CFNB metal-free redox catalyst and preparation method and application thereof

Abstract

The invention discloses a CFNB metal-free redox catalyst and a preparation method and application thereof, and belongs to the technical field of electrochemical catalytic materials, the CFNB metal-free redox catalyst is composed of a carbon material co-doped with three heterogeneous elements of fluorine, nitrogen and boron, and has a three-dimensional cross-linked nano network structure; the preparation method comprises the following steps: jointly dissolving the polyalcohol ether borate, the polydopamine and the polyvinylidene fluoride hexafluoropropylene copolymer in N-N dimethylformamide according to a mass ratio of (1-5): (1-5): (1-5), and stirring until the materials are uniformly mixed; the obtained mixed solution is subjected to electrostatic spinning, the spinning voltage is 12-18 kV, the receiving distance is 15-20 cm, the flow velocity is 0.05-5 mL / h, and an aluminum foil serves as a receiving base material; the obtained spinning product is subjected to carbonization treatment in an inert atmosphere, calcination is conducted for 1-4 h at the calcination temperature of 700-950 DEG C, and the CFNB metal-free oxygen reduction catalyst is obtained and has better catalytic activity and stability.

Description

Technical Field

[0001] This invention relates to the field of electrochemical catalytic materials technology, and in particular to a CFNB metal-free redox catalyst, its preparation method, and its application. Background Technology

[0002] As a highly efficient and clean energy technology, fuel cells' performance is limited by the slow kinetics of the oxygen reduction reaction at the cathode. Currently, platinum-based catalysts hinder the commercialization of fuel cells due to their high cost and poor stability. While non-metallic doped carbon materials can partially replace precious metals in existing technologies, they still suffer from insufficient conductivity and inadequate exposure of active sites. For example, the nitrogen-boron co-doped carbon fiber catalyst disclosed in Chinese patent CN117306024A has a complex preparation process and poor alkali resistance. Electrospinning technology can prepare nanofiber materials with high specific surface area, but single-element doping makes it difficult to optimize charge distribution and catalytic activity. Therefore, developing a multi-element co-doped, simple-to-prepare, and suitable-for-alkaline-environment-efficient oxygen reduction catalyst is of great significance. Summary of the Invention

[0003] Technical problem solved: In view of the problems existing in the prior art, the present invention provides a metal-free CFNB redox catalyst, its preparation method and application, which significantly improves oxygen reduction activity and stability through the three-dimensional nano-network structure of F, N and B co-doped carbon materials.

[0004] Technical solution: The present invention provides a CFNB metal-free redox catalyst, wherein the catalyst is composed of carbon material co-doped with three heterogeneous elements, namely fluorine, nitrogen and boron, and has a three-dimensional cross-linked nanonetwork structure.

[0005] Preferably, the specific surface area of ​​the carbon material is 600-800 m². 2 / g.

[0006] This invention discloses a method for preparing the above-mentioned metal-free oxygen reduction catalyst for CFNB, comprising the following steps:

[0007] Step 1: Dissolve polyol ether borate, polydopamine and polyvinylidene fluoride hexafluoropropylene copolymer in N,N dimethylformamide at a mass ratio of (1-5):(1-5):(1-5) and stir at 40-90℃ until the mixture is homogeneous.

[0008] Step 2: Electrospin the mixture obtained in Step 1. The spinning voltage is 12-18kV, the receiving distance is 15-20cm, the flow rate is 0.05-5mL / h, and aluminum foil is used as the receiving substrate.

[0009] Step 3: The spinning product obtained in Step 2 is carbonized under an inert atmosphere at a calcination temperature of 700-950℃ for 1-4 hours to obtain the CFNB metal-free oxygen reduction catalyst.

[0010] Preferably, the stirring temperature in step 1 is 60°C.

[0011] Preferably, the calcination temperature in step 3 is 900℃ and the calcination time is 2h.

[0012] The present invention also discloses the application of the above-mentioned CFNB metal-free oxygen reduction catalyst in the oxygen reduction reaction of fuel cell cathode. The catalyst exhibits an oxygen reduction onset potential ≥0.85V in alkaline electrolyte and a current density retention rate ≥90% after 10,000 seconds.

[0013] Compared with the prior art, the present invention achieves the following technical effects:

[0014] 1. The CFNB metal-free oxygen reduction catalyst of the present invention utilizes a three-dimensional cross-linked nanonetwork structure prepared from polypolyol ether borate, polydopamine, and polyvinylidene fluoride hexafluoropropylene copolymer to provide a high specific surface area, which efficiently promotes oxygen adsorption and mass transfer. F doping adjusts the hydrophilicity of the catalyst layer, and the highly polarized CF bonds enhance the conductivity and alkali resistance of the material. B doping can adjust the electrically neutral structure around carbon, promoting oxygen adsorption. N and B synergy can optimize the charge distribution. Co-doping of N, B, and F can improve the charge C bond polarization, charge and spin distribution, and improve the catalytic activity and stability of the catalyst. The oxygen reduction performance of this catalyst under alkaline conditions is close to that of commercial platinum carbon, and its stability is even better.

[0015] 2. The preparation process of the present invention is simple and low in cost. The fiber membrane is obtained by electrospinning and then calcined. The manufacturing process is safer and suitable for large-scale production. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the preparation process of the CFNB metal-free oxygen reduction catalyst of the present invention.

[0017] Figure 2 This is a scanning electron microscope image of the CFNB metal-free oxygen reduction catalyst prepared in Example 2 of the present invention;

[0018] Figure 3 Linear sweep voltammetry curve of the CFNB metal-free oxygen reduction catalyst prepared in Example 2 of this invention;

[0019] Figure 4 The attached figure shows the nitrogen adsorption and desorption process of the CFNB metal-free oxygen reduction catalyst prepared in Example 2 of this invention.

[0020] Figure 5Cyclic voltammetry curves of the CFNB metal-free oxygen reduction catalysts prepared in Examples 1-11 and Comparative Example 1 of this invention;

[0021] Figure 6 This is a comparison graph showing the percentage loss of current density between the CFNB metal-free oxygen reduction catalyst prepared in Example 2 and the commercial catalyst platinum-carbon, tested after 10,000 s at a constant voltage of -0.35V and a stirring speed of 1600 rpm. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will be described in conjunction with the accompanying drawings. Figures 1-6 The technical solutions of the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0023] This invention discloses a CFNB metal-free redox catalyst, wherein the catalyst is composed of carbon material co-doped with three hetero-elements: fluorine, nitrogen, and boron, and has a three-dimensional cross-linked nanonetwork structure; the specific surface area of ​​the carbon material is 600-800 m². 2 / g.

[0024] like Figure 1 As shown, this invention discloses a method for preparing a metal-free oxygen reduction catalyst for CFNB, comprising the following steps:

[0025] Step 1: Dissolve polypolyol ether borate, polydopamine and polyvinylidene fluoride hexafluoropropylene copolymer in N,N dimethylformamide at a mass ratio of (1-5):(1-5):(1-5) and stir at 40-90℃ until uniformly mixed (stirring temperature can be 40℃, 50℃, 60℃, 70℃, 80℃ and 90℃).

[0026] Step 2: Electrospin the mixture obtained in Step 1. The spinning voltage is 12-18kV, the receiving distance is 15-20cm, the flow rate is 0.05-5mL / h, and aluminum foil is used as the receiving substrate.

[0027] Step 3: The spinning product obtained in Step 2 is carbonized under an inert atmosphere. The calcination temperature is 700-950℃ (calcination temperature can be 700℃, 800℃, 900℃ and 950℃), and the calcination time is 1-4h (calcination time can be 1h, 2h, 3h and 4h, depending on the selection), to obtain the CFNB metal-free oxygen reduction catalyst.

[0028] The present invention also discloses the application of a CFNB metal-free oxygen reduction catalyst in the oxygen reduction reaction at the cathode of a fuel cell. The catalyst exhibits an oxygen reduction initiation potential ≥0.85V in an alkaline electrolyte and a current density retention rate ≥90% after 10,000 seconds.

[0029] The catalyst samples were subjected to performance testing. Cyclic voltammetry curves were obtained using an Autolab PGSTAT302N telephone workstation. Specific test conditions were as follows: a three-electrode system with Ag / AgCl as the reference electrode, platinum wire as the counter electrode, and a glassy carbon electrode loaded with the catalyst as the working electrode; the scan rate was 10 mV / s. The working electrode was prepared by dissolving 5 mg of catalyst in a mixture of 20 mL isopropanol and 40 μL of Nafion (5% solution, purchased from DuPont), ultrasonically dispersing the solution, and then adding 10 μL dropwise to the glassy carbon electrode. After drying at room temperature, this became the working electrode. During cyclic voltammetry testing, nitrogen and oxygen were separately introduced into a 0.1 M KOH electrolyte solution to create a nitrogen / oxygen atmosphere. Before testing, the electrode was cycled 30 times in the electrolyte solution to activate it, and then the test was performed. The chronoamperometry curves of the catalyst samples were measured using an Autolab PGSTAT302N telephone workstation. The test conditions were as follows: a three-electrode system with Ag / AgCl as the reference electrode, a platinum sheet as the counter electrode, and a rotating disk electrode loaded with the catalyst as the working electrode; 0.1M KOH as the electrolyte solution; and a scan rate of 10 mV / s. The working electrode was prepared by dissolving 5 mg of catalyst in a mixture of 20 mL isopropanol and 40 μL of Nafion (5% solution, purchased from DuPont), ultrasonically dispersing the mixture, and then adding 10 μL dropwise to the rotating disk electrode. After drying at room temperature, this became the working electrode. The chronoamperometry curves were measured under the following conditions: a constant potential of -0.35 V and a rotation speed of 1600 rpm, measuring the change in current over 10,000 s.

[0030] The present invention will be further described with reference to the following specific embodiments.

[0031] Example 1: 2g of polyol ether borate, 1g of polydopamine and 1g of polyvinylidene fluoride hexafluoropropylene copolymer were dissolved in 50ml of NN dimethylformamide and stirred until homogeneous at a stirring temperature of 60℃. Electrospinning was performed using aluminum foil as the receiving substrate at a voltage of 14kV, a receiving distance of 15cm and a flow rate of 0.1mL / h. The resulting spun product was placed in a tube furnace and calcined at 900℃ for 2h under an inert atmosphere to obtain the CFNB metal-free oxygen reduction catalyst.

[0032] Example 2: 2g of polyol ether borate, 1g of polydopamine and 2g of polyvinylidene fluoride hexafluoropropylene copolymer were dissolved in 50ml of NN dimethylformamide and stirred until homogeneous at a stirring temperature of 60℃. Electrospinning was performed using aluminum foil as the receiving substrate at a voltage of 14kV, a receiving distance of 15cm and a flow rate of 0.1mL / h. The resulting spun product was placed in a tube furnace and calcined at 900℃ for 2h under an inert atmosphere to obtain the CFNB metal-free oxygen reduction catalyst.

[0033] Figure 2 The image shown is a scanning electron microscope image of the CFNB metal-free oxygen reduction catalyst prepared in Example 2. It can be seen that the carbon material used in this catalyst has a good three-dimensional cross-linked nanonetwork structure. The existence of the three-dimensional network connects the various layers, and the interlayer pore structure can provide abundant active sites.

[0034] Figure 3 The linear sweep voltammetry curve for the CFNB metal-free oxygen reduction catalyst prepared in Example 2 shows that, under alkaline conditions, the catalyst sample prepared in Example 2 has a half-wave potential of 0.844 V and a limiting current density of 5.691 mA·cm⁻¹. -2 It exceeds that of commercial platinum-carbon (half-wave potential 0.830V, limiting current density 5.006mAcm-2).

[0035] Figure 4 The attached figure shows the nitrogen adsorption and desorption process of the CFNB metal-free oxygen reduction catalyst prepared in Example 2. Figure 4 Typical type IV mesoporous curves demonstrate that the synthesized F, N, and B-doped carbon materials possess high specific surface area and favorable mesoporous structure. According to the IUPAC classification standard, the nitrogen adsorption-desorption isotherms of all catalysts belong to type IV(a). This structure with high surface area and micro-mesoporous features is beneficial for mass transfer of reactants and exposes more active sites.

[0036] Depend on Figure 3 , Figure 5 As shown in Table 1, the F, N, and B doped carbon material of Example 2 exhibits significant oxygen reduction properties, with an oxygen reduction potential of 0.866 V, a half-wave potential of 0.844 V, and a limiting current density of 5.691 mA·cm⁻¹. -2 It surpasses commercial platinum-carbon.

[0037] Example 3: 2g of polyol ether borate, 1g of polydopamine and 5g of polyvinylidene fluoride hexafluoropropylene copolymer were dissolved in 50ml of NN dimethylformamide and stirred until homogeneous at a stirring temperature of 60℃. Electrospinning was performed using aluminum foil as the receiving substrate at a voltage of 14kV, a receiving distance of 15cm and a flow rate of 0.1mL / h. The resulting spun product was placed in a tube furnace and calcined at 900℃ for 2h under an inert atmosphere to obtain the CFNB metal-free oxygen reduction catalyst.

[0038] Example 4: 2g of polyol ether borate, 1g of polydopamine and 2g of polyvinylidene fluoride hexafluoropropylene copolymer were dissolved in 50ml of NN dimethylformamide and stirred until homogeneous at a stirring temperature of 40℃. Electrospinning was performed using aluminum foil as the receiving substrate at a voltage of 14kV, a receiving distance of 15cm and a flow rate of 0.1mL / h. The resulting spun product was placed in a tube furnace and calcined at 900℃ for 2h under an inert atmosphere to obtain the CFNB metal-free oxygen reduction catalyst.

[0039] Example 5: 2g of polyol ether borate, 1g of polydopamine and 2g of polyvinylidene fluoride hexafluoropropylene copolymer were dissolved in 50ml of NN dimethylformamide and stirred until homogeneous at a stirring temperature of 90℃. Electrospinning was performed using aluminum foil as the receiving substrate at a voltage of 14kV, a receiving distance of 15cm and a flow rate of 0.1mL / h. The resulting spun product was placed in a tube furnace and calcined at 900℃ for 2h under an inert atmosphere to obtain the CFNB metal-free oxygen reduction catalyst.

[0040] Example 6: 2g of polyol ether borate, 1g of polydopamine and 2g of polyvinylidene fluoride hexafluoropropylene copolymer were dissolved in 50ml of NN dimethylformamide and stirred until homogeneous at a stirring temperature of 60℃. Electrospinning was performed using aluminum foil as the receiving substrate at a voltage of 12kV, a receiving distance of 20cm and a flow rate of 5mL / h. The resulting spun product was placed in a tube furnace and calcined at 900℃ for 2h under an inert atmosphere to obtain the CFNB metal-free oxygen reduction catalyst.

[0041] Example 7: 2g of polyol ether borate, 1g of polydopamine and 2g of polyvinylidene fluoride hexafluoropropylene copolymer were dissolved in 50ml of NN dimethylformamide and stirred until homogeneous at a stirring temperature of 60℃. Electrospinning was performed using aluminum foil as the receiving substrate at a voltage of 18kV, a receiving distance of 17cm and a flow rate of 3mL / h. The resulting spun product was placed in a tube furnace and calcined at 900℃ for 2h under an inert atmosphere to obtain the CFNB metal-free oxygen reduction catalyst.

[0042] Example 8: 2g of polyol ether borate, 1g of polydopamine and 2g of polyvinylidene fluoride hexafluoropropylene copolymer were dissolved in 50ml of NN dimethylformamide and stirred until homogeneous at a stirring temperature of 60℃. Electrospinning was performed using aluminum foil as the receiving substrate at a voltage of 14kV, a receiving distance of 15cm and a flow rate of 0.1mL / h. The resulting spun product was placed in a tube furnace and calcined at 950℃ for 1h under an inert atmosphere to obtain the CFNB metal-free oxygen reduction catalyst.

[0043] Example 9: 2g of polyol ether borate, 1g of polydopamine and 2g of polyvinylidene fluoride hexafluoropropylene copolymer were dissolved in 50ml of NN dimethylformamide and stirred until homogeneous at a stirring temperature of 60℃. Electrospinning was performed using aluminum foil as the receiving substrate at a voltage of 14kV, a receiving distance of 15cm and a flow rate of 0.1mL / h. The resulting spun product was placed in a tube furnace and calcined at 700℃ for 4h under an inert atmosphere to obtain the CFNB metal-free oxygen reduction catalyst.

[0044] Example 10: 1g of polyol ether borate, 5g of polydopamine and 2g of polyvinylidene fluoride hexafluoropropylene copolymer were dissolved in 50ml of NN dimethylformamide and stirred until homogeneous at a stirring temperature of 60℃. Electrospinning was performed using aluminum foil as the receiving substrate at a voltage of 14kV, a receiving distance of 15cm and a flow rate of 0.1mL / h. The resulting spun product was placed in a tube furnace and calcined at 900℃ for 2h under an inert atmosphere to obtain the CFNB metal-free oxygen reduction catalyst.

[0045] Example 11: 5g of polyol ether borate, 3g of polydopamine, and 3g of polyvinylidene fluoride hexafluoropropylene copolymer were dissolved in 50ml of NN dimethylformamide and stirred until homogeneous at a stirring temperature of 60℃. Electrospinning was performed using aluminum foil as the receiving substrate at a voltage of 14kV, a receiving distance of 15cm, and a flow rate of 0.1mL / h. The resulting spun product was placed in a tube furnace and calcined at 900℃ for 2h under an inert atmosphere to obtain the CFNB metal-free oxygen reduction catalyst.

[0046] Comparative Example 1: 2g of polyol ether borate and 1g of polyvinylidene fluoride hexafluoropropylene copolymer were dissolved in 50ml of N-N dimethylformamide and mixed and stirred at 60℃ until homogeneous; using aluminum foil as the receiving substrate, electrospinning was performed under the conditions of 14kV voltage, 15cm receiving distance and 0.1mL / h flow rate; the resulting spun product was placed in a tube furnace and calcined at 900℃ for 2h under an inert atmosphere to obtain CB metal-free oxygen reduction catalyst.

[0047] The electrochemical performance comparison results of the catalysts prepared in Examples 1-11 of this invention and the catalyst prepared in Comparative Example 1 are shown in Table 1.

[0048] Table 1. Comparison of the electrochemical performance of the catalysts prepared in Examples 1-11 with that prepared in Comparative Example 1:

[0049]

[0050] As shown in Table 1, the initial potential of Examples 1-11 is greater than 0.8V, the half-wave potential is greater than 0.7V, and the limiting current density is greater than 4mA / cm². 2 This indicates that the F, N, and B doped carbon material used in this invention exhibits significant oxygen reduction properties. Under alkaline conditions, the half-wave potential of Example 2 is 0.866 V, and the limiting current density is 5.691 mA / cm². -2 This exceeds the commercial platinum-carbon (half-wave potential 0.830V, limiting current density 5.006 mA / cm²) parameters. -2 The relevant data of other embodiments are close to those of commercial platinum carbon; the oxygen reduction potential of Comparative Example 1 is only 0.655V and the half-wave potential is only 0.705V, indicating that the oxygen reduction performance of B-doped carbon material alone is poor under alkaline conditions. The comparison proves that the conductivity and alkali resistance of the material can be improved by doping with fluorine in the embodiments, which is conducive to oxygen adsorption and further improves the catalytic activity of the catalyst.

[0051] Figure 5 Cyclic voltammetry curves of the CFNB metal-free oxygen reduction catalysts prepared in Examples 1-11 and Comparative Example 1 show that the catalysts prepared in O2 saturated electrolyte all showed obvious reduction peaks, indicating that all samples have certain catalytic ability. In addition, the redox peak positions of Example 2 are all positively shifted compared to the positive reduction peak positions of other examples, and the peak of Example 2 shows a higher oxygen reduction potential.

[0052] Figure 6 This is a comparison graph showing the percentage loss of current density between the CFNB metal-free oxygen reduction catalyst prepared in Example 2, the commercial catalyst platinum-carbon, and Comparative Example 1, tested after 10000 s under alkaline conditions: constant voltage -0.35V, stirring speed 1600 rpm. Figure 6 It can be seen that after testing for 10,000 s, the catalyst current density of Example 2 was retained at 95.81%, while that of the commercial platinum-carbon catalyst was 86.65%, and that of the B-doped carbon material alone was 83.47%. This proves that the alkali resistance of the material can be improved by doping with fluorine, indicating that the catalyst has better stability than the commercial platinum-carbon catalyst.

[0053] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A metal-free redox catalyst for CFNB, characterized in that, The catalyst is composed of carbon material co-doped with three heterogeneous elements: fluorine, nitrogen, and boron, and has a three-dimensional cross-linked nanonetwork structure.

2. The CFNB metal-free redox catalyst according to claim 1, characterized in that, The specific surface area of ​​the carbon material is 600-800 m². 2 / g.

3. A method for preparing the CFNB metal-free oxygen reduction catalyst as described in claim 1, characterized in that, Includes the following steps: Step 1: Dissolve polyol ether borate, polydopamine and polyvinylidene fluoride hexafluoropropylene copolymer in N,N dimethylformamide at a mass ratio of (1-5):(1-5):(1-5) and stir at 40-90℃ until the mixture is homogeneous. Step 2: Electrospin the mixture obtained in Step 1. The spinning voltage is 12-18kV, the receiving distance is 15-20cm, the flow rate is 0.05-5mL / h, and aluminum foil is used as the receiving substrate. Step 3: The spinning product obtained in Step 2 is carbonized under an inert atmosphere at a calcination temperature of 700-950℃ for 1-4 hours to obtain the CFNB metal-free oxygen reduction catalyst.

4. The method for preparing the CFNB metal-free redox catalyst according to claim 3, characterized in that, The stirring temperature in step 1 is 60°C.

5. The CFNB metal-free redox catalyst according to claim 1, characterized in that, The calcination temperature in step 3 is 900℃, and the calcination time is 2 hours.

6. The application of the CFNB metal-free oxygen reduction catalyst according to claim 1 in the oxygen reduction reaction at the cathode of a fuel cell.

7. The application according to claim 6, characterized in that, The catalyst exhibits an oxygen reduction initiation potential ≥0.85V in an alkaline electrolyte and a current density retention rate ≥90% after 10,000 seconds.

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