A sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst and its preparation and application

Abstract

This invention discloses a sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst and its preparation and application. The preparation process involves: 1) dissolving iron dimer and zinc nitrate fully in methanol solvent, followed by ultrasonic dispersion to obtain a mixed solution; 2) dissolving an organic nitrogen source in methanol solvent, followed by ultrasonic dispersion to obtain a mixed solution, then adding this to the mixed solution from step 1), mixing thoroughly, centrifuging, washing, drying, and pyrolysis to obtain a dry powder; 3) mixing the dry powder with an organic sulfur source, grinding, and calcining at high temperature to obtain the sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst. The synthesis method of this invention is simple, the raw materials are readily available, and the obtained sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst can effectively form a structure with diatomic iron sites. Furthermore, an appropriate concentration of sulfur atom doping can effectively anchor the diatomic iron active sites, thereby regulating the coordination environment of the active center, exhibiting oxygen reduction reaction performance comparable to commercial Pt-based catalysts.

Description

Technical Field

[0001] This invention relates to the field of catalytic material synthesis technology, and particularly to a sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst and its preparation and application. Background Technology

[0002] Fuel cells have attracted significant research interest because they directly convert hydrogen and oxygen into water, achieving high-efficiency energy conversion while reducing environmental pollution. However, the slow kinetics of the oxygen reduction reaction (ORR) at the cathode greatly limit the development of fuel cells, necessitating the loading of catalysts at the cathode to improve the energy conversion efficiency of fuel cells.

[0003] While traditional platinum-based catalysts can effectively promote the oxygen reduction reaction, they suffer from problems such as limited reserves, high cost, and dissolution and loss during the catalytic process. Therefore, finding a non-precious metal electrocatalyst with high activity, high stability, and high selectivity is beneficial for the widespread adoption of fuel cells.

[0004] Numerous studies have shown that nitrogen-doped carbon materials with diatomic iron dispersion not only ensure that active sites are well dispersed on the material, but also leverage the synergistic effect between the two metallic iron atoms to maximize atom utilization and achieve ORR performance comparable to platinum-based catalysts. Furthermore, doping non-precious metal materials with heteroatoms (nitrogen, boron, sulfur, phosphorus, etc.) can alter the distribution of catalyst charge density and optimize the adsorption energy of reaction intermediates on the catalyst surface.

[0005] However, few studies have combined diatomic regulation and heteroatomic doping strategies, and the cumbersome synthesis steps are not conducive to maintaining the coordination environment at the diatomic sites and effectively regulating the active sites, thus increasing the cost of commercial process technologies.

[0006] Therefore, developing an oxygen reduction reaction catalyst based on a diatomic iron catalyst and doped with heteroatoms is beneficial to effectively maintain the diatomic sites of iron at a low cost, while regulating the coordination environment of the active center, thereby improving the oxygen reduction reaction performance and increasing the reaction scale of fuel cells. Summary of the Invention

[0007] The purpose of this invention is to provide a sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst, its preparation, and its application. The raw materials used in this invention are readily available, the operation process is simple, and the resulting material exhibits outstanding electrocatalytic oxygen reduction activity.

[0008] The application of the sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst prepared in this invention in the oxygen reduction reaction at the cathode of a fuel cell.

[0009] In this invention, sulfur doping significantly improves the electrocatalytic oxygen reduction activity of the original diatomic iron catalyst, meaning that the sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst can be effectively applied as an electrocatalyst for oxygen reduction reaction.

[0010] This invention is achieved through the following technical solution:

[0011] A method for preparing a sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst, characterized by comprising the following steps:

[0012] Step 1: Dissolve the iron dimer and zinc nitrate thoroughly in methanol solvent, and then disperse by ultrasonication to obtain mixed solution A;

[0013] Step 2: Dissolve the organic nitrogen source in methanol solvent, disperse it by ultrasound to obtain mixed solution B, then add it to mixed solution A obtained in step 1, mix thoroughly, centrifuge, wash and dry, and obtain dry powder through pyrolysis treatment;

[0014] Step 3: Mix the dry powder obtained in Step 2 with the organic sulfur source, grind it, and then calcine it at high temperature to obtain a sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst.

[0015] The iron dimer in step one is cyclopentadienyl dicarbonyl iron dimer, and the zinc nitrate is zinc nitrate Zn(NO3)2·6H2O containing water of crystallization.

[0016] The organic nitrogen source in step two is dimethylimidazole;

[0017] The organic sulfur source in step three is thioaminourea.

[0018] The molar ratio of zinc nitrate in step one to the organic nitrogen source in step two is 1:(4-6);

[0019] The mass ratio of the iron dimer in step one to the organic sulfur source in step three is 1:(5-20).

[0020] The mass-to-volume ratio of iron dimer to methanol solvent in step one is (0.02–0.06) g / 100 mL;

[0021] In step two, the mass-to-volume ratio of the organic nitrogen source to the methanol solvent is (4.4–4.8) g / 100 mL.

[0022] The thorough mixing in step two refers to sonicating mixed solution A and mixed solution B at room temperature until the solution color changes from transparent to white, and then continuing to stir at room temperature for 4-5 hours.

[0023] The high-temperature roasting in step three refers to roasting at 950-1000℃ in a nitrogen atmosphere for 2-3 hours.

[0024] The pyrolysis treatment in step two refers to acid washing and drying after high-temperature roasting;

[0025] Pickling refers to acid immersion treatment, with an immersion temperature of 20-30℃ and an immersion time of 12-14 hours. The acid used in the pickling operation is dilute hydrochloric acid or dilute sulfuric acid, preferably dilute sulfuric acid; the concentration of the acid is 2-3 mol / L.

[0026] The drying conditions are: drying at 60-80℃ for 12-14 hours.

[0027] This invention relates to the application of sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalysts in the oxygen reduction reaction at the cathode of fuel cells, particularly the oxygen reduction reaction at the cathode of fuel cells.

[0028] Compared with the prior art, the present invention has the following advantages and effects:

[0029] (1) This invention mainly uses zinc nitrate, dimethylimidazole, and thioaminourea as raw materials, which are inexpensive and readily available. Among them, the zeolite imidazole ester framework material formed by zinc nitrate and dimethylimidazole has a large specific surface area, high porosity, controllable pore size and good structural stability, which is conducive to the efficient loading of diatomic iron sites and is widely used in the field of electrocatalysis. Thioaminourea, as an organic sulfur source, can undergo complexation reaction with metal ions to generate stable complexes, which is conducive to the rational control of the coordination environment of metal ions, thereby enhancing the oxygen reduction reaction performance.

[0030] (2) The synthesis process of the present invention is simple and easy to operate, and the loss of materials during the preparation process is small.

[0031] (3) In the catalyst prepared by the present invention, the active sites are doped in the carbon skeleton in the form of diatomic iron. The high dispersion of sulfur atoms provides a sufficient sulfur source for the catalyst. Furthermore, the introduction of thioaminourea can effectively anchor iron atoms, thereby regulating the coordination environment at the active sites and exhibiting excellent oxygen reduction activity. Attached Figure Description

[0032] Figure 1 The X-ray diffraction patterns are those of the products obtained in Examples 2-6.

[0033] Figure 2 This is a spherical aberration corrected transmission electron microscope image of the product obtained in Example 5.

[0034] Figure 3 Linear scan curves of the products obtained in Examples 2-6. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation methods and protection scope of the present invention are not limited thereto.

[0036] Example 1

[0037] A method for preparing a precursor (denoted as Fe@ZIF-8) of a nitrogen-doped porous carbon-supported diatomic iron catalyst includes the following steps:

[0038] 6.0 mg of cyclopentadienyl dicarbonyl iron dimer and 1.19 g of Zn(NO3)2·6H2O were weighed and added sequentially to 30 mL of methanol solvent. The mixture was ultrasonically dispersed for 10 min to obtain mixed solution A. 1.314 g of dimethylimidazole was weighed and added to 30 mL of methanol solvent. After ultrasonic dispersion for 10 min, mixed solution B was obtained. Mixed solution B was added to mixed solution A, and the mixture was ultrasonically dispersed again for 1 h until the solution changed from transparent to a white suspension. The mixture was stirred at room temperature for 4 h, centrifuged, washed with deionized water and ethanol, and dried in an oven at 70 °C for 12 h to obtain a white solid. The solid was then transferred to a tube furnace and calcined at a nitrogen atmosphere at a heating rate of 5 °C / min from room temperature to 1000 °C for 2 h. After natural cooling to room temperature, a black solid was obtained. The obtained solid was impregnated with 2 mol / L dilute sulfuric acid at 25 °C for 12 h, then washed with deionized water and ethanol, and dried in an oven at 70 °C for 12 h, and labeled as Fe@ZIF-8.

[0039] Example 2

[0040] A method for preparing a nitrogen-doped porous carbon-supported diatomic iron catalyst (denoted as Fe2-NC) specifically includes the following steps:

[0041] Fe@ZIF-8 was placed in a ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 1000℃ at a heating rate of 5℃ / min and calcined for 2 hours. After naturally cooling to room temperature, black solid Fe2-NC was obtained.

[0042] Example 3

[0043] A method for preparing a sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst (denoted as Fe2-NCS-1) specifically includes the following steps:

[0044] Weigh 30 mg of Fe@ZIF-8 solid and 30 mg of thiourea and grind them in a mortar until the powder is evenly mixed. Place the powder in a tube furnace and heat it from room temperature to 1000℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and calcine for 2 hours. After naturally cooling to room temperature, the black solid obtained is Fe2-NCS-1.

[0045] Example 4

[0046] A method for preparing a sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst (denoted as Fe2-NCS-2) specifically includes the following steps:

[0047] Weigh 30 mg of Fe@ZIF-8 solid and 60 mg of thiourea and grind them in a mortar until the powder is evenly mixed. Place the powder in a tube furnace and heat it from room temperature to 1000℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and calcine for 2 hours. After naturally cooling to room temperature, the black solid obtained is Fe2-NCS-2.

[0048] Example 5

[0049] A method for preparing a sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst (denoted as Fe2-NCS-3) specifically includes the following steps:

[0050] Weigh 30 mg of Fe@ZIF-8 solid and 90 mg of thiourea and grind them in a mortar until the powder is evenly mixed. Place the powder in a tube furnace and heat it from room temperature to 1000°C at a rate of 5°C / min under a nitrogen atmosphere and calcine for 2 hours. After naturally cooling to room temperature, the black solid obtained is Fe2-NCS-3.

[0051] Example 6

[0052] A method for preparing a sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst (denoted as Fe2-NCS-4) specifically includes the following steps:

[0053] Weigh 30 mg of Fe@ZIF-8 solid and 120 mg of thiourea and grind them in a mortar until the powder is evenly mixed. Place the powder in a tube furnace and heat it from room temperature to 1000℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and calcine for 2 hours. After naturally cooling to room temperature, the black solid obtained is Fe2-NCS-4.

[0054] The phase composition of the products obtained in Examples 2-6 was characterized by X-ray powder diffraction using a Bruker D8 X-ray powder diffractometer (Germany). The results are as follows: Figure 1 As shown in the figure, no characteristic diffraction peaks of Fe-related species were detected in the obtained products, indicating that there was no aggregation of metal particles in the material, and Fe atoms were highly dispersed on the catalyst surface. Comparison of the spectra of Fe2-NC and Fe2-NCS-x (x=1-4) materials further demonstrates that S atom doping does not cause Fe particle aggregation.

[0055] The product obtained in Example 5 was characterized by aberration-corrected transmission electron microscopy (AC-TEM) using a JEOL NEOARM 200F spherical aberration-corrected transmission electron microscope manufactured by ThermoFisher Scientific, USA. Figure 2 As can be seen, adjacent bright spots appear in most positions of the catalyst, exhibiting a diatomic iron structure. This result indicates that there is no aggregation of metallic Fe particles on the catalyst surface, and the Fe atoms are highly dispersed on the catalyst surface, consistent with the results of the X-ray diffraction pattern. Moreover, this preparation method successfully introduces sulfur while synthesizing a diatomic iron site structure, which can fully utilize the synergistic effect between adjacent active sites in the electrocatalytic oxygen reduction reaction.

[0056] The products obtained in Examples 2–6 were analyzed by linear sweep voltammetry (LSV) using an IGS-6030 electrochemical workstation from Guangzhou Yingsi Sensor Technology Co., Ltd. The test medium was 0.1 mol / L potassium hydroxide solution, the scan rate was 10 mV / s, the rotation speed of the rotating disk electrode was 1600 rpm, and the half-wave potential was selected as the comparative standard for evaluating the electrochemical oxygen reduction performance.

[0057] Figure 3 The linear voltammetric scan curves of the products obtained in Examples 2-6 are shown, with the potential values ​​on the horizontal axis based on the reversible hydrogen electrode (RHE). After gradually increasing the S content in the initial Fe2-NC, the half-wave potential values ​​of Examples 3-5 were all higher than those of Fe2-NC (0.851V vs. RHE) (Table 1), and Fe2-NCS-3 had the highest half-wave potential value (0.882V vs. RHE), indicating that appropriate sulfur atom doping can effectively improve the oxygen reduction catalytic performance of the diatomic iron catalyst. When the S content was further increased, the half-wave potential value of Fe2-NCS-4 began to decrease (0.840V vs. RHE), even falling below that of the initial Fe2-NC. This indicates that introducing excessive sulfur atoms weakens the oxygen reduction reaction activity of the original catalyst. This may be because excessive sulfur atoms cover the iron active sites on the catalyst surface, weakening the interaction between iron and reaction intermediates, leading to a slower oxygen reduction reaction process and reduced oxygen reduction performance.

[0058] Table 1. Onset potential and half-wave potential of the products obtained in Examples 2-6 in 0.1 mol / L potassium hydroxide solution.

[0059]

[0060] In summary, the sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst of this invention can effectively form a structure with diatomic iron sites, and an appropriate concentration of sulfur atom doping can effectively anchor the diatomic iron active sites, thereby regulating the coordination environment of the active center. The sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst of this invention can significantly improve the electrocatalytic oxygen reduction performance of the material and is expected to replace traditional commercial Pt-based catalysts.

[0061] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst, characterized in that, Includes the following steps: Step 1: Dissolve the iron dimer and zinc nitrate thoroughly in methanol solvent, and then disperse by ultrasonication to obtain mixed solution A; Step 2: Dissolve the organic nitrogen source in methanol solvent, disperse it by ultrasound to obtain mixed solution B, then add it to mixed solution A obtained in step 1, mix thoroughly, centrifuge, wash and dry, and obtain dry powder through pyrolysis treatment; Step 3: Mix the dry powder obtained in Step 2 with the organic sulfur source, grind it, and then calcine it at high temperature to obtain a sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst. The iron dimer in step one is cyclopentadienyl dicarbonyl iron dimer, and the zinc nitrate is zinc nitrate Zn(NO3)2·6H2O containing water of crystallization; The organic nitrogen source in step two is dimethylimidazole; The organic sulfur source in step three is thioaminourea; The molar ratio of zinc nitrate in step one to the organic nitrogen source in step two is 1:(4~6). The mass ratio of the iron dimer in step one to the organic sulfur source in step three is 1:(5~20). The high-temperature roasting in step three refers to roasting at 950-1000℃ in a nitrogen atmosphere for 2-3 hours.

2. The method for preparing the sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst according to claim 1, characterized in that, The mass-to-volume ratio of iron dimer to methanol solvent in step one is (0.02~0.06) g / 100mL; The mass-to-volume ratio of the organic nitrogen source to the methanol solvent in step two is (4.4~4.8) g / 100mL.

3. The method for preparing the sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst according to claim 1, characterized in that, The thorough mixing in step two refers to sonicating mixed solution A and mixed solution B at room temperature until the solution color changes from transparent to white, and then continuing to stir at room temperature for 4-5 hours.

4. The method for preparing the sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst according to claim 1, characterized in that, The pyrolysis treatment in step two refers to acid washing and drying after high-temperature roasting; Pickling refers to acid immersion treatment, with an immersion temperature of 20-30℃ and an immersion time of 12-14 hours; the acid used in the pickling operation is dilute hydrochloric acid or dilute sulfuric acid; the acid concentration is 2-3 mol / L; The drying conditions are: drying at 60-80℃ for 12-14 hours.

5. A sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst, characterized in that... It is obtained by the preparation method described in any one of claims 1-4.

6. The application of the sulfur-nitrogen co-doped porous carbon-supported diatomic iron catalyst as described in claim 5 in the oxygen reduction reaction at the cathode of a fuel cell.

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