A nitrogen-boron doped carbon fiber catalyst, a preparation method and application thereof

Abstract

The application discloses a nitrogen and boron doped carbon fiber catalyst and a preparation method and application thereof, and belongs to the field of oxygen reduction electrocatalyst preparation. Polyacrylonitrile (PAN) and boric acid are dissolved in an organic solvent to obtain a spinning slurry. The spinning slurry is used to prepare a fiber structure catalyst precursor by using an electrostatic spinning machine, and then the catalyst precursor is subjected to high-temperature crosslinking treatment in air and high-temperature carbonization treatment in a reducing gas to obtain nitrogen and boron doped carbon fiber which can be used as an electrocatalyst for catalyzing hydrogen peroxide production. The fiber network structure provides a high specific surface and good electrical conductivity, which is conducive to improving the electrochemical performance of the material. The nitrogen and boron doped carbon fiber catalyst prepared by the application has high hydrogen peroxide selectivity, and the process is simple and the conditions are mild.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of oxygen reduction electrocatalysts, and particularly relates to a nitrogen-boron doped carbon fiber catalyst and a preparation method and application thereof. BACKGROUND

[0002] Electrospinning is an important method for preparing ultra-fine fibers and non-woven fabrics in the world in the past 20 years, and has realized the preparation of nanofibers of different polymers in the range of several nanometers to several hundred nanometers. The nanofiber materials prepared by electrospinning have shown great application potential in the fields of optoelectronics, sensors, electrochemical electrodes, catalysts, environment and biomedicine.

[0003] Carbon fiber is a carbon material mainly composed of carbon elements, which is generally derived from the high-temperature pyrolysis of various organic matters such as polyacrylonitrile. Carbon fiber is widely used in the research of electrochemical energy technology due to its high specific surface area, good electrical conductivity, easy preparation, chemical corrosion resistance and other advantages.

[0004] Hydrogen peroxide (H2O2) is a multifunctional and clean harmless oxidant, which is used in medical disinfection, textile bleaching, wastewater treatment, chemical synthesis, semiconductor cleaning and waste gas treatment in various industries. Electrochemical synthesis of hydrogen peroxide as a decentralized hydrogen peroxide production method, combined with renewable energy electrolysis of water to produce hydrogen, can realize the in-situ production of hydrogen peroxide on demand, avoiding the difficulties and dangers of centralized production, transportation and storage of hydrogen peroxide, and has very important strategic and practical value.

[0005] Catalysts are the key factors affecting the selectivity and reaction rate of the electrochemical synthesis of hydrogen peroxide. Although noble metal catalysts have excellent performance, their high price and resource scarcity limit their commercialization potential. Non-metallic heteroatom doped carbon materials as catalysts have the advantages of low cost, good controllability and high stability, and have attracted more and more attention in the production of hydrogen peroxide by oxygen reduction. However, the non-metallic doped carbon materials still have the disadvantages of low catalytic activity and low hydrogen peroxide selectivity under acidic conditions, and effective doping strategies are needed to improve the activity and selectivity. The preparation methods of heteroatom doped carbon materials are divided into carbon material surface modification and carbonization of heteroatom-containing polymers. The former has a low doping amount. The template method is often used in the carbonization of heteroatom-containing polymers to obtain a high specific surface area, but the subsequent template removal step is complicated and the chemical reagents used will pollute the environment. SUMMARY

[0006] In order to solve the problems existing in the prior art, the application provides a nitrogen-boron doped carbon fiber catalyst and a preparation method and application thereof. The synthesized fiber has uniform size and good electrochemical performance.

[0007] In order to achieve the above object, the technical scheme realized by the present application is:

[0008] In the first aspect, the present application provides a preparation method of nitrogen and boron doped carbon fiber catalyst, comprising the following steps:

[0009] (1) dissolving polyacrylonitrile (PAN) and boric acid in an organic solvent to obtain an electrospinning precursor solution;

[0010] (2) electrospinning the electrospinning precursor solution obtained in step (1);

[0011] (3) crosslinking the product obtained in step (2) in air;

[0012] (4) further carbonizing the product obtained in step (3) in a reducing atmosphere to obtain a nitrogen and boron doped carbon fiber catalyst.

[0013] Further, in step (1) of the above technical scheme, the mass-volume ratio of polyacrylonitrile to organic solvent is 0.01-0.2 g / mL; and the mass ratio of boric acid to polyacrylonitrile is 0.2-2:1.

[0014] Preferably, in step (1), the mass-volume ratio of polyacrylonitrile to organic solvent is 0.05-0.1 g / mL; and the mass ratio of boric acid to polyacrylonitrile is 0.05-1.

[0015] Further, in step (2) of the above technical scheme, the high voltage of electrospinning is 15-25 kV, the discharge rate is 0.1-1 mL / h, and the distance from the needle to the drum is 10-25 cm.

[0016] Further, in step (3) of the above technical scheme, the crosslinking temperature is 200-380℃, the holding time is 1-12 h, and the heating rate is 2-10℃ / min.

[0017] Preferably, in step (3), the crosslinking temperature is 220-280℃, the holding time is 2-5 h, and the heating rate is 1-5℃ / min.

[0018] Further, in step (4) of the above technical scheme, the reducing atmosphere is H2+Ar; the carbonization temperature is 500-900℃, the holding time is 2-12 h, and the heating rate is 1℃ / min-5℃ / min.

[0019] Preferably, the carbonization temperature is 600-800℃, and further preferably 750℃; the holding time is 3-10 h, and further preferably 3 h; and the heating rate is 2℃ / min-3℃ / min.

[0020] In a second aspect, the present application provides a nitrogen and boron doped carbon fiber catalyst prepared by the preparation method.

[0021] In a third aspect, the present application provides an application of the nitrogen and boron doped carbon fiber catalyst in a two-electron electrocatalytic oxygen reduction synthesis of hydrogen peroxide.

[0022] Advantages:

[0023] The preparation method of the present application is simple, and a higher specific surface area can be obtained without using a template method; the electrode can be directly spun, avoiding the spraying process of the catalyst. The electrostatic spinning method used in the present application can directly obtain a carbon material with a larger specific surface area without a template; in addition, effective doping can be performed by adding heteroatom molecules in the precursor polymer, and the process is simple and has potential for practical application.

[0024] The process of the present application is simple and mild, and the prepared nitrogen and boron doped carbon fiber catalyst is doped with nitrogen and boron atoms, which can be applied to the electro synthesis of hydrogen peroxide. The nitrogen and boron doped carbon fiber catalyst prepared by the present application has a fiber network structure, provides a higher specific surface and good electrical conductivity, and is beneficial to improve the electrochemical performance of the material. The boron atoms can be reduced using a reducing atmosphere, the adsorption energy of the active sites and oxygen reduction intermediates is adjusted, the activity and selectivity of oxygen reduction to produce hydrogen peroxide are improved, and the selectivity of hydrogen peroxide can be more than 95%. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a scanning electron microscope picture of the nitrogen and boron doped carbon fiber catalyst of Example 1.

[0026] Figure 2 It is a scanning electron microscope picture of the nitrogen and boron doped carbon fiber catalyst of Example 2.

[0027] Figure 3 It is an i-v curve of the rotating ring-disk electrode test of the nitrogen and boron doped carbon fiber catalyst of Example 1.

[0028] Figure 4 It is an i-v curve of the rotating ring-disk electrode test of the nitrogen and boron doped carbon fiber catalyst of Example 2.

[0029] Figure 5 It is an i-v curve of the rotating ring-disk electrode test of the nitrogen and boron doped carbon fiber catalyst of Comparative Example 1.

[0030] Figure 6 It is a hydrogen peroxide selectivity-voltage curve of the rotating ring-disk electrode test of the nitrogen and boron doped carbon fiber catalyst of Example 1.

[0031] Figure 7 It is a hydrogen peroxide selectivity-voltage curve of the rotating ring-disk electrode test of the nitrogen and boron doped carbon fiber catalyst of Example 2.

[0032] Figure 8 The hydrogen peroxide selectivity-voltage curve of the hydrogen peroxide selectivity of the nitrogen and boron doped carbon fiber catalyst rotating ring disc electrode test of Comparative Example 1. DETAILED DESCRIPTION

[0033] The application will be further described in the following specific examples, which are only descriptive and not limiting, and cannot limit the protection scope of the application.

[0034] Example 1

[0035] A preparation method of a nitrogen and boron doped carbon fiber catalyst, comprising the following steps:

[0036] 1) Dissolve 1.0 g of polyacrylonitrile and 0.5 g of boric acid in 10 mL of N,N-dimethylformamide to form a transparent solution to obtain an electrospinning precursor solution.

[0037] 2) Electrospin the electrospinning precursor solution obtained in step 1). The high voltage is 25 kV, the discharge rate is 0.2 mL / h, and the distance from the needle to the drum is 20 cm.

[0038] 3) High-temperature crosslinking treatment of the spinning product obtained in step 2) in air. The crosslinking temperature is 220°C, the holding time is 3h, and the heating rate is 5°C / min.

[0039] 4) Further carbonization treatment of the product obtained in step 3) in a 5% H2+Ar atmosphere, the carbonization temperature is 750°C, the heating rate is 5°C / min, and the holding time is 3h, to obtain a nitrogen and boron doped carbon fiber catalyst.

[0040] Test results:

[0041] The product was subjected to scanning electron microscopy, and the results are as Figure 1 , the fiber diameter is about 200 nm, and the morphology is uniform.

[0042] The product was subjected to rotating ring disc electrode test, and the test conditions were: 0.5 mol / L sulfuric acid solution as electrolyte, disc electrode loading amount was 0.1 mg cm -2 , and the rotation speed was 1600 rpm. The results are as Figure 3 and Figure 6 , the initial potential is about 0.5V vs. RHE, and the hydrogen peroxide selectivity is more than 95% in the potential range of 0.05-0.2V vs. RHE.

[0043] Example 2

[0044] A preparation method of a nitrogen and boron doped carbon fiber catalyst, comprising the following steps:

[0045] 1) Dissolve 1.0 g of polyacrylonitrile and 1.0 g of boric acid in 10 mL of N,N-dimethylformamide to form a transparent solution to obtain an electrospinning precursor solution.

[0046] 2) Electrospin the electrospinning precursor solution obtained in step 1). The high voltage is 25 kV, the discharge rate is 0.2 mL / h, and the distance from the needle to the drum is 20 cm.

[0047] 3) High-temperature crosslinking treatment of the spinning product obtained in step 2) in air. The crosslinking temperature is 220°C, the holding time is 3 h, and the heating rate is 5°C / min.

[0048] 4) Further carbonization treatment of the product obtained in step 3) in a 5% H2+Ar atmosphere, the carbonization temperature is 750°C, the heating rate is 5°C / min, and the holding time is 3 h, to obtain a nitrogen-boron-doped carbon fiber catalyst.

[0049] Test results:

[0050] The product was subjected to scanning electron microscopy, and the results are shown in Figure 2 , the fiber diameter is about 250 nm, and the morphology is uniform.

[0051] The product was subjected to a rotating ring-disk electrode test, and the test conditions were as follows: 0.5 mol / L sulfuric acid solution as electrolyte, disk electrode loading of 0.1 mg cm -2 , and rotation speed of 1600 rpm. The results are shown in Figure 4 and Figure 7 , the initial potential is about 0.5 V vs. RHE, and the hydrogen peroxide selectivity is more than 95% in the potential range of 0.05-0.2 V vs. RHE.

[0052] Comparative Example 1

[0053] A method for preparing a nitrogen-boron-doped carbon fiber catalyst, comprising the following steps:

[0054] 1) Dissolve 1.0 g of polyacrylonitrile and 0.5 g of boric acid in 10 mL of N,N-dimethylformamide to form a transparent solution to obtain an electrospinning precursor solution.

[0055] 2) Electrospin the electrospinning precursor solution obtained in step 1). The high voltage is 25 kV, the discharge rate is 0.2 mL / h, and the distance from the needle to the drum is 20 cm.

[0056] 3) High-temperature crosslinking treatment of the spinning product obtained in step 2) in air. The crosslinking temperature is 220°C, the holding time is 3 h, and the heating rate is 5°C / min.

[0057] 4) The product obtained in step 3) is further carbonized at 750℃ under Ar atmosphere, with a heating rate of 5℃ / min and a holding time of 3h, to obtain a nitrogen and boron doped carbon fiber catalyst.

[0058] Test results:

[0059] The product is subjected to a rotating ring-disk electrode test, with a test condition of 0.5mol / L sulfuric acid solution as electrolyte, a disk electrode loading of 0.1mg cm -2 , and a rotating speed of 1600rpm. The results are shown in Figure 5 and Figure 8 , with an onset potential of about 0.5V vs. RHE and a hydrogen peroxide selectivity of less than 70% in a potential range of 0.05-0.2V vs. RHE.

[0060] By comparing the data of Examples 1-2 and Comparative Example 1, it is proved that the use of a reducing atmosphere in the present application can reduce boron atoms, adjust the adsorption energy of active sites and oxygen reduction intermediates, improve the activity and selectivity of oxygen reduction to produce hydrogen peroxide, and the hydrogen peroxide selectivity can be more than 95%.

[0061] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. The application of a nitrogen-boron-doped carbon fiber catalyst in the two-electron electrocatalytic oxygen reduction synthesis of hydrogen peroxide, characterized in that, The preparation method of nitrogen-boron-doped carbon fiber catalyst includes the following steps: (1) Dissolve polyacrylonitrile and boric acid in an organic solvent to obtain an electrospinning precursor solution; (2) Electrospin the electrospinning precursor solution obtained in step (1); (3) The product obtained in step (2) is subjected to crosslinking treatment in air; (4) The product obtained in step (3) is further carbonized in a reducing atmosphere to obtain a nitrogen-boron-doped carbon fiber catalyst. In step (3), the crosslinking temperature is 200~380℃, the holding time is 1~12h, and the heating rate is 2~10℃ / min; In step (4), the reducing atmosphere is H2+Ar; the carbonization temperature is 500~900℃, the holding time is 2~12h, and the heating rate is 1℃ / min~5℃ / min.

2. The application of the nitrogen-boron-doped carbon fiber catalyst according to claim 1 in the two-electron electrocatalytic oxygen reduction synthesis of hydrogen peroxide, characterized in that, In step (1), the mass-volume ratio of polyacrylonitrile to organic solvent is 0.01~0.2 g / mL; the mass ratio of boric acid to polyacrylonitrile is 0.2~2:

1.

3. The application of the nitrogen-boron-doped carbon fiber catalyst according to claim 1 in the two-electron electrocatalytic oxygen reduction synthesis of hydrogen peroxide, characterized in that, In step (2), the high voltage of electrospinning is positive voltage of 15~25kV, the output rate is 0.1~1mL / h, and the distance from the needle to the roller is 10~25cm.

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