A method for preparing wrinkled graphene-based single-atom catalyst by atomization pyrolysis and its application

Abstract

A method for preparing wrinkled graphene-based single-atom catalysts by atomization pyrolysis comprises the following steps: (1) preparing a graphene oxide suspension solution and uniformly mixing it with a metal precursor solution to obtain a mixed solution; (2) atomizing and pyrolyzing the mixed solution to obtain a wrinkled spherical graphene oxide-based metal single-atom catalyst; and (3) calcining the wrinkled spherical graphene oxide-based metal single-atom catalyst under an inert or reducing atmosphere to regulate the coordination environment of the single atoms and obtain the wrinkled spherical graphene-based metal single-atom catalyst. The suspension is atomized by an atomizer and subjected to heat treatment to achieve batch preparation of wrinkled spherical graphene single-atom catalysts with controllable size. The physicochemical properties of the graphene carrier, such as wrinkle degree, specific surface area, electrochemical active area, hydrophilicity, as well as the electronic structure and intrinsic catalytic properties of the single atoms, can be flexibly regulated.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a wrinkled graphene-based metal adsorption catalyst. Background Art

[0002] Single-atom catalysts play a crucial role in modern industry, and graphene-based single-atom catalysts have attracted widespread research interest in recent years. Since its discovery by Novoselov and Geim in 2010, graphene has been used in various fields, including drug delivery, photoelectrocatalysis, solar cells, and energy storage systems, due to its large theoretical specific surface area (SSA of approximately 2600 m2 / g), good electrical conductivity, excellent mechanical properties and foldability, and high thermal conductivity. With these advantages, graphene is considered an ideal substrate material for supporting the active sites of single-atom catalysts. However, when used as a substrate, graphene often faces problems such as stacking of graphene atoms, masking of active sites, and a sudden drop in specific surface area, resulting in a serious mismatch between the graphene substrate and the expected properties.

[0003] In the catalytic reaction process of fuel cells, metal-air batteries, carbon dioxide conversion, etc., the utilization rate of active sites and the transport of substances are crucial to the performance of the catalyst. However, traditional preparation methods, such as high-temperature calcination method [such as CN113368845A "Single-atom-loaded carbon-based catalyst and its preparation method and application" and CN113842904A "A tungsten single-atom catalyst with a graphene substrate, its preparation method and use"], use graphene as a substrate and adopt a special atmosphere high-temperature calcination method to prepare graphene-based single-atom catalysts. However, this method cannot avoid the stacking and aggregation between graphene layers during the freeze-drying process, resulting in the embedding of active sites and reducing the atomic utilization rate; Similar preparation methods, such as microwave methods (e.g., CN113921833A, "Composite Materials Based on Metal Single Atoms and Graphene, Preparation Methods, and Applications thereof") and Joule heating methods (e.g., CN113151861A, "Method for Thermal Shock Synthesis of Carbon-Supported Single Atom Catalysts and Carbon-Supported Single Atom Catalysts"), employ freeze-drying or other drying methods to obtain aerogel or powdered precursors followed by post-processing. These methods all face the problem of stacking or agglomeration between graphene layers, which masks active sites and hinders their full utilization and material transport. Therefore, a large number of research teams are currently conducting in-depth research on the morphology control of graphene oxide to address these challenges. For example, CN202110265767.7 "A directional porous single-atom carbon film electrode, its preparation method and application" first prepares a hydrogel through hydrothermal treatment, and then regulates its internal pore structure through freeze-drying; 10.1002 / adma.202103740 "Highly Efficient Cellular Acoustic Absorber of Graphene Ultrathin Drums" converts graphene oxide sheets into graphene foam through hydroplastic foaming to achieve the regulation of graphene micromorphology; these studies all use special treatment methods to process flaky graphene oxide to obtain wrinkles to prevent stacking between graphene layers, increase the exposure of active sites, and optimize material transfer, but the formation of three-dimensional gel-like or foam-like graphene still cannot avoid the problem of stacking between graphene layers, and also introduces new challenges, such as easy collapse of the structure, cumbersome preparation methods, complex production processes, and inability to prepare in large quantities. At the same time, CN101993065B "A method for preparing graphene powder" uses a uniformly exfoliated graphene oxide suspension solution, atomization drying technology, and then non-expansion heat treatment to obtain spherical wrinkled graphene powder. This method can effectively control the morphology of graphene, and the production process has realized the industrial mass production of wrinkled spherical graphene; this technology does not load single atoms, and has different electronic structures and reaction active centers from single-atom loaded graphene materials, and cannot meet the application needs of the existing market.

[0004] In summary, the graphene-based single-atom catalysts prepared by traditional methods currently face the problems of low atom utilization and limited mass transfer due to interlayer stacking problems. There are currently no reports on a simple, convenient and scalable method for preparing graphene single-atom catalysts without stacking or agglomeration. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology and provide a method for preparing wrinkled graphene-based single-atom catalysts by atomization pyrolysis and its application.

[0006] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0007] A method for preparing a wrinkled graphene-based single-atom catalyst by atomization pyrolysis comprises the following steps:

[0008] (1) preparing a graphene oxide suspension solution, and uniformly mixing the graphene oxide suspension solution with a metal precursor solution to obtain a mixed solution;

[0009] (2) atomizing and pyrolyzing the mixed solution to obtain a wrinkled spherical graphene oxide-based metal single atom catalyst;

[0010] (3) calcining the wrinkled spherical graphene oxide-based metal single-atom catalyst under an inert or reducing atmosphere to regulate the coordination environment of the single atom and obtain the wrinkled spherical graphene-based metal single-atom catalyst.

[0011] This application adopts atomization pyrolysis technology, which can not only form a wrinkled spherical morphology and increase the specific surface area of ​​graphene oxide, but also form a single-atom catalyst due to the high-temperature treatment during the atomization pyrolysis process; subsequent high-temperature and long-term calcination regulates the electronic structure of the single-atom catalyst and realizes the reduction of graphene.

[0012] Preferably, the preparation of the graphene oxide suspension solution in step (1) adopts a thermal expansion oxidation method.

[0013] Preferably, the thermal expansion oxidation method specifically comprises the following steps:

[0014] (1) Graphite flakes are intercalated with concentrated sulfuric acid and concentrated nitric acid, and heated to expand to obtain expanded graphite powder;

[0015] (2) pre-oxidizing the expanded graphite powder using a strong oxidant;

[0016] (3) performing an oxidative intercalation treatment on the product using concentrated sulfuric acid and potassium permanganate;

[0017] (4) Wash with water and dialyze to obtain a graphene oxide suspension solution.

[0018] Preferably, the strong oxidant is potassium disulfate and phosphorus pentoxide.

[0019] Preferably, the metal precursor solution in step (1) includes a precursor solution of one or more metals among iron, cobalt, nickel, copper, zinc, platinum, ruthenium or iridium, and the mass of the metal in the metal precursor solution is 0.01-3% of the total mass of graphene oxide.

[0020] Preferably, the atomization pyrolysis in step (2) is performed using an ultrasonic atomizer, and the oscillation frequency of the ultrasonic atomizer is 1.7 MHz or 2.4 MHz, and its power can also be adjusted.

[0021] The mixed solution is atomized into small droplets using an ultrasonic atomizer. After high-temperature treatment, capillary action causes the two-dimensional graphene to shrink, forming wrinkles. Simultaneously, the high temperature partially reduces the graphene oxide, anchoring the metal atoms. During this operation, the oscillation frequency can be adjusted to control the size of the droplets, thereby controlling the size of the final product particles.

[0022] Preferably, the atomized mixed solution is pyrolyzed in an inert atmosphere. During the pyrolysis process, the concentration of the graphene oxide suspension is 0.1-5 mg / ml, and the pyrolysis temperature is 350-1100°C.

[0023] The concentration of the graphene oxide suspension can be between 0.1 and 5 mg / ml, which will affect the degree of wrinkling. The carrier gas flow rate can be in any range, but will affect the degree of wrinkling and yield of the product. The heating temperature is 350-1100°C, which will affect the degree of reduction and wrinkling of the graphene oxide.

[0024] Planar two-dimensional graphene tends to stack during the drying process, resulting in a reduction in specific surface area and electrochemically active area. However, wrinkling effectively prevents stacking of graphene sheets. Therefore, compared to unwrinkled graphene, wrinkled spherical graphene increases specific surface area and electrochemically active area. The wrinkled surface produces nanoscale ridges, which can achieve the regulation of hydrophilicity and hydrophobicity.

[0025] Preferably, the temperature of the high-temperature calcination in step (3) is 300-1100° C., and the calcination atmosphere is Ar / NH 3 atmosphere or Ar / H 2 atmosphere.

[0026] The calcination temperature can be from the spray temperature to 1100 ° C, and the calcination time can be from 0 min to several hours. The calcination atmosphere can achieve heterogeneous atom doping (Ar / NH3 atmosphere) and oxidation and reduction treatment of the sample (Ar / H2 atmosphere) through different atmospheres.

[0027] The electronic structure and intrinsic catalytic properties of single atoms can be manipulated by adjusting the secondary calcination temperature, treatment time, and atmosphere. This manipulation of the electronic structure of single atoms can lead to improved catalytic activity and selectivity for specific reactions, making the catalysts prepared by this method applicable to a wider range of reactions.

[0028] Under the same technical concept, the present invention also provides an application of a wrinkled graphene-based single-atom catalyst, which is used in an electrocatalytic process, a photocatalytic process or a thermal catalytic process.

[0029] Preferably, the electrocatalytic process includes any one of a water electrolysis hydrogen production reaction, a fuel cell reaction, an air battery reaction or a carbon dioxide reduction reaction.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The suspension is atomized by an atomizer and heat treated to achieve batch preparation of size-controllable wrinkled spherical graphene single-atom catalysts. The physicochemical properties of the graphene support, such as wrinkle degree, specific surface area, electrochemical active area, hydrophilicity and hydrophobicity, as well as the single-atom electronic structure and intrinsic catalytic properties, can be flexibly controlled.

[0032] (2) Normal drying or freeze-drying techniques will cause the two-dimensional graphene to stack, reducing the active area and covering the active sites. The advantage of this patent is that it uses the atomization process to form a mixture of two-dimensional graphene oxide and metal precursors into wrinkled graphene spheres loaded with single atoms, which can effectively prevent the stacking of two-dimensional graphene, increase atomic utilization and material transmission;

[0033] (3) The wrinkled spherical graphene single-atom catalyst prepared by this method can be used to catalyze different reaction processes, including electrocatalytic processes (such as water electrolysis hydrogen production reaction, fuel cell reaction, air battery reaction, carbon dioxide reduction reaction) and thermal catalytic processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 、 Figure 2 This is an electron microscope image of the morphology of wrinkled graphene loaded with single atoms at the atomization heat treatment temperature of Example 1;

[0036] Figure 3 、 Figure 4This is an electron microscope image of the morphology of wrinkled graphene loaded with single atoms at the atomization heat treatment temperature of Comparative Example 1;

[0037] Figure 5 This is a size distribution diagram of wrinkled graphene loaded with single atoms at the atomization heat treatment temperature of Example 1;

[0038] Figure 6 This is the size distribution diagram of the wrinkled graphene loaded with single atoms at the atomization heat treatment temperature of Comparative Example 1;

[0039] Figure 7 The BET specific surface area distribution diagram of wrinkled graphene loaded with single atoms at different atomization heat treatment temperatures in Example 1, Comparative Example 1, and Comparative Example 2;

[0040] Figure 8 The contact angle test graphs of wrinkled graphene loaded with single atoms at different atomization heat treatment temperatures for Example 1, Comparative Example 1, and Comparative Example 2;

[0041] Figure 9 XRD test patterns of wrinkled graphene loaded with single atoms at different atomization heat treatment temperatures in Example 1, Comparative Example 1, and Comparative Example 2;

[0042] Figure 10 These are Raman test images of wrinkled graphene loaded with single atoms at different atomization heat treatment temperatures in Example 1, Comparative Example 1, and Comparative Example 2;

[0043] Figure 11 This is the HAADF-STEM image of the wrinkled graphene loaded with single atoms under atomization heat treatment in Example 1;

[0044] Figure 12 This is a performance comparison chart of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 in oxygen reduction two-electron electrocatalytic applications. DETAILED DESCRIPTION

[0045] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0046] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0047] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0048] Example 1:

[0049] A method for preparing a wrinkled graphene-based single-atom catalyst by atomization pyrolysis comprises the following steps:

[0050] In the first step, the graphite flakes are evenly exfoliated and oxidized into a stable graphene oxide suspension solution; the cobalt metal precursor solution and the graphene oxide solution are evenly mixed using a cell crusher or an ultrasonic machine;

[0051] In the second step, an ultrasonic atomizer (1.7MHz) is used to uniformly atomize the mixed cobalt metal precursor solution and graphene oxide solution. Ar gas is used to carry the atomized precursor into the heating zone and perform high-temperature atomization heat treatment at 700°C. Due to the evaporation of the liquid, capillary action causes the two-dimensional graphene to shrink and form wrinkles. At the same time, the functional groups on the surface of the graphene oxide are detached to form vacancies. The cobalt metal precursor combines with the vacancies to achieve the anchoring of cobalt metal single atoms. In the third step of the preparation process, the degree of wrinkling of the graphene carrier can be controlled by changing the conditions such as the concentration of the graphene oxide suspension, the atomization frequency, the carrier gas flow rate, and the heating temperature.

[0052] In the third step, a conventional tubular furnace was used for calcination at 800°C for 1.5h. The calcination atmosphere was an Ar / NH3 mixed gas with a gas ratio of 150sccm:50sccm. The graphene oxide was thermally reduced to graphene, and the coordination environment of the cobalt single atom was regulated to finally obtain a wrinkled spherical graphene-based single-atom catalyst.

[0053] The graphene oxide suspension mentioned in the preparation method is prepared by thermal expansion oxidation method, which mainly includes the following steps:

[0054] ① Use concentrated sulfuric acid and concentrated nitric acid to intercalate graphite flakes, and then expand them at high temperature (1100℃) to obtain expanded graphite powder;

[0055] ② Pre-oxidation of expanded graphite powder using potassium persulfate and phosphorus pentoxide;

[0056] ③ The above product is then subjected to oxidation intercalation treatment using concentrated sulfuric acid and potassium permanganate;

[0057] ④ The product is washed with water and dialyzed to obtain a graphene oxide suspension.

[0058] Comparative Example 1:

[0059] The remaining steps are the same as those in Example 1, and the temperature of the atomization heat treatment is 300°C.

[0060] Comparative Example 2:

[0061] The remaining steps were the same as those in Example 1, except that the atomization heat treatment was not performed and freeze-drying was used.

[0062] Comparative Example 3:

[0063] The remaining steps are the same as those in Example 1, except that the cobalt precursor solution is replaced with an equal volume of deionized water.

[0064] The performance test of the products obtained in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 was carried out. The test results are as follows: Figures 1-12 shown.

[0065] like Figure 1 、 Figure 2 As shown in Example 1, the high temperature (700°C) atomization heat treatment of the metal precursor and graphene mixed solution resulted in a product (Co single atom-loaded highly wrinkled graphene) with a greater degree of shrinkage, and the size of the wrinkled graphene spheres was mainly distributed around 400nm. By regulating the heat treatment temperature, the degree of wrinkling can be effectively controlled; Figure 3 and Figure 4 As shown, the product obtained by low-temperature (300°C) atomization heat treatment in Comparative Example 1 (Co single-atom loaded low-wrinkle graphene) shrinks significantly less, and the size of the wrinkled graphene spheres is mainly distributed around 600nm.

[0066] like Figure 5 、 6 As shown in the figure, the BET specific surface area test results show that the BET specific surface area increases significantly after atomization and heat treatment. Through the comparison of BET specific surface area values, the BET specific surface area of ​​Co single atom-loaded highly wrinkled graphene spheres is about four times greater than that of Co single atom-loaded planar graphene. This result strongly proves that the synthesis method effectively prevents the stacking and aggregation between graphene layers during the preparation process.

[0067] like Figure 7 As shown in the figure, graphene with different wrinkle degrees obtained by different atomization heat treatment temperatures exhibits significantly different hydrophilic and hydrophobic properties in the contact angle test. Figure 8 As shown in the figure, as the atomization heat treatment temperature increases, the contact angle of the sample increases, indicating better hydrophilicity. In contrast, the contact angle of the sample without atomization heat treatment is smaller, indicating stronger hydrophobicity. This property can be used to effectively control the contact between the sample and the electrolyte in practical applications, achieving control of the gas-liquid-solid interface, thereby achieving higher current and product selectivity.

[0068] like Figure 9 As shown in Figure 2, the XRD test data shows that with the increase of the atomization heat treatment temperature, the characteristic peak signal of graphene (002) is significantly weakened, indicating that the atomization heat treatment operation is beneficial to increase the interlayer spacing of graphene and reduce the stacking and agglomeration between graphene layers during the preparation of single-atom catalysts. At the same time, Figure 10As shown in the figure, it can be seen from the Raman spectral data that the different degrees of wrinkling have little effect on the degree of defects and graphitization of graphene, indicating that the regulation of physicochemical properties such as hydrophilicity and hydrophobicity can be achieved by simply changing the degree of wrinkling.

[0069] like Figure 11 As shown, the catalyst prepared in Example 1 can be characterized by high-angle annular dark field imaging-scanning transmission electron microscopy (HAADF-STEM) images, and the elements are evenly distributed, and the metal atoms exist in the form of single atoms.

[0070] like Figure 12 As shown, by comparing the electrochemical catalytic performance of samples with different wrinkling degrees and metal-free highly wrinkled graphene spheres in the oxygen reduction two-electron production of hydrogen peroxide reaction, it was found that Co single-atom-loaded highly wrinkled graphene spheres have better electrochemical activity and hydrogen peroxide selectivity. Its performance advantage is attributed to the fact that Co single-atom-loaded highly wrinkled graphene spheres have better properties to prevent stacking and aggregation, which gives them higher atomic utilization, as well as better material transport capabilities, which gives them higher hydrogen peroxide selectivity. The above conclusions strongly support that the Co single-atom-loaded wrinkled graphene catalyst prepared by the strategy described in this patent has very good electrocatalytic performance in the field of oxygen reduction two-electron production of hydrogen peroxide. At the same time, it can also be expected that other metal single-atom-loaded wrinkled graphene catalysts can also exhibit good performance in other electrochemical reactions.

Claims

1. An application of a wrinkled graphene-based single-atom catalyst prepared by atomization pyrolysis in the oxygen reduction two-electron production of hydrogen peroxide reaction, characterized in that: The method for preparing wrinkled graphene-based single-atom catalyst by atomization pyrolysis comprises the following steps: (1) preparing a graphene oxide suspension solution and uniformly mixing it with a metal precursor solution to obtain a mixed solution, wherein the metal precursor solution includes a precursor solution of one or more metals selected from the group consisting of iron, cobalt, nickel, copper, zinc, platinum, ruthenium, and iridium; (2) atomizing and pyrolyzing the mixed solution, wherein the concentration of the graphene oxide suspension is 0.1-5 mg / ml and the pyrolysis temperature is 350-1100° C. to obtain wrinkled spherical graphene oxide-based metal single atom catalyst; (3) calcining the wrinkled spherical graphene oxide-based metal single-atom catalyst under an inert or reducing atmosphere to regulate the coordination environment of the single atom and obtain the wrinkled spherical graphene-based metal single-atom catalyst.

2. The use of the wrinkled graphene-based single-atom catalyst prepared by atomization pyrolysis as claimed in claim 1 in the oxygen reduction two-electron production of hydrogen peroxide reaction, characterized in that: The preparation of the graphene oxide suspension solution described in step (1) adopts a thermal expansion oxidation method.

3. The use of the wrinkled graphene-based single-atom catalyst prepared by atomization pyrolysis in the oxygen reduction two-electron production of hydrogen peroxide as claimed in claim 2, characterized in that: The thermal expansion oxidation method specifically comprises the following steps: (1) Using concentrated sulfuric acid and concentrated nitric acid to intercalate graphite flakes, heating and expanding them to obtain expanded graphite powder; (2) Pre-oxidizing the expanded graphite powder using a strong oxidant; (3) oxidative intercalation treatment of the above product with concentrated sulfuric acid and potassium permanganate; (4) Wash with water and dialyze to obtain a graphene oxide suspension solution.

4. The use of the wrinkled graphene-based single-atom catalyst prepared by atomized pyrolysis in the oxygen reduction two-electron production of hydrogen peroxide according to claim 3, characterized in that: The strong oxidants are potassium disulfate and phosphorus pentoxide.

5. The use of the wrinkled graphene-based single-atom catalyst prepared by atomization pyrolysis as claimed in claim 1 in the oxygen reduction two-electron production of hydrogen peroxide reaction, characterized in that: The mass of the metal in the metal precursor solution in step (1) is 0.01-3% of the total mass of graphene oxide.

6. The use of the wrinkled graphene-based single-atom catalyst prepared by atomization pyrolysis in the oxygen reduction two-electron production of hydrogen peroxide according to claim 1, characterized in that: The atomization in the atomization pyrolysis in step (2) is performed using an ultrasonic atomizer, and the oscillation frequency of the ultrasonic atomizer is 1.7 MHz or 2.4 MHz.

7. The use of the wrinkled graphene-based single-atom catalyst prepared by atomization pyrolysis in the oxygen reduction two-electron production of hydrogen peroxide according to claim 6, characterized in that: The atomized mixed solution is pyrolyzed in an inert atmosphere.

8. The use of the wrinkled graphene-based single-atom catalyst prepared by atomization pyrolysis in the oxygen reduction two-electron production of hydrogen peroxide according to claim 1, characterized in that: The calcination temperature in step (3) is 300-1100° C., and the calcination atmosphere is Ar / NH 3 atmosphere or Ar / H 2 atmosphere.

Images