 prepared in Comparative Examples 1 and 3, and the coated catalytic electrode TF-4 obtained by coating the powdered catalyst P100 prepared in Comparative Example 4 onto commercial hydrophobic carbon paper in slurry form as cathodes. The electrochemical experiments were carried out in an O2-saturated 0.1 mol / L KOH electrolyte using a CHI760E electrochemical workstation. Platinum (Pt) foil and Ag / AgCl (saturated KCl aqueous solution) were used as the counter and reference electrodes, respectively. Throughout the testing process, an H-electrolysis cell was used, with an electrolyte volume of 30 mL in the cathode chamber and an electrode area of ​​1... 1cm 2 .

[0058] Set to a constant current density of 40 mA / cm² 2 To detect Faraday efficiency and the concentration of generated H2O2.

[0059] The electrocatalytic material was set to a constant potential of -1.0V (vs. Ag / AgCl) and cycled stably for 24 hours to detect the cumulative H2O2 production concentration.

[0060] Figure 8 Six catalytic electrodes were tested in 0.1 M KOH electrolyte at a current of 40 mA / cm². 2 The Faraday efficiency (FE) curve and H2O2 formation concentration at current density after 0.5 h of electrolysis are shown. Figure 8 As shown, samples JP-1 and JP-2 have high hydrogen peroxide production and high Faraday efficiency, and can accumulate a certain amount of hydrogen peroxide. The Faraday efficiency is ~90%, with JP-1 being better. Compared to JP-1 and JP-2, TF-1 showed a significant decrease in both Faradaic efficiency and H2O2 formation concentration. This was mainly because when excessive polypyrrole was loaded onto the carbon nanotube film, most of the pores in the carbon nanotube network were filled, leaving only the surface to participate in the electrocatalytic preparation of H2O2. TF-2 showed a slight decrease in both Faradaic efficiency and H2O2 formation concentration compared to JP-1 and JP-2, presumably due to insufficient polypyrrole loading and the detachment of particulate polypyrrole with poor adhesion from the carbon nanotube conductive network. TF-3 exhibited the worst Faradaic efficiency and H2O2 formation concentration, primarily because a large amount of particulate polypyrrole coated the surface of the carbon nanotube film, failing to contact the carbon nanotube conductive network. TF-4 had a Faradaic efficiency close to that of TF-1, but a lower formation concentration. This is attributed to the benefits of in-situ polymerization forming a continuous conductive network compared to powder coating. Figure 9 Using sample JP-1 obtained in Example 1 as the catalytic electrode, the amperometric curve and hydrogen peroxide (H2O2) concentration change graph were obtained by stable cycling in 0.1M KOH electrolyte at a constant potential of -1.0V (vs. Ag / AgCl) for 24 hours. This shows that the H2O2 yield of the electrode material JP-1 prepared by the preferred preparation method of the present invention is quite constant and stable, and after 24 hours of catalysis, the cumulative H2O2 concentration reaches 2.5 g / L.

[0061] 3. Stability test of catalytic electrode structure: First, the JP-1 and TF-4 electrode sheets were ultrasonicated in pure water for 30 min. Then, the two electrode sheets were dried in a 60℃ oven. Finally, they were subjected to an electrolysis in 0.1M KOH electrolyte at 40 mA / cm². 2 Electrolysis was performed at a current density for 0.5 hours, and the concentration of H2O2 generated was tested. The results are as follows: Figure 10As shown, the electrocatalytic performance of the JP-1 electrode hardly diminished under continuous ultrasonic conditions, while the TF-4 electrode showed a significant decline in electrocatalytic performance. This was caused by the electrocatalyst P100, which was attached to the carbon paper substrate by a slurry coating, detaching from the carbon paper substrate after continuous generation. This indicates that the polypyrrole catalyst prepared by the in-situ polymerization process of JP-1 has a significant advantage in bonding with the carbon nanotube conductive network substrate.

[0062] 4. Comparison of catalytic electrode preparation processes: Examples 1, 2, and Comparative Examples 1-3 employ an in-situ polymerization process of polypyrrole on a carbon nanotube film with a continuous conductive network structure, which allows for the direct preparation of self-supporting catalytic electrodes after polymerization. In contrast, the electrocatalytic material P100 prepared in Comparative Example 4 is a powder material and cannot be used directly as a catalytic electrode. It needs to be coated onto commercial hydrophobic carbon paper with a conductive network in the form of a slurry to prepare the catalytic electrode, making the electrode preparation process more complex.

[0063] The above are merely preferred embodiments 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.

Claims

1. A method for preparing a carbon-based electrocatalytic material with a continuous network self-supporting structure, characterized in that, Includes the following steps: Step 1: Clean the carbon nanotube film, put the cleaned carbon nanotube film into a hydrogen peroxide aqueous solution for activation, disperse pyrrole evenly in water and add it to the hydrogen peroxide aqueous solution soaking the carbon nanotube film, add ammonium persulfate and perform ultrasonic dispersion. Step 2: The mixture system of carbon nanotube films obtained in Step 1 is refrigerated and allowed to stand. Step 3: Dry the mixed liquid system of soaked carbon nanotube film obtained in Step 2 to obtain carbon nanotube film material loaded with polypyrrole. Step 4: The carbon nanotube film material loaded with polypyrrole obtained in Step 3 is ultrasonically cleaned. Step 5: Anneal the material obtained in Step 4 to obtain the carbon-based electrocatalytic material with a continuous network self-supporting structure.

2. The method for preparing a carbon-based electrocatalytic material with a continuous network self-supporting structure according to claim 1, characterized in that, In step 1, the thickness of the carbon nanotube film is ≥1μm.

3. The method for preparing a carbon-based electrocatalytic material with a continuous network self-supporting structure according to claim 1, characterized in that, In step 1, the relationship between the mass of pyrrole added and the area of ​​the carbon nanotube film is 0~3 mg / cm². 2 And it is not 0.

4. The method for preparing a carbon-based electrocatalytic material with a continuous network self-supporting structure according to claim 1, characterized in that, In step 1, the mass concentration of the hydrogen peroxide aqueous solution is ≥10%; Activation time ≥ 1 min; The mass ratio of pyrrole to ammonium persulfate is 1:(1~5). The mass ratio of hydrogen peroxide to ammonium persulfate in the hydrogen peroxide aqueous solution is greater than 3:

1.

5. The method for preparing a carbon-based electrocatalytic material with a continuous network self-supporting structure according to claim 1, characterized in that, In step 2, the temperature of the refrigerated stand is higher than the freezing point of the system.

6. The method for preparing a carbon-based electrocatalytic material with a continuous network self-supporting structure according to claim 1, characterized in that, In step 4, the ultrasonic cleaning time is ≥2 min.

7. The method for preparing a carbon-based electrocatalytic material with a continuous network self-supporting structure according to claim 1, characterized in that, In step 5, the annealing process is carried out in an inert gas environment, the annealing temperature is 200~500℃, and the holding time is ≥0.5h.

8. A carbon-based electrocatalytic material with a continuous network self-supporting structure, characterized in that, It is prepared according to any one of claims 1 to 7.

9. The application of a carbon-based electrocatalytic material with a continuous network self-supporting structure as described in claim 8 in the preparation of hydrogen peroxide, characterized in that, The carbon-based electrocatalytic material with a continuous network self-supporting structure is directly used as the working electrode.

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