A method for synthesizing zinc oxide-etched iron-cobalt alloy-doped carbon nanofibers for electrocatalysis

Abstract

This invention relates to a method for synthesizing iron-cobalt alloy-doped carbon nanofibers for electrocatalysis using zinc oxide etching, belonging to the technical field of electrode materials and catalysts. The preparation method includes the following steps: 1) mixing DMF (dimethylformamide), PMDA (pyromellitic dianhydride), and ODA (4,4-diaminodiphenyl ether) in a certain proportion to prepare a PAA (polyamic acid) spinning solution; 2) preparing PAA nanofibers from the PAA spinning solution using an electrostatic melt-blowing device; 3) imidizing the PAA nanofibers using a programmed temperature rise method to obtain PI nanofibers; 4) impregnating the PI nanofibers in a salt solution; 5) carbonizing the impregnated PI nanofibers with a large number of metal ions on their surface in an inert atmosphere using a certain temperature rise program to obtain iron-cobalt alloy-doped carbon nanofibers. The iron-cobalt alloy-doped carbon nanofibers prepared by this method exhibit excellent performance as an ORR / OER bifunctional electrocatalyst and have wide applications.

Description

Technical Field

[0001] This invention relates to a method for synthesizing zinc oxide-etched iron-cobalt alloy-doped carbon nanofibers for electrocatalysis, belonging to the technical field of electrode materials and catalysts. Background Technology

[0002] Non-renewable energy sources such as coal, oil, and natural gas are gradually being depleted with rapid societal development. Extensive use of fossil fuels can easily cause irreversible damage to the ecological environment. However, renewable energy sources such as wind and solar power require energy storage systems to ensure stable power output. Zinc-air batteries, with their stable discharge curves and large capacity, are being extensively studied as a low-cost, high-efficiency, and environmentally friendly energy storage device.

[0003] Electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the main reactions involved in zinc-air battery technology. Chinese patent CN116344848A discloses a FeNi-NC composite electrochemical catalyst based on MOFs structure applied to the cathode catalysis of ORR in zinc-air batteries, but single-functional catalysts have certain limitations. Noble metal Pt-based materials exhibit excellent electrocatalytic activity for ORR, but their OER activity is weak; noble metal Ru and Ir-based materials are highly efficient OER electrocatalysts, but their ORR activity is poor. Chinese patent CN115513476A discloses a method for preparing a carbon-supported high-loading noble metal electrocatalyst, but the high cost and low availability of noble metal-based catalysts also hinder their widespread application in zinc-air batteries. Therefore, developing high-performance, low-cost ORR / OER bifunctional electrocatalysts can help overcome the limitations of high cost and single activity of noble metal-based electrocatalysts, improve catalytic efficiency, and has broad application prospects.

[0004] One-dimensional carbon nanofibers, composed of carbon elements, possess advantages such as high aspect ratio, large specific surface area, excellent electrical conductivity, and low cost as electrocatalysts. While these advantages facilitate rapid electron transport in specific directions, single carbon nanofibers are insufficient to provide enough active sites for ORR and OER catalytic processes. Therefore, it is necessary to further introduce electrocatalytically active materials to enhance the catalytic performance of one-dimensional carbon nanomaterials. However, during the carbonization process, a carbon film easily forms on the surface of the introduced active material, preventing some active sites from being fully exposed to the electrolyte and reducing the catalyst's catalytic efficiency. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to design and prepare a low-cost, non-precious metal-based catalyst to replace precious metals as the catalytic active material. Its ingenious process design fully exposes the active material on the surface of carbon nanofibers, further enhancing its electrocatalytic performance. Zinc oxide is introduced into the material through an impregnation-high-temperature carbonization process. During carbonization, the zinc oxide reacts with the carbon film covering the iron-cobalt alloy surface and then vaporizes, thereby destroying the carbon film coating the iron-cobalt alloy particles on the carbon nanofibers. The fully exposed iron-cobalt alloy surface provides numerous reaction sites, thereby enhancing the catalytic performance and efficiency of the carbon nanofibers. To achieve the above objective, the present invention provides a method for preparing iron-cobalt alloy-doped carbon nanofibers etched with zinc oxide, characterized by the following steps:

[0006] (1) Preparation of PAA (polyamic acid) precursor spinning solution: DMF (dimethylformamide), PMDA (pyromellitic dianhydride), and ODA (4,4-diaminodiphenyl ether) are mixed evenly in a certain proportion to prepare the spinning solution;

[0007] (2) Preparation process of PAA nanofibers: PAA nanofibers are prepared by using an electrostatic meltblowing device to prepare the spinning solution prepared in step (1).

[0008] (3) PAA precursor nanofiber impregnation process: The PAA nanofibers prepared in step (2) were impregnated in a solution with a total salt concentration of 0.225 mol / L. -1 PAA nanofibers loaded with metal ions were obtained by soaking the nanofibers in a mixed salt solution of ferric nitrate, cobalt nitrate, and zinc acetate in a molar ratio of 1:1:1 for 12 hours and then drying them overnight at 60°C.

[0009] (4) The PAA nanofibers loaded with metal ions prepared in step (3) are placed in an air atmosphere at 1°C for 1 min. -1 The temperature was increased to 300℃ and held for 1 hour to carry out the imidization reaction, thereby obtaining PI nanofibers loaded with a large number of metal ions.

[0010] (5) Preparation of zinc oxide etching of iron-cobalt alloy doped carbon nanofibers: The PI nanofibers loaded with a large number of metal ions in step (4) were subjected to nitrogen atmosphere at 3℃ min -1 The temperature was increased to 900℃ and carbonized at a certain rate, and then held for 1 hour to obtain zinc oxide etched iron-cobalt alloy doped carbon nanofibers. Attached Figure Description

[0011] Figure 1 A method for preparing carbon nanofibers doped with iron-cobalt alloy by etching with zinc oxide.

[0012] Figure 2 This is a scanning electron microscope image of melt-blown PAA nanofibers.

[0013] Figure 3 Scanning transmission electron microscope image of zinc oxide etching of iron-cobalt alloy doped carbon nanofibers;

[0014] Figure 4 Transmission electron microscope images of iron-doped, iron-cobalt alloy-doped, and iron-cobalt alloy-doped carbon nanofibers etched with zinc oxide at different temperatures;

[0015] Figure 5 XRD patterns of iron-cobalt alloy-doped carbon nanofibers etched with zinc oxide at different temperatures;

[0016] Figure 6 The test data are for the oxygen reduction reaction performance of iron-doped, iron-cobalt alloy-doped, and iron-cobalt alloy-doped carbon nanofiber electrocatalysts etched with zinc oxide at different temperatures.

[0017] Figure 7 The test data are for the oxygen evolution reaction performance of iron-doped, iron-cobalt alloy-doped, and iron-cobalt alloy-doped carbon nanofiber electrocatalysts etched with zinc oxide at different temperatures. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0019] Example 1

[0020] (1) In this invention, it is first necessary to prepare a PAA precursor spinning solution. The specific steps are as follows: 2.68g ODA is added to 14.4g DMF, and 2.92g PMDA is added in batches while stirring. The solution is stirred for 12h to obtain the final PAA homogeneous spinning solution.

[0021] (2) Add the spinning solution prepared in step (1) above to the electrostatic melt-blowing device. Maintain a distance of 80 cm between the 1 mm diameter spinning needle and the fiber receiving device, and control the air pressure at the outlet between 0.2 and 0.25 MPa. Use a booster to make the spinning solution extrusion speed 0.15 mL / min. -1 The spinning voltage is 20kV. Under the combined action of a rapid airflow and a high-voltage electrostatic field, the spinning solution can be fully stretched, ultimately forming PAA nanofibers on the collecting plate.

[0022] (3) The PAA nanofibers prepared in step (2) were placed in a solution with a total salt concentration of 0.225 mol / L. -1 PAA nanofibers loaded with a large number of metal ions were obtained by soaking them in a mixed salt solution of ferric nitrate, cobalt nitrate and zinc acetate in a molar ratio of 1:1:1 for 12 hours and then drying them overnight at 60°C.

[0023] (4) The PAA nanofibers loaded with metal ions prepared in step (3) are placed in an air atmosphere at 1°C for 1 minute. -1 The temperature was increased to 300℃ and held for 1 hour to carry out the imidization reaction, resulting in PI nanofibers loaded with a large number of metal ions.

[0024] (5) The PI nanofibers prepared in step (4) were placed in a N2 atmosphere at 3℃ for 3 min. -1 The temperature was increased to 900℃ to carbonize the carbon nanofibers, which were then doped with iron-cobalt alloy.

[0025] (6) Air electrode preparation parameters: 4 mg of iron-cobalt alloy-doped carbon nanofiber sample was dispersed in a mixture of 250 μL DMF and 250 μL deionized water, and then 40 μL of 5% Nafion solution was added dropwise. The mixture was ultrasonically dispersed for 30 min to obtain the electrocatalyst. The catalyst was then loaded onto a glassy carbon electrode by drop coating for electrochemical testing.

[0026] Example 2

[0027] (1) In this invention, it is first necessary to prepare a PAA precursor spinning solution. The specific steps are as follows: 2.68g ODA is added to 14.4g DMF, and 2.92g PMDA is added in batches while stirring. The solution is stirred for 12h to obtain the final PAA homogeneous spinning solution.

[0028] (2) Add the spinning solution prepared in step (1) above to the electrostatic melt-blowing device. Maintain a distance of 80 cm between the 1 mm diameter spinning needle and the fiber receiving device, and control the air pressure at the outlet between 0.2 and 0.25 MPa. Use a booster to make the spinning solution extrusion speed 0.15 mL / min. -1 The spinning voltage is 20kV. Under the combined action of a rapid airflow and a high-voltage electrostatic field, the spinning solution can be fully stretched, ultimately forming PAA nanofibers on the collecting plate.

[0029] (3) The PAA nanofibers prepared in step (2) are placed in a solution with a concentration of 0.075 mol / L. -1 After soaking in a ferric nitrate solution for 12 hours, the PAA nanofibers loaded with a large number of metal ions were obtained by drying at 60°C overnight.

[0030] (4) The iron-loaded PAA nanofibers prepared in step (3) are in an air atmosphere at 1°C for 1 min. -1 The temperature was increased to 300℃ and held for 1 hour to carry out the imidization reaction, resulting in PI nanofibers loaded with a large number of metal ions.

[0031] (5) The PI nanofibers prepared in step (4) are placed in a N2 atmosphere at 3℃ for 3 min. -1The temperature was raised to 900℃ for carbonization to obtain iron-doped carbon nanofibers.

[0032] (6) Air electrode preparation parameters: 4 mg of iron-doped carbon nanofiber sample was dispersed in a mixture of 250 μL DMF and 250 μL deionized water, and then 40 μL of 5% Nafion solution was added dropwise. The mixture was ultrasonically dispersed for 30 min to obtain the electrocatalyst. The catalyst was then loaded onto a glassy carbon electrode by drop coating for electrochemical testing.

[0033] Example 3

[0034] (1) In this invention, the first step is to prepare a PAA precursor spinning solution. The specific steps are as follows: 2.68g ODA is added to 14.4g DMF, and 2.92g PMDA is added in batches while stirring. The solution is stirred for 12h to obtain the final PAA homogeneous spinning solution.

[0035] (2) Add the spinning solution prepared in step (1) to the electrostatic melt-blowing device. Maintain a distance of 80 cm between the 1 mm diameter spinning needle and the fiber receiving device, and control the air pressure at the outlet between 0.2 and 0.25 MPa. Use a booster to achieve an extrusion speed of 0.15 mL / min for the spinning solution. -1 The spinning voltage is 20kV. Under the combined action of a rapid airflow and a high-voltage electrostatic field, the spinning solution can be fully stretched, ultimately forming PAA nanofibers on the collecting plate.

[0036] (3) The PAA nanofibers prepared in step (2) were subjected to a total salt concentration of 0.15 mol / L. -1 PAA nanofibers loaded with a large number of metal ions were obtained by soaking them in a 1:1 mixed salt solution of ferric nitrate and cobalt nitrate for 12 hours and then drying them overnight at 60°C.

[0037] (4) The PAA nanofibers loaded with iron and cobalt ions prepared in step (3) are placed in an air atmosphere at 1°C for 1 minute. -1 The temperature was increased to 300℃ and held for 1 hour to carry out the imidization reaction, resulting in PI nanofibers loaded with a large number of metal ions.

[0038] (5) The PI nanofibers prepared in step (4) were placed in a N2 atmosphere at 3℃ for 3 min. -1 Carbonization was carried out by heating to 900℃ to obtain iron-cobalt alloy-doped carbon nanofibers.

[0039] (6) Air electrode preparation parameters: 4 mg of iron-cobalt alloy-doped carbon nanofiber sample was dispersed in a mixture of 250 μL DMF and 250 μL deionized water, and then 40 μL of 5% Nafion solution was added dropwise. The mixture was ultrasonically dispersed for 30 min to obtain the electrocatalyst. The catalyst was then loaded onto a glassy carbon electrode by drop coating for electrochemical testing.

[0040] Example 4

[0041] (1) In this invention, the PAA precursor spinning solution needs to be prepared first. The specific steps are as follows: 2.68g ODA is dissolved in 14.4g DMF, and 2.92g PMDA is added one by one while stirring. The PAA spinning solution is obtained by stirring for 12h.

[0042] (2) Add the spinning solution prepared in step (1) to the electrostatic melt-blowing device. Maintain a distance of 80 cm between the spinning needle (1 mm inner diameter) and the fiber receiving device, and control the air pressure at the outlet between 0.2 and 0.25 MPa. Use a booster to achieve an extrusion speed of 0.15 mL / min. -1 The spinning voltage is 20kV. Under the simultaneous action of a rapid airflow and a high-voltage electrostatic field, the spinning solution can be fully stretched, ultimately forming PAA nanofibers on a collecting plate. Collecting the fibers on the collecting plate yields the PAA nanofibers.

[0043] (3) The PAA nanofibers prepared in step (2) were placed in a solution with a total salt concentration of 0.225 mol / L. -1 PAA nanofibers loaded with metal ions were obtained by soaking them in a mixed salt solution of ferric nitrate, cobalt nitrate and zinc acetate in a ratio of 1:1:1 for 12 hours and then drying them overnight at 60°C.

[0044] (4) The PAA nanofibers loaded with metal ions prepared in step (3) are placed in an air atmosphere at 1°C for 1 min. -1 The temperature was increased to 300℃ and held for 1 hour to carry out the imidization reaction, thereby obtaining PI nanofibers loaded with a large number of metal ions.

[0045] (5) The PI nanofibers prepared in step (4) were placed in a N2 atmosphere at 3℃ for 3 min. -1 The temperature was increased to 800℃ to carbonize the carbon nanofibers, which were co-doped with iron-cobalt alloy and zinc oxide.

[0046] (6) Electrode preparation: 4 mg of sample was dispersed in a mixture of 250 μL DMF and 250 μL deionized water, and then 40 μL of 5% Nafion solution was added dropwise. The mixture was ultrasonically dispersed for 30 min to obtain a uniform electrocatalyst dispersion. This dispersion was then loaded onto a glassy carbon electrode by drop coating for subsequent electrochemical testing.

[0047] Performance testing:

[0048] The zinc oxide etching process for iron-cobalt alloy-doped carbon nanofibers disclosed in this application is characterized by the introduction of a zinc source after the iron-cobalt alloy is generated through an impregnation-carbonization process. During the carbonization heating process, the zinc oxide generated reacts with carbon atoms in the carbon film on the surface of the iron-cobalt alloy to produce metallic zinc and carbon oxides. Metallic zinc has a melting point of 419℃ and a boiling point of 907℃. During the carbonization heating process, the zinc evaporates and diffuses into the ambient atmosphere, disrupting the carbon film coating of the uniformly loaded iron-cobalt alloy particles on the carbon nanofiber surface. Because the zinc oxide etching catalyst for iron-cobalt alloy-doped carbon nanofibers reduces the obstruction of the carbon film, the number of reactive sites increases, thus exhibiting excellent ORR / OER performance.

[0049] This method ensures that the carbon film coating on the surface of the iron-cobalt alloy grown on carbon nanofibers is destroyed, providing a large number of active sites and enhancing the electrocatalytic conversion efficiency.

[0050] Figure 1 A method for preparing zinc oxide-etched iron-cobalt alloy doped carbon nanofibers is presented. The zinc oxide-etched iron-cobalt alloy doped carbon nanofiber electrocatalyst is obtained using a melt-blowing, impregnation-carbonization process.

[0051] Figure 2 This is a scanning electron microscope image of solution-blown PAA nanofibers. This image demonstrates that, under appropriate conditions, the PAA nanofiber precursor was successfully prepared using the solution-blowing method.

[0052] Figure 3 This is a scanning transmission electron microscope (STEM) image of iron-cobalt alloy-doped carbon nanofibers etched with zinc oxide. The image demonstrates that under carbonization conditions at 900℃, the surface of the iron-cobalt alloy-doped carbon nanofibers possesses numerous micropores and mesopores. Part of the carbon film is consumed, exposing the active sites.

[0053] Figure 4 Transmission electron microscopy (TEM) images show iron-doped, iron-cobalt alloy-doped, and iron-cobalt alloy-doped carbon nanofibers etched with zinc oxide at different temperatures. The carbon nanofiber surfaces are all loaded with a large number of metal nanoparticles. For iron-doped and iron-cobalt alloy-doped carbon nanofibers, the metal particles are coated with a carbon film. However, the addition of zinc reduces or even eliminates the carbon film on the metal nanoparticle surface, increasing the exposed area of ​​active sites and thus providing more reaction sites.

[0054] Figure 5The image shows the XRD patterns of iron-cobalt alloy-doped carbon nanofibers etched with zinc oxide at different temperatures. The figure shows that at a carbonization temperature of 800℃, the zinc source in the catalyst produces a peak representing zinc oxide, indicating the formation of zinc oxide. At a carbonization temperature of 900℃, the zinc oxide peak disappears, leaving only the peak representing the iron-cobalt alloy. This indicates that under calcination conditions at 900℃, zinc oxide reacts with carbon to produce metallic zinc and carbon monoxide. Firstly, metallic zinc has a melting point of 419℃ and a boiling point of 907℃; it melts into a liquid and evaporates as zinc vapor, diffusing into the ambient atmosphere. Secondly, some of the carbon on the surface of the iron-cobalt alloy nanoparticles is converted into carbon oxides and diffuses into the ambient atmosphere, exposing the iron-cobalt alloy surface, increasing the number of electrocatalytic active sites, and thus enhancing the electrocatalytic conversion efficiency.

[0055] Figure 6 The figure presents test data for the oxygen reduction reaction (ORR) performance of iron-doped, iron-cobalt alloy-doped, and zinc oxide-etched iron-cobalt alloy-doped carbon nanofiber electrocatalysts at different temperatures. As shown in the figure, the half-wave potential of this catalyst is 0.84 V. This half-wave potential is significantly higher than that of iron-doped carbon nanofibers (0.68 V), iron-cobalt alloy-doped carbon nanofibers (0.78 V), and zinc oxide and iron-cobalt alloy co-doped carbon nanofibers (0.82 V). This indicates that metal alloy doping can enhance the activity of the electrocatalyst, and the addition of zinc reduces the carbon film coating on the alloy surface, further improving the ORR catalytic performance.

[0056] Figure 7 This data represents the performance test results of iron-doped, iron-cobalt alloy-doped, and zinc oxide-etched iron-cobalt alloy-doped carbon nanofiber electrocatalysts at different temperatures for oxygen evolution reaction. As shown in the figure, at 10 mA / cm²... -2 At a given current density, compared to iron-doped carbon nanofibers with almost no OER performance and iron-cobalt alloy-doped carbon nanofibers with an overpotential of 390 mV, the zinc oxide-etched iron-cobalt alloy-doped carbon nanofiber catalyst exhibits a potential of 1.53 V, i.e., an overpotential of 300 mV. This indicates that the catalyst possesses good ORR / OER bifunctional catalytic activity and is suitable for zinc-air batteries.

[0057] Example 1 is the preferred embodiment of this application, and Examples 2-4 also exhibited certain performance after the above performance tests. Therefore, in summary, the zinc oxide-etched iron-cobalt alloy-doped carbon nanofibers in this application combine the following advantages: (1) carbon nanofibers have strong conductivity, large specific surface area, and many attachable active sites; (2) metallic zinc has a low melting point and low boiling point, and can react with carbon to reduce the influence of carbon film coating on the surface of active materials; (3) iron-cobalt alloy has strong OER / ORR catalytic ability. Therefore, the electrocatalytic ability of iron-doped carbon nanofibers, iron-cobalt alloy-doped carbon nanofibers, and zinc oxide-etched iron-cobalt alloy-doped carbon nanofibers increases sequentially. The carbon nanofiber framework provides conductive pathways and a large number of attachable sites; the fully exposed iron-cobalt alloy provides a large number of active sites for ORR / OER reactions, greatly enhancing the oxygen electrocatalytic energy of the electrode material.

Claims

1. A method for synthesizing carbon nanofibers doped with iron-cobalt alloy for electrocatalytic etching using zinc oxide. Its features include the following steps: (1) Preparation of polyamic acid precursor spinning solution: Dimethylformamide, pyromellitic dianhydride and 4,4-diaminodiphenyl ether are mixed evenly in a certain proportion to prepare spinning solution; (2) Preparation process of polyamic acid nanofibers: The spinning solution prepared in step (1) is used to prepare polyamic acid nanofibers by electrostatic melt blowing device. (3) Polyamic acid precursor nanofiber impregnation process: The polyamic acid nanofibers prepared in step (2) were immersed in a salt solution and dried after soaking for 12 hours; the total concentration of the impregnation salt solution used was 0.225 mol·L⁻¹. -1 A mixed salt solution of ferric nitrate:cobalt nitrate:zinc acetate in a ratio of 1:1:1; (4) Imidization of impregnated polyamic acid nanofibers: The polyamic acid nanofibers prepared in step (3) after being impregnated with salt solution are heated and kept at a temperature in air by a programmed heating process to obtain PI nanofibers loaded with a large number of metal ions. (5) Preparation of iron-cobalt alloy-doped carbon nanofibers by zinc oxide etching: The imidized precursor nanofibers prepared in step (4) were carbonized under a nitrogen atmosphere at a certain temperature to obtain iron-cobalt alloy-doped carbon nanofibers; the carbonization program was 3℃·min -1 Heat to 900℃ and keep warm for 1 hour.

2. The method for synthesizing zinc oxide-doped carbon nanofibers for electrocatalytic etching of iron-cobalt alloys as described in claim 1, characterized in that: The polyamic acid nanofibers were prepared by extruding the spinning solution at a rate of 0.15 mL / min. -1 The outlet air pressure is 0.2 MPa.

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