A porous carbon catalyst with continuous support of single-atom iron and its preparation method

Abstract

This invention proposes a continuously supported porous carbon catalyst with single-atom iron and its preparation method, belonging to the technical field of single-atom catalysts, to solve the technical problem of low atom utilization in single-atom catalysts. This invention uses a mixed solution of ferric oxide and polyamic acid as a spinning precursor solution, and prepares the porous carbon catalyst with supported single-atom iron through five steps: electrospinning, vacuum drying, pre-oxidation, heat treatment, and acid etching. The required raw materials are abundant. Ferric oxide serves as a pore template, giving the material a rich pore structure, and also acts as an iron source, uniformly dispersed on the material surface. This invention significantly increases the specific surface area, increases the loading of more active sites, and solves the problem of low loading of single metal atoms.

Description

Technical Field

[0001] This invention belongs to the technical field of single-atom catalysts, and particularly relates to a porous carbon catalyst with continuously supported single-atom iron and its preparation method. Background Technology

[0002] With technological advancements, people's living standards have greatly improved. There is an urgent need to develop a low-cost, high-density, and environmentally friendly energy source. Over the past few decades, in order to achieve high reactivity, durability, and selectivity in reactions, researchers have explored various materials, including noble metals, transition metals, and metal-free carbon, as electrocatalysts.

[0003] However, their high cost, low atom utilization, structural instability, and susceptibility to oxidation during catalysis severely limit their commercial application. Therefore, developing a novel, efficient, stable, and inexpensive catalyst is of great significance in order to better accelerate reaction kinetics.

[0004] Among various novel catalysts, single-atom catalysts (SACs) have attracted considerable attention due to their high atom utilization efficiency, low coordination environment of single-atom centers, and unique quantum size effects. However, SACs still suffer from low metal loading, which limits the number of active sites for the oxygen reduction reaction. Furthermore, due to their high surface energy, individual metal atoms tend to aggregate into larger metal particles. Therefore, constructing highly metal-loaded SACs as high-performance catalysts remains a significant challenge. Summary of the Invention

[0005] To address the technical problem of low atom utilization in single-atom catalysts, this invention proposes a porous carbon catalyst with continuously supported single-atom iron and its preparation method, which further enhances the internal catalytic sites by increasing the specific surface area of ​​the fibers.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] A method for preparing a porous carbon catalyst with continuously supported single-atom iron includes the following steps:

[0008] (1) Prepare a polyamic acid solution and mix it with Fe2O3 powder to obtain a spinning precursor solution;

[0009] (2) Prepare fiber membranes by electrospinning the spinning precursor solution;

[0010] (3) The fiber membrane was calcined and carbonized to obtain Fe3O4 carbon fiber;

[0011] (4) Fe3O4 carbon fibers are dispersed in acid and etched to obtain a porous carbon catalyst.

[0012] The polyamic acid solution is prepared by: preparing a 4,4'-diaminodiphenyl ether solution, and then adding pyromellitic dianhydride to react and obtain a polyamic acid solution; the molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride is 1:(1-2).

[0013] The preparation method of the Fe2O3 powder is as follows: sodium hydroxide solution is added to ferric chloride hexahydrate solution, followed by sodium sulfate solution. Finally, the resulting ferric hydroxide gel is subjected to hydrothermal reaction. The product is washed and dried to obtain ferric oxide powder.

[0014] The concentration of the ferric chloride hexahydrate solution is 1–4 mol / L; the concentration of the sodium hydroxide solution is 3–6 mol / L; the concentration of the sodium sulfate solution is 0.2–1 mol / L; the volume ratio of the ferric chloride hexahydrate solution, sodium hydroxide solution, and sodium sulfate solution is 1:(1-2):0.1; the hydrothermal reaction temperature is 80–150℃, and the time is 3–10 days.

[0015] In step (1), Fe2O3 powder is first dispersed in the same solvent as the polyamic acid solution, and then mixed with the polyamic acid solution to prepare a spinning precursor solution. The solvent is N-N-dimethylacetamide.

[0016] The concentration of polyamic acid in the spinning precursor solution is 5-10 wt%, and the mass ratio of polyamic acid to Fe2O3 powder is 1:

[0017] (1-3).

[0018] The conditions for the electrospinning process are: spinning speed 0.5-2.5 mL / h, voltage 8-20 kV, and receiving distance 10-20 cm.

[0019] The calcination and carbonization includes pre-oxidation and carbonization. The pre-oxidation temperature is 180-300℃ and the time is 1-3h. The carbonization is first calcined at 250-400℃ for 1-3h, and then calcined at 700-1000℃ for 1-3h. The calcination atmosphere is an inert gas.

[0020] The acid is hydrochloric acid, with a concentration of 2–6 mol / L, and the etching time is 12–48 h.

[0021] The beneficial effects of this invention are:

[0022] (1) This invention uses Fe2O3 as a template and iron source, and utilizes electrospinning technology to control the microstructure of the material to obtain fibers with a continuous and uniformly dispersed iron source. Fe3O4 carbon fibers are acid-etched to obtain a porous carbon catalyst with continuously supported single-atom iron, increasing the specific surface area of ​​the material and also increasing the number of internal catalytic sites. Therefore, the catalyst in this invention has a multi-cavity structure, which is more conducive to the continuous and uniform dispersion of single iron atoms, thereby exposing more catalytic active sites and accelerating the reaction rate of ions, further ensuring faster charge exchange and transport of the single-atom iron catalyst during the reaction process.

[0023] (2) The porous carbon catalyst with continuous supported single-atom iron prepared by the present invention has a uniform and well dispersed morphology, a simple preparation process, convenient operation, and is capable of large-scale production.

[0024] (3) This invention achieves uniform dispersion of the iron source on the surface and inside the material, and after subsequent processing, a porous carbon catalyst with continuous single-atom iron is finally obtained, which improves the problem of low atom utilization and opens up a new path for the development of highly active catalysts. At the same time, the catalyst developed in this work also brings great prospects for the development of various energy storage and conversion devices. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a scanning electron microscope image of PAA / Fe2O3 fibers.

[0027] Figure 2 This is a scanning electron microscope image of C@Fe3O4 fibers.

[0028] Figure 3 This is a scanning electron microscope image of Fe-SAC.

[0029] Figure 4 This is a transmission electron microscope image of Fe-SAC.

[0030] Figure 5 Aberration-corrected high-angle annular dark-field scanning transmission electron microscope image of Fe-SAC. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] A porous carbon catalyst with continuously supported single-atom iron, the preparation method comprising the following steps:

[0034] S1: Add 100 mL of a 2 mol / L ferric chloride hexahydrate solution (FeCl3·6H2O) to a 250 mL three-necked flask and stir in an oil bath at 75 °C for 10 minutes. Then, add 100 mL of a 5.4 mol / L sodium hydroxide solution (NaOH) dropwise, and continue stirring for 30 minutes. Next, add 10 mL of a 0.6 mol / L sodium sulfate solution (Na2SO4). Finally, place the resulting ferric hydroxide gel in a constant temperature oven at 100 °C and allow it to grow for 8 days. Remove the supernatant, collect the red product, wash it three times with ethanol and deionized water, and then dry the product at 60 °C for 12 hours to obtain a deep red ferric oxide (Fe2O3) powder with a peanut-like shape.

[0035] S2: At room temperature, 2.155 g of 4,4'-diaminodiphenyl ether (ODA) was first added to 30 mL of NN-dimethylacetamide (DMAC), and mechanically stirred until the solute was completely dissolved. While stirring at 350 r / min, 2.395 g of pyromellitic dianhydride (PMDA) was then added to the above solution in small, repeated additions. The reaction was allowed to proceed for 6 hours to obtain a 14 wt% polyamic acid (PAA) solution.

[0036] S3: Add 3.2g of Fe2O3 powder to 5g of DMAC and stir magnetically until homogeneous. Then add 10g of PAA solution to the mixture and continue stirring to obtain a spinning precursor solution with a PAA concentration of 7.7wt%.

[0037] S4: Transfer 10 mL of the spinning precursor solution for electrospinning. Use a commercially available 18-inch spinneret. # Stainless steel needles were used, the spinning speed was adjusted to 1.7 mL / h, the DC voltage was 18 kV, the distance between the spinneret and the receiver was kept at 15 cm, and spinning was continued for about 6 hours to obtain a fiber membrane of polyamic acid coated with ferric oxide (PAA / Fe2O3). Figure 1 The results show that PAA / Fe2O3 fibers have a continuous network structure, with Fe2O3 particles uniformly distributed inside the fibers as an iron source.

[0038] S5: The PAA / Fe2O3 fiber membrane was dried under vacuum at 100℃ for 1 hour, then transferred to a muffle furnace at 250℃ for pre-oxidation for 2 hours, followed by calcination at 350℃ for 2 hours under argon atmosphere, and then further heated to 800℃ for calcination for 2 hours. Afterwards, it was naturally cooled to room temperature to obtain Fe3O4 carbon fiber (C@Fe3O4 fiber). Figure 2 This demonstrates that the fibers still maintain their network structure, and the Fe2O3 particles did not undergo significant changes after high-temperature calcination.

[0039] S6: The obtained Fe3O4 carbon fiber was etched with 60 mL of 4 mol / L hydrochloric acid solution for 24 hours, washed with deionized water until neutral, and dried at a constant temperature of 60℃ for 24 hours to obtain a porous carbon catalyst with continuous single-atom iron support. Figure 3 The etching clearly shows that the Fe3O4 particles were successfully etched, forming a cavity structure with pores spaced approximately 500 nm apart and pore walls about 100 nm thick. This increases the specific surface area of ​​the catalyst and improves the loading of metal single atoms. Figure 4 The transmission electron microscopy images further revealed that the layered cavity structure of Fe-SAC not only exposes a large number of active sites, but also reduces the flow resistance of gas and liquid, and accelerates charge transfer and mass transfer. Figure 5 The aberration-corrected electron microscopy images show a large number of isolated and dispersed bright spots, indicating that the iron source is uniformly dispersed on the surface and inside the catalyst, proving that the iron source exists in the form of single atoms.

[0040] Example 2

[0041] A porous carbon catalyst with continuously supported single-atom iron, the preparation method comprising the following steps:

[0042] S1: Add 100 mL of a 1 mol / L ferric chloride hexahydrate solution (FeCl3·6H2O) to a 250 mL three-necked flask and stir in an oil bath at 75 °C for 10 minutes. Then, add 100 mL of a 3 mol / L sodium hydroxide solution (NaOH) dropwise, and continue stirring for 30 minutes. Next, add 10 mL of a 0.2 mol / L sodium sulfate solution (Na2SO4). Finally, place the resulting ferric hydroxide gel in an oven at 80 °C and allow it to grow for 10 days. Remove the supernatant, collect the red product, wash it three times with ethanol and deionized water, and then dry the product at 60 °C for 12 hours to obtain a deep red ferric oxide (Fe2O3) powder with a peanut-like shape.

[0043] S2: At room temperature, first add 2.155 g of 4,4'-diaminodiphenyl ether (ODA) to 30 mL of NN-dimethylacetamide (DMAC) and stir mechanically until the solute is completely dissolved. Then, while stirring at 350 r / min, add 3.59 g of pyromellitic dianhydride (PMDA) in small, repeated additions to the above solution. React for 6 hours to obtain a polyamic acid (PAA) solution.

[0044] S3: Add 1.4g of Fe2O3 powder to 16.6g of DMAC and stir magnetically until homogeneous. Then add 10g of PAA solution to the mixture and continue stirring to obtain a spinning precursor solution with a PAA concentration of 5wt%.

[0045] S4: Transfer 10 mL of the spinning precursor solution for electrospinning. Use a commercially available 18-inch spinneret. # Stainless steel needles were used, the spinning speed was adjusted to 0.5 mL / h, the DC voltage was 8 kV, and the distance between the spinneret and the receiver was kept at 10 cm. Spinning was continued for about 6 hours to obtain a fiber membrane of polyamic acid coated with ferric oxide (PAA / Fe2O3).

[0046] S5: The PAA / Fe2O3 fiber membrane was dried under vacuum at 100℃ for 1 hour, then transferred to a muffle furnace at 180℃ for pre-oxidation for 3 hours, followed by calcination at 300℃ for 2 hours under argon atmosphere, and then further heated to 700℃ for 1 hour. Afterwards, it was naturally cooled to room temperature to obtain Fe3O4 carbon fiber (C@Fe3O4 fiber).

[0047] S6: The obtained Fe3O4 carbon fiber was etched with 60 mL of 2 mol / L hydrochloric acid solution for 48 hours, washed with deionized water until neutral, and dried at a constant temperature of 60℃ for 24 hours to obtain a porous carbon catalyst with continuous single-atom iron support.

[0048] Example 3

[0049] A porous carbon catalyst with continuously supported single-atom iron, the preparation method comprising the following steps:

[0050] S1: Add 200 mL of a 3 mol / L ferric chloride hexahydrate solution (FeCl3·6H2O) to a 500 mL three-necked flask and stir in an oil bath at 75 °C for 10 minutes. Then, add 100 mL of a 4 mol / L sodium hydroxide solution (NaOH) dropwise, and continue stirring for 30 minutes. Next, add 10 mL of a 0.5 mol / L sodium sulfate solution (Na2SO4). Finally, place the resulting ferric hydroxide gel in a constant temperature oven at 120 °C and allow it to grow for 5 days. Remove the supernatant, collect the red product, wash it three times with ethanol and deionized water, and then dry the product at 60 °C for 12 hours to obtain a deep red ferric oxide (Fe2O3) powder with a peanut-like shape.

[0051] S2: At room temperature, 2.155 g of 4,4'-diaminodiphenyl ether (ODA) was first added to 30 mL of NN-dimethylacetamide (DMAC), and mechanically stirred until the solute was completely dissolved. While stirring at 350 r / min, 2.395 g of pyromellitic dianhydride (PMDA) was then added to the above solution in small, repeated additions. The reaction was allowed to proceed for 6 hours to obtain a 14 wt% polyamic acid (PAA) solution.

[0052] S3: Add 2.8g of Fe2O3 powder to 1.2g of DMAC and stir magnetically until homogeneous. Then add 10g of PAA solution to the mixture and continue stirring to obtain a spinning precursor solution with a PAA concentration of 10wt%.

[0053] S4: Transfer 10 mL of the spinning precursor solution for electrospinning. Use a commercially available 18-inch spinneret. # Stainless steel needles were used, the spinning speed was adjusted to 2 mL / h, the DC voltage was 15 kV, the distance between the spinneret and the receiver was kept at 15 cm, and spinning was continued for about 5 hours to obtain a fiber membrane of polyamic acid coated with ferric oxide (PAA / Fe2O3).

[0054] S5: The PAA / Fe2O3 fiber membrane was dried under vacuum at 100℃ for 1 hour, then transferred to a muffle furnace at 230℃ for pre-oxidation for 3 hours, followed by calcination at 250℃ for 1 hour under argon atmosphere, and then further heated to 800℃ for calcination for 3 hours. Afterwards, it was naturally cooled to room temperature to obtain Fe3O4 carbon fiber (C@Fe3O4 fiber).

[0055] S6: The obtained Fe3O4 carbon fiber was etched with 60 mL of 6 mol / L hydrochloric acid solution for 12 hours, washed with deionized water until neutral, and dried at a constant temperature of 60℃ for 24 hours to obtain a porous carbon catalyst with continuous single-atom iron support.

[0056] Example 4

[0057] A porous carbon catalyst with continuously supported single-atom iron, the preparation method comprising the following steps:

[0058] S1: Add 150 mL of a 4 mol / L ferric chloride hexahydrate solution (FeCl3·6H2O) to a 500 mL three-necked flask and stir for 10 minutes in an oil bath at 75 °C. Then, add 100 mL of a 6 mol / L sodium hydroxide solution (NaOH) dropwise, and continue stirring for 30 minutes. Next, add 10 mL of a 1 mol / L sodium sulfate solution (Na2SO4). Finally, place the resulting ferric hydroxide gel in a constant temperature oven at 150 °C and allow it to grow for 3 days. Remove the supernatant, collect the red product, wash it three times with ethanol and deionized water, and then dry the product at 60 °C for 12 hours to obtain a deep red ferric oxide (Fe2O3) powder with a peanut-like shape.

[0059] S2: At room temperature, 2.155 g of 4,4'-diaminodiphenyl ether (ODA) was first added to 30 mL of NN-dimethylacetamide (DMAC), and mechanically stirred until the solute was completely dissolved. While stirring at 350 r / min, 2.395 g of pyromellitic dianhydride (PMDA) was then added to the above solution in small, repeated additions. The reaction was allowed to proceed for 6 hours to obtain a 14 wt% polyamic acid (PAA) solution.

[0060] S3: Add 4.2g of Fe2O3 powder to 3.3g of DMAC and stir magnetically until homogeneous. Then add 10mL of PAA solution to the mixture and continue stirring to obtain a spinning precursor solution with a PAA concentration of 8wt%.

[0061] S4: Transfer 10 mL of the spinning precursor solution for electrospinning. Use a commercially available 18-inch spinneret. # Stainless steel needles were used, the spinning speed was adjusted to 2.5 mL / h, the DC voltage was 20 kV, the distance between the spinneret and the receiver was kept at 20 cm, and spinning was continued for about 3 hours to obtain a fiber membrane of polyamic acid coated with ferric oxide (PAA / Fe2O3).

[0062] S5: The PAA / Fe2O3 fiber membrane was dried under vacuum at 100℃ for 1 hour, then transferred to a muffle furnace at 300℃ for pre-oxidation for 2 hours, followed by calcination at 400℃ for 2 hours under argon atmosphere, and then further heated to 1000℃ for 1 hour. Afterwards, it was naturally cooled to room temperature to obtain Fe3O4 carbon fiber (C@Fe3O4 fiber).

[0063] S6: The obtained Fe3O4 carbon fiber was etched with 60 mL of 4 mol / L hydrochloric acid solution for 24 hours, washed with deionized water until neutral, and dried at a constant temperature of 60℃ for 24 hours to obtain a porous carbon catalyst with continuous single-atom iron support.

[0064] This invention successfully prepared a continuous porous carbon catalyst, Fe-SAC, supported on single-atom iron using electrospinning technology, opening a new avenue for the development of highly active catalysts. The continuous porous structure increases its specific surface area, facilitating maximum Fe atom utilization and full exposure of active sites, while also enhancing the intrinsic activity of the Fe metal sites. Furthermore, the unique characteristic of fiber materials as catalysts lies in their ability to not only increase active sites but also promote electron transport through fiber pathway guidance effects to achieve excellent catalytic activity. Simultaneously, this work opens a new pathway for the preparation of highly active catalysts and presents great promise for the development of various energy storage and conversion devices.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a porous carbon catalyst with continuously supported single-atom iron, characterized in that, Includes the following steps: (1) Prepare a polyamic acid solution and mix it with Fe2O3 powder to obtain a spinning precursor solution; (2) Prepare fiber membranes by electrospinning the spinning precursor solution; (3) The fiber membrane is calcined and carbonized to obtain Fe3O4 carbon fiber; (4) Fe3O4 carbon fibers were dispersed in acid and etched to obtain a porous carbon catalyst; The concentration of polyamic acid in the spinning precursor solution is 5-10 wt%, and the mass ratio of polyamic acid to Fe2O3 powder is 1:(1-3). In step (1), Fe2O3 powder is first dispersed in the same solvent as the polyamic acid solution, and then mixed with the polyamic acid solution to prepare a spinning precursor solution. The solvent is N,N-dimethylacetamide. The calcination and carbonization includes pre-oxidation and carbonization. The pre-oxidation temperature is 180~300℃ and the time is 1~3h. The carbonization is first calcined at 250~400℃ for 1~3h, and then calcined at 700~1000℃ for 1~3h. The calcination atmosphere is an inert gas. The acid is hydrochloric acid, with a concentration of 2-6 mol / L, and the etching time is 12-48 h.

2. The method for preparing a porous carbon catalyst with continuously supported single-atom iron according to claim 1, characterized in that, The polyamic acid solution is prepared by: preparing a 4,4'-diaminodiphenyl ether solution, and then adding pyromellitic dianhydride to react and obtain a polyamic acid solution; the molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride is 1:(1~2).

3. The method for preparing a porous carbon catalyst with continuously supported single-atom iron according to claim 2, characterized in that, The preparation method of the Fe2O3 powder is as follows: sodium hydroxide solution is added to ferric chloride hexahydrate solution, followed by sodium sulfate solution. Finally, the resulting ferric hydroxide gel is subjected to hydrothermal reaction. The product is washed and dried to obtain ferric oxide powder.

4. The method for preparing a porous carbon catalyst with continuously supported single-atom iron according to claim 3, characterized in that, The concentration of the ferric chloride hexahydrate solution is 1~4 mol / L; the concentration of the sodium hydroxide solution is 3~6 mol / L; the concentration of the sodium sulfate solution is 0.2~1 mol / L; the volume ratio of the ferric chloride hexahydrate solution, sodium hydroxide solution, and sodium sulfate solution is 1:(1-2):0.1; the hydrothermal reaction temperature is 80~150 ℃, and the time is 3~10 days.

5. The method for preparing a porous carbon catalyst with continuously supported single-atom iron according to claim 1, characterized in that, The conditions for the electrospinning process are: spinning speed 0.5~2.5mL / h, voltage 8~20 kV, and receiving distance 10~20cm.

6. A porous carbon catalyst with continuously supported single-atom iron prepared by the method according to any one of claims 1-5.

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