A preparation method of a high-performance in-situ sulfur-doped Fe-N-C catalyst based on a substituent group strategy

Abstract

The application discloses a preparation method of a high-performance in-situ sulfur-doped Fe-N-C catalyst based on a substituent strategy. The method adopts the substituent strategy, uses 2,4-diaminobenzene sulfonic acid as a nitrogen and sulfur source, uses iron chloride hexahydrate as a metal source, uses ammonium persulfate as an oxidant, and uses a chemical oxidation polymerization coordination pyrolysis strategy to prepare a high-performance in-situ sulfur-doped Fe-NSC catalyst. The Fe-NCS catalyst prepared by the application presents a fluffy porous structure, has a high specific surface area and rich mesoporous structure, which provides a short path for effective ion transmission and increases the accessibility of reaction active sites, thereby ensuring the rapid reaction. Electrochemical tests show that the Fe-NCS catalyst exhibits excellent oxygen reduction activity, cycle stability and methanol tolerance in an alkaline condition.

Description

Technical Field

[0001] This invention belongs to the field of cathode electrocatalysis 4e − The field of oxygen reduction reaction (ORR) catalyst preparation technology specifically relates to a method for preparing a high-performance in-situ sulfur-doped Fe-NC catalyst based on a substituent strategy. Background Technology

[0002] To meet current energy demands and address the increasingly serious environmental pollution problem, my country urgently needs to cultivate and develop clean and sustainable new energy technologies, such as fuel cells and rechargeable zinc-air batteries. Among these, the cathode oxygen reduction reaction (ORR) is a key reaction in zinc-air batteries, determining the battery's final performance and cost. However, due to the slow kinetics of the ORR reaction, electrocatalysts are necessary to effectively lower the activation barrier of the four-electron pathway, thereby improving conversion efficiency. Currently, platinum-based materials remain the most effective ORR electrocatalysts. However, platinum is expensive, scarce, and has poor catalyst durability, thus hindering the large-scale application of zinc-air battery systems. Therefore, developing inexpensive and stable metal-free ORR catalysts is of great significance for reducing the cost of zinc-air batteries and promoting their large-scale application. Among the many high-performance, low-cost novel electrocatalysts widely explored, non-precious metal / nitrogen / carbon (M / NC) materials have become the research frontier of ORR catalysis due to their high-density active site distribution, high intrinsic catalytic activity, high stability, and selectivity. Therefore, it is essential to optimize ORR performance by rationally designing the morphology and porous structure of M / NC materials to generate more active sites, faster mass transport paths, and higher surface area.

[0003] Generally, Fe-NC materials exhibit higher ORR activity compared to other metal-derived M / NC electrocatalysts, making them the most likely alternative to platinum-based catalysts. Nitrogen-containing carbon materials, due to their nitrogen-rich structure, excellent electrical conductivity, good chemical stability, tunable structure, and abundant pore structure, have become ideal supports for the preparation of Fe-NC electrocatalysts. Furthermore, heteroatom doping (such as N, B, P, and F) is favored by researchers because it can lead to charge redistribution in the carbon matrix, thereby improving catalytic activity. However, due to the synergistic effect between different heteroatoms, carbon co-doped with different heteroatoms exhibits better catalytic activity than carbon doped with a single heteroatom. Nevertheless, since the doping site is difficult to control during material preparation, the influence of heteroatom doping site on catalytic activity still needs further investigation. Recent studies have found that the controllable carbonization of conjugated polymers containing N or S heteroatoms is an effective method for preparing heteroatom-doped carbon materials.

[0004] This invention employs a substituent strategy, leveraging the structural advantages of phenylenediamine. By loading sulfonic acid groups onto its unique benzene ring structure, in-situ N and S co-doping of the catalyst is achieved. By controlling the number and position of substituents, the electronic structure and coordination environment of the catalytic material are modulated, thus preparing a Fe-NC catalyst with high catalytic performance. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a simple, low-cost, and high-performance in-situ sulfur-doped Fe-NC catalyst based on a substituent strategy. This method uses a substituent strategy, with 2,4-diaminobenzenesulfonic acid as the nitrogen and sulfur source, ferric chloride hexahydrate as the metal source, and ammonium persulfate as the oxidant. A chemical oxidation-polymerization coordination pyrolysis strategy is used to prepare the high-performance in-situ sulfur-doped Fe–NSC catalyst.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for preparing a high-performance in-situ sulfur-doped Fe-NC catalyst based on a substituent strategy, characterized by the following specific steps:

[0007] Step S1: 2,4-Diaminobenzenesulfonic acid, nano-silica and FeCl3•6H2O are dispersed in hydrochloric acid solution at a low temperature of 0~4℃. After stirring and mixing evenly, solution A is obtained. Then ammonium persulfate is added to hydrochloric acid solution and ultrasonicated to obtain solution B which is evenly dispersed. Solution B is added to solution A and oxidative polymerization reaction is carried out at a low temperature of 0~4℃ to obtain material A.

[0008] Step S2: Let the material A obtained in step S1 stand for aging, then transfer it to a forced-air drying oven for thorough drying. After it cools naturally to room temperature, grind it thoroughly to obtain material B.

[0009] Step S3: Transfer the material B obtained in step S2 to a corundum boat and place it in a high-temperature tube furnace for carbonization. Under the protection of nitrogen atmosphere, raise the temperature from room temperature to 800-900℃ at a heating rate of 2-8℃ / min and hold the temperature for 60-180min. Then, cool it naturally to room temperature to obtain material C.

[0010] Step S4: The material C obtained in step S3 is transferred to a hydrofluoric acid solution for immersion, then washed repeatedly with deionized water until the filtrate is neutral. The resulting filter cake is then transferred to a forced-air drying oven for drying, ultimately yielding the target product, an in-situ sulfur-doped Fe-NC catalyst with a specific surface area of ​​922.1 m². 2 g −1 It also has a rich mesoporous structure, which is beneficial for accelerating the material transport process during the reaction and promoting the exposure of active sites.

[0011] Further specifying, the feeding ratio of 2,4-diaminobenzenesulfonic acid, nano-silica and FeCl3•6H2O in step S1 is 8~10mmol:1~2g:0.2~0.3g.

[0012] Further specifying, the molar concentration of the hydrochloric acid solution in step S1 is 0.5~2 mol / L.

[0013] Further specifying, the aging time of material A in step S2 is 10~14h.

[0014] Further specifying, the mass fraction of the hydrofluoric acid solution in step S4 is 10wt%~20wt%.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0016] 1. This invention utilizes the non-covalent interaction of polymer carbon materials to anchor metal Fe atoms, thereby effectively inhibiting the aggregation of metal atoms during high-temperature pyrolysis. Through the chemical oxidative polymerization reaction between phenylenediamine monomers and ammonium persulfate, in-situ doping of N and S dual heteroatoms in carbon materials is successfully achieved. Furthermore, through synergistic effects, the electronic structure of the central metal atom and the electronic structure and density of the adjacent carbon matrix are adjusted, thereby enhancing the intrinsic catalytic activity of the in-situ sulfur-doped Fe-NC catalyst.

[0017] 2. This invention employs a substituent strategy to explore the effects of the number and position of heteroatoms and the modification of multiple heteroatoms on the structure and performance of catalysts by controlling the number and position of substituents, and aims to establish the correlation between catalyst activity and the structure of nitrogen and sulfur / carbon precursors.

[0018] 3. The in-situ sulfur-doped Fe-NC catalyst prepared by this invention exhibits a loose porous structure with a high specific surface area and abundant mesoporous structures. This provides short pathways for efficient ion transport and increases the accessibility of reactive sites, ensuring rapid reaction. Electrochemical tests show that this in-situ sulfur-doped Fe-NC catalyst exhibits excellent oxygen reduction activity, cycling stability, and methanol tolerance under alkaline conditions. Attached Figure Description

[0019] Figure 1 The molecular structural formulas of the nitrogen source and nitrogen and sulfur source corresponding to Fe-NC electrocatalysts D1-D4 prepared in Example 1 and Comparative Examples 1-3 are shown.

[0020] Figure 2 The image shows a transmission electron microscope (TEM) image of the Fe-NC electrocatalyst D3 prepared in Example 1.

[0021] Figure 3The X-ray diffraction patterns are of Fe-NC electrocatalysts D1-D4 prepared in Example 1 and Comparative Examples 1-3.

[0022] Figure 4 The nitrogen adsorption-desorption curve of Fe-NC electrocatalyst D3 prepared in Example 1 is shown.

[0023] Figure 5 The pore size distribution diagram is shown for Fe-NC electrocatalyst D3 prepared in Example 1.

[0024] Figure 6 The cyclic voltammetry curves are for Fe-NC electrocatalysts D1-D4 prepared in Example 1 and Comparative Examples 1-3.

[0025] Figure 7 Linear sweep voltammetry curves of Fe-NC electrocatalysts D1-D4 prepared in Example 1 and Comparative Examples 1-3 are shown.

[0026] Figure 8 Linear sweep voltammetry curves of Fe-NC electrocatalyst D3 prepared in Example 1 and commercial reference sample Pt / C.

[0027] Figure 9 Cyclic voltammetry curves, methanol resistance graphs, and stability graphs of the Fe-NC electrocatalyst D3 prepared in Example 1. Detailed Implementation

[0028] The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.

[0029] Example 1

[0030] Step S1: 9.25 mmol 2,4-DBAS (2,4-diaminobenzenesulfonic acid), 1 g nano SiO2 and 0.25 g FeCl3•6H2O were dispersed in 16 mL of 1 M hydrochloric acid solution at a low temperature of 0~4℃. After stirring for 60 min, solution A was obtained. Then, 11.56 mmol APS was added to 4 mL of 1 M hydrochloric acid solution and sonicated for 10 min to obtain a uniformly dispersed solution B. Solution B was slowly added dropwise to solution A and subjected to oxidative polymerization reaction at a low temperature of 0~4℃ for 12 h to obtain material A.

[0031] Step S2: Let the material A obtained in step S1 stand for aging for 12 hours, then transfer it to an 80℃ forced-air drying oven for thorough drying. After it cools naturally to room temperature, grind it thoroughly to obtain material B.

[0032] Step S3: Transfer the material B obtained in step S2 to a corundum boat and place it in a high-temperature tube furnace for carbonization. Under nitrogen atmosphere protection, raise the temperature from room temperature to 900℃ at a heating rate of 5℃ / min and hold the temperature for 120min. Then, allow it to cool naturally to room temperature to obtain material C.

[0033] Step S4: Transfer the material C obtained in step S3 to 250 mL of 10 wt% hydrofluoric acid solution and soak for 24 h. Then wash it several times with deionized water until the filtrate is neutral. Then transfer the obtained filter cake to a 60 °C forced-air drying oven and dry for 12 h to obtain the final target product Fe-NC catalyst D3.

[0034] Comparative Example 1

[0035] Step S1: 9.25 mmol m-PD (m-phenylenediamine), 1 g nano-SiO2 and 0.25 g FeCl3•6H2O were dispersed in 16 mL of 1 M hydrochloric acid solution at a low temperature of 0~4℃. After stirring for 60 min, solution A was obtained. Then, 11.56 mmol APS was added to 4 mL of 1 M hydrochloric acid solution and sonicated for 10 min to obtain a uniformly dispersed solution B. Solution B was slowly added dropwise to solution A and subjected to oxidative polymerization reaction at a low temperature of 0~4℃ for 12 h to obtain material A.

[0036] Step S2: Let the material A obtained in step S1 stand for aging for 12 hours, then transfer it to an 80℃ forced-air drying oven for thorough drying. After it cools naturally to room temperature, grind it thoroughly to obtain material B.

[0037] Step S3: Transfer the material B obtained in step S2 to a corundum boat and place it in a high-temperature tube furnace for carbonization. Under nitrogen atmosphere protection, raise the temperature from room temperature to 900℃ at a heating rate of 5℃ / min and hold the temperature for 120min. Then, allow it to cool naturally to room temperature to obtain material C.

[0038] Step S4: Transfer the material C obtained in step S3 to 250 mL of 10 wt% hydrofluoric acid solution and soak for 24 h. Then wash it several times with deionized water until the filtrate is neutral. Then transfer the obtained filter cake to a 60 °C forced-air drying oven and dry for 12 h to obtain the final target product Fe-NC catalyst D1.

[0039] Comparative Example 2

[0040] Step S1: 9.25 mmol p-PD (p-phenylenediamine), 1 g nano SiO2 and 0.25 g FeCl3•6H2O were dispersed in 16 mL of 1 M hydrochloric acid solution at a low temperature of 0~4℃. After stirring for 60 min, solution A was obtained. Then, 11.56 mmol APS was added to 4 mL of 1 M hydrochloric acid solution and sonicated for 10 min to obtain a uniformly dispersed solution B. Solution B was slowly added dropwise to solution A and subjected to oxidative polymerization reaction at a low temperature of 0~4℃ for 12 h to obtain material A.

[0041] Step S2: Let the material A obtained in step S1 stand for aging for 12 hours, then transfer it to an 80℃ forced-air drying oven for thorough drying. After it cools naturally to room temperature, grind it thoroughly to obtain material B.

[0042] Step S3: Transfer the material B obtained in step S2 to a corundum boat and place it in a high-temperature tube furnace for carbonization. Under nitrogen atmosphere protection, raise the temperature from room temperature to 900℃ at a heating rate of 5℃ / min and hold the temperature for 120min. Then, allow it to cool naturally to room temperature to obtain material C.

[0043] Step S4: Transfer the material C obtained in step S3 to 250 mL of 10 wt% hydrofluoric acid solution and soak for 24 h. Then wash it several times with deionized water until the filtrate is neutral. Then transfer the obtained filter cake to a 60 °C forced-air drying oven and dry for 12 h to obtain the final target product Fe-NC catalyst D2.

[0044] Comparative Example 3

[0045] Step S1: 9.25 mmol 2,5-DBAS (2,5-diaminobenzenesulfonic acid), 1 g nano SiO2 and 0.25 g FeCl3•6H2O were dispersed in 16 mL of 1M hydrochloric acid solution at a low temperature of 0~4℃. After stirring for 60 min, solution A was obtained. Then, 11.56 mmol APS was added to 4 mL of 1M hydrochloric acid solution and sonicated for 10 min to obtain a uniformly dispersed solution B. Solution B was slowly added dropwise to solution A and subjected to oxidative polymerization reaction at a low temperature of 0~4℃ for 12 h to obtain material A.

[0046] Step S2: Let the material A obtained in step S1 stand for aging for 12 hours, then transfer it to an 80℃ forced-air drying oven for thorough drying. After it cools naturally to room temperature, grind it thoroughly to obtain material B.

[0047] Step S3: Transfer the material B obtained in step S2 to a corundum boat and place it in a high-temperature tube furnace for carbonization. Under nitrogen atmosphere protection, raise the temperature from room temperature to 900℃ at a heating rate of 5℃ / min and hold the temperature for 120min. Then, allow it to cool naturally to room temperature to obtain material C.

[0048] Step S4: Transfer the material C obtained in step S3 to 250 mL of 10 wt% hydrofluoric acid solution and soak for 24 h. Then wash it several times with deionized water until the filtrate is neutral. Then transfer the obtained filter cake to a 60 °C forced-air drying oven and dry for 12 h to obtain the final target product Fe-NC catalyst D4.

[0049] ORR activity testing procedure: A certain amount of the powdered Fe-NC catalyst D3 sample was weighed using an electronic balance and mixed evenly with 5wt% Nafion, high-purity water, and anhydrous ethanol. The mixture was then sonicated for several minutes to obtain a homogeneous catalyst ink. The surface of the glassy carbon electrode was polished with alumina polishing powder until it was smooth and free of any stains or scratches. It was then cleaned with high-purity water and dried with air. A suitable amount of the sonicated catalyst ink was pipetted onto the cleaned glassy carbon electrode and allowed to air dry at room temperature to complete the preparation of the working electrode. The same method was used to prepare the working electrodes for the Fe-NC catalysts D1, D2, and D4 samples, which were then used as a control for the Fe-NC catalyst D3 sample. All electrochemical tests used a three-electrode system: an Hg / HgO electrode as the reference electrode, a platinum sheet electrode as the counter electrode, and a 0.1M KOH solution as the electrolyte. During cyclic voltammetry (CV) testing, the working electrode was a 3 mm diameter glassy carbon electrode coated with a specific volume and concentration of active material (the catalyst ink prepared above). Before testing, the electrode was saturated with oxygen / nitrogen, and the scan rate was 10 mV / s. -1 The scanning range is -0.8V to 0.2V. When performing linear sweep voltammetry (LSV) testing, the working electrode is a glassy carbon electrode with a diameter of 5mm coated with a certain volume and concentration of active material (the catalyst ink prepared above). Before the test, it is saturated with oxygen / nitrogen. During the test, the rotation speed is 1600rpm, and the scanning speed and scanning range are the same as the CV conditions described above.

[0050] The physical characterization of the high-performance in-situ sulfur-doped Fe-NC catalyst D3 constructed based on the substituent strategy is as follows: Figure 3 As shown, it has a high specific surface area of ​​922.1 m². 2 g −1 , Figure 4 The pore size distribution diagram shows that it also possesses abundant mesoporous structure, which is beneficial for accelerating mass transport during the reaction process and promoting the exposure of active sites. Electrochemical characterization tests are as follows: Figure 5 As shown, under alkaline conditions, the peak potential of the CV curve of Fe-NCS catalyst D3 is 0.86V (vs. RHE), which is better than that of control samples D1, D2 and D4. Figure 7 The LSV test results shown indicate that the half-wave potential (E) of the Fe-NC catalyst D3 under alkaline conditions is...1 / 2 The oxidation-reduction (OR) value was 0.83 V (vs. RHE), exhibiting oxygen reduction activity comparable to commercial Pt / C. The high activity of the catalyst is mainly attributed to the effective anchoring of metal Fe atoms by the amino groups of the phenylenediamine polymer, resulting in abundant reactive sites. Furthermore, the supported sulfonic acid groups enabled in-situ doping of S atoms, and the synergistic effect of the two heteroatoms effectively enhanced the catalyst's catalytic performance.

[0051] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are only illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from the scope of the principles of the present invention, and all such changes and modifications fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-performance in-situ sulfur-doped Fe-NC catalyst based on a substituent strategy, characterized in that... The specific steps are as follows: Step S1: 2,4-Diaminobenzenesulfonic acid, nano-silica and FeCl3•6H2O are dispersed in hydrochloric acid solution at a low temperature of 0~4℃. After stirring and mixing evenly, solution A is obtained. Then ammonium persulfate is added to hydrochloric acid solution and ultrasonicated to obtain solution B which is evenly dispersed. Solution B is added to solution A and oxidative polymerization reaction is carried out at a low temperature of 0~4℃ to obtain material A. Step S2: Let the material A obtained in step S1 stand for aging, then transfer it to a forced-air drying oven for thorough drying. After it cools naturally to room temperature, grind it thoroughly to obtain material B. Step S3: Transfer the material B obtained in step S2 to a corundum boat and place it in a high-temperature tube furnace for carbonization. Under the protection of nitrogen atmosphere, raise the temperature from room temperature to 800-900℃ at a heating rate of 2-8℃ / min and hold the temperature for 60-180min. Then, cool it naturally to room temperature to obtain material C. Step S4: The material C obtained in step S3 is transferred to a hydrofluoric acid solution for immersion, then washed repeatedly with deionized water until the filtrate is neutral. The resulting filter cake is then transferred to a forced-air drying oven for drying, ultimately yielding the target product, an in-situ sulfur-doped Fe-NC catalyst with a specific surface area of ​​922.1 m². 2 g −1 It also has a rich mesoporous structure, which is beneficial for accelerating the material transport process during the reaction and promoting the exposure of active sites.

2. The method for preparing a high-performance in-situ sulfur-doped Fe-NC catalyst based on a substituent strategy according to claim 1, characterized in that: The feeding ratio of 2,4-diaminobenzenesulfonic acid, nano-silica and FeCl3•6H2O in step S1 is 8~10mmol:1~2g:0.2~0.3g.

3. The method for preparing a high-performance in-situ sulfur-doped Fe-NC catalyst based on a substituent strategy according to claim 1, characterized in that: The molar concentration of the hydrochloric acid solution in step S1 is 0.5~2 mol / L.

4. The method for preparing a high-performance in-situ sulfur-doped Fe-NC catalyst based on a substituent strategy according to claim 1, characterized in that: The material A in step S2 is left to stand for aging for 10 to 14 hours.

5. The method for preparing a high-performance in-situ sulfur-doped Fe-NC catalyst based on a substituent strategy according to claim 1, characterized in that: The hydrofluoric acid solution in step S4 has a mass fraction of 10wt% to 20wt%.

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